You noted the main physical differences in the 490 vs. 590. Lam used the 590
primarily for oxide/nitride etches using CF4 and other gases. The 490 was used
for etching using chlorine processes such as for polysilicon. They are both top
powered and the graphite on the 590 can tend to generate particles through time
and needs to be replaced as a consumable. No such problem with the anodized
version on the 490. In my opinion the 490 was a great polysilicon etch tool but
the 590 was a marginal oxide etcher. I think Tegal made a better oxide etcher in
the Tegal 903e. Bob Henderson