Thomas,

I work with SU-8 layers about a third your thickness, but I can talk
from my experience:

When you say high-pass, you pass high frequencies or high wavelengths,
you should be passing high wavelengths.  365nm (i-line) is the
wavelength that you want.

My pattern never appears until after PEB.  Your pattern probably did
without the filter because SU-8 is very sensitive below 360nm and it
probably got way overexposed.

Two more things to try to prevent your wrinkling:

First, you may be under exposing.  You need to measure the power from
your lamp at 365nm.  Make sure you are using this number to calculate
the time and not the total exposure power. Power from the G-line won't
affect SU-8 and you should be filtering out any DUV.

Second, you may be baking the top of your resist in the exposure step,
especially if you are going for 900 seconds straight.  I usually do 10
seconds exposure followed by 1 minute cool down then 10 more seconds
exposure, etc.

That's about all I can think of.

Greg

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Thomas KF Lei
Sent: Wednesday, July 02, 2003 12:38 PM
To: General MEMS discussion
Subject: Re: [mems-talk] SU-8 problem

Greg Reimann,

Thank you for your suggestions.
Actually, I tried using hot plate before. But I also have the same
symptoms.
When PEB temperature goes over 60C, the surface of SU-8 becomes
wrinkling
every time.
And I would like to ask whether the SU-8 pattern appears after exposure
before PEB?
I tried two cases:
board band UV: after 10secs exposure, SU-8 pattern appears before PEB.
board band UV with WB-360 fiter(360nm high pass): after 900secs
exposure,
SU-8 pattern doesn't appear before PEB.
Thank you very much.

Regards,
Thomas

----- Original Message -----
From: "Greg Reimann" 
To: "'General MEMS discussion'" 
Sent: Wednesday, July 02, 2003 11:41 PM
Subject: RE: [mems-talk] SU-8 problem


> Thomas,
>
> Try switching at least your soft bake to a hot-plate. Microchem wrote
> all of its specs with hotplates in mind, so in an oven you may not be
> baking of all of the solvent, or more likely given your symptoms, you
> are baking off the top layer of solvent and trapping the rest in lower
> layers which dissolve in the develop.
>
> Since a hot plate heats from the bottom, this is less likely to
happen.
>
> Greg Reimann
> Boston University
>
> -----Original Message-----
> From: mems-talk-bounces+gjreiman=bu.edu@memsnet.org
> [mailto:mems-talk-bounces+gjreiman=bu.edu@memsnet.org] On Behalf Of
> Thomas KF Lei
> Sent: Wednesday, July 02, 2003 8:16 AM
> To: mems-talk@memsnet.org
> Subject: [mems-talk] SU-8 problem
>
> Dear collegues,
>
> I have some problems in doing MicroChem SU-8 2075 PR on Si. My process
> is:
> spin 500rpm and 3000rpm 30secs
> soft bake: 95C 15mins in oven
> UV explore with filter WB-360: 300secs
> PEB: 95C 10mins in oven
> Develop: about 10mins
>
> I found that the surface of SU-8 becomes wrinkling after PEB and my
> pattern peer off after develop. Can anyone give me some suggestions?
> Thank you very much.
>
> Thomas
>
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