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US-12625090-B2 - Imaging optical arrangement to image an object illuminated by X-rays

US12625090B2US 12625090 B2US12625090 B2US 12625090B2US-12625090-B2

Abstract

An imaging optical arrangement serves to image an object illuminated by X-rays. An imaging optics serves to image a transfer field in a field plane into a detection field in a detection plane. A layer of scintillator material is arranged at the transfer field. A stop is arranged in a pupil plane of the imaging optics. The imaging optics has an optical axis. A center of a stop opening of the stop is arranged at a decentering distance with respect to the optical axis. Such imaging optical arrangement ensures a high quality imaging of the object irrespective of a tilt of X-rays entering the transfer field. The imaging optical arrangement is part of a detection assembly further comprising a detection array and an object mount. Such detection assembly is part of a detection system further comprising an X-ray source.

Inventors

  • Johannes Ruoff
  • Juan Atkinson Mora
  • Thomas Anthony Case
  • Heiko Feldmann
  • Christoph Hilmar GRAF VOM HAGEN
  • Thomas Matthew Gregorich
  • Gerhard Krampert

Assignees

  • CARL ZEISS SMT GMBH
  • Carl Zeiss X-Ray Microscopy Inc.

Dates

Publication Date
20260512
Application Date
20240216
Priority Date
20210915

Claims (20)

  1. 1 . A detection system for an X-ray inspection of an object, the detection system comprising: an X-ray source for generating X-rays, an object mount to hold the object, an object displacement drive, wherein the object mount is movable relative to the X-ray source via the object displacement drive along at least one lateral object displacement direction in the object plane, a layer of scintillator material arranged in a transfer field, wherein X-rays from the X-ray source produce a projection image on the layer of scintillator material via radiographically shading casting, an imaging optics to image the transfer field into a detection field in a detection plane, at least one stop being movable via a stop displacement drive, and a control device with a drive control unit being in a signal connection with the at least one of stop displacement drive and the object displacement drive for synchronizing a movement of the stop displacement drive and a movement of the object displacement drive.
  2. 2 . The detection system of claim 1 , wherein an object side numerical aperture of the imaging optics which is defined by the stop opening is larger than 0.4.
  3. 3 . The detection system of claim 1 , wherein an angle between the X-rays entering the transfer field and an optical axis of the imaging optics is between 0 deg and 80 deg.
  4. 4 . The detection system of claim 1 , wherein the object mount and/or the at least one stop is movable along at least one linear displacement direction.
  5. 5 . The detection system of claim 1 , wherein the object mount and/or the at least one stop is movable along at least one circular direction.
  6. 6 . The detection system of claim 1 , wherein the at least one stop is configured such that the stop aperture is variable in size.
  7. 7 . The detection system of claim 1 , further comprising at least one stop exchange mount to exchange between different stops.
  8. 8 . The detection system of claim 1 , wherein no X-ray optics is present to influence a direction of the X-rays between the X-ray source and the layer of scintillator material.
  9. 9 . The detection system of claim 1 , wherein the control device has a lookup table configured to store data with respect to a dependency between actions of the stop displacement drive and actions of the object displacement drive.
  10. 10 . The detection system of claim 9 , wherein the control device is configured to use the data stored in the lookup table to control the stop displacement drive and the object displacement drive.
  11. 11 . The detection system of claim 1 , wherein the X-ray source is an open transmissive source or a liquid metal jet source.
  12. 12 . The detection system of claim 1 , wherein the at least one stop is a shield stop having a shield stop aperture transmissive for the X-rays, the shield stop being arranged in an X-ray path of X-rays between the X-ray source and the object mount, the shield stop being movable via the stop displacement drive along at least one displacement direction.
  13. 13 . The detection system of claim 1 , wherein the at least one stop is arranged in a pupil plane of the imaging optics and forming a pupil stop.
  14. 14 . The detection system of claim 13 , wherein a center of a stop opening of the pupil stop is arranged at a decentering distance with respect to an optical axis of the imaging optics.
  15. 15 . The detection system according to claim 14 , wherein the stop displacement drive is configured as a decentering drive to translate the pupil stop in the pupil plane.
  16. 16 . The detection system of claim 14 , wherein the decentering distance is at least 10% of a width of the stop opening.
  17. 17 . The detection system of claim 14 , wherein a lateral displacement of the X-ray source with respect to the object mount and the decentering distance of the center of the stop opening are balanced such that X-rays entering the transfer field run parallel to chief imaging rays of imaging light within the imaging light path.
  18. 18 . The detection system of claim 13 , wherein the stop displacement drive is configured to axially move the pupil stop.
  19. 19 . The detection system of claim 13 , wherein the imaging optics includes a movable optical element.
  20. 20 . The detection system of claim 13 , wherein the stop is an annular pupil stop.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of and claims priority under 35 U.S.C. § 120 from PCT Application No. PCT/EP2022/070678, filed on Jul. 22, 2022, which claims priority from U.S. patent application Ser. No. 17/402,819, filed on Aug. 16, 2021, published as US 2023/0050439, U.S. patent application Ser. No. 17/402,822, filed on Aug. 16, 2021, now U.S. Pat. No. 11,817,231, German Patent Application No. 10 2021 210 175.5, filed on Sep. 15, 2021, and German Application No. 10 2021 210 174.7, filed on Sep. 15, 2021. The entire contents of each of these priority applications are incorporated herein by reference. TECHNICAL FIELD The invention refers to an imaging optical arrangement to image an object illuminated by X-rays. Further, the invention refers to a detection assembly including such an imaging optical arrangement and to a detection system including such a detection assembly. Further, the invention refers to an X-ray inspection method using such a detection system. BACKGROUND An imaging optical arrangement to image an object illuminated by X-rays is known from U.S. Pat. No. 7,057,187 B1, from U.S. Pat. No. 7,130,375 B1 and from U.S. Pat. No. 9,129,715 B2. Further, from DE 10 2018 209 570 A1 a method and a device to produce a three-dimensional image is known. US 2021/0012499 A1 discloses methods and systems for detecting defects in devices using X-rays. In the article of S. Gondrom et al., NDT.net—July 1999, Vol. 4, No. 7, Digital computed laminography and tomosynthesis including functional principles and industrial applications are disclosed. DE 42 28 082 C1 discloses an optical stop. US 2016/0088205 A1 discloses Multiplexed Fourier Ptychography imaging systems and methods. US 2018/0164690 A1 discloses an imaging optical unit for EUV projection lithography. US 2017/0131528 A1 discloses an imaging optical unit for a metrology system for examining a lithography mask. US 2012/0154823 A1 discloses a position detection apparatus, an exposure apparatus and a method of manufacturing. SUMMARY In a general aspect, the invention establishes an imaging optical arrangement which enables a high quality imaging of the object irrespective of X-rays entering the transfer field in an oblique or tilted manner. The above aspect is achieved by an imaging optical arrangement configured to image an object illuminated by X-rays, in which the imaging optical arrangement includes an imaging optics to image a transfer field in a field plane into a detection field in a detection plane via an imaging light path, a layer of scintillator material arranged at the transfer field, and a stop being arranged in a pupil plane of the imaging optics. The imaging optics has an optical axis, and a center of a stop opening of the stop is arranged at a decentering distance with respect to the optical axis. It has been realized by the inventors, that a stop arranged at a decentering distance with respect to the optical axis of the imaging optics of the imaging optical arrangement makes it possible to adapt such decentering distance to an angle of an oblique or tilted entry of X-rays to the transfer field of the imaging optics. With a respective decentering of the stop opening, a mean spot size of the imaging spots of points of origin from different positions of the layer of scintillator material can be kept advantageously small. This gives a good imaging from the transfer field to the detection field even in case of obliquely entering rays on the layer of scintillator material. The stop opening of the stop of the imaging optical arrangement defines a pupil of the imaging optics. In particular, it is possible to image object structures, which are smaller than 20 μm, smaller than 10 μm and in particular which are smaller than 1 μm. Examples for such structures are Cu—Cu hybrid bonding structures between microchips and substrate conductor paths. In particular, direct bonds between single dies or between a whole wafer onto a substrate wafer can be inspected. In particular, a 3D tomographic reconstruction of an object sample under investigation by combining several 2D images taken from different directions is possible. A decentering distance that is at least 10% of a width of the stop opening has proven to be good adapted to typical space requirements of detection systems and detection assemblies including such an imaging optical arrangement. The decentering distance can be larger than 10% of the stop opening width and can amount to 15%, 20%, 25%, 30%, 35%, 40% or even a larger fraction of the stop opening width. The decentering distance can be a continuous function of an angle of incidence of the X-ray illumination of the object. After measuring such X-ray angle of incidence, for a given imaging optical arrangement, a decentering distance value can be stored, e.g., in a look-up table to be adjusted within the imaging optics. The stop opening of the stop can be a circular opening. In this case, the width of the sto