Method of spatially aligning patterning device and substrate

Abstract

A method of spatially aligning a patterning device and a substrate, where the patterning device and the substrate are separated by an optical path comprising one or more movable optical components, the method comprising: projecting a beam of radiation from the patterning device along the optical path; -performing a displacement of the one or more movable optical components along a predetermined trajectory; -determining, during the displacement of the one or more movable optical components, an optical property of the radiation beam received by the sensor on the substrate table supporting the substrate at a plurality of times; -spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of times.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22178555.3 filed on June 13, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a method of spatially aligning a patterning device and a substrate in a lithographic apparatus, wherein the patterning device and the substrate are separated by an optical path comprising one or more movable optical components. Background Art

[0004] A lithographic apparatus is a machine 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 at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0005] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of the radiation determines the minimum size of a feature that can be formed on the substrate. Compared to a lithographic apparatus that may use radiation with a wavelength of 193 nm, for example, a lithographic apparatus that uses extreme ultraviolet (EUV) radiation with a wavelength in the range of 4-20 nm (e.g., 6.7 nm or 13.5 nm) may be used to form smaller features on a substrate.

[0006] In order to accurately pattern the substrate with the pattern of the patterning device, it is necessary to accurately align the substrate and the patterning device. To this end, it is known to determine the alignment position between the patterning device and the substrate or the substrate table holding the substrate by projecting a pattern or image of one or more marks present on the patterning device onto a sensor arranged on the substrate table holding the substrate. Typically, this alignment process involves projecting the pattern along an optical path including one or more optical components (such as mirrors or lenses). During this alignment process, the optical components are typically held in fixed positions. In the event that these components are displaced or need to be displaced during a subsequent patterning or exposure process, it has been found that the determined alignment position may be defective or inaccurate, which may result in overlay errors during the patterning process. Summary of the invention

[0007] It is an object of the present invention to provide improved alignment between a patterning device and a substrate, in particular when movable optical components are used during a patterning process in a lithographic apparatus.

[0008] According to a first aspect of the present invention, there is provided a method of spatially aligning a patterning device and a substrate, wherein the patterning device and the substrate are separated by an optical path comprising one or more movable optical components, the method comprising:

[0009] - projecting a radiation beam from said patterning device along said optical path;

[0010] - performing a displacement of said one or more movable optical components along a predetermined trajectory;

[0011] - determining, at a plurality of time instants during displacement of the one or more movable optical components, an optical property of a radiation beam received by a sensor on a substrate table supporting the substrate;

[0012] - spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of time instants.

[0013] According to a second aspect of the present invention, there is provided a device, the device comprising:

[0014] - a support structure configured to support a patterning device;

[0015] - a substrate table configured to support a substrate;

[0016] - a projection system comprising a plurality of movable optical components providing an optical path between the patterning device and the substrate;

[0017] - a positioning system configured to position the patterning device, the substrate and the movable optical component of the projection system;

[0018] - a position measurement system configured to measure the position of the support structure, the substrate table and the movable optical component of the projection system;

[0019] - a control unit configured to control the positioning system;

[0020] - wherein the apparatus is configured to receive a radiation beam to illuminate the patterning device, and wherein the control unit is configured to control the apparatus to perform the method of spatially aligning the patterning device and the substrate according to the first aspect of the invention.

[0021] According to a third aspect of the present invention, there is provided a device, comprising:

[0022] - a support structure configured to support a patterning device;

[0023] - a substrate table configured to support a substrate;

[0024] - a projection system comprising a plurality of movable optical components providing an optical path between the patterning device and the substrate;

[0025] - a positioning system configured to position the patterning device, the substrate and the movable optical component of the projection system;

[0026] - a position measurement system configured to measure the position of the support structure, the substrate table and the movable optical component of the projection system;

[0027] - a control unit configured to control the positioning system;

[0028] wherein the apparatus is configured to project a radiation beam from the patterning device along the optical path onto the substrate table supporting the substrate; and

[0029] The control unit is configured as follows:

[0030] - controlling the positioning system to perform a displacement of the one or more movable optical components along a predetermined trajectory;

[0031] - determining, at a plurality of time instants, an optical property of a radiation beam received by a sensor on the substrate table during displacement of the one or more movable optical components;

[0032] - determining an alignment position of the patterning device and the substrate based on the optical characteristics determined at the plurality of time instants. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0034] Figure 1 A lithographic system comprising a lithographic apparatus and a radiation source according to the present invention is depicted;

[0035] Figure 2 A system for performing the alignment method according to the invention is depicted;

[0036] Figure 3 schematically shows a trajectory representing the displacement of the substrate table during alignment measurement;

[0037] Figure 4 schematically shows a 2D diagram of an optical property determined by a sensor during an alignment measurement;

[0038] Figure 5a and Figure 5b schematically shows a trajectory that can be used to perform the alignment method according to the invention;

[0039] Figure 6 A device according to the invention is shown schematically. DETAILED DESCRIPTION

[0040] Figure 1 A lithographic system according to the invention is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to provide the EUV radiation beam B to the lithographic apparatus LA. The lithographic 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.

[0041] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Thereby, the illumination system IL may comprise a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide a desired cross-sectional shape and a desired intensity distribution for the EUV radiation beam B. The illumination system IL may comprise other mirrors or arrangements in addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11.

[0042] After this adjustment, the EUV radiation beam B interacts with the pattern forming 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. To this end, the projection system PS may include a plurality of mirrors 13, 14, which are configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. According to the present invention, the mirrors 13, 14 may also refer to movable optical components that can be displaced or moved, for example during a patterning process or an exposure process and during an alignment process. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image having features that are smaller than the corresponding features on the pattern forming device MA. For example, a reduction factor of 4 or 8 may be applied. Although in Figure 1 The projection system PS is shown in FIG. 2 with only two mirrors 13 , 14 , but the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0043] 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 pattern previously formed on the substrate W.

[0044] The lithographic apparatus LA as shown in the figure further comprises a control unit CU. In general, the control unit CU may be configured to control the operation of the lithographic apparatus. In particular, the control unit CU may, for example, be configured to control 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 may be configured to control the lithographic apparatus to perform a method of spatially aligning the pattern forming device MA and the substrate W according to the present invention. To this end, the control unit CU may, for example, be configured to also control the positions of the mirrors 13, 14 of the projection system PS. In addition, as will be described in detail below, the control unit CU may be configured to control the appropriate positioning of the pattern forming device PA, the substrate table WT and the optical components of the projection system PS so as to perform a plurality of alignment measurements, whereby for each alignment measurement, the movable optical components 13, 14 of the projection system PS are arranged in predetermined positions.

[0045] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, the illumination system IL and / or the projection system PS.

[0046] For example, Figure 1 The radiation source SO shown in FIG. 1 is of a type that may be referred to as a laser produced plasma (LPP) source. The laser system 1 (which may, for example, include a CO 2 The laser emitter 3 is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn), provided by, for example, a fuel emitter 3. Although described below with tin, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may, for example, be a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards the plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. The deposition of laser energy into the tin causes a tin plasma 7 to be generated in the plasma formation region 4. During de-excitation and recombination of electrons with ions of the plasma, radiation including EUV radiation is emitted from the plasma 7.

[0047] EUV radiation from the plasma is collected and focused by a collector 5. For example, the collector 5 comprises a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may be an elliptical configuration with two foci. As described below, the first focus may be at the plasma formation region 4, and the second focus may be at the intermediate focus 6.

[0048] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or beam expanders and / or other optical devices. The laser system 1, the radiation source SO and the beam delivery system may together be considered a radiation system.

[0049] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image at the intermediate focus 6 of a plasma present in the plasma formation region 4. The image at the intermediate focus 6 serves 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 adjacent to an opening 8 in an enclosure 9 of the radiation source SO.

[0050] Although Figure 1 The radiation source SO is depicted as a laser produced plasma (LPP) source, but any suitable source may be used to produce EUV radiation, such as a discharge produced plasma (DPP) source or a free electron laser (FEL).

[0051] In order to accurately pattern a substrate (such as substrate W) with a pattern on a patterning device (such as patterning device MA), accurate spatial alignment of the substrate and the patterning device is required. Performing an alignment process between the patterning device and the substrate is known and typically involves projecting a pattern or image of one or more marks present on the patterning device onto a sensor disposed on a stage holding 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).

[0052] In known photolithography processes, the position of the optical component in the optical path is in a fixed position. In addition, in subsequent exposure or patterning processes, the optical component is usually also kept in the fixed position.

[0053] The present invention relates to determining the alignment position between a patterning device and a substrate, wherein optical components arranged in the optical path between the patterning device and the substrate are movable rather than being in a fixed position.

[0054] Figure 2 An arrangement comprising a patterning device and a substrate is schematically shown, in which the present invention may be applied.

[0055] Figure 2Schematically a patterning device MA arranged on a support or structure MT and a substrate W arranged on a substrate table WT are shown. In the arrangement shown, the patterning device MA is configured to receive a radiation beam B (e.g. provided by an illumination system or illuminator) and to project a patterned radiation beam B' towards the substrate W or substrate table WT via an optical path OP. In the arrangement 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, for example, form a projection system 110 (similar to Figure 1 The patterning device MA is part of a projection system PS of the embodiment of the present invention. In order 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, for example, be patterned with a pattern or image of a mark present on the patterning device MA. The patterned radiation beam B' may then be detected by an alignment sensor 150 on the substrate table WT during the alignment process in order to establish the relative position of the patterning device MA and the substrate table WT. In the case where 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 will also be known. In the arrangement shown, the position of the optical component 100 is measured using a position measurement system 120, which may likewise form part of the projection system 110. The position measurement system 120 may, for example, be an interferometer-based measurement system or an encoder-based measurement system. In the arrangement shown, the position measurement system 120 is configured to measure the position of the optical component 100 relative to the frame 130 of the projection system 110.

[0056] In one embodiment, the position measurement system 120 may 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 may be configured to measure the position of the optical component in 6 degrees of freedom (6 DOF). To this end, the position measurement system 120 may include multiple measurement systems. In one embodiment, for each optical component 100, the position measurement system 120 may, for example, include a set of interferometers (e.g., 6 interferometers) to measure the position of the optical component in 6 DOF.

[0057] According to the present invention, Figure 2 The schematically shown projection system 110 is intended to project a patterned radiation beam (i.e., a radiation beam patterned by a patterning device MA) onto a substrate W during use. According to one aspect of the invention, the optical components 100 of the projection system 110 are configured to be displaced during a patterning process or an exposure process. During the patterning process or the exposure process, accurate alignment between the patterning device and the substrate is required to ensure that the patterned radiation beam is projected onto a desired position on the substrate W.

[0058] The inventors of the present invention have observed that in case the optical components do not have a fixed position but are arranged to be displaceable or movable, in particular during a patterning process or an exposure process, applying known alignment methods in which the optical components arranged in the optical path between the patterning device and the substrate are held in a fixed position when determining the spatial alignment between the patterning device and the substrate does not result in an accurate alignment. The inventors have thought that such inaccuracies in the determined alignment may be caused by inaccuracies in the applied position measurement system 120 for measuring the position of the movable optical component arranged in the optical path between the patterning device and the substrate.

[0059] The present invention provides a solution to reduce this inaccuracy.

[0060] As described above, the position measurement system 120 for measuring the position of the optical component 100 arranged 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 pattern or image of the mark projected onto the substrate table WT, in particular onto the alignment sensor 150, is not at the desired or expected position.

[0061] In an embodiment of the present invention, the positioning error of the movable optical component 100 is considered to be caused by the cyclic error of the applied position measurement. As is generally known to those skilled in the art, a position measurement system, in particular an optical position measurement system (such as an interferometer-based measurement system or an encoder-based measurement system) may be affected by so-called cyclic errors. For example, the cyclic error e(x) of such a position measurement system can be modeled by a combination of one or more sinusoidal components, wherein the sinusoidal components have a position measurement system (e.g., Figure 2 The periodicity of an integer fraction of the wavelength λ used by the position measurement system 120 schematically shown in FIG.

[0062] As an example, the cyclic error e(x), as a function of the length x of the measuring beam of the position measuring system, can be expressed as:

[0063] (1)

[0064] In equation (1), the amplitude a1-a4 and the phase φ1-φ4 are generally unknown. In the given example, the cyclic error e(x) may, for example, represent a cyclic error of a position measurement system 120 for measuring the position of the movable optical component 100 in the x-direction, the cyclic error e(x) comprising 4 components. In particular, the cyclic error e(x) is described as a combination of λ / 4, λ / 8, λ / 12 and λ / 16 sinusoidal components, where λ is the wavelength of the position measurement system. In one embodiment, the wavelength λ may, for example, be the wavelength of a laser source of the position measurement system. With regard to the amplitude a1-a4 and the phase φ1-φ4 of the cyclic error e(x), it may be noted that these parameters may be different for each component or subsystem of the position measurement system 120. As Figure 2 As shown, the position measurement system 120 may include different components or subsystems, each configured to measure the position of one of the movable optical components 100. Therefore, the cyclic errors of the position measurements of these different components may have different magnitudes and / or phases.

[0065] Note that, in general, there can be an error equation similar to equation (1) for each position measurement system for each measured degree of freedom. For example, setting Figure 2 The projection system 110 shown in comprises 8 movable optical components 100 whose positions are measured over 6 DOF, then the positioning error of such a system can be characterized by 48 equations similar to equation (1). Thus, when performing an alignment process using such a projection system 110 including a position measurement system with the indicated cyclic errors, each degree of freedom of each optical component may be affected by a cyclic error according to equation (1).

[0066] 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 substrate table WT.

[0067] According to a first aspect of the invention, a method of spatially aligning a patterning device and a substrate is proposed, wherein the patterning device and the substrate are separated by an optical path comprising one or more movable optical components, the method involving shifting the one or more optical components along a predetermined trajectory during alignment measurements.

[0068] According to said first aspect of the invention, a method is proposed for displacing one or more optical components along a predetermined trajectory during alignment measurements, rather than performing alignment measurements with the optical components arranged in fixed positions.

[0069] In known alignment methods, as discussed above, an alignment position between a substrate and a patterning device is determined by projecting a radiation beam from the patterning device along an optical path towards a substrate table supporting the substrate. In particular, the projected radiation beam may be, for example, a radiation beam reflected from the patterning device, and the projected radiation beam comprises an image of a mark on the patterning device. The patterned radiation beam may then be projected towards a substrate table configured to support the substrate, for example via an optical path comprising one or more movable optical components. In particular, the patterned radiation beam may be projected towards an alignment sensor, such as the alignment sensor 150 described above. In order to determine the alignment position, the substrate table supporting the substrate is typically displaced so that the substrate table is displaced relative to the radiation beam or the patterned radiation beam, and more specifically, the alignment sensor on the substrate table is displaced relative to the radiation beam. Figure 3 A typical displacement of the substrate table for determining the aligned position of the patterning device relative to the substrate or substrate table is shown. Figure 3 A trajectory representing the displacement of a substrate table during a typical alignment measurement (e.g., a trajectory in a vertical XZ or YZ plane) is schematically shown, wherein optical components arranged in or along the optical path are considered to be in fixed positions. Such a trajectory is also referred to as a warehouse scan. As can be seen, the trajectory includes shifting the substrate table in a horizontal direction (i.e., in the X or Y direction) within a specific range, as indicated by reference numeral 501, and shifting the substrate table in a vertical direction or Z direction, as indicated by reference numeral 502, thereby generating different vertical positions or Z positions to perform a horizontal shift or scan. During the performance of the shift or scan, the alignment sensor may measure optical properties of a radiation beam or patterned radiation beam impinging on the alignment sensor (e.g., alignment sensor 150) at different times. Based on the optical properties captured at different times, a 2D map or matrix representing the optical properties may be determined or derived, for example. Figure 4 Such a 2D diagram is shown schematically. Figure 4 Measured optical properties (e.g., intensity) of a radiation beam as a function of the X and Z positions of a substrate table are schematically shown. Profile 600 represents locations having the same value of the optical property. Using mathematical modeling techniques (such as interpolation or curve or surface fitting), an optimal value of the optical property measured across the scan area can be determined. The location where the optimal value occurs (e.g., Figure 4 Position X in opt ) is regarded as the alignment position. In particular, the position where the optimal value of the optical characteristic occurs can be regarded as the alignment position of the pattern forming device and the alignment sensor mounted on the substrate stage. In combination with the positioning data of the substrate on the substrate stage, the alignment position of the pattern forming device and the substrate can be determined.

[0070] According to the first aspect of the invention, one or more movable optical components arranged in the optical path between the patterning device and the substrate table are not kept in a fixed position during alignment measurements, but are displaced along a predetermined trajectory. In particular, according to the first aspect of the invention, at least one of the one or more movable optical components arranged in the optical path between the patterning device and the substrate table is displaced along a predetermined trajectory during alignment measurements.

[0071] The method of spatially aligning a patterning device and a substrate according to the first aspect of the invention comprises projecting a radiation beam from the patterning device along an optical path. For example, the radiation beam may be a patterned radiation beam as described above.

[0072] The method also includes performing a displacement of at least one of the one or more movable optical components along a predetermined trajectory. In one embodiment, such displacement of the one or more movable optical components can cause the radiation beam to be displaced relative to the substrate. It will be appreciated by those skilled in the art that displacement of the optical components in the optical path between the pattern forming device and the substrate will generally result in displacement of the radiation beam relative to the substrate or a substrate table holding the substrate. In the case of applying a patterned radiation beam (e.g., a radiation beam including an image of a mark present on the pattern forming device), the aerial image of the mark will be displaced relative to the substrate or the substrate table due to the displacement of the one or more movable optical components along the optical path. Note that in the present invention, the displacement of the movable optical component can be rotation, translation, or a combination thereof. However, it is noted that when multiple optical components are each displaced along a predetermined trajectory, the displacement of the radiation beam along the optical path generated can cause the radiation beam irradiated onto the substrate table or the aerial image of the radiation received by the substrate table to remain substantially stationary. Based on known optical properties of the movable optical component and the known geometry of the optical path, the trajectory for the movable optical component may be chosen such that movement or displacement of the movable optical component along the chosen trajectory does not shift the radiation beam or the aerial image of the radiation beam relative to the substrate table.

[0073] The alignment method according to the first aspect of the invention further comprises determining, at a plurality of moments, an optical property of a radiation beam received by a sensor on a substrate table supporting the substrate during the displacement of the one or more movable optical components. Compared to known alignment methods, in which optical components along the optical path are kept in fixed positions during the measurement of the optical property of the radiation beam at different moments, the method according to the first aspect of the invention proposes to displace the one or more movable optical components along a predetermined trajectory while performing a plurality of measurements of the optical property of the radiation beam. As will be explained in more detail below, by performing a plurality of measurements of the optical property during the displacement of the 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 out or at least reduced.

[0074] Once the optical properties of the radiation beam are determined at different times during the displacement of the one or more movable optical components, the patterning device and the substrate can be spatially aligned based on the optical properties determined at multiple times. Based on the optical properties determined at multiple times, for example, an optimal value of the optical property can be found, which is associated with the aligned position of the patterning device and the substrate. For example, this can be done using similar mathematical modeling techniques as described above (e.g., interpolation or curve or surface fitting).

[0075] As mentioned above, the present invention aims to provide improved or more accurate spatial alignment of a patterning device and a substrate. In particular, the present invention aims to reduce any adverse effects on alignment caused by measurement errors of one or more position measurement systems used to measure the position of a movable optical component. An example of such a measurement error is a cyclic error.

[0076] In the alignment method according to the first aspect of the invention, during the performance of the alignment measurement, 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, it is possible to average out or reduce the effects of cyclic errors of the position measurement system associated with the optical components.

[0077] Typically, when a movable optical component or the like is to be displaced, a positioning system (e.g., comprising one or more actuators or motors) is used to perform the desired displacement. Typically, such a positioning system receives as feedback a signal from a position measurement system indicating the position of the optical component. When a displacement of the optical component along a predetermined trajectory is to be performed, the positioning system will use the position measurement signal from the position measurement system as feedback to generate a force acting on the optical component to perform the desired displacement along the predetermined trajectory. When the position measurement signal is imperfect, for example due to cyclic errors of the position measurement system, the actual trajectory followed by the optical component will deviate from the desired predetermined trajectory; the actual trajectory followed will be affected by the cyclic errors. By performing alignment measurements during the displacement of the optical component (e.g., comprising Figure 3 The effect of cyclic errors on the determined alignment positions is averaged out or at least reduced. As an example, the predetermined trajectory along which one or more movable optical components are displaced may, for example, span one or more periods of the cyclic error of the position measurement system used to measure the position of the movable optical component.

[0078] In one embodiment, multiple movable optical components are displaced along respective predetermined trajectories instead of only one optical component being displaced. Note that the selection of which optical components need to be displaced can be evaluated based on the impact of cyclic error on the alignment accuracy of each optical component.

[0079] The method of spatially aligning a patterning device and a substrate according to the first aspect of the invention may be implemented in different ways.

[0080] In a first embodiment of the alignment method according to the first aspect of the invention, the predetermined trajectory along which the 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. In embodiments of the invention, such a horizontal displacement of the aerial image of the radiation beam relative to the substrate table may be used at least in part to replace a horizontal displacement of the substrate table relative to the radiation beam, such as, for example Figure 3 The horizontal shift shown is a horizontal shift of 501.

[0081] In a more detailed example of the first embodiment, the predetermined trajectory along which the one or more movable optical components are displaced is selected to perform a series of multiple substantially horizontal displacements of the aerial image of the radiation beam relative to the substrate table. By doing so, horizontal displacements of the substrate table such as are performed during a typical alignment measurement (e.g. Figure 3The horizontal shift 501 shown need not be performed by the stage. Instead, the substantially horizontal shift required during the warehouse scan is provided by a series of horizontal shifts of the aerial image of the radiation beam. The series of substantially horizontal shifts of the aerial image of the radiation beam relative to the substrate table may, for example, be configured to span the same horizontal shifts as when performing the above. Figure 3 The range of the aerial image of the radiation beam relative to the substrate table may therefore span a range similar to that performed by the substrate table during a warehouse scan as shown. Figure 3 The range shown is X 1 –X 0 A series of horizontal shifts may be a series of movements or shifts alternating in substantially opposite directions.

[0082] In an embodiment, a substrate table supporting a substrate may be configured to perform a substantially vertical shift during a series of horizontal shifts of the aerial image of the radiation beam relative to the substrate table. Such substantially vertical shifts may be substantially continuous shifts, or may be discrete or stepwise shifts. In the latter case, the stepwise vertical shifts may be similar to Figure 3 In this case, the displacement of the generated radiation beam relative to the substrate table is equal to Figure 3 The warehouse scan shown is similar. Figure 5a Such resulting displacements are schematically illustrated in FIG. 1 . In the former case, a combination of a series 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 produce a displacement such as Figure 5b The trajectory is schematically shown in . Note that Figure 5a and Figure 5b The trajectory shown, the horizontal shift of the trajectory is caused by the shift of the aerial image of the radiation beam, while the vertical shift is caused by the substrate table. According to the invention, during the shift of one or more movable optical components, the optical properties of the radiation beam received by the sensor on the substrate table are determined at a plurality of time instants. Figure 5a and Figure 5b In FIG, the aerial image of the radiation beam and the relative position of the substrate table at these multiple time instants are represented by points 700. By determining the optical properties of the radiation beam at the indicated positions 700, a 2D map of the optical properties can be made and the positions corresponding to optimal values ​​of the optical properties can be determined.

[0083] In a first embodiment of the alignment method according to the first aspect of the invention, a desired horizontal shift of the aerial image of the radiation beam relative to the substrate table is achieved using a shift of one or more movable optical components, so that a horizontal scan of the substrate table can be at least partially omitted, e.g. corresponding to Figure 3 The horizontal shift 501 is shown in FIG.

[0084] In a second embodiment of the alignment method according to the first aspect of the invention, the method does not rely on the displacement of one or more movable optical components to cause a displacement of the aerial image of the radiation beam relative to the substrate table. In the second embodiment of the alignment method according to the first aspect of the invention, the displacement of one or more movable optical components along a predetermined trajectory may cause a displacement of the aerial image of the radiation beam relative to the substrate table, or may cause the radiation beam to remain stationary relative to the substrate table. In order to achieve the latter option, it may be necessary to shift multiple movable optical components along multiple predetermined trajectories and configure the shifts or trajectories so that the combined shifts of the movable optical elements do not cause the radiation beam impinging on the substrate table or the aerial image of the radiation beam. In such an arrangement, in which the radiation beam remains substantially stationary relative to the substrate table, the substrate table may be configured to be shifted along other predetermined trajectories, the other displacements of the substrate table causing the substrate table to shift relative to the radiation beam. In one embodiment, the other predetermined trajectories performed by the substrate table may correspond to the substrate table performing such displacements relative to the radiation beam. Figure 3 In this embodiment, other predetermined trajectories may include a plurality of different vertical positions (e.g., Figure 3 However, it is noted that according to the first aspect of the invention, the displacement of the substrate table along other predetermined trajectories is performed during the displacement of the one or more movable optical components. Thus, cyclic errors of a position measurement system for measuring the position of the one or more movable optical components can be averaged out or reduced.

[0085] In another embodiment of the first aspect of the invention, the displacement of one or more movable optical components is set so that the aerial image of the radiation beam is displaced relative to the substrate table. The alignment method in this embodiment does not use this displacement of the aerial image of the radiation beam to perform alignment measurements, but rather includes performing a displacement of the substrate table, which at least partially compensates or follows the displacement of the aerial image of the radiation beam relative to the substrate table caused by the displacement of one or more movable optical components. In this embodiment, the substrate table can therefore follow the aerial image of the radiation beam that is displaced due to the displacement of one or more movable optical components along a predetermined trajectory. In order to perform the necessary measurements of the optical properties, a scanning movement or displacement can be superimposed on the following movement. In this embodiment, the displacement of the substrate table (which can be referred to as a displacement along a further predetermined trajectory) can include the following components:

[0086] a following trajectory corresponding to a displacement of the aerial image of the radiation beam relative to the substrate table caused by a displacement of the one or more movable optical components, and

[0087] A scan-like trajectory during which optical properties of the received radiation beam are determined at a plurality of time instants.

[0088] In one embodiment, the scan-like trajectory may be similar to Figure 3 Thus, the quasi-scanning trajectory may include a plurality of substantially horizontal displacements of the substrate table at a corresponding plurality of different vertical positions. Alternatively, the quasi-scanning trajectory may be similar to Figure 5b The trajectory shown.

[0089] In an embodiment of the alignment method according to the first aspect of the invention, the predetermined trajectory followed by the one or more movable parts spans at least one period of the cyclic error of the position measurement of the movable optical component. As discussed in detail above, such a cyclic error may include multiple components, each component having a different period, for example see equation (1). In one embodiment, the predetermined trajectory followed by the one or more movable parts spans at least one period of the cyclic error component with the longest period. In one embodiment, the predetermined trajectory spans multiple periods of the cyclic error.

[0090] For completeness, it may be pointed out that in an embodiment, the displacement of the movable optical component may also result in a substantially vertical displacement of 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. Figure 3 , the vertical shift of the aerial image caused by the shift of the movable optical component may thus at least partially replace the vertical shift of the substrate table 502. In such an embodiment, the vertical shift of the aerial image relative to the substrate table or the alignment sensor may be caused by the shift of the movable optical component, while the horizontal shift of the aerial image relative to the substrate table may be caused by a shift of the substrate table in the horizontal direction, a shift of the movable optical component causing a horizontal shift of the aerial image of the radiation beam, or a combination thereof, as explained above.

[0091] The present invention can also be Figure 6 The invention is specifically implemented in the device schematically shown in FIG. Figure 6The device 200 schematically shown in the figure comprises a support or support structure MT configured to support a pattern forming device MA, a substrate table WT configured to support a substrate W, and a projection system 210. In the arrangement shown, the device 200 is configured to receive a radiation beam B to illuminate the pattern forming device MA. The radiation beam B can be provided, for example, by an illumination system or illuminator. The projection system 210 of the device 200 comprises a set of movable optical components 210.1, thereby providing an optical path between the pattern forming device MA and the substrate table WT or substrate W. In order to spatially align the pattern forming device MA with the substrate W, or to determine the alignment position between the pattern forming device and the substrate, during use, the patterned radiation beam B' can be patterned with a pattern or image of a mark present on the pattern forming device MA. Then, during the alignment process, the patterned radiation beam B' can be detected by the alignment sensor 150 on the substrate table WT to establish the relative position of the pattern forming device MA and the substrate table W. The apparatus 200 further comprises a position measurement system 220, which is configured to determine or measure the position of the support structure, the substrate table, and the movable optical components of the projection system 210. 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 part of the same frame, or may be different frames. The applied position measurement system may be, for example, an interferometer-based measurement system or an encoder-based measurement system.

[0092] The device 200 as shown also includes a positioning system 280, which is configured to position the pattern forming device, the substrate and the movable optical components of the projection system. In the embodiment shown, the positioning system 280 includes a first positioning system 280.1 for positioning the support structure MT supporting the pattern forming device. The first positioning system 280.1 may, for example, include one or more motors and / or actuators (e.g., electromagnetic motors or actuators) to position the support structure MT and the pattern forming device. As an example, the first positioning system 280.1 may, for example, include a linear motor for providing coarse positioning of the support structure MT and a group of actuators for providing fine positioning of the support structure MT. The positioning system 280 also includes a second positioning system 280.2 for positioning the substrate table WT supporting the substrate W. As an example, the second positioning system 280.2 may, for example, include a planar motor or a group of linear motors for providing coarse positioning of the substrate table WT in a horizontal plane and a group of actuators for providing fine positioning of the substrate table WT. By 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.

[0093] As shown, the positioning system 280 used in the device 200 also includes a set of actuators 280.3 as a third positioning system 280.3 for positioning the movable optical component 210.1 of the projection system 210. For example, such actuators 280.3 can be electromagnetic actuators or piezoelectric actuators or a combination thereof. The actuators 280.3 can be configured to position the movable optical component 210.1 on 6 DOF, for example. The device 200 also includes a control unit 290, which can be embodied as a computer, a controller, a microcontroller, etc. The control unit 290 is configured to control the positioning system so as to accurately position the pattern forming device MA, the substrate W and the movable optical component 210.1. To this end, the control unit 290 can generate an output signal 290.1 ​​to control 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 (eg a signal obtained from the position measurement system 220), eg the signal 290.2 being indicative of the position of the patterning device MT, the substrate W and the movable optical component 210.1.

[0094] The apparatus 200 according to the invention is further configured to perform any method of spatially aligning the patterning device MT and the substrate W according to the invention, which method is explained in detail above.

[0095] In particular, the control unit 290 of the device 200 may be configured to:

[0096] - controlling the positioning system 280 to perform a displacement of one or more movable optical components 210.1 along a predetermined trajectory;

[0097] - determining, at a plurality of time instants, an optical property of the radiation beam received by a sensor on the substrate table during displacement of the one or more movable optical components; and

[0098] - determining an alignment position of a patterning device and a substrate based on said optical characteristics determined at said plurality of time instants.

[0099] In an embodiment, the apparatus according to the invention may be incorporated in a lithography system, such system further comprising a radiation source and an illumination system or illuminator.

[0100] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible 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, etc.

[0101] Although specific reference may be made herein to embodiments of the invention in the context of lithographic equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of a mask inspection equipment, a metrology equipment, or any equipment that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These equipment may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0102] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0103] 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 by 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 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 in the present invention as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and that these actions are in fact generated by a computing device, a processor, a controller, or other devices that execute firmware, software, routines, instructions, etc., and that performing such operations may cause an actuator or other device to interact with the physical world.

[0104] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in a manner other than that described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be clear to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method of spatially aligning a patterning device and a substrate, wherein the patterning device and the substrate are separated by an optical path including one or more movable optical components, the method comprising: - projecting a radiation beam from said patterning device along said optical path; - performing a displacement of said one or more movable optical components along a predetermined trajectory; - determining, at a plurality of time instants during displacement of the one or more movable optical components, an optical property of a radiation beam received by a sensor on a substrate table supporting the substrate; - spatially aligning the patterning device and the substrate based on the optical properties determined at the plurality of time instants. 2 . The method of claim 1 , wherein the radiation beam is a patterned radiation beam comprising a pattern of marks arranged on the patterning device.

3. A method according to any one of the preceding claims, wherein the optical characteristic is the intensity of the patterned radiation beam.

4. The method according to any one of the preceding claims, further comprising: - performing a displacement of the substrate table along a further predetermined trajectory, the displacement of the substrate table causing a displacement of the substrate table relative to the radiation beam.

5. The method of claim 4, wherein the displacement of the substrate table relative to the radiation beam comprises: A plurality of substantially horizontal shifts at a corresponding plurality of different vertical positions.

6. A method according to claim 4 or 5, wherein a shift of the one or more movable optical components causes a shift of the aerial image of the radiation beam relative to the substrate table, and wherein the shift of the substrate table relative to the radiation beam at least partially compensates for or follows the shift of the aerial image of the radiation beam relative to the substrate table caused by the shift of the one or more movable optical components.

7. A method according to any one of the preceding claims, wherein the predetermined trajectory spans at least one period of a cyclic error in the position measurement of the one or more movable optical components.

8. A method according to any one of the preceding claims, wherein displacement of the one or more movable optical components along the predetermined trajectory causes a series of multiple substantially horizontal displacements of the aerial image of the radiation beam relative to the substrate table.

9. The method according to claim 8, further comprising: - During the displacement of the one or more movable optical components, a substantially vertical displacement of the substrate table is performed.

10. The method of claim 9, wherein the substantially vertical shift is a substantially continuous shift or a step-wise shift.

11. A device comprising: - 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 providing 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 component of the projection system; - a position measurement system configured to measure the position of the support structure, the substrate table and the movable optical component of the projection system; - a control unit configured to control the positioning system; - wherein the apparatus is configured to receive a radiation beam to illuminate the patterning device, and wherein 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 the preceding claims.

12. A device, comprising: - 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 providing 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 component of the projection system; - a position measurement system configured to measure the position of the support structure, the substrate table and the movable optical component of the projection system; - a control unit configured to control the positioning system; wherein the apparatus is configured to project a radiation beam from the patterning device along the optical path onto the substrate table supporting the substrate; and The control unit is configured as follows: - controlling the positioning system to perform a displacement of the one or more movable optical components along a predetermined trajectory; - determining, at a plurality of time instants, an optical property of a radiation beam received by a sensor on the substrate table during displacement of the one or more movable optical components; - determining an alignment position of the patterning device and the substrate based on the optical characteristics determined at the plurality of time instants.

13. Apparatus according to claim 11 or 12, wherein the predetermined trajectory spans at least one period of a cyclic error of the position measurement system.

14. A lithography system comprising the apparatus according to claim 11, 12 or 13, and - A radiation source and an irradiation system for generating a radiation beam.

15. The lithography system of claim 14, wherein the radiation source is an EUV radiation source and / or wherein the movable optical component is an EUV mirror.

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