Copper Encapsulated Ultra-Thin NbN Films and Damascene Structures on 300 mm Si Wafers

In this report, the development of reactively sputtered ultra-thin niobium nitride (NbN) films and their fabrication into patterned structures using 193 nm optical lithography on 300 mm scale is presented. The target composition of NbN film with Cu encapsulation showed a critical temperature ( T_c ) of ∼9.5 K (at a thickness of ∼50 nm), with <7% across-wafer variation in room temperature sheet resistance. Using this film composition, damascene structures of 3–20 nm NbN film thickness and 100–3000 nm width, encapsulated by copper, were fabricated on 300 mm Si wafer. These were measured to determine the dependence of the critical current ( I_c ) as a function of film thickness. The variation of T_c of copper encapsulated NbN as a function of Nb to N ratio, and position on the wafer is reported, along with the variation of T_c and I_c as a function of linewidth. These results underscore the potential of ultra-thin NbN films deposited over a large area, for a broad range of applications in quantum computing, photon detection and superconducting circuits operating at GHz frequencies.