Apparatus for and method of measuring surface shape of an object

• US 20030067609A1
• Filed: 09/23/2002
• Published: 04/10/2003
• Est. Priority Date: 09/21/2001
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Morita, Nobuhiro
• Granted Patent: US 6,885,460 B2
• Time in Patent Office: Days
• US Class Current: 356/512
• 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 that emits light to illuminate said object;

an interference optical system that generates interference fringes between a reference fraction of said light and a reflective fraction of said light reflected by said object;

an imaging capturing unit that captures said interference fringes and outputs interference fringe data; and

a computer unit that

obtains 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,

obtains first surface shape data, based on the in-focus principle, indicating the surface shape of said object by 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, using said amplitude data,

obtains second surface shape data, based on the interference principle, indicating the surface shape of said object, using said phase data, and

obtains 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.

3. The apparatus as claimed in claim 1, wherein said computer unit obtains an entirely in-focus image of said object, the entire region of which is in focus, based on the in-focus principle, using said amplitude data or said phase data in order to obtain said first surface shape data.

4. The apparatus as claimed in claim 3, wherein said computer unit replaces an in-focus image of a micro region in said entirely in-focus image, with an item of said phase data at a position closest to said in-focus position.

5. The apparatus as claimed in claim 3, wherein said computer unit obtains said first surface data by performing Fresnel'"'"'s diffraction calculation using said in-focus position and focus image of a micro region.

6. 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 the wavelength of said light.

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

of the wavelength of said light.

8. The apparatus as claimed in claim 1, wherein said computer unit, when combining said first surface shape data with said second surface shape data, determines an order m in a formula “

m λ

(λ

/2)+δ

”

(m;

order, λ

;

wavelength, δ

;

said second surface shape data).

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

10. The apparatus as claimed in claim 1, wherein said light source emits pulses of light to illuminate said object.

11. The apparatus as claimed in claim 1, wherein said interference optical system converts 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.

12. The apparatus as claimed in claim 1, wherein

said interference optical system further comprises a magnification adjustment unit that changes the magnification of said interference optical system;

and

said magnification adjustment unit can adjust measurement resolution or measurement range in the directions of said optical axis.

13. The apparatus as claimed in claim 12, wherein the magnification of said interference optical system is adjustable in the manner where the curvature of said reflective fraction of said light and the curvature of said reference fraction of said light are interlocked and substantially equalized.

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

a light source that emits light to illuminate said object;

an interference optical system that generates interference fringes between a reference fraction of said light and a reflective fraction of said light reflected by said object;

an imaging capturing unit that captures said interference fringes and outputs interference fringe data; and

a computer unit that

obtains 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,

obtains first surface shape data, based on the in-focus principle, indicating the surface shape of said object by 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, using said phase data,

obtains second surface shape data, based on the interference principle, indicating the surface shape of said object, using said phase data, and

obtains 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 the steps of:

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, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said amplitude data;

obtaining, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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.

16. The method as claimed in claim 14, wherein the step of obtaining said first surface shape data creates an entirely in-focus image of said object, the entire region of which is in focus, based on the depth-from-focus principle, using said amplitude data or said phase data in order to obtain said first surface shape data.

17. The method as claimed in claim 16, wherein in-focus images of micro regions in said entirely in-focus image are replaced 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.

18. The method as claimed in claim 16, wherein, in the step of obtaining said first surface data, in-focus images of micro regions in said entirely in-focus image are obtained by performing Fresnel'"'"'s diffraction calculation using said in-focus distance determined by the focusing level.

15. A method of measuring surface shape of an object, comprising the steps of:

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, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said phase data;

obtaining, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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 that causes a computer to:

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

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

calculate, 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;

obtain, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said amplitude data;

obtain, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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.

21. 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, based on the depth-from-focus principle, using said amplitude data or said phase data in order to obtain said first surface shape data.

22. The computer program as claimed in claim 21, 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.

23. The computer program as claimed in claim 21, 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.

20. A computer program that causes a computer to:

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

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

calculate, 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;

obtain, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said phase data;

obtain, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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 readable recording medium including a computer program, wherein the computer program causes a computer to:

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

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

calculate, 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;

obtain, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said amplitude data;

obtain, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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.

26. The computer readable recording medium 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, based on the depth-from-focus principle, using said amplitude data or said phase data in order to obtain said first surface shape data.

27. The computer readable recording medium as claimed in claim 26, 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.

28. The computer readable recording medium as claimed in claim 26, 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.

25. A computer readable recording medium including a computer program, wherein said computer program causes a computer to:

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

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

calculate, 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;

obtain, based on the depth-from-focus principle, first surface shape data indicating the shape of said object by determining the focusing level using said phase data;

obtain, based on the interference measurement principle, second surface shape data indicating the surface shape of said object 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.