If you use pure SF6 (no O2) you should get an isotropic profile.

Roger Shile

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Jie Zou
Sent: Sunday, June 08, 2008 9:45 PM
To: General MEMS discussion
Subject: [mems-talk] RIE on SOI

Hi,

To make a movable structure, I need to etch through the device layer. I
tested the ICP-RIE recipe on a Si wafer and got an isotropic profile
(1um/min). But when I applied this recipe to the SIMOX SOI wafer (200nm
device layer and 350nm oxide layer), I only get an anisotropic profile
and
can't make any undercutting. Is it related to the SOI wafer? Would a
bonded
wafer be better? My supervisor prefer a smart-cut type SOI wafer, but I
can't find any vendor in US selling that.

I have tuned my recipe many times and didn't get improvement. I
increased
the source (ICP) power and lower the bias power.

My recipe is 48 sccm SF6, 32 sccm O2, source power (ICP): 160W, bias
power:
360W, Pressure: 80mTorr. It gives an anisotropic profile.

Thanks a lot.

Best,
Jay