ElectroHolography Laboratory

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====SOP – Photolithography using SU 8 - 2002====

===Tentative SOP developed using bake numbers from the CMUT paper===

  - Clean wafer by using the Anelva RIE plasma etcher
  - Spin on SU 8 using 1mL of resist for each 25 mm of substrate diameter. 
    - 500 rpm for 5-10s acceleration 100rpm/s
    - 3000 rpm for 30s acceleration of 300 rpm/s (Hawkin’s group uses 1500rpm for 30s at 300rpm/s)
    - 4000 rpm for 2 s at 3000 rpm/s (Edge bead removal) 
  - Soft bake (Hawkin’s group uses ramping, but maybe preheated is better?)
    - 65 C for 3 min
    - 95 C for 3 min
    - 65 C for 3 min
  - Expose
      - Settings: 
        - Short program
        - Hard contact 
        - Manual align for markers if not the first mask
        - Alignment gap: 50 microns
        - Alignment check: on
        - Negative resist 
    - Center stage and microscope by going to first mask, then align stage, then going back to manual align. OR go out of the short program and click the button that says align stage. 
    - Put the wafer down align the flat side with the line on the pillar. 
      - Vacuum on
    - Put down mask
      - The side the metal was deposited on is the side that goes toward the mask
      - Vacuum on
    - If not first mask and you are manually aligning, get the alignment marks to this position by focusing, rotating, and panning. Identify the mark positions on both the mask and the wafer. Then move the wafer so that the marks look like this:{{alignment_marker_pattern.png}}
    - Once the alignment marks are in place, move the wafer so that the top and bottom markers are overlapping. 
    - If the feature size is small enough, then move to the fine-tuning alignment markers and repeat the process of focusing. Instead of panning at this resolution, use the single-step setting on the right joy stick and change the step size to one micron or so. 
    - Click the expose button
      - Alignment check
        - If the alignment is not as good as intended, click the realign button and repeat the alignment process until it is as aligned as possible.
        - If it is as good as intended, click the continue button on the joy stick
  - Post Exposure Bake
    - 65 C for 3 min
    - 95 C for 3 min
    - 65 C for 3 min
  - Develop
    - 35 s in the SU8 developer (Check this time)
    - Rinse with Acetone and IPA (I’m not sure about the acetone yet) 
  - Hard Bake
    - 65 C for 2 min
    - 95 C for 4 min
    - 65 C for 2 min
ElectroHolography Laboratory

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