Daniel,

One idea that comes to mind would be the use of spray coating to form a
conformal coating across the bottom, sidewalls, and top of the trench
structure.  Since sidewalls are extremely difficult to expose, if you
were to use a negative tone material instead, it would be a relatively
simple matter to expose the top/bottom surfaces while leaving the
sidewalls with little to no exposure.  During develop, the material on
the sidewalls would dissolve, leaving the sidewalls bare. At this point,
isotropic doping would only enter the sidewalls.

What are the dimensions of your trench structure?

Best Regards,
Chad Brubaker

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Thursday, May 04, 2006 4:24 PM
To: [email protected]
Subject: [mems-talk] forming boron and arsenic doped sidewalls in a
siliconwafer

I am trying to form boron and arsenic doped sidewalls in trenches in a
silicon wafer.  I thought of doing reactive ion or electrochemical
etching of the trench bottom after isotropic doping, but I'm worried
that the reaction will be hard to time correctly because the silicon
underneath would etch much faster than the doped layer.  Any thoughts
you have on the most efficient process to form doped sidewalls would be
greatly appreciated.