Johannes,
years ago we used a process calles PCM that might work for you.
coat the wafer with PMMA to planerize ans softbake. on top, coat a thin
layyer of Brewer Science bottom ARC and bake it.
on top, you coat your resist and softbake it.
you then expose and develop the photoresist using a negative mask. you do a
post Develop I-line flood expose to the resist.
then you flood expose the pmma with a colimated 248nm light. the resist +
ARC acts a conformable mask for the PMMA.  develop the remaining positive
resist and arc and then develop the PMMA using xylene. if your groove walls
are close to the geometry you might need to add a bottom ARC (can be evaped
metal) on thr sustrate below the pmms to avoid sie exposure due to
reflections.
good luck

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

>
> 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?