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 wit h an additional RF-discharge resulting in ion bombardment of the growi ng 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 ene rgies 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 determ ined 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% hav e been achieved and a layered structure [hexagonal boron nitride (h-BN ) interlayer between substrate and c-BN film] typical for c-BN film de position, was observed. The films are nearly stoichiometric with littl e boron enrichment as determined by XPS analysis. Using pure argon dis charges without any molecular nitrogen leads to boron-rich films and s uppression of the cubic phase. High compressive stress is present in r egions of c-BN formation. leading to partial delamination and cracking of the films. Micro-Raman analysis showed only peaks characteristic f or h-BN, even in regions of c-BN growth, indicating that c-BN is nanoc rystalline, which is confirmed by XRD measurements. (C) 1998 Elsevier Science S.A.