Dear Xinbing,

A quick reference (M.Kohler,Etching in Microsystem Technology, Wiley-VCH,
1999) says :

NaOH 0.24mol/l
H2O2 0.17mol/l
Temp: 5 Celcius
Etch Rate 1.7nm/s
(H. Beneking 1991)

Also

Citric Acid 2.4mol/l
H2O2 1.4mol/l
Temp: 18 Celcius
Etch Rate : 3nm/s
(C. Juang 1990)

I have no idea about NaOH solution, but citric acid seems not to roughen the
surface more.  And how rough can it make in 60nm depth :)

Slower etch rates may(?) be possible with lower H2O2 content and lower
temperature I guess.

Best of Luck.

Oray Orkun Cellek
Middle East Technical University
EE-Dept.
Ankara, Turkey

>From: Xinbing Liu 
>Reply-To: [email protected]
>To: [email protected]
>Subject: [mems-talk] Slow wet etch of GaAs?
>Date: Fri, 22 Feb 2002 10:43:15 -0500
>
>Hi,
>
>I need to remove about 60 nm thick of GaAs from a GaAs wafer.  I read
>that GaAs can be wet etched in H2O2/H2SO4 solutions, but the etch rate
>seems too high for me, couple of microns per minute.  Does anyone have a
>recipe for slow etch so I can control the thickness removed?  I also
>need smooth surface after etching.
>
>Any help is appreciated.
>
>Xinbing Liu
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