Hi Roger,

Quintel makes a double sided/ double mask - aligner which works in essence as
you have described . It's the Q1200 series. It allows 2 masks to be aligned to
each other and for them to be separated (without losing alignment) and a wafer
coated on both sides inserted between them, and the masks brought back
together (without losing mask to mask alignment) . It has two UV light sources
so both sides can be exposed simultaneously

Regards

Vince Wilson
Quintel  Europe
5, Trevor Drive
Bromham
Bedford MK43 8PH
UK
Phone +44 1234 82 4660
Fax  +44 870 161 2969
e-mail [email protected]
Message: 1
Date: Wed, 20 Feb 2002 10:11:20 -0800
From: "Roger Shile" 
To: 
Subject: [mems-talk] Re: Is there a way to align both sides of wafer
Reply-To: [email protected]

I will attempt to describe another alternative for creating front to back
aligned patterns:

Use a fixture in which the front and back masks are mounted on fixtures which
will hold the masks face to face, where they can be aligned using adjustment
screws.

After the masks are aligned, the fixture is opened and the wafer, coated with
resist on both sides is placed between the two masks and the fixture closed.

After one side of the assembly is exposed, it is flipped over and the other
side exposed.

Years ago I used such a fixture made by PTI, a small company in the Chicago
area.  In this implementation the fixture opened on precision hinges like a
book,  the masks held with tape on opposite sides.  I aligned the two masks
with the "book" closed using adjustment screws to move one mask, while
viewing
alignment marks with a jewlers loupe.  Alignment was probably only as good as
a couple of mils.

Another way I've seen this done is with two separate mask holders,  pins in
one holder fitting into holes on the other holder, and the wafer sandwiched
in
between.

Roger Shile