Influence of coating parameters on the structure and properties of Al 2O 3 layers reactively deposited by means of pulsed magnetron sputtering

Abstract

It has been shown already that pulsed reactive magnetron sputtering (PMS) allows to deposit crystalline, hard and transparent Al 2O 3 layers. In this paper, correlations between process parameters, structure and properties of these layers are investigated. The deposition of the layers took place on steel at substrate temperatures ( T s) of 290–770°C. The sputtering power was varied in the range of 11–17 kW, and the substrate bias was 50 V. With increasing substrate temperature and sputtering power, a phase transition takes place from amorphous Al 2O 3 via λ-Al 2O 3 into α-Al 2O 3. At the highest sputtering power, textured γ-Al 2O 3 occurs already at T s≈350°C. The formation of α-Al 2O 3 starts at 670°C, and practically pure α-Al 2O 3 is present at the highest substrate temperature. The substrate bias has a substantial influence on the ratio of the phase fractions of γ-Al 2O 3 and α-Al 2O 3. Linked with the formation of crystalline phases is an increases in hardness from 10 up to 22 GPa. In addition, a pronounced increase in residual stresses of the layers can be observed. Pulsed magnetron sputtering permits to coat substrate materials with hard, crystalline aluminum oxide that could not be treated up to now because the substrate temperatures were too high.