Trends for Future Silicon Technology

In addition to three-terminal devices such as metal oxide semiconductor (MOS) transistors and bipolar transistors, the introduction of four-terminal devices such as neuron MOS transistor is essentially required for the realization of intelligent ULSI systems which is most crucial for electronics in the 21st century. Four-terminal devices will allow us to make ULSI hardware more flexible, real-time programmable, and thus more intelligent based on binary multi-valued analog-merged hardware computation algorithm. For such systems to work, we must establish high-accuracy device fabrication processes based on the concept of ultraclean technology. The simultaneous fulfillment of three principles, viz. ultraclean wafer surface, ultraclean processing environment, and perfect process-parameter control, is the key to high-performance processes for fabricating advanced subhalf-micron and subquarter-micron ULSI devices. Advanced process technologies have been realized for the first time by ultraclean processing, making it possible to establish total low-temperature processing, such as gate oxidation at 450°C, implanted region anneal at 450°C, BPSG film reflow at 450°C and single-crystal silicon epitaxy with simultaneous doping at 300°C by introducing very well regulated ion bombardment during processing which is most essential for obtaining high-performance subhalf-micron and subquarter-micron ULSI.