Structure and Fabrication of Field-effect Transistor for Alleviating Short-channel Effects and/or Reducing Junction Capacitance

Abstract

An IGFET ( 40 or 42 ) has a channel zone ( 64 or 84 ) situated in body material ( 50 ). Short-channel threshold voltage roll-off and punchthrough are alleviated by arranging for the net dopant concentration in the channel zone to longitudinally reach a local surface minimum at a location between the IGFET's source/drain zones ( 60 and 62 or 80 and 82 ) and by arranging for the net dopant concentration in the body material to reach a local subsurface maximum more than 0.1 μm deep into the body material but not more than 0.1 μm deep into the body material. The source/drain zones ( 140 and 142 or 160 and 162 ) of a p-channel IGFET ( 120 or 122 ) are provided with graded-junction characteristics to reduce junction capacitance, thereby increasing switching speed.

1 - 94 . (canceled) 
     
     
         95 . A structure comprising a pair of opposite-polarity field-effect transistors formed from a semiconductor body having an upper surface, each transistor comprising:
 a channel zone situated in body material of the semiconductor body;   a pair of source/drain zones situated in the semiconductor body along its upper surface, laterally separated by the channel zone, and forming respective pn junctions with the body material, the body material having a net dopant concentration that reaches at least two vertically separate local subsurface maxima along an imaginary line that extends generally perpendicular to the body's upper surface through the channel zone and into underlying matter of the body material, each local subsurface maximum in the body material's net dopant concentration extending continuously laterally so as to underlie at least part of each source/drain zone;   a gate dielectric layer overlying the channel zone; and   a gate electrode overlying the gate dielectric layer above the channel zone; wherein the net dopant concentration of the body material for one of the transistors reaches a third such local subsurface maximum.   
     
     
         96 . A structure as in  claim 95  wherein each local subsurface maximum in the net dopant concentration of the body material for each transistor underlies substantially all of each of its source/drain zones. 
     
     
         97 . A structure as in  claim 95  wherein the net dopant concentration of the body material for the other of the transistors also reaches a third such local subsurface maximum. 
     
     
         98 . A structure as in  claim 97  wherein each local subsurface maximum in the net dopant concentration of the body material for each transistor underlies substantially all of each of its source/drain zones. 
     
     
         99 . A structure as in  claim 95  wherein the net dopant concentration of the body material for a specified one of the transistors longitudinally reaches a local surface minimum along the body's upper surface in the channel zone of the specified transistor at a location between its source/drain zones. 
     
     
         100 . A structure as in  claim 99  wherein the net dopant concentration of the body material for the specified transistor increases in moving along the body's upper surface from the location of the local surface minimum of the body material for the specified transistor toward each of its source/drain zones. 
     
     
         101 . A structure as in  claim 99  wherein the net dopant concentration of the body material for the specified transistor increases in moving along the body's upper surface from the location of the local surface minimum of the body material for the specified transistor toward only one of its source/drain zones. 
     
     
         102 . A structure as in  claim 95  wherein one of the source/drain zones of one of the transistors comprises a main portion and a more lightly doped lateral extension extending toward the other of the source/drain zones of that transistor. 
     
     
         103 . A structure as in  claim 95  wherein each of the source/drain zones of one of the transistors comprises a main portion and a more lightly doped lateral extension such that the channel zone of that transistor is terminated by the lateral extensions along the body's upper surface. 
     
     
         104 . A structure as in  claim 95  wherein one of the source/drain zones of each of the transistors comprises a main portion and a more lightly doped lateral extension extending toward the other of the source/drain zones of that transistor. 
     
     
         105 . A structure as in  claim 95  wherein each of the source/drain zones of each of the transistors comprises a main portion and a more lightly doped lateral extension such that the channel zone of that transistor is terminated by the lateral extensions along the body's upper surface. 
     
     
         106 . A structure comprising a pair of opposite-polarity field-effect transistors formed from a semiconductor body having an upper surface, each transistor comprising:
 a channel zone situated in body material of the semiconductor body, a channel surface depletion region extending along the body's upper surface into the channel zone so as to reach a maximum thickness at a location in the channel zone;   a pair of source/drain zones situated in the semiconductor body along its upper surface, laterally separated by the channel zone, and forming respective pn junctions with the body material, the body material having a net dopant concentration that reaches at least two vertically separate local subsurface maxima along an imaginary line that extends generally perpendicular to the body's upper surface through the channel zone and into underlying matter of the body material, each local subsurface maximum in the body material's net dopant concentration occurring at a location below the location of the channel surface depletion region at its maximum thickness, each non-shallowest local subsurface maxima in the body material's net dopant concentration extending continuously laterally so as to underlie at least part of each source/drain zone;   a gate dielectric layer overlying the channel zone; and   a gate electrode overlying the gate dielectric layer above the channel zone; wherein the net dopant concentration of the body material for one of the transistors reaches a third such local subsurface maximum.   
     
     
         107 . A structure as in  claim 106  wherein each non-shallowest local subsurface maximum in the net dopant concentration of the body material for each transistor underlies substantially all of each of its source/drain zones. 
     
     
         108 . A structure as in  claim 106  wherein the net dopant concentration of the body material for the other of the transistors also reaches a third such local subsurface maximum. 
     
     
         109 . A structure as in  claim 108  wherein each non-shallowest local subsurface maximum in the net dopant concentration of the body material for each transistor underlies substantially all of each of its source/drain zones. 
     
     
         110 . A structure as in  claim 106  wherein the shallowest local subsurface maximum in the net dopant concentration of the body material for a specified one of the transistors also extends continuously laterally so as to underlie at least part of each of its source/drain zones. 
     
     
         111 . A structure as in  claim 110  wherein each local subsurface maximum in the net dopant concentration of the body material for the specified transistor underlies substantially all of each of its source/drain zones. 
     
     
         112 . A structure as in  claim 106  wherein the net dopant concentration of the body material for a specified one of the transistors longitudinally reaches a local surface minimum along the body's upper surface in the channel zone of the specified transistor at a location between its source/drain zones. 
     
     
         113 . A structure as in  claim 112  wherein the net dopant concentration of the body material for the specified transistor increases in moving along the body's upper surface from the location of the local surface minimum of the body material for the specified transistor toward each of its source/drain zone. 
     
     
         114 . A structure as in  claim 112  wherein the net dopant concentration of the body material for the specified transistor increases in moving along the body's upper surface from the location of the local surface minimum of the body material for the specified transistor toward only one of its source/drain zones. 
     
     
         115 . A structure as in  claim 106  wherein one of the source/drain zones of one of the transistors comprises a main portion and a more lightly doped lateral extension extending toward the other of the source/drain zones of that transistor. 
     
     
         116 . A structure as in  claim 106  wherein each of the source/drain zones of one of the transistors comprises a main portion and a more lightly doped lateral extension such that the channel zone of that transistor is terminated by the lateral extensions along the body's upper surface. 
     
     
         117 . A structure as in  claim 106  wherein one of the source/drain zones of each of the transistors comprises a main portion and a more lightly doped lateral extension extending toward the other of the source/drain zones of that transistor. 
     
     
         118 . A structure as in  claim 106  wherein each of the source/drain zones of each of the transistors comprises a main portion and a more lightly doped lateral extension such that the channel zone of that transistor is terminated by the lateral extensions along the body's upper surface.