Very small critical current spreads in Nb/Al-AlOx/Nb integrated circuits using low-temperature and low-stress ECR PECVD silicon oxide films

We have developed a new Nb/Al-AlOx/Nb IC process with very small critical current spread. Low-temperature and low-stress ECR (Electron Cyclotron Resonance) PECVD (Plasma Enhanced Chemical Vapor Deposition) silicon oxide films have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputtered silicon oxide. Since ECR PECVD silicon oxide films have superiority in quality over e-beam evaporated silicon monooxide films and extremely low damage to underlayers compared to sputtered films, our Nb/Al-AlOx/Nb IC quality and yield have been improved greatly. The critical current spreads (maximum to minimum) are less than 1%(/spl sigma/<0.2%) on chip and less than 4%(/spl sigma/<0.7%) cross a four-inch wafer for 5 /spl mu/m/spl times/5 /spl mu/m junctions. Even for high critical current density (/spl sim/10 kA/cm/sup 2/) small junctions (1.5 /spl mu/m x 1.5 /spl mu/m) the on-chip spread is only about 4%(/spl sigma/<0.7%). High quality Nb/Al-AlOx/Nb ICs have been fabricated and demonstrated.