Correlation between structure and properties of reactively deposited Al 2O 3 coatings by pulsed magnetron sputtering

Abstract

It has already been shown that substrate temperature and plasma density have a pronounced influence on the formation of crystalline Al 2O 3 phases. This paper deals with the correlation between structure and properties of reactively sputtered Al 2O 3 layers. The layers were deposited at substrate temperatures between 300 and 800 °C. The structure was investigated by XRD and cross-section TEM. With increasing substrate temperature, a phase transition from amorphous into α Al 2O 3 via γ Al 2O 3 is observed. An enhancement of the plasma density shifts the formation of crystalline phases to lower substrate temperatures. It would appear that the growth of the crystalline layers starts with the formation of globulitic γ crystallites. With increasing layer thickness, columnar γ crystallites with a lateral grain size of about 60 to 100 nm and a pronounced (110) fiber texture occur. In addition, wedge-shaped α crystallites are present. With increasing layer thickness these α crystallites reach a lateral grain size of about 1μm. The SAD investigations indicate that a grain epitaxy between the γ and the α phase is present. The properties of the layers, e.g. hardness and chemical stability, depend strongly on the occurrence of crystalline phases.