Hi, Thank you, Mike.
I use diluted HCL(2:1), and the AlGaAs contains 80%Al.
I need to undercut 8um. So, the 0.1um/min etch rate will take 80mins, which
may be too long for the photoresist.
I will try baking the wafer before spin and HCl(1:1) to see whether there is
any improvements.

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Michael Yakimov
Sent: Friday, January 25, 2002 8:37 AM
To: [email protected]
Subject: RE: [mems-talk] How to prevent the ethant from creeping along
the interface between photoresist and semiconductor material?


What is the concentration of HCl? composition of AlGaAs?
from our experience, we found that photoresist may haveadhesion problems
with concentrated  (36%) HCl, baking the wafer before spin  and photoresist
hard bake before etrching slightly improve the situation.. Diluted HCL (1:1)
has no adhesion problems- but I'm not sure about the etch rate.
 For higher Al content you may try to use diluted BHF. I don't have the
reference right now, but for diluted BHF ( BHF(6:1) :DI = 1:20 the etch rate
for 85%Al is about 0.1 um/min, and it has no problems with photoresist
adhesion

Mike

> -----Original Message-----
> From: Qingwei Mo [SMTP:[email protected]]
> Sent: Thursday, January 24, 2002 8:14 PM
> To:   Mems-Talk
> Subject:      [mems-talk] How to prevent the ethant from creeping along
> the interface between photoresist and semiconductor material?
>
> Hi, I am trying to etch the AlGaAs under a GaAs layer using HCl. The
> AlGaAs
> is exposed to the etchant at the sidewall of a trech. To protect the most
> part of the trench, I covered the whole thing with photoresist AZ4330.
> There
> is only a small opening left to let the echant in. However, what I found
> is,
> somehow, the etchant creeped along the interface between the photoresist
> and
> the sidewall. And etch away the material they are not supposed to. I have
> tried both wet etch are RIE to make the sidewall, it doesn't change much.
> Anyone has any idea, or similar experience? Is there something wrong with
> the sidewall or the recipe of the photoresist?
>
> Thanks a lot for your help
>
> Qingwei
>
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