CMOS image sensor devices

1. A pixel for CMOS image sensor device, comprising:

a substrate comprising a first well region formed in a top portion of the substrate, having a first conductivity type and a first doping concentration;

a plurality of shallow trench isolation (STI) structures formed in the first well region, defining at least one pixel region over the substrate;

a second well region formed in a potion of the first well region of the pixel region, having a second conductivity type opposite to the first conductivity type;

a top surface region formed in a top portion of the second well region, having the first conductivity type and a second doping concentration; and

a MOS transistor formed on portions of the pixel region, having a pair of source/drain regions formed in the first well region, wherein the source/drain regions are formed of the second conductivity type and one of the source/drain regions physically connects the second well region and the top surface region, and the second well region is formed with a depth greater than that of the STI structure adjacent thereto.

2. The pixel as claimed in claim 1 , wherein the second doping concentration is greater than the first doping concentration.

3. The pixel as claimed in claim 1 , wherein the second well region covers a bottom corner of one of the STI structures adjacent thereto.

4. The pixel as claimed in claim 1 , wherein the first conductivity type is P type and the second conductivity type is N type.

5. The pixel as claimed in claim 1 , wherein the substrate further comprises a third well region underlying the first well region and the third well region has the first conductivity type and a third doping concentration greater than that of the first doping concentration.

6. The pixel as claimed in claim 5 , wherein the second well region covers a bottom corner of one of the STI structures adjacent thereto and reaches a boundary between the first and third well regions.

7. A CMOS image sensor device, comprising:

at least one pixel of claim 1 ;

an interconnect structure overlying the substrate, overlying the MOS transistor;

a color filter layer overlying the interconnect structure, comprising at least one color filter region substantially align to the underlying pixel region; and

at least one microlens overlying the color filter layer and substantially aligning to the underlying pixel region.

8. The CMOS image sensor device as claimed in claim 7 , wherein the second doping concentration is greater than the first doping concentration.

9. The CMOS image sensor device as claimed in claim 7 , wherein the second well region covers a bottom corner of one of the STI structures adjacent thereto.

10. The CMOS image sensor device as claimed in claim 7 , wherein the first conductivity type is F type and the second conductivity type is N type.

11. The CMOS image sensor device as claimed in claim 7 , wherein the substrate further comprises a third well region underlying the first well region and the third well region has the first conductivity type and a third doping concentration greater than that of the first doping concentration.

12. The CMOS image sensor device as claimed in claim 10 , wherein the first well region covers a bottom corner of one of the STI structures adjacent thereto and reaches a boundary between the first and third well regions.

13. The CMOS image sensor device as claimed in claim 7 , wherein the color filter layer is defined into red, green and blue regions.

14. A CMOS image sensor device, comprising:

at least one pixel of claim 1 ;

an interconnect structure overlying the substrate, overlying the MOS transistor;

a color filter layer overlying a side of the substrate not having the MOS transistor formed thereon;

at least one microlens overlying the color filter layer and substantially aligning to the pixel region.

15. The CMOS image sensor device as claimed in claim 14 , wherein the second doping concentration is greater than the first doping concentration.

16. The CMOS image sensor device as claimed in claim 14 , wherein the second well region covers a bottom corner of one of the STI structures adjacent thereto.

17. The CMOS image sensor device as claimed in claim 14 , wherein the first conductivity type is P type and the second conductivity type is N type.

18. The CMOS image sensor device as claimed in claim 14 , wherein the substrate further comprises a third well region underlying the first well region and contacting the color filter layer, and the third well region has the first conductivity type and a third doping concentration greater than that of the first doping concentration.

19. The CMOS image sensor device as claimed in claim 18 , wherein the second well region covers a bottom corner of one of the STI structures adjacent thereto and reaches a boundary between the first and third well regions.

20. The CMOS image sensor device as claimed in claim 14 , wherein the color filter layer is defined into red, green and blue regions.

21. The CMOS image sensor device as claimed in claim 14 , wherein the CMOS image sensor device has an optical path of bout 50000-70000 Å, ranging from the microlens to the top surface region of the pixel.