Highly selective argon–oxygen ion beam etching process for Pb alloys

Abstract

We report an ion-beam subtractive etch process for patterning the Pb-alloy counter electrode of superconducting Josephson tunnel junction devices. There is no resist on the wafer during the critical steps of cleaning and oxidizing the Nb base electrode to form the tunnel barrier, in contrast to the usual case of lift-off patterning. To remove the undesired PbAuIn, we use a 500-eV argon beam with 5%–10% oxygen, which etches Pb alloy about ten times faster than the underlying SiO and Nb. In contrast, a pure argon beam gives a selectivity of only ∼2 against SiO. The added oxygen enhances the selectivity for etching PbAuIn by decreasing the etch rate of materials which are more readily oxidized.