We proposed a novel process for improving cubic boron nitride (c-BN) film properties coated on Si substrates, using a magnetically enhanced plasma ion plating (MEP-IP) method. The method has two features: 1) To realize a stable anode current, the deposition of an insulating BN film on the anode electrode was controlled by adjusting the anode electrode temperature, and 2) a stable substrate current was generated by high-density Ar/N2 plasma with a stable anodic current to promote the reaction between N radicals and B atoms evaporated onto the substrate. To prevent the delamination of the c-BN film from the substrate, a structure of the c-BN/t-BN/a-BN/B/Ti/TiN/Ti/substrate was designed. It was found that the hardness defined by the Knoop indenter increased with an increase in the substrate voltage, and simultaneously the friction coefficient decreases. The electrical capacitance measurement revealed superior interface property for the BN/TiN/Si stack structure after air exposure (the permittivity of the stack structure is ∼13.8). We also confirmed the long-term stability of the c-BN film hardness to be 3000 to 4000 HK after a five-year exposure. These results confirmed that no delamination occurred in the c-BN structure fabricated by the present MEP-IP method.
The optical constants of boron nitride (BN) films on Si substrates were systematically investigated using spectroscopic ellipsometry. BN films with a wide variety of atomic compositions (B/N ratios) and bonding phases (sp2/sp3 ratios) were synthesized using a reactive plasma-assisted coating method, which consists of magnetically confined vacuum-arc discharge and electron-beam evaporation. A wide range of optical constants were assigned to various BN films via a model fitting procedure employing the Tauc–Lorentz optical model. The estimated film thicknesses corresponded with those determined using scanning electron microscopy. The optical constants of the films were found to be significantly dependent on their respective atomic compositions, which shows a transition from the semiconducting to the insulating phase in BN films in response to the deposition conditions. Ion bombardment during the film growth induced an increase in the refractive index along with an increase in the amount of the sp3 phase. Furthermore, the extinction coefficient increased substantially in the ultraviolet region in response to the generation of defects in the BN nano-network structures.
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