High aspect ratio and low capacitance through-silicon-vias (TSVs) with polymer insulation layers
Polymer insulation layers (liners) have several potential advantages in terms of capacitance and reliability over conventional silicon dioxide for through-silicon-via (TSV) applications. This paper reports the development and measurement results of a TSV using poly (propylene carbonate) (PPC) polymer as the insulation layers. To address the challenge in coating thin and uniform PPC liners on the sidewalls of high aspect-ratio vias, a spin-on technique using vacuum treatment and solvent refill is developed to prevent formation of air bubbles in the vias, and using this technique circular vias with aspect-ratio as high as 9:1 have been coated with uniform PPC layers. Based on these results, TSVs with thick PPC polymer liners have been fabricated and the capacitance and the current leakage are measured. Thanks to the relatively large thickness and the low dielectric constant of PPC liners, the TSV capacitance density is about 2.45nF/cm2 and the leakage current is around 40nA/cm2 at 5V voltage, indicating that replacing silicon dioxide with PPC as liners considerably reduces TSV capacitance. The preliminary results demonstrate the feasibility of fabrication of high aspect ratio and low capacitance TSVs with polymer liners.
capacitance through-silicon-via (tsv) poly (propylene carbonate) (ppc) polymer liner three-dimensional integration