Semiconductor imaging device and fabrication process thereof

Abstract

A semiconductor imaging device includes a photodetection region formed of a diffusion region of a first conductivity type formed in an active region of a silicon substrate at a first side of a gate electrode such that a top part thereof is separated from a surface of the silicon substrate and such that an inner edge part invades underneath a channel region right underneath the gate electrode, a shielding layer formed of a second conductivity type at a surface of the silicon substrate at the first side of the gate electrode such that an inner edge part thereof is aligned with a sidewall surface of the gate electrode at the first side, a floating diffusion region formed in the active region at a second side of the gate electrode, and a channel region formed right underneath said gate electrode, wherein the channel region includes a first channel region part formed adjacent to the shielding layer and a second channel region part formed adjacent to the floating diffusion region, wherein the second channel region part contains an impurity element with a concentration level lower than the impurity concentration level of the first channel region part.

1 . A semiconductor imaging device, comprising: 
 a silicon substrate defined with an active region;    a gate electrode formed on said silicon substrate in correspondence to a channel region in said active region via a gate insulation film;    a photodetection region formed of a diffusion region of a first conductivity type, said photodetection region being formed in said active region at a first side of said gate electrode such that a top part thereof is separated from a surface of said silicon substrate and such that an inner edge part invades underneath a channel region right underneath said gate electrode;    a shielding layer formed of a diffusion region of a second conductivity type, said shielding layer being formed in said active region at said surface of said silicon substrate at said first side of said gate electrode such that an inner edge part thereof is aligned with a sidewall surface of said gate electrode at said first side, said shielding layer being formed so as to cover a part of said photodetection region located at said first side of said gate electrode,;    a floating diffusion region formed of a diffusion region of said first conductivity type, said floating diffusion region being formed in said active region at a second side of said gate electrode; and    a channel region formed of a diffusion region of said second conductivity type, said channel region being formed in said active region right underneath said gate electrode,    said channel region comprising:    a first channel region part having said second conductivity type, a first end of said first channel region part being formed adjacent to said shielding layer, another end of said first channel region part invading to a region right underneath said gate electrode and covering a part of said photodetection region invading underneath said channel region; and    a second channel region part having said second conductivity type and formed adjacent to said floating diffusion region,    said first channel region part containing an impurity element of said second conductivity type with an impurity concentration level lower than an impurity concentration level in said shielding layer,    said second channel region part containing said impurity element with a concentration level lower than said impurity concentration level of said first channel region part.    
   
   
       2 . The semiconductor imaging device as claimed in  claim 1 , wherein said shielding layer contains said impurity element in a substantially uniform impurity concentration level at least in a part covering said photodetection region at said first side of said gate electrode.  
   
   
       3 . The semiconductor imaging device as claimed in  claim 1 , wherein there is formed an intermediate region underneath said first channel region part between said first channel region part and said photodetection region such that said intermediate region has an impurity concentration level substantially identical to said impurity concentration level of said second channel region part.  
   
   
       4 . The semiconductor imaging device as claimed in  claim 1 , wherein there is formed a third channel region part between said first channel region part and said second channel region part such that said third channel region part has an impurity concentration level intermediate of said first and second channel region parts.  
   
   
       5 . The semiconductor imaging device as claimed in  claim 1 , wherein said first and second channel region parts forming together a potential gradient in said channel region such that said potential gradient is inclined as a whole toward said floating diffusion region.  
   
   
       6 . A semiconductor imaging device, comprising: 
 a silicon substrate defined with an active region;    a gate electrode formed on said silicon substrate in correspondence to a channel region in said active region via a gate insulation film;    a photodetection region formed of a diffusion region of a first conductivity type, said photodetection region being formed in said active region at a first side of said gate electrode such that a top part thereof is separated from a surface of said silicon substrate and-such that an inner edge part invades underneath a channel region right underneath said gate electrode;    a shielding layer formed of a diffusion region of a second conductivity type, said shielding layer being formed in said active region at said surface of said silicon substrate at said first side of said gate electrode such that an inner edge part thereof is aligned with a sidewall surface of said gate electrode at said first side, said shielding layer being formed so as to cover a part of said photodetection region located at said first side of said gate electrode,;    a floating diffusion region formed of a diffusion region of said first conductivity type, said floating diffusion region being formed in said active region at a second side of said gate electrode; and    a channel region formed of a diffusion region of said second conductivity type, said channel region being formed in said active region right underneath said gate electrode,    said channel region comprising:    a first channel region part having said second conductivity type, a first end of said first channel region part being formed adjacent to said shielding layer, another end of said first channel region part invading to a region right underneath said gate electrode and covering a part of said photodetection region invading underneath said channel region; and    a second channel region part having said second conductivity type and formed adjacent to said floating diffusion region,    said first channel region part containing an impurity element of said second conductivity type with an impurity concentration level lower than an impurity concentration level in said shielding layer,    said second channel region part containing an impurity element of said first conductivity type and an impurity element of said second conductivity type, such that a carrier concentration level of said second conductivity type is larger in said first channel region part than in said second channel region part.    
   
   
       7 . The semiconductor imaging device as claimed in  claim 6 , wherein a bottom edge of said photodetection region is formed at a depth deeper than a bottom edge of a device isolation structure defining said active region.  
   
   
       8 . The semiconductor imaging device as claimed in  claim 7 , wherein there is formed a well of said second conductivity type around said photodetection region so as to define said photodetection region with a depth exceeding a bottom edge of said device isolation structure but not exceeding a bottom edge of photodetection region.  
   
   
       9 . A photodetection method that uses a semiconductor imaging device, said semiconductor photodetection device comprising: silicon substrate defined with an active region; a gate electrode formed on said silicon substrate in correspondence to a channel region in said active region via a gate insulation film; a photodetection region formed of a diffusion region of a first conductivity type, said photodetection region being formed in said active region at a first side of said gate electrode such that a top part thereof is separated from a surface of said silicon substrate and such that an inner edge part invades underneath a channel region right underneath said gate electrode; a shielding layer formed of a diffusion region of a second conductivity type, said shielding layer being formed in said active region at said surface of said silicon substrate at said first side of said gate electrode such that an inner edge part thereof is aligned with a sidewall surface of said gate electrode at said first side, said shielding layer being formed so as to cover a part of said photodetection region located at said first side of said gate electrode; a floating diffusion region formed of a diffusion region of said first conductivity type, said floating diffusion region being formed in said active region at a second side of said gate electrode; and a channel region formed of a diffusion region of said second conductivity type, said channel region being formed in said active region right underneath said gate electrode, said channel region comprising: a first channel region part having said second conductivity type, a first end of said first channel region part being formed adjacent to said shielding layer, another end of said first channel region part invading to a region right underneath said gate electrode and covering a part of said photodetection region invading underneath said channel region; and a second channel region part having said second conductivity type and formed adjacent to said floating diffusion region, said first channel region part containing an impurity element of said second conductivity type with an impurity concentration level lower than an impurity concentration level in said shielding layer, said second channel region part containing said impurity element with a concentration level lower than said impurity concentration level of said first channel region part, 
 said photodetection method comprising the step of applying a voltage of +0.3-0.7V to said gate electrode in a photoreception mode thereof.    
   
   
       10 . A photodetection method that uses a semiconductor imaging device, said semiconductor imaging device comprising: a silicon substrate defined with an active region by a device isolation structure; a gate electrode formed on said silicon substrate in correspondence to a channel region in said active region via a gate insulation film; a photodetection region formed of an n-type diffusion region, said photodetection region being formed in said active region at a first side of said gate electrode such that a top part thereof is separated from a surface of said silicon substrate and such that an inner edge part invades into a region under a channel region right underneath said gate electrode; a shielding layer formed of a p-type diffusion region, said shielding layer being formed in said active region at said first side of said gate electrode at a surface of said silicon substrate such that an inner edge thereof is aligned to a sidewall surface of said gate electrode at said first side, said shielding layer being formed so as to cover at least a part of said photodetection region located at said first side of said gate electrode; a floating diffusion region formed of an n-type diffusion region, said floating diffusion region being formed in said active region at a second side of said gate electrode; and a channel region formed of a p-type diffusion region, said channel region being formed in said active region right underneath said gate electrode, 
 said photodetection method comprising the step of applying a voltage of −0.5-−2V to said gate electrode in a photoreception mode thereof.    
   
   
       11 . A method of fabricating a semiconductor imaging device, comprising the steps of: 
 forming a first diffusion region of a first conductivity type at a surface of a silicon substrate by introducing an impurity element of said first conductivity type into an active region defined on said silicon substrate such that said first diffusion region is formed over an entire surface of said active region with a first depth and a first impurity concentration level;    forming a photodetection region of a second conductivity type underneath said first diffusion region, by covering a first part of said first diffusion region by a first mask pattern and introducing an impurity element of a second conductivity type into said active region in overlapping relationship with said first diffusion region while using said first mask pattern as a mask, such that said impurity element of said second conductivity type is introduced to a second depth deeper than said first depth;    forming a second diffusion region of said first conductivity type on said photodetection region, by introducing an impurity element of said first conductivity type into said active region in overlapping relationship with said photodetection region while using said first mask pattern as a mask to a depth of said first depth or shallower, such that said second diffusion region contains said impurity element of said first conductivity type with a second impurity concentration level higher than in said first diffusion region;    forming a gate electrode on said silicon substrate via a gate insulation film such that said gate electrode covers a boundary of said first diffusion region and said second diffusion region;    forming a shielding layer of a diffusion region of said first conductivity type at a surface of said second diffusion region, by introducing an impurity element of said first conductivity element into said active region while using said gate electrode and a second mask pattern covering a part of said active region at a side opposite to said photodetection region with regard to said gate electrode as a mask, such that said shielding layer contains said impurity element of said first conductivity type with a third impurity concentration level larger than said second impurity concentration level; and    forming a floating diffusion region of said second conductivity type by introducing an impurity element of said second conductivity type into said active region while using said gate electrode and a third mask pattern covering a part of said active region at a side of said photodetection region with respect to said gate electrode as a mask.    
   
   
       12 . The method as claimed in  claim 11 , wherein said step of forming said second diffusion region comprises plural ion implantation process steps for introducing an impurity element of said first conductivity type with an oblique angle to a substrate of said silicon substrate, said plural ion implantation process steps being conducted while changing a direction of injection of said impurity element.  
   
   
       13 . A method of fabricating a semiconductor imaging device, comprising the steps of: 
 forming a first diffusion region of a first conductivity type in an active region defined on a silicon substrate by a device isolation region, by introducing thereto an impurity element of a first conductivity type with a first depth deeper than a bottom edge of said device isolation region;    forming a second diffusion region of a second conductivity type on a surface of said first diffusion region, by introducing an impurity element of a second conductivity type with a second, shallower depth;    forming a well having said second conductivity type and defining a photodetection region of said imaging device in said first diffusion region, by forming a first mask pattern on said active region in correspondence to said photodetection region so as to cover a first region in which said photodetection region is to be formed and by introducing an impurity element of said second conductivity type into said active region to a depth deeper than said bottom edge of said device isolation region but not exceeding a bottom edge of said first diffusion region while using said first mask pattern as a mask;    forming a second region of said second conductivity type but having a carrier concentration level lower than a carrier concentration level of said first region, by introducing an impurity element of said first conductivity type into said active region to said second depth while using said first mask pattern as a mask to said second depth such that said second region is formed in a part of said active region not covered by said first mask pattern;    forming a gate electrode on said silicon substrate via a gate insulation film so as to cover a part of a boundary between said first and second parts;    forming a shielding layer having said second conductivity type and a carrier concentration level higher than said first part in said active region, by covering a part of said active region opposite to said photodetection region with respect to said gate electrode by a third mask pattern, and by introducing a second impurity element to said active region in overlapping relationship with said second diffusion region while using said gate electrode and said third mask pattern as a mask; and    forming a floating diffusion region of said first conductivity type in said active region at a side opposite to said photodetection region by introducing thereto an impurity element of said first conductivity type.