Imaging device
View Patent ↗First diffusion region constituting a photodiode in each pixel stores carriers generated according to incident light. Second diffusion region is formed at a surface of the first diffusion region to cover a peripheral part of the first diffusion region. In the peripheral part of the first diffusion region, crystal defects tend to occur by a process of forming an isolation region and a gate electrode, so that dark current noise tends to occur. The second diffusion region functioning as a protection layer prevents crystal defects in a manufacturing process. The second diffusion region isn't formed on a center of the surface of the first diffusion region where crystal defects don't tend to occur. In the first diffusion region where the second diffusion region isn't formed, the thickness of a depletion layer increases, which improves light detection sensitivity. This improves detection sensitivity of the photodiode without increasing the dark current noise.
1. An imaging device, comprising a plurality of pixels each including a photodiode, wherein
the each pixel comprises:
a first diffusion region of a first conductive type which constitutes a storing part of optical carriers in the photodiode;
a transfer transistor which uses the first diffusion region as a source electrode, whose gate electrode is formed in a position adjacent to the first diffusion region via an insulating film, and which transfers the optical carriers stored in the photodiode to a drain electrode; and
a second diffusion region of a second conductive type which is formed at a surface of a peripheral part of the first diffusion region to cover the peripheral part and has a polarity opposite to that of the first conductive type, wherein the first diffusion region includes a center part exposed at a surface of the photodiode, the center part being located inside of the peripheral part.
2. The imaging device according to claim 1 , further comprising
an isolation region which is formed apart from the first diffusion region around a partial peripheral part other than a portion adjacent to the gate electrode of the peripheral part, wherein
the second diffusion region is formed from the partial peripheral part to the isolation region.
3. The imaging device according to claim 1 , wherein
in the first diffusion region, an area of a region exposed at the surface is larger than an area of a region covered with the second diffusion region.
4. The imaging device according to claim 1 , wherein
the each pixel comprises:
a reset transistor whose source electrode is connected to the drain electrode of the transfer transistor and drain electrode is connected to a voltage supply line;
a source follower transistor whose gate electrode is connected to a floating diffusion node being the drain electrode of the transfer transistor and the source electrode of the reset transistor and which outputs a pixel signal from a source electrode; and
a contact region which connects the floating diffusion node and the gate electrode of the source follower transistor to each other.
5. The imaging device according to claim 1 , wherein
an impurity concentration of the second diffusion region is higher than an impurity concentration of the first diffusion region.
6. The imaging device according to claim 1 , wherein
the first conductive type is an n type, and the second conductive type is a p type.
7. The imaging device according to claim 1 , further comprising
a micro lens which is formed above the first diffusion region of the each pixel to gather light incident on the each pixel in the first diffusion region.
8. An imaging device, comprising a plurality of pixels each including a photodiode, wherein
the each pixel comprises:
a first diffusion region of a first conductive type which constitutes a storing part of optical carriers in the photodiode;
a transfer transistor which uses the first diffusion region as a source electrode, whose gate electrode is formed in a position adjacent to the first diffusion region via an insulating film, and which transfers the optical carriers stored in the photodiode to a drain electrode;
a second diffusion region of a second conductive type which is formed at a surface of the first diffusion region to cover a partial peripheral part other than a portion adjacent to the gate electrode of a peripheral part of the first diffusion region and has a polarity opposite to that of the first conductive type; and
a third diffusion region of the first conductive type which is formed in the peripheral part on a gate electrode side of the first diffusion region in an inner part of the first diffusion region and has an impurity concentration higher than an impurity concentration of the first diffusion region.
9. The imaging device according to claim 8 , further comprising
an isolation region which is formed apart from the first diffusion region around the partial peripheral part, wherein
the second diffusion region is formed from the partial peripheral part to the isolation region.
10. An imaging device, comprising a plurality of pixels each including a photodiode, wherein
the each pixel comprises:
a first diffusion region of a first conductive type which constitutes a storing part of optical carriers in the photodiode;
a transfer transistor which uses the first diffusion region as a source electrode, whose gate electrode is formed in a position adjacent to the first diffusion region via an insulating film, and which transfers the optical carriers stored in the photodiode to a drain electrode;
a second diffusion region of a second conductive type which is formed at a surface of the first diffusion region to cover a partial peripheral part other than a portion adjacent to the gate electrode of a peripheral part of the first diffusion region and has a polarity opposite to that of the first conductive type; and
a third diffusion region of the first conductive type which is formed in the peripheral part on a gate electrode side of the first diffusion region at the surface of the first diffusion region and has an impurity concentration higher than an impurity concentration of the first diffusion region.
11. An imaging device, comprising a plurality of pixels each including a photodiode, wherein
the each pixel comprises:
a first diffusion region of a first conductive type which constitutes a storing part of optical carriers in the photodiode;
a transfer transistor which uses the first diffusion region as a source electrode, whose gate electrode is formed in a position adjacent to the first diffusion region via an insulating film, and which transfers the optical carriers stored in the photodiode to a drain electrode;
a second diffusion region of a second conductive type which is formed at a surface of the first diffusion region to cover a partial peripheral part other than a portion adjacent to the gate electrode of a peripheral part of the first diffusion region and has a polarity opposite to that of the first conductive type; and
a plurality of third diffusion regions of the first conductive type which is sequentially formed toward the gate electrode inside the second diffusion region at the surface of the first diffusion region and have impurity concentrations higher than an impurity concentration of the first diffusion region, wherein
the nearer the gate electrode, the higher the impurity concentration of the third diffusion region becomes.
12. The imaging device according to claim 8 , wherein
in the first diffusion region, an area of a region exposed at the surface is larger than an area of a region covered with the second diffusion region.
13. The imaging device according to claim 8 , wherein
the each pixel comprises:
a reset transistor whose source electrode is connected to the drain electrode of the transfer transistor and drain electrode is connected to a voltage supply line;
a source follower transistor whose gate electrode is connected to a floating diffusion node being the drain electrode of the transfer transistor and the source electrode of the reset transistor and which outputs a pixel signal from a source electrode; and
a contact region which connects the floating diffusion node and the gate electrode of the source follower transistor to each other.
14. The imaging device according to claim 8 , wherein
an impurity concentration of the second diffusion region is higher than an impurity concentration of the first diffusion region.
15. The imaging device according to claim 8 , wherein
the first conductive type is an n type, and the second conductive type is a p type.
16. The imaging device according to claim 8 , further comprising
a micro lens which is formed above the first diffusion region of the each pixel to gather light incident on the each pixel in the first diffusion region.