Anodization. But make sure the back side of your wafers is hightly doped to
ensure ohmic contact and the front side will have the pores.  The size of
the pores will of course depend on the current density, time, type of substrate,
illumination and so on.

Maybe this is the way to go.

nimo

________________________________
From: ANIRBAN SARKAR 
To: mems-talk@memsnet.org
Sent: Fri, September 17, 2010 10:49:25 PM
Subject: [mems-talk] Porous Silicon recipe

Hello all,

I have been trying to generate porous silicon for our project but I am not
being able to obtain porous Silicon in the range of 50nm to 200nm.
I am requesting some insight in the recipe of generation of porous Si.

Any help will be gladly appreciated.

Thanks
Anirban