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DE-102023205136-B4 - Method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object using an optical measuring system

DE102023205136B4DE 102023205136 B4DE102023205136 B4DE 102023205136B4DE-102023205136-B4

Abstract

Method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object (5), wherein the replicating is carried out using an optical measuring system of a metrology system (2), - where the optical measuring system -- a lighting optic (9) for illuminating the object (5) --- with a pupillary diaphragm (10) of the illumination optics (9) in the area of an illumination pupil in a pupillary plane (11) and -- has an imaging optic (20) for imaging the object (5) onto an image plane (29), - wherein the object (5) can be moved perpendicular to an object plane (4) by the following steps: - Providing at least one pupil diaphragm (10) for specifying several measurement illumination settings generated by moving the pupil diaphragm (10) in the pupil plane (11), - Taking aerial measurement images I meas in the image plane (29) for different displacement positions of the object (5) perpendicular to the object plane (4) at the different measurement illumination settings, wherein the different measurement illumination settings are specified by displacement of the pupil aperture (10), - Reconstructing a complex mask transfer function M from the recorded measurement aerial images I meas , - Determining a 3D aerial image I sim of the optical production system as a result of the simulation procedure from the reconstructed mask transfer function M and a given illumination setting σ target of the optical production system, - the reconstruction takes into account that the progressions of the aperture edges (39) of the at least one pupil aperture (10) that effectively determine the respective measurement illumination setting change depending on the displacement position of the pupil aperture (10) beyond a mere displacement of the aperture edge (39).

Inventors

  • Alexander Winkler
  • Klaus Gwosch
  • Markus Koch

Assignees

  • CARL ZEISS SMT GMBH

Dates

Publication Date
20260513
Application Date
20230601

Claims (12)

  1. Method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object (5), wherein the replicating is carried out by means of an optical measuring system of a metrology system (2), - wherein the optical measuring system comprises -- an illumination optic (9) for illuminating the object (5) --- with a pupil aperture (10) of the illumination optic (9) in the region of an illumination pupil in a pupil plane (11) and -- an imaging optic (20) for imaging the object (5) into an image plane (29), - wherein the object (5) is displaceable perpendicular to an object plane (4), comprising the following steps: - providing at least one pupil aperture (10) for specifying several measurement illumination settings generated by displacing the pupil aperture (10) in the pupil plane (11), - taking measurement aerial photographs I meas in the image plane (29) for different displacement positions of the object (5) perpendicular to the object plane (4) at the different measurement illumination settings, wherein the different measurement illumination settings are specified by displacement of the pupil aperture (10), - Reconstructing a complex mask transfer function M from the recorded measurement aerial images I meas , - Determining a 3D aerial image I sim of the optical production system as a result of the reconstruction procedure from the reconstructed mask transfer function M and a specified illumination setting σ target of the optical production system, - wherein the reconstruction takes into account that the progressions of aperture edges (39) of the at least one pupil aperture (10) that effectively act to specify the respective measurement illumination setting change beyond a mere displacement of the aperture edge (39) when the respective measurement illumination setting is specified, depending on the displacement position of the pupil aperture (10).
  2. Procedure according to Claim 1 , characterized in that shadowing effects due to a finite thickness of a base body (41) of the pupil diaphragm (10) are taken into account in a determination of a change in the course of the aperture edges (39) of the at least one pupil diaphragm (10) when specifying the measurement illumination settings.
  3. Procedure according to Claim 1 or 2 , characterized in that in a determination of a change in the course of the aperture edges (39) of the at least one pupil aperture (10) when specifying the measurement illumination settings, shadowing effects due to a principal beam angle (CRAi) of illumination of the object (5) in the optical production system, which is greater than 4°, are taken into account.
  4. Procedure according to one of the Claims 1 until 3 , characterized in that a field-dependent determination of a change in the course of the aperture edges of the at least one pupil aperture (10) is carried out when the measurement illumination settings are specified.
  5. Procedure according to one of the Claims 1 until 4 , characterized in that a field dependence of imaging properties of an imaging optic of the optical production system is included in a determination of a change in the course of the aperture edges of the at least one pupil aperture (10) when specifying the measurement illumination settings.
  6. Procedure according to one of the Claims 1 until 5 , characterized in that at least one of the following correction terms is included in the reconstruction of the mask transfer function M: - a calculated aerial image ( I s i m ( r → , z , x m ) ) at the associated defocus value and field height, which is generated by simulating an image with the imaging optics of the optical production system including reconstructed spectra of the object (5), and/or - a calculated aerial image ( I s i m ( r → , z , q → ) ) at the associated defocus value, which is generated by simulating an image with the measuring imaging optics (20) including the reconstructed spectra.
  7. Procedure according to one of the Claims 1 until 6 , characterized in that a pupil diaphragm (10) is used in the acquisition of the measurement aerial images, the shape of which is optimized by means of the following process steps: - specification (45) of a starting diaphragm shape (10 dc ) of the pupil diaphragm (10) as an initial design candidate for reproduction, - modification (46) of the starting diaphragm shape (10 dc ) so that a modified diaphragm shape (10 dcnew ) is created which differs from the last specified diaphragm shape (10 dc ), - verification (48) of at least one manufacturing boundary condition with regard to the manufacture of the modified diaphragm shape (10 dcnew ) and repetition of the "modify" and "verify" steps until the verification (48) shows compliance with the manufacturing boundary condition, - determination (49) of a degree of conformity between the illumination and imaging properties of the optical Production system and the illumination and imaging properties of the optical measuring system, as soon as the manufacturing boundary conditions are met, - Repeat the steps “ Modify ”, “Check” and “Determine” until the conformity quality reaches a predetermined optimization criterion, which is checked via a query step (50), - Manufacturing (52) a target aperture shape resulting from reaching the optimization criterion as an optimized pupil aperture shape (39) after reaching the optimization criterion.
  8. Procedure according to Claim 7 , characterized in that the aperture boundary (39) is optimized separately for several field areas and in particular for several field heights (x m ), resulting in several pupil apertures (10) which can each be used to replicate the properties of the optical production system in the corresponding field area.
  9. Metrology system (2) for carrying out a procedure according to one of the Claims 1 until 8 , - wherein the optical measuring system comprises an illumination optic (9) for illuminating the object (5) with a pupil aperture (10) in the region of an illumination pupil in a pupil plane (11) and an imaging optic (20) for imaging the object (5) in the image plane (29), - with a selection device for selecting at least one pupil aperture from a plurality of pupil apertures.
  10. Metrology system according to Claim 9 , - wherein the optical measuring system has a displacement drive (16) for displacing the pupillary diaphragm (10) in at least one displacement direction in the pupillary plane (11), - wherein the optical measuring system has an object holder (17) that can be displaced by actuator perpendicular to an object plane (4).
  11. Metrology system according to Claim 9 or 10 , characterized in that the optical measuring system has a displacement drive (25) for displacing an imaging pupil diaphragm (23) which is arranged in the region of a pupil of the imaging optics (20) in at least one displacement direction in a pupil plane (22) of the imaging optics (20).
  12. Metrology system according to one of the Claims 9 until 11 , characterized in that the selection device has an aperture magazine with a plurality of pupil apertures (10) each with different aperture edge shapes and/or aperture edge orientations for specifying different measurement illumination settings.

Description

The invention relates to a method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object, wherein the replicating is carried out using an optical measuring system or a metrology system. The invention further relates to a metrology system for carrying out such a method. Such a method and a metrology system for it are known from the DE 10 2019 208 552 A1 , the DE 10 2019 206 651 B4 and from the DE 10 2019 215 800 A1 A metrology system for the three-dimensional measurement of an aerial image of a lithography mask is known from the WO 2016/012 426 A1 . The DE 10 2013 219 524 A1 describes a device and a method for determining the image quality of an optical system, as well as an optical system itself. In the DE 10 2013 219 524 A1 A phase retrieval method for determining a wavefront based on the imaging of a pinhole is described. From the article by Martin et al., "A new system for a wafer lever CD metrology on photomasks," Proceedings of SPIE - The International Society for Optical Engineering, 2009, 7272, a metrology system for determining a critical dimension (CD) at the wafer level is known. The DE 102 20 815 A1 and the DE 102 20 816 A1 They describe a reflective X-ray microscope and an inspection system for examining objects with wavelengths ≤ 100 nm. WO 2016/012 426 A1 discloses a method for the three-dimensional measurement of a 3D aerial image of a lithography mask. WO 2012/028 303 A1 It reveals an optical system for EUV projection lithography. US 9,176,390 B2 discloses a method for adjusting a lighting system of a projection exposure system for projection lithography. US 2013/0083321 A1 discloses a device for EUV imaging and an operating method for this purpose. US 2013/0063716 A1 Disclosing an illumination optic for a metrology system for examining an object with EUV illumination light and a metrology system with such an illumination optic. The article by Totzeck et al., "How to describe polarization influence on imaging," Proceedings of SPIE, 2005, 23, deals with the description of a polarization influence on an image. The subsequently published DE 10 2022 200 372 A1 discloses a method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object using an optical measuring system. The subsequently published DE 10 2021 213 827 A1 discloses a method for optimizing a pupil aperture shape to replicate the illumination and imaging properties of an optical production system when illuminating and imaging an object using an optical measuring system. DE 10 2021 205 541 A1 discloses a method for determining the imaging quality of an optical system when illuminated with illumination light within an entrance pupil to be measured. DE 10 2021 205 328 B3 discloses a method for determining the imaging quality of an optical system when illuminated with illumination light within a pupil to be measured and a metrology system for this purpose. It is an object of the present invention to improve a method for replicating the illumination and imaging properties of an optical production system when illuminating and imaging an object using an optical measuring system. This problem is solved according to the invention by a replication method with the features specified in claim 1. According to the invention, it has been recognized that capturing aerial images using multiple pupil apertures, in particular capturing aerial images in several measurement positions of a pupil aperture previously selected to best replicate the illumination setting of the optical production system, makes it possible to improve the overall accuracy of the reconstruction method and, in particular, to reduce artifacts, especially those dependent on the illumination angle, in the reconstructed complex mask transfer function, i.e., the transfer function of the imaged object. 3D mask effects can then be correctly taken into account. This can be considered when examining lithography masks, especially masks used for EUV lithography. By taking into account the dependence of an effective aperture edge profile on a respective displacement position of the pupillary diaphragm used in the measurement, whereby this consideration goes beyond the pure displacement-related shift of the aperture edge contour, the The accuracy of the 3D aerial image of the optical production system determined via the simulation is ensured. If the pupillary diaphragm is repositioned during the acquisition of the measurement aerial images in such a way that an outer diaphragm boundary, which in particular defines a numerical illumination aperture, remains constant in its position, this can be taken into account in the simulation process and simplify the modeling of the respective edge contour of the pupillary diaphragm in the current measurement position. The provided pupillary diaphragm is a diaphragm of the illumination optics, wherein the pupillary d