EUV light source with coupling device

Abstract

The present 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 coupling device (6) for coupling the first laser beam (3) and the second laser beam (5), and further comprising a beam guidance device (7) for jointly guiding the first laser beam (3) and the second laser beam (5) into a target region (8) to generate EUV radiation (9). The coupling device (6) is designed to supply the first laser beam (3) and the second laser beam (5) to the beam guidance device (7) for joint beam guidance via common optical elements (21, 13, 18) with spatial separation and lateral offset (ΔL).

Description

[Technical Field]

[0001] The present 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 coupling device for coupling the first laser beam and the second laser beam; and a beam guidance device for jointly guiding the first laser beam and the second laser beam into a target region in order to generate EUV radiation.

[0002] An EUV light source is a radiation source that functions to emit EUV radiation. EUV radiation is understood to mean electromagnetic radiation with wavelengths of 5 nm to 30 nm. EUV radiation has found applications particularly in the semiconductor industry. Compared to lithography equipment currently widely used and operating at wavelengths in the UV wavelength range, the use of EUV radiation for microlithography manufacturing enables the reliable production of components with significantly smaller structural sizes, and therefore results in a corresponding improvement in performance.

[0003] The EUV light sources described above are suitable for generating EUV radiation by an LPP (Laser-Generated Plasma) process. In such EUV light sources, a target material, typically a metal, especially tin, is supplied in droplet form within the target area by a supply device. In each case, the droplet is first irradiated with one, two, or optionally three or more prepulses. The prepulses of the prepulse laser source prepare the droplet for irradiation by the main pulse, and in particular, they function to heat the droplet, expand it, vaporize it, and / or generate a plasma. Subsequent irradiation of the droplet with the main pulse of the main pulse laser beam functions to transition the target material into a plasma state. When the plasma components recombine, EUV radiation is emitted.

[0004] To generate EUV radiation, at least one prepulse, usually at least two, and the main pulse must be guided to approximately the same focal position within the target region. It is advantageous if the collision angles between the prepulse and the main pulse within the target region, or between two or more prepulses, deviate from each other as small as possible. In principle, two or more laser beams can be guided into the target region via different optical units and focused within the target region via different focusing optical units. However, the space required for these optical units is quite large, complicating constructive solutions with small relative collision angles between the two laser beams.

[0005] US10,932,350B2 proposes combining a pre-pulsed laser beam and a main-pulsed laser beam, or both pre-pulsed laser beams, in a beam combiner to focus them via a common focusing optical unit within the plasma generation region or on the target material. The beam combiner can be designed to be wavelength-selective, for example, to reflect the pre-pulsed laser beam and transmit the main-pulsed laser beam.

[0006] EUV beam generators having two beam sources for emitting two laser beams, designed to combine or superimpose two laser beams, are described in US10,932,350B2, as well as, for example, WO2015 / 036024A1 and WO2015 / 036025A1.

[0007] WO2015 / 036025A1 describes an EUV radiation generator having a beam guidance device having a superposition device that superimposes two laser beams entering a vacuum chamber through two different apertures for joint beam guidance toward a target region. In WO2015 / 036025A1, superposition is understood to mean that the two laser beams have a common beam axis after superposition and propagate coaxially along the common beam axis. The superposition device can be designed as a reflective optical element, for example, located within the vacuum chamber, having a first surface region for reflecting a first laser beam and a second surface region for reflecting a second laser beam, surrounding the first surface region in an annular manner. [Background technology]

[0008] In contrast, the object of the present invention was to provide the above-described type of EUV light source that enables guiding two (or more) laser beams into a target area with low requirements for installation space and optical components, and in particular, simplifies the coordination of the laser beams with respect to each other.

[0009] Summary of the present invention This objective is achieved by the above-described type of EUV light source, in which the coupling device is designed to supply the first and second laser beams to the beam guide device via a common optical unit in a spatially separated manner and with a lateral offset for joint beam guidance. The coupling device may also be designed to supply additional third, fourth, and other laser beams to the beam guide device in a spatially separated manner and with a lateral offset for joint beam guidance.

[0010] For various reasons, it has proven advantageous when the first and second laser beams are not spatially superimposed within the coupling device for joint beam induction, i.e., when they do not have a common beam axis after coupling, such as in the usual case with polarization superposition (e.g., by a polarization coupler), wavelength superposition (e.g., by a grating), temporal superposition (e.g., by an acousto-optic modulator), or coaxial superposition as described in WO2015 / 036025A1. Joint beam induction using such spatial superposition with a common beam axis results in thermally induced deformation or thermally induced change in optical density, which usually leads to a degradation of image quality and affects all laser beams.

[0011] With polarization superposition, an additional problem arises: the superposition leads to losses in the polarization combiner. Furthermore, with polarization superposition, polarization can no longer be used to isolate the laser source from back-emission. The back-emission of the first laser beam also leads to potential interference with the second laser beam, and vice versa. When coupling by wavelength superposition, laser beams of different wavelengths are required, but the availability of corresponding laser sources with the required pulse shape and power density may not exist. Moreover, optical units that are sufficiently good at transmitting and reflecting both the CO2 laser radiation (approximately 10.6 μm wavelength) typically used for the main pulsed laser beam (see below) and the solid-state laser radiation (approximately 1 μm wavelength) typically used for the pre-pulsed laser beam are difficult to produce, and therefore always lead to increased absorption in the optical elements, and thus to a decrease in image quality. At the wide-ranging wavelengths specified above, the pre-pulsed laser beam and the main pulsed laser beam are typically guided through separate optical units, so that the separate optical units allow for almost aberration-free imaging of the pre-pulse while maintaining the high average power of the main pulse.

[0012] In the EUV light source according to the present invention, spatial superposition with lateral offset occurs in the coupling device, i.e., the laser beams exit the coupling device in a spatially separated state with a lateral offset. The two laser beams pass together, but along different laterally offset beam paths, through the optical units or optical elements of the beam guidance device (e.g., a deflection and focusing optical unit). In the near-field within the beam guidance device, the laser beams are typically collimated and substantially parallel (with a lateral offset). In the far-field (after focusing by the focusing optical unit), the laser beams are focused on a target region at approximately the same focal position. The joint beam guidance in the beam guidance device reduces the space required to guide the laser beams into the target region. In addition, by slightly tilting the first and second laser beams relative to each other in the near-field, their relative positions in the far-field (after focusing) can be adjusted or set (see below).

[0013] In one embodiment, the first laser source is a prepulsed laser source for emitting a prepulsed laser beam, and the second laser source is a main pulsed laser source for emitting a main pulsed laser beam or a further prepulsed laser source for emitting a further prepulsed laser beam. A coupling device can be used to couple the prepulsed laser beam and the main pulsed laser. Alternatively, the coupling device can couple a prepulsed laser beam with an additional prepulsed laser beam. It is also apparent that the coupling device can be designed to supply three or more prepulsed laser beams or at least two prepulsed laser beams and a main pulsed laser beam to a beam guidance device for joint beam guidance in a spatially separated manner and with a lateral offset.

[0014] The wavelength of the prepulse laser beam, and therefore the wavelength of the prepulse, is referred to as the prepulse wavelength, and the wavelength of the main pulse beam, and therefore the wavelength of the main pulse, is referred to as the main pulse wavelength. The main pulse laser source is, for example, a CO2 laser having a main pulse wavelength of about 10.6 μm, and the prepulse laser source is, for example, a solid-state laser which can have a prepulse wavelength of about 1 μm. Compared to the use of a prepulse laser source in the form of an additional CO2 laser, the use of a prepulse laser source in the form of a solid-state laser has the advantages of higher conversion efficiency and almost aberration-free focusing of the laser beam to the droplet. In particular, the reasons for this are that a short pulse duration and focusing of the prepulse to the target material are achieved thereby, and the prepulse has different absorption behavior from the main pulse. In principle, the main pulse laser source is a solid-state laser, and it is also possible that the main pulse laser source has a main pulse wavelength of about 1 μm, 2 μm, or 5 μm. When multiple prepulse laser sources are used, they can each have the same prepulse wavelength, or (usually slightly) different prepulse laser wavelengths, for example, 1030 nm (Yb:YAG laser) and 1064 nm (Nd:YAG laser).

[0015] In one embodiment, the first wavelength of the first laser beam and the second wavelength of the second laser beam deviate from each other by up to 70 nm, preferably up to 50 nm, and / or the first wavelength of the first laser beam and the second wavelength of the second laser beam are within the wavelength range of 350 nm to 5 μm, preferably 500 nm to 2.5 μm.

[0016] As described above, an optical unit that transmits or reflects two wavelengths typically has increased absorbance. When the wavelengths of the two laser beams are relatively close to each other, this usually does not play a significant role. This is especially true for the pre-pulse wavelengths of 1030 nm and 1064 nm specified above. In principle, the deviation between the two wavelengths may also be greater than that specified above, in which case the two laser beams can be guided through a common optical unit of the beam guidance device. In the case of a transmissive optical unit, this usually needs to be in close proximity to each other and can be used with the same substrate and coating, in particular in the form of an anti-reflective coating (see below). For example, when using a suitable substrate material, e.g., quartz glass, the laser beam can also be guided through a common transmissive optical unit having wavelengths significantly different from those specified above. When the main pulse wavelength is of a similar magnitude to the pre-pulse wavelength, (at least one) pre-pulse laser beam and the main pulse laser beam can also be guided toward the target region through a common optical unit.

[0017] In a further embodiment, the beam guiding device comprises at least one transmissive optical unit having an anti-reflection coating, the anti-reflection coating being designed to suppress reflection of a first laser beam of a first wavelength and reflection of a second laser beam of a second wavelength, and / or the transmissive optical unit is formed from fused silica. For example, in the case of a transmissive optical unit in the form of a lens, reflection when entering or exiting the substrate material leads to a reduction in transmittance, which is why an anti-reflection coating is applied to such an optical unit. The anti-reflection coating is typically optimized to suppress reflection of a wavelength corresponding to the wavelength of the impinging laser radiation. If the wavelengths of the two laser beams are significantly different from each other, it may be useful to apply an anti-reflection coating to the surface of the transmissive optical unit, and the coating is optimized to suppress reflection of the two wavelengths of the two laser beams. For example, in this case, the first wavelength can be about 515 nm and the second wavelength can be about 1 μm, or the first wavelength can be about 1 μm and the second wavelength can be about 2 μm.

[0018] For example, the use of fused silica as a material for the transmissive optical unit of the beam guiding device in the form of a lens is advantageous because this material has a relatively high transmittance in a wide wavelength range from about 350 nm to about 2.5 μm.

[0019] It is clear that the beam guiding device can comprise not only transmissive optical units but also, for example, reflective optical units in the form of mirrors. For example, the focusing optical unit of the beam guiding device can be fully or partially realized in the form of a reflective optical unit. The reflective optical unit can be provided with a coating optimized for reflection at both wavelengths.

[0020] In a further embodiment, the first laser beam impinges on the coupling device in a first beam direction, and the second laser beam impinges on the coupling device in a second beam direction different from the first beam direction. The different beam directions facilitate guiding the laser beams along spatially separated beam paths to the coupling device. In this case, the coupling device is typically designed to change the first and / or second beam direction in order to orient the laser beams substantially parallel to each other. The beam direction can be changed at the coupling device, for example, by refraction in (at least) one transmissive optical element or, for example, by deflection in (at least) one reflective optical element, particularly a deflecting mirror beam. In the event that an odd number of beams enter the coupling device, the central beam can pass through the coupling device, for example, without its beam direction being changed by the coupling device.

[0021] In one embodiment, the coupling device is designed to orient the first laser beam and the second laser beam parallel to each other. For the purposes of the present application, a parallel orientation means that the beam directions of the laser beams deviate from each other by less than 0.2° when leaving the coupling device. As explained above, the positions of the laser beams in the far field can be adjusted by slightly tilting the beam directions of the laser beams at the front of the coupling device, which leads to a slight deviation from the parallel orientation of the laser beams after the coupling device. However, the tilt should be selected so as not to become too large, otherwise the laser beams can no longer be jointly guided through the optical elements of the beam guiding device.

[0022] In further embodiments, the coupling device comprises at least one prism. In particular, the coupling device may consist of prisms. Because the refractive index of the prism material is wavelength-dependent, for coupling two or more laser beams using a prism, it is advantageous or essential that they have the same or similar wavelengths. When two laser beams are precisely coupled, the prism may have a (flat) prism surface that acts as, for example, a beam inlet surface, and the laser beams collide in a spatially offset manner. In this case, the angles of incidence of the two laser beams to the prism surface may have the same magnitude but different signs. The two laser beams exit two further prism surfaces, each oriented at a wedge angle with respect to the prism surface that acts as the beam inlet surface. By appropriately selecting the beam direction, wedge angle, and refractive index of the prism material, the two laser beams can be oriented parallel to each other or at a desired angle as they pass through the prism. The prism may be a symmetrical prism with a substantially triangular base, and the wedge angles of the two prism surfaces that act as the beam exit surfaces are equal in magnitude to the beam entrance surface, although this is not necessarily the case. If the beam paths of the laser beams intersect before the laser beam strikes the coupling device, this may be advantageous in reducing the aperture of the subsequent optical unit. Depending on the optical unit configuration, it may also be advantageous if the laser beams do not intersect before the laser beam strikes the coupling device.

[0023] In further embodiments, the EUV light source comprises a first beam directional adjustment device for adjusting the first beam direction of a first laser beam, and / or a second beam directional adjustment device for adjusting the second beam direction of a second laser beam. When three or more laser beams are coupled, it is clear that three or more beam directional adjustment devices may be present. As described above, adjusting the beam direction of laser beams can be advantageous because by slightly tilting the beam directions relative to each other in the near field, the focal positions of laser beams focused relative to each other within a target region can be set or adjusted. To adjust the beam direction, the beam directional adjustment device may have an adjustable deflection device in the form of, for example, a deflection mirror, which is designed to be movable, for example, tiltable.

[0024] In further embodiments, the EUV light source comprises a first magnifying device for varying, in particular adjusting, the beam diameter of a first laser beam, and / or a second magnifying device for varying, in particular adjusting, the beam diameter of a second laser beam. Different beam diameters can be generated for beams at focal positions within a target region by specifying different beam diameters for the first (collimated) laser beam and the second (collimated) laser beam, although cofocusing via the optical elements of the focusing devices inherently requires the same focal length. For example, by doubling the beam diameter of the laser beam, a focused beam diameter twice as large can be generated within the target region. In the context of this application, the magnifying device is also understood to mean a device that can reduce the beam diameter. The magnifying device may be designed to vary the beam diameter of a laser beam in a manner in which the diameter is not adjustable, for example, by using a beam telescope. However, it is also possible for the magnifying device to be designed to adjust the beam diameter. In this case, the magnifying device typically has at least one optical element that is movable, e.g., displaceable, within the beam path.

[0025] In further embodiments, the target region is located within a vacuum chamber, and the coupling device is located outside the vacuum chamber. To generate plasma, and therefore EUV radiation, it is necessary to place the target region, in which the target material is provided in droplet form, within a vacuum environment. As described above, at least one pre-pulsed laser beam and a main-pulsed laser beam typically have significantly different wavelengths. Therefore, the vacuum chamber usually has separate windows for the passage of the pre-pulsed laser beam and the main-pulsed laser beam, each window allowing passage at the pre-pulsed and main-pulsed laser wavelengths, respectively. If the main-pulsed laser has a main-pulse wavelength that is the same size as the pre-pulse wavelength (e.g., about 1 μm), then the pre-pulsed and main-pulsed laser beams can pass through a common window.

[0026] In further embodiments, the beam guidance device includes a focusing optical unit for focusing a first laser beam and a second laser beam into a target region, the focusing optical unit preferably located in a vacuum chamber. As described above, typically, in order to generate EUV radiation in the target region, it is necessary to focus at least one pre-pulsed laser beam and a main-pulsed laser beam within the target region. Focusing of two or more pre-pulsed laser beams using a focusing optical unit is usually performed at the same focal length, i.e., the pre-pulsed laser beams are not focused to different degrees by the focusing optical unit. However, focusing of the main-pulsed laser beam can be performed at different focal lengths if necessary.

[0027] In a further embodiment, the EUV light source includes a spatially resolved back-reflected detector for detecting radiation reflected back from a target region. When EUV radiation is generated within a target region, portions of the focused pre-pulse and main-pulse laser beams are reflected back from the target material in the form of tin droplets. The reflected radiation propagates backward through a beam guidance device and can be analyzed using a spatially resolved detector, such as a camera. Based on the position of the back-reflected radiation or the pre-pulse or main-pulse laser beam on the spatially resolved detector, conclusions can be drawn regarding the position of the droplets within the target region. Guiding the two laser beams through a common optical unit allows for the use of a large numerical aperture to measure the position of each droplet during imaging onto the detector.

[0028] In further embodiments, the EUV light source includes a spatially resolved detector located downstream of the coupling device in the beampath for detecting a first laser beam and a second laser beam, and in particular for detecting the lateral offset between the first and second laser beams. In this embodiment, the laser beams in the forward beampath are analyzed downstream of the coupling device, as also described in US10,932,350B1. For example, with the assistance of a spatially resolved detector in the form of a camera, the lateral offset or relative position of (at least one) pre-pulsed laser beam and the main-pulsed laser beam, or of two or more pre-pulsed laser beams relative to each other, can be determined. The relative positions of the individual beams correspond to the beam positions in the target region or at the focal point, since, assuming suitable scaling, typically only a common optical unit is used after the coupling device (see above). The EUV light source may include an evaluation device for determining the relative focal position of the laser beams in the target region based on the lateral offset.

[0029] In further embodiments, the beam guidance device includes at least one beam splitter device for deflecting back-reflected radiation from a target region onto a back-reflected detector, and / or for deflecting portions of a first laser beam and a second laser beam onto a spatially resolved detector. While the deflection of back-reflected radiation and portions of the laser beams can be performed by the same beam splitter device, this is not absolutely necessary. The beam splitter device can be designed to deflect the largest possible proportion of back-reflected radiation onto the spatially resolved detector.

[0030] In further embodiments, the common beam guidance device has an optical unit in the form of a telescopic configuration. The telescopic configuration is designed to allow the correct beam diameter to be set in the far field for a given input beam and a given output focal length (determined by distance and, in particular, not being shorter). The telescopic configuration is typically located in the beam path upstream of the vacuum chamber.

[0031] Further features and advantages of the present invention arise from the following description of exemplary embodiments of the invention and the claims, with reference to drawings illustrating important details to the invention. Each feature can be realized individually by itself or as a plurality in any desired combination of modifications of the invention.

[0032] Exemplary embodiments are illustrated in schematic diagrams and described in the following description. [Brief explanation of the drawing]

[0033] [Figure 1] A schematic representation of an EUV light source is shown, which has a coupling device for coupling a first prepulsed laser beam and a second prepulsed laser beam in a spatially separated manner and with a lateral offset, and a beam guidance device for guiding the first prepulsed laser beam and the second prepulsed laser beam into a target region via a common optical element.

[0034] The figure shows the pre-pulse wavelength λ of approximately 1030 nm. V1 A first laser source (hereinafter referred to as the first prepulsed laser source) 2 in the form of a solid-state laser for emitting the first laser beam (hereinafter referred to as the first prepulsed laser beam) 3, and a second prepulsed wavelength λ of 1064 nm. V2 The present invention relates to an EUV light source 1 comprising a second laser source (hereinafter referred to as the second prepulsed laser source) 4 in the form of a second solid-state laser for emitting a second laser beam (hereinafter referred to as the second prepulsed laser beam) 5. The EUV light source 1 also comprises a coupling device 6 that functions to couple the first prepulsed laser beam 3 and the second prepulsed laser beam 5, and a beam guidance device 7 for jointly guiding the first prepulsed laser beam 3 and the second prepulsed laser beam 5 into the target region 8 to generate EUV radiation 9 which is emitted by a target material 10 in the form of tin droplets, located within the target region 8. The target region 8 having the target material 10 is located within a vacuum chamber 11 in which a supply device (not shown) provides the target material 10 in the form of tin droplets, and the target material 10 moves along a predetermined trajectory through the vacuum chamber 11 and the target region 8. The focal positions of the first prepulse laser beam 3 and the second prepulse laser beam, not shown in the figure, are within the target region 8 and are slightly offset from each other in order to strike the target material 10 in the form of a tin droplet. For the sake of simplification with respect to the following considerations, we assume that the focal positions of the first prepulse laser beam 3 and the second prepulse laser beam 5 correspond to the positions of the target material 10. For the passage of the first prepulse laser beam 3 and the second prepulse laser beam 5, the vacuum chamber 11 has an opening with a window 11a. A main pulse laser beam (not shown) generated by a main pulse laser source in the form of a CO2 laser with a main pulse wavelength of 10.6 μm is also focused over the target region 8 within the vacuum chamber 11.

[0035] As can be seen in the figure, the first prepulsed laser beam 3 from the first prepulsed laser source 2 and the second prepulsed laser beam 5 from the second prepulsed laser source 4 are emitted in a collimated manner and collide with a coupling device 6, which is designed in the form of a prism 6a in the example shown. The first beam direction (first prepulsed beam direction) R of the prepulsed laser beam 3 collides with the beam inlet surface 12a of the prism 6a in a spatially offset manner. V1 and the second beam direction (second prepulse beam direction) R of the second prepulse laser beam 5 V2 These are different from each other. The coupling device 6 in the form of a prism 6a is designed to orient the first prepulsed laser beam 3 and the second prepulsed laser beam 5 parallel to each other. When the beams exit the prism 6a at the beam exit surfaces 12b and 12c, the first prepulsed laser beam 3 and the second prepulsed laser beam 5 are oriented parallel to each other. The parallel orientation is determined by the angle formed between the beam exit surfaces 12b and 12c and the beam inlet surface 12a, and the beam direction R, taking into account the refractive index of the material of the prism 6a. V1 , R V2 This is achieved through a favorable selection.

[0036] As can be seen in the figure, the first prepulsed laser beam 3 and the second prepulsed laser beam 5 are spatially separated as they exit the coupling device 6, with a lateral offset or distance ΔL from each other. The lateral offset ΔL is maintained during the joint guidance (in the near field) of the first prepulsed laser beam 3 and the second prepulsed laser beam 5 in the beam guidance device 7 and is simply eliminated after the first prepulsed laser beam 3 and the second prepulsed laser beam 5 are focused by the focusing optical unit 13, which focuses the first prepulsed laser beam 3 and the second prepulsed laser beam 5 onto (slightly different) focal positions or target material 8 within the target region 8.

[0037] As can be seen in the figure, the EUV light source 1 also has a first prepulse beam direction R of the first prepulse laser 3. V1It also has a first beam direction adjustment device (hereinafter referred to as the first prepulse beam direction adjustment device) 14 for adjusting the [direction]. The prepulse beam direction adjustment device 14 has three tiltable deflection mirrors 15a to 15c that can change the first prepulse beam direction R V1 EUV light source 1 also has a second beam direction adjustment device (hereinafter referred to as the second prepulse beam direction adjustment device) 16 for adjusting the second prepulse beam direction R V2 of the second prepulse laser 5. The second prepulse beam direction adjustment device 16 has three tiltable deflection mirrors 17a to 17c that can change the second prepulse beam direction R V2 By slightly tilting the first prepulse beam direction R V1 and the second prepulse beam direction R V2 in the near field, the focal position of the first prepulse laser beam 3 focused in the target area 8 by the focusing optical unit 13 and the focal position of the second prepulse laser beam 5 can be adjusted relative to each other. In addition, the focal positions of the first prepulse laser beam 3 and the second prepulse laser beam 5 can be jointly changed by a tiltable deflection mirror 18 arranged downstream of the focusing optical unit 13 in the beam path.

[0038] EUV light source 1 also has a first expansion device (first prepulse expansion device) 19, which is a combination of beam expansion and beam focusing optical elements, for changing the beam diameter d V1 of the first prepulse laser beam 3, and in the example shown, for expanding it. In the beam path of the second prepulse laser beam 5, a second expansion device (second prepulse expansion device) 20 is provided for changing the beam diameter d V2 of the second prepulse laser beam 5. The second prepulse expansion device 20 also has beam expansion and beam focusing optical elements. In the example shown in the figure, the beam diameter d V1The beam diameter d of the second prepulsed laser beam 5 is substantially doubled by the first prepulsed expansion device 19. V2 This is substantially halved by the second prepulse expansion device 20. Both the first prepulse expansion device 19 and the second prepulse expansion device 20 reduce the beam diameter d V1 d V2 It is designed not only to change the beam, but also to adjust it. For this purpose, the distance between beam expanding or beam focusing optical elements can be changed.

[0039] beam diameter d V d V2 By changing the beam diameter d of the first prepulsed laser beam 3 and the second prepulsed laser beam 5, the different focal diameters of the first prepulsed laser beam 3 and the second prepulsed laser beam 5 can be adjusted within the target region 8, however, cofocusing by the focusing optical unit 13 can only be performed at the same focal length. V1 When it is magnified by a factor of two, the beam diameter d is reduced to half, as shown in the figure. V1 This can be generated at the focal position within the target region 8. The beam diameter d of the second prepulsed laser beam 5 V2 When the diameter is reduced by half, as shown in the figure, the beam diameter d is twice as large, provided that the two laser sources 2 and 4 each have the same beam quality. V2 This can be generated at the focal point within the target region 8.

[0040] The beam guidance device 7 also has a telescopic configuration 21 that functions to set the correct beam diameter in the far field for a given input beam and a given output focal length.

[0041] The EUV light source 1 also has a spatially resolved backreflection detector 22 designed in the form of a camera. The backreflection detector 22 functions to detect radiation 23 reflected from the back of a target region 8, more precisely from a target material 10. The reflected radiation 23 passes through a beam guidance device 7 in opposite beam directions to the first prepulsed laser beam 3 and the second prepulsed laser beam 5. A beam splitter 24 is used to deflect or decouple the reflected radiation 23 in the direction of the backreflection detector 22. The beam splitter 24 can be designed polarization-selectively and / or wavelength-selectively to deflect the reflected radiation 23 away from the target region 8. The deflection of the reflected radiation 23 makes it possible to determine the position of the target material 10 in the form of a tin droplet within the target region 8. An optical unit connected to the backreflection detector 22 or upstream thereof enables detection with a high numerical aperture.

[0042] The beam splitter device 24 also functions to deflect a portion (output) of the first prepulsed laser beam 3 and the second prepulsed laser beam 5 onto the spatially resolved detector 25 after passing through the coupling device 6. In the example shown, the spatially resolved detector 25 is designed in the form of a camera. With the assistance of the spatially resolved detector 25, a lateral offset ΔL between the first prepulsed laser beam 3 and the second prepulsed laser beam 5 can be detected. By an evaluation device (not shown), the relative position or distance of the focal positions of the first prepulsed laser beam 3 and the second prepulsed laser beam 5 within the target region 8 can be inferred based on the lateral offset ΔL, since only the jointly used optical elements 21, 13, and 18 are used in the beam guidance device 7 after the beam splitter 24.

[0043] The beam guidance device 7 also, in principle, has separate optical elements for guiding the first prepulsed laser beam 3 and the second prepulsed laser beam 5, but this increases the installation space and the number of components required. However, the use of separate optical elements results in significantly different prepulsed wavelengths λ V1 , λ V2This may be necessary. For this reason, a main pulsed laser beam (CO2 laser beam), not shown in the image, having a main pulse wavelength of approximately 10.6 μm, is typically guided through a separate optical unit (not shown) of the beam guidance device 7, and usually passes through its own window into the vacuum chamber 11. For example, if the main pulsed laser source is a solid-state laser having a main pulse wavelength of, for example, approximately 1 μm, 2 μm, or approximately 5 μm, and the main pulse wavelength of the main pulsed laser beam does not deviate excessively from the pre-pulse wavelength, the main pulsed laser beam can be coupled with the first pre-pulsed laser beam 3 for co-beam guidance in the beam guidance device 7 of the type described above in the coupling device 6, instead of the second pre-pulsed laser beam 5 shown in the figure.

[0044] Unlike as shown in the figure, the telescope configuration 21 and the focusing optical unit 13 do not have lens elements and may have reflective optical elements or mirrors. Unlike as shown in the figure, three or more laser beams can also be guided to the coupling device 6 via separate beam paths. Three or more laser beams may be, for example, three or more pre-pulsed laser beams, but it is also possible that two or more pre-pulsed laser beams and a main-pulsed laser beam are coupled at the coupling device 6. In the latter case, the coupling device 6 typically forms two or more spatially separated pre-pulsed laser beams with a lateral offset from each other and one main-pulsed laser beam.

[0045] Two or more prepulse wavelengths λ V1 , λ V2 If the wavelengths deviate significantly from each other, an anti-reflective coating can be applied to the transmission optical units 21 and 13 of the beam guidance device 7, and the coating is applied to the first pre-pulse wavelength λ V1 To suppress reflection to and the second prepulse wavelength λ V2It is configured or optimized to suppress reflection to the light. For example, quartz glass can be used as the material for the transmissive optical units 21 and 13. The reflective optical unit of the beam guidance device 7, for example, the deflection mirror 18, is configured to suppress reflection to the light. V1 , λ V2 It is optimized for reflection.

Claims

1. EUV light source (1), - 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 coupling device (6) for coupling the first laser beam (3) and the second laser beam (5), - A beam guidance device (7) for jointly guiding the first laser beam (3) and the second laser beam (5) into a target region (8) in order to generate EUV radiation (9), An EUV light source characterized in that the coupling device (6) is designed to supply the first laser beam (3) and the second laser beam (5) to the beam guidance device (7) for joint beam guidance via a common optical unit (21, 13, 18) in a spatially separated manner and having a lateral offset (ΔL).

2. The EUV light source according to claim 1, wherein the first laser source is a prepulsed laser source (2) for emitting a prepulsed laser beam (3), and the second laser source is a main pulsed laser source for emitting a main pulsed laser beam, or an additional prepulsed laser source (4) for emitting an additional prepulsed laser beam (5).

3. The first wavelength (λ) of the first laser beam (3) Ｖ１ ) and the second wavelength (λ) of the second laser beam (5) Ｖ２ ) deviate from each other by up to 70 nm, preferably up to 50 nm, and / or the first wavelength (λ) of the first laser beam (3) Ｖ１ ) and the second wavelength (λ) of the second laser beam (5) Ｖ２ The EUV light source according to claim 1 or 2, wherein the wavelength range is 350 nm to 5 μm, preferably 500 nm to 2.5 μm.

4. The beam guidance device (7) comprises at least one transmissive optical unit (21, 13) having an anti-reflective coating, wherein the anti-reflective coating has a first wavelength (λ Ｖ１ ) suppresses the reflection of the first laser beam (3) at the second wavelength (λ Ｖ２ An EUV light source according to any one of claims 1 to 3, wherein the second laser beam (5) is designed to suppress reflection of the second laser beam (5), and / or the transmissive optical unit (21, 13) is formed of quartz glass.

5. The first laser beam (3) collides with the coupling device (6) in a first beam direction (R Ｖ１ ), and the second laser beam (5) collides with the coupling device (6) in a second beam direction (R Ｖ１ ) different from the first beam direction (R Ｖ２ ). The EUV light source according to any one of claims 1 to 4.

6. The EUV light source according to any one of claims 1 to 5, wherein the coupling device (6) is designed to orient the first laser beam (3) and the second laser beam (5) parallel to each other.

7. The EUV light source according to any one of claims 1 to 6, wherein the coupling device includes at least one prism (6a).

8. The first beam direction (R) of the first laser beam (3) Ｖ１ A first beam direction adjustment device (14) for adjusting the second beam direction (R) of the second laser beam (5), and / or the second beam direction (R) of the second laser beam (5). Ｖ２ The EUV light source according to any one of claims 1 to 7, further comprising a second beam direction adjustment device (16) for adjusting the beam.

9. The beam diameter (d) of the first laser beam (3) Ｖ１ A first magnification device (19) for changing, in particular for adjusting, the beam diameter (d) of the second laser beam (5). Ｖ２ The EUV light source according to any one of claims 1 to 8, further comprising a second magnification device (20) for particularly adjusting, for changing ).

10. The EUV light source according to any one of claims 1 to 9, wherein the target region (8) is located inside the vacuum chamber (11) and the coupling device (6) is located outside the vacuum chamber (11).

11. The EUV light source according to any one of claims 1 to 10, wherein the beam guidance device (7) has a focusing optical unit (13) for focusing the first laser beam (3) and the second laser beam (5) into the target region (8), and the focusing optical unit (13) is preferably located in a vacuum chamber (11).

12. The EUV light source according to any one of claims 1 to 11, further comprising a spatially resolved backreflection detector (22) for detecting radiation (23) backreflected from the target region (8).

13. The EUV light source according to any one of claims 1 to 12, further comprising a spatially resolved detector (25) positioned in the beampath after the coupling device (6) for detecting portions of the first laser beam (3) and the second laser beam (5), and in particular for detecting the lateral offset (ΔL) between the first laser beam (3) and the second laser beam (5).

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

15. The EUV light source according to any one of claims 1 to 14, wherein the beam guidance device (7) has an optical unit in the form of a telescope configuration (21).

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