Hi,
I didn't see the black color on the etched Si surface.
Anyhow, if there exists native oxide on Si, it is possible for the etch rate
to be delayed. What you can do is putting your sample into very diluted HF
solution like 100:1 that dose not etch your mask much.
J. Kim

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of LSujatha
Sent: Friday, September 01, 2006 9:13 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] KOH etching

Dear friends,
When I am doing KOH etching of Silicon with silicon dioxide mask in 30%
solution I am getting the black color in the place of silicon to be etched
and hence the etching starts very late. the etching time becomes almost
twice.Can anyone tell the reason for this black color formation? How to
avoid?
Temperature is 75 degrees Centigrade.