Abstract: A method of manufacturing a display device includes: providing a glass including an edge region and an inner region; arranging a light source under the glass; setting a center position of the light source to correspond to an inside of the edge region or an inside of the inner region of the glass; directing light into the glass by using the light source; and detecting a defect in the edge region of the glass by receiving light passing through the glass by using a detection camera.

Abstract: In a method for determining 3D coordinates of at least one predetermined point of an object, the object is arranged in a measurement region and a variable illumination source projects a variable pattern onto the object arranged in the measurement region. An image recording apparatus which is arranged in a previously known relationship with respect to the illumination source records an image of at least one section of the object illuminated by the variable illumination source. The at least one predetermined point is detected in the recorded image. The 3D coordinates of the at least one predetermined point are determined from the recorded image, taking into account the previously known relationship of the image recording apparatus with respect to the illumination source, if a check of the recorded image reveals that the at least one predetermined point is marked in the recorded image by a feature of the variable pattern.

Abstract: There is provided a system for inspecting an edge area of a transparent media, the transparent media having a decoration on a surface, the system includes: an illuminator to direct light to the transparent media for inspection, wherein the illuminator directs light to the transparent media at an oblique angle relative to a surface of the transparent media which is opposite the surface with the decoration; an optical element to capture light transmitted through the transparent media; and a sensor to obtain an image from the light captured by the optical element. There is also provided a method for inspecting an edge area of a transparent media, where the transparent media has a decoration on a surface.

Abstract: One embodiment relates to an apparatus that includes an illumination source (102) for illuminating a target substrate (106), objective optics (108) for projecting the EUV light which is reflected from the target substrate, and a sensor (110) for detecting the projected EUV light. The objective optics includes a first mirror (202,302, or 402) which is arranged to receive and reflect the EUV light which is reflected from the target substrate, a second mirror (204, 304, or 404) which is arranged to receive and reflect the EUV light which is reflected by the first mirror, a third mirror (206, 306, or 406) which is arranged to receive and reflect the EUV light which is reflected by the second mirror, and a fourth mirror (208, 308, or 408) which is arranged to receive and reflect the EUV light which is reflected by the third mirror.

Abstract: A method of assessing a model of a substrate is presented. A scatterometry measurement is taken using radiation at a first wavelength. The wavelength of the radiation is then changed and a further scatterometry measurement taken. If the scatterometry measurements are consistent across a range of wavelengths then the model is sufficiently accurate. However, if the scatterometry measurements change as the wavelength changes then the model of the substrate is not sufficiently accurate.

Abstract: A measurement system scans the given surface of a tire component (e.g., a brush-finished tread or buffed tire casing) to electronically measure data points corresponding to vertical and horizontal coordinates along the given surface. Associated computer processors electronically calculate the slope at a plurality of different locations by determining the degree of steepness (e.g., rise over run, angle or grade) between selected ones of the first and second coordinates and electronically comparing at least one slope-based parameter to one or more predetermined levels to determine a characterization defining one or more of surface adhesion fitness, finishing brush wear level and brush bristle placement location. Slope may be determined between every adjacent pair of data points or between selected data points (e.g., identified local maximum and minimum). The at least one-slope based parameter compared to the predetermined levels may correspond to the slopes themselves or to a calculated average slope value.

Abstract: In one embodiment, a surface inspection system comprises a radiation source that emits a broadband radiation beam, a radiation directing assembly to target radiation onto a surface of an object, the radiation directing assembly comprising a radiation collection assembly to collect radiation reflected from the surface of the object, the radiation collection assembly comprising at least one multi-chip detector array assembly positioned within a field of view of the inspection system.

Abstract: Disclosed is a method for inspecting defects of optical layer elements of a display device. The method includes steps of: scanning a selected optical layer element of the display device by a scanning light beam at a predetermined scan angle, wherein the optical layer element is selected from a polarizing layer, a filter layer, an alignment layer, a liquid crystal layer, a thin film transistor substrate layer, a light diffusion layer, a light guide layer, or a combination thereof; retrieving a light pattern generated by scanning the selected optical layer element; generating an inspecting result information according to the light pattern in relation to the selected optical layer element; and analyzing the optical layer element regarding defect conditions according to the inspecting result information.

Abstract: The disclosure relates to a scanning device for detecting the contour of an object. The scanning device has a light source for generating a light pattern on the surface area of the object, and a camera for detecting the light pattern on the surface area of the object. The disclosure describes that the one light source includes at least one incoherent spot light source, and that between the at least one spot light source and the object, a shadow caster defines the light pattern on the surface area of the object. The disclosure also relates to a method for detecting the contour of an object.

Abstract: A device for inspecting a polycrystalline silicon layer that is crystallized by receiving irradiated laser beams on a front side of the polycrystalline silicon layer includes: a light source configured to emit inspection beams to a rear side of the polycrystalline silicon layer; a light inspector configured to inspect the inspection beams reflected at the rear side of the polycrystalline silicon layer; and a controller that controls the light source and the light inspector.

Abstract: A surface layer formed of a composite material is stacked on the surface of a core layer formed of a foam synthetic resin material, and an arrester portion is provided in an interface region between the surface layer and the core layer to prevent the progression of delamination between the surface layer and the core layer. Optical fibers with grating portions are embedded inside the arrester and along the surface layer, and the spectra of reflected light from the optical fibers are compared to detect the occurrence position of a crack between the surface layer and the core layer.

Abstract: A system for measuring an optical spectral response of a photoelectric DUT includes a spectrally programmable light source including a broadband light source, a dispersive element for dispersing the light, and a spatial light modulator for controlling an intensity and a spectra of the light to provide a spectrally programmable light beam. A light distributing device is coupled to receive the spectrally programmable light beam and includes a light distributing structure for distributing the spectrally programmable light beam in a known ratio to a first area and a second area. A reference detector is positioned at the first area, and the DUT is positioned at the second area. Data acquisition electronics and a processor receive simultaneously generated output signals from the DUT and the reference detector to correct for intensity variation in the spectrally programmable light beam in determining the optical spectral response of the DUT.

Abstract: A system and method for monitoring a physiological parameter includes a garment that includes a fabric that exhibits both a light transmission property and a light reflection property. The amount of light transmitted through the fabric relative to the amount of light reflected by the fabric changes when the fabric stretches in response to motion, such as the motion induced by physiological activity (e.g., heart rate). The system includes at least one source of radiation having wavelength(s) in the range of 400 to 2200 nanometers and at least one detector responsive to such incident radiation. The source and detector are associated with the fabric such that the reception of incident radiation by the detector is directly affected by a change in the amount of light transmitted through the fabric relative to the amount of light reflected by the fabric when the fabric stretches.

Abstract: One embodiment relates to an apparatus that includes an illumination source (102) for illuminating a target substrate (106), objective optics (108) for projecting the EUV light which is reflected from the target substrate, and a sensor (110) for detecting the projected EUV light. The objective optics includes a first mirror (202,302, or 402) which is arranged to receive and reflect the EUV light which is reflected from the target substrate, a second mirror (204, 304, or 404) which is arranged to receive and reflect the EUV light which is reflected by the first mirror, a third mirror (206, 306, or 406) which is arranged to receive and reflect the EUV light which is reflected by the second mirror, and a fourth mirror (208, 308, or 408) which is arranged to receive and reflect the EUV light which is reflected by the third mirror.

Abstract: Disclosed is a device for inspecting a bonded wafer using laser, which has a simple structure to facilitate an operation of the device and can detect an interface defect of the bonded wafer economically and highly reliably. To this end, the device for inspecting the bonded wafer using laser includes a laser unit, a laser diffusion unit, and a detection unit. If the device of inspecting the bonded wafer using laser according to the present invention is used, it is possible to advantageously inspect a wafer interface at a magnification desired by an inspector. In addition, the device has a simple structure, and thus it is advantageously easy to operate the device.

Abstract: The invention relates to a method and an apparatus for detecting cracks in semiconductor substrates, such as silicon wafers and solar cells. The method and apparatus are based on the detection of light deflected at a crack.

Abstract: A photomask inspection method that identifies a foreign particle such as dirt on a photomask with high sensitivity by suppressing erroneous identification due to an influence of noise is provided. The photomask inspection method includes acquiring image data of a photomask having regions with different layer structures on a surface thereof, creating inverted image data by subtracting the image data from pixel value data of the regions, creating offset inverted image data by raising pixel values of the inverted image data by a fixed amount, creating normalized correlation image data by computing a normalized correlation of the offset inverted image data and an offset Gaussian distribution-type kernel, and identifying foreign particles by comparing the normalized correlation image data and a predetermined threshold.

Abstract: Previously used examination devices and methods mostly operate with reflected visible or UV light to analyze microstructured samples of a wafer (38), for example. The aim of the invention is to increase the possible uses of said devices, i.e. particularly in order to represent structural details, e.g. of wafers that are structured on both sides, which are not visible in VIS or UV because coatings or intermediate materials are not transparent. Said aim is achieved by using IR light as reflected light while creating transillumination (52) which significantly improves contrast in the IR image, among other things, thus allowing the sample to be simultaneously represented in reflected or transmitted IR light and in reflected visible light.

Abstract: A garment and system includes a monitoring fabric that exhibits a light reflection property and substantially no light transmission property when the fabric is illuminated with light having wavelength(s) in the range of 400 to 2200 nanometers. The amount of useful light reflected by the fabric into an aperture of acceptance defined with respect to an imaginary axis extending from the fabric relative to the amount of light lost to the aperture of acceptance detectably changes when the fabric stretches in response to motion, as the motion induced by physiological activity (e.g., heart rate). The system includes at least one radiation source and at least one radiation detector, with the detector disposed in the aperture of acceptance.

Abstract: Disclosed herein is a method of inspecting defects in a circuit pattern of a substrate. At least one laser beam radiation unit for radiating a laser beam onto an inspection target circuit pattern of a substrate in a non-contact manner is prepared. A probe beam radiation unit for radiating a probe beam onto a connection circuit pattern to be electrically connected to the inspection target circuit pattern in a non-contact manner is prepared. The laser beam is radiated onto the inspection target circuit pattern using the laser beam radiation unit. The probe beam is radiated onto the connection circuit pattern using the probe beam radiation unit, thus measuring information about whether the probe beam is diffracted, and a diffraction angle. Accordingly, the method can solve problems such as erroneous measurements caused by contact pressure and can reduce the time required for measurements.

Abstract: Apparatus for optical inspection includes an illumination assembly, including multiple parallel rows of light sources for emitting light and illumination optics associated with each row for directing the light onto an object under inspection. The multiple parallel rows include at least a first row with first illumination optics including a first array of prisms that are configured to reflect the light emitted by the light sources in the first row, and at least a second row with second illumination optics including a second array of prisms that are configured to refract the light emitted by the light sources in the second row. An imaging assembly is configured to capture an image of the object under illumination by the multiple parallel rows of the light sources.

Abstract: A surface defect data display and management system comprises a risk score calculation unit for calculating the magnitude of an influence a surface defect on a wafer detected by a wafer inspection system or review system has upon a reduction in the yield of a final product as a risk score of the surface defect based on a defect size of the surface defect on the wafer and a pattern concentration obtained from design data of a pattern figure nearby a location corresponding to the position of the surface defect, and a correlation graph and defect image display unit for preparing a correlation graph showing the correlation between the defect size and the risk score of each defect, displaying the prepared correlation graph on the display apparatus and displaying additionally a defect image list of one or more defects selected by using the correlation graph.

Abstract: A spatial mask printer may be used in conjunction with an optical inspection tool. The tool can be used to obtain a Fourier image of an inspected object, and a filter mask image can be designed to block certain aspects of the object's image in the Fourier plane corresponding to repetitive aspects of the imaged object. The filter mask image can then be printed and used in the tool during the inspection process. The mask image may be designed by hand or by computer and may be stored for later use. Filters may be automatically placed into the optical path of the inspection tool by a filter wheel, or may be housed in other filter banks. The printer may be configured to operate in a clean room environment, and may be integrated into the optical inspection tool.

Abstract: In a measuring system, a method for evaluating parameters of a workpiece includes measuring a periodic structure, such as a grating, on the workpiece to produce image data. An orientation of features in the image data, produced by higher order diffractions from the periodic structure, is identified. An orientation of the periodic structure is determined based on the orientation of the features in the image data. The image data is then modified, based on the orientation of the periodic structure, to correlate with, and for comparison to, simulated image data to ascertain parameters of the workpiece. Alternatively, optical components in the measuring system, or the workpiece itself, are adjusted to provide a desired alignment between the optical components and the periodic structure. A microstructure on the workpiece may then be measured, and the resulting image data may be compared to the simulated image data to ascertain parameters of the microstructure.

Abstract: A garment and system includes a monitoring fabric comprising a first plurality of reflective yarns knitted or woven with a second plurality of stretchable yarns. The fabric exhibits both a light transmission property and a light reflection property. The amount of light transmitted through the fabric relative to the amount of light reflected by the fabric changes when the fabric stretches in response to motion, such as the motion induced by physiological activity (e.g., heart rate). The system includes at least one source of radiation having wavelength(s) in the range of 400 to 2200 nanometers and at least one detector responsive to such incident radiation. The source and detector are associated with the fabric such that the reception of incident radiation by the detector is directly affected by a change in the amount of light transmitted through the fabric relative to the amount of light reflected by the fabric when the fabric stretches.

Abstract: There is provided a defect inspecting apparatus, which includes an irradiating optical system of irradiating a light beam on a surface of a face plate of a disk mounted on a stage to scan the surface of the face plate, a light-receiving optical system of receiving specular reflection light that has transmitted a shading filter with a shading difference that changes an amount of the specular reflection light from the face plate resulting from the light beam irradiated on the disk, and a processing unit of identifying defects on the surface of the face plate from the change in amount of the specular reflection light that has transmitted a filter, so that a size and a height of the defect can be measured with high accuracy when irregular defects are determined, which is not easily achieved by a conventional lens effect.

Abstract: Disclosed are methods and apparatus for inspecting a sub-resolution assist features (SRAF) on a reticle. A test flux measurement for a boundary area that encompasses a width and a length portion of a test SRAF is determined, and at least one reference flux measurement for one or more boundary areas of one or more reference SRAF's is determined. The test flux measurement is compared with the reference flux measurements. The comparison is used to then determine whether the test SRAF is undersized or oversized. If the test SRAF is determined to be oversized, it may then be determined whether the test SRAF is defective based on the comparison using a first threshold.

Abstract: A system and method for inspecting a machined surface. The method includes acquiring optical information of the machined surface from a predefined orientation. Further, the method includes comparing one or more parameters of the optical information with a corresponding one or more reference parameters. Furthermore, the method includes assessing a quality of the machined surface based on the comparison.

Abstract: Fourier filters, inspection systems, and systems for fabricating Fourier filters are provided. One Fourier filter configured for use in an inspection system includes a substrate that is substantially transparent to light from a specimen illuminated by the inspection system. The Fourier filter also includes an array of patterned features formed on the substrate. The patterned features are formed of one or more pigments on the substrate. The patterned features are configured to block light reflected and diffracted from structures on the specimen and to allow light scattered from defects on the specimen to pass through the substrate.

Abstract: A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The system features a variable scan speed beam scanning subsystem, preferably using an acousto-optic deflector, with beam compensation, so that variable scanning speeds can be achieved. Also included are methods and systems for improving the signal to noise ratio by use of scatter reducing complements, and a system and method for selectively and repeatedly scanning a region of interest on the surface in order to provide additional observations of the region of interest.

Abstract: An optical plate having an exit pupil array or a lens array aligned at a predetermined pitch is disposed at the front of a display. A test pattern is supplied to the display to light a pixel corresponding to the predetermined pitch. A first optical element transmits a light from an inspection position of the optical plate. A second optical element coaxially disposed on the first optical element, focuses the light from the first optical element. An image from the light focused at the second optical element is obtained. A three-dimensional position at the inspection position of the optical plate relative to the display or a predetermined period of the optical plate is calculated from a position and a period of luminance distribution of the image, and a distance between the optical plate and the first optical element. Whether the three-dimensional position or the predetermined period is within a threshold is inspected.

Abstract: An object of the present invention is to provide a pattern measuring method and an electron microscope that achieve truly high measurement throughput by achieving both precise location of a measurement target position and high-speed movement of the scanning position of an electron beam to the measurement target position.

Abstract: An illumination beam irradiation apparatus for use in pattern inspection systems is disclosed, which is less in deterioration of optical components and in attenuation of illumination light. The illumination apparatus includes a light source which yields a fundamental wave, a beam-shaper unit which performs beam-shaping of the fundamental wave so that this wave has a prespecified shape, and a pattern generator unit which operates, upon receipt of the beam-shaped fundamental wave, to convert this incoming wave into illumination light with a shorter wavelength to thereby generate illumination light of a prespecified shape. The illuminator also includes an image relay unit for guiding the illumination light that was generated by the pattern generator to fall onto a workpiece under inspection, such as a photomask or else.

Abstract: According to a mask defect inspection data generating method, a distance between inspection areas neighboring in a predetermined direction is calculated based on inspection area control information defined in photomask inspection data. It is determined whether or not the calculated distance between inspection areas is less than a predetermined distance. When it is determined that the distance between inspection areas is less than a predetermined distance, the inspection area is combined to produce an optimization inspection area. The produced optimization inspection area information is defined in inspection layout data for making a reference in die-to-database defect inspection.

Abstract: A garment and system includes a monitoring fabric comprising a first plurality of reflective yarns knitted or woven with a second plurality of stretchable yarns. The fabric exhibits both a light transmission property and a light reflection property. The amount of light transmitted through the fabric relative to the amount of light reflected by the fabric changes when the fabric stretches in response to motion, such as the motion induced by physiological activity (e.g., heart rate). The system includes at least one source of radiation having wavelength(s) in the range of 400 to 2200 nanometers and at least one detector responsive to such incident radiation. The source and detector are associated with the fabric such that the reception of incident radiation by the detector is directly affected by a change in the amount of light transmitted through the fabric relative to the amount of light reflected by the fabric when the fabric stretches.

Abstract: A material independent profiler system and method for measuring a slope on the surface of an object such as a thin film disk, a silicon wafer, or a glass substrate is disclosed.

Abstract: A garment and system includes a monitoring fabric that exhibits a light reflection property and substantially no light transmission property when the fabric is illuminated with light having wavelength(s) in the range of 400 to 2200 nanometers. The amount of useful light reflected by the fabric into an aperture of acceptance defined with respect to an axis extending from the fabric relative to the amount of light lost to the aperture of acceptance detectably changes when the fabric stretches in response to motion, as the motion induced by physiological activity (e.g., heart rate). The system includes at least one radiation source and at least one radiation detector, with the detector disposed in the aperture of acceptance.

Abstract: An inspecting method inspects an optical stacked structure having a reflection layer and at least one light transmitting thin film sequentially stacked on a substrate. The inspecting method irradiates inspection light on the optical stacked structure from a side provided with the light transmitting thin film, measures a light intensity of reflected light from each layer, that changes depending on a change in an optical path length to each layer, and inspects a thickness of the light transmitting thin film based on the light intensity of reflected light for a specific wavelength.

Abstract: In a measuring system, a method for evaluating parameters of a workpiece includes measuring a periodic structure, such as a grating, on the workpiece to produce image data. An orientation of features in the image data, produced by higher order diffractions from the periodic structure, is identified. An orientation of the periodic structure is determined based on the orientation of the features in the image data. The image data is then modified, based on the orientation of the periodic structure, to correlate with, and for comparison to, simulated image data to ascertain parameters of the workpiece. Alternatively, optical components in the measuring system, or the workpiece itself, are adjusted to provide a desired alignment between the optical components and the periodic structure. A microstructure on the workpiece may then be measured, and the resulting image data may be compared to the simulated image data to ascertain parameters of the microstructure.

Abstract: An object of the invention is to provide a defect inspection method which can prevent the failure in detecting a defect, caused by saturation of a pattern signal obtained by inspecting an inspected object, so that the investigation of the cause for defect occurrence can be done earlier. To achieve this object, according to an embodiment of the invention, there is provided a defect inspection that irradiates laser light on an inspected object having a pattern formed thereon, detects a signal from the inspected object and thereby detects a defect, the inspection including: inputting pattern information contained in layout data on the inspected object; determining based on the inputted pattern information, at least one of arrangement, repetitiveness and density for each of a plurality of inspected areas of the inspected object; estimating a saturation level of the detected signal based on the determination result; and determining a transmittance condition so that the signal does not saturate.

Abstract: An optical plate having an exit pupil array or a lens array aligned at a predetermined pitch is disposed at the front of a display. A test pattern is supplied to the display to light a pixel corresponding to the predetermined pitch. A first optical element transmits a light from an inspection position of the optical plate. A second optical element coaxially disposed on the first optical element, focuses the light from the first optical element. An image from the light focused at the second optical element is obtained. A three-dimensional position at the inspection position of the optical plate relative to the display or a predetermined period of the optical plate is calculated from a position and a period of luminance distribution of the image, and a distance between the optical plate and the first optical element. Whether the three-dimensional position or the predetermined period is within a threshold is inspected.

Abstract: A surface inspection system, as well as related components and methods, are provided. The surface inspection system includes a beam source subsystem, a beam scanning subsystem, a workpiece movement subsystem, an optical collection and detection subsystem, and a processing subsystem. The system features a variable scan speed beam scanning subsystem, preferably using an acousto-optic deflector, with beam compensation, so that variable scanning speeds can be achieved. Also included are methods and systems for improving the signal to noise ratio by use of scatter reducing complements, and a system and method for selectively and repeatedly scanning a region of interest on the surface in order to provide additional observations of the region of interest.

Abstract: A method for using light to indicate locations of inconsistencies on a composite structure. The method generally includes electronically accessing positional data defining one or more inconsistency locations on a composite structure. The positional data may be extracted from a part fabrication file containing numerical control (NC) data that may be used by a material placement machine to fabricate the composite structure. A light source directs light at the composite structure to illuminate the inconsistency locations as defined by the positional data. The information needed by the light source may be stored in a lookup table accessed by a processor of a vision detection system. The light allows the inconsistency locations to be noted for later action.

Abstract: A method of inspecting an inspection pattern using a statistical inference function is disclosed. The inference function is generated in relation to optical reference signal data and reference pattern characteristic data for a plurality of reference patterns formed by a unit process of interest on reference substrates.

Abstract: A method of inspecting a light-management film comprises reflecting light from an overhead light source off a first side of the light-management film and examining the light-management film for defects; directing transmission light from a backlight source through a second side of the light-management film to the first side and examining the light-management film for defects; reflecting light from the overhead light source off the second side of the light-management film and examining the light-management film for defects; directing transmission light from the backlight source through the first side of the light-management film to the second side and examining the light-management film for defects; and measuring a location of each of the examined defects in the light-management film.

Abstract: The invention provides a device to inspect an illumination optical device and a method to inspect an illumination optical device that make it possible to efficiently inspect illumination optical devices and to control manufacturing cost. A lens array inspecting device is provided with a light source device to emit a parallel luminous flux, lens array holders to retain lens arrays, which are test objects that split the parallel luminous flux into a plurality of partial luminous fluxes, and a ground glass on which the optical images of the luminous fluxes emitted through the lens arrays are projected. On the ground glass, a parting frame appropriate to a design illumination region is formed. Therefore, whether the lens arrays are defective or non-defective can be determined by checking whether the optical images projected onto the ground glass include the area of the parting frame.

Abstract: Methods, apparatus and systems for the detection of defects in transparent substrates such as glass sheets are disclosed. The methods, apparatus and systems are capable of detecting optical path length variations in transparent substrates smaller than 100 nm.

Abstract: An apparatus for feature detection of a test object includes at least one light source module and at least one image capturing unit. The light source module provides light to illuminate a test region of the test object, and includes a substrate, a set of light-emitting components, and a light-focusing unit. The light-emitting components are mounted on the substrate for emitting light in parallel directions that are generally transverse to the substrate. The light-focusing unit is to be disposed between the light-emitting components and the test object, receives the light emitted by the light-emitting components, and focuses the light on the test region of the test object. The image capturing unit captures an image of the test object at the test region.

Abstract: Methods, apparatus and systems for the detection of defects in transparent substrates such as glass sheets are disclosed. The methods, apparatus and systems are capable of detecting optical path length variations in transparent substrates smaller than 100 nm.

Abstract: We disclose several instrument architectures for the measurement of arbitrary phase retardation on advanced lithography photomasks. These architectures combine traditional interferometric techniques with high-magnification UV microscopy. Features are interrogated using a multitude of phase probes, formed by a imaging a number of variable apertures back-illuminated by phase-coherent beams, onto the surface of the photomask with a given demagnification. The size, spacing, and orientation of the phase probes may be adjusted to suit photomask feature geometries. Means are provided to vary the relative optical phase between the phase probes. These phase probes both reflect from and transmit through the photomask; the stationary, non-localized interference fringes, formed in the regions of phase probe electric field overlap, contain information on the optical path difference between the two probes.