Andrea,

If you can increase Au thickness, most likely your problem will be solved.
In the past, I've protected poly-Si features by Cr/Au. Cr is necessary for
adhesion (anywhere from 50 to 200 is common).
For my purpose half micron Au was almost sufficient, but still had about 10%
or so yield loss (KOH penetrated through Au). One micron thick Au was
perfectly protecting poly underneath.

Please note that depending on your topography, surface conditions,
deposition tool, and even Au purity (I used 99.99% Au) you may end up using
thinner, or thicker Au. I'd suggest at least 2-3kA evaporated Au or 4-5 kA
sputtered Au for a polished Si.

Good luck

E.



On Fri, Apr 2, 2010 at 10:40 AM, Andrea Mazzolari wrote:

> Hi all,
>
> i need to thermal evaporate a metallic mask on a polished silicon wafer.
> The mask should withstand 40% KOH etch for 5 hours.
> I tried 20/30 Cr/Au, but it seams that it is not working: after about 1
> hour etch many pinholes are generated in the Cr/Au layer, KOH penetrates
> such pinholes and etch silicon.
>
> Any suggestion on how to improve the resistance of Cr/Au layer ?
> Any alternative to Cr/Au ?
>
> Thanks,
> Andrea