Method for simulating the illumination and imaging properties of an optical production system during illumination and imaging of an object by means of an optical measurement system - Patents.com

Abstract

When simulating the illumination and imaging properties of an optical production system when illuminating and imaging an object by means of an optical measurement system of a metrology system, first an optical measurement system is provided that has an illumination optical unit for illuminating an object and a pupil diaphragm (10), in particular a displaceable pupil diaphragm, and has an imaging optical unit for imaging the object into an image plane. When simulating these properties of the optical production system by means of the optical measurement system, first a plurality of pupil diaphragms (10) are provided. Then, a measured aerial image with the plurality of pupil diaphragms (10) is recorded. From the recorded measured aerial images, a complex mask transfer function is reconstructed, and from this function and the illumination settings of the optical production system, a 3D aerial image is determined. This provides an improved simulation method.

Description

[Technical field]

[0001] This patent application claims the priority of DE 102022200372.1 A1, the content of which is incorporated herein by reference.

[0002] The present invention relates to a method for simulating the illumination and imaging properties of an optical production system during illumination and imaging of an object by means of an optical measurement system.Furthermore, the present invention relates to a metrology system for carrying out such a method. [Background technology]

[0003] Such a method and a metrology system for this purpose are known from DE 102019208552 A1 and DE 102019215800 A1. A metrology system for measuring the aerial image of a lithographic mask in three dimensions is known from WO 2016 / 012426 A1. DE 102013219524 A1 describes an apparatus and a method for determining the imaging quality of an optical system, as well as an optical system. DE 102013219524 A1 describes a phase search method for determining a wavefront based on the imaging of a pinhole. The expert paper by Martin et al. "A new system for a wafer lever CD metrology on photomasks", proceedings of SPIE - The International Society for Optical Engineering, 2009, 7272 describes a metrology system for determining wafer-level critical dimensions (CD). Summary of the Invention

[0004] It is an object of the invention to provide an improved method for simulating the illumination and imaging properties of an optical production system when illuminating and imaging an object by means of an optical measurement system.

[0005] According to the invention, this object is achieved by a simulation method having the features set forth in claim 1.

[0006] According to the invention, it has been found that recording measured aerial images with multiple pupil stops, in particular at multiple measurement positions of a pupil stop preselected for the best possible simulation of the illumination settings of the optical production system, offers the possibility of improving the overall accuracy of the simulation method and in particular offers the option of reducing illumination angle-dependent artifacts, in particular illumination angle-dependent artifacts in the reconstructed complex mask transfer function, i.e. illumination angle-dependent artifacts in the transfer function of the imaged object. It is then possible to properly take into account the effects of 3D masks. When inspecting lithographic masks, in particular masks used for EUV lithography, the effects of 3D masks can be taken into account.

[0007] Within the scope of the simulation method, it is possible to precisely select a pupil diaphragm from among a number of pupil diaphragms provided, which may differ with respect to the pupil diaphragm aperture border shape and / or the pupil diaphragm aperture border orientation. Alternatively, it is also possible to select and use different pupil diaphragms in order to specify different measurement positions. The provided pupil diaphragms may in particular specify at least one of the following illumination settings: quadrupole, C-quad, dipole, annular, conventional illumination settings. The skilled person will find examples of such settings, inter alia, in WO 2012 / 028303. Firstly, within the scope of the preparation of the imaging method, the best focal plane (defocus value z m=0). The z-increment when determining the 3D aerial image in the last step of the simulation method, i.e. when determining the aerial image from the reconstructed mask transfer function and the illumination settings of the optical production system, may be different from the defocus value that may have been specified initially in the simulation method. The pixel size of the recorded measured aerial image may be sampled to fit the desired pixel resolution.

[0008] The target pupil aperture that can be specified, and its target aperture boundary shape, may relate to a plurality or otherwise numerous individual illumination or pupil spots, i.e. a plurality of apertures, for example arranged in a grid. Such illumination or pupil spots may provide an illumination setting that is used within the scope of production illumination. The illumination setting may be set, for example, through an illumination optical unit having a field facet mirror and a pupil facet mirror.

[0009] The displacement drive as claimed in claim 2 has proven its value for reproducibly specifying the pupil diaphragm measurement position. Correspondingly, this applies to an object holder which is displaceable perpendicularly to the object plane.

[0010] Different aperture boundary shapes and / or aperture boundary orientations of the provided pupil aperture, as claimed in claim 3, increase the versatility when carrying out the simulation method.

[0011] The simulation method according to claim 4 with the aid of a qualified algorithm has proved particularly valuable. With the aid of an object holder displaceable by an actuator and a displacement drive for displacing the pupil diaphragm, the defocus value and / or the pupil diaphragm measurement position can be specified. Piezo drives and / or stepper motor drives can be used as displacement drives or displacement actuators.

[0012] The recording of measured aerial images as claimed in claim 5 has proven its worth in practice.

[0013] The central measurement position and the plurality of offset measurement positions as claimed in claim 6 have proven their worth within the scope of practical implementation of the simulation method. In the central measurement position, a pupil diaphragm is arranged in the center of the utilized pupil of the optical measurement system. Two to ten offset measurement positions, in particular two to five, for example three or four offset measurement positions, can be provided. The offset measurement positions can be arranged uniformly distributed in the circumferential direction around the central measurement position. The offset measurement positions can be displaced in a Cartesian coordinate direction or otherwise in a quadrant direction relative to the central measurement position. The measurement positions can be arranged randomly in the circumferential direction or on one or more radii, in particular on two or three different radii. It is also possible to arrange the measurement positions completely randomly within the measurement pupil or otherwise partially outside the measurement pupil. Where a random arrangement is mentioned above, the random arrangement can be determined by using an algorithmic random function.

[0014] The defocus value / measurement position combinations as claimed in claim 7 have proven their worth in practice. It has been found that for each defocus value it is not necessary to cover all pupil diaphragm measurement positions specified within the method. This shortens the measurement time.

[0015] The method for selecting a pupil diaphragm as claimed in claim 8 ensures the best possible simulation of a target pupil diaphragm using a selected pupil diaphragm. For each pupil spot, illumination light is present in the illumination pupil. Within the selection method, a distance qualification of the assigned pupil spot of the target diaphragm boundary shape for the respective pupil diaphragm can be performed. Within the selection method, a merit function can be defined and minimized.

[0016] The modelling of the illumination direction dependent mask spectrum as claimed in claim 9 has proven its value during the reconstruction, since it helps to reduce the number of degrees of freedom present during the optimization within this reconstruction.

[0017] The displacement of the imaging pupil diaphragm as claimed in claim 10 extends the modelling possibilities within the scope of the simulation method.

[0018] The reconstruction as claimed in claim 11 leads to particularly good simulations.

[0019] The result of the simulation method as claimed in claim 12 is an option for the aerial image description that also depends on the chief ray angle of illumination by the optical production system. Thus, when determining the 3D aerial image, different illumination chief ray angles of the production system may be taken into account. This increases the power of the simulation method.

[0020] The advantages of the measurement system as claimed in claims 13 to 15 correspond to the advantages already explained above with reference to the method claims.

[0021] A selection device with a diaphragm storage unit as claimed in claim 16 advantageously enables a pupil diaphragm selection step of the simulation method. In particular, this selection can be performed with the aid of a robotic actuation system, which takes the respective selected pupil diaphragm from the diaphragm storage unit and moves it to its position of use in the pupil plane. The selection device further ensures that the last used pupil diaphragm is replaced by the newly selected pupil diaphragm. In that case, in particular, the last used pupil diaphragm can be returned from its position of use to the diaphragm storage unit by the robotic actuation system.

[0022] The aperture of the diaphragm, ie the aperture of the illumination pupil diaphragm and / or the imaging pupil diaphragm, may be variably addressable, for example in the form of an iris diaphragm.

[0023] The metrology system may include a light source for illumination light. This type of light source may be configured as an EUV light source.

[0024] The EUV wavelength of the light source may be in the range between 5 nm and 30 nm. Light sources in the DUV wavelength range are also possible, for example around 193 nm.

[0025] In the following, exemplary embodiments of the invention are explained in more detail with reference to the drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 shows very diagrammatically a side view of a measurement system for simulating the illumination and imaging characteristics of an optical production system when illuminating and imaging an object, the measurement system comprising an illumination optical unit and an imaging optical unit, both of which are shown very diagrammatically in each case. [Figures 2A-2D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 3A-3D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 4A-4D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 5A-5D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figures 6A-6D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 7A-7D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 8A-8D] 5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 9A-9D]5A-5C show different variants of the measurement system pupil diaphragm which can be arranged in the region of the illumination pupil of the illumination optical unit; [Figure 10] FIG. 2 illustrates an example of an illumination setting for a simulated optical production system, where the illumination setting is represented by an intensity distribution across an illumination pupil in a pupil plane of the optical production system. [Figures 11A-11I] FIG. 10 shows an embodiment of a sequence of measurement positions for one of the pupil diaphragms according to FIGS. 2 to 9 using the example of the pupil diaphragm according to FIG. 2B, which measurement position sequence is used in a method executed by a metrology system for simulating the illumination and imaging characteristics of an optical production system when illuminating and imaging an object using an optical measurement system of the metrology system. [Fig. 12A-12F] 11A to 11I show another embodiment of the sequence of measurement positions of the measurement system pupil diaphragm in a similar representation to that of FIGS. 11A to 11I. [Figures 13A-13I] 11A to 11I show another embodiment of the sequence of measurement positions of the measurement system pupil diaphragm in a similar representation to that of FIGS. 11A to 11I. [Figures 14A-14C] 11A to 11I show another embodiment of the sequence of measurement positions of the measurement system pupil diaphragm in a similar representation to that of FIGS. 11A to 11I. [Figure 15] FIG. 7B shows a comparison in pupil coordinate representation between a target illumination setting of a production system that is intended to be approximated by the measurement system pupil aperture and candidate pupil apertures using an example of a measurement system pupil aperture corresponding to the pupil aperture according to FIG. 7A, which comparison is part of an algorithm for selecting at least one measurement system pupil aperture from among a plurality of provided pupil apertures. [Figure 16] FIG. 2 is a plan view of a periodic dual test structure arranged at XVI of the measurement system according to FIG. 1. [Figure 17] 17 shows the field distribution of the electromagnetic field of the illumination light at XVII in FIG. 1 on the illumination light beam path after illumination of the test structure, similar to the plan view according to FIG. 16. [Figure 18]FIG. 18 shows the diffraction spectrum of the test structure in FIG. 1VIII on the illumination light beam path, also in the plan view according to FIG. [Figure 19] FIG. 19 shows, in a similar representation to FIG. 18, the diffraction spectrum cut off at the edges by the aperture stop of the measurement system, said aperture stop being XIX in FIG. 1. [Figure 20] FIG. 20 shows a diffraction spectrum including wavefront effects shown as contour lines due to the imaging optical unit of the measurement system, in a similar representation to FIG. 19, as a spectrum measured in the region of the exit pupil of the imaging optical unit at XX in FIG. 1. [Figure 21] 17 shows the complex field distribution of the illumination light at XXI in FIG. 1 on the imaging light beam path after illumination of the spatially resolved detection device of the measurement system in a plan view similar to FIG. 17. [Figure 22] 22 is a diagram showing, in a similar manner to FIG. 21, the illumination light intensity measured by a detection device at the position of the detection device XXII in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] For ease of representation of positional relationships, a Cartesian xyz coordinate system is used hereafter. In Fig. 1, the x-axis extends into the drawing perpendicular to the plane of the drawing. The y-axis extends to the left in Fig. 1. The z-axis extends vertically upwards in Fig. 1.

[0028] In a view corresponding to a longitudinal section, Figure 1 shows the beam path of EUV illumination or imaging light 1 in a metrology system 2 in order to simulate by means of an optical measurement system of the metrology system 2 the illumination and imaging properties of an optical production system when illuminating and imaging an object, in this case a test structure 5 arranged in an object field 3 of an object plane 4.

[0029] An example of a test structure 5 is shown in the plan view of Fig. 16. The test structure 5 is periodic in one dimension, in particular along the y coordinate, for example. The test structure 5 is implemented as a binary test structure having absorbing lines 6 and in each case alternating multilayer lines 7 that reflect the illumination light 1. The lines 6, 7 are vertical structures, for example vertical structures extending along the y direction.

[0030] The metrology system 2 is used to analyze a three-dimensional (3D) aerial image (aerial image metrology system). One application is to simulate the aerial image of a lithography mask in the way that its aerial image would also appear in an optical production system of a production projection exposure apparatus, for example in a scanning apparatus. To that end, in particular the imaging quality of the metrology system 2 itself can be measured and optionally adjusted. The analysis of the aerial image can then serve to determine the imaging quality of a projection optical unit of the metrology system 2 or else in particular the imaging quality of a projection optical unit in a projection exposure apparatus. Measuring systems are known from WO 2016 / 012426, US 2013 / 0063716 (see FIG. 3 therein), DE 10220815 A1 (see FIG. 9 therein), DE 10220816 A1 (see FIG. 2 therein) and US 2013 / 0083321 A1.

[0031] The illumination light 1 is reflected and diffracted at the test structure 5. In the case of central initial illumination, the plane of incidence of the illumination light 1 is parallel to the yz plane.

[0032] The EUV illumination light 1 is generated by an EUV light source 8. The light source 8 can be a laser plasma source (LPP; laser produced plasma) or a discharge source (DPP; discharge produced plasma). In principle, a synchrotron-based light source can also be used, for example a free electron laser (FEL). The operating wavelength of the EUV light source can be a wavelength in the range between 5 nm and 30 nm. In principle, in a variant of the measurement system 2, instead of the light source 8, a light source with a different operating light wavelength can also be used, for example a light source with an operating wavelength of 193 nm.

[0033] An illumination optical unit 9 of the measurement system 2 is arranged between the light source 8 and the test structure 5. The illumination optical unit 9 serves to illuminate the test structure 5 to be examined with a defined illumination intensity distribution over the entire object field 3 and at the same time with a defined illumination angle distribution which illuminates the field points of the object field 3. Such an illumination angle distribution is also called the illumination setting.

[0034] The respective illumination angle distribution of the illumination light 1 is specified through a pupil diaphragm 10 arranged in a pupil plane 11 of the illumination optical unit. The pupil diaphragm 10 is also called a sigma diaphragm.

[0035] 2A-9B show possible embodiments of such a pupil diaphragm 10, which can be used as alternatives in the illumination optical unit 9 of the measurement system 2 to specify the illumination settings. Components and features corresponding to those already described with respect to the preceding figures will not be discussed in detail again in the subsequent figures, and where applicable, such components and features will be indicated using the same reference numbers in the subsequent figures.

[0036] Figure 2A shows a pupil diaphragm 10 with a single central pass pole I. The radius of this pass pole I is approximately one quarter of the diameter of the peripheral aperture stop portion 14 of the pupil diaphragm 10. A central illumination angle for an object field 3 with a relatively small angular variation is selected through the pupil diaphragm 10 according to Figure 2A.

[0037] Further variants of the pupil diaphragm 10 with central passage poles I of increasing radii are shown in Figures 2B to 2D. When using the pupil diaphragm 10 according to Figures 2D to 2D, the object field illumination angle variation increases accordingly. The pupil diaphragm 10 according to Figure 2D provides a conventional illumination setting in which light can pass substantially unhindered through the pupil plane 11 of the illumination optical unit of the measurement system 2.

[0038] Figure 3A shows a variant of a pupil diaphragm 10 with a ring-shaped passing portion I arranged around a round central obscuration diaphragm portion 12. The inner diameter of the ring-shaped passing pole I of the pupil diaphragm according to Figure 3A is approximately the same in size as the outer diameter of the illumination pole I of the pupil diaphragm 10 according to Figure 2A. The outer diameter of the ring-shaped passing pole I of the pupil diaphragm 10 according to Figure 3A is approximately twice this size.

[0039] Figure 3B shows a variant of the pupil diaphragm 10, in which, in comparison with Figure 2A, the outer diameter of the ring-shaped passing pole I is about 2.5 times the inner diameter. The central obscuration diaphragm part 10 of the pupil diaphragm 10 according to Figure 3B is the same size as the central obscuration diaphragm part 10 of the pupil diaphragm 10 according to Figure 3A.

[0040] Figure 3C shows a variant of the pupil diaphragm 10 with a ring-shaped pass pole I with an inner diameter that is approximately twice the size in comparison with the inner diameter of Figures 3A and 3B and an outer diameter that is only slightly larger than the outer diameter of the pass pole I according to Figure 3B. This results in a correspondingly larger central obscuration diaphragm section 12.

[0041] Figure 3D shows an illumination pupil 10 with a ring-shaped illumination pole I, the thickness of which corresponds approximately to that of the embodiment according to Figure 3C, in which the diameter of the ring-shaped illumination pole I is maximized, so that only a comparatively thin aperture stop portion 14 remains on the edge side. This results in a correspondingly large central obscuration stop portion 12, which is larger in the embodiment according to Figure 3D than in the embodiment according to Figure 3C.

[0042] A corresponding annular illumination setting can be realized using the embodiment of the pupil diaphragm 10 according to FIGS. 3A to 3D.

[0043] 4A shows a bipole pupil diaphragm 10 implemented as a x2pole. The two poles I and II are in each case round and in each case have a diameter that corresponds to the diameter of the central passing pole I of the pupil diaphragm 10 according to FIG. 2A.

[0044] Figure 4B shows a bipole pupil diaphragm 10 implemented as a y bipole with poles I, II which correspond in terms of their shape and size to the poles I, II of the embodiment according to Figure 4A. The pupil diaphragm 10 according to Figure 4B can be generated by rotating the pupil diaphragm 10 according to Figure 4A by 90° around an axis parallel to the z-axis.

[0045] FIG. 4C shows another embodiment of a x2-pole pupil stop 10 with pass poles I, II having a rectangular embodiment with an x / y aspect ratio of approximately 1 / 4.

[0046] FIG. 4D shows a y-doublet pupil diaphragm 10 which corresponds to the x-doublet pupil diaphragm 10 according to FIG. 4C.

[0047] 5A shows a x2-pole pupil diaphragm 10 with each open pole I, II having a circumferential extent of approximately 90°. Again, a central obscuration diaphragm portion 12 is located between the two through poles I, II.

[0048] FIG. 5B now shows a y-dipole pupil diaphragm 10 which corresponds to the x-dipole pupil diaphragm 10 according to FIG. 5A.

[0049] FIG. 5C shows a x2-pole pupil stop 10 in which the individual poles I, II are implemented as lobules, i.e. each has a biconvex shape.

[0050] FIG. 5D shows a y2pole pupil diaphragm 10 which corresponds to the x2pole pupil diaphragm 10 according to FIG. 5C.

[0051] Figure 6A shows an embodiment of a quadrupole pupil diaphragm 10 with four round pass poles I, II, III and IV arranged in quadrants, the diameter of which corresponds to the diameter of the pass pole I of the pupil diaphragm 10 according to Figure 2A.

[0052] Figure 6B shows a variant of the pupil diaphragm 10 that can be generated from the variant according to Figure 6A by twisting it by 45° around an axis parallel to the z-axis, in which the four poles I to IV are thus arranged as a superposition of the x2-pole pupil diaphragm and the y2-pole pupil diaphragm according to Figures 4A and 4B.

[0053] FIG. 6C shows a variant of the corresponding quadrupole pupil stop 10, also with square pass poles I-IV arranged in quadrants.

[0054] Next, FIG. 6D shows an arrangement corresponding to FIG. 6B, but with the square pass poles I to IV rotated by 45° compared to FIG. 6C.

[0055] Figure 7A shows a variant of a quadrupole pupil diaphragm 10 with sector-type poles I to IV arranged in quadrants each having a circumferential extent of approximately 45°. The connecting pieces 13 between adjacent passing poles I to IV of the pupil diaphragm 10 according to Figure 7A likewise have a circumferential extent of approximately 45° in each case. In this case too, a central obscuration diaphragm part 12 is located in the center of the pupil diaphragm 10 according to Figure 7A.

[0056] FIG. 7B shows a quadrupole pupil diaphragm 10 corresponding to the embodiment according to FIG. 7A, which can be generated by a rotation of 45° around an axis parallel to the x-axis.

[0057] FIG. 7C shows a variant of the quadrupole pupil diaphragm 10 with pass poles I-IV in the form of leaflets arranged on the edge side near the aperture diaphragm portion 14 along a circumferential direction around the diaphragm center.

[0058] FIG. 7D shows a variant of the quadrupole pupil diaphragm corresponding to the variant according to FIG. 7C, which can be produced by a rotation of 45° around an axis parallel to the z-axis.

[0059] Figure 8A shows a hexapole pupil diaphragm 10 with six round passing poles I-VI arranged uniformly distributed along the circumferential direction around the diaphragm center. The diameter of the poles I-VI corresponds to the diameter of the passing pole I of the pupil diaphragm 10 according to Figure 2A. The distance between two adjacent poles I-VI is approximately 1 / 3 of the pole diameter.

[0060] As measured from the x-coordinate of the pupil stop 10 in FIG. 8A, the six poles are located at 30°, 90°, 150°, 210°, 270° and 330°.

[0061] FIG. 8B shows a variant of the hexapole pupil diaphragm 10 which corresponds to the hexapole pupil diaphragm 10 according to FIG. 8A, except that in the embodiment according to FIG. 8B the edge contours of the pass poles I to VI are square.

[0062] Figure 8C shows a variant of the hexapole pupil diaphragm 10 which corresponds to the hexapole pupil diaphragm 10 according to Figure 8A, except that in the embodiment according to Figure 8C the edge contours of the pass poles I to VI are of sector type. The circumferential extent of the sector type pass poles I to VI is approximately 30°, which in each case coincides with the circumferential extent of the connecting pieces between adjacent pass poles I to VI.

[0063] FIG. 8D shows a variant of the hexapole pupil diaphragm 10 which corresponds to the hexapole pupil diaphragm 10 according to FIG. 8A, except that in the embodiment according to FIG. 8D the edge contours of the pass poles I to VI are approximately triangular on the side of the edge near the aperture diaphragm portion 14.

[0064] FIG. 9A shows a variant of the hexapole pupil diaphragm 10 which can be generated from the variant according to FIG. 8A through a rotation of 30° around an axis parallel to the z-axis.

[0065] FIG. 9B shows a variant of the hexapole pupil diaphragm 10 which can be generated from the variant according to FIG. 8B through a rotation of 30° around an axis parallel to the z-axis.

[0066] FIG. 9C shows a variant of the hexapole pupil diaphragm 10 which can be generated from the variant according to FIG. 8C through a rotation of 30° about an axis parallel to the z-axis.

[0067] FIG. 9D shows a variant of the hexapole pupil diaphragm 10 which can be generated from the variant according to FIG. 8D through a rotation of 30° around an axis parallel to the z-axis.

[0068] The pupil diaphragm 10 of the illumination optical unit 9 is implemented as a driven displaceable diaphragm arranged in front of the object plane 4 on the illumination light beam path 15 of the illumination light 1. A drive unit used for drivingly displacing the pupil diaphragm 10 is shown at 16 in FIG. 1. By means of the drive unit 16, also called a displacement drive, this pupil diaphragm can be displaced along the x-coordinate and / or the y-coordinate. Through the drive unit 16, a fine setting along the z-coordinate is also possible for adjusting the alignment of the arrangement plane of the pupil diaphragm 10 with respect to the pupil plane 11 of the illumination optical unit. Furthermore, the drive unit 16 can also be designed such that it is possible to tilt the diaphragm around at least one tilt axis parallel to the x-axis and / or parallel to the y-axis. Furthermore, the diameter of the obscuration diaphragm portion 12 and / or the aperture diaphragm portion 14 and / or the size of the poles I; I, II; I, II, III, IV; I, II, III, IV, V, VI of the respective embodiment of the pupil diaphragm 10 may be specifiable in a settable manner, in particular in a settable driven manner.

[0069] With the aid of a displacement drive 16, the selected pupil diaphragm 10 is moved in the pupil plane 11 to a pupil coordinate k x and k y It is possible to displace the gyroscope along

[0070] The displacement drive 16 may further comprise a diaphragm exchange unit by means of which a particular pupil diaphragm 10 is exchanged for another particular pupil diaphragm 10. To that end, the diaphragm exchange unit may remove the respective selected pupil diaphragm from the diaphragm storage unit and return the exchanged diaphragm to this diaphragm storage unit.

[0071] The test structure 5 is held by an object holder 17 of the measurement system 2. The object holder 17 cooperates with an object displacement drive 18 to displace the test structure 5, in particular along the z coordinate.

[0072] After reflection from the test structure 5, the electromagnetic field of the illumination light 1 has a distribution 19 shown in the plan view of Figure 18, which corresponds to the plan view of Figure 17. In the field distribution 19, the amplitude and phase values ​​correspond to the absorption lines 6 and multilayer lines 7 of the test structure 5.

[0073] The illumination light 1 reflected by the test structure 5 enters the imaging or projection optical unit 20 of the measurement system 2 .

[0074] Due to the periodicity of the test structure 5, a diffraction spectrum 21 arises in the pupil plane of the projection optical unit 20 (see FIG. 18).

[0075] The diffraction spectrum 21 has a central 0th diffraction order of the test structure 5. Additionally, Figure 18 also shows the + / -1st and + / -2nd diffraction orders of the diffraction spectrum 21.

[0076] 18 appear in this form in a pupil plane of the optical system of the measurement system 2, for example in an entrance pupil plane 22 of the projection optical unit 20. In this entrance pupil plane 22 an aperture stop 23 of the projection optical unit 20 is arranged, which defines the edge boundary of an entrance pupil 24 of the projection optical unit 20. The aperture stop 23 is also called the imaging pupil stop of the measurement system 2.

[0077] The imaging pupil diaphragm 23 is operatively connected to a displacement drive 25 whose function corresponds to that of the displacement drive 16 for the sigma diaphragm 10 .

[0078] FIG. 19 shows the entrance pupil 24 and three diffraction orders of the diffraction spectrum 21 located within the entrance pupil 24 in the initial illumination angle distribution, specifically the 0th and + / -1st diffraction orders.

[0079] 20 shows the distribution of the intensity of the illumination / imaging light 1 in the exit pupil plane of the projection optical unit 20. As an image of the entrance pupil 24 an exit pupil 26, shown in FIG.

[0080] Pupils 24 (see FIG. 19) and 26 (see FIG. 20) are elliptical. In alternative designations, pupils 22, 24 may have different deviations from circular through a suitable aperture stop 21, and possibly these pupils are at least approximately circular. The pupil radius can be calculated as the average radius. For example, such alternative pupils may have elliptical embodiments with an aspect ratio between the semi-axes ranging between 1 and, for example, 3. In embodiments not shown here, pupils 24 and 26 may be circular.

[0081] Firstly, the images of the -1, 0 and +1 diffraction orders and secondly the imaging contribution of the optical system, specifically the projection optical unit 20, contribute to the intensity distribution in the exit pupil 26. This imaging contribution, elucidated by the dashed contours in Fig. 20, can be described by the optical system transfer function, which will be explained later. Due to the unavoidable imaging aberrations of the optical system, there is a measurable intensity of the illumination / imaging light 1 in the exit pupil 26, even in the areas around several diffraction orders.

[0082] The projection optical unit 20 images the test structure 5 towards a spatially resolved detection device 27 of the metrology system 2. The detection device 27 takes the form of a camera, in particular a CCD camera or a CMOS camera.

[0083] The projection optical unit 20 is implemented as a magnification optical unit. The magnification of the projection optical unit 20 may be greater than 10, greater than 50, greater than 100 or even greater. Typically, this magnification is less than 1000.

[0084] In a manner corresponding to FIG. 18, FIG. 21 shows a complex field distribution 28 of the illumination / imaging light 1 in the area of ​​the image plane 29 in which the detector device 27 is located.

[0085] 22 shows the intensity distribution 31 of the illumination / imaging light 1 measured by the camera 27 in the image field 30 of the image plane 29. The image of the absorption line 6 is present in the intensity distribution 31 as a substantially low intensity dark line 32, and the image of the multilayer line 7 is present in the intensity distribution 31 as a much higher intensity emission line 33.

[0086] In order to simulate the illumination and imaging properties of the optical production system when illuminating and imaging an object by the optical measurement system 1 of the metrology system 2 using the example of the test structure 5, the following procedure is carried out: Firstly, a number of pupil diaphragms 10 are provided, in each case with different diaphragm boundary shapes, in order to specify correspondingly different measurement illumination settings. This is carried out by providing the pupil diaphragm 10, for example in the form of the pupil diaphragm 10 of Figures 2A to 9D, in a diaphragm storage unit accessible to a diaphragm exchange unit, which may be part of the displacement drive 16.

[0087] A target pupil aperture is then specified having a target aperture boundary shape derived from the illumination settings of the optical production system to be simulated. The target pupil aperture can be an arrangement of a plurality or multiple individual pupil or aperture spots, where the intensity of the individual illumination or pupil spots typically varies between the individual spots.

[0088] 10 shows a first example of an illumination setting of an optical production system to be simulated. This production illumination setting in the pupil plane of an illumination optical unit of the optical production system is provided through a fly's eye integrator with a field facet mirror and a pupil facet mirror and comprises a number of intensity spots 34 arranged in a grid-like manner in an illumination pupil plane 35 of the production illumination optical unit. The intensity spots 34 may have different intensities, so that illumination light from different illumination directions may be incident on the object field 3 with correspondingly different intensities.

[0089] Similarly, in FIG. 15, the pupil coordinate k x ,k y10 shows a target pupil diaphragm 36 in a pupil plane having a target diaphragm boundary shape which is specified in a manner dependent on the illumination settings of the optical production system to be simulated, for example in a manner dependent on the illumination settings according to FIG. 10.

[0090] The target pupil aperture 36 can be specified through defining a suitable aperture contour, in particular a continuous aperture contour, which can be described, for example, by a chain of polygons.

[0091] These successive apertures are then approximated by a finite number of pupil spots 37 within the aperture, which are shown as examples in Figure 15.

[0092] For this particular example of Figure 15, the aperture contour of the aperture in Figure 7A was used as the measurement aperture, and the aperture contour of the aperture in Figure 5A was used as the target setting. The finer the grid of the illumination spot, the more accurately the actual aperture shape can be approximated.

[0093] Figure 15 shows a grid of pupil spots 37 (stars in Figure 15) arranged within a specified target pupil stop 36. This grid arrangement of pupil spots 37 can take into account shadowing, particularly shadowing as a result of the required web of the pupil stop.

[0094] Then, from among the provided pupil apertures 10, at least one pupil aperture 10 derived from this target pupil aperture 36 is selected by an algorithm which identifies the deviation between the aperture boundary shape of each of the provided pupil apertures 10 and the target aperture boundary shape of the target pupil aperture 36. For this purpose, the selected pupil aperture 10 currently under examination (also called pupil aperture to be identified later) can be decomposed within its aperture boundary into a number of pupil spots 38 arranged in a grid, represented by circles in FIG.

[0095] The scope of the qualification includes determining the degree of similarity between the target illumination pupil (hereinafter sometimes denoted as "T") and the possible measurement aperture 10 (hereinafter sometimes denoted as "M"). For example, this can be performed by calculating an overlap function Q.

[0096]

number

[0097] The operators "∩", "∪" and "\" correspond to the intersection (∩), union (∪) and relative complement (\) operators from set theory. In this case, the intersection M1∩M2 of sets / areas M1 and M2 is intended to mean the sets / areas that are contained in both M1 and M2, i.e. corresponds to the overlapping area of ​​M1 and M2. The union M1∪M2 of sets / areas M1 and M2 describes the sets / areas that are contained in M1 or M2, i.e. corresponds to the total area covered by M1 or M2. The relative complement M1\M2 of sets / areas M1 and M2 describes the sets / areas that are covered by M1 but not contained in M2.

[0098] For example, the area function A can be implemented as counting the illumination spots in the pupil. To that end, the target illumination pupil and the measurement pupil contain the same grid. Typically, this grid corresponds to the pupil facet grid in the scanning device on which the target illumination pupil is sampled (see FIG. 10). Then, the number of spots present in both illumination pupils (first term in the above formula) is counted, as well as the spots that are confined to only one of the two pupils (second and third terms in the above formula). Alternatives to this could be a comparison of the local spot density or the average local brightness.

[0099] Selection of the pupil diaphragm 10 therefore involves a comparison between the pose of the pupil spot 37 of the target diaphragm boundary shape and the pose of the pupil spot 38 of the provided pupil diaphragm 10 .

[0100] In addition, multiple defocus values ​​z m (see FIG. 1) is designated as the z-distance of the position of the object holder 17 from the object plane 4 (parallel to the xy-plane).

[0101] Furthermore, a number of measurement positions (k x ,k y ) is specified within the scope of this simulation method.

[0102] Next, the specified defocus value z m and the measurement position (k x ,k y 22. For each of the combinations of the defocus values ​​z(x,y) in the image plane 29, a measured aerial image I(x,y) in the form of an intensity distribution 31 according to FIG. 22 is recorded. m For each recording of the measurement aerial image I(x,y), the specified defocus value z m At least one of the defocus values ​​z m For this, a plurality of measurement positions (k x ,k y ) is the subject of this review.

[0103] The sequence of FIG. 11A to FIG. 11I is for one defocus value z m A total of nine measurement positions (k x ,k y 2B) in which a pupil diaphragm 10 according to FIG. 2B has been chosen to specify a conventional illumination setting. The position of the pass pole I of the pupil diaphragm 10 relative to the position of the imaging pupil diaphragm 23 in each case is shown.

[0104] 11A shows the pupil diaphragm 10 located in the center of the imaging pupil diaphragm 23. In this starting position according to FIG.

[0105] In comparison with the imaging pupil stop 23, FIG. 11B shows a positive k x 3 shows the pupil diaphragm 10 displaced by specified increments in the direction.

[0106] In comparison with the central position according to Fig. 11A, the following sequence of Figs. 11C to 11I shows in each case other displacements of the pupil diaphragm 10, displaced by 45° in the circumferential direction starting from the position according to Fig. 11B. The measurement positions according to Figs. 11C, 11E, 11G and 11I therefore show the pupil diaphragm 10 in the positions of the four quadrants I to IV. The measurement positions according to Figs. 11B, 11D, 11F and 11H are the positions of the Cartesian displacement position +k x , +k y , -k x , -k y 1 shows the pupil diaphragm 10 at .

[0107] Measurement position of pupil diaphragm 10 (k x ,k y ) is shown in Figures 12A to 12F. This sequence of measurement positions 12A to 12F corresponds to the measurement positions according to Figures 11D, 11E, 11C, 11G, 11I and 11H.

[0108] 13A to 13I show the measurement position (k x ,k y ) sequence.

[0109] FIG. 13A also shows the pupil diaphragm 10 located at the center of the imaging pupil diaphragm 23. In comparison with the imaging pupil diaphragm 23, FIG. 13B shows the pupil diaphragm 10 at a positive k x 3 shows the pupil diaphragm 10 displaced by specified increments in the direction.

[0110] For the imaging pupil stop 23, FIG. 13C shows a positive k y 1 shows the pupil diaphragm 10 displaced by the same increment in the x-direction.

[0111] For the imaging pupil stop 23, FIG. 13D shows a negative k starting from the central position according to FIG. 13A. x 1 shows the pupil diaphragm 10 displaced by the same increment in the x-direction.

[0112] For the imaging pupil stop 23, FIG. 13E shows a negative k starting from the central position according to FIG. 13A. y 1 shows the pupil diaphragm 10 displaced by given increments in the direction.

[0113] Measurement position (k x ,k y ) are shown in Fig. 13F-13I. The circumferential positions of the pupil diaphragm 10 relative to the imaging pupil diaphragm 23 correspond to the positions according to Fig. 11C, 11E, 11G and 11I. In contrast to these positions, the pupil diaphragm 10 in the sequence according to Fig. 13F-13I is pushed radially out of the aperture of the imaging pupil diaphragm 23, yet only the inner part of the passing spot I of the pupil diaphragm 10 overlaps with the aperture of the imaging pupil diaphragm 23. In this case, the illumination light can traverse an area slightly more than half the area of ​​the passing spot I. This gives the completed sequence according to Fig. 13A-13I with two displacement radii.

[0114] 14A to 14C show the measurement positions (k x ,ky 14A to 14C correspond to the measurement positions in FIGS. 11B, 11E and 11G.

[0115] The selection of the respective measurement position sequence, or optionally a subset of these sequences, is performed based on the arrangement of the individual structures of the test structure 5 and / or based on the illumination settings of the optical production system to be simulated. For example, the measurement position sequence can be selected in a manner similar to the aperture selection algorithm (see above), considering all aperture positions of the sequence and selecting the sequence that maximizes the overlap of the measurement sequence with the target illumination pupil.

[0116] Positivities of the pupil diaphragm 10 which differ from the central position with respect to the relative pose with respect to the imaging pupil diaphragm 23 are also called offset measurement positions. Within the measurement position sequence, 2 to 10 such offset measurement positions can be covered, which is typically 2 to 5 offset measurement positions, for example 3 or 4 offset measurement positions. The offset measurement positions can be arranged uniformly distributed in the circumferential direction. To reduce the measurement time, it is also possible to use only a subset of the shown measurement plans (FIGS. 11 to 14), for example using every other measurement position.

[0117] The specified defocus value z m are all measured with the help of the respective measurement position sequences. In alternative embodiments, only one defocus value or the individual defocus values ​​z m For only one defocus value z, it is possible to use the entire respective measurement position sequence, and for other defocus values ​​z m , the measured aerial images are recorded for a smaller number of measurement positions of the pupil diaphragm relative to the imaging pupil diaphragm 23. In the extreme case, for example, the complete measurement position sequence is covered and only one defocus value z m For each measurement aerial image, it is possible to record only one image, while for other specified defocus values ​​z mIn the case of the measurement of the aerial image I at each measurement position, in particular in the case of the centrally located pupil diaphragm 10, meas Record only (x,y).

[0118] For example, the following combinations of defocus value / measurement location: m and a plurality of measurement positions (k x ,k y ), i.e. in particular the combination of a central measurement position and a number of offset measurement positions, as well as defocus values ​​z min , z max And these positions z min , z max Exactly one central measurement position (k x ,k y ) combination can be recorded.

[0119] The complex mask transfer function is then reconstructed from the entire set of measured aerial images recorded with the selected pupil diaphragm 10. A similar reconstruction step is also described in DE 10 2019215800 A1.

[0120] This reconstruction is carried out within the scope of a modelled description, in which the projection optical unit 20 of the measurement system 2 with its illumination settings specified by the pupil diaphragm 10 is represented by an illumination direction passing through the pupil diaphragm 10.

[0121]

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[0122] Each illumination direction produces a complex-valued field distribution in the object plane (4) as a result of its interaction with the test structure 5.

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[0123]

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[0124]

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[0125] The purpose here is to mask the spectrum

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[0126] The reconstructed spectrum can then be used to simulate any other lighting setting.

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[0127] As an optimization problem

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[0128] Lighting Direction

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[0129] The simplest solution is the Hopkins approximation, which assumes that this spectrum shifts by the same amount when the illumination direction shifts, i.e.

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[0130] Spectrum and Lighting Direction

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[0131] in this case,

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[0132] As an example, the function

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[0133] Within the scope of the reconstruction of the complex mask transfer function M, the mask spectrum depends on the illumination direction

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[0134] Then, a mask spectrum is calculated that minimizes the difference between the measured aerial image and the simulated aerial image.

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[0135] Thus, for the Hopkins approximation, the number of free parameters increases by only N, where N is typically small.

[0136] This direction-dependent reconstructed spectrum is used to determine the target illumination setting σ target and target defocus z target Simulated aerial image of I sim It is possible to calculate

[0137]

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[0138] Equation (6) then gives the simulated aerial image I sim and the measured aerial images I meas which can be used to reconstruct the mask spectrum M and thus the complex mask transfer function.

[0139] From equation (6), the reconstructed mask transfer function M and the illumination setting σ of the optical production system are target With the help of the 3D aerial image can be calculated. In this way it is possible to see what the aerial image of the test structure 5 would look like if it were imaged by an optical production system.

[0140] In a variant of this simulation method, several different pupil diaphragms 10 are used to measure various measurement positions (k x ,k y ) can also be specified.

[0141] To prepare for this simulation method, it is possible to record an aerial image stack to ascertain which z pose of the object plane 4 provides an optimally sharp image in the image plane 29 (the zero z pose).

[0142] Aerial image I sim The z increment used in equation (6) when determining z is the defocus value z specified within this simulation method. m may be different from.

[0143] To match the desired pixel resolution, the recorded measured aerial image I meas The pixel size of may be resampled.

[0144] In the simulation method, a plurality of k of the imaging pupil diaphragm 23 x ,k y The position can also be set through the displacement drive 25 .

[0145] It is therefore possible to take into account the imaging aberrations of the optical measurement system, in particular the imaging aberrations of the imaging optical unit 20 of the metrology system 2, when reconstructing the mask transfer function.

[0146] 3D aerial image I meas Determination and / or simulated aerial image I sim The calculation of may be performed using an illumination chief ray angle different from the illumination chief ray angle of the reconstruction of the mask transfer function.

[0147] To select a respective pupil diaphragm 10 from among the offered pupil diaphragms 10, which in each case have different diaphragm boundary shapes and / or diaphragm boundary orientations, the measuring system 2 has a selection device, not shown in detail in the drawings, which has a diaphragm storage unit, in which a plurality of pupil diaphragms 10, which in each case have different diaphragm boundary shapes and / or diaphragm boundary orientations, are stored in order to specify correspondingly different measurement illumination settings.

[0148] In a selection step of the simulation method, the last inserted pupil diaphragm is first removed from its position of use in the pupil plane 11 and fed to a diaphragm storage unit in the selection device with the aid of an actuator system of the selection device, in particular with the aid of a robotic actuator system. Subsequently, the pupil diaphragm 10 selected according to the simulation method is selected from the diaphragm storage unit and inserted into its position of use in the pupil plane 11 with the aid of the robotic actuator system.

Claims

1. A method for simulating illumination and imaging properties of an optical production system during illumination and imaging of an object (5) by means of an optical measurement system of a metrology system (2), comprising: - said optical measurement system is an illumination optical unit (9) for illuminating said object (5), k x , k y the illumination optical unit (9) having a pupil stop (10) in the region of an illumination pupil in a pupil plane (11) and an imaging optical unit (20) for imaging the object (5) into an image plane (29), The method comprises the following steps: - providing a plurality of pupil diaphragms (10) for specifying different measurement illumination settings; - measured aerial image I in the image plane (29) by the pupil stops (10) meas recording (x,y); - the recorded measured aerial image (I meas ) reconstructing a complex mask transfer function (M); As a result of the simulation method, the reconstructed mask transfer function (M) and the illumination settings of the optical production system (σ target ) from the 3D aerial image (I sim ) determining A method comprising:

2. The optical measurement system measures the pupil diaphragm (10) by k x and / or k y 2. The method according to claim 1, characterized in that the optical measurement system comprises a displacement drive (16) for displacing in the x-y direction, and the optical measurement system comprises an object holder (17) displaceable perpendicularly to the x-y object plane (4) by an actuator.

3. 3. The method according to claim 1, wherein the pupil diaphragms (10) in each case have different diaphragm boundary shapes and / or diaphragm boundary orientations in order to specify correspondingly different measurement illumination settings.

4. The method further comprises the steps of: - the illumination setting of the optical production system (σ target specifying a target pupil aperture (36) having a target aperture boundary shape derived from the target aperture boundary shape; - selecting at least one pupil diaphragm (10) from among said plurality of pupil diaphragms by means of an algorithm which determines the deviation between said diaphragm boundary shape of each of said pupil diaphragms (10) and said target diaphragm boundary shape; a number of defocus values ​​z as the z distance of the object holder position from said xy object plane (4); m Specifying a number of measurement positions (k) of the at least one selected pupil diaphragm (10); x , k y ) and The method according to any one of claims 1 to 3, characterized in that it comprises:

5. The measured aerial image I meas (x, y) is the specified defocus value (z m ) and the designated measurement position (k x , k y ) for each of a plurality of combinations of the specified defocus value z m The measured aerial images (I meas For each of the records, the designated defocus value z m At least one of the defocus values ​​z m For a plurality of the specified measurement positions (k x , k y 5. The method of claim 4, wherein the method is directed to

6. The specified measurement position (k x , k y 6. The method of claim 4, wherein the measurement points include a central measurement location and a plurality of offset measurement locations surrounding the central measurement location.

7. The measured aerial image (I meas ) for at least the following defocus value / measurement position combinations: - central defocus value (z m ) and a plurality of measurement positions (k x , k y ) in combination with the central defocus value (z m ) maximally offset from the central defocus value (z m ) on either side of the defocus value (z min , z max ) and exactly one measurement position (k x , k y ) in combination with The method according to any one of claims 4 to 6, characterized in that the information is recorded for

8. 8. The method according to claim 4, characterized in that when selecting the pupil diaphragm (10), a comparison is performed between the position of a pupil spot (37) of the target diaphragm boundary shape and the position of a pupil spot (38) of the offered pupil diaphragm (10).

9. During the reconstruction of the complex mask transfer function (M), the illumination direction [0010] The method according to any one of claims 1 to 8, characterized in that the mask spectrum dependent on , is modelled as a product of an illumination direction independent mask spectrum and an illumination direction dependent correction function.

10. The optical measurement system comprises an imaging pupil diaphragm (23) in the pupil region of the imaging optical unit (20), a number of measurement positions of the imaging pupil diaphragm (23) are designated, and the measurement aerial image (I meas 10. The method according to claim 1, wherein a plurality of designated measurement positions of the imaging pupil diaphragm (23) are set when recording the image of interest.

11. Method according to any one of the preceding claims, characterized in that imaging aberrations of the optical measurement system are taken into account when reconstructing the mask transfer function (M).

12. Said 3D aerial image (I sim 12. The method according to claim 1, wherein the mask transfer function (M) is determined using an illumination chief ray angle different from the illumination chief ray angle used in the reconstruction of the mask transfer function (M).

13. A measurement system (2) for carrying out the method according to any one of claims 1 to 12, comprising: - said optical measurement system is an illumination optical unit (9) for illuminating said object (5), k x , k y the illumination optical unit (9) having a pupil stop (10) in the region of an illumination pupil in a pupil plane (11) and an imaging optical unit (20) for imaging the object (5) into the image plane (29), Measurement system (2).

14. - the optical measurement system measures the pupil diaphragm (10) at k x and / or k y A displacement drive device (16) for displacing in a direction, said optical measurement system comprises an object holder (17) displaceable perpendicular to the xy object plane (4) by an actuator; The measurement system of claim 13.

15. The optical measurement system measures an imaging pupil stop (23) arranged in the pupil region of the imaging optical unit (20) k x and / or k y 15. The measuring system according to claim 13 or 14, further comprising a displacement drive (25) for displacing in the direction.

16. 16. The measuring system according to claim 13, characterized in that the selection device for selecting at least one pupil diaphragm from among a plurality of pupil diaphragms comprises a diaphragm storage unit which comprises a plurality of pupil diaphragms (10), the plurality of pupil diaphragms (10) having in each case different diaphragm border shapes and / or diaphragm border orientations in order to specify correspondingly different measurement illumination settings.

Images