Stsetch Deep RIE Operating Instructions
Basic System and Process Description
The STS is an ICP (Inductively Charged Plasma) etch system which uses the ‘Bosch’ process to
etch deeply into silicon or polysilicon. During the etching process gases toggle in user set cycles
of SF6 (to etch anisotropically) and C4F8 (to deposit a sidewall protecting polymer or passivate
the wafer surface).
A description of the tool may be found at:
http://snf.stanford.edu/Equipment/stsetch/stsetchgeninfo.html
Labmembers requesting training on stsetch must be familiar with this information.
Labmembers should also have read over the following Frequently Asked Questions prior to
hands-on training with a staff member:
http://snf.stanford.edu/Equipment/stsetch/stsfaqs.html
Description of Software and Definition of Action Buttons
The software displays four windows in normal run mode; two informational schematic windows
(ICP and Machine View) and two task windows (Transfer and Process Control-ICP). Let’s go
over each of the windows;
ICP View; this window show the requested and actual set points for gas flow, RF power and
matching values while to system is etching a wafer.
Machine View; this window displays the wafer status, load-lock and chamber pressure.
Transfer; this window is where the users requests via buttons that a wafer be loaded, unloaded,
the load-lock be vented, or the loading process be aborted. There is also a close button which will
close the window altogether. To restore the window after an accidental close go to the toolbar
and look for the window in either Control Panel or Window.
Process Control-ICP; this is the window where the users loads, edits or creates a recipe and
controls the actual etch process. These are the buttons and there functions;
 Chamber LU; this is a leak-up test used mostly used by the maintenance staff.
 Process; this button starts the recipe selected.
 Abort; is a hard stop of a running process. The tool goes into idle mode without going
through the usual pump and purge cycles.
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Hold; suspends the recipe by turning off the clock, RF and gases. If pressed it
will turn into Resume to start the recipe (and count down clock).
Skip; moves the recipe to the next step. It is a kinder gentler way of aborting a
program as it will allow the tool to go through the usual pump/purge steps.
Close; is defined above in Transfer.
Stand By Conditions
1.  Verify the turbo pump is on by checking the electronics rack located behind the
pump. The third panel from the top marked Pfeiffer Vacuum has a digital read
out window. It should read 390-400Hz. If it drops below 390, please use coral to
report it as a problem.
2.  Look around the loading deck for any notes. There may be a message asking
the next user of the tool remove a wafer from the chamber. A proper storage
container should be available for the wafer.
3.  The load-lock should be under vacuum and the machine indicates there is a
wafer on the chuck. There probably isn't a wafer there, unless the last user left a
message about the wafer.
Load and Edit a Program
1) After enabling stsetch, click on the aqua colored recipe name found on the far left-hand side of
the Process-ICP window. This will open the file that contains all the recipes. Search the file until
you find the desired recipe. Be careful; many recipes have very similar names. Be sure to choose
the correct one.
► This loads the recipe.
2) Click on ‘Recipe’ on the left hand side of the window. This will bring up the chosen recipe.
3) The file should open on the page containing the Standby Step parameters. This step is run
automatically before and after the etching step. Most recipes have this step set to these values;
Standby Gas-ARGON
Flow Rate
0sccm
(Ar is not even plumbed to the tool)
Pumpdown Time 00:00:20
Purge Time
00:00:10
Pump Out Time 00:00:20
Base Pressure 4mT
Pressure Trip 94mT
(The pressure operating range)
4) Click on the tab labeled General to get to these input fields;
Pumpdown Time
Gas Stabilization
Process Time
Pump Out Time
00:00:30
00:00:10
(variable)
00:00:30
(User defined time)
Parameter Switching  (The box must be checked for the Bosch process)
○ Etch First
○ Pass First
(User chooses whether to etch or passivation first)
Etch Time
Pass Time
Overrun
(This is where both gases, SF6 and C4F8 are on at the same time)
5) Click on Pressure to get to the pressure page. APC (automatic Pressure Control) is set to
manual. It’s a long story, but we lost the ability to use APC when the turbo pump was upgraded.
The APC setting is a percentage of how open the valve is. A one percent change is significant.
Base Pressure 1mT
Pressure Trip 94mT
(This is a change from the Standby page)
6) Click on the Gases to get to the gases page
SF6 Flow Tol%
C4F8 Flow Tol%
(Tolerance should be set to around 20% to avoid an error)
7) Click on RF to get this page. There are two generator sources, Coil and Platen (chuck). The
coil generator is on for both the etch and passivation steps, but the platen generator is on only
during the etch step. This gives directionality to the plasma and creates approximately 90°
sidewalls.
Platen Generator
Etch
Passivate
Power
(Typical value is about 120W. This is actually only 12W as there 10X scale)
Tolerance
Coil Generator
Power
Tolerance
Etch
Passivate
(Typical value is 600W. The 10X scale is off)
In both cases the matching should be chosen and the Load and Tune set to 50%.
8) Click Endpoint to get to the endpoint page. We do not have an endpoint detector on the
system, so the disabled box is checked.
► This completes the review of a recipe.
NOTE: We strongly encourage to user to check his/her recipe before every use. Any user can
change any parameter of any recipe at any time. Please protect your work by verifying the recipe
is correct.
If you change a parameter of a recipe, for example Time, please use the EXIT option on the
toolbar to exit. As you do this you will be asked if you want to saves changes. Answer yes. You
will then be show the file you are about to change. Answer yes. You will be prompted that the
file exists and asked if you want to over write it. Answer yes.
►This completes the editing of a recipe. For more information about recipes, please refer to the
More on Recipes section of these instructions.
Starting an Etch
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The load lock should be under vacuum. The Machine View window will show a wafer
loaded into the chamber. There really isn’t one loaded. You will need to push UNLOAD
and once the loader arm is back in position, the VENT button to vent the load lock.
Load your wafer into the load lock with the flat at the 9:00 position if the wafer indent on
the loading plate is imagined to be a clock face. This assures that the flat of the wafer
will not be under a clamp finger and avoids breaking the wafer, or worse, breaking the
clamp finger.
Click on LOAD in the transfer window. This will start pumping down the load lock and
will position the wafer on the chuck in the process chamber.
Once loading has occurred, push PROCESS in the Process Control-ICP window.
Following the stand-by step, the plasma will ignite and etching has started. You can
verify this by looking into the chamber. Note; the plasma will appear to flicker. This is
good. What you are seeing is the gases and RF changing as per the Bosch process.
Once the etching is complete the stand-by step will again pump and purge the chamber.
When completed, UNLOAD will become an option in the transfer window. Click it to
remove the wafer from the chamber.
Once the wafer is back in the load lock click on VENT to vent the load lock and remove
the wafer.
You are now back to tool’s stand-by condition. You may disable the etcher or continue
etching more wafers.
The Paperwork
Users of the tool are asked to fill out the log form located in the binder near the tool. You will be
asked for the following information;
Date, Name Program used.
Each Run Time- this is mostly for you so there is a record of your etch times if you did multiple
etches.
Total Time = total RF time for all your runs during that session.
He Pressure and He Flow- these are two checks of the He backside cooling system. He pressure
should be about 9 Torr. He flow should be about 2.8 Sccm. What is really being checked here is
that those numbers are steady and not fluctuating. If they are, there is a He leak. This means the
He is escaping and you wafer is getting hot, you lost control of the etch and it is no longer
anisotropic.
To fix this problem do the following;
 Stop the etching by clicking on SKIP in the process control-CP window.
 Unload and vent.
 Take a look at the back of the wafer for any resist, particles, or pieces that might interfere
with the maintaining a good pressure seal on the chuck.
 Remove to make sure the back of the wafer is clean and re-LOAD the wafer.
 Check to see that the He pressure and flow are steady.
You may have to do this procedure more that once. Examine the wafer carefully; there may be
small cracks or you may have punched through a feature.
Chamber Pressure Passivation/Etch- you are asked to note the chamber pressure during the
etching as a check status of the vacuum system. This can be an indicator that the lines are
beginning to constrict and needs attention.
Used Holder?- did you use the wafer holder during the etching.
Wafer #’s- in order to look at the log of the etching run we will need to have the wafer number.
There is no time/date stamp. The number is located in the transfer window.
More on Recipes
There are four staff maintained recipes; DEEP, SMOODEEP, SMOOSHAL, FASTDEEP and
O2CLEAN. This means that users are welcome to use these recipes, but if any parameter is
changed besides Time, the user is requested to write their own recipe.
Here are the four recipes with a basic explanation of why they were created and when a user
might want to use them;
Recipe Name
DEEP
Etch
Passivation
SF6 Flow- 130 sccm
C4F8 Flow- 85 sccm
RF Coil- 600W
RF Coil- 600W
RF Platen- 12W
RF Platen-0W
Time- 12 secs
Time- 7 secs
This is a basic Bosch process recipe. It has been the starting point for many users who have gone
on to customize and write their own recipes. The etch rate is very much dependant on the size of
the features to be etched and the amount of wafers surface that is exposed silicon. Recent testing
using patterns with about 15-20% exposed silicon has the etch rate at about 1.8-2.0µ/min.
Users are very strongly encouraged to establish the etch rate of critical features for each patterns
(mask level) etched.
Recipe Name
SMOODEEP
Etch
SF6 Flow- 130 sccm
RF Coil- 600W
RF Platen- 12W
Time- 9 secs
Passivation
C4F8 Flow- 85 sccm
RF Coil- 600W
RF Platen- 0W
Time- 7 secs
This recipe was developed in an effort to smooth out the ‘scalloped’ side walls when using the
DEEP recipe. In DEEP there are roughly 10 scallops per micron of etch depth. SMOODEEP has
a faster gas toggle rate and hence there are more scallops per micron.
Recipe Name
SMOOSHAL
Etch
SF6 Flow- 130 sccm
RF Coil- 600W
RF Platen- 12W
Time- 6 secs
Passivation
C4F8 Flow- 120 sccm
RF Coil- 600W
RF Platen- 0W
Time- 5 secs
SMOOSHAL is a recipe to be used for etch depths of less than 20µ.
Recipe Name
O2CLEAN
Etch
O2 Flow- 40 sccm
RF Coil- 600W
RF Platen- 80W
Time- 30 mins
O2CLEAN is a recipe that is used primarily after the chamber has been exposed to air, say, after a
broken wafer has been cleaned up. Users are encouraged to use it before critical etches, but need
to be advised to also run the desired etch program for 10-15 mins after O2CLEAN to condition or
season the chamber. The clean is also done before running the process quals.