Tungsten Through-Silicon Via Technology for Three-Dimensional LSIs

Tungsten through-silicon via (W-TSV) technology is investigated for the fabrication of three-dimensional (3D) LSI chips having low-resistive TSVs with a width less than 3 µm. In our 3D integration technology, completed two-dimensional (2D) LSI chips including metal–oxide–semiconductor field-effect transistors (MOSFETs) and metal wirings are vertically stacked through a number of short vertical interconnections called TSV with lengths ranging from several microns to several tens of microns. The W-TSV technology is mainly divided into three low-temperature processes: deep-trench etching, dielectric layer formation, and filling with a conductive material. We successfully formed deep Si trenches through a 6-µm-thick SiO₂ dielectric layer by the modified Bosch process. The depth of the resulting Si trenches with a dielectric layer is approximately 40 µm. A SiO₂ layer was formed at the bottom and on the sidewall of the Si trenches by sub-atmospheric chemical vapor deposition (SACVD) method using tetraethylorthosilicate (TEOS) and O₃. In addition, we succeeded in uniformly depositing a conformal W metal layer by time-modulated W-CVD method at 300 °C.