Growth and characterization of cubic boron nitride thin films

Abstract

Boron nitride (BN) thin films have been grown on [100] oriented single crystal Si, diamond, Cu and Ni substrates by ion beam assisted deposition using electron beam evaporation of boron together with simultaneous bombardment by nitrogen and argon ions. Characterization by Fourier-transform infrared spectroscopy and high-resolution transmission electron microscopy showed that the films on Si and diamond consisted of initial noncubic (amorphous and hexagonal BN) layers, followed by the growth of cubic BN (c-BN). This growth sequence was attributed primarily to increasing compressive intrinsic stress with increased film thickness. Increasing the substrate temperature above 400 °C led to the onset of c-BN at a greater film thickness while increased ion flux resulted in earlier growth of this phase. These results may be explained by the relaxation of the intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300 °C) is required for nucleation and growth of single phase c-BN by this technique. It is believed that the interstitial Ar observed in Rutherford backscattering spectrometry studies is primarily responsible for the stress generation in the films. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.