CMOS image sensor and manufacturing method thereof

1. A CMOS (complementary metal oxide semiconductor) image sensor comprising:

a semiconductor substrate on which a device isolation region and an active region are defined;

a photodiode region formed on the active region;

a conductive plug formed at the photodiode region for connecting the photodiode region to a metal wiring; and

a transistor formed enclosing the conductive plug, wherein the perimeter of the conductive plug is completely surrounded by the transistor.

2. The CMOS image sensor according to claim 1 , wherein the perimeter of the conductive plug has a square shape.

3. A CMOS (complementary metal oxide semiconductor) image sensor comprising:

a semiconductor substrate on which a device isolation region and an active region are defined;

a photodiode region formed on the active region;

a transistor region formed on the active region, wherein the transistor region is horizontally arranged with the photodiode region;

a conductive plug making a contact with a top surface of the photodiode region;

a transistor formed on the transistor region wherein a portion of the transistor extends into the photodiode region around the perimeter of the conductive plug to provide an enclosing portion of the transistor on the photodiode region; and

an interlayer dielectric formed on the semiconductor substrate including the transistor, wherein the conductive plug is formed in a contact hole in the interlayer dielectric.

4. The CMOS image sensor according to claim 3 , wherein the perimeter of the conductive plug has a square shape.

5. The CMOS image sensor according to claim 3 , wherein the transistor comprises a gate insulating layer, a gate electrode, and an insulating layer sidewall.

6. The CMOS image sensor according to claim 5 , wherein a part of the conductive plug is enclosed by the interlayer dielectric, and another part of the conductive plug is enclosed by the insulating layer sidewall of the transistor.