Surface growth mechanism of cubic boron nitride thin films prepared by plasma-enhanced chemical vapor deposition

Abstract

Chemical species in the low-pressure inductively coupled plasma for cubic boron nitride (cBN) film deposition using B2H6, N2, He and Ar as reactant gases were investigated by quadrupole mass spectrometry. B2H6 was found to be ionized totally, while N2 was only partially ionized. The species in plasma were Ar, He, N2 molecules and Ar+, He+, N+, N+2, B+, BxH+y, H+ and H+2 ions, no H and N radical was detected by appearance potential mass spectrometry. The introduction of H2 and N2 gases into the deposition system was found to produce a large mount of H radicals and excited N*2 molecules, which suppressed the cBN formation by reacting with the growth surface. The etching and sputtering of cBN and turbostraotic boron nitrde (tBN) by H2 and Ar plasmas were also evaluated, and we did not find that the tBN is selectively etched or sputtered. Moreover, high-resolution transmission electron microscopy of as-deposited cBN on the edge of ultrathin silicon flake substrate showed that the surface of as-deposited cBN film was composed of cBN {111} nanofacets, and no thin sp2-bonded boron nitride surface layer was observed. Our results suggest that cBN nucleates and then grows on the top surface in chemical vapor deposition systems, and the processes of cBN surface nucleation and growth in the present system was also discussed simply.