Configuration and fabrication of semiconductor structure in which source and drain extensions of field-effect transistor are defined with different dopants

A structure comprising a field-effect transistor provided along an upper surface of a semiconductor body having body material of a first conductivity type, the transistor comprising:

• a channel zone of the body material;
• a source and a drain situated in the semiconductor body along its upper surface, laterally separated by the channel zone, and being of a second conductivity type opposite to the first conductivity type so as to form respective pn junctions with the body material;
• a gate dielectric layer overlying the channel zone;
• and
• a gate electrode overlying the gate dielectric layer above the channel zone, the source comprising a main source portion and a more lightly doped lateral source extension laterally continuous with the main source portion, the drain comprising a main drain portion and a more lightly doped lateral drain extension laterally continuous with the main drain portion, the source and drain extensions extending laterally under the gate electrode so as to terminate the channel zone along the body's upper surface and being respectively largely defined by source-extension and drain-extension semiconductor dopants of the second conductivity type, the source-extension dopant being of higher atomic weight than the drain-extension dopant.