Wisconsin Center for Applied Microelectronics
1550 Engineering Drive
Phone: 608/262-6877
BOE / HF BENCH
AND CASCADE RINSER
OPERATION
Rev. 2/12/16
PURPOSE OF THE TOOL: Wet etch of silicon oxide in buffered or unbuffered HF
MATERIAL RESTRICTIONS:
Every member of the WCAM labs has the right to expect that our tools are free of
contaminants that could be dangerous, or that could affect process results. Therefore, every lab
member is personally responsible for ensuring that every material he wants to use is specifically
allowed in the specific tool where he wants to use it.
All materials allowed for use in the BOE/HF bench are listed in the Allowed Materials list,
available in the “Chemicals in the Lab” section of the WCAM Website. Go to
wcam.engr.wisc.edu for more information.
Chemicals may be prohibited from use in a tool on grounds of safety or contamination.
Generally, the only liquid chemicals allowed at this bench are HF and buffered oxide etch (BOE).
No solvents or bases are allowed at the BOE/HF bench.
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SAFETY PROTOCOLS:
As you learned during your training at this bench, hydrofluric acid (HF) is one of the most
dangerous substances that members of the WCAM labs interact with directly. Each user must
pay close, continuous attention to following all safety protocols while using this wet bench.
The list below summarizes the protocols you learned during training. You are responsible for
remembering and following your training, as well as for thinking on your own about the effects
of your actions at this tool.
The central concern for using a corrosives bench is to KEEP THE CHEMICALS IN THE BENCH
and KEEP THE CHEMICALS OFF PEOPLE.
Properties of Hydrofluoric Acid (HF)

HF is a weakly-ionizing acid; it
penetrates tissue easily and can
spread to other parts of the body

Exposure may not immediately
produce pain or visible effects

HF absorbed into your skin can
enter your blood and stop your
heart

HF corrodes and damages skin, muscle, bone, and other tissues

ANY suspected exposure to HF is a medical emergency. Your response in the first few
minutes may make the difference between life and death. Remember and follow the
emergency response training you received when you were certified to use this tool.

A Material Safety Data Sheet (MSDS) for HF can be found in the binders in the
gowning room
SEE ALSO HF exposure procedures under Emergency Response
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SAFETY PROTOCOLS continued
Personal Protective Equipment (PPE) Protocols
Any time you interact with the wet bench in any way – even to just check on the
progress of your etch – you must wear full PPE, including a face shield, a chemicalresistant apron, and chemical-resistant gloves.

Face shield: Tighten the head strap on the shield, so it cannot fall off and knock over a
chemical container. Wear the shield in the down position, covering your face. Never
touch the shield while wearing chem gloves.

Chemical-resistant apron: Choose the correct size chem apron. Tie or snap it at top
and bottom, so it cannot fall open and interfere with your work. Place damaged
aprons on the bottom shelf of the apron rack; place contaminated aprons in the wet
bench. Never put aprons in the trash.

Chemical-resistant gloves:
o Label your gloves with your name and their application (acid, base, solvent)
o Any time your hands reach inside the corrosives bench, you must wear chem
gloves; any time you touch controls on the outside of the bench, or other
things outside the bench, you must not wear chem gloves.
o Before putting on your gloves, inspect them, and test them for leaks
o Do not reach directly into chemicals, even with gloves on
o Rinse your gloves often while working
o Extend the safe lifetime of your gloves by always storing them in a sealed bag.
Label the bag with your name and the gloves’ application (acid, base, solvent).
o If your gloves become discolored or cracked, or begin to leak, stop using them
immediately. See WCAM staff for disposal and replacement.
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SAFETY PROTOCOLS continued
Protocols for Working at the Bench

Handling chemicals:
o Touch the doors of the chemical cabinets only with your cleanroom gloves,
never with your chem gloves
o When carrying chemicals from the cabinet to the bench, wear full PPE. Touch
the chemical jugs only with chem gloves. Carry with two hands: One on the
handle, and one beneath the jug
o Pour with two hands, one on the handle and one beneath the jug
o Use only as much of the chemical as you actually need

Chemical containers and sample handling:
o HF etches glass. You must use plastic or Teflon containers
o HF etches metal, such as metal tweezers
o Any open container of chemical, anywhere in the lab, must always be labeled
with the owner’s name and the chemical it contains.
o The wet benches are not storage areas; do not leave unused containers of
chemicals in them
o WCAM provides plastic wafer cassettes, baskets, and wands at each
corrosives bench. To minimize contamination, do not move them from bench
to bench. If something is missing, ask staff; don’t take it from another bench

Waste disposal:
o Place empty chemical jugs in the jug cart, never in the trash. You do not need
to rinse them out.
o Put broken glass or wafer pieces in the red bucket at the end of the bay
o Cleanroom wipers that have been used in the acid bench must be discarded in
the plastic “corrosives” trash can, not the metal “solvent” trash can
o Acids allowed at this bench may be disposed of by pouring them down the
bench drain while running lots of water
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SAFETY PROTOCOLS continued
Emergency Response Protocols
Your life and health are more important than your sample!

Exhaust failure: If the exhaust alarm on the bench sounds, or if the exhaust pressure
difference gauge exceeds its setpoints, you must immediately:
1) Make your bench safe. Dispose of chemicals in open containers, cover open
chem baths, and turn off any heaters
2) Leave the lab (not just the bay you are working in) by way of the gown room
3) Notify staff

Fire or Toxic Gas alarm: If either of these alarms sounds, you must immediately:
1) Leave the cleanroom by the nearest exit, usually the door at the end of the
bay. Go directly into the hall. Do not take time to log out of CRESS. Do not
take time to go through the gowning room and ungown. Just leave your
clearnroom suit on.
2) Leave the building. This is a state law; failure to evacuate can have legal
consequences
3) Go to the meeting point at the corner of Breese and University, near the
large church
4) Remain at the meeting point until WCAM staff check your name against lab
occupancy recover your cleanroom suit for laundering.

Chemical spills

EPO
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Etch Bath
1. Log onto CRESS.
2. Lift white tank lid and check acid level in tank. At idle the level should be halfway in tank.
3. Turn ON the ETCH BATH PUMP.
 6:1 BOE in the left tank
 15:1 BOE in the right tank
4. On ETCH BATH 1 timer:
 Press and hold STOP/RESET — then press START.
The Setup light is lit.
 Display flashes CS and 00:00 for clock setpoint.
 Use  keys to set time in minutes:seconds.
 Press STOP/RESET. The time is now ready.
5. Insert wafers in the either 3-inch or 4-inch wafer holder.
Pieces should be locked in the basket and then the basket
placed inside the 3-inch wafer holder.
Use only the BOE
6. Don all PPE – apron, face shield and 1 chemical glove –
holders or basket.
before transferring basket in the etch bath.
7. With chemical gloved hand, lift off the white tank lid and
Do not use holders or
set aside.
baskets from other
8. With chemical gloved hand, slowly lower holder/basket
process benches.
into acid tank.
9. With nitrile gloved hand, press START on the
controller to begin the timer.
10. With chemical gloved hand, replace the white tank
lid.
11. Rinse chemical glove.
12. At the end of set time, press STOP/RESET to stop
alarm.
13. Don all the PPE – apron, face shield and chemical
gloves – before removing holder/basket from acid
tank.
14. Lift off the white tank lid and set aside.
15. Go to RINSER procedures.
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Trouble Shooting Tip #1:
If solution doesn’t cascade
through the filter, try
turning off then on.
Trouble Shooting Tip #2:
Add more BOE solution to
the tank.
Cascade Rinser
#1
#2
#3
1. While wearing PPE slowing lift wafer holder/basket from Etch Bath. Hold above
tank to allow dripping of acid solution to stop before moving wafer holder/basket to
cascade rinser.
2. Lower holder/basket into #1 compartment of cascade rinser.
3. Replace the white tank lid to the acid bath.
4. Carefully rinse bench top surface to remove any acid drips.
5. Rinse chemical gloves and remove to operate rinse controller.
6. With chemical gloves off, push START on RINSER controller.
5-minute rinse cycle begins
5-second pre-alarm before end of rinse cycle
7. Push STOP/RESET to stop alarm.
8. Push STOP/RESET to reset rinser timer.
9. Slowly lift holder/basket from #1 compartment and move to #2 compartment.
10. Push START on RINSER controller.
5-minute rinse cycle begins
5-second pre-alarm before end of rinse cycle
11. Push STOP/RESET to stop alarm.
12. Push STOP/RESET to reset rinser timer.
13. Slowly lift holder/basket from #2 compartment and move to #3 compartment.
14. Push START on RINSER controller.
5-minute rinse cycle begins
5-second pre-alarm before end of rinse cycle
15. Push STOP/RESET to stop alarm.
16. Push STOP/RESET to reset rinser timer.
17. The rinse is complete. Lift holder/basket from #3 compartment and set on
perforated deck.
18. Go to the drying procedures.
Technique #1: Manually holding wafer or piece with tweezers and blow dry
with nitrogen gun.
Technique #2: For full wafers only. Automatically dry wafers by transferring
rinsed wafers into holder for Verteq spin dryer. Follow operating procedures.
19. Stored BOE/HF wafer holders/basket in cascade rinser.
Do not remove holders and use at other process benches.
LOG OFF CRESS
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