Method for automated testing of the modulation transfer function in image sensors

• US 7,215,361 B2
• Filed: 09/17/2003
• Issued: 05/08/2007
• Est. Priority Date: 09/17/2003
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Shah, Joey, Altice, Peter P. Jr., Reuven, Moshe, Robinson, Donald E., Duesman, Kevin, Bruce, Jeffrey, Jenkins, Ed
• Primary Examiner(s): LEE, MICHAEL
• Application Number:
  US10/663,709
• Publication Number:
  US 20050057655A1
• Time in Patent Office: 1,329 Days
• Field of Search: 348/187, 348/188, 348/175, 348/178, 348/241, 348/248, 348/249, 348/250, 356/124.5
• US Class Current: 348/187
• CPC Class Codes: G01R 31/2829 Testing of circuits in sensor or actuator systems testing of apparatus for measuring electric or magnetic variables G01R35/00; testing of indicating or recording apparatus G01D; in airbag systems B60R21/0173; checking gas analysers G01N33/007; monitoring or fail-safe circuits for electromagnets H01F7/1844
• CPC Class Codes: H01L 21/76805 the opening being a via or contact hole penetrating the underlying conductor
• CPC Class Codes: H01L 23/53238 Additional layers associated with copper layers, e.g. adhesion, barrier, cladding layers
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H01L 27/14627 Microlenses
• CPC Class Codes: H01L 27/14636 Interconnect structures
• CPC Class Codes: H01L 27/14687 Wafer level processing
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 31/022408 for devices characterised by at least one potential jump barrier or surface barrier
• CPC Class Codes: H04N 17/002 for television cameras

Abstract

A method for automatically measuring the modulation transfer function of an imager is disclosed. A opaque mask is placed over selected columns and rows of the imager during fabrication. In the course of an automated process, photons are uniformly shone over the image sensor. The amount of the input signal that flows from the unmasked pixel cells to the masked pixel cells can then be measured and the modulation transfer function can be determined.

Claims

1. A method of testing a modulation transfer function (MTF) of an imager comprising photosensitive cells, the method comprising:

exposing the imager to a photon source;

measuring an output of first and second photosensitive cells, wherein the first cell is blocked from the photon source by a layer of opaque material formed within the imager; and

calculating the MTF using the measured outputs.

2. The method of claim 1, wherein said first and second photosensitive cells are adjacent.

3. The method of claim 1, wherein said method occurs during an automated testing process.

4. The method of claim 3, wherein said method occurs during probe testing of an imager array.

5. The method of claim 1, wherein said photon source has an intensity below photosensitive cell saturation intensity.

6. The method of claim 1, wherein said opaque material forms a mask for a plurality of photosensitive cells of an imager array.

7. The method of claim 6, wherein said masking is formed during fabrication of said imager array.

8. The method of claim 6, wherein said opaque mask covers a predetermined number of rows on at least one edge of said imager array.

9. The method of claim 6, wherein said opaque mask covers a predetermined number of columns on at least one edge of said imager array.

10. The method of claim 6, wherein said opaque mask covers a predetermined number of rows and columns on at least two edges of said imager array.

11. The method of claim 6, wherein said opaque mask covers a predetermined number of rows and columns on four edges of said imager array.

12. The method of claim 1, wherein said measuring includes the averaging of output signals from a first column and averaging the output signal from a second column of adjacent photosensitive cells.

13. The method of claim 1, wherein said opaque material is comprised of a metal.

14. The method of claim 1 further comprising aligning an edge of said opaque material between a row or column of said imager.

15. The method of claim 1, wherein said imager is a CMOS imager.

16. The method of claim 1, wherein said imager is a CCD imager.

17. A method of testing a modulation transfer function (MTF) of an imager comprising photosensitive cells, the method comprising:

exposing a first imager to a collimated photon source;

measuring an output of first and second adjacent photosensitive cells, wherein the first cell is blocked from the photon source by a layer of opaque material;

calculating the MTF using the measured output to form a test standard;

exposing the first imager to a non-collimated photon source;

measuring an output of first and second adjacent photosensitive cells, wherein the first cell is blocked from the photon source by a layer of opaque material;

calculating the MTF using the measured output for the test using the non-collimated photon source;

comparing results of said first standardizing test with results of said second test using a non-collimated photon source; and

determining whether said results attained with said second test using the non-collimated photon source are within an acceptable error margin as compared with the result attained with said first standardizing test.

18. The method of claim 17 further comprising aligning an edge of said opaque material between a row or column of photosensitive cells of said imager.

19. The method of claim 17 further comprising performing said second test on a plurality of second imagers if said test using the first imager is within an acceptable error margin.

20. The method of claim 17, wherein said method occurs during an automated testing process.

21. The method of claim 20, wherein said method occurs during probe testing of an imager array.

22. The method of claim 17, wherein said opaque material is comprised of a metal.

23. The method of claim 17, wherein said collimated and non-collimated photon source has an intensity below photosensitive cell saturation intensity.

24. The method of claim 17, wherein said imager is a CMOS imager.

25. The method of claim 17, wherein said imager is a CCD imager.

26. A method of testing a modulation transfer function (MTF) of an imager comprising photosensitive cells, the method comprising:

exposing a first and second predetermined number of photosensitive cells in at least one of a row and column of adjacent photosensitive cells of the imager to a photon source, wherein the first predetermined number of photosensitive cells are blocked from the photon source by a layer of opaque material formed within the imager;

measuring an output of the first and second predetermined number of photosensitive cells; and

calculating the MTF using the measured outputs.

27. The method of claim 26 further comprising aligning an edge of said opaque material between a row or column of said imager.

28. The method of claim 26, wherein said method occurs during an automated testing process.

29. The method of claim 28, wherein said method occurs during probe testing of an imager array.

30. The method of claim 26, wherein said first and second measuring comprise averaging measurements taken from said plurality of blocked photosensitive cells and averaging measurements taken from a plurality of unblocked photosensitive cells.

31. The method of claim 26, wherein said opaque material forms a mask for a plurality of photosensitive cells of an imager array.

32. The method of claim 31, wherein said opaque material is comprised of a metal.

33. The method of claim 31, wherein said forming comprises masking said at least one photosensitive cell during fabrication of said imager array.

34. The method of claim 31, wherein said opaque mask covers a predetermined number of rows and columns on at least one edge of said imager array.

35. The method of claim 26, wherein said imager is a CMOS imager.

36. The method of claim 26, wherein said imager is a CCD imager.

37. A method of testing a modulation transfer function (MTF) of an imager comprising photosensitive cells, the method comprising:

exposing a first imager to a collimated photon source;

measuring an output of a first row or column and a second row or column of adjacent photosensitive cells, wherein the first row or column of cells are blocked from the photon source by a layer of opaque material;

calculating the MTF using the measured outputs to form a test standard;

exposing the first imager to a non-collimated photon source;

measuring an output of said first row or column and said second row or column of adjacent photosensitive cells;

calculating the MTF using the measured outputs for the test using the non-collimated photon source;

comparing results of said first standardizing test with results of said second test using a non-collimated photon source; and

determining whether said results attained with said second test using the non-collimated photon source are within an acceptable error margin as compared with the result attained with said first standardizing test.

38. The method of claim 37 further comprising aligning an edge of said opaque material between a row or column of said imager.

39. The method of claim 37 further comprising performing said test on a plurality of second imagers if said test using the first imager is within an acceptable error margin.

40. The method of claim 37, wherein said method occurs during an automated testing process.

41. The method of claim 40, wherein said method occurs during probe testing of an imager array.

42. The method of claim 37, wherein said opaque material is comprised of a metal.

43. The method of claim 37, wherein said collimated and non-collimated photon source has an intensity below photosensitive cell saturation intensity.

44. The method of claim 37, wherein said imager is a CMOS imager.

45. The method of claim 37, wherein said imager is a CCD imager.

46. A computer program stored on a computer readable storage medium for operating a computer to perform a method of testing an imager array, the method comprising:

exposing the imager to a photon source;

measuring an output of first and second photosensitive cells, wherein the first cell is blocked from the photon source by a layer of opaque material formed within the imager; and

calculating the MTF using the measured outputs.

47. The computer program of claim 46, wherein said first and second cells are adjacent.

48. The computer program of claim 47, wherein a plurality of photosensitive cells blocked by said opaque material are measured and a plurality of photosensitive cells not blocked by said opaque material, adjacent to said blocked photosensitive cells are measured.

49. The computer program of claim 48, wherein said measuring includes the averaging of output signals from a first column and averaging the output signal from a second column of adjacent photosensitive cells.

50. A computer program stored on a computer readable storage medium for operating a computer to perform a method of testing an imager array, the method comprising:

exposing a first and second predetermined number of photosensitive cells in at least one of a row and column of adjacent photosensitive cells of the imager to a photon source, wherein the first predetermined number of photosensitive cells are blocked from the photon source by a layer of opaque material formed within the imager;

measuring an output of the first and second predetermined number of photosensitive cells; and

calculating the MTF using the measured outputs.

51. The computer program of claim 50, wherein said measurements taken from said plurality of photosensitive cells blocked by said opaque material are averaged and said plurality of photosensitive cells not blocked by said opaque material, adjacent to said blocked photosensitive cells are averaged.

52. A test system for an imager array containing photosensitive cells, the test system comprising:

a light source for exposing at least a portion of the imager array to photons;

a processor coupled to an output of first and second adjacent photosensitive cells of said array, wherein the first cell is blocked from the photon source by a layer of opaque material formed within the imager, said processor determining a modulation transfer function of said imager array from the output signal of said blocked and unblocked photosensitive cells.

53. The system of claim 52, wherein said imager contains an opaque material which defines said blocked and unblocked photosensitive cells.

54. The system of claim 52, wherein a plurality of photosensitive cells blocked by said opaque material are measured and a plurality of photosensitive cells not blocked by said opaque material, adjacent to said blocked photosensitive cells are measured.

55. The system of claim 54, wherein said measurements taken from said plurality of photosensitive cells blocked by said opaque material are averaged and said plurality of photosensitive cells not blocked by said opaque material, adjacent to said blocked photosensitive cells are averaged.

56. The system of claim 52, wherein said light source has an intensity below photosensitive cell saturation intensity.

57. A test system for an imager array containing photosensitive cells, the test system comprising:

a light source for exposing at least a portion of the imager array to photons;

a processor coupled to an output of a first and second predetermined number of photosensitive cells in at least one of a row and column of adjacent photosensitive cells of said array, wherein the first predetermined number of photosensitive cells are blocked from the light source by a layer of opaque material formed within the imager, said processor determining a modulation transfer function of said imager array from the output signal of said blocked and unblocked photosensitive cells.

58. The system of claim 57, wherein said imager contains an opaque material which defines said blocked and unblocked photosensitive cells.

59. The system of claim 57, wherein said determining averages said output from said plurality of photosensitive cells blocked by said opaque material and averages said output from said plurality of photosensitive cells not blocked by said opaque material, adjacent to said blocked photosensitive cells are averaged.

60. The system of claim 57, wherein said light source has an intensity below photosensitive cell saturation intensity.