Jörn-Steffen Liebig

Influence of process parameters on the structure and the properties of ZrO2 coatings deposited by reactive pulsed magnetron sputtering (PMS)

Abstract Thin ZrO2 layers in the thickness range between 100 and 150 nm were deposited by reactive pulsed magnetron sputtering (PMS). The influence of the sputtering Ar pressure and of the target to substrate distance on structure and properties of the films were investigated. The structure of the layers was determined by grazing angle XRD. At low sputtering pressure of 0.3 Pa, the low temperature stable monoclinic modification of ZrO2 is deposited, while at a sputtering pressure of 3.5 Pa, the high-temperature cubic phase of ZrO2 can be obtained. Atomic force microscopy investigations have shown that with higher sputtering pressures the roughness of the deposited layers is increased. The residual stresses were also drastically influenced by the sputtering pressure. In the layers deposited at low sputtering pressures of approximately 0.3 Pa very high compressive stresses of up to 1800 MPa are present. With further increase of sputtering pressure these high compressive residual film stresses were decreased down to low tensile stresses of approximately 150 MPa. After a storage time of 1 month in air only small changes in the film stress values were measured. The hardness and Youngs modulus of the layers were determined by nanoindentation techniques at an indentation depth of 20 nm. The results show that with increasing sputtering pressure the hardness and the Youngs modulus of the layers are decreased from approximately 12.3 to 6.2 GPa and from approximately 173 GPa to 150 GPa, respectively. The refractive index (at λ=550 nm) of the layer deposited at low sputtering pressure is 2.2. With increasing sputtering pressure the refractive index is shifted to 2.1. The thickness of a surface roughness layer calculated by effective medium approximation is increased with increasing sputtering pressure from 2.5 to 11.5 nm.