Niobium and Aluminum Josephson Junctions Fabricated with a Damascene CMP Process

Paper in proceeding, 2012

We report on the fabrication of Josephson junction and superconducting bridges using a damascene CMP process applied for a first time to superconductors. The demonstrated industrial reliability of damascene CMP processes on large scale semiconductor circuits is a major incentive for our research that should allow large numbers of nanometric Josephson junctions to be fabricated in both Nb and Al, the two main material employed in superconducting quantum computing (qubit) and RSFQ electronics fabrication.We carried out a Chemical-Mechanical Polishing (CMP) process on Nb and Al films deposited on a SiO2 layer patterned with trenches of 100 to 300 nm of nominal depth. The process formed long bridges, 1 to 4 μm wide. The susceptibility and resistive transitions showed that CMP has no observable influence on superconductivity.We have also developed a hybrid technique that uses Al/Al2O3/Al shadow evaporation in the trenches before the damascene CMP process. This allows for high quality “in-situ” junction oxidation with the size reduction benefit provided by the damascene CMP process. We easily reach junctions sizes near 0.5 μm2 which are difficult to fabricate by other methods.We describe these techniques and report on measurements on large bridges and junctions and on the fabrication and measurements of Al and Nb nanobridges.