Abstract: In a lithographic projection apparatus, a grating spectral filter is used to filter an EUV projection beam. The grating spectral filter is preferably a blazed, grazing incidence, reflective grating. Cooling channels may be provided in or on the rear of the grating spectral filter. The grating spectral filter may be formed of a material effectively invisible to the desired radiation.

Abstract: A process for recognizing a colorless or color-reduced register mark by recording reflected or remitted electromagnetic radiation, particularly of visible or invisible light such that the register mark can be more reliably identified with particularity. The register mark is given an environment contrasting with the register mark, preferably installed beneath it, that absorbs an amount of radiation different from the amount the register mark itself and/or an absorptive ground absorbs.

Abstract: An exposure device in which a device for insertion or removal of the microscope for mask marks is not necessary, and in which the arrangement of the device is simplified is achieved by the provision of a microscope for mask marks in a workpiece carrier which can move in unison with the workpiece carrier. Furthermore, a reference mark is provided in the light incidence part of the microscope for determining the mask marks. The relation between the positions of the microscope for workpiece marks, the microscope for mask marks and the workpiece carrier is confirmed beforehand using this reference mark. In the positioning of the mask relative to the workpiece, the workpiece carrier is moved and the microscope for workpiece marks determines the position of the workpiece mark. Then, the workpiece carrier is moved and the microscope for mask marks determines the projection position of the mask mark. The workpiece carrier is driven such that the two agree with one another.

Abstract: A method for determining the relative motion of a surface with respect to a measurement device including placing a partially transmitting object, which is part of the measuring device, adjacent to the surface; illuminating the surface with incident illumination, which does not constitute an interference pattern, such that the illumination is reflected from portions of the surface, wherein at least part of at least one of the incident and reflected illumination passes through the object; detecting the illumination reflected from the surface, and generating a detected signal; and determining the relative motion of the surface parallel to the surface, from the detected signal.

Abstract: Alignment to buried marks is carried out by using electromagnetic radiation to induce waves in the layers covering the buried layer. The acoustic or thermal waves cause reflectivity changes and displacements in the surface whose position and/or time dependence reveals the true position of the buried alignment mark. The buried alignment mark may be revealed by mapping the thickness of covering layers in its vicinity, e.g. by measuring the time dependence of the decay of a standing wave induced in the covering layers or by measuring the delay time of echoes of a travelling wave created at interfaces between different ones of the covering layers. Alternatively, a travelling wave can be created over the whole area of the mark so that echoes off the top and bottom of the buried mark carry positive and negative images of the mark; these cause reflectivity differences and displacements when they reach the surface which can be aligned to.

Abstract: An optical alignment system for controlling the position of a laser beam through an optical train. The optical alignment system includes a semiconductor laser source for the generation of an alignment beam, and a beam steering device to manipulate the position of the alignment beam on a multi-element detector. The semiconductor laser is driven to mode hop at a frequency greater than the upper frequency limit of the multi-element detector. Driving the semiconductor laser to mode hop at a frequency greater than the upper frequency limit of the multi-element detector results in a more uniform alignment beam as seen by the detector, as the alignment beam becomes an average of all the operational modes of the semiconductor laser. A more uniform alignment beam results in improved accuracy of the alignment system.

Abstract: An illumination system and exposure apparatus and method involving illuminating a surface over an illumination field (IF) having an arcuate shape. The illumination system comprises a light source (54) for providing a light beam (100), and an optical integrator (56). The optical integrator comprises a first reflective element group (60) having an array of first optical elements (E) each having an arcuate profile corresponding to the arcuate shape of the illumination field. Each of the first optical elements has an eccentric reflecting surface (RSE) comprising an off-axis section of either a spherical surface (S) or an aspherical surface (ASE). The array of first optical elements is designed so as to form a plurality of arcuate light beams (108) capable of forming a plurality of light source images (I).

Abstract: In order to find the positional relation between the reference coordinate system XY which defines the movement of a substrate W and the arrangement coordinate system &agr;&bgr; which corresponds to a plurality of divided areas on the substrate W divided by street lines S&agr; and S&bgr;, the substrate W and an observation field are moved relatively. By allowing position detecting method marks Mk on the substrate W to visit the observation field, the street lines S&agr; and S&bgr; are detected in the observation field during the observation field. According to the results of the detection, an approximate arrangement coordinate system is corrected. The positional relation between the reference coordinate system XY and the arrangement coordinate system &agr;&bgr; is caught with high accuracy enough to allow the observation field to visit the position detection mark (Mk).

Abstract: A planar wafer-level packaging method is provided for a laser and a monitor photo detector. The laser and photo detector are affixed to a planar substrate. The planar substrate provides electrical connections to the components. A lens cap with a microlens is formed and affixed to the substrate with a seal. The lens cap forms a hermetically sealed cavity enclosing the laser and photo detector. The inside surface of the lens cap has a reflective coating with a central opening over the emitting aperture of the laser. The central opening has an anti-reflective coating. Light from the laser is directed and shaped by the lens cap to couple into an external light guide. Residual light from the edge of the laser reflects off the inside surface of the lens cap and is incident upon the photo detector. In an alternate method, the laser may be packaged using flip-chip assembly.

Abstract: In a lithographic apparatus, a reference grating 11 mounted on the wafer table WT is illuminated with a measurement beam 20 incident in a direction independent of wafer table tilt. The diffraction orders are detected by detector 30 and used to determine the lateral shift in the wafer table resulting from a non-zero Abbe arm, and hence the Abbe arm, for calibration purposes. The detector 30 may be a detector also used for off-axis alignment of the wafer and wafer table.

Abstract: A confocal three dimensional inspection system, and process for use thereof, allows for inspecting of bumps and other three dimensional (3D) features on wafers and other semiconductor substrates. The sensor eliminates out of focus light using a confocal principal to improve depth response. This process and system creates multiple parallel confocal optical paths along a line. The out of focus light is eliminated by placing an aperture at a plane which is a conjugate focal plane to the surface of the sample. The result is that the sensor produces a signal only when the sample surface is in a narrow focal range.

Abstract: In an off-axis levelling procedure a height map of the substrate is generated at a measurement station. The height map is referenced to a physical reference surface of the substrate table. The physical reference surface may be a surface in which is inset a transmission image sensor. At the exposure station the height of the physical reference surface is measured and related to the focal plane of the projection lens. The height map can then be used to determine the optimum height and/or tilt of substrate table to position the exposure area on the substrate in best focus during exposure. The same principles can be applied to (reflective) masks.

Abstract: A method for performing optical adjustments of an exposure apparatus is based on an exposure apparatus having a light source for generating illumination light for exposure, and illumination optics for irradiating a mask with the illumination light generated from the exposure light source so as to imprint a mask pattern on a substrate base.

Abstract: In an overlay measurement mark comprising an inner box and an outer box located at a predetermined area on a mask through which patterns are formed on a semiconductor device, the improvement of an overlay mark that extends the overlay measurement range comprising: in-focused marks means printed at an optimal or ideal focal plane level from an illumination source, and de-focused marks means located at a different focus level from the optimal focal plane to provide image placement shift of the de-focused marks larger than that of the in-focused marks means to enable measurement of the shift of de-focused marks that are not attributable to a mechanical alignment error to be determined with greater accuracy.

Abstract: The present invention accomplishes an evaluation of image formation performance in which the influence of a coat is accurately reflected. According to the present invention, for the evaluation of image formation performance of an optical system obtained is a pupil transmittance distribution (a distribution of light transmittance on an exit pupil surface) of a light beam that enters an image point to be evaluated of the optical system. At least one of a rotational symmetrical component, an odd symmetrical component, and an even symmetrical component is extracted from the obtained pupil transmittance distribution as an evaluation index.

Abstract: Linewidth variations and bias that result from MEF changes and reticle linewidth variations in a printed substrate are controlled by correcting exposure dose and partial coherence at different spatial locations. In a photolithographic device for projecting an image of a reticle onto a photosensitive substrate, an adjustable slit is used in combination with a partial coherence adjuster to vary at different spatial locations the exposure dose received by the photosensitive substrate and partial coherence of the system. The linewidth variance and horizontal and vertical or orientation bias are calculated or measured at different spatial locations with reference to a reticle, and a corrected exposure dose and partial coherence is determined at the required spatial locations to compensate for the variance in linewidth and bias on the printed substrate. Improved printing of an image is obtained, resulting in the manufacture of smaller feature size semiconductor devices and higher yields.

Abstract: A method and system to measure misalignment error between two overlying or interlaced periodic structures are proposed. The overlying or interlaced periodic structures are illuminated by incident radiation, and the diffracted radiation of the incident radiation by the overlying or interlaced periodic structures are detected to provide an output signal. The misalignment between the overlying or interlaced periodic structures may then be determined from the output signal.

Abstract: An illumination system used in photolithography for the manufacture of semiconductors having an array optical element with different illumination regions corresponding or matched to different line width variations printed on a photosensitive substrate. The array optical element may be a filter, diffractive optical element, or micro lens array having illumination regions producing different types of illumination properties or characteristics. Each of the illumination regions are matched or correspond to a respective region on the reticle to provide optimized exposure of a photosensitive resist covered wafer. The optical element of the present invention may be used to tailor a conventional illumination system to the unique characteristics of the projection optics used in the photolithographic system, thereby compensating for vertical and horizontal bias or variations in line width for features oriented in the vertical and horizontal direction.

Abstract: A first cylindrical lens and a first linear sensor are constructed on the X axis, a second cylindrical lens and a second linear sensor are constructed on the Y axis, the X and Y axes are orthogonal, and the image width of a beam spot formed by each of the first and second cylindrical lenses is larger than each pixel of the corresponding first and second linear sensors.

Abstract: An optical tool includes a tool body that is transparent to light. Pluralities of parallel opaque lines on the body form a first outline in the shape of the square, and a second outline in the shape of a square which is centrally located relative to and within the first-mentioned square. Each pair of adjacent parallel lines has therebetween a first region that allows transmission of light therethrough without changing phase thereof, and a second region alongside the first region that allows transmission of light therethrough while shifting the phase thereof by 90°. The phase shifting and non-phase shifting regions are positioned so that the images of the outlines provided by a lens on an object shit in position a substantial amount as the distance between the lens and the object is changed.

Abstract: Misalignment error between two periodic structures such as two overlay targets placed side-by-side is measured. The two structures are illuminated by coherent radiation and the positive and negative diffraction beams of the input beam by the two structures are detected to discover the optical phase difference between the positive and negative diffraction beams. The misalignment between the two structures may then be ascertained from the phase difference.

Abstract: A passive alignment technique is disclosed to facilitate accurate positioning of components of an optical assembly. In one aspect, a method includes directing light onto components of an optical assembly in which a first component includes a first pattern of marks with a first frequency and a second component includes a second pattern of marks with a second different frequency. An optical signal corresponding to the superposition of the first and second patterns is detected. Based on the detected optical signal, a determination may be made as to whether the first and second components are properly positioned with respect to one another.

Abstract: A test fixture for testing circuit components includes at least one test bar, at least one tray, a test pedestal, a transportable test stage, a pickup collet, a first camera, and a second camera. Each test bar contains at least one circuit component. Each tray contains at least one test bar. The test pedestal is adapted to hold at least one test bar. The transportable test stage includes at least one tray and the test pedestal. The transportable test stage transports the circuit component under test from the pickup collet to the test site and return. The trays and test pedestal are in a fixed position with respect to the test stage. The pickup collet picks up test bars from the trays and the test pedestal. The pickup collet also places the test bars in the trays and on the test pedestal. The first camera is used to visually align the pickup collet and components on the test stage, and read test bar identification codes. The second camera is used to visually align the test bars with a test site.

Abstract: A high-performance projection exposure apparatus and method which can adjust optical characteristics which are rotationally asymmetric with respect to the optical axis of projection optical system and which remain in the projection optical system. In exemplary embodiments, the projection exposure apparatus includes an illumination optical system, a projection optical system and a plurality of optical elements. The illumination optical system illuminates a first object, and the projection optical system projects an image of the first object onto a second object under a predetermined magnification. The optical elements are set between the first object and the second object, and has rotationally asymmetric powers with respect to an optical axis of the projection optical system. Consequently, the optical elements can correct an optical characteristic rotationally asymmetric with respect to the optical axis of the projection optical system remaining in the projection optical system.

Abstract: Alignment to buried marks is carried out by using electromagnetic radiation to induce waves in the layers covering the buried layer. The acoustic or thermal waves cause reflectivity changes and displacements in the surface whose position and/or time dependence reveals the true position of the buried alignment mark. The buried alignment mark may be revealed by mapping the thickness of covering layers in its vicinity, e.g. by measuring the time dependence of the decay of a standing wave induced in the covering layers or by measuring the delay time of echoes of a travelling wave created at interfaces between different ones of the covering layers. Alternatively, a travelling wave can be created over the whole area of the mark so that echoes off the top and bottom of the buried mark carry positive and negative images of the mark; these cause reflectivity differences and displacements when they reach the surface which can be aligned to.

Abstract: A light barrier or light barrier grid has two housings in which a light source and a light receiver are arranged. In addition, an apparatus for aligning the two housings is provided. For this purpose, the first housing includes an alignment light emitter, while a mirror is arranged in the second housing. An alignment beam generated by the alignment light emitter is reflected by the mirror onto itself, or nearly onto itself.

Abstract: In a method for controlling a processing apparatus, an error value between an input value of the processing apparatus for processing a subject to be processed, and a measurement value obtained by measuring the subject being processed is obtained. A correction value is computed for correcting the input value of the processing apparatus in the direction of decreasing the error value, and the values are managed as processing data to be utilized in computing a next correction value. Previous processing data having a history identical to that of the subject loaded to the processing apparatus is searched, and a current bias correction value is predicted from a plurality of most recent correction values having the identical history. Also, a current random correction value is predicted by means of a neural network on the basis of a plurality of most recent random correction values. The predicted bias correction value is summed with the random correction value as a current correction value of the processing apparatus.

Abstract: A system for manufacturing a semiconductor device which predicts a difference in registration error between a circuit pattern and an overlay mark from a pattern dimension, illumination conditions and the wave aberration of an exposure lens, feeds a correction value based on the predicted difference back to an exposure device and modifies an overlay inspection data control limit.

Abstract: The object of the present invention is to provide a mark detection method, an exposure method, a device manufacturing method, a mark detection apparatus, an exposure apparatus, and a device manufactured by the use of the exposure apparatus, which are capable of reducing a position measurement error in a short time even in the case where a sampling interval must be set to about 0.2 times or more of a lower limit of a minimum periodic component. In the present invention, a mark formed on an object is irradiated with a detection beam, an image of the mark is picked up through an image-forming system, the image of the mark formed on an image pickup device is converted into an electrical image signal, a signal related to the image signal is output at predetermined sampling intervals, and a signal related to the image signal is interpolated in a cycle equal to or less than the predetermined sampling interval.

Abstract: A fast wafer positioning method for optical metrology includes three main steps. In the first step, an initial measurement recipe is constructed for the host system and target wafer. In the next step, the host system performs a test run using the initial measurement and the target wafer. In this step, the initial measurement recipe is refined to eliminate positioning errors produced by the host system. In the final step, the refined measurement recipe is used by the host system to process production wafers (e.g., as part of a production environment). This is performed using the information included in the refined measurement recipe without reference to optical images of the wafers being processed.

Abstract: An illumination optical system for illuminating a mask using light from a light source includes a shape varying mechanism for continuously making a shape of an effective light source variable, wherein the shape varying mechanism includes a first stop plate that has a first aperture part for allowing the light to pass through the first aperture part, and a second stop plate that has second aperture part for allowing the light that has passed through the first stop plate through the second aperture part.

Abstract: A wafer stage assembly, wafer table servo control system, and method for operating the same, are provided for use in combination with a projection lens assembly in a semiconductor wafer manufacturing process. The wafer stage assembly includes a wafer stage base supporting a wafer stage to position the semiconductor wafer, a wafer table connected to the wafer stage to support the wafer, a plurality of sensors, and an actuator. The sensors include a first sensor to determine a position of an exposure point on the wafer relative to the projection lens assembly, and a second sensor to determine a position of a focal point of the projection lens assembly relative to the exposure point. To increase focusing properties of the projection lens assembly, in response to the determined positions of the exposure point and the focal point, the actuator moves the wafer table so that the exposure point substantially coincides with the focal point.

Abstract: The optimized band saw feed speed system of this invention is associated with a saw mill carriage reciprocable past a band saw by a power drive motor. The feed speed control system utilizes a first laser line arranged to allow video scanning of the diameter profile of a log on the carriage for measuring the impending depth of cut by the band saw blade as the carriage moves the log through the band saw. A second laser line is arranged to show on the band saw blade for detecting the lateral deviation of the blade from its path. A video camera is arranged to cover the diameter of a log on the carriage and to view the laser line projections and control the speed of the power drive motor of the carriage, to provide optimum speed of movement of the log through the band saw.

Abstract: A bonding apparatus that includes a bonding tool through which a wire passes and which performs bonding on a workpiece, a position detection camera which takes images of the workpiece, a reference member which is disposed in a specified position, and an optical assembly which conducts the image of the tool and reference member to the position detection camera. A lens used in the position detection camera and a lens installed in the optical assembly are arranged so that such lenses construct an afocal optical system.

Abstract: A system and method having applications in semiconductor areas for accurate die placement on a substrate that takes into account any positional offset from the reference position due to variations caused by thermal change and other nonrandom systemic effects. The system includes an offset alignment tool having a plurality of internal reflection surfaces and located below a vision plane of the substrate, and an optical detector to receive an indirect image of a bottom surface of the die through the alignment tool, such that the die is accurately positioned on the substrate based on the indirect image received by the optical detector. The method comprises the steps of providing a cornercube offset alignment tool having a plurality of total internal reflection surfaces below a vision plane of the die, and receiving an indirect image of the die tool through the cornercube offset tool.

Abstract: A controller of an optical axis aligning apparatus carries out quadric surface approximation with a plane parallel to a connecting end face of an optical component or an optical fiber, in order to align the emission axis of the optical component and the optical axis of the optical fiber in connecting the component and the fiber, and then carries out quadric function approximation in the direction of an axis perpendicular to the plane related to the quadric surface approximation, thereby securely finding a maximum light quantity point at a lower frequency of stage operation in the aligning apparatus to shorten the tact time for optical axis alignment.

Abstract: An exposure apparatus for exposing a photoresist film formed on a semiconductor substrate includes a plurality of reticle stages on which respective reticles can be supported at the same time. The reticles can be selectively and hence, successively, positioned along the optical axis of the apparatus that extends from the light source of the apparatus to a substrate stage. One region of the photoresist film is exposed to light directed through the first reticle. Then the second reticle stage is aligned and another region of the photoresist film is exposed to light directed through the second reticle.

Abstract: A system and method are used to calibrate a focus portion of an exposure section of a lithography tool. A wafer is exposed so that a resulted or formed patterned image is tilted with respect to the wafer. The tilting can be imposed based on controlling a wafer stage to tilt the wafer or a reticle stage to tilt the reticle. The wafer is developed. Characteristics of the tilted patterned image are measured with a portion of the lithography tool to determine focus parameters of an exposure system. The portion can be an alignment system. The measuring step can measure band width and/or band location of the tilted patterned image. Sometimes, more than one patterned image is formed on the wafer, then the measuring step can measure distance between bands and shifting of the bands with respect to a central axis of the wafer. The focus parameters can be focus tilt errors and/or focus offset. The focus parameters are used to perform calibration.

Abstract: An article of manufacture bearing an alignment target having at least one of the following attributes: it has no significant rotational symmetry; it has no significant orientation self-similarity or size self-similarity; it is not primarily composed of circles, circular arcs, straight lines, or right angles; and it may have other unique attributes. In one embodiment, the specific alignment targets are shapes consisting of at least one “generalized polar polygon.” Such a figure will include radial lines, circular arcs, and spiral segments when drawn in the Cartesian plane. In another embodiment, the specific alignment targets are members of a family of “fan” shapes.

Abstract: Photolithographic processes require alignment of substrate to mask prior to exposure. Alignment accuracy becomes critical as feature size diminishes. For alignment tolerances above 1 &mgr;m, off-axis camera-based techniques are acceptable, but require frequent calibration. Through the lens (TTL) on-axis alignment is much preferred, not requiring frequent calibrations and having superior alignment accuracies, even though usually more complicated and expensive. This invention provides a simple, easy to incorporate TTL, on-axis alignment technique for alignment accuracies of 1 &mgr;m, such as scan-and-repeat patterning systems that employ a unitary mask-substrate stage and a folded projection imaging system. There is a master alignment mark adjacent to the mask, which is imaged onto a phosphor screen with the same radiation as is to be used for patterning.

Abstract: An apparatus and method for detecting mispositioned wafers attributable to transfer shift of the wafer are disclosed. A calibration wafer has a target region comprising a pattern of optically distinguishable features from which is determined the position of the calibration wafer within the chamber subsequent to its transfer therein. Preferably, the features comprise a pattern of colors that can be detected by spectroscopy. A preferred form and manner of providing such color features is by way of dielectric thin film filters.

Abstract: A way to average alignment measurements that obtains the advantage of multiple alignment marks per shot without requiring actual measurement of all alignment marks on all wafers of a batch. All alignment marks on all sampled shots are measured and averaged on the first wafer of a batch. The offset between a single sampled alignment mark and the average total offset for the wafer is characterized and applied when that alignment mark is sampled on succeeding wafers.

Abstract: A scanning type projection exposure apparatus including an illumination optical system having a slit which can change an illumination area width in the scanning direction, excluding a portion of this area. The light intensity at a portion located in correspondence with a slit area is detected, and the detection result is used to control the exposure amount with respect to a wafer. The scanning type projection exposure apparatus can control the exposure amount precisely. In the exposure apparatus, the illumination area width in the scanning direction can be changed in order to make uniform the exposure amount in a direction perpendicular to the scanning direction.

Abstract: An exposure method according to the present invention includes a first step of forming on a substrate an alignment mark including a concave and convex pattern; a second step of forming a coat over said alignment mark and the other area on said substrate; a third step of flattening said coat; and a fourth step of applying a photosensitive material on said coat flattened by said third step and projecting a mask pattern thereto. The alignment mark is formed by said concave and convex pattern arranged with a pitch which is smaller than the predetermined value between adjacent convex portions having a width of not less than a predetermined value.

Abstract: A large scale polarizer comprises one or more quartz substrate parts formed as a rectangle, a triangle, or a parallelogram, and a polarizer holder supporting the quartz substrate part. The polarizer holder may be in a lattice structure holding a plurality of quartz substrate parts. A polarizer system employing the large scale polarizer comprises a lens making an incident light to a parallel light, the large scale polarizer, and a moving control part coupled to and moving the large scale polarizer.

Abstract: A method and apparatus for aligning the axis of a mirror of a carbon in ash sensor. The method first executes a series of steps that causes a stepper motor connected to an axis of the mirror to move the mirror through a first coarse alignment procedure and then executes a second series of steps that that moves the mirror through a second fine alignment procedure.

Abstract: In an exposure apparatus, a main controller calculates the thickness of a light transmitting protective member that protects a pattern surface of a mask, based on detection signals of a first and second reflection beams of a detection beam irradiated from an irradiation system, reflected off the front and back surfaces of the protective member, and received by a photodetection system. This makes exposure that takes into account the variation in the image forming state of the image pattern depending on the calculated thickness of the protective member possible. Accordingly, exposure with high precision is possible, without the difference in thickness of the protective member protecting the pattern surface of the mask affecting the exposure. In addition, when the incident angle of the detection beam is optimized, setting a detection offset in the photodetection system, or resetting the origin will not be necessary.

Abstract: The correct handover position between the gripper and the e-chuck is located using a light source and a 2-D photosensor. As the e-chuck is in the loading position it can be driven forwards or backwards in the beam direction by rotating the main whisper scan rotor. The line drawn across the 2-D array by a spot of light from the light source passing through a hole in a flag attached to the e-chuck is recorded. Similarly, the line drawn by a spot of light from the same source passing through a hole in the flag attached to the gripper is also recorded. The point of intersection is the ideal transfer point. For transfer the e-chuck is then driven to this point which can be checked from the 2-D sensor. The gripper is then also driven to the same point and alignment can be checked using the light source and sensor.

Abstract: A method of detecting focus information about an image projecting optical system includes performing mark projection through the optical system, and, based on illumination lights having different chief ray incidence directions, the mark projection is carried out so that mark images formed by the illumination lights, respectively, are superposed one upon another approximately upon an imaging plane, and detecting focus information about the optical system on the basis of information related to a deviation between the mark images superposed.

Abstract: A virtual gauging system for use in a lithographic process is described that includes means for gauging a region at a surface of a wafer when the region is located away from an axis of illumination producing wafer surface data, while other portions of the wafer are being illuminated. The system also includes means for converting the wafer surface data into wafer correction data and means for adjusting a separation distance between an exposure lens and the region at the surface of the wafer based on the correction data when the region is located at the axis of illumination. The means for gauging includes at least two wafer surface gauges located on opposite sides of an illumination slot.