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
>>> [email protected] 02/20/02 01:45AM >>>
Hello Martin,
Here's a little trick, but it's probably not accurate enough. I used it
with little samples, not whole wafers. (1) The sample is stuck frontside
down with dental wax on a glass slide and photoresist is spun on (make sure
the resist not only covers the sample backside but also a good part of the
glass slide as well). (2) Turn sample over.
(3) Now the mask is aligned to the sample frontside and the resist exposed
through the glass slide (... the resist on the sample backside is not
exposed). (4) After development turn sample over. (5) Align the mask to the
patterns in the sourrounding resist on the glass slide. (6) Expose and
develop the previously unexposed resist on the sample backside. Regards,
-- Werner
_______________________________________________
[email protected] mailing list: to unsubscribe or change your list
options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.mems-exchange.org/
