INITIAL GROWTH-PROCESS OF EPITAXIAL DIAMOND THIN-FILMS ON CBN SINGLE-CRYSTALS

The initial growth process of diamond thin films formed by dc plasma chemical vapor deposition on cubic boron nitride (cBN) surfaces of {111}B, {111}N and {100} has been investigated by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). On the {111}B surface, it is observed that the carbonaceous layer decorates the edge of the terrace, and the epitaxial islands of diamond grow in the decorated regions. Most of the islands grow laterally until their size exceeds about 100 nm across. On the other hand, on the {111}N surface, neither the formation of carbonaceous layer nor epitaxy of diamond has been observed. The difference in the manner of growth on these two surfaces is roughly explained when the strength relationships of the chemical bonds formed on the substrate surfaces are taken into account. On the {100} surface, the formation of a carbonaceous layer has also been observed, together with the formation of pyramidal diamond islands. The carbonaceous layer plays an important role in the epitaxial nucleation of diamond.