Nanometer-Scale Stress Field Evaluation of Cu/ILD Structure by Cathodoluminescence Spectroscopy

Engineering of the residual stress fields related to the backend process of LSI devices with Cu interconnects is required together with the adoption of low-k materials that have quite low Young's modulus. We measured the nano-scale residual stresses stored within interlayer dielectric (ILD) films according to a cathodoluminescence (CL) piezo-spectroscopic technique. The SiO2 film (k = 4.1) produced a sharp and stable spectrum, which well suited for the analysis of stress distribution on the surface. We confirmed that stresses in ILD could be successfully detected with less than 50 nm spatial resolution and that a higher chemical mechanical polishing (CMP) downward pressure led to a shift toward the tensile side of the residual stress field stored in the ILD film. We also carried out line-scan analyses of a cross section as well as a surface of the sample. Furthermore, we performed thermal stress analyses by FEM and made a comparison with the CL results. The tensile stress peak neighboring a Cu line observed by CL spectroscopy showed the same tendency as with the thermal stress field calculated by the FEM.