hi kathleen,

this just an german link: http://de.wikipedia.org/wiki/Bosch-Prozess .

perhaps it helps a little bit. shortly the process can be described as a
changing of etching and passivating, means: you etch with DRIE (deep
reactive ion etching), then you passivate (the sidewalls) to protect an
underetch, then you do again a DRIE, passivating, DRIE, etc.  => until you
reach the depth you need.

this is a presentation with some pics (unfortunately in german...):

http://www.imtek.de/anwendungen/content/upload/vorlesung/2006/mst_t

&p_06__schichtabtragung_durch_aetzen_(16.01.2006).pdf#search=%22Bosch-Prozes
s%22

if you have some additional questions, do not hezitate to contact me.

best regards,
michael
  _____

Michael Prömpers

Dipl.-Ing. Elektrotechnik, Mikrosystemtechnik
Institut für Bio- und Nanotechnologie, Bioelektronik (IBN2-BE)
Forschungszentrum Jülich GmbH
D-52425 Jülich

Tel: +49 (0) 2461 61 2635
Fax: +49 (0) 2461 61 8733

http://www.fz-juelich.de/ibn/ISG2