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WO-2026093323-A1 - METHOD FOR INSPECTING MICROLITHOGRAPHIC PHOTOMASKS, COMPUTER PROGRAM PRODUCT, SYSTEM FOR INSPECTING A MICROLITHOGRAPHIC PHOTOMASK, METHOD FOR REPAIRING A MICROLITHOGRAPHIC PHOTOMASK AND METHOD OF MICROLITHOGRAPHY

WO2026093323A1WO 2026093323 A1WO2026093323 A1WO 2026093323A1WO-2026093323-A1

Abstract

Method for inspecting a microlithographic photomask (17), wherein with the aid of a mask inspection device comprising an illumination lens (16) and a projection lens (22), the image of a photomask (17) illuminated by means of the illumination lens (16) is projected by the projection lens (22) onto an image sensor (24) of a camera (23) arranged in the image plane of the projection lens (22). The photomask (17) is placed on a positioning system (26) that is designed to displace the photomask (17). The photomask (17) is displaced using the positioning system (26) such that the image sensor (24) captures a first image line (101) that corresponds to a first region on the photomask (17). The photomask (17) is displaced using the positioning system (26) such that the image sensor (24) captures a second image line (102) that corresponds to a second region on the photomask (17). There is an overlap (200) between the first region and the second region such that the first and the second image line (101, 102) comprise a piece of image information regarding a structure of the photomask (17) arranged within the overlap (200). A defect detection method is applied to the piece of image information in the first image line (101) in order to determine a first piece of defect information. A defect detection method is applied to the piece of image information in the second image line (102) in order to determine a second piece of defect information. The first piece of defect information is compared with the second piece of defect information in order to determine a piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200). The invention also relates to a system for inspecting a microlithographic photomask, a computer program product, a method for repairing a microlithographic photomask and a method of microlithography.

Inventors

  • TABBONE, GILLES
  • FROEHLICH, BJOERN
  • Freytag, Alexander
  • BRAUER, BJOERN
  • NGUYEN, XUAN TRUONG

Assignees

  • CARL ZEISS SMT GMBH

Dates

Publication Date
20260507
Application Date
20251028
Priority Date
20241030

Claims (20)

  1. 1. Method for inspecting a microlithographic photomask (17) , wherein with the aid of a mask inspection device comprising an illumination lens (16) and a projection lens (22) , the image of a photomask (17) illuminated by means of the illumination lens (16) is projected by the projection lens (22) onto an image sensor (24) of a camera (23) arranged in the image plane of the projection lens (22) , comprising the following steps: a) placing the photomask (17) on a positioning system (26) that is designed to displace the photomask (17) ; b) displacing the photomask (17) using the positioning system (26) such that the image sensor (24) captures a first image line (101) that corresponds to a first region on the photomask (17) ; c) displacing the photomask (17) using the positioning system (26) such that the image sensor (24) captures a second image line (102) that corresponds to a second region on the photomask (17) , with there being an overlap (200) between the first region and the second region such that the first and the second image line (101, 102) comprise a piece of image information regarding a structure of the photomask (17) arranged within the overlap (200) ; d) applying a defect detection method to the piece of image information in the first image line (101) in order to determine a first piece of defect information; e) applying a defect detection method to the piece of image information in the second image line (102) in order to determine a second piece of defect information; f) comparing the first piece of defect information with the second piece of defect information in order to determine a piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200) .
  2. 2. Method according to Claim 1, wherein the first image line (101) is captured by virtue of the positioning system (26) displacing the photomask (17) in a positive X-direction and wherein the second image line (102) is captured by virtue of the positioning system (26) displacing the photomask (17) in the positive or negative X-direction.
  3. 3. Method according to Claim 2, wherein the capture of the second image line is preceded by the positioning system (26) displacing the photomask (17) in a Y-direction such that an overlap parameter is less than 1.
  4. 4. Method according to Claim 3, wherein the overlap parameter is less than 0.1, preferably less than 0.05, further preferably less than 0.02 and further preferably less than 0.01.
  5. 5. Method according to any of the preceding claims, wherein the overlap (200) corresponds to a region on the photomask (17) that is specified on the basis of a specified region.
  6. 6. Method according to any of the preceding claims, wherein the determined piece of information regarding the correctness is compared with an expected correctness.
  7. 7. Method according to Claim 6, wherein the comparison between the determined piece of information regarding the correctness and the expected correctness is used to determine a piece of calibration information for the mask inspection device and/or a defect detection method, in order to reduce a deviation between the determined piece of information regarding the correctness and the expected correctness.
  8. 8. Method according to any of the preceding claims, wherein the overlap (200) is specified on the basis of structures to be registered.
  9. 9. Method according to any of the preceding claims, wherein steps b) and c) are repeated in order to capture a plurality of pairs of first and second image lines (101, 102) and wherein steps d) to f) are performed on the basis of a specified rate for a subset of the plurality of pairs of first and second image lines (101, 102) .
  10. 10. Method according to any of the preceding claims, wherein a defect candidate in the first or second piece of defect information is verified by a defect candidate in the respective other piece of defect information such that the piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200) then states that an actual defect is present if a certain defect candidate is present in the first and in the second piece of defect information.
  11. 11. Method according to any of Claims 1 to 6, wherein the piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200) then states that an actual defect is present if a certain defect candidate is present in the first or in the second piece of defect information.
  12. 12. Method according to either of Claims 10 and 11, wherein the information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200) comprises a piece of reliability information.
  13. 13. Method according to Claim 12, wherein the piece of reliability information specifies the number of pieces of defect information in which a certain defect candidate is present.
  14. 14. Method according to either of Claims 12 and 13, wherein a setting of the mask inspection device is modified in response to the piece of reliability information.
  15. 15. Method according to any of the preceding claims, wherein a specified piece of identity information is used to determine whether a defect candidate in the first piece of defect information corresponds to a defect candidate in the second piece of defect information.
  16. 16. Method according to Claim 15, wherein the piece of identity information states that two defect candidates are identical if they have the same centre or are arranged within a certain radius on the photomask (17) or have the same shape or if a shape difference lies within a certain shape tolerance .
  17. 17. Method according to any of the preceding claims, wherein the piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (200) and/or the piece of reliability information is output, preferably acoustically, visually, as a database entry or as a text file.
  18. 18. Method according to any of the preceding claims, wherein at least one defect detection method comprises the application of a trained model from machine learning, with the input of the model comprising an image line (101, 102, 103) or a section of an image line and the output of the model comprising a piece of defect information. 31
  19. 19. Method according to any of the preceding claims, wherein the photomask (17) is displaced using the positioning system (26) such that the image sensor (24) captures a third image line (103) that corresponds to a third region on the photomask (17) , with there being an overlap (300) between the first region and the third region and also between the second region and the third region such that the first, the second and the third image line (101, 102, 103) comprise the image information regarding the structure of the photomask (17) arranged within the overlap (300) , and wherein the third piece of defect information is also compared with the first piece of defect information and the second piece of defect information in order to determine the piece of information regarding the correctness of the structure of the photomask (17) arranged within the overlap (300) .
  20. 20. Method according to Claim 19, wherein at least one image line is combined from two overlaid image lines.

Description

CZVS 151PW0 28 . 10 . 2025/PH Method for inspecting mi cr ©lithographic photomasks , computer program product , system for inspecting a mi cr ©lithographic photomask , method for repairing a mi cr ©lithographic photomask and method of microlithography [ 0001 ] The invention relates to a method for inspecting a mi- crolithographic photomask . The invention also relates to a computer program product , a system for inspecting a microlith- ographic photomask, a method for repairing a microlithographic photomask and a method of microlithography . [ 0002 ] Photomasks are used in microlithographic proj ection exposure apparatuses used to produce components such as integrated circuits with particularly small structures . The photomask illuminated by very short-wave extreme ultraviolet radiation (EUV radiation) is imaged onto a lithography obj ect in order to trans fer the mask structure to the lithography ob- j ect . [ 0003 ] To ensure a high quality of the image generated on the lithography obj ect , it is necessary for the photomask to be true to si ze and not adversely af fected by structural defects . It is known practice to subj ect photomasks to an inspection, either prior to operation in a microlithographic proj ection exposure apparatus or during an interruption of operation . To this end, what is known as an aerial image of a portion of the photomask is created using a mask inspection system, the photomask in the process being imaged not on a lithography obj ect but on an image sensor of an EUV camera . Using the imaging onto the image sensor as a basis , it is possible to use a defect detection method to make an assessment as to whether the photomask is without defects . Defect detection methods are known in the prior art . [ 0004 ] For example , a defect may consist in a structure part of the photomask or the distance between two structure parts not being suf ficiently wide . Additionally, a structure part may comprise a locali zed defect not provided for in the envisaged design of the photomask or an unwanted "bridge" to an adj acent structure part . During an exposure of a mask comprising a mask defect , the defect would be imaged on the light-sensitive layer as an irregular shadow or bright region and, following the subsequent processing steps , would also be found in the component ultimately produced . Various repair methods that can be used to remove defects or at least reduce these to a harmless level are known from the prior art . For this purpose , a material of the photomask is typically removed, added and/or structurally modi fied during a repair step . To this end, an electron beam or an ion beam may be used to influence the photomask, for example . Relatively long straight defects may also be removed by mechanical action ( scratching) . The use of a laser is also possible but usually not precise enough . [ 0005 ] Any undetected defect on a photomask left unrepaired may render an entire batch of components produced unusable . Hence , it is desirable that preferably no defect remains undetected during the inspection of microlithographic photomasks so that all defects actually present can be repaired . [ 0006 ] Defect detection methods may ascertain a piece of defect information that comprises one or more defect candidates . A defect candidate is a detected potential defect in the structure of the photomask . Defect detection methods applied during a mask inspection typically have high sensitivity and low speci ficity . The sensitivity is the probability that an actual defect is in fact present at a detected defect candidate . The speci ficity is the probability that no actual defect is in fact present should no defect candidate be detected . Accordingly, the defect detection methods are typically designed such that all actual defects present are detected while accepting a few detected defect candidates at which no actual defect is present . In other words , the applied defect detection methods typically have a low " false negative rate" and a high " false positive rate" . As explained above , the low false negative rate is desired so that preferably no actual defects present remain undetected . However, the high false positive rate is disadvantageous because it is typically a human who performs the last assessment of the detected defect candidates before the photomask is repaired, and so the human could be presented with numerous defect candidates where no actual defect on the photomask is present ; this is time-consuming and expensive . [ 0007 ] The problem addressed by the invention is that of presenting a method and a computer program product for inspecting microlithographic photomasks , in which the aforementioned disadvantages are reduced . The problem is solved by the features of the independent claims . Advantageous embodiments are specified in the dependent claims . [ 0008 ] In a method according to the invention for inspecting a microlithographic photomask and with the aid of a ma