Crack-Free Fabrication and Electrical Characterization of Coaxial Ultra-Low-Resistivity-Silicon Through-Silicon-Vias

Ultra-low-resistivity-silicon (ULRS) coaxial through-silicon-vias (TSVs) employ silicon pillar as the central conductor, which simplifies the fabrication process and exhibits good electrical characteristics. However, microcracks that may appear on silicon pillars degrade the reliability and electrical properties. In this work, the main cause of microcracks is investigated experimentally and an optimized fabrication process is proposed to avoid microcracks, which includes a two-step chemical mechanical polishing for frontside Benzocyclobutene overburden layer removal and a two-step backside TSVs reveal process featuring mechanical grinding with a safety margin followed by chemical mechanical polishing. Utilizing the proposed method, crack-free ULRS coaxial TSVs were successfully fabricated. In addition, the electrical properties of TSVs including I-V curves and S-parameters were characterized under various temperatures, and the results demonstrates that the coaxial TSVs exhibit good impedance matching and low insertion loss up to 50 GHz even under 125°C.