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Low Capacitance Through-Silicon-Vias With Uniform Benzocyclobutene Insulation Layers

Low capacitance is critical to the electric performance of through-silicon-vias (TSVs). This paper reports the development of a low capacitance TSVs by replacing silicon dioxide insulation layers (liners) with benzocyclobutene (BCB) polymer. The BCB liner TSVs are fabricated by etching deep annular trenches on substrates, void-free filling the trenches with BCB polymer, selective etching the silicon post in the annular trenches, and filling the via with copper. Key fabrication processes including void-free BCB polymer filling in deep trenches, BCB chemical mechanical planarization, and selective etching of silicon post to BCB are developed. TSVs with BCB liners are successfully fabricated and the electrical performance is measured. The measurement results show that the capacitance of the BCB liner TSVs is around 42 fF, and the leakage currents to substrates and to neighboring TSVs are 2.2 pA and 1.1 pA at 10 V voltage, respectively. These preliminary results demonstrate the feasibility of the proposed fabrication technology and the efficacy of BCB liners in reducing TSV capacitance.