i would go with the TMAH option: 25% or a more diluted solution, high
Temperature, sonication; you may need to remove any native oxide
before etching the silicon.

i have also used a diluted solution of ammonia, 200-500:1 NH4OH:H2O,
room temperature, it just depends how much silicon you want to etch.

cheers!


On Thu, Feb 5, 2009 at 2:51 PM, Brian Stahl  wrote:
> Hello Peter,
>
> What are you trying to etch?  Aqueous solutions of TMAH (tetramethylammonium
> hyroxide) and EDP (ethylene diamine pyrocatechol) also etch silicon
> anisotropically, and there's plenty of literature out there on both.  TMAH
> is particularly useful because it isn't as toxic as EDP and you generally
> don't have metal ion contamination.  Here's an excellent article that covers
> almost the whole gamut: Kovacs, Maluf, and Petersen: "Bulk Micromaching of
> Silicon," Proceedings of the IEEE, Volume 86, Number 8, August 1988.

--
_fmaya