Hi, all.

I am writing to see if someone has the experience working with 495 PMMA
A6 from Micro Chem.

I exposed the PMMA A6 with Raith 150 system, after a spinning speed of
4000rpm for 30s and a prebake @180C for 30min, with which I should get a
thickness between 300nm and 350nm. However, I found that I needed an
area dose of 500 uc/um2 or even larger to get a clear image. The
acceleration voltage I used was 20KV. I wonder why I need such a huge
dose. Does any of you have a similar experience? or did I do anything
wrong? Thanks.

Regards,
Zhanghua