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 field-effect transistor comprising:
 a channel zone situated in body material of a semiconductor body having an upper surface;   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 channel zone having a channel length extending along the body's upper surface from one of the source/drain zones to the other of the source/drain zones;   a gate dielectric layer overlying the channel zone; and   a gate electrode overlying the gate dielectric layer above the channel zone, the body material and source/drain zones comprising semiconductor dopant atoms and semiconductor material, the dopant atoms being distributed in the semiconductor material in such a way that the transistor has a threshold voltage which depends on the channel length at a given set of post-layout fabrication process conditions for the transistor so as to reach a maximum absolute value V TAM  at a value L C  of the channel length, to be at least 0.03 volt less than V TAM  in absolute value when the channel length is approximately 0.3 μm greater than L C , and to be materially decreasing with increasing channel length when the channel length is approximately 1.0 μm greater than L C .   
     
     
         96 . A structure as in  claim 95  wherein the threshold voltage is at least 0.08 volt less than V TAM  in absolute value at the given set of fabrication process conditions when the channel length is approximately 1.0 μm greater than L C . 
     
     
         97 . A structure as in  claim 95  wherein the threshold voltage is at least 0.1 volt less than V TAM  in absolute value at the given set of fabrication process conditions when the channel length is approximately 1.0 μm greater than L C . 
     
     
         98 . A structure as in  claim 95  wherein the threshold voltage materially decreases with increasing channel length when the channel length is approximately 5.0 μm greater than L C . 
     
     
         99 . A structure as in  claim 98  wherein the threshold voltage is at least 0.15 volt less than V TAM  in absolute value at the given set of fabrication process conditions when the channel length is approximately 5.0 μm greater than L C . 
     
     
         100 . A structure as in  claim 95  wherein L C  is no greater than 1.0 μm and wherein the threshold voltage materially decreases with increasing channel length when the channel length is at least 10 μm. 
     
     
         101 . A structure as in  claim 100  wherein the threshold voltage materially decreases with increasing channel length when the channel length is at least 20 μm. 
     
     
         102 . A structure as in  claim 95  wherein the channel zone has a net dopant concentration whose average value generally decreases as the channel length increases at the given set of fabrication process conditions. 
     
     
         103 . A structure as in  claim 95  wherein a pocket portion of the body material extends along at least one of the source/drain zones so as to encompass part of the channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of the channel zone. 
     
     
         104 . A structure as in  claim 103  wherein a further pocket portion of the body material extends along the other of the source/drain zones so as to encompass part of the channel zone up to the body's upper surface, the further pocket portion being more heavily doped than adjacent material of the channel zone. 
     
     
         105 . A structure as in  claim 95  wherein the first source/drain zone comprises a first main portion and a more lightly doped first lower portion underlying, and vertically continuous with, the first main portion. 
     
     
         106 . A structure as in  claim 105  wherein the second source/drain zone comprises a second main portion and a more lightly doped second lower portion underlying, and vertically continuous with, the second main portion. 
     
     
         107 . A structure comprising a plurality of like-polarity insulated-gate field-effect transistors formed from a semiconductor body having an upper surface and having respective channel lengths of multiple different values of at least a value L C , each transistor comprising first and second source/drain zones situated in the semiconductor body along its upper surface, laterally separated by a channel zone of body material of the semiconductor body, and forming respective pn junctions with the body material, the channel length of each transistor extending between its source/drain zones along the body's upper surface, the body material and the source/drain zones of the transistors comprising semiconductor dopant atoms and semiconductor material, the dopant atoms being distributed in the semiconductor material in such a way that the transistors have respective threshold voltages which have a group characteristic of depending on channel length so as to reach a maximum absolute value V TAM  when channel length equals L C , to be at least 0.03 volt less than V TAM  in absolute value when channel length is approximately 0.3 μm greater than L C , and to be materially decreasing with increasing channel length when the channel length is approximately 1.0 μM greater than L C , the transistors being formed at their respective channel lengths substantially simultaneously according to a set of post-layout fabrication process conditions which are substantially identical from transistor to transistor for all such fabrication process conditions that significantly affect the transistor threshold voltages. 
     
     
         108 . A structure as in  claim 107  wherein the group characteristic for the threshold voltages includes being at least 0.1 volt less than V TAM  in absolute value when the channel length is approximately 1.0 μm greater than L C . 
     
     
         109 . A structure as in  claim 107  wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is approximately 5.0 μm greater than L C . 
     
     
         110 . A structure as in  claim 109  wherein the group characteristic for the threshold voltages includes being at least 0.15 volt less than V TAM  in absolute when the channel length is approximately 5.0 μm greater than L C . 
     
     
         111 . A structure as in  claim 107  wherein L C  is no greater than 1.0 μm and wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is at least 10 μm. 
     
     
         112 . A structure as in  claim 111  wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is at least 20 μm. 
     
     
         113 . A structure as in  claim 107  wherein the first source/drain zone of a specified one of the transistors comprises a first main portion and a more lightly doped first lower portion underlying, and vertically continuous with, the first main portion. 
     
     
         114 . A structure as in  claim 107  wherein the second source/drain zone of the specified transistor comprises a second main portion and a more lightly doped second lower portion underlying, and vertically continuous with, the second main portion. 
     
     
         115 . A structure comprising a plurality of like-polarity field-effect transistors formed from a semiconductor body so as to have respective threshold voltages dependent on transistor channel length, 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 channel zone having a channel length along the body's upper surface from one of the source/drain zones to the other of the source/drain zones;   a gate dielectric layer overlying the channel zone; and   a gate electrode overlying the gate dielectric layer above the channel zone, the transistors having multiple different values for their channel lengths and being formed at those channel lengths substantially simultaneously according to a set of post-layout fabrication process conditions which are substantially identical from transistor to transistor for all such fabrication process conditions that significantly affect the threshold voltages, the body material and source/drain zones of the transistors comprising semiconductor dopant atoms and semiconductor material, the dopant atoms being distributed in the semiconductor material in such a way that the threshold voltages have a group characteristic of reaching a maximum absolute value V TAM  at a value L C  of channel length, of being at least 0.03 volt less than V TAM  in absolute value when channel length is approximately 0.3 μm greater than L C , and of materially decreasing with increasing channel length when the channel length is approximately 1.0 μm greater than L C .   
     
     
         116 . A structure as in  claim 115  wherein the group characteristic for the threshold voltages includes being at least 0.08 volt less than V TAM  in absolute value when the channel length is approximately 1.0 μm greater than L C . 
     
     
         117 . A structure as in  claim 115  wherein the group characteristic for the threshold voltages includes being at least 0.1 volt less than V TAM  in absolute value when the channel length is approximately 1.0 μm greater than L. 
     
     
         118 . A structure as in  claim 115  wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is approximately 5.0 μm greater than L. 
     
     
         119 . A structure as in  claim 118  wherein the group characteristic for the threshold voltages includes being at least 0.15 volt less than V TAM  in absolute value when the channel length is approximately 5.0 μm greater than L C . 
     
     
         120 . A structure as in  claim 115  wherein L C  is no greater than 1.0 μm and wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is at least 10 μm. 
     
     
         121 . A structure as in  claim 120  wherein the group characteristic for the threshold voltages includes materially decreasing with increasing channel length when the channel length is at least 20 μm. 
     
     
         122 . A structure as in  claim 115  wherein the channel zones have respective net dopant concentrations whose respective average values generally decrease as the respective channel lengths increase at the set of fabrication process conditions. 
     
     
         123 . A structure as in  claim 115   claim 120  wherein a pocket portion of the body material extends along at least one of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         124 . A structure as in  claim 123  wherein a further pocket portion of the body material extends along the other of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the further pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         125 . A structure as in  claim 115  wherein the first source/drain zone of a specified one of the transistors comprises a first main portion and a more lightly doped first lower portion underlying, and vertically continuous with, the first main portion. 
     
     
         126 . A structure as in  claim 125  wherein the second source/drain zone of the specified transistor comprises a second main portion and a more lightly doped second lower portion underlying, and vertically continuous with, the second main portion. 
     
     
         127 - 140 . (canceled) 
     
     
         141 . A structure as in  claim 95  wherein semiconductor dopant atoms distributed in the semiconductor material of the channel and source/drain zones substantially cause the threshold voltage to vary as recited in  claim 95  at the given set of post-layout fabrication process conditions. 
     
     
         142 . A structure as in  claim 95  wherein at least one of the source/drain zones comprises a main portion and a more lightly doped lateral extension extending toward the other of the source/drain zones. 
     
     
         143 . A structure as in  claim 95  wherein a pocket portion of the body material extends along substantially only one of the source/drain zones so as to encompass part of the channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of the channel zone. 
     
     
         144 . A structure as in  claim 104  wherein (i) the channel zone has a net dopant concentration that longitudinally reaches a local surface minimum along the body's upper surface at a location between the source/drain zones and (ii) the local surface minimum occurs approximately at a single point along an imaginary line extending longitudinally between the source/drain zones along the body's upper surface such that the pocket portions merge together. 
     
     
         145 . A structure as in  claim 107  wherein semiconductor dopant atoms distributed in the semiconductor material of the channel and source/drain zones of the transistors substantially cause their threshold voltages to have the group characteristic recited in  claim 107 . 
     
     
         146 . A structure as in  claim 107  wherein at least 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. 
     
     
         147 . A structure as in  claim 107  wherein a pocket portion of the body material extends along substantially only one of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         148 . A structure as in  claim 107  wherein a pocket portion of the body material extends along at least one of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         149 . A structure as in  claim 148  wherein a further pocket portion of the body material extends along the other of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the further pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         150 . A structure as in  claim 149  wherein (i) the channel zone of a specified one of the transistors has a net dopant concentration that longitudinally reaches a local surface minimum along the body's upper surface at a location between the source/drain zones of the specified transistor and (ii) the local surface minimum occurs approximately at a single point along an imaginary line extending longitudinally between the source/drain zones of the specified transistor along the body's upper surface such that the pocket portions of the specified transistor merge together. 
     
     
         151 . A structure as in  claim 115  wherein semiconductor dopant atoms distributed in the semiconductor material of the channel and source/drain zones of the transistors substantially cause their threshold voltages to have the group characteristic recited in  claim 115 . 
     
     
         152 . A structure as in  claim 115  wherein at least 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. 
     
     
         153 . A structure as in  claim 115  wherein a pocket portion of the body material extends along substantially only one of the source/drain zones of each transistor so as to encompass part of that transistor's channel zone up to the body's upper surface, the pocket portion being more heavily doped than adjacent material of that transistor's channel zone. 
     
     
         154 . A structure as in  claim 124  wherein (i) the channel zone of a specified one of the transistors has a net dopant concentration that longitudinally reaches a local surface minimum along the body's upper surface at a location between the source/drain zones of the specified transistor and (ii) the local surface minimum occurs approximately at a single point along an imaginary line extending longitudinally between the source/drain zones of the specified transistor along the body's upper surface such that the pocket portions of the specified transistor merge together.