I want to reflow microposit S1813 photoresist around some 700-1000 um tall structures, so that the tips of these have almost no resist left on them. Any tips on how to do this?
Hello Carl,
I've used several different hard bakes depending on the etchant when using S1813 as an etch mask. These have ranged from 100oC (oven) to 115oC (hotplate with covering petri dish - trying to minimise temperature gradient). Times have ranged from 1 (hotplate) to 25 minutes (oven) so my suggestion would be to try temperatures higher than this.
I too cannot find much information on Shipley's S1800 series (S1813) temperature characteristics, but as a comparison, looking at MicroChem's lithography troubleshooter, they suggest up to 150oC (Sections K2 and K5 for example) as hard bakes for their resists, with 130oC being the resist's nominal softening point:
http://www.microchemicals.com/technical_information/TroubleShooter_EN.pdf
My suggestion would be to use some test samples, increasing the temperature and work your way up until you get satisfactory results.
Is it possible to work the other way? Maybe spin a thinner film and then etch the structures down to give you what you want? Without fully understanding what you are trying to achieve or what the substrate is, it's hard to give any other suggestions.
Hope you manage to work something out,
Jules
Hi, and thanks a lot Jules. What I am attempting is to cover some pyramidal microstructures covered in thin oxide, and then expose the tip for etching away the oxide and do metallization. It seems that 130 C in a convection oven for 30 minutes does the job with a pretty thin resist, close to what you suggested.
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