Depth-sensitive strain analysis of a W/Ta/W trilayer

Abstract

The high-resolution x-ray diffraction technique was used to determine the entire strain tensor as a function of x-ray penetration depth in a 400 nm W/Ta/W trilayer, which consisted of 150 nm W, 100 nm Ta, and 150 nm W. The strain tensor was calculated in a laboratory reference frame to determine the variation of in-plane strains, εxx and εyy, and the normal strain εzz, as a function of x-ray penetration depth. Two different methods were then used to determine the strains εxx, εyy, and εzz in each layer of trilayer, and both indicated that the strain states in the W layers were the same, and that the strains εxx and εyy in the W and Ta layer were the same magnitude. The difference between the Ta and W arose with the normal strain, εzz, and was due to a Poisson contraction effect. The average residual stresses in the trilayer were determined with the HRXRD data, and also with sin2ψ and a substrate curvature technique, double-crystal diffraction topography. All three techniques indicated that the average biaxial stress in the trilayer was approximately 1.0 GPa.