Multiple layer confocal interference microscopy using wavenumber domain reflectometry and background amplitude reduction and compensation

• US 6,480,285 B1
• Filed: 03/16/2000
• Issued: 11/12/2002
• Est. Priority Date: 01/28/1997
• Status: Expired due to Fees

• Current Assignee: Zetetic Institute
• Original Assignee: Zetetic Institute
• Inventors: Hill, Henry A.
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US09/526,847
• Time in Patent Office: 971 Days
• Field of Search: 356/492, 356/497, 356/508, 356/511, 356/450, 356/491
• US Class Current: 356/492
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G01B 9/02042 Confocal imaging
• CPC Class Codes: G01B 9/04 Measuring microscopes
• CPC Class Codes: G02B 21/004 fixed arrays, e.g. switchable aperture arrays
• CPC Class Codes: G02B 21/0056 based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
• CPC Class Codes: G02B 21/006 focusing arrangements; selection of the plane to be imaged
• CPC Class Codes: G02B 21/0068 arrangements using polarisation
• CPC Class Codes: G02B 21/008 Details of detection or image processing, including general computer control
• CPC Class Codes: G11B 7/005 Reproducing G11B7/0065 takes precedence
• CPC Class Codes: G11B 7/14 specially adapted to record on, or to reproduce from, more than one track simultaneously

Abstract

An in-focus image of an information-bearing region within and/or on a substance is discriminated from an out-of-focus image so as to reduce errors in image information of the substance by producing a probe beam and a reference beam from a wideband point source, producing antisymmetric spatial properties in the reference beam, converting the probe beam to a beam focused to a line in the region, producing an in-focus return probe beam, and producing antisymmetric spatial properties in the in-focus return probe beam. Then the in-focus return probe beam is spatially filtered and focused to a line image in a detector plane of a detector system. The reference beam is spatially filtered and focus to a line image in the detector plane. A beam from an out-of focus image point is spatially filtered. The line image of the spatially filtered reference beam is interfered with the spatially filtered beam from the out-of-focus image point and the line image of the spatially filtered in-focus return probe beam. A complex amplitude of the spatially filtered in-focus return probe beam is detected as an interference term between line image of the spatially filtered reference beam and the line image of the spatially filtered in-focus return probe beam by means of the detector system. An amplitude of an interference term between the spatially filtered out-of-focus image beam and the line image of the spatially filtered reference beam is thereby substantially reduced, and reduces statistical and systematic errors in data produced by the detector system to represent the image information of the region. The image information is acquired as either one-dimensional or two-dimensional data arrays wherein the elements of the arrays are obtained substantially simultaneously. The substance is scanned to generate images of dimensionalities greater than the one-dimensional or two-dimensional data arrays.

Claims

1. A method for discriminating an in-focus image from an out-of-focus image so as to reduce errors in information representing the in-focus image, comprising the steps of:

(a) producing a probe beam and a reference beam from an array of monochromatic point radiation sources;

(b) producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points;

(c) producing antisymmetric spatial properties in the in-focus return probe beam;

(d) producing an in-focus reference beam;

(e) producing antisymmetric spatial properties in the in-focus reference beam;

(f) interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points;

(g) interfering the in-focus reference beam with the in-focus return probe beam;

(h) reducing systematic and statistical errors in data produced by a detector to represent the information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam.

2. The method of claim 1 wherein the step (h) includes detecting the in-focus reference beam as a non-linear function of the amplitude of the in-focus reference beam and using that amplitude in determining the complex amplitude of the in-focus return probe beam from the amplitudes of the interference terms.

3. The method of claim 1 including providing an optical disk, wherein the array of in-focus image points is in and/or on the optical disk.

4. The method of claim 1 including providing in situ tissue of a human or animal subject, wherein the array of in-focus image points is in and/or on the in situ tissue.

5. The method of claim 1 including providing excised biopsy tissue of a human or animal subject, wherein the array of in-focus image points is in and/or on the excised biopsy tissue.

6. The method of claim 1 including providing a reference surface having a fixed relationship to the array of in-focus image points and performing steps (b) through (h) for in-focus reference image points located on the reference surface, and determining locations of the array of in-focus image points relative to the reference surface.

7. The method of claim 3 including providing relative mechanical translation between an optical disk and the probe beam to allow steps (b) through (h) to be performed for other portions of the optical disk at the in-focus image points.

62. The method of claim 4 including providing relative mechanical translation between in situ tissue of a human or animal subject and the probe be to allow steps (b) through (h) to be performed for other portions of the in situ tissue at the in-focus image points.

63. The method of claim 5 including providing relative mechanical translation between excise biopsy tissue of a human or animal subject and the probe beam to allow steps (b) through (h) to be performed for other portions of the in situ tissue at the in-focus image points.

77. The method of claim 1 including providing a substance, wherein the array of in-focus image points is in and/or on the substance.

8. A method for discriminating an in-focus image from an out-of-focus image so as to reduce errors in information representative of the in-focus image, comprising the steps of:

(a) producing a probe beam and a reference beam from an array of monochromatic point radiation sources;

(b) producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points, the in-focus return probe beam including a plurality of in-focus return sub-beams, each in-focus return sub-beam being associated with at least one in-focus image point of the array;

(c) producing antisymmetric spatial properties in each in-focus return sub-beam;

(d) producing an in-focus reference beam including a plurality of in-focus reference sub-beams, each in-focus reference sub-beam being associated with an in-focus return sub-beam, respectively;

(e) producing antisymmetric spatial properties in each in-focus reference sub-beam;

(f) interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points;

(g) interfering the in-focus reference beam with the in-focus return probe beam;

(h) reducing systematic and statistical errors in data produced by a detector array to represent the information being determined by detecting the complex amplitudes of the in-focus return sub-beams as interference data by means of detector elements, respectively, of the detector array wherein the interference data comprises interference terms between corresponding in-focus reference sub-beams and in-focus return probe sub-beams and other interference terms of substantially reduced amplitudes between out-of-focus image beams associated with out-of-focus image points, respectively, and corresponding in-focus reference sub-beams.

9. The method of claim 8 wherein the step (h) includes detecting the in-focus reference beam as a non-linear function of the amplitude of the in-focus reference beam and using that amplitude in determining the complex amplitude of the in-focus return probe beam from the amplitudes of the interference terms.

10. A method for discriminating an in-focus image from an out-of-focus image so as to reduce errors in information representative of the in-focus image, comprising the steps of:

(a) producing a probe beam and a reference beam from a wideband point radiation source;

(b) producing an in-focus reference beam;

(c) producing antisymmetric spatial properties in the in-focus reference beam;

(d) passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line;

(e) producing an in-focus return probe beam;

(f) producing antisymmetric spatial properties in the in-focus return probe beam;

(g) spatially filtering the in-focus return probe beam;

(h) passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector;

(i) spatially filtering the in-focus reference beam;

(j) passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane;

(k) spatially filtering a beam from a plurality of out-of-focus image points;

(l) passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element;

(m) interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points;

(n) interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam; and

(o) reducing systematic and statistical errors in data produced by a detector to represent the information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam.

11. The method of claim 10 wherein the step (o) includes detecting the in-focus reference beam as a non-linear function of the amplitude of the in-focus reference beam and using that amplitude in determining the complex amplitude of the in-focus return probe beam from the amplitudes of the interference terms.

12. The method of claim 10 including providing an optical disk, wherein the target line is in and/or on the optical disk.

13. The method of claim 10 including providing in situ tissue of a human or animal subject, wherein the target line is in and/or on the in situ tissue.

14. The method of claim 10 including providing excised biopsy tissue of a human or animal subject, wherein the target line is in and/or on the excised biopsy tissue.

15. The method of claim 10 wherein step (a) includes producing the probe beam and the reference beam from an array of wideband point radiation sources.

16. The method of claim 10 including providing a reference surface near or on the target line and performing steps (b) through (o) for in-focus reference image points located on the reference surface and determining locations of the in-focus image points near or on the target line relative to the reference surface.

17. The method of claim 12 including providing relative mechanical translation between the optical disk and the probe beam to allow steps (b) through (o) to be performed for other portions of the optical disk at the target line.

18. The method of claim 12 wherein step (d) includes passing the probe beam through at least one grating wherein the target line is substantially parallel to a major surface of the optical disk.

19. The method of claim 12 wherein the target line of step (d) is substantially perpendicular to a major surface of the optical disk.

20. The method of claim 19 including performing Fourier transforms on the data produced by the detector to convert the interferometric data to determine information stored at predetermined depths along the target line.

64. The method of claim 13 including providing relative mechanical translation between the in situ tissue and the probe beam to allow steps (b) through (o) to be performed for other portions of the in situ tissue at the target line.

65. The method of claim 14 including providing relative mechanical translation between the excised biopsy tissue and the probe beam to allow steps (b) through (o) to be performed for other portions of the excised biopsy tissue at the target line.

66. The method of claim 13 wherein step (d) includes passing the probe beam through at least one grating wherein the target line is substantially parallel to a major surface of the in situ tissue.

67. The method of claim 14 wherein step (d) includes passing the probe beam through at least one grating wherein the target line is substantially parallel to a major surface of the excised biopsy tissue.

68. The method of claim 13 wherein the target line of step (d) is substantially perpendicular to a major surface of the in situ tissue.

69. The method of claim 14 wherein the target line of step (d) is substantially perpendicular to a major surface of the excised biopsy tissue.

78. The method of claim 10 including providing a substance, wherein the target line is in and/or on the substance.

79. The method of claim 10 wherein step (a) includes producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein step (d) includes converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein step (h) includes converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein step (j) includes converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

21. A method for discriminating an in-focus image from an out-of-focus image so as to reduce errors in determining information represented by information representative of the in-focus image, comprising the steps of:

(a) producing a probe beam and a reference beam from a wideband point radiation source;

(b) producing an in-focus reference beam;

(c) producing antisymmetric spatial properties in the in-focus reference beam;

(d) converting the probe beam to a beam focused to a target line;

(e) producing an in-focus return probe beam;

(f) producing antisymmetric spatial properties in the in-focus return probe beam;

(g) spatially filtering the in-focus return probe beam;

(h) converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector;

(i) spatially filtering the in-focus reference beam;

(j) converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane;

(k) spatially filtering a beam from a plurality of out-of-focus image points;

(l) interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points;

(m) interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam; and

(n) reducing errors in data produced by the detector to represent the information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam.

22. The method of claim 21 wherein the step (n) includes detecting the converted spatially filtered in-focus reference beam as a non-linear function of the amplitude of the converted spatially filtered in-focus reference beam and using that amplitude in determining the complex amplitude of the in-focus return probe beam from the amplitude of the interference term.

23. The method of claim 21 including providing an optical disk, wherein the target line is in and/or on the optical disk.

24. The method of claim 21 including providing in situ tissue of a human or animal subject, wherein the target line is in and/or on the in situ tissue.

25. The method of claim 21 including providing excised biopsy tissue of a human or animal subject, wherein the target line is in and/or on the excised biopsy tissue.

26. The method of claim 21 wherein step (a) includes producing the probe beam and the reference beam from an array of wideband point radiation sources.

27. The method of claim 21 including providing a reference surface in fixed relationship to the target line and performing steps (b) through (n) for in-focus reference image points located on the reference surface, and determining the location of the target line relative to the reference surface.

28. The method of claim 21 including providing relative mechanical translation between the substance and the probe beam to allow steps (b) through (n) to be performed for other portions of the substance.

29. The method of claim 23 wherein step (d) includes passing the probe beam through at least one grating, wherein the target line is substantially parallel to a major surface of the optical disk.

30. The method of claim 21 including performing Fourier transforms on the interferometric data produced by the detector to convert the data to determine information representative of conditions at predetermined points along the target line.

31. The method of claim 23 wherein the target line is substantially perpendicular to a major surface of the optical disk.

70. The method of claim 21 including providing a substance, wherein the target line is in and/or on the substance.

71. The method of claim 70 wherein step (d) includes passing the probe beam through at least one grating, wherein the target line is substantially parallel to a major surface of the substance.

72. The method of claim 70 wherein the target line is substantially perpendicular to a major surface of the substance.

73. The method of claim 72 wherein the substance includes one of the group including an optical disk, in situ tissue of a human or animal subject, and excised biopsy tissue of a human or animal subject.

80. The method of claim 21 wherein step (a) includes producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein step (d) includes converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein step (h) includes converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein step (j) includes converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

32. A system for use in profiling the surface of a wafer, the system comprising:

(a) a stage for supporting the wafer;

(b) an illumination system for imaging spatially patterned radiation onto the wafer;

(c) a gauged positioning control system for adjusting the position of the stage relative to the imaged radiation;

(d) an interferometry system for measuring the position of the wafer relative to the imaged radiation; and

(e) an identification mark sub-system for identifying an alignment mark in an information-bearing region, the identification mark sub-system including means for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, the discriminating means including

(1) means for producing a probe beam and a reference beam from an array of monochromatic point radiation sources,

(2) means for producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points,

(3) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(4) means for producing an in-focus reference beam,

(5) means for producing antisymmetric spatial properties in the in-focus reference beam,

(6) means for interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points,

(7) means for interfering the in-focus reference beam with the in-focus return probe beam, and

(8) means for reducing systematic and statistical errors in data produced by a detector to represent the information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam.

33. A metrology system for use in measuring overlay accuracy of a lithography stepper or scanner in fabricating an integrated circuit on a wafer, the metrology system comprising:

(a) a gauge-controlled stage for measuring the relative positions of a first pattern in a first information-bearing region on a first level of the integrated circuit and a second pattern in a second information-bearing region on a second level of the integrated circuit;

(b) a wafer handling system including the stage, for supporting the wafer; and

(c) a microscope system for viewing the patterns to compare the relative positions of the first pattern and the second pattern, the microscope including

(1) means for producing a probe beam and a reference beam from an array of monochromatic point radiation sources,

(2) means for producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points,

(3) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(4) means for producing an in-focus reference beam,

(5) means for producing antisymmetric spatial properties in the in-focus reference beam,

(6) means for interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points,

(7) means for interfering the in-focus reference beam with the in-focus return probe beam, and

(8) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam.

34. A metrology system for use in measuring defects in a mask to be used in fabrication of an integrated circuit, the metrology system comprising:

(a) a gauge-controlled stage for supporting the mask;

(b) a microscope system for imaging the mask and producing a first digital representation of pattern features of the mask, the microscope system including

(1) means for producing a probe beam and a reference beam from an array of monochromatic point radiation sources,

(2) means for producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points,

(3) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(4) means for producing an in-focus reference beam,

(5) means for producing antisymmetric spatial properties in the in-focus reference beam,

(6) means for interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points,

(7) means for interfering the in-focus reference beam with the in-focus return probe beam, and

(8) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam;

(c) a memory system for storing an accurate second digital representation of the pattern features of the mask; and

(d) a processor coupled to the memory system and the microscope system for comparing the first and second digital representations of the mask image to determine defects of the mask.

35. The metrology system of claim 34 wherein the second digital representation represents the pattern features of an ideal mask.

36. The metrology system of claim 34 wherein the second digital representation includes data obtained by operating the microscope system to image a reference mask having essentially no defects.

37. A system for producing an image of an information-bearing region with reduced sensitivity to motion of a substance containing the information-bearing region, the system comprising:

(a) a support structure supporting the substance;

(b) a microscope system for imaging the information-bearing region, the microscope system including

(1) means for producing a probe beam and a reference beam from an array of monochromatic point radiation sources,

(2) means for producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points,

(3) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(4) means for producing an in-focus reference beam,

(5) means for producing antisymmetric spatial properties in the in-focus reference beam,

(6) means for interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points,

(7) means for interfering the in-focus reference beam with the in-focus return probe beam, and

(8) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam,

wherein a predetermined one-dimensional or two-dimensional section of the information-bearing region produced by the microscope system is substantially independent of motion of the substance relative to the microscope system.

38. The system of claim 37 wherein all of the image points of a predetermined one-dimensional or two-dimensional section of the information-bearing region are acquired substantially simultaneously.

39. A system for producing an image of an information bearing surface of a substance having an external surface to control a spatial relationship between the system and the external surface, the system comprising;

a) a support structure supporting the substance;

b) a microscope system for imaging the profile of the external surface and determining the spatial relationship between the external surface and the system, the microscope system including

(1) means for producing a probe beam and a reference beam from an array of monochromatic point radiation sources,

(2) means for producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points,

(3) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(4) means for producing an in-focus reference beam,

(5) means for producing antisymmetric spatial properties in the in-focus reference beam,

(6) means for interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points,

(7) means for interfering the in-focus reference beam with the in-focus return probe beam, and

(8) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam; and

c) a processor controlling the location of the microscope system relative to the external surface in accordance with the determined spatial relationship to prevent physical contact of the microscope system with the external surface.

40. The system of claim 39 wherein the processor controls the location of the microscope system on a real time basis.

41. The system of claim 40 wherein the processor operates to maintain the microscope system at least a predetermined distance from the external surface.

42. A system for use in fabricating integrated circuitry on a wafer, the system comprising:

(a) a stage for supporting the wafer;

(b) an illumination system for imaging spatially patterned radiation onto the wafer;

(c) a gauged positioning control system for adjusting the position of the stage relative to the imaged radiation;

(d) an interferometry system for measuring the position of the wafer relative to the imaged radiation; and

(e) an identification mark sub-system for identifying an alignment mark in an information-bearing region, the identification mark sub-system including means for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, the discriminating means including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element,

(13) means for interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points,

(14) means for interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam, and

(15) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam.

81. The system of claim 42 wherein element (e)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (e)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (e)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (e)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

43. A metrology system for use in measuring overlay accuracy of a lithography stepper or scanner in fabricating an integrated circuit on a wafer, the metrology system comprising:

(a) a gauge-controlled stage for measuring the relative positions of a first pattern in a first information-bearing region on a first level of the integrated circuit and a second pattern in a second information-bearing region on a second level of the integrated circuit;

(b) a wafer handling system including the stage, for supporting the wafer; and

(c) a microscope system for viewing the patterns, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element,

(13) means for interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points,

(14) means for interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam, and

(15) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam.

82. The metrology system of claim 43 wherein element (c)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (c)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (c)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (c)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

44. A metrology system for use in measuring defects in a mask to be used in fabrication of an integrated circuit, the metrology system comprising:

(a) a gauge-controlled stage for supporting the mask;

(b) a microscope system for imaging the mask and producing a first digital representation of pattern features of the mask, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element,

(13) means for interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points,

(14) means for interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam, and

(15) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam;

(c) a memory system for storing an accurate second digital representation of the pattern features of the mask; and

(d) a processor coupled to the memory system and the microscope system for comparing the first and second digital representations of the mask image to determine defects of the mask.

45. The metrology system of claim 44 wherein the second digital representation includes data representing the pattern features of an ideal mask.

46. The metrology system of claim 44 wherein the second digital representation includes data obtained by operating the microscope system to image a reference mask having essentially no defects.

83. The metrology system of claim 44 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

47. A system for producing an image of an information-bearing region, with reduced sensitivity to motion of a substance containing the information-bearing region, the system comprising:

(a) a support structure supporting the substance;

(b) a microscope system for imaging the information-bearing region, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element,

(13) means for interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points,

(14) means for interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam, and

(15) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam,

wherein a predetermined one-dimensional or two-dimensional section of the information-bearing region produced by the microscope system is substantially independent of motion of the substance relative to the microscope system.

48. The system of claim 47 wherein all of the image points of a predetermined one-dimensional or two-dimensional section of the information-bearing region are acquired substantially simultaneously.

84. The system of claim 47 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

49. A system for producing an image of an information bearing surface of a substance having an external surface to control a spatial relationship between the system and the external surface, the system comprising;

a) a support structure supporting the substance;

b) a microscope system for imaging the profile of the external surface and determining the spatial relationship between the external surface and the system, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element,

(13) means for interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points,

(14) means for interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam, and

(15) means for reducing systematic and statistical errors in data produced by a detector to represent information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam; and

c) a processor controlling the location of the microscope system relative to the external surface in accordance with the determined spatial relationship to prevent physical contact of the microscope system with the external surface.

50. The system of claim 49 wherein the processor controls the location of the microscope system on a real time basis.

51. The system of claim 50 wherein the processor operates to maintain the microscope system at least a predetermined distance from the external surface.

85. The system of claim 49 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

52. A system for use in fabricating integrated circuitry on a wafer, the system comprising:

(a) a stage for supporting the wafer;

(b) an illumination system for imaging spatially patterned radiation onto the wafer;

(c) a gauged positioning control system for adjusting the position of the stage relative to the imaged radiation;

(d) an interferometry system for measuring the position of the wafer relative to the imaged radiation; and

(e) an identification mark sub-system for identifying an alignment mark in an information-bearing region, the identification mark sub-system including means for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, the discriminating means including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for converting the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points,

(13) means for interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam, and

(14) means for reducing errors in data produced by the detector to represent information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam.

86. The system of claim 52 wherein element (e)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (e)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (e)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (e)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

53. A metrology system for use in measuring overlay accuracy of a lithography stepper or scanner in fabricating an integrated circuit on a wafer, the metrology system comprising:

(a) a gauge-controlled stage for measuring the relative positions of a first pattern in a first information-bearing region on a first level of the integrated circuit and a second pattern in a second information-bearing region on a second level of the integrated circuit;

(b) a wafer handling system including the stage, for supporting the wafer; and

(c) a microscope system for viewing the patterns to compare the relative positions of the first pattern and the second pattern, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for converting the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points,

(13) means for interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam, and

(14) means for reducing errors in data produced by the detector to represent information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam.

87. The metrology system of claim 53 wherein element (c)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (c)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (c)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (c)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

54. A metrology system for use in measuring defects in a mask to be used in fabrication of an integrated circuit, the metrology system comprising:

(a) a gauge-controlled stage for supporting the mask;

(b) a microscope system for imaging the mask and producing a first digital representation of pattern features of pattern features of the mask, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for converting the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points,

(13) means for interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam, and

(14) means for reducing errors in data produced by the detector to represent information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam;

(c) a memory system for storing an accurate second digital representation of the pattern features of the mask; and

(d) a processor coupled to the memory system and the microscope system for comparing the first and second digital representations of the mask image to determine defects of the mask.

55. The metrology system of claim 54 wherein the second digital representation includes data representing the pattern features of an ideal mask.

56. The metrology system of claim 54 wherein the second digital representation includes data obtained by operating the microscope system to image a reference mask having essentially no defects.

88. The metrology system of claim 54 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

57. A system for producing an image of an information-bearing region, with reduced sensitivity to motion of a substance containing the information-bearing region, the system comprising:

(a) a support structure supporting the substance;

(b) a microscope system for imaging the information-bearing region, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for converting the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points,

(13) means for interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam, and

(14) means for reducing errors in data produced by the detector to represent information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam,

wherein a predetermined one-dimensional or two-dimensional section of the information-bearing region produced by the microscope system is substantially independent of motion of the substance relative to the microscope system.

58. The system of claim 57 wherein all of the image points of a predetermined one-dimensional or two-dimensional section of the information-bearing region are acquired substantially simultaneously.

89. The system of claim 57 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

59. A system for producing an image of an information surface of a substance having an external surface to control a spatial relationship between the system and the external surface, the system comprising;

a) a support structure supporting the substance;

b) a microscope system for imaging the profile of the external surface and determining the spatial relationship between the external surface and the system, the microscope system including

(1) means for producing a probe beam and a reference beam from a wideband point radiation source,

(2) means for producing an in-focus reference beam,

(3) means for producing antisymmetric spatial properties in the in-focus reference beam,

(4) means for converting the probe beam to a beam focused to a target line in the information-bearing region,

(5) means for producing an in-focus return probe beam,

(6) means for producing antisymmetric spatial properties in the in-focus return probe beam,

(7) means for spatially filtering the in-focus return probe beam,

(8) means for converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector,

(9) means for spatially filtering the in-focus reference beam,

(10) means for converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane,

(11) means for spatially filtering a beam from a plurality of out-of-focus image points,

(12) means for interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points,

(13) means for interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam, and

(14) means for reducing errors in data produced by the detector to represent information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam; and

c) a processor controlling the location of the microscope system relative to the external surface in accordance with the determined spatial relationship to prevent physical contact of the microscope system with the external surface.

60. The system of claim 59 wherein the processor controls the location of the microscope system on a real time basis.

61. The system of claim 60 wherein the processor operates to maintain the microscope system at least a predetermined distance from the external surface.

90. The system of claim 59 wherein element (b)(1) includes means for producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein element (b)(4) includes means for converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein element (b)(8) includes means for converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein element (b)(10) includes means for converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

74. A method for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, comprising the steps of:

(a) producing a probe beam and a reference beam from an array of monochromatic point radiation sources;

(b) producing an in-focus return probe beam by directing the probe beam to an array of in-focus image points;

(c) producing antisymmetric spatial properties in the in-focus return probe beam;

(d) producing an in-focus reference beam;

(e) producing antisymmetric spatial properties in the in-focus reference beam;

(f) interfering the in-focus reference beam with a beam from a plurality of out-of-focus image points;

(g) interfering the in-focus reference beam with the in-focus return probe beam;

(h) reducing systematic and statistical errors in data produced by a detector to represent the information being determined by detecting the complex amplitude of the in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the in-focus reference beam and the in-focus return probe beam and another interference term of substantially reduced amplitude between the out-of-focus image beams associated with out-of-focus image points and corresponding portions of the in-focus reference beam.

75. A method for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, comprising the steps of:

(a) producing a probe beam and a reference beam from a wideband point radiation source;

(b) producing an in-focus reference beam;

(c) producing antisymmetric spatial properties in the in-focus reference beam;

(d) passing the probe beam through a dispersal element to convert the probe beam to a beam focused to a target line in the information-bearing region;

(e) producing an in-focus return probe beam;

(f) producing antisymmetric spatial properties in the in-focus return probe beam;

(g) spatially filtering the in-focus return probe beam;

(h) passing the spatially filtered in-focus return probe beam through a dispersal element to convert it to a beam focused to a line in a detector plane of a detector;

(i) spatially filtering the in-focus reference beam;

(j) passing the spatially filtered in-focus reference beam through a dispersal element to convert it to a beam focused to the line in the detector plane;

(k) spatially filtering a beam from a plurality of out-of-focus image points;

(l) passing the spatially filtered beam from the plurality of out-of-focus image points through a dispersal element;

(m) interfering the spatially filtered in-focus reference beam with the spatially filtered beam from the out-of-focus image points;

(n) interfering the spatially filtered in-focus reference beam with the spatially filtered in-focus return probe beam; and

(o) reducing systematic and statistical errors in data produced by a detector to represent the information being determined by detecting the complex amplitude of the spatially filtered in-focus return probe beam as interference data by means of detector elements of the detector wherein the interference data comprises an interference term between the spatially filtered in-focus reference beam and the spatially filtered in-focus return probe beam and another interference term of a substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the spatially filtered in-focus reference beam.

91. The method of claim 75 wherein step (a) includes producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein step (d) includes converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein step (h) includes converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein step (j) includes converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.

76. A method for discriminating an in-focus image of an information-bearing region in and/or on a substance from an out-of-focus image so as to reduce errors in determining information represented by the information-bearing region in and/or on the substance, comprising the steps of:

(a) producing a probe beam and a reference beam from a wideband point radiation source;

(b) producing an in-focus reference beam;

(c) producing antisymmetric spatial properties in the in-focus reference beam;

(d) converting the probe beam to a beam focused to a target line in the information-bearing region;

(e) producing an in-focus return probe beam;

(f) producing antisymmetric spatial properties in the in-focus return probe beam;

(g) spatially filtering the in-focus return probe beam;

(h) converting the spatially filtered in-focus return probe beam to a beam focused to a line in a detector plane of a detector;

(i) spatially filtering the in-focus reference beam;

(j) converting the spatially filtered in-focus reference beam to a beam focused to the line in the detector plane;

(k) spatially filtering a beam from a plurality of out-of-focus image points;

(l) interfering the converted spatially filtered in-focus reference beam with the spatially filtered beam from the plurality of out-of-focus image points;

(m) interfering the converted spatially filtered in-focus reference beam with the converted spatially filtered in-focus return probe beam; and

(n) reducing errors in data produced by the detector to represent the information being determined by detecting by means of the detector the spatially filtered in-focus return probe beam as interference data comprising an interference term between the converted spatially filtered in-focus reference beam and the converted spatially filtered in-focus return probe beam and another interference term of substantially reduced amplitude between the spatially filtered beam from the plurality of out-of-focus image points and the converted spatially filtered in-focus reference beam.

92. The method of claim 76 wherein step (a) includes producing the probe beam and the reference beam from a linear array of wideband point radiation sources, wherein step (d) includes converting the probe beam to a plurality of beams focused to a plurality of target lines, respectively, in the information-bearing region, the plurality of beams corresponding to the wideband point radiation sources, respectively, wherein step (h) includes converting the spatially filtered in-focus return probe beam to a plurality of beams corresponding to the wideband point radiation sources, respectively, focused to a plurality of lines, respectively, in the detector plane, and wherein step (j) includes converting the spatially filtered in-focus reference beam to a plurality of beams focused to the plurality of lines, respectively, in the detector plane.