Growth of Topological Semimetal Cobalt Monosilicide for Scaled Back-End-of-Line Interconnects

The resistivity of conventional metal interconnects increases rapidly with decreasing size which causes high energy consumption with severe signal delay. Electron scattering at surfaces and grain boundaries are found to be the main causes of this size effect. Topological semimetals, which can effectively suppress electron scattering at surfaces, are believed to be promising candidates to replace currently used conventional metals. CoSi, a topological semimetal with multifold fermions, possesses unique topologically protected surface states that are expected to decrease resistivity at scaled dimensions where surface transport dominates.<br/>Here, we demonstrate the growth of CoSi thin films and single-crystal CoSi nanowires. CoSi thin film growth is achieved on c-plane sapphire and GaN substrates by MBE. Multiple characterization techniques including RHEED, HRXRD, and Raman microscopy are utilized for optimizing growth conditions and realizing single-phase CoSi thin film growth. CoSi nanowires are obtained by co-depositing Co and Si on HOPG substrates via MBE. By carefully controlling the Co flux and growth temperature, the CoSi nanowire dimensions and yield can be controlled and the single-crystal and single-phase nature of the CoSi nanowire are confirmed by TEM and EDX. We also demonstrate a new approach to transferring CoSi nanowires from the HOPG substrate to another carrier wafer by only introducing and freezing DI water. And four-probe devices were made on transferred nanowires via electron beam lithography for measuring the CoSi nanowire resistivity. We will discuss both the thin film and nanowire results, including the impact of in-plane texturing as well as the benefits of the nanowire synthesis. We will discuss resistivity vs. dimension and provide an outlook for using CoSi as scaled interconnects. This work was supported by IMPACT, a center in nCORE, a Semiconductor Research Corporation (SRC) program.