Surface sulfurization of liner and ruthenium metallization to reduce interface scattering for Low-Resistance interconnect

Abstract

Ruthenium with a low resistivity, high melting temperature and short electron mean free path has been considered to replace copper as the next-generation interconnect metallization. However, its ascending resistivity with linewidth scaling because of the diffuse scattering of electrons at the interface with dielectrics or liners is a concern. Thus, in this study, sulfurization was applied on the surface of titanium-tantalum nitride and ruthenium films to form an ultrathin sulfide layer to reduce interface scattering. The microstructure, chemical composition, bonding configuration, and stability of the layer were characterized, and the resistivity scaling of the ruthenium films was examined. Microscopic observations suggested a crystalline TiTaSx layer formed on the titanium-tantalum nitride films while RuS2 formed on the ruthenium films, both of which changed the binding state/energy of the metals. With the surface sulfurization, the interface scattering of electrons for the ruthenium films was effectively reduced to elevate the specularity parameter from 0.2 to 0.9 and lessen the resistivity scaling for at least 40 % at a thickness of below 10 nm, without a marked loss of interfacial adhesion. However, an increase in contact resistance of molybdenum to the surface-sulfurized ruthenium films needs to be considered.