Dear Alik,

I am pleased you are making headway with the SU-8 process and would like to
offer my services to you...I do have a couple of questions that may help in
sorting out the issues you currently have :

1) Can you tell me the type of mask you are using to expose through ? We
recommend the use of Chrome on glass or quartz as this vastly improves the edge
acuity with SU-8. If you are using anything other than this you may be getting
some UV transmission through the masked off areas and therefore partially
exposing SU-8. SU-8 is a very high contrast resist and as such even a small
amount of UV exposure will generate enough acid to cause crosslinking during
PEB.

2) Do you know if the output energy is being measured at 365nm or at another
wavelength ? If not you could be either overexposing or underexposing the film.

3) What is the substrate you are coating the SU-8 onto ? For some 'special'
substrates different exposure conditions are required in order to create just
enough acid to enable sufficient crosslinking during PEB, for example Au, Cu and
Glass/Quartz.

Other than the comments above your process looks sound and should be generating
good results.

If you have any additional comments or would like to discuss your problems
directly with me please do not hesitate to contact me....

Best regards,

Mark Shaw
Technical Sales & Applications Support
MicroChem Corp.

Tel : 617-965-5511 ext 308
Fax: 617-831-2354


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Message: 1
Date: Thu, 07 Aug 2003 17:13:05 -0400
From: Alik Widge 
Subject: [mems-talk] Another SU-8 question
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii; format=flowed

Folks,

Yes, I'm still working on the SU-8 problem (and thanks to the folks from
MicroChem and EV Group who sent me some process sheets). At this point,
I've got it down such that I can spin the layer to the thickness I want and
expose it such that it doesn't fall off the wafer, but I'm having a problem
in the final development step. Here's my process (roughly):

- Spin on SU-8 2007 to 10 um thickness
- Prebake 1 min @ 65 degC, 2 min @ 95 degC
- Expose 32 seconds @ 3.3 mW/cm2
- Postbake 1 min @ 65 degC, 2 min @ 95 degC
- Develop by immersion with agitation, isopropanol rinse

My problem is that even after long developments with vigorous agitation,
the SU-8 is not gone from the trenches between my structures; there is
clearly a thin dark film of it left. I have tried reducing bake times,
reducing exposure times, and so on, and all these do is push my wafers into
being undercrosslinked and cause the SU-8 to lift up off the surface or
dissolve during the development step.

Has anyone experienced this problem before, and if so, is there a known
solution?

Alik



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