Hi Pavel,
thanks for your answer.

I've tried it out but the result was that I didn't get any etching at all.

I'm using a wafer holder with Au-contacts inside (for contacting the
n-Epi-Layer on the p substrate).
As Aux-electrode I'm using Platinum-wire, the same for the
reference-electrode.

I've applyed +0.9V to the n-Epi (against the ref.-electrode) and get a
current of about 25uA slowly increasing to 32uA (in 4 hours).
(The voltage applyed to the Aux-electrode lies in between 0.95V and 1.1V)


As there wasn't any significant increase of current as assumed (the
etching should have been finished at this time) I stopped and had a look
at it - I can't see any etch progress.

So the etch-stop-system in general seems to work (?) but obviously too
good/early?!? Etching stopps already at the p-substrate...

So what is wrong?

Can anyone help? Thank you!


Mark P.


Pavel Neuzil wrote:
> the etch rate is given only by the KOH concentration
> and temperature. As the technique is called
> Electrochemical Etch Stop, the etching is indeed
> chemical and it is only stopped by an electrochemical
> oxidation of the N layer once the layer is exposed to
> the solution. A few volts is enough to stop the
> etching, higher voltage would also work but most
> likely your PN junction will not be able to hold it
> due to the defects. Typically people use 3 or 4
> electrode systems in potentiostat configuration, which
> is definitely better than just a simple power supply.
>
> The Aux (counter) electrode can be Platinum as it is a
> stable metal. The most important part is a wafer
> holder to prevent the front side of the wafer to be in
> contact with the KOH. There are a few vendors of
> systems suitable for KOH etching with an EC etch stop
> option.
>
> In case you need a wafer holder (and a simple
> potentiostat), we can help you out as we manufacture
> two different types of wafer holders for the EC
> etching (Etch stop) with quite a few clones as well as
> the potentiostat.
> Pavel
>
> _____________________________________________________


> I'm looking for a way to get a membrane by etching Si
> (thin n-layer on
> p
> substrate) anisotropically in KOH using an
> electrochemical etch-stop
> techinque.
>
> How much voltage have to be applied between the
> KOH-solution and the
> n-layer?