The single flux quantum (SFQ) circuit with Josephson Junction is a promising candidate for high-performance computing due to its high speed and low loss dissipation. In order to improve the integration of SFQ circuit chips, the three-dimensional multi-chip module (3D-MCM) technology would be an effectively way. Through silicon via (TSV) is an important interconnection technology for realizing 3D-MCM. However, superconducting integrated circuits have low-temperature operating conditions (4.2 K) and weak signals (mV), which bring the new requirement and challenges for the vertical interconnection of 3D-MCM, i.e. The TSV interconnect should preferably be superconductive so as to ensure the lowest-loss transmission of the chip-to-chip SFQ signals.
To achieve superconducting TSVs, we proposed a niobium-based vertical TSV method. We achieved vertical TSVs with low-roughness TSV sidewalls by DRIE process, and eliminated the scallop pattern defects by thermal oxidation process and BOE etching process; then we used double-side magnetron sputtering method to deposit niobium (Nb) thin films inside the TSVs, and completed the interconnections between Nb-TSVs by Nb redistribution layer (RDL) on the double side of the interposer wafer. The electrical tests showed that the superconducting transition temperature (Tc) of the fabricated Nb-TSV reaches 6.2 K and the critical current (Ic) of Nb-TSV exceeds 100 mA, which can meet the requirements of superconducting integrated circuits.