Actuator array, in particular for substrate table and lithographic apparatus, and piezoelectric actuator control circuit arrangement

Abstract

An actuator array comprising a plurality of actuator units (AC), each actuator unit comprising: at least one actuator (ACT); a switch assembly (SA) configured to switch power to the actuator; and a control circuit (CC) connected to the switching assemblies and configured to control the switching assemblies, and having a serial control input (SCI), a power line (PL) connected to at least the switching assemblies of each cell, and a control line (CL) connected to the serial control input of each cell to transmit control data to the control circuit. The control line may be integrated with the power line, and the actuator may be of the piezoelectric type. The actuator array may be incorporated in a substrate table or a lithographic apparatus. Also disclosed is a feedback control circuit arrangement comprising a piezoelectric actuator (ACT; CPZ) in parallel with a reference capacitor (Cref), where the actuator and capacitor are located at locations remote from its control circuitry (CC, AMP).

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European Application No. 22210952.2, filed on December 1, 2022, and European Application No. 23160035.4, filed on March 3, 2023. The entire contents of these European applications are incorporated herein by reference. Technical field

[0003] The present invention relates to actuator arrays, substrate tables including such actuator arrays, actuator units, and lithographic apparatuses. Background art

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

[0005] As semiconductor manufacturing processes continue to advance, for decades, while the size of circuit elements has been continuously decreasing, the amount of functional elements (such as transistors) per device has been steadily increasing, following a trend commonly known as “Moore’s law.” To keep up with Moore’s law, the semiconductor industry is seeking technologies that can produce ever-smaller features. To project a pattern onto a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. A lithographic apparatus using extreme ultraviolet (EUV) radiation (having a wavelength in the range of 4 nm to 20 nm, e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on a substrate compared to a lithographic apparatus using, for example, radiation having a wavelength of 193 nm.

[0006] The lithographic apparatus may include a substrate table for supporting the substrate. The substrate table may include a substrate holding surface, which may for example be formed by the top surfaces of a plurality of protrusions. Since the substrate may thus be supported by the top surfaces of the plurality of protrusions, the contact surface between the substrate on the one hand and the substrate table on the other hand may be small. The substrate table may include a plurality of actuators for moving the protrusions or a subset of the protrusions, for example in a vertical direction, for example capable of lifting the substrate or compensating for any unevenness of the substrate. The actuators may for example include piezoelectric actuators. The actuators may be individually controllable, for example capable of taking into account the unevenness of the substrate or capable of lifting the substrate in a particular sequence: for example, the central protrusion may first be lifted to hold the substrate, after which more peripheral protrusions are actuated to lift, such that the substrate can be contacted in a defined manner, for example.

[0007] Using a large number of protrusions and a correspondingly large number of actuators, driving the actuators may involve a large number of electrical conductors (such as wires) to the substrate table. On the one hand, the wires may impede the ability of the substrate table to move, accelerate, etc., and on the other hand, they may transmit forces, vibrations or other disturbances to the substrate table.

[0008] Multiplexing can provide some improvements as the number of wires can be reduced. For example, by having a single high voltage line and a low voltage signal for addressing a single cell for each multiplexing, the number of connections can be reduced. However, for a large array of cells with, for example, hundreds or thousands of actuators, the number of connections may still be significant. Moreover, the larger the multiplexing, the longer the time it takes to update each cell, since the multiplexing can address each cell once at a time. Therefore, holding capacitors or other buffers must be significant in capacitance and size (which may again require longer addressing to fully charge) to hold, for example, a desired potential during the addressing cycle.

[0009] Over time, the requirements for lithographic apparatus tend to increase. Larger substrates are to be processed, which may require an increase in the size of the substrate table. In addition, the substrate processing time will be reduced, which may translate into increased speed and acceleration of the substrate table. In addition, the accuracy can be increased, such that patterns can be projected onto the substrate with a smaller line width. Summary of the Invention

[0010] In view of the above, it is an object of the present invention to provide a substrate table that facilitates meeting the increasing requirements for lithographic apparatus.

[0011] According to one aspect of the present invention, there is provided an actuator array, comprising:

[0012] a plurality of actuator units, each actuator unit comprising

[0013] at least one actuator,

[0014] a switch assembly configured to switch electrical power to the at least one actuator,

[0015] a control circuit connected to the switch assembly and configured to control the switch assembly and including a serial control input,

[0016] a power line connected to at least the switch assembly of each actuator unit for powering at least the switch assembly of each actuator unit, and

[0017] a control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

[0018] According to one aspect of the present invention, there is provided a substrate table including a plurality of protrusions configured to support a substrate, the substrate table including an actuator array according to the present invention, wherein the actuators of the actuator array are configured to actuate at least a subset of the protrusions.

[0019] According to one aspect of the present invention, there is provided a lithographic apparatus including a substrate table according to the present invention. According to another aspect of the present invention, there is provided a lithographic apparatus including an actuator array according to the present invention.

[0020] According to one aspect of the present invention, there is provided an actuator unit including:

[0021] a piezoelectric actuator;

[0022] a reference capacitor connected in series with the piezoelectric actuator;

[0023] a control circuit configured to control the piezoelectric actuator and the reference capacitor;

[0024] a feedback line configured to provide a reference capacitor voltage representative of the voltage across the reference capacitor to the control circuit;

[0025] wherein the piezoelectric actuator and the reference capacitor are arranged at a first location and the control circuit is arranged at a second location, wherein the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location.

[0026] According to one aspect of the present invention, there is provided a substrate table including a plurality of protrusions configured to support a substrate, the substrate table including an actuator unit according to the present invention, wherein the actuator of the actuator unit is configured to actuate at least one of the protrusions.

[0027] According to one aspect of the present invention, there is provided a lithographic apparatus including an actuator unit according to the present invention.

[0028] According to one aspect of the present invention, there is provided an actuator array including:

[0029] a plurality of actuator units, each actuator unit including

[0030] at least one piezoelectric actuator,

[0031] a reference capacitor connected in series with the piezoelectric actuator,

[0032] a switch assembly configured to switch power to the at least one actuator,

[0033] a control circuit connected to the switch assembly and configured to control the switch assembly and including a serial control input,

[0034] a feedback line configured to provide a reference capacitor voltage representing the voltage across the reference capacitor to the control circuit,

[0035] wherein the piezoelectric actuator and the reference capacitor are arranged at a first location and the control circuit is arranged at a second location, wherein the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location,

[0036] a power line connected to at least the switch assembly of each actuator unit for powering at least the switch assembly of each actuator unit, and

[0037] a control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

[0038] According to one aspect of the present invention, there is provided a substrate table including a plurality of protrusions configured to support a substrate, the substrate table including an actuator array according to the present invention, wherein the actuators of the actuator array are configured to actuate at least a subset of the protrusions.

[0039] According to one aspect of the present invention, there is provided a lithographic apparatus including an actuator array or a substrate table according to the present invention. Description of the Drawings

[0040] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0041] Figure 1 A schematic overview of a lithographic apparatus according to an embodiment of the invention is depicted;

[0042] Figure 2 Depicted Figure 1 A detailed view of a part of the lithographic apparatus;

[0043] Figure 3 A position control system, which is part of a positioning system according to an embodiment of the invention, is schematically depicted;

[0044] Figure 4 A part of an actuator array according to an embodiment of the invention is schematically depicted;

[0045] Figure 5 A part of an actuator array according to another embodiment of the invention is schematically depicted;

[0046] Figure 6 A part of an actuator array according to yet another embodiment of the invention is schematically depicted;

[0047] Figure 7 A top view of a piezoelectric layer including a plurality of actuators that can be employed in an embodiment of the invention is depicted;

[0048] Figure 8 A side view of a part of an actuator array according to yet another embodiment of the invention is schematically depicted;

[0049] Figure 9 An actuator unit is schematically depicted;

[0050] Figure 10 An actuator unit according to an embodiment of the invention is schematically depicted;

[0051] Figure 11 An actuator unit according to another embodiment of the invention is schematically depicted; and

[0052] Figure 12 A part of an actuator array according to another embodiment of the invention is schematically depicted. Detailed Description

[0053] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and EUV radiation (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm).

[0054] As used in this invention, the term "reticle", "mask" or "patterning device" can be broadly interpreted to mean a general patterning device that can be used to endow an incoming radiation beam with a patterned cross-section corresponding to a pattern to be created in a target portion of a substrate. In this context, the term "light valve" can also be used. Examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays in addition to classical masks (transmission or reflection, binary, phase-shifting, hybrid, etc.).

[0055] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA includes: an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation); a reticle support (e.g., a reticle stage) MT configured to support a patterning device (e.g., a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., a portion including one or more dies) of the substrate W.

[0056] In operation, the illumination system IL receives the radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for guiding, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL can be used to condition the radiation beam B to have a desired spatial intensity distribution and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0057] The term "projection system" PS as used in the present invention should be broadly interpreted to cover various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof. Any term "projection lens" used herein may be considered synonymous with the more general term "projection system" PS.

[0058] The lithographic apparatus LA may be of the type in which at least a portion of the substrate is covered by an immersion liquid having a relatively high refractive index (e.g. water) in order to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US 6952253, which is incorporated herein by reference.

[0059] The lithographic apparatus LA may also be of the type having two or more substrate supports WT (also referred to as "dual platforms"). In such a "multi-platform" machine, the substrate supports WT can be used in parallel, and / or another substrate W on another substrate support WT can be used for exposing a pattern on another substrate W while the steps of preparing the substrate W on one of the substrate supports WT located in the substrate support are being carried out for a subsequent exposure of the substrate W.

[0060] In addition to the substrate support WT, the lithographic apparatus LA may also include a measurement platform. The measurement platform 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 platform may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system providing the immersion liquid. The measurement platform may move under the projection system PS when the substrate support WT is moved away from the projection system PS.

[0061] In operation, the radiation beam B is incident on a patterning device (e.g. a mask) MA held on the mask support MT and is patterned by the pattern (design layout) presented on the patterning device MA. After 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. By means of the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (in Figure 1(not explicitly depicted in [the figure]) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as illustrated occupy dedicated target portions, the marks can be located in the spaces between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, these substrate alignment marks are referred to as scribe alignment marks.

[0062] To illustrate the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, the y-axis and the z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is referred to as an Rx rotation. A rotation about the y-axis is referred to as an Ry rotation. A rotation about the z-axis is referred to as an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system is not limited to the present invention and is only used for illustration. As an alternative, another coordinate system (such as, a cylindrical coordinate system) can be used to illustrate the present invention. The directions of the Cartesian coordinate system can be different, for example, such that the z-axis has a component along the horizontal plane.

[0063] Figure 2 shows Figure 1 A more detailed view of a part of the lithographic apparatus LA. The lithographic apparatus LA can be provided with a base frame, a balancing 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 can support a part of the position measurement system PMS. The metrology frame MF is supported by the base frame via the vibration isolation system IS. The vibration isolation system IS is arranged to prevent or reduce the propagation of vibrations from the base frame to the metrology frame MF.

[0064] A second positioner PW is arranged to accelerate the substrate support WT by a driving force between the substrate support WT and the balancing mass BM. The driving force accelerates the substrate support WT in a desired direction. Due to the conservation of momentum, the driving force is also applied to the balancing mass BM in an equal magnitude but in a direction opposite to the desired direction. Typically, the mass of the balancing mass BM is significantly larger than the masses of the moving parts of the second positioner PW and the substrate support WT.

[0065] In an embodiment, the second positioner PW is supported by the balance mass BM. For example, wherein the second positioner PW includes a planar motor for levitating the substrate support WT on the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, wherein the second positioner PW includes a linear motor and wherein the second positioner PW includes bearings (such as gas bearings) for levitating the substrate support WT on the base frame.

[0066] The position measurement system PMS may include any type of sensor adapted to determine the position of the substrate support WT. The position measurement system PMS may include any type of sensor adapted to determine 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 has a combined system of an interferometer and an encoder. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor, or an inductive sensor. The position measurement system PMS may determine the 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 stage WT and / or the mask support MT by measuring the position or by measuring the time derivative of the position (such as velocity or acceleration).

[0067] The position measurement system PMS may include an encoder system. The encoder system is known from, for example, U.S. Patent Application US2007 / 0058173A1 filed on September 7, 2006, which is hereby incorporated by reference. The encoder system includes 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 originate 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 generated by diffracting the original radiation beam with the grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam with the grating, the primary radiation beam needs to have a different diffraction order from the secondary radiation beam. Different diffraction orders are, for example, +1 order, -1 order, +2 order, and -2 order. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. The sensor in the encoder head determines the phase or the phase difference of the combined radiation beam. The sensor generates a signal based on the phase or the 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 arranged on the substrate structure WT. The other of the encoder head and the grating may be arranged on the metrology frame MF or the base frame. For example, a plurality of encoder heads are arranged on the metrology frame MF, whereby the grating is arranged on the top surface of the substrate support WT. In another example, the grating is arranged on the bottom surface of the substrate support WT, and the encoder head is arranged below the substrate support WT.

[0068] The position measurement system PMS may include an interferometer system. The encoder system is known from, for example, U.S. Patent Application US6,020,964 filed on July 13, 1998, which is hereby incorporated by reference. The interferometer system may include a beam splitter, a mirror, a reference mirror, and a sensor. The radiation beam is split by the beam splitter into a reference beam and a measurement beam. The measurement beam propagates to the mirror and is reflected back to the beam splitter by the mirror. The reference beam propagates to the reference mirror and is reflected back to the beam splitter by the reference mirror. At the beam splitter, the measurement beam and the reference beam are combined into a combined radiation beam. The combined radiation beam is incident on the sensor. The combined radiation beam is the incident beam on the sensor. The sensor generates a signal based on the phase or the phase or the frequency. The signal represents the displacement of the mirror. In an embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to the metrology frame MF. In an embodiment, the measurement beam and the reference beam are combined into a combined radiation beam by additional optical components instead of the beam splitter.

[0069] The first positioner PM may include a long - stroke module and a short - stroke module. The short - stroke module is arranged to move the mask support MT relative to the long - stroke module with high accuracy over a small movement range. The long - stroke module is arranged to move the short - stroke module relative to the projection system PS with relatively low accuracy over a large movement range. Using the combination of the long - stroke module and the short - stroke module, the first positioner PM is capable of moving the mask support MT relative to the projection system PS with high accuracy over a large movement range. Similarly, the second positioner PW may include a long - stroke module and a short - stroke module. The short - stroke module is arranged to move the wafer support WT relative to the long - stroke module with high accuracy over a small movement range. The long - stroke module is arranged to move the short - stroke module relative to the projection system PS with relatively low accuracy over a large movement range. Using the combination of the long - stroke module and the short - stroke module, the second positioner PW is capable of moving the wafer support WT relative to the projection system PS with high accuracy over a large movement range.

[0070] The first positioner PM and the second positioner PW are each provided with an actuator for moving the mask support MT and the wafer support WT, respectively. The actuator may be a linear actuator for providing a driving force along a single axis (e.g., the y - axis). A plurality of 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 wafer 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 type actuator having the at least one magnet respectively coupled to the wafer support WT and the mask support MT. The actuator may be a moving - coil type actuator having the at least one coil respectively coupled to the wafer support WT and the mask support MT. The actuator may be a voice - coil actuator, a magnetoresistive actuator, a Lorentz actuator, or a piezoelectric actuator, or any other suitable actuator.

[0071] The lithographic apparatus LA includes a position control system PCS, such as Figure 3is schematically depicted. 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 the actuator ACT. The actuator ACT can be an actuator having the first positioner PM or the second positioner PW. The actuator ACT drives the facility P, which can include the substrate support WT or the mask support MT. The output of the facility P is a position quantity, such as position, velocity, or acceleration. The position quantity is measured by the position measurement system PMS. The position measurement system PMS generates a signal that is a position signal representing the position quantity of the facility P. The setpoint generator SP generates a signal that is a reference signal representing the desired position quantity of the facility P. For example, the reference signal represents the desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms the input to the feedback controller FB. Based on the input, the feedback controller FB provides at least a portion of the drive signal to the actuator ACT. The reference signal can form the input to the feedforward controller FF. Based on the input, the feedforward controller FF provides at least a portion of the drive signal to the actuator ACT. The feedforward FF can utilize information related to the dynamic characteristics of the facility P, such as mass, stiffness, resonance modes, and natural frequencies.

[0072] Figure 4 A schematic diagram depicting a portion of an actuator array according to an embodiment of the present invention is shown. The actuator array includes a power line PL and a control line CL, which are integrated in this example to form a single conductor. The power line supplies power to a plurality of actuator units AC, each actuator unit including at least one actuator ACT, a switch assembly SA connected to the actuator ACT and the power line PL to supply power from the power line to the actuator, and a control circuit CC. The control circuit CC is connected to the switch assembly to control the switching of the switch assembly. The switch assembly includes a serial control input SCI connected to the control line, and in this example, the control line is integrated with the power line, that is, the control line and the power line are the same electrical conductor. In this example, the switch assembly includes a charging switch CS connected between the power line and the switch assembly output and a discharging switch DS connected between the switch assembly output and ground. The actuator unit also includes an inductor or other low-pass filter LPF that connects the switch assembly output to the actuator. The switch of the switch assembly can include a controllable switch, such as a transistor, for example, a field effect transistor.

[0073] The switch of the switch assembly is controlled by a control device. For example, the switch is alternately driven into a conducting state, thereby driving the charging switch into a conducting state as long as the actuator is connected to the power line via an inductor, and driving the discharging switch into a conducting state as long as the actuator is connected to ground via an inductor. Thus, the actuator can be alternately charged and discharged. The ripple of the switch can be suppressed or at least reduced by an inductor or other low-pass filter. The duty cycle of the switch, i.e., the duty cycles of activating the charging switch and the discharging switch, can be set to enable setting the actuator voltage between the power supply voltage of the power line and ground.

[0074] The actuator can include, for example, a piezoelectric actuator. Setting the actuator voltage can enable controlling the actuation (e.g., displacement) of the piezoelectric actuator. Figure 4 Three actuator units in the actuator unit are depicted, namely actuator unit 1, actuator unit 2, and actuator unit N. It will be understood that multiple actuator units can be driven, whereby a single conductor power line and a single control line can be used, or as in a preset embodiment, a combined power line and control line can be used.

[0075] The power line can supply a power supply voltage to the actuator unit. Control data can be superimposed, for example, in the form of a high-frequency signal. Each actuator unit can include, for example, a high-pass filter, such as a capacitor, connected between the serial control input of the control unit and the power line to filter the DC or low-frequency power voltage of the combined power and control on a single line, so as to enable sending the serial control data to the control unit of the actuator unit. The control data can be sent in the form of serial control data.

[0076] Instead of a combined power line and control line, separate power lines and control lines can be used.

[0077] Control data can be addressed to one or more of the actuator units. For example, a corresponding address can be assigned to each actuator unit. The address can be stored in the control circuit of the actuator unit. For example, each actuator unit is provided with a unique address, or a group of actuator units is provided with the same address. The control data can be sent by sending the address of the actuator unit to which the control data is directed via the control line, and the control data. For example, the address can be sent, and the control data can be sent after the address. The sending can be, for example, before a start bit or a synchronization bit, and can include an end bit or a synchronization bit after the sending of the address and / or the control data. The address can be sent as binary data. The control data can be sent as binary data. The sending at the control line is received by all actuator units, in particular by all control units of the actuator units. One or more control units whose address corresponds to the sent address can respond to the sending by executing the control data. The control data can, for example, include actuator variables such as actuator drive signal amplitude. The control data can, for example, include an actuator drive voltage value or an actuator PWM duty cycle value. The control circuit can drive the switching component in accordance with the control data in response to the control data addressed to it. In the case where multiple control circuits have been assigned the same address, these control circuits can all respond to the control data addressed to these control circuits, i.e., the control data addressed to these actuator units.

[0078] In an embodiment, the control data can be broadcast to multiple actuator units simultaneously. The control circuit of the actuator unit can be configured to respond to the broadcast, which addresses the control data associated with the broadcast to multiple actuator units. Thereby, for example, multiple actuators can be actuated simultaneously.

[0079] For illustrative purposes, Figure 4 three actuator units are depicted, and Figure 5 and Figure 6 each depict two actuator units. In reality, hundreds, thousands, or tens of thousands of actuator units can be included in an actuator array.

[0080] Figure 5FIG. depicts another embodiment of an actuator array according to the present invention. The actuator array also includes a power line PL and a control line CL, which are integrated into a single combined power and control line and are connected to a plurality of actuator units AC. The power line is powered by a power supply PRS, and a control system CS for sending a serial control signal to the actuator units is connected in series with the power supply. Each actuator unit includes an actuator ACT, a switch assembly SA, and a control circuit CS for driving the switch assembly. In this embodiment, the switch assembly includes a switching mode converter. The switching mode converter is configured to convert the power line voltage at the power line into an actuator voltage to drive the actuator. In this example, the switching mode converter includes a boost 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 through its first inductor terminal and is connected to the second switch connected between the second inductor terminal and ground through its second inductor terminal. The second switch is connected between the second inductor terminal and the actuator. The control circuit is connected to the first switch and the second switch to control these switches to enter the conducting state and the non-conducting state, respectively. For example, the control circuit operates the first switch and the second switch at the boost converter switching frequency, whereby when the second switch is conducting, the inductor current increases due to the power line voltage across the inductor, and when the second switch is driven to stop conducting, the inductor voltage at the second inductor terminal rises due to the inductive characteristics of the inductor, and the first switch is driven to the conducting state to connect the second inductor terminal to the actuator. Accordingly, a boost converter is provided, which is configured to provide an actuator voltage that exceeds the power line voltage to the actuator. Thus, a high actuator voltage can be provided while keeping the power line voltage at a lower level. The duty cycle of the switching of the first switch and the second switch can be set such that the actuator voltage can be controlled. Accordingly, each actuator can be driven at a corresponding actuator voltage by a corresponding control circuit that controls the duty cycles of the corresponding first switch and second switch of the actuator unit. As another example of controlling the switches by the control circuit, in the absence of a resistive load, a stable output voltage (c.q. piezoelectric charge) can be achieved as follows. Increasing the output voltage can be achieved by first closing the second switch SSW. This charges the inductor to a current level and energy that depends on the supply voltage, switch activation time, and inductor value. When the second switch SSW is deactivated, the first switch FSW closes, which transfers the inductor energy to a load capacitor included by a piezoelectric element (with or without its series reference capacitor), thereby increasing the load voltage. Reducing the output voltage can be performed by activating the first switch FSW. In the case where the output voltage is greater than the supply voltage, this results in an energy return from the load capacitor (i.e., the piezoelectric actuator), thereby reducing its voltage by an amount that depends on the supply and load voltages, switch activation time, and inductor value.When the first switch FSW is deactivated, the second switch SSW takes over the accumulated inductor current and releases it into the power supply without further affecting the output voltage. The overall result can be that the load voltage can be controlled in energy quanta defined by the voltage and initial activation time of the SSW for increasing the output voltage and the FSW for decreasing the output voltage. Additionally, when the load voltage needs to be stabilized, it may not be necessary to activate the switches, which can avoid dissipation of switching and conduction losses in the switching elements. Assuming that changes in the output voltage can occur only sparsely in time, this can significantly reduce the magnetic head load on the wafer and the wafer stage.

[0081] As Figure 5 further depicted, the control circuit is connected to the control line (in this example, the combined power line and control line) through a high-pass filter HPF (such as a capacitor in this example) to enable serial control data while blocking the DC power supply voltage at the combined power line and control line. The high-pass filter is connected to the serial control input of the control circuit to enable passing the serial control data to the serial control input.

[0082] The control circuit and the switch assembly can be included in an integrated circuit, such as an application-specific integrated circuit ASIC or a field-programmable gate array FPGA, which can facilitate a compact implementation of each actuator unit.

[0083] In an embodiment, the converter can be a bidirectional converter. When the control circuit drives the converter to increase the actuator voltage, power is drawn from the power line by the bidirectional converter. When the control circuit drives the converter to decrease the actuator voltage, electrical energy is fed back into the power line by the bidirectional converter, thereby reducing the power consumption of the actuator array.

[0084] Figure 6 Another embodiment of the actuator array according to the present invention is depicted. The actuator array also includes a power line PL and a control line CL, which are integrated into a single combined power line and control line, connected to a plurality of actuator units AC, each actuator unit including an actuator ACT, a switch assembly SA, and a control circuit CC for driving the switch assembly. In this embodiment, the switch assembly includes a switched-mode converter. The switched-mode converter is configured to convert the power line voltage at the power line into an actuator voltage to drive the actuator. In this example, the switched-mode converter includes a boost converter, i.e., a boost converter formed by an inductor L, a plurality of first switches FSW, and a second switch SSW. The inductor is connected to the power line through its first inductor terminal and to the second switch connected between the second inductor terminal and ground through its second inductor terminal. The first switch is connected between the second inductor terminal and the corresponding actuator. AndFigure 5 Compared with the embodiments depicted in Figure 6 the embodiments depicted in can be capable of driving multiple actuators through the same control circuit.

[0085] For example, the control circuit operates the first switch and the second switch at the boost converter switching frequency, whereby when the second switch is turned on, the inductor current increases due to the power line voltage across the inductor, and when the second switch is driven to stop conducting, the inductor voltage at the second inductor terminal rises due to the inductive characteristic of the inductor, and one of the first switches is driven to the on state to connect the second inductor terminal to the corresponding actuator associated with the respective first switch. Accordingly, a boost converter is provided, which is configured to supply an actuator voltage exceeding the power line voltage to the actuator. Switching all the first switches of the actuator unit at the boost converter switching frequency in the on state can enable the same actuator voltage to be supplied to all the actuators of the actuator unit. Alternatively, the actuators of the actuator unit can be driven one by one, whereby the control circuit drives the second switch and one of the first switches associated with one of the actuators at the switching frequency to drive the corresponding actuator. As will be understood from the above reference Figure 5 the description of, the first switch and the second switch are the same as those of the embodiments described in reference Figure 5 and are driven in anti-phase. After driving one actuator of the actuator unit for a plurality of repetitive time periods at the boost converter switching frequency, the desired actuator voltage can be applied to the actuator, after which the control circuit can stop the switching of one of the first switches. Thus, the first switches can be operated sequentially one by one to drive the corresponding actuators of the actuator unit sequentially one by one. For each of the actuators, setting the duty ratio of the switching of the corresponding first switch and second switch can enable the corresponding actuator voltage to be controlled. Accordingly, each actuator of the actuator unit can be driven at the corresponding actuator voltage by the control circuit, which controls the duty ratio of the corresponding first switch associated with the corresponding actuator and the second switch of the actuator unit. As another example of the control circuit controlling the switches, as referred to above in reference Figure 5As described, in the absence of a resistive load, a stable output voltage (c.q. piezoelectric charge) can be achieved as follows. Increasing the output voltage can be achieved by first closing the second switch SSW. This charges the inductor to a current level and energy that depends on the supply voltage, the switch activation time, and the inductor value. When the second switch SSW is deactivated, the first switch FSW is closed, which transfers the inductor energy to the load capacitor included by the piezoelectric element (with or without its series reference capacitor), thereby increasing the load voltage. Reducing the output voltage can be performed by activating the first switch FSW. In the case where the output voltage is greater than the supply voltage, this results in an energy return from the load capacitor (i.e., the piezoelectric actuator), thereby reducing its voltage by an amount that depends on the supply and load voltages, the switch activation time, and the inductor value. When the first switch FSW is deactivated, the second switch SSW takes over the accumulated inductor current and releases it to the power supply without further affecting the output voltage. The overall result can be that the load voltage can be controlled in energy quanta defined by the voltage and initial activation time of the SSW for increasing the output voltage and the FSW for reducing the output voltage. Additionally, when the load voltage needs to be stabilized, it may not be necessary to activate the switches, which can avoid the dissipation of switching and conduction losses in the switch elements. Assuming that the change in the output voltage can occur only sparsely in time, this can significantly reduce the magnetic head load on the wafer and the wafer stage.

[0086] To drive multiple actuators of an actuator unit individually, each actuator at its actuator voltage, the control circuit of the actuator unit can be assigned multiple addresses, e.g., a corresponding address for each actuator. The addresses of the actuators can be stored in the memory of the control circuit. Thus, the actuator assembly can be configured to send control data for the multiple actuators of the control circuit to each of the addresses of the actuators of the control circuit via the control lines by serial transmission.

[0087] In the actuator array described in reference Figure 4 、 Figure 5 and Figure 6 the actuators can be piezoelectric actuators having an inherent actuator capacitance. The actuator capacitance can be used as a holding circuit to hold the actuator voltage supplied to the actuator. Thus, when the actuator has been driven by the operation of the switches of the switch assembly, the actuator can hold the actuator voltage until the actuator is driven again by its actuator capacitance. Therefore, since the actuators of the actuator units in Figure 6 can be addressed one by one via the serial control lines of the serial control, the actuators can be driven one by one correspondingly, thereby holding the actuator voltage until the next drive of the same actuator. The holding capacitance can be increased by providing a capacitor in parallel with the actuator.

[0088] Figure 7 Depicts a top view of a plurality of actuators ACT that can be included in an actuator array according to the present invention. The actuators can be piezoelectric actuators, each piezoelectric actuator being configured to actuate a node. The top surface of the node can provide a substrate-bearing surface. Power lines and control lines or combined power line / control lines can be arranged substantially parallel to the plane of the substrate-bearing surface, for example, below the substrate-bearing surface SCS, to facilitate electrical connection of the actuator units to the power lines and control lines respectively. The actuators can be configured, for example, in the vertical direction, i.e., in the Z direction, so as to actuate the nodes in a direction substantially perpendicular to the substrate-bearing surface. The actuators can also be configured to actuate the nodes in a direction parallel to the substrate-bearing plane, for example, in the X direction or the Y direction, for example, in combination with actuation in the Z direction. For example, the actuators can be configured to actuate the nodes in the Z direction, the X direction, the Y direction, the Z direction and the X direction, the Z direction and the Y direction, the X direction and the Y direction, or the Z direction, the X direction and the Y direction. Generally, throughout this document, the actuators can be configured to actuate in the vertical direction, i.e., in the Z direction, in the X direction or in the Y direction. The X and Y directions define a substantially horizontal plane. In another embodiment, generally, throughout this document, the actuators can be configured to actuate in any combination of the X, Y, and Z directions, for example, in the Z direction, in the X direction, in the Y direction, in the Z and X directions, in the Z and Y directions, in the Z, X, and Y directions, or in the X and Y directions.

[0089] According to an embodiment of the present invention, a substrate table includes a plurality of nodes configured to support a substrate, the substrate table including an actuator array as described above, wherein the actuators of the actuator array are configured to actuate at least a subset of the nodes. The lithographic apparatus can include a lithographic apparatus substrate table and / or an actuator array according to the present invention.

[0090] According to the present invention, the actuators can be configured to actuate (i.e., move and / or generate force) in any direction. For example, the actuators can be configured to actuate in the vertical direction. As another example, the actuators can be configured to actuate in the horizontal direction. As yet another example, the actuators can be configured to actuate in the horizontal and vertical directions, such as in the x, y, and z directions.

[0091] In the above example of the substrate table, the actuators can be configured to move the substrate in the vertical direction, in the horizontal direction, or in the horizontal and vertical directions. For example, the actuators can be configured to actuate in three dimensions. By actuating the substrate in the horizontal direction, the actuators can position the substrate in the horizontal plane, which can help reduce overlay errors in the lithographic apparatus.

[0092] The actuator can include any type of actuator. For example, in the case of a piezoelectric actuator, a shear actuator can be used to actuate in the horizontal direction. For example, the substrate table according to the present invention includes a plurality of protrusions configured to support a substrate, the substrate table including an actuator array as described above, wherein the actuators of the actuator array are configured to actuate at least a subset of the protrusions in the vertical and horizontal directions. Actuating the protrusions in the horizontal direction, for example using a shear actuator, can enable reduction of overlay errors.

[0093] Figure 8 Another embodiment is depicted, in which the mirror MR includes a mirror surface MRS, and the mirror is provided with a plurality of actuators ACT, which are arranged on a carrier CR and configured to apply a force on a ceramic substrate CRS that can hold the mirror MR. The ceramic substrate CRS is arranged between the plurality of actuators and the mirror. Power lines and control lines or combined power line / control lines can be provided to be substantially parallel to the plane of the mirror surface, for example, below the mirror surface, to facilitate electrical connection of the actuator units to the power lines and control lines respectively. The mirror can be included in a projection system of a lithographic apparatus.

[0094] Figure 9 At least a part of an actuator unit including a piezoelectric actuator ACT is depicted, the piezoelectric actuator having a capacitance indicated by C piezo 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. Thus, the control circuit and the amplifier form a feedback loop in response to the setpoint signal to drive the actuator.

[0095] The actuator unit further includes a reference capacitor C refWhen the reference capacitor and the piezoelectric actuator form a capacitively coupled series connection, the actuator drive current supplied by the amplifier to the piezoelectric actuator also flows through the reference capacitor. Since the capacitance of the reference capacitor can be accurately known, the voltage across the reference capacitor can accurately reflect the charge held by the reference capacitor. Since the reference capacitor and the piezoelectric actuator are in series connection and are subject to the same actuator current, the charge held by the reference capacitor will reflect the charge held by the piezoelectric actuator. In an embodiment, a resistor is placed in parallel with the actuator and the reference capacitor to obtain the defined low-frequency behavior. The resistor in parallel with the actuator and the reference capacitor can result in a cut-off frequency below which the charge amplifier effectively behaves as a voltage amplifier and is thus capable of providing the defined and desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the high-frequency voltage gain defined by the capacitors (i.e., the capacitances of the actuator and the reference capacitor).

[0096] The piezoelectric actuator may exhibit hysteresis, resulting in a non-linearity between the actuator drive signal and the displacement (position, force) of the piezoelectric actuator. It has been observed that the degree of hysteresis can vary, depending on whether voltage drive, current drive or charge drive is used. More specifically, it has been observed that in the case of charge drive, the hysteresis can be smaller compared to voltage drive. By means of the reference capacitor, charge drive can be achieved, whereby the feedback signal supplied to the controller is obtained from the voltage across the reference capacitor.

[0097] As Figure 9 depicted, the actuator is arranged at a first location, while the control circuit, amplifier and reference capacitor are arranged at a second location remote from the first location. A cable, such as a coaxial cable, extends between the first and second locations to supply an actuator drive signal to one terminal of the actuator and to connect the other terminal of the actuator in series with the reference capacitor. The parasitic capacitance between the conductors of the cable can extend along the length of the cable and is symbolically indicated by C1 and C2 between the conductors in Figure 9 . The series resistance of the conductors of the cable is symbolically represented by R 1a , R 2a , R 3a in one conductor and by R 1b , R 2b , R 3b in the other conductor.

[0098] As referenced Figure 9The described configuration can work satisfactorily as long as the capacitances of the actuator and the reference capacitor are large compared to the parasitic capacitance of the cable. In the case where the distance between the control circuit and the actuator (i.e., the distance between the first part and the second part) increases, the cable capacitance may increase due to the increased cable length. The movement of the actuator may cause a change in the parasitic capacitance of the cable, which may affect the charge control, especially when the cable capacitance is relatively large. In addition, such a large cable capacitance in parallel with the actuator may affect the described charge control because the larger the cable capacitance relative to the actuator capacitance, the more charge will be absorbed by the cable, thus deviating from the charge control, which may increase the hysteresis. The above effects may be further exacerbated due to a decrease in the actuator capacitance, for example, due to a piezoelectric actuator of a smaller size, resulting in a relatively larger capacitance of the cable.

[0099] Figure 10 An embodiment of an actuator unit according to the present invention is depicted, the actuator unit being different from the actuator unit depicted and referenced Figure 9 as in Figure 9 described in that the reference capacitor is arranged at the first part, i.e., at the part of the actuator.

[0100] Figure 10 At least a part of an actuator unit including a piezoelectric actuator ACT is depicted, the piezoelectric actuator having a capacitance indicated by C piezo 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 the actuator setpoint signal SET and the 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. Thus, the control circuit and the amplifier form a feedback loop in response to the setpoint signal to drive the actuator.

[0101] The actuator unit further includes a reference capacitor C refAs explained above, when the reference capacitor and the piezoelectric actuator form a capacitively coupled series connection, the actuator drive current supplied by the amplifier to the piezoelectric actuator also flows through the reference capacitor. Since the capacitance of the reference capacitor can be accurately known, the voltage across the reference capacitor can accurately reflect the charge held by the reference capacitor. Since the reference capacitor and the piezoelectric actuator are in series connection and are subject to the same actuator current, the charge held by the reference capacitor will reflect the charge held by the piezoelectric actuator. In an embodiment, a resistor is placed in parallel with the actuator and the reference capacitor to obtain a defined low-frequency behavior. The resistor in parallel with the actuator and the reference capacitor can result in a cut-off frequency below which the charge amplifier effectively behaves as a voltage amplifier and is thus capable of providing a defined and desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the high-frequency voltage gain defined by the capacitors (i.e., the capacitances of the actuator and the reference capacitor). The resistor can be placed at the amplifier, i.e., at the second location, and / or locally at the actuator and the reference capacitor, i.e., at the first location.

[0102] As Figure 10 depicted in, the actuator and the reference capacitor are arranged at a first location, while the control circuit and the amplifier are arranged at a second location remote from the first location. A cable such as a coaxial cable extends between the first location and the second location. Via the actuator line of the cable, i.e., the conductor of the cable, the actuator drive signal is provided to one terminal of one of the actuator and the reference capacitor. The other terminal of one of the actuator or the reference capacitor is connected in series with one terminal of the other of the actuator and the reference capacitor. The other terminal of the other of the actuator and the reference capacitor is connected to electrical ground via the return conductor of the cable (also referred to as the return line of the cable). A feedback signal representing the voltage across the reference capacitor is provided from the first location to the second location by the feedback line FL of the cable. Similar to Figure 9 , the parasitic capacitance between the conductors of the cable can extend along the length of the cable and is symbolically indicated by C1 and C2 between the conductors in Figure 10 . The series resistance of the conductors of the cable is symbolically represented by R 1a , R 2a , R 3a in one conductor and by R 1b , R 2b , R 3b in the other conductor.

[0103] In Figure 10In the embodiment depicted, the terminal of the reference capacitor connected to the actuator is connected to the feedback line, i.e., directly providing a feedback signal to the control circuit. Since the cable capacitance can affect the measurement of the charge held by the actuator, for example, via the cable capacitance of the feedback line of the cable, in a similar manner as described above with reference to Figure 9 sensitivity may occur.

[0104] In Figure 11 the embodiment depicted, the actuator unit further includes a preamplifier PA at a first location, which amplifies the reference capacitor voltage across the reference capacitor. The voltage gain of the preamplifier can be one or more than one, and the preamplifier actually buffers the reference capacitor voltage. The preamplifier can include a high-impedance preamplifier input. The output of the preamplifier is connected to the feedback line of the cable and provides a feedback signal to the control circuit. As a result of the combination of the preamplifier, the influence of the cable on the feedback signal can be at least reduced. In an embodiment, a resistor is placed in parallel with the actuator and the reference capacitor to obtain a defined low-frequency behavior. The resistor in parallel with the actuator and the reference capacitor can result in a cut-off frequency below which the charge amplifier actually behaves as a voltage amplifier and is thus able to provide a defined and desired low-frequency behavior. For example, the low-frequency voltage gain defined by the resistor is set to the same value as the high-frequency voltage gain defined by the capacitor (i.e., the capacitance of the actuator and the reference capacitor). In accordance with Figure 11 the configuration, the resistors can be placed separately at the actuator and the reference capacitor, i.e., at the first location.

[0105] The charge control using a reference capacitor connected in series with the actuator and arranged near the actuator can also be employed in the embodiment as described above with reference to Figures 4 to 6 The example is schematically depicted in Figure 12 and will be explained with reference to Figure 12 A height schematic diagram of an actuator unit similar to the actuator unit described above with reference to Figure 12 is depicted, which is provided with a reference capacitor and the charge control as described above with reference to Figure 5 Thus, in addition to what has been described with reference to Figure 10 and Figure 11 the actuator unit further includes a reference capacitor C Figure 5 connected in series with the actuator ACT. The actuator (i.e., the piezoelectric actuator) and the reference capacitor can be arranged at the first location, while the control circuit and the switch assembly are arranged at a second location remote from the first location. As referred to in ref As in reference Figure 11As described, the preamplifier PRA can be used to buffer the reference capacitor voltage that forms the feedback signal. The control circuit CC can utilize the feedback signal representing the charge in the reference capacitor and thus the charge in the piezoelectric actuator to drive the switch assembly SA. The control circuit can derive the setpoint from the data obtained at the serial control input SCI. The actuator unit also includes a modulator MOD, which is electrically connected to the control circuit to be driven by the control circuit. The modulator is configured to drive the first switch and the second switch of the switch assembly to charge and discharge the piezoelectric actuator, respectively. Although in Figure 12 the preamplifier is depicted as being located near the control circuit, the preamplifier can be located near the actuator and the reference capacitor, i.e., at the first location instead of the second location. Charge control according to Figure 12 added to the embodiment described with reference to Figures 4 to 6 can provide accurate driving of the piezoelectric actuator because the described charge control may be less sensitive to actuator hysteresis and because the arrangement of the reference capacitor close to the piezoelectric actuator (i.e., at the same end of the cable interconnecting the actuator and the control circuit) can reduce the adverse effects of cable parasitics such as cable capacitance on accuracy. In an embodiment according to Figure 12 similar to the embodiment according to Figures 4 to 6 , compared to the cable lengths in the embodiments of Figure 10 and Figure 11 , the cable length can be relatively small. In other words, in an embodiment according to Figure 12 similar to the embodiment according to Figures 4 to 6 , compared to the distance between the first location and the second location in the embodiments of Figure 10 and Figure 11 , the distance between the first location and the second location can be relatively small. In the embodiments described with reference to Figures 4 to 6 and Figure 12 , the power lines and control lines can enable the distribution of power and control data such that the control circuit and the switch can be positioned closer to the actuator, which can result in a shorter cable to the actuator, i.e., a shorter distance between the first location and the second location.

[0106] This document describes multiple sets of embodiments, namely, a first set of embodiments described with reference to Figures 4 to 6 , a second set of embodiments described with reference to Figures 9 to 10 , and a reference Figure 11A third set of described embodiments. The actuator can be a piezoelectric actuator. Unless the actuator is specifically identified as a piezoelectric actuator, the actuator can be any other suitable actuator, such as any other capacitive actuator. The actuators in the first, second, and third sets of inventions can be the same as each other, or they can also be different from each other. Thus, the actuator in the first set of inventions can be identified as the first actuator, the actuator in the second set of inventions can be identified as the second actuator, and the actuator in the third set of inventions can be identified as the third actuator.

[0107] The actuator units in the first, second, and third sets of inventions can be the same as or different from each other. Thus, the actuator unit in the first set of inventions can be identified as the first actuator unit, the actuator unit in the second set of inventions can be identified as the second actuator unit, and the actuator unit in the third set of inventions can be identified as the third actuator unit.

[0108] The control circuits described in the first, second, and third sets of inventions can be the same as or different from each other. Thus, the control circuit in the first set of inventions can be identified as the first control circuit, the control circuit in the second set of inventions can be identified as the second control circuit, and the control circuit in the third set of inventions can be identified as the third control circuit.

[0109] Although specific reference may be made herein to the use of a lithographic apparatus in IC manufacture, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, the guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0110] Although specific reference is made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention can be used in other apparatuses. Embodiments of the invention can form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). These apparatuses are generally referred to as lithographic tools. Such lithographic tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0111] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be understood that, where the context allows, the invention is not limited to optical lithography and can be used in other applications, such as imprint lithography.

[0112] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof, as circumstances permit. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium and executable by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine, such as a computing device. For example, machine-readable magnetic storage media may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash storage devices; electrical, optical, acoustic, or other forms of propagated signals (such as carrier waves, infrared signals, digital signals, etc.). Additionally, in this document, firmware, software, routines, and instructions may be described as performing certain actions. However, it should be understood that such descriptions are for convenience only, and these actions are actually generated by a computing device, processor, controller, or other device that executes the firmware, software, routines, instructions, etc., and doing so enables the actuator or other device to interact with the physical world.

[0113] While specific embodiments of the present invention have been described above, it will be understood that the present invention may be practiced in ways different from those described. The above description is intended to be exemplary, not restrictive. Other aspects of the present invention are set forth in the following numbered aspects.

[0114] 1. An actuator array, comprising:

[0115] A plurality of actuator units, each actuator unit comprising:

[0116] At least one actuator,

[0117] A switch assembly configured to switch power to the at least one actuator,

[0118] A control circuit connected to the switch assembly and configured to control the switch assembly and including a serial control input,

[0119] A power line connected to at least the switch assembly of each actuator unit for powering at least the switch assembly of each actuator unit, and

[0120] A control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

[0121] 2. The actuator array according to aspect 1, wherein the control line is integrated with the power line, and wherein each actuator unit includes a high-pass filter connected between the power line and the serial control input.

[0122] 3. The actuator array according to any one of the foregoing aspects, wherein the switch assembly includes a switching mode converter.

[0123] 4. The actuator array according to aspect 3, each actuator unit including a plurality of actuators, wherein for each of the plurality of actuators of each actuator unit, the switching mode converter includes a respective first switch associated with a respective one of the plurality of actuators of the actuator unit.

[0124] 5. The actuator array according to aspect 4, wherein the control circuit is configured to operate the switching mode converter to sequentially power the plurality of actuators of each actuator unit by sequentially operating the first switches associated with the respective actuators of the plurality of actuators of the actuator unit in an on state.

[0125] 6. The actuator array according to any one of aspects 3 to 5, wherein the switching mode converter includes a bidirectional converter.

[0126] 7. The actuator array according to any one of the foregoing aspects, wherein the voltage line includes a conductive plane.

[0127] 8. The actuator array according to any one of the foregoing aspects, wherein each actuator includes a piezoelectric actuator.

[0128] 9. The actuator array according to any one of the foregoing aspects, wherein each of the control circuits in the control circuit is associated with a respective address, and wherein the control circuit is configured to be individually addressable by addressing control data to the respective address via the control line.

[0129] 10. The actuator array according to any one of the foregoing aspects, wherein each of the control circuits is configured to be addressable by broadcasting control data via the control line.

[0130] 11. The actuator array according to any one of the foregoing aspects, wherein the control circuit includes one of an ASIC, an FPGA, or a PCB.

[0131] 12. The actuator array according to any one of the foregoing aspects, further comprising a control transmitter configured to send serial control data to the actuator unit via the control line.

[0132] 13. The actuator array according to any one of the foregoing aspects, wherein the switch assembly includes the switching mode converter, and the switching mode converter includes:

[0133] An inductor,

[0134] at least one first switch configured to electrically connect the inductor to the at least one actuator, and

[0135] a second switch configured and arranged to electrically connect the inductor between the power line and ground,

[0136] wherein the control circuit is configured to alternately:

[0137] operate the second switch in an on state to electrically connect the inductor between the power line and ground so that inductor current can flow between the power line and ground, and operate the first switch in an off state, and

[0138] operate the second switch in an off state and operate the first switch in an on state to electrically connect the inductor to the at least one actuator.

[0139] 14. A substrate table comprising a plurality of protrusions configured to support a substrate, the substrate table comprising an actuator array according to any one of the foregoing aspects, wherein the actuators of the actuator array are configured to at least actuate a subset of the protrusions.

[0140] 15. The substrate table according to aspect 14, wherein the control lines are integrated with the power lines and extend in a plane substantially parallel to the substrate holding surface defined by the protrusions.

[0141] 16. A lithographic apparatus comprising a substrate table according to aspect 14 or 15.

[0142] 17. A lithographic apparatus comprising an actuator array according to any one of aspects 1 to 13.

[0143] 18. An actuator unit comprising:

[0144] a piezoelectric actuator;

[0145] a reference capacitor connected in series with the piezoelectric actuator;

[0146] a control circuit configured to control the piezoelectric actuator and the reference capacitor;

[0147] a feedback line configured to provide a reference capacitor voltage representing the voltage across the reference capacitor to the control circuit;

[0148] Wherein the piezoelectric actuator and the reference capacitor are arranged at a first location, and the control circuit is arranged at a second location, wherein the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location.

[0149] 19. The actuator unit according to aspect 18, wherein the actuator unit further comprises a preamplifier, the preamplifier being arranged at the first location and configured to amplify the voltage across the reference capacitor, an output terminal of the preamplifier being connected to the feedback line, the preamplifier being configured to output the amplified reference capacitor voltage onto the feedback line.

[0150] 20. The actuator unit according to aspect 18 or 19, wherein the actuator unit further comprises:

[0151] a switch assembly configured to switch power to a series connection of the piezoelectric actuator and the reference capacitor,

[0152] the control circuit being connected to the switch assembly and configured to control the switch assembly.

[0153] 21. The actuator unit according to any one of aspects 18 to 20, wherein the actuator unit further comprises an amplifier configured to drive a series connection of the piezoelectric actuator and the reference capacitor, wherein the control circuit is connected to the amplifier and configured to control the amplifier.

[0154] 22. The actuator unit according to aspect 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 comprising 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.

[0155] 23. A substrate table comprising a plurality of protrusions configured to support a substrate, the substrate table comprising the actuator unit according to any one of aspects 18 to 22, wherein the actuator of the actuator unit is configured to actuate at least one of the protrusions.

[0156] 24. A lithographic apparatus comprising the substrate table according to aspect 23.

[0157] 25. A lithographic apparatus comprising the actuator unit according to any one of aspects 18 to 22.

[0158] 26. An actuator array, comprising:

[0159] A plurality of actuator units, each actuator unit comprising:

[0160] At least one piezoelectric actuator,

[0161] A reference capacitor, the reference capacitor being connected in series with the piezoelectric actuator,

[0162] A switch assembly configured to switch power to the at least one piezoelectric actuator,

[0163] A control circuit connected to the switch assembly and configured to control the switch assembly and including a serial control input,

[0164] A feedback line configured to provide a reference capacitor voltage representing the voltage across the reference capacitor to the control circuit,

[0165] Wherein the piezoelectric actuator and the reference capacitor are arranged at a first location, and the control circuit is arranged at a second location, wherein the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location,

[0166] A power line connected to at least the switch assembly of each actuator unit for powering at least the switch assembly of each actuator unit, and

[0167] A control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

[0168] 27. The actuator array according to aspect 26, wherein each actuator unit further comprises a preamplifier arranged at the first location and configured to amplify the voltage across the reference capacitor, an output of the preamplifier being connected to the feedback line, the preamplifier being configured to output the amplified reference capacitor voltage onto the feedback line.

[0169] 28. The actuator array according to aspect 26 or 27, wherein each actuator unit further comprises 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.

[0170] 29. The actuator array according to any one of aspects 26 to 28, wherein the control line is integrated with the power line, and wherein each actuator unit includes a high-pass filter connected between the power line and the serial control input.

[0171] 30. The actuator array according to any one of the foregoing aspects 26 or 29, wherein the switching component includes a switched-mode converter.

[0172] 31. The actuator array according to aspect 30, each actuator unit including a plurality of actuators, wherein for each of the plurality of actuators in each actuator unit, the switched-mode converter includes a respective first switch associated with a respective one of the plurality of actuators in the actuator unit.

[0173] 32. The actuator array according to aspect 31, wherein the control circuit is configured to operate the switched-mode converter to sequentially power each of the plurality of actuators in each actuator unit by sequentially operating the first switches associated with the respective actuators in the plurality of actuators in the actuator unit in an on state.

[0174] 33. The actuator array according to any one of aspects 26 to 32, wherein the switched-mode converter includes a bidirectional converter.

[0175] 34. The actuator array according to any one of the foregoing aspects 26 to 33, wherein the voltage line includes a conductive plane.

[0176] 35. The actuator array according to any one of the foregoing aspects 26 to 34, wherein each actuator includes a piezoelectric actuator.

[0177] 36. The actuator array according to any one of the foregoing aspects 26 to 35, wherein each control circuit in the control circuit is associated with a respective address, and wherein the control circuit is configured to be individually addressable by addressing control data to the respective address via the control line.

[0178] 37. The actuator array according to any one of the foregoing aspects 26 to 36, wherein each of the control circuits is configured to be addressable by broadcasting control data via the control line.

[0179] 38. The actuator array according to any one of the foregoing aspects 26 to 37, wherein the control circuit includes one of an ASIC, an FPGA, or a PCB.

[0180] 39. The actuator array according to any one of the foregoing aspects 26 to 38 further includes a control transmitter configured to send serial control data to the actuator units via the control lines.

[0181] 40. The actuator array according to any one of the foregoing aspects 26 to 39, wherein the switch assembly includes the switch mode converter, and the switch mode converter includes:

[0182] An inductor,

[0183] At least one first switch configured to electrically connect the inductor to the at least one actuator, and

[0184] A second switch configured and arranged to electrically connect the inductor between the power line and ground,

[0185] Wherein the control circuit is configured to alternately:

[0186] Operate the second switch in the on state to electrically connect the inductor between the power line and ground so that the inductor current can flow between the power line and the ground, and operate the first switch in the off state, and

[0187] Operate the second switch in the off state and operate the first switch in the on state to electrically connect the inductor to the at least one actuator.

[0188] 41. A substrate table includes a plurality of protrusions configured to support a substrate, and the substrate table includes the actuator array according to any one of the foregoing aspects 26 to 40, wherein the actuators of the actuator array are configured to actuate at least a subset of the protrusions.

[0189] 42. The substrate table according to aspect 41, wherein the control lines are integrated with the power lines and extend in a plane substantially parallel to the substrate holding surface defined by the protrusions.

[0190] 43. A lithographic apparatus includes the substrate table according to aspect 41 or 42.

[0191] 44. A lithographic apparatus includes the actuator array according to any one of the foregoing aspects 26 to 40.

Claims

1. An actuator array, comprising: A plurality of actuator units, each actuator unit comprising: At least one actuator, A switching component configured to switch power to the at least one actuator, A control circuit connected to the switching component and configured to control the switching component and including a serial control input, A power line connected to at least the switching component of each actuator unit for powering at least the switching component of each actuator unit, and A control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

2. The actuator array according to claim 1, wherein The control line is integrated with the power line, and wherein each actuator unit includes a high-pass filter connected between the power line and the serial control input.

3. The actuator array according to any one of the preceding claims, wherein, The switching component includes a switched-mode converter.

4. The actuator array according to any one of the preceding claims, wherein, The voltage line includes a conductive plane.

5. The actuator array according to any one of the preceding claims, wherein, Each control circuit in the control circuit is associated with a corresponding address, and wherein the control circuit is configured to be individually addressable by addressing control data to the corresponding address via the control line.

6. The actuator array according to any one of the preceding claims, wherein, Each control circuit in the control circuit is configured to be addressable by broadcasting control data via the control line.

7. The actuator array according to any one of the preceding claims, further comprising a control transmitter configured to send serial control data to the actuator units via the control line.

8. A substrate stage, comprising a plurality of protrusions configured to support a substrate, the substrate stage including the actuator array according to any one of the preceding claims, wherein the actuators of the actuator array are configured to actuate at least a subset of the protrusions.

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

10. An actuator unit, comprising: A piezoelectric 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 representing the voltage across the reference capacitor to the control circuit; Wherein the piezoelectric actuator and the reference capacitor are arranged at a first location, and the control circuit is arranged at a second location, wherein the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location.

11. The actuator unit according to claim 10, wherein, The actuator unit further includes a preamplifier arranged at the first location and configured to amplify the voltage across the reference capacitor, an output of the preamplifier of the preamplifier is connected to the feedback line, and the preamplifier is configured to output the amplified reference capacitor voltage to the feedback line.

12. The actuator unit according to claim 10 or 11, wherein, The actuator unit further includes: A switching component configured to switch power to a series connection of the piezoelectric actuator and the reference capacitor. The control circuit, which is connected to the switching component and configured to control the switching component.

13. An actuator array, comprising: A plurality of actuator units, each actuator unit comprising At least one piezoelectric actuator, A reference capacitor that is connected in series with the piezoelectric actuator, A switching component configured to switch power to the at least one actuator, A control circuit connected to the switching component and configured to control the switching component and comprising a serial control input, A feedback line configured to provide a reference capacitor voltage representing the voltage across the reference capacitor to the control circuit; Wherein the piezoelectric actuator and the reference capacitor are arranged at a first location, and the control circuit is arranged at a second location, where the second location is remote from the first location, and wherein the feedback line extends between the first location and the second location, A power line connected to at least the switching component of each actuator unit for powering at least the switching component of each actuator unit, and A control line connected to the serial control input of the control circuit of each actuator unit to send control data to the control circuit of at least one of the actuator units.

14. The actuator array according to claim 13, wherein, Each actuator unit further comprises a preamplifier arranged at the first location and configured to amplify the voltage across the reference capacitor, an output of the preamplifier being connected to the feedback line, the preamplifier being configured to output the amplified reference capacitor voltage onto the feedback line.

15. The actuator array according to claim 13 or 14, wherein, Each actuator unit further comprises a cable electrically connected to the piezoelectric actuator and the reference capacitor, the cable extending between the first location and the second location, and the cable comprising 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.

Images