Ion-surface interactions and limits to silicon epitaxy at low temperatures

Citation

Murty, M. V. Ramana (1995) Ion-surface interactions and limits to silicon epitaxy at low temperatures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1vkn-xh33. https://resolver.caltech.edu/CaltechETD:etd-10262007-111208

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Low temperature (T [...] 400°C) deposition of Si on Si(001) proceeds epitaxially up to a finite thickness followed by a crystal-state-amorphous-state transition. An atomistic model, the twin-boundary/facet (TBF) mechanism, has been proposed for this transition. The increase in surface roughness during film growth has been directly tied to the breakdown of epitaxy. The mechanism involves the nucleation of a twin boundary on a {111} facet (produced by roughening). When the twinned region meets a different part of the perfect crystal, it inevitably leads to the formation of five- and seven-member rings. These act as nucleation sites for amorphous silicon. Adsorbates such as carbon and oxygen can dramatically increase the surface roughness even at small coverages ([...] 0.01 ML). They thus play an indirect role by accelerating the surface roughening rate. Films with improved crystalline quality were deposited by ion beam-assisted molecular beam epitaxy. Atomic force microscopy revealed that the main effect of low energy [...] ion irradiation was surface smoothing. Molecular dynamics simulations suggest that epitaxy on hydrogen-terminated silicon surfaces (at high hydrogen coverage) proceeds by subplantation of the incident Si atom and segregation of [...] units. The remarkable success of sputter deposition in growing epitaxial films on a dihydride-terminated Si(001) surface is explained by the very rapid rise in the subplantation probability with the incident Si atom energy. An empirical interatomic potential has been developed to describe Si-H interactions. This can be used, with caution, for classical molecular dynamics investigations of hydrogen-terminated silicon surfaces, chemical vapor deposition of silicon and hydrogenated amorphous silicon. A technique for low temperature Si(001)-2x1 substrate preparation was developed to complement the various low temperature processes that are being developed for device fabrication. This was achieved by low energy noble gas ion ([...] or [...]) irradiation of a nominally dihydride-terminated Si(001)-1x1 surface. Reconstructed Si(001)-2x1 surfaces were prepared at temperatures as low as 100°C. Silicon films deposited on such surfaces were epitaxial.

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