Solid-state imaging device and imaging system

1. A solid-state imaging device comprising:

a plurality of pixels each of which includes:

a photoelectric conversion portion which photoelectrically converts incident light to generate a signal charge;

a charge holding portion that accumulates the signal charge transferred from the photoelectric conversion portion;

a floating diffusion region to which the signal charge of the charge holding portion is transferred;

a first transfer gate configured to transfer the signal charge from the photoelectric conversion portion to the charge holding portion; and

a second transfer gate configured to transfer the signal charge from the charge holding portion to the floating diffusion region,

wherein:

the photoelectric conversion portion includes a first semiconductor region of a first conductivity type, and a second semiconductor region of a second conductivity type including a majority carrier of a polarity of the signal charge formed under the first semiconductor region,

the charge holding portion includes a third semiconductor region of the first conductivity type, and a fourth semiconductor region of the second conductivity type formed under the third semiconductor region,

in a first cross section including the photoelectric conversion portion, the charge holding portion and the first transfer gate, a first side edge of the fourth semiconductor region on the photoelectric conversion portion side is provided between the second semiconductor region and a first side edge of the third semiconductor region on the photoelectric conversion portion side,

in a second cross section including the charge holding portion, the floating diffusion region and the second transfer gate, a second side edge of the fourth semiconductor region on the floating diffusion region side is provided between the floating diffusion region and a second side edge of the third semiconductor region on the floating diffusion region side, and

a plane including the first cross section is different and distant from a plane including the second cross section.

2. The solid-state imaging device according to claim 1 , wherein the fourth semiconductor region has a higher impurity concentration than the second semiconductor region.

3. The solid-state imaging device according to claim 1 , wherein an area of the charge holding portion is larger than an area of the photoelectric conversion portion.

4. The solid-state imaging device according to claim 1 , wherein the charge holding portion further has a fifth semiconductor region of the first conductivity type, which is formed in contact with a bottom of the fourth semiconductor region.

5. The solid-state imaging device according to claim 1 , wherein the photoelectric conversion portion further has a sixth semiconductor region which is formed in contact with an end of the first semiconductor region at a side of the charge holding portion, and has a lower impurity concentration than the first semiconductor region.

6. The solid-state imaging device according to claim 1 , wherein the charge holding portion further has a seventh semiconductor region of the first conductivity type, which is formed in contact with an end of the third semiconductor region at a side of the floating diffusion region, and has a lower impurity concentration than the third semiconductor region.

7. The solid-state imaging device according to claim 1 , wherein the charge holding portion further has an eighth semiconductor region of the first conductivity type, which is formed in contact with an end of the third semiconductor region at a side of the photoelectric conversion portion, and has a lower impurity concentration than the third semiconductor region.

8. The solid-state imaging device according to claim 1 , wherein the charge holding portion further has a ninth semiconductor region of the second conductivity type, which is arranged in a vicinity of an end of the third semiconductor region at a side of the floating diffusion region.

9. The solid-state imaging device according to claim 1 , wherein the charge holding portion further has a tenth semiconductor region of the second conductivity type, which is arranged in a vicinity of an end of the third semiconductor region at a side of the photoelectric conversion portion.

10. The solid-state imaging device according to claim 5 , wherein the sixth semiconductor region extends to a region below the first transfer gate.

11. The solid-state imaging device according to claim 8 , wherein the ninth semiconductor region extends to a region below the second transfer gate.

12. The solid-state imaging device according to claim 9 , wherein the tenth semiconductor region extends to a region below the first transfer gate.

13. The solid-state imaging device according to claim 1 , wherein the first transfer gate extends to an upper part of the charge holding portion.

14. The solid-state imaging device according to claim 1 , wherein,

in the first cross section, a part of the fourth semiconductor region is provided under the first transfer gate, and

in the second cross section, a part of the fourth semiconductor region is provided under the second transfer gate.

15. The solid-state imaging device according to claim 14 , wherein a p-n junction between the third semiconductor region and the fourth semiconductor region is positioned at a different depth from a p-n junction between the first semiconductor region and the second semiconductor region.

16. The solid-state imaging device according to claim 1 , wherein the fourth semiconductor region and the floating diffusion region are isolated by a semiconductor region of the first conductivity type.

17. An imaging system comprising:

the solid-state imaging device according to claim 1 ; and

an optical system which forms an object image on the solid-state imaging device.

18. The solid-state imaging device according to claim 1 , wherein a first line included in the first cross section and a second line included in the second cross section are offset from each other.