Prefurnace Clean Sink (PFC Sink) - Login | Nanolab, UCLA

Superusers:
Prefurnace Clean Sink (PFC Sink)
You-Sheng (Wilson) Lin
Tom Lee
1.0 SCOPE
PREPARED BY:You Sheng Lin, Nanolab Staff
9-14-06
NRFS-8
This document establishes the procedures for wafer cleaning in the Prefurnace Cleaning Sink
located in the RTA aisle (see figure 1). There are 2 constant temperature baths located in the
center-right side of the deck and identified as Bath 1 and Bath 2. Normally there will be either
a Piranha solution or an RCA Step 1 NH4OH solution in Bath 1, and a RCA Step 2 HCl
solution in Bath 2. One HF sink located in the center-left side of the deck. All work at the PFC
Sink is designed to achieve high purity cleanliness requirements for the Nanolab's high
temperature furnace systems.
Caution: Do not use any organic materials in or around the PFC Sink. Organically coated
wafers, i.e. photoresist, must be removed at another hood, prior to processing at the PFC
Sink.

#3
Dump Rinse
2.0 APPLICABLE DOCUMENTS
Figure 1
MSDS for sulfuric acid, hydrogen peroxide, hydrochloric acid, ammonium hydroxide,
hydrofluoric acid. All the MSDS documents are stored at the table next to the entrance of the
Nanolab.
3.0 MATERIALS AND EQUIPMENT
Chemical Bath Controllers
Dump Rinse Controllers
#2
Chemical Bath
# 1
Properly exhausted PFC Sink exhaust system as noted on the Magnehelic gauge (see figure 2).

Materials:
Fig 2
1. Dedicated constant temperature baths, either Bath 1 or Bath 2, depending
on process
2. Temperature controller, located in PFC top plenum area, identified as Bath
1 or Bath 2 controller
3. Required chemicals (see individual specification for each chemical bath
process)
4. Acid safe gloves
5. Face Shield
6. Acid apron
7. Teflon cassette
8. Graduated cylinder or clean beaker
9. Prefurnace Clean Sink (PFC) Fume Hood
10. Dry N2 gun or Verteq spin dryer (depending on wafer size and condition)
Note: No broken, fractured or wafer pieces are allowed in the Verteq spin dryer system,
rather these pieces or wafers should be dried with the nitrogen blow gun.

4.0 GENERAL
Note: Follow all safety procedures for handling, pouring, and disposing of
chemicals.
Note: This procedure is to be conducted only within the exhausting PFC Sink fume
hood.
Materials: Use only the clean quartz constant temperature bath identified as Bath 1 or
Bath 2. Use dedicated materials for any piece that comes in direct contact with the acid
solutions. Keep the wafer carrier handles with the wafer carrier in the chemical baths.
5.0 PROCESS PREPARATION
5.1 Select bath and wafer cassettes
1. There are two chemical baths located on the center-right side of the PFC sink (see figure
1).
CAUTION: Do not use any of the colored cassettes e.g., black or
orange. (These are not Teflon)
2. For 4 inch, use a full 4 inch cassette and they are located in the storage cart under the
fumehood. (See Figure 3)
Figure 3
3. Single wafer Teflon carriers are available for single 2.5" or quartered wafers, or for
irregularly shaped substrates.

5.2 Chemical Bath Replacement (STAFF ONLY)
1. Confirm bath is below 40 o C (turn on bath power to see current temperature).
2. Contact Nanolab staff to replace the bath.
5.3 Pour Chemicals
NOTE: At this point you must be wearing safety glasses, safety shield, acid apron and acid
gloves. (See Figure 4)
Figure 4
You must decide which Prefurnace cleaning process is desired, as this will effect which
chemical bath you will use, as well as what chemicals you will use. (See Figure 5) For gate
interface oxidation runs (Dry OX), the RCA procedure is recommended, using

Figure 5
1. RCA Process Bath 1: DI Water (H2O) : Ammonium Hydroxide (NH4OH) :
Hydrogen Peroxide (H2O2) 5:1:1 ratio.
a. 6000 ml DI Water
b. 1200 ml Ammonium Hydroxide
c. 1200 ml Hydrogen Peroxide (Refresh solution with 250 ml H2O2, each usage)
d. Heat the solution to 90 o C. The solution should begin to bubble vigorously as it
approaches 90 o C. If not, wait a little longer and/or add more hydrogen peroxide. If
the solution does not bubble, there is a problem contact Nanolab management.
2. RCA Process Bath 2: DI Water (H2O) : Hydrochloric Acid (HCl) : Hydrogen
Peroxide (H2O2) 5:1:1 ratio.
a. 5000 ml DI Water
Dump Rinsers
b. 1000 ml Hydrochloric Acid
Bath 2
HCl Only
Bath 1
Piranha or NH4OH
c. 1000 ml Hydrogen Peroxide (Refresh solution with 250 ml H2O2, each usage)
d. Heat the solution to 85 o C. The solution should begin to bubble vigorously as it

approaches 85 o C. If not, wait a little longer and/or add more hydrogen peroxide. If
the solution does not bubble, there is a problem contact Nanolab management.
3. Piranha Process Bath 1: Sulfuric Acid (98%) (H2SO4) : Hydrogen Peroxide
(H2O2) 17:1 ratio.
6.0 PROCEDURE
6.1 Sample Loading
a. (2 bottles @ 15 lb. each) Sulfuric Acid (~7400ml)
b. 425 ml Hydrogen Peroxide (Refresh solution with 250 ml H2O2, each usage)
c. Heat the solution to 100 o C. The solution should begin to bubble vigorously as it
approaches 100 o C. If not, wait a little longer and/or add more hydrogen peroxide.
If the solution does not bubble, there is a problem contact Nanolab management.
1. Place wafers in white Teflon cassette and secure the Teflon handle to the cassette. NOTE:
For a polysilicon run, include a silicon wafer with 1000 Å of oxide to be used as a
thickness monitor on the Nanospec. Record the monitor number in the polysilicon
logbook.
6.2 Wafer cleaning and rinsing
1. Piranha (or RCA 1) Cleaning Procedure:
a. Turn on Power buttons for constant temperature baths 1 & 2. Press Hold to turn
off the HOLD LED to begin the heating sequence.
b. Verify that the solution in chemical bath 1 is Piranha solution. This is verified by
looking for the recent bath entry in the log book.
c. If the bath is different than Piranha, please contact Nanolab Staff.
Note 1: If you replace or change the type of chemical bath solution, remember to fill in the
logbook.
Note 2: To make more Piranha solution chemical for Bath 1: pour 2 new sulfuric acid
bottles (15 pounds each) into the empty Bath 1 quartz pot. Using a graduated cylinder or a
clean beaker, measure 425ml of H2O2 (hydrogen peroxide). Allow solution to come to
temperature (100 o C) prior to inserting wafers. We use a 17:1 ratio for our Piranha
solution. :
Note 3: To make more RCA Step 1 chemical for the bath: using graduated cylinder or a
clean beaker, measure 6000ml of DI water; 1200ml of NH4OH (ammonium hydroxide);
and 1200ml of H2O2 (hydrogen peroxide). Allow solution to come to temperature prior to
inserting wafers. We use a 5:1:1 ratio.

d. Remove the top cover of the chemical bath 1. Refresh the solution with 250 ml
hydrogen peroxide (H2O2), unless the solution was made immediately prior to
usage. Make sure the bath temperature is less than 30C.
CAUTION: Do not overfill the bath, use the aspirator (figure 6) to remove some
chemical prior to adding the hydrogen peroxide.
Figure 6
e. Verify it is at 90 o C prior to usage then immerse the cassette in Bath 1. (see figure
7 below). Press Timer on the Bath 1 controller to activate the 10 minute timer.

Figure 7
Hot Pot Lid
Chemical Bath
Dump Rinser
f. After 10 minutes, move the wafers to the dump rinser in front of the hotpot and
close the lid on the dump riser. Turn off the chemical bath controller by hitting
POWER and hit START on the appropriate dump rinse controller. Dump rinse
controllers are set for 5 dump cycles, and will require about 10 minutes to finish
the rinsing process.
g. For the RCA 2 clean process, after the wafers are rinsed in dump rinser 1, refresh
the HCl bath (bath 2) with 250ml of hydrogen peroxide and at 90 o C perform the
HCl step ONLY USING BATH 2. Bath 2 has its own controller (see figure 1), so
follow the procedures in 6.2.a above and verify it is at 90 o C prior to usage. After
the 10 minutes minimum in bath 2, turn off the power by hitting POWER. Then
move the wafers into dump rinser 2 (directly in front of bath 2) and hit START on
dump rinse controller 2.
Note: If you need to make (or
replace) the HCl solution in Bath 2, follow procedure in 5.2. Then, using the
graduated cylinder or a clean beaker, add 5000ml H2O (DI water); add 1000ml
HCl (hydrochloric acid); and 1000ml of H2O2 (hydrogen peroxide). Allow the
solution to come up to 90 o C prior to inserting your wafers and carrier. We use a
5:1:1 ratio.
h. If an HF dip is required (figure 8), remove wafers in carrier from the dump rinser
and remove the lid of the cascade rinser on left of PFC sink deck. The chemical is
DI:HF (10:1 ratio) or BOE (NH4F:HF: 6:1). CAUTION: Never place hot

wafers in the HF tank. Always finish the dump rinse step and ensure that the
wafers are at room temperature. Set the wafer carrier with handle into the HF
solution for the desired time. Turn on the cascade rinser and nitrogen bubbler for
the rinsing step.(See Figure 8). When finished, turnoff both cascade bubble and
water, then dry the wafers as discussed in 6.3 below.
NOTE: HF is a separate training; only trained users can use HF bath.
Figure 8
HF or BOE
Rinse Bath
Cascade Bubble and Water
Rinse Controller

Fill out logbook: Enter run number, date, your name, new bath or refresh, comments.
Drying the wafers: Fill out Logbook for Verteq Spin Dryer System
Note: Only 4 inch wafers carriers can go into the Verteq Spin Dryer System. 3 inch
wafers can be spun dry only in the modified 3 inch carrier inserted into a standard 4
inch carrier.
4 inch wafer full cassettes
NOTE: Make sure all wafers are sitting straight in the cassette, no cross slotting, before
starting rinse/dry.
1. Immediately place the boat into top chamber (H-bar forward) and select the proper recipe
(Recipe 0) and press START. Step 1 of Recipe 0 is a 3 minute heated DI rinse, followed
by step 2, 10 minutes of heated nitrogen for the dry. When the recipe is complete, remove
the wafers to load the furnaces.
2. Wafers are allowed to stay in dryer no longer than a half hour.
Minispec: You-Sheng (Wilson) Lin (yousheng@seas.ucla.edu)
©2006 UCLA, The Nanoelectronics Research Facility, Los Angeles, CA, USA. All rights reserved.