An improved etching process used for the fabrication of submicron Nb/AlOx/Nb Josephson junctions

摘要

It is important to develop a reliable and reproducible fabrication process of submicron Nb/AlOx/Nb Josephson junctions to improve the integration level and the operating speed of the Josephson LSI circuit. For this purpose, we have developed an improved etching process by introducing a dummy etching process and using a scanning electron microscope (SEM) as an etching end-point detector. The dummy etching process improves the anisotropy of a reactive ion etching (RIE) process using CF4. The etching residue around a junction is detected easily and correctly by the SEM observation. We have successfully fabricated Nb/AlOx/Nb Josephson junctions with critical current density of 104 A/cm2 using the cross-line patterning (CLIP) method and electron beam lithography, where the junction size was varied from 2 μm to 0.5 μm at 0.1 μm intervals. High-quality submicron junctions for integrated circuits with suitable critical current variations were obtained.