Apparatus and method for controlling droplet formation

Abstract

An apparatus and method for controlling droplet formation for generating EUV radiation includes an apparatus for generating a laser beam directed toward an irradiation region and a droplet source. The droplet source includes a capillary having a nozzle and an electrically actuated element for generating a disturbance in a liquid source material within the capillary. The droplet source generates a stream that breaks into droplets that, as they progress toward the irradiation region, coalesce into larger droplets. The electrically actuated element is driven by a waveform associated with at least one resonance of the droplet source that controls the droplet generation / coalescence process.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 843,712, filed May 6, 2019, entitled APPARATUS FOR AND METHOD OF CONTROLLING DROPLET FORMATION, which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to extreme ultraviolet ("EUV") light sources and methods of operating the same. These light sources provide EUV light by creating a plasma from a source material. In one application, EUV light can be collected and used in a photolithography process to produce semiconductor integrated circuits. Background Art

[0004] A patterned EUV beam can be used to expose a resist-coated substrate, such as a silicon wafer, to create extremely small features in the substrate. Extreme ultraviolet light (sometimes also called soft x-rays) is generally defined as electromagnetic radiation with a wavelength in the range of approximately 5nm-100nm. One particular wavelength of interest in lithography is 13.5nm.

[0005] Methods of generating EUV light include, but are not necessarily limited to, converting a source material into a plasma state having chemical elements that have emission lines in the EUV range. These elements may include, but are not limited to, xenon, lithium, and tin.

[0006] In one such method, generally referred to as laser produced plasma ("LPP"), the desired plasma can be generated by irradiating a source material (e.g., in the form of droplets, streams, or wires) with a laser beam. In another method, generally referred to as discharge produced plasma ("DPP"), the desired plasma can be generated by placing a source material having an appropriate emission line between a pair of electrodes and causing a discharge between the electrodes.

[0007] One technique for generating droplets involves melting a source material, such as tin, and then forcing it through an orifice, such as an orifice having a diameter of about 0.5 μm to about 30 μm, under high pressure to produce a stream that results in droplets having droplet velocities in the range of about 30 m / s to about 150 m / s. Under most conditions, naturally occurring instabilities (e.g., noise) in the stream exiting the orifice cause the stream to break into droplets in a process known as Rayleigh breakup. These droplets may have different velocities and may combine with each other in flight to coalesce into larger droplets.

[0008] In the EUV generation process considered here, it is desirable to control the breakup / coalescence process. For example, in order to synchronize the droplets with the optical pulses of the LPP drive laser, a repetitive disturbance with an amplitude exceeding the amplitude of random noise can be applied to the continuous stream. By applying the disturbance at a frequency that is the same as the repetition rate of the pulsed laser or its higher harmonics, the droplets can be synchronized with the laser pulses. For example, the disturbance can be applied to the stream by coupling an electro-actuating element (such as a piezoelectric material) to the stream and driving the electro-actuating element with a periodic waveform. In one embodiment, the diameter of the electro-actuating element contracts and expands (on the order of nanometers). This dimensional change is mechanically coupled to the capillary, which undergoes a corresponding contraction and expansion in diameter. The column of liquid source material (e.g., molten tin) inside the capillary also contracts and expands in diameter (as well as expands and contracts in length) to induce velocity disturbances in the stream at the nozzle outlet.

[0009] As used herein, the term "electroactuated element" and its derivatives refer to a material or structure that undergoes a dimensional change when subjected to a voltage, an electric field, a magnetic field, or a combination thereof, and includes, but is not limited to, piezoelectric materials, electrostrictive materials, and magnetostrictive materials. Apparatus and methods for controlling droplet streams using electroactuated elements are disclosed, for example, in U.S. Patent Application Publication No. 2009 / 0014668 A1, entitled "Laser Produced Plasma EUV Light Source Having a Droplet Stream Produced Using a Modulated Disturbance Wave," published on January 15, 2009, and U.S. Patent No. 8,513,629, entitled "Droplet Generator with Actuator-Induced Nozzle Cleaning," issued on August 20, 2013, both of which are incorporated herein by reference in their entireties. Summary of the Invention

[0010] The following presents a simplified summary of one or more embodiments to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is neither intended to identify key or critical elements of all embodiments nor to delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0011] According to one aspect, a source material dispenser includes a capillary tube and an electro-actuated element mechanically coupled to and coaxially arranged with the capillary tube. At least one dimension of at least one of the capillary tube and the electro-actuated element is selected such that the source material dispenser exhibits a resonant mode at a frequency component of a periodic control signal. The resonant mode may be a thickness mode of the piezoelectric and capillary mechanical stack. The capillary tube and the electro-actuated element may be sized such that they resonate at a common frequency in the thickness direction. The resonant mode may be an elastic length mode. The length of the electro-actuated element may be selected such that, when the source material fills the capillary tube, the resonant frequency and wavelength of the electro-actuated element are substantially the same as the frequency and wavelength of an acoustic harmonic of the source material. The electro-actuated element may be a piezoelectric element.

[0012] According to another aspect, an apparatus includes a source material dispenser comprising a capillary tube and an electro-actuating element mechanically coupled to and coaxially arranged with the capillary tube to form a capillary electro-actuating element system; and a signal generator electrically coupled to the electro-actuating element to supply a control signal comprising a periodic signal having a frequency component matched to at least one resonant mode of the capillary electro-actuating element system. The periodic control signal may have a sinusoidal wave component whose frequency matches a thickness mode of the capillary electro-actuating element system. The periodic control signal may have a coherent ultrasonic component whose frequency and wavelength match an elastic length mode of the source material dispenser. The electro-actuating element may be a piezoelectric element. The control signal may cause the electro-actuating element to generate a longitudinal wave in the capillary tube having a frequency substantially the same as the wave component. The longitudinal wave propagates along the length of the capillary tube to displace the tip of the capillary tube in an axial direction to promote Rayleigh breakup of a source material jet exiting a nozzle orifice in the capillary tip.

[0013] According to another aspect, a method includes the following steps: providing a source material dispenser, the source material dispenser comprising a capillary having a nozzle and an electro-actuated element mechanically coupled to and coaxially arranged with the capillary; supplying a control signal to the source material dispenser, the control signal having a component having a frequency substantially equal to a frequency of a resonant mode of the source material dispenser; and supplying a liquid source material to the source material dispenser, the liquid source material being discharged from the nozzle in a stream, the stream being controlled by the control signal to at least one of breakup into droplets and coalescence of the droplets. The resonant mode may be a thickness mode. The resonant mode may be an elastic length mode. The control signal may have at least one sinusoidal component having a frequency matched to the thickness mode of the system comprising the capillary and the electro-actuated element. The control signal may have a coherent ultrasonic component having a frequency and a wavelength matched to the elastic length mode of the source material dispenser. The electro-actuated element may be a piezoelectric element. The control signal can cause the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in an axial direction to promote Rayleigh breakup of the tin jet exiting the nozzle orifice in the capillary tip.

[0014] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments, are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the methods and systems of embodiments of the present invention by way of example and not limitation. Together with the detailed description, the drawings serve to explain the principles and enable one skilled in the relevant art(s) to make and use the methods and systems presented herein. In the drawings, like reference numerals indicate like or functionally similar elements.

[0016] Figure 1 is a schematic, not to scale, illustration of the general broad concept of a laser produced plasma EUV radiation source system according to one aspect of the embodiments.

[0017] Figure 2 is a diagram of an apparatus for distributing source material according to an aspect of an embodiment.

[0018] Figures 3A to 3C is a diagram of thickness mode resonance in an apparatus for distributing source material according to an aspect of an embodiment.

[0019] Figure 4 is a diagram of an apparatus for distributing source material according to an aspect of an embodiment.

[0020] Figure 5 is a diagram of an apparatus for distributing source material according to an aspect of an embodiment.

[0021] Figure 6 is a flowchart of a method of distributing source material according to an aspect of an embodiment.

[0022] Other features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are set forth herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein. DETAILED DESCRIPTION

[0023] Various embodiments will now be described with reference to the accompanying drawings, in which like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, many specific details are set forth in order to facilitate a thorough understanding of one or more embodiments. However, it may be apparent in some or all instances that any embodiment described below can be implemented without adopting the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form to facilitate the description of one or more embodiments. A simplified summary of one or more embodiments is presented below to provide a basic understanding of the embodiments. This summary is not an extensive overview of all envisioned embodiments and is neither intended to identify key or important elements of all embodiments nor to describe the scope of any or all embodiments.

[0024] However, before describing such embodiments in more detail, it is helpful to present an example environment in which embodiments of the present invention may be implemented. In the following description and claims, terms such as "upward," "downward," "top," "bottom," "vertical," and "horizontal" may be used. These terms are intended to illustrate relative directions only, not any direction relative to gravity.

[0025] First refer to Figure 1 , a schematic diagram of an exemplary EUV radiation source (e.g., a laser-generated plasma EUV radiation source 10) according to one aspect of an embodiment of the present invention is shown. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may be, for example, a pulsed gas discharge CO2 laser source that generates a radiation beam 12 having a wavelength typically below 20 μm (e.g., in the range of about 10.6 μm to about 0.5 μm or less). The pulsed gas discharge CO2 laser source may have DC or RF excitation operating at high power and high pulse repetition rate.

[0026] The EUV radiation source 10 also includes a source delivery system 24 for delivering source material in the form of droplets or a continuous liquid stream. In this example, the source material is a liquid, but it can also be a solid or a gas. The source material can be made of tin or a tin compound, but other materials can also be used. In the depicted system, the source material delivery system 24 introduces droplets 14 of source material into the interior of a cavity (e.g., a vacuum chamber) 26 to an irradiation region 28, where the source material can be irradiated to produce a plasma. In some cases, an electric charge is placed on the source material to allow the source material to be steered toward or away from the irradiation region 28. It should be noted that, as used herein, an irradiation region is an area where irradiation of the source material can occur, and is an irradiation region even when no irradiation actually occurs. The EUV light source can also include a beam focusing and steering system 32, as will be described below in conjunction with Figure 2 Explained in more detail.

[0027] In the system shown, the components are arranged so that the droplets 14 travel substantially horizontally. The direction from the laser source 22 toward the irradiation region 28 (i.e., the nominal propagation direction of the beam 12) can be referred to as the Z-axis. The path taken by the droplets 14 from the source material delivery system 24 to the irradiation region 28 can be referred to as the X-axis. Thus, Figure 1 Furthermore, while a system is depicted in which droplets 14 travel substantially horizontally, one of ordinary skill in the art will appreciate that other arrangements in which droplets travel vertically or at an angle relative to gravity (between and including 90 degrees (horizontal) and 0 degrees (vertical)) may be used.

[0028] The EUV radiation source 10 may further include an EUV light source controller system 60, which may further include a laser ignition control system 65 and a beam steering system 32. The EUV radiation source 10 may further include a detector, such as a source position detection system, which may include one or more droplet imagers 70 that generate an output indicating the absolute position of a source droplet or a relative position, for example, relative to the irradiation area 28, and provide the output to the source position detection feedback system 62.

[0029] The source position detection feedback system 62 can use the output of the droplet imager 70 to calculate the source position and trajectory, from which the target error can be calculated. The source error can be calculated on a droplet-by-drop basis or on an average basis or on some other basis. The target error can then be provided as an input to the light source controller system 60. In response, the light source controller system 60 can generate a control signal, such as a laser position, direction, or timing correction signal, and provide the control signal to the laser beam steering system 32. The laser beam steering system 32 can use the control signal to change the position and / or focal length of the laser beam focal spot within the cavity 26. The laser beam steering system 32 can also use the control signal to change the geometry of the interaction between the beam 12 and the droplet 14. For example, the beam 12 can be caused to be offset from the center or to strike the droplet 14 at an angle of incidence other than directly oncoming.

[0030] like Figure 1 As shown, the source material delivery system 24 may include a source delivery control system 90. The source delivery control system 90 is operable to adjust the path of the target droplet 14 through the irradiation area 28 in response to a signal (e.g., the target error described above) or some quantity derived from the target error provided by the light source controller system 60. This can be achieved, for example, by repositioning the point at which the source delivery mechanism 92 releases the target droplet 14. The droplet release point can be repositioned, for example, by tilting the source delivery mechanism 92 or by offsetting the source delivery mechanism 92. The source delivery mechanism 92 extends into the cavity 26 and is preferably supplied with source material from an external source and connected to a gas source to place the source material under pressure in the source delivery mechanism 92.

[0031] continue Figure 1The radiation source 10 may also include one or more optical elements. In the following discussion, the collector 30 is used as an example of such an optical element, but the discussion is also applicable to other optical elements. The collector 30 may be a normal incidence reflector, for example implemented as a multilayer mirror (MLM), with an additional thin barrier layer (e.g., B4C, ZrC, Si3N4, or C) deposited at each interface to effectively block thermally induced interlayer diffusion. Other substrate materials may also be used, such as aluminum (Al) or silicon (Si). The collector 30 may be in the form of an oblate ellipsoid with a central aperture to allow the laser radiation 12 to pass through and reach the irradiation area 28. The collector 30 may be in the shape of an ellipsoid, for example, having a first focus at the irradiation area 28 and a second focus at a so-called intermediate point 40 (also referred to as intermediate focus 40), where the EUV radiation can be output from the EUV radiation source 10 and input to, for example, an integrated circuit lithography scanner or stepper 50 that uses the radiation, for example to process a silicon wafer workpiece 52 using a reticle or mask 54 in a known manner. The mask 54 can be transmissive or reflective. For EUV applications, the mask 54 is typically reflective. The silicon wafer workpiece 52 is then additionally processed in a known manner to obtain an integrated circuit device.

[0032] Figure 1 The device may also include a temperature sensor 34, such as a thermocouple located within the cavity 26, to measure the local temperature of the gas within the cavity 26, ie, the temperature at the sensor. Figure 1 One temperature sensor is shown, but it will be apparent that additional temperature sensors may be used. The temperature sensor 34 generates a signal indicative of the measured temperature and supplies it as an additional input to the light source controller system 60. The light source controller system 60 bases its control signal supplied to the beam steering system 32 at least in part on the temperature signal.

[0033] Figure 2 Components of a simplified source delivery mechanism 92 are illustrated in a schematic format. As shown therein, the source delivery mechanism 92 can include a capillary 94 that holds a fluid 96 (e.g., molten tin) under pressure. Also shown, the capillary 94 can be formed with a nozzle 98 that allows the pressurized fluid 96 to flow through the nozzle 98, establishing a continuous stream 100 that subsequently breaks up into droplets 102. The source delivery mechanism 92 shown also includes a subsystem for generating a disturbance in the fluid 96 having an electrically actuated element 104 operably coupled to the fluid 96 and a signal generator 106 that drives the electrically actuated element 104.

[0034] As further described below, waveforms with different amplitudes, frequencies, or shapes can be used to drive the electro-actuated element 104 to generate droplets for EUV output. The electro-actuated element 104 creates disturbances in the fluid 96 that generate droplets with different initial velocities, causing at least some adjacent droplet pairs to coalesce before reaching the irradiation region. The ratio of initial droplets to coalesced droplets can be 2, 3, or more, and in some cases, tens, hundreds, or more.

[0035] More specifically, when a fluid (e.g., source material) 96 first exits a nozzle 98, the source material is in the form of a steady stream 100 with a disturbed velocity. The stream 100 breaks up into a series of micro-droplets having different velocities. The micro-droplets coalesce into intermediate-sized droplets, called subcoalesced droplets, which have different velocities relative to each other. The subcoalesced droplets then coalesce into droplets 102 having a desired final size. The number of subcoalesced steps can vary. The distance from the nozzle 98 to the point where the droplets reach their final coalesced state is the coalescence distance L. Thus, control of the breakup / coalescing process involves controlling the flow and droplets so that the flow breaks up into droplets, which then coalesce sufficiently before reaching the irradiation zone, and with a frequency corresponding to the pulse rate of the laser used to irradiate the coalesced droplets.

[0036] Control of some aspects of droplet coalescence can be achieved by applying a square wave voltage signal to an electrically actuated element 104 in the form of a piezoelectric actuator to stimulate droplet coalescence. The piezoelectric element can be mounted coaxially with a capillary tube, and the capillary tube can be made of a material such as glass. In the following discussion, a piezoelectric actuator and a glass capillary tube will be used as specific examples, but it will be apparent to one of ordinary skill in the art that other types of actuators can be used and that the capillary tube can be made of materials other than or in addition to glass.

[0037] The square wave can be composed of multiple high-frequency components. These can indirectly promote the sub-coalescence of droplets necessary for Rayleigh breakup and fully coalesced 50 kHz droplets, but do not provide a means to directly control these processes.

[0038] Sine-wave excitation of a piezoelectric actuator, whose frequency matches the thickness mode of the coaxial piezoelectric / capillary system, generates a longitudinal wave of the same frequency, which propagates along the length of the capillary to displace the capillary nozzle in the axial direction. This directly promotes Rayleigh breakup of the tin jet exiting the nozzle orifice. Furthermore, coherent ultrasonic excitation with a frequency in the range of approximately 100 kHz to approximately 1 MHz can be applied to the piezoelectric actuator, which is coaxially arranged with the capillary and mechanically coupled to the capillary. The elastic length mode of the piezoelectric actuator can be matched in frequency and wavelength to the acoustic harmonics of the desired sub-coalescence droplet frequency in the liquid source material in the capillary. This provides a means of directly controlling the coalescence process.

[0039] Regarding the crushing, the thickness of the piezoelectric actuator and the capillary can be set so that they each resonate at a common frequency in the thickness direction. Figures 3A to 3B Middle picture. Figure 3A The profile of the first order thickness mode of the capillary 94 at λ / 4 is shown. Figure 3B The profile of the electro-actuated element 104 is shown having a third-order thickness mode resonance at 5λ / 4. Figure 3C The profile of the overall third-order thickness mode of the capillary / piezoelectric system 300 at 3λ / 2 is shown.

[0040] In the case where the capillary and piezoelectric are configured as such, and as Figure 4 As shown, system thickness modes 400 generate longitudinal waves 402 in the glass capillary 94 that propagate along the capillary axis to displace the capillary nozzle 98 by a distance D. These longitudinal waves thus induce axial displacement of the nozzle 98, providing a direct means of controlling the Rayleigh breakup of the source material flow. By decomposing the system thickness modes into multiple component-level thickness modes, a system can be designed to resonate at an optimal Rayleigh breakup frequency by selecting a frequency-tuned piezoelectric and the glass capillary thickness. For example, the resonant frequency can be in the range of approximately 4 MHz to 6 MHz.

[0041] An impedance sweep can be performed on the system to identify the frequency f1 of the thickness mode resonance. A control signal can be generated having a first component at this frequency and an additional sinusoidal component for controlling coalescence. In other words, the additional sinusoidal component can be composed of multiple (two or more) sinusoidal waves whose frequencies, amplitudes (voltages), and relative phases are selected to completely coalesce the droplets within the desired coalescence length. For example, the second component can be a 600 kHz sinusoidal wave and a 50 kHz sinusoidal wave. For example, the voltage amplitude of the first component at a frequency of approximately 4.2 MHz can be selected to minimize droplet velocity jitter.

[0042] Thus, according to one aspect of the embodiment, an acoustic wave is generated to propagate through the capillary in the axial direction, thereby displacing the nozzle orifice in the axial direction at a designed frequency to promote controlled Rayleigh breakup of the tin jet. High-frequency Rayleigh droplets are first generated at a sine wave frequency that matches the system piezoelectric / capillary thickness mode, then sub-coalesced at an intermediate sine wave frequency (e.g., 600 kHz), and then fully coalesced using another sine wave (e.g., using a combination of three sine waves).

[0043] Regarding the control of coalescence, such as Figure 5As shown, the length of the electro-actuated element 104 coaxially coupled to the capillary 94 can be designed to target specific resonant frequencies and wavelengths corresponding to acoustic harmonics of the fluid 96 (e.g., tin) within the capillary 94. For example, the second-order length mode resonance 500 of the piezoelectric element at 2λ / 2 can be used to target the acoustic harmonics of tin, as shown by trace 502 at ((2n-1)λ / 4). More specifically, and also by way of example only, if the length of the electro-actuated element 104 is approximately 6 mm, then after accounting for the coaxial capacitive fringing effect that reduces the total effective actuation length, the piezoelectric second length mode is approximately 500 kHz and has a wavelength of approximately 2.6 mm. For a system using a capillary tube with a length of approximately 20 mm, the (19λ / 4) frequency and wavelength can be calculated to be approximately 516 kHz and 2.6 mm, respectively. By matching the frequency and wavelength of the piezoelectric element and the liquid source material in the capillary tube, the transfer of electrical energy to the axial jet velocity perturbation at the target frequency can be maximized. This linearizes the droplet generator breakup process, resulting in more precise droplet spacing and also enables more deterministic control of the droplet formation process.

[0044] Thus, according to one aspect of the embodiment, coherent excitation of a capillary filled with an active material using a coaxially bonded piezoelectric actuator whose design length is selected to elastically resonate at a frequency and wavelength common to desired acoustic harmonics in the ultrasonic (100 kHz to 1 MHz) frequency range is used to control the droplet coalescence process.

[0045] According to another aspect, a method of controlling the breakup and / or subsequent agglomeration of a source material stream is disclosed. Figure 6 In step S10, a source material dispenser is provided, wherein the source material dispenser is sized and configured as described above to have a resonance at the frequency of the control signal to be applied. For example, the selection can be to select a thickness mode resonance of the dispenser to cause an axial displacement of the dispenser nozzle to control the process of the stream leaving the nozzle breaking into droplets. The selection can also be used to match the longitudinal resonance of the piezoelectric with the acoustic harmonics of the liquid source material filling the capillary to control coalescence. In step S20, a control signal is applied to the source material dispenser, wherein the frequency component of the control signal is selected to match the resonant characteristics that the source material dispenser has been constructed to exhibit. In step S30, the source material is supplied to the dispenser. It will be understood that, depending on the specific application, the step of supplying the source material can be performed before the step of supplying the control signal.

[0046] The present invention has been described above with the aid of functional building blocks that illustrate the implementation of specified functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined in this article. Alternative boundaries can be defined as long as the specified functions and their relationships are properly performed.

[0047] The foregoing description of specific embodiments is so comprehensive as to demonstrate the generality of the invention that others, by applying knowledge in the art, can readily modify and / or adapt such specific embodiments for various applications without undue experimentation and without departing from the general concepts of the invention. Therefore, based on the teachings and guidance set forth herein, such adaptations and modifications are intended to be within the meaning and scope equivalent to the disclosed embodiments. It is to be understood that the wording or terminology herein is for descriptive purposes and not for limiting purposes, and therefore, the wording or terminology of this specification is to be interpreted by those skilled in the art in accordance with the teachings and guidance. The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined solely in accordance with the appended claims and their equivalents.

[0048] Further aspects of the invention are set out in the following numbered clauses:

[0049] 1. A source material distributor, comprising:

[0050] capillary tubes; and

[0051] an electro-actuating element mechanically coupled to the capillary and arranged coaxially with the capillary,

[0052] At least one dimension of at least one of the capillary tube and the electro-actuating element is selected such that the source material dispenser has a resonant mode at a frequency component of a periodic control signal.

[0053] 2. The source material dispenser of clause 1, wherein the resonant mode is a thickness mode of the capillary tube together with the electro-actuating element.

[0054] 3. A source material dispenser according to clause 1 or 2, wherein the capillary tube and the electro-actuating element are sized such that the capillary tube and the electro-actuating element each resonate at a common frequency in the thickness direction.

[0055] 4. The source material dispenser of clause 1 , wherein the resonant mode is an elastic length mode.

[0056] 5. The source material dispenser of clause 4, wherein the length of the electro-actuated element is selected such that when source material fills the capillary tube, the resonant frequency of the electro-actuated element is substantially the same as the frequency of an acoustic harmonic of the source material.

[0057] 6. A source material dispenser according to any one of clauses 1 to 5, wherein the electrically actuated element comprises a piezoelectric element.

[0058] 7. A device comprising:

[0059] a source material dispenser comprising a capillary tube and an electro-actuating element mechanically coupled to and coaxially arranged with the capillary tube to form a capillary electro-actuating element system; and

[0060] A signal generator is electrically coupled to the electro-actuating element to supply a control signal, wherein the control signal includes a periodic signal having a frequency component that matches at least one resonant mode of the capillary electro-actuating element system.

[0061] 8. The device of clause 7, wherein the periodic control signal has a sinusoidal component having a frequency matched to a thickness mode of the capillary electro-actuating element system.

[0062] 9. Apparatus according to clause 7, wherein the periodic control signal has a coherent ultrasonic component matched in frequency and wavelength to the elastic length mode of said source material dispenser.

[0063] 10. The device of clause 7, wherein the electro-actuating element comprises a piezoelectric element.

[0064] 11. An apparatus according to item 7, wherein the control signal causes the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in an axial direction to promote Rayleigh breakup of the source material jet leaving the nozzle orifice in the capillary tip.

[0065] 12. A method comprising the steps of:

[0066] providing a source material dispenser comprising a capillary having a nozzle and an electro-actuation element mechanically coupled to and coaxially arranged with the capillary;

[0067] supplying a control signal to the source material dispenser, the control signal having a component having a frequency substantially equal to a frequency of a resonant mode of the source material dispenser; and

[0068] A liquid source material is supplied to the source material dispenser, the liquid source material being discharged from the nozzle in a stream, at least one of the stream being broken up into droplets and the droplets being coalesced as controlled by the control signal.

[0069] 13. The method of clause 12, wherein the resonant mode is a thickness mode of the capillary together with the electro-actuating element.

[0070] 14. The method of clause 12, wherein the resonant mode is an elastic length mode.

[0071] 15. The method of clause 12, wherein the control signal has at least one periodic wave component having a frequency matched to a thickness mode of a system comprising the capillary and the electro-actuating element.

[0072] 16. The method of clause 12, wherein the control signal has a coherent ultrasonic component that matches in frequency and wavelength the elastic length mode of the source material dispenser.

[0073] 17. The method of clause 12, wherein the electro-actuating element is a piezoelectric element.

[0074] 18. A method according to item 12, wherein the control signal causes the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in an axial direction to promote Rayleigh breakup of the tin jet exiting the nozzle orifice in the capillary tip.

Claims

1. A source material distributor, comprising: capillary; as well as an electro-actuating element mechanically coupled to the capillary and arranged coaxially with the capillary, At least one dimension of at least one of the capillary tube and the electro-actuating element is selected so that the source material dispenser has a resonant mode at a frequency component of the periodic control signal, The periodic control signal causes the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component of the periodic control signal, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in the axial direction to promote Rayleigh breakup of a jet of source material exiting a nozzle orifice in the capillary tip. 2 . The source material dispenser of claim 1 , wherein the resonant mode is a thickness mode of the capillary tube together with the electro-actuated element. 3 . The source material dispenser of claim 2 , wherein the capillary tube and the electro-actuated element are sized such that the capillary tube and the electro-actuated element each resonate at a common frequency in a thickness direction. 4 . The source material dispenser of claim 1 , wherein the capillary tube and the electro-actuated element are sized such that the capillary tube and the electro-actuated element each resonate at a common frequency in a thickness direction.

5. The source material dispenser of claim 1, wherein the resonant mode is an elastic length mode.

6. The source material dispenser of claim 5, wherein the length of the electro-actuated element is selected such that when source material fills the capillary tube, a resonant frequency of the electro-actuated element is substantially the same as a frequency of an acoustic harmonic of the source material.

7. The source material dispenser of claim 1, wherein the electrically actuated element comprises a piezoelectric element.

8. The source material dispenser of claim 4, wherein the electrically actuated element comprises a piezoelectric element.

9. A device comprising: a source material dispenser comprising a capillary tube and an electro-actuating element mechanically coupled to the capillary tube and coaxially arranged with the capillary tube to form a capillary electro-actuating element system; as well as a signal generator electrically coupled to the electro-actuating element for supplying a control signal, the control signal comprising a periodic signal having a frequency component matched to at least one resonant mode of the capillary electro-actuating element system, The control signal causes the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component of the control signal, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in an axial direction to promote Rayleigh breakup of a jet of source material exiting a nozzle orifice in the capillary tip.

10. The device of claim 9, wherein the control signal has a sinusoidal wave component having a frequency matched to a thickness mode of the capillary electro-actuating element system.

11. The apparatus of claim 9, wherein the control signal has a coherent ultrasonic component that matches in frequency and wavelength the elastic length mode of the source material dispenser.

12. The device of claim 9, wherein the electrically actuated element comprises a piezoelectric element.

13. A method comprising the steps of: providing a source material dispenser comprising a capillary having a nozzle and an electro-actuation element mechanically coupled to and coaxially arranged with the capillary; supplying a control signal to the source material dispenser, the control signal having a component having a frequency substantially equal to a frequency of a resonant mode of the source material dispenser; as well as supplying a liquid source material to the source material dispenser, the liquid source material being discharged from the nozzle in a stream, at least one of the stream breaking up into droplets and the droplets coalescing being controlled by the control signal, The control signal causes the electro-actuated element to generate a longitudinal wave in the capillary having a wave frequency substantially the same as the frequency of the wave component of the control signal, the longitudinal wave propagating along the length of the capillary to displace the tip of the capillary in an axial direction to promote Rayleigh breakup of a tin jet exiting a nozzle orifice in the capillary tip. The method of claim 13 , wherein the resonant mode is a thickness mode of the capillary tube together with the electro-actuating element. The method of claim 13 , wherein the resonant mode is an elastic length mode. 16 . The method of claim 13 , wherein the control signal has at least one periodic wave component having a frequency matched to a thickness mode of a system including the capillary tube and the electro-actuating element.

17. The method of claim 13, wherein the control signal has a coherent ultrasonic component that matches in frequency and wavelength the elastic length mode of the source material dispenser. The method according to claim 13 , wherein the electrically actuated element is a piezoelectric element.

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