Residual stress and adhesion in ion-assisted hafnia coatings on glass*

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Abstract
Thin film mechanical properties are strongly influenced by the features of the employed deposition technique. Ion beam-assisted evaporation permits good control of the parameters involved in the process and offers several advantages in processing coatings with expected performance. In this paper, the generation of residual stresses depending on the ion bombardment conditions and their effect on the adhesion behaviour of hafnium dioxide IBAD thin films were investigated. Stresses, which were tensile or compressive depending on the momentum parameter RE1/2 values, where R is the ion-to-atom arrival ratio and E is the ion energy, were measured with a mechanical profilometer by the curvature change of the sample before and after the deposition. The scratch test technique was used to evaluate the adhesion failure load (Lc) of the HfO2 thin films and is correlated with the stress present in the samples themselves. The analysed samples showed an increase in critical load as the momentum parameter value increased. Moreover, the coating microstructure, which also depends on the deposition conditions, was analysed by X-ray diffraction in order to investigate the possible correlation of tensile or compressive stress with the two film structures for different values of the momentum parameter.