Solid state imaging device and method for manufacturing the same
View Patent ↗A solid state imaging device includes a transfer transistor for transferring signal charges generated by photoelectric conversion to a floating diffusion layer, a reset transistor for resetting a potential of the floating diffusion layer, and an amplifying transistor for outputting a signal corresponding to the potential of the floating diffusion layer. A low concentration impurity region having an impurity concentration lower than that of the first conductivity type semiconductor region is formed in part of a surface portion of the first conductivity type semiconductor region which is located below a gate electrode of the amplifying transistor and serves as a well region of the amplifying transistor.
1. A solid state imaging device comprising:
a transfer transistor for transferring signal charges generated by photoelectric conversion to a floating diffusion layer;
a reset transistor for resetting a potential of the floating diffusion layer; and
an amplifying transistor for outputting a signal corresponding to the potential of the floating diffusion layer, wherein
the solid state imaging device includes
a first conductivity type semiconductor region serving as a well region of the amplifying transistor, and
a low concentration impurity region which is formed in part of a surface portion of the first conductivity type semiconductor region below a gate electrode of the amplifying transistor, and has an impurity concentration lower than that of the first conductivity type semiconductor region.
2. The solid state imaging device of claim 1 , wherein
the low concentration impurity region is substantially an intrinsic semiconductor region.
3. The solid state imaging device of claim 1 , wherein
the low concentration impurity region has an impurity concentration of 3×10 16 cm 3 or lower.
4. The solid state imaging device of claim 1 , wherein,
the low concentration impurity region has an impurity concentration of ½ or lower of the impurity concentration of the first conductivity type semiconductor region.
5. The solid state imaging device of claim 1 , wherein,
the low concentration impurity region is formed in a region ranging from an interface with a gate insulating film of the amplifying transistor to a depth of 60 nm.
6. The solid state imaging device of claim 1 , wherein,
an STI is formed in part of the first conductivity type semiconductor region between the transfer transistor and the amplifying transistor.
7. A method for manufacturing a solid state imaging device including a transfer transistor for transferring signal charges generated by photoelectric conversion to a floating diffusion layer, a reset transistor for resetting a potential of the floating diffusion layer, and an amplifying transistor for outputting a signal corresponding to the potential of the floating diffusion layer, the method comprising:
(a) forming a first conductivity type semiconductor region serving as a well region of the amplifying transistor on a substrate; and
(b) implanting a second conductivity type impurity to a surface portion of the first conductivity type semiconductor region to form a low concentration impurity region having an impurity concentration lower than that of the first conductivity type semiconductor region and serving as a channel region of the amplifying transistor.
8. The method for manufacturing a solid state imaging device of claim 7 , wherein
the implantation (b) is performed before the formation (a).
9. The method for manufacturing a solid state imaging device of claim 7 , wherein
the low concentration impurity region is substantially an intrinsic semiconductor region.
10. The method for manufacturing a solid state imaging device of claim 7 , wherein
the second conductivity type impurity is arsenic or phosphorus.