Low-Capacitance Through-Silicon-Vias With Combined Air/SiO2 Liners

Through-silicon-vias (TSVs) with air-gap insulators have the advantages of low capacitance and low thermal stress. This paper reports the design, fabrication, and characterization of new TSVs with combined air/SiO₂ insulators. Sacrificial technologies based on heat decomposition of poly(propylene carbonate) and reactive ion etching of benzocyclobutene have been developed to fabricate uniform and high aspect-ratio air gaps. Air gaps with a thickness of 0.8 μm and an aspect ratio of 62.5:1 have been successfully fabricated. Measurement results show that the SiO₂ liner is able to eliminate the impacts of residues of the sacrificial polymers, and the TSVs with air/SiO₂ have low capacitances and leakage currents at both room temperature and high temperature, constant minimum capacitance, and good temperature stability.