Hi Ameya,

>From my experience, anything on the surface would cause problem in spin coating
photoresist. Even a very small dust or bubble can leave a spike line or fringes
on the photoresist. If you have to use the uneven surface, there is a technology
called 'spray coating' you can give a try. But I am not sure how good it is.
Good luck.

Yingtao

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of ameya g
Sent: 10 November 2009 08:04
To: General MEMS discussion
Subject: [mems-talk] Photolithography on a rough surface

Hello everyone,

I need some advice regarding photolithography on a patterened surface.
I have a 4 inch Si wafer that has 30 um deep and 20 um wide trenches all
over the wafer. This uneven topography makes it difficult to uniformly spin
and develop the photoresist (AZ3312 and AZ4330). Extensive fringing is
visible due to the non-uniform film and the measured thickness varies
from 0.1 um to 4 um. The problem is compounded by the fact that my
smallest linewidth is 1 um.

Has anyone faced a similar issue before? Is there any polymer I could
use to fill and level the trenches? Any advice on how to attain a uniform
film on such a heavily patterened wafer will be greatly appreaciated.

Thank you,
-Ameya