Multi-trench region for accumulation of photo-generated charge in a CMOS imager

• US 6,611,037 B1
• Filed: 08/28/2000
• Issued: 08/26/2003
• Est. Priority Date: 08/28/2000
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): Wilson, Allan R.
• Application Number:
  US09/650,432
• Time in Patent Office: 1,093 Days
• Field of Search: 257/448, 257/461-466
• US Class Current: 257/466
• CPC Class Codes: H01L 27/14601 Structural or functional details thereof
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14687 Wafer level processing
• CPC Class Codes: H01L 27/14689 MOS based technologies
• CPC Class Codes: H01L 31/035281 Shape of the body
• CPC Class Codes: H01L 31/03529 Shape of the potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/103 the potential barrier being of the PN homojunction type
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

A multiple-trench photosensor for use in a CMOS imager having an improved charge capacity. The multi-trench photosensor may be either a photogate or photodiode structure. The multi-trench photosensor provides the photosensitive element with an increased surface area compared to a flat photosensor occupying a comparable area on a substrate. The multi-trench photosensor also exhibits a higher charge capacity, improved dynamic range, and a better signal-to-noise ratio. Also disclosed are processes for forming the multi-trench photosensor.

Claims

1. A photosensor for use in an imaging device, said photosensor comprising:

a doped layer of a first conductivity type formed in a substrate;

a plurality of trenches formed in said doped layer to define a photosensitive area, each of said plurality of trenches having sidewalls and a bottom;

a doped region of a second conductivity type formed at the sidewalls and bottom of each of said plurality of trenches; and

an insulating layer formed over said doped region.

2. The photosensor of claim 1, wherein the photosensor is a photodiode sensor.

3. The photosensor of claim 2, wherein the insulating layer has a thickness of at least 30 Angstroms.

4. The photosensor of claim 1, wherein each of said plurality of trenches has a depth within the range of approximately 0.05 to 10 μ

m.

5. The photosensor of claim 1, wherein said plurality of trenches comprises two trenches.

6. The photosensor of claim 1, further comprising a conductive layer formed on substantially all of an upper surface of said insulating layer for gating the collection of charges in said doped region.

7. The photosensor of claim 6, wherein the insulating layer has a thickness within the range of approximately 20 to 500 Angstroms.

8. The photosensor of claim 6, wherein the photosensor is a photogate sensor.

9. The photosensor of claim 6, wherein the conductive layer is a doped polysilicon layer.

10. The photosensor of claim 6, wherein the conductive layer is a layer of indium tin oxide.

11. The photosensor of claim 6, wherein the conductive layer is a layer of tin oxide.

12. The photosensor of claim 6, wherein the conductive layer is a doped layer of a second conductivity type.

13. The photosensor of claim 6, wherein the conductive layer is substantially transparent to light radiation.

14. The photosensor of claim 6, wherein the conductive layer has a thickness within the range of approximately 200 to 4000 Angstroms.

15. The photosensor of claim 1, wherein the insulating layer is a silicon dioxide layer.

16. The photosensor of claim 1, wherein the insulating layer is a silicon nitride layer.

17. The photosensor of claim 1, wherein the insulating layer is a layer of ONO.

18. The photosensor of claim 1, wherein the insulating layer is a layer of ON.

19. The photosensor of claim 1, wherein the insulating layer is a layer of NO.

20. The photosensor of claim 1, wherein the first conductivity type is p-type, and the second conductivity type is n−

type.

21. The photosensor of claim 1, wherein the doped region is formed by a process of multiple angled ion implantation.

22. The photosensor of claim 21, wherein the process comprises four orthogonal angled implants at a dose of 1×

10¹² to 1×

10¹⁶ ions/cm², wherein a resist is placed on top of the substrate while implanting, and wherein the angle of implantation for each angled implant is greater than θ

_C, where tan θ

_C=[(t+d)/(w)], where t is the thickness of the resist, d is the depth of said plurality of trenches, and w is the width of said plurality of trenches.

23. The photosensor of claim 22, wherein the dose of each implant is 1×

10¹³ to 1×

10¹⁵ ions/cm².

24. The photosensor of claim 21, wherein the dose of each implant is 5×

10¹³ ions/cm².

25. A photogate sensor for use in an imaging device, said photogate sensor comprising:

a doped layer of a first conductivity type formed in a substrate;

a plurality of trenches formed in said doped layer to define a photosensitive area, each of said plurality of trenches having sidewalls and a bottom;

a doped region of a second conductivity type formed at the sidewalls and bottom of each of said plurality of trenches;

an insulating layer formed on substantially all of an upper surface of said doped region; and

a light radiation-transparent electrode formed on substantially all of an upper surface of said insulating layer for gating the collection of charges in said doped region.

26. The photogate sensor of claim 25, wherein each of said plurality of trenches has a depth within the range of approximately 0.05 to 10 μ

m.

27. The photogate sensor of claim 25, wherein said plurality of trenches comprises two trenches.

28. The photogate sensor of claim 25, wherein the first conductivity type is p-type, and the second conductivity type is n−

type.

29. The photogate sensor of claim 25, wherein the insulating layer has a thickness within the range of approximately 20 to 500 Angstroms.

30. The photogate sensor of claim 25, wherein the insulating layer is a layer of silicon dioxide.

31. The photogate sensor of claim 25, wherein the insulating layer is a layer of silicon nitride.

32. The photogate sensor of claim 25, wherein the insulating layer is a layer of ONO.

33. The photogate sensor of claim 25, wherein the insulating layer is a layer of ON.

34. The photogate sensor of claim 25, wherein the insulating layer is a layer of NO.

35. The photogate sensor of claim 25, wherein the radiation-transparent electrode has a thickness within the range of approximately 200 to 4000 Angstroms thick.

36. The photogate sensor of claim 25, wherein the radiation-transparent electrode is a layer of doped polysilicon.

37. The photogate sensor of claim 25, wherein the radiation-transparent electrode is a layer of indium tin oxide.

38. The photogate sensor of claim 25, wherein the radiation-transparent electrode is a layer of tin oxide.

39. The photogate sensor of claim 25, wherein the radiation-transparent electrode is doped to a second conductivity type.

40. The photogate sensor of claim 39, wherein the first conductivity type is p-type, and the second conductivity type is n−

type.

41. The photogate sensor of claim 25, wherein said doped region comprises multiple angled ion implants.

42. The photogate sensor of claim 41, wherein said multiple angled ion implants comprise four orthogonal angled implants having a dose of 1×

10¹² to 1×

10¹⁶ ions/cm², and having an angle greater than θ

_C, where tan θ

_C=[(t+d)/(½

w)], where t is the thickness of a resist, d is the depth of said plurality of trenches, and w is the width of said plurality of trenches.

43. The photogate sensor of claim 42, wherein the dose of each implant is 1×

10¹³ to 1×

10¹⁵ ions/cm².

44. The photogate sensor of claim 42, wherein the dose of each implant is 5×

10¹³ ions/cm².