Method for spatially aligning a patterning device and a substrate

Abstract

A method for spatially aligning a patterning device and a substrate separated by an optical path comprising one or more movable optical components includes projecting a radiation beam from the patterning device along the optical path, executing a displacement of the one or more movable optical components along a predetermined trajectory, determining optical properties of the radiation beam received by a sensor on a substrate table supporting the substrate at a plurality of instances during the displacement of the one or more movable optical components, and spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of instances.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the priority of European application 22178555.3 filed on June 13, 2022, the entire content of which is incorporated herein by reference.

[0002] [Technical Field] The present invention relates to a method for spatially aligning a patterning device and a substrate separated by an optical path including one or more movable optical components in a lithographic apparatus.

Background Art

[0003] A lithographic apparatus is a device configured to apply a desired pattern onto a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern in a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on a substrate.

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be formed on the substrate. A lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 - 20 nm (e.g., 6.7 nm or 13.5 nm) may be used, for example, to form smaller features on a substrate than a lithographic apparatus using radiation having a wavelength of 193 nm.

Summary of the Invention

Problems to be Solved by the Invention

[0005] To accurately pattern a substrate with the pattern of a patterning device, an accurate alignment of the substrate and the patterning device is required. To that end, an alignment position between the patterning device and the substrate or a substrate table holding the substrate is determined by projecting an image of a pattern or one or more markers present on the patterning device onto a sensor disposed on a substrate table holding the substrate. Typically, such an alignment process involves projecting a pattern along an optical path comprising one or more optical components such as mirrors or lenses. During such an alignment process, the optical components are typically held in a fixed position. It has been found that if these components are displaced (or need to be displaced) during a subsequent patterning or exposure process, the determined alignment position is impaired or becomes inaccurate, potentially resulting in overlay errors during the patterning process.

[0006] It is an object of the present invention to provide an improved alignment between a patterning device and a substrate, particularly when a movable optical component is used during a patterning process in a lithographic apparatus.

Means for Solving the Problem

[0007] According to a first aspect of the present invention, there is provided a method of spatially aligning a patterning device and a substrate separated by an optical path comprising one or more movable optical components. The method comprises projecting a radiation beam from the patterning device along the optical path, performing displacement of the one or more movable optical components along a predetermined trajectory, determining optical properties of the radiation beam received by a sensor on a substrate table supporting the substrate at a plurality of instants during displacement of the one or more movable optical components, and spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of instants.

[0008] According to a second aspect of the present invention, an apparatus is provided. The apparatus comprises a support structure configured to support a patterning device, a substrate table configured to support a substrate, a projection system comprising a plurality of movable optical components configured to provide an optical path between the patterning device and the substrate, a positioning system configured to position the patterning device, the substrate and the movable optical components of the projection system, a position measurement system configured to measure the positions of the support structure, the substrate table and the movable optical components of the projection system, and a control unit configured to control the positioning system. The apparatus is configured to receive a radiation beam for illuminating the patterning device, and the control unit is configured to control the apparatus to perform a method for spatially aligning the patterning device and the substrate according to the first aspect of the present invention.

[0009] According to a third aspect of the present invention, an apparatus is provided. The apparatus comprises a support structure configured to support a patterning device, a substrate table configured to support a substrate, a projection system comprising a plurality of movable optical components configured to provide an optical path between the patterning device and the substrate, a positioning system configured to position the patterning device, the substrate and the movable optical components of the projection system, a position measurement system configured to measure the positions of the support structure, the substrate table and the movable optical components of the projection system, and a control unit configured to control the positioning system. The apparatus is configured to project a radiation beam from the patterning device along the optical path onto the substrate table supporting the substrate. The control unit is configured to control the positioning system to execute a displacement of one or more movable optical components along a predetermined trajectory, to determine optical properties of the radiation beam received by a sensor on the substrate table at a plurality of instants during the displacement of the one or more movable optical components, and to determine an alignment position of the patterning device and the substrate based on the optical properties determined at the plurality of instants.

Brief Description of the Drawings

[0010] Embodiments of the invention are described below by way of example only, with reference to the following accompanying schematic drawings. FIG. 1 shows a lithography system according to the present invention, comprising a lithography apparatus and a radiation source. FIG. 2 shows a system for performing an alignment method according to the present invention. FIG. 3 schematically shows a trajectory representing the displacement of a substrate table during alignment measurement. FIG. 4 schematically shows a 2D map of optical properties determined by a sensor during alignment measurement. FIGS. 5a and 5b schematically show trajectories that can be applied to perform an alignment method according to the present invention. FIG. 6 schematically shows an apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] FIG. 1 shows a lithography system according to the present invention, comprising a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0012] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Additionally, the illumination system IL may include a facet field mirror device 10 and a facet pupil mirror device 11. The facet field mirror device 10 and the facet pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or instead of the facet field mirror device 10 and the facet pupil mirror device 11.

[0013] After being conditioned in this way, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. According to the invention, the mirrors 13, 14 may be represented as movable optical components that can be displaced or actuated, for example, during the patterning or exposure process and during the alignment process. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’ to form an image having features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. The projection system PS is illustrated in FIG. 1 as having only two mirrors 13, 14, but the projection system PS may include a different number of mirrors (for example, six or eight mirrors).

[0014] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B’ with the previously formed pattern on the substrate W.

[0015] A lithographic apparatus LA as shown further comprises a control unit CU. Generally, the control unit CU can be configured to control the operation of the lithographic apparatus. In particular, the control unit CU can be configured to control, for example, the positioning of the support structure MT and / or the positioning of the substrate table WT. According to the present invention, the control unit CU can be configured to control the lithographic apparatus so as to perform the method according to the present invention for spatially aligning the patterning device MA and the substrate W. To that end, the control unit CU can also be configured to control, for example, the positions of the mirrors 13, 14 of the projection system PS. Further, as will be described in detail below, the control unit CU performs a plurality of alignment measurements and controls the proper positioning of the optical components of the patterning device PA, the substrate table WT, and the projection system PS such that the movable optical components 13, 14 of the projection system PS are arranged at predetermined positions for each of the alignment measurements.

[0016] In the radiation source SO, the illumination system IL, and / or the projection system PS, a relatively low vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure sufficiently lower than atmospheric pressure, may be provided.

[0017] The radiation source SO shown in FIG. 1 may be of a type that may be represented, for example, as a laser-produced plasma (LPP) source. For example, a laser system 1 that may include a CO2 laser is provided to input energy via a laser beam 2 into a fuel such as tin (Sn) provided from a fuel emitter 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may be, for example, liquid, or may be, for example, a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct tin in the form of droplets along a trajectory toward the plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. The input of laser energy into the tin generates a tin plasma 7 in the plasma formation region 4. During the deexcitation and recombination of electrons and plasma ions, radiation including EUV radiation is emitted from the plasma 7.

[0018] The EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 includes, for example, a near-normal incidence radiation collector 5 (often more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (for example, EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration having two foci. As will be described later, the first focus may be in the plasma formation region 4, and the second focus may be in the intermediate focus 6.

[0019] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO by a beam delivery system (not shown) that includes, for example, suitable steering mirrors and / or a beam expander, and / or other optical elements. The laser system 1, the radiation source SO, and the beam delivery system may be interpreted together as a radiation system.

[0020] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused onto an intermediate focus 6 in order to form an image of the plasma existing in the plasma formation region 4 at the intermediate focus 6. The image at the intermediate focus 6 functions as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near the aperture 8 itself in the closed structure 9 of the radiation source SO.

[0021] FIG. 1 shows a radiation source SO as a laser-produced plasma (LPP) source, although any suitable source such as a discharge-produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[0022] In order to accurately pattern the substrate of the substrate W with a pattern on a patterning device such as the patterning device MA, an accurate spatial alignment of the substrate and the patterning device is required. Performing an alignment process between the patterning device and the substrate is generally known and typically involves projecting an image of a pattern or one or more markers present on the patterning device onto a sensor disposed on an object table that holds the substrate. Typically, such an alignment process involves projecting the pattern along an optical path that includes one or more optical components such as mirrors or lenses.

[0023] In known lithography processes, the position of the optical components in the optical path is a fixed position. In addition, the optical components are typically maintained at the fixed position also during subsequent exposure or patterning processes.

[0024] The present invention relates to determining an alignment position between a patterning device and a substrate when an optical component disposed in an optical path between the patterning device and the substrate is movable rather than remaining in a fixed position.

[0025] Figure 2 schematically shows an arrangement including a patterning device and a substrate to which the present invention can be applied.

[0026] Figure 2 schematically shows a patterning device MA arranged on a support or support structure MT and a substrate W arranged on a substrate table WT. In the arrangement as shown, the patterning device MA is configured to receive a radiation beam B provided, for example, by an illumination system or illuminator, and project a patterned radiation beam B' through an optical path OP towards the substrate W or the substrate table WT. In the arrangement as shown, the optical path between the patterning device MA and the substrate W comprises a plurality of movable optical components 100. The set of optical components 100 may constitute, for example, a part of a projection system 110 similar to the projection system PS of FIG. 1. To align the patterning device MA with the substrate W or to determine the alignment position between the patterning device and the substrate, the patterned radiation beam B' may be patterned, for example, with an image of a pattern or marker present on the patterning device MA. And the patterned radiation beam B' may be detected by an alignment sensor 150 on the substrate table WT during an alignment process to establish the relative position of the patterning device MA and the substrate table WT. If the position of the substrate W relative to the substrate table WT is known, the alignment position between the patterning device MA and the substrate W is also known. In the arrangement as shown, a position measurement system 120, which may similarly constitute a part of the projection system 110, is used to measure the position of the optical components 100. The position measurement system 120 may be, for example, an interferometer-based measurement system or an encoder-based measurement system. In the arrangement as shown, the position measurement system 120 is configured to measure the position of the optical components 100 relative to the frame 130 of the projection system 110.

[0027] In one embodiment, the position measurement system 120 can be configured to measure the position of the optical component 100 in one or more degrees of freedom. In one embodiment, the position measurement system 120 can be configured to measure the position of the optical component in six degrees of freedom (6 DOF). To that end, the position measurement system 120 can include a plurality of measurement systems. In one embodiment, the position measurement system 120 can include, for example, a set of interferometers (e.g., six interferometers) for measuring the position of each optical component 100 in 6 DOF.

[0028] According to the present invention, a projection system 110 as schematically shown in FIG. 2 projects, in use, a beam of patterned radiation, i.e., a radiation beam patterned by a patterning device MA, onto a substrate W. According to an aspect of the present invention, the optical component 100 of the projection system 110 is configured to be displaced during a patterning or exposure process. During the patterning or exposure process, an accurate alignment between the patterning device and the substrate is required to ensure that the patterned radiation beam is projected onto a desired location on the substrate W.

[0029] The inventors of the present invention have observed that the application of known alignment approaches in which the spatial alignment between the patterning device and the substrate is determined while the optical components disposed in the optical path between the patterning device and the substrate are kept in a fixed position does not result in an accurate alignment when the optical components do not have a fixed position and are, in particular, provided to be displaceable or movable during the patterning or exposure process. It has been found by the inventors that this inaccuracy in the determined alignment can be caused by inaccuracies in the applied position measurement system 120 used to measure the position of the movable optical components disposed in the optical path between the patterning device and the substrate.

[0030] The present invention provides a solution to mitigate this inaccuracy.

[0031] As described above, the position measurement system 120 applied to measure the position of the optical component 100 disposed in the optical path between the patterning device MA and the substrate W may have inaccuracies. The position of the optical component 100 measured by the position measurement system 120 may not correspond to the actual position of the optical component. Due to this error, the position of the image of the pattern or marker projected onto the substrate table WT (particularly, on the alignment sensor 150) is not in the desired or expected location.

[0032] In one embodiment of the present invention, it is interpreted that the positioning error of the movable optical component 100 is caused by the cyclic error of the applied position measurement. As is generally known to those skilled in the art, position measurement systems, particularly optical position measurement systems such as interferometer-based measurement systems or encoder-based measurement systems, may be affected by what is known as cyclic error. The cyclic error e(x) of such a position measurement system can be modeled, for example, by a combination of one or more sine components. Here, the sine components have a periodicity that can be expressed as an integer fraction of the wavelength λ applied by the position measurement system (for example, the position measurement system 120 schematically shown in FIG. 2).

[0033] As an example, the cyclic error e(x) may be expressed as follows as a function of the length x of the measurement beam of the position measurement system.

Equation

[0034] In general, error equations similar to Equation (1) may exist for each degree of freedom measured by each position measurement system. For example, assuming that the projection system 110 shown in FIG. 2 comprises eight movable optical components 100 whose positions are measured in 6 DOF, the positioning error of such a system may be characterized by 48 equations similar to Equation (1). Thus, when an alignment process is performed in such a projection system 110 including a position measurement system having the shown cyclic error, each degree of freedom of each optical component may be affected by the cyclic error according to Equation (1).

[0035] According to the present invention, a method has been devised for more accurately determining the alignment position between the patterning device MA and the substrate W or the substrate table WT.

[0036] According to a first aspect of the present invention, a method for spatially aligning a patterning device and a substrate is provided. The patterning device and the substrate are separated by an optical path comprising one or more movable optical components. The method involves one or more displacements of the optical components along a predetermined trajectory during an alignment measurement.

[0037] According to the first aspect of the present invention, instead of performing an alignment measurement with an optical component arranged at a fixed position, a method is proposed in which one or more of the optical components are displaced along a predetermined trajectory during the alignment measurement.

[0038] In a known alignment method, as described above, the alignment position between the substrate and the patterning device is determined by projecting a radiation beam from the patterning device along the optical path towards the substrate table that supports the substrate. In particular, the projected radiation beam may be, for example, a radiation beam that is reflected from the patterning device and includes an image of a marker on the patterning device. And the patterned radiation beam can be projected towards a substrate table configured to support the substrate via an optical path including one or more movable optical components. In particular, the patterned radiation beam can be projected towards an alignment sensor such as alignment sensor 150 as described above. To determine the alignment position, typically, the substrate table that supports the substrate is displaced to cause a displacement of the substrate table with respect to the radiation beam or the patterned radiation beam, more specifically, a displacement of the alignment sensor on the substrate table with respect to the radiation beam. A typical displacement of the substrate table used to determine the alignment position of the patterning device with respect to the substrate or the substrate table is shown in FIG. 3. FIG. 3 schematically shows a trajectory, for example, in the vertical XZ or YZ plane, representing the displacement of the substrate table during a typical alignment measurement, where it is interpreted that the optical components arranged on or along the optical path are in a fixed position. Such a trajectory is also known as a warehouse scan. As shown, the trajectory involves displacing the substrate table over a specific range in the horizontal direction, i.e., the X or Y direction, indicated by reference numeral 501, and displacing the substrate table in the vertical or Z direction, indicated by reference numeral 502, resulting in different vertical positions or Z positions for performing the horizontal displacement or scan. During the execution of the displacement or scan, the alignment sensor may measure the optical properties of the radiation beam or the patterned radiation beam hitting the alignment sensor (e.g., alignment sensor 150) at different instants. Based on the optical properties captured at different instants, for example, a 2D map or matrix representing the optical properties can be determined or obtained. FIG. 4 schematically shows such a 2D map.FIG. 4 schematically shows the measured optical characteristics, e.g., the intensity of the radiation beam as a function of the X and Z positions of the substrate table. The contour lines 600 indicate locations having the same value for the optical characteristics. Optimal values of the measured optical characteristics across the scanned area may be determined using mathematical modeling techniques such as interpolation or curve or surface fitting. The location where the optimal value occurs, e.g., location X in FIG. 4. opt may be interpreted as the alignment position. In particular, the position where the optimal value of the optical characteristics occurs may be interpreted as the alignment position of the alignment sensor mounted on the patterning device and the substrate table. In combination with data regarding the positioning of the substrate on the substrate table, the alignment positions of the patterning device and the substrate may be determined.

[0039] According to a first aspect of the present invention, one or more movable optical components disposed in the optical path between the patterning device and the substrate table are not kept in a fixed position and are displaced along a predetermined trajectory during the alignment measurement. In particular, according to a first aspect of the present invention, at least one of the one or more movable optical components disposed in the optical path between the patterning device and the substrate table is displaced along a predetermined trajectory during the alignment measurement.

[0040] A method of spatially aligning a patterning device and a substrate according to a first aspect of the present invention comprises projecting a radiation beam from the patterning device along the optical path. The radiation beam may be, for example, a patterned radiation beam as described above.

[0041] The method further comprises performing at least one displacement of one or more movable optical components along a predetermined trajectory. In one embodiment, such displacement of one or more movable optical components may result in a displacement of the radiation beam relative to the substrate. As will be understood by those skilled in the art, displacement of an optical component in the optical path between the patterning device and the substrate typically results in a displacement of the radiation beam relative to the substrate or the substrate table holding the substrate. In the case of the application of a patterned radiation beam (e.g., a radiation beam comprising an image of a marker present on the patterning device), the aerial image of the marker is displaced relative to the substrate or the substrate table due to the displacement along the optical path of one or more movable optical components. It should be noted that within the scope of the present invention, the displacement of the movable optical component may be a rotation, a translation, or a combination thereof. However, when a plurality of optical components each perform a displacement along a predetermined trajectory, the resulting displacement along the optical path of the radiation beam may be such that the radiation beam hitting the substrate table, or the aerial image of the radiation received by the substrate table, remains substantially stationary. Based on the known optical properties of the movable optical component and the known geometry of the optical path, a trajectory for the movable optical component can be selected such that the movement or displacement of the movable optical component along the selected trajectory does not result in a displacement of the radiation beam or the aerial image of the radiation beam relative to the substrate table.

[0042] The alignment method according to a first aspect of the present invention further comprises determining the optical properties of a radiation beam received by a sensor on a substrate table supporting a substrate at a plurality of instants during the displacement of one or more movable optical components. In contrast to known alignment methods in which the optical components along the optical path are kept in a fixed position at different instants during the measurement of the optical properties of the radiation beam, the method according to the first aspect of the present invention proposes to perform a plurality of measurements of the optical properties of the radiation beam while displacing one or more movable optical components along a predetermined trajectory. As will be explained in more detail below, by performing a plurality of measurements of the optical properties during the displacement of one or more movable optical components, the influence of cyclic errors in the position measurement of the one or more movable optical components can be averaged or at least mitigated.

[0043] When the optical properties of the radiation beam are determined at different instants during the displacement of one or more movable optical components, the patterning device and the substrate can be spatially aligned based on the optical properties determined at the plurality of instants. Based on the optical properties determined at the plurality of instants, for example, an optimum value of the optical properties related to the alignment position of the patterning device and the substrate can be found. This can be done, for example, using similar mathematical modeling techniques as described above (e.g., interpolation or curve or surface fitting).

[0044] The present invention aims to provide an improved or more accurate spatial alignment of the patterning device and the substrate, as described above. In particular, the present invention aims to reduce the adverse effect on alignment caused by measurement errors of the position measurement system or the system applied to measure the position of the movable optical component. An example of such a measurement error is a cyclic error.

[0045] In the alignment method according to the first aspect of the present invention, an alignment measurement is performed, during which one or more movable optical components are displaced along a predetermined trajectory. It has been observed that by displacing one or more movable optical components during the alignment measurement, averaging or mitigation of the effects of cyclic errors of the position measurement system associated with the optical components can be achieved.

[0046] Typically, when a movable optical component or the like is displaced, for example, a positioning system comprising one or more actuators or motors is used to effect the desired displacement. Such a positioning system typically receives, as feedback, a signal from a position measurement system indicating the position of the optical component. When the displacement of the optical component along the predetermined trajectory is to be performed, the positioning system uses the position measurement signal from the position measurement system as feedback to generate a force acting on the optical component to effect the desired displacement along the predetermined trajectory. For example, when the position measurement signal is corrupted due to cyclic errors of the position measurement system, the actual trajectory followed by the optical component deviates from the desired predetermined trajectory (the actual trajectory followed is affected by cyclic errors). During the displacement of the optical component, by performing an alignment measurement (for example, an alignment measurement comprising a warehouse scan as illustrated in FIG. 3), the effect of cyclic errors on the determined alignment position is averaged or at least mitigated. As an example, the predetermined trajectory along which one or more movable optical components are displaced can span one or more periods of cyclic errors of the position measurement system applied to measure the position of the movable optical component.

[0047] In one embodiment, not only one optical component but also a plurality of movable optical components are displaced along their respective predetermined trajectories. Note that the selection of the optical components that need to be displaced may be determined based on the impact of cyclic errors on the alignment accuracy for each optical component.

[0048] The method for spatially aligning a patterning device and a substrate according to the first aspect of the present invention can be implemented in different manners.

[0049] In a first embodiment of the alignment method according to the first aspect of the present invention, a predetermined trajectory along which one or more movable optical components are displaced is selected such that the displacement of the one or more movable optical components results in a displacement of the radiation beam relative to the substrate table. As an example, the displacement of the one or more movable optical components may result in a substantially horizontal displacement of the aerial image of the radiation beam relative to the substrate table. Such a horizontal displacement of the aerial image of the radiation beam relative to the substrate table may be at least partially used in one embodiment of the present invention instead of a horizontal displacement of the substrate table relative to the radiation beam (for example, the horizontal displacement 501 shown in FIG. 3).

[0050] In a more detailed example of the first embodiment, a predetermined trajectory along which one or more movable optical components are displaced is selected to result in a sequence of a plurality of substantially horizontal displacements of the aerial image of the radiation beam relative to the substrate table. By doing so, the horizontal displacement of the substrate table (such as that exemplified by the horizontal displacement 501 in FIG. 3) that is performed during a typical alignment measurement need not be performed by the stage. Rather, the substantially horizontal displacements required during the warehouse scan are provided by the sequence of horizontal displacements of the aerial image of the radiation beam. The sequence of substantially horizontal displacements of the aerial image of the radiation beam relative to the substrate table may be configured to cover a similar range as that performed by the substrate table when performing a warehouse scan as exemplified in FIG. 3, for example. For this reason, the sequence of horizontal displacements of the aerial image of the radiation beam relative to the substrate table may extend over a range X1 to X0 as shown in FIG. 3. The sequence of horizontal displacements may also be an alternating sequence of movements or displacements in substantially opposite directions.

[0051] In one embodiment, a substrate table supporting a substrate may be configured to perform a displacement substantially perpendicular during a sequence of horizontal displacements of the aerial image of the radiation beam relative to the substrate table. Such a substantially perpendicular displacement may be a substantially continuous displacement or a discrete or stepped displacement. In the latter case, the stepped vertical displacement may be a vertical displacement 502 as shown in FIG. 3. In such a case, the resulting displacement of the radiation beam relative to the substrate table is similar to the warehouse scan shown in FIG. 3. Such a resulting displacement is schematically shown in FIG. 5a. In the former case, a combination of a sequence of substantially horizontal displacements of the aerial image of the radiation beam relative to the substrate table and a substantially continuous vertical displacement of the substrate table may result in a trajectory as schematically shown in FIG. 5b. Regarding the trajectories shown in FIGS. 5a and 5b, the horizontal displacement of the trajectory is due to the displacement of the aerial image of the radiation beam, and the vertical displacement is provided by the substrate table. According to the present invention, the optical properties of the radiation beam received by a sensor on the substrate table are determined at a plurality of instants during the displacement of one or more movable optical components. In FIGS. 5a and 5b, the relative positions of the aerial image of the radiation beam and the substrate table at these plurality of instants are indicated by dots 700. By determining the optical properties of the radiation beam at the indicated positions 700, a 2D map of the optical properties can be created and the location corresponding to the optimum value of the optical properties can be determined.

[0052] In a first embodiment of the alignment method according to the first aspect of the present invention, the displacement of one or more movable optical components is used to achieve the required horizontal displacement of the aerial image of the radiation beam relative to the substrate table so that the horizontal scanning of the substrate table (e.g., corresponding to the horizontal displacement 501 shown in FIG. 3) can be at least partially omitted.

[0053] In a second embodiment of the alignment method according to the first aspect of the present invention, the method does not depend on the displacement of one or more movable optical components in causing the displacement of the aerial image of the radiation beam relative to the substrate table. In a second embodiment of the alignment method according to the first aspect of the present invention, the displacement of one or more movable optical components along a predetermined trajectory may cause the displacement of the aerial image of the radiation beam relative to the substrate table, or may result in a radiation beam that remains stationary relative to the substrate table. To realize the latter option, a plurality of movable optical elements are displaced along a plurality of predetermined trajectories, and the displacement or trajectory may be configured such that the combined displacement of the movable optical elements does not cause the displacement of the radiation beam hitting the substrate table or the aerial image of the radiation beam. In such a configuration where the radiation beam remains substantially stationary relative to the substrate table, the substrate table may be configured to perform a further displacement along a predetermined trajectory. Here, the further displacement of the substrate table causes the displacement of the substrate table relative to the radiation beam. In one embodiment, the further predetermined trajectory executed by the substrate table may correspond to, for example, a substrate table that performs a warehouse scan as shown in FIG. 3 with respect to the radiation beam. In such an embodiment, the further predetermined trajectory may comprise a plurality of substantially horizontal displacements at a plurality of different vertical positions, for example, as shown in FIG. 3. However, according to the first aspect of the present invention, the displacement of the substrate table along the further predetermined trajectory is executed during the displacement of one or more movable optical components. As a result, the cyclic error of the position measurement system applied to measure the position of one or more movable optical components can be averaged or alleviated.

[0054] In another embodiment of the first aspect of the present invention, it is assumed that the displacement of one or more movable optical components results in the displacement of the aerial image of the radiation beam relative to the substrate table. Instead of using the displacement of the aerial image of this radiation beam to perform the alignment measurement, the alignment method in this embodiment comprises performing a displacement of the substrate table that at least partially compensates for, or at least partially follows, the displacement of the aerial image of the radiation beam relative to the substrate table brought about by the displacement of one or more movable optical components. For this purpose, in such an embodiment, the substrate table may track the aerial image of the radiation beam displaced due to the displacement of one or more movable optical components along a predetermined trajectory. To perform the measurement of the required optical properties, a scanning movement or displacement may be superimposed on the tracking movement. In such an embodiment, the displacement of the substrate table, which may be represented as a further displacement along a predetermined trajectory, may comprise the following components. - A tracking trajectory corresponding to the displacement of the aerial image of the radiation beam relative to the substrate table brought about by the displacement of one or more movable optical components - A trajectory such as a scan in which the optical properties of the received radiation beam are determined at a plurality of instants

[0055] In one embodiment, a trajectory such as a scan may be similar to a warehouse scan as schematically shown in FIG. 3. For this purpose, a trajectory such as a scan may comprise a plurality of substantially horizontal displacements of the substrate table at a plurality of different vertical positions. Alternatively, a trajectory such as a scan may be similar to the trajectory shown in FIG. 5b.

[0056] In one embodiment of the alignment method according to the first aspect of the present invention, a predetermined trajectory followed by one or more movable components extends over at least one period of the cyclic error in the position measurement of the movable optical component. As previously described in detail, such cyclic errors may comprise a plurality of components each having a different period (see, for example, Equation (1)). In one embodiment, the predetermined trajectory followed by one or more movable components extends over at least one period of the cyclic error component having the longest period. In one embodiment, the predetermined trajectory extends over a plurality of periods of the cyclic error.

[0057] For the sake of completeness, it may be noted that in one embodiment, the displacement of the movable optical component may also result in a displacement substantially perpendicular to the aerial image of the radiation beam. In such an embodiment, the displacement of the movable optical component may at least partially replace the vertical movement of the substrate table during the alignment measurement. For this reason, referring to FIG. 3, the vertical displacement of the aerial image caused by the displacement of the movable optical component may at least partially replace the vertical displacement 502 of the substrate table. In such an embodiment, while the vertical displacement of the aerial image with respect to the substrate table or the alignment sensor may be caused by the displacement of the movable optical component, the horizontal displacement of the aerial image with respect to the substrate table may be caused by the displacement of the substrate table in the horizontal direction, the displacement of the movable optical component that causes the horizontal displacement of the aerial image of the radiation beam, or a combination thereof, as previously described.

[0058] The present invention may be embodied in an apparatus as schematically shown in FIG. 6. An apparatus 200 as schematically shown in FIG. 6 comprises a support or support structure MT configured to support a patterning device MA, and a substrate table WT configured to support a substrate W and a projection system 210. In the arrangement shown, the apparatus 200 is configured to receive a radiation beam B for illuminating the patterning device MA. The radiation beam B may be provided, for example, by an illumination system or illuminator. The projection system 210 of the apparatus 200 comprises a set of movable optical components 210.1 that provide an optical path between the patterning device MA and the substrate table WT or the substrate W. In order to spatially align the patterning device MA with the substrate W, or to determine an alignment position between the patterning device and the substrate, a patterned radiation beam B' may be patterned with an image of a pattern or marker present on the patterning device MA during use. And the patterned radiation beam B' may be detected by an alignment sensor 150 on the substrate table WT during an alignment process in order to establish a relative position between the patterning device MA and the substrate table WT. The apparatus 200 further comprises a position measurement system 220 configured to determine or measure the positions of the support structure, the substrate table and the movable optical components 210 of the projection system. In the embodiment shown, the position measurement system comprises a first system 220.1 for measuring the position of the movable optical components 210.1 relative to the frame 230 of the projection system 210. In the embodiment shown, the position measurement system comprises a second system 220.2 for measuring the position of the support system MT relative to the frame 260 of the apparatus 200. In the embodiment shown, the position measurement system comprises a third system 220.3 for measuring the position of the substrate table WT relative to the frame 270 of the projection system 210. The frames 230, 260 and 270 may be parts of the same frame or different frames. The position measurement system applied may be, for example, an interferometer-based measurement system or an encoder-based measurement system.

[0059] An apparatus 200 as shown further comprises a positioning system 280 configured to position a patterning device, a substrate, and a movable optical component of a projection system. In an embodiment as shown, the positioning system 280 comprises a first positioning system 280.1 for positioning a support structure MT that supports the patterning device. The first positioning system 280.1 may comprise, for example, one or more motors and / or actuators (e.g., electromagnetic motors or actuators) for positioning the support structure MT and the patterning device. As an example, the first positioning system 280.1 may comprise, for example, a linear motor for providing a coarse positioning of the support structure MT and a set of actuators for providing a fine positioning of the support structure MT. The positioning system 280 further comprises a second positioning system 280.2 for positioning a substrate table WT that supports the substrate W. As an example, the second positioning system 280.2 may comprise, for example, a set of planar motors or linear motors for providing a coarse positioning of the substrate table WT in a horizontal plane and a set of actuators for providing a fine positioning of the substrate table WT. Using such positioning systems 280.1 and 280.2, the patterning device MA and the substrate W may be positioned, for example, in 6 DOF.

[0060] As shown, the positioning system 280 applied in the apparatus 200 further includes, as a third positioning system 280.3, a set of actuators 280.3 for positioning the movable optical component 210.1 of the projection system 210. Such actuators 280.3 may be, for example, electromagnetic or piezoelectric actuators or a combination thereof. The actuator 280.3 may be configured, for example, to position the movable optical component 210.1 in 6 DOF. The apparatus 200 further includes a control unit 290 that may be embodied as, for example, a computer, a controller, a microcontroller, etc. The control unit 290 is configured to control the positioning system to accurately position the patterning device MA, the substrate W, and the movable optical component 210.1. To that end, the control unit 290 can generate an output signal 290.1 for controlling the positioning system 280 (in particular, the motor or actuator of the positioning system 280). To generate the output signal 290.1, the control unit 290 may be configured to receive an input signal 290.2 (for example, a signal obtained from the position measurement system 220). Here, the signal 290.2 represents, for example, the positions of the patterning device MT, the substrate W, and the movable optical component 210.1.

[0061] The apparatus 200 according to the present invention is further configured to perform any of the methods for spatially aligning the patterning device MT and the substrate W according to the present invention, which have been described in detail above.

[0062] In particular, the control unit 290 of the apparatus 200 may be configured to control the positioning system 280 to execute the displacement of one or more movable optical components 210.1 along a predetermined trajectory, to determine the optical characteristics of the radiation beam received by a sensor on the substrate table at a plurality of instants during the displacement of the one or more movable optical components, and to determine the alignment positions of the patterning device and the substrate based on the optical characteristics determined at the plurality of instants.

[0063] In one embodiment, the apparatus according to the invention may be integrated into a lithography system, which further comprises a radiation source and an illumination system or illuminator.

[0064] Although specific reference may be made in this text to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0065] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of any apparatus for measuring or processing an object such as a mask inspection apparatus, a metrology apparatus, or a wafer (or other substrate) or mask (or other patterning device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or atmospheric (non-vacuum) conditions.

[0066] Although specific reference to the use of embodiments of the present invention may have been made in the context of optical lithography, it is understood that the present invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0067] When the context permits, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may be implemented as instructions stored on a machine-readable medium that may be read and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a device (e.g., a computing device). For example, the machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical / optical / acoustic or other form of transmitted signals (e.g., carrier waves, infrared signals, digital signals, etc.). Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, such descriptions are merely for convenience and such actions are actually caused by computing devices, processors, controllers or other devices that execute firmware, software, routines, instructions, etc., and may interact with the physical world through actuators or other devices.

[0068] Although specific embodiments of the invention have been described above, it is understood that the invention may be practiced in ways different from those described. The foregoing description is for the purpose of non-limiting illustration. Thus, it will be apparent to those skilled in the art that changes may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method for spatially aligning a patterning device and a substrate separated by an optical path including one or more movable optical components, comprising: projecting a radiation beam from the patterning device along the optical path; executing displacement of the one or more movable optical components along a predetermined trajectory; determining optical properties of the radiation beam received by a sensor on a substrate table supporting the substrate at a plurality of instances during the displacement of the one or more movable optical components; spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of instances. A method comprising the above steps.

2. The method according to claim 1, wherein the radiation beam is a patterned radiation beam comprising a pattern of markers disposed on the patterning device.

3. The method according to claim 1 or 2, wherein the optical property is the intensity of the patterned radiation beam.

4. The method according to any one of claims 1 to 3, further comprising executing displacement of the substrate table along a further predetermined trajectory, resulting in displacement of the substrate table with respect to the radiation beam.

5. The method according to claim 4, wherein the displacement of the substrate table with respect to the radiation beam comprises a plurality of substantially horizontal displacements at a plurality of different vertical positions.

6. The displacement of the one or more movable optical components results in displacement of an aerial image of the radiation beam with respect to the substrate table, and the displacement of the substrate table with respect to the radiation beam at least partially compensates for or at least partially follows the displacement of the aerial image of the radiation beam with respect to the substrate table caused by the displacement of the one or more movable optical components. The method according to claim 4 or 5.

7. The method according to any one of claims 1 to 6, wherein the predetermined trajectory is at least over one period of a cyclic error in position measurement of the one or more movable optical components.

8. The displacement of the one or more movable optical components along the predetermined orbit results in a sequence of a plurality of substantially horizontal displacements of the aerial image of the radiation beam with respect to the substrate table, according to the method of any one of claims 1 to 7.

9. The method according to claim 8, further comprising performing a substantially vertical displacement of the substrate table during the displacement of the one or more movable optical components.

10. The method according to claim 9, wherein the substantially vertical displacement is a substantially continuous displacement or a stepped displacement.

11. A support structure configured to support a patterning device, A substrate table configured to support a substrate, A projection system comprising a plurality of movable optical components that provide an optical path between the patterning device and the substrate, A positioning system configured to position the patterning device, the substrate, and the movable optical components of the projection system, A position measurement system configured to measure the positions of the support structure, the substrate table, and the movable optical components of the projection system, A control unit configured to control the positioning system, An apparatus comprising: The apparatus is configured to receive a radiation beam for illuminating the patterning device, The control unit is configured to control the apparatus to perform the method of spatially aligning the patterning device and the substrate according to any one of claims 1 to 10. Apparatus.

12. A support structure configured to support a patterning device, A substrate table configured to support a substrate, A projection system comprising a plurality of movable optical components that provide an optical path between the patterning device and the substrate, A positioning system configured to position the patterning device, the substrate, and the movable optical components of the projection system, A position measurement system configured to measure the positions of the support structure, the substrate table, and the movable optical components of the projection system, A control unit configured to control the positioning system, An apparatus comprising: The apparatus is configured to project a radiation beam from the patterning device onto the substrate table supporting the substrate along the optical path, The control unit, controls the positioning system to execute displacement of the one or more movable optical components along a predetermined trajectory, determines optical properties of the radiation beam received by a sensor on the substrate table at a plurality of instants during the displacement of the one or more movable optical components, determines alignment positions of the patterning device and the substrate based on the optical properties determined at the plurality of instants, is configured to perform, apparatus. **Claim 13** The apparatus according to claim 11 or 12, wherein the predetermined trajectory is at least over one period of a cyclic error of the position measurement system. **Claim 14** An apparatus according to any one of claims 11 to 13, a radiation source and an illumination system for generating the radiation beam, a lithography system comprising. **Claim 15** The lithography system according to claim 14, wherein the radiation source is an EUV radiation source and / or the movable optical component is an EUV mirror.

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