Johannes,

It depends on your method of exposure.  If you are using a contact/proximity
mask aligner, your maximum depth would be ~25 µm. If you were using some sort of
projection system, you should be able to focus on the bottom of the cavity
regardless of the depth of the cavity, although this assumes you are using a 1µm
thick resist, which in and of itself is difficult to achieve in a cavity, unless
you can use spray coating.

Without spray coating, you are most likely partially (or fully) filling up the
cavity.  In this case, you don't typically rely on better than 3:1 aspect ratio
(except with special resists), so you'd be limited to a 15µm layer of resist
(25µm at the outside).



Best Regards,
Chad Brubaker


-----Original Message-----
From: Johannes Grether
Subject: [mems-talk] lithography in deep grooves

Hello,

I want to pattern structures in deep grooves and got problems with the focus.
Does anybody know about the maximal depth to create structures with dimensions
of about 5 um, or know how to increase the focus?