Hi Ali,

We use a ICP/RIE system, a PT 770 at the very lowest pressure it can run
(2 mT) and a chemistry consisting of 13 sccm of BCl3, 3 sccm Cl2 and 5
sccm of Ar. ICP power ~ 250 W and RIE power ~125 to 175 W. Etch results
give in general very smooth sidewalls, but there is some selectivity
between AlAs and GaAs. This shows up as a staircase cross-section at the
bottom of your etch trench or via. You can improve this by adding BCl3
and removeing Cl2, which will give you a flatter bottom, but slow your
etch rate. We have had excellent results before with an ECR etcher using
a similar gas mixture but a lower pressure. I think, however, that the
mask material you use is much more important; PR must be thick and have
nice vertical sidewalls also, I have not too much experience with metal,
but it seems to me that the edge roughness will be transferred directly
into your sidewall so if you do so, lift off is probably better than a
wet etch to pattern your metal mask.

hope this helps.

Regards,

Jobert van Eisden

Graduate student
College of Nanoscale Science and Engineering
SUNY Albany
Albany, NY, 12203


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of ahajjiah@vt.edu
Sent: Wednesday, December 06, 2006 1:26 PM
To: General MEMS discussion
Subject: [mems-talk] Need help with some processing recipe (if possible)

Dear Mems Community,

I am in the process of forming the optical cavity in micro-cavity
GaAs/AlGaAS lasers by wet and/or dry etching? As a result, i would like
to know how to form a smooth/vertical optical cavity? If anybody has
some experience in doing so, it would be appreciated if he/she can give
me some hints on how to proceed. In other words, What are the optimum
processing conditions to get a smooth and vertical optical cavity?