New to the list.  I searched through the archives and didn't find this
question, but if its there and anyone can point me to the thread I'd be
obliged.  Anyway, here we go:

Performing some relatively deep RIE of SiO2 using an aluminum mask.
Problem is that mask is eroding more than we'd like (it's not
sacrificial), even after trying to tweak the recipe.  What we are
looking at now are ways to 'harden' this aluminum mask such that the
unwanted milling will be reduced.  The mask is only 15m thick (not
negotiable), and we need the majority of the mask to remain aluminum for
functionality after processing.  What we had in mind was enhancing the
oxidation of the aluminum, making for a thicker Al2O3 layer at the top
of the metal than the normal native oxide.  Even though it is likely to
still be milled away, the thicker oxide should last longer and result in
less overall aluminum milling.  Not sure on thickness requirements, as I
don't quite know the etch selectivity between Al2O3 and Al, but the
normal process is currently milling away about 30-40% of the thickness,
so we'd probably want to find the optimum somewhere between the native
2.5nm and 250nm.

Here's the problem:  I've been hunting through the literature trying to
find something for Aluminum like the SiO2 oxidation curves that I could
find in 5 minutes if I needed to.  Basically, I need to know aluminum
oxide thickness as a function of time _at elevated temperatures_, and so
far I've been coming up short.  Would anyone out there be able to point
me to the appropriate reference, or at least in the right direction?

Also, I've seen that plasma oxidation could be another option instead of
thermal oxidation, and possibly a better one since it wouldn't require
temperatures as high, and we could keep the wafer in the closed system
for both processes.  Any advice on this would be greatly appreciated as
well.

If providing more info would be helpful, I'd be happy to do so.  Thanks.