This is what I used to etch Cr.  It should be safe with oxide.  You need
to check if it is OK with PMMA.  There are also commercial etchants you
can buy.

Nichrome Etch: 155 g (NHb4)2Ce(NO3)6  (Ceric Ammonium Nitrate) + 60 ml
HNO3 + 985 ml H2O

TK


-----Original Message-----
From: Leyla Soleymani [mailto:l.soleymani@utoronto.ca]
Sent: Thursday, March 15, 2007 10:10 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Using Chrome as etch mask

Hi,

I am using ebeam lithography to open holes in SiO2. PMMA is my resist
but it is not a good etch mask so I am using a layer of chrome on top
of the SiO2 and below PMMA as an etch mask. Does anyone know what
Chrome etchant I should use that does not attack PMMA or SiO2? Also
does buffered oxide etch attack Cr? I would really appreciate some
help on this issue.