Reactive ionized magnetron sputtering of crystalline alumina coatings

Ionized magnetron sputtering has been used to deposit alumina films containing orthorhombic κ-alumina at substrate temperatures as low as 320 °C. An inductively coupled Ar/O₂/Al radio frequency discharge was used to effectively ionize not only the Ar but, more importantly, also the Al and O₂. In this study it was shown that ion irradiation of stainless steel reduces the temperature of formation of crystalline alumina phases significantly. The ion energy influenced by the substrate bias potential has a strong influence on the phase composition of the deposited films. Monoclinic θ-alumina-containing films were obtained at substrate temperatures as low as 180 °C. Furthermore, it was found that if the substrate bias potential is raised to -90 V, the resulting film structure is amorphous.