An inorganic shadow-mask platform for Josephson junction fabrication

A reliable production of high-quality Josephson junctions and pristine superconducting materials is critical in the applications of superconducting quantum circuits. The widely applied shadow-evaporation technique based on organic resist, nevertheless, imposes stringent requirements on the process thermal budget such that only low-melting-point material systems such as aluminum Josephson junctions can be fabricated. On the other hand, it also forbids any aggressive in situ treatment process on either the substrate surface or the as-deposited materials. To resolve this challenge and to further improve the process versatility of the shadow-evaporation technique, we demonstrate a simple and robust inorganic shadow-mask platform based on a silicon compound that helps to increase the thermal budget and reduce the sensitivity of mask materials to various process steps. Using the conventional aluminum junction as a proof-of-concept, we managed to complete a full process flow including mask fabrication, junction evaporation, and mask lift-off, where the yielded aluminum transmon devices revealed expected coherent properties. We believe such a technique serves as a new opportunity for device engineering and paves the way for future exploration of other superior material systems.