I am doing some work with adding on a thin layer of PDMS that is diluted with a solvent (DCM, THF, 1,4-Dioxane) on a silicon wafer by spin-coating or drop coating. My problem is that I have noticed that I have bubbles on the backside of the layer and I am having problem with curing it without getting bubbles. It is either cavities of the solvent getting evaporated during curing or bubbles as I might have to high temperature?
I usually cure at 100 deg. but I have also tried curing at boiling temperature of the solvent and then later at 100 deg.
I usually have the ratio of 1:10 or 1:15 of the agent:elastomer. I add 1:6 ratio of the PDMS:solvent. DCM has boiling point of 40 deg. and THF has a boiling point of around 66 deg.
I am not sure what to do? I need a thin (few micrometer) nice homogeneous layer (without cavities or bubbles) that is molded into my structures of the wafer. My structures are in the size of micrometers in size.