Target supply system, extreme ultraviolet light generation device, and method for manufacturing electronic devices

Abstract

To provide a target supply system that suppresses generation of a defective target formation.SOLUTION: A target supply system comprises: a target generating part which fuses a solid target substance inside thereof to generate a liquid target substance, and ejects the liquid target substance; a loading mechanism which loads the solid target substance into the target generating part; a heater which is arranged for the target generating part; a sensor which detects the temperature of the target generating part; and a processor which controls loading timing at which the solid target substance is loaded into the target generating part, feedback-controls the heater on the basis of the current temperature detected by the sensor, and feed-forward controls the heater on the basis of the loading timing while feedback-controlling the heater.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present disclosure relates to a target supply system, an extreme ultraviolet light generating apparatus, and a method for manufacturing an electronic device.

Background Art

[0002] In recent years, with the miniaturization of semiconductor processes, the miniaturization of transfer patterns in optical lithography of semiconductor processes has been rapidly progressing. In the next generation, microfabrication of 10 nm or less will be required. For this reason, the development of an exposure apparatus combining an EUV light generating apparatus that generates extreme ultraviolet (EUV) light with a wavelength of about 13 nm and a reduced projection reflection optics is expected.

[0003] As an EUV light generating apparatus, the development of an LPP (Laser Produced Plasma) type apparatus in which plasma generated by irradiating a target substance with pulsed laser light is used has been progressing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0005] A target supply system according to one aspect of this disclosure comprises: a target generation unit that melts a solid target material internally to generate a liquid target material and discharges the liquid target material; a feeding mechanism that feeds the solid target material into the target generation unit; a heater disposed in the target generation unit; a sensor that detects the temperature of the target generation unit; and a processor that controls the feeding timing at which the solid target material is fed into the target generation unit, provides feedback control of the heater based on the current temperature detected by the sensor, and provides feedforward control of the heater based on the feeding timing while providing feedback control of the heater.

[0006] A method for manufacturing an electronic device according to one aspect of the present disclosure includes: a target supply system comprising: a target supply system comprising: a target supply system comprising: a target supply system comprising: a target supply system comprising: a laser device comprising: a laser device comprising: a laser device comprising: a laser device comprising: a laser device comprising: a laser device comprising: a laser device comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing mirror comprising: an EUV focusing device

[0007] A method for manufacturing an electronic device according to one aspect of the present disclosure includes: a target supply system comprising: a target generation unit that generates a liquid target material by melting a solid target material internally and discharges the liquid target material; a feeding mechanism for feeding a solid target material into the target generation unit; a heater disposed in the target generation unit; a sensor for detecting the temperature of the target generation unit; and a processor that controls the feeding timing at which the solid target material is fed into the target generation unit, provides feedback control of the heater based on the current temperature detected by the sensor, and provides feedforward control of the heater based on the feeding timing while providing feedback control of the heater; a laser device that irradiates pulsed laser light onto the liquid target material discharged from the target supply system and reaching a predetermined region; and an EUV focusing mirror that focuses extreme ultraviolet light emitted from the plasma generated in the predetermined region. The method includes irradiating a mask with extreme ultraviolet light generated by an extreme ultraviolet light generation device to inspect for defects in the mask, selecting a mask using the inspection results, and exposing and transferring a pattern formed on the selected mask onto a photosensitive substrate. [Brief explanation of the drawing]

[0008] Some embodiments of this disclosure are described below, merely as examples, with reference to the accompanying drawings. [Figure 1] Figure 1 shows a schematic configuration of an LPP-type EUV light generation system. [Figure 2] Figure 2 schematically shows the configuration of the target supply system in the comparative example. [Figure 3] Figure 3 shows the configuration of the load lock chamber and solid target supply valve, and their operation is shown in combination with Figure 4. [Figure 4] Figure 4 shows the configuration of the load lock chamber and solid target supply valve, and their operation is shown in combination with Figure 3. [Figure 5] Figure 5 is a flowchart of the EUV photogeneration processor in the comparative example. [Figure 6]Figure 6 is a flowchart of the input control processor in the comparative example. [Figure 7] Figure 7 is a flowchart of temperature control of a large tank using a temperature control processor in a comparative example. [Figure 8] Figure 8 is a flowchart of temperature control of a small tank using a temperature control processor in a comparative example. [Figure 9] Figure 9 is a flowchart of nozzle temperature control by a temperature control processor in a comparative example. [Figure 10] Figure 10 is a block diagram of temperature control in the comparative example. [Figure 11] Figure 11 shows the results of a simulation of the temperature change of the liquid target substance inside the small tank in the comparative example. [Figure 12] Figure 12 is a flowchart of the input control processor in the first embodiment. [Figure 13] Figure 13 is a flowchart of temperature control of a small tank by a temperature control processor in the first embodiment. [Figure 14] Figure 14 is a block diagram of temperature control in the first embodiment. [Figure 15] Figure 15 shows the results of a simulation of the temperature change of the liquid target substance inside the small tank in the first embodiment. [Figure 16] Figure 16 is a flowchart of the input control processor in the second embodiment. [Figure 17] Figure 17 is a flowchart of temperature control of a large tank by a temperature control processor in the second embodiment. [Figure 18] Figure 18 is a flowchart of nozzle temperature control by the temperature control processor in the second embodiment. [Figure 19] Figure 19 is a block diagram of temperature control in the second embodiment. [Figure 20] Figure 20 is a flowchart of the nozzle temperature control by the temperature control processor in the third embodiment. [Figure 21] FIG. 21 is a block diagram of temperature control in the third embodiment. [Figure 22] FIG. 22 shows the result of simulating the temperature change of the liquid target substance inside the small tank in the third embodiment. [Figure 23] FIG. 23 is a flowchart of the temperature control of the small tank by the temperature control processor in the fourth embodiment. [Figure 24] FIG. 24 is a block diagram of temperature control in the fourth embodiment. [Figure 25] FIG. 25 shows the result of simulating the temperature change of the liquid target substance inside the small tank in the fourth embodiment. [Figure 26] FIG. 26 shows the result of simulating the temperature change of the liquid target substance inside the small tank in the fifth embodiment. [Figure 27] FIG. 27 schematically shows the configuration of an exposure apparatus connected to an EUV light generation system. [Figure 28] FIG. 28 schematically shows the configuration of an inspection apparatus connected to an EUV light generation system. Embodiment

[0009] <Content> 1. Overall description of EUV light generation system 11 1.1 Configuration 1.2 Operation 2. Comparative example 2.1 Configuration 2.1.1 Reservoir tank C1 2.1.2 Load lock chamber C2 2.1.3 Target generation unit 260 2.1.4 Details of load lock chamber C2 and solid target supply valve VT2 2.2 Operation 2.2.1 Operation of EUV light generation processor 5 2.2.2 Input control of solid target substance 27a 2.2.3 Temperature control of large tank 7lt 2.2.4 Temperature control of small tank 7st 2.2.5 Temperature control of nozzle 7nz 2.2.6 Block Diagram 2.3 Challenges of the Comparative Example 3. Suppression of temperature drop through feedforward control 3.1 Operation 3.1.1 Control of input of solid target material 27a 3.1.2 Temperature control of the large 7lt tank 3.1.3 Temperature control of small 7-stroke tank 3.1.4 Temperature control of nozzle 7nz 3.1.5 Block Diagram 3.2 Simulation Results 3.3 Effect 4. Example where feedforward control is selectable. 4.1 Operation 4.1.1 Control of input of solid target material 27a 4.1.2 Temperature control of the large 7lt tank 4.1.3 Temperature control of small 7st tank 4.1.4 Temperature control of nozzle 7nz 4.1.5 Block Diagram 4.2 Effect 5. Example of feedforward control of the temperature of the small tank 7st and nozzle 7nz. 5.1 Operation 5.1.1 Input control of solid target material 27a 5.1.2 Temperature control of the large 7lt tank 5.1.3 Temperature control of small 7st tank 5.1.4 Temperature control of nozzle 7nz 5.1.5 Block Diagram 5.2 Simulation Results 5.3 Effect 6. Example of feedforward control using the current correction value fcst(t) 6.1 Operation 6.1.1 Control of input of solid target material 27a 6.1.2 Temperature control of the large 7lt tank 6.1.3 Temperature control of small 7st tank 6.1.4 Temperature control of nozzle 7nz 6.1.5 Block Diagram 6.2 Simulation Results 6.3 Effect 7. Example where the waveform of the current correction value fcst(t) is a square wave. 8. Other

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. The embodiments described below are examples of the disclosure and are not intended to limit the scope of this disclosure. Furthermore, not all configurations and operations described in each embodiment are necessarily essential to the configurations and operations of this disclosure. The same reference numerals are used for identical components, and redundant descriptions are omitted.

[0011] 1. Overall description of the EUV light generation system 11 1.1 Configuration Figure 1 schematically shows the configuration of an LPP-type EUV light generation system 11. The EUV light generator 1 is used together with a laser device 3. In this disclosure, the system including the EUV light generator 1 and the laser device 3 is referred to as the EUV light generation system 11. The EUV light generator 1 includes a chamber 2 and a target supply system 26. The chamber 2 is a sealable container. The target supply system 26 supplies a target 27 containing a target material into the chamber 2. The target material may include tin, terbium, gadolinium, lithium, xenon, or any combination of two or more of these.

[0012] The wall of chamber 2 is provided with a through-hole. This through-hole is covered by a window 21, through which pulsed laser light 32 output from the laser device 3 passes. Inside chamber 2, an EUV focusing mirror 23 with a spheroidal reflective surface is positioned. The EUV focusing mirror 23 has a first and a second focal point. A multilayer reflective film is formed on the surface of the EUV focusing mirror 23, in which molybdenum and silicon are alternately layered. The EUV focusing mirror 23 is positioned such that its first focal point is located in the plasma generation region 25 and its second focal point is located in the intermediate focal point 292. A through-hole 24 is provided in the center of the EUV focusing mirror 23, through which pulsed laser light 33 passes.

[0013] The EUV light generation apparatus 1 includes an EUV light generation processor 5, a target sensor 4, etc. The EUV light generation processor 5 is a processing unit that includes a memory 501 in which a control program is stored, and a CPU (central processing unit) 502 that executes the control program. The EUV light generation processor 5 is specially configured or programmed to perform various processes included in this disclosure. The target sensor 4 detects at least one of the presence, trajectory, position, and velocity of the target 27. The target sensor 4 may also have an imaging function.

[0014] Furthermore, the EUV light generator 1 includes a connecting section 29 that connects the inside of the chamber 2 with the inside of the EUV light utilization device 6. An example of the EUV light utilization device 6 will be described later with reference to Figures 27 and 28. Inside the connecting section 29, there is a wall 291 with an aperture formed therein. The wall 291 is positioned such that its aperture is located at the second focal point of the EUV focusing mirror 23.

[0015] Furthermore, the EUV light generation device 1 includes a laser light transmission device 34, a laser light focusing mirror 22, a target retrieval unit 28 for retrieving the target 27, and the like. The laser light transmission device 34 includes an optical element for defining the transmission state of the pulsed laser light 32, and an actuator for adjusting the position, orientation, etc., of this optical element.

[0016] 1.2 Operation Referring to Figure 1, the operation of the EUV light generation system 11 will be explained. The pulsed laser light 31 output from the laser device 3 passes through the laser light transmission device 34 and enters the chamber 2 as pulsed laser light 32, passing through the window 21. The pulsed laser light 32 travels through the chamber 2 along the laser light path, is reflected by the laser light focusing mirror 22, and is irradiated onto the target 27 as pulsed laser light 33.

[0017] The target supply system 26 outputs the target 27 toward the plasma generation region 25 inside the chamber 2. The target 27 is irradiated with pulsed laser light 33. The target 27, irradiated with pulsed laser light 33, becomes plasma, and synchrotron radiation 251 is emitted from the plasma. The EUV light contained in the synchrotron radiation 251 is reflected by the EUV focusing mirror 23 with a higher reflectivity than light in other wavelength ranges. The reflected light 252, which includes the EUV light reflected by the EUV focusing mirror 23, is focused at an intermediate focusing point 292 and output to the EUV light utilization device 6. Note that multiple pulses contained in the pulsed laser light 33 may be irradiated onto a single target 27.

[0018] The EUV photogeneration processor 5 controls the entire EUV photogeneration system 11. The EUV photogeneration processor 5 processes the detection results of the target sensor 4. Based on the detection results of the target sensor 4, the EUV photogeneration processor 5 controls the timing of the output of the target 27, the output direction of the target 27, etc. Furthermore, the EUV photogeneration processor 5 controls the oscillation timing of the laser device 3, the direction of propagation of the pulsed laser beam 32, the focusing position of the pulsed laser beam 33, etc. The various controls described above are merely examples, and other controls may be added as needed.

[0019] 2. Comparative Examples 2.1 Configuration Figure 2 schematically shows the configuration of a target supply system 26 according to a comparative example. The comparative examples in this disclosure are forms that the applicant recognizes as being known only to the applicant, and are not known examples acknowledged by the applicant. As shown in Figure 2, the target supply system 26 according to the comparative example includes a reservoir tank C1, a load lock chamber C2, a target generation unit 260, a target supply processor 60, a measuring device 61, a pressure regulator 62, a temperature control processor 63, and a feeding control processor 64.

[0020] The target supply processor 60 is a processing unit that includes a memory 601 in which a control program is stored and a CPU 602 that executes the control program. The target supply processor 60 is specially configured or programmed to perform various processes included in this disclosure. The target supply processor 60 transmits control signals to the pressure regulator 62 and the temperature control processor 63.

[0021] 2.1.1 Reservoir Tank C1 The reservoir tank C1 is a container for holding a solid target material 27a, such as tin. The solid target material 27a may be, for example, spherical particles of approximately the same size. Alternatively, it may be particles of a shape other than spherical. The temperature inside the reservoir tank C1 is lower than the melting point of the target material. The gas pressure inside the reservoir tank C1 is approximately the same as atmospheric pressure.

[0022] The measuring device 61 is located at the lower end of the reservoir tank C1 in the direction of gravity. The reservoir tank C1 is connected to the solid target supply pipe 41 via the measuring device 61, and the solid target supply pipe 41 is connected to the load lock chamber C2. A solid target supply valve VT1 is located in the solid target supply pipe 41.

[0023] Under normal circumstances, the measuring device 61 stops supplying the solid target material 27a to the solid target supply pipe 41. The weighing device 61 can weigh the solid target material 27a supplied from the reservoir tank C1 and pass it towards the load lock chamber C2. Weighing the solid target material 27a includes counting the number of particles of the solid target material 27a. The weighed solid target material 27a moves by gravity and passes through the solid target supply pipe 41 and the solid target supply valve VT1 to the load lock chamber C2. Once a predetermined amount of solid target material 27a has passed through, the weighing device 61 stops the passage of the solid target material 27a.

[0024] 2.1.2 Load Lock Chamber C2 The load lock chamber C2 is a container configured to accommodate the solid target material 27a supplied from the reservoir tank C1. The temperature inside the load lock chamber C2 is lower than the melting point of the target material.

[0025] The load lock chamber C2 is connected to the solid target supply pipe 42, which is connected to the target generation unit 260. A solid target supply valve VT2 is located in the solid target supply pipe 42. The configuration of the load lock chamber C2 and the solid target supply valve VT2 will be described later with reference to Figures 3 and 4.

[0026] The solid target supply valves VT1 and VT2 are normally closed, and the other is opened only when one is closed. That is, when the solid target material 27a is moved from the reservoir tank C1 to the load lock chamber C2 via the measuring device 61, the solid target supply valve VT1 is temporarily opened while the solid target supply valve VT2 is closed. Also, when the solid target material 27a is introduced from the load lock chamber C2 to the target generation unit 260, the solid target supply valve VT2 is temporarily opened while the solid target supply valve VT1 is closed. This suppresses the flow of gas inside the target generation unit 260 toward the reservoir tank C1.

[0027] The feed control processor 64 is a processing unit that includes a memory 641 in which a control program is stored and a CPU 642 that executes the control program. The feed control processor 64 constitutes the processor in this disclosure. The feed control processor 64 is specially configured or programmed to perform various processes included in this disclosure. The feed control processor 64 controls the measuring instrument 61, the solid target supply valves VT1 and VT2, and the adjustment mechanism 66, described later, which is located inside the load lock chamber C2. The measuring instrument 61, the solid target supply valves VT1 and VT2, and the adjustment mechanism 66 constitute the feed mechanism in this disclosure.

[0028] 2.1.3 Target generation unit 260 The target generation unit 260 is a device that melts solid target material 27a, which is introduced from the load lock chamber C2 via the solid target supply pipe 42, to generate liquid target material 27b, and then discharges the liquid target material 27b as the target 27.

[0029] The target generation unit 260 includes a large tank 7lt, a small tank 7st, and a nozzle 7nz. The large tank 7lt melts a solid target material 27a inside to produce a liquid target material 27b. The small tank 7st passes the liquid target material 27b produced in the large tank 7lt towards the nozzle 7nz. The nozzle 7nz discharges the liquid target material 27b produced in the large tank 7lt. A filter F is placed between the large tank 7lt and the small tank 7st. The filter F is a plate with numerous fine through holes and prevents solid matter mixed inside the large tank 7lt from flowing into the small tank 7st. The large tank 7lt corresponds to the first tank in this disclosure, and the small tank 7st corresponds to the second tank in this disclosure. However, the large tank 7lt does not have to be larger than the small tank 7st.

[0030] In this disclosure, the region of the target generation unit 260 that includes the large tank 7lt is referred to as the first region, and the region of the target generation unit 260 that includes the nozzle 7nz is referred to as the second region. The boundary between the first region and the second region may be defined by the position of the filter F, in which case the small tank 7st would be included in the second region, but the disclosure is not limited thereto.

[0031] Heaters 8lt, 8st, and 8nz are located in the large tank 7lt, the small tank 7st, and the nozzle 7nz, respectively. Heaters 8lt, 8st, and 8nz are connected to power supplies 82lt, 82st, and 82nz, respectively, and heat the inside of the target generation unit 260 to a predetermined temperature higher than the melting point of the target substance. The temperature inside the target generation unit 260 is controlled by controlling the power supplies 82lt, 82st, and 82nz based on the output of sensors 80lt, 80st, and 80nz, which are located in the heaters 8lt, 8st, and 8nz, respectively. Sensor 80lt is located in heater 8lt and is not in contact with the large tank 7lt or the liquid target substance 27b inside it. However, the temperature of the large tank 7lt and the temperature of the liquid target substance 27b inside it may be so high in thermal conductivity that they can be considered to be approximately the same as the temperature of heater 8lt and can be measured by sensor 80lt. Sensors 80st and 80nz are located on heaters 8st and 8nz, respectively, and are not in contact with the small tank 7st, nozzle 7nz, or the liquid target substance 27b inside them. However, the thermal conductivity of the small tank 7st and nozzle 7nz is similar, and their respective temperatures may be measurable by sensors 80st and 80nz. Alternatively, sensors 80lt, 80st, and 80nz may be directly attached to the large tank 7lt, small tank 7st, and nozzle 7nz, respectively.

[0032] In this disclosure, one heater located in a first region of heaters 8lt, 8st, and 8nz is referred to as the first heater, and one heater located in a second region of heaters 8lt, 8st, and 8nz is referred to as the second heater. For example, heater 8lt corresponds to the first heater, and either heater 8st or 8nz corresponds to the second heater. Alternatively, either heater 8lt or 8st corresponds to the first heater, and heater 8nz corresponds to the second heater. Alternatively, heater 8lt corresponds to the first heater, heater 8st corresponds to the second heater, and heater 8nz corresponds to the third heater.

[0033] The large tank 7lt is connected to a pressure regulator 62 via gas piping. The pressure regulator 62 is connected to a gas cylinder G1. Gas cylinder G1 contains high-pressure noble gases such as argon and helium as pressurized gases. The pressure regulator 62 adjusts the gas pressure supplied from gas cylinder G1 and supplies it to the large tank 7lt. The gas pressure inside the large tank 7lt is lower than the gas pressure supplied from gas cylinder G1 and higher than atmospheric pressure.

[0034] The small tank 7st is located between the large tank 7lt and the nozzle 7nz. The nozzle 7nz is positioned at the lower end of the target generation unit 260 in the direction of gravity. The tip of the nozzle 7nz opens into the chamber 2 (see Figure 1). The liquid target substance 27b inside the target generation unit 260 is discharged from the opening at the tip of the nozzle 7nz due to the difference between the gas pressure supplied from the pressure regulator 62 and the gas pressure inside the chamber 2. When the nozzle 7nz is vibrated by a piezoelectric element (not shown), the jet-like liquid target substance 27b discharged from the nozzle 7nz separates into droplets, forming the target 27.

[0035] The temperature control processor 63 is a processing unit that includes a memory 631 in which a control program is stored and a CPU 632 that executes the control program. The temperature control processor 63 constitutes the processor in this disclosure. The temperature control processor 63 is specially configured or programmed to perform various processes included in this disclosure. The temperature control processor 63 determines the current values ​​of the heaters 8lt, 8st, and 8nz based on the temperature of the target generation unit 260 detected by sensors 80lt, 80st, and 80nz, and controls the power supplies 82lt, 82st, and 82nz.

[0036] 2.1.4 Details of Load Lock Chamber C2 and Solid Target Supply Valve VT2 Figures 3 and 4 show the configuration of the load lock chamber C2 and the solid target supply valve VT2, respectively, and their operation is shown in combination with Figures 3 and 4. The adjustment mechanism 66 included in the load lock chamber C2 includes a receiving plate 66a and an actuator 66b. The receiving plate 66a is located near the lower end of the load lock chamber C2 in the direction of gravity. The actuator 66b is configured to switch the adjustment mechanism 66 between a first state shown in Figure 3 and a second state shown in Figure 4 by moving the receiving plate 66a.

[0037] In the first state, the receiving plate 66a is positioned to block the connection from the load lock chamber C2 to the solid target supply pipe 42. This prevents the solid target material 27a from moving toward the solid target supply valve VT2. In the second state, the receiving plate 66a is positioned away from the connection point between the load lock chamber C2 and the solid target supply pipe 42. This allows the solid target material 27a to move toward the solid target supply valve VT2. The adjustment mechanism 66 is normally in the first state, and is temporarily in the second state when moving the solid target material 27a toward the solid target supply valve VT2.

[0038] The solid target supply valve VT2 is composed of a ball valve including, for example, a ball portion V2a and a body portion V2b. By rotating the ball portion V2a inside the body portion V2b in the direction of arrow R, it is switched between a closed state shown in Figure 3 and an open state shown in Figure 4. In the closed state, the flow of gas from the target generation unit 260 to the load lock chamber C2 is suppressed, and in the open state, the introduction of the solid target material 27a from the load lock chamber C2 to the target generation unit 260 is permitted.

[0039] 2.2 Operation 2.2.1 Operation of EUV light generation processor 5 Figure 5 is a flowchart of the EUV light generation processor 5 in the comparative example. EUV light is generated when the EUV light generation processor 5 operates the EUV light generation system 11 as follows.

[0040] In S1, the EUV photogeneration processor 5 starts the EUV photogeneration system 11. Starting the EUV photogeneration system 11 includes starting various power supplies included in the EUV photogeneration system 11, starting various processors, purging gases and vacuuming within the various devices, etc.

[0041] In S2, the EUV photogeneration processor 5 instructs the input control processor 64 to begin input control of the solid target material 27a. The input control of the solid target material 27a is repeated after it starts in S2, for example, until EUV photogeneration is completed. The input control of the solid target material 27a will be described later with reference to Figure 6.

[0042] In S3, the EUV photogeneration processor 5 sends a control signal to the target supply processor 60, causing the temperature control processor 63 to start temperature control of the large tank 7lt, the small tank 7st, and the nozzle 7nz. After starting in S3, the temperature control is repeated, for example, until EUV photogeneration is completed. The temperature control will be described later with reference to Figures 7 to 9.

[0043] In S4, the EUV photogeneration processor 5 causes the target supply processor 60 to start supplying targets. Target supply is initiated, for example, by the pressure regulator 62 adjusting the gas pressure inside the large tank 7lt to a high pressure.

[0044] In S5, the EUV light generation processor 5 performs processing for EUV light generation. EUV light generation is performed by controlling the laser device 3 and the laser light transmission device 34, etc., so that pulsed laser light 33 is irradiated onto the target 27 at the timing when the target 27 reaches the plasma generation region 25 (see Figure 1).

[0045] In S6, the EUV light generation processor 5 determines whether to continue EUV light generation. If EUV light generation is to be continued (S6: YES), the EUV light generation processor 5 returns to S5. If EUV light generation is not to be continued (S6: NO), the EUV light generation processor 5 terminates the process in this flowchart.

[0046] 2.2.2 Input control of solid target material 27a Figure 6 is a flowchart of the input control processor 64 in the comparative example. The solid target material 27a is fed into the target generation unit 260 as follows.

[0047] In S21, the input control processor 64 determines whether the amount of liquid target substance 27b inside the large tank 7lt is below a set value. The amount of liquid target substance 27b is determined by the output of a liquid level sensor (not shown) located in the large tank 7lt. If the amount of liquid target substance 27b is below the set value (S21: YES), the input control processor 64 proceeds to S22. If the amount of liquid target substance 27b is greater than the set value (S21: NO), the input control processor 64 proceeds to S26. The input timing is controlled by waiting without inputting the solid target substance 27a until the amount of liquid target substance 27b becomes below the set value.

[0048] In S22, the input control processor 64 controls the weighing device 61 and the solid target supply valve VT1 to weigh out one solid target particle 27a at a time and move them to the load lock chamber C2.

[0049] In S23, the input control processor 64 determines whether a predetermined amount of solid target material 27a has moved to the load lock chamber C2. If the predetermined amount of solid target material 27a has not moved (S23: NO), the input control processor 64 returns to S22. If the predetermined amount of solid target material 27a has moved (S23: YES), the input control processor 64 proceeds to S25. The amount of solid target material 27a input is controlled by continuing to weigh it until the predetermined amount of solid target material 27a has moved.

[0050] In S25, the input control processor 64 controls the adjustment mechanism 66 inside the load lock chamber C2 and the solid target supply valve VT2 to input the solid target material 27a into the large tank 7lt.

[0051] In S26, the input control processor 64 determines whether to continue the input control of the solid target material 27a. For example, if the EUV light generation processor 5 determines to continue EUV light generation, it is determined that the input control of the solid target material 27a will also be continued. If the input control of the solid target material 27a is to be continued (S26: YES), the input control processor 64 returns to S21. If the input control of the solid target material 27a is not to be continued (S26: NO), the input control processor 64 terminates the processing in this flowchart.

[0052] Through this operation, the solid target material 27a, which is contained inside the reservoir tank C1 at near atmospheric pressure, is introduced into the high-pressure target generation unit 260. Even if the liquid target material 27b inside the target generation unit 260 is consumed, the target material can be replenished without replacing the target generation unit 260, thus reducing the downtime of the EUV light generator 1.

[0053] 2.2.3 Temperature control of the large 7lt tank Figure 7 is a flowchart of the temperature control of the large tank 7lt by the temperature control processor 63 in the comparative example. The temperature of the large tank 7lt is feedback controlled as follows.

[0054] In S301, the temperature control processor 63 determines whether the temperature control cycle for the large tank 7lt has elapsed. If the control cycle has elapsed (S301: YES), the temperature control processor 63 proceeds to S302. If the control cycle has not elapsed (S301: NO), the temperature control processor 63 proceeds to S312. In S302, the temperature control processor 63 reads the target temperature SVlt of the large tank 7lt from the memory 631.

[0055] In S306, the temperature control processor 63 reads the current temperature PVlt of the large tank 7lt detected by the sensor 80lt. In S307, the temperature control processor 63 calculates the temperature deviation elt between the target temperature SVlt and the current temperature PVlt using the following formula. elt=SVlt-PVlt In S308, the temperature control processor 63 performs PID control calculations to calculate the current value Clt of the heater 8lt.

[0056] In S311, the temperature control processor 63 outputs a heater control signal for heater 8lt using the current value Clt. In S312, the temperature control processor 63 determines whether to continue temperature control of the large tank 7lt. For example, if the EUV light generation processor 5 determines to continue EUV light generation, it is determined that temperature control should also be continued. If temperature control is to be continued (S312: YES), the temperature control processor 63 returns to S301. If temperature control is not to be continued (S312: NO), the temperature control processor 63 terminates the processing in this flowchart.

[0057] 2.2.4 Temperature control of small 7st tank Figure 8 is a flowchart of the temperature control of the small tank 7st by the temperature control processor 63 in the comparative example. The temperature control of the small tank 7st is equivalent to the temperature control of the large tank 7lt described with reference to Figure 7, but with the following points replaced. Replace step numbers starting with "S3" with step numbers starting with "S4". Replace the target temperature SVlt for the large tank (7lt) with the target temperature SVst for the small tank (7st). The specific numerical values ​​for target temperatures SVlt and SVst may be the same. Replace the current temperature PVlt of the large tank 7lt with the current temperature PVst of the small tank 7st. Replace the temperature deviation elt with the temperature deviation est. Replace the current value Clt for heater 8lt with the current value Cst for heater 8st.

[0058] 2.2.5 Temperature control of nozzle 7nz Figure 9 is a flowchart of the temperature control of nozzle 7nz by the temperature control processor 63 in the comparative example. The temperature control of nozzle 7nz is equivalent to the temperature control of the large tank 7lt described with reference to Figure 7, but with the following points replaced. Replace step numbers starting with "S3" with step numbers starting with "S5". Replace the target temperature SVlt of the large tank 7lt with the target temperature SVnz of nozzle 7nz. The specific numerical values ​​for target temperatures SVlt and SVnz may be the same. Replace the current temperature PVlt of the large tank 7lt with the current temperature PVnz of nozzle 7nz. Replace the temperature deviation elt with the temperature deviation enz. Replace the current value Clt for heater 8lt with the current value Cnz for heater 8nz.

[0059] 2.2.6 Block Diagram Figure 10 is a block diagram of temperature control in a comparative example. Temperature control is performed independently for the large tank 7lt, the small tank 7st, and the nozzle 7nz. Temperature deviations elt, est, and enz are calculated from the target temperatures SVlt, SVst, and SVnz and the current temperatures PVlt, PVst, and PVnz of the large tank 7lt, the small tank 7st, and the nozzle 7nz, respectively. PID control calculations using the temperature deviations elt, est, and enz are used to calculate the current values ​​Clt, Cst, and Cnz for the heaters 8lt, 8st, and 8nz. Heaters 8lt, 8st, and 8nz convert electrical energy corresponding to the current values ​​Clt, Cst, and Cnz into thermal energy. This thermal energy, along with the disturbance when the solid target material 27a is introduced into the large tank 7lt, affects the current temperatures PVlt, PVst, and PVnz. The current temperatures PVlt, PVst, and PVnz are detected and fed back by sensors 80lt, 80st, and 80nz.

[0060] 2.3 Challenges of the Comparative Example Figure 11 shows the results of a simulation of the temperature change of the liquid target substance 27b inside the small tank 7st in the comparative example. The horizontal axis shows the elapsed time from the timing of adding the solid target substance 27a, and the vertical axis shows the temperature deviation relative to the temperature of the liquid target substance 27b at the timing of adding the solid target substance 27a. The amount of liquid target substance 27b remaining inside the target generation unit 260 before adding the solid target substance 27a is 50 cm³. 3 The amount of solid target material 27a to be introduced is 0.35 cm³. 3 That's what I decided.

[0061] The liquid target material 27b loses heat of fusion to the solid target material 27a, causing its temperature to decrease. Subsequently, the temperature of the liquid target material 27b is restored by feedback control of heaters 8lt, 8st, and 8nz. If the temperature decrease is within an acceptable range, the liquid target material 27b discharged from nozzle 7nz forms an ideal droplet-shaped target 27. However, if it falls outside the acceptable range, target formation failure may occur. For example, a decrease of 0.1°C may result in target formation failure.

[0062] 3. Suppression of temperature drop through feedforward control A first embodiment will be described below. The configuration of the target supply system 26 according to the first embodiment may be the same as that described with reference to Figure 2.

[0063] 3.1 Operation 3.1.1 Control of input of solid target material 27a Figure 12 is a flowchart of the input control processor 64 in the first embodiment. The process shown in Figure 12 differs from the process shown in Figure 6 in the following respects.

[0064] When a predetermined amount of solid target material 27a has moved to the load lock chamber C2 (S23:YES), the input control processor 64 proceeds to S24a. In S24a, the input control processor 64 notifies the temperature control processor 63 of the timing and amount of solid target material 27a to be input. Subsequently, in S25, the solid target material 27a is input into the large tank 7lt.

[0065] 3.1.2 Temperature control of the large 7lt tank Temperature control for the large 7lt tank can be done using the same feedback control as shown in Figure 7.

[0066] 3.1.3 Temperature control of small 7-stroke tank Figure 13 is a flowchart of the temperature control of the small tank 7st by the temperature control processor 63 in the first embodiment. The process shown in Figure 13 differs from the process shown in Figure 8 in the following respects.

[0067] In S402, after reading the target temperature SVst of the small tank 7st, in S404a, the temperature control processor 63 calculates a correction value fst(t) for the temperature of the small tank 7st by feedforward control calculation. The correction value fst(t) is calculated based on the timing and amount of solid target material 27a to be added, received from the input control processor 64. The correction value fst(t) is a function of time shown by the following formula. fst(t) = N·Ast·exp(-t / τst) Here, N is the amount of solid target material 27a added, Ast is the control gain, t is the elapsed time from the timing of adding the solid target material 27a, and τst is the time constant. The correction value fst(t) is a function that decays and approaches 0 as the elapsed time t increases.

[0068] In S405a, the temperature control processor 63 calculates the corrected target temperature SVstr by adding a correction value fst(t) to the target temperature SVst of the small tank 7st. The target temperature SVst is an example of a first target value in this disclosure, and the corrected target temperature SVstr is an example of a second target value in this disclosure. Feedback control is performed in S406-S411. At this time, in S407a, the corrected target temperature SVstr is used to calculate the temperature deviation est, so feedforward control is performed along with the feedback control. The feedforward control is performed in accordance with the control cycle of the feedback control.

[0069] 3.1.4 Temperature control of nozzle 7nz The temperature control of nozzle 7nz can be performed using the same feedback control as shown in Figure 9.

[0070] 3.1.5 Block Diagram Figure 14 is a block diagram of temperature control in the first embodiment. In the first embodiment, the input control processor 64 transmits the input timing and amount of solid target material 27a to the temperature control processor 63. The temperature control processor 63 calculates a correction value fst(t) by feedforward control calculation based on the input timing and amount, and calculates a corrected target temperature SVstr by adding the correction value fst(t) to the target temperature SVst of the small tank 7st. Feedback control and feedforward control are performed by performing feedback control of the heater 8st of the small tank 7st based on the corrected target temperature SVstr.

[0071] Regarding the temperature of the large tank 7lt and the nozzle 7nz, feedforward control based on the timing and amount of injection is not required, and feedback control may be performed as in the comparative example.

[0072] 3.2 Simulation Results Figure 15 shows the results of a simulation of the temperature change of the liquid target substance 27b inside the small tank 7st in the first embodiment. The temperature of the liquid target substance 27b decreases after the solid target substance 27a is added, and then recovers through feedback control.

[0073] Figure 15 also shows the temperature correction value fst(t) for the small tank 7st. The time constant τst of the correction value fst(t) is set to, for example, about 10 seconds, and the temperature of the liquid target material 27b is lowest after the correction value fst(t) has become virtually zero. The next solid target material 27a is introduced into the target generation unit 260 only after that.

[0074] In the comparative example, the temperature drop of the liquid target substance 27b was 0.1°C or more, whereas in the first embodiment, feedforward control was performed, resulting in a temperature drop of less than 0.1°C. Since the temperature drop is within an acceptable range, the occurrence of target formation defects is suppressed. This allows for stable generation of EUV light.

[0075] 3.3 Effect (1) According to the first embodiment, the target supply system 26 comprises a target generation unit 260, a feeding mechanism, a heater 8st, a sensor 80st, a feeding control processor 64, and a temperature control processor 63. The target generation unit 260 melts solid target material 27a internally to generate liquid target material 27b and discharges the liquid target material 27b. The feeding mechanism includes, for example, a measuring instrument 61, solid target supply valves VT1 and VT2, and an adjustment mechanism 66, and feeds solid target material 27a into the target generation unit 260. The heater 8st is located in the target generation unit 260. The sensor 80st detects the temperature of the target generation unit 260. The feeding control processor 64 controls the feeding timing at which solid target material 27a is fed into the target generation unit 260. The temperature control processor 63 feedforward controls the heater 8st based on the feeding timing while feedback controlling the heater 8st based on the current temperature PVst detected by the sensor 80st. According to this, by feedback-controlling the heater 8st and performing feedforward control based on the timing of introducing the solid target material 27a, temperature fluctuations when the solid target material 27a is introduced can be suppressed, and the formation of the target 27 can be stabilized.

[0076] (2) According to the first embodiment, the temperature control processor 63 feedforward controls the heater 8st so that the temperature of the target generation unit 260 drops to less than 0.1°C. According to this, the occurrence of target formation defects can be suppressed.

[0077] (3) According to the first embodiment, the temperature control processor 63 feedforward controls the heater 8st in accordance with the control cycle of the feedback control of the heater 8st. According to this, by aligning the control cycles, it is possible to suppress the increase in the computational complexity of control calculations.

[0078] (4) According to the first embodiment, the temperature control processor 63 reads the target temperature SVst from the target generation unit 260, and calculates the corrected target temperature SVstr by adding a correction value fst(t) including a feedforward element to the target temperature SVst. The temperature control processor 63 further performs feedback control of the heater 8st based on the corrected target temperature SVstr and the current temperature PVst. According to this, by adding a correction value fst(t) to the target temperature SVst and performing feedback control, the increase in computational complexity due to the addition of feedforward control can be suppressed.

[0079] (5) According to the first embodiment, the input control processor 64 controls the amount of solid target material 27a to be input into the target generation unit 260, and the temperature control processor 63 calculates a correction value fst(t) based on the input amount. According to this method, the amount of solid target material 27a to be introduced can be known before the introduction of the solid target material 27a, and the correction value fst(t) can be calculated in a timely manner. Furthermore, it is possible to avoid situations where the amount introduced is too large, making it impossible to suppress temperature fluctuations, or where the amount introduced is too small, causing the solid target supply valve VT2 to be opened and closed frequently and shortening its lifespan.

[0080] (6) According to the first embodiment, the temperature control processor 63 brings the correction value fst(t) closer to 0 while providing feedback control to the heater 8st. According to this, feedforward control can be performed only for the necessary period while feedback control is performed on heater 8st.

[0081] (7) According to the first embodiment, the input control processor 64 controls the next input timing so that the solid target material 27a is input to the target generation unit 260 when the correction value fst(t) is substantially zero. According to this approach, the next feedforward control is started when the correction value fst(t) is effectively zero, thus avoiding the complexity of the feedforward control calculation.

[0082] (8) According to the first embodiment, the target generation unit 260 includes a first region for melting a solid target material 27a internally to generate a liquid target material 27b, and a second region including a nozzle 7nz for discharging the liquid target material 27b generated in the first region. The target generation unit 260 includes a heater 8lt located in the first region and a heater 8st located in the second region. The temperature control processor 63 performs feedforward control while feedback controlling at least one of the heaters 8lt and 8st. According to this, the optimal control can be selected for each region within the target generation unit 260.

[0083] In the first embodiment, a case was described in which the heater 8st of the small tank 7st is controlled by feedforward control while also being controlled by feedback control, and the heater 8lt of the large tank 7lt and the heater 8nz of the nozzle 7nz are controlled by feedback control. However, the disclosure is not limited thereto. At least one of the heaters 8lt, 8st, and 8nz may be controlled by feedforward control while also being controlled by feedback control, and the rest may be controlled by feedback control. Furthermore, the small tank 7st may not be provided. In that case, for example, the heater 8lt of the large tank 7lt may be feedback controlled, and the heater 8nz of the nozzle 7nz may be feedforward controlled while also being feedback controlled.

[0084] (9) According to the first embodiment, the temperature control processor 63 performs feedback control on the heater 8lt and feedforward control on the heater 8st while performing feedback control on it. According to this, stabilizing the temperature of the small tank 7st, which is close to the nozzle 7nz, can stabilize the formation of the target 27.

[0085] (10) According to the first embodiment, a filter F is placed between the first region and the second region. According to this, the temperature of the second region can be stabilized when the solid target material 27a is introduced into the first region. In other respects, the first embodiment may be the same as the comparative example.

[0086] 4. Example where feedforward control is selectable. A second embodiment will be described below. The configuration of the target supply system 26 according to the second embodiment may be the same as that described with reference to Figure 2.

[0087] 4.1 Operation 4.1.1 Control of input of solid target material 27a Figure 16 is a flowchart of the input control processor 64 in the second embodiment. The process shown in Figure 16 differs from the process shown in Figure 12 in the following respects.

[0088] When a predetermined amount of solid target material 27a moves to the load lock chamber C2 (S23:YES), the input control processor 64 proceeds to S24c. In S24c, the input control processor 64 notifies the temperature control processor 63 of the timing and amount of solid target material 27a to be introduced, as well as the location to be controlled via feedforward. Subsequently, in S25, the solid target material 27a is introduced into the large tank 7lt.

[0089] The areas subject to feedforward control may be determined according to the amount of solid target material 27a introduced, or they may be selected by the user. In the second embodiment, the heater 8st of the small tank 7st is always subjected to feedforward control, and it is selectable whether or not to perform feedforward control on the heater 8lt of the large tank 7lt and the heater 8nz of the nozzle 7nz.

[0090] 4.1.2 Temperature control of the large 7lt tank Figure 17 is a flowchart of the temperature control of the large tank 7lt by the temperature control processor 63 in the second embodiment. The process shown in Figure 17 differs from the process shown in Figure 7 in the following respects.

[0091] In S302, after reading the target temperature SVlt of the large tank 7lt, in S303c, the temperature control processor 63 determines whether or not to perform feedforward control on the heater 8lt of the large tank 7lt. If the large tank 7lt is a target of feedforward control in the process shown in Figure 16, the temperature control processor 63 determines to perform feedforward control (S303c:YES) and proceeds to S304b. If the large tank 7lt is not a target of feedforward control, the temperature control processor 63 determines not to perform feedforward control (S303c:NO) and proceeds to S306.

[0092] In S304b, the temperature control processor 63 calculates a correction value flt(t) for the temperature of the large tank 7lt by feedforward control calculation. The correction value flt(t) is calculated based on the timing and amount of solid target material 27a to be added, which are received from the input control processor 64. The correction value flt(t) is a function of time, as shown by the following formula. flt(t) = N·Alt·exp(-t / τlt) Here, Alt is the control gain and τlt is the time constant. The correction value flt(t) is a function that decays and approaches 0 as time t elapses.

[0093] In S305b, the temperature control processor 63 calculates the corrected target temperature SVltr by adding a correction value flt(t) to the target temperature SVlt of the large tank 7lt. The target temperature SVlt is an example of a first target value in this disclosure, and the corrected target temperature SVltr is an example of a second target value in this disclosure. In S307b, when calculating the temperature deviation elt, the corrected target temperature SVltr is used.

[0094] 4.1.3 Temperature control of small 7st tank The temperature control of the small tank 7st can be achieved using a combination of feedback control and feedforward control, similar to that shown in Figure 13.

[0095] 4.1.4 Temperature control of nozzle 7nz Figure 18 is a flowchart of the temperature control of nozzle 7nz by the temperature control processor 63 in the second embodiment. The temperature control of nozzle 7nz corresponds to the temperature control of the large tank 7lt described with reference to Figure 17, with the following points replaced. Replace step numbers starting with "S3" with step numbers starting with "S5". Replace the target temperature SVlt for the large tank 7lt with the target temperature SVnz for nozzle 7nz. Replace the temperature correction value flt(t) for the large tank 7lt with the temperature correction value fnz(t) for the nozzle 7nz. Replace the correction target temperature SVltr for the large tank 7lt with the correction target temperature SVnzr for nozzle 7nz. Replace the current temperature PVlt of the large tank 7lt with the current temperature PVnz of nozzle 7nz. Replace the temperature deviation elt with the temperature deviation enz. Replace the current value Clt for heater 8lt with the current value Cnz for heater 8nz.

[0096] The correction value fnz(t) is a function of time given by the following formula. fnz(t) = N·Anz·exp(-t / τnz) Here, Anz is the control gain and τnz is the time constant. The correction value fnz(t) is a function that decays and approaches 0 as time t elapses.

[0097] The set values ​​of the control gains Alt, Ast, and Anz for calculating the correction values ​​flt(t), fst(t), and fnz(t) may be different from each other. The set values ​​of the time constants τlt, τst, and τnz for calculating the correction values ​​flt(t), fst(t), and fnz(t) may also be different from each other.

[0098] 4.1.5 Block Diagram Figure 19 is a block diagram of temperature control in the second embodiment. In the second embodiment, the power-on control processor 64 notifies the temperature control processor 63 of the target location for feedforward control.

[0099] If the large tank 7lt is the target of feedforward control, the temperature control processor 63 uses the corrected target temperature SVltr, corrected by the correction value flt(t), to perform feedback control of the heater 8lt of the large tank 7lt. If the large tank 7lt is not the target of feedforward control, feedback control is performed in the same manner as in the comparative example.

[0100] If the nozzle 7nz is the target of feedforward control, the temperature control processor 63 uses the corrected target temperature SVnzr, corrected by the correction value fnz(t), to perform feedback control of the heater 8nz of the nozzle 7nz. If the nozzle 7nz is not the target of feedforward control, feedback control is performed in the same manner as in the comparative example.

[0101] The small tank 7st is always subject to feedforward control, and the temperature control processor 63 uses the corrected target temperature SVstr, which has been corrected by the correction value fst(t), to perform feedback control of the heater 8st of the small tank 7st.

[0102] 4.2 Effect (11) According to the second embodiment, at least one of the heaters 8lt and 8nz is selectable to be feedforward controlled while being feedback controlled. According to this, the optimal control can be selected depending on the situation, such as the amount of solid target material 27a that is input.

[0103] In the second embodiment, the case in which the heater 8st of the small tank 7st is always controlled by feedforward control was described, but the disclosure is not limited thereto. It may be possible to select whether or not to control the heater 8st of the small tank 7st by feedforward control.

[0104] (12) According to the second embodiment, the temperature control processor 63 performs feedforward control of the heater 8lt using a first set value such as a time constant τlt while performing feedback control of the heater 8st. It also performs feedforward control of the heater 8st using a second set value such as a time constant τst that is different from the first set value while performing feedback control of the heater 8st. According to this, the feedforward control settings can be changed for each region, enabling precise temperature control. In all other respects, the second embodiment may be the same as the first embodiment.

[0105] 5. Example of feedforward control of the temperature of the small tank 7st and nozzle 7nz. A third embodiment will be described below. The configuration of the target supply system 26 according to the third embodiment may be the same as that described with reference to Figure 2.

[0106] 5.1 Operation 5.1.1 Input control of solid target material 27a The input control of the solid target material 27a can be the same as in Figure 12.

[0107] 5.1.2 Temperature control of the large 7lt tank Temperature control for the large 7lt tank can be done using the same feedback control as shown in Figure 7.

[0108] 5.1.3 Temperature control of small 7st tank The temperature control of the small tank 7st can be achieved using a combination of feedback control and feedforward control, similar to that shown in Figure 13.

[0109] 5.1.4 Temperature control of nozzle 7nz Figure 20 is a flowchart of the temperature control of the nozzle 7nz by the temperature control processor 63 in the third embodiment. The process shown in Figure 20 differs from the process shown in Figure 9 in the following respects.

[0110] In S502, after reading the target temperature SVnz of the nozzle 7nz, in S504b, the temperature control processor 63 calculates a correction value fnz(t) for the temperature of the nozzle 7nz by feedforward control calculation. The correction value fnz(t) is calculated based on the feeding timing and amount of solid target material 27a received from the feeding control processor 64. The correction value fnz(t) may be the same as that described in the second embodiment. The set values ​​for the time constant τnz and control gain Anz used to calculate the temperature correction value fnz(t) for nozzle 7nz may be larger than the set values ​​for the time constant τst and control gain Ast used to calculate the temperature correction value fst(t) for small tank 7st. The correction value fnz(t) may be a function that decays more slowly than the correction value fst(t).

[0111] In S505b, the temperature control processor 63 calculates a corrected target temperature SVnzr by adding a correction value fnz(t) to the target temperature SVnz of the nozzle 7nz. The target temperature SVnz is an example of a first target value in this disclosure, and the corrected target temperature SVnzr is an example of a second target value in this disclosure. In S507b, when calculating the temperature deviation enz, the corrected target temperature SVnzr is used.

[0112] 5.1.5 Block Diagram Figure 21 is a block diagram of temperature control in the third embodiment. In the third embodiment, the temperature control processor 63 adds a correction value fnz(t), calculated by feedforward control calculation based on the input timing and input amount, to the target temperature SVnz of the nozzle 7nz. Based on the corrected target temperature SVnzr to which the correction value fnz(t) has been added, feedback control of the heater 8nz of the nozzle 7nz is performed.

[0113] For the temperature of the large 7lt tank, feedforward control based on the timing and amount of input is not required, and feedback control may be performed as in the comparative example.

[0114] 5.2 Simulation Results Figure 22 shows the results of a simulation of the temperature change of the liquid target substance 27b inside the small tank 7st in the third embodiment. The temperature of the liquid target substance 27b decreases after the solid target substance 27a is added, and then recovers through feedback control.

[0115] Figure 22 shows the temperature correction value fst(t) for the small tank 7st and the temperature correction value fnz(t) for the nozzle 7nz. The time constant τst for the correction value fst(t) is set to approximately 10 seconds, for example, and the time constant τnz for the correction value fnz(t) is set to approximately 20 seconds. The temperature of the liquid target material 27b is lowest after both the correction value fst(t) and the correction value fnz(t) have become substantially zero. The next solid target material 27a is introduced into the target generation unit 260 only after this point.

[0116] The temperature decrease of the liquid target material 27b is slight compared to the temperature decrease in the first embodiment. Because the temperature decrease is slight, the occurrence of target formation defects is suppressed. This allows for stable generation of EUV light.

[0117] 5.3 Effect (13) According to the third embodiment, the target generation unit 260 includes a large tank 7lt, a nozzle 7nz, and a small tank 7st between them, wherein a heater 8lt is provided in the large tank 7lt, a heater 8st is provided in the small tank 7st, and a heater 8nz is provided in the nozzle 7nz. According to this, by placing heaters in the large tank 7lt, the small tank 7st, and the nozzle 7nz, precise temperature control becomes possible. In other respects, the third embodiment may be the same as the first embodiment.

[0118] As described in the first to third embodiments, the small tank 7st may always be a target of feedforward control. The nozzle 7nz may be subject to feedback control only, as described in the first embodiment; it may be selectable to use feedforward control, as described in the second embodiment; or it may always be subject to feedforward control, as described in the third embodiment.

[0119] 6. Example of feedforward control using the current correction value fcst(t) A fourth embodiment will be described below. The configuration of the target supply system 26 according to the fourth embodiment may be the same as that described with reference to Figure 2.

[0120] 6.1 Operation 6.1.1 Control of input of solid target material 27a The input control of the solid target material 27a can be the same as in Figure 12.

[0121] 6.1.2 Temperature control of the large 7lt tank Temperature control for the large 7lt tank can be done using the same feedback control as shown in Figure 7.

[0122] 6.1.3 Temperature control of small 7st tank Figure 23 is a flowchart of the temperature control of the small tank 7st by the temperature control processor 63 in the fourth embodiment. The process shown in Figure 23 differs from the process shown in Figure 8 in the following respects.

[0123] In S408, the current value Cst of heater 8st is calculated by PID control calculation using the target temperature SVst and the current temperature PVst. Then, in S409d, the temperature control processor 63 calculates a correction value fcst(t) for the heater 8st current by feedforward control calculation. The correction value fcst(t) is calculated based on the timing and amount of solid target material 27a that is fed in, as received from the feeding control processor 64. The correction value fcst(t) is a function of time shown by the following formula. fcst(t)=N·Acst·exp(-t / τcst) Here, Acst is the control gain and τcst is the time constant. The correction value fcst(t) is a function that decays and approaches 0 as time t elapses.

[0124] In S410d, the temperature control processor 63 calculates a corrected current value Cstr by adding a correction value fcst(t) to the current value Cst of the heater 8st. The current value Cst corresponds to the first current value in this disclosure, and the corrected current value Cstr corresponds to the second current value in this disclosure. When outputting a heater control signal in S411, the corrected current value Cstr is used.

[0125] 6.1.4 Temperature control of nozzle 7nz The temperature control of nozzle 7nz can be performed using the same feedback control as shown in Figure 9.

[0126] 6.1.5 Block Diagram Figure 24 is a block diagram of temperature control in the fourth embodiment. In the fourth embodiment, the temperature control processor 63 adds a correction value fcst(t), calculated by a feedforward control calculation based on the input timing and input amount, to the heater 8st current value Cst, calculated by a PID control calculation. The heater 8st is controlled using the corrected current value Cstr, to which the correction value fcst(t) has been added.

[0127] Regarding the temperature of the large tank 7lt and the nozzle 7nz, feedforward control based on the timing and amount of injection is not required, and feedback control may be performed as in the comparative example.

[0128] 6.2 Simulation Results Figure 25 shows the results of a simulation of the temperature change of the liquid target substance 27b inside the small tank 7st in the fourth embodiment. The temperature of the liquid target substance 27b decreases after the solid target substance 27a is added, and then recovers through feedback control.

[0129] Figure 25 also shows the correction value fcst(t) for the heater 8st current. The time constant τcst of the correction value fcst(t) is set to, for example, about 100 seconds, and the temperature of the liquid target material 27b, which has decreased, recovers after the correction value fcst(t) has become substantially zero. The next solid target material 27a is introduced into the target generation unit 260 only after that.

[0130] In the comparative example, the temperature drop of the liquid target substance 27b was 0.1°C or more, whereas in the fourth embodiment, it was less than 0.1°C. Because the temperature drop is within an acceptable range, the occurrence of target formation defects is suppressed. Furthermore, in the fourth embodiment, it is possible to reduce the overshoot after the temperature has recovered following an initial drop. This allows for more stable generation of EUV light.

[0131] 6.3 Effect (14) According to the fourth embodiment, the temperature control processor 63 reads the target temperature SVst from the target generation unit 260 and calculates the current value Cst of the heater 8st by performing a feedback control calculation based on the target temperature SVst and the current temperature PVst. The temperature control processor 63 calculates a corrected current value Cstr by adding a correction value fcst(t) including a feedforward element to the current value Cst and controls the heater 8st according to the corrected current value Cstr. According to this, by adding a correction value fcst(t) to the current value Cst and performing feedback control, the increase in computational complexity due to the addition of feedforward control can be suppressed.

[0132] (15) According to the fourth embodiment, the input control processor 64 controls the amount of solid target material 27a to be input into the target generation unit 260, and the temperature control processor 63 calculates a correction value fcst(t) based on the input amount. According to this method, the amount of solid target material 27a to be introduced can be known before the introduction of the solid target material 27a, and the correction value fcst(t) can be calculated in a timely manner. Furthermore, it is possible to avoid situations where the amount introduced is too large, making it impossible to suppress temperature fluctuations, or where the amount introduced is too small, causing the solid target supply valve VT2 to be opened and closed frequently and shortening its lifespan.

[0133] (16) According to the fourth embodiment, the temperature control processor 63 controls the heater 8st according to the correction current value Cstr and brings the correction value fcst(t) closer to 0. According to this, feedforward control can be performed only for the necessary period while feedback control is performed on heater 8st.

[0134] (17) According to the fourth embodiment, the input control processor 64 controls the next input timing so that the solid target material 27a is input to the target generation unit 260 when the correction value fcst(t) has become substantially zero. According to this approach, the next feedforward control is started when the correction value fcst(t) is effectively zero, thus avoiding the complexity of the feedforward control calculation.

[0135] In the fourth embodiment, a case in which the heater 8st of the small tank 7st is feedforward controlled has been described, but the disclosure is not limited thereto. The heater 8lt of the large tank 7lt or the heater 8nz of the nozzle 7nz may also be feedforward controlled using a corrected current value. It may be possible to select whether or not to perform feedforward control on each of the heaters 8lt, 8st, and 8nz. In other respects, the fourth embodiment may be the same as the first embodiment.

[0136] 7. Example where the waveform of the current correction value fcst(t) is a square wave. Figure 26 shows the results of a simulation of the temperature change of the liquid target substance 27b inside the small tank 7st in the fifth embodiment.

[0137] Figure 26 also shows the correction value fcst(t) for the heater 8st current. In the fifth embodiment, the correction value fcst(t) is not an attenuating function, but a square wave as shown in the following equation. fcst(t) = N·Ac(0≦t≦T) fcst(t)=0(t<0,T <t) Here, Ac is the control gain and T is the time width of the square wave. Using a square wave makes it easier to calculate the correction value fcst(t). The time width T is set to, for example, about 200 seconds, and the temperature of the liquid target material 27b is lowest after the correction value fcst(t) has become virtually zero. The next solid target material 27a is introduced into the target generation unit 260 even later.

[0138] The temperature of the liquid target substance 27b does not decrease significantly during the period when the correction value fcst(t) is a constant value N·Ac, and may even increase sharply. However, it may decrease when the correction value fcst(t) switches to 0. The temperature change of the liquid target substance 27b can be adjusted by changing the control gain Ac and the time width T of the square wave. In all other respects, the fifth embodiment may be the same as the fourth embodiment.

[0139] 8. Other Figure 27 schematically shows the configuration of the exposure apparatus 6a connected to the EUV light generation system 11. In Figure 27, the exposure apparatus 6a, which is an EUV light utilization apparatus 6 (see Figure 1), includes a mask irradiation unit 608 and a workpiece irradiation unit 609. The mask irradiation unit 608 illuminates the mask pattern on the mask table MT via a reflective optical system using EUV light incident from the EUV light generation system 11. The workpiece irradiation unit 609 images the EUV light reflected by the mask table MT onto a workpiece (not shown) placed on the workpiece table WT via a reflective optical system. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist. The exposure apparatus 6a exposes the workpiece to EUV light reflecting the mask pattern by synchronously moving the mask table MT and the workpiece table WT in parallel. By transferring a device pattern onto a semiconductor wafer through this exposure process, an electronic device can be manufactured.

[0140] Figure 28 schematically shows the configuration of the inspection device 6b connected to the EUV light generation system 11. In Figure 28, the inspection apparatus 6b, which is an EUV light utilization apparatus 6 (see Figure 1), includes an illumination optical system 603 and a detection optical system 606. The illumination optical system 603 reflects EUV light incident from the EUV light generation system 11 and irradiates the mask 605 placed on the mask stage 604. The mask 605 here includes mask blanks before a pattern is formed. The detection optical system 606 reflects the EUV light from the illuminated mask 605 and forms an image on the light-receiving surface of the detector 607. The detector 607, having received the EUV light, acquires an image of the mask 605. The detector 607 is, for example, a TDI (time delay integration) camera. Based on the image of the mask 605 acquired through the above process, defects in the mask 605 are inspected, and a mask suitable for the manufacture of an electronic device is selected using the inspection results. Then, the pattern formed on the selected mask can be exposed and transferred onto a photosensitive substrate using the exposure apparatus 6a to manufacture an electronic device.

[0141] The above description is intended to be illustrative, not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the embodiments of this disclosure without departing from the claims. It will also be apparent to those skilled in the art that the embodiments of this disclosure can be used in combination.

[0142] Terms used in this specification and throughout the claims should be interpreted as "non-limiting" unless otherwise specified. For example, the terms "include" or "contained" should be interpreted as "not limited to those described as included." The term "possess" should be interpreted as "not limited to those described as possessing." The indefinite article "one" should be interpreted as "at least one" or "one or more." The term "at least one of A, B, and C" should be interpreted as "A," "B," "C," "A+B," "A+C," "B+C," or "A+B+C." Furthermore, it should be interpreted as including combinations of these with anything other than "A," "B," and "C."

Claims

1. A target generation unit that melts a solid target material internally to produce a liquid target material and discharges the liquid target material, The target generation unit includes an input mechanism for introducing the solid target material, A heater arranged in the target generation unit, A sensor for detecting the temperature of the target generation unit, It is a processor, The timing at which the solid target material is introduced into the target generation unit is controlled. The heater is feedback controlled based on the current temperature detected by the sensor. The heater is controlled by feedback control, and the heater is controlled by feedforward control based on the timing of activation. The aforementioned processor, A target supply system equipped with, A laser device that irradiates the liquid target substance, which has been discharged from the target supply system and reached a predetermined area, with pulsed laser light. An EUV focusing mirror that focuses extreme ultraviolet light emitted from the plasma generated in the predetermined region, An extreme ultraviolet light generating device equipped with [a specific feature].

2. An extreme ultraviolet light generating apparatus according to claim 1, The processor feedforward controls the heater so that the temperature of the target generation unit drops to less than 0.1°C. Extreme ultraviolet light generator.

3. An extreme ultraviolet light generating apparatus according to claim 1, The processor performs feedforward control of the heater in accordance with the control cycle of the heater's feedback control. Extreme ultraviolet light generator.

4. An extreme ultraviolet light generating apparatus according to claim 1, The aforementioned processor, The first target value of the temperature of the target generation unit is read, A second target value is calculated by adding a correction value including a feedforward element to the first target value. The heater is feedback controlled based on the second target value and the current temperature. Extreme ultraviolet light generator.

5. An extreme ultraviolet light generating device according to claim 4, The aforementioned processor, The amount of the solid target material introduced into the target generation unit is controlled. The correction value is calculated based on the input amount. Extreme ultraviolet light generator.

6. An extreme ultraviolet light generating device according to claim 4, The processor controls the heater with feedback while bringing the correction value closer to zero. Extreme ultraviolet light generator.

7. An extreme ultraviolet light generating apparatus according to claim 6, The processor controls the feeding timing such that the solid target material is fed into the target generation unit when the correction value is substantially zero. Extreme ultraviolet light generator.

8. An extreme ultraviolet light generating apparatus according to claim 1, The target generation unit includes a first region for melting the solid target material internally to generate the liquid target material, and a second region including a nozzle for discharging the liquid target material generated in the first region. The heater includes a first heater located in the first region and a second heater located in the second region. The aforementioned processor, Feedforward control is performed while feedback control is performed on at least one of the first and second heaters. Extreme ultraviolet light generator.

9. An extreme ultraviolet light generating apparatus according to claim 8, The aforementioned processor, The first heater is controlled by feedback, The second heater is controlled by feedforward control while also being controlled by feedback control. Extreme ultraviolet light generator.

10. An extreme ultraviolet light generating device according to claim 9, A filter is placed between the first region and the second region. Extreme ultraviolet light generator.

11. An extreme ultraviolet light generating apparatus according to claim 8, The aforementioned processor, At least one of the first and second heaters is selectable to either perform feedforward control while performing feedback control. Extreme ultraviolet light generator.

12. An extreme ultraviolet light generating apparatus according to claim 8, The aforementioned processor, The first heater is controlled using a first setpoint while feedback control is performed, The second heater is controlled using a second set value different from the first set value, while feedback control is performed on the second heater. Extreme ultraviolet light generator.

13. An extreme ultraviolet light generating apparatus according to claim 8, The first region includes the first tank, The second region further includes a second tank between the first tank and the nozzle, The heater further includes a third heater located in the second region, The second heater is located in the second tank, and the third heater is located in the nozzle. Extreme ultraviolet light generator.

14. An extreme ultraviolet light generating apparatus according to claim 1, The aforementioned processor, The target temperature of the target generation unit is read, The first current value of the heater is calculated by a feedback control calculation based on the target temperature and the current temperature. A second current value is calculated by adding a correction value including a feedforward element to the first current value. The heater is controlled according to the second current value. Extreme ultraviolet light generator.

15. An extreme ultraviolet light generating apparatus according to claim 14, The aforementioned processor, The amount of the solid target material introduced into the target generation unit is controlled. The correction value is calculated based on the input amount. Extreme ultraviolet light generator.

16. An extreme ultraviolet light generating apparatus according to claim 14, The processor controls the heater according to the second current value and brings the correction value closer to zero. Extreme ultraviolet light generator.

17. An extreme ultraviolet light generating apparatus according to claim 16, The processor controls the feeding timing such that the solid target material is fed into the target generation unit when the correction value is substantially zero. Extreme ultraviolet light generator.

18. A method for manufacturing electronic devices, A target generation unit that melts a solid target material internally to produce a liquid target material and discharges the liquid target material, The target generation unit includes an input mechanism for introducing the solid target material, A heater arranged in the target generation unit, A sensor for detecting the temperature of the target generation unit, It is a processor, The timing at which the solid target material is introduced into the target generation unit is controlled. The heater is feedback controlled based on the current temperature detected by the sensor. The heater is controlled by feedback control, and the heater is controlled by feedforward control based on the timing of activation. The aforementioned processor, A target supply system equipped with, A laser device that irradiates the liquid target substance, which has been discharged from the target supply system and reached a predetermined area, with pulsed laser light. An EUV focusing mirror that focuses extreme ultraviolet light emitted from the plasma generated in the predetermined region, Extreme ultraviolet light is generated by an extreme ultraviolet light generation device equipped with the following: Extreme ultraviolet light is output to the exposure device, In order to manufacture electronic devices, extreme ultraviolet light is exposed onto a photosensitive substrate in the exposure apparatus. A method for manufacturing electronic devices, including the following.

19. A method for manufacturing electronic devices, A target generation unit that melts a solid target material internally to produce a liquid target material and discharges the liquid target material, The target generation unit includes an input mechanism for introducing the solid target material, A heater arranged in the target generation unit, A sensor for detecting the temperature of the target generation unit, It is a processor, The timing at which the solid target material is introduced into the target generation unit is controlled. The heater is feedback controlled based on the current temperature detected by the sensor. The heater is controlled by feedback control, and the heater is controlled by feedforward control based on the timing of activation. The aforementioned processor, A target supply system equipped with, A laser device that irradiates the liquid target substance, which has been discharged from the target supply system and reached a predetermined area, with pulsed laser light. An EUV focusing mirror that focuses extreme ultraviolet light emitted from the plasma generated in the predetermined region, Extreme ultraviolet light generated by an extreme ultraviolet light generator is irradiated onto the mask to inspect for defects in the mask. Using the results of the above inspection, select a mask. The pattern formed on the selected mask is then exposed and transferred onto a photosensitive substrate. A method for manufacturing electronic devices, including the following.

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