I used to use a black anodised chuck on a MA56 contact aligner with
transparent substrates with no problems.
Exposure energy should be kept to a minimum to provide a reliable process.
If the problem was just related to the transparency of the substrate, I
would expect the effect to be present across the entire wafer, not just the
edges.
What contact mode are you using (soft/hard or vacuum)? check that the
fringing is not due to contact problems on the SiC.
Check that the optics are delivering good uniformity right up to the wafer
edges.
Do you have a large edge bead on the resist which is holding off the mask?
Is your resist uniformity ok?

Regards

Steve

-----Original Message-----
From: Yuzhu Li [mailto:yuzhul@eden.rutgers.edu]
Sent: 03 June 2004 19:17
To: mems-talk@memsnet.org
Subject: [mems-talk] optical fringe effect for transparent substrate


I am using 3-inch SiC substrate for fine linewidth lithagraphy on SUSS
MJB3. PR 5214, eith positive process or image reversal. There band
formation on wafer edge, those band areas are poorly developed. The
puzzle is when I use 3-inch Si then no such band.
        Also I have same problem with 2-inch SiC wafer on 2-inch chuck. But
There
is no problem when I use 2-inch SiC wafer on 3-inch chuck. But MJB3 only
support upto 3-inch chuck!
        Using black tapes to cover wafer chuck doesn't help.
I wonder anti-reflective coating will do any good? But it will complicate
process...
Anyone doing litha on transparent substrate has any advice? Thanks.


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