Eric,

One trick, we used a long time ago - was to add an IR camera to the
trinocular, and use the light from the tungsten lamps (which includes enough
IR) to see the backside.  This can be done on a standard aligner ( we did it
on a old Kasper/Quintel Contact printer ). The IR from the tungsten lamps
will reflect off the bottom chuck, and the reflected light will be visible
in the IR camera. This of course assumes you are using silicon without IR
blocking metals or other layers on the surface. We were able to perform very
tight alignments (~1-2 um) with this technique.  The IR Cameras are a little
expensive, but if you look hard you can find them slightly used.  We did
have to have a special trinocular coupling made.

This is the cheap way to do it, but it worked great.

Good Luck,
Charles Ellis...


----- Original Message -----
From: "Eric Johnson" 
To: 
Sent: Tuesday, February 19, 2002 9:45 AM
Subject: Re: [mems-talk] Is there a way to align two sides of wafer


> You can do this with front to back through wafer alignment.  Karl Suss and
> Quintel have front to back options for most of their aligners.
>
> Eric G. Johnson, PhD
> Assistant Professor of Optics
> School of Optics/CREOL
> University of Central Florida
> P.O. Box 162700
> 4000 Central Florida Blvd
> Orlando, FL 32816-2700
> (407)823-6803
> Fax 823-6880
>
> >>> [email protected] 2/19/2002 9:32:36 AM >>>
> Dear Mems group,
>
> I have a single side mask aligner.  Is there a method by which this
aligner
> can be used to align features on both sides of the wafer?
>
> Thanks for your assistance.
>
> Marty
>
> Martin O. Patton
> Senior Research Engineer
> Essential Research Incorporated
> 6410 Eastland Road
> Cleveland, Ohio 44142
> www.er.com
> (440) 816-9850
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