Ion-assisted sputter-deposition of superconducting NbN thin films on silicon

NbN is an attractive material for superconducting metallization of electronic devices due to its relatively high critical temperature of superconducting transition of 16 K. In this study, we demonstrate ion assisted reactive magnetron sputter deposition of superconducting NbN thin films directly on Si without the need for elevated deposition temperatures. The highest TC achieved is 13 K. Two key factors determining the low temperature behavior are identified. The film morphology, specifically the density, influences the room temperature electron transport and the residual resistivity ratio. The degree of microstructural disorder, described as the crystallite size or microstrain, determines the critical temperature. Partial ionization of the film forming species results in both densification and increased crystallite size with beneficial impact on the film performance.