durusmail: mems-talk: TMAH Etching
TMAH Etching
2002-05-24
Full Name
2002-05-26
chakravarthy.S.Yamarthy
2002-05-28
Gang Li
2002-05-28
il-seok Son
2002-05-28
chakravarthy.S.Yamarthy
2002-05-29
il-seok Son
2002-05-28
Michael D Martin
2002-05-28
BERAUER,FRANK (HP-Singapore,ex7)
2002-05-28
chakravarthy.S.Yamarthy
2002-05-30
Michael D Martin
TMAH Etching
il-seok Son
2002-05-29
Chakry,



I used powder form of silicic acid from Fisher scientific.

I add 40 g/liter of SA in 5 % TMAH solution, which is lower concentration
than yours.

The recipe is from Kovacs' article. Aluminium passivation is always working.

As you know, the etching rate of each crystal orientation is slightly
different depends on the concentration.



I am sorry but I am still confused with some part of your mail.

First, would you let me know what gms means?

Did you mean "mg" ,"ml", or none of them?

If it does not make huge difference, I would think "gms" as "ml".

You made 10 % TMAH 710 mg and added DI water later.

So, the TMAH that you are using is not 10 % TMAH, is it?



The following are very good articles for TMAH. I believe there are plenty of
good references out there.

[1] Tabata,O. pH-controlled TMAH Etchants For Silicon Micromachining,
Transducer 95

[2] Klaassen,E. Reay,R. Kovacs,G. Diode-based thermal r.m.s. converter with
on-chip circuitry fabricated using CMOS technology,
Sensors-and-Actuators-A-(Physical), Vol.A52:1-3, p.33-40, March-April, 1996.

I hope these articles are helpful.



I have a question for Michael D Martin.

Would you tell me how long you etched the MOSIS chip?

In other word, how deep did you etch the silicon?

What is the longest TMAH etching that you performed without any damage on
MOSIS chip?

Please, give me all the details.

Thanks.



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


----- Original Message -----
From: "chakravarthy.S.Yamarthy" 
To: 
Sent: Tuesday, May 28, 2002 2:10 PM
Subject: Re: [mems-talk] TMAH Etching


> 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
> _______________________________________________
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