Effect of photomask pattern shape for a junction counter-electrode on critical current uniformity and controllability in Nb/AlO/sub x//Nb junctions

The authors evaluated the effect of photomask pattern shape for a counter-electrode on critical current I/sub c/ uniformity and controllability in Nb/AlOx/Nb junctions. Circular, square, and 2 kinds of optical proximity correction (OPC) square patterns were used as the mask pattern shape. Although there was no difference in the I/sub c/ uniformity between square and OPC junctions, the OPC junctions exhibited smaller shrinkage in junction size than the square junction. In addition, the OPC junctions improved the chip-to-chip variation in the shrinkage. The circular junction exhibited the smallest variation in the shrinkage, and had an advantage in I/sub c/ uniformity for smaller than 1.0 /spl mu/m/sup 2/ junctions in comparison with the other junctions. The shrinkage of the circular junction was the largest of all the junctions. This paper describes the recommended choice of the photomask pattern shape for several Nb LSI technologies.