The present invention is directed to the provision of an interferometer and a phase shift amount measuring apparatus that can precisely operate in the EUV region. The interferometer according to the invention comprises an illumination source for generating an illumination beam, an illumination system for projecting the illumination beam emitted from the illumination source onto a sample, and an imaging system for directing the reflected beam by the sample onto a detector. The illumination system includes a first diffraction grating for producing a first and second diffraction beams which respectively illuminate two areas on the sample where are shifted from each other by a given distance, and the imaging system includes a second grating for diffracting the first and second diffraction beams reflected by the sample to produce a third and fourth diffraction beams which are shifted from each other by a given distance.

A method for high-accuracy wavefront measurement based on grating shearing interferometry, which adopts a grating shearing interferometer system comprising an illuminating system, an optical imaging system under test, an object plane diffraction grating plate, an image plane diffraction grating plate, a two-dimensional photoelectric sensor, and a calculation processing unit. The object plane diffraction grating plate and the image plane diffraction grating plate are respectively arranged on the object plane and the image plane of the optical imaging system under test. The shearing phase of 1.sup.st-order diffracted beam and −1.sup.st-order diffracted beam is exactly extracted through phase shifting method, and the original wavefront is obtained by carrying out reconstruction algorithm according to a shear ratio of 2s, such that the accuracy of wavefront measurement of the optical imaging system under test is improved, wherein s is the shear ratio of the grating shearing interferometer.

A method for high-accuracy wavefront measurement based on grating shearing interferometry, which adopts a grating shearing interferometer system comprising an illuminating system, an optical imaging system under test, an object plane diffraction grating plate, an image plane diffraction grating plate, a two-dimensional photoelectric sensor, and a calculation processing unit. The object plane diffraction grating plate and the image plane diffraction grating plate are respectively arranged on the object plane and the image plane of the optical imaging system under test. The shearing phase of 1.sup.st-order diffracted beam and −1.sup.st-order diffracted beam is exactly extracted through phase shifting method, and the original wavefront is obtained by carrying out reconstruction algorithm according to a shear ratio of 2s, such that the accuracy of wavefront measurement of the optical imaging system under test is improved, wherein s is the shear ratio of the grating shearing interferometer.

A metrology system includes a first beam analysis system for analyzing at least one first measurement beam that was coupled from the excitation laser beam before a reflection on the target material and a second beam analysis system for analyzing at least one second measurement beam that was coupled from the excitation laser beam after a reflection on the target material. Each of the first beam analysis system and the second beam analysis system has at least one wavefront sensor system.

Projection objective wave-front aberration detecting device and a detecting method thereof, wherein the projection objective wave-front aberration detecting device comprises a light source and illuminating system, an object plane grating, an object plane displacement stage, a measured projection objective, an image plane grating, a two-dimensional photoelectric sensor, an image plane displacement stage and a control processing unit. According to the invention, by controlling the length of the object plane grating line, or the periodic structure of the object plane grating perpendicular to the shearing diffraction direction, or the object plane grating to adopt a sinusoidal grating, or the image plane grating to adopt an amplitude-phase hybrid grating, the complexity of an interference field is reduced, and the wave-front aberration detection speed and precision are improved, and the precision and speed of in-situ wave-front aberration detection can be improved.

A method for wavefront measurement of optical imaging system based on grating shearing interferometry, the grating shearing interferometer comprising: a light source and illumination system, an optical imaging system to be tested, a one-dimensional diffraction grating plate, a two-dimensional diffraction grating plate, a two-dimensional photoelectric sensor and a computing unit. The one-dimensional diffraction grating plate and the two-dimensional diffraction grating plate are respectively placed on the object side and the image side of the optical imaging system to be tested. By collecting N sets of interferograms with a $\frac{2\pi }{N}$
phase-shifting interval (where, $N=2\left(\mathrm{fix}\left(\frac{\mathrm{ceil}\left(1/s\right)}{2}\right)+1\right),$
s is the shear ratio of the grating shearing interferometer), combined with a certain phase retrieval algorithm, the influence of all high-order diffraction beams on the phase retrieval accuracy is eliminated, and finally the wavefront measurement accuracy for the optical imaging system is improved.

Projection objective wave-front aberration detecting device and a detecting method thereof, wherein the projection objective wave-front aberration detecting device comprises a light source and illuminating system, an object plane grating, an object plane displacement stage, a measured projection objective, an image plane grating, a two-dimensional photoelectric sensor, an image plane displacement stage and a control processing unit. According to the invention, by controlling the length of the object plane grating line, or the periodic structure of the object plane grating perpendicular to the shearing diffraction direction, or the object plane grating to adopt a sinusoidal grating, or the image plane grating to adopt an amplitude-phase hybrid grating, the complexity of an interference field is reduced, and the wave-front aberration detection speed and precision are improved, and the precision and speed of in-situ wave-front aberration detection can be improved.

A method for wavefront measurement of optical imaging system based on grating shearing interferometry, the grating shearing interferometer comprising: a light source and illumination system, an optical imaging system to be tested, a one-dimensional diffraction grating plate, a two-dimensional diffraction grating plate, a two-dimensional photoelectric sensor and a computing unit. The one-dimensional diffraction grating plate and the two-dimensional diffraction grating plate are respectively placed on the object side and the image side of the optical imaging system to be tested. By collecting N sets of interferograms with a

[00001]$\frac{2.Math.}{N}$

phase-shifting interval (where,

[00002]$N=2.Math.\left(\mathrm{fix}\left(\frac{\mathrm{ceil}\left(1/s\right)}{2}\right)+1\right),$

s is the shear ratio of the grating shearing interferometer), combined with a certain phase retrieval algorithm, the influence of all high-order diffraction beams on the phase retrieval accuracy is eliminated, and finally the wavefront measurement accuracy for the optical imaging system is improved.

The imaging quality of an optical imaging system is interferometrically measured. A wavefront measurement has a first imaging scale .sub.1 in a first direction and a second imaging scale .sub.2 in a second, perpendicular direction. The second imaging scale differs from the first imaging scale by a scale ratio (.sub.1/.sub.2)1 (anamorphic imaging system). A first measurement structure (MS1) on a first structure carrier arranged on the object side of the imaging system has a two-dimensional mask structure suitable for shaping the coherence of measurement radiation. A second measurement structure (MS2) on a second structure carrier arranged on the image side of the imaging system has a diffraction grating. The first and second measurement structures are mutually adapted, taking account of the scale ratio so that an interference pattern arises upon imaging the first measurement structure onto the second measurement structure using the anamorphic imaging system.

A shearing interferometer includes first and second shearing plates disposed opposite to each other. The first shearing plate includes a first front surface and a first back surface, and splits an input beam input to the first front surface into first and second beams reflected at the first front and back surfaces, respectively. The second shearing plate includes a second front surface and a second back surface. The second shearing plate splits the first beam into third and fourth beams reflected at the second front and back surfaces, respectively, and splits the second beam into fifth and sixth beams reflected at the second front and back surfaces, respectively. Each of the first and second shearing plates has a thickness which limits a phase delay between the fourth beam and the fifth beam to a degree determined to allow interference to occur between the fourth beam and the fifth beam.