Plasma Processes for Vertical Niobium Nitride Superconducting Through Silicon Vias

Superconducting through silicon vias are emerging as a key interconnect technology to realise a scalable superconducting quantum computing platform. Integration of semiconductor technology into quantum devices is becoming more common whilst quantum devices are taking advantage of novel combinations of plasma processes and materials to realise more qubits and denser integration. In this letter, plasma processes for fabrication of superconducting niobium nitride TSVs have been developed by means of deep silicon etching, plasma polishing and atomic layer deposition. Key steps were experimentally investigated for their impact on etching and deposition results. The underlying mechanisms have been analysed to optimise the whole process flow. Sidewall topography significantly influenced conformality of niobium nitride deposition into deep features. As a result, high-quality vertical superconducting through silicon vias were obtained with a transition temperature of 10.7 K.