> 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?

In my measurements with this etchant the photoresist etch rate was zero
(or it might have even swelled slightly).
Try OCG (formerly KTI) 820 or similar in this series of resists
or
Shipley Microposit 1822 or similar in this series.
Silicon dioxide is slowly etched.
Silicon nitride is barely etched.
Titanium is etched.
Chromium is not etched.

        --Kirt Williams Agilent Technologies