if you have the option to use DRIE that will be the best option.  if not then
you can use HF in different concentrations; mostly 50% with water.  that will be
isotropic and not anisotropic; that means not vertical wall but will be smooth
enough i guess.

i hope this helps.
Nimo

--- On Sun, 8/16/09, renil kumar  wrote:

From: renil kumar 
Subject: [mems-talk] KOH etch
To: "General MEMS discussion" 
Date: Sunday, August 16, 2009, 8:35 PM

Hi all,

              I want to etch smooth vertical walls of depth 70 um in <110>
oriented silicon. what is the best etch recipe to get a smooth wall of width 5um
and a depth of 70um. any suggestion would be appreciated well, thanking you