Metrology and control system

Abstract

A metrology and control system (100, 400, 500) for a laser beam in an EUV radiation source is disclosed. The system includes an optical pickup (405, 540, 550) configured to measure a forward beam (410, 510, 520, 530) directed towards a target location (420, 535) and a return beam (415) reflected from the target location. The system also includes operable optical devices (425, 430, 435, 465, 475, 555, 560, 565) configurable to direct and focus the forward beam to the target location and to align the measurement plane of the optical pickup with the target location. The operable optical devices are disposed before and after the optical pickup in the path of the forward beam, and the operable optical devices are controlled in response to measurements of the forward beam and the return beam by the optical pickup.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims priority to European Application No. 22184227.1, filed on July 11, 2022, the entire disclosure of which is incorporated herein by reference.

[0002]

[0002] The present invention relates to a metrology and control system for a laser beam in an EUV radiation source and a related method for controlling a laser in an EUV radiation source for a lithographic apparatus.

Background Art

[0003]

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

[0004]

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation can determine the minimum size of the features that can be formed on the substrate. A lithographic apparatus using extreme ultraviolet (EUV) radiation in the range of 4 - 20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than a lithographic apparatus using radiation with a wavelength of 193 nm.

[0005]

[0005] An EUV radiation source can generate EUV radiation, where the EUV radiation source may be of a type that can be referred to as a laser - produced plasma (LPP) source. In such an LPP source, a laser system can be arranged to deposit energy into the fuel in a plasma - forming region via one or more laser beams. The deposition of laser energy into the fuel can create a plasma that emits EUV radiation.

[0006]

[0006] In some examples, the laser system may be configured to supply one or more prepulses and / or vaporization pulses to the fuel to deform and dilute the fuel respectively prior to a subsequent main pulse for generating a plasma. Such prepulses and vaporization pulses may provide a way to optimize the mass density and distribution of the fuel prior to interaction with the subsequent main pulse.

[0007]

[0007] Metrology and control tools may be implemented to monitor and control the laser system to ensure an efficient and optimized process for plasma generation.

[0008]

[0008] However, the position of the fuel in the plasma formation region may vary over time, increasing the complexity of directly maintaining the focus of the laser system on the fuel.

[0009]

[0009] Further, the metrology system may need to be adapted to accommodate a substantial range of measurements resulting from such variations in fuel position. In some examples, due to variations in the position of the fuel, the measurement plane of the metrology system may not exactly coincide with where the laser system is focused on the fuel.

[0010]

[0010] Therefore, it is also desirable to provide metrology and control solutions that can accurately and precisely monitor and control the focusing of one or more laser beams on the fuel in the plasma formation region, suitable for use in an EUV radiation source.

[0011]

[0011] Accordingly, an aim of at least one embodiment of at least one aspect of the present disclosure is to prevent or at least mitigate at least one of the drawbacks of the prior art identified above. Further examples of the prior art are as follows.

SUMMARY OF THE INVENTION

[0012]

[0012] According to a first embodiment of the present disclosure, a metrology and control system for a laser beam in an EUV radiation source is provided. The system comprises an optical pickup configured to measure a forward beam directed towards a target location and a return beam reflected from the target location.

[0013]

[0013] The system also comprises an operable optical device configurable to direct and focus the forward beam towards the target location and to align the measurement plane of the optical pickup with the target location.

[0014]

[0014] The operable optical device is disposed before and after the optical pickup in the path of the forward beam, and the operable optical device is controlled in response to measurements of the forward beam and the return beam by the optical pickup.

[0015]

[0015] Advantageously, the disclosed system enables the target location to be maintained within the rear focal plane of the focusing optics of the system, as will be explained in more detail below, particularly by implementing operable optical devices both before and after the optical pickup.

[0016]

[0016] That is, the operation before the optical pickup enables all important beam characteristics, such as steering, direction, beam size / numerical aperture (NA), and beam curvature, to be controlled into the focusing section of the system, so that the focus of the beam will ultimately be exactly within the rear focal plane of the lens.

[0017]

[0017] The operation after the optical pickup ensures that the target location is positioned exactly within the rear focal plane of the focusing optics by measuring the return beam, for example, the radiation reflected from the fuel at the target location.

[0018]

[0018] The operable optical device may comprise at least one device for controlling the wavefront curvature and / or the diameter of the forward beam.

[0019]

[0019] At least one of the devices may be disposed in front of the optical pickup in the path of the forward beam.

[0020]

[0020] Advantageously, an operable optical device configured to control the curvature and / or diameter of the beam in front of the optical pickup enables maintaining the target location in the rear focal plane while keeping the laser focused on the target location.

[0021]

[0021] Each operable optical device may comprise at least one of a deformable mirror, a position controllable mirror, and a position controllable lens.

[0022]

[0022] Measurement of the forward beam and the return beam by the optical pickup may comprise measurement of the wavefronts of the forward beam and the return beam. Measurement of the forward beam and the return beam by the optical pickup may comprise measurement of the positions of the forward beam and the return beam.

[0023]

[0023] The optical pickup may comprise a first sensor for measuring the forward beam, a second sensor for measuring the return beam, a beam splitting device for directing a part of the forward beam onto the first sensor, and a surface for directing the return beam onto the second sensor. The surface for directing the return beam onto the second sensor may be a reflective surface, for example a surface configured to reflect the return beam. The surface may be the surface of the beam splitting device. The surface may be a further surface of the beam splitting device different from the surface on which the forward beam is incident during use, i.e., the rear surface of the beam splitting device.

[0024]

[0024] The optical pickup may include a first focusing device for focusing the forward beam onto a first sensor. The optical pickup may include a second focusing device for focusing the return beam onto a second sensor. The first and second focusing devices may be configured to match at least one optical focal length of the operable optical devices for focusing the forward beam onto a target location.

[0025]

[0025] That is, when the target location is exactly in the rear focal plane, as realized by the operable optical device after the optical pickup, both the first focusing device and the second focusing device may match the forward beam focal length, and thus the location of the focus of the beam with respect to the target location can be determined.

[0026]

[0026] Advantageously, by effectively matching the optical characteristics of the optical pickup to be equivalent to those of the focusing optics, the metrology and control system can correctly measure the forward beam characteristics particularly relevant to the focusing optics. This can minimize the crosstalk of the beam position error of the forward beam regarding the laser-to-fuel target performance.

[0027]

[0027] The operable optical device may include a plurality of devices that can be arranged after the optical pickup in the path of the forward beam and configured to center the return beam on the second sensor.

[0028]

[0028] Advantageously, by centering the beam on the sensor, the required sensor range can be minimized because the sensors operate near the center of the range. Further, the sensors may exhibit an improved linear response near the center of the measurement range.

[0029]

[0029] The metrology and control system may include operable position controllable mirrors arranged before and after the optical pickup in the path of the forward beam for steering the forward beam.

[0030]

[0030] The metrology and control system may comprise a plurality of optical pickups, each optical pickup being configured to measure one or more forward beams directed towards respective target locations and one or more respective return beams reflected from the respective target locations. The metrology and control system may comprise an operative optical device configurable to direct and focus each forward beam to a respective target location and to align the measurement plane of each optical pickup with the respective target location. The operative optical device may be disposed before and after each optical pickup in the path of each forward beam, and the operative optical device may be controlled in response to the measurement of one or more forward beams and each return beam by each optical pickup.

[0031]

[0031] According to a second aspect of the present disclosure, there is provided a radiation source for an EUV lithography apparatus, the radiation source comprising a metrology and control system according to the first aspect, a fuel ejector for ejecting fuel at a target location, and a laser configured to generate a forward beam that is reflected as a return beam by the fuel.

[0032]

[0032] As described above, the fuel may be in liquid form, for example in the form of droplets ejected along a trajectory towards a plasma formation region. The trajectories of the droplets may vary slightly between droplets. Advantageously, the disclosed radiation source, and in particular the disclosed metrology and control system, effectively enables tracking of the position of the droplets, for example the target location for focusing the forward beam, whereby the position and focus of the forward beam can be appropriately adjusted to optimize plasma generation.

[0033]

[0033] The radiation source may comprise a first laser configured to generate a prepulse forward beam for deforming the fuel, a second laser configured to generate a vaporization pulse forward beam for diluting the fuel, and a third laser configured to generate a main pulse forward beam for generating EUV plasma from the fuel. The metrology and control system may be configured to direct and focus each forward beam onto the fuel at the target location and align the measurement plane with each target location.

[0034]

[0034] According to a second aspect of the present disclosure, there is provided a method of controlling a laser in a radiation source for an EUV lithography apparatus, the method comprising configuring an operable optical device to direct and focus a forward beam of the laser onto the fuel at the target location and to align the measurement plane of the optical pickup with the target location, the operable optical device being disposed before and after the optical pickup in the path of the forward beam, and the operation of the optical device being controlled in response to measurement by the optical pickup of the forward beam and the return beam reflected from the fuel at the target location.

[0035]

[0035] The method may comprise operating at least one operable optical device to control the wavefront curvature and / or the diameter of the forward beam.

[0036]

[0036] The forward beam comprises at least one of a prepulse forward beam for deforming the fuel, a vaporization pulse forward beam for diluting the fuel, and / or a main pulse forward beam for generating EUV plasma from the fuel.

[0037]

[0037] The above summary is intended to be merely illustrative and non - limiting. The present disclosure includes one or more corresponding aspects, embodiments, or features, whether specifically recited (including being claimed) alone or in various combinations, alone or in combination. Features defined above according to any aspect of the present disclosure or features defined below in relation to any specific embodiment of the present disclosure may be utilized alone or in combination with any other defined features in any other aspect or embodiment or to form further aspects or embodiments of the present disclosure.

Brief Description of the Drawings

[0038]

[0038] Embodiments of the present invention will be described below merely by way of example with reference to the accompanying schematic diagrams.

[0039]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0040]

[0039] Figure 1 shows a lithography system comprising a radiation source SO and a lithography apparatus LA. 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 comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0041]

[0040] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. To this end, the illumination system IL can comprise a facet field mirror device 10 and a facet pupil mirror device 11. The facet field mirror device 10 and the facet pupil mirror device 11 together impart a desired cross-sectional shape and a desired intensity distribution to the EUV radiation beam B. The illumination system IL can comprise other mirrors or devices in addition to or instead of the facet field mirror device 10 and the facet pupil mirror device 11.

[0042]

[0041] After being conditioned in this way, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. 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 can comprise a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B’, thereby forming an image of features smaller than the corresponding features in the patterning device MA. For example, reduction factors of 4 or 8 can be applied. The projection system PS is shown in Figure 1 as having only two mirrors 13, 14, but the projection system PS can comprise various numbers of mirrors (e.g., 6 or 8 mirrors).

[0043]

[0042] The substrate W can include a pre-formed pattern. In such a case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B’ with the pre-formed pattern on the substrate W.

[0044]

[0043] A relative vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure much lower than atmospheric pressure, can be supplied into the radiation source SO, the illumination system IL, and / or the projection system PS.

[0045]

[0044] The radiation source SO shown in FIG. 1 is of a type that may be referred to as, for example, a laser-produced plasma (LPP) radiation source. A laser system 1, which may include, for example, a CO2 laser, is arranged to deposit energy via a laser beam 2 onto a fuel such as tin (Sn) supplied, for example, from a fuel dispenser 3. Although tin is referred to in the following description, any suitable fuel may be used. The fuel can be, for example, in liquid form or, for example, a metal or an alloy. The fuel dispenser 3 can comprise a nozzle configured to direct, for example, tin in the form of droplets along a trajectory towards the plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. Deposition of the laser energy onto the tin generates a tin plasma 7 in the plasma formation region 4. During de-excitation and recombination of electrons by plasma ions, radiation including EUV radiation is emitted from the plasma 7.

[0046]

[0045] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 can include, for example, a near-normal incidence radiation collector 5 (more generally sometimes referred to as a normal incidence radiation collector). The collector 5 can have a multilayer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm, etc.). The collector 5 can have an elliptical configuration with two foci. As will be discussed below, the first of the foci can be in the plasma formation region 4 and the second of the foci can be at an intermediate focus 6.

[0047]

[0046] The laser system 1 may be spatially separated from the radiation source SO. In such a case, the laser beam 2 can be passed from the laser system 1 to the radiation source SO by a beam delivery system (not shown) including, for example, suitable guiding mirrors and / or beam expanders and / or other optical systems. The laser system 1, the radiation source SO, and the beam delivery system can all be regarded as a radiation system.

[0048]

[0047] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at the intermediate focus 6 to form an image of the plasma existing in the plasma formation region 4 at the intermediate focus 6. The image of the intermediate focus 6 acts as a virtual radiation source of the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is positioned at or near the opening 8 of the closed structure 9 of the radiation source SO.

[0049]

[0048] Although FIG. 1 illustrates the radiation source SO as a laser-produced plasma (LPP) radiation source, EUV radiation may be generated using any suitable radiation source such as a discharge-produced plasma (DPP) radiation source or a free electron laser (FEL).

[0050]

[0049] FIG. 1 also shows a metrology and control system 100 for analyzing fuel such as tin (Sn) provided from the fuel dispenser 3 and for controlling the laser system 1 to deposit energy on the fuel via the laser beam 2, as will be described in more detail below with reference to the exemplary embodiments of FIGS. 4 and 5.

[0051]

[0050] FIG. 2 illustrates an example of an optical pickup 200 in use in a prior art metrology system. FIG. 2 also shows an optical device 220 for focusing the forward beam 210 at the target location 225, as will be described in more detail below.

[0052]

[0051] The optical pickup 200 includes a first beam splitting device 205 for guiding a part of the forward beam 210 onto the first sensor 215 through a first focusing device 235 for focusing the forward beam 210 onto the first sensor 215.

[0053]

[0052] In the example of FIG. 2, the first focusing device 235 is shown as a convex lens, but it will be understood that in other examples, the first focusing device 235 may comprise a plurality of lenses and / or optical elements.

[0054]

[0053] The forward beam 210 can be a beam from a laser such as a laser configured to provide a prepulse to the fuel at the target location 225.

[0055]

[0054] The first sensor 215 may comprise a plurality of pixels and can be, for example, at least a quad pixel design. Thus, the first sensor 215 can be configured to determine the relative position and / or size and / or intensity of the incident beam, the forward beam 210. For example, by comparing the intensities of the radiation incident on each pixel of the first sensor 215, the relative position and size of the focus of the forward beam 210 on the first sensor 215 can be determined.

[0056]

[0055] A further part of the forward beam 210 passes through the beam splitting device 205 and proceeds towards the optical device 220 for focusing the forward beam 210 onto the target location 225.

[0057]

[0056] In this example, the optical device 220 is shown as a convex lens, but it will be understood that in other examples, the optical device 220 may comprise a plurality of lenses and / or optical elements.

[0058]

[0057] In use, fuel such as a tin droplet can be at the target location 225. At least a part of the forward beam 210 can be reflected by the fuel at the target location 225 as a return beam 230.

[0059]

[0058] The return beam 230 is collimated by an optical device 220, such as one or more lenses, and then is incident on the reflecting surface of the optical pickup 200. In the example of FIG. 2, the reflecting surface is the surface of the first beam splitting device 205, but in other examples, the reflecting surface may be implemented as a separate device.

[0060]

[0059] The reflecting surface reflects the return beam 230 toward the second sensor 240 via a second focusing device 245 for focusing the forward beam 210 onto the first sensor 215.

[0061]

[0060] In the example of FIG. 2, the second focusing device 245 is also represented as a convex lens, but it will be understood that in other examples, the second focusing device 245 may comprise a plurality of lenses and / or optical elements.

[0062]

[0061] The second sensor 240 may be substantially the same as the first sensor 215. That is, in the example, the second sensor 240 may comprise a plurality of pixels, for example, it may be at least a quad pixel design. Thus, the second sensor 240 may be configured to determine the relative position and / or size and / or intensity of the incident return beam 230. For example, by comparing the intensity of the radiation of the return beam 230 incident on each pixel of the first sensor, the relative position and size of the focus of the return beam 230 on the second sensor 240 can be determined.

[0063]

[0062] A second beam splitter 250 is also provided in the path of the portion of the forward beam 210 that is guided by the first beam splitting device 205 toward the first sensor 215. The second beam splitter 250 can guide a part of the forward beam 210 onto the third sensor 255.

[0064]

[0063] During use, the position of the forward beam 210 on the first sensor 215 measured by the first sensor 215 may indicate the position of the focus of the forward beam 210 at the main focus, for example, the target location 225.

[0065]

[0064] During use, the position of the return beam 230 on the second sensor 240 measured by the second sensor 240 may indicate the position of the fuel, for example, the tin droplets, at the main focus, for example, the target location 225.

[0066]

[0065] Therefore, if the position of the forward beam 210 measured by the first sensor 215 coincides with the position of the return beam 230 measured by the second sensor 240, the forward beam 210 is focused on the fuel at the target location 225.

[0067]

[0066] The third sensor 255 may indicate the x - y position of the forward beam 210.

[0068]

[0067] During use, if the position of the forward beam 210 measured by the first sensor 215 does not coincide with the position of the return beam 230 measured by the second sensor 240, an operable optical device may be operated to adjust the forward beam so as to align the focus of the forward beam 210 with the fuel at the target location 225.

[0069]

[0068] However, the implementation of such an optical pickup 200 in a metrology system may be insufficient to measure and compensate for various degrees of freedom of the forward beam incident on the fuel as the target location 225, especially due to variations in the position of the target location 255 during use.

[0070]

[0069] Such degrees of freedom are shown in FIG. 3, which illustrates various examples of the degrees of freedom of the forward beam guided through an optical device 320 equivalent to the optical device 220 of FIG. 2.

[0071]

[0070] Plane 305 is illustrated, which may represent the plane where the target should be located. Plane 305 is orthogonal to the optical axis 315 of the optical device 320.

[0072]

[0071] In the first example, the forward beam 310a can be directed through the optical device 320. For purposes of illustration, the optical device 320 is represented as a convex lens, but in other examples, it will be understood that the optical device 320 may comprise one or more lenses and / or optical elements.

[0073]

[0072] In the first example, the forward beam 310a is inclined in the x - y plane with respect to the optical axis 315 of the optical device 320. Thus, the focus of the forward beam 310a by the optical device 320 is offset from the plane 305, for example, in the +x direction.

[0074]

[0073] In the illustrated exemplary use case, such an inclination of the forward beam 310a as it approaches the optical device 320 offsets the forward beam 310a in the +x direction from the plane 305. When used in a metrology and control system for a prepulse laser beam in an EUV radiation source, such an offset can non - ideally deform and / or misorient the fuel target. For example, ideally, the fuel droplets can be uniformly deformed to increase the surface area available for subsequent vaporization pulses and / or main pulses. However, such an offset of the prepulse incident on the fuel can non - uniformly deform and / or misorient the fuel droplets.

[0075]

[0074] In the second example, the forward beam 310b can be directed through the optical device 320.

[0076]

[0075] In the second example, the forward beam 310b is offset in the x-y plane from the optical axis 315 of the optical device 320. In this specific example, the forward beam 310b is offset in the +x direction. Thus, the focal plane of the forward beam 310b by the optical device 320 can be inclined with respect to the plane 305.

[0077]

[0076] When used in a metrology and control system for a prepulse laser beam in an EUV radiation source, such an offset of the focus of the forward beam 310b can non-ideally deform and / or misorient the fuel target.

[0078]

[0077] In the third example, the forward beam 310c can be directed through the optical device 320.

[0079]

[0078] In the third example, the wavefront of the forward beam 310c is curved with respect to the optical device 320. That is, the forward beam 310c is a non-ideally collimated forward beam 320c. Thus, the focus of the forward beam 310c by the optical device 320 can be offset in the -z direction from the plane 305.

[0080]

[0079] In the illustrated exemplary use case, the curvature of the wavefront of the forward beam 310c offsets the focus of the forward beam 310c in the -z direction from the target location. When used in a metrology and control system for a prepulse laser beam in an EUV radiation source, such an offset of the focus can non-ideally deform and / or misorient the fuel target. Specifically, such an offset can affect the size of the deformed fuel target.

[0081]

[0080] Finally, in the fourth example, the forward beam 310d can be directed through the optical device 320.

[0082]

[0081] In the fourth example, the width of the forward beam 310d, which is equivalent to the numerical aperture, for example, the beam waist, is excessively large. Optical elements such as the optical device 320 can generally exhibit lower optical performance towards the periphery of the optical surface and better optical performance towards the center of the optical surface aligned with the optical axis 315. Thus, an excessively wide forward beam 310d can also affect the depth of focus and / or the beam waist in the plane 305, thereby resulting in non-ideal deformation and / or orientation of the fuel target during use.

[0083]

[0082] A metrology and control system for a laser beam in an EUV radiation source according to an embodiment of the present disclosure can compensate for the above-described degrees of freedom of the forward beams 310a - d, as described below with reference to FIGS. 4 and 5.

[0084]

[0083] FIG. 4 illustrates an example of a metrology and control system 400 according to an embodiment of the present disclosure. In the example, the metrology and control system 400 may be implemented as the metrology and control system 100 of FIG. 1.

[0085]

[0084] The metrology and control system 400 includes an optical pickup 405. The optical pickup 405 is configured to measure a forward beam 410 directed towards the target location 420 and a return beam 415 reflected from the target location 420.

[0086]

[0085] The metrology and control system 400 includes a plurality of operable optical devices 425, 430, 435, 465, 475 that are configurable to direct and focus the forward beam 410 to the target location 420 and align the measurement plane of the optical pickup 405 with the target location 420, as will be described in more detail below. Specifically, the operable optical devices 425, 430, 435, 465, 475 are disposed before and after the optical pickup 405 in the path of the forward beam 410, and the operable optical devices are controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405.

[0087]

[0086] The exemplary metrology and control system 400 includes a laser 495 configured to provide the forward beam 410. For purposes of non-limiting illustration only, the laser 495 is configured to provide a forward beam 410 suitable for use as a prepulse to optimize the mass density and / or distribution of fuel within an EUV radiation source prior to interaction with one or more subsequent vaporization pulses and / or main pulses. It will be understood that the exemplary metrology and control system 400 described may be suitable for use with the vaporization pulses or main pulses described above. Further, the metrology and control systems embodying the disclosed invention may be suitable for use with two or more of the prepulse, vaporization pulse, or main pulse, as will be described in more detail below with reference to the exemplary metrology and control system 500 of FIG. 5.

[0088]

[0087] The exemplary metrology and control system 400 of FIG. 4 includes a first operable optical device 425. The first operable optical device 425 is disposed before the optical pickup 405 in the path of the forward beam 410. The first operable optical device 425 is controlled by a first operable optical device controller 480.

[0089]

[0088] The first actuatable optical device 425 can be configured to control the wavefront curvature of the forward beam 410. In an example, the first actuatable optical device 425 is additionally or alternatively configured to control the diameter of the forward beam 410.

[0090]

[0089] Thus, the first actuatable optical device controller 480 is shown in FIG. 4 as a "Beam-spatial d, c controller", where "d" refers to the width of the forward beam 410 and "c" refers to the curvature of the wavefront of the forward beam 410.

[0091]

[0090] The first actuatable optical device 425 may comprise a plurality of devices such as one or more lenses. The position and / or characteristics of the first actuatable optical device 425 may be configurable, for example actuatable. That is, the position and / or characteristics of one or more of the plurality of devices forming the first actuatable optical device 425 may be configurable.

[0092]

[0091] In one example, the first actuatable optical device 425 may comprise one or more lenses, and the position of the one or more lenses may be adjusted. That is, the first actuatable optical device 425 may comprise one or more position-controllable lenses. An actuator such as a servo motor may be configurable to control the position of the one or more lenses.

[0093]

[0092] In another example, the first actuatable optical device 425 may additionally or alternatively comprise one or more deformable lenses. In one example, the optical characteristics of such a deformable lens may be adjusted by means for controlling the pressure in a fluid applied to one or more components of the deformable lens, such as the optical surface of the lens or a component for adjusting the tension within the lens.

[0094]

[0093] In use, the first operable optical device 425 can be configured to compensate for the curvature of the wavefront of the forward beam 410, as described above with reference to the third example of the forward beam 310c directed towards the plane 305. That is, the operation of the first operable optical device 425 for controlling the curvature of the wavefront of the forward beam 410 can be controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405.

[0095]

[0094] Similarly, the first operable optical device 425 can be configured to adjust the width of the forward beam 310, for example to reduce the numerical aperture, as described above with reference to the fourth example of the forward beam 310d directed towards the plane 305. That is, the operation of the first operable optical device 425 for controlling the width of the forward beam 310 can be controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405.

[0096]

[0095] The exemplary metrology and control system 400 includes a second operable optical device 430. The second operable optical device 430 is disposed in the path of the forward beam 410 in front of the optical pickup 405. The second operable optical device 430 is disposed in the path of the forward beam 410 after the first operable optical device 425. The second operable optical device 430 is controlled by a second operable optical device controller 485.

[0097]

[0096] The second operable optical device 430 is a mirror, for example a reflective surface suitable for reflecting radiation having the wavelength of the forward beam 410.

[0098]

[0097] In an example, the second operable optical device 430 is a position controllable mirror. That is, the tilt of the second operable optical device 430 can be adjusted by an actuator such as a servo motor.

[0099]

[0098] In another example, the second actuatable optical device 430 may comprise a deformable mirror. The optical properties of such a deformable mirror may be adjusted by means for controlling the pressure in a fluid applied to one or more components of the deformable mirror, such as the rear surface of the deformable mirror.

[0100]

[0099] In use, the second actuatable optical device 430 may be configured to compensate for the offset of the forward beam 410 with respect to the optical axis of the second actuatable optical device 430, as described above with reference to a second example of the forward beam 310b directed towards the plane 305. That is, the actuation of the second actuatable optical device 430 for controlling the offset of the forward beam 410 may be controlled in response to the measurement of the forward beam 410 and the return beam 415 by the optical pickup 405, and the measurement of the forward beam 410 and the return beam 415 by the optical pickup 405 may comprise the measurement of the wavefront and / or position of the forward beam 410 and the return beam 415.

[0101] [000100] Thus, the second actuatable optical device controller 485 is shown as the "Beam position X-Y controller" in FIG. 4, where the controller 185 is configured to adjust the position of the forward beam 410 in the X-Y plane (shown in FIG. 3) to compensate for the offset of the forward beam 410 by the second actuatable optical device 430.

[0102] [000101] The exemplary metrology and control system 400 comprises a third actuatable optical device 435. The third actuatable optical device 435 is disposed in the path of the forward beam 410 in front of the optical pickup 405. The third actuatable optical device 435 is controlled by a third actuatable optical device controller 490.

[0103] [000102] The third operable optical device 435 is a mirror for reflecting the forward beam 410. In the example, the third operable optical device 435 is a position-controllable mirror. That is, the tilt of the third operable optical device 435 can be adjusted by an actuator such as a servo motor. In other examples, the third operable optical device 435 may comprise a deformable mirror.

[0104] [000103] In use, the third operable optical device 435 may be configured to compensate for the tilt of the forward beam 410 with respect to the optical axis, as described above with reference to the first example of the forward beam 310a directed towards the plane 305. The operation of the third operable optical device 435 to compensate for the effect of the tilt of the forward beam 410 may be controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405.

[0105] [000104] Accordingly, the second operable optical device 430 and the third operable optical device 435 can be effectively used to steer the forward beam 410.

[0106] [000105] The third operable optical device controller 490 is shown as the "Beam tilt Rx, Ry controller" in FIG. 4, where the third optical device controller 490 configures the third operable optical device 435 to compensate for the tilt of the forward beam 410.

[0107] [000106] Only three operable devices 425, 430, 435 are shown in front of the optical pickup 405 in the path of the forward beam 410, but this is for illustrative purposes only. In other examples within the scope of the present disclosure, one or more additional operable devices may be implemented in front of the optical pickup 405 in the path of the forward beam 410 to control the tilt and / or position and / or width and / or curvature of the forward beam 410.

[0108] [000107] The optical pickup 405 includes a first sensor 440 for measuring the forward beam 410, a second sensor 445 for measuring the return beam 415, a beam splitting device 450 for guiding a part of the forward beam 410 onto the first sensor 440, and a reflecting surface for guiding the return beam 415 onto the second sensor 445. The optical pickup 405 also includes a first focusing device 455 for focusing the forward beam 410 onto the first sensor 440 and a second focusing device 460 for focusing the return beam 415 onto the second sensor 455.

[0109] [000108] The first sensor 440, the second sensor 445, the beam splitting device 450, the reflecting surface, the first focusing device 455, and the second focusing device 460 generally correspond to the first sensor 215, the second sensor 240, the beam splitting device 205, the reflecting surface, the first focusing device 235, and the second focusing device 245 of the pickup 200 in FIG. 2, and thus will not be described in further detail for the sake of brevity.

[0110] [000109] The exemplary metrology and control system 400 also includes a fourth operable optical device 465. The fourth operable optical device 465 is disposed after the optical pickup 405 in the path of the forward beam 410. The fourth operable optical device 465 is disposed in the path of the return beam 415.

[0111] [000110] The fourth operable optical device 465 is a mirror for reflecting the forward beam 410 and the return beam 415. In the example, the fourth operable optical device 465 is a position controllable mirror. That is, the tilt of the fourth operable optical device 465 can be adjusted by an actuator such as a servo motor. In other examples, the fourth operable optical device 465 may include a deformable mirror.

[0112] [000111] Thus, the fourth operable optical device 465, in conjunction with the second operable optical device 430 and the third operable optical device 435, can be effectively used to steer the forward beam 410.

[0113] [000112] Also, the fourth operable optical device 465 can be configured to center the return beam 415 on the second sensor 445 of the optical pickup 405. By centering the return beam 415 on the second sensor 445, the range required by the second sensor 445 can be minimized, and the second sensor 445 can operate within a region of the sensor that exhibits a relatively high linear response near the center of the available range.

[0114] [000113] A further optical device 470 within the paths of the forward beam 410 and the return beam 415 is also illustrated, and for illustrative purposes, this further optical device 470 is a mirror. In other examples, the further optical device 470 may be an operable optical device 470.

[0115] [000114] The exemplary metrology and control system 400 also includes a fifth operable optical device 475. The fifth operable optical device 475 is disposed after the optical pickup 405 within the path of the forward beam 410. The fifth operable optical device 475 is disposed within the path of the return beam 415.

[0116] [000115] Only two operable devices 465, 475 are shown after the optical pickup 405 within the paths of the forward beam 410 and the return beam 415, but this is for illustrative purposes only. In other examples within the scope of the present disclosure, one or more additional operable devices can be implemented after the optical pickup 405 within the path of the forward beam 410 to control the tilt and / or position and / or width and / or curvature of the forward beam 410 on the target location 420, and to direct the return beam towards the second sensor 445 to center the return beam on the second sensor 445.

[0117] [000116] The fifth operable optical device 475 is disposed after the optical pickup 405 in the paths of the forward beam 410 and the return beam 415. In the example, the fifth operable optical device 475 is disposed after the fourth operable optical device 465 in the path of the forward beam 410.

[0118] [000117] The exemplary fifth operable optical device 475 includes an operable lens. In use, the fifth operable optical device 475 can be operated to focus the forward beam 410 onto the fuel at the target location 410, thereby also ensuring that the measurement plane of the optical pickup 405 is aligned with the target location 410.

[0119] [000118] Also, the optical focal length of the fifth drivable optical device 475 is configured to match that of the first focusing device 455 and the second focusing device 460 of the optical pickup 405. Thus, by operating the fifth operable optical device 475 to focus the forward beam 410 onto the fuel at the target location 410, for example ensuring that the target location 410 is exactly in the rear focal plane, both the first focusing device 455 and the second focusing device 460 that match the focal length of the forward beam 410 can provide an indication that the location of the focus of the forward beam 410 is exactly at the target location 420.

[0120] [000119] The fourth and fifth operable optical devices 465, 475 are controlled by a fourth operable optical device controller 499. The fourth operable optical device controller 499 is shown in FIG. 4 as a "Laser to droplet X, Y, Z controller". This is because the fourth controller 499 can operate the fourth and fifth operable optical devices 465, 475 to control the steering and positioning of the focus of the forward beam 410 in the x, y, and z directions shown in FIG. 3.

[0121] [000120] That is, the fourth and fifth operable optical devices 465, 475 can control the position of the focus of the forward beam 410 in the x, y, and z directions so as to ensure that the forward beam 410 accurately impinges on the fuel at the target location to optimize the EUV plasma generation process in the EUV radiation source. By controlling the focus of the forward beam 410 in this way, the fourth and fifth operable optical devices 465, 475 also ensure that the return beam 415 reflected by the fuel at the target location 420 can be guided towards the center of the second sensor 445.

[0122] [000121] FIG. 5 illustrates an example of a metrology and control system 500 according to a further embodiment of the present disclosure. FIG. 5 is included to provide an example of the metrology and control system 400 of FIG. 4 applied to a plurality of laser beams in an EUV radiation source. In the example, the metrology and control system 500 may be implemented as the metrology and control system 100 of FIG. 1.

[0123] [000122] An exemplary metrology and control 500 system comprises a first laser 505 configured to generate a prepulse forward beam 510 for deforming fuel, a second laser 515 for generating a vaporization pulse forward beam 520 for diluting fuel, and a third laser 525 configured to generate a main pulse forward beam 530 for generating EUV plasma from the fuel.

[0124] [000123] The metrology and control system 500 is configured to direct each forward beam 510, 520, 530 onto the fuel at the target location 535 and to align the measurement plane with the target location 535.

[0125] [000124] It will be appreciated that in use, the prepulse forward beam 510, the vaporization pulse forward beam 520, and the main pulse forward beam 530 may be sequentially provided with each beam comprising one or more pulses.

[0126] [000125] In use, each forward beam 510, 520, 530 is directed towards a potentially moving dynamic fuel target. Thus, it will be appreciated that the target location 535 may vary, for example, each of the target location 535 and the forward beams 510, 520, 530 may be different.

[0127] [000126] The first optical pickup 540 is configured to measure the prepulse forward beam 510 directed towards the fuel droplet at the target location 535 and the prepulse return beam reflected from the target location 535.

[0128] [000127] The first optical pickup 540 is also configured to subsequently measure the vaporization pulse forward beam 520 directed towards the fuel droplet at the target location 535 and the vaporization pulse return beam reflected from the target location 535.

[0129] [000128] The second optical pickup 550 is configured to measure the main pulse forward beam 530 directed toward the fuel droplets at the target location 535 and the main pulse return beam reflected from the target location 535.

[0130] [000129] A plurality of actuatable optical devices are illustrated, and those actuatable optical devices can be configured to direct and focus each of the forward beams 510, 520, 530 to their respective target locations 535 and to align the measurement planes of their respective optical pickups 540, 550 with their respective target locations 535.

[0131] [000130] As described above with reference to the exemplary system of FIG. 4, the plurality of actuatable optical devices can comprise, for example, one or more deformable mirrors, position controllable mirrors, and / or position controllable lenses.

[0132] [000131] As described above with reference to the exemplary metrology and control system 400 of FIG. 4, the actuatable optical devices are disposed before and after the first and second optical pickups 540, 550 within the respective paths of each of the forward beams 510, 520, 530, and the actuatable optical devices are controlled in response to one or more measurements of each of the forward beams 510, 520, 530 and each return beam by their respective optical pickups 540, 550.

[0133] [000132] Specifically, a first operable device 555 that may include one or more operable optical elements is provided to control the wavefront curvature and / or the diameter of the prepulse forward beam 510, and the first operable device 555 is disposed in front of the first optical pickup 540 in the path of the prepulse forward beam 510. Also, a second operable device 560 that may include one or more operable optical elements is provided to control the wavefront curvature and / or the diameter of the vaporization pulse forward beam 520, and the second operable device 560 is disposed in front of the first optical pickup 540 in the path of the vaporization pulse forward beam 510. Also, one or more third operable devices 565, each of which may include one or more operable optical elements, are provided to control the wavefront curvature and / or the diameter of the main pulse forward beam 530, and the one or more third operable devices 565 are disposed in front of the second optical pickup 545 in the path of the main pulse forward beam 510.

[0134] [000133] As described above with reference to FIG. 4, various additional operable optical devices are provided to control the tilt and position for each of the forward beams 510, 520, 530.

[0135] [000134] Although the present text specifically refers to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein has other uses. Other possible uses are in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0136] [000135] Although embodiments of the present invention are specifically referred to in this specification in relation to a lithographic apparatus, embodiments of the present invention can also be used in other apparatuses. Embodiments of the present invention may form part of any apparatus for measuring or processing an object such as a mask inspection apparatus, a metrology apparatus, or a wafer (or other substrate) or mask (or other patterning device). These apparatuses are sometimes generally referred to as lithography tools. Such lithography tools can use vacuum conditions or ambient (non-vacuum) conditions.

[0137] [000136] Although the above specifically refers to the use of embodiments of the present invention in relation to optical lithography, the present invention may also be used in other applications such as, for example, imprint lithography, and is understood not to be limited to optical lithography where the context permits.

[0138] [000137] Where context permits, embodiments of the present invention can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention can also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can 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 propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, such descriptions are for convenience only, and such actions actually result from computing devices, processors, controllers, or other devices that execute firmware, software, routines, instructions, etc., and it should be understood that actuators or other devices can interact with the physical world when executing.

[0139] [000138] While specific embodiments of the present invention have been described above, it will be understood that the invention can be practiced in ways other than those described. The above description is exemplary and not limiting. Thus, it will be apparent to those skilled in the art that the present invention as described can be modified without departing from the scope of the claims.

Claims

1. A metrology and control system (100, 400, 500) for a laser beam in an EUV radiation source, comprising: An optical pickup (405, 540, 550) configured to measure a forward beam (410, 510, 520, 530) directed towards a target location (420, 535) and a return beam (415) reflected from the target location; An operable optical device (425, 430, 435, 465, 475, 555, 560, 565) configured to direct and focus the forward beam towards the target location and align the measurement plane of the optical pickup with the target location; Comprising: The operable optical device is disposed before and after the optical pickup in the path of the forward beam, and the operable optical device is controlled in response to the measurement of the forward beam and the return beam by the optical pickup. A system.

2. The metrology and control system (100, 400, 500) of claim 1, wherein the operable optical device comprises at least one device (425, 555, 560, 565) for controlling the wavefront curvature and / or the diameter of the forward beam (410, 510, 520, 530).

3. The metrology and control system (100, 400, 500) of claim 2, wherein the at least one device (425, 555, 560, 565) is disposed before the optical pickup (405, 540, 550) in the path of the forward beam.

4. Each operable optical device (425, 430, 435, 465, 475, 555, 560, 565) comprises: A deformable mirror; A position controllable mirror; A position controllable lens; The metrology and control system (100, 400, 500) according to any one of claims 1 to 3, comprising at least one of the above.

5. The measurement of the forward beam (410, 510, 520, 530) and the return beam (415) by the optical pickup (405, 540, 550) comprises the measurement of the wavefront and / or position of the forward beam and the return beam. The metrology and control system (100, 400, 500) according to any one of claims 1 to 4.

6. The optical pickup (405, 540, 550) is A first sensor (440) for measuring the forward beam (410); A second sensor (445) for measuring the return beam (415); A beam splitting device (450) for guiding a part of the forward beam onto the first sensor; A surface for guiding the return beam onto the second sensor; The metrology and control system (100, 400, 500) according to any one of claims 1 to 5, comprising the above.

7. The optical pickup (405, 540, 550) comprises a first focusing device (455) for focusing the forward beam (410) onto the first sensor (440) and a second focusing device (460) for focusing the return beam (415) onto the second sensor (445), and the first and second focusing devices are configured to match at least one optical focal length of the operable optical device (475) for focusing the forward beam onto the target location (420). The metrology and control system (100, 400, 500) of claim 6.

8. The operable optical device (425, 430, 435, 465, 475, 555, 560, 565) is disposed after the optical pickup (405, 540, 550) in the path of the forward beam (410, 510, 520, 530) and comprises a plurality of devices (465, 475) configurable to center the return beam (415) on the second sensor (445). The metrology and control system (100, 400, 500) of claim 6 or 7.

9. The metrology and control system (100, 400, 500) according to any one of claims 1 to 8, comprising operable position-controllable mirrors (430, 435, 465) disposed before and after the optical pickup (405, 540, 550) in the path of the forward beam (410, 510, 520, 530) for steering the forward beam.

10. A plurality of optical pickups (540, 550), each configured to measure one or more forward beams (510, 520, 530) guided towards respective target locations (535) and one or more respective return beams reflected from the respective target locations; An operable optical device (555, 560, 565) configured to direct and focus each forward beam to the respective target location and align the measurement plane of each optical pickup with the respective target location. Comprising: The operable optical device is disposed before and after each optical pickup in the path of each forward beam, and the operable optical device is controlled in response to the measurement of the one or more forward beams and each return beam by the respective optical pickup. A metrology and control system (500) according to any one of claims 1 to 9. **Claim 11** A radiation source (SO) for an EUV lithography apparatus (LA), A metrology and control system (100, 400, 500) according to any one of claims 1 to 10, A fuel injector (3) for discharging fuel at the target location, A laser (1) configured to generate the forward beam reflected as the return beam by the fuel, A radiation source comprising: **Claim 12** A first laser (505) configured to generate a prepulse forward beam (510) for deforming the fuel, a second laser (515) for generating a vaporization pulse forward beam (520) for thinning the fuel, and a third laser (525) configured to generate a main pulse forward beam (530) for generating EUV plasma from the fuel. Comprising: The metrology and control system (100, 500) is configured to direct and focus each forward beam to the fuel at the target location (535) and align the measurement plane with the respective target location. The radiation source (SO) of claim 11. **Claim 13** A method of controlling a laser in a radiation source (SO) for an EUV lithography apparatus (LA), Configuring an operable optical (425, 430, 435, 465, 475, 555, 560, 565) device to direct and focus the forward beam (410, 510, 520, 530) of the laser to the fuel at the target location (420, 535) and align the measurement plane of the optical pickup (405, 540, 550) with the target location. Comprising: The method, wherein the actuatable optical device is disposed before and after the optical pickup in the path of the forward beam, and the operation of the optical device is controlled in response to measurement by the optical pickup of the forward beam and the return beam reflected from the fuel at the target location.

14. The method according to claim 13, comprising the step of operating at least one actuatable optical device (425, 555, 560, 565) to control the wavefront curvature and / or the diameter of the forward beam (410, 510, 520, 530).

15. The forward beam is a prepulse forward beam (510) for deforming the fuel, a vaporization pulse forward beam (520) for diluting the fuel, and / or a main pulse forward beam (530) for generating an EUV plasma from the fuel The method according to claim 13 or 14, comprising at least one of the foregoing.

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