hi, Dan:
       According to my knowledge, 0.5um lot-to-lot accuracy will be really hard
for most of the silicon etching process. But you may try "etch-stop" technology.
The process will be more complicated and you may need special treated wafer.
Hope this helps.

  Guocheng Shao

"Chilcott, Dan W"  wrote:
  To All,

I am looking for a well controlled isotropic silicon etch for etching 2 um deep
features. I do not believe that a timed plasma etch would be controlled enough
for this application. I am looking for a control of better than 0.5 um from lot
to lot and across the wafer. Any ideas?