Spectroscopic ellipsometric study of boron nitride thin films

Abstract

Thin films of boron nitride (BN) have the following interesting properties as a promising alternative to diamond in optical, electronic and mechanical applications: mechanical hardness (c-BN), low density, chemical inertness, high optical transparency, high thermal conductivity and high electrical resistivity. However, these attractive properties depend strongly on the deposition conditions.We present the optical characterization by spectroscopic (UV-visible) ellipsometry of thin BN films obtained under different conditions on c-Si and NiCr substrates. The deposition techniques were RF plasma enhanced chemical vapor deposition (PECVD) and RF magnetron sputtering. The PECVD films were obtained by glow discharge decomposition of a mixture of NH3 and B2H6 in a RF plasma reactor. The sputtered films were deposited from a h-BN target in an Ar + N2 RF discharge, varying the N2 concentration in the gas process from 35% to 90%. All the films were deposited at a substrate temperature of 300 °C.The ellipsometric measurements were carried out by spectroscopic ellipsometry in the UV-visible range (1.5–5.2 eV). A dispersive model for the complex refractive index was used to analyze the ellipsometric data. The sample structure (overlayer|film| interface|substrate) was determined using a multilayer model and the effective medium approximation. The results show that the films have very high transparency, a high refractive index (greater than 1.9) and obvious microstructural variations depending on the deposition conditions.