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

Through silicon vias (TSV) are the enabling components in the emerging 2.5D and 3D integration microelectronic 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 more suitable properties and simpler processing compared to the tradition silicon dioxide (SiO2) liner. Recently we reported a novel low-k polymer that can be conformally coated on the surface of the holes as the TSV liner by spin coating. Theaspect ratio (depth over diameter) of TSV used in previous studied was 2:1. However, in many applications such as CMOS image sensor, Si interposer and 3D integrated circuits, TSV with higher aspect ratio have been broadly adopted. In this paper, we report the successful conformal coating of polymer liner in TSV with aspect ratio over 5:1 by spin coating. In atypical experiment, the polymer were coated on array of TSVs with 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 TSV opening, 3.0 μm on the sidewall of TSV, and 9.0 μm at the bottom of the TSV. The top surface roughness of the polymer on the sidewall was measured to be below 5 nm by atomic force microscope, while the sidewall roughness was well below 50 nm under observation of high resolution SEM. The ultra-low surface roughness could facilitate the facile complete metal filling inside TSV. In the paper, we also demonstrate the conformal coating of the polymer in high-aspect-ratio TSV with various diameter from 30 μm to 100 μm. The challenges in the conformal coating as the aspect ratio of TSV increases are discussed. The dielectric constant of the polymer was measured to be 3.2 in frequency range of 10 to 100 kHz, with dissipation 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.