Metrology Method and Apparatus, and Device Manufacturing Method
First Claim
1. A method of measuring asymmetry in a periodic structure formed by a lithographic process on a substrate, the method comprising:
- using the lithographic process to form a periodic structure on the substrate;
a first measurement step 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 part of non-zero order diffracted radiation while excluding zero order diffracted radiation;
a second measurement step 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 part of the non-zero order diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure; and
using a difference in intensity values derived from the detected first and second images together to determine the asymmetry in the profile of the periodic structure,wherein the first and second measurement steps are performed using different optical paths within a measurement optical system, andat least one correction, applied either to the first and second image intensity values or to the calculated difference between them, for reducing an influence on the determined asymmetry of the difference in optical paths between the first and second measurement steps.
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Accused Products
Abstract
Methods are disclosed for measuring target structures formed by a lithographic process on a substrate. A grating or other structure within the target is smaller than an illumination spot and field of view of a measurement optical system. The position of an image of the component structure varies between measurements, and a first type of correction is applied to reduce the influence on the measured intensities, caused by differences in the optical path to and from different positions. A plurality of structures may be imaged simultaneously within the field of view of the optical system, and each corrected for its respective position. The measurements may comprise first and second images of the same target under different modes of illumination and/or imaging, for example in a dark field metrology application. A second type of correction may be applied to reduce the influence of asymmetry between the first and second modes of illumination or imaging, for example to permit a more accurate overly measurement in a semiconductor device manufacturing process.
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Citations
18 Claims
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1. A method of measuring asymmetry in a periodic structure formed by a lithographic process on a substrate, the method comprising:
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using the lithographic process to form a periodic structure on the substrate; a first measurement step 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 part of non-zero order diffracted radiation while excluding zero order diffracted radiation; a second measurement step 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 part of the non-zero order diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure; and using a difference in intensity values derived from the detected first and second images together to determine the asymmetry in the profile of the periodic structure, wherein the first and second measurement steps are performed using different optical paths within a measurement optical system, and at least one correction, applied either to the first and second image intensity values or to the calculated difference between them, for reducing an influence on the determined asymmetry of the difference in optical paths between the first and second measurement steps. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An inspection apparatus configured for measuring asymmetry in a periodic structure on a substrate, the inspection apparatus comprising:
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an illumination arrangement operable to deliver first and second beams of radiation to the substrate for use in first and second measurements; a detection arrangement operable during the first and second measurements to form and detect respective first and second images of the substrate using radiation diffracted from the substrate; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are effective to stop zero order diffracted radiation contributing to the first and second images, and are configurable to form first and second images using first and second parts respectively of the non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation, a computational arrangement operable to determine the asymmetry using a difference in intensity values derived from the first and second images, the computational arrangement is operable when calculating the difference to apply a correction for reducing an influence on the determined asymmetry of a difference between first and second optical paths, that are used within the inspection apparatus for the first and second measurements respectively. - View Dependent Claims (11, 12)
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13. A method of measuring properties of a target structure formed by a lithographic process on a substrate, the method comprising:
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using the lithographic process to form a structure on the substrate; forming and detecting an image of the structure through an optical system while illuminating the structure with a beam of radiation; using intensity values derived from the detected image together to determine at least one parameter of the structure, wherein the image of the structure is smaller than an image field of the optical system, and detecting a position of the image within the image field, and applying a correction to reduce an influence on the measured properties of a difference in optical paths between positions. - View Dependent Claims (14)
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15. An inspection apparatus for measuring properties of a target structure formed by a lithographic process on a substrate, the inspection apparatus comprising:
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an illumination arrangement operable to deliver a radiation beam to the substrate; a detection arrangement operable to form and detect an image of the structure through an optical system while the illumination arrangement is illuminating the structure with a radiation beam; and a computational arrangement operable; to use intensity values derived from the detected image together to determine at least one property of the structure; to detect a position of the image within the image field when the image of the structure is smaller than an image field of the optical system; and in response to detected position, to apply a correction to reduce an influence on the measured property of differences in optical paths associated with different image positions. - View Dependent Claims (16)
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17. 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 first and second beams of radiation to the substrate for use in first and second measurements; a detection arrangement operable during the first and second measurements to form and detect respective first and second images of the substrate using radiation diffracted from the substrate; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are effective to stop zero order diffracted radiation contributing to the first and second images, and are configurable to form first and second images using first and second parts respectively of the non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation, a computational arrangement operable to determine the asymmetry using a difference in intensity values derived from the first and second images, the computational arrangement is operable when calculating the difference to apply a correction for reducing an influence on the determined asymmetry of a difference between first and second optical paths, that are used within the inspection apparatus for the first and second measurements 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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18. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including:
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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 the lithographic process to form a periodic structure on the substrate; a first measurement step 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 part of non-zero order diffracted radiation while excluding zero order diffracted radiation; a second measurement step 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 part of the non-zero order diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure; and using a difference in intensity values derived from the detected first and second images together to determine the asymmetry in the profile of the periodic structure, wherein the first and second measurement steps are performed using different optical paths within a measurement optical system, and at least one correction, applied either to the first and second image intensity values or to the calculated difference between them, for reducing an influence on the determined asymmetry of the difference in optical paths between the first and second measurement steps, and controlling the lithographic process for later substrates in accordance with the result of the inspection method.
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Specification