Photolithography Processes

Photolithography

AZ1512

  1. Spin coat AZ1512
    • 200 rpm at 10 rpm/s for 60s
    • 3000 rpm at 1250 rpm/s for 60s
  2. Bake at 100 °C for 1 minute
  3. Expose at 80 mJ/cm2
    • Use Channel B (405nm)
  4. Develop in AZ300 for 1 minute

The adhesion of AZ1512 to Si is not very good.

LOR5A/AZ1512 Bilayer

  1. Dehydration bake at 170 °C for 5 minutes
  2. Cool by blowing with N2
  3. Spin coat LOR5A
    • 2500 rpm at 1250 rpm/s for 60s for a 600nm thick film
  4. Bake at 170 °C for 5 minutes
  5. Cool by blowing with N2
  6. Spin coat AZ1512
  7. Bake at 100 °C for 1 minute
  8. Expose at 80 mJ/cm2
  9. Develop in MF-319
    • Immerse for 1 minute to completely develop AZ1512
    • Further development will undercut the LOR5A at a rate of 4 nm/s

This bilayer resist system is used to produce an undercut beneath the AZ1512 resist pattern as shown below. This undercut facilitates lift-off.

LOR5A/AZ1512 Bilayer with undercut

Transparency mask

Substrate: Transparency/Carbon?

  1. Draw patterns
    1. KLayout is a free layout software
    2. Save using the *.gds format
    3. Draw within a 5x7 area
  2. Send pattern file to outputcity.com
    1. Answer some of their questions (tone and emulsion side)
    2. They will send you a PDF image of the pattern
    3. Confirm the PDF image of the pattern

Transparency masks are much cheaper than glass photomasks and you can get them the next day. The main limitation is the 10 μm resolution. If you plan to use the transparency mask quite often, it may be worth it to copy it onto a glass photomask blank since glass masks are more durable and can be cleaned.

Making a glass mask from a plastic mask

A verbose process recipe can be found here.

Substrate: Glass(Soda-lime or Quartz)/Cr/AZ1518(1um)

  1. Acquire photomask blank from vendor
    1. nanofilm.com is a good source
  2. Acquire plastic mask from vendor
    1. outputcity.com is a good source
    2. 10 um resolution
  3. Check plastic mask for defect
  4. Place photomask blank on the mask aligner chuck
  5. Place plastic mask on top of the photomask blank, pattern side down
  6. Place a blank mask on top of plastic mask to weigh it down and keep it flat
  7. Expose at 70 mJ/cm2
  8. Post exposure bake at 105°C for 50 seconds on a hot plate
  9. Develop by immersing with agitation in AZ MIF 300 for 60 seconds
  10. Rinse in DI water and blow dry with nitrogen
  11. Etch the Cr by immersing with agitation in CEP-200 for 180 seconds
  12. Rinse in DI water and blow dry with nitrogen
  13. Strip the residual resist by immersing in piranha for 30 minutes
  14. Rinse in DI water and blow dry with nitrogen