I started working on SU-8 few months ago, I also face same problem of adhesion after the spin coating step before soft bake. Whole SU-8 get shrinked at the centre...i tried all cleaning steps....RCA-1 cleaning, HF oxide removal and then bake at hotplate for 15min. But still its not adhere.... i dont have primer yet. I want to know what are the main reason for poor adhesion on silicon????????????????? also suggest me ideas
Usually adhesion is very good on silicon. I just use 30% HF treatment for 40s and bake 5 min at 180 C.
Maybe the wafer is too hydrophobic, treat the wafer with plasma before spin-coating?
https://www.researchgate.net/publication/259044379_A_protocol_for_improving_fabrication_yield_of_thin_SU-8_microcantilevers_for_use_in_an_aptasensor
Article A protocol for improving fabrication yield of thin SU-8 micr...
Agree with Mr. Li, it is something to do with your silicon wafer type. Hope you are using standard p-type Si wafer without additional coatings by default.
You can try boiling silicon for 10 min into Caro acid (Pirania) and applying adhesion promoter based on HMDS after this (HMDS:PGMEA 1:4). This scheme have to be without HF threatment.
Another point to consider is the bake duration. try to put that as optimize as possible.
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