Target supply apparatus

Abstract

The present invention provides a system comprising: a conduit including an orifice configured to be fluidly coupled to a reservoir and for discharging molten target material; an actuator including at least a first partition and a second partition located between the first partition and the orifice, wherein movement of the first partition and the second partition is transmitted to an interior of the conduit; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition. The second actuation signal has a frequency higher than that of the first actuation signal.

Description

[Technical Field]

[0001] This invention relates to a target supply device. The target supply device can be used to generate targets in an extreme ultraviolet (EUV) light source. [Previous Technology]

[0002] The target device can be used to generate a flow or jet of fluid material. For example, a nozzle device can be used to generate a target that is converted into an ultraviolet (EUV) light emission.

[0003] EUV light can be, for example, electromagnetic radiation with wavelengths of 100 nanometers (nm) or less (sometimes referred to as soft X-rays) and including wavelengths of, for example, 20 nm or less, light between 5 and 20 nm or between 13 and 14 nm, which can be used in photolithography processes to produce minute features in a substrate (e.g., a silicon wafer) by initiating polymerization in a resist layer. Methods for generating EUV light include, but are not limited to, converting materials containing elements such as xenon, lithium, or tin into a plasma state using emission spectra in the EUV range. In one such method, often referred to as laser-generated plasma (LPP), the desired plasma can be generated by irradiating a target material, for example, in the form of droplets, plates, strips, streams, or clusters, with an amplified beam, which may be referred to as a driving laser. For this process, the plasma is typically generated in a sealed container, such as a vacuum chamber, and various types of measuring devices are used to monitor the plasma. [Summary of the Invention]

[0004] In one embodiment, the system includes: a conduit including an orifice configured to be fluidly coupled to a reservoir and for emitting molten target material; an actuator including at least a first partition and a second partition located between the first partition and the orifice, wherein movement of the first partition and the second partition is transmitted to an interior of the conduit; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition. The second actuation signal has a higher frequency than the first actuation signal.

[0005] Implementation may include one or more of the following features.

[0006] The second partition can be smaller than the first partition.

[0007] The system may also include a plurality of actuator electrodes. In such embodiments, at least one actuator electrode may be associated with each of the first partition and the second partition; each of the first actuation signal and the second actuation signal may include an electrical signal having a spectrum; and, in order to apply a specific actuation signal to a specific partition of the actuator, the controller may be configured to apply an electrical signal to the actuator electrode associated with the specific partition. The spectrum of the at least one electrical signal may include more than one frequency.

[0008] The actuator may include a single piece of material mounted to the exterior of one of the conduits; the actuator electrodes may be located on the exterior of one of the actuators, and the actuator electrodes may be spatially separable from each other. In some embodiments, the actuator includes a sleeve comprising: a first end; a second end; an inner wall extending from the first end to the second end and mechanically coupled to the exterior of the conduit; the second end being closer to the orifice than the first end; the first partition of the actuator being a first portion of one of the sleeves, and the second partition of the actuator being a second portion of one of the sleeves; and at least one surface feature formed on the exterior of the actuator between the first partition and the second partition, and each surface feature being configured to provide partial mechanical isolation between the first partition and the second partition. The at least one surface feature may include at least one groove recessed into the outer surface. The at least one surface feature may include a plurality of grooves; each groove may surround the sleeve; and each groove may have a groove shape.

[0009] The system may also include a grounding electrode located at the first end of the sleeve and on the inner wall. One of the plurality of grooves is located between the grounding electrode and the first partition. In some embodiments, at least one of the plurality of grooves has a different shape than at least another groove. The diameter of the outer wall of the sleeve may be smaller at the second end than at the first end. In some embodiments, each actuator electrode surrounds an associated partition. Furthermore, in some embodiments, a minimum frequency in the spectrum of the second actuation signal is greater than a maximum frequency in the spectrum of the first actuation signal. A maximum frequency in the second spectrum may be greater than a maximum frequency in the first spectrum.

[0010] The controller is configured to apply the first actuation signal and the second actuation signal, which may include configuring the controller to control an electrical signal generator to generate the first actuation signal and the second actuation signal and apply them to the respective first and second partitions. Each of the first actuation signal and the second actuation signal may include at least one sine wave.

[0011] The system may also include the electrical signal generator.

[0012] The molten target material can emit extreme ultraviolet light when it is in a plasma state.

[0013] The first section of the actuator may include a first actuator and the second actuator may be different from the first actuator. The system may also include a diaphragm in mechanical communication with the interior of one of the conduits; and the second actuator may be mechanically coupled to the diaphragm. The system may include a motion transmission block between the first actuator and the second actuator. The first actuator may include a stack of actuating elements.

[0014] In another embodiment, the method includes: fluidly coupling an orifice of a conduit to a reservoir holding molten target material; applying pressure to the reservoir to cause the molten target material to flow in the conduit; applying a first actuation signal to a first section of an actuator mechanically coupled to the conduit, the first actuation signal having a first spectrum; and applying a second actuation signal to a second section of the actuator. The second actuation signal has a second spectrum, and the second spectrum includes frequencies higher than the first spectrum.

[0015] Implementation may include one or more of the following features.

[0016] A third actuation signal may be applied to a third partition of the actuator, the third actuation signal having a third spectrum.

[0017] In another embodiment, the system includes: a conduit including an orifice configured to be fluidly coupled to a reservoir and to emit molten target material; a one-piece actuator mechanically coupled to the conduit, the one-piece actuator including a plurality of individually controllable zones; and a controller configured to apply a single actuation signal to each of at least one first zone and one second zone.

[0018] In some implementations, a groove is formed in the outer surface of one of the single-piece actuators between the first partition and the second partition, and the groove is configured to partially mechanically decouple the first partition and the second partition.

[0019] In another embodiment, the system includes: a conduit including an orifice configured to be fluidly coupled to a reservoir and to emit molten target material; an actuator mechanically coupled to the conduit, the actuator including a plurality of individually controllable partitions including at least a first partition and a second partition, the second partition being located between the first partition and the orifice; and the second partition being smaller than the first partition; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition.

[0020] The second actuation signal includes at least one frequency that is greater than all frequencies in the first actuation signal.

[0021] In another embodiment, the actuator includes: an actuator body comprising: a grounded partition configured to be electrically connected to a reference potential; and a plurality of controllable partitions. Each controllable partition is configured to receive a control signal, and in operation, the controllable partitions are configured to be mechanically coupled to a conduit such that movement of the controllable partitions generates pressure waves in an internal region of the conduit.

[0022] Implementation may include one or more of the following features. The actuator body may include a single piece of material; the grounding partition and the plurality of controllable partitions are part of the single piece of material; and the single piece of material may be a plurality of spatial features; and the grounding partition may be separated from the plurality of controllable partitions by one of the plurality of spatial features, and each controllable partition may be separated from a nearest controllable partition by one of the plurality of spatial features.

[0023] At least one of these controllable zones may be a single material that does not directly contact other controllable zones or any of the zones.

[0024] The actuator body may include a substantially cylindrical sidewall configured to surround one of the conduits.

[0025] Implementations of any of the technologies described above may include: an EUV light source, a target supply system, a method, a procedure, a controller, or a control system, apparatus, or device acting on an actuator or target supply device. Details of one or more implementations are set forth below in the accompanying drawings and description. Other features will be apparent from the description and drawings and from the scope of the claims.

Implementation Method

[0027] Referring to FIG1, a block diagram of an EUV light source 100 including a supply system 110 is shown. A target stream 121 of the supply system 110 delivers a target 121p to a plasma formation location 123 within a vacuum chamber 109. The target 121p includes a target material, which is any material that emits EUV light 197 when in a plasma state. For example, the target material may include water, tin, lithium, and / or xenon. The plasma formation location 123 receives a beam 106. The beam 106 is generated by an optical source 105 and delivered to the vacuum chamber 109 via an optical path 107. The interaction between the beam 106 and the target material in the target 121p generates plasma 196 that emits EUV light 197.

[0028] The supply system 110 includes a conduit 114 defining an orifice 119. The conduit 114 is mounted to the supply system 110 via a nozzle mount or housing 117. The interior of the conduit 114 and the orifice 119 are fluidly coupled to a reservoir 112 that holds target material under pressure P. When the pressure P exceeds the pressure in the vacuum chamber 109, the target material flows into the conduit 114 and exits the orifice 119 as a jet or continuous stream 124 of target material. The jet 124 of target material breaks down into individual droplets, which coalesce into a stream 121 of larger droplets reaching the plasma formation location 123. The conduit 114 is coupled to an actuator 193 controlled by a controller 190. Movement of the actuator 193 is transmitted to the conduit 114 to generate acoustic waves within the conduit 114.

[0029] The controller 190 may include, for example, an electronic processing module, electronic storage, and / or a function or signal generator for generating control signals. In some implementations, the controller 190 controls individual devices (such as voltage or current sources) to generate control signals applied to the actuator 192. For example, the controller 190 may control a voltage source to generate control signals in the form of voltage and / or current signals having specific amplitude, frequency, and / or phase values.

[0030] Controller 190 controls the characteristics of the motion of actuator 193 (e.g., amplitude and / or frequency), and thus also controls the characteristics of the acoustic waves inside conduit 114. The rate at which larger coalesced droplets reach plasma formation location 123 is determined by the characteristics of the acoustic waves inside conduit 114. Therefore, by controlling the actuation of conduit 114, controller 190 is also configured to control the properties of droplets in stream 121. The final target can be generated, for example, at a frequency between 40 and 300 kHz, and can travel toward plasma formation location 123, for example, at a speed between 40 and 120 meters per second (m / s) or up to 500 m / s. The spatial separation between two adjacent targets in the target stream 121 can be, for example, between 1 and 3 millimeters (mm). 50 to 300 initial droplets (also called Rayleigh droplets) can coalesce to form a single larger target.

[0031] The actuator 193 has two or more partitions that are individually controlled by the controller 190. As discussed below, having two or more individually controllable partitions improves the performance of the actuator 193 and the supply system 110.

[0032] In the example of FIG1, actuator 193 includes a first partition 194a and a second partition 194b. The second partition 194b is located between the orifice 119 and the first partition 194a. In the example of FIG1, the second partition 194a is relatively close to the orifice 119 and the first partition 194a is relatively far from the orifice 119. Each partition 194a and 194b receives respective control signals 192a and 192b from controller 190.

[0033] Control signals 192a and 192b have different characteristics. For example, each of control signals 192a and 192b may be a voltage signal with a different frequency band. In some embodiments, control signal 192a includes a plurality of sinusoidal voltage signals with frequencies between 50 kHz and 1 MHz, and control signal 192b includes a plurality of sinusoidal voltage signals with frequencies between 1 MHz and 20 MHz. Other embodiments are possible. For example, each control signal 192a and 192b may be a square wave or a triangular wave. Control signals 192a and 192b are periodic and have a frequency at which the coalescing target reaches the plasma formation position 123. That is, control signals 192a and 192b are periodic, which is equal to the frequency at which the coalescing target reaches the plasma formation position 123. For example, each of control signals 192a and 192b can be an electrical signal with a spectrum that includes only the fundamental frequency (the frequency at which the target arrives at position 12) and its harmonics. Controller 190 can be implemented as more than one separate controller or can control individual functions or signal generators. In such implementations, signals 192a and 192b are synchronized to the same clock to avoid phase drift between signals 192a and 192b.

[0034] The performance and availability of the supply system 110 are improved by using two or more controllable partitions (partitions 194a and 194b in this example). For example, driving the actuator 193 with various partitions of different control signals increases the bandwidth of the driveable actuator 193 compared to driving the actuator 193 with a single control signal. In methods where the actuator 193 lacks two or more individually controllable partitions, the actuator 193 is driven with a single control signal having a relatively large bandwidth (e.g., 50 kHz to 20 MHz). The single control signal can be amplified; however, amplifiers have finite gain bandwidth characteristics, where the gain of the amplifier decreases as the bandwidth of the signal to be amplified increases. Therefore, adequately amplifying all frequencies in a single control signal is relatively challenging. On the other hand, each of the control signals 192a and 192b can be amplified by a separate amplifier. Therefore, greater amplification of the control signals 192a and 192b is possible.

[0035] Furthermore, to increase the amount of EUV light 197 produced, the pressure P is increased, the droplets in the stream 121 are spaced further apart, and the velocity of the jet 124 is increased by increasing the bandwidth of the driving actuator 193. For example, at a pressure P of 275 bar, the bandwidth of the control signal is 50 kHz to 5 MHz. However, at a pressure P of 1400 bar, the bandwidth of the control signal is 100 kHz to 20 MHz. In the supply system 110, the relatively large bandwidth for a pressure P of 1400 bar is split between sections 194a and 194b, rather than being applied to the conduit 114 with a single control signal. Driving each section 194a and 194b with separate control signals 192a and 192b allows the actuator 193 to be driven efficiently and effectively over a wider frequency range, and with simpler electronics.

[0036] In addition, although partitions 194a and 194b are mechanically coupled, they are spatially different. This configuration allows certain frequency bands to be delivered to specific portions of actuator 193, and allows for greater control over the formation of stream 122 and more efficient use of actuator 193.

[0037] Furthermore, in some embodiments, partitions 194a and 194b have different shapes and / or sizes. For example, actuator 193 may be a ceramic material, such as lead zirconate titanate (PZT). When such materials are driven at high frequencies (e.g., 10 MHz) or higher, the current required to obtain the same charge on the PZT increases. If the piezoelectric drive electronics cannot provide that current, the larger current requirement may become a problem. The current required to drive the PZT is given by I = C*dV / dt, and dV / dt increases with frequency. Therefore, the current required to drive the PZT increases with frequency. The capacitance of the PZT depends on its thickness and area. The capacitance (C) of the PZT in farads is given by C = (1500 × free space permittivity × width × length) / thickness.

[0038] On the other hand, at low frequencies, a smaller current is required. By using separate partitions 194a and 194b, the actuator 193 can be configured so that partitions 194a and 194b are of different sizes to address the challenges posed by the frequency characteristics of the actuator 193 material. For example, partition 194a can be a relatively large PZT, and partition 194b can be a relatively small PZT. The larger partition 194a is driven at a relatively low frequency and generates large volume fluctuations in the target material inside the conduit 114.

[0039] Therefore, by manufacturing partition 194b as a relatively small PZT, the capacitance of the PZT is smaller, and the amount of current required to drive the PZT at high frequencies is reduced. In this way, actuator 193 can be driven effectively and efficiently at multiple frequencies. For example, driving partition 194b at a frequency different from that of partition 194a can result in twice the actuation amount at the frequency of control signal 192a (due to the ability to amplify low-frequency signals relatively easily) and ten times the actuation amount at the frequency of control signal 192b (due to the reduction caused by capacitance).

[0040] The configuration shown in Figure 1 is an example, and other implementations are possible. For example, the conduit 114 may be a capillary, such as capillary 214 shown in Figures 2, 3, and 4. In these implementations, the nozzle housing or mount 117 attaches the capillary to the vacuum chamber 109 and fluidly couples the capillary to the reservoir 112. In these implementations, the conduit 114 extends from the nozzle mount or housing 117 and is not necessarily contained within the mount or housing 117. In the example shown in Figure 1, the conduit extends substantially along the X direction. However, in some implementations, the conduit 114 has a more complex path and extends in more than one direction. The figure shows a conduit 514 with a more complex path.

[0041] Figure 2A is a side cross-sectional block diagram of the target forming device 216 in the XZ plane. Figure 2B is a cross-sectional view of the target forming device 216 in the YZ plane taken along line 2B'-2B' of Figure 2A. The target forming device 216 can be used in the EUV light source 100 (Figure 1). The target forming device 216 includes a capillary 214. The capillary 214 includes a sidewall 230 that extends along the X direction from a first end 231 to a second end 232. The sidewall 230 is a three-dimensional object that is generally cylindrical. The sidewall 230 can be made of, for example, glass or quartz.

[0042] The sidewall 230 includes an inner surface 233 and an outer surface 239. The inner surface 233 defines an inner region 238 in fluid communication with a nozzle 235 at a first end 231. The nozzle 235 narrows along the -X direction to define an orifice 219. In operation, the inner region 238 is fluidly coupled to a reservoir of target material (such as reservoir 112 in FIG. 1), and the molten target material flows in the inner region 238 and passes through the orifice 219 in the -X direction.

[0043] The outer surface 239 is mechanically coupled to the actuator assembly 293. The outer surface 239 may be mechanically coupled to the actuator assembly 293 by, for example, an adhesive (such as, a benzo[a] resin, a resin containing benzo[a] resin, a bismaleimide resin, a cyanate ester resin or a resin containing a cyanate ester), by mechanical fasteners, or by direct contact (e.g., an interference fit) between the outer surface 239 and the actuator assembly 293.

[0044] The actuator assembly 293 includes an actuator body 291 and electrodes 295a, 295b and 295g. Referring also to FIG2B, the actuator body 291 is generally cylindrical and includes an inner wall 285 and an outer surface 286. The inner wall 285 defines an aperture surrounding a portion of the outer surface 239 of the capillary 214.

[0045] The actuating body 291 is made of a material capable of moving the sidewall 230. For example, the actuating body 291 may be a piezoelectric ceramic material, such as lead zirconate titanate (PZT), that changes shape in response to the application of voltage. The movement of the actuating body 291 causes a corresponding displacement of the sidewall 230 by radial contraction and expansion. The radial contraction and expansion cause acoustic or pressure waves in the internal region 238.

[0046] The actuating body 291 has a first partition 294a, a second partition 294b, and a grounding partition 294g. The first partition 294a and the second partition 294b are separate controllable partitions. The first partition 294a is located between the second partition 294b and the grounding partition 294g. The second partition 294b is the partition closest to the orifice 219. The radial thicknesses of the first partition 294a, the second partition 294b, and the grounding partition 294g are substantially the same. However, compared to the first partition 294a, the second partition 294b extends a shorter distance along the X direction. Therefore, the second partition 294b has a smaller material (e.g., PZT) volume than the first partition 294a.

[0047] Electrode 295g is located on a portion of the outer surface 286 adjacent to the grounding partition 294g. Electrode 295g also extends along the edge 284 of the actuator body 291 and along the inner wall 285. During operation of the target forming apparatus 216, electrode 295g is electrically connected to ground or a reference voltage.

[0048] Electrode 295a is located on a portion of the outer surface 296 adjacent to the first partition 294a. Electrode 295b is located on a portion of the outer surface 296 adjacent to the second partition 294b. Electrodes 295a, 295b, and 295g may be coated on the outer surface 296 and attached to the outer surface 296 by means of mechanical fasteners and / or by means of conductive adhesives.

[0049] The actuating body 291 includes spatial features 288a and 288b on its outer surface 286. Spatial feature 288a provides separation between electrodes 295g and 295a, and spatial feature 288b provides separation between electrodes 295a and 295b. The actuating body 291 is a single piece of material or a collection of material parts that are joined during use. Therefore, the grounding partition 294g, the first partition 294a, and the second partition 294b are mechanically coupled. However, spatial feature 288a provides partial mechanical decoupling or partial mechanical isolation between the grounding partition 294g and the first partition 294a, and spatial feature 288b provides partial mechanical decoupling or partial mechanical isolation between the first partition 294a and the second partition 294b.

[0050] In the example shown, spatial features 288a and 288b are notches formed on the outer surface 286. Notches 288a and 288b have a semi-circular cross-section and surround the outer surface 286. In other words, in the example of FIG. 2A, notches 288a and 288b are recessed rings surrounding the actuating body 291. However, spatial features 288a and 288b can take any form that provides partial mechanical isolation between adjacent sections. For example, spatial features 288a and 288b can be notches with a triangular, rectangular, square, or irregular cross-section instead of a semi-circular cross-section. Furthermore, spatial features 288a and 288b can protrude from the outer surface 296 rather than be recessed into the outer surface 296. Additionally, spatial features 288a and 299b can extend less than the entire circumference of the actuating body 291. In some implementations (such as those shown in Figure 3), spatial features 288a and 288b do not have the same size and do not have the same spatial characteristics.

[0051] During operation, the controller 190 (FIG. 1) provides a first control signal 192a to the first electrode 295a, causing the first partition 294a to move according to the first control signal 192a. For example, the first control signal 192a may include a sinusoidal voltage signal having a frequency between 50 kHz and 1 MHz, and the application of the first control signal 192a causes the first partition 294a to vibrate at such a frequency. The controller 190 provides a second control signal 192b to the second electrode 295b, causing the second partition 294b to move according to the second control signal 192b. For example, the second control signal 192b may include a sinusoidal voltage signal having a frequency between 1 MHz and 20 MHz, and the application of the second control signal 192b causes the second partition 294b to vibrate at such a frequency.

[0052] Because the first partition 294a and the second partition 294b are not completely mechanically isolated, some frequencies applied to the first partition 294a propagate to the second partition 294b, and vice versa. However, spatial feature 288b reduces such crosstalk, so that the first partition 294a vibrates primarily due to the application of the first control signal 192a and the second partition 294b vibrates primarily due to the application of the second control signal 192b. Therefore, the target forming apparatus 216 includes two separate controllable partitions (partitions 294a and 294b), and the characteristics of the control signal applied to each partition can be varied to make the movement of the actuator body 291 more finely controllable. The vibration of partitions 294a and 294b generates corresponding pressure waves or sound waves in the target material in the internal region 238 to promote droplet formation at frequencies and sizes suitable for application.

[0053] Figure 3 is a side cross-sectional block diagram of the target forming device 316 in the XZ plane. The target forming device 316 can be used in the EUV light source 100 to generate a stream 122 (Figure 1). The target forming device 316 includes a capillary tube 214 and an actuator assembly 393. The actuator assembly 393 includes an actuator body 391 and a grounding partition 394g, a first partition 394a, and a second partition 394b. The first partition 394a is located between the grounding partition 394g and the second partition 394b. The actuator body 391 includes an outer surface 386 and an inner wall 385. The actuator body 391 also includes spatial features 388a and 388b on the outer surface 386.

[0054] Except that spatial features 388a and 388b are not the same size and shape, actuator assembly 393 is similar to actuator assembly 293. Spatial feature 388a is a notch in outer surface 386. Spatial feature 388a has a semi-circular cross-section and surrounds actuator body 391. Spatial feature 388b is also a notch in outer surface 386, but spatial feature 388b extends further into outer surface 386 than spatial feature 388a and has a different cross-sectional shape. Spatial feature 388b has an asymmetrical arcuate cross-section, having a first side 381a and a second side 381b. The first side 381a and the second side 381a are curves or arcs that form the larger arc defining spatial feature 388b.

[0055] The first side 381a extends further from the inner wall 385 than the second side 381b. Therefore, the first partition 394a has a thicker radial dimension than the second partition 394b. The second partition 394b has a smaller extent in the X direction and therefore a smaller volume compared to the first partition 394b. Because the spatial feature 388b extends deeper into the outer surface 386, the first partition 394a and the second partition 394b are connected by a relatively thin portion of the actuator body 291. Compared to spatial features 288b (FIG. 2A) and 388a, spatial feature 388b provides more mechanical separation between adjacent partitions. Therefore, although the first partition 394a and the second partition 394b are physically connected, spatial feature 388b provides additional mechanical isolation and separation, making the first partition 394a and the second partition 394b more mechanically separated than the first partition 294a and the second partition 294b.

[0056] In operation, the grounding electrode 395g (located on a portion of the outer surface 386 adjacent to the grounding partition 394g), edge 384, and inner wall 385 are electrically connected to ground or a reference potential. Electrode 395a is located on a portion of the outer surface 386 adjacent to the first partition 394a. Electrode 395b is located on a portion of the outer surface 386 adjacent to the second partition 394b. Electrodes 395a and 395b receive control signals 191a and 192b, respectively, from controller 190 (FIG. 1). The relatively small size of the second partition 394b allows it to be driven efficiently at higher frequencies (e.g., 1 to 20 MHz).

[0057] Other implementations of actuator assemblies 293 and 393 are possible. For example, actuator assemblies 292 and / or 392 may include more than two individually controllable zones. For example, actuator bodies 291 and / or 391 may include three, four, or more than four zones associated with electrodes receiving control signals from controller 190. In other words, actuator assemblies 293 and / or 393 may be configured to be controlled using three, four, or more individual frequency bands.

[0058] Actuator assemblies 293 and 393 include separate actuator bodies 291 and 391 made of a single material. However, in other embodiments, the actuator assembly includes a plurality of discrete or different actuator bodies. Figures 4, 5 and 7 illustrate examples of such actuator assemblies.

[0059] Figure 4 is a side cross-sectional block diagram of the target forming device 416 in the XZ plane. The target forming device 416 can be used in the EUV light source 100 to generate a stream 122 (Figure 1).

[0060] The target forming apparatus 416 includes a capillary 214 and an actuator assembly 493. The actuator assembly 493 includes a grounding partition 494g, a first partition 494a, and a second partition 494b. The first partition 494a is located between the grounding partition 494g and the second partition 494b. Each of the grounding partition 494g, the first partition 494a, and the second partition 494b is a discrete body of an actuating material. For example, each of these partitions may be a ring of PZT material surrounding and mechanically coupled to the outer wall 239 of the capillary 214. The grounding partition 494g, the first partition 494a, and the second partition 494b are positioned along the sidewall 230 such that they do not directly contact each other.

[0061] In operation, a grounding electrode 495g extending on the grounding partition 494g and along the outer surface 239 of the sidewall 230 is electrically connected to ground or a reference potential. Electrode 495a is on the first partition 494a. Electrode 495b is on the second partition 494b. Electrodes 495a and 495b receive control signals 191a and 191b from the controller 190 (FIG. 1), respectively. In the example shown in FIG. 4, the second partition 494b has a smaller volume than the first partition 494a. The relatively smaller volume of the second partition 494b allows it to be driven efficiently at higher frequencies (e.g., 1 to 20 MHz).

[0062] Other implementations are possible. For example, the target forming apparatus 416 may have a grounding partition 494g and a first partition 494a on a single piece of material and be partially mechanically isolated by a spatial feature such as spatial feature 388a. In such implementations, the second partition 494b is a separate piece of material and does not directly touch the first partition 494a or the grounding partition 494g. Furthermore, although the target forming apparatus 416 is shown as having two partitions (first partition 494a and second partition 494b) that receive control signals from the controller 190, the target forming apparatus 416 may implement additional partitions configured to receive control signals from the controller 190 (or another controller).

[0063] Figure 5 is a side cross-sectional block diagram of the target forming device 516 in the XZ plane. The target forming device 516 can be used in the EUV light source 100 to generate a stream 122 (Figure 1). The target forming device 516 includes an actuator assembly 593 and a conduit 514 held in a mounting assembly or housing 511. The housing 511 holds the actuator assembly 593 and the conduit 514 and can be used to mount the target forming device 516 to a vacuum chamber such as the chamber 109 of Figure 1.

[0064] The conduit 514 includes an internal region 538 configured to be fluidly coupled to a reservoir such as reservoir 112 (FIG. 1). The internal region 538 may be fluidly coupled to the reservoir by means of a hole drilled through housing 511 or by a channel (not shown) formed in housing 511. The conduit 514 has a substantially T-shape, including a region 514a extending in the Z direction (and may extend in the YZ plane) and a region 514b extending in the X direction. Region 514b narrows toward an orifice 519 through which the target material can pass. Region 514a is in fluid contact with diaphragm 512. Diaphragm 512 is flexible and movable, and movement of diaphragm 512 generates pressure waves in internal region 538. Diaphragm 512 may be part of housing 511, or diaphragm 512 may be a separate element attached to housing 511. The outer casing 511 and the diaphragm 512 may be made of, for example, molybdenum, tantalum or tungsten.

[0065] The actuator assembly 593 includes a first partition 594a and a second partition 594b. The first partition 594a and the second partition 594b are shown in diagonal shading. The first partition 594a and the second partition 594b are made of an actuating material such as PZT. The first partition 594a and the second partition 594b are discrete partitions and do not directly touch each other. The first partition 594a and the second partition 594b are three-dimensional objects and may have, for example, circular, rectangular, or square shapes in the YZ plane. The first partition 594a and the second partition 594b may be continuous objects and may not include openings, holes, or other features that can be used to position partition 594a or partition 594b around another object. The first partition 594a and the second partition 594b may have different shapes in the YZ plane. In the example shown in FIG. 5, the second partition 594b has a smaller spatial volume than the first partition 594a.

[0066] The actuator assembly 593 includes a positioning mechanism 571 configured to position and hold the first partition 594a. The positioning mechanism 571 may include, for example, a pre-tensioned wedge and / or spacer that hold the first partition 594a in place while also allowing the first partition 594a to change shape.

[0067] The actuator assembly 593 also includes a block 572 between the second partition 594b and the first partition 594a. The block 572 has a face 572a and a tip 572b. The tip 572b extends away from the face 572a in the -X direction and is narrower than the face 572a in the Z direction. The face 572a contacts the first partition 594a. The second partition 594b is mounted on the tip 572b. The tip 572b contacts the diaphragm 512. The tip 572b is shaped to guide vibrations from the movement of the first partition 594a to the diaphragm 512.

[0068] During operation, control signals 191a and 191b from controller 190 (FIG. 1) are provided to the first partition 494a and the second partition 494b, respectively, to control the movement of these partitions. The vibrations of the first partition 594a and the second partition 594b are transmitted from the top 572b to the diaphragm 512. Therefore, the diaphragm 512 vibrates based on the frequency of the vibrations of the first partition 594a and the second partition 594b. The vibration of the diaphragm 512 causes corresponding sound waves in the internal region 538.

[0069] The actuator assembly 593 may include additional elements. For example, the actuator assembly 593 may include one or more electrodes on each partition 594a and 594b. The actuator assembly 593 may include more than one controllable partition, and therefore may include more PZT than shown in FIG. 5.

[0070] Figure 6 is a side cross-sectional block diagram of the actuator assembly 693, which is an example implementation of the actuator assembly 593 in which the first partition 594a is implemented as a stack 694 of PZT disks. The stack 694 may include 10, 50, 100 or more thin PZT disks. The disks may have a circular cross-section in the YZ plane. The stack 694 may have a range of about 2 mm to 10 mm in the X direction. The stack 694 may be held together by a compressive force provided by the positioning mechanism 571 along the X direction.

[0071] Figure 7 is a side cross-sectional block diagram of a target forming apparatus 716 in the XZ plane. The target forming apparatus 716 can be used in an EUV light source 100 to generate a stream 122 (Figure 1). The target forming apparatus 716 includes a conduit 714 defining an internal region 738 and an orifice 719. The conduit 714 is generally conical and narrows toward the orifice 719 in the -X direction. The target forming apparatus 716 also includes various mounting elements or housings 711. The mounting elements or housings 711 are used to house the components of the target forming apparatus 716 and to mount the target forming apparatus 716 to a vacuum chamber such as a vacuum chamber 109.

[0072] The target forming apparatus 716 also includes partitions 794a and 794b, each of which is a ring of PZT material mounted to the outer surface 733 of the conduit 714. Partition 794a has a larger radius and a greater longitudinal thickness than partition 794b. Therefore, partition 794b has a smaller volume than partition 794b. Of partitions 794a and 794b, partition 794b is closer to the orifice 719.

[0073] During operation, control signals 191a and 191b from controller 190 (FIG. 1) are provided to leads 777 and 778, respectively. Leads 777 and 778 may be wires or cables. Lead 777 is electrically connected to an electrode (not shown) on the first partition 794a, and lead 778 is electrically connected to an electrode (not shown) on the second partition 794b. Control signals 191a and 191b control the movement of partitions 794a and 794b, respectively. Vibrations of the first partition 794a and the second partition 794b are transmitted to the internal space 738 and generate sound waves in the internal area 538.

[0074] Any of the target forming devices 216, 316, 416, 516 and 716 discussed above can be used in an EUV light source. Referring to Figure 8, an implementation of the LPP EUV light source 800 is shown. Any of the nozzle assemblies discussed above can be used as part of the supply system 825 in the light source 800.

[0075] An LPP EUV light source 800 is formed by irradiating a target mixture 814 at a plasma formation location 805 with a magnified beam 810 traveling along a beam path toward the target mixture 814. The target material discussed in FIG1 and the target in the stream 121 discussed in FIG1 may be or include the target mixture 814. The plasma formation location 805 is located inside 807 of a vacuum chamber 830. When the magnified beam 810 irradiates the target mixture 814, the target material within the target mixture 814 is converted into a plasma state having an emission spectrum in the EUV range. The generated plasma has certain characteristics depending on the composition of the target material within the target mixture 814. These characteristics may include the wavelength of the EUV light generated by the plasma and the type and amount of debris released from the plasma.

[0076] The light source 800 also includes a supply system 825 that delivers, controls, and directs a target mixture 814 in the form of droplets, streams, solid particles or clusters, solid particles contained within droplets, or solid particles contained within streams. The target mixture 814 includes target materials such as water, tin, lithium, xenon, or any material that has an emission spectrum in the EUV range when converted to a plasma state. For example, elemental tin can be used as pure tin (Sn); as tin compounds such as SnBr4, SnBr2, SnH4; or as tin alloys such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of such alloys. The target mixture 814 may also include impurities such as non-target particles. Thus, in the absence of impurities, the target mixture 814 is made solely of the target material. The target mixture 814 is delivered by the supply system 825 into the interior 807 of the chamber 830 and to the plasma formation location 805.

[0077] The light source 800 includes a driving laser system 815, which generates an amplified beam 810 due to population inversion within one or more gain media of the laser system 815. The light source 800 includes a beam delivery system between the laser system 815 and the plasma formation position 805, the beam delivery system including a beam transport system 820 and a focusing assembly 822. The beam transport system 820 receives the amplified beam 810 from the laser system 815, and, as needed, directs and adjusts the amplified beam 810 and outputs the amplified beam 810 to the focusing assembly 822. The focusing assembly 822 receives the amplified beam 810 and focuses the beam 810 onto the plasma formation position 805.

[0078] In some embodiments, the laser system 815 may include one or more optical amplifiers, lasers, and / or lamps for providing one or more master pulses and, in some cases, one or more pre pulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength with high gain, an excitation source, and internal optics. The optical amplifier may or may not have a laser mirror or other feedback device forming a laser cavity. Thus, the laser system 815 generates an amplified beam 810 even in the absence of a laser cavity, attributable to population inversion in the gain medium of the laser amplifier. Furthermore, the laser system 815 may generate an amplified beam 810 as a coherent laser beam in the presence of a laser cavity to provide sufficient feedback to the laser system 815. The term "amplified beam" encompasses one or more of the following: light from the laser system 815 that is merely amplified but not necessarily coherent laser oscillation, and light from the laser system 815 that is amplified and is also coherent laser oscillation.

[0079] The optical amplifier in the laser system 815 may include a fill gas (including CO2) as a gain medium and may amplify light at wavelengths between about 9100 nm and about 11000 nm, particularly at about 10600 nm, by a gain of greater than or equal to 800 times. Suitable amplifiers and lasers for use in the laser system 815 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices, which are used, for example, to generate radiation at about 9300 nm or about 10600 nm by DC or RF excitation operating at relatively high power (e.g., 10 kW or higher) and high pulse repetition rate (e.g., 40 kHz or higher). The pulse repetition rate may be, for example, 50 kHz. The optical amplifier in the laser system 815 may also include a cooling system, such as water, for use when the laser system 815 is operated at higher power.

[0080] The light source 800 includes a collector mirror 835 having an aperture 840 to allow the magnified beam 810 to pass through and reach the plasma formation position 805. The collector mirror 835 may be, for example, an ellipsoidal mirror having a primary focal point at the plasma formation position 805 and a secondary focal point (also referred to as an intermediate focal point) at an intermediate position 845, wherein EUV light can be output from the light source 800 and the EUV light can be input to, for example, an integrated circuit lithography tool (not shown). The light source 800 may also include an open-ended hollow conical shield 850 (e.g., a gas cone) that tapers from the collector mirror 835 toward the plasma formation position 805 to reduce the amount of plasma-generated debris entering the focusing assembly 822 and / or the beam delivery system 820, while allowing the magnified beam 810 to reach the plasma formation position 805. For this purpose, airflow can be provided in the shield, which is directed to plasma forming position 805.

[0081] The light source 800 may also include a master controller 855, which is connected to the droplet position detection feedback system 856, the laser control system 857, and the beam control system 858. The light source 800 may include one or more target or droplet imagers 860, which provide an output indicating the position of the droplet, for example, relative to the plasma formation location 805, and provide this output to the droplet position detection feedback system 856, which can, for example, calculate the droplet position and trajectory, and calculate the droplet positioning error from the droplet position and trajectory on a droplet-by-droplet basis or on average. The droplet positioning detection feedback system 856 therefore provides the droplet positioning error as an input to the master controller 855. Therefore, the master controller 855 can provide, for example, a laser positioning, orientation, and timing correction signal to a laser control system 857 that can be used to control, for example, the laser timing circuit, and / or to a beam control system 858, which controls the shaping of the amplified beam positioning and beam delivery system 820 to change the position and / or focus of the beam focusing point within the chamber 830.

[0082] The supply system 825 includes a target material delivery control system 826 operable to modify the release point of droplets, such as those released by a target material supply device 827, in response to a signal, for example, from a master controller 855, to correct for errors in the droplets reaching the desired plasma formation location 805. The target material supply device 827 may be or include any of the target formation devices and / or actuators discussed above.

[0083] Additionally, the light source 800 may include light source detectors 865 and 870, which measure one or more EUV light parameters, including but not limited to pulse energy, energy distribution varying according to wavelength, energy within a specific wavelength band, energy outside a specific wavelength band, and angular distribution and / or average power of EUV intensity. The light source detector 865 generates a feedback signal for use by the main controller 855. The feedback signal may, for example, indicate errors in parameters such as timing and focal length in the proper interception of droplet laser pulses at the appropriate location and time for effective and efficient EUV light generation.

[0084] The light source 800 may also include a guiding laser 875, which can be used to align or assist in directing the amplified beam 810 to the plasma formation position 805. In conjunction with the guiding laser 875, the light source 800 includes a measurement system 824 disposed within a focusing assembly 822 to sample a portion of the light from the guiding laser 875 and the amplified beam 810. In other embodiments, the measurement system 824 is disposed within a beam delivery system 820. The measurement system 824 may include an optical element for sampling or redirecting a subset of the light, the optical element being made of any material capable of withstanding the power of the guiding laser beam and the amplified beam 810. A beam analysis system is formed by a measurement system 824 and a master controller 855, because the master controller 855 analyzes the light sampled by the self-guided laser 875 and uses this information to adjust the components in the focusing assembly 822 via the beam control system 858.

[0085] Therefore, in summary, the light source 800 generates an amplified light beam 810, which is guided along a beam path to irradiate the target mixture 814 at the plasma formation location 805 to convert the target material within the mixture 814 into plasma emitting light in the EUV range. The amplified light beam 810 operates at a specific wavelength (also referred to as a driving laser wavelength) determined based on the design and properties of the laser system 815. Furthermore, the amplified light beam 810 can be a laser beam when the target material provides sufficient feedback back to the laser system 815 to generate coherent laser light, or when the driving laser system 815 includes suitable optical feedback to form a laser cavity.

[0086] The embodiments may be further described using the following clauses: 1. A system comprising: a conduit including an orifice configured to be fluidly coupled to a reservoir and for discharging molten target material; an actuator including at least a first partition and a second partition located between the first partition and the orifice, wherein movement of the first partition and the second partition is transmitted to an interior of the conduit; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition, wherein the second actuation signal has a higher frequency than the first actuation signal. 2. The system of clause 1, wherein the second partition is smaller than the first partition. 3. The system of claim 1, further comprising a plurality of actuator electrodes; wherein at least one actuator electrode is associated with each of the first partition and the second partition; each of the first actuation signal and the second actuation signal comprises an electrical signal having a spectrum; and in order to apply a specific actuation signal to a specific partition of the actuator, the controller is configured to apply an electrical signal to the actuator electrode associated with the specific partition. 4. The system of claim 3, wherein the spectrum of at least one electrical signal comprises more than one frequency. 5. The system of claim 3, wherein the actuator comprises a single piece of material mounted to the exterior of one of the conduits; the actuator electrodes are located on the exterior of one of the actuators, and the actuator electrodes are spatially separated from each other. 6. The system of claim 5, wherein the actuator comprises a sleeve including: a first end; a second end; an inner wall extending from the first end to the second end and mechanically coupled to the exterior of the conduit; the second end being closer to the orifice than the first end; the first section of the actuator being a first portion of the sleeve, and the second section of the actuator being a second portion of the sleeve; and at least one surface feature formed on the exterior of the actuator between the first section and the second section, wherein each surface feature is configured to provide partial mechanical isolation between the first section and the second section. 7. The system of claim 6, wherein the at least one surface feature includes at least one groove recessed into the outer surface. 8. The system of claim 7, wherein the at least one surface feature includes a plurality of grooves; each groove surrounds the sleeve; and each groove has a groove shape. 9. The system of claim 8, further comprising a grounding electrode located at the first end of the sleeve and on the inner wall; and wherein one of the plurality of grooves is located between the grounding electrode and the first partition. 10. The system of claim 9, wherein at least one of the plurality of grooves has a different shape than at least another groove. 11. The system of claim 10, wherein the diameter of the outer wall of the sleeve is smaller at the second end than at the first end. 12. The system of claim 3, wherein each actuator electrode surrounds an associated partition.13. The system of claim 3, wherein a minimum frequency in the spectrum of the second actuation signal is greater than a maximum frequency in the spectrum of the first actuation signal. 14. The system of claim 1, wherein configuring the controller to apply the first actuation signal and the second actuation signal includes configuring the controller to control an electrical signal generator to generate the first actuation signal and the second actuation signal and apply them to respective first and second partitions. 15. The system of claim 14, further comprising the electrical signal generator. 16. The system of claim 14, wherein each of the first actuation signal and the second actuation signal comprises at least one sine wave. 17. The system of claim 1, wherein the molten target material emits extreme ultraviolet light when in a plasma state. 18. The system of claim 1, wherein the first partition of the actuator comprises a first actuator and the second actuator comprises a second actuator different from the first actuator. 19. The system of claim 18, wherein the system further includes a diaphragm in internal mechanical communication with one of the conduits; and the second actuator is mechanically coupled to the diaphragm. 20. The system of claim 19, further including a motion transmission block between the first actuator and the second actuator. 21. The system of claim 20, wherein the first actuator includes a stack of actuating elements. 22. The system of claim 3, wherein a maximum frequency in the second spectrum is greater than a maximum frequency in the first spectrum. 23. A method comprising: fluidly coupling an orifice of a conduit to a reservoir holding a molten target material; applying pressure to the reservoir to cause the molten target material to flow in the conduit; applying a first actuation signal to a first section of an actuator mechanically coupled to the conduit, the first actuation signal having a first spectrum; and applying a second actuation signal to a second section of the actuator, wherein the second actuation signal has a second spectrum, and the second spectrum includes frequencies higher than the first spectrum. 24. The method of claim 23, further comprising: applying a third actuation signal to a third section of the actuator, wherein the third actuation signal has a third spectrum. 25. A system comprising: a conduit including an orifice configured for fluid coupling to a reservoir and for emitting molten target material; a one-piece actuator mechanically coupled to the conduit, the one-piece actuator including a plurality of individually controllable zones; and a controller configured to apply a separate actuation signal to each of at least one first zone and one second zone. 26. The system of claim 25, wherein a groove is formed in an outer surface of the one-piece actuator between the first zone and the second zone, and the groove is configured to partially mechanically decouple the first zone from the second zone.27. A system comprising: a conduit including an orifice configured for fluid coupling to a reservoir and for emitting molten target material; an actuator mechanically coupled to the conduit, the actuator including a plurality of individually controllable partitions, wherein the plurality of individually controllable partitions includes at least one first partition and a second partition, the second partition being located between the first partition and the orifice; and the second partition being smaller than the first partition; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition. 28. The system of claim 27, wherein the second actuation signal includes at least one frequency greater than all frequencies of the first actuation signal. 29. An actuator comprising: an actuator body comprising: a grounding partition configured to be electrically connected to a reference potential; and a plurality of controllable partitions, wherein each controllable partition is configured to receive a control signal, and wherein, in operation, the controllable partitions are configured to be mechanically coupled to a conduit such that movement of the controllable partitions generates a pressure wave in an internal region of the conduit. 30. The actuator of claim 29, wherein the actuator body comprises a single piece of material; the grounding partition and the plurality of controllable partitions are parts of the single piece of material; and the single piece of material comprises a plurality of spatial features; and the grounding partition is separated from the plurality of controllable partitions by one of the plurality of spatial features, and each controllable partition is separated from a nearest controllable partition by one of the plurality of spatial features. 31. The actuator of clause 29, wherein at least one of the controllable zones is a separate material element that does not directly contact the other controllable zones or any of the zones. 32. The actuator of clause 29, wherein the actuator body includes a substantially cylindrical sidewall configured to surround one of the conduits.

[0087] The above-described embodiments and other embodiments fall within the scope of the following patent application. [Simplified Explanation of the Diagram]

[0026] Figure 1 is a block diagram of an example of an EUV light source. Figure 2A is a side cross-sectional block diagram of an example of a target forming device in the XZ plane. Figure 2B is a cross-sectional view of the target forming device of Figure 2A in the YZ plane, taken along line 2B'-2B'. Figure 3 is a side cross-sectional block diagram of another example of a target forming device in the XZ plane. Figure 4 is a side cross-sectional block diagram of another example of a target forming device in the XZ plane. Figure 5 is a side cross-sectional block diagram of another example of a target forming device in the XZ plane. Figure 6 is a side cross-sectional block diagram of an example of an actuator assembly. Figure 7 is a side cross-sectional block diagram of another example of a target forming device in the XZ plane. Figure 8 is a block diagram of an example of an EUV light source.

Claims

1. A target supply system comprising: a conduit including an orifice configured to be fluidly coupled to a reservoir and for discharging molten target material; an actuator including at least a first partition and a second partition located between the first partition and the orifice, wherein movement of the first partition and the second partition is transmitted to an interior of the conduit; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition, wherein the second actuation signal has a frequency higher than the first actuation signal.

2. The system of request item 1, wherein the second partition is smaller than the first partition.

3. The system of claim 1, further comprising a plurality of actuator electrodes; wherein at least one actuator electrode is associated with each of the first partition and the second partition; each of the first actuation signal and the second actuation signal comprises an electrical signal having a spectrum; and in order to apply a specific actuation signal to a specific partition of the actuator, the controller is configured to apply an electrical signal to the actuator electrode associated with the specific partition.

4. The system of claim 3, wherein the spectrum of at least one electrical signal contains more than one frequency.

5. The system of claim 3, wherein the actuator comprises a single piece of material mounted to the outside of one of the conduits; the actuator electrodes are located on the outside of one of the actuators, and the actuator electrodes are spatially separated from each other.

6. The system of claim 5, wherein the actuator includes a sleeve comprising: a first end; a second end; an inner wall extending from the first end to the second end and mechanically coupled to the exterior of the conduit; the second end being closer to the orifice than the first end; the first partition of the actuator being a first portion of the sleeve, and the second partition of the actuator being a second portion of the sleeve; and at least one surface feature being formed on the exterior of the actuator between the first partition and the second partition, wherein each surface feature is configured to provide partial mechanical isolation between the first partition and the second partition.

7. The system of claim 6, wherein the at least one surface feature comprises at least one groove recessed into the outer surface.

8. The system of claim 7, wherein the at least one surface feature comprises a plurality of grooves; each groove surrounds the sleeve; and each groove has a groove shape.

9. The system of claim 8, further comprising a grounding electrode located at the first end of the sleeve and on the inner wall; and wherein one of the plurality of recesses is located between the grounding electrode and the first partition.

10. The system of claim 9, wherein at least one of the plurality of grooves has a different shape than at least another groove.

11. The system of claim 10, wherein the diameter of the outer wall of the sleeve is smaller at the second end than at the first end.

12. The system of claim 3, wherein each actuator electrode surrounds an associated partition.

13. The system of claim 3, wherein a minimum frequency in the spectrum of the second actuation signal is greater than a maximum frequency in the spectrum of the first actuation signal.

14. The system of claim 1, wherein the controller is configured to apply the first actuation signal and the second actuation signal includes the controller being configured to control an electrical signal generator to generate the first actuation signal and the second actuation signal and apply them to the respective first partition and second partition.

15. The system of claim 14 further includes the electrical signal generator.

16. The system of claim 14, wherein each of the first actuation signal and the second actuation signal comprises at least one sine wave.

17. The system of claim 1, wherein the molten target material emits extreme ultraviolet light when in a plasma state.

18. The system of claim 1, wherein the first partition of the actuator includes a first actuator and the second partition includes a second actuator different from the first actuator.

19. The system of claim 18, wherein the system further includes a diaphragm in internal mechanical communication with one of the conduits; and the second actuator is mechanically coupled to the diaphragm.

20. The system of claim 19 further includes a motion transfer block between the first actuator and the second actuator.

21. The system of claim 20, wherein the first actuator comprises a stack of actuating elements.

22. The system of claim 3, wherein one of the maximum frequencies in the second spectrum is greater than one of the maximum frequencies in the first spectrum.

23. A method of supplying a target material, comprising: fluidly coupling an orifice of a conduit to a reservoir holding molten target material; applying pressure to the reservoir to cause the molten target material to flow in the conduit; applying a first actuation signal to a first section of an actuator mechanically coupled to the conduit, the first actuation signal having a first spectrum; and applying a second actuation signal to a second section of the actuator, wherein the second actuation signal has a second spectrum and the second spectrum includes frequencies higher than the first spectrum.

24. The method of claim 23, further comprising: applying a third actuation signal to a third partition of the actuator, wherein the third actuation signal has a third spectrum.

25. A target supply system comprising: a conduit including an orifice configured to be fluidly coupled to a reservoir and for discharging molten target material; a one-piece actuator mechanically coupled to the conduit, the one-piece actuator including a plurality of individually controllable zones; and a controller configured to apply a single actuation signal to each of at least one first zone and one second zone.

26. The system of claim 25, wherein a groove is formed in the outer surface of one of the single-piece actuators between the first partition and the second partition, and the groove is configured to partially mechanically decouple the first partition and the second partition.

27. A target supply system comprising: a conduit including an orifice configured to be fluidly coupled to a reservoir and for discharging molten target material; an actuator mechanically coupled to the conduit, the actuator including a plurality of individually controllable partitions, wherein the plurality of individually controllable partitions includes at least a first partition and a second partition, the second partition being located between the first partition and the orifice; and the second partition being smaller than the first partition; and a controller configured to apply a first actuation signal to the first partition and a second actuation signal to the second partition.

28. The system of claim 27, wherein the second actuation signal includes at least one frequency greater than all frequencies of the first actuation signal.

29. An actuator comprising: an actuator body comprising: a grounding partition configured to be electrically connected to a reference potential; and a plurality of controllable partitions, wherein each controllable partition is configured to receive a separate control signal, and wherein, in operation, the controllable partitions are configured to be mechanically coupled to a conduit such that movement of the controllable partitions generates pressure waves in an internal region of the conduit.

30. The actuator of claim 29, wherein the actuator body comprises a single piece of material; the grounding partition and the plurality of controllable partitions are part of the single piece of material; and the single piece of material comprises a plurality of spatial isolation features; and the grounding partition is separated from the plurality of controllable partitions by one of the plurality of spatial isolation features, and each controllable partition is separated from a nearest controllable partition by one of the plurality of spatial isolation features.

31. The actuator of claim 29, wherein at least one of the controllable zones is a separate material that does not directly contact the other controllable zones or any of the zones.

32. The actuator of claim 29, wherein the actuator body includes a substantially cylindrical sidewall configured to surround one of the conduits.

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