Ebeam Lithography on SiN membrane

Dear labmembers,

I'm wondering if anyone have experience with ebeam lithography on SiN
membranes? Our chips have ~200nm SiN membrane on top of silicon. What's the
relation between spin speed and resist thickness? And what's the easy way to
measure the resist thickness in the fab? I found there's no standard program
in Nanometrics for measuring resist on SiN membrane.

Any input will be appreciated.

Thanks,
Bing