Fabrication process, experimental results, and application for an elemental level vertically intergrated circuit (ELVIC)

Abstract

A new double-layered stacked LSI fabrication process has been developed for the purpose of realizing short fabrication turn-around time, high fabrication yield, and high integration density. This process, which is named “Elemental Level Vertical Integrated Circuit (ELVIC)” technology, puts two conventionally made LSI chips face to face and bonds them by thermal compression. The process includes, in addition to the conventional LSI fabrication process, vertical interconnection (VI) formation in the upper and lower LSI layers, planarization of both upper and lower layer surfaces, and inter-level connections using pressure and heat. In the experimental version, about 52 000 10X10μm2 Au-on-Ti VIs were connected on a 5×5 mm2 chip. Each pair of mated VIs was measured and had a tensile strength of 4 mg · force. A two-layer, 31-stage inter-CMOS/bulk ring oscillator consisting of p-channel MOSFETs on the upper layer and n-channel MOSFETs on the lower layer has been built. Propagation delay time per stage is 1.86 ns at the supply voltage of 5 V. ELVIC technology can produce a variety of benefits such as high production yield, doubling integration density, latchup-free CMOS LSIs, radiation-damage-free LSIs, multifunction, and complete mixing of bipolar, CMOS, and GaAs technologies.