RADIO-FREQUENCY ION PLATING-INDUCED PHASE-TRANSITION FROM H-BN TO NANOCRYSTALLINE C-BN

Boron nitride thin films were deposited by unbalanced r.f. magnetron sputtering from a hexagonal boron nitride (h-BN) target and by r.f. ion plating at low gas pressures. The content of cubic boron nitride (c-BN) is determined by IR spectroscopy to be higher than 90%. The grain size derived from X-ray diffraction (XRD) is in the region of 5 nm. Furthermore, the films are characterized by Auger electron spectroscopy (AES) and stress measurements. The deposition of the cubic phase is only possible in a small range of boron to nitrogen ratio (0.9 < B/N < 1.1). The film-forming particles (flux Phi(n)) are mainly neutral boron and nitrogen atoms with typical sputtering energies of a few electronvolts, and the plating particles (flux Phi(i)) are argon and krypton ions with a well defined energy up to 140 eV. The current density is more than 2 mA cm(-2), as determined from energy and mass analysis. The arrival ratio Phi(i)/Phi(n) is approximately 20. The high ion current density causes a substrate temperature of about 510 K, and external substrate heating allows us to raise the temperature to 800 K. The c-BN formation depends mostly on the r.f. substrate bias and slightly on the substrate temperature and the rare gas masses. The results are compared with TRIM calculations. The film properties are discussed on the basis of the subplantation model.