Hi Jeeva,

I am very curious about this phenomenom because now I am looking for a
method to get rough surface, say, 1um deep and 1um serparation.  I know a
method called black silicon method.  It is a dry etch of silicon, and
because of some native oxide or dusts on the silicon wafer, they serve as
micron masks in the RIE(reactive ion etching), so after the etching, the
surface will be rough, grass like surface.  Then the surface will become
balck since the incident light is trapped inside the "grass".  That's why
this method is called black silicon method.  I think the result of your
experiment has the same reason.

What I want to know is, was your wafer bare silicon? did you cleaned your
wafer before the KOH etching? how long had your wafer exposed to air before
your experiment? what's the exactly roughness of your sample, like the depth
and spacing of those spurs?

If you could tell me some details about it, it would be highly appreciated.

Thanks very much.

Duan


On 2/14/06, jeeva S  wrote:
>
> Hi all,
>   Few days back I sent a mail to the group saying that a silicon sample
> (subjected to wet etching) was black on the surface.
> I corrected it from some of your replies asking me to use 40grams of KOH
> with 100ml of DI water and 2 ml of IPA. I got a perfect silicon wet etched
> sample. Thanks for all your help.
>
> Now that I got a perfect wet etched sample, I was wondering why was it
> black
> on the surface when I used 10 grams of KOH. Is it because of KOH and
> Silicon
> reaction?     In that case, teflon coated on silicon substrate will not be
> affected by this KOH. But my sample as a whole was blackened on the
> surface.(My sample is teflon coated silicon substrate with patterns on
> teflon layer)
>
> I request you to explain me the reason for the blackening.