Growth and characterisation of boron nitride thin films

Boron nitride layers were deposited using ion beam assisted deposition with different ion energies (0.5 or 1.5 keV) and normal angle of incidence on silicon wafers heated to 400 degrees C. By mounting the electron beam evaporator at an angle of 56 degrees to the normal of the substrate, it was possible to investigate the influence of the continuously changing ion-to-atom ratio on the grown modification and, subsequently, to determine the properties of the BN films. The coatings were characterised using polarised IR reflection spectroscopy, heavy ion elastic recoil detection and microhardness measurement (Vickers indenter). The dynamic hardness of the Si substrate could be almost doubled with an approximately 1000-Angstrom thick c-BN coating. The transition determined by IR spectroscopy from non-cubic to cubic growth could be clearly resolved across the 3-inch silicon substrate. As soon as the spectra recorded with p-polarised light exhibited the reflection band of the cubic phase at 1100 cm(-1), an additional feature appeared in the in-plane stretching h-BN mode near 1580 cm(-1). The two features of the h-BN LO band might be due to the layered growth of the BN system corresponding to two different dielectric constants of the h-BN layer near the interface and at the sp(2)-bonded grain boundaries of the c-BN-containing overlayer. Furthermore, coatings with a high cubic fraction exhibited a stoichiometric boron-to-nitrogen ratio with small oxygen and hydrogen contaminations.