Effect of thin film stress on the elastic strain energy of coherent Cr thin film on substrate has been calculated by applying Eshelby's inclusion theory taking into account both the anisotropy and inhomogeneity. The elastic strain energy is more significantly influenced by the magnitude of 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 has an effect to raise the elastic strain energy at all film orientations and causes for the (200)Cr orientation to have the smallest elastic strain energy at a sufficiently large compressive stress. This suggests a possibility that a coherent Cr thin film on substrate can exhibit a (200) texture due to a development of high thin film stress during an early period of sputter deposition. Concerning an incoherent Cr thin film on substrate, the elastic strain energy is mostly determined by that due to a 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 hundreds of 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 thin film during an early period of sputter deposition plays an important role in determining its texture.
The texture and stress of sputtered Cr thin films on Si substrates have been investigated for various deposition conditions. The measurement of stress variation with Ar pressure indicates that a maximum tensile stress occurs at an intermediate pressure. As the substrate temperature and bias increase, the stress of Cr thin film decreases and the texture of Cr thin film changes from (110) to (200). This result is in good agreement with the prediction of our calculation.
Variation of surface undulation of thin film on substrate has been simulated using Discrete Atom Method(DAM) as a function of the magnitude of coherent misfit. The results are in accord with the thermodynamic critical wavelength suggested by Srolovitz considering the total energy of thin film as the sum of surface energy and elastic strain energy. The larger the misfit, the shorter the wavelength of surface undulation. The waves of surface undulation was observed when misfit is larger than a critical value. The observation of surface undulation of Cr thin film using Atomic Force Microscope(AFM) indicated that its wavelength became shorter with the increase of the thin film stress. This suggests that the misfit between Cr thin film and Si substrate is so small that thin film stress becomes a dominating factor in determining the elastic strain energy of Cr thin film. A new DAM program was developed so that it can handle the stress problem in addition to the misfit problem. The result showed that the thin film stress exerts a similar effect on the surface undulation as the misfit does. Further development of DAM program has been explored so that one can simulate a bi-layer thin film problem. The result showed that thin film stress on top layer plays a more important role in determining the surface undulation.
