Thanks for the info.  I sounds like I better avoid Ti as an adhesion layer,
as I will be etching through a Si wafer ~10 hr in KOH.

I am trying to do wafer level gold thermocompression bonding.  So far I
haven't had much success using Au with a Cr adhesion layer.  I have heard
that the Cr can diffuse through the Au and cause problems.  An alternative
would be to use a Pt diffusion barrier between the Cr and the Au.

Can someone advise me as to how thick the Pt should be to prevent diffusion
of Cr into the Au at 300-350 degC, 1-24 hr?

Roger Shile

----- Original Message -----
From: "Kirt & Erika Zipf-Williams" 
To: "General MEMS discussion" 
Sent: Wednesday, March 26, 2003 1:57 PM
Subject: Re: [mems-talk] Ti attack by KOH


> I tried Ti in 33% KOH at 80 C.
> It became soft. After ~30 min, the apparent etch rate was 62 nm/min.
> Ti under Au may end up being OK, however.
>
> You might use Cr instead.
> For Cr, I measured a slow etch rate of 4.2 nm/min in the same solution.
> 100 nm Au with 10 nm Cr as an adhesion layer worked fine for ~1 hour of
KOH
> etching.
>
> The other popular adhesion layer, 10Ti/90W, did not fare well, being
etched
> at > 300 nm/min.
>
>     --Kirt Williams, Ph.D.   consultant
>
> ----- Original Message -----
> From: Roger Shile 
> To: MEMS Discussion Group 
> Sent: Tuesday, March 25, 2003 12:51 PM
> Subject: [mems-talk] Ti attack by KOH
>
>
> > Can someone tell me if titnanium can be used as an adhesion layer for
gold
> when the metalization will be subjected to a long KOH etch?
> > In my experience, chemistries that etch Si, such as HF and fluorine
based
> plasmas, will also etch Ti.  I therefore suspect that KOH will etch Ti,
but
> haven't found any published data.
> >
> > Roger Shile
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