Resist Process Information
P(MMA-MAA) Copolymer
Spin-Speed Thickness Data
Typical PMMA BiLayer Process Parameters
1. Clean substrate - bake, solvents + bake, O2 plasma, or piranha etch.
First / Bottom Layer - More sensitive, either lighter molecular weight or copolymer.
2. Dispense resist.
3. Spin bottom layer of resist, 60 seconds.
4. Bake resist, hotplate, 180 C, 180 seconds.
Second / Top Layer - Less sensitive, thinner, usually heavier molecular weight, 950K PMMA.
5. Dispense resist.
6. Spin bottom layer of resist, 60 seconds.
7. Bake resist, hotplate, 180 C, 180 seconds.
8. Expose. Dosing ranges from 200-500 µC/cm^2, depending on substrate, feature size and density.
9. Develop. 60-120 seconds. MIBK:IPA, either 1:1 or 1:3.
10. Rinse, IPA, 15 seconds. N2 dry.
Notes
- HMDS does not generally help adhesion. Cleaning the substrate with piranha or an O2 plasma (ie, barrel ash) will help adhesion.
- If possible, a very brief, light O2 descum prior to metallization is helpful.
- During metallization, line up sample very carefully to get line-of-sight deposition. Your substrate surface must be perpendicular to the deposition source. You may be surprised to find that even a very small mis-alignment will cause your deposited material to be shifted, and in worse cases, no material whatsoever to reach your wafer surface.
OK:
BAD:
- PMMA and Copolymer can be stripped in Dichloromethane/DCM, NMP, Acetone (ok), or an O2 plasma.
- When stripping or during liftoff, be sure to keep the substrate completely wet at all times, until after final rinsing in IPA is completed, or you will have a hard-to-remove residue.
Example
Here is an example bilayer resist recipe:
Bottom Layer: P(MMA-MAA) EL8, Spin 3000 rpm, 120 seconds.
Top Layer: PMMA, A4, 3000 rpm, 120 sec.
Develop 1:1 MIBK:IPA, 60 sec
Vendor Information
See the vendor information sheet here.