Patrick:
I would suggest using SU-8 photoresist. I have found it to be very selective for
deep etch applications. Also since the profile is anisotropic you will get good
final results in your etched substrate. You might also want to investigate a
more aggressive etch chemistry like SF6 + O2. You should be able to obtain
3-4000 angstroms/min etch rate and the SU-8 at say 8 microns thickness should
hold up well. You can give me a call if you want more information. Bob Henderson
602-206-6154

-----Original Message-----
From: Patrick Lu 
To: General MEMS discussion 
Sent: Sat, 20 Aug 2005 22:59:19 -0700
Subject: [mems-talk] needed: durable etch mask for making gratings in quartz

i'm interested in etching gratings that are about 1 um deep with about 300nm
feature sizes in a quartz substrate. i prefer a dry etch because i want my
sidewalls to be as vertical as possible (and since my etch depth exceeds my
horizontal feature sizes, a wet etch will undercut significantly). i'm
finding it challenging to do this with photoresist/PMMA--to get those fine
feature sizes, i'm forced to use resist that is not more than a micron, but
to get those depths i think i need resist that is at least 3 um deep. i've
heard of cases of people using chrome as a mask for etching quartz. can
anyone confirm the effectiveness of this or suggest any other materials? i
need a thin, durable etch mask.

i've actually tried using 50nm of chrome as a mask during a CF4/O2 plasma
etch. I didn't expect the gases to attack the chrome at all, but I found
that the chrome didn't hold up during the etch.