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Study of Vacuum-Assisted Spin Coating of Polymer Liner for High-Aspect-Ratio Through-Silicon-Via Applications

This paper provides a new approach for the formation of polymer liner for low-k high-aspect-ratio through-silicon-vias involved in via-last backside-via 3-D integration applications. The approach mentioned, referred to as vacuum-assisted spin coating technique in this paper, is formed by combining a conventional spin coating technique and a vacuum treatment. Silicon blind vias with a diameter of 6 μm and an aspect ratio of ~8 were conformably coated on their sidewall with polyimide liner with the minimum step coverage ~30% by this approach. Impacts of via geometric parameters and wafer sizes on step coverage were investigated. Electrical characteristics were evaluated with a trench capacitor structure of which the insulator layer was formed by the vacuum-assisted spin coating technique. The minimum capacitance density of 5.3 nF/cm2 and the leakage current density of ~3 nA/cm2 at a biased voltage of 5 V were obtained. The proposed vacuum-assisted spin coating technique is a simple, feasible, and cost-effective approach for 3-D integration applications.