Fabrication of three-dimensional IC using `cumulatively bonded IC´ (CUBIC) technology

A technology is proposed for the fabrication of three-dimensional integrated circuits (3D-ICs) having a large number of device layers, referred to as `cumulatively bonded IC´ (CUBIC) technology wherein several thin-film devices are bonded cumulatively. The technology was used to fabricate a two-active-layer device having a bulk-Si NMOSFET lower layer and a thinned NMOSFET upper layer. The CUBIC technology, essentially a face-to-back device bonding technology, is applicable to fabricating 3D-ICs having more than three active-device layers. The process consists of two subprocesses-wafer thinning and thin-film lamination. Preferential polishing was used for wafer thinning and bump/tool contacts were used for device-to-device vertical interconnections