Electron beam bunch injection system and extreme ultraviolet light source

Abstract

Embodiments of the present disclosure relate to an electron bunch injection system and an extreme ultraviolet (EUV) light source. The electron bunch injection system comprises a photocathode electron gun, a linear accelerator and a beam expansion ring. The photocathode electron gun is configured to generate a string of electron bunches with a specific temporal structure and a specific charge amount, the linear accelerator is configured to accelerate the string of electron bunches generated by the electron gun and ensure that the emittance of the string of electron bunches is within a certain range, and the beam expansion ring is configured to expand a plurality of electron bunches to form a continuous electron bunch with a length of at least 1 ns. The injection system can provide a high-current uniform electron source for an accelerator-type EUV light source device, thereby achieving an average EUV output power of the order of kW.

Description

Technical Field

[0001] Embodiments of this disclosure generally relate to the field of accelerators, and more specifically, to electron beam injection systems and extreme ultraviolet (EUV) light sources, particularly EUV light sources for lithography machines. Background Technology

[0002] With the further development of integrated circuit technology, photolithography continues to evolve towards more microscopic scales. In photolithography, extreme ultraviolet (EUV) light can be used to create very small features in a substrate (e.g., a silicon substrate). EUV light can be electromagnetic radiation with wavelengths of approximately 50 nm or smaller (sometimes also called soft X-rays), for example, light with a wavelength of approximately 13 nm. Therefore, EUV light sources have become a key component in photolithography machines, and the development of EUV light sources has become a crucial technology in photolithography machines. Summary of the Invention

[0003] Embodiments of this disclosure provide an electron beam injection system and an extreme ultraviolet light source.

[0004] In a first aspect of this disclosure, an electron bundle injection system is provided. The electron bundle injection system includes a beam-spreading ring configured to spread a plurality of electron bundles to form a continuous electron bundle with a length of at least 1 ns.

[0005] In a second aspect of this disclosure, an extreme ultraviolet (EUV) light source is provided. The EUV light source includes a storage ring and an electron bundle injection system according to the first aspect, the electron bundle injection system being configured to inject the continuous electron bundles into the storage ring.

[0006] In a third aspect of this disclosure, a lithography machine is provided. The lithography machine includes an extreme ultraviolet light source according to a second aspect of this disclosure.

[0007] The summary section is provided to present the chosen concepts in a simplified form, which will be further described in the detailed description below. The summary section is not intended to identify key or principal features of this disclosure, nor is it intended to limit the scope of this disclosure. Attached Figure Description

[0008] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0009] Figure 1 A schematic diagram of a system according to some embodiments of the present disclosure is shown.

[0010] Figure 2The temporal structure of an electron beam string generated by an electron gun according to some embodiments of the present disclosure is shown.

[0011] Figure 3 The temporal structure of an electron beam string after passing through a linear accelerator is shown according to some embodiments of the present disclosure.

[0012] Figure 4 The temporal structure of a continuous electron beam cluster after beam spreading by a beam spreading ring is shown according to some embodiments of the present disclosure.

[0013] Figure 5 The relationship between the energy output of the electron gun and the laser activation time is shown in some embodiments of the present disclosure.

[0014] Figure 6 The relationship between the energy output of the electron gun and the laser activation time is shown in some embodiments of the present disclosure.

[0015] Figure 7 Information on beam energy dissipation and energy obtained by injecting a beam at different times according to some embodiments of the present disclosure is shown.

[0016] Figure 8 Information on beam energy dissipation and energy obtained by injecting a beam at different times, taking into account laser jitter, is shown according to some embodiments of the present disclosure.

[0017] Figure 9 The feed power waveforms according to some embodiments of this disclosure are shown.

[0018] Figure 10 A power combining system according to some embodiments of the present disclosure is shown.

[0019] Figure 11 Waveforms and simulated waveforms obtained by a power combining system according to some embodiments of the present disclosure are shown.

[0020] Figure 12 A magnetic focusing structure of a beam-spreading ring according to some embodiments of the present disclosure is shown.

[0021] Figure 13 A schematic diagram of the timing of an electron beam according to some embodiments of the present disclosure is shown.

[0022] Figure 14 It shows according to Figure 13 The illustrated embodiment shows the time structure of the electron beam cluster generated from the electron gun.

[0023] Figure 15 It shows according to Figure 13 The illustrated embodiment shows the opening and closing timing of the injected magnet and the extracted magnet.

[0024] Figure 16 A schematic diagram of the timing of an electron beam according to some embodiments of the present disclosure is shown.

[0025] Figure 17 It shows according to Figure 16 The illustrated embodiment shows the opening and closing timing of the injected magnet and the extracted magnet.

[0026] Figure 18 A schematic diagram of the timing of an electron beam according to some embodiments of the present disclosure is shown.

[0027] Figure 19 It shows according to Figure 18 The illustrated embodiment shows the opening and closing timing of the injected magnet and the extracted magnet.

[0028] Figure 20 and Figure 21 It shows Figure 18 A schematic diagram of the injection scheme is shown.

[0029] Figure 22 A schematic diagram of the timing of an electron beam according to some embodiments of the present disclosure is shown.

[0030] Figure 23 It shows according to Figure 22 The illustrated embodiment shows the time structure of the electron beam cluster generated from the electron gun.

[0031] Figure 24 It shows according to Figure 22 The illustrated embodiment shows the opening and closing timing of the injected magnet and the extracted magnet.

[0032] Figure 25 and Figure 26 It shows Figure 22 A schematic diagram of the injection scheme is shown. Detailed Implementation

[0033] The principles of this disclosure will now be described with reference to several exemplary embodiments illustrated in the accompanying drawings. While preferred embodiments of this disclosure are shown in the drawings, it should be understood that these embodiments are described merely to enable those skilled in the art to better understand and implement this disclosure, and are not intended to limit the scope of this disclosure in any way.

[0034] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0035] Figure 1 A schematic diagram of a system 100 according to an embodiment of the present disclosure is shown. (As...) Figure 1 As shown, the system 100 includes an electron bundle storage ring, also called the main storage ring or main ring. The main ring can be a steady-state micro-bundling (SSMB) storage ring or an accelerator storage ring. The main ring includes four symmetrical deflection structures 102 and four straight segments 104 connecting the deflection structures 102. Electron bundle injectors 124 and electron bundle extractors 126 can be arranged on the straight segments 104. The electron bundle injector 124 is used to inject electron bundles into the main ring, and may include, for example, an injection magnet. The electron bundle extractor 126 is used to extract electron bundles from the main ring, and may include, for example, an extraction magnet. The electron bundles can achieve steady-state micro-bundling in the main ring to generate high average power extreme ultraviolet (EUV) light as an EUV source.

[0036] like Figure 1 As shown, system 100 also includes an electron bundle injection system for injecting electron bundles into the main ring. The electron bundle injection system includes a beam-spreading ring comprising four symmetrical deflection structures 106 and four linear segments 108 connecting the deflection structures 106. Electron bundle injectors 120 and electron bundle extractors 122 can be arranged on the linear segments 108. Electron bundle injectors 120 are used to inject electron bundles into the beam-spreading ring; for example, they may include injection magnets. Electron bundle extractors 122 are used to extract electron bundles from the beam-spreading ring; for example, they may include extraction magnets. The electron bundles extracted by electron bundle extractors 122 can be injected into the main ring via electron bundle injectors 124.

[0037] In some embodiments, the electron bundle injection system can provide continuous electron bundle injection to the SSMB storage ring, for example, continuous electron bundles with a length of at least 1 ns, for example, continuous electron bundles with a length of at least 10 ns, for example, continuous electron bundles with a length of at least 100 ns. In some embodiments, continuous electron bundle injection with a high average current intensity can be provided to the SSMB storage ring. For example, the average current intensity can be greater than 1 A.

[0038] In some embodiments, in order to achieve a continuous electron beam, the momentum compression factor of the beam-spreading ring can be at least 0.1m, for example, at least 1m.

[0039] like Figure 1 As shown, system 100 may further include an electron gun 130 for generating an electron beam and a linear accelerator 140 for accelerating the electron beam generated by the electron gun. The accelerated electron beam can be injected into the beam-spreading ring via an electron bundle injector 120. This electron bundle injection system can inject a continuous bundle with a high average current intensity into the main ring, with an average current intensity exceeding 1 Å. When the main ring is a steady-state micro-bundle storage ring, EUV radiation output with an average power greater than 1 kW can be achieved.

[0040] The following description will be made in conjunction with specific embodiments. It should be understood that the numerical values ​​in the following specific embodiments are generally provided as examples only and are not intended to limit the scope of this disclosure, and any other suitable numerical values ​​may be used instead.

[0041] Figure 2 The pulse timing structure of an electron beam string generated by an electron gun 130 according to some embodiments of the present disclosure is shown. In this example, the electron beam string comprises multiple electron beams spaced approximately 0.3 ns apart, and the length of the electron beam string is approximately 100 ns. It should be understood that this pulse timing structure is provided as an example only, and the electron gun 130 may also generate electron beam strings with any other suitable pulse timing structure.

[0042] Figure 3 The pulse-time structure of an electron beam string output by a linear accelerator 140 according to some embodiments of the present disclosure is shown. The linear accelerator 140 can accelerate the electron beam string to a specific energy and can ensure that parameters such as the lateral dimensions and energy dispersion of the electron beam string are within a specific range. In this example, the linear accelerator 140 substantially maintains the pulse-time structure of the electron beam string generated by the electron gun 130. For example, the electron beam string output by the linear accelerator 140 comprises multiple pulsed beams, with an interval of approximately 0.3 ns between the electron beams and a length of approximately 100 ns.

[0043] Figure 4 The temporal structure of the electron beam output from the beam-spreading ring according to some embodiments of the present disclosure is shown. For example... Figure 4 As shown, the length of this electron beam can be approximately 100 ns, that is, essentially equal to... Figure 2 and Figure 3 The length of the electron beam strand shown.

[0044] In one embodiment, the electron gun 130 may be a photocathode electron gun. The photocathode electron gun can generate electron beams with a specific charge. The linear accelerator 140 can accelerate these electron beams to a specific energy and ensure that parameters such as the lateral dimensions and energy dispersion of the electron beams are within a specific range (depending on the requirements of the beam-spreading ring and the main storage ring injection system). The beam-spreading ring is used to spread the electron beams, shaping them into a longitudinally uniform continuous beam with a specific time structure. Alternatively, the electron gun 130 may also be a thermionic electron gun.

[0045] A photocathode electron gun is a device that generates electron beams, capable of producing electron beams with specific charge amounts and time structures as required. Taking an S-band photocathode microwave electron gun as an example, if a uniformly distributed electron beam with an average current of 1 A and a pulse length of approximately 100 ns (about 30 m) is to be injected into the main storage ring in a single pass, the electron gun needs to generate approximately 300 electron beam strings, each with a charge of approximately 350 pC, and the spacing between the beam strings is approximately 0.33 ns (about 10 cm). Figure 2 As shown.

[0046] Considering beam dynamics, the photocathode microwave electron gun of the embodiments of this disclosure needs to provide a continuous beam with a high average current intensity. This high-average-current-intensity continuous beam carries away a significant amount of stored energy from the electron gun. For a typical electron gun fed by a square-wave pulse, the power carried away by the beam is faster than its replenishment. This results in the beam head receiving the highest energy. When the beam tail enters the accelerating structure, the stored energy in the accelerating structure has decreased considerably. Therefore, the lower energy received at the beam tail leads to a very large energy deviation between the center beams, which is known as the "beam loading effect" in the accelerator field. Currently, a compensation scheme for the beam loading effect in the electron gun is still lacking.

[0047] In some embodiments, the beam load effect in the electron gun can be compensated by pre-injection. The field-building process in the electron gun is a process of continuously increasing the stored energy until saturation. If the laser is turned on during the field-building process, causing the photocathode to emit photoelectrons, the rate of increase in stored energy during the field-building process can be roughly matched with the rate at which the electron beam carries away the stored energy, thus minimizing the energy difference between the clusters.

[0048] In some embodiments, the electron gun was simulated according to the parameters shown in the table below. The simulation results are as follows: Figure 5 and Figure 6 As shown, the energy of the final beam is obtained by turning on the laser at different times to emit an electron beam from the photocathode and inject it into the electron gun. Figure 6 for Figure 5 An enlarged view of section 502.

[0049]

[0050] like Figure 6 As shown, the short lines at different baseline levels represent the energies of the 100ns electron beam injected at different times. It can be seen that if the injection time is too early, the beam head energy will be low while the tail energy will be high. This is because the rate of energy increase within the electron gun is faster than the rate at which the beam carries away the stored energy. If the injection time is too late, the beam head energy will be low while the tail energy will be high. This is because the rate of energy increase within the electron gun is slower than the rate at which the beam carries away the stored energy. Therefore, there exists an optimal injection time that minimizes beam energy dissipation.

[0051] Figure 7 Detailed information on beam energy dissipation and energy obtained from the injected beam at different times is shown. For example... Figure 7 As shown, when the microwave power is fed into the range electron gun and the electron beam is injected 1068 ns later, the beam energy dissipation is minimal, at which point it is only 0.0003334, which meets the system's energy dissipation requirements.

[0052] Figure 8 This shows detailed information on beam energy dissipation and energy at different times, with a random error (average error of 5%) introduced into the charge amount of each bundle. Figure 8 As shown, when injected at the same time, the beam energy dissipation is approximately 0.0005, which still meets the system requirements. Therefore, slight fluctuations in laser power have little impact on the compensation of beam load effects.

[0053] In some embodiments, the linear accelerator 130 may be a traveling-wave electron linear accelerator. For example, when providing a continuous beam with a high average current intensity, the "beam load effect" is more pronounced. In some embodiments, the beam load effect can be compensated by amplitude modulation of the feed power. The feed power waveform required to compensate for the beam load effect can be determined through theoretical calculations. Figure 9 The required feed power waveform is shown when a 100 ns beam is accelerated to 30 MeV after passing through a SLAC-type 3m long accelerating tube. (Example:) Figure 9As shown, line 902 represents the required feed power waveform. If the power is fed according to the required waveform, the resulting 100ns beam energy is as shown in line 910, with no energy dissipation. If the beam load effect is ignored and the power is still fed according to line 902, then the beam energy is as shown in line 904, continuously increasing because the fed power is constantly increasing. Line 906 represents the difference between lines 904 and 910, which represents the power carried away by the beam. Line 908 represents the beam intensity, that is, a beam with an average current intensity of 1A over 100ns.

[0054] In some embodiments, this can be achieved by combining microwave signals generated by different microwave power sources. Figure 9 The waveform is shown by line 902. Specifically, a first microwave power source can generate a first microwave power output, and a second microwave power source can generate a second microwave power output. The second microwave power output can have the same waveform as the first microwave power output, but with a specific phase difference. The first and second microwave signals are then combined using a coupler (e.g., a 3dB coupler) to generate a target microwave signal that compensates for the beam load effect of multiple electron beam clusters. For example, waveform modulation can be achieved by modulating the phase difference and / or intensity difference between the second and first microwave signals, thereby realizing... Figure 9 The target waveform is shown by line 902 in the diagram.

[0055] Figure 10 A schematic diagram of a dual-speed tube power combining system according to some embodiments of the present disclosure is shown. For example... Figure 10 As shown, the low-level system 1002 can output two microwave signals. For example, the low-level system 1002 can control the phase of the two microwave signals with an accuracy of 10 ns. Figure 10 As shown, the power waveforms of the two microwave signals can be the same, but their phases are different. Then, klystrons 1004 and 1006 can be operated in the saturation region, thus acting as two amplifiers to amplify the square wave signal from the low-level system 1002, while maintaining the same phase as the low-level system 1002. The two power signals are then combined using a 3dB coupler 1008. The working principle of the 3dB coupler 1008 can be expressed by the following formula:

[0056]

[0057] in It is the phase difference between the two input power sources, so the final output amplitude can be controlled by controlling the phase of the two inputs, thus obtaining... Figure 9The target waveform is shown by line 902 in the diagram. The resulting microwave signal can be provided to the acceleration structure 1012 (e.g., linear accelerator 140) or other load 1010.

[0058] Figure 11 It shows according to Figure 10 The experimental system obtained waveforms, where the straight line represents the theoretically required power waveform obtained through calculation. It can be seen that the two waveforms are basically in agreement before the power decreases. Since the actual waveform has a certain fall time, the power cannot decrease immediately. However, this less-than-ideal fall edge has little impact on compensating for the beam load effect, because the embodiments of this disclosure mainly compensate for the beam load effect through the preceding slowly rising waveform. When the power decreases, the beam has already completely passed through the accelerating structure. The energy dissipation of the beam can be calculated from the obtained power waveform. By averaging several data points, the center energy deviation between the beam clusters is found to be around 0.05%, which meets the system requirements.

[0059] A beam-spreading ring can expand an electron beam with a specific time structure into a continuous beam with a uniform longitudinal distribution. The longitudinal coordinates of the electron beam are generally defined as (z, δ), where z represents the longitudinal positional deviation of the electrons within the beam relative to the standard particle, and δ is the energy deviation of the electrons within the beam relative to the standard particle. Due to the energy deviation, the longitudinal position of the electrons will also deviate from that of the standard particle, denoted as... .in It is the momentum compressibility factor of the segment of the magnetic focusing element through which the electrons pass. This refers to the initial position deviation of the electron. To unwind an electron beam with a specific time structure into a continuous beam with a uniform longitudinal distribution, the electron beams of two adjacent beam strings in a macropulse train with a specific time structure can be overlapped. In some embodiments, the distance between the beam strings is approximately 10 cm, and the electron beam energy dispersion requirement is below 0.1%, therefore, it is necessary to provide… It must be at least 100 meters or more. In an accelerator, it's difficult for a straight structure to provide such a large [depth / depth]. Therefore, this can be achieved using a storage ring.

[0060] For example, in designing a single-cycle energy supply When the storage ring is about 1m long, the electron beam can be rotated about 100 times in the storage ring to flatten the original electron beam with time structure into a continuous beam with uniform longitudinal distribution.

[0061] Figure 12 A magnetic focusing structure of a beam-spreading ring according to some embodiments of the present disclosure is shown. For example... Figure 12 As shown, the three different shapes represent dipole, tetrapole, and hexapole iron, respectively, and the solid black lines represent straight sections. This storage ring... With a depth of approximately 1.4m, an S-band radio frequency cavity (RF cavity) can be added to relieve pressure on upstream devices.

[0062] According to embodiments of this disclosure, continuous bundle injection with high average current intensity can be provided for storage rings (e.g., steady-state micro-bundle storage rings). In this way, high average power light sources can be generated in steady-state micro-bundle storage rings or synchrotron radiation storage rings. For example, kW-level average power light source output can be generated in SSMB storage rings, thereby realizing high-power EUV light sources for EUV lithography machines.

[0063] The control scheme of an electron beam injection system according to some embodiments of the present disclosure will be described below. Figure 13 A schematic diagram illustrating the timing of electron bundles according to some embodiments of the present disclosure is shown. In these embodiments, the beamforming ring does not contain a radio frequency cavity, and the electron gun provides a string of electron bundles with a total length of approximately 100 ns at a time, with an interval of approximately 0.3 ns between the bundles and a charge of approximately 350 pC for each bundle. For example, the electron bundles are accelerated to an energy of 400 MeV by a linear accelerator, and it is necessary to maintain the transverse normalized emittance of the electron bundles below 1 mm·mrad, the energy dispersion of a single bundle not exceeding 0.05%, and the center energy deviation between bundles not exceeding 0.1%. The bundle string accelerated by the linear accelerator is further injected into the beamforming ring and runs in the beamforming ring for approximately 100 revolutions, spreading into a long pulse train with a longitudinally uniform distribution and a length of approximately 100 ns. Finally, the long pulse train is injected into the main ring of the storage ring.

[0064] like Figure 13 As shown, in the main storage ring, all electron beam clusters need to be renewed every 10 seconds. The photocathode electron gun operates at the S-band frequency, i.e., 2856 MHz. Figure 14 It shows according to Figure 13 The illustrated embodiment shows the time structure of a 100 ns long electron beam string generated from the electron gun. Each electron beam has a charge of approximately 350 pC. The time structure remains essentially unchanged after the electrons are accelerated by a linear accelerator, similar to... Figure 14 The results are basically the same.

[0065] Figure 15 The opening and closing timing of the injection magnet and the extraction magnet is shown. (As shown) Figure 15 As shown, the opening time of the injection magnet is 100 ns, which is approximately the same as the length of the electron beam string. The transition time between opening and closing the injection magnet is less than 100 ns, and the transition time between opening and closing the extraction magnet is also less than 100 ns, in order to complete the transition as quickly as possible. In addition, the time between opening the injection magnet and the extraction magnet is approximately 15-25 μs, which basically corresponds to the cyclotron time of the electron beam in the beam spreading ring.

[0066] It should be understood that the above figures are provided as examples only, and those skilled in the art can use any other suitable figures to achieve the same result.

[0067] Figure 16 A schematic diagram illustrating the timing of electron beam clusters according to some embodiments of the present disclosure is shown. Figures 13-15 The embodiments shown are different, in Figure 16 In this embodiment, the beam-spreading ring includes a radio frequency (RF) cavity, such as an S-band RF cavity. The electron gun provides a single electron beam string with a total length of approximately 100 ns, with an interval of approximately 0.3 ns between the electron beam strings, and each electron beam string has a charge of approximately 350 pC. For example, the electron beam strings are accelerated to an energy of 400 MeV by a linear accelerator. Due to the presence of the RF cavity, the requirement for the lateral emittance of the electron beam strings can be reduced to 10 mm·mrad, and the requirement for beam dispersion can be reduced to one-thousandth, with the center dispersion deviation between beam strings not exceeding two-thousandths. The beam string accelerated by the linear accelerator is further injected into the beam-spreading ring and stored there until a steady state is reached (e.g., approximately 2 seconds). Then, the RF cavity is shut off to spread the electron beam strings, running for approximately 200 cycles, resulting in a longitudinally uniformly distributed long pulse train of approximately 100 ns in length. Finally, the long pulse train is injected into the main storage ring.

[0068] The photocathode electron gun operates in the S-band, i.e., 2856 MHz, and the time structure of the electron beam it generates is similar to... Figure 14 The results are essentially the same. The charge of each electron beam is approximately 350 pC. The electrons are accelerated by a linear accelerator, and the time structure remains essentially unchanged, similar to... Figure 14 The results are basically the same.

[0069] Figure 17 The opening and closing timing of the injection magnet and the extraction magnet is shown. (As shown) Figure 17 As shown, the on-time of the injection magnet is 100 ns, which is approximately the same as the length of the electron beam string. The transition time between the on and off of the injection magnet is less than 100 ns, and the transition time between the on and off of the extraction magnet is also less than 100 ns, in order to complete the transition as quickly as possible.

[0070] The RF cavity is opened when the injection magnet is turned on. The RF cavity is then turned off approximately 1-2 seconds after the injection magnet is turned off. After the RF cavity is turned off, the electron beam is spread for approximately 100 μs, after which the extraction magnet can be turned on to extract the spread electron beam.

[0071] Figure 18 A schematic diagram illustrating the timing of an electron beam loop according to some embodiments of the present disclosure is shown. In these embodiments, the beam-spreading loop includes a radio frequency cavity, for example, an S-band radio frequency cavity. Figures 13-17 The embodiments shown are different, in Figure 18 In the illustrated embodiment, the electron gun provides electron beams of approximately 100 ns in multiple stages, for example, by injecting the beam-spreading ring in ten stages. The timing structure of the electron beams is related to... Figure 14 The results are essentially the same, except that the spacing between electron bundles is approximately 0.3 ns, and the charge of each bundle is approximately 35 pC. The electron bundles are accelerated to an energy of 400 MeV by a linear accelerator. The requirement for the transverse emittance of the electron bundles can be reduced to 10 mm·mrad, and the requirement for bundle energy dispersion can be reduced to one-thousandth, with the center energy dispersion deviation between bundles not exceeding two-thousandths. The bundles accelerated by the linear accelerator are further injected into a beam-spreading ring. After each storage in the beam-spreading ring until a steady state is reached, the next electron bundle is injected until all electron bundles have reached a steady state in the beam-spreading ring. Then, the RF cavity is shut off, and the electron bundles are spread into long pulses of approximately 100 ns in length, with a uniform longitudinal distribution. Finally, they are injected into the main storage ring. Figures 13-17 Compared to the embodiments shown, Figure 18 The embodiments shown can further reduce beam load effects in electron guns and linear accelerators.

[0072] exist Figure 18 In the illustrated embodiment, the photocathode electron gun operates at the S-band frequency, i.e., 2856 MHz. The time structure of the electron beam string is... Figure 14 The results are essentially the same, except that the spacing between electron clusters is approximately 0.3 ns, and the charge of each electron cluster is approximately 35 pC. The electrons are accelerated by a linear accelerator, and the time structure remains essentially unchanged.

[0073] Figure 19 The opening and closing timing of the injection magnet and the extraction magnet is shown. (As shown) Figure 19 As shown, after opening the RF cavity, the injection magnet is opened 10 times, with an interval of about 1-2 seconds between each opening. Then the RF cavity is closed, and after the electron beam is spread for about 100μs, the extraction magnet can be opened to extract the spread electron beam.

[0074] Figure 20 and Figure 21 It shows Figure 18 The diagram shows a beam-spreading scheme. Each time the beam is injected from the linear accelerator into the beam-spreading ring, it must correspond perfectly with the beam stored in the beam-spreading ring in the longitudinal position.

[0075] Figure 22A schematic diagram illustrating the timing of electron bundles according to some embodiments of the present disclosure is shown. In these embodiments, the beam-spreading ring includes a radio frequency cavity, such as an S-band radio frequency cavity. A photocathode electron gun provides electron bundle strings of approximately 100 ns in length in multiple injections, for example, in ten injections into the beam-spreading ring, with an interval of approximately 3 ns between electron bundles and a charge of approximately 350 pC for each bundle. The electron bundles are accelerated to an energy of 400 MeV by a linear accelerator, reducing the requirement for lateral emittance of the electron bundles to 10 mm·mrad and the requirement for energy dispersion of the bundles to one-thousandth, with the center energy dispersion deviation between bundles not exceeding two-thousandths. The bundle strings accelerated by the linear accelerator are further injected into the beam-spreading ring. After each injection into the beam-spreading ring until a steady state is reached, the next electron bundle string is injected until all electron bundles have reached a steady state in the beam-spreading ring. Then, the radio frequency cavity is shut off to spread the electron bundles, running for approximately 200 cycles, resulting in a longitudinally uniformly distributed long pulse train of approximately 100 ns in length. Finally, the expanded electron beam is injected back into the main storage ring. This embodiment is similar to... Figure 18 The embodiments shown are similar, which can reduce the beam load effect in the electron gun and linear accelerator, and can reduce the operating frequency of the electron gun to around 285MHz, making the corresponding laser readily available.

[0076] In this embodiment, the photocathode microwave electron gun operates at a frequency of 285.6 MHz. Figure 23 The temporal structure of a 100 ns long electron beam string generated from an electron gun is shown. In this embodiment, the interval between electron beam strings is approximately 3 ns, and the charge of each electron beam string is approximately 350 pC. The temporal structure remains essentially unchanged after the electrons are accelerated by a linear accelerator.

[0077] Figure 24 It shows according to Figure 22 The opening and closing timing of the injection magnet and the extraction magnet in the illustrated embodiment. Figure 24 and Figure 19 Basically the same, however, the synchronization requirements during each injection are different. Figure 19 The embodiments shown are different. Figure 25 and Figure 26 As shown Figure 22 A schematic diagram of the injection scheme is shown. (As shown) Figures 25-26 As shown, each time the beam is injected from the linear accelerator into the beam-splitting ring, it is sequentially offset from the beam stored in the beam-splitting ring in the longitudinal position, for example, approximately one cycle of the S-band.

[0078] The above description is merely an optional embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0079] Although the claims in this application have been formulated for specific combinations of features, it should be understood that the scope of this disclosure also includes any novel feature or any novel combination of features, whether express or implied or generalized herein, whether or not it relates to the same scheme in any of the claims currently claimed.

Claims

1. A system for electron bunch injection for an extreme ultraviolet (EUV) light source, comprising: a debunching ring configured to debunch a plurality of continuous electron bunches to form a continuous electron bunch having a length of at least 1 ns. 2.The system of claim 1, wherein the continuous electron bunch has a length of at least 10 ns. 3.The system of claim 2, wherein the continuous electron bunch has a length of at least 100 ns. 4.The system of claim 1, wherein a momentum compression factor of the debunching ring is at least 0.1 m. 5.The system of claim 4, wherein the momentum compression factor of the debunching ring is at least 1 m. 6.The system of claim 1, wherein the debunching ring is configured to make the plurality of continuous electron bunches revolve in the debunching ring for multiple turns to form the continuous electron bunch. 7.The system of claim 1, further comprising: an electron gun configured to generate the plurality of continuous electron bunches; and a linear accelerator configured to accelerate the plurality of continuous electron bunches generated by the electron gun to a specified energy and inject the plurality of continuous electron bunches into the debunching ring. 8.The system of claim 7, wherein during a field building process of the electron gun, the electron gun emits electrons to compensate for a beam loading effect in the electron gun. 9.The system of claim 7, wherein the linear accelerator further comprises: a first microwave power source configured to generate a first microwave power output; a second microwave power source configured to generate a second microwave power output having a same waveform as the first microwave power output but having a specified phase difference from the first microwave power output by a low-level system; and a coupler configured to synthesize the first microwave power output and the second microwave power output to generate a target microwave power output that compensates for a beam loading effect of the plurality of continuous electron bunches. 10.The system of claim 1, wherein the debunching ring comprises a radio frequency (RF) cavity, an injection magnet and an extraction magnet, and the debunching ring is configured to: inject the plurality of continuous electron bunches into the debunching ring through the injection magnet when the RF cavity is turned on; debunch the plurality of continuous electron bunches through the debunching ring to obtain the continuous electron bunch when the RF cavity is turned off. 11.The system of claim 10, wherein an up-down edge of the injection magnet and the extraction magnet is no more than 100 ns and a flat top part is no less than 100 ns. 12.The system of claim 10, wherein the debunching ring is configured to: inject the plurality of continuous electron bunches into the debunching ring through one injection when the RF cavity is turned on. 13.The system of claim 10, wherein the debunching ring is configured to: inject the plurality of continuous electron bunches into the debunching ring through multiple injections when the RF cavity is turned on.

14. The system of claim 13, wherein each of the multiple injections corresponds at a longitudinal position of the debunching ring.

15. The system of claim 13, wherein each of the multiple injections is sequentially offset at a longitudinal position of the debunching ring.

16. An extreme ultraviolet light source, comprising: a storage ring; and a system for electron bunch injection according to any of claims 1-15, the system configured to inject the continuous electron bunch into the storage ring.

17. The extreme ultraviolet light source of claim 16, wherein the storage ring comprises a steady-state microbunch storage ring.

18. A lithography machine, comprising: the extreme ultraviolet light source of claim 16 or 17. ​

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