Controlled droplet generator nozzle environment to improve reliability

Abstract

An apparatus and method are disclosed for controlling the environment around a nozzle orifice of a droplet generator in a source system for generating extreme ultraviolet (EUV) radiation, wherein the amount of oxygen-containing gas in the nozzle orifice environment is controlled to reduce the formation of oxides that may potentially interfere with the operation of the droplet generator.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Application No. 63 / 431,481, filed on December 9, 2022, entitled "CONTROLLED DROPLET GENERATOR NOZZLE ENVIRONMENT TO IMPROVE RELIABILITY", the entire content of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to extreme ultraviolet radiation generators that generate light by exciting a source material, and more particularly to devices, systems, and methods for dispensing the source material in such extreme ultraviolet radiation generators. Background Art

[0004] Extreme ultraviolet ("EUV") radiation, e.g., electromagnetic radiation having a wavelength of about 50 nm or less (sometimes also referred to as soft x-rays) and including light having a wavelength of about 13 nm, is used in a lithography process to create extremely small features in and on a substrate such as a silicon wafer.

[0005] Methods for generating EUV radiation include, but are not limited to, changing the physical state of a source material to a plasma state. Source materials include elements having emission lines in the EUV range, such as xenon, lithium, or tin. In one such method, commonly referred to as laser-produced plasma ("LPP"), the desired plasma is generated by irradiating a source material in the form of, e.g., droplets or clusters of the source material with an amplified laser beam referred to as a drive laser beam. For this process, the plasma is typically generated in a sealed container such as a vacuum chamber and monitored using various types of metrology equipment.

[0006] EUV radiation can be generated in a multi-step process in which a target (e.g., a droplet of the source material) is impacted by one or more pulses of conditioning radiation before reaching the irradiation site, the conditioning radiation conditioning or preparing the target for a final phase change at the irradiation site. Conditioning in this context can include changing the shape of the droplet, e.g., flattening the droplet, or changing the distribution of the droplets, e.g., at least partially dispersing some of the droplets into a mist, or even a partial phase change. Pulses prior to the main heating pulse are referred to as conditioning pulses and include pre-pulses, rarefaction pulses, and pedestal pulses, whether generated by the main drive laser or another laser.

[0007] A technique for generating droplets involves melting a target or source material such as tin and then forcing the liquid tin through an orifice of relatively small diameter, such as an orifice having a diameter of from about 0.5 μm to about 30 μm, under high pressure to produce a stream of droplets. In most cases, in a process called Rayleigh breakup, instabilities that occur naturally in the stream leaving the orifice, e.g., noise, will cause the stream to break up into droplets. These droplets can have varying velocities and can combine with each other as they travel in the stream to coalesce into larger droplets. To generate EUV light, the frequency of the droplets is controlled to match the frequency of the driving laser.

[0008] The droplet generator places the droplets at the primary focus of a collector mirror, where they will be irradiated to produce EUV. The droplets must reach the primary focus within certain spatial and temporal stability criteria, i.e., have a repeatable position and timing within acceptable bounds. They must also reach at a given frequency and velocity. In addition, the droplets must be fully coalesced, which means the droplets must be monodisperse (have uniform size) and reach a given driving frequency.

[0009] The very small orifices in the nozzle of the droplet generator are prone to clogging by source material by-products. For example, when tin is used as the source material, if oxidation contaminants (such as O2 gas and H2O vapor or any native oxide from a tin-wetted surface) can reach any tin within the nozzle, tin oxide (SnO x ) particles can form. Oxidation of the free surface of tin can occur inside the nozzle (especially during a cold restart when the tin retracts due to shrinkage) or right at the orifice. These tin oxides do not melt at the operating temperature of the droplet generator and will clog the nozzle. This can lead to droplet generator startup failures (failures during initial operation) and droplet generator cold restart failures (failures in restarting the droplet generator after an idle period). Thus, for at least some applications, it is advantageous to control the humidity and oxygen levels around the nozzle orifice.

[0010] In this context, a need for the presently disclosed subject matter has arisen. SUMMARY OF THE INVENTION

[0011] The following is a concise summary that provides a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify any key or critical elements of any embodiment nor to delineate the scope of any embodiment. Its sole purpose is to present some concepts related to one or more embodiments as a prelude to the more detailed description presented below.

[0012] According to one aspect of an embodiment, a droplet generator system for an extreme ultraviolet (EUV) radiation source is disclosed. The droplet generator system includes: a nozzle housing; a nozzle having an outlet hole positioned in the housing, the outlet hole being adapted to selectively fluidly communicate with a supply source of a liquid EUV source material and being adapted to transport the EUV source material into a chamber of the EUV radiation source; and a valve fluidly communicating with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is fluidly communicated with the chamber, and in the second state, the interior of the housing is not fluidly communicated with the chamber. The nozzle is adapted to transport the EUV source material along a path passing through the valve to the chamber, and wherein the valve is adapted to keep the path in an open state when the valve is in the first state and keep the path in a closed state when the valve is in the second state.

[0013] The valve can be a gate valve. The valve is adapted to switch between the first state and the second state in response to a control signal. The droplet generator system may further include a sensor arranged to sense whether the valve is in the first state or the second state. The droplet generator system may further include an inlet fluidly communicating with the interior of the housing and adapted to be connected to a source of purge gas.

[0014] The purge gas can include Ar + H2. The purge gas can include an inert gas. The inert gas can include at least one of nitrogen and argon. The droplet generator system may further include a purge gas cleaner arranged to clean the purge gas.

[0015] According to another aspect of an embodiment, a droplet generator system for an extreme ultraviolet (EUV) radiation source is disclosed. The droplet generator system includes: a nozzle housing; a nozzle having an outlet hole positioned in the housing, the outlet hole being adapted to selectively fluidly communicate with a supply source of a liquid EUV source material and transport the EUV source material into a chamber of the EUV radiation source; a valve fluidly communicating with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is fluidly communicated with the chamber, and in the second state, the interior of the housing is not fluidly communicated with the chamber. A supply source of purge gas, selectively fluidly communicating with the interior of the housing; and a vacuum pump, selectively fluidly communicating with the interior of the housing.

[0016] The vacuum pump can be a turbomolecular vacuum pump or a scroll vacuum pump. The droplet generator system may further include a high-conductivity conduit arranged to connect the interior of the housing to the turbomolecular vacuum pump.

[0017] According to another aspect of an embodiment, a component for purifying the environment of a nozzle outlet of a droplet generator in an extreme ultraviolet (EUV) radiation source is disclosed. The component includes: a housing that is disposed around the nozzle outlet and encloses the nozzle outlet except for an opening for a droplet path through which droplets are delivered to a chamber of the EUV radiation source; a source of purifying gas that is selectively in fluid communication with the interior of the housing; and a pump that is selectively in fluid communication with the interior of the housing and is adapted to evacuate the housing.

[0018] The purifying gas may include Ar + H2. The purifying gas may include an inert gas. The purifying gas may include at least one of nitrogen and argon. The component may further include a purifying gas cleaner arranged to clean the purifying gas.

[0019] The pump may include a roughing pump. The pump may include a turbo molecular pump or a scroll vacuum pump. The pump may be fluidly connected to the interior of the housing through a high conductance line.

[0020] The component may further include a valve disposed in the droplet passageway that has a first state and a second state. In the first state, the interior of the housing is fluidly connected to the chamber. In the second state, the interior of the housing is not fluidly connected to the chamber. And wherein the source of purifying gas and the pump are adapted to perform cyclic purification, including at least supplying purifying gas to the interior of the housing when the droplet generator is depressurized and the valve is in the second state, and performing continuous purification by supplying purifying gas to the interior of the housing when the droplet generator is depressurized and the valve is in the first state. The valve may be a gate valve.

[0021] According to another aspect of an embodiment, a method for controlling the environment of a nozzle of a droplet generator in an extreme ultraviolet (EUV) radiation source is disclosed. The method includes: disposing the nozzle in a housing; determining whether the droplet generator is depressurized; and if it is determined that the droplet generator is depressurized, sending a signal to activate the disposed valve to isolate the nozzle from the chamber of the EUV radiation source.

[0022] The method may further include, after sending the signal to activate the valve to isolate the nozzle from the chamber of the EUV radiation source, determining whether the valve operates in response to the signal to isolate the nozzle from the chamber. The method may further include, if it is determined that the valve does not operate in response to the signal to isolate the nozzle from the chamber, performing cyclic purification of the housing by cycling between supplying purifying gas to the housing and evacuating the housing.

[0023] The purge gas may include Ar + H2. The purge gas may include an inert gas. The purge gas may include at least one of nitrogen and argon. The method may further include cleaning the purge gas before supplying the purge gas to the housing. The method may further include: if it is determined that the valve does not operate in response to the signal to isolate the nozzle from the chamber, performing continuous purging of the housing by continuously supplying the purge gas to the housing.

[0024] The purge gas may include Ar + H2. The purge gas may include an inert gas. The purge gas may include at least one of nitrogen and argon. The method may further include cleaning the purge gas before supplying the purge gas to the housing. The method may further include: if it is determined that the valve does operate in response to the signal to isolate the nozzle from the chamber, evacuating the housing. The housing may be evacuated using a turbomolecular vacuum pump or a scroll vacuum pump.

[0025] The method may further include evacuating the housing after sending a signal to activate the arranged valve to isolate the nozzle from the chamber of the EUV radiation source.

[0026] Other embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structures and operations of the various embodiments, will be described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings incorporated herein and forming a part of the specification illustrate the presently disclosed subject matter and, together with the specification, further serve to explain the principles of the presently disclosed subject matter and enable a person of ordinary skill in the relevant art to make and use the presently disclosed subject matter.

[0028] Figure 1 is a partial schematic functional block diagram of an overall general concept of a laser-produced plasma EUV radiation source system (such as one aspect that may implement an embodiment).

[0029] Figure 2A is a schematic diagram of a system for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0030] Figure 2B is a schematic diagram of a system for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0031] Figure 3A and Figure 3B is a schematic diagram of a valve according to one aspect of an embodiment, which may be used in a system for controlling the environment around the nozzle orifice of a droplet generator.

[0032] Figure 4 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0033] Figure 5 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0034] Figure 6 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0035] Figure 7 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0036] Figure 8 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0037] Figure 9 is a flowchart showing the steps of a process for controlling the environment around the nozzle orifice of a droplet generator according to one aspect of an embodiment.

[0038] The additional features and advantages of the disclosed apparatus and method, as well as the structure and operation of various embodiments of the disclosed apparatus, are described in detail below with reference to the accompanying drawings. The disclosed apparatus and method are not limited to the specific embodiments described herein. These embodiments are presented herein for illustrative purposes only. Other embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein. Detailed Description

[0039] Various embodiments are described below with reference to the accompanying drawings, in which like reference numerals are always used to denote like elements. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, in some or all instances, it will be apparent that the following embodiments may be practiced without the use of the specific design details described below.

[0040] Figure 1 is a schematic diagram of an example of an EUV radiation source, such as a laser-produced plasma EUV radiation source 10. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may be, for example, a pulsed gas discharge CO2 laser source that produces a radiation pulse beam 22b having a wavelength generally below 20 μm, such as in the range of about 11 μm to about 9 μm or less. The pulsed gas discharge CO2 laser source may have DC or RF excitation operating at high power and high pulse repetition rate.

[0041] The EUV radiation source 10 also includes a source material delivery system 24 for delivering the source material in the form of droplets or a continuous liquid stream. In this example, the source material is liquid, but it can also be solid. The source material can consist of tin or a tin compound, but other materials can also be used. In the described system, the source material delivery system 24 introduces droplets 14 of the source material into the interior of the vacuum chamber 26 to the irradiation region 28, where the droplets 14 can be irradiated to generate a plasma. It should be noted that the irradiation region used here is the region where the source material irradiation occurs, and it is the irradiation region even when the irradiation does not actually occur. The EUV light source 10 also includes a beam focusing and steering system 32.

[0042] In the example shown, the components are arranged such that the droplets 14 travel substantially horizontally. The direction from the laser source 22 towards the irradiation region 28, i.e., the nominal propagation direction of the beam 22b, can be taken as the Z-axis. The path of the droplets 14 from the source material delivery system 24 to the irradiation region 28 can be taken as the X-axis. Thus, Figure 1 the view of is perpendicular to the XZ plane. Although a system in which the droplets 14 travel substantially horizontally has been described, those of ordinary skill in the art will understand that other arrangements can be used, in which the droplets 14 travel vertically or at an angle between 90 degrees (horizontal) and 0 degrees (vertical) and including 90 degrees (horizontal) and 0 degrees (vertical) relative to gravity.

[0043] The EUV radiation source 10 can also include an EUV light source controller system 60 and a laser emission control system 65 as well as a beam steering system 32. The EUV radiation source 10 can also include a detector such as a target position detection system, which can include one or more droplet imagers 70 that generate an output indicating the absolute or relative position of the target droplet, e.g., relative to the irradiation region 28, and provide this output to the target position detection feedback system 62. The target position detection feedback system 62 can use the output of the droplet imager 70 to calculate the target position and trajectory, whereby the target error can be calculated.

[0044] Figure 1 The illustrated EUV radiation source 10 also includes an adjustment laser 23 for generating an adjustment beam 23b. The adjustment beam 23b consists of pulses whose main drive pulses prepare the target for subsequent heating. The adjustment pulses can change the shape or distribution of the target. It includes pulses that are variously referred to as prepulses, pedestal pulses, and rarefaction pulses. The adjustment pulses from the adjustment laser 23 must hit the target in an optimal manner. For this purpose, the laser beam steering system 32 has the ability to manipulate the adjustment beam 23b generated by the adjustment laser 23.

[0045] As Figure 1As shown, the source material delivery system 24 may include a target delivery control system 90. The target delivery control system 90 may adjust the path of the target 14 through the irradiation region 28 in response to a signal provided by the system controller 60 (e.g., a target error or some quantity derived from the target error). This may be achieved, for example, by repositioning the point at which the target delivery mechanism 92 releases the droplets 14. The droplet release point may be repositioned, for example, by tilting or moving the target delivery mechanism 92. The target delivery mechanism 92 extends into the chamber 26 and preferably supplies source material and gas from an external source to place the source material in the target delivery mechanism 92 under pressure. The EUV radiation source 10 also includes a source material catcher 80 that catches and holds the source material that has not been evaporated to limit contamination from such source material.

[0046] Continuing to refer to Figure 1 , the EUV radiation source 10 may also include one or more optical elements. In the following discussion, the collector 30 is used as an example of such an optical element, but the discussion also applies to other optical elements. The collector 30 may be a normal incidence reflector, for example, implemented as a multilayer mirror ("MLM") having an additional thin barrier layer, such as B4C, ZrC, Si3N4, or C, deposited at each layer interface to effectively block thermally induced interlayer diffusion. The collector 30 may be in the form of an ellipsoid of revolution, having a central aperture to allow the beam 22b and the conditioning beam 23b to pass through and reach the irradiation region 28. The collector 30 may have a first focus at the irradiation region 28 and a second focus at a so-called intermediate point 40 (also referred to as the intermediate focus 40), where EUV radiation may be output from the EUV radiation source 10 and input into, for example, an integrated circuit lithography scanner or stepper 50. The integrated circuit lithography scanner or stepper 50 uses the radiation, for example, to process a silicon wafer workpiece 52 in a known manner using a reticle or mask 54. The silicon wafer workpiece 52 is then further processed in a known manner to obtain an integrated circuit device.

[0047] Maintaining the EUV radiation source 10 sometimes requires performing maintenance actions during which the droplet generator is deactivated, i.e., no droplets of source material need to be released. These maintenance actions include, for example, replacing the collector 30 in the EUV chamber 26 or emptying the source material catcher 80 or software or firmware upgrades. Another example of such a maintenance action is droplet generator exchange. During such an exchange, all surfaces near the nozzle are exposed to air and may reabsorb water. In addition, the droplet generator has a large number of vacuum seals. For these seals, the leak rate, outgassing (for polymer seals), and O2 permeation affect the partial pressures of water vapor and oxygen in the vicinity of the nozzle (i.e., in the nozzle environment). There are also other sources of oxygen-containing gases in the vessel, such as tin capture seals.

[0048] Thus, during these maintenance operations, there is potentially a problem of oxygen in the nozzle orifice environment oxidizing the tin in and around the nozzle orifice to form tin oxide. Oxygen can be present as molecular oxygen or as part of an oxygen-containing gas such as water vapor. The melting temperature of these tin oxides is higher than the operating temperature of the droplet generator and thus remains solid, creating a risk that they will clog the nozzle or interfere with the operation of the droplet generator.

[0049] To mitigate this risk, according to one aspect of the embodiment, during periods when the droplet generator is inactive, the droplet generator is maintained in a "thermal isolation state". In this state, the droplet generator is depressurized but maintained at or near its operating temperature, and the nozzle orifice environment is isolated from the main chamber that generates EUV radiation. The droplet generator is maintained at a high temperature ("hot") to avoid precipitation of oxides in the tin. The isolation of the thermal isolation state can be achieved, for example, by placing a valve such as a gate valve in the path of the droplet from the nozzle orifice to the main chamber. A gate valve, also known as a sluice valve, is a valve that opens by lifting a barrier (gate) out of the fluid path. In addition, the nozzle environment is contained in a housing that is sealed so that it can be purged or evacuated or some combination of these measures to reduce the amount of oxygen in the nozzle orifice environment. Here and elsewhere, "purging" refers to introducing a second gas to displace the first gas from the nozzle orifice environment, and "evacuating" refers to removing gas from the nozzle orifice environment.

[0050] It should be understood that the gate valve is merely one example of the type of valve that can be used as the path valve disclosed herein. Other types of valves, such as large-diameter diaphragm valves, can also be used.

[0051] For example, in some embodiments, the gate valve that separates the droplet generator from the main EUV source container is closed, and the environment around the nozzle orifice is cyclically purged. Here, "cyclically purging" means that the system is configured to repeatedly cycle the nozzle orifice environment between phases. These phases can include (1) a lower-pressure vacuum phase and (2) a higher-pressure purging phase, where a purging gas is introduced to dilute the water and oxygen that have leaked into the nozzle environment from sources such as outgassing and vacuum leaks. In some embodiments, the pressure in the high-pressure phase is higher than atmospheric pressure. One of ordinary skill in the art will understand that the terms "vacuum state" and "vacuum" mean a partial vacuum (very low pressure), since an absolute vacuum is not achievable. The cyclic purging can have three phases, including a pumping evacuation phase, a purging phase, and an exhaust phase.

[0052] The droplet generator can be safely maintained in this thermal isolation state for an extended period of time, while significantly reducing the risk of forming SnO x particles in the nozzle.

[0053] Operating parameters for cyclic purging, such as minimum and maximum pressures during different phases (such as the purging phase of the cycle, the pumping evacuation phase of the cycle, and the venting phase of the cycle, if used), the number of cycles per unit time, and the relative durations of the cycle phases are typically selected to optimize (e.g., minimize) the H2O and O2 partial pressures.

[0054] In some embodiments, the nozzle environment is enclosed within a housing, which can be part of an existing structure for other purposes, such as a flight tube assembly provided to protect the flight of the target material leaving the nozzle orifice. Here, terms such as "enclosed" and "sealed" mean that, except for the opening through which the droplets exit the housing, except for the inlet and outlet as described below, and except for inevitable leakage, the nozzle environment is effectively isolated. Other parts of the flight tube assembly or droplet generator assembly may be provided with dedicated features to direct the flow of the purge gas and facilitate effective purging in the volume around the nozzle orifice.

[0055] The purge gas can be any gas that displaces and dilutes any oxygen-containing gas in the nozzle environment without itself interacting detrimentally with the conditions or operation of components in that environment. For example, the purge gas can be an inert gas such as nitrogen, argon, or it can be hydrogen. The purge gas can be a mixture of an inert gas such as argon and molecular hydrogen (i.e., Ar + H2). The advantage of such a gas mixture is that in some systems, it is already used for other purposes in the droplet generator. Using a partial amount of hydrogen instead of pure hydrogen helps to reduce oxides without incurring the complexity and cost of providing hydrogen safety facilities. According to one aspect of an embodiment, the purge gas is purified before use.

[0056] There are situations where an isolation valve provided in the droplet channel becomes partially blocked and cannot be fully closed. For example, this can occur when a phenomenon called "tin writing" occurs, where tin accumulates inside or near the isolation valve and interferes with the operation of the isolation valve. To overcome this problem, in some embodiments, whenever the droplet generator is depressurized and the isolation valve is blocked and cannot be closed, the nozzle orifice environment is controlled by performing continuous purging instead of cyclic purging. In other words, the purge pressure is maintained and not alternated with intermediate evacuation phases. This continuous purging is maintained until droplets are needed and the droplet generator is switched from the idle state to the active operating state.

[0057] In some embodiments, a system for performing nozzle environment purification can be integrated with a gas nozzle for droplet acceleration. Gas acceleration of droplets generated by a droplet generator has been considered a way to increase droplet velocity without having to increase the drive gas pressure. For example, U.S. Patent No. 8,598,551, entitled "EUV Radiation Source Comprising a Droplet Accelerator and Lithographic Apparatus," issued December 3, 2013 to inventors named Mestrom et al., discloses an EUV radiation source that includes a droplet accelerator configured to use gas to accelerate droplets. Additionally, International Application Publication No. WO 2022 / 002662, entitled "Apparatus for and Method of Accelerating droplets in a Droplet Generator of an EUV Source," published January 6, 2022 to inventors named Ershov et al., discloses an apparatus in which droplets are subjected to an air stream that entrains and accelerates the droplets.

[0058] All patent applications, patents, and printed publications cited herein are incorporated herein by reference in their entirety, unless there is any definition, disclaimer of subject matter, or conflict, and unless the incorporated material is inconsistent with the explicit disclosure herein, in which case the language of this disclosure shall govern.

[0059] According to another aspect of an embodiment, instead of performing a cyclic or continuous purification of the isolated nozzle environment, a pumping system can be used to create a vacuum state inside the isolation housing such that when the isolation valve is closed and the droplet generator is depressurized (idling) at a high operating temperature, water vapor and oxygen can be efficiently removed from the nozzle environment. This can be achieved by providing a pumping system connected to the inside of the housing through a conduit. If a large amount of gas needs to be pumped, the pumping system can include a roughing pump, such as a scroll pump, or a high-capacity turbomolecular vacuum pump or another vacuum pump with a high pumping rate to achieve a very high vacuum, or a combination of a roughing pump and a high-performance pump.

[0060] In some embodiments, the conduit connecting the isolated nozzle environment and the pumping system can be a high-conductivity conduit. Generally, flow resistance is generated due to external friction between gas molecules and the wall surface and internal friction (viscosity) between the gas molecules themselves. In vacuum technology, the reciprocal of flow resistance, conductance C, is typically used. Conductance has the dimension of volumetric flow rate and is usually expressed in standard liters per second. Here, the hydraulic diameter of the high-conductivity conduit is selected to be large compared to the length of the high-conductivity conduit to provide a very high conductivity.

[0061] Figure 2A Schematic diagram of a system 100 for controlling the environment of a nozzle orifice of a droplet generator according to an aspect of an embodiment. Figure 2A The system shown includes a nozzle 110 having a nozzle orifice 120. The nozzle 110 and the nozzle orifice 120 are positioned within a housing 140. As described above, the housing 140 can be part of an existing structure such as a flight tube. The housing 140 can also be part of a device for supplying gas to accelerate a droplet stream 14 emitted from the nozzle orifice 120. The droplet stream 14 enters the EUV source chamber 26 through a valve 150 that can be a gate valve.

[0062] Figure 2A Also shown is a pump 180 fluidly connected (i.e., in fluid communication) to the interior 145 of the housing 140 through a conduit 185. Here, the phrases "fluidly connected to" and "in fluid communication with" are intended to mean that there is a path for fluid to pass through. The pump 180 can be a roughing pump or can be a high-volume pump such as a turbomolecular pump or a combination of both types of pumps. The conduit 185 can be configured as a high-conductivity conduit.

[0063] Figure 2A Also shown is a purge gas supply source 160 in fluid communication with a purge gas control unit 165, which supplies purge gas to a purge gas inlet 170. The purge gas is then carried into the housing interior 145 through a purge gas conduit 175. The purge gas can be an inert gas such as a mixture of argon and molecular hydrogen.

[0064] Figure 2A The arrangement shown includes a control line 157 that carries a signal for controlling whether the valve 150 is in a first state or a second state. In the first state, the housing interior 145 is in fluid communication with the EUV source chamber 26 (i.e., open, thereby allowing the droplet stream 14 emitted from the nozzle orifice 120 to pass through), and in the second state, the housing interior 145 is not in fluid communication with the EUV source chamber 26 (i.e., closed). Also shown is a data line 155 that carries a signal from the valve 150 indicating whether the valve 150 is open or closed. This can be a simple binary "open / closed" signal or can be a signal indicating the degree of a partially open or partially closed position. The signal carried by the data line 155 is used to determine whether the gate 150 is fully open or only partially open in response to an "open" control signal carried by the control line 157.

[0065] Figure 2AThe arrangement shown also includes a control line 167 that controls the purge gas controller 165 to determine whether purge gas from the purge gas supply source 160 is supplied to the purge gas inlet 170. Thus, the interior 145 of the housing is selectively fluidly connected to the purge gas supply source 160 in the sense that the connected “open / closed” state is selectable.

[0066] Figure 2B System 105 is shown where the pump 180 and the purge gas supply source 160 share a common inlet inside the housing 140. Specifically, the pump 180 and the purge gas supply source 160 are selectively connected to the inlet 192 by a valve 195. The valve 195 can be a three-way valve that is also connected to the atmosphere exhaust device 190. The inlet 192 communicates with the interior of the housing 140 through a conduit 197. System 105 can be used, for example, for a three-stage cycle of purifying, including a pumping evacuation stage, a purging stage, and an exhaust stage.

[0067] Figure 2B The system 105 shown also includes a purge gas cleaner 162 that is arranged to clean the purge gas before the purge gas passes into the interior of the housing 140. The purge gas cleaner 162 is included in the system 105 such that cleaning can be performed close in time and physically to when the purge gas is used to ensure that any oxygen-containing gas such as water vapor in the cleaned purge gas remains at a low concentration.

[0068] Figure 3A and Figure 3B is a diagram showing the operation of the valve 150 according to one aspect of an embodiment. In Figure 3A it, the valve 150 is configured as a gate valve having a gate 200. In Figure 3A the state shown, the valve 150 is open while the gate 200 is moved out of the passage through which the droplet stream 14 travels from the interior 145 of the housing to the chamber 26. Figure 3A An actuator 210 and a sensor 220 are also shown in it. The actuator 210 moves the gate 200 into and out of the closed position, and the sensor 220 can be configured as a valve position sensor that detects whether the gate 200 is in the open position, the closed position, or some intermediate position. In Figure 3B it, the gate 200 has been moved to a position isolating the interior 145 of the housing from the chamber 26 by a control signal applied to the actuator 210 through the control line 157.

[0069] The sensor 220 provides a valve state signal on the data line 155 indicating whether the valve 150 is open or closed. According to one embodiment, the valve state signal is used to determine whether a command to close the valve 150 has been successfully executed. For example, due to tin contamination on the gate 200, the gate 200 may not present Figure 3BThe fully closed position shown. This valve status information can be used to determine the characteristics of the nozzle orifice environment control operation to be performed.

[0070] Figure 4 FIG. is a flowchart showing an operation mode of a system for controlling the nozzle orifice environment according to an aspect of an embodiment. In step S10, it is determined whether the droplet generator (abbreviated as "DGEN" in the figure) is idle by determining whether the droplet generator has been depressurized. Generally, liquid target material is supplied to the droplet generator under pressure. During the idle period of the droplet generator, i.e., when droplet delivery is not invoked, this pressure is removed. If the determination in step S10 is negative, no action is taken. If the determination in step S10 is positive, then in step S20, the valve is closed, thereby isolating the interior of the droplet generator near the nozzle orifice from the EUV source chamber. Then, in step S30, a cyclic purge of the droplet generator nozzle orifice environment is performed. As described above, the cyclic purge is a purge performed using multiple cycles, each cycle including a stage of evacuating the housing using a vacuum pump, followed by a stage of supplying a purge gas to the housing.

[0071] Figure 5 FIG. is a flowchart showing another operation mode of a system for controlling the nozzle orifice environment according to an aspect of an embodiment. Again, in step S10, it is determined whether the droplet generator has been depressurized. If the determination in step S10 is negative, no action is taken. If it is determined in step S10 that the droplet generator has been depressurized, then in step S40, it is determined whether the valve can be closed. For example, this step S40 can be performed by providing a signal to attempt to close the valve and then determining whether the valve has closed in response to the signal. If the valve cannot be closed, for example, due to being blocked, then in step S50, a continuous purge is applied to the droplet generator nozzle environment. Here, "continuous" means that the purge gas is continuously supplied to the interior of the housing without an intervening evacuation stage. This continuous purge in step S50 continues until the droplet generator is invoked again to generate droplets and droplet generation begins in step S60. If it is determined in step S60 that droplets have not been generated, then the continuous purge in step S50 continues. However, if it is determined in step S60 that droplets are being generated, then in step S70, the continuous purge of the droplet generator nozzle environment is stopped.

[0072] Figure 6It is a flowchart showing another operation mode of a system for controlling the nozzle orifice environment according to an aspect of an embodiment. Again, in step S10, it is determined whether the droplet generator has been depressurized. If the determination in step S10 is negative, no action is taken. If it is determined in step S10 that the droplet generator has been depressurized, then in step S40, it is determined whether the valve can be closed. If the valve cannot be closed, then in step S50, continuous purging is applied to the nozzle environment of the droplet generator. This continuous purging in step S50 continues until the droplet generator is called again to generate droplets, and droplet generation starts in step S60. If it is determined in step S60 that no droplets have been generated, then continuous purging continues in step S50. However, if it is determined in step S60 that droplets are being generated, then the continuous purging of the nozzle environment of the droplet generator is stopped in step S70.

[0073] If it is determined in step S40 that the valve can be closed, then in step S20, the valve is closed, thereby isolating the interior of the droplet generator near the nozzle orifice from the EUV source chamber. Then, in step S30, cyclic purging of the nozzle orifice environment of the droplet generator is performed. Then in step S80, it is determined whether droplets are needed, that is, whether the droplet generator is reactivated. If it is determined in step S80 that droplets are not needed yet, then cyclic purging continues in step S30. However, if it is determined in step S80 that droplets are needed, then the cyclic purging of the nozzle environment of the droplet generator is stopped in step S90 and the valve is opened.

[0074] Figure 7 It is a flowchart showing another operation mode of a system for controlling the nozzle orifice environment according to an aspect of an embodiment. In step S10, it is determined whether the droplet generator is idle by determining whether the droplet generator has been depressurized. If the determination in step S10 is affirmative, then in step S120, the valve is closed, thereby isolating the interior of the droplet generator near the nozzle orifice from the EUV source chamber. Then, in step S130, the nozzle environment of the droplet generator is evacuated. This process can be modified by adding steps to confirm valve closure in step S120 and not performing the evacuation step S130 if valve closure is not confirmed.

[0075] Figure 8It is a flowchart showing another operation mode of a system for controlling the nozzle orifice environment according to an aspect of an embodiment. In step S10, it is determined whether the droplet generator is idle by determining whether the droplet generator has been depressurized. If the determination in step S10 is affirmative, the nozzle environment of the droplet generator is evacuated in step S200. In step S210, it is determined whether the valve isolating the nozzle environment of the droplet generator from the interior of the chamber can be closed. If so, the valve is closed in step S220, thereby isolating the interior of the droplet generator near the nozzle orifice from the EUV source chamber. Then, in step S230, cyclic purging of the droplet generator nozzle orifice environment is performed. Then it is determined in step S240 whether droplets are needed, that is, whether the droplet generator is activated. If it is determined in step S240 that droplets are not yet needed, cyclic purging continues in step S230. However, if it is determined in step S240 that droplets are needed, cyclic purging of the droplet generator nozzle environment is stopped and the valve is opened in step S250.

[0076] If it is determined in step S210 that the valve cannot be closed, the nozzle environment of the droplet generator continues to be evacuated in step S260. The evacuation in step S260 continues until it is determined in step S270 that the droplet generator is called again to generate droplets. If it is determined in step S270 that droplets are not yet needed, the evacuation continues in step S260. However, if it is determined in step S270 that droplets are needed, the evacuation of the droplet generator nozzle environment is stopped in step S280.

[0077] In some embodiments, the step of determining whether the valve can be closed can be performed before starting to evacuate the nozzle environment of the droplet generator. Figure 9 It is a flowchart describing such a process. In step S10, it is determined whether the droplet generator is idle by determining whether the droplet generator has been depressurized. If the determination in step S10 is affirmative, it is determined in step S210 whether the valve isolating the nozzle environment of the droplet generator from the interior of the chamber can be closed. If so, the valve is closed in step S220, thereby isolating the interior of the droplet generator near the nozzle orifice from the EUV source chamber. Then, in step S230, cyclic purging of the droplet generator nozzle orifice environment is performed. Then it is determined in step S240 whether droplets are needed, that is, whether the droplet generator is activated. If it is determined in step S240 that droplets are not yet needed, cyclic purging continues in step S230. However, if it is determined in step S240 that droplets are needed, cyclic purging of the droplet generator nozzle environment is stopped and the valve is opened in step S250.

[0078] If it is determined in step S210 that the valve cannot be closed, evacuation of the droplet generator nozzle environment is initiated in step S270. The evacuation in step S270 continues until it is determined in step S280 that droplets are required to be generated by the droplet generator. If it is determined in step S280 that droplets are not yet required, evacuation continues in step S270. However, if it is determined in step S280 that droplets are required, evacuation of the droplet generator nozzle environment is stopped in step S290.

[0079] This disclosure has been made in terms of functional building blocks that illustrate specific functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined herein. Alternative boundaries can be defined so long as the specified functions and their relationships are appropriately performed. For example, the control module functionality can be divided among several systems or at least partially performed by the overall control system.

[0080] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe every conceivable combination of components or methods for the purpose of describing the foregoing embodiments, but one of ordinary skill in the art will recognize that many other combinations and permutations of the various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims. Additionally, insofar as the terms "including" are used in the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising" as that term is interpreted when used as a transitional word in the claims. Further, although the elements of the aspects and / or embodiments described may be described or claimed in the singular, the plural is covered unless expressly stated to be limited to the singular. Additionally, all or part of any aspect and / or embodiment may be used in conjunction with all or part of any other aspect and / or embodiment, unless otherwise noted.

[0081] These embodiments may be further described using the following clauses:

[0082] 1. A droplet generator system for an extreme ultraviolet (EUV) radiation source, the droplet generator system comprising:

[0083] A nozzle housing;

[0084] A nozzle having an exit hole positioned within the housing, the exit hole being adapted to be selectively in fluid communication with a supply source of liquid EUV source material and adapted to deliver the EUV source material into a chamber of the EUV radiation source; and

[0085] A valve, in fluid communication with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is in fluid communication with the chamber, and in the second state, the interior of the housing is not in fluid communication with the chamber.

[0086] 2. The droplet generator system according to clause 1, wherein the nozzle is adapted to convey the EUV source material along a path from the outlet hole through the valve into the chamber, and wherein the valve is adapted to maintain the path in an open state when the valve is in the first state and to maintain the path in a closed state when the valve is in the second state.

[0087] 3. The droplet generator system according to clause 1, wherein the valve is a gate valve.

[0088] 4. The droplet generator system according to clause 1, wherein the valve is adapted to switch between the first state and the second state in response to a control signal.

[0089] 5. The droplet generator system according to clause 1, further comprising a sensor arranged to sense whether the valve is in the first state or the second state.

[0090] 6. The droplet generator system according to clause 1, further comprising an inlet in fluid communication with the interior of the housing and adapted to be connected to a purge gas source.

[0091] 7. The droplet generator system according to clause 6, wherein the purge gas comprises Ar + H2.

[0092] 8. The droplet generator system according to clause 6, wherein the purge gas comprises an inert gas.

[0093] 9. The droplet generator system according to clause 8, wherein the inert gas comprises at least one of nitrogen and argon.

[0094] 10. The droplet generator system according to clause 6, further comprising a purge gas cleaner arranged to clean the purge gas.

[0095] 11. A droplet generator system for an extreme ultraviolet (EUV) radiation source, the droplet generator system comprising:

[0096] A nozzle housing;

[0097] A nozzle having an outlet hole positioned in the housing, the outlet hole being adapted to be selectively in fluid communication with a supply source of liquid EUV source material and adapted to convey the EUV source material into a chamber of the EUV radiation source;

[0098] A valve, in fluid communication with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is in fluid communication with the chamber, and in the second state, the interior of the housing is not in fluid communication with the chamber;

[0099] A source of purge gas, selectively in fluid communication with the interior of the housing; and

[0100] A vacuum pump, selectively in fluid communication with the interior of the housing.

[0101] 12. The droplet generator system according to clause 11, wherein the vacuum pump is a turbomolecular vacuum pump or a scroll vacuum pump.

[0102] 13. The droplet generator system according to clause 11, wherein the vacuum pump is a turbomolecular vacuum pump, and further includes a high-conductivity conduit arranged to connect the interior of the housing to the turbomolecular vacuum pump.

[0103] 14. A component for purifying the environment of a nozzle outlet of a droplet generator in an extreme ultraviolet (EUV) radiation source, the component comprising:

[0104] A housing, disposed around the nozzle outlet and enclosing the nozzle outlet except for an opening for the droplet path, through which droplets are conveyed to a chamber of the EUV radiation source;

[0105] A source of purge gas, selectively in fluid communication with the interior of the housing; and;

[0106] A pump, selectively in fluid communication with the interior of the housing and adapted to evacuate the housing.

[0107] 15. The component according to clause 14, wherein the purge gas includes Ar + H2.

[0108] 16. The component according to clause 14, wherein the purge gas includes an inert gas.

[0109] 17. The component according to clause 14, wherein the purge gas includes at least one of nitrogen and argon.

[0110] 18. The component according to clause 14, further comprising a purge gas cleaner arranged to clean the purge gas.

[0111] 19. The component according to clause 14, wherein the pump includes a roughing pump.

[0112] 20. The assembly according to clause 14, wherein the pump comprises a turbomolecular vacuum pump or a scroll vacuum pump.

[0113] 21. The assembly according to clause 14, wherein the pump is fluidly connected to the interior of the housing through a high-conductivity pipeline.

[0114] 22. The assembly according to clause 14, further comprising a valve disposed in the droplet path, the valve having a first state and a second state, in the first state, the interior of the housing is fluidly connected to the chamber, in the second state, the interior of the housing is not fluidly connected to the chamber, and wherein the source of the purifying gas and the pump are adapted to:

[0115] When the droplet generator is depressurized and the valve is in the second state, perform a cyclic purge including at least supplying purifying gas to the interior of the housing, and

[0116] When the droplet generator is depressurized and the valve is in the first state, perform a continuous purge by supplying purifying gas to the interior of the housing.

[0117] 23. The assembly according to clause 22, wherein the valve is a gate valve.

[0118] 24. A method for controlling the environment of a nozzle of a droplet generator in an extreme ultraviolet (EUV) radiation source, the method comprising:

[0119] Disposing the nozzle in a housing;

[0120] Determining whether the droplet generator is depressurized; and

[0121] If it is determined that the droplet generator is depressurized, sending a signal to activate the disposed valve to isolate the nozzle from the chamber of the EUV radiation source.

[0122] 25. The method according to clause 24, further comprising, after sending the signal to activate the disposed valve to isolate the nozzle from the chamber of the EUV radiation source, determining whether the valve operates in response to the signal to isolate the nozzle from the chamber.

[0123] 26. The method according to clause 25, further comprising, if it is determined that the valve does not operate in response to the signal to isolate the nozzle from the chamber, performing a cyclic purge of the housing by cycling between supplying purifying gas to the housing and evacuating the housing.

[0124] 27. The method of clause 26, wherein the purifying gas comprises Ar + H2.

[0125] 28. The method of clause 26, wherein the purifying gas comprises an inert gas.

[0126] 29. The method according to clause 26, wherein the purifying gas comprises at least one of nitrogen and argon.

[0127] 30. The method according to clause 26, further comprising purifying the purifying gas before supplying the purifying gas to the housing.

[0128] 31. The method according to clause 25, further comprising, if the determination is that the valve fails to operate in response to the signal to isolate the nozzle from the chamber, performing continuous purging of the housing by continuously supplying purifying gas to the housing.

[0129] 32. The method according to clause 31, wherein the purifying gas comprises Ar + H2.

[0130] 33. The method according to clause 31, wherein the purifying gas comprises an inert gas.

[0131] 34. The method according to clause 31, wherein the purifying gas comprises at least one of nitrogen and argon.

[0132] 35. The method according to clause 31, further comprising cleaning the purifying gas before supplying the purifying gas to the housing.

[0133] 36. The method according to clause 25, further comprising evacuating the housing if the determination is that the valve does operate in response to the signal to isolate the nozzle from the chamber.

[0134] 37. The method according to clause 36, wherein evacuation of the housing is performed using a turbomolecular vacuum pump or a scroll vacuum pump.

[0135] 38. The method according to clause 24, further comprising evacuating the housing after sending a signal to activate the arranged valve to isolate the nozzle from the chamber of the EUV radiation source.

[0136] The above-described embodiments and other embodiments are within the scope of the appended claims.

[0137] The above embodiments and other embodiments are within the scope of the appended claims.

Claims

1. A droplet generator system for an extreme ultraviolet (EUV) radiation source, the droplet generator system comprising: A nozzle housing; A nozzle having an outlet hole positioned in the housing, the outlet hole being adapted to be selectively in fluid communication with a supply source of a liquid EUV source material and being adapted to transport the EUV source material into a chamber of the EUV radiation source; And A valve in fluid communication with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is in fluid communication with the chamber, and in the second state, the interior of the housing is not in fluid communication with the chamber.

2. The droplet generator system according to claim 1, wherein the nozzle is adapted to transport the EUV source material along a path from the outlet hole through the valve into the chamber, and wherein the valve is adapted to keep the path in an open state when the valve is in the first state and in a closed state when the valve is in the second state.

3. The droplet generator system according to claim 1, wherein the valve is a gate valve.

4. The droplet generator system according to claim 1, wherein the valve is adapted to switch between the first state and the second state in response to a control signal.

5. The droplet generator system according to claim 1, further comprising a sensor arranged to sense whether the valve is in the first state or the second state.

6. The droplet generator system according to claim 1, further comprising an inlet in fluid communication with the interior of the housing and adapted to be connected to a source of a purge gas.

7. The droplet generator system according to claim 6, wherein the purge gas comprises an inert gas, and wherein the inert gas comprises at least one of nitrogen and argon.

8. The droplet generator system according to claim 6, further comprising a purge gas scrubber arranged to purify the purge gas.

9. A droplet generator system for an extreme ultraviolet (EUV) radiation source, the droplet generator system comprising: A nozzle housing; A nozzle having an outlet hole positioned in the housing, the outlet hole being adapted to be selectively in fluid communication with a supply source of a liquid EUV source material and being adapted to transport the EUV source material into a chamber of the EUV source; A valve in fluid communication with the interior of the housing and the chamber, the valve having a first state and a second state, in the first state, the interior of the housing is in fluid communication with the chamber, and in the second state, the interior of the housing is not in fluid communication with the chamber; A supply source of a purge gas selectively in fluid communication with the interior of the housing; And A vacuum pump selectively in fluid communication with the interior of the housing.

10. The droplet generator system according to claim 9, wherein the vacuum pump is a turbomolecular vacuum pump or a scroll vacuum pump.

11. The droplet generator system according to claim 9, wherein the vacuum pump is the turbomolecular vacuum pump, and further includes a high-conductivity conduit arranged to connect the interior of the housing to the turbomolecular vacuum pump.

12. A method of controlling the environment of a nozzle of a droplet generator in an extreme ultraviolet (EUV) radiation source, the method comprising: arranging the nozzle in a housing; determining whether the droplet generator is depressurized; and if it is determined that the droplet generator is depressurized, sending a signal to activate a valve arranged to isolate the nozzle from a chamber of the EUV radiation source.

13. The method according to claim 12, further comprising, after sending the signal to activate the valve to isolate the nozzle from the chamber of the EUV radiation source, performing a determination as to whether the valve operates in response to the signal to isolate the nozzle from the chamber.

14. The method according to claim 13, further comprising: If the determination is that the valve does not operate in response to the signal to isolate the nozzle from the chamber, performing a cyclic purge of the housing by cycling between supplying a purge gas to the housing and evacuating the housing.

15. The method according to claim 14, wherein the purge gas includes an inert gas, and wherein the purge gas includes at least one of nitrogen and argon.

16. The method according to claim 14, further comprising purifying the purge gas before supplying the purge gas to the housing.

17. The method according to claim 13, further comprising: If the determination is that the valve does not operate in response to the signal to isolate the nozzle from the chamber, performing a continuous purge of the housing by continuously supplying the purge gas to the housing.

18. The method according to claim 13, further comprising: If the determination is that the valve does not operate in response to the signal to isolate the nozzle from the chamber, evacuating the housing.

19. The method according to claim 18, wherein the housing is evacuated using a turbomolecular vacuum pump or a scroll vacuum pump.

20. The method according to claim 12, further comprising evacuating the housing after sending the signal to activate the valve arranged to isolate the nozzle from the chamber of the EUV radiation source.

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