Device for providing excitation energy for a target material for generating EUV radiation, system for generating EUV radiation, and method for operating a device for providing excitation energy for a target material for generating EUV radiation

Abstract

The invention relates to a device (10) for generating EUV radiation, comprising: a laser beam source (12) for generating a pulsed laser beam (16), and a beam deflection apparatus (24) which is designed to deflect the pulsed laser beam (16), in particular for the purpose of generating the EUV radiation onto the target material (26). The beam deflection apparatus (24) has at least one mirror unit (28) having a mirror element (32). The mirror element (32) can be optically switched by means of a light beam (34) between a reflecting state and a transmitting state. The mirror element (32) is designed to reflect the pulsed laser beam (16) in the reflecting state, and to transmit the pulsed laser beam (16) in the transmitting state.

Description

[0001] Device for providing excitation energy for a target material for generating EUV radiation, system for generating EUV radiation and method for operating a device for providing excitation energy for a target material for generating EUV radiation

[0002] The invention relates to a device for providing excitation energy for a target material for generating EUV radiation, a system for generating EUV radiation and a method for operating a device for generating UV radiation.

[0003] Extreme ultraviolet radiation (EUV radiation) enables the precise and high-accuracy imaging of fine structures, which is why EUV radiation is frequently used in lithography, which is often referred to as E UV lithography. Due to the advantage of precise and high-accuracy imaging of fine structures, EUV lithography is typically used for microchip production.

[0004] In EUV lithography, EUV radiation is often generated by directing excitation energy, for example, using a laser beam, onto a target material, such as a tin droplet. Upon impact, the laser beam transforms the target material into a plasma state, generating EUV radiation.

[0005] The laser beam for generating EUV radiation is often generated using a laser beam source that has at least one optical switch for switching the laser beam. Such an optical switch can, for example, ensure that EUV radiation is provided quickly and reliably when needed and for the duration of the optical switch's actuation, in particular without the time-consuming switching of the laser beam source on and off. In particular, such an optical switch can be used to generate laser pulses, and these laser pulses can be tuned to the target material, in particular to a trajectory and shape of the target material when the target material is in the form of a tin droplet.

[0006] In devices known from the prior art, an acousto-optical modulator is often used as an optical switch. Such an acousto-optical modulator typically has a transparent solid through which the laser beam is guided along a first propagation direction. If an optical grating is created in the transparent solid using sound waves, the laser beam can be diffracted by this grating, thereby deflecting the laser beam such that it propagates along a second propagation direction different from the first propagation direction. In a system for generating EUV radiation, this deflection can, for example, occur such that the laser beam strikes the target material along the second propagation direction.However, this deflection can also occur in such a way that the laser beam travels along the second propagation direction, for example, into a detection device or a so-called beam dump. Within such a beam dump, the laser beam can, for example, become dead due to a multitude of reflections.

[0007] The object of the invention is to provide a device for providing excitation energy for a target material for generating EUV radiation, a system for generating EUV radiation and a method for operating a device for providing excitation energy for a target material for generating EUV radiation, by means of which a rapid and reliable provision of EUV radiation is made possible.

[0008] The invention solves this problem by providing a device for providing excitation energy for a target material for generating EUV radiation having the features of claim 1, a system for generating EUV radiation having the features of claim 9 and a method having the features of claim 10. Advantageous developments and / or embodiments of the invention are described in the dependent claims.

[0009] A device according to the invention for providing excitation energy for a target material to generate EUV radiation comprises a laser beam source and a beam deflection device. The laser beam source is designed to generate a pulsed laser beam. The beam deflection device is configured to deflect the pulsed laser beam. The beam deflection device can, in particular, be configured to direct the laser beam onto a target material for the purpose of generating EUV radiation. The beam deflection device comprises at least one mirror unit with a mirror element. The mirror element can be optically switched, in particular by means of a light beam, between a reflective state and a transmissive state.The mirror element is configured to reflect the pulsed laser beam in the reflective state and to transmit the pulsed laser beam in the transmitting state.

[0010] The EUV radiation can be generated using the target material.

[0011] Advantageously, the optical switching allows the switching time for transitioning the mirror element between the reflective state and the transmissive state to be less than 200 fs (femtoseconds), in particular 100 fs. Therefore, the optical switching of the mirror element allows it to be quickly and reliably transitioned between the reflective state and the transmissive state. This enables a particularly fast and reliable provision of EUV radiation. Due to the rapid switching between the reflective state and the transmissive state, the laser beam can also be shaped, for example, with regard to an intensity profile and / or a pulse duration and / or a pulse width.

[0012] A further aspect of the device can be that the optical switching of the mirror element can be carried out several times in succession at a high switching frequency, which is why high switching frequencies can be realized in a simple and compact design by means of the mirror element and the optical switching.

[0013] A further aspect of the device can be that the mirror element is designed for comparatively low to comparatively medium power levels, so that the pulsed laser beam with an average power between approximately 10 W and approximately 500 W, preferably approximately 50 W to approximately 250 W, more specifically preferably 75 W to 125 W or 100 W, can be guided over the mirror element. Additionally or alternatively, a further aspect of the device can be that the mirror element is designed for high power levels. In particular, the pulsed laser beam with an average power of over 5 kW (kilowatts), preferably over 10 kW, can be guided over the mirror element and, depending on its condition, can be reflected or transmitted by the mirror element without damaging the mirror element.

[0014] The pulsed laser beam can be guided over the mirror unit, in particular over the mirror element. The pulsed laser beam can be guided over the mirror unit, in particular over the mirror element, once or multiple times, for example three or four times.

[0015] In the reflective state, the mirror element can be configured to reflect at least 80%, preferably 95% or 99%, of the laser beam's power. In the transmissive state, the mirror element can be configured to transmit at least 80%, preferably 95% or 99%, of the laser beam's power impinging on the mirror element.

[0016] Optically switchable can be understood to mean that the mirror element can be switched between the reflective state and the transmissive state by means of the light beam, in particular a laser beam.

[0017] Free charge carriers can be generated in the mirror element by means of the light beam, in particular by absorption of the light beam. The free charge carriers can form an electron-hole plasma within the mirror element. The electron-hole plasma can be reflective to electromagnetic radiation with a frequency lower than the plasma frequency of the electron-hole plasma. As a result, the mirror element can act as a metallic mirror for the electromagnetic radiation when the electron-hole plasma is formed. In other words, the mirror element can be an efficient metallic mirror for the electromagnetic radiation when irradiated with the light beam.

[0018] The laser beam may have a frequency that is lower than the plasma frequency of the electron-hole plasma that is formed when the mirror element is irradiated with the light beam.

[0019] The light beam can be designed to generate the electron-hole plasma when it strikes the mirror element. The light beam can exhibit a top-hat-shaped or Gaussian intensity distribution in cross-section, with a top-hat-shaped intensity distribution being advantageous. In addition, the light beam can also exhibit other intensity distributions not explicitly mentioned.

[0020] The light beam can be a pulsed light beam. The impingement of the pulses of the pulsed light beam on the mirror element can be coordinated with the impingement of the pulsed laser beam on the mirror element. For example, the pulses of the pulsed light beam can impinge on the mirror element before the pulses of the pulsed laser beam impinge on the mirror element. A pulse duration of the pulses of the pulsed light beam can be shorter, longer, or equal to a pulse duration of the pulses of the pulsed laser beam, wherein the pulse duration of the pulses of the pulsed light beam is preferably shorter than the pulse duration of the pulses of the pulsed laser beam. For example, the pulse duration of the pulses of the pulsed light beam can be in the femtosecond range, picosecond range, or nanosecond range.

[0021] The light beam can have a power, in particular an average power, of 50 W to 10 kW (kilowatts), in particular 75 W to 5 kW and preferably 100 W to 2.5 kW, particularly preferably 100 W to 1 kW.

[0022] The pulsed light beam may have a pulse repetition frequency equal to a pulse repetition frequency of the pulsed laser beam.

[0023] Using the light beam, the mirror element can be switched such that between two pulses of the pulsed laser beam that follow one another immediately one after the other, the mirror element is switched twice between the reflective state and the transmissive state. In other words, the mirror element can be switched to the reflective state or the transmissive state for each pulse of the pulsed laser beam using the light beam.

[0024] A beam path of the light beam and a beam path of the laser beam of the laser beam source may differ from each other.

[0025] The light beam can be directed onto the mirror element from multiple sides. The light beam can be guided over the mirror element multiple times. By guiding the light beam over the mirror element multiple times, the absorption of the light beam by the mirror element can be advantageously increased.

[0026] In the reflective state of the mirror element, the pulsed laser beam can be deflected by reflection at the mirror element, in particular deflected onto a target material, and in the transmissive state of the mirror element, the pulsed laser beam can transmit the mirror element and thus not be deflected, in particular not deflected onto the target material. Alternatively, in the transmissive state of the mirror element, the pulsed laser beam can be directed, for example, onto the target material by transmission through the mirror element, and in the reflective state of the mirror element, the pulsed laser beam can be reflected by the mirror element and thus not be directed onto the target material.

[0027] When the pulsed laser beam strikes the target material, the pulsed laser beam can convert the target material into a plasma state. EUV radiation can be generated when the target material is converted into the plasma state. In other words, EUV radiation can be generated when the target material is irradiated with the laser beam. In other words, the laser beam can be designed to generate EUV radiation when it strikes the target material.

[0028] The pulsed laser beam 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.

[0029] The laser beam source may include at least one laser oscillator for generating the laser beam and a number of laser amplifiers for amplifying the laser beam. The mirror element may be arranged between the laser oscillator and a laser amplifier of the laser beam source. Alternatively, the mirror element may be arranged downstream of the laser beam source in a propagation direction of the laser beam.

[0030] The laser beam source may comprise a solid-state laser and / or a gas laser, in particular a CO2 laser.

[0031] For example, the laser beam source can comprise the solid-state laser for generating pre-pulses with a wavelength in a range of 1 pm (micrometer) to 3 pm, and the CO2 laser for generating main pulses with a wavelength in a range of 10 pm to 11 pm, in particular 10.6 pm. Each main pulse can be preceded in time, in particular shortly before, by a pre-pulse.

[0032] The pre-pulse can prepare the target material for the impact of the main pulse on the target material, so that when the main pulse hits the target material, as large a proportion of the main pulse as possible is converted into EU radiation.

[0033] The pre-pulse may have a lower laser power than the main pulse.

[0034] The power, in particular the average power, of the laser beam may be at least 500 W, in particular at least 1 kW or 10 kW.

[0035] The beam deflection device can be configured to deflect the laser beam from the laser beam source to the target material. The beam deflection device can comprise a plurality of optical components, in particular lenses and / or mirrors.

[0036] Preferably, the beam deflection device can comprise at least one controllable mirror, for example, a galvanometer mirror. The controllable mirror can be used to change, in particular adjust, the path of the laser beam. The controllable mirror can be arranged in the path of the laser beam downstream of or upstream of the mirror element.

[0037] The mirror element can be disk-shaped. Disk-shaped means that the mirror element has the shape of a cylinder whose radius is many times greater than its thickness.

[0038] The mirror element can have an anti-reflective coating on one side for a wavelength of the laser beam from the laser beam source and / or for a wavelength of the light beam. The anti-reflective coating can be suitable for reducing the reflectance of the laser beam and / or the light beam at interfaces of the mirror element. The laser beam and / or the light beam can impinge on the side of the element before passing through the mirror element. The mirror element can have a highly reflective coating for the wavelength of the laser beam from the laser beam source and / or for the wavelength of the light beam on a further side opposite the side. The highly reflective coating can have a reflectance for the wavelength of the laser beam from the laser beam source and / or for the wavelength of the light beam of at least 90%, preferably 95% or 98%.The laser beam and / or the light beam can hit the other side after passing through the mirror element.

[0039] In a further development of the device, the mirror unit has a light source for generating the light beam for optically switching the mirror element between the reflective state and the transmissive state.

[0040] The light source can comprise a laser diode, a fiber laser, a disk laser, and / or a lamp-pumped rod laser. In particular, the light source can comprise a GaAs laser diode, an AlGaAs laser diode, a Q-switched solid-state laser, preferably a Q-switched Nd:YAG laser and / or a frequency-doubled Nd:YAG laser.

[0041] In a further development of the device, the light beam is designed to optically switch the mirror element in such a way that a beam path of the pulsed laser beam from the laser beam source to the target material and a beam path of a portion of the pulsed laser beam reflected by the target material differ from each other at least in sections.

[0042] This advantageously prevents the portion of the pulsed laser beam reflected by the target material from impairing process efficiency or stability, or even damaging the laser beam source. The laser beam source could be damaged if the portion of the pulsed laser beam reflected by the target material travels back along the laser beam path and is amplified by the laser amplifier of the laser beam source to such an extent that the laser oscillator is damaged. This can be prevented by the mirror element.

[0043] A further aspect may be that the mirror element can act and / or be used as an insulator to protect the laser beam source from the portion of the pulsed laser beam reflected by the target material by enabling different beam paths of the pulsed laser beam and the portion of the pulsed laser beam reflected by the target material.

[0044] In other words, the light beam can be designed to optically switch the mirror element in such a way that the pulsed laser beam and the portion of the pulsed laser beam reflected by the target material are spatially separated from one another at least in sections by means of the mirror element.

[0045] The mirror element can be arranged such that the pulses of the pulsed laser beam and the pulses of the portion of the pulsed laser beam reflected by the target material do not strike the mirror element at the same time.

[0046] The mirror element can have the transmitting state for each pulse of the pulsed laser beam and the reflecting state for each pulse of the portion of the pulsed laser beam reflected by the target material. Alternatively, the mirror element can have the reflecting state for each pulse of the pulsed laser beam and the transmitting state for each pulse of the portion of the pulsed laser beam reflected by the target material. Advantageously, this allows the pulsed laser beam and the portion of the pulsed laser beam reflected by the target material to be separated from each other with a high contrast ratio.

[0047] Preferably, a beam path of the pulsed laser beam before passing the mirror element and a beam path of the portion of the pulsed laser beam reflected by the target material after passing the mirror element can differ from each other.

[0048] In a further development of the device, the light beam is designed to optically switch the mirror element in such a way that each pulse of the pulsed laser beam is divided by means of the mirror element into a reflected pulse component and a transmitted pulse component.

[0049] Advantageously, this allows the impingement of an unwanted pulse portion of a pulse of the pulsed laser beam onto the target material to be suppressed or completely avoided. This allows for more efficient generation of EUV radiation and / or higher quality of the generated EUV radiation. The light beam can be configured to optically switch the mirror element such that the unwanted pulse portion and a desired pulse portion of the pulse of the pulsed laser beam are separated from one another. This enables the desired pulse portion of the pulse of the pulsed laser beam to be directed onto the target material. The unwanted pulse portion cannot at least partially impinge on the target material.

[0050] The unwanted pulse component can be, for example, an unwanted pre-pulse, an unwanted post-pulse and / or an unwanted pulse podium.

[0051] In a further development of the device, the mirror element is formed, in particular entirely, from a semiconductor material. Advantageously, the material properties of the semiconductor material can allow the mirror element to be optically switched between the reflective state and the transmissive state by means of the light beam.

[0052] The mirror element can also be called a semiconductor mirror.

[0053] The semiconductor material can have a fundamental band gap energy that is greater than the photon energy of the laser beam from the laser beam source. Advantageously, this allows the laser beam from the laser beam source to pass through the mirror element with virtually no absorption when the mirror element is in the transmitting state.

[0054] The semiconductor material can be, for example, germanium or silicon.

[0055] The semiconductor material can be, for example, a binary semiconductor. Preferably, the semiconductor material can be gallium arsenide or indium phosphide.

[0056] The semiconductor material can have a semiconductor structure. The semiconductor structure can be designed to create an electric field for localizing charge carriers in the mirror element, preferably at an interface of the semiconductor structure. The semiconductor structure can be a pn junction or two adjacent semiconductor layers with different doping types and / or densities. Advantageously, this makes it possible to adapt a charge carrier density and / or a lifetime of the charge carriers, in particular electrons. The semiconductor material can have a semiconductor heterostructure. The semiconductor material can have a quantum well for localizing charge carriers, in particular electrons. The semiconductor material can have a layer of a semiconductor with a smaller band gap, which is embedded between two layers of a semiconductor with a larger band gap.The semiconductor material can comprise a layer of gallium arsenide embedded between two layers of aluminum gallium arsenide. This advantageously allows for the adaptability of the charge carrier density and / or lifetime of the charge carriers, particularly electrons.

[0057] In a further development of the device, the mirror unit has a cooling element for cooling the mirror element. The mirror element is arranged on the cooling element. This advantageously protects the mirror element from damage due to thermal expansion. The cooling element can be made of aluminum, brass, or copper. The cooling element can be designed so that a cooling fluid, in particular cooling water, can flow through it for the purpose of cooling the mirror element.

[0058] In a further development of the device, the mirror element is wedge-shaped.

[0059] One side and a further side opposite the other side can be at an angle to each other. In other words, the side and the further side are not parallel to each other. The laser beam and / or the light beam can strike the side of the element before passing through the mirror element. The laser beam and / or the light beam can strike the further side after passing through the mirror element.

[0060] The side can be designed as the front side of the mirror element and the other side can be designed as the back side of the mirror element.

[0061] The wedge-shaped design of the mirror element makes it possible to ensure that a reflection of the laser beam at the front of the mirror element and a reflection of the laser beam at the back of the mirror element propagate at different angles to one another. The wedge-shaped design of the mirror element makes it possible to ensure that a reflection of the light beam at the front of the mirror element and a reflection of the light beam at the back of the mirror element propagate at different angles to one another. In a further development of the device, the mirror element is arranged such that an angle of incidence of the pulsed laser beam on the mirror element, in particular before the pulsed laser beam strikes the target material, is equal to the Brewster angle. This advantageously reduces or completely prevents unwanted reflection of the pulsed laser beam from the mirror element.

[0062] A system according to the invention for generating EUV radiation comprises a device for providing excitation energy for a target material, having some or all of the features mentioned above for the device, and the target material. In the case of the system, the device is configured to introduce excitation energy, in particular by means of a laser beam, into the target material to generate EUV radiation.

[0063] The system may comprise a vacuum chamber. The vacuum chamber may have an interior space. The target material may be arranged in the interior space. The vacuum chamber may have a vacuum state. In the vacuum state, a vacuum may prevail in the interior of the vacuum chamber.

[0064] The target material can be a metal, for example, tin. The target material can be formed as droplets, for example, as tin droplets.

[0065] A method according to the invention is suitable for operating a system for generating EUV radiation. A device for providing excitation energy for a target material, in particular with some or all of the features listed above for the device, and the target material are provided. The device comprises a mirror unit with a mirror element. The mirror element is optically switchable between a reflective state and a transmissive state.The method comprises the steps of: generating a pulsed laser beam; and directing the pulsed laser beam for the purpose of generating the EUV radiation onto the target material by switching the mirror element between the reflective state and the transmissive state, wherein the mirror element is configured to reflect the pulsed laser beam in the reflective state and to transmit the pulsed laser beam in the transmissive state. In particular, the method can be suitable for operating the device described above. The description of the device described above can also apply accordingly to the method.

[0066] In a further development of the method, the switching of the mirror element takes place in such a way that the beam path of the pulsed laser beam before passing the mirror element and the beam path of a portion of the pulsed laser beam reflected by the target material after passing the mirror element differ from each other at least in sections.

[0067] In a further development of the method, the mirror element is switched for the purpose of splitting each pulse of the pulsed laser beam into a reflected pulse portion and a transmitted pulse portion by means of the mirror element.

[0068] 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:

[0069] Fig. 1 is a schematic representation of a device for generating EUV radiation,

[0070] Fig. 2 is a schematic representation of a mirror unit of the device of Fig. 1,

[0071] Fig. 3 is a schematic representation of a variant of the mirror unit of Fig. 2, and

[0072] Fig. 4 is a schematic flow chart of a method for operating the device of

[0073] Fig. 1.

[0074] Fig. 1 shows a device 10 for providing excitation energy for a target material for generating EUV radiation. A system comprising the device 10 for generating EUV radiation is not separately shown in the figures.

[0075] The device 10 has a laser beam source 12. The laser beam source 12 has a laser oscillator 14 in the form of a CO2 laser for generating a pulsed laser beam 16 with a wavelength of 10.6 pm, which propagates along a propagation direction 18.

[0076] The laser beam 16 is shown in Fig. 1 with a solid line.

[0077] The laser beam source 12 has a first laser amplifier 20 and a second laser amplifier 22 for amplifying the pulsed laser beam 16. The pulsed laser beam 16 passes through the two laser amplifiers 20, 22. After leaving the laser beam source 12 and before entering the first laser amplifier 20, the pulsed laser beam 16 has an average power of approximately 100 W. After leaving the second laser amplifier 22, the pulsed laser beam 16 has an average power of over 10 kW.

[0078] The device 10 has a beam steering device 24. The beam steering device 24 has a plurality of optical components in the form of lenses and mirrors for directing the pulsed laser beam 16 from the laser beam source 12 onto a target material 26 of the device 10 for the purpose of generating the EUV radiation. For reasons of clarity, not all lenses and mirrors of the beam steering device 24 are shown in Fig. 1.

[0079] The beam steering device 24 has a mirror unit 28. The mirror unit 28 has a light source 30 and a mirror element 32. The light source 30 is designed as a fiber laser. The light source 30 is designed to generate a light beam 34 in the form of a laser beam. The light beam 34 is shown in Fig. 1 with a dashed line. The light beam 34 has, for example, a wavelength of only approximately 1 pm. The light beam 34 has an average power of 100 W. The light beam 34 is a pulsed light beam. The light beam 34 propagates in a propagation direction 36.

[0080] The mirror element 32 is disk-shaped. The mirror element 32 is made entirely of a semiconductor material. In the illustrated embodiment, the semiconductor material is germanium.

[0081] The light beam 34 is designed for optically switching the mirror element 32 between a reflective state and a transmissive state. In other words, the mirror element 32 is optically switchable between the reflective state and the transmissive state by means of the light beam 34. When a pulse of the pulsed light beam 34 strikes the mirror element 32, free charge carriers are generated in the mirror element 32 by absorption of the light beam 34. The free charge carriers form an electron-hole plasma within the mirror element 32. The electron-hole plasma makes the mirror element 32 reflective to electromagnetic radiation with a frequency that is lower than a plasma frequency of the electron-hole plasma. The mirror element 32 can act as a metallic mirror for the electromagnetic radiation.

[0082] The laser beam 16 of the laser beam source 12 has a frequency that is lower than a plasma frequency of the electron-hole plasma that is created when a pulse of the light beam 34 strikes the mirror element 32. As a result, the laser beam 16 is reflected by the mirror element 32 when the mirror element 32 is irradiated with the light beam 34.

[0083] The mirror element 32 is in the reflective state when a pulse of the light beam 34 strikes the mirror element 32, particularly when the electron-hole plasma is formed in the mirror element 32. In the reflective state, the mirror element 32 is designed to reflect the pulsed laser beam 16, preferably to reflect at least 99% of an average power of the laser beam 16.

[0084] When the light beam 34 does not strike the mirror element 32, particularly when no pulse of the light beam 34 strikes the mirror element 32, the electron-hole plasma dissipates and the mirror element 32 becomes transparent to the wavelength of the laser beam 16. In other words, the mirror element 32 is in the transmitting state. In the transmitting state, at least 98% of the average power of the laser beam 16 striking the mirror element 32 can be transmitted through the mirror element 32.

[0085] The mirror element 32 has an anti-reflective coating for the wavelength of the laser beam 16 and the light beam 34 on one side, which is impinged by the laser beam 16, and on a further side opposite the other side. Each anti-reflective coating is suitable for reducing the reflectance of the laser beam 16 and the light beam 34 at the interface between the mirror element 32 and its surroundings. The mirror element 32 is arranged such that, in the reflective state, the mirror element 32 directs the laser beam 16 onto the target material 26. The reflective state of the mirror element 32 is shown in Fig. 1.

[0086] The target material 26 is formed as tin droplets. The target material 26 is arranged in an interior space 38 of a vacuum chamber 40 of the device 10. The vacuum chamber 40 is in a vacuum state. In the vacuum state, a vacuum prevails in the interior space 38 of the vacuum chamber 40.

[0087] When the pulsed laser beam 16 strikes the target material 26, the pulsed laser beam 16 transforms the target material 26 into a plasma state. EUV radiation is generated when the target material 26 is transformed into the plasma state. The laser beam 16 is designed to generate EUV radiation upon impact with the target material 26.

[0088] When the pulsed laser beam 16 strikes the target material 26, a portion of the pulsed laser beam 16 is reflected by the target material 26. The portion of the pulsed laser beam 16 reflected by the target material 26 is shown in dashed lines in Fig. 1. The portion of the pulsed laser beam 16 reflected by the target material 26 propagates in a propagation direction 42. The portion of the pulsed laser beam 16 reflected by the target material 26 travels back along the beam path of the pulsed laser beam 16 from the mirror element 32 to the target material 26 and strikes the mirror element 32.

[0089] The mirror element 32 is arranged such that the pulses of the pulsed laser beam 16 and the pulses of the portion of the pulsed laser beam 16 reflected by the target material 26 do not strike the mirror element 32 at the same time.

[0090] The pulsed light beam 34 and the pulsed laser beam 16 have the same pulse repetition frequency. The impingement of the pulses of the pulsed light beam 34 on the mirror element 32 is coordinated with the impingement of the pulses of the pulsed laser beam 16 on the mirror element 32. The mirror element 32 is switched to the reflective state for each pulse of the pulsed laser beam 16 by means of the light beam 34. After at least a portion of a pulse of the pulsed laser beam 16 has been reflected by the mirror element 32, the mirror element 32 is in the transmissive state. The pulses of the portion of the pulsed laser beam 16 reflected by the target material 26 impinge on the mirror element 32 in the transmissive state.The portion of the pulsed laser beam 16 reflected by the target material 26 passes through the mirror element 32 without being reflected and then strikes a beam trap 44 for reliably blocking the portion of the pulsed laser beam 16 reflected by the target material 26.

[0091] In other words, the pulsed light beam 34 is designed to optically switch the mirror element 32 such that a beam path of the pulsed laser beam 16 before passing the mirror element 32 and a beam path of the portion of the pulsed laser beam 16 reflected by the target material 26 after passing the mirror element 32 differ from one another.

[0092] This can prevent the portion of the pulsed laser beam 16 reflected by the target material 26 from entering the laser beam source 12. In other words, the mirror element can act as an insulator to protect the laser beam source 12 from the portion of the pulsed laser beam 16 reflected by the target material 26.

[0093] Fig. 1 shows that the mirror element 32 is arranged between the second laser amplifier 22 and the target material 26.

[0094] In an alternative embodiment not shown, the mirror element is arranged between the first laser amplifier and the second laser amplifier, wherein the mirror element in the reflective state reflects the laser beam such that the laser beam is coupled into the second laser amplifier.

[0095] In a further alternative embodiment, not shown, the mirror element is arranged between the laser oscillator and the first laser amplifier, wherein the mirror element in the reflective state reflects the laser beam in such a way that the laser beam is coupled into the first laser amplifier.

[0096] Fig. 2 shows the mirror unit 28. Fig. 2 schematically illustrates that a pulse 46 of the pulsed laser beam 16 has a desired pulse portion 48 and an undesired pulse portion 50 before passing the mirror element 32. In the illustrated embodiment, the undesired pulse portion 50 is an undesired pre-pulse. In an alternative embodiment not shown, the undesired pulse portion may additionally or alternatively comprise a pulse pedestal or a post-pulse.

[0097] The pulses of the pulsed light beam 34 switch the mirror element 32 such that each pulse of the pulsed laser beam 16 is split into a reflected pulse portion and a transmitted pulse portion by the mirror element 32. In the illustrated embodiment, the reflected pulse portion is, for example, the desired pulse portion 48, and the transmitted pulse portion is the undesired pulse portion 50.

[0098] The pulses of the pulsed light beam 34 impinge on the mirror element 32 in such a way that at the time the unwanted pulse portion 50 impinges on the mirror element 32, the mirror element 32 is in the transmitting state and the unwanted pulse portion 50 is transmitted by the mirror element 32. At the time the desired pulse portion 48 impinges on the mirror element 32, the mirror element 32 is in the reflecting state and the desired pulse portion 48 is reflected by the mirror element 33. As a result, the unwanted pulse portion 50 is separated, in particular spatially, from the desired pulse portion 48 by means of the pulsed light beam 34 and the mirror element 32. In other words, the propagation direction 18 of the desired pulse portion 48 and a propagation direction 52 of the undesired pulse portion 50 differ from each other after passing the mirror element 32.As a result, the desired pulse portion 48 can be directed onto the target material 26 without the unwanted pulse portion 50. Advantageously, the generation of EUV radiation cannot be negatively influenced by the unwanted pulse portion 50.

[0099] In an alternative embodiment not shown, the reflected pulse portion may be the unwanted pulse portion and the transmitted pulse portion may be the desired pulse portion.

[0100] Fig. 2 shows that the mirror element 32 is arranged such that an angle of incidence 54 of the pulsed laser beam 16 onto the mirror element 32 is equal to the Brewster angle. This can reduce unwanted reflection of the pulsed laser beam 16 from the mirror element 32.

[0101] Fig. 3 shows a further embodiment of the mirror unit 28 of Fig. 2, wherein the same reference numerals are used for identical and functionally equivalent elements and in this respect reference can be made to the explanations of the embodiment of Figs. 1 to 2, so that essentially only the existing differences are discussed.

[0102] Fig. 3 shows that the mirror unit 28 has a cooling element 56 for cooling the mirror element 32. The cooling element 56 is made of copper and has cooling water flowing through it for the purpose of cooling the mirror element 32. The mirror element 32 is arranged on the cooling element 56.

[0103] A side 58 of the mirror element 32, which faces the cooling element 56, has a highly reflective coating for the wavelength of the laser beam 16 and the wavelength of the light beam 34. The side 58 facing the cooling element 56 can also be referred to as the back side of the mirror element 32. The highly reflective coating has a reflectance of at least 95% for the wavelength of the laser beam and the wavelength of the light beam.

[0104] The mirror element 32 is wedge-shaped. In other words, the side 58 and a side 60 of the mirror element 32 opposite the side 58 extend at an angle to each other. The side 60 opposite the rear side 58 can be referred to as the front side of the mirror element 32.

[0105] In the illustrated embodiment, the angle between the front side 60 and the rear side 58 is 5°. Alternatively, the angle can be 3° or 10°.

[0106] The wedge-shaped design of the mirror element 32 ensures that the laser beam 16 is reflected at the front side 60 for directing the laser beam 16 onto the target material 26 when the mirror element 32 is in the reflective state. The portion of the laser beam 16 reflected by the target material 26 strikes the back side 58 of the mirror element 32 and is directed onto the beam trap 44 by the highly reflective coating when the mirror element 32 is in the transmissive state.

[0107] Fig. 4 shows an exemplary sequence of a method for operating a previously described device 10 of Fig. 1 for generating EUV radiation. The method comprises the steps: a) generating the pulsed laser beam 16; and b) directing the pulsed laser beam 16 for the purpose of generating the EU radiation onto the target material 26 by switching the mirror element 32 between the reflective state and the transmissive state, wherein the mirror element 32 is configured to reflect the pulsed laser beam 16 in the reflective state and to transmit the pulsed laser beam 16 in the transmissive state. The switching of the mirror element 32 takes place in such a way that the beam path of the pulsed laser beam 16 before passing the mirror element 32 and the beam path of the portion of the pulsed laser beam 16 reflected by the target material 26 after passing the mirror element 32 differ from one another.In addition, the switching of the mirror element 32 for the purpose of splitting each pulse of the pulsed laser beam 16 into the reflected pulse portion and the transmitted pulse portion is carried out by means of the mirror element 32.

Claims

Patent claims 1. A device (10) for providing excitation energy for a target material (26) for generating EUV radiation, comprising: a laser beam source (12) for generating a pulsed laser beam (16), and a beam deflection device (24) which is configured to deflect the pulsed laser beam (16), in particular for the purpose of generating the EUV radiation onto a target material (26), wherein the beam deflection device (24) has at least one mirror unit (28) with a mirror element (32), wherein the mirror element (32) is optically switchable between a reflective state and a transmissive state by means of a light beam (34), wherein the mirror element (32) is configured to reflect the pulsed laser beam (16) in the reflective state and to transmit the pulsed laser beam (16) in the transmissive state.

2. Device (10) according to claim 1, wherein the mirror unit (28) has a light source (30) for generating the light beam (34) for optically switching the mirror element (32) between the reflective state and the transmissive state.

3. Device (10) according to one of the preceding claims, wherein the light beam (34) is designed to optically switch the mirror element (32) such that a beam path of the pulsed laser beam (16) from the laser beam source (12) to the target material (26) and a beam path of a portion of the pulsed laser beam (16) reflected by the target material (26) differ from one another at least in sections.

4. Device (10) according to one of the preceding claims, wherein the light beam (34) is designed to optically switch the mirror element (32) in such a way that each pulse of the pulsed laser beam (16) is divided by means of the mirror element (32) into a reflected pulse portion and a transmitted pulse portion.

5. Device (10) according to one of the preceding claims, wherein the mirror element (32) is formed from a semiconductor material.

6. Device (10) according to one of the preceding claims, wherein the mirror unit (28) has a cooling element (56) for cooling the mirror element (32), wherein the mirror element (32) is arranged on the cooling element (56).

7. Device (10) according to one of the preceding claims, wherein the mirror element (32) is wedge-shaped.

8. Device (10) according to one of the preceding claims, wherein the mirror element (32) is arranged such that an angle of incidence (54) of the pulsed laser beam (16) onto the mirror element (32) is equal to the Brewster angle.

9. A system for generating EUV radiation, comprising a device (10) for providing excitation energy for a target material (26) according to one of the preceding claims and the target material (26), wherein the device (10) is configured to introduce excitation energy into the target material (26) to generate EUV radiation.

10. A method for operating a system for generating EUV radiation, wherein a device (10) for providing excitation energy for a target material (26) and the target material (26) are provided, wherein the device (10) has a mirror unit (28) with a mirror element (32), wherein the mirror element (32) is optically switchable between a reflective state and a transmissive state, wherein the method comprises the steps of: generating a pulsed laser beam (16), and Deflecting the pulsed laser beam (16), in particular for the purpose of generating the EUV radiation onto a target material (26), by switching the mirror element (32) between the reflective state and the transmissive state, wherein the mirror element (32) is designed to reflect the pulsed laser beam (16) in the reflective state and to transmit the pulsed laser beam (16) in the transmissive state.

11. The method according to claim 10, wherein the switching of the mirror element (32) is carried out in such a way that the beam path of the pulsed laser beam (16) before passing the mirror element (32) and the beam path of a portion of the pulsed laser beam (16) reflected by the target material (26) after passing the mirror element (32) differ from one another at least in sections.

12. The method according to claim 10 or 11, wherein the switching of the mirror element (32) for the purpose of splitting each pulse of the pulsed laser beam (16) into a reflected pulse portion and a transmitted pulse portion is carried out by means of the mirror element (32).

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