Image sensor

1. An image sensor, comprising:

a substrate having a first surface;

a first device isolation region in the substrate and adjacent to the first surface of the substrate, the first device isolation region defining a unit pixel;

a transfer gate on the first surface of the substrate at an edge of the unit pixel;

a photoelectric conversion part in the substrate and adjacent to a first side surface of the transfer gate; and

a floating diffusion region in the substrate and adjacent to a second side surface of the transfer gate, the second side surface opposing the first side surface,

a second device isolation region in the substrate below the floating diffusion region and doped with impurities having a first conductivity,

wherein the first device isolation region is spaced apart from the second side surface of the transfer gate,

wherein the substrate and the first device isolation region are doped with impurities having the first conductivity,

wherein a first impurity concentration of the first device isolation region is greater than a second impurity concentration of the substrate, and

wherein a third impurity concentration of the second device isolation region is equal to the first impurity concentration of the first device isolation region.

2. The image sensor of claim 1 , wherein the second device isolation region contacts the first device isolation region.

3. The image sensor of claim 1 , wherein the first device isolation region is spaced apart from the floating diffusion region.

4. The image sensor of claim 1 , further comprising:

a first impurity doped region in the substrate and overlapping the transfer gate,

wherein the photoelectric conversion part comprises a first photoelectric conversion region doped with impurities having a second conductivity opposite to the first conductivity, and

wherein the first impurity doped region extends into the first photoelectric conversion region.

5. The image sensor of claim 4 ,

wherein the photoelectric conversion part further comprises a second photoelectric conversion region in the substrate and adjacent to a second surface of the substrate that is opposite to the first surface of the substrate, and

wherein the second photoelectric conversion region overlaps the first photoelectric conversion region and is doped with impurities having the first conductivity.

6. The image sensor of claim 5 ,

wherein the photoelectric conversion part further comprises a third photoelectric conversion region between the first photoelectric conversion region and the second photoelectric conversion region,

wherein the third photoelectric conversion region is doped with impurities having the second conductivity, and

wherein a fourth impurity concentration of the third photoelectric conversion region is less than a fifth impurity concentration of the first photoelectric conversion region.

7. The image sensor of claim 1 , further comprising:

a deep device isolation pattern extending from a second surface of the substrate that is opposite to the first surface of the substrate towards the first surface of the substrate and overlapping the first device isolation region and/or the floating diffusion region.

8. The image sensor of claim 1 , further comprising:

a shallow device isolation pattern extending from the first surface of the substrate towards a second surface of the substrate that is opposite to the first surface of the substrate and in contact with the first device isolation region.

9. The image sensor of claim 8 , further comprising:

a first source/drain region and a second source/drain region adjacent to each other in the substrate,

wherein the shallow device isolation pattern is spaced apart from the unit pixel and is between the first source/drain region and the second source/drain region.

10. An image sensor, comprising:

a substrate having a first surface;

a first device isolation region in the substrate and adjacent to the first surface of the substrate, the first device isolation region defining a unit pixel;

a sub-isolation region on the unit pixel in the substrate, wherein the sub-isolation region is spaced apart from the first device isolation region and separates the unit pixel into a first sub-pixel and a second sub-pixel;

a first sub-transfer gate on the first surface of the substrate, adjacent to a first corner of the first sub-pixel, wherein the first corner of the first sub-pixel is adjacent to the second sub-pixel;

a second sub-transfer gate on the first surface of the substrate, adjacent to a second corner of the second sub-pixel, wherein the second corner of the second sub-pixel is adjacent to the first sub-transfer gate;

a floating diffusion region in the substrate and adjacent to the first sub-transfer gate and the second sub-transfer gate; and

a first impurity doped region in the substrate and overlapping the first and second sub-transfer gates,

wherein the first device isolation region and the sub-isolation region are spaced apart from the floating diffusion region,

wherein the substrate, the first device isolation region, and the first impurity doped region are doped with impurities having a first conductivity, and

wherein a first impurity concentration of the first impurity doped region is greater than a second impurity concentration of the substrate and less than a third impurity concentration of the first device isolation region.

11. An image sensor, comprising:

a substrate having a first surface;

a first device isolation region in the substrate and adjacent to the first surface of the substrate, the first device isolation region defining a unit pixel;

a sub-isolation region on the unit pixel in the substrate, wherein the sub-isolation region is spaced apart from the first device isolation region and separates the unit pixel into a first sub-pixel and a second sub-pixel;

a first sub-transfer gate on the first surface of the substrate, adjacent to a first corner of the first sub-pixel, wherein the first corner of the first sub-pixel is adjacent to the second sub-pixel;

a second sub-transfer gate on the first surface of the substrate, adjacent to a second corner of the second sub-pixel, wherein the second corner of the second sub-pixel is adjacent to the first sub-transfer gate;

a floating diffusion region in the substrate and adjacent to the first sub-transfer gate and the second sub-transfer gate; and

a second device isolation region below the floating diffusion region and doped with impurities having a first conductivity,

wherein the first device isolation region is doped with impurities having the first conductivity,

wherein the first device isolation region and the sub-isolation region are spaced apart from the floating diffusion region, and

wherein a second impurity concentration of the second device isolation region is equal to a first impurity concentration of the first device isolation region.

12. The image sensor of claim 11 , wherein the second device isolation region contacts the first device isolation region.