CMOS image sensor and method of fabrication

• US 6,946,715 B2
• Filed: 02/19/2003
• Issued: 09/20/2005
• Est. Priority Date: 02/19/2003
• Status: Expired due to Fees

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Hong, Sungkwon (Chris)
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): HOANG, QUOC DINH
• Application Number:
  US10/367,825
• Publication Number:
  US 20040161868A1
• Time in Patent Office: 944 Days
• Field of Search: 257/440, 257/293
• US Class Current: 257/440
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/14645 Colour imagers
• CPC Class Codes: H01L 27/14647 Multicolour imagers having a stacked pixel-element structure, e.g. npn, npnpn or MQW elements
• CPC Class Codes: H01L 31/035236 Superlattices; Multiple quantum well structures
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A CMOS imaging device including a two pixel detection system for red, green, and blue light. One pixel detects red and blue light and another pixel detects green light. The detection of red and blue is based on wavelength and the device is structured such that in the red/blue pixel, detection of blue light is at a shallow substrate depth, while detection of red is at a deeper substrate depth. The pixel array is structured such that the red/blue pixel is adjacent to the green pixel and alternates between red/blue and green pixels. The invention is also related to methods of forming such an imager array and pixels.

Claims

1. A two color pixel comprising:

a substrate having a surface;

a first color component photoconversion device located below the surface of said substrate at a first absorption depth for a first wavelength of light; and

a second color component photoconversion device located below the surface of said substrate at a second absorption depth for a second wavelength of light;

wherein said first color component photoconversion device and said second color component photoconversion device overlap vertically within said substrate such that the first color component photoconversion device is located closer to the surface of the substrate than the second color component photoconversion device and said first and second color component photoconversion devices are spaced apart vertically by a region of said substrate which does not produce photogenerated charges; and

a two-color output processing circuit respectively coupled to said first and second color component photoconversion devices, said processing circuit being configured to output signals corresponding to respective charges produced by said first and second color component photoconversion devices.

2. The two color pixel of claim 1 wherein said first and second color component photoconversion devices are photodiodes.

3. The two color pixel of claim 2 wherein said first and second photodiodes are PIN photodiodes.

4. The two color pixel of claim 1 wherein said first color component photoconversion device is a blue light sensor.

5. The two color pixel of claim 4 wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μ

m to about 1.0 μ

m from a top surface of the substrate.

6. The two color pixel of claim 1 wherein said second color component photoconversion device is a red light sensor.

7. The two color pixel of claim 6 wherein said red light sensor has a p-n junction located at a depth of about 2.0 μ

m or greater from a top surface of the substrate.

8. The two color pixel of claim 6 wherein said red light sensor has a p-n junction located at a depth of about 5.0 μ

m or greater from a top surface of the substrate.

9. The two color pixel of claim 1 further comprising an isolation region for minimizing lateral charge transfer of charges generated by said first color component photoconversion device into a region in said substrate which receives charges generated by said second color component photoconversion device.

10. The two color pixel of claim 9 wherein said isolation region is a shallow trench isolation region.

11. The two color pixel of claim 1 wherein said first color component photoconversion device is part of a four transistor pixel circuit comprising a transfer transistor, a reset transistor, a source follower transistor and a row select transistor.

12. The two color pixel of claim 11, wherein said first color component photoconversion device further comprises a doped region that is configured to receive charge transferred from the first color component photoconversion device.

13. The two color pixel of claim 12, wherein said doped region is doped n+.

14. The two color pixel of claim 12, wherein said doped region is a floating diffusion region.

15. The two color pixel of claim 12, further comprising a transfer gate configured to gate charge between said first color component photoconversion device and said doped region.

16. The two color pixel of claim 1 wherein said second color component photoconversion device is part of a four transistor pixel circuit comprising a transfer transistor, a reset transistor, a source follower transistor and a row select transistor.

17. The two color pixel of claim 16, wherein said second color component photoconversion device further comprises a first doped region configured to receive charge transferred from the second color component photoconversion device.

18. The two color pixel of claim 17, wherein said first doped region is doped n−

.

19. The two color pixel of claim 17 wherein said first doped region connects said second color component photoconversion device to a second doped region configured to receive charge transferred from the second photoconversion device.

20. The two color pixel of claim 19 wherein said second doped region is doped n+.

21. The two color pixel of claim 19 wherein said second doped region is a floating diffusion region.

22. The two color pixel of claim 19, wherein said second color component photoconversion device comprises a transfer gate configured to gate charge between said second photoconversion device and said second doped region.

23. The two color pixel of claim 1 wherein said first color component photoconversion device is part of a three transistor pixel circuit comprising a reset transistor, a source follower transistor, and a row select transistor.

24. The two color pixel of claim 23 wherein charges generated by said first color component photoconversion device are transferred to a doped region.

25. The two color pixel of claim 24 wherein said doped region is doped n+.

26. The two color pixel of claim 24 wherein said doped region is a floating diffusion region.

27. The two color pixel of claim 1 wherein said second color component photoconversion device is part of a three transistor pixel circuit comprising a reset transistor, a source follower transistor, and a row select transistor.

28. The two color pixel of claim 27, wherein said second color component photoconversion device comprises a first doped region configured to receive charge transferred from the second color component photoconversion device.

29. The two color pixel of claim 28 wherein said first doped region is doped n−

.

30. The two color pixel of claim 28 wherein said first doped region connects said second color component photoconversion device to a second doped region configured to receive charge transferred from the second color component photoconversion device.

31. The two color pixel of claim 30 wherein said second doped region is doped n+.

32. The two color pixel of claim 30 wherein said second doped region is a floating diffusion region.

33. The two color pixel of claim 1 wherein a doped region connects said first color component photoconversion device to a ground circuit.

34. The two color pixel of claim 33 wherein said doped region is a p+ doped region.

35. The two color pixel of claim 1 wherein a doped region connects said second color component photoconversion device to a ground circuit.

36. The two color pixel of claim 35 wherein said doped region is a p+ doped region.

37. The two color pixel of claim 1 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top.

38. The two color pixel of claim 37 wherein said respective charge generating region of the first color component photoconversion device occupies a smaller area than said respective charge generating region of the second color component photoconversion device when viewed from the top.

39. The two color pixel of claim 1 wherein doped said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in shape when viewed from the top.

40. An array of pixel sensor cells comprising:

a substrate having a top surface and comprising a plurality of first and second pixels arranged into an array of rows and columns;

said first pixel comprising a first color component photoconversion device located below the top surface of said substrate at a first depth corresponding to a first absorption depth for a first wavelength of light and a second color component photoconversion device located below the top surface of said substrate at a second depth corresponding to a second absorption depth for a second wavelength of light;

said first color component photoconversion device and said second color component photoconversion device overlapping vertically within said substrate such that the first color component photoconversion device is located closer to the top surface of the substrate than the second color component photoconversion device and said first and second color component photoconversion devices are spaced from one another by a region of said substrate which does not produce photogenerated charges; and

wherein said second pixel comprises a third color component photoconversion device for a third wavelength of light.

41. The array of claim 40 wherein said first pixel senses red and blue colors of light.

42. The array of claim 40 wherein said first color component photoconversion device is a blue light sensor.

43. The array of claim 42 wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μ

m to about 1.0 μ

m from the top surface of the substrate.

44. The array of claim 40 wherein said second color component photoconversion device is a red light sensor.

45. The array of claim 44 wherein said red light sensor has a p-n junction located at a depth of about 2.0 μ

m or greater from the top surface of the substrate.

46. The array of claim 44 wherein said red light sensor has a p-n junction located at a depth of about 5.0 μ

m or greater from the top surface of the substrate.

47. The array of claim 40 further comprising an isolation region for minimizing lateral charge transfer of charges generated by said first color component photoconversion device into a region in said substrate which receives charges generated by said second color component photoconversion device.

48. The array of claim 40 wherein a doped region connects said first color component photoconversion device to a ground circuit.

49. The array of claim 48 wherein said doped region is a p+ doped region.

50. The array of claim 40 wherein a doped region connects said second color component photoconversion device to a ground circuit.

51. The device array of claim 50 wherein said doped region is a p+ doped region.

52. The array of claim 40 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top.

53. The array of claim 52 wherein said respective charge generating region of the first color component photoconversion device occupies a smaller area than said said respective charge generating region of the second color component photoconversion device when viewed from the top.

54. The array of claim 40 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in shape when viewed from the top.

55. The array of claim 40 wherein each said second pixel senses green color of light.

56. The array of claim 40 wherein said first and second pixels are arranged in a checkerboard pattern.

57. An imaging system comprising:

an array of pixel cells arranged in rows and columns, each said pixel cell being configured to generate at least one voltage at a diffusion node responsive to detected light intensity by the cell, said array of pixel cells comprising a plurality of first pixel cells and a plurality of second pixel cells, said first and second pixel cells being arrayed in an alternating pattern in said array;

each of said first pixel cells comprising a first color component photoconversion device located below the surface of a substrate at a first depth corresponding to a first absorption depth for a first wavelength of light and a second color component photoconversion device located below the surface of said substrate at a second depth corresponding to a second absorption depth for a second wavelength of light;

said first color component photoconversion device and said second color component photoconversion device overlapping vertically within said substrate such that the first color component photoconversion device is located closer to the surface of the substrate than the second color component photoconversion device, said first and second color component photoconversion devices being vertically spaced from one another by a region of said substrate which does not produce photogenerated charges; and

wherein each of said second pixel cells comprises a third color component photoconversion device for a third wavelength of light.

58. The system of claim 57 wherein each said first pixel cell senses red and blue colors of light.

59. The system of claim 57 wherein said first color component photoconversion device is a blue light sensor.

60. The system of claim 59 wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μ

m to about 1.0 μ

m from a top surface of the substrate.

61. The system of claim 57 wherein said second color component photoconversion device is a red light sensor.

62. The system of claim 61 wherein said red light sensor has a p-n junction located at a depth of about 2.0 μ

m or greater from a top surface of the substrate.

63. The system of claim 61 wherein said red light sensor has a p-n junction located at a depth of about 5.0 μ

m or greater from a top surface of the substrate.

64. The system of claim 57 wherein each second pixel senses a green color of light.

65. The system of claim 57 further comprising an isolation region configured to prevent lateral transfer of charges generated by said first color component photoconversion device into a region in said substrate which receives charges generated by said second color component photoconversion device.

66. The system of claim 57 wherein a doped region connects said first color component photoconversion device to a ground circuit.

67. The system of claim 66 wherein said doped region is a p+ doped region.

68. The system of claim 57 wherein a doped region connects said second color component photoconversion device to a ground circuit.

69. The system of claim 68 wherein said doped region is a p+ doped region.

70. The system of claim 57 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top.

71. The system of claim 70 wherein said respective charge generating region of the first color component photoconversion device occupies a smaller area than said respective charge generating region of the second color component photoconversion device when viewed from the top.

72. The system of claim 57 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in shape when viewed from the top.

73. An imager device, comprising:

a doped layer formed in a substrate;

an array of first and second pixel cells formed in said doped layer;

wherein each of said first pixel cells comprises a first color component photoconversion device located below the surface of said substrate at a first depth corresponding to a first absorption depth for a first wavelength of light and a second color component photoconversion device located below the surface of said substrate at a second depth corresponding to a second absorption depth for a second wavelength of light;

wherein said first color component photoconversion device and said second color component photoconversion device overlap vertically within said substrate such that the first color component photoconversion device is located closer to the surface of the substrate than the second color component photoconversion device and said first and second color component photoconversion devices are vertically spaced from one another by a region of said substrate which does not produce photogenerated charges; and

wherein each of said second pixel cells comprises a third color component photoconversion device for a third wavelength of light.

74. The imager device of claim 73 wherein each said first pixel cell senses red and blue colors of light.

75. The imager device of claim 73 wherein said first color component photoconversion device is a blue light sensor.

76. The imager device of claim 75 wherein said blue light sensor has a p-n junction located at a depth of from about 0.5 μ

m to about 1.0 μ

m from a top surface of the substrate.

77. The imager device of claim 73 wherein said second color component photoconversion device is a red light sensor.

78. The imager device of claim 77 wherein said red light sensor has a p-n junction located at a depth of about 2.0 μ

m or greater from a top surface of the substrate.

79. The imager device of claim 77 wherein said red light sensor has a p-n junction located at a depth of about 5.0 μ

m or greater from a top surface of the substrate.

80. The imager device of claim 73 wherein each said second pixel senses green color of light.

81. The imager device of claim 73 further comprising an isolation region configured to prevent lateral transfer of charges generated by said first color component photoconversion device into a region in said substrate which receives charges generated by said second color component photoconversion device.

82. The imager device of claim 73 wherein a doped region connects said first color component photoconversion device to a ground circuit.

83. The imager device of claim 82 wherein said doped region is a p+ doped region.

84. The imager device of claim 73 wherein a doped region connects said second color component photoconversion device to a ground circuit.

85. The imager device of claim 84 wherein said doped region is a p+ doped region.

86. The imager device of claim 73 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in size when viewed from the top.

87. The imager device of claim 86 wherein said respective charge generating regions of the first color component photoconversion device occupies a smaller area than said respective charge generating region of the second color conversion photoconversion device when viewed from the top.

88. The imager device of claim 73 wherein said first and second color component photoconversion devices comprise respective charge generating regions that are not coincident in shape when viewed from the top.