Quantum efficiency improvements in active pixel sensors

• US 6,005,619 A
• Filed: 10/06/1997
• Issued: 12/21/1999
• Est. Priority Date: 10/06/1997
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Photobit Corporation (Micron Technology, Inc.)
• Inventors: Fossum, Eric R.
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): WILSON, JACQUELINE B
• Application Number:
  US08/944,794
• Time in Patent Office: 806 Days
• Field of Search: 348/297, 348/298, 348/308, 348/309, 348/310, 348/306, 348/315, 257/233, 257/291, 257/292
• US Class Current: 348/315
• 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 27/14623 Optical shielding

Abstract

Quantum efficiency in an active pixel sensor improved by proper sizing and shaping of the contacts. The photodiode elements are formed of special shapes that are optimized for obtaining diffusion of charge, rather than obtaining the charge directly. Photogates are formed with a thinned polysilicon covering.

Claims

1. An image sensor, comprising:

a plurality of pixel areas, each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open bv the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element,

wherein said photodiode is in the shape of a bar extending from an edge of the pixel towards a center of the pixel.

2. An image sensor, comprising:

a plurality of pixel areas, each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open by the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element,

wherein said photodiode is in the shape of only a portion of a ring.

3. An image sensor, comprising:

a plurality of pixel areas, each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open by the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element,

wherein said photodiode extends along a diagonal of said pixel.

4. An image sensor, comprising:

a plurality of pixel areas, each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open by the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element,

wherein said photodiode is in the shape of an H.

5. An image sensor, comprising:

a plurality of pixel areas, each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open by the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element,

wherein said photodiode is in the shape of an X.

6. An image sensor, comprising:

a plurality of pixel areas, each pixel area formed on a substrate of a type that can receive impinging light, and react to said impinging light to form a changed substrate portion that can diffuse, each said pixel area including a circuitry area and a photodiode area, said circuitry area including at least a buffer transistor therein and at least one circuit other than said buffer transistor, said buffer transistor and said at least one other circuit being formed of MOS, said photodiode area including a photodiode element therein, said photodiode element having a geometrical shape which is optimized for obtaining diffusion of said changed substrate portion, rather than for obtaining the light directly.

7. An image sensor as in claim 6, wherein said photodiode takes less than an entire amount of space left open by the circuitry area.

8. A sensor as in claim 7 wherein said photodiode is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode.

9. A sensor as in claim 7 wherein said photodiode is in the shape of a bar extending from an edge of the pixel towards a center of the pixel ending near a center of said pixel.

10. A sensor as in claim 7 wherein said photodiode is in the shape of only a portion of a ring.

11. A sensor as in claim 7 wherein said photodiode extends along the diagonal of said pixel.

12. A sensor as in claim 7 wherein said photodiode is in the shape of a ring, a center of the ring being a center of the pixel.

13. A sensor as in claim 7 wherein said photodiode is in the shape of an H.

14. A sensor as in claim 7 wherein said photodiode is in the shape of an X.

28. An image sensor as in claim 6, wherein said photodiode element is itself formed of an opaque material.

29. An image sensor as in claim 28, wherein said photodiode element is formed of polycide.

15. An image sensor, comprising:

a plurality of pixel areas, each pixel area formed on a substrate of a type that can receive impinging light, each said pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein said photodiode element itself formed of an opaque material that blocks light from directly reaching said photodiode element.

16. A sensor as in claim 15, wherein said opaque material is polycide.

17. An image sensor as in claim 15 wherein said photodiode element takes less than an entire amount of space left open by the circuitry area.

18. A sensor as in claim 15 wherein said photodiode is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode.

19. A sensor as in claim 18 wherein said photodiode is in the shape of a bar extending from an edge of the pixel towards a center of the pixel.

20. A sensor as in claim 18 wherein said photodiode is in the shape of a portion of a ring.

21. A sensor as in claim 18 wherein said photodiode extends along the diagonal of said pixel.

22. A sensor as in claim 18 wherein said photodiode is in the shape of a ring, a center of the ring being a center of the pixel.

23. A sensor as in claim 18 wherein said photodiode is in the shape of an H.

24. An image sensor, comprising:

a plurality of pixel areas, each pixel area formed on a substrate of a type that can receive impinging light and react to said impinging light to form electron hole pairs, each said pixel area including a photodiode area, said photodiode area including a photodiode element therein, said photodiode element itself being formed of an opaque polycide, said photodiode element having a shape which is optimized for obtaining diffusion of said electron hole pairs, rather than for obtaining the light directly.

25. An image sensor, comprising:

a plurality of pixel areas, each pixel area formed on a substrate of a type that can receive impinging light, and react to said impinging light, each said pixel area including a circuitry area and a photogate area, said photogate area covered by a layer of polysilicon less than 400 Å

in thickness.

26. An image sensor, comprising:

a plurality of pixel areas each pixel area including a circuitry area and a photodiode area, said photodiode area including a photodiode element therein, said photodiode element taking less than an entire amount of space left open by the circuitry area, wherein said photodiode element is located in a position on said substrate which includes a plurality of collection areas in said substrate which are substantially equidistant from said photodiode element, wherein said photodiode element is itself formed of an opaque material.

27. An image sensor as in claim 26, wherein said photodiode element is formed of polycide.

30. An image sensor, comprising:

a plurality of pixel areas, each pixel area formed on a substrate of a type that can receive impinging light, each said pixel area including a light receptor therein that is itself formed of an opaque material that blocks light from directly reaching said light receptor.

32. A method as in claim 30, wherein said photosensitive element is a photodiode.

33. A device as in claim 30, wherein said shaping comprises forming said photodiode into the shape of a bar extending from an edge of the pixel toward a center of the pixel and ending near a center of the pixel.

34. A method as in claim 30, wherein said shaping comprises shaping said photosensitive element into the portion of only a portion of a ring.

35. A method as in claim 30, further comprising shaping said photodiode to form a shaped photodiode along a diagonal of the pixel.

36. A method as in claim 30, further comprising shaping said photosensitive element into the shape of an H.

31. A method of forming an image sensor, comprising:

defining a plurality of pixel areas, each pixel area including a circuitry area for electronic circuitry including at least a buffer transistor and at least one circuit other than said buffer transistor, said buffer transistor and said at least one other circuit being formed of MOS, and an photosensitive area including a photosensitive element therein;

shaping said photosensitive element such that it takes less than an entire amount of space left open by the circuitry area;

forming a substrate of a type that can react to impinging radiation to form a changed substrate portion that can diffuse;

shaping said photosensitive element to a geometric shape that optimizes diffusing of said changed substrate portion; and

allowing said changed portion to diffuse into said photosensitive element.