Abstract: A system and method for cleaning an optical element of an EUV optical system is disclosed. The system and method may include receiving design data of one or more samples. The system and method may include simulating a plurality of irradiance distributions at a plane of an EUV optical sub-system based on the design data and one or more parameters. The system and method may include aggregating the plurality of irradiance distributions to generate an aggregated irradiance distribution. The system and method may include determining a predicted contaminate distribution based on both the aggregated irradiance distribution and a contaminate growth rate. The system and method may include determining a cleaning recipe for the one or more optical elements based on the predicted contaminate distribution.

Abstract: An extreme ultraviolet (EUV) light source includes a vacuum chamber with a rotating target assembly therein. The rotating target assembly has an annular groove with a distal wall relative to an axis of rotation. The distal wall includes a porous region. The rotating target assembly is rotated to form a target by centrifugal force with a layer of molten metal on a distal wall of an annular groove in the rotating target assembly.

Abstract: A photomask includes a plurality of distinctly patterned regions to provide different respective intensities of extreme ultraviolet (EUV) light in response to illumination with an EUV beam. The photomask may be part of a system that also includes a time-delay-integration (TDI) inspection tool with an EUV light source and a TDI sensor. The EUV light source is to generate the EUV beam. The photomask is to be loaded into the TDI inspection tool. The system further includes a reference intensity detector to be mounted in the TDI inspection tool to measure intensities of EUV light collected from the photomask.

Abstract: To calibrate a TDI photomask inspection tool, a photomask with a plurality of distinctly patterned regions is loaded into the tool. The plurality of distinctly patterned regions is successively illuminated with an EUV beam of light. While illuminating respective distinctly patterned regions, respective instances of imaging of the respective distinctly patterned regions are performed using a TDI sensor in the inspection tool. While performing the respective instances of imaging, a reference intensity detector is used to measure reference intensities of EUV light collected from the photomask. Based on the results of the respective instances of imaging and the measured reference intensities of EUV light, linearity of the TDI sensor is determined.

Abstract: An acousto-optic modulator (AOM) laser frequency shifter system includes a laser configured to generate an incident beam, a first optical splitter optically coupled to the laser and configured to split the incident beam into at least one portion of the incident beam, at least one phase-shift channel optically coupled to the first optical splitter and configured to generate at least one frequency-shifted beam with an acousto-optic modulator (AOM) from the at least one portion of the incident beam received from the first optical splitter, and a second optical splitter configured to receive the at least one frequency-shifted beam from the at least one phase-shift channel and configured to direct the at least one frequency-shifted beam to an interferometer configured to acquire an interferogram of a sample with the at least one frequency-shifted beam.

Abstract: Heights on a surface of a photomask are measured using broadband light interferometry. The heights include heights of patterned areas of the photomask. A focal map is produced from the measured heights on the surface of the photomask. To produce the focal map, the measured heights of the patterned areas are adjusted based on fill factors for the patterned areas. The photomask is inspected for defects, using the focal map.

Abstract: An optical system with aberration correction is disclosed. The optical system may include an illumination source. The optical system may include a detector. The optical system may include one or more collection optics configured to image a sample onto the detector based on illumination from the illumination source. The optical system may include two or more aberration correction plates located in one or more pupil planes of the one or more collection optics. The two or more aberration correction plates may provide at least partial correction of two or more linearly-independent aberration terms. Any particular one of the two or more aberration correction plates may have a spatially-varying thickness profile providing a selected amount of correction for a single particular aberration term of the two or more linearly-independent aberration terms.

Abstract: A photomask-inspection system includes a vacuum chamber and a stage, disposed in the vacuum chamber, to support a photomask and to translate the photomask horizontally and vertically. The system also includes an EUV objective, disposed in the vacuum chamber, to collect EUV light from the photomask to inspect the photomask for defects and an optical height sensor, at least partially disposed in the vacuum chamber, to measure heights on a surface of the photomask. The system further includes a stage controller to translate the stage horizontally and vertically in accordance with a focal map for the photomask produced using the measured heights on the surface of the photomask.

Abstract: Reference and test waves are directed in a common path mode in a fiber tip diffraction interferometer. A first fiber can be used to generate the reference wave and a second fiber can be used to generate the test wave. Each fiber can include a single mode fiber tip that defines a wedge at an end without a coating on end surface or a tapered fiber tip. The fiber tip diffraction interferometer can include an aplanatic pupil imaging lens or system disposed to receive both the test wave and the reference wave and a sensor configured to receive both the test wave and the reference wave.

Abstract: Disclosed are methods and apparatus for inspecting a photolithographic reticle. A plurality of reference far field images are simulated by inputting a plurality of reference near field images into a physics-based model, and the plurality of reference near field images are generated by a trained deep learning model from a test portion of the design database that was used to fabricate a test area of a test reticle. The test area of a test reticle, which was fabricated from the design database, is inspected for defects via a die-to-database process that includes comparing the plurality of reference far field reticle images simulated by the physic-based model to a plurality of test images acquired by the inspection system from the test area of the test reticle.

Abstract: Disclosed are methods and apparatus for inspecting a photolithographic reticle. A near field reticle image is generated via a deep learning process based on a reticle database image produced from a design database, and a far field reticle image is simulated at an image plane of an inspection system via a physics-based process based on the near field reticle image. The deep learning process includes training a deep learning model based on minimizing differences between the far field reticle images and a plurality of corresponding training reticle images acquired by imaging a training reticle fabricated from the design database, and such training reticle images are selected for pattern variety and are defect-free.

Abstract: An inspection system includes an illumination source configured to generate extreme ultraviolet (EUV) light, illumination optics to direct the EUV light to a sample within a range of off-axis incidence angles corresponding to an illumination pupil distribution, collection optics to collect light from the sample in response to the incident EUV light within a range of collection angles corresponding to an imaging pupil distribution, and a detector configured to receive at least a portion of the light collected by the collection optics. Further, a center of the illumination pupil distribution corresponds to an off-axis incidence angle along a first direction on the sample, and at least one of the illumination pupil distribution or the imaging pupil distribution is non-circular with a size along the first direction shorter than along a second direction perpendicular to the first direction.

Abstract: An acousto-optic modulator (AOM) laser frequency shifter system includes a laser configured to generate an incident beam, a first optical splitter optically coupled to the laser and configured to split the incident beam into at least one portion of the incident beam, at least one phase-shift channel optically coupled to the first optical splitter and configured to generate at least one frequency-shifted beam with an acousto-optic modulator (AOM) from the at least one portion of the incident beam received from the first optical splitter, and a second optical splitter configured to receive the at least one frequency-shifted beam from the at least one phase-shift channel and configured to direct the at least one frequency-shifted beam to an interferometer configured to acquire an interferogram of a sample with the at least one frequency-shifted beam.

Abstract: Reference and test waves are directed in a common path mode in a fiber tip diffraction interferometer. A first fiber can be used to generate the reference wave and a second fiber can be used to generate the test wave. Each fiber can include a single mode fiber tip that defines a wedge at an end without a coating on end surface or a tapered fiber tip. The fiber tip diffraction interferometer can include an aplanatic pupil imaging lens or system disposed to receive both the test wave and the reference wave and a sensor configured to receive both the test wave and the reference wave.

Abstract: Heights on a surface of a photomask are measured using broadband light interferometry. The heights include heights of patterned areas of the photomask. A focal map is produced from the measured heights on the surface of the photomask. To produce the focal map, the measured heights of the patterned areas are adjusted based on fill factors for the patterned areas. The photomask is inspected for defects, using the focal map.

Abstract: To calibrate a TDI photomask inspection tool, a photomask with a plurality of distinctly patterned regions is loaded into the tool. The plurality of distinctly patterned regions is successively illuminated with an EUV beam of light. While illuminating respective distinctly patterned regions, respective instances of imaging of the respective distinctly patterned regions are performed using a TDI sensor in the inspection tool. While performing the respective instances of imaging, a reference intensity detector is used to measure reference intensities of EUV light collected from the photomask. Based on the results of the respective instances of imaging and the measured reference intensities of EUV light, linearity of the TDI sensor is determined.

Abstract: A metrology system for measuring wave-front aberration of an extreme ultraviolet (EUV) mask inspection system is disclosed. The test mask includes a substrate formed from a material having substantially no reflectivity for EUV illumination, and one or more patterns formed on the substrate, the one or more patterns having a reflective portion configured to reflect EUV illumination, positioned in a common plane with an absorption portion having substantially no reflectivity for EUV illumination, on or above the substrate.

Abstract: An inspection system includes an illumination source configured to generate extreme ultraviolet (EUV) light, illumination optics to direct the EUV light to a sample within a range of off-axis incidence angles corresponding to an illumination pupil distribution, collection optics to collect light from the sample in response to the incident EUV light within a range of collection angles corresponding to an imaging pupil distribution, and a detector configured to receive at least a portion of the light collected by the collection optics. Further, a center of the illumination pupil distribution corresponds to an off-axis incidence angle along a first direction on the sample, and at least one of the illumination pupil distribution or the imaging pupil distribution is non-circular with a size along the first direction shorter than along a second direction perpendicular to the first direction.

Abstract: Disclosed are methods and apparatus for inspecting an extreme ultraviolet (EUV) reticle using an optical inspection tool. An inspection tool having a pupil filter positioned at an imaging pupil is used to obtain a test image or signal from an output beam that is reflected and scattered from a test portion of an EUV test reticle. The pupil filter is configured to provide phase contrast in the output beam. A reference image or signal is obtained for a reference reticle portion that is designed to be identical to the test reticle portion. The test and reference images or signals are compared and it is determined whether the test reticle portion has any candidate defects based on such comparison. For each of a plurality of test reticle portions of the reticle, the operations for using the inspection tool, obtaining a reference image or signal, comparing, and determining are repeated. A defect report is generated based on any candidate defects that have been determined to be present.

Abstract: Block-to-block reticle inspection includes acquiring a swath image of a portion of a reticle with a reticle inspection sub-system, identifying a first occurrence of a block in the swatch image and at least a second occurrence of the block in the swath image substantially similar to the first occurrence of the block and determining at least one of a location, one or more geometrical characteristics of the block and a spatial offset between the first occurrence of the block and the at least a second occurrence of the block.