Formation of Polymer Insulation Layer (Liner) on Through Silicon Vias (TSV) with High Aspect Ratio over 5:1 by Direct Spin Coating

Abstract

Through silicon vias (TSV) are the enablingcomponents in the emerging 2.5D and 3D integrationmicroelectronic packaging. The insulation layer, i.e. the liner, plays the key role in determining the performance of TSV. Polymer liner are receiving a growing attention for its moresuitable properties and simpler processing compared to thetradition silicon dioxide (SiO2) liner. Recently we reported anovel low-k polymer that can be conformally coated on thesurface of the holes as the TSV liner by spin coating. Theaspect ratio (depth over diameter) of TSV used in previousstudied was 2:1. However, in many applications such as CMOSimage sensor, Si interposer and 3D integrated circuits, TSVwith higher aspect ratio have been broadly adopted. In thispaper, we report the successful conformal coating of polymerliner in TSV with aspect ratio over 5:1 by spin coating. In atypical experiment, the polymer were coated on array of TSVswith diameter of 30 µm, depth of 160 µm and spacing of 80 µm. The thickness of polymer after hard baking were measured as8.0 µm on the top surface of Si, 3.5 µm at the corner of the TSVopening, 3.0 µm on the sidewall of TSV, and 9.0 µm at thebottom of the TSV. The top surface roughness of the polymeron the sidewall was measured to be below 5 nm by atomic forcemicroscope, while the sidewall roughness was well below 50 nmunder observation of high resolution SEM. The ultra-lowsurface roughness could facilitate the facile complete metalfilling inside TSV. In the paper, we also demonstrate theconformal coating of the polymer in high-aspect-ratio TSVwith various diameter from 30 µm to 100 µm. The challengesin the conformal coating as the aspect ratio of TSV increasesare discussed. The dielectric constant of the polymer wasmeasured to be 3.2 in frequency range of 10 to 100 kHz, withdissipation factor of 0.02. Thermogravimetric analysis showeda half decomposition temperature of 600 °C in the air. Differential scanning calorimetry showed a glass transitiontemperature of 230 °C. The reported results demonstrate thesuperior properties of the polymer as TSV liner in a broadrange of application. More importantly, the simple processapproach of the polymer using only spin coating make it apromising approach in TSV manufacturing with highthroughput and economic viability.