Unit pixel of image sensor and image sensor including the same

1. A pixel unit comprising:

a semiconductor substrate having first and second opposite major surfaces at upper and lower portions thereof, respectively;

a photoelectric conversion region within the semiconductor substrate;

an isolation region comprising dielectric material surrounding the photoelectric conversion region, and wherein the dielectric material extends substantially vertically in an axial direction away from the first surface of the semiconductor substrate to the level of the second surface of the semiconductor substrate in the pixel unit, the dielectric material has an end surface coplanar with the second surface of the semiconductor substrate, and an entire outer circumferential portion of the photoelectric conversion region contacts the isolation region; and

a transfer gate extending substantially vertically in the axial direction away from the first surface of the semiconductor substrate to a location adjacent the photoelectric conversion region.

2. The pixel unit of claim 1 , wherein the dielectric material has a refractive index lower than that of the semiconductor substrate.

3. The pixel unit of claim 2 , further comprising a polysilicon region within the dielectric material of the isolation region.

4. The pixel unit of claim 2 , wherein the semiconductor substrate contains impurities of a conductivity type, and further comprising a doped surface layer surrounding the dielectric material of the isolation region, and wherein the doped surface layer contains impurities of the opposite conductivity type as the photoelectric conversion region but at a higher density.

5. The pixel unit of claim 2 , wherein the dielectric material contains negative fixed charges.

6. The pixel unit of claim 1 , wherein part of the transfer gate extends into the photoelectric conversion region.

7. The pixel unit of claim 1 , wherein the transfer gate is cup-shaped or pillar-shaped.

8. The pixel unit of claim 1 , further comprising a first impurity region under the photoelectric conversion region, the photoelectric conversion region containing impurities of a first-conductivity type, and the first impurity region containing the same type of impurities as the photoelectric conversion region but at a lower density than the photoelectric conversion region.

9. The pixel unit of claim 1 , further comprising:

a color filter disposed on the second surface of the semiconductor substrate.

10. The pixel unit of claim 9 , further comprising:

a dielectric layer interposed between the second surface of the semiconductor substrate and the color filter.

11. The pixel unit of claim 10 , wherein the dielectric layer includes negative fixed charges.

12. The pixel unit of claim 1 , wherein the photoelectric conversion region has impurities of a first conductivity type and is spaced from the first surface of the semiconductor substrate towards the second surface of the semiconductor substrate.

13. The pixel unit of claim 9 , further comprising:

a micro lens disposed on the color filter.

14. The pixel unit of claim 13 , wherein the micro lens is a convex lens having such a curvature that light incident on the micro lens is focused through the color filter and onto the photoelectric conversion region by the micro lens.

15. The pixel unit of claim 1 , wherein the photoelectric conversion region collects photo-charges in response to incident light, and configured such that a leakage component of the incident light is reflected internally at a sidewall surface of the isolation region, and a reflection component of the incident light reaches the photoelectric conversion region.