Method for determining a manufacturing space image of an object to be measured

Abstract

In order to determine a manufacturing aerial image of an object under test due to illuminating and imaging under illumination and imaging conditions of an optical manufacturing system, a measurement aerial image (17) of the object under test is first captured (17). This is done under illumination and imaging conditions of an optical measurement system, which conditions comprise predefined measurement illumination settings. Data of the measurement aerial image are generated in the process of capturing. An object structure of the object under test is reconstructed (18) from the data of the captured measurement aerial image by a reconstruction algorithm. Data of the reconstructed object structure are generated in the process of reconstruction. An aerial image is simulated (19) from the data of the reconstructed object structure under illumination and imaging conditions of the optical manufacturing system. The conditions comprise manufacturing illumination settings, which are different from the measurement illumination settings. This leads to a determination method, in which the requirements of the optical measurement system used in the determination method are reduced, even under stringent illumination and imaging conditions of the optical manufacturing system.

Description

[0001] Cross-reference to Related Applications

[0002] The content of the German patent application DE 10 2019 208 552.0 is incorporated herein by reference. TECHNICAL FIELD

[0003] The invention relates to a method for determining a manufacturing space image of an object to be measured, wherein the manufacturing space image results from an illumination and imaging under illumination and imaging conditions of an optical manufacturing system. Furthermore, the invention relates to a metrology system comprising an optical measurement system for carrying out the method. BACKGROUND

[0004] A metrology system is known from US 2017 / 0131 528 A1 (parallel document WO 2016 / 0124 425 A2) and from US 2017 / 0132782 A1. WO 2017 / 207 297 A1 discloses a method for predicting imaging results of a photolithographic mask. SUMMARY

[0005] It is an object of the invention to develop a determination method of the type mentioned in the introduction, such that even under stringent illumination and imaging conditions of an optical manufacturing system, the requirements on the optical measurement system used in the determination method are alleviated.

[0006] According to the invention, this object is achieved by a determination method having the features specified in claim 1.

[0007] According to the invention, it has been recognized that even for stringent illumination and imaging conditions of an optical manufacturing system, a manufacturing space image can be determined using an optical measurement system in which a different measurement illumination setting is used compared to the manufacturing illumination setting. The measurement illumination setting can then be configured such that it can be realized more simply within the optical measurement system, the result of which is that the overall requirements on the optical measurement system are relaxed. In particular, it is possible to simulate a manufacturing space image which would not be possible, or would be difficult, to realize in the measurement setup, since this would require, for example, a stop structure which cannot be manufactured, or which is difficult to manufacture, in the measurement setup.

[0008] Based on the simulated manufacturing space image, i.e. based on the result of the determination method, the object structure of the measured object can be optimized until the simulated manufacturing space image corresponds to the predefined space image. Thus, the determination method can be part of an iterative procedure for optimizing the object structure until it has been optimized for the illumination and imaging conditions of the optical manufacturing system used to generate the image structure, which in turn is the starting point for producing a corresponding structure semiconductor component with very high resolution, for example, if the optical manufacturing system is used for producing micro- or nano-structured semiconductor components.

[0009] The measurement illumination setting comprises a predefined numerical illumination aperture of the optical measurement system. The predefined illumination aperture is predefined by an edge profile of an illumination pupil.

[0010] In the determination method, it is possible to use a reconstruction method of the object structure known from the technical article "Method for Retrieval of the Three-Dimensional Object Potential by Inversion of Dynamical Electron Scattering" by Van den Broek et al., Phys. Rev. Lett 109, 245502 (2012) and from WO 2017 / 207 297 Al.

[0011] For example, in the optimization of the object structure, object defects can be identified and selectively repaired.

[0012] It has proven worthwhile to predefine the measurement illumination setting by a setting diaphragm according to claim 2.

[0013] The manufacturing illumination setting with the elliptical edge profile of the illumination pupil according to claim 3 is an example of a strict manufacturing illumination setting.

[0014] In contrast, this applies equally to a free-form or SMO (Source Mask Optimization) illumination setting according to claim 3. Such a free-form illumination setting cannot be described with any of the standardized illumination settings "traditional", "annular", "dipole" or "multipole", but is distinguished by a free adjustment of the configuration of the pupil areas hit by the illumination light within the illumination pupil. With regard to the SMO method, reference is made to the technical article "Source mask optimization methodology (SMO) and application to real full chip optical proximity corrections" by D. Zhang et al., Proceedings SPIE 8326, Optical Microlithography XXV, 83261V (13 March 2012).

[0015] The manufacturing illumination setting with varying illumination intensity according to claim 5 is a further example of a strict manufacturing illumination setting. The minimum illumination intensity can be more than 1% or more than 10% of the maximum illumination intensity. The minimum illumination intensity can be less than 50% of the maximum illumination intensity.

[0016] The manufacturing illumination setting according to claim 6 has proven to be worthwhile in optical manufacturing systems. The individual areas illuminated within the illumination pupil can be configured separately from one another.

[0017] It is hardly or not at all possible to predefine such a manufacturing illumination setting by setting a diaphragm, since the production costs for such a type of setting diaphragm, if such a setting diaphragm is producible at all, would be very high.

[0018] The individual area configuration or individual area arrangement according to claims 7 to 9 is likewise proven to be worthwhile when a manufacturing illumination setting is predefined. The individual areas can have a circular boundary; however, this is not mandatory.

[0019] The advantages of the metrology system according to claim 10 correspond to the advantages already explained above with reference to the converging method according to the application.

[0020] The metrology system can measure a lithography mask provided for a projection exposure, which serves to produce semiconductor components with a very high structure resolution, which is for example better than 30 nm, in particular can be better than 10 nm.

[0021] The metrology system according to claim 11 is flexibly usable. The metrology system can comprise a plurality of changeable setting diaphragms, which can be exchanged for one another in an automated manner by means of a changeover mount. BRIEF DESCRIPTION OF DRAWINGS

[0022] Hereinafter, exemplary embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the drawings:

[0023] Figure 1 A metrology system for determining an aerial image of an object to be measured in the form of a lithography mask is schematically shown, comprising an illumination system, an imaging optical unit and a spatially resolving detection device;

[0024] Figure 2 shows the sequence of the main method steps of the method in which the Figure 1 A metrology system for determining an aerial image of an object to be measured, which is a result of illumination and imaging under the illumination and imaging conditions of the optical manufacturing system;

[0025] Figure 3 More detailed but still schematically shown is the use of Figure 1 imaging the photolithography mask using an imaging optical unit of a metrology system; and

[0026] Figure 4 A schematic visualization of the input variables that influence the determined manufacturing aerial image is shown, namely in particular data concerning the optical manufacturing system for imaging the object to be measured, data concerning the reconstructed object structure, and data concerning the optical manufacturing system with manufacturing illumination settings that differ from those according to Figure 1 Data on the lighting conditions of optical manufacturing systems (measurement lighting settings of metrology systems). DETAILED DESCRIPTION

[0027] Figure 1 The beam path of EUV illumination light or imaging light 1 in the metrology system 2 is shown in a cross-sectional view corresponding to a meridional section. The illumination light 1 is generated by an EUV light source 3 .

[0028] To facilitate the presentation of positional relationships, the Cartesian xyz coordinate system is used below. Figure 1 In the , the x-axis is perpendicular to and extends from the drawing plane. The y-axis is Figure 1 The z-axis extends to the right. Figure 1 Extending upward.

[0029] The light source 3 can be a laser plasma source (LPP; laser produced plasma) or a discharge source (DPP; discharge produced plasma). In principle, synchrotron-based light sources, such as free electron lasers (FELs), can also be used. The operating wavelength of the illumination light 1 can be in the range between 5 nm and 30 nm. In principle, in the case of variants of the projection exposure apparatus 2, it is also possible to use light sources for certain other operating wavelengths, for example for an operating wavelength of 193 nm.

[0030] In a illumination optical unit (not shown in more detail) of the illumination system of the metrology system 2 to which the light source 3 belongs, the illumination light 1 is conditioned to provide a certain illumination setting 5 of the illumination, i.e. a certain illumination angle distribution. This illumination setting 5 corresponds to a certain intensity distribution of the illumination light 1 in an illumination pupil of the illumination optical unit of the illumination system 4.

[0031] An example of an illumination setting 5 is schematically shown in Figure 1 with a web and with a total of four illumination poles 6 which are substantially in the shape of quadrants. In fact, there is an illumination pupil arrangement of the illumination setting 5 which is perpendicular to Figure 1 the drawing plane in and perpendicular to the propagation direction of the illumination light 1 through the illumination pupil.

[0032] In the illumination pupil, in each case at the position of the illumination poles 6 there is a predefined illumination intensity, and otherwise there is no illumination intensity. The illumination setting 5 can be predefined by a setting diaphragm 7 which transmits the illumination light 1 at the position of the illumination poles 6 and blocks the illumination light around the illumination poles 6. An example of such a setting diaphragm 7 is a metal plate with through-holes which exactly correspond in shape to the illumination poles 6. The setting diaphragm is arranged in the pupil plane of the illumination optical unit of the metrology system 2.

[0033] By means of the exchange support 7a shown, the setting diaphragm 7 can be exchanged for an exchange setting diaphragm for changing the respective measurement illumination setting. Figure 1

[0034] Instead of the four-pole illumination setting 5 shown, it is also possible to predefine other illumination settings within the metrology system 2, for example a conventional illumination setting (in which in fact all illumination angles are used for object illumination, in particular apart from illumination angles close to normal or average incidence onto the object to be illuminated), a ring illumination setting (which overall has small illumination angles, i.e. illumination angles close to normal or average incidence, which can itself be omitted), or a dipole illumination setting (in which the individual poles can each have a "small leaflet" profile, i.e. substantially corresponding to the edge profile of a cross section through a lenticular lens element), by correspondingly using differently shaped and / or distributed through-holes.

[0035] The illumination system 4 together with an imaging optical unit or projection optical unit 8 forms an optical measurement system 9 of the metrology system 2.

[0036] In the case of the respective setting of the illumination setting 5, the illumination light 1 illuminates an object field 10 of an object plane 11 of the metrology system 2. A lithography mask 12 (also called reticle) is arranged as a reflective object in the object plane 11. The object plane 11 extends parallel to the xy plane.

[0037] In the following, the main steps of the method are explained with the aid of Figure 3 In the drawing plane of Figure 3 In the drawing plane of

[0038] As shown schematically in Figure 1 The illumination light 1 is reflected from the lithography mask 12 and enters the entrance pupil of the imaging optics 8 in the entrance pupil plane. The entrance pupil of the imaging optics 8 can have a circular or an elliptical boundary.

[0039] Within the imaging optics 8, the illumination or imaging light 1 propagates between the entrance pupil plane and an exit pupil plane. The circular exit pupil of the imaging optics 8 is located in the exit pupil plane.

[0040] The imaging optics 8 images the object field 10 into an image field 14 in an image plane 15 of the metrology system 2. The magnification imaging ratio during the imaging by the imaging optics 8 is larger than 500. Depending on the embodiment of the imaging optics 8, the magnification imaging ratio can be larger than 100, can be larger than 200, can be larger than 250, can be larger than 300, can be larger than 400, and can also be significantly larger than 500. The imaging ratio of the imaging optics 8 is typically smaller than 2000.

[0041] The imaging optics 8 is used to image a portion of the object 12 into the image plane 15.

[0042] A spatially resolving detection device 16 of the metrology system 2 is arranged in the image plane 15. This can include a CCD camera.

[0043] The metrology system 2 with the optical measurement system 9 is used to perform a method to determine a spatial image of the object 12 to be measured as a result of the illumination and imaging under the illumination and imaging conditions of an optical manufacturing system of an EUV projection exposure apparatus (not shown). Thus, with the aid of the metrology system 2, a spatial image of the object 12 produced by the optical manufacturing system of the manufacturing projection exposure apparatus can be simulated or emulated.

[0044] The main steps of this method are explained in the following with the aid of Figure 2 and Figure 4

[0045] In a capturing step 17, the metrology system 2 captures a measurement spatial image I(x,y) of the object 12 to be measured with the illumination and imaging conditions of the optical measurement system 9. In this case, the measurement spatial image is captured with a predefined measurement illumination setting, for example the illumination setting 5. During this capturing, intensity data I(x,y) of the measurement spatial image are produced.

[0046] ​The subsequent reconstruction step 18 of the decision method consists in reconstructing the transfer function T of the object 12 to be measured from the data I(x,y) captured of the measurement space image by means of a reconstruction algorithm. Mask The object structure 13 at (x, y) is generated during this reconstruction step 18. This object structure reconstruction algorithm from captured measurement aerial image data is described in the technical article "Method for Retrieval of the Three-Dimensional Object Potential by Inversion of Dynamical Electron Scattering" by Van den Broek et al., Phys. Rev. Lett 109, 245502 (2012). This reconstruction algorithm can also be applied to photolithography masks. In this case, reference is made to WO 2017 / 207 297 A1.

[0047] In a subsequent simulation step 19 of the decision method, the object structure 13 is reconstructed according to the data T under the illumination and imaging conditions of the optical production system. Mask , simulating the electric field EI(x,y) of the manufacturing aerial image (i.e., the aerial image obtained by manufacturing the optical manufacturing system of the projection exposure apparatus). The illumination and imaging conditions of the optical manufacturing system include the manufacturing illumination setting 19a (see Figure 4 ), which is different from the measurement lighting system 5.

[0048] By way of example Figure 4 The manufacturing lighting setup 19a shown in has a circular edge profile 20. Alternatively, a manufacturing lighting setup having an edge profile that deviates from a circular shape, for example having an elliptical edge profile, may be used.

[0049] Figure 4 The illustrated manufacturing lighting setup 19a is a free-form lighting setup. This free-form lighting setup cannot be described using the standardized lighting setups "conventional," "annular," "dipole," or "multipole." The free-form manufacturing lighting setup 19a has a plurality of illuminated individual regions 21 within an edge contour 20 of the manufacturing illumination pupil. The individual regions 21 are arranged as selected grid points of a dot grid that completely covers the illumination pupil within the edge contour.

[0050] Each illuminated individual area 21 has the same typical diameter.The typical diameter of an individual area 21 may be in the range between 0.5% and 10% of the total pupil area.

[0051] The illuminated individual areas 21 can have a circular boundary. The illuminated individual areas 21 are arranged within the edge contour 20 in a manner that is irregularly distributed over the illumination pupil. The illuminated individual areas 21 are arranged within the edge contour 20 in a manner that is distributed over the illumination pupil with a different surface density.

[0052] In the case of the illumination setting 19a, all illuminated individual areas are illuminated with the same illumination intensity. In the case of an alternative manufacturing illumination setting, the illumination intensity can vary continuously over the illumination area of the illumination pupil in the range between a minimum illumination intensity and a maximum illumination intensity, wherein the minimum illumination intensity is greater than 0.

[0053] In the case of a manufacturing illumination setting that additionally corresponds to the manufacturing illumination setting 19a, such a variation of the illumination intensity can be achieved by illuminating different individual areas 21 with different illumination intensities. In this case, certain of the individual areas 21 can be illuminated using the maximum illumination intensity, and others can be illuminated using a lower illumination intensity, for example 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 1% of the maximum illumination intensity. In this case, different graduated illumination intensities can be used to illuminate different individual areas 21, or possibly a continuous variation of the illumination intensity. In the case of graduated illumination intensities, two steps, three steps, four steps, five steps, six steps, seven steps, eight steps, nine steps, ten steps or even more steps can be used.

[0054] The simulation of the manufacturing aerial image I(x, y) is also influenced by data relating to the imaging conditions of the projection optical unit 22 of the manufacturing projection exposure apparatus. In the case of the measurement projection optical unit 8 of the metrology system 2, the imaging conditions are known. Figure 4 The manufacturing projection optical unit 22 is shown schematically at the left-hand side of Fig. 1, which is generally very different from the measurement projection optical unit 8 of the metrology system 2. Alternatively, a measurement projection optical unit that corresponds to the manufacturing projection optical unit can also be used.

[0055] The image-side numerical aperture of the manufacturing projection optical unit 22 can be in the range between 0.3 and 0.9, for example 0.33, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7. The imaging factor of the manufacturing projection optical unit 22 can be less than 1, so that the manufacturing projection optical unit 22 images the object structure 13 into the image field 26 of the manufacturing projection exposure apparatus in a demagnifying manner. This demagnification can be for example four times, resulting in an imaging ratio of 0.25. Other imaging ratios in the range between 0.1 and 0.5 are also possible.

[0056] In addition to the manufacturing illumination setting 19a, the simulation step 19 is also influenced by further illumination conditions of the optical manufacturing system that manufactured the projection exposure apparatus, in particular by the device functions of the illumination system 23 of the manufacturing projection exposure apparatus. The device functions are influenced by data of the EUV light source and by data of the illumination and projection optical unit of the manufacturing projection exposure apparatus. Such data are, for example, data on the uniformity of the illumination, i.e. data that represent a measure of the degree of correspondence between the actual illumination intensity on the object field to be illuminated and the desired illumination intensity. The data can further contain data on the photon noise of the light source 3.

[0057] In addition, the simulation step 19 can additionally be influenced by the specific further properties of the coating of the object to be measured and / or of the substrate on which the object is imaged by the manufacturing system. The corresponding optical data can be the absorption coefficients of the absorption layers and / or of the multilayer.

[0058] Figure 4 The input variables that influence the simulation of the manufactured aerial image I are elucidated. They contain the transfer function T POB of the manufacturing projection optical unit 22 Mask , the transfer function T illu of the object structure 13 decided during the reconstruction step 18, and the illumination conditions E I (u,v) of the manufacturing illumination system 23 that contains the manufacturing illumination setting 19a. In this case, u and v are coordinates in the frequency domain. The simulation is schematically shown by the block 27 in Figure 4 .

[0059] In addition, the decision method (schematically designated by the element symbol 28 in Figure 4 ) can additionally be influenced by system-specific effects, i.e. by aberrations that are measured during the system adjustment and during the processes that prepare the decision method, by uniformity data and by data on the photon noise that are estimated from the data of the measured aerial image I(x,y) and are optionally included in the calculation. This step that contains the system-specific effects is illustrated at 24 in Figure 4 . Overall, the decided aerial image I = |E 2 of the object to be measured 12 is produced by the illumination and imaging under the illumination and imaging conditions of the optical projection system with the manufacturing projection optical unit 22 according to the following equation:

[0060] E I (x,y) = FT -1 [T POB x FT[T Mask (x',y') x FT -1 [E illu (u,v)]]]

[0061] In this case, FT denotes the Fourier transform, FT -1 denotes the inverse Fourier transform. u and v denote the pupil coordinates of the manufacturing illumination setting 19a and of the manufacturing projection system 23, respectively, in the frequency domain.

[0062] By way of example, the determination method makes it possible to determine spatial images for significantly more complex manufacturing illumination settings in the manner of the illumination setting 19a with the aid of the measurement illumination setting 5, which can be implemented using a setting diaphragm 7 produced at relatively low cost (in Figure 4 ). As a result, the design requirements with respect to the setting diaphragm 7 of the metrology system 2 are reduced.

[0063] The measurement spatial images I are captured in three dimensions. For this purpose, the object 12 is moved stepwise in the z direction by means of the object displacement device 12a, which is shown schematically in Figure 1 , such that, on the basis of the image transfer from the object plane 11 to the image plane 15 of this z displacement, a z step z i is produced for the region around the image plane 15. A plurality of 2D spatial images I(x, y, z i ) is produced. Subsequently, a 3D measurement spatial image (I(x, y, z)) is produced from the plurality of 2D spatial images. The image plane 15 is also referred to as the measurement plane.

Claims

1. A method for determining a manufacturing aerial image (I(x,y)) of an object under test (12) caused by illuminating and imaging under illumination and imaging conditions of an optical manufacturing system (22, 23), comprising the steps of: - capturing (17) a measurement aerial image (I(x,y)) of the object under test (12) under illumination and imaging conditions of an optical measurement system (9), said conditions comprising a predefined measurement illumination setting (5), wherein data of the measurement aerial image (I(x,y)) are generated during the capturing (17); - reconstructing (18) the object structure (13) of the object under measurement (12) from the captured data of the measurement space image (I(x,y,z)) by a reconstruction algorithm, wherein data (T Mask ) of the reconstructed object structure (13) are generated during the reconstruction (18); and - simulating (19) the manufactured aerial image (I(x,y)) from the data (T Mask ) of the reconstructed object structure (13) under illumination and imaging conditions (T POB , illu ) of the optical manufacturing system (22, 23), said conditions comprising manufacturing illumination settings (19a) which are different from the measurement illumination settings (5), wherein the optical manufacturing system (22, 23) is a different optical system than the optical measurement system (9).

2. The method of claim 1, wherein, The measurement illumination setting (5) is predefined by a settable diaphragm (7).

3. The method according to claim 1 or 2, characterized in that The manufacturing illumination setting (19a) has an elliptical edge profile of the illumination pupil.

4. The method according to any one of claims 1 to 3, characterized in that, The manufacturing illumination setting (19a) is a freeform or source mask optimization (SMO) illumination setting.

5. The method according to any one of claims 1 to 4, characterized in that, The manufacturing illumination setting (19a) has an illumination intensity on the illuminated area of the illumination pupil, which varies in a range between a minimum illumination intensity and a maximum illumination intensity, wherein the minimum illumination intensity is greater than 0.

6. The method according to any one of claims 1 to 5, characterized in that, The manufacturing illumination setting (19a) has a plurality of illuminated individual areas (21) within the illumination pupil.

7. The method of claim 6, wherein, Each of the illuminated individual areas (21) has the same typical diameter.

8. The method of claim 6 or 7, characterized in that, The illuminated individual areas (21) are arranged in a manner that is irregularly distributed over the illumination pupil.

9. The method according to any one of claims 6 to 8, characterized in that, The illuminated individual areas (21) are arranged in a manner that is distributed over the illumination pupil with a different surface density.

10. A metrology system (2) comprising an optical measurement system (9) for carrying out the method of any one of claims 1 to 9: - comprising an illumination system (4) comprising an illumination optical unit for illuminating the object under test (12) with a predefined illumination setting (5), - comprising an imaging optical unit (8) for imaging a portion of the object (12) into a measurement plane (15), and - comprising a spatially resolving detection device (16) arranged in the measurement plane (15).

11. The metrology system of claim 10, wherein, A settable diaphragm (7) for predefining the measurement illumination setting (5).

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