SPR 220 7.0

SPR 220 is our most commonly used photoresist, especially for RIE. SPR 220 7.0 is for filmes thicker than 5µm.

Process

1. Dehydrate and apply HMDS
2. Spin
   • Initial Spin at 100RPM for 10 Seconds
   • Final Spin at approximately 1500RPM for 30 Seconds
3. Soft bake
   • Use 2 Hotplates - 90°C 30 sec → 115°C 6 min. Move quickly between hotplates so wafer does not cool.
   • Let sample cool in a cassette or somewhere it can cool slowly, NOT on cold metal table. Cooling the wafer too quickly can cause the resist to crack.
4. Wait ≥ 20 min (rehydration)
5. Expose
   • Aligner - 26 sec (silicon)
6. Wait ≥ 60 min (outgassing)
7. Post Exposure Bake
   • Use 2 Hotplates - 90°C 30 sec → 115°C 3 min. 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. Cooling the wafer too quickly can cause the resist to crack.
8. Develop
   • AZ300 - 60 sec
   • AZ726 DP 80-80 sec

Characterization

Softbake

A wafer was spun and the thickness was measured at intervals of 60 seconds using the NanoSpec 6100. After 6 minutes (360 seconds) the thickness of the photoresist stays the same indicating the solvents have been removed.

Wait time between Exposure and Post Exposure Bake

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

Post Exposure Bake

Develop

Troubleshooting

Bubbles in resist after spinning

• If you are manually dispensing, the syringe may need to be degassed.
  1. Wrap the syringe in aluminum foil and place in a beaker of water.
  2. Put the beaker into an ultrasonic tank and sonicate for ~10 min at room temp to degas.

Cracking Resist

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.

Small bubbles form during DRIE

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

1. Flood Expose Sample for 45 sec on MA/BA6
2. Wait >1hr
3. DRIE

Resist peeling during DRIE

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

1. After mounting sample remove from hotplate.
2. Let cool for at least 5 minutes.

Technical Data Sheet

• Data Sheet