(cmp)
Chemical-Mechanical Polisher
2.0
Purpose
The Strausbaugh CMP tool is a chemical-mechanical polisher
primarily used for polishing polysilicon and silicon dioxide films on 4"
and 6” wafers. The system processes wafers serially with manual loading and
unloading of each wafer. The chemical-mechanical polishing process uses the
combination of chemical and mechanical polishing to planarize wafer surfaces.
Materials that can be polished right now are: various oxides, nitride,
polysilicon, and polysilicon-germanium.
No metal is allowed in CMP as of now.
3.0
Scope
The tool consists of a polishing table, polishing overarm,
load/unload station, and pad
conditioning device. The load/unload station centers the wafer and holds the
wafer with vacuum before the polishing overarm picks up the wafer. The load/unload station also has a sprayer
for cleaning the wafer after polishing.
The polishing over arm holds the wafer in the wafer carrier, which
includes a pad underneath the wafer.
The quill can spray air and water through the pad, or hold the wafer
with vacuum. Backpressure is applied
during polishing through the holes in the wafer pad.
The polishing over arm can exert down force up to 15 psi, and
backpressure up to 1 psi less than the down force (larger back-pressures might
blow the wafer off the chuck during polishing, damaging both the machine and
the wafer).
The polishing overarm is connected to the overarm spindle and the
eccentric wheel, which controls the lateral travel of the arm across the pad
during polishing. The travel is set by
adjusting a bolt attached to the overarm spindle – this adjustment should only
be made by Microlab staff
The polishing pad is glued onto the polishing table. The pad, (we are currently using a
IC1000/SUBA IV composite pad) is made of a felt-like material adhered to a
stiff back structure. If the pad ever
dries out, the residual slurry will stick in the pad fibers and destroy the
pad. It is critical that the wafer
carrier pad and the polishing pad are never dry.
The conditioning arm is used to condition (brush) the table during or
in preparation for
wafer polishing. This arm automatically retires to the rinse
bowl located behind the machine after polishing is completed.
The slurry consists of DI water, KOH, ~ 200 nm diameter silicon
dioxide particles. When the slurry
dries it is difficult or impossible to remove, so it is important that all
wafer surfaces stay wet until they are properly cleaned.
Wafers are cleaned in CMPWC, a dedicated machine for post-cmp
clean. Please refer to its manual (Chapter 10.2)
for the operation procedure. In the
case CMPWC is down or unavailable, there is a blue box labeled CMP transfer.
This box can be used to transfer wafers underwater to the Microlab for cleaning
after polishing. Cleaning can be done
in spindryer 3, recipe 2, or sink 8 piranha and rinse.
4.0
Applicable Documents
CMP
Process Characterization Report 1999
5.0
Definitions & Process Terminology
N/A
6.0
Safety
N/A
7.0
Statistical/Process Notes
N/A
8.0
Available Process, Gases, Process Notes
N/A
9.0
Equipment Operation
9.1
Check the machine setup. The label on the machine indicates
whether it is set up for either 4” or 6” operation. If change is desired,
e-mail cmp@silicon2 and request a tooling change. Be sure to include 4” or 6”
in your request. Cmp users will be notified when this change can be made.
9.2
Enable the CMP on the wand.
9.3
The machine should be in the Wet Idle process. Press Stop Wet Idle, then press Exit
Wet Idle to exit this mode.
9.4
Log out idle user and log in:
►
Choose the Login from the menu.
►
Press Log Off to log out the user idle.
►
Login with your own username and password.
►
Make sure the Chuck vacuum meter reads more than 500, otherwise
report the fault and refrain from using the tool.
9.5
Prepare the system for polishing:
►
Turn the valves on the DI water and slurry lines to the slurry configuration
as shown on the diagram by the slurry tank.
9.6
Prime slurry lines:
►
Load recipe: slurry.prime -- this recipe is used to prime
the lines with slurry.
►
Go to Auto mode -- download recipe.
►
Make sure table is clear.
►
Press start conditioning button: conditioning arm moves out
and onto the table, slurry line begins to dispense. Slurry should start
dripping onto the table after ~ 2 minutes. The conditioning ends after three
minutes.
►
No dummy wafer needed for slurry line prime as the polish overarm
should stay over the table throughout the process.
9.7
Process your wafers:
►
You are now ready to process. Go back to recipe page and load oxide.std.00 (for
standard thermal oxide, LTO, PSG polishing on 4”) or 6ox6.00 (for
standard thermal oxide, LTO, PSG polishing on 6”).
►
Go to Auto mode -- DO NOT SAVE YOUR RECIPE MODIFICATIONS --
download recipe.
Note: If
you need to change any parameter other than the time, you will need prior
approval from the staff (see the Appendix).
►
Put in your device wafers and press start polish.
9.8
Purge slurry lines:
►
Turn the valves on the water and slurry lines back to the
original configuration as
shown on the diagram by the slurry tank.
►
Go to recipe page, and load rinse.purge recipe.
►
Go to Auto mode, press start conditioning.
9.9
Clean off all surfaces -- dried slurry is difficult or impossible
to clean!
9.10
Thoroughly rinse the load station, the spindle, and the table.
MAKE SURE the WHOLE table is covered with water.
9.11
Log out.
9.12
Log in user: idle, password: (blank).
9.13
Go to wet idle page.
9.14
MAKE SURE TO CHECK Enable Quill Flush, Enable Chuck Speed, Enable Table Rinse.
9.15
Press Start Wet Idle.
9.16
Disable CMP on the wand.
9.17
See Chapter 10.2
on how to use CMPWC in conjunction with CMP to clean your wafers.
10.0
Troubleshooting
10.1
I forgot to put a wafer on the chuck before starting a recipe,
now it is just sitting there looking for a wafer, what do I do?
Press the Stop polishing button on the screen. Go
to the Manual page
on the computer, and press the arm position button to move the polish arm
back above the table.
Now you can open the front door of the chamber and
place a wafer on the wafer load chuck,
then press Start Polishing
again.
10.2
There is a wafer on the load chuck, but the machine keeps
turning the vacuum on and off, as if
it cannot find the wafer.
The vacuum is probably not strong
enough. Wait a
few seconds and the pump should start to pump down the vacuum chamber.
10.3
I forgot to run the wet idle and then left for the weekend.
Is this a problem?
YES -- if the pad ever dries out it must be replaced. This costs ~
$300 for the pad, plus about 3 hours of technician time. DO NOT FORGET TO RUN THE WET IDLE!
10.4 Helpful
Suggestions (by Emmanuel Quévy, 7/04)
10.4.1
Local Non-uniformity
Many users complain about non-uniformity, which is really Within
Die Non Uniformity (WIDNU), not within wafer non-uniformity.
Local non-uniformity occurs because of the uneven distribution of
patterns to be planarized (up areas) and non-planarized patterns (down
areas) within the die. This non-uniformity is reproduced everywhere on the
wafer, and is really a matter of design. What I did to trick this was that I
included dummy structures on my design to roughly get a uniform distribution of
Up and Down areas (~ 50%). I got way better results than what I did with previous
designs.
But it is still not enough, since I do not
have a hard etch stop. So, at this point, other parameters to play with
are the speed of the pad, and the down force applied. Basically, each design
requires a little trimming of the recipe to minimize WIDNU. I can improve that
by modifying the recipe a little.
10.4.2
Within Wafer Non-Uniformity
Down force is a very efficient parameter when within wafer
uniformity is critical. Less down force, however, produces a lower removal rate
but does provide better uniformity.
Example: My run with CMP went absolutely
fine. No scratches whatsoever, and the wafers never went off the pad. I
planarized 2 µm of SiGe with a removal rate of 0.2 µm/min roughly. Cross wafer
and cross load Uniformity is really good (~1%) provided that you rotate your
wafer. I did 6 times 2 min, each time rotated the wafer on the load station by
60 degrees.
10.4.3
Monitoring
For any monitoring purpose, I would advise
to just run blanket removals on oxide and poly-Si, and measure uniformity to
assess the machine is operating as expected.
11.0
Figures & Schematics
Standard Recipes
oxide.std.00
|
Step |
1 |
2 |
3 |
4 |
5 |
|
Time (sec) |
15 |
5 |
5 |
60 |
15 |
|
Down Force (psi) |
0 |
2 |
6 |
6 |
2 |
|
Table RPM |
100 |
100 |
100 |
100 |
100 |
|
Chuck RPM |
10 |
10 |
10 |
10 |
10 |
|
Back Pressure (psi) |
-2 |
-2 |
-2 |
1 |
-2 |
|
Table Temp (ºC) |
30 |
30 |
30 |
30 |
30 |
|
Slurry 1 (ml/min) |
50 |
50 |
50 |
50 |
0 |
|
Rinse (on/off) |
off |
off |
off |
off |
on |
6ox6.00
|
Step |
1 |
2 |
3 |
4 |
5 |
|
Time (sec) |
0 |
15 |
5 |
60 |
4 |
|
Down Force (psi) |
0 |
0 |
3 |
6 |
0 |
|
Table RPM |
33 |
33 |
33 |
33 |
15 |
|
Chuck RPM |
15 |
15 |
15 |
15 |
15 |
|
Back Pressure (psi) |
-2 |
-2 |
-2 |
2 |
-2 |
|
Table Temp (ºC) |
30 |
30 |
30 |
30 |
30 |
|
Slurry 1 (ml/min) |
50 |
100 |
100 |
125 |
0 |
|
Rinse (on/off) |
off |
Off |
off |
off |
on |
Poly.polish
|
Step |
1 |
2 |
3 |
4 |
|
Time (sec) |
15 |
2 |
20 |
5 |
|
Down Force (psi) |
0 |
5 |
8 |
0 |
|
Table RPM |
24 |
24 |
24 |
24 |
|
Chuck RPM |
6 |
6 |
6 |
6 |
|
Back Pressure (psi) |
-2 |
-1 |
1 |
-2 |
|
Table Temp (ºC) |
30 |
30 |
30 |
30 |
|
Slurry 1 (ml/min) |
100 |
100 |
100 |
100 |
|
Rinse (on/off) |
off |
off |
off |
on |
rinse.purge
|
Step |