Residual stress of aluminum thin films measured by X-ray and curvature methods

The residual stress in aluminum thin films sputtered on silicon substrates was measured by the X-ray diffraction method and the curvature method. Aluminum thin films have a fiber texture with a fiber axis of [111] direction perpendicular to the film surface. In the X-ray method, the residual stress in the films was determined from the strain measurements by using Al 222 and 311 diffractions. The residual stress of as-sputtered films was equi biaxial tension. The magnitude remained invariant with film thickness and was nearly equal to the value obtained by the curvature method. On the other hand, the residual stress measured by the two methods were different for the films annealed at temperatures above the sputtering temperature (423K). The stress value measured by the X-ray method decreased with annealing temperature; the value by the curvature method had a maximum for the case of annealing at 473K. Line broadening of X-ray diffraction profiles of as-sputtered films was found to increase with increasing thickness. Line broadening increased by annealing at temperatures above the sputtering temperature.