Investigation of etching techniques for superconductive Nb/Al-Al/sub 2/O/sub 3//Nb fabrication processes

Wet etching, CF/sub 4/ and SF/sub 6/ reactive ion etching (RIE), RIE/wet hybrid etching, Cl-based RIE, ion milling and liftoff techniques have been investigated for use in superconductive Nb/Al-Al/sub 2/O/sub 3//Nb fabrication processes. High-quality superconductor-insulator junctions have been fabricated using a variety of these etching methods; however, each technique offers distinct tradeoffs for a given process an wafer design. In particular, it was shown that SF/sub 6/ provides an excellent RIE chemistry for low-voltage anisotropic etching of Nb with high selectivity to Al. The SF/sub 6/ tool has greatly improved the trilevel resist junction insulation process. Excellent repeatability, selectivity with respect to quartz, and submicron resolution make Cl/sub 2/+BCl/sub 3/+CHCl/sub 3/ RIE a very attractive process for trilayer patterning.<>