On the potential of tungsten as next-generation semiconductor interconnects

Abstract

The continuous scaling of copper (Cu) interconnects produced two major shortcomings–a severe resistivity size effect and material reliability issues. Tungsten (W), with the expected reduction in resistivity size effect due to its shorter electron mean free path and improved reliability due to its high activation energy for diffusion, is a worthwhile candidate to replace Cu. In this article, the potential of W for future interconnects is critically discussed by reviewing the current status of W technology, including various W processing methods and the resulting phases, resistivity and microstructure. The compatibility of W with the back-end-of-line processes in CMOS devices is also discussed. The resistivity of W and Cu wires at similar nanoscale is compared based on the Fuchs-Sondheimer surface scattering model and Mayadas-Shatzkes grain boundary scattering model using the reported scattering parameters (p = 0.11 and R = 0.42 for W, and p = 0.52 and R = 0.43 for Cu), which shows that the resistivity of W wires is predicted to exhibit lower resistivity than that of Cu wires at line-widths below ~15 nm. Finally, anisotropy in the resistivity size effect in W wires is discussed, with a suggested method to reduce wire resistivity.