Mirror module, laser device and method for producing a mirror module

Abstract

The invention relates to a mirror module (10) for reflecting a laser beam (104) with a phase shift between a P-polarization component and an S-polarization component of the laser beam (104). The mirror module (10) comprises a substrate unit (12) and a layer system (14) fixedly connected to the substrate unit (12). The layer system (14) comprises an amorphous partial layer system (32) and a crystalline partial layer system (34). The amorphous partial layer system (32) is formed by alternating amorphous layers (16, 18) having different refractive indices. The crystalline partial layer system (34) is formed by alternating crystalline layers (20, 22) having different refractive indices.

Description

[0001] Mirror module, laser device and method for producing a mirror module

[0002] Description

[0003] The invention relates to a mirror module, a laser device and a method for producing a mirror module.

[0004] Extreme ultraviolet radiation (EUV radiation) enables the particularly precise and high-accuracy imaging of fine structures, which is why EUV radiation is frequently used in lithography, which can therefore be referred to as EUV lithography. Due to the advantage of precise and high-accuracy imaging of fine structures, EUV lithography is typically used for the production of microchips.

[0005] The EUV radiation for EUV lithography can be generated using a laser device. The laser device typically includes a laser beam generation assembly for generating a laser beam, a beam steering device, and a target chamber in which a target material is arranged.

[0006] The EUV radiation can be generated by directing and / or focusing the laser beam onto the target material using the beam steering device. In other words, the beam steering device can be configured to direct and / or focus the laser beam from the laser beam generation arrangement onto the target material. For this purpose, the beam steering device can comprise a plurality of optical components, in particular lenses and / or mirror modules.

[0007] When the laser beam hits the target material, the material can be transformed into a plasma state by the laser beam, generating EUV radiation. In other words, the target material can emit EUV radiation when irradiated by the laser beam.

[0008] A vacuum condition is preferably established in the target chamber. The target material can be a metal, for example, tin. The target material can be formed as droplets, for example, as tin droplets. Forming the target material as tin droplets can be particularly advantageous for generating EUV radiation due to the high yield of EUV radiation.

[0009] The laser beam generating arrangement may comprise a number of laser beam sources, for example, 1, 2, or 3. Each laser beam source may be configured to generate a laser beam. The laser beams from the laser beam sources may form the laser beam of the laser beam generating arrangement.

[0010] If the laser beam generating arrangement has two or more laser beam sources, the wavelengths of the laser beams of the laser beam sources may be equal in magnitude or may differ from each other.

[0011] For example, the laser beam generating arrangement can comprise a CO2 laser and a solid-state laser, wherein the CO2 laser provides a laser beam with a wavelength of 9 pm to 11 pm, preferably 10.6 pm (micrometers), and the solid-state laser provides a laser beam with a wavelength in a range of 1 pm to 3 pm, preferably 1.01 to 1.08 pm.

[0012] The laser beam generation arrangement may comprise a number of laser amplifiers, for example, 1, 3, 4, or 6. Each laser amplifier may be configured to amplify the power of a laser beam from a laser beam source. For example, the laser beam generation device may comprise a CO2 laser amplifier for amplifying the power of the laser beam from the CO2 laser and / or a solid-state laser amplifier for amplifying the power of the laser beam from the solid-state laser.

[0013] For example, the laser beam of the CO2 laser can have an average power of over 5 kW (kilowatts), preferably over 10 kW, after passing through the CO2 laser amplifier.

[0014] Typically, a CO2 laser amplifier or a CO2 laser can have a frame device that accommodates, in particular supports, a plurality of components for the purpose of guiding a laser beam through the CO2 laser amplifier or CO2 laser. The components can include, for example, quartz tubes, mirror modules, and / or lenses. A gaseous laser-active medium, in particular a gas mixture of carbon dioxide (CO2), nitrogen (N2), and helium (He), can be arranged in the quartz tubes. The gaseous laser-active medium can be brought into an energetic state by means of high-frequency electrical signals or high-frequency alternating current. The high-frequency electrical signals or the high-frequency alternating current can have a frequency in the megahertz or gigahertz range. In the energetic state, the laser-active medium can generate and / or amplify a laser beam.By generating and / or amplifying the laser beam, the laser-active medium can be converted from the energetic state to its original state.

[0015] The laser beam of the laser beam generation arrangement can be a pulsed laser beam. The pulsed laser beam can have pre-pulses and main pulses. Each main pulse can be preceded in time, particularly shortly before, by a pre-pulse. The pre-pulse can have a lower laser power than the main pulse. The pre-pulses and the main pulses can be generated using the same laser beam source or different laser beam sources.

[0016] It has been found to be particularly advantageous if the laser beam of the laser beam generating arrangement has a pre-pulse with a wavelength in a range from 1 pm to 3 pm, preferably 1.01 to 1.08 pm, and a main pulse with a wavelength in a range from -9 pm to 11 pm, in particular 10.6 pm.

[0017] The pre-pulse can prepare the target material for the impingement of the main pulse on the target material, so that when the main pulse impinges on the target material, as large a portion of the main pulse as possible is converted into EUV radiation. In particular, the pre-pulse can be designed to influence the target material, for example, to heat, expand, vaporize, ionize, and / or convert the target material into the plasma state.

[0018] The main pulse can convert a major part of the target material influenced by the pre-pulse into the plasma state and thus generate EUV radiation.

[0019] The laser beam can be a polarized laser beam. The beam steering device can have at least one mirror module for steering the laser beam from the laser beam generation arrangement onto the target material. The mirror module can have a phase shift, in particular a predetermined or desired phase shift. A value of the phase shift typically indicates a change between a P-polarization component and an S-polarization component of the laser beam, which the mirror module causes upon reflection of the polarized laser beam. The P-polarization component and the S-polarization component of the laser beam can each relate to a plane of incidence of the laser beam striking the mirror module. In particular, a direction of incidence of the laser beam striking the mirror module and a normal on the mirror module can define the plane of incidence.

[0020] For example, the mirror module can have a predefined phase shift of 0°. This means that when the polarized laser beam is reflected by the mirror module, the mirror module does not cause a change in polarization. In other words, the polarization of the laser beam cannot be influenced by the mirror module. Advantageously, this allows the polarization of the laser beam before being deflected by the mirror module and the polarization of the laser beam after being deflected by the mirror module to be the same.

[0021] Alternatively, the specified phase shift of a mirror module can deviate from 0°. This results in a change in polarization by reflecting the polarized laser beam off the mirror module. If the mirror module causes a phase shift of greater than or equal to 2°, in particular 3° or 5°, such a mirror module can be referred to as a phase-shifting mirror.

[0022] In particular, the phase shift of a mirror module can have a value of 90°, although any other phase shift values, in particular in a range from 5°, preferably 3°, 2°, or 0°, to 180°, are also conceivable. Mirror modules with a phase shift value close to 0° are often used in order to avoid changing the polarization state of the laser beam as much as possible. A phase shift of 90° can be understood as a phase shift of λ / 4. Thus, the mirror module with the phase shift of 90° can reflect a linearly polarized laser beam, which is incident on the phase-shifting mirror in such a way that the P-polarization component and the S-polarization component are equal in their amounts, as a circularly polarized laser beam. In laser devices, mirror modules are often used over which the laser beam is guided at an angle of incidence of 45° and which have a phase shift of 0°.If the laser device causes an undesired change in the polarization of the laser beam, additional mirror modules designed as phase-shifting mirrors can be used to direct the laser beam with a predetermined polarization onto the target material.

[0023] The mirror module can be designed to be reflective for a wavelength of the laser beam. Reflective design can be understood to mean that the mirror module is designed to reflect the laser beam with a reflectance of over 98%, preferably 99% or 99.5%.

[0024] During the manufacture of the mirror module, production-related fluctuations may occur which may lead to a deviation from the specified phase shift or target phase shift of the mirror module.

[0025] US 2014 / 0063606 A1 discloses a mirror array comprising a carrier substrate. The carrier substrate is curved with a radius of curvature between 0.1 m and 10 m or between 1 km and 10 km. Furthermore, the mirror array comprises a plurality of alternating monocrystalline semiconductor layers of a first and a second type. The layers of the first type have a higher refractive index than the layers of the second type, thereby forming a Bragg mirror. The semiconductor layers are attached to the curved carrier substrate. By forming the Bragg mirror using alternating monocrystalline semiconductor layers, the mirror array can exhibit low absorption.

[0026] The invention is based on the object of providing a mirror module that has improved properties, in particular that has improved insensitivity to manufacturing defects, for example in the form of production-related fluctuations. Furthermore, the invention is based on the object of providing a laser device with the mirror module and a method for producing the mirror module. The invention solves this problem by providing a mirror module with the features of claim 1, a laser device with the features of claim 11, and a method with the features of claim 12. Advantageous embodiments and further developments of the invention emerge from the dependent claims.

[0027] A mirror module according to the invention is designed for reflecting a laser beam with a, in particular predetermined or desired, phase shift between a P-polarization component and an S-polarization component of the laser beam. The mirror module comprises a substrate unit and a layer system. The layer system is firmly connected to the substrate unit. The layer system comprises an amorphous partial layer system and a crystalline partial layer system. The amorphous partial layer system is formed by alternating amorphous layers of different refractive indices. The crystalline partial layer system is formed by alternating crystalline layers of different refractive indices.

[0028] Advantageously, the combination of an amorphous partial layer system and a crystalline partial layer system allows the mirror module to be manufactured precisely, cost-effectively, and quickly. The crystalline partial layer system makes the mirror module more tolerant to production-related variations, in particular to deviations from at least one target layer thickness of an amorphous layer in the amorphous partial layer system. In particular, the crystalline partial layer system ensures that, when production-related variations occur in the layer system, a deviation in the phase shift is smaller than in a mirror module without the crystalline partial layer system.

[0029] Another aspect of the mirror module may be that the crystalline sub-layer system can be manufactured with smaller production-related fluctuations than the amorphous sub-layer system. This advantageously allows for larger production-related fluctuations in the manufacture of the amorphous sub-layer system without the phase shift of the mirror module exceeding a specified limit.

[0030] The phase shift, in particular the predetermined or desired phase shift, between the P-polarization component and the S-polarization component of the laser beam can have a value in a range from 0° to 180°. The angle of incidence of the laser beam onto the mirror module can have a value in a range from 0° to 90°. In particular, the angle of incidence can have a value in a range from 0° to 5° or 30° to 60°. The angle of incidence of the laser beam onto the mirror module can preferably be 45°.

[0031] The laser beam can be a laser beam from a CCh laser. The power of the laser beam can be in a first range from 50 W (watts) to 300 W, in particular 100 W to 200 W, and / or in a second range from 8 kW (kilowatts) to 50 kW, in particular 10 kW to 30 kW. The wavelength of the laser beam can be in a range from 9 pm to 12 pm, in particular 10 pm to 11 pm. For example, the wavelength of the laser beam can be 10.6 pm.

[0032] The mirror module can be designed as a Bragg mirror.

[0033] Reflecting the laser beam can be understood to mean that the mirror module is designed to reflect the laser beam with a reflection factor of more than 98%, preferably 99% or 99.5%.

[0034] In particular, the mirror module can be designed to reflect the laser beam at an angle of incidence of 45° with a reflection factor of more than 98% and to effect a phase shift, in particular a predetermined or desired phase shift, of 0°.

[0035] The substrate unit can be disk-shaped, particularly cylindrical. Disk-shaped means that the radius of the substrate unit is several times greater than its thickness.

[0036] The substrate unit can be made of silicon, quartz glass, sapphire, diamond, SiC, low-expansion ceramics, germanium or gallium arsenide.

[0037] The substrate unit may have a curvature in a range from 0.1 m (meters) to 10 m, from 10 m to 10 km (kilometers) or from 1 km to 10 km.

[0038] The layer system can be formed from alternating layers of different refractive indices. The layers of the layer system can be referred to as thin layers. A thin layer can be understood as a layer whose thickness ranges from 20 nm (nanometers) to 600 pm.

[0039] The layer system can be designed to reflect the laser beam through constructive interference. For example, a portion of the laser beam can be reflected at each interface between two adjacent layers of different refractive indices. The individual layers can have a layer thickness such that the reflected portions of the laser beam constructively interfere with each other. The individual layers of the layer system can differ from one another in their layer thicknesses.

[0040] The layer system, in particular the amorphous partial layer system, can be arranged directly on the substrate unit. The layer system can be supported by the substrate unit. The substrate unit can serve as a carrier for the layer system. The substrate unit can be coated with the amorphous partial layer system.

[0041] The layer system can be configured to effect a phase shift with an amount in a range from 0° to 180° between the P-polarization component or the S-polarization component. In particular, the layer system can be configured to effect a phase shift with an amount in a range from 0° to 2° or 5° to 180°, in particular 10° to 160°.

[0042] By a suitable choice of layer thicknesses of the individual layers of the layer system, the mirror module can have the, in particular, predetermined or desired, phase shift.

[0043] The individual amorphous layers of the amorphous sub-layer system can be formed from an amorphous material, a polycrystalline material, or a semi-crystalline material. An amorphous layer can be a layer whose building blocks, in particular atoms, ions, or molecules, form an irregular pattern, in particular without any ordered structures. Preferably, the building blocks of the amorphous layer cannot be arranged in a repeating arrangement.

[0044] The amorphous sub-layer system can comprise a plurality of dielectric layers. The amorphous sub-layer system can be produced by physical vapor deposition (PVD), in particular sputtering or ion plating.

[0045] The amorphous partial layer system can comprise a number of amorphous layers of the first type and a number of amorphous layers of the second type. The amorphous layers of the first type and the amorphous layers of the second type can differ in their refractive indices. The amorphous layers of the first type can have a higher refractive index than the amorphous layers of the second type, particularly for a wavelength of the laser beam. The amorphous layers of the first type and the amorphous layers of the second type can be arranged alternately next to one another. This can form a sequence of amorphous layers with alternating refractive indices. In other words, the amorphous partial layer system can comprise amorphous layers arranged alternately next to one another with high and low refractive indices.

[0046] At least one amorphous layer, in particular all amorphous layers, of the amorphous partial layer system can be formed from a material which comprises, in particular is, ThF4, YbFs, YF3, BaF2, LaFs, CeFs, ZnS, ZnSe or Ge.

[0047] The amorphous layers of the second type can be formed, for example, from a material comprising, in particular, ThF4, YbFs, or YF3. A refractive index of ThF4, YbFs, or YF3 for a wavelength of 10.6 pm can be in a range from 1.3 to 1.5.

[0048] The amorphous layers of the first type can be formed, for example, from a material that includes, in particular, Ge. A refractive index of Ge for a wavelength of 10.6 pm can be in a range of 3.95 to 4.05.

[0049] The amorphous layers of the first type or the amorphous layers of the second type can be formed, for example, from a material that comprises, in particular, ZnS or ZnSe. A refractive index of ZnS or ZnSe for a wavelength of 10.6 pm can be in a range from 2.15 to 2.45.

[0050] The amorphous layers of the first type can have the same layer thickness or different layer thicknesses. The amorphous layers of the second type can have the same layer thickness or different layer thicknesses. The individual crystalline layers of the crystalline sub-layer system can be formed from a crystalline material. A crystalline layer can be a layer whose building blocks, in particular atoms, ions, or molecules, form a regular pattern, in particular have an ordered structure. Preferably, the building blocks of the crystalline layer can be regularly arranged in a crystal II structure.

[0051] The term crystalline can be understood as single-crystal.

[0052] The crystalline sub-layer system can comprise a plurality of crystalline layers, in particular epitaxially grown layers. The crystalline sub-layer system can be produced using an epitaxial process, in particular molecular beam epitaxy (abbreviation: MBE) or metal-organic chemical vapor deposition (abbreviation: MOCVD). The production process for the crystalline sub-layer system can have lower manufacturing tolerances than the production process for the amorphous sub-layer system.

[0053] At least one crystalline layer, in particular all crystalline layers, of the crystalline partial layer system can be formed as a single-crystalline or monocrystalline layer.

[0054] The crystalline sub-layer system can have a number of crystalline layers of the first type and a number of crystalline layers of the second type. The crystalline layers of the first type and the crystalline layers of the second type can differ in their refractive indices. The crystalline layers of the first type can have a higher refractive index than the crystalline layers of the second type. The crystalline layers of the first type and the crystalline layers of the second type can be arranged alternately next to one another. This can form a sequence of crystalline layers with alternating refractive indices. In other words, the crystalline sub-layer system can have crystalline layers arranged next to one another, alternating between high and low refractive indices.

[0055] At least one crystalline layer, in particular all crystalline layers, of the crystalline sub-layer system can be formed from a semiconductor material. At least one crystalline layer, in particular all crystalline layers, of the crystalline sub-layer system can be formed from a material that comprises, in particular is, GaAs or AlGaAs. A refractive index of GaAs or AlGaAs for a wavelength of 10.6 pm can have a value in a range from 2.6 to 2.8, in particular 2.7.

[0056] The crystalline layers of the first type can have the same layer thickness or different layer thicknesses. The crystalline layers of the second type can have the same layer thickness or different layer thicknesses.

[0057] A further aspect of the mirror module can be that a deviation from the, in particular predetermined or desired, phase shift of the mirror module due to manufacturing-related fluctuations can be reduced or completely avoided by the combination of crystalline partial layer system and amorphous partial layer system.

[0058] A further aspect of the mirror module may be that the crystalline partial layer system can achieve a higher degree of reflection of the mirror module and / or a lower absorption of the laser beam in the layer system.

[0059] In a further development of the mirror module, the amorphous sub-layer system is arranged between the crystalline sub-layer system and the substrate unit. This can simplify the manufacturing process. First, the amorphous sub-layer system can be attached to the substrate unit before the crystalline sub-layer system is attached to the amorphous sub-layer system. The amorphous sub-layer system can be arranged directly on the substrate unit. The crystalline sub-layer system can be arranged directly on the amorphous sub-layer system.

[0060] In a further development of the mirror module, the number of crystalline layers of the crystalline sub-layer system is greater than the number of amorphous layers of the amorphous sub-layer system. This allows for particularly high insensitivity to production-related fluctuations.

[0061] In a further development of the mirror module, the amorphous sub-layer system is formed from at least four amorphous layers. Additionally or alternatively, the crystalline sub-layer system is formed from at least eight crystalline layers. Such a number of layers can be particularly advantageous for achieving the phase shift while simultaneously maintaining high insensitivity to production-related fluctuations. The amorphous sub-layer system can be formed from at least 10, in particular at least 14 or 20, amorphous layers. The crystalline sub-layer system can be formed from at least 22, in particular 28 or 32, crystalline layers.

[0062] In a further development of the mirror module, the mirror module has a suppression factor of greater than or equal to 3, in particular 4 or 5. The suppression factor describes, for a layer thickness error of 3%, in particular +3%, of the amorphous partial layer system, a ratio of a deviation from the, in particular predetermined or desired, phase shift of the mirror module without the crystalline partial layer system to a deviation from the, in particular predetermined or desired, phase shift of the mirror module with the crystalline partial layer system.

[0063] The layer thickness error can occur due to manufacturing-related variations. The layer thickness error can be a positive layer thickness error. A positive layer thickness error can mean that a layer thickness is thicker than intended.

[0064] The layer thickness error can describe a deviation from a target thickness of the entire amorphous partial layer system, a deviation from a target layer thickness of a single amorphous layer of the amorphous partial layer system, a deviation from all target layer thicknesses of the amorphous layers of the first type or a deviation from all target layer thicknesses of the amorphous layers of the second type.

[0065] For example, all amorphous layers of the first type can have a layer thickness error of 3% such that the layer thickness of each amorphous layer of the first type is 3% thicker than intended. As a result of the layer thickness error, a deviation from the, in particular predetermined or desired, phase shift of the mirror module with the crystalline partial layer system can be 0.5°. Without the crystalline partial layer system, a deviation from the, in particular predetermined or desired, phase shift as a result of the layer thickness error can be 3°. The suppression factor can be determined by dividing the deviation from the, in particular predetermined or desired, phase shift of the mirror module without the crystalline partial layer system by the deviation from the, in particular predetermined or desired, phase shift of the mirror module with the crystalline partial layer system. In this example, the suppression factor can be 6.In a further development of the mirror module, the amorphous partial layer system has a bonding layer. The crystalline partial layer system is firmly bonded to the bonding layer. Advantageously, the bonding layer can simplify the arrangement of the crystalline partial layer system on the amorphous partial layer system. The bonding layer can be formed from a material that includes, in particular is, ThF4, YbFs, YF3, BaF2, LaFs, CeFs, ZnS, ZnSe, or Ge. The bonding layer can be formed from a material that differs from a material of the amorphous layers of the first type and / or the amorphous layers of the second type.

[0066] In a further development of the mirror module, the crystalline sub-layer system is connected to the amorphous sub-layer system by wringing and / or bonding. Advantageously, the wringing and / or bonding can create a permanent and stable connection between the crystalline sub-layer system and the amorphous sub-layer system. No additional material, such as an adhesive, may be required for the wringing and / or bonding. The wringing can also be referred to as pushing.

[0067] The bonding process may include an annealing step. The annealing step may involve heating to a temperature of up to 700°C, particularly in a range of 200°C to 700°C.

[0068] In a further development of the mirror module, the crystalline sub-layer system and the amorphous sub-layer system are connected by van der Waals forces and / or a covalent bond. A covalent bond can be an atomic bond, an electron pair bond, or a homopolar bond.

[0069] In a further development of the mirror module, the substrate unit is designed as a metallic mirror, in particular for reflecting the laser beam. This advantageously allows a higher reflectivity of the mirror module to be achieved. The metallic mirror can be designed as a metal disc. The metallic mirror, in particular the disc, can be made of aluminum, silicon, copper, or silicon carbide.

[0070] The substrate unit can have a mirror surface. The mirror surface can be designed to reflect the laser beam. The mirror surface can be a polished metallic surface. The layer system, in particular the amorphous partial layer system, can be arranged, in particular attached, in particular directly, to the mirror surface of the substrate unit.

[0071] In a further development of the mirror module, the substrate unit has a metal coating for reflecting the laser beam. The layer system, in particular the amorphous partial layer system, is arranged on the metal coating. This advantageously allows metallic mirrors to be provided cost-effectively. The metal coating can form the mirror surface. The metal coating can be designed as an aluminum coating, silver coating, or gold coating. The layer system, in particular the amorphous partial layer system, can be arranged, in particular attached, in particular directly, on the metal coating of the substrate unit.

[0072] A laser device according to the invention for generating EUV radiation by directing a laser beam onto a target material comprises a laser beam generating arrangement and a beam steering device. The laser beam generating arrangement is designed to generate the laser beam. The beam steering device is suitable for directing the laser beam from the laser beam generating arrangement onto the target material. The beam steering device comprises at least one mirror module as described above for directing the laser beam.

[0073] The laser device may include a target chamber in which the target material is disposed. The target chamber may be a vacuum chamber.

[0074] The beam steering device can, for example, comprise 5, 10, 15 or 20 mirror modules as described above.

[0075] Each mirror module of the beam steering device can be designed to reflect the laser beam with a reflection factor of over 98%.

[0076] A method according to the invention for producing a mirror module as described above comprises the steps of: producing the amorphous partial layer system on the substrate unit; producing the crystalline partial layer system on a carrier substrate; detaching the crystalline partial layer system from the carrier substrate; and applying the crystalline partial layer system to the amorphous partial layer system. The amorphous partial layer system can be produced using a physical vapor deposition process, in particular sputtering or evaporation. These processes can be enhanced with ion support.

[0077] The crystalline partial layer system can be produced by means of an epitaxial process, in particular molecular beam epitaxy or metal-organic chemical vapor deposition.

[0078] A surface of the carrier substrate may be polished.

[0079] The attachment of the crystalline sub-layer system to the amorphous sub-layer system can be done by wringing and / or bonding.

[0080] Further advantages and advantageous embodiments of the invention can be gathered from the figures, their description, and the claims. All features disclosed in the figures, their description, and the claims can be essential to the invention both individually and in any combination. They show:

[0081] Fig. 1 is a schematic representation of a mirror module,

[0082] Fig. 2 is a schematic representation of another embodiment of a

[0083] mirror module,

[0084] Fig. 3 is a schematic representation of another embodiment of a

[0085] mirror module,

[0086] Fig. 4 is a schematic representation of a laser device with the mirror module of Fig. 1 , and

[0087] Fig. 5 is a schematic flow chart of a method for manufacturing a mirror module of Fig. 1.

[0088] Fig. 1 shows a mirror module 10. The mirror module 10 is designed to reflect a laser beam, in particular with a reflectance of over 98, preferably 99% or 99.X%, where X can be any integer value in the range 1 to 9. The laser beam can have a wavelength in a range from 1 pm to 3 pm, preferably 1.01 to 1.08 pm, and / or in a range from 10 pm to 11 pm, in particular 10.6 pm. For example, the wavelength of the laser beam can be 10.6 pm.

[0089] The mirror module 10 is designed to reflect the laser beam with a phase shift of 0°. Therefore, the mirror module 10 does not affect the polarization of the laser beam. The polarization of the laser beam is the same before and after reflection by the mirror module 10.

[0090] The mirror module has a substrate unit 12. The substrate unit 12 is cylindrical.

[0091] In an alternative embodiment (not shown), the substrate unit is formed from a metal. The metal can be aluminum, silicon, silicon carbide, or copper. Thus, the substrate unit can be a metallic mirror. The metallic mirror can have a mirror surface for reflecting the laser beam. The mirror surface can be a polished metallic surface.

[0092] The mirror module 10 has a layer system 14. The layer system 14 is arranged directly on the substrate unit 12 and is firmly connected to the substrate unit 12. The layer system 14 is designed to effect, or in particular, to prevent, the phase shift. The phase shift is 0°.

[0093] The layer system 14 is formed from alternating layers 16, 18, 20, 22 with different refractive indices and different layer thicknesses 24, 26, 28, 30. At each interface between two adjacent layers 16, 18, 20, 22 of different refractive indices, a portion of the laser beam is reflected, with the layer thicknesses 24, 26, 28, 30 of the individual layers being selected such that the reflected portions of the laser beam constructively interfere with each other. As a result, the layer system 14 reflects the laser beam by constructive interference.

[0094] Additionally, the refractive indices and layer thicknesses 24, 26, 28, 30 of layers 16, 18, 20, 22 of layer system 14 are selected such that the reflected laser beam exhibits the phase shift. Layer system 14 has an amorphous sub-layer system 32 and a crystalline sub-layer system 34.

[0095] The amorphous sub-layer system 32 is arranged between the crystalline sub-layer system 34 and the substrate unit 12. The amorphous sub-layer system 32 is arranged directly on the substrate unit 12. There is a touching contact between the amorphous sub-layer system 32 and the substrate unit 12. The amorphous sub-layer system 32 is attached to the substrate unit 12.

[0096] The crystalline sub-layer system 34 is arranged directly on the amorphous sub-layer system 32. There is a touching contact between the crystalline sub-layer system 34 and the amorphous sub-layer system 32. The crystalline sub-layer system 34 is attached to the amorphous sub-layer system 32. The crystalline sub-layer system 34 is connected to the amorphous sub-layer system 32 by bonding.

[0097] The amorphous sub-layer system 32 is formed by alternating amorphous layers 16, 18 of different refractive indices. Each amorphous layer 16, 18 of the amorphous sub-layer system 32 is a layer produced by physical vapor deposition. Each amorphous layer 16, 18 of the amorphous sub-layer system 32 is a dielectric layer.

[0098] The amorphous partial layer system 32 has a number of amorphous layers of the first type 18 and a number of amorphous layers of the second type 16. The amorphous layers of the first type 18 and the amorphous layers of the second type 16 differ from each other at least in their refractive indices.

[0099] In the illustrated embodiment, the amorphous layers of the first type 18 have a higher refractive index than the amorphous layers of the second type 16. The amorphous layers of the first type 18 have a refractive index for a wavelength of 10.6 pm with a value in a range of 3.95 to 4.05. The amorphous layers of the first type 18 are formed from Ge. The amorphous layers of the second type 16 have a refractive index for a wavelength of 10.6 pm with a value in a range of 2.15 to 2.45. The amorphous layers of the second type 16 are formed from ZnS. The amorphous layers of the first type 18 and the amorphous layers of the second type 16 are arranged alternately, in particular alternately, next to one another. This forms a sequence of amorphous layers 16, 18 with alternating refractive indices.

[0100] The layer thicknesses 26 of the first-type amorphous layers 18 differ from one another. The layer thicknesses 24 of the second-type amorphous layers 16 differ from one another.

[0101] Fig. 1 shows that the amorphous partial layer system 32 is formed by four amorphous layers 16, 18.

[0102] The crystalline sub-layer system 34 is formed by alternating crystalline layers 20, 22 of different refractive indices. For reasons of clarity, only four crystalline layers 20, 22 are shown in Fig. 1. Each crystalline layer 20, 22 of the crystalline sub-layer system 34 is a layer produced using an epitaxial process. Each crystalline layer 20, 22 has a crystal structure.

[0103] The crystalline sub-layer system 34 has a number of crystalline layers of the first type 22 and a number of crystalline layers of the second type 20. The crystalline layers of the first type 22 and the crystalline layers of the second type 20 differ from each other in their refractive indices.

[0104] In the illustrated embodiment, the first-type crystalline layers 22 have a higher refractive index than the second-type crystalline layers 20. The first-type crystalline layers 22 have a refractive index for a wavelength of 10.6 pm with a value in a range of 2.6 to 2.8, in particular 2.7. The first-type crystalline layers 22 are formed from GaAs. The second-type crystalline layers 20 have a refractive index for a wavelength of 10.6 pm with a value in a range of 3.2 to 3.35. The second-type crystalline layers 20 are formed from AlGaAs.

[0105] The crystalline layers of the first type 22 and the crystalline layers of the second type 20 are arranged alternately, in particular alternatingly, next to one another. This forms a sequence of crystalline layers 20, 22 with alternating refractive indices. The layer thicknesses 30 of the crystalline layers of the first type 22 differ from one another. The layer thicknesses 28 of the crystalline layers of the second type 20 differ from one another.

[0106] The layer thicknesses 24, 26 of the amorphous layers 16, 18 and the layer thicknesses 28, 30 of the crystalline layers 20, 22 are selected depending on the refractive indices of the amorphous layers 16, 18 and the refractive indices of the crystalline layers 20, 22 such that the laser beam is reflected from the layer system 14 with a reflectance of more than 98%, preferably 99%, and the reflected laser beam has a phase shift after reflection.

[0107] In the illustrated embodiment of Fig. 1, the crystalline sub-layer system 34 is formed by eight crystalline layers 20, 22. As a result, the number of crystalline layers 20, 22 of the crystalline sub-layer system 34 is greater than the number of amorphous layers 16, 18 of the amorphous sub-layer system 34.

[0108] The mirror module 10 has a suppression factor UDF of greater than 3. The suppression factor UDF describes a ratio of a deviation AOK from the phase shift of the mirror module 10 without the crystalline sub-layer system 34 to a deviation AMK from the phase shift of the mirror module 10 with the crystalline sub-layer system 34 when a layer thickness error of +3% occurs in the amorphous sub-layer system 32. Consequently, the suppression factor UDF satisfies the condition: UDF = AOK / AMK.

[0109] A layer thickness error of +3% can be understood to mean that the thickness of the entire amorphous partial layer system 32 is 3% greater than the target thickness of the entire amorphous partial layer system 32, that the thickness of a single amorphous layer 16, 18 of the amorphous partial layer system 32 is 3% greater than the target thickness of the single amorphous layer 16, 18 of the amorphous partial layer system 32, that the thicknesses of all the layer thicknesses of the amorphous layers of the first type 18 are 3% greater than the target thicknesses of the amorphous layers of the first type 18, or that the thicknesses of all the layer thicknesses of the amorphous layers of the second type 16 are 3% greater than the target thicknesses of the amorphous layers of the second type 16. In the illustrated embodiment of Fig.1, it is assumed that all amorphous layers of the first type 18 are 3% thicker than the target layer thicknesses of the amorphous layers of the first type 18. The deviation AOK is determined by forming an absolute value of a difference between the phase shift of the mirror module 10 without the layer thickness error of +3% and the phase shift of the mirror module 10 without the crystalline sub-layer system 34 and with the layer thickness error of +3%. The deviation AMK is determined by forming an absolute value of a difference between the phase shift of the mirror module 10 without the layer thickness error of +3% and the phase shift of the mirror module 10 with the layer thickness error of +3%.

[0110] In the initial example shown in Fig. 1, a value of 1° is determined for the deviation AOK and a value of 0.25° for the deviation AMK. This results in a suppression factor UDF of 4.

[0111] Consequently, by means of the combination of amorphous sub-layer system 32 and crystalline sub-layer system 34, an improved insensitivity to fluctuations in the layer thicknesses of the amorphous sub-layer system 32 is achieved.

[0112] Fig. 2 shows a further embodiment of the mirror module 10 of Fig. 1, wherein the same reference numerals are used for identical and functionally equivalent elements and in this respect reference can be made to the above explanations regarding the embodiment of Fig. 1, so that essentially only the existing differences are discussed.

[0113] The substrate unit 12 has a support element 36 and a metal coating 38 for reflecting the laser beam. The support element 36 is coated with the metal coating 38.

[0114] The carrier element 36 can be made of silicon, quartz glass, sapphire, germanium or gallium arsenide.

[0115] The metal coating 38 can be an aluminum coating, a silver coating, or a gold coating. In the illustrated embodiment, the metal coating 38 is a gold coating. The substrate unit 12 has a mirror surface 40 formed by the metal coating 38.

[0116] The layer system 14 is arranged on the metal coating 38, in particular the mirror surface 40, and is attached to the metal coating 38.

[0117] Fig. 3 shows a further embodiment of the mirror module 10 of Fig. 1, wherein the same reference numerals are used for identical and functionally equivalent elements and in this respect reference can be made to the above explanations regarding the embodiment of Fig. 1, so that essentially only the existing differences are discussed.

[0118] Fig. 3 shows that the amorphous sub-layer system 32 has a connecting layer 42. The crystalline sub-layer system 34 is firmly connected to the connecting layer 42.

[0119] The connecting layer 42 has a layer thickness 44. The layer thickness 44 is greater than the other layer thicknesses 24, 26 of the amorphous partial layer system 32.

[0120] The interconnect layer 42 is a layer produced by physical vapor deposition. The interconnect layer 42 is a dielectric layer.

[0121] The connecting layer 42 has a refractive index that differs from the refractive index of the first-type amorphous layers 18 and from the refractive index of the second-type amorphous layers 16. In other words, the connecting layer 42 is a third-type amorphous layer.

[0122] The bonding layer 42 can be formed from a material that includes, in particular, ThF4, YbF5, YF3, BaF2, LaF5, CeF5, ZnS, ZnSe, or Ge. In the illustrated starting example in Fig. 3, the bonding layer 42 is formed from ThF4.

[0123] In a further embodiment not shown, the mirror module can comprise the bonding layer and the metal coating. In other words, the mirror module of the embodiment not shown can comprise the features of the mirror module of Fig. 2 and the features of the mirror module of Fig. 3. Fig. 4 shows a laser device 100 for generating EUV radiation by directing a laser beam 104 onto a target material 110. The laser device 100 has a laser beam generation arrangement 102 for generating a laser beam 104 and a beam steering device 108. The target material 110 for generating EUV radiation is arranged in a target chamber 106. The beam steering device 108 is configured to direct the laser beam 104 from the laser beam generation arrangement 102 onto the target chamber 106, in particular onto the target material 110. The beam steering device 108 has the mirror module 10 of Fig.1 for directing the laser beam 104. The angle of incidence of the laser beam 104 onto the mirror module 10 is 45°. The mirror module 10 reflects the laser beam 104 with a phase shift of 0° between the P-polarization component and the S-polarization component of the laser beam 104. This ensures that the reflection of the laser beam 104 by the mirror module 10 does not affect the polarization of the laser beam 104, and the laser beam 104 impinges on the target material 110 without any change in polarization.

[0124] Fig. 5 shows an exemplary sequence of a method for producing the mirror module 10 of Fig. 1. The method comprises the steps: a) producing the amorphous partial layer system 32 on the substrate unit 12; b) producing the crystalline partial layer system 34 on a carrier substrate; c) detaching the crystalline partial layer system 34 from the carrier substrate; d) applying the crystalline partial layer system 34 to the amorphous partial layer system 32.

[0125] Steps c) and d) can be performed simultaneously or sequentially.

[0126] Applying the crystalline sub-layer system 34 to the amorphous sub-layer system 32 may include bonding the crystalline sub-layer system 34 to the amorphous sub-layer system 32. Bonding may include the steps of: arranging the crystalline sub-layer system 34 to the amorphous sub-layer system 32; pressing the crystalline sub-layer system 34 to the amorphous sub-layer system 32; and heating the crystalline sub-layer system 34 and the amorphous sub-layer system 32 to a temperature in a range of 200°C to 700°C.

Claims

Patent claims 1. A mirror module (10) for reflecting a laser beam (104) with a, in particular predetermined or desired, phase shift between a P-polarization component and an S-polarization component of the laser beam (104), in particular for a laser device for generating EUV radiation by directing a laser beam (104) onto a target material (110), comprising: a substrate unit (12), and a layer system (14) which is firmly connected to the substrate unit (12), wherein the layer system (14) has an amorphous partial layer system (32) and a crystalline partial layer system (34), wherein the amorphous partial layer system (32) is formed by alternating amorphous layers (16, 18) of different refractive indices, wherein the crystalline partial layer system (34) is formed by alternating crystalline layers (20, 22) of different refractive indices.

2. Mirror module (10) according to claim 1, wherein the amorphous partial layer system (32) is arranged between the crystalline partial layer system (34) and the substrate unit (12).

3. Mirror module (10) according to one of the preceding claims, wherein a number of the crystalline layers (20, 22) of the crystalline partial layer system (34) is greater than a number of the amorphous layers (16, 18) of the amorphous partial layer system (32).

4. Mirror module (10) according to one of the preceding claims, wherein the amorphous partial layer system (32) is formed from at least 4 amorphous layers (16, 18), and / or wherein the crystalline partial layer system (34) is formed from at least 8 crystalline layers (20, 22).

5. Mirror module (10) according to one of the preceding claims, wherein the mirror module (10) has a suppression factor of greater than or equal to 3, in particular 4 or 5, wherein the suppression factor describes a ratio of a deviation from the, in particular predetermined or desired, phase shift of the mirror module (10) without the crystalline partial layer system (34) to a deviation from the, in particular predetermined or desired, phase shift of the mirror module (10) with the crystalline partial layer system (34) when the amorphous partial layer system (32) has a layer thickness error of 3%.

6. Mirror module (10) according to one of the preceding claims, wherein the amorphous partial layer system (32) has a connecting layer (42), wherein the crystalline partial layer system (34) is firmly connected to the connecting layer (42).

7. Mirror module (10) according to one of the preceding claims, wherein the crystalline partial layer system (34) is connected to the amorphous partial layer system (32) by wringing and / or bonding.

8. Mirror module (10) according to one of the preceding claims, wherein the crystalline partial layer system (34) and the amorphous partial layer system (32) are connected to one another by means of van der Waals forces and / or by means of a covalent bond.

9. Mirror module (10) according to one of the preceding claims, wherein the substrate unit (12) is designed as a metallic mirror.

10. Mirror module (10) according to one of the preceding claims, wherein the substrate unit (12) has a metal coating (38) for reflecting the laser beam (104), wherein the layer system (14) is arranged on the metal coating (38).

11. Laser device (100) for generating EUV radiation by directing a laser beam (104) onto a target material (110), comprising: a laser beam generating arrangement (102) for generating the laser beam (104), and a beam steering device (108) for directing the laser beam (104) from the laser beam generating arrangement (102) onto the target material (110), wherein the beam steering device (108) comprises at least one mirror module (10) according to one of the preceding claims for steering the laser beam (104) from the laser beam generating arrangement (102) onto the target material (110).

12. A method for producing a mirror module (10) according to one of the preceding claims Claims 1 to 10, wherein the method comprises the steps: Producing the amorphous partial layer system (32) on the substrate unit (12), Producing the crystalline partial layer system (34) on a carrier substrate, Detaching the crystalline partial layer system (34) from the carrier substrate, and - Applying the crystalline partial layer system (34) to the amorphous partial Shift system (32).

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