Process and apparatus for in-situ qualification of master patterns used in patterning systems

• US 4,758,094 A
• Filed: 05/15/1987
• Issued: 07/19/1988
• Est. Priority Date: 05/15/1987
• Status: Expired due to Term

• Current Assignee: KLA Instruments, Corporation
• Original Assignee: KLA Instruments, Corporation
• Inventors: Wihl, Tim S., Yasher, Frank D.
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US07/050,994
• Time in Patent Office: 431 Days
• Field of Search: 356/394, 356/398, 356/237, 358/101, 358/106, 355/53, 437/20, 437/229
• US Class Current: 356/394
• CPC Class Codes: G03F 1/84 Inspecting

Abstract

A process and apparatus for qualifying a reticle, master pattern, or the like, in-situ as it is used in a system for photolithographically creating an image on a substrate, including the steps of coating a transparent substrate with a layer of transparent photoresist material, placing the coated substrate with a layer of transparent photoresist material, placing the coated substrate on a substrate supporting means, using a source of illumination in combination with a reticle, or master pattern, to create an image of the reticle, or master pattern, on the substrate, thereby exposing the photo resist coated on the surface thereof, removing the substrate from the supporting means, developing the exposed photoresist to produce a transparent patterned mask on the surface of the substrate, said patterned mask corresponding to the pattern on the reticle, or master pattern, and, in combination with the substrate, forming a monitor object, inspecting the monitor object by passing light through both the transparent masked and transparent unmasked areas of the substrate to detect defects, and using the detected defects as a measure of the quality of the reticle or master pattern.

Claims

1. A process for qualifying a reticle, master pattern, or the like, in-situ as it is used in a system for photolithographically creating an image on a substrate, such system normally including a source of illumination, a reticle or master pattern, and a substrate supporting means, comprising the steps of:

coating a transparent substrate with a layer of transparent photoresist material;

placing the coated substrate on the substrate supporting means;

using the source of illumination in combination with the reticle, or master pattern, to create an image of the reticle, or master pattern, on the substrate, thereby exposing the photoresist coated on the surface thereof;

removing the substrate from the supporting means;

developing the exposed photoresist to produce a transparent patterned mask on the surface of the substrate, said patterned mask corresponding to the pattern on the reticle, or master pattern, and in combination with the substrate, forming a monitor object;

inspecting the monitor object by passing light through both the transparent masked and transparent unmasked areas of the substrate to detect defects; and

using the detected defects as a measure of the quality of the reticle or master pattern.

2. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 and further including the step of providing an opaque border around at least a substantial portion of the perimeter of the substrate before it is coated with the photoresist material, said border being used to facilitate automatic handling of the monitor object.

3. A process for qualifying a reticle, master pattern, or the like, as recited in claim 2 and further including the step of providing the substrate with a coating that is transmissive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

4. A process for qualifying a reticle, master pattern, or the like, as recited in claim 2 and further including the step of providing the substrate with a coating that is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

5. A process for qualifying a reticle, master pattern, or the like, as recited in claim 2 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

6. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 and further including the step of providing the substrate with a coating that is transmissive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

7. A process for qualifying a reticle, master pattern, or the like as recited in claim 6 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

8. A process for qualifying a reticle, master pattern, or the like as recited in claim 1 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

9. A process for qualifying a reticle, master pattern, or the like, as recited in claim 8 and further including the step of providing the substrate with a coating that is transmissive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

10. A process for qualifying a reticle, master pattern, or the like, as recited in claim 9 and further including the step of providing an opaque border around at least a substantial portion of the perimeter of the substrate before it is coated with the photoresist material, said border being used to facilitate automatic handling of the monitor object.

11. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 wherein the transparent substrate is made of a material selected from the group of materials including glass, quartz, sapphire and borosilicate.

12. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 wherein the substrate is transparent to predetermined wavelengths of light used to inspect the monitor object and is opaque to other predetermined wavelengths of light.

13. A process for qualifying a reticle, master pattern, or the like, as recited in claim 12 wherein the photoresist material is transparent to predetermined wavelengths of light used to inspect the monitor object and is opaque to other predetermined wavelengths of light.

14. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 wherein the photoresist material is transparent to predetermind wavelengths of light used to inspect the monitor object and is opaque to other predetermined wavelengths of light.

15. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 wherein during inspection of the monitor object light is passed through the masked and unmasked areas of the substrate in a manner so as to create an image having bands signifying the edges of the masked areas.

16. A process for qualifying a reticle, master pattern, or the like, as recited in claim 15 wherein the bands created by the monitor object are compared to corresponding dark bands of a reference.

17. A process for qualifying a reticle, master pattern, or the like, as recited in claim 15 wherein said bands are created using darkfield illumination of the monitor object.

18. A process for qualifying a reticle, master pattern, or the like, as recited in claim 15 wherein said bands are created using brightfield illumination of the monitor object.

19. A process for qualifying a reticle, master pattern, or the like, as recited in claim 15 wherein the inspection is made using a sampling system having a pixel size approximately equal to or smaller than the width of a band.

20. A process for qualifying a reticle, master pattern, or the like, as recited in claim 1 wherein an optical system having a predetermined numerical aperture is used to pass light through the monitor object during inspection thereof.

21. A process for qualifying a reticle, master pattern, or the like, as recited in claim 20 wherein said predetermined numerical aperture is large enough to provide an image having a high contrast band and small enough that the optical system has sufficient depth of field to accommodate the thickness of the patterned mask.

22. A process for qualifying a reticle, master pattern, or the like, as recited in claim 21 wherein the inspection is made using a sampling system having a pixel size approximately equal to or smaller than the width of a band.

23. A monitor object for use in qualifying a particular recticle, master pattern, or the like, in-situ as it is used in a system for photolithographically creating an image on a product object, comprising:

a substrate which is transparent to predetermined visible wavelenths of light and has physical dimensions generally corresponding to those of said particular product object to be qualified using said monitor object; and

a coating of transparent photoresist material covering at least one surface of substrate, said coating being used to produce a transparent patterned mask on the surface of said substrate when photolithographically exposed to illumination passed through the reticle or master pattern, whereby light may be passed through the transparent masked and transparent unmasked areas of the sustrate to create an image which may be compared to a reference to detect defects in said reticle or master pattern.

24. A monitor object as recited in claim 23 and further comprising means forming an opaque substrate border around at least a portion of the perimeter of said substrate for facilitating the automatic handling of the monitor object.

25. A monitor object as recited in claim 24 and further comprising a coating on said substrate that is transmisssive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

26. A monitor object as recited in claim 24 and further comprising a coating on said substrate that is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitoring object.

27. A monitor object as recited in claim 24 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and or focussing of the monitor object.

28. A monitor object as recited in claim 23 and further comprising a coating that is transmissive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

29. A monitor object as recited in claim 28 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

30. A monitor object as recited in claim 23 wherein the substrate is transmissive of predetermined wavelengths used for inspection purposes and is absorptive of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

31. A monitor object as recited in claim 30 and further comprising a coating that is transmissive of predetermined wavelengths used for inspection purposes and is reflective of other predetermined wavelengths used for automatic handling and/or focussing of the monitor object.

32. A monitor object as recited in claim 31 and further comprising means forming an opaque border around at least a portion of the perimeter of the substrate, said border being used to facilitate automatic handling of the monitor object.

33. A monitor object as recited in claim 23 wherein the transparent substrate is made of a material selected from the group of materials including glass, quartz, sapphire and borosilicate.

34. A monitor object as recited in claim 23 wherein the substrate is transparent to wavelengths of light used to inspect the monitor object.

35. A monitor object as recited in claim 34 wherein the photoresist material is transparent to wavelengths of light used to inspect the monitor object.

36. A monitor object as recited in claim 23 wherein the photoresist material is transparent to wavelengths of light used to inspect the monitor object.

37. A process for inspecting an object consisting of a transparent substrate, having formed thereon regions of transparent material, for the purpose of determining that the boundaries of the regions are accurately defined, comprising the steps of:

passing light through the object to form an image thereof wherein the boundaries of the regions appear as bands; and

comparing the bands to a reference to locate variances exceeding predetermined criteria.

38. A process for inspecting an object as recited in claim 37 wherein the step of passing light through the object is accomplished by

illuminating the object with a beam of light having a predetermined angle of convergence;

collecting the light passing through the object and focussing it upon a detector to detect the level of light transmission of the object on a pixel by pixel basis.

39. A process for inspecting an object as recited in claim 37 wherein the step of comparing the bands to a reference includes the steps of identifying each pixel falling within the bands and comparing the level of light transmitted therethrough to a reference.

40. A process for inspecting an object as recited in claim 37 wherein the step of passing light through the object is accomplished using an image forming system having a numerical aperture large enough to provide an image having high contrast bands and small enough that the optical system has sufficient depth of field to accommodate the thickness of the transparent material.

41. A process for inspecting an object as recited in claim 40 wherein the detected level of light of each pixel is obtained using a sampling system having a pixel size approximately equal to or smaller than the width of a band.

42. A process for inspecting an object consisting of a transparent substrate, having formed thereon regions of transparent material, for the purpose of determining that the boundaries of the regions are accurately defined, comprising the steps of:

passing light through the object to form an image thereof wherein the boundaries of the regions appear as bands; and

comparing the bands to a reference to determine the accuracy of their definition.

43. A process for inspecting an object as recited in claim 42 wherein the step of passing light through the object is accomplished by

illuminating the object with a beam of light having a predetermined angle of convergence;

collecting the light passing through the object and focussing it upon a detector to detect the level of light transmission of the object on a pixel by pixel basis.

44. A process for inspecting an object as recited in claim 42 wherein the step of comparing the bands to a reference includes the steps of identifying each pixel falling within the bands and comparing the level of light transmitted therethrough to a reference.

45. A process for inspecting an object as recited in claim 42 wherein the step of passing light through the object is accomplished using an image forming system having a numerical aperture large enough to provide an image having high contrast bands and small enough that the optical system has sufficient depth of field to accommodate the thickness of the transparent material.

46. A process for inspecting an object as recited in claim 45 wherein the detected level of light of each pixel is obtained using a sampling system having a pixel size approximately equal to or smaller than the width of a band.

47. A process for inspecting an object consisting of a transparent substrate, having formed thereon regions of transparent material, for the purpose of determining that the boundaries of the regions are accurately defined, comprising the steps of:

passing light through the object to form an image thereof wherein the boundaries of the regions appear as bands; and

inspecting the image to determine whether or not a particular characteristic of the bands is consistent with a predetermined criteria.

48. A process for inspecting an object as recited in claim 47 wherein the step of passing light through the object is accomplished by illuminating the object with a beam of light having a predetermined angle of convergence;

collecting the light passing through the object and focussing it upon a detector to detect the level of light transmission of the object on a pixel by pixel basis.

49. A process for inspecting an object as recited in claim 47 wherein the step of comparing the bands to a reference includes the steps of identifying each pixel falling within the bands and comparing the level of light transmitted therethrough to a reference.

50. A process for inspecting an object as recited in claim 47 wherein the step of passing light through the object is accomplished using an image forming system having a numerical aperture large enough to provide an image having high contrast bands and small enough that the optical system has sufficient depth of field to accommodate the thickness of the transparent material.

51. A process for inspecting an object as recited in claim 50 wherein the detected level of light of each pixel is obtained using a sampling system having a pixel size approximately equal to or smaller than the width of a band.