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 c urrent spread. Low-temperature and lour-stress ECR (Electron Cyclotron Reso nance) PECVD (Plasma Enhanced Chemical Vapor Deposition) silicon oxide film s have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputte red silicon oxide. Since ECR PECVD silicon oxide films have superiority in quality over e-beam evaporated silicon monooxide films and extremely low da mage to underiayers compared to sputtered films, our Nb/Al-AlOx/Nb IC quali ty and yield have been improved greatly. The critical current spreads (maxi mum to minimum) are less than 1% (sigma < 0.2%) on chip and less than 4% (s igma < 0.7%) cross a four-inch wafer for 5 mu\m x 5 mu m junctions. Even fo r high critical current density (similar to 10 kA/cm(2)) small junctions (1 .5 mu m x 1.5 mu m) the on-chip spead is only about 4% (sigma < 0.7%). High quality Nb/Al-AlOx/Nb ICs have been fabricated and demonstrated.