Dear Chakry,

pH is a good indicator for aluminum passivatoin in doped TMAH.
You have to keep the pH at 12.
If the pH is higher than 12, such as 12.3, you can literally see the
aluminum disappearing.
If the pH is lower than 12, the etching rate of silicon is decreased.
You can find this information from many articles about TMAH.
You might need to put more chemical that you  are currently using in order
to drop the pH.

Some of your descriptions are not clear to me.
Would you describe more in detail about your recipe?
What does  "40% SA aqueous solution" mean?
Is this silicic acid?
Also, how did you make 40% SA solution?
Would you tell me how many gram of what chemical you put in a liter of water
or TMAH solution?
What is the resource for this recipe?
Is there any specific reason for using 10% TMAH solution?
I cannot tell much about it based on your description.


__________________________________________________________
Il-seok  Son (Sunny)
Dept. of Electrical and Computer Engineering
University of Wisconsin - Madison, SonicMEMS
__________________________________________________________

----- Original Message -----
From: "chakravarthy.S.Yamarthy" 
To: 
Sent: Sunday, May 26, 2002 3:57 PM
Subject: [mems-talk] TMAH Etching


> Dear friends,
>
> i am trying to do TMAH etching of silicon under the
> cantilever beam  made of (silicon
> dioxide+polysilicon).
>
> We have used the solution of TMAH(10% w/w in
> water)+SA(40% aqueous solution)+Ammonium peroxy
> disulphate(APODS about 1.25gms).
>
> we have heated the entire solution @ 80 degree
> centigrade and chips were etched in this solution.
>
> But,we could see that Al bond pads,which were opened
> thru silicon dioxide passivation layer(9000 Angs)were
> attacked by the etching solution.
>
> Can anyone of u please suggest me any good etching
> technique for silicon that should not attack Aluminum.
>
> thanks
> Chakry
>
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