High-rate reactive DC magnetron sputtering of oxide and nitride superlattice coatings

Abstract

Over the past 10 years, there have been three major advancements in reactive sputtering technology that now make it possible to deposit both conductive and non-conductive fully-dense films at high rates. These three advances are unbalanced magnetron sputtering, partial pressure control of the reactive gas, and pulsed dc power. Multicathode unbalanced magnetron sputtering systems provide a dense secondary plasma that is used for producing a well-adhered, fully dense film that is difficult to achieve with conventional magnetron sputtering. Online automatic partial pressure control of the reactive gas prevents the poisoning of the target surface during deposition, which leads to compound film deposition rates that approach or are equal to those for the pure metal rate. Pulsed dc power, where the polarity of the voltage on the sputtering target is alternately switched briefly between negative and positive, prevents arcing on the target surface during the deposition of nonconducting films. With both pulsed dc power and partial pressure control of the reactive gas, films such as aluminum oxide can now be deposited reactively at rates up to 78% of the pure metal rate. The reactive unbalanced magnetron sputtering process is used to deposit polycrystalline nitride superlattice films such as TiN/NbN or TiN/VN with hardnesses exceeding 50 GPa, which is more than double the hardness of either component in the multilayered film. The nitride superlattice work is being extended to oxide films, and initial results are encouraging. Nanometer scale, multilayer Al 2O 3/ZrO 2 and Y 2O 3/ZrO 2 films have been deposited at high rates. The Al 2O 3/ZrO 2 films are amorphous and optically clear, whereas the Y 2O 3/ZrO 2 films are crystalline as well as being optically clear.