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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