Targeted delivery system

Abstract

A target delivery system for an extreme ultraviolet (EUV) light source is disclosed. The system includes a conduit including an aperture configured to be fluidly coupled to a reservoir; an actuator configured to be mechanically coupled to the catheter such that movement of the actuator is transmitted to the catheter; and a control system coupled to the actuator, the control system configured to determine an indication of a pressure applied to the target material in the reservoir, and control movement of the actuator based on the determined indication of the applied pressure. Also, techniques for operating the provisioning system are disclosed. For example, one or more characteristics of the supply system are determined, and an actuator mechanically coupled to the supply system is controlled based on the one or more determined characteristics such that the aperture of the supply system remains substantially free of material damage during operational use.

Description

[0001] This application is a divisional application filed on the international application date of January 9, 2020, entered the Chinese national phase on July 16, 2021, with application number 202080009683.0 and invention name “Target Delivery System”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Application No. 62 / 793,813, filed on January 17, 2019, entitled “TARGETED DELIVERY SYSTEM,” and U.S. Application No. 62 / 913,552, filed on October 10, 2019, entitled “TARGETED DELIVERY SYSTEM,” both of which are incorporated herein by reference in their entirety. Technical Field

[0004] The present disclosure relates to a targeted delivery system for an extreme ultraviolet (EUV) light source. Background Art

[0005] Extreme ultraviolet (“EUV”) light—e.g., electromagnetic radiation having a wavelength of 100 nanometers (nm) or less (sometimes also referred to as soft X-rays) and including light having a wavelength of, for example, 20 nm or less, between 5 nm and 20 nm, or between 13 nm and 14 nm—can be used in photolithography processes to create extremely small features in a substrate such as a silicon wafer by initiating polymerization in a resist layer.

[0006] Methods of generating EUV light include, but are not limited to, converting materials including elements such as xenon, lithium, or tin that have emission lines in the EUV range in a plasma state. In one such method, often referred to as laser produced plasma ("LPP"), the desired plasma may be generated by irradiating a target material in the form of droplets, sheets, ribbons, streams, or clusters of material using an amplified beam, which may be referred to as a drive laser. For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of metrology equipment. Summary of the invention

[0007] In one aspect, a target delivery system for an extreme ultraviolet (EUV) light source includes a conduit including a hole configured to be fluidically coupled to a reservoir; an actuator configured to be mechanically coupled to the conduit so that movement of the actuator is transmitted to the conduit; and a control system coupled to the actuator, the control system configured to determine an indication of pressure applied to a target material in the reservoir and to control movement of the actuator based on the determined indication of the applied pressure.

[0008] Implementations may include one or more of the following features. The control system may also be configured to compare the determined indication of the applied pressure with a threshold, and the control system being configured to control the movement of the actuator based on the determined indication of the applied pressure may include: the control system is configured to control the movement of the actuator based on the comparison. The movement of the actuator may generate a displacement in the conduit wall and an acoustic wave inside the conduit, and the threshold may be related to the amplitude of the acoustic wave. The control system being configured to control the actuator based on the comparison may include: the control system is configured to only cause the actuator to generate a displacement in the conduit wall if the determined indication of the applied pressure is greater than the threshold. The threshold may be a threshold pressure between zero and an operating pressure, and the operating pressure may be an amount of pressure applied to the target material in the reservoir during operation of the EUV light source. The acoustic wave may include a maximum amplitude, and the threshold may be defined by the maximum amplitude. The threshold may be a threshold pressure in the range of 200 pounds per square inch (PSI) to 1000 pounds. The control system may also include one or more electronic processors, and a non-transitory computer-readable storage medium coupled to the one or more electronic processors.

[0009] In some implementations, the control system is configured to control movement of the actuator based on the determined indication of applied pressure, including: the control system is configured to provide a modulation signal to the actuator based on the determined indication of applied pressure, the modulation signal being sufficient to cause the actuator to produce a displacement in the conduit wall. The actuator may include a piezoelectric modulator, and the modulation signal may include an electrical signal sufficient to cause the shape of the piezoelectric modulator to change.

[0010] The control system may also include an electrical switch configured to be coupled to the actuator, and wherein the electrical switch is configured to receive an indication of applied pressure, the electrical switch being configured to have a particular possible state of a plurality of possible states at a particular time, the electrical switch allowing the modulated signal to reach the actuator in a state less than all of the plurality of states, the particular state of the electrical switch at a particular time being determined by the received indication of applied pressure, and the control system being configured to determine the indication of applied pressure includes determining that the electrical switch is in a particular state. The indication of applied pressure may be received from a separate pressure switch coupled to the reservoir. The received indication of applied pressure may include an analog signal received directly from a pressure sensor. The received indication of applied pressure may include an electronic signal generated by instructions executed by an electronic processor.

[0011] In some implementations, an interior surface of the conduit is configured to be exposed to the target material, and the interior surface is substantially free of defects to reduce cavitation in the target material.At least a portion of the interior surface can be flame polished.

[0012] The control system being configured to determine the indication of the pressure applied to the target material may include the control system being configured to analyze the indication from a pressure sensor configured to measure the applied pressure.

[0013] In another aspect, a targeted delivery system for an extreme ultraviolet (EUV) light source includes a conduit including an aperture configured to be fluidically coupled to a reservoir; an actuator configured to be mechanically coupled to the conduit such that movement of the actuator is transmitted to the conduit; a signal generator configured to provide a modulated signal to the actuator sufficient to cause the actuator to move; and a control system coupled to the actuator and the signal generator, the control system configured to control one or more characteristics of the modulated signal, thereby controlling one or more characteristics of the movement of the actuator, such that, when used, the aperture is substantially free of material damage.

[0014] Implementations may include one or more of the following features. One or more characteristics may include the frequency content of the modulation signal, and the control system may be configured to control the frequency content of the modulation signal. The control system may be configured to reduce the amplitude of components in the modulation signal whose frequencies are below a frequency threshold. The mechanically coupled actuator and catheter may form an actuator-catheter assembly, and the control system may be configured to reduce the amplitude of components in the modulation signal at frequencies associated with: an eigenmode of the actuator-catheter assembly or its harmonics and subharmonics.

[0015] The one or more characteristics may include an amplitude of the modulation signal, and the control system is configured to control the amplitude of the modulation signal. The control system may be configured to maintain the amplitude of the modulation signal below an amplitude limit. The amplitude limit may be a peak-to-peak amplitude limit.

[0016] The hole can remain substantially crack-free.

[0017] The aperture may be defined by the end of the conduit.

[0018] The conduit may be coupled to the structure defining the aperture.

[0019] In another aspect, a target delivery system for an extreme ultraviolet (EUV) light source includes a reservoir configured to hold a mixture including a target material and inclusion particles; a conduit including a hole configured to be fluidically coupled to the reservoir; an actuator configured to be mechanically coupled to the reservoir so that movement of the actuator is transmitted to the reservoir; and a control system coupled to the actuator, the control system configured to control movement of the actuator so that inclusion particles in the mixture move toward a surface of the mixture.

[0020] Implementations may include one or more of the following features. The actuator may be an ultrasonic actuator. The target delivery system may also include a gas delivery system configured to deliver a flowing gas across the surface of the mixture. The flowing gas may include at least one component configured to react with the inclusion particles, thereby removing at least some of the inclusion particles from the surface. The target material may include molten tin, the inclusion particles may include tin oxide particles, and the flowing gas may include hydrogen. The movement of the actuator may be controlled so that cavitation is induced in the mixture and the inclusion particles are moved toward the surface by bubbles formed around the particles by cavitation.

[0021] The targeted delivery system may further include one or more filters located between the reservoir and the well, the filters configured to substantially prevent the inclusion particles from reaching the well.The inclusion particles may have a diameter of 1 micrometer (μm) or less.

[0022] The inclusion particles may include tin oxide particles.

[0023] In another aspect, a method of operating a targeted supply system of an EUV light source includes: determining one or more characteristics of the supply system; and controlling an actuator mechanically coupled to the supply system based on the determined one or more characteristics so that an aperture of the supply system remains substantially free of material damage during operational use.

[0024] Implementations of any of the techniques described above may include EUV light sources, target supply systems, methods, processes, devices or apparatuses. Details of one or more implementations are set forth in the accompanying drawings and the following description. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a block diagram of an example of an EUV light source including a supply system.

[0026] Figure 2A is a side cross-sectional view of an example of a target forming structure.

[0027] Figure 2B yes Figure 2A A top cross-sectional view of a target forming structure.

[0028] FIG. 3A to FIG. 3C and Figure 4 It has multiple control systems Figure 1 Block diagram of an example of an EUV light source.

[0029] Figure 5 is a block diagram of another example of an EUV light source.

[0030] Figure 6 is a flow chart of an example of a process for operating a supply system for an EUV light source.

[0031] Fig. 7A and Figure 7B is a block diagram of an example of a lithographic apparatus.

[0032] Figure 8 is a block diagram of an example of an EUV light source. DETAILED DESCRIPTION

[0033] refer to Figure 1 , a block diagram of an EUV light source 100 including a supply system 110 is shown. The supply system 110 emits a stream of targets 121 such that the targets 121p are delivered to a plasma formation location 123 in a vacuum chamber 109. The targets 121p include a target material, which is any material that emits EUV light when in a plasma state. For example, the target material may include tin, lithium, or xenon. The plasma formation location 123 receives a light beam 106. The light 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 light beam 106 and the target material in the target 121p produces a plasma 196 that emits EUV light.

[0034] The supply system 110 may include a capillary 114 having a hole 119. The hole 119 is located at the end of the capillary 114 and forms the outlet of the capillary 114. The capillary 114 may be made of, for example, fused silica or glass in the form of quartz. The capillary 114 is shown in more detail in the inset (in Figure 1 The side wall 150 of the capillary 114 passes through (in Figure 1 109 is a schematic diagram of a vacuum chamber 109 in which a plurality of vacuum chambers 109 are provided. The vacuum chamber 109 is provided with a plurality of vacuum chambers 109 and ... 4 SnBr 2 SnH 4; Tin alloys, such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys are used. The target mixture may also include impurities such as non-target particles or inclusion particles 117. Inclusion particles 117 may be, for example, tin oxide (SnO 2 ) particles or tungsten (W) particles.

[0035] The target mixture 111 is a liquid material that can flow in the capillary 114. For example, in an implementation where the target mixture 111 includes a metal (such as tin) that is solid at room temperature, the metal is melted and is in a liquid state in the target mixture 111. Under certain conditions, cavitation bubbles may be formed in the target mixture 111. Bubbles may damage the capillary 114 and / or the hole 119. The following is a discussion of techniques for reducing or eliminating bubble formation. When the pressure p is greater than the Laplace pressure, the target mixture 111 flows through the capillary 114 and is ejected into the chamber 109 through the hole 119. The Laplace pressure is the pressure difference between the inside and outside of a curved surface that forms a boundary between a gas region and a liquid region. The pressure difference is caused by the surface tension of the interface between the liquid and the gas. When the pressure p is greater than the Laplace pressure, the target mixture 111 leaves the hole 119 as a continuous jet 124.

[0036] The jet 124 breaks up into individual targets (e.g., droplets) according to the Rayleigh-Plateau instability of the liquid jet. The breakup of the jet 124 is controlled by vibrating the capillary 114 using the actuator 132 so that the individual droplets coalesce into larger droplets that arrive at the plasma formation location 123 at a desired rate. The movement of the actuator 132 deforms the sidewall 150 of the capillary 114, thereby generating acoustic waves in the target mixture 111 located in the capillary 114. When the disturbance of the acoustic pressure amplitude in the target mixture 111 in the capillary 114 exceeds the pressure p applied to the reservoir 112, cavitation (that is, bubble formation) may occur in the target mixture 111. For example, during the startup process when the pressure p increases from a low startup pressure to an operating pressure, during the shutdown process when the pressure p decreases from the operating pressure to the startup pressure, or when the pressure p unexpectedly decreases during operation, the disturbance of the acoustic pressure amplitude in the target mixture 111 may exceed the pressure p.

[0037] When conditions are favorable for cavitation, the initial bubble may continue to grow over time as more and more residual gas dissolved in the target material diffuses toward the bubble; the gas diffusion and alternating acoustic pressure that contribute to the creation of a bubble of critical size eventually cause the bubble to collapse. The collapse of the bubble can generate a high-speed liquid jet that can be directed toward the wall of the capillary; as a result, a large local pressure (e.g., 1 gigapascal (GPa)) large enough to damage the capillary 114 can be generated. Therefore, the formation of bubbles in the target mixture 111 may cause damage (e.g., cracks) to the sidewall 150 or the hole 119.

[0038] Such damage may result in reduced performance of the supply system 110 and the EUV light source 100. For example, when the hole 119 is damaged, the size of the droplets in the stream 121 is different from the expected size and the droplets do not reach the plasma formation region 123 as expected. Moreover, damage on the edge of the hole 119 may cause the jet 124 to be emitted from the hole 119 at a certain angle, so that the droplets in the stream 121 are not directed to the plasma formation location 123 at all. Therefore, damage to the hole 119 may cause the light beam 106 to fail to irradiate the droplets and produce less EUV light or no EUV light. Therefore, when cracks are formed on the hole 119, the performance of the EUV light source 100 may be reduced.

[0039] In some existing systems and technologies, material damage to the capillary 114 and / or the hole 119 is believed to be caused entirely by hard particles (such as, for example, tungsten particles and tin oxide particles) passing through the capillary 114 and the hole 119. As discussed above, these particles may be located in the target mixture 111. Although these particles can be removed by conventional mechanical filtering techniques, material damage may still occur due to cavitation in the target mixture 111. Therefore, preventing or reducing cavitation can contribute to the robust operation of the EUV light source 100. In the EUV light source 100, the control system 160 is used to prevent or reduce the occurrence of cavitation. Several implementations of the control system 160 and techniques for reducing or eliminating cavitation in the target mixture 111 are discussed below. Before discussing the techniques for reducing or eliminating cavitation, the operation and structure of the supply system 110 are discussed in more detail.

[0040] The actuator 132 is coupled to the control system 160 via a control link 162. Figure 1 , FIG. 3A to FIG. 3C , Figure 4 and Figure 5In , the dashed lines indicate the communication paths or links along which the electrical signals including data and information flow. The control system 160 may include or be coupled to a function generator, an electronic processor (not shown), and / or an electronic storage device (not shown) for performing the functions of the control system 160. The control link 162 is any type of connection capable of transmitting data from the control system 160 to the actuator 132. For example, the control link 162 may be a wired connection and / or a wireless connection configured to transmit electronic signals and commands between the control system 160 and the actuator 132. The control system 160 generates a signal that, when applied to the actuator 132 or an element associated with the actuator 132, causes the actuator 132 to move. For example, the actuator 132 may be a piezoelectric ceramic material that changes shape based on an applied voltage. In these implementations, the control system 160 generates a signal that is delivered to a function generator (not shown) that applies a waveform to the actuator 132. The amplitude and / or polarity of the waveform applied to the actuator 132 is based on a signal from the control system 160. Due to the mechanical coupling between the capillary 114 and the actuator 132, when the actuator 132 moves or vibrates, the sidewall 150 is deformed. Thus, the capillary 114 undergoes movement or vibration corresponding to the movement of the actuator 132.

[0041] The motion of the actuator 132 is used to control the characteristics of the droplets arriving at the plasma formation location 123. The control system 160 can provide a signal having at least a first frequency and a second frequency component via the control link 162, thereby driving the actuator 132 to vibrate at the first frequency and the second frequency. The first frequency can be in the megahertz (MHz) range. Vibrating the capillary 114 at the first frequency causes the jet 124 to break up into relatively small targets of desired size and speed. The second frequency is lower than the first frequency, and the second frequency is the frequency of the target when it is fully formed, thereby matching the frequency of the pump laser pulse of the EUV light source. For example, the second frequency can be in the kilohertz (kHz) range. The second frequency is used to adjust the speed of the target in the flow and promote droplet coalescence. Driving the capillary 114 at the second frequency causes a target group to be formed. In any given target group, different targets travel at different speeds. Targets with higher speeds can coalesce with targets with lower speeds to form larger coalesced targets that constitute the target stream 121. The distances separating these larger targets from each other are greater than the distances separating the uncoalesced droplets. The larger separation distance helps mitigate the effect of the plasma formed by one target on the trajectory of subsequent targets in target stream 121. After coalescence, the targets in target stream 121 are approximately spherical and are on the order of 30 micrometers (μm).

[0042] By vibrating the capillary 114 in this manner, a target can be generated, for example, at a frequency between 40 kHz and 300 kHz and can travel toward the plasma formation location 123 at a speed between 40 meters per second (m / s) and 120 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 millimeter (mm) and 3 mm. It may be necessary to merge 50 initial droplets to 300 initial droplets (also called Rayleigh droplets) to form a single larger target.

[0043] Typically, more than two frequencies are used in the target jet modulation signal. The introduction of additional spectral components of the modulation signal allows for a better controlled and faster (more efficient) droplet coalescence process. Typically, these additional frequencies are higher order harmonics of the desired frequency of the droplets and are selected from the range between the second frequency (frequencies in the kHz range) and the first frequency (frequencies in the MHz range). The modulation waveform may consist of a number of deliberately selected sinusoidal waves aligned in phase and amplitude, or a periodic waveform (such as, for example, a pulse wave, a sawtooth wave, or a sine wave) containing high frequency harmonics of the desired droplet frequency ("second frequency").

[0044] Figure 2A is a side cross-sectional view of the target forming structure 216 in the XZ plane. Figure 2B It is along Figure 2A 2B′-2B′ is a top cross-sectional view of the target forming structure 216 in the YZ plane.

[0045] It can be possible to use EUV light source 100 ( Figure 1 ) uses a target forming structure 216 instead of the capillary 114, the actuator 132, and the adhesive 134. The target forming structure 216 includes the capillary 214, which is mechanically coupled to the actuator 232 by the adhesive 234 (shown in cross-hatching). The adhesive 234 is any type of adhesive capable of mechanically coupling the capillary 214 and the actuator 232. For example, the adhesive 234 can be a benzoxazine resin, a resin containing benzoxazine, a cyanate resin, a resin containing cyanate, a bismaleimide-based adhesive, or an epoxy resin.

[0046] Capillary 214 includes a sidewall 250 extending from a first end 251 to a second end 252 along the X direction. Sidewall 250 is a three-dimensional object that is generally cylindrical. Sidewall 250 includes an inner surface 253 and an outer surface 254. Inner surface 253 defines an inner region 258 ( Figure 2A and Figure 2B), the inner region is in fluid communication with a nozzle 255 at the first end 251. The nozzle 255 is along the -X direction to define the hole 219. In operation, the inner region 258 is fluidly coupled to a reservoir (such as a Figure 1 reservoir 112), and the target mixture flows in the inner region 258 of the capillary 214 and through the hole 219 in the -X direction.

[0047] Defects on the inner surface 253 and / or the hole 219, such as, for example, microcracks, dents, recesses, and particles, can serve as nucleation sites that promote cavitation and bubble formation in the target mixture 111. To reduce or eliminate the formation of these bubbles, the inner surface 253 and the hole are made substantially free of defects. For example, the inner surface 253 and the hole 119 may be flame polished. Flame polishing is a technique for polishing the rough edge of a glass object by applying a flame to the edge.

[0048] exist Figure 2A and Figure 2B In the example of , the actuator 232 is a cylinder having an outer actuator surface 235 and an inner actuator surface 236. The inner actuator surface 236 defines an open central area extending along the X direction. The inner actuator surface 236 surrounds the outer surface 254. The actuator 232 is made of any material that can move the sidewall 250. For example, the actuator 232 can be a piezoelectric ceramic material, such as lead zirconate titanate (PZT) that changes shape in response to an applied voltage. By changing shape, the PZT also deforms the sidewall 250 of the capillary 214. For example, the actuator 232 can vibrate or squeeze the sidewall 250 of the capillary 214.

[0049] refer to Figure 3A , a block diagram of an EUV light source 100 having a control system 360A is shown. The control system 360A is a control system 160 ( Figure 1 ) is an example of an implementation method.

[0050] The control system 360A is coupled to the reservoir 112 and the actuator 132. The control system 360A controls the actuator 132 based on the pressure p applied to the target mixture 111. For example, the control system 360A can control the actuator 132 such that the actuator 132 vibrates the capillary 114 only when the pressure p is greater than a threshold pressure. The threshold pressure is a pressure that is lower than the operating pressure. The operating pressure is the value of the pressure p during typical operation when the light source 100 is generating EUV light. The operating pressure can be, for example, from 3000 (psi) to 15000 (psi) or higher. The threshold pressure can be, for example, from 200 psi to 1000 psi. Thus, the control system 360A can prevent the capillary 114 from vibrating unless the pressure p is greater than 200 psi, greater than 500 psi, or greater than 1000 psi. The exact value of the threshold pressure is defined by the maximum amplitude of the pressure wave generated by the actuator in the capillary. By preventing the capillary 114 from vibrating when the pressure p is relatively low, the control system 360A prevents or reduces cavitation.

[0051] The control system 360A can be implemented in a variety of ways, and two examples are discussed with respect to Figure 3B and Figure 3C two examples.

[0052] Figure 3B is a block diagram of an EUV light source 100 having a control system 360B. The control system 360B is an implementation of the control system 360A. The control system 360B is coupled to a pressure system 370 that pressurizes the reservoir 112. The pressure system 370 includes a pressure equipment system 373 that includes, for example, pumps, gas supplies, valves, and / or other equipment capable of increasing, decreasing, or maintaining the pressure p applied to the target mixture 111 in the reservoir 112.

[0053] The pressure system 370 also includes a communication interface 372 that is coupled to a data link 371. The pressure system 370 and the control system 360B are coupled via the data link 371. The data link 371 is any type of communication channel through which data, information, and / or commands can be provided, and the data link 371 can be a wired connection or a wireless connection. The pressure system 370 can provide the value of the applied pressure p (or an indication of the value of the applied pressure p) to the control system 360B via the data link 371, or the control system 360B can retrieve the value of the pressure p from the pressure system 370. In some implementations, the pressure system 370 includes a pressure sensor (not shown) that measures the applied pressure p. In other implementations, the pressure system 370 is calibrated to apply a specific pressure p, and the pressure system 370 provides information related to the applied pressure p without measuring the actually applied pressure p.

[0054] The control system 360B is implemented using an electronic processor 361B, an electronic memory 362B, and an I / O interface 363B. The I / O interface 363B is an interface of any type that allows the control system 360B to receive or send information or data. For example, the I / O interface 363B can be a keyboard, a mouse, or other computer peripherals that enable an operator to operate and / or program the control system 360B. The I / O interface 363B can include a device that generates a perceptible alarm, such as a light or a speaker. Further, the I / O interface 363B can include a communication interface, such as a universal serial port (USB), a network connection, or any other interface that allows communication with the control system 360B.

[0055] Electronic processor 361B includes one or more processors suitable for executing computer programs (such as general-purpose microprocessors or special-purpose microprocessors), and any one or more processors of any type of digital computer. Typically, the electronic processor receives instructions and data from a read-only memory, a random access memory (RAM), or both. Electronic processor 361B can be any type of suitable electronic processor.

[0056] Electronic storage device 362B can be a volatile memory, such as RAM, or a non-volatile memory. In some implementations, electronic storage device 362B includes non-volatile and volatile parts or components. Electronic storage device 362B can store data and information for operating control system 360B. For example, electronic storage device 362B can store information about the operation of supply system 110 and / or pressure system 370. In some implementations, electronic storage device 362B stores the value of pressure p that should be applied during typical operation of supply system 110. Moreover, electronic storage device stores threshold value. The threshold value is a value that is a pressure below or related to the pressure at which cavitation is known to occur or may occur. For example, the threshold value can be a pressure expressed in PSI or a value related to the following pressure (such as a voltage value generated by a switch or electrical device), under which cavitation is known to occur or may occur.

[0057] Additionally, the electronic storage device 362B stores instructions (e.g., in the form of a computer program) that, when executed, cause the electronic processor 361B to provide an electrical signal (e.g., a modulation signal or an excitation signal) to the actuator 132 so that the actuator 132 vibrates the capillary 114. The electronic storage device 362B can store information sufficient to cause the electronic processor 361B to generate a modulation signal with a variety of different characteristics. For example, the control system 360B can generate a modulation signal that is a sinusoidal voltage signal with a specific maximum and minimum amplitude and frequency, or a square wave with a specific duty cycle, maximum amplitude and minimum amplitude, or a combination of such waveforms. In this way, the control system 360B can also perform as a function generator.

[0058] Electronic storage 362B also stores instructions (e.g., in the form of a computer program) that implement various analyses related to preventing cavitation or reducing the occurrence of cavitation. For example, electronic storage 362B may store instructions for analyzing a pressure value from pressure system 370 and comparing that value to a threshold value stored in electronic storage 362B. Electronic storage 362B may also include instructions related to the operation of supply system 110 that are dependent on the comparison between the stored threshold value and the value of pressure p indicated by pressure system 370.

[0059] Electronic storage device 362B also stores instructions, such as a computer program, that, when executed, cause electronic processor 361B to communicate with components in supply system 110 and / or pressure system 370. For example, electronic storage device 362B stores instructions that cause electronic processor 361B to provide modulated signals via link 162 that are sufficient to cause actuator 132 to vibrate capillary tube 114 only when the pressure provided from pressure system 370 is greater than a stored threshold pressure.

[0060] In some implementations, the control system 360B also includes an electrical switch 381 that is used to control the flow of modulated signals to the actuator 132. The electrical switch 381 has multiple states, less than all of which allow signals from the control system 360B to reach the actuator 132. For example, the electrical switch 381 can have an ON state in which the switch 381 passes electrical signals from the control system 360B to the actuator 132 and an OFF state in which the switch 381 does not allow modulated signals from the control system 360B to reach the actuator.

[0061] Figure 3C 360C is another embodiment of the implementation of the control system 360A. The control system 360C includes an electrical switch 381. Figure 3CIn an implementation of , the electrical switch 381 is used to directly control the operation of the function generator 384 , which provides a modulation signal to the actuator 132 via the link 162 .

[0062] The electrical switch 381 is coupled to the pressure indicator 383 and the function generator 384. The electrical switch 381 receives an indication of the amount of pressure p from the pressure indicator 383. The switch 381 has a plurality of states, and the state of the switch 381 is determined by the pressure p received from the pressure indicator. In at least one state, the switch 381 prevents the modulation signal generated by the function generator 384 from reaching the actuator 132. In at least one other state, the switch 381 allows the modulation signal generated by the function generator 384 to reach the actuator 132. For example, the electrical switch 381 can enable the output signal in the function generator 384 in one state but not in another state. In another example, the electrical switch 381 disconnects the electrical path between the function generator 384 and the actuator 132 in one state and closes the electrical path in another state. In this implementation, the modulation signal can only reach the actuator when the electrical path is closed. Therefore, the control system 360C controls the operation of the actuator 132 (therefore controlling the vibration of the capillary 114) based on the pressure p.

[0063] The pressure indicator 383 is any type of device capable of generating an electrical signal (e.g., voltage and / or current) representing the value of the pressure p. In some implementations, the pressure indicator 383 is a pressure sensor that directly measures the pressure p and generates an electrical signal representing the measured pressure p. In these implementations, the electrical signal from the pressure indicator 383 is a current or voltage having an amplitude indicating the amount of the measured applied pressure p. The amplitude of the electrical signal from the pressure sensor is sufficient to cause the electrical switch 381 to change state. For example, the electrical signal may be a voltage signal, and the electrical switch 381 may be a transistor or a diode that allows current to flow only when the amplitude of the voltage signal is above a certain value.

[0064] In other implementations, a pressure switch is used as the pressure indicator 383. A pressure switch is a switch that closes an electrical circuit when a predetermined fluid pressure is reached at the input of the pressure switch. The pressure switch may be, for example, a capsule that includes a moving element such as a bellows, a piston, or a diaphragm that moves or deforms based on the pressure at the input of the pressure switch. When the predetermined pressure is reached or exceeded, the movement or deformation causes the electrical contacts to make physical contact, thereby closing the pressure switch.

[0065] In an implementation using a pressure switch as the pressure indicator 383, the input of the pressure switch is coupled to the reservoir 112 so that when the pressure p applied to the target mixture 111 is greater than a predetermined fluid pressure, the pressure switch is closed. The output of the pressure switch is coupled to the electrical switch 381. When the pressure switch is closed (i.e., when the pressure p of the target mixture 111 is greater than a predetermined pressure), the electrical switch 381 is in a state in which the electrical switch 381 allows the modulation signal generated by the function generator 384 to reach the actuator 132. For example, in some implementations, when the pressure switch is closed, the electrical switch 381 is in the following state: conducting current and allowing current to flow to the function generator so that the function generator is powered and generates a modulation signal, which is delivered to the actuator 132 via the link 162. In these implementations, when the pressure switch is disconnected (i.e., when the pressure p is lower than a preset pressure), the electrical switch 381 is disconnected and does not conduct current or provide current to the function generator 384. Therefore, when the pressure p is lower than the predetermined pressure, the function generator 384 is not powered and no modulation signal is generated, nor is the modulation signal delivered to the actuator 132 .

[0066] Figure 4 4 is a block diagram of an EUV light source 100 having a control system 460. The control system 460 is a control system 160 ( Figure 1 The control system 460 reduces or prevents cavitation in the target mixture 111 flowing in the capillary 114 by controlling the frequency at which the actuator 132 vibrates and controlling the frequency content of the modulation signal applied to the actuator 132.

[0067] As discussed above, during typical operation, the actuator 132 is driven by an electrical waveform that is composed to promote droplet coalescence to produce individual droplets that arrive at the plasma formation location 123 at a desired rate and have a desired size. The modulation signal used to drive the actuator 132 can include components at frequencies that do not contribute to droplet coalescence. Moreover, modulating the actuator 132 using these other frequencies can increase the chance of cavitation. For example, modulating the actuator 132 at a relatively low frequency that is different from the desired frequency of fully coalesced droplets can increase the chance of cavitation because the cavitation acoustic power density threshold in the target material is a function of the modulation frequency (that is, for lower modulation frequencies, the cavitation acoustic power density threshold is lower, so cavitation is more likely to occur at lower modulation frequencies). Therefore, in some implementations, the control system 460 is configured to remove or reduce the amplitude of components in the modulation signal that are below the frequency threshold and do not contribute critically to the droplet coalescence process.

[0068] The mechanically coupled actuator 132 and capillary 114 form a target forming structure associated with an eigenmode, which is a normal vibration mode of the structure formed by the mechanically coupled actuator 132 and capillary 114. Driving the actuator 132 with a modulated signal including a frequency associated with an eigenmode of the structure, a harmonic of an eigenmode of the structure, or a subharmonic of an eigenmode of the structure increases the likelihood of cavitation. For example, in a case where the actuator 132 is a tube structure (such as a capillary structure with respect to FIG. 1 ), the actuator 132 may be driven by a modulated signal having a frequency associated with the eigenmode of the structure, a harmonic of an eigenmode of the structure, or a subharmonic of an eigenmode of the structure. Figure 2A and Figure 2B In the implementation of the actuator 232 discussed, driving the actuator 132 at frequencies consistent with the length or longitudinal mode mechanical resonance of the actuator 132 (typically in the range of 200 kHz to 600 kHz) can increase the likelihood of cavitation in the target mixture 111 because the amplitude of the acoustic waves at these frequencies is greater due to resonance effects for a given modulation voltage.

[0069] The control system 460 is configured to remove or reduce the amplitude of frequencies associated with the structure of the combined capillary 114 and actuator 132, the eigenmodes of the actuator 132, and / or the capillary 114. For example, the mechanical characteristics of the actuator 132 and the capillary 114 may be evaluated during manufacturing, and the frequencies to be avoided or minimized are stored in the electronic storage device 462. During operational use, the control system 460 removes or filters the frequencies from the modulation signal before applying the modulation signal to the actuator 132.

[0070] The control system 460 includes an electronic processor 461, an electronic storage device 462, and an I / O interface 463. The electronic processor 461 is any type of electronic processor 461 capable of processing data and executing instructions. The control system 460 may include more than one electronic processor 461. The electronic storage device 462 is any type of electronic memory and may include volatile components and / or non-volatile components. The I / O interface 463 is any type of interface that allows an operator or external device to communicate with the control system 460. Figure 3B Similar to the control system 360B discussed above, the control system 460 can be configured to act as a function generator. Thus, the control system 460 can generate a modulation signal (eg, a voltage signal and / or a current signal) for modulating or driving the actuator 132.

[0071] The electronic storage device 462 stores instructions, such as instructions in the form of a computer program, that control the frequency content of the modulated signal generated by the control system 460. For example, the electronic storage device 462 may store a threshold frequency value that is used as a minimum frequency value for the modulated signal generated by the control system 460. In another example, the electronic storage device 462 stores instructions to analyze and filter the modulated signal so that unwanted frequency components are removed or reduced in amplitude before being provided to the actuator 132. In yet another example, the electronic storage device 462 stores a minimum amplitude value that represents the maximum amplitude that the reduced frequency component may have. The minimum amplitude value may be a peak-to-peak value and / or a maximum value.

[0072] Undesirable drive frequencies may vary between different instances of the supply system 110. Therefore, the mechanical properties of the supply system 110 are evaluated during the manufacturing or assembly process. In some implementations, the operator of the EUV light source 100 can increase or change the frequencies to be avoided or minimized as needed during the service life of the EUV light source 100. In other implementations, a machine-readable tag (such as a radio frequency identification (RFID) tag) on ​​the supply system 110 contains information specific to the supply system 110 (such as undesirable drive frequencies). Reading the tag using an appropriate device (e.g., an RFID reader) enables information about the supply system 110 to be saved in the control system 460 and used during operation of the supply system 110.

[0073] Figure 5 is a block diagram of EUV light source 500. EUV light source 500 and EUV light source 100 ( Figure 1 ), except that the EUV light source 500 includes a supply system 510 that includes an actuator 532 that is mechanically mounted to the reservoir 112. The EUV light source 500 uses ultrasonic filtration and / or mechanical filtration to remove or reduce inclusion particles 117 in the target mixture 111. As discussed above, particulate material can act as a nucleation site for cavitation, so it is desirable to remove inclusion particles 117 from the target mixture 111 before the mixture 111 reaches the hole 119. The liquid target mixture 111 held in the reservoir 112 includes a target material (e.g., molten tin) and inclusion particles 117. The inclusion particles 117 may include, for example, tin oxide (SnO 2 ) particles. The inclusion particles 117 are particles that are not target materials and are not required to generate the plasma 196. Therefore, the inclusion particles 117 can be removed from the target mixture 111 without affecting the generation of EUV light.

[0074] In some implementations, the supply system 510 includes one or more filters 592 located between the reservoir 112 and the hole 119. The filter 592 has an opening that is smaller than the diameter of most of the inclusion particles 117. For example, the filter 592 can be formed of a solid metal block material that includes through holes with a diameter smaller than the diameter of the inclusion particles 116; and / or the filter 592 can be made of a mesh material or a sintered material. The filter 592 is positioned so that the target mixture 111 interacts with the filter 592 and the liquid target material flows through the filter 592. Most of the inclusion particles 117 cannot flow through the filter 592 and therefore do not reach the hole 119.

[0075] Filter 592 is designed to capture small particles (e.g., down to about 20 nanometers (nm) in size). Filters used in EUV supply systems are typically designed to capture particles with a size in the range of 1 μm to 10 μm, which is approximately the diameter of hole 119. Therefore, a filter designed to capture particles with a size in the range of 1 μm to 10 μm is typically used to prevent clogging of the nozzle hole. However, filter 592 is also intended to capture smaller particles with a size less than 1 μm. For example, filter 592 can be designed to capture particles with a size of 20 nm. Because cavitation can be promoted by nucleation sites in the form of nanometer-sized particles, filter 592 is designed to capture such small particles. Therefore, filter 592 is intentionally different from the filters typically used in EUV supply systems.

[0076] Alternatively or additionally, ultrasonic filtration techniques are used to remove or reduce the inclusion particles 117. Ultrasonic filtration is a technique for removing or locating particulate debris present in a fluid by applying an ultrasonic modulated signal to the fluid.

[0077] The actuator 532 is mechanically coupled to the wall 594 of the reservoir 112. The control system 560 provides a modulation signal to the actuator 532 via a data link 562. The actuator 532 is driven at an ultrasonic frequency (e.g., 20 kHz to 30 kHz). Driving the actuator 532 generates pressure waves in the target mixture 111 in the reservoir 112. In the case where the acoustic power is high enough, the pressure waves generate cavitation bubbles that attach to small particles, which carry the particles to the surface 595 due to buoyancy. Unless there is a significant convective flow 112 of the target material due to a large temperature gradient in the reservoir, the inclusion particles 117, once located at the surface 595, remain at the surface 595 because the density of the oxide is lower than that of the target material itself. Therefore, under typical operating conditions and when the target mixture 111 is not completely discharged from the reservoir 112, the inclusion particles 117 remain at the surface 595 and do not flow into the capillary 114 or the pore 119. Thus, cavitation is reduced in the capillary 114. This cleaning is only performed periodically for short periods of time when the EUV light source 500 is not used to generate EUV light.

[0078] exist Figure 5 In the example of , EUV light source 500 includes a gas supply system 590. Gas supply system 590 emits gas that flows over surface 595. Gas supply system 590 includes components configured to control, regulate, and / or generate flowing gas. For example, gas supply system 590 may include a gas tank, a tube, a valve, a pipe, and / or a pump containing gas.

[0079] The gas flowing out of the gas supply system 590 is a gas that reacts with the inclusion particles 117 (which have moved toward the surface 595). For example, in the case where the inclusion particles 117 are tin oxide (SnO 2 ) particles, a gas supply system generates hydrogen gas that flows across surface 595. The hydrogen gas reacts with the tin oxide inclusion particles 117 to form molecules of tin and water, which are removed from surface 595.

[0080] refer to Figure 6 , a flow chart of process 600 is shown. Process 600 is an example of a process for operating a supply system of an EUV light source in a manner that avoids or reduces the occurrence of cavitation in capillary 114. By reducing or eliminating the occurrence of cavitation, process 600 helps ensure that hole 119 remains undamaged during operational use. Process 600 can be performed by any of control systems 160, 360A, 360B, 360C, 460, and 560. Process 600 is discussed with respect to supply system 110 and supply system 510.

[0081] Determine (610) one or more characteristics of the supply system 110. The characteristic may be related to pressure. For example, the applied pressure p may be measured by a pressure sensor or determined by a pressure switch. In another example, the characteristic is a threshold pressure below which the actuator 132 will not operate.

[0082] In some implementations, the characteristic is related to the frequency of vibration of the capillary 114. In these implementations, the characteristic may be a threshold frequency. The threshold frequency is the lowest frequency at which the capillary 114 can vibrate without cavitation occurring. The threshold frequency may be determined during the manufacture or assembly of the supply system 110, or the threshold frequency may be determined by the end user in the field. The characteristic related to frequency may also be related to the physical structure of the supply system 110. For example, cavitation is more likely to occur when the capillary 114 vibrates at the frequency of an eigenmode of the structure formed by the actuator 132 and the capillary 114 or at a harmonic or sub - harmonic of that eigenmode.

[0083] In some implementations, the characteristic is related to the configuration of the supply system. For example, the characteristic may be related to whether an actuator (such as the actuator 532 shown in the supply system 510) is coupled to the reservoir 112.

[0084] The actuator mechanically coupled to the supply system 110 is controlled such that the orifice 119 remains substantially free of material damage (620). For example, the actuator 132 may be controlled based on the amount of the applied pressure p. In another example, the actuator 132 may be controlled such that the capillary 114 does not vibrate in response to excitation having a particular frequency component or range of frequency components. In yet another example, the actuator 532 is controlled to provide ultrasonic vibrations to the target mixture 111 in the reservoir to cause the inclusion particles 117 to move to the surface 595.

[0085] Additionally, more than one technique may be used to prevent or reduce cavitation. For example, the applied pressure p may be used to control the actuator 132, as discussed with respect to FIG. 3A to FIG. 3C and the frequency content of the modulation signal provided to the actuator 132 may be controlled, as discussed with respect to Figure 4 Moreover, the ultrasonic filtration and / or mechanical filtration discussed with respect to Figure 5 may also be used in conjunction with FIG. 3A to FIG. 3C and / or Figure 4 the techniques discussed. Finally, any of the control systems discussed above and any of the supply systems discussed above may be used with the target forming structure 216 ( Figure 2A and Figure 2B ) rather than with the actuator 132 and the capillary 114.

[0086] The damage of conduits and holes caused by cavitation is not uniquely attributed to the target supply system in the configuration described above. The same problem may occur in supply systems with other configurations, and the same mitigation measures can be applied to supply systems in other common configurations. For example, the target supply system may include a conduit for the target material made of a high-strength metal or ceramic material rather than a glass capillary. In these implementations, the conduit is coupled to an orifice plate with a small hole, which is designed to output the target material in the form of a liquid jet that is broken into droplets. In this configuration, the modulation of the liquid jet can be completed by a mechanically preloaded piezoelectric actuator that generates sound waves in the target material by vibrating the conduit wall or a film, and the film can be introduced in the design of the supply system for ease of modulation. Moreover, the actuator can have a tubular shape, or can have any other shape suitable for effectively exciting sound waves in the target material located in the conduit. For example, the shape of the actuator can have the shape of a disk or a stack of disks. The action of the actuator can be enhanced by an acoustic (Helmholtz type) resonator that can be formed in the conduit.

[0087] Fig. 7A and Figure 7B is an example of an EUV lithography apparatus in which the control system and / or supply system discussed above may be used. Figure 8 is an example of an EUV light source that may use the control system and / or supply system discussed above.

[0088] Fig. 7A is a block diagram of a lithographic apparatus 700 including a source collector module SO. The lithographic apparatus 700 includes:

[0089] • An illumination system (illuminator) IL configured to condition a radiation beam B (eg EUV radiation).

[0090] a support structure (e.g., mask table) MT constructed to support a patterning device (e.g., mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0091] a substrate table (e.g., wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and

[0092] • A projection system (eg, a reflective projection system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more chips).

[0093] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0094] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as, for example, whether the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may, for example, be a frame or a stage, which may be fixed or movable as desired. The support structure may ensure that the patterning device is in a desired position, for example relative to a projection system.

[0095] The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a pattern to a cross-section of a radiation beam so as to form a pattern in a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer in a device created in the target portion such as an integrated circuit.

[0096] The patterning device may be a transmissive patterning device or a reflective patterning device. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the matrix of mirrors.

[0097] Depending on the exposure radiation being used or other factors such as the use of a vacuum, like the illumination system IL, the projection system PS may include various types of optical components, such as refractive components, reflective components, magnetic components, electromagnetic components, electrostatic components, or other types of optical components, or any combination thereof. It may be desirable to use a vacuum for EUV radiation, as other gases may absorb too much radiation. Therefore, a vacuum environment may be provided to the entire beam path with the aid of vacuum walls and a vacuum pump.

[0098] exist Fig. 7A and Figure 7B In the example of , the apparatus is a reflective apparatus (e.g. employing a reflective mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more patterning device tables). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0099] refer to Fig. 7A , the illuminator IL receives a beam of extreme ultraviolet radiation from a source collector module SO. Methods of generating EUV light include, but are not limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) in which one or more emission lines are in the EUV range. In one such method - generally referred to as laser produced plasma ("LPP") - the desired plasma is generated by irradiating a fuel (such as a droplet, stream, or cluster of a material having the desired line emitting elements) with a laser beam. The source collector module SO may be a laser ( Fig. 7A The laser is a part of an EUV radiation system (not shown) for providing a laser beam to excite the fuel. The resulting plasma emits output radiation, for example, EUV radiation, which is collected using a radiation collector disposed in the source collector module. The laser and source collector module may be separate entities, for example, when carbon dioxide (CO 2 ) laser is used to provide a laser beam for fuel excitation.

[0100] In this case, the laser is not considered to form part of the lithographic apparatus, and the radiation beam is delivered from the laser to the source collector module by means of a beam delivery system, which includes, for example, appropriate guiding mirrors and / or a beam expander. In other cases, the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator (commonly referred to as a DPP source).

[0101] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (typically referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may include various other components, such as a faceted field mirror device and a faceted pupil mirror device. The illuminator IL may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0102] A radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device. After reflection from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved, for example, so as to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to precisely position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W can be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0103] The depicted device can be used in at least one of the following modes:

[0104] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT remain substantially stationary while an entire pattern imparted to the radiation beam is projected once onto a target portion C (that is, a single static exposure). The substrate table WT is then shifted in the X-direction and / or Y-direction so that a different target portion C can be exposed.

[0105] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0106] 3. In another mode, the support structure (e.g. mask table) MT is kept substantially stationary, thereby holding the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, the radiation source is pulsed and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applicable to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array of the type mentioned above.

[0107] Combinations and / or variations of the above-described modes of use or entirely different modes of use may also be employed.

[0108] Figure 7BThe implementation of a lithographic apparatus 700 is shown in more detail, and the lithographic apparatus 700 includes a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged so that a vacuum environment can be maintained in an enclosure 720 of the source collector module SO. The systems IL and PS are also contained in their own vacuum environments. The EUV radiation emitting plasma 2 can be formed by a laser-generated LPP plasma source. The function of the source collector module SO is to transfer the EUV radiation beam 20 from the plasma 2 so that it is focused in a virtual source point. The virtual source point is usually referred to as an intermediate focus (IF), and the source collector module is arranged so that the intermediate focus IF is located at or near a hole 721 in the enclosure 720. The virtual source point IF is an image of the radiation emitting plasma 2.

[0109] From the aperture 721 at the intermediate focus IF, the radiation traverses an illumination system IL which, in this example, comprises a faceted field mirror device 22 and a faceted pupil mirror device 24. These devices form a so-called "fly's eye" illuminator which is arranged to provide a desired angular distribution of the radiation beam 21 at the patterning device MA and a desired uniformity of radiation intensity at the patterning means MA (as indicated by reference numeral 760). Following reflection of the beam 21 at the patterning device MA held by the support structure (mask table) MT, a patterned beam 26 is formed and the projection system PS images the patterned beam 26 via reflective elements 28, 30 onto a substrate W held by a substrate table WT. In order to expose a target portion C on the substrate W, radiation pulses are generated while the substrate table WT and the patterning device table MT perform synchronized movements to scan a pattern on the patterning device MA through an illumination slit.

[0110] Each system IL and PS is arranged in its own vacuum environment or near-vacuum environment, which is defined by an enclosure similar to enclosure 720. There may generally be more elements in illumination system IL and projection system PS than those shown. Further, there may be more mirrors than those shown. For example, in addition to Figure 7B In addition to the reflective elements shown, there may be one to six additional reflective elements in the illumination system IL and / or the projection system PS.

[0111] Considering the source collector module SO in more detail, a laser energy source including a laser 723 is arranged to deposit laser energy 724 into a fuel including a target material. The target material can be any material that emits EUV radiation in a plasma state, such as xenon (Xe), tin (Sn) or lithium (Li). Plasma 2 is a highly ionized plasma with an electron temperature of tens of electron volts (eV). Higher energy EUV radiation may be generated by other fuel materials (e.g., terbium (Tb) and gadolinium (Gd). The energy radiation generated during the de-excitation and recombination of these ions is emitted from the plasma, collected by the near normal incidence collector 3 and focused on the aperture 721. Plasma 2 and aperture 721 are located at the first and second focal points of the collector CO, respectively.

[0112] although Figure 7B The collector 3 shown is a single curved reflector, but the collector may take other forms. For example, the collector may be a Schwarzschild collector having two radiation collecting surfaces. In one embodiment, the collector may be a grazing incidence collector comprising a plurality of substantially cylindrical reflectors nested within each other.

[0113] To deliver a fuel, such as liquid tin, a droplet generator 726 is disposed within the enclosure 720, arranged to excite a high frequency stream 728 of droplets toward a desired location of the plasma 2. The droplet generator 726 may be a target forming structure 216 and / or a target forming device formed by the actuator 132 and the capillary 114. In operation, laser energy 724 is delivered in synchronization with the operation of the droplet generator 726 to deliver a pulse of radiation to convert each fuel droplet into a plasma 2. The delivery frequency of the droplets 2 may be several kilohertz, for example, 50 kHz. In practice, the laser energy 724 is delivered in at least two pulses: a pre-pulse with limited energy is delivered to the droplet before the droplet reaches the plasma location so as to vaporize the fuel material into a small cloud, and then a main pulse of laser energy 724 is delivered to the cloud at the desired location to generate the plasma 2. A trap 730 is provided on the opposite side of the enclosure 720 to capture fuel that is not converted into plasma for whatever reason.

[0114] The droplet generator 726 includes a reservoir 701 containing a fuel liquid (e.g., molten tin) and a filter 769, and a nozzle 702. The nozzle 702 is configured to eject droplets of the fuel liquid toward a location where the plasma 2 is formed. The droplets of the fuel liquid may be ejected from the nozzle 702 by a combination of pressure within the reservoir 701 and vibration applied to the nozzle by a piezoelectric actuator (not shown).

[0115] As will be known to those skilled in the art, in order to measure and describe the geometry and behavior of the device, its various components, and the radiation beams 20, 21, and 26, reference axes X, Y, and Z may be defined. At each portion of the device, a local reference system for the X, Y, and Z axes may be defined. Figure 7B In the example of FIG. 1 , the Z axis is roughly aligned with the directional optical axis O at a given point in the system and is roughly perpendicular to the plane of the patterning device (mask) MA and to the plane of the substrate W. In the source collector module, the X axis is roughly aligned with the direction of the fuel flow 728, and the Y axis is roughly aligned with the direction of the fuel flow 728. Figure 7B On the other hand, near the support structure MT holding the mask MA, the X-axis is generally transverse to the scanning direction aligned with the Y-axis. For convenience, Figure 7B In this region of the schematic view of the X-axis points out of the paper, as indicated by the marker. These representations are conventional in the art and are adopted herein for convenience. In principle, any reference frame can be chosen to describe the device and its behavior.

[0116] Many additional components used in the operation of the source collector module and the lithographic apparatus 500 as a whole are present in a typical apparatus, although not shown herein. These include arrangements for reducing or mitigating the effects of contamination within the closed vacuum, for example, to prevent deposits of fuel material from damaging or impairing the performance of the collector 3 and other optical devices. Other features present but not described in detail are all sensors, controllers and actuators involved in controlling the various components and subsystems of the lithographic apparatus 700.

[0117] refer to Figure 8 , shows an implementation of the LPP EUV light source 800. The light source 800 can be used as a source collector module SO in the lithography apparatus 700. Furthermore, Figure 1 The light source 105 may be part of the driving laser 815. The driving laser 815 may be used as the laser 723 ( Figure 7B ).

[0118] The LPP EUV light source 800 is formed by irradiating a target mixture 814 at a plasma formation location 805 using an amplified light beam 810 traveling along a beam path toward the target mixture 814. Figure 1 The target materials discussed and the Figure 1The target in the target stream 121 in question can be or include a target mixture 814. The plasma formation location 805 is within the interior 807 of the vacuum chamber 830. When the amplified light beam 810 strikes the target mixture 814, the target material within the target mixture 814 is converted into a plasma state of an element having emission lines in the EUV range. The generated plasma has certain properties that depend on the composition of the target material within the target mixture 814. These properties can include the wavelength of EUV light generated by the plasma and the type and amount of debris released from the plasma.

[0119] The light source 800 includes a drive laser system 815 that generates an amplified light beam 810 due to a 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 location 805, the beam delivery system including a beam transport system 820 and a focusing assembly 822. The beam transport system 820 receives the amplified light beam 810 from the laser system 815, and steers and modifies the amplified light beam 810 as needed and outputs the amplified light beam 810 to the focusing assembly 822. The focusing assembly 822 receives the amplified light beam 810 and focuses the beam 810 to the plasma formation location 805.

[0120] In some implementations, the laser system 815 may include one or more optical amplifiers, lasers, and / or lamps for providing one or more main pulses, and in some cases one or more pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying the desired wavelength at high gain, an excitation source, and internal optical devices. The optical amplifier may or may not have a laser reflector or other feedback device that forms a laser cavity. Therefore, even if there is no laser cavity, the laser system 815 will produce an amplified light beam 810 due to the population inversion in the gain medium of the laser amplifier. Moreover, if there is a laser cavity to provide sufficient feedback to the laser system 815, the laser system 815 can produce an amplified light beam 810 as a coherent laser beam. The term "amplified light beam" covers one or more of the following: light from the laser system 815 that is only amplified and not necessarily coherent laser oscillation, and light from the laser system 815 that is amplified and is also coherent laser oscillation.

[0121] The optical amplifier in the laser system 815 may include a fill gas as a gain medium, the fill gas including CO 2, and can amplify light at wavelengths between about 9100 nm and about 11000 nm (particularly at about 10600 nm) with a gain of greater than or equal to 800 times. Suitable amplifiers and lasers for laser system 815 may include pulsed laser devices, such as pulsed gas discharge CO 2 A laser device, for example, by DC or RF excitation, operates at a relatively high power (e.g., 10 kW or more) and a high pulse repetition rate (e.g., 40 kHz or more) to generate radiation at about 9300 nm or about 10600 nm. The pulse repetition rate can be, for example, 50 kHz. The optical amplifier in the laser system 815 can also include a cooling system such as water, which can be used when operating the laser system 815 at a higher power.

[0122] The light source 800 includes a collector mirror 835 having an aperture 840 to allow the amplified light beam 810 to pass through and reach the plasma formation location 805. The collector mirror 835 may be, for example, an elliptical mirror having a primary focus at the plasma formation location 805 and a secondary focus (also referred to as an intermediate focus) at an intermediate location 845, where EUV light may be output from the light source 800 and may be input into, 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 location 805 to reduce the amount of plasma generated debris entering the focusing assembly 822 and / or the beam delivery system 820 while allowing the amplified light beam 810 to reach the plasma formation location 805. To this end, a gas flow directed toward the plasma formation location 805 may be provided in the shield.

[0123] The light source 800 may also include a main controller 855 connected to a droplet position detection feedback system 856, a laser control system 857, and a beam control system 858. The light source 800 may include one or more target or droplet imagers 860 that provide an output indicating the position of a droplet, for example, relative to the plasma formation location 805, and provide the output to the droplet position detection feedback system 856, which may, for example, calculate a droplet position and trajectory, from which a droplet position error may be calculated dropwise or on an average basis. Thus, the droplet position detection feedback system 856 provides the droplet position error as an input to the main controller 855. Thus, the main controller 855 can provide laser position, direction, and timing correction signals to, for example, a laser control system 857, which can be used, for example, to control a laser timing circuit, and / or a beam control system 858, which can be used, for example, to control the position and shaping of the amplified light beam of the beam delivery system 820 to change the position and / or focal length of the beam focal spot within the chamber 830.

[0124] The supply system 825 includes a target material delivery control system 826 that is operable in response to signals from the main controller 855 to, for example, modify the release point of droplets as released by the target material supply device 827 to correct errors in droplets reaching the desired plasma formation location 805.

[0125] Additionally, the light source 800 may include light source detectors 865 and 870 that measure one or more EUV light parameters including, but not limited to, pulse energy, distribution of energy with wavelength, energy within a particular wavelength band, energy outside a particular wavelength band, and angular distribution of EUV intensity and / or average power. 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 focusing of laser pulses to accurately intercept droplets at the right place and time for effective and efficient production of EUV light.

[0126] The light source 800 may also include a guide laser 875, which may be used to align various segments of the light source 800 or to help steer the amplified light beam 810 to the plasma formation location 705. In conjunction with the guide laser 875, the light source 800 includes a metrology system 824 placed within the focusing assembly 822 to sample a portion of the light from the guide laser 875 and the amplified light beam 810. In other implementations, the metrology system 824 is placed within the beam delivery system 820. The metrology system 824 may include an optical element that samples or redirects a subset of the light, such optical element being made of any material that can withstand the power of the guide laser beam and the amplified light beam 810. Since the main controller 855 analyzes the sampled light from the guide laser 875 and uses this information to adjust components within the focusing assembly 822 through the beam control system 858, a beam analysis system is formed by the metrology system 824 and the main controller 855.

[0127] Thus, in summary, the light source 800 generates an amplified light beam 810 directed along a beam path to irradiate a target mixture 814 at a plasma formation location 805 to convert a target material within the mixture 814 into a plasma that emits light in the EUV range. The amplified light beam 810 operates at a specific wavelength (also referred to as a drive laser wavelength) determined based on the design and characteristics of the laser system 815. Additionally, the amplified light beam 810 can be a laser beam when the feedback provided by the target material is sufficient to return into the laser system 815 to produce coherent laser light or if the drive laser system 815 includes suitable optical feedback to form a laser cavity.

[0128] Other aspects of the invention are set out in the following numbered clauses.

[0129] 1. A targeted delivery system for an extreme ultraviolet (EUV) light source, the system comprising:

[0130] a conduit comprising an aperture configured to be fluidly coupled to a reservoir;

[0131] an actuator configured to be mechanically coupled to the catheter such that movement of the actuator is transmitted to the catheter; and

[0132] A control system, coupled to the actuator, the control system being configured to:

[0133] determining an indication of the pressure applied to the target material in the reservoir, and

[0134] Movement of the actuator is controlled based on the determined indication of applied pressure.

[0135] 2. A target delivery system according to claim 1, wherein the control system is also configured to compare the determined indication of the applied pressure with a threshold, and the control system is configured to control the movement of the actuator based on the determined indication of the applied pressure, including: the control system is configured to control the movement of the actuator based on the comparison.

[0136] 3. The targeted delivery system of clause 2, wherein movement of the actuator generates displacement in the catheter wall and acoustic waves inside the catheter, and the threshold is related to the amplitude of the acoustic waves.

[0137] 4. A target delivery system according to clause 3, wherein the control system is configured to control the actuator based on the comparison includes: the control system is configured to only cause the actuator to displace in the catheter wall if the determined indication of the applied pressure is greater than a threshold value.

[0138] 5. The target delivery system of clause 4, wherein the threshold comprises a threshold pressure between zero and an operating pressure, and the operating pressure is an amount of pressure applied to the target material in the reservoir during operation of the EUV light source.

[0139] 6. The targeted delivery system of clause 5, wherein the acoustic wave comprises a maximum amplitude and the threshold pressure is defined by the maximum amplitude.

[0140] 7. The targeted delivery system of clause 5, wherein the threshold pressure is selected from the range of 200 to 1000 pounds per square inch (PSI).

[0141] 8. The targeted delivery system according to clause 5, wherein the control system further comprises:

[0142] one or more electronic processors; and

[0143] A non-transitory computer-readable storage medium coupled to one or more electronic processors.

[0144] 9. A target delivery system according to claim 1, wherein the control system is configured to control the movement of the actuator based on an indication of the applied pressure, including: the control system is configured to provide a modulation signal to the actuator based on the indication of the applied pressure, the modulation signal being sufficient to cause the actuator to produce a displacement in the catheter wall.

[0145] 10. The targeted delivery system of clause 9, wherein the actuator comprises a piezoelectric modulator and the modulation signal comprises an electrical signal sufficient to cause a change in shape of the piezoelectric modulator.

[0146] 11. The targeted delivery system of clause 1, wherein the control system further comprises an electrical switch configured to be coupled to the actuator, and wherein

[0147] The electrical switch is configured to receive an indication of the applied pressure,

[0148] The electrical switch is configured to have one of a plurality of possible states at a particular time,

[0149] The electrical switch allows the modulated signal to reach the actuator in less than all of the plurality of states,

[0150] The particular state of the electrical switch at a particular time is determined by the received indication of the applied pressure, and

[0151] The control system being configured to determine an indication of a pressure applied to a target material in the reservoir includes the control system being configured to determine that the electrical switch is in a particular state.

[0152] 12. The targeted delivery system of clause 11, wherein the indication of the applied pressure is received from a separate pressure switch coupled to the reservoir.

[0153] 13. The targeted delivery system of clause 11, wherein the received indication of applied pressure comprises an analog signal received directly from a pressure sensor.

[0154] 14. The targeted delivery system of clause 11, wherein the received indication of applied pressure comprises an electronic signal generated by instructions executed by an electronic processor.

[0155] 15. The targeted delivery system of clause 1, wherein an interior surface of the conduit is configured to be exposed to the target material, and the interior surface is substantially free of defects to reduce cavitation in the target material.

[0156] 16. The targeted delivery system of clause 15, wherein at least a portion of the interior surface is flame polished.

[0157] 17. The targeted delivery system of clause 1, wherein the control system is configured to determine an indication of pressure applied to the target material comprises: the control system is configured to analyze an indication from a pressure sensor configured to measure the applied pressure.

[0158] 18. A targeted delivery system for an extreme ultraviolet (EUV) light source, the system comprising:

[0159] a conduit comprising an aperture configured to be fluidly coupled to a reservoir;

[0160] an actuator configured to be mechanically coupled to the catheter such that movement of the actuator is transmitted to the catheter;

[0161] a signal generator configured to provide a modulated signal to the actuator, the modulated signal being sufficient to cause the actuator to move; and

[0162] A control system, coupled to the actuator and the signal generator, the control system being configured to:

[0163] One or more characteristics of the modulation signal, and thereby one or more characteristics of the movement of the actuator, are controlled such that, in use, the aperture remains substantially free of material damage.

[0164] 19. The targeted delivery system of clause 18, wherein the one or more characteristics include a frequency content of the modulated signal, and the control system is configured to control the frequency content of the modulated signal.

[0165] 20. The targeted delivery system of clause 19, wherein the control system is configured to reduce the amplitude of components of the modulated signal having frequencies below a frequency threshold.

[0166] 21. A target delivery system according to claim 19, wherein the mechanically coupled actuator and catheter form an actuator-catheter assembly, and the control system is configured to reduce the amplitude of components in the modulated signal at frequencies associated with: eigenmodes of the actuator-catheter assembly, or harmonics and subharmonics thereof.

[0167] 22. The targeted delivery system of clause 18, wherein the one or more characteristics include an amplitude of the modulation signal, and the control system is configured to control the amplitude of the modulation signal.

[0168] 23. The targeted delivery system of clause 22, wherein the control system is configured to maintain the amplitude of the modulated signal below an amplitude limit.

[0169] 24. The targeted delivery system of clause 23, wherein the amplitude limitation is a peak-to-peak amplitude limitation.

[0170] 25. The targeted delivery system of clause 18, wherein the pores remain substantially crack-free.

[0171] 26. The targeted delivery system of clause 18, wherein the aperture is defined by an end of the catheter.

[0172] 27. The targeted delivery system of clause 18, wherein the catheter is coupled to a structure defining the aperture.

[0173] 28. A targeted delivery system for an extreme ultraviolet (EUV) light source, the system comprising:

[0174] a reservoir configured to contain a mixture including a target material and inclusion particles;

[0175] a conduit comprising an aperture configured to be fluidly coupled to a reservoir;

[0176] an actuator configured to be mechanically coupled to the reservoir such that movement of the actuator is transferred to the reservoir; and

[0177] A control system, coupled to the actuator, the control system being configured to:

[0178] The movement of the actuator is controlled so that inclusion particles in the mixture move toward the surface of the mixture.

[0179] 29. The targeted delivery system of clause 28, wherein the actuator comprises an ultrasonic actuator.

[0180] 30. The targeted delivery system of clause 28, further comprising a gas delivery system configured to deliver a flowing gas across a surface of the mixture.

[0181] 31. The targeted delivery system of clause 30, wherein the flowing gas comprises at least one component configured to react with the inclusion particles to remove at least some of the inclusion particles from the surface.

[0182] 32. A targeted delivery system according to clause 31, wherein

[0183] Target materials include molten tin,

[0184] The inclusion particles include tin oxide particles, and

[0185] The flowing gas includes hydrogen.

[0186] 33. The targeted delivery system of clause 32, wherein the movement of the actuator is controlled such that cavitation is induced in the mixture and the content particles are moved toward the surface via bubbles formed around the particles by cavitation.

[0187] 34. The targeted delivery system of clause 28, wherein the targeted delivery system further comprises one or more filters located between the reservoir and the well, the filters configured to substantially prevent particles of the contents from reaching the well.

[0188] 35. The targeted delivery system of clause 28, wherein the diameter of the inclusion particles is 1 micrometer (μm) or less.

[0189] 36. The targeted delivery system of clause 28, wherein the inclusion particles comprise tin oxide particles.

[0190] 37. A method of operating a target supply system of an EUV light source, the method comprising:

[0191] determining one or more characteristics of the supply system; and

[0192] An actuator mechanically coupled to the supply system is controlled based on the determined one or more characteristics such that the aperture of the supply system remains substantially free of material damage during operational use.

Claims

1. A targeted delivery system for an extreme ultraviolet (EUV) light source, the system include: a conduit comprising an aperture configured to be fluidly coupled to a reservoir; an actuator configured to be mechanically coupled to the catheter such that movement of the actuator is transmitted to the catheter; a signal generator configured to provide a modulation signal to the actuator, the modulation signal being sufficient to cause the actuator to move; as well as a control system coupled to the actuator and the signal generator, the control system being configured to: One or more characteristics of the modulation signal, and thereby one or more characteristics of the movement of the actuator, are controlled such that, in use, the aperture remains substantially free of material damage.

2. The targeted delivery system of claim 1, wherein the one or more characteristics include a frequency content of the modulated signal, and the control system is configured to control the frequency content of the modulated signal. 3 . The targeted delivery system of claim 2 , wherein the control system is configured to reduce the amplitude of components of the modulated signal having frequencies below a frequency threshold.

4. A target delivery system according to claim 2, wherein the mechanically coupled actuator and catheter form an actuator-catheter assembly, and the control system is configured to reduce the amplitude of the component of the modulated signal at the frequency associated with the following items: the eigenmode of the actuator-catheter assembly or its harmonics and subharmonics. 5 . The targeted delivery system of claim 1 , wherein the one or more characteristics include an amplitude of the modulation signal, and the control system is configured to control the amplitude of the modulation signal.

6. The targeted delivery system of claim 5, wherein the control system is configured to maintain the amplitude of the modulated signal below an amplitude limit.

7. The targeted delivery system of claim 6, wherein the amplitude limitation comprises a peak-to-peak amplitude limitation.

8. The targeted delivery system of claim 1, wherein the pores remain substantially free of cracks.

9. The targeted delivery system of claim 1, wherein the aperture is defined by an end of the catheter.

10. The targeted delivery system of claim 1, wherein the catheter is coupled to a structure defining the aperture.

11. A targeted delivery system for an extreme ultraviolet (EUV) light source, the system include: a reservoir configured to contain a mixture including a target material and inclusion particles; a conduit comprising an aperture configured to be fluidly coupled to the reservoir; an actuator configured to be mechanically coupled to the reservoir such that movement of the actuator is transferred to the reservoir; as well as a control system coupled to the actuator, the control system being configured to: The movement of the actuator is controlled so that the inclusion particles in the mixture move toward the surface of the mixture.

12. The targeted delivery system of claim 11, wherein the actuator comprises an ultrasonic actuator.

13. The targeted delivery system of claim 11, further comprising a gas delivery system configured to deliver a flowing gas across the surface of the mixture.

14. The targeted delivery system of claim 13, wherein the flowing gas comprises at least one component configured to react with the inclusion particles to thereby remove at least some of the inclusion particles from the surface.

15. The targeted delivery system of claim 14, wherein The target material includes molten tin, The inclusion particles include tin oxide particles, and The flowing gas includes hydrogen.

16. The targeted delivery system of claim 15, wherein the movement of the actuator is controlled such that cavitation is induced in the mixture and the inclusion particles are moved toward the surface via bubbles formed around the particles by the cavitation.

17. The targeted delivery system of claim 11, wherein the targeted delivery system further comprises one or more filters located between the reservoir and the pores, the filters being configured to substantially prevent the content particles from reaching the pores.

18. The targeted delivery system of claim 11, wherein the inclusion particles have a diameter of 1 micrometer (μm) or less.

19. The targeted delivery system of claim 11, wherein the inclusion particles comprise tin oxide particles.

20. A method of operating a target supply system of an EUV light source, the method include: determining one or more characteristics of the supply system; as well as An actuator mechanically coupled to the supply system is controlled based on the determined one or more characteristics such that the aperture of the supply system remains substantially free of material damage during operational use.

Images