Evolution of surface roughness and texture during low-temperature film deposition.

Abstract

Low temperature film growth involves a competition between the energetics and kinetics of atom motion. Energetics determine the lowest energy (equilibrium) sites for atom attachment to the growing layer. Kinetics dictate the rate and manner of atom motion. At low temperatures, kinetics typically limit atom mobility and prevent the system from reaching equilibrium. Nevertheless, microstructures are often characterized by metastable growth shapes (i.e. facets, grain shape anisotropies). This dissertation addresses how growth shapes influence microstructural evolution in Si limited thickness epitaxy (LTE) and texturing of Mo films. Specific goals included, developing a methodology to measure surface roughening in-situ, determining the role of surface topography and roughness in Si LTE, identifying the correct model for Si LTE, identifying the parameters which control texture evolution, determining how in-plane texture scales with film thickness, and developing a model to explain in-plane texturing. These goals are addressed sequentially in the dissertation. Reflection high energy electron diffraction and transmission electron microscopy (TEM) analyses of surface roughening were used to investigate Si (100) LTE. Si LTE was characterized by a saturation roughness ($\rm E\sb{act} -0.31\ \pm\ 0.1$ eV) near the crystalline/amorphous transition, and the formation of critically-sized Si $\{111\}$ facets. Growth on these facets results in nucleation of amorphous Si. On high-indexed Si $\{hkl\}$ surfaces (investigated using a CoSi$\sb2$ template technique) pre-existing Si $\{111\}$ facets accelerated the transition to amorphous growth. It is concluded that all Si LTE phenomena involve growth on critically-sized Si $\{111\}$ facets. Texturing during Mo film growth was investigated with TEM, x-ray pole figures and grazing incidence x-ray scattering. Experiments revealed that in-plane texturing is a competitive grain growth process which requires an obliquely incident flux and anisotropic Mo grain shapes. In the texturing model, self-shadowing results in anisotropic in-plane growth rates from obliquely incident fluxes. Anisotropic surface free energy and diffusion cause faceted elongated Mo grains to form. It is shown that both the self-shadowing and grain shape anisotropies are required for an in-plane texture to evolve. In conclusion, both Si LTE and Mo texturing are linked to specific features in the growth shapes: stable $\{111\}$ facets in Si, and elongated faceted grain shapes in Mo.