DEPOSITION OF CUBIC BORON-NITRIDE THIN-FILMS BY ION-BEAM-ENHANCED DEPOSITION

Boron nitride (BN) films were deposited on single-crystal silicon by ion-beam-enhanced deposition (IBED). A sputter-deposited film was produced by ion-beam sputtering of a boron target with a 1 kV, 100 mA argon ion beam, and an ion-beam mixture of nitrogen and argon was used to bombard concurrently the growing film. BN phases in the deposited films were investigated as a function of the bombarding ion energy (Ei) and current density (Ji). Ei and Ji, which were in the range 300-1200 eV and 40-200 μA cm-2 respectively, were controlled independently. The boron deposition rate was held constant at 2000 Å h-1. The characterization of the films was performed by Fourier transform IR (FT-IR) spectroscopy, transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). The concurrent bombardment of the ion beam has a strong influence on the formation of cubic BN (c-BN). Mainly single-phase c-BN is formed within a certain range of Ei and Ji. Critical minimum values of Ei and Ji (Ec and Jc) exist for the formation of c-BN between 300 and 400 eV and 60 and 80 μA cm-2 respectively. With an increase in Ei, the deposited films change from sp2-bonded BN (possibly turbostratic hexagonal BN (t-BN)) to c-BN. A sudden change is also observed in the dependence of the BN phase on Ji. It is concluded that Ec is the threshold energy for the formation of c-BN in the thermal spike induced by the bombarding ion. The dependence of the nitrogen to boron ratio on Ji suggests that a stoichiometric nitrogen content is necessary for the formation of c-BN and Jc corresponds to the critical nitrogen flux. At the maximum values of the Ei range, deposition of a mixture of c-BN and sp2-bonded BN takes place due to radiation damage by the bombarding ions. At the maximum values of the Ji range, net film deposition does not occur and the substrate is sputtered by the ion beam. © 1992.