Other Applications and Summary

Abstract

Due to the similarities between allotropic pairs of diamond—graphite and cubic boron nitride—hexagonal boron nitride (cBN-hBN), the new kind of phase diagram can also be used for activated CVD cBN processes. Figures 9.1 and 9.2 are projective nonequilibrium phase diagrams calculated on the basis of our coupling model [9.1–9.3] for activated (by hot filament, plasma torch, and/or r.f. plasma, ...) cBN growth from BN-H-Cl and BN-H-F systems, respectively, in the range of total pressure p = 10−105 Pa and substrate temperature T = 1200−1500 K. There are three typical phase regions: (i) gas region or no deposition region, (ii) possible cBN growth region or cBN stable region (filled by oblique lines), and (iii) non-cBN deposition region (filled by net-like pattern). One must keep the total composition of the system inside the cBN stable region for growing cBN crystals or films. However, the possible cBN growth region is much narrower in comparison with the diamond growth region in the corresponding phase diagrams for the activated CVD diamond process. The possible cBN growth region seems to be a line in both Figs. 9.1 and 9.2, but it is really a region, as shown amplified in the small circles. That is perhaps the reason why cBN is much more difficult to prepare under low pressure, although activated CVD processes for cBN are very similar to those for diamond. For instance, the hot filament process has been used very easily and stably for the activated CVD diamond process, but a similar hot filament process must be enhanced by a simultaneous r.f. plasma or bias for cBN growth, as reported by F. Zhang, Z. Song, Y. Guo, G. Chen [9.4, 9.5].