MICROSTRUCTURE OF CUBIC BORON-NITRIDE THIN-FILMS GROWN BY ION-ASSISTED PULSED-LASER DEPOSITION

A microstructural study of boron nitride films grown by ion-assisted p ulsed laser deposition is presented. Fourier transform infrared spectr oscopy, electron-energy-loss spectroscopy, and electron-diffraction me asurements indicate that within the ion-irradiated region on the subst rate, the film consists of a high fraction of the cubic phase (cBN) wi th a small amount of the turbostratic phase; outside the irradiated re gion, only the turbostratic phase is detected. Conventional and high-r esolution electron microscopic observations show that the cBN is in th e form of twinned crystallites, up to 40 nm in diameter. Particulates, formed by the laser ablation process, reduce the yield of cBN in the irradiated regions by shadowing local areas from the ion beam. The fil ms exhibit a layered structure with an approximately 30-nm-thick layer of oriented turbostratic material forming initially at the silicon su bstrate followed by the cBN. The observations of oriented turbostratic material and twinned cBN crystallites are discussed in relation to a previously proposed compressive stress-induced mechanism for cBN synth esis by ion-assisted film deposition.