EUV drive laser for generating an EUV light-emitting plasma, a facility for exposing a semiconductor substrate coated with a light-sensitive coating to EUV light and a method for generating a combined excitation beam

Abstract

The present invention relates to an EUV-driven laser (10) for generating a plasma (14) of a target material, the plasma emitting EUV light (12), the EUV-driven laser comprising: a first beam source (16) configured to generate a first excitation beam (20) having a first wavelength, and a second beam source (18) configured to generate a second excitation beam (22) having a second wavelength. The EUV-driven laser (10) has a first pump source and a second pump source (24, 26) configured to supply pump energy to the two beam sources (16, 18) respectively, such that the two excitation beams (20, 22) are generated without scattering by converting their respective pump energies. Furthermore, the EUV-driven laser (10) has a first amplifier device (28) and a second amplifier device (30), each having an amplifier unit (32) having at least one optical amplifier (34), wherein the optical amplifier (34.i) is configured to amplify the two excitation beams (20, 22) accordingly to form an amplified excitation beam (36, 38). According to the invention, the EUV-driven laser (10) has: a combining unit (42) configured to combine the amplified excitation beams (36, 38) to form a combined excitation beam (40); and a focusing unit (43) configured to focus the combined excitation beam (40) onto a target (14). Furthermore, according to the invention, the first excitation beam and the second excitation beam (20, 22) and / or the two amplified excitation beams (36, 38) have different wavelengths in the range of 1600 nm to 2300 nm.

Description

Technical Field

[0001] This invention relates to an EUV-driven laser for generating a plasma for a target material, the plasma emitting EUV light, the EUV-driven laser having: a) A first beam source configured to generate a first excitation beam having a first wavelength. b) A second beam source configured to generate a second excitation beam having a second wavelength. c) A first pump source and a second pump source, the first pump source and the second pump source being configured to supply pump energy to the two beam sources respectively, such that the two excitation beams are generated without scattering by converting their respective pump energies. d) A first amplifier device and a second amplifier device, each having an amplifier unit having at least one optical amplifier, wherein the optical amplifier is configured to amplify the two excitation beams accordingly to form an amplified excitation beam.

[0002] The present invention also relates to a device for exposing a semiconductor substrate coated with a photosensitive coating to EUV light.

[0003] The present invention also relates to a method for generating a combined excitation beam for generating a plasma of a target material that emits EUV light. Background Technology

[0004] In the fabrication of integrated circuits (microchips), a typically single-crystal semiconductor substrate (hereinafter referred to as a wafer) is coated with a layer in a relatively early manufacturing step, which is then structured in subsequent manufacturing steps. This structured structure acts as a mask in subsequent manufacturing steps, allowing the etching of functional layers located beneath the coating, doping with foreign atoms (e.g., by ion implantation), or the introduction of foreign materials into the structured structure (e.g., by LIGA and stripping).

[0005] The purpose of these methods is to produce transistors and conductive regions that connect the transistors to each other on the wafer, etc. Various methods can be used to introduce structure into the coating.

[0006] For example, in photolithography, the coating is implemented as a photosensitive coating, specifically as a photoresist. Here, the photoresist is exposed in a specific pattern to light of a specific wavelength to which the photoresist is sensitive. This light can affect the chemical properties of the exposed areas of the photoresist, such as the solubility of the exposed areas in the developer solution. There are photoresists in which the exposed areas polymerize, i.e., the solubility of the exposed areas increases compared to the unexposed areas (negative photoresists). Additionally, there are photoresists in which the exposed areas become more soluble than the unexposed areas (positive photoresists). In either case, in order to form a structure in the photoresist and thus a mask for the functional layer located beneath the photoresist, the more soluble areas in the photoresist are removed using a developer solution.

[0007] In order to introduce a specific pattern into the photoresist, a mask element (hereinafter referred to as a photomask) is usually placed between the light source and the wafer. The mask element is configured to be a negative or positive image of the structure to be formed on the photoresist, depending on the photoresist used (negative or positive photoresist).

[0008] In conventional photolithography, photomasks are either placed directly on the photoresist or positioned directly above it, spaced apart from it, such that the photomask and the resulting structure on the photoresist are proportional to each other. Since photomasks can only be scaled to a limited size, they are essentially limited to structural dimensions of a few hundred nanometers. Because smaller structures enable microchips to have significantly higher performance per unit area or volume (as this allows for more transistors to be implemented in a consistently smaller area), there is a general trend towards shrinking structural dimensions to absolute physical limits.

[0009] For this reason, projection lithography facilities are now commonly used, in which focusing optics are typically arranged between the photomask and the photoresist, allowing the photomask to be significantly reduced in size and projected onto the photoresist. This makes photomasks cheaper to manufacture because the structure of the photomask does not need to be so small. On the other hand, this also allows for the imaging of significantly smaller structures on the wafer compared to conventional photolithography. Then, for example, the structures obtained on the photomask and the photoresist can exist in a ratio of 5:1 or higher. The photomask itself can be constructed as an absorptive photomask or a reflective photomask.

[0010] Because the reduced image of the photomask on the photoresist does not cover the entire wafer, existing methods typically employ a "step-repeating" approach: exposing the wafer at a first exposure position, moving it a certain distance, and then exposing it again at a second exposure position. This process is repeated in these known methods until a portion of the wafer is covered with the same structure.

[0011] After the photoresist has been removed from areas that are more soluble than the developer solution and the underlying functional layer has been treated (e.g., by etching), the photoresist is typically removed from the functional layer through a process called "stripping".

[0012] For multilayer microchips, the projection exposure method described above can be performed up to one hundred times on the same microchip.

[0013] EUV lighting fixtures and EUV generation Besides reducing the size of photomasks and using focusing optics, another way to reduce the size of patterns on wafers is to expose them with light of shorter wavelengths.

[0014] In a method known according to the prior art, extreme ultraviolet light (EUV light) with a wavelength range of about 8 nm to about 15 nm is generated, wherein the main part of the EUV light is at 13.5 nm, and the EUV light is guided onto the photoresist by means of EUV projection optics and EUV focusing optics of a projection exposure facility.

[0015] EUV light generation facilities for this purpose mainly include: an EUV-driven laser, by means of which at least one excitation beam can be generated; a target generator; and an EUV light generation chamber. Typically, a pulsed high-power laser is used as the EUV-driven laser, while a droplet generator is used as the target generator, by means of which droplets of the target material are injected into the EUV light generation chamber. To avoid damage to the system due to particle contamination, a high vacuum can be maintained within the EUV light generation chamber under the processing gas atmosphere of existing applications, wherein hydrogen (H2) or helium (He) is particularly suitable as the processing gas.

[0016] In methods known according to the prior art, tin (Sb) is frequently used as the target material. Besides tin (Sb), targets including xenon (Xe), gold (Au), and / or lithium (Li) are also possible. To increase the amount of emitted EUV light, droplets generated by a droplet generator can be excited, for example, first with a first excitation beam (pre-pulse) and then with a second excitation beam (main pulse), wherein the two excitation beams can be two independent beams, or they can be generated by splitting a single beam. In principle, EUV light can be generated by a single excitation beam; the second excitation beam is therefore not absolutely necessary. However, in methods known according to the prior art, the conversion efficiency—i.e., the ratio of input laser power to generated EUV power—is significantly improved by using a second excitation beam.

[0017] Since conversion efficiency depends on a variety of factors, for clarity, the term overall conversion efficiency will be used below. Therefore, it is clear that what is being addressed is the net ratio of the power of the excitation beam to the power of the produced EUV light.

[0018] This is because in these known methods, excitation with a pre-pulse results in the pretreatment of the target droplet. Currently, this pretreatment involves the target droplet forming an approximately disk-shaped form due to the energy input through the pre-pulse, thereby relatively increasing the surface area of ​​the target droplet that can be excited by the second excitation beam. The main pulse then encounters the pretreated target droplet, thereby exciting the pretreated target droplet. In known methods, this excitation involves generating an ionized gas of the target—if the target is a tin material, this generates tin plasma. This tin plasma then emits EUV light required to form the structure in the photoresist.

[0019] In another known method, for further pretreatment, a third excitation beam in the form of a rarefied pulse can be used, which impinges on the target droplet between the pre-pulse and the main pulse. In this known method, the rarefied pulse causes the volume of the target droplet (which forms a disk shape through the pre-pulse) to become rarefied or increased, approaching a target cloud, where the term "cloud" is not equivalent to the gaseous state of the material or the vapor state of the target. Using such a rarefied pulse further improves the conversion efficiency.

[0020] Rare pulses can be generated by splitting a first excitation beam into a prepulse and a rarefaction pulse. However, rarefaction pulses can also be generated using a separate beam source, or even by splitting a single excitation beam into a prepulse, a rarefaction pulse, and a main pulse. Furthermore, it is also possible for the rarefaction pulse to form part of the main pulse, which precedes the main pulse in time and can be distinguished temporally with respect to its time-varying intensity distribution. In this case, the term pedestal is typically used.

[0021] EUV-driven lasers are also conceivable, in which more than three excitation beams are used to excite the target and generate EUV light.

[0022] In each of the above cases, the main pulse impacts the target droplet with a power ranging from 20 kW to 50 kW.

[0023] EUV driven laser Existing EUV driven lasers can have a beam source, a pump source, an amplifier device with multiple optical amplifiers, and a focusing unit.

[0024] A beam source can generate an excitation beam, which is then amplified at specific points along an optical path by multiple optical amplifiers to produce an amplified excitation beam.

[0025] If more than one beam is used in the existing technical method to generate EUV light, then a separate beam source can exist for each excitation beam (prepulse, sparse pulse, and main pulse), i.e., a prepulse beam source, a sparse pulse beam source, and a main pulse beam source.

[0026] In known methods, the term "pulse" refers to a beam of light that has a relatively short duration and therefore a start and end time, is part of a large number of sequentially occurring beams of the same type, and is generated by a pulsed laser. The duration of a pulse can be in the range of microseconds, nanoseconds, picoseconds, or femtoseconds. Lasers operating in continuous wave (CW) mode must be distinguished from these.

[0027] If one, two, three or more separate beam sources are used to generate an excitation beam or pre-pulse, sparse pulse and / or main pulse, these beam sources can generate excitation beams with the same or different wavelengths and the same or different intensities, modes, beam caustics and / or polarizations, or the excitation beams can bombard target droplets with the same or different wavelengths and the same or different intensities, modes, beam caustics and / or polarizations.

[0028] For example, in conventional EUV-driven lasers, it is known to use solid-state lasers as prepulse beam sources for the prepulse. Such known solid-state lasers generate prepulses with wavelengths of about 1 µm. Solid-state lasers can also be used as sparse pulse beam sources, which, for example for metrological purposes, preferably have wavelengths different from the prepulse, also about 1 µm.

[0029] CO2 lasers are typically used as the main pulse beam source for the main pulse, producing a main pulse with a wavelength of approximately 10.6 µm.

[0030] Problems arising from existing technology The known drawbacks of EUV-driven lasers, as understood in the current technology, are that the power of the excitation beam or irradiation beam can only be increased with exceptionally high development and cost due to the complexity of the laser and the special design requirements of optical amplifiers, particularly CO2 amplifiers, which use gas mixtures as the active medium. There has long been a desire to increase the power of the excitation beam, especially since the relatively high power input to the target droplet leads to a relatively high power gain in the generated EUV light. If more EUV light could be quantitatively obtained, the yield of structured wafers per unit time could be increased.

[0031] Therefore, it is desirable to move away from the conventional approach of using optical amplifiers with gas mixtures as the active medium; however, alternatives known in the art to generate EUV-driven lasers with an excitation beam of 10.6 µm wavelength have not been a focus of development to date, since the conversion efficiency is relatively highest in the wavelength range of 10 µm to 11 µm. Summary of the Invention

[0032] Therefore, the object of the present invention is to provide the EUV driven laser described above, which overcomes the disadvantages of the prior art mentioned above.

[0033] According to the present invention, this objective is achieved by the EUV-driven laser mentioned at the beginning, wherein, e) EUV driven lasers include: - A combining unit configured to combine amplified excitation beams to form a combined excitation beam. - A focusing unit configured to focus the combined excitation beam onto the target material. f) The first excitation beam and the second excitation beam and / or two amplified excitation beams have different wavelengths in the range of 1600 nm to 2300 nm.

[0034] In EUV-driven lasers that generate excitation beams in the wavelength range of 1600 nm to 2300 nm, the overall conversion efficiency is significantly lower than that of CO2 EUV-driven lasers known in the prior art and described above. This is due to the wavelength-specific self-absorption of EUV light by the generated plasma. In other words, with the same power input, relatively less net EUV light can be provided for wafer exposure when the target is excited with lower wavelength light, which is also true for the region of this invention. However, in the case of known CO2 EUV-driven lasers, the target must be pretreated accordingly to achieve this relatively high overall conversion efficiency.

[0035] However, according to the present invention, it is recognized that targets typically used for these shorter wavelengths have higher absorption rates than those known in the prior art for longer wavelengths, and that by independently generating at least two excitation beams, separately amplifying the at least two excitation beams in an optical amplifier, and then combining the amplified excitation beams into a combined excitation beam, the relatively low conversion efficiency compared to known CO2 EUV driven lasers can be compensated, and the combined excitation beam can even deliver significantly higher power to the target than using previously known EUV driven lasers and corresponding methods, without the need for corresponding pretreatment of the target.

[0036] According to the invention, it is also recognized that excitation beams with different wavelengths in the range of 1600 nm to 2300 nm have significantly higher conversion efficiencies than excitation beams with wavelengths in, for example, the range of 900 nm to 1100 nm, because in this range, the self-absorption of the generated plasma to the generated EUV light is even higher and therefore more difficult to compensate for. Therefore, the invention—in other words—is based on the understanding that the wavelength range of the excitation beam according to the invention has optimal overall conversion efficiency, and that the combination of excitation beams is advantageous.

[0037] Advantageously, the excitation beam has different wavelengths in the range of 1800 nm to 2100 nm, particularly in the range of 1900 nm to 2050 nm, and especially preferably in the range of 1900 nm to 2000 nm.

[0038] In this context, wavelength is understood as the average wavelength of the emission range of the beam source.

[0039] Optical amplifiers are preferably connected in parallel.

[0040] Different combinations of wavelengths of the excitation beam within this range are conceivable and possible, such as 1900 nm and 1910 nm, 1910 nm and 1920 nm, or 1920 nm and 1930 nm, etc. — where the ten-step step here is purely illustrative and chosen for the purpose of explanation.

[0041] Of course, EUV-driven lasers are not limited to a first and a second beam source (including associated components), but can also include a large number of beam sources. Essentially, this can be a modular system that uses beam source devices and amplifier devices that can produce amplified excitation beams with different spectra, and then a combining unit amplifies the amplified excitation beams to form a combined excitation beam.

[0042] The specific number of beam sources used and their associated components is theoretically unlimited, meaning that the power of the combined excitation beams reaching the target is theoretically scalable.

[0043] It is particularly advantageous if the EUV-driven laser has advanced features that are subsequently followed: a) Optical amplifiers include at least one solid-state amplifier, particularly an optical fiber amplifier, and / or b) In each case, at least one optical preamplifier is arranged in front of the corresponding amplifier device in the respective propagation directions of the two excitation beams, and / or c) Each beam source includes a solid-state laser and / or a semiconductor laser.

[0044] If each amplifier unit includes at least one optical amplifier configured as a solid-state amplifier, then the maximum achievable power of the combined excitation beam can theoretically be scaled arbitrarily because the overhead required to install additional optical amplifiers in each amplifier unit is relatively small. Therefore, the power gain of the generated EUV light can theoretically be scaled arbitrarily.

[0045] The "scatterless" reference mentioned at the beginning regarding the conversion of pump energy from the pump source into two excitation beams is understood to mean that, when the EUV-driven laser is in operation, the main portion of the excitation beam is generated through stimulated emission. In other words, when the EUV-driven laser is in operation, the main portion of the excitation beam is generated by producing photons in the wavelength range of 1600 nm to 2300 nm within the population-inverted state of the beam source. These photons are generated through stimulation of atoms and / or molecules and / or through spontaneous emission that induces a chain reaction within the excited atoms and / or molecules.

[0046] However, "scatterless" is not understood to mean that, when the EUV-driven laser is in operation, the main portion of the excitation beam is generated directly or indirectly by inelastic scattering of light by atoms and / or molecules. In other words, specifically, when the EUV-driven laser is in operation, an excitation beam generated "scatterless" is not said to be generated if the main portion of the excitation beam is generated only or primarily by Raman scattering.

[0047] Advantageously, each optical preamplifier includes at least one solid-state preamplifier and / or one semiconductor preamplifier.

[0048] Preferably, each of the two excitation beams can be directly generated by converting its corresponding pump energy. By omitting possible intermediate steps in the generation of the excitation beams, power loss, such as that caused by elastic scattering, can be avoided.

[0049] Furthermore, the pump energy is preferably either optical pump energy or electric pump energy. Preferably, the pump energy is electric pump energy in the form of an electric field. In the case of a solid-state laser, optical pump energy is also possible, i.e., in the form of a pump beam provided by a laser diode, the wavelength of which is different from the wavelength of the excitation beam emitted by the beam source.

[0050] It is advantageous when the solid-state amplifier and / or optical preamplifier each comprise: a) At least one crystal amplifier or crystal preamplifier, said at least one crystal amplifier or crystal preamplifier having a crystal substrate doped with a first active medium, and / or b) At least one fiber amplifier or fiber preamplifier, wherein the at least one fiber amplifier or fiber preamplifier has an optical waveguide doped with a second active medium.

[0051] Furthermore, it is advantageous when the first and second active media are identical. If the active media are identical in both the crystal (preamplifier) ​​and the fiber (preamplifier), it can be particularly ensured that the amplified excitation beam comprises highly monochromatic light, and therefore has no or only negligible beam components with wavelengths deviating from the wavelength of the excitation beam.

[0052] It is advantageous when the beam source, pump source, and / or one, more, or all optical amplifiers or optical preamplifiers are doped with an active medium. It is also advantageous when the active medium is identical in the beam source, pump source, and / or one, more, or all optical amplifiers.

[0053] Preferably, the active medium comprises holmium (Ho) or thulium (Tm). In the case of a first active medium and a second active medium, these active media may further comprise holmium (Ho) and / or thulium (Tm). Pure thulium (Tm) doping is preferred, but mixed doping with thulium (Tm) and holmium (Ho) at different relative concentrations in the material to be doped is also conceivable and possible. Thulium and holmium can emit light in the range of approximately 1600 nm to 2300 nm when excited. In addition to the two active media mentioned, the active medium may also comprise other lanthanide elements. Depending on the lanthanide elements included in the active medium and their proportions, the emission spectrum of the active medium, the beam quality of the emitted excitation beam, and / or the beam profile can be adjusted.

[0054] Advantageously, the crystal substrate comprises a crystal material from the group consisting of YAG, YAP, YLF, Lu2O3, LuAG, and LuLF. Preferably, the crystal substrate comprises YLF as the crystal material. Therefore, the crystal amplifier or crystal preamplifier can be configured as a Tm:YAG, Tm:YAP, Tm:YLF, Tm:Lu2O3, Tm:LuAG, Tm:LuLF, Ho:YAG, Ho:YAP, Ho:YLF, Ho:Lu2O3, or Ho:LuAG (preamplifier) ​​amplifier, wherein Tm:YLF is preferred.

[0055] Advantageously, the optical waveguide includes at least one amorphous material that is transparent to the excitation beam, said at least one amorphous material being derived from the group consisting of SiO2, Al2O3, MgO, B2O3, CaO, and Na2CO3. Therefore, the fiber amplifier or fiber preamplifier can be constructed as a Tm: SiO2-, Al2O3-, MgO-, B2O3-, CaO-, Na2CO3 fiber amplifier or fiber preamplifier.

[0056] Alternatively, the beam source is a semiconductor laser, each of which has a laser emitter, wherein each laser emitter comprises a semiconductor material or an alloy of the semiconductor material, wherein the semiconductor material is selected from the group consisting of GaAs, GaP, InAs, InP, and InGaAsP.

[0057] The beam source can be configured as a main pulse beam source device, the combined excitation beam can be a main pulse, and the pump source can be configured as a main pulse pump source device. The EUV-driven laser also includes: a) A prepulse beam source device, wherein the prepulse beam source device is configured to generate a prepulse. b) A pre-pulse pump source device configured to supply pump energy to the pre-pulse beam source device, such that the pre-pulse is generated without scattering by converting the pump energy. in, c) The prepulse beam source device has at least one prepulse beam source, and the prepulse pump source device has at least one prepulse pump source, wherein the prepulse pump source is configured to supply pump energy to the prepulse beam source. d) The pre-pulse for pre-treating the target and the main pulse for generating the plasma of the target can be directed onto the target, wherein the plasma emits EUV light.

[0058] Furthermore, it is advantageous when EUV-driven lasers also possess the following characteristics: a) A sparse pulse beam source device configured to generate sparse pulses. b) A sparse pulse pump source device configured to supply pump energy to a pre-pulse beam source device such that sparse pulses are generated without scattering by converting the pump energy. in, c) The sparse pulse beam source device has at least one sparse pulse beam source, and the sparse pulse pump source device has at least one sparse pulse pump source, wherein the sparse pulse pump source is configured to pump pump energy to the sparse pulse beam source. d) The sparse pulse between the pre-pulse and the main pulse can be directed toward the target for sparse application.

[0059] Advantageously, the target is further pretreated during exposure to the rarefied pulse, thereby advantageously increasing the target's absorption coefficient relative to the main pulse, and thus increasing the conversion efficiency from input laser power to generated EUV power. The rarefied pulse can pretreat the target, for example, by changing its shape or temperature.

[0060] Preferably, each optical amplifier in the amplifier unit is provided with at least one pulse shaping unit and / or beam shaping unit behind it in the corresponding propagation direction of the excitation beam. At least one optical amplifier, preferably multiple or all optical amplifiers, may additionally be provided with a second pulse shaping unit and / or beam shaping unit behind the beam splitter device in the propagation direction. Therefore, the excitation beam can be shaped temporally, spectrally, and / or with respect to intensity distribution before entering the amplifier device or after leaving the amplifier device.

[0061] The pulse shaping unit and / or beam shaping unit may include a phase shift module, a Q-switching module, an intensity modulation module, and / or a polarization module. Additionally or alternatively, the pulse shaping unit and / or beam shaping unit may have a spectral expansion or limitation module, by means of which the spectral range of the excitation beam and / or the amplified excitation beam and / or the combined excitation beam can be expanded or limited.

[0062] Preferably, the combining units are configured to combine the amplified excitation beams with each other in the spectrum.

[0063] Preferably, each amplifier unit may be assigned a combination unit, each combination unit being configured to combine the amplified excitation beams assigned to it with each other in the spectrum.

[0064] According to an advantageous configuration, at least one beam splitter device can be provided, by means of which at least one excitation beam in the excitation beam can be split into two or more partial beams. The beam splitter device can also split two or more excitation beams (if additional beam sources are present) into two or more partial beams respectively. In such a case, the partial beams can be individually amplified in an amplifier device assigned to each beam source to form an amplified partial beam.

[0065] The amplified excitation beam and / or amplified partial beam can be combined with each other through a combination unit, so that... a) The amplified excitation beam and / or amplified partial beams propagate parallel to each other and side by side along the propagation direction with essentially no overlap. or b) The amplified excitation beam and / or amplified portions of the beam overlap spatially and temporally to achieve beam overlap.

[0066] The amplified excitation beams can be combined, for example, spectrally, such that portions of the beams do not overlap or overlap only to a negligible degree, while extending parallel and side-by-side along a common propagation direction. Furthermore, it is also possible to combine the beams spectrally such that the amplified excitation beams overlap spatially and temporally.

[0067] When amplified excitation beams are combined spectrally, it is advantageous to arrange one or more additional polarization modulation units for each beam source within the corresponding beam path of the amplified excitation beams to reduce power loss due to potential adverse, i.e. weakened, interactions between the amplified excitation beams caused by different polarizations.

[0068] According to another aspect of the invention, the problem mentioned at the beginning is solved by the following: a facility for exposing a semiconductor substrate coated with a photosensitive coating to EUV light, characterized in that the facility has an EUV-driven laser having some or all of the features listed above associated with the EUV-driven laser, wherein a pump source, a beam source, and an amplifier device are arranged in a first facility region, and a focusing unit is arranged in a second facility region, and wherein a beam transmission system is provided that is capable of transmitting the combined excitation beam from the amplifier device to the focusing unit.

[0069] Facility areas can be facility levels located at different heights within the facility and separated from each other, for example, by facility ceilings or facility floors.

[0070] According to another aspect of the invention, the problem mentioned at the beginning is also solved by: a method for generating a combined excitation beam for generating a plasma of a target material that emits EUV light, wherein the method uses an EUV-driven laser having some or all of the features mentioned above for an EUV-driven laser. Attached Figure Description

[0071] The embodiments of the present invention will now be described in more detail with the aid of the accompanying drawings. In the drawings: Figure 1 A first embodiment of an EUV-driven laser is shown, the EUV-driven laser having: two beam sources capable of generating a first excitation beam and a second excitation beam with different wavelengths, wherein each beam source can be supplied with pump energy by a pump source; two amplifier devices capable of amplifying the two excitation beams into amplified excitation beams accordingly; a combining unit; and a focusing unit. Figure 2 A second embodiment of an EUV-driven laser is shown. Compared with the first embodiment, the second embodiment has an additional beam source, an additional pump source, and an additional amplifier device, and the excitation beam generated by the beam source can be split into multiple partial beams by means of a beam splitter device. Figure 3 A third embodiment of an EUV-driven laser is shown, which, compared to the second embodiment, includes three additional beam sources, three additional pump sources, and an additional combination unit. Figures 4a to 4c A possible implementation of the combination unit for spectral “side-by-side” combination of partial beams is shown; Figures 5 to 9 Several possible implementations of the combining unit are shown, by means of which the spectral "fill aperture" combination of a portion of the beam can be achieved.

[0072] Of course, the present invention is not limited to the embodiments shown. The embodiments illustrated in the figures are merely specific examples of the invention. Those skilled in the art will recognize embodiments of the invention not explicitly shown.

[0073] List of reference numerals 10 EUV driven laser 12 EUV light 14 Target Material 16 First beam source 18 Second beam source 20 First excitation beam 22 Second excitation beam 24 First Pump Source 26 Second Pump Source 28 First Amplifier Device 30 Second Amplifier Device 32 Amplifier Units 34.i Optical Amplifier 36 First amplified excitation beam 38 Second amplified excitation beam 40 combinations of excitation beams 42 Combined Units 43 Focusing Unit 44.i Other beam sources 46.i Other pump sources 48.i Other amplifier devices 50.i Another excitation beam 52.i Beam Splitter Device 54.i Partial Beam 56.i Amplified portion of the beam 58 Optical waveguide 60. Direction of dissemination 62-core fiber 64 Fibrous Body 66 optical guidance channels 68.i Pulse shaping unit and / or beam shaping unit 70 Second Combination Unit 72.i Combined amplified portion of the beam 74 Final Combined Beam 76 Reflective Optical Elements 78 Third Combination Unit 80.i Amplified Combined Beam 82 "Side by Side" Combination 84 Filling aperture 86 Diffraction apparatus 88 Diffractive optical elements 90 Second diffractive optical element 92a First Focusing Optical Element 92b Second Focusing Optical Element 94 Stepped reflective optical elements 96 Third Focusing Optical Element 98 mirror device 100 dichroic mirror Detailed Implementation

[0074] Figures 1 to 3Each embodiment of an EUV-driven laser, generally designated 10, is schematically illustrated. The EUV-driven laser 10 is configured to generate a plasma in a target 14 that emits EUV light 12. A method is described in this document in which target plasma is generated by inputting optical power into the target 14, which in turn generates EUV light 12; the target plasma is sometimes referred to as LPP (laser-generated plasma).

[0075] The EUV-driven laser 10 has a first beam source 16 and a second beam source 18, wherein the first beam source 16 is configured to generate a first excitation beam 20, and the second beam source 18 is configured to generate a second excitation beam 22. Additionally, the EUV-driven laser 10 has a first pump source 24 and a second pump source 26, wherein the first pump source 24 is configured to supply pump energy to the first beam source 16, and the second pump source 26 is configured to supply pump energy to the second beam source 18. The supply of energy to the beam sources 16 and 18 in the EUV-driven laser 10 is performed such that the excitation beams 20 and 22 are generated without scattering by converting their respective pump energies. This means, for example, that the main portions of the excitation beams 16 and 18 are generated without using an optical parametric oscillator (OPO) and without generating higher harmonics.

[0076] For clarity, the same structures in the following figures are not always provided with figure reference numerals.

[0077] Furthermore, the EUV-driven laser 10 has a first amplifier device 28 and a second amplifier device 30, each amplifier device having only one amplifier device in operation. Figure 2 , Figure 3 and Figure 4a The amplifier unit 32 shown in the figures, and at least one optical amplifier 34 shown only in these figures, are also shown. The optical amplifier 34 is configured to amplify the excitation beams 20, 22 into amplified excitation beams 36, 38 respectively.

[0078] In order to generate a combined excitation beam 40 from the amplified excitation beams 36, 38, according to the invention, the EUV-driven laser 10 further includes a combining unit 42. To achieve this, the combining unit 42 may have one or more beam combiners, not specifically shown.

[0079] According to the present invention, the EUV driven laser 10 has a focusing unit 43 by means of which the combined excitation beam 40 can be focused onto the target 34.

[0080] According to the present invention, the first excitation beam and the second excitation beams 16, 18, as well as two amplified excitation beams 36, 38, have wavelengths that differ from each other in the range of 1600 nm to 2300 nm. Compared to known EUV-driven lasers 10, which mostly use CO2 gas mixtures as the active medium and can generate excitation beams with wavelengths of about 10.6 µm, the conversion efficiency—the efficiency of converting the optical power introduced into the target by the excitation beam into EUV power—is significantly lower. However, the EUV-driven laser 10 according to the present invention can operate more energy-efficiently. This is mainly due to the fact that no radio frequency generator is required to excite the CO2 gas mixture, and no complex gas recirculation and renewal cycle is needed.

[0081] According to the present invention, the lower conversion efficiency of the EUV-driven laser 10 can be compensated for by separately and independently amplifying at least two excitation beams 16 and 18 having wavelengths different from each other in the range of 1600 nm to 2300 nm in the optical amplifier 34 of the amplifier devices 28 and 30, and combining the amplified excitation beams 36 and 38 using the combining unit 42 to form a combined excitation beam 40. Compared to using EUV-driven lasers known according to the prior art, this makes it possible to achieve significantly higher power of the combined excitation beam 40, exceeding the absolute physical load limit of the individual optical amplifier 34.

[0082] According to existing technology, laser power in the range of 20 kW to 50 kW is known, and the laser power ultimately reaches the target 14 and is introduced into the target. By generating at least two excitation beams 16, 18, amplifying the at least two excitation beams individually, and then combining the at least two excitation beams using the combining unit 42, arbitrarily high laser power can theoretically be achieved, only limited, for example, by the absorption characteristics of the optics used in the EUV-driven laser 10.

[0083] Figure 2 and Figure 3 The embodiments shown also include, by way of example, at least one additional beam source 44.i, at least one additional pump source 46.i, and at least one additional amplifier device 48.i, wherein i corresponds to the consecutive designations of the additional beam source 44.i, pump source 46.i, or amplifier device 48.i. Thus, a first additional beam source is designated, for example, by reference numeral 44.1, a second additional beam source by reference numeral 44.2, and so on. For clarity, elements subsequently designated by this consecutive designation are not always provided with reference numerals in the figures. The same principle applies if alternative reference numerals are assigned using scheme "Xi".

[0084] also, Figure 2 and Figure 3 The amplifier unit 32 of the embodiment of the EUV-driven laser 10 shown has a plurality of optical amplifiers 34.i connected in parallel, wherein i again corresponds to the sequential numbering of the optical amplifiers. Each additional beam source 44.i generates an additional excitation beam 50.i, wherein the additional excitation beam 50.i and the two excitation beams 20, 22 have wavelengths that are different from each other in the range of 1600 nm to 2300 nm, and are generated without scattering by converting the pump energy of the pump source 46.i.

[0085] Figure 2 and Figure 3 The embodiments in the text also include a beam splitter device 52.i for each beam source 16, 18, 44.i, each of which is configured to split the excitation beams 20, 22, 50.i generated by the beam sources 16, 18, 44.i into multiple partial beams 54.i. Each beam splitter device 52.i may have one or more beam splitters not specifically shown.

[0086] In these embodiments, each optical amplifier 34.i is configured to amplify at least one portion of the partial beam 54.i to form an amplified partial beam 56.i. In other words, each optical amplifier 34.i can amplify at least one assigned partial beam 54.i to produce an amplified partial beam 56.i.

[0087] In all of these embodiments, the optical amplifier 34.i is configured as a fiber amplifier, and the beam sources 16, 18, and 44.i are configured as solid-state lasers. Therefore, the pump sources 24, 26, and 46.i are optical pump sources in the form of semiconductor laser diodes, which can supply optical pump energy to the solid-state lasers 16, 18, and 44.i. The solid-state lasers 16, 18, and 44.i are exemplarily configured here as Tm:YLF lasers. In embodiments not specifically shown, the solid-state lasers 16, 18, and 44.i may also include different dopants: crystal combinations. In other embodiments not specifically detailed, the beam sources 16, 18, and 44.i are each configured as semiconductor lasers in the form of laser diodes, and therefore are not optically pumped, but electrically pumped by means of an electric field.

[0088] In this invention, each of the optical amplifiers 34.i configured as fiber optic amplifiers has an optical waveguide 58 in the form of an optical fiber. Each optical waveguide can independently and separately receive a portion of the beam 54.i and guide it through the corresponding distance along the propagation direction 60.

[0089] Alternative sites, replacing, including, Figure 4a and Figure 4bThe multiple individual fiber amplifiers 34.i shown can also be configured as a multi-core fiber 62, comprising a fiber body 64, each containing a light guiding channel 66 that functions as an optical fiber. In this case, the light guiding channel 66 serves not only as a light guiding element but also as an optical amplifier 34.i. Using such a multi-core fiber 62 is advantageous because it significantly reduces the structural overhead required to couple partial beams 54.i into and out of the optical amplifiers 34.i. Furthermore, this allows for substantial savings in structural space. With proper design, partial beams 54.i can be guided through the multi-core fiber 62, allowing them to be amplified to form amplified partial beams 56.i that are substantially independent of each other.

[0090] In this invention, each optical waveguide 58 or multi-core optical fiber 62 is doped with an active medium, by means of which the excitation beam 40 of a portion of the beam 54.i or possibly a combination thereof can be amplified.

[0091] The active medium may specifically include thulium (Tm), holmium (Ho), or combinations of these lanthanides. Thulium (Tm) has proven advantageous in beam generation and amplification, which is why the active medium in this case includes thulium (Tm).

[0092] In embodiments not specifically shown, the EUV-driven laser 10 includes at least one additional beam source besides beam sources 16, 18, and 44.i, wherein beam sources 16, 18, and 44.i collectively constitute a main pulse beam source device, and the at least one additional beam source is constructed as a pre-pulse beam source device. In another embodiment not specifically shown, the EUV-driven laser 10 includes at least one additional independent beam source, which is here constructed as a sparse pulse beam source device. Therefore, these EUV-driven lasers 10 thus include a main pulse pump source device, a pre-pulse pump source device, and (if applicable) a sparse pulse pump source device, wherein each pump source device supplies pump energy to the beam source of its corresponding beam source device. The pre-pulse pump source device can generate a beam referred to as a pre-pulse, while the sparse pulse beam source device can generate a beam referred to as a sparse pulse. Before the main pulse, both beams can be directed onto the target 14 to increase the power gain of the generated EUV light 12.

[0093] exist Figure 2 and Figure 3In one embodiment, each optical amplifier 34.i is assigned a pulse shaping unit and / or a beam shaping unit 68.i in the propagation direction 60, behind the beam splitter device 52.i; specifically, in the present invention, in the propagation direction 60, behind the combining unit 42.i. Alternatively, in embodiments not specifically shown, pulse shaping units and / or beam shaping units 68.i may also be assigned to amplifier units 32 or amplifier devices 28, 30, 48.i. Similarly, pulse shaping units and / or beam shaping units 68.i may be placed in the propagation direction 60, behind the beam splitter device 52.i and in front of the amplifier devices 28, 30, 48.i. Therefore, the partial beam 54.i can be shaped into the amplified partial beam 56.i in terms of time, spectrum and / or intensity distribution with respect to the amplified partial beam 56.i before entering the amplifier devices 28, 30, 48.i or (as in the present invention) after leaving the amplifier devices.

[0094] We will now discuss this in detail. Figure 2 The embodiment shown is illustrated. In this case, the EUV-driven laser 10 has three beam sources 16, 18, and 44.1, each of which can generate separate excitation beams 20, 22, and 50.1 without scattering by converting the pump energy provided by the corresponding pump sources 24, 26, and 46.1. Therefore, the EUV-driven laser 10 has five separate optical amplifiers 34.1 to 34.5 each configured as fiber amplifiers, or optionally, amplifier units 32 configured as multi-core optical fibers 62, wherein optical guiding channels 66 are formed within the multi-core optical fibers 62. In the propagation direction 60, behind the amplifier units 32 of the three amplifier devices 28, 30, and 48.1, between the respective amplifier devices 28, 30, and 48.1 and the corresponding combination unit 42 for combining the excitation beams 40, a second combination unit 70 is arranged for each amplifier unit 32. The amplifier devices are each assigned to beam sources 16, 18, and 44.1. By means of the second combination unit, the amplified partial beams 56.i emitted from the amplifier units 32 can be combined to form amplified excitation beams 36 and 38, which are constructed in this invention as combined amplified partial beams 72.i. The combined amplified partial beams 72.i are then combined by means of the combination unit 42 to form the combined excitation beam 40, which in this progressive combination can also be referred to as the final combined beam 74.

[0095] The combining unit 42 has multiple reflective optical elements 76 for combining the combined amplified partial beams 72.i.

[0096] Now we will discuss the basis Figure 3An embodiment of the EUV-driven laser 10 is described. In this embodiment, a total of six separate beam sources 16, 18, 44.1 to 44.4 are used as an example, each of which can generate a separate excitation beam 20, 22, 50.1 to 50.4, wherein each excitation beam 20, 22, 50.1 to 50.4 has a different wavelength from each other in the range of 1600 nm to 2300 nm. The beam sources 16, 18, 44.1 to 44.4 are supplied with pump energy by pump sources 24, 26, 46.1 to 46.4, which is directly converted without scattering.

[0097] In this embodiment, a plurality of second combination units 70 are arranged in the propagation direction 60, behind amplifier devices 28, 30, 48.1 to 48.4 and in front of combination unit 42 for combining excitation beams 40 or final combined beams 74. Each of the second combination units can combine five partial beams 54.i into a combined amplified partial beam 72.i. Next in the propagation direction 60 are two third combination units 78, each of which can combine three combined amplified partial beams 72.1 to 72.3 to produce amplified excitation beams 36 and 38 configured as amplified combined beams 80.1 and 80.2.

[0098] exist Figure 3 In one embodiment, a pulse shaping unit and / or a beam shaping unit 68.i are arranged between the second combination unit 70 and the third combination unit 78.

[0099] from Figures 4a to 9 It can be seen that the amplified portion of the beam 56.i can be combined with each other in different ways using combination units 42, 70, and 78. From Figures 4a to 4c It can be seen that the combined beams can propagate in a basically parallel and side-by-side manner along the propagation direction of 60°. Figure 4c In this invention, this can be referred to as a “side-by-side” combination 82.

[0100] However, as Figures 5 to 9 The partial beam 56.i shown can also be spatially and temporally overlapped and amplified. Because the excitation beams 20, 22, 50.i and the amplified partial beam 56.i have different wavelengths from each other, there is essentially no interference during this spatial and temporal overlap; that is, neither constructive nor destructive interference occurs. However, this does produce the disadvantage that the beams cannot amplify each other through constructive interference. However, this also has the advantage that the beams do not interfere destructively with each other, provided that the beams have a corresponding phase difference. In each of these embodiments, this can be referred to as "fill aperture" 84. Figure 5 , Figure 6 and Figure 7In the case of combination units 42, 70, 78, there is a diffraction device 86 by means of which the filling aperture 84 is achieved, wherein the diffraction device 86 has at least one diffraction optical element 88, such as a diffraction grating.

[0101] exist Figure 5 In the embodiment described, the filling aperture 84 is achieved by guiding the amplified partial beam 56.i at different angles onto the diffractive optical element 88. The amplified partial beam 56.i is shown in this and subsequent figures only as an example and for clarity. Similarly, these embodiments can of course also involve amplified excitation beams 36, 38, combined amplified partial beams 72.i, and / or amplified combined beams 80.i. The statements below concerning only the amplified partial beam 56.i apply accordingly to the other beams mentioned. Different wavelengths are deflected to different degrees, for example, at the grating, and thus transmitted into the filling aperture 84.

[0102] exist Figure 6 In one embodiment, the amplified partial beams 56.i extending parallel to each other are focused onto a second diffractive optical element 90 via a diffractive optical element 88. In this particular example, the second diffractive optical element transforms the amplified partial beams 56.i into a combined excitation beam 40, a combined amplified partial beam 72.i, or an amplified combined beam 80.i.

[0103] exist Figure 7 In the embodiment, focusing optical elements 92a and 92b, in the form of lenses, are located in the propagation direction, in front of and behind the diffractive optical element 88, by means of which the amplified partial beam 56.i, extending parallel to each other, is guided onto the stepped reflective optical element 94 (in this invention, in the form of a stepped mirror). The amplified partial beam 56.i is guided onto the second diffractive optical element 90 by means of a third focusing optical element 96 following the stepped reflective optical element 94 in the propagation direction 60, thereby transforming the amplified partial beam 56.i into a combined excitation beam 40, a combined amplified partial beam 72.i, or an amplified combined beam 80.i. This arrangement reduces the "chirp" that may be applied to the amplified excitation beam 56.i.

[0104] On the contrary, Figure 8 In one embodiment, a mirror device 98 having a plurality of dichroic mirrors 100 is used to combine amplified partial beams 56.i to form a combined excitation beam 40, a combined amplified partial beam 56.i, or an amplified combined beam 80.i.

Claims

1. An EUV-driven laser (10) for generating a plasma (14) of a target material, the plasma emitting EUV light (12), the EUV-driven laser having: a) A first beam source (16), the first beam source being configured to generate a first excitation beam (20) having a first wavelength. b) A second beam source (18), which is configured to generate a second excitation beam (22) having a second wavelength. c) A first pump source and a second pump source (24, 26), the first pump source and the second pump source being configured to supply pump energy to the two beam sources (16, 18) respectively, such that the two excitation beams (20, 22) are generated without scattering by converting their respective pump energies. d) A first amplifier device (28) and a second amplifier device (30), each having an amplifier unit (32) having at least one optical amplifier (34), wherein, An optical amplifier (34.i) is configured to amplify the two excitation beams (20, 22) accordingly to form an amplified excitation beam (36, 38). Its features are, e) The EUV-driven laser (10) comprises: - Combination unit (42), the combination unit is configured to combine the amplified excitation beams (36, 38) to form a combined excitation beam (40). - A focusing unit (43) configured to focus the combined excitation beam (40) onto the target (14). f) The first excitation beam and the second excitation beam (20, 22) and / or the two amplified excitation beams (36, 38) have wavelengths that are different from each other in the range of 1600 nm to 2300 nm.

2. The EUV-driven laser according to claim 1, characterized in that, a) The optical amplifier (34.i) includes at least one solid-state amplifier, particularly an optical fiber amplifier, and / or b) At least one optical preamplifier is arranged in front of the corresponding amplifier device (28, 30) in the respective propagation direction (60) of the two excitation beams (20, 22), and / or c) Each of the beam sources (16, 18) comprises a solid-state laser and / or a semiconductor laser.

3. The EUV-driven laser according to claim 2, characterized in that, Each of the optical preamplifiers includes at least one solid-state preamplifier and / or one semiconductor preamplifier.

4. The EUV-driven laser according to any one of the preceding claims, characterized in that, The two excitation beams (20, 22) are each generated directly by converting their corresponding pump energy.

5. The EUV-driven laser according to any one of the preceding claims, characterized in that, The pump energy is either optical pump energy or electrical pump energy.

6. The EUV-driven laser according to any one of claims 2 to 5, characterized in that, Each of the solid-state amplifier and / or the optical preamplifier includes: a) At least one crystal amplifier or crystal preamplifier, said at least one crystal amplifier or crystal preamplifier having a crystal substrate doped with a first active medium, and / or b) At least one fiber amplifier or fiber preamplifier, the at least one fiber amplifier or fiber preamplifier having an optical waveguide (58) doped with a second active medium.

7. The EUV-driven laser according to claim 6, characterized in that, The first active medium and the second active medium are the same.

8. The EUV-driven laser according to any one of the preceding claims, characterized in that, The beam source (16, 18, 44.i), pump source (24, 26, 46.i) and / or one, more or all of the optical amplifiers (34.i) or optical preamplifiers are doped with active media.

9. The EUV-driven laser according to any one of the preceding claims, characterized in that, The beam sources (16, 18, 44.i) are configured as a main pulse beam source device, the combined excitation beam (40) is a main pulse, and the pump sources (24, 26, 46.i) are configured as a main pulse pump source device. The EUV-driven laser (10) further includes: a) A prepulse beam source device, wherein the prepulse beam source device is configured to generate a prepulse. b) A pre-pulse pump source device configured to supply pump energy to the pre-pulse beam source device, such that the pre-pulse is generated without scattering by converting the pump energy. in, c) The prepulse beam source device has at least one prepulse beam source, and the prepulse pump source device has at least one prepulse pump source, wherein the prepulse pump source is configured to supply pump energy to the prepulse beam source. d) The pre-pulse for pre-treating the target (14) and the main pulse for generating plasma of the target (14) can be directed onto the target (14), wherein the plasma emits EUV light (12).

10. The EUV-driven laser according to any one of the preceding claims, characterized in that, At least one pulse shaping unit and / or beam shaping unit (68.i) is arranged in the corresponding propagation direction (60) of the excitation beam (20, 22, 50.i) and behind the corresponding beam source (16, 18, 44.i).

11. The EUV-driven laser according to any one of the preceding claims, characterized in that, At least one optical amplifier (34.i) of the amplifier unit (32) is provided with at least one pulse shaping unit and / or beam shaping unit (68.i) behind the corresponding optical amplifier (34.i) in the corresponding propagation direction (60) of the excitation beam (20, 22, 50.i).

12. The EUV-driven laser according to any one of the preceding claims, characterized in that, The combining unit (42) is configured to combine the amplified excitation beams (36, 38) with each other in the spectrum.

13. An apparatus for exposing a semiconductor substrate coated with a photosensitive coating to EUV light (12), characterized in that, The facility has an EUV driven laser (10) according to any one of claims 1 to 12, wherein the pump source (24, 26, 46.i), the beam source (16, 18, 44.i), the amplifier device (28, 30, 48.i) and the combining unit (42) are arranged in a first facility area, and the focusing unit (43) is arranged in a second facility area, and wherein a beam transmission system is provided, the beam transmission system being capable of transmitting the combined excitation beam (40) from the combining unit (42) to the focusing unit (43).

14. A method for generating a combined excitation beam (40) for generating a plasma of a target (14) emitting EUV light (12), characterized in that, Use the EUV driven laser (10) according to any one of claims 1 to 12.

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