THRESHOLDS FOR THE PHASE FORMATION OF CUBIC BORON NITRIDE THIN FILMS

We introduce a phase diagram for boron nitride film growth. It is based on studies of the influence of the ion energy and substrate temperature on the phase formation using mass-selected ion-beam deposition of ${\mathrm{B}}^{+}$ and ${\mathrm{N}}^{+}$ ions. For the formation of the cubic phase we find threshold values of 125 eV for the ion energy and 150 \ifmmode^\circ\else\textdegree\fi{}C for the substrate temperature. Furthermore, we find a characteristic ion energy and substrate temperature dependence of the compressive stress, yielding low stress values for high energies and/or temperatures. c-BN nucleation and growth is attributed to a subsurface process qualitatively described by the subplantation model.