Diffraction stress analysis in fiber-textured TiN thin films grown by ion-beam sputtering: Application to (001) and mixed (001)+(111) texture

Abstract

The present study concerns the analysis by x-ray diffraction (XRD) of the residual stresses in fiber-textured TiN thin films grown by sputter deposition. We present an extension of the stress model of Kamminga et al. [J. Appl. Phys. 88, 6332 (2000)] to the case of sputtered thin films having a crystallographic growth texture. The state of stress is triaxial and includes an intrinsic hydrostatic component due to volumetric distortion in the growing layer caused by ion-bombardment-induced point defects, and a biaxial component imposed by the substrate on which the film adheres. Numerical illustration of the model is given for TiN films having a (001) or a mixed (001)+(111) growth texture. It is shown that in the presence of triaxial stresses, the dependence of the lattice parameter with sin2 ψ is still linear, but the stress-free lattice parameter a0 can no longer be determined from the classical strain-free direction. Nevertheless, a direct determination of a0 can be obtained graphically from the intersection of the sin2 ψ lines plotted for films with different hydrostatic stresses. When films exhibit a mixed texture, the sin2 ψ lines plotted for each subset of grains do not intersect exactly at a0. The present model is then used to analyze the XRD results of TiN fiber-textured thin films grown by a dual-ion-beam sputtering technique. The crystallite group method was used to measure the strain of crystallites having different specific fiber axis directions. The evolution of the microstructure, preferred orientation, and state of stress have been studied as a function of the film thickness, deposition temperature, and acceleration voltage Va of the Ar/N2 assistance beam. It is shown that the preferred orientation gradually changes from (001) to (111) as the thickness of the TiN films increases, with a crossover occurring between 150 and 200 nm. For films grown at T=25 °C, no significant changes in the orientational crossover or the state of stress were observed when Va was varied from 25 to 150 V. Stress analysis of TiN films having a mixed (001)+(111) texture indicates that (111) grains are more stressed than (002) ones. The present results suggest that the strain is not the dominant factor in controlling the development of preferred orientation in these films, the governing process being rather competitive growth.