Carson,

SU-8 is negative tone and so exposed regions should remain after development.

For SU-8 2035 with a 50um thickness I'm currently using an exposure dose of
around 270mj/cm^2 which in your case gives a time of 13.5 seconds.

Are you using an optical filter to attenuate components below ~350nm? In the
early stages of my SU-8 work I was using a broadband exposure source i.e. with
power below 350nm, which lead to very poor results. If this is the case for you
I would recommend obtaining a Hoya UV-34 filter to remove these components.

Hope this helps,

Novak

 -----Original Message-----
From:   mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]  On
Behalf Of laetitia philippe
Sent:   Wednesday, December 08, 2004 9:02 AM
To:     MEMS-talk@memsnet.org
Subject:        [mems-talk] SU8 exposure time

Hello All,



I am trying to find the best exposure time for a SU8-2035 with a

thickness of around 50 um

This is not looking to be very easy. I am working with a UV i-line 365

nm, with 20 mW/cm2



For high exposure time (up to 100s ), I see that my structure does not

developp at all, i.e. the exposed polymer is not removed in the

developper although the sutructre is clearly visible with a color difference

between the exposed and non exposed part



For reasonnable exposure time (20 s), I have a good developpment but I

have always a resulting mould that is small as my mask. i.e some

feature of my pattern of 200 um would lead to only 100 um cavity in my

developped polymer and so one.



Finally, when I go down to 7 seconds, I have a good resulting mould,

with much better dimensions, but I have enormous stress on my polymer and

sometimes delamination which makes me thing I am under exposing of

course





Could someone share his own experience about that? especially about the

over-exposure'?



Many thanks

Carson



_____________________________________

Novak Farrington
Institute of Microwaves and Photonics
School of Electronic and Electrical Engineering
University of Leeds
Leeds LS2 9JT
UK

Mob. 0790 9948673
Fax. +44 (0)113 343 7265
email: eennf@leeds.ac.uk