METHOD FOR FABRICATING MOS DEVICES WITH A MULTIPLICITY OF THRESHOLDS ON A SINGLE SEMICONDUCTOR TRATE

摘要

The process includes the steps of doping selected portions of the substrate with a dopant of conductivity-determining type opposite the conductivity type of the substrate to form source and drain regions for a plurality of semiconductor devices. A first conductivity-determining type impurity is then introduced into the substrate at the surface thereof in regions corresponding to a first set of selected devices and not in regions corresponding to a second set of selected devices. A second conductivity type determining impurity is then introduced into the substrate of the surface thereof in regions corresponding to the second set of selected devices. The second conductivity type determining impurity is also introduced in regions corresponding to at least some of the first set of selected devices. There may be a third set of selected devices where neither of the conductivity type determining impurities are introduced. The source, drain and gate electrodes for each devices are then formed.