Ion induced stress generation in arc-evaporated TiN films

Abstract

The influence of Ti ion bombardment on the intrinsic stress and microstructure of TiN films during deposition by arc evaporation of Ti in pure N2 has been investigated. Ions with an average charge of +1.6 were accelerated from the arc discharge by a negative substrate bias Vs between 5 and 540 V which yielded a steady-state substrate temperature between 300 and 600 °C, respectively. The compressive intrinsic stresses in the films, as determined by the x-ray-diffraction (XRD) sin2 ψ method after subtracting the thermal stress contribution at room temperature, changed abruptly from 1.9 to a maximum of 6.5 GPa as Vs increased from 5 to 100 V. The compressive stress then decreased monotonically to ∼1.6 GPa as Vs increased to 540 V. Broadening of XRD peaks (β) showed accompanying inhomogeneous strain with a maximum values for Vs=100 V. Cross-sectional transmission electron microscopy showed a dense columnar film microstructure. Electron microdiffraction showed a distorted structure within the same columns for Vs=100 V and better defined grains for Vs=500 V. The observed reduction in intrinsic stress with increasing Ti ion energy is in addition to what is normally observed in sputter-deposited TiN films with the same ion energy range of predominantly Ar-ion bombardment. A comparison with published work of magnetron sputtered TiN showed that defects created by Ti ions are more easily annihilated than defects created using Ar ions. Ar atoms tend to be strongly bound to lattice defects and forming thermally stable complexes and prevent stress relief at high Vs as is observed for arc-evaporated films. The obtained results are compared to models for stress generation during steady-state conditions in the competition between collisionally induced point defect formation and defect annihilation during deposition.