Jay,

There is about 1nm of native oxide on the SOI wafer. It is possible that is
what is causing the undercutting of the Cr.

HF last or back-sputter the silicon before chrome deposition may help

Best regards,
Glenn

-----Original Message-----
From: Jie Zou [mailto:zoujiepku@gmail.com]
Sent: Thursday, April 29, 2010 10:34 PM
To: General MEMS discussion
Subject: [mems-talk] Cr/Au structure under HF etch


Hi folks,

I defined a gold pattern by e-beam lithography and lift-off. The gold was
evaporated on the SOI with ~8nm Cr as the adhesion. After several other
fabrications (mainly DRIE), I had some free-standing gold structures sitting
on a silicon structure made by the device layer of a SOI wafer. My last step
was to release the whole structure by HF etching the buried oxide layer. I
used 49% HF for 3min to achieve the necessary undercutting to make sure my
structure was free. However part of the gold structure was peeled off.

How can I improve it? Is there another adhesion layer that can resist HF
better? I tried BOE instead of 49% HF. It didn't help much.

Thanks a lot.

Jay