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 -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of leiwangsdu Sent: 11 February 2010 01:02 To: mems-talk Subject: [mems-talk] Help for photoresist coating Hello, everyone. I use the positive photoresist to do some lithography. I have a big problem. My samples are rectangular which have dimensions 10mm*15mm After the resist spinning, I found that the resist film around the edge of the sapmle is thicker than the resist in the center. This produces a gap when the contact exposure is applied. And the resist profile is not good enough after the development. I shall be highly obliged if anyone can help me out in this and provide some advices. Thanks in advance Yours sincerely, Lei Wang