RESIDUAL-STRESS IN STABILIZED ZIRCONIA THIN-FILMS PREPARED BY RF MAGNETRON SPUTTERING

Calcia-stabilized zirconia thin films were deposited by r.f. magnetron sputtering onto 2 inch <111) silicon substrates. Three samples of cub ic phase, with thicknesses 0.36, 0.72 and 1.08 mu m were deposited und er the same operating conditions, and both thickness uniformity and su rface roughness were controlled accurately by profilometry. The consid erable residual stress held present in the samples was studied by two very different techniques: measurement of the substrate curvature by p rofilometry, and measurement of the thin film lattice strain by X-ray diffraction (XRD). The adopted XRD parallel beam geometry permitted al so study of the texture developed; the main orientation was such that the angle between [ Ill] directions of Si and CaO-ZrO2 was about 13 de grees, with a fraction of crystallites grown along [111]Si\[111]ZrO2. Residual stress values as high as 3 GPa were measured but, as is typic al of many highly textured physically vapour deposited films, the sin( 2) psi method gave different stress values along different crystallogr aphic directions and the trend of interplanar distances d(hkl) vs. sin (2) psi was not always linear. The main reason for this behaviour is t he anistropy of the thin him elastic constants, which has a strong eff ect particularly in highly textured materials. XRD data were evaluated following a recently proposed procedure which takes into account elas tic anisotropy and thin film preferred orientations. The residual stre ss measured by XRD methods was systematically higher than that obtaine d from curvature measurements: this difference is discussed with refer ence to the hypotheses of the two methods and the nature of the stress in the film/substrate composite system.