Electron microscopy of interfaces in chemical vapour deposition diamond films on silicon

Abstract

Abstract The structure of interfaces in diamond films grown on Si(100) has been investigated by transmission electron microscopy for the early stages of microwave-assisted chemical vapour deposition. Using conditions optimized for achieving so-called highly-oriented diamond films the depositions were performed in two steps, a bias-enhanced nucleation step and a subsequent growth step. Characteristic for the early deposition stages is the self-organized formation of regular arrays of predominantly {111}-facetted Si substrate surface grooves and islands elongated along [110] and [110] directions. Subsequently, an interlayer of nanocrystalline β-silicon carbide islands forms, followed by the formation of epitaxially oriented diamond nanocrystals with high fractions of {111} interfaces. High-resolution electron microscopy of the interface regions depicts arrays of terminating {111} diamond planes at an average ratio of five diamond to four SiC lattice planes which corresponds to a remaining lattice mismatch of 2.3%. The orientation relationships between the lattices may be described by a coincidence site lattice model if the elastic lattice distortions are taken into account. Only small fractions of amorphous inclusions are present near interfaces, essentially consisting of amorphous carbon as could be deduced from analyses of the C K edge fine structure in electron energy loss spectra. The observations are compared with cases for which diamond nucleation directly on silicon has been obtained.