In the sputtering of Niobium by reactive DC sputtering in order to try to get NbO2, does the niobium oxidize before reaching the substrate, or after it reaches the substrate it oxidizes?
I suppose it is also related to target-substrate distance.
If you sputtering gas consists of Ar+O2,
then definitely deposited specie on the substrate will be oxidised, provided you have an optimum power and deposition rate.
Very high powers can result in high deposition rates, and probably yield a metal rich oxide film.
To get a good oxide deposit, you can try sputtering in 100% oxygen, and preferably rf sputtering, and some substrate temperature to ensure the formation a crystalline Nb2O5.
K. Sreenivas
It depends on the quality of both the target and the sputtering environment One possibility is that the target surface might have oxidized already or oxidation might occur during the sputtering process if the system is contaminated with oxygen. Or as you mentioned there might be oxidation at the target.
It is essential to have a thorough control of the air in the system at all times so as to know exactly where the oxidation transpires,
Dear Ali Fakih,
The both oxidation process occur during niobium DC
sputtering depend on Oxygen to Argon ratio gas ratio, DC plasma parameters and bias voltage. However, perfect niobium oxide thin film would`t be an easily achieved process using this technique. Alternatively, you have to use RF sputtering of niobium oxide target in Oxygen rich medium.
Dear Ali,
It all depends on the deposition pressure. And oxidation (oxide molecule formation) in the gas phase must at all cost be avoided. Indeed, such molecules are much heavier than atoms and also tend to agglomerate into nanparticles, which finally deposit on the bottom of your vacuum chamber (and are also entering the vacuum pumps which they can destroy over time). If you work in a reasonable pressure range (say somewhere between 1.E-03 mbar and 1.E-02 mbar), the sputtered Nb metal particles will oxidize (i.e. react with atomic oxygen) upon condensing on the substrate. Choose your pressure to get more or less into a neutral instrinsic stress situation in the deposited coating. By the way: the selection of exact sputter pressure should be in line with the target-subtrate distance: choose it so that the mean free path is about equal to or larger than this T-S distance.
In my experience when we sputter reactively with oxygen from a metallic target, the deposition speed is lowered tremendously, indicating that oxidation already happens to the surface of the metal target. However I can immagine that also some oxidation occurs in the gas phase or on the substrate. Which effect is dominant will probably depend on the deposition speed.
To crystalline the film without heating you could either reduce the gas pressure or add a bias to your substrate; in the case of glass substrate you would need an RF bias
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