Chapter 2.1
Cleaning Procedures
1.0
Introduction
All cleaning procedures must be performed correctly, otherwise
wafers and labware are likely to become contaminated rather than clean. Never
touch a wafer with your hands, and always use clean tweezers. Use stainless
steel tweezers for non-acid work and Teflon® holders for acid work.
Use DI water only for any cleaning and rinsing in the lab.
2.0
Cleaning Laboratory Ware
Correct and thorough cleaning of Pyrex, Teflon® or
polypropylene ware (beakers, petri dishes, wafer boxes, thermometers, stirring
rods, etc.), is very important. All cleaning is to be done in the Chemical Room
of the Old Lab (Room 432C and cleaned at sink432C.)
2.1
Scrub all items to be used in the lab in Nova Clean NC-1
with a brush.
2.2
Rinse thoroughly in running DI water for two minutes.
2.3
Perform the water break test: submerge the item in DI water
and observe the film of draining water.
On a clean surface it will remain unbroken and fairly uniform.
Contaminants will cause breaks or sharp irregularities such as islands
to appear in the color fringes and droplets remain on the surface.
2.4
Allow to drain and dry chemical ware in the oven on an aluminum
foil sheet, under an IR lamp or with a nitrogen gun.
3.0
Cleaning Tweezers
3.1
Degrease
Degrease all new stainless and Teflon® tweezers as
follows prior to cleaning:
►
5 minutes rinse in acetone
►
1 minute rinse in running DI water
3.2
Cleaning
3.2.1
Metal and Teflon® Tweezers - Removal of Organics
Use acetone as per Section 3.1, to remove residual organic
contaminants.
4.0
Wafer Handling and Cleaning
To minimize contamination from the tweezers, never allow the rinse
or dip to touch the tweezers before it touches the wafer. Rinse or blow-dry
toward the tweezers.
4.1
Standard Wafer Cleaning in the VLSI Area
(Removal of residual
organic and metal contaminants:)
4.1.1
Piranha clean for 10 minutes at sink6.
4.1.2
Rinse wafers in the sink6 QDR (quick dump/rinse) which is
currently set for two dump/rinse cycles.
4.1.3
Final rinse until water resistivity reaches 10 megohm-cm.
4.1.4
Place in the sink6 SRD (spin-rinse/dryer) for a final rinse and
dry cycle. Water resistivity should reach 12 or more after this step.
4.2
Thin Oxide Film Removal
Dip in 10:1 H2O : HF until front and back of wafer dewet.
Pulling the wafer from the water leaves an absolutely water free surface with
only a drop or two on the lowest edge. If this test fails, reclean.
4.3
RCA Clean (widely used in industry)
*This procedure is optional.
RCA-1 - Removes organic residues
5 H2O (DI Water)
1 NH4OH (Ammonium Hydroxide)
1 H2O2 (Hydrogen Peroxide)
RCA-2 - Removes metallic residues
6 H2O (DI Water)
1 HCl2 (Hydrochloric Acid)
1 H2O2 (Hydrogen
Peroxide)
Process
5 min. in RCA-1 at 70ºC
5 min. in DI water rinse
5 min. in RCA-2 at 70ºC
DI water rinse to 10 megohm-cm
5.0
Quartzware Cleaning Procedure
Hydrofluoric acid (HF) is extremely dangerous. Always wear
chemical-resistant gloves on top of your surgical gloves, rubber apron and eye
protection(safety goggles plus face shield) when you work with it. Test your
gloves for leaks by inflating them with the N2 gun to twice their size and
immersing in a water bath. If any bubbles of escaping gas are observed throw
the glove away.
5.1
For all quartzware, it is essential that oils (from fingerprints)
or other organic contaminants be removed by wiping with trichloroethane
followed by acetone.
5.2
The cleaning solution consists of 5% HF : 95% DI water.
5.3
Rinse well in DI water. Dry under IR lamp or in oven.
6.0
Tystar Dummy Cleaning Procedure
6.1
Wafer Identification
All dummy wafers are specific to a furnace and should be scribed
on the back with the furnace number. Each furnace deposits a different film as
follows: tystar9 and tystar18: silicon
nitride; tystar 11 and tystar16: doped and undoped silicon dioxide. Each film
requires a different method of removal as described below. If you are unsure
what film/s is/are on a dummy wafer, contact Sia Parsa, Process Engineering
Manager.
6.2
Tystar9(Silicon Nitride)
6.2.1
Make sure that the dummies are scribed on the back with the tylan
name. If not, scribe TYSTAR 9 on the back.
6.2.2
Load wafers into a sink7 cassette and dip in 5:1 HF for about 15
seconds. (If necessary, fill the left non-MOS bath at sink7 with the 5:1 BHF.
Rinse the wafers thoroughly in the sink7 non-MOS clean QDR.
6.2.3
Place cassette in phosphoric acid bath located in the right side
heated bath of sink 7.
6.2.4
Turn the heater on and check that the set point is at 160ºC.
6.2.5
Leave the cassette in the bath for about 24 hours. (Longer may
cause surface damage to wafer characterized by a clouding of the smooth surface
and recognizable polish marks. Damaged wafers should be thrown out.)
6.2.6
Remove, rinse, and dry the wafer cassette.
6.2.7
At this point the wafers may be stored for piranha cleaning in the
original Tystar dirty box. If so, label the box accordingly.
6.2.8
Standard piranha clean in sink 8 then sink 6.
6.2.9
Place clean, stripped dummies in clean tystar9 dummy box.
6.3
Tystar10 and 16 (Polysilicon)
6.3.1
If the dummies are new, dummies must be scribed on the back with
the tystar name. If not, scribe them.
6.3.2
Dummies to be reworked must be sorted. Those with obvious stress
lines should be discarded.
6.3.3
Make special silicon etch if not made already 2200ml Water:2200ml
Nitric Acid:90ml HF. This should be made in the left heated bath at sink7.If
the etch is already made up, add 15ml HF prior to etching.
6.3.4
Turn on the heater. The setpoint should be around 80-85ºCThe
heater greatly increases the etch rate. Place cassette of dummies in etch. The
time of the etch will vary but it should never exceed 7 minutes. The
sacrificial nitride layer may etch away resulting in surface damage. Surface
damage is characterized by a clouding of the smooth surface and recognizable
polish marks. The etch is very nonuniform so look out for thinning of the
nitride layer. The etch is done when the wafers are brilliantly colored purple
or yellow.
6.3.5
Remove, rinse, and dry the cassette. Inspect the wafers. If the
wafer color is a light blue or the shade of a bare wafer, set wafer aside to be
coated with nitride.
6.3.6
At this point the wafers may be stored for piranha cleaning in the
original Tystar 11 or 16 dirty dummy box. If so, label the box accordingly.
6.3.7
Standard piranha clean in sink 8 then sink 6.
6.3.8
Place clean, stripped dummies in the clean tystar 11 or 16 dummy
box.
6.3.9
After a standard clean, dummies not previously coated with nitride
or those that need to be recoated should be coated in tystar ylan11 dummies
only!) or tylan18 (tylan16 dummies only!) using the recipe SNITC with a
deposition time of 50 minutes Place dummies in the CLEAN tylan 11 or 16 dummy
box.
6.4
Tystar 11 and 12 (LTO & PSG)
6.4.1
Make sure that the dummies are scribed on the back with the tystar
name, If not, scribe them.
6.4.2
Dip in 5:1 BHF (sink8) until wafers dewet. This usually takes at least
30 minutes. The time may be longer if the wafers have a very thick film on
them. (The etch rate of fresh 5:1 BHF is about 1000A/min.)
6.4.3
Remove and rinse the cassette.
6.4.4
At this point the wafers may be stored for piranha cleaning in the
original tystar 12 or 20 dirty dummy box. If so, label the box accordingly.
6.4.5
Standard piranha clean in sink 8 then sink 6.
6.4.6
Place clean, stripped dummies in CLEAN tystar 12 or 20 dummy box.
Note: If you do not have the time to clean the dummies in both sink 8
and 6, don't just clean them in sink8 and put them back into the dirty box.
This defeats the cleaning you just did. If you find it necessary to split up
the cleanings, use a separate clean box. Do not use the clean tylan box.
6.5
Tystar 17 (Low Stress Nitride)
Note: Tystar 17 dummies are to be replaced every 4 weeks. Calendar
mail will be sent as a reminder.
6.5.1
Retrieve new dummies.
6.5.2
Scribe the tystar number on the back of the dummies.
6.5.3
Standard piranha clean in sink 8 then sink 6.
6.5.4
Place clean dummies in CLEAN Tystar 17 box or directly into
Tystar17.
7.0
Tystar Dummy Unload Procedure
7.1
Furnace Status
Check the status of the furnace. It must be in the standby mode
before you can unload the dummies. You can check the status at the furnace
itself by pressing the STATUS (7) key, or by accessing the tycom on the wand
under Equipment Communication--Tystar furnace interface. For tystar9 the
standby program is called 9STNBYA. For tystar11 it
is called 11STNBYA, for
tystar12 the standby program is called 12STNBYA, and for tystar16 it is
called 16STNBYA Tystar20 and Tystar18 are not monitored through the
tycom, but have their own display panels. (See the Tystar18 and Tystar20
manual, Chapter 5.9 for procedures.)
7.2
Venting the Furnace
The furnaces will be under vacuum in the standby mode, and will need
to be vented to atmosphere in order to open them. This can be done at the
furnace by pressing the ACK (acknowledge) button on the furnace control panel.
For tystar9 the ACK button must be pressed twice, for the other two furnaces
only once. You should here a loud squealing sound from the back of the
furnace as the furnace begins to vent. You can also check that the furnace is
back- filling (venting) by pressing the STATUS button until the time countdown
is displayed. The backfill step counts down for 00:07:00 (7 minutes), except
for tystar16 where it backfills for 00:04:00Soon after the furnace begins
venting, a loud alarm will sound. This is silenced by pushing the appropriate
ALARM ACK button below the furnace control panels. When the seven minutes are
up, the furnace will alarm to indicate the END of the process, and you can
silence this alarm by pressing the ACK button. Located on the TYSTAR Furnace
Controller Panel are the controls for retracting and sending in the cantilever
holding the wafer boats. This is labeled BOAT CONTROL and has 3 buttons labeled
IN, OUT, and STOP Press the OUT button to bring the cantilever out of the
furnace.
7.3
Unloading the Dummies
For tystar9, the wafers are held in quartz cassettes. Remove all
the dummies using the vacuum wand and place in the quartz cassette at the
furnace until the dummies cool. When the dummies are cool, place them in the
box labeled for dirty dummies. These can now be cleaned according to the Dummy
Clean Procedure. For tystar11, tystar12, and tystar16 the wafers are held in
quartz cages. The top portion of the cage must be removed using the
quartz-tipped fork- like tool found at the furnaces. Place the tool with the
lid in the metal plate holder located at the furnaces. The dummies can now be
removed and placed in the quartz cassettes to cool. When they have cooled,
place them in the appropriately labeled dirty dummy box, and later clean them
according to the procedures outlined for dummy cleaning. Replace all dummies
with clean ones.
7.4
Returning the Furnace to STANDBY
Press the IN button on the BOAT LOAD CONTROL panel to return the
cantilever to the furnace (make sure that the cantilever is in completely).
Press the RUN button on the furnace control panel to start the standby program.
Press the STATUS (7) button until the panel displays the standby recipe name
(9STNBYA for tystar9, 11STNBYA for tystar11, 12STNBYA for tystar12
16STNBYA for tystar16). Report on the
WAND in the comments section for each furnace that clean dummies have been
installed in the furnaces.
Teflon® is a registered
trademark of DuPont.