Polymer Liner Formation in High Aspect Ratio Through-Silicon-Vias for 3-D Integration
Replacing silicon dioxide with polymers that have low dielectric constants as the insulation (liner) materials is of great help in reducing the capacitive coupling of throughsilicon-vias and improving the reliability. This paper presents the fabrication of uniform poly propylene carbonate (PPC) polymer liners in high aspect ratio trenches by addressing the difficulty in coating PPC layers on via inner walls. A unique spin-coating method is developed by using vacuum treatment and solvent refill techniques for PPC liner formation for circular and annular trenches. Vacuum treatment and solvent refill facilitate PPC filling in high aspect ratio vias by preventing formation of air bubbles in the vias. By investigating the flow behaviors of PPC precursors and optimizing the spin-coating parameters, an optimal fabrication process is achieved. Using this newly developed technique as well as the optimized processing parameters, uniform PPC liners are successfully fabricated on the inner walls of circular vias with coating aspect ratio greater than 9:1 and the annular vias with filling aspect ratio of 24:1.