Is it possible for you to deposit an adhesion layer first? Chromium and titanium are common materials used for this.

Dear Aaron,

Thank you for your answer. The problem is I can only benefit is the metal makes direct contact with the semiconductor. So depositing an adhesion layer would not be feasible.

It is not clear what method you were using for the deposition of the metal. The first approach I'd try is that suggested earlier but you mention it's not applicable here (why, by the way?)

Alternatively, when using sputtering, the conditions can be tuned to induce a bit of intermixing/implant of the impinging ions into the substrate, which could improve adhesion (and can be detrimental to other interface properties - but sometimes they are not important)

Last, most semiconductors form a native oxide in air. Usually it is the oxide that hampers adhesion. Removal of the oxide right before metal deposition can significantly increase adhesion. 

Dear Lior,

I am sputtering depositing gold and (hopefully) platinum onto TiO2 particles; hence oxide layer is not the problem. I could try increasing the current, but it would also enhance the deposition rate which is already pretty high, and I need a layer less than 10 nm. 

Any other suggestions are welcome.

Two additional suggestions:

Heat the substrate prior to deposition. Ideally, inside the chamber. Annealing at ~150C can help desorb moisture and contaminants that can reduce adhesion (although for Pt on oxides it is already intrinsically low).

If you can reverse the polarity of the sputter process, before deposition, i.e. briefly bombarding the substrate with the Ar plasma, and then switch the polarity back to normal sputtering - this can help make the surface more reactive and it may help Pt to adhere better. It may also affect the electronic property at the interface (but not necessarily for the worse)

Try to sputter the Au or Pt at the lowest pressure possible. You will get neutral atoms with the highest energy impinging on the Si and as a result of that better adhesion. Noble metals in general adhere very bad to Si or SiO2 covered Si . As suggested if you can do a sputter etch prior to the sputter deposiiton you remove oxides and absorbed water. This will enhance adhesion. My experience is that Au en Pt could adhere for a while but slowly delaminate again since there is no intrinsic bonding. The best thing to do is apply a heat treatment with a rapid thermal anneal (e.g.400C, 20 s). Both Au en Pt will then diffuse a bit into the Si and you have a very good adhesion.

Dear all,

Thank you for your kind suggestions. 

Hi Aditya,

reading back the comments I see you want to sputter noble metals on TiO2. I was in the presumption it was Si. Adhesion on TiO2 of these mateirals will be hard without a adhesion layer. The best thing you can do is use a sputteretch for cleaning and low pressures for sputtering. Annealing might help but as I suggested but this will work for Si, I don't know if it works for TiO2.

Hi,

Try sputter etch the TiO2 surface using Ar. Also us the pulse bias in order to improve the adhesion (TiO2 being not very good conductor) during deposition, elevated temp during deposition will  help for adhesion.

During deposition of TiO2 particles are you using some sort of drum arrangement to coat the particles from all sides?

Pretreatment by vacuum  plasma can help. 

Aditya,

You said you were sputtering into a petri dish. Can you reverse the process? Can you deposit your Pt/Au alloy onto an insulating substrate, and then apply your TiO2 particles? I am assuming you are doing some type of solgel process. Below i have attached a link to a paper by Puangrat Kajitvichyanukul that discusses adhesion of TiO2 to glass slides. Perhaps some of the information contained will be useful for you.

Sincerely,

George

http://cmuj.cmu.ac.th/sites/default/files/pdf/2002-2006/Volume%204,%20Number%201,%20Special%20Issue/15_Effect%20of%20Acetyl%20Acetone%20on%20Property%20of%20TiO2%20Thin%20Film.pdf