COALESCENCE AND OVERGROWTH OF DIAMOND GRAINS FOR IMPROVED HETEROEPITAXY ON SILICON(001)

Heteroepitaxial [001]-oriented diamond films with considerably increas ed lateral grain size and strongly improved orientational perfection c ould be prepared by microwave plasma-assisted chemical vapor depositio n using a [001]-textured growth process on Si (001) substrates followe d by a [110] step-flow growth process. The diamond films were characte rized by atomic force microscopy, scanning electron microscopy, and tr ansmission electron microscopy. The results indicate that the diamond crystals increase their lateral dimensions at the (001) film surface e ither by coalescence of grains combined with a termination of the prop agation of grain boundaries or by changing the grain boundary plane or ientations from preferentially vertical to preferentially parallel dir ections with respect to the (001) growth faces. In the second case, th e grains with relatively large angle deviation from the ideal epitaxia l orientation are overgrown by those with relatively small angle devia tion. As a result, the degree of orientational. perfection of the film s improves considerably in comparison to that of films prepared by the established process of [001]-textured growth. The presence of boron i n the gas phase was found to strongly enhance the step-flow lateral gr ain growth. It was possible to achieve deposition of a thin boron-dope d diamond film characterized by a full width at half maximum value of the measured tilt angle distribution of only 2.1 degrees. (C) 1998 Ame rican Institute of Physics.