Problems in homoepitaxial growth of diamonds using CVD method and ways to solve them

The CVD technology of homoepitaxial growth of single-crystal diamond has experienced significant difficulties for more than a decade. Long-term morphologically stable epitaxy of the crystal is not possible: as the crystal grows, a surface relief develops; over time, polycrystals inevitably appear on the growth surface, a polycrystalline ‘rim’ grows on the edges, and structural perfection of the material is not achieved. Productive epitaxy on the $\{111\}$ faces is impossible due to unavoidable twinning. Considered an achievement is the growth of 1–2 mm of epitaxial material in a single session on a well-prepared facet vicinal to (001). To obtain significant growth of a crystal, it is necessary to periodically extract it from the reactor, trim the polycrystalline rim along the perimeter, and re-polish the growth surface for a new growth session. The brilliant prospects of using CVD diamond are still very poorly realized. These problems urgently require a solution. It is now clear that the structural perfection of the material is inextricably linked with the achievement of morphologically stable epitaxial growth. To analyze the mechanism of growth of single-crystal diamond using the CVD method, a model of layered growth was used. It provided a description of such key components of the growth surface as sources of layered growth and a stairway of growth ledges. The morphological instability of layered growth is mainly due to (a) positive feedback related to the action of a boundary diffusion layer with a large concentration gradient of growth radicals and (b) the Ehrlich–Schwoebel barrier for the movement of adatoms over the growth step edge. Morphological instability of homoepitaxial diamond growth primarily manifests itself in the grouping of steps (with the formation of macrosteps), meandering of steps, emergence of hillocks and mounds, and formation of depressions. These destructive phenomena have been shown to arise and develop during epitaxy on the faces close to $\{100\}$. The development of the growth surface relief inevitably leads to the appearance of twins on it, i.e., to the breakdown of epitaxy. Diagnosing mechanisms of morphological instability of diamond epitaxy by means of the CVD method made it possible to suggest ways to eliminate it. They include: (a) the creation of controlled sources of layered growth; (b) the preparation of a growth ledge stairway by correct polishing of growth faces; (c) the choice of the optimal vicinal angle of growth surfaces; and (d) the selection of supersaturation conditions for morphologically stable operation of layered growth sources and the development of growth layers.