I don't know the exact parameter you should use with an Oxford RIE. But,
SF6 is probably a no-no. Now, to increase selectivity, you can either
reduce mask erosion or increase etch rate. I would go for the later.

Try higher power then. What kind of source do you have? Coil or plate?
Here's the link to recipes from Stanford for your information.
http://snf.stanford.edu/Process/PlasmaEtch/Oxide.html



Best,
ShuTing
UCLA, Electrical Engineering


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Sungjun Lee
Sent: Monday, July 14, 2003 9:28 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Wet and Dry Etching.


Dear all:

MEMS is not my major but I need to do a simple process. Recently, I have
worked SiO2 etching using a PMMA etch mask(100nm thickness). My goal is
to etch SiO2 about 400A depth.(There should be PMMA alive for the
lift-off process) About 300nm is the width of lines written by e-beam
lithography.

In wet etching with 25:1 HF, I failed to get some good results. (PMMA
was peeled off at around 120 seconds, and the etch depth is less than
100A during this time) Does anyone who use my condition in wet etching?

We have a Oxford Etcher(plasmalab 80+).
The 100nm-PMMA is nearly wiped-out in my conditions:
CF4(40sccm) + O2(5sccm) under 50mtorr, 50W for 90 seconds.
Now, I can use some other gases, Ar, SF6, and CHF3.
Is there someone who try to other conditions?

Could you please give your invaluable comments to me?

Thanks in advance.

Sungjun / Graduate Student.


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