Study on resistivity size effect of ruthenium and molybdenum for the next-generation interconnect material

Abstract

the resistivity of copper thin film rapidly increases from 39nm due to the prominent effects of surface and grain boundary scattering, resulting in power consumption and RC delay of the semiconductor device. One of the possible solutions is to replace the interconnect material. Ru and Mo are receiving a high interest as candidate materials for next-generation interconnect, which is expected to be more conductive than copper. Here, we investigate the resistivity size effect of copper, ruthenium and molybdenum thin films to quantify and compare their resistivity at nanoscale. Experimental resistivity ρ vs d is explained by introducing the four independent resistivity factors, which are from bulk, surface, grain boundary and impurity scattering, in which the theoretical values of electron mean free path were utilized and the complete diffuse scattering (p=0) was assumed. As a result, for as-deposited Ru and Mo thin films deposited by sputtering, it was found that the resistivity increase by impurity had a great effect on the total resistivity. After the annealing process, the crystallinity and crystalline size of the thin film increased, and the total resistivity was greatly reduced. It was confirmed that the resistivity increase by grain boundary mainly affects to the total resistivity. Therefore, it is essential to develop a deposition method capable of producing a high-purity metal with large crystallinity and grains in order to fabricate a Ru and Mo interconnect with a resistivity lower than that of copper in the nanoscale.

Copper has been used in the semiconductor industry as an interconnect material thanks to its high conductivity and reliability. However, as the scaling of interconnect pitch progresses below 10nm, several limitations of copper are coming up. The most crucial issue is the increase of the resistivity