Abstract: A method, involving illuminating at least a first periodic structure of a metrology target with a first radiation beam having a first polarization, illuminating at least a second periodic structure of the metrology target with a second radiation beam having a second different polarization, combining radiation diffracted from the first periodic structure with radiation diffracted from the second periodic structure to cause interference, detecting the combined radiation using a detector, and determining a parameter of interest from the detected combined radiation.

Abstract: An overlay metrology target (600, 900, 1000) contains a plurality of overlay gratings (932-935) formed by lithography. First diffraction signals (740(1)) are obtained from the target, and first asymmetry values (As) for the target structures are derived. Second diffraction signals (740(2)) are obtained from the target, and second asymmetry values (As?) are derived. The first and second diffraction signals are obtained using different capture conditions and/or different designs of target structures and/or bias values. The first asymmetry signals and the second asymmetry signals are used to solve equations and obtain a measurement of overlay error. The calculation of overlay error makes no assumption whether asymmetry in a given target structure results from overlay in the first direction, in a second direction or in both directions. With a suitable bias scheme the method allows overlay and other asymmetry-related properties to be measured accurately, even in the presence of two-dimensional overlay structure.

Abstract: Methods and apparatuses for measuring a plurality of structures formed on a substrate are disclosed. In one arrangement, a method includes obtaining data from a first measurement process. The first measurement process including individually measuring each of the plurality of structures to measure a first property of the structure. A second measurement process is used to measure a second property of each of the plurality of structures. The second measurement process includes illuminating each structure with radiation having a radiation property that is individually selected for that structure using the measured first property for the structure.

Abstract: A substrate has three or more overlay gratings formed thereon by a lithographic process. Each overlay grating has a known overlay bias. The values of overlay bias include for example two values in a region centered on zero and two values in a region centered on P/2, where P is the pitch of the gratings. Overlay is calculated from asymmetry measurements for the gratings using knowledge of the different overlay bias values and an assumed non-linear relationship between overlay and target asymmetry, thereby to correct for feature asymmetry. The periodic relationship in the region of zero bias and P/2 has gradients of opposite sign. The calculation allows said gradients to have different magnitudes as well as opposite sign. The calculation also provides information on feature asymmetry and other processing effects. This information is used to improve subsequent performance of the measurement process, and/or the lithographic process.

Abstract: An overlay measurement (OV) is based on asymmetry in a diffraction spectrum of target structures formed by a lithographic process. Stack difference between target structures can be perceived as grating imbalance (GI), and the accuracy of the overlay measurement may be degraded. A method of predicting GI sensitivity is performed using first and second images (45+, 45?) of the target structure using opposite diffraction orders. Regions (ROI) of the same images are used to measure overlay. Multiple local measurements of symmetry (S) and asymmetry (A) of intensity between the opposite diffraction orders are made, each local measurement of symmetry and asymmetry corresponding to a particular location on the target structure. Based on a statistical analysis of the local measurements of symmetry and asymmetry values, a prediction of sensitivity to grating imbalance is obtained. This can be used to select better measurement recipes, and/or to correct errors caused by grating imbalance.

Abstract: An overlay metrology target (T) is formed by a lithographic process. A first image (740(0)) of the target structure is obtained using with illuminating radiation having a first angular distribution, the first image being formed using radiation diffracted in a first direction (X) and radiation diffracted in a second direction (Y). A second image (740(R)) of the target structure using illuminating radiation having a second angular illumination distribution which the same as the first angular distribution, but rotated 90 degrees. The first image and the second image can be used together so as to discriminate between radiation diffracted in the first direction and radiation diffracted in the second direction by the same part of the target structure. This discrimination allows overlay and other asymmetry-related properties to be measured independently in X and Y, even in the presence of two-dimensional structures within the same part of the target structure.

Abstract: A method including obtaining a fit of data for overlay of a metrology target for a patterning process as a function of a stack difference parameter of the metrology target; and using, by a hardware computer, a slope of the fit (i) to differentiate a metrology target measurement recipe from another metrology target measurement recipe, or (ii) calculate a corrected value of overlay, or (iii) to indicate that an overlay measurement value obtained using the metrology target should be used, or not be used, to configure or modify an aspect of the patterning process, or (iv) any combination selected from (i)-(iii).

Abstract: A property of a target structure is measured based on intensity of an image of the target. The method includes (a) obtaining an image of the target structure; (b) defining a plurality of candidate regions of interest, each candidate region of interest comprising a plurality of pixels in the image; (c) defining an optimization metric value for the candidate regions of interest based at least partly on signal values of pixels within the region of interest; (d) defining a target signal function which defines a contribution of each pixel in the image to a target signal value. The contribution of each pixel depends on (i) which candidate regions of interest contain that pixel and (ii) optimization metric values of those candidate regions of interest.

Abstract: In an illumination system (12, 13) for a scatterometer, first and second spatial light modulators lie in a common plane and are formed by different portions of a single liquid crystal cell (260). Pre-polarizers (250) apply polarization to first and second radiation prior to the spatial light modulators. A first spatial light modulator (236-S) varies a polarization state of the first radiation in accordance with a first programmable pattern. Second spatial light modulator (236-P) varies a polarization state of the second radiation accordance with a second programmable pattern. A polarizing beam splitter (234) selectively transmits each of the spatially modulated first and second radiation to a common output path, depending on the polarization state of the radiation. In an embodiment, functions of pre-polarizers are performed by the polarizing beam splitter.

Abstract: A method including evaluating a plurality of substrate measurement recipes for measurement of a metrology target processed using a patterning process, against stack sensitivity and overlay sensitivity, and selecting one or more substrate measurement recipes from the plurality of substrate measurement recipes that have a value of the stack sensitivity that meets or crosses a threshold and that have a value of the overlay sensitivity within a certain finite range from a maximum or minimum value of the overlay sensitivity.

Abstract: A metrology target formed by a lithographic process on a substrate includes a plurality of component gratings. Images of the target are formed using +1 and ?1 orders of radiation diffracted by the component gratings. Regions of interest (ROIs) in the detected image are identified corresponding the component gratings. Intensity values within each ROI are processed and compared between images, to obtain a measurement of asymmetry and hence overlay error. Separation zones are formed between the component gratings and design so as to provide dark regions in the image. In an embodiment, the ROIs are selected with their boundaries falling within the image regions corresponding to the separation zones. By this measure, the asymmetry measurement is made more tolerant of variations in the position of the ROI. The dark regions also assist in recognition of the target in the images.

Abstract: A display system (1) for generating a picture in accordance with image information (10) derived from a video signal has a light modulation device (20), an illumination device (30) and a control circuit (40) for driving both devices. The algorithm implemented in the control circuit (40) distributes the image information (10) over the light modulation device (20) and the illumination device (30) in order to minimize the power consumption of the display system.

Abstract: In an illumination system (12, 13) for a scatterometer, first and second spatial light modulators lie in a common plane and are formed by different portions of a single liquid crystal cell (260). Pre-polarizers (250) apply polarization to first and second radiation prior to the spatial light modulators. A first spatial light modulator (236-S) varies a polarization state of the first radiation in accordance with a first programmable pattern. Second spatial light modulator (236-P) varies a polarization state of the second radiation accordance with a second programmable pattern. A polarizing beam splitter (234) selectively transmits each of the spatially modulated first and second radiation to a common output path, depending on the polarization state of the radiation. In an embodiment, functions of pre-polarizers are performed by the polarizing beam splitter.

Abstract: A spectral purity filter includes a body of material, through which a plurality of apertures extend. The apertures are arranged to suppress radiation having a first wavelength and to allow at least a portion of radiation having a second wavelength to be transmitted through the apertures. The second wavelength of radiation is shorter than the first wavelength of radiation. The body of material is formed from a material having a bulk reflectance of substantially greater than or equal to 70% at the first wavelength of radiation. The material has a melting point above 1000° C.

Abstract: A property of a target structure is measured based on intensity of an image of the target. The method includes (a) obtaining an image of the target structure; (b) defining a plurality of candidate regions of interest, each candidate region of interest comprising a plurality of pixels in the image; (c) defining an optimization metric value for the candidate regions of interest based at least partly on signal values of pixels within the region of interest; (d) defining a target signal function which defines a contribution of each pixel in the image to a target signal value. The contribution of each pixel depends on (i) which candidate regions of interest contain that pixel and (ii) optimization metric values of those candidate regions of interest.

Abstract: A method, involving illuminating at least a first periodic structure of a metrology target with a first radiation beam having a first polarization, illuminating at least a second periodic structure of the metrology target with a second radiation beam having a second different polarization, combining radiation diffracted from the first periodic structure with radiation diffracted from the second periodic structure to cause interference, detecting the combined radiation using a detector, and determining a parameter of interest from the detected combined radiation.

Abstract: An inspection apparatus includes an optical system, which has a radiation beam delivery system for delivering radiation to a target, and a radiation beam collection system for collecting radiation after scattering from the target. Both the delivery system and the collection system comprise optical components that control the characteristics of the radiation and the collected radiation. By controlling the characteristics of one or both of the radiation and collected radiation, the depth of focus of the optical system may be increased.

Abstract: A property of a target structure is measured based on intensity of an image of the target. The method includes (a) obtaining an image of the target structure; (b) defining (1204) a plurality of candidate regions of interest, each candidate region of interest comprising a plurality of pixels in the image; (c) defining (1208, 1216) an optimization metric value for the candidate regions of interest based at least partly on signal values of pixels within the region of interest; (d) defining (1208, 1216) a target signal function which defines a contribution of each pixel in the image to a target signal value. The contribution of each pixel depends on (i) which candidate regions of interest contain that pixel and (ii) optimization metric values of those candidate regions of interest.

Abstract: A metrology target formed by a lithographic process on a substrate includes a plurality of component gratings. Images of the target are formed using +1 and ?1 orders of radiation diffracted by the component gratings. Regions of interest (ROIs) in the detected image are identified corresponding the component gratings. Intensity values within each ROI are processed and compared between images, to obtain a measurement of asymmetry and hence overlay error. Separation zones are formed between the component gratings and design so as to provide dark regions in the image. In an embodiment, the ROIs are selected with their boundaries falling within the image regions corresponding to the separation zones. By this measure, the asymmetry measurement is made more tolerant of variations in the position of the ROI. The dark regions also assist in recognition of the target in the images.

Abstract: A substrate has a plurality of overlay gratings formed thereon by a lithographic process. Each overlay grating has a known overlay bias. The values of overlay bias include for example two values in a region centered on zero and two values in a region centered on P/2, where P is the pitch of the gratings. Overlay is calculated from asymmetry measurements for the gratings using knowledge of the different overlay bias values, each of the overall asymmetry measurements being weighted by a corresponding weight factor. Each one of the weight factors represents a measure of feature asymmetry within the respective overlay grating. The calculation is used to improve subsequent performance of the measurement process, and/or the lithographic process. Some of the asymmetry measurements may additionally be weighted by a second weight factor in order to eliminate or reduce the contribution of phase asymmetry to the overlay.