Questions about the Si wet etching process in SOI wafer

jim kruger jimkruger at
Fri Jul 8 12:20:59 PDT 2011

TMAH is very selective to the thin native SiO2 on all Si, much more than KOH.  I am guessing that your SOI had a little more SiO2 than your test wafer.
Use a 50:1 HF dip for 30 or 60 sec (60 sec =~ 50A) just before the TMAH, rinse but no need to dry, just into the TMAH.  I don't think the doping plays much roll until very high levels of Boron.

--- On Fri, 7/8/11, Donkoun Lee <dlee76 at> wrote:

From: Donkoun Lee <dlee76 at>
Subject: Questions about the Si wet etching process in SOI wafer
To: wbgen-hpr at
Date: Friday, July 8, 2011, 11:12 AM

Hi all:

Recently, I used the 25% TMAH in order to wet-etch the Si layer in SOI wafer.
Before etching a SOI wafer, when I used a Si wafer for the reference, the Si wafer was well etched.
However, when I used the SOI wafer, the Si layer (device layer) in SOI wafer was not etched at all:

The condition I used is like below:
Temperature: 45 oC
Concentration of TMAH: 25%
The Si thickness in SOI wafer: 30 ~ 50 nm

I also used the higher temperature, like ~ 70 oC. But, I could not etch the Si layer in SOI wafer.
Si layer is P-type. However, the doping concentration is around 10^15/cm2. 
Furthermore, I double checked out the orientation of the Si layer and the orientation was (001)

Could you give me a tip for solving this problem?

Thank you.
Kind Regards,
Donkoun Lee
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