EUV light source having a combination device

Abstract

The invention relates to an EUV light source (1), comprising: a first laser source (2) for emitting a first laser beam (3), a second laser source (4) for emitting a second laser beam (5), a combination device (6) for combining the first laser beam (3) and the second laser beam (5), and also a beam-guiding device (7) for jointly guiding the first laser beam (3) and the second laser beam (5) into a target region (8) for generating EUV radiation (9). The combination device (6) is designed to supply the beam-guiding device (7) with the first laser beam (3) and the second laser beam (5) for joint beam guidance via common optical elements (21, 13, 18) with spatial separation and a lateral offset (∆L).

Description

[0001] EUV light source with a combination device

[0002] Background of the invention

[0003] The invention relates to an EUV light source, comprising: a first laser source for emitting a first laser beam, a second laser source for emitting a second laser beam, a combination device for combining the first laser beam and the second laser beam, and a beam guiding device for jointly guiding the first laser beam and the second laser beam into a target area for generating EUV radiation.

[0004] An EUV light source is a radiation source used to emit EUV radiation. EUV radiation is defined as electromagnetic radiation with a wavelength between 5 nm and 30 nm. EUV radiation is used primarily in the semiconductor industry. Compared to currently common lithography systems, which operate at wavelengths in the UV wavelength range, the use of EUV radiation for microlithographic manufacturing allows for the reliable production of components with significantly smaller feature sizes, thus leading to a corresponding increase in performance.

[0005] The EUV light source described here is suitable for generating EUV radiation using an LPP (“Laser Produced Plasma”) process. With such an EUV light source, a target material, which is typically a metal, in particular tin, is provided in the target area by means of a provision device, usually in droplet form. Each droplet is first irradiated with one, two, or possibly more than two pre-pulses. The pre-pulse or pre-pulses of a respective pre-pulse laser source serve to prepare the droplet for irradiation with the main pulse, in particular to heat the droplet, expand it, vaporize it, and / or generate a plasma. The subsequent irradiation of each droplet with a main pulse of a respective main pulse laser beam serves to convert the target material into the plasma state.When the components of the plasma recombine, EUV radiation is emitted.

[0006] To generate EUV radiation, at least one pre-pulse, usually at least two pre-pulses, and the main pulse must be directed to approximately the same focus position in the target area. It is advantageous if the angle of incidence of the pre-pulse and the main pulse, or the angle of incidence of two or more pre-pulses, in the target area differ as little as possible. In principle, the two or more laser beams can be guided into the target area via different optics and focused in the target area via different focusing optics. However, the space required for these optics is considerable, making a design solution with small relative angles of incidence of the two laser beams complex.

[0007] US 10,932,350 B2 proposes combining a pre-pulse laser beam and a main pulse laser beam, or two pre-pulse laser beams, in a respective beam combiner in order to focus both beams via a common focusing optics in a plasma generation region or on the target material. The beam combiner can be wavelength-selective and, for example, reflect the pre-pulse laser beam and transmit the main pulse laser beam.

[0008] EUV beam generation devices with two beam sources for emitting two laser beams, which are designed to combine or superimpose the two laser beams, are described in addition to US 10,932,350 B2, for example, also in WO 2015 / 036024 A1 and WO 2015 / 036025 A1. WO 2015 / 036025 A1 describes an EUV radiation generation device with a beam guiding device that has a superposition device that superimposes two laser beams, which enter a vacuum chamber through two different openings, for joint beam guidance towards the target area. In WO 2015 / 036025 A1, superimposition is understood to mean that the two laser beams have a common beam axis after superimposition and propagate coaxially along the common beam axis.The superposition device can, for example, be designed as a reflective optical element arranged in the vacuum chamber, which has a first surface area for reflecting the first laser beam and a second surface area surrounding the first in a ring shape for reflecting the second laser beam.

[0009] Object of the invention

[0010] In contrast, the object of the invention was to provide an EUV light source of the type mentioned above which makes it possible to guide two (or more) laser beams into the target area with little requirement of installation space and optical components and in particular to simplify the adjustment of the laser beams to each other.

[0011] Subject of the invention

[0012] This object is achieved by an EUV light source of the type mentioned above, in which the combination device is designed to supply the first laser beam and the second laser beam for joint beam guidance to the beam guidance device via shared optics, spatially separated and with a lateral offset. The combination device can also be designed to additionally supply a third, fourth, ... laser beam for joint beam guidance to the beam guidance device, spatially separated and with a lateral offset.

[0013] For various reasons, it has proven advantageous if the first laser beam and the second laser beam are not spatially superimposed in the combination device for joint beam guidance, i.e. if they do not have a common beam axis after combination, as is usually the case with superposition by polarization (e.g. by means of a polarization coupler), wavelength superposition (e.g. by means of a grating), temporal superposition (e.g. by means of an acousto-optical modulator) or the coaxial superposition described in WO 2015 / 036025 A1. Joint beam guidance using such a local superposition with a common beam axis would result in thermally induced deformations or thermally induced changes in optical density, which usually lead to a deterioration in imaging quality, affecting all laser beams.

[0014] With polarization superposition, there is the additional problem that the superposition leads to losses at the polarization combiner. Furthermore, with polarization superposition, polarization can no longer be used to isolate the laser sources from backward-facing radiation.

[0015] Backward-directed radiation from the first laser beam also potentially influences the second laser beam, and vice versa. When combining by wavelength superposition, laser beams of different wavelengths are necessary, but the availability of corresponding laser sources with the required pulse shapes and power densities may not be available. Furthermore, optics that sufficiently transmit and reflect both CO2 laser radiation (~10.6 pm wavelength), which is typically used for the main pulse laser beam (see below), and solid-state laser radiation (~1 pm wavelength), which is typically used for the pre-pulse laser beam, are difficult to manufacture and therefore always lead to increased absorption in the optical elements, thus also deteriorating the image quality.At the widely separated wavelengths specified above, the pre-pulse laser beam and the main pulse laser beam are typically guided via separate optics, as this enables a largely aberration-free imaging of the pre-pulse while maintaining a high average power of the main pulse.

[0016] In the EUV light source according to the invention, local superposition with a lateral offset takes place in the combination device, i.e. the laser beams emerge from the combination device spatially separated and with a lateral offset. The two laser beams pass through the optics or the optical elements of the beam guiding device (e.g. deflection and focusing optics) together, but along different, laterally offset beam paths. In the near field, the laser beams within the beam guiding device are typically collimated and essentially parallel (with a lateral offset). In the far field (after focusing by means of focusing optics), the laser beams are focused in the target area at approximately the same focus position. The joint beam guidance in the beam guiding device reduces the space required to guide the laser beams into the target area.In addition, by slightly tilting the first laser beam and the second laser beam relative to each other in the near field, their relative position in the far field (after focusing) can be adjusted or set (see below).

[0017] In one embodiment, the first laser source is a pre-pulse laser source for emitting a pre-pulse laser beam, and the second laser source is a main pulse laser source for emitting a main pulse laser beam or a further pre-pulse laser source for emitting a further pre-pulse laser beam. The combination device can be used to combine a pre-pulse laser beam and the main pulse laser beam. Alternatively, it is possible for the combination device to combine a pre-pulse laser beam and a further pre-pulse laser beam. It is understood that the combination device can also be designed to supply more than two pre-pulse laser beams, or at least two pre-pulse laser beams and the main pulse laser beam, to the beam guiding device for joint beam guidance, spatially separated and with a lateral offset.

[0018] The wavelength of the respective pre-pulse laser beam and thus of the pre-pulses is referred to as the pre-pulse wavelength, while the wavelength of the main pulse laser beam and thus of the main pulses is referred to as the main pulse wavelength. The main pulse laser source is, for example, a CO2 laser with a main pulse wavelength of approximately 10.6 pm, while the pre-pulse laser source is, for example, a solid-state laser that can have a pre-pulse wavelength of approximately 1 pm. The use of a pre-pulse laser source in the form of a solid-state laser has the advantage of higher conversion efficiency and largely aberration-free focusing of the laser beam on the droplet compared to the use of a pre-pulse laser source in the form of another CO2 laser.This is due, among other things, to the fact that short pulse durations and a sharp focus of the pre-pulses on the target material are achieved, and that the pre-pulses have a different absorption behavior than the main pulses. It is also possible for the main pulse laser source to be a solid-state laser and for the main pulse laser beam to have a main pulse wavelength on the order of approximately 1 pm, 2 pm, or 5 pm. If multiple pre-pulse laser sources are used, they can each have the same pre-pulse wavelength or (usually slightly) different pre-pulse laser wavelengths, for example, 1030 nm (Yb:YAG laser) and 1064 nm (Nd:YAG laser).

[0019] In one embodiment, a first wavelength of the first laser beam and a second wavelength of the second laser beam differ from each other by no more than 70 nm, preferably by no more than 50 nm and / or the first wavelength of the first laser beam and the second wavelength of the second laser beam are in a wavelength range between 350 nm and 5 pm, preferably between 500 nm and 2.5 pm.

[0020] As described above, optics that transmit or reflect two wavelengths generally have increased absorption. If the wavelengths of the two laser beams are relatively close to each other, this effect generally plays a minor role. This is particularly the case for the pre-pulse wavelengths of 1030 nm and 1064 nm specified above. In principle, the deviation between the two wavelengths can also be greater than stated above, although in this case the two laser beams can be guided via common optics of the beam guidance device. For transmissive optics, this generally requires that the two wavelengths are so close to each other that the same substrates and coatings, particularly in the form of anti-reflective coatings (see below), can be used. For example, when using a suitable substrate material, e.g.For example, when using quartz glass, laser beams can be guided through shared transmissive optics whose wavelengths differ significantly more than stated above. If the main pulse wavelength is of a similar order of magnitude to the pre-pulse wavelength(s), the (at least one) pre-pulse laser beam and the main pulse laser beam can also be guided toward the target area through shared optics.

[0021] In a further embodiment, the beam guiding device has at least one transmissive optic with an anti-reflective coating, which is designed to suppress reflections of the first laser beam at the first wavelength and to suppress reflections of the second laser beam at the second wavelength, and / or the transmissive optic is made of quartz glass. With transmissive optics, e.g. in the form of lenses, reflections upon entry into the substrate material or exit from the substrate material generally lead to a reduction in transmission, which is why anti-reflective coatings are applied to such optics. Anti-reflective coatings are typically optimized to suppress reflections at a wavelength that corresponds to the wavelength of the incident laser radiation.In the event that the wavelengths of the two laser beams differ significantly, it may be useful to apply an anti-reflective coating to the surface of a transmitting optic that is optimized to suppress reflections at both wavelengths of the two laser beams. For example, in this case, the first wavelength may be approximately 515 nm and the second wavelength approximately 1 pm, or the first wavelength may be approximately 1 pm and the second wavelength approximately 2 pm.

[0022] The use of quartz glass as a material for transmissive optics of the beam guiding device, e.g. in the form of lenses, is advantageous because this material has a comparatively high transmission in a wide wavelength range from approx. 350 nm to approx. 2.5 pm.

[0023] It is understood that the beam guiding device can comprise not only transmitting optics but also reflective optics, e.g., in the form of mirrors. For example, a focusing optic of the beam guiding device can be implemented entirely or partially in the form of reflective optics. The reflective optics can be provided with a coating optimized for the reflection of both wavelengths.

[0024] In a further embodiment, the first laser beam impinges on the combination device with a first beam direction, and the second laser beam impinges on the combination device with a second beam direction that differs from the first beam direction. The different beam directions simplify guiding the laser beams along spatially separated beam paths to the combination device. In this case, the combination device is typically designed to change the first and / or second beam direction in order to align the laser beams substantially parallel to one another. The change in the beam direction in the combination device can occur, for example, by refraction at (at least) one transmitting optical element or by beam deflection, for example, at (at least) one reflective optical element, in particular at a deflecting mirror.In the event that an odd number of beams enter the combination device, the beam in the middle can, for example, pass through the combination device without its beam direction being changed by the combination device.

[0025] In one embodiment, the combination device is designed to align the first laser beam and the second laser beam parallel to one another. For the purposes of this application, parallel alignment means that the beam directions of the laser beams deviate from one another by less than 0.2° upon exiting the combination device. As described above, by slightly tilting the beam directions of the laser beams upstream of the combination device, their position in the far field can be adjusted, which leads to a slight deviation from the parallel alignment of the laser beams downstream of the combination device. However, the tilt should not be chosen to be too great, since otherwise the laser beams can no longer be guided together via the optical elements of the beam guiding device. In a further embodiment, the combination device has at least one prism.In particular, the combination device can consist of a prism. Since the refractive index of the prism material is wavelength-dependent, it is advantageous or necessary for two or more laser beams to have the same or similar wavelengths when combining them using a prism. If exactly two laser beams are to be combined, the prism can, for example, have a (flat) prism surface that serves as the beam entrance surface and onto which the laser beams impinge in a spatially offset manner. In this case, the angles of incidence of the two laser beams onto the prism surface can, for example, have the same magnitude but a different sign. The two laser beams exit at two further prism surfaces, each of which is aligned at a wedge angle to the prism surface that serves as the beam entrance surface.With a suitable choice of beam directions, the respective wedge angle, and the refractive index of the prism material, the two laser beams can be aligned parallel or at a desired angle to each other as they pass through the prism. The prism can be a symmetrical prism with an essentially triangular base, in which the wedge angles of the two prism surfaces serving as beam exit surfaces are equal in relation to the beam entry surface, but this is not necessarily the case. It can be advantageous if the beam paths of the laser beams cross before they hit the combiner, as this reduces the aperture on the downstream optics. Depending on the optics configuration, it can also be advantageous if the laser beams do not cross before they hit the combiner.

[0026] In a further embodiment, the EUV light source comprises a first beam direction adjustment device for adjusting the first beam direction of the first laser beam and / or a second beam direction adjustment device for adjusting the second beam direction of the second laser beam. It is understood that if three or more laser beams are combined, three or more beam direction adjustment devices may be present. As described above, it may be advantageous to adjust the respective beam direction of the laser beams, since by slightly tilting the beam directions relative to one another in the near field, the focus positions of the focused laser beams relative to one another in the target area can be adjusted or aligned.For adjusting the beam direction, the respective beam direction adjusting device can have adjustable deflection devices, for example in the form of deflection mirrors or the like, which are designed to be movable, for example tiltable.

[0027] In a further embodiment, the EUV light source comprises a first expansion device for changing, in particular for adjusting, a beam diameter of the first laser beam and / or a second expansion device for changing, in particular for adjusting, a beam diameter of the second laser beam. By defining different beam diameters for the first (collimated) laser beam and the (collimated) second laser beam, different beam diameters can be generated for the beams at the respective focus position in the target area, although the joint focusing via the optical element(s) of the focusing device naturally requires an identical focusing focal length. For example, a focused beam diameter that is a factor of 2 larger can be generated in the target area by a beam diameter of the respective laser beam that is a factor of 2 smaller.For the purposes of this application, an expansion device also includes a device that can reduce the beam diameter. The respective expansion device can be configured to change the beam diameter of the respective laser beam without allowing adjustment of the respective diameter, e.g., using a beam telescope. However, it is also possible for the respective expansion device to be configured to adjust the beam diameter. In this case, the expansion device typically comprises at least one optical element that is movable, for example, displaceable, in the respective beam path.

[0028] In a further embodiment, the target area is located in a vacuum chamber and the combination device is located outside the vacuum chamber. In order to generate the plasma and thus the EUV radiation, it is necessary to arrange the target area, in which the target material is provided in droplet form, in a vacuum environment. As described above, the at least one pre-pulse laser beam and the main pulse laser beam typically have significantly different wavelengths. The vacuum chamber therefore generally has its own window for the passage of the pre-pulse laser beam(s) and the main pulse laser beam, which window allows passage at the respective pre-pulse or main pulse laser wavelength. In the event that the main pulse laser beam has a main pulse wavelength that is in the same order of magnitude as the pre-pulse wavelength(s) (e.g., approximately 1 pm), the passage of the pre-pulse laser beam(s) can be achieved.the pre-pulse laser beams and the main pulse laser beam pass through a common window.

[0029] In a further embodiment, the beam guiding device has focusing optics for focusing the first laser beam and the second laser beam into the target area, wherein the focusing optics are preferably arranged in the vacuum chamber. As described above, it is typically necessary to focus the at least one pre-pulse laser beam and the main pulse laser beam in the target area in order to generate the EUV radiation there. The focusing of two or more pre-pulse laser beams with the aid of the focusing optics is generally carried out with the same focal length, i.e. the pre-pulse laser beams are not focused to different degrees by the focusing optics. The focusing of the main pulse laser beam, however, can optionally be carried out with a different focal length.

[0030] In a further embodiment, the EUV light source comprises a spatially resolving back-reflection detector for detecting radiation reflected back from the target area. When the EUV radiation is generated in the target area, a portion of the focused pre-pulse and main-pulse laser beams is reflected back from the target material in the form of tin droplets. The reflected radiation propagates back through the beam guiding device and can be analyzed using a spatially resolving detector, e.g., a camera. Based on the back-reflected radiation or the position of the pre-pulse laser beam(s) or the main-pulse laser beam on the spatially resolving detector, conclusions can be drawn about the position of the droplet in the target area. Guiding the two laser beams via shared optics makes it possible to use a large numerical aperture to measure the position of each droplet during imaging onto the detector.

[0031] In a further embodiment, the EUV light source has a spatially resolving detector arranged in the beam path downstream of the combination device for detecting the first laser beam and the second laser beam, in particular for detecting the lateral offset between the first laser beam and the second laser beam. In this embodiment, an analysis of the laser beams in the leading beam path takes place downstream of a combination device, as is also described in US 10,932,350 B1. With the aid of the spatially resolving detector, e.g. in the form of a camera, the lateral offset or the relative position(s) of the (at least one) pre-pulse laser beam and the main pulse laser beam or of the two or more pre-pulse laser beams to one another can be determined. The relative positions of the individual beams correspond - assuming suitable scaling - to the positions of the beams in the target area orat the respective focus position, since after the combination device, typically only common optics are used (see above). The EUV light source can have an evaluation device to determine the relative focus positions of the laser beams in the target area based on the lateral offset.

[0032] In a further embodiment, the beam guiding device comprises at least one beam splitter device for redirecting the radiation reflected back from the target area to the back-reflection detector and / or for redirecting a portion of the first laser beam and the second laser beam to the spatially resolving detector. The redirection of the back-reflected radiation and the portion of the laser beams can be performed at one and the same beam splitter device, but this is not mandatory. The beam splitter device can be configured to redirect the largest possible portion of the back-reflected radiation to the spatially resolving detector.

[0033] In another embodiment, the common beam guiding device comprises optics in the form of a telescope arrangement. The telescope arrangement serves to adjust the correct beam diameter in the far field for a given input beam and a given output focal length (which is determined by the distances and, in particular, cannot be shorter). The telescope arrangement is typically arranged in the beam path upstream of the vacuum chamber.

[0034] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details essential to the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0035] drawing

[0036] Examples of embodiments are shown in the schematic drawing and are explained in the following description.

[0037] Figure a schematic representation of an EUV light source with a combination device for combining a first pre-pulse laser beam and a second pre-pulse laser beam spatially separated and with lateral offset, as well as with a beam guiding device for guiding the first pre-pulse laser beam and the second pre-pulse laser beam via common optical elements into a target area.

[0038] The figure shows an EUV light source 1 which has a first laser source (hereinafter referred to as first pre-pulse laser source) 2 in the form of a solid-state laser for emitting a first laser beam (hereinafter referred to as first pre-pulse laser beam) 3 at a pre-pulse wavelength Avi of approximately 1030 nm and a second laser source (hereinafter referred to as second pre-pulse laser source) 4 in the form of a second solid-state laser for emitting a second laser beam (hereinafter referred to as second pre-pulse laser beam) 5 at a second pre-pulse wavelength Xv2 of 1064 nm.The EUV light source 1 also includes a combination device 6, which serves to combine the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5, as well as a beam guiding device 7 for jointly guiding the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 into a target area 8 to generate EUV radiation 9, which is emitted by a target material 10 in the form of a tin droplet arranged in the target area 8. The target area 8 with the target material 10 is located in a vacuum chamber 11, in which a supply device (not shown) supplies the target material 10 in the form of tin droplets, which move along a predetermined trajectory through the vacuum chamber 11 and through the target area 8.The focus positions of the first pre-pulse laser beam 3 and the second pre-pulse laser beam, which are not shown in the figure and which deviate only slightly from one another in order to hit the target material 10 in the form of the tin droplet, are located in the target area 8. For the sake of simplicity, the following considerations assume that the focus positions of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 correspond to the position of the target material 10. The vacuum chamber 11 has an opening with a window 11a for the passage of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5. A main pulse laser beam (not shown in the figure), which is generated by a main pulse laser source in the form of a CO2 laser with a main pulse wavelength of 10.6 pm, is also focused on the target area 8 in the vacuum chamber 11.

[0039] As can also be seen in the figure, the first pre-pulse laser beam 3 from the first pre-pulse laser source 2 and the second pre-pulse laser beam 5 from the second pre-pulse laser source 4 are emitted in a collimated manner and impinge in a collimated manner on the combining device 6, which in the example shown is in the form of a prism 6a. A first beam direction (first pre-pulse beam direction) Rvi of the pre-pulse laser beam 3 and a second beam direction (second pre-pulse beam direction) RV2 of the second pre-pulse laser beam 5, which impinge spatially offset on a beam entry surface 12a of the prism 6a, differ from one another. The combining device 6 in the form of the prism 6a is designed to align the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 parallel to one another.Upon exiting the prism 6a at a respective beam exit surface 12b, 12c, the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 are aligned parallel to each other. The parallel alignment is achieved by a suitable selection of the angles formed by the respective beam exit surface 12b, 12c with the beam entry surface 12a, as well as the respective beam directions Rvi, Rv2, taking into account the refractive index of the material of the prism 6a.

[0040] As can also be seen in the figure, the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 are spatially separated upon exiting the combination device 6 and have a lateral offset or distance AL from each other. The lateral offset AL is maintained during the joint guidance of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 (in the near field) in the beam guidance device 7 and is only canceled after the focusing of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 by means of a focusing optics 13, which focuses the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 at a (slightly different) focus position in the target area 8 or onto the target material 8.

[0041] As can also be seen in the figure, the EUV light source 1 also has a first beam direction adjustment device (hereinafter referred to as the first pre-pulse beam direction adjustment device) 14 for adjusting the first pre-pulse beam direction Rvi of the first pre-pulse laser beam 3. The pre-pulse beam direction adjustment device 14 comprises three tiltable deflection mirrors 15a-c, which make it possible to change the first pre-pulse beam direction Rvi. The EUV light source 1 also has a second beam direction adjustment device (hereinafter referred to as the second pre-pulse beam direction adjustment device) 16 for adjusting the second pre-pulse beam direction Rv2 of the second pre-pulse laser beam 5. The second pre-pulse beam direction adjustment device 16 comprises three tiltable deflection mirrors 17a-c, which make it possible to change the second pre-pulse beam direction Rv2.By slightly tilting the first pre-pulse beam direction Rvi and the second pre-pulse beam direction Rv2 in the near field, the focus positions of the first pre-pulse laser beam 3, which is focused in the target area 8 by the focusing optics 13, and the second pre-pulse laser beam 5 can be adjusted relative to one another. In addition, the focus positions of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 can be changed jointly by means of a tiltable deflection mirror 18 arranged in the beam path downstream of the focusing optics 13. The EUV light source 1 also has a first expansion device (first pre-pulse expansion device) 19 with a combination of a beam-expanding and a beam-converging optical element in order to change a beam diameter dvi of the first pre-pulse laser beam 3, in the example shown, to increase it.In the beam path of the second pre-pulse laser beam 5, a second expansion device (second pre-pulse expansion device) 20 is arranged for changing a beam diameter dv2 of the second pre-pulse laser beam 5. The second pre-pulse expansion device 20 also has a beam-expanding and a beam-converging optical element. In the example shown in the figure, the beam diameter dvi of the first pre-pulse laser beam 3 is essentially doubled by the first pre-pulse expansion device 19, and the beam diameter dv2 of the second pre-pulse laser beam 5 is essentially halved by the second pre-pulse expansion device 20. Both the first pre-pulse expansion device 19 and the second pre-pulse expansion device 20 are designed not only to change the respective beam diameter dvi, dv2, but also to adjust them. For this purpose, the distance between the respective beam-expanding orbeam converging optical elements.

[0042] By changing the beam diameters dv, dv2, different focus diameters of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 can be set in the target area 8, although joint focusing by means of the focusing optics 13 can naturally only be achieved with an identical focal length. With the enlargement of the beam diameter dvi of the first pre-pulse laser beam 5 by a factor of two, as shown in the figure, a beam diameter dvi reduced by half can be generated at the focus position in the target area 8. With the reduction of the beam diameter dv2 of the second pre-pulse laser beam 5 by half, as shown in the figure, a beam diameter dv2 larger by a factor of two can be generated at the focus position in the target area 8, provided that the two laser sources 2, 4 each have the same beam quality.The beam guiding device 7 also has a telescope arrangement 21 which serves to set the correct beam diameter in the far field for a given input beam and a given output focal length.

[0043] The EUV light source 1 also has a spatially resolving back-reflection detector 22, which is designed in the form of a camera. The back-reflection detector 22 serves to detect radiation 23 reflected back from the target area 8, more precisely from the target material 10. The back-reflected radiation 23 passes through the beam guiding device 7 with a reverse beam direction relative to the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5. A beam splitter 24 serves to deflect or decouple the back-reflected radiation 23 toward the back-reflection detector 22. The beam splitter 24 can be designed to be polarization-selective and / or wavelength-selective in order to deflect the back-reflected radiation 23 from the target area 8. The detection of the back-reflected radiation 23 makes it possible to determine the position of the target material 10 in the form of the tin droplet within the target area 8. The back-reflection detector 22 orThe optics connected upstream of this enable detection with a high numerical aperture.

[0044] The beam splitter device 24 also serves to deflect a (power) portion of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 onto a spatially resolving detector 25 after passing through the combination device 6. In the example shown, the spatially resolving detector 25 is designed in the form of a camera. With the aid of the spatially resolving detector 25, the lateral offset AL between the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 can be detected. By means of an evaluation device (not shown), the relative position or distance of the focus positions of the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5 in the target area 8 can be deduced from the lateral offset AL, since the beam guiding device 7 following the beam splitter 24 exclusively uses shared optical elements 21, 13, 18.

[0045] The beam guiding device 7 can in principle also have separate optical

[0046] Elements for guiding the first pre-pulse laser beam 3 and the second pre-pulse laser beam 5, but this increases the installation space and the number of components required. The use of separate optical elements may, however, be necessary if the pre-pulse wavelengths Avi, Xv2 are significantly different. For this reason, the main pulse laser beam (not shown in the figure), which is generated with a main pulse wavelength of approx. 10.6 pm (CO2 laser beam), is typically guided via a separate optics of the beam guiding device 7 (not shown in the figure) and usually enters the vacuum chamber 11 through its own window. In the event that the main pulse wavelength of the main pulse laser beam does not deviate too greatly from the pre-pulse wavelength(s), e.g. because the main pulse laser source is a solid-state laser with a main pulse wavelength of, for example, approx. 1 pm, 2 pm or approx.5 pm, this can be combined with the first pre-pulse laser beam 3 for common beam guidance in the beam guidance device 7 in the manner described above in the combination device 6 instead of the second pre-pulse laser beam 5 shown in the figure.

[0047] Contrary to what is shown in the figure, the telescope arrangement 21 and the focusing optics 13 may not have lens elements, but rather reflective optical elements or mirrors. Contrary to what is shown in the figure, three or more laser beams can also be guided to the combination device 6 via separate beam paths. The three or more laser beams can, for example, be three or more pre-pulse laser beams, but it is also possible for two or more pre-pulse laser beams and the main pulse laser beam to be combined in the combination device 6. In the latter case, the combination device 6 typically forms two or more spatially separated pre-pulse laser beams and one main pulse laser beam, each of which has a lateral offset from one another.

[0048] In the event that the two pre-pulse wavelengths Avi, Av2 differ significantly from one another, an anti-reflection coating can be applied to the transmissive optics 21, 13 of the beam guiding device 7. This anti-reflection coating is designed or optimized to suppress reflections at both the first pre-pulse wavelength Avi and the second pre-pulse wavelength Av2. For example, quartz glass can be used as the material for the transmissive optics 21, 13. Reflective optics of the beam guiding device 7, e.g., the deflection mirror 18, can be provided with a coating optimized for the reflection of both pre-pulse wavelengths Avi, Av2.

Claims

Patent claims 1. EUV light source (1), comprising: - a first laser source (2) for emitting a first laser beam (3), - a second laser source (4) for emitting a second laser beam (5), - a combination device (6) for combining the first laser beam (3) and the second laser beam (5), and - a beam guiding device (7) for the joint beam guiding of the first laser beam (3) and the second laser beam (5) into a target area (8) for generating EUV radiation (9), characterized in that the combination device (6) is designed to supply the first laser beam (3) and the second laser beam (5) to the beam guiding device (7) for the joint beam guiding via common optics (21, 13, 18) spatially separated and with a lateral offset (AL).

2. EUV light source according to claim 1, wherein the first laser source is a pre-pulse laser source (2) for emitting a pre-pulse laser beam (3) and the second laser source is a main pulse laser source for emitting a main pulse laser beam or a further pre-pulse laser source (4) for emitting a further pre-pulse laser beam (5).

3. EUV light source according to claim 1 or 2, wherein a first wavelength (Avi) of the first laser beam (3) and a second wavelength (Av2) of the second laser beam (5) differ from one another by not more than 70 nm, preferably by not more than 50 nm and / or wherein the first wavelength (Avi) of the first laser beam (3) and the second wavelength (Av2) of the second laser beam (5) are in a wavelength range between 350 nm and 5 pm, preferably between 500 nm and 2.5 pm.

4. EUV light source according to one of the preceding claims, in which the beam guiding device (7) comprises at least one transmissive optic (21, 13) with an anti-reflective coating which is designed to suppress reflections of the first laser beam (3) at the first wavelength (Avi) and to suppress reflections of the second laser beam (5) at the second wavelength (Av2), and / or in which the transmissive optics (21, 13) are formed from quartz glass.

5. EUV light source according to one of the preceding claims, in which the first laser beam (3) impinges on the combination device (6) with a first beam direction (Rvi) and in which the second laser beam (5) impinges on the combination device (6) with a second beam direction (Rv2) different from the first beam direction (Rvi).

6. EUV light source according to one of the preceding claims, wherein the combination device (6) is designed to align the first laser beam (3) and the second laser beam (5) parallel to one another.

7. EUV light source according to one of the preceding claims, wherein the combining device comprises at least one prism (6a).

8. EUV light source according to one of the preceding claims, further comprising: a first beam direction adjusting device (14) for adjusting the first beam direction (Rvi) of the first laser beam (3) and / or a second beam direction adjusting device (16) for adjusting the second beam direction (Rv2) of the second laser beam (5).

9. EUV light source according to one of the preceding claims, further comprising: a first expansion device (19) for changing, in particular for adjusting, a beam diameter (dvi) of the first laser beam (3) and / or a second expansion device (20) for changing, in particular for adjusting, a beam diameter (dv2) of the second laser beam (5).

10. EUV light source according to one of the preceding claims, wherein the target region (8) is located in a vacuum chamber (11) and the combination device (6) is located outside the vacuum chamber (11).

11. EUV light source according to one of the preceding claims, wherein the beam guiding device (7) has a focusing optics (13) for focusing the first laser beam (3) and the second laser beam (5) into the target area (8), wherein the focusing optics (13) is preferably arranged in the vacuum chamber (11).

12. EUV light source according to one of the preceding claims, further comprising: a spatially resolving back-reflection detector (22) for detecting radiation (23) reflected back from the target area (8).

13. EUV light source according to one of the preceding claims, further comprising: a spatially resolving detector (25) arranged in the beam path after the combination device (6) for detecting a portion of the first laser beam (3) and the second laser beam (5), in particular for detecting the lateral offset (AL) between the first laser beam (3) and the second laser beam (5).

14. EUV light source according to one of claims 12 or 13, further comprising: at least one beam splitter device (24) for deflecting the radiation (23) reflected back from the target area (8) onto the back-reflection detector (22) and / or for deflecting a portion of the first laser beam (3) and the second laser beam (5) onto the spatially resolving detector (25).

15. EUV light source according to one of the preceding claims, wherein the beam guiding device (7) has an optic in the form of a telescope arrangement (21).

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