Yours is a real problem. Aluminum oxide is very difficult to rie etch. It
requires toxic gases such as boron trichloride and chlorine. The etch rate is
very slow. A more realistic approach would be to use ion beam etching or
reactive sputter etch. Using this methold would allow you to sputter away the
material that doesn't react well in an rie mode. The problem is the masking
material that you would use. If it is photoresist, the resist will etch away
faster than the underlying material you are etching. I would suggest a thick
photoresist like SU-8 or other to accomplish this. We make sputter etch tools
if you have an interest but I would need to know more about what you are
trying to accomplish such as depth of etch size of features ect to be able to
suggest a process solution. You can call me for more details if you wish at
480-55801156  Bob Henderson