FABRICATION OF HIGH-QUALITY, DEEP-SUBMICRON NB/ALOX/NB JOSEPHSON-JUNCTIONS USING CHEMICAL-MECHANICAL POLISHING

A reliable process based on Chemical Mechanical Polishing (CMP) has been developed for the fabrication of high quality, deep-submicron Nb/AlOx/Nb Josephson junctions on 2 inch wafers. The Nb counter electrode is defined using low pressure SF6 reactive ion etching (RIE) with a mask of SiO, which is thermally evaporated through a bilayer resist stencil patterned by electron beam lithography. After RIE, the entire wafer is coated with SiO, which is then planarized using CMP (which also removes the etch mask) to expose the counter electrode. This technique has produced high quality (V-m similar or equal to 60 mV for J(c) of 2 kA/cm(2)) junctions with areas as small as 0.003 mu m(2) demonstrating that the process does not degrade the junction quality. Junctions with critical currents of 22 mu A and areas of 0.006 mu m(2) have been fabricated from trilayers with J(c) > 300 kA/cm(2).