Focused beam spectroscopic ellipsometry method and system

• US 6,734,967 B1
• Filed: 02/11/1999
• Issued: 05/11/2004
• Est. Priority Date: 01/19/1995
• Status: Expired due to Term

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Chen, Xing, Piwonka-Corle, Timothy R., Lacomb, Lloyd J. Jr., Scoffone, Karen F., Stehle, Jean-Louis, Rey, John-Pierre, Zahorski, Dorian
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US09/248,876
• Time in Patent Office: 1,916 Days
• Field of Search: 356/369
• US Class Current: 356/369
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06

Abstract

A method and system for spectroscopic ellipsometry employing reflective optics to measure a small region of a sample by reflecting radiation (preferably broadband UV, visible, and near infrared radiation) from the region. The system preferably has an autofocus assembly and a processor programmed to determine from the measurements the thickness and/or complex refractive index of a thin film on the sample. Preferably, only reflective optics are employed along the optical path between the polarizer and analyzer, a sample beam reflects with low incidence angle from each component of the reflective optics, the beam is reflectively focused to a small, compact spot on the sample at a range of high incidence angles, and an incidence angle selection element is provided for selecting for measurement only radiation reflected from the sample at a single, selected angle (or narrow range of angles). The focusing mirror preferably has an elliptical shape to reduce off-axis aberrations in the focused beam. Some embodiments include both a spectrophotometer and an ellipsometer integrated together as a single instrument. In such instrument, the spectrophotometer and ellipsometer share a radiation source, and radiation from the source can be focused by either the spectrophotometer or the ellipsometer to the same focal point on a sample. Preferred embodiments of the ellipsometer employ a rotating, minimal-length Rochon prism as a polarizer, and include a spectrometer with an intensified photodiode array to measure reflected radiation from the sample, and a reference channel (in addition to a sample channel which detects radiation reflected from the sample).

Claims

1. A method for performing spectroscopic ellipsometry measurements on a sample, including:

(a) polarizing broadband radiation to produce a sampling beam by means of a polarizer;

(b) focusing the sampling beam to a small spot on the sample;

(c) collecting radiation of the sampling beam that has been modified by the sample, wherein said focusing and/or collecting use(s) optics that comprises a reflective element;

(c1) analyzing the collected radiation by means of an analyzer, thereby producing an output beam;

(d) detecting the output beam to provide a detected output;

wherein relative rotational motion is caused between the polarizer and analyzer during the detection; and

(e) processing the detected output to determine phase changes of polarization state caused by reflection by the sample.

2. The method of claim 1, wherein (b) includes focusing the sampling beam to a spot on the sample less than 40 by 40 microns in dimensions.

3. The method of claim 1, wherein (b) includes reflectively focusing the sampling beam to the spot so that the sampling beam is a converging beam whose rays are incident on the sample in a substantial range of high incident angles.

4. The method of claim 3, said method also including:

(f) selecting for detection, from reflection of said converging sampling beam from the sample within a substantial range of reflection angles, only radiation reflected from the sample at a subrange of said substantial range of reflection angles, and blocking radiation in said substantial range of reflection angles but not within the subrange.

5. The method of claim 4, wherein said subrange is a narrow range of angles near Brewster'"'"'s angle of crystalline silicon.

6. The method of claim 4, wherein (f) includes:

selecting an aperture in the shape of an elongated slit at a position at which the aperture determines said subrange of said substantial range of reflection angles.

7. The method of claim 3, said substantial range of high incidence angles includes a range from about 63.5 to 80.5 degrees.

8. The method of claim 1, wherein said processing determines the ellipsometric parameters of the sample.

9. The method of claim 1, wherein said processing processes the detector output to determine changes of polarization state in amplitude and phase caused by the sample.

10. The method of claim 1, further comprising providing broadband radiation from a combination of a tungsten lamp and a deuterium lamp, or a xenon arc lamp.

11. The method of claim 1, wherein said detecting employs a detector including an intensified photodiode array or a CCD array.

12. The method of claim 1, said detecting measuring deep into the UV range.

13. The method of claim 1, wherein said detecting measures radiation of wavelengths in the UV, visible and infrared wavelength bands.

14. The method of claim 13, wherein said detecting measures radiation of wavelengths substantially in the range of 230 to 850 nm.

15. A spectroscopic ellipsometer for measuring a sample, including:

a source which emits broadband radiation;

a polarizer that polarizes the broadband radiation, to produce a sampling beam;

illumination optics that focuses the sampling beam to a small spot on the sample;

a collector that collects radiation of the sampling beam that has been modified by the sample, the optics or the collector comprising a reflective element;

an analyzer that analyzes the collected radiation, thereby producing an output beam;

a detector detecting the output beam to provide an output, wherein relative rotational motion is caused between the polarizer and analyzer during the detection; and

a processor processing the detector output to determine phase changes of polarization state caused by reflection by the sample

16. The ellipsometer of claim 15, wherein said element focuses the sampling beam to a spot less than 40 by 40 microns in dimensions.

17. The ellipsometer of claim 15, wherein said element focuses the sampling beam to the spot so that the sampling beam is a converging beam whose rays are incident on the sample in a substantial range of high incident angles.

18. The ellipsometer of claim 17, further comprising a reflection angle selection element for detecting, from reflection of said sampling beam from the sample within a substantial range of reflection angles, only radiation reflected from the sample at a subrange of said substantial range of reflection angles, and blocking radiation in said substantial range of reflection angles but not within the subrange.

19. The ellipsometer of claim 18, wherein said substantial range of reflection angles is a range corresponding to a range of incident angles of the sampling beam from about 63.5 degrees to about 80.5 degrees.

20. The ellipsometer of claim 18, wherein said subrange is a narrow range of angles near Brewster'"'"'s angle of crystalline silicon.

21. The ellipsometer of claim 18, wherein the reflection angle selection element includes a device selecting an aperture in the shape of an elongated slit and placing it at a position at which the aperture determines said subrange of said substantial range of reflection angles.

22. The ellipsometer of claim 21, wherein the device includes an apertured plate with a slit therethrough.

23. The ellipsometer of claim 22, said device also including an actuator that moves the apertured plate in a direction in a plane of incidence of said radiation reflected from the sample to a position at which the slit determines said narrow range of said reflection incident angles.

24. The ellipsometer of claim 17, said substantial range of high incidence angles includes a range from about 63.5 to 80.5 degrees.

25. The ellipsometer of claim 15, wherein the sampling beam has an elongated cross-section, and wherein the element includes an ellipsoidal focusing mirror which reflectively focuses the sample beam to a small, substantially square spot on the sample.

26. The ellipsometer of claim 15, wherein said processor processes the detector output to determine changes of polarization state in amplitude and phase caused by the sample.

27. The ellipsometer of claim 15, wherein said source includes a combination of a tungsten lamp and a deuterium lamp, or a xenon arc lamp.

28. The ellipsometer of claim 15, said detector including an intensified photodiode array or a CCD array.

29. The ellipsometer of claim 15, said detector measuring deep into the UV range.

30. The ellipsometer of claim 15, said polarizer or analyzer including a Rochon prism.

31. The ellipsometer of claim 15, said detector measures radiation of wavelengths in the UV, visible and infrared wavelength bands.

32. The ellipsometer of claim 30, said detector measures radiation of wavelengths substantially in the range of 230 to 850 nm.

33.The ellipsometer of claim 15, wherein said processor determines the ellipsometric parameters of the sample.

33. A method for performing spectroscopic ellipsometry measurements on a sample, including:

(a) polarizing broadband radiation to produce a sampling beam;

(b) focusing the sampling beam to a small spot on the sample;

(c) analyzing radiation of the sampling beam that has been modified by the sample, thereby producing an output beam, wherein said focusing and/or analyzing use(s) optics that includes a reflective element;

(d) detecting the output beam to provide a detected output; and

(e) processing the detected output to determine a change in relative phase between two polarization states caused by reflection by the sample.

34. The method of claim 34, wherein said processing determines the ellipsometric parameters of the sample.

35. A spectroscopic ellipsometer for measuring a sample, including:

a source which emits broadband radiation;

a polarizer that polarizes the broadband radiation, to produce a sampling beam;

optics that focuses the sampling beam to a small spot on the sample;

an analyzer that analyses radiation of the sampling beam that has reflected from the sample, thereby producing an output beam, said analyzer comprising a collector that collects radiation, said collector and/or said optics comprising a reflective element, wherein said sampling and/or output beam are/is reflected from said element(s) at a low incidence angle of not more than 30 degrees;

detector means for detecting the output beam to provide an output; and

means for processing the detector means output to determine changes of polarization state in amplitude and phase caused by reflection by the sample.

36. The ellipsometer of claim 36, wherein said processor determines the ellipsometric parameters of the sample.

37. A spectroscopic instrument for measuring a sample, said instrument comprising:

a spectroscopic ellipsometer and a spectrophotometer, said spectroscopic ellipsometer comprising;

a source which emits broadband radiation;

a polarizer that polarizes the broadband radiation, to produce a sampling beam;

optics that focuses the sampling beam to a small spot on the sample;

an analyzer that analyses radiation of the sampling beam that has been modified by the sample, thereby producing an output beam, said analyzer comprising a collector that collects radiation, said collector and/or said optics comprising a reflective element, wherein said collector and/or optics cause(s) radiation from the sampling beam to be incident on or reflected from said element(s) at a low incidence angle of not more than 30 degrees;

a detector detecting the output beam at a plurality of wavelengths to provide an output, wherein relative rotational motion is caused between the polarizer and analyzer during detection; and

a processor processing the detector output to determine a reflectance spectrum and phase changes of polarization state caused by refelection by the sample.

38. The instrument of claim 38, wherein said element focuses the sampling beam to a spot on the sample less than 40 by 40 microns in dimensions.

39. The instrument of claim 38, wherein said element focuses the sampling beam to the spot so that the sampling beam is a converging beam whosed rays are incident on the sample in a substantial range of high incident angles.

40. The instrument of claim 38, further comprising a reflection angle selection element for detecting, from reflection of said sampling beam from the sample within a substantial range of reflection angles, only radiation reflected from the sample at a subrange of said substantial range of reflection angles, and blocking radiation in said substantial range of reflection angles but not within the subrange.

46. The instrument of claim 38, wherein the sampling beam has an elongated cross-section, and wherein the element includes an ellipsoidal focusing mirror which reflectively focuses the sample beam to a small, substantially square spot on the sample.

47. The instrument of claim 38, wherein said processor processes the detector output to determine changes of polarization state in amplitude and phase caused by the sample.

48. The instrument of claim 38, wherein said source includes a combination of a tungsten lamp and a deuterium lamp, or a xenon arc lamp.

49. The instrument of claim 38, said detector including an intensified photodiode array or a CCD array.

50. The instrument of claim 38, said detector measuring deep into the UV range.

51. The instrument of claim 38, said substantial range of high incidence angles includes a range from about 63.5 to 80.5 degrees.

52. The instrument of claim 38, said polarizer or analyzer including a Rochon prism.

53. The instrument of claim 38, wherein said detector measures radiation of wavelengths in the UV, visible and infrared wavelength bands.

55. The instrument of claim 38, said source also supplying radiation for operation of the spectrophotometer.

56. The instrument of claim 38, wherein each of said spectroscopic ellipsometer and said spectrophotometer has an optical path between a radiation source and a detector, said spectroscopic ellipsometer and said spectrophotometer sharing a common optical path for at least a portion of their respective optical paths.

58. The instrument of claim 38, wherein said spectroscopic ellipsometer and said spectrophotometer are operable simultaneously.

59. The instrument of claim 38, wherein said spectrophotometer has a reference channel.

60. The instrument of claim 38, wherein said spectroscopic ellipsometer and said spectrophotometer detect radiation from the sample of wavelengths in the UV, visible and infrared wavelength bands.

61. The instrument of claim 38, wherein said spectroscopic ellipsometer and said spectrophotometer detect radiation from the sample in substantially overlapping wavelength bands.

63. The instrument of claim 38, wherein each of said spectroscopic ellipsometer and said spectrophotometer has a processor processing a detector output, said spectroscopic ellipsometer and said spectrophotometer sharing a common processor.

64. The instrument of claim 38, wherein each of said spectroscopic ellipsometer and said spectrophotometer has optics, the optics of said spectroscopic ellipsometer and of said spectrophotometer illuminating substantially the same area of the sample.

65. The instrument of claim 38, further comprising an autofocus device, wherein said device is operable in combination with either one of said spectroscopic ellipsometer and said spectrophotometer or with both.

68. The instrument of claim 38, wherein each of said autofocus device and said spectrophotometer has an optical path between a radiation source and a detector, said device and said spectrophotometer sharing a common optical path for at least a portion of their respective optical paths.

72. The instrument of claim 38, wherein said processor determines the ellipsometric parameters of the sample.

41. The instrument of claim 41, wherein said substantial range of reflection angles is a range corresponding to a range of incident angles of the sampling beam from about 63.5 degrees to about 80.5 degrees.

42. The instrument of claim 41, wherein said subrange is a narrow range of angles near Brewster'"'"'s angle of crystalline silicon.

43. The instrument of claim 41, wherein the reflection angle selection element includes a device selecting an aperture in the shape of an elongated slit and placing it at a position at which the aperture determines said subrange of said substantial range of reflection angles.

44. The instrument of claim 44, wherein the device includes an apertured plate with a slit therethrough.

45. The instrument of claim 45, said device also including an actuator that moves the apertured plate in a direction in a plane of incidence of said radiation reflected from the sample to a position at which the slit determines said narrow range of said reflection incident angles.

54. The instrument of claim 54, wherein said detector measures radiation of wavelengths substantially in the range of 230 to 850 nm.

57. The instrument of claim 57, each of said spectroscopic ellipsometer and said spectrophotometer has a reflective element, said spectroscopic ellipsometer and said spectrophotometer sharing a common radiation source and a common reflective element, said common optical path including an optical path between the common source and the common reflective element.

62. The instrument of claim 62, wherein said substantially overlapping wavelength band includes wavelengths of about 230 to about 830 nm.

66. The instrument of claim 66, wherein said autofocus device includes a camera.

67. The instrument of claim 66, wherein said autofocus device includes a focus detector.

69. The instrument of claim 69, wherein each of said autofocus device and said spectrophotometer has optical components in its respective optical path, and wherein said autofocus device and said spectrophotometer share common optical components, said common optical components including a radiation source.

70. The instrument of claim 70, said common optical components including a reflective objective focusing radiation originating from a source to the sample and collecting radiation reflected by the sample for detection by the device and by the spectrophotometer.

71. The instrument of claim 71, wherein each of said autofocus device and said spectrophotometer has a detector, said common optical components including a beam divider that divides the radiation collected by the reflective objective and provides a portion of such collected radiation to the detector of the device and another portion of such collected radiation to the detector of the spectrophotometer.

73. A method for measuring a sample, comprising:

(a) polarizing broadband radiation to produce a sampling beam;

(b) focusing the sampling beam to a small spot on the sample using optics that includes a reflective element;

(c) collecting radiation of the sampling beam that has been modified by the sample, thereby producing an output beam, wherein said focusing and/or collecting use(s) optics that comprises a reflective element and said sampling and/or output beam ar/is reflected from said element(s) at a low incidence angle of not more than 30 degrees;

;

(c1) analyzing the output beam;

(d) detecting the analyzed output beam to provide a detected output;

(e) processing the detected output to determine changes of polarization state caused by reflection by the sample; and

(f) obtaining a reflectance spectrum of said sample.

74. The method of claim 74, wherein said focusing focuses the sampling beam to a spot on the sample less than 40 by 40 microns in dimensions.

75. The method of claim 74, wherein said focusing focuses the sampling beam to the spot so that the sampling beam is a converging beam whose rays are incident on the sample in a substantial range of high incident angles.

80. The method of claim 74, wherein said processing processes the detector output to determine changes of polarization state in amplitude and phase caused by the sample.

81. The method of claim 74, further comprising providing broadband radiation from a combination of a tungsten lamp and a deuterium lamp, or a xenon arc lamp for producing the sampling beam.

82. The method of claim 74, wherein said detecting employs a detector including an intensified photodiode array or a CCD array.

83. The method of claim 74, said detecting measuring deep into the UV range.

84. The method of claim 74, wherein said detecting measures radiation of wavelengths in the UV, visible and infrared wavelength bands.

86. The method of claim 74, wherein said changes of polarized state and the reflectance spectrum are acquired substantially simultaneously.

87. The method of claim 74, further comprising providing broadband radiation for producing the sampling beam and for obtaining the reflectance spectrum.

88. The method of claim 74, wherein said reflectance spectrum obtained is a relative reflectance spectrum.

89. The method of claim 74, wherein said changes of polarized state and the reflectance spectrum are acquired at wavelengths in the UV, visible and infrared wavelength bands.

90. The method of claim 74, wherein said changes of polarized state and the reflectance spectrum are acquired over substantially overlapping wavelength bands.

92. The method of claim 74, wherein said obtaining employs a processor, and wherein said obtaining and processing are performed by the same processor.

93. The method of claim 74, further comprising autofocusing the sample when (a)-(d) or when (f) is performed, or when both are performed.

94. The method of claim 74, wherein (a)-(d), the autofocusing and the obtaining in (f) are performed using radiation from a common radiation source.

95. The method of claim 74, wherein the autofocusing and the obtaining are performed using common optical components, said common optical components including a common radiation source.

98. The method of claim 74, wherein said processing determines the ellipsometric parameters of the sample.

76. The method of claim 76, further including selecting for detection, from reflection of said converging sampling beam from the sample within a substantial range of reflection angles, only radiation reflected from the sample at a subrange of said substantial range of reflection angles, and blocking radiation in said substantial range of reflection angles but not within the subrange.

79. The method of claim 76, said substantial range of high incidence angles includes a range from about 63.5 to 80.5 degrees.

77. The method of claim 77, wherein said subrange is a narrow range of angles near Brewster'"'"'s angle of crystalline silicon.

78. The method of claim 77, wherein said selecting selects an aperture in the shape of an elongated slit at a position at which the aperture determines said subrange of said substantial range of reflection angles.

85. The method of claim 85, wherein said detecting measures radiation of wavelengths substantially in the range of 230 to 850 nm.

91. The method of claim 91, wherein said substantially overlapping wavelength band includes wavelengths of about 230 to about 830 nm.

96. The method of claim 96, said common optical components including a reflective objective, each of said autofocusing and the obtaining includes focusing radiation originating from a common source to the sample and collecting radiation reflected by the sample using the objective and detecting the collected radiation.

97. The method of claim 97, wherein said autofocusing and obtaining include dividing the radiation collected by the reflective objective into a portion from which the reflectance spectrum is obtained, and another portion, and deriving focusing information from said another portion.

99. A spectroscopic ellipsometer for measuring a sample, including:

a source which emits broadband radiation;

a polarizer that polarizes the broadband radiation;

to produce a sampling beam;

illumination optics that focuses the sampling beam to small spot on the sample,;

a collector that collects radiation of the sampling beam that has been modified by the sample, the optics or the collector comprising a reflective element;

an analyzer that analyzes the collected radiation, thereby producing an output beam;

a detector detecting the output beam to provide an output; and

a processor processing the detector output to determine a change in relative phase between two polarization states caused by reflection by the sample.

100. The ellipsometer of claim 100, wherein said processor determines the ellipsometric parameters of the sample.

101. The ellipsometer of claim 100, wherein said processor determines the ellipsometric parameters of the sample.

102. A spectroscopic ellipsometer for measuring a sample, including:

polarizing broadband radiation to produce a sampling beam;

focusing the sampling beam to a small spot on the sample using optics;

collecting radiation of the sampling beam that has reflected from the sample by means of a collector, said collector and/or said optics comprising a reflective element, wherein said sampling and/or output beam are/is reflected from said element(s) at a low incidence angle of not more than 30 degrees;

analyzing the collected radiation thereby producing an output beam,

detecting the output beam to provide an output; and

processing the output to determine changes of polarization state in amplitude and phase caused by reflection by the sample.