kathleen,

The Bosch process is used to make etches, sometimes
very narrow ~ 50 um with high aspect ratio.

Basically, you have a manifold that has a Florine
based etchant, that isotropically etches your
substrate.  Then a passivant is introduced into the
manifold that "passivates and protects" the sidewalls,
and then the Anisotropy of the next phase of Florine
or etchant preferentially removes the bottom of the
etched holes, leaving the sidewall unchanged.

This process is repeated and there are "scallops" when
you do SEMS on the vias.  This has been used in many
R&D fabs and likely in production fabs as well.

University of Albany Nanotech is one place you can
find out more information on this.

Regards,

John
Cyan Systems
--- "Holmes, Kathleen"  wrote:

> I'm a newbie in the mems business. Would someone
> please explain the
> Bosch process, or direct me to some literature?
> Thanks