Patent Publication Number: US-2022213981-A1

Title: Fluid control device and method for fluid control in an extreme ultraviolet light source

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Application No. 62/852,685, filed May 24, 2019 and titled FLUID CONTROL DEVICE AND METHOD FOR FLUID CONTROL IN AN EXTREME ULTRAVIOLET LIGHT SOURCE, which is incorporated herein in its entirety by reference. 
    
    
     TECHNICAL FIELD 
     The disclosed subject matter relates to a fluid control device and a method for fluid control that can be used in a laser produced plasma extreme ultraviolet light source. 
     BACKGROUND 
     Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers. 
     Methods to produce EUV light include, but are not necessarily limited to, converting a material that has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range in a plasma state. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment. 
     SUMMARY 
     In some general aspects, a two-mode fluid control device includes: a structure defining a valve cavity and three fluid ports fluidly coupled to the valve cavity, a first fluid port configured to be fluidly coupled to a vacuum pump, a second fluid port configured to be fluidly coupled to a fluid supply, and a third fluid port configured to be fluidly coupled to a hermetic interior of a body; and a single plunger valve within the valve cavity and configured to move between first and second modes while maintaining the hermetic interior of the body. The first mode corresponds to a vacuum mode in which the plunger valve is open such that a first fluid flow path is open between the hermetic interior and the first fluid port and fluid is free to pass between the vacuum pump and the hermetic interior. The second mode corresponds to a pressure mode in which the plunger valve is closed such that the first fluid port is blocked from the hermetic interior by the plunger valve and a second fluid flow path is open between the hermetic interior and the second fluid port. 
     Implementations can include one or more of the following features. For example, the first fluid port can have a first cross-sectional area that provides a first fluid conductance and the second fluid port can have a second cross-sectional area that provides a second fluid conductance, the first cross-sectional area being greater than the second cross-sectional area. The first cross-sectional area can be at least twice the size of, at least five times the size of, at least ten times the size of, at least fifty times the size of, or about one hundred times the size of the second cross-sectional area. 
     The second mode can be a default mode in which the plunger valve is at its equilibrium position. The fluid control device can include a biasing device in physical communication with the plunger valve and configured to bias the plunger valve to the second mode. 
     When the plunger valve is in the second mode and is closed, a seal can be formed that separates the vacuum pump from the hermetic interior and the plunger valve is exposed to a pressure above atmospheric pressure. The seal can strengthen or remain at a constant strength while the plunger valve is in the second mode due to pressure applied against the plunger valve from the fluid supply. 
     In the vacuum mode, a pressure within the hermetic interior can be maintained below atmospheric pressure, and in the pressure mode, a pressure within the hermetic interior can be maintained above atmospheric pressure. In the vacuum mode, a pressure within the hermetic interior can be maintained at high or ultra-high vacuum in which molecular flow dominates within first fluid flow path and the hermetic interior. In the vacuum mode, a pressure within the hermetic interior can be maintained below 101 kilopascals (kPa), and in the pressure mode, a pressure within the hermetic interior can be maintained above 10 megapascals (MPa). In various implementations, the vacuum mode is suitable to support pressures below, for example, 10 kPa, 3 kPa, or 1 kPa. In various implementations, the pressure mode is suitable to support pressures above, for example, 5 MPa, 10 MPa, or 24 MPa. 
     Fluid can be free to pass from the hermetic interior to the vacuum pump when the plunger valve is in the first mode. 
     The plunger valve can be configured to move between the first and second modes by linearly translating between the first and second modes without rotation. The fluid control device can include an actuator in physical communication with the plunger valve and configured to control the translation of the plunger valve between the first and second modes. The actuation can include linear motion by a rotatable threaded rod, a push/pull bar or cable, a lever, a solenoid, or a piston (that can be pneumatic or hydraulic). 
     A hermetic seal can be formed between the structure and the body. 
     The second fluid port can be fluidly coupled to a fluid supply of gas. The gas can be an inert gas that includes one or more of a noble gas and a molecular gas. 
     While in the first mode, a first fluid volume that includes the hermetic interior and a first portion of the valve cavity can be formed. And, while in the second mode, a second fluid volume that includes the hermetic interior and a second portion of the valve cavity can be formed, the second fluid volume being smaller than the first fluid volume. 
     The plunger valve can be a solid volume or mass of material such that any fluid flow path remains exterior to the plunger valve. 
     In other general aspects, a target apparatus for an extreme ultraviolet (EUV) light source includes a target generator including a reservoir defining a hollow interior configured to contain target material that produces EUV light when in a plasma state and a nozzle structure defining an opening that is in fluid communication with the hollow interior; and a two-mode valve device hermetically sealed to the reservoir. The two-mode valve device includes: a structure defining a valve cavity and three fluid ports fluidly coupled to the valve cavity, a first fluid port of a first extent being fluidly coupled to a vacuum pump, a second fluid port of a second extent being fluidly coupled to a fluid supply, the first extent being at least ten times the size of the second extent, and a third fluid port being fluidly coupled to the reservoir interior; and a single plunger valve within the valve cavity and configured to move between first and second modes without opening the reservoir interior. The first mode corresponds to a vacuum mode in which the plunger valve is open such that a first fluid flow path is open between the reservoir interior and the first fluid port. The second mode corresponds to a pressure mode in which the plunger valve is closed such that a second fluid flow path is open between the reservoir interior and the second fluid port. 
     Implementations can include one or more of the following features. For example, the hollow interior can be held at a pressure above 10 megapascals (MPa) when the plunger valve is in the pressure mode. The pressure within the hollow interior of the reservoir can be greater than a pressure at the exterior when the plunger valve is in the pressure mode. 
     A pressure within the hollow interior can be controlled at least in part by the mode of the two-mode valve device. 
     The first fluid port can be hermetically separated from the hollow interior by the plunger valve when the plunger valve is in the second mode. 
     In other general aspects, a method includes controlling a fluid state in a hermetic interior of a body using one of two operationally-isolated control modes, the two control modes including a vacuum control mode and a high pressure control mode. In the vacuum control mode, fluid is conducted from the hermetic interior of the body at a first conductance such that the hermetic interior reaches a target vacuum pressure. In the high pressure control mode, fluid is conducted into the hermetic interior of the body at a second conductance such that the hermetic interior reaches a target high pressure that is above atmospheric pressure, the first conductance being at least twice the second conductance. The method also includes switching between the vacuum control mode and the high pressure control mode including moving a single plunger valve between a first mode corresponding to the vacuum control mode in which the plunger valve is open and a second mode corresponding to the high pressure control mode in which the plunger valve is closed and forms a seal. The hermetic interior of the body is maintained throughout the switching. 
     Implementations can include one or more of the following features. For example, the method can also include, prior to conducting fluid into the hermetic interior of the body at the second rate of flow while in the high pressure control mode, forming the seal to thereby separate a vacuum pump from the hermetic interior. The fluid can be conducted into the hermetic interior of the body at the second rate of flow while in the high pressure control mode by exposing the plunger valve to the target high pressure. 
     The target vacuum pressure can be below 101 kilopascals (kPa) and fluid can be conducted from the hermetic interior of the body after switching to the vacuum control mode at the first conductance such that the hermetic interior of the body reaches the target vacuum pressure in less than four hours, less than an hour, less than 15 minutes, or less than a minute. 
     The switch to the vacuum control mode can include opening the plunger valve and forming a first fluid volume that includes the hermetic interior and a first portion of a valve cavity in which the plunger valve is seated. The switch to the high pressure control mode can include closing the plunger valve and forming a second fluid volume that includes the hermetic interior and a second portion of the valve cavity, the second fluid volume being smaller than the first fluid volume. 
     Prior to controlling the fluid state in the hermetic interior of the body, the method can include inserting a solid mass of material into an interior of the body and sealing the interior to form the hermetic interior in which the solid mass is located. The fluid state in the hermetic interior of the body can be controlled by: conducting fluid that includes one or more contaminants from the hermetic interior while in the vacuum control mode; and if the concentration of each contaminant inside the hermetic interior is below a respective threshold concentration, then closing the plunger valve to halt vacuum control mode, melting the solid mass of material, and switching to high pressure control mode after the solid mass of material has melted. The fluid can be conducted into the hermetic interior until a pressure in the hermetic interior rises above a threshold pressure at which the melted target material viscously flows out of an opening fluidly coupled to the hermetic interior during high pressure control mode. 
     The method can include biasing the plunger valve to the first state. 
     The method can include biasing the plunger valve to the second state. 
     The first conductance can be at least five times, at least ten times, at least fifty times, or about one hundred times the second conductance. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a block diagram of a fluid control device in fluid communication with and for controlling a hermetic interior of a body, the fluid control device in a vacuum mode; 
         FIG. 1B  is a block diagram of the fluid control device of  FIG. 1A  in a pressure mode; 
         FIG. 1C  is a schematic illustration of a plunger valve of the fluid control device in the pressure mode of  FIG. 1B , the plunger valve being seated and movable in a valve cavity defined by a structure of the fluid control device of  FIGS. 1A and 1B ; 
         FIG. 2A  is a schematic illustration of an implementation of a face seal formed between the plunger valve and the structure of the fluid control device of  FIGS. 1B and 1C ; 
         FIG. 2B  is a schematic illustration of an implementation of a conical seal formed between the plunger valve and the structure of the fluid control device of  FIGS. 1B and 1C ; 
         FIG. 3A  is a cross-sectional illustration of an implementation of a fluid control device of  FIG. 1A  while in a vacuum mode; 
         FIG. 3B  is a cross-sectional illustration of the implementation of the fluid control device of  FIG. 3A  while in a pressure mode; 
         FIG. 3C  is a schematic illustration of a plunger valve of the fluid control device in the pressure mode of  FIG. 3B , the plunger valve being seated and movable in a valve cavity defined by a structure of the fluid control device of  FIGS. 3A and 3B  and showing a piston-bore type seal formed between the plunger valve and the structure; 
         FIG. 4  is a block diagram of a target apparatus of an extreme ultraviolet (EUV) light source in which a fluid control device that can be the fluid control device of  FIGS. 1A and 1B  is used in the target apparatus; 
         FIG. 5  is a flow chart of a procedure performed for controlling a fluid state within the hermetic interior of the body using the fluid control device of  FIGS. 1A and 1B  or  FIGS. 2A-3C ; 
         FIGS. 6A-6F  show steps of a procedure performed for controlling a fluid state within a hollow interior of a reservoir of the target apparatus of  FIG. 4 ; and 
         FIG. 7  is a block diagram of an implementation of a lithography apparatus that receives EUV light output from the EUV light source of  FIG. 4 . 
     
    
    
     DESCRIPTION 
     Referring to  FIGS. 1A and 1B , a fluid control device  100  is configured to be in fluid communication with and is used to control a hermetic interior  105  defined within a body  110 , the hermetic interior  105  being effectively sealed off or isolated from an external environment  115 . The two-mode fluid control device  100  switches between two modes: an open mode in which a relatively large fluid conductance out of the hermetic interior  105  is possible and a closed mode in which a relatively smaller fluid conductance into the hermetic interior  105  is possible. The switching can be performed while maintaining the hermetic interior  105  in its hermetically-isolated state. The fluid that can be conducted into and out of the hermetic interior  105  can be in a gas state or a liquid state. 
     The fluid control device  100  includes a structure  120  defining a valve cavity  125  in which a single plunger valve  130  is seated and is movable. Thus, the fluid control device  100  performs the functions described herein solely with the use of only one plunger valve  130 , thus reducing complexity and cost. The structure  120  defines three fluid ports  135 ,  140 ,  145  fluidly coupled to the valve cavity  125 . The first fluid port  135  is configured to be fluidly coupled to a vacuum pump  137 , the second fluid port  140  is configured to be fluidly coupled to a supply  142  of fluid, and the third fluid port  145  is configured to be fluidly coupled to the hermetic interior  105  of the body  110 . The plunger valve  130  is within the valve cavity  125  and is configured to move between first and second modes while maintaining the hermetic interior  105  of the body  110 . 
     The first mode, which is shown in  FIG. 1A , corresponds to a vacuum mode in which the plunger valve  130  is in an open status such that a first fluid flow path FP 1  is open between the hermetic interior  105  and the first fluid port  135  and fluid is free to pass between the vacuum pump  137  and the hermetic interior  105 . For example, in the first mode, fluid is free to pass from the hermetic interior  105  to the vacuum pump  137 . The second mode, which is shown in  FIG. 1B , corresponds to a pressure mode in which the plunger valve  130  is in a closed status such that the first fluid port  135  is blocked from the hermetic interior  105  by the plunger valve  130  and a second fluid flow path FP 2  is open between the hermetic interior  105  and the second fluid port  140 . The plunger valve  130  is in the closed status or closed when it is sealed to the structure  120  such that fluid is unable to pass around the plunger valve  130 . 
     Moreover, while in the first mode, a first fluid volume FV 1  that includes the hermetic interior  105  and a first portion of the valve cavity  125  is formed; while in the second mode, a second fluid volume FV 2  that includes the hermetic interior  105  and a second and smaller portion of the valve cavity  125  is formed. The first fluid volume FV 1  includes the first fluid port  135 , the valve cavity  125 , the third fluid port  145 , and the hermetic interior  105 . The second fluid volume FV 2  includes the valve cavity  125 , the second fluid port  140 , the third fluid port  145 , and the hermetic interior  105 . The second fluid volume FV 2  is smaller than the first fluid volume FV 1 , as is evident from  FIGS. 1A and 1B . The second fluid volume FV 2  does not include the first fluid port  135 . 
     The structure  120  is a suitably rigid solid structure that is able to maintain both a vacuum (while in the vacuum mode) that is less than atmospheric pressure and a high pressure that is greater than atmospheric pressure (when in the pressure mode). The vacuum maintained in the hermetic interior  105  and also in the valve cavity  125  during vacuum mode can be a high or ultra-high vacuum in which molecular flow dominates within first fluid flow path FP 1  and the hermetic interior  105 . For example, in the vacuum mode, a pressure within the hermetic interior  105  can be maintained or held below 101 kilopascals (kPa). Moreover, the pressure maintained in the hermetic interior  105  and the valve cavity  125  during the pressure mode can be above atmospheric pressure, or can be above 10 megapascals (MPa). 
     Thus, the structure  120  (including the parts of the structure  120  that form the fluid ports  135 ,  140 ,  145 ) should be made of a material that has low or minimal outgassing such as stainless steel, aluminum, titanium, for example. 
     The plunger valve  130  is controllable to move between the two modes, and when in the second mode, the plunger valve  130  is sealed to an interior wall  121  ( FIG. 1C ) of the structure  120  to thereby prevent fluid from flowing into the first fluid port  135 . The plunger valve  130  is a solid mass such that all possible fluid flow paths remain exterior to the body of the plunger valve  130  and there are not paths that pass through or within the plunger valve  130 . Additionally, the plunger valve  130 , like the structure  120 , should be made of a rigid material that is able to withstand both a vacuum (while in the vacuum mode) that is less than atmospheric pressure and a high pressure that is greater than atmospheric pressure (when in the pressure mode) and also has low or minimal outgassing. The plunger valve  130  can be made of stainless steel, aluminum, titanium, for example. 
     The plunger valve  130  is configured to move between the first and second modes by linearly translating along a direction  133  (depicted by an arrow that is labeled  133  in  FIG. 1C ) that extends between the first and second modes. The direction  133  along which the plunger valve  130  can translate is either parallel with the +Z direction or parallel with the −Z direction. Moreover, the plunger valve  130  can be configured to perform such translation without any rotational motion. The plunger valve  130  moves under the control of an actuator  152  that maintains the position of the plunger valve  130  within the valve cavity  125  and also physically translates the plunger valve along the direction  133 . 
     As discussed above, in the first mode, a relatively large fluid conductance out of the hermetic interior  105  is possible. A relatively large fluid conductance out of the hermetic interior  105  in the first mode means that the fluid conductance through the first fluid port  135  (which is fluidly coupled to the hermetic interior  105  in the first mode) is much greater than the fluid conductance through the second fluid port  140  (which is fluidly coupled to the hermetic interior  105  at least in the second mode). The fluid conductance through a port (such as the first and second fluid ports  135 ,  140 ) is generally proportional (and can be directly proportional) to a cross-sectional area of that port, where the cross-sectional are is taken along the plane that is perpendicular to the general direction of fluid flow through that port. Thus, a first cross-sectional area  138  in the first fluid port  135  is much larger than a second cross-sectional area  143  of the second fluid port  140 . In this example, the cross section of the first and second ports  135 ,  140  has a circular shape, but other shapes such as, for example, polygonal or asymmetric are possible. 
     In some implementations, the first cross-sectional area  138  is at least twice the size of the second cross-sectional area  143 ; in other implementations, the first cross-sectional area  138  is at least five times the size of the second cross-sectional area  143 ; in still further implementations, the first cross-sectional area  138  is at least ten times the size of the second cross-sectional area  143 ; and in other implementations, the first cross-sectional area  138  is at least fifty times the size of the second cross-sectional area  143 . Lastly, in still other implementations, the first cross-sectional area  138  is about one hundred times the size of the second cross-sectional area  143 . 
     In order for the fluid control device  100  to maintain the hermetic interior  105  of the body  110  during switching between the first and second modes, the structure  120  forms a hermetic seal  150  with the body  110  at the location at which the structure  120  and the body  110  attached to each other. The hermetic seal  150  can be any seal that can withstand both the vacuum pressures present during the vacuum mode and the high pressures present during the high pressure mode. For example, the hermetic seal  150  can be a gasket seal between the structure  120  and the body  110 , in which the gasket is made of soft metal such as copper and the edges of the structure  120  and the body  110  that sandwich the gasket have a knife edge to thereby maintain integrity in the ultra-high vacuum range. 
     The vacuum pump  137  can be any vacuum pump suitable to remove matter from the hermetic interior  105  so that a pressure within the hermetic interior  105  drops below a threshold pressure sufficiently quickly and adequately to support operating requirements on the hermetic interior  105 . In the example above, in which the threshold pressure is in the high or ultra-high vacuum range, a suitable vacuum pump  137  can include one or more of the following type of pump: turbomolecular, ion, titanium sublimation, non-evaporative getter and/or cryopumps. Additionally, the vacuum pump  137  can include a pair of pumps that are used in distinct stages of operation. For example, the vacuum pump  137  can also include a mechanical pump that is initially fluidly coupled to the first fluid port  135  to perform a first rough pump down to an intermediate low pressure. 
     The fluid supply  142  can be a tank including an output port  144  that is fluidly coupled to the second fluid port  140 , and a gate valve or some suitable fluid control valve can be positioned in the output port  144  to control how much fluid is directed from the fluid supply  142  to the second fluid port  140 . In some implementations, the fluid control valve in the output port  144  remains open even during the vacuum mode in order to provide certain fluids to the hermetic interior  105  during the vacuum mode. 
     The fluid supplied by the fluid supply  142  to the hermetic interior  105  can be a fluid that is compatible for the application in which the hermetic interior  105  is used. The fluid supplied by the fluid supply  142  to the hermetic interior  105  can be a gas such as an inert gas, which can include one or more of a noble gas and a molecular gas. For example, the gas can be nitrogen, argon, a mixture of argon and hydrogen, hydrogen, or helium. 
     As discussed above, and as also shown in  FIG. 1C , when the plunger valve  130  is in the second mode and is closed ( FIG. 1B ), a seal  132  is formed that separates the vacuum pump  137  from the hermetic interior  105 , such seal  132  being formed by compressing an elastic member  136  ( FIG. 1A ) between the plunger valve  130  and a wall or walls of the structure  120 , such as the narrowing wall  121  of the structure  120 . The seal  132  is formed from a squeezing force applied between the plunger valve  130  and the narrowing wall  121  of the structure  120  that is directed away (shown by an arrow labeled  134 ) from the hermetic interior  105  generally along the −Z direction. 
     Moreover, in this second mode, the plunger valve  130  is exposed to a pressure above atmospheric pressure (and can be substantially higher than atmospheric pressure) at the side facing the hermetic interior  105  due to the pressure from the fluid in the second fluid flow path FP 2 . Thus, the pressure applied to the plunger valve  130  from the fluid supply  142  applies an additional force to the plunger valve  130  that, depending on the design of the seal  132 , adds to the force along the direction  134 , and this additional force can strengthen or maintain the seal  132  between the plunger valve  130  and the wall of the structure  120  and/or impart a greater force that maintains the plunger valve  130  in the second mode and closed. 
     The seal  132  shown in  FIGS. 1B and 1C  is depicted in a generic manner. In various implementations, the seal  132  can be a face seal, a conical seal, or a piston-bore seal, or any modifications to these seals. The seal  132  needs to be able to withstand many cycling motions of the plunger valve  132  between the two modes of operation without requiring the elastic member  136  to be replaced. 
     Referring to  FIG. 2A , in some implementations, the seal  132  is a face seal  232 A. The face seal  232 A is a seal in which two parallel surfaces compress an elastic member  236 A (gasket) along the sealing direction (which is parallel with the Z direction), where the elastic member  236 A is seated in an O-ring groove formed in a wall  231 A of the plunger valve  230 A. Specifically, the elastic member  236 A is compressed between an interior wall  221 A of the structure  220 A and the wall  231 A (which is an axial face) of the plunger valve  230 A. In this implementation, increasing the pressure along the direction  134  (due to the fluid flow from the fluid supply  142 ) compresses the gasket  236 A and increases the performance of the seal  232 A. The elastic material of the gasket  232 A may need to be protected from excess strain that could lead to degradation or failure of the seal  232 A. This protection can be provided by a hard stop that limits the compression, such as using an O-ring groove formed in the wall  231 A having a specific depth. Additionally, in this implementation, the additional force from the fluid flow imparts a greater force that maintains the plunger valve  230 A in the second mode and therefore closed. 
     Referring to  FIG. 2B , in other implementations, the seal  132  is a conical seal  232 B. In the conical seal  232 B, a plunger valve  230 B is designed with a draft angle (that is larger on the side at which pressure is applied and thus is larger facing the fluid port  145 ) at a wall  231 B that matches the conical shape of interior wall  221 B. The elastic member  236 B (which can be a gasket) can be seated in an O-ring groove formed in the wall  231 B. In this implementation, increasing the pressure along the direction  134  (due to the fluid flow from the fluid supply  142 ) also compresses the gasket  236 B and increases the performance of the seal  232 B. The elastic material of the elastic member  232 B may need to be protected from excess strain that could lead to degradation or failure of the seal  232 B. This protection can be provided by a hard stop that limits the compression, such as using an O-ring groove formed in the wall  231 B having a specific depth. Additionally, in this implementation, the additional force from the fluid flow imparts a greater force that maintains the plunger valve  230 B in the second mode and therefore closed. 
     Referring to  FIGS. 3A-3C , an implementation  300  of the fluid control device  100  includes a plunger valve  330  seated in a valve cavity  325  defined within a structure  320  that is hermetically sealed by way of seal  350  to the body  110 . In this implementation, as shown more clearly in  FIG. 3C , a seal  332  is formed by compressing a sealing mechanism (which can be an elastic member)  336  between a wall  331  (which is a radial sidewall) of the plunger valve  330  and an interior cylindrical wall  321  of the structure  320 . The seal  332  is a part of a piston-bore type seal, in which the sealing mechanism  336  seals radially between the plunger valve  330  and the interior wall  321 . 
     The structure  320  includes the three ports  335 ,  340 ,  345  in fluid communication with respective vacuum pump  337 , fluid supply  342 , and hermetic interior  105 . As with the fluid control device  100 , the plunger valve  330  is configured to move between two modes by translating along the direction  133  (depicted by the arrow) that extends between the first and second modes and is either parallel with the +Z direction or parallel with the −Z direction. Moreover, the plunger valve  330  performs such translation without any rotational motion (that is, rotational motion about the Z direction). 
     The fluid control device  300  further includes an actuator  352  in physical communication with the plunger valve  330 , the actuator  352  being configured to control the translation of the plunger valve  330  along the direction  133  between the first and second modes. The movement of the actuator  352  affects the translation of the plunger valve  330 . The actuator  352  is moved under control of a control device  354 , which can be an automatic device or a manual device. For example, the control device  354  can be a human (manual). As another example, the control device  354  can be an electromechanical device that adjusts the position of the actuator  352 . The actuator  352  can be a rotatable threaded rod that linearly translates when rotated, a lever, a push/pull bar or cable, a solenoid, or a piston (which can be pneumatic or hydraulic). The motion of the actuator  352  can be restricted or limited along a direction perpendicular to the Z direction by being seated in an opening of the structure  320 , and such interface between the actuator  352  and the opening of the structure  320  includes a seal  353 . The combination of the seal  353  (between the actuator  352  and the structure  320 ) and the seal  332  (between the plunger valve  330  and the structure  320 ) forms the piston-bore type seal. 
     Moreover, the actuator  352  can be sealed within a baffle  356  that separates the valve cavity  325  from the actuator  352 . That is, the valve cavity  325  does not include the volume within the baffle  356 . The baffle  356  is attached at one end to the structure  320  and at another end to the plunger valve  330 . The baffle  356  can optionally provide some control over the motion of the plunger valve  330  by, for example, dampening the motion of the plunger valve  330  or biasing the plunger valve  330 . The baffle  356  also can be utilized to inhibit or prevent rotational motion (that is, rotational motion about the Z direction) because the baffle  356  is fixed at one end to the plunger valve  330  and at the other end to the structure  320 . 
     In this implementation, the plunger valve  330  includes an O-ring groove for receiving the sealing mechanism  336  (such as a gasket) and this gasket  336  is pressed between the wall  321  of the structure and the sidewall  331  (labeled in  FIGS. 3A and 3C ) of the plunger valve  330  when the plunger valve  330  is in the second mode, as shown in  FIGS. 3B and 3C . 
     Additionally, in some implementations, the second mode can be configured as a default mode in which the plunger valve  330  is at an equilibrium (or stable) position. For example, the plunger valve  330  can be biased along the direction  134  (away from the hermetic interior  105  and parallel with the −Z direction) to thereby rest in a position that seals the vacuum pump  337  from the hermetic interior  105 . A biasing device  358  is shown in block diagram form in  FIGS. 3A and 3B . The biasing device  358  can be configured to maintain the plunger valve  330  in the second mode (sealing). 
     In other implementations, the first mode is configured as a default mode in which the plunger valve  330  is at an equilibrium position. In these implementations, the biasing device  358  biases (or maintains) the plunger valve  330  in the first mode. 
     The biasing device  358  can be any device that sets the equilibrium position of the plunger valve  330 . For example, the biasing device  358  can be a mechanical object able to store energy such as a spring or a piston attached to the plunger valve  330  or to the actuator  352 . The resting position of the spring can correspond to the equilibrium position of the plunger valve  330 . 
     Referring to  FIG. 4 , in some implementations, a fluid control device  400  (which can be the fluid control device  100  or  300 ) is used in a target apparatus  460  of an extreme ultraviolet (EUV) light source  462  that supplies EUV light  464  to an output apparatus  466  (which can be a photolithography apparatus). The target apparatus  460  includes one or more fluid devices for holding or moving target material  406 . 
     In the implementation of  FIG. 4 , the target apparatus  460  includes a single reservoir  410 . In other implementations, it is possible for the target apparatus  460  to include a plurality of reservoirs and one or more tanks for storage of fluid. A reservoir  410  is basically a pressure-controlled vessel into which target material  406  is placed and thereafter used by the EUV light source  462 . The reservoir  410  can be formed of forged molybdenum or other suitable low-outgassing materials. 
     The target apparatus  460  includes the reservoir  410 , which defines a hollow interior  405  configured to contain the target material that produces EUV light when in a plasma state, and a nozzle structure  468  defining an opening  470  that is in fluid communication with the hollow interior  405  and opens into an interior  416  of a vacuum chamber. The target apparatus  460  includes the fluid control device  400 , which is hermetically sealed to the reservoir  410 . The fluid control device  400  is designed like the fluid control devices  100 ,  300 , and thus includes three fluid ports, a first fluid port fluidly coupled to the vacuum pump  437 , a second fluid port fluidly coupled to the fluid supply  442 , and the third fluid port  445  fluidly coupled to the reservoir interior  405 . The fluid control device  400  also includes the single plunger valve  420  within the valve cavity and configured to move between first and second modes without opening the reservoir interior  405 . The reservoir  410  can include a cover or port  411  that is removable to enable fresh target material (in solid form) to be added to the interior  405 . When the cover or port  411  is removed from the reservoir  410 , the interior  405  of the reservoir  410  is exposed to contaminants and atmospheric pressure that may be present in the environment  415 . 
     Aspects of the EUV light source  462  are described next. The EUV light source  462  includes an EUV light collector  472  arranged relative to a target space at which one or more radiation pulses  474  interact with targets  476  that are ejected or forced out of the nozzle structure  468  under control of the pressure within the reservoir interior  405 . The EUV light collector  472  collects the EUV light  473  that is emitted from the plasma that is formed from the interaction of the radiation pulses  474  with the target  476 . 
     Each of the targets  476  is made up of the target material (supplied to the reservoir interior  405 ). The targets  476  are converted at least partially to plasma through their interaction with the radiation pulses  474 . The targets  476  can be in the form of a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target material, or solid particles contained within a portion of a liquid stream. The target material  406  can include for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target material  406  can be the element tin, which can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys. 
     In use, the hollow interior  405  can be maintained at a pressure above 10 megapascals (MPa) when the plunger valve  420  is in the pressure mode (which is the mode that is shown in  FIG. 4 ). Moreover, when the plunger valve  420  is in the pressure mode (as shown in  FIG. 4 ), the pressure within the hollow interior  405  of the reservoir  410  is greater than a pressure within the interior  416  of the vacuum chamber. In this way, the stream of targets  476  is forced out of the nozzle structure  468  and directed toward the target space. 
     Because the fluid control device  400  uses only a single plunger valve  420  for both modes of operation (vacuum mode and high pressure mode), it can be designed with a smaller overall volume, and thus is easier to arrange relative to the reservoir  410  in the EUV light source  462 , where space is limited. Moreover, because the fluid control device  400  is simple to use, and has a streamlined design, it is less expensive, lighter, and easier to maintain than prior systems that provide both vacuum and high pressure modes. Because the fluid control device  400  provides excellent and high fluid conductance while in the vacuum mode, the fluid control device  400  can be utilized after a restart of the target apparatus  460 . A restart of the target apparatus  460  occurs after the hollow interior  405  of the reservoir  410  has been opened to atmospheric environment. By opening the hollow interior  405  of the reservoir  410 , the hollow interior  405  can become contaminated with unwanted matter, and before the hollow interior  405  of the reservoir  410  can start operation again (to supply targets  476  to the target space), the hollow interior  405  must be de-contaminated, which may generally include an evacuation of the hollow interior  405 , and this can be done with the fluid control device  400 , which can perform the de-contamination at a must shorter time scale than prior systems. 
     Referring to  FIG. 5 , a procedure  580  is performed for controlling a fluid state within the hermetic interior  105  of the body  110  using the fluid control device  100 . Reference is made to the fluid control device  100  of  FIG. 1  but the procedure  580  can be performed by the fluid control device  300  or  400 . The procedure  580  can be halted whenever the hermetic interior  105  needs to be opened to the environment. 
     The procedure  580  includes controlling the fluid state in the hermetic interior  105  using one of two operationally-isolated control modes ( 582 ). The two control modes include the first mode, which is the vacuum control mode ( 584 ), and the second mode, which is the high pressure control mode ( 586 ). In the vacuum control mode ( 584 ), fluid is conducted from the hermetic interior  105  of the body  110  at the first conductance such that the hermetic interior  105  reaches a target vacuum pressure P TV . The target vacuum pressure P TV  is below atmospheric pressure, and thus is below about 101.325 kilopascals (kPa). In the high pressure control mode ( 586 ), fluid is conducted into the hermetic interior  105  of the body  110  at the second conductance such that the hermetic interior  105  reaches a target high pressure P TH . The target high pressure P TH  is above atmospheric pressure, and thus is above about 101.325 kilopascals (kPa). Moreover, as discussed above, the first conductance (which is through the first fluid port  135 ) larger than (for example, at least twice the size of) the second conductance (which is through the second fluid port  140 ). 
     The procedure  580  includes switching between the vacuum control mode ( 584 ) and the high pressure control mode ( 586 ). 
     If current operation is the vacuum control mode ( 584 ), then there is a determination ( 588 ) as to whether the mode needs to be switched to the high pressure control mode ( 586 ). For example, if the pressure within the hermetic interior  105  has reached the target vacuum pressure P TV , then the determination may be that the mode needs to be switched. As another example, the determination ( 588 ) for when to switch to the high pressure control mode ( 586 ) could be based on another aspect of the hermetic interior  105 , such as a concentration of matter within the hermetic interior  105 . The determination ( 588 ) as to whether to switch to high pressure control mode ( 586 ) can be made by an operator or by a process implemented in software. The determination ( 588 ) can be based on measurements that are performed by sensors associated with the hermetic interior  105 , and the result of the determination can be actuation of components of the fluid control device  100  or it can be a display or conveyance of values to the operator. As another example, the determination ( 588 ) for when to switch to the high pressure control mode ( 586 ) could be based on a control signal that is triggered or initiated, for example, by an assessment that a de-contamination procedure has been concluded, or an assessment that high-pressure operations are ready to commence, or other factors, or combinations thereof. 
     If the mode does not need to be switched from vacuum control mode ( 584 ) to high pressure control mode ( 586 ) ( 588 ), then the vacuum control mode ( 584 ) continues. If the mode does need to be switched from vacuum control mode ( 584 ) to high pressure control mode ( 586 ) ( 588 ), then the plunger valve  130  is moved from the first mode corresponding to the vacuum control mode ( 584 ) in which the plunger valve  130  is open to the second mode corresponding to the high pressure control mode ( 586 ) in which the plunger valve  130  is closed and forms the seal  132  ( 590 ). For example, and with reference to  FIGS. 3A and 3B , the actuator  352  can be moved under control of the control device  354  along the Z direction, and the motion of the actuator  352  causes the plunger valve  330  to be moved along the Z direction. During this movement ( 590 ), the hermetic interior  105  of the body  110  is maintained. 
     The seal  132  that is formed ( 590 ) separates the vacuum pump  137  from the hermetic interior  105 . The seal  132  is formed ( 590 ) prior to conducting the fluid into the hermetic interior  105  from the fluid supply  142  during operation of the high pressure control mode ( 586 ). Moreover, the plunger valve  130  is exposed to the higher pressure (and ultimately the target high pressure P TH  when that is reached) while the fluid is conducted into the hermetic interior  105  of the body  110 . 
     If current operation is the high pressure control mode ( 586 ), then there is a determination ( 592 ) as to whether the mode needs to be switched to the vacuum control mode ( 584 ). The determination ( 592 ) can be externally driven by other system usage, needs, and controls (such as related to the hermetic interior  105 ). For example, the determination ( 592 ) can occur at the end of an operation cycle or in the event of a pressure leak from the hermetic interior  105 . If the mode does not need to be switched from high pressure control mode ( 586 ) to vacuum control mode ( 584 ) ( 592 ), then high pressure control mode ( 586 ) continues. If the mode does need to be switched from high pressure control mode ( 586 ) to vacuum control mode ( 584 ) ( 592 ), then the plunger valve  130  is moved from the second mode corresponding to the high pressure control mode ( 586 ) in which the plunger valve  130  is closed to the first mode corresponding to the vacuum control mode ( 584 ) in which the plunger valve  130  is open ( 594 ). For example, and with reference to  FIGS. 3A and 3B , the actuator  352  can be moved along the −Z direction under control of the control device  354  and the motion of the actuator  352  causes the plunger valve  330  to be moved along the −Z direction. During this movement ( 594 ), the hermetic interior  105  of the body  110  is maintained. 
     The procedure  580  can begin ( 596 ) after the body  110  has been sealed to form the hermetic interior  105 . At this beginning state, in some implementations, the hermetic interior  105  is first pumped down to the target vacuum pressure PTV during vacuum control mode ( 584 ) in order to remove any contaminants that were in the hermetic interior  105  due to it previously being opened to environment. 
     Depending on the design of the hermetic interior  105  and the body  110 , fluid is conducted from the hermetic interior  105  of the body  110  after switching to the vacuum control mode ( 584 ) or after beginning ( 596 ) such that the hermetic interior  105  of the body  110  reaches the target vacuum pressure P TV  in less than four hours, less than an hour, less than 15 minutes, or less than a minute. 
     Thus, for example, with reference to the fluid control device  400  of  FIG. 4 , the procedure  580  begins operation in vacuum control mode ( 584 ) after the hollow interior  405  is sealed off from the environment  415 . Because the fluid control device  400  includes a first fluid port  435  that has a much larger conductance than the second fluid port  440 , it is possible to reach the target vacuum pressure P TV  in a relatively rapid fashion, for example, in a few minutes or even less than a minute. 
     Specifically, and with reference to  FIGS. 6A-6F , prior to the hollow interior  405  being sealed off from the environment  415  and also prior to operation in vacuum control mode ( 584 ), a solid mass  607  of target material  406  is inserted into the interior  405  of the reservoir  410  after the cover  411  has been removed ( FIG. 6A ). In this particular implementation, the fluid control device  400  is integrated within the cover  411 , although it is alternatively possible for the fluid control device  400  to be integrated into a wall of the reservoir  410 . The cover  411  is replaced ( FIG. 6B ) and the cover  411  and fluid control device  400  are sealed to the reservoir  410  to form the hollow interior  405 . Next, because the hollow interior  405  was previously opened to the environment  415  and contaminants may be present within the hollow interior  405 , the procedure  580  beings controlling the fluid state in the hollow interior  405  by first conducting fluid that includes one or more contaminants out of the hollow interior  405  while operating in vacuum control mode  584  using the vacuum pump  437  ( FIG. 6C ). 
     Once the concentration of each contaminant inside the hollow interior  405  drops below a respective threshold concentration, then vacuum control mode ( 584 ) is halted, the plunger valve  420  is closed ( 590 ) ( FIG. 6D ), and the solid mass  607  of target material  406  is melted ( FIG. 6E ). The fluid control device  400  operates in high pressure control mode ( 586 ) after the target material  406  has been melted by conducting fluid into the hollow interior  405  from the fluid source  442  ( FIG. 6F ). Once the pressure within the hollow interior  405  rises above a target high pressure P TH , the melted target material  406  viscously flows through the opening  470  of the nozzle structure  468  and into the interior  416  of the vacuum chamber. 
     Referring to  FIG. 7 , an implementation  766  of the lithography apparatus  466  is shown. The lithography apparatus  766  exposes a substrate (which can be referred to as a wafer) W with an exposure beam B. The lithography apparatus  766  includes a plurality of reflective optical elements R 1 , R 2 , R 3 , a mask M, and a slit S, all of which are in an enclosure  10 . The enclosure  10  is a housing, tank, or other structure that is capable of supporting the reflective optical elements R 1 , R 1 , R 2 , the mask M, and the slit S, and is also capable of maintaining an evacuated space within the enclosure  10 . 
     The EUV light  464  enters the enclosure  10  and is reflected by the optical element R 1  through the slit S toward the mask M. The slit S partly defines the shape of the distributed light used to scan the substrate W in a lithography process. The dose delivered to the substrate W or the number of photons delivered to the substrate W depends on the size of the slit S and the speed at which the slit S is scanned. 
     The mask M also may be referred to as a reticle or patterning device. The mask M includes a spatial pattern that represents the features that are to be formed in a photoresist on a substrate W. The EUV light  464  interacts with the mask M. The interaction between the EUV light  364  and the mask M results in the pattern of the mask M being imparted onto the EUV light  464  to form the exposure beam B. The exposure beam B passes through the slit S and is directed to the substrate W by the optical elements R 2  and R 3 . An interaction between the substrate W and the exposure beam B exposes the pattern of the mask M onto the substrate W, and the photoresist features are thereby formed at the substrate W. The substrate W includes a plurality of portions  20  (for example, dies). The area of each portion  20  in the Y-Z plane is less than the area of the entire substrate W in the Y-Z plane. Each portion  20  may be exposed by the exposure beam B to include a copy of the mask M such that each portion  20  includes the electronic features indicated by the pattern on the mask M. 
     The lithography apparatus  766  can include a lithography control system  30  that is in communication with a control apparatus (not shown) of the EUV light source  462 . 
     Other aspects of the invention are set out in the following numbered clauses.
     1. A two-mode fluid control device comprising:   

     a structure defining a valve cavity and three fluid ports fluidly coupled to the valve cavity, a first fluid port configured to be fluidly coupled to a vacuum pump, a second fluid port configured to be fluidly coupled to a fluid supply, and a third fluid port configured to be fluidly coupled to a hermetic interior of a body; and 
     a single plunger valve within the valve cavity and configured to move between first and second modes while maintaining the hermetic interior of the body; 
     wherein the first mode corresponds to a vacuum mode in which the plunger valve is open such that a first fluid flow path is open between the hermetic interior and the first fluid port and fluid is free to pass between the first fluid port and the hermetic interior and the second mode corresponds to a pressure mode in which the plunger valve is closed such that the first fluid port is blocked from the hermetic interior by the plunger valve and a second fluid flow path is open between the hermetic interior and the second fluid port.
     2. The two-mode fluid control device of clause 1, wherein the first fluid port has a first cross-sectional area that provides a first fluid conductance and the second fluid port has a second cross-sectional area that provides a second fluid conductance, the first cross-sectional area being greater than the second cross-sectional area.   3. The two-mode fluid control device of clause 2, wherein the first cross-sectional area is at least twice the size of, at least five times the size of, at least ten times the size of, at least fifty times the size of, or about one hundred times the size of the second cross-sectional area.   4. The two-mode fluid control device of clause 1, wherein the second mode is a default mode in which the plunger valve is at its equilibrium position.   5. The two-mode fluid control device of clause 4, further comprising a biasing device in physical communication with the plunger valve and configured to bias the plunger valve to the second mode.   6. The two-mode fluid control device of clause 1, wherein, when the plunger valve is in the second mode and is closed, a seal is formed that separates the vacuum pump from the hermetic interior and the plunger valve is exposed to a pressure above atmospheric pressure.   7. The two-mode fluid control device of clause 6, wherein the seal strengthens or remains constant while the plunger valve is in the second mode due to pressure applied against the plunger valve from the fluid supply.   8. The two-mode fluid control device of clause 1, wherein, in the vacuum mode, a pressure within the hermetic interior is held below atmospheric pressure, and in the pressure mode, a pressure within the hermetic interior is held above atmospheric pressure.   9. The two-mode fluid control device of clause 1, wherein, in the vacuum mode, a pressure within the hermetic interior is held at high or ultra-high vacuum in which molecular flow dominates within first fluid flow path and the hermetic interior.   10. The two-mode fluid control device of clause 1, wherein, in the vacuum mode, a pressure within the hermetic interior is held below 101 kilopascals (kPa), and in the pressure mode, a pressure within the hermetic interior is held above 10 megapascals (MPa).   11. The two-mode fluid control device of clause 1, wherein, when the plunger valve is in the first mode, fluid is free to pass from the hermetic interior to the vacuum pump.   12. The two-mode fluid control device of clause 1, wherein the plunger valve is configured to move between the first and second modes by linearly translating between the first and second modes without rotation.   13. The two-mode fluid control device of clause 12, further comprising an actuator in physical communication with the plunger valve and configured to control the translation of the plunger valve between the first and second modes.   14. The two-mode fluid control device of clause 13, wherein the actuator comprises a rotatable threaded rod, a push/pull bar, a cable, a lever, a piston, or a solenoid.   15. The two-mode fluid control device of clause 1, wherein a hermetic seal is formed between the structure and the body.   16. The two-mode fluid control device of clause 1, wherein the second fluid port is fluidly coupled to a fluid supply of gas.   17. The two-mode fluid control device of clause 16, wherein the gas is an inert gas that includes one or more of a noble gas and a molecular gas.   18. The two-mode fluid control device of clause 1, wherein:   

     while in the first mode, a first fluid volume that includes the hermetic interior and a first portion of the valve cavity is formed; and 
     while in the second mode, a second fluid volume that includes the hermetic interior and a second portion of the valve cavity is formed, the second fluid volume being smaller than the first fluid volume.
     19. The two-mode fluid control device of clause 1, wherein the plunger valve is a solid volume such that any fluid flow path remains exterior to the plunger valve.   20. A target apparatus for an extreme ultraviolet (EUV) light source, the target apparatus comprising:   

     a target generator comprising a reservoir defining a hollow interior configured to contain target material that produces EUV light when in a plasma state and a nozzle structure defining an opening that is in fluid communication with the hollow interior; and 
     a two-mode valve device hermetically sealed to the reservoir, the two-mode valve device comprising: 
     a structure defining a valve cavity and three fluid ports fluidly coupled to the valve cavity, a first fluid port of a first extent being fluidly coupled to a vacuum pump, a second fluid port of a second extent being fluidly coupled to a fluid supply, the first extent being at least ten times the size of the second extent, and a third fluid port being fluidly coupled to the reservoir interior; and 
     a single plunger valve within the valve cavity and configured to move between first and second modes without opening the reservoir interior, the first mode corresponding to a vacuum mode in which the plunger valve is open such that a first fluid flow path is open between the reservoir interior and the first fluid port and the second mode corresponding to a pressure mode in which the plunger valve is closed such that a second fluid flow path is open between the reservoir interior and the second fluid port.
     21. The apparatus of clause 20, wherein the hollow interior is held at a pressure above 10 megapascals (MPa) when the plunger valve is in the pressure mode.   22. The apparatus of clause 21, wherein when the plunger valve is in the pressure mode, the pressure within the hollow interior of the reservoir is greater than a pressure at the exterior.   23. The apparatus of clause 20, wherein a pressure within the hollow interior is controlled at least in part by the mode of the two-mode valve device.   24. The target apparatus of clause 20, wherein the first fluid port is hermetically separated from the hollow interior by the plunger valve when the plunger valve is in the second mode.   25. A method comprising:   

     controlling a fluid state in a hermetic interior of a body using one of two operationally-isolated control modes, the two control modes including a vacuum control mode and a high pressure control mode; 
     in the vacuum control mode, conducting fluid from the hermetic interior of the body at a first conductance such that the hermetic interior reaches a target vacuum pressure; 
     in the high pressure control mode, conducting fluid into the hermetic interior of the body at a second conductance such that the hermetic interior reaches a target high pressure that is above atmospheric pressure, the first conductance being at least twice the second conductance; and 
     switching between the vacuum control mode and the high pressure control mode including moving a single plunger valve between a first mode corresponding to the vacuum control mode in which the plunger valve is open and a second mode corresponding to the high pressure control mode in which the plunger valve is closed and forms a seal, wherein the hermetic interior of the body is maintained throughout the switching.
     26. The method of clause 25, further comprising, prior to conducting fluid into the hermetic interior of the body at the second rate of flow while in the high pressure control mode, forming the seal to thereby separate a vacuum pump from the hermetic interior.   27. The method of clause 26, wherein conducting fluid into the hermetic interior of the body at the second rate of flow while in the high pressure control mode comprises exposing the plunger valve to the target high pressure.   28. The method of clause 25, wherein the target vacuum pressure is below 101 kilopascals (kPa) and fluid is conducted from the hermetic interior of the body after switching to the vacuum control mode at the first conductance such that the hermetic interior of the body reaches the target vacuum pressure in less than four hours, less than an hour, less than 15 minutes, or less than a minute.   29. The method of clause 25, wherein:
 
switching to the vacuum control mode comprises opening the plunger valve and forming a first fluid volume that includes the hermetic interior and a first portion of a valve cavity in which the plunger valve is seated; and
   

     switching to the high pressure control mode comprises closing the plunger valve and forming a second fluid volume that includes the hermetic interior and a second portion of the valve cavity, the second fluid volume being smaller than the first fluid volume.
     30. The method of clause 25, wherein, prior to controlling the fluid state in the hermetic interior of the body, inserting a solid mass of material into an interior of the body and sealing the interior to form the hermetic interior in which the solid mass is located, and controlling the fluid state in the hermetic interior of the body comprises:   

     in the vacuum control mode, conducting fluid that includes one or more contaminants from the hermetic interior; 
     if the concentration of each contaminant inside the hermetic interior is below a respective threshold concentration, then closing the plunger valve to halt vacuum control mode, melting the solid mass of material, and switching to high pressure control mode after the solid mass of material has melted.
     31. The method of clause 30, wherein, during high pressure control mode, fluid is conducted into the hermetic interior until a pressure in the hermetic interior rises above a threshold pressure at which the melted target material viscously flows out of an opening fluidly coupled to the hermetic interior.   32. The method of clause 25, further comprising biasing the plunger valve to the second state.   33. The method of clause 25, wherein the first conductance is at least five times, at least ten times, at least fifty times, or about one hundred times the second conductance.