Fabrication and structure of asymmetric field-effect transistors using L-shaped spacers

A method of fabricating a field-effect transistor from a semiconductor body having body material of a first conductivity type, the method comprising:

• defining a gate electrode above, and vertically separated by a gate dielectric layer from, a portion of the body material intended to be a channel zone such that the gate electrode has opposite source-side and drain-side lateral sides;
• introducing pocket semiconductor dopant of the first conductivity type into the body material to define a precursor source-side pocket portion of the body material more heavily doped than laterally adjacent material of the body material and substantially extending below only the source-side one of the gate electrode's lateral sides using the gate electrode and any material along its lateral sides as a dopant-blocking shield;
• providing a source-side spacer along the gate electrode's source-side lateral side such that the source-side spacer comprises (i) a source-side vertically extending dielectric spacer portion situated along the gate electrode, (ii) a source-side laterally extending dielectric spacer portion continuous with the source-side vertically extending spacer portion and situated along the semiconductor body, and (iii) a source-side filler spacer portion largely occupying the space between the source-side vertically and laterally extending spacer portions;
• subsequently introducing main source/drain (“S/D”) semiconductor dopant of a second conductivity type opposite to the first conductivity type into the semiconductor body to define main source and drain portions of the second conductivity type using the gate electrode, the source-side spacer, and any other material along the gate electrode's lateral sides as a dopant-blocking mask for largely preventing the main S/D dopant from entering the channel zone such that (i) the channel zone is situated between the main source and drain portions and (ii) a further source-side pocket portion of the first conductivity type comprises material of at least part of the precursor pocket portion and extends to the main source portion for causing the channel zone to be longitudinally asymmetric;
• subsequently largely removing the source-side filler spacer portion;
• and
• forming a pair of electrical contacts respectively to the main source and drain portions.

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 gate dielectric layer overlying the channel zone;
• a gate electrode overlying the gate dielectric layer above the channel zone and having opposing first and second lateral sides;
• first and second source/drain (“S/D”) zones situated in the semiconductor body along its upper surface, laterally separated by the channel zone, extending respectively below the gate electrode's first and second lateral sides, 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 pocket portion of the body material more heavily doped than laterally adjacent material of the body material extending largely along only the first S/D zone and into the channel zone so as to cause the channel zone to be asymmetric with respect to the S/D zones;
• a first spacer situated laterally along the gate electrode's first lateral side and comprising (i) a first vertically extending dielectric spacer portion situated along the gate electrode and (ii) a second laterally extending dielectric spacer portion continuous with the first vertically extending spacer portion and situated along the semiconductor body so as to generally form an L with the first vertically extending spacer portion;
• and
• a pair of electrical contacts respectively to the S/D zones.

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 gate dielectric layer overlying the channel zone;
• a gate electrode overlying the gate dielectric layer above the channel zone and having opposing source-side and drain-side lateral sides;
• a source and a drain situated in the semiconductor body along its upper surface, laterally separated by the channel zone, extending respectively below the gate electrode's source-side and drain-side lateral sides, 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 pocket portion of the body material more heavily doped than laterally adjacent material of the body material extending largely along only the source and into the channel zone so as to cause the channel zone to be asymmetric with respect to the source and drain;
• a source-side spacer situated laterally along the gate electrode's source-side lateral side and comprising (i) a source-side vertically extending dielectric spacer portion situated along the gate electrode and (ii) a source-side laterally extending dielectric spacer portion continuous with the source-side vertically extending spacer portion and situated along the semiconductor body so as to generally form an L with the source-side vertically extending spacer portion;
• and
• a pair of electrical contacts respectively to the source and drain.