The trick is how to dope sidewall only. Have to deposited mask on top and
bottom, but not on sidewall. What is the dimention of your trench and mesa?

You can create SiN spacer on sidewall only, then thermal oxidation, so oxide
only forms on top and bottom. Then selectively remove SiN spacer, exposing
sidewall. Now you have oxide on top and bottom serving as diffuion mask,
then use gas furnace isotropic doping.

> 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.
>
> Thanks,
>
> Daniel
>
>