My first tip for coating of SU-8 2100 would be to use a resist system
with an integrated cover, but it sounds as if you are doing so already.

A second critical factor is that, if you have a bowl cover, you also
need to ensure that you are turning off the exhaust in the bowl while it
is closed (otherwise, you create a low-grade vacuum in the chamber,
which is pretty much the exact opposite of the effect you want to
achieve).

If you are using a rest period, then it is best to do it with the bowl
closed, to prevent drying of the outside surface (thus, fixing it in
place).

A final recommendation (and this goes way back) - increase your bake
time.  SU-8 resin has a Tg of 55C, which means that during the bake (at
95C), the material is re-flowable. If you just leave it in a level
hotplate for a longer period of time, the material will be more able to
planarize itself.

Best Regards,
Chad Brubaker


-----Original Message-----
From: riyaz pasha shaik
Sent: Monday, September 19, 2005 11:29 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] SU 8 2100 Thickness Level Uniformity

Hai every one,
                I am working on SU 8 2100  to get 500microns as
thickness
on the substrate, I have tried few spin speeds and spin time's for
achieving 500microns,I want to get the thickness uniformity of SU 8
resist
on wafer with minimum deviation on the whole wafer...

1) Does any one have any idea whether uniformity of  SU 8 resist level
has major effect  during resting period after spin coat or during Soft
bake?

 2) During resting period (after spin coating) should I leave the resist
wafer close with lid to get better reflow of resist on the whole wafer.

I would be thankfull for the people who has posted their valuable
suggestion to my post..