I am working with lift off technique with a negative photoresist (AZ nLOF2020) which is a cresol novolak based one.
The baking and post-exposure baking are done at 100ºC for 60s and the exposure is under 60 mJ/cm². I believe that is more than enough to avoid the excess of cross-linking. During the deposition of the film, the wafer temperature does not exceed 60ºC.
The manufacturer recommends to do the strip with DMSO (dimethylsulfoxide) or NMP (N-methyl-pyrrolidone) at 80ºC. However I am not able to completely remove the photoresist and I observe a strong adhesion between it and the wafer (SiO2 coated). Some parts are easily removed while another are strongly adhered.
Some remarks:
- I tried: DMSO, NMP, PGMEA, and Acetone at different temperatures and times
- The film I work with is a glassy semiconductor and it is sensitive to basic media (including DMSO).
- Ultrasound bath helps to remove the photoresist but also removes the film
Does anyone experience something similar with negative photoresist? Could I try another solvent?
I worked with negative photoresist for many years. Sometimes acetone was good enough, but usually something stronger, like NMP, was necessary. For very stubborn photoresist, I had to use AZ300T or oxygen plasma. I'm not sure what semiconductor you are using, but I know for a fact that AZ300T will slowly etch GaAs, so be mindful of that.
Thank you Alan Farrell
I am working with AsSe (glassy) and the DMSO etches it. I am trying to do it with acetone or NMP... I will take a look on the AZ300T.
Hello,
I have tried Remover PG from micro-chem, it is an NMP based solution. It worked really well with AZnLof when heated up to 80 C. Make sure not to use Acetone, it makes it harder to remove the resist.
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