I found if you just leave the resist-coated wafer dry in room temperature in
stead of prebake, the crack would be less or even disappear. The room dry
photoresist is still OK for the following litho process.

Just curious, how much is the smallest size do you want to pattern the
resist on the PDMS? And how is it working?

Good luck,

Hongjun Zeng, Ph.D
Microfabrication Application Laboratory (MAL)
University of Illinois at Chicago