A bilayer diffusion barrier of Ru/WSixNy for advanced Cu interconnects

Bilayers of Ru (7 nm)/WSixNy (8 nm) prepared by sputtering were investigated as diffusion barriers between Cu and Si for direct-platable Cu interconnects. Four different WSixNy films were prepared by using various N2/Ar flow rate ratios during sputtering of a WSi2.7 target. Sheet resistance measurements and X-ray diffractometry analysis showed that Ru/WSixNy bilayer diffusion barriers prevented Cu diffusion during 30 min of annealing at temperatures of up to 550-750 °C, while the Ru single layer of the same thickness (15 nm) failed after annealing at 400 °C by the formation of copper silicide due to the diffusion of Cu into Si. It was shown that the performances of bilayer diffusion barriers were improved as the nitrogen content in the WSixNy films was increased, which can be explained based on the results from transmission electron microscopy and X-ray photoelectron spectroscopy analysis of WSixNy films deposited with different N2/Ar flow rate ratios. From the results, the SiN and WN chemical bonds are strengthened as the N contents in the WSixNy films are increased by increasing the N2 flow rate during the deposition. The results indicate that the formation of both SiN and WN bonds will give an effective diffusion barrier against Cu diffusion.