Abstract: An apparatus for optical measurement of an object, especially for measuring movement, is provided, which includes an interferometer for measuring movements along the measurement beam of the interferometer, as well as a confocal auto-focus microscope. The interferometer is coupled in the beam path of the confocal auto-focus microscope, such that the measurement beam of the interferometer is simultaneously the focusing beam of the microscope. Here, it is guaranteed that the interferometric movement measurement is always performed at the focal point of the microscope that is used. This enables automatic correction of the Guoy effect for objectives with high numerical aperture. In addition, for the use of a scanning confocal auto-focus microscope, data sets of test objects can also be measured, which comprise their vibrational behavior, height profile, and optionally also their in-plane movement behavior.

Abstract: Described are a multiple channel interferometric surface contour measurement system and methods of determining surface contour data for the same. The measurement system includes a multiple channel interferometer projector, a digital camera and a processor. Fringe patterns generated by spatially separate channels in the projector are projected onto an object surface to be measured. The digital camera acquires images of the fringe patterns and the processor determines surface contour data from the fringe patterns. More specifically, fringe numbers arc determined for points on the object surface based on image data. The fringe numbers are modified according to collinear adjustment values so that the modified fringe numbers correspond to a common, collinear axis for the interferometer projector. After unwrapping the modified fringe numbers, the unwrapped values are modified by the collinear adjustment values to obtain accurate fringe numbers for the pixels in each interferometer channel.

Abstract: Provided are methods to be carried out prior to, while, and/or after performing a photolithographic process to a wafer that involve wafer misalignment assessment. The method involves obtaining curvature and/or deformation information of a surface of the wafer over a plurality of locations so as to obtain a curvature map of the wafer. The curvature map is processed to obtain a stress map of the wafer. The stress map is used to determine displacement of a layer of the wafer. The displacement information is used to determine a degree of misalignment in the photolithographic process.

Abstract: Disclosed is a system including: (i) an interferometer configured to direct test electromagnetic radiation to a test surface and reference electromagnetic radiation to a reference surface and subsequently combine the electromagnetic radiation to form an interference pattern, the electromagnetic radiation being derived from a common source; (ii) a multi-element detector; (iii) one or more optics configured to image the interference pattern onto the detector so that different elements of the detector correspond to different illumination angles of the test surface by the test electromagnetic radiation; and (iv) an electronic processor coupled to the detector, wherein the electronic processor is configured to process information measured by the detector to determine information about a test object having the test surface. The measurements made by the detector elements provide ellipsometry/reflectometry data for the test surface.

Abstract: An integrated interference scanning method, mainly used to integrate the respective advantages of VSI and PSI measurements, hereby achieving the characteristic of high precision and limitless measurement range. In particular, the slope correction factor and the displacement correction factor between the VSI measurement and PSI measurement may be utilized to execute the integration calculation of the height data arrays of the VSI and PSI, so that the scanning procedure may be achieved through merely using the wideband light source of the interference scanning system, as such reducing the errors and complexity of the interference scanning system.

Abstract: A method estimates a nonlinearity profile of a material. The method includes providing a magnitude of a transform of a measured nonlinearity profile measured from the material. The method further includes providing an estimated phase term of the transform of the measured nonlinearity profile. The method further includes multiplying the magnitude and the estimated phase term to generate an estimated transform. The method further includes calculating an inverse transform of the estimated transform. The method further includes calculating a real component of the inverse transform to generate an estimated nonlinearity profile.

Abstract: A method of measuring topology of functional liquid in a pixel, in which thickness or volume of the functional liquid in the pixel is measured by a surface topology measuring apparatus comprising: measuring surface topologies in which surface topology of the functional liquid in the pixel and surface topology of the bank are measured by the surface topology measuring apparatus, and measurement parameters regarding the surface topologies are generated; adding a bank height in which a height parameter of a height of the bank is added to the measurement parameter of a surface of the functional liquid in the pixel of the measurement parameter generated; and calculating topology in which the thickness or the volume of the functional liquid in the pixel is calculated based on the added measurement parameter of the surface of the functional liquid in the pixel and the measurement parameter of the surface of the bank.

Abstract: A method is disclosed which includes: using a scanning interferons dry system, generating a sequence of phase-shifted interferometry images at different scan positions of an object comprising a buried surface, identifying a scan position corresponding to a position of best focus for the buried surface based on the sequence of phase-shifted interferometry images of the object, and generating a final image based on the phase-shifted interferometry images and the scan position, where the interferometric fringes in the final image are reduced relative to the interferometric fringes in the phase-shifted interferometry images.

Abstract: An apparatus for assessing topology of a surface of a target including an optical source for generating a probe laser beam. The apparatus also includes a means for scanning the probe laser beam across at least a portion of the surface of the target and a beamsplitter for redirecting a return signal toward the means for detecting the return signal in a substantially quadrature condition. A quadrature interferometric method for determining the presence or absence of a target analyte in a sample comprising a laser probe beam having a wavelength ? and a waist wo to probe at least a portion of a substrate having a reflecting surface that includes at least a first region having a layer of recognition molecules specific to the target analyte and a second region that does not include a layer of recognition molecules specific to the target analyte.

Abstract: An apparatus is disclosed which includes an interferometry system configured to operate in a first mode to produce a first set of multiple interferometry signals corresponding to different illumination angles of a test object by test light and in a second mode produce a second set of multiple interferometry signals corresponding to different surface locations of a test object. An electronic processor coupled to the interferometry system is configured to receive the first set of interferometry signals and programmed to compare information derivable from the first set of multiple interferometry signals to information corresponding to multiple models of the test object to determine information related to one or features of the test object, and output the information. In some embodiments, the features include an under-resolved feature.

Abstract: A method of interferometric imaging includes a) focusing an interference pattern of a surface of an object onto a digital micromirror device, b) reflecting interfered electromagnetic radiation from a first plurality of mirrors of the digital micromirror device onto a detector, and recording the integrated intensity of the reflected interferometric radiation, repeating step b) for a second plurality of mirrors, and computing the interference pattern of the surface of the object from the recorded integrated intensities.

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: A method for determining at least one of distortion and de-focus for an optical imaging system. The method includes determining wavefront aberrations in a pupil plane of the optical imaging system by a wavefront measurement method, determining focus offset measured values in an xy-direction and/or z-direction for one or more different illumination settings by a test pattern measurement method with imaging and comparative evaluation of test patterns for the optical imaging system, and determining values for one or more aberration parameters that relate to the distortion and/or image surface from a prescribed relationship between the determined wavefront aberrations and the determined focus offset measured values.

Abstract: An eye tracking system includes an eye camera and a scene camera for supplying video data to interlace electronics indicative of an image of the user's eye and an image of the scene observed by the user. A frame grabber is provided for digitizing the video data and for separating the eye and scene data into two processing channels, and a spot location module determines the location of a reference spot formed on the user's eye. The module includes an adaptive threshold and spot identification sub-modules for indicating parts of the eye camera image which have higher brightness, and for selecting a valid reference spot. A pupil location module determines the user's line of gaze, and a display for indicating the user's point of regard from the user's line of gaze determined by the pupil and spot location modules.

Abstract: Methods and apparatus for three-dimensional imaging of a sample. A source is provided of a beam of substantially collimated light characterized by a temporally dependent spectrum. The beam is focused in a plane characterized by a fixed displacement along the propagation axis of the beam, and scattered light from the sample is superposed with a reference beam derived from the substantially collimated source onto a focal plane detector array to provide an interference signal.

Abstract: A surface profiling apparatus and method. Broadband light is directed along sample and reference paths such that light reflected by a region of a sample surface and light reflected by a reference surface interfere. A mover effects relative movement between the sample and reference surfaces along a scan path. A detector senses a series of light intensity values representing interference fringes produced by the region of the sample surface during the movement. A data processor processes the intensity values as they are received during a measurement operation to produce data indicating the position of a coherence peak, and, after completion of a measurement operation, uses this coherence peak position data to obtain data indicative of the height of the surface region. The data processor includes a correlator for correlating intensity values with a correlation function to provide correlation data to enable the position of a coherence peak to be identified.

Abstract: An interferometric measuring device for three-dimensional measurement of shapes on an object to be measured having: a beam splitter receiving via an input light path, and splitting into measuring and reference light paths, light from a light source; an image pick-up, to which light reflected from the object and from a reference and brought into interference can be supplied via an output light path for conversion into electrical signals; an evaluation unit for determining the surface shape from the signals; and an adaptation device adapting the light intensity or interfering light signals. For increased measuring precision, the measuring device is configured to measure planar regions of the surface which extend over at least the measuring device's lateral resolution and the adaptation device is configured for adjusting the intensity of the light and/or the signals by locally varying reflective properties of the surface with respect to the measuring optics.

Abstract: A phase shift interferometer (100) has an illuminating optical system (200) that emits a P-wave and an S-wave, a collimator lens (110), a reference half mirror (120), a pinhole plate (130) having a pinhole (131), and a phase shift interference fringe acquiring section (300) that allows an object light and a reference light contained in the light beam passed through the pinhole (131) interfere with each other in four different phases to acquire interference fringes with different phases. In the S-wave, only the reference light (SR) reflected by the reference half mirror (120) is passed through the pinhole (131), and the object light (SM) reflected by a surface-to-be-measured is blocked by the pinhole plate (130). In the P-wave, only the object light (PM) reflected by the surface-to-be-measured is passed through the pinhole (131), and the reference light (PR) reflected by the reference half mirror (120) is blocked by the pinhole plate (130).

Abstract: An optical tomographic imaging apparatus capable of obtaining a high resolution tomographic image rapidly. In the apparatus, light beams having different wavelength ranges with portions of the ranges overlapping with each other are outputted from light source units, each of which is split into measuring and reference beams in each of the beam splitting units. A reflected beam reflected from a measuring object when the measuring beams are irradiated onto the measuring object is combined with the respective reference beams in the respective beam combining units, and a plurality of interference beams generated when the reflected beam is combined with the respective reference beams is detected in the respective interference light detection units, thereby interference signals are generated and a tomographic image is generated using the generated interference signals.

Abstract: Deterioration of the resolution of tomographic images obtained by optical tomography measurement is prevented. Interference signals, which are obtained when a light beam L is emitted, are divided into a plurality of divided interference signals each having different wavelength bands. Spectral analysis is administered for each of the plurality of divided interference signals, to obtain a plurality of pieces of intermediate tomographic data. The plurality of pieces of intermediate tomographic data are employed to obtain tomographic data, a tomographic image is generated based on the tomographic data, then displayed.

Abstract: An ophthalmic surgical microscope (100) has a microscope main objective (101) and a viewing beam path (105) which passes through the microscope main objective (101) for visualizing an object region. The ophthalmic surgical microscope (100) includes an OCT-system (140) for recording images of the object region (108). The OCT-system (140) includes an OCT-scanning beam (142) which is guided via a scan mirror arrangement (146) to the object region (108). An optic element (147) is provided between the scan mirror arrangement (146) and the microscope main objective (101). This optic element (147) bundles the OCT-scanning radiation exiting from the scan mirror arrangement (146) and transfers the same into a beam path which passes through the microscope main objective (101). Alternatively or in addition, the ophthalmic surgical microscope (100) includes an ophthalmoscopic magnifier lens (132) which can be pivoted into and out of the viewing beam path (105) and the OCT-scanning beam path (142).

Abstract: In general, in one aspect, the invention features methods that include interferometrically monitoring a distance between an interferometry assembly and a measurement object along each of three different measurement axes while moving the measurement object relative to the interferometry assembly. The methods also include monitoring an orientation angle of the measurement object with respect to a rotation axis non-parallel to the three different measurement axes while the measurement object is moving, determining values of a parameter for different positions of the measurement object from the monitored distances, wherein for a given position the parameter is based on the distances of the measurement object along each of the three different measurement axes at the given position, and deriving information about a surface figure profile of the measurement object from a frequency transform of at least the parameter values.

Abstract: Three-dimensional shape measuring instrument (white interferometer) for measuring the three-dimensional shape of an object to be measured by using white interference fringes, which detects the position where the amplitude of the white interference fringes takes on a maximum value with high accuracy in a short calculation processing time. An envelope distribution of the amplitude of the white interference fringes produced by the interference between the returning light from a reference mirror (6) and the returning light from an object (7) to be measured is determined, and an approximate position where the contrast of the white interference fringes is the highest is determined using this envelope distribution.

Abstract: A digitized image of an object may include representations of portions of the object that are obscured, occluded or otherwise unobservable. The image may be a multi-dimensional visual representation of dentition. Characteristics of the dentition and its surfaces, contours, and shape may be determined and/or analyzed. A light may be directed toward and reflected from the dentition. The reflected light may be combined with a reference to determine characteristics of the dentition, including obscured areas such as subgingival tissue.

Abstract: An imaging system for imaging an object point to an image point, the system including: a beam splitter positioned to receive light rays from the object point and separate each of a plurality of rays into a transmitted portion and a reflected portion, the transmitted portions defining a first set of rays and the reflected portions defining a second set of rays; and an array of independently positionable reflecting elements forming a reflecting surface positioned to receive one of the sets of rays from the beam splitter and focus that set of rays towards the image point via the beam splitter.

Abstract: A device and a method are used for measuring the surface topography and a wave aberration of a lens system. The device is fitted with a first measuring system containing a light source radiating a first light beam of a first wavelength, and a detector which captures the first light beam which is reflected on the lens system. In addition the device has a second measuring system containing a light source for radiating a second light beam of a second wavelength and a detector for capturing the second light beam transmitted by the lens system. A diffractive optical element is disposed in a common beam path of the first measuring system and second measuring system. The optical element adapts the respective wave-front course of the first light beam and the second light beam in a wavelength-selective manner.

Abstract: A system and method for coherent optical inspection are described. In one embodiment, an illuminating beam illuminates a sample, such as a semiconductor wafer, to generate a reflected beam. A reference beam then interferes with the reflected beam to generate an interference pattern at a detector, which records the interference pattern. The interference pattern may then be compared with a comparison image to determine differences between the interference pattern and the comparison image. According to another aspect, the phase difference between the reference beam and the reflected beam may be adjusted to enhance signal contrast. Another embodiment provides for using differential interference techniques to suppress a regular pattern in the sample.

Abstract: A method for determining a surface profile of an object is described. The method typically includes providing a surface profile (e.g., a height profile) of a test object measured by an interferometric profiler. Information related to field- and object orientation-dependent systematic errors of the interferometric profiler is provided. The surface profile is corrected based on the field- and orientation-dependent errors. Also described is a method for determining the field- and orientation-dependent errors of a profiler.

Abstract: Disclosed is an interferometry analysis method that includes comparing information derivable from multiple interferometry signals corresponding to different surface locations of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parameterized by a series of characteristics that relate to one or more under-resolved lateral features of the test object; and outputting information about the under-resolved surface feature based on the comparison.

Abstract: A method including: providing a low coherence scanning interferometry data for at least one spatial location of a sample having multiple interfaces, wherein the data is collected using a low coherence scanning interferometer having an illumination geometry and an illumination frequency spectrum, and wherein the data comprises a low coherence scanning interferometry signal having multiple regions of fringe contrast corresponding to the multiple interfaces; and determining a distance between at least one pair of interfaces based on a distance between the corresponding regions of fringe contrast and information about the illumination geometry.

Abstract: Methods and systems are disclosed for analyzing a scanning interferometry signal. A scanning interferometry signal is provided that is produced by a scanning interferometer for a first location of a test object (e.g., a sample having a thin film). A model function of the scanning interferometry signal is provided which is produced by the scanning interferometer. The model function is parametrized by one or more parameter values. The model function is fit to the scanning interferometry signal for each of a series of shifts in scan position between the model function and the scanning interferometry signal by varying the parameter values. Information is determined about the test object (e.g., a surface height or height profile, and/or a thickness or thickness profile for a thin film in the test object) at the first location based on the fitting.

Abstract: A repairing method for a surface profile is provided. The intensity on the waveform of the interference diagrams or the existence of envelope on the waveform of the interference diagram are used to decide whether the respected pixel is located in a dark area on the surface profile or not. Then, mark the pixel located in the dark area. Afterward, repair the marked pixel by using the surrounding effective pixels on the surface profile.

Abstract: A surface profile measuring method using a broad bandwidth light source illuminating a sample surface and a reference surface through a splitter is provided. By changing a distance between the sample surface and the reference surface with a constant step, an interference diagram with a waveform composed of interference data points depicting a relationship of surface height versus illumination intensity is generated. In the beginning, a first data point with greatest illumination intensity is selected from the interference data points on the waveform. Then, a second data point is selected from the data points on the waveform within a predetermined range centered at the first data point to have the waveform showing best quality of symmetry. Then, a peak of a fringe defined by the second data point and its neighboring data points is estimated by using phase compensating approach.

Abstract: A method for measuring a thickness of a coating of a constructional unit, in particular a heat-compatible coating on a component of a gas turbine, includes measuring coordinates of the constructional unit three-dimensionally with a measuring device, in particular an optical scanner, before and after the coating, a thermal distortion of the constructional unit being recorded during the coating and the thickness of the coating being determined from a comparison of the measured constructional unit coordinates before and after the coating. The thermal distortion of the constructional unit is taken into account in the thickness determination of the coating by a comparison with at least one reference point at an uncoated location.

Abstract: A surface texture measuring instrument provided with a near-field measuring unit (30) including a near-field probe (33) that forms a near-field light at a tip end thereof when a laser beam is irradiated, a laser source (35) that generates the laser beam to be irradiated on the near-field probe (33), a detection element (38) that detects scattering effect of the near-field light generated when the near-field probe (33) is moved close to a workpiece (1), and an actuator (32) that displaces the near-field probe (33) and the workpiece (1) in a direction moving close to/away from each other, includes: a laser length-measuring unit (20) that measures a relative distance between a reference position and the workpiece (1) in the vicinity of the tip end of the near-field probe (33) or a relative distance between the reference position and the near-field probe (33).

Abstract: A compact monolithic quadrature detector generates four signals from an input beam including orthogonally polarized object and reference beam components provided by an interferometer. The single input beam may be split into four output beams using a first beam splitting interface between two prisms, reflections at two air interface surfaces of the prisms, and a second beam splitting element. Different respective predetermined phase shifts may be imposed on the respective output beams by coatings on the beam splitting surfaces, which impart a different phase shift to the components of a transmitted beam as compared to a reflected beam. The four relatively phase shifted output beams may be directed through polarizers onto respective detectors to provide four signals usable to eliminate many common mode errors and determine the phase difference between the components of the original input beam with high accuracy.

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: In general, the invention relates to the design and fabrication of optical devices suitable for use in methods and systems associated with phase-shift interferometry.

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: To determine the profile of an integrated circuit structure, a signal is measured off the structure with a metrology device. The measured signal is compared to signals in a virtual profile library. The comparison is stopped if matching criteria are met. A subset of a virtual profile data space is determined when the matching criteria are not met. The subset is determined using profile data space associated with the library. A virtual profile signal of the subset is selected. Virtual profile shape/parameters are determined based on the virtual profile signal. A difference is calculated between the measured and virtual profile signals. The difference is compared to virtual profile library creation criteria. If the criteria are met, then the structure is identified using virtual profile data, which includes the virtual profile shape/parameters, associated with the virtual profile signal. Or, if the criteria are not met, then a corrective action is applied.

Abstract: A method and apparatus for detecting stray particles upon a relatively smooth surface by measuring the amount of collimated light reflected from the surface from clear areas of the surface and from particles resting on the surface. Optical pick-up units similar to those used in DVD's and CD's can be used. A method for detecting defective depressions is also covered.

Abstract: An optical system includes a photolithography system, a low coherence interferometer, and a detector. The photolithography system is configured to illuminate a portion of an object with a light pattern and has a reference surface. The low coherence interferometer has a reference optical path and a measurement optical path. Light that passes along the reference optical path reflects at least once from the reference surface and light that passes along the measurement optical path reflects at least once from the object. The detector is configured to detect a low coherence interference signal including light that has passed along the reference optical path and light that has passed along the measurement optical path. The low coherence interference signal is indicative of a spatial relationship between the reference surface and the object.

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: Frequency-scanning interferometry is used for measuring test objects having multiple surface regions. The regions are distinguished and can be measured based on different measuring criteria. Interference data is gathered for the imageable portion of the test object from a plurality of interference patterns taken over substantially the same imageable portion at different measuring beam frequencies. The interference data is evaluated to determine topographical measures of associated points on the test object. The topographical measures are compared against a benchmark to distinguish between points on the test object that are within a first of the surface regions from points on a boundary separating the first surface region from one or more other surface regions of the imageable portion of the test object. The interference data of points within the first surface region are further evaluated to a higher accuracy.

Abstract: In general, in one aspect, the invention features methods that include interferometrically monitoring a distance between an interferometry assembly and a measurement object along each of three different measurement axes while moving the measurement object relative to the interferometry assembly, determining values of a first parameter and a second parameter for different positions of the measurement object from the monitored distances, wherein for a given position the first parameter is based on the monitored distances of the measurement object along each of the three different measurement axes at the given position, and for a given position the second parameter is based on the monitored distance of the measurement object along each of two of the measurement axes at the given position, and deriving information about a surface figure profile of the measurement object from the first and second parameter values.

Abstract: In general, in one aspect, the invention features methods that include interferometrically monitoring a distance between an interferometry assembly and a measurement object along each of three different measurement axes while moving the measurement object relative to the interferometry assembly, determining values of a parameter for different positions of the measurement object from the monitored distances, wherein for a given position the parameter is based on the distances of the measurement object along each of the three different measurement axes at the given position, and deriving information about a surface figure profile of the measurement object from a frequency transform of at least the parameter values.

Abstract: A method includes providing scanning interferometry data for a test object, the data including intensity values for each of multiple scan positions for each of different spatial locations of the test object, the intensity values for each spatial location defining an interference signal for the spatial location, the intensity values for a common scan position defining a data set for that scan position. The method includes providing a scan value for each scan position, wherein increments between the scan values are non-uniform, transforming at least some of the interference signals into a frequency domain with respect to the scan values, and determining information about the test object based on the transformed interference signals.

Abstract: An apparatus for detecting the surface profile of a test object includes a light source, a beam splitter, a reflective component, a sensor, and a computing device. The light source emits a light beam. The beam splitter divides the light beam into reference and probing beams. The reference beam is reflected by the reflective component back to the beam splitter. The reflective component is configured so that components of the reflected reference beam travel at different optical path lengths to the beam splitter. The probing beam is reflected by the test object back to the beam splitter. The beam splitter combines the reflected reference and probing beams to result in a heterodyne light beam. The sensor converts the heterodyne light beam into a corresponding electrical signal. The computing device records the converted electrical signal. A method for detecting the surface profile of the test object is also disclosed.

Abstract: A surface of a dynamic object such as a polygon mirror is measured to determine configuration. In measuring the surface configuration, a light is emitted onto the surface, and interference stripes are analyzed to determine the surface configuration. In analysis of the interference stripes, a correct sign for the peak frequency is required so as to measure a configuration at a high precision level without much prior preparation. The correct sign is obtained in a substantially improved manner by using a relationship between the object light that has been reflected by an object to be measured and the reference light that has been emitted from the light source.

Abstract: A structure formed on a wafer can be examined by directing an incident pulse at the structure, the incident pulse being a sub-picosecond optical pulse. A diffraction pulse resulting from the incident pulse diffracting from the structure is measured. A characteristic of the profile of the structure is then determined based on the measured diffraction pulse.