Methods and scatterometers, lithographic systems, and lithographic processing cells
First Claim
1. A method of determining a focus of a lithographic apparatus used in a lithographic process on a substrate, the method comprising:
- forming a periodic structure on the substrate, the periodic structure comprising at least one feature having a profile which has an asymmetry, the asymmetry depending on the focus of the lithographic apparatus on the substrate;
stopping, using a stop arrangement and an illumination arrangement together, zero order diffracted radiation from contributing to a first image and a second image of the periodic structure;
detecting a first image of the periodic structure while illuminating the periodic structure with a first beam of radiation from the illumination arrangement to generate a first measurement, the first image being formed using a first part of non-zero order diffracted radiation while excluding zero order diffracted radiation;
detecting a second image of the periodic structure while illuminating the periodic structure with a second beam of radiation from the illumination arrangement to generate a second measurement;
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;
determining the asymmetry in the profile of periodic the structure based on the first and second images detected in the first and second measurements; and
providing an indication of the focus on the substrate based on the determined asymmetry and a relationship between the focus and the determined asymmetry.
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Accused Products
Abstract
In a method of determining the focus of a lithographic apparatus used in a lithographic process on a substrate, the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has an asymmetry in the printed profile which varies as a function of the focus of the lithographic apparatus on the substrate. A first image of the periodic structure is formed and detected while illuminating the structure with a first beam of radiation. The first image is formed using a first part of non-zero order diffracted radiation. A second image of the periodic structure is formed and detected while illuminating the structure with a second beam of radiation. The second image is formed using a second part of the non-zero order diffracted radiation which is symmetrically opposite to the first part in a diffraction spectrum. The ratio of the intensities of the measured first and second portions of the spectra is determined and used to determine the asymmetry in the profile of the periodic structure and/or to provide an indication of the focus on the substrate. In the same instrument, an intensity variation across the detected portion is determined as a measure of process-induced variation across the structure. A region of the structure with unwanted process variation can be identified and excluded from a measurement of the structure.
119 Citations
24 Claims
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1. A method of determining a focus of a lithographic apparatus used in a lithographic process on a substrate, the method comprising:
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forming a periodic structure on the substrate, the periodic structure comprising at least one feature having a profile which has an asymmetry, the asymmetry depending on the focus of the lithographic apparatus on the substrate; stopping, using a stop arrangement and an illumination arrangement together, zero order diffracted radiation from contributing to a first image and a second image of the periodic structure; detecting a first image of the periodic structure while illuminating the periodic structure with a first beam of radiation from the illumination arrangement to generate a first measurement, the first image being formed using a first part of non-zero order diffracted radiation while excluding zero order diffracted radiation; detecting a second image of the periodic structure while illuminating the periodic structure with a second beam of radiation from the illumination arrangement to generate a second measurement;
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;determining the asymmetry in the profile of periodic the structure based on the first and second images detected in the first and second measurements; and providing an indication of the focus on the substrate based on the determined asymmetry and a relationship between the focus and the determined asymmetry. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An angularly resolved scatterometer configured to determine a focus of a lithographic apparatus used in a lithographic process on a substrate, wherein the lithographic process is used to form a structure on the substrate, the structure comprising at least one feature having a profile which has an asymmetry, the asymmetry depending on the focus of the lithographic apparatus on the substrate, the scatterometer comprising:
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an illumination arrangement configured 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 structure 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, while the first and second images are formed using first and second parts respectively of non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and a computational arrangement configured to determine the asymmetry for the feature from the first and second images and/or to use the determined asymmetry and a relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A lithographic system comprising:
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 on to a substrate; and an angularly resolved scatterometer configured to determine a focus of the lithographic system used in a lithographic process on the substrate, wherein the lithographic process is used to form a structure on the substrate, the structure comprising at least one feature having a profile which has an asymmetry which depends on the focus of the lithographic system on the substrate, the scatterometer comprising; an illumination arrangement configured 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 structure using radiation diffracted from the substrate; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are configured to stop zero order diffracted radiation contributing to the first and second images, while the first and second images are formed using first and second parts respectively of non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and a computational arrangement configured to determine the asymmetry for the feature from the first and second images and/or to use the determined asymmetry and a relationship between the focus and the asymmetry or each feature to provide an indication of the focus on the substrate.
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22. A lithographic cell comprising:
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a coater arranged to coat a substrate with a radiation sensitive layer; a lithographic apparatus arranged to expose images onto the radiation sensitive layer of the substrate; a developer arranged to develop images exposed by the lithographic apparatus; and an angularly resolved scatterometer configured to determine a focus of the lithographic apparatus used in a lithographic process on the substrate, wherein the lithographic process is used to form a structure on the substrate, the structure comprising at least one feature having a profile which has an asymmetry, the asymmetry depending on the focus of the lithographic apparatus on the substrate, the scatterometer 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 structure using radiation diffracted from the substrate; and a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are configured to stop zero order diffracted radiation contributing to the first and second images, while the first and second images are formed using first and second parts respectively of non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and a computational arrangement configured to determine the asymmetry for the feature from the first and second images and/or to use the determined asymmetry and a relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate.
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23. An angularly resolved scatterometer configured to determine a focus of a lithographic apparatus used in a lithographic process on a substrate, wherein the lithographic process is used to form a structure on the substrate, the structure comprising at least one feature having a profile which has an asymmetry, the asymmetry depending on the focus of the lithographic apparatus on the substrate, the scatterometer comprising:
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an illumination device configured to produce a beam of radiation; a masking device arranged such that the beam of radiation produced by the illumination device and directed onto the substrate through the masking device will illuminate the structure within a first range of angles; a detection device configured to detect an image produced by radiation diffracted from the structure; a stop device between the substrate and the detection device, the masking device and stop device together being effective to stop zero order diffracted radiation and a part of higher order diffracted radiation from being detected, wherein the masking device and the substrate are configured to rotate relative to each other about their respective optical axes such that after the relative rotation the structure is illuminated within a second range of angles, the second range being diametrically opposed to the first range within a cross section of the beam of radiation, and wherein the detection device is configured to measure different portions of the image produced by the diffracted radiation produced by directing the beam of radiation onto the structure through the stop device before and after the rotation of the masking device and the substrate relative to each other about their respective optical axes; and a computational device configured to determine the asymmetry for the feature from the different portions of the image measured before and after the rotation of the device and the substrate relative to each other or to use the determined asymmetry and a relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate. - View Dependent Claims (24)
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Specification