Stabilization of tetragonal ZrO2 by oxygen plasma treatment of sputtered ZrCu and ZrAl thin films

Abstract

The stabilization of tetragonal zirconium dioxide (zirconia) by doping at room temperature has already been carried out with dopant materials like Y or Mg. Also alternative dopants like Al and Cu have been investigated using reactive sputtering processes at elevated temperatures with oxygen as a reactive gas. In the present work we investigate if stabilization is possible by dopants like Al and Cu which are added by means of non-reactive sputtering in a dual cathode magnetron sputtering device. Because it is expected that the stabilization depends on the dopant concentration, the Zr coatings were produced with a dopant gradient. So it was possible to investigate many different compositions with only few samples. This dopant gradient could be produced with a modification of the substrate holder in the sputtering chamber where a small wall partially shadows the vapor beam of the dopant. After production of the metallic ZrAl and ZrCu samples, first their chemical composition was determined by energy dispersive X-ray spectroscopy in a scanning electron microscope. Then they were treated with oxygen plasma. Depth profiles were recorded by Auger electron spectroscopy to investigate the progress of the oxidation. For crystallographic analysis X-ray diffraction was used. The surface morphology was measured with an atomic force microscope.The results show that the stabilization worked successfully with Cu while for Al no formation of the tetragonal phase was observed and the films remained essentially amorphous. The results show that oxygen plasma treatment is a viable and fast way to transform doped metallic Zr films into tetragonal Zirconia.