Hi Mark,
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

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Dear MEMS-Group,

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 can this be done?
What kind of electrodes can be used (Pt?, Au?) in KOH?
How much voltage have to be applied between the
KOH-solution and the
n-layer?
Will there be a difference in the etch-rate compared
to the normal
etch-rate in KOH?



Thanks for your answers
Mark



=====
Pavel Neuzil
CTO SiMEMS Pte Ltd

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