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

Abstract

To simulate the characteristics of the optical generation system, an optical measurement system is used, which includes an illumination optical unit for an object to be imaged with a pupil stop in the region of the illumination pupil and an imaging optical unit for imaging the object. To optimize the pupil stop shape of the pupil stop, first, a starting aperture shape of the pupil stop is predefined (30) as an initial design candidate for the simulation. The starting aperture shape is modified (31) and at least one manufacturing boundary condition of the corresponding modified aperture shape is checked (33). The "modifying" and "checking" steps are repeated until the checking (33) step indicates compliance with the boundary conditions. A matching quality between the characteristics of the optical generation system and the characteristics of the optical measurement system is determined (34), the matching quality is queried (35), and the "modifying", "checking" and "determining" steps are repeated until a predefined optimization criterion is reached. A target aperture shape resulting from the target aperture shape resulting in the minimum merit function value E in the optimization is manufactured (37) as an optimized pupil stop shape after the optimization criterion is reached. This results in a simulation of the illumination and imaging properties of the optical generation system that is as free as possible from deviations during illumination and imaging of an object by the optical measurement system.

Description

[Technical Field]

[0001] This patent application claims priority to German patent application DE 10 2021 213 827.6, the content of which is incorporated herein by reference.

[0002] The present invention relates to a method for optimizing a pupil diaphragm shape for simulating the illumination and imaging properties of an optical production system during illumination and imaging of an object by an optical measurement system, and further to a pupil diaphragm optimized by such a method, and to a measurement system including at least one such pupil diaphragm. [Background technology]

[0003] A metrology system for three-dimensionally measuring the aerial image of a lithography mask is known from WO 2016 / 012 425 and WO 2016 / 012 426. A corresponding metrology system and method for three-dimensionally determining the aerial image of a lithography mask is known from DE 10 2019 206 651. DE 10 2013 219 524 describes a device and method for determining the imaging quality of an optical system, as well as an optical system. DE 10 2013 219 524 describes a phase retrieval method for determining a wavefront based on the imaging of a pinhole. DE 10 2017 210 164 describes a method and an adjustment device for adjusting the imaging behavior of a projection lens. A method for compensating for lens heating in a projection exposure apparatus is known from U.S. Pat. No. 9,746,784. An optical generation system, particularly one having an anamorphic projection optical unit, is known, for example, from U.S. Patent Application Publication No. 2020 / 0272058. A further variant of the optical generation system is known from WO 2009 / 100 856. DE 10 2008 001 553 discloses a component for setting a scan-integrated illumination energy in the object plane of a microlithography projection exposure apparatus. EP 0 674 778 discloses a process and device for creating a dose pattern for generating a structured surface. DE 103 52 040 and WO 2005 / 045 503 disclose aperture and / or filter arrangements for optical devices, particularly microscopes.

[0004] Known metrology systems, in terms of the setup of the illumination optical unit and / or the setup of the imaging optical unit, sometimes differ significantly from the corresponding illumination setup and imaging optical components in the optical generation system to be simulated, in particular because the setup of the metrology system cannot be achieved at the same cost in terms of design and energy as the setup of the optical generation system. Summary of the Invention

[0005] Therefore, it is an object of the present invention to provide a method for optimizing the shape of a pupil diaphragm used in a metrology system, which optimization method results in a simulation of the illumination and imaging characteristics of the optical generation system with as little deviation as possible during illumination and imaging of an object by the optical measurement system of the metrology system, despite differences in the illumination and imaging optical components.

[0006] This object is achieved according to the invention by an optimization method having the features of claim 1.

[0007] The present invention recognizes, in particular, that mathematical or numerical modeling of an optical system allows for a global qualitative determination of the influence of changes in the aperture shape of the pupil diaphragm on the illumination and imaging characteristics of the optical system with such accuracy that aperture shape optimization is possible. The target aperture shape resulting from the final manufacturing step of the optimization method ensures a highly accurate simulation of the illumination and imaging characteristics of the optical generation system during illumination and imaging of an object by the optical measurement system. More complex illumination settings and / or complex imaging characteristics of the optical generation system, such as anamorphic imaging of the projection optical unit of the optical generation system, can be taken into account and simulated during the alignment quality determination in the optimization method. For anamorphic imaging of the projection optical unit, reference is made to U.S. Pat. No. 9,366,968. In particular, illumination-side pupil obscuration of the optical measurement system, which is necessary due to the structural definition, can be taken into account during the optimization method. This illumination-side obscuration of the optical measurement system can then be corrected or compensated for by the target aperture shape. Even the effect of the necessary studs required for the mechanical structure of the pupil diaphragm of the optical measurement system can be taken into account. When examining the manufacturing boundary conditions, specifications regarding the freestanding configuration of the diaphragm shape, the minimum stud stud width, the minimum diaphragm aperture diameter, and the maximum curvature of the diaphragm edge portion can be taken into account. This avoids situations where an optimization solution that cannot be manufactured is found. Furthermore, particularly central obscuration of the exit pupil of the imaging optical unit of the optical generation system (which is often found in optical generation systems) can be taken into account in the context of the optimization method. In this case, the central obscuration of the exit pupil of the optical generation system can be taken into account by the central aperture of the NA aperture stop of the imaging optical unit of the measurement system. Even different imaging exit pupil apodization between one optical generation system and another optical measurement system can be taken into account.

[0008] The optimization method can in particular be carried out in such a way that the structural configuration of the object to be imaged is taken into account, thus taking into account the varying optical properties associated with different structures.

[0009] Differences in configuration between the illumination pupil of an optical generation system, which is regularly constructed from a large number of individual spots, and the illumination pupil of an optical measurement system of a measurement system, which has a regularly and continuously illuminated area, can likewise be taken into account.

[0010] Alternatively, the optimization method can function in such a way that specific object structures do not affect the method. In particular, optical generation systems with large image-side numerical apertures (image-side numerical apertures greater than 0.5) can be simulated with good quality.

[0011] The inspection method for inspecting compliance with manufacturing boundary conditions according to claim 2 has proven to be valuable in practice. The requirements regarding the manufacturing quality can be predefined by predefining the size of the peripheral area to be inspected in each case. This avoids situations in particular where excessively narrow splices or excessively large curvatures of the aperture edges result along the respective inspection section of the target aperture shape, i.e. after inspection has been carried out along the entire aperture edge of the target aperture shape.

[0012] A pixel-by-pixel arrangement of the surrounding area to be inspected during inspection of the manufacturing boundary conditions according to claim 3 has proven to be valuable in practice. The size of the pixel can be chosen according to the achievable manufacturing resolution.

[0013] Instead of pixel-based inspection of the manufacturing boundary conditions of the pupil diaphragm shape, a polygonal boundary may be used as the desired boundary shape, in which case a curvature estimate (the rounding radius of the diaphragm shape) can be derived from the angles of the line segments of the polygons adjacent to each other.

[0014] Taking into account the pupil alignment between the optical generation system on the one hand and the optical measurement system on the other hand according to claim 4 has proven to be valuable to ensure a sufficient alignment quality determination, where information about the respective illumination pupil and / or the respective imaging pupil may be used depending on the boundary conditions of the optical systems involved.

[0015] The merit function value calculation according to claim 5 simplifies the numerical modeling of the match quality determination in the context of the optimization method. The size of the pupil overlap region can be varied in the context of the match quality determination. This can be done depending on the selected boundary conditions of the optical system involved. The required degree of match quality can be precisely influenced by predefining the size of the pupil overlap regions used in determining the match quality and their number and distribution across the illumination pupil. This predefinition can be done in particular depending on the illumination and imaging characteristics of the optical generation system to be simulated.

[0016] Instead of an overlap-based merit function, the matching quality may also be achieved by a direct imaging simulation that takes into account a large number of test imagings. In connection with such a direct imaging simulation, deviations in directly corresponding imaging parameters, in particular the critical dimension (CD) or imaging telecentricity, can be evaluated, and the matching between the optical generation system and the optical measurement system can be guaranteed.

[0017] The illumination and imaging parameters according to claim 6 have proven to be valuable in practice, as they are well adapted to the typical imaging characteristics or imaging aberrations of the optical system involved. Further illumination and imaging parameters can also be used, such as parameters that compare the possible structure resolutions (critical dimensions, CD) along two mutually perpendicular coordinates. One example of such a parameter is the so-called HV (horizontal / vertical) asymmetry. A parameter that predefines a lower limit for the pupil transmission may also be used in connection with the matching quality determination.

[0018] The optimization loop according to claim 7 makes it possible to use known optimization methods, one example of which is simulated annealing. Other optimization methods known in the technical literature can also be used. The total calculation time or else the quality of the match with the optimization criterion can be chosen as the termination criterion.

[0019] The simulation of the illumination and imaging properties of the optical generation system is improved by taking into account the field dependence of the object illumination according to claim 8. The field dependence can be taken into account by averaging the pupil of the optical generation system over the respective field and / or by determining the matching quality in connection with an optimization method for all field points or for a selected field point region.

[0020] The advantages of the pupil diaphragm according to claim 9 correspond to those already explained above with reference to the optimization method according to the invention.

[0021] In the case of a free-form pupil diaphragm according to claim 10, this correspondingly allows for a large degree of design freedom for simulating the optical properties of the optical production system. A free-form pupil diaphragm is a pupil diaphragm whose diaphragm boundary has no distinct axes and / or planes of symmetry. In the case of a free-form pupil diaphragm, even multiple rotational symmetries do not exist.

[0022] The advantages of the measurement system according to claim 11 correspond to those already explained above with reference to the optimization method and the pupil diaphragm optimized thereby.

[0023] An exchange holder according to claim 12 allows for the use of different pupil diaphragms in the optical measuring system of the metrology system.

[0024] A metrology system with a correspondingly optimized pupil diaphragm has proven to be particularly valuable in the use according to claim 13. Different imaging scales of the projection optical unit of the optical production system in mutually perpendicular directions may be taken into account in connection with the manufacturing steps with different scaling in these two directions.

[0025] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. [Brief explanation of the drawings]

[0026] [Figure 1]FIG. 1 is a highly schematic plan view of a measurement system for simulating a target wavefront of an imaging optical generation system when an object is illuminated with illumination light, with the line of sight perpendicular to the plane of incidence; the measurement system includes an optical measurement system having an illumination optical unit for illuminating the object and an imaging optical unit for imaging the object, the illumination optical unit and the imaging optical unit each being shown highly schematic. [Figure 2] FIG. 1 is a plan view of a sigma stop for placement in a pupil plane of an illumination optical unit of a metrology system. [Figure 3] 3 is a plan view of a NA stop for placement in a pupil plane of an imaging optical unit of an optical measurement system of a metrology system, similar to FIG. 2. FIG. [Figure 4] FIG. 10 is a diagram illustrating the instantaneous overlap between the illumination pupil and the pupil of an imaging optical unit of an optical system including an illumination optical unit and an imaging optical unit, for elucidating a method for optimizing the matching quality between the illumination and imaging characteristics of the optical generation system and the illumination and imaging characteristics of the optical measurement system. [Figure 4A] FIG. 1 shows the illumination pupil of the optical production system (left) and the projection optical unit exit pupil (right) simulated by a metrology system for optical properties. [Figure 4B] FIG. 4B shows the sigma pupil stop shape (left) and the NA aperture stop shape (right) of the optical measurement system for simulating the pupil configuration according to FIG. 4A found in connection with the stop shape optimization method. [Figure 5] FIG. 10 shows a detail of the pupil stop shape of an illumination optical unit of an optical measurement system for determining how to inspect at least one manufacturing boundary condition, illustrating an acceptable path for a peripheral inspection portion of the stop shape that satisfies the manufacturing boundary condition. [Figure 6] 6 is a diagram similar to FIG. 5, showing an example of an inspection portion of a draw shape that does not satisfy the manufacturing boundary conditions. FIG. [Figure 7] 1 is a flow diagram of a method for optimizing a pupil stop shape to simulate the illumination and imaging characteristics of an optical production system during illumination and imaging of an object by an optical measurement system. [Figure 8] FIG. 10 shows an example of a target aperture shape resulting during the optimization method, shown in pupil coordinates (angular space). [Figure 9] 9 shows a broken detail from a manufactured metal sheet having a target drawing shape based on the angular space results from FIG. 8, showing additional alignment marking openings. DETAILED DESCRIPTION OF THE INVENTION

[0027] For ease of presentation of positional relationships, a Cartesian xyz coordinate system is used below. In Figure 1, the x-axis extends out of the drawing, perpendicular to the plane of the drawing. The y-axis extends to the right in Figure 1. The z-axis extends upward in Figure 1.

[0028] In a view corresponding to a meridional section, Figure 1 shows the illumination and imaging properties of an imaging optical generation system when an object is illuminated with illumination light 1, in particular the beam path of EUV illumination light or imaging light 1 in a metrology system 2 for simulating a target wavefront. In the imaging optical unit of the optical measurement system of the metrology system 2, a test structure 5 in the form of a reticle or lithography mask (see Figure 2) arranged in an object field 3 in an object plane 4 is imaged using the EUV illumination light 1. In the following, the test structure 5 is also referred to as object or sample.

[0029] The metrology system 2 is used to analyze a three-dimensional (3D) aerial image (aerial image metrology system). Applications include simulating the aerial image of a lithography mask as it would appear in a production projection exposure apparatus, e.g., a scanner. Such metrology systems are known from WO 2016 / 012 426, U.S. Patent Application Publication No. 2013 / 0063716 (see FIG. 3 therein), DE 102 20 815 (see FIG. 9 therein), DE 102 20 816 (see FIG. 2 therein), and U.S. Patent Application Publication No. 2013 / 0083321.

[0030] The illumination light 1 is reflected by the object 5. The plane of incidence of the illumination light 1 is parallel to the yz plane.

[0031] The EUV illumination light 1 is generated by an EUV light source 6. The light source 6 can be a laser plasma source (LPP; laser-produced plasma) or a discharge source (DPP; discharge-produced plasma). In principle, it is also possible to use a synchrotron-based light source, for example a free electron laser (FEL). The operating wavelength of the EUV light source can be in the range between 5 nm and 30 nm. In principle, in one variant of the measurement system 2, it is also possible to use a light source with a different operating wavelength of light, for example a light source with an operating wavelength of 193 nm, instead of the light source 6.

[0032] Depending on the embodiment of the measurement system 2, the latter may be used for reflective or otherwise transparent objects 5. One example of a transparent object is a pinhole diaphragm.

[0033] An illumination optical unit 7 of the measurement system 2 is arranged between the light source 6 and the object 5. The illumination optical unit 7 serves to illuminate the object 5 to be inspected with a defined illumination intensity distribution across the object field 3 and at the same time with a defined illumination angle distribution, in which field points of the object field 3 are illuminated. This illumination angle distribution is also referred to hereinafter as illumination aperture or illumination setting.

[0034] The illumination aperture is delimited by a sigma aperture stop 8 of the illumination optical unit 7, which is arranged in the illumination optical unit pupil plane 9 and predefines the illumination pupil therein. The sigma aperture stop 8 is hereinafter also referred to as a sigma stop. The sigma aperture stop 8 defines the peripheral boundary of the beam of illumination light 1 incident thereon. Alternatively or additionally, the sigma aperture stop 8 and / or the stop of the imaging optical unit can also block the illumination light beam from the inside, i.e., function as an obscuration stop. The corresponding stop can have an inner stop body, which accordingly blocks the inner beam, connected to the outer stop support by several ribs, for example four ribs.

[0035] Figure 2 shows one embodiment of the sigma stop 8 in a plan view from the viewing direction II in Figure 1. The coordinate σ shown in Figure 2 x , σ y spreads in the illumination optical unit pupil plane 9 in the angle space and corresponds to the coordinates x and y in FIG. 1. The sigma illumination diaphragm 8 has four support bones 81 to 84, which are attached to the peripheral diaphragm support 8 T and inner occlusion shading body 8 O Extending like spokes between the inner shading body 8 O Supports the bone support part 8 i and Career 8 T and inner occlusion shading body 8 O Between the Sigma aperture 8, σ x / σ y Four openings corresponding to the four quadrants of the coordinate system8 I , 8 II , 8 III , and 8 IV The obscured illumination of the measurement system is predefined by the sigma diaphragm 8 according to FIG.

[0036] The sigma aperture diaphragm 8 can be displaced in a defined manner in the illumination optical unit pupil plane 9, i.e. parallel to the xy-plane, by means of a displacement drive 8a. The diaphragm displacement drive 8a is an actuator for predefining the illumination settings when illuminating the object 5.

[0037] In addition to the displacement drive 8a, the measurement system 2 has an exchange holder 8b, by means of which it is possible to exchange the respective sigma diaphragm 8 with a replacement sigma diaphragm 8'. The exchange holder 8b makes it possible to transfer the currently used sigma diaphragm 8 to the diaphragm magazine, select a replacement sigma diaphragm from the diaphragm magazine, and transfer this selected sigma diaphragm to the place of the current sigma diaphragm in the pupil plane 9 of the illumination optical unit.

[0038] After reflecting off the object 5, the illumination or imaging light 1 enters the imaging or projection optical unit 10 of the optical measurement system of the metrology system 2. Similar to the illumination aperture, there is a projection optical unit aperture predefined by a NA aperture stop 11 in the entrance pupil 12 of the projection optical unit 10 in FIG.

[0039] The entrance pupil 12 is optically conjugate to the illumination pupil of the illumination optical unit 7 .

[0040] FIG. 3 is a view similar to FIG. 2, again showing a plan view of the NA aperture stop 11.

[0041] The support members 111, 112, 113, and 114 are provided to support the aperture support of the NA aperture diaphragm 11 and the central obscuration shielding body 11 of the NA aperture diaphragm 11. O Connect to the occlusion shielding body 11 O simulates the central obscuration of the imaging optical unit of the optical production system to be simulated.

[0042] The aperture material of the apertures 8, 11 may be metal.

[0043] The entrance pupil 12 is an example of a projection optical unit pupil plane of the projection optical unit 10. The NA aperture stop 11 may also be arranged at the exit pupil of the projection optical unit 10. The NA aperture stop 11 is displaceable in a defined manner within the projection optical unit pupil plane 12, i.e. parallel to the xy plane, by a displacement drive 13. The displacement drive 13 is also an actuator for predefining the illumination settings.

[0044] Typically, the sigma aperture stop 8 and the NA aperture stop 11 are aligned relative to each other so that the central ray of the illumination light 1 and its reflection from the test structure 5 hits both stops centrally. The sigma aperture stop 8 and the NA aperture stop 11 may be centered relative to each other.

[0045] The imaging optical unit 10 to be measured serves to image the object 5 towards a spatially resolved detection device 14 of the measurement system 2. The detection device 14 is designed, for example, as a CCD detector. A CMOS detector can also be used. The detection device 14 is arranged in an image plane 15 of the projection optical unit 10.

[0046] The detection device 14 is signal-connected to a digital image processing device 17 .

[0047] The pixel spatial resolution of the detection device 14 in the xy plane is determined by the numerical aperture (NA) of the entrance pupil 12 to be measured in the coordinate directions x and y. x , N.A. y ) can be predefined to be inversely proportional to the pixel spatial resolution, which is regularly λ / 2NA in the x-coordinate direction. x is smaller than λ / 2NA and is regularly y where λ is the wavelength of the illumination light 1. The pixel spatial resolution of the detection device 14 is also smaller than NA x , N.A. y Regardless, it can be implemented using square pixel dimensions.

[0048] The spatial resolution of the detection device 14 can be increased or decreased by resampling. Detection devices with pixels having different dimensions in the x and y directions are also possible.

[0049] The object 5 is carried by an object holder or holder 18. The holder 18 can be displaced, on the one hand parallel to the xy-plane and, on the other hand, perpendicular to this plane, i.e., in the z-direction, by means of a displacement drive or actuator 19. The displacement drive 19, like the overall operation of the measurement system 2, is controlled by a central control device 20, which is signal-connected to the components to be controlled in a manner not further specified.

[0050] The optical setup of the metrology system 2 serves for the most accurate possible simulation or emulation of illumination and imaging in the course of projection exposure of an object 5 during projection lithography manufacturing of semiconductor components. The optical measurement system of the metrology system 2 serves to simulate the illumination and imaging properties, in particular the target wavefront, of the imaging optical generation system of the projection exposure apparatus used in this case.

[0051] 1 shows, in each case using dashed lines, various possible arrangement planes of the test structure 5 in the region of the object plane 4. During operation of the measurement system 2, the test structure 5 is measured at different distance positions z m , each sub-aperture 10i is illuminated with a predefined illumination angle distribution, and the intensity I(x, y, z m ) are the distances z m The measurement result I(x, y, z m ) is also called the aerial image.

[0052] focal plane z m The number of λ can be between 2 and 20, for example between 10 and 15. In this case, the number of Rayleigh units (NA / λ) 2 ) for the total displacement in the z direction.

[0053] 1 also schematically shows an exit pupil 21 of the projection optical unit 13. The entrance pupil 12 and the exit pupil 21 of the imaging optical unit 10 are both elliptical. Alternatively, the two pupils 12, 21 may have circular boundaries.

[0054] The imaging optical units 10 of the metrology system 2 are of identical construction, ie have the same imaging scale in the x and y directions.

[0055] 1 shows at the bottom three measurement results of the detection device 14, again in an xy-plane view, the central measurement result showing an image representation of the test structure 5 when placed in the object plane 4, and the other two measurement results showing image representations in which the test structure 5 is displaced once in the positive z direction and once in the negative z direction compared to the z coordinate of the object plane 4. The spatial image of the test structure 5 results from the totality of the measurement results assigned to each z coordinate.

[0056] The pupil stop shape of the sigma illumination stop 8 is optimized in connection with a simulation of the illumination and imaging characteristics of the optical generation system during illumination and imaging of the object 5 by the optical measurement system of the metrology system 2. Part of this optimization method is to determine the match quality between the illumination and imaging characteristics of one optical generation system and the illumination and imaging characteristics of the optical measurement system of the other metrology system 2 using a particular stop shape of the sigma stop 8. The value of at least one merit function is calculated in connection with determining this match quality. The merit function is influenced by a comparison of optical illumination and imaging parameters between a pupil overlap region of the illumination pupil and the imaging pupil of one optical generation system and a corresponding pupil overlap region of the illumination pupil with the used stop shape of the sigma stop 8 and the imaging pupil with the used NA aperture stop 11 of the optical measurement system.

[0057] FIG. 4 illustrates such a pupil overlap area A between the illumination pupil, which may be the entrance pupil 12, and the imaging pupil, which may be the exit pupil 21. r,φ Shows.

[0058] Center Z of Exit Pupil 21 Ar,φ are Cartesian coordinates

number

number

[0059] Such pupil overlap area A r,φ In connection with determining the alignment quality with the aid of

number

number

[0060]

number

[0061] With regard to the definition of the parameter CD, reference is made to US Pat. No. 9,176,390.

[0062] The T term (according to equation (2)) represents the integral over the overlap region A, said integral being again weighted by the distance value σφ. In this formulation of the T term, for simplicity, it is assumed that there is no apodization in the exit pupils 11 or 21, respectively. This T term correlates to the imaging parameter imaging telecentricity, which can include the sensitivity of offset object structures as a function of the defocus position of the substrate on which the object is imaged.

[0063] For a given pupil stop shape of the sigma stop 8, all possible overlap areas A r,φWhen determining the match quality of the following optimization rules are applied:

number

[0064] The optimization rules according to equations (3) and (4) are usually not achieved. When determining the matching quality, the aperture shape of the candidate design dc is varied until the optimization rules (3) and (4) yield a minimum.

[0065] In addition to the optimization variables D and T, further variables that correlate with additional illumination and / or imaging parameters may also be used in determining the match quality. One example of such a variable is:

number

[0066] To determine the HV term according to the above equation (5), the coordinate origin Z B Two defined overlapping regions A that are rotated 90° relative to each other around r,φ and Br,φ (see FIG. 4) To calculate the integral of the overlap region B, the overlap between, for example, the entrance pupil 12 and the correspondingly rotated exit pupil 21′ by 90° is taken into account.

[0067] Then, there is a corresponding optimization provision for the HV term.

number

[0068] 4A and 4B show two pupil pairs of the optical generation system (FIG. 4A) on the one hand and the optical measurement system of the metrology system 2 (FIG. 4B) on the other hand, which are compared with each other in the context of the alignment quality determination described above, particularly in relation to FIG. 4.

[0069] Figure 4A shows, on the left, the illumination of the illumination pupil for an x-dipole illumination setup, and, on the right, the exit pupil of a projection optical unit of an optical projection system with a central, approximately elliptical pupil obscuration.

[0070] The illumination setting of the optical generation system to be simulated (see the left side of FIG. 4A) can consist of a number of individual spots in the illumination pupil, corresponding to the faceted configuration of the illumination optical unit of the optical generation system, for example, a configuration with field facet mirrors and pupil facet mirrors, or a configuration in which a MEMS mirror configuration is used in the illumination optical unit. The size of each individual spot on the left side of FIG. 4A is a measure of the brightness of this individual spot, i.e., the illumination intensity from the illumination direction assigned to this individual spot.

[0071] Figure 4B shows on the left the target aperture shape (obtained by the optimization method) of the sigma diaphragm 8 for the simulation of the illumination and imaging characteristics of an optical production system with the illumination setting and exit pupil according to Figure 4A. On the right, Figure 4B shows the exit pupil of the imaging optical unit of the optical measurement system with the central obscuration created by the NA diaphragm 11 (see also Figure 3).

[0072] The method for optimizing the pupil stop shape of the sigma stop 8 includes testing at least one manufacturing boundary condition for each candidate design of the stop shape. One example of such testing of manufacturing boundary conditions is described in more detail below with reference to Figures 5 and 6.

[0073] Aperture shape design candidate 8 dc are considered and peripheral inspection areas 23, 24 are shown in Figures 5 and 6. The resolution of the manufacturing method is such that the individual pixels 25 of the diagrams according to Figures 5 and 6 i The individual pixels25 are shown in dark or hatched areas. i represents a possibly continuous aperture material that blocks illumination / imaging light 1, and each open individual pixel 25 i represents a possibly continuous iris opening (illumination / imaging light transmission).

[0074] Therefore, in relation to the inspection method, the aperture shape design candidate 8 dc The whole, also called the starting or modified aperture shape, is described as a regular bitmap with pixel discretization.

[0075] To define the roundness of each test portion 23, 24, i.e. its curvature, in a locally pixel-based manner, a surrounding area with a defined radius r is defined around each pixel 25 of the bitmap. i This is shown for pixels 251, 252 and 253 in Figures 5 and 6. Each surrounding pixel region 261, 262, 263 to be evaluated, highlighted with different hatching, is square and in each case includes five individual pixels 251, 252, 253 along both coordinates x and y. iThe central individual pixel to be considered, for example 251, and the surrounding pixel region, for example 261, are arranged in rows and columns.

[0076] The following provisions will be examined during the evaluation:

[0077] Each pixel region 26 around the individual pixel under consideration has an "aperture material" or "aperture opening" of an opposite state with respect to the central individual pixel under consideration. i Individual pixels within 25 i The sum of the rounded up numbers is (2r+1) 2 / 2 is less than.

[0078] Therefore, if r=2, this sum must be less than 13, because the comparison numbers are always integers, and (2r+1) 2 Unless / 2 yields an integer, it is rounded up to the next higher integer.

[0079] The corresponding evaluation shows that the individual pixels 251 have aperture material and there are nine individual pixels 251 in the pixel area 261 that represent aperture openings, so that the requirement "a number less than 13" is met, and correspondingly, it is also met for the individual pixels 252 (=aperture openings) (the number of individual pixels 251 in the pixel area 262 made of aperture material = 8, i.e. less than 13), so that the above requirement is met for the individual pixels 251 and 252.

[0080] This requirement is met by the fact that in individual pixels 253, each pixel 253 represents an aperture opening, and pixel area 263 contains a total of 16 individual pixels 253 representing aperture material. i is not satisfied because

[0081] Therefore, pixel area 26 i , i.e., each central individual pixel 25 iA check is made to see whether the surrounding area around the central region behaves with sufficient probability in exactly the same way as the central region with respect to the transmission of illumination light.

[0082] Thus, inspection of the manufacturing boundary conditions in this manner shows that it is possible to manufacture peripheral test portion 23 in the area of ​​individual pixels 251 and 252, but not peripheral test portion 24 in the area of ​​individual pixel 253. These manufacturing boundary conditions are applied to all individual pixels 251 and 252. i Then the above mentioned rules are applied to all individual pixels 25 i The locally formulated prescription for each test part 23, 24 results in a manufacturable aperture shape of the sigma aperture 8. dc This shows that the respective aperture shapes of the various aperture shapes vary only locally and therefore in each case only a corresponding small inspection portion of the overall aperture shape has to be inspected for manufacturability.

[0083] The minimum hole diameter and, for example, the minimum draw-in bone width can be predefined via the selection of the radius r.

[0084] When checking the manufacturing boundary conditions, it is also possible to take into account oblique illumination of the sigma diaphragm, in which case the elliptical shape of the sigma diaphragm 8 results in, for example, a circular entrance pupil 12. In this regard, in the case of the bitmap representations from FIGS. 5 and 6, the individual pixels 25 i The x and y ranges of can be chosen to be unequal to each other.

[0085] The field dependence of the object illumination of the optical generation system can be taken into account when determining the quality of the match between the illumination and imaging characteristics of the optical generation system on the one hand and the illumination and imaging characteristics of the optical measurement system of the metrology system 2 on the other hand. This then takes into account that in the optical generation system, an object point is affected by a different intensity distribution of the illumination light over the illumination angle compared to object points that are further away from it.

[0086] This consideration of field variations is due to the strong influence of the illumination intensity on the coordinates of the considered target pupil (the illumination pupil of the optical generation system). t ) can be achieved by replacing it with the target pupil field average value averaged over the entire object field 3. Alternatively, during the scanning of the optical generating optical system, it is possible to minimize the optimization rule according to the above equations (3), (4), and (6) for all field coordinates, in particular for all x field coordinates perpendicular to the object displacement direction y. Therefore, the pupil overlap area A r,φ,x A field-dependent boundary of .gt. may also occur.

[0087] An example of an overall method for optimizing the pupil stop shape of the sigma stop 8 to simulate the illumination and imaging characteristics of the optical generation system during illumination and imaging of the object 5 by the optical measurement system of the metrology system 2 is described below with reference to the flowchart of Figure 7.

[0088] In the predefined step 30, first, sigma stop 8, 8 dc The starting aperture shape of is selected as the initial design candidate for the simulation.

[0089] In the context of optimization, this starting aperture shape 8 dc is modified in a modification step 31, resulting in a modified aperture shape 8 that is slightly changed with respect to the boundary shape. dcnew occurs in the generation step 32.

[0090] In the inspection step 33, this corrected aperture shape 8 dcnew However, this modified aperture shape 8 dcnew 5 and 6. The inspection step allows the modified aperture shape 8 to be inspected to see whether it satisfies at least one manufacturing boundary condition for the manufacture of the modified aperture shape 8. dcnewIf at least one peripheral inspection portion 23, 24 of the drawing is shown not to satisfy the manufacturing boundary conditions (decision "N" in the inspection step 33), the modification step 31 and the generation step 32 are repeated. This is done for the next given modified drawing shape 8 dcnew This is done until the test step 33 indicates compliance with the predefined manufacturing boundary conditions (verdict "Y" in test step 33).

[0091] The determining step 34 then involves determining the match quality between the illumination and imaging characteristics of the optical generation system and the illumination and imaging characteristics of the optical measurement system, with the aid of the match quality determination explained above, in particular with reference to Figure 4 and equations (1)-(6).

[0092] In general, since the match specifications according to equations (3), (4), and (6) do not all simultaneously equal zero, a merit function E can be used during the match quality determination. This merit function can be written in the usual way as a weighted error minimization as follows:

[0093]

number

[0094] The merit function E is, in addition, sigma stop 8 dcnew This can be extended by the minimum transmittance requirement of

[0095] In addition to the target illumination pupil of the optical production system, determining step 34 may also be influenced by the pupil transfer function of the optical production system and the pupil transfer function of the optical measurement system of metrology system 2 .

[0096] To this end, the D term defined above in relation to equation (1) can be written as follows:

number

[0097] The apodization of the exit pupil 11 or 21, respectively, can then be taken into account by this means.

[0098] During the decision step 34, the fit to an optimization criterion is queried in an optimization query step 35. One example of such an optimization criterion is the Boltzmann criterion of simulated annealing.

number

[0099] As long as the Boltzmann criterion is satisfied, i.e., the optimization has not yet terminated (determination Y in query step 35), the current aperture shape 8 dcnew is the initial drawing shape 8 for the next modification to be performed in the pre-definition step 36 dcThe control parameter β is also increased in a predefining step 36. In this way, the optimization criterion is strengthened in relation to the predefining step 36. The method then continues to a modification step 31, where steps 32 to 35 are repeated until the optimization query step 35 indicates that the Boltzmann criterion is no longer satisfied or the control parameter β is greater than the predefined value (query result N in query step 35).

[0100] Therefore, if the optimization criterion is then achieved in the optimization query step 35 (query result N), a sigma aperture 8 having the target aperture shape that resulted in the minimum merit function value E in the optimization is manufactured in the manufacturing step 37.

[0101] Such a target aperture shape 38 in pupil coordinates of the pupil plane 9 is shown in the top left of FIG.

[0102] The resulting actual aperture contour of the sigma aperture 8 is shown in the bottom right of Figure 9. For example, the aperture opening boundary 39 of the sigma aperture 8, which can be used to simulate a dipole illumination setup of an optical production system, has a freeform configuration that is only vaguely reminiscent of the actual dipole shape of the illumination setup to be simulated.

[0103] In addition, FIG. 9 also shows a further diaphragm opening 40 which is an alignment aid for positioning the sigma diaphragm 8 in the pupil plane 9 .

[0104] Next, after correctly aligning and inserting the manufactured sigma aperture 8 into the optical measurement system using the target aperture shape, the metrology system 2 is then able to measure the object or test structure 5 under illumination and imaging conditions that optimally model the illumination and imaging conditions of the optical generation system.

Claims

1. 1. A method for optimizing a pupil diaphragm shape (39) for simulating illumination and imaging properties of an optical production system during illumination and imaging of an object (5) by an optical measurement system, comprising: the optical measurement system comprises an illumination optical unit (7) for the object (5) with a pupil stop (8) in the region of an illumination pupil with the pupil stop shape (39) to be optimized, and an imaging optical unit (10) for imaging the object (5), a starting diaphragm shape (8) of the pupil diaphragm (8) as an initial design candidate for simulating the illumination and imaging properties of the optical production system; dc ) (30) predefining - The most recent predefined aperture shape (8 dc ) different modified aperture shape (8 dcnew ) to generate the initial drawing shape (8 dc ) (31); - the modified aperture shape (8 dcnew checking (33) at least one manufacturing boundary condition for the manufacturing of the product (i.e., the product of the product), and repeating the "modifying" and "checking" steps until the checking (33) step indicates compliance with the manufacturing boundary condition; - determining (34) the quality of the match between the illumination and imaging characteristics of the optical generation system and the illumination and imaging characteristics of the optical measurement system once the manufacturing boundary conditions have been met; repeating the "correcting", "checking" and "determining" steps until the quality of the match reaches a predefined optimization criterion that is checked by a query step (35); - after achieving said optimization criterion, producing (37) as optimized pupil diaphragm shape (39) the target diaphragm shape resulting from the achievement of said optimization criterion; A method comprising:

2. During the step of checking (33) the manufacturing boundary conditions of the peripheral test portions (23, 24) of the pupil stop shape, the conformity to local boundary conditions is checked, in which case the central region (25) 1 , 25 2 , 25 3 ) around the peripheral area (26) of each of said peripheral inspection portions. i ) in terms of the transmission of the illumination light (1), 1 ~25 3 ) and each of the surrounding areas (26 i ) a predefined percentage of said central region (25 1 ~25 3 2. The method of claim 1, wherein the local boundary condition is satisfied when the local boundary condition behaves exactly like

3. The central region (25 1 ~25 3 ) and the surrounding area (26 i 3. The method of claim 2, wherein the pixels are arranged as rows and columns of pixels.

4. 2. The method according to claim 1, characterized in that the step of determining (34) the quality of the alignment is affected by checking the alignment between the illumination and / or imaging pupil of the optical generation system and the illumination and / or imaging pupil of the optical measurement system.

5. A method as described in claim 2, characterized in that the step of determining (34) the alignment quality is affected by checking the alignment between the illumination and / or imaging pupil of the optical generation system and the illumination and / or imaging pupil (12, 21, 21') of the optical measurement system.

6. determining (34) the quality of the match by the pupil overlap area (A) of the illumination pupil and the imaging exit pupil of said optical production system r,φ )and, the illumination pupil (12) with the stop shape used and the corresponding pupil overlap area (A) of the imaging aperture (11) for predefining the imaging exit pupil (21, 21') of the optical measurement system; r,φ )and The value of the merit function (E) affected by the comparison of the optical illumination and imaging parameters (D, T, HV) between a plurality of pupil overlap regions (A) each covering the entire illumination pupil is calculated. r,φ 6. The method of claim 5, wherein the method is performed by calculating:

7. below - the pupil overlap region (A r,φ ) the integrated intensity (I) (D) of the illumination light (1) passing through the illumination pupil at - the pupil overlap region (A r,φ The telecentricity parameter (σ) of the illumination light (1) passing through the illumination pupil at φ ) weighted integral intensity (I)(T) 7. The method of claim 6, wherein is used as the optical illumination and imaging parameter.

8. As soon as said predefined optimization criterion is achieved, the optimization routine continues as follows: - strengthening (36) said optimization criterion; - performing the "correcting", "checking" and "determining" steps again until the match quality reaches the enhanced optimization criterion; repeating said "enhance" and "run again" steps until a termination criterion checked in said query step (35) is achieved; 3. The method according to claim 1 or 2, characterized in that:

9. 3. The method according to claim 1, wherein the dependence of the distribution of the illumination angle of the illumination of the object (5) over the illuminated object field (3) is taken into account when determining the matching quality.

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