Vacuum Design Constraints and Considerations - Owens Design

Vacuum Design Constraints and
Considerations
Martin P. Aalund, Ph.D.

Summary
• Intro to Vacuum Technology
– History
– Terminology
– Levels of Vacuums
– Cluster Tools
• The Vacuum barrier, How do you Cross it?
– Robotics
– Motion Across The Barrier
– Data and Electrically
• Design Consideration
– How do we Maintain it
– Virtual Leaks
– Material Compatibility
• Out gassing

Intro to Vacuum Technology
• History
• Why do we need Vacuums
• Terminology
• Levels of Vacuums
• Cluster Tools
• Robots

Vacuum History
• Evangelista Torricelli was the first person credited with creating
a vacuum 1643 and also invented the barometer. This was in
an attempt understand why a suction pump could only raise
water to 32 feet.
• Robert Boyle (1627-1691) used a von Guericke pump,
improved by the young Robert Hooke, to investigate the
vacuum and the general properties of gases and gas pressure
• England. Papin invented the Pressure Cooker
• Currently one of the most impressive bits of artificial emptiness
is created in the particle accelerators. The large electronpositron
collider (LEP) at CERN gets down to a pressure of 10-
12 Torr or 1.3*10-10 Pa This corresponds to a particle density
of about 1011 hydrogen molecules per cubic meter.
• To a first approximation the average density of the universe is
about 1 hydrogen atom per m3

Why do we need Vacuum
• Limits Contamination
– No Airborne Contamination
– Limits Cross Contamination
• Control Chemistries
– Slows Oxidation
– Allows for Controlled Atmospheres
• Many process can be made more predictable or require a vacuum to
function
– Plasma Production
– Metallization: Metal is evaporated and deposited onto a substrate
– Etch
– Deposition
– Sputtering
– Ion Implantation
– E-beam
• Metrology
• Inspection

Terminology
• Vacuum:
– A volume of Space Substantially void of matter
(Wikepedia)
– a space partially exhausted (as to the highest
degree possible) by artificial means (as an air
pump) (Websters)
• Manometer: Liquid scale used to measure
vacuum or pressure usually in Inches or mm
• torr: A unit of measurement for pressure:
torr
= 1mm_Hg torr = 1.32× 10 − 3 atm
P 1
P 2
∆P
torr
= 0.039in_Hg torr = 133.32Pa
• (it is named after Evangelista Torricelli)
• Virtual Leek: A void or trapped volume that
slowly released material into a vacuum.
Examples include Blind wholes with screws etc.

Terminology
• Atmospheric pressure is variable based on weather and location, but is
standardized at 101.325 kPa (760 Torr)
• Low vacuum, also called rough vacuum or coarse vacuum, is vacuum that can
be achieved or measured with rudimentary equipment such as a household
vacuum cleaner. Can be measure with a simple manmometer
• Medium vacuum is vacuum that can be achieved with a single pump, but is
too low to measure with a liquid or mechanical manometer. It can be measured
with a McLeod gauge, thermal gauge or a capacitive gauge.
• High vacuum is vacuum where the mean free path of residual gases is longer
than the size of the chamber or of the object under test. High vacuum usually
requires multi-stage pumping and ion gauge measurement. Some texts
differentiate between high vacuum and very high vacuum.
• Ultra high vacuum requires baking the chamber to remove trace gases, and
other special procedures.
• Deep space is generally much more empty than any artificial vacuum that we
can create. But it is not uniform and has areas of gas that may be quite dense.
• Perfect vacuum is an ideal state that cannot be obtained in a lab, nor even in
outer space.
• AMC: Airborne Molecular Contaminates: Gaseous Atoms, Molecules, or
clusters

AMCs
• Can be emitted from Cables, Plastic or Electrometric Parts
• Airborne molecular Include
– Acids: HCl, HF, SO x , NO x , etc.
– Basis: Amonias: Amines, etc
– Condensates: Phthalic Ester, Siloxane, Etc
– Dopants: Boron, Phosphorous
• AMC Related Problems include
– Yield Loss
– Corrosion of metal surfaces on the wafer
– Surface Pollution
• Haze on wafers
• Haze on optics
– Changes in contact resistance
• AMC Control
– Use materials with High Molecular weight and Low Volatility
– Use High Purity Materials
– Control Cross Contamination during Manufacturing and Installation
• Outgassing Measurements
– Testing is performed in vacuum. Sample from 100 to 300 grams in placed in special aluminum boat
and heated to 398K inside a copper container with a 6.3 mm hole for 24 hours. A Chromium plated
disk is placed in front of a 6.3 mm hole.
– TML Total Mass Loss
– CVCM Collected Volatile Condensable Material
– WVR Water Vapor Regained (Exposed to 50% Humidity for 24 Hours)

Levels of Vacuum
Name
Atmospheric Pressure (variable)
Low, Rough or Course Vacuum
Medium Vacuum
High Vacuum
Ultra High Vacuum
Extremely High Vacuum
Outer Space
Perfect Vacuum
Start torr (Pa)
760 (101.325 kPa)
760 (101kPa)
25 (3kPa)
1x10 -3 (100nPa)
1X10 -9 (100mPa)
1x10 -12 (100pPa)
1x10 -6 (100uPa)
0 (0)
Stop torr (Pa)
25 (3kPa)
1x10 -3 (100mPa)
1x10 -9 (100pPa)
1x10 -12
3x10- 17 (3fPa)

Vacuum Cluster
Challenges
• Process Challenges
– Time to purge
– Temperature
– Chemistries
• Clusters used for
alternate
atmospheres
• Operate near strong
electro-magnetic
fields
– No magnetic
signature
– Static electricity
• Moving the Wafer
Vacuum Robot
High Vacuum
Process
Chambers
Integrated
Process
Chambers
Orienter / Degas
Low Vacuum
Wafer Cassette Loadlocks
Process
Chambers
Cool-Down/
PreClean
Chambers
Orienter / Degas

Vacuum Robots
• Very high reliability
• Operate in vacuum
– 10-8 Torr
– Material compatibility
– No virtual leaks
• Low profile
– MESC compatibility
– Minimize chamber volume
• Sophisticated controls
– Increase wafer throughput
– Prevent wafer slippage
– Time optimized trajectories
• 7 to 9" arm links

Robot ARM Types
• Frog Leg
– More Bearings
– Second Wafer Moves at Low Speed
– Higher Throughput for Same Accel
• SCARA
– Simple Design
– Must Have Bands or Belts in Vacuum
– Speed of Extension limited by Second Wafer
• Four-Bar Linkage
– No Bands
– More Bearings

Vacuum Robot Vendors
Vendor
Brooks
IDE
Rorze
Genmark
Yaskawa
JEL
AITEC
Sankyo
Models
Mag 7
RR452, RR713
AVR3000
SVHR3163, STVHR4000,
DVHR3200
AR-SV300, AR-WV300
SR8600
Technology
Permanent Magnet
Ferrofluidic Seals
Ferrofluidic Seals,
Only in Japan
Ferrofluidic Seals
Single and Dual
Single and Dual Arm

Motion and Vacuum
• Cannot use a vacuum ∆P chuck
to hold a substrate
– Edge Grip
– Highly Optimized Motion
– Special Materials
• Motion can be created either
inside or outside the vacuum
barrier, both create challenges.
• We will look at some of these
challenges for robotics, but could
be applied to any general device.

The Vacuum barrier, How do you Cross
• Mechanically
– How do We transmit Motion or Torque Across the
Barrier
• Electrically
– Need to get Signals and Power Across the Barrier
• Information
– Need to See and measure things
• Quarts
• Encoders
• Lasers

Two Main Choices
• Create Motion in the vacuum
• Create Motion outside of vacuum and then
provide feed through transferring motion to
the vacuum.
– Bellows
– Ferro fluidic Seals
– Lip Seals
– Mag Coupling

Permanent Magnet
•Pros
•Good Vacuum Isolation
•Simple Design
•Cons
•Bearings in Vacuum
•Magnets and epoxy in vacuum
•Can Stack for extra DOF
•Brooks has Patent
Vacuum
Flux
N
Magnet Flux
S
Magnet Flux
Flux
Bearings

Bearing
Magnetic Coupling
•Pros
•Good Vacuum Isolation
•Cons
•Bearings in Vacuum
•Magnets and epoxy in vacuum
•Two air gaps produces control and
stiffness issues
•Can Stack for extra DOF
•AMAT has Patent
Vacuum
Flux
S
Magnet Flux
N
S
Magnet Flux
Flux
S N N
Magnet Flux
Magnet Flux

Ferrofluidic Seals
•Pros
•No Bearing in Vacuum
•Motor and Sensors can be standard
•Cons
•Seal can Burp during pump down
•Seal can Outgas
•Reliability of Seal
•Concentric shaft for added DOFs
•Used by Yaskawa, Brooks has some
Patents via Smartmachines
Vacuum
N
S
Magnet Flux
Magnet Flux
Magnet Flux
Magnet Flux
Magnet Flux
Magnet Flux
N
S
Ferrofluidic Liquid
Flux
N
Magnet Flux
S
Magnet Flux
Flux
Bearings

Harmonic Drive
•Pros
•Motor and Sensors can be standard
•Gear Reduction reduces motor and
sensor costs.
•Cons
•Bearings in Vacuum
•Flex Spline Circular Spline Interface
in Bearing
•Costs
Circular Spline
Vacuum
Flex Spline
Wave Generator

Placing Motor in Vacuum
• Standard Motors not suitable for less than 10^-4 Torr.
– bearing grease,
– paper slot liners,
– conformal coatings,
– winding insulation
• Lubricants are not suitable and will vaporize resulting in bearing failures and
fouling other components.
• Some lubricants boil off very quickly others such as Silicon don’t vaporize as
fast but create low level contamination on all components and are very hard to
clean.
• Cooling. How do we get the heat out.
– Heat Sink
– Heat Pipes
– Radiation
• Micro Leaks due to construction
– Laminations
– Non Vented Screws.
• Micro Environments make create voltage discharge paths

Electrical Challenges in A Vacuum
• Insulation
• Getting rid of heat
• Out gassing
• Exiting the Vacuum

Electrically
• Exposed conductors should be insulated
– Arcing can be an Issue
• Vacuum approved Solders
• Virtual Leaks
• Electronics Components in Vacuum
– Enclosing
• Enclose in Box
• Must monitor pressure
• Shields device from vacuum (issue for some chips)
• Prevents Out gassing
– Potting
• Completely cover with Potting material such as vacuum compatible
epoxy.
• Should Minimize area by placing in recess
• Whole assembly often must be scrapped if there is a component failure
• Can actually improve heat transfer.
– Venting
• Same as Enclosing, but vent supplied to atmosphere.

Out gassing in Cables
• Construction
– Stranded Cables can have
voids between wires creating
virtual leaks
– Trapped Air can cause Cable
Ruptures and expose Interior
materials
• Materials
– Must select Materials that
have low Out gassing.

Position Information
• Type of Rotary Actuator
– Encoders
• Easy to Interface
• Lower Cost
– Revolvers
• Absolute Position
• Robust
– Capacitive Encoders
• Low Cost
• Absolute and Incremental
• Could be Made Vacuum Compatible
– In Vacuum
• Disc in Vacuum Sensor Outside
• Use Quarts viewing Window (Adds Costs)
• New Vacuum Compatible Read heads can be placed in vacuum

Use a Window to View Sensor
Code Wheel
Sensor Window
Quarts Windows
Vacuum Barrier

Design Consideration
• How do we Maintain it
– Virtual Leaks
– Material Compatibility
– Out gassing

Pump down Speed is Critical
How do we optimize it
• Minimize the Volume
• Eliminating the cracks, crevices and other areas that
trap gasses
• Fine machine finishes hold less air
• Porous metals typically require cleaning and sealing
• Machined metals are preferable to castings
• Avoid Leaks and Virtual Leaks
– Leaks: Leaks can take the form of air leaking through seals,
or air or other contaminates leaking from contained volume
or voids.
– Vent Screw
• Select the correct Components

How To Select Materials
• Out-gassing
– Evaporation
– Sublimation
• Thermal Compatibility
• Use

Material Compatibility
Carefully Selected
Wet Lubricants
Vacuum Lubricants
Dry Lubricant
Low Vacuum (Mechanical Pump)
High Vacuum Turbo Pump
Many
Commercial
Plastics
Limited Plastics
Most Natural Materials
Must be eliminated
No Plastics
ATM
10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9

Vacuum Lubricants
• Solid
– MoS2 (molybdenum disulphide) Good down to 10 -12 torr
– WS2 (Tungsten Disulfide)
– Lubricant is often provided by cage or Spacer.
• Grease/Oil
– TorrLube Good Down to 10 -9 torr
– Fomblin Y perfluoroalkylpolyether (PFPE)
– Isoflex
– Krytox (PFPE)
– Barrierta

Common Materials
• Stainless Steal
– Strength
– Corrosion Resistance
– Available in Magnetic and Non-Magnetic Forms
– Common Alloys Include
• Xxx Mag
• XXx non Mag
• Aluminum
– Good Stiffness To Weight Ration
– Easily machined
– Non Magnetic
• Common Alloys Include
• Ceramics
– Chemical Resistance
– Temperature Resistance
– Thermal and Electrical Insulation
– Alumina
– Quarts
– Beryllium Oxide?
• Plastics
– PolyBenzImidazole (Celazole) High Temp, Brittle, Hard to Machine. Bushings, Bearings, Rollers
– Polyimide
• Vespel High Temp, Expensive
• Duration, Lower Cost than Vespel, similar Properties
– PolyAmide-Imide (Torlon) Low Thermal Expansion, typically used for Insulators, spaces. Can be glass filled.
– PTFE

Low Outgassing Plastics
• PolyBenzImidazole
– Celazole® is the highest temperature-capable plastic available. However, it is very brittle (almost ceramic-like) and quite
difficult to machine. That said, is it frequently used for bushings, bearings, rollers, and spacers in extreme environments.
Polyimide
– DuPont Vespel® SP-1 is one of the most-used high-temperature plastic materials used in applications where high-purity
and electrical properties are needed. Vespel is frequently used in ultra-clean semiconductor and chemical applications. It
is also one of the most expensive materials sold, but is flight-approved for NASA, USAF and other aerospace agencies.
– Duratron® XP is the first real alternative to Vespel ... it was developed specifically to replace Vespel in extreme
applications at a slightly lower price. It contains less than 1% metallic impurities as measured using the ICP-MS test
standard. Duratron XP is ideal for use in high-energy gas plasma etch and strip processes.
• PolyAmide-Imide
– Unfilled Torlon® 4203 has high dielectric properties and low thermal expansion, and is much less expensive than some
advanced polymers. Torlon 4203 is typically used for insulators, spacers, and mechanical parts up to 520°F.
– Torlon 5530 (30% glass-filled) is typically used for applications where dimensional stability over a wide temperature
range is needed, as with temperature test sockets, nests, and fixtures. : Torlon's moisture absorption is a bit high, so
critical dimensional stability can be an issue.
• Semitron® ESd 500HR (filled PTFE)
Semitron® ESd 500HR is antistatic/conductive PTFE. This material is relatively clean, readily machinable,
dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other
applications where static generation may cause failures and/or errors in production environments. PTFE
has good mechanical properties up to approximately 500°F.
• Neoflon® PCTFE (PolyChloroTetraFluoroEthylene)
PCTFE exhibits high chemical resistance, low and high temperature capability, resistance to most
chemicals (including strong acids and bases), low friction, electrical and thermal insulation, and
"slipperiness".

Low Outgassing Plastics
• PEEK (PolyEtherEtherKetone)
PEEK is pure, easily machinable, chemically resistant, stable, and also has relatively low outgassing
values. PEEK has good mechanical properties, but will not take temperatures over 350°F, so it may not
have the mechanical or thermal performance needed.
• Techtron® PPS (PolyPhenylene Sulfide)
Techtron® PPS is easily machined to close tolerance, has excellent mechanical, thermal and chemical
stability and has one of the lowest outgassing thermoplastic material. Techtron PPS is generally a bit less
expensive than PEEK or Torlon, but will not take as high temperatures.
• Ultem® PEI (PolyEtherImide)
Ultem® has good dielectric properties and low thermal expansion, and is considerably less expensive than
some other polymers. PEI is also clean and stable, but is not particularly resistant to chemicals or solvents
. PEI has good mechanical properties up to approximately 410°F.
• Semitron® ESd 410C (filled PEI)
Semitron® ESd 410C is antistatic/conductive PEI. This material is relatively clean, readily machinable,
dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other
applications where static generation may cause failures and/or errors in production environments. PEI has
good mechanical properties up to approximately 340°F.
• Ertalyte® PET-P (Polyethylene Terephthalate)
Ertalyte® offers the dimensional stability of acetal with the wear resistance of nylon. Ertalyte® PET-
Polyester is clean, chemically resistant, stable, PET-P is considerably less expensive than most of the
other materials listed above, but may not have the mechanical or thermal performance needed for all
applications.
• Semitron® ESd 225 (filled acetal)
Semitron® ESd 225 is antistatic/conductive acetal. This material is relatively clean, readily machinable,
dissipates static electricity reliably ... as a result it is used in test handling equipment, fixtures, and other
applications where static generation may cause failures and/or errors in production environments. Acetal
has good mechanical properties up to approximately 180°F.

Bearings
• Ball
• Cross Roller
• Magnetic
• Chamberlink Actuator
– Puts Bearing on Outside

Bearings
• EXAMPLE A:
– RINGS: Stainless Steel
BALLS: Stainless Steel
RETAINER: Vespel® or PEEK
LUBRICATION: Solid, MOS2. Solid, WS2 (Tungsten
Disulfide)
FEATURES: Clean, high temperature, corrosion resistant,
solid lubricated, inexpensive.
• EXAMPLE B
– RINGS: Stainless Steel
BALLS: Solid Lube Coated Stainless Steel
RETAINER: PEEK
LUBRICATION: Solid, MOS2
FEATURES: Clean, high temperature, corrosion resistant,
solid lubricated, increased life, increased performance, more
expensive.

Materials Information
• Good Information Available
• Use Your Suppliers
• Use the Web
– NASA
• http://outgassing.nasa.gov/

References
• Low Outgassing Cables for Clean Room
– HITACHI CABLE REVIEW No.24 (AUGUST
2005)
• http://outgassing.nasa.gov/
• http://en.wikipedia.org/wiki/Main_Page

Backups

Design Considerations
• reliability,
• product safety,
• efficiency,
• response time,
• flexibility, and
• maintenance issues.
• Thermal

Summary
Cost
Patent
Clean
Proven
Stiffness
Magnetic
Coupling
10
10
5
3
10
Ferro Fluidic
9
3
10
3
3
Permanent
Magnets
7
10
5
3
4
Harmonic Drive
8
3
7
5
2

How do we create a Vacuum
• This vacuum is produced by pumping air out
of a chamber or chambers
• At pressures above 10 -6 Torr a standard
Mechanical Pump can be used.
• At pressures below 10 -6 Torr a standard
turbo pumps are often used.

Types of Vacuum Pumps
• Positive Displacement (.1Pa)
– Diaphragm
– Piston Pump
– Scroll Pump
– Gear Pump
• Momentum Transfer (
– Diffusion (10-8 to 1 pascals )
– Turbo Molecular (intermediate
vacuum (~10-4) up to
ultra-high vacuum levels (~10-10 Torr). )
• Entrapment
– Cryopumps
– Ion pump
– Sorption Pumps

Cluster
Vacuum
Loadlocks
Vacuum
Robot
Vacuum Transport
Chamber
View From Front End (EFEM
Interface)
Top View Looking Towards
Front End

Vacuum Challenges
• Operating in vacuum
– Limits material selection
– Limits lubrication
– No out gassing
• Motion across vacuum barrier
– Ferofluidic seals
– Magnetic coupling
– Cooling
• No Vacuum to Grip
– Highly optimized motion
– Special materials
• Reliability

• Methods of Getting Power Across
– Ferofluidic seals
– Magnetic coupling
– Cooling
• Operating in vacuum
– Limits material selection
– Limits lubrication
– No out gassing
• Reliability

How do we create a Vacuum
• This vacuum is produced by pumping air out
of a chamber or chambers
• At pressures above 10 -6 Torr a standard
Mechanical Pump can be used.
• At pressures below 10 -6 Torr a standard
turbo pumps are often used.

Sin/Cosine

Linked Slides

Median Speed
• Friction between silicon and
stainless steel is about .24 G
• Must Grip the Wafer to move
faster, or use a polymer to
increase Friction
• We must limit the acceleration
of the robot when it has a
wafer on either end-effector.
– Thus the Kinematics of the robot
may affect the overall
Throughput.

Paschen’s Law

Resolver
• Uses an AC signal to excite the rotor winding.
• Stator has two windings at 90 degrees to each other.
• As the rotor turns the coupling to the two windings will change
• Can have multiple poles, but you lose absolute capability.
• Converters usually are analog and can be expensive, $200 for 14-16 bits.
• Rotor current normally passed through an inductive coupling.
• Could be placed in vacuum environment.
Cosine
Reference
Sin