Interferometer and phase shift amount measuring apparatus with diffraction gratings to produce two diffraction beams

1. An interferometer comprising:

an illumination source for generating an illumination beam,

an illumination system for projecting the illumination beam emitted from the illumination source onto a sample so as to illuminate two areas of the sample where the two areas are laterally shifted from each other by a given distance,

a detector for receiving radiation beams reflected by the two areas of the sample, and

an imaging system for directing the radiation beams reflected by the two areas of the sample onto the detector,

wherein said illumination system includes a first diffraction grating for diffracting the illumination beam emitted from the illumination source to produce first and second diffraction beams, wherein said two areas of the sample are illuminated by the first and second diffraction beams, respectively, and

wherein said imaging system includes a second diffraction grating for diffracting the first and second diffraction beams reflected by the sample to produce a third and a fourth diffraction beams which are laterally shifted from each other, and

wherein an interference image consisting of the third and fourth diffraction beams is formed on the detector,

wherein said first and second diffraction gratings each comprise a phase diffraction grating for producing at least two higher order diffraction beams higher than zero-th beam,

wherein said phase grating includes a grating pattern defined by two spatial frequency components, and

wherein said grating pattern is defined by logical sum of the two spatial frequency components.

2. The interferometer of claim 1 , wherein the first diffraction beam and the second diffraction beam generated by the first diffraction grating illuminate the two areas of the sample coherently.

3. The interferometer of claim 1 , wherein said first diffraction beam and the second diffraction beam generated by the first diffraction grating are projected obliquely relative to a sample surface, and wherein

said second diffraction grating diffracts the first diffraction beam and the second diffraction beam reflected by the sample surface.

4. The interferometer of claim 1 , wherein the interference image formed on the detector includes phase difference information corresponding to a path-length difference between the first diffraction beam and the second diffraction beam generated by the first diffraction grating.

5. The interferometer of claim 4 , wherein said interference image formed on the detector includes phase difference information corresponding to the variation in height of the sample surface.

6. The interferometer of claim 1 , wherein the first and second diffraction gratings comprise a grating having the same structure, and wherein

the first diffraction grating is arranged at a pupil position of the illumination system or in the vicinity of the pupil position, and the second diffraction grating is arranged at the pupil position or in the vicinity of the imaging system.

7. The interferometer of claim 1 , wherein an objective system is arranged in the paths between the sample and the first and second diffraction gratings, and wherein

the first and second diffraction beams emitted from the first diffraction grating are directed onto the sample through the objective system, and the first and second diffraction beams emitted from the sample are directed onto the second diffraction grating through the objective system.

8. The interferometer of claim 1 , wherein a field stop is arranged in the path between the illumination source and the first diffraction grating to project the image of the field stop onto the sample.

9. The interferometer of claim 1 , wherein said sample is supported on a stage having a tilting mechanism for tilting the sample, and wherein

the tilting mechanism performs a fringe-scan for the first and second diffraction beams by scanning the tilted angle of the stage.

10. An interferometer comprising:

illumination source for generating an illumination beam,

an illumination system for projecting the illumination beam emitted from the illumination source onto a sample so as to illuminate two areas of the sample where the two areas are laterally shifted from each other by a given distance,

a detector for receiving radiation beams reflected by the two areas of the sample, and

an imaging system for directing the radiation beams reflected by the two areas of the sample onto the detector,

wherein said illumination system includes a first diffraction grating for diffracting the illumination beam emitted from the illumination source to produce first and second diffraction beams, wherein said two areas of the sample are illuminated by the first and second diffraction beams, respectively, and

wherein said imaging system includes a second diffraction grating for diffracting the first and second diffraction beams reflected by the sample to produce third and fourth diffraction beams which are laterally shifted from each other, and

wherein an interference image consisting of the third and fourth diffraction beams is formed on the detector, and

wherein said first and second diffraction grating comprise a phase diffraction grating for producing at least two higher order diffraction beams higher than zero-th beam, and

wherein said phase diffraction grating is a phase diffraction grating of reflection type comprising a substrate in which grating grooves having depth of λ/4 are formed based on the grating pattern and a reflection film formed on the substrate, λ being a wavelength of the illumination beam.

11. The interferometer of claim 10 , wherein a photomask of reflection type used in extremely ultraviolet lithography (EUVL) is used as the sample, and an EUV source whose emission peak wavelength is 13.5 nm is used as the illumination source.

12. An interferometer comprising:

an illumination source for generating an illumination beam,

an illumination system for projecting the illumination beam emitted from the illumination source onto a sample so as to illuminate two areas of the sample where the two areas are laterally shifted from each other by a given distance,

a detector for receiving radiation beams reflected by the two areas of the sample, and

an imaging system for directing the radiation beams reflected by the two areas of the sample onto the detector,

wherein said illumination system includes a first diffraction grating for diffracting the illumination beam emitted from the illumination source to produce first and second diffraction beams, wherein said two areas of the sample are illuminated by the first and second diffraction beams, respectively, and

wherein said imaging system includes a second diffraction grating for diffracting the first and second diffraction beams reflected by the sample to produce third and fourth diffraction beams which are laterally shifted from each other, and

wherein an interference image consisting of the third and fourth diffraction beams is formed on the detector, and

wherein an objective system is arranged in the paths between the sample and the first and second diffraction gratings, and

wherein the first and second diffraction beams emitted from the first diffraction grating are directed onto the sample through the objective system, and the first and second diffraction beams emitted from the sample are directed onto the second diffraction grating through the objective system, and

wherein said objective system comprises a plane mirror and two concave mirrors,

wherein a focus point of the objective system is set at infinity, and

wherein one half area of the objective system forms a part of the illumination system and the remaining half area forms a part of the imaging system.