Method for examining a substrate body for a component in a lithography apparatus, substrate body and lithography apparatus

Abstract

Method for examining a substrate body (108) for a component (102) in a lithography apparatus (1), including the steps of: a) creating (S1) at least one marking (112) in an interior (114) of the substrate body (108), b) transmitting (S3) an ultrasonic signal (134) and receiving an ultrasonic signal (136) reflected off the at least one marking (112), and c) ascertaining (S4), in spatially resolved fashion, one or more parameters (P) of the substrate body (108) on the basis of the received ultrasonic signal (136).

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1

[0003] METHOD FOR EXAMINING A SUBSTRATE BODY FOR A COMPONENT IN A LITHOGRAPHY APPARATUS, SUBSTRATE BODY AND LITHOGRAPHY APPARATUS

[0004] The present invention relates to a method for examining a substrate body for a component in a lithography apparatus, such a substrate body and a lithography apparatus having such a substrate body.

[0005] The content of the priority application DE 10 2024209 082.4 is incorporated by reference in its entirety.

[0006] Microlithography is used for producing microstructured component parts, for example integrated circuits. The microlithography process is performed using a lithography apparatus, which comprises an illumination system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0007] Driven by the desire for ever smaller structures in the production of integrated circuits, EUV lithography apparatuses which use light at a wavelength in the range of 0.1 nm to 30 nm, in particular 13.5 nm, are currently being developed. Since most materials absorb light at this wavelength, such EUV lithography apparatuses require the use of reflective optics units, i.e. mirrors, instead of refractive optics units, i.e. lens elements, as used previously.

[0008] A problem that arises in the process is that the mirrors heat up as a consequence of absorbing the radiation emitted by the EUV light source. This may lead to a thermal deformation of the mirrors. Furthermore, an optical coating of the mirrors might also degrade as a result of an increase in temperature. Both thermal deformations of the mirrors and damage to their optical coatings may adversely affect the imaging properties of the mirrors.

[0009] The imaging quality of projection systems of an EUV lithography apparatus depends greatly on the quality of the mirror material. A material with a very small coefficient of thermal expansion is used for the mirror substrates in order to reduce aberrations due to the mirrors heating. In particular, a deformation of the mirror material as a function of a temperature increase is minimal and / or zero at the so-called zero-crossing temperature of the coefficient of thermal expansion of Carl Zeiss SMT GmbH

[0010] 2 the mirror material. Variations in the coefficient of thermal expansion or in the zero-crossing temperature within the mirror substrate volume have a direct effect on aberrations caused by mirror heating.

[0011] Against this background, a problem addressed by the present invention is that of providing an improved method for examining a substrate body for a component in a lithography apparatus.

[0012] According to a first aspect, a method is proposed for examining a substrate body for a component in a lithography apparatus. The method comprises the steps of: a) creating at least one marking in an interior of the substrate body, b) transmitting an ultrasonic signal and receiving an ultrasonic signal reflected off the at least one marking, and c) ascertaining, in spatially resolved fashion, one or more parameters of the substrate body on the basis of the received ultrasonic signal.

[0013] With the aid of the method, a parameter that varies over the volume of the substrate body of a component in a lithography apparatus, or a plurality of such parameters, may be easily ascertained in spatially resolved fashion. In particular, at least one marking is created in the interior of the substrate body. As a result, the substrate volume is divided into a plurality of volume elements (voxels) in relation to a reflection of the ultrasonic signal. This is because, firstly, the ultrasonic signal radiated into the substrate body from a top side is reflected off a base of the substrate body opposite the top side and thus contains information regarding the volume region of the substrate body traversed from the top side to the base. Secondly, the ultrasonic signal radiated into the substrate body from the top side is reflected off the at least one marking and thus contains information regarding the volume region traversed from the top side to the at least one marking. In the case of exactly one marking, the substrate body is thus divided into exactly two volume elements, one from the top side to the marking and a second from the marking to the base. In the case of a plurality of markings, the substrate body is divided accordingly into a plurality of volume elements. For each volume element, the one or more parameters may be ascertained separately on the basis of the corresponding reflected ultrasonic signal components, and so the parameter / parameters can be ascertained in spatially resolved fashion. It follows that a spatial resolution when ascertaining the parameter / parameters can be increased with an increased number of the markings - especially if the markings are distributed uniformly over the substrate body. Carl Zeiss SMT GmbH

[0014] 3

[0015] The lithography apparatus (projection exposure apparatus) may be an EUV lithography apparatus. EUV stands for "extreme ultraviolet" and refers to a wavelength of the operating light of between 0.1 nm and 30 nm, in particular 13.5 nm. The lithography apparatus can also be a DUV lithography apparatus. DUV stands for "deep ultraviolet" and denotes a wavelength of the operating light of between 30 nm and 250 nm. The lithography apparatus comprises an illumination system and a projection system. In particular, using the lithography apparatus, the image of a mask (reticle) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0016] For example, the component in the lithography apparatus is an optical component, e.g. a mirror or a lens element, or a mechanical component, e.g. a mount or the like.

[0017] The component is preferably used in a projection optics unit of the projection exposure apparatus. However, the component can also be used in an illumination system.

[0018] The substrate body is a three-dimensional body in particular. The substrate body is a solid body in particular. For example, the one or more parameters of the substrate body ascertained in step c) of the method are parameters and / or properties of a material of the substrate body (i.e. material parameters or material properties). For example, the substrate body contains variations in the one or more parameters over the volume of the substrate body. These variations can be ascertained using the proposed method. In other words, a spatial distribution of the one or more parameters over the volume of the substrate body is ascertained using the proposed method.

[0019] An extent of an inhomogeneity of the relevant parameter can be ascertained on the basis of the one or more parameters of the substrate body ascertained in a spatially resolved fashion. This can be used to check a quality of the substrate body. For example, a suitability of the substrate body for a predetermined use in the lithography apparatus can be checked on the basis of the ascertained extent of an inhomogeneity of the relevant parameter.

[0020] Purely by way of example, a material of the substrate body contains titanium- doped glass, and a coefficient of thermal expansion of the substrate body is Carl Zeiss SMT GmbH

[0021] 4 ascertained in spatially resolved fashion in step c). That is to say, a spatial distribution of the coefficient of thermal expansion over the volume of the substrate body is ascertained. Should it be ascertained that the inhomogeneities of the coefficient of thermal expansion are smaller than a predetermined threshold value, then it is possible to ascertain that the examined substrate body is suitable - e.g. without further adaptations - for use as a mirror substrate of a mirror in the lithography apparatus. Should it be ascertained that the inhomogeneities of the coefficient of thermal expansion are greater than a predetermined threshold value, then the substrate body and / or its surface may be subject to a suitable treatment on the basis of the ascertained spatial distribution of the coefficient of thermal expansion in order to compensate for the ascertained inhomogeneities of the coefficient of thermal expansion.

[0022] For example, the at least one marking contains a modification to a material of the substrate body. For example, the at least one marking contains one or more tears in a material of the substrate body. The at least one marking for example comprises a plurality of tears in a material of the substrate body that are arranged within a substantially spherical volume.

[0023] The at least one marking being created in the interior of the substrate body also means that it is attached and / or arranged in the interior of the substrate body.

[0024] In particular, the at least one marking is created, i.e. arranged, in the interior of the substrate body only. No markings are created on the surface of the substrate body. One could also say that the at least one marking is created in such a way in step c) that the surface of the substrate body is free from the at least one marking.

[0025] For example, the at least one marking is created at at least one position in the interior of the substrate body ascertained in advance. Moreover, the one or more parameters of the substrate body are ascertained on the basis of the received ultrasonic signal and, additionally, on the basis of the position ascertained in advance. For example, a time of flight of the ultrasonic signal (e.g. up to the at least one marking) is ascertained on the basis of the ultrasonic signal received. Furthermore, a speed of propagation of the ultrasonic signal in the substrate body, in particular in each volume element of the substrate body, is ascertained, e.g. on the basis of the ascertained time of flight and the position of the at least one marking ascertained in advance. Thereupon, the one or more parameters may be ascertained on the basis of the ascertained speed of propagation of the ultrasonic signal. Carl Zeiss SMT GmbH

[0026] 5

[0027] In particular, the ultrasonic signal is transmitted and received by an ultrasonic sensor device. The received ultrasonic signal is an echo signal of the transmitted ultrasonic signal in particular. The received ultrasonic signal contains a reflection signal for each reflection (e.g. off the at least one marking and / or the base of the substrate body) in particular.

[0028] In particular, the received ultrasonic signal is a time -dependent function. For example, the received ultrasonic signal contains a time curve of a sensor voltage output by the ultrasonic sensor device. The sensor voltage specifies the reception signal intensity, i.e. the sonic pressure, measured by the ultrasonic sensor device. For each reflection, the ultrasonic signal received contains e.g. an increase in the amplitude of the received signal intensity (i.e. a maximum and / or a peak in the received signal intensity as a function of time) as a corresponding echo signal. Hence, the associated time may be identified as reception time of this echo signal. The time of flight can be ascertained therefrom.

[0029] For example, the ultrasonic sensor device has an accuracy of 100 ns or better, 10 ns or better, 5 ns or better, 1 ns or better and / or 0.1 ns (i.e. 100 ps) or better.

[0030] In other words, the ultrasonic sensor device is configured to ascertain the time of flight of the ultrasonic signal, for example with the specified accuracy. However, the ultrasonic sensor device may also have a different accuracy in relation to a time measurement.

[0031] For example, the substrate body may be examined using an ultrasonic signal as a longitudinal wave and / or as a transverse wave.

[0032] For example, longitudinal waves and transverse waves have different speeds, and the ascertained speeds can also be converted into other parameters. For example, the material property known as Young's modulus can be ascertained from the speed of sound of a longitudinal wave. Furthermore, the material property known as shear modulus for example can be ascertained from the speed of sound of a transverse wave.

[0033] Whether a longitudinal wave or a transverse wave is created with the aid of the ultrasonic device depends on the direction of movement of an oscillator in the ultrasonic device. A longitudinal wave is formed if the oscillator oscillates in parallel with the direction of propagation of the wave. A transverse wave is formed if the oscillator oscillates perpendicular to the direction of propagation of the wave. Moreover, a transverse wave may also be created in the substrate body by virtue Carl Zeiss SMT GmbH

[0034] 6 of an ultrasonic longitudinal wave being radiated at a surface of the substrate body at an angle not equal to 90° (e.g. at an angle of 45°), i.e. not in perpendicular fashion. Then, an ultrasonic transverse wave is formed within the substrate body should the inclined ultrasonic longitudinal wave be incident on the surface of the substrate body.

[0035] For example, a control device ascertains the parameter / parameters.

[0036] For processing the received ultrasonic signal, the control device may optionally also be configured in such a way that signals with a low signal-to-noise ratio are extracted from the ultrasonic signal. For example, the substrate body may be traversed (i.e. scanned and / or raster scanned) using a measuring head of the ultrasonic sensor device in order to detect an increase in the reflection signal when the measuring head approaches a marking and a reduction in the reflection signal when the measuring head moves away from the marking ("synthetic aperture focusing technique", SAFT). However, other techniques for extracting signals with a low signal-to-noise ratio may also be applied, e.g. a pulse compression, in which an outgoing pulse is cross correlated with the echo.

[0037] For example, the method is carried out with the aid of an examination apparatus that comprises a marking creation device for creating the at least one marking, the ultrasonic sensor device and the control device.

[0038] According to an embodiment, the at least one marking comprises at least one engraving.

[0039] In particular, the at least one marking contains a local modification to the material at the location of the corresponding marking. For example, the at least one marking contains a physical and / or chemical modification to the material at the location of the corresponding marking.

[0040] According to a further embodiment, the at least one marking is created by means of a laser engraving process.

[0041] The laser engraving process allows the at least one marking to be created as a very small marking (e.g. 100 gm or smaller, 50 gm or smaller, 10 gm or smaller and / or 1 gm or smaller). Hence, the substrate body may be examined virtually non -destructively using the method. Carl Zeiss SMT GmbH

[0042] 7

[0043] During the laser engraving process, the at least one marking is created at a location in the interior of the substrate body ascertained in advance, in particular by heating a material of the substrate body by means of a laser beam. In this case, the material of the substrate body is heated locally in the region of a focus of the radiated-in laser light. The power density of the laser beam at the location of the marking to be applied may be so strong that the material melts there. Applying a strongly focused laser beam allows the heat input into the material to be very restricted locally. If a pulsed laser beam is additionally used, it is also possible to significantly restrict the heat input into the material in terms of time. Since the material of the substrate body is strongly heated only locally at the location of the marking to be applied, while adjacent regions of the material are not heated, tears and / or fractures in the material arise at the location of the marking to be applied.

[0044] For example, the applied laser beam has a wavelength in the range from 380 nm to 1400 nm (visible light and near infrared). For example, the applied laser beam has a wavelength in the range from 500 nm to 570 nm (green light). For example, the applied laser beam has a wavelength in the range from 780 nm to 1400 nm (near infrared light). For example, the applied laser beam has a wavelength of 1030 nm. However, the applied laser beam may also have any other wavelength.

[0045] For example, the applied laser beam is a pulsed laser beam. For example, a pulse length is 6.5 ps. However, a pulse length of the applied laser beam may also have any other value.

[0046] For example, the applied laser beam is very strongly focused and thus has a small laser spot size (i.e. a small beam cross section) at the processing location (i.e. at the location of the marking to be applied). It could also be said that the applied laser beam has a large divergence angle. The divergence angle is defined as the angle about which the laser beam widens in the far field; in this context, the beam waist (which corresponds to the laser spot size at the processing point) is used as reference. That is to say, the smaller the laser spot size at the processing point, the greater the divergence angle.

[0047] As a result of the small laser spot size a very high energy density may be provided at the location of the marking to be applied, whereas virtually no laser energy arrives at locations adjacent thereto.

[0048] Exemplary values for the laser spot size are 50 pm or less, 10 pm or less and / or 1 pm or less. Carl Zeiss SMT GmbH

[0049] 8

[0050] Exemplary values for the numerical aperture, which depends on the divergence angle, are 0.1 or more, 0.5 or more and / or 0.8 or more.

[0051] According to a further embodiment, a predetermined laser wavelength is applied in the laser engraving process, and the substrate body is transparent to the predetermined laser wavelength.

[0052] For example, the at least one marking can be created using a laser wavelength in the visible spectral range in the case of a glass material and / or a transparent plastic (e.g. Plexiglas).

[0053] For example, the at least one marking can be created using a laser wavelength in the infrared spectral range in the case of a silicon material (e.g. single-crystal silicon). In particular, silicon is transparent to infrared light, even though it is nontransparent (opaque) to visible light.

[0054] According to a further embodiment, a size of the at least one marking is 100 gm or less, 50 gm or less, 30 gm or less, 10 gm or less, 5 gm or less and / or 1 gm or less.

[0055] As a result of the at least one marking created in the interior of the substrate body being very small, the substrate body may be examined virtually non-de- structively using the method.

[0056] In embodiments, a size of the at least one marking is for example at least 1 gm and / or at least 5 gm in order to allow a detection of the at least one marking using ultrasound.

[0057] For example, the size of the at least one marking is a maximum external dimension of the at least one marking. The at least one marking may have e.g. a substantially circular shape; in that case, the size of the at least one marking for example is a diameter of the at least one marking.

[0058] According to a further embodiment, a plurality of the markings that divide the substrate body into a plurality of volume elements are created in the interior of the substrate body. Moreover, the received reflected ultrasonic signal has a corresponding reflected signal component for each marking. Furthermore, the one or more parameters for each volume element are ascertained on the basis of the corresponding reflected signal component. Carl Zeiss SMT GmbH

[0059] 9

[0060] A spatial resolution during the examination of the substrate body may be increased as a result. Hence the distribution of the one or more parameters of the substrate body may be ascertained with a higher spatial resolution.

[0061] Merely by way of example, it is possible to create 100 markings or more, 500 markings or more and / or 1000 markings or more in the substrate body.

[0062] In this document, "a plurality of markings" refers to a plurality of the at least one marking in particular.

[0063] In particular, the plurality of markings are arranged at a distance from one another.

[0064] A respective spacing between the plurality of markings defines a spatial resolution when ascertaining the parameter / parameters in step S4 in particular. In particular, the spatial resolution is higher when the respective spacing between the plurality of markings is smaller.

[0065] A spacing between two adjacent markings is e.g. 0.005 cm or more, 0.01 cm or more, 0.05 cm or more, 0.1 cm or more, 0.5 cm or more, 1 cm or more, 2 cm or more and / or 3 cm or more. In addition to that or instead, a spacing between two adjacent markings is e.g. 3 cm or less, 2 cm or less, 1 cm or less, 0.5 cm or less and / or 0.1 cm or less.

[0066] Moreover, a respective size of the plurality of markings may be multiple times (e.g. 10 times or more, 50 times or more and / or 100 times more) smaller than a distance between (e.g. in each case) two adjacent markings of the plurality of markings. This facilitates the detection of the markings in the deeper planes of the substrate body by means of ultrasound in step S3.

[0067] Furthermore, the number of volume elements may for example be greater than the number of markings since the transmitted ultrasonic signal is also reflected off the base of the substrate body, whereby this gives rise to at least one additional volume element.

[0068] According to a further embodiment, a plurality of the markings are created in the interior of the substrate body and are arranged accordingly at or adjacent to grid points of a regular three-dimensional grid. Carl Zeiss SMT GmbH

[0069] 10

[0070] The spatial distribution of the one or more parameters can be ascertained better by way of a uniformly distributed arrangement of the plurality of markings.

[0071] An arrangement of the plurality of markings at grid points of a regular three-dimensional grid means that, in particular, the plurality of markings are arranged at uniform distances from one another.

[0072] Some of the plurality of markings may also be arranged not exactly on the grid points of the grid but adjacent thereto. For example, some of the plurality of markings may be arranged at a distance from the respective grid point by an offset that is a multiple (e.g. two to ten times) of the size of said markings. This facilitates the detection using the ultrasonic signal. In particular, the plurality of markings may be arranged in the interior of the substrate body in such a way that, when projected onto a plane perpendicular to the incoming radiation direction of the ultrasonic signal, they are all arranged spaced apart from one another.

[0073] According to a further embodiment, a position of the at least one marking is ascertained, and the one or more parameters of the substrate body are ascertained on the basis of the ascertained position, and the position of the at least one marking is ascertained on the basis of operating parameters of a laser when creating the at least one marking, and / or the position of the at least one marking is ascertained on the basis of an optical measurement.

[0074] By ascertaining the position of the at least one marking, the speed of sound for the at least one marking may be ascertained from the ascertained position and the measured time of flight of the ultrasonic signal.

[0075] The operating parameters of the laser when creating the at least one marking for example include a position of a laser head of the laser (e.g. in three spatial directions that span a three-dimensional space and / or in relation to a rotation about the three spatial directions), a working distance of the laser from the at least one marking, a degree of focusing of the laser (i.e. the divergence angle of the laser), a wavelength of the laser or the like.

[0076] For example, the optical measurement includes an interferometric measurement. For example, the optical measurement is performed with the aid of one or more interferometers. In particular, the optical measurement is carried out before step c). Furthermore, the optical measurement may be carried out before or after step b). Carl Zeiss SMT GmbH

[0077] 11

[0078] As a result of optically measuring the position of the at least one marking, the corresponding position can be ascertained even more accurately. Consequently, the one or more parameters of the substrate body can be ascertained even better therewith (in particular with a greater accuracy in relation to the spatial coordinate). For example, the optical measurement of the position of the at least one marking may be carried out in addition to the ascertainment of the position of the at least one marking on the basis of the operating parameters of the laser.

[0079] Purely by way of example, a first ascertainment of the position of all markings of the at least one marking may be ascertained on the basis of the operating parameters of the laser. Furthermore, a second ascertainment of the position may for example be performed only for a few of the markings (alternatively also for all markings) by means of an optical measurement. Then, a systematic error of the first ascertainment of the position can be ascertained and taken into account, based on a comparison between the second ascertainment of the position and the first ascertainment of the position.

[0080] According to a further embodiment, a speed of sound in the substrate body is determined in spatially resolved fashion on the basis of the received ultrasonic signal, and the one or more parameters of the substrate body are ascertained on the basis of the determined speed of sound.

[0081] The speed of sound in the substrate body is ascertained in particular on the basis of the position of the at least one marking and an ascertained time of flight of the ultrasonic signal for the corresponding marking. In particular, the speed of sound is ascertained in the volume element, which is defined by a respective marking, on the basis of the position of the at least one marking and the ascertained time of flight of the ultrasonic signal in the event of a reflection off the corresponding marking. Consequently, a spatially dependent speed of sound can be ascertained for each of the at least one marking. Thereupon, the spatially dependent parame- ter / parameters of the substrate body may be ascertained from the spatially dependent speed of sound.

[0082] According to a further embodiment, a material of the substrate body comprises glass, high-performance glass, titanium-doped glass, silicon and / or plastic.

[0083] In particular, a high-performance glass comprises a material with a low (e.g. ultralow) coefficient of thermal expansion. For example, the coefficient of thermal expansion of a high-performance glass is within a range of ±20 ppb / K (parts per Carl Zeiss SMT GmbH

[0084] 12 billion per Kelvin), ±15 ppb / K, ±10 ppb / K and / or ±5 ppb / K at a desired operating temperature. However, the coefficient of thermal expansion of the high-performance glass may also be within a different range. In such a high-performance glass, changes in the geometric shape and in the dimensions on account of temperature changes occur to only a very small degree.

[0085] Examples of a material for the high-performance glass encompass a titanium- doped glass, e.g. a glass material made of TiC^'SiC^, in which the ultralow coefficient of thermal expansion is realized by varying the concentration of TiC>2 (e.g. a substrate material sold by Corning Inc. under the trademark "ULE" for "ultralow expansion"). A further example of a high-performance glass is a Li2O-A12Os- SiC>2 glass ceramic (sold by Schott under the trademark "Zerodur") with a crystalline phase, in which the ultralow coefficient of thermal expansion is realized by uniformly distributed nanocrystals in a residual glass phase.

[0086] A material of the substrate body containing silicon may be a silicon single crystal, for example, which is used for mirror substrates. Silicon is transparent to infrared light in particular.

[0087] A material of the substrate body containing plastic could be Plexiglas, for example, or any other plastic that is transparent to selected wavelengths of the laser light.

[0088] According to a further embodiment, the one or more parameters of the substrate body comprise: one or more mechanical, thermal and / or acoustic parameters, and / or a coefficient of thermal expansion, a zero-crossing temperature, a Young's modulus, a shear modulus, a Poisson number and / or an acoustic impedance.

[0089] In particular, all parameters of the substrate body (e.g. material parameters and / or material properties) that have an influence on the propagation of sound and hence the speed of sound in a material of the substrate body may be ascertained using the method.

[0090] The coefficient of thermal expansion specifies a change in the geometric shape and the dimensions of a material in the case of a temperature change. For example, the coefficient of thermal expansion is a linear coefficient of thermal expansion, which specifies a change in material length as a function of a change in temperature. Carl Zeiss SMT GmbH

[0091] 13

[0092] The coefficient of thermal expansion itself is temperature -dependent, i.e. a temperature-dependent function. At its zero-crossing temperature (ZCT), the coefficient of thermal expansion has a zero crossing in its temperature dependence, in the proximity of which there is no thermal expansion, or only a negligible thermal expansion, of the material in the case of a change in temperature.

[0093] Young's modulus (modulus of elasticity) specifies the proportional relationship between applied stress and arising strain in the deformation of the substrate body in the event of a linear elastic behaviour.

[0094] The shear modulus (modulus of rigidity) specifies the relationship between applied shear stress and arising shear distortion (shear angle, sliding) in the event of a linear elastic behaviour.

[0095] The Poisson number describes the transverse contraction behaviour of the substrate body.

[0096] Purely by way of example, a material of the substrate body contains titanium- doped glass, and a spatially resolved coefficient of thermal expansion of the substrate body is ascertained in step c). For titanium-doped glass, the coefficient of thermal expansion can be ascertained in particular from the speed of sound of the ultrasonic signal since the speed of sound in the substrate body depends on the titanium content.

[0097] A further example is that of a material of the substrate body comprising a glass ceramic with the crystalline phase (e.g. "Zerodur") and a spatially resolved coefficient of thermal expansion of the substrate body being ascertained in step c). For a glass ceramic with a crystalline phase, the coefficient of thermal expansion can be ascertained on the basis of the speed of sound of the ultrasonic signal because the speed of sound in the substrate body depends on the presence of crystalline and amorphous phases.

[0098] According to a further embodiment, step b) is carried out with the aid of a scanning acoustic microscope.

[0099] The substrate a body may be raster-scanned using the scanning acoustic microscope (SAM). Carl Zeiss SMT GmbH

[0100] 14

[0101] According to a further embodiment, the component in the lithography apparatus is a mirror in the lithography apparatus, and the substrate body is a body of a mirror substrate of the mirror.

[0102] A substrate body for a component in the lithography apparatus is proposed according to a second aspect. The substrate body comprises at least one marking at at least one predetermined position in an interior of the substrate body, wherein the at least one marking is configured to reflect an ultrasonic signal.

[0103] According to a third aspect, a lithography apparatus is proposed. The lithography apparatus comprises a component having a substrate body as described above.

[0104] According to a further aspect, a computer program product is proposed, the latter comprising commands which, upon execution of the program by at least one computer, cause said computer to carry out at least a part of the above-described method. For example, the computer program product is configured to receive the reflected ultrasonic signal from an ultrasonic sensor device. For example, the computer program product is configured to carry out step c) of the method.

[0105] A computer program product, such as e.g. a computer program means, can be provided or supplied for example as a storage medium, such as e.g. a memory card, a USB stick, a CD-ROM, a DVD, or else in the form of a downloadable file from a server in a network. For example, in a wireless communications network, this can be effected by transferring an appropriate file with the computer program product or the computer program means.

[0106] According to a further aspect, an examination apparatus is proposed for examining a substrate body for a component in a lithography apparatus. The examination apparatus comprises: a marking creation device as described above, an ultrasonic sensor device as described above and a control device as described above.

[0107] ”A(n)" should not necessarily be understood as a restriction to exactly one element in the present case. Rather, there may also be multiple elements, for example two, three or more. Any other numeral used here should also not be understood as a restriction to exactly the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless indicated otherwise.

[0108] The embodiments and features described for the method apply, mutatis mutandis, to the proposed substrate body and the lithography apparatus. Carl Zeiss SMT GmbH

[0109] 15

[0110] Further possible implementations of the invention also comprise non-explicitly mentioned combinations of features or embodiments described hereinabove or hereinafter with regard to the exemplary embodiments. A person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the invention.

[0111] Further advantageous configurations and aspects of the invention are the subject matter of the dependent claims and of the exemplary embodiments of the invention described below. The invention is explained in detail hereinafter on the basis of preferred embodiments with reference to the accompanying figures.

[0112] Fig. 1 shows a schematic meridional section of a projection exposure apparatus for EUV projection lithography, according to one embodiment;

[0113] Fig. 2 shows an optical component of the projection exposure apparatus from Fig. 1 according to one embodiment;

[0114] Fig. 3 shows a flowchart for elucidating a method for examining a substrate body for a component in a projection exposure apparatus, according to one embodiment;

[0115] Fig. 4 shows a substrate body of the component from Fig. 2 according to one embodiment during a method step of the method from Fig. 3;

[0116] Fig. 5 shows a substrate body of the component from Fig. 2 according to one embodiment while markings are created;

[0117] Fig. 6 shows a marking of the substrate body from Fig. 4 or 5 according to one embodiment;

[0118] Fig. 7 shows a view similar to Fig. 5, wherein volume elements assigned to the markings are labelled; and

[0119] Fig. 8 shows a view similar to Fig. 7, wherein an ultrasonic examination of the markings is elucidated.

[0120] In the figures, identical or functionally identical elements have been provided with the same reference signs, unless indicated otherwise. It should also be noted that the illustrations in the figures are not necessarily to scale. Carl Zeiss SMT GmbH

[0121] 16

[0122] Fig. 1 shows an embodiment of a projection exposure apparatus 1 (lithography apparatus), in particular an EUV lithography apparatus. In addition to a light source or radiation source 3, an embodiment of an illumination system 2 of the projection exposure apparatus 1 has an illumination optics unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 may also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not comprise the light source 3.

[0123] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable by way of a reticle displacement drive 9, in particular in a scanning direction.

[0124] Fig. 1 shows, for explanation purposes, a Cartesian coordinate system with an x- direction x, a ydirection y, and a z-direction z. The x-direction x runs perpendicularly into the plane of the drawing. The ydirection y runs horizontally, and the z- direction z runs vertically. The scanning direction in Fig. 1 runs in the ydirection y. The z-direction z runs perpendicularly to the object plane 6.

[0125] The projection exposure apparatus 1 comprises a projection optics unit 10. The projection optics unit 10 serves for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. In an alternative, an angle that differs from 0° is also possible between the object plane 6 and the image plane 12.

[0126] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by way of a wafer displacement drive 15, in particular in the ydirection y. The displacement firstly of the reticle 7 by way of the reticle displacement drive 9 and secondly of the wafer 13 by way of the wafer displacement drive 15 can be implemented so as to be mutually synchronized.

[0127] The light source 3 is an EUV radiation source. The light source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. The used radiation 16 has in particular a wavelength in the range of between 5 nm and 30 nm. The light source 3 may be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It may also be a synchrotron-based radiation source. The light source 3 may be a free electron laser (FEL). Carl Zeiss SMT GmbH

[0128] 17

[0129] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 may be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The illumination radiation 16 may be incident on the at least one reflection surface of the collector 17 with grazing incidence (Gl), i.e. at angles of incidence of greater than 45°, or with normal incidence (Nl), i.e. at angles of incidence of less than 45°. The collector 17 may be structured and / or coated, firstly to optimize its reflectivity for the used radiation and secondly to suppress extraneous light.

[0130] Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics unit 4.

[0131] The illumination optics unit 4 comprises a deflection mirror 19 and, disposed downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a plane deflection mirror or, in an alternative to that, a mirror with a beam -influencing effect going beyond the pure deflection effect. In an alternative to that or in addition, the deflection mirror 19 may be in the form of a spectral filter that separates a used light wavelength of the illumination radiation 16 from extraneous light at a different wavelength. Should the first facet mirror 20 be arranged in a plane of the illumination optics unit 4 which is optically conjugate to the object plane 6 as a field plane, this facet mirror is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which can also be referred to as field facets. Only some of these first facets 21 are illustrated in Fig. 1 by way of example.

[0132] The first facets 21 may take the form of macroscopic facets, in particular rectangular facets or facets with an arc-shaped or part-circular edge contour. The first facets 21 may take the form of plane facets or, in an alternative to that, convexly or concavely curved facets.

[0133] As is known for example from DE 10 2008 009 600 Al, the first facets 21 themselves can also each be composed of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 may take the form of a microelectromechanical system (MEMS system) in particular. For details, reference is made to DE 10 2008 009 600 Al. Carl Zeiss SMT GmbH

[0134] 18

[0135] The illumination radiation 16 propagates horizontally, i.e. in the ydirection y, between the collector 17 and the deflection mirror 19.

[0136] In the beam path of the illumination optics unit 4, a second facet mirror 22 is disposed downstream of the first facet mirror 20. Should the second facet mirror 22 be arranged in a pupil plane of the illumination optics unit 4, this facet mirror is also referred to as a pupil facet mirror. The second facet mirror 22 may also be spaced apart from a pupil plane of the illumination optics unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 Al, EP 1 614 008 Bl, and US 6,573,978.

[0137] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0138] The second facets 23 can likewise be macroscopic facets, which can for example have a round, rectangular or hexagonal boundary, or can alternatively be facets composed of micromirrors. For details in this regard, reference is likewise made to DE 10 2008 009 600 Al.

[0139] The second facets 23 may have plane reflection surfaces or, in an alternative to that, convexly or concavely curved reflection surfaces.

[0140] The illumination optics unit 4 thus forms a doubly faceted system. This fundamental principle is also referred to as a fly's eye integrator.

[0141] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optics unit 10. In particular, the second facet mirror 22 may be arranged so as to be tilted in relation to a pupil plane of the projection optics unit 10, as described for example in DE 10 2017 220 586 Al.

[0142] The second facet mirror 22 is used to image the individual first facets 21 into the object field 5. The second facet mirror 22 is the last beam-shaping mirror or actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

[0143] In a further embodiment (not illustrated) of the illumination optics unit 4, a transfer optics unit contributing in particular to the imaging of the first facets 21 into the object field 5 may be arranged in the beam path between the second facet Carl Zeiss SMT GmbH

[0144] 19 mirror 22 and the object field 5. The transfer optics unit may have exactly one mirror or, in an alternative to that, two or more mirrors, which are arranged one behind another in the beam path of the illumination optics unit 4. The transfer optics unit may in particular comprise one or two normal-incidence mirrors (NI mirrors) and / or one or two grazing-incidence mirrors (GI mirrors).

[0145] In the embodiment shown in Fig. 1, the illumination optics unit 4 has exactly three mirrors downstream of the collector 17, specifically the deflection mirror 19, the first facet mirror 20, and the second facet mirror 22.

[0146] In a further embodiment of the illumination optics unit 4, the deflection mirror 19 may also be omitted, and so the illumination optics unit 4 may then have exactly two mirrors downstream of the collector 17, specifically the first facet mirror 20 and the second facet mirror 22.

[0147] The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or using the second facets 23 and a transfer optics unit is, as a rule, only approximate imaging.

[0148] The projection optics unit 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

[0149] In the example illustrated in Fig. 1, the projection optics unit 10 comprises six mirrors Ml to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are likewise possible. The projection optics unit 10 is a doubly obscured optics unit. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics unit 10 has an image-side numerical aperture which is greater than 0.5 and which may also be greater than 0.6 and which, for example, may be 0.7 or 0.75.

[0150] Reflection surfaces of the mirrors Mi may take the form of free-form surfaces without an axis of rotational symmetry. In an alternative to that, the reflection surfaces of the mirrors Mi may take the form of aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics unit 4, the mirrors Mi may have highly reflective coatings for the illumination radiation 16. These coatings may be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon. Carl Zeiss SMT GmbH

[0151] 20

[0152] The projection optics unit 10 has a large object-image offset in the ydirection y between a ycoordinate of a centre of the object field 5 and a ycoordinate of the centre of the image field 11. This object-image offset in the ydirection y can be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.

[0153] In particular, the projection optics unit 10 may have an anamorphic design. It has in particular different imaging scales Bx, By in the x- and y- directions x, y. The two imaging scales Bx, By of the projection optics unit 10 are preferably (Bx, By) = (+ / -0.25, + / -0.125). A positive imaging scale B means imaging without image inversion. A negative sign for the imaging scale B means imaging with image inversion.

[0154] The projection optics unit 10 consequently leads to a reduction in size with a ratio of 4'1 in the x-direction x, i.e. in a direction perpendicular to the scanning direction.

[0155] The projection optics unit 10 leads to a reduction in size of 8H in the ydirection y, i.e. in the scanning direction.

[0156] Other imaging scales are likewise possible. Imaging scales with the same sign and the same absolute value in the x-direction x and ydirection y are also possible, for example with absolute values of 0.125 or of 0.25.

[0157] The number of intermediate image planes in the x-direction x and in the ydirection y in the beam path between the object field 5 and the image field 11 can be the same or can differ, depending on the embodiment of the projection optics unit 10. Examples of projection optics units with different numbers of such intermediate images in the x-direction x and ydirection y are known from US 2018 / 0074303 Al.

[0158] In each case, one of the second facets 23 is assigned to exactly one of the first facets 21 for forming in each case an illumination channel for illuminating the object field 5. This may yield in particular illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the first facets 21. The first facets 21 create a plurality of images of the intermediate focus on the second facets 23 respectively assigned to them.

[0159] The first facets 21 are each imaged onto the reticle 7 by an assigned second facet 23 with images overlaid over one another for the purpose of illuminating the Carl Zeiss SMT GmbH

[0160] 21 object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity may be achieved by overlaying different illumination channels.

[0161] The illumination of the entrance pupil of the projection optics unit 10 can be defined geometrically by an arrangement of the second facets 23. The intensity distribution in the entrance pupil of the projection optics unit 10 can be set by selecting the illumination channels, in particular the subset of the second facets 23, which guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

[0162] A likewise preferred pupil uniformity in the region of sections of an illumination pupil of the illumination optics unit 4 which are illuminated in a defined manner may be achieved by a redistribution of the illumination channels.

[0163] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics unit 10 are described below.

[0164] The projection optics unit 10 may have in particular a homocentric entrance pupil. The latter may be accessible. It may also be inaccessible.

[0165] The entrance pupil of the projection optics unit 10 regularly cannot be exactly illuminated with the second facet mirror 22. In the case of an imaging process of the projection optics unit 10 which telecentrically images the centre of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect in a single point. However, it is possible to find an area in which the spacing of the aperture rays that is determined in pairs becomes minimal. This area represents the entrance pupil or an area conjugate thereto in real space. In particular, this area exhibits a finite curvature.

[0166] It may be the case that the projection optics unit 10 has different poses of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, in particular an optical structural element of the transfer optics unit, should be provided between the second facet mirror 22 and the reticle 7. By means of this optical element, the different poses of the tangential entrance pupil and the sagittal entrance pupil may be taken into account.

[0167] In the arrangement of the components of the illumination optics unit 4 illustrated in Fig. 1, the second facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optics unit 10. The first facet mirror 20 is Carl Zeiss SMT GmbH

[0168] 22 arranged so as to be tilted with respect to the object plane 6. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the second facet mirror 22.

[0169] Fig. 2 shows an optical system 100 (e.g. a part of an optical system 100) having an optical component 102 according to one embodiment. The optical component 102 comprises a substrate 104 and an optically active surface 106. In particular, the substrate 104 comprises a three-dimensional substrate body 108. For example, the optical component 102 is a mirror having a mirror substrate 104 and a reflective surface 106.

[0170] For example, the optical system 100 is a projection optics unit 10 of the EUV lithography apparatus 1 (Fig. 1). However, the optical system 100 might also be an illumination optics unit 4 of the lithography apparatus 1, for example.

[0171] For example, the optical component 102 is one of the mirrors Ml to M6 of the projection optics unit 10 (Fig. 1). For example, the optical component 102 might also be one of the mirrors 19, 20, 22 of the illumination optics unit 4 (Fig. 1).

[0172] Although not shown in the figures, the optical component 102 might also be a mirror or a lens element of a DUV lithography apparatus.

[0173] Although not shown in the figures, the component 102 might also be a mechanical component - rather than an optical component - of the lithography apparatus 1.

[0174] It is desirable to examine the component 102 in view of mechanical, thermal and / or acoustic parameters.

[0175] For example, the optical component 102 might heat up due to irradiation by operating light 16 (e.g. EUV light 16 of the lithography apparatus 1, Fig. 1) and absorption of the operating light 16. This may lead to a thermal deformation of the optical component 102. Aberrations of the optical component 102 or of the optical system 100 comprising the optical component 102 might arise on account of this thermal deformation.

[0176] High-quality substrate material 110 is used for the substrate 104, i.e. the substrate body 108, in order to reduce thermal deformation and aberrations connected therewith. In particular, the material 110 of the substrate body 108 has a Carl Zeiss SMT GmbH

[0177] 23 very small coefficient of thermal expansion p. In particular, the material 110 has a zero-crossing temperature ZCT of the coefficient of thermal expansion p at which a thermal deformation of the material 110 on account of a temperature increase is minimal and / or zero. Purely by way of example, the material 110 is tita- nium-doped glass.

[0178] On account of inhomogeneities of the material 110 of the substrate body 108 (e.g. an inhomogeneous distribution of a titanium content), the coefficient of thermal expansion p and / or the zero-crossing temperature ZCT of the substrate 104 might not be distributed homogeneously over the substrate body 108 but instead have variations Ap, AZCT as a function of the location r on the substrate body 108. The location r of the substrate body 108 is for example a location in the three-dimensional space spanned by the directions x', y' and z'. A value (e.g. a mean) of the coefficient of thermal expansion p or of the zero-crossing temperature ZCT of the material 110 and the variations Ap of the coefficient of thermal expansion p as function of location r and the variations AZCT of the zero-crossing temperature ZCT as a function of location r, respectively, have an immediate influence on aberrations of the optical component 102.

[0179] A method for examining a substrate body 108 for a component 102 in a lithography apparatus 1 according to one embodiment is described below with reference to Figures 3 to 8. Any desired parameters of the substrate body 108 that influence the speed of sound may be examined using the method.

[0180] In a first step Si of the method, at least one marking 112 is created in an interior 114 of the substrate body 108, as illustrated in Fig. 4.

[0181] For example, the at least one marking 112 comprises at least one engraving 116, e.g. a laser engraving. For example, the at least one marking 112 is created with the aid of a marking creation device 118 (Fig. 5).

[0182] For example, the at least one marking 112 is created in step Si by means of a laser engraving process. In this case, the marking creation device 118 (Figure 5) comprises a laser for transmitting a laser beam 120. For example, a strongly focused laser beam 120 is used in the laser engraving process. For example, the laser beam 120 has a large divergence angle a, whereby strong focusing onto a small beam cross section is attained at the processing location 122.

[0183] As a result of the laser beam 120 focused at the respective processing location 122 in the interior 114 of the substrate body 108, the material 110 of the Carl Zeiss SMT GmbH

[0184] 24 substrate body 108 is heated strongly locally at the respective processing location 122. As a result, there is a local modification 124 (Fig. 6) of the material 110 of the substrate body 108 at the respective processing location 122. For example, the modification 124 comprises a plurality of tears 126 in the material 110, some of which are labelled by a reference sign in Fig. 6. The modification 124 is restricted to a substantially circular region 128, for example.

[0185] For example, the at least one marking 112 has a size G (Fig. 6) of 100 gm or less, 50 gm or less, 30 gm or less and / or 10 gm or less. On account of the very small size G of the at least one marking 112, the method may also be referred to as quasi non -destructive.

[0186] During the laser engraving process, a laser beam 120 having a predetermined laser wavelength X (Fig. 5) is for example applied. Moreover, the substrate body 108, 208 is for example transparent to the predetermined laser wavelength X.

[0187] For example, a strongly focused laser beam 120 with a very large divergence angle a is applied in the laser engraving process.

[0188] As illustrated in Fig. 5, a plurality of markings 212 may also be created in the interior 214 of the substrate body 208 during step Si. In Fig. 5, the substrate body 208 is shown during a processing with the marking creation device 118. By way of example, eight markings 212 have already been created, some of which have been provided with a reference sign. By way of example, a total of 24 markings 212 are envisaged for the substrate body 208 in Fig. 5. However, substantially more markings 212 (e.g. 500 or more and / or 1000 or more markings 212) may be envisaged. The more markings 212 are produced, the greater the spatial resolution becomes in the subsequent ultrasonic examination in step S3.

[0189] For example, the plurality of markings 212 are arranged spaced apart from one another! see distances Al, A2 between respective adjacent markings 212 in Fig. 7.

[0190] As shown in Fig. 5, the plurality of markings 212 can be arranged accordingly at grid points 216 of a regular three-dimensional grid 218. In Fig. 5, four of the grid points 216 have been provided with a reference sign in an exemplary manner.

[0191] Optionally, some of the plurality of markings 212, 212' might also not be arranged exactly at the grid points 216 of the grid 218 but be displaced from these Carl Zeiss SMT GmbH

[0192] 25 by a small offset B - as illustrated by way of example for the marking 212' in Fig.

[0193] 5. This facilitates the detection of the markings 212, 212' in subsequent step S3.

[0194] Should exactly one marking 112 be created in step Si (Fig. 4), then this divides the substrate body 108 into two corresponding volume elements 130 (130a, 130b) for the subsequent ultrasonic examination in step S3.

[0195] Should a plurality of markings 212 be created in step Si (Figs 5, 7), then this divides the substrate body 208 into a plurality of corresponding volume elements 230 (Fig. 7) for the subsequent ultrasonic examination in step S3. In Fig. 7, some of the volume elements 230 have been provided with a reference sign by way of example.

[0196] A position C (first position C) of the at least one marking 112, 212 can also be ascertained in step Si (Figs 4, 5). The position C of the at least one marking 112, 212 is for example ascertained on the basis of operating parameters (e.g. the divergence angle a, the laser wavelength X and / or other setting parameters) of a laser 118 when creating the at least one marking 112, 212.

[0197] The position D (second position D) of the at least one marking 112, 212 is ascertained on the basis of an optical measurement in an optional second step S2 of the method. For example, the position D (second position D) of the at least one marking 112, 212 is ascertained on the basis of an interferometric measurement with the aid of an interferometer 132 (Fig. 5). As a result, the position C, D of the at least one marking 112, 212 can be ascertained more accurately.

[0198] Step S2 can be performed before or after step S3.

[0199] The substrate body 108, 208 is examined with the aid of ultrasound in a third step S3 of the method. In particular, an ultrasonic signal 134 (Fig. 4) is transmitted, and an ultrasonic signal 136 reflected off the at least one marking 112 is received. For example, the ultrasonic signal 134 is transmitted and received by an ultrasonic sensor device 138 (Fig. 8), e.g. a scanning acoustic microscope 140.

[0200] In the example of Fig. 4, a marking 112 was created in the interior 114 of the substrate body 108. The ultrasonic signal 134 transmitted by the ultrasonic sensor device 138 is reflected off the base 142 of the substrate body 108 (reflected ultrasonic signal 136 with signal component 136a). Moreover, the ultrasonic signal 134 transmitted by the ultrasonic sensor device 138 is reflected off the marking 112 in the substrate body 108 (reflected ultrasonic signal 136 with signal Carl Zeiss SMT GmbH

[0201] 26 component 136b). The ultrasonic signal component 136a reflected off the base 142 thus contains information regarding the volume region 130a. Moreover, the ultrasonic signal component 136b reflected off the marking 112 contains information regarding the volume region 130b. In particular, the signal component 136a contains information regarding the time of flight from a surface of the substrate body 108 to the base 142. Furthermore, the signal component 136b contains information regarding the time of flight from the surface to the marking 112. If the time of flight of the signal component 136b is subtracted from the time of flight of the signal component 136a, the time of flight from the marking 112 to the base 142 is obtained. By using the distances between the surface and the marking 112 and between the marking 112 and the base 142, which are known in advance, it is now possible to ascertain the speed of sound in the volume region 130a and in the volume region 130b, respectively.

[0202] In the example of Figs 5, 7 and 8, a plurality of markings 212 were created in the interior 214 of the substrate body 208. The ultrasonic signal 234 transmitted by the ultrasonic sensor device 138 is reflected off the base 242 of the substrate body 208. Moreover, the ultrasonic signal 234 transmitted by the ultrasonic sensor device 138 is reflected off each marking 212 in the substrate body 208 (reflected ultrasonic signal 236 with signal components 236a to 236c from the markings 212a- 212c). The signal component 236a of the ultrasonic signal 236 reflected off the marking 212a contains information regarding the volume region 230a. Likewise, the signal component 236b of the ultrasonic signal 236 reflected off the marking 212b contains information regarding the volume region 230b. Moreover, the signal component 236c of the ultrasonic signal 236 reflected off the marking 212c contains information regarding the volume region 230c. A similar statement applies to the remaining markings 212 and volume elements 230 (without reference sign) in Fig. 8.

[0203] In Figs 7 and 8, only three of the markings 212 (212a to 212c) and three of the volume elements 230 (230a to 230c) have been provided with a reference sign for reasons of clarity. Furthermore, the ultrasonic signals 234, 236 for only three of the markings 212 are shown and provided with a reference sign in Fig. 8.

[0204] In a fourth step S4 of the method, one or more parameters P of the substrate body 108, 208 are ascertained in spatially resolved fashion on the basis of the received ultrasonic signal 136, 236.

[0205] In particular, the received ultrasonic signal 136, 236 with the plurality of reflected signal components 136a, 136b (Fig. 4) and 236a to 236c (Fig. 8), Carl Zeiss SMT GmbH

[0206] 27 respectively, is evaluated in step S4. The received ultrasonic signal 136, 236 is transmitted to a control device 144 (Fig. 8), e.g. by the ultrasonic sensor device 138. The received ultrasonic signal 136, 236 is analysed and evaluated, e.g. by the control device 144. For example, the control device 144 is configured to ascertain a respective signal time of flight on the basis of the ultrasonic signal 136, 236 with the plurality of reflected signal components 136a, 136b or 236a to 236c. Hence, a speed of sound V (Va to Vc in Fig. 8) can be ascertained on an individual basis for each volume element 130, 230 by taking account of the position C, D, ascertained in advance, of the corresponding marking 112, 212. Thereupon, the one or more parameters P of the substrate body 108, 208 are ascertained on the basis of the ascertained speed of sound V (Va to Vc). Hence, the one or more parameters P (Pa to Pc) of the substrate body 108, 208 can be ascertained separately for each volume element 130, 230 (i.e. 130a to 130b in Fig. 4 or 230a to 230c in Fig. 8). Purely by way of example, a coefficient of thermal expansion p is ascertained as parameter Pa to Pc for each volume element 230 in Fig. 8. However, one or more other parameters of the substrate body 208 may also be ascertained in step S4 - in addition to the coefficient of thermal expansion p or instead of it.

[0207] For example, the optical system 100 and / or the component 102 may also be used in a DUV lithography apparatus.

[0208] Although the present invention has been described on the basis of exemplary embodiments, it is modifiable in diverse ways.

[0209] Carl Zeiss SMT GmbH

[0210] 28

[0211] LIST OF REFERENCE SIGNS

[0212] 1 Projection exposure apparatus

[0213] 2 Illumination system

[0214] 3 Light source

[0215] 4 Illumination optics unit

[0216] 5 Object field

[0217] 6 Object plane

[0218] 7 Reticle

[0219] 8 Reticle holder

[0220] 9 Reticle displacement drive

[0221] 10 Projection optics unit

[0222] 11 Image field

[0223] 12 Image plane

[0224] 13 Wafer

[0225] 14 Wafer holder

[0226] 15 Wafer displacement drive

[0227] 16 Illumination radiation

[0228] 17 Collector

[0229] 18 Intermediate focal plane

[0230] 19 Deflection mirror

[0231] 20 First facet mirror

[0232] 21 First facet

[0233] 22 Second facet mirror

[0234] 23 Second facet

[0235] 100 Optical system

[0236] 102 Component

[0237] 104 Mirror substrate

[0238] 106 Surface

[0239] 108 Substrate body

[0240] 110 Material

[0241] 112 Marking

[0242] 114 Interior

[0243] 116 Engraving

[0244] 118 Marking creation device

[0245] 120 Laser beam

[0246] 122 Processing location

[0247] 124 Modification

[0248] 126 Tear

[0249] 128 Region Carl Zeiss SMT GmbH

[0250] 29

[0251] 130 Volume element

[0252] 130a, 130b Volume element

[0253] 132 Interferometer

[0254] 134 Ultrasonic signal

[0255] 136 Ultrasonic signal

[0256] 136a, 136b Signal component

[0257] 138 Ultrasonic sensor device

[0258] 140 Scanning acoustic microscope

[0259] 142 Base

[0260] 144 Control device

[0261] 208 Substrate body

[0262] 212, 212' Marking

[0263] 212a-212c Marking

[0264] 214 Interior

[0265] 216 Grid point

[0266] 218 Grid

[0267] 230 Volume element

[0268] 230a-230c Volume element

[0269] 234 Ultrasonic signal

[0270] 236 Ultrasonic signal

[0271] 236a-236c Signal component

[0272] 242 Base a Angle

[0273] Ap Variation in the coefficient of thermal expansion

[0274] AZCT Variation in the zero-crossing temperature

[0275] X Wavelength

[0276] P Coefficient of thermal expansion

[0277] Al Distance

[0278] A2 Distance

[0279] B Offset

[0280] C Position

[0281] Ca- Cc Position

[0282] D Position

[0283] G Size

[0284] M1-M6 Mirrors

[0285] P Parameter

[0286] Pa-Pc Parameters

[0287] Location Carl Zeiss SMT GmbH

[0288] 30

[0289] S1-S4 Method step

[0290] V Speed of sound

[0291] Va-Vc Speed of sound

[0292] ZCT Zero-crossing temperature

Claims

Carl Zeiss SMT GmbH31CLAIMS1. Method for examining a substrate body (108) for a component (102) in a lithography apparatus (1), including the steps of: a) creating (Si) at least one marking (112) in an interior (114) of the substrate body (108), b) transmitting (S3) an ultrasonic signal (134) and receiving an ultrasonic signal (136) reflected off the at least one marking (112), and c) ascertaining (S4), in spatially resolved fashion, one or more parameters (P) of the substrate body (108) on the basis of the received ultrasonic signal (136).

2. Method according to Claim 1, wherein the at least one marking (112) comprises at least one engraving (116).

3. Method according to Claim 1 or 2, wherein the at least one marking (112) is created by means of a laser engraving process.

4. Method according to Claim 3, wherein a predetermined laser wavelength (X) is applied in the laser engraving process, and the substrate body (108) is transparent to the predetermined laser wavelength (X).

5. Method according to any of Claims 1 to 4, wherein a size (G) of the at least one marking (112) is 100 gm or less, 50 gm or less, 30 gm or less, 10 gm or less, 5 gm or less or 1 gm or less.

6. Method according to any of Claims 1 to 5, wherein a plurality of the markings (212, 212a-212c) that divide the substrate body (208) into a plurality of volume elements (230, 230a-230c) are created in the interior (214) of the substrate body (208), the received reflected ultrasonic signal (236) has a corresponding reflected signal component (236a-236c) for each marking (212, 212a-212c), and the one or more parameters (P, Pa-Pc) for each volume element (230, 230a- 230c) are ascertained on the basis of the corresponding reflected signal component (236a-236c).

7. Method according to any of Claims 1 to 6, wherein a plurality of the markings (212) are created in the interior (214) of the substrate body (208) and are arranged accordingly at or adjacent to grid points (216) of a regular three-dimensional grid (218).Carl Zeiss SMT GmbH328. Method according to any of Claims 1 to 7, wherein a position (C, D) of the at least one marking (112) is ascertained, and the one or more parameters (P) of the substrate body (108) are ascertained on the basis of the ascertained position (C, D), and the position (C) of the at least one marking (112) is ascertained on the basis of operating parameters (a, X) of a laser (118) when creating the at least one marking (112), and / or the position (D) of the at least one marking (112) is ascertained on the basis of an optical measurement.

9. Method according to any of Claims 1 to 8, wherein a speed of sound (V) in the substrate body (108) is determined in spatially resolved fashion on the basis of the received ultrasonic signal (136), and the one or more parameters (P) of the substrate body (108) are ascertained on the basis of the determined speed of sound (V).

10. Method according to any of Claims 1 to 9, wherein a material (110) of the substrate body comprises glass, high-performance glass, titanium -doped glass, silicon and / or plastic.

11. Method according to any of Claims 1 to 10, wherein the one or more parameters (P) of the substrate body (108) include: one or more mechanical, thermal and / or acoustic parameters, and / or a coefficient of thermal expansion (p), a zero-crossing temperature (ZCT), a Young's modulus, a shear modulus, a Poisson number and / or an acoustic impedance.

12. Method according to any of Claims 1 to 11, wherein step b) is carried out with the aid of a scanning acoustic microscope (140).

13. Method according to any of Claims 1 to 12, wherein the component (102) in the lithography apparatus (1) is a mirror (M1-M6) in the lithography apparatus (1), and the substrate body (108) is a body of a mirror substrate (104) of the mirror (M1-M6).

14. Substrate body (108) for a component (102) in a lithography apparatus (1), comprising at least one marking (112) at at least one predetermined position (C) in an interior (114) of the substrate body (108), wherein the at least one marking (112) is configured to reflect an ultrasonic signal (134).Carl Zeiss SMT GmbH3315. Lithography apparatus (1) having a component (102) with a substrate body (108) according to Claim 14.

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