Nucleation and growth of cubic boron nitride films produced by ion-assisted pulsed laser deposition

摘要

We are studying the boron nitride system using a pulsed excimer laser to ablate from hexagonal BN (cBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25--800C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N(sub 2) source gases to produce BN films with a high percentage of sp(sup 3)-bonded cBN. In order to optimize growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp(sup 3)-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30--40 mn. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm(sup (minus)1) and the position decreases with growth time to a constant value of 1085 cm(sup (minus)1). Since in bulk cBN this IR mode appears at 1065 cm(sup (minus)1), a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.