Chromium fluoride is not very volatile and thus
chromium is not chemically etched in a plasma with fluorine radicals.
Improved attempts to plasma etch Cr have used chlorine and oxygen.

My experience using chromium as a mask for oxide with fluorine-based
chemistry
in a parallel-plate RIE system is that the Cr mask erodes a lot faster
at high power, while only giving say a 2X increase in oxide etch rate.
The higher power corresponds to high sheath voltage and thus high
ion-bombardment energy of the wafer.

For an ICP system, to reduce the Cr erosion rate,
try turning down the platen power to reduce ion-bombardment energy.

> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
> Sent: Thursday, December 13, 2001 10:49 AM
> To: [email protected]
> Cc: [email protected]
> Subject: [mems-talk] Oxide to Chrome Selectivity - something to ponder
>
>
> Dear MEMs enthusiasts,
>       I have a friend, based in The Netherlands, who is using
> Chrome as a
> hardmask (limited to this) for dry etching
> deep 'silicon dioxide'. He is using, as far as I am aware,
> Fluorine based
> chemistry of only ..F4 at 50mTorr
> in 'Bright Mode' (ICP mode).
>
> He has found that the chrome begins to erode substantially
> once the Chrome
> is broken through into the oxide.
>
> I think it could be due to Cr2O3 or CrO3 formation from
> oxygen, liberated
> during the oxide etch?
>
> Without having to embark on a 2K Factorial DOE, any
> suggestions as to how he
> could improve on the Oxide to Chrome selectivity?
>
> Perhaps, increasing  pressure to reduce Chrome etchrate?
>
>
> suggestions or known effects from experience  would be appreciated.
>
> Best Regards,
>
> Philip Lau
>
>
>
>
>
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