I'm using soft-lithography to build SU8 master on silica wafer. Currently, I am spin-coating SU8 for 50um thickness, soft bake then expose under UV for 1st layer for 50um then hard bake. Upon complete hard bake, I spin-coat SU8 for another 50um thickness, soft bake then expose under UV with 2nd layer for 50um then hard bake and develop. I was wondering if this is the best method for series of soft-lithography. Can I simply spin-coat 100um SU8 then soft bake and expose under UV for 1st layer of 50um then consecutively expose under UV for 2nd layer of 50um then hard bake?
It is definitely the correct method, you risk freeze-out of your donor carriers and contamination of your UV lamp by the epoxy mask otherwise. Here is a diagram that I believe will enlighten you :
There is no problem exposing 100 or more microns of SU-8 at once but you can't do it differently masks unless the bottom layer pattern is also always in the top layer. This implies that you will have over hanging structures in your SU-8 which can be hard to part with cast material. Maybe you could look into greyscale lithography as well.
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