Hello Ali, when you mean etching to the substrate do you mean all the way
through the active region.  Normal BA lasers are isolated only by etching
the contact layer and perhaps some of the cladding.

Also, is it necessary for you to put metal first?  Its seems easier to use
photolithography to isolate, than pattern again and deposit the metal with a
lift-off.  There should be no reason to etch the metal on a BA laser.

If you need do a metal first process, can you use a different gold etch such
as iodine based?  Also, you could use 1:8:80 sulf:peroxide:water for etching
the AlGaAs. I don't have much experience with more durable resist-Im sure
someone will provide feedback on that.

Good luck,

Scott



-----Original Message-----
From: ahajjiah [mailto:ahajjiah@vt.edu]
Sent: Tuesday, May 30, 2006 10:08 AM
To: General MEMS discussion; mems-talk
Subject: [mems-talk] Help with Processing AlGaAs Broad Area Lasers


Dear All,

I am currently trying to process Broad Area Lasers on 1cm2 AlGaAs sample. On

the Epi side i am depositing Ti/Au by e-beam evaporation. Then using
photolithography to create openings on the sample to isolate the devices
from
each other by etching all the way to the substrate using wet etching. The
photoresist i am using is a positive photoresist (S1813).

My problem is this:

I know that (3 HCl:1 HNO3) will etch Au and AlGaAs and HF will etch Ti, but
my
photoresist will not hold against either etchants. As a result, my
photoresist
will not cover and protect the areas i don't want to be etched.

Can someone please suggest a solution for my problem?