This limitation of the oxide etch (Al and CMOS in general) is also one of the
reasons people move over to a silicon release layer. You can then use xenon
difluoride which has zero attack on Al (and most other metals). Using XeF2 and a
silicon release layer you can have Al that  is still be reflective or makes a
perfect contact or is exactly the thickness you started with. XeF2 works with
any form of silicon (poly, amorphous, crystalline). As an added bonus it shows
high selectivity to all the other CMOS materials you may be using, shows good
selectivity to a wide range of dielectrics (as good as 1000 to 1 for oxide) and
does not attack polymers (like photo resist).

If you have any questions about using XeF2 and Si as a release layer for your
application you can contact me directly at XACTIX.

David Springer
XACTIX, Inc.
412 381 3195
[email protected]



>>  This is one of the famous limitations in trying to
 >>  integrate standard CMOS with MEMS, and leads people to
 >>  use gold as a metal system rather than Aluminum.
 >>  You can try a 1:1 mixture of BHF and Ethylene Glycol
 >>  this usually reduces the attack of Al somewhat.
 >>  good luck

 >>  Dave Kharas Ph.D.
 >>  Sarcon Microsystems @Sarnoff Corp.


 >>  > From: "bobo" 
 >>  > Subject: [mems-talk] Etching SiO2 without affecting
 >>  > Aluminum
 >>  > Date: Thu, 15 May 2003 12:30:50 +0800
 >>  > To: 
 >>  >
 >>  > Dear all,
 >>  > does anyone knows what wet etchant can etching
 >>  > silicon dioxide without etching aluminum at the same
 >>  > time?   Thanks.
 >>  >


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