Metrology Method and Inspection Apparatus, Lithographic System and Device Manufacturing Method
First Claim
1. A method comprising:
- using a lithographic process to form a periodic structure on a substrate;
a first measurement comprising forming and detecting a first image of the periodic structure, while illuminating the structure with a first beam of radiation, the first image being formed using a first selected part of diffracted radiation;
a second measurement comprising forming and detecting a second image of the periodic structure, while illuminating the structure with a second beam of radiation, the second image being formed using a second selected part of the diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure;
using a difference in intensity values derived from the detected first and second images together to determine a property of the periodic structure; and
controlling a spatial light modulator to apply a varying non-binary optical attenuation over the first and second selected parts of the diffracted radiation prior to forming the first and second images respectively.
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Accused Products
Abstract
Methods are disclosed for measuring target structures formed by a lithographic process on a substrate. A grating structure within the target is smaller than an illumination spot and field of view of a measurement optical system. The optical system has a first branch leading to a pupil plane imaging sensor and a second branch leading to a substrate plane imaging sensor. A spatial light modulator is arranged in an intermediate pupil plane of the second branch of the optical system. The SLM imparts a programmable pattern of attenuation that may be used to correct for asymmetries between the first and second modes of illumination or imaging. By use of specific target designs and machine-learning processes, the attenuation patterns may also be programmed to act as filter functions, enhancing sensitivity to specific parameters of interest, such as focus.
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Citations
23 Claims
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1. A method comprising:
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using a lithographic process to form a periodic structure on a substrate; a first measurement comprising forming and detecting a first image of the periodic structure, while illuminating the structure with a first beam of radiation, the first image being formed using a first selected part of diffracted radiation; a second measurement comprising forming and detecting a second image of the periodic structure, while illuminating the structure with a second beam of radiation, the second image being formed using a second selected part of the diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure; using a difference in intensity values derived from the detected first and second images together to determine a property of the periodic structure; and controlling a spatial light modulator to apply a varying non-binary optical attenuation over the first and second selected parts of the diffracted radiation prior to forming the first and second images respectively. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An inspection apparatus comprising:
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an illumination arrangement operable to deliver conditioned beams of radiation to the substrate for use in measurements; a detection arrangement operable during such measurements to form and detect respective images of the substrate using radiation diffracted from the substrate the illumination arrangement and the detection arrangement forming a measurement optical system; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are operable to select which part of a diffraction spectrum of the diffracted radiation contributes to each image, and wherein the detection arrangement further comprises a spatial light modulator operable to apply a varying optical attenuation over the selected part of the diffracted radiation prior to forming the first and second images respectively. - View Dependent Claims (19, 20, 21)
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22. A lithographic system comprising:
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a lithographic apparatus comprising; an illumination optical system arranged to illuminate a pattern; a projection optical system arranged to project an image of the pattern onto a substrate; and an inspection apparatus comprising, an illumination arrangement operable to deliver conditioned beams of radiation to the substrate for use in measurements; a detection arrangement operable during such measurements to form and detect respective images of the substrate using radiation diffracted from the substrate the illumination arrangement and the detection arrangement forming a measurement optical system; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are operable to select which part of a diffraction spectrum of the diffracted radiation contributes to each image, and wherein the detection arrangement further comprises a spatial light modulator operable to apply a varying optical attenuation over the selected part of the diffracted radiation prior to forming the first and second images respectively, wherein the lithographic apparatus is arranged to use the measurement results from the inspection apparatus in applying the pattern to further substrates.
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23. A method of manufacturing devices comprising:
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a device pattern is applied to a series of substrates using a lithographic process; inspecting at least one periodic structure formed as part of or beside the device pattern on at least one of the substrates using an inspection method comprising, using a lithographic process to form a periodic structure on a substrate; a first measurement comprising forming and detecting a first image of the periodic structure, while illuminating the structure with a first beam of radiation, the first image being formed using a first selected part of diffracted radiation; a second measurement comprising forming and detecting a second image of the periodic structure, while illuminating the structure with a second beam of radiation, the second image being formed using a second selected part of the diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure; using a difference in intensity values derived from the detected first and second images together to determine a property of the periodic structure; and controlling a spatial light modulator to apply a varying non-binary optical attenuation over the first and second selected parts of the diffracted radiation prior to forming the first and second images respectively; and controlling the lithographic process for later substrates in accordance with the result of the inspection method.
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Specification