I should have put this info in the first post, but here's something I
had mentioned in one of the followups. Wish this was a newsgroup or had
a web archive, then I could just point to a link...(oh, using RIE):
> We're using a foundry service (through MOSIS) that gives us a standard 5
> metal layer CMOS chip back. We define the top level interconnect metal
> for use as a post processing etch mask. So, the aluminum mask is a
> must, and can't modify it to any great extent. The depth of the etch is
> such that we are beginning to see ARDE effects, and need the lower
> pressure/higher bias to clear out the SiO2 from the bottom of the
> trenches. So, mainly looking at options for modifying the aluminum
> (i.e., oxidizing or something) to increase its sputtering resistance.
> We would like the aluminum layer to still be mostly aluminum when we're
> done, and it's only 1micron thick to start with. So, we need something
> that will controllably oxidize 100-300nm. Most anodization schemes I've
> looked at are likely to turn the whole layer into Al2O3 in a very short
> time. maybe I'm wrong. I started looking a bit at plasma oxidation, and
> it would be very nice if we could do it in the RIE, as then we wouldn't
> have to break vacuum. We could even oxidize a bit, etch, oxidize some
> more, etc. But I have no idea where to start as far as plasma
> parameters, and oxidation times are concerned. If they are
> self-limiting that would be great, because then we could set up the
> conditions, and the thickness wouldn't be very sensitive to exposure
> time. Another reason I'm shying away from the wet processes for
> oxidation is that the majority of the milling occurs at the end of the
> etch when we have to drop pressure and turn up the bias to clear out the
> last of the SiO2. At that point I wouldn't want to put the chip in a
> wet environment if I didn't have to. We could possibly even wait to do
> the oxidation until this point, but all of that means I need to find
> some rate temp dependence data, and so far I've come up short :)