Solid-state image sensor, production method for solid-state image sensor, and camera using solid-state image sensor

• US 20050006676A1
• Filed: 05/11/2004
• Published: 01/13/2005
• Est. Priority Date: 05/15/2003
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Watanabe, Takanori
• Granted Patent: US 7,227,206 B2
• Time in Patent Office: Days
• US Class Current: 257/290
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers

Abstract

A solid-state image sensor includes, in each pixel, a p-type well provided on a semiconductor substrate, a photodiode provided in the p-type well, a transfer gate for transferring photocharges accumulated in the photodiode, and an n-type diffusion region for receiving the transferred photocharges. The photodiode includes a first n-type accumulation region, and a second n-type accumulation region having a concentration higher than that of the first accumulation region and provided at a position deeper than the first accumulation region. The first accumulation region extends toward an end of the transfer gate, and the second accumulation region is separate from the transfer gate.

Claims

1. A solid-state image sensor comprising in each pixel:

a semiconductor region of a first conductive type provided on a semiconductor substrate;

a photodiode provided in the semiconductor region;

a transfer gate for transferring photocharges accumulated in the photodiode; and

a diffusion region for receiving the transferred photocharges;

wherein the photodiode includes a first accumulation region composed of a semiconductor of a second conductive type, and a second accumulation region provided in contact with the first accumulation region and at a position deeper than the first accumulation region, and composed of a semiconductor of the second conductive type, and

wherein the first accumulation region extends toward and end of the transfer gate, and the second accumulation region is separate from the transfer gate.

2. A solid-state image sensor according to claim 1, wherein a part of the first accumulation region reaches a surface of the semiconductor region.

3. A solid-state image sensor according to claim 1, wherein the semiconductor region serves as a first semiconductor region, and a second semiconductor region of the first conductive type is provided on a front side of the photodiode and in contact with the first accumulation region.

4. A solid-state image sensor according to claim 3, wherein the following condition is satisfied:

Rp2≦

Xj

where Rp2 represents the mean range for the first accumulation region, and Xj represents the depth of the junction between the first accumulation region and the second semiconductor region.

5. A solid-state image sensor according to claim 4, wherein the following condition is satisfied:

Rp2≦

Xj<

Rp1

where Rp1 represents the mean range for the second accumulation region.

6. A solid-state image sensor according to claim 1, wherein an impurity that defines the second conductive type of the second accumulation region is arsenic.

7. A solid-state image sensor according to claim 1, wherein an impurity that defines the second conductive type of the first accumulation region is arsenic.

8. A solid-state image sensor according to claim 3, wherein the second semiconductor region is provided separate from an end of the transfer gate.

9. A camera having a solid-state image sensor, wherein the solid-state image sensor comprises in each pixel:

a semiconductor region of a first conductive type provided on a semiconductor substrate;

a photodiode provided in the semiconductor region;

a transfer gate for transferring photocharges accumulated in the photodiode; and

a diffusion region for receiving the transferred photocharges;

wherein the photodiode includes a first accumulation region composed of a semiconductor of a second conductive type, and a second accumulation region provided in contact with the first accumulation region and at a position deeper than the first accumulation region, and composed of a semiconductor of the second conductive type, and

wherein the first accumulation region extends toward and end of the transfer gate, and the second accumulation region is separate from the transfer gate.

10. A production method for a solid-state image sensor comprising, for each pixel, the steps of:

providing a semiconductor region of a first conductive type on a semiconductor substrate;

providing a photodiode in the semiconductor region;

providing a transfer gate for transferring photocharges accumulated in the photodiode; and

providing a diffusion region for receiving the transferred photocharges,

wherein the step of providing a photodiode includes providing a first accumulation region composed of a semiconductor of a second conductive type, and providing a second accumulation region in contact with the first accumulation region and at a position deeper than the first accumulation region, and composed of a semiconductor of the second conductive type, and

wherein the step of providing a photodiode further includes forming the first accumulation region by ion implantation satisfying 0°

≦

α

<

90° and

270°

<

α

≦

360°

, and forming the second accumulation region by ion implantation satisfying 90°

≦

α

≦

270°

, where a represents an angle defined between an x-axis, indicating a gate length direction of the transfer gate, and a projected ion implantation direction, obtained by projecting an ion implantation direction onto an xy-plane including the x-axis and a y-axis indicating a gate width direction of the transfer gate.

11. A production method according to claim 10, wherein the ion implantation for forming the first accumulation region is performed at α

=0°

, and the ion implantation for forming the second accumulation region is performed at α

=90°

or 270°

.

12. A production method according to claim 10, wherein the semiconductor region serves as a first semiconductor region, the method further comprising the step of providing a second semiconductor region of the first conductive type on a front side of the photodiode and in contact with the first accumulation region.

13. A production method according to claim 12, further comprising forming an offset portion by performing ion implantation for the second semiconductor region with a side spacer placed at an end of the transfer gate.

14. A production method according to claim 12, further comprising an offset portion between the second semiconductor region and the transfer region in a self-alignment manner by performing ion implantation for the second semiconductor region in a direction to make a shadow of the transfer gate on the photodiode.

15. A production method according to claim 10, wherein the first accumulation region is formed by arsenic implantation.

16. A production method according to claim 10, wherein the second accumulation region is formed by arsenic implantation.