Backside silicon wafer design reducing image artifacts from infrared radiation

• US 20070031988A1
• Filed: 08/03/2005
• Published: 02/08/2007
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Karasev, Igor, Agranov, Gennadiy
• Granted Patent: US 7,576,361 B2
• Time in Patent Office: Days
• US Class Current: 438/60
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• 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 27/1462 Coatings
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/14685 Process for coatings or optical elements
• CPC Class Codes: H01L 31/0232 Optical elements or arrangements associated with the device H01L31/0236 takes precedence; for photovoltaic cells H01L31/054; for photovoltaic modules H02S40/20

Abstract

Imaging devices having reduced image artifacts are disclosed. The image artifacts in the imaging devices are reduced by redirecting, absorbing or scattering IR radiation that passes through the imaging device substrate away from dark pixels.

Claims

1. An imager comprising:

an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate, said pixel cells including imaging pixel cells and dark current pixel cells; and

a layer formed on a second surface of said substrate for reducing the amount of light reflecting from said second surface back to said dark current pixel cells.

2. The imager according to claim 1, wherein said layer is an anti-reflective coating.

3. The imager according to claim 2, wherein said anti-reflective coating is a deposited anti-reflective coating.

4. The imager according to claim 2, wherein said anti-reflective coating is a layered structure of titanium nitride and aluminum.

5. The imager according to claim 2, wherein said anti-reflective coating is a formed from TiO₂.

6. The imager according to claim 2, wherein said anti-reflective coating has a thickness from about 0.1 μ

m to about 5 μ

m.

7. The imager according to claim 2, further comprising an absorption layer formed over said anti-reflective coating.

8. The imager according to claim 7, wherein said absorption layer absorbs IR radiation at the wavelength of between about 800 to about 1150 nm.

9. The imager according to claim 7, wherein said absorption layer is formed from materials selected from the group consisting of Ge, SiGe, and SiC.

10. The imager according to claim 7, wherein said absorption layer has a thickness from about 2 μ

m to about 5 μ

m.

11. The imager according to claim 1, wherein said layer is an absorption layer.

12. The imager according to claim 11, wherein said absorption layer absorbs IR radiation at the wavelength of between about 800 to about 1150 nm.

13. The imager according to claim 12, wherein said absorption layer is formed from materials selected from the group consisting of Ge, SiGe, and SiC.

14. The imager according to claim 12, wherein said absorption layer is formed of germanium.

15. The imager according to claim 14, wherein said absorption layer has a thickness from about 2 μ

m to about 5 μ

m.

16. An imager comprising:

a substrate having a first surface and a second surface; and

an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate, said pixel cells including imaging pixel cells and dark current pixel cells;

wherein said second surface has surface abrasions formed therein for reducing the amount of light reflecting from said second surface back to said dark current pixel cells.

17. The imager according to claim 16, wherein said surface abrasions include perpendicular roughenings.

18. The imager according to claim 16, wherein said surface abrasions include shaped gratings formed therein.

19. The imager according to claim 18, wherein said shaped gratings are formed at an angle of from about 10 to about 75 degrees to said second surface.

20. The imager according to claim 18, wherein said shaped gratings are formed at an angle of from about 20 to about 55 degrees to said second surface.

21. An imager comprising:

an array of pixel sensor cells comprising a plurality of active pixel cells and dark current pixel cells formed at a first surface of a substrate, wherein said active pixel cells and said dark current pixel cells are separated in said substrate by a predetermined distance.

22. The imager according to claim 21, wherein said distance is calculated by the following formula:

2·

D·

tan(α

)

where D is the thickness of said substrate and α

is the maximum angle of the IR radiation into said substrate.

23. The imager according to claim 22, further comprising an absorption layer formed over said dark pixels and said separation distance.

24. The imager according to claim 23, wherein said absorption layer is formed from materials selected from the group consisting of Ge, SiGe, and SiC.

25. The imager according to claim 23, further comprising a non-transparent layer formed over said absorption layer.

26. The imager according to claim 25, wherein said non-transparent layer is formed from a metal.

27. The imager according to claim 26, wherein said metal is selected from the group consisting of tungsten and aluminum.

28. A processor system comprising:

an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate, said pixel cells including imaging pixel cells and dark current pixel cells; and

a layer formed on a second surface of said substrate for reducing the amount of light reflecting from said second surface back to said dark current pixel cells; and

a processor for receiving and processing data representing the image.

29. The processor system according to claim 28, wherein said arrays and said processor are formed on a single substrate.

30. The processor system according to claim 28, wherein said layer is an anti-reflective coating.

31. The processor system according to claim 30, herein said anti-reflective coating is a deposited antireflective coating.

32. The processor system according to claim 30, wherein said anti-reflective coating is a layered structure of titanium nitride and aluminum.

33. The processor system according to claim 30, wherein said anti-reflective coating is a formed from TiO₂.

34. The processor system according to claim 30, wherein said imager further comprises an absorption layer formed over said anti-reflective coating.

35. The processor system according to claim 34, wherein said absorption layer absorbs IR radiation at the wavelength of between about 800 to about 1150 nm.

36. The processor system according to claim 35, wherein said absorption layer is formed from materials selected from the group consisting of Ge, SiGe, and SiC.

37. The processor system according to claim 28, wherein said layer is an absorption layer.

38. The processor system according to claim 37, wherein said absorption layer absorbs IR radiation at the wavelength of between about 800 to about 1150 nm.

39. The processor system according to claim 37, wherein said absorption layer is formed from materials selected from the group consisting of Ge, SiGe, and SiC.

40. A processor system comprising:

a substrate having a first surface and a second surface;

an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate, said pixel cells including imaging pixel cells and dark current pixel cells;

wherein said second surface has surface abrasions formed therein for reducing the amount of light reflecting from said second surface back to said dark current pixel cells; and

a processor for receiving and processing data representing the image.

41. The processor system according to claim 40, wherein said arrays and said processor are formed on a single substrate.

42. The processor system according to claim 40, wherein said surface abrasions include perpendicular roughenings.

43. The processor system of claim 40, wherein said surface abrasions include shaped gratings formed therein.

44. The processor system according to claim 43, wherein said shaped gratings are formed at an angle of from about 10 to about 75 degrees to said second surface.

45. The processor system according to claim 43, wherein said shaped gratings are formed at an angle of from about 35 to about 45 degrees to said second surface

46. A processor system comprising:

an array of pixel sensor cells comprising a plurality of active pixel cells and dark pixel cells formed at a first surface of a substrate, wherein said active pixel cells and said dark pixel cells are separated in said substrate by a predetermined distance; and

a processor for receiving and processing data representing the image.

47. The processor system of claim 46, wherein said arrays and said processor are formed on a single substrate.

48. The processor system according to claim 47, wherein said distance is calculated by the following formula:

2·

D·

tan(α

)

where D is the thickness of said substrate and α

is the maximum angle of the IR radiation into said substrate.

49. The processor system according to claim 46, further comprising an absorption layer formed over said dark pixels and said separation distance.

50. The processor system according to claim 49, further comprising a non-transparent layer formed over said absorption layer.

51. A method of reducing image artifacts in an imaging device, said method comprising the steps of:

minimizing the amount of IR radiation that penetrates the substrate of the imaging device and reflects to dark pixels in said imaging device to reduce image artifacts in said imager.

52. The method according to claim 51, wherein IR radiation is minimized by providing an imaging substrate having an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate;

an anti-reflective coating formed on a second surface of said substrate and an absorption layer formed over said anti-reflective coating.

53. The method according to claim 51, wherein IR radiation is minimized by providing an imaging substrate having an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate and an absorption layer formed on a second surface of said substrate.

54. The method according to claim 51, wherein IR radiation is minimized by providing a substrate having a first surface and a second surface with an array of pixel sensor cells comprising a plurality of pixel cells formed at a first surface of a substrate;

wherein said second surface has surface abrasions formed therein.

55. The method according to claim 54, wherein said surface abrasions include perpendicular roughenings.

56. The method according to claim 55, wherein said surface abrasions are formed by CMP.

57. The method according to claim 54, wherein said surface abrasions include shaped gratings formed therein.

58. The method according to claim 51, wherein IR radiation is minimized by providing an imager having an array of pixel sensor cells comprising a plurality of active pixel cells and dark pixel cells formed at a first surface of a substrate, wherein said active pixel cells and said dark pixel cells are separated in said substrate by a predetermined distance.

59. The method according to claim 58, wherein said distance is calculated by the following formula:

2·

D·

tan(α

)

where D is the thickness of said substrate and α

is the maximum angle of the IR radiation into said substrate.