Coalescence and overgrowth of diamond grains for improved heteroepitaxy on silicon (001)

Heteroepitaxial [001]-oriented diamond films with considerably increased lateral grain size and strongly improved orientational perfection could be prepared by microwave plasma-assisted chemical vapor deposition using a [001]-textured growth process on Si (001) substrates followed by a [110] step-flow growth process. The diamond films were characterized by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that the diamond crystals increase their lateral dimensions at the (001) film surface either by coalescence of grains combined with a termination of the propagation of grain boundaries or by changing the grain boundary plane orientations from preferentially vertical to preferentially parallel directions with respect to the (001) growth faces. In the second case, the grains with relatively large angle deviation from the ideal epitaxial orientation are overgrown by those with relatively small angle deviation. As a result, the degree of orientational perfection of the films improves considerably in comparison to that of films prepared by the established process of [001]-textured growth. The presence of boron in the gas phase was found to strongly enhance the step-flow lateral grain growth. It was possible to achieve deposition of a thin boron-doped diamond film characterized by a full width at half maximum value of the measured tilt angle distribution of only 2.1°.