Precise patterning technique for Nb junctions using optical proximity correction

In the fabrication process of Nb junctions, a precise and reliable lithography technique for a small junction area is needed to realize a wide-operating-margin circuit. We propose a patterning technique for micron or submicron Nb junctions using optical proximity correction (OPC). In the i-line optical lithography process, scattering bars and serifs are added to the photomask patterns for small junction area. Nb junctions ranging in size from 0.5-μm square to 2.0-μm square were successfully fabricated using this technique. For a square junction pattern, variations of junction critical current and shrinkage of the junction size are improved using OPC