Hi Renil

Have you examined the percipitates carefully, for example, understand
SEM? How does the surface look? Is the exposed silicon etched at all?
What masking material were you using? Have you cleaned your wafers
thoroughly before the KOH step?

You should probably also try a higher concentration, say 45%.

Best
Leo

On Wed, Aug 19, 2009 at 6:16 AM, renil kumar wrote:
> Hi all
>           I am making some grating layers on <110> oriented silicon. I had to
etch 30 um down to the silicon wafer to form vertical walls of 5 um width. the
openig was also 5um. for that i aligned the features along the (111) flat. I was
trying to etch the exposed silicon using 20 % wt KOH solution at 76 degrees and
i used 85% KOH salt. after few minutes of etching it produced a black
precipitate over the etched portion and stopped the further etching. i was also
tried with 30% KOH solution at 75 degrees. that time also the precipitate was
formed and further etching was stopped. does anyone know about it and any
suggestion regarding this will be highly appreciated. thanks i advance.
>
>  renil

--
Xiaoguang "Leo" Liu
Birck Nanotechnology Center,
Purdue University,
1205 W.State Street, West Lafayette, IN, 47906 USA
liu79@purdue.edu