Photodiode with improved charge capacity

1. A method for forming a photodiode cathode in an integrated circuit imager including:

defining and implanting a photodiode cathode region with a photodiode cathode implant dose of an n-type dopant species; and

defining and implanting an edge region of the photodiode cathode regions region with a photodiode cathode edge implant dose of an n-type dopant species to form a region of higher impurity concentration than the photodiode cathode impurity concentration.

2. The method of claim 1 wherein the dopant species used to dope both the photodiode cathode region and the edge region of the photodiode cathode region is phosphorous.

3. The method of claim 1 wherein the dopant species used to dope both the photodiode cathode region and the edge region of the photodiode cathode region is arsenic.

4. The method of claim 1 wherein the photodiode cathode implant dose is between about 1×10e12/cm 2 and about 5×10e13/cm 2 .

5. The method of claim 1 wherein the photodiode cathode edge implant dose is between about 1×10e12/cm 2 and about 4×10e13/cm 2 .

6. A method for forming a photodiode cathode in an integrated circuit imager including:

defining and implanting a photodiode cathode region with a photodiode cathode edge implant dose of a dopant species of a first conductivity type; and

defining and implanting a center region of the photodiode cathode regions with an implant dose of a dopant species of a second conductivity type opposite that of the first conductivity type to form a partially counterdoped photodiode cathode center region.

7. The method of claim 6 wherein the first conductivity type is n-type.

8. The method of claim 7 wherein the dopant species of the first conductivity type is phosphorous.

9. The method of claim 7 wherein the dopant species of the first conductivity type is arsenic.

10. The method of claim 8 wherein the photodiode cathode implant dose is between about 1×10e12/cm 2 and about 5×10e13/cm 2 .

11. The method of claim 8 wherein the dopant species of the second conductivity type is boron.

12. The method of claim 11 wherein the dose of the dopant of the second conductivity type is between about 1×10e12/cm 2 and about 4×10e13/cm 2 .

13. The method of claim 6 wherein defining the center region comprises defining a center region within the photodiode cathode region that is smaller than the photodiode cathode region.

14. The method of claim 13 wherein defining the center region comprises defining a center region that is self aligned to the photodiode cathode region.

15. The method of claim 14 wherein defining a center region that is self aligned to the photodiode cathode region includes forming a spacer in an aperture in a mask used to define the photodiode cathode region.

16. A method for forming a photodiode cathode in an integrated circuit imager including:

defining and implanting a photodiode cathode region with a photodiode cathode implant dose of an n-type dopant species; and

defining and implanting corner regions of the photodiode cathode region with a photodiode cathode corner implant dose of an n-type dopant species to form a region of higher impurity concentration than the photodiode cathode impurity concentration.

17. The method of claim 16 wherein the dopant species is n-type.

18. The method of claim 16 wherein the dopant species is phosphorous.

19. The method of claim 16 wherein the dopant species is arsenic.

20. The method of claim 16 wherein the photodiode cathode corner implant dose is between about 1×10e12/cm 2 and about 5×10e13/cm 2 .

21. The method of claim 16 wherein the photodiode cathode corner implant dose is between about 1×10e12/cm 2 and about 4×10e13/cm 2 .