| Safety: |
Acid protective gear MUST be worn when working
at this sink and when transporting or handling chemicals. An
acid-proof apron, sleeve guards, acid-proof gloves (atop the
normal clean room gloves), and an acid face mask (with the
face shield DOWN) worn over safety glasses, are all required.
ALWAYS know the location of the nearest eye wash and safety
shower.
Before using the acid-hood, verify that the exhaust is working.
The louvers must be open, and the plastic shields must be
down. Note: The louvers have been set for proper flow, and
must not be adjusted. Never, for any reason, put your head
inside the acid-hood1s working area.
Chemicals must be transported to and from the acid hood
using the chemical cart. Handling of chemical bottles, beakers,
or other vessels must always be done with dry acid-gloved
hands. Typically, acids should be added last to solutions.
The chemicals used in the acid-hood are all dangerous to
touch or inhale. HF acid is very dangerous and HF burns are
particularly hazardous. An insidious aspect of HF burns is
that there may not be any discomfort until long after exposure.
These burns are extremely serious and may result in bone
tissue damage. If you contact HF, flush the area well and
be sure to work under and around your fingernails, then apply
calcium glutamate to skin burn. Fingernails and cuticles
are the classic areas where people receive burns, having
washed off the HF without washing under their nails. If washed
off within a few minutes of exposure, immediately followed
by application of the gel, HF may do no harm. Remember, HF
may not produce any burning sensation until after it has
already done damage. A physician should look at all HF burns.
In case of chemical exposure, call for help to the person
nearest you and tell them to call the MIT campus police (dial
100). While you are speaking to the person nearest you, get
to the nearest shower or eyewash as fast as possible. Exposure
of the eyes requires flushing with water for at least 15
minutes. As a precaution, all exposures to the eye will require
a visit to an emergency room for a check up. Contact a staff
member as soon as possible for assistance or call 100. Exposure
of the skin requires immediate removal of all contaminated
clothing. Rinse under the shower for 15 minutes. Contact
a staff member as soon as possible for assistance or call
100.
|
| Procedure: |
NOTE: Operation will be demonstrated using
the "Piranha" cleaning Process, in a "CMOS" contamination
category.
- Check Equipment Reservations in CORAL to insure that
you reserved the correct machine in the correct facility
for the correct date. Another user may have reservations;
it is your responsibility to honor them, if this is the
case.
- Use the "Engage" command in CORAL for
the equipment that you are about to use; use this command
BEFORE you start the operation. Insure that the correct
facility is set (TRL) and that your lot name is entered
correctly.
NOTE: Contamination control is of extreme importance in all TRL equipment.
You must know what contamination level your wafers classify into, and
use labware and equipment of the same classification. Broadly, the
lab and this machine are separated into "GOLD" (red-tagged)
and "CMOS" contamination categories. Wafers and labware classified
as "GOLD"
are not allowed in the dump-rinse, so you will need to rinse your wafers
inside a separate bath of DI water in the acid-hood. There is a dedicated "GOLD" spin-rinse-dry
and aspirator, and you need use dedicated "GOLD" tweezers
and wands when handling these wafers.
- Place wafers in the appropriately marked teflon wafer
carrier; use the correct teflon handle for the process
you are about to perform.
- Gown up with apron, face shield, arm protectors and rubber
gloves. Thin vinyl gloves and clean room suits do not provide
protection against corrosive and hazardous chemicals.
Never touch the inside of a process tank or a teflon wafer carrier
with your hands, especially if wearing the rubber gloves, as these
gloves are extremely dirty by processing standards, and would contaminate
your lot and those following you. Instead, use the vertical or horizontal
teflon handles.
- Get chemicals from the chemical "pass-through" and
use the cart to transport them to the acid-hood. Note:
Use the small amounts of chemicals left in the bottles
by previous users before proceeding to open a new bottle.
- Place the appropriate quartz tank, which matches the
contamination level of your wafers and teflon labware inside
the acid-hood. A piranha is always processed in a quartz
tank, since it would destroy most polypropylene or polyethylene
plastic tanks and contaminate your wafers (conversely,
all HF processes, such as BOE, must be done in plastic
as they would etch a glass tank). You may process in the
sink or on a solid surface inside the hood, but you may
not process within one foot of the front edge of the hood
for both spill and exhaust flow safety reasons.
- Add hydrogen peroxide. In a piranha, the ratio of hydrogen
peroxide to sulfuric acid is 1:3, which can be approximated.
Due to dangers inherent in pouring these chemicals, we
don't normally measure this ratio exactly. Always open
and close ALL chemical bottles within the confines of the
acid-hood, as most spilling of chemicals occurs in the
transfer of chemical bottles. When pouring, keep the bottom
of the bottle from protruding out of the hood enclosure,
so any drips do not land on you or on the floor. If you
need to measure critical chemical volumes, graduated cylinders
are stored above the hood. Processing is not allowed in
these dedicated measuring vessels, and they MUST be cleaned
and returned immediately after use.
- Add sulfuric acid to a level that would cover the wafers.
Let the solution stand for several minutes.
- Place wafers inside the beaker. Typically, we leave
wafers in piranhas for10 minutes, although you may need
more time if your wafers are not completely clean at the
end of this time. If your wafers appear to need more than
20 minutes in piranha, you may need to aspirate out the
solution and start again with a new mixture. You must never
end a piranha before your wafers are completely clean.
If you do so, you would be leaving the tank in a dirty,
unclean, state, and your wafers would contaminate all following
equipment such as the dump-rinse and the SPIN-DRYER.
- Before you remove carrier/wafers from acid mixture for
rinsing, press the RESET then START buttons on the dump
rinse tank. The rinse tank has been set for 3 cycles. After
two cycles, or after the water resistively has exceeded
1 mega-ohm, place your wafers inside the dump rinse tank
and press RESET then START again. Do not remove the wafers
until either 3 cycles have completed or until the resistively
is above 1 mega-ohm again.
- Wash and dry gloved hands while wafers are rinsing to
avoid dragging chemical to other areas.
- An audio/visual warning (flashing digital readout) will
sound at the end of the third rinse cycle. Press RESET
and STOP buttons twice to reset the rinse tank and silence
the alarm.
- Remove the wafer carrier from the tank. Avoid dropping
any acidic/other contamination from the glove onto your
clean wafers, and proceed directly into a SPIN DRYER to
prevent the wafers from air-drying.
- Dry wafers in the appropriate SPIN DRYER next to the
acid-hood. (140 sec rinse, 240 sec dry). If you do not
use the "rinse" cycle in any MTL SPIN DRYER,
you must do a rinse and dry run with dummy wafers, after
removing your wafers, to rinse out any contamination or
corrosives which may have been deposited while drying your
wafers.
- Remove wafers from carrier and return all carriers and
holders to their proper shelf.
- Aspirate acids from the beaker in the acid hood.
- Rinse and aspirate the interior of the beaker at least
3 times. Rinse the outside of the beaker and place upside-down
on fabwipes on the counter to briefly dry. Return all labware
to the original shelf location before you leave the area.
- Rinse the tip of the aspirator with DI Water and put
it away.
- Inspect bottles for chemical drips and wash if necessary.
- Rinse counter with DI water from the water gun.
- Return all chemicals to the "pass-through".
- Wash acid gloves and hang up to dry.
- Remove safety attire and place it in its proper location.
- "DISENGAGE MACHINE" in CORAL.
|
Technical
Staff Only 
