Hi,

You can use Sulfuric/Hydrogen Peroxide, like 98:2 very little peroxide,
use a hard mask. Or use a resist mask and use PA-11 which is
Water:Hydrogen Peroxide:Ammonium Hydroxide use a ratio of 80:10:10. If
you need to keep certain features like MESA's then adjust the pH using
the NH4OH and you can make great mesa structures. To get it going faster
add more H2O2 and NH4OH.

Rick


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of deepa sree
Sent: Wednesday, August 23, 2006 3:04 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Deep GaAs etching

Hi

I need to etch 3-4 mils of GaAs. I need to chemically etch it due to
lack of facilities. Can anyone suggest a suitable masking layer and a
fast chemical etchant that does this?