Method and an apparatus for measuring the flying height with sub-nanometer resolution

• US 6,590,667 B1
• Filed: 07/24/2000
• Issued: 07/08/2003
• Est. Priority Date: 07/27/1999
• Status: Active Grant

• Current Assignee: National Science Council
• Original Assignee: National Science Council
• Inventors: Shiue, Shuen-Chen, Lee, Jau-Hu, Lee, Chih-Kung, Lee, Shu-Sheng, Wu, Jiun-Yan
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): SEVER, ANDREW T
• Application Number:
  US09/624,685
• Time in Patent Office: 1,079 Days
• Field of Search: 356/491-493, 356/503-505, 356/507, 356/496, 356/369, 356/243.3, 356/364
• US Class Current: 356/507
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: G11B 5/6011 Control of flying height
• CPC Class Codes: G11B 7/122 Flying-type heads, e.g. analogous to Winchester type in magnetic recording
• CPC Class Codes: G11B 7/1387 using the near-field effect
• CPC Class Codes: G11B 7/22 Apparatus or processes for the manufacture of optical heads, e.g. assembly

Abstract

A method and apparatus is claimed for measuring the distance between a slider and a transparent disk with sub-nanometer resolution. The flying height is measured by applying ellipsometry. The measurement is done by: providing a sampling light beam with adjustable initial polarization state by phase modulation, and with variable incident angles relative to the air film and reflecting the sampling light off of the specimen at a detection site forming a reflected light beam that is then reflected at the detection site again and then guided to both detectors for detecting the intensity and phase change of the light beam to determine the gap'"'"'s thickness as well as passing some light to a microscope used for observation of the detecting site on the specimen.

Claims

1. A method for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, comprising steps of:

a) providing a sampling light beam with adjustable initial polarization state by phase modulation, and with variable incident angles, which is controlled by an optical control subsystem, relative to said air film and forming a first reflected light beam of said sampling light beam relative to said air film;

b) guiding said first reflected light beam of said sampling light beam through said optical control subsystem to form a return light beam traveling in the opposite direction to said first reflected light beam, wherein said return light beam being incident to the specimen again at said detecting site, therefore a second reflected light beam of said returned light beam is formed, while said second reflected light beam exits from the said optical control subsystem in the opposite direction to the said sampling light beam, it is to form a signal light beam;

c) guiding said signal light beam through an analyzer and the detectors for detection of intensity and phase change of said signal light beam; and

d) partially dividing said signal light beam to form an observing light beam, which is guided to a microscope and used as a light source for observation of said detecting site on said specimen.

2. The method according to claim 1, wherein said transparent disk is a glass disk.

3. The method according to claim 1, wherein said distance is to be measured less than one wavelength of said linear polarizing light.

4. The method according to claim 1, wherein said slider is made of non-dielectric material.

5. The method according to claim 1, wherein said slider is in static state relative to said transparent disk while said sampling light beam is incident onto a surface of said slider.

6. The method according to claim 1, wherein said slider is in motion relative to said transparent disk while said sampling light beam is incident onto a surface of said slider.

7. The method according to claim 1, wherein said incident light beam of said return light beam exits from said optical control subsystem to becomes a signal light beam traveling along the same path but in the opposite direction to said sampling light beam and at least twice reflecting from said detecting site.

8. The method according to claim 1, wherein said observing light beam is used for said microscope as a light source of observation on detecting site as well as for the auto-collimation of said sampling light beam.

9. A method for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, comprising steps of:

a) providing a sampling light beam with adjustable initial polarization state by phase modulation, and with variable incident angles, which is controlled by an optical control subsystem, relative to said air film and forming a first reflected light beam of said sampling light beam relative to said air film;

b) guiding said first reflected light beam of said sampling light beam through said optical control subsystem to form a return light beam traveling in the opposite direction to said first reflected light beam, wherein said return light beam being incident to the specimen again at said detecting site, therefore a second reflected light beam of said returned light beam is formed, while said second reflected light beam exits from the said optical control subsystem in the opposite direction to the said sampling light beam, it is to form a signal light beam;

c) guiding said signal light beam through an analyzer and the detectors for detection of intensity and phase change of said signal light beam;

d) partially dividing said signal light beam to form an observing light beam, which is guided to a microscope and used as a light source for observation of said detecting site on said specimen;

e) partially dividing said sampling light beam to form a reference light beam, which is guided to a reference light beam analyzer for measuring light intensity and phase change of said reference light beam as a calibration reference of non-linear phase retardation and non-uniform absorption in said phase modulator; and

f) providing a polarization state control method utilizing intensity and phase change of said reference light beam as parameters to accurately control the polarization state of said sampling light beam.

10. The method according to claim 9, wherein said transparent disk is a glass disk.

11. The method according to claim 9, wherein said distance is to be measured less than one wavelength of said linear polarizing light.

12. The method according to claim 9, wherein said slider is made of non-dielectric material.

13. The method according to claim 9, wherein said slider is in static state relative to said transparent disk while said sampling light beam is incident onto a surface of said slider.

14. The method according to claim 9, wherein said slider is in motion relative to said transparent disk while said sampling light beam is incident onto a surface of said slider.

15. The method according to claim 9, wherein said incident light beam of said return light beam exits from said optical control subsystem to becomes a signal light beam traveling along the same path but in the opposite direction to said sampling light beam and at least twice reflecting from said detecting site.

16. The method according to claim 9, wherein said observing light beam is used for said microscope as a light source of observation on detecting site as well as for the auto-collimation of said sampling light beam.

17. The method according to claim 9, wherein control of polarization state of said sampling beam is done by a open-loop control.

18. The method according to claim 9, wherein control of polarization state of said sampling beam is done by a close-loop control.

19. An apparatus for measuring the distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, comprising:

a linear polarizing light source subsystem of which light intensity is to be tuned and initial linear polarization state is provided thereof to form a sampling light beam;

a phase modulator for the control of phase change of said sampling light beam to vary initial polarization state of said linear polarizing light source;

an optical control subsystem, which comprises a beam-bending element for guiding said sampling light beam incident to the detecting site in various angles, a carrier carrying and moving the said beam-bending element, and an optical component set comprising a focusing element and a normal reflection element, wherein said focusing element is used to guide said sampling light beam passing through said transparent disk to form a first reflected light beam at a detecting site of said specimen, and wherein said normal reflection element is used to normally reflect said first reflected light beam to form a return light beam traveling along the same path but in the direction opposite to said sampling light beam, therefore, a second reflected light beam of said return light beam at said detecting site is formed, while said second reflected light beam exits from the said optical control subsystem in the opposite direction to the said sampling light beam, it is to form a signal light beam; and

a signal analysis subsystem for detecting light intensity and phase change of said signal light beam.

20. The apparatus according to claim 19, wherein said linear polarizing light source subsystem is simply a monochromatic, linear polarized light.

21. The apparatus according to claim 19, wherein said linear polarizing light source subsystem is composed of a diode laser and a linear polarizer.

22. The apparatus according to claim 19, wherein said linear polarizing light source subsystem further is composed of a light emitted diode (LED) and a linear polarizer.

23. The apparatus according to claim 19, wherein said phase modulator is a liquid crystal panel.

24. The apparatus according to claim 19, wherein said phase modulator is a photo-elastic phase modulator.

25. The apparatus according to claim 19, wherein said phase modulator is an optical compensator.

26. The apparatus according to claim 19, wherein said phase modulator is a half waveplate.

27. The apparatus according to claim 19, wherein said phase modulator is a quarter waveplate.

28. The apparatus according to claim 19, wherein said beam-bending element is a reflective mirror.

29. The apparatus according to claim 19, wherein said beam-bending element is a triangular prism.

30. The apparatus according to claim 19, wherein said beam-bending element is a penta prism.

31. The apparatus according to claim 19 wherein said carrier is a single-axis motion stage driven by a stepping motor.

32. The apparatus according to claim 19, wherein said carrier is a single-axis motion stage driven by a DC motor.

33. The apparatus according to claim 19, wherein said focusing element is a focusing mirror and said normal reflection element is a plane reflective mirror.

34. The apparatus according to claim 19, wherein said focusing element is a concave pseudo-paraboloidal mirror and said normal reflection element is a concave pseudo-spherical mirror.

35. The apparatus according to claim 19, wherein said signal analysis subsystem is composed of an analyzer and a photo detector.

36. The apparatus according to claim 35, wherein said focusing element is a concave pseudo-paraboloidal mirror and said normal reflection element is a concave pseudo-spherical mirror.

37. An apparatus for measuring a distance between a sliding object and a transparent disk with sub-nanometer resolution, wherein the distance is regarded as a nanometer specimen, comprising:

a linear polarizing light source subsystem of which light intensity is to be tuned and initial linear polarization state is provided thereof to form a sampling light beam;

a phase modulator for the control of phase change of said sampling light beam to vary initial polarization state of said linear polarizing light source;

an optical control subsystem, which comprises a beam-bending element for guiding said sampling light beam incident to the detecting site in various angles, a carrier carrying and moving the said beam-bending element, and an optical component set comprising a focusing element and a normal reflection element, wherein said focusing element is used to guide said sampling light beam passing through said transparent disk to form a first reflected light beam at a detecting site of said specimen, and wherein said normal reflection element is used to normally reflect said first reflected light beam to form a return light beam traveling along the same path but in the direction opposite to said sampling light beam, therefore, a second reflected light beam of said return light beam at said detecting site is formed, while said second reflected light beam exits from the said optical control subsystem in the opposite direction to the said sampling light beam, it is to form a signal light beam;

a signal analysis subsystem for detecting light intensity and phase change of said signal light beam;

a reference analysis subsystem for detection of light intensity and polarization state variation of said reference light beam and calibration of non-linear phase retardation and non-uniform absorption in said phase modulator to accurately control said polarization state of said sampling light beam; and

a transfer function calibration device for detection of unknown ellipsometric parameters of said optical system.

38. The apparatus according to claim 37, wherein said linear polarizing light source subsystem is simply a monochromatic, linear polarized light.

39. The apparatus according to claim 37, wherein said linear polarizing light source subsystem is composed of a diode laser and a linear polarizer.

40. The apparatus according to claim 37, wherein said linear polarizing light source subsystem further is composed of a light emitted diode (LED) and a linear polarizer.

41. The apparatus according to claim 37, wherein said phase modulator is a liquid crystal panel.

42. The apparatus according to claim 37, wherein said phase modulator is a photo-elastic phase modulator.

43. The apparatus according to claim 37, wherein said phase modulator is an optical compensator.

44. The apparatus according to claim 37, wherein said phase modulator is a half waveplate.

45. The apparatus according to claim 37, wherein said phase modulator is a quarter waveplate.

46. The apparatus according to claim 37, wherein said beam-bending element is a reflective mirror.

47. The apparatus according to claim 37, wherein said beam-bending element is a triangular prism.

48. The apparatus according to claim 37, wherein said beam-bending element is a penta prism.

49. The apparatus according to claim 37, wherein said carrier is a single-axis motion stage driven by a stepping motor.

50. The apparatus according to claim 37, wherein said carrier is a single-axis motion stage driven by a DC motor.

51. The apparatus according to claim 37, wherein said focusing element is a focusing mirror and said normal reflection element is a plane reflective mirror.

52. The apparatus according to claim 37, wherein said signal analysis subsystem is composed of an analyzer and a photo detector.

53. The apparatus according to claim 37, wherein said reference analysis subsystem is composed of an analyzer, a first photo detector and a second photo detector.

54. The apparatus according to claim 37, wherein said transfer function calibration device is a convex pseudo-spherical mirror.