Structural investigation of the bias-enhanced nucleation and growth of diamond films by microwave plasma chemical vapor deposition

Transmission electron microscopy (TEM), transmission electron diffraction (TED), atomic force microscopy (AFM), and scanning electron microscopy have been used to investigate the initial nucleation process and growth behavior of diamond films by microwave plasma chemical vapor deposition. TED examination revealed epitaxial relations between the β-SiC and the Si, and the diamond and the β-SiC, which depended on the bias-enhanced nucleation (BEN) time and methane (CH₄) concentration. The highly oriented (001) diamond films were obtained after 25 min BEN for 4% CH₄ and 20 min BEN for 8% CH₄. TEM revealed the β-SiC crystallites 2-25 nm across and the diamond crystallites 3-40 nm in size which depended on the CH₄ concentration and the BEN time. As the BEN time increased, the density of the β-SiC cyrstallites increased from ∼2.7 × 10¹¹ to ∼3.4 × 10¹² cm², while that of the diamond crystallites varied from ∼2.0 × 10⁹ to ∼4.0 × 10¹⁰ cm^-2. Discrepancy between the densities obtained using TEM and AFM is discussed. It is shown that the heteroepitaxially oriented diamond crystallites are critically important for the growth of the highly (001)-oriented diamond films, although the heteroepitaxially oriented β-SiC crystallites could serve as nucleation sites for the growth of the diamond films.