Method for evaluating measurement values of an aberration of a projection lens
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-26
- Publication Date
- 2026-03-11
AI Technical Summary
The existing methods for evaluating aberrations in projection lenses for microlithography are inefficient, leading to increased measurement time and reduced productivity due to the need for frequent interruptions during the exposure process, while also limiting the accuracy of imaging error corrections.
A method that uses a fit function with a polynomial function and a further term including rigid body sensitivities to extrapolate aberration measurements from a limited number of field points, allowing for high-precision corrections and accounting for system drifts caused by heating, thereby reducing measurement interruptions and improving accuracy.
This approach enables rapid and accurate aberration measurements across multiple field points, maintaining high productivity and improving the precision of manipulator corrections, even when considering aberrations induced by system drifts.
Smart Images
Figure EP2024061570_07112024_PF_FP_ABST
Abstract
Description
Method for evaluating measured values of an aberration of a projection lens This application claims priority from German patent application 10 2023 1 1 1 478.6 filed on May 3, 2023. The entire disclosure of this patent application is incorporated by reference into this application. Background of the invention The invention relates to a method for evaluating measured values of at least one aberration of a projection objective of a projection exposure apparatus for microlithography, a method for operating such a projection exposure apparatus and a projection exposure apparatus for microlithography. To ensure the most precise possible imaging of mask structures onto a substrate, a projection lens with the lowest possible wavefront aberrations is required. Projection lenses are therefore equipped with manipulators that allow wavefront errors to be corrected by changing the state of individual optical elements of the projection lens. Examples of such a change in state include: a change in position in one or more of the six rigid body degrees of freedom of the optical element in question, exposure to heat and / or cold on the optical element, and deformation of the optical element. Typically, the aberration characteristics of the projection lens are measured regularly for this purpose, and if necessary, changes in the aberration characteristics between individual measurements are determined by simulation. This allows, for example, lens heating effects to be mathematically accounted for.The calculation of the manipulator changes to be carried out to correct the aberration characteristics is carried out by means of a travel-generating optimization algorithm, which. also referred to as a "manipulator change model." Such optimization algorithms are described, for example, in WO 2010 / 034674 A1. In order to correct the imaging errors of the projection lens that develop during exposure with the highest possible accuracy, the aforementioned regular measurement of the aberration characteristics is usually performed at a number of field points of the projection lens. However, the measurement time increases with the number of field points measured. Since the exposure process of semiconductor wafers must be interrupted for aberration measurement, the productivity of the projection exposure system decreases with the number of field points measured. Therefore, conventionally, only a limited number of field points are measured. Underlying task It is an object of the invention to provide methods and a projection exposure apparatus of the type mentioned at the outset, with which the aforementioned problems can be solved and, in particular, the imaging errors that develop during the exposure operation of the projection exposure apparatus can be corrected with improved accuracy and, at the same time, the productivity of the projection exposure apparatus can be maintained at a high level. Inventive solution The above-mentioned object can be achieved according to the invention, for example, with a method for evaluating measured values of at least one aberration of a projection lens of a projection exposure apparatus for microlithography, which aberration is measured at a plurality of field points in a field plane of the Projection lens, wherein the projection lens comprises a plurality of optical elements for guiding an exposure radiation and a manipulator system with which at least one of the optical elements can be manipulated in at least one degree of freedom of movement to execute a rigid body movement.The method comprises the following steps: providing a fit function which comprises a polynomial function as a function of two variables in the form of the location coordinates defining the field plane and a further term, wherein the further term comprises rigid body sensitivities for a plurality of locations in the field plane, each of which describes a dependence of the at least one aberration on a degree of freedom of movement controllable by the manipulator system at the respective locations, and extrapolating the measured values determined at the plurality of field points to further field points of the projection lens by fitting the fit function to the determined measured values. A field point of a projection lens is a point in a field plane of the projection lens. A field plane is particularly suitable for a substrate plane of the projection lens, i.e., a plane into which mask structures of a lithography mask are imaged and in which a substrate, in particular a semiconductor substrate, is therefore arranged. The polynomial dependent on two variables can also be referred to as a bivariate polynomial. According to one embodiment, the manipulator system is configured to manipulate a plurality of the optical elements, in particular all optical elements, in at least one degree of freedom of movement, in particular in several, preferably all, degrees of freedom of movement, in order to execute a rigid body movement. The respective sensitivity thus describes, for at least one location in the field plane, a dependence of at least one aberration on the degrees of freedom of movement of the manipulator system. The degrees of freedom of movement can, for example, be all rigid body degrees of freedom of the optical elements, ie Translations and rotations of the optical elements with respect to all three spatial dimensions. By providing a fitting function with the polynomial function and the further term described according to the invention and extrapolating the measured values determined at the majority of field points to further field points of the projection lens by fitting the fitting function, the interruption of the exposure operation required for aberration measurement can be kept short. At the same time, the fit function allows for the use of highly accurate aberrations of other field points, in addition to the aberrations of the measured field points, for the manipulator correction. By incorporating the additional term with at least one sensitivity in the fit function, aberrations caused by system drifts that occur simultaneously with the heating of the optical elements can be better accounted for when fitting to the measured values. Generating the aberrations of other field points with high accuracy also improves the accuracy of the manipulator correction. According to one embodiment, the further term comprises a plurality of rigid-body sensitivities for the at least one location in the field plane. These describe a dependence of the at least one aberration on a plurality of degrees of freedom of movement controllable by the manipulator system at the respective location. According to a further embodiment, the further term comprises one or more rigid body sensitivities for several locations in the field plane. According to a further embodiment, the degrees of freedom of movement of the manipulator system each comprise at least one translational degree of freedom and at least one rotational degree of freedom of several of the optical elements. According to a further embodiment, the at least one aberration comprises one or more Zernike coefficients of a wavefront error of the projection lens. According to a further embodiment, the polynomial function of the fit function is configured to model a component of the field-point-dependent distribution of the aberration, which is generated by shape deviations of the optical elements. The shape deviation can be caused, in particular, by inhomogeneous temperature distributions in the optical elements. According to a further embodiment, the polynomial function of the fit function is a two-dimensional polynomial of at least third degree. This means that the polynomial function contains at least one term in which the sum of the powers of the two function variables, e.g., x and y, is three, e.g., x 3 , x 2 y, or y 3 . According to a further embodiment, when extrapolating the measured values, extrapolated values are determined both for the field points at which the measured values were determined and for the further field points by fitting the fit function to the measured values. Furthermore, according to the invention, a method for operating a projection exposure system for microlithography with a projection objective comprising a plurality of optical elements and a manipulator system is provided. The method comprises the following steps: determining measured values of at least one aberration of the projection objective at a plurality of field points in a field plane of the projection objective; evaluating the determined measured values using the method according to one of the embodiments described above to determine extrapolated values of the at least one aberration at further field points; and determining a travel command for the manipulator system for correcting the at least one aberration using the extrapolated values. According to one embodiment of the method according to the invention for operating a projection exposure system, the travel command is determined by means of an optimization process. According to one embodiment of the method according to the invention for evaluating measured values or of the method according to the invention for operating a projection exposure system, the projection exposure system is designed for operation in the EUV wavelength range. Furthermore, the invention provides a projection exposure system for microlithography. This comprises a projection lens for imaging mask structures onto a substrate having a plurality of optical elements, a manipulator system configured to manipulate at least one of the optical elements in at least one degree of freedom to execute a rigid-body movement, a measuring module for determining measured values of at least one aberration of the projection lens at a plurality of field points in a field plane of the projection lens, and an extrapolation device for extrapolating the measured values determined at the plurality of field points to further field points of the projection lens, with a fitting module configured to fit a fitting function to the determined measured values.The fit function comprises a polynomial function depending on two variables in the form of the spatial coordinates defining the field plane, as well as a further term. The further term comprises rigid body sensitivities for several locations in the field plane, each of which describes a dependence of the at least one aberration on a degree of freedom of movement controllable by the manipulator system at the respective locations. According to one embodiment of the projection exposure system, the extrapolation device further comprises an aberration value determination module which is configured to determine aberration values for the further field points based on the fitted fit function. According to a further embodiment, the projection exposure system is designed for operation in the EUV wavelength range. The features specified with regard to the above-mentioned embodiments, exemplary embodiments or embodiment variants, etc. of the inventive method for evaluating measured values or the inventive method for operating a projection exposure system can be transferred accordingly to the projection exposure system according to the invention, and vice versa. These and other features of the embodiments according to the invention are explained in the description of the figures and the claims. The individual features can be implemented either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments that are independently protectable and whose protection may only be claimed during or after the application is filed. Brief description of the drawings The above and other advantageous features of the invention are illustrated in the following detailed description of exemplary embodiments of the invention with reference to the accompanying schematic drawings. It shows: Fig. 1 shows an illustration of an embodiment of a projection exposure system for microlithography according to the invention with a measuring module for determining measured values of a wavefront aberration at a plurality of field points and an extrapolation device for extrapolating the measured values to further field points, and Fig. 2 shows a detailed representation of the extrapolation device according to Fig. 1. Detailed description of embodiments according to the invention In the exemplary embodiments or embodiments or variants described below, functionally or structurally similar elements are provided with the same or similar reference numerals wherever possible. Therefore, to understand the features of the individual elements of a specific embodiment, reference should be made to the description of other exemplary embodiments or the general description of the invention. To facilitate the description, a Cartesian xyz coordinate system is shown in the drawing, from which the respective positional relationships of the components shown in the figure are derived. In Fig. 1, the y-direction runs perpendicular to the plane of the drawing, the x-direction to the right, and the z-direction upward. Fig. 1 shows an embodiment of a projection exposure system 10 for microlithography. The projection exposure system 10 is designed for operation in the EUV wavelength range, i.e., with electromagnetic radiation having a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.8 nm. All optical elements of the projection exposure system 10 are therefore designed as mirrors. However, the invention is not limited to projection exposure systems in the EUV wavelength range. Further embodiments according to the invention are designed, for example, for operating wavelengths in the UV range, such as 365 nm, 248 nm, or 193 nm. At least some of the optical elements are then configured as conventional transmission lenses. The projection exposure system 10 comprises an exposure radiation source 12 for generating exposure radiation 14. In the present case, the exposure radiation source 12 is designed as an EUV source and can, for example, a plasma radiation source. The exposure radiation 14 first passes through an illumination system 16 and is directed by it onto a mask 18. The illumination system 16 is configured to generate different angular distributions of the exposure radiation 14 impinging on the mask 18. Depending on a lighting setting desired by the user, also called a "lighting setting," the illumination system 16 configures the angular distribution of the exposure radiation 14 impinging on the mask 18. Examples of selectable lighting settings include so-called dipole illumination, annular illumination, and quadrupole illumination. The mask 18 has mask structures for imaging onto a substrate 32 in the form of a semiconductor wafer arranged in a field plane 33 and is displaceably mounted on a mask displacement stage 20. The mask 18 can, as shown in Fig. 1, be designed as a reflection mask or, alternatively, particularly for UV lithography, also be configured as a transmission mask. In this exemplary embodiment, the exposure radiation 14 is reflected by the mask 18 and then passes through a projection lens 22, which is configured to image the mask structures onto the substrate 32. The exposure radiation 14 is guided within the projection lens 22 by means of a plurality of optical elements. The projection lens 22 has four optical elements E1 to E4 in the form of mirrors. All optical elements are movably mounted. For this purpose, each of the optical elements E1 to E4 is assigned a respective mechanical manipulator M1 to M4. The manipulators M1, M2, and M3 each enable a displacement of the assigned optical elements E1, E2, and E3 essentially in the x-direction and thus essentially parallel to the plane in which the respective reflective surface of the optical elements lies. The manipulator M4 is configured to tilt the optical element E4 by rotating it about a tilt axis 38 arranged parallel to the y-axis. This changes the angle of the reflecting surface of E4 relative to the incident Radiation changes. Further degrees of freedom for the manipulators are conceivable. For example, a displacement of a respective optical element transverse to its optical surface or a rotation about a reference axis perpendicular to the reflecting surface can be provided. According to one embodiment, each of the optical elements E1 to E4 can be manipulated in all six rigid body degrees of freedom, i.e., in the three translational degrees of freedom (x, y, and z directions) and the three rotational degrees of freedom (rotations with respect to the x, y, and z axes). In other words, the manipulator system formed by the manipulators M1 to M4 enables the movement of the optical elements E1 to E4 in one or more degrees of freedom, which can also be referred to as rigid body degrees of freedom. All degrees of freedom that can be adjusted at the various optical elements E1 to E4 by means of the manipulator system formed by the manipulators M1 to M4 are denoted by the index i in Fig. 2 (reference numeral 68). Here, i = {1, 2, ... where imax is the sum of all degrees of freedom of movement of the manipulators M1 to M4, so the largest possible value for imax is 24, i.e. four times the six rigid body degrees of freedom per manipulator M1 to M4. Generally speaking, each of the manipulators M1 to M4 shown here is intended to effect a displacement of the associated optical element E1 to E4 by executing a rigid-body movement along a predetermined travel path w1 to W4. Each of these travel paths w1 to W4 can, for example, combine translations in different directions, tilts, and / or rotations in any desired manner. In other words, the travel paths w1 to W4 comprise the control instructions for all degrees of freedom i of the manipulators M1 to M4. In addition, manipulators can also be provided which are configured to carry out a different type of change in a state variable of the assigned The adjustment of the optical element can be carried out by appropriate actuation of the manipulator, for example, by subjecting the optical element to a specific temperature distribution or a specific force distribution. In this case, the travel w can be characterized by a change in the temperature distribution at the optical element or by the application of a local voltage to an optical element designed as a deformable lens or a deformable mirror. As an example of a manipulator for applying a specific temperature distribution to an optical element, a heating device, referred to as manipulator M5, is assigned to the optical element E3 in Fig. 1. The optical element E3 is designed as a mirror with a mirror substrate 24 and a reflective surface 26. Fig. 1 also shows a schematic detailed view of the optical element E3. The surface 26 comprises a surface section 28, beneath which a compacted volume section 30 is arranged. By compacting the volume section 30, for example, a predetermined surface shape of the surface section 28 is realized very precisely. The heating device M5 serves, depending on a control signal in the form of a travel distance ws, for the location-dependent heating of the surface section 28 in order to influence the relaxation of the compacted volume section 30. For this purpose, the heating device M5 comprises an irradiation device with an infrared laser and a deflection device for guiding the laser beam over the entire area of the surface section 28. In this case, the surface section 28 is scanned line by line or in a spiral shape with infrared light 48. Depending on the predetermined local intensity, a corresponding residence time of the laser beam is provided at each position on the surface section 28. Alternatively, another electromagnetic radiation can also be used to heat the surface section 28. The substrate 32 is displaceably mounted on a substrate displacement stage 34. In the illustrated embodiment, the projection exposure system 10 is designed as a so-called scanner. During exposure of a substrate 32, the substrate is displaced by the substrate displacement stage 34 in a displacement direction 40, in the illustrated case in the negative x-direction, and the mask 18 is displaced by the mask displacement stage 20 in the opposite displacement direction 41, in the illustrated case in the positive x-direction. During exposure of the substrate 32, a scanner slot 44 is then moved over the substrate 32, and a field on the substrate 32 is exposed in a scanning process. Alternatively, the projection exposure system 10 can be designed as a so-called stepper. Furthermore, a measuring module 36 for determining measured values 50 of at least one aberration of the projection lens 22 at various field points 52 is arranged next to the substrate 32 on the substrate displacement stage 34. In the present exemplary embodiment, the measuring module 36 is configured as a wavefront measuring device for measuring wavefront deviations or wavefront errors of the projection lens 22, represented by Zernike coefficients. These measurements are performed, for example, using phase-shifting interferometry techniques, such as shearing interferometry or point diffraction interferometry. Alternatively, the measuring module 36 can also be used to measure aberrations in the form of lithographic errors, such as overlay errors and / or focus errors. In the present embodiment, the measuring module 36 determines a vector b of Zernike coefficients as measured values 50 at each measured field point 52. In Fig. 1, six measured field points 52 are shown as an example in the area of the scanner slot 44. These are designated by the counting variable m, where m ranges from 1 to rn m ax = 6 runs ( m = {1,2, ... m max}) - see Fig. 2 top left). The vector set bm thus denotes mmax vectors b, which contain a predetermined selection of Zernike coefficients Zj, for example all Zernike coefficients Z1 , Z2, ... , Zjmax up to the Zernike coefficient with the index jmax, include (j= {1,2, •••jmax} )■ In the present application, as for example in the sections
[0125] until
[0129] by US 2013 / 0188246A1, which is taken from, for example, Chapter 13.2.3 of the textbook “Optical Shop Testing”, 2 ndEdition (1992) by Daniel Malacara, Ed. John Wiley & Sons, Inc. known Zernike functions Z" according to the so-called fringe sorting are denoted by Zj, where bj are the Zernike coefficients assigned to the respective Zernike polynomials (also called "Zernike functions"). The fringe sorting is illustrated, for example, in Table 20-2 on page 215 of the "Handbook of Optical Systems", Vol. 2 by H. Gross, 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. A wavefront deviation W at a point in the image plane of the projection lens is developed as a function of the polar coordinates (p, 4>) in the pupil plane as follows: While the Zernike polynomials are denoted by Zj, i.e., with a subscript j, the Zernike coefficients in term (2) are denoted by bj. It should be noted here that in the scientific community, the Zernike coefficients bj are often denoted by Zj, i.e., with a normally placed subscript, such as Z5 and Z6 for astigmatism. This notation is also used in this text, for example, in expression (1). The measured values 50 in the form of the vectors bm measured at the field points 52 are transmitted to an extrapolation device 54, which serves to extrapolate the measured values 50 to further field points 56 of the projection lens 22. The further field points 56 are shown in Fig. 1 as small circles in the area of the substrate-side field plane 33 illuminated by the scanner slot 44, while the measured field points 52 are shown as filled points. The same representation can be found in Fig. 2 bottom left, where amax = 9 further field points 56 are shown. For these, the numbering of the measured field points 52 explained above is continued (1 to rrimax = 6), so that the further field points 56 are assigned the numbers 7 to 15 (rnmax+1, rnmax+2 ...). The extrapolation device 54 provides an enlarged value set 74 of aberrations in the form of a vector set bv, which includes respective vectors b with the corresponding, above-mentioned, Zernike coefficients for both the measured field points 52 and the further field points 56. According to one embodiment, the vector set bv for the measured field points 52 comprises the measured values 50, i.e. the vector set bm , as well as extrapolated aberration values 76 for the further field points 56 in the form of a vector set be. In this case, be comprises a total of e Vectors b: According to a further embodiment, which is not shown graphically, the vector set bv also includes the extrapolated aberration values for the measured field points 52, ie in this case bv = b e and the vector set b e includes a total of e = {1,2, ... , m max +a max} vectors b. As shown in Fig. 2, the extrapolation device 54 comprises a fitting module 58 and an aberration value determination module 60. The fitting module 58 is configured to fit a fitting function 62 to the determined measured values 50 (vector set bm). According to one embodiment, the fitting function 62 is as follows: Here, Zj(x,y) denotes a field-point dependent distribution 63 of the aberration in the form of all Zernike coefficients listed in bm depending on the location coordinates x and y in the field plane 33. The fit function 62 according to (4) includes a polynomial function 64 and with a further term 66. The polynomial function 64 is a two-dimensional function depending on the spatial coordinates x and y defining the field plane 33. In the present embodiment, the polynomial function 64 is a two-dimensional polynomial of the third degree, ie the polynomial function 64 contains at least one term, in the present case the terms Cj,ex 2 y and Cj,?x 3 , in which the sum of the powers of the two function variables x and y is three. The polynomial function 64 is configured to represent a component of the field point-dependent Aberration distribution Zj(x,y), which is generated by shape deviations of the optical elements E1 to E4, to be modeled. The further term 66 comprises for each Zernike coefficient Zj and each degree of freedom i of the manipulator system formed by the manipulators M1 to M4 a rigid body sensitivity Sij(x,y) (reference symbol 70) as well as a sensitivity coefficient Si (reference symbol 72), the sum being formed from the products of Si and Sij(x,y). The rigid body sensitivities Sij(x,y) each describe a dependence of an aberration in the form of the respective Zernike coefficient Zj on the respective degree of freedom i. As explained above, i denotes the degrees of freedom that can be controlled by the manipulator system formed by the manipulators M1 to M4. The rigid body sensitivities Sij(x,y) are each a two-dimensional function depending on the position coordinates x and y of the field plane 33. This two-dimensional function can also be discretized, ie the rigid body sensitivities Sij(x,y) can each be represented by a set of discrete values specified for certain field points, ie Sij(x,y)= ...}. Since the rigid body sensitivities Sij(x,y) are indexed with i and j, the term 66 includes a plurality of rigid body sensitivities for each location in the field plane 33. The fitting function 62 is fitted to the measured values 50 in the fitting module 58 using a specially adapted fitting algorithm. As a result of the fitting, a set of coefficients Cj,i , Cj,2 , Cj,3 , Cj,4 , Cj,5 , Cj,6 , and Cj,7 , or a matrix C with j columns and 7 rows, in which the matrix elements are the coefficients, is determined for each Zernike coefficient Zj. Furthermore, the fitting algorithm determines a set of sensitivity coefficients Si for the respective degrees of freedom i of the manipulator system formed by the manipulators M1 to M4. Finally, the aberration value determination module 60 determines the relevant Zernike coefficients at the further field points 56, ie the vectors b at the further field points (x m_ max+1 , ym_max+1 ), (Xm_max+2, ym_max+ 2), .. . (Xm_max+a_max, ym_max+a_max) and thus the vector set be according to the above-mentioned first embodiment. Thus, the extrapolation device 54 represents the vector set bv from the vectors bm of the measured field points 52 and the vectors b determined by extrapolation. e the additional field points 56 are available. As already mentioned above, according to a further embodiment, the vectors b for the field points 52 can also be newly determined by extrapolation from the aberration value determination module 60, so that the vector set b e includes extrapolated vectors b for both field points 52 and 56. In this case, the vector set bv with the enlarged value set 74 of aberrations corresponds to the vector set b e . As illustrated in Fig. 1, the vector set bv with the aberration values for the expanded number of field points 52 and 56 is transmitted to a correction signal determiner 78. This is configured to determine, on the basis of the vector set bv, a travel command w (reference number 82) with travel distances wi to ws for the manipulators M1 to M5. This means that the correction signal determiner 78 determines travel distances wi to W4 specifying rigid body movements of the mechanical manipulators M1 to M4, as well as a travel distance ws that specifies an intensity distribution of a heating energy for the heating device M5. The travel command 82 is shown in Fig. 1 as a vector w. The correction signal detector 78 can, for example, use an optimization algorithm to determine the travel distances wi to ws. According to one embodiment, the optimization algorithm serves to optimize a quality function 80, also called the merit function, taking into account at least one constraint. According to one embodiment, the optimization algorithm according to the invention is configured to solve the following optimization problem: Here ll^ w " Nh is the quality function 80 and A is a sensitivity matrix which describes the relationship between an adjustment of the manipulators M1 to M5 by a standard travel Wi° and a resulting change of bv. The above description of exemplary embodiments, embodiments, and variants is to be understood as exemplary. The disclosure thus made enables those skilled in the art, on the one hand, to understand the present invention and the associated advantages, and, on the other hand, also encompasses obvious variations and modifications of the described structures and methods within the understanding of those skilled in the art. Therefore, all such variations and modifications, insofar as they fall within the scope of the invention as defined in the appended claims, as well as equivalents, are intended to be covered by the claims. List of reference symbols 10 projection exposure system 12 Exposure radiation source 14 Exposure radiation 16 Lighting system 18 Mask 20 mask transfer platform 22 Projection lens 24 Mirror substrate 26 Surface 28 Surface section 30 compacted volume section 32 Substrat 33 Field level 34 Substrate transfer stage 36 measuring module 38 Tilting axis 40 Direction of movement of the substrate transfer stage 41 Direction of movement of the mask transfer stage 42 Lighting setting 44 Scanner slot 48 infrared light 50 measured values bm 52 surveyed field points 54 Extrapolation device 56 additional field points 58 Fitting module 60 Aberration value determination module 62 Fit function 63 field-point dependent distribution of aberration 64 polynomial function 66 further term 68 degrees of freedom of movement of the manipulators M1 to M4 70 Rigid body sensitivity 72 Sensitivity coefficient 74 increased set of aberrations bv 76 extrapolated aberration values b e 78 correction signal detectors 80 quality function 82 Travel command E1 - E4 optical elements M1 - M4 mechanical manipulators M5 heating device W1 - W5 travel ranges
Claims
Claims 1. A method for evaluating measured values (50) of at least one aberration of a projection lens (22) of a projection exposure system (10) for microlithography, which were determined at a plurality of field points (52) in a field plane (33) of the projection lens, wherein the projection lens comprises a plurality of optical elements (E1-E4) for guiding an exposure radiation (14) and a manipulator system (M1-M4) with which at least one of the optical elements can be manipulated in at least one degree of freedom (68) to execute a rigid body movement, the method comprising the following steps: - Providing a fit function (62) which comprises a polynomial function (64) as a function of two variables in the form of the location coordinates defining the field plane and a further term (66), wherein the further term comprises rigid body sensitivities (70) for several locations in the field plane, each of which describes a dependence of the at least one aberration (63) on a degree of freedom of movement (68) controllable by the manipulator system at the respective locations, and - Extrapolating the measured values (50) determined at the majority of field points (52) to further field points (56) of the projection lens by fitting the fit function to the determined measured values.
2. The method according to claim 1, wherein the further term (66) comprises a plurality of rigid body sensitivities (70) for the at least one location in the field plane (33).
3. Method according to claim 1 or 2, wherein the further term (66) comprises one or more rigid body sensitivities (70) for a plurality of locations in the field plane (33).
4. Method according to one of the preceding claims, in which the degrees of freedom of movement (68) of the manipulator system (M1 -M4) each comprise at least one translational degree of freedom and at least one rotational degree of freedom of several of the optical elements (E1 -E4).
5. Method according to one of the preceding claims, wherein the at least one aberration comprises one or more Zernike coefficients (63) of a wavefront error of the projection lens (22).
6. Method according to one of the preceding claims, wherein the polynomial function (64) of the fit function is configured to model a component of the field point-dependent distribution (63) of the aberration generated by shape deviations of the optical elements.
7. Method according to one of the preceding claims, wherein the polynomial function (64) of the fit function is a two-dimensional polynomial of at least third degree.
8. Method according to one of the preceding claims, wherein when extrapolating the measured values (50), extrapolated values are determined both for the field points (52) at which the measured values were determined and for the further field points (56) by fitting the fit function to the measured values.
9. A method for operating a projection exposure system (10) for microlithography with a projection objective (22) comprising a plurality of optical elements (E1 -E4) and a manipulator system (M1 -M4), the method comprising the following steps: - determining measured values (50) of at least one aberration of the projection lens at a plurality of field points (52) in a field plane (33) of the projection lens, - evaluating the determined measured values using the method according to one of the preceding claims to determine extrapolated values (74) of the at least one aberration at further field points (56), - Determining a travel command (82) for the manipulator system to correct the at least one aberration using the extrapolated values (74).
10. The method according to claim 9, wherein the determination of the travel command (82) is carried out by means of an optimization process.
11. Method according to one of the preceding claims, wherein the projection exposure system (10) is designed for operation in the EUV wavelength range.
12. Projection exposure system (10) for microlithography with: - a projection lens (22) for imaging mask structures onto a substrate (32) with a plurality of optical elements (E1 -E4), - a manipulator system (M1 -M5) configured to manipulate at least one of the optical elements (E1 -E4) in at least one degree of freedom of movement to execute a rigid body movement, - a measuring module (36) for determining measured values (50) of at least one aberration of the projection lens at a plurality of field points (52) in a field plane (33) of the projection lens, and - an extrapolation device (54) for extrapolating the measured values determined at the plurality of field points to further field points of the projection lens, with a fitting module (58) which is configured to fit a fitting function to the determined measured values, wherein the fitting function comprises a polynomial function as a function of two variables in the form of the location coordinates defining the field plane and a further term which comprises rigid body sensitivities for a plurality of locations in the field plane, each of which describes a dependence of the at least one aberration on a degree of freedom of movement controllable by the manipulator system at the relevant locations.
13. Projection exposure system according to claim 12, wherein the extrapolation device further comprises an aberration value determination module (60) which is configured to determine aberration values for the further field points (56) on the basis of the fitted fit function (62).
14. Projection exposure system according to claim 13, which is designed for operation in the EUV wavelength range.