The design and modification of a sputter system for DC reactive sputtering of alumina and zirconia thin films

Abstract

Yttria-stabilized zirconia (7% YSZ) is the most used material for thermal barrier coatings (TBCs) to reduce the conductive heat transfer on turbine blades, but it is not resistant to infrared radiation. In order to reduce radiation heat transfer, alternating materials, such as alumina and zirconia, can be used to fabricate multi-layer coatings in which each layer is optimized to reflect a targeted range of wavelength. This research aims to fabricate these multi-layer coatings by reactive magnetron sputtering. Reactive magnetron sputtering is the sputtering of an elemental target in the presence of a reactive gas that will react with the target material to form a compound on the substrate. Although reactive magnetron sputtering has high deposition rate, a major disadvantage of reactive magnetron sputtering is target poisoning, which leads to very low deposition rates. In this research the flow control of reactive gas method has been used to complement the setup of the current sputtering system. First, pure aluminum and zirconium thin films are deposited and analyzed for film structure and properties. Then, alumina and zirconia thin films are reactively sputtered. The films are analyzed using XRD and SEM to determine the crystallography and surface structure. The XRD results of the metallic thin films for aluminum and zirconium shows the peaks corresponding to FCC and HCP crystal structure, respectively. The XRD results of the alumina and zirconia films do not contain any peaks, indicating an amorphous structure. XPS results give elemental compositions for the films from which the stoichiometry can be determined. The composition of the films is analyzed for before and after ion etching of the surface. The XPS results concluded that the films were under stoichiometric. More experiments need to be performed to determine the best ratio of inert and reactive gas in order to produce stoichiometric films. Modifying the current system could help to improve the quality of the films by utilizing a pulsed-DC power source, an arc suppression system, the partial pressure control of the reactive gas, and other instruments to properly measure the film properties.