System and method for irradiating a fuel target

Abstract

A laser system arranged to irradiate a fuel target at a target destination with a laser pulse. The laser system is arranged to generate a plurality of sub-pulses having a predetermined pulse length, the plurality of sub-pulses being combined in time to form the laser pulse having a certain duration. The laser system further comprises at least one optical element arranged to spatially separate each of the sub-pulses to be incident on the fuel target at a corresponding target destination.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European application 24167180.9, filed on 28 March 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a laser system and a method for irradiating a fuel target in a plasma formation region. The laser system can form a portion of a laser-generated plasma (LPP) radiation source. The LPP radiation source can generate extreme ultraviolet (EUV) radiation and can form a portion of a photolithography system. Background Technology

[0004] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. Lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project a pattern from a patterning apparatus (e.g., a mask) onto a radiation-sensitive material (resist) layer disposed on a substrate.

[0005] To project a pattern onto a substrate, a photolithography apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Compared to a photolithography apparatus using radiation with a wavelength of, for example, 193 nm, a photolithography apparatus using extreme ultraviolet (EUV) radiation with wavelengths in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on the substrate.

[0006] EUV radiation used in lithography equipment can be generated by a laser-generated plasma (LPP) radiation source. Within the LPP radiation source, a laser beam can be used to irradiate fuel droplets (fuel targets) to generate plasma that will emit EUV radiation.

[0007] The laser beam used to irradiate the fuel droplets is expected to generate high EUV source power. A seed (or driving) laser system can be used to provide a pulsed laser beam, which is then amplified using an optical amplifier. The optical amplifier increases the power of the pulsed laser beam. The amplified pulsed laser beam is incident on the fuel droplets, thereby generating EUV radiation.

[0008] CO2-driven lasers are an option, but they require one or more pre-pulses to deform the fuel droplets into a more favorable shape for optimal laser absorption and EUV emission. Alternative driving lasers exist, such as 1 μm or 2 μm solid-state lasers. However, they also present problems that make them less preferred or challenging in their use.

[0009] It may be desirable to provide a laser system and a method for irradiating fuel targets in a way that is not disclosed or implied by the prior art, overcoming problems associated with the prior art. Summary of the Invention

[0010] According to a first aspect of the invention, a laser system is provided, the laser system being arranged to irradiate a fuel target at a target destination using laser pulses, wherein the laser system is arranged to generate a plurality of subpulses having a predetermined pulse length, the plurality of subpulses being combined in time to form the laser pulse having a specific duration, and wherein the laser system further includes at least one optical element, the at least one optical element being arranged to spatially separate each of the subpulses for incident on the fuel target at a corresponding target destination.

[0011] Advantageously, the subpulses can be better positioned in space to achieve an optimal intensity distribution of EUV generation across the entire propulsion trajectory of the fuel target. This can allow for increased EUV source power (e.g.) without involving improvements in conversion efficiency (CE) or even further increases in pressure within the droplet launcher.

[0012] The fuel target can be a fuel droplet from a fuel emitter. The temporal combination of subpulses means that relatively long single pulses are not required. Combining the subpulses means that the desired power level can be achieved. The laser pulse causes a significant propulsion of the fuel target (droplet) during the laser pulse. For some embodiments of the optical system, this significant propulsion of the droplet may not be desirable for EUV radiation collection.

[0013] Multiple optical elements can exist. One or more optical elements focus the subpulses (i.e., each subpulse laser beam) at a different spatial point (compared to other subpulses). This allows the fuel target to move over time, for example, from one corresponding target destination (relative to one subpulse) to another corresponding target destination (relative to another subpulse). That is, the corresponding target destinations can be considered to be at different locations over time. The movement of the fuel target is mainly due to the effect of the subpulses incident on the fuel target (i.e., z-kick). It is necessary to consider the movement of the fuel target over time because the total time (a specific duration) of the laser pulses (i.e., the combination of subpulses) is longer than that of previous laser systems, and therefore the droplets move relatively farther, which needs to be taken into account accordingly.

[0014] The laser system may include multiple sub-modules, each of which is configured to sequentially emit corresponding sub-pulses at different times, such that the sub-pulses are combined approximately continuously in time to generate the laser pulse.

[0015] Subpulses can be emitted toward the fuel target at different times, rather than all at once. Submodules can be emitted at different times. Each submodule can be considered an independent laser. Each submodule can be switched on for the duration of a subpulse of a predetermined pulse length. Each submodule can be switched on and off at different times.

[0016] The laser system may include at least one of the following: 2 to 20 sub-modules, 10 to 20 sub-modules, 2 to 15 sub-modules, 10 to 15 sub-modules, 2 sub-modules, 3 sub-modules, and 10 sub-modules.

[0017] The submodule can be a solid-state laser module. The submodule can be a fiber laser system. The submodules can be arranged for coherent beam combining. Coherent beam combining of fiber laser systems is possible. The laser system can be arranged for spatial beam combining or polarization beam combining between submodules.

[0018] The sub-pulse can be partially superimposed in time with the corresponding neighboring sub-pulse.

[0019] This can produce a smooth overall time-domain distribution. The subpulse length and emission time of each subpulse can be individually optimized to produce the desired overall time-domain distribution.

[0020] The laser pulse can have a roughly flat-topped time-domain distribution.

[0021] The laser pulse can be considered as having a box-shaped profile in the time domain.

[0022] The subpulse may have a roughly flat-topped spatial beam distribution at the corresponding target destination. The subpulse may have a Gaussian beam profile.

[0023] The generally flat-topped spatial beam distribution can be considered as a constant intensity across the cross-section of the laser beam. The spatial distribution and instantaneous intensity can be optimized to maximize conversion efficiency and in-band EUV energy at output.

[0024] The at least one optical element may include at least one of the following: an optical element, a telescope, a lens, multiple lenses, a convex lens, a concave lens, a mirror, a curved mirror, and multiple mirrors.

[0025] One or more optical elements can control the beam size and divergence.

[0026] The pulse length of each sub-pulse can be at least one of the following: substantially the same; in the range of 10 ns to 30 ns per sub-pulse; in the range of 10 ns to 100 ns per sub-pulse; in the range of 60 ns to 100 ns per sub-pulse; in the range of 200 ns to 300 ns per sub-pulse; 20 ns; and 100 ns.

[0027] The pulse length of each sub-pulse can be shorter than the duration of the laser pulse. The pulse length of each sub-pulse can be optimized individually.

[0028] The pulse length of the laser pulse can be at least one of the following: in the range of 100 ns to 300 ns; and 200 ns.

[0029] It should be understood that the laser pulses mentioned here are combined laser pulses (a combination of multiple sub-pulses).

[0030] The laser pulse may have a wavelength of at least one of the following: in the range of 1.5 to 3 μm; and 2 μm.

[0031] The subpulse may have a wavelength of at least one of the following: in the range of 1.5 to 3 μm; and 2 μm.

[0032] The laser pulse may have a power of at least one of the following: in the range of 60 to 100 kW; and 50 kW.

[0033] It should be understood that the laser pulses mentioned here are combined laser pulses (a combination of multiple sub-pulses). The sub-pulses may have a power in the range of 6 to 10 kW per sub-pulse; or in the range of 60 to 100 kW per sub-pulse. Each submodule can deliver 5 kW sub-pulses.

[0034] The laser system may include an optical arrangement configured to generate the sub-pulses from the incident pulse.

[0035] The incident pulse can be at least one of the following: a main pulse; a main pulse from a main pulse module; one or more sub-pulses; or one or more sub-pulses from at least one of the multiple sub-modules.

[0036] The optical arrangement may include at least one electro-optic modulator configured to split the incident pulse into the sub-pulses.

[0037] The optical arrangement may include at least one polarization splitting optical element configured to separate the subpulses into different paths.

[0038] The polarization splitting optical element may include at least one of the following: a polarization beam splitter, a thin-film polarizer, and a crystal polarizer.

[0039] The electro-optic modulator can be configured to preferably switch the polarization of the incident pulse approximately midway through the incident pulse.

[0040] The electro-optic modulator can be configured to switch the polarization of the incident pulse approximately instantaneously or gradually over time.

[0041] The electro-optic modulator can be configured to preferably change the divergence of the incident pulse at a predetermined time or gradually over time.

[0042] The optical arrangement can be configured to generate a corresponding subpulse from another subpulse in the subpulse.

[0043] The optical arrangement may include a plurality of electro-optic modulators, wherein at least one of the plurality of electro-optic modulators may be configured to split another sub-pulse in the sub-pulse to generate the corresponding sub-pulse.

[0044] The optical arrangement may include a plurality of polarization-splitting optical elements, wherein at least one of the plurality of polarization-splitting optical elements may be configured to separate another sub-pulse and the corresponding sub-pulse.

[0045] The optical arrangement can be configured to merge the subpulses onto the same path after the subpulses have been transmitted through the corresponding optical elements arranged to spatially separate the subpulses.

[0046] The optical arrangement may include at least one polarization combining optical element or at least one combining electro-optic modulator configured to combine the subpulses onto the same path.

[0047] The optical arrangement may include a final optical system located after the respective optical elements arranged to spatially separate the subpulses, preferably wherein the final optical system may be at an angle relative to each other.

[0048] The optical arrangement can be configured to generate subpulses from the merged subpulses.

[0049] The optical arrangement may include at least two electro-optic modulators. At least one electro-optic modulator (and at least one polarization splitting optical element) may be located after (e.g., on the same optical path) another electro-optic modulator (and another polarization splitting optical element). The at least one electro-optic modulator may be configured to split the merged subpulse into the subpulse.

[0050] According to a second aspect of the invention, a laser-generated plasma radiation source is provided, comprising: a fuel emitter operable to provide a fuel target at a plasma formation region; and a laser system as described above.

[0051] According to a third aspect of the present invention, a photolithography system is provided, comprising: a laser-generated plasma radiation source as described above; and a photolithography apparatus.

[0052] The lithography equipment can be an EUV lithography equipment.

[0053] According to a fourth aspect of the invention, a method is provided comprising: generating a plurality of subpulses having a predetermined pulse length; temporally combining the plurality of subpulses to form a laser pulse having a specific duration; and spatially separating each of the subpulses using at least one optical element of the laser system for incident on a fuel target located at a corresponding target destination.

[0054] The method may further include sequentially emitting corresponding sub-pulses from multiple sub-modules at different times, such that the sub-pulses are combined approximately continuously in time to generate the laser pulse.

[0055] The method may also include generating the sub-pulse from the incident pulse using an optical configuration.

[0056] According to a fifth aspect of the invention, a computer program is provided that includes computer-readable instructions configured to cause a processor to perform the methods described above.

[0057] According to a sixth aspect of the present invention, a computer-readable medium carrying a computer program as described above is provided.

[0058] According to a seventh aspect of the present invention, a computer device is provided, comprising: a memory storing processor-readable instructions; and a processor arranged to read and execute the instructions stored in the memory; wherein the processor-readable instructions include instructions arranged to control the computer to perform the methods described above. Attached Figure Description

[0059] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic diagrams, in which:

[0060] Figure 1 A lithography system, including lithography equipment and a radiation source, is schematically depicted.

[0061] Figure 2 A laser system according to an embodiment of the present invention is schematically depicted;

[0062] Figure 3 A graph depicting the relationship between the power and time of a sub-pulse generated by a laser system according to an embodiment of the present invention;

[0063] Figure 4 A graph depicting the spatial intensity of a sub-pulse generated by a laser system according to an embodiment of the present invention;

[0064] Figure 5 A method for using a laser system in a photolithography system according to an embodiment of the present invention is described;

[0065] Figure 6 A laser system according to an embodiment of the present invention is schematically depicted;

[0066] Figure 7 A graph depicting the voltage of the electro-optic modulator over time and the beam intensity levels of the two sub-pulses generated by the laser system over time according to an embodiment of the present invention;

[0067] Figure 8 A graph depicting the voltage of the electro-optic modulator over time at different voltage switching times according to an embodiment of the present invention, and the beam intensity levels of the two sub-pulses generated by the laser system over time;

[0068] Figure 9 A laser system according to an embodiment of the present invention is schematically depicted;

[0069] Figure 10 A laser system according to an embodiment of the present invention is schematically depicted;

[0070] Figure 11 A laser system according to an embodiment of the present invention is schematically depicted;

[0071] Figure 12 A laser system according to an embodiment of the present invention is schematically depicted. Detailed Implementation

[0072] Figure 1A lithography system including a radiation source SO and a lithography apparatus LA is shown. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an irradiation system IL, a support structure MT configured to support a pattern forming apparatus MA (e.g., a mask), a projection system PS, and a substrate stage WT configured to support a substrate W.

[0073] The irradiation system IL is configured to adjust the EUV radiation beam B before it is incident on the pattern forming apparatus MA. Additionally, the irradiation system IL may include a faceted field mirror assembly 10 and a faceted pupil mirror assembly 11. Together, the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11 provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. In addition to or in place of the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11, the irradiation system IL may include other mirrors or devices.

[0074] After such adjustment, the EUV radiation beam B interacts with the patterning apparatus MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. A projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate stage WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image with features smaller than the corresponding features on the patterning apparatus MA. For example, a reduction factor of 4 or 8 may be applied. Although in Figure 1 The projection system PS is illustrated as having only two mirrors 13 and 14, but the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0075] The substrate W may include a previously formed pattern. In this case, the photolithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

[0076] A relative vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure far below atmospheric pressure, can be provided in the radiation source SO, the irradiation system IL, and / or the projection system PS.

[0077] Figure 1The radiation source SO shown belongs to the type that can be referred to as a laser-generated plasma (LPP) source, for example. The laser system 1 is arranged to store energy via a laser beam 2 into a fuel, such as tin (Sn), supplied from a fuel emitter 3, for example. Although tin is mentioned in the following description, any suitable fuel can be used. The fuel can be, for example, in liquid form and can be, for example, a metal or alloy. The fuel emitter 3 may include a nozzle configured to guide tin, for example, in droplet form, along a trajectory toward the plasma forming region 4. The laser beam 2 is incident on the tin at the plasma forming region 4. Storing laser energy in the tin generates tin plasma 7 at the plasma forming region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during electron de-excitation and ion recombination with the plasma.

[0078] Collector 5 collects and focuses EUV radiation from the plasma. Collector 5 includes, for example, a near-normal incident radiation collector 5 (sometimes more commonly referred to as a normal incident radiation collector). Collector 5 may have a multi-layered mirror structure arranged to reflect EUV radiation (e.g., EVU radiation with a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two foci. The first foci may be located at the plasma formation region 4, and the second foci may be located at the intermediate foci 6, as discussed below.

[0079] Laser system 1 can be spatially separated from radiation source SO. In such a case, laser beam 2 can be transmitted from laser system 1 to radiation source SO by means of a beam delivery system (not shown) including, for example, suitable directional mirrors and / or beam expanders and / or other optical devices. Laser system 1, radiation source SO, and beam delivery system can be considered together as a radiation system.

[0080] The radiation reflected by collector 5 forms an EUV radiation beam B. EUV radiation beam B is focused at intermediate focal point 6 to form an image of the plasma present in plasma formation region 4 at intermediate focal point 6. The image at intermediate focal point 6 serves as a virtual radiation source for irradiating system IL. Radiation source SO is arranged such that intermediate focal point 6 is located at or near opening 8 in the enclosure structure 9 of radiation source SO.

[0081] exist Figure 2 The laser system 1 is depicted schematically in more detail and illustrated with dashed lines. The laser system 1 can be considered as a seed laser system (or a driving laser system). The laser system 1 includes multiple sub-modules: a first sub-module 20A (in...) Figure 2 The topmost part is shown), the second submodule 20B (in Figure 2 (shown in the middle) and the third submodule 20C (in Figure 2(Seen at the bottom). Multiple submodules 20A, 20B, and 20C are each configured to emit a corresponding subpulse 22 of a predetermined pulse length. Each submodule 20A, 20B, and 20C can be considered a separate laser emitting the subpulse 22. The subpulses 22 are combined to form a laser beam 2 (which can be referred to as a laser pulse). Although in Figure 2 The diagram shows three submodules 20A, 20B, and 20C, but it should be understood that more or fewer submodules may exist. For example, there may be only two submodules or there may be ten submodules.

[0082] Laser pulse 2 is incident on plasma formation region 4 (in Figure 2 The laser pulse 2 is shown as a droplet 26 (more commonly referred to as a fuel target) in the image (shown as a dashed line). The laser pulse 2 can be considered a combined laser pulse. That is, sub-pulses 22 are combined to form laser pulse 2. Specifically, sub-pulses 22 with predetermined pulse lengths are combined temporally to form laser pulse 2 with a specific duration. Each of the sub-modules 20A, 20B, and 20C is configured to sequentially emit a corresponding sub-pulse 22 at different times, such that the sub-pulses 22 are combined temporally in a substantially continuous manner to generate laser pulse 2. The temporal combination of sub-pulses 22 from multiple sub-modules 20A, 20B, and 20C means that there is no relatively long single pulse from a single laser module.

[0083] Instead of firing all the sub-pulses at once, sub-pulses 22 can be emitted toward the droplet 26 at different times. In an embodiment, each sub-module 20A, 20B, 20C can be turned on for the duration of a sub-pulse 22 of a predetermined pulse length. Each sub-module 20A, 20B, 20C is turned on and off at different times to generate the desired combined laser pulse 2.

[0084] In this embodiment, submodules 20A, 20B, and 20C are solid-state laser modules and are fiber laser systems. Submodules 20A, 20B, and 20C are arranged for coherent beam combining of the fiber laser system. Laser system 1 can be arranged for spatial beam combining or polarization beam combining among submodules 20A, 20B, and 20C. It should be understood that in other embodiments, the submodules can be different types of laser modules.

[0085] In this embodiment, each sub-pulse 22 has a wavelength of 2 μm (approximately 2 μm). Therefore, the (combined) laser pulse 2 also has a wavelength of 2 μm. It should be understood that in other embodiments, the wavelength of the laser beam can be different. For example, the wavelengths of the sub-pulse 22 and the laser pulse 2 can be in the ranges of 1.5 μm to 3 μm, 1 μm to 5 μm, 1 μm to 3 μm, 1.5 μm to 5 μm, greater than 1 μm, greater than 1.5 μm, less than 3 μm, and / or less than 5 μm. When compared to a 10.6 μm CO2-driven laser, a 1 μm solid-state driven laser can have a significantly lower conversion efficiency (CE) (but even with a lower CE, it can still operate precisely). However, this is not a problem for a 2 μm solid-state laser-driven laser. In fact, using a laser with a wavelength of 2 μm instead of, for example, a 10.6 μm CO2-driven laser has many advantages. The first advantage is its high "wall-plug efficiency," which is the efficiency of converting electrical energy into laser energy. The second advantage is the fact that the 2 μm driven laser can operate without any pre-pulses. The third advantage is that the 2 μm driven laser can achieve significantly higher single-pulse energy. This can potentially increase EUV source power without involving improvements in conversion efficiency (CE) or further increasing the pressure in the droplet emitter.

[0086] For a 2 μm driven laser, target pre-shaping is not required, and instead, a relatively long (e.g., ~200 ns) master pulse (or laser pulse) is used compared to a 10.6 μm CO2 driven laser, which can have a master pulse length of ~60 ns. This relatively long pulse will cause a significant propulsion of the droplet during the laser pulse, resulting in a significant path for plasma probing along the laser caustic curve. Such a “z-jump” distance can be up to 800 μm. However, using multiple sub-modules 20A, 20B, 20C and combining the sub-pulses 22 in the manner described to generate a combined laser beam 2 allows for the adaptation of this significant propulsion, as will be explained in more detail.

[0087] Subpulses 22 can be directed to plasma formation region 4 using beam steering. For example, in this embodiment, optical components 28 are used to align subpulses 22 with each other. Because subpulses 22 are temporally separated, coherent combination is not possible. Therefore, polarization combination or spatial combination can be used. For polarization combination, if more than two beams (subpulses 22) are being combined, an electro-optic modulator (EOM) may be required. Other components may be needed for combining the subpulses. For simplicity of illustration, in Figure 2The active polarization component is omitted, and only the general optical component 28 is shown schematically. It should be understood that, depending on the type of combination used (e.g., polarization or spatial), these optical components 28 can be any optical elements that combine the sub-pulses 22 as needed. Furthermore, in this embodiment, the mirror 30 is used to guide the (combined) laser pulse 2 to the plasma formation region 4.

[0088] The laser system 1 includes corresponding optical elements 32 arranged to spatially separate each sub-pulse 22 for incident on a droplet 26 located at a corresponding target destination. In this embodiment, the optical elements 32 form a telescope (shown schematically). The telescope includes convex and concave lenses. It should be understood that in other embodiments, the optical elements 32 may be different. For example, in other embodiments, the optical elements 32 may be lenses, multiple lenses, mirrors, curved mirrors, multiple curved mirrors, or multiple mirrors. One or more optical elements can control the beam size and divergence.

[0089] Optical element 32 focuses sub-pulses 22 (i.e., each sub-pulse laser beam) onto a different spatial point in the plasma formation region 4 (compared to other sub-pulses). This allows droplets 26 to move over time, for example, from one corresponding target destination (relative to one sub-pulse) to another corresponding target destination (relative to another sub-pulse). That is, the corresponding target destinations can be considered to be in different locations over time.

[0090] This is Figure 2 As shown in the diagram, Figure 2 The diagram shows multiple target destinations 34A, 34B, and 34C for droplet 26, corresponding to each corresponding sub-pulse 22 from each of the respective sub-modules 20A, 20B, and 20C. More specifically, the first sub-module 20A has a corresponding target destination 34A (shown in dashed lines) where droplet 26 is located. The second sub-module 20B has a corresponding target destination 34B, where droplet 26 will be located when a sub-pulse 22 from the second sub-module 20B reaches that location. Finally, the third sub-module 20C has a corresponding target destination 34C, where droplet 26 will be located when a sub-pulse 22 from the third sub-module 20C reaches that location. Each sub-pulse 22 from the respective sub-modules 20A, 20B, and 20C will be focused onto the corresponding target destination 34A, 34B, or 34C. For example, a sub-pulse 22 from the second sub-module 20B will be focused onto target destination 34B.

[0091] Typically, the first submodule 20A will be aligned and configured to provide the desired intensity at the target location of droplet 26 (i.e., target destination 34A), where droplet 26 is located at the target location at the correct time. The next laser submodules 20B and 20C provide subsequent subpulses 22 at the actual target location of droplet 26 at the correct time (i.e., target destinations 34B and 34C). It should be understood that the acceleration of droplet 26 (i.e., the target) will need to be considered as it increases sequentially. This is because each time subpulse 22 is incident on droplet 26, the droplet is given a further jolt and is thus propelled more rapidly.

[0092] The movement of droplet 26 over time is primarily due to the effect of subpulse 22 incident on droplet 26 and providing a propulsion source in the z-direction (i.e., z-jump). Lateral movement can also be considered because droplet 26 can be emitted in the y-direction at a significant velocity (e.g., ~100 m / s). This means that during the duration of laser pulse 2 (e.g., 200 ns), there exists a lateral displacement (~perpendicular to the light propagation direction) of a certain distance (e.g., ~20 μm). This lateral displacement is still small (but not negligible) compared to the z-displacement (which can be ~800 μm). Therefore, movement in both the z and y directions can be considered when subpulse 22 is focused on the corresponding target destinations 34A, 34B, and 34C. The effect of gravity on droplet 26 can be ignored because its contribution to the movement of droplet 26 is negligible. For some embodiments of the optical system, significant propulsion of droplet 26 may not be desirable for EUV radiation collection.

[0093] It is necessary to consider the movement of droplet 26 over time because the total time (specific duration) of laser pulse 2 (i.e., the combination of sub-pulses 22) is longer than that of the previous laser system, and therefore the droplet moves relatively farther, which needs to be taken into account accordingly. For example, the specific duration of laser pulse 2 could be ~200 ns instead of, for example, ~60 ns in the previous laser system. The advantage of having multiple sub-pulses 22 instead of a single long laser pulse (from a single laser module) means that the sub-pulses 22 can be better spatially positioned (e.g., compared to a single laser pulse) to obtain the optimal intensity distribution of EUV generation over the entire propulsion trajectory of droplet 26. Using a larger number of sub-modules (e.g., ten sub-modules instead of...) Figure 2 The three sub-modules described in the text mean that each sub-pulse can have a relatively short pulse length, and there will be an even better spatial distribution of sub-pulses 22 in order to obtain further improvement on the optimal intensity distribution of EUV generation across the entire propulsion trajectory.

[0094] In this embodiment, the pulse length of each sub-pulse 22 is approximately the same (i.e., lasts for approximately the same duration). Typically, the pulse length of each sub-pulse 22 is shorter than the duration of the laser pulse 2. In an embodiment with ten sub-modules, each sub-pulse 22 lasts, for example, ~20 ns. Therefore, this provides a pulse length of ~200 ns for the (combined) laser pulse 2. It should be understood that in other embodiments, with different numbers of sub-modules, the duration of each sub-pulse can be different and can be tailored to the desired length of the combined laser beam. For example, the pulse length of the sub-pulse can be in the range of 10 ns to 30 ns / sub-pulse, in the range of 10 ns to 100 ns / sub-pulse, in the range of 60 ns to 100 ns / sub-pulse, or in the range of 200 ns / sub-pulse to 300 ns / sub-pulse. As an example, if there are only two or three (3) sub-modules, the sub-pulses from these two or three sub-modules can be in the range of 60 ns to 100 ns. More typically, the length of a subpulse can be approximately ~200 ns / subpulse to 300 ns / subpulse. The pulse length of a (combined) laser pulse can range from 100 ns to 300 ns. The pulse length of a subpulse can be optimized individually. When using different numbers of submodules (e.g., 10 or 3 submodules), the total pulse length will be the same. The pulse length will be set by selecting the initial droplet size and laser intensity.

[0095] In one embodiment, each submodule 20A, 20B, 20C delivers 5 kW of power. In an embodiment with, for example, ten submodules and each submodule delivering 5 kW of power, the (combined) laser pulse 2 has a power of 50 kW. It should be understood that in other embodiments, for example, with a different number of submodules, the power provided by each submodule can be different and can be adapted to the desired power of the combined laser beam. For example, subpulse 22 can have a power in the range of 6 to 10 kW. Thus, laser pulse 2 can have a power in the range of 60 to 100 kW. More typically, the power of a subpulse can be approximately ~60 to 100 kW per number of subpulses. It should be understood that the laser pulse 2 mentioned herein refers to the combined laser pulse 2 (a combination of multiple subpulses 22) – this can be referred to as the total continuous wave (CW) power. This is different from the power of subpulse 22 – which can be referred to as the pulse intensity. In an embodiment, there may be, for example, two subpulses from two 40 kW submodules (lasers), which are combined into an 80 kW laser pulse. Each of the two 40 kW submodules can generate a 100 ns subpulse that is combined into a 200 ns laser pulse with two focal points. It should be understood that in some embodiments, the subpulse can be formed from multiple incident subpulses. These incident subpulses can be generated by the incident submodules. For example, five incident subpulses from five 5 kW incident submodules can be combined to form a 100 ns 25 kW subpulse (effectively forming a 25 kW submodule), which is then combined with another 100 ns 25 kW subpulse (effectively forming a second 25 kW submodule) to form a 200 ns 50 kW laser pulse.

[0096] Figure 3The graph shows the power of subpulse 22 over time. In this embodiment, there are four subpulses 22 instead of three (i.e., four sub-modules). The graph illustrates how multiple individual subpulses 22 can be superimposed in time to produce a smooth overall temporal intensity distribution. In this embodiment, the shape formed by each subpulse 22 is an isosceles trapezoid, and it can be seen that the first subpulse begins before the second subpulse has completed, and there is a superposition segment O (shown by the dotted line). Thus, for example, while the power of the first subpulse has decreased to approximately the midpoint, the power of the second subpulse has increased to approximately the midpoint. Therefore, the combination of the first and second subpulses, which at this point spans the entire superposition segment O, adds up to approximately the same power level as each subpulse 22 when at its maximum power level. Thus, the (combined) laser pulse 2 will have a generally flat-topped temporal distribution. The (combined) laser pulse 2 can be considered as having an overall box-shaped profile or distribution in the temporal domain, and more specifically, in this example, forming an overall isosceles trapezoidal shape (shown by the dashed line). It should be understood that in other embodiments, the shape of the subpulse in the time domain may be different and may be optimized for specific situations.

[0097] Figure 4 The graph shows the spatial intensity of sub-pulse 22. Figure 4 Only one subpulse is shown, but it should be understood that this also applies to the other subpulses. It can be seen that subpulse 22 has a roughly flat-topped spatial beam distribution at the droplet 26 located, for example, at the corresponding target destination 34A. That is, the intensity of the subpulse is essentially at the level of the diameter of the droplet 26. Although the roughly flat-topped spatial beam distribution of subpulse 22 is... Figure 2 The diameter of the sub-pulse is shown to be approximately the same as that of the droplet, but it should be understood that this is merely an example, and it can have a diameter approximately larger than that of the droplet, for example, up to 2 or even 3 times larger. A roughly flat-top spatial beam distribution can be considered as a constant intensity across the cross-section of the laser beam. The spatial distribution and instantaneous intensity can be optimized to maximize conversion efficiency and output in-band EUV energy. It should be understood that sub-pulse 22 does not need to have a roughly flat-top spatial beam distribution. In other embodiments, the sub-pulse can have a different distribution, such as a Gaussian distribution (i.e., a Gaussian beam). Laser pulse 2 can be of the flat-top type, with relatively good beam quality and resolution. As an example, given a 100 μm flat top (e.g., 20 μm resolution at its edges at 1.88 μm), approximately 0.1 NA (numerical aperture) (resolution ~λ / NA) might be required. This would translate to a depth of field DoF (DoF ~λ / 2NA² = 100 μm), after which most of the advantageous characteristics of flat-top beam delivery would disappear.

[0098] Figure 5The illustration shows a method 100 for irradiating the fuel target (e.g., droplet 26) located at the target destinations 34A, 34B, and 34C using a laser pulse 2.

[0099] In the first step 102, three sub-modules 20A, 20B, and 20C generate multiple (three) sub-pulses 22 with predetermined pulse lengths.

[0100] In the second step 104, multiple sub-pulses 22 are combined in time to form a (combined) laser pulse 2 with a specific duration.

[0101] In the third step 106, each of the three sub-pulses 22 is spatially separated using the corresponding optical element 32 of the laser system 1 to be incident from the corresponding sub-modules 20A, 20B, 20C onto the fuel target (droplet 26) located at the corresponding target destinations 30A, 30B, 30C.

[0102] Figure 6 The illustration shows another embodiment of the present invention. Specifically, Figure 6 A laser system 40 is shown, including a main pulse system 42 (which can be considered as a main module or main pulse module). The main pulse module 42 is configured to emit a main pulse 44 (which can be referred to as an incident pulse). The main pulse module 42 can be considered as a laser that emits the incident pulse 44.

[0103] It should be understood that aspects of this embodiment can be combined with other embodiments as previously described. For example, the incident pulse 44 may be a result of the previously described submodules. The laser system 40 includes an optical arrangement configured to generate subpulses from the incident pulse 44. In particular, in this embodiment, an electro-optic modulator (EOM) 46 is provided for splitting the incident pulse 44 into subpulses (first subpulse 48A and second subpulse 48B), and a polarization beam splitter (PBS) 50 is configured to separate the subpulses 48A and 48B into different paths. The first subpulse 48A is shown as a solid line, and the second subpulse 48B is shown as a dashed line. More generally, the polarization beam splitter (PBS) can be considered as a polarization splitting optical element. It should be understood that the polarization beam splitter (PBS) is merely an example, and other polarization splitting optical elements, such as thin-film polarizers and crystal polarizers, can be used.

[0104] EOM 46 is configured to switch the polarization of the incident pulse 44, and this allows PBS 50 to split subpulses 48A, 48B into different paths, since PBS 50 transmits P-polarized light and reflects S-polarized light. More specifically, EOM 46 switches the polarization approximately halfway through the incident pulse 44, meaning that the first half of the incident pulse 44 (which becomes the first subpulse 48A) is P- or S-polarized light, and the second half of the incident pulse 44 (which becomes the second subpulse 48B) is the other of P- or S-polarized light. It should be understood that in other embodiments, the polarization can be switched at different times during the incident pulse 44 (e.g., midway through the first half or midway through the second half).

[0105] The first sub-pulse 48A is transmitted through the PBS 50 along the first path toward the optical system 52A (which may more generally be referred to as one or more optical elements). The second sub-pulse 52B is reflected by the PBS 50 along the second path (different from the first path) toward the optical system 52B (which may more generally be referred to as one or more optical elements). In other words, the second sub-pulse 48B is redirected to a different path than the first sub-pulse 48A (which is shown as the lower path). The optical systems 52A and 52B are arranged to spatially separate each sub-pulse of the sub-pulses 48A and 48B to be incident on the droplet 26 (more generally referred to as the fuel target) at the corresponding respective target destination (the first image i1 and the second image i2 (i.e., different image positions)). The optical systems 52A and 52B provide similar Figure 2 The functionality of the optical element 32 of the laser system 1 in the embodiment.

[0106] A polarization beam combiner (PBC) 54 is provided to combine the second sub-pulse 48B back onto the same path as the first sub-pulse 48A after the sub-pulses 48A and 48B have passed through the optical systems 52A and 52B. More generally, the polarization beam combiner (PBC) can be considered as a polarization combining optical element. It can be thought of at the PBC 54 that the sub-pulses 48A and 48B (having predetermined pulse lengths) are combined in time to form a laser pulse 58 with a specific duration. The sub-pulses 48A and 48B together can be considered as the (master) laser pulse 58.

[0107] A reflector 56 (more generally, an optical component) is provided to direct the second subpulse 48B to the optical system 52B and to the PBC 54.

[0108] The final optical system 60 is provided to focus both sub-pulses 48A and 48B (now on the same path and forming laser pulse 58) onto their respective target destinations i1 and i2. It will be understood that the second sub-pulse 48B (which has followed the lower path) has a different position along the z-axis. Since this will take effect later during laser pulse 58, it will be better aligned with droplet 26, which will move toward this position during the z-jump of laser pulse 58. Thus, switching the polarization using EOM 46 allows for a time-resolved position of droplet 26 after the (main) laser pulse 58 jump.

[0109] Figure 7 (Upper graph) shows the voltage of EOM 46 over time, and (lower graph) shows the beam intensity levels of the first sub-pulse 48A and the second sub-pulse 48B over time.

[0110] like Figure 7 As shown in the upper graph, the polarization of the incident beam 44 is achieved by switching the voltage of EOM 46 from a low value (e.g., 0) to a high value (e.g., 7 kV). It should be understood that 7 kV is merely an example, and the high voltage will depend on the EOM used. In some embodiments, polarization can be achieved by switching the voltage from a high value to a low value. In this embodiment, the voltage switching from low to high is approximately instantaneous (i.e., the switching from one polarization to another is discrete) or at least can be achieved as quickly as possible. However, as in... Figure 7 As can be seen in the lower curve of the graph, during this switching time, there is a certain overlap between the first sub-pulse 48A (solid line) and the second sub-pulse 48B (dashed line).

[0111] Figure 8 (The upper graph) shows the voltage of EOM 46 over time, and (the lower graph) shows the beam intensity levels of the first sub-pulse 48A and the second sub-pulse 48B over time at different voltage switching times. That is, as Figure 8 As shown in the upper plot, the polarization of the incident beam 44 is achieved by gradually switching the voltage of EOM 46 from a low value (e.g., 0) to a high value (i.e., the voltage of EOM 46 slowly increases over time). This means that the ratio between the intensities at two different image positions i1, i2 can also change slowly. Therefore, the switching from one polarization to another does not need to be discrete. This aspect provides more control over the main pulse properties on the z-jump of droplet 26 (and avoids interference since the two images have opposite polarizations).

[0112] Figure 9 The diagram shows four image positions i1 to i4 instead of Figure 6The embodiments of the two image positions i1 and i2 shown are illustrated. Here, the laser system 40' includes an optical arrangement with three EOMs 46 (also referred to as P1, P2, P3) and three corresponding PBSs 50. Similarly, there are three corresponding PBCs 54.

[0113] The first EOM 46 (i.e., P1) splits the incident pulse 44 into a first sub-pulse 48A and a second sub-pulse 48B, while the corresponding PBS 50 separates the first sub-pulse 48A and the second sub-pulse 48B into different paths. Similarly, the second EOM 46 (i.e., P2) splits the first sub-pulse 48A to generate a third sub-pulse 48C, while the corresponding PBS 50 separates the first sub-pulse 48A and the third sub-pulse 48C into different paths. Likewise, the third EOM 46 (i.e., P3) splits the second sub-pulse 48B to generate a fourth sub-pulse 48D, while the corresponding PBS 50 separates the second sub-pulse 48B and the fourth sub-pulse 48D into different paths.

[0114] There are corresponding optical systems 52A, 52B, 52C, and 52D for each of the sub-pulses 48A, 48B, 48C, and 48D.

[0115] In this embodiment, two additional EOMs (which will be referred to as combined electro-optic modulators CEOM 46', also known as P2 (mirror) and P3 (mirror)) with opposite polarization effects exist after optical systems 52A to 52D, which similarly allow subpulses 48A, 48B, 48C, and 48D to be combined into a single path. Thus, laser system 40' can provide four different focusing (image) positions i1 to i4 for the (main) laser pulse 58, thereby providing even greater control over the beam properties at the z position.

[0116] Figure 10 An embodiment of laser system 40'' is shown, wherein at least some of the sub-pulses 48A to 48D may not be merged (i.e., they are not spatially superimposed but separated by a small angular difference). More specifically, the first sub-pulse 48A and the third sub-pulse 48C are not merged with the second sub-pulse 48B and the fourth sub-pulse 48D. In this embodiment, there are two different final optical systems 60A, 60B that are angular to each other. This means that at least one of CEOM and PBC may not be required. This is in contrast to Figure 9 The embodiments will be simpler electronically, but more complex optically / mechanically. Figure 10 The sub-pulses 48A to 48D may not be in conjunction with Figure 9 They are merged in the same sense, but they are superimposed in space by means of small-angle alignment. Therefore, it can be considered that the final optical systems 60A and 60B perform this functionality to this extent.

[0117] Figure 11 An embodiment of the laser system 40''' is shown, wherein the optical systems are connected in series. That is, the optical arrangement allows four sub-pulses 48A to 48D to be obtained using only two EOMs 46. This would be simpler electronically, but would make the different focal points dependent on all the optical systems, and thus more optically complex than other embodiments.

[0118] The optical arrangement is configured such that the first sub-pulse 48A and the second sub-pulse 48B, formed using the first EOM 46 (i.e., P1), are each transmitted through optical systems 52A and 52B. Sub-pulses 48A and 48B from the first EOM 46 are then merged before being transmitted through the second EOM 46 (i.e., P2). This then forms a third sub-pulse 48C and a fourth sub-pulse 48D, which are subsequently transmitted through optical systems 52C and 52D, respectively, and then merged before the final optical system 60 focuses all four sub-pulses 48A to 48D (currently on the same path and forming laser pulse 58) to their respective target destinations i1, i2, i3, and i4. It should be understood that, effectively, the first sub-pulse 48A and the second sub-pulse 48B are also transmitted through optical systems 52C and 52D, respectively.

[0119] Figure 12 An embodiment of the laser system 40'''' is shown, in which the properties of the EOM are used in a different manner. Since the voltage applied to the EOM changes its refractive index, it can also be used as a type of lens as the diverging / converging beam passes through it. Thus, in this embodiment, the EOM 46 changes the beam divergence at specific times (or gradually), thereby altering the beam properties at the position of the droplet 26. In this embodiment, two sub-pulses 48A, 48B are formed with two corresponding image positions i1, i2.

[0120] While specific references can be made to the use of lithography equipment in IC manufacturing within this document, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0121] Where circumstances permit, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc. Additionally, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and these actions are actually caused by a computing device, processor, controller, or other means of executing firmware, software, routines, instructions, etc., and may cause actuators or other means to interact with the physical world in performing such operations.

[0122] The following are part of this disclosure.

[0123] 1. A laser system arranged to irradiate a moving fuel target with laser pulses.

[0124] The laser system is arranged to generate a plurality of sub-pulses having a predetermined pulse length, the plurality of sub-pulses being combined in time to form the laser pulse, and

[0125] The laser system further includes at least one optical element arranged to spatially separate the subpulses to be incident on the moving fuel target at different points along the path of the moving fuel target.

[0126] 2. The laser system according to aspect 1, wherein the laser system comprises a plurality of sub-modules, each of the plurality of sub-modules being configured to sequentially emit corresponding sub-pulses at different times, such that the sub-pulses are combined substantially continuously in time to generate the laser pulse.

[0127] 3. The laser system according to aspect 2, comprising at least one of the following: 2 to 20 sub-modules, 10 to 20 sub-modules, 2 to 15 sub-modules, 10 to 15 sub-modules, 2 sub-modules, 3 sub-modules, and 10 sub-modules.

[0128] 4. The laser system according to any of the foregoing aspects, wherein the subpulse is partially superimposed in time with a corresponding neighboring subpulse.

[0129] 5. The laser system according to any of the foregoing aspects, wherein the laser pulses have a generally flat-topped time-domain distribution.

[0130] 6. The laser system according to any of the foregoing aspects, wherein the subpulse has a generally flat-topped spatial beam distribution at the corresponding target destination.

[0131] 7. The laser system according to any of the foregoing aspects, wherein the at least one optical element comprises at least one of an optical element, a telescope, a lens, a plurality of lenses, a convex lens, a concave lens, a mirror, a curved mirror, and a plurality of mirrors.

[0132] 8. The laser system according to any of the foregoing aspects, wherein the pulse length of each subpulse is at least one of the following: substantially the same; in the range of 10 ns to 30 ns; in the range of 10 ns to 100 ns; in the range of 60 ns to 100 ns; in the range of 200 ns / subpulse number to 300 ns / subpulse number; 20 ns; and 100 ns.

[0133] 9. The laser system according to any of the foregoing aspects, wherein the pulse length of the laser pulse is at least one of the following: in the range of 100 ns to 300 ns; and 200 ns.

[0134] 10. The laser system according to any of the foregoing aspects, wherein the laser pulse has a wavelength of at least one of the following: in the range of 1 μm to 5 μm, in the range of 1 μm to 3 μm, in the range of 1.5 μm to 5 μm, in the range of 1.5 μm to 3 μm, greater than 1 μm, greater than 1.5 μm, less than 3 μm, less than 5 μm, and approximately 2 μm.

[0135] 11. The laser system according to any of the foregoing aspects, wherein the laser pulse has a power of at least one of the following: in the range of 60 to 100 kW; and 50 kW.

[0136] 12. The laser system according to any of the foregoing aspects, wherein the laser system includes an optical arrangement configured to generate the sub-pulse from the incident pulse.

[0137] 13. The laser system according to aspect 12, wherein the optical arrangement includes at least one electro-optic modulator configured to split the incident pulse into the sub-pulses.

[0138] 14. The laser system according to aspect 13, wherein the optical arrangement includes at least one polarization splitting optical element configured to separate the subpulses into different paths.

[0139] 15. The laser system according to aspect 13 or 14, wherein the electro-optic modulator is configured to preferably switch the polarization of the incident pulse approximately midway through the incident pulse.

[0140] 16. The laser system according to aspect 15, wherein the electro-optic modulator is configured to switch the polarization of the incident pulse substantially instantaneously or gradually over time.

[0141] 17. The laser system according to aspect 13 or 14, wherein the electro-optic modulator is configured to preferably change the divergence of the incident pulse at a predetermined time or gradually over time.

[0142] 18. The laser system according to any one of aspects 12 to 17, wherein the optical arrangement is configured to generate a corresponding subpulse from another subpulse in the subpulse.

[0143] 19. The laser system according to aspect 18, wherein the optical arrangement includes a plurality of electro-optic modulators, wherein at least one of the plurality of electro-optic modulators is configured to split another sub-pulse of the sub-pulse to generate the respective sub-pulse.

[0144] 20. The laser system according to aspect 19, wherein the optical arrangement includes a plurality of polarization-splitting optical elements, wherein at least one of the plurality of polarization-splitting optical elements is configured to separate another sub-pulse and the corresponding sub-pulse.

[0145] 21. A laser system according to any one of aspects 12 to 20, wherein the optical arrangement is configured to merge the subpulses onto the same path after the subpulses have been transmitted through corresponding optical elements arranged to spatially separate the subpulses.

[0146] 22. The laser system according to aspect 21, wherein the optical arrangement includes at least one polarization combining optical element or at least one combining electro-optic modulator configured to combine the subpulses into the same path.

[0147] 23. The laser system according to any one of aspects 12 to 22, wherein the optical arrangement includes a final optical system located after the respective optical elements arranged to spatially separate the subpulses, preferably wherein the final optical system is at an angle relative to each other.

[0148] 24. The laser system according to any one of aspects 21 to 23, wherein the optical arrangement is configured to generate subpulses from merged subpulses.

[0149] 25. A laser-generated plasma radiation source, comprising:

[0150] A fuel emitter, operable to provide a fuel target at a plasma formation region; and a laser system according to any one of aspects 1 to 24.

[0151] 26. A photolithography system, comprising:

[0152] The laser-generated plasma radiation source according to aspect 25; and

[0153] Photolithography equipment.

[0154] 27. The lithography system according to aspect 26, wherein the lithography equipment is an EUV lithography equipment.

[0155] 28. A method for irradiating a fuel target located at a target destination using a laser pulse, the method comprising:

[0156] Generate multiple sub-pulses with a predetermined pulse length;

[0157] The multiple sub-pulses are combined in time to form the laser pulse having a specific duration, and

[0158] Each subpulse in the subpulse is spatially separated using at least one optical element of the laser system so that it is incident on the fuel target at the corresponding target destination.

[0159] 29. The method according to aspect 28 further includes sequentially emitting corresponding sub-pulses from multiple sub-modules at different times, such that the sub-pulses are combined substantially continuously in time to generate the laser pulse.

[0160] 30. The method according to aspect 28 or 29 further includes generating the sub-pulse from the incident pulse using an optical arrangement.

[0161] 31. A computer program comprising computer-readable instructions configured to cause a processor to perform the method according to any one of aspects 28 to 30.

[0162] 32. A computer-readable medium carrying a computer program according to aspect 31.

[0163] 33. A computer device, comprising:

[0164] Memory, which stores processor-readable instructions; and

[0165] A processor, the processor being configured to read and execute instructions stored in the memory;

[0166] The processor-readable instructions described therein include instructions arranged to control the computer to perform the method according to any one of aspects 28 to 30. While specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in other ways than those described. The above description is intended to be illustrative and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. A laser system configured to irradiate a moving fuel target with laser pulses. The laser system is arranged to generate a plurality of sub-pulses having a predetermined pulse length, the plurality of sub-pulses being combined in time to form the laser pulse, and The laser system further includes at least one optical element arranged to spatially separate the subpulses to be incident on the moving fuel target at different points along the path of the moving fuel target.

2. The laser system according to claim 1, wherein, The laser system includes multiple sub-modules, each of which is configured to sequentially emit corresponding sub-pulses at different times, such that the sub-pulses are combined approximately continuously in time to generate the laser pulse.

3. The laser system according to any of the preceding claims, wherein, The sub-pulse is partially superimposed in time with its corresponding neighboring sub-pulse.

4. The laser system according to any of the preceding claims, wherein, The sub-pulse has a roughly flat-topped spatial beam distribution at the corresponding target destination.

5. The laser system according to any of the preceding claims, wherein, The pulse length of each sub-pulse is at least one of the following: substantially the same; in the range of 10 ns to 30 ns; in the range of 10 ns to 100 ns; in the range of 60 ns to 100 ns; in the range of 200 ns / sub-pulse number to 300 ns / sub-pulse number; 20 ns; and 100 ns.

6. The laser system according to any of the preceding claims, wherein, The pulse length of the laser pulse is at least one of the following: in the range of 100 ns to 300 ns; and 200 ns.

7. The laser system according to any of the preceding claims, wherein, The laser pulse has a wavelength of at least one of the following: in the range of 1 μm to 5 μm, in the range of 1 to 3 μm, in the range of 1.5 μm to 5 μm, in the range of 1.5 μm to 3 μm; greater than 1 μm; greater than 1.5 μm; less than 3 μm; less than 5 μm; and approximately 2 μm.

8. The laser system according to any of the preceding claims, wherein, The laser system includes an optical arrangement configured to generate the sub-pulses from the incident pulse.

9. The laser system according to claim 8, wherein, The optical arrangement includes at least one of the following: An electro-optic modulator configured to split the incident pulse into the sub-pulses; and A polarization splitting optical element configured to separate the sub-pulses into different paths.

10. The laser system according to claim 9, wherein, The electro-optic modulator is configured to: Preferably, the polarization of the incident pulse is switched approximately midway through the incident pulse; The polarization of the incident pulse is switched approximately instantaneously or gradually over time.

11. The laser system according to claim 9, wherein, The electro-optic modulator is configured to preferably change the divergence of the incident pulse at a predetermined time or gradually over time.

12. The laser system according to any one of claims 8 to 11, wherein, The optical arrangement is configured to generate a corresponding subpulse from another subpulse in the subpulse.

13. The laser system according to claim 12, wherein, The optical arrangement includes a plurality of electro-optic modulators, wherein at least one of the plurality of electro-optic modulators is configured to split another sub-pulse in the sub-pulse to generate the corresponding sub-pulse, and / or The optical arrangement includes a plurality of polarization-splitting optical elements, wherein at least one of the plurality of polarization-splitting optical elements is configured to separate another sub-pulse and the corresponding sub-pulse.

14. The laser system according to any one of claims 8 to 13, wherein, The optical arrangement is configured to merge the subpulses onto the same path after the subpulses have been transmitted through corresponding optical elements arranged to spatially separate the subpulses, wherein the optical arrangement includes at least one polarization combining optical element or at least one combining electro-optic modulator configured to merge the subpulses onto the same path.

15. The laser system according to any one of claims 8 to 14, wherein, The optical arrangement includes a final optical system located after the respective optical elements arranged to spatially separate the sub-pulses, preferably wherein the final optical system is at an angle relative to each other.

16. The laser system according to any one of claims 14 to 15, wherein, The optical arrangement is configured to generate subpulses from the merged subpulses.

17. A laser-generated plasma radiation source, comprising: A fuel launcher, operable to provide a fuel target at a plasma formation region; And the laser system according to any one of claims 1 to 16.

18. A photolithography system, comprising: The laser-generated plasma radiation source according to claim 17; and The lithography equipment is an EUV lithography equipment.

19. A method for irradiating a fuel target located at a target destination using a laser pulse, the method comprising: Generate multiple sub-pulses with a predetermined pulse length; The multiple sub-pulses are combined in time to form the laser pulse having a specific duration, and Each subpulse in the subpulse is spatially separated using at least one optical element of the laser system so that it is incident on the fuel target at the corresponding target destination.

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