Fabrication technologies for three-dimensional integrated circuits

The MIT approach to 3D VLSI integration is based on low-temperature Cu-Cu wafer bonding. Device wafers are bonded in a face-to-back manner, with short vertical vias and Cu-Cu pads as the inter-wafer throughway. In our scheme, there are several reliability criteria, which include: (a) structural integrity of the Cu-Cu bond; (b) Cu-Cu contact electrical characteristics; and (c) process flow efficiency and repeatability. In addition, CAD tools are needed to aid in design and layout of 3DICs. This paper discusses recent results in all these areas.