Plasma-surface interactions in deposition of silicon thin films: An atomic-scale analysis

Hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon grown by plasma deposition through SiHu containing discharges are widely used in solar cells and thin film transistors for flat panel displays. Developing deposition strategies for improving film quality requires a better fundamental understanding of the radical-surface interaction mechanisms. Atomic-scale computer simulations of the deposition process allow for direct monitoring of kinetic phenomena that occur on the deposition surface on a nanoscopic scale and help elucidate reaction mechanisms that lead to film deposition, defect formation, and hydrogen incorporation. In this study, a systematic analysis is conducted of the interactions of chemically reactive radicals originating in the plasma with Si surfaces during plasma deposition from SiH ₄/H₂ discharges based on recently developed classical force fields and ab initio calculations. The theoretical results are compared with experimental data and are used to discuss additional experimental work in the literature.; Our simulation study employs a hierarchical approach that combines molecular-dynamics (MD) simulations for reaction identification and mechanistic understanding aided by molecular-statics (MS) and Monte Carlo (MC) simulations for sample preparation, surface characterization, and reaction analysis. Chemical reaction energetics is analyzed based on a conjugate gradient minimization scheme to quench MD-generated trajectories and construct the corresponding reaction paths. Description of interatomic interactions in the Si:H system is based on the Tersoff potential for silicon, as extended by Ohira and coworkers to account for the presence of hydrogen. In addition to analysis based on the above classical potential, the energetics of the radical-surface interactions at the initial stage of growth are verified through ab initio pseudopotential calculations employing cluster models within the framework of density-functional theory (DFT).; Surface interactions with isolated radicals during the initial stage of growth for each surface at submonolayer coverage are studied in detail to determine the surface chemical reactivity and its implications for the deposited film properties. The adsorption sites for the SiH_x (x = 1,2,3) radicals are identified on the pristine and H-terminated Si(001)-(2 x 1) surfaces: the energetics of adsorption determined by the classical potential agree well with our ab initio calculations. Also, the interactions of minority plasma species such as SinHm clusters with these surfaces are analyzed systematically. In addition, ultrafast rate deposition of a-Si:H from each of the SiH _x radicals has been simulated through MD by repeatedly impinging the corresponding radical onto H-terminated Si(001)-(2 x 1) surfaces. (Abstract shortened by UMI.)...