System and method for determining a shape of a surface of an object and method of manufacturing an object having a surface of a predetermined shape

• US 20060215177A1
• Filed: 03/10/2006
• Published: 09/28/2006
• Est. Priority Date: 03/11/2005
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Inventors: Doerband, Bernd
• Granted Patent: US 7,522,292 B2
• Time in Patent Office: Days
• US Class Current: 356/609
• CPC Class Codes: G01B 11/2509 Color coding
• CPC Class Codes: G01B 2210/50 Using chromatic effects to achieve wavelength-dependent depth resolution
• CPC Class Codes: G01M 11/005 Testing of reflective surfaces, e.g. mirrors
• CPC Class Codes: G01M 11/025 by determining the shape of the object to be tested measuring contours or curvatures by optical means G01B11/24
• CPC Class Codes: G01M 11/0271 by using interferometric methods

Abstract

A system and method for determining a shape of a surface comprises a chromatic imaging optics for generating a dispersion in a measuring light. Colour information contained in measuring light emerging from the surface to be tested and received by a detector may be used to determine the shape of the surface to tested.

Claims

1. A method of determining a shape of a surface of an object, the method comprising:

generating measuring light of plural different wavelengths;

directing the measuring light onto the surface of the object through a chromatic illuminating optics such that the measuring light is incident at plural locations of the surface, wherein, at each said location, a direction of incidence of measuring light of a first wavelength differs from a direction of incidence of measuring light of a second wavelength by more than 1 arcmin;

directing a portion of measuring light reflected from the surface of the object onto a light detecting surface of a detector through an imaging optics, wherein more than one third of the reflected measuring light of the plural different wavelengths entering the imaging optics is blocked from being incident on the light detecting surface of the detector;

detecting wavelength dependent distributions of an intensity of the measuring light incident on the detector; and

determining a shape of the surface of the object based upon the detected wavelength dependent distributions of intensity.

2. The method according to claim 1, wherein the reflected measuring light entering the imaging optics is blocked from being incident on the light detecting surface of the detector by a beam stop having an aperture of a predefined shape.

3. The method according to claim 1, wherein the measuring light of the plural different wavelengths is incident on the surface of the object at a same time, and wherein the detecting of the wavelength dependent distributions of intensity comprises a spectral analysis of the measuring light having traversed the imaging optics.

4. The method according to claim 1, wherein the measuring light of the plural different wavelengths is incident on the surface of the object at a same time, and wherein the detecting of the wavelength dependent distributions comprises subsequent detection of distributions of an intensity of the measuring light at the different wavelengths.

5. The method according to claim 1, wherein the generating of the measuring light of plural different wavelengths comprises generating of the measuring light of a single wavelength range at a time and subsequently changing the wavelength range of the generated measuring light.

6. The method according to claim 1, further comprising generating reference light and directing the reference light onto the detector to be superimposed thereon with the portion of the measuring light reflected from the surface of the object.

7. The method according to claim 6, wherein the determining of the shape of the surface of the object comprises analyzing an interference pattern generated by the superimposed reference light and measuring light.

8. The method according to claim 6, wherein the reference light is generated by reflecting a portion of the generated measuring light from a reference surface disposed upstream of the surface of the object in a beam path of the measuring light to be incident on the surface of the object.

9. The method according to claim 1, wherein the illuminating optics and the imaging optics each have plural optical elements, and wherein at least one optical element is a component of both the illuminating optics and the imaging optics.

10. The method according to claim 1, wherein the chromatic illuminating optics comprises a diffractive grating.

11. The method according to claim 10, wherein the diffractive grating is a component of both the illuminating optics and the imaging optics.

12. The method according to claim 10, wherein the diffractive grating is disposed outside of the imaging optics.

13. The method according to claim 1, wherein the chromatic illuminating optics has a beam cross section at a position of a beam path of the measuring light to be incident on the surface of the object, wherein measuring light of different non-overlapping wavelength bands traverses the beam cross section in respective different non-overlapping regions of the cross section.

14. The method according to claim 1, wherein the non-overlapping regions of the cross section are ring shaped.

15. A method of determining a shape of a surface of an object, the method comprising:

generating measuring light of different wavelengths to be incident on the surface of the object from different directions of incidence;

allowing measuring light emerging from an extended region of the surface to traverse an imaging optics;

detecting a light intensity of each of plural groups of rays of the measuring light having traversed the imaging optics, wherein each group of rays has associated therewith a range of wavelengths of its rays and a range of angles of the rays relative to a predetermined direction,

wherein the groups are selected such that the detected light intensities of less than one half of all the groups are greater than twice a background intensity; and

determining a shape of the extended region of the surface of the object based upon the detected intensities.

16. The method according to claim 15, wherein the detecting of light intensities comprises allowing only a portion of the measuring light having traversed the imaging optics to traverse an aperture provided in a beam stop, and detecting light intensities of the portion of the measuring light having traversed the aperture.

17. The method according to claim 15, wherein the selecting of groups of rays comprises using a position sensitive detector having a plurality of spaced apart detector elements.

18. The method according to claim 15, wherein the generating of the measuring light to be incident on the surface of the object comprises directing the measuring light through the imaging optics.

19. The method according to claim 18, wherein the measuring light emerging from the surface is measuring light reflected from the surface.

20. A method of manufacturing an object having a surface of a target shape, the method comprising:

generating measuring light of plural different wavelengths;

directing the measuring light onto the surface of the object through a chromatic illuminating optics such that the measuring light is incident at plural locations of the surface, wherein, at each said location, a direction of incidence of measuring light of a first wavelength differs from a direction of incidence of measuring light of a second wavelength by more than 1 arcmin;

directing a portion of measuring light reflected from the surface of the object onto a light detecting surface of a detector through an imaging optics, wherein more than one third of the reflected measuring light of the plural different wavelengths entering the imaging optics is blocked from being incident on the light detecting surface of the detector;

detecting wavelength dependent distributions of an intensity of the measuring light incident on the detector;

determining deviations of a shape of the surface of the object based upon the detected wavelength dependent distributions of intensity; and

processing the surface of the object based on the determined deviations.

21. The method according to claim 20, wherein the reflected measuring light entering the imaging optics is blocked from being incident on the light detecting surface of the detector by a beam stop having an aperture of a predefined shape.

22. The method according to claim 20, wherein the measuring light of the plural different wavelengths is incident on the surface of the object at a same time, and wherein the detecting of the wavelength dependent distributions of intensity comprises a spectral analysis of the measuring light having traversed the imaging optics.

23. The method according to claim 20, wherein the measuring light of the plural different wavelengths is incident on the surface of the object at a same time, and wherein the detecting of the wavelength dependent distributions comprises subsequent detection of distributions of an intensity of the measuring light at different wavelengths.

24. The method according to claim 20, wherein the generating of the measuring light of plural different wavelengths comprises generating of the measuring light of a single wavelength range at a time and subsequently changing the wavelength range of the generated measuring light.

25. The method according to claim 20, further comprising generating reference light and directing the reference light onto the detector to be superimposed thereon with the portion of the measuring light reflected from the surface of the object.

26. The method according to claim 25, wherein the determining of the shape of the surface of the object comprises analyzing an interference patter generated by the superimposed reference light and measuring light.

27. The method according to claim 20, wherein the chromatic illuminating optics comprises a diffractive grating.

28. The method of claim 20, wherein the target shape is an aspherical shape.

29. The method according to claim 20, wherein the processing of the surface of the object comprises at least one of milling, grinding, loose abrasive grinding, polishing, ion beam figuring, magneto-rheological figuring, and finishing the surface of the object.

30. The method according to claim 29, wherein the finishing comprises applying a coating to the surface.

31. The method according to claim 30, wherein the coating comprises at least one of a reflective coating, an anti-reflective coating and a protective coating.

32. A system for measuring a shape of a surface of an object, the system comprising:

a light source for generating measuring light within a broad wavelength range;

a chromatic illuminating optics for directing the measuring light onto the surface of the object, wherein the chromatic illuminating optics has a front surface of an optical element disposed closest to the object to be measured, and wherein a dispersion of the chromatic illuminating optics is such that, at each of plural locations on the front surface, an emission direction of measuring light of a first wavelength differs from an emission direction of measuring light of a second wavelength by more than 1 arcmin;

an imaging optics for imaging the surface of the object onto a light detecting surface of a detector, wherein the imaging optics comprises a beam stop having an aperture disposed within a beam path of the imaging optics, the aperture having a cross section of a size which is smaller than a third of a size of an effective cross section of the beam path of the imaging optics upstream of the beam stop; and

a spectral selector transmitting only measuring light within a narrow wavelength range, wherein the spectral selector is disposed in a beam path of the measuring light between the light source and the detector.

33. The system according to claim 32, wherein the spectral selector is disposed in the beam path of the measuring light upstream of the illuminating optics.

34. The system according to claim 32, wherein the spectral selector is disposed in the beam path of the measuring light downstream of the imaging optics.

35. The system according to claim 32, wherein the spectral selector comprises an interference filter.

36. The system according to claim 32, wherein the chromatic illuminating optics comprises a diffractive grating.

37. The system according to claim 32, further comprising an interferometer having a measuring arm including the imaging optics and a reference arm including a reflecting reference surface.

38. The system according to claim 37, wherein the reference surface is disposed in the imaging optics.

39. The system according to claim 34, wherein a coherence length of the measuring light is shorter than an optical path length between the reference surface and a front surface of the illuminating optics disposed closest to the optical surface to be tested.

40. A system for measuring a shape of a surface of an object, the system comprising:

an imaging optics;

a beam stop having an aperture;

a test piece mount configured to mount the object such that the surface of the object is disposed at a distance from a position which is conjugate to the aperture with respect to the imaging optics;

a position sensitive detector to detect measuring light emerging from the surface of the object and having traversed the imaging optics and the aperture;

a light source for generating measuring light within a broad wavelength range;

a chromatic illuminating optics for directing the measuring light onto the surface;

a spectral selector to select, from the broad wavelength range, an adjustable narrow wavelength range of the measuring light to be incident on the position sensitive detector, wherein a ratio of a width of the narrow wavelength range over a width of the broad wavelength range is less than ¼

; and

a controller configured to control the spectral selector such that plural different narrow wavelength ranges are subsequently adjusted and to receive a representation of light intensities detected by the position sensitive detector for each of the plural different narrow wavelength ranges.

41. The system according to claim 40, wherein the spectral selector comprises a controller of the light source to adjust an emission wavelength thereof.

42. The system according to claim 40, wherein the spectral selector comprises a spectral filter disposed in a beam path of the measuring light between the light source and the surface of the object.

43. The system according to claim 40, wherein the spectral selector comprises a spectral filter disposed in a beam path of the measuring light between the surface of the object and the position sensitive detector.

44. The system according to claim 40, wherein the chromatic illuminating optics comprises a diffractive grating.

45. The system according to claim 40, further comprising an interferometer having a measuring arm including the imaging optics and a reference arm including a reflecting reference surface.

46. The system according to claim 45, wherein the reference surface is provided by the imaging optics.

47. The system according to claim 46, wherein a coherence length of the measuring light is shorter than an optical path difference between the reference surface and the optical surface of the object.

48. A method of determining a shape of a surface of an object, the method comprising:

generating measuring light of different wavelengths to be incident on the surface of the object from different directions of incidence;

detecting wavelength dependent distributions of an intensity of the measuring light reflected from the object; and

determining a shape of the surface of the object based upon the detected wavelength dependent distributions of intensity.

49. The method according to claim 48, wherein the detecting comprises detecting the wavelength dependent distributions of the intensity of the measuring light which is reflected from the object and which has traversed an aperture of a beam stop configured to block at least one half of the measuring light reflected from the object to be detected.

50. A system for measuring a shape of a surface of an object, the system comprising:

a light source for generating measuring light within a wavelength range;

an illuminating optics for directing the measuring light onto the surface of the object;

an imaging optics for imaging the surface of the object onto a light detecting surface of a detector;

wherein the illuminating optics and the imaging optics are configured such that first and second aspherical optical surfaces can be disposed relative to the illuminating optics, wherein corresponding locations of the first and second aspherical optical surfaces are imaged onto same locations on the light detecting surface of the detector, and wherein orientations of the first and second surfaces at the corresponding locations may differ by more than arcsin (λ

min/2p), wherein;

λ

min is a smallest wavelength of the measuring light, and

p is a pitch of detector pixels in the light detecting surface of the detector.