Submicrometer patterning of YBa 2Cu 3O 7−x

Abstract

Because no reactive ion etching process for the high T c material YBa 2Cu 3O 7−x (YBCO) exists, it is difficult to get deep submicrometer patterns with a single layer resist process. To solve this problem we used a multilayer masking technique. The mask is a carbon/titanium/PMMA trilayer and is structured using e-beam lithography and reactive ion etching (RIE). The YBCO is structured with Ar ion beam etching (IBE) using the patterned carbon layer as a mask. An excellent etch selectivity was obtained for the complete process. For some applications it is necessary to place short YBCO bridges across a grain boundary of a bicrystal (Josephson junction). Because the electron beam can not detect the grain boundary, a procedure to align the e-beam pattern within about ± 250 nm with respect to the grain boundary has been developed and is presented in this paper. The 3 μm long Josephson junctions created by this structuring and etching procedures show excellent superconducting properties for widths down to 360 nm. At 77 K, no deviation of the critical current density or specific resistance of these Josephson junctions was observed.