Visual inspection and verification system

• US 6,757,645 B2
• Filed: 08/07/1998
• Issued: 06/29/2004
• Est. Priority Date: 09/17/1997
• Status: Expired due to Term

• Current Assignee: Synopsys Merger Holdings LLC (Synopsys Incorporated)
• Original Assignee: Numerical Technologies Inc. (Synopsys Incorporated)
• Inventors: Wang, Yao-Ting, Chang, Fang-Cheng, Pati, Yagyensh C., Karklin, Linard N.
• Primary Examiner(s): Jones, Hugh
• Assistant Examiner(s): FERRIS III, FRED O
• Application Number:
  US09/130,996
• Publication Number:
  US 20020019729A1
• Time in Patent Office: 2,153 Days
• Field of Search: 703/13, 716/19, 716/21
• US Class Current: 703/13
• CPC Class Codes: G03F 1/26 Phase shift masks [PSM]; PSM blanks; Preparation thereof
• CPC Class Codes: G03F 1/36 Masks having proximity correction features; Preparation thereof, e.g. optical proximity correction [OPC] design processes
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/0004 Industrial image inspection

Abstract

A method and apparatus for inspecting a photolithography mask for defects is provided. The inspection method comprises providing a defect area image to an image simulator wherein the defect area image is an image of a portion of a photolithography mask, and providing a set of lithography parameters as a second input to the image simulator. The defect area image may be provided by an inspection tool which scans the photolithography mask for defects using a high resolution microscope and captures images of areas of the mask around identified potential defects. The image simulator generates a first simulated image in response to the defect area image and the set of lithography parameters. The first simulated image is a simulation of an image which would be printed on a wafer if the wafer were to be exposed to an illumination source directed through the portion of the mask. The method may also include providing a second simulated image which is a simulation of the wafer print of the portion of the design mask which corresponds to the portion represented by the defect area image. The method also provides for the comparison of the first and second simulated images in order to determine the printability of any identified potential defects on the photolithography mask. A method of determining the process window effect of any identified potential defects is also provided for.

Claims

1. A method of inspecting a mask used in lithography for defects, the method comprising:

locating a portion of said mask which contains a potential defect;

providing a defect area image as a first input, wherein said defect area image comprises an image of said portion of said mask;

providing a first set of lithography parameters;

generating a first simulated image in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters;

providing a reference description of said portion of said mask;

providing a reference image, wherein said reference image comprises a representation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said second mask comprises a mask described by said reference description;

generating a first process window related output in response to said first simulated image;

generating a second process window related output in response to said reference image; and

comparing said first process window related output with said second process window related output.

2. The method of inspecting a mask used in lithography for defects of claim 1 wherein providing said defect area image comprises:

providing a set of potential defect criteria;

scanning said mask for features whose characteristics fall within said set of potential defect criteria; and

generating said defect area image in response to said scanning of said mask, wherein said defect area image comprises an image of a portion of said mask comprising at least one feature whose characteristics fall within said set of potential defect criteria.

3. The method of inspecting a mask used in lithography for defects of claim 2 wherein said mask is scanned by a device comprising one of a group of devices including an optical microscope, a scanning electron microscope, a focus ion beam microscope, an atomic force microscope and a near-field optical microscope.

4. The method of inspecting a mask used in lithography for defects of claim 1, wherein said defect area image comprises a digital representation of said defect area image.

5. The method of inspecting a mask used in lithography for defects of claim 1, wherein said illumination source comprises a visible illumination source.

6. The method of inspecting a mask used in lithography for defects of claim 1, wherein said illumination source comprises a non-visible illumination source.

7. The method of inspecting a mask used in lithography for defects of claim 1, wherein said first set of lithography parameters comprises data representing at least one parameter of a group of parameters including numerical aperture, wavelength, sigma, lens aberration, defocus and critical dimension.

8. The method of inspecting a mask used in lithography for defects of claim 1, wherein said mask comprises a bright field mask design.

9. The method of inspecting a mask used in lithography for defects of claim 1, wherein said mask comprises a dark field mask design.

10. The method of inspecting a mask used in lithography for defects of claim 1, wherein said mask comprises a phase shifting mask.

11. The method of inspecting a mask used in lithography for defects of claim 1, comprising:

providing a set of photoresist process parameters as a third input; and

generating a second simulated image in response to said third input, wherein said second simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

12. The method of inspecting a mask used in lithography for defects of claim 11 wherein said set of photoresist process parameters comprises data representing at least one parameter of a group of parameters including thickness, contrast, pre-bake time, post-bake time, development time, photoresist concentration, developer solution concentration, and light absorption of photoresist.

13. The method of inspecting a mask used in lithography for defects of claim 1, wherein the step of generating said first simulated image has been calibrated to a set of photoresist process parameters such that said first simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

14. The method of inspecting a mask used in lithography for defects of claim 11 comprising:

providing a set of etching process parameters as a fourth input; and

generating a third simulated image in response to said fourth input, wherein said third simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

15. The method of inspecting a mask used in lithography for defects of claim 14 wherein said set of etching process parameters comprises data representing at least one parameter of a group of parameters including etching time, etching method, and concentration.

16. The method of inspecting a mask used in lithography for defects of claim 1, wherein the step of generating said first simulated image has been calibrated to a set of etching process parameters such that said first simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

17. The method of inspecting a mask used in lithography for defects of claim 1, wherein said reference description comprises a physical mask which has been determined to be free from defects.

18. The method of inspecting a mask used in lithography for defects of claim 1, wherein providing said reference image comprises generating said reference image in response to said reference description, wherein said reference image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said second mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters.

19. The method of inspecting a mask used in lithography for defects of claim 18 wherein said reference description comprises data in a format comprising at least one of a group of data formats including GDS-II, MEBES, CFLAT, digitized and discretized data.

20. The method of inspecting a mask used in lithography for defects of claim 1 wherein generating said first process window related output comprises:

providing a set of wafer image acceptance criteria; and

generating a range of values for at least one optical parameter comprising said first set of lithography parameters, wherein within said range said first simulated image falls one of inside and outside said set of wafer image acceptance criteria.

21. The method of inspecting a mask used in lithography for defects of claim 20 wherein generating said second process window related output comprises:

generating a second range of values for said at least one optical parameter comprising said first set of lithography parameters, wherein within said second range said reference image falls one of inside and outside said set of wafer image acceptance criteria.

22. The method of inspecting a mask used in lithography for defects of claim 21 wherein said first set of lithography parameters comprises data representing at least one of a group of parameters including numerical aperture, wavelength, sigma, lens aberration, defocus and critical dimension.

23. The method of inspecting a mask used in lithography for defects of claim 1, wherein the method is performed by a machine executing a program of instructions tangibly embodied in a program storage device readable by said machine.

24. The method of inspecting a mask used in lithography for defects of claim 23 wherein said program storage device comprises a hard disk drive.

25. The method of inspecting a mask used in lithography for defects of claim 23 wherein said program storage device comprises a server.

26. An apparatus for inspecting a mask used in lithography for defects, the apparatus comprising:

data storage receiving a defect area image as a first input, wherein said defect area image comprises an image of said portion of said mask and receiving a first set of lithography parameters as a second input; and

an image simulator that generates a first simulated image in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions;

data storage receiving a reference description of said portion of said mask; and

an image simulator that generates a reference image in response to said reference description, wherein said reference image comprises a representation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions, and wherein said second mask comprises a mask described by said reference description; and

an image comparator that compares said first simulated image with said reference image, wherein said image comparator generates a first process window related output and a second process window related output, and wherein said image comparator compares said first process window related output with said second process window related output.

27. The apparatus for inspecting a mask used in lithography for defects of claim 26, comprising:

a resource for receiving a set of potential defect criteria;

a scanning resource which scans said mask for features whose characteristics fall within said set of potential defect criteria; and

a resource for generating said defect area image, wherein said defect area image comprises an image of a portion of said mask comprising at least one feature whose characteristics fall within said set of potential defect criteria.

28. The apparatus for inspecting a mask used in lithography for defects of claim 27 wherein said scanning resource comprises one of a group of devices including an optical microscope, a scanning electron microscope, a focus ion beam microscope, an atomic force microscope and a near-field optical microscope.

29. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said defect area image comprises a digital representation of said defect area image.

30. The apparatus for inspecting a mask used in lithography for defects of claim 26, Wherein said illumination source comprises a visible illumination source.

31. The apparatus for inspecting a mask used in lithography for defects of claim 26 Wherein said illumination source comprises a non-visible illumination source.

32. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said first set of lithography parameters comprises data representing at least one parameter of a group of parameters including numerical aperture, wavelength, sigma, lens aberration, defocus and critical dimension.

33. The apparatus for inspecting a mask used in lithography for defects of claim 26, herein said mask comprises a bright field mask design.

34. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said mask comprises a dark field mask design.

35. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said mask comprises a phase shifting mask.

36. The apparatus for inspecting a mask used in lithography for defects of claim 26, comprising:

a resource for receiving a set of photoresist process parameters as a third input; and

a resource for generating a second simulated image in response to said third input, wherein said second simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

37. The apparatus for inspecting a mask used in lithography for defects of claim 36 wherein said set of photoresist process parameters comprises data representing at least one parameter of a group of parameters including thickness, contrast, pre-bake time, post-bake time, development time, photoresist concentration, developer solution concentration, and light absorption of photoresist.

38. The apparatus for inspecting a mask used in lithography for defects of claim 26 wherein said image simulator has been calibrated to a set of photoresist process parameters such that said first simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

39. The apparatus for inspecting a mask used in lithography for defects of claim 36 comprising:

a resource for receiving a set of etching process parameters as a fourth input; and

a resource for generating a third simulated image in response to said fourth input, wherein said third simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

40. The apparatus for inspecting a mask used in lithography for defects of claim 39 wherein said set of etching process parameters comprises data representing at least one parameter of a group of parameters including etching time, etching method, and concentration.

41. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said image simulator has been calibrated to a set of etching process parameters such that said first simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

42. The apparatus for inspecting a mask used in lithography for defects of claim 26 wherein said reference description comprises a physical mask which has been determined to be free from defects.

43. The apparatus for inspecting a mask used in lithography for defects of claim 26, wherein said resource for providing said reference image comprises said image simulator apparatus generating said reference image in response to said reference description, wherein said reference image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said second mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions.

44. The apparatus for inspecting a mask used in lithography for defects of claim 43 wherein said reference description comprises data in a format comprising at least one of a group of data formats including GDS-II, MEBES, CFLAT, digitized and discretized data.

45. The apparatus for inspecting a mask used in lithography for defects of claim 26 wherein generating said first process window related output comprises:

providing a set of wafer image acceptance criteria; and

generating a range of values for at least one optical parameter comprising said first set of lithography parameters, wherein within said range said first simulated image falls one of inside and outside said set of wafer image acceptance criteria.

46. The method of inspecting a mask used in lithography for defects of claim 45 wherein generating said second process window related output comprises:

generating a second range of values for said at least one optical parameter comprising said first set of lithography parameters, wherein within said second range said reference image falls one of inside and outside said set of wafer image acceptance criteria.

47. The apparatus for inspecting a mask used in lithography for defects of claim 46 wherein said first set of lithography parameters comprises data representing at least one of a group of parameters including numerical aperture, wavelength, sigma, lens aberration, defocus and critical dimension.

48. The apparatus for inspecting a mask used in lithography for defects of claim 26, the apparatus comprising a computer program product comprising a computer usable medium having a computer readable program code embodied therein for causing a computer to inspect a mask used in lithography for defects.

49. The apparatus for inspecting a mask used in lithography for defects of claim 48 wherein said computer usable medium comprises a hard disk drive.

50. The apparatus for inspecting a mask used in lithography for defects of claim 48 wherein said computer usable medium comprises a server.

51. A program storage device readable by a machine, tangibly embodying a program of instructions executable by said machine to perform method steps to inspect a mask used in lithography, the method comprising:

supporting location of a portion of said mask which contains a potential defect;

receiving a defect area image as a first input, wherein said defect area image comprises an image of said portion of said mask;

receiving a first set of lithography parameters;

generating a first simulated image in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters;

providing a reference description of said portion of said mask;

providing a reference image, wherein said reference image comprises a representation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said second mask comprises a mask described by said reference description;

generating a first process window related output in response to said first simulated image;

generating a second process window related output in response to said reference image; and

comparing said first process window related output with said second process window related output.

52. The program storage device readable by a machine of claim 51, wherein said generating of said first simulated image has been calibrated to a set of photoresist process parameters such that said first simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

53. The program storage device readable by a machine of claim 51, wherein said generating of said first simulated image has been calibrated to a set of etching process parameters such that said first simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

54. The program storage device readable by a machine of claim 51, wherein the method further comprises analyzing said first simulated image for defects on said mask.

55. The program storage device readable by a machine of claim 51, wherein said program storage device comprises a hard disk drive.

56. The program storage device readable by a machine of claim 51, wherein said program storage device comprises a server.

57. A computer program product, comprising:

a computer usable medium having a computer readable program code embodied therein for causing a computer to inspect a mask used in lithography for defects, the computer readable program code comprising;

computer readable program code that reads a defect area image of a portion of said mask as a first input;

computer readable program code that reads a first set of lithography parameters;

computer readable program code that generates a first simulated image in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters;

computer readable program code that receives a reference description of said portion of said mask;

computer readable program code that provides a reference image, wherein said reference image comprises a simulation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions, and wherein said second mask comprises a mask described by said reference description; and

computer readable program code that generates a first process window related output in response to said first simulated image, generates a second process window related output in response to said reference image, and compares said first process window related output with said second process window related output.

58. The computer program product of claim 57, wherein said computer readable program code that generates said first simulated image has been calibrated to a set of photoresist process parameters such that said first simulated image comprises a simulation of an image which would be printed on said wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography conditions, and wherein said wafer comprises a coating of photoresist material characterized by said set of photoresist process parameters.

59. The computer program product of claim 57, wherein said computer readable program code that generates said first simulated image has been calibrated to a set of etching process parameters such that said first simulated image comprises a simulation of an image which would be transferred on said wafer if said wafer were etched in accordance with said etching process parameters after said exposure to said illumination source.

60. The computer program product of claim 57, comprising a computer readable program code that analyzes said first simulated image for defects on said mask.

61. The computer program product of claim 57, wherein said computer usable medium comprises a hard disk drive.

62. The computer program product of claim 57, wherein said computer usable medium comprises a server.

63. A method of inspecting a mask used in lithography for defects, the method comprising:

providing a mask inspection tool;

providing a set of potential defect criteria to the mask inspection tool;

scanning said mask with said mask inspection tool for features whose characteristics fall within said set of potential defect criteria;

generating a defect area image as a first input, wherein said defect area image comprises an image of a portion of said mask which contains a potential defect;

providing a first set of lithography parameters;

generating a first simulated image with said simulator apparatus in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters;

providing a reference description of said portion of said mask;

providing a reference image, wherein said reference image comprises a representation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said second mask comprises a mask described by said reference description;

generating a first process window related output in response to said first simulated image;

generating a second process window related output in response to said reference image; and

comparing said first process window related output with said second process window related output.

64. An apparatus for inspecting a mask used in lithography for defects, the apparatus comprising:

an inspection tool, wherein said inspection tool locates a portion of said mask which contains a potential defect and generates a defect area image, wherein said defect area image comprises an image of said portion of said mask which contains said potential defect;

a resource for receiving said defect area image as a first input;

a resource for receiving a first set of lithography parameters;

an image simulator that generates a first simulated image in response to said first input, wherein said first simulated image comprises a simulation of an image which would be printed on a wafer if said wafer were exposed to an illumination source directed through said portion of said mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters;

a resource for receiving a reference description of said portion of said mask;

a resource for providing a reference image, wherein said reference image comprises a simulation of an image that would be printed on a wafer if said wafer were exposed to an illumination source directed through a second mask, wherein the characteristics of said illumination source comprise said first set of lithography parameters, and wherein said second mask comprises a mask described by said reference description; and

a resource that generates a first process window related output in response to said first simulated image, generates a second process window related output in response to said reference image, and compares said first process window related output with said second process window related output.