Method of determining optical properties of optical system

Abstract

In order to determine optical properties of an optical system having an illumination system to illuminate an object field and a projection system to image the object field into an image field, the following steps are performed: providing illumination of the object field via an illumination pupil comprising a plurality of pupil spots. An optical element having an optical surface including a plurality of shifted optical regions is provided that enables individual directional displacements of illumination beams entering respective shifted optical regions according to the respective shifted optical regions. The individual directional shifts are calibrated by measuring pupil spot shifts caused by the shifted optical region for each of pupil spots of a plurality of individual field points within the object field in the illumination beam path after the optical element via the measurement pupil (4). The optical property to be determined is then calculated from the measured pupil spot shift. The resulting determination method is robust in obtaining the desired optical properties.

Description

[0001] This application claims priority to German patent application DE 10 2023 203 312.7, the content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present invention relates to a method of determining an optical property 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

[0003] From US 2013 / 0271636 A1 a method of determining an apodization property of an optical system is known. SUMMARY

[0004] It is an object of the present invention to develop a method of determining an optical property in order to be robust in obtaining a proper result of the optical property to be determined.

[0005] This object is achieved by the method according to claim 1.

[0006] By means of the calibration of the individual directional displacements of the plurality of displaced optical areas of the optical element with the illumination pupil comprising the plurality of pupil spots an information basis for the later calculation of the optical property is provided which in particular comprises information about the inhomogeneity of the desired individual directional displacement of the respective displaced optical area. Then, manufacturing tolerances with respect to the optical element and in particular with respect to the displaced optical areas of the optical element can be assessed and compensated during the determination method and in particular based on the information obtained in the calculation step. After having obtained potential deviations of the individual directional displacements of the plurality of displaced optical areas from the desired values, the other steps of the optical property determination method can be used which are known in the art but are now used together with the calibrated directional displacement data.

[0007] With the method comprising the calibration the pupil displacement characteristics can be measured directly and thus enable decoupling of the projection system effects on the optical property to be determined from the illumination system effects on the optical property to be determined during the calculation.

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

[0009] An example of the optical property to be determined is an apodization of the optical system. Another optical property which can be determined via the method is a two-dimensional attenuation of the optical system.

[0010] The calculation step can use a measurement with full pupil after the calibration step. This measurement with full pupil can not use a pupil with a plurality of pupil spots but a pupil with uniform or continuous illumination. Alternatively, the measurement with full pupil can use a plurality of individual pupil spots.

[0011] The optical element can have at least two shifted optical areas.

[0012] The calibration step can be repeated after a given time span. This can minimize undesired influences of the effect of the optical element on the illumination beam, in particular due to drift or due to comparable effects.

[0013] The calibration of the individual directional shifts can be done relying on the pupil spots.

[0014] The calibration of the individual directional shifts reduces errors originating from manufacturing errors of the shifted optical areas, in particular from manufacturing tolerances. Furthermore, errors caused by a drift of the shift effect of the shifted optical areas over time are reduced. Furthermore, a placement error of the optical element can be reduced. Furthermore, a curvature error of the optical element can be reduced.

[0015] The use of an illumination pupil with multiple pupil spots during the calibration step enables a measurement of deviations originating from such manufacturing / placement / drift errors.

[0016] With the calibration of the individual directional shifts, a translational deviation of the respective pupil spot from a given value as well as an azimuthal displacement of the respective pupil spot can be calibrated.

[0017] During the calibration and calculation steps of the method, the angular displacement of each pupil spot from the shifted optical areas can be analyzed, stored and used within the method. The detection and localization of the shifted pupil spots can be done via fitting algorithms like "local maxima", Gaussian or Lorentzian fitting.

[0018] With regard to the determination of the apodization, in particular, the apodization effect of the illumination system can be separated from the apodization effect of the projection system in order to achieve tight apodization tolerances independent from the illumination system on the one hand and independent from the projection system on the other hand.

[0019] The optical element with multiple shifted optical areas can be inserted into the beam path between the illumination system and the projection system of the optical system. The multiple shifted optical areas then introduce a defined new set of illumination angles in the projection system, which set is different from the initial set defined by the multiple pupils. With this new set of illumination angles, access to the optical properties of the projection system, in particular to the apodization properties, independent from the optical properties of the illumination system is given.

[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 with regard to the number of shift types of the shifted optical areas.

[0021] The quality of the calibration step of the method is further improved according to the non-shifted optical area of ​​claim 2. The non-shifted optical area may be embodied as a pinhole in the optical element.

[0022] A wedge as a shifted optical zone according to claim 3 has been shown to be effective in methods for determining apodization properties. In this regard, reference is made to US 2013 / 0271636 A1. The wedge's tilt can be in the range of 10 mrad to 55 mrad. This tilt can be measured relative to a plane perpendicular to the optical axis of the optical system. The wedge tilt can be selected so that, after the corresponding directional shift, the illumination beam subjected to this directional shift remains in another beam path of the optical system within the numerical aperture of the optical system. Depending on the accuracy of the measurement system used to measure the corresponding pupil spot shift, tilt angles of less than 10 mrad are possible. If the numerical aperture of the optical system is sufficiently large, wedge tilt angles greater than 55 mrad are also possible.

[0023] As an alternative or in addition to displacement via a wedge, it is also possible to use a grating, in particular a linear grating. Such a linear grating can be moved laterally, i.e. perpendicularly to the path of the illumination plan. This translational movement can be gradual and is also referred to as a shearing movement.

[0024] The angular differences between the wedge-shaped orientations deviating from the angular differences between the rectangular orientations known in the art have proven useful for determining apodization properties according to claim 4. During the calibration step of the method, this deviation can be compensated.

[0025] For example, angular differences that are integer multiples of 90 degrees provide four different wedge orientations (0 degrees, 90 degrees, 180 degrees, and 270 degrees) and four types of wedge bodies, respectively. 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, the wedge bodies may have orientations of 5 degrees, 10 degrees, 15 degrees, 30 degrees, or 45 degrees relative to one another. Thus, there may be more than four types of wedge orientations, for example, six or eight types. There may even be a greater number of wedge orientation types.

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

[0027] The grid arrangement of multiple pupil spots according to claim 5 has proven to be effective. This grid arrangement can be generated via a pupil generating device which can comprise pupil facet mirrors and / or a pupil microlens array and / or a plurality of pinholes in the pupil plane.

[0028] The calibration information map according to claim 6 is helpful for identifying a calibrated optical element which can then be used without the need for repeating the calibration step. The measure of the pupil spot shift is a separate directional shift of the respective illumination beam.

[0029] The inclusion of a Ronchi test according to claim 7 by using the illumination beam for diffraction via at least one grating area enables Ronchi test measurements. 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). According to this Ronchi test measurement, phase, shift and modulation data can be obtained which can further be used for obtaining e.g. the apodization properties of the optical system. The grating area can be part of the optical element. The respective grating area can be attributed to the respective one of the shifted optical areas. The order of the arrangement of the grating area and the optical shifted area along the beam path of the respective illumination beam depends on the respective embodiment of the optical apparatus. The grating area can follow the optical shifted area or the optical shifted area can follow the grating area along such beam path.

[0030] The use of at least one optical polarizer during the method according to claim 8 enables the determination of the diattenuation of the optical system. The optical polarizer can be moved between different polarizer positions, thereby imposing different polarization states on the illumination beam. The optical polarizer can be a linear polarizer. The optical polarizer can be driven by a controlled drive unit for the controlled setting of a given polarization state.

[0031] The use of the optical analyzer according to claim 9 is further helpful, in particular for determining the diattenuation of the optical system.

[0032] It is a further object of the present invention to improve an optical apparatus which is capable of performing such an optical property determination method.

[0033] Such an object is met by the optical apparatus having the features of claim 10.

[0034] The advantages of such an optical apparatus correspond to the advantages of the above described optical property determination method. In particular, the optical apparatus can be designed to perform such a method.

[0035] The optical device according to claim 11 allows for an automatic calibration step according to the above described method.

[0036] The optical device with a calculation module according to claim 12 enables an automatic calculation step within the above described method. The use of a Ronchi grating according to claim 13 as the respective grating area during this method has the advantages mentioned here.

[0037] The use of the optical polarizer according to claim 14 and the optical analyzer according to claim 15 gives the advantages mentioned above with respect to claims 8 and 9. BRIEF DESCRIPTION OF DRAWINGS

[0038] In the following exemplary embodiments of the present application are described by means of the enclosed drawings:

[0039] Figure 1 An optical lithography apparatus is shown, comprising an optical device with an optical system comprising an illumination system for illuminating a light field and a projection system for imaging the light field into an image field, the optical device being able to determine optical properties of the optical system;

[0040] Figure 2 Variations of the beam path through the optical device are shown schematically;

[0041] Figure 3 A top view of an optical element with an optical surface comprising a plurality of wedges and a further plurality of pinholes as part of an optical device is shown, the optical element being used in a method for determining optical properties of the optical system;

[0042] Figure 4 A cross section of one of the wedges of the optical element of Figure 3 is shown, and further depicts the beam path of individual rays through the wedge causing a shift of the ray direction, wherein also a part of the substrate of the optical element carrying the wedge is shown;

[0043] Figure 5 Another embodiment of a wedge is shown on a substrate of an optical element, wherein the wedge is fixed on the substrate via an adhesive structure;

[0044] Figures 6 to 8 is a top view of different embodiments of an adhesive structure that can be used to adhere a wedge according to Figure 5 to a substrate;

[0045] Figure 9 is a perspective view of another embodiment of one of the wedges of an optical element;

[0046] Figure 10Displaying an intensity distribution of an illumination light via an illumination pupil comprising a plurality of pupil spots arranged as a grid within a circular pupil for use in a method of determining optical properties of an optical system;

[0047] Figure 11 Displaying a measurement of pupil spot displacements caused by illumination by an optical element having a pupil intensity distribution according to Figure 10 wherein the possible pupil spot displacements attributed to the respective pupil spot positions are indicated;

[0048] Figure 12 Amplifying different pupil spot displacement possibilities introduced by different kinds of wedges on the optical element;

[0049] Figure 13 Displaying another arrangement of an optical device in a view similar to Figure 2 enables determining an attenuation property of the optical system;

[0050] Figure 14 Schematically displaying a guiding of a light beam path through components of another embodiment of an optical device, the optical device further comprising a Ronchi grating as part of the device to determine optical properties of the optical system;

[0051] Figure 15 Displaying a diffraction scheme of a Ronchi grating embodiment of Figure 14 in a view similar to Figure 14 ;

[0052] Figures 16 to 18 Displaying a positional relationship between a linear grating (source grating) structure of a grating according to Figure 14 and Figure 15 and a linear grating (source grating) structure of a Ronchi grating of a chessboard arrangement shape of a sensor device, the Ronchi grating showing a first shear direction x caused by different translational positions of the linear grating with respect to the Ronchi grating along a first shear direction x;

[0053] Figures 19 to 21 Displaying a positional relationship between a Ronchi grating of another embodiment of an optical element according to Figures 16 to 18 and Figure 14 and Figure 15 with different linear grating structure orientations, shown for three positional relationships along another shear direction y, similar to

[0054] Figure 22 Displaying a phase signal measured by one pixel of a sensor device in a relative position according to one of Figures 16 to 18 and / or Figures 19 to 21 . DETAILED DESCRIPTION

[0055] This specification discloses one or more embodiments that incorporate the features of the application. The disclosed embodiments are only examples of the application. The scope of the application is not limited to the disclosed embodiment(s). The application is defined by the claims appended hereto.

[0056] The described embodiment(s) and the specification can use terms such as "one embodiment," "an embodiment," "example embodiment," etc., to describe various embodiments. Such terms are not to be construed as necessarily referring to the same embodiment(s). Furthermore, when used throughout this specification, the word "comprising" or variations such as "comprise" or "comprises" means a non-exclusive inclusion, such that a process or method that comprises more steps can also consist only of those steps. Also, the term "coupled" or variations such as "couples," "coupling," and "coupled to," mean a direct or indirect connection between two or more elements, which can or can not be physical.

[0057] Embodiments of the application can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the application can also be implemented 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 form readable by a machine (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, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0058] However, before describing such embodiments in further detail, it is instructive to present an example environment in which embodiments of the application can be implemented.

[0059] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein can have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat-panel displays such as liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” in this text can be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrates referred to herein can be processed, before or after exposure, in one or more treatment processes such as trim etching, resist removal, and / or the application of a layer of insulation onto the substrate. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrates can be processed more than once, for example to create multiple layers of the IC, such that the term substrate as used herein can also refer to a substrate that already includes a number of processed layers.

[0060] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0061] The term “patterning device” used herein should be interpreted in its broadest sense as a device that can be used in the patterning of a radiation beam, either directly or indirectly. It should be noted that the pattern imparted to the radiation beam can not completely correspond to the desired pattern in the target portion of the substrate. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being patterned, such as an integrated circuit.

[0062] The patterning device 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 mask types such as binary, alt -phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Programmable mirror arrays are an example of a programmable reflection device. An example of such an array includes a matrix of small mirrors, each of which can be individually tilted so as to steer the incoming radiation in different directions; in this manner, the reflected beam can be patterned.

[0063] The support structure holds the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support can use mechanical clamping, vacuum, or other clamping techniques, e.g. electrostatic clamping in vacuum. The support structure can be a frame or a table, for example, which can be fixed or movable, as required, and which can ensure the patterning device is at a desired position, e.g. with respect to the projection system. Throughout this document the term "reticle" or "mask" can be considered synonymous with the more general term "patterning device".

[0064] The term "projection system" used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic and / or electromagnetic, and any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion fluid or the use of a vacuum. Any use of the term "projection lens" herein can be considered as synonymous with the more general term "projection system".

[0065] The illumination system or illuminator can also include various types of optical components, including refractive, reflective, and catadioptric optical components for directing, shaping, or controlling the beam of radiation, and such components can also be referred to below, collectively or singularly, as a "lens".

[0066] The lithographic apparatus can be of a type that includes two or more substrate tables (and / or two or more support structures) that are held at the same environment, for example at the same pressure. Such an apparatus is known as a twin-twin or twin-twin-twin lithographic apparatus.

[0067] The lithographic apparatus can also be of a type that includes two or more substrate tables (and / or two or more support structures) that are held at the same environment, for example at the same pressure. Such an apparatus is known as a twin-twin or twin-twin-twin lithographic apparatus.

[0068] Figure 1A lithographic apparatus LA according to an embodiment of the application is schematically illustrated. The apparatus includes an illumination system IL configured to condition a radiation beam B (e.g., UV radiation), a support structure, such as a mask table MT, configured to hold a patterning device, such as a mask MA, and connected to a first positioning device PM configured to accurately position the patterning device in accordance with a desired pattern. The apparatus also includes a projection system PS configured to project a pattern imparted to the beam B by patterning device MA on the patterning device in a field plane OF onto a target portion C of the substrate W in an image plane 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 connected to a second positioning device PW configured to accurately position the substrate in accordance with a desired pattern.

[0069] The illumination system can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0070] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example, 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 can be a frame or table, for example, which can be fixed or movable as required. The support structure can ensure that the patterning device is at a desired position, for example, in terms of alignment and levelness.

[0071] The term“patterning device” should be interpreted in its broadest form as referring to any device that can be used to impart a pattern in a radiation beam to form a pattern in a target portion of a substrate. The pattern imparted to the radiation beam can correspond to a particular functional layer in a device, such as an integrated circuit, that is created in the target portion.

[0072] The patterning device 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 mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. Programmable mirror arrays are an example of static masks. Programmable mirror arrays have small mirrors on a matrix arrangement that can be individually tilted so as to steer the incoming radiation beam in different directions.

[0073] Like the illumination system, the projection system can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It can be desired to use a vacuum for EUV radiation since gas molecules can absorb too much radiation. A vacuum environment can therefore be used for the beam path in the lithography apparatus. Some gas can be provided in parts of the lithography apparatus, for example to allow for cooling of the optical components in the lithography apparatus.

[0074] As shown in Figure 1 , the apparatus is a transmissive apparatus employing a transmissive mask MA. Alternatively, the apparatus can be a reflective one employing a programmable mirror array.

[0075] The illuminator IL receives a radiation beam from a radiation source SO. The illuminator IL comprises an adjustment device AD configured to set the outer and / or inner radial extent of the beam, an integrator IN, and a condenser CO. The source SO will generally be a laser, for example a single- or two-UV-molecule laser. For purposes of simplicity of explanation, in Figure 1 , a single source SO is shown, and the source SO can include two lasers, or alternatively a plurality of sources SO can be provided, each having a single laser, the beams of which are combined before or after entering the projection system PS. A beam delivery system BD, for example comprising suitable directional mirrors and / or a beam expander, is also provided. The source SO and the beam delivery system BD combine to form a radiation system that presents a suitable radiation beam to the projection system. It will be appreciated that the radiation beam B includes radiation from at least one laser. It will also be appreciated that the beam can include alternating radiation pulses from at least one laser.

[0076] The projection system PS can include a diaphragm having an adjustable aperture for setting the numerical aperture of the projection system PS at the wafer level to a selected value.

[0077] ​A radiation beam B is incident upon the patterning device MA held on the support structure MT. This patterning device reversibly alters the intensity of the radiation beam B to form a pattern in the beam of radiation. The beam of radiation B, after traversing the patterning device, passes through the projection system PS which focuses the beam onto a target portion C of the substrate W. The support structure MT and the substrate W are moved synchronously so that a pattern imparted to the beam is transferred to a layer of radiation-sensitive material onto the substrate W. One support structure (the mask table) is connected to a first positioner PM, which is capable of precise positioning in the X, Y directions. The other support structure (the substrate table) is connected to a second positioner PW, which is capable of precise positioning in the X and Y directions. During use, the support structures MT and the substrate table WT are kept essentially stationary, except during a transition period, while the pattern imparted to the beam is transferred to a layer of radiation-sensitive material onto the substrate W. During the transfer of a pattern to the substrate W, the support structures MT and the substrate table WT are kept essentially stationary, except that the support structures MT and the substrate table WT can be moved:

[0078] The depicted apparatus can be used in at least one of the following modes:

[0079] 1. In step mode, the support structure (for example, the mask table) MT and the substrate table WT are kept essentially stationary, except that the support structure (for example, the mask table) MT is moved to a different position, i.e. the support structure (for example, the mask table) MT and the substrate table WT are kept essentially stationary and the entire pattern imparted to the beam is transferred to the target portion C at once. The support structure (for example, the mask table) MT is then moved by one

[0080] 2. In scan mode, the support structure (for example, the mask table) MT and the substrate table WT are scanned synchronously so that the pattern imparted to the beam is transferred to a target portion C (i.e. the entire pattern is transferred in a single dynamic movement of the support structure (for example, the mask table) MT and the substrate table WT). The speed and direction of the substrate table WT relative to the support structure (for example, the mask table) MT can be determined by the (de-) magnification and the image reversal characteristics of the projection system PS.

[0081] 3. In another mode, the support structure (for example, the mask table) MT holding the programmable patterning device is kept essentially stationary, and the substrate table WT is moved or scanned while a pattern imparted to the beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is used and the programmable patterning device is updated as desired either at the end of each movement of the substrate table WT or, more commonly, in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as the programmable mirror array described above.

[0082] Combinations and / or variations on the above-described modes of use or entirely different modes of use can also be employed. A known problem with conventional apparatuses is the problem of apodization when the beam path passes through the projection system PL. Apodization is a known optical phenomenon which can result in the angular intensity distribution of the light beam being non-uniform, in particular the intensity falling off at the edges of the light beam. Apodization can be caused by a variation of the illumination intensity distribution which is caused by the lens material or the lens properties of the lenses of the optical apparatus. Apodization of the lenses becomes more and more important, in particular in systems using a complementary phase shift mask. Such a mask is usually illuminated by a coherent light beam, wherein the light is concentrated around the optical axis of the system. The diffracted light will not contain a zero order beam and will be directed more towards the edges of the aperture of the system. The spacing between these diffracted beams (and thus the distance to the optical axis) is proportional to the resolution of the features being imaged. Apodization can lead to similar dose errors, depending on the resolution of the lines being imaged. It is therefore important to be able to measure the lens apodization and the differences in lens apodization in one apparatus which can drift over time and between systems.

[0083] In order to measure the apodization accurately, the light distribution on the reticle level has to be known in order to compare it to the light distribution on the wafer level. Currently, in known apodization determination techniques, it is assumed that the light distribution on the reticle level has a uniform distribution for example, but this is not necessarily the case. One solution to this could be to measure the light distribution on the reticle level directly, but this can not be possible or easy. The present invention proposes at least in some embodiments an alternative solution in which multiple shifted copies of the same light distribution are measured with different parts of the lens.

[0084] Figure 2 The basic idea behind the apodization measurement is schematically shown. In this respect, reference is also made to US 2013 / 0271636 A1. In addition to the apodization measurement, with the optical apparatus described hereinafter, further optical properties of the optical system of such an optical apparatus can be determined. Examples of such further optical properties include the two-way attenuation of the optical system.

[0085] Figure 2 The illumination pupil 1 of the illumination system IL and the projection pupil 2 of the projection system PS are shown. The illumination system IL and the projection system PS constitute Figure 1 the optical system of the projection exposure apparatus shown.

[0086] An optical element (e.g. a reticle, a mask or a master) 3 is placed between an illumination pupil 1 of the illumination system IL and a projection pupil 2 of the projection system, wherein the optical element 3 is usually located in a focal plane of the illumination system IL. In other words, the optical element 3 is located in an object plane at the object field OF where the mask MA will be located in use. The optical element 3 comprises a coating (e.g. a chromium layer), a plurality of pinholes arranged in the coating such that radiation can pass through the optical element 3 via the pinholes, and a plurality of sub-elements (wedges 5) to displace the radiation. Those sub-elements are also denoted as displaced optical areas. The non-displaced beam paths are depicted with a first hatching. The displaced beam paths are depicted with a second, different hatching.

[0087] Below the projection system PS a sensor device 4a is provided comprising a sensor module SM comprising a camera with a camera pupil 4. The pinholes for measuring the camera pupil 4 are usually located in the same plane as the plane where the substrate W will be located in use, i.e. in an image plane at the image field IF of the projection system PS. The camera of the sensor device 4a can be placed in a far field plane without imaging optics, or can be located in a pupil plane with imaging optics.

[0088] Figure 3 The structure of the optical element 3 is shown 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 direction. Each wedge 5 is provided on a substrate 3a of the optical element 3. The pinholes 6 located between the wedges 5 can be used as a reference. Pinholes are also provided below each wedge 5, Figure 3 not shown in Figure 5 indicated by exemplary pinholes "x" in

[0089] The pinholes 6 are provided in a coating at a surface of the optical element 3. The coating can be e.g. a chromium layer. Further, other reticle features can be provided on the coating, e.g. a grating structure, or instead of the coating. These other reticle features can also be located below the wedges 5.

[0090] A more detailed illustration of a wedge 5 is shown in Figure 4 Figure 4 A portion of the substrate 3a of the optical element 3 is also schematically shown. The wedge 5 is arranged at a surface of the optical element 3, wherein a first surface 10 faces the substrate 3a of the optical element 3. A second surface 11 of the wedge 5 opposite to the first surface 10 is inclined with an angle a. When a radiation beam exits the wedge 5 at the first surface 10, a radiation beam hitting the second surface 11 will experience a change of direction Φ2-Φ1 as a function of the wedge inclination angle a. The plane in which the inclination or the inclination angle a is measured represents the wedge orientation of the respective wedge 5 with respect to a reference plane. In the example shown in​Figure 4 In embodiments of the application, such a tilt angle reference plane is the xz-plane, and the tilt of the respective wedge 5 is thus in the positive x-direction. The position and orientation of the respective tilt angle reference plane is also referred to as wedge orientation in the following.

[0091] To fix the sub-elements (wedges) 5 to the surface of the optical element 3, the sub-elements 5 can be clamped by clamping means arranged at the surface.

[0092] The fixing of the sub-elements 5 can alternatively or additionally be done by an adhesive 15 provided between the sub-elements 5 and the surface of the optical element 3, as shown in the embodiment shown in Figures 6 to 8 .

[0093] Preferably, the adhesive 15 is provided at the periphery (edge region) of the sub-element 5 outside the optical path. Thus, the adhesive 15 does not interact with the radiation used for e.g. an apodization measurement. In case the adhesive 15 is provided at 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.

[0094] For example, when two parallel spacers 15 (see Figure 6 ) are provided or spacers are provided at four corners, there is a risk that unwanted contaminants (e.g. dust particles) are captured under the sub-element 5, in particular at the pinhole under the wedge 5.

[0095] The use of the adhesive 15 at additional edge regions for fixing the sub-element can reduce the chance that particles are captured between the sub-element 5 and the optical element 3. For example, the adhesive can be provided at three edge regions or at four edge regions, Figure 7 and Figure 8 .

[0096] With four edge regions provided with adhesive 15 (or spacers), a closed space can be formed. In case the optical element 3 and thus also the sub-element 5 is subjected to pressure changes, such a configuration can not be preferred. Pressure changes can occur during a load sequence in a lithography apparatus LA, for example, when the local environment is evacuated. A pressure difference between the closed space and the local environment can cause stress to the spacer 15 and / or the sub-element 5. To control the pressure in the space under the sub-element 5 and to prevent dust particles from entering this space, a vent port 16 can be provided in at least one of the spacers, as shown in Figure 7 and Figure 8 . The vent port forming a labyrinth seal 16 allows a 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 considered as physically open but optically closed.

[0097] Figure 9 A perspective view showing an exemplary embodiment of one of the wedges 5.

[0098] Figure 3 A perspective view showing the respective wedge 5 of an observer facing Figure 3 The wedge-shaped second surface 11 of the respective wedge 5 can be tilted in four main directions, i.e. it can be tilted in the positive or negative x-direction or in the positive or negative y-direction. Furthermore, a tilt along the bisector between + / -x and + / -y coordinates is also possible, which is indicated via a diagonal tilt defining line 11a in Figure 3

[0099] In Figure 2 The pupil generating device 20, which is schematically shown in

[0100] Figure 10 An example of an intensity distribution of the illumination light 19 over the illumination pupil 1 is shown. This intensity distribution of the illumination pupil 1 comprises a plurality of pupil spots 21 i j The number i of rows and the number j of columns of such a grid arrangement can be in the range between 1 and 500, for example in the range between 10 and 50. In the shown embodiment, these numbers i and j are about 20, respectively. The illumination pupil 1 has at least two separate pupil spots 21. By using a measurement sequence with different pupil spots, it is also possible to use a single pupil spot 21 during a single measurement step of such a sequence.

[0101] In case of a pupil facet mirror or a microlens array design of the pupil generating device 20, each of the pupil spots 21 i j may be generated via exactly one pupil facet or via exactly one microlens. As a further alternative, the pupil generating device 20 can comprise a plurality of pinholes in the plane of the illumination pupil 1.

[0102] The optical system comprising the illumination system IL and the projection system PS, the source SO, the pupil generating device 20, the optical element 3 and the sensor arrangement 4a are part of an optical apparatus for determining the apodization properties of the optical system.

[0103] ​Other parts of the optical device OA (compare Figure 2 ) are the calibration module 22 and the calculation module 23.

[0104] The calibration module 22 serves to calibrate the individual directional displacements Φ2-Φ1 of the respective wedges or displaced optical zones 5, as explained in more detail below. The calibration module 22 is in signal connection with the sensor device 4a.

[0105] The calculation module 23 is used to calculate the apodization properties of the optical system based on the measured pupil spot shift, which is caused by the shifted optical area (i.e., the wedge 5 of the optical element 3), as also explained in more detail below. The calculation module 23 is in signal connection with the sensor device 4a and the calibration module 22.

[0106] Figure 11 and Figure 12 An exemplary possible pupil spot shift is shown, which can be introduced into the pupil spot 21 by the wedge 5 of the optical element 3. i j , and can be measured via the sensor device 4a, in particular for a plurality of individual field points.

[0107] Multiple measurement spots 24 i j Each of them represents a pupil spot 21 imaged by the sensor device 4a after it has undergone a pupil spot shift by interaction with the shifting optical region (ie the see-through wedge 5 of the optical element 3). i j A measure of the strength of one of the

[0108] Depending on the respective tilted orientation of the wedge surface 11 of the wedge 5, four different offset directions of the pupil spot shift are possible. Figure 12 The initial unshifted position 240 is formed by the pupil spot 21 which has not undergone pupil spot shifting. i j Measurement spots 24 i j This unshifted measurement spot 240 is for example formed by a pupil spot 21 passing through the optical element 3 via one of the pinholes 6. i j produce.

[0109] exist Figure 12 The four main pupil spot offset directions further indicated in FIG are represented as 24 +x ,twenty four -x ,twenty four +y and 24 -y The four main pupil spot shift directions correspond to the four main tilt directions of the wedge 5 of the optical element 3 .

[0110] The optical device OA (in particular with Figure 2 the optical element 3) operates as follows:

[0111] Via the source SO and the pupil generating device 20, the illumination of the object field of the lithography apparatus LA is provided via the illumination pupil 1 comprising a plurality of pupil spots 21 i j .

[0112] Furthermore, the optical element 3 is provided with an optical surface having a plurality of shifted optical regions 5, i.e. the wedges 5.

[0113] Via the sensor device 4a and the calibration module 22, the optical device OA calibrates the individual directional offset Φ2-Φ1of the respective wedge 5 of the optical element by measuring the pupil spot shift, i.e. by measuring the respective measurement spot 24 i j corresponding to the pupil spot 21 i j . The measurement spot 24 i j is part of the camera pupil 4, i.e. part of the measurement pupil of the sensor device 4a.

[0114] The measure of the pupil spot shift is the individual directional offset Φ2-Φ1of the respective illumination beam, as explained above in particular with reference to Figure 4 .

[0115] This calibration step is done for a plurality of individual field points within the object field OF of the lithography apparatus LA.

[0116] During the calibration step, also a reference beam can be measured which enters the pinhole 6, i.e. the non-shifted optical region of the optical element 3.

[0117] Furthermore, the non-shifted optical region of the optical element 3 can be realized via a flat element, i.e. a flat “wedge” having parallel entrance and exit optical surfaces. Such a flat “wedge” can have the same optical path length as the “real” wedge 5.

[0118] After such a calibration, the to-be-determined apodization properties are calculated from the measured pupil spot shifts.

[0119] Due to the calibration step of the determination method, directional deviations of the pupil spot shifts 24 +-x , 24 +-y deviating from the main directions of the coordinates x and y can be compensated. Such a shift deviation is indicated in Figure 12 by the dashed arrow having the deviation angle δ.

[0120] During the calibration step, a mapping is created in which a respective pupil spot shift is attributed to a respective pupil spot 21 i j and the respective field point actually measured.

[0121] As an alternative to the use of a wedge, a blazed diffraction grating optimized for use at a specific wavelength can also be used.

[0122] The measurement of the light intensity at adjacent points obtained by the sensor module contains data related to the difference in apodization of two adjacent portions of the projection system pupil and can be passed to a digital processing device which then reconstructs the total apodization map. This can be done using the same techniques as used in shearing interferometry where the wavefront difference between shifted copies of the wavefront is measured. From these copies, the original wavefront can be reconstructed. See, for example, Daniel Malacara, “Optical Shop Testing” (2nd Edition), John Wiley & Sons (1992), which is incorporated herein by reference in its entirety. It will be appreciated that the data from the sensor module will be sent to a processing device which can comprise a computer processing device running software implementing the necessary algorithms.

[0123] Figure 13 Another embodiment of the optical apparatus OA comprising a pupil generating apparatus and an optical element having a shifted optical area and further comprising a sensor device is shown in a depiction similar to Figure 2 as explained above with respect to Figures 1 to 12 The components and functions already discussed with respect to these previous figures are denoted with the same reference signs or drawing numbers and are not described in detail again.

[0124] Figure 13 The optical apparatus OA of Fig. 4 comprises an additional optical polarizer 31 in the beam path of the optical apparatus OA upstream of the integrator IN of the illumination system IL.

[0125] The optical polarizer 31 is embodied as a linear polarizer. The optical polarizer 31 imposes a polarization of 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 the respective wedge-shaped body 5, resulting in the individual directional shifts as described above.

[0126] The optical polarizer 31 is pivotable about an axis 32 which can coincide with the optical axis of the optical apparatus OA. This pivoting motion is driven by a drive unit 33 of the optical polarizer 31. This drive unit 33 is in signal connection with the main control unit CU of the lithography apparatus LA (see Figure 1). With the control unit CU, a desired linear polarization state of the illumination light 19 path in the polarizer 31 can be achieved.

[0127] Via the controllable optical polarizer 31 and the above-mentioned measurement scheme, a polarization-dependent measurement of the optical properties of the optical apparatus OA, in particular a determination of the diattenuation of the optical system, in particular of the illumination system IL and the projection system PS, is possible with the sensor device 4a.

[0128] This diattenuation measurement does not necessarily require an illumination pupil 1 with multiple pupil spots 21. Alternatively, this diattenuation measurement is also possible by using a conventional pupil with a uniform intensity of the illumination light 19 across the illumination pupil 1.

[0129] By using a Ronchi grating, a measurement of the optical properties of the optical system, in particular a measurement of the apodization properties of the illumination system IL and / or the projection system PS, is also possible. Details of this principle measurement method using such a Ronchi grating can be found in J. Braat et al., "Improved Ronchi test with extended source, J. Opt. Soc. Am. A, Vol. 16, No. 1, pp. 131-140 (1999)" and US 2002 / 0145717 Al.

[0130] Reference is made to Figures 14 to 20 Further discussion is made in the Ronchi test method for determining the properties of an optical system and a corresponding equipped optical apparatus using a Ronchi grating.

[0131] Figure 14 The optical element sequence between the object plane in which the object field OF is arranged and the sensor device 4a is schematically shown. The components and functions corresponding to the components and functions already discussed above with respect to Figures 1 to 13 The components and functions corresponding to the components and functions already discussed above with respect to

[0132] In the object plane, a linear grating 36 is arranged, which has a plurality of parallel linear grating structures to diffract the illumination light 19. Such grating structures extend perpendicular to Figure 14 the drawing plane of the schematic drawing. In Figure 14 In an embodiment of the linear grating 36, such linear structures extend along the y-direction. This linear grating 36 serves as a source grating for the Ronchi measurement scheme.

[0133] In the beam path of the illumination light 19 down to the linear grating 36 is the projection system PS.

[0134] The Ronchi grating 35 is arranged in the beam path of the illumination light 19 between the projection system PS and the sensor device 4a.

[0135] The linear grating 36 is connected to a phase stepping actuator 36c to translate the linear grating 36 in a shear direction perpendicular to its linear structure, as shown in FIG. Figure 14 As shown by double arrow 36b.

[0136] The Ronchi grating 35 is implemented as a checkerboard configuration having a two-dimensional array of grating structures in two directions x and y.

[0137] The sensor device 4a has a Figure 14 The sensor pixel array in the xy plane.

[0138] Figure 15 Shown Figure 14 Measuring principle of the arrangement:

[0139] When the linear grating 36 steps through Figure 15 When the incident illumination light 19 is directed in the x-direction in FIG, the incident illumination light 19 is then deflected into the linear grating diffraction directions 361, 362 and 363 according to the step phase within one period of the linear grating.

[0140] The Ronchi grating 35 further divides these incident linear grating diffraction directions 361 into Ronchi grating diffraction orders 351 +1 、351 -1 、351 -1 The linear grating diffraction direction 362 is diffracted by the Ronchi grating into Ronchi grating diffraction order 352 +1 、352 0 、352 -1 The linear grating diffraction direction 363 is diffracted by the Ronchi grating 35 into the Ronchi grating diffraction order 353 +1 、353 0 、353 -1 .

[0141] Figures 16 to 21 The projection in the z direction shows, on the one hand, the superposition of the grating structures of the linear gratings 36 of the corresponding regions of the optical element 3 , ie the xy positional relationship, and on the other hand, the superposition of the checkerboard arrangement of the Ronchi gratings 35 .

[0142] Figure 16 The linear grating 36 extending along the y direction is shown. Figure 15 The xy positional relationship between the grating structures of the Ronchi grating 35 in the linear grating diffraction direction 361.

[0143] Figure 17 The corresponding relative positions of the linear direction 36 and the Ronchi grating 35 resulting in the linear grating diffraction direction 362 are shown.

[0144] Figure 18The corresponding relative positions of the linear grating 36 and the Ronchi grating 35 leading to the linear grating diffraction directions 363 are shown.

[0145] Figures 19 to 21 The corresponding positional xy relationship between the linear grating structure 36 of the linear grating 36 extending in the x direction and the Ronchi grating 35 is shown, since the linear grating 36 is obtained along the y direction in Figures 19 to 21 Figure 15 The diffraction orders are accordingly spread as explained above with respect to the linear diffraction directions 361, 362, 363, but now in the yz plane.

[0146] Figure 22 Intensity measurements of individual Ronchi tests with the relative lateral orientation according to Figures 16 to 18 Figure 22 also represent the results along the second shear direction y of the relative lateral position according to Figures 19 to 21 Figure 22 The intensities measured by exactly one pixel of the sensor device 4a during the relative shear movement of the linear grating 36 with respect to the Ronchi grating 35 in the x or y direction are shown. P1, P2 and P3 correspond to the intensity measurements of this sensor pixel at three different shear positions. The number of measurement points Pi can vary and can be greater than three or, alternatively, can be much greater than three to improve the measurement accuracy.

[0147] For each pixel of the sensor device 4a, a corresponding phase curve can be fitted, resulting in an exact phase detection.

[0148] This Ronchi measurement scheme can be performed without a wedge structure, such as the wedge 5 on the optical element 3.

[0149] The measurement points P1 to P3 give complete information about the process of the expected sinusoidal signal S, i.e. its modulation M, its offset O and its phase P. From these data, using the Ronchi test algorithm, the apodization properties of the optical system comprising the illumination system IL and the projection system PS can be obtained. In particular, the offset O is used to determine the apodization of the projection system PS in the case of the entire apodization measurement sequence using linear gratings sheared in the x direction and the y direction as described above.

[0150] ​​​It will be appreciated that aspects of the application can be implemented in any convenient way, including by suitable hardware and / or software. For example, appropriate hardware components can be used to create an apparatus arranged to implement the application. Alternatively, programmable apparatus can be programmed to carry out embodiments of the application. The application therefore also provides suitable computer programs for implementing aspects of the application. Such computer programs can be carried on suitable carrier media including tangible carrier media (for example hard disks, CD ROMs etc) and intangible carrier media such as communications signals.

[0151] While specific embodiments of the application have been described above, it will be appreciated that the application can be practiced otherwise than as described. The description is not intended to limit the application.

[0152] It will be appreciated that the detailed description section, and not the summary and abstract sections, is intended to explain the application. The summary and abstract sections can set forth one or more but not all exemplary embodiments of the present application as contemplated by the inventors, and thus, are not intended to limit the application and the appended claims in any way.

[0153] The application has been described above by way of functional building blocks illustrating the implementation of specified functions and relationships of the parts thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships of the parts are appropriately performed.

[0154] The foregoing description of specific embodiments will so fully reveal the general nature of the application that others can modify and / or adapt for various applications such specific embodiments without undue experimentation and without departing from the general concept of the application. Therefore, it is intended that the disclosure set forth herein be considered as a representative embodiment of the application and be considered techniques capable of broad application. Consequently, numerous modifications and adaptations thereof will be apparent to those skilled in the art without departing from the general concept of the application. The specific embodiments are to be considered in their application to the described exemplary process. Therefore, the scope of the application is indicated by the appended claims rather than being indicated by the specification.

[0155] The breadth and scope of the present application should not be limited by any of the above-described exemplary embodiments, but should be defined in accordance with the following claims and their equivalents.

Claims

1. A method for determining optical properties of an optical system comprising an illumination system (IL) for illuminating an object field (OF) and a projection system (PS) for imaging the object field (OF) into an image field (IF), the method comprising the following steps: - providing illumination of the object field (OF) via an illumination pupil (1) comprising a plurality of pupil spots (21), - providing an optical element (3) having an optical surface, said optical surface comprising a plurality of shifting optical areas (5), said shifting optical areas (5) effecting an individual directional shift (Φ2-Φ1; δ) of an illumination light beam (19) entering the respective shifting optical area (5), depending on the respective shifting optical area (5), - calibrating the individual directional shifts (Φ2-Φ1; δ) by measuring, for each of a plurality of pupil spots (21) within the object field (OF), a pupil spot shift caused by the shifted optical region (5) via a measurement pupil (4) in the path of the illumination beam (19) after the optical element (3), - Using the calibrated individual directional shifts to calculate the optical property to be determined from the measurement.

2. The method according to claim 1, wherein The optical element (3) comprises at least one non-displaced optical area (6) which does not impart a directional shift to an illumination light beam (19) entering the non-displaced optical area (6), wherein a reference illumination light beam (19) entering the non-displaced optical area (6) is also measured during the calibration step.

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

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

5. The method according to any one of claims 1 to 4, wherein A 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 said calibration step, a map is created in which respective pupil spot shifts are attributed to respective pupil spots (21) and respective field points.

7. The method according to any one of claims 1 to 6, wherein The optical element (3) comprises at least one grating region which diffracts an illumination light beam (19) entering such grating region and further passing through one of the shifted optical regions (5) of the optical element (9), wherein the method comprises a Ronchi test to obtain the optical property 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 for applying polarization of an illumination beam (19) entering the shifted optical region (5), the optical polarizer being used to determine the transmittance of the optical element (3) for two different polarization states of the illumination beam (19), wherein the method comprises measuring the transmittance data and thereby obtaining the bidirectional attenuation of the optical system.

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

10. An optical device having an optical system comprising an illumination system (IL) for illuminating an object field (OF) and a projection system (PS) for imaging the object field (OF) into an image field (IF), the optical device comprising: a light source (SO) for generating an illumination light beam (19) for illuminating the object field (OF) via the illumination system (IL), - pupil generating means (20) as part of the illumination system (IL) for providing illumination of the object field (OF) via an illumination pupil (1) comprising a plurality of pupil spots (21), - an optical element (3) having an optical surface comprising a plurality of shifting optical areas (5) which effect an individual directional shift (Φ2-Φ1; δ) of the illumination light beam (19) entering the respective shifting optical area (5), - a sensor device (4a) for measuring, for each of the pupil spots at a plurality of individual field points within the object field (OF), a pupil spot shift produced by a different shifting optical region (5) via a measurement pupil (4) in the path of the illumination beam (19) after the optical element (3).

11. The optical device according to claim 10, comprising a calibration module (22) for calibrating the individual directional displacements (Φ2-Φ1; δ), the calibration module (22) being in signal connection with the sensor device (4a).

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

13. Optical device according to any one of claims 10 to 12, comprising a Ronchi grating as part of the optical element (3).

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

15. The optical device according to claim 14, comprising an optical analyzer for determining the transmittance of the optical element (3) for two different polarization states of the illumination light beam (19).

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