I've had this problem before, of etching silicon in TMAH with gold in
contact with the silicon.  We've had some luck attaching a wire to the gold
(we used a teflon coated wire and a gold plated tip, with a blob of rubber
cement over the solder joint, which should not be exposed to the TMAH) and
biasing it relative to the metal can we were etching it in.  I've forgotten
the polarity of the bias, but it was on the order of a few volts, with
minimal current draw.

If you're using an insulating etch beaker, I'm not sure how you would do the
biasing.

David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
Ph: (703) 961-9573 x206
Fax:(703) 961-9576

-----Original Message-----
From: mems-talk-bounces+nemeth=sophiawireless.com@memsnet.org
[mailto:mems-talk-bounces+nemeth=sophiawireless.com@memsnet.org]On
Behalf Of Massimiliano Decarli
Sent: Tuesday, November 18, 2003 11:52 AM
To: General MEMS discussion
Subject: Re: [mems-talk] metal? etch mask for TMAH


Hy Martina,
Your problem is that gold/silicon combination forms a galvanic cell.
In fact this tecnique is already used and it is called galvanic etch stop.
Here you can find more on this topic:
http://www.dimes.tudelft.nl/1998/s2/c2/c2-1-fundamentals.html

Max


From: "Martyna" 
To: 
Sent: Tuesday, November 18, 2003 11:50 AM
Subject: ITCSpam: [mems-talk] metal? etch mask for TMAH


> Hello,
>
> Does anybody know if gold mask can be used for TMAH etching? I have 1000 A
gold layer (with 100 A Cr) on a Si wafer. I used 5% TMAH and etch for half
an hour. The result is much below the typical etch rate.
>
> Before etching I removed native oxide with HF.
>
> Thank you for your help
>
> Martyna
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