Dear Richard,
=20
SU-8 absorbs MUCH more at 320 nm than at 365 nm. Look at the SU-8 =
datasheet.=20
A rough estimate is that the absorption is 4 orders of magnitude higher.
If you are aiming for an SU-8 thickness of 100 micrometer, it will be =
practically impossible for you to get enough light at the lower parts of =
the SU-8 layer. During postbake you will end up with a few micrometer =
thick structures floating on an unexposed  "sea" of SU-8.
Your structures will curve because of a stress gradient across the =
exposed layer. This is due to the exposure dose gradient across the =
layer. The top part of your SU-8 will be massively overexposed, and I =
think you consequently will see very poor 2D structure definition.
=20
320 nm lasers should not be used for SU-8 exposure, unless it is for =
very thin layers.
=20
Jacques Jonsmann
=20
=20

________________________________

Fra: [email protected] p=E5 vegne af Richard Chang
Sendt: ti 17-01-2006 19:19
Til: General MEMS discussion
Emne: [mems-talk] SU-8 layer is curved up during postbake



Hi, All,

   I expose a thick SU-8 2100 layer with a 320nm laser. After postbake, =
I
found out the layer is curved up.
   The picture is shown in the link below.

   http://base.google.com/base/items?oid=3D15423750006658009412

   We used a broadband UV  before for exposure and we never have the =
problem
like this with the same layer of SU-8.
   Any suggestion would be appreciated.
   Thank you.