Chapter 2.8
Sink8 (Non-MOS Clean)
(sink8)
1.0
Title
Sink8 (Non-MOS
Clean)
2.0 Purpose
This
document has specific information about VLSI sink8. Wet sink 8
provides two sets of heated baths: one for aluminum etch and one for “dirty”
piranha, one 5:1 HF tank and one quick dump rinse station (QDR). The aluminum
etch bath is on the left; the 5:1 BHF tank is in the center; the “dirty”
piranha bath is on the right.
3.0
Scope
Wet sink8 is the first piranha clean. It is to be used for
cleaning wafers prior to sink6 piranha clean. NON-MOS processed wafers shall be
cleaned in sink8 first, then go into sink6 as a furnace pre-clean step. MOS
processed wafers, which went through the photoresist strip step, should also be
cleaned in sink8 prior to their pre-clean steps in sink6.
4.0
Applicable Documents
Chapter 2.1 of
the lab manual, which explains wafer boxes, tweezers, and other tool cleaning
prior to using VLSI sink.
5.0
Definitions and Process Terminology
5.1 Full Plenum Lockout Alarm: Early warning
alarm indicating sink drain failure.
5.2 Quick dump Rinse (QDR): DI
water station programmed to rinse wafers to an acceptable resistivity level
(>10 Mega Ohm-cm), and to get rid of excess acid and/or contaminant.
Therefore, it is very important to make sure cassette/wafers go through full
QDR cycle/s, as any remaining acid can easily ruin the consequent SRD machine
and/or contaminate other equipment in the lab, particularly the furnaces.
5.3
Spin Rinse Dryer (SRD):
DI water rinse followed by a spin dry cycle.
5.4
Clear Teflon cassette:
Clear Teflon® cassette with name “MEMS” drilled on their side. These
cassettes are dedicated for NON-MOS processing.
6.0
Safety
Follow the general safety
guidelines for the lab, the safety rules outlined in Chapter 1.2
and the following:
6.1 This sink contains heated
aluminum etchant, BHF acid and Piranha (heated sulfuric acid); therefore,
appropriate safety attire should be worn while working at this station. This means
chemically resistant gloves should be worn on top of the surgical gloves, plus
a face shield and apron must be worn at all times while working at or around
sink8.
6.2
Do not adjust the
heater controllers as they have been preset to produce proper temperatures for
the piranha bath and aluminum etch.
6.3
Glove Wash: Rinse gloves with
deck hose in utility sink.
6.4
EPO red button:
Cuts power to the sink in emergencies. Report promptly on FAULTS.
6.5
The de-ionized (DI) water deck hose for the sinks is ALWAYS
available for emergencies; it provides a good safety backup in the event of
exposure to chemicals.
7.0
Statistical
Process Data
N/A
8.0
Available
Processes, Glove Policy, and Process Notes
8.1 Processing
Aluminum etch, Piranha clean and BHF dip are available at this
sink as well as the quick dump rinse process to a desired resistivity for both
4" and 6” wafers. Clear “MEMS”
Teflon 4” cassettes, 6” cassettes and designated “MEMS” Teflon®
handles are available by the station. The same cassettes should be used in this
sink, then put them into the SRD for the final rinse. The clear Teflon
cassettes are properly balanced for the SRD by sink8.
8.2
Chemical
location
All
sink8 chemicals are purchased premixed. They are available in the C-lockers in
the front lobby. Additional sink8 chemicals can be found in the C-locker in
service chase CV2 also (located between sink 6 and 7 in the VLSI area of the
lab).
8.3
Glove
and Safety Attire Policy
Whenever
you are handling chemicals and/or place wafers into the chemical baths, you
must wear appropriate safety attire:
chemical-resistant gloves on top of surgical gloves, apron and face
shield. Whenever handling any cassettes or handles from VLSI sink8, the poly
gloves (clear gloves) MUST be worn on top of whichever gloves you already have on.
Example 1: surgical gloves/poly gloves
Example 2: surgical gloves/chemical-resistant gloves/poly gloves
Never
touch any surface while wearing chemical-resistant gloves that other lab members
may come into contact with, such as table tops, door handles, computer
keyboards, face shields, aprons, etc. If you need to step away from the sink at
anytime, rinse off gloves at the glove wash, dry with techni-cloths and put
away in your drawer until you are ready to resume your work at the sink.
8.4
Process Notes
The
VLSI Sink 8 is maintained for NON-MOS clean processes. Staff changes the chemicals in sink8
regularly (as listed on Table 1, below). If it appears that any of the
solutions have been contaminated, notify a staff member (or e-mail
processtaff at silicon.eecs.berkeley.edu
to change it, and post the problem report on FAULTS.
Hint:
If there is a ring around any of the rinse tanks after you remove your wafers,
you have contaminated the tank, cassette and handle. Report the contamination
on FAULTS immediately.
|
Bath |
Chemicals |
Portions |
|
Right Heated Bath Center Non-Heated Tank Left Heated Bath |
“Dirty” Sulfuric Acid (Piranha*) 5:1 Buffered HF Aluminum Etch |
6000 ml (6 liters) 6000 ml 6000 ml |
Table 1
►
Piranha is made by adding 100 ml of hydrogen peroxide to the
sulfuric acid bath. Use the 100 ml beaker kept next to the hydrogen peroxide bottle
on the table adjacent to the sink. You must add the hydrogen peroxide just
before immersing every batch of wafers. After cleaning your wafers in piranha,
they must rinse in the QDR station. Rinse the wafers until the resistivity
reading is 10 M OHM-CM or higher.
►
Sink8 is for cleaning wafers after a photoresist plasma strip
step; wafers can then be cleaned in sink6 in preparation for a furnace process.
8.5
Wafer Breakage
in the Sink
If you
accidentally break a wafer in either the piranha baths or the HF tanks, first
try to retrieve the broken wafer pieces by using the 10” long Fluoroware
tweezers located on the worktable next the sink. DO NOT PUT METAL TWEEZERS INTO
THE BATHS OR TANKS.
If the wafer pieces cannot be retrieved by this method, you will need
to turn off the heater and let bath cool to 100ºC. Next, drain the piranha. Thoroughly rinse the bath with DI water;
then drain the DI. Retrieve all pieces of broken wafers; rinse; drain once
more; refill the bath with fresh suphuric, then turn the heater back on. Report
the chemical change on FAULTS.
If there is an issue with the solutions in these heated tanks,
report a sink problem via the WAND. Microlab staff will respond, change baths,
and clear the FAULT.
9.0
Sink Operation
The
sink operation is relatively easy, however special care must be taken not to
contaminate this MEMS clean station and subsequent processes. The piranha and
HF sinks are set up much like sink6. QDR stations are programmed to run two
complete DI fill/rinse cycles with wafers submerged in the water at the end of
the program.
9.1 Control
Key Description
There are
three control/displays at this station (see Figures 1-3). Most of the time,
members should only need to use the DUMP RINSER control pad marked as “UFT
–48-8 ”. This is the control pad for the quick dump (QDR) station, which is
currently set for two dump rinse cycles. Wafers are initially showered with DI
water followed by two DI fill-dump cycles. These cycles end with wafers
submerged in the water for operator to extract and place them in the SRD.
During the QDR cycle, the resistivity can be monitored via the UFT-223
RESISTIVITY MONITOR control panel. Piranha bath temperature can also be read on
the right UFT-820 TEMPERATURE CONTROLLER display.
UFT-820 TEMPERATURE CONTROLLER (Figure 3)
POWER ON/OFF Turns on/off the master power for the
temperature controller (Figure3).
HEATER ON/OFF Turns on/off the heated piranha bath.
TIMER RUN Starts the timer.
TIMER STOP/RESET Stops or resets the timer.
ALARM SIL - Silences the timer and other
alarm conditions.
-
Cancels flashing alpha code in the
displays.
- Examines
the process set point and the Time Preset.
DRAIN Press twice to empty
the baths/tanks. Make sure chemical baths are sufficiently cooled down before
draining. To only drain a small amount, press the DRAIN button twice, then once
again when you want to stop the draining.
PROG Access
to change or step through various setup parameters.
SAVE Permanently
save the system setup parameters.
RESET This
key is utilized to exit the PROGRAM mode.
UFT-223 RESISTIVITY MONITOR (Figure 1)
UP/DSPLY Toggles
between resistivity and temperature readings.
DOWN/CHAN Toggles between the viewing of
channel 1 and channel 2. Since there is
only one QDR in sink8, UFT-223 Resistivity Monitor is locked to Channel 1.
RETURN/SIL Silence the alarm. Exit the set
up mode.
UFT-48-8 DUMP RINSER (Figure
2)
START Activates
the dump rinse cycle/ Reactivates dump rinse cycle.
RESET -
Deactivates the Dump Rinser.
-
Silences alarm.
-
Automatically reset itself in preparation for another run.
-
Exits program mode.
HOLD When the system is
running, it halts the operation temporarily. When it is in STANDBY mode, it
dumps the tank manually.
PROG Parameters
to be written in the EEPROM memory.
9.2
Control Key
Functions for Overall Sink Operations (Figure
4)
POWER ON Main
power on for top control panels.
EPO Big
red button for emergency stop on the entire sink operation.
SILENCE ALARM Silence the plenum flush lockout alarm.
ALARM RESET Reset the plenum flush system.
9.3
Control Panel
Programs are shown in Appendix 2
The parameter
codes for the programs on the UFT-223 resistivity monitors, UFT-820 temperature
controllers and UFT-48-8 quick dump rinsers are listed in Tables 2-5 in Section
12.2. The parameter codes are not to be altered by the Microlab members. Please
only use them as your reference check.
9.4
Basic Piranha Clean
Piranha is an excellent oxidant capable of
removing most organic contaminants.
9.4.1
Add 100 ml hydrogen peroxide to the heated sulfuric acid bath,
which is kept at 120ºC to activate (spike) the piranha (see Figure
3 for more details on the temperature controller display).
9.4.2
Piranha clean wafers for 10 minutes.
9.4.3
DI water rinse your wafers by carefully lifting the cassette out
of the (piranha) bath, and holding it above the bath until it stops dripping
before placing them in the quick dump rinse station.
9.4.4
Start the DI rinse in the QRD station per the instructions
provided in Section 9.5.1 to 9.5.6 and make sure you reach proper resistivity
level.
9.4.5
HF dip if desired; however, make sure to run another DI rinse in
QDR by repeating Section 8.5.1 to 8.5.6.
Note: Repeat
the rinse cycle as described above after each acid clean step done in sink8
(aluminum etch, piranha or BHF).
9.5
Quick Dump Rinse
Operation
This is a two cycle DI dump/rinse
process that is needed to bring wafers to above 10 M OHM-CM resistivity before
one can proceed to next step in the spin rinse dryer. Proceed as follows:
9.5.1
Place wafers in the QDR
tank: it should initially have no water in it.
9.5.2
Press RESET (if status
light is blinking), and then START button to activate the dump rinse cycle (see
Figure 2 for keypad schematic).
9.5.3
Monitor the resistivity
by selecting the proper resistivity channel on the RESISTIVITY MONITOR control
pad (Figure 1). Select proper channel by pressing CHAN
button (channel 1 for the QDR #1 on the right station). Make sure M OHM-CM
light is on when selecting this measurement mode. Water temperature or
resistivity can be monitored on the same LED display by selecting/deselecting
one or the other display mode via DSPLY button.
9.5.4
Make sure your
resistivity reading is 10 M OHM-CM or greater than 10 M OHM-CM at the end of
your dump rinse cycle before going into SRD. If not, repeat the rinse program.
9.5.5
Upon the completion of
two rinse cycles in the QDR, remove wafers from the bath and place them in the
spin rinse dryer (SRD) station for the final rinse dry cycle. 6” wafer cassette
goes in the top SRD and 4” wafer cassette goes in the lower SRD. Make sure to
place the cassette with H-bar facing in. Dump the QDR water by pressing the HOLD
button, then the RESET button. As soon as the water is drained, close
the lid. Leave the QDR with no water in it and with closed lid, before leaving
the station.
9.5.6
Final resistivity
should be greater than 12 M OHM-CM for the SRD during its rinse cycles.
9.6
Sink8 Chemicals
Chemicals used at sink 8 can be found in the C-locker in service
chase CV2 (located between rooms V1 and V2).
Silicon etch bath had temporarily moved to sink 7. If you use the last of the silicon etch,
return the empty bottle to the tall white acid cabinet next to sink 432C in the
old lab, and bring a fresh bottle into the VLSI locker.
No empty bottles may be returned to this locker, left on the floor
in the chase, on the floor in the vicinity of the sinks, or underneath the
sinks. All empty bottles MUST be taken to sink 432C in the old lab to be rinsed
and disposed of properly.
Face shields, surgical gloves, and aprons
must be worn at all times when working with chemicals.
9.7
Important Operational Notes
Metal tweezers are NOT to be used at this sink! Use the vacuum
wand to load and unload wafers. The spin/rinse dryer next to Sink 8 can only be
used with the cassettes from Sink 8- each sink has its own set of
cassettes! Transferring cassettes from
one sink to another introduces contaminants.
After wafers have been piranha cleaned, DI water
rinsed (QDR) and spun dry (SRD), inspect each wafer under the inspection light,
which is mounted on the wall at each sink. If any particles are found on the
wafers, post it as problem on FAULTS.
Extra cassettes and handles for Sink 8 are stored in a
blue bin labeled "extra cassettes for sink8" located on the worktable
in V2 (next to Sink 8). If a sink8 cassette and/or white handle appears to be contaminated,
please observe the following procedure:
9.7.1
Remove the contaminated piece from sink8 immediately;
transfer your wafers into a clean cassette from the worktable next to Sink 8.
9.7.2
Place the contaminated cassette into the blue bin on the
process table against the wall in V2 labeled
"contaminated cassettes”.
Note: If the cassette and/or handle have been
dropped on the floor, label it as such. Contaminated cassette/handle will be
removed from the VLSI area for the next scheduled RCA 1 and RCA2 clean.
Clean up: Always leave the working area of the VLSI
sinks as you would like to find it. Wipe all work surfaces of the sink with
Techno-cloth lint-free towels. If a
solution is needed later, label it with name, date, time, contents, when you
will return, and where you can be reached.
Keep C-lockers closed.
10.0
Troubleshooting
Guidelines
10.1 Rinse
cycle stopped in the middle QDR cycles:
Press RESET/HOLD buttons to dump the water out, then press RESET/START
buttons to restart the quick dump rinse cycles.
10.2 Cannot
reach resistivity above 10 M Ohm-cm in QDR: Go through another rinse program (2 cycles). If resistivity is
still below specification limit, then change the cassette and try the rinse
cycle again (dirty cassettes need to be RCA cleaned by staff). If it still
cannot make the resistivity, then there may be other issues involved. Stop and
report it on FAULTS.
10.3
–LO-: Display
indicates that the resistivity reading is below the system minimum.
10.4
Err: Display
indicates that the sensor reading is erroneous. The sensor has exceeded a
reasonable value on the resistivity display or a malfunction in the sensor on
the temperature display.
10.5
Status
Indicators on Temperature Control Panel (Figure 3):
Red LED
will light up to indicate a problem:
HGH TEMP OVER
TEMP DEFFECTIVE SYSTEM
SENSOR FAULT
LOW TEMP LOW
LIQUID POWER HEAT
FAILURE
10.6
Sink System
Status Indicators (located on top of
the sink panel)
LOW PURGE Red indicator light will come on when there is low
air purge to cool off electronics for the sink.
PLENUM L/L Red indicator light will come on when the plenum
liquid level is too high.
ASPIRATOR Red indicator light will come on when aspirator is in use.
DRAIN Red indicator light will come on when acid is
draining.
PLENUM L/L HIGH: If it sounds, push the ALARM
SILENCE button on the sink, and notify the process staff and post the
problem on FAULTS as a full plenum lockout is an early warning alarm indicating
sink drain failure.
The area under the deck of a wet process
station (sink) is known as the plenum. This area receives the water and
chemicals when they drain from the tanks and the utility sink. When the level
of water in the plenum reaches 3 inches, a float activated switch opens a valve
and the waste is removed. Should the water rise too high in the plenum because
of a failure of the system, all sources of water to the sink are shut off and
the alarm will sound. This is to prevent an overflow. If the user silences the
alarm, it will again sound when the problem is solved and the water level has
returned to normal.
10.7
If EPO is
pushed, follow instructions:
10.7.1
Pull out EPO button.
10.7.2
Open head case pull
down breaker switch and then lift up.
10.7.3
Push button on front of
sink that says on.
10.7.4
Push power button on
heater controller.
10.7.5
Push heat button on
controller.
Spin Rinse/Dryer HElp
Messages
|
HELP-0 Power
Failure
|
The
power failed while the unit was operating. Check the electrical lines in the
unit, and for a blown fuse. Press START to reset the microprocessor.
The rinser/dryer indexes the rotor and resets to the beginning of the
interrupted cycle. |
|
HELP-1 Bladder Pressure |
There
is inadequate nitrogen pressure to inflate the door seal. Check the door
bladder, the nitrogren pressure, and the pressure switch. Be sure there is
20-21 psi on RG2 and that the pressure switch turns off when the pressure
reaches 17-18 psi. |
|
HELP-2 Nitrogen Pres |
There
is insufficient pressure in the system nitrogen line. Check the nitrogen
pressure switch (PSW1). It should be set to approximately 13 psi. Check the
system line for leaks. Be sure that the pressure at RG1 is 23 psi dynamic.
Check the Clean Coil thermostat and reset if necessary. |
|
HELP-3 Door Open |
The
door is not completely closed. Check the door. If the door is properly
aligned, check the micro-swtich actuating arm. |
|
HELP-4 Index Failure |
The
unit is not able to index the rotor. Check the rotor positioner. |
|
HELP-5 Excessive Speed |
The
rotor speed has exceeded 3400 RPM. Retry the cycle a few minutes. If the
problem persists, there is a hardware problem. Call maintenance or VERTEQ for
assistance. |
11.0
Figures
and Schematics
Figure 1
Figure 2
Figure 3
Figure 4
12.0
Appendices
12.1 RCA
1 and RCA 2 Clean Tanks
The heated baths and rinse tanks in sink 6
and sink 8 in the VLSI area are periodically RCA1 and RCA2 cleaned as follows:
|
|
||
|
DI water NH4OH H2O2 |
5 parts 1 part 1 part |
4250 ml 850 ml 850 ml |
|
RCA 2 |
||
|
DI water HCl H2O2 |
6 parts 1 part 1 part |
4500 ml 750 ml 750 ml |
Piranha is a mixture of sulfuric acid and hydrogen peroxide and
is used to remove organic residues. It can be made in small batches as follows:
►
5 parts H2SO4
► 1 part H2O2
Note: Always add peroxide to sulfuric acid, never vice versa! This
is a self-heating solution.
12.2 Sink
8 Controller Programs
|
|
UFT-820
Temperature Controller for Heated Piranha Bath |
|
UFT-48-8
Dump Rinsers |
||||
|
SP1 |
10.00 |
|
C5 |
10:00 |
|
CY |
2 |
|
SS1 |
12.00 |
|
PA | ||||