Increasing the temp of the resist will increase the thickness at the center.
Lowering the exhaust( if you have exhaust) will lower the thickness at the
edge. Are you doing an EBR (edge bead removal)? May be hard to do on a
rectangle though.


Robert

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Y.Tian
Sent: Thursday, February 11, 2010 9:07 AM
To: General MEMS discussion
Subject: Re: [mems-talk] Help for photoresist coating

It is normal to have resist thicker near the edge than the centre, that's
the physics of the spin coating. You can not completely avoid it. What I can
suggest, you can try to leave the sample on a nice flat surface for few
minutes once you done the spin coating. Bear in mind the photoresist is a
kind of liquid anyway, this will allow part of the liquid flow back from the
edge to the central part. Then you can do the baking afterwards. The other
thing is your sample is so small, why don't you try to spinning coating a
larger area then dice into smaller pieces?

Yingtao