Actuator array, substrate table and lithography tool

Abstract

The actuator array includes a plurality of actuator cells (AC), each cell including at least one actuator (ACT), a switch assembly (SA) configured to switch power to the actuator, and a control circuit (CC) connected and configured to control the switch assembly and having a serial control input (SCI), a power line (PL) connected to at least the switch assembly of each cell and supplying power to at least the switch assembly, and a control line (CL) connected to the serial control input of each cell for transmitting control data to the control circuit. The control line may be integral with the power line, and the actuator may be piezoelectric. The actuator array may be integrated into the substrate table or the lithographic apparatus. Also, a reference capacitor (C ref ) and a piezoelectric actuator (ACT; C PZ ) is disclosed, where the actuator and capacitor are located remotely from their control circuits (CC, AMP).

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22210952.2 filed December 1, 2022, and European Application No. 23160035.4 filed March 3, 2023, both of which are incorporated by reference in their entirety into this specification. [Background technology]

[0002] The present invention relates to an actuator array, a substrate table including such an actuator array, , and and lithography tool Regarding.

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project a pattern (often referred to as a "design layout" or "design") in 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 advance, the dimensions of circuit elements have continually decreased, while the amount of functional elements (e.g., transistors) per device has steadily increased for decades, following a trend commonly referred to as "Moore's Law." To accommodate Moore's Law, the semiconductor industry pursues technologies that enable the creation of increasingly smaller features. To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form smaller features on a substrate than lithography apparatuses using radiation having a wavelength of, for example, 193 nm, lithography apparatuses using extreme ultraviolet (EUV) radiation may be used, having wavelengths in the range of 4 nm to 20 nm, e.g., 6.7 nm or 13.5 nm.

[0005]

[0005] The lithographic apparatus may include a substrate table for supporting a substrate. The substrate table may include a substrate holding surface that may be formed, for example, by the upper surfaces of multiple burls. This allows the substrate to be supported by the upper surfaces of multiple burls, thereby reducing the contact surface between one substrate and another substrate table. The substrate table may include multiple actuators for moving the burls or a subset of the burls, for example, vertically, for example, to lift the substrate or to compensate for non-flatness of the substrate. The actuators may include, for example, piezo actuators. The actuators may be individually controllable, for example, to take into account non-flatness of the substrate or to lift the substrate in a specific order, for example, to lift a central burl first to hold the substrate, and then actuate and lift more peripheral burls, for example, to allow contact with the substrate in a predetermined manner.

[0006]

[0006] Using a large number of burls and a correspondingly large number of actuators, driving the actuators may require a large number of electrical conductors (e.g. wires) to the substrate table, which on the one hand may impede the ability of the substrate table to move, accelerate, etc., and on the other hand may transmit forces, vibrations or other disturbances to the substrate table.

[0007]

[0007] Multiplexing can offer some improvement because it can reduce the number of wires. For example, having a single high-voltage line per multiplex and low-voltage signals for addressing individual cells can reduce the number of connections. However, for large cell arrays, e.g., with hundreds or thousands of actuators, the number of connections can still be significant. Also, because a multiplex addresses each cell one at a time, the larger the multiplex, the longer it takes to update each cell. Therefore, hold capacitors and other buffers must be significant in capacitance and size, e.g., to maintain a desired potential over an addressing cycle (which, again, may require long addressing periods to fully charge).

[0008]

[0008] The demands on lithographic apparatus tend to increase over time. Larger substrates are processed, which may require the size of the substrate table to increase. Furthermore, substrate processing times are reduced, which may lead to increases in the speed and acceleration of the substrate table. Furthermore, precision can be increased, making it possible to project patterns onto the substrate with smaller line widths. Summary of the Invention

[0009]

[0009] In light of the above, it is an object of the present invention to provide a substrate table that facilitates increasing requirements on a lithographic apparatus.

[0010] According to one aspect of the present invention, there is provided an actuator array, comprising: The actuator array is a plurality of actuator cells, each actuator cell comprising: - at least one piezo actuator - a reference capacitor in series with the piezo actuator a switch assembly configured to switch power to at least one actuator; a control circuit connected to the switch assembly and configured to control the switch assembly, the control circuit including a serial control input; a plurality of actuator cells, a feedback line configured to provide a reference capacitor voltage representative of the voltage across the reference capacitor to the control circuit, a feedback line, wherein the piezoelectric actuator and the reference capacitor are disposed at a first location, the control circuit is disposed at a second location, the second location is spaced apart from the first location, and the feedback line extends between the first location and the second location; a power line connected to at least the switch assembly of each actuator cell for powering at least the switch assembly of each actuator cell; a control line connected to a serial control input of the control circuit of each actuator cell for transmitting control data to the control circuit of at least one of the actuator cells; Includes:

[0011]

[0011] According to one aspect of the present invention, there is provided a substrate table including a plurality of burls configured to support a substrate, the substrate table including an actuator array according to the present invention, the actuators of the actuator array being configured to actuate at least a subset of the burls.

[0012]

[0012] According to one aspect of the invention, a lithography system including a substrate table according to the invention is provided. tool According to a further aspect of the present invention, there is provided a lithography system including an actuator array according to the present invention. tool is provided. [Brief explanation of the drawings]

[0013] [000 13 ] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which: [Figure 1] 1 depicts a schematic overview of a lithographic apparatus according to an embodiment of the invention; [Figure 2] 2 illustrates a detailed view of a portion of the lithographic apparatus of FIG. 1; [Figure 3] 1 illustrates a schematic diagram of a position control system as part of a positioning system according to an embodiment of the present invention; [Figure 4] 1 illustrates a schematic representation of a portion of an actuator array according to an embodiment of the present invention; [Figure 5] 10A and 10B schematically illustrate a portion of an actuator array according to another embodiment of the present invention; [Figure 6] 10 is a schematic illustration of a portion of an actuator array according to yet another embodiment of the present invention; [Figure 7] FIG. 1 illustrates a top view of a piezoelectric layer including multiple actuators that may be used in embodiments of the present invention. [Figure 8] 10A and 10B schematically illustrate a side view of a portion of an actuator array according to yet another embodiment of the present invention; [Figure 9] 1 illustrates a schematic diagram of an actuator cell. [Figure 10] 1 illustrates a schematic diagram of an actuator cell according to an embodiment of the present invention; [Figure 11] 10 illustrates a schematic representation of an actuator cell according to another embodiment of the present invention; [Figure 12] 10A and 10B schematically illustrate portions of an actuator array according to further embodiments of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0014] [000 14 ] The terms "radiation" and "beam" are used herein to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5-100 nm).

[0015] [000 15] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross-section to an incident radiation beam 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 the classic mask (which may be transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0016] [000 16 1 schematically depicts 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. UV radiation, DUV radiation or EUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer 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 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.

[0017] [000 17In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via the 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, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0018] [000 18 ] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic-optical systems, electromagnetic-optical systems and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or a vacuum. Where the term "projection lens" is used herein, it may be considered as synonymous with the more general term "projection system" PS.

[0019] [000 19 ] The lithographic apparatus LA may be of a type in which at least a portion of the substrate is covered with a liquid having a relatively high refractive index (e.g. water) so as to fill a space between the projection system PS and the substrate W, which is also known as immersion lithography. Further information on immersion techniques is given in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0020] [000 20] 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 a substrate W located on one of the substrate supports WT may have preparation steps for a subsequent exposure of the substrate W performed while other substrates W on other substrate supports WT are being used to expose patterns on other substrates W.

[0021] [000 21 ] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged 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 arranged to clean part of the lithographic apparatus, for example part of the projection system PS or part of the system for providing immersion liquid. When the substrate support WT is remote from the projection system PS, the measurement stage may be moved below the projection system PS.

[0022] [000 221 ] In operation, the radiation beam B is incident on the patterning device MA (e.g., a mask), which is held on the mask support MT, and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The second positioner PW and position measurement system IF can be used to accurately move the substrate support WT, for example, to position various target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly further position sensors (not explicitly shown in FIG. 1 ), can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0023] [000 23 ] To clarify the invention, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The x- and y-axes define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is not a limitation of the invention and is used for clarity only. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane.

[0024] [000 24] Figure 2 shows a more detailed view of a portion of the lithographic apparatus LA of Figure 1. The lithographic apparatus LA may comprise a base frame BF, a balance mass BM, a metrology frame MF, and a vibration isolation system IS. The metrology frame MF supports the projection system PS. Additionally, the metrology frame MF may support part of the position measurement system PMS. The metrology frame MF is supported by the base frame BF via the vibration isolation system IS. The vibration isolation system IS is positioned to prevent or reduce vibrations from propagating from the base frame BF to the metrology frame MF.

[0025] [000 25 ] The second positioner PW is positioned to accelerate the substrate support WT by providing a driving force between the substrate support WT and the balance mass BM. The driving force accelerates the substrate support WT in a desired direction. Due to conservation of momentum, the driving force is also applied to the balance mass BM with the same magnitude but in a direction opposite to the desired direction. Typically, the mass of the balance mass BM is significantly greater than the mass of the second positioner PW and the moving part of the substrate support WT.

[0026] [000 26 In one embodiment, the second positioner PW is supported by the balance mass BM. For example, the second positioner PW includes a planar motor for levitating the substrate support WT above the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, the second positioner PW includes a linear motor, and the second positioner PW includes a bearing, such as a gas bearing, for levitating the substrate support WT above the base frame BF.

[0027] [000 27] The position measurement system PMS may comprise any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may comprise any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor, such as an interferometer or an encoder. The position measurement system PMS may comprise a combined interferometer and encoder system. The sensor may also be another type of sensor, such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS may determine a position relative to a reference (e.g. the metrology frame MF or the projection system PS). The position measurement system PMS may determine the position of the substrate table WT and / or the mask support MT by measuring the position or by measuring a time derivative of the position, such as the velocity or acceleration.

[0028] [000 28] The position measurement system PMS may comprise an encoder system. Encoder systems are known, for example, from U.S. Patent Application No. 2007 / 0058173 A1, filed September 7, 2006, which is incorporated herein by reference. The encoder system comprises an encoder head, a grating, and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam and the secondary radiation beam are derived from the same radiation beam (i.e., the original radiation beam). At least one of the primary radiation beam and the secondary radiation beam is produced by diffracting the original radiation beam with a grating. If both the primary radiation beam and the secondary radiation beam are produced by diffracting the original radiation beam with a grating, the primary radiation beam must have a different diffraction order from the secondary radiation beams. The different diffraction orders are, for example, +1st order, -1st order, +2nd order, and -2nd order. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal represents the position of the encoder head relative to the grating. One of the encoder head and the grating may be disposed on the substrate structure WT. The other of the encoder head and the grating may be disposed on the metrology frame MF or the base frame BF. For example, multiple encoder heads are disposed on the metrology frame MF, while one grating is disposed on the top surface of the substrate support WT. In another example, one grating is disposed on the bottom surface of the substrate support WT, and one encoder head is disposed below the substrate support WT.

[0029] [000 29] The position measurement system PMS may comprise an interferometer system. Interferometer systems are known, for example, from U.S. Pat. No. 6,020,964, filed July 13, 1998, which is incorporated herein by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror, and a sensor. The radiation beam is split into a reference beam and a measurement beam by the beam splitter. The measurement beam propagates to the mirror and is reflected by the mirror back to the beam splitter. The reference beam propagates to the reference mirror and is reflected by the reference mirror back to the beam splitter. At the beam splitter, the measurement beam and the reference beam combine into a combined radiation beam. The combined radiation beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. The signal represents the displacement of the mirror. In one embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to a metrology frame MF. In one embodiment, the measurement and reference beams are combined into a combined radiation beam by an additional optical component rather than a beam splitter.

[0030] [000 30The first positioner PM may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with low accuracy relative to the projection system PS. The combination of the long-stroke module and the short-stroke module enables the first positioner PM to move the mask support MT over a large range of movement with high accuracy relative to the projection system PS. Similarly, the second positioner PW may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the substrate support WT over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with low accuracy relative to the projection system PS. The combination of the long-stroke module and the short-stroke module enables the second positioner PW to move the substrate support WT over a large range of movement with high accuracy relative to the projection system PS.

[0031] [000 31The first positioner PM and the second positioner PW each include an actuator for moving the mask support MT and the substrate support WT, respectively. The actuator may be a linear actuator for providing a driving force along a single axis (e.g., the y-axis). Multiple linear actuators may be applied to provide driving forces along multiple axes. The actuator may be a planar actuator for providing driving forces along multiple axes. For example, the planar actuator may be arranged to move the substrate support WT with six degrees of freedom. The actuator may be an electromagnetic actuator including at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying a current to the at least one coil. The actuator may be a moving magnet actuator, which has at least one magnet coupled to the substrate support WT and the mask support MT, respectively. The actuator may be a moving coil actuator, which has at least one coil coupled to the substrate support WT and the mask support MT, respectively. The actuator may be a voice coil actuator, a reluctance actuator, a Lorentz actuator, a piezoelectric actuator, or any other suitable actuator.

[0032] [000 32The lithographic apparatus LA includes a position control system PCS, which is shown schematically in FIG. 3. The position control system PCS includes a setpoint generator SP, a feedforward controller FF, and a feedback controller FB. The position control system PCS provides a drive signal to an actuator ACT. The actuator ACT may be an actuator of the first positioner PM or the second positioner PW. The actuator ACT drives a plant P, which may include a substrate support WT or a mask support MT. The output of the plant P is a position quantity, such as a position, velocity, or acceleration. The position quantity is measured by a position measurement system PMS. The position measurement system PMS generates a signal, which is a position signal representing the position quantity of the plant P. The setpoint generator SP generates a signal, which is a reference signal representing a desired position quantity of the plant P. For example, the reference signal represents a desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms an input to the feedback controller FB. Based on this input, the feedback controller FB provides at least a portion of the drive signal for the actuator ACT. The reference signal may form an input to the feedforward controller FF. Based on its input, the feedforward controller FF provides at least a portion of the drive signal for the actuator ACT. The feedforward FF may utilize information about the mechanical characteristics of the plant P, such as mass, stiffness, resonant modes and natural frequencies.

[0033] [000 33FIG. 4 illustrates a schematic diagram of a portion of an actuator array according to one embodiment of the present invention. The actuator array includes a power line PL and a control line CL, which in this example are integrated and form a single conductor. The power line provides power to a plurality of actuator cells AC, each of which includes at least one actuator ACT, a switching assembly SA connected to the actuator ACT and the power line PL to provide power to the actuator from the power line, and a control circuit CC. The control circuit CC is connected to the switching assembly to control the switching of the switching assembly. The switching assembly includes a serial control input SCI connected to the control line, which in this example is integrated with the power line (i.e., the control line and the power line are the same electrical conductor). In this example, the switch assembly includes a charge switch CS connected between the power line and the switching assembly output, and a discharge switch DS connected between the switching assembly output and ground. The actuator cell further includes an inductor or other low-pass filter LPF connecting the switching assembly output to the actuator. The switches of the switching assembly may include controllable switches such as transistors (e.g., field-effect transistors).

[0034] [000 34 ] The switches of the switching assembly are controlled by a control device. For example, the switches are alternately driven to a conductive state, such that driving the charge switch to a conductive state connects the actuator to the power line via an inductor, and driving the discharge switch to a conductive state connects the actuator to ground via an inductor. Thus, the actuator can be alternately charged and discharged. Switching ripple can be suppressed or at least reduced by an inductor or other low-pass filter. By setting the switching duty cycle (i.e., the duty cycle for activating the charge switch and the discharge switch), it can be possible to set the actuator voltage between the power supply voltage of the power line and ground.

[0035] [000 35 ] The actuators may include, for example, piezoelectric actuators. Setting an actuator voltage may allow for control of the actuation (e.g., displacement) of the piezoelectric actuators. Figure 4 illustrates three of the actuator cells: actuator cell 1, actuator cell 2, and actuator cell N. It will be appreciated that multiple actuator cells may be driven and that a single conductor power line and a single control line may be used, or, as in this embodiment, multiple power and control lines may be used.

[0036] [000 36 ] The power lines may provide a power supply voltage to the actuator cells. Control data may be superimposed, for example, in the form of a high-frequency signal. Each actuator cell may include a high-pass filter, such as a capacitor, connected between the power lines and the serial control input of the control unit to remove DC or low-frequency power voltages from the combined power and control on the single line, thereby enabling serial control data to be transmitted to the control unit of the actuator cell. The control data may be transmitted in the form of serial control data.

[0037] [000 37 ] Separate power and control lines may be used instead of combined power and control lines.

[0038] [000 38] Control data may be addressed to one or more of the actuator cells. For example, each actuator cell may be assigned a respective address. The address may be stored in the control circuitry of the actuator cell. For example, each actuator cell may be given a unique address, or a group of actuator cells may be given the same address. Control data may be transmitted by transmitting the address of the actuator cell to which the control data is directed and the control data over the control lines. For example, the address may be transmitted followed by the control data. For example, a start bit or synchronization bit may precede the transmission, and the transmission may include an end bit or synchronization bit after the transmission of the address and / or control data. The address may be transmitted as binary data. The control data may be transmitted as binary data. The transmission on the control lines is received by all actuator cells, particularly all control units of the actuator cells. The control unit or units whose address corresponds to the transmitted address may respond to the transmission by executing the control data. The control data may include, for example, an actuator variable, such as an actuator drive signal magnitude. The control data may include, for example, an actuator drive voltage value or an actuator PWM duty cycle value. The control circuits are responsive to control data addressed to them to drive the switching assemblies in accordance with the control data. If multiple control circuits are assigned the same address, then all of those control circuits are responsive to control data addressed to those control circuits (i.e., addressed to those actuator cells).

[0039] [000 39In one embodiment, the control data may be broadcast to multiple actuator cells simultaneously. The control circuitry of the actuator cells may be configured to respond to the broadcast addressing the control data associated with the broadcast to multiple actuator cells, thereby allowing multiple actuators to be actuated, for example, simultaneously.

[0040] [000 40 4 illustrates three actuator cells, and Figures 5 and 6 each illustrate two actuator cells for illustrative purposes. In practice, hundreds, thousands, or tens of thousands of actuator cells may be included in an actuator array.

[0041] [000 415 illustrates another embodiment of an actuator array according to the present invention. The actuator array also includes power lines PL and control lines CL, which are combined into a single composite power and control line and connected to a plurality of actuator cells AC. The power lines are powered by a power source PRS, and a control system CS, which transmits serial control signals to the actuator cells, is connected in series with the power source. Each actuator cell includes an actuator ACT, a switch assembly SA, and a control circuit CS for driving the switch assembly. In this embodiment, the switching assembly includes a switch-mode converter. The switch-mode converter is configured to convert a power line voltage at the power line to an actuator voltage for driving the actuator. In this example, the switch-mode converter includes a step-up converter (i.e., a boost converter formed by an inductor L, a first switch FSW, and a second switch SSW). The inductor is connected to the power line using its first inductor terminal and to a second switch using its second inductor terminal, which connects between the second inductor terminal and ground. The second switch connects between the second inductor terminal and the actuator. A control circuit is connected to the first switch and the second switch and controls the switches to a conductive state and a non-conductive state, respectively. For example, the control circuit operates the first switch and the second switch at a boost converter switching frequency, such that when the second switch is conducting, the inductor current increases due to the power line voltage across the inductor, while when the second switch is driven to stop conducting, the inductor voltage at the second inductor terminal increases due to the inductance of the inductor, and the first switch is driven to a conductive state to connect the second inductor terminal to the actuator. Accordingly, a step-up converter is provided that is configured to provide an actuator voltage that exceeds the power line voltage to the actuator. As a result, a high actuator voltage can be provided while maintaining the power line voltage at a low level.By setting the duty cycle of the switching of the first switch and the second switch, it may be possible to control the actuator voltage. Accordingly, each actuator can be driven with a respective actuator voltage by a respective control circuit that controls the duty cycle of each of the first and second switches of the actuator cell. As another example of controlling the switches by a control circuit, when there is no resistive load, a stable output voltage (in this case, a piezo charge) can be achieved as follows: First, the output voltage can be increased by closing the second switch SSW. This causes the inductor to charge to a current level and energy that depend on the supply voltage, the switch activation time, and the inductor value. After disabling the second switch SSW, the first switch FSW is closed to transfer the inductor energy to the load capacitor included in the piezo (with or without its reference capacitor in series), thereby increasing the load voltage. Enabling the first switch FSW can reduce the output voltage. When the output voltage is greater than the supply voltage, this causes a backflow of energy from the load capacitor (i.e., the piezo actuator), and therefore its voltage decreases by an amount that depends on the supply and load voltages, the switch activation time, and the inductor value. After the first switch FSW is disabled, the second switch SSW takes over the built-up inductor current, releasing it to supply without further affecting the output voltage. The overall result can be that the load voltage can be controlled in a quantum of energy defined by the voltage and the initial enable times of the SSW to increase the output voltage and the FSW to decrease the output voltage. Furthermore, if the load voltage needs to be stable, there is no need to enable the switch, avoiding switching and conduction losses in the switch elements. Assuming that output voltage changes occur only sparsely in time, this can significantly reduce the thermal load on the wafer and wafer table.

[0042] [000 425, the control circuit is connected to the control lines (in this example the combined power and control lines) by a high pass filter HPF, such as a capacitor in this example, to allow the serial control data to pass while blocking the DC supply voltage on the combined power and control lines. The high pass filter is connected to the serial control input of the control circuit to allow the serial control data to pass to the serial control input.

[0043] [000 43 ] The control circuitry and switching assembly may be contained within an integrated circuit, such as an application specific integrated circuit (ASIC) or a field programmable gate array, which can facilitate compact packaging of each actuator cell.

[0044] [000 44 In one embodiment, the converter may be a bidirectional converter. When the control circuit drives the converter to increase the actuator voltage, the bidirectional converter draws power from the power line. When the control circuit drives the converter to decrease the actuator voltage, the bidirectional converter puts power back into the power line, thereby reducing the power consumption of the actuator.

[0045] [000 45] FIG. 6 illustrates a further embodiment of an actuator array according to the present invention. The actuator array similarly includes a power line PL and a control line CL, which are integrated into a single composite power line and control line, and which are connected to a plurality of actuator cells AC, each of which includes an actuator ACT, a switch assembly SA, and a control circuit CC for driving the switch assembly. In this embodiment, the switching assembly includes a switch-mode converter configured to convert a power line voltage at the power line into an actuator voltage for driving the actuator. In this example, the switch-mode converter includes a step-up converter (i.e., a boost converter formed by an inductor L, a plurality of first switches FSW, and a plurality of second switches SSW). The inductor is connected to the power line using its first inductor terminal and to a second switch connecting the second inductor terminal to ground using its second inductor terminal. The first switch connects the second inductor terminal to a respective actuator. Compared to the embodiment illustrated in FIG. 5, the embodiment illustrated in FIG. 6 may enable multiple actuators to be driven by the same control circuit.

[0046] [000 46For example, the control circuit operates the first switch and the second switch at a boost converter switching frequency, such that when the second switch is conducting, the inductor current increases due to the power line voltage across the inductor, while when the second switch is driven to stop conducting, the inductor voltage at the second inductor terminal increases due to the inductance of the inductor, and one of the first switches is driven to a conductive state to connect the second inductor terminal to a respective actuator associated with the respective first switch. Accordingly, a step-up converter configured to provide actuators with an actuator voltage that exceeds the power line voltage is provided. By simultaneously switching all of the first switches of the actuator cells to a conductive state at the boost converter switching frequency, it may be possible to provide the same actuator voltage to all of the actuators of the actuator cells. Alternatively, the actuators of the actuator cells may be driven one at a time, whereby the control circuit drives the second switch and one of the first switches associated with one of the actuators at a switching frequency to drive the corresponding actuator. As can be seen from the above description with reference to FIG. 5, the first switch and the second switch are driven in antiphase, similar to the embodiment described with reference to FIG. 5. After driving one actuator of the actuator cells for multiple repetition periods of the boost converter switching frequency, a desired actuator voltage may be applied to the actuator, after which the control circuit can stop switching one of the first switches. Thus, the first switches can be operated one by one in sequence to drive each actuator of the actuator cells one by one in sequence. By setting the duty cycle of the switching of the respective first switch and second switch for each one of the actuators, it may be possible to control the respective actuator voltage.Accordingly, each actuator of the actuator cell can be driven with a respective actuator voltage by a control circuit that controls the duty cycle of the respective first switch associated with each actuator and the second switch of the actuator cell. As described above with reference to FIG. 5, as another example of control of the switches by the control circuit, when there is no resistive load, a stable output voltage (in this case, piezo charge) can be achieved as follows: First, the output voltage can be increased by closing the second switch SSW. This causes the inductor to charge to a current level and energy that depend on the supply voltage, the switch activation time, and the inductor value. After disabling the second switch SSW, the first switch FSW is closed to transfer the inductor energy to the load capacitor included in the piezo (with or without its reference capacitor in series), thereby increasing the load voltage. Enabling the first switch FSW can result in a reduction of the output voltage. When the output voltage is greater than the supply voltage, this causes a backflow of energy from the load capacitor (i.e., the piezo actuator), and therefore its voltage decreases by an amount that depends on the supply and load voltages, the switch activation time, and the inductor value. After the first switch FSW is disabled, the second switch SSW takes over the built-up inductor current, releasing it to supply without further affecting the output voltage. The overall result can be that the load voltage can be controlled in a quantum of energy defined by the voltage and the initial enable times of the SSW to increase the output voltage and the FSW to decrease the output voltage. Furthermore, if the load voltage needs to be stable, there is no need to enable the switch, avoiding switching and conduction losses in the switch elements. Assuming that output voltage changes occur only sparsely in time, this can significantly reduce the thermal load on the wafer and wafer table.

[0047] [000 47] To separately drive the multiple actuators of one actuator cell (each with its own actuator voltage), the control circuit of the actuator cell can be assigned multiple addresses (e.g., a respective address for each actuator). The addresses of the actuators can be stored in a memory of the control circuit. Thus, the actuator assembly can be configured to transmit control data for the multiple actuators of the control circuit to each one of the addresses of the actuators of the control circuit by serial transmission via the control lines.

[0048] [000 48 4, 5, and 6, the actuators may be piezo actuators having an intrinsic actuator capacitance. The actuator capacitance may be used as a holding circuit to hold the actuator voltage provided to the actuator. Thus, when an actuator is activated by operation of a switch in the switching assembly, the actuator may maintain the actuator voltage by virtue of its actuator capacitance until the actuator is activated again. Thus, serial control via serial control lines may address the actuators in the actuator cells of FIG. 6 one at a time, thereby activating the actuators one at a time and holding the actuator voltage until the next activation of the same actuator. The holding capacitance may be increased by providing a capacitor in parallel with the actuator.

[0049] [000 497 illustrates a top view of multiple actuators ACT that may be included in an actuator array according to the present invention. The actuators may be piezoelectric actuators, each configured to actuate a burl. The top surfaces of the burl may provide a substrate transport surface. Power and control lines, or combined power / control lines, may be provided as a plane substantially parallel to the substrate transport surface (e.g., below the substrate transport surface SCS) to facilitate electrically connecting the actuator cells to the power and control lines, respectively. The actuators may be configured, for example, to actuate the burl in a vertical direction (i.e., the Z direction), and thus in a direction substantially perpendicular to the substrate transport surface. The actuators may also be configured to actuate the burl in a direction parallel to the substrate transport surface (e.g., the X direction or the Y direction), for example, in combination with actuation in the Z direction. For example, the actuators may be configured to actuate the burl in the Z direction, the X direction, the Y direction, the Z and X directions, the Z and Y directions, the X and Y directions, or the Z, X and Y directions. Generally, throughout this document, actuators may be configured to actuate in the vertical direction (i.e., the Z direction), the X direction, or the Y direction. The X and Y directions define a substantially horizontal plane. In alternative embodiments, generally throughout this document, actuators may be configured to actuate in any combination of the X, Y, and Z directions (e.g., the Z direction, the X direction, the Y direction, the Z and X directions, the Z and Y directions, the Z, X, and Y directions, or the X and Y directions).

[0050] [000 50 According to an embodiment of the invention, the substrate table includes a plurality of burls configured to support the substrate, and the substrate table includes an actuator array as described above, the actuators of the actuator array being configured to actuate at least a subset of the burls. A lithographic apparatus may include a lithographic apparatus substrate table and / or actuator array according to the invention.

[0051] [000 51] In accordance with the present invention, an actuator may be configured to actuate (i.e., generate movement and / or force) in any direction. For example, an actuator may be configured to actuate vertically. As another example, an actuator may be configured to act horizontally. As yet another example, an actuator may be configured to act in horizontal and vertical directions, such as the x, y, and z directions.

[0052] [000 52 In the substrate table example above, the actuators may be configured to move the substrate vertically, horizontally, or horizontally and vertically. For example, the actuators may be configured to actuate in three dimensions. By actuating the substrate horizontally, the actuators may position the substrate in a horizontal plane, which may help reduce overlay errors in the lithographic apparatus.

[0053] [000 53 ] The actuators may include any type of actuator. For example, in the case of piezo actuators, shear actuators may be used to actuate a shear actuator in a horizontal direction. For example, a substrate table according to the present invention includes a plurality of burls configured to support a substrate, the substrate table including an actuator array as described above, the actuators of the actuator array being configured to actuate at least a subset of the burls in a vertical and horizontal direction. Actuating the burls in a horizontal direction (for example using shear piezo actuators) may enable overlay errors to be reduced.

[0054] [000 548 illustrates another embodiment, in which a mirror MR includes a mirror surface MRS and is provided with a plurality of actuators ACT arranged on a carrier CR and configured to apply forces to a ceramic substrate CRS that may hold the mirror MR. The ceramic substrate CRS is arranged between the plurality of actuators and the mirror. Power and control lines, or combined power / control lines, may be provided in a plane substantially perpendicular to the mirror surface (e.g., below the mirror surface) to facilitate electrically connecting the actuator cells to the power and control lines, respectively. The mirror may be included in a projection system of a lithographic apparatus.

[0055] [000 55 9 shows an actuator cell including a piezo actuator ACT, piezo 1 illustrates at least a portion of an actuator cell having a capacitance indicated by , and a driver for driving the actuator. The driver includes a control circuit CC and an amplifier AMP driven by an output signal of the control circuit. The difference between an actuator setpoint signal SET and a feedback signal FBS is provided to the control circuit, and the output of the control circuit is connected to the amplifier. The amplifier is configured to provide an actuator drive signal to the actuator. In this manner, the control circuit and amplifier form a feedback loop that drives the actuator in response to the setpoint signal.

[0056] [000 56 The actuator cell further includes a reference capacitor C electrically connected in series with the piezoelectric actuator. refBecause the reference capacitor and the piezoelectric actuator form a series-connected capacitance, the actuator drive current provided by the amplifier to the piezoelectric actuator also flows through the reference capacitor. Because the capacitance of the reference capacitor is accurately known, the voltage across the reference capacitor can accurately reflect the charge held by the reference capacitor. Because the reference capacitor and the piezoelectric actuator are connected in series and experience the same actuator current, the charge held by the reference capacitor will reflect the charge held by the piezoelectric actuator. In one embodiment, to obtain a defined low-frequency behavior, a resistor is placed in parallel with the actuator and reference capacitor. The resistor in parallel with the actuator and reference capacitor can provide a cutoff frequency below which the charge amplifier effectively behaves as a voltage amplifier, thus providing the defined, desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the higher-frequency voltage gain defined by the capacitor (i.e., the capacitance of the actuator and reference capacitor).

[0057] [000 57 ] Piezoelectric actuators may exhibit hysteresis, causing a nonlinearity between the actuator drive signal and the excursion (position, force) of the piezo actuator. It has been observed that the degree of hysteresis may vary depending on whether voltage drive, charge drive, or current drive is used. More specifically, it has been observed that charge drive may result in less hysteresis compared to voltage drive. Charge drive may be implemented with a reference capacitor, whereby the feedback signal provided to the controller is derived from the voltage across the reference capacitor.

[0058] [000 589, the actuator is located at a first location, while the control circuit, amplifier, and reference capacitor are located at a second location remote from the first location. A cable, such as a coaxial cable, extends between the first and second locations to provide an actuator drive signal to one terminal of the actuator and connect the other terminal of the actuator in series with the reference capacitor. Parasitic capacitance between the conductors of the cable may extend along the length of the cable and is symbolically represented in FIG. 9 by C1 and C2 between the conductors. The series resistance of the conductors of the cable is the sum of the R 1a , R 2a , R 3a and R of the other conductor 1b , R 2b , R 3b It is symbolically represented by

[0059] [000 59 ] The configuration described with reference to FIG. 9 may function satisfactorily as long as the capacitance of the actuator and reference capacitor is large compared to the parasitic capacitance of the cable. If the difference between the control circuit and the actuator (i.e., the difference between the first location and the second location) increases, the cable capacitance may increase due to an increase in cable length. Actuator movement may result in a change in the cable's parasitic capacitance, which may affect charge control, especially if the cable capacitance is relatively large. Furthermore, a large cable capacitance in parallel with such an actuator may affect the described charge control, since the larger the cable capacitance relative to the actuator capacitance, the more charge is absorbed by the cable, thus deviating from charge control and increasing hysteresis. The above effect may be further exacerbated by a decrease in actuator capacitance, for example, due to the smaller size of the piezoelectric actuator, further increasing the relative cable capacitance.

[0060] [000 60] Figure 10 illustrates an embodiment of an actuator cell according to the present invention, which differs from the actuator cell illustrated in and described with reference to Figure 9 in that the reference capacitor is located at a first location (i.e., the location of the actuator).

[0061] [000 61 ] FIG. 10 shows an actuator cell including a piezo actuator ACT, piezo 1 illustrates at least a portion of an actuator cell having a capacitance indicated by , and a driver for driving the actuator. The driver includes a control circuit CC and an amplifier AMP driven by an output signal of the control circuit. The difference between an actuator setpoint signal SET and a feedback signal FBS is provided to the control circuit, and the output of the control circuit is connected to the amplifier. The amplifier is configured to provide an actuator drive signal to the actuator. In this manner, the control circuit and amplifier form a feedback loop that drives the actuator in response to the setpoint signal.

[0062] [000 62 The actuator cell further includes a reference capacitor C electrically connected in series with the piezoelectric actuator. refAs explained above, because the reference capacitor and the piezoelectric actuator form a series-connected capacitance, the actuator drive current provided by the amplifier to the piezoelectric actuator also flows through the reference capacitor. Because the capacitance of the reference capacitor is accurately known, the voltage across the reference capacitor can accurately reflect the charge held by the reference capacitor. Because the reference capacitor and the piezoelectric actuator are connected in series and experience the same actuator current, the charge held by the reference capacitor will reflect the charge held by the piezoelectric actuator. In one embodiment, to obtain a defined low-frequency behavior, a resistor is placed in parallel with the actuator and reference capacitor. The resistor in parallel with the actuator and reference capacitor can provide a cutoff frequency below which the charge amplifier effectively behaves as a voltage amplifier, thus providing the defined, desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the higher-frequency voltage gain defined by the capacitor (i.e., the capacitance of the actuator and reference capacitor). The resistor may be located locally at the amplifier (ie, the second location) and / or at the actuator and reference capacitor (ie, the first location).

[0063] [000 63] As illustrated in FIG. 10, the actuator and reference capacitor are located at a first location, while the control circuitry and amplifier are located at a second location remote from the first location. A cable, such as a coaxial cable, extends between the first and second locations. An actuator drive signal is provided to one terminal of one of the actuator and reference capacitor via the cable's actuator line (i.e., the cable's conductor). The other terminal of one of the actuator or reference capacitor is connected in series with one terminal of the other of the actuator and reference capacitor. The other terminal of the other of the actuator and reference capacitor is connected to electrical ground via the cable's return conductor, also referred to as the cable's return line. A feedback signal representing the voltage across the reference capacitor is provided from the first location to the second location by the cable's feedback line FL. As in FIG. 9, parasitic capacitance between the cable's conductors may extend along the length of the cable and is symbolically represented in FIG. 10 by C1 and C2 between the conductors. The series resistance of the cable's conductors is calculated by multiplying the R 1a , R 2a , R 3a and R of the other conductor 1b , R 2b , R 3b It is symbolically represented by

[0064] [000 64 10, the terminals of the reference capacitor connected to the actuator are connected to the feedback line, i.e., provide a feedback signal directly to the control circuit. Sensitivity may appear, for example, via the cable capacitance of the feedback line of the cable, in a similar manner as described above with reference to FIG. 9, as the cable capacitance may affect the measurement of the charge held by the actuator.

[0065] [000 65In the embodiment illustrated in FIG. 11 , the actuator cell further includes a preamplifier PA in a first location, which amplifies the reference capacitor voltage across the reference capacitor. The preamplifier may have a voltage gain of one or more, and the preamplifier actually buffers the reference capacitor voltage. The preamplifier may include a high-impedance preamplifier input. The preamplifier output is connected to the feedback line of the cable and provides a feedback signal to the control circuit. As a result of incorporating the preamplifier, the effect on the feedback line of the cable can be at least reduced. In one embodiment, a resistor is placed in parallel with the actuator and reference capacitor to obtain a defined low-frequency behavior. The resistor in parallel with the actuator and reference capacitor can provide a cutoff frequency below which the charge amplifier actually behaves as a voltage amplifier, thus providing the defined, desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the higher-frequency voltage gain defined by the capacitor (i.e., the capacitance of the actuator and reference capacitor). In a configuration according to FIG. 11, a resistor may be placed at the actuator and the reference capacitor (ie, at the first location), respectively.

[0066] [000 66 Charge control using a reference capacitor in series with and located close to the actuator can also be used in the embodiments described above with reference to Figures 4 to 6. An example is shown schematically in, and will be described with reference to, Figure 12, which illustrates a highly schematic view of an actuator cell similar to the actuator cell described above with reference to Figure 5, with the reference capacitor and charge control described above with reference to Figures 10 and 11. Thus, in addition to what has been described with reference to Figure 5, the actuator cell may also include a reference capacitor C in series with the actuator ACT. refThe actuator (i.e., the piezoelectric actuator) and reference capacitor may be located at a first location, while the control circuit and switch assembly are located at a second location remote from the first location. As described with reference to FIG. 11, the preamplifier PRA may be used to buffer the reference capacitor voltage forming the feedback signal. The control circuit CC may drive the switch assembly SA using a feedback signal representing the charge on the reference capacitor, and therefore the charge on the piezoelectric actuator. The control circuit may derive a set point from data acquired at the serial control input SCI. The actuator cell further includes a modulator MOD electrically connected to the control circuit so as to be driven by the control circuit. The modulator is configured to drive the first and second switches of the switching assembly to charge and discharge the piezoelectric actuator, respectively. While FIG. 12 illustrates the preamplifier being located close to the control circuit, the preamplifier may instead be located close to the actuator and reference capacitor, i.e., located at the first location instead of the second location. Adding charge control according to FIG. 12 to the embodiments described with reference to FIGS. 4-6 can provide accurate actuation of a piezoelectric actuator because the described charge control can be less sensitive to actuator hysteresis and locating the reference capacitor close to the piezoelectric actuator (i.e., both at the same end of the cable connecting the actuator and control circuitry) can reduce the adverse effects on accuracy due to cable parasitics, such as cable capacitance. In the embodiment according to FIG. 12, similar to the embodiments according to FIGS. 4-6, the cable length can be relatively short compared to the cable length in the embodiments of FIGS. 10 and 11. In other words, in the embodiment according to FIG. 12, similar to the embodiments according to FIGS. 4-6, the distance between the first and second locations can be relatively short compared to the distance between the first and second locations in the embodiments of FIGS. 10 and 11.In the embodiments described with reference to Figures 4-6 and 12, the power and control lines may allow for the distribution of power and control data, allowing the control circuitry and switches to be positioned closer to the actuator, which may result in shorter cables to the actuator, i.e., shorter distances between the first and second locations.

[0067] [000 67 ] This document describes several groups of embodiments, namely, a first group of embodiments described with reference to FIGS. 4-6, a second group of embodiments described with reference to FIGS. 9-10, and a third group of embodiments described with reference to FIG. 11. The actuators may be piezoelectric actuators. Unless an actuator is specifically specified as a piezoelectric actuator, the actuator may be any other suitable actuator, such as any other capacitive actuator. The actuators in the first, second, and third groups of the present invention may be the same or different from one another. Thus, an actuator in the first group of the present invention may be identified as a first actuator, an actuator in the second group of the present invention may be identified as a second actuator, and an actuator in the third group of the present invention may be identified as a third actuator.

[0068] [000 68 The actuator cells in the first, second and third groups of the present invention may be the same or different from one another. Thus, the actuator cells in the first group of the present invention may be identified as first actuator cells, the actuator cells in the second group of the present invention may be identified as second actuator cells, and the actuator cells in the third group of the present invention may be identified as third actuator cells.

[0069] [000 69The control circuits in the first, second, and third groups of the present invention may be the same or different from one another. Thus, the control circuit in the first group of the present invention may be identified as a first control circuit, the control circuit in the second group of the present invention may be identified as a second control circuit, and the control circuit in the third group of the present invention may be identified as a third control circuit.

[0070] [000 70 ] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein have other possible applications, including the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0071] [000 71 ] Although specific reference is made herein to embodiments of the invention in the context of lithography apparatus, embodiments of the invention may also be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus are sometimes referred to generically as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0072] [000 72 ] Although particular reference has been made above to the use of embodiments of the present invention in the context of optical lithography, it will be understood that the present invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0073] [000 73] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and, in doing so, may cause actuators or other devices to interact with the physical world.

[0074] [000 74 While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. Other aspects of the invention are set forth in the following numbered clauses: 1.- A plurality of actuator cells, each actuator cell comprising: - at least one actuator a switch assembly configured to switch power to at least one actuator; a control circuit connected to the switch assembly and configured to control the switch assembly, the control circuit including a serial control input; a plurality of actuator cells, a power line connected to at least the switch assembly of each actuator cell for powering at least the switch assembly of each actuator cell; and a control line connected to a serial control input of the control circuit of each actuator cell for transmitting control data to the control circuit of at least one of the actuator cells; an actuator array including: 2. An actuator array as described in clause 1, wherein the control lines are integral with the power lines and each actuator cell includes a high frequency pass filter connected between the power line and the serial control input. 3. An actuator array as described in any one of clauses 1-2, wherein the switch assembly includes a switch mode converter. 4. The actuator array of clause 3, including a plurality of actuators per actuator cell, and wherein the switch mode converter includes, for each one of the plurality of actuators per actuator cell, a respective first switch associated with each one of the plurality of actuators of the actuator cell. 5. The actuator array of clause 4, wherein the control circuit is configured to operate the switch-mode converter to sequentially power the plurality of actuators in each actuator cell by sequentially operating a first switch associated with each one of the plurality of actuators in the actuator cell in a conductive state. 6. The actuator array of any one of clauses 3 to 5, wherein the switch mode converter comprises a bidirectional converter. 7. The actuator array of any one of clauses 1 to 6, wherein the voltage lines include a conductive surface. 8. The actuator array of any one of clauses 1 to 7, wherein each actuator comprises a piezo actuator. 9. An actuator array as described in any one of clauses 1 to 8, wherein each of the control circuits is associated with a respective address, and the control circuits are configured to be individually addressable by addressing control data via control lines to the respective addresses. 10. An actuator array as described in any one of clauses 1 to 9, wherein each of the control circuits is configured to be addressable by broadcasting control data over the control lines. 11. An actuator array according to any one of clauses 1 to 10, wherein the control circuitry comprises one of an ASIC, an FPGA or a PCB. 12. An actuator array as described in any one of clauses 1 to 11, further comprising a control transmitter configured to transmit serial control data to the actuator cells via the control lines. 13. The switch assembly includes a switch converter; The switch converter is -Inductor at least one first switch configured to electrically connect the inductor to the at least one actuator; and a second switch constructed and arranged to electrically connect the inductor between the power line and ground; and the control circuit includes: - operating the second switch in a conductive state to electrically connect the inductor between the power line and ground and allow an inductor current to flow between the power line and ground, and operating the first switch in a non-conductive state; and - operating the second switch in a non-conductive state and the first switch in a conductive state to electrically connect the inductor to the at least one actuator. 13. The actuator array of any one of clauses 1 to 12, configured to alternate between: 14. A substrate table comprising a plurality of burls configured to support a substrate, the substrate table comprising an actuator array according to any one of clauses 1 to 13, the actuators of the actuator array being configured to actuate at least a subset of the burls. 15. A substrate table according to clause 14, wherein the control lines are integral with the power lines and extend in a plane substantially parallel to the substrate holding surface defined by the burls. 16. A lithographic apparatus comprising a substrate table according to clause 14 or 15. 17. A lithographic apparatus comprising an actuator array according to any one of clauses 1 to 13. 18. Piezo actuator and a reference capacitor in series with the piezoelectric actuator; a control circuit configured to control the piezoelectric actuator and the reference capacitor; a feedback line configured to provide a reference capacitor voltage representative of the voltage across the reference capacitor to the control circuit; An actuator cell comprising: An actuator cell, wherein the piezo actuator and reference capacitor are disposed at a first location, the control circuit is disposed at a second location, the second location is spaced apart from the first location, and the feedback line extends between the first location and the second location. 19. The actuator cell of clause 18, wherein the actuator cell further includes a preamplifier disposed at a first location and configured to amplify the voltage across the reference capacitor, a preamplifier output of the preamplifier connected to a feedback line, and the preamplifier configured to output the amplified reference capacitor voltage on the feedback line. 20. The actuator cell is further comprising a switch assembly configured to switch power to the series connection of the piezoelectric actuator and the reference capacitor; 20. An actuator cell according to clause 18 or 19, wherein the control circuit is connected to the switch assembly and configured to control the switch assembly. 21. An actuator cell as described in any one of clauses 18 to 20, wherein the actuator cell further includes an amplifier configured to drive the series connection of the piezoelectric actuator and the reference capacitor, and the control circuit is connected to the amplifier and configured to control the amplifier. 22. An actuator cell as described in clause 19 or 21, further comprising a cable electrically connected to the piezoelectric actuator and the reference capacitor, the cable extending between the first location and the second location and including an actuator line connected to one of the actuator and the reference capacitor, and a return line connected to the other of the actuator and the reference capacitor. 23. A substrate table comprising a plurality of burls configured to support a substrate, the substrate table comprising an actuator cell according to any one of clauses 18 to 22, the actuator of the actuator cell being configured to actuate at least one of the burls. 24. A lithographic apparatus comprising a substrate table according to clause 23. 25. A lithographic apparatus comprising an actuator cell according to any one of clauses 18 to 22. 26.- A plurality of actuator cells, each of which comprises: - at least one piezo actuator - a reference capacitor in series with the piezo actuator a switch assembly configured to switch power to at least one actuator; a control circuit connected to the switch assembly and configured to control the switch assembly, the control circuit including a serial control input; a feedback line configured to provide a reference capacitor voltage representative of a voltage across a reference capacitor to a control circuit, the piezoelectric actuator and the reference capacitor being disposed at a first location, the control circuit being disposed at a second location, the second location being remote from the first location, and the feedback line extending between the first location and the second location. a plurality of actuator cells, a power line connected to at least the switch assembly of each actuator cell for powering at least the switch assembly of each actuator cell; and a control line connected to a serial control input of the control circuit of each actuator cell for transmitting control data to the control circuit of at least one of the actuator cells; an actuator array including: 27. An actuator array as described in clause 26, wherein each actuator cell further includes a preamplifier disposed at a first location and configured to amplify the voltage across the reference capacitor, a preamplifier output of the preamplifier being connected to a feedback line, and the preamplifier being configured to output the amplified reference capacitor voltage onto the feedback line. 28. An actuator array as described in clause 26 or 27, wherein each actuator cell further includes a cable electrically connected to the piezoelectric actuator and the reference capacitor, the cable extending between the first location and the second location and including an actuator line connected to one of the actuator and the reference capacitor, and a return line connected to the other of the actuator and the reference capacitor. 29. An actuator array as described in any one of clauses 26 to 28, wherein the control lines are integral with the power lines and each actuator cell includes a high frequency pass filter connected between the power line and the serial control input. 30. An actuator array as described in any one of clauses 26 or 29, wherein the switch assembly includes a switch mode converter. 31. The actuator array of clause 30, including a plurality of actuators per actuator cell, and wherein the switch mode converter includes, for each one of the plurality of actuators per actuator cell, a respective first switch associated with the respective one of the plurality of actuators of the actuator cell. 32. The actuator array of clause 31, wherein the control circuit is configured to operate the switch-mode converter to sequentially power the plurality of actuators per actuator cell by sequentially operating in a conductive state a first switch associated with each one of the plurality of actuators in the actuator cell. 33. An actuator array according to any one of clauses 26 to 32, wherein the switch mode converter comprises a bidirectional converter. 34. An actuator array according to any one of clauses 26 to 33, wherein the voltage lines comprise conductive surfaces. 35. An actuator array according to any one of clauses 26 to 34, wherein each actuator comprises a piezo actuator. 36. An actuator array as described in any one of clauses 26 to 35, wherein each of the control circuits is associated with a respective address, and the control circuits are configured to be individually addressable by addressing control data via control lines to the respective addresses. 37. An actuator array according to any one of clauses 26 to 36, wherein each of the control circuits is configured to be addressable by broadcasting control data over the control lines. 38. An actuator array according to any one of clauses 26 to 37, wherein the control circuitry comprises one of an ASIC, an FPGA or a PCB. 39. An actuator array according to any one of clauses 26 to 38, further comprising a control transmitter configured to transmit serial control data to the actuator cells via the control lines. 40. The switch assembly includes a switch mode converter; Switch mode converters are -Inductor at least one first switch configured to electrically connect the inductor to the at least one actuator; and a second switch constructed and arranged to electrically connect the inductor between the power line and ground; and the control circuit includes: - operating the second switch in a conductive state to electrically connect the inductor between the power line and ground and allow an inductor current to flow between the power line and ground, and operating the first switch in a non-conductive state; and - operating the second switch in a non-conductive state and the first switch in a conductive state to electrically connect the inductor to the at least one actuator. 40. The actuator array of any one of clauses 26 to 39, configured to alternate between: 41. A substrate table comprising a plurality of burls configured to support a substrate, the substrate table comprising an actuator array according to any one of clauses 26 to 40, the actuators of the actuator array being configured to actuate at least a subset of the burls. 42. A substrate table according to clause 41, wherein the control lines are integral with the power lines and extend in a plane substantially parallel to the substrate holding surface defined by the burls. 43. A lithographic apparatus comprising a substrate table according to clause 41 or 42. 44. A lithographic apparatus comprising an actuator array according to any one of clauses 26 to 40.

Claims

1. a plurality of actuator cells, each actuator cell comprising: at least one actuator a switch assembly configured to switch power to said at least one actuator; a control circuit connected to said switch assembly and configured to control said switch assembly, said control circuit including a serial control input; a plurality of actuator cells, - a power line connected to at least said switch assembly of each actuator cell for powering at least said switch assembly of each actuator cell; and a control line connected to the serial control input of the control circuit of each actuator cell for transmitting control data to the control circuit of at least one of the actuator cells; an actuator array including:

2. 2. The actuator array of claim 1, wherein the control lines are integral with the power lines, and each actuator cell includes a high frequency pass filter connected between the power line and the serial control input.

3. The actuator array of any one of claims 1 to 2, wherein the switch assembly includes a switch mode converter.

4. The actuator array according to any one of claims 1 to 3, wherein the voltage lines include a conductive surface.

5. 5. An actuator array according to claim 1, wherein each of the control circuits is associated with a respective address, and the control circuits are configured to be individually addressable by addressing control data to the respective addresses via the control lines.

6. An actuator array according to any preceding claim, wherein each of the control circuits is arranged to be addressable by broadcasting control data over the control lines.

7. An actuator array according to any preceding claim, further comprising a control transmitter configured to transmit serial control data to the actuator cells via the control lines.

8. 8. A substrate table comprising a plurality of burls configured to support a substrate, the substrate table comprising an actuator array according to any one of claims 1 to 7, the actuators of the actuator array being configured to actuate at least a subset of the burls.

9. A lithographic apparatus comprising an actuator array according to any one of claims 1 to 8.

10. A piezo actuator; a reference capacitor connected in series with the piezoelectric actuator; a control circuit configured to control the piezoelectric actuator and the reference capacitor; a feedback line configured to provide a reference capacitor voltage to the control circuit, the reference capacitor voltage being representative of the voltage across the reference capacitor; An actuator cell comprising: An actuator cell, wherein the piezo actuator and the reference capacitor are disposed at a first location, the control circuit is disposed at a second location, the second location is spaced apart from the first location, and the feedback line extends between the first location and the second location.

11. 11. The actuator cell of claim 10, wherein the actuator cell further comprises a preamplifier disposed at the first location and configured to amplify the voltage across the reference capacitor, a preamplifier output of the preamplifier connected to the feedback line, and the preamplifier configured to output the amplified reference capacitor voltage onto the feedback line.

12. The actuator cell includes: - further comprising a switch assembly configured to switch power to the series connection of the piezo actuator and the reference capacitor; An actuator cell according to claim 10 or 11, wherein the control circuit is connected to the switch assembly and configured to control the switch assembly.

13. a plurality of actuator cells, each actuator cell comprising: at least one piezo actuator a reference capacitor connected in series with the piezo actuator; a switch assembly configured to switch power to said at least one actuator; a control circuit connected to said switch assembly and configured to control said switch assembly, said control circuit including a serial control input; a feedback line configured to provide a reference capacitor voltage representative of a voltage across the reference capacitor to the control circuit, the piezo actuator and the reference capacitor being located at a first location, the control circuit being located at a second location, the second location being remote from the first location, and the feedback line extending between the first location and the second location. a plurality of actuator cells, - a power line connected to at least said switch assembly of each actuator cell for powering at least said switch assembly of each actuator cell; and a control line connected to the serial control input of the control circuit of each actuator cell for transmitting control data to the control circuit of at least one of the actuator cells; an actuator array including:

14. 14. The actuator array of claim 13, wherein each actuator cell further includes a preamplifier disposed at the first location and configured to amplify the voltage across the reference capacitor, a preamplifier output of the preamplifier connected to the feedback line, the preamplifier configured to output the amplified reference capacitor voltage onto the feedback line.

15. 15. The actuator array of claim 13 or 14, wherein each actuator cell further includes a cable electrically connected to the piezoelectric actuator and the reference capacitor, the cable extending between the first location and the second location and including an actuator line connected to one of the actuator and the reference capacitor, and a return line connected to the other of the actuator and the reference capacitor.

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