The role of hydride coverage in surface-limited thin-film growth of epitaxial silicon and germanium

Abstract

The connection between the hydride coverage and thin-film growth rate was investigated by a kinetic model consisting of the elementary reaction steps of source gas chemisorption and hydrogen desorption in silicon and germanium epitaxial thin-film growth from silanes and germanes. A generalized form of the model for steady-state conditions was used to extract the kinetic parameters of the elementary reaction steps from experimental film growth data in the literature. Three-dimensional plots of the growth rate as a function of the substrate temperature and the source gas flux were used to summarize the trends in steady-state surface-limited thin-film growth using the kinetic parameters extracted by the model. The three-dimensional plots show that: (1) each of the elementary reaction steps is dominantly dependent only on a single external growth parameter, and (2) in the transition region where neither of the elementary steps is clearly dominant the growth rates exhibit a complex dependence on the growth parameters. The kinetic parameters for the elementary reaction steps are found to be in good agreement with the values obtained by independent (nonfilm growth) surface studies. The insight gained by modeling the hydride coverage in thin-film growth led to development of digital epitaxy, an alternative growth method to atomic layer epitaxy of group IV materials. Digital epitaxy is accomplished through cyclic repetition of alternating chemisorption and hydrogen desorption stages.