Abstract: The invention features an apparatus including a first portion defining an optical axis and configured to connect to an optical fiber, a second portion having a reference surface configured to connect with a terminal, and a third portion between the first and second portions. The third portion bends more easily than either the first or second portion to permit adjustable alignment of the optical axis relative to the reference surface.

Abstract: A method including comparing information derivable from a scanning interferometry signal for a first surface location of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parametrized by a series of characteristics for the test object. The derivable information being compared may relate to a shape of the scanning interferometry signal for the first surface location of the test object.

Abstract: Methods and apparatus that combine the techniques of reversal (or self-calibration) to provide a low spatial frequency measurement of a part shape, independent of systematic errors in the staging used to move the part and small aperture interferometry to provide high spatial frequency information on a large part. The low spatial frequency is used to establish the rigid body motions (e.g., tip, tilt, and piston for a plano object) to be applied to the individual sub-apertures of interferometric data in stitching them together to give a full map at high resolution of the whole part. No overlap between sub-apertures is required.

Abstract: Interferometric scanning method(s) and apparatus for measuring optics either having aspherical surfaces or that produce aspherical wavefronts. A test optic is aligned and moved with respect to a scanning axis relative to the origin of a known spherical wavefront that is generated with a reference surface to intersect the test optic at the apex of the aspherical surface and at radial zones where the spherical wavefront and the aspheric surface possess common tangents. The test surface is imaged onto a space resolving detector to form interferograms containing phase information about the differences in optical path length between the reference surface and the test surface while the axial distance which the test optic moves relative to the spherical reference surface is interferometrically measured. The deviation in the shape of the aspheric surface from its design in a direction normal to the aspheric surface is determined and reported.

Abstract: An apparatus including: (i) an interferometer positioned to derive measurement and reference wavefronts from a source of electromagnetic radiation, wherein the interferometer is configured to direct the measurement wavefront to reflect from a measurement surface and the reference wavefront to reflect from a reference surface, and further directs reflected measurement and reflected reference wavefronts to overlap with one another and to form an interference pattern; (ii) an auxiliary optic having a curved reflective surface positioned to redirect the measurement wavefront between the interferometer and the measurement surface; and (iii) a translation stage, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a zero optical path length difference between the measurement and reference wavefronts, and wherein the translation stage is configured to scan the optical measur

Abstract: An apparatus includes an interferometer having a polarizing beam splitter to split an input beam into a measurement beam and a reference beam, the measurement beam contacting a measurement object, the reference beam contacting a reference object. The interferometer includes at least one thin retarder on a surface of the interferometer.

Abstract: An interferometry system includes an interferometer to split an input beam into a measurement beam and at least one other beam. The interferometer directs the measurement beam along a measurement path that includes at least two passes to a measurement object, and overlaps the measurement beam with the other beam after the measurement beam completes the at least two passes. The path of the measurement beam is sheared during the first and second passes when the measurement object moves along a direction orthogonal to a portion of the measurement path that contacts the measurement object. The interferometry system includes optics to redirect the measurement beam after the first pass and before the second pass so that shear imparted during the second pass cancels shear imparted during the first pass.

Abstract: In general, in one aspect, the invention features an interferometer assembly for use in a lithography tool used for fabricating integrated circuits on a wafer, wherein the lithography tool includes a support structure and a stage for positioning the wafer relative to the support structure, the interferometer assembly including an interferometer configured to direct a measurement beam between the stage and the support structure and combine the measurement beam with another beam to form an output beam which includes a phase related to a position of the stage relative to the support structure, wherein the interferometer is mechanically secured to the lithography tool through an interferometer surface selected to cause the phase of the output beam to be insensitive to thermal changes of the interferometer over a range of temperatures.

Abstract: A computer-based stroboscopic interferometric microscope system for measuring the topography of a microscopic vibratory object includes an interferometric microscope equipped with a multiple-color (e.g., LED) or white-light source, a mechanical scanning apparatus for varying the optical path difference between the vibratory object and a reference surface, a camera having a two-dimensional detector array, and digital signal processing apparatus for determining surface height from interference data. Interferograms for each of the detector image points in the field of view are generated simultaneously by scanning the object in a direction approximately perpendicular to the object surface illuminated stroboscopically while recording detector data in digital memory.

Abstract: A test surface of a test object is measured with respect to a reference surface to generate a first relative surface measurement, where the test surface is in a first position relative to the reference surface. The test surface is measured with respect to the reference surface to generate a second relative surface measurement, where the test surface is in a second position relative to the reference surface different from the first position. Estimates of a rotationally varying part of a measurement of the test surface and a rotationally varying part of a measurement of the reference surface are provided. An estimate of a rotationally invariant part of the measurement of the test surface is calculated at a plurality of radial values based on a combination of the relative surface measurements, the provided estimates, and a difference between the first and second relative positions.

Abstract: Methods and related systems for determining properties of optical systems (e.g., interferometers) and/or optical elements (e.g., lenses and/or lens systems) are described. For example, information related to an optical thickness mismatch of an interferometer can be determined by providing scanning interferometry data. The data typically include obtaining one or more interference signals each corresponding to a different spatial location of a test object. A phase is determined for each of multiple frequencies of each interference signal. The information related to the optical thickness mismatch is determined based on the phase for each of the multiple frequencies of the interference signal(s).

Abstract: A method including: imaging test light emerging from a test object over a range of angles to interfere with reference light on a detector, wherein the test and reference light are derived from a common source; for each of the angles, simultaneously varying an optical path length difference from the source to the detector between interfering portions of the test and reference light at a rate that depends on the angle at which the test light emerges from the test object; and determining an angle-dependence of an optical property of the test object based on the interference between the test and reference light as the optical path length difference is varied for each of the angles.

Abstract: An apparatus including: a multi-axis interferometry system configured to receive an input beam and direct at least two beams derived from the input beam to contact different locations on a measurement object to monitor changes in an angular orientation of the measurement object; a beam steering assembly having a beam steering element positioned to direct the input beam into the interferometry system and a positioning system to selectively orient the beam steering element relative to the interferometry system; and a control circuit which during operation orients the beam steering element based on the changes in the angular orientation of the measurement object monitored by the interferometry system.

Abstract: Conical surfaces (and other complex surface shapes) can be interferometrically characterized using a locally spherical measurement wavefront (e.g., spherical and aspherical wavefronts). In particular, complex surface shapes are measured relative to a measurement point datum. This is achieved by varying the radius of curvature of a virtual surface corresponding to a theoretical test surface that would reflect a measurement wavefront to produce a constant optical path length difference (e.g., zero OPD) between the measurement and reference wavefronts.

Abstract: A method including comparing information derivable from a scanning interferometry signal for a first surface location of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parametrized by a series of characteristics for the test object. The derivable information being compared may relate to a shape of the scanning interferometry signal for the first surface location of the test object.

Abstract: An interferometry method includes: imaging test light reflected from at least a first portion of a test surface to interfere with reference light on a camera and form an interference pattern, wherein the imaging defines a depth of focus for the light reflected from the test surface, and wherein the test light and reference light are derived from a common source; varying an optical path length difference between the test light and reference light over a range larger than the depth of focus, wherein the optical path length difference corresponds to a difference between a first optical path between the common source and the camera for the test light and a second optical path between the common source and the camera for the reference light; and maintaining the first portion of the test surface within the depth of focus as the optical path length difference is varied.

Abstract: A microlithography method includes: interferometrically measuring information about a position of a microlithography stage with respect to each of multiple metrology axes during a photolithographic exposure cycle; analyzing the position information to determine correction factors indicative of a local slope on a side of the stage used to reflect an interferometric measurement beam and optical gradients caused by environmental effects produced by the photolithographic exposure cycle; and applying the correction factors to subsequent interferometric measurements of the stage.

Abstract: A method including: generating a sequence of phase-shifted interferometry images of an object surface relative to a reference surface; and calculating an unequally weighted average of the phase-shifted interferometry images to produce a final image. The final image can be useful as a lateral metrology image. The method may further include calculating a surface topography image from the sequence of phase-shifted interferometry images. Embodiments further include apparatus related to the method.

Abstract: The invention features a system and method for reducing the contribution of cyclic errors to an interferometric position measurement of a movable stage. An initial interferometric position measurement of the stage is averaged with at least one additional measurement corresponding to a displacement(s) of the stage from its initial position. The displacements are selected to reduce the overall cyclic error contribution to an average position measurement. As a result, the average position of the stage can be measured more accurately than any of its individual positions. The average position can be used to more accurately determine the average position of an alignment mark on a wafer carried by the stage. Furthermore, the averaging described above can be applied to additional interferometric measurement axes.

Abstract: An interferometric apparatus includes: a polarizing beam-splitting interface positioned to separate an input beam into two orthogonally polarized beams; and interferometer optics positioned to receive a first set of beams derived from one of the orthogonally polarized beams and a second set of beams derived from the other of the orthogonally polarized beams. The interferometer optics are configured to direct each beam in the first set to contact different locations of a measurement object at least once, and subsequently combine each beam in the first set with a corresponding beam from the second set of beams to produce a corresponding output beam comprising information about changes in the position of the measurement object with respect to a different degree of freedom.