It has been done.  We did it with an excimer on a
standard pressure sensor diaphram.  We got a hole
about 40um diameter.  It wasn't very clean and round.

Kirthi Roberts wrote:
>
> Dear MEMS enthusiasts,
>
> Has anyone laser drilled holes on a 50-100
> micrometer thick silicon membrane, to get a roughly
> cylindrical cavity. I need holes of diameter of
> about 50 micrometers on a Silicon membrane of the
> above mentioned thickness. If anyone knows of any
> publications in this area or can offer any advice or
> tips, I would much appreciate if you could send them
> to me.
>
> Thanks in advance,
>
> Kirthi Roberts
>
> --
> __________________________________
> Kirthi Roberts
> School of Engineering Science
> Simon Fraser University
> Vancouver,
> Canada
> e-mail : [email protected]
>