Fabrication of Al-Based Superconducting High-Aspect Ratio TSVS for Quantum 3D Integration

We describe a microfabrication process that, thanks to a specifically tailored sidewall profile, enables for the first-time wafer-scale arrays of high-aspect ratio through-silicon vias (TSVs) coated with DC-sputtered Aluminum, achieving at once superconducting and CMOS-compatible 3D interconnects. Void-free conformal coating of up to $500\ \mu\mathrm{m}$-deep and $50\ \mu\mathrm{m}$-wide vias with a mere $2\ \mu\mathrm{m}$-thick layer of Al, a widely available metal in for IC manufacturing, was demonstrated. Single-via electric resistance as low as $468 \mathrm{m}\Omega$ at room temperature and superconductivity at 1.25 K were measured by a cross-bridge Kelvin resistor structure. This work establishes the fabrication of functional superconducting interposers suitable for 3D integration of high-density silicon-based quantum computing architectures.