Matt,

a well known method to overcome your alignment problem is the usage of back
side alignment (BSA). Especially when your resist layers are very thick, BSA
is an easy and more accurate way to align all of your front side litho
layers to a common reference pattern on the back side of your wafer. Of
course, this would require an additional process step to print the reference
alignment targets on the back side, but, once created, they can be used to
align all of the front side layers.

I do not know if your exposure tool is equipped with or can be upgraded with
BSA, but there are several suppliers of maskaligners offering this option.
Please feel free to contact me if you are interested in receiving further
information about BSA.

Best Regards,

Frank.

--------------------------------------------
SUSS MicroTec
Applications Manager RSC Europe
Frank Runkel
Schleissheimer Str. 90
85748 Garching
Germany
Fon     +49 89 32007 - 302
Fax     +49 89 32007 - 390
email   f.runkel@suss.de


> ------------------------------
>
> Message: 4
> Date: Mon, 16 Aug 2004 15:22:11 +0100
> From: "Matthew Davies" 
> Subject: [mems-talk] Double depth SU-8
> To: 
> Message-ID: <001d01c4839c$6bec94a0$ec8cc593@bagger>
> Content-Type: text/plain;     charset="Windows-1252"
>
> Hi all
>
> I'm trying to find out if there is an easy method for seeing developed
> SU-8 through another layer of SU-8.  We are trying to make devices
> requiring double depth processing and the aligning of the photomask for
> the second layer is very difficult as we are currently unable to see the
> developed SU-8 on the bottom layer.  At the moment we need to
> overdevelop the bottom SU-8 layer until cracks appear at which point we
> can see the cracks through the top layer of SU-8.
>
> Any suggestions would be much appreciated.
>
> Thanks all
>
> Matt Davies
> STRC, University of Hertfordshire
>
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