Method and apparatus utilizing an optical stage for topographic surface analysis

• US 5,568,256 A
• Filed: 04/21/1994
• Issued: 10/22/1996
• Est. Priority Date: 04/21/1993
• Status: Expired due to Fees

• Current Assignee: Fraunhofer-Gesellschaft ZUR Forderung Der Angewandten Forschung EV
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Uhlmann, Eckart, Holger, Fritz, Korner, Klaus, Nyarsik, Lajos, Spur, Gunter
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US08/230,772
• Time in Patent Office: 915 Days
• Field of Search: 356/345, 356/349, 356/353, 356/354, 356/359, 356/360, 356/371
• US Class Current: 356/512
• CPC Class Codes: G01B 11/303 using photoelectric detection means
• CPC Class Codes: G01B 9/025 Double exposure technique

Abstract

A method and apparatus for topographic surface analysis including at leastne light source for radiating light, a first light-distributing surface of a first diffraction grating for receiving light from the at least one light source and for reflecting a first bundle of light under normal optical conditions and a second bundle of light formed by diffraction of the first order. A first optical stage is provided for projecting the first and second bundles from the first light-distributing surface in an optically conjugated form onto an object surface to be analyzed of a sample. Light representing the object surface is sharply projected via the first optical stage onto a second light-distributing surface of a second diffraction grating. A second optical stage projects diffracted bundles of light from the second light-distributing surface onto a detector which detects radiation and enables topographic analysis of the object surface.

Claims

1. Apparatus for topographic analysis of a surface comprising at least one light source for radiating divergent light, a first light-distributing surface of a first diffraction grating for receiving light from the at least one light source and for reflecting a first bundle of light under normal optical conditions and a second bundle of light formed by diffraction of the first order, a first optical stage for projecting the first and second bundles from the first light-distributing surface in an optically conjugated form onto an object surface to be analyzed of a sample, light representing the object surface being sharply projected via the first optical stage onto a second light-distributing surface of a second diffraction grating, and a detector for receiving diffracted bundles of light from the second light-distributing surface projected by a second optical stage for detecting radiation enabling topographic analysis of the object surface.

2. Apparatus according to claim 1, wherein the at least one light source is a light source module having a rotating focusing screen on which an extended spot is illuminated.

3. Apparatus according to claim 1, wherein at least one of the first and second diffraction gratings is at least one of a multiline grating, reflecting diffraction grating and holographic reflecting grating, and is located on one of a straight and a curved surface.

4. Apparatus according to claim 1, wherein at least one of the first and second diffraction gratings has a grating period selected so that an obliquely incident light beam in the first order of diffraction is radiated substantially orthogonally relative to a grating surface.

5. Apparatus according to claim 1, wherein at least one of the first and second diffraction gratings is a multi-line reflecting diffraction grating having a grating structure located on a surface matched with the object surface.

6. Apparatus according to claim 5, wherein the object surface is convex and the grating structure is disposed on a concave surface.

7. Apparatus according to claim 1, wherein at least one of the first and second light-distributing surfaces have grating structures with different grating periods.

8. Apparatus according to claim 7, wherein on each line of the grating structures having different grating periods include a small grating period and fine gratings have a higher grating period.

9. Apparatus according to claim 8, wherein the small grating period include 10 lines/mm and the higher grating period include 1,000 lines/mm.

10. Apparatus according to claim 1, wherein at least one of the first and second light-distributing surfaces is connected to a computer-controlled microtranslator for enabling application of a phase shift technique.

11. Apparatus according to claim 1, further comprising a reflector associated with the object surface and arranged in a substantially orthogonal relationship thereto so that one of a compensating plane through the object surface and a combination of the reflector and the object surface form a roof edge.

12. Apparatus according to claim 1, wherein the first optical stage is configured as a 4 f-type system.

13. Apparatus according to claim 1, wherein the second optical stage is disposed at a same angle as the first optical stage so as to create an arrangement which is symmetrical relative to the object surface in terms of an axial provision of the first and second optical stages.

14. Apparatus according to claim 1, wherein the at least one light source is interchangeable in position with a position of the detector so as to enable coverage of surface areas which are shaded.

15. Apparatus according to claim 1, wherein the first light-distributing surface is disposed obliquely relative to an optical axis of the first optical stage, and the object surface is disposed equally obliquely relative to the optical axis of the first optical stage so that light radiated from the first light source onto the first light-distributing surface arrives obliquely on the object surface to be analyzed via the first optical stage, and the first light-distributing surface and the object surface are optically conjugated.

16. Apparatus for analyzing a topography of a surface by strip projection comprising at least one light source for radiating light, at least one light-distributing surface for receiving light irradiated from the at least one light source, at least one optical stage, an object surface to be analyzed of a sample, and a detector for detecting radiation of the object surface to be analyzed, the at least one light-distributing surface being disposed obliquely relative to an optical axis of the at least one optical stage, and the object surface being disposed equally obliquely relative to the optical axis of the at least one optical stage so that light radiated from the at least one light source onto the at least one light-distributing surface arrives obliquely on the object surface via the at least one optical stage, and the at least one light-distributing surface and the object surface are optically conjugate.

17. Apparatus according to claim 16, wherein the object surface to be analyzed is illuminated by an oblique light beam at a wide angle.

18. Apparatus according to claim 16, wherein an image of the object surface in an area of the detector presents a geometric similarity with the object surface.

19. Apparatus according to claim 16, further comprising means for one of manually entering and iteratively and automatically determining an optimum sensitivity in the measurement of the object surface.

20. Apparatus according to claim 16, wherein the at least one optical stage includes a first optical stage of a 4 f-type system having a reflecting diffraction grating providing the at least one light-distributing surface which includes a first light-distributing surface and a second light-distributing surface, wherein a beat created between the reflecting diffraction grating and an image of the reflecting diffraction grating as the first light-distributing surface is projected onto the object surface of the sample and reflected back to the reflecting diffraction grating as the second light-distributing surface, and a beat image is projected onto a detector by a second optical stage for enabling analysis of shape.

25. A dual beam interferometer according claim 20, wherein the optical path-folding stage is an optical reflecting system having a highly planar reflecting surface.

21. A dual beam interferometer comprising a light source, a beam splitter surface at which a reference beam and object beams of an object beam bundle are generated, an object surface, at least one optical path-folding stage and at least one optical stage for projecting a course of the object and reference beams, at least one interference means having an interference pattern recordable via a further optical stage by a CCD camera connected to a computer, the at least one optical path-folding stage being provided with a computer-controlled adjusting element so that an optical path difference in the course of the object and reference beams, following the object surface between the reference beam and the object beams of the object beam bundle, is set approximately to zero.

22. A dual beam interferometer according claim 21, wherein the at least one optical stage is provided in the course of the reference beam and the object beams of the object beam bundle following the object surface and having an optical axis extending substantially in parallel to a beam axis.

23. A dual beam interferometer according claim 21, wherein the interference means include a light-distributing surface producing one of a light-diffusing and light-diffracting effect.

24. A dual beam interferometer according to claim 23, wherein the light-distributing surface is a holographic reflecting grating.

26. Apparatus for analyzing a shape of a surface comprising at least one light source for providing a light beam, a beam splitter system for splitting the light beam at least once to create two sub-beams and for generating a lateral shear in one of the two sub-beams relative to the other of the two sub-beams, and means for focusing the two sub-beams onto a sample so as to generate two sub-beams by reflection, and a beam recombination system for recombining the sub-beams and for at least one of reducing or eliminating lateral shear between the sub-beams.

27. Apparatus according to claim 26, wherein the beam splitter system for generating lateral shear includes a Michelson'"'"'s interferometer having at least two retro-reflectors, one polarization-dependent splitting layer, and one nonpolarizing layer, wherein the sub-beams are focused by projection so as to interfere with each other.

28. A method of analyzing the shape of a surface, comprising the steps of splitting a light beam bundle at least once so as to create two sub-beams, one of the two sub-beams having a lateral shear relative to the other of the two sub-beams and the two sub-beams being focused at least once for arrival at a sample in the form of sub-beams so as to generate two sub-beams by reflection, recombining the sub-beams so as to at least one of reduce or eliminate the lateral shear between the sub-beams, and focusing the sub-beams by projection so as to interfere with each other.

29. A method according to claim 28, further comprising the step of evaluating by electronic image processing techniques at least one order of interference which occurs.