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

Abstract

We describe a microfabrication process that, thanks to a specifically tailored sidewall profile, enables for the firsttime 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 μmdeep and 50 μm-wide vias with a mere 2 μm-thick layer of Al, a widely available metal in for IC manufacturing, was demonstrated. Single-via electric resistance as low as 468 mΩ 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 highdensity silicon-based quantum computing architectures.

Highly-Conformal Sputtered Through-Silicon Vias With Sharp Superconducting Transition

“…To facilitate the penetration of the plasma within the TSVs during the sputtering process, a funneled TSV profile in the shape of a wine glass was introduced in 300 µm-thick Si wafers ( Fig. 2b) [16]. This pseudo-hemispherical funnel was 50 µm deep and had a diameter of 120 µm at the wafer surface side.…”

“…Several works in literature have described a variety of approaches to deploy superconducting interposers [6]- [14], including our previous investigations [15], [16]. Foxen et al [7] used indium bumps as electrical interconnects between two planar devices with aluminum wiring.…”

“…We have previously demonstrated the fabrication of high aspect-ratio (HAR) superconducting TSVs using sputtered aluminum [15], [16]. Sputter deposition is a physical vapor deposition technique used for the deposition of thin films.…”