Semiconductor imaging device and fabrication process thereof

A method of fabricating a semiconductor imaging device, comprising:

• 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 regions;
• forming a shielding layer having said second conductivity type and a carrier concentration level higher than said second diffusion region below said gate electrode 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.