Performance recovery method of EUV light generation system, EUV light generation system, and processor

Abstract

To provide a performance recovery method of an EUV light generation system which generates EUV light by irradiating a target with a pulse laser beam.SOLUTION: A performance recovery method of an EUV light generation system executes a first evaluation step of evaluating performance of EUV light while generating the EUV light at constant repetition frequency during a first period, executes an adjustment step of adjusting the performance when an evaluation result by the first evaluation step is not within a normal range, then executes the first evaluation step as a confirmation step, executes a second evaluation step of evaluating the performance of the EUV light while generating the EUV light at the repetition frequency during a second period longer than the first period, when the evaluation result by the confirmation step is within a normal range, ends the processing when the evaluation result by the confirmation step is not within the normal range, and evaluates an index related to a position where a target is irradiated with a pulse laser beam in the first evaluation step and the second evaluation step.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a method for recovering the performance of an EUV light generation system, an EUV light generation system, and a processor.

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 a semiconductor exposure apparatus that combines an apparatus for generating extreme ultraviolet (EUV) light having a wavelength of about 13 nm and a reduction projection reflective optical system is expected.

[0003] As an EUV light generation system, the development of a system including an LPP (Laser Produced Plasma) type EUV light generation apparatus in which plasma generated by irradiating a target substance with laser light is used is in progress.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] A method for restoring the performance of an EUV light generation system according to one aspect of the present disclosure is a method for restoring the performance of an EUV light generation system that generates EUV light by irradiating a target with pulsed laser light. The method includes performing a first evaluation step of evaluating the performance of EUV light while generating EUV light at a constant repetition frequency during a first period. If the evaluation result by the first evaluation step is not within the normal range, an adjustment step of adjusting the performance is performed, and then the first evaluation step is performed as a confirmation step. If the evaluation result by the confirmation step is within the normal range, a second evaluation step of evaluating the performance of EUV light while generating EUV light at the repetition frequency during a second period longer than the first period is performed. If the evaluation result by the confirmation step is not within the normal range, the process is terminated. In the first evaluation step and the second evaluation step, an index related to the irradiation position of the pulsed laser light on the target is evaluated.

[0006] An EUV light generation system according to one aspect of the present disclosure is an EUV light generation system that generates EUV light by irradiating a target with pulsed laser light. The system includes a processor. The processor performs a first evaluation step of evaluating the performance of EUV light while generating EUV light at a constant repetition frequency during a first period. If the evaluation result by the first evaluation step is not within the normal range, an adjustment step of adjusting the performance is performed, and then the first evaluation step is performed as a confirmation step. If the evaluation result by the confirmation step is within the normal range, a second evaluation step of evaluating the performance of EUV light while generating EUV light at the repetition frequency during a second period longer than the first period is performed. If the evaluation result by the confirmation step is not within the normal range, the process is terminated. In the first evaluation step and the second evaluation step, an index related to the irradiation position of the pulsed laser light on the target is evaluated.

[0007] A processor according to one aspect of the present disclosure is a processor used in an EUV light generation system that generates EUV light by irradiating a target with pulsed laser light. The processor executes a first evaluation step of evaluating the performance of EUV light while generating EUV light at a constant repetition frequency during a first period. If the evaluation result by the first evaluation step is not within the normal range, an adjustment step of adjusting the performance is executed, and then the first evaluation step is executed as a confirmation step. If the evaluation result by the confirmation step is within the normal range, a second evaluation step of evaluating the performance of EUV light while generating EUV light at the repetition frequency during a second period longer than the first period is executed. If the evaluation result by the confirmation step is not within the normal range, the process is terminated. In the first evaluation step and the second evaluation step, an index related to the irradiation position of the pulsed laser light on the target is evaluated.

Brief Description of the Drawings

[0008] Some embodiments of the present disclosure will be described below by way of example only with reference to the accompanying drawings.

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[0009] <Content> 1. Overall Description of EUV Light Generation System 1.1 Configuration 1.2 Operation 2. EUV Light Generation System According to Comparative Example 2.1 Configuration 2.2 Operation 2.3 Problems 3. EUV Light Generation System According to First Embodiment 3.1 Configuration 3.2 Operation 3.3 Actions and Effects 4. EUV Light Generation System According to Second Embodiment 4.1 Configuration 4.2 Operation 4.3 Actions and Effects

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. Also, not all of the configurations and operations described in each embodiment are essential as the configurations and operations of the present disclosure. Note that the same reference numerals are assigned to the same components, and redundant descriptions are omitted.

[0011] 1. Overall Description of EUV Light Generation System 1.1 Configuration FIG. 1 schematically shows the configuration of an EUV light generation system 11 of the LPP method. The EUV light generation apparatus 1 is used together with a laser apparatus 3. In the present disclosure, a system including the EUV light generation apparatus 1 and the laser apparatus 3 is referred to as an EUV light generation system 11. The EUV light generation apparatus 1 includes a chamber 2 and a target supply device 25. The chamber 2 is a sealable container. The target supply device 25 supplies a target 27 into the chamber 2. The material of the target 27 may include tin, terbium, gadolinium, lithium, xenon, or any combination of two or more of them.

[0012] A through hole is provided in the wall of the chamber 2. The through hole is blocked by a window 21, and the pulsed laser light 31 output from the laser apparatus 3 passes through the window 21. Inside the chamber 2, an EUV condenser mirror 23 having a reflective surface in the shape of a rotational ellipsoid is disposed. The EUV condenser mirror 23 has first and second foci. A multilayer reflective film in which molybdenum and silicon are alternately laminated is formed on the surface of the EUV condenser mirror 23. The EUV condenser mirror 23 is arranged such that its first focus is located in the plasma generation region R1 and its second focus is located at the intermediate focus point IF. A through hole 24 is formed in the central portion of the EUV condenser mirror 23, and the pulsed laser light 31 passes through the through hole 24.

[0013] The EUV light generation apparatus 1 includes a processor 5, a target sensor 4, etc. The target sensor 4 detects the presence, trajectory, position, speed, etc. of the target 27. The target sensor 4 may have an imaging function.

[0014] Further, the EUV light generation apparatus 1 includes a connection portion 29 that communicates the inside of the chamber 2 with the inside of an external device 6. Inside the connection portion 29, a wall 291 having an aperture 293 formed therein is provided. The wall 291 is arranged such that the aperture 293 is located at the second focus of the EUV condenser mirror 23. For example, the external device 6 is an exposure apparatus.

[0015] Furthermore, the EUV light generation apparatus 1 includes a laser light transmission apparatus 50, a laser light condensing optical system 60, and a target recovery unit 28 for recovering the target 27. The laser light transmission apparatus 50 includes an optical element for defining the transmission state of the laser light, and an actuator for adjusting the position, posture, etc. of this optical element.

[0016] Furthermore, inside the chamber 2, buffer gas is supplied from a buffer gas supply apparatus (not shown) in order to protect the EUV condensing mirror 23 from fragment debris generated during plasma generation. Inside the chamber 2, the buffer gas supplied from the supply port of the buffer gas supply apparatus flows in the direction of a dust removal apparatus (not shown), forming a flow field. The buffer gas is hydrogen, nitrogen, or a noble gas such as helium or argon.

[0017] 1.2 Operation Referring to FIG. 1, the operation of an exemplary LPP-type EUV light generation system 11 will be described. The pulsed laser light 31 output from the laser apparatus 3 passes through the laser light transmission apparatus 50, passes through the window 21, and enters the chamber 2. The pulsed laser light 31 that has entered the chamber 2 travels inside the chamber 2 along the laser light path, is condensed by the laser light condensing optical system 60, and is irradiated onto the target 27.

[0018] The target supply apparatus 25 outputs the target 27 toward the plasma generation region R1 inside the chamber 2. The target 27 is irradiated with the pulsed laser light 31. The target 27 irradiated with the pulsed laser light 31 is turned into plasma, and radiation light 32 is emitted from the plasma. The EUV light 33 included in the radiation light 32 is selectively reflected by the EUV condensing mirror 23. The EUV light 33 reflected by the EUV condensing mirror 23 is condensed at the intermediate focus point IF and output to the external apparatus 6. Note that a plurality of pulses included in the pulsed laser light 31 may be irradiated onto one target 27.

[0019] The processor 5 controls the entire EUV light generation system 11. Based on the detection results of the target sensor 4, the processor 5 controls the timing at which the target 27 is output, the output direction of the target 27, and the like. Further, the processor 5 controls the oscillation timing of the laser device 3, the traveling direction of the pulsed laser light 31, the focusing position, and the like. The various controls described above are merely examples, and other controls may be added as necessary.

[0020] 2. EUV Light Generation System According to Comparative Example 2.1 Configuration

[0021] FIG. 2 shows the configuration of the EUV light generation system 11 according to the comparative example. The EUV light generation apparatus 1 according to the comparative example includes a laser energy sensor 58, a beam sensor 70, a target size sensor 80, and an EUV energy sensor 82 in addition to a chamber 2, a target supply device 25, a processor 5, a target sensor 4, a laser light transmission device 50, and a laser light focusing optical system 60.

[0022] The laser device 3 outputs a plurality of pulsed laser lights 31 to irradiate one target 27 supplied to the plasma generation region R1. As the plurality of pulsed laser lights 31, for example, a prepulse laser light 31a and a main pulse laser light 31b are output in this order. Hereinafter, the prepulse laser is denoted as "PPL", and the main pulse laser is denoted as "MPL".

[0023] The laser device 3 includes a PPL device 3a that outputs PPL light 31a and an MPL device 3b that outputs MPL light 31b. The PPL device 3a is composed of a YAG laser device or a laser device using Nd:YVO 4 The MPL device 3b is composed of, for example, a CO 2 laser device. Note that the MPL device 3b may be composed of a YAG laser device or a laser device using Nd:YVO 4

[0024] Processor 5 includes an EUV light generation processor 5a and a target processor 5b. The EUV light generation processor 5a controls the laser device 3, the laser light transmission device 50, etc. The target processor 5b controls the target supply device 25.

[0025] The EUV light generation processor 5a is constituted by, for example, a CPU (Central Processing Unit). The EUV light generation processor 5a executes the above various processes based on a program stored in a built-in or connected memory. Some or all of the functions of the EUV light generation processor 5a may be realized using integrated circuits typified by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0026] The target supply device 25 includes a tank 251, a nozzle 252, a heater 253, a pressure regulator 254, and a piezo element 255. The heater 253, the pressure regulator 254, and the piezo element 255 are controlled by the target processor 5b.

[0027] The target sensor 4 is configured to include a light receiving element or an imaging element, an illumination device, and a high-speed shutter, and detects the passing timing, generation interval, speed, etc. of the target 27 passing through the target detection region R2, and outputs a detection signal to the EUV light generation processor 5a. Hereinafter, a signal representing the timing when the target 27 passes through the target detection region R2 is referred to as a "target passing timing signal". The target passing timing signal is included in the detection signal output by the target sensor 4.

[0028] The laser light transmission device 50 includes reflection control mirrors 51, 52, high reflection mirrors 53, 55, a combiner element 56, and beam splitters 54, 57.

[0029] The reflection control mirror 51 includes a high-reflection mirror 511 and a stage 512. The high-reflection mirror 511 is mounted on the stage 512 and is disposed at a position where the PPL light 31a output from the PPL device 3a is incident. The stage 512 is an actuator that changes the angle of the high-reflection mirror 511. The stage 512 is controlled by the EUV light generation processor 5a.

[0030] The reflection control mirror 52 includes a high-reflection mirror 521 and a stage 522. The high-reflection mirror 521 is mounted on the stage 522 and is disposed at a position where the MPL light 31b output from the MPL device 3b is incident. The stage 522 is an actuator that changes the angle of the high-reflection mirror 521. The stage 522 is controlled by the EUV light generation processor 5a.

[0031] The high-reflection mirror 53 is disposed at a position where the PPL light 31a reflected by the reflection control mirror 51 is reflected and incident on the combiner element 56.

[0032] The beam splitter 54 is disposed in the optical path of the MPL light 31b reflected by the reflection control mirror 52. The beam splitter 54 is configured to reflect the MPL light 31b with a high reflectivity and transmit a part of the MPL light 31b toward the laser energy sensor 58.

[0033] The high-reflection mirror 55 is disposed at a position where the MPL light 31b reflected by the beam splitter 54 is reflected and incident on the combiner element 56.

[0034] The reflection control mirror 51 and the high-reflection mirror 53 are arranged such that the PPL light 31a can be incident on the laser light condensing optical system 60 with the target optical performance. The reflection control mirror 52 and the beam splitter 54 are arranged such that the MPL light 31b can be incident on the laser light condensing optical system 60 with the target optical performance. Here, the optical performance refers to the position or angle of the optical axis.

[0035] The laser energy sensor 58 is disposed in the optical path of the MPL light 31b that passes through the beam splitter 54. The laser energy sensor 58 measures the energy of the MPL light 31b that has passed through the beam splitter 54 and outputs the measured value to the EUV light generation processor 5a. The laser energy sensor 58 is not limited to the above arrangement. The laser energy sensor 58 may be arranged such that any high-reflection mirror disposed in the optical path of the MPL light 31b is changed to a beam splitter and the transmitted light thereof can be measured.

[0036] The combiner element 56 is an element that reflects the PPL light 31a and transmits the MPL light 31b. The combiner element 56 is, for example, a polarization beam combiner that combines the optical paths of the PPL light 31a and the MPL light 31b whose polarization directions are orthogonal. The optical path of the PPL light 31a reflected by the combiner element 56 and the optical path of the MPL light 31b transmitted through the combiner element 56 are combined so as to substantially coincide. Note that the combiner element 56 may be configured to reflect the MPL light 31b and transmit the PPL light 31a.

[0037] The PPL light 31a and the MPL light 31b whose optical paths are combined by the combiner element 56 enter the beam splitter 57. The beam splitter 57 reflects a part of the PPL light 31a and the MPL light 31b and makes it enter the laser light condensing optical system 60, and transmits the other part and makes it enter the beam sensor 70. Note that the beam splitter 57 may be configured to transmit a part of the PPL light 31a and the MPL light 31b and make it enter the laser light condensing optical system 60, and reflect the other part and make it enter the beam sensor 70. Hereinafter, for convenience of explanation, the PPL light 31a and the MPL light 31b may be simply referred to as pulsed laser light 31 without distinction.

[0038] The laser light condensing optical system 60 is disposed inside the chamber 2. The laser light condensing optical system 60 is on the optical path of the pulsed laser light 31 that has passed through the window 21 and is disposed between the window 21 and the plasma generation region R1. The laser light condensing optical system 60 includes a laser light condensing mirror 221 and a manipulator 224.

[0039] The laser light focusing mirror 221 reflects the pulsed laser light 31 that has passed through the window 21 and focuses it on the plasma generation region R1. The laser light focusing mirror 221 is mounted on the manipulator 224. The laser light focusing mirror 221 is composed of an off-axis parabolic mirror 222 and a plane mirror 223. Here, the off-axis parabolic mirror 222 is a concave mirror. Note that the off-axis parabolic mirror 222 may be a convex mirror, and an elliptical mirror may be used instead of the plane mirror 223.

[0040] The manipulator 224 is a stage that adjusts at least one of the position and orientation of the laser light focusing mirror 221 so that the pulsed laser light 31 irradiates the target 27. The manipulator 224 is controlled by the EUV light generation processor 5a.

[0041] The beam sensor 70 includes a beam splitter 71, a first optical axis sensor 72, and a second optical axis sensor 73. The beam splitter 71 is an element that reflects the PPL light 31a and transmits the MPL light 31b. The beam splitter 71 is, for example, a polarization beam splitter that separates the optical paths of the PPL light 31a and the MPL light 31b with orthogonal polarization directions. The PPL light 31a separated by the beam splitter 71 enters the first optical axis sensor 72, and the MPL light 31b enters the second optical axis sensor 73.

[0042] The first optical axis sensor 72 is a sensor that detects the optical performance of the PPL light 31a. The second optical axis sensor 73 is a sensor that detects the optical performance of the MPL light 31b. The first optical axis sensor 72 and the second optical axis sensor 73 each output the detection value of the optical performance to the EUV light generation processor 5a.

[0043] Alternatively, a beam splitter may be disposed in the optical path through which only the PPL light 31a propagates, and the first optical axis sensor 72 may be disposed such that a part of the PPL light 31a transmitted or reflected by the beam splitter is incident thereon. Further, a beam splitter may be disposed in the optical path through which only the MPL light 31b propagates, and the second optical axis sensor 73 may be disposed such that a part of the MPL light 31b transmitted or reflected by the beam splitter is incident thereon.

[0044] The beam sensor 70 measures the optical performance of the pulsed laser light 31 immediately before it enters the chamber 2 so that the pulsed laser light 31 enters the chamber 2 with the target optical performance. In this comparative example, the beam sensor 70 measures the optical performance of the pulsed laser light 31 immediately before it enters the laser light condensing optical system 60.

[0045] The target size sensor 80 is attached to the chamber 2. The target size sensor 80 includes an imaging element, and by imaging the plasma generation region R1, it measures the size of a secondary target described later and outputs the measured value to the EUV light generation processor 5a.

[0046] The EUV energy sensor 82 is attached to the chamber 2. The EUV energy sensor 82 measures the energy of the EUV light 33 included in the emitted light 32 emitted by the target 27 in the plasma generation region R1 and outputs the measured value to the EUV light generation processor 5a. Note that a plurality of EUV energy sensors 82 may be provided. Hereinafter, the energy of the EUV light 33 is referred to as "EUV energy".

[0047] 2.2 Operation The operation of the EUV light generation system 11 according to the comparative example will be described. First, the EUV light generation processor 5a outputs set values such as the pulse energy, pulse width, and pulse waveform of the PPL light 31a to the PPL device 3a. Further, the EUV light generation processor 5a outputs set values such as the pulse energy, pulse width, and pulse waveform of the MPL light 31b to the MPL device 3b.

[0048] The target processor 5b controls the heater 253 of the target supply device 25, and heats the material of the target 27 in the tank 251 to a temperature higher than its melting point to melt it. In this comparative example, the material of the target 27 is tin, and the tank 251 is filled with molten liquid tin.

[0049] When the EUV light generation device 1 receives a signal requesting the generation of EUV light from the external device 6, it transmits a droplet generation signal to the target processor 5b. When the target processor 5b receives the droplet generation signal, it controls the pressure in the tank 251 to a predetermined pressure via the pressure regulator 254. As a result, a jet of liquid tin is output from the nozzle 252 at a constant speed.

[0050] The target processor 5b applies a voltage of a predetermined waveform to the piezo element 255 fixed to the nozzle 252 so that droplets of the target 27 are generated from the jet of liquid tin at a predetermined frequency. As a result, the jet of liquid tin output from the nozzle 252 is atomized into droplets. Then, a droplet-shaped target 27 having a predetermined diameter is generated by the combination of a plurality of droplets. The target 27 is generated at a constant generation interval.

[0051] The target sensor 4 detects the timing when the target 27 passes through the target detection region R2, and outputs a target passing timing signal representing the detected timing to the EUV light generation processor 5a. The target sensor 4 may detect the generation interval of the target 27 and the speed of the target 27, and output a detection signal to the EUV light generation processor 5a.

[0052] The EUV light generation processor 5a generates a first light emission trigger signal delayed by a first delay time from the target passing timing signal, and outputs it to the PPL device 3a. The PPL device 3a outputs PPL light 31a having a target pulse energy, pulse width, and pulse waveform in response to the first light emission trigger signal.

[0053] The PPL light 31a is reflected by the reflection control mirror 51, the high reflection mirror 53, the combiner element 56, and the beam splitter 57 in the laser light transmission device 50, and is incident on the laser light condensing optical system 60. The PPL light 31a is condensed by the laser light condensing optical system 60 and irradiated onto the target 27. Note that the droplet-shaped target 27 irradiated with the PPL light 31a is also referred to as the "primary target".

[0054] By the irradiation of the PPL light 31a, the primary target is destroyed and becomes a "secondary target" that diffuses in a mist shape. Here, the mist shape means a state in which microdroplets, clusters, etc. are diffused due to the primary target being destroyed by the PPL light 31a.

[0055] The EUV light generation processor 5a generates a second light emission trigger signal that is delayed by a second delay time from the target passage timing signal and outputs it to the MPL device 3b. The MPL device 3b outputs MPL light 31b having a target pulse energy, pulse width, and pulse waveform in response to the second light emission trigger signal.

[0056] The MPL light 31b is reflected by the reflection control mirror 52, the beam splitter 54, and the high reflection mirror 55 in the laser light transmission device 50, passes through the combiner element 56, and is reflected by the beam splitter 57, thereby being incident on the laser light condensing optical system 60. The MPL light 31b is condensed by the laser light condensing optical system 60 and irradiated onto the target 27 as the secondary target. As a result, the secondary target is turned into plasma, and the radiation light 32 including the EUV light 33 is generated.

[0057] The MPL light 31b that has passed through the beam splitter 54 is incident on the laser energy sensor 58. The laser energy sensor 58 measures the energy of the MPL light 31b and outputs the measured value to the EUV light generation processor 5a.

[0058] The PPL light 31a that has passed through the beam splitter 57 is incident on the beam sensor 70, reflected by the beam splitter 71, and then incident on the first optical axis sensor 72. The first optical axis sensor 72 measures the optical performance of the PPL light 31a and outputs the measured value to the EUV light generation processor 5a.

[0059] The MPL light 31b that has passed through the beam splitter 57 is incident on the beam sensor 70, passes through the beam splitter 71, and is then incident on the second optical axis sensor 73. The second optical axis sensor 73 measures the optical performance of the MPL light 31b and outputs the measured value to the EUV light generation processor 5a.

[0060] The EUV light generation processor 5a controls the angle of the reflection control mirror 51 so that the optical performance of the PPL light 31a measured by the first optical axis sensor 72 reaches the target value. Further, the EUV light generation processor 5a controls the angle of the reflection control mirror 52 so that the optical performance of the MPL light 31b measured by the second optical axis sensor 73 reaches the target value.

[0061] In addition, the target size sensor 80 measures the size of the secondary target after the PPL light 31a irradiates the primary target and outputs the measured value to the EUV light generation processor 5a. The EUV energy sensor 82 measures the EUV energy after the MPL light 31b irradiates the secondary target and outputs the measured value to the EUV light generation processor 5a.

[0062] Figure 3 shows an example of the operation of the EUV light generation system 11 according to the comparative example. In Figure 3, the vertical axis of the graph represents EUV energy, and the horizontal axis represents time.

[0063] The EUV light generation system 11 may output EUV light 33 by burst operation. The burst operation is an operation that repeats a burst period TA during which EUV light 33 is output at a certain repetition frequency and a pause period TB during which EUV light 33 is not output. During the burst period TA, EUV light 33 is output. During the pause period TB, the output of the pulsed laser light 31 is stopped, or the propagation of the pulsed laser light 31 to the plasma generation region R1 is suppressed.

[0064] The burst pattern is defined by data including any one or more of EUV energy, repetition frequency, number of pulses, duty cycle DT, and number of bursts during the burst period TA. The burst pattern may be specified from an external device 6.

[0065] The duty cycle DT is the ratio of the burst period TA to one cycle T of the burst. Specifically, the duty cycle DT is expressed as DT = [TA / (TA + TB)] × 100. The unit of the duty cycle DT is percent.

[0066] When the optical axis of the pulsed laser light 31 focused on the plasma generation region R1 during burst operation deviates from the center of the target 27, problems such as a decrease in EUV energy occur. Since it is difficult to directly measure the deviation between the optical axis of the pulsed laser light 31 and the center of the target 27, the EUV light generation processor 5a controls the energy of the MPL light 31b so as to maintain the EUV energy constant. For example, the EUV light generation processor 5a controls the energy of the MPL light 31b so that the measured value of the EUV energy by the EUV energy sensor 82 is within a predetermined range. Hereinafter, the pulse energy of the MPL light 31b in the plasma generation region R1 is referred to as "MPL energy".

[0067] It is not easy to maintain the EUV energy constant only by controlling the MPL energy. Therefore, the EUV light generation processor 5a performs laser irradiation position control using the average value of the EUV energy or E3σ, which is an index representing the temporal variation of the EUV energy. Further, the EUV light generation processor 5a may perform laser irradiation position control using CE, which is an index representing the conversion efficiency of the MPL energy to the EUV energy. CE is a value obtained by dividing the average value of the EUV energy by the MPL energy. Hereinafter, E3σ is referred to as "E3σ".

[0068] For example, E3σ is calculated by the following formula (1). The unit of E3σ is percent.

[0069]

Number

[0070] Here, σ is the standard deviation of EUV energy for a plurality of pulses included in a unit time. μ is the average value of EUV energy for a plurality of pulses included in a unit time. Therefore, in this case, E3σ represents the value obtained by multiplying the coefficient of variation by 3 and expressing it as a percentage.

[0071] The EUV light generation processor 5a may adjust a plurality of elements of the EUV light generation system 11 so that the output performance of the EUV light 33 becomes a desired value. Such adjustment is called performance recovery. The EUV light generation processor 5a performs performance recovery, for example, in the following cases. For example, the EUV light generation processor 5a performs performance recovery when an error for protecting the device is reported and the laser irradiation is stopped in a continuous operation state. For example, the error is reported when a certain amount or more of fragment debris is generated. Also, the EUV light generation processor 5a performs performance recovery when receiving a signal from the external device 6 indicating that the performance of the EUV light 33 does not meet the required performance. Furthermore, the EUV light generation processor 5a performs performance recovery when the EUV light generation system 11 is maintained. Maintenance includes replacement of the EUV condenser mirror 23, replacement of the target supply device 25, and the like.

[0072] FIG. 4 shows the flow of the performance recovery process according to the comparative example. When the generation of the EUV light 33 stops due to the reporting of an error or the like, various factors can be considered. Therefore, as shown in FIG. 4, the performance recovery process includes a plurality of steps. Actually, the performance recovery process includes 10 or more steps.

[0073] First, as adjustment steps regarding the target 27, the EUV light generation processor 5a executes target diameter adjustment (step S10), droplet coupling adjustment (step S11), and synchronization timing adjustment (step S12).

[0074] The target diameter adjustment is a process of adjusting the frequency of the voltage waveform applied by the target processor 5b to the piezo element 255, using the speed of the target 27 detected by the target sensor 4 as an index. The diameter of the target 27 changes according to the frequency of the voltage waveform.

[0075] The droplet coupling adjustment is a process of adjusting the voltage waveform applied by the target processor 5b to the piezo element 255, using the generation interval of the target 27 detected by the target sensor 4 as an index. For example, in the droplet coupling adjustment, the duty of the voltage waveform is adjusted. The coupling state of the droplets changes according to the duty of the voltage waveform.

[0076] The synchronization timing adjustment is a process of adjusting the first delay time and the second delay time for generating the first light emission trigger signal and the second light emission trigger signal, using the passing timing of the target 27 detected by the target sensor 4 as an index.

[0077] Next, the EUV light generation processor 5a performs adjustment of the irradiation position of the PPL light 31a (step S13), adjustment of the irradiation position of the MPL light 31b (step S14), and performance evaluation of the EUV light 33 (step S15) in a short burst with a short burst period TA. In a short burst, adjustment can be performed ignoring the influence of the thermal load. The thermal load refers to, for example, the amount of heat generated by plasma heating. With the change in the density of the buffer gas due to plasma heating, the position of the target 27 fluctuates.

[0078] The adjustment of the irradiation position of the PPL light 31a is a process of adjusting the irradiation position of the PPL light 31a with respect to the primary target, using the size of the secondary target measured by the target size sensor 80 as an index. For example, the EUV light generation processor 5a controls the manipulator 224 to change the position of the laser light condensing optical system 60, thereby adjusting the irradiation position of the PPL light 31a. The size of the secondary target changes according to the irradiation position of the PPL light 31a.

[0079] The adjustment of the irradiation position of the MPL light 31b is a process of adjusting the irradiation position of the MPL light 31b with respect to the secondary target using CE as an index. For example, the EUV light generation processor 5a adjusts the irradiation position of the MPL light 31b by controlling the stage 522 to change the attitude of the high-reflection mirror 521. CE changes according to the irradiation position of the MPL light 31b.

[0080] The performance evaluation of the EUV light 33 is a process of evaluating the performance of the EUV light 33 using the average value of EUV energy, E3σ, or CE in one burst period as an index.

[0081] Next, the EUV light generation processor 5a performs the adjustment of the irradiation position of the PPL light 31a (step S16), the adjustment of the irradiation position of the MPL light 31b (step S17), and the performance evaluation of the EUV light 33 (step S18) in a long burst with a long burst period TA. In a long burst, adjustment including the influence of the position variation of the target 27 due to the heat load can be performed.

[0082] The adjustment of the irradiation position of the PPL light 31a, the adjustment of the irradiation position of the MPL light 31b, and the performance evaluation of the EUV light 33 in a long burst are the same as in the case of a short burst except that the length of the burst period TA is different.

[0083] 2.3 Problems As described above, in the EUV light generation system 11 according to the comparative example, it is necessary to execute 10 or more steps every time the performance recovery process is performed. This performance recovery process may take several hours. Therefore, when the generation of the EUV light 33 stops due to an error report or the like, it is difficult to quickly return to a state where the performance of the EUV light 33 is ensured by performing the performance recovery process. Thus, it has become an issue to realize a quick return to a state where the performance of the EUV light 33 is ensured.

[0084] 3. EUV Light Generation System According to the First Embodiment The EUV light generation system 11 according to the first embodiment will be described. Components similar to those described above are denoted by the same reference numerals, and redundant descriptions are omitted unless otherwise specified.

[0085] 3.1 Configuration FIG. 5 shows the configuration of the EUV light generation system 11 according to the first embodiment. The configuration of the EUV light generation system 11 according to this embodiment is the same as that of the comparative example, except that the EUV light generation processor 5a is configured to execute a performance recovery process based on the performance recovery program 5c stored in the memory.

[0086] 3.2 Operation The operation of the EUV light generation system 11 according to the first embodiment will be described. The operation of the EUV light generation system 11 according to the first embodiment is the same as that of the comparative example, except for the performance recovery process.

[0087] FIG. 6 shows the flow of the performance recovery process according to the first embodiment. In this embodiment, when the generation of the EUV light 33 stops due to an error report or the like, the EUV light generation processor 5a executes the performance recovery process shown in FIG. 6 based on the performance recovery program 5c. Hereinafter, the evaluation of the performance of the EUV light 33 evaluates an index related to the irradiation position of the pulsed laser light 31 on the target 27. This index is the average value of the EUV energy, E3σ, or CE in one burst period.

[0088] In this embodiment, first, the EUV light generation processor 5a evaluates the performance of EUV light 33 in a long burst and closed loop (step S20). Here, the long burst and closed loop are irradiation conditions simulating the state where the EUV light generation system 11 is continuously operating. For example, the long burst is a burst operation having a burst period TA of about 1 second. The pause period TB is greater than 1 second, and the duty cycle DT is less than 50%. The number of pulses included in the burst period TA is about 20,000. The closed loop means performing feedback control to maintain the EUV energy constant. In step S20, the MPL energy, the irradiation position of the PPL light 31a, and the irradiation position of the MPL light 31b are feedback controlled.

[0089] The EUV light generation processor 5a determines whether the evaluation result obtained in step S20 is within the normal range (step S21). Here, the evaluation result being within the normal range means that the measured values of the above-mentioned indicators are within the normal range. When the evaluation result is within the normal range (step S21: YES), the EUV light generation processor 5a ends the performance recovery process.

[0090] When the evaluation result is not within the normal range (step S21: NO), the EUV light generation processor 5a evaluates the performance of EUV light 33 in a short burst and open loop (step S22). Here, the short burst and open loop are short-term irradiation conditions in which the influence of the thermal load can be ignored. For example, the short burst is a burst operation having a burst period TA of 0.01 milliseconds or more and 10 milliseconds or less. The pause period TB is greater than 1 second, and the duty cycle DT is less than 50%. In the open loop, EUV light 33 is generated without performing feedback control to maintain the EUV energy constant. In this case, the EUV light generation processor 5a does not perform feedback control of the MPL energy by keeping the set value of the MPL energy applied to the MPL device 3b constant, and evaluates the performance of EUV light 33 using the above-mentioned indicators. The burst period TA of the short burst is an example of the "first period" according to the technology of the present disclosure.

[0091] The EUV light generation processor 5a determines whether the evaluation result obtained in step S22 is within the normal range (step S23). This normal range may be different from that in step S21 in the case of a closed loop. Note that steps S22 and S23 are an example of the "first evaluation step" according to the technology of the present disclosure.

[0092] When the evaluation result of the EUV light generation processor 5a is within the normal range (step S23: YES), without performing the adjustment step and confirmation step described later, the process proceeds to step S27.

[0093] When the evaluation result of the EUV light generation processor 5a is not within the normal range (step S23: NO), it performs a short burst and open loop to execute the adjustment step described later (step S24). After that, the EUV light generation processor 5a evaluates the performance of the EUV light 33 again in a short burst and open loop (step S25).

[0094] The EUV light generation processor 5a determines whether the evaluation result obtained in step S25 is within the normal range (step S26). This normal range is the same as the normal range in step S23. Note that steps S25 and S26 are an example of the "confirmation step" according to the technology of the present disclosure.

[0095] When the evaluation result is within the normal range (step S26: YES), the EUV light generation processor 5a proceeds to step S27. On the other hand, when the evaluation result is not within the normal range (step S26: NO), the EUV light generation processor 5a ends the performance recovery process as an abnormal end.

[0096] In step S27, the EUV light generation processor 5a evaluates the performance of the EUV light 33 in a long burst and open loop manner. For example, the long burst is a burst operation having a burst period TA of 50 milliseconds or more and 10 seconds or less. The pause period TB is greater than 1 second, and the duty cycle DT is less than 50%. Step S27 is the same as step S22 except that the burst period TA is different. The burst period TA of the long burst is an example of the "second period" according to the technology of the present disclosure.

[0097] The EUV light generation processor 5a determines whether the evaluation result obtained in step S27 is within the normal range (step S28). This normal range may be different from that in the case of the closed loop in step S21. Note that steps S27 and S28 are an example of the "second evaluation step" according to the technology of the present disclosure.

[0098] When the evaluation result is within the normal range (step S28: YES), the EUV light generation processor 5a ends the performance recovery process as an abnormal end. This is because it is considered that the evaluation result in the closed loop is out of the normal range due to an unknown cause, and it is considered that it is difficult to recover the performance of the EUV light 33 in this performance recovery process, that is, further adjustment is required. Note that when a YES determination is made in step S28, instead of ending abnormally, the performance evaluation in a long burst and closed loop (step S20) may be executed again. When the evaluation result after re-executing the performance evaluation in a long burst and closed loop (step S20) is within the normal range (step S21: YES), the performance recovery process is ended, and when the evaluation result is not within the normal range (step S21: NO), it may be ended abnormally.

[0099] When the evaluation result is not within the normal range (step S28: NO), the EUV light generation processor 5a executes an adjustment process described later in a long burst and open loop (step S29). After that, the EUV light generation processor 5a evaluates the performance of the EUV light 33 again in a long burst and open loop (step 30).

[0100] The EUV light generation processor 5a determines whether the evaluation result obtained in step S30 is within the normal range (step S31). This normal range is the same as the normal range in step S28. Note that steps S30 and S31 are examples of the "second confirmation step" according to the technology of the present disclosure.

[0101] If the evaluation result of the EUV light generation processor 5a is within the normal range (step S31: YES), the performance recovery process ends. On the other hand, if the evaluation result of the EUV light generation processor 5a is not within the normal range (step S31: NO), the performance recovery process ends as an abnormal termination.

[0102] Note that when the EUV light generation processor 5a terminates abnormally, for example, it issues an abnormality report by displaying a message notifying the abnormality to an external monitor.

[0103] FIG. 7 shows an example of the adjustment process (step S24) in a short burst and open loop. In this adjustment process, the EUV light generation processor 5a performs the irradiation position adjustment of the PPL light 31a (step S240) and the irradiation position adjustment of the MPL light 31b (step S241). These irradiation position adjustments are the same as steps S13 and S14 shown in FIG. 4 described in the comparative example. The irradiation position adjustment of the PPL light 31a (step S240) and the irradiation position adjustment of the MPL light 31b (step S241) may be alternately executed a plurality of times. The irradiation position adjustment in a short burst and open loop is a rough adjustment for adjusting the irradiation position with low accuracy because it is performed under irradiation conditions in which the influence of the position variation of the target 27 due to the thermal load can be ignored.

[0104] FIG. 8 shows an example of the adjustment process (step S29) in a long burst and open loop. In this adjustment process, the EUV light generation processor 5a performs adjustment of the irradiation position of the PPL light 31a (step S290) and adjustment of the irradiation position of the MPL light 31b (step S291). These irradiation position adjustments are the same as steps S16 and S17 shown in FIG. 4 described in the comparative example. The adjustment of the irradiation position of the PPL light 31a (step S290) and the adjustment of the irradiation position of the MPL light 31b (step S291) may be alternately performed a plurality of times. The irradiation position adjustment in a long burst and open loop is a fine adjustment for adjusting the irradiation position with high accuracy because it is performed under irradiation conditions including the influence of the position variation of the target 27 due to the heat load. However, the adjustment amount in the case of a long burst is smaller than that in the case of a short burst.

[0105] 3.3 Operations and Effects When the generation of the EUV light 33 stops due to the reporting of an error or the like, various factors can be considered. In this embodiment, an evaluation process is executed for the factors that should be preferentially confirmed, and an adjustment process and a confirmation process are executed according to the evaluation result in the evaluation process. In this embodiment, an evaluation process is executed with the irradiation position of the pulsed laser light 31 with respect to the target 27 as a factor that should be preferentially confirmed. Specifically, in this embodiment, a short-term first evaluation process is executed, and if the evaluation result is not within the normal range, an adjustment process and a confirmation process are executed. As a result of the confirmation process, if the evaluation result is within the normal range, a long-term second evaluation process is executed, and if the evaluation result is not within the normal range, the process ends. In this way, in this embodiment, the number of processes executed in the performance recovery process can be reduced, so that when the generation of the EUV light 33 stops due to the reporting of an error or the like, it is possible to quickly return to a state where the performance of the EUV light 33 is ensured.

[0106] 4. EUV Light Generation System According to the Second Embodiment Next, the EUV light generation system 11 according to the second embodiment will be described.

[0107] 4.1 Configuration The configuration of the EUV light generation system 11 according to the second embodiment is the same as that of the first embodiment, except that the content of the processing defined in the performance recovery program 5c is different.

[0108] 4.2 Operation The operation of the EUV light generation system 11 according to the second embodiment will be described. The operation of the EUV light generation system 11 according to the second embodiment is the same as that of the comparative example, except for the performance recovery process.

[0109] FIGS. 9 and 10 show the flow of the performance recovery process according to the second embodiment. In the present embodiment, before the performance recovery process according to the first embodiment, the evaluation of the target performance and the evaluation of the laser performance are performed. When the target performance and the laser performance are within the normal range, the performance recovery process according to the first embodiment is executed. Here, the target performance refers to the performance of the target 27. The laser performance refers to the performance of the pulsed laser light 31. The target performance is acquired by the target sensor 4. The laser performance is the optical performance described in the comparative example and is acquired by the beam sensor 70.

[0110] In the present embodiment, when the generation of the EUV light 33 stops due to an error report or the like, the EUV light generation processor 5a executes the evaluation of the target performance (step S40) and the evaluation of the laser performance (step S50). Step S40 is an example of the "third evaluation step" according to the technology of the present disclosure. Step S50 is an example of the "fourth evaluation step" according to the technology of the present disclosure.

[0111] In step S40, the EUV light generation processor 5a evaluates each index using the speed and generation interval of the target 27 as indexes, respectively. The EUV light generation processor 5a determines whether each evaluation result is within the normal range (step S41). This normal range varies for each index. Note that the number of indexes related to the target performance may be one or more.

[0112] If the evaluation results for all indicators are within the normal range (step S41: YES), the EUV light generation processor 5a transfers the process to step S43.

[0113] If any of the evaluation results of the EUV light generation processor 5a are not within the normal range (step S41: NO), it performs an adjustment for the indicator that is not within the normal range (step S42). For example, if the speed of target 27 is not within the normal range, it performs the target diameter adjustment described in the comparative example. Also, if the generation interval of target 27 is not within the normal range, it performs the droplet combination adjustment described in the comparative example. When an adjustment is performed, the adjusted indicator is evaluated again. After step S42, the EUV light generation processor 5a transfers the process to step S43.

[0114] In step S50, the EUV light generation processor 5a evaluates the laser performance using the position or angle of the optical axis of the pulsed laser light 31 as an indicator. Specifically, the indicators of laser performance are obtained for each of the PPL light 31a and the MPL light 31b. Note that energy, divergence, pulse width, etc. may also be used as indicators of laser performance. There may be one or more indicators related to laser performance. After step S50, the EUV light generation processor 5a transfers the process to step S43.

[0115] In step S43, the EUV light generation processor 5a determines whether the target performance and the laser performance are within the normal range (step S43). If the evaluation result for any of the indicators of the target performance and the laser performance is not within the normal range (step S43: NO), it ends the performance recovery process as an abnormal end.

[0116] If the evaluation results for all indicators of the target performance and the laser performance are within the normal range (step S43: YES), the EUV light generation processor 5a transfers the process to step S20. The process of transferring to step S20 is the same as the performance recovery process according to the first embodiment.

[0117] 4.3 Function and Effect In this embodiment, when the target performance and the laser performance are within the normal range, a performance recovery process for EUV light 33 is executed. Therefore, compared with the first embodiment, the probability of the abnormal termination of the performance recovery process decreases, that is, the success rate of the performance recovery improves.

[0118] In this embodiment, evaluations of both the target performance and the laser performance are executed, but evaluations of only one of the target performance and the laser performance may be executed. Also, steps S41 and S42 may be omitted.

[0119] The above description is intended as an illustration and not a limitation. Thus, it will be apparent to those skilled in the art that various changes may be made to each embodiment of the present disclosure without departing from the scope of the appended claims.

[0120] The terms used throughout this specification and the appended claims are to be construed as "non-limiting" terms. For example, the terms "comprising" or "included" should be construed as not being limited to those described as being included. The term "having" should be construed as not being limited to those described as having. Also, the modifier "one" described in this specification and the appended claims should be construed to mean "at least one" or "one or more". Also, the term "at least one of A, B, and C" should be construed as "A", "B", "C", "A + B", "A + C", "B + C", or "A + B + C", and further should be construed to include combinations with things other than "A", "B", and "C".

Claims

1. A method for recovering the performance of an EUV light generation system that generates EUV light by irradiating a target with pulsed laser light, comprising: Performing a first evaluation step of evaluating the performance of the EUV light while generating the EUV light at a constant repetition frequency during a first period; When the evaluation result by the first evaluation step is not within the normal range, after performing an adjustment step of adjusting the performance, the first evaluation step is performed as a confirmation step; When the evaluation result by the confirmation step is within the normal range, performing a second evaluation step of evaluating the performance of the EUV light while generating the EUV light at the repetition frequency during a second period longer than the first period; When the evaluation result by the confirmation step is not within the normal range, the process is terminated; In the first evaluation step and the second evaluation step, evaluating an index related to the irradiation position of the pulsed laser light on the target; A method for recovering the performance of an EUV light generation system, including the above.

2. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: The index is an average value of the energy of the EUV light or a value representing the temporal variation of the energy of the EUV light.

3. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: The index is a value obtained by dividing the average value of the energy of the EUV light by the pulse energy of the pulsed laser light.

4. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: The first period is 0.01 milliseconds or more and 10 milliseconds or less.

5. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: The second period is 50 milliseconds or more and 10 seconds or less.

6. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: When the evaluation result by the first evaluation step is within the normal range, it includes performing the second evaluation step.

7. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: Before the first evaluation step, performing a third evaluation step of evaluating the performance of the target, and when the evaluation result of the third evaluation step is within the normal range, performing the first evaluation step.

8. The method for recovering the performance of an EUV light generation system according to Claim 1, wherein: Before the first evaluation step, performing a fourth evaluation step of evaluating the performance of the pulsed laser light, and when the evaluation result of the fourth evaluation step is within the normal range, performing the first evaluation step.

9. A method for recovering the performance of an EUV light generation system according to claim 1, comprising: Before the first evaluation step, performing a third evaluation step of evaluating the performance of the target and a fourth evaluation step of evaluating the performance of the pulsed laser light, and if both the evaluation result of the third evaluation step and the evaluation result of the fourth evaluation step are within a normal range, performing the first evaluation step.

10. A method for recovering the performance of an EUV light generation system according to claim 7, comprising: In the third evaluation step, evaluating the speed or generation interval of the target.

11. A method for recovering the performance of an EUV light generation system according to claim 8, comprising: In the fourth evaluation step, evaluating the position or angle of the optical axis of the pulsed laser light.

12. An EUV light generation system that generates EUV light by irradiating a target with pulsed laser light, comprising: A processor, The processor: Performs a first evaluation step of evaluating the performance of the EUV light while generating the EUV light at a constant repetition frequency during a first period; If the evaluation result from the first evaluation step is not within the normal range, after performing an adjustment step of adjusting the performance, performs the first evaluation step as a confirmation step; If the evaluation result from the confirmation step is within the normal range, performs a second evaluation step of evaluating the performance of the EUV light while generating the EUV light at the repetition frequency during a second period longer than the first period; If the evaluation result from the confirmation step is not within the normal range, ends the process; In the first evaluation step and the second evaluation step, evaluating an index related to the irradiation position of the pulsed laser light on the target; An EUV light generation system.

13. A processor used in an EUV light generation system that generates EUV light by irradiating a target with pulsed laser light, comprising: Performs a first evaluation step of evaluating the performance of the EUV light while generating the EUV light at a constant repetition frequency during a first period; If the evaluation result from the first evaluation step is not within the normal range, after performing an adjustment step of adjusting the performance, performs the first evaluation step as a confirmation step; If the evaluation result from the confirmation step is within the normal range, performs a second evaluation step of evaluating the performance of the EUV light while generating the EUV light at the repetition frequency during a second period longer than the first period; If the evaluation result from the confirmation step is not within the normal range, ends the process; In the first evaluation step and the second evaluation step, a processor that evaluates an index related to the irradiation position of the pulsed laser light on the target. Processor.

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