STRUCTURE AND FABRICATION OF FIELD-EFFECT TRANSISTOR HAVING SOURCE/DRAIN EXTENSION DEFINED BY MULTIPLE LOCAL CONCENTRATION MAXIMA

摘要

An insulated-gate field-effect transistor (100W) has a source (980) and a drain (242) laterally separated by a channel zone (244) of body material (180) of a semiconductor body. A gate electrode (262) overlies a gate dielectric layer (260) above the channel zone. A more heavily doped pocket portion (250) of the body material normally extends largely along only the source so that the IGFET is an asymmetric device. The source has a main source portion (980M) and a more lightly doped lateral source extension (980E). The semiconductor dopant which defines the source reaches multiple local concentration maxima in defining the source extension. The procedure involved in defining the source extension with semiconductor dopant that reaches two such local concentration maxima enables source/drain extensions of mutually different characteristics for three insulated-gate field-effect transistors to be defined in only two source/drain-extension doping operations.