SUBMICROMETER PATTERNING OF YBA2CU3O7-X

Because no reactive ion etching process for the high T-c material YBa2 Cu3O7-x (YBCO) exists, it is difficult to get deep submicrometer patte rns with a single layer resist process. To solve this problem we used a multilayer masking technique. The mask is a carbon/titanium/PMMA tri layer and is structured using e-beam lithography and reactive ion etch ing (RIE). The YBCO is structured with A-ion beam etching (IBE) using the patterned carbon layer as a mask. An excellent etch selectivity wa s obtained for the complete process. For some applications it is neces sary to place short YBCO bridges across a grain boundary of a bicrysta l (Josephson junction). Because the electron beam can not detect the g rain 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 mu m long Josephson junctions created b y this structuring and etching procedures show excellent superconducti ng properties for widths down to 360 nm. At 77 K, no deviation of the critical current density or specific resistance of these Josephson jun ctions was observed.