I am trying to achieve a tunable undercut profile by using bi-layer resist stack PMMA(Top)/PMMA-ZEP 2:1 Ratio(Bottom). I am pretty new to fabrication; hence, I am not sure how do I mix the PMMA and ZEP together?
You could put your PMMA/ZEP 2:1 mixture in a beaker, and then you can use a magnetic stirrer for say 5-10 min to homogenise your solution.
Don't know if you solved your problem...
Don't mix the PMMA with resist. Tuneable undercut can be done by PMMA bake temperature and time. The higher the bake, the less undercut during develop. To determine bake time and temperatures, spin wafers and bake at different times and temperatures and then develop them away timing the time to clear. You can also do PMMA coats with each layer baked at a different temperature and/or time.
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