Hi Mikael,

Is your Cr layer deposited via sputtering or thermal evaporation? The
former would produce a more dense and protective layer. I have no
experience with thermally deposited layers, however, these would
include a greater defect density, and hence more high-energy sites
that are susceptible to general chemical attack. Sputtered layers are
more dense and continuous and so would have a better protective
effect. Normally the stable Cr2O3 native layer that rapidly forms on
the Cr surface under ambient conditions has a low etch rate -
sufficient to make Cr a good and very stable masking layer in HF (Ar
and Pt are alternatives). I am surprised that the Cr/Ar double layer
did not survive either: this suggests to me the quality of the
layer(s) is not sufficient. Does your mask dissolve or peel?

Unfortunately I have no quantitative data on the etch rate of
sputtered Cr layers in BHF, however, I know 500 Ångströms was
sufficient in my case as a masking layer when etching thermal oxide
with a thickness of 1.2 um (~30 mins).

Best regards,

Michael



>Hi!

>How long are you able to etch with just chromium as a mask? I've done
some fast tests with
>chromium and chromium/gold but I've never been able to etch very deep
without the chromium
>being dissolved by the HF :(

>/mikael