Hi All,

I am trying to do a double-layer SU8 50 process. Both layers are rather thick,
i.e. more than 250 um. I finished the first layer by following the recommended
recipe and, as suggested by some researchers, I only did a short post exposure
bake at 70 C to form a weak crosslink. The first layer was finished nicely and
no visible crack was spotted. Then, I spun coating the second layer SU8 and left
it resting for few hours before sofe bake. However, after leaving the second
layer SU8 for few hours, I found lots of cracks occurred in the first layer. I
was able to complete the process and the crack did not cause substantial damage
to the structure so far. But, I still don't think it's a good sign for the
quality of the structure.

Anybody has an idea how these cracks occurred in the first layer?

Thanks,
Yingtao
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