Photolithography

Pay attention to all the process parameters (how long is the piranha wet etch; what is the exposure time for a given UV exposure system). These parameters may not be given in the data sheet and depend on where you are going to perform the photolithography steps. You will need these parameters for “debugging” if the process goes wrong. The following are 2 protocols developed by your fellow classmates.

SU-8 Protocol Recipe #1

01   Substrate Preparation: Clean Substrate

Using piranha wet etch (H₂SO₄ and H₂O₂)

Using De-ionized water rinse

02   Coat SU-8

Using SU-8 2015 spin at 2000 rpm for 30 s with accelerationof 300 rpm/s

03   Edge Bead Removal (EBR)

Using small stream of solvent (MicroChem’s EBR PG) to remove thick bead

04   Soft Bake

Using a uniformity thermal hotplate to warm the soft bake

Soft bake for 3~4 min and control temperature at 95 °C

Remove wafer and Cool down wafer to room temperature

Return wafer to hotplate and repeat cool down and heat up to remove “wrinkle”

05   Exposure

Expose wafer under Ultraviolet at the wavelength of 350 nm

Exposure energy is 140~160 mJ/cm²

For silicon wafer, we choose 1X dose

06   Post Exposure Bake

Using hotplate to back wafer for 4~5 min at 95 °C

07   Development

Using MicroChem’s as SU-8 developer to develop SU-8 for 3~4 min

08   Rinse and Dry

Spray and wash the developed wafer with fresh solution for 10 s

Second spray and wash with Isopropyl Alcohol for 10 s

Using pressure air with filter (or N₂) to dry wafer

09   Hard Bake (Optional)

Hard bake wafer 150 °C for 5~30 min to anneal any crack

10   Removal (Optional)

Using MicroChem’s Remover PG with OmniCoat to lift off SU-8

Control temperature at 50~80 °C and immerse wafer for 30~90 min in Remover.

Also can use Plasma removal (200 W, 80 sccm O₂, 8 sccm CF₄, 100 mtorr, 10 °C)

SU-8 Protocol Recipe #2