Systems for cleaning optical surfaces of overlay inspection systems are disclosed. In particular, systems for optical-path coupling of light for in-situ photochemical cleaning in projection imaging systems are disclosed. A system for cleaning optical surfaces of overlay inspection systems includes a first illumination source, a detector, a set of illumination optics, and a set of imaging optics. In some embodiments, the system may include at least one of a second illumination source and a third illumination source, each of which may be configured to cause or aid the removal of contaminants from one or more optical surfaces of the system.

An extreme ultraviolet (EUV) collector inspection apparatus includes a light blocking cover covering a front surface of an EUV collector to be inspected and providing a space portion in which external light is blocked, a light source in the space portion, the light source having a pillar shape extending along a central axis of the EUV collector, the light source configured to output irradiated light ranging from an ultraviolet (UV) band to a visible light (VIS) band, and a spectrometer above the light source and configured to detect a spectrum of reflected light from the irradiated light reflected from the front surface of the EUV collector. The apparatus or a controller associated therewith may be configured to inspect a contamination state of the front surface of the EUV collector based on the spectrum of reflected light.

A method for inspecting an extreme ultraviolet (EUV) light source includes: removing a collector mirror of the EUV light source from a collector chamber; installing an inspection apparatus within the collector chamber, the apparatus including a selectively extendable and retractable member and a camera at one end of the member; operating a first actuator to extend the member along a path through the interior chamber of the EUV light source, thereby moving the camera to a given position within the interior chamber of the EUV light source; operating a second actuator to pan the camera about an axis of rotation, thereby establishing a given camera orientation within the interior of the EUV light source; and, capturing an image of the interior chamber of the EUV light source with the camera while the camera is at the given position and orientation established by the operation of the first and second actuators.

A lithography apparatus is disclosed, which comprises a mirror having at least two mirror segments which are joined together in such a way that an interspace is formed between the mirror segments, and a sensor for detecting the relative position of the mirror segments, wherein the sensor is arranged in the interspace between the mirror segments.

A method for controlling a vibrating optical element of a lithographic system the optical element having a predetermined number of degrees of freedom comprises: detecting a number of displacements of the optical element, each displacement corresponding to a degree of freedom, wherein the number of detected displacements is larger than the number of degrees of freedom; for each displacement according to a degree of freedom, generating a sensor signal corresponding to a movement in a degree of freedom; wherein the optical element moves as a function of a rigid body transformation matrix, the optical element movement including a first type of movement and a second type of movement; and modifying the sensor signals as a function of a modified transformation matrix, wherein the modified transformation matrix at least partially reduces at least one eigen mode or resonance of one of the first type of movements or the second type of movements.

An extreme ultraviolet (EUV) collector inspection apparatus and method capable of precisely inspecting a contamination state of an EUV collector and EUV reflectance in accordance with the contamination state are provided. The EUV collector inspection apparatus includes a light source arranged in front of an EUV collector to be inspected and configured to output light in a visible light (VIS) band from UV rays, an optical device configured to output narrowband light from the light, and a camera configured to perform imaging from an UV band to a VIS band. An image by wavelength of the EUV collector is obtained by using the optical device and the camera and a contamination state of the EUV collector is inspected.

A spheroidal mirror reflectivity measuring apparatus for extreme ultraviolet light may include an extreme ultraviolet light source, an optical system, and a first photosensor. The extreme ultraviolet light source may be configured to output extreme ultraviolet light to a spheroidal mirror that includes a spheroidal reflection surface. The optical system may be configured to allow the extreme ultraviolet light to travel to the spheroidal reflection surface via a first focal position of the spheroidal mirror. The first photosensor may be provided at a second focal position of the spheroidal mirror, and may be configured to detect the extreme ultraviolet light that has passed through the first focal position and then has been reflected by the spheroidal reflection surface.

Disclosed is an illumination system for delivering incoherent radiation to a metrology sensor system. Also disclosed is an associated metrology system and method. The illumination system comprises a spatial filter system for selective spatial filtering of a beam of said incoherent radiation outside of a module housing of the metrology sensor system. At least one optical guide is provided for guiding the spatially filtered beam of incoherent radiation to the metrology sensor system, the at least one optical guide being such that the radiation guided has a substantially similar output angle as input angle.

A measurement illumination optical unit guides illumination light into an object field of a projection exposure apparatus for EUV lithography. The illumination optical unit has a field facet mirror with a plurality of field facets and a pupil facet mirror with a plurality of pupil facets. The latter serve for overlaid imaging in the object field of field facet images of the field facets. A field facet imaging channel of the illumination light is guided via any one field facet and any one pupil facet. A field stop specifies a field boundary of an illumination field in the object plane. The illumination field has a greater extent along one field dimension than any one of the field facet images. At least some of the field facets include tilt actuators which help guide the illumination light into the illumination field via various field facets and one and the same pupil facet.

The invention relates to a method for compensating at least one defect of an optical system which includes introducing an arrangement of local persistent modifications in at least one optical element of the optical system, which does not have pattern elements on one of its optical surfaces, so that the at least one defect is at least partially compensated.