Measurement of Residual Stress Distribution in Sputtered Cu Thin Films by X-Ray Method

Three kinds of copper thin films were fabricated by RF-magnetron sputtering. The target power was selected to be 10 and 150W to change the properties of the films. Thin glass sheet was used as a substrate. For the target power of 150W, the deposition time was selected to be 7 and 40min. The thickness was 0.6μm and 2.9μm, and the grain size measured was 243nm and 450nm, respectively. The grain size of thicker film was larger than that of thinner one. On the other hand, for the target power of 10W, the thickness and grain size were 2.4μm and 54nm, respectively. The grain size depends on the target power, too. The residual stress distribution in the films was measured by X-ray method. Several methods such as the grazing incidence X-ray diffraction method, the constant penetration depth method and the conventional sin2ψ method were adopted. The measured weighted average stress increased with increasing depth. After taking the maximum value at about 0.3μm from the surface, the value decreased with increasing depth. The stress distribution near the surface in the films deposited at 150W was almost identical irrespective of thickness. On the other hand, for the target power of 10W, the stress distribution shifted to compression side. The reason could be explained by the effect of the thermal residual stress. The real stress distribution was estimated by using the optimization technique. The stress took the maximum value at 0.5μm from the surface, and was compressive near the substrate.