Method for determining the optical properties of an optical system

Abstract

This provides a method for determining the optical properties of an optical system. [Solution] To determine the optical properties of an optical system having an illumination system that illuminates an object field of view and a projection system that images the object field of view into an image field of view, the following steps are taken: Illumination of the object field of view is provided through an illumination pupil containing a plurality of pupil spots. An optical element is provided having an optical surface containing a plurality of shift optical regions. The plurality of shift optical regions result in a separate directional shift of the illumination beam incident on each shift optical region, depending on each shift optical region. For a plurality of distinct field of view points in the object field of view, the individual directional shifts are calibrated for each pupil spot by measuring the pupil spot shift resulting from the shift optical region via a measuring pupil (4) in the path of the illumination beam after the optical element. From the measured pupil spot shifts, the optical properties to be determined are calculated. The resulting determination method is robust to obtaining the desired optical properties.

Description

[Technical Field]

[0001] This application claims priority to German Patent Application No. DE10 2023 203 312.7, the contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for determining the optical properties of an optical system. Furthermore, the present invention relates to an optical device having an optical system comprising an illumination system and a projection system. [Background technology]

[0003] A method for determining the apodization characteristics of an optical system is known from U.S. Patent Application Publication No. 2013 / 0271636. [Overview of the Initiative]

[0004] The present invention aims to develop a method for determining optical properties that is robust in obtaining appropriate results for the optical properties to be determined.

[0005] Such an objective is achieved by the method according to claim 1.

[0006] Calibrating the individual directional shifts resulting from multiple shift optical regions of an optical element by using an illumination pupil containing multiple pupil spots provides an information base for subsequent calculations of optical properties, particularly information about the non-uniformity of the desired individual directional shifts of each shift optical region. Manufacturing tolerances of the optical element, and especially those relating to the shift optical regions of the optical element, can be evaluated and compensated in the determination method, particularly based on the information obtained in the calculation step. After obtaining the potential deviations from desired values ​​of the individual directional shifts of the multiple shift optical regions, further steps of optical property determination methods, known from the art but now used with the calibrated directional shift data, can be used.

[0007] By using a method including calibration, it is possible to directly measure the pupil shift characteristics, and thus, during calculation, the effect of the projection system on the determined optical characteristics can be separated from the effect of the illumination system.

[0008] In particular, the selected optical characteristics of the illumination system and / or the projection system of the optical system can be determined.

[0009] An example of the determined optical characteristic is the apodization of the optical system. Further optical characteristics that can be determined by the method are the diattenuation of the optical system.

[0010] In the calculation step, measurements using the entire pupil may be used after the calibration step. Such measurements using the entire pupil do not use a pupil having a plurality of pupil spots, but may use a pupil that is uniformly or continuously illuminated. Alternatively, in measurements using the entire pupil, a plurality of separate pupil spots may also be used.

[0011] The optical element can have at least two shift optical regions.

[0012] The calibration step can be repeated after a given period. This can minimize the undesired effects, particularly with respect to the effect of the optical element on the illumination beam due to drift or equivalent effects.

[0013] [[ID=2四十八]]The calibration of the individual direction shifts can be performed depending on the pupil spots.

[0014] By calibrating the individual direction shifts, errors resulting from manufacturing errors of the shift optical region, particularly manufacturing tolerances, are reduced. Further, errors resulting from the drift of the shift effect of the shift optical region over time are reduced. Further, the alignment error of the optical element can be reduced. Further, the bending error of the optical element can be reduced.

[0015] By using an illumination pupil having a plurality of pupil spots during the calibration step, deviations resulting from such manufacturing / placement / drift errors can be measured.

[0016] By calibrating the individual direction shifts, the translational deviation of each pupil spot from a given value and the azimuthal displacement of each pupil spot can be calibrated.

[0017] During the calibration and calculation steps of the method, the angular displacement from the shift optical region of each pupil spot can be analyzed, saved, and used within the method. The detection and localization of the shift of each shifted pupil spot can be performed via a fitting algorithm such as "maximum value", Gaussian fit, or Lorentz fit.

[0018] Regarding the determination of apodization, in particular, it is possible to separate the apodization effect of the illumination system from the apodization effect of the projection system in order to achieve strict apodization tolerances independently for the illumination system on the one hand and the projection system on the other hand.

[0019] An optical element having a plurality of shift optical regions can be inserted into the beam path between the illumination system and the projection system of the optical system. Then, the plurality of shift optical regions introduce a defined new set of illumination angles into the projection system, which is different from the initial set defined by the plurality of pupils. This new set of illumination angles provides access to the optical characteristics of the projection system, particularly the apodization characteristics, independently of the optical characteristics of the illumination system.

[0020] The optical element can be designed to be inserted into the beam path of the optical system in at least two different orientations. This reduces the requirements regarding the number of shift types of the shift optical regions.

[0021] The non-shift optical region according to claim 2 further improves the quality of the calibration step of the method. The non-shift optical region can be embodied as a pinhole in the optical element.

[0022] The wedge as a shift optical region according to claim 3 has been proven effective in the apodization characterization method, referred to in this respect as U.S. Patent Application Publication No. 2013 / 0271636. The wedge tilt can be in the range of 10 mrad to 55 mrad. Such tilts can be measured with respect to a plane perpendicular to the optical axis of the optical system. The wedge tilt can be selected so that, after each directional shift, the illumination beam that has undergone such a directional shift is still within its numerical aperture in the further beam path of the optical system. Any tilt angle smaller than 10 mrad is possible, depending on the accuracy of the measurement system that measures each pupil spot shift. If the numerical aperture of the optical system is sufficiently large, wedge tilt angles larger than 55 mrad are also possible.

[0023] In addition to or instead of shifting via wedges, such shifts can also be achieved using grids, particularly linear grids. Such linear grids can be moved laterally, i.e., perpendicular to the path of the lighting scheme. Such translational movement can be stepwise and is also called shearing movement.

[0024] The angular difference between wedge orientations according to claim 4, which deviates from right-angle wedges known in the art, has been proven useful in determining apodization characteristics. Such deviations can be compensated for during the calibration step of the method.

[0025] For example, an angular difference that is an integer multiple of 90 degrees gives four different wedge orientations (0 degrees / 90 degrees / 180 degrees / 270 degrees) and four corresponding types of wedges. In further embodiments of the optical element, different or additional wedge orientations of 45 degrees, 135 degrees, 225 degrees, and / or 315 degrees may be provided. In further examples, wedges have orientations of 5 degrees, 10 degrees, 15 degrees, 30 degrees, or 45 degrees relative to each other. As a result, there may be more than four types of wedge orientations, such as six or eight types. Even more than a certain number of wedge orientations may exist.

[0026] By using optical elements that can be inserted into the beam path of the optical system in at least two orientations, the number of wedge orientations required can be reduced. For example, a 90-degree wedge orientation can be converted to a 270-degree wedge orientation by rotating the entire optical element by 180 degrees.

[0027] The grid arrangement of multiple pupil spots according to claim 5 has been proven effective. Such a grid arrangement can be generated via a pupil generation device. The pupil generation device may include a pupil facet mirror and / or a pupil microlens array and / or multiple pinholes in the pupil plane.

[0028] The calibration information map according to claim 6 helps to determine whether the calibrated optical element is suitable, and that calibrated optical element can then be used without the need to repeat the calibration step. The measure of pupil spot shift is the individual directional shift of each illumination beam.

[0029] By using diffraction of the illumination beam through at least one optical grating region, a Ronchi test measurement is made possible by including a Ronchi test according to claim 7. The Ronchi test is described in J. Braat et al. "Improved Ronchi test With extended source" (J. opt. Soc. Am.A, Vol.16, No.1, pp.131-140 (1999)). Phase, offset, and modulation data can be obtained from such Ronchi test measurements, which can further be used, for example, to obtain the apodization characteristics of the optical system. An optical grating region may be part of an optical element. Each optical grating region may be comprised of each region of a shifted optical region. The arrangement of the optical grating regions and optical shift regions along the beam path of the illumination beam depends on each embodiment of the optical device. Along such a beam path, the optical grating regions may follow the optical shift regions, or the optical shift regions may follow the optical grating regions.

[0030] By using at least one optical polarizer in the method according to claim 8, it becomes possible to determine the diatenation of the optical system. The optical polarizer can move between different polarizer positions to make the illumination beam into different polarization states. The optical polarizer may be a linear polarizer. The optical polarizer may be driven by a controlled drive unit for controlled setting of a given polarization state.

[0031] Using the optical analyzer according to claim 9 is particularly useful for determining the diatenation of an optical system.

[0032] A further objective of the present invention is to improve an optical apparatus capable of performing such an optical property determination method.

[0033] Such an objective is achieved by an optical device having the features of claim 10.

[0034] The advantages of such optical devices correspond to the advantages of the optical property determination methods described above. In particular, optical devices can be designed to perform such methods.

[0035] The optical apparatus according to claim 11 enables the automatic calibration step by the method described above.

[0036] An optical apparatus having a calculation module according to claim 12 enables an automated calculation step within the method described above. Using a Ronchi grating according to claim 13 as each corresponding optical grating region in the method provides the advantages described herein.

[0037] Using the optical polarizer according to claim 14 and the optical analyzer according to claim 15 provides the advantages described above with respect to claims 8 and 9.

[0038] Exemplary embodiments of the present invention will be described below with reference to the enclosed figures. [Brief explanation of the drawing]

[0039] [Figure 1] This figure shows a lithography apparatus that includes an optical system comprising an illumination system for illuminating the optical field and a projection system for imaging the optical field onto the image field, and an optical device capable of determining the optical characteristics of the optical system. [Figure 2] This diagram schematically shows variations in the beam path through the optical device. [Figure 3] A plan view of an optical element having an optical surface comprising a plurality of wedges and a further plurality of pinholes as part of an optical device, wherein the optical element is used in a method for determining the optical properties of an optical system. [Figure 4] Figure 3 shows a cross-section of one of the multiple wedges of the optical element, further illustrating the beam paths of individual rays passing through the wedge that causes the ray direction shift, and also showing a portion of the substrate of the optical element supporting that wedge. [Figure 5] This figure shows another embodiment of a wedge on a substrate for an optical element, where the wedge is fixed to the substrate via an adhesive structure. [Figure 6] Figure 5 is a top view of a different embodiment of an adhesive structure that can be used to bond a wedge to a substrate. [Figure 7] Figure 5 is a top view of a different embodiment of an adhesive structure that can be used to bond a wedge to a substrate. [Figure 8] Figure 5 is a top view of a different embodiment of an adhesive structure that can be used to bond a wedge to a substrate. [Figure 9] This is a perspective view of one of several wedges of an optical element, or another embodiment. [Figure 10] This diagram shows the intensity distribution of illumination light through an illumination pupil, which has multiple pupil spots arranged as a grid within a circular pupil. The illumination pupil is used in methods for determining the optical properties of an optical system. [Figure 11] Figure 10 shows the measurement results of pupil spot shift resulting from the illumination of an optical element with pupil intensity distribution, illustrating the possible pupil spot shifts caused by each pupil spot position. [Figure 12] This diagram expands on the possibilities of different pupil spot shifts caused by different types of wedges on optical elements. [Figure 13] This figure is similar to Figure 2 and shows a further arrangement of optical devices that can determine the attenuation characteristics of the optical system. [Figure 14] This diagram schematically shows components that guide the beam path through another embodiment of the optical apparatus, which further includes a ronch grating, as part of the apparatus for determining the optical properties of the optical system. [Figure 15] This figure is similar to Figure 14 and shows the diffraction scheme of the Ronchi grating embodiment in Figure 14. [Figure 16] Figures 14 and 15 show the positional relationship between the linear grid (source grid) structure of the grid and the linear grid (source grid) structure of the launch grid in the shape of a checkerboard arrangement of sensor devices, illustrating the positional relationship that shows the first shear direction x caused by different translational positions of the linear grid with respect to the launch grid along the first shear direction x. [Figure 17] Figures 14 and 15 show the positional relationship between the linear grid (source grid) structure of the grid and the linear grid (source grid) structure of the launch grid in the shape of a checkerboard arrangement of sensor devices, illustrating the positional relationship that shows the first shear direction x caused by different translational positions of the linear grid with respect to the launch grid along the first shear direction x. [Figure 18] Figures 14 and 15 show the positional relationship between the linear grid (source grid) structure of the grid and the linear grid (source grid) structure of the launch grid in the shape of a checkerboard arrangement of sensor devices, illustrating the positional relationship that shows the first shear direction x caused by different translational positions of the linear grid with respect to the launch grid along the first shear direction x. [Figure 19] Similar to Figures 16-18, the positional relationships between the rach grating and the rach grating of further embodiments of the optical element according to Figures 14 and 15, which have different linear lattice structure orientations, are shown for three positional relationships along a different shear direction y. [Figure 20]Similar to Figures 16-18, the positional relationships between the rach grating and the rach grating of further embodiments of the optical element according to Figures 14 and 15, which have different linear lattice structure orientations, are shown for three positional relationships along a different shear direction y. [Figure 21] Similar to Figures 16-18, the positional relationships between the rach grating and the rach grating of further embodiments of the optical element according to Figures 14 and 15, which have different linear lattice structure orientations, are shown for three positional relationships along a different shear direction y. [Figure 22] This figure shows the phase signal measured at one pixel of a sensor device at a relative position as shown in Figures 16-18 and / or Figures 19-21. [Modes for carrying out the invention]

[0040] This specification discloses one or more embodiments incorporating features of the present invention. The disclosed embodiments are merely illustrative of the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the appended claims.

[0041] The embodiments described, and references in the specification such as “one embodiment,” “a certain embodiment,” and “exemplary embodiment,” indicate that the embodiments described may include certain features, structures, or characteristics, but not all embodiments necessarily include certain features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiments. Moreover, when certain features, structures, or characteristics are described in relation to one embodiment, it is understood that it is within the knowledge of those skilled in the art to bring about such features, structures, or characteristics in relation to other embodiments, whether explicitly described or not.

[0042] Embodiments of the present invention can be realized by hardware, firmware, software, or any combination thereof. Embodiments of the present invention can also be realized as instructions stored on a machine-readable medium, which can be read and executed by one or more processors. A machine-readable medium can include any mechanism for storing or transmitting information in a machine-readable format (e.g., a computing device). For example, a machine-readable medium can include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagating signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and instructions may be described herein as performing specific actions. However, such descriptions are for convenience only, and it should be understood that in practice, such actions result from a computing device, processor, controller, or other device executing firmware, software, routines, instructions, etc.

[0043] However, before describing such embodiments in more detail, it is useful to present exemplary environments in which embodiments of the present invention may be implemented.

[0044] While this text may specifically refer to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein may have other applications, such as the manufacture of integrated optical systems, induction and detection patterns for magnetic domain memory, liquid crystal displays (LCDs), thin-film magnetic heads, and the like. Those skilled in the art will understand that in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered synonymous with the more general terms “substrate” or “target portion,” respectively. The substrates referred to herein may be processed before or after exposure, for example, in a track (typically a tool for coating a layer of resist onto the substrate and growing the exposed resist) or in a measuring or inspection tool. Where applicable, this disclosure herein may apply to such and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example, to create a multilayer IC, and therefore the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

[0045] As used herein, the terms “radiation” and “beam” encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths of 365, 248, 193, 157, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range of 5 to 20 nm), as well as particle beams such as ion beams and electron beams.

[0046] As used herein, the term “patterning device” should be broadly interpreted to refer to a device that can be used to impart a pattern to a radiation beam in its cross-section in order to create a pattern on a target portion of a substrate. It should be noted that the pattern imparted to the radiation beam may not precisely correspond to the desired pattern on the target portion of the substrate. Generally, the pattern imparted to the radiation beam corresponds to a specific functional layer of the device to be created on the target portion, such as an integrated circuit.

[0047] Patterning devices can be transparent or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well-known in lithography and include various mask types such as binary, alternating phase shift, and decaying phase shift, as well as various hybrid mask types. In an example of a programmable mirror array, a matrix arrangement of small mirrors is employed, and by tilting each small mirror individually, the incident radiation beam can be reflected in different directions, thus patterning the reflected beam.

[0048] A support structure holds the patterning device. The support structure holds the patterning device depending on the orientation of the patterning device, the design of the lithography apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. Mechanical clamps, vacuum, or other clamping techniques, such as electrostatic clamps under vacuum conditions, can be used for support. The support structure may be a frame or a table, and may be fixed or movable as needed, for example, to ensure that the patterning device is in a desired position with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0049] As used herein, the term “projection system” should be interpreted broadly to encompass various types of projection systems, including refractive optics, reflective optics, and reflective-refractive optics, depending on other factors such as the exposure radiation used and the use of immersion solutions or vacuum. Any use of the term “projection lens” herein may be considered synonymous with the more general term “projection system.”

[0050] Lighting systems or illuminators can also encompass various types of optical components, including refractive, reflective, and refractorious optical components for directing, shaping, or controlling beams of radiation, and such components may also be referred to collectively or singularly as “lenses” below.

[0051] A lithography apparatus may be of a type having two or more substrate tables (and / or two or more support structures). In such a "multi-stage" machine, additional tables may be used in parallel, or preparation steps may be performed on one or more tables while one or more other tables are being used for exposure.

[0052] The lithography apparatus may be of a type that immerses the substrate in a liquid with a relatively high refractive index, such as water, to fill the space between the final element of the projection system and the substrate. Immersion techniques for increasing the numerical aperture of the projection system are well known in this art.

[0053] Figure 1 schematically shows a lithography apparatus LA according to one embodiment of the present invention. The apparatus includes an illumination system IL adapted to condition a beam B of radiation (such as UV radiation), and a support structure such as a mask table MT connected to a first positioning device PM configured to hold a patterning device such as a mask MA and to precisely position the patterning device relative to a projection system PS. The projection system PS is adapted to image the pattern applied to the beam B by the patterning device MA within the object field OF of the projection system PS onto a target portion C of a substrate W in the image field IF. The apparatus also includes a substrate table such as a wafer table WT configured to hold a substrate W such as a resist-coated wafer and to be connected to a second positioning device PW configured to precisely position the substrate relative to the projection system PS.

[0054] Illumination systems may include various types of optical components, such as refracting, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0055] The support structure MT holds the patterning device MA depending on the orientation of the patterning device, the design of the lithography apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or table that can be fixed or movable as needed. The support structure can ensure that the patterning device is in the desired position relative to the projection system, for example.

[0056] The term "patterning device" should be broadly interpreted to refer to any device that can be used to impart a pattern to a radiation beam in its cross-section, so as to create a pattern on a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer of the device to be created on the target portion, such as an integrated circuit.

[0057] Patterning devices can be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well-known in lithography and include various mask types such as binary, alternating phase shift, and decaying phase shift, as well as various hybrid mask types. In an example of a programmable mirror array, a matrix arrangement of small mirrors is employed, and by tilting each small mirror individually, the incident radiation beam can be reflected in different directions. The tilted mirrors give a pattern to the radiation beam reflected by the mirror matrix.

[0058] The projection system, like the illumination system, can include various types of optical components, such as refracting, reflecting, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, depending on other factors such as the exposure radiation used and the use of vacuum. Since gases can absorb too much radiation, it is desirable to use a vacuum for EUV radiation. Therefore, a vacuum environment can be provided throughout the beam path using vacuum walls and vacuum pumps. By supplying gas to parts of the lithography apparatus, for example by utilizing a gas flow, the possibility of contaminants reaching the optical components of the lithography apparatus can be reduced.

[0059] As shown in Figure 1, this device is a transmissive type using a transmissive mask MA. Alternatively, the device may be a reflective type using a programmable mirror array.

[0060] The illuminator IL receives a radiation beam from the radiation source SO. The illuminator IL comprises a tuning device AD ​​configured to set an outer and / or inner radial range, an integrator IN, and a capacitor CO. The radiation source SO includes at least one laser, e.g., one or two UV excimer lasers. For the sake of illustrative purposes of Figure 1, a single radiation source SO is shown, and the radiation source SO may include both lasers, or alternatively, multiple radiation source SOs may be provided, each having a single laser, whose beams are combined before or after entering the projection system PS. Also provided is a beam delivery system BD, e.g., including a suitable directional mirror and / or beam expander. The radiation source SO and beam delivery system BD combine to form a radiation system that presents a suitable radiation beam to the projection system. It will be understood that the beam B of this radiation includes radiation from at least one laser. It will also be understood that the beam may include alternating pulses of radiation from at least one laser.

[0061] The projection system PS may include a diaphragm having an adjustable transparent aperture used to set the numerical aperture of the projection system PS at the wafer level to a selected value.

[0062] A beam of radiation B is incident on a patterning device MA held on a support structure MT. After traversing the patterning device, the beam of radiation B passes through a projection system PS, which focuses the beam onto a target portion C on the substrate W. A second positioning device PW and a position sensor IF (e.g., an interferometer device) can be used to precisely move the substrate table WT to position various target portions C along the path of beam B. Similarly, a first positioning device PM and another position sensor, along with alignment marks M1, M2, and P1 and P2, can be used to precisely position the patterning device MA relative to the path of beam B and the substrate W. Generally, the movement of the support structure MT and the substrate table WT is achieved using long-stroke modules for coarse positioning and short-stroke modules for fine positioning. However, in the case of a stepper (rather than a scanner), the support structure may be connected only to short-stroke actuators or may be fixed.

[0063] The illustrated device can be used in at least one of the following modes: 1. In step mode, the support structure (e.g., mask table) MT and substrate table WT are essentially stationary, while the entire pattern applied to the radiation beam is projected onto the target portion C in one pass (i.e., single static exposure). The substrate table WT is then shifted in the X and / or Y directions to allow exposure of different target portions C. 2. In scanning mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously, while the pattern applied to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g., mask table) MT can be determined by the (reduction) scaling and image inversion characteristics of the projection system PS. 3. In another mode, the support structure (e.g., mask table) MT is essentially stationary, holding the programmable patterning device, while the substrate table WT is moved or scanned, and the pattern applied to the radiation beam is projected onto the target portion C. In this mode, a pulsed radiation source is generally used, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between continuous radiation pulses during scanning. This operating mode can be readily applied to maskless lithography utilizing programmable patterning devices, such as the programmable mirror arrays of the type described above.

[0064] Combinations and / or variations of the above usage modes, or entirely different usage modes, may also be used. A known problem with conventional devices is the problem of apodization as a beam path through the projection system PL. Apodization is a known optical phenomenon that can result in a non-uniform angular intensity distribution of a light beam, particularly an attenuation of intensity at the edges of the beam. Apodization can be caused by changes in the illumination intensity distribution due to the lens material and lens properties of the lenses of the optical device. Lens apodization is becoming increasingly important, especially in systems using complementary phase-shift masks, for example. Such masks are typically illuminated by a coherent light beam in which the light is concentrated around the optical axis of the system. The diffracted light does not contain a zero-order beam and is directed closer to the edges of the system's aperture. The separation between these diffracted beams (and therefore the distance to the optical axis) is proportional to the resolution of the imaged feature. Apodization can cause similar dose errors depending on the resolution of the imaged line. Therefore, it is important to be able to measure both lens apodization and the difference between lens apodization in a single device where drift can occur over time and between systems.

[0065] To accurately measure apodization, it is necessary to know the optical distribution at the reticle level and compare it to the optical distribution at the wafer level. Current known apodization determination techniques assume that the optical distribution at the reticle level is (for example) uniform, but this is not always the case. One solution to this is to directly measure the optical distribution at the reticle level, but this may not be possible or easy. The present invention presents an alternative solution in which, in at least some embodiments, multiple shifted copies of the same optical distribution are measured at different parts of the lens.

[0066] Figure 2 schematically illustrates the basic concept behind apodization measurement, also known as U.S. Patent Application Publication No. 2013 / 0271636. In addition to apodization measurement, further optical properties of the optical system of such an optical system can be determined using the optical devices described below herein. An example of such further optical properties is diatenation of the optical system.

[0067] Figure 2 shows the illumination pupil 1 of the illumination system IL and the projection pupil 2 of the projection system PS. The illumination system IL and the projection system PS constitute the optical system of the projection exposure apparatus shown in Figure 1.

[0068] An optical element (such as a reticle, mask, or original) 3 is positioned between the illumination pupil 1 of the illumination system IL and the projection pupil 2 of the projection system, and the optical element 3 is typically located at the focal plane of the illumination system IL. In other words, when in use, the optical element 3 is positioned in the object plane of the object field of view OF where the mask MA will be located. The optical element 3 comprises a coating layer (e.g., a chromium layer), a plurality of pinholes arranged in the coating layer, the plurality of pinholes arranged so that radiation can pass through the optical element 3, and a plurality of sub-elements (wedges 5) that shift the radiation. These sub-elements are also shown as shift optical regions. Unshifted beam paths are represented by a first hatching. Shifted beam paths are represented by a second, different hatching.

[0069] Below the projection system PS, a sensor device 4a is provided, which includes a sensor module SM containing a camera having a camera pupil 4. The pinhole for measuring the camera pupil 4 is located in the same plane as the plane in which the substrate W would normally be located when in use, i.e., the image plane in the image field of view IF of the projection system PS. The camera of the sensor device 4a can be positioned in the far field of view plane without imaging optical components, or it can be positioned in the pupil plane with imaging optical components.

[0070] Figure 3 shows the structure of the optical element 3 in more detail. The optical element 3 comprises an array of optical wedges 5 and pinholes 6 arranged in a regular array in the x and y directions. Each wedge 5 is positioned on the substrate 3a of the optical element 3. The pinholes 6 between the wedges 5 can be used as a reference. Pinholes are also provided below each wedge 5 (not shown in Figure 3) to allow radiation impacting the optical element 3 to pass towards the projection system PS. The pinholes below the wedges 5 are shown as an exemplary pinhole "x" in Figure 5.

[0071] The pinhole 6 is provided in the coating layer on the surface of the optical element 3. The coating may be, for example, a chromium layer. Furthermore, other reticle features, such as a lattice structure, can be provided on or instead of the coating layer. These other reticle features may also be located beneath the wedge 5.

[0072] Figure 4 shows a more detailed view of the wedge 5. Figure 4 also schematically shows a portion of the substrate 3a of the optical element 3. The wedge 5 is positioned on the surface of the optical element 3 with its first surface 10 facing the substrate 3a of the optical element 3. The second surface 11 of the wedge 5, opposite to the first surface 10, is inclined at an angle α. A radiation beam striking the second surface 11 experiences a change in direction Φ2-Φ1 as a function of the wedge inclination angle α when the radiation beam exits the wedge 5 at the first surface 10. The plane on which the inclination angle or inclination angle α is measured represents the wedge orientation of each wedge 5 with respect to a reference plane. In the embodiment of Figure 4, such an inclination angle reference plane is the xz plane, and therefore the inclination of each wedge 5 is in the positive x direction. The location and orientation of each inclination angle reference plane are hereafter referred to as the wedge orientation.

[0073] To fix the sub-element (wedge) 5 to the surface of the optical element 3, the sub-element 5 can be clamped by clamping means positioned on the surface.

[0074] The sub-element 5 can be fixed by an adhesive 15 provided between the sub-element 5 and the surface of the optical element 3, as shown in the embodiments in Figures 6 to 8, either by means of an adhesive 15.

[0075] Preferably, the adhesive 15 is provided around the sub-element 5 outside the optical path (edge ​​region). This prevents the adhesive 15 from interacting with radiation used, for example, in apodization measurements. When the adhesive 15 is provided in the edge region, the adhesive forms a spacer. Thus, a partially closed space is formed between the sub-element 5 and the substrate 3a of the optical element 3.

[0076] For example, when two parallel spacers 15 are provided (see Figure 6), or when spacers are provided at all four corners, there is a risk that undesirable contaminants (e.g., dust particles) may become trapped in pinholes beneath the sub-element 5, particularly beneath the wedge 5.

[0077] Using adhesive 15 in additional edge regions to fix the sub-elements may reduce the likelihood of particles becoming trapped between the sub-elements 5 and the optical elements 3. For example, adhesive can be applied to three or four edge regions (Figures 7 and 8).

[0078] Providing adhesive 15 (or spacers) to the four edge regions can create a closed space. Such a configuration may be undesirable if the optical element 3 (and therefore the sub-element 5 as well) is subjected to pressure changes. Pressure changes can occur, for example, during the loading sequence of the lithography apparatus LA when the local environment is vacuumed. The pressure difference between the closed space and the local environment can cause stress on the spacers 15 and / or sub-element 5. To control the pressure in the space below the sub-element 5 and prevent dust particles from entering this space, a vent port 16 can be provided in at least one of the spacers, as shown in Figures 7 and 8. The vent port, which forms a labyrinth seal 16, allows gas flow between the closed space and the local environment but prevents dust particles from entering the closed space. The vent port 16 can be thought of as physically open but optically closed.

[0079] Figure 9 shows a perspective view of one exemplary embodiment of a plurality of wedges 5.

[0080] Figure 3 shows that the wedge-bound second surface 11 of each wedge 5 facing the viewer of Figure 3 can be inclined in four principal directions; that is, it can be inclined in the positive or negative x direction, or in the positive or negative y direction. Furthermore, inclination along the bisector between the positive / negative x coordinate and the positive / negative y coordinate is also possible, which is shown by the diagonal inclination modifying line 11a in Figure 3.

[0081] The pupil generation device 20, schematically shown in Figure 2, is located within the integrator IN of the illumination system IL. The pupil generation device 20 is in the beam path of the illumination light 19, upstream of the illumination pupil 1. Such a pupil generation device 20 may include a field facet mirror and a pupil facet mirror, where each pupil facet of the pupil facet mirror can define a pupil spot within the illumination pupil 1. In particular, when using illumination light wavelengths that are not in the EUV range but are in the DUV range, such a pupil generation device may have another configuration known in the art, in particular, including at least one microlens array.

[0082] Figure 10 shows an example of the intensity distribution of illumination light 19 across the illumination pupil 1. Such an intensity distribution of illumination pupil 1 is represented by multiple pupil spots 21 arranged as a grid with i rows and j columns. i j This includes the number of rows i and the number of columns j in one grid arrangement can be in the range of 1 to 500, for example, in the range of 10 to 50. In the shown embodiment, these numbers i and j are each close to 20. The illumination pupil 1 has at least two distinct pupil spots 21. A single pupil spot 21 can also be used during a single measurement step of such a sequence by using a sequence of measurements with different pupil spots.

[0083] In the case of pupil facet mirror or microlens array design of pupil generation device 20, pupil spot 21 i j Each of these can be generated via exactly one pupil facet or exactly one microlens. As a further alternative, the pupil generation device 20 may include multiple pinholes in the plane of the illuminated pupil 1.

[0084] The optical system, including the illumination system IL and the projection system PS, the radiation source SO, the pupil generation device 20, the optical element 3, and the sensor device 4a are part of the optical apparatus that determines the apodization characteristics of the optical system.

[0085] As a further part of this optical device OA (see FIG. 2), there are a calibration module 22 and a calculation module 23.

[0086] The calibration module 22 calibrates the individual directional shifts Φ2 - Φ1 of each wedge or shift optical region 5, as will be described in more detail below. The calibration module 22 is signal-connected to the sensor device 4a.

[0087] The calculation module 23 calculates the apodization characteristics of the optical system from the measured pupil spot shift resulting from the shift optical region of the optical element 3, i.e., the wedge 5, as will also be described in more detail below. The calculation module 23 is signal-connected to the sensor device 4a and the calibration module 22.

[0088] FIGS. 11 and 12 show exemplary possible pupil spot shifts that can be introduced by the wedge 5 of the optical element 3 into the pupil spot 21 i j and can be measured via the sensor device 4a, particularly for a plurality of distinct field points.

[0089] Each of the plurality of measurement spots 24 i j represents a measurement of the intensity of one of the pupil spots 21 after experiencing a pupil spot shift due to the interaction with the shift optical region of the optical element 3, i.e., each wedge 5, using the sensor device 4a. i j i

[0090] Depending on the respective tilt orientation of the tilted wedge surface 11 of the wedge 5, four different shift directions of the pupil spot shift are possible, which are shown enlarged in FIG. 12. The initial non-shifted position 240 is the measurement spot 24 of the pupil spot 21 that has not experienced a pupil spot shift. j i j ​​This is shown. Such an unshifted measurement spot 240 is, for example, the pupil spot 21 that passed through the optical element 3 through one of the pinholes 6. i j It is brought about by.

[0091] The four primary pupil spot shift directions further shown in Figure 12 are 24 +x ,twenty four -x ,twenty four +y , and 24 -y This is shown. These four primary pupil spot shift directions correspond to the four primary inclination directions of the wedge 5 of the optical element 3.

[0092] The optical device OA (see Figure 2 in particular) operates as follows: Multiple pupil spots 21 are generated via the light source SO and pupil generation device 20. i j Illumination of the object field of view OF of the lithography apparatus LA is provided via the illumination pupil 1, which includes the pupil.

[0093] Furthermore, an optical element 3 is provided having multiple shift optical regions 5, i.e., an optical surface having a wedge 5.

[0094] The optical device OA measures pupil spot shift, i.e., pupil spot 21, via the sensor device 4a and calibration module 22. i j Each of the 24 measurement spots corresponds to i j By measuring this, the individual directional shifts Φ2-Φ1 caused by each wedge 5 of the optical element are calibrated. Measurement spot 24 i j This is the camera pupil 4, which is part of the measurement pupil of the sensor device 4a.

[0095] The pupil spot shift is measured by the individual directional shift Φ2-Φ1 of each illumination beam, as described above with reference to Figure 4 in particular.

[0096] This calibration step is performed for multiple distinct field-of-view points within the object field of view (OF) of the lithography apparatus LA.

[0097] During the calibration step, the reference beam incident on the pinhole 6, i.e., incident on the non-shifted optical region of the optical element 3, can also be measured.

[0098] Furthermore, the non-shifted optical region of the optical element 3 can be realized through a flat element, i.e., a flat "wedge" having parallel incident and exit optical surfaces. Such a flat "wedge" may have the same optical path length as the "actual" wedge 5.

[0099] After this calibration, the apodization characteristics are calculated from the measured pupil spot shift.

[0100] This calibration step of the determination method determines the pupil shift 24, which deviates from the principal directions of coordinates x and y. +-x ,twenty four +-y It is possible to compensate for the directional deviation. Such a shift deviation is shown in Figure 12 by a dashed arrow with a deviation angle δ.

[0101] During the calibration step, each pupil spot shift is adjusted to each pupil spot 21 i j A map is then created based on each field of view point of the actual measurement.

[0102] Instead of using an optical wedge, it is also possible to use a blazed diffraction grating optimized for use at a specific wavelength.

[0103] Measurements obtained by a sensor module of light intensity at adjacent points, including data related to the apodization difference between two adjacent parts of the projection system pupil, are passed to a digital processing means, from which the entire apodization map can be reconstructed. This can be done using the same technique as the algorithm used in shearing interferometry, where the wavefront difference between displaced copies of a wavefront is measured. The original wavefront can then be reconstructed from these copies. See, for example, "Optical Shop Testing" (2nd edition) by Daniel Malacara (Wiley & Sons (1992)), which is incorporated herein by reference in its entirety. It will be understood that the data from the sensor module is sent to a processing means, which may include a computer processing means running software that executes the necessary algorithms.

[0104] Figure 13, in a diagram similar to Figure 2, shows another embodiment of the optical apparatus OA, which includes a pupil generation device and an optical element having a shift optical region, as described above for Figures 1 to 12, and further includes a sensor device. The parts and functions already described with respect to these previous figures have the same reference numerals or reference numerals and will not be described in detail again.

[0105] The optical device OA in Figure 13 includes an additional optical polarizer 31 located upstream of the integrator IN of the illumination system IL and in the beam path of the optical device OA.

[0106] The optical polarizer 31 is implemented as a linear polarizer. The optical polarizer 31 polarizes the illumination light 19 in the beam path upstream of the integrator IN. With the polarization state determined by the optical polarizer 31, the illumination light 19 then enters the optical element 3 and each wedge 5, resulting in individual directional shifts as described above.

[0107] The optical polarizer 31 is capable of pivoting around an axis 32, which may coincide with the optical axis of the optical device OA. This pivoting motion is driven by a drive unit 33 of the optical polarizer 31. This drive unit 33 is signal-connected to the main control unit CU of the lithography device LA (see Figure 1). The control unit CU can achieve the desired linear polarization state of the illumination light 19 path within the polarizer 31.

[0108] Through the controllable optical polarizer 31 and the measurement scheme described above, the sensor device 4a can be used to measure the polarization dependence of the optical properties of the optical device OA, and in particular to determine the diatenation of the optical system, especially the illumination system IL and the projection system PS.

[0109] Such diatennosis measurements do not necessarily require an illuminated pupil 1 having multiple pupil spots 21. Alternatively, such diatennosis measurements can also be performed using a conventional pupil having a uniform intensity of illumination light 19 across the entire illuminated pupil 1.

[0110] The measurement of the optical properties of an optical system, particularly the apodization properties of the illumination system (IL) and / or projection system (PS), can be further enhanced by using a Ronchi grating. Details of the fundamental measurement method using such a Ronchi grating can be found in "Improved Ronchi test with extended source" by J. Braat et al. (J. opt. Soc. Am. A, Vol.16, No. 1, pp. 131-140 (1999)) and U.S. Patent Application Publication No. 2002 / 0145717.

[0111] The use of a launch grating in the launch test method for determining the characteristics of the optical system and the optical devices equipped with it will be further explained with reference to Figures 14 to 20.

[0112] Figure 14 schematically shows the arrangement of optical elements between the object plane on which the object field of view OF is located and the sensor device 4a. Components and functions corresponding to those already described in Figures 1-13 are indicated by the same reference numbers and will not be described in detail again.

[0113] A linear grid 36 having multiple parallel linear grid structures is arranged on the object plane to diffract illumination light 19. Such a grid structure extends perpendicular to the drawing plane in the schematic diagram of Figure 14. In the embodiment of Figure 14, such linear structures of the linear grid 36 extend along the y-direction. This linear grid 36 functions as a source grid in the launch measurement scheme.

[0114] A projection system PS is located in the beam path of the downward illumination light 19 directed onto the linear grid 36.

[0115] A launch grating 35 is positioned between the projection system PS and the sensor device 4a in the beam path of the illumination light 19.

[0116] The linear grid 36 is connected to a phase stepping actor 36c that translates the linear grid 36 in a shearing direction perpendicular to its linear structure (indicated by a double arrow 36b in Figure 14).

[0117] The rawn grid 35 is embodied as a checkerboard configuration having a two-dimensional array of grid structures in both directions x and y.

[0118] The sensor device 4a has an array of sensor pixels arranged in the xy plane of Figure 14.

[0119] Figure 15 shows the measurement principle for the arrangement in Figure 14.

[0120] When linear diffraction 36 is introduced in the x-direction of Figure 15, the incident illumination light 19 is subsequently deflected in the linear lattice diffraction directions 361, 362, and 363, depending on the stepping phase within one period of the linear lattice.

[0121] The Ronchi grating 35 uses these incident linear grating diffraction directions 361 to determine the Ronchi grating diffraction order 351. +1 ,351 0 ,351 -1 Further division. Linear grating diffraction direction 362 is determined by the Ronch grating, Ronch grating diffraction order 352 +1 ,352 0 ,352 -1 It is diffracted in the linear lattice diffraction direction 363, with the Ronchi lattice diffraction order 353. +1 ,353 0 ,353 -1 It is diffracted.

[0122] Figures 16 to 21 show the superposition, i.e., the xy positional relationship, of the linear grid structure 36 in each region of the optical element 3 and the checkerboard arrangement of the rawn grid 35 in a projection along the z direction.

[0123] Figure 16 shows the xy positional relationship between the lattice structure of the linear lattice 36 extending in the y direction and the lattice structure of the ronch lattice 35, which result in the linear lattice diffraction direction 361 in Figure 15.

[0124] Figure 17 shows the relative position between the linear direction 36 and the ronch grating 35, which results in the linear grating diffraction direction 362.

[0125] Figure 18 shows the relative positions between the linear grating 36 and the ronchi grating 35, which result in the linear grating diffraction direction 363.

[0126] Figures 19 to 21 show the linear lattice structure 36 of the linear lattice 36 extending in the x direction, which corresponds to the linear diffraction directions 361, 362, and 363 described above in relation to Figure 15, and the positional xy relationship between the linear lattice structure 36 of the linear lattice 36 extending in the x direction and the Ronch lattice 35, which then leads to diffraction orders that spread in the yz plane.

[0127] Figure 22 shows the intensity measurement results of a launch test using the relative lateral orientation shown in Figures 16-18, i.e., along the first shear direction x. Figure 22 also shows the results of the relative lateral position along the second shear direction y, as shown in Figures 19-21. Figure 22 shows the intensity measured at exactly one pixel of the sensor device 4a during the relative shearing motion of the linear grid 36 with respect to the launch grid 35 along the x or y direction. P1, P2, and P3 correspond to the intensity measurement results of this sensor pixel at three different shearing positions. The number of measurement points Pi may vary and may be more than 3, or much more than 3 to improve measurement accuracy.

[0128] A corresponding phase curve can be fitted to each pixel of the sensor device 4a, resulting in accurate phase detection.

[0129] Such a launch measurement scheme may be performed without a wedge structure such as the wedge 5 on the optical element 3.

[0130] Measurement points P1 to P3 provide complete information about the expected sine signal S, i.e., its modulation M, offset O, and phase P. From this data, the apodization characteristics of the optical system, including the illumination system IL and projection system PS, can be obtained using the Launch test algorithm. In particular, as described above, if the entire apodization measurement sequence using a linear grating is sheared in the x and y directions, the offset O is used to determine the apodization of the projection system PS.

[0131] It will be understood that embodiments of the present invention can be implemented in any convenient way, including by using appropriate hardware and / or software. For example, a device configured to implement the present invention can be made using appropriate hardware components. Alternatively, an embodiment of the present invention can be implemented by programming a programmable device. Accordingly, the present invention also provides appropriate computer programs for implementing embodiments of the present invention. Such computer programs can be carried on appropriate carrier media, including tangible carrier media (such as hard disks and CD-ROMs) and intangible carrier media such as communication signals.

[0132] While specific embodiments of the present invention are described above, it will be understood that the present invention may be carried out in ways other than those described. The description is not intended to limit the present invention.

[0133] It should be understood that the section "Modes for Carrying Out the Invention," rather than the "Summary of the Invention" and "Abstract" sections, is intended to be used to interpret the claims. The "Summary of the Invention" and "Abstract" sections may define one or more exemplary embodiments of the invention as envisioned by the inventor, but not all of them. Therefore, they are not intended to limit the invention and the appended claims in any way.

[0134] The present invention is described above using functional components that illustrate the implementation of specific functions and their relationships. For the sake of clarity, the boundaries of these functional components are arbitrarily defined herein. Alternative boundaries can be defined, as long as the specified functions and their relationships are adequately performed.

[0135] The above description of specific embodiments fully illustrates the general nature of the invention, and therefore, others can readily modify and / or adapt such specific embodiments for various uses without requiring excessive experimentation and without departing from the general concept of the invention, by applying knowledge within the art of the present invention. Such adaptations and modifications are therefore intended to be within the meaning and scope of equivalents of the disclosed embodiments based on the teachings and guidance presented herein. Expressions or terms herein are for illustrative purposes only and not for limitation, and it should be understood that such terms or expressions herein should be interpreted by those skilled in the art in light of the teachings and guidance.

[0136] The scope and breadth of the present invention should not be limited to any of the exemplary embodiments described above, but should be defined only by the following claims and their equivalents.

Claims

1. A method for determining the optical properties of an optical system comprising an illumination system (IL) that illuminates an object field of view (OF) and a projection system (PS) that forms an image of the object field of view (OF) onto an image field of view (IF), - A step of providing illumination of the object field of view (OF) through an illumination pupil (1) including multiple pupil spots (21), - A step of providing an optical element (3) having an optical surface including a plurality of shift optical regions (5), wherein the plurality of shift optical regions (5) depend on each of the shift optical regions (5) and the individual directional shift (Φ) of the illumination beam (19) incident on each of the shift optical regions (5). 2 -Φ 1 The steps that bring about δ) and provide, - For each of the pupil spots (21) within a plurality of separate field of view points in the object field of view (OF), the pupil spot shift arising from the shift optical region (5) is measured via the measuring pupil (4) in the path of the illumination beam (19) after the optical element (3), thereby determining the individual directional shift (Φ 2 -Φ 1 The steps include: 1) Calibrating δ) and - A step of calculating the optical properties to be determined from the measured values ​​using the calibrated individual directional shifts. Methods that include...

2. The method according to claim 1, wherein the optical element (3) includes at least one non-shift optical region (6), the at least one non-shift optical region (6) does not cause a directional shift of the illumination beam (19) incident on such non-shift optical region (6), and a reference illumination beam (19) incident on the non-shift optical region (6) is also measured during the calibration step.

3. The method according to claim 1 or 2, wherein the provided optical element (3) includes a plurality of wedges having different wedge orientations as the shift optical region (5).

4. The method according to claim 3, wherein the angles between adjacent orientations of the wedges are different by integer multiples of 45 degrees.

5. The method according to any one of claims 1 to 4, wherein the plurality of pupil spots (21) of the provided illumination pupil (1) are arranged as a grid.

6. The method according to any one of claims 1 to 5, wherein during the calibration step, a map is created in which each pupil spot shift is generated by each pupil spot (21) and each field of view point.

7. The method according to any one of claims 1 to 6, wherein the optical element (3) includes at least one optical grating region, the at least one optical grating region causes diffraction of an illumination beam (19) incident on such optical grating region and further passing through one of the shift optical regions (5) of the optical element (9), and the method includes a launch test to obtain the optical properties to be determined.

8. The method according to any one of claims 1 to 7, wherein the optical system (1) comprises at least one optical polarizer that causes polarization of an illumination beam (19) incident on such a shift optical region (5), and an analyzer is used to determine the transmission of the optical element (3) for two different polarization states of the illumination beam (19), the method comprising the measurement of such transmission data from which the diatenation of the optical system is obtained.

9. The method according to claim 8, wherein during the measurement of the transmission data, an additional optical analyzer is used to determine the transmission of the optical element for two different polarization states of the illumination beam (19).

10. An optical device having an optical system comprising an illumination system (IL) for illuminating an object field of view (OF) and a projection system (PS) for forming an image of the object field of view (OF) onto an image field of view (IF), - A light source (SO) for generating an illumination beam (19) that illuminates the object field of view (OF) via the illumination system (IL), - A pupil generating device (20) that provides illumination of the object field of view (OF) via an illuminated pupil (1) including a plurality of pupil spots (21) as part of the illumination system (IL), - An optical element (3) having an optical surface including a plurality of shift optical regions (5), wherein the plurality of shift optical regions (5) depend on each of the shift optical regions (5) and the individual directional shift (Φ) of the illumination beam (19) incident on each of the shift optical regions (5). 2 -Φ 1 Optical element (3) that brings about δ, - A sensor device (4a) that measures pupil spot shift resulting from different shift optical regions (5) for each of the pupil spots for a plurality of separate field of view points within the object field of view (OF) via a measuring pupil (4) in the path of the illumination beam (19) after the optical element (3) and An optical device equipped with the following features.

11. The individual directional shifts (Φ 2 -Φ 1 The optical apparatus according to claim 10, comprising a calibration module (22) for calibrating δ, wherein the calibration module (22) is signal-connected to the sensor device (4a).

12. The optical apparatus according to claim 11, further comprising a module (23) that calculates the optical properties of the optical system from pupil measurement data using the calibrated individual directional shifts, wherein the module (23) is signal-connected to the sensor device (4a) and the calibration module (22).

13. The optical apparatus according to any one of claims 10 to 12, comprising a ronchi grating which is part of the optical element (3).

14. The optical apparatus according to any one of claims 10 to 13, comprising an optical polarizer for polarizing an illumination beam (19) incident on the optical element.

15. The optical apparatus according to claim 14, further comprising an optical analyzer that determines the transmission of the optical element (3) for two different polarization states of the illumination beam (19).

Images