SYSTEM, LITHOGRAPHIC APPARATUS AND METHOD

Abstract

A system for measuring a beam, the system including a measurement device configured to measure the beam and determine a signal based on the measured beam, and a fluid supply device configured to provide a fluid as a fluid flow to or around the beam, the system configured to calculate noise in the signal and adjust parameters of the fluid that make up the fluid flow such that the calculated noise is reduced.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to Dutch Application No. 2025372, filed April 20, 2020, and U.S. Provisional Application No. 63 / 013,170, filed April 21, 2020, both of which are incorporated by reference in their entireties.

[0002] [Technical field] The present disclosure relates to a system for measuring a beam, a lithographic apparatus comprising the system and a method for measuring a beam. [Background technology]

[0003] A lithographic apparatus is a machine used to form a desired pattern on a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (which can also be called a "design layout" or "design") from a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., wafer).

[0004] As semiconductor manufacturing processes continue to improve, the amount of functional elements, such as transistors, per device has been steadily increasing for decades while the dimensions of circuit elements have been continually decreasing, following a trend commonly referred to as "Moore's Law". To keep up with Moore's Law, the semiconductor industry is pursuing technologies that allow for the creation of smaller features. To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation defines the minimum size of features that may be patterned on the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0005] The lithographic apparatus may include an illumination system for providing a projection beam of radiation, and a support structure for supporting a patterning device. The patterning device may serve to impart the projection beam with a pattern in its cross-section. The apparatus may include a projection system for projecting the patterned beam onto a target portion of a substrate.

[0006] In a lithographic apparatus, the substrate to be exposed (which may be called a production substrate) may be held on a substrate support (often also called a wafer table), which may be moveable relative to the projection system.

[0007] Prior to the exposure step, one or more properties of the substrate are detected during a detection phase. At least one of the one or more properties may be detected by an alignment system. For example, the surface topography of the substrate may be measured during the detection phase. This process is often called leveling or leveling scan. Additionally or alternatively, the detected property may be the position of an alignment mark on the substrate, for example relative to other alignment marks provided on a substrate support on which the substrate is supported. This process is called alignment or alignment scan. The properties detected during the detection phase are used during the exposure phase to ensure correct focusing of the patterned radiation beam on the substrate and / or to ensure correct positioning of the patterned radiation beam on the substrate. Summary of the Invention [Problem to be solved by the invention]

[0008] The measurement radiation beam is used to determine a position of the substrate support relative to the projection system, the alignment system and / or a plurality of alignment systems or an intermediate structure such as a grid or reference frame configured to cooperate with an encoder system. A grid is sometimes called a grating plate.

[0009] The measurement radiation beam in some lithographic apparatus (such as atmospheric lithographic apparatus) passes through a gas along the path of the radiation. Local variations in one or more characteristics of the gas through which the measurement radiation beam passes can affect the measurement radiation beam and lead to measurement errors. The system can protect the measurement radiation beam from such variations by using a purge gas (e.g. air). Unfortunately, purging cannot prevent all environmental gas (e.g. air) from entering the path of the measurement radiation beam. Disturbances to the path of the measurement radiation beam can be reduced by controlling the temperature and / or humidity offset between the purge gas and the ambient gas. Thus, one method measures the temperature and / or humidity of the purge gas using a temperature sensor, while another method measures the environmental gas through which the measurement radiation beam passes. In this way, one or more characteristics of the purge gas can be controlled to reduce or minimize disturbances to the measurement radiation beam that may affect the measurement accuracy. However, this may be cumbersome and impractical to achieve. It is therefore an object of one or more embodiments described herein to provide a system for accurate measurements using a measurement radiation beam, for example, without implementing such cumbersome and / or impractical methods.

[0010] One object is to provide a system for measuring a beam, which allows improving the accuracy of the measurement. [Means for solving the problem]

[0011] In an embodiment, a system for measuring a beam is provided, the system comprising a measurement device configured to measure the beam and determine a signal based on the measured beam, and a fluid supply device configured to provide a fluid as a fluid flow to or around the beam, the system configured to calculate noise in the signal and adjust parameters of the fluid constituting the fluid flow such that the calculated noise is reduced.

[0012] According to an embodiment, there is provided a lithographic apparatus comprising such a system.

[0013] According to an embodiment, there is provided a method of reducing noise in a system for measuring a beam, the method comprising providing a beam, providing a fluid as a fluid flow to or around the beam, measuring the beam, determining a signal based on the measured beam, calculating noise in the signal, and adjusting parameters of the fluid such that the calculated noise is reduced.

[0014] Further embodiments, features, and advantages, as well as the structure and operation of the various embodiments, features and advantages are described in detail below with reference to the accompanying drawings.

[0015] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: [Brief description of the drawings]

[0016] [Figure 1] 1 depicts a schematic overview of a lithographic apparatus;

[0017] [Diagram 2] FIG. 2 is a cross-sectional view of a substrate support.

[0018] [Diagram 3] FIG. 3 is a plan view of the substrate support of FIG. 2;

[0019] [Figure 4] 1 depicts a schematic overview of a lithographic apparatus;

[0020] [Diagram 5] FIG. 2 is a cross-sectional view of a substrate support.

[0021] [Figure 6] 1 is a cross-sectional view of a patterning device.

[0022] [Figure 7] 1 is a cross-sectional view of a system and a substrate.

[0023] [Figure 8] 1 depicts a schematic overview of a lithographic apparatus;

[0024] [Figure 9] 1 depicts a schematic overview of a lithographic apparatus;

[0025] [Figure 10] Figure 10a is a cross-section of the system and Figure 10b shows the grid.

[0026] [Figure 11] FIG. 2 is a cross-sectional view of the system.

[0027] [Figure 12] FIG. 2 shows in a flow chart the steps involved in the method.

[0028] [Figure 13] FIG. 2 shows in a flow chart the steps involved in the method.

[0029] The illustrated features are not necessarily to scale and are not intended to be limiting in size and / or arrangement as depicted. It should be understood that the figures include optional features that may not be essential to the invention. Furthermore, not all features of the system and / or lithographic apparatus are depicted in each figure, and only some components relevant to the description of a particular feature may be shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In this document, the terms "radiation", "beam" and "beam of radiation" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. having wavelengths at or near 436, 405, 365, 355, 248, 193, 157, 126 or 13.5 nm), as well as particle beams such as ion beams and electron beams.

[0031] The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0032] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to any general patterning device that can be used to impart an incident radiation beam with a patterned cross-section that corresponds to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Besides traditional masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0033] Fig. 1 illustrates a schematic diagram of a lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system (also called an illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation or DUV radiation), a patterning device support (e.g. a mask table) MT configured to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a substrate table) WT constructed to hold a substrate (e.g. a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support WT according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The substrate support WT may alternatively be called a substrate stage.

[0034] In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, to direct, shape and / or control the radiation. The illuminator IL may be used to condition the radiation beam B such that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0035] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, appropriate to the exposure radiation being used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein can be considered as synonymous with the more general term "projection system" PS.

[0036] The lithographic apparatus may be of a type in which at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, e.g. water, so as to fill an immersion space between the projection system PS and the substrate. This is also referred to as immersion lithography. More details on immersion techniques are given in U.S. Patent No. 6,952,253, which is incorporated herein by reference in its entirety.

[0037] The lithographic apparatus may be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or while preparation steps for a subsequent exposure of a substrate W are performed on a substrate W placed on one substrate support WT, another substrate W on another substrate support WT is used for exposing a pattern onto the other substrate W.

[0038] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown in Figure 1). The measurement stage is configured to hold a sensor and / or a cleaning device. The sensor may be configured to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be configured to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for providing immersion liquid. When the substrate support WT is away from the projection system PS, the measurement stage may move directly underneath the projection system PS.

[0039] In operation, a radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on the patterning device support MT, and is patterned by a pattern (design layout) present on the patterning device MA. After traversing the patterning device MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of a substrate W. With the aid of the second positioner PW and the first position measurement system PMS1, the substrate support WT can be precisely moved, e.g. such that different target portions C are positioned at a focused and aligned position in the path of the radiation beam B. Similarly, the first positioner PM and possibly further position sensors (not explicitly shown in Figure 1) may be used to precisely position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may also be located in spaces between the target portions. The substrate alignment marks P1, P2, when located between the target portions C, are known as scribe-line alignment marks.

[0040] The depicted lithographic apparatus can be used in scan mode, i.e. as a scanner. In scan mode, the patterning device support MT and the substrate support WT are scanned synchronously while a patterned radiation beam is projected onto a target portion C (i.e. single dynamic exposure). The velocity and direction of the substrate support WT relative to the patterning device support MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0041] In this specification, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y and z. Each of these three axes is orthogonal to the other two. Rotation around the x axis is called Rx rotation. Rotation around the y axis is called Ry rotation. Rotation around the z axis is called Rz rotation. The x and y axes define a horizontal plane, and the z axis is vertical. The Cartesian coordinate system is not a limitation of the invention, but is used merely for clarity. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used for clarity of the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z axis has a component along the horizontal plane.

[0042] Prior to the exposure phase, one or more properties of the substrate W may be detected during a detection phase. The surface topography of the substrate W may be measured during the detection phase (often referred to as leveling or a leveling scan). Additionally or alternatively, the positions of substrate alignment marks P1, P2 on the substrate W relative to alignment marks on the substrate support WT may be measured during the detection phase (often referred to as alignment or an alignment scan). Properties detected during the detection phase are used during the exposure phase to ensure correct focusing of the patterned radiation beam B on the substrate W and / or to ensure correct positioning of the patterned radiation beam on the substrate W.

[0043] It will be appreciated that in a lithographic apparatus, various components need to be positioned with a very high degree of precision. For example, during the exposure phase and during the detection phase, the position of the substrate support WT relative to the reference system RF may be determined. A position measurement system (such as a first position measurement system PMS1) may be provided for determining the position of the substrate support WT relative to the reference system RF. The position measurement system may determine the position of the substrate support WT relative to the reference system RF via a path of radiation (i.e. a measurement beam) between the substrate support WT and the reference system RF. By knowing (i) the position of the substrate support WT relative to the reference system RF, (ii) the position of the reference system RF relative to the projection system PS, and (iii) the position of the substrate W relative to the substrate support WT, the position of the substrate W relative to the patterned radiation beam B may be determined.

[0044] In a normal atmospheric environment of a lithography machine, thermal loads from one or more components in the vicinity of the position measurement system will generate temperature, pressure and / or humidity disturbances in a gas (e.g. air) through which the measurement beam passes. A reflected measurement beam affected by these disturbances will have measurement errors leading to overlay errors and / or reduced focus performance. Thus, variations (e.g. temperature, pressure and / or humidity) in the environment through which the measurement beam passes can affect the measurement accuracy.

[0045] Some measurement systems purge gas in the same direction as the measurement beam to provide a protected volume through which the measurement beam travels. Unfortunately, purging cannot prevent all ingress of environmental gas into the protected volume. There is a high probability that there will be a temperature and / or humidity offset between the purge gas and the ambient gas, which will perturb the measurement beam and lead to measurement errors. In an ideal case, the humidity and / or temperature of the purge gas would be the same as the ambient gas. Some systems use thermal optimization of the environment by measuring the temperature (and / or humidity) of the relevant areas and adjusting them to achieve a thermally matched level. Specifically, to try to address the problem, some systems use at least one sensor, e.g., a temperature sensor and / or humidity sensor to measure the temperature and / or humidity of the purge gas, and at least one other sensor to measure the temperature and / or humidity of the surrounding ambient gas. However, the implementation of this process is currently cumbersome and impractical.

[0046] It would therefore be beneficial to provide a system that can be used to accurately measure a radiation beam (e.g., a measurement beam) in a system where the temperature and / or humidity fluctuates within the medium through which the radiation beam (e.g., a measurement beam) passes. Desirably, the system would measure the radiation beam (e.g., a measurement beam) in a manner that is more practical to implement. The measurement beam can be used to determine the positions of various components, thus allowing for accurate determination of the relative positions of different components with increased accuracy. Some, but not all, possible applications of such a system are described below. It will be appreciated that these examples relate to lithographic apparatus due to the need for very high accuracy. However, the system can be used in any other apparatus and devices that measure distances and / or positions, for example any metrology tool.

[0047] An embodiment of the invention provides a system for measuring a beam. As will be further explained below, the system may be provided in a variety of locations and / or devices. This system may be the same as or part of the position measurement system described above.

[0048] The beam used is any beam that can be measured using the system. The beam may be at least one selected from a measurement beam, a light beam, an optical beam, a radiation beam, or a projection beam. There is overlap in some of these definitions. Any of these beams may be used interchangeably where appropriate.

[0049] The term "measurement beam" is used throughout the following description. The term "measurement beam" refers to any suitable beam that can be measured by the system, and therefore this term is interchangeable with the term "beam". The beam may be a beam emerging from a radiation source. Alternatively, the beam may be a projection beam, i.e. the beam may be at least a part of a beam from a projection system PS. For example, the beam may be the radiation beam B mentioned above.

[0050] Different types of beams may be used. The measurement beam may be a radiation beam. Thus, as mentioned above, the measurement beam may include all types of electromagnetic radiation, including ultraviolet radiation, as well as particle beams, such as ion beams or electron beams. The measurement beam may be a light beam, or may otherwise be referred to as an optical beam.

[0051] The system comprises a measurement device configured to measure the measurement beam. The measurement device may comprise any suitable sensor capable of detecting the measurement beam. For example, the measurement device may comprise an optical sensor. The measurement device may be an encoder / position device, a levelling device, an alignment device, etc.

[0052] The measurement device is configured to determine a signal based on the measured measurement beam. The signal may be an electronic signal that is output from the sensor. The signal corresponds to the measurement beam, such that variations in the measurement beam lead to variations in the signal. For example, the signal may be proportional to the measurement beam. In this way, the signal can be used to represent the measured measurement beam.

[0053] The system may comprise a source for emitting a measurement beam. The source may be part of a measurement device and / or a measurement sensor. The source may be any source capable of emitting a suitable measurement beam. The source may be a radiation source, i.e. the source of the radiation beam used for the measurement.

[0054] The system includes a fluid supply device configured to provide a fluid. The fluid supply device can provide the fluid as a fluid stream. The fluid stream may be provided along the measurement beam such that the fluid is provided substantially along the length of the measurement beam. The fluid supply device may comprise a fluid supply unit that contains the fluid. The fluid supply device may comprise at least one opening through which the fluid can be provided as a fluid stream. The fluid stream may alternatively be referred to as a fluid shower, a fluid barrier or a fluid curtain. The fluid stream may be provided as a purge gas as mentioned above (insofar as it is provided at or around the measurement beam as described below). The fluid may be a gas or a liquid or a combination of gas and liquid. By way of example only, the fluid may be air, which may optionally be purified or filtered.

[0055] The fluid flow may be provided to the measurement beam. For example, the fluid flow may be provided such that it is transverse to the measurement beam, i.e. the optical axes of the fluid flow and the measurement beam are non-parallel to each other. In this case, it is preferred that the fluid flow is provided substantially perpendicular to the measurement beam. Alternatively, the fluid flow may be provided around the measurement beam. In this case, the fluid flow may be provided to form a fluid barrier or fluid curtain around the measurement beam. In this way, the fluid surrounding the measurement beam can be controlled.

[0056] The system is configured to calculate the noise of the signal. For example, the system may perform one or more processing steps on the beam to determine the noise of the signal. The system may comprise a processor to determine the noise. There are various different ways in which the noise may be determined from the measurement beam. Any suitable method may be used. By way of example only, the noise may be determined by measuring the measurement beam when the relevant components (e.g., a source configured to emit the measurement beam, a sensor configured to detect the measurement beam, and a component that reflects the measurement beam) remain stationary. When the relevant components are stationary, a stable (i.e., unchanging) measurement beam is expected, and thus a stable signal is expected. However, noise will be present in the signal due in part to fluctuations in temperature and / or humidity of the medium through which the measurement beam passes. By processing this signal, for example by examining the power spectral density, certain frequencies of the signal that are known to be associated with temperature and / or humidity fluctuations can be examined. This allows the noise to be determined. As indicated above, one or more other methods for determining noise may alternatively or additionally be used.

[0057] The processor used to determine the noise of the signal may be part of the measurement device. The processor may determine any of several types of noise, for example, the noise of the raw signal, the noise of the filtered signal, and / or the noise of the processed signal. The processor may process noise from multiple signals, for example, by combining with one or more other optical sensors. The processor may be used with any type of noise and / or may be focused on a particular frequency region.

[0058] The system may further be configured to adjust a parameter of the fluid constituting the fluid flow to reduce the calculated noise. For example, the system may be configured to calculate the noise when the parameter is at a first value, and the system may be configured to adjust the parameter and determine whether the noise increases or decreases. Depending on the variation in the noise when the parameter is adjusted, the system may be configured to adjust the parameter to reduce the noise. One method is described in more detail below. Alternatively, a relationship between the parameter and the noise of the measured signal corresponding to the beam may be known. In this case, the parameter can be adjusted to a value corresponding to a reduced amount of noise. Desirably, the parameter will be adjusted to a point where the noise is minimal.

[0059] As described above, the system may attempt to match the temperature of the purge gas to that of the ambient gas by measuring the temperature of the supply of the ambient gas. However, the temperature of this supply gas may rise when in the vicinity of the substrate support WT, for example due to heat radiated from at least one component. Thus, the measurement of the temperature may be inaccurate. The same applies to the measurement of humidity, which may have a higher inaccuracy. Certain embodiments of the invention described herein may address one or more problems that may arise because the system may not rely on temperature and / or humidity measurements to match the purge conditions. As explained, the system directly measures the noise of the signal that causes an error in the refractive index of the measured measurement beam, and then adjusts at least one parameter of the fluid that constitutes the fluid flow to generate a measurement system with a reduced amount of noise, preferably a minimal amount of noise. In other words, the system does not need to perform additional measurements of one or more specific parameters of the supplied fluid, but adjusts selected parameters to reduce the noise, which is used to reduce the errors associated with the above-mentioned inaccuracies.

[0060] There may be various advantages associated with one or more of the embodiments described herein. If during diagnostics, calibration is deemed to be the source of an error, one parameter needs to be reset to address the calibration issue. Additionally, an embodiment of the system may effectively skip interim factors (e.g., measuring the temperature of the supply gas) and go straight to higher level factors (i.e., noise), resulting in a more direct and reliable optimization test and improving overlay performance. This may improve the accuracy of the measurement system without one or more additional sensors, providing an alternative option to hardware solutions. This means that one or more additional sensors may not be necessary, reducing costs. It is noted that measurements made by the present system may be more robust than measurements made by other systems, as noise is desirably reduced to a minimum by parameter adjustment. Therefore, other direct and indirect environmental factors that affect noise may be considered.

[0061] The parameter adjusted by the system may be at least one selected from temperature, pressure, humidity, fluid composition (e.g., O2, N2, or CO2), and / or CO2 content. Each of these parameters may affect the refractive index of the medium through which the measurement beam passes. Each parameter may have a different effect on the refractive index.

[0062] It is desirable for the temperature to be controlled because of ease of implementation. The temperature of the fluid may be controlled by using at least one heater in or adjacent to the fluid supply and / or by flowing a cooling fluid adjacent to the fluid supply. The temperature of the fluid can be regulated by using at least one heat exchanger in combination with a temperature controlled fluid. For example, a conditioned gas (e.g., conditioned air) may be used with a temperature controlled liquid (e.g., water) via a heat exchanger. For example, one or more Peltier elements may be used, optionally in combination with at least one heater, to condition the fluid. This may be done directly or indirectly via one or more heat exchangers using a liquid.

[0063] Adjustment of the fluid composition may be performed by including additional fluids having different refractive indices in the fluids that make up the fluid stream. For example, adjustment of the fluid composition can be performed by adding additional lines with additional fluids to the fluid supply, for example by using a mixing valve that can be controlled to add the appropriate amount of additional fluid.

[0064] The system may comprise a number of measuring devices and / or fluid supply devices. The measuring devices may have corresponding fluid supply devices, for example, there may be one fluid supply device per measuring device. There may be multiple measuring devices per fluid supply device, or multiple fluid supply devices per measuring device. There may be four measuring devices and corresponding fluid supply devices, and the four measuring devices are configured to determine the position of the measuring devices. The system comprising the devices may form a position measurement system. This is described below in relation to figures 1, 2 and 3.

[0065] A further advantage is that the system can be used in a wide variety of scenarios: it can be used as part of any optical measurement system that is purged, i.e. where fluid is provided as a fluid stream, and although these examples relate to use in a lithographic apparatus, the system can be used in any suitable apparatus.

[0066] Within a lithographic apparatus the system may be used in any suitable location, for example the system may be used in a substrate support position sensor, an alignment sensor, a level sensor, a patterning device position sensor and / or any other component where distance measurements are performed.

[0067] More specifically, the measurement apparatus may be located on the patterning device support MT, on a patterning device reference system opposite the patterning device support MT, on a substrate support WT configured to support a substrate W, or on a reference system RF opposite the substrate support WT. Any reference to opposite the substrate support WT is interchangeable with opposite the substrate W which may be located on the substrate support WT.

[0068] The system may be provided on a single component, i.e. the measurement device and the fluid supply may be formed on the same component. Alternatively, the system may be provided on multiple components, i.e. different parts of the system may be provided on different components. For example, if the measurement device is on the substrate support WT, the fluid supply may be arranged on the substrate support WT, or alternatively the fluid supply may be arranged on the reference system RF facing the substrate W / substrate support WT. If the measurement device is on the reference system RF facing the substrate W / substrate support WT, the fluid supply may be arranged on the reference system RF facing the substrate W / substrate support WT, or alternatively the fluid supply may be arranged on the substrate support WT. If the measurement device is on the patterning device support MT, the fluid supply may be arranged on the patterning device support MT, or alternatively the fluid supply may be arranged on the patterning device reference system facing the patterning device support MT. If the measurement device is on the patterning device reference system opposite the patterning device support MT, the fluid provider may be located on the patterning device reference system opposite the patterning device support MT, or alternatively the fluid provider can be located on the patterning device support MT. Other combinations in which the measurement device is located on the same component as the fluid provider or on a different component can be more generally envisaged.

[0069] An embodiment in which the measurement device is arranged on the substrate support WT is described below in relation to Figures 1, 2 and 3. An embodiment in which the measurement device is arranged on a position measuring system opposite the substrate support WT is described below in relation to Figures 4 and 5. An embodiment in which the measurement device is arranged on a patterning device reference system opposite the patterning device support MT is described below in relation to Figure 6. An embodiment in which multiple measurement devices are arranged opposite the substrate W is shown in Figure 7.

[0070] An embodiment of a system for measuring a measurement beam is shown in Fig. 2 and Fig. 3. In particular, Fig. 2 and Fig. 3 show an embodiment in which measurements are made to determine the position of the substrate support WT relative to the reference system RF. Fig. 2 and Fig. 3 show a side view and a top view of the substrate support WT, respectively. The system shown in Fig. 2 comprises a radiation output (e.g., radiation source) 20 for emitting a measurement beam 50. The system comprises a measurement device comprising a sensor (e.g., input to a sensor detector, sensor detector, etc.) 40 for detecting the measurement beam. The measurement beam 50 is projected towards a grid G ​​of the reference system RF. For reference, the grid G ​​is shown in Fig. 1 as being located on the reference system RF. In this embodiment, the position of the grid G ​​relative to the projection system PS is known. In the illustrated embodiment, the reference system RF may be realized by a reference frame, here denoted by the same acronym RF. The position of the grid G ​​relative to the reference frame RF is known and may be fixed or not. The relative position of the reference frame RF relative to the projection system PS is known. The position of the reference frame RF relative to the projection system PS may or may not be fixed. In this way, the grid G ​​is at a known position relative to the projection system PS. The measurement beam 50 is reflected and / or refracted by the grid G ​​back to the sensor 40. The measurement beam 50 travels along a radiation path. The sensor 40 is configured to detect the measurement beam 50 and is used to indicate the position and / or movement of the grid G ​​relative to the radiation output 20 and / or the sensor 40. The sensor 40 measures the displacement of the substrate table WT relative to the grid G. Thus, the position of the substrate support WT relative to the projection system PS can be determined. This is possible because the position of the grid G ​​relative to the projection system PS is known as described above.

[0071] Each pair of radiation outputs 20 and sensors 40 are most conveniently located at a respective one of the corners of the substrate support WT, for example as shown in FIG. 3, which is described separately below. This convenient location occurs because the center of the substrate support WT is occupied by the substrate W. Furthermore, a pair of diametrically arranged pairs are involved in determining the angular displacement of the substrate support WT about an axis parallel to the Z-axis (see FIG. 1). The greater the distance between the diametrically arranged pairs, the more accurately the angular displacement can be determined. For further background, see, for example, U.S. Pat. No. 7,602,489, which is incorporated herein by reference in its entirety.

[0072] 3 illustrates the use of four radiation outputs 20 with four corresponding sensors 40, it will be appreciated that any suitable number of radiation outputs 20 and / or sensors 40 may be used in the system. Additionally, the radiation outputs 20 and / or sensors 40 may be located in any suitable or advantageous location depending on other components, such as components on the substrate support WT.

[0073] As described above, the system uses a measurement beam 50. The measurement beam 50 travels along the path of the radiation. As described above, the ambient gas through which the measurement beam passes along the path of the radiation may affect the measurement beam 50. As described above, several factors may affect how the measurement beam 50 propagates through the gas. For example, the temperature of the gas, the humidity of the gas, and / or the composition of the gas are factors that may affect the refractive index of the gas. Local variations in one or more of these factors and / or turbulence in the gas may result in non-uniformity in the refractive index of the gas. The measurement beam 50 passing through the gas is affected by the variations in the refractive index. For example, the changes in the refractive index may change the trajectory of the measurement beam 50. Additionally or alternatively, the changes in the refractive index may introduce wavefront errors into the measurement beam 50. The measurement errors may be caused by the variations in the refractive index along the path of the radiation. The measurement errors may lead to positioning inaccuracies in the positioning of one or more components of the lithographic apparatus (e.g. the substrate support WT). Any inaccuracy in such positioning may change the placement of the patterned radiation beam B on the substrate W, which may have adverse effects on overlay and / or focus.

[0074] Arrangements are placed in suitable locations to attempt to reduce variations in the refractive index of the gas in a volume traversed by the path of the radiation. For example, in one embodiment a fluid supply 3 is provided. The fluid supply 3 is configured to provide fluid as a fluid flow to or around the measurement beam 50. Thus, one or more parameters of the gas in the volume through which the measurement beam 50 passes can be controlled.

[0075] In this embodiment, the fluid supply device 3 ejects a fluid from at least one opening 30 in the surface of the substrate support WT. The fluid may be a barrier gas and may form a gas curtain 13 that prevents the flow of ambient gas on one side of the gas curtain 13. The gas curtain 13 may be provided around a volume such that the gas inside the volume is effectively separated from the ambient gas outside the volume. The gas inside the volume may be adjusted to be more uniform than the gas outside the volume. The gas curtain 13 formed by the fluid flow may thus be used to provide a barrier around a volume traversed by the path of the radiation of the measurement beam 50. This protects the measurement beam 50 from the effects of changes in the ambient gas outside the volume. The gas inside the volume is called protected gas.

[0076] As shown in Figure 2, the system may comprise a number of measurement devices and / or fluid supply devices 3. The substrate support WT is shown at an imaging location below the projection system PS. However, in an embodiment, at least one fluid supply device 3 may instead be part of the reference system RF and, together with the radiation output 20 and the sensor 40, may be mounted substantially stationary relative to the projection system PS (e.g. housed on the reference frame RF). In that embodiment, the grid G ​​is not part of the reference system RF but moves with the substrate support WT and is at a known position relative to the substrate support WT (e.g. fixed to the substrate support WT).

[0077] In an embodiment, a grid G, which is part of the reference system RF, is additionally located at the measurement location. One or more properties of the substrate W mounted on the substrate support WT, such as the position of the substrate W on the substrate support WT, the surface topography of the substrate W, etc., can be measured at the measurement location. In this embodiment, the grid G ​​may be located above the substrate support WT (as in the main embodiment described above) or may be located on the substrate support WT as explained in the previous paragraph.

[0078] Four fluid supply devices 3 can be seen on the substrate support WT in FIG. 3. Other objects not shown may be included on the substrate support WT, for example a substrate holder configured to hold a substrate W or one or more other different types of sensors. In this embodiment, each fluid supply device 3 is configured to provide a gas curtain 13 that operates to reduce the inflow of ambient gas into a volume traversed by a path of radiation between the substrate support WT and the reference system RF. Each of the illustrated fluid supply devices 3 comprises at least one opening 30 in the substrate support WT. The at least one opening 30 in the substrate support WT is adapted for a flow of fluid as a fluid flow. Specifically, in this case the fluid is a barrier gas from the at least one opening 30 for establishing a fluid flow, where the fluid flow forms a gas curtain 13 that surrounds a portion of the volume traversed by the path of radiation. Although four fluid supply devices 3 and four corresponding measurement devices are shown, it will be understood that any suitable number of fluid supply devices 3 and corresponding measurement devices may be used, i.e. there may be a smaller or larger number.

[0079] FIG. 3 shows an embodiment of one or more fluid supply devices 3. In this embodiment, a plurality of individual openings 30 are provided on the top surface of the substrate support WT and surround the radiation output 20 and the sensor 40. The controller 100 individually controls the flow of fluid (e.g., gas barrier) from each opening 30 of the fluid supply device 30. The controller 100 controls the velocity of fluid exiting each of the openings 30 for each individual opening 30. The velocity of fluid for each individual opening 30 may be the same for each of the plurality of openings 30. Alternatively, the velocity of fluid for each individual opening 30 may differ between the openings 30. For example, any of the openings 30 aligned with the radiation output 20 and / or the sensor 40 in the main direction of movement of the substrate support WT may have a higher fluid flow rate than the other openings 30. The controller 100 varies the velocity of fluid for each opening 30 during the exposure phase compared to at least a part of the detection phase (e.g., a sub-phase of the leveling scan). Because (i) the velocity of the substrate support WT relative to the reference system RF is lower during the exposure phase than during a portion of the detection phase, and (ii) the time taken between changes in the direction of movement of the substrate support WT is lower during the exposure phase than during at least a portion of the detection phase (e.g. a sub-phase of the levelling scan), the control unit 100 reduces the velocity of the fluid exiting each opening 30 during the exposure phase compared to a portion of the detection phase (e.g. a sub-phase of the levelling scan). As a result, the acoustic disturbance generated by the fluid during the exposure phase is lower than if the velocity of the fluid from each of the openings 30 relative to each opening 30 during the exposure phase was not lower.

[0080] 3 shows multiple openings 30 per fluid supply 3, there may alternatively be a single elongated opening 30. Multiple elongated openings 30 may also be provided.

[0081] 3 has been described above with reference to the velocity relative to the opening 30 as it exits the opening 30. However, in some embodiments, the controller 100 may control the amount of barrier gas exiting the opening 30 per unit time.

[0082] As with the embodiment of FIG. 3 and all other embodiments, the system is configured to control at least one parameter of the fluid. More specifically, the control unit 100 may be configured to control the at least one parameter. Alternatively, a separate control or control device (not shown) may be used to control the at least one parameter. As mentioned above, the at least one parameter may be one or more selected from temperature, pressure, humidity, fluid composition, and / or CO2 content. The at least one parameter is controlled based on a calculated noise of the signal. Additionally, the at least one parameter may be changed depending on whether it is in an exposure phase or a particular part of a detection phase (e.g., a sub-phase of a leveling scan). The control unit 100 may be provided in combination with any embodiment of the invention, such as those shown in the other figures.

[0083] As explained in relation to figures 2 and 3, the fluid may be provided as a fluid flow surrounding the measurement beam 50. However, different configurations may be provided. In particular, the fluid flow may be provided to the measurement beam 50. In other words, the fluid flow may be provided such that it crosses the measurement beam 50, for example the optical axes of the fluid flow and the measurement beam may be non-parallel to each other and cross each other. In this case, the fluid flow is desirably provided substantially perpendicular to the measurement beam 50. In the embodiment shown in figures 2 and 3, this can be implemented by providing the fluid supply device 3 to have at least one outlet for the fluid between the substrate support WT and the grid G. In this example, the fluid supply device 3 may have at least one outlet and / or an elongated outlet arranged between the substrate support WT and the grid G. The at least one outlet and / or the elongated outlet may be arranged to provide the fluid along the length of the measurement beam 50. An example of this arrangement of the fluid flow / fluid supply device 130 relative to the measurement beam 50 is shown in figure 5. Although the systems in Figures 4 and 5 are in different positions than Figures 2 and 3, it will be understood that the systems shown in Figures 2 and 3 can be adapted to provide a fluid flow across the measurement beam 50 as shown in Figures 4 and 5.

[0084] Further embodiments are shown in Figures 4 and 5, where the first position measurement system PMS1 described above is replaced by a second position measurement system PMS2. The second position measurement system PMS2 may function in a similar manner to the first position measurement system PMS1. A detailed close-up of the second position measurement system PMS2 is shown in Figure 5. It will be understood that although these position measurement systems are shown in different versions of the lithographic apparatus, they can be used in combination.

[0085] Figure 5 includes similar features as those shown and described in connection with Figures 2 and 3. To avoid repetition, features that are the same as those shown in Figures 2 and 3 will not be described again. However, it will be understood that the systems shown in Figures 4 and 5 may include any of the features of Figures 2 and 3, as desired, as described in connection with those figures.

[0086] The difference between the system shown in Figures 2 and 3 and the system shown in Figure 4 relates to the position of the system in the lithographic apparatus. In particular, the system in Figures 4 and 5 may be part of a second position measurement system PMS2 arranged on the reference system RF. As shown, the second position measurement system PMS2 may be arranged on a side of the substrate support WT, for example in the horizontal plane of the substrate support WT. In this case, the position of the second position measurement system PMS2 is known relative to the projection system PS, for example due to the reference system RF. There may be multiple measurement devices and / or fluid supply devices 130 used to determine the position of the substrate support WT.

[0087] Additionally, the systems of Figures 2 and 3 differ from those of Figures 4 and 5 due to the manner in which fluid is provided in relation to the measurement beam 50. As described in relation to Figures 2 and 3, the fluid may be provided by the system such that a fluid stream 113 intersects the measurement beam 50 as shown in Figure 5. Alternatively, the system may be provided as shown in Figure 5, except that a fluid supply 130 may be provided to surround the measurement beam, i.e., with the fluid provided as shown in Figures 2 and 3.

[0088] Although FIG. 1 shows a first position measurement system PMS1 and FIG. 4 shows a second position measurement system PMS2, it will be understood that these position measurement systems are interchangeable and can be provided in combination with each other and include any combination of the features described in the above embodiments.

[0089] Figure 6 includes similar features as those shown and described in connection with Figures 2, 3 and 5. To avoid repetition, features that are the same as those shown in Figures 2, 3 and 5 will not be described again. However, it will be understood that the system shown in Figure 6 may include any of the features of Figures 1-5, if desired, as described in connection with those figures.

[0090] The difference between the systems shown in Figures 2 and 3 and the system shown in Figure 6 relates to the position of the system within the lithographic apparatus. In particular, the system in Figure 6 may be part of a patterning device reference system 110 facing the patterning device support MT. In this case, the position of the patterning device reference system 110 facing the patterning device support MT is known relative to the projection system PS. There may be multiple measurement devices and / or fluid supply devices 130 used to determine the position of the patterning device support MT.

[0091] Fluid may be provided to the measurement beam 50 as shown in Figures 4 and 5 and by the fluid supply 130 on the right side of Figure 6. Alternatively, fluid may be provided around the measurement beam 50 as shown in Figures 2 and 3 and by the fluid supply 30 on the left side of Figure 6. It will be appreciated that if multiple fluid supply devices are provided, the configuration of the multiple fluid supply devices in the system may be different as shown in Figure 6. Alternatively, if multiple fluid supply devices are provided, the system may provide fluid in the same way in all of the multiple fluid supply devices. For example, all fluid supply devices may provide fluid to the measurement beam 50 as on the right side of Figure 6, or all fluid supply devices may provide fluid around the measurement beam 50 as on the left side of Figure 6.

[0092] Most of the above embodiments describe the fluid being provided to the measurement beam 50 as a fluid stream. It will be appreciated that where multiple measurement beams 50 are provided, the fluid may be provided to multiple such measurement beams 50, for example where multiple measurement devices are provided as described in relation to FIG. 7 or where one measurement device utilises multiple measurement beams 50.

[0093] Figure 7 includes similar features as those shown and described in connection with Figures 2-5. To avoid repetition, the same features shown in Figures 2-5 will not be described again. However, it will be understood that the system shown in Figure 7 may include any of the features of Figures 1-6, as desired and as described in connection with those figures.

[0094] 7 may be disposed on a reference system RF facing the substrate W when in position, where the system is configured to provide fluid to a space between the at least one measurement device and the substrate W.

[0095] There may be multiple measurement devices and / or multiple fluid supply devices. In particular, the fluid supply device 230 is configured to provide fluid to a first measurement beam 50A from the first sensor output 20A that is detected by the first measurement device 40A. Additionally, the fluid supply device 230 is configured to provide fluid to a second measurement beam 50B from the second sensor output 20B that is detected by the second measurement device 40B. In this case, the first sensor 20A may be an alignment sensor. In this case, the second sensor 20B may be a level sensor. It will be understood that the sensors used here are merely examples and other sensors and detectors may be used.

[0096] The system shown in Figure 7 comprises at least one barrier 60 which is used to direct the fluid flow. In this case, the fluid which constitutes the fluid flow is directed over the barrier 60, between the lower surface of the barrier 60 and the substrate W. This helps to ensure that the fluid flow is provided to the first measurement beam 50A and the second measurement beam 50B.

[0097] The fluid supply 230 may include multiple outlets, as shown and described on the left and right sides of FIG. 7. The fluid supply 230 may control the outlets to eject the same amount of fluid or different amounts of fluid. For example, an outlet on the left side of the fluid supply 230 may eject less than 50% of the fluid and an outlet on the right side of the fluid supply 230 may eject more than 50% of the fluid. For example, one of the multiple outlets of the fluid supply 230 may eject 40% or less of the fluid, or 30% or less of the fluid, or 20% or less of the fluid. For example, one or more of the other outlets (e.g., corresponding outlets) of the fluid supply 230 may eject 60% or more of the fluid, or 70% or more of the fluid, or 80% or more of the fluid.

[0098] In some embodiments above, the apparatus is described as having the radiation output 20 and the sensor 40 housed in the substrate support WT, with the grid G ​​on the substrate support WT. An embodiment is equally applicable to another configuration with the grid G ​​on the substrate support WT and the radiation output 20 and the sensor 40 housed in the reference system RF as in FIG. 8. An embodiment is equally applicable to another configuration with the grid G ​​on the substrate support WT and the radiation output 20 and the sensor 40 housed (e.g. attached to another reference system) below the substrate support WT. For example, the other reference system may be an L-bar LRF as shown in FIG. 9. The L-bar LRF may optionally be connected to the reference system RF described above. In this case, the grid G ​​may be arranged on the underside of the substrate support WT so as to face the radiation output 20 and the sensor 40. An embodiment is equally applicable to another configuration with the radiation output 20 and the sensor 40 on the substrate support WT and the grid G ​​housed below the substrate support WT, with the grid G ​​attached to a different reference system, e.g. an L-bar LRF. In this case, the radiation output 20 and the sensor 40 may be arranged on the underside of the substrate support WT such that they face the grid G.

[0099] The grid G ​​used in any of the above described embodiments may alternatively be referred to as a grating and may comprise any suitable configuration, for example a scale, a reflective grating, a diffractive grating, etc. Thus, the grid G ​​may be any suitable component that enables measurements, such as a 1D encoder grating plate or a 2D encoder grating plate.

[0100] In any of the above embodiments, the measurement device used may have the same features and / or be similarly arranged as in PCT Patent Application Publications WO2009-014252A1 and / or WO2013-073538, each of which is incorporated herein by reference in its entirety.

[0101] In an embodiment, the measurement device may be located on the reference frame RF or on any element facing the substrate W / substrate support WT as in some of the configurations described above. Figures 10a and 10b show a measurement device using a measurement beam 50 combined with a grid G ​​(as described above). The grid G ​​may be located on the substrate support WT. As in the above embodiment, the radiation output 20 may provide the measurement beam 50. In this embodiment, the radiation output 20 may emit the measurement beam 50 in a direction that is at an angle of 45 degrees to the Y and Z axes. Optionally, the measurement device may include a lens 70 positioned along the optical axis of the measurement beam 50 emitted from the radiation output 20.

[0102] The measurement device may optionally include any combination of a polarizing beam splitter 71 (whose splitting surface is parallel to the XZ plane), reflecting mirrors 72 and 73, lenses 74 and 75, quarter-wave plates (i.e., λ / 4 plates) 76 and 77, reflecting mirrors 78 and 79, etc. In this case, the reflecting mirror 73 may be disposed at a position symmetrical to the reflecting mirror 72 with respect to the splitting surface of the polarizing beam splitter 71. Similarly, the condenser lenses 74 and 75, the λ / 4 plates 76 and 77, and the reflecting mirrors 78 and 79 may also be disposed at positions symmetrical to each other with respect to the splitting surface of the polarizing beam splitter 71. The measurement system may include a polarizer (analyzer), a sensor 40 (such as a photodetector), etc. The sensor 40 may be disposed on a return optical path of the reflected diffracted radiation of the measurement beam 50 via the splitting surface of the polarizing beam splitter 71.

[0103] In the measurement device, the radiation output 20 may emit, optionally via a lens 70, a measurement beam 50 which may be incident on a polarizing beam splitter 71. The measurement beam 50 may be split into two beams 50C and 50D by polarization. In this case, the P-polarized component of the measurement beam 50 may be transmitted through the polarizing beam splitter 71 to form the measurement beam 50C. Furthermore, the S-polarized component of the measurement beam 50 may be reflected at a separation surface of the polarizing beam splitter 71 to form the measurement beam 50D. The measurement beams 50C and 50D (which are components of the measurement beam 50) may be reflected by reflecting mirrors 72 and 73, respectively, and may be incident on a grid G, which in this case may comprise a reflective grating RG as shown in FIG. 10b.

[0104] The measurement devices described herein may function as described in further detail in PCT Patent Application Publication WO2009-014252A1, which is incorporated herein by reference in its entirety.

[0105] In an embodiment, at least one of the systems as shown in Figure 11 may be provided. As further shown in Figure 11, an exposure apparatus, such as a projection system PS, may be provided in combination with at least one system as described in any of the above embodiments. The projection system PS may be as described above. The system used as described below may be located in any of the configurations described in U.S. Patent Application Publication US2019-377270, the entire contents of which are incorporated herein by reference, and in particular with reference to Figure 9 of US2019-377270.

[0106] The system may include a measurement device having a first radiation output 20a and a first sensor 40a, and a first fluid supply device 3a. The system may include a measurement device having a second radiation output 20b and a second sensor 40b, and a second fluid supply device 3b. The system may include a measurement device having a third radiation output 20c and a third sensor 40c, and a third fluid supply device 3c. The system may include a measurement device having a fourth radiation output 20d and a fourth sensor 40d, and a fourth fluid supply device 3d. The system may include a measurement device having a fifth radiation output 20e and a fifth sensor 40e, and a fifth fluid supply device 3e.

[0107] Multiple systems may be provided as shown in Figure 11. Any, some or all of the systems shown in Figure 11 may be provided.

[0108] As shown in Figure 11, the exposure apparatus, for example the projection system PS, is supported by a reference frame RF. In an embodiment, the exposure apparatus is moveable relative to the reference frame RF.

[0109] In an embodiment, the system including the first radiation output 20a, the first sensor 40a, and the first fluid supply device 3a is provided with a first grid G1. The stationary support 210 includes recesses for holding the first radiation output 20a, the first sensor 40a, and the first fluid supply device 3a. The first grid G1 is arranged on a bottom surface of a first substrate support WT1 configured to support a substrate (omitted in the drawings for simplicity). The first radiation output 20a and the first sensor 40a face the first grid G1 while the first substrate support WT1 is at or near the fourth radiation output 20d and the fourth sensor 40d (described separately below), and are configured to provide (or generate) a first signal representative of position information of the first substrate support WT1. The first radiation output 20a and the first sensor 40a may be an encoder head system including multiple encoder heads and / or including one or more other position sensors other than the encoder heads, for example one or more capacitive or interferometric sensors.

[0110] The first radiation output 20a and the first sensor 40a may be coupled to the stationary support 210 via dynamic isolators, for example as described in U.S. Patent Application Publication US2019-377270, which is incorporated by reference in its entirety. The positions of the first radiation output 20a and the first sensor 40a may be maintained relative to a reference. The reference may be the fourth radiation output 20d and the fourth sensor 40d or the projection system PS.

[0111] In an embodiment, the system comprising the second radiation output 20b, the second sensor 40b and the second fluid supply device 3b is provided with a second grid G2. The second grid G2 is arranged on a bottom surface of a second substrate support WT2 configured to support a substrate (omitted in the drawings for simplicity). The second radiation output 20b and the second sensor 40b are arranged facing the second grid G2 to provide (or generate) a second signal representative of position information of the second substrate support WT2. The second radiation output 20b and the second sensor 40b are arranged facing the second grid G2 to provide (or generate) a second signal representative of position information of the second substrate support WT2 while the second substrate support WT2 is at or near the projection system PS. The second radiation output 20b and the second sensor 40b may be an encoder head system comprising multiple encoder heads and / or comprising one or more other position sensors other than encoder heads, for example one or more capacitive or interferometric sensors.

[0112] The second radiation output 20b and the second sensor 40b may be mounted on a measurement arm, such as the L-shaped bar LRF (see FIG. 9) mentioned above. The measurement arm may be mounted to the reference frame RF and may extend below the second substrate support WT2. The second radiation output 20b and the second sensor 40b may be positioned along the optical axis O of the projection system PS.

[0113] The second substrate support WT2 and the first substrate support WT1 may exchange positions such that the first radiation output 20a and the first sensor 40a face the second grid G2 and the second radiation output 20b and the second sensor 40b face the first grid G1. In that situation, the first radiation output 20a and the first sensor 40a may provide (or generate) a first signal representative of position information of the second substrate support WT2. In that situation, the second radiation output 20b and the second sensor 40b may provide (or generate) a second signal representative of position information of the first substrate support WT1.

[0114] In an embodiment, a system including the third radiation output 20c, the third sensor 40c and the third fluid supply device 3c is provided with a third grid G3. The third grid G3 is arranged on a bottom surface of a third substrate support WT3 configured to support a substrate (omitted in the drawings for simplicity). The third radiation output 20c and the third sensor 40c are arranged to face the third grid G3 to provide (or generate) a third signal representative of position information of the third substrate support WT3. The third radiation output 20c and the third sensor 40c are arranged to face the third grid G3 and provide a third signal representative of position information of the third substrate support WT3 while the third substrate support WT3 is supported by the exchange mechanism 208.

[0115] The exchange mechanism 208 may provide the third substrate support WT3 to the transport part 204 and remove the third substrate support WT3 from the transport part 204. The transport part 204 is arranged to support the second substrate support WT2 while in the vicinity of the exposure apparatus. The transport part may be configured to support any of the first substrate support WT1, the second substrate support WT2 and the third substrate support WT3.

[0116] The third radiation output 20c and the third sensor 40c may be an encoder head system comprising multiple encoder heads and / or comprising one or more other position sensors other than encoder heads, for example one or more capacitive or interferometric sensors.

[0117] The third radiation output 20c and the third sensor 40c may be attached to a further measurement arm, such as the L-shaped bar LRF mentioned above (see FIG. 9). The further measurement arm may be attached to the reference frame RF and may extend below the third substrate support WT3.

[0118] The third substrate support WT3 may take the position of the second substrate support WT2 such that the second radiation output 20b and the second sensor 40b face the third grid G3. In that situation, the second radiation output 20b and the second sensor 40b may provide (or generate) a second signal representative of position information of the third substrate support WT3.

[0119] In an embodiment, a system is provided that includes a fourth radiation output 20d, a fourth sensor 40d and a fourth fluid supply device 3d. The fourth radiation output 20d and the fourth sensor 40d are used to provide measurement information of the substrate (i.e. configured to measure the substrate). The projection system PS and the fourth radiation output 20d and the fourth sensor 40d are separate from each other. The fourth radiation output 20d and the fourth sensor 40d may be any suitable device that is configured to provide measurement information of the substrate (i.e. configured to measure the substrate).

[0120] In an embodiment, a system is provided comprising a fifth radiation output 20e, a fifth sensor 40e and a fifth fluid supply 3e, the fifth radiation output 20e and the fifth sensor 40e configured to provide further measurement information of the substrate (i.e. configured to perform further measurements of the substrate).

[0121] The fifth radiation output 20e and the fifth sensor 40e are closer to the projection system PS than the fourth radiation output 20d and the fourth sensor 40d. The fourth radiation output 20d and the fourth sensor 40d are farther from the projection system PS than the fifth radiation output 20e and the fifth sensor 40e. The fifth radiation output 20e and the fifth sensor 40e may be similar to the fourth radiation output 20d and the fourth sensor 40d and may provide similar information about the substrate. For example, the fifth radiation output 20e and the fifth sensor 40e may be the same type of measurement device as the fourth radiation output 20d and the fourth sensor 40d, but the fourth radiation output 20d and the fourth sensor 40d may provide more accurate information about the substrate than the fifth radiation output 20e and the fifth sensor 40e by taking a longer measurement time. In other words, the fifth radiation output 20e and the fifth sensor 40e may complete the measurement of the substrate in a shorter time. The fifth radiation output 20e and the fifth sensor 40e may perform measurements of the substrate while the second substrate support WT2 is supported by the transporter 204.

[0122] The information provided by the fifth radiation output 20e and the fifth sensor 40e may be used to determine the z-position of the surface of the substrate relative to an image plane of the exposure apparatus. The fifth radiation output 20e and the fifth sensor 40e may comprise a leveling sensor system that provides information about the height profile of the substrate, e.g., the flatness of the substrate. The leveling sensor system may be referred to as an autofocus system. The information about the height profile of the substrate may be used to determine the positional relationship of the substrate and the patterning device MA, as described in U.S. Patent Application Publication US2019-377270, which is incorporated herein by reference in its entirety.

[0123] The information of the fifth radiation output 20e and the fifth sensor 40e may be used to determine the x- and y-position of the substrate relative to a reference mark of the patterning device MA, e.g. an image of one or more patterning device alignment marks M1, M2. Additionally or alternatively, the fifth radiation output 20e and the fifth sensor 40e may provide information about the position of one or more substrate alignment marks P1, P2 on the substrate. In other words, the fifth radiation output 20e and the fifth sensor 40e may measure the position of one or more substrate alignment marks P1, P2 on the substrate. The information about the position of one or more substrate alignment marks P1, P2 may be used to determine the position of one or more substrate alignment marks P1, P2 relative to each other or to compare said information with reference information. The fifth radiation output 20e and the fifth sensor 40e may be part of a substrate alignment sensor system providing information about in-plane deformations of the substrate. The fifth radiation output 20e and the fifth sensor 40e may comprise a plurality of alignment sensors as described in US Patent Application Publication US2009-233234, which is incorporated herein by reference in its entirety. In other words, the substrate alignment sensor system may comprise a plurality of such alignment sensors. Alternatively, the substrate alignment sensor system may comprise a single alignment sensor. Information about the in-plane deformation may be used to position the substrate at a particular x and y position during exposure of a particular target portion C and generate an image at the correct x and y position on the substrate, as described in US Patent Application Publication US2019-377270, which is incorporated herein by reference in its entirety.

[0124] It should be noted that in the embodiment shown in Figure 11, all of the fluid providers are shown in a position to provide fluid as a fluid stream surrounding the beam, as described with respect to Figures 2 and 3. The fluid providers shown in Figure 11 may provide fluid in any suitable manner, for example, may comprise fluid providers configured to provide fluid as a fluid stream to the beam (rather than surrounding the beam). Thus, any, some or all of the systems as shown in Figure 11 may be adapted to vary the position of the fluid providers relative to the respective radiation outputs and sensors, for example, as shown and described with respect to Figure 5.

[0125] In any of the above embodiments, the measurement device may or may not include a radiation source. For example, an external source of radiation may be used. For example, at least a portion of the projection beam may be redirected to the sensor. Thus, any description relating to a measurement device may include a sensor that does not have a radiation source, and any radiation source may be replaced with an external radiation source that is not part of the measurement device to provide the measurement beam 50.

[0126] An embodiment of the invention comprises a method for reducing noise in a system for measuring a measurement beam 50. The system may be a system of an embodiment of the invention described in relation to any of the above embodiments or variants. Thus, the system for measuring the measurement beam 30 may be configured to perform a method as shown in FIG. 12 below.

[0127] The method comprises providing a measurement beam 50 (step S01), providing a fluid to the measurement beam 50 as a fluid flow (step S02), and measuring the measurement beam 50 to determine a signal based on the measurement beam 50 (step S03). The method further comprises calculating a noise in the signal based on the measurement beam 50 (step S04). The method further comprises adjusting a parameter of the fluid to reduce the calculated noise (step S05). At least one parameter may be adjusted, e.g. multiple parameters may be adjusted, although the method may be effective when only a single parameter is adjusted. As discussed above, reducing noise is beneficial as it correlates to reducing errors associated with, e.g., variations in the refractive index of a medium through which the measurement beam 50 passes.

[0128] The method relies on adjusting the parameters based on the calculated noise. Thus, to effectively reduce the noise, the effect of parameter adjustment on the noise should be known. Most generally, the method comprises obtaining information indicative of a relationship between the parameters and the noise. The relationship between the parameters and the noise can be known from previous tests or data. Thus, the system may include, for example, a memory storage in communication with the control unit 100 and storing the data of the relationship between the parameters and the noise. The method may include, for example, receiving data from an external source and obtaining the relevant data. Alternatively, the method may include determining the relationship between the parameters and the calculated noise.

[0129] The method may be configured to determine the relationship as shown in FIG. 13 below. If the method includes determining the relationship, this may include performing a first measurement of the measurement beam 50 and calculating the noise of the corresponding signal (step S11). When the first measurement is performed, the parameter is at a known value, i.e. the first value. This provides a first link between the noise of the signal and the parameter of the fluid, i.e. when the parameter is at the first value. A further measurement is performed to determine how the calculated noise varies with the parameter. Thus, the method may include adjusting the parameter of the fluid to a value different from the first value (step S12) and performing a second measurement of the measurement beam 50 and calculating the noise of the corresponding signal (step S13). When the second measurement is performed, the parameter is at a known value, i.e. the second value. This provides a second link between the noise of the signal and the parameter of the fluid, i.e. when the parameter is at the second value. This may continue until a suitable number of measurements have been performed. The minimum number of measurements performed is two. However, it is desirable to be higher as the more measurements made the more accurately the relationship can be determined, which is desirable as it means that the optimum set point can be more accurately determined.

[0130] After each measurement, the method would include a step of determining whether the number of measurements performed has reached a predetermined value (step S14). If it is determined that the number of measurements has not reached the predetermined value (S14=N), the relevant steps would be repeated. Specifically, if the predetermined value has not been reached, the method would include a further step of adjusting the parameter (step S12), measuring the measurement beam 50 and calculating the noise of the corresponding signal (step S13), and separately determining whether the number of measurements has reached a predetermined value (step S14). This would be repeated until the number of measurements reaches the predetermined value (step S14=Y). The predetermined value may be based on how many data points are needed to determine the relationship between the parameter and the noise. To a certain extent, the more measurements, the more accurately the relationship can be determined. However, after a certain amount of relevant data has been collected, additional measurements will not significantly improve the accuracy of the relationship. Thus, the predetermined value would be a balance of the number of measurements needed to determine the relationship while avoiding less useful measurements being performed.

[0131] If the number of measurements is determined to be equal to (or greater than) the predetermined value (step S14=Y), the method includes interpolating the calculated noise with the parameter measured by the measurement beam 50 and calculating a relationship between the parameter and the calculated noise (step S15). For example, if the data points are considered on a graph, the interpolation may include providing a best-fit line. Any known technique for interpolating the data points to provide an estimated relationship between the parameter and the noise may be used.

[0132] The method may include determining one or more optimal settings for the parameter based on the relationship between the parameter and the calculated noise. The one or more optimal settings for the given parameter may correspond to substantially minimal noise. For example, the method may include determining a value for the given parameter at which the relationship between the given parameter and the noise indicates that the minimum noise will be. This may be determined in any suitable manner, such as by determining a minimum value for the noise indicated by the relationship and determining a predicted value for the parameter at which this minimum noise occurs. The method may include adjusting the parameter to have an optimal value, i.e., at which the noise is substantially minimal for variations in that parameter. Of course, the method may also include adjusting one or more various parameters based on the one or more optimal values ​​for each parameter.

[0133] Preferably, the steps of the above-described methods are performed in the order described herein.

[0134] The system can be configured to function during or after an existing thermal calibration setup. This is advantageous to reduce the penalty on setup time or availability. In a lithographic apparatus, the calibration of modules in the apparatus can be performed through temperature modulation in the system during the process of testing the thermal optimization of the substrate support. In an embodiment, instead of separately measuring the temperature of the surrounding environment, it is possible to obtain the output of the refractive index error during the substrate support optimization test and find the thermally optimized state from the refractive index error readings, i.e. the calculated noise. One or more different parameters of the fluid (e.g., purge gas) can be adjusted to reduce, preferably minimize, the noise. For example, the temperature and / or humidity may be adjusted to reduce, preferably minimize, the calculated noise.

[0135] Combining temperature calibration and noise reduction related measurements may save hardware design efforts, costs and production time availability. For example, an optimization test of the substrate support WT may be adjusted through conditioning liquids of different temperatures until an optimal temperature is achieved for the substrate support WT and the system providing immersion liquid in the immersion lithography apparatus. The change in temperature of this conditioning liquid will indirectly affect the temperature of the fluids that make up the fluid flow. Each time this happens, the measurement device can measure the measurement beam 50, determine the signal and calculate the noise of the signal (corresponding to the refractive index error). At the end of this new test, in addition to the matching information obtained from the substrate support WT matching test, an output of the noise (representing the refractive index error) for different fluid temperatures will be obtained. The optimal thermal point can be obtained by this (corresponding to the minimum noise) and can be adjusted accordingly through the setting of one or more parameters of the fluid, such as temperature and / or humidity.

[0136] In the above embodiments, the term "measurement beam" refers to a beam that can be measured using the system. In most examples, the measurement beam is a beam emerging from an output of a measurement device, e.g. the radiation output 20. Alternatively or additionally, the measurement beam may be a projection beam, i.e. the beam may be at least a part of a beam from the projection system PS. For example, the beam may be the radiation beam B mentioned above. Thus, the system may be used to measure a projection beam.

[0137] As will be appreciated from the above embodiments, the system described in relation to any of the Figures and having any of the variations described above may be part of a lithographic apparatus that can be used in a device manufacturing method for irradiating a substrate W using a projection beam of radiation, such as radiation beam B.

[0138] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein may have other applications, such as integrated optical systems, guiding and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion", respectively. Substrates referred to herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), metrology tools, and / or inspection tools. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Additionally, a substrate may be processed more than once, for example to create multi-layer ICs, and thus the term substrate as used herein may refer to a substrate that already includes one or more processed layers.

[0139] 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 understood that the invention may be used in other applications and is not limited to optical lithography, where the context permits. For example, the invention may be used in imprint lithography, in which a topography of a patterning device defines a pattern to be created on a substrate. The topography of the patterning device is pressed into a layer of resist supplied to the substrate and the resist is cured by application of electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in the resist after the resist has hardened.

[0140] As will be appreciated by one of ordinary skill in the art, the present application may be embodied as a system, method, or computer program product. Accordingly, aspects of the present application may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, which may all be referred to generally herein as a "circuit," "module," or "system." Furthermore, aspects of the present application may take the form of a computer program product embodied in any one or more computer-readable medium(s) having computer usable program code embodied therein.

[0141] Any combination of one or more computer readable media may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or any suitable combination thereof. More specific examples (non-exhaustive list) of computer readable media may include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or flash memory), an optical fiber, a portable compact disk read only memory (CDROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In the context of this document, a computer readable storage medium may be any tangible medium that can store or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0142] A computer-readable signal medium may include a propagated data signal in which computer-readable program code is embodied, for example in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, for example, but not limited to, electromagnetic, optical, or any suitable combination thereof. A computer-readable signal medium is not a computer-readable storage medium, but may be any computer-readable medium that can communicate, propagate, or transfer a program for use by or in connection with an instruction execution system, apparatus, or device.

[0143] The computer code embodied on a computer readable medium may be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber cable, radio frequency (RF), etc., or any suitable combination thereof.

[0144] Computer program code for performing one or more operations for aspects of the present application may be written in any combination of one or more programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), and the connection to the external computer may be made (e.g., through the Internet using an Internet Service Provider).

[0145] The computer program instructions may be loaded into a computer, other programmable data processing apparatus, or other device and may generate a computer-implemented process such that a series of operational steps are executed on the computer, other programmable apparatus, or other device to provide a process for implementing the functions / operations identified in the flowchart and / or block diagram blocks by the instructions executed on the computer or other programmable apparatus.

[0146] As mentioned above, it will be appreciated that the exemplary embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. In one example embodiment, the mechanisms of the exemplary embodiments may be implemented in software or program code, including but not limited to firmware, resident software, microcode, etc.

[0147] A data processing system suitable for storing and / or executing program code will include at least one processor coupled directly or indirectly to memory elements via a system bus. The memory elements may include local memory used during actual execution of the program code, mass storage, and cache memory that provides temporary storage of at least some of the program code to reduce the number of times code needs to be retrieved from mass storage during execution.

[0148] Input / output or I / O devices (including but not limited to keyboards, displays, pointing devices, etc.) may be coupled to the system either directly or through intervening I / O controllers. Network adapters may also be connected to the system to enable the data processing system to be connected to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the network adapters currently available.

[0149] Whilst specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0150] The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications can be made to the invention as described without departing from the scope of the claims.

Claims

1. 1. A system for measuring a beam, comprising: a measurement device configured to measure the beam and determine a signal based on the measured beam; a fluid supply configured to provide a fluid as a fluid stream to or around the beam; the system is configured to calculate noise in the signal and adjust parameters of the fluid constituting the fluid flow such that the calculated noise is reduced; A system in which the calculated noise of the signal is based on measurements of a single beam.

2. The parameters may be temperature, pressure, humidity, fluid composition and / or CO ２ The system of claim 1 , comprising at least one selected from the following:

3. The system of claim 1 or 2, wherein the system comprises at least four measurement devices and corresponding fluid supply devices, the at least four measurement devices being configured to determine the position of the measurement devices.

4. 4. The system of claim 1, wherein the measurement apparatus is configured to be positioned on a patterning device support configured to support a patterning device, a patterning device reference system opposite the patterning device support, a substrate support configured to support a substrate, or a reference system opposite the substrate support.

5. The system of claim 1 , wherein the beam is at least one selected from a measurement beam, a light beam, an optical beam, a radiation beam, or a projection beam.

6. A lithographic apparatus comprising a system according to any one of claims 1 to 5.

7. A reference system; a substrate support configured to support a substrate; a grid on the substrate support, The lithographic apparatus of claim 6 , wherein the radiation output and the sensor are contained in the reference system above or below the substrate support.

8. The lithographic apparatus of claim 7 , wherein the reference system comprises an L-shaped bar coupled to the reference system.

9. The lithographic apparatus of claim 8 , wherein the grid is positioned on a lower surface of the substrate support facing the radiation output and the sensor.

10. 1. A method for reducing noise in a system for measuring a beam, comprising: providing said beam; providing a fluid as a fluid stream to or around the beam; measuring the beam and determining a signal based on the measured beam; calculating the noise of said signal; and adjusting parameters of the fluid such that the calculated noise is reduced; A method, wherein the calculated noise of the signal is based on measurements of a single beam.

11. The method of claim 10 , further comprising determining a relationship between the parameter and the calculated noise.

12. Determining the relationship includes: i) performing measurements of said beams and calculating the noise of the corresponding signals; ii) adjusting a parameter of said fluid, re-running the measurement of said beam and calculating the noise of the corresponding signal; iii) determining whether the number of measurements performed reaches a predetermined value; repeating steps ii) and iii) if it is determined that the number of measurements has not reached the predetermined value; 12. The method of claim 11, further comprising: if the number of measurements is determined to be greater than or equal to the predetermined value, interpolating the calculated noise with values ​​of the parameter at which the beam was measured to determine a relationship between the parameter and the calculated noise.

13. 13. The method of claim 11 or 12, further comprising determining one or more optimal settings of the parameters based on a relationship between the parameters and the calculated noise, the one or more optimal settings corresponding to substantially minimal noise.

14. The parameters may be temperature, pressure, humidity, fluid composition, and / or CO ２ The method according to any one of claims 11 to 13, comprising at least one selected from the following:

15. 15. The method according to any one of claims 11 to 14, wherein the beam is at least one selected from a measurement beam, a light beam, an optical beam, a radiation beam or a projection beam.

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