Nucleation and initial growth phase of diamond thin films on (100) silicon

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Abstract
The nucleation of diamond on silicon (100) in a methane-in-hydrogen microwave plasma has been investigated by atomic-force microscopy, scanning electron microscopy, and reflection high-energy electron diffraction (RHEED). The nucleation of diamond was performed by application of an electrical substrate potential. It was found that three-dimensional nonfacetted islands are initially formed whose sizes increase with the deposition time. In spite of their very small sizes of a few nanometers, RHEED reveals that the islands are of crystalline-diamond structure. An induction time of about 6.5 min was necessary for the diamond nucleation, which is partly caused by the formation of a silicon-carbide surface layer due to the carbon diffusion into the substrates. The time dependence of nucleation density was investigated and fitted with a model kinetics, which considers the formation, destruction, and capture of active sites, germs, and nuclei. Analyses of the first-nearest-neighbor distance distributions reveal the formation of a depletion zone of nuclei around the existing islands. These results confirm the role of the adatom diffusion improved by the bias-enhanced ion bombardment. Analyses of the island-size and the island-height distributions show constant growth rate at the beginning of the diamond deposition. From the nearly constant ratios of the island height to island size, independent of the nucleation time, one can deduce that the thermodynamics accounts not only for the growth mode, but also for the island shape during deposition. The bias-enhanced ion bombardment during deposition may also increase the diffusion of the surface atoms of the islands, allowing the system to approach equilibrium.