Hi Andrea,

I have done some times this type of aligning. If you have an UV aligner, you can
probably find IR (infrared) botton on machine. You need just use this feature to
align backside of the wafer with front side. The only important thing is that
you cannot see any feature on front side except metals. Al is a good metal that
you can use. So, first you need to evaporate some Al marks on the top and then
you can see them by IR and align back with Al marks. Just be careful, don't use
IR much, just press the botton when you need to see marks, because it generates
heat and heat wafer.
I believe the resolution of back aligning by IR is not as the same as front
side, because you cannot see every thing like front side. however, I think you
can align 10 um feature easily.

Good luck,
Reza Rashidi,

Mechanical Engineering
University of British Columbia

________________________________
From: Andrea Mazzolari 
To: General MEMS discussion 
Sent: Sunday, January 18, 2009 2:37:25 AM
Subject: [mems-talk] front back photolitography

Hello all,
i need to perform front and back photolitography.

On each side of a 4'' silicon wafer i need to realize geometries of size
10um. Geometries on the opposite wafer faces must be aligned with the best
possible accuracy.
Here we don't have the possibility to realize front-back photolitography
and so i plan to ask to some company to do the job for me.

Which is the best precision accuracy which can be obtained on the market ?

Best regards,
Andrea