Mechanisms of intrinsic stress generation in amorphous carbon thin films prepared by magnetron sputtering

Amorphous carbon (a-C) films have been deposited on biased silicon substrates at room temperature by conventional and unbalanced magnetron sputtering from a graphite target in pure argon discharges. The flux and energy of positive ions striking the surface of growing films were determined as functions of the substrate bias voltage by grid probe measurements. The flux of neutral carbon atoms condensed on Si substrates was deduced from Rutherford backscattering spectroscopy measurements. The mass density of a-C films, the argon concentration and intrinsic stress in these films were investigated as functions of the substrate bias voltage, i.e. the energy of positive ions impinging on the film surface. The similarity between the variations of the mass density and argon concentration as the substrate bias voltage was increased suggests that the increase in mass density was likely caused by the argon incorporation in the films. The intrinsic stress level was essentially dependent on the energy of positive ions striking the film surface. The experimental values of the intrinsic stress were compared with the values predicted by models of intrinsic stress generation in thin films reported in the literature. The good agreement between experimental and theoretical values of the intrinsic stress in a-C films sputter-deposited using conventional and unbalanced magnetron modes contributes to assess the validity of the model proposed by Davis. (C) 1997 Elsevier Science S.A.