Fabrication and Understanding of Superconducting Damascene Structures for Quantum Devices

Superconducting materials transmit electrical current without resistance and eliminate Joule heating. Quantum devices, on the other hand, operate at cryogenic temperatures, where even a small amount of heat can cause perturbation and compromise overall performance. Therefore, superconducting wirings are needed for the interconnections and integration of quantum devices. Copper damascene structures, which are tiny copper or other metal elements embedded in a dielectric layer with a planarized surface, are used in conventional semiconductor circuits to enable the fabrication of multilayer interconnect networks. These structures are fabricated using specialized chemistry and optimized electrochemical processes to fill metals into tiny features. However, the chemistry and processes used to fabricate damascene structures have been limited to a small number of non-superconducting metals. This project will focus on two innovative approaches to fabricate damascene structures from superconducting metals, systematically study the chemistry and process used in their fabrication, and provide an understanding of the superconducting properties and long-term stability of such damascene structures for quantum circuits. The goal is to enable a manufacturable process for the integration of quantum devices into large-scale circuits and to provide a viable path toward achieving the long-term performance and reliability of quantum circuits. Collaborations with a local children’s museum and local high schools will be further strengthened to promote awareness of science and engineering education and career opportunities among K-12 students and their parents. The research results will contribute to the development of new modules for undergraduate- and graduate-level courses in device fabrication and electrochemical engineering. Organic additives play a critical role in enabling superconformal electrodeposition of metals into high aspect ratio features. Suppressor molecules create a higher deposition rate at the bottom of a feature than at the top. This enables the bottom-up filling of copper (Cu) damascene structures, which are ubiquitously used as the interconnects in semiconductor circuits. This project leverages a class of polymer suppressors for the electrodeposition of tin (Sn) and indium (In), both of which are superconductors, to enable the fabrication of superconducting damascene structures. In parallel, this project explores an alternative approach that aims to convert the conventional Cu damascene structures into superconducting structures through solid-state reactions. The project aims to provide a fundamental understanding of: i) the effects of electrolyte chemistry and deposition process on the nucleation and growth of Sn to promote defect-free filling of damascene features; ii) the effects of thermal processing, volumetric confinement, and impurity incorporation on the formation, evolution, and distribution of intermetallic compounds within damascene structures during solid-state reaction; iii) the electrical properties of the resulting damascene structures and how the nanoscale dimension and the surrounding materials influence the superconductivity through the proximity effect; and iv) the effects of electrolyte chemistry on the co-deposition and distribution of bismuth (Bi) within damascene structures, as well as how the Bi dopants impact the superconductivity and long-term reliability of the structures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.