Isa,
For only two layers, the box in a box alignment marks work very well. The
first mark is just a square. The second mark is a window that goes around
the first square, and is larger by a gap that is just a few times bigger
than your alignment tolerance (so no more than 2 or 3 microns for 0.5 micron
tolerance). The overall size of the square should be large enough to
comfortable fit in the field of view.
Typically, I do a bunch of these marks to go from coarse alignment to fine
alignment. The largest squares I use are 200 microns on a side with 25
micron gaps, going down to 5 micron squares with 1 micron gaps. This
simplifies finding the alignment marks in the begining. The sizes you
choose will depend on your first later process (does it grow or shrink the
mask pattern? Is there a minimum feature size?), your magnification, and
your illumination (how well can you see the first layer marks?).
But as a rule of thumb, square in a box works great. Make the gap 2 to 3
times bigger than the desired alignment tolerance. Don't forget coarse
alignment marks, and put in more marks than you need, as they don't take up
much space.
Good luck!
David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
Ph: (703) 961-9573 x206
Fax:(703) 961-9576
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On
Behalf Of Isa Kiyat
Sent: Friday, March 12, 2004 2:34 AM
To: General MEMS discussion
Subject: [mems-talk] Alignment marks
I am designing a photomask. I will have a two step lithography with maximum
0.5 um tolerance. I need your suggestions about the kind of alignment marks
I should use (shape, dimension any experience will help) . Thanks.
=================================
Isa Kiyat
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