Hi Ramesh,

I am not sure if I totally understand your problem but I can suggest you an
etching method that removes thermal SiO2 without affecting aluminum. HF vapor
phase etching is very selective if the right parameters are chosen. I pattern
SiO2 using a aluminum mask in the etcher of idonus (www.idonus.com), which is
dedicated for research labs having an moderate price. Even aluminum membranes
can be fabricated by removing a sacrificial SiO2 layer. However, photo resist
does not work for masking.

Hope this could help you!

Michael