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Electroless Gold Plating of Semiconductor Substrates

Hi

I'm developing X-ray and Gamma Ray detectors using novel high density semiconductor substrates. To function well a great deal of attention needs to be paid to the properties of the electrical contacts made to the semiconductor. Recently I've tried depositing gold contacts via thermal evaporation and sputtering, typically of 100-200nm thickness, but both methods have had issues with adhesion and non-uniformities. I would now like to try electroless deposition of gold (of similar thickness) onto the semiconductor surface to see if this is any better.

The semiconductor substrate that I'm using is Cadmium Telluride (CdTe). Substrates are typically prepared through mechanical lapping and polishing with alumina suspensions followed by a final chemo-mechanical polish using a Bromine Methanol solution; this leaves a clean surface on which to deposit.

The main restrictions that I have are that the material cannot be heated >100 °C, I cannot use adhesion layers such as nickel as this effects detector performance, the surface chemistry cannot be significantly altered (although removal of cadmium, tellurium or the addition of oxygen may be acceptable) and I'm unable to use cyanide based chemicals in our labs.

From the literature I see that some people have used Gold (III) Chloride + Hydrogen Peroxide to deposit gold while others have used Gold (III) Chloride with H2O, HCl and Ethyle Glycol; typically this is followed by a low temperature annealing step to aid adhesion. I would be extremely grateful for any opinions people may have on any of these methods or any other suggestions on how to carry out this electroless deposition.

Many Thanks in advance!

Matt Veale
Scientist - London, UK
September 28, 2011