Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction

Measurements of residual stresses in textured thin films have always been problematic. In this article, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin(2)psi method. Instead of using the Bragg-Brentano (B-B) or Seemarm-Bohlin geometry, the proposed method utilizes an asymmetrical diffraction geometry for which the X-ray beam is incident at a grazing angle gamma to the sample surface, while the angle psi is the tilt angle of the sample surface as defined by the conventional sin(2)psi method. Basic equations involved in the X-ray residual stress analysis are described, along with exemplified experimental data. Analysis shows that, for an isotropic medium, strain measured using this grazing-incidence geometry assumes a linear relationship with the geometrical parameter cos(2)alphasin(2)psi, where the angle alpha is a constant and is defined as the Bragg angle at psi=0degrees, theta(o), minus the grazing incidence angle gamma, i.e. alpha = theta(o) - gamma. The grazing-incidence diffraction geometry effectively increases the irradiation volume from a thin-film specimen, thereby giving rise to higher intensity for high-angle Bragg peaks than the conventional B-B geometry. The proposed analysis has another advantage, in that the inhomogeneous sample casts little effect on the residual stress results when compared to the traditional sin(2)psi method. (C) 2002 Elsevier Science B.V. All rights reserved.