Dear Li,

I use a color patterned alignment mark such as a metal or oxide under my
SU-8 layers to align with.  This allows for easy alignment of SU-8 at any
thickness.

Secondly,  you do not need to develop both layers at once. The 50um SU-8
layer will flow into the 7um pattern just fine and it will level itself off
during the prebake.  If the multilayer process gives you any problems,
simply flood expose the first layer after development and prior to coating
the 2nd.  This will further crosslink the resist making it impermiable to
the developer.

Hope this helps,

John D. Williams
Department of Mechanical Engineering
Louisiana State University


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Message: 7
Date: Wed, 26 Nov 2003 14:36:11 -0500 (EST)
From: DARREN S GRAY 
Subject: [mems-talk] RE: about 2 level soft lithography
To: mems-talk@memsnet.org
Message-ID:

Content-Type: TEXT/PLAIN; charset=ISO-8859-1

Dear Li,

Since SU-8 is transparent, you need to align the mask to alignment marks
on your wafer.
In general, you don't want to develop the first layer of SU8 because
the resulting topology will make it difficult to spin-coat the second
layer of SU8.
For more information on multilayer soft lithography, I would recommend
Tien et al, PNAS, Feb. 2002.

Darren Gray
Graduate Student
Johns Hopkins University

Hi all,

I^Òm working on 2-level PDMS structure fabrication so that I should spin
SU-8 twice. But I met a problem when I align the two layers. Since the two
layers are both SU-8 and SU-8 seemed transparent, it really hard to
observe
the alignment mark under the microscope during the alignment process. My
first layer is about 7um, second layer is 50um. Did anybody met this
problem? Any ideas about this?

Another issue is that according to some papers from Whitesides group, they
said the first SU-8 should not be developed. I couldn't find the reason
why
the first layer should not be developed. Is there anybody can give me
hints
for this issue? I tried developed and undeveloped the first layer.
Developed can be a little bit better, but still not enough to clearly
observe under microscope.

Thank for your help.

Li Wang
412-2682514
Carnegie Mellon University






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