Stepper 1 (GCA 6300) - Standard Operating Procedure

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 [10,1]
2. Type MODE and scroll down through options
3. Select the chuck size. Use 100 for 4" substrates and 3 for 3" or smaller substrates.This number is used for telling the system where the chuck center is.
4. DO NOT change any parameters in here, except the chuck size
5. Log out using LOG OUT
6. At the colon sign type LOG IN [10,xxx], and hit enter. ( xxx-your account )
7. Type ORIG and hit enter. This resets the laser interferometer position measurement system and moves the stage through its entire motion.

Reticle Loading and Unloading

The alignment of the reticle (mask) to the system is critical for achieving reproducible alignment.  System alignment marks on the reticle are located near the right and left edges of the mask and are 103 mm apart so they do not get exposed within the 100 mm exposure area of the mask.  These marks are put on automatically by Photronix and the gds file can be obtained from Brian Thibeault if you use a different vendor. Use the following procedure to align the mask correctly to the system.

Loading the reticle:

1. Unlock spindle and swing lamp column to middle position so that the lens is exposed.
2. Place mask chrome side down so that wording appears correct ( as seen in L-edit file).
3. Swing lamp column so that objective can be used to align mask, DO NOT tighten spindle lock at this time.
4. Using your hands and looking through microscope, shift and rotate mask so that the “crosses” are roughly aligned
5. Tighten spindle lock. This releases a vacuum holder onto the top of the mask so that the mask may be precisely aligned.
6. Looking through microscope, use alignment knobs (x,y) to translate and rotate(Θ) the mask into position.  First focus the objective by using the knob on top of the microscope.  Use the right alignment mark for the x-axis alignment and both alignment marks for the y-axis and rotation alignments.  NOTE: To get best and fastest results approach alignment from one direction, do not try to wiggle back and forth about the alignment position. Backlash in the mechanics can make this frustrating. You should see equal amounts of light in between all lines when the mask is aligned well (within 0.1 um).
7. Once mask is aligned, pull the reticle vacuum button to the left of the lens column. The reticle is now vacuumed to the system.
8. Use the stencil (usually L-shape mask cover), to cover part of the mask plate that you do NOT want to be exposed. If you have just one layer on your mask plate, you do not need to use the stencil. There are also blade apertures that could be used. The knobs on the lamp column  (X,Y) can be adjusted to 100,75,50 and 25% to be open. Fully open blade apertures would be at 100%
9. You are now ready to proceed with a focus job, map job, or exposure job.
10. This part is important: If alignments are critical, do not just brush through this procedure.  The global alignment requires good, precise alignment of the reticle with the system in order to work correctly.  The local alignment system can adjust for local X and Y misalignment, but not rotational errors.

Unloading the reticle:

1. Unlock spindle and swing lamp column to middle position so that the lens is exposed.
2. Pull the reticle vacuum button to the left of the lens column. Unload the reticle from the system.
3. Swing the lamp column back. Tighten spindle lock.

Wafer Loading

1. Attach the appropriate chuck to the system. ( Link: How to select proper chuck)
2. Place your wafer centered on the chuck, noting the orientation. If you are doing an alignment step, make sure to place the wafer in the same orientation and as best as possible in the same location as the first exposure.  The set screws in the chuck can help to get reproducible placement of the wafer.  When the wafer is in place, flip the right vacuum switch upwards to hold the sample.
3. Place the sample chuck onto the stage, again trying to be repeatable, and flip the left vacuum switch upwards to hold the chuck.
4. Now you are ready to do an exposure job.

Running a JOB-Normal Operation

1. At the colon sign type LOG IN [10,xxx], and hit enter. ( xxx-your account )
2. Load the sample on chuck and then on stage
3. The command you will use for Global alignment is:
4. EXEC jobname\passname and hit enter.
5. (See bellow “Wafer alignment to system" - for Global Alignment , and " Wafer alignment to mask"- for Local Alignment (DFAS)” )
6. Type in the desired exposure time.
7. Type in desired focus offset.
8. Press RESET on the small keyboard.
9. Press MAN and S/C simultaneously.
10. Wait about 5-10 seconds.
11. Press MAN.
12. Sample will move to alignment position/do global alignment.

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

The joysticks and focus knobs are used in this part of the exposure sequence to align the wafer to the system.  The sequence of operations will depend on whether or not you use standard alignment keys (global alignment mark) 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 joysticks have a double speed.  Press joystick far for the high speed, shallow for the low speed.  To change the joystick speed hit letter "O" on the main keyboard. The joystick speed can be in range from 1-10 (1- slowest, 10-fastest). 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 knob to get a crisp image (knob on top of the microscope piece).
2. Align the right alignment mark using the position joystick.
3. Use the Theta joystick to rotate the left image into position. [Positive Theta = CW , Negative Theta= CCW rotation of chuck]. 
4. If you run out of theta alignment, you will need to adjust your sample on the chuck by hand, and continue with alignment until aligned very well.
5. The left image is used for theta only. The right image is used for x, and y alignment
6. Repeat process until satisfied with the alignment.  You can obtain better than 0.2 um alignment consistently if you are careful with reticle and global alignment.

Non-Standard Alignment Keys:

1. Adjust the focus knob to get a crisp image (knob on top of the microscope piece)
2. Align the right mark using the position joystick.
3. Press "A" on the main keyboard to toggle to the left alignment mark.
4. Use the Theta joystick 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 by hand, and continue with alignment until aligned very well.
6. The left image is used for theta only. The right image is used for x, and y alignment.
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 right alignment mark before pressing " EXP", BL orientation - make sure you are on 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 for Local Alignment (DFAS:

MAP jobname\mapxx, passname

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".

Running a FOCUS and\or EXPOSURE matrix

 The system is calibrated weekly on 4 inch Si wafers using resist SPR 955-0.9 and standard chuck (4”-500um). Your substrate type, thickness, and resist may require different focus and exposure setting than the standard calibration. A focus and\or exposure matrix should be done for each resist, to tweak your process relative to the calibration baseline. Once the process is optimized for a specific resist, the exposure time\focus will not change in future , since the lamp power is hold constant all the time.

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

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

1. Before doing an EXPO job, LOG IN to [10,1] and type “MODE” – set the correct chuck size for the substrate (4” wafer-would be 100)
2. LOG OUT form [10,1], and LOG IN to your account [10,xxx]
3. Use the command EXPO jobname\passname and hit enter
4. You can use one of your already defined jobs\passes with your highest resolution mask to optimize the process.
5. Enter starting row within array specified in the pass (for example : 1)
6. 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)
7. Enter starting column within array specified in the pass (for example:1)
8. Enter ending column within the array specified in the pass(for example:6)
9. Enter either F=to vary the focus , E= to vary the exposure , or R for both (to increment focus for each row and exposure for each column within the array)
10. Enter the parameters as prompted by the computer. They will differ based on which option is chosen
11. Press RESET on the small keyboard, and then the MAN and S\C simultaneously
12. Wait a few seconds and press MAN again
13. If you are doing an aligned test (like for exposure on top of a mesa) align the wafer now, press “EXPOSE”
14. If you are NOT doing an aligned test, just press “EXPOSE”
15. The command EXPO will shoot a specified serpentine array based on the parameters in your job\pass (first exposure - upper left corner)
16. When exposure is finished, follow the recipe (post exposure bake if needed) with development. Please take your time for inspection, and select best exposure time and focus.
17. The computer will ask you for the best row and column. Enter row and column number
18. The computer will then tell you the focus and exposure based on the row and column you input
19. 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)
20. Unload the mask plate, and LOG OUT.