We use to use 2000 Angstroms of SiO2 as a mask and etch 5 micron cavities
(1/8 inch in diameter) to form pressure sensing diaphragms. We used to mix
7000 ml Nitric Acid (HNO3) and 60 ml Hydrofluoric Acid (HF) at room
temperature. To improve the etch rate repeatability we would drop a diced
raw chip of Silicon into the mixture about a minute before we would etch,
and we would bubble Carbon Dioxide through the mixture to provide agitation.
Etch rate was about 0.6 microns per minute and etch depth was very
controllable. This was for a commercial application and yield was VERY
important.

Phil Klauder
Work 215-646-7400  x2151
Home 215-643-5853
Home [email protected]


-----Original Message-----
From: li gang [mailto:[email protected]]
Sent: Monday, November 05, 2001 3:50 AM
To: [email protected]
Subject: [mems-talk] isotropic wet silicon etching.


Dear all:

  Could you please share some isotropic wet silicon etching experience
with me? I want to know the volume ratio of the HF:HNO3:HAC ,the etching
rate and the mask. According to my reference, the etching rate of silicon
is too quick (7 um/min) with SiO2 mask. I wonder if there is another good
volume ratio to provide slower (less than 1um/min) silcion etching still
with SiO2 as the mask.

Thanks in advance,

Regards,

Li Gang

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