A novel reactive magnetron sputtering technique for producing insulating oxides of metal alloys and other compound thin films

Abstract

Problems associated with reactive magnetron sputtering from elemental (i.e. non-compound) targets have been successfully solved in this work. The elements of this achievement are: (i) the use of mid-frequency (i.e. 40 kHz) AC power in the floating mode, between two magnetrons, allowed the reactive sputtering process to be arc-free and hence eliminating the undesired effects of arcing in reactive sputtering such as driving the process to become unstable, creating defects in the films and reducing the target lifetime. (ii) The combination of DC and mid-frequency AC power in a novel way using a filter to protect the DC power supply from the AC one (or the independently DC powered magnetrons method) permitted the composition of the produced films to be easily and independently manipulated by varying the magnitude of power applied to each magnetron. (iii) The use of very fast feedback methods to automatically control the admission rate of oxygen into the sputtering chamber (i.e. plasma emission monitoring or voltage control) allowed the stoichiometry of the deposited films to be independently controlled. This also allowed the deposition rate of the sputtered films to be high. (iv) Sputtering from two magnetrons made the production of alloys or multi-element compounds, which are either difficult or impossible to be formed from single targets, an easy task. (v) Substrate rotation enhanced atomic level mixing of the film constituents. The stoichiometry of the film was controlled by plasma emission monitoring or voltage control on one magnetron, and dopants were added by sputtering from the other magnetron. This means that the former magnetron served two purposes; the first was to sputter metal and oxidise it, and the second purpose was to oxidise the metal sputtered from the other magnetron. This novel technique opens the door wide for investigating virtually all potentially promising thin oxide films. Using this technique, a large range of alloy-oxide films was deposited at high rates. In fact, the independent control of both the metallic composition and stoichiometry was very valuable in identifying the optimum properties of these films. That is, giving transparent films of different refractive indices for optical applications. Furthermore, such a technique may also be capable of investigating other types of thin films (e.g. hard coatings, semiconducting films, superconducting films, etc.).