Structure and fabrication of asymmetric field-effect transistor having asymmetric channel zone and differently configured source/drain extensions

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 doped with composite semiconductor dopant of a second conductivity type opposite to the first conductivity type such that the source and drain are of the second 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 lateral extensions both extending laterally under the gate electrode so as to terminate the channel zone along the body's upper surface, the drain extension being more lightly doped than the source extension, the dopant of the second conductivity type having a concentration that locally reaches a subsurface maximum concentration in each lateral extension, the maximum concentration of the drain extension averagely occurring deeper below the body's upper surface than the maximum concentration of the source extension, 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 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;
• first and second source/drain (“S/D”) zones 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, each S/D zone comprising a main S/D portion and a more lightly doped lateral S/D extension laterally continuous with the main S/D portion and extending laterally under the gate electrode such that the channel zone is terminated by the S/D extensions along the body's upper surface, the S/D extension of the second S/D zone extending further laterally under the gate electrode than the S/D extension of the first S/D zone, a pocket portion of the body material more heavily doped than laterally adjacent material of the body material extending largely along only the first of the S/D zones and into the channel zone so as to cause the channel zone to be asymmetric with respect 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 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 lateral extensions both extending laterally under the gate electrode so as to terminate the channel zone along the body's upper surface, the drain extension extending further laterally below the gate electrode than the source extension, 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 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;
• and
• subsequently introducing (i) semiconductor dopant of the first conductivity type into at least the intended channel-zone portion of the body material and (ii) composite semiconductor dopant of a second conductivity type opposite to the first conductivity type into the semiconductor body such that (a) the composite dopant of the second conductivity type forms first and second source/drain (“S/D”) zones of the second conductivity type laterally separated by the channel zone, (b) each S/D zone comprises a main S/D portion and a more lightly doped lateral S/D extension laterally continuous with the main S/D portion and extending laterally under the gate electrode, (c) the channel zone is terminated by the S/D extensions directly below the gate dielectric layer, (d) the S/D extension of the second S/D zone is more lightly doped than the S/D extension of the first S/D zone and extends deeper into the semiconductor body than the S/D extension of the first S/D zone, and (e) a pocket portion of the body material more heavily doped than laterally adjacent material of the body material and defined at least partially by the dopant of the first conductivity type extends largely along only the first of the S/D zones and into the channel zone so as to cause the channel zone to be asymmetric with respect to the S/D zones.

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;
• and
• subsequently introducing (i) semiconductor dopant of the first conductivity type into at least the intended channel-zone portion of the body material and (ii) composite semiconductor dopant of a second conductivity type opposite to the first conductivity type into the semiconductor body such that (a) the composite dopant of the second conductivity type forms a source and a drain of the second conductivity type laterally separated by the channel zone, (b) the source comprises a main source portion and a more lightly doped lateral source extension laterally continuous with the main source portion, (c) the drain comprises a main drain portion and a more lightly doped lateral drain extension laterally continuous with the main drain portion, (d) the lateral extensions both extend laterally under the gate electrode so as to terminate the channel zone directly below the gate dielectric layer, (e) the drain extension is more lightly doped than the source extension and extends deeper into the semiconductor body than the source extension, and (f) a pocket portion of the body material more heavily doped than laterally adjacent material of the body material and defined at least partially by the dopant of the first conductivity type extends 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 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;
• and
• introducing (i) semiconductor dopant of the first conductivity type into at least the intended channel-zone portion of the body material and (ii) composite semiconductor dopant of a second conductivity type opposite to the first conductivity type into the semiconductor body such that (a) the composite dopant of the second conductivity type forms first and second source/drain (“S/D”) zones of the second conductivity type laterally separated by the channel zone, (b) each S/D zone comprises a main S/D portion and a more lightly doped lateral S/D extension laterally continuous with the main S/D portion and extending laterally under the gate electrode, (c) the channel zone is terminated by the S/D extensions directly below the gate dielectric layer, (d) the S/D extension of the second S/D zone extends further laterally under the gate electrode than the S/D extension of the first S/D zone, and (e) a pocket portion of the body material more heavily doped than laterally adjacent material of the body material and defined at least partially by the dopant of the first conductivity type extends largely along only the first of the S/D zones and into the channel zone so as to cause the channel zone to be asymmetric with respect to the S/D zones.

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;
• and
• introducing (i) semiconductor dopant of the first conductivity type into at least the intended channel-zone portion of the body material and (ii) composite semiconductor dopant of a second conductivity type opposite to the first conductivity type into the semiconductor body such that (a) the composite dopant of the second conductivity type forms a source and a drain of the second conductivity type laterally separated by the channel zone, (b) the source comprises a main source portion and a more lightly doped lateral source extension laterally continuous with the main source portion, (c) the drain comprises a main drain portion and a more lightly doped lateral drain extension laterally continuous with the main drain portion, (d) the lateral extensions both extend laterally under the gate electrode so as to terminate the channel zone directly below the gate dielectric layer, (e) the drain extension extends further laterally under the gate electrode than the source extension, and (f) a pocket portion of the body material more heavily doped than laterally adjacent material of the body material and defined at least partially by the dopant of the first conductivity type extends 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.