Hello all,
To be specific, I want to reduced the surface roughness of the sidewalls of SU8.
I attached a picture to help everyone understand what I mean. This is a side view of a 125 um high object made from SU8-2025 and its reflection from glass substrate. The vertical 'lines' is what I call 'roughness'. Because they are vertical, I think that this happens during UV curing through a mask.
I couldn't find a tech support contact on Microchem website.
Thank you in advance.
Elena,
the best method to produce mirror like flat surfaces is the mechanical chemical polishing CMP. This method is applied straight forward for the planarization of substrate during the integrated circuit fabrication. But for your geometry it may need special tools.
Best wishes
You might consider using a filter to cut out the wavelength below 350nm during UV exposure. This is useful when you are using a wideband UV-source. Also increasing the postbake time together with decreasing the temperature might work. By the way, the SU8-2025 is made for thicknesses up to ~80 um. Did you spincoat multiple layers to achieve a thickness of 125 um? Or did you use a rpm of less than 1000?
Thank you for the answers. Yes, I tested rpm of 640 for 30 s, and all my structures were 125-126 um high. I measured that under a stereo microscope. I was, however, thinking of making a thinner layer, prebaking, making another layer, prebaking, and then exposing and so on.
I do use a filter.
I already tried the following PEB: 10 min @ 65 degrees, 40 min @ 90 degrees and 4 hours of cooling with temperature ramp of 18 degrees/hour. That SEEMS to help somewhat. I also noticed that glycerol drops have to be completely wiped after exposure. SU8 has to be dry.
Also, I should add that sonicating the glycerol also helps to get rid of air bubbles invisible to the eye. These bubbles my show up as 'rings' on SU8 surface or circular distortions on channel boundaries. I once deliberately left some glycerol on SU8 during PEB and SU8 right under it never developed. It softened, though.
Here is he result of the PEB above, with use of dessicated glycerol
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