Hello Leo,

Thirty years ago, I was routinely etching 1.5um of thermal oxide in BOE
(buffered oxide etch --NH4F, HF, H2O) using negative photoresist (Waycoat, I
think).  Good luck.

Roger Brennan

Applications Director
Solecon Labs
770 Trademark Drive
Reno, NV 89521-5926
Work: roger@Solecon.com
Work: 775-853-5900 ext 108


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org]On Behalf Of Xiaoguang "Leo" Liu
Sent: Thursday, April 19, 2007 3:42 PM
To: General MEMS discussion
Subject: [mems-talk] Thick SiO2 etch


Dear all

For one of my projects, I need to pattern thick thermal oxide of
1.5um. I used 49%HF:DI = 1:6 as the etchant and 20um AZ9260 as a mask
(the reason of using this thick resist is that I need to do a through
wafer Deep RIE after patterning the SiO2).

The etching of the oxide takes more than half an hour in the etchant.
My problem is that the photoresist can not stand the HF solution and
start to peel off (especially the smaller features) after about 20min.
HF also attacks the photoresist reducing the overall thickness of the
photoresist, which can impact my later DRIE process.

Could anybody illuminate me with a better method to etch the oxide
layer without destroying the photoresist?