Hi Zhiyan,

to avoid cracks on SU-8 during development you have to adopt a relaxation
time between the post exposure bake and the development. I made good
experience with waiting overnight. You also have to cool down the wafers
slowly after the softbake and also after the PEB.
The best alternative to prevent cracks is to design the mask without
corners. Because these produce the cracks.

best regards,
Ulrike Schoembs