Lithography system

Abstract

A lithography system comprising a lithography apparatus and a radiation source, wherein the radiation source comprises a fuel ejector capable of providing a fuel target to a plasma formation region, and further comprises a laser system operable to provide a laser beam that generates EUV radiation used to expose a substrate by being incident on the fuel target, the laser system comprising a seed laser and a laser beam amplification system comprising a series of optical amplifiers and a controller, the controller configured to operate the last of the series of optical amplifiers at a power level less than the maximum power level of the last optical amplifier during exposure of an exposure area of ​​the substrate.

Description

Technical Field

[0001] (Cross - reference to related applications)

[0001] This application claims priority to European Application No. 23174642.1, filed on May 22, 2023, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present invention relates to a lithography system. The lithography system may comprise an extreme ultraviolet (EUV) radiation source and a lithography apparatus.

Background Art

[0003]

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithography apparatus can project a pattern in a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on the substrate.

[0004]

[0004] To project a pattern onto a substrate, the lithography apparatus can use electromagnetic radiation. The wavelength of this radiation is within the range of 4 - 20 nm that determines the minimum size of the features that can be formed on the substrate. For example, when using a lithography apparatus using extreme ultraviolet (EUV) radiation having a wavelength of 6.7 nm or 13.5 nm, smaller features can be formed on the substrate than when using a lithography apparatus using radiation with a wavelength of 193 nm.

[0005]

[0005] EUV radiation for a lithography apparatus may be generated by a laser - produced plasma (LPP) radiation source. In the LPP radiation source, a laser beam provided by a laser system may be used to irradiate fuel droplets, generating a plasma that emits EUV radiation.

[0006]

[0006] The laser beam used to illuminate the fuel droplets is preferably high-power. A laser beam amplification system amplifies the laser beam to provide this high power. A laser beam amplification system can use a considerable amount of energy.

[0007]

[0007] In some cases, it is desirable to provide a laser beam amplification system that addresses the problem of high energy consumption or the challenges associated with the prior art by a method not disclosed or suggested in the prior art. [Overview of the project]

[0008]

[0008] According to a first aspect of the present invention, a lithography system is provided comprising a lithography apparatus and a radiation source, wherein the radiation source comprises a fuel ejector operable to provide a fuel target to a plasma formation region, and a laser system operable to provide a laser beam that generates EUV radiation used to expose a substrate, the laser system comprising a seed laser and a laser beam amplification system comprising a series of optical amplifiers and a controller, the controller configured to operate the last of the series of optical amplifiers at a power level less than the maximum power level of the last optical amplifier during exposure of an exposure area of ​​the substrate.

[0009]

[0009] Advantageously, by operating the last optical amplifier at a power level below the last optical amplifier's maximum power level, the efficiency of laser beam amplification is improved (compared to when the last optical amplifier was operating at its maximum power level).

[0010]

[0010] The controller may operate the last optical amplifier in the series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series.

[0011]

[0011] The laser beam amplification system may include four optical amplifiers.

[0012]

[0012] The controller may be configured to operate the last optical amplifier at less than 90% of the last optical amplifier's maximum power level during exposure of the exposure area.

[0013]

[0013] The controller may be configured to operate the last optical amplifier at less than 80% of the maximum power of the last optical amplifier during exposure of the exposure area.

[0014]

[0014] The controller may be further configured to operate the second-to-last optical amplifier in a series at a power level less than 100% of the maximum power level during exposure of the exposure area.

[0015]

[0015] The controller may be configured to operate the second-to-last optical amplifier in the series at a power level lower than the power level relative to the maximum power level of each of the upstream optical amplifiers in the series during exposure of the exposure area.

[0016]

[0016] The controller may be configured to simultaneously adjust the power levels of the optical amplifiers in a series.

[0017]

[0017] The controller may be configured to modulate the power level of the last of the series of optical amplifiers based on the power of the amplified laser beam output from the last optical amplifier and / or based on the power of the EUV radiation provided by the radiation source.

[0018]

[0018] The controller may be configured to modulate the power level of each of the optical amplifiers in the series based on the power of the amplified laser beam output from the last optical amplifier.

[0019]

[0019] The lithography system may further include a photodetector configured to provide an output indicating the power of the amplified laser beam output from the final optical amplifier.

[0020]

[0020] The controller may be configured to further reduce the power delivered to the last of the series of optical amplifiers when the substrate is not exposed.

[0021]

[0021] According to a second aspect of the present invention, a lithography system is provided comprising a lithography apparatus and a radiation source, wherein the radiation source comprises a fuel ejector operable to provide a fuel target to a plasma formation region, and a laser system operable to provide a laser beam that generates EUV radiation used to expose a substrate, the laser system comprising a seed laser and a laser beam amplification system comprising a series of optical amplifiers and a controller, the controller configured to operate the last of the series of optical amplifiers at a power level relative to the maximum power level that is lower than the power level relative to the respective maximum power levels of the other optical amplifiers in the series.

[0022]

[0022] Advantageously, efficiency is improved by operating the last optical amplifier at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series. This may be applied while the exposure area is exposed or when the exposure area is not exposed.

[0023]

[0023] The controller may be configured to operate the last photoamplifier at a lower power level during exposure of the exposure area of ​​the substrate.

[0024]

[0024] The controller may operate the penultimate optical amplifier in the series at a relative power level with respect to the maximum power level that is lower than the relative power level with respect to each of the upstream optical amplifiers in the series.

[0025]

[0025] The controller may be configured to operate the penultimate optical amplifier at a lower power level during exposure of the exposed area of the substrate.

[0026]

[0026] According to a third aspect of the present invention, there is provided a method of amplifying a laser beam used to generate EUV radiation during exposure of an exposed area of a substrate, the method comprising receiving the laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last optical amplifier in the series operates at a power level less than the maximum power level of the last optical amplifier.

[0027]

[0027] Advantageously, this can improve efficiency.

[0028]

[0028] According to a fourth aspect of the present invention, there is provided a method of amplifying a laser beam used to generate EUV radiation, the method comprising receiving the laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last optical amplifier in the series operates at a relative power level with respect to the maximum power level that is lower than the relative power level with respect to each of the other optical amplifiers in the series.

[0029]

[0029] Advantageously, this can improve efficiency.

[0030]

[0030] The features of different aspects of the present invention may be combined with each other.

Brief Description of the Drawings

[0031]

[0031] Embodiments of the present invention will be described by way of example only with reference to the accompanying schematic diagrams.

[0032] [Figure 1] A schematic diagram of a lithography system comprising a lithography apparatus and a radiation source according to one embodiment of the present invention is shown. [Figure 2] A schematic diagram of a laser system that constitutes part of one embodiment of the present invention is shown. [Figure 3] The operation of a laser beam amplification system according to one embodiment of the present invention is schematically shown. [Figure 4] The operation of a laser beam amplification system according to another embodiment of the present invention is schematically shown. [Figure 5] The operation of a laser beam amplification system according to another embodiment of the present invention is schematically shown. [Modes for carrying out the invention]

[0033]

[0032] Figure 1 shows a lithography system according to one embodiment of the present invention. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply this EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask or reticle), a projection system PS, and a substrate table WT configured to support a substrate W.

[0034]

[0033] The illumination system IL is configured to adjust the EUV radiation beam B before it is incident on the patterning device MA. Therefore, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together, the faceted field mirror device 10 and the faceted pupil mirror device 11 provide the EUV radiation beam B having a desired cross-sectional shape and a desired intensity distribution. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11, or instead of them, the illumination system IL may include other mirrors or devices.

[0035]

[0034] After being adjusted in this manner, the EUV radiation beam B interacts with the patterning device MA. This interaction results in the generation of a patterned EUV radiation beam B'. The 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 have multiple mirrors 13, 14 which are configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS can form an image of a feature smaller than the corresponding feature on the patterning device MA by applying a reduction factor to the patterned EUV radiation beam B'. For example, a reduction factor of 4 or 8 can be applied. In Figure 1, the projection system PS is shown having only two mirrors 13, 14, but the projection system PS may include a different number of mirrors (e.g., 6 or 8 mirrors).

[0036]

[0035] The substrate W may contain a previously formed pattern. If this is the case, the lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the previously formed pattern on the substrate W.

[0037]

[0036] A small amount of gas (e.g., hydrogen) at a relative vacuum, i.e., a pressure well below atmospheric pressure, may be provided within the radiation source SO, the illumination system IL, and / or the projection system PS.

[0038]

[0037] The radiation source SO shown in Figure 1 is of a type that may be called, for example, a laser-generated plasma (LPP) source. The radiation source includes a laser system 1 according to an embodiment of the present disclosure. The laser system 1 may include, for example, a CO2 laser and is configured to impart energy to a fuel, such as tin (Sn), provided from, for example, a fuel ejector 3, via a pulsed laser beam 2. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may be, for example, a liquid, or it may be, for example, a metal or an alloy. The fuel ejector 3 may include a nozzle configured to eject tin, for example, in the form of droplets, along a trajectory toward a plasma-forming region 4. The laser pulsed beam 2 is incident on the tin in the plasma-forming region 4. The deposition of laser energy into the tin generates a tin plasma 7 in the plasma-forming region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during the de-excitation and recombination of electrons with ions in the plasma.

[0039]

[0038] The pulsed laser beam 2 incident on the tin in the plasma formation region 4 may be referred to as the main laser beam or main pulsed laser beam. Each individual pulse of this pulsed laser beam 2 may be referred to as a main pulse.

[0040]

[0039] Before the main laser beam 2 is incident on the tin in the plasma-forming region 4, another pre-pulse laser beam may be incident on the tin. The pre-pulse laser beam may act to change the shape of the tin and increase the conversion efficiency when the main pulse is incident on the tin (next). One or more additional pulses may be used. The pre-pulse laser beam and one or more additional pulses may be provided by different lasers, for example. The pre-pulse laser beam and one or more additional pulses may propagate along one or more beam paths different from the beam path of the main laser beam.

[0041]

[0040] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration with two foci. As will be discussed below, the first of the foci may be in the plasma-forming region 4, and the second of the foci may be in an intermediate focus 6.

[0042]

[0041] The laser system 1 may be spatially separated from the radiation source SO. In this case, the main laser beam 2 can be delivered from the laser system 1 to the radiation source SO with the help of a beam delivery system (not shown) equipped with, for example, a suitable guide mirror and / or beam expander, and / or other optical components. The laser system 1, the radiation source SO, and the beam delivery system can together be considered as a radiation system.

[0043]

[0042] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6, forming an image of the plasma in the plasma-forming region 4 at the intermediate focus 6. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is positioned such that the intermediate focus 6 is located at or near the aperture 8 of the closed structure 9 of the radiation source SO.

[0044]

[0043] The laser system 1 comprises a seed laser system 20 and a laser beam amplification system 21 according to the embodiment of the present disclosure, as schematically shown in Figure 2. A beam steering system 26 is also shown that can deliver the resulting main laser beam 2 to the plasma formation region 4 (see Figure 1).

[0045]

[0044] The seed laser system 20 provides seed laser pulses to the laser beam amplification system 21. The laser beam amplification system 21 comprises four optical amplifiers 22-25 and a controller 28. The optical amplifiers 22-25 may be alternatively referred to as laser beam amplifiers or optical amplifiers. The optical amplifiers 22-25 are arranged in series, with the first optical amplifier 22 amplifying the laser beam output by the seed laser system 20, the second optical amplifier 23 providing further amplification of the laser beam output from the first optical amplifier 22, the third optical amplifier 24 providing further amplification of the amplified laser beam output from the second optical amplifier 23, and the fourth optical amplifier 25 providing further amplification of the laser beam output from the third optical amplifier 24. In this way, the four optical amplifiers 22-25 apply four amplification stages to the laser beam, which are arranged in series and each increases the power of the laser beam. The laser beam output from the fourth and final optical amplifier 25 passes through the beam steering system 26. The beam steering system 26 guides the amplified laser beam toward the plasma formation region 4 (see Figure 1), and the amplified laser beam is incident on the fuel droplets to generate EUV radiation. The amplified laser beam is a pulsed laser beam and may also be referred to as the main pulsed laser beam 2.

[0046]

[0045] The controller 28 controls the power supplied to the optical amplifiers 22-25. The controller 28 may also control the power of the laser beam output from the seed laser system 20. The controller may be configured to individually adjust the power supplied to each optical amplifier 22-25. The optical sensor 30 receives a portion of the amplified laser beam 2 and provides an output signal indicating the power of the amplified laser beam. The controller 28 modulates the power supplied to the optical amplifiers 22-25. The modulation may be based on the output signal provided by the optical sensor 30 (or another sensor), for example, by reference to a desired value. For example, the EUV radiation source controller may issue a command requesting a desired power for the main pulse laser beam 2. The modulation applied by the controller 28 may attempt to maintain the power of the main pulse laser beam 2 at that desired power. The EUV radiation source may use the EUV sensor to determine the requested desired power of the main pulse laser beam 2. The controller 28 may modulate the power supplied to the seed laser system 20 according to the requested desired power. The modulation of the power supplied to the seed laser system 20 and the power supplied to the optical amplifiers 22-25 may be performed simultaneously.

[0047]

[0046] In an embodiment (not shown), an optical sensor may be provided between the second-to-last optical amplifier 24 and the last optical amplifier 25. In this case, the output provided by the optical sensor may be adjusted to take into account the power level provided to the last optical amplifier 25. The adjustment may be converted into a value that represents the power of the amplified laser beam output from the last optical amplifier 25.

[0048]

[0047] Figure 2 shows four optical amplifiers 22-25, but a different number of optical amplifiers may be provided. In general, a series of optical amplifiers may be provided.

[0049]

[0048] Figure 3 schematically shows the operation of a laser beam amplification system 21 according to one embodiment of the present invention. The laser beam amplification system 21 amplifies the laser beam emitted by the seed laser system 20 (see Figure 2) to meet the requirements of the lithography apparatus LA (see Figure 1). During the operation of the lithography apparatus LA, the radiation beam B is projected onto the exposure area on the substrate W. The substrate W is then moved to different positions so that different exposure areas on the substrate receive the patterned radiation beam B. During this movement between different exposure areas of the substrate W, the radiation beam B continues to be supplied by the radiation source SO. A masking blade (not shown) provided adjacent to the patterning device MA is closed during the movement of the substrate W to shield the radiation beam B from entering the substrate W. The masking blade is opened when the substrate W moves to a position for exposure of the next exposure area of ​​the substrate.

[0050]

[0049] During exposure of an exposure area on the substrate, it may be desirable to provide the EUV radiation beam B at a high power. This is because higher power allows the substrate to be exposed faster than at lower power, thus increasing the throughput of the lithography apparatus LA. When no exposure area is exposed, it may be desirable to operate the radiation source SO at a lower power. This reduces the power consumption of the radiation source and may improve the power stability of the radiation source when starting exposure of the next exposure area.

[0051]

[0050] While it may be desirable to provide the EUV radiation beam at high power during exposure of the exposure area, the power of the EUV radiation beam may be less than the maximum possible power. Similarly, the power of the main pulse laser beam 2 may be less than the maximum possible power. There are several possible reasons for this. One possible reason is that the controller 28 needs some room to increase the power of the main pulse laser beam in order to adjust the power of the main pulse laser beam 2 and maintain the power at a desired value. Therefore, the main pulse laser beam 2 should not be at its maximum possible power in order to allow such power increases. Another possible reason is that it may be desirable to expose the exposure area at a power less than the maximum possible power. This is the case, for example, in the requirements of a particular lithography recipe, or when performing a second exposure on a previously exposed area to correct previous exposure errors.

[0052]

[0051] In one embodiment of the present invention, the last optical amplifier 25 of the series of optical amplifiers operates at less than 100% of the maximum power level of the last optical amplifier during exposure of the substrate exposure area. When the last optical amplifier 25 is operating at a power level below its maximum power level, an improvement in the overall efficiency of the laser beam amplification system 21 is obtained. The overall efficiency can be thought of as relating to the power consumption of the laser beam amplification system 21. Power consumption is also referred to as wall-plug power. The improvement in overall efficiency corresponds to a reduction in the wall-plug power required to obtain a given power of the main pulse laser beam 2.

[0053]

[0052] In one embodiment of the present invention, the last optical amplifier 25 of the series of optical amplifiers operates at less than 90% of the maximum power level of the last optical amplifier during exposure of the substrate exposure area. In one embodiment of the present invention, the last optical amplifier 25 of the series of optical amplifiers operates at less than 80% of the maximum power level of the last optical amplifier during exposure of the substrate exposure area.

[0054]

[0053] In the embodiment shown in Figure 3, all four optical amplifiers 22-25 operate at, for example, 85% of their maximum power level during exposure of the substrate exposure area. Sensor 30 provides an output signal indicating the power of the laser beam 2 output from the last optical amplifier 25. This output signal is provided to controller 28. Controller 28 modulates the power supplied to each optical amplifier 22-25 based on the output signal provided by the optical sensor 30. Thus, a feedback loop is provided in which the power supplied to the optical amplifiers 22-25 is modulated based on the output from the optical sensor 30. In the embodiment shown in Figure 3, the optical amplifiers 22-25 each operate at the same power level. In other words, controller 28 increases or decreases the power level at which the optical amplifiers 22-25 operate in a synchronized manner.

[0055]

[0054] The power levels mentioned in relation to Figure 3 (and other figures) are not absolute values, but percentages representing the power level relative to the maximum power level at which each optical amplifier 22-25 can operate. The maximum power level of an optical amplifier is determined by the physical properties of the optical amplifier. For example, optical amplifiers 22-25 may be CO2 gas optical amplifiers. The power supplied to the CO2 gas optical amplifier may include the RF power supplied to the electrodes. The RF power excites the CO2 gas, provides energy to the CO2 gas, and is then transmitted to the laser beam (amplifies the laser beam). The maximum power level of the CO2 gas optical amplifier is achieved when the laser beam does not provide any further amplification even if additional power is supplied to the optical amplifier (the population inversion of the CO2 gas cannot be increased any further). In general, the maximum power level of an optical amplifier can be interpreted as the power level supplied to the optical amplifier so that the amplification of the laser beam is maximized (i.e., the laser beam does not provide any further amplification even if the power supplied to the optical amplifier is further increased).

[0056]

[0055] The absolute power supplied to each of the optical amplifiers 22-25 may be different. For example, the maximum power that can be supplied to the last optical amplifier 25 may be greater than the maximum power that can be supplied to the first optical amplifier 22. The last optical amplifier 25 may be configured to use more power than the first optical amplifier 22 because the power of the laser beam amplified by the last optical amplifier is greater than the power of the laser beam when amplified by the first optical amplifier. As an example, the maximum power level (e.g., RF power) on which each optical amplifier operates is 50 kW for the first optical amplifier 22, 86 kW for the second optical amplifier 23, 116 kW for the second-to-last optical amplifier 24, and 140 kW for the last optical amplifier 25. The wall-plug power supplied to the optical amplifiers may be greater than these powers because the conversion efficiency to RF power (or power of a different gain medium) is not 100%. For example, the conversion efficiency to RF power may be around 80%, meaning that the wall-plug power supplied to the optical amplifiers is about 20% greater than the RF power value.

[0057]

[0056] Figure 3 shows the optical amplifiers 22-25 operating at 85% of their maximum power levels, but the optical amplifiers may operate at different power levels. Generally, the optical amplifiers 22-25 may operate at less than 90% of their maximum power levels on average (during exposure of the substrate exposure area). The optical amplifiers may operate, for example, between 80% and 90% of their maximum power levels on average (during exposure of the substrate exposure area).

[0058]

[0057] In the embodiment shown in Figure 3, the controller 28 simultaneously adjusts the power levels of the optical amplifiers 22-25. The power levels at which the optical amplifiers 22-25 operate may be changed by the controller 28, but any changes are applied simultaneously to all of the optical amplifiers.

[0059]

[0058] In other embodiments, the controller may individually adjust the power levels of the optical amplifiers 22 to 25.

[0060]

[0059] In some embodiments, the power level at which the last optical amplifier operates (relative to its maximum power level) may be lower than the power levels at which the other optical amplifiers operate (relative to their maximum power levels). This may improve the overall efficiency of the laser beam amplification system 21. The efficiency improvement may be applied during the exposure of the substrate exposure area. The efficiency improvement may also be applied between exposures of the substrate exposure area.

[0061]

[0060] In some embodiments, the power level (relative to its maximum power) at which the second-to-last optical amplifier operates may be lower than the power level (relative to their maximum power) at which the upstream optical amplifiers operate. This may further improve the overall efficiency of the laser beam amplification system 21. The efficiency improvement may be applied during the exposure of the substrate exposure area. The efficiency improvement may also be applied between exposures of the substrate exposure area.

[0062]

[0061] The power levels of the last optical amplifier 25 and, if necessary, the other optical amplifiers 22-24 may be modulated based on the signal received from the photodetector 30. That is, a feedback loop may be formed using the photodetector 30 to control the power levels of the last optical amplifier 25 (and, if necessary, the other optical amplifiers 22-24). The feedback loop may be configured to provide a desired power level of the laser beam 2, for example, to compensate for fluctuations in the power of the radiated beam B during exposure of a substrate exposure area.

[0063]

[0062] An alternative embodiment is schematically shown in Figure 4. In this embodiment, the first, second, and third optical amplifiers 22-24 all operate at 87% of their maximum power levels (during substrate exposure area exposure). The last optical amplifier 25 operates at 83% of its maximum power level. The power levels shown in Figure 4 may be average power levels, and the power levels may be modulated based on feedback signals provided by the optical sensor 30 (as in the other embodiments). The power levels of the optical amplifiers 22-25 are controlled by the controller 28.

[0064]

[0063] In this embodiment, the last optical amplifier 25 in the series operates at a lower power level than the other optical amplifiers 22-24 in the series. The power level values ​​shown in Figure 4 are merely examples, and other power levels may be used. In general, the power level at which the last optical amplifier 25 operates may be lower than the power levels at which the other optical amplifiers 22-24 in the series operate. This can improve the overall efficiency of the laser beam amplification system 21.

[0065]

[0064] The power level at which the second-to-last optical amplifier 24 operates may be lower than the power level at which the upstream optical amplifiers 22 and 23 in the series operate. This may further improve the overall efficiency of the laser beam amplification system 21.

[0066]

[0065] In conventional configurations, during exposure of the substrate exposure area, the power level of the last of the series of optical amplifiers 25 is set to 100%. This approach has been adopted based on the understanding that modulating the power level of the last optical amplifier 25 would destabilize the power of the laser beam 2 supplied to the EUV radiation source SO, and as a result, the EUV radiation beam B itself would likely become unstable. However, surprisingly, it has been found that operating the last optical amplifier 25 at a power level of less than 100% does not destabilize the power of the laser beam 2.

[0067]

[0066] In one embodiment, the radiation source SO further comprises at least one additional laser (not shown) configured to provide a pulse that is incident on the fuel droplets before the main laser beam pulse. This additional pulse may be referred to as a prepulse. The prepulse is delivered to the plasmaforming region 4 via a beam path that does not include a series of optical amplifiers 22-25. In conventional radiation sources, the prepulse propagates through a series of optical amplifiers, which complicates the operation of the optical amplifiers and can contribute to power instability of the main laser beam when the last optical amplifier is operated at a power level below its maximum power level. However, in some embodiments of the present invention, the prepulse does not pass through a series of optical amplifiers 22-25, so that the power instability of the laser beam that could otherwise occur when the last optical amplifier 25 is operated at a power level below its maximum power level is not present.

[0068]

[0067] In one embodiment, the power supplied to one or more of the optical amplifiers 22-25 may be reduced when the substrate exposure area is not being exposed (for example, when the substrate is being moved between exposure areas). An example of this is shown in Figure 5. In Figure 5, when the substrate exposure area is not being exposed, each of the optical amplifiers 22-25 is operating at 58% of its maximum power level. The power levels of the optical amplifiers 22-25 are controlled by a controller 28 that receives a signal from the lithography apparatus LA indicating that the substrate exposure area is not being exposed.

[0069]

[0068] The value of 58% is merely an example, and the optical amplifiers 22-25 may operate at other power levels. Generally, when the substrate exposure area is not exposed, the power levels of the optical amplifiers 22-25 may be less than 65% of the maximum power level of the optical amplifiers. The power level may be less than 60% of the maximum power level. Different optical amplifiers 22-25 may operate at different power levels. The last optical amplifier may operate at the same power level as or lower than the power levels of the other optical amplifiers.

[0070]

[0069] It was found that when the last optical amplifier 25 operates at a power level below its maximum power level, an improvement in the overall efficiency of the laser beam amplification system 21 is obtained. Since optical amplifiers 22-25 use a considerable amount of power, this improvement in efficiency leads to a significant cost reduction. Surprisingly, it was found that even in this manner, no significant instability occurs in the power of the laser beam with respect to the output from the series of optical amplifiers 22-25.

[0071]

[0070] Furthermore, it was found that when the second-to-last optical amplifier 24 operates at a power level below its maximum power level, a further improvement in the overall efficiency of the laser beam amplification system 21 can be obtained. This improvement in efficiency also leads to a significant cost reduction.

[0072]

[0071] Generally, the overall efficiency of the laser beam amplification system 21 is achieved when the last optical amplifier 25 is operated below its maximum power level, and, if necessary, when the second to last optical amplifier 24 is operated below its maximum power level.

[0073]

[0072] Embodiments of the present invention can result in energy savings of at least 20kW. Embodiments of the present invention can result in energy savings of 40kW or more.

[0074]

[0073] In some embodiments, one or more prepulses may pass through a series of optical amplifiers 22-25. In this case, it may become more difficult to control the power stability of the amplified main laser beam 2.

[0075]

[0074] Where permitted by context, 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 in a machine-readable medium that can be read and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, the machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, propagating signals of electrical, optical, acoustic or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing specific actions. However, such descriptions are merely for convenience, and it should be understood that such actions actually originate from a computing device, processor, controller, or other device that performs the firmware, software, routines, instructions, etc., and that in the process, actuators or other devices may interact with the material world.

[0076]

[0075] Although this text specifically refers to the use of lithography equipment in the manufacture of ICs, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like.

[0077]

[0076] Although embodiments of the present invention are referred to in the context of lithography apparatus in this text, embodiments of the present invention may also be used in other apparatuses. Embodiments of the present invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be referred to as lithography tools. Such lithography tools may be used under vacuum conditions or ambient (non-vacuum) conditions.

[0078]

[0077] Although specific embodiments of the present invention have been described above, it will be clear that the present invention can be practiced in ways other than those described. The above description is intended to be illustrative and not limiting. Accordingly, it will be obvious to those skilled in the art that the described invention can be modified without departing from the claims set forth below.

[0079]

[0078] Clause 1. A lithography system comprising a lithography apparatus and a radiation source, The radiation source comprises a fuel ejector operable to provide a fuel target to a plasma-forming region, and further comprises a laser system operable to provide a laser beam that generates EUV radiation used to expose the substrate when incident on the fuel target. A lithography system comprising a seed laser and a laser beam amplification system with a series of optical amplifiers and a controller, wherein the controller is configured to operate the last of the series of optical amplifiers at a power level below the maximum power level of the last optical amplifier during exposure of an exposure area of ​​a substrate. 2. The lithography system as described in Clause 1, wherein the controller is configured to operate the last optical amplifier in the series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series. 3. The lithography system according to Clause 1 or Clause 2, comprising four optical amplifiers for the laser beam amplification system. 4. The lithography system as described in any of clauses 1 to 3, wherein the controller is configured to operate the last light amplifier at less than 90% of the maximum power level of the last light amplifier during exposure of the exposure area. 5. The lithography system as described in any of clauses 1 to 4, wherein the controller is configured to operate the last light amplifier at less than 80% of the maximum power of the last light amplifier during exposure of the exposure area. 6. The lithography system as described in any of clauses 1 to 5, wherein the controller is further configured to operate the second-to-last light amplifier in a series at a power level less than 100% of the maximum power level during exposure of the exposure area. 7. The lithography system as described in Clause 6, wherein the controller is configured to operate the second-to-last optical amplifier in a series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the upstream optical amplifiers in the series during exposure of the exposure area. 8. The lithography system described in any of clauses 1 to 7, wherein the controller is configured to simultaneously adjust the power levels of the optical amplifiers in a series. 9. The lithography system according to any one of the clauses 1 to 8, wherein the controller is configured to modulate the power level of the last optical amplifier in a series based on the power of the amplified laser beam output from the last optical amplifier and / or based on the power of the EUV radiation provided by the radiation source. 10. The lithography system as described in Clause 7, wherein the controller is configured to modulate the power level of each of the optical amplifiers in the series based on the power of the amplified laser beam output from the last optical amplifier. 11. The lithography system according to any one of the clauses 1 to 10, further comprising a photodetector configured to provide an output indicating the power of the amplified laser beam output from the final optical amplifier. 12. The lithography system according to any one of clauses 1 to 11, wherein the controller is configured to further reduce the power delivered to the last of the series of optical amplifiers when the substrate is not exposed. 13. A lithography system comprising a lithography apparatus and a radiation source. The radiation source comprises a fuel ejector operable to provide a fuel target to a plasma-forming region, and further comprises a laser system operable to provide a laser beam that generates EUV radiation used to expose the substrate when incident on the fuel target. A lithography system comprising a seed laser and a laser beam amplification system having a series of optical amplifiers and a controller, wherein the controller is configured to operate the last of the series of optical amplifiers at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series. 14. The lithography system as described in Clause 13, wherein the controller is configured to operate the last light amplifier at a lower power level during exposure of the exposure area of ​​the substrate. 15. The lithography system according to Clause 13 or 14, wherein the controller is configured to operate the second-to-last optical amplifier in the series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the upstream optical amplifiers in the series. 16. The lithography system as described in Clause 15, wherein the controller is configured to operate the second-to-last optical amplifier at a lower power level during exposure of the exposure area of ​​the substrate. 17. A method for amplifying a laser beam used to generate EUV radiation during exposure of an exposure area of ​​a substrate, the method comprising receiving a laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last of the series of optical amplifiers operates at a power level less than the maximum power level of the last optical amplifier. 18. A method for amplifying a laser beam used to generate EUV radiation, the method comprising receiving a laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last of the series of optical amplifiers operates at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series.

Claims

1. A lithography system comprising a lithography apparatus and a radiation source, The radiation source comprises a fuel ejector operable to provide a fuel target to a plasma-forming region, and further comprises a laser system operable to provide a laser beam that generates EUV radiation used to expose a substrate when incident on the fuel target. The laser system comprises a seed laser and a laser beam amplification system having a series of optical amplifiers and a controller, wherein the controller is configured to operate the last of the series of optical amplifiers at a power level less than the maximum power level of the last optical amplifier during exposure of an exposure area of ​​a substrate.

2. The lithography system according to claim 1, wherein the controller is configured to operate the last of the series of optical amplifiers at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series.

3. The lithography system according to any one of claims 1 to 2, wherein the controller is configured to operate the last optical amplifier at less than 90%, more preferably less than 80%, of the maximum power level of the last optical amplifier during exposure of the exposure area.

4. The lithography system according to any one of claims 1 to 3, wherein the controller is further configured to operate the second-to-last of the series of optical amplifiers at a power level of less than 100% of the maximum power level during exposure of the exposure area.

5. The lithography system according to claim 4, wherein the controller is configured to operate the second-to-last optical amplifier of the series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the upstream optical amplifiers of the series during exposure of the exposure area.

6. The lithography system according to any one of claims 1 to 5, wherein the controller is configured to simultaneously adjust the power levels of the optical amplifiers in the series.

7. The lithography system according to any one of claims 1 to 6, wherein the controller is configured to modulate the power level of the last of the series of optical amplifiers based on the power of the amplified laser beam output from the last optical amplifier and / or based on the power of the EUV radiation provided by the radiation source.

8. The lithography system according to claim 5, wherein the controller is configured to modulate the power level of each of the series of optical amplifiers based on the power of the amplified laser beam output from the last optical amplifier.

9. The lithography system according to any one of claims 1 to 8, further comprising a photodetector configured to provide an output indicating the power of the amplified laser beam output from the last optical amplifier.

10. The lithography system according to any one of claims 1 to 9, wherein the controller is configured to further reduce the power delivered to the last of the series of optical amplifiers when the substrate is not exposed.

11. A lithography system comprising a lithography apparatus and a radiation source. The radiation source comprises a fuel ejector operable to provide a fuel target to a plasma-forming region, and further comprises a laser system operable to provide a laser beam that generates EUV radiation used to expose a substrate when incident on the fuel target. The laser system comprises a seed laser and a laser beam amplification system having a series of optical amplifiers and a controller, wherein the controller is configured to operate the last of the series of optical amplifiers at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series.

12. The lithography system according to claim 11, wherein the controller is configured to operate the last light amplifier at a lower power level during exposure of the exposure area of ​​the substrate.

13. The lithography system according to claim 11 or 12, wherein the controller is configured to operate the second-to-last optical amplifier in the series at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the upstream optical amplifiers in the series.

14. The lithography system according to claim 13, wherein the controller is configured to operate the second-to-last optical amplifier at a lower power level during exposure of the exposure area of ​​the substrate.

15. A method for amplifying a laser beam used to generate EUV radiation during exposure of an exposure area of ​​a substrate, the method comprising receiving the laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last of the series of optical amplifiers operates at a power level less than the maximum power level of the last optical amplifier.

16. A method for amplifying a laser beam used to generate EUV radiation, the method comprising receiving the laser beam and amplifying the laser beam using a series of optical amplifiers, wherein the last of the series of optical amplifiers operates at a power level relative to the maximum power level that is lower than the power level relative to the maximum power level of each of the other optical amplifiers in the series.

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