Image sensor applied with device isolation technique for reducing dark signals and fabrication method thereof

1 . An image sensor, comprising:

a logic unit; and

a light collection unit in which a plurality of photodiodes is formed, wherein the photodiodes are isolated from each other by a field ion-implantation region formed under a surface of a substrate and an insulation layer formed on the surface of the substrate.

2 . The image sensor as recited in claim 1 , wherein the substrate and the field ion-implantation region are formed of a first conductive type and the photodiode is formed of a second conductive type.

3 . The image sensor as recited in claim 1 , wherein the insulation layer is an oxide layer grown by a thermal process.

4 . The image sensor as recited in claim 1 , wherein the logic unit includes an insulation layer for device isolation formed by a local oxidation of silicon (LOCOS) technique and a shallow trench isolation (STI) technique.

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

a logic unit; and

a pixel array unit in which a plurality of photodiodes is formed, wherein the photodiodes are isolated from each other by a field ion-implantation region formed under a surface of a substrate and an insulation layer formed on the surface of the substrate.

6 . The CMOS image sensor as recited in claim 5 , wherein the substrate and the field ion-implantation region are formed of a first conductive type and the photodiode is formed of a second conductive type.

7 . The CMOS image sensor as recited in claim 5 , wherein the logic unit includes an insulation layer for device isolation formed by one of a LOCOS technique and a STI technique.

8 . The CMOS image sensor as recited in claim 5 , wherein the insulation layer is an oxide layer grown by a thermal process.

9 . The CMOS image sensor as recited in claim 5 , wherein the insulation layer is formed with a predetermined thickness in consideration of ion-implantation energy used in a subsequent ion-implantation process.

10 . A method for forming a device isolation structure in an image sensor including a light collection unit and a logic unit, comprising the steps of:

forming an insulation layer pattern on a substrate in a field region of the light collection unit;

forming an insulation layer for device isolation in a field region of the logic unit by performing one of a LOCOS technique and a STI technique; and

forming a field ion-implantation region under a surface of the substrate in the field region of the light collection unit.

11 . The method as recited in claim 10 , wherein the insulation layer pattern is formed in a manner to have inclined sidewalls.

12 . The method as recited in claim 10 , wherein the step of forming the insulation layer pattern includes the steps of:

stacking an oxide layer and a nitride layer on a substrate;

forming a mask pattern on the nitride layer, the mask pattern opening an active region of the light collection unit;

performing a dry etching process and a subsequent wet etching process to the nitride layer and the oxide layer by using the mask pattern as an etch mask; and

removing the mask pattern and the nitride layer.

13 . The method as recited in claim 10 , wherein an undercut is formed at a bottom portion of each sidewall of the nitride layer patterned by the dry etching process.

14 . The method as recited in claim 10 , wherein the oxide layer is made to remain in a thickness ranging from about 600 Å to about 700 Å during the dry etching process.

15 . The method as recited in claim 12 , wherein the oxide layer is grown by a thermal process.