Do you have to periodically replenish the (NH4)2S2O8?  I read somewhere
(JVST A 18(2) p.738 May Apr 2000) that with low concentrations of TMAH,
hillocks would form and etching would eventually stop if (NH4)2S2O8 wasn't
added at least ~ every 40 minutes.

Roger Shile

----- Original Message -----
From: 
To: "General MEMS discussion" 
Sent: Wednesday, June 11, 2003 8:23 AM
Subject: Re: [mems-talk] TMAH Etchant


> Usually people will first doped the TMAH with Si before
> etching the wafer. The dissolved Si will form a passive
> layer on the Al to protect it form etching.
>
> A popular forumla is TMAH(25%) : H2O : Si : (NH4)2S2O8 ( 200
> g : 800 g : 16 g : 5 g ). I have tried it before and it
> works!
>
> First you have to put 2 635um Si wafer into 200ml TMAH
> solution and 800ml H20 at 85oC until all the Si is
> completely dissoved. It takes about 1 days. After that add
> 5g of (NH4)2S2O8 into the mixtures. Then the solution is
> ready to use. Remember, use the solution as soon as
> possible, because the lifetime of the solution is quite
> short (1-2days).
>
> Enjoy!
>
> > Dear MEMS members,
> >
> > I am looking for the information regarding TMAH
> > etching that does not attack Al bond pads.
> >
> > can i get any article regarding this.
> >
> > Your suggestions would be highly helpful.
> >
> > thanks
> > Kris
> >
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> Best Regards,
> Kin
>
>
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