Control method for target supply device, and target supply device

A control method for a target supply device may employ a target supply device, provided in an EUV light generation apparatus including an image sensor, that includes a target generator having a nozzle and configured to hold a target material and a pressure control unit configured to control a pressure within the target generator, and the method may include outputting the target material in the target generator from a nozzle hole in the nozzle by pressurizing the interior of the target generator using the pressure control unit, determining whether or not a difference between an output direction of the target material outputted from the nozzle hole that is detected by the image sensor and a set direction is within a predetermined range, and holding the pressure in the target generator using the pressure control unit until the difference falls within the predetermined range.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2012-199775 filed Sep. 11, 2012.

BACKGROUND

1. Technical Field

The present disclosure relates to control methods for target supply devices and to target supply devices.

2. Related Art

In recent years, semiconductor production processes have become capable of producing semiconductor devices with increasingly fine feature sizes, as photolithography has been making rapid progress toward finer fabrication. In the next generation of semiconductor production processes, microfabrication with feature sizes at 60 nm to 45 nm, and further, microfabrication with feature sizes of 32 nm or less will be required. In order to meet the demand for microfabrication with feature sizes of 32 nm or less, for example, an exposure apparatus is needed in which a system for generating EUV light at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system.

Three kinds of systems for generating EUV light are known in general, which include a Laser Produced Plasma (LPP) type system in which plasma is generated by irradiating a target material with a laser beam, a Discharge Produced Plasma (DPP) type system in which plasma is generated by electric discharge, and a Synchrotron Radiation (SR) type system in which orbital radiation is used to generate plasma.

SUMMARY

A control method for a target supply device according to an aspect of the present disclosure may employ a target supply device, provided in an EUV light generation apparatus including an image sensor, that includes a target generator having a nozzle and configured to hold a target material and a pressure control unit configured to control a pressure within the target generator, and the method may include outputting the target material in the target generator from a nozzle hole in the nozzle by pressurizing the interior of the target generator using the pressure control unit, determining whether or not a difference between an output direction of the target material outputted from the nozzle hole that is detected by the image sensor and a set direction is within a predetermined range, and holding the pressure in the target generator using the pressure control unit until the difference between the output direction and the set direction falls within the predetermined range.

A target supply device according to another aspect of the present disclosure may be provided in an EUV light generation apparatus including an image sensor, and the device may include a target generator, a pressure control unit, and a control unit. The target generator may include a nozzle and may be configured to hold a target material. The pressure control unit may be configured to control a pressure in the target generator. The control unit may be configured to control the pressure control unit and output the target material in the target generator from a nozzle hole in the nozzle by pressurizing the interior of the target generator, determine whether or not a difference between an output direction of the target material outputted from the nozzle hole that is detected by the image sensor and a set direction is within a predetermined range, and hold the pressure in the target generator until the difference between the output direction and the set direction falls within the predetermined range.

DETAILED DESCRIPTION

Hereinafter, selected embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments to be described below are merely illustrative in nature and do not limit the scope of the present disclosure. Further, the configuration(s) and operation(s) described in each embodiment are not all essential in implementing the present disclosure. Note that like elements are referenced by like reference numerals and characters, and duplicate descriptions thereof will be omitted herein.

Contents

2. Overview of EUV Light Generation System

3. EUV Light Generation Apparatus Including Target Supply Device

3.1 First Embodiment

3.2 Second Embodiment

According to an embodiment of the present disclosure, a control method for a target supply device may employ a target supply device, provided in an EUV light generation apparatus including an image sensor, that includes a target generator having a nozzle and configured to hold a target material and a pressure control unit configured to control a pressure within the target generator, and the method may include outputting the target material in the target generator from a nozzle hole in the nozzle by pressurizing the interior of the target generator using the pressure control unit, determining whether or not a difference between an output direction of the target material outputted from the nozzle hole that is detected by the image sensor and a set direction is within a predetermined range, and holding the pressure in the target generator using the pressure control unit until the difference between the output direction and the set direction falls within the predetermined range.

According to an embodiment of the present disclosure, a target supply device may be provided in an EUV light generation apparatus including an image sensor, and the device may include a target generator, a pressure control unit, and a control unit. The target generator may include a nozzle and may be configured to hold a target material. The pressure control unit may be configured to control a pressure in the target generator. The control unit may be configured to control the pressure control unit and output the target material in the target generator from a nozzle hole in the nozzle by pressurizing the interior of the target generator, determine whether or not a difference between an output direction of the target material outputted from the nozzle hole that is detected by the image sensor and a set direction is within a predetermined range, and hold the pressure in the target generator until the difference between the output direction and the set direction falls within the predetermined range.

2. Overview of EUV Light Generation System

FIG. 1schematically illustrates an exemplary configuration of an LPP type EUV light generation system. An EUV light generation apparatus1may be used with at least one laser apparatus3. Hereinafter, a system that includes the EUV light generation apparatus1and the laser apparatus3may be referred to as an EUV light generation system11. As shown inFIG. 1and described in detail below, the EUV light generation system11may include a chamber2and a target supply device7. The chamber2may be sealed airtight. The target supply device7may be mounted onto the chamber2, for example, to penetrate a wall of the chamber2. A target material to be supplied by the target supply device7may include, but is not limited to, tin, terbium, gadolinium, lithium, xenon, or any combination thereof.

The chamber2may have at least one through-hole or opening formed in its wall, and a pulse laser beam32may travel through the through-hole/opening into the chamber2. Alternatively, the chamber2may have a window21, through which the pulse laser beam32may travel into the chamber2. An EUV collector mirror23having a spheroidal surface may, for example, be provided in the chamber2. The EUV collector mirror23may have a multi-layered reflective film formed on the spheroidal surface thereof. The reflective film may include a molybdenum layer and a silicon layer, which are alternately laminated. The EUV collector mirror23may have a first focus and a second focus, and may be positioned such that the first focus lies in a plasma generation region25and the second focus lies in an intermediate focus (IF) region292defined by the specifications of an external apparatus, such as an exposure apparatus6. The EUV collector mirror23may have a through-hole24formed at the center thereof so that a pulse laser beam33may travel through the through-hole24toward the plasma generation region25.

The EUV light generation system11may further include an EUV light generation controller5and a target sensor4. The target sensor4may have an imaging function and detect at least one of the presence, trajectory, position, and speed of a target27.

Further, the EUV light generation system11may include a connection part29for allowing the interior of the chamber2to be in communication with the interior of the exposure apparatus6. A wall291having an aperture292may be provided in the connection part29. The wall291may be positioned such that the second focus of the EUV collector mirror23lies in the aperture292formed in the wall291.

The EUV light generation system11may also include a laser beam direction control unit34, a laser beam focusing mirror22, and a target collector28for collecting targets27. The laser beam direction control unit34may include an optical element (not separately shown) for defining the direction into which the pulse laser beam32travels and an actuator (not separately shown) for adjusting the position and the orientation or posture of the optical element.

With continued reference toFIG. 1, a pulse laser beam31outputted from the laser apparatus3may pass through the laser beam direction control unit34and be outputted therefrom as the pulse laser beam32after having its direction optionally adjusted. The pulse laser beam32may travel through the window21and enter the chamber2. The pulse laser beam32may travel inside the chamber2along at least one beam path from the laser apparatus3, be reflected by the laser beam focusing mirror22, and strike at least one target27as a pulse laser beam33.

The target supply device7may be configured to output the target(s)27toward the plasma generation region25in the chamber2. The target27may be irradiated with at least one pulse of the pulse laser beam33. Upon being irradiated with the pulse laser beam33, the target27may be turned into plasma, and rays of light251including EUV light may be emitted from the plasma. At least the EUV light included in the light251may be reflected selectively by the EUV collector mirror23. EUV light252, which is the light reflected by the EUV collector mirror23, may travel through the intermediate focus region292and be outputted to the exposure apparatus6. Here, the target27may be irradiated with multiple pulses included in the pulse laser beam33.

The EUV light generation controller5may be configured to integrally control the EUV light generation system11. The EUV light generation controller5may be configured to process image data of the target27captured by the target sensor4. Further, the EUV light generation controller5may be configured to control at least one of: the timing when the target27is outputted and the direction into which the target27is outputted. Furthermore, the EUV light generation controller5may be configured to control at least one of: the timing when the laser apparatus3oscillates, the direction in which the pulse laser beam33travels, and the position at which the pulse laser beam33is focused. It will be appreciated that the various controls mentioned above are merely examples, and other controls may be added as necessary.

3. EUV Light Generation Apparatus Including Target Supply Device

3.1 First Embodiment

In a control method for a target supply device according to a first embodiment of the present disclosure, the output of the target material in the target generator from the nozzle hole in the nozzle may be carried out by outputting the target material as a jet, and the determination as to whether or not the difference between the output direction of the target material and the set direction is within the predetermined range may be carried out by determining whether or not a difference between a trajectory of the target material outputted as a jet and a set trajectory is within a predetermined range.

In a target supply device according to the first embodiment of the present disclosure, the control unit may output the target material in the target generator from the nozzle hole in the nozzle by outputting the target material as a jet, and may determine whether or not the difference between the output direction of the target material and the set direction is within the predetermined range by determining whether or not a difference between a trajectory of the target material outputted as a jet and a set trajectory is within a predetermined range.

FIG. 2schematically illustrates the configuration of an EUV light generation apparatus that includes the target supply device according to the first embodiment as well as a second embodiment that will be described later.FIG. 3schematically illustrates the configuration of the target supply device according to the first embodiment.

An EUV light generation apparatus1A may, as shown inFIG. 2, include the chamber2and a target supply device7A. The target supply device7A may include a target generation section70A and a target control apparatus80A. The laser apparatus3and an EUV light generation controller5A may be electrically connected to the target control apparatus80A.

As shown inFIGS. 2 and 3, the target generation section70A may include a target generator71A, a pressure control section72A, a temperature control section73A, and a piezoelectric section75A.

The target generator71A may include a tank711A for holding a target material270in its interior. The tank711A may be cylindrical in shape. A nozzle712A for outputting the target material270in the tank711A to the chamber2as the targets27may be provided in the tank711A. The target generator71A may be provided so that the tank711A is positioned outside of the chamber2and the nozzle712A is positioned inside of the chamber2.

It is preferable for the nozzle712A to be configured of a material that has a low wettability with the target material270. A “material that has a low wettability to the target material270” may specifically be a material whose angle of contact with the target material270is greater than 90°. The material having an angle of contact greater than or equal to 90° may be one of SiC, SiO2, Al2O3, molybdenum, tungsten, and tantalum.

A nozzle hole713A of the nozzle712A may have an inner wall surface714A (seeFIG. 4A) and an opening715A (seeFIG. 4A). The inner wall surface714A may be formed in a cylindrical shape so that an axis of the nozzle hole713A matches an axis of the nozzle712A. The opening715A may be provided at a first end of the nozzle hole713A.

Depending on how the chamber2is arranged, it is not necessarily the case that a pre-set output direction for the target27(the axial direction of the nozzle712A (called a “set output direction10A”)) will match a gravitational direction10B. The configuration may be such that the target27is outputted horizontally or at an angle relative to the gravitational direction10B. Note that the first embodiment describes a case in which the chamber2may be arranged so that the set output direction10A and the gravitational direction10B match.

As shown inFIGS. 2 and 3, an inert gas bottle721A may be connected, via a pipe727A, to an end719A of the tank711A. The pipe727A may be connected at a first end to the inert gas bottle721A. The pipe727A may be connected to the end719A so that a second end of the pipe727A is located within the tank711A. Through such a configuration, an inert gas within the inert gas bottle721A can be supplied to the interior of the target generator71A.

The pressure control section72A may be provided in the pipe727A. The pressure control section72A may include a first valve V1, a second valve V2, and a pressure sensor722A.

The first valve V1may be provided in the pipe727A.

A pipe728A may be connected to a location of the pipe727A that is closer to the tank711A than the first valve V1. The pipe728A may be connected at a first end to a side surface of the pipe727A. A second end of the pipe728A may be open. The second valve V2may be provided partway along the pipe728A.

The first valve V1and the second valve V2may be gate valves, ball valves, butterfly valves, or the like. The first valve V1and the second valve V2may be the same type of valve, or may be different types of valves.

The target control apparatus80A may be electrically connected to the first valve V1and the second valve V2. The first valve V1and the second valve V2may switch, independent from each other, between open and closed states based on a signal sent from the target control apparatus80A.

When the first valve V1opens, an inert gas from the inert gas bottle721A can be supplied to the interior of the target generator71A via the pipe727A. When the second valve V2closes, the inert gas present in the pipe727A can be prevented from being discharged to the exterior of the pipe727A from the second end of the pipe728A. Accordingly, when the first valve V1opens and the second valve V2closes, a pressure in the target generator71A can rise to the same pressure as the pressure in the inert gas bottle721A. Thereafter, the pressure in the target generator71A can be held at the same pressure as the pressure in the inert gas bottle721A.

When the first valve V1closes, an inert gas from the inert gas bottle721A can be prevented from being supplied to the interior of the target generator71A via the pipe727A. When the second valve V2opens, the inert gas present in the pipe727A can be discharged to the exterior of the pipe727A from the second end of the pipe728A as a result of a pressure difference between the interior of the pipe727A and the exterior of the pipe727A. Accordingly, when the first valve V1closes and the second valve V2opens, the pressure in the target generator71A can drop.

A pipe729A may be connected to a location of the pipe727A that is closer to the tank711A than the pipe728A. The pipe729A may be connected at a first end to a side surface of the pipe727A. The pressure sensor722A may be provided in a second end of the pipe729A. The target control apparatus80A may be electrically connected to the pressure sensor722A. The pressure sensor722A may detect a pressure of the inert gas present in the pipe729A and may send a signal corresponding to the detected pressure to the target control apparatus80A. The pressure within the pipe729A can be essentially the same as the pressure in the pipe727A and the pressure in the target generator71A.

The temperature control section73A may be configured to control the temperature of the target material270within the tank711A. The temperature control section73A may include a heater731A, a heater power source732A, a temperature sensor733A, and a temperature controller734A. The heater731A may be provided on an outer circumferential surface of the tank711A. The heater power source732A may cause the heater731A to produce heat by supplying power to the heater731A based on a signal from the temperature controller734A. As a result, the target material270within the tank711A can be heated via the tank711A.

The temperature sensor733A may be provided on the outer circumferential surface of the tank711A, toward the location of the nozzle712A, or may be provided within the tank711A. The temperature sensor733A may be configured to detect a temperature primarily at a location where the temperature sensor733A is installed as well as the vicinity thereof in the tank711A, and to send a signal corresponding to the detected temperature to the temperature controller734A. The temperature at the location where the temperature sensor733A is installed and at the vicinity thereof can be essentially the same temperature as the temperature of the target material270within the tank711A.

The temperature controller734A may be configured to output, to the heater power source732A, a signal for controlling the temperature of the target material270to a predetermined temperature, based on a signal from the temperature sensor733A.

The piezoelectric section75A may include a piezoelectric element751A and a power source752A. The piezoelectric element751A may be provided on an outer circumferential surface of the nozzle712A within the chamber2. Instead of the piezoelectric element751A, a mechanism capable of applying vibrations to the nozzle712A at high speeds may be provided. The power source752A may be electrically connected to the piezoelectric element751A via a feedthrough753A. The power source752A may be electrically connected to the target control apparatus80A.

The target generation section70A may generate a jet27A as a continuous jet, and may be configured so that the targets27are produced by vibrating the jet27A outputted from the nozzle712A.

As shown inFIG. 3, a first target sensor41A and a second target sensor42A may be provided in the chamber2. The first target sensor41A and the second target sensor42A may correspond to an image sensor of the present disclosure.

The first target sensor41A may be provided to the side of the target generator71A in a −X direction (inFIG. 3, the left side). The second target sensor42A may be provided to the side of the target generator71A in a −Y direction (inFIG. 3, the far side in the depth direction). The first target sensor41A and the second target sensor42A may be provided so as to be capable of detecting the jet27A outputted from the nozzle712A, from the −X direction and the −Y direction, respectively.

The first target sensor41A and the second target sensor42A may be electrically connected to the target control apparatus80A. The first target sensor41A and the second target sensor42A may respectively send, to the target control apparatus80A, signals corresponding to a detected form of the jet27A.

The target control apparatus80A may serve as a controller according to the present disclosure. A timer81A may be electrically connected to the target control apparatus80A. The target control apparatus80A may control the temperature of the target material270in the target generator71A by sending a signal to the temperature controller734A. The target control apparatus80A may control the pressure in the target generator71A by sending signals to the first valve V1and the second valve V2of the pressure control section72A.

FIG. 4Ais a diagram illustrating an issue in the first embodiment, and illustrates a state in which the target supply device is not outputting a jet.FIG. 4Bis a diagram illustrating the stated issue, and illustrates a state in which the target supply device is outputting the jet.FIG. 5is a flowchart illustrating a control method for the target supply device.FIG. 6is a timing chart illustrating the control method for the target supply device.FIG. 7Aillustrates a state in which the target supply device is not outputting the jet.FIG. 7Bis a diagram illustrating a state in which the target supply device is outputting the jet, and illustrates a state in which a trajectory of the jet deviates from a set trajectory.FIG. 7Cis a diagram illustrating a state in which the target supply device is outputting the jet, and illustrates a state in which the trajectory of the jet essentially matches the set trajectory.FIG. 7Dillustrates a state in which the output of the jet has been stopped from the state shown inFIG. 7C.

Note that the following describes a control method for the target supply device7A using a case where the target material270is tin as an example. The target control apparatus80A may receive a signal sent from the pressure sensor722A and determine a pressure within the target generator71A based on the received signal. The target control apparatus80A may receive a signal sent from the timer81A and determine a time based on the received signal.

First, an issue that the control method for the target supply device of the first embodiment solves will be described.

An operator of the EUV light generation apparatus1may install a new target generator71A, or a target generator71A that has undergone maintenance, in the chamber2.

The target control apparatus80A of the target supply device7A may, as indicated inFIG. 4A, heat the target material270until the target material270melts by controlling the temperature control section73A. The target control apparatus80A may set the pressure in the target generator71A to a pressure PJ in order to output the jet27A. The pressure PJ may be greater than or equal to 1 MPa and less than or equal to 10 MPa. When the pressure in the target generator71A reaches the pressure PJ, the jet27A can be outputted from the nozzle hole713A of the nozzle712A as indicated inFIG. 4B.

At this time, a trajectory C1of the jet27A may deviate from a set trajectory CA. The set trajectory CA may be set to match the center axis of the nozzle712A. A reason why the trajectory C1deviates from the set trajectory CA can be postulated as follows.

When the target material270is pushed out under the pressure in the target generator71A from the state shown inFIG. 4A, the inner wall surface714A of the nozzle712A can have a region that makes contact with the target material270and a region that does not make contact with the target material270. In this case, the region of the inner wall surface714A that has made contact with the target material270can be more easily wetted by the target material270. As a result, it is possible for the target material270to traverse only part of the inner wall surface714A and reach only part of the opening715A. For example, it is possible for the target material270to traverse only a region of the inner wall surface714A that is on the right side shown inFIG. 4Band reach only a region of the opening715A that is on the right side. When the target material270that has reached only the region on the right side is then outputted as the jet27A, the trajectory C1of the jet27A may deviate to the right from the set trajectory CA.

If the target control apparatus80A then applies vibrations to the nozzle712A by controlling the piezoelectric section75A while the jet27A whose trajectory C1has deviated from the set trajectory CA is being outputted, the targets27generated by the vibrations may be outputted in an unintended direction.

To solve such an issue, the control method for the target supply device7A shown inFIGS. 5 and 6may be carried out before starting the process for outputting the targets27in order to generate the EUV light.

With the nozzle712A located within the chamber2and the interior of the chamber2being in a vacuum state, the target control apparatus80A of the target supply device7A may perform a process such as that shown inFIG. 5as a pre-process for the process carried out to generate the targets27.

The target control apparatus80A may set the pressure in the target generator71A to a pressure PL (step S1). The target control apparatus80A may adjust the apertures of the first valve V1and the second valve V2of the pressure control section72A by sending signals to the first valve V1and the second valve V2. Through this, the inert gas in the inert gas bottle721A can be supplied to the target generator71A, and the pressure in the target generator71A can rise to the pressure PL at a time T0, as shown inFIG. 6. The pressure PL may be of a magnitude that positions an end area of the target material270at the opposite end of the nozzle hole713A to the end on which the opening715A is located (that is, an upper end), as shown inFIG. 7A. The pressure PL may, for example, be less than or equal to atmospheric pressure, and may be 0.05 MPa.

As shown inFIG. 5A, the target control apparatus80A may set the temperature controller734A to a target temperature Ts that is greater than or equal to a melting point Tm of tin (step S2). The melting point Tm of tin may be 232° C. The target temperature Ts may be, for example, 280° C. to 350° C. As a result of the processing indicated in step S2, a temperature T of the target material270in the target generator71A can rise.

The target control apparatus80A may determine whether or not the temperature T of the target material270within the target generator71A is within a predetermined temperature range (step S3). The predetermined temperature range may be greater than or equal to a minimum temperature Tsmin and less than or equal to a maximum temperature Tsmax. The target temperature Ts, corresponding to a median value of the predetermined temperature range, may be 315° C.

When it is determined in step S3that the standard for determination has been met, the target control apparatus80A may continue this temperature control as-is (step S4). However, when it is determined in step S3that the standard for determination has not been met, the target control apparatus80A may carry out the process of step S2. When the process of step S2is carried out, in the case where the temperature T is lower than the minimum temperature Tsmin, the temperature of the target material270can rise. In the case where the temperature T is higher than the maximum temperature Tsmax, the temperature of the target material270can drop.

The target control apparatus80A may set the pressure in the target generator71A to the pressure PJ (step S5). The target control apparatus80A may adjust the apertures of the first valve V1and the second valve V2by sending signals to the first valve V1and the second valve V2. The pressure PJ may be of a magnitude that outputs the target material270in the target generator71A from the nozzle712A as the jet27A. As described above, the pressure PJ may be greater than or equal to 1 MPa and less than or equal to 10 MPa.

When the process of step S5is carried out, the pressure in the target generator71A can begin to rise at a time T1and reach the pressure PJ at a time T2, as indicated inFIG. 6. When the pressure in the target generator71A reaches the pressure PJ, the target material270can be pressurized and the jet27A can be outputted from the nozzle hole713A as indicated inFIG. 7B. At this time, as described above, the trajectory C1of the jet27A may deviate from the set trajectory CA.

The first target sensor41A and the second target sensor42A may monitor the jet27A as indicated inFIG. 5(step S6). The first target sensor41A and the second target sensor42A can monitor (detect) the jet27A from the −X direction and the −Y direction, respectively. The first target sensor41A and the second target sensor42A may respectively send, to the target control apparatus80A, signals corresponding to monitoring results (detection results) for the jet27A.

The target control apparatus80A may calculate the direction of the jet27A (step S7). Based on the signals sent from the first target sensor41A and the second target sensor42A, the target control apparatus80A may calculate an output state of the jet27A occurring when the jet27A is monitored from the −X direction and the −Y direction. The target control apparatus80A may calculate the direction of the jet27A as the trajectory C1based on the calculated output state. At this time, the target control apparatus80A can calculate the direction of the jet27A at a high level of accuracy based on the monitoring results from the two different directions obtained by the first target sensor41A and the second target sensor42A.

The target control apparatus80A may determine whether or not an angle Δθ formed between the trajectory C1of the jet27A outputted from the nozzle hole713A and the set trajectory CA is within a predetermined angular range (step S8). The determination as to whether or not the angle Δθ is within the predetermined angular range indicated inFIG. 7Bmay be carried out by determining whether or not the absolute value of the angle Δθ is less than or equal to a threshold angle Δθmax. The threshold angle Δθmax may be several degrees (for example, 0°≦Δθmax≦3°).

Here, as shown inFIG. 7B, if the output of the jet27A is continued with the trajectory C1of the jet27A deviated from the set trajectory CA, the region of the inner wall surface714A that makes contact with the target material270can gradually spread along the circumferential direction of the nozzle hole713A. As a result, the target material270can make contact with the entire inner wall surface714A and can reach the entire opening715A along the entire area of the inner wall surface714A. When the target material270that has reached the entire opening715A is outputted as the jet27A, the trajectory C1of the jet27A can essentially match the set trajectory CA, as indicated inFIG. 7C. In other words, the absolute value of the angle Δθ can be essentially zero.

When it is determined that the standard for determination in step S8has not been met, the target control apparatus80A may carry out the process of step S6, as indicated inFIG. 5. For example, in the case where the jet27A is being outputted in the manner indicated inFIG. 7B, it can be determined that the angle Δθ is not within the predetermined angular range.

On the other hand, in the case where it has been determined that the standard for the determination in step S8is met, the target control apparatus80A may set the pressure in the target generator71A to the pressure PL (step S9). For example, the target control apparatus80A can determine that the angle Δθ is within the predetermined angular range in the case where the jet27A is being outputted in the manner indicated inFIG. 7Cat a time T3indicated inFIG. 6.

When the process of step S9is carried out, the pressure in the target generator71A can begin to drop at a time T4and reach the pressure PL at a time T5, as indicated inFIG. 6. During the period leading up to the pressure in the target generator71A reaching the pressure PL, the output of the jet27A can be stopped with the target material270making contact with the entire inner wall surface714A, as indicated inFIG. 7D.

After this, the target control apparatus80A may generate the targets27by controlling the target generation section70A, in order to generate the EUV light. Here, because the entire inner wall surface714A is more easily wetted by the target material270as a result of the aforementioned control method for the target supply device7A, the output of the jet27A can be started with the target material270making contact with the entire inner wall surface714A, as indicated inFIG. 7D. As a result, the jet27A can be outputted with the trajectory C1thereof essentially matching the set trajectory CA, and the targets27can be outputted in an intended direction (that is, toward the plasma generation region25).

As described thus far, the target control apparatus80A performs, as a pre-process for the process for outputting the targets27, a process for holding the pressure in the target generator71A at the pressure PJ until a difference between the output direction of the target material270outputted from the nozzle hole713A and a set direction falls within a predetermined range, and thus the targets27can be properly outputted after the pre-process has been carried out.

The targets27can be properly outputted as a continuous jet by the target control apparatus80A determining whether or not the angle Δθ formed between the trajectory C1of the jet27A and the set trajectory CA is within the predetermined angular range.

3.2 Second Embodiment

In a control method for a target supply device according to a second embodiment of the present disclosure, the output of the target material in the target generator from the nozzle hole in the nozzle may be carried out by pushing out the target material from the nozzle hole and causing the target material to adhere to a leading end of the nozzle, and the determination as to whether or not the difference between the output direction of the target material and the set direction is within the predetermined range may be carried out by determining whether or not a difference between a center position of the target material that adheres to the leading end of the nozzle and a center axis of the nozzle hole is within a predetermined range.

In a target supply device according to the second embodiment of the present disclosure, the control unit may output the target material in the target generator from the nozzle hole in the nozzle by pushing out the target material from the nozzle hole and causing the target material to adhere to a leading end of the nozzle, and may determine whether or not the difference between the output direction of the target material and the set direction is within the predetermined range by determining whether or not a difference between a center position of the target material that adheres to the leading end of the nozzle and a center axis of the nozzle hole is within a predetermined range.

FIG. 8schematically illustrates the configuration of the target supply device according to the second embodiment.FIG. 9schematically illustrates the configuration of a nozzle in the target supply device.

As shown inFIG. 8, an EUV light generation apparatus1B according to the second embodiment may employ the same configuration as the EUV light generation apparatus1A of the first embodiment, with the exception of a target generation section70B of a target supply device7B and a target control apparatus80B.

In the second embodiment, the chamber2may be arranged so that the set output direction10A and the gravitational direction10B match.

The target generation section70B may include a target generator71B, the pressure control section72A, the temperature control section73A, and an electrostatic extraction section75B.

As shown inFIGS. 8 and 9, the target generator71B may include a tank711B. The tank711B may be cylindrical in shape. A nozzle712B may be provided in the tank711B. The target generator71B may be provided so that the tank711B is positioned outside of the chamber2and the nozzle712B is positioned inside of the chamber2.

The nozzle712B may include a nozzle main body713B, a holding portion714B, and an output portion715B. The nozzle main body713B may be provided so as to protrude into the chamber2from a lower surface of the tank711B. The holding portion714B may be provided on a leading end of the nozzle main body713B. The holding portion714B may be formed as a cylinder whose diameter is greater than that of the nozzle main body713B.

The output portion715B may be formed as an approximately circular plate. The output portion715B may be held by the holding portion714B so as to be affixed to a leading end surface of the nozzle main body713B. A circular truncated cone-shaped protruding portion716B may be provided in a central area of the output portion715B. The output portion715B may be provided so that the protruding portion716B protrudes into the chamber2.

The protruding portion716B may be provided so as to make it easier for an electrical field to concentrate thereon. A nozzle hole717B may be provided in the protruding portion716B, in approximately the center of a leading end portion that configures the upper surface of the circular truncated cone in the protruding portion716B. The diameter of the nozzle hole717B may be 6 to 15 μm. The nozzle hole717B may have an inner wall surface717B1(seeFIG. 10A) and an opening717B2(seeFIG. 10A). The inner wall surface717B1may be formed in a cylindrical shape so that an axis of the nozzle hole717B matches an axis of the nozzle712B. The opening717B2may be provided at a first end of the inner wall surface717B1. It is preferable for the output portion715B to be configured of a material that has a low wettability to the target material270. Alternatively, at least the surface of the output portion715B may be coated with a material having a low wettability. The material having a low wettability may be the same material indicated in the first embodiment as the material of the nozzle712A.

The tank711B, the nozzle712B, and the output portion715B may be configured of electrically insulated materials. In the case where these elements are configured of materials that are not electrically insulated materials, for example, metal materials such as molybdenum, an electrically insulated material may be disposed between the chamber2and the target generator71B, between the output portion715B and a first electrode751B (mentioned later), and so on. In this case, the tank711B and a pulsed voltage generator753B, mentioned later, may be electrically connected.

Meanwhile, a target27B may adhere to a leading end of the protruding portion716B prior to being extracted from the protruding portion716B by the electrostatic extraction section75B.

Two through-holes710B may be provided in the holding portion714B. The through-holes710B may be provided so that the target27B adhering to the leading end of the protruding portion716B can be monitored by the first target sensor41A and the second target sensor42A.

The electrostatic extraction section75B may include the first electrode751B, a second electrode752B, the pulsed voltage generator753B, and a voltage source754B. As will be described later, the targets27B may be extracted from the output portion715B by utilizing a potential difference between a potential of the first electrode751B and a potential of the second electrode752B.

A circular through-hole755B may be formed in the center of the first electrode751B. The first electrode751B may be held by the holding portion714B so that a gap is formed between the first electrode751B and the output portion715B. It is preferable for the first electrode751B to be held so that a center axis of the through-hole755B and an axis of the protruding portion716B match. The targets27B can pass through the circular through-hole755B. The first electrode751B may be electrically connected to the pulsed voltage generator753B via a feedthrough758B.

The second electrode752B may be disposed in the target material270within the tank711B. The second electrode752B may be electrically connected to the voltage source754B via a feedthrough759B.

The pulsed voltage generator753B and the voltage source754B may be grounded. The pulsed voltage generator753B and the voltage source754B may be electrically connected to the target control apparatus80B.

In the following, descriptions of operations identical to those in the first embodiment will be omitted.

FIG. 10Ais a diagram illustrating an issue in the second embodiment, and illustrates a state in which the target supply device is not generating targets.FIG. 10Bis a diagram illustrating the stated issue, and illustrates a state prior to a target generated by the target supply device being discharged by an electrostatic extraction section.FIG. 11is a flowchart illustrating a control method for the target supply device.FIG. 12is a flowchart illustrating the control method for the target supply device, and illustrates a process continuing from the process shown inFIG. 11.FIG. 13is a timing chart illustrating the control method for the target supply device.FIG. 14Aillustrates a state when the target supply device is not generating targets.FIG. 14Bis a diagram illustrating a state prior to a target generated by the target supply device being discharged by the electrostatic extraction section, and illustrates a state in which a center position of the target deviates from a center axis of a nozzle hole.FIG. 14Cis a diagram illustrating a state prior to a target generated by a target supply device being discharged by an electrostatic extraction section, and illustrates a state in which a center position of the target essentially matches a center axis of a nozzle hole.FIG. 14Dillustrates a state in which the generation of targets has been stopped from the state shown inFIG. 14C.

First, an issue that the control method for the target supply device of the second embodiment solves will be described.

After, for example, a new target generator71B has been installed in the chamber2, the target control apparatus80B of the target supply device7B may, as indicated inFIG. 10A, heat the target material270until the target material270melts. The target control apparatus80B may set a pressure in the target generator71B to a pressure PS in order to generate the targets27B. When the pressure in the target generator71B reaches the pressure PS, the target material270may break the surface tension of the target material270at the nozzle hole717B. As a result, the target material270can be pushed out from the nozzle hole717B, and the target27B can be generated at the leading end of the protruding portion716B, as shown inFIG. 10B. In the case where the nozzle hole717B is 10 μm in diameter, the pressure PS may be 0.25 MPa.

At this time, a center position C2of the target27B may deviate from a center axis CB of the nozzle hole717B. The center axis CB of the nozzle hole717B may be set to match the center axis of the nozzle712B. A reason why the center position C2deviates from the center axis CB of the nozzle hole717B can be postulated as follows.

When the target27B is generated due to the pressure in the target generator71B, a region that makes contact with the target27B and a region that does not make contact with the target27B may be present in a ring-shaped region on the inner edge side of a leading end surface718B of the protruding portion716B. In this case, the region, of the ring-shaped region on the inner edge side of the leading end surface718B, that has made contact with the target27B can be more easily wetted by the target material270. As a result, the center position C2of the target27B may deviate to the right from the center axis CB of the nozzle hole717B, for example as indicated inFIG. 10B.

When the target27B whose center position C2has deviated from the center axis CB of the nozzle hole717B is extracted by the electrostatic extraction section75B, the target27B may be outputted in an unintended direction.

To solve such an issue, the control method for the target supply device7B shown inFIGS. 11 and 12may be carried out before starting the process for extracting the targets27B in order to generate the EUV light.

The target control apparatus80B of the target supply device7B may carry out the same processes as those in steps S1to S5according to the first embodiment.

When the process of step S1is carried out, the pressure in the target generator71A can rise to the pressure PL at the time T0, as shown inFIG. 13. The pressure PL may be of a magnitude that positions an end area of the target material270at the opposite end of the inner wall surface717B1in the nozzle hole717B to the end on which the opening717B2is located (that is, the upper end), as shown inFIG. 14A.

When the process of step S5is carried out, the pressure in the target generator71B can begin to rise at a time T11and reach the pressure PJ at a time T12, as indicated inFIG. 13. When the pressure in the target generator71B reaches the pressure PJ, the target material270can be pressurized and a jet (not shown) can be outputted from the nozzle hole717B.

When the pressure in the target generator71B reaches the pressure PJ, the target control apparatus80B may start measuring time using the timer81A as indicated inFIG. 11(step S11). The target control apparatus80B may determine whether or not a measured time Kt measured by the timer81A is both longer than a minimum time Kmin and shorter than a maximum time Kmax (step S12). The minimum time Kmin and the maximum time Kmax may be several minutes to several tens of minutes. In other words, the length of time from the time T12to a time T13(mentioned later) may be several minutes to several tens of minutes.

When it is determined that the standard for determination in step S12has not been met, the target control apparatus80B may carryout the process of step S12. In other words, in the case where it has been determined that the standard for the determination in step S12is not met, the target control apparatus80B may carry out the process of step S12again after a predetermined amount of time has elapsed. In the case where it has been determined that the standard for the determination in step S12is met, the target control apparatus80B may set the pressure in the target generator71B to the pressure PS, as indicated inFIG. 12(step S13).

When the processes of steps S11to S13are carried out, the pressure in the target generator71B can begin to drop at the time T13and reach the pressure PS at a time T14, as indicated inFIG. 13. The output of the jet can be stopped between the time T13and the time T14. Furthermore, when the pressure in the target generator71B reaches the pressure PS, the target27B can be formed at the leading end of the protruding portion716B. The target27B can gradually grow (that is, can gradually develop) while the pressure in the target generator71B is held at the pressure PS.

The target control apparatus80B may determine whether or not a diameter D of the target27B is within a predetermined set range, as indicated inFIG. 12(step S14). The predetermined set range may be a size at which the entire opening717B2of the nozzle hole717B is covered by the target27B. The predetermined set range may be greater than or equal to a minimum value Dmin and less than or equal to a maximum value Dmax. The minimum value Dmin may be 100 μm. The maximum value Dmax may be 1 mm.

A method such as that described hereinafter may be employed as a method through which the target control apparatus80B detects the diameter D of the target27B.

The first target sensor41A and the second target sensor42A may detect the shape of the target27B that gradually grows, and may respectively send signals corresponding to the detection results to the target control apparatus80B. The first target sensor41A and the second target sensor42A may detect the shape of the target27B every predetermined amount of time. Based on the signals sent from the first target sensor41A and the second target sensor42A, the target control apparatus80B may determine whether or not the diameter D of the target27B is within the predetermined set range.

As another method, a relationship between the time required for the pressure in the target generator71B to reach the pressure PS and the diameter D of the target27B may be found experimentally. A minimum time at which the diameter D reaches the minimum value Dmin and a maximum time at which the diameter D reaches the maximum value Dmax may then be found based on the results of the experiment, and the minimum and maximum times may then be stored in a memory (not shown). The target control apparatus80B may use the timer81A to measure the amount of time that has elapsed after the pressure in the target generator71B has reached the pressure PS, and when the elapsed time is greater than or equal to the minimum time and less than or equal to the maximum time, the diameter D of the target27B may be determined to be within the predetermined set range.

However, when the target control apparatus80B has determined that the standard for determination in step S14has not been met, the target control apparatus80B may carry out the process of step S14. In other words, in the case where it has been determined that the standard for the determination in step S14is not met, the target control apparatus80B may carry out the process of step S14again after a predetermined amount of time has elapsed.

In the case where the target control apparatus80B has determined that the standard for the determination in step S14has been met, the first target sensor41A and the second target sensor42A may monitor the target27B that adheres to the protruding portion716B (step S15).

The target control apparatus80B may calculate the center position C2of the target27B based on the monitoring results from the first target sensor41A and the second target sensor42A (step S16).

Based on the signals sent from the first target sensor41A and the second target sensor42A, the target control apparatus80B may calculate an adherence position of the target27B when the target27B is monitored from the −X direction and the −Y direction. The target control apparatus80B may calculate the center position C2of the target27B based on the calculated adherence position. Here, the target control apparatus80B can calculate the center position C2at a high level of accuracy based on the monitoring results from the first target sensor41A and the second target sensor42A.

The target control apparatus80B may determine whether or not a difference ΔC between the center position C2of the target27B and the center axis CB of the nozzle hole717B is within a predetermined range (step S17). The determination as to whether or not the difference ΔC is within the predetermined range indicated inFIG. 14Bmay be carried out by determining whether or not the absolute value of the difference ΔC is less than or equal to a threshold ΔCmax. The threshold ΔCmax may be several μm.

In the case where it has been determined that the standard for the determination in step S17has not been met, the target control apparatus80B may carry out the processes of step S5and steps S11to S17until the standard for the determination has been met.

When the processes of step S5and steps S11to S17have been carried out, the pressure in the target generator71B can rise from the pressure PS to the pressure PJ from, for example, a time T15to a time T16, a time T19to a time T20, and a time T23to a time T24, as indicated inFIG. 13.

From the time T16to a time T17, the time T20to a time T21, and the time T24to a time T25, the pressure in the target generator71B can be held at the pressure PJ and the jet can be outputted from the nozzle hole717B. The target27B that adheres to the protruding portion716B can be outputted into the chamber2as the jet is outputted.

From the time T17to a time T18, the time T21to a time T22, and the time T25to a time T26, the pressure in the target generator71B can be reduced from the pressure PJ to the pressure PS and the output of the jet can be stopped.

The target27B can gradually grow from the time T18to the time T19, the time T22to the time T23, and the time T26to a time T27.

By repeatedly outputting the jet and growing the target27B in this manner, the target material270can gradually spread along the circumferential direction of the leading end surface718B. As a result, the target material270can make contact with the entire ring-shaped region on the inner edge side of the leading end surface718B, and as shown inFIG. 14C, the target27B can grow on the protruding portion716B so that the center position C2and the center axis CB of the nozzle hole717B essentially match.

In the case where it has been determined that the standard for the determination in step S17is met, the target control apparatus80B may set the pressure in the target generator71B to the pressure PL, as indicated inFIG. 12(step S9). For example, in the case where, at the time T27indicated inFIG. 13, the target27B adheres to the protruding portion716B so that the center position C2and the center axis CB of the nozzle hole717B essentially match as indicated inFIG. 14C, the target control apparatus80B can determine that the difference ΔC is within the predetermined range. In the state shown inFIG. 14C, the entire ring-shaped region on the inner edge side of the leading end surface718B can be easily wetted by the target material270.

When the process of step S9is carried out, the pressure in the target generator71B can begin to drop at a time T28and reach the pressure PL at a time T29, as indicated inFIG. 13. The target27B can be pulled into the nozzle hole717B during the period leading up to the pressure in the target generator71A reaching the pressure PL, and as shown inFIG. 14D, a state can be achieved in which the target material270makes contact with the entire inner wall surface717B1of the nozzle hole717B and the target27B does not adhere to the protruding portion716B.

After this, the target control apparatus80B may continuously extract the targets27B from the output portion715B by using the potential difference between the first electrode751B and the second electrode752B, in order to generate the EUV light. Here, because the entire ring-shaped region on the inner edge side of the leading end surface718B is more easily wettable by the target material270as a result of the aforementioned control method for the target supply device7B, the target27B can be generated at the protruding portion716B in order for the center position C2and the center axis CB of the nozzle hole717B essentially to be matched. As a result, the target27B can be extracted in an intended direction (that is, toward the plasma generation region25).

As described above, by the target control apparatus80B determining whether or not the difference ΔC between the center position C2of the target27B and the center axis CB of the nozzle hole717B is within the predetermined range, the target27B can be properly outputted in a configuration in which the target27B is extracted by utilizing the potential difference between the first electrode751B and the second electrode752B.

Note that the following configurations may be employed as the control method for a target supply device.

In the first embodiment, rather than monitoring the jet27A using the first target sensor41A and the second target sensor42A, vibrations may be applied to the nozzle712A that is outputting the jet27A and the targets27generated using these vibrations may be monitored. In this case, instead of determining the deviation of the trajectory C1of the jet27A relative to the set trajectory CA, the deviation of the trajectory of the targets27relative to the set trajectory CA may be determined.

Although two target sensors (the first target sensor41A and the second target sensor42A) are provided in the first and second embodiments, one target sensor, or three or more target sensors, may be provided instead.

In the first and second embodiments, the target supply device7A and the target supply device7B may cause the target material270to harden by lowering the temperature from the states shown inFIGS. 7D and 14D, respectively. After this, the target supply device7A and the target supply device7B may heat the target material270to melt and output the targets27, extract the targets27B, and so on in order to generate the EUV light.

In the first embodiment, an on-demand system that generates targets by using a piezoelectric element or the like to apply a compressive force to the nozzle712A may be employed as the target supply device.

The above-described embodiments and the modifications thereof are merely examples for implementing the present disclosure, and the present disclosure is not limited thereto. Making various modifications according to the specifications or the like is within the scope of the present disclosure, and other various embodiments are possible within the scope of the present disclosure. For example, the modifications illustrated for particular ones of the embodiments can be applied to other embodiments as well (including the other embodiments described herein).

The terms used in this specification and the appended claims should be interpreted as “non-limiting.” For example, the terms “include” and “be included” should be interpreted as “including the stated elements but not limited to the stated elements.” The term “have” should be interpreted as “having the stated elements but not limited to the stated elements.” Further, the modifier “one (a/an)” should be interpreted as “at least one” or “one or more”.