DIAMOND AND RELATED MATERIALS Cubic boron nitride (c-BN) was deposited on silicon substrates using electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) employing Ar–He–N2–H2–BF3 gas precursors at 780 °C. In situ X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM) measurements indicated that c-BN nucleated and grew on a hexagonal boron nitride (h-BN) layer that initially formed on the substrate. The minimum and maximum bias applied to the sample that yielded c-BN growth was investigated by in situ XPS. Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD), and XPS were employed to determine the chemical composition of the produced films, while XPS and in situ ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the electronic structure of film surfaces. The bandgap of the c-BN films was estimated to be 6.2 ± 0.2 eV from XPS measurements. In situ UPS measurements indicated that as-deposited c-BN films exhibited a negative electron affinity (NEA). The surface continued to exhibit an NEA after H2 plasma treatment performed at 650 °C and annealing at 780 °C. Analysis of surface bonding using a surface dipole model suggests that H-terminated N surface sites could be responsible for the observed NEA character.
Fig. 5. Transmission electron microscopy image of a c-BN film after 4 h of deposition. First, an h-BN layer grows on the top of the silicon substrate. After the h-BN layer reached approximately 40 nm in thickness, polycrystalline c-BN nucleated and grew on top of the h-BN layer. The polycrystalline c-BN layer was approximately 20 nm thick.