Development of ultra-low capacitance through-silicon-vias (TSVs) with air-gap liner

This paper presents the development of ultra-low capacitance TSVs using air-gap to replace conventional SiO₂ as the insulating liners. Two polymer sacrificial technologies, including Benzocyclobutene (BCB) etching and Propylene Carbonate (PPC) pyrolysis, have been developed to successfully realize the air-gap TSVs. The capacitance-voltage (C-V) characteristics and the leakage current have been measured to evaluate the electrical performances of the air-gap TSVs, and the thermal-mechanical stress has been studies with ANSYS. The measurement results show that the air-gap TSVs have a capacitance density around 0.6 nF/cm² at the maximum depletion region, and the leakage current is less than 1×10^-1 A at 20 V biased voltage, indicating that air-gaps are able to achieve low capacitance and good insulating property. The simulation results show that the air-gap is effective to reduce the thermal stresses in the silicon substrate, which is beneficial for devices performance.