Resist-free fabrication of Josephson junctions using stencil lithography

Organic residues remaining after fabrication are a source of qubit decoherence in superconducting quantum processors. Post-fabrication surface cleaning of organic residues cannot be performed as it risks damaging the conventional Al-based Josephson junctions. To address this limitation, we develop an alternative fabrication approach based on stencil lithography. A reusable hard mask (stencil) is used to transfer patterns directly onto the base chip, eliminating the need for resist-based processing on the device surface. Stencils defining the JJ geometry are fabricated, and shadow evaporation is demonstrated. An additional stencil allows evaporation of Al contact patches (also called bandages) and prior argon-ion milling to improve the contact between junction electrodes and transmon capacitor pads (Ta). Finally, we provide an update on our effort to fabricate multi-transmon quantum processors using this method.