Evolution of microstructure and residual stress in sputtered chromium and chromium(x) nitrogen(y) thin films.

Abstract

This dissertation examines several fundamental aspects of sputtered films, including chemistry, structure, texture, residual stress and growth morphology. The systems considered are Cr films, C_xN_y films and Ta films. In the first system, the studies focus on some of the unique microstructural features of Cr films. These films develop well-organized anisotropic microstructures and <italic>in-plane</italic> texture. A texture turnover with thickness has been revealed. The <italic>out-of-plane</italic> preferred orientation changes from [110] to [111], and conformally, the <italic>in-plane</italic> preferred orientations vary as well. A new methodology has been developed, in which an anisotropic <italic>in-plane</italic> stress distribution in a thin film can be determined. This approach has been applied to the Cr films. The anisotropic stresses in these films are related to the evolution of anisotropic microstructure and <italic>in-plane</italic> texture. The studies of reactively sputtered Cr_xN_y thin films concentrate on phase formation, microstructure, texture, residual stress and growth morphology. It has been shown that these characteristics are predominantly affected by nitrogen flows. The phases identified in the films include Cr, hexagonal Cr₂N, and cubic Cr_xN_y, depending on deposition conditions. The composition of the cubic phase exhibits a wide homogeneity span as indicated by large variations of its lattice parameter. At certain nitrogen flow, a nano-crystalline, N-deficient Cr_xN_y film can be obtained. The Cr_xN_y films deposited at high nitrogen flows develop both <italic>out-of-plane</italic> texture and <italic>in-plane</italic> texture. In these films, the elongated grains align crystallographically, forming well-defined microstructures. A new experimental apparatus, which utilizes white beam transmission Laue topography and concomitant radiography, has been developed and applied to study cracking/delamination of thin films. Using the systems, the sputtered Ta and CrN films have been studied, and their failures are related to different types of stress development, respectively. This work has demonstrated for the first time that <italic>in situ</italic> observation via x-ray topography/radiography is a useful means for observing stress induced film failures of different modes in a real time fashion.