Solid-state image sensing device

1. A solid-state image sensing device provided with photoelectric conversion films stacked above a semiconductor substrate, comprising:

first impurity regions of a first conduction type electrically connected to the photoelectric conversion films and provided in a surface of the semiconductor substrate for accumulating signal charges generated in the photoelectric conversion films;

second impurity regions of the first conduction type provided under the first impurity regions and lower in density than the first impurity regions for accumulating the signal charges accumulated in the first impurity regions;

signal charge reading regions for reading the signal charges accumulated in the second impurity regions; and

third impurity regions of a second conduction type provided in the surface of the semiconductor substrate and between the first impurity regions and the signal charge reading regions and reverse to the first conduction type.

2. The solid-state image sensing device according to claim 1 , further comprising fourth impurity regions of the second conduction type provided between the first impurity regions and the second impurity regions.

3. The solid-state image sensing device according to claim 2 , wherein part of the second impurity regions dig into the signal charge reading regions.

4. The solid-state image sensing device according to claim 3 , wherein the third impurity regions are provided to surround the first impurity regions respectively.

5. The solid-state image sensing device according to claim 2 , wherein the third impurity regions are provided to surround the first impurity regions respectively.

6. The device of claim 2 , wherein the third impurity regions are directly adjacent to each of the first, second and fourth impurity regions.

7. The device of claim 2 , wherein an electrical potential of the fourth impurity regions is fixed.

8. The device of claim 7 , wherein the fourth impurity regions are lower in density than a p-well layer.

9. The solid-state image sensing device according to claim 1 , wherein part of the second impurity regions dig into the signal charge reading regions.

10. The solid-state image sensing device according to claim 9 , wherein the third impurity regions are provided to surround the first impurity regions respectively.

11. The solid-state image sensing device according to claim 1 , wherein the third impurity regions are provided to surround the first impurity regions respectively.

12. The device of claim 1 , wherein the third impurity regions are directly adjacent to each of the first and second impurity regions.

13. The device of claim 1 , wherein the second impurity regions are provided completely inside the semiconductor substrate below the surface of the substrate.

14. A method for reading a signal charge from a solid-state image sensing device, the solid-state image sensing device being provided with photoelectric conversion films stacked above a semiconductor substrate, and comprising,

first impurity regions of a first conduction type electrically connected to the photoelectric conversion films and provided in a surface of the semiconductor substrate for accumulating signal charges generated in the photoelectric conversion films;

second impurity regions of the first conduction type provided under the first impurity regions and completely inside the semiconductor substrate and lower in density than the first impurity regions for accumulating the signal charges accumulated in the first impurity regions;

signal charge reading regions for reading the signal charges accumulated in the second impurity regions; and

third impurity regions of a second conduction type provided in the surface of the semiconductor substrate and between the first impurity regions and the signal charge reading regions and reverse to the first conduction type, in which the third impurity regions are in contact with other impurity regions,

wherein the method comprises reading out the signal charges generated by photoelectric conversion and accumulated in the first impurity regions via the second impurity regions and an inside of the semiconductor substrate.

15. The method according to claim 14 , wherein fourth impurity regions of the second conduction type are provided between the first impurity regions and the second impurity regions, and signal charges accumulated in the first impurity regions and overflowing are once accumulated in the second impurity regions and the signal charges accumulated in the second impurity regions are read out to a transfer portion.

16. The method according to claim 15 , wherein when the signal charges are read out, the second impurity regions are depleted.

17. The method according to claim 14 , wherein a part of the second impurity regions is provided inside the signal charge reading regions.