Kinetics and morphology of homoepitaxial diamond growth by chemical vapor deposition
Rawles, Robin E.
D'Evelyn, Mark P.
Doctor of Philosophy thesis
To address the relative lack of understanding concerning growth mechanisms for diamond chemical vapor deposition (CVD), this work explores kinetics of diamond epitaxy--growth on single-crystal substrates--and morphology of diamond surfaces--CVD films and natural and synthetic diamond after hydrogen plasma treatment. Optical Fizeau interferometry was implemented for in situ growth-rate measurements, providing a facile and sensitive means of systematically studying diamond growth kinetics. Fizeau interferometry was also used for non-contact temperature measurement of diamond single crystals, and the index of refraction variation with temperature was determined. Kinetics of diamond (100) homoepitaxy was investigated--in particular, the effects of oxygen on epitaxial growth and etching was studied, in conjunction with the nanometer-scale film morphology. Addition of oxygen to the hot-filament reactor had similar effects for growth conditions containing 0.5% or 1% methane in hydrogen. Growth rates at lower temperatures increased relative to samples grown without oxygen, proceeded through a maximum, and then decreased until etching was observed at high temperatures. Increased etching of diamond and non-diamond carbon was also observed for hydrogen with oxygen than for hydrogen alone. Oxygen addition improved the crystallinity of CVD diamond films deposited on silicon, as characterized by scanning electron microscopy (SEM). Without oxygen such films had polycrystalline features with relatively smooth (100) and rather rough (111) facets--with oxygen these films had both smooth (100) and (111) facets. Growth rates for diamond (100) and (111), with and without oxygen, were measured simultaneously using in situ Fizeau interferometry. The ratio of the two growth rates was then correlated with the nanometer-scale morphology, characterized by atomic force microscopy (AFM). Oxygen addition affected the (100) growth rate only; (100) epilayers were smooth for growth without oxygen but contained defects and penetration twins for growth with oxygen. The (111) epilayers from growth with and without oxygen were highly defective. Single-crystal diamonds, with and without CVD epilayers, and natural and synthetic diamond powders were treated in hydrogen plasmas, and examined by AFM and SEM. Evidence for a possible role of diffusion of surface species during diamond growth was observed.
Physical chemistry; Engineering; Materials science