Evaluation procedures for wafer bonding and thinning of interconnect test structures for 3D ICs

Electrical and mechanical impacts of wafer bonding and thinning processes required for three-dimensional (3D) IC fabrication have been evaluated with interconnect structures. In addition to the bonding and thinning required for a two-level 3D IC stack, an additional bonding and thinning process is used along with dielectric glue ashing to expose the previously tested interconnect structures. This procedure permits evaluation of bonding and thinning integrity without inter-wafer interconnect processing. Promising results on wafers with oxide interlevel dielectric (ILD) have been obtained, while some damages observed with the porous low-k ILD.