Spectroscopic ellipsometry characterization of boron nitride films synthesized by a reactive plasma-assisted coating 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.