Chapter 6.04
CPA Sputtering System
(cpa)
1.0
Title
CPA Sputtering System
2.0
Purpose
This document has specific operation and process information about
the CPA 9900 Sputtering System. It can RF
sputter etch clean native oxide on substrates and sputter Ti, Al/ 2% Si, Ni and
W films on both 4” and 6” wafers.
3.0
Scope
The CPA 9900 sputtering system has four targets for DC magnetron
sputtering, an RF sputter etch station for pre-cleaning substrates of native
oxide, and load-locked, heated end stations.
The targets currently available are:
Ti Location #1
Al/2% Si Location #2 99.999%
Pure
Ni Location
#3
W Location #4
These targets are labeled on the front of the system. Dedicated pallets are provided for each metal
film that will be sputtered. They are
stored in the storage unit below the right loading station and clearly labeled
on front of the case door. Do not mix pallets. This will cause cross contamination issues.
The system has the ability to sputter targets sequentially. It is
equipped with a 10-inch cryopump and has a base pressure of 2 x 10E-7
Torr. Substrates processed in this tool must be inorganic, low vapor pressure
materials.
4.0
Applicable
Documents
5.0
Definitions and
Process Terminology
6.0
Safety
6.1
Make sure pallets are all the way into the elevator before closing the
load lock gate valve.
6.2
Turn on the water to a target before turning on the DC power to the
target.
6.3
Turn off the ion gauge before opening the throttle valve (gas will flow
with open throttle).
7.0
Statistical/Process
Data
CPA statistical data are posted under the process monitoring
section of the Microlab home page.
8.0
Available
Process, Gases, Process Notes
Available Process
8.1
Four Targets are currently available for
sputtering (Ti, Al/2%Si, Ni and W).
Process Notes
8.2
The CPA's linear design has three major
sections; two load locks, end chambers, and a main process chamber. The CPA
elevator (right load lock) can hold up to 9 pallets, at slots below the top
dummy pallet. Each pallet can hold nine
4" wafers or four 6” wafers. The
pallets may be loaded at either end of the system. Since there is not enough
room to open the chamber door fully for load and unload pallets in the left L/L
station, it is recommended to return the pallets to the right L/L station for
loading and unloading. An elevator in
the load locks automatically loads the pallets onto a constant-speed conveyer
which moves them from the load lock, the pallets moving through the main
process chamber to the opposite load lock and automatically sputtering the
wafers in the process. The conveyor or track may be reversed for multi-pass or
sequential deposition.
8.3
Substrates processed in this tool must be
inorganic, low vapor pressure materials in the standard mode of operation.
8.4
High vapor pressure materials, polymers,
photoresist and organics maybe permitted in this tool, but only following
process/application review and approval by Process Engineering Manager. Failure
to do so could result in cryopump damage beyond repair, which means long CPA
down time, and tens of thousands of dollars in cryopump replacement cost.
8.5
Kapton tape may be used in CPA with power
setting, at or below 1000 W. Make sure to give enough delays for multiple
passes to cool down the substrates, and never exceed the 1000 W power on any of
the recipe setting/target material, while using Kapton tape.
8.6
Dedicated
pallets are provided for each metal film. Please do not mix the pallets in the
storage unit or during sputtering. Mixing pallets will cause cross
contamination issues, hence, profoundly impact/destroy other members'
device/products in the Microlab. Moreover,
cross-contaminated pallet cannot efficiently be cleaned by our metal
etch/cleaner, and will have to be replaced at a cost.
9.0
Equipment
Operation
9.1
Enable the system on the Wand. If you are
going to use the aluminum target, enable cpa.
9.2
Operation of the system is automated when
the AUTO MODE LED's are lit on the Left Load Lock (left L/L), Right Load Lock
(right L/L), and the Main Chamber of the AUTOMATIC VACUUM CONTROLLER, located
in the center of the system. Most members however, use the tool in manual mode
(Auto/manual mode is flipped to manual) on the same panel. In either automatic
or Manual mode of operation if any of the
MAINT LEDs (maintenance LED's) or Alarm LED’s are lit, then DO NOT operate the
system. Report the problem on the Wand.
9.3
Check the right side and left side L/L
heaters (labeled 'SUBSTRATE TEMP CONTROLLER') to see if they are on (warm to
the touch). Ask staff to turn them on, if they are not. Do not adjust the
setting.
9.4
Vent the right L/L station as per follows:
9.4.1
Turn off the ion gauge.
9.4.2
Push the STANDBY button either over the
right L/L, on the L/L Control panel, or by using the Automatic Vacuum
Controller. This closes the L/L gate valve, isolating the chamber from the rest
of the system.
9.4.3
Wait for the L/L gate valve to close --
you will hear a distinct clank when it does. This takes approximately
10-15 seconds.
9.4.4
Push the VENT button to bring the L/L
chamber to atmosphere. If you vent too soon (while gate valve is open), you
might raise the pressure of the chamber.
9.4.5
Unlatch the chamber door.
9.5
Check to make sure that an empty pallet is
sitting in the top slot of the elevator assembly. It will catch any flakes
falling from the top chain and protect the wafers on the pallets underneath
from being contaminated.
9.6
By using the raise/lower switch above the
L/L raise the elevator so it is near the top of the chamber. When you reach the
top the upper limit LED (on the L/L Control panel) will light up.
9.7
Place your process wafers on a pallet(s)
and slide it into a slot in the elevator; make sure it is level and in the
center of the elevator. Check pallets again to insure they are level -- it is
easy to misalign them. Manually (using the raise/lower switch) move the
elevator down until the bottom pallet is ONE SPACE above the tracks (if not
already there). Make sure to follow material compatibility/process rules noted
in sections 8.3-8.5, before proceeding to the next step.
9.8
Close the L/L door and, while holding
firmly, press the PUMP button on the L/L Control panel. Wait for the pump to
kick in, and check that the L/L door is held firmly by the vacuum. The gate
valve of the load station will automatically open and the system will cross
over into hi-vac at ~200 mTorr.
9.9
When crossover into high vacuum is
complete (you can hear the cryo kick in), you may turn on the ion gauge.
The following steps can be done while the system is pumping down
(about 15 - 30 minutes):
9.10 The
opposite L/L chamber must be prepared for receiving processed pallets. Lower
the pallet elevator to the bottom position, enough to get the processed pallets
in, by using the RAISE/LOWER switch to lower.
9.11 If
you are going to use the AUTO MODE (most users run in MANUAL), set the pallet
count (i.e., the number of pallets to be run), on the Automatic Pallet Transfer
as follows:
9.11.1 Set
the AUTO/MANUAL MODE in the center of the Automatic Pallet Transfer Controller
switch to AUTO.
9.11.2 Push
the COUNT UP button on the Right Station panel of the Pallet Controller,
chamber pallets are in.
9.11.3 Toggle
the COUNT SET/COUNT RESET switch on the Right Station panel to the COUNT SET
side until the desired number of pallets is reached on the LED readout.
9.11.4 Press
COUNT DOWN, the direction outgoing pallets are to index.
9.11.5 Toggle
the COUNT SET/COUNT RESET switch on the receiving Left Station panel to COUNT
RESET to zero the Pallet Count LEDs. Press the COUNT UP button, the direction
for incoming pallet to index.
9.12 Set
SPEED SELECT switch to VARIABLE.
9.13
Set the TRACK SPEED setting as necessary.
You can use the following equation to get an idea of the speed you will need:
R = TS/WP (R * WP) / T = TS ( R * W /P ) / T = S (see
handwritten notes on next page)
where
R = rate in A/min/Kw A / min * kW
T = film thickness in A
W = width of target in cm (12.065 cm)
S = track speed in cm/min.
P = power in kW
The current process parameters and the Deposition Constant
you need to determine the required track speed for a given thickness are listed
in the header which appears when enabling the CPA, also updated at the
Microlab process monitoring web site. The film thickness can be obtained by
dividing the Constant by the track speed for the process condition. In
addition to proper pre-sputter and good pressure, lowering the track speed will
also improve film quality.
Below is an example of process parameters:
Aluminum/2% Silicon
Power: 4.5
kWatts
Pressure: 6
mTorr
Constant: 86,000
A*cm/min.
Example: 16 cm/min. gives ~
5100 A of Al/Si
Note: The constant
changes with target usage.
Tungsten
Power: 3.0
kWatts
Pressure: 20
mTorr
Constant: 30,000
A*cm/min.
Example: 30 cm/min. gives
~1000 A of W
Note : The
constant changes with target usage.
Note : The track speed is inversely proportional to
the thickness, and the power is directly proportional to thickness. Keep track
speed above 9 cm/min. Perform at least two passes to prevent substrate
overheating and keep power out of the extreme upper and lower ends for
consistent results.
9.14 Set
TRACK TRAVEL DIRECTION to REVERSE (i.e., to the left).
9.15 Wait
for the pressure to reach a minimum of 5 x 10E-7 Torr on the ion
gauge readout.
Make sure that the target you want to sputter has been selected:
targets 1 or 3 are selected by a toggle switch on the top power supply panel.
Target #2 has its own supply.
9.16 Select
High or Low process pressure via the pneumatic switch above the etch controller.
Turn off the ion gauge and push the THROTTLE button on the Main Chamber section
of the Automatic Vacuum Controller. This will turn on the process gas. Wait for
the pressure to stabilize, 15 to 30 seconds.
9.17 Turn
the GAS FLOW ADJUST knob, located below target #2, to set the Process Gas FLOW
LED display. If your pressure needs are not met for a given gas flow, report it
on the wand and have a staff member adjust the throttle valve for you. The
throttle valve can be adjusted manually to any pressure.
9.18 Initiate
cooling water to your target by using the rotating lever know on the right-hand
side of the machine (as you’re facing the front of the machine). A green button
will light up, showing that water is flowing, and only then will it allow you
to turn on the DC power. If the DC power switch does not work, perhaps the
machine is not enabled, or the cooling water flow is low.
Note: If you do not turn on the target cooling
water, you will not be able to strike a plasma! Adjust the power level by using
the CONTROL knob. Observe plasma through viewport and make sure it looks
stable. The color of the plasma is bluefish. For a good quality film, it is
recommended that the target be pre-sputtered before use. Pre-sputter the target
for 3-5 minutes. If a target has not been used for several weeks, it may be
necessary to pre-sputter for a longer time period to remove any native oxides
or contaminates.
Note: If the target is arcing, it needs to be
conditioned. Do not run the machine. Report the problem on the computer.
9.19 Push
the green START button on the Automatic Pallet Transfer Controller to begin
your process. When the pallet lowers down to the chain track, if placed
incorrectly if may start rotating on the track, becoming stuck on the vertical
rollers.
It will then be impossible to move it
backwards or forwards. If your pallet does start to rotate on the track,
immediately return to the load lock.* Open the L/L and check to make sure the
pallet is not warped. Next, if the pallet is not warped, reposition it
correctly.
To move things along more rapidly, you may leave the SPEED SELECT
in the FIXED position (80 cm/min.) until your dummy pallet gets to the target
and at that point switch it to the VARIABLE position to get the desired process
track speed. Be sure to switch the speed BEFORE your wafers arrive at the
target, about an inch from the deposition chamber, to insure a uniform metal
layer. Pallets will move sequentially under the targets and end up in the left
load lock.
9.20 Pallet
removal may begin once all the pallets are in the L/L.
Note: If
you want to run another pass, proceed with a) below, reset per step 10 for
opposite direction, push throttle, turn on P.S. and push start.
9.20.1 Turn
off the power of the D.C. power supply and push the PUMP button on the Main
Chamber section of the Automatic Vacuum Controller. This will turn off the
process gas and open the high vacuum valve. To avoid breaking the gate valve by
cranking the pallet, make sure that ALL the pallets are in the L/L, then stop
the track by setting the TRACK TRAVEL DIRECTION switch to the center position.
9.20.2 Press
STANDBY on the left End Station L/L Control panel or on the Automatic Vacuum
Control panel. This will close the end station L/L valve.
9.20.3 WAIT
until you hear the L/L gate valve close and press VENT to backfill the end
station to atmosphere.
9.20.4 Unlatch
end chamber door.
9.20.5 Remove
pallets from end station from the bottom up to prevent particles from
contaminating your samples.
9.20.6 Close
door and latch.
9.20.7 Push
PUMP while pressing FIRMLY on the L/L door to insure it is closed and check to
see it seals properly. This will rough out the chamber and cross over to high
vacuum automatically. To prevent debonding, make sure that you have run the
cooling water at least 5 minutes after turning off power to your target.
9.21 When
you are finished,
9.21.1 Turn
on the ion gauge tube, to monitor machine pressure.
9.21.2 Make
sure the RF sputter etch controller is left in MANUAL. This will disable it.
9.22 Disable
the system and enter your process parameters and results in comments.
Note: Every time the
targets are changed and the chambers are exposed to air, the targets have to be
reconditioned. This is done by a staff member.
Optional
RF Sputter Etch System Description
The sputter etch system consists of three control components: an
ENI RF power supply located on the bottom right hand side of CPA, a RF
matching/tuning box that sits on top of the sputter etch chamber, and the
sputtering etch control panel located on the upper left hand side (on top of
the ion gauge controller).
The front panel of the ENI RF power supply has three toggle
switches, a power adjust dial, a power meter, and four led lights. The AC line
toggle switch should always be on. The RF power toggle switch should be
off/remote. One can toggle meter switch to either forward or reverse to monitor
the forward or reflected RF power during sputtering etch. The power adjust dial
is used for set RF power.
The RF matching/tuning box has three toggle switches and two
meters. The auto/manual toggle switch should be on manual. Usually one need not
adjust the tune and load, since they have been optimized at 42 and 78
respectively. The bias is not working.
The sputtering etch control panel can only run in manual mode (the
toggle switch should be on manual). The position toggle switch is used to set
sputtering target electrode position. The red RF ON and green RF OFF push
buttons turn on/off the RF power. Other switches and push buttons are not used.
One important feature of the sputtering etch system requires all
users' attention. That is the sputter electrode is made of copper. If there is
a gap between the electrode and the pallet, and the plasma is on, the electrode
will be sputtered too. The sputtered copper atoms will contaminate the whole
chamber and the wafers inside. This situation usually occurs if one lowers the
pallet position or switch to the auto mode on the sputtering etch control panel
while the RF power is on.
RF Sputter Etch Operating Procedure
1. Enable
the system on the wand and load your wafers as per operating procedure defined
in Section 2. Only one pallet of up to none wafers can be processed at any
given time, although you can load more than one pallet into the load lock. Make
sure that the pallets are not warped. It is a good idea to use an empty pallet
first to check whether the system is working and to set the RF power.
2. Check
toggle switch settings and LEDs on all three control units.
ENI RF Power Supply:
AC line: on
Meter: forward
RF Power: off/remote.
Only the AC on led should
be on.
RF Matching/Tuning Box:
Manual mode
Tune meter at 42
Load meter at 78.
Sputtering Etch Control Panel:
Manual mode
Down led (red) on
If position 1 or 2 led
(green) are on, push the toggle switch to lower once.
3. Set
the track speed to the fixed speed (80 cm/min).
4. Turn
on the track in the reverse direction (to the left). This will turn the Track
Fwd light on, on the Sputter Etch control panel.
5. Next
set Platform Position switch to position 1. (Lift switch once). This raises a
stop for the pallet.
6. Lower
the pallet onto the moving track in the L/L. Run pallet out until it reaches
the stop. Once it has stopped moving, stop the drive chain.
7. Lift
(raise) the switch again to raise the platform to position 2. Check to see if
the pallet is positioned well on the electrode through the load lock window.
Only two ends of the pallet can be seen. The center should be sitting inside
the electrode.
If you can see the center edge of the pallet, return it to the
load lock and resend it. If you still can see the center edge, the pallet may
be misaligned or warped. Usually, you can not strike a plasma with this
pallets. Even worse, if you strike a plasma, the electrode will be sputtered
too. Unload the pallet and check it for warp. If it is bad, mark it then report
on wand. Staff will handle the warped pallet.
8. Turn
off the ion gauge (filament).
9. Press
throttle valve switch to start gas flow.
10. Adjust
the gas flow to 7 mtorr. This should require a flow rate of ~200 sccm.
11. Press
If there is no plasma, return the pallet to the load lock and repeat
from step (2). If there is no plasma again, unload your wafers and report on
the wand.
12. When
your desired sputter time is completed, press RF OFF button (green) on the
sputter etch control panel to turn off power.
If the plasma cannot be turned off by the pushing RF OFF button,
check the RF POWER toggle switch on the ENI RF power supply. If it is on,
switch it to off/remote, then push the RF OFF button. If you still cannot turn
off plasma, call staff immediately. Do not lower the pallets. Doing so will
only contaminate your wafers and the whole chamber with copper.
13. Toggle
the platform position switch down once to lower the pallet to the normal
position. Make sure to turn on the drive chain. You can then proceed with
sputtering dep of your desired film or reverse the track direction to unload
your wafers for a sputter only etch process.
Remember only one pallet should be sent through the machine at a
time when using the Sputter Etch.
14. Wafer
unloading and equipment log off: You can also refer to operational procedure
section for more detail explanation.
14.1
Turn off the Ar gas by hitting the pump
button for the main chamber.
14.2
Once the gas has exited and pallet(s) are
in the right L/L then the standby button can be pressed. This lowers a
door that isolate the L/L..
14.3
Hit the vent button and release the
door latch.
14.4
Remove wafers when door opens and return
pallets to the designated slots in the storage unit.
14.5
Close the L/L door.
14.6
Turn on the Ion gauge (filament) and
disable the machine.
FBSputter Etch Process
Example:
Power: 400
W
Pressure: 7
mT (200 Ar flow)
Time: 5
minutes
Total wet oxide film removed
(1000 A test wafers): 63 A
Note: This
process gets the pallet quite hot; when the pallet was removed it was almost
too hot to hold, so temp probably reached 100ºC. Allow a few minutes to cool down before
unloading it.
14
Troubleshooting
Guidelines
15
Figures &
Schematics
16
Appendix
*** Test run data
for Al sputter etch on CPA ***
At 200 watts the etch rate of Al is ~12-13
Angstroms/min.
Pressure = 6 mTorr , Argon flow = ~50 sccm
This is slightly less than the rate for Al2O3 (sapphire), i.e.,15
A/min.
*** Low Power Titanium (Ti) and Tungsten (W) Deposition Recipes ***
Ti deposition:
Power = 1.5 kW
Pressure = 7 mT
Track speed = 30 cm/min
Dep rate ~ 600 A/pass
W Deposition Recipe:
Power = 2.0 kW
Pressure = 10 mT
Track speed = 35 cm/min
Dep rate ~ 1000 A/pass
Target Inventory:
AlSi (99.999% pure), Ti, W (99.999% pure)
CPA Study Guide
Be sure to know:
1.
Which materials are NOT allowed in cpa
2.
Maintenance LEDs
3.
Pre-Start-up checks
4.
Ion gauge when it should be on or off
5.
Venting the load-lock
6.
How to obtain process parameters for Al
deposition
7.
Base pressure
8.
Throttle
9.
Using the viewport
10.
Track speed
11.
Loading and unloading pallets.
12.
Troubleshooting problem pallets.
13.
Target pre-sputtering.
14.
Setting the target.
15.
Typical film quality problems and
troubleshooting them.
16.
DC power supply, and cooling water.
17. What
plasma is; how it is used.