Standard Operating Procedures
1
Attach Sample
Attach the ST:O sample(s) to the throwaway silicon wafer:
- Use the ruler and the fine tip sharpie to make straight lines where you want the samples to go. Make these lines parallel to the flat edge of the silicon wafer; this will make it easier to align later. If doing more than one ST:O sample, make sure they are placed exactly 1.4 cm apart vertically or horizontally to line up with the mask.
- Add a small dot of super glue near the center of the sample and carefully drop into place.
- Let the super glue dry until ST:O no longer moves around when nudged with the tweezers. Putting it on the hot plate can speed up the drying process.
Tip
If any super glue gets on the surface of the sample, wet a Kim wipe with acetone and carefully remove it.
2
Plasma Clean
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- Plasma clean the sample for 1 minute using the plasma cleaner in the cleanroom. This removes any excess surface gunk (especially hydrocarbons from fingerprints, etc.)
Note
Follow the instructions as posted near the machine. Start the timer once you strike the plasma.
3
Apply Photoresist
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- Center the wafer on the spinner and turn on the vacuum.
- Under select process, select Program 12 (5000rpm, 1 min) -- the settings for the "Davis Group".
- Apply 5 drops of HMDS to each 1 cm sample.
Warning
Immediately after doing so, close the lid and press "Start". Waiting too long will cause it to spread and dry unevenly.
- Apply at least 20 drops of AZ3330 to each sto square. Immediately after doing so, close the lid and press "Start".
- Check to make sure the coat of AZ3330 has covered the entirety of the sample(s). A little waviness is not bad but use your best judgment. If it looks too messy, clean it off with acetone on the other spinner around the corner. Then go back to step 3.
- If you are satisfied, place the sample on the hot plate and do a pre-exposure bake at 90C for 1 minute.
4
Light Exposure
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- Keep these settings on the screen. You can move to the other screen by tapping the blue Launch UV Exposure button.
- Now move to the physical control panel.
- Press EDIT PARAMETER button.
- Using the X arrow keys to move between parameters and the Y arrow keys to modify parameter, set:
- Exp. Time to 10.0 sec
- Al. Gap 50
- Wec type cont
- Exposure type ‘soft’
- Press EDIT PARAMETER again to continue.
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- Once the settings have been established, press CHANGE MASK to load mask.
- Put mask dark side up (the machine will flip it over), and press ENTER to turn on the vacuum.
- Flip mask stage in and then click CHANGE MASK again.
Caution
Don’t trust the holding clip. Use your other hand to hold the mask.
- Press LOAD and pull out wafer stage to load wafer.
- Press ENTER to turn on sample vacuum.
- Move in slide and press ENTER.
- Align sample.
Tip
You want the sample edge to be straight in line with the mask. You should be able to see the 1 cm square sample under the mask. Move the mask so the 1 cm sample lines up with one of the 1 cm squares on the mask. The microscope screen is usually not needed to do this.
Big silver knob in the back is moving the wafer (11 turns to move 1 cm sample from one side of the mask square to the other). Silver knobs in front moves mask.
Big silver knob in the back is moving the wafer (11 turns to move 1 cm sample from one side of the mask square to the other). Silver knobs in front moves mask.
- Before exposing click ALIGN/CONT/EXP.
- Press EXPOSURE once it's done aligning.
Warning
The microscope will raise, and the light will move forward and expose for 10 seconds. Do not look straight at the light.
- Remove wafer
- Once it lights up, press UNLOAD
- Pull out wafer stage
- Click ENTER to turn off the vacuum and remove the wafer
- Remove mask
- Press CHANGE MASK and pull out stage
- Carefully flip it over and set it next to the exposure machine
- Press ENTER to turn vacuum off and remove mask
5
Develop Pattern
- Place the sample on the hot plate for a 1-minute post-exposure bake at 90 C.
- Place the wafer into the development holder (looks like a plastic arrow) and slide down the tab to hold it in place.
Caution
Check the AZ300M developer solution. If it is too dark in color, you can pour it into the waste container and replace it with new solution. Make sure to check the label to make sure it is the correct chemical to develop AZ3330.
- Submerge wafer in the solution and agitate slightly for 30 seconds.
- Rinse with deionized water and blow dry.
- Check the pattern under the optical microscope in the NE corner.
Note
If not sufficiently developed, resubmerge in the solution for an additional 30 seconds to repeat the development and check cycle until the pattern is sufficiently developed.
If the pattern was not aligned correctly, if you overdevelop, or if there is something else wrong with it, you can still rinse off the photoresist with acetone on the spinner and go back to step 3. You can also develop it for longer if the acetone doesn't work completely, but end with acetone before the plasma clean.
If the pattern developed correctly, congratulations, you are done with the photolithography!
If the pattern was not aligned correctly, if you overdevelop, or if there is something else wrong with it, you can still rinse off the photoresist with acetone on the spinner and go back to step 3. You can also develop it for longer if the acetone doesn't work completely, but end with acetone before the plasma clean.
If the pattern developed correctly, congratulations, you are done with the photolithography!
Tip
There is an optical microscope in the basement of the Eyring Science Center that you can sometimes check your pattern on. To save a screenshot off that microscope, put the screenshot in This PC > Desktop > DATA > Sandberg Group.