be sure that your wafer is free of any oxide or other
contamination..
if very small amount of oxide islands remain it will
create silicon grass or a rough surface as you've
experienced.. (same happened to me)

you may dip your substrate in BOE buffer or clean the
surface in a plasma for a short amount of time before
the KOH etch..

this method solved my problem..


jeeva S  wrote:  Hi all,
   I did KOH (anisotropic ) wet etching of silicon. I
used 10g of KOH
pellets and mixed it with 100ml of DI water at 65 deg.
Then I immersed the Silicon substrate in this
solution. After one
minute (as
it was the time limit for 1 micron depth of substrate)
when I removed
the
substrate from this solution, it was rough on the
surface and also it
was
darkened (Black colored rough surface).
Can anyone explain me why this has happened and give
me correct
procedure
for the KOH wet etching with composition of KOH and
water?