Thermal annealing of RF sputtered NbN

The effects of thermal annealing on RF sputtered NbCN films and completed NbN-based tunnel junctions has been investigated. The starting films were RF sputtered at temperatures from 150°C to 650°. After a vacuum anneal at 600°C for six hours the transition temperature reached a maximum of 14.6K and depended only on the carbon concentration, for those films deposited at 200°C and 400°C. Vacuum annealing for one hour at temperatures of 900°C or more caused the formation of additional phases. Rapid thermal annealing, RTA, at temperatures from 600°C to 1200°C for times from one to 100 sec resulted in increased Tcwith increased annealing temperature. The maximum Tcproduced by RTA was 16.6K. The lattice parameter of annealed δ -phase NbCN was decreased toward the accepted value of 4.41 Å. Resistivity of the annealed films decreased except when the films cracked during annealing. RTA for 10 sec at 750°C of a completed NbN/Si/NbN edge junction increased the electrode gaps but for NbN/Si/Nb planar junctions the sum gap decreased. Microshorts also appeared in both types of junctions after annealing.