A method for optimizing the pupil aperture shape to simulate the illumination and imaging properties of an optical generation system during illumination and imaging of an object by an optical measurement system

Abstract

To simulate the properties of an optical generation system, an optical measurement system is used that includes an illumination optical unit for an object to be imaged and an imaging optical unit for imaging the object, having a pupil aperture in the region of the illumination pupil. To optimize the pupil aperture shape of the pupil aperture, first, a starting pupil aperture shape of the pupil aperture is predefined as an initial design candidate for the simulation (30). The starting pupil aperture shape is modified (31), and at least one manufacturing boundary condition of the corresponding modified pupil aperture shape is checked (33). The "modifying" step and the "checking" step are repeated until the check (33) reveals a conformity to the boundary condition. The matching quality between the properties of the optical generation system and the properties of the optical measurement system is determined (34), and the "modifying" step, the "checking" step, and the "determining" step are repeated until the matching quality achieves a predefined optimization criterion—the benefit is inquired about (35). The target aperture shape obtained from the target aperture shape generated with the minimum merit function value (E) during optimization is manufactured as the optimized aperture shape after achieving the optimization criteria (37). This causes the optical measurement system to simulate the illumination and imaging properties of the optical generation system—without possible deviations—during the illumination and imaging of the object.

Description

Technology Field

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

[0002] The present invention relates to a method for optimizing a pupil aperture shape to simulate the illumination and imaging properties of an optical generation system during illumination and imaging of an object by an optical measurement system. Furthermore, the present invention relates to a pupil aperture optimized by such a method and a measurement system comprising at least one such pupil aperture. Background Technology

[0003] A metrology system for measuring an aerial image of a lithography mask in three dimensions is known from WO 2016 / 012 425A2 and WO 2016 / 012 426A1. A corresponding metrology system and method for determining an aerial image of a lithography mask in three dimensions is known from DE 10 2019 206 651A1. DE 10 2013 219 524A1 describes an optical system and a device and method for determining the imaging quality of an optical system. DE 10 2013 219 524A1 describes a phase recovery method for determining a wavefront based on the imaging of a pinhole. DE 10 2017 210 164B4 describes a method for adjusting the imaging behavior of a projection lens and an adjustment device. A method for compensating for lens heating in a projection exposure device is known from US 9,746,784B2. In particular, an optical generation system having an anamorphic projection optical unit is known, for example, from US 2020 / 0272058A1. Further variations of the optical generation system are known from WO 2009 / 100 856A1. DE 10 2008 001 553A1 discloses a component for setting scan-integrated illumination energy in the object plane of a microlithography projection exposure device. EP 0 674 778B1 discloses a process and a device for generating a dosage pattern for the generation of a structured surface. DE 103 52 040A1 and WO 2005 / 045 503A1 disclose aperture and / or filter arrangements for optical devices, in particular microscopes.

[0004] With respect to the setup of its illumination optical unit and / or its imaging optical unit, a known measurement system is, in some cases, very different from the setup of the corresponding illumination and imaging optical components of the optical generation system to be simulated. This is, in fact, because the setup of the measurement system cannot be realized at the same cost in terms of design and energy as the setup of the optical generation system. The problem to be solved

[0005] Therefore, the object of the present invention is to provide a method for optimizing the pupil aperture shape by an optical measurement system of a measurement system for use in a measurement system that causes the simulation of the illumination and imaging properties of an optical generation system during illumination and imaging of an object—possibly without deviation—despite differences existing in the illumination and imaging optical components. means of solving the problem

[0006] This objective is achieved according to the present invention by an optimization method having the characteristics specified in claim 1.

[0007] According to the present invention, it has been recognized that, particularly due to mathematical or numerical modeling of the optical system, the influence of changes in the aperture shape of the pupil aperture on the illumination and imaging properties of the optical system can be quantitatively and entirely determined with such precision that aperture shape optimization is likely achieved by this means. The target aperture shape that causes the final manufacturing step process of the optimization method ensures the simulation of the illumination and imaging properties of the optical generation system during the illumination and imaging of the object by an optical measurement system having high precision. More complex illumination settings of the optical generation system and / or complex imaging properties of the optical generation system, such as anamorphic imaging of the projection optical unit of the optical generation system, may be considered and simulated during the determination of matching quality during the optimization method. For anamorphic imaging of the projection optical unit, refer to US 9,366,968B2. In particular, the illumination-side pupil obscuration of the optical measurement system required due to structural specifications may be considered, for example, during the optimization method. This illumination-side compression of the optical measurement system can be corrected or compensated by the target aperture shape. The influence of the necessary webs required for the mechanical configuration of the pupil aperture of the optical measurement system can be further considered. Specifications regarding the self-supporting configuration of the aperture shape, minimum aperture web width, minimum aperture hole diameter, and maximum curvature of the aperture edge can be considered when checking manufacturing boundary conditions. This avoids situations where there is an optimization solution that cannot be manufactured. The specific center compression of the exit pupil of the imaging optical unit of the optical generation system—which often occurs in optical generation systems—can even be considered in the context of the optimization method. In this case, the center compression of the exit pupil of the optical generation system can be considered by the center aperture of the NA aperture in the imaging optical unit of the measurement system.On the one hand, different imaging output pupil apodizations between the optical generation system and the optical measurement system can be considered.

[0008] The optimization method can be implemented to specifically consider the structural configuration of the object to be imaged. Optical properties that vary with respect to different structures can be taken into account accordingly.

[0009] The difference between the configuration of the illumination pupil of an optical generating system that is regularly composed of multiple individual apertures and the illumination pupil of an optical measuring system that has a regularly continuously illuminated area can be likewise considered.

[0010] Alternatively, the optimization method can also function so 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 excellent quality.

[0011] It has been proven that the inspection method for checking compliance with manufacturing boundary conditions according to claim 2 is actually valuable. Requirements regarding manufacturing quality can be predetermined by predetermining the size of the surrounding area to be inspected. This advantage avoids situations in which an excessively narrow web or excessively large curvature of the aperture edge occurs along each inspection section, that is, along the entire aperture edge of the target aperture shape after inspection.

[0012] It has been proven that the pixel-by-pixel arrangement of pixels in the surrounding area being inspected during the inspection of manufacturing boundary conditions according to claim 3 is actually valuable. The size of the pixels can be selected according to the achievable manufacturing resolution.

[0013] Instead of pixel-based checks of manufacturing boundary conditions for pupil aperture shape, polygonal boundaries can be used as desired boundary shapes; in such cases, curvature estimation (rounding radius of aperture shape) can be derived from the angles of polygonal line segments adjacent to each other.

[0014] It has been proven that considering pupil matching between an optical generating system on the one hand and an optical measuring system on the other, according to claim 4, is valuable for ensuring sufficient matching quality determination. Information of each illumination pupil and / or each imaging pupil may be used depending on the boundary conditions of the optical system involved herein.

[0015] Calculation of the merit function value according to claim 5 simplifies the numerical modeling of the matching quality determination in an optimization method environment. The size of the pupil overlap region may vary in the determination environment. This advantage may be achieved depending on the selected boundary conditions of the accompanying optical system. The degree of matching quality required may be finely influenced by predefining the size of the pupil overlap region used when determining the matching quality, as well as its number and distribution over the illuminated pupil. Such predefinition may be influenced particularly by the illumination and imaging properties of the optical generation system being simulated.

[0016] Instead of a superposition-based merit function, matching quality can also be realized by direct imaging simulations of a large number of test images considered. In such a direct imaging simulation environment, deviations of corresponding imaging parameters, particularly the critical dimension (CD) or imaging telecentrity, can be evaluated directly, and 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 because they fit well with the typical imaging properties or imaging aberrations of the optical system they entail. Additional illumination and imaging parameters, such as parameters that compare possible structural resolutions (critical dimensions (CD)) along two mutually perpendicular coordinates, may also be used. An example of such a parameter is the so-called HV (Horizontal / Vertical) asymmetry. Parameters that predefine a lower limit for pupil transmission may also be used in the matching quality determination environment.

[0018] Optimization methods known through the optimization loop according to claim 7 may be used. An example of this is simulated annealing. Other optimization methods known in the technical literature may also be used. Total computation time or other quality of compliance with optimization criteria may also be selected as termination criteria.

[0019] Considering the field dependency of object illumination according to claim 8 improves the simulation of illumination and imaging properties of an optical generation system. Field dependency can be considered by averaging the pupils of the optical generation system over each field and / or by determining the matching quality in the environment of the optimization method for all field points or for a selected field point region.

[0020] The advantages of the pupil aperture according to claim 9 correspond to those previously described with reference to the optimization method according to the present invention.

[0021] In the case of a freeform pupil aperture according to claim 10, this provides many corresponding design degrees of freedom for simulating the optical properties of the generation system. A freeform pupil aperture is a pupil aperture having aperture boundaries that do not have distinct symmetry axes and / or symmetry planes. Even, multifold rotational symmetry does not exist in the case of a freeform pupil aperture.

[0022] The advantages of the measurement system according to claim 11 correspond to those previously described with reference to the optimization method and the pupil aperture optimized thereby.

[0023] Due to the exchange holder according to claim 12, different pupil apertures can be used in the optical measurement system of the measurement system.

[0024] A measurement system having a correspondingly optimized pupil aperture has been proven to be particularly valuable when used according to claim 13. Different imaging scales of the projection optical unit of the optical generating system in mutually perpendicular directions can be considered in the environment of the manufacturing stage due to different scaling in these two directions.

[0025] Exemplary embodiments of the present invention will be described in more detail below with reference to the drawings. Brief explanation of the drawing

[0026] FIG. 1 illustrates a highly schematic plan view in the field of view perpendicular to the incident plane of a measurement system for simulating the target wavefront of an imaging optical generation system when an object is illuminated by an illumination light, the measurement system comprising an optical measurement system having an illumination optical unit for illuminating an object and an imaging optical unit for imaging an object, wherein the illumination optical unit and the imaging optical unit are each shown in a highly schematic manner. Figure 2 shows a plan view of a sigma aperture for placement in the pupil plane of an illumination optical unit of a measurement system. FIG. 3 illustrates a plan view of an NA aperture to be placed in the pupil plane of an imaging optical unit of an optical measurement system of a measurement system, in an example similar to FIG. 2. FIG. 4 schematically illustrates the instantaneous overlap between the pupil of the imaging optical unit and the illumination pupil of an optical system including an illumination optical unit and an imaging optical unit, in order to explain a method for optimizing the matching quality between the illumination and imaging properties of an optical generation system and an optical measurement system. FIG. 4a illustrates the illumination pupil (left) and projection optical unit emission pupil (right) of an optical generation system that are simulated for their optical properties by a measurement system. FIG. 4b illustrates the sigma pupil aperture shape (left) and NA aperture aperture shape (right) of the optical measurement system of the measurement system for simulating the pupil configuration according to FIG. 4a confirmed in the aperture shape optimization method environment. FIG. 5 illustrates details of the aperture shape of the pupil of an illumination optical unit of an optical measurement system for explaining a method for checking at least one manufacturing boundary condition, and illustrates an acceptable course of the edge inspection part of the aperture shape that satisfies the manufacturing boundary condition. FIG. 6 illustrates an example of an inspection part of an aperture shape that does not satisfy manufacturing boundary conditions in an example similar to FIG. 5. Figure 7 illustrates a flowchart of a method for optimizing the pupil aperture shape by an optical measurement system to simulate the illumination and imaging properties of an optical generation system during illumination and imaging of an object. FIG. 8 illustrates an example of a target aperture shape generated during an optimization method, represented in pupil coordinates (angle space). FIG. 9 illustrates a suspended detail from a manufactured metal sheet having a target aperture shape based on the angular space result according to FIG. 8, and an additional alignment indication opening is illustrated. Specific details for implementing the invention

[0027] To facilitate the presentation of positional relationships, an orthogonal xyz-coordinate system is used thereafter. In FIG. 1, the x-axis runs perpendicular to the plane of the drawing and extends outward from this plane. The y-axis runs toward the right side of FIG. 1. In FIG. 1, the z-axis runs upward.

[0028] In the drawing corresponding to the meridional section, FIG. 1 illustrates the beam path of the EUV illumination light or imaging light (1) in the measurement system (2) for simulating the illumination and imaging properties of the imaging optical generation system, in particular the target wavefront, when an object is illuminated by the illumination light (1). In the imaging optical unit of the optical measurement system of the measurement system (2), a test structure (5) in the form of a reticle or lithography mask (compare FIG. 2) placed in the object field (3) on the object plane (4) is imaged using the EUV illumination light (1). Hereinafter, the test structure (5) is also referred to as an object or sample.

[0029] A measurement system (2) is used to analyze a three-dimensional (3D) aerial image (aerial image measurement system). The application includes a simulation of an aerial image of a lithography mask in such a way that the aerial image also appears in a generated projection exposure device, such as a scanner. Such a measurement system is known from WO 2016 / 012 426A1, from US 2013 / 0063716A1 (compare with FIG. 3), from DE 102 20 815A1 (compare with FIG. 9), from DE 102 20 816A1 (compare with FIG. 2), and from US 2013 / 0083321A1.

[0030] The illumination light (1) is reflected from the object (5). The incident plane of the illumination light (1) is parallel to the yz-plane.

[0031] EUV illumination light (1) is generated by an EUV light source (6). This light source (6) may be a laser-produced plasma (LPP) source or a discharge-produced plasma (DPP) source. In principle, a synchrotron-based light source, such as a free electron laser (FEL), may also be used. The wavelength of use of the EUV light source may be in the range between 5 nm and 30 nm. In principle, in one variation of the measurement system (2), a light source for a different wavelength of light, such as a light source for a wavelength of 193 nm, may also be used instead of the light source (6).

[0032] Depending on an embodiment of the measurement system (2), the measurement system (2) may be used for a reflective or other transmissive object (5). An example of a transmissive object is a pinhole aperture.

[0033] An illumination optical unit (7) of the measurement system (2) is positioned between the light source (6) and the object (5). The illumination optical unit (7) is responsible for illuminating the object (5) to be inspected with a defined illumination intensity distribution over the object field (3) and, at the same time, a defined illumination angle distribution in which a field point of the object field (3) is illuminated. This illumination angle distribution is also referred to as an illumination aperture or illumination setting.

[0034] The illumination aperture is delimited by the sigma aperture aperture (8) of the illumination optical unit (7), which is positioned on the illumination optical unit pupil plane (9) to pre-define the illumination pupil therefrom. The sigma aperture aperture (8) is also referred to as the sigma aperture hereafter. The sigma aperture aperture (8) marginally delimits the beam of illumination light (1) incident thereon. Alternatively or additionally, the sigma aperture aperture (8) and / or the aperture of the imaging optical unit may also shadow the illumination light beam from within. That is, it may operate as an apscuration aperture. The corresponding aperture may have an inner aperture body that shadows the inner beam accordingly, and this aperture body is connected to an outer aperture support body by a plurality of webs, for example, by four webs.

[0035] FIG. 2 illustrates an embodiment of a sigma aperture (8) as a plan view from the viewing direction (II) of FIG. 1. The coordinates (σ) exemplified in FIG. 2 x , σ y ) extends across the illumination optical unit pupil plane (9) in angular space and corresponds to the coordinates (x and y) of FIG. 1. The sigma illumination aperture (8) has four webs (81 to 84), and these webs are edge aperture supports (8 T ) and internal compression shielding body (8 O Extended in a spoke manner between ) supports this compression shielding body. Web (8 i ), carrier(8 T ) and internal compression shielding body (8 O Between ), the sigma aperture (8) is σ x / σ y - 4 openings corresponding to the 4 quadrants of the coordinate system (8 I , 8 II , 8 III and 8 IVIt has ). The abscured illumination of the measurement system is predetermined by the sigma aperture (8) according to FIG. 2.

[0036] The sigma aperture aperture (8) can be displaced by a displacement drive (8a) in a predetermined manner in the illumination optical unit pupil plane (9), that is, parallel to the xy-plane. The aperture displacement drive (8a) is an actuator for predetermining the illumination settings when illuminating an object (5).

[0037] In addition to the displacement drive unit (8a), the measurement system (2) has an exchange holder (8b), and by this exchange holder (8b), each sigma aperture (8) can be replaced with a replacement sigma aperture (8'). In each case, the exchange holder (8b) can transfer the sigma aperture (8) currently in use to the aperture magazine and select a replacement sigma aperture from the aperture magazine and transfer the selected sigma aperture to the position of the current sigma aperture on the illumination optical unit pupil plane (9).

[0038] After reflection from the object (5), the illumination or imaging light (1) is incident on the imaging optical unit or projection optical unit (10) of the optical measurement system (2). In a manner similar to the illumination aperture, there is a projection optical unit aperture predetermined by the NA aperture aperture (11) at the incident pupil (12) of the projection optical unit (10) of FIG. 1.

[0039] The incident pupil (12) is optically paired with respect to the illumination pupil of the illumination optical unit (7).

[0040] FIG. 3 once again illustrates a plan view of the NA aperture aperture (11) as an example similar to FIG. 2.

[0041] The web (111, 112, 113, 114) is an aperture support of the NA aperture (11) and a center compression shielding body (11) of the NA aperture (11) O Connect to ). Abscuration shielding body (11O ) simulates the central compression of the imaging optical unit of the optical generation system to be simulated.

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

[0043] The incident pupil (12) is an example of the projection optical unit pupil plane of the projection optical unit (10). The NA aperture aperture (11) may also be placed at the exit pupil of the projection optical unit (10). The NA aperture aperture (11) may be displaced by a displacement drive (13) in a defined manner from the projection optical unit pupil plane (12), that is, parallel to the xy-plane. The displacement drive (13) is also an actuator for pre-defining the lighting settings.

[0044] Typically, the sigma aperture (8) and the NA aperture (11) are aligned with respect to each other so that the two apertures collide at the center with the center ray of the illumination light (1) and reflect off the test structure (5). The sigma aperture (8) and the NA aperture (11) can be centered with respect to each other.

[0045] The imaging optical unit (10) to be measured serves to image the object (5) toward the spatially resolving detection device (14) of the measurement system (2). The detection device (14) is designed, for example, as a CCD detector. A CMOS detector may also be used. The detection device (14) is placed on the image plane (15) of the projection optical unit (10).

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

[0047] The pixel space resolution of the detection device (14) in the xy-plane is the numerical aperture (NA) of the incident pupil (12) to be measured in the coordinate directions (x and y). x , NA yIt can be predetermined to be inversely proportional to ). In the x-coordinate direction, this pixel-space resolution is regularly λ / 2NA x It is less than, and in the y-coordinate direction, this is λ / 2NA y It is less than. In this case, λ is the wavelength of the illumination light (1). The pixel space resolution of the detection device (14) is also NA x , NA y It can be implemented as a squared pixel dimension independently of.

[0048] The spatial resolution of the detection device (14) can be increased or decreased by resampling. A detection device of pixels having different dimensions in the x- and y- directions is also possible.

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

[0050] The optical settings of the measurement system (2) serve to simulate or emulate the most accurate possible simulation of illumination and imaging during the projection exposure of an object (5) during the projection-lithographic manufacturing of a semiconductor component. The optical measurement system of the measurement system (2) serves to simulate the illumination and imaging properties of the imaging optical generation system of the projection exposure device used in this case, and in particular, the target wavefront.

[0051] FIG. 1 illustrates several possible placement planes of the test structure (5) in the area of ​​the object plane (4) using dotted lines in each case. During the operation of the measurement system (2), the test structure (5) is, sub-aperture (10 iDifferent distance positions (z) of the test structure (5) with respect to the object plane (4) using a lighting angle distribution each predetermined by ) m Illuminated in ), intensity (I(x, y, z m )) is each distance position (z m ) is recorded on an image plane (15) in a spatial resolution manner. This measurement result (I(x, y, z m )) is also called an aerial image.

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

[0053] In addition to the incident pupil (12), FIG. 1 also schematically shows the outgoing pupil (21) of the projection optical unit (13). Both the incident pupil (12) and the outgoing pupil (21) of the imaging optical unit (10) are elliptical. Alternatively, the two pupils (12, 21) may also have rounded boundaries.

[0054] The imaging optical unit (10) of the measurement system (2) is isomorphic, that is, it has the same imaging scale in the x- and y- directions.

[0055] FIG. 1 illustrates three measurement results of the detection device (14) once again in an xy-plane view from the bottom, with the central measurement result showing an image display of the test structure (5) when placed on the object plane (4), and the other two measurement results being displaced once in the positive z-direction and once in the negative z-direction compared to the z-direction of the object plane (4). The aerial image of the test structure (5) is generated from the total measurement results assigned to each z-coordinate.

[0056] In a simulation environment of the illumination and imaging properties of an optical generation system during illumination and imaging of an object (5) by the optical measurement system of the measurement system (2), the pupil aperture shape of the sigma illumination aperture (8) is optimized. As part of this optimization method, a matching quality is determined between the illumination and imaging properties of the optical generation system on one hand and the illumination and imaging properties of the optical measurement system of the measurement system (2) on the other hand, using a specific aperture shape of the sigma aperture (8). The value of at least one merit function is calculated in the environment of this matching quality determination. This merit function is influenced, on the one hand, by a comparison of optical illumination and imaging parameters between the pupil overlap area of ​​the illumination pupil and the imaging pupil of the optical generation system and the corresponding pupil overlap area of ​​the illumination pupil having the aperture shape of the sigma aperture (8) used by the optical measurement system.

[0057] FIG. 4 shows such a pupil overlap region between an illumination pupil (12), which may be an incident pupil (12), and an imaging pupil (21), which may be an exit pupil (21). ) city.

[0058] The center of the shooting pupil (21) ) is orthogonal coordinates( , It is located in ). Cartesian coordinates (σ x , σ y Instead of ), the polar coordinates exemplified in FIG. 4 can also be selected. In this case, σ φ is the center (Z) of the light pupil (12) B ) and the center (Z) of the shooting pupil (21) A It represents the distance between ). φ is, for example, σ, as shown in FIG. 4. y - Axis and distance (σ φ Represents the angle between ). In the example case, φ is 90°.

[0059] Such pupil overlapping region ( In an environment where matching quality is determined using ), multiple scanned support points ( , Evaluates overlap in ). The following evaluation terms are used in this case:

[0060] (1)

[0061] (2)

[0062] D is the respective pupil overlap area here ( Strength over ) (I(σ x ,σ y This is a term that describes the simple sum of )). This D term (according to mathematical formula (1)) corresponds to the image dimension (CD (critical dimension)), that is, the width of the structure along a predetermined direction.

[0063] For the definition of the parameter (CD), please refer to US9,176,390B.

[0064] This T term (according to mathematical formula (2)) represents the integral over the overlapping region (A), and this integral is again the distance value (σ φ It is weighted by ). In this formula for the term T, for simplification, it is assumed that each of the outgoing pupils (11 or 21) does not have apodization. This term T corresponds to the imaging parameter imaging telecentrity. This may include the sensitivity of the object structure offset as a function of the defocus position of the substrate on which the object is imaged.

[0065] For a given pupil aperture shape of the sigma aperture (8), all possible overlapping regions ( The following optimization specifications are applied when determining the matching quality for ):

[0066]

[0067] In this case, dc represents the currently considered aperture shape of each design candidate, namely the sigma aperture (8). t represents the target illumination pupil of the optical generation system, in particular a projection exposure device in the form of a scanner.

[0068] Optimization specifications according to mathematical formulas (3) and (4) are generally not achieved. When determining the matching quality, the aperture shape of the design candidate (dc) changes until the optimization specifications (3) and (4) yield a minimum value.

[0069] In addition to the optimization variables (D and T), additional variables correlated with additional lighting and / or imaging parameters are also used when determining matching quality. Examples of such variables include the following:

[0070] (5)

[0071] This HV term is correlated with the imaging variable "HV asymmetry," which quantifies the difference in critical dimension (CD) along the vertical and horizontal dimensions. The HV term may be of interest depending on the structure to be imaged in the object (5), such as the horizontal or vertical line to be imaged, particularly when it has the same period and the same target CD, or otherwise in the case of a so-called contact hole, i.e., a structure having an xy aspect ratio of 1 in the region. HV asymmetry is the difference between two CDs, i.e., the CD in the case of the horizontal (h) and vertical (v) lines. h - CD v or in the case of a contact hole having a range in the x- and y- directions, CD x - CD y It can be understood as.

[0072] The verification of the HV term according to the preceding mathematical formula (5) is the coordinate origin (Z B Two defined overlapping regions rotating 90° relative to each other around the center ( and It involves calculating the difference between two D terms according to mathematical formula (1) at the position (compare with FIG. 4). To calculate the integral in the overlap region (B), the overlap between the incident pupil (12) and the exit pupil (21') rotated correspondingly by, for example, 90° is considered.

[0073] Regarding the HV clause, there is also a corresponding optimization specification:

[0074]

[0075] After the comparison calculation is executed, the used nested area ( ) covers the entire illumination pupil of the optical generation system on one side, and the illumination optical unit (7) of the measurement system (2) on the other side.

[0076] FIGS. 4a and FIGS. 4b illustrate two pairs of pupils, one on the one hand, of an optical generation system (Fig. 4a), and the other on the other, of an optical measurement system (Fig. 4b) of a measurement system (2), and these pairs of pupils are compared with each other in the matching quality determination environment described above, particularly in relation to FIG. 4.

[0077] FIG. 4a shows the illumination of the illumination pupil for an x-dipole illumination setup on the left. FIG. 4a shows the emission pupil of the projection optical unit of an optical projection system having a centered, approximately elliptical pupil compression on the right.

[0078] The simulated lighting setup of the optical generation system (compare left side of Fig. 4a) may be composed of multiple individual spots in the lighting pupil corresponding to the faucet configuration of the lighting optical unit of the optical generation system, such as a configuration having a field faucet mirror and a pupil faucet mirror, or a configuration in which a MEMS mirror configuration is used within the lighting optical unit. The size of each individual spot in Fig. 4a on the left is a measure of the brightness of this individual spot, that is, the intensity of the lighting from the lighting direction assigned to this individual spot.

[0079] FIG. 4b shows, on the left, the target aperture shape obtained by the optimization method of the sigma aperture (8) for simulating the illumination and imaging properties of an optical generation system having an illumination setting and an exit pupil according to FIG. 4a. FIG. 4b shows, on the right, the exit pupil of the imaging optical unit of an optical measurement system having a central compression generated by the NA aperture (11) (also compare with FIG. 3).

[0080] The optimization method for the pupil aperture shape of the sigma aperture (8) involves the step of checking at least one manufacturing boundary condition for each design candidate of the aperture shape. An example of such checking of the manufacturing boundary condition will be described in more detail below with reference to FIGS. 5 and FIGS. 6.

[0081] The edge inspection portions (23, 24) are aperture shape design candidates (8) exemplified in FIGS. 5 and 6. dc ) considers. The resolution performance of the manufacturing method is the individual pixel (25) of the example according to FIGS. 5 and 6. i This becomes evident by the range of ). Individual pixels (25) depicted darkly or diagonally. i ) represents an aperture material that is as continuous as possible and blocks illumination / imaging light (1), and open individual pixels (25 i ) represents an aperture opening (transmission of illumination / imaging light) that is as continuous as possible.

[0082] In the environment of the inspection method, the overall aperture shape design candidate (8), also called the starting or modified aperture shape. dc ) is described accordingly as a regular bitmap in pixel discretization.

[0083] To define the circularity, i.e., the curvature, of each inspection section (23, 24) locally in a pixel-based manner, the surrounding area having a defined radius (r) is each pixel (25) of the bitmap iIt is evaluated for ). This advantage is illustrated for pixels (251, 252, and 253) in FIGS. 6. Each evaluated surrounding pixel area (261, 262, and 263), highlighted by different diagonal lines, is square, and in each case, five individual pixels (25) along two coordinates (x, y) i It has a range of ). For example, the central individual pixel to be considered is 251, and the surrounding pixel area is 261, arranged in rows and columns.

[0084] The following standards are checked during the evaluation:

[0085] Each pixel area (26) around the individual pixel considered having the opposite state, "aperture material" or "aperture opening" i Individual pixels (25) within ) i The rounded sum for the central individual pixels considered above is (2r + 1) 2 Less than / 2.

[0086] In the case of r=2, this sum must therefore be less than 13, since the comparison digit is always an integer, (2r + 1) 2 This is because unless / 2 yields an integer, it is rounded to the next larger integer.

[0087] According to the corresponding evaluation, the aforementioned specification is satisfied for individual pixels (251 and 252), because individual pixels (251) have aperture material and nine individual pixels (251) representing aperture openings exist in the pixel area (261), and as a result, the specification, "number of less than 13," is satisfied, and this advantage is also satisfied correspondingly for individual pixels (252) (=aperture openings) (the number of individual pixels (251) in the pixel area (262) composed of aperture material is 8, i.e., less than 13).

[0088] This requirement is not satisfied for individual pixels (253), which represent aperture openings and a total of 16 individual pixels (25) representing aperture materials. i This is because ) exists in the pixel area (263).

[0089] Accordingly, pixel area (26 i ), that is, each central individual pixel (25 i ) Check to establish whether the surrounding area behaves like the central area with respect to the transmission of illumination light with sufficient probability.

[0090] Accordingly, according to the inspection of manufacturing boundary conditions according to this method, an edge inspection portion (23) can be manufactured in the area of ​​individual pixels (251 and 252), but an edge inspection portion (24) cannot be manufactured in the area of ​​individual pixels (253). These manufacturing boundary conditions correspond to all individual pixels (25 i The previously described specifications are checked for every individual pixel (25 i The requirement that ) must be satisfied at this time calculates a manufacturable aperture shape for the sigma aperture (8). According to the specifications locally formulated for each inspection section (23, 24), aperture shape design candidates (8 dc Each aperture shape of ) changes only locally, and accordingly, in each case, only a small inspection part corresponding to the entire aperture shape must be checked for manufacturability.

[0091] The minimum hole diameter and, for example, the minimum aperture web width can be predetermined by the selection of the radius (r).

[0092] When checking manufacturing boundary conditions, in the case where the elliptical shape of the sigma aperture (8) causes, for example, a round incident pupil (12), oblique illumination of the sigma aperture can also be considered. In this regard, in the case of the bitmap representation of FIGS. 5 and FIGS. 6, the x- and y- ranges of individual pixels (25i) can be selected so that they are not the same as each other.

[0093] When determining the matching quality between the lighting and imaging properties of the optical generation system on one hand and the lighting and imaging properties of the optical measurement system of the measurement system (2) on the other, the field dependency of the object lighting of the optical generation system can be taken into account. This advantage is that, in the optical generation system, the object point is considered to collide with a different intensity distribution of the lighting light across the lighting angle compared to the separated object point.

[0094] This consideration of field change is a term (I) for the collision of illumination intensity of the coordinates of the considered target pupil (I of the illumination pupil of the optical generation system). t This can be realized by replacing the target pupil field average, which is averaged over the entire object field (3). For all field coordinates, particularly for all x-field coordinates perpendicular to the object displacement direction (y) during scanning of the optical generating device, the optimization specifications according to the preceding mathematical formulas (3), (4), and (6) can be minimized. Accordingly, the pupil overlap area ( Field-dependency boundaries of ) may also occur.

[0095] An example of an overall method for optimizing the pupil aperture shape of a sigma aperture (8) for simulating the lighting and imaging properties of an optical generation system during lighting and imaging of an object (5) by the optical measurement system of the measurement system (2) will be described below with reference to the flowchart according to FIG. 7.

[0096] In the pre-defining step (30), first, the starting aperture shape (8) of the sigma aperture (8) dc ) is selected as an initial design candidate for this simulation.

[0097] In an optimized environment, this starting aperture shape (8 dc ) is modified in the modification step (31) and the modified aperture shape (8) that has changed slightly with respect to the boundary shape. dcnewIt occurs in the step (32) that generates )

[0098] In the inspection step (33), this modified aperture shape (8 dcnew ) This modified aperture shape (8 dcnew It is checked to establish whether at least one manufacturing boundary condition regarding the manufacturing of ). This can be done using the inspection method described above with reference to FIGS. 5 and 6. By this inspection step, the modified aperture shape (8 dcnew If at least one edge inspection portion (23, 24) of ) does not satisfy the manufacturing boundary condition (determined in the inspection step (33), "N"), the modification step (31) and the generation step (32) are repeated. This is, at this time, the modified aperture shape (8 dcnew The inspection step (33) for ) is performed until it reveals that it conforms to a predetermined manufacturing boundary condition (determination of the inspection step (33), "Y").

[0099] The determining step (34) involves determining the matching quality between the illumination and imaging properties of the optical generation system and the illumination and imaging properties of the optical measurement system. This is done using the matching quality determination described above, with reference to FIG. 4 and mathematical formulas (1) through (6).

[0100] A merit function (E) can be used during the determination of matching quality, because, generally, the matching specifications according to mathematical equations (3), (4), and (6) do not all become zero at the same time. This merit function can usually be written as a weighted error minimization as follows:

[0101] (7)

[0102] I is the sigma aperture (8) to be evaluated by the merit function here. dcnew Represents the aperture shape of ). trepresents the target illumination pupil of the optical generation system, which is the intended optimization target. D and T represent the evaluation terms discussed earlier in relation to equations (3) and (4). Furthermore, the merit function (E) can also be extended, for example, by the evaluation term (HV) (compared to equations (5) and (6)).

[0103] The merit function (E) is the sigma aperture (8 dcnew It can be further extended by the requirements for minimum penetration of ).

[0104] In addition to the target illumination pupil of the optical generation system, the determining step (34) may also be influenced by the pupil transfer function of the optical measurement system of the measurement system (2) and the pupil transfer function of the optical generation system.

[0105] To this end, the previously defined term D in conjunction with mathematical formula (1) can be written as follows:

[0106]

[0107] P is the energetic proportion of the apodization function, that is, the Pupil transfer function.

[0108] Each apodization of the output pupil (11 or 21) can be considered by this means at this time.

[0109] In the process of the decision step (34), compliance with the optimization criteria is inquired about in the optimization inquiry step (35). An example of such an optimization criterion is the Boltzmann criterion of simulated annealing:

[0110]

[0111] In this case, r is a uniformly distributed random number from the interval [0,1[ (the exact value "1" is excluded from this interval accordingly), and β is a control parameter that increases further during the simulated annealing optimization process. E(dc new) and E(dc) are merit functions that occur for the aperture shape of the sigma aperture (8) during the last and preceding optimization steps.

[0112] As long as the Boltzmann criterion is satisfied, that is, as long as optimization has not yet been concluded (determined Y in the inquiry stage (35)), the current aperture shape (8 dcnew ) is the initial aperture shape (8) for the next modification dc It is set to ), and this subsequent modification is executed in the predefined step (36). The control parameter (β) is also increased in the predefined step (36). The optimization criterion is accordingly strengthened in the environment of the predefined step (36). Eventually, this method is repeated until it is revealed by the optimization inquiry step (35) that the Boltzmann criterion is no longer satisfied or that the control parameter (β) is greater than the predefined value (inquiry result N in the inquiry step (35)).

[0113] Therefore, if the optimization criteria are achieved in the optimization inquiry stage (35) (inquiry result N), a sigma aperture (8) having a target aperture shape generated by the minimum merit function value (E) during optimization is manufactured in the manufacturing stage (37).

[0114] Such a target aperture shape (38) in pupil coordinates of the pupil plane (9) is shown in the upper left of FIG. 8.

[0115] The actual aperture contour of the sigma aperture (8) obtained as a result therefrom is illustrated in the bottom right of FIG. 9. The boundary (39) of the aperture opening of the sigma aperture (8), which can be used to simulate a dipole lighting setup of an optical generation system, has, for example, a freeform configuration, and this configuration only slightly resembles the actual dipole geometric shape of the lighting setup to be simulated.

[0116] In addition, FIG. 9 further illustrates an additional aperture opening (40) which is an alignment aid for positioning the sigma aperture (8) in the pupil plane (9).

[0117] At this time, the target aperture shape of the manufactured sigma aperture (8) is accurately aligned and inserted into the optical measurement system, and the measurement system (2) can measure the object or test structure (5) under such lighting and imaging conditions that are optimally modeled with respect to the lighting and imaging conditions of the optical generation system.

Claims

Claim 1 A method for optimizing a pupil aperture shape (39) for simulating the illumination and imaging properties of an optical generation system during illumination and imaging of an object (5) using an optical measurement system, wherein the optical measurement system comprises: an illumination optical unit (7) for the object (5) having a pupil aperture (8) in an area of ​​the illumination pupil having the pupil aperture shape (39) to be optimized, and an imaging optical unit (10) for imaging the object (5), and the method comprises the following steps: a starting aperture shape (8) of the pupil aperture (8). dc Step (30) of pre-defining ) as an initial design candidate for the above simulation, - the most recently pre-defined aperture shape (8 dc ) and different modified aperture shape (8 dcnew The starting aperture shape (8) to create ) dc Step (31) for modifying ) - the modified aperture shape (8 dcnew A step (33) of checking at least one manufacturing boundary condition that must be satisfied regarding the manufacturing of ), and a step of repeating the "modifying" step and the "checking" step until the checking step (33) reveals compliance with the manufacturing boundary condition, - as soon as the modified aperture shape (8) meets the manufacturing boundary condition dcnew A method comprising: a step (34) of determining a matching quality between the illumination and imaging properties of the optical generating system and the illumination and imaging properties of the optical measuring system with respect to ), a step of repeating the steps of “modifying,” “checking,” and “determining” until the matching quality achieves a predetermined optimization criterion—which is checked by the inquiry step (35)—and a step (37) of manufacturing the target aperture shape obtained from the achievement of the optimization criterion as the optimized pupil aperture shape (39) after the optimization criterion has been achieved. Claim 2 In claim 1, compliance with local boundary conditions is checked during the step (33) of checking manufacturing boundary conditions for the edge inspection portions (23, 24) of the pupil aperture shape, wherein, in this case, the peripheral area (26) of each inspection portion arranged around the central area (251, 252, 253) i Regarding ), these peripheral areas are checked to establish whether they behave only like the central areas (251 to 253) with respect to the transmission of illumination light (1), and each of the peripheral areas (26) of a predetermined ratio i A method characterized in that the local boundary condition is satisfied if ) behaves only like the central region (251 to 253). Claim 3 In claim 2, the central region (251 to 253) and the peripheral region (26 i A method characterized by ) being arranged as pixels in rows and columns. Claim 4 A method according to claim 1, wherein the step (34) of determining the matching quality is influenced by the confirmation of a matching between the illumination and / or imaging pupil of the optical generating system and the illumination and / or imaging pupil (12, 21, 21') of the optical measuring system. Claim 5 In claim 4, the step (34) of determining the matching quality comprises a plurality of pupil overlapping areas each covering the entire lighting pupil ( Regarding ),- the pupil overlap area of ​​the illumination pupil and the imaging emission pupil of the optical generating system ( ) and, - corresponding pupil overlap area of ​​an illumination pupil (12) having an aperture shape used with an imaging aperture (11) to predefine the imaging emission pupil (21, 21') of the optical measurement system ( A method characterized by being realized by calculating the value of a merit function (E) influenced by a comparison of optical illumination and imaging parameters (D, T, HV) between ). Claim 6 In claim 5, the following:- the pupil overlapping region ( The integral intensity (I)(D) of the illumination light (1) passing through the illumination pupil in ) and / or - the pupil overlap area ( - Telecentrity parameter (σ) of the illumination light (1) passing through the illumination pupil in ) φ A method characterized by using an integrated intensity (I)(T) weighted by ) as an optical illumination and imaging parameter. Claim 7 A method according to claim 1, wherein as soon as a predetermined optimization criterion is achieved, the optimization routine continues as follows: - a step of strengthening the optimization criterion (36); - a step of executing the "modifying" step, the "checking" step, and the "determining" step once again until the matching quality is achieved through the enhanced optimization criterion; - a step of repeating the "strengthening" step and the "executing once again" step until a termination criterion is achieved - which is checked by the optimization inquiry step (35). Claim 8 A method according to claim 1, characterized in that the dependency of the distribution of the illumination angle of the object (5) on the illuminated object field (3) is taken into account when determining the matching quality. Claim 9 A pupil aperture (8) optimized by the method described in any one of claims 1 to 8. Claim 10 A pupil aperture according to claim 9, characterized in that the pupil aperture shape (39) is implemented as a freeform aperture boundary. Claim 11 A measurement system (2) comprising at least one pupil aperture (8) optimized by the method described in claim 1, wherein the optical measurement system of the measurement system (2) comprises an illumination optical unit (7) for the object (5) having the pupil aperture (8) optimized for an area of ​​the illumination pupil, and an imaging optical unit (10) for imaging the object (5). Claim 12 A measuring system according to claim 11, characterized by an exchange holder for the pupil aperture (8). Claim 13 A measurement system according to claim 11, configured for use in simulating the illumination-imaging properties of an optical generation system having an anamorphic projection optical unit.

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