Measurement and control system

Abstract

A measurement 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 toward a target site (420, 535) and a return beam (415) reflected from the target site. The system also includes an actuatable optical device (425, 430, 435, 465, 475, 555, 560, 565) that can be configured to direct and focus the forward beam onto the target site and align a measurement plane of the optical pickup with the target site. The actuatable optical device is disposed in the path of the forward beam before and after the optical pickup, and the actuatable optical device is controlled in response to measurements of the forward beam and the return beam by the optical pickup.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application 22184227.1 filed on July 11, 2022, and the entire contents of this European application are incorporated herein by reference. Technical Field

[0003] The present invention relates to a measurement and control system for a laser beam in an EUV radiation source, and an associated method of controlling a laser in an EUV radiation source for a lithographic apparatus. Background Art

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

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

[0006] The EUV radiation source may generate EUV radiation, wherein the EUV radiation source may be of a type that may be referred to as a laser produced plasma (LPP) source. In such an LPP source, a laser system may be configured to deposit energy into a fuel at a plasma formation region via one or more laser beams. The deposition of laser energy into the fuel may generate a plasma that emits EUV radiation.

[0007] In some examples, the laser system can be configured to provide one or more pre-pulses and / or vaporization pulses to the fuel to deform and rarefy the fuel, respectively, prior to a subsequent main pulse used to generate the plasma. Such pre-pulses and vaporization pulses can provide a means to optimize the mass density and distribution of the fuel prior to interacting with a subsequent main pulse.

[0008] Metrology and control tools may be implemented to monitor and control the laser system to ensure an efficient and optimized process of plasma generation.

[0009] However, the location of the fuel at the plasma formation region may change over time, increasing the complexity of maintaining the focus of the laser system directly on the fuel.

[0010] Furthermore, the metrology system may need to be adapted to accommodate the relatively large measurement range due to such variations in fuel position. In some examples, due to variations in fuel position, the measurement plane of the metrology system may not exactly match where the laser system is focused on the fuel.

[0011] It would also be desirable, therefore, to provide a metrology and control scheme suitable for use in an EUV radiation source and capable of accurately and precisely monitoring and controlling the focus of one or more laser beams on the fuel at the plasma formation region.

[0012] Therefore, it is an object of at least one embodiment of at least one aspect of the present disclosure to obviate or at least mitigate at least one of the above-identified disadvantages of the prior art.Other examples of the prior art are as follows. Summary of the invention

[0013] 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 includes an optical pickup configured to measure a forward beam directed toward a target site and a return beam reflected from the target site.

[0014] The system also includes an actuatable optical device that can be configured to direct and focus the forward beam onto the target site and align a measurement plane of the optical pickup with the target site.

[0015] The actuatable optical devices are disposed in the path of the forward beam before and after the optical pickup and are controlled in response to measurements of the forward beam and the return beam by the optical pickup.

[0016] Advantageously, the disclosed system, and in particular by implementing actuatable optics before and after the optical pickup, enables the target site to be maintained in the back focal plane of the focusing optics of the system, as described in more detail below.

[0017] That is, actuation prior to the optical pickup enables all significant beam properties such as steering, direction, beam size / numerical aperture (NA) and beam curvature to be controlled into the focusing portion of the system so that the focus of the beam ends up being exactly in the back focal plane of the lens.

[0018] Actuation after the optical pickup ensures that the target site is exactly positioned in the back focal plane of the focusing optics by means of measuring the return beam (eg radiation reflected from the fuel at the target site).

[0019] The actuatable optical device may comprise at least one device for controlling the wavefront curvature of the forward beam and / or the diameter of the forward beam.

[0020] The at least one device may be arranged before the optical pickup in the path of the forward beam.

[0021] Advantageously, an actuatable optical arrangement configured to control beam curvature and / or diameter prior to the optical pickup enables maintaining the target site in the back focal plane while maintaining the laser focused on the target site.

[0022] Each actuatable optical device may comprise at least one of: a deformable mirror; a position controllable mirror; a position controllable lens.

[0023] The measuring of the forward beam and the return beam by the optical pickup may include measuring of wavefronts of the forward beam and the return beam. The measuring of the forward beam and the return beam by the optical pickup may include measuring of positions of the forward beam and the return beam.

[0024] The optical pickup may include: a first sensor for measuring the forward beam; a second sensor for measuring the return beam; a beam splitter for directing a portion 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, such as a surface configured to reflect the return beam. The surface may be a surface of the beam splitter. The surface may be a surface of the beam splitter that is different from another surface of the beam splitter on which the forward beam is incident during use. That is, the surface may be the rear surface of the beam splitter.

[0025] The optical pickup may include a first focusing device for focusing the forward beam on the first sensor. The optical pickup may include a second focusing device for focusing the return beam on the second sensor. The first focusing device and the second focusing device may be configured to match the optical focal length of at least one of the actuable optical devices for focusing the forward beam onto the target site.

[0026] That is, when the target site is exactly in the back focal plane - as achieved by an actuatable optical device after the optical pickup - then both the first focusing device and the second focusing device can match the forward beam focal length and therefore determine the position of the focus of the beam relative to the target site.

[0027] Advantageously, by effectively matching the optical properties of the optical pickup to be equivalent to the focusing optics, the measurement and control system can correctly measure forward beam properties particularly related to the focusing optics. This can minimize the crosstalk of beam position errors of the forward beam on the laser to fuel target performance.

[0028] The actuatable optical devices may include a plurality of devices disposed after the optical pickup in the path of the forward beam and configurable to center the return beam on the second sensor.

[0029] Advantageously, by centering the beam on the sensor, the required sensor range can be minimized because the sensors all operate close to the center of the range. In addition, the sensor can exhibit an improved linear response close to the center of the measurement range.

[0030] The measurement and control system may comprise actuatable position-controllable mirrors arranged in the path of the forward beam before and after the optical pickup for steering the forward beam.

[0031] The measurement and control system may include a plurality of optical pickups, each of which is configured to measure one or more forward beams directed toward a corresponding target location and one or more corresponding return beams reflected from the corresponding target location. The measurement and control system may include an actuable optical device, which may be configured to direct and focus each forward beam onto the corresponding target location and align the measurement plane of the corresponding optical pickup with the corresponding target location. The actuable optical device may be arranged before and after each optical pickup in the path of each forward beam, and the actuable optical device may be controlled in response to the measurement of the one or more forward beams and each return beam by the corresponding optical pickup.

[0032] According to a second aspect of the present disclosure, a radiation source for EUV lithography equipment is provided, the radiation source comprising: the measurement and control system according to the first aspect; a fuel emitter, the fuel emitter being used to emit fuel to the target site; and a laser, the laser being configured to generate a forward beam, the forward beam to be reflected by the fuel as the return beam.

[0033] As described above, the fuel may be in liquid form, and may be, for example, in the form of droplets emitted along a trajectory towards the plasma formation region. The trajectory of the droplets may vary slightly between droplets. Advantageously, the disclosed radiation source, and in particular the disclosed measurement and control system, effectively enables tracking of the position of the droplets, for example for focusing a target location of the forward beam, and thereby the position and focus of the forward beam may be adjusted accordingly to optimize plasma generation.

[0034] The radiation source may include a first laser configured to generate a pre-pulse forward beam for deforming the fuel, a second laser configured to generate a vaporization pulse forward beam for rarefying the fuel, and a third laser configured to generate a main pulse forward beam for generating EUV plasma from the fuel. The measurement and control system may be configured to direct and focus each forward beam onto the fuel at the target site and align a measurement plane with the corresponding target site.

[0035] According to a second aspect of the present disclosure, there is provided a method for controlling a laser in a radiation source for EUV lithography equipment, the method comprising: configuring an actuatable optical device to guide and focus a forward beam of the laser onto fuel at a target site and aligning a measurement plane of an optical pickup device with the target site, wherein the actuatable optical device is arranged before and after the optical pickup device in the path of the forward beam, and wherein actuation of the optical device is controlled in response to measurement by the optical pickup device of the forward beam and a return beam reflected from the fuel at the target site.

[0036] The method may comprise the step of actuating at least one actuatable optical device to control the wavefront curvature of the forward beam and / or the diameter of the forward beam.

[0037] The forward beam includes at least one of: a pre-pulse forward beam for deforming the fuel; a vaporization pulse forward beam for rarefying the fuel; and / or a main pulse forward beam for generating EUV plasma from the fuel.

[0038] The above content of the invention is intended to be exemplary only and not restrictive. The present disclosure includes one or more corresponding aspects, embodiments or features, either individually or in various combinations, whether or not specifically stated (including claimed) in the combination or individually. It should be understood that the features defined above according to any aspect of the present disclosure or below with respect to any specific embodiment of the present disclosure can be used alone or in combination with any other defined features in any other aspect or embodiment, or used to form another aspect or embodiment of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0040] - Figure 1 Depicting a lithography system including a lithography apparatus and a radiation source and implementing a metrology and control system according to an embodiment of the present disclosure;

[0041] - Figure 2 Describes an example of an optical pickup used in a prior art metrology system;

[0042] - Figure 3 Describe various examples of degrees of freedom in the forward beam;

[0043] - Figure 4 Describes an example of a measurement and control system according to an embodiment of the present disclosure; and

[0044] - Figure 5 An example of a measurement and control system according to another embodiment of the present disclosure is depicted. DETAILED DESCRIPTION

[0045] Figure 1 A lithographic system is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic 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.

[0046] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In addition, the illumination system IL may include a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide a desired cross-sectional shape and a desired intensity distribution to the EUV radiation beam B. In addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11, the illumination system IL may also include other mirrors or arrangements.

[0047] After being thus conditioned, 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 the purposes described, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is Figure 1 1. Although illustrated in FIG. 1 as having only two mirrors 13, 14, the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0048] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns an image formed by the patterned EUV radiation beam B′ with a pattern previously formed on the substrate W.

[0049] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL and / or in the projection system PS.

[0050] Figure 1 The radiation source SO shown in is, for example, of a type that may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn), provided from, for example, a fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory toward a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. The deposition of laser energy into the tin generates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons and ions of the plasma.

[0051] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 includes, for example, a near normal incidence radiation collector 5 (sometimes more generally 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 ellipsoidal configuration having two focal points. A first of the focal points may be at the plasma formation region 4, and a second of the focal points may be at the intermediate focus 6, as discussed below.

[0052] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directional mirrors and / or a beam expander and / or other optical devices. The laser system 1, the radiation source SO and the beam delivery system may together be considered a radiation system.

[0053] 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 to form an image at the intermediate focus 6 of a plasma present at the plasma formation region 4. The image at the intermediate focus 6 serves as a virtual radiation source for illuminating the system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 in an enclosure 9 of the radiation source SO.

[0054] Although Figure 1 The radiation source SO is depicted as a laser produced plasma (LPP) source, but any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[0055] Figure 1 Also depicted is a measurement and control system 100 for analyzing a fuel such as tin (Sn) provided from a fuel emitter 3 and for controlling a laser system 1 to deposit energy into the fuel via a laser beam 2, as described below with reference to Figure 4 and Figure 5 Example embodiments are described in more detail.

[0056] Figure 2 An example of an optical pickup 200 used in a prior art metrology system is depicted. Figure 2 Also shown is an optical arrangement 220 for focusing the forward beam 210 onto a target site 225, as described in more detail below.

[0057] The optical pickup 200 comprises a first beam splitting device 205 for directing a portion of the forward beam 210 onto a first sensor 215 via a first focusing device 235 for focusing the forward beam 210 onto the first sensor 215 .

[0058] exist Figure 2 In the example of , the first focusing device 235 is represented as a convex lens, but it should be understood that in other examples, the first focusing device 235 may include multiple lenses and / or optical elements.

[0059] The forward beam 210 may be a beam from a laser, such as a laser configured to provide a pre-pulse to the fuel at the target site 225 .

[0060] The first sensor 215 may include a plurality of pixels, for example, may be a four-pixel design. Thus, the first sensor 215 may be configurable to determine the relative position and / or size and / or intensity of the incident beam forward beam 210. For example, by comparing the intensity of 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 may be determined.

[0061] Another portion of the forward beam 210 continues through the beam splitting device 205 toward the optical device 220 , which is used to focus the forward beam 210 onto a target site 225 .

[0062] In this example, the optical device 220 is shown as a convex lens, but it should be understood that in other examples, the optical device 220 may include multiple lenses and / or optical elements.

[0063] In use, a fuel such as tin droplets may be at the target site 225. At least a portion of the forward beam 210 may be reflected by the fuel at the target site 225 as a return beam 230.

[0064] The return beam 230 is collimated by the optical device 220 (eg, one or more lenses), and then incident on the reflective surface of the optical pickup 200. Figure 2 In the example of , the reflective surface is a surface of the first beam splitting device 205, but in other examples, the reflective surface may be implemented as a separate device.

[0065] The reflective surface reflects the return beam 230 towards the second sensor 240 via a second focusing device 245 for focusing the forward beam 210 onto the first sensor 215 .

[0066] exist Figure 2 In the example of , the second focusing device 245 is also represented as a convex lens, but it should be understood that in other examples, the second focusing device 245 may include multiple lenses and / or optical elements.

[0067] The second sensor 240 may be substantially the same as the first sensor 215. That is, in an example, the second sensor 240 may include a plurality of pixels, for example, may be at least a four-pixel design. As such, the second sensor 240 may be configurable 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 may be determined.

[0068] A second beam splitter 250 is also disposed in the path of the portion of the forward beam 210 directed by the first beam splitting device 205 toward the first sensor 215. The second beam splitter 250 may direct a portion of the forward beam 210 onto a third sensor 255.

[0069] In use, the position of the forward beam 210 on the first sensor 215 as measured by the first sensor 215 may indicate the focal position of the forward beam 210 at a primary focus (eg, at the target site 225 ).

[0070] In use, the position of the return beam 230 on the second sensor 240 as measured by the second sensor 240 may indicate the position of the fuel (eg, tin droplets) at the primary focus (eg, the target site 225).

[0071] As such, if the position of the forward beam 210 measured by the first sensor 215 matches 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 site 225 .

[0072] The third sensor 255 may give an indication of the xy position of the forward beam 210 .

[0073] In use, if the position of the forward beam 210 measured by the first sensor 215 does not match the position of the return beam 230 measured by the second sensor 240 , the actuatable optical device may be actuated to adjust the forward beam to align the focus of the forward beam 210 with the fuel at the target site 225 .

[0074] However, such an implementation of the optical pickup 200 in a metrology system may not be sufficient to measure and compensate for the various degrees of freedom in the forward beam incident on the fuel as target site 225, particularly due to variations in the position of the target site 255 in use.

[0075] Figure 3 The degree of freedom is shown in Figure 1. Figure 3 Depicts various examples of degrees of freedom in a forward beam directed through an optical device 320, which is equivalent to Figure 2 Optical device 220.

[0076] A plane 305 is depicted which may represent the plane in which the target is to be positioned. The plane 305 is orthogonal to the optical axis 315 of the optical device 320 .

[0077] In a first example, the forward beam 310a may be directed through the optical device 320. For purposes of illustration, the optical device 320 is shown as a convex lens, but it is understood that in other examples, the optical device 320 may include one or more lenses and / or optical elements.

[0078] In a first example, the forward beam 310a is tilted in the xy plane relative to the optical axis 315 of the optical device 320. Thus, the focus of the forward beam 310a generated by the optical device 320 is offset from the plane 305, for example, in the +x direction.

[0079] In the depicted example use case, this tilt of the forward beam 310a as it approaches the optical device 320 causes the forward beam 310a to be offset from the plane 305 in the +x direction. When used in a metrology and control system for a pre-pulse laser beam in an EUV radiation source, this offset can cause the fuel target to be deformed and / or oriented non-ideally. For example, ideally, the fuel droplets can be uniformly deformed to increase the available surface area for subsequent vaporization and / or main pulses. However, this offset in the pre-pulse incident on the fuel can cause the fuel droplets to be deformed and / or oriented non-uniformly.

[0080] In a second example, the forward beam 310 b may be directed through the optical device 320 .

[0081] In the second example, the forward beam 310b is offset from the optical axis 315 of the optical device 320 in the xy plane. In a specific example, the forward beam 310b is offset in the +x direction. As such, the focal plane of the forward beam 310b generated by the optical device 320 can be tilted relative to the plane 305.

[0082] When used in a metrology and control system for a pre-pulse laser beam in an EUV radiation source, such a shift in the focus of the forward beam 310b may cause a non-ideal deformation and / or orientation of the fuel target.

[0083] In a third example, the forward beam 310 c may be directed through the optical device 320 .

[0084] In the third example, the wavefront of the forward beam 310c is curved relative 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 generated by the optical device 320 may be offset from the plane 305 in the -z direction.

[0085] In the depicted example use case, the curvature of the wavefront of the forward beam 310c causes the focus of the forward beam 310c to shift from the target site in the -z direction. In the use of a measurement and control system for a pre-pulse laser beam in an EUV radiation source, such a shift in the focus may cause the fuel target to be non-ideally deformed and / or oriented. In particular, such a shift may affect the size of the deformed fuel target.

[0086] Finally, in a fourth example, the forward beam 310 d may be directed through the optical device 320 .

[0087] In the fourth example, the width of the forward beam 310d equivalent to the numerical aperture (e.g., beam waist) is too large. Optical elements such as optical device 320 may generally exhibit poorer optical performance toward the periphery of the optical surface and better optical performance toward the center of the optical surface aligned with optical axis 315. As such, an excessively wide forward beam 310d may also affect the depth of focus and / or beam waist at plane 305, thereby causing non-ideal deformation and / or orientation of the fuel target in use.

[0088] The measurement and control system for the laser beam in the EUV radiation source according to the embodiment of the present disclosure can compensate for the above-mentioned degrees of freedom in the forward beams 310a to 310d, as described below with reference to Figure 4 and Figure 5 as described.

[0089] Figure 4 An example of a measurement and control system 400 according to an embodiment of the present disclosure is depicted. In an example, the measurement and control system 400 may be implemented as Figure 1 Measurement and control system 100.

[0090] The measurement and control system 400 comprises an optical pickup 405. The optical pickup 405 is configured to measure a forward beam 410 directed towards a target site 420 and a return beam 415 reflected from the target site 420.

[0091] The measurement and control system 400 includes a plurality of actuatable optical devices 425, 430, 435, 465, 475, which can be configured to direct and focus the forward beam 410 onto the target site 420 and align the measurement plane of the optical pickup 405 with the target site 420, as described in more detail below. In particular, the actuatable 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 are controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405.

[0092] The example measurement and control system 400 includes a laser 495 configured to provide a forward beam 410. For purposes of non-limiting example only, the laser 495 is configured to provide a forward beam 410 suitable for use as a pre-pulse for use in optimizing the mass density and / or distribution of fuel in the EUV radiation source prior to interaction with subsequent one or more vaporization pulses and / or main pulses. It should be understood that the described example measurement and control system 400 can be adapted for use with the above-described vaporization pulses or main pulses. In addition, the measurement and control system embodying the disclosed invention can be adapted for use with more than one of the pre-pulses, vaporization pulses, or main pulses, as described below with reference to Figure 5 An example measurement and control system 500 is described in greater detail.

[0093] Figure 4 The example measurement and control system 400 includes a first actuatable optical device 425. The first actuatable optical device 425 is disposed before the optical pickup 405 in the path of the forward beam 410. The first actuatable optical device 425 is controlled by a first actuatable optical device controller 480.

[0094] The first actuatable optical device 425 may be configured to control a curvature of a wavefront of the forward beam 410. In an example, the first actuatable optical device 425 may additionally or alternatively be configured to control a diameter of the forward beam 410.

[0095] Thus, the first actuable optical device controller 480 Figure 4 denoted as “beam space 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 .

[0096] The first actuatable optical device 425 may include a plurality of devices, such as one or more lenses. The position and / or properties of the first actuatable optical device 425 may be configurable, e.g., actuatable. That is, the position and / or properties of one or more of the plurality of devices forming the first actuatable optical device 425 may be configurable.

[0097] In an example, the first actuatable optical device 425 may include one or more lenses, wherein the position of the one or more lenses may be adjusted. That is, the first actuatable optical device 425 may include 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.

[0098] In another example, the first actuatable optical device 425 may additionally or alternatively include one or more deformable lenses. In an example, the optical properties of such a deformable lens may be adjusted by means for controlling pressure in a fluid applied to one or more components of the deformable lens, such as an optical surface of the lens or a component for adjusting tension in the lens.

[0099] In use, the first actuatable optical device 425 may 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 toward the plane 305. That is, the actuation of the first actuatable optical device 425 may be controlled in response to the measurement of the forward beam 410 and the return beam 415 by the optical pickup 405 to control the curvature of the wavefront of the forward beam 410.

[0100] Similarly, the first actuatable 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 toward the plane 305. That is, the actuation of the first actuatable optical device 425 can be controlled in response to the measurement of the forward beam 410 and the return beam 415 by the optical pickup 405 to control the width of the forward beam 310.

[0101] The example measurement and control system 400 includes a second actuatable optical device 430. The second actuatable optical device 430 is disposed before the optical pickup 405 in the path of the forward beam 410. The second actuatable optical device 430 is disposed after the first actuatable optical device 425 in the path of the forward beam 410. The second actuatable optical device 430 is controlled by a second actuatable optical device controller 485.

[0102] The second actuatable optical device 430 is a mirror, for example a reflective surface adapted to reflect radiation having the wavelength of the forward beam 410 .

[0103] In the example, the second actuatable optical device 430 is a position-controllable mirror, that is, the tilt of the second actuatable optical device 430 can be adjusted by an actuator such as a servo motor.

[0104] In other examples, the second actuatable optical device 430 may include 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 back surface of the deformable mirror.

[0105] In use, the second actuatable optical device 430 may be configured to compensate for a deviation of the forward beam 410 relative to the optical axis of the second actuatable optical device 430, as described above with reference to the second example of the forward beam 310b being directed towards the plane 305. That is, actuation of the second actuatable optical device 430 may be controlled in response to measurement of the forward beam 410 and the return beam 415 by the optical pickup 405 to control the deviation of the forward beam 410, wherein the measurement of the forward beam 410 and the return beam 415 by the optical pickup 405 may include measurement of the wavefront and / or position of the forward beam 410 and the return beam 415.

[0106] Thus, the second actuable optical device controller 485 Figure 4 4. The controller 185 is denoted as a "beam position XY controller" in the figure, wherein the controller 185 configures the second actuatable optical device 430 to adjust the position of the forward beam 410 in the XY plane (eg, Figure 3 ) to compensate for the deviation of the forward beam 410.

[0107] The example measurement and control system 400 comprises a third actuatable optical device 435. The third actuatable optical device 435 is arranged before the optical pickup 405 in the path of the forward beam 410. The third actuatable optical device 435 is controlled by a third actuatable optical device controller 490.

[0108] The third actuable optical device 435 is a mirror for reflecting the forward beam 410. In an example, the third actuable optical device 435 is a position-controllable mirror. That is, the tilt of the third actuable optical device 435 can be adjusted by an actuator such as a servo motor. In other examples, the third actuable optical device 435 may include a deformable mirror.

[0109] In use, the third actuatable optical device 435 may be configured to compensate for a tilt of the forward beam 410 relative to the optical axis, as described above with reference to the first example of the forward beam 310a being directed towards the plane 305. That is, actuation of the third actuatable optical device 435 may be controlled in response to measurements of the forward beam 410 and the return beam 415 by the optical pickup 405 to compensate for the effects of the tilt of the forward beam 410.

[0110] As such, the second actuatable optical device 430 and the third actuatable optical device 435 may be effectively used to steer or manipulate the forward beam 410 .

[0111] The third actuable optical device controller 490 is Figure 4 denoted as “beam tilt Rx, Ry controller”, wherein the third actuatable optical device controller 490 configures the third actuatable optical device 435 to compensate for the tilt of the forward beam 410 .

[0112] Although only three actuatable devices 425, 430, 435 are depicted in the path of the forward beam 410 before the optical pickup 405, it should be understood that this is for illustrative purposes only, and in other examples within the scope of the present disclosure, one or more other actuatable devices may be implemented in the path of the forward beam 410 before the optical pickup 405 for controlling the tilt and / or position and / or width and / or curvature of the forward beam 410.

[0113] 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 directing a portion of the forward beam 410 onto the first sensor 440, and a reflecting surface for directing 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.

[0114] The first sensor 440, the second sensor 445, the beam splitting device 450, the reflective surface, the first focusing device 455 and the second focusing device 460 correspond substantially to Figure 2 The first sensor 215, the second sensor 240, the beam splitting device 205, the reflective surface, the first focusing device 235 and the second focusing device 245 of the pickup member 200 are described in further detail for the sake of brevity.

[0115] The example measurement and control system 400 also includes a fourth actuatable optical device 465. The fourth actuatable optical device 465 is disposed in the path of the forward beam 410 after the optical pickup 405. The fourth actuatable optical device 465 is disposed in the path of the return beam 415.

[0116] The fourth actuable optical device 465 is a mirror for reflecting the forward beam 410 and the return beam 415. In an example, the fourth actuable optical device 465 is a position-controllable mirror. That is, the tilt of the fourth actuable optical device 465 can be adjusted by an actuator such as a servo motor. In other examples, the fourth actuable optical device 465 may include a deformable mirror.

[0117] As such, the fourth actuatable optical device 465 , along with the second actuatable optical device 430 and the third actuatable optical device 435 , can be effectively used to steer or manipulate the forward beam 410 .

[0118] Furthermore, the fourth actuatable 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 required range of the second sensor 445 can be minimized, and the second sensor 445 can be operated close to the center of the usable range and in a region of the sensor that exhibits a relatively high linear response.

[0119] Also depicted are further optical devices 470 in the paths of the forward beam 410 and the return beam 415 , wherein for purposes of illustration, the further optical devices 470 are mirrors. In other examples, the further optical devices 470 may be actuatable optical devices 470 .

[0120] The example measurement and control system 400 also includes a fifth actuatable optical device 475. The fifth actuatable optical device 475 is disposed in the path of the forward beam 410 after the optical pickup 405. The fifth actuatable optical device 475 is disposed in the path of the return beam 415.

[0121] Although only two actuatable devices 465, 475 are depicted after the optical pickup 405 in the path of the forward beam 410 and the return beam 415, it should be understood that this is for illustrative purposes only, and in other examples within the scope of the present disclosure, one or more additional actuatable devices may be implemented after the optical pickup 405 in the path of the forward beam 410 for use in controlling the tilt and / or position and / or width and / or curvature of the forward beam 410 on the target site 420, and for directing the return beam toward the second sensor 445 and centering the return beam on the second sensor 445.

[0122] The fifth actuatable optical device 475 is disposed after the optical pickup 405 in the path of the forward beam 410 and the return beam 415. In an example, the fifth actuatable optical device 475 is disposed after the fourth actuatable optical device 465 in the path of the forward beam 410.

[0123] The example fifth actuatable optical device 475 comprises an actuatable lens. In use, the actuatable fifth actuatable optical device 475 can be actuated to focus the forward beam 410 on the fuel at the target site 410, thereby also ensuring that the measurement plane of the optical pickup 405 is aligned with the target site 410.

[0124] Furthermore, the optical focal length of the fifth actuatable optical device 475 is configured to match the optical focal lengths of the first focusing device 455 and the second focusing device 460 of the optical pickup 405. Thus, by actuating the fifth actuatable optical device 475 to focus the forward beam 410 on the fuel at the target site 410, for example, to ensure that the target site 410 is exactly in the back focal plane, both the first focusing device 455 and the second focusing device 460 (which match the forward beam 410 focal length) can provide an indication that the location of the focus of the forward beam 410 is exactly at the target site 420.

[0125] The fourth actuable optical device 465 and the fifth actuable optical device 475 are controlled by a fourth actuable optical device controller 499. The fourth actuable optical device controller 499 is Figure 4 4 is represented as “laser to droplet X, Y, Z controller” because the fourth controller 499 can actuate the fourth actuatable optical device 465 and the fifth actuatable optical device 475 to control the steering and positioning of the focus of the forward beam 410 in the x, y and z directions, as shown in FIG. Figure 3 As indicated in .

[0126] That is, the fourth actuatable optical device 465 and the fifth actuatable optical device 475 can control the position of the focus of the forward beam 410 in the x, y and z directions to ensure that the forward beam 410 is accurately incident on the fuel at the target site 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 actuatable optical device 465 and the fifth actuatable optical device 475 also ensure that the return beam 415 reflected by the fuel at the target site 420 can be directed toward the center of the second sensor 445.

[0127] Figure 5 An example of a measurement and control system 500 according to another embodiment of the present disclosure is depicted. Figure 5 To provide multiple laser beams used in EUV radiation sources Figure 4 In an example, the measurement and control system 500 may be implemented as Figure 1 Measurement and control system 100.

[0128] The example measurement and control 500 system includes a first laser 505 configured to generate a pre-pulsed forward beam 510 for deforming a fuel, a second laser 515 for generating a vaporization pulsed forward beam 520 for rarefying the fuel, and a third laser 525 configured to generate a main pulsed forward beam 530 for generating EUV plasma from the fuel.

[0129] The measurement and control system 500 is configured to direct and focus each forward beam 510 , 520 , 530 onto the fuel at a target site 535 and to align a measurement plane with the target site 535 .

[0130] It will be appreciated that, in use, the pre-pulse forward beam 510, the vaporization pulse forward beam 520 and the main pulse forward beam 530 may be provided sequentially, wherein each beam comprises one or more pulses.

[0131] In use, each forward beam 510, 520, 530 is directed toward a dynamic fuel target that may be in motion. As such, it should be understood that the target location 535 may vary, for example, the target location 535 of each of the forward beams 510, 520, 530 may be different.

[0132] The first optical pickup 540 is configured to measure the pre-pulse forward beam 510 directed toward the fuel droplets at the target site 535 , and the pre-pulse return beam reflected from the target site 535 .

[0133] The first optical pickup 540 is also configured to subsequently measure a vaporization pulse forward beam 520 directed toward the fuel droplets at the target site 535 , and a vaporization pulse return beam reflected from the target site 535 .

[0134] The second optical pickup 550 is configured to measure the main pulse forward beam 530 directed towards the fuel droplets at the target site 535 , and the main pulse return beam reflected from the target site 535 .

[0135] A plurality of actuatable optical devices are depicted, wherein the actuatable optical devices are configurable to direct and focus each forward beam 510 , 520 , 530 onto a respective target site 535 and to align a measurement plane of a respective optical pickup 540 , 550 with the respective target site 535 .

[0136] As mentioned above Figure 4 As described in the example system of , the plurality of actuatable optical devices may include, for example, one or more deformable mirrors, position controllable mirrors, and / or position controllable lenses.

[0137] The actuatable optical device is disposed before and after the first optical pickup 540 and the second optical pickup 550 in the path of each respective forward beam 510, 520, 530, and is controlled in response to one or more measurements of each of the forward beams 510, 520, 530, and each return beam by the respective optical pickup 540, 550, as described above with reference to Figure 4 An example measurement and control system 400 is described.

[0138] In particular, a first actuatable device 555, which may include one or more actuatable optical elements, is provided for controlling the wavefront curvature of the pre-pulse forward beam 510 and / or the diameter of the pre-pulse forward beam 510, wherein the first actuatable device 555 is arranged before the first optical pickup 540 in the path of the pre-pulse forward beam 510. In addition, a second actuatable device 560, which may include one or more actuatable optical elements, is provided for controlling the wavefront curvature of the vaporization pulse forward beam 520 and / or the diameter of the vaporization pulse forward beam 520, wherein the second actuatable device 560 is arranged before the first optical pickup 540 in the path of the vaporization pulse forward beam 510. In addition, one or more third actuatable devices 565, each of which may include one or more actuatable optical elements, are provided for controlling the wavefront curvature of the main pulse forward beam 530 and / or the diameter of the main pulse forward beam 530, wherein the one or more third actuatable devices 565 are arranged before the second optical pickup 545 in the path of the main pulse forward beam 510.

[0139] As mentioned above Figure 4 As described, various additional actuatable optical devices are provided to control the tilt and position for each forward beam 510 , 520 , 530 .

[0140] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include 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, etc.

[0141] Although specific reference may be made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0142] Although specific reference may be made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications such as imprint lithography where the context permits.

[0143] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; a propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.) in electrical, optical, acoustic, or other form, etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and that these actions actually result from a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc. and that, when performing such operations, may cause an actuator or other device to interact with the physical world.

[0144] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A measurement and control system (100, 400, 500) for a laser beam in an EUV radiation source, the measurement and control system comprising: an optical pickup (405, 540, 550) configured to measure a forward beam (410, 510, 520, 530) directed toward a target site (420, 535) and a return beam (415) reflected from the target site; and an actuatable optical device (425, 430, 435, 465, 475, 555, 560, 565) which can be configured to direct and focus the forward beam onto the target site and to align a measurement plane of the optical pickup with the target site, wherein the actuatable optical device is arranged before and after the optical pickup in the path of the forward beam and is controlled in response to measurements of the forward beam and the return beam by the optical pickup.

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

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

4. The measurement and control system (100, 400, 500) according to any of the preceding claims, wherein: Each actuatable optical device (425, 430, 435, 465, 475, 555, 560, 565) includes at least one of the following: Deformable mirror; Position controllable reflector; Position controllable lens.

5. The measurement and control system (100, 400, 500) according to any of the preceding claims, wherein: 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.

6. The measurement and control system (100, 400, 500) according to any of the preceding claims, wherein: The optical pickup element (405, 540, 550) comprises: a first sensor (440), the first sensor being used to measure the forward beam (410); a second sensor (445), the second sensor being configured to measure the return beam (415); A beam splitter (450) for directing a portion of the forward beam to the first sensor; and A surface is provided for directing the return beam onto the second sensor.

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

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

9. A measurement and control system (100, 400, 500) according to any preceding claim, comprising actuatable position-controllable mirrors (430, 435, 465) arranged 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. The measurement and control system (500) according to any preceding claim, comprising: a plurality of optical pickups (540, 550), each optical pickup configured to measure one or more forward beams (510, 520, 530) directed toward a corresponding target site (535) and one or more corresponding return beams reflected from the corresponding target site; and an actuatable optical device (555, 560, 565) which can be configured to direct and focus each forward beam onto the respective target site and to align a measurement plane of the respective optical pickup element with the respective target site, wherein the actuatable optical device is arranged before and after each optical pickup in the path of each forward beam and is controlled in response to measurements of the one or more forward beams and each return beam by the corresponding optical pickup.

11. A radiation source (SO) for EUV lithography equipment (LA), the radiation source comprising: A measurement and control system (100, 400, 500) according to any preceding claim; A fuel launcher (3), the fuel launcher being used to launch fuel to the target location; as well as A laser (1) is configured to generate a forward beam to be reflected by the fuel as the return beam.

12. The radiation source (SO) according to claim 11, comprising: a first laser (505) configured to generate a pre-pulse forward beam (510) for deforming the fuel; a second laser (515) for generating a vaporizing pulsed forward beam (520) for diluting the fuel; and a third laser (525) configured to generate a main pulse forward beam (530) for generating EUV plasma from the fuel, And wherein the measurement and control system (100, 500) is configured to direct and focus each forward beam onto the fuel at a target location (535) / the target location (535) and align a measurement plane / the measurement plane with the corresponding target location.

13. A method of controlling a laser in a radiation source (SO) for an EUV lithography apparatus (LA), the method comprising: an actuatable optical device (425, 430, 435, 465, 475, 555, 560, 565) is configured to direct and focus a forward beam (410, 510, 520, 530) of the laser onto the fuel at a target site (420, 535) and to align a measurement plane of an optical pickup (405, 540, 550) with the target site, wherein the actuatable optical device is arranged before and after the optical pickup in the path of the forward beam, and wherein actuation of the optical device is controlled in response to measurement of the forward beam and a return beam reflected from the fuel at the target site by the optical pickup.

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

15. The method according to claim 13 or 14, wherein: The forward beam includes at least one of the following: a pre-pulse forward beam (510) for deforming the fuel; A vaporizing pulse forward beam (520) for enleaning the fuel; and / or A main pulse forward beam (530) is used to generate EUV plasma from the fuel.

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