Stepper 2 (AutoStep 200) Operating Procedures

Work In Progress This article is still under construction. It may contain factual errors. Content is subject to change.

Cleaning the back-side of wafer

If the back side of wafer has some resist residue or particulates, this can cause errors in the interpreted best focus point since the wafer surface may be at a different height.

1. Make sure all work surfaces/spin chucks/hot plates are cleaned! Don’t use wipes, instead use cleaned steel surfaces.
2. Spin coat resist following the recipe for spinning/baking specific resist.
3. Check back-side of wafer thoroughly for resist residue/particulates before loading into system!
4. If you see particulates, try to blow off with high N2 flow first, you may need a razor blade to remove stubborn particles.
5. If you see resist residue, do next:
   1. Place wafer upside down in POLOS spinner using non-contact chuck.
   2. Set spin speed to 2000rpm.
   3. Spin wafer, wait until at top speed.
   4. Squirt Acetone on sample back for 3 seconds. Followed by ISO for 3 sec.
   5. Spin Dry while blowing with N2.
6. Load the wafer on chuck and then stage.

Logging into computer and checking the system

The system administrator will set up a directory for you to LOG IN and use the stepper at the time of training.

1. At the colon log into the system using LOG IN [10,xxx] where xxx is your account number.
2. Type CHUCK
3. You need to select C-change chuck size. Use 2 for 2” diameter wafers, 3 for 3” diameter wafers, 100 for 4” diameter wafers, and 142 smaller substrates ( ¼ of 2” or smaller parts). This number is used for telling the system where the chuck center is and for wafer auto leveling.
4. After select proper chuck, use Q- quit when done.
5. FOR STAFF AND EXPERIENCED USERS ONLY: Type SETUP and hit enter. Align the target and press “expose”. We use it as a method to verify all sub systems are operating properly and to reset system focus before an exposure job is performed.

Reticle Loading and Unloading

Loading the reticle:

 Mask Alignment on this system is automatic. You need to have the square marks on the top and bottom of the mask. These are put on automatically by Photronix and the gds file can be obtained from Brian Thibeault if you use a different vendor. There are 10 reticle box positions on the elevator. Slot 1 is dedicated for a calibration mask. Slots 2-10 are available for your use. Slots will NOT be dedicated for any users.

1. Load the reticle into a box with chrome side down (insert photo shown in the figure 1.)
2. Type RMSL on the main computer at the colon prompt.
3. Swing the reticle forks 90 degrees away from the reticle elevator.
4. Pull out knob, insert box in one of the slots (2-10), release knob to hold   box.
5. Make sure the box is sitting properly in place.
6. Hit Enter on the computer and the system will map the reticles.
7. On them main monitor you will get information about the reticle name and the slot# it is loaded (if the reticle does not have a name it will say just NONE)

Unloading the reticle:

 At the end of each job you need to unload the mask

1. Type RMSR on the main computer at the colon prompt.
2. Wait for the reticle to be loaded back in the reticle box.
3. Type RMSL on the main computer at the colon prompt.
4. Get your reticle from  the reticle box
5. NOTE: NEVER try to manually unload the reticle (as you would in GCA 6300 Stepper #1). Always use commands.

Loading a wafer into the system

1. Attach the appropriate chuck to the system. ( insert link "How to select proper chuck")
2. Make sure you know your substrate thickness and wafer diameter.
3. TARGET thickness is : 12.150mm +/- 0.1mm (TARGET= Chuck thickness+ Substrate thickness)
4. Each chuck has two numbers on top side (for example 100mm/500um) showing wafer diameter, and substrate thickness. ( insert link with TARGET thickness )
5. Place a wafer centered on the chuck, noting the orientation (major flat always touching two front screws, minor flat touching the screw either on left or right side)
6. If you are doing an alignment step, make sure to place the wafer in the same orientation as it was in the first exposure.
7. The set screws in the chuck can help to get reproducible placement of the wafer.
8. When the wafer is in place, flip the chuck vacuum switch upwards to hold the sample.
9. Place the sample chuck onto the stage, again trying to be repeatable, and flip the stage vacuum switch upwards to hold the chuck.
10. If your sample is thin (150um thinner than the number on top side of chuck), then you need to use SHIM ( we have 130,180, 230, 260um metal shims)
11. If you need a shim with different thickness you can try cutting some shim stock (stored in drawer next to Autostep200).
12. Be careful when placing the chuck on to the system. Do not set the chuck onto the built-in reticle on the left side of the stage.
13. Make sure the chuck vacuum is properly holding the chuck in place (it can tip forwards before the vacuum holds it in place).
14. At this stage type AWLT Jobname\Passname. This will test the auto-leveling of your wafer ( auto-leveling cannot be done on pieces smaller then ¼ of 2”, so when writing the program make sure that you at the LEVELER batch size input value -1( TURN off leveling).
15. At "START AWH" (automatic wafer handling) prompt, press MANUAL button.
16. Press MANUAL again.
17. Choose “N” to answer to all questions ( if not sure, use what is default value (*)).
18. If you have an auto focus error or leveling error, the system will tell you.

Running a JOB- Normal Operation

1. At the colon sign type LOG IN [10, xxx], and hit enter ( xxx- your account)
2. Make sure you have loaded the reticle as described above.
3. Make sure you have loaded the wafer as described above.
4. Type EXEC jobname\passname and hit enter. (See “Wafer alignment to mask / Local Alignment (DFAS)” below for local alignment job syntax)
5. Type in the desired exposure time if different
6. Type in desired focus offset.
7. Reticle T: 0
8. Reticle Bar Code: Enter a bar code name if you have one on the mask, otherwise, hit Enter.
9. Floor#:  Enter the elevator slot number where you put your reticle ( it could be any # (2-9), #1- only for SETUP mask).
10. If MATCH was enabled, the system loads the reticle and you will see the left screen perform the InSitu-Match routine on your mask.
11. Press MANUAL key when “Start AWH” prompt is seen.
12. Press MANUAL again as prompted
13. Sample will move to alignment position/do global alignment.

• Wafer alignment to system / Global (Manual Operation Only)

The keyboard alone is used in this part of the exposure sequence to align the wafer to the system.  The sequence of operations you do will depend on whether or not you used standard alignment keys or not.  If you placed the sample close to the position you did during the first exposure, you should see an alignment mark in the right side of the screen.  If not, you will need to find this mark using the position joystick by following a spiraling outward from the initial position. Pressing “F” repeatedly on the keyboard will do this spiral finding for you automatically. The red arrows on the number keys indicate the direction of movement for each keystroke.  There are also + and -theta (angle) keys for rotation.   Inc and Dec are used for microscope focus.  The enter key on the numeric keypad changes from fast to slow movement.   To change the joystick speed hit O on the main keyboard.  Once the alignment mark is found follow one of the following procedures. Most of the time we use Non-Standard Alignment keys:

Standard Alignment Keys:

1. Adjust the focus (Inc and Dec keys) to get a crisp image (you might have to change speed with the Fast/Slow key).
2. Align the right mark using the numeric keys labeled with arrows.
3. Use the Theta keys to rotate the left image into position. Positive Theta = clockwise rotation of chuck.  If you run out of theta alignment, you will need to adjust your sample on the chuck.
4. The left image is used for theta only.
5. Repeat process until satisfied with the alignment. You can obtain better than 0.2 um alignment consistently if you are careful.

Non-Standard Alignment Keys:

1. Adjust the focus (Inc and Dec keys) to get a crisp image (you might have to change speed).
2. Align the right mark using the numeric keys labeled with arrows.
3. Press "A" on the main keyboard to toggle to the left alignment mark.
4. Use the Theta keys to rotate the left image into position. [Positive Theta= CW, Negative Theta=CCW rotation of chuck]
5. If you run out of theta alignment, you will need to adjust your sample on the chuck.
6. The left image is used for theta only.
7. Press "A" again to move to the right alignment mark
8. Again adjust the right alignment mark
9. Repeat process until position and Theta are acceptable.
10. Always use your RIGHT alignment mark (right side of monitor) for alignment. Once alignment is finished, you have two option for pieces (quarters): BR orientation, and BL orientation.
11. BR orientation - make sure you are on the right alignment mark before pressing "EXP", BL orientation - make sure you are on the left alignment mark before pressing "EXP"
12. After global alignment, press EXP on small keyboard and the job will be executed.
13. Remove the sample from the stage when done.
14. Develop resist and inspect in microscope for alignment (if needed)
15. Computer may ask for next wafer.  To escape out of this press CTRL C followed by A and the enter key to abort out of the loop. If you have another wafer with the same job\pass, you can do it now without aborting.

• Wafer alignment to mask / Local Alignment (DFAS) :

The best way to use this is to use a mapping routine followed by a shoot using the corrections given by the map.  A mapping routine should be set-up in your mapping pass. Usually we do not map all dies, just selected ones. You could selected in each row few dies. The mapping pass should have a name different then any other pass. It could be named mapxx or some other name (for example: local). Make sure you specify die x die is to be used and that you have the correct key offsets for the global and local alignment marks.  The command you will use is:

MAP jobname\mapxx,passname

1. Proceed as normal. Find a global alignment mark and do your best alignment. The first pass (mapxx) is the mapping pass. The system will do mapping, using dies that are selected in mapping pass. It will look for DFAS alignment mark in each die, and make corrections. When asked to make corrections, say yes. After corrections are applied, the exposure job will be performed shooting the pass named " passname". Follow instructions on screen when using this function.
2. Remove the sample from the stage when done. (If Match was enabled, you will have to wait until the match is done again.  It will do this before asking you for the next wafer). Develop resist and inspect in microscope for alignment (if needed)
3. Computer will ask for next wafer.  To escape out of this press CTRL C followed by A and the enter key to abort out of the loop.  If you have another wafer with the same job\pass, you can do it now without aborting by placing it on the chuck and hitting MANUAL.

Running a FOCUS and\or EXPOSURE matrix

The system is calibrated weekly on 4 inch Si wafers using the standard chuck (4”-500um). Your substrate type, thickness, and resist may require different focus and exposure setting than the standard calibration.

A focus-exposure optimization should be done for each resist, to tweak your process relative to the calibration baseline. You can use one of your already defined jobs\passes with your highest resolution mask to optimize the process.

The command EXPO will shoot a specified serpentine array based on the parameters in your job\pass. The focus and\or exposure can be varied across this

array to determine the optimum focus relative to the baseline. One focus step is equal to 0.1 um of focus depth. FOCUS OFFSET is an INTEGER!

+1=0.1um of lens movement up from the wafer é

-1=0.1um of lens movement down toward the wafer ê 

1. 1.   Before doing an EXPO job, type the “CHUCK” – set the chuck size that is correct for your substrate (4” wafer-would be 100)
2. 2.    Use the command EXPO jobname\passname and hit enter
3. 3.    Enter starting row within array specified in the pass (for example : 1)
4. 4.   Enter ending row within the array specified in the pass (for example:6, depending how big is die size, and how many dies can fit in X direction)
5. 5.    Enter starting column within array specified in the pass (for example:1)
6. 6.    Enter ending column within the array specified in the pass(for example:6)
7. 7.   Enter either F=to vary the focus , or E= to vary the exposure , or R for both (to increment focus for each row and exposure for each column within the array)
8. 8.   Enter the parameters as prompted by the computer. They will differ based on which option is chosen
9. 9.   “Start AWH” process – press MANUAL when prompted
10. 10.  Press the MANUAL again
11. 11.  If you are doing an aligned test (like for exposure on top of a mesa) align the wafer now, press “EXPOSE”
12. 12.  If you are NOT doing an aligned test, just press “EXPOSE”
13. 13. When done, do PEB, and development according to the process and inspect in the microscope.  Please take your time for inspection.
14. 14. The computer will ask you for the best row and column. Enter row and column number
15. 15. The computer will then tell you the focus and exposure based on the row and column you input
16. 16. Do not update system focus ! Input a focus offset into your own exposure job. (If you update the system focus, you must change it back using the MODE command)
17. 17.  Unload the mask plate, and LOG OUT