Wafer-on-wafer (WOW) stacking with damascene-contact TSV for 3D integration

Through-silicon via (TSV) module-process based on wafer-on-wafer (WOW) stacking has been developed. Stacking wafers were thinned down to 20 μm, and TSVs with a diameter of 30 μm were fabricated to connect inter-wafers without electrical failure in chain TSV interconnects. The TSVs were constructed with the damascene technique. Multi-wafer stacking was realized by planarizing TSV-heads with a diamond bit of a surface planer. A wafer bonding process was optimized to suppress void formation and alignment shift after adhesive cure. According to our simulation, thinner wafers and a thinner adhesive layer create less stress on a device under the TSV.