Three-dimensional CMOS IC's Fabricated by using beam recrystallization

A three-dimensional (3-D) CMOS integrated circuit with a structure, in which one type of transistor is fabricated directly above a transistor of the opposite type with separate gates and an insulator in between, has successfully been fabricated by using laser beam recrystallization. Seven-stage ring oscillators fabricated in the 3-D structure have a propagation delay of 8.2 ns. In the present experiment, a double-layer of silicon-nitride and phospho-silicate-glass (PSG) film has been used as an intermediate insulating layer between the top and the bottom devices. This CMOS structure and the process technology we have developed here can be the basis for realizing a multilayered 3-D device composed of vertically stacked transistors with separate gates and an insulating layer in between.