Abstract: An interferometry method for determining information about a test object includes directing test light to the test object positioned at a plane, wherein one or more properties of the test light vary over a range of incidence angles at the plane, the properties of the test light being selected from the group consisting of the spectral content, intensity, and polarization state; subsequently combining the test light with reference light to form an interference pattern on a multi-element detector so that different regions of the detector correspond to different angles of the test light emerging from the test object, wherein the test and reference light are derived from a common source; monitoring the interference pattern using the multi-element detector while varying an optical path difference between the test light and the reference light; determining the information about the test object based on the monitored interference pattern.

Abstract: In general, in a first aspect, the invention features a system including an interferometer configured to direct test light to an overlay target and subsequently combine it with reference light to form an interference pattern, the test and reference light being derived from a common source, a multi-element detector, one or more optics to image the overlay target on the multi-element detector; and an electronic processor in communication with the multi-element detector. The overlay target includes a first pattern and a second pattern and the electronic processor is configured to determine information about the relative alignment between the first and second patterns.

Abstract: An encoder interferometry system includes an interferometer positioned to receive first and second beams having different frequencies, in which the interferometer has at least one polarizing beam splitting element for directing the first beam along a measurement path to define a measurement beam and the second beam along a reference path to define a reference beam. The encoder interferometry system further includes a encoder scale positioned to diffract the measurement beam at least once, a detector positioned to receive the measurement and reference beams after the measurement beam diffracts from the encoder scale, and an output component positioned to receive the measurement and reference beams before they reach the detector and deflect spurious portions of the first and second beam away from the detector.

Abstract: A method for determining information about changes along a degree of freedom of an encoder scale includes directing a first beam and a second beam along different paths and combining the first and second beams to form an output beam, where the first and second beams are derived from a common source, the first and second beams have different frequencies, where the first beam contacts the encoder scale at a non-Littrow angle and the first beam diffracts from the encoder scale at least once; detecting an interference signal based on the output beam, the interference signal including a heterodyne phase related to an optical path difference between the first beam and the second beam; and determining information about a degree of freedom of the encoder scale based on the heterodyne phase.

Abstract: Methods and apparatuses for performing the same, where the methods include obtaining, from an interferometer, a time-varying interference signal S(t) based on a combination of a first beam and a second beam, the first beam being diffracted from an encoder scale, in which at least one of the encoder scale and the interferometer is moveable with respect to the other, obtaining one or more error correction signals based on one or more errors that modify the time-varying interference signal S(t), and outputting information about a change in a position of the encoder scale relative to the interferometer based on the time-varying interference signal S(t) and the one or more error correction signals.

Abstract: Methods for forming a three-dimensional image of a test object include directing light to a surface of best-focus of an imaging optic, where the light has an intensity modulation in at least one direction in the surface of best-focus, scanning a test object relative to the imaging optic so that a surface of the measurement object passes through the surface of best-focus of the imaging optic as the test object is scanned, acquiring, for each of a series of positions of the test object during the scan, a single image of the measurement object using the imaging optic, in which the intensity modulation of the light in the surface of best-focus is different for successive images, and forming a three-dimensional image of the test object based on the acquired images.

Abstract: Systems are disclosed that include an interferometer configured to direct test light to an overlay test pad and subsequently combine it with reference light, the test and reference light being derived from a common source, one or more optics configured to direct at least a portion of the combined light to a multi-element detector so that different regions of the detector correspond to different illumination angles of the overlay test pad by the test light, the detector being configured to produce an interference signal based on the combined light, and an electronic processor in communication with the multi-element detector. The overlay test pad comprises a first patterned structure and a second patterned structure and the electronic processor is configured to determine information about the relative alignment between the first and second patterned structures based on the interference signal.

Abstract: An imaging interferometer includes optics defining an interferometric cavity, in which the optics include a first beam-splitting optic positioned to separate an input beam into a test beam and a reference beam, a second beam-splitting optic positioned to transmit the test beam to the test surface, receive the test beam back from the test surface, and thereafter recombine the test beam with the reference beam, and a third optic positioned to direct the reference beam from the first optic to the second optic. The interferometric cavity defines a virtual reference surface positioned along a path for the reference beam between the second and third optics. The interferometer also includes an imaging channel positioned to receive the recombined test and reference beams, where the imaging channel includes an imaging detector, and at least one imaging element configured to image the test surface and the virtual reference surface onto the detector.

Abstract: A method includes fitting a function to a subset of reflectivity data comprising values for the reflectivity of a test object for different wavelengths, different scattering angles, and/or different polarization states; determining values for the function at certain wavelengths and scattering angles and/or polarization states; and determining information about the test object based on the determined values.

Abstract: A method for determining information about a test object includes combining two or more scanning interference signals to form a synthetic interference signal; analyzing the synthetic interference signal to determine information about the test object; and outputting the information about the test object. Each of the two or more scanning interference signals correspond to interference between test light and reference light as an optical path length difference between the test and reference light is scanned, wherein the test and reference light are derived from a common source. The test light scatters from the test object over a range of angles and each of the two or more scanning interferometry signals corresponds to a different scattering angle or polarization state of the test light.

Abstract: A method includes comparing a scanning interferometry signal obtained for a location of a test object to each of multiple model signals corresponding to different model parameters for modeling the test object, wherein for each model signal the comparing includes calculating a correlation function between the scanning interferometry signal and the model signal to identify a surface-height offset between the scanning interferometry signal and the model signal and, based on the identified surface-height offset, calculating a height-offset compensated merit value indicative of a similarity between the scanning interferometry signal and the model signal for a common surface height. The method further includes, based on the respective merit values for the different model signals, determining a test object parameter at the location of the test object.

Abstract: A lapping or polishing machine includes a material having a first finishing surface to process a surface of a work item, a measuring tool to measure a contour of the first finishing surface, and a conditioning tool having a second finishing surface to process the first finishing surface to reduce a difference between the measured contour and a desired contour of the first finishing surface.

Abstract: In certain aspects, interferometry methods are disclosed that include providing one or more interferometry signals for a test object, wherein the interferometry signals correspond to a sequence of optical path difference (OPD) values which are not all equally spaced from one another because of noise, providing information about the unequal spacing of the sequence of OPD values, decomposing each of the interferometry signals into a contribution from a plurality of basis functions each corresponding to a different frequency and sampled at the unequally spaced OPD values, and using information about the contribution from each of the multiple basis functions to each of the interferometry signals to determine information about the test object.

Abstract: An apparatus includes an interferometer configured to generate an interference pattern by combining test light from a test object with reference light reflected from a reference object, the interferometer being further configured to direct at least a first part of a monitor test beam to the test object at a first incident angle and at least a second part of a monitor reference beam to the reference object at a second incident angle, and recombine the first part and the second part of the monitor beams after they reflect from the test and reference surfaces to interfere with one another and form a monitor pattern, where the first and second angles cause the monitor pattern to have spatial interference fringes, and wherein a change in the position of the interference fringes is indicative of a change in a relative position between the test and reference objects.

Abstract: A method for determining a spatial property of an object includes obtaining a scanning low coherence interference signal from a measurement object that includes two or more interfaces. The scanning low coherence interference signal includes two or more overlapping low coherence interference signals, each of which results from a respective interface. Based on the low coherence interference signal, a spatial property of at least one of the interfaces is determined. In some cases, the determination is based on a subset of the low coherence interference signal rather than on the entirety of the signal. Alternatively, or in addition, the determination can be based on a template, which may be indicative of an instrument response of the interferometer used to obtain the low coherence interference signal.

Abstract: In certain aspects, disclosed methods include directing test light reflected from an object to form an image of the object on a detector, where the object includes a diffractive structure. The test light at the detector includes both specularly and non-specularly reflected light from the diffractive structure, and the diffractive structure is under-resolved in the image. The method further includes directing reference light to interfere with the test light at the detector where the reference and test light being derived from a common source, varying an optical path length difference between the test and reference light, acquiring an interference signal from the detector while varying the optical path length difference, and determining information about the diffractive structure based on the interference signal and on predetermined information derived from a mathematical model of light reflection from a model diffractive structure.

Abstract: An optical assembly for use in an interferometer is provided. The optical assembly includes first and second partially reflective surfaces positioned along an optical axis and oriented at different non-normal angles to the optical axis. The second partially reflective surface is configured to receive light transmitted through the first partially reflective surface along the optical path, transmit a portion of the received light to a test object to define measurement light for the interferometer and reflect another portion of the received light back towards the first partially reflective surface to define reference light for the interferometer. The reference light makes at least one round trip path between the second and first partially reflective surfaces.

Abstract: A method for determining information about changes along a degree of freedom of an encoder scale includes directing a first beam and a second beam along different paths and combining the first and second beams to form an output beam, where the first and second beams are derived from a common source, the first and second beams have different frequencies, where the first beam contacts the encoder scale at a non-Littrow angle and the first beam diffracts from the encoder scale at least once; detecting an interference signal based on the output beam, the interference signal including a heterodyne phase related to an optical path difference between the first beam and the second beam; and determining information about a degree of freedom of the encoder scale based on the heterodyne phase.

Abstract: In general, in one aspect, the invention features apparatus that includes a broadband scanning interferometry system including interferometer optics for combining test light from a test object with reference light from a reference object to form an interference pattern on a detector, wherein the test and reference light are derived from a common light source. The interferometry system further includes a scanning stage configured to scan an optical path difference (OPD) between the test and reference light from the common source to the detector and a detector system including the detector for recording the interference pattern for each of a series of OPD increments, wherein the frequency of each OPD increment defines a frame rate. The interferometer optics are configured to produce at least two monitor interferometry signals each indicative of changes in the OPD as the OPD is scanned, wherein the detector system is further configured to record the monitor interferometry signals.

Abstract: A method and a system for measuring the relief of an object are described herein. The system includes a grid projecting for projecting a grid, an image acquisition apparatus that includes a camera, and a computer. Providing a reference object having common elements with the object to measure, the method includes the steps of a) positioning the grid at three different known positions relative to the camera and the common elements; b) for each position of the grid, projecting the grid unto the reference object and, with the camera, taking an image of the reference object to yield three images having values for each pixel of the camera and c) computing the reference object phase for each pixel using the three reference object intensity values for the corresponding pixel. Steps a), b) and c) are repeated by replacing the reference object by the object to be measured.