SPR 220 is our most commonly used photoresist, especially for RIE. The lab stocks SPR 220 (3.0) for general use, in the ACS 200 cluster tool, and in the CEE 200X photoresist spinner 1 & CEE 200X photoresist spinner 2. For films thicker then 5µm SPR 220 (7.0) is also available from the LNF Store and in the CEE 200X photoresist spinner 1.

Process

Dehydrate and apply HMDS
CEE 200X photoresist spinner 1, 10um recipe
Soft bake
- Use 2 Hotplates - 30 seconds @ 90°C, 6 minutes (360 seconds) at 115°C. Move quickly between hotplates to wafer does not cool.
- Let sample cool in a cassette or somewhere it can cool slowly. NOT on cold metal table.
Wait ≥ 20 min
Expose
- MA/BA 6 - Aligner -26 sec (silicon)
Wait ≥60 min
Bake 115°C for
- Use 2 Hotplates - 30 seconds @ 90°C, 3 minutes (180 seconds) at 115°C. Move quickly between hotplates to wafer does not cool.
- Let sample cool in a cassette or somewhere it can cool slowly. NOT on cold metal table.
Develop
- ACS - AZ300 - ?? sec
- CEE - AZ726 DP 80-80 sec

Characterization

There are still some bubbles after 50 minutes so wait time needs to be greater than 50 minutes.

This has been traced back to how you cool your sample. Best results have been seen with the following options.

Place sample in a 25 wafer carrier well away from the table and let sit for 2-3 minutes (this is what is used for the characterization work)
These are options that other cleanroom users use. They may affect other aspect ration and exposure conditions.
- Step down to a 90°C hotplate for 30 seconds after 115°C step and then place on a wipe folded in quarters.
- Step down to a 90°C hotplate for 60 seconds, step down to a 65°C hotplate for 60 sec, cool on a stack of wipes.

This could be potentially be caused by UV exposure and simultaneous heating during the DRIE step creating N2 bubble. After develop

This is has been tracked back to cooling after mounting your sample for DRIE.