[mems-talk] su8 fabrication problem

[Gwennou Coupier]

I can confirm that one can often get rid of the cracks with a final 
hard bake (e.g. 2 hours, 135°C, in oven, not hotplate for 50 microns 
thick SU8.).
This might be surprising, but it works. The explanation would be that 
the SU8 have a glassy behavior at sufficiently high temperature. The 
temperature might depend on the resist you use. Consequently, do not 
let it in the oven too long, otherwise it could broaden your object.

On Fri, 27 Apr 2007 09:52:05 +0100
  Gareth Jenkins <gjenkins at f2s.com> wrote:
> At what point do the wrinkles occur? Possible causes are uneven 
>hotplate temperature or too rapid ramping / cooling.
> Pitting can be due to insufficient dehydration of the wafer prior to 
>spinning, contaminants (either on the wafer surface or within the 
>SU-8) or bubbles during dispensing onto the wafer.
> As for the cracks, often these are too shallow to be a problem but 
>are usually caused during the post exposure bake. Use a lower 
>temperature bake and/or ensure rapid heating and cooling is avoided. 
>Alternatively, I have also heard that a hard bake step sometimes 
>closes these cracks.

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Gwennou Coupier
Laboratoire de Spectrom&#233;trie Physique
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