Understanding radical-surface interactions in plasma deposition of silicon thin films through atomistic simulations

Hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) thin films are widely used in large area electronic devices such as solar cells and flat-panel displays. These thin films are grown by plasma deposition from silane-hydrogen (SiH₄/H₂) discharges. A variety of reactive species from the plasma impinge on the deposition surface during film growth. Understanding the resulting physicochemical surface processes is crucial for controlling the film's structural and electronic properties. In this dissertation, an integrated atomic-scale computational analysis of the fundamental interactions of the radicals (SiH_x, x = 1–3) and H atoms with a-Si:H deposition surfaces is presented. This approach combines molecular-dynamics (MD), molecular-statics, and Monte Carlo simulations with quantum mechanical density-functional-theory calculations of surface reaction energetics. The a-Si:H deposition process is modeled through MD simulations on initial H-terminated crystalline Si substrate surfaces through repeated impingement of individual radical precursors. Surface chemical reactions during film growth, as well as the evolution of the films' structure, surface morphology and roughness, surface reactivity, and surface composition and their roles in governing film properties is discussed.; While amorphous silicon is commonly used, nanocrystalline silicon exhibits superior properties such as higher electron mobilities. nc-Si:H films are deposited when SiH₄ discharges are heavily diluted with H ₂, or when as-deposited a-Si:H films are exposed to an H₂ plasma. Though it is well known that H atoms from the plasma play an important role in nc-Si:H deposition, the fundamental atomic-scale mechanism has remained a puzzle. The atomic-scale mechanism of H-induced crystallization of a-Si:H analyzed through MD simulations of H atom interactions with a-Si:H films is discussed in detail through various structural characterizations and detailed analysis. Experimental measurements of the surface silicon hydride composition based on in situ infrared spectroscopy and results from atomistic simulations are synergistically used to understand the thin film deposition process.