X-Ray Measurement of Residual Stress in Patterned Aluminum Thin Films Sputtered on Silicon Wafers.

Abstract

A new method of X-ray stress measurement was proposed for measuring the triaxial residual stress in thin films of cubic polycrystals having the[111]fiber texture with the fiber axis perpendicular to the film surface. The elastic deformation of poly crystals is assumed to follow Reuss or Voigt models. The method was applied to measure the residual stress in patterned aluminum(Al) thin films sputtered on silicon single crystal wafers. The strain was measured from Al 222 and 311 diffractions obtained by Cr-Kα radiation. The values of in-plane residual stresses σ11 σ22 and σ12 and out-of-plane normal residual stress, σ33 were determined from the measured strains by using the fundamental formulae derived on the basis of Reuss and Voigt models. The residual stress in unpatterned thin films was equi-biaxial tension and the magnitude did not vary with the film thickness. The residual stress in patterned thin films was tensile, and its magnitude decreased with increasing ratio of line thickness to line width. The residual stress perpendicular to the line pattern was smaller than the parallel stress.