Reactive ion etching of Nb/A1O_x/Nb for Josephson technology

Abstract

We describe a process for defining and etching Nb/A1Ox/Nb Josephson junctions on 125 mm wafers using standard optical lithographic stencils and low pressure chlorine plasma in a single wafer reactive ion etching tool. The process exhibits selectivities to SiO2 in excess of 10:1 and can be tailored to produce niobium lines with either sloped or vertical profiles. During the etch, the chlorine plasma emission intensity is monitored, providing a distinct signature when etching through the thin AlOx layer and a sharp indication of endpoint as the underlying SiO2 is reached. The etch sequence is programmed to maintain the wafer temperature below 100°C at all times. This process has been used to fabricate a variety of Josephson devices using 2.0 μm groundrules and high quality Josephson junctions as small as 0.5 μm2 in area. In a variation on this process, using direct write electron-beam lithography, we have fabricated niobium features as small as 0.15 μm. © 1991.