Thermally grown SiO2 works rather well for nitric-HF.

Silicon nitride has also been used.  Do a search for "isotropic etch problem".


-----Original Message-----
From:   Zigurts Majumdar [SMTP:majumdar@uiuc.edu]
Sent:   Friday, February 01, 2002 9:15 AM
To:     mems-talk@memsnet.org
Subject:        [mems-talk] [Q] Mask for isotropic silicon wet etch? (fwd)

Hi,

I am trying to isotropically wet etch silicon using a 126:60:5 HNO3:H20:NH4F
etchant (as described by Williams and Muller, J. of MEMS 1996).  The etchant
appears to work well, but masks made of AZ5214 do not.  In less than
15 minutes, the AZ5214 layer has visibly thinned and formed holes.

Can anyone recommend a more durable mask (PR, metal, both or otherwise) for
this etchant?

Thanks!

Ziggy
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