A wavefront of a light beam that exits an acousto-optic material is estimated; a control signal for an acousto-optic system that includes the acousto-optic material is generated, the control signal being based on the estimated wavefront of the light beam; and the control signal is applied to the acousto-optic system to generate a frequency-chirped acoustic wave that propagates in the acousto-optic material, the frequency-chirped acoustic wave forming a transient diffractive element in the acousto-optic material, an interaction between the transient diffractive element and the light beam adjusting the wavefront of the light beam to compensate for a distortion of the wavefront of the light beam, the distortion of the wavefront being at least partially caused by a physical effect in the acousto-optic material.

Metrology apparatus and methods are disclosed. In one arrangement, a substrate is inspected. A source beam of radiation emitted by a radiation source is split into a measurement beam and a reference beam. A first target is illuminated with the measurement beam, the first target being on the substrate. A second target is illuminated with the reference beam, the second target being separated from the substrate. First scattered radiation is collected from the first target and delivered to a detector. Second scattered radiation is collected from the second target and delivered to the detector. The first scattered radiation interferes with the second scattered radiation at the detector. The first target comprises a first pattern. The second target comprises a second pattern, or a pupil plane image of the second pattern. The first pattern is geometrically identical to the second pattern, the first pattern and the second pattern are periodic and a pitch of the first pattern is identical to a pitch of the second pattern, or both.

One pair each of a Y linear motor (a total of four) on the +X side and the X side that drive a reticle stage include one pair each of a stator section (a total of four) and three each of a mover section (a total of six) on the +X side and the X side. In this case, the three each of the mover sections on the +X side and the X side configure one each of a mover. The mover section located in the center in the Z-axis direction of each of the movers is used in common by each pair of the Y linear motors. Therefore, the weight of the mover section (reticle stage) of the reticle stage device is reduced, which allows a higher acceleration. Further, the mover section located in the center in the Z-axis direction of each of the movers coincides with a neutral plane of the reticle stage.

An illumination system of a microlithographic projection exposure apparatus includes a spatial light modulator which varies an intensity distribution in a pupil surface. The modulator includes an array of mirrors that reflect impinging projection light into directions that depend on control signals applied to the mirrors. A prism, which directs the projection light towards the spatial light modulator, has a double pass surface on which the projection light impinges twice, namely a first time when leaving the prism and before it is reflected by the mirrors, and a second time when entering the prism and after it has been reflected by the mirrors. A pupil perturbation suppressing mechanism is provided that reduces reflections of projection light when it impinges the first time on the double pass surface, and/or prevents that light portions being a result of such reflections contribute to the intensity distribution in the pupil surface.

An actuator to displace, for example a mirror, provides movement with at least two degrees of freedom by varying the currents in two electromagnets (370). A moving part includes a permanent magnet (362) with a magnetic face constrained to move over a working area lying substantially in a first plane perpendicular to a direction of magnetization of the magnet. The electromagnets have pole faces lying substantially in a second plane closely parallel to the first plane, each pole face substantially filling a quadrant of the area traversed by the face of the moving magnet. A ferromagnetic shield (820) is provided around the moving part and has at least one interruption (822) to reduce the influence of adjacent actuators or stray fields while also minimizing attraction between the permanent magnet (362) and the shield (820).

An illumination optical unit for EUV projection lithography illuminates an object field with illumination light. The illumination optical unit has a first facet mirror including a plurality of first facets on a first mirror carrier. Disposed downstream of the first facet mirror is a second facet mirror including a plurality of second facets arranged on a second mirror carrier around a facet arrangement center. Partial beams of the illumination light are guided superposed on one another into the object field, respectively via illumination channels which have one of the first facets and one of the second facets. Second maximum angle facets are arranged at the edge of the second mirror carrier. The second maximum angle facets predetermine maximum illumination angles of the illumination light which deviate maximally from a chief ray incidence on the object field.

An optical system (10) includes an arrangement for splitting a source beam into a measurement beam and a reference beam. The reference beam is reflected off a reflective element (42) which mounted on a delay line (44). A target (35) scatters the radiation from the measurement beam. The scattered radiation and the reference beam are brought to interfere on a detector (40) by calibrating the delay line (44). The detected interference pattern is Fourier-transformed and filtered to select a region of interest around a side-band of the Fourier-transformed interference pattern in order to remove noise caused by stray radiation that hits the detector.

When a reticle is first used, the reticle is loaded in a projection exposure device and measured by either oblique measurement or random measurement, thereby avoiding the fear of uneven sampling and determining the reticle transmittance of the entire reticle as the parent population, without increasing the sampling count. The same effect can be obtained by making the measurement spot size, which is fixed in general, variable and by changing the angle of incidence in relation to the measurement spot size.

When a reticle is first used, the reticle is loaded in a projection exposure device and measured by either oblique measurement or random measurement, thereby avoiding the fear of uneven sampling and determining the reticle transmittance of the entire reticle as the parent population, without increasing the sampling count. The same effect can be obtained by making the measurement spot size, which is fixed in general, variable and by changing the angle of incidence in relation to the measurement spot size.

Microlithography projection objectives for imaging into an image plane a pattern arranged in an object plane are described with respect to suppressing false light in such projection objectives.