Patrick,

Xenon difluoride (XeF2) is highly selective to Si compared to SiO2.  Just
make sure there is NO moisture in your system (such as from outgassing from
your vacuum chamber walls), otherwise you might form HF which will attack
your SiO2 and some metals.  The etch is mostly isotropic.  However, by
etching in bursts, you can increase the lateral etch rate which can be
useful for undercutting structures.  If you lack processing equipment, a
XeF2 etching apparatus can be constructed quite easily and inexpensively
with a vacuum chamber, vacuum pump, tubing, hand valves, pressure gauge,
exhaust port (very important for safety) and a container for the XeF2
crystals.  There have been a number of publications on this technique,
especially as a post processing etch step for MEMS devices fabricated in
CMOS processes, such as through MOSIS.

Sincerely,

Robert Dean

At 03:48 PM 11/25/02 +0100, you wrote:
>Dear all
>
>I am interesseted in etching Si with SiO2 as an etch mask. Does anyone
>know of a dry or wet etch that can be used?
>
>All comments are highly apriciated
>
>Patrick
>
>
>
>
>
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