SPR 955

SPR 955 is an I-line series of photoresists developed by microchem, it's similar to SPR 220 but is formulated for thinner viscosities and higher resolution. We've been able to consistently get 500nm gratings in 0.97µm of SPR 955 in the stepper, on silicon. The 0.97µm thickness was chosen because it's one of the peaks listed in the datasheets swing curve.

Processes

SPR 955 (0.97µm)

1. Vapor prime wafer with HMDS
2. Spin 0.97µm in ACS, CEE 200X #1 or CEE 100CB
3. Bake at 100°C for 90 sec
4. Verify thickness if possible, for thin resists small thickness variations drastically change the necessary exposure dose.
5. Expose

Material	Stepper	Contact Aligner	Notes
Silicon	0.30 sec	5.5 sec
500nm SiO2
Borosilicate	0.30-0.34		Severe sidewall degradation <1µm due to back reflection

1. Bake at 110°C for 90 sec
2. Develop
   • ACS 200 cluster tool - AZ 300 for 25 sec
   • CEE Developer - AZ 726 25-25 sec double puddle

Notes: When photoresist is this thin the swing curve will have a larger effect; small thickness variations will have a larger change in the necessary exposure. Also at the end of the process you will have closer to .9-.94µm of resist. The softbake needs to be at 100C, not 115. Doing the softbake at 115 will burn out a lot of the PAC's, increasing dose to clear by ~40% (.24 sec vs .17 sec on the stepper).

These gratings are on silicon and exposed via the stepper:

Process Curves

This plot shows the ideal exposure time for several develops in the ACS. The 0.3 sec exposure with a AZ 300 25 sec develop in the ACS seems to be a good point.

The next plot shows the CD loss vs the amount of defocus in the stepper. ±900nm is about the limit before it's no longer going to work. Larger features will of course have a wider focus range.

Technical Data Sheet

SPR 955 Datasheet

Safety Data Sheet

• SDS