DS 7-7R 17-12R Semiconductor Fabrication Facilities ... - FM Global

REFERENCE DOCUMENT 

FM Global 7-7R 

Property Loss Prevention Data Sheets 17-12R 

SEMICONDUCTOR FABRICATION FACILITIES 

Table of Contents 

January 2003 

Page1of38 

1.0 SCOPE ................................................................................................................................................... 3 

2.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................... 3 

2.1 Process Hazards ............................................................................................................................. 3 

2.1.1 Gases (General) .................................................................................................................... 3 

2.1.1.1 Silane ......................................................................................................................... 6 

2.1.1.2 Dichlorosilane ............................................................................................................ 6 

2.1.1.3 Trichlorosilane ............................................................................................................ 6 

2.1.1.4 Chlorine Trifluoride ..................................................................................................... 6 

2.1.1.5 Hydrogen ................................................................................................................... 7 

2.1.2 Photoresist, Developer and Rinse ........................................................................................ 7 

2.1.3 Plastic Wet Benches ............................................................................................................. 8 

2.1.4 Plastic Ductwork .................................................................................................................... 8 

2.1.5 Vacuum Pumps ..................................................................................................................... 9 

2.1.6 Ion Implanters ...................................................................................................................... 10 

2.1.6.1 Ion Implanter HVDC Power Supply ......................................................................... 10 

2.1.6.2 Ion Implanter Isolation Transformer ......................................................................... 10 

2.1.6.3 Ion Implanters — National Electric Code (NEC) Requirements for 

Transformers ............................................................................................................ 11 

2.1.6.4 American National Standard for Transformers - C57.12.22-1989 ........................... 11 

2.1.6.5 Ion Implanter Loss Experience ................................................................................ 12 

2.1.7 Diffusion ............................................................................................................................... 12 

2.1.8 Spill Hazard ......................................................................................................................... 12 

2.2 Fire Hazards of Wet Benches ....................................................................................................... 13 

2.2.1 Fire Tests Conducted by FM Approvals on Wet Benches .................................................. 13 

2.3 FM Approvals Cleanroom Materials Flammability Test Protocol (Class 4910) ............................. 14 

2.4 FM Approved Duct Systems .......................................................................................................... 14 

2.5 Fire Hazards of Stockers ............................................................................................................... 15 

2.6 Silane Gas ..................................................................................................................................... 15 

2.7 Electrical Exposure ........................................................................................................................ 16 

2.8 Deionized (DI) Water Systems ...................................................................................................... 16 

3.0 PROCESS OVERVIEW ........................................................................................................................ 16 

3.1 Effluent Gas Conditioning Systems ............................................................................................... 21 

3.2 Cleanroom Overview ..................................................................................................................... 21 

3.3 Processing Tools ............................................................................................................................ 24 

3.3.1 Chemical Mechanical Polish ............................................................................................... 25 

3.3.2 Alcohol Vapor Dryers ........................................................................................................... 25 

3.3.3 Reprocessors ...................................................................................................................... 25 

3.3.4 Mini-Environment Enclosures .............................................................................................. 25 

3.3.5 Vacuum Pumps ................................................................................................................... 26 

3.4 Bulk Chemical Distribution ............................................................................................................. 26 

3.5 Liquid Damage Exposures ............................................................................................................ 26 

3.6 Protection Against Theft ................................................................................................................ 27 

3.7 Uninterruptible Power Supply Overview ........................................................................................ 28 

4.0 OTHER APPLICABLE CODES AND STANDARDS ........................................................................... 28 

4.1 United States Building Code ......................................................................................................... 28 

4.2 NFPA 318 ....................................................................................................................................... 29 

©2003 Factory Mutual Insurance Company. All rights reserved. No part of this document may be reproduced, 

stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical, 

photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company. 

Page

7-7R 


17-12R SEMICONDUCTOR FABRICATION FACILITIES 

Page 2 

4.3 SEMI S-2 ....................................................................................................................................... 29 

4.4 International Codes ........................................................................................................................ 30 

4.5 ISO International Cleanroom Standards ........................................................................................ 31 

4.5.1 ISO 14644-1 Air Cleanliness Classification .......................................................................... 32 

5.0 SEMICONDUCTOR TERMINOLOGY .................................................................................................. 33 

6.0 BIBLIOGRAPHY ................................................................................................................................... 38 

List of Figures 

Fig. 1. Process gas distribution arrangements ............................................................................................. 4 

Fig. 2. Wet bench free burn test. ................................................................................................................. 13 

Fig. 3. Flow diagram of semiconductor fabrication. ..................................................................................... 17 

Fig. 4. Semiconductor fabrication facility systems diagram. ........................................................................ 18 

Fig. 5. Clean bay service aisle. .................................................................................................................... 22 

Fig. 6. Tool service corridor. ......................................................................................................................... 23 

Fig. 7. Various arrangements of a wet bench and associated fume exhaust ductwork. ............................ 24 

List of Tables 

Table 1. Gases Used in Fabrication ............................................................................................................. 5 

Table 2. Silane Mixtures ................................................................................................................................. 6 

Table 3. Flammable and Combustible Liquids Used in Fabrication .............................................................. 8 

Table 4. Process Reactions ........................................................................................................................... 9 

Table 5. Vacuum Applications Used in Fabrication ...................................................................................... 10 

Table 6. Material Nomenclature and Use .................................................................................................... 14 

Table 7. Common Nonflammable Semiconductor Process Liquids ........................................................... 26 

Table 8. Possible Water Damage Sources ................................................................................................. 27 

Table 9. Selected airborne particulate cleanroom classes for cleanrooms and cleanzones 

defined by ISO 14644-1 ................................................................................................................. 32 

Table 10. Comparison between different Cleanroom Class Standards ....................................................... 32 

©2003 Factory Mutual Insurance Company. All rights reserved.

1.0 SCOPE 

This reference data sheet describes the process flow and processing tools used to fabricate semiconductors. 

Included is an overview of the requirements of other applicable codes used by the industry at the national 

and international levels. Basic terminology used by the industry is provided along with a bibliography of 

reference material. 

2.0 SUPPORT FOR RECOMMENDATIONS 

2.1 Process Hazards 

The process hazards of manufacturing semiconductor devices involve extensive use of toxic, highly corrosive 

and flammable gases and liquids. The extensive use of combustible plastics adds to the high risk of fire 

loss. Because process equipment is expensive and the product in process is extremely susceptible to fire, 

smoke, and water damage, great potential exists for substantial dollar loss from fire, even though the fire may 

be contained in a very small area. 

2.1.1 Gases (General) 

REFERENCE DOCUMENT 7-7R 

SEMICONDUCTOR FABRICATION FACILITIES 17-12R 

Page 3 

Table 1 lists gases and the associated processes in which the gases are used. The overall system for the 

distribution of process gases is shown in Figure 1. 





Page 4 

Fig. 1. Process gas distribution arrangements 1 . 

Notes: 

(1) Does not represent any single configuration, but many possible configurations. 

(2) Section of piping between the gas cabinet and process tool can range in length from a few feet (meters) to several 

hundred feet (meters). 

(3) See Figures 8 and 9 in Data Sheet 7-7/17-12 for actual illustrations. 

(4) Exhaust fans where applicable. 




Page 5 

Table 1. Gases Used in Fabrication 

Gas Process Hazard 

Ammonia (NH 3) VX FTC 

Arsenic Pentafluoride (AsF 5) I TC 

Argon (Ar) COEDVMX I 

Arsine (AsH 3) CEDIV FT 

Boron Trichloride (BCl 3) DIX TC 

Boron Trifluoride (BF 3) DI T 

Carbon Dioxide (CO 2) V I 

Carbon Monoxide (CO) EM FT 

Carbon Tetrachloride (Ccl 4) X CT 

Chlorine (Cl 2) X CT 

Chlorine Trifluoride (CLF 3) D TCO 

Diborane (B 2H 6) EDV FPT 

Dichlorosilane (SiH 2Cl 2) EV F(T)C, P 

Dimethylzinc ((CH 3) 2Zn) V FT 

Disilane (Si 2H 6) V F 

Fluorocarbons (various Freon compounds & others) X I 

Germane (GeH 4) EV FT 

Hydrogen (H 2) COEDIVX F 

Hydrogen Chloride (HCl) OEX TC 

Hydrogen Selenide (H 2Se) I FT 

Hydrogen Sulfide (H 2S) V T 

Nitrogen (N 2) OEDIVX I 

Nitrogen Trifluoride (NF 3) X T 

Nitrous Oxide (N 2O) V O 

Oxygen (O 2) ODVX O 

Phosgene (COCl 2) CEDIV FT 

Phosphine (PH 3) CEDIV FPT 

Phosphorous Pentafluoride (PF 5) I TC 

Silane (SiH 4) EIV FP 

Silicon Tetrachloride (SiCL 4) EVX TC 

Silicon Tetrafluoride (SiF 4) IX TC 

Sulphur Hexafluoride (SF 6) X I 

Trichlorosilane (SiHCl 3) EV F(T)C 

Trimethylsilane ((CH 3) 5Si 4) V F 

Tungsten Hexafluoride (WF 6) V (T)C 

Xenon (Xe) X I 

KEY for Table 1. 

PROCESS 

C — crystal growth (silicon, gallium arsenide compounds) 

O — thermal oxidation 

E — epitaxy 

D — thermal diffusion 

I — ion implantation 

V — chemical vapor deposition (aluminum, polysilicon, silicon dioxide, silicon nitride, silicides, tungsten) 

M — metalization 

X — etching (aluminum, chromium, III-V compounds, ion milling, metal silicides and refractory metals, photoresist, polysilicon, silicon 

dioxide, silicon nitride) 

HAZARD 

F — flammable 

P — pyrophoric 

T — toxic (T)-toxic byproducts 

C — corrosive 

I — inert 

O — oxidizer 



2.1.1.1 Silane 

Silane, which is discussed in detail under Section 2.6, more so than other gases used in semiconductor manufacturing, 

can lead to severe exposures. It is a stable gas but is pyrophoric, that is, under certain conditions, 

it can spontaneously ignite. 

The trend today is to use higher concentrations of silane. In addition, silane is being used as a carrier gas 

for arsine and phosphine. In the event of a leak, the pyrophoric silane reaction would likely consume the 

poisonous arsine and phosphine. The process properties of silane mixtures can be found in Table 2. 

Percent Silane 

Table 2. Silane Mixtures 

Carrier Gas Hazard 

2.0 Inert Flammable 

>1.0 Any Flammable 

>2.0 Hydrogen Pyrophoric 

>3.0 Inert Pyrophoric 

2.1.1.2 Dichlorosilane 

Dichlorosilane (DCS) is a pyrophoric, toxic, corrosive and colorless gas. Its boiling point is 47°F (8.3°C). 

The minimum autoignition temperature is 111°F (44°C). 

DCS is used for a variety of chemical vapor deposition reactions. It is used to form epitaxial layers as well 

as silicon dioxide, silicon nitride, and polysilicon layers. 

DCS tends to slowly decompose during storage. This is only a problem in the presence of heat and/or catalysts 

such as amines or Lewis acids. Decomposition products are silane, monochlorosilane, trichlorosilane 

and silicon tetrachloride. 

Due to the corrosive nature of DCS, there is concern regarding its effect on carbon steel cylinders and valves. 

Therefore, no more than a 12-month shelf life is recommended. 

Minimum ignition energy (MIE) is 0.0154 mJ (second to hydrogen which is the lowest measured MIE). 

Combustion produces amorphous silica, water, hydrogen chloride gas, and chlorine. 

Due to its low vapor pressure (9 psi [0.6 bar]) and concern about proper distribution flow, there is a preference 

in the industry to locate process cylinders of DCS close to the process tool to minimize the length of distribution 

pipe. However, this results in process DCS cylinders being located in service chases and subfabs 

which, in turn, results in an unnecessary exposure to the cleanroom, process tools and related support 

equipment. 

Some facilities have overcome the low vapor pressure distribution flow issue by insulating and heat tracing 

the distribution piping. This allows them to locate process DCS cylinders in properly arranged process gas 

distribution rooms which do not expose the cleanroom, process tools and related support equipment. 

2.1.1.3 Trichlorosilane 

Another chlorinated silane gas is trichlorosilane (TCS) which is used to produce polycrystalline silicon and 

to form silicon epitaxial layers. With a boiling point of 89°F (32°C) and a flash point of 7°F (–14°C), TCS is 

normally found in liquid form. 

2.1.1.4 Chlorine Trifluoride 



Page 6 

Chlorine trifluoride is used to clean chemical vapor deposition (CVD) reactor chambers. It is a corrosive, colorless 

gas and a powerful oxidizer, which immediately ignites many organic compounds. It also ignites many 

metals at elevated temperatures, and reacts violently with water. Chlorine trifluoride is hypergolic, which 

means that it ignites organic fuels on contact. No ignition source or air is required. 

The installation of automatic sprinklers in gas cabinets containing chlorine trifluoride is not recommended 

due to its extreme reactivity with water. The reaction products with water include hydrogen fluoride, chlorine 

dioxide, hydrogen chloride and other hazardous by-products. In the event of a release, water is the major 


eaction source for chlorine trifluoride because it is normally readily available in the surroundings. Exposure 

to chlorine trifluoride in the presence of a relative humidity of 50% has been shown to cause significant 

corrosion in a short period of time to materials. 

Since chlorine trifluoride decomposes instantaneously when exposed to atmospheric conditions (moist air), 

the compound in its original form cannot be monitored or detected. The presence of chlorine trifluoride must 

be sensed through one of its by-products. 

Electrochemical detectors or paper tapes are two methods being successfully used to detect chlorine trifluoride 

through its by-products. Hydrogen fluoride (HF) is the major by-product of chlorine trifluoride reactions 

with moist air, however, detectors based on hydrogen fluoride do not have the capability to sense very low concentrations 

of HF (less than 0.1 ppm). For this reason, detectors calibrated for HF should only be used to 

detect high quantity chlorine trifluoride leaks. In critical areas where life safety is required, detectors calibrated 

for chlorine dioxide provide the most accurate indication of chlorine trifluoride. 

Detection based on HF, HCL, chlorine or fluorine are not recommended as they will not provide accurate 

detection at TLV or sub-TLV values of chlorine trifluoride. 

In air, chlorine trifluoride reacts rapidly with oxygen and water to form highly toxic and corrosive products, 

such as hydrogen fluoride, hydrogen chloride, fluorine, chlorine and chlorine dioxide. 

2.1.1.5 Hydrogen 

Hydrogen gas is widely used and is the primary carrier for the dopant gases such as silane, phosphine, arsine, 

diborane, etc. It can be found in both cylinder and cryogenic form. Even though the flammable and explosive 

properties of hydrogen are well documented, there have been numerous adverse incidents involving 

this gas. These incidents generally involve some kind of leak and ignition of the gas by many different sources. 

2.1.2 Photoresist, Developer and Rinse 



Page 7 

‘‘Photoresist,’’ its developer, and rinse make up the largest volume of flammable liquids used within the 

semiconductor fabrication area. A list of flammable/combustible liquids used in fabrication can be found in 

Table 3. The handling of flammable photoresist, developer and rinse in plastic containers represents a severe 

fire hazard. Large scale fire tests by FM Approvals have shown flammable liquids in plastic containers to 

be a severe fire hazard and special fire protection is warranted in accordance with Loss Prevention Data Sheet 

7-29. 



Table 3. Flammable and Combustible Liquids Used in Fabrication 

Solvent Name Classification 

Acetone IB 

Butyl Acetate IC 

Chlorobenzene IB 

Developer Ethylene Glycol IIIB 

Ethyl Lactate IB 

Ethylene Glycol Monomethyl Ether II 

Formaldehyde IIIA 

HMDS (Hexamethyldisilazane) IC 

Isopropyl Alcohol IB 

Methyl alcohol IB 

Methyl Ethyl Ketone IB 

Methyl Isobutyl Ketone IB 

N-Methyl Pyrrolidone II 

Phenol IIIA 

Photoresist IB, IC 

Propanol IB 

Tetraethylorthosilicate (TEOS) II 

Toluene IB 

1,1,1-Trichloroethylene IIIB 

1,1,1-Trichloroethane IIIB 

Trichlorobenzene IIIB 

Xylene IC 

The storage of flammable/combustible photoresist, developer and rinse within the fabrication area creates 

an unnecessary exposure to the cleanroom and process tools. If storage of these liquids inside the cleanroom 

is absolutely necessary, such storage should be arranged in accordance with Section 2.2.5 of the Data 

Sheet 7-7/17-12. 

The developing, rinsing, and etching portions of the fabrication process are typically performed in plastic 

work stations called wet benches (Figs. 17 and 18 in Data Sheet 7-7/17-12). Process liquids (both flammable 

and nonflammable) are often heated by using hot plates, electric immersion heaters, liquid heat transfer 

systems or steam heated bench inserts; more modern wet benches may use in-line, infrared heaters 

which are safer. 

2.1.3 Plastic Wet Benches 

There have been numerous and very costly fires involving the ignition of plastic wet benches by immersion 

heaters and hot plates. Once the plastic wet bench is ignited, the fire is usually drawn into the fume exhaust 

ductwork system. Depending on the combustibility of the ductwork, a fire involving the ductwork will then 

develop. 

2.1.4 Plastic Ductwork 



Page 8 

Plastic ductwork, such as fiberglass reinforced polyester (FRP), polyvinyl chloride (PVC), and polypropylene 

(PP) have been typically used to exhaust fumes of corrosive and flammable vapors and gases. In addition, 

fume exhaust systems have scrubbers constructed of FRP and PVC. During the doping and deposition 

processes (Table 4), unreacted silane and hydrogen gas are sometimes exhausted directly into the plastic 

ductwork. Numerous duct fires have started when unreacted silane and hydrogen gas ignited inside the 

ductwork. These fires have damaged from 1 to 100 ft (0.30 to 30.5 m) of ductwork. The amount of damage 

depends on the combustibility of the ductwork, intensity of the ignition source, size of the duct, physical 

arrangement (horizontal/vertical) of the ductwork system, presence or absence of combustible vacuum pump 

oil condensate and, most importantly, the presence or absence of internal automatic sprinkler protection. 


3 SiH4 Silane 

3 SiH2Cl2 Dichlorosilane 

SiH 4 

Silane 

SiH 4 

Silane 

SiH 4 

Silane 

SiH 2Cl 2 

Dichlorosilane 

SiH 4 

Silane 

SiH 2Cl 2 

Dichlorosilane 

SiHCl 3 

Trichlorosilane 

+ 4 NH3 Ammonia 

+ 10 NH3 Ammonia 

+ Heat 

Heat 

+ 4 CO2 Carbon 

Dioxide 

+ CO 

Carbon 

Monoxide 

+ 2 N2O Nitrous Oxide 

→ Si 

Silicon 

→ Si 

Silicon 

+ H 2 

Hydrogen 

Table 4. Process Reactions 

Chemical Vapor Deposition 

Silicon Nitride 

→ Si3N4 + 12 H2 Silicon Nitride 

Hydrogen 

→ Si 3N 4 

Silicon Nitride 

Poly Silicon 

→ Si (poly) 

Polysilicon 

Silicon Dioxide 

→ SiO2 Silicon Dioxide 

→ SiO2 Silicon 

Dioxide 

→ SiO2 Silicon 

Dioxide 

Epitaxy 

Pyrolytic Decomposition of Silane 

+ 2 H2 Hydrogen 

Reduction of Dichlorosilane 

+ 2 HCl 

Hydrogen 

Chloride 

Hydrogen Reduction of Trichlorosilane 

→ Si 

Silicon 

+ 6 NH 4Cl 

Ammonium 

Chloride 

+ 2 H 2 

Hydrogen 

+ 4 CO 

Carbon 

Monoxide 

+ 2 H2 Hydrogen 

+ 2 N 2 

Nitrogen 

+ 3 HCl 

Hydrogen 

Chloride 

+ 6 H 2 

Hydrogen 

+ 2 H 2O 

Water 

+ 2 HCl 

Hydrogen 

Chloride 

Various studies and loss experience have shown that if the fume exhaust ductwork does not collapse during 

a fire, the fume exhaust system will effectively remove smoke and heat. However, if the ductwork collapses, 

smoke contamination of the cleanroom is usually widespread. Once products of combustion are 

released from a collapsed duct, the cleanroom recirculating air system will pick up these products, and distribute 

them throughout the cleanroom in seconds. The need to keep the fume exhaust ductwork intact is critical. 

(See Section 2.4. FM Approved Duct Systems.) 

2.1.5 Vacuum Pumps 



Page 9 

Many of the semiconductor process reactions are performed under a vacuum as shown in Table 5. These 

include low pressure chemical vapor deposition and epitaxy. Vacuum pumps typically induce a vacuum on the 

process chamber while the source gas is injected into the chamber for deposition. A problem exists when residue 

hydrocarbon pump oil mist collects in the exhaust ductwork and ignites by an ignition source such as 

unreacted silane gas. This scenario has resulted in several high dollar loss fires in past years. 



Table 5. Vacuum Applications Used in Fabrication 

Fabrication 

heat treat (vacuum chucks and ovens) 

photoresist coat/softbake (vacuum chucks and ovens) 

align and expose (vacuum chucks) 

develop (some dry vacuum processes) 

hardbake (vacuum chucks and ovens) 

etch (plasma etch—vacuum)* 

photoresist strip (plasma O 2—vacuum) 

Deposition/Growth/Dopants 

low pressure CVD (vacuum)* 

plasma-enhanced LPCVD (vacuum)* 

photochemical LPCVD (vacuum)* 

low pressure epitaxy (vacuum)* 

ion implant (vacuum)* 

Metalization 

evaporation (vacuum) 

sputtering (vacuum) 

low pressure CVD (vacuum) 

Thermal Oxidation 

low pressure (vacuum)* 

Anneal/Drive-In 

low pressure furnace (vacuum) 

rapid thermal process (vacuum) 

laser annealing (vacuum) 

*Process may use flammable/pyrophoric gases 

2.1.6 Ion Implanters 

Ion implanters (Fig. 23 in Data Sheet 7-7/17-12) are used to modify surface characteristics of silicon wafers 

by accelerating dopant ions of various materials to embed them into the surface of the silicon wafer. The 

total voltage of the ion source with respect to ground determines the energy of the ions, which in turn determines 

the depth of penetration of the ions into the wafer. 

Ion implanters are located in the cleanroom. The working components of an implanter are surrounded by 

an enclosure usually of sandwich panel construction consisting of a conductive inner surface, a plastic or balsa 

wood core, one or more thin layers of lead shielding and a plastic composite exterior. 

Most implanters utilize one or more transformers to deliver ac power and high voltage dc (HVDC) to sections 

of the implanter which are not at ground potential. 

2.1.6.1 Ion Implanter HVDC Power Supply 

The HVDC required by the implanter are produced by power supplies within the enclosure. The HVDC power 

supply transformer may be either oil filled or dry type and is usually rated at 5 to 10 kVA. If oil filled, it may 

contain from 20 to 40 gal (75 to 151 liters) of oil. Since the high voltage power supply provides the HVDC, 

it must remain in the ion implanter enclosure. If the power supply includes an oil filled transformer, the best 

solution is to replace the transformer with a dry type transformer. 

2.1.6.2 Ion Implanter Isolation Transformer 



Page 10 

The purpose of the isolation transformer is to isolate the ac power input from the high dc voltage section of 

the ion implanter. The transformers have ratings from 5 to 75 kVA. They may operate with isolation voltages 

in excess of 100 kV between their primary and secondary windings. These transformers are mineral 

oil insulated and may contain from 15 to 200 gal (57 to 757 liters). 

Nominal ac input is 208 V or 480 V. The transformer secondary voltage is usually 208 V ac plus the dc bias. 

The transformer secondary neutral is connected to the sections of the implanter which are not at ground 

potential (electrostatic shield) and whose potential is at 100 kV or higher. The total transformer secondary 

voltage is therefore 208 V ac biased at 100 kV dc or higher. 

Mineral oil filled power supply and isolation transformers used in ion implanters do not have ANSI standard 

nameplates and do not appear to be constructed to any ANSI transformer standard. The transformers may 

not have a pressure relief device. They may not have an oil sampling valve where oil samples could be pulled 


for dielectric and dissolved gas in oil analysis. Isolation transformers experience both high temperatures and 

high voltages so testing to detect gassing is critical. The transformer tank withstand strength is unknown. Isolation 

transformers with a 208 V primary are electrically protected by 240 V circuit breakers similar to what 

is used in the home. These breakers may have interruption capability as low as 10,000 amps. Fault currents 

higher than this may occur and breakers of larger interrupting capability will be required. Current limitation 

is not provided on the primary. Ground fault protection is not feasible on the secondary because the 

transformer neutral is connected to the HVDC. 

2.1.6.3 Ion Implanters — National Electric Code (NEC) Requirements for Transformers 

Oil insulated transformers installed indoors must be installed in accordance with the provisions of the NEC. 

The following is quoted directly from NFPA 70-1996, National Electrical Code, Article 450 Transformers and 

Transformer Vaults: 

Article 450-26. Oil-insulated Transformers Installed Indoors. ‘‘Oil-insulated transformers installed indoors shall 

be installed in a vault constructed as specified in Part C of this article.’’ There are several exceptions to this 

rule. Exception 1 and 2 may be applicable. 

‘‘Exception No. 1: Where the total capacity does not exceed 112.5 kVA, the vault specified in Part C of this 

article shall be permitted to be constructed of reinforced concrete not less than 4 in. (102 mm) thick.’’ 

‘‘Exception No. 2: Where the nominal voltage does not exceed 600, a vault shall not be required if suitable 

arrangements are made to prevent a transformer oil fire from igniting other materials, and the total capacity 

in one location does not exceed 10 kVA in a section of the building classified as combustible, or 75 kVA 

where the surrounding structure is classified as fire-resistant construction.’’ 

The phrase ‘‘total capacity’’ in the above refers to adding the kVA of all of the transformers in the section 

of a building. If one had 4 transformers each rated 30 kVA, the ‘‘total capacity’’ would be 120 kVA. A vault 

in accordance with Article 450, Part C. Transformer Vaults of the NEC would therefore be required. 

At the May, 1998 NFPA meeting an exception to NFPA 70, National Electric Code, Article 450 ‘‘Transformers 

and Transformer Vaults’’ was granted. This exception was submitted by the implanter manufacturers and 

reads as follows: 

‘‘Section 450-26, Exception No.4: A transformer that is an integral part of charged particle accelerating equipment 

having a total rating not exceeding 75 kVA shall be permitted to be installed without a vault in a building 

or room of noncombustible or fire-resistant construction, provided suitable arrangements are made to 

prevent a transformer oil fire from spreading to other combustible material.’’ 

This exception effectively allows oil filled ion implanter transformers up to 75 kVA rating to be allowed in a 

cleanroom. By this exception, multiple implanters containing several hundred gallons of mineral oil each could 

be located in the same room. 

Changes to the exception may still result as it is currently being challenged. 

2.1.6.4 American National Standard for Transformers - C57.12.22-1989 



Page 11 

The following excerpted sections from the ANSI C57.12.22 – 1989 standard are provided below and form 

the basis for the electric safeguard recommendations (see recommendation 2.5.13.1.2 in Data Sheet 7-7/17- 

12) concerning oil filled transformers in ion implanters. 

7.5.2 A replaceable valve shall be provided to relieve pressures that build up slowly in excess 

of normal operating pressures. These excess pressures may be due to overloads, high ambient 

temperatures, external secondary faults, and incipient faults in the low voltage winding. When 

relieving these excess pressures, the valve shall emit only a negligible amount of oil. The valve 

shall be furnished in the low-voltage compartment on the tank wall above the 140°C top oil level, 

by the manufacturer’s calculation, and shall be located so as not to interfere with use of the lowvoltage 

terminals or the operating handle of the low-voltage circuit breaker. The inlet port shall 

be ¼ inch or larger NPT ( or NF thread with gasket), sized for specified minimum flow rate. Exposed 

parts shall be of weather-and corrosion-resistant materials. Gaskets and O-rings shall withstand 

oil vapor and 105°C temperature continuous under operation conditions as described in 

ANSI/IEEE C57.91-1981 and ANSI/IEEE C57.92-1981, without seizing or deteriorating, for the life 

of the transformer. The valve shall have a pull ring for manually reducing pressure to atmospheric 

using a standard hook-stick and shall be capable of withstanding a static pull force of 25 lb 



(11.34 kg) for one minute without permanent deformation. The valve shall withstand a static force 

of 100 lb (45.36 kg) for one minute applied normal to its longitudinal axis at the outermost extremity 

of the body. When specified, the venting port, on the outward side of the valve head set, shall 

be protected to prevent entry of dust, moisture, and insects before and after the valve has actuated; 

or a weather-cap-type indicator shall be provided, which will remain attached to the valve 

and provide positive indication to an observer that the valve has operated. Venting and sealing 

characteristics shall be as follows: 

7.6 Tanks 

Cracking pressure: 10 psig ± 2 psig 

Resealing pressure: 6 psig minimum. 

Zero leakage from resealing pressure to –8 psig. 

Flow at 15 psig: 35 SCFM minimum (where SCFM 

is flow at cubic feet per minute corrected for air 

pressure of 14.7 psi and air temperature of ° 21.1C) 

7.6.1 The tank shall be of sufficient strength to withstand a pressure of 7 psig without permanent 

distortion; and 15 psig without rupturing or affecting cabinet security as described in ANSI 

C57.12.28-1988. A 1-inch NPT upper plug (or cap) for filling and pressure testing shall be provided 

in the low voltage compartment. A 1-inch NPT drain plug (or cap) for transformers rated 

75-500 kVA and 1-inch NPT drain valve with built-in sampling device for transformers rated 750- 

2500 kVA shall be provided in the low-voltage compartment. Suitable means for indicating the correct 

liquid level at 25°C shall be provided. 

2.1.6.5 Ion Implanter Loss Experience 

No fires have been reported in mineral oil insulated transformers in cleanrooms. However, all of the major 

fire loss experience in the five year period analyzed in Data Sheet 5-4 Transformers has involved mineral oil 

insulated transformers. During this period there were 13 fires involving mineral oil filled transformers inside 

buildings. In all but four incidents, damage was limited to the transformer, adjacent cable and switchgear. 

In four incidents damage was substantially larger than expected. One incident involved damage to the automatic 

sprinkler system. The loss of protection resulted in damage to switchgear and cable in this large room. 

In a second incident, wall and ceiling penetrations were not sealed. This resulted in fire and smoke damage 

to an MCC room above the transformer room. The other two incidents involved PCB contamination. The 

cost of cleanup of PCB contamination in an industrial facility would probably be on the order of magnitude 

of the cost of cleanup of heavy smoke deposits in a cleanroom. 

2.1.7 Diffusion 

The high process temperature (1652°F–2372°F [900°C– 1300°C]) and use of process gases such as 

phosphine, arsine, diborane, boron trichloride in a hydrogen carrier makes diffusion one of the most hazardous 

processes in the manufacture of semiconductor devices. A vertical furnace used in the diffusion process 

is shown in Figure 24 (see Data Sheet 7-7/17-12). Numerous adverse incidents have occurred and 

generally business interruption was considerable since diffusion is the workhorse of the doping process. 

These incidents included ignition of unreacted pyrophoric and/or flammable gases, ignition of combustible 

vacuum pump oil residue and backstreaming of vacuum pump oil. A foreline trap or antibackstreaming device 

should be installed between the vacuum pump and quartz tube in all diffusion furnaces where backstreaming 

is thought to be possible. This device is an optically dense, wool type filter barrier reinforced with copper 

or stainless steel mesh. The filter will cause the oil to condense and drop back into the vacuum pump. 

2.1.8 Spill Hazard 



Page 12 

The use of hydrofluoric, sulfuric, hydrochloric, nitric and other acids constantly presents a spill hazard 

potential. Certain cleanroom designs utilize a perforated raised floor and/or an open waffle slab (see Figs. 

4 and 5 in Data Sheet 7-7/17-12). A spill of these acids through such open floors could contaminate the cleanroom 

via the recirculating air system or cause corrosion damage to equipment below. In addition, a spill of 

flammable liquids through open floors could result in a flammable liquids fire below the floor. 


2.2 Fire Hazards of Wet Benches 

Wet benches (see Figs. 17 and 18 in Data Sheet 7-7/17-12) are used in the semiconductor industry for the fabrication 

of integrated circuits. Due to exposure to atmospheres which corrode metal, wet benches are typically 

constructed from plastic material; polypropylene (PP) or fire-retardant polypropylene (FRPP) have been 

commonly used in the United States. Polyvinylchloride (PVC) is commonly used in Japan and is increasingly 

being used in facilities operated by Japanese companies in the United States. Wet benches also contain 

a considerable amount of electrical equipment which represent a potential ignition source. Over the past 

10 years, 40 wet bench fires have been reported to FM Global. 

2.2.1 Fire Tests Conducted by FM Approvals on Wet Benches 



Page 13 

FM Approvals has conducted extensive fire testing on plastic wet benches to evaluate fire propagation and 

fire suppression. For these tests, 8 ft (2.4 m) long, open face-style wet benches were used. 

The first of these tests was a free burn test conducted under the FM Approvals fire products collector. The 

objective of these tests was to evaluate fire propagation within a bench constructed of polypropylene once 

ignition had been established in the bench. This test showed that fire developed rapidly after an incubation 

time of approximately 10 minutes. Peak heat release rate exceeded 10 MW and the entire bench was consumed 

during the test. Figure 2 shows the bench at peak fire involvement. 

Fig. 2. Wet bench free burn test. 

Fire suppression tests were conducted on wet benches placed in a mockup cleanroom facility constructed at 

FM Global Research. In this facility, typical cleanroom ventilation and wet bench exhaust systems were 

installed, so that typical air velocities and flow rates could be maintained in both the room and wet bench. 

All fire suppression tests were conducted with the room ventilation system and wet bench exhaust system in 

full operation. Three different fire suppression systems were tested: fine water spray (FWS), carbon dioxide 

(CO 2), and FM-200. These suppression systems were tested with fires of different sizes placed at the 

bench working surface and subsurface areas. Fire tests were also conducted with FWS in unventilated 



spaces. Results of these tests were successful and formed the basis for design and installation protection criteria 

offered for each of these systems in this data sheet. 

2.3 FM Approvals Cleanroom Materials Flammability Test Protocol (Class 4910) 

FM Approvals has developed a specification test standard titled FM Approvals Cleanroom Materials Flammability 

Test Protocol (Class 4910). This standard evaluates the fire hazard of materials used in environments 

which are highly sensitive to thermal and nonthermal damage, such as the interiors of cleanrooms 

in the semiconductor industry. All requirements in the standard must be met for materials to be acceptable 

in cleanrooms. 

The protocol uses three small-scale tests and a large-scale validation test if needed. Small-scale tests 

performed in the FM Approvals Flammability Apparatus are: 

Ignition Tests 

Fire Propagation Tests 

Combustion Tests 

This is a performance-based test protocol. Based on results of the three small-scale tests, the following 

indexes are determined for each material tested: 

1. Fire Propagation Index (FPI): this index is determined based on the fire propagation tests conducted and 

represents the rate at which the surface of the material is involved on fire. Nonpropagating materials have 

FPI values at or below 6.0 (m/s 1/2 )/(kW/m) 2/3 . 

2. Smoke Development Index (SDI): this index is defined as the product of the FPI index and the yield of 

smoke for a given material. SDI is an indicator of the smoke contamination of the environment expected during 

fire propagation. Materials expected to limit smoke contamination have SDI of 0.4 [(m/s 1/2 )(g/g)(kW/m) 2/3 ] 

or less. 

Materials that are FM Approvals Specification Tested to meet the flammability protocol criteria require high 

heat fluxes to be ignited; once ignited these materials may burn locally in the ignition area, but they will not 

propagate a fire beyond the ignition zone. Smoke and corrosive products generated from the combustion 

of these materials is reduced, minimizing nonthermal damage. 

Table 6 lists material nomenclature and use in cleanrooms. 

Plastic 

Table 6. Material Nomenclature and Use 

Use in Cleanrooms 

Polypropylene (PP) wet benches, ductwork, wafer boxes, process equipment enclosures, wall panels 

Fire Retardant Polypropylene (FRPP) wet benches, process equipment enclosures 

Polyvinylchloride (PVC) wet benches, ductwork, process piping, process equipment enclosures 

Polyvinylidene Fluoride (PVDF) process piping, chemical baths 

Polyether ether ketone (PEEK) wafer carriers 

Fiberglass Reinforced Plastic (FRP) ductwork, scrubbers, wall panels 

Polycarbonate (PC) mini-environment enclosures, valve manifold boxes, wafer boxes 

Polymethymethacrylate (PMMA) mini-environment enclosures, valve manifold boxes 

Polyethylene (PE) process piping, process equipment enclosures, wafer boxes 

Perfluoroalkoxy (PFA) process piping, chemical baths 

Polytetrafluoroethylene (PTFE) wet benches, coating on stainless steel ductwork 

Polyphenylene Oxide (PPO) exhaust ducts 

Polyoxymethylene, or Delrin (POM) not used in cleanrooms except for fire protection fine water spray nozzles 

2.4 FM Approved Duct Systems 



Page 14 

FM Approvals approves duct systems designed for general purpose use in exhausting noncombustible corrosive 

fumes, vapors and/or smoke. In cleanrooms of the semiconductor industry FM Approved Duct Systems 

can be utilized without the need for automatic sprinkler protection subject to the restrictions shown in 

the Approval Guide, a publication of FM Approvals. 


FM Global Research does not limit vertical runs of duct to any particular length. FM Global Research limits 

the height of the riser to the actual height that was tested. While most manufacturers have chosen to test 

15 ft (4.6 m), several manufacturers have successfully tested risers longer than 15 ft (4.6 m) as shown in the 

Approval Guide. 

Compatibility of the duct system for the end use application is determined by the manufacturer of the duct system; 

however, further investigation is underway into the methods used to determine the compatibility of duct 

systems to the end use application. This is necessary because of the many variables and the lack of 

consistent pass/fail criteria used in industry today. 

While there have been no failures documented by FM Global for Approved ducts used and installed as 

described in this data sheet, failures of FM Approved ducts have been reported when the duct system was 

used to handle corrosive liquids or when condensate was allowed to accumulate in the duct system; failures 

have also been reported for duct systems installed with improperly prepared joints. In both these conditions, 

the duct systems were being utilized outside their intended use or were not installed according to 

the manufacturers’ recommendations. 

2.5 Fire Hazards of Stockers 

Stockers (see Fig. 22 in Data Sheet 7-7/17-12) are self-contained storage units located inside cleanrooms. 

Stockers are used for storage of in-process and finished wafers and masks. Wafers are commonly stored 

in plastic boxes which are placed in open storage shelves along the side walls of the stocker. Wafer boxes 

are normally arranged one deep in each tier; each tier is approximately 1 ft (0.30 m) high and the storage normally 

fills the entire height of the unit. Masks are typically stored in clear plastic cases also placed in a shelf 

arrangement. 

Wafer stockers typically have a total width of 4.0 ft (1.2 m), a total height of 12 ft (3.6 m) with lengths varying 

for 8 ft (2.4 m) to 18 ft (5.4 m), normally in 2 ft (0.60 m) increments. Mask stockers are typically smaller 

than wafer stockers. 

Abundant fuel (the plastic boxes) is present in wafer and mask stockers and the most likely ignition sources 

are from electrical equipment and components inside the stocker. 

Protection guidelines for stockers are based on full scale fire tests conducted by FM Approvals on a simulated 

wafer stocker. 

2.6 Silane Gas 



Page 15 

Silane (SiH 4) is a pyrophoric gas whose mixture with air can self ignite at room temperature. Silane can be 

found in gas cabinets and open manifold racks and is used in various processing tools such as furnaces 

and epitaxial reactors. 

FM Global Research has conducted novel studies on the behavior of accidental releases of 100 percent 

silane and a 10 percent mixture of silane and nitrogen inside enclosures. These studies have dispelled several 

myths about silane behavior and have shown that self ignition of silane following an accidental release 

is a complex phenomenon, governed by many variables such as the line pressure and diameter, and size 

and geometry of the release. Self ignition of the gas immediately following an accidental leakage (start-up) 

or at flow shut-off is expected to occur, for example, in about 50 percent of those cases where the release 

is from a 1/4-in. (6.4 mm) diameter line with pressures within 100 to 300 psig (7 to 21 bars). The ignition probability 

increases significantly at line pressure below 50 psig (3.5 bars). The studies have also shown that 

self ignition may not occur at all times immediately following an accidental release of silane or silane mixtures. 

Mixtures that do not immediately ignite following an accidental release may self ignite at flow shutoff 

or, if the concentration is allowed to go beyond critical values, unstable mixtures may be formed which will 

result in bulk autoignition with catastrophic consequences. 

The recommendations in this data sheet cover all ignition scenarios that might occur during accidental 

releases of silane. When applied, the recommendations will limit damage to the cabinet of origin. Compliance 

with the recommendations will help control the maximum pressure rise inside the enclosure and exhaust 

duct system following self ignition of the gas at flow startup or at flow shutoff. Compliance with the recommendations 

will also prevent silane concentrations from reaching critical limits where the mixture is unstable 

and bulk autoignition would occur. 



Accidental releases followed by self ignition of the gas will generate a pressure rise inside the enclosure 

and a localized fire that can be kept confined to the cabinet of origin by installing automatic sprinkler protection 

inside the gas cabinet per section 2.2.12, Process Gas Cabinets in Data Sheet 7-7/17-12. 

Gas cylinders containing silane are required by code (Uniform Fire Code and others) to be equipped with 

a restrictive flow orifice (RFO) in the CGA fitting. The RFO is intended to limit the flow of gas in the event of 

a failure of the pressure regulator. Current code requirements are for RFO’s with a diameter of 0.010 in. 

(0.25 mm) or less. 

The work conducted by FM Global Research has provided new insights on the behavior of silane and on 

the RFO effects on the accidental discharge of a line. Based on the results of this work and, on the current 

trend in the industry for better usage of silane, the use of RFOs with diameters of 0.020 in. (0.50 mm) is 

likely in the near future. 

2.7 Electrical Exposure 

Clean and reliable electrical power (see Fig. 6 in Data Sheet 7-7/17-12) is the most critical utility at a semiconductor 

facility. Because most process tools are microprocessor controlled, a voltage dip of more than 

10% (nominal voltage), lasting for more than 5-10 cycles will cause the process tools to abort their cycle run. 

This will typically result in spoilage of any wafers in the tool, in addition to downtime to return the tool to production. 

This could take from a few minutes to 12 to 48 hours depending on the type of tool. Tools with cryogenic 

pumps, as well as steppers generally take the longest to restart. 

These voltage dips can be caused by utility switching operations, recloser operation, or on-site electrical 

equipment failures. These can also result in total power outage to the plant or a portion of the plant. There 

are various choices of technology combinations available today for critical power users. Nearly all configurations 

will satisfy the need to protect critical loads by isolating them from disturbances coming from the utility 

supply grid. 

The bottom line goal is that no failure of a single piece of equipment (transformer, cable, breaker and/or switchgear 

line-up, junction box, etc.) should result in extended downtime of the fab, while maintaining clean stable 

power to the production tools and facilities equipment. 

Fab production demands often require that these facilities operate 365 days a year without any major shutdowns. 

If this is the case, the electrical system will have to be designed such that all electrical system maintenance 

can be performed with no disturbance to operation of the fab. This means all areas of the electrical 

system can be shut down and power can still be fed to the fab through redundant equipment, thus production 

can continue. 

2.8 Deionized (DI) Water Systems 

DI water is different than most other water systems. Because this is ultrapure water, it can only be stored 

for about 6 to 8 hours before it becomes contaminated with bacteria to the point that it cannot be used. For 

this reason, there will be no large storage tanks of final DI water and this water must be produced on a 

continual basis. 

3.0 PROCESS OVERVIEW 



Page 16 

Producing a state-of-the-art semiconductor device, also known as an integrated circuit (IC) or ‘‘chip,’’ is truly 

an extraordinary process. Silicon, a fundamental component of sand, is a tetravalent, nonmetallic element 

that occurs in combined form as the earth’s second most abundant element next to oxygen. It is processed 

through several hundred steps into devices which are used in a wide range of applications. 

Silicon has the same crystalline structure as a diamond, but it is only as hard as glass. It is also a semiconductor 

which means it is halfway between a conductor which carries electricity easily (like the copper wire 

used in domestic lighting circuits) and an insulator which prevents electricity from flowing (like the plastic 

sheath around the wires). Its conductivity can be easily altered by adding minute ‘‘dopants’’ to its crystalline 

structure. Other semiconductor materials include gallium arsenide, germanium, indium arsenide and a 

combination of sapphire and silicon. The use of silicon is currently the most popular, but gallium arsenide technology 

is rapidly gaining popularity. This is because gallium arsenide can move electricity faster than silicon 

and can generate light impulses, which silicon cannot do. 

Flow and system diagrams of semiconductor fabrication are shown in Figures 3 and 4. 




Page 17 

Notes: 

1. Optional step, almost all facilities purchase wafers from an outside supplier. 

2. Masks may be supplied from an outside supplier. 

3. Mask may be replaced with direct writing on wafers (not very common). 

4. Most of the time these operations are performed at other facilities. 

Fig. 3. Flow diagram of semiconductor fabrication. 





Page 18 

Fig. 4. Semiconductor fabrication facility systems diagram. 

In addition to the production of electronic circuits, electro-optical and electro-magnetic devices are also produced. 

These devices are made on wafers in cleanrooms with similar processes. Photocells for converting 

light energy to electrical energy and sensors for measuring UV, visible, and IR electromagnetic waves 

are made using the deposition, photolithography, and etching processes. Electromagnetic devices, such as 

read-write heads for magnetic disc drives are also made using similar processes in cleanrooms. 

Crystal production involves the growing of silicon crystals in electrically heated, argon-atmosphere vacuum 

furnaces operating at a temperature above 1400°F (760°C). As with all crystal growing, a seed crystal is 

required to set the process in motion. When the growing process is complete, the silicon ingot is brought to 

room temperature and the seed is removed from the crystal. Years ago the diameter of the ingot was only 

1/2 in. (13 mm). Six in. (150 mm) and 8 in. (200 mm) ingots are common today and 12 in. (300 mm) versions 

are in the development stages. 

In the cut and grind operation, the ends of the polysilicon crystal are removed and the uneven exterior is 

ground to achieve uniformity. The silicon ingot is then sliced into wafers. This can be done using either 

multiwire saws that make numerous cuts at once, or with a diamond edge circular saw. These slice the ingot 

into 14 to 30 mil (0.36 to 0.76 mm) wafers. (This is about the thickness of a business card.) About 28 wafers 

are cut from each inch of the ingot. 

After slicing, the wafers are lapped to remove the saw marks. The wafers are mounted to the equipment 

which features an abrasive slurry on a revolving disc. An acid etch process performed in plastic wet benches 

follows to remove the lap marks. 

Wafers are then polished with a diamond paste to a mirror-like finish. Finally, the wafers are either given a 

thin surface layer of silicon dioxide in an oxidation furnace (metal oxide semiconductor [MOS] process) or silicon 

in a epitaxial reactor (bipolar process). At this point, the wafers are ready for building the circuits on 




Page 19 

the silicon substrate. Most chip manufacturers purchase wafers from an outside supplier, but some facilities 

make a small portion of wafers needed for processing. 

Gallium arsenide crystal is more brittle and it is more difficult to grow a single crystal than silicon; so 2 in. 

(50 mm), 3 in. (75 mm), and 4 in. (100 mm) wafers are typically used. Gallium arsenide circuits are sometimes 

grown on germanium wafers due to the lower cost of germanium. 

Mask production involves transferring a large circuit drawing to a glass plate called a mask. The mask contains 

hundreds of exact reproductions of the original art work and is used later to recreate the pattern on 

the wafer surface. Each mask contains the pattern for a single layer of the circuit, so many masks are used 

to fabricate the entire integrated circuit or chip. The mask surface may be an emulsion, chrome, iron oxide 

or silicon monoxide. Most masks are fabricated from chrome on glass. Two different techniques used to produce 

masks are known as reticle and electron beam technology. 

The circuit design process starts with a determination of the functioning of the circuit. A logic diagram of the 

circuit is developed and then translated to a schematic diagram which shows the location of the various components. 

The circuit components are then translated to their relative final dimensions, as they will be formed 

in and on the wafer surface. A sophisticated computer-aided design (CAD) system then draws a composite 

picture of the circuit surface showing all of the sublayer patterns. 

The reticle is a miniaturized reproduction of one layer of the circuit. The actual size of the pattern on the 

reticle is normally ten times the final size (10 X) of the pattern on the wafer. A reticle is an emulsion or chrome 

photo plate that is selectively exposed to light in a pattern generator. The computer tape from the digitizing 

operation instructs the shutter system to open and close, exposing the reticle in the exact pattern of the 

original drawing. 

The pattern on the reticle is transferred to the mask in the step and a repeat operation. The reticle is positioned 

over one corner of the photoresist coated mask blank and a light source transfers the pattern on the 

reticle into the photoresist. After the first pattern is transferred, the machine ‘‘steps’’ the reticle to the next position 

and repeats the pattern in the next location. This process continues until the entire mask surface is filled 

with the reticle pattern. 

Electron beam technology is used to make masks which produce more advanced circuits. An electron beam 

writer is similar to a scanning electron microscope. The coated mask is placed in a vacuum chamber and 

an electron beam directed at it. The pattern information stored on the tape at the digitizing operation is used 

to direct the electron beam to the correct locations to expose the photoresist. The pattern is written onto 

the mask without a reticle. 

The fabrication or main part of the process involves repeated steps of photoresist, masking, etching, doping, 

and deposition. These processes are typically performed in cleanrooms. Photoresist and its developer are 

the largest volume solvents within the fabrication area. Negative photoresist is a photosensitive polymer suspended 

in a flammable organic solvent base such as xylene or toluene. It is used to coat the wafer in preparation 

for transferring the pattern of the circuit from the mask to the wafer. The wafers are coated by 

dispensing a small quantity of photoresist on the wafer and rapidly rotating on a ‘‘spinner’’ which spreads a 

thin uniform layer. Photoresist materials are classified as either negative or positive resists, depending on 

whether the solubility in the developer decreases (negative) or increases (positive) upon exposure to a UV 

light source. Since photoresist is sensitive to light, it is shipped, stored and dispensed to the areas in brown 

glass or plastic bottles. 

Photoresist adjuncts, a variety of chemical liquids and gases, are used to promote the adhesion of the photoresist 

coating to the wafer. Hexamethyldisilazane (HMDS) is the most widely used chemical for adhesion 

and is spun onto the wafer surface prior to photoresist application. 

After the wafers are coated with photoresist, they are ‘‘soft baked’’ to evaporate a portion of the solvents in 

the photoresist. Methods used to soft bake include hot plates and the following different type ovens: convection, 

vacuum, moving belt IR, microwave and conduction belt. After the baking has been concluded, the 

actual photomask process takes place. 

Photomasking is a process of alignment and exposure. The different types of equipment used for this process 

can vary in size, overall appearance, method of operation and equipment cost. This equipment includes 

contact aligners, projection aligners, and wafer steppers. The function is the same in that the wafer is placed 

onto this machine and a specific patterned ‘‘mask plate’’ is placed over the wafer. The wafer is then aligned 





Page 20 

with the mask plate, and then exposed through the action of the shutter of the machine opening to allow ultraviolet 

light to hit the unmasked portion of the wafer. 

After the wafer has been aligned and exposed, the next step is developing. In developing a wafer, a machine 

similar to a ‘‘spinner’’ is used. The developing is done by chemicals which are sprayed down onto the wafer. 

This spray washes away the nonexposed resist (areas where the light was not allowed to pass through the 

mask plate) while the exposed or ‘‘polymerized’’ resist remains. The preferred developing chemical for negative 

photoresist is xylene. A Stoddard solvent may also be used in certain cases. Positive photoresist is developed 

in an alkaline solution, such as potassium hydroxide or sodium hydroxide. 

Other flammable solvents are also used in the wafer fabrication process. Butyl acetate and isopropyl alcohol 

will be used as washes for wafers after they have been developed with negative resist. D.I. water is more 

commonly used with positive photoresist as a post develop wash. 

Etching removes layers of silicon dioxide, metals and polysilicon as well as resists, according to desired 

patterns delineated by the resist. The two major categories of etching are wet and dry chemical. Wet etching 

is predominantly used and involves solutions containing the etchants (usually an acid mixture) at the 

desired strengths, which react with the materials to be removed. Plastic wet benches and plastic fume exhaust 

ductwork are typically used in wet etching operations (Figures 17 and 18 of Data Sheet 7-7/17-12). Dry etching 

involves the use of reactive gases (hydrogen chloride, ammonia, etc.) under vacuum in a highly energized 

chamber, which also removes the desired layers not protected by resist. 

To form the junctions where current will flow, a controlled number of impurities or dopants must be introduced 

into a selected region of the wafer either by diffusion or ion implantation. Diffusion is a high temperature 

(1652°F to 2372°F [900°C to 1300°C]) process in which certain chemicals (dopants) are introduced into 

the surface layer of the semiconductor material to change its electrical characteristics. Diffusion is the most 

established method of applying dopant material. Ion implantation is a technique for doping impurity atoms into 

an underlying substrate by accelerating the selected dopant ion towards the silicon target through an electrical 

field. Ion implantation is often preferred over standard diffusion methods because it is more precise, 

faster and less expensive. Annealing usually is required following ion implantation because of the structural 

damage caused by bombardment of the substrate by the accelerated ions. 

The need for annealing after ion implantation led to the development of a technology called Rapid Thermal 

Processing (RTP). This process, which takes place in seconds, eliminated the need for a minutes-long 

process in a tube furnace, which had undesirable side effects of migration of dopant atoms within the wafer. 

Also, every time a wafer is heated near diffusion temperatures and then cooled down, crystal dislocation 

forms, which can result in circuit failures. In the single wafer RTP tool, radiation heating (usually from tungsten 

halogen lamps) is very rapid and the body of the wafer never comes up to temperature. Annealing can 

take place without undesirable side effects. The trend to small feature sizes on wafers has also lead to thinner 

layers. Thermally grown gate oxide layers now may be less than 100 Angstroms thick. RTO ( Rapid Thermal 

Oxidation) tools are similar to the RTP annealing tools but have an oxygen atmosphere in the chamber 

rather than an inert gas. RTP technology is now used in various oxide, nitride and silicon layer processes. 

Deposition is the process of placing additional layers onto the wafer surface, either by epitaxial or chemical 

vapor deposition (CVD). Chemical vapor deposition is the process of forming a thin film on a substrate by 

the chemical reaction of various gases. CVD is usually promoted by heating the substrate, either at atmospheric 

pressure, or low pressure (LPCVD). Epitaxy is the process of depositing a crystalline layer having the 

same structure as the substrate. Epitaxy represents a special form of chemical vapor deposition. Often, 

epitaxial layers are grown with intentionally added impurities such as boron or phosphorus. These change 

the electrical conductivity of the crystalline silicon. Some of the more common process reactions can be found 

in Table 6 of Data Sheet 7-7/17-12. 

The photoresist, masking, etching, doping and deposition processes are repeated many times until the complete 

circuit is produced. 

After the final diffusion step, the devices which have been fabricated into the silicon wafer must be connected 

together to perform circuit functions. This process is known as metalization. Metalization provides a 

means of wiring or interconnecting the uppermost layers of integrated circuits by depositing complex patterns 

of conductive material, which route electrical energy within the circuits. To do this, a conductive metal is either 

sputtered or evaporated over the front of the wafer. A photoresist pattern is then aligned over the metal and 

some of it is etched away, leaving the desired metal coverage. The most common metals used for metalization 

are: aluminum, nickel, chromium, gold, copper, silver, titanium, tungsten and platinum. 


The final step in wafer form of integrated circuit manufacturing is testing. During the electrical test, (e.g., 

‘‘die sort,’’ ‘‘wafer sort,’’ ‘‘wafer probe’’), each circuit or die is tested for its ability to perform the operations 

for which it was designed. As each die or chip is tested, a computer records certain information about it. If a 

die is not acceptable, that is, if it fails any one or more of the tests, a small droplet of ink is automatically 

placed on the die so that when the wafer is separated into individual die the bad or ‘‘inked’’ die can be 

discarded. 

3.1 Effluent Gas Conditioning Systems 

After the various gases are used in the semiconductor manufacturing process, the resulting effluent must 

be neutralized prior to discharge. Current disposal methods include dilution systems, scrubber systems, 

adsorption systems and thermal processing systems. 

Dilution systems lower the concentration of exiting gas streams by flooding them with an inert gas such as 

nitrogen. Although dilution systems reduce the concentration of pyrophoric/flammable gases so they will not 

burn, the systems are not reliable for handling unexpected surges and dumps which create higher than 

expected gas flows. 

Another problem with dilution systems is that the exiting gas stream can include combustible vacuum pump 

oil that has been carried into the duct system. Since dilution systems cannot treat the vacuum pump oil, a significant 

amount of oil can build up inside the ducts. This oil buildup provides a source of fuel which, when 

ignited, has caused significant fire damage to ductwork. Even with demisters in the lines, oil will continue to 

be carried in the exiting gas streams because demisters lose their removal efficiency over time. 

Scrubbing is another method of conditioning the exhaust effluent. Scrubbers are grouped into two classifications. 

The first classification is a water scrubber used for conditioning exhaust streams containing water 

soluble gases such as hydrogen chloride, ammonia, etc. The second classification is a chemical scrubber 

used for conditioning exhaust streams containing gases which are nonsoluble in water such as silane, phosphine, 

arsine, etc. Chemicals such as sodium hydroxide or potassium permanganate are added to water 

to form a solution which is effective for scrubbing gases which are not soluble in water. 

Adsorption is the physical adhesion of gas molecules to the surfaces of solid substances with which they 

are in contact. Generally, adsorption methods are useful for applications where only small quantities of materials 

are produced, because the capacity of adsorption systems typically lack the ability to process large 

amounts of effluent in a short period of time. In addition, the adsorption medium needs to be recharged either 

by replacing the medium, desorbing with heat or oxidizing the volatile organic compounds with ozone. 

Thermal processing is a method of controlled combustion of the gaseous exhaust effluent. Commercial systems 

actively induce ignition of the spent process gases. These systems use heat to bring about ignition, 

either with a heater element or by direct flame contact. There are also thermal processors which dispose of 

volatile organic solvent vapors from flammable liquids such as acetone, isopropyl alcohol, etc. 

Finally, burn-boxes are proprietary in-house burn chambers designed with the assumption that pyrophoric 

materials will mix with air, and the desired burning will take place. However, there have been some unexpected 

and damaging results from using burn boxes. Some units have allowed spent gases to accumulate to 

explosive levels and the damage has been extensive from the reactive force. 

3.2 Cleanroom Overview 



Page 21 

The fabrication or main part of the semiconductor manufacturing process is performed in Class 1–10,000 

cleanrooms, see Figures 5 and 6. (Class number is the number of particles, 0.5 microns in size, per cubic 

foot of air. In comparison, normal unfiltered air is the equivalent of Class 5 million and smoke is Class 1 billion 

and up.) The two basic methods of constructing a cleanroom are the built-in-place method and the modular 

method. 

Built-in-place rooms are based on a custom design and all construction is on site. These rooms are the most 

practical approach for larger, permanent installations. Prefabricated or modular construction uses manufactured, 

modular components that can be connected to one another in a variety of ways. In either modular 

or built-in-place construction, the mechanical systems must be custom designed and installed. The cleanroom 

air handling includes the air make-up system and the air recirculation system. There are many different 

room arrangements. Figures 1 through 5 of Data Sheet 7-7/17-12 show the more common arrangements 

being used today. 





Page 22 

Fig. 5. Clean bay service aisle. 

The air flow velocity in the cleanroom ranges from 40 to 100 ft/min (0.20 to 0.51 m/sec). Typical air flow volumes 

for new cleanrooms, whether recirculated at work stations, modules, or large global air systems, range 

from about 20 to 50 cfm/ft 2 (0.57 to 1.4 m 3 /min) of cleanroom. This assumes that 60 percent of the cleanroom 

is a service corridor with less stringent requirements. 

The method of returning the air from the cleanroom to the recirculation fans is accomplished by sidewall 

vents (Figs. 2 and 3 of Data Sheet 7-7/17-12), a perforated raised floor (Fig. 4 of Data Sheet 7-7/17-12), 

or a perforated raised floor opening into a basement plenum (Fig. 5 of Data Sheet 7-7/17-12). 

Sidewall return refers to the use of openings in the walls of the work area as the path for air return. A perforated 

raised floor is from 1 to 4 ft (0.3 to 1.2 m) above the structural floor and forms a plenum underneath 

the walking level for air return. Finally, perforations in the structural floor allows air flow directly to the basement 

which is used as an air plenum. 




Page 23 

Fig. 6. Tool service corridor. 

The air supplied to the cleanroom is usually a mixture of recirculated air and make-up air which compensates 

for leakage and exhaust losses. Since the recirculated air is cleaner and closer to the temperature and 

humidity requirements, a high ratio (80 to 95 percent) of recirculated-to-make-up air is provided. 

The concept of laminar air flow is used in nearly all semiconductor cleanrooms. Laminar flow occurs when 

air is made to flow in unidirectional layers when air flow velocities are maintained above 70 ft/min 

(0.36 m/sec). As the air flows from the supply side (usually the ceiling) to the return side (either a perforated 

floor or sidewall vent), particulate matter is ‘‘washed’’ away in a shower of air. 

The laminar flow cleanroom requires an air flow rate between 70 to 110 ft/min (0.36 to 0.56 m/sec) The average 

Class 100 room will operate at 90 ft/min (0.46 m/sec). If this room has a 9-ft high (2.7 m) ceiling, ten 

air changes per minute or 600 per hour would occur. 

The cleanroom is typically kept under a positive pressure in the range of about 0.15 in. W.G. (water gauge) 

(0.04 kPa). This is done because if there is any air leakage, or if a door or other passage is opened, the 

exchange of air will be from the inside to the outside. If outside air were to rush in, it would bring millions of 

airborne contaminates with it. 

In a vertical laminar flow (VLF) work station or hood (Fig. 7 and Figs. 1 through 4 of Data Sheet 7-7/17-12), 

the air enters from above and moves vertically downward over the work area. These stations are used in recirculating 

applications, or where fumes are generated, and must be removed and exhausted. The use of a 

VLF work station can reduce the size of the central air system and simultaneously provide a source of high 

velocity, filtered air to the work area. 

In the past, as more critical particulate control became necessary, the VLF hood approach had several drawbacks. 

But this problem was solved by dividing the fabrication area into separate tunnels or bays. Today, 

HEPA filters built into the ceilings serve the same purpose. 



High Efficiency Particular Air (HEPA) filters are built into an extended surface configuration by folding filter 

media into pleats and housing it in a frame. The media is a matte of glass fibers held together with binder 

resins which filter over 99 percent of the particles attempting to pass through it. The combustibility of the HEPA 

and ULPA (ultrahigh particulate air) filter modules varies depending on the media, binder resins, and frame 

materials. 

The pressure drop through a HEPA filter is typically 0.5 in. W.G. After extended use, depending upon the cleanliness 

of the air passing through the filter and the amount of prefiltration used, the pressure drop will increase 

to 1 in. W.G. and beyond and must be replaced. In the event of a cleanroom fire, if the HEPA filters are 

exposed to fire products of combustion, the filters might experience an unacceptable pressure drop and need 

to be replaced. 

3.3 Processing Tools 



Page 24 

Fig. 7. Various arrangements of a wet bench and associated fume exhaust ductwork. 

This section gives an overview of some of the tools and support equipment used in the semiconductor 

fabrication process. 


3.3.1 Chemical Mechanical Polish 

Chemical Mechanical Polish (CMP) or planarization, was developed as a method of dealing with the variation 

in wafer surface topography which results from the increasing numbers of layers. These topography 

effects, combined with requirements of the sub-half micron geometries of modern integrated circuit production, 

make it more difficult to achieve resolution of small image sizes due to light reflection and the thinning 

of resist layers over steps on the wafer surface. CMP levels the entire surface of the wafer using polishing pads 

and slurries. Typically the CMP tool consists of two main units: 

1. The polishing machine, including the platen, vacuum system wafer carrier, rotor motor and alignment 

system. 

2. The post CMP cleaning system used to scrub the wafer removing traces of chemicals and surface 

contamination. 

Typically the polishing machine is constructed of, or clad in, polypropylene and has a clear plastic enclosure 

around the operating surface creating shielded combustible spaces. During CMP, the back side of the 

wafer is attached to a plastic film held inside a rotating carrier. The front side of the wafer is then pressed 

against a textured pad soaked with an abrasive slurry. The simultaneous chemical and mechanical actions 

are applied to the surface of the wafer, removing 0.2 micron to 2 micron of material. 

With increasing use of tool integration, environmental enclosures and other techniques, it is likely that CMP 

will become part of the cleanroom. 

3.3.2 Alcohol Vapor Dryers 

An alcohol vapor dryer is a drying system for semiconductor products. It operates by replacing de-ionized 

water with isopropyl alcohol (IPA) which is then evaporated, leaving the product clean, dry, and static-free. 

Because the equipment uses IPA vapors instead of liquid, this drying process is very suited to products having 

deep, narrow surface features. 

A typical vapor dryer is constructed as two cabinets. The first cabinet contains the drying tank, along with 

the necessary operator interfaces and hardware control features. The second cabinet encloses a canister 

containing IPA and additional hardware controls. The two cabinets are connected by electrical cables and 

plumbing lines. 

3.3.3 Reprocessors 

Reprocessors are on-site distillation systems which enable wafer fabrication facilities to recycle various liquid 

chemicals. Sulfuric and hydrofluoric acid are the main acids recycled due to their ultra high purity requirements, 

large consumption volumes, high cost and disposal challenge. Isopropyl alcohol is also being recycled 

for these reasons. 

The reprocessors consist of self-contained distillation systems which concentrate and purify the used liquid 

before returning it to the distribution system. 

3.3.4 Mini-Environment Enclosures 



Page 25 

Advances in semiconductor technology have enabled the industry to reach extremely complex levels in the 

various manufacturing processes. These advances require higher and higher levels of cleanliness. Rather 

than raising the level of cleanliness of the entire fabrication area, many times the individual process is isolated 

in a mini-environment enclosure where the cleanliness of the particular processing step is increased, 

but not the surrounding area. Sometimes referred to as ‘‘wafer isolation technology,’’ this process separates 

the process (tool) from cleanroom personnel and the remainder of the cleanroom environment. This 

technology helps increase yields, reduce defect density, reduce start-up time of processes, positively impact 

costs associated with manufacturing, and increase efficiency. 

Some mini-environment enclosures will have their own dedicated air supply, but most merely utilize cleanroom 

air. Some may actually operate at different pressures (slightly higher) than the surrounding cleanroom. 

They will usually have their own HEPA or ULPA filter systems to improve the air quality to the tool 

they are associated with. 



Mini-environment enclosures will most always create shielded areas which are not adequately protected by 

cleanroom sprinkler systems. The protection guidelines developed by FM Global for specific tools and equipment 

address the need to provide internal protection to mitigate the shielding problem when a minienvironment 

enclosure is provided around that tool. 

3.3.5 Vacuum Pumps 

Data Sheet 7-7 recommends that a foreline trap be installed to prevent oil backstreaming and damage to 

the furnace. Backstreaming can occur as a furnace tube or reactor chamber cools and pressure drops in the 

tube relative to pressure at the vacuum pump. This can allow oil mist from the vacuum pump to be drawn 

back into the furnace or reactor if the mechanical pump vanes can turn backwards. 

Mechanical pumps typically have a ratchet or other mechanism that prevents the pump from turning backwards. 

If, during a pump maintenance teardown and rebuild, the ratchet is inadvertently omitted during reassembly, 

then the pump could turn backwards, causing a potential problem. Diffusion pumps are also 

susceptible to backstreaming but are not usually directly connected to a furnace tube. The use of a dry type 

vacuum pump or one lubricated with an inert fluid eliminates the fire exposure. 

3.4 Bulk Chemical Distribution 

A chemical delivery system filters, blends and transports chemicals through tubing/piping to the point-ofuse 

where controllers regulate the flow rate and pressure of delivery. This system includes the means to pressurize 

a chemical and control its distribution throughout the fab. It consists of a source of chemical, or storage 

vessel, a chemical delivery module and a piping system. 

Fluoropolymer tubing and components are typically used for acidic and caustic chemicals. 

The most common method of liquid transfer is by local distribution systems which are generally located in 

the service chases close to the equipment they serve. A liquid source supply and piping connected directly 

to the process equipment is provided. Liquids are manually delivered to these systems. 

Bulk chemical distribution systems represent a greater exposure than local distribution systems due to long 

runs of pressurized distribution piping which results in a much larger liquid release scenario. 

3.5 Liquid Damage Exposures 

The most common causes of liquid release from distribution systems include items such as component failure 

on distribution piping, corrosion of fittings, and physical damage caused by personnel. When a liquid 

is released from its distribution system, contaminants can be quickly picked up by the cleanroom air handling 

system and distributed throughout the cleanroom space served by the air handling system. Depending on 

the type and amount of the liquid released, contamination of the cleanroom space, in-process product and 

process equipment is probable. 

The spread of airborne contaminants can be minimized following a spill by shutdown of the recirculating air 

system, operation of the smoke/contaminant control system and proper action by the Emergency 

Organization. 

Hydrochloric Acid (HCL) 

Sulfuric Acid (H 2SO 4) 

Nitric Acid (HNO 2) 

Hydrofluoric Acid (HF) 

Phosphoric Acid (H 3PO 4) 

Acetic Acid (CH 3COOH) 

Chromic Phosphoric Acid (CrPO 4) 

Hydrogen Peroxide (H 2O 2) 

Sodium Hydroxide (NaOH) 

Potassium Hydroxide (KOH) 

Ammonium Hydroxide (NH 4OH) 



Page 26 

Table 7. Common Nonflammable Semiconductor Process Liquids 


Chill Water Supply/Return 

Heating Water Supply/Return 

Humidification Systems 

Deionized Water Systems 

Sanitary Hot/Cold Sprinkler 

Rain/Roof Drains 

Condensation 

Equipment Cooling 

Scrubber System 

3.6 Protection Against Theft 

Table 8. Possible Water Damage Sources 

Theft of small high value electronic components has been a major problem in the last three years. Products 

such as processors are often in short supply when they are introduced and sold at a premium, making them 

an attractive product to thieves who can easily resell them on the black market. Memory products fell into 

a similar category but a significant price drop in 1996 reduced thefts considerably. 

The activities which curtail thefts are as follows: 

• Access control to sites and buildings 

• Reliable security systems 

• Employee controls 

• Adequate stock control systems 

• Access control to sites and buildings 

Site fences and barriers with manned or unmanned vehicle control points located at entrances and exits 

can be a significant deterrent to thieves. Where the layout of a site does not permit such controls, the use 

of barriers and speed control devices near loading docks can prevent ram raids. 

All visitors and employees should wear badges and visitors should be escorted at all times. 

Reliable security systems 

A security system is only as good as the people who respond to it and also depends on the original goal 

of the system designer. As a result, security systems should be under regular review to ensure that the changing 

needs of the site are being met. Closed circuit television (CCTV) with remote or duplicate recording of 

images, intruder alarms using a mixture of detection devices and airport style detection arches can all be used 

to tailor a security system to a particular site’s needs. 

Employee controls 

Theft by, or aided by, employees has been a significant problem in many countries. Carefully selecting new 

employees can help, but physical measures including enforcing access control restrictions, the wearing of 

employee badges, locating employee lockers away from production areas and providing employees with 

pocketless uniforms can all play a part in reducing theft by employees. 

Adequate stock control systems 

Related to employee control is stock control. High value shipments should receive special attention upon 

their arrival and dispatch, ideally with witnessed checking of the contents of packages. 

Without these vital checks it is difficult, if not impossible to trace the source of losses downstream. A typical 

system of incoming inspection includes immediate shipment counting by store personnel watched by security. 

The parts would then be stored in a secure area and inventory records updated. Whenever parts are 

then issued to the next stage, the issuer and receiver should check and sign for the parts to ensure that there 

is an effective audit trail. 

Special Exposures 



Page 27 

In 1995 and early 1996, the U.K. experienced a new phenomenon—theft of memory chips and processors 

from personal computers located in offices. Because new memory was in short supply and the black market 

for stolen memory chips was significant, office buildings with a PC on every desk became prime targets 

for thieves. Computers were often severely damaged by thieves who ripped open units to get at the 



easily removable memory boards. Losses of $15,000 were a daily occurrence in many cities; some of the largest 

losses reached in excess of $500,000. 

3.7 Uninterruptible Power Supply Overview 

Uninterruptible power is accomplished in several ways: 

a. Static switches. A static switch is a solid state device which can have 2 to 3 input sources but just 

one output. The inputs are typically odd and even feeders, but some switches now come with a third source, 

which can be an emergency generator. In this case, the emergency generator should be set to automatically 

start upon loss of one switch source. 

The output off these static switches would then go to a bus or breaker panel which supplies fab production 

tools. If either of the input sources to the switch were lost, the switch digitally transfers to the alternate 

input source in less than 1/4 cycle. This is well below the switching time threshold that would affect 

production tools (5 to 10 cycles). 

This arrangement is best suited for plants with very reliable utility sources from alternate substations. 

This arrangement is very good at protecting the production tools from shutting down due to minor power 

interruptions (lasting a few seconds), or total loss of power from one utility source. This arrangement does 

not protect the facility at all if both utility power sources were lost, unless the three source static switches 

are provided, and these are typically used only on critical systems. 

b. Diesel no-break systems. This method employs an AC motor driving an AC generator. The generator 

in turn supplies the critical loads. There is also a diesel engine connected onto this unit which performs 

as the primary driver if utility power were lost. The method used to bridge the time to start the engine 

and bring it up to load carrying condition is with the use of internally stored kinetic energy, so the output 

of the generator never changes. These systems provide clean continuous, extended power outage protection 

which enables the plant to avoid surges and sags in their critical power load. If this type of system 

is used, some of the redundancy in the electrical system to this machine can be eliminated, because this 

machine can function for long periods of time. 

c. Static UPS Modules, with or without emergency generator sets. This is a typical standard UPS system 

where an AC source is rectified to DC to power a battery bank. This DC battery power is then inverted 

back to an AC source and feeds the fab tools. During normal operations, utility power is fed to the power 

supply. If this power is lost, the batteries provide power for the system. The two major drawbacks are 

the large physical size of the battery banks needed to supply the power demand of the fab tools and the 

limiting time the batteries can supply power. This arrangement provides good protection against power 

blips, but battery capacity usually limits the duration of the outage to less than an hour. 

d. Hybrid rotary UPS modules, with or without emergency generator sets. 

4.0 OTHER APPLICABLE CODES AND STANDARDS 

4.1 United States Building Code 



Page 28 

Building and fire codes are the two basic model codes adopted and enforced by government officials designated 

as the ‘‘authority having jurisdiction’’ (AHJ) in the U.S. Three different codes are used in three areas 

of the U.S.: 

• Northeast: the Building Officials and Code Administrators (BOCA), the National Building Code (NBC) and 

National Fire Prevention Code 

• Southeast: the Southern Building Code Congress International (SBCCI), the Standard Building Code, and 

the Standard Fire Code 

• West of the Mississippi River: generally the Uniform Building Code (UBC) and Uniform Fire Code (UFC) 

of the International Congress of Building Officials (ICBO). 

The electrical code in use in the U.S. is the National Electric Code (NEC), reprinted as NFPA 70, augmented 

by NFPA 79, Electrical Standard for Industrial Machinery. Process tools and equipment are typically 

reviewed for compliance with NFPA 70, Section 90-7, Examination of Equipment for Safety. Review for 

compliance with these codes is typically done by third party firms or by company personnel specifically hired 

to validate equipment compliance with company standards. 


Typically, these codes have separate chapters or articles that specifically govern the semiconductor industry. 

Examples: in the UBC a special occupancy class H-6 has been designated for the semiconductor industry; 

in the UFC, Article 51 and in the BOCA Fire Code, Chapter 15 address the semiconductor industry 

specifically. 

The scope statements of these model codes illustrate the difference between them and FM Global standards. 

The codes are designed to provide minimum standards primarily focused on safeguarding the life and 

health of people while FM Global provides property damage loss prevention and control engineering. 

A fire incident which resulted in no loss of life or injuries might be acceptable in a semiconductor fabricating 

facility from a code standpoint. However, that same incident, which might only have opened two automatic 

sprinkler heads, could be a 20 or 30 million-dollar loss and totally unacceptable from a property 

conservation viewpoint. 

A brief look at the code requirements versus FM Global standards for the semiconductor industry illustrates 

the following differences. 

1. It is only since the 1994 UFC that a 0.010 in. (0.254 mm) RFO is required. FM Global has recommended 

the RFO, automated cylinder valves, and high ventilation airflows since 1990. 

2. Fire codes require automatic sprinklers in combustible ducts 10 in. (0.25 m) diameter and larger with an 

exception for 12 ft (3.6 m) of ductwork below the ceiling. FM Global recommends (1) using ducts not needing 

sprinkler protection; (2) not using ducts of certain materials such as PVC or polypropylene and sprinkler 

protection in all combustible ducts. 

3. Smoke/contaminant control systems are not addressed as required in the model codes but are recommended 

for all semiconductor fabricating areas by FM Global. 

4. Automatic sprinkler protection for the horizontal surface of a wet bench plus within 2 ft (0.6 m) of the duct 

connection to the bench is the requirement of the UFC. FM Global recommends protection for the surface 

and all interior compartments with a detector-activated suppression system to limit the loss to far less than 

would be expected in a wet bench fire controlled by sprinkler protection alone. 

4.2 NFPA 318 

The NFPA 318 Standard for the Protection of Cleanrooms was first published in 1992. It is currently in its 

third revision process with reissue in mid 2000. The requirements of NFPA 318 are far more comprehensive 

and detailed than the model codes. Generally, Data Sheet 7-7/17-12 and NFPA 318 are very similar, 

because property damage loss prevention is a recognized component of the Purpose section of NFPA 318. 

One important difference between NFPA 318 and Data Sheet 7-7/17-12 is the NFPA 318 requirements are not 

retroactive. Therefore, there are no protection requirements for existing combustible wet benches, for 

example. Since its first issue, NFPA 318 has instead contained a basic requirement that tools be of noncombustible 

construction. A broad exception, loophole allowing plastics where corrosive process chemicals exist 

will hopefully be closed in the next edition by restricting plastic materials to those which meet the 

FM Approvals Cleanroom Materials Flammability Test Protocol. 

4.3 SEMI S-2 



Page 29 

Semiconductor Equipment and Materials International (SEMI) is an organization dedicated to providing guidelines 

to the manufacturers of equipment used by the semiconductor industry. The SEMI S-2 standard is a 

broad tool safety guideline which includes a section number 19 on Fire Protection. 

Section 19 gives no definitive guidance on fire protection and references the UL-94 test as a basis for determining 

the need for fire protection in a tool. SEMI S-2 is now being revised and section 19 will be replaced 

by a new SEMI safety standard, SEMI 2697 Document. 

This new Tool Fire Protection Standard includes a flow chart for use in determining appropriate tool fire 

protection. Parameters to consider include tool construction materials, chemicals used in the tool, safety 

controls on the tool, and the need for detection and/or suppression systems. UL 94 compliance is no longer 

the focal point of the tool fire protection considerations. 



4.4 International Codes 

There are no specific codes in use which control the semiconductor industry outside of the U.S. Each country 

has its own Building Regulations (U.K.) or similar, but these do not specifically address semiconductor loss 

prevention or firesafety issues. As a result, it is possible that although the UBC and UFC may be used in 

the initial designs for many fabs, the standards may be compromised during construction to the lower local 

codes. 

In all cases, the international building codes are lifesafety based, typically geared to enable safe evacuation 

of occupants in a short period of time. In the U.K., the use of British standards for installations such as 

electrical installations (BS7671, 16th Edition Wiring Regulations) is not mandatory, however a designer applying 

them is ‘‘deemed to satisfy’’ the building regulations if they are used. If an alternative standard is used, the 

designer has to justify that deviation showing that it is at least as good as the equivalent British standard. 

1. Sprinkler installations in the United Kingdom are often specified to meet LPC (Loss Prevention Council 

‘‘Rules for Automatic Sprinkler Installations’’ adopted by British Standards Institution as BS 5305 Part 2). However 

the use of FM Global standards for sprinkler installation is usually acceptable. These are also often 

the basis of sprinkler codes in commonwealth countries. 

2. European CE Union Mark 

On 1 January 1995 a set of European Union (EU) directives became effective. They require a wide range 

of products to have the ‘‘CE’’ mark. The intent is to ensure that products entering the EU countries comply 

with general safety and environmental regulations. 

Each product with a CE mark will have a technical file which contains the following information: 

a. Overall drawing of the equipment together with control circuit drawings. 

b. Full detailed documentation to show that the equipment conforms to Environmental Health and Safety 

(EHS) requirements, which include: 

i. Principles of safety integration. 

ii. Safety and reliability of control systems. 

iii. Control devices. 

iv. Protection against other hazards. 

v. Fire and explosion. 

vi. Emissions of dust, gases etc. (maintenance, indicators, warning devices, warning or residual risks) 

c. A list of the EHS regulations, standards and other technical specifications used in the design of the 

equipment. 

d. Methods adopted to eliminate hazards. 

e. Relevant technical reports or certificates issued by a competent body or laboratory. 

f. A list of the harmonized standards and a technical report giving results of tests. 

g. Equipment operation instructions. 

3. There are three main directives: 

a. The Machinery Directive, 

b. The Electrical Directive 

c. The Low Voltage Directive (73/23/EEC): Mandatory from 1/1/97 

Conformance Requirements (Article 2) 

i. Equipment must be ‘‘safe’’ 



Page 30 

ii. Equipment must be constructed in accordance with good engineering practice. 

iii. Equipment must conform with the principle elements of the safety objective (annex I) 


Conformance can be demonstrated by one of the following methods. 

i. Conformance with a harmonized standard. 

ii. Conformance with an International standard. 

iii. Conformance with a National standard. 

iv. Conformance with ‘‘Low Voltage’’ directive Article 2 

The SEMI organization is attempting to incorporate the CE Marking directives into the Semi revision to the 

S2-93 standard and a CE Marking Interest Group has been formed. 

The following is an overview of fire protection code issues in countries located in the Asia-Pacific Region: 

Taiwan—Fire protection standard is per local code (somewhat like Japanese standard). For some newer fabs, 

the plant fire protection systems are designed to NFPA and SEMI S-2. This is also acceptable to the local 

authorities. 

Hong Kong—fire protection design has to meet LPC (U.K.) standard. If fire protection design is to NFPA/ 

FM Global standard, there should generally be no problem, because the NFPA/FM Global standard is usually 

more conservative. Singapore—fire protection design is to local code (which is actually the Australian 

code and quite similar to LPC (U.K.) standard). If fire protection is to NFPA/FM Global standard, there should 

generally be no problem, because the NFPA/FM Global standard is usually more conservative. 

Malaysia—there is no local standard though LPC (U.K.) standard is more widely used. Using the NFPA/ 

FM Global standard should not pose a problem. 

Philippines—there is a local code which closely follows the NFPA standard. Using the FM Global standard 

should not pose a problem. 

Thailand—there is no local code. The use of NFPA/FM Global standard should not pose a problem. 

4.5 ISO International Cleanroom Standards 

Following steps towards international harmonization of cleanroom standards in 1990, with the establishment 

of an European Technical Committee (CEN/TC 243 Cleanroom Technology), the International Organization 

for Standardization Technical Committee was set up in 1993 (ISO/TC 209 Cleanrooms and associated 

controlled environments). As a result, working groups were set up to deal with seven specific areas that will 

be developed into globally recognized standards. The CEN and ISO technical committees have harmonized 

their list of work items and as a result of the way in which the ISO and CEN organizations work, all standards 

developed by ISO/TC 209 will be submitted to the parallel approval procedure, resulting in the standards being 

eventually adopted by the national standards collections of the 18 CEN member countries at the same time 

as being accepted by the 85 voting members of the ISO. 

The working groups are outlined below: 

WG 1: Air Cleanliness classification (UK) 

WG 2: Biocontamination and biocontamination control (France) 

WG 3: Metrology and testing methods (Japan) 

WG 4: Design and Construction (Germany) 

WG 5: Cleanroom Operation (USA) 

WG 6: Terms, definitions and units (Switzerland) 

WG 7: Mini-environments and isolators (USA) 

(The country in brackets holds the convenership of the working group.) 



Page 31 

The ISO standards and their date of approval for issue as a draft international standard are as follows: 

ISO 14644-1 Air Cleanliness classification 03-96 

ISO 14644-2 Specification for testing cleanrooms to prove continued compliance with ISO 14644-1 04-97 

ISO 14644-3 Metrology and test methods 04-98 

ISO 14644-4 Design, Construction and start-up of cleanroom facilities 10-97 

ISO 14644-5 Operation of cleanroom systems 09-98 

ISO 14644-6 Isolators and transfer devices 04-99 

ISO 14702 Terms, definitions and units 04-99 



To overcome the interim period until the standards are approved, CEN has decided to publish an European 

Prestandard ENV 1631 Cleanroom Technology — Design construction and operation of cleanrooms and 

clean airdevices, which will be automatically withdrawn once the ISO standards 14644-4 and -5 are approved 

and published. 

4.5.1 ISO 14644-1 Air Cleanliness Classification 

The new ISO air cleanliness classification is based on the following formula: 

C n =10 N (0.1/D) 2.08 

where C n = max. number of particles per m 3 meter with a diameter equal to or larger than the particles under 

consideration, rounded to the nearest whole number, using no more than three significant digits 

N = The ISO classification number 

D = The diameter of the particles under consideration 

0.1 = A constant with dimensions in microns. 

The following tables show the relationship between the ISO classification and the particle size and a comparison 

between the ISO classification and the commonly used US 209E classification system. 

While it is likely that the previous form to describe a cleanroom classification, i.e., Class 1, Class 10, etc., 

will continue to used for some time, increasingly cleanrooms will be specified using the international terms, 

defined in ISO14644-1. 

Table 9. Selected airborne particulate cleanroom classes for cleanrooms and cleanzones defined by ISO 14644-1 

Maximum concentration limits (particles/m3 of air) for particles equal to and larger than the considered 

sizes (in nanometers) shown below (concentration limits are calculated in accordance with formula 1) 

ISO Classification Number (N) 100 nm 200 nm 300 nm 500 nm 1000 nm 5000 nm 

ISO Class 1 10 2 

ISO Class 2 100 24 10 4 

ISO Class 3 1000 237 102 35 8 

ISO Class 4 10000 2370 1020 352 83 

ISO Class 5 100000 23700 10200 3520 832 29 

ISO Class 6 1000000 237000 102000 35200 8320 293 

ISO Class 7 352000 83200 2930 

ISO Class 8 3520000 832000 29300 

ISO Class 9 35200000 8320000 293000 

Particles per m 3 

greater than or 

equal to 0.5 

microns 

US 209E 

(1992) 

Table 10. Comparison between different Cleanroom Class Standards 

US 209E 

(Imperial 

Equivalent) 



Page 32 

EEC 

cGMP 

1989 

France 

AFNOR 

1989 

Germany 

VDI 2083 

1990 

UK 

BS 5295 

1989 

Japan JIS 

B 9920 

1989 

ISO EN 

14644-1 

1998 DIS/FDIS 

1 

3.5 0 2 2 

10 M1.0 

35 M1.5 1 1 3 3 

100 M2.0 

353 M2.5 10 2 4 4 

1,000 M3.0 

3,530 M3.5 100 A + B 4,000 3 E or F 5 5 

10,000 M4.0 

35,300 M4.5 1,000 4 G or H 6 6 

100,000 M5.0 

353,000 M5.5 10,000 C 400,000 5 J 7 7 

1,000,000 M6.0 

3,530,000 M6.5 100,000 D 4,000,000 6 K 8 8 

10,000,000 M7.0 

100,000,000 M7.5 1,000,000 40,000,000 L 9 9 


5.0 SEMICONDUCTOR TERMINOLOGY 

Alignment—The positioning of a mask or reticle with respect to the wafer. 

Anneal—A high temperature processing step (usually the last one), designed to repair defects in the crystal 

structure of the wafer. 

APCVD—Atmospheric Pressure Chemical Vapor Deposition 

Art work—The large CAD (computer aided design) drawings of the various layers of a circuit. It is used to 

make the master mask for each layer. 

Ashing—Process in which photoresist is removed from the wafer by heating it and turning it to ash. 

Automated Cylinder Valve (ACV)—The best form of ESOV, this is a normally closed, pneumatically held 

open valve assembly that replaces the manual valve on top of the gas cylinder. This allows for automatic opening 

and closing of the valve by an automated gas cabinet purge program, and automatic shut down of the 

gas cylinder in response to detection of a gas leak, for example. 

Bipolar—Literally, having two poles. A transistor consisting of a base, emitter and collector. It has both N 

and P type carriers present. 

Boat—A vessel, usually made of quartz or silicon used for holding wafers during high temperature furnace 

processing. 

Bonding—The connecting of a wire from the package leads to the pads (bonding pads) of the circuit. 

BPSG—Borophosphosilicate glass. 

Bubbler—An apparatus in which a carrier gas is transmitted through a heated liquid causing portions of 

the liquid to be transported with the gas. 

Buffered Oxide Etch—A mix of hydrogen fluoride (HF) and ammonium fluoride (NH 4F) used to promote 

oxide etching at a slow, controlled rate. 

Burn-in—Term given to heat soaking components to determine operational reliability at elevated 

temperatures or temperature fluctuations. 

Carrier—A vessel made of plastic used for holding wafers (typically 25) during nonprocessing times. 

CGA—Compressed Gas Association. 

Chip (Die)—The sliver of silicon on which the tiny devices of the integrated circuit are formed. 

Contact Aligner—An aligner tool which clamps the wafer and mask into a tight contact before the resist 

exposure cycle. 

Cleanroom Environment—An enclosed area where the amount and size of particulate matter in air, 

temperature, humidity, and pressure are closely controlled. 

Cluster tool—Several process stations or tools served by one loading-unloading chamber and wafertransport 

system. 

CMP—Chemical Mechanical Polishing—A wafer flattening and polishing process that combines chemical 

removal with mechanical buffing. Used for polishing/flattening wafers after crystal growing and wafer 

planarization during the wafer fabrication process. 

CMOS—Complementary metal oxide semiconductor. 

Coke Cans–A noncombustible, pressurized canister containing photoresist or developer which feeds the 

spinner in the masking operation. These canisters are usually pressurized with nitrogen and are equipped 

with metallic or plastic tubes connected to the spinners. 

Contact Aligner—An aligner tool that clamps the wafer and mask into a tight contact before the resist 

exposure cycle. 

CVD—Chemical Vapor Deposition. 



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Deep Ultraviolet (DUV)—A light wavelength often used to expose photoresist which has the advantage of 

an ability to produce smaller image widths. 



Deionized Water—Water which has had all charged particles removed. Commonly called ‘‘D.I. water,’’ it is 

used throughout the entire manufacturing process. 

Deposition—The depositing or laying down of various chemicals on wafers, generally done in a high 

temperature furnace or evaporator. 

Developer—Chemical used to remove areas defined in the masking and exposure step of wafer fabrication. 

DIE—See Chip. 



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Diffusion—The fab process whereby high temperature furnaces are used to drive dopant material into the 

wafer. 

DIP (Dual In-line Package)—A rectangular circuit package, with leads coming out of the long sides and 

bent down to fit onto a socket. 

Dopant—Chemical ‘‘impurities’’ used to regulate the current flow in integrated circuit junctions. Usually put 

on the wafer via furnaces, implants, or CVD systems and later diffused further into the wafer by heat. 

Dry Etch—Generally used in place of the acid bathing technique to produce more uniform pattern definition, 

particularly with smaller geometries, as is necessary for VLSI processing. 

Emergency Shut Off Valve (ESOV)—A valve located in the gas piping train, usually close to the cylinder 

CGA fitting, which can be closed either automatically or manually in response to a gas emergency. For 

example, automatic closure might result from a signal from the gas monitoring system; manual closure can be 

done from the gas cabinet EMO button. 

EPI—(i.e. epitaxy)—A special process for growing additional layers of silicon on wafers. Usually either silane 

or silicon tetrachloride is used at a high temperature in a reactor. 

Evaporation—The vaporizing of a material such as aluminum or gold and subsequent depositing of the 

vapor on the wafers. 

Expose—In masking after proper alignment of mask to wafer, light is allowed to activate or polymerize the 

photoresist on the wafer much like exposing film in a camera. 

FAB—Fabrication i.e., wafer fabrication area is called FAB or ‘‘Wafer fab.’’ 

FET (Field-Effect Transistor)—A unipolar transistor consisting of a source, gate and drain, whose action 

depends on the flow of majority carriers past the gate from source to drain. 

Fume Scrubber—Equipment used to clean the fumes which evolve during the wafer fabrication process. Usually, 

the exhaust hood, furnace exhaust, etc. in the wafer fabrication process are vented to a fume scrubber. 

The scrubber is required by the environmental authorities. 

Furnace—Generally refers to high temperature cylinders used for depositions and diffusions in wafer fab. 

Crystal growing machines are also referred to as furnaces. 

Glassification—Process used to place an environmentally safe protective coating on the completed semiconductor. 

This hard surface is the final process before the individual chips are cut from the silicon wafers and 

tested for operational capabilities. 

Hard Bake—Generally, in masking, the baking of wafers at about 150°C (302°F) to remove moisture and 

provide for better adhesion of the photoresist after develop and prior to etch. 

HPM—Hazardous Production Material—A solid, liquid or gas that has a degree of hazard ranking in health, 

flammability or reactivity of 3 or 4 as ranked by Uniform Fire Code Standard 79-3 and which is used directly 

in research, laboratory or production processes which have, as their end product, materials which are not 

hazardous. 

HEPA Filter—High Efficiency Particulate Air Filter capable of filtering out 99.97 percent of particles greater 

than 0.3 microns in diameter. 

Integrated Circuit (IC)—An array of transistors and other components on a piece of semiconductor material. 

Ion Implantation—A process of introducing charged dopant ions into the semiconductor. These ions, usually 

boron or phosphorus, are accelerated and driven into the surface of the semiconductor wafer. 


Junction—The interface at which the conductivity type of a circuit material changes from P-type to N-type 

or vice versa. 

Jungle—Generally, the entire collection of tubes, lines, bubblers, injectors, etc. found at the back end of 

a diffusion or deposition system. Also called a source cabinet. 

Laminar Flow Hoods—The hoods used in cleanrooms where it is important to maintain laminar airflow 

characteristics throughout a given space. 

Lapping—Process of removing the saw marks on the raw wafers once they are sliced from the polysilicon 

ingot. 

LPCVD—Low Pressure Chemical Vapor Deposition (Furnace). 

Manufacturing Electron Beam Exposure System (MEBES)—An electron beam lithography machine used 

to make masks. The circuit design is programmed into the MEBES machine. The MEBES reduces the circuit 

pattern size to that of a chip and transfers this design onto the master mask. This design is duplicated 

many times to form a grid on the master mask. This mask provides the basic pattern which is exposed onto 

the silicon wafer. 

Mask—A glass plate covered with an array of patterns used on the photo-masking process. Each pattern consists 

of opaque and clear areas that respectively prevent or allow light to pass. The mask surface may be 

emulsion, chrome, iron oxide, silicon, or a number or other materials. 

Masking—The fab process whereby each layer of the process is photographically transposed onto the wafer. 

MBE—Molecular Beam Epitaxy. An evaporation rather than a CVD process. An electron beam is directed 

into the center of the target material, which it heats to the liquid state. In this state, atoms evaporated out 

of the material, exit the cell through an opening, and deposit on the wafers. MBE has found production use 

in the fabrication of special microwave devices and for compound semiconductors such as gallium arsenide. 

Micron—Equal to one millionth of a meter. Used in measuring thickness of material or line width at various 

steps of processing. 

Microprocessors—A single semiconductor device which carries out the processing tasks in a digital system. 

Its development made the microcomputer possible. A microprocessor incorporates both the arithmetic logic 

unit and the control unit—components previously requiring separate dedicated devices. 

Mil—Equal to 0.001 in. (0.03 mm). Used in measuring thickness and width at various steps of processing. 

Mini-environment—An environment that maintains wafer cleanliness by storing, transporting, and loading or 

unloading wafers in small, clean enclosures. 

MOCVD—Metal Organic Chemical Vapor Deposition, one of the latest options for CVD of compound materials. 

A Group III halide (gallium) is formed in the hot zone and the gallium arsenide compound is deposited 

in the cold zone. In the metallorganic process for gallium arsenide, trimethylgallium is metered into the 

reaction chamber along with arsine to form gallium arsenide. 

MOS—Metal Oxide Semiconductor. 

MOSFET—Metal Oxide Semiconductor Field Effect Transistor. 



Page 35 

Nitride—(Si 3N 4) Short for silicon nitride, used to form an insulation layer on a circuit. 

Optoelectronics—The technology which mixes solid state electronics and optics. 

Organometallic Compounds—Organic compounds in which metal atoms have replaced one or more hydrogen 

atoms. The hazards vary, but most of the materials are flammable liquids or solids. Most are very reactive 

and some will react with air or moisture at room temperature. Examples of some organometallic 

compounds include trimethylaluminum, diethylzinc, and trimethylgallium. 

Oxidation—The process which combines oxygen and heat with a silicon wafer in a furnace to produce a 

layer of silicon dioxide (‘‘oxide’’). Also done in a CVD process using silane. 

Oxide—Silicon dioxide. Grown on a wafer, oxide is used as a deterrent to dopant penetration in deposition 

and diffusion processes. Also used as part of the structure of the circuit or as a final protective layer (glass). 





Page 36 

Package—The finished integrated circuit unit which consists of the chip fastened to a frame inside a ceramic 

or plastic case whose metal leads can be inserted into printed circuit boards. Can also refer to the case only. 

Passivation—Usually a silicon dioxide or silicon nitride layer put over an existing layer of the wafer to protect 

against moisture, contamination and abrasion. 

Pass-through—An enclosure installed in a wall with a door on each side that allows chemicals, production 

materials, equipment and parts to be transferred from one side of the wall to the other. 

Pattern Generator—Optical or E-Beam tool used to make the mask plates or reticles. 

PECVD—Plasma Enhanced Chemical Vapor Deposition. 

Pellicle—A protective film covering on a frame adhered to a mask plate which keeps contaminants off the 

mask surface. 

Photoresist—A light-sensitive, frequently flammable liquid which is sprayed on the wafer, exposed and developed 

to make the circuit image during the wafer fabrication process. Similar to film in an ordinary camera 

in its sensitivity to light. 

Plasma—A high energy gas made up of ionized particles. 

Plasma Etcher—A machine in which a high energy RF field excites the gas molecules in the chamber to 

a high level causing a reaction in which unprotected sections of an oxide layer are removed. 

Plasma Etching—An etching process which accomplishes results similar to the chemical etch mechanism 

reaction using an etching gas instead of a wet chemical. 

Polishing—The process whereby a mirror-like finish is put on raw wafers after slicing. 

Poly—Polycrystalline silicon. Usually grown in layers epitaxially to form part of the circuit structure. Also the 

raw material for the melt for crystal growth. 

Projection/Promixity—Masking exposure methods in which the wafer and mask plate have no contact, 

thus lengthening the mask usage due to less contamination of the mask plate. 

Puller—Furnace for growing silicon crystals. Refers to the process of pulling the crystal out of the molten 

silicon. 

Pyrophoric—A substance which ignites spontaneously in air below 130°F (54°C). 

RCA Clean—A multiple-step process to clean wafers before oxidation; named after RCA, the company that 

developed the procedure. Chemicals used include mixtures of water, hydrogen peroxide and ammonium 

hydroxide (step 1) or hydrochloric acid (step 2). 

Reactive Ion Etching (RIE)—An etching process that combines plasma and ion beam removal of the surface 

layer. The etchant gas enters the reaction chamber and is ionized. The individual molecules accelerate 

to the wafer surface. At the surface, the top layer removal is achieved by the physical and chemical 

removal of the material. 

Reticle—A miniature reproduction of one layer of a circuit drawing on an emulsion or chrome covered glass 

plate. Typically 5xor10xinsize it will be reduced and reproduced many times on a mask blank. 

RTO (Rapid Thermal Oxidation)—An RTP technology used to grow very thin (usually less than 100 

Angstorms) MOS gate oxide layers. 

RTP (Rapid Thermal Processing)—A process usually using high intensity tungsten halogen lamps to heat 

and cool a wafer in seconds. 

Seed—In crystal growing a piece of single-crystal structured silicon which upon contact with the melt (molten 

poly-silicon) starts a crystal or ingot to be grown which has same single-crystal structure as that of the seed. 

SEM—Scanning Electron Microscope. Used in examining portions of circuit by allowing the viewer to see 

an image as much as 15,000 times its actual size. 

Semiconductor—An element such as silicon or germanium intermediate in electrical conductivity between 

the conductors and the insulators. 

Slicing—The cutting of a silicon crystal in a saw in order to make wafers on which ICs will be made. 


Soft Baking—A heating process used to evaporate a portion of the solvents in resist. The term ‘‘soft’’ 

describes the still soft resist after baking. The solvents are evaporated to achieve two results: to avoid retention 

of the solvent in the resist film and to increase the surface adhesion of the resist to the wafer. 

Spin—The operation and development in a spinner machine where photoresist or developer is applied to 

a wafer and rotated at high speed so that a uniform film coating results. 

Sputter—Method of depositing various types of thin metal films on wafers by ion bombardment of a target. 

Standard Mechanical Interface (SMIF)—A system that allows the mating of portable clean wafer boxes 

(called pods) to the clean microenvironment loading stations of process tools. 

Step & Repeat—In making mask plates a step-and-repeat camera (‘‘stepper’’) is used to transform the pattern 

image of the reticle onto the surface of the plate. In some fab processing, a stepper is used to project 

the reticle’s image directly onto the resist spun wafer and does not employ a mask plate (also called DSW for 

Direct-Step-On-The-Wafer). 

Strip—In fab, refers to the stripping of the photoresist after etch usually in a wet chemical bath or in a plasma 

chamber. 

Substrate—The silicon wafer. 

Tape Automatic Bonding (TAB)—Chip-to-package connection process in which the package leads are 

formed on a flexible tape and all the lead fingers are bonded to the chip in one action. 

Tetraethylorthosilicate (TEOS)—A chemical source for the deposition of silicon dioxide. A combustible liquid 

(flash point 125°F [52°C]) replacement for silane. 

Tool—Any device, storage container, work station, or process machine used in a cleanroom. 

Torr—In vacuum systems the remaining pressure inside the chamber after pumpdown is a measure of 

atmospheric pressure expressed in Torr (Torr = 1/760 of atmospheric pressure). 

Transition Piece—That portion of a work station exhaust plenum attached to the rear of a work station. 

This portion of the plenum is connected to the fume exhaust branch duct. 

ULPA Filter—Ultrahigh-Efficiency Particulate Air Filter, capable of filtering out 99.999 percent of particles 

greater than 0.3 microns in diameter. 

VLF—Vertical Laminar Flow. 



Page 37 

VLSI (Very Large Scale Integration)—A chip manufacturing process which enables a high density of 

transistors and circuits typically 100,000 to 1,000,000 devices per chip. 

Wafer—The silicon disc sliced from a crystal on which integrated circuits are manufactured. Also called a 

substrate or starting material. 

Wafer Box—A plastic box with a hinged opening top used to hold carriers with wafers during non-processing 

times. 

Wafer Fab—The area in which circuits are manufactured, usually consisting of masking, diffusion, deposition, 

and other operations which will transform a polished wafer into hundreds of chips. 

Wafer Sort—The step after wafer fabrication during which the electrical parameters of integrated circuits 

are tested for functionality. Probes contact the pads of the circuit to conduct the test leading to the name 

‘‘prober’’ for the equipment that performs electrical tests on each die site of completed wafers. 

Wire Bonding—An assembly step in which thin gold or aluminum wires are attached between the die bonding 

pads and the lead connections in the package. 

Yield—The amount of good products compared to the total possible good products, i.e., on a wafer which 

has 100 possible chips and 65 are found to be good, then the yield = 65 percent. Or if a ‘‘run’’ of wafers has 

50 wafers to start and 41 wafers are finished, the run has a yield of 82 percent. 



6.0 BIBLIOGRAPHY 

The following codes, standards and publications provide additional information: 

BOCA National Fire Prevention Code, 1993, Chapter 15: Hazardous Production Material Facilities 

National Fire Protection Association (NFPA) 

• Standard No. 45-1986 Edition: Fire Protection for Laboratories Using Chemicals 

• Standard No. 90A-1985 Edition: Installation of Air Conditioning and Ventilation Systems 

• Standard No. 91-1983 Edition: Blower and Exhaust Systems for Dust, Stock and Vapor Removal or 

Conveying 

• Standard No. 318-1998: Protection of Cleanrooms 

Pletsch, William, Integrated Circuits—Making the Miracle Chip, California: Pletsch & Associates, 1985 

Semiconductor Equipment and Materials International, SEMI S2-93, Safety Guidelines for Semiconductor 

Manufacturing Equipment. 

Uniform Fire Code, 1997 

• Article 51—Semiconductor Fabrication Facilities 

• Article 74—Compressed Gases 

• Article 80—Hazardous Materials 



Page 38 

Van Zant, Peter. Microchip Fabrication: A Practical Guide to Semiconductor Processing, Third Edition, New 

York: McGraw-Hill Publishing Company, 1997

DS 7-7R 17-12R Semiconductor Fabrication Facilities ... - FM Global

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