Cr is ok for masking oxide.  The problem might be:

 Cr layer is not thick enough.  PECVD-SiO2 is relatively porous, to mask a
porous layer, thick etch mask is required (3500 - 5000 angstrom depend on
the quality of oxide film) .

And I think TMAH is not a good candidate for oxide etch.

Perhaps you can use photoresist to mask oxide and use BOE to etch oxide.


Yinbao Yang
NRCORP
yxy11@po.cwru.edu