Growth anisotropy and self-shadowing: A model for the development of in-plane texture during polycrystalline thin-film growth

Abstract

The development of a preferred crystallographic orientation in the plane of growth, an in-plane texture, is addressed in a model that incorporates anisotropic growth rates of a material and self-shadowing. Most crystalline materials exhibit fast growth along certain crystallographic directions and slow growth along others. This crystallographic growth anisotropy, which may be due to differences in surface free energy and surface diffusion, leads to the evolution of specific grain shapes in a material. In addition, self-shadowing due to an obliquely incident deposition flux leads to a variation in in-plane grain growth rates, where the “fast” growth direction is normal to the plane defined by the substrate normal and the incident flux direction. This geometric growth anisotropy leads to the formation of elongated grains in the plane of growth. Neither growth anisotropy alone can explain the development of an in-plane texture during polycrystalline thin-film growth. However, whenever both are present (i.e., oblique incidence deposition of anisotropic materials), an in-plane texture will develop. Grains that have “fast” crystallographic growth directions aligned with the “fast” geometric growth direction overgrow grains that do not exhibit this alignment. Furthermore, the rate of texturing increases with the degree of each anisotropy. This model was used to simulate in-plane texturing during thin-film deposition. The simulation results are in excellent quantitative agreement with recent experimental results concerning the development of in-plane texture in sputter deposited Mo films.