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 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: 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 diffraction measurement target that has at least a first sub-target and at least a second sub-target, and wherein (1) the first and second sub-targets each include a pair of periodic structures and the first sub-target has a different design than the second sub-target, the different design including the first sub-target periodic structures having a different pitch, feature width, space width, and/or segmentation than the second sub-target periodic structure or (2) the first and second sub-targets respectively include a first and second periodic structure in a first layer, and a third periodic structure is located at least partly underneath the first periodic structure in a second layer under the first layer and there being no periodic structure underneath the second periodic structure in the second layer, and a fourth periodic structure is located at least partly underneath the second periodic structure in a third layer under the second layer.

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 laser-based light source includes a laser device configured to generate laser light of a predetermined laser wavelength and emit this laser light as a laser beam. A light-conversion device is configured to convert at least part of the laser light into converted light and a laser-output sensor is configured to determine a laser-output signal proportional to the output of laser light emitted by the laser device. Further, a converted-light sensor is configured to determine a converted-light signal proportional to the output of converted light emitted by the light-conversion device. A controller is configured to receive the laser-output signal and the converted-light signal, to determine a safe-to-operate parameter, based on the laser-output signal and the converted-light signal, and to control the operation of the laser-based light source based on a comparison of the safe-to-operate parameter with a at least one predefined threshold.

Abstract: A spectral purity filter is configured to allow transmission therethrough of extreme ultraviolet (EUV) radiation and to refract or reflect non-EUV secondary radiation. The spectral purity filter may be part of a source module and/or a lithographic apparatus.

Abstract: A transmissive spectral purity filter is configured to transmit extreme ultraviolet radiation. The spectral purity filter includes a filter part having a plurality of apertures configured to transmit extreme ultraviolet radiation and to suppress transmission of a second type of radiation. Each aperture has been manufactured by an anisotropic etching process.

Abstract: Disclosed is a device manufacturing method, and accompanying inspection and lithographic apparatuses. The method comprises measuring on the substrate a property such as asymmetry of a first overlay marker and measuring on the substrate a property such as asymmetry of an alignment marker. In both cases the asymmetry is determined. The position of the alignment marker on the substrate is then determined using an alignment system and the asymmetry information of the alignment marker and the substrate aligned using this measured position. A second overlay marker is then printed on the substrate; and a lateral overlay measured on the substrate of the second overlay marker with respect to the first overlay marker using the determined asymmetry information of the first overlay marker.

Abstract: According to an aspect of the present invention, a spectral purity filter includes an aperture, the aperture being arranged to diffract a first wavelength of radiation and to allow at least a portion of a second wavelength of radiation to be transmitted through the aperture, the second wavelength of radiation being shorter than the first wavelength of radiation, wherein the aperture has a diameter greater than 20 ?m.

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 method of forming a spectral purity filter having a plurality of apertures configured to transmit extreme ultraviolet radiation and suppress transmission of a second type of radiation, in which trenches are formed in a base material in a pattern corresponding to the walls to be formed between the apertures. The trenches are filled with a grid material to form walls of the grid material, and the base material is selectively removed until the grid material is exposed and forms the spaces between the walls of the grid material for the apertures.

Abstract: A radiation source includes an uncapped Mo/Si multilayer mirror, and a cleaning apparatus configured to remove a deposition comprising Sn on the uncapped Mo/Si multilayer mirror. The cleaning apparatus is configured to provide a gas comprising one or more of H2, D2 and HD and one or more additional compounds selected from hydrocarbon compounds and/or silane compounds in at least part of the radiation source, to produce hydrogen and/or deuterium radicals and radicals of the one or more additional compounds, from the gas, and to supply the hydrogen and/or deuterium radicals and radicals of the one or more additional compounds to the uncapped Mo/Si multilayer mirror to remove at least part of the deposition.

Abstract: A radiation source includes an uncapped Mo/Si multilayer mirror, and a cleaning apparatus configured to remove a deposition comprising Sn on the uncapped Mo/Si multilayer mirror. The cleaning apparatus is configured to provide a gas comprising one or more of H2, D2 and HD and one or more additional compounds selected from hydrocarbon compounds and/or silane compounds in at least part of the radiation source, to produce hydrogen and/or deuterium radicals and radicals of the one or more additional compounds, from the gas, and to supply the hydrogen and/or deuterium radicals and radicals of the one or more additional compounds to the uncapped Mo/Si multilayer mirror to remove at least part of the deposition.

Abstract: A light output device includes first and second light sources, and a partly transparent mirror arranged between the light sources. The partly transparent mirror, during operation, receives substantially all light emitted by the first and second light sources, and reflects part of the light emitted by the first light source and transmits part of the light emitted by the second light source, and vice versa, such that the light from the first light source is superimposed onto the light from the second light source following reflection/transmission at the partly transparent mirror.

Abstract: A metal component (262M, 300M) is designed for use in an EUV lithography apparatus, for example as a spectral purity filter (260) or a heating element (300) in a hydrogen radical generator. An exposed surface of the metal is treated (262P, 300P) to inhibit the formation of an oxide of said metal in an air environment prior to operation. This prevents contamination of optical components by subsequent evaporation of the oxide during operation of the component at elevated temperatures.

Abstract: A method for removal of a deposition on an uncapped multilayer mirror of an apparatus. The method includes providing a gas that includes one or more of H2, D2, and DH, and one or more additional compounds selected from hydrocarbon compounds and/or silane compounds in at least part of the apparatus; producing hydrogen and/or deuterium radicals and radicals of the one or more additional compounds, from the gas; and bringing the uncapped multilayer mirror with deposition into contact with at least part of the hydrogen and/or deuterium radicals and the radicals of the one or more additional compounds to remove at least part of the deposition.

Abstract: Proposed is a light sensor (1), comprising at least one wavelength selective photo-detector (10), a lens (20) and an aperture (30).The wavelength selective photo-detector allows detecting light within a predefined wavelength range falling on the sensor. The lens project light on the photo-detector and the aperture defines a field of view of the light sensor. The photo-detector (10), the lens (20), and the aperture (30) are arranged in a telecentric configuration. Advantageously, this allows light to impinge on the wavelength selective photo-detector within a predefined range of angles irrespective of the direction of the light incident on the aperture, thus removing the angle dependent response of the wavelength selective photo-detector.

Abstract: According to an aspect of the present invention, a spectral purity filter includes an aperture, the aperture being arranged to diffract a first wavelength of radiation and to allow at least a portion of a second wavelength of radiation to be transmitted through the aperture, the second wavelength of radiation being shorter than the first wavelength of radiation, wherein the aperture has a diameter greater than 20 ?m.

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.