Dear Sunny,

Thanks alot for ur suggestions.

40% SA is silicic acid in water.we could able to get
the chemical from alfa aesar company.u can get that
chemical directly from that company.

the mixture consists of

10%TMAH solution(710gms)+40% sio2(100gms)+DI
water(110gms).......MIXTURE (I)

The above mixture was heated heated for 80 degree
centigrade and stirred continously.after the mixture
appears to be void of white precipitate i.e,completely
clear

Ammonium peroxy Disulphate(APODS)(1.25gms)+10ml of DI
water was prepared separately.

The above APODS mixture along with 20 ml of 10% TMAH
was added to MIXTURE(I) at regular intervals and
silicon chips were etched.The Aluminum bond pads were
attacked.

APODS was added to reduce the hillocks.

SA was added to maintain the PH of the entire mixture.

Can u suggest me which chemical am i need to add  to
the mixture to maintain the proper PH.

Thanks
Chakry(AMSTC,AUBURN-AL)
--- il-seok Son  wrote:
> 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
> >
> > =====
> > To Know That We Know What We Know,And That We Do
> Not Know,What We Do Not
> > Know:That Is The True Knowledge.
> > Confucius
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=====
To Know That We Know What We Know,And That We Do Not Know,What We Do Not
Know:That Is The True Knowledge.
Confucius
Yahoo! - Official partner of 2002 FIFA World Cup
http://fifaworldcup.yahoo.com