Polycrystalline TiN films deposited by reactive bias magnetron sputtering: Effects of ion bombardment on resputtering rates, film composition, and microstructure

Abstract

Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used to investigate the effects of ion irradiation during growth on the deposition rate, composition, and microstructure of single-phase polycrystalline NaCl-structure TiNx films deposited by reactive magnetron sputtering with a negative substrate bias voltage Vs. The layers were deposited on thermally oxidized Si(001) substrates in mixed Ar+4% N2 discharges at a total pressure of 4.2 mTorr. Varying Vs between 0 and 1800 V resulted in incident ion-to-Ti atom flux ratios of 0.3 to 0.6 at the film growth surface and increases in the substrate temperature Ts (initially Ts=300 °C) of 40 to 200 °C. The Ti resputtering yield increased from ≤0.02 (Vs≤100 V) to 0.30 (Vs=1800 V) Ti atoms per incident ion (primarily Ar+), while the N/Ti ratio in as-deposited films increased from 1.03 for Vs=0 V to 1.12 for 100 V≤Vs≤400 V and then decreased to ≂0.95 as Vs was raised to 1800 V. Trapped Ar concentrations ranged from ≤0.5 at.% (Vs=0) to ≂5.5 at.% (Vs=1800 V). However, the Ar was not randomly dispersed in films grown with Vs≳1000 V and gas bubbles were observed. Film lattice parameters a0 were found to vary from the bulk value of 0.4240 nm at Vs=0 to a maximum of 0.4295 nm at Vs=800 V and then decrease to 0.4265 nm at Vs=1800 V. Voided grain boundaries were observed in films grown with Vs≤120 V. The use of higher substrate biases initially resulted densification of grain boundaries with a corresponding decrease in average grain size. However, with Vs≥800 V, the films again became less dense and increased intragranular defect densities were observed.