Image sensor and method of fabricating same

1. An image sensor, comprising:

a substrate having a first surface and an opposing second surface and including unit pixels respectively having photoelectric conversion regions;

a semiconductor pattern disposed in a first trench defining the unit pixels, the semiconductor pattern including a first semiconductor layer provided on an inner surface of the first trench and a second semiconductor layer provided on the first semiconductor layer; and

a first contact provided on the second surface and connected to the semiconductor pattern,

wherein a height of the first semiconductor layer from a bottom surface of the first trench is less than a height of the second semiconductor layer from the bottom surface of the first trench.

2. The image sensor of claim 1 , wherein a bottom surface of the semiconductor pattern is coplanar with the second surface of the substrate.

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

a device isolation pattern provided adjacent to the first surface to fill a second trench of the substrate, wherein a top surface of the second semiconductor layer is disposed at a level between a bottom surface of the device isolation pattern and the second surface of the substrate.

4. The image sensor of claim 1 , wherein a first width of the second semiconductor layer adjacent to the first surface is greater than a second width of the second semiconductor layer adjacent to the second surface.

5. The image sensor of claim 1 , wherein the first and second semiconductor layers include poly silicon doped with first conductivity type impurities, and

the first conductivity type is one of N-type and P-type.

6. The image sensor of claim 1 , wherein a vertical distance from the first surface of the substrate to the first semiconductor layer ranges from 50 nm to 2000 nm.

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

an oxide pattern provided between the first and second semiconductor layers to at least partially cover an interface between the first and second semiconductor layers.

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

a first light-blocking pattern which covers an inner surface of a third trench of the substrate and is connected to the first contact, wherein the first contact fills an inner space of the third trench.

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

micro lenses provided on the second surface,

wherein the first trench extends from the second surface toward the first surface, the bottom surface of the first trench is disposed at a level between the first surface and the second surface, and the first semiconductor layer covers the bottom surface of the first trench.

10. An image sensor, comprising:

a substrate having a first surface and an opposing second surface and including a plurality of unit pixels;

color filters and micro lenses provided on the second surface of the substrate;

a pixel isolation pattern disposed in a first trench defining the unit pixels and penetrating the substrate, the pixel isolation pattern including a first oxide layer covering an inner surface of the first trench, a first semiconductor layer, and a second semiconductor layer; and

a first contact connected to the first and second semiconductor layers,

wherein the first semiconductor layer has a first side surface and an opposing second side surface, and

a distance between the first and second side surfaces in a horizontal direction increases with decreasing distance to the first surface of the substrate.

11. The image sensor of claim 10 , wherein a first height of the first semiconductor layer from the second surface is less than a second height of the second semiconductor layer from the second surface.

12. The image sensor of claim 10 , wherein the second semiconductor layer is disposed between the first and second side surfaces of the first semiconductor layer.

13. The image sensor of claim 10 , wherein the second semiconductor layer includes a first portion and a second portion and vertically extends toward the second surface of the substrate,

the first portion contacts the first oxide layer, and

the second portion is spaced apart from the first oxide layer by the first semiconductor layer interposed therebetween.

14. The image sensor of claim 10 , wherein a thickness of the first semiconductor layer adjacent to the first surface of the substrate is less than a thickness of the second semiconductor layer adjacent to the second surface of the substrate.

15. The image sensor of claim 10 , wherein a vertical distance from the first surface of the substrate to the first semiconductor layer is greater than a vertical distance from the first surface to the second semiconductor layer.

16. The image sensor of claim 10 , wherein a ratio between a vertical height of the first semiconductor layer and a vertical height of the pixel isolation pattern ranges from 3/4 to 5/6.

17. The image sensor of claim 10 , further comprising an oxide pattern, wherein the oxide pattern is disposed between the first and second semiconductor layers.

18. The image sensor of claim 10 , wherein the substrate comprises a pixel region, a pad region, and an optically black region between the pixel region and the pad region,

the first contact is disposed in the optically black region, and

a first light-blocking pattern is provided between the first contact and the substrate and is connected to the first and second semiconductor layers.

19. The image sensor of claim 10 , wherein the first and second semiconductor layers comprise poly silicon are doped with impurities of first conductivity type, and

a concentration of the first conductivity type impurities is higher in the first semiconductor layer than in the second semiconductor layer.

20. An image sensor, comprising

a substrate having a first surface and an opposing second surface and including a pixel region with a plurality of unit pixels, an optically black region, and a pad region;

a pixel isolation pattern filling a first trench of the substrate and defining the unit pixels, the pixel isolation pattern including a first oxide layer covering an inner surface of the first trench, a first semiconductor layer, and a second semiconductor layer;

color filters provided on the second surface of the substrate;

micro lenses provided on the color filters;

transfer transistors and logic transistors provided on the first surface;

a device isolation pattern provided adjacent to the first surface to fill a second trench of the substrate;

an interlayer insulating layer provided on the first surface;

interconnection lines provided in the interlayer insulating layer and electrically connected to the transfer and logic transistors;

a first light-blocking pattern and a first contact provided on the optically black region; and

a second light-blocking pattern and a second contact provided on the pad region,

wherein the first contact is connected to the first light-blocking pattern and the first and second semiconductor layers.