  Nanofabrication techniques for superconducting qubits rely on resist-based
masks patterned by electron-beam or optical lithography. We have developed an
alternative nanofabrication technique based on free-standing silicon shadow
masks fabricated from silicon-on-insulator wafers. These silicon shadow masks
not only eliminate organic residues associated with resist-based lithography,
but also provide a pathway to better understand and control surface-dielectric
losses in superconducting qubits by decoupling mask fabrication from substrate
preparation. We have successfully fabricated aluminum 3D transmon
superconducting qubits with these shadow masks and found coherence quality
factors comparable to those fabricated with standard techniques.
