Measurement system and method for characterizing a patterning device

Abstract

A method for determining surface parameters of a pattern forming device is provided, comprising the following steps: positioning the pattern forming device relative to the path of an exposure radiation beam using a first measurement system; setting the pattern forming device at a first focal plane of a chromatic lens arranged in a second measurement system; irradiating a portion of the surface of the pattern forming device with radiation passing through the chromatic lens, wherein the radiation includes multiple wavelengths; determining the position of the irradiated portion of the pattern forming device in a first direction and a second direction; collecting at least a portion of the radiation reflected by the pattern forming device through the chromatic lens; measuring the intensity of the collected portion of the radiation as a function of wavelength to obtain spectral information of the irradiated area; and determining the surface parameters of the pattern forming device at the determined position based on the spectral information.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application 19201296.1 filed on October 3, 2019, and the entire contents of said European application are incorporated herein by reference. Technical Field

[0003] The present invention relates to measurement systems and methods for characterizing a patterning device and in particular for measuring geometrical and surface properties of a patterning device. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] As semiconductor manufacturing processes continue to advance, the size of circuit elements has continued to decrease over the decades, while the amount of functional elements such as transistors per device has steadily increased, following a trend commonly referred to as "Moore's Law". In order to keep up with Moore's Law, the semiconductor industry is chasing technologies that can produce smaller and smaller features. In order to project a pattern onto a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365nm (i-line), 248nm, 193nm, and 13.5nm. Compared to lithography equipment using radiation with a wavelength of, for example, 193nm, lithography equipment using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4nm to 20nm (e.g., 6.7nm or 13.5nm) can be used to form smaller features on a substrate.

[0006] It is desirable to provide accurate control of the pattern of the substrate transferred to the lithographic apparatus so as to meet the requirements of uniformity and overlap of critical dimensions. This control is not limited to the pattern as set on the pattern forming device or projection system (such as lens and / or reflector), but this control can also be related to the shape of the pattern forming device itself. That is, the surface flatness of the pattern forming device may affect the pattern projected to the substrate. Although the sensor arranged at the platform (such as wafer platform or measurement platform) can be used to obtain the position information of the pattern forming device, the position information is usually limited by the measurement performed near the four edges of the pattern forming device. In order to improve the accurate control of the pattern, the surface position information in the exposure field of the pattern forming device is required, and the surface position information cannot be obtained in situ with the current sensor or method. The shape information in the exposure field of the pattern forming device or the patterning area of ​​the pattern forming device can be obtained by means of the interferometric measurement system as described in WO2017 / 153085A1. However, these types of interferometric measurement systems have the disadvantage of being sensitive to environmental changes, which may lead to erroneous measurement results.

[0007] It is an object of the present invention to provide an apparatus and a method for characterizing a patterning device which overcomes the limitations as mentioned above. Summary of the invention

[0008] It is an object of the present invention to provide a measurement system and method for characterizing a patterning device.The measurement system is configured for measuring geometrical and surface properties of a patterning device.

[0009] This objective is achieved by a method for determining a surface parameter of a patterning device. The method comprises the following steps: loading the patterning device onto a mask support arranged in a lithographic apparatus; positioning the patterning device relative to a path of an exposure radiation beam using a first measurement system; arranging the patterning device at a first focal plane of a chromatic lens arranged in a second measurement system; arranging the patterning device at a first focal plane of a chromatic lens; irradiating a portion of the surface of the patterning device with radiation passing through the chromatic lens, the radiation comprising a plurality of wavelengths; determining the position of the irradiated portion in a first direction and a second direction; collecting at least a portion of the radiation reflected by the patterning device through the chromatic lens; measuring the intensity of a portion of the collected portion of the radiation as a function of wavelength at a second focal plane of the chromatic lens to obtain spectral information; and determining the surface parameter of the patterning device at the determined position based on the spectral information. Positioning (or aligning) the patterning device is to prepare the patterning device for exposure of a substrate. By arranging the patterning device at the first focal plane of the chromatic lens and by measuring the radiation reflected at the first focal plane at the second focal plane, only radiation focused at a target by the chromatic lens will be recorded. That is, the chromatic aberration lens can provide strong chromatic aberration to radiation that interacts with the chromatic aberration lens. This has the advantage of focusing radiation comprising different wavelengths at different distances (or different focal planes) of the chromatic aberration lens. This gives the advantage that the chromatic aberration lens does not have to be moved to ensure that the focus position of radiation comprising multiple wavelengths is located at the surface or interface of the patterning device.

[0010] According to the invention, the method is repeated a number of times, wherein for each repetition a different part of the surface of the patterning device is illuminated. This can be achieved by moving the patterning device relative to the chromatic aberration lens in at least the first direction or the second direction. Thus, the patterning device can be scanned in one or more directions. Based on the spectral information received during the scanning movement as a function of the position of the patterning device, spatial information of the patterning device can be obtained. A surface parameter map can be determined based on the information collected during the scanning.

[0011] The recorded surface parameters may be determined by the optical properties of the surface. Hence, the surface parameters may thus be a measure of the optical properties of the illuminated portion (parts or regions) of the patterning device. According to the invention, the method may be used to determine at least the optical properties of the patterning device, such as transmittance, reflectivity and / or absorptivity.

[0012] The present invention also provides a method for determining the expected heating effect of a patterning device by using an optical property as input using a heating model. The heating model can be a mask heating model and / or a lens or lens heating model. The optical property can be used to derive the amount of radiation absorbed by the patterning device during an exposure sequence within a lithography process. The absorptivity depends on the local properties of the patterning device. Based on the amount of absorbed radiation, a model (e.g. a finite element model) can be used to derive the (expected) thermal load at the patterning device. The thermal load may cause shape and / or optical changes to the patterning device.

[0013] According to the invention, the method can be used to determine the axial distance between the illuminated portion at the patterning device and the chromatic lens. Due to the chromatic behavior of the lens, the wavelength can be used as a scale for measuring the distance between the chromatic lens and the surface of the patterning device. Therefore, by determining the wavelength of the collected and measured radiation, information on the axial distance (in the third direction) can also be obtained.

[0014] The present invention also provides a method for determining the shape of a patterning device based on an axial distance. By measuring the axial distance as a function of spatial position (e.g. as a function of position in a two-dimensional plane, preferably in a plane substantially parallel to the surface of the patterning device), a height map or map of the patterning device, or a surface topography map or map can be obtained. From such a map or map, the local and / or global shape of the patterning device can be determined.

[0015] According to the present invention, the method may also be used to perform patterning device shape compensation. The method further comprises performing at least one of the following adjustments based on the determined shape of the patterning device: adjusting the position of the patterning device by applying a translation to the patterning device, and adjusting the orientation of the patterning device by applying a rotation to the patterning device. The translation of the patterning device may be in the z direction. The rotation of the patterning device may be an Rx rotation and / or an Ry rotation.

[0016] Shape compensation may also be achieved by adjusting the shape of the patterning device by applying a mechanical load to the patterning device based on the determined shape.

[0017] According to the present invention, a method for compensating for the heating effect of a pattern forming device is provided. The method further comprises the following steps: calculating the expected shape change of the pattern forming device based on the determined surface parameter map or diagram and the exposure settings to be used for the exposure of the substrate to determine the expected heating effect of the pattern forming device; defining the (lens or lens) settings of the projection lens by means of a lens model to compensate for the expected shape change of the pattern forming device; and applying the defined settings before and / or during exposure. The heating effect may include optical aberrations. That is, the optical elements (transmitting elements and reflective elements) within the projection lens are typically configured to be adjusted. Therefore, the optical aberrations within the optical path can be changed or compensated by adjusting one or more settings of the optical elements. This can be done via position and / or orientation changes of these elements or by changing the refractive index of the transmitting element.

[0018] The invention also comprises a method of imaging a pattern provided at a pattern forming device onto a substrate by means of a projection system under the control of data representing a surface topography map or diagram of the pattern forming device according to the method for determining the shape of the pattern forming device.

[0019] In an embodiment, a lithographic apparatus comprises a measurement system for characterizing a patterning device, wherein the measurement system comprises: a radiation source arranged to provide radiation having a plurality of wavelengths; at least one chromatic lens arranged in at least one spectral confocal sensor, the at least one chromatic lens being configured to illuminate an area of ​​the patterning device with the provided radiation, and wherein the at least one chromatic lens being configured to collect at least a portion of the radiation reflected by the patterning device disposed at a first focal plane of the at least one chromatic lens; a detector arranged at a second focal plane of the at least one chromatic lens, wherein the detector is configured to detect at least a portion of the collected radiation and to provide an intensity signal as a function of wavelength in response to the detected radiation; and a processor for determining a characteristic of the patterning device at the illuminated area. The chromatic lens may provide a strong chromatic aberration to radiation interacting with the chromatic lens. This has the advantage of focusing radiation comprising different wavelengths at different distances (or different focal planes) of the chromatic lens. This gives the advantage that the chromatic lens does not have to be moved to ensure that the focus position of the radiation comprising a plurality of wavelengths is located at a surface or interface of the patterning device. Thus, a patterning device arranged in a lithographic apparatus can be characterized in situ. Measurements and characterization can be performed before and / or during a wafer exposure sequence. This has the advantage that the patterning device can be monitored in real time. The measurement results can be used directly in order to compensate for changes in parameters of the patterning device caused by the exposure step. This can include shape changes and optical changes caused, for example, by thermal loads of the incident radiation used for exposure.

[0020] The detector may be a spectrometer arranged to obtain spectral information of the radiation detected by the detector.

[0021] Multiple spectral confocal sensors can be arranged to form a sensor array. Thus, multiple locations or areas can be measured simultaneously.

[0022] The characteristic of the patterning device is at least one of an axial distance between the patterning device and the chromatic lens, and an optical property. By using the measurement system according to the invention, the distance between the chromatic lens arranged in the spectral confocal sensor and the patterning device can be determined based on the intensity signal as a function of the wavelength. The wavelength can be used as a measure of the axial distance. The optical property can be the transmittance, reflectivity and / or absorptivity of the patterning device at the illuminated area. This has the advantage that not only the shape of the patterning device can be measured, but also the (local and / or global) optical properties can be determined.

[0023] In an embodiment of the invention, multi-wavelength radiation (or radiation having multiple wavelengths) is provided by a radiation source comprising a broadband radiation source or a plurality of radiation sources. A measurement system provided with radiation from a broadband radiation source has the advantage that a single radiation source is used to provide radiation of multiple wavelengths. Therefore, only control of one radiation source is required. Using multiple radiation sources can be cost-effective.

[0024] According to an embodiment, the measurement system may be arranged at the top of a lens within the lithographic apparatus.The measurement system may also be arranged at a frame close to a support configured to support the patterning device.

[0025] According to an embodiment, the measurement system may be arranged in an inspection apparatus. The inspection apparatus may be configured to inspect and / or qualify the patterning device. Information obtained in the inspection apparatus may be provided to another system, such as a lithographic apparatus or an apparatus arranged to manufacture the patterning device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0027] Figure 1 A schematic overview diagram depicting a lithographic apparatus;

[0028] Figure 2A A non-planar pattern forming device is shown;

[0029] Figure 2B and Figure 2C illustrates the interaction of exposure radiation with a non-planar transmissive patterning device and a non-planar reflective patterning device, respectively;

[0030] Figure 3 An embodiment of the present invention is illustrated;

[0031] Figure 4 depicts a schematic layout of a spectral confocal sensor that may be used in embodiments of the present invention;

[0032] Figure 5 Schematic illustrations depicting embodiments of the present invention;

[0033] Figure 6 depicts a schematic cross-section of a patterning device;

[0034] Figure 7 An embodiment of the present invention is illustrated;

[0035] Fig. 8A , Figure 8B and Figure 8C illustrates different sensor array configurations according to the present invention;

[0036] Fig. 9A An illustration of a patterning device including a non-uniform material layer density;

[0037] Fig. 9B depicts a schematic diagram illustrating a spectral recording of radiation received by a spectral confocal sensor;

[0038] Fig.10 A method for compensating for reticle heating is schematically illustrated. DETAILED DESCRIPTION

[0039] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365nm, 248nm, 193nm, 157nm or 126nm) and extreme ultraviolet radiation (EUV, e.g., having a wavelength in the range of about 5nm to 100nm).

[0040] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be produced in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0041] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation), a mask support (e.g. a mask stage) MT configured to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer stage) WT configured to hold a substrate (e.g. a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0042] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL may be used to condition (expose) the radiation beam B to have a desired spatial and angular intensity distribution in a cross-section of the radiation beam B at the plane of the patterning device MA.

[0043] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0044] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid, e.g. water, having a relatively high refractive index, so as to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US6952253, incorporated herein by reference.

[0045] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or steps for preparing a substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT while another substrate W on another substrate support WT is used for exposing a pattern on the other substrate W.

[0046] In addition to the substrate support WT, the lithographic apparatus LA may also comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean parts of the lithographic apparatus, for example a part of the projection system PS or a part of the system for providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0047] In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be precisely moved, for example in order to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly a further position sensor (which is located in the substrate support WT) are arranged to move the substrate support WT to a desired position. Figure 1 The patterning device MA may be positioned relative to the path of the radiation beam B using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 (as shown) occupy dedicated target portions, the marks may be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0048] To illustrate the present invention, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes, i.e., an x-axis, a y-axis, and a z-axis. Each of the three axes is orthogonal to the other two axes. A rotation around the x-axis is called an Rx rotation. A rotation around the y-axis is called an Ry rotation. A rotation around the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in a vertical direction. The Cartesian coordinate system does not limit the present invention, but is only used for illustration. The direction of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane.

[0049] In known lithographic apparatus and methods, lithographic errors may occur that affect important parameters of the lithographic process, such as critical dimension uniformity or overlap. One of the reasons is the unevenness of the pattern forming device MA. That is, during the operational use of the lithographic apparatus LA, the surface of the pattern forming device MA may be (partially) bent or tilted due to interaction with the support platform (or mask support T), due to gravity and / or due to reaction forces acting on the pattern forming device MA. In addition, the shape or surface of the pattern forming device MA may change during the exposure of a wafer batch. It will be appreciated by those skilled in the art that obtaining information about the pattern forming device MA (and in particular surface position information) can be beneficial for limiting lithographic errors.

[0050] Figure 2A The problem solved by the present invention is illustrated. The surface 11 of the patterning device 10 which can be provided with a pattern deviates from a (virtual) planar surface 11A, as indicatively illustrated by the dashed lines which represent a flat surface in the xy plane. Figure 2A , Figure 2B and Figure 2C As shown in the figure, the deviation (or deformation) is exaggerated to illustrate the effect. In practice, the deviation may be in the nanometer or (sub) micrometer range. Figure 2A In the presented case, the patterned surface 11 has a so-called concave shape which may be caused, for example, by the support platform T due to the clamping for positioning the patterning device 10. The patterned surface 11 may also have a convex shape (not shown), for example, due to gravity. The actual shape of the patterned surface 11 may vary across the surface. This means that the surface shape may be different from one part to another - a local surface shape. Furthermore, the surface deformation in the x-direction may be different from the surface deformation in the y-direction.

[0051] Figure 2B and Figure 2C The effects of a patterning device 10 having a curved patterned surface 11 for a transmission patterning device and a reflection patterning device are depicted, respectively. In these examples, the concave surface interacts with a first radiation beam 12 (e.g., exposure radiation B). Note: The effect is not limited to concave surfaces. The surface can have any shape as mentioned above. As illustrated, the first radiation beam 12 is deflected from the ideal radiation path 13 due to the curvature of the patterned surface 11, thereby producing a radiation path illustrated by the second radiation beam 14. This may cause a position shift and / or a focus shift of the second radiation beam relative to the ideal radiation path 13. The transmission or reflection patterning device can be used for exposure using DUV or EUV radiation, respectively.

[0052] Exposure radiation propagating through a path deviating from the ideal radiation path 13 may result in a shifted and / or deformed pattern projected at the substrate W. Thus, if no countermeasures are provided, the surface topography of the patterning device 10 may introduce lithographic errors and thereby affect IC features.

[0053] Figure 3 A first embodiment of the present invention is illustrated. A pattern forming device 20 is positioned above a lens top plate 23 (e.g. above a projection system PS) and is arranged to move relative to a slit region 22 (as illustrated by arrow S) through which a radiation beam B can pass (e.g. during exposure). At the lens top plate 23, a spectral confocal sensor 24 is positioned. The spectral confocal sensor 24 comprises a chromatic aberration lens 25 (e.g. a hyperchromatic lens) which can provide strong chromatic aberration to radiation interacting with the chromatic aberration lens 25. Such a chromatic aberration lens 25 has the advantage of focusing radiation comprising different wavelengths at different distances from the chromatic aberration lens 25. Providing radiation having multiple wavelengths to the spectral confocal sensor 24 (e.g. provided by a broadband radiation source) can cause the multiple wavelengths to be focused at different axial distances from the chromatic aberration lens 25, such as by Figure 3 The chromatic aberration lens 25 can focus radiation having a first wavelength at the patterned surface 21 of the patterning device 20, as illustrated by the first focal line 26A. The focus of radiation having a second wavelength may not be located at the patterned surface 21, as illustrated by the second focal line 26B.

[0054] The spectral confocal sensor 24 can be embedded in the lens top plate 23, such as by Figure 3 In another embodiment, the spectral confocal sensor 24 may be positioned at the surface of the lens top plate 23 .

[0055] The top plate 23 may be provided with one or more spectral confocal sensors 24 .

[0056] In another embodiment, the spectral confocal sensor 24 may be disposed at a frame different from the lens top plate 23, for example, at a frame configured to support the first positioner PM or at a frame arranged between the projection system PS and the pattern forming device MA. The frame may be provided with one or more spectral confocal sensors 24.

[0057] Channel 27 may include one or more optical fibers to provide radiation from a radiation source (eg, a broadband radiation source) to spectral confocal sensor 24 .

[0058] The spectral confocal sensor 24 may include a plurality of optical elements, which may include lenses, mirrors, beam splitters, filters and / or prisms.

[0059] Figure 4 A more detailed diagram shows that the lens top plate 23 can be provided (eg Figure 3) or the functionality of the spectral confocal sensor 24 at the frame. The spectral confocal sensor 34 can receive radiation from a radiation source 40, which is configured to provide measurement radiation 41 of multiple wavelengths. The multi-wavelength radiation 41 can be provided by an off-site light source and can be directed toward the spectral confocal sensor 34 via an optical channel, such as an optical fiber or an arrangement of optical elements, such as lenses and mirrors. In an alternative configuration, the radiation source 40 can be arranged in the spectral confocal sensor 34. The radiation 41 can be provided by the radiation source 40 to interact with the beam splitter 42 for the first time or first. Different optical elements, such as lenses and / or mirrors, can be arranged between the radiation source 40 and the beam splitter 42. An optical element 43, such as a mirror, can be positioned in the optical path to direct the radiation toward the (multi) chromatic aberration lens 35. Due to the chromatic aberration properties of the chromatic aberration lens 35, i.e., axial dispersion, each wavelength of the radiation interacting with the chromatic aberration lens 35 has a different focal length. The chromatic aberration lens 35 can be arranged to project the multi-wavelength radiation 41 onto the target 30. Projection lines 36 illustrate the chromatic aberration properties of the chromatic aberration lens 35, wherein each focal line 36 represents a radiation path of radiation having a different wavelength. A portion of the target, such as an interface or surface 31 of the target 30, may be located at a first focal plane of the chromatic aberration lens 35. The measurement radiation focused at the portion of the target 30 includes measurement radiation having a single wavelength or measurement radiation having a narrow spectral range.

[0060] A portion of the projected radiation may be reflected by the target 30. At least a portion of the reflected radiation is collected by the chromatic aberration lens 35. Due to the confocal arrangement of the sensor 34, only the radiation focused at the target interface or surface 31 will pass through a confocal aperture 45 arranged at a second confocal plane of the chromatic aberration lens 35. The confocal aperture 45 may be arranged in front of a spectrometer 46. The spectrometer 46 may be positioned close to the second focal plane of the chromatic aberration lens 35 to receive at least a portion of the reflected radiation 44. With the aid of the spectrometer 46, which typically includes a grating, a lens arrangement and an array detector, spectral information of at least a portion of the reflected radiation 44 (received radiation 47) received by the spectrometer 46 is determined.

[0061] The spectrometer 46 may provide a signal 48 including spectral information of the received radiation 47 (i.e., the reflected and returned radiation that passes through the confocal aperture 45 after interacting with the target 30). The spectral information may be intensity data for each wavelength of the received and measured radiation 47. By acquiring the spectral information of the received radiation 47, the axial distance information (or depth) of the target 30 relative to the chromatic aberration lens 35 is obtained without mechanically (re)positioning the lens 35 relative to the target 30. This has the advantage that the confocal sensor 34 does not require moving parts or components to ensure that the focus position of the radiation (which is used to measure the axial distance) is located at the surface or interface 31 of the target 30.

[0062] The spectral confocal sensor 34 may (additionally) include one or more optical components (eg lenses and mirrors) to steer, direct and / or shape the radiation beam.

[0063] The multi-wavelength radiation 41 may be provided by a broadband radiation source (e.g. a white light source). The multi-wavelength radiation 41 may also be provided by a plurality of radiation sources, each providing a measurement radiation having a narrow spectral range, for example each radiation source having a wavelength range (or bandwidth) of 1 nm to 10 nm, and thus forming a radiation source 40 having a wide spectral range. Each of the multiple radiation sources may be a laser or an LED, etc. Different measurement radiation beams may be combined by means of an optical combiner.

[0064] The measurement range and the measurement precision or accuracy of the spectral confocal sensor 34 are determined by the spectral range of the provided radiation 41 and the amount of axial dispersion of the (poly)chromatic lens 35. This means that a person skilled in the art can select specific wavelengths, wavelength ranges and chromatic lenses for optimizing sensor performance. For example, with a measurement range of 0.1 mm to 0.3 mm, the spectral confocal sensor 34 can achieve a measurement resolution of approximately 10 nm.

[0065] It will be appreciated by those skilled in the art that, for example, the lens top plate 23 including the spectral confocal sensor 34 may enable an axial position or axial distance measurement of the patterning device 20 positioned within the measurement range of the spectral confocal sensor 34. In addition, during a scanning movement (e.g., a scanning movement in the first direction and / or the second direction) of the patterning device 20, for example, during exposure of the substrate W, a position (in a third direction (e.g., z-direction)) or depth scan on the surface of the patterning device 20 may be performed with the aid of the spectral confocal sensor 34.

[0066] The spectral confocal sensor 34 may also be arranged at a support different from the lens top plate 23. The spectral confocal sensor may be arranged at a platform supporting the pattern forming device 20, but the platform is not a moving part or component during exposure. The spectral confocal sensor 34 may be arranged at a frame close to the pattern forming device.

[0067] The spectral information provided by the spectrometer 46 can be obtained by Figure 4 49 is illustrated in the schematic diagram depicted in FIG. Spectral information may include information on the intensity of the radiation per wavelength. Wavelength may be viewed as a scale for measuring the distance between the chromatic aberration lens 35 and the target 30 (e.g., patterning device 20, MA) (axial position or distance of the target). In addition, the received intensity (spectral intensity information) may provide a measure of the (local) reflectivity of the surface 31 at the focus position (first focal plane) of the received radiation 47.

[0068] In addition to the radiation with a wavelength focused at the surface 31 of the target 30 and measured by the spectrometer 46, radiation with a different wavelength can be measured by the spectrometer 46. That is, depending on the dispersion of the chromatic aberration lens 35 and the size of the aperture 45, radiation with a wavelength different from the radiation focused at the first focal plane and the second focal plane can strike the spectrometer 46. This can generate a (spectral) background signal. With the help of a (multi)chromatic aberration lens 35 with a relatively high dispersion and / or with a relatively narrow aperture 45, such background signals can be suppressed. Even with the (spectral) background signal, the received spectral intensity information can also be used to characterize the target 30. That is, the intensity peaks in the recorded spectrum can provide a measure for characterizing the surface of the target of interest.

[0069] The controller may be used to control the one or more spectral confocal sensors 34 or to control a measurement device that includes the one or more spectral confocal sensors 34. This may include control of the radiation source 40 and the spectrometer 46. The same controller or a different controller may be used to change the position of the patterning device 20 relative to the one or more spectral confocal sensors 34.

[0070] The processor may be used to process the spectral information provided by the signal 48. The processor may be configured to receive (relative) position information in order to associate the measured spectral information with a position or location within the system or apparatus at the patterning device 20. This may include the axial distance between the surface of the target 30 (or patterning device 20) that interacts with the measurement radiation and the chromatic aberration lens 35.

[0071] Figure 5 A schematic diagram depicting an embodiment of the present invention. A support 53, such as a lens top plate 23, may include more than one spectral confocal sensor configured to provide more than one measurement radiation beam 56. Note: For clarity, Figure 5 More than one spectral confocal sensor is not shown in the figure. For example, more than one spectral confocal sensor can be arranged in one or more arrays. A first array of spectral confocal sensors can be arranged at a first portion of the support 53 located on one side of the slit region 52, and a second array can be arranged at a second portion of the support 53, for example, located on the opposite side of the slit region 52. Figure 5 Two exemplary arrays are shown, each array being formed of three spectral confocal sensors and indicated by an array of radiation cones 56. The number of spectral confocal sensors per array and the number of arrays may differ as indicated by Figure 5 The number of schematic diagrams is shown. It is contemplated that, for example, five or seven spectral confocal sensors may be arranged per array. Fewer or more spectral confocal sensors may be arranged in each sensor array. Each sensor array may be configured to measure multiple axial distances from the pattern forming device 50.

[0072] The patterning device 50 may include a patterned surface 51 that may be positioned to align with a spectral confocal sensor (e.g., Figure 3 and Figure 4 , or in the field of view of the at least one chromatic aberration lens of the spectral confocal sensor 24, 34 illustrated in the figure. Therefore, the multi-wavelength radiation projected by the at least one chromatic aberration lens can be projected onto the patterned surface 51 of the pattern forming device 50. Preferably, the at least one spectral confocal sensor can be arranged so that the radiation spot of the at least one spectral confocal sensor can be projected onto or interact with an area on the pattern forming device 50 including a measurement pattern 59 (e.g., mask alignment marks M1, M2). The measurement pattern 59 is typically measured by a parallel-lens interferometer, for example, arranged at a wafer stage or a measurement stage, to measure the shape and / or position of the pattern forming device 50. Measuring the same area (or pattern) by means of a first measurement system including, for example, an interferometer (i.e., an interferometric measurement system) and a second measurement system including a spectral confocal sensor can advantageously calibrate and / or correlate the two measurement systems.

[0073] For example, the patterning device 50 may have a barrel shape. Such a barrel shape may be measured by both the first measurement system and the second measurement system, which may be used to calibrate one system relative to the other.

[0074] In the case where parts of the pattern forming device 50 are not measured by one of the first and second measurement systems, it may also be beneficial to provide the missing information by using the data of the other measurement system to obtain a complete measurement data set. This may not be limited to the areas that can be measured by both measurement systems. The first measurement system may be limited to measurements at the area including the measurement pattern 59, while the second measurement system may measure the area including the measurement pattern 59 and the area between the measurement patterns 59. Thus, not only can the two systems be calibrated, but also shape and position information of areas that are not usually measured by the common measurement system is received. An improved (shape) model of the pattern forming device 50 may be obtained.

[0075] The patterning device 50 may be moved relative to the array of spectral confocal sensors, such as by Figure 5 . Thus, the patterned surface 51 of the patterning device 50 facing the sensor array can be scanned. Based on the received spectral information as a function of the scanning position of the patterning device relative to the sensor array, spatial information of the patterning device 50, such as a surface height map or map, and a surface density map or map at the patterned surface 51 of the patterning device 50 can be obtained.

[0076] Figure 6An enlargement of a schematic cross section of a patterning device 60 is depicted including a patterned surface 61. The patterned surface 61 may include a patterned layer 63 including chromium or another radiation absorbing material disposed on a surface 62 of a support material, such as a quartz material. The patterned layer 63 may have a thickness of typically on the order of 100 nm. Thus, portions of the patterned layer 63 may be viewed as regions having a height of approximately 100 nm disposed on, for example, a bare quartz material.

[0077] Using a spectral confocal sensor with a measurement range of 0.1mm to 0.3mm and a measurement precision or accuracy of about 10nm, a height step of the order of 100nm can be resolved. That is, a first radiation with a first wavelength reflected at, for example, a bare quartz material can be received by a spectrometer 46. A second radiation with a second wavelength reflected at a patterned layer portion 63 (e.g., a chrome portion) can also be received by a spectrometer. Both the first radiation and the second radiation can be displayed graphically. Two peaks can be presented by a chart 49, wherein the first peak is at a first wavelength and the second peak is at a second wavelength. Therefore, the multi-wavelength radiation interacting with different parts of the pattern forming device 60 will have different spectral records, each spectral record corresponding to a specific part. Therefore, different parts can be distinguished spectrally. The wavelength difference between the first wavelength and the second wavelength as recorded is a measure of the difference in axial position (axial distance) between, for example, a quartz portion 62 and a portion of the patterned layer 63. This means that the local thickness of the patterned layer 63 can be measured.

[0078] In some cases, the pattern forming device 60 may be provided with a (partially) transparent pellicle membrane 64, wherein the pellicle membrane is arranged to face the patterned surface 61 to prevent contaminants from staying on the patterned surface 61. Alternatively, the contaminant particles may stay on the pellicle membrane 64. The pellicle membrane 64 may be provided with a frame ( Figure 6 The pellicle membrane 64 is arranged to the patterning device 60 (not shown). Typically, the pellicle membrane 64 is arranged a few millimeters from the patterning surface 61 so that the pellicle membrane 64 is out of the focal plane of the patterning device 60. Thus, the influence of particles during exposure is reduced.

[0079] pass Figure 7 The support 73 is provided with one or more spectral confocal sensors 74, such as Figure 4 In one embodiment, a plurality of spectral confocal sensors 74 are arranged in an array configuration, thereby forming a sensor array (e.g., Figure 5). Each of the spectral confocal sensors may be configured to provide a radiation cone 76 to interact with a patterning device 70 at a focal plane of at least one confocal lens that may be arranged in the sensor array 74. The patterning device 70 may be held on a mask support MT that is configured to move the patterning device 70 in at least one direction, for example the y direction as illustrated by the arrow S. Thus, the patterning device 70 may be moved relative to the sensor array 74 such that the area of ​​the patterning device 70 that interacts with the radiation provided by the spectral confocal sensor 74 is changed by the relative movement. During the relative movement, the radiation spot of at least one spectral confocal sensor arranged in the sensor array 74 strikes the patterned surface 71 of the patterning device 70. Thus, the patterned surface 71 is scanned and measured along the direction of the relative movement (illustrated by the arrow S). With the aid of a plurality of spectral confocal sensors 74, the patterned surface 71 may be measured at different surface locations simultaneously. This may advantageously minimize the measurement time and / or increase spatial surface position information, such as surface information density and surface curvature.

[0080] In one embodiment, the sensor array 74 can be configured to form a single linear array of sensors disposed at a single side of the slit region 72. The linear array of sensors can be configured such that the linear array is arranged perpendicular to the scan direction. For example, the linear array can be arranged along the x-direction. The linear array can also be arranged in a direction that forms an angle between 45 degrees and 90 degrees relative to the scan direction. Thus, the entire surface of the pattern forming device or a portion thereof can be scanned in one scan (or stroke).

[0081] By measuring the axial distance as a function of spatial position, for example as a function of position in a two-dimensional plane, preferably as a function of position in an (xy) plane substantially parallel to the surface of the patterning device 70, a height map or map, or a surface topography map or map of the patterning device 70 may be obtained. From such a map or map, the local and / or global shape of the patterning device 70 may be determined.

[0082] During operation of the lithographic apparatus LA, the pattern forming device 70 performs a scanning movement relative to the slit area 72 (illustrated by arrow S). Typically, the stroke of this movement is determined by the area of ​​the patterned surface 71 and the position of the measurement pattern 79 at the pattern forming device 70. Since the slit area 72 and the sensor array 74 are spatially separated, the pattern forming device 70 needs to be moved beyond a moving window as typically used during system operation (e.g., during exposure) to ensure that the sensor array 74 is able to measure both the area including the patterned surface 71 and the measurement pattern 79. In order not to extend the moving window significantly beyond a window as typically used during system operation, the sensor array 74 (including a plurality of spectral confocal sensors) may be arranged by a dual sensor array including a first sensor array and a second sensor array. For example, the first sensor array may be arranged at one side of the slit area 72 and the second sensor array may be configured at a second side of the slit area 72 (e.g., the opposite side of the slit area), as shown by Figure 7 Thus, the first sensor array may measure a first portion of the patterning device 70 and the second sensor array may measure a second portion of the patterning device 70. The first portion and the second portion of the patterning device 70 may be selected in such a way as to cover an area of ​​interest.

[0083] Furthermore, when the first and second parts at least partially overlap, the overlapping parts may be used to calibrate the first and second sensor arrays relative to each other. Thus, it is also ensured that the region of interest is fully measured by the sensor array 74.

[0084] The sensor array 74 may be arranged in such a way that the radiation spot 76 of the one or more spectral confocal sensors is configured to interact with one or more metrology patterns 79, M1, M2 provided at the patterning device 70 when the patterning device 70 is held on the mask support MT. Measuring the same area (e.g. measuring the same metrology pattern) by means of a first measurement system comprising an interferometer (i.e. an interferometric sensor) and a second measurement system comprising the spectral confocal sensor 74 may advantageously calibrate and / or correlate the two measurement systems.

[0085] like Figure 7 The sensor array 74 shown in FIG. 7 can be arranged in a linear array. Alternatively, the sensor array 74 can have a Fig. 8A . This can advantageously avoid optical crosstalk between adjacent sensors. That is, radiation projected by a first chromatic aberration lens may be scattered at the surface of the target (patterning device) and received by a second chromatic aberration lens (e.g., an adjacent lens). This may lead to incorrect analysis of the spectral intensity information.

[0086] In another embodiment, the spectral confocal sensors positioned at the outer sides of the sensor (line) array 74 are displaced relative to the central spectral confocal sensor, as indicated by Figure 8B Such a sensor array configuration can be used, for example, to match a metrology pattern layout at the surface of a patterning device. That is, the metrology pattern is sometimes positioned along the long side of the exposure field of the patterning device.

[0087] If Figure 7 , Fig. 8A and Figure 8B The illustrated sensor array may include spectral confocal sensors that are arranged equidistantly relative to each other. Thus, a sensor array with a single pitch is formed. In the case of an equidistant arrangement, surface information with spatial uniformity can be obtained.

[0088] In another embodiment, the sensors may not be arranged equidistantly. The sensors may be arranged with a variable pitch within the array. This may be beneficial in situations where surface information at a first area needs to be denser than at a second area.

[0089] Figure 8C Another embodiment according to the present invention is shown. According to the present invention, the sensor array may include a first sub-array 74A and a second sub-array 74B. The first sub-array 74A may be arranged so that the patterned surface of the pattern forming device 70 is at the focal plane of the chromatic aberration lens arranged in the first sub-array 74A. The second sub-array 74B may be arranged so that the pellicle membrane 75 provided at the pattern forming device 70 is at the focal plane of the chromatic aberration lens arranged in the second sub-array 74B. Since the spacing distance between the pattern forming devices 60, 70 and the pellicle membrane 64, 75 is typically a few millimeters, the pellicle membrane is not within the working range of the first sub-array 74A. The same is true for the pattern forming devices 60, 70, which will be located outside the working range of the second sub-array 74B. Since the pellicle membrane is (partially) transparent, the first sub-array is able to sense the surface of the pattern forming device 70 with slight or negligible influence of the pellicle membrane 75. As Figure 8C As illustrated in FIG. 1 , this embodiment has the advantage that position and shape measurements can be made simultaneously for the patterning device 70 and the pellicle surface 75 by means of the sensor array 74 .

[0090] Those skilled in the art will appreciate that the position of the first spectral confocal sensor at the support, such as the lens top plate (23, 53), can be changed. For example, one or more mutual distances between sensors arranged into a sensor array and the distance between the pattern forming device and the sensor array can be changed to optimize the measurement and / or customize the sensor array for the area of ​​interest.

[0091] Fig. 9A A patterning device 80 is shown comprising a patterned area 81. The patterned area 81 may, for example, comprise a non-uniform absorptivity layer or a non-uniform chrome layer, as illustrated by the greyscale variation across the patterned area 81. When measuring at the patterned surface 81 by means of a spectral confocal sensor, multiple wavelengths may be received and detected by the spectrometer, as illustrated by Fig. 9B , as illustrated by the two peaks in the depicted graph. The actual number of peaks recorded is determined by the material composition and / or layer configuration. Therefore, more than two peaks may be recorded. In this example, the first peak 87 may correspond to, for example, radiation interacting with the patterned chrome layer 63, and the second peak 88 may correspond to radiation interacting with the support material 62 (e.g., quartz material). The first peak 87 and the second peak 88 are recorded due to the axial dispersion length of the chromatic aberration lens. The spectral difference between the peaks is a measure of the local thickness of the patterned layer 63. Since the focus of the measurement beam typically has a finite size, both (portions of) the patterned layer 63 and (portions of) the support material 62 may be measured. That is, the actual spot size of the multi-wavelength radiation beam that interacts with the target determines the measured area. Depending on the spot size, different material portions (and therefore different materials) may interact with the measurement radiation, which may produce more than one intensity peak, as indicated by Fig. 9B As shown.

[0092] Since the spot of radiation provided by the chromatic aberration lens has a finite size, the measured intensity is determined by the (averaged) reflectivity of the area within the radiation spot. This means that the amplitude of the peak can be a measure of the local material density. During a scan on the patterned surface 81, the amplitude of one or more peaks may vary. By comparing the relative amplitudes (the measured amplitude corresponds to the position at the measured target), information about the local material density and its variations can be obtained. The spot size can determine the spatial sensitivity of the sensor. And therefore, the spatial resolution can be determined by the spot size.

[0093] comprising a plurality of spectral confocal sensors (e.g. in accordance with Figure 4 The sensor array 84 of the illustrated sensor (spectral confocal sensor) can be used to obtain surface information of the patterning device 80 with high spatial resolution. Thus, a two-dimensional material density map or map can be obtained. The information about the local and global material density can in turn be used to calculate the local and global transmittance, reflectivity and / or absorptivity of the patterning device 80. Thus, a two-dimensional map or map of the optical properties of the patterning device 80 can be generated.

[0094] Instead of deriving the pattern distribution using a mask design file (e.g. a GDSII file), the required material density map or map can be obtained during the (pre) exposure sequence (in situ). That is, during the exposure step, the pattern forming device 80 held by a support (e.g. a mask support T) is moved relative to the sensor array 84. By recording the reflected and received radiation as provided by one or more spectral confocal sensors, a density map or map can be obtained in parallel with the exposure. The density map or map can also be determined by surface information obtained at a time before the exposure step. In both cases, the density map or map can be used in a feed-forward control to define and set exposure characteristics, such as the (local) intensity of the exposure radiation B and / or the lens or lens settings of the projection system PS.

[0095] The sensor array 84 may be based on Figure 7 , Fig. 8A , Figure 8B and Figure 8C of sensor array 74.

[0096] A lithographic apparatus according to the invention comprising a spectral confocal sensor or an array of spectral confocal sensors (e.g. Figure 1 The lithographic apparatus LA) illustrated in FIG. 1 may use the sensor at various stages during an exposure sequence. This may be before, during and / or after the exposure sequence.

[0097] At the first stage of an exposure sequence, e.g. before the substrate W is illuminated by patterned radiation, the spectral confocal sensor (array) may be used to measure an initial shape and / or initial optical properties of the patterning device MA. At the beginning of a wafer batch, the exposure radiation B may not have interacted with the patterning device MA yet. Therefore, the patterning device may be considered to be (relatively) cold. The first or initial measurement may provide information representative of the cold shape of the patterning device MA.

[0098] At a second stage in the exposure sequence, e.g. after a first exposure or a series of exposures, a second measurement providing a secondary shape and / or a secondary optical property of the patterning device MA may be performed. After interaction with the exposure radiation B, the patterning device MA may be heated due to the exposure radiation B. Hence, the patterning device is in a heated (or warm) state. Hence, the second measurement provides information representative of the heated shape of the patterning device MA.

[0099] The information obtained by the first and second measurements can be used to calculate the shape change of the pattern forming device MA as a function of time (transient behavior) and the exposure sequence. Finite element methods can be used to model the properties of the pattern forming device MA by using the shape measurement results as input to the model. The model can be a mask heating model and / or a lens or lens heating model. The output of the model may include instructions about the positioning of optical elements within the projection system PS (for example, the position and orientation of lenses and / or mirrors arranged in the projection system PS) and the arrangement of the pattern forming device MA.

[0100] Reticle heating may cause deformation of the patterned area that may vary over time, typically indicated as an XY grid distortion. Knowledge of the surface parameters of the patterning device, including optical properties (e.g., reflectivity, transmittance, and absorptivity) and surface curvature (axial distance), can be used to determine adjustments to the position of the patterning device MA by applying translations (e.g., in the x, y, and / or z directions) and to determine the orientation of the patterning device MA by applying rotations (e.g., Rx rotations and / or Rz rotations) to at least partially compensate for the torque.

[0101] Information representing the cold shape and the heated shape, or the difference between the cold shape and the heated shape, of the patterning device MA can be used for shape compensation with the aid of the mask support MT. The mask support MT can be actively controlled to compensate for the exposure induced shape changes. This can be done, for example, by moving the patterning device MA in the z direction and / or by providing an Rx rotation and / or an Ry rotation.

[0102] Information representing the cold shape and the heated shape, or the difference between the cold shape and the heated shape, of the patterning device MA may be used for shape compensation by means of a reticle bender using a mechanical load applied to the patterning device MA.

[0103] Fig.10 A method is shown for compensating for heating or warming of the patterning device MA (also referred to as reticle heating or warming), for example based on information of the pattern density at the patterning device MA within the lithographic apparatus LA. At a first step 90, a spectral confocal sensor array (e.g., as provided by Fig. 9AThe illustrated sensor array 84) scans the surface of the patterning device, preferably the surface including the patterned surface 81. Thus, surface position information of the scanned surface can be obtained. The surface position information can be obtained by means of a single scan, but multiple scans can be beneficial to improve the measurement precision or accuracy. At a second step 91, a surface density map or map is calculated based on the surface position information (obtained at the first step 90). The surface density map or map can include the spatial distribution of the absorbing coating and / or the reflective layer at the patterning device MA. At a third step 92, the surface density map or map is combined with information of the (expected) exposure settings 93. In particular, the dose and irradiation settings of the exposure radiation (e.g., the radiation beam B) are used at the third step 92. The surface density map or map is used to estimate the reflectivity and / or transmittance of the patterning device MA and / or the absorptivity of the patterning device MA when interacting with the exposure radiation. This can be based on the local and / or more global pattern density of the absorbing coating and / or the reflective layer. Thus, the mask heating effect caused by the exposure can be calculated. The reticle heating effect can be characterized by optical aberrations, including shape deformations of the pattern forming device MA. The expected shape deformations can be calculated with the aid of a thermomechanical model of the pattern forming device. For a reflective pattern forming device MA, for example, to be used in an EUV lithography system, a surface density map or diagram can be used to estimate the reflectivity and absorptivity of the pattern forming device MA. At a fourth step 94, the expected reticle shape effects, which may include reticle heating, are sent to a correction model, such as a lens or lens model. The correction model can be used to define the lens or lens settings within the projection system PS to compensate for the expected optical changes of the pattern forming device MA. Optical compensation can be achieved with the aid of (semi-) active optical elements, such as lenses and / or mirrors. This can include a correction model for reticle heating, which is used to calculate compensation for the exposure scanning trajectory of the lens (or lens) and the platform.

[0104] The optical elements within the projection system PS (which may be transmissive or reflective elements) are typically configured to be adjusted. Thus, optical aberrations within the optical path used during exposure of the substrate may be altered or compensated for by adjusting one or more settings of the optical elements. This may be done by changing the position and / or orientation of these elements or by changing the refractive index of the transmissive element.

[0105] The processor can be used to manipulate and perform Fig.10 Each individual step is illustrated. The processor may be part of the lithographic apparatus LA. The processor may be at a remote location.

[0106] The desired optical compensation can be achieved with the aid of (semi-)active reticle manipulation, for example by shaping the reticle with the aid of a reticle bender.

[0107] In another embodiment, the surface density map or diagram of the patterning device obtained at step 91 can be used as a direct input to the lens or lens model. That is, based on the (local) density information of the patterning device, an estimation of the local dose (or radiation density) within the projection system can be made. Furthermore, this can enable an estimation of the radiation-induced lens or lens heating on which the lens or lens settings depend. In other words, based on the received density information, the knowledge of the projected pattern can be used to define the optical lens or lens settings to include lens or lens heating corrections.

[0108] Similar to lens or camera heating, the heating of the substrate W (ie, wafer heating) depends on the local transmittance and / or reflectivity of the patterning device. Fig.10 The illustrated method can also be used to compensate for heating effects at substrate level. In the case of wafer heating compensation, Fig.10 At a fourth step 94 of the illustrated method, an expected substrate shape (e.g., radiation-induced deformation of the substrate) may be calculated based on the information received at the previous step. The expected substrate shape may be sent to a correction model, including, for example, a lens or lens model. The correction model may be used to define a lens or lens setting within the projection system to compensate for expected changes in the substrate W. Optical compensation may be achieved with the aid of (semi-)active optical elements (e.g., lenses and / or mirrors). This may include a correction model for wafer heating, which is used to calculate compensation for the exposure scan trajectory of the lens (or lens) and the stage.

[0109] In another embodiment, the method may be used to compensate for both reticle and wafer heating effects.It may be beneficial to define in the correction model lenses or lens settings that initiate compensation for effects caused by reticle heating as well as by wafer heating.

[0110] Referring to the above figure, the slit area can be defined and formed by additional elements or systems. That is, the actual slit area is usually not defined by the lens top plate, support or frame. As illustrated by the figure, the lens top plate, support or frame can be arranged to coincide with the position of the slit area.

[0111] According to an embodiment of the invention, a measurement system for characterizing a pattern forming device comprising one or more spectral confocal sensors as described above may be arranged in a lithographic apparatus. For example, the measurement system is arranged in a lens top plate.

[0112] In another embodiment, the inspection apparatus comprises a measurement system according to the invention. The inspection apparatus may be configured to inspect and / or qualify the patterning device. The information obtained by the inspection apparatus may be provided to another system, such as a lithographic apparatus or an apparatus arranged to manufacture the patterning device. The inspection apparatus may be arranged to interact with the lithographic apparatus (or manufacturing apparatus) as a separate apparatus or as a supplement to the lithographic apparatus (or manufacturing apparatus).

[0113] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0114] Although embodiments of the present invention may be specifically mentioned herein in the context of a lithographic apparatus, embodiments of the present invention may be used in other apparatuses. Embodiments of the present invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes a target such as a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0115] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism or mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include: a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), and the like. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and such actions are actually caused by a computing device, a processor, a controller, or other devices that execute firmware, software, routines, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0116] Aspects of the invention are set out in the following aspects.

[0117] 1. A method for determining surface parameters of a pattern forming device, the method comprising the following steps: loading the pattern forming device onto a mask support arranged in a lithography device; positioning the pattern forming device relative to the path of an exposure radiation beam using a first measurement system; setting the pattern forming device at a first focal plane of a chromatic lens arranged in a second measurement system; irradiating a portion of the surface of the pattern forming device with radiation passing through the chromatic lens, the radiation comprising a plurality of wavelengths; determining the position of the irradiated portion in a first direction and a second direction; collecting at least a portion of the radiation reflected by the pattern forming device through the chromatic lens; measuring the intensity of the collected portion of the radiation as a function of wavelength at the second focal plane of the chromatic lens to obtain spectral information; and determining the surface parameters of the pattern forming device at the determined position based on the spectral information.

[0118] 2. The method according to aspect 1 further includes: repeating multiple times: irradiating a portion of the surface, determining the position of the irradiated portion, collecting at least a portion of the reflected radiation, measuring the intensity of the collected portion, and determining the surface parameters, wherein a different portion of the surface of the pattern forming device is irradiated for each repetition by moving the pattern forming device relative to the chromatic aberration lens in at least the first direction or the second direction.

[0119] 3. The method according to clause 2, further comprising determining a surface parameter map or map of the patterning area at the patterning device.

[0120] 4. A method according to clause 2 or 3, wherein the surface parameters include at least optical properties at the illuminated portion.

[0121] 5. The method of clause 4, wherein the optical property is at least one of reflectivity, transmittance, and absorptivity.

[0122] 6. The method according to clause 4 or 5, further comprising determining an expected heating effect of the patterning device by using a heating model with the optical property as input.

[0123] 7. The method according to clause 2 or 3, wherein the surface parameters include at least an axial distance between the illuminated portion and the chromatic aberration lens in a third direction.

[0124] 8. The method of clause 7, further comprising determining a shape of the patterning device based on the axial distance.

[0125] 9. The method of clause 7 or 8, further comprising using the axial distance as a function of the determined position to produce a surface topography map or graph of the patterning device.

[0126] 10. A method for performing shape compensation of a pattern forming device, comprising the steps according to aspect 8, the method also comprising performing at least one of the following adjustments based on the determined shape of the pattern forming device: adjusting the position of the pattern forming device by applying a translation to the pattern forming device, and adjusting the orientation of the pattern forming device by applying a rotation to the pattern forming device.

[0127] 11. A method for performing shape compensation of a patterning device, comprising the steps according to aspect 8, the method further comprising adjusting the shape of the patterning device by applying a mechanical load to the patterning device based on the determined shape.

[0128] 12. A method for compensating for a heating effect of a pattern forming device, comprising the steps according to aspect 5, the method further comprising: calculating an expected shape change of the pattern forming device based on a determined surface parameter map or diagram and an exposure setting to be used for exposure of a substrate to determine an expected heating effect of the pattern forming device; defining settings of a projection lens or lens with the aid of a lens or lens model to compensate for the expected shape change of the pattern forming device; and applying the defined settings before and / or during exposure.

[0129] 13. A method according to clause 12, wherein the heating effect comprises an aberration.

[0130] 14. A method of imaging a pattern provided at a patterning device onto a substrate by means of a projection system under the control of data representing a map or diagram of the surface topography of the patterning device according to clause 9.

[0131] 15. A lithographic device comprising a measurement system for characterizing a pattern forming device, the measurement system comprising: a radiation source, the radiation source being arranged to provide radiation having multiple wavelengths; at least one chromatic aberration lens, the at least one chromatic aberration lens being arranged in at least one spectral confocal sensor, the at least one chromatic aberration lens being configured to illuminate an area of ​​the pattern forming device with the provided radiation, and wherein the at least one chromatic aberration lens is configured to collect at least a portion of the radiation reflected by the pattern forming device disposed at a first focal plane of the at least one chromatic aberration lens; a detector, the detector being arranged at a second focal plane of the at least one chromatic aberration lens, wherein the detector is configured to detect at least a portion of the collected radiation and to provide an intensity signal as a function of wavelength in response to the detected radiation; and a processor, the processor being used to determine characteristics of the pattern forming device at the illuminated area.

[0132] 16. The lithographic apparatus of clause 15, wherein the plurality of spectral confocal sensors are arranged to form a sensor array.

[0133] 17. The lithographic apparatus according to clause 15 or 16, wherein the radiation source comprises at least one of a broadband radiation source and a plurality of radiation sources.

[0134] 18. A lithographic apparatus according to any one of clauses 15 to 17, wherein the characteristic of the patterning device is at least one of an optical property, and an axial distance between the patterning device and the chromatic aberration lens.

[0135] 19. The lithographic apparatus of clause 16, wherein the sensor array comprises a first array of spectral confocal sensors arranged at a first side of the slit region, and a second array of spectral confocal sensors arranged at a second side of the slit region.

[0136] 20. A lithographic device according to any one of aspects 15 to 17, wherein a first chromatic aberration lens is arranged at a first axial distance from the pattern forming device, and a second chromatic aberration lens is arranged at a second axial distance from the pattern forming device, wherein the second axial distance is different from the first axial distance.

[0137] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative, not restrictive. All described variant embodiments may be combined if the combination of all described variant embodiments is not limited from a technical perspective. Therefore, it will be appreciated by those skilled in the art that the described invention may be modified without departing from the scope of the claims set forth below.

Claims

1. A method for determining a surface parameter of a pattern forming device, the method comprising the following steps: loading the patterning device onto a mask support arranged in a lithographic apparatus; positioning the patterning device relative to a path of an exposure radiation beam using a first measurement system; placing the patterning device at a first focal plane of a chromatic aberration lens arranged in a second measurement system; illuminating a portion of a surface of the patterning device with radiation that passed through the chromatic aberration lens, the radiation comprising a plurality of wavelengths; determining a position of the illuminated portion in a first direction and a second direction; collecting at least a portion of the radiation reflected by the patterning device through the chromatic aberration lens; measuring the intensity of the collected portion of the radiation as a function of wavelength at a second focal plane of the chromatic aberration lens to obtain spectral information; as well as The surface parameter of the patterning device at the determined position is determined based on the spectral information.

2. The method according to claim 1, further comprising: repeating a plurality of times: illuminating a portion of the surface, determining the position of the illuminated portion, collecting at least a portion of the reflected radiation, measuring the intensity of the collected portion, and determining said surface parameter, wherein for each repetition, a different portion of the surface of the patterning device is illuminated by moving the patterning device relative to the chromatic aberration lens in at least the first direction or the second direction.

3. The method of claim 2, further comprising determining a surface parameter map of the patterned area at the patterning device. The method according to claim 2 , wherein the surface parameters comprise at least optical properties at the illuminated portion. The method of claim 4 , wherein the optical property is at least one of reflectivity, transmittance, and absorptivity.

6. The method of claim 4, further comprising determining an expected heating effect of the patterning device using a heating model with the optical property as input.

7. The method according to claim 2 or 3, wherein the surface parameters include at least an axial distance between the illuminated portion and the chromatic aberration lens in a third direction.

8. The method of claim 7, further comprising determining a shape of the patterning device based on the axial distance.

9. The method of claim 7, further comprising generating a surface topography map of the patterning device using the axial distance as a function of the determined position.

10. A method for compensating for heating effects of a pattern forming device, comprising the method according to claim 5, the method for compensating for heating effects of a pattern forming device further comprising: calculating an expected shape change of the patterning device based on the determined surface parameter map and exposure settings to be used for exposure of the substrate to determine an expected heating effect of the patterning device; defining settings of a projection lens by means of a lens model to compensate for said expected shape change of said patterning device; as well as The defined settings are applied before and / or during the exposure. The method of claim 10 , wherein the heating effect comprises an aberration.

12. A lithographic apparatus comprising a measurement system for characterizing a patterning device, the measurement system comprising: a radiation source arranged to provide radiation having a plurality of wavelengths; at least one chromatic lens, the at least one chromatic lens being arranged in at least one spectral confocal sensor, the at least one chromatic lens being configured to illuminate a region of the patterning device with the provided radiation, and wherein the at least one chromatic lens is configured to collect at least a portion of the radiation reflected by the patterning device disposed at a first focal plane of the at least one chromatic lens; a detector disposed at a second focal plane of the at least one chromatic aberration lens, wherein the detector is configured to detect at least a portion of the collected radiation and to provide an intensity signal as a function of wavelength in response to the detected radiation; and A processor is provided for determining a characteristic of the patterning device at the illuminated area.

13. The lithographic apparatus of claim 12, wherein a plurality of spectral confocal sensors are arranged to form a sensor array.

14. A lithographic apparatus according to claim 12 or 13, wherein the characteristic of the patterning device is at least one of an optical property, and an axial distance between the patterning device and the chromatic aberration lens.

15. A lithographic device according to claim 12 or 13, wherein a first chromatic aberration lens is arranged at a first axial distance from the pattern forming device, and a second chromatic aberration lens is arranged at a second axial distance from the pattern forming device, wherein the second axial distance is different from the first axial distance.

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