Properties of cubic boron nitride thin films deposited by a hybrid RF-PLD-technique

In the hybrid RF-PLD-technique pulsed laser deposition is combined with an additional RF-discharge resulting in ion bombardment of the growing film due to DC-self-biasing of the substrate electrode. The DC-bins voltage is in the order of some hundreds of volts, leading to ion energies in the order of some hundreds of electron volts. The ion current to the substrate is typically in the order of 10 mu A/cm(2) as determined by the Langmuir probe technique. FTIR (Fourier transform infrared) spectroscopy reveals that the cubic phase is formed only in regions on the film surface where an ion-to-atom arrival ratio of about 0.5 is present. Maximum cubic boron nitride (c-BN) contents of about 60% have been achieved and a layered structure [hexagonal boron nitride (h-BN) interlayer between substrate and c-BN film] typical for c-BN film deposition, was observed. The films are nearly stoichiometric with little boron enrichment as determined by XPS analysis. Using pure argon discharges without any molecular nitrogen leads to boron-rich films and suppression of the cubic phase. High compressive stress is present in regions of c-BN formation. leading to partial delamination and cracking of the films. Micro-Raman analysis showed only peaks characteristic for h-BN, even in regions of c-BN growth, indicating that c-BN is nanocrystalline, which is confirmed by XRD measurements. (C) 1998 Elsevier Science S.A.