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 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 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 detecting 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
18 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 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 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 detecting 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. 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 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 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 detecting 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