Effect of thin film stress on the elastic strain energy of Cr thin film on substrate

Abstract

The effect of thin film stress on the elastic strain energy of a coherent Cr thin film on a substrate has been calculated by applying Eshelby's inclusion theory taking into account both the anisotropy and inhomogenity. The elastic strain energy is more significantly influenced by the magnitude of the coherent misfit than by the film orientation, which explains why the (200) Cr texture can develop on the (200) MgO seed layer. The application of compressive stress to a film showing a positive dilatational misfit with a constant magnitude raises the elastic strain energy at all film orientations and causes the (200) Cr orientation to have the smallest elastic strain energy at a sufficiently large compressive stress. This suggests the possibility that a coherent Cr thin film on a substrate can exhibit a (200) texture due to the development of high thin film stress during the early period of sputter deposition. The elastic strain energy of an incoherent Cr thin film on a substrate is mostly determined by that due to the thin film stress itself and is always the smallest at the (200) Cr orientation, unlikely from the coherent thin film. Although this energy is normally negligibly small compared with the elastic strain energy due to a coherent misfit, it can nevertheless attain a critical energy range for a texture change from the (110) to (200) Cr at thin film stresses more than several hundred MPa. This explains why the (200) Cr texture is promoted over the (110) on amorphous NiP coating on applying either a mechanical texturing or a bias of negative voltage during sputter deposition. All of these analyses strongly suggest that the thin film stress developed in a thin film during the early period of sputter deposition plays an important role in determining its texture.