I am looking for other people's ideas for alignment marks.  I am using a
Karl Suss MJB3 aligner and I want at least 0.5 micron accuracy.  The marks
I am using consist of a ~100micron feature for rough alignment, and then a
vernier.  The vernier consists of five rectangles, 2 microns wide, and
separated by 5 microns.  The rectangles on the second mask are separated by
5.5 microns in such a way that when alignment is correct, the center
rectangles align.  When alignment is 0.5micron off, the rectangle one from
center is aligned.  It looks like this (excuse the crude drawing):

   O     O     O     O     O       base vernier
O      O      O      O       O    top vernier (aligned)

These marks can get me to better than 0.5micron, but I have to almost be in
vacuum contact before I can see my alignment clearly.  I have thought of
better alignment marks, but at $600/mask I want to get it right the first
time.  I am wondering if it would work better if the top marks were
larger/smaller than the bottom marks (I am using a dark field mask) or if I
would still be able to get as good of an alignment if my marks were say
5microns wide so I could see through them without being in very close
contact.  If anyone has a CAD/PDF design of marks that work for them,
please e-mail me.  Thanks.

Glen Landry