Apparatus for and method of measuring surface shape of an object

• US 6,885,460 B2
• Filed: 09/23/2002
• Issued: 04/26/2005
• Est. Priority Date: 09/21/2001
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Morita, Nobuhiro
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): Lyons, Michael A.
• Application Number:
  US10/251,830
• Publication Number:
  US 20030067609A1
• Time in Patent Office: 946 Days
• Field of Search: 356/511, 356/512, 356/513, 356/514
• US Class Current: 356/514
• CPC Class Codes: G01B 11/2441 using interferometry

Abstract

An apparatus for measuring an object'"'"'s surface shape that obtains complex amplitude at a plurality of positions substantially in the directions of the optical axis of the light reflected by the object and calculates the first surface shape of the object by the depth-from-focus principle. On the other hand, using the phase data of the complex amplitude, the apparatus can measure a micro shape in the sub-fringe order by ordinary laser interference measurement. The first surface shape data are applied to a region including a step of a height greater than ½ of the light'"'"'s wavelength and second surface shape data are applied to the other region.

Claims

1. An apparatus for measuring surface shape of an object, comprising:

a light source configured to emit light to illuminate said object;

an interference optical system configured to generate interference fringes between a reference fraction of said light and a reflective fraction of said light reflected by said object;

an imaging capturing unit configured to capture said interference fringes and output interference fringe data; and

a computer unit configured to

obtain phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light at a plurality of positions in the directions of the optical axis of said reflective fraction of said light using said interference fringe data,

obtain first surface shape data indicating the surface shape of said object using said amplitude data by calculating an in-focus distance at each micro region of a plurality of micro regions and determining an in-focus position in the directions of the optical axis of said reflective fraction of said light, at which said reflective fraction of said light comes into focus,

obtain second surface shape data indicating the surface shape of said object using said phase data by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region, and

obtain third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

2. The apparatus as claimed in claim 1, wherein said computer unit is further configured to obtain an entirely in-focus image of said object, the entire region of which is in focus, using at least one of said amplitude data and said phase data in order to obtain said first surface shape data.

3. The apparatus as claimed in claim 2, wherein said computer unit is further configured to replace an in-focus image of each micro region in said entirely in-focus image, with an item of said phase data at a position closest to said in-focus position.

4. The apparatus as claimed in claim 2, wherein said computer unit is further configured to obtain said first surface data by performing Fresnel'"'"'s diffraction calculation using said in-focus position and focus image of a micro region.

5. The apparatus as claimed in claim 1, wherein magnification of said interference optical system is set at a value at which the resolution of said interference optical system in the directions of the axis of said reflective light becomes smaller than ½

of a wavelength of said light.

6. The apparatus as claimed in claim 1, wherein the plurality of positions at which said computer unit is configured to obtain said phase data and said amplitude data are arranged at intervals less than ½

of a wavelength of said light.

7. The apparatus as claimed in claim 1, wherein said computer unit, when combining said first surface shape data with said second surface shape data, is further configured to determine an order m in a formula “

m×

(λ

/2)+δ

”

(m;

order, λ

;

wavelength, δ

;

said second surface shape data).

8. The apparatus as claimed in claim 1, wherein said interference fringes are superposed with a carrier frequency.

9. The apparatus as claimed in claim 1, wherein said light source is further configured to emit pulses of light to illuminate said object.

10. The apparatus as claimed in claim 1, wherein said interference optical system is further configured to convert said reference fraction of said light and said reflective fraction of said light reflected by said object into respective spherical waves that have substantially the same curvature at a position where said image capturing unit captures said interference fringes.

11. The apparatus as claimed in claim 1, wherein

said interference optical system further comprises a magnification adjustment unit configured to change the magnification of said interference optical system;

and

said magnification adjustment unit adjusts at least one of measurement resolution and measurement range in the directions of said optical axis.

12. The apparatus as claimed in claim 11, wherein the magnification adjustment unit is further configured to interlock and substantially equalize the curvature of said reflective fraction of said light and the curvature of said reference fraction of said light.

13. An apparatus for measuring surface shape of an object, comprising:

a light source configured to emit light to illuminate said object;

an interference optical system configured to generate interference fringes between a reference fraction of said light and a reflective fraction of said light reflected by said object;

an imaging capturing unit configured to capture said interference fringes and output interference fringe data; and

a computer unit configured to

obtain phase data indicating the phase of said reflective fraction of said light at a plurality of positions in the directions of the optical axis of said reflective fraction of said light using said interference fringe data,

obtain first surface shape data indicating the surface shape of said object using said phase data by calculating an in-focus distance at each micro region of a plurality of micro regions and determining an in-focus position in the directions of the optical axis of said reflective fraction of said light, at which said reflective fraction of said light comes into focus,

obtain second surface shape data indicating the surface shape of said object using said phase data by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region, and

obtain third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

14. A method of measuring surface shape of an object, comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by determining a focusing level using said amplitude data and calculating an in-focus distance at each micro region of a plurality of micro regions;

obtaining second surface share data indicating the surface shape of said object using said phase data by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region; and

obtaining third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

15. The method as claimed in claim 14, wherein said obtaining first surface shape data creates an entirely in-focus image of said object, using at least one of said amplitude data and said phase data in order to obtain said first surface shape data.

16. The method as claimed in claim 15, wherein said obtaining first share data includes replacing in-focus images of micro regions in said entirely in-focus image with said phase data of said micro regions at a position closest to an in-focus position.

17. The method as claimed in claim 15, wherein, said obtaining first surface shape data includes performing Fresnel'"'"'s diffraction calculation using said in-focus distance determined by the focusing level to obtain in-focus images of micro regions in said entirely in-focus image.

18. A method of measuring surface shape of an object, comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by calculating an in-focus distance at each micro region of a plurality of micro regions and determining a focusing level using said phase data;

obtaining second surface shape data indicating the surface shape of said object by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region using said phase data; and

obtaining third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

19. A computer program, which when executed by the computer system causes the computer system to perform a method comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by determining a focusing level using said amplitude data and calculating an in-focus distance at each micro region of a plurality of micro regions;

obtaining second surface shape data indicating the surface shape of said object using said phase data by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region; and

obtaining third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

20. The computer program as claimed in claim 19, wherein the computer program further causes said computer to create an entirely in-focus image of said object, the entire region of which is in focus, using at least one of said amplitude data and said phase data in order to obtain said first surface shape data.

21. The computer program as claimed in claim 20, wherein the computer program further causes said computer to replace in-focus images of micro regions in said entirely in-focus image with said phase data of said micro regions at a position closest to said in-focus position in order to obtain said first surface shape data.

22. The computer program as claimed in claim 20, wherein the computer program further causes said computer to obtain in-focus images of micro regions in said entirely in-focus image by performing Fresnel'"'"'s diffraction calculation using said in-focus distance determined by the focusing level.

23. A computer program, which when executed by the computer system causes the computer system to perform a method comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by calculating an in-focus distance at each micro region of a plurality of micro regions and determining a focusing level using said phase data;

obtaining second surface shape data indicating the surface shape of said object by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region using said phase data; and

obtain third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

24. A computer program product storing program instructions for execution on a computer system, which when executed by the computer system causes the computer system to perform a method comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by determining a focusing level using said amplitude data and calculating an in-focus distance at each micro region of a plurality of micro regions;

obtaining second surface shape data indicating the surface shape of said object using said phase data by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region; and

obtaining third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

25. The computer program product as claimed in claim 24, wherein the computer program further causes said computer to create an entirely in-focus image of said object, the entire region of which is in focus, using at least one of said amplitude data and said phase data in order to obtain said first surface shape data.

26. The computer program product as claimed in claim 25, wherein the computer program further causes said computer to replace in-focus images of micro regions in said entirely in-focus image with said phase data of said micro regions at a position closest to said in-focus position in order to obtain said first surface shape data.

27. The computer program product as claimed in claim 25, wherein the computer program further causes said computer to obtain in-focus images of micro regions in said entirely in-focus image by performing Fresnel'"'"'s diffraction calculation using said in-focus distance determined by the focusing level.

28. A computer program product storing program instructions for execution on a computer system, which when executed by the computer system causes the computer system to perform a method comprising:

capturing an image of interference fringes generated by a reflective fraction of light reflected by an object and a reference fraction of said light;

generating interference fringe data using the captured image of said interference fringes;

calculating, using the generated interference fringe data, phase data indicating the phase of said reflective fraction of said light and amplitude data indicating the amplitude of said reflective fraction of said light, at a plurality of positions in the directions of the optical axis of said reflective fraction of said light;

obtaining first surface shape data indicating the shape of said object by calculating an in-focus distance at each micro region of a plurality of micro regions and determining a focusing level using said phase data;

obtaining second surface shape data indicating the surface shape of said object by assigning the in-focus distance of each micro region of the plurality of micro regions and calculating a complex amplitude of each micro region using said phase data; and

obtain third surface shape data indicating the surface shape of said object by combining or comparing said first surface shape data with said second surface shape data.

29. An apparatus for measuring surface shape of an object, comprising:

a light source configured to emit light to illuminate said object;

an interference optical system configured to generate interference fringes between a reference fraction of said light and a reflective fraction of said light reflected by said object;

an imaging capturing unit configured to capture said interference fringes and output interference fringe data; and

a computer unit configured to

obtain first surface shape data by determining an in-focus distance for a plurality of micro regions by calculating a complex amplitude at a reproduction distance using Fresnel'"'"'s diffraction calculation for each micro region, obtaining an in-focus measure of the amplitude data of the complex amplitude for each micro region, and converting the in-focus distance into said first surface shape data,

calculate an order at each pixel of a plurality of pixels,

obtain second surface shape data by assigning the in-focus distance of each micro region as a reproduction distance, calculating the complex amplitude of each micro region by Fresnel'"'"'s diffraction calculation, and converting phase data at each pixel of the plurality of pixels into said second surface shape data, and

obtain third surface shape data indicating the surface shape of said object by at least one of combining and comparing said first surface shape data with said second surface shape data.