↵Standard Operation Procedure for Spin Coating
Purpose: to uniformly spin resist or polymer onto a sample
Location: Pettit or Marcus cleanrooms
Chemicals: photoresist, acetone
Supplies Needed: spinner, spinner chuck, pipettes, aluminum foil, texwipes, bottle carriers, hot plate or oven, tweezers
Setup Procedures:
1. Set the hotplate or oven to the temperature needed for your pre-bake.
2. Make sure that your wafer is clean (see previous section).
3. Line the spinner bowl with aluminum foil, if necessary.
4. Choose the appropriate chuck so that your sample covers the entire chuck.
5. Properly line up the chuck with the shaft of the spinner. Do NOT force a chuck onto the shaft if it is not lined up.
6. Make sure that any screws are tight and not protruding above the chuck
7. Program your parameters according to the recipe on the photoresist data sheet.
Number of Substrates: 1
Process Parameters:
1. Place you sample on the spinner chuck
2. Run your recipe without photoresist to test the vacuum
3. Dispense your resist in two possible ways:
a. For a thinner resist, pipette from the amber bottle. Do NOT place a pipette in a stock bottle
b. For a thicker resist, pour from the amber bottle directly to your wafer. Do NOT pour directly from a provided stock bottle.
4. When dispensing your photoresist:
a. Make sure the resist is at room temperature
b. Remove any particles or bubbles in the resist
c. Dispense in a continuous stream, close to you wafer
d. Dispense only enough resist to coat your sample
5. Close the lid to the spinner (if it has one)
6. After starting the recipe, close the fumehood door.
7. Throw any pipettes used for dispensing resist in the labeled solvent trash cans.
8. Once the recipe is complete, remove your sample and place on the preset hotplate or oven rack.
9. Set a timer for your pre-exposure bake.
10. Clean the spinner and chuck with acetone and texwipes
a. Take the chuck off of the spinner to clean it
b. Throw all texwipes used into the solvent waste container
11. Close the fumehood door when you are done cleaning the spinner
12. Photoresist will be on your gloves, so they need to be changed immediately when you are done cleaning the spinner
13. When your hotplate/ oven timer goes off, set your samples on a texwipe on a counter to cool before returning them to the sample box.
General Dose Guide
The dosage required will often vary on a case-by-case basis. It depends on the type of resist, the thickness of the resist, and the intensity of the radiation (which itself varies on the exposure tool). Exposure tools at the IEN have intensity probes that are used to determine the intensity of the radiation. Sometimes, a log is present at the tool for users to record the measured intensity at a particular time. This can remove the need to measure the intensity everytime the tool is used.
The exposure time can be calculated by taking the dosage (found on the photoresist datasheet) and dividing it by the intensity measured. If possible, the intensity can be measure through the mask. If there is not a large enough clearfield space to accommodate the sensor, subtract 1.0 mW/cm2 to account for the intensity lost traveling through the mask. The intensity loss can vary depending on the mask material, so that value should be looked up before exposure if unable to measure through the mask.
Standard Operation Procedure for Alignment & Exposure
Purpose: to align the mask to the layers of processing under the photoresist or to simply expose resist through a mask
Location: Pettit and Marcus Cleanrooms
Supplies Needed: mask, mask holder, correct size wafer chuck, tweezers, blue tape (if necessary)
Setup Procedures:
1. Choose the proper exposure wavelength on the mask aligner tool and the intensity measurement tool.
2. Place the sensor of the intensity measurement tool in the center of the mask aligner chuck
a. If possible, measure the intensity through the mask.
i. Place the mask on top of the sensor so that dark space does not cover the sensor
b. If not enough clearfield space, measure with the sensor alone
i. Start a lamp test and not the intensity reading
ii. Calculate the exposure time by taking the dosage found on the photoresist data sheet and dividing by the measured intensity.
c. Be sure to subtract 1.0 mW/cm2 from the measured intensity to account for loss from the mask if not able to measure through the mask
iii. Program the calculated time into the recipe on the mask aligner
Number of Substrates: 1
Process Procedures:
1. Load your mask onto the properly sized mask holder with the chrome side up, and then turn on the mask vacuum
2. Load the mask holder into the mask aligner. The chrome side should now be facing down.
3. Choose the mask aligner chuck so that you sample will not hang over the edges
4. Load the mask aligner chuck
5. Load your sample onto the chuck
a. If your sample does not cover the entire chuck, use blue tape to cover the rest
b. Cut a hole in the blue tape slightly smaller than your sample size
i. Cut the blue tape on a counter or table away from the mask aligner
ii. Do not cut on the chuck
iii. Do not cut the vacuum bladder for the vacuum chucks
6. Load your sample into the mask aligner
7. Align your sample as needed and expose
8. Unload your sample
9. Transfer you sample to the hotplate or oven for a post-exposure back, if needed.
10. Unload your mask
Standard Operation Procedure for Development
Purpose: to remove exposed positive resist and unexposed negative resist
Location: general purpose fumehoods
Chemicals: developer
Supplies Needed: glass or Pyrex dish, PPE, timer, tweezers, bottle carrier, developer, texwipes, fumehood, chemical warning labels
Setup Procedures:
1. Look up the development time and developer type on the photoresist data sheet
2. Fill out a chemical warning label with the name of the developer being used
3. Find a plastic or glass container that will fit your sample
4. Using a bottle carrier, bring a bottle of developer to the fumehood you will be working at
5. Pour enough developer into the container to cover your sample
Number of Substrates: 1
Process Procedures:
1. Set a timer for development
2. Place your sample in the container and start the timer
3. Slightly agitate the container while developing
4. Stop developing once your timer has ended or when you no longer see photoresist coming off the sample
a. If you are unsure if your sample is finished developing, check it under a microscope with a UV filter
b. Under-developed features will have wide corners and thin spaces or a “rainbow” pattern where the resist is still in the feature
c. Over-developed features will have a rounded corners and thin lines
d. If you need to develop for more than the time on the data sheet states, add extra time in small increments, continuously checking under the microscope
5. Take your sample out of the developer and rinse under gently running DI water
6. Place your sample on a texwipe and blow dry with the nitrogen gun. Use a sweeping motion while working from one side of the sample to the opposite side.
7. Dispose of base developer in the sink with plenty of running city water. Solvent developers should be disposed of in the solvent waste jug.
8. Rinse the development container with DI water.
Comments:
a. Under –exposed is better than over-exposed
b. Be sure to note any differences in development times for later use
Baking
Resist Stripping