Reactive magnetron sputter deposition of (Ti,Cu)N nano-crystalline thin films: modeling of particle and energy flux toward the substrate

Abstract

Ternary (Ti,Cu)N thin films were deposited by reactive dc magnetron sputtering on Si (111), glass slide, quartz and potassium bromide (KBr) substrates in molecular nitrogen ambient. This work has provided insight into the effects of substrate temperature, nitrogen content and particle and energy flux toward the substrate on the characteristics of (Ti,Cu)N films. Structural analysis of the films was identified by the x-ray diffraction (XRD) technique. Crystalline quality and phase stability are strongly dependent on substrate temperature. Ti-accommodated Cu3N structure results in lattice constant expansion and (100) preferential orientation. The bonding environment in these films was obtained by Fourier transform infrared (FTIR) spectroscopy. The surface morphology and chemical composition of the films were studied by using a scanning electron microscope (SEM)/energy dispersive x-ray spectroscopy (EDX). The films were aggregated as spherical grains. The atomic titanium to copper (Ti : Cu) ratio of (Ti,Cu)N films was less than that of the original target. An optical study was performed by vis–near-IR transmittance spectroscopy. The film thickness, refractive index and extinction coefficient were extracted from the measured transmittance. The as-deposited (Ti,Cu)N films are direct semiconductors with bandgap energy in the range of 2.57–3.23 eV. Nitrogen richness acts as an acceptor center and injects holes into the valence band (excited semiconductor). The amount of N attracted by the films was calculated using a model based on chemical bonding and the solubility process. Energy and angular contributions of sputtering yield were extracted from the existing literature to obtain a prediction about the atomic Ti : Cu ratio. By means of transport and range of ions in matter (TRIM.SP) Monte-Carlo simulation, the particle reflection coefficient of reflected N-neutrals was calculated. The initial energy of reflected N-neutrals and the sputtered particle at the substrate were estimated using a simple binary collision model and distribution weighted average, respectively. Their final energy was evaluated by energy dissipation considerations during mass transport through the gas phase. The total energy flux at the substrate during sputter deposition was estimated in order to assess the surface temperature during film growth.