Laser imaging system for inspection and analysis of sub-micron particles

• US 5,963,314 A
• Filed: 10/15/1996
• Issued: 10/05/1999
• Est. Priority Date: 06/17/1993
• Status: Expired due to Term

• Current Assignee: Ultrapointe Corp. (Lumentum Holdings Inc.)
• Original Assignee: Ultrapointe Corp. (Lumentum Holdings Inc.)
• Inventors: Fairley, Christopher R., Crane, Dale E., Hansen, Hans J., Lee, Ken K., Worster, Bruce W.
• Primary Examiner(s): Hardy, David B.
• Application Number:
  US08/730,254
• Time in Patent Office: 1,085 Days
• Field of Search: 350/237, 250/562, 250/563, 250/571, 250/572, 356/388, 356/394, 356/376
• US Class Current: 356/237.2
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01R 31/311 of integrated circuits G01R31/31728 takes precedence
• CPC Class Codes: G02B 21/006 focusing arrangements; selection of the plane to be imaged

Abstract

A laser imaging system is used to analyze defects on semiconductor wafers that have been detected by patterned wafer defect detecting systems (wafer scanners). The laser imaging system replaces optical microscope review stations now utilized in the semiconductor fab environment to examine detected optical anomalies that may represent wafer defects. In addition to analyzing defects, the laser imaging system can perform a variety of microscopic inspection functions including defect detection and metrology. The laser imaging system uses confocal laser scanning microscopy techniques, and operates under class 1 cleanroom conditions and without exposure of the wafers to operator contamination or airflow. Unlike scanning electron microscopes (SEMs) that have previously been used for defect analysis, the laser imaging system will not damage samples or slow processing, costs significantly less to implement than an SEM, can produce a three dimensional image which provides quantitative dimensional information, and allows sub-surface viewing of defects lying beneath dielectric layers. The laser imaging system is adaptable to cluster or in-situ applications, where examination of defects or structures during on-line processing can be performed.

Claims

1. An imaging system comprising:

means for supporting a semiconductor wafer to be imaged by the imaging system;

means for inspecting the wafer to determine the efficacy of a process previously performed on the wafer, the inspecting means including;

means for emitting laser light of a plurality of wavelengths;

means for directing the laser light toward the supporting means;

means for measuring a first intensity of laser light reflected from a plurality of points on a surface of the wafer to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface; and

means for storing the plurality of test values;

means for comparing the stored plurality of test values to a plurality of reference values to identify differences between the test values and the reference values, wherein the differences between the test and reference values indicate the presence of an optical anomaly; and

means for analyzing the differences to determine the nature and origin of the anomaly.

2. The imaging system of claim 1, wherein the analyzing means is capable of determining whether the anomaly was caused by a contaminant.

3. The imaging system of claim 2, wherein the analyzing means further comprises means for determining at least one material of which the contaminant is constituted.

4. The imaging system of claim 1, wherein the analyzing means is capable of determining whether the anomaly was caused by a deformation of the wafer.

5. The imaging system of claim 1, wherein the analyzing means further comprises means for determining at least one dimension of the anomaly.

6. The imaging system of claim 1, wherein the analyzing means further comprises means for determining a location of the anomaly on the wafer.

7. The imaging system of claim 1, further comprising means for isolating the wafer within a region of the system, wherein air within the region conforms to Class 1 cleanroom conditions.

8. The imaging system of claim 7, further comprising means for remotely loading and unloading the wafer onto and off of the supporting means such that the air within the region conforms to Class 1 cleanroom conditions.

9. The imaging system of claim 1, wherein the imaging system can resolve features on the wafer as small as approximately 0.1 microns.

10. The imaging system of claim 1, wherein the means for emitting laser light includes an ultraviolet laser.

11. The imaging system of claim 1, wherein the imaging system renders images of the wafer in false color.

12. A microscope for imaging a surface of an object, the microscope comprising:

a stage for supporting the object;

a laser imaging system configured to provide a three-dimensional image of the surface, the laser imaging system including;

a laser light source for emitting a beam of laser light;

a lens arranged to be between the laser light source and the stage, the lens having a focal plane;

a beam scanner for scanning the beam and for directing the scanned beam toward the stage through the lens; and

a first photodetector for measuring the intensity of laser light reflected from the surface of the object, wherein the measured intensity of laser light reflected from the surface is at a maximum intensity when the surface lies in the focal plane of the lens; and

a white-light imaging system for imaging the surface simultaneous with the laser imaging system, the white-light imaging system including;

a white light source for emitting white light toward the stage; and

a second photodetector for measuring the intensity of white light reflected from the surface.

13. The microscope of claim 12, further comprising a filter for preventing laser light from impinging upon the second photodetector and for allowing white light to impinge upon the second photodetector.

14. The microscope of claim 12, wherein the laser imaging system further comprises a first display for displaying the laser light image of the surface, and the white-light imaging system further comprises a second display for displaying the white-light image of the surface.

15. The microscope of claim 14, wherein the laser light image of the surface can be displayed as a three-dimensional view.

16. The microscope of claim 12, wherein the laser imaging system further comprises a polarizer for polarizing the laser light and a cross polarized filter.

17. A microscope for imaging a surface of an object, the microscope comprising:

a stage for supporting the object;

a laser imaging system for imaging the surface, the laser imaging system including;

a laser light source for emitting a beam of laser light;

a lens arranged to be between the laser light source and the stage, the lens having a focal plane;

a beam scanner for scanning the beam and for directing the scanned beam toward the stage through the lens; and

a first photodetector for measuring the intensity of laser light reflected from the surface of the object, wherein the measured intensity of laser light reflected from the surface is at a maximum intensity when the surface lies in the focal plane of the lens; and

a white-light imaging system for imaging the surface simultaneous with the laser imaging system, the white-light imaging system including;

a white light source for emitting white light toward the stage; and

a second photodetector for measuring the intensity of white light reflected from the surface;

wherein one of the laser light or the white light is to be emitted at a first wavelength for causing fluorescence of a particular material in or on the surface such that the one of the laser light or white light is reflected from the material at a second wavelength, and

wherein the microscope further comprises a filter for allowing light of the second wavelength to pass through the filter and for preventing light of the first wavelength from passing through the filter.

18. An imaging system for detection or analysis of defects in or on an object to be imaged, the system comprising:

a stage for supporting the object;

a source of polarized light of a first polarity, the source for directing polarized light toward the stage, whereby the polarized light impinges upon the object when the object is supported by the stage;

a pinhole aperture positioned between the light source and the stage such that a portion of the light of a first polarity travels through the pinhole aperture toward the stage;

a lens, mounted between the source of polarized light and the stage, for focusing the portion of the light of the first polarity to a focal point of the lens;

a photodetector for measuring the intensity of light reflected from the object when the object is supported by the stage, wherein the intensity of light reflected from the object is at a maximum intensity when a surface of the object and the focal point are coincident; and

a filter, positioned between the stage and the photodetector, for changing the polarization of reflected light so that the polarization of light reflected by the surface is of a second polarity different from the first polarity.

19. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

a stage for supporting the wafer to be inspected;

a light source for emitting a beam of light;

a beam scanner for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

a photodetector for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first region of memory for storing the plurality of test values;

a second region of memory for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on a reference surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values diagnose whether an optical anomaly is present on the wafer and

wherein the optical anomaly provides an indication of the efficacy of the process.

20. The system of claim 19, further comprising a processor capable of processing the test values to provide display data to a first display, thereby enabling the first display to produce an image of the wafer surface.

21. The system of claim 20, further comprising a white-light imaging system for simultaneously providing a white-light image of the wafer surface.

22. The system of claim 19, further comprising a third region of memory for storing a group of difference values, the group of difference values representing the differences between corresponding test and reference values.

23. The system of claim 22, wherein the means for comparing may be used to analyze the group of difference values to determine at least one material that caused the anomaly.

24. The system of claim 22, wherein the means for comparing may be used to analyze the group of difference values to determine at least one dimension of the anomaly.

25. The system of claim 22, further comprising a hood for encapsulating the stage and the wafer, wherein air within the hood conforms to Class 1 cleanroom conditions.

26. The system of claim 25, further comprising a robot for remotely loading and unloading the wafer onto and off of the stage such that air within the hood conforms to Class 1 cleanroom conditions.

27. The system of claim 19, further comprising collimating optics between the light source and the beam scanner.

28. The system of claim 19, wherein the light source is a laser.

49. The system of claim 19 wherein the reference values are not generated from the wafer.

29. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

a stage for supporting the wafer to be inspected;

a light source for emitting a beam of light;

a beam scanner for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

a photodetector for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first region of memory for storing the plurality of test values;

a second region of memory for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on a reference surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values indicate the presence of an optical anomaly, and

wherein the optical anomaly provides an indication of the efficacy of the process,

said system further comprising a third region of memory for storing a group of difference values, the group of difference values representing the differences between corresponding test and reference values, and

wherein the means for comparing may be used to analyze the group of difference values to determine a location of the anomaly on the wafer, the location being defined by X, Y, and Z coordinates.

30. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

a stage for supporting the wafer to be inspected;

a laser light source for emitting a beam of light, wherein the laser light source is capable of emitting light of a plurality of wavelengths;

a beam scanner for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

a photodetector for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first region of memory for storing the plurality of test values;

a second region of memory for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on a reference surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values indicate the presence of an optical anomaly, and

wherein the optical anomaly provides an indication of the efficacy of the process.

31. A method of locating an optical anomaly on a test surface, wherein the test surface is contained within a test volume represented by a Cartesian coordinate system having x, y, and z axes describing a set of unique x-y-z coordinates, the method comprising the steps of:

scanning the test surface in the test volume with a focussed beam so that the focal point of the focussed beam coincides, in turn, with each unique x-y-z coordinate within the test volume;

determining, for each unique x-y-z coordinate in the test volume, a reflected intensity of the focussed beam to create a set of reflected intensity values; and

comparing the set of reflected intensity values to a set of reference values to determine whether the set of reflected intensity values is different from the set of reference values;

wherein differences between the set of reflected intensity values and the set of reference values indicate the presence of an optical anomaly.

32. The method of claim 31, wherein the focussed beam comprises white light.

33. The method of claim 31, wherein the focussed beam comprises at least one beam of laser light.

34. The method of claim 31 further comprising the steps of:

determining, for each column of points specified by a unique x-y coordinate of the test volume, the z coordinate resulting in a maximum reflected intensity of the focussed beam;

storing all the locations along the z axes of all unique x-y coordinates to form a set of z test data representing a three-dimensional image of the test surface; and

comparing the set of z test data with a set of z reference data to determine whether the set of z test data is different from the set of z reference data.

35. The method of claim 34, wherein the light source provides white light.

36. The method of claim 34, wherein the light source provides at least one beam of laser light.

37. A method comprising the steps of:

generating three-dimensional microscope image data representing a semiconductor wafer;

comparing the three-dimensional microscope image data to reference three-dimensional image data; and

characterizing structures on the semiconductor wafer based on the step of comparing.

38. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

means for supporting the wafer to be inspected;

means for emitting a beam of light;

means for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

means for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first memory means for storing the plurality of test values;

a second memory means for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on the wafer surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values diagnose whether an optical anomaly is present on the wafer, and

wherein the optical anomaly provides an indication of the efficacy of the process.

39. The system of claim 38, further comprising a means for processing the test values to provide display data to a display means, thereby enabling the display means to produce an image of the wafer surface.

40. The system of claim 39, further comprising a means for simultaneously providing a white-light image of the wafer surface.

41. The system of claim 38, further comprising a third memory means for storing a group of difference values, the group of difference values representing the differences between corresponding test and reference values.

42. The system of claim 41, wherein the means for comparing may be used to analyze the group of difference values to determine at least one material that caused the anomaly.

43. The system of claim 41, wherein the means for comparing may be used to analyze the group of difference values to determine at least one dimension of the anomaly.

44. The system of claim 41, further comprising a means for encapsulating the stage and the wafer, wherein air within the encapsulating means conforms to Class 1 cleanroom conditions.

45. The system of claim 44, further comprising a means for remotely loading and unloading the wafer onto and off of the stage such that air within the hood conforms to Class 1 cleanroom conditions.

46. The system of claim 38, wherein the light-emitting means is a laser.

50. The system of claim 38 wherein the reference values are not generated from the wafer.

47. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

means for supporting the wafer to be inspected;

means for emitting a beam of light;

means for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

means for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first memory means for storing the plurality of test values;

a second memory means for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on the wafer surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values indicate the presence of an optical anomaly, and

wherein the optical anomaly provides an indication of the efficacy of the process,

said system further comprising a third memory means for storing a group of difference values, the group of difference values representing the differences between corresponding test and reference values; and

wherein the means for comparing may be used to analyze the group of difference values to determine a location of the anomaly on the wafer, the location being defined by X, Y, and Z coordinates.

48. A system for inspecting a semiconductor wafer to determine the efficacy of a wafer process previously performed, the system comprising:

means for supporting the wafer to be inspected;

a laser capable of emitting light of a plurality of wavelengths;

means for scanning the beam and directing the scanned beam toward the stage, wherein the stage is arranged such that a portion of the scanned beam will be reflected from a plurality of points on a surface of the wafer to be inspected;

means for measuring the intensity of the reflected portion of the scanned beam from the plurality of points on the wafer surface to define a plurality of test values, each of the test values representing the intensity of light reflected from one of the plurality of points on the wafer surface;

a first memory means for storing the plurality of test values;

a second memory means for storing a plurality of reference values, each of the reference values representing the intensity of light reflected from one of a plurality of points on a reference surface; and

means for comparing ones of the plurality of test values with corresponding ones of the plurality of reference values to identify differences between corresponding ones of the test and reference values,

wherein the differences between corresponding ones of the test and reference values indicate the presence of an optical anomaly, and

wherein the optical anomaly provides an indication of the efficacy of the process.

51. A method comprising the steps of:

generating three-dimensional microscope image data representing a workpiece bearing an integrated circuit pattern;

comparing the three-dimensional microscope image data to reference three-dimensional image data; and

characterizing structures on the workpiece based on the step of comparing.