Seeded lateral epitaxial laser-recrystallization of silicon film on SiO2 is applied to fabricate 3-dimensional (3-D) integrations: 3-D CMOS 7-stage ring oscillators. Top p-channel Si-gate SOI MOSFET's are fabricated in the seeded recrystallized silicon directly above bottom n-channel Si-gate bulk MOSFET's with insulator in between. The recrystallized silicon at the seed region can be utilized for buried contact to interconnect bottom and top MOSFET's. At the arsenic implantation step to fabricate source and drain of the bottom MOSFET's, ions are not implanted into the seed region to prevent heavy doping and crystal disorder there; otherwise the dopant diffuses laterally and residual crystal disorder disturbs the epitaxial recrystallization. After the laser-recrystallization, the seed region is implanted with phosphorus to interconnect the top and bottom MOSFET's.
The Ar+ laser irradiation is performed with a 10 W power, a 50 μm spot size, a 13 cm/s scanning speed and a 13 μm step at 400 °C in air. Propagation delay of 460 psec is obtained for the seven stage 3-D CMOS ring oscillator at a power supply voltage of 17 V for a channel length of 3 μm and a channel width of 18 μm. In the seeded SOI films, grain boundary generation and crystal orientation can be controlled.