EUV driver laser for generating a plasma state that emits an EUV light beam, system for exposing a photosensitive coating, use of the EUV driver laser, method for generating a plasma state that emits an EUV light beam, and method for exposing a photosensitive coating

Abstract

The invention relates to an EUV driver laser (10) for generating a plasma state of a target material (68) which emits an EUV light beam (18), comprising: a plurality of laser beam sources (22) for generating a plurality of laser beams (24); a combination device (62) for combining the plurality of laser beams (24) to form an excitation beam (64) for generating the plasma state; and a focusing device (66) for focusing the excitation beam (64) onto the target material (68) for generating the plasma state. Each laser beam source (22) has a mirror (26), a coupling-out mirror (28), a laser-active medium (30) which is arranged between the mirror (26) and the coupling-out mirror (28), and a photonic structure (34) which is designed to determine at least one beam parameter of the laser beam (24). The mirror (26) faces a first broad side (38) of the laser-active medium (30). The coupling-out mirror (28) faces a second broad side (40) of the laser-active medium (30).

Description

[0001] EUV driver laser for generating an EUV light beam emitting plasma state, apparatus for exposing a photosensitive coating, use of the EUV driver laser, method for generating an EUV light beam emitting plasma state and method for exposing a photosensitive coating

[0002] Description

[0003] The invention relates to an EUV driver laser for generating an EUV light beam emitting plasma state, a system for exposing a photosensitive coating, a use of the EUV driver laser, a method for generating an EUV light beam emitting plasma state and a method for exposing a photosensitive coating.

[0004] Extreme ultraviolet (EUV) light beams enable the highly precise and accurate imaging of fine structures, which is why EUV light beams are frequently used in lithography, a process that can therefore be called EUV lithography. Due to the advantage of precise and highly accurate imaging of fine structures, EUV lithography is suitable for the production of integrated circuits, especially for the manufacture of microchips.

[0005] In the fabrication of integrated circuits, semiconductor substrates, typically also called wafers and often monocrystalline, transistors, and conductive areas that connect the transistors are produced. For this purpose, the wafer is frequently coated with a layer, and the coating is then patterned. The patterning can act as a mask, allowing a functional layer to be created within the wafer, for example, by etching, doping with foreign atoms, or introducing foreign materials. Doping with foreign atoms can be achieved, for example, by ion implantation. Introducing foreign materials can be achieved, for example, by LIGA and lift-off. In lithography, the patterning of the coating is typically achieved by exposing the coating to light.The coating can be a photosensitive coating, specifically a photoresist. The photoresist can be exposed to light of a specific wavelength, to which it is sensitive, in a particular pattern. Typically, the exposed and unexposed areas differ in their solubility, which is why the photoresist can be removed from the wafer using a developer solution, either in the exposed or the unexposed areas. This localized removal of the photoresist creates the pattern that acts as a mask.

[0006] An EUV light beam is typically used to expose the coating. The EUV light beam can be generated, for example, by a system comprising an EUV driver laser and a target chamber. The EUV driver laser can be configured to generate an excitation beam. A target material can be arranged in the target chamber. The EUV light beam can be generated by irradiating the target material with the excitation beam. Upon impact of the excitation beam on the target material, it can be brought into a plasma state, thus generating the EUV light beam.

[0007] Typically, an EUV driver laser uses at least one CO2 laser to generate the excitation beam. CO2 lasers are gas lasers that require regular and complex maintenance to ensure the excitation beam has the required beam parameters necessary for generating the EUV light beam.

[0008] The invention is based on the objective of providing an EUV driver laser, a system, a use of the EUV driver laser, a method for generating an EUV light beam emitting plasma state and a method for exposing a photosensitive coating, each of which has improved properties, in particular being cost-effective.

[0009] The invention solves this problem by providing an EUV driver laser with the features of claim 1, a system with the features of claim 13, a use with the features of claim 14, a method for generating an EUV light beam emitting plasma state with the features of claim 15, and a method for exposing a photosensitive coating with the features of claim 16. Advantageous embodiments and further developments of the invention are set forth in the dependent claims.

[0010] An EU driver laser according to the invention is configured for generating an EU light-emitting plasma state of a target material. The EUV driver laser comprises a plurality of laser beam sources, a combination device, and a focusing device. The plurality of laser beam sources are configured for generating a plurality of laser beams. The combination device is configured for combining the plurality of laser beams into a single excitation beam, in particular a single excitation beam, for generating the plasma state. The focusing device is configured for focusing the excitation beam onto the target material for generating the plasma state. Each laser beam source comprises a mirror, an output coupler, a laser-active medium, and a photonic structure. The laser-active medium is arranged between the mirror and the output coupler.The photonic structure is configured to determine, and in particular to define, at least one beam parameter of the laser beam. The mirror, in particular a mirror surface of the mirror, faces a first broad side of the laser-active medium. The output coupler, in particular a mirror surface of the output coupler, faces a second broad side of the laser-active medium.

[0011] Advantageously, the photonic structure enables the generation of laser beams with beam parameters that allow for a reduction in the number of components required to construct the EUV driver laser. This reduces the complexity of the EUV driver laser, thereby decreasing the effort required for its alignment. By reducing the number of components and the effort required for alignment, costs are saved, making the EUV driver laser cost-effective.

[0012] Another advantage is that by positioning the mirror and the output coupler on opposite sides of the laser-active medium, a compact design of the EUV driver laser is possible. In particular, the space requirement of the EUV driver laser can be significantly reduced compared to an EUV driver laser using a CO2 laser, thus reducing space costs. The target material can be a metal, such as tin. The target material can be in the form of droplets, for example, tin droplets. Forming the target material as tin droplets can be particularly advantageous for generating an EUV light beam due to the high yield of EUV radiation.

[0013] The excitation beam can be designed to, upon impact with the target material, convert it into a plasma state in such a way that the EUV light beam is generated. In other words, the target material can emit the EUV light beam when irradiated with the excitation beam.

[0014] The excitation beam can be a pulsed beam. Every laser beam can be a pulsed beam. The pulses of any pulsed laser beam can be generated, for example, by modulating the electrical energy supplied to each laser beam source for generating the laser beam.

[0015] The excitation beam can have an average power of over 20 kW (kilowatts), preferably over 25 kW. With such characteristics, the plasma state of the target material can be generated particularly easily and effectively. Furthermore, each laser beam can have an average power in the range between 20 W (watts) and 250 W, in particular between 50 W and 175 W, preferably between 75 W and 125 W.

[0016] Every laser beam can be a single-mode laser beam. Every laser beam can have a diffraction coefficient M. 2 exhibiting a diffraction coefficient of 2 or less than 2. Preferably, each laser beam can have a diffraction coefficient M. 2 with a value in the range of 1 to 1.4. The excitation beam can be a single-mode laser beam. The excitation beam can have a diffraction coefficient M. 2 of equal to or less than 2, particularly in a range of 1 to 1.4.

[0017] The focusing device can include at least one lens or at least one curved mirror for focusing the excitation beam onto the target material. In particular, the curved mirror of the focusing device can be a concave mirror. Focusing the excitation beam onto the target material allows for a high power density on the target material, resulting in a greater yield of EUV radiation. The combination device can be configured to form the excitation beam by spatially superimposing multiple laser beams. This spatial superimposition of multiple laser beams can result in the excitation beam being a single laser beam. In particular, the excitation beam can be formed such that the beam cross-sections of the laser beams largely overlap.Furthermore, the combination device can also be designed to form the excitation beam by spatially combining the majority of laser beams in such a way that the laser beams propagate parallel to each other and alongside each other along a propagation direction.

[0018] The EUV driver laser may include a beam guidance device. The beam guidance device may be configured to guide the laser beams from the laser beam sources to the combination device and / or to guide the excitation beam from the combination device to the focusing device. The beam guidance device may include multiple optical components, in particular lenses and / or mirrors.

[0019] The laser-active medium can be referred to as the laser-active material. Every laser beam source can be designed as a solid-state laser. The laser-active medium of every laser beam source can be in a solid state. The laser-active medium can be a semiconductor laser material. In particular, the laser-active medium can be formed from a semiconductor laser material. The laser-active medium can be produced by epitaxial growth.

[0020] The laser-active medium can be composed of a material containing holmium, thulium, gallium arsenide, gallium antimonide, gallium nitride, or indium phosphide. In particular, a laser-active medium containing gallium antimonide can be advantageous for generating a laser beam with a wavelength in the range between 1600 nm (nanometers) and 2300 nm, especially between 1800 nm and 2100 nm.

[0021] The laser-active medium can be configured to convert electrical power, preferably directly, into optical power. For example, the laser-active medium can generate the laser beam by recombination of electrons and holes. Advantageously, this allows the excitation beam to be generated efficiently with low electrical power consumption, making the EUV driver laser energy-efficient. This, in turn, reduces the operating costs of the EUV driver laser.

[0022] In particular, the efficiency for generating the excitation beam using the EUV driver laser can be greater than 25%, especially 30%. The efficiency for generating the excitation beam can describe the ratio of the excitation beam power to the electrical power consumed by the laser beam sources for generating the laser beams.

[0023] The output coupler mirror can be designed to reflect for a wavelength of the laser beam with a reflectance of over 80%, preferably 90%, 95%, 98% or 99%.

[0024] The mirror can be designed to reflect the laser beam at a wavelength of over 98%, 99%, or 99.5%. The reflectance of the mirror can be higher than that of the output coupler.

[0025] The output coupler and / or the mirror can each be a plane mirror. The output coupler and / or the mirror can each be a Bragg mirror. The output coupler and / or the mirror can each be formed by a system of alternating layers with different refractive indices. The layers of the system can be referred to as thin films. A thin film can be defined as a film whose thickness is in the range of 20 nm to 600 pm.

[0026] The output mirror and / or the mirror can each be arranged on the laser-active medium, particularly directly. The mirror and / or the output mirror can each be arranged on the laser-active medium in a contacting manner. In particular, the laser-active medium can be coated with the output mirror and / or the mirror. Preferably, the first broad side of the laser-active medium can be coated with the mirror and the second broad side with the output mirror. Advantageously, this allows each laser beam source to be designed compactly, thereby reducing the space requirement of the EUV driver laser.

[0027] The output coupler and the mirror can form a resonator for the laser beam source. The laser-active medium can be located within the resonator. The emission direction of each laser beam source, from which the laser beam is emitted, can be oriented orthogonally to the output coupler and / or the mirror.

[0028] The laser-active medium can extend along an X, Y, and Z direction. The X direction can be orthogonal to the Y direction. The Z direction can be orthogonal to both the X and Y directions. The Z direction can also be parallel to the emission direction.

[0029] The extent of the laser-active medium in the Z-direction can be less than its extent in the X-direction and / or Y-direction. The extent of the laser-active medium in the X-direction and / or Y-direction can be more than five times, and in particular ten times, its extent in the Z-direction. The extent of the laser-active medium in the Z-direction can range from 30 pm (micrometers) to 1 mm (millimeters), and in particular from 250 pm to 850 pm.

[0030] The laser-active medium can be disk-shaped. The diameter of the disk-shaped laser-active medium can be more than five times, and in particular ten times, its thickness. The disk-shaped laser-active medium can be arranged such that its thickness and extent in the Z-direction are equal.

[0031] The first and second broadsides of the laser-active medium can be aligned parallel to each other. The first and / or the second broadside can each be aligned parallel to a plane spanned by the X and Y directions. The first and / or the second broadside can each be planar.

[0032] A value for the area of ​​a surface of the laser-active medium on the first broadside and / or a value for the area of ​​a surface of the laser-active medium on the second broadside can be greater than a value for the sum of area units of the remaining sides excluding the first broadside and excluding the second broadside.

[0033] Every laser beam source can have a photonic element that exhibits the photonic structure at least partially, and in particular completely. The photonic element can be located between the output coupler and the mirror. Alternatively or additionally, the photonic structure can be integrated into the mirror, the output coupler, and / or the laser-active medium. The photonic structure can be two-dimensional. The photonic structure can be configured as a photonic crystal lattice or as a metamaterial.

[0034] The photonic crystal lattice can be designed to determine, in particular to fix, the beam parameter of the laser beam by means of diffraction and / or interference.

[0035] A photonic crystal lattice can be understood as an arrangement with spatially periodic dielectricity. This spatially periodic dielectricity can be achieved by combining at least two materials with different dielectrics. The photonic crystal lattice can have a unit cell. It can be formed by a regularly repeating arrangement of the unit cell. The photonic crystal lattice can exhibit a regular change in the refractive index. It can also have a periodic arrangement of holes, particularly air holes, in a solid material.

[0036] The metamaterial can exhibit a permeability to electric and magnetic fields due to its structure, which differs from the permeability to electric and magnetic fields of the material(s) from which the metamaterial is formed. This can be achieved through specially designed, usually periodic, microscopically fine structures of electrically or magnetically active material(s). The metamaterial can exhibit a negative real part of the complex refractive index.

[0037] The statement that the photonic structure is designed to determine at least the beam parameter can be understood to mean that the photonic structure is the cause of the laser beam having the beam parameter. In particular, the photonic structure can cause the laser beam to have the beam parameter.

[0038] The beam parameter can be a polarization of the laser beam, a wavelength of the laser beam, the diffraction coefficient M 2 and / or the degree of collimation of the laser beam. The degree of collimation can describe whether the laser beam is emitted from the laser source in a collimated state.

[0039] For example, the presence of the photonic structure allows the laser beam to have a predetermined polarization, wavelength, diffraction coefficient, and / or collimation. Every laser beam source can have a first electrode and a second electrode. The two electrodes are configured to be connected to an electrical energy source, in particular a current source. The two electrodes can serve to supply, in particular, impart electrical energy from the electrical energy source to the laser-active medium. By supplying, in particular imparting, electrical energy to the laser-active medium, the laser-active medium can convert the electrical energy into optical energy, thereby generating the laser beam.

[0040] The first electrode can be arranged on the mirror. The mirror can be positioned between the first electrode and the laser-active medium. The second electrode can be arranged on the output coupling mirror. The output coupling mirror can be positioned between the second electrode and the laser-active medium. The second electrode can have a breakthrough. The breakthrough can form an exit aperture for the laser beam. The second electrode can be annular in shape.

[0041] The first electrode and / or the second electrode can be made of a material containing at least 40%, preferably 60%, copper.

[0042] The EU driver laser can include a waveguide device for guiding the laser beams to the combination device via waveguide. The waveguide device can be designed as a photonically integrated circuit.

[0043] In a further development of the EU driver laser, the photonic structure of each laser beam source is arranged at least sectionally, and in particular completely, between the laser-active medium and the output coupler mirror. Additionally or alternatively, the photonic structure of each laser beam source is arranged at least sectionally, and in particular completely, between the laser-active medium and the mirror. Additionally or alternatively, the laser-active medium of each laser beam source has the photonic structure at least sectionally, and in particular completely. Advantageously, this allows the photonic structure to be arranged within the resonator formed by the mirror and the output coupler mirror. This allows the photonic structure to increase resonator losses for unwanted modes of the resonator, so that the resonator losses for a number of desired modes are low.

[0044] If the photonic structure is arranged at least partially between the laser-active medium and the mirror and / or between the laser-active medium and the output coupler, any laser beam source can incorporate the photonic element. The photonic structure can be arranged between the laser-active medium and the mirror by placing the photonic element between the laser-active medium and the mirror. The photonic structure can also be arranged between the laser-active medium and the output coupler by placing the photonic element between the laser-active medium and the output coupler. This allows the photonic structure to be separated from the laser-active medium. An electron barrier layer can be arranged between the photonic element and the laser-active element.

[0045] If only the laser-active medium of each laser beam source exhibits the photonic structure, the laser-active medium can advantageously extend from the mirror to the output coupler, thereby giving the resonator a higher fill factor with the laser-active medium. This allows for higher gain and / or higher output power of each laser beam source.

[0046] In a further development of the EU driver laser, the photonic structure of each laser beam source is designed to ensure that the laser beam is emitted in a collimated state. Advantageously, this eliminates the need for lenses to collimate the laser beams, thereby reducing the manufacturing costs of the EU driver laser. Furthermore, this reduces the complexity of the EU driver laser, simplifying its adjustment. In particular, if a laser beam source should fail, it can be replaced or exchanged with a new one with less effort, especially since the new laser beam source only requires adjustment in the X and Y directions.

[0047] Due to its structure within the resonator, the photonic structure can cause the lowest losses for the laser beam in the collimated state.

[0048] For example, the photonic structure can be formed from an arrangement of holes, especially air holes, which, due to their arrangement relative to each other in the resonator, cause the lowest losses for the laser beam in the collimated state.

[0049] In a further development of the EUV driver laser, the mirror, the output coupling mirror, the laser-active medium, and the photonic structure are inextricably integrated in each laser beam source. Advantageously, this eliminates the need for adjustment of the mirror, the output coupling mirror, and the laser-active medium relative to each other.

[0050] The mirror, the output coupling mirror, the photonic structure and the laser-active medium can be designed as one, in particular a single, component.

[0051] The mirror, the output coupling mirror, the photonic structure and the laser-active medium can be attached to each other.

[0052] In a further development of the EU driver laser, each laser beam source has a heat sink for dissipating heat generated during laser beam generation. The heat sink is arranged on the mirror, in particular attached to it, so that heat from the laser-active medium can be conducted through the mirror into the heat sink. During laser beam generation, heat can be generated in the laser-active medium, which is dissipated by means of the heat sink to prevent damage to the laser-active medium. In particular, at least 60%, preferably 80%, of the heat generated during laser beam generation can be conducted through the mirror into the heat sink.

[0053] The mirror can be positioned between the heat sink and the laser-active medium. The heat sink can be made of a material containing at least 40% copper or at least 80% aluminum. The heat sink, the mirror, the output coupling mirror, and the laser-active medium can be designed as a single component, particularly a single, integrated component. The heat sink can be designed to allow flow of a cooling fluid. The cooling fluid can be air or water.

[0054] The heat sink can be electrically conductive. This allows the heat sink to act as the first electrode. Advantageously, this enables the heat sink to perform a dual function: dissipating the heat generated during laser beam production and simultaneously supplying the laser-active medium with electrical energy. The heat sink can have a connection for attaching an electrical conductor.

[0055] In a further development of the EUV driver laser, the laser-active medium comprises a plurality, in particular at least 5 or 20, of thin layers. This allows the laser-active medium to be configured to convert electrical energy into optical energy. The laser-active medium can comprise a number of thin layers of the first kind and a number of thin layers of the second kind. The thin layers of the first kind and the thin layers of the second kind can differ from each other in one property. The laser-active medium can be formed by an alternating arrangement of a thin layer of the first kind and a thin layer of the second kind.

[0056] For example, thin films of the first kind can be designed to bind electrons. Thin films of the second kind can be designed to bind holes. This allows photons to be emitted from the laser-active medium when electrical energy is applied, through recombination of the electrons and holes, which then form the laser beam.

[0057] Thin films of the first kind and thin films of the second kind can each be formed from a semiconductor material or semiconductor laser material.

[0058] In an alternative development of the EUV driver laser, the EUV driver laser is amplifierless, meaning it lacks an optical amplifier for amplifying the laser beams and / or the excitation beam. In other words, the laser beams can be supplied in such a large number that the excitation beam generated by the combination device can be directed directly onto the target material without one or more further optical amplification steps. Advantageously, this further reduces the complexity and material costs of the EUV driver laser. In particular, optical components required when an optical amplifier is present can be eliminated. Furthermore, this simplifies the alignment required during the manufacturing of the EUV driver laser.

[0059] Laser beam amplification can refer to increasing the power output of the laser beams, for example, the average power or the peak pulse power. Once a laser beam leaves its source, it cannot undergo any optical amplification, particularly in terms of power.

[0060] Advantageously, the EUV driver laser has a sufficient number of laser beam sources such that the excitation beam combined from the laser beams has sufficient power to generate the plasma state. In other words, the laser beam sources are designed to generate laser beams with such power that the excitation beam combined from the laser beams has sufficient power to generate the plasma state. Amplification, in particular power amplification, of the laser beams after they leave the laser beam sources is unnecessary. The optical amplifier can be referred to as a laser amplifier.

[0061] In an advanced version of the EUV driver laser, the combination unit is designed to combine the laser beams into the excitation beam using either coherent or non-coherent beam combinations. Advantageously, coherent beam combinations, due to constructive interference, can achieve higher excitation beam power, particularly a higher peak pulse power, compared to non-coherent beam combinations. Conversely, non-coherent beam combinations, because phase matching between the laser beams is not required, simplify the design of the EUV driver laser compared to coherent beam combinations.

[0062] In a further development of the EUV driver laser, the combination unit is designed to combine the laser beams into the excitation beam using spectral beam combination, polarization-beam combination, intensity-beam combination, or spatial beam combination. These combination principles have proven particularly suitable for combining the laser beams into the excitation beam for generating the plasma state. In particular, these combination principles can be especially suitable for a power range, especially a pulse energy range, required for generating the plasma state.

[0063] In spectral beam combination, the laser beams can differ in their wavelength. The combination device can include a grating. The laser beams can strike the grating at different angles of incidence. The grating can be configured to diffract the laser beams by a reflection angle, depending on their wavelength. This reflection angle can be the same for all laser beams. In other words, the grating can diffract all laser beams in the same direction, thus forming the excitation beam.

[0064] In polarization-beam combination, the combination device can have a number of polarizers. Each laser beam can be linearly polarized. Each polarizer can combine two mutually orthogonally polarized laser beams. For example, the polarizer can be configured to transmit the polarization of one laser beam and reflect the polarization of the other. The polarizer can be configured to form a combined laser beam exiting the polarizer by spatially superimposing the two laser beams. The combined laser beam can be a linearly polarized laser beam. The combined laser beam can be combined with another polarizer in the combination device and another combined laser beam to form the excitation beam.Alternatively, the combination device can have a single polarizer that forms the excitation beam from two laser beams.

[0065] In spatial beam combining, the combining device can have a number of beam splitters through which the laser beams travel in opposite directions. Each beam splitter can combine at least two laser beams. For example, the combining device can have at least one fiber optic beam splitter. A laser beam can be injected into each of the two outputs of the fiber optic beam splitter, and these two beams emerge from one input of the fiber optic beam splitter as a combined laser beam. In other words, the combining device can be implemented using waveguides.

[0066] In a further development of the EUV driver laser, the EUV driver laser features a carrier unit. The majority of the laser beam sources are attached to this carrier unit. Advantageously, the carrier unit enables a modular design for the EUV driver laser. If one or more laser beam sources fail, the carrier unit, along with the laser beam sources, can be removed from the EUV driver laser and replaced with another carrier unit containing functional laser beam sources. This simplifies maintenance and / or repair of the EUV driver laser. In particular, the EUV driver laser can be back in operation more quickly after a defect occurs, thus reducing downtime. Consequently, the short downtimes make the EUV driver laser cost-effective to operate.

[0067] The support unit can be plate-shaped. In particular, the support unit can be designed as a mounting plate. The mounting plate can be an optical tabletop or optical breadboard. The width and / or length of the support unit can be more than five times, in particular ten times, its thickness. The support unit can have a thickness in the range of 4 mm to 15 mm, in particular 5 mm to 10 mm.

[0068] The carrier unit can be detachably attached to a base plate of the EUV driver laser. At least one other component of the EUV driver laser, for example the combination unit, can be attached to the base plate of the EUV driver laser.

[0069] In a further development of the EUV driver laser, the number of laser beam sources is in the range of 2 to 1000, in particular 4 to 20, preferably 5 to 10. Such a number of laser beam sources has proven to be sufficient for generating the plasma state.

[0070] In a further development of the EUV driver laser, the excitation beam has a wavelength in the range of 1600 nm to 4000 nm, particularly 1800 nm to 3000 nm, preferably 1800 nm to 2400 nm. Advantageously, such a wavelength range can be generated cost-effectively using the laser beam sources described above. Furthermore, a particularly high yield of EUV radiation can be achieved with such a wavelength range by generating the plasma state. Therefore, such a wavelength range can be particularly suitable for EUV power scaling.

[0071] An apparatus according to the invention is designed for exposing a photosensitive coating using an EUV light beam. The photosensitive coating is supported by a semiconductor substrate. The apparatus comprises a previously described EUV driver laser and a target chamber in which the target material for generating the EUV light beam is arranged. Advantageously, the EUV light beam can be generated efficiently using the apparatus. In particular, the apparatus can be configured to generate the EUV light beam with a wavelength or with an average wavelength of less than 6 nm.

[0072] The previously given description of the target chamber, the target material and / or the photosensitive coating can apply to identical or corresponding features of the system.

[0073] The target chamber can be designed as a vacuum chamber. The target chamber can be filled with hydrogen at a pressure of 1 Pa (Pascal) to 10⁻¹⁰.15 Pa, preferably 10' 3 Pabis 10- 12 Pa, be filled. Alternatively, the target chamber can be in a vacuum state. In this vacuum state, a vacuum can exist within the interior of the target chamber.

[0074] The system may include a holding device for holding the semiconductor substrate coated with the photosensitive coating.

[0075] The system may include an EUV steering device. The EUV steering device may be configured to direct the EUV light beam onto the holding device, in particular onto the semiconductor substrate held by the holding device.

[0076] The majority of laser beam sources and the combination unit can be arranged in a first system area. The focusing unit and the target chamber can be arranged in a second system area. The first and second system areas can be configured as distinct system levels. The height levels of the first system area and the second system area can differ from each other.

[0077] The photosensitive coating can be called a photoresist. The photosensitive coating can consist of a polymer base and a photosensitive substance. The polymer base can, for example, be a phenol-formaldehyde resin and / or a polymethyl methacrylate. The photosensitive substance can, for example, be a diazonaphthoquinone and / or an acrylate.

[0078] One use according to the invention relates to the exposure of a photosensitive coating supported by a semiconductor substrate using a previously described EUV driver laser or apparatus. An EUV light beam generated by the previously described EUV driver laser or apparatus may be particularly suitable for exposing the photosensitive coating.

[0079] A method according to the invention serves to generate an EUV light-emitting plasma state of a target material. The method comprises: generating a plurality of laser beams by means of a plurality of laser beam sources, wherein each laser beam source has a mirror, an output mirror, a laser-active medium arranged between the mirror and the output mirror, and a photonic structure configured to determine at least one beam parameter of the laser beam, wherein the mirror faces a first broad side of the laser-active medium, and the output mirror faces a second broad side of the laser-active medium; combining the plurality of laser beams into an excitation beam for generating the plasma state; and generating the plasma state by irradiating the target material with the excitation beam.

[0080] The EUV driver laser and / or the system described above can be configured to perform the method. In particular, the method can be configured to operate the EUV driver laser and / or the system described above. The description given above of the EUV driver laser and / or the system can apply to identical or functionally equivalent features of the method, and / or vice versa.

[0081] A method according to the invention serves to expose a photosensitive coating which is supported by a semiconductor substrate.The method comprises: generating a plurality of laser beams by means of a plurality of laser beam sources, each laser beam source comprising a mirror, an out-coupler mirror, a laser-active medium arranged between the mirror and the out-coupler mirror, and a photonic structure configured to determine at least one beam parameter of the laser beam, the mirror facing a first broadside of the laser-active medium, and the out-coupler mirror facing a second broadside of the laser-active medium; combining the plurality of laser beams into an excitation beam for generating the plasma state; generating the EUV light beam by irradiating the target material with the excitation beam; and exposing the photosensitive coating by directing the EUV light beam onto the photosensitive coating.

[0082] The previously described system can be configured to execute the process. In particular, the process can be configured to operate the previously described system. The previously given description of the system can apply to identical or functionally equivalent features of the process and / or vice versa.

[0083] Further advantages and advantageous embodiments of the invention can be seen 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. Figure 1 shows a schematic representation of a system for exposing a photosensitive coating using an EUV light beam.

[0084] Fig. 2 is a schematic representation of a cross-section of a laser beam source of the system of Fig. 1, and

[0085] Fig. 3 shows a schematic representation of a cross-section of another embodiment of a laser beam source.

[0086] Fig. 1 shows a system 500 with an EUV driver laser 10 and a target chamber 12.

[0087] The system 500 is used to fabricate integrated circuits on a wafer 14, which has the form of a semiconductor substrate. For this purpose, the wafer 14 is coated with a coating 16. The coating 16 is a photoresist. The photoresist is exposed using an EUV light beam 18 from the system 500. Before striking the coating 18, the EUV light beam 18 passes through a mask 20, which locally shades the EUV light beam 18. This exposes the coating 18 with a specific pattern, resulting in exposed and unexposed areas. The exposed and unexposed areas differ in their solubility. Therefore, the photoresist 16 can be removed from the exposed areas using a developing solution, but cannot be removed from the unexposed areas using the developing solution.After removal of the exposed photoresist, a structure forms on the coating 16, which acts as a local mask on the wafer 14. The masking of individual areas enables the fabrication of a functional layer in the wafer 14, for example by etching the unmasked areas, and thus the fabrication of integrated circuits.

[0088] Exposure is carried out using the EUV light beam 18, which is generated by the system 500. The system has the EUV driver laser 10 for generating the EUV light beam 18.

[0089] The EUV driver laser 10 has a plurality of laser beam sources 22. In the initial example shown, the EUV driver laser 10 has five laser beam sources 22. However, it is also conceivable that the EUV driver laser 10 has more or fewer laser beam sources 22.

[0090] Fig. 2 shows a cross-section of a laser beam source 22 of the EUV driver laser 10. All laser beam sources 22 of the EUV driver laser 10 are shown here as examples of identical construction. However, the laser beam sources 22 can also be at least partially different from one another and, for example, emit laser beams 24 with different wavelengths and / or polarizations.

[0091] The laser beam source 22 serves to generate a single laser beam 24. The laser beam 24 is a pulsed beam. The pulses of the pulsed laser beam 24 are generated by modulating the electrical energy supplied to the laser beam source 22 for generating the laser beam 24. The laser beam 24 has an average power of 40 W. The wavelength of the laser beam 24 is in the range of 1900 to 2100 nm. The laser beam 24 is a single-mode laser beam whose diffraction coefficient M 2has a value that is less than 1.3.

[0092] The laser beam source 22 has a mirror 26, an output coupling mirror 28, a laser-active medium 30, and a photonic element 32. The photonic element 32 has a photonic structure 34.

[0093] The output coupler 28 and the mirror 26 form a resonator for the laser beam source 22. The mirror 26 is designed to be reflective with a reflectance of over 99.5% for the wavelength of the laser beam. The output coupler 28 serves to couple the laser beam 24 out of the resonator. Therefore, the reflectance of the output coupler 28 is lower than that of the mirror 26. The output coupler 28 can be designed to be reflective with a reflectance of over 95% for the wavelength of the laser beam.

[0094] The output coupler 28 and the mirror 26 are each planar, specifically designed as a planar mirror. The output coupler 28 and the mirror 26 are each formed from a layer system of alternating layers with different refractive indices. The output coupler 28 and the mirror 26 are each Bragg mirrors.

[0095] The laser-active medium 30 is arranged within the resonator, or in other words between the output coupling mirror 28 and the mirror 26.

[0096] The laser-active medium 30 is designed as a solid. Therefore, the laser beam source 22 can be referred to as a solid-state laser. The laser-active medium 30 is formed from a semiconductor laser material. The laser-active medium 30 has a plurality, for example, 3 or 4, of thin layers of gallium antimonide. The laser-active medium 30 is designed to convert electrical power directly into optical power by recombination of electrons and holes, thereby generating the laser beam 24. This allows for an efficiency of over 25% for generating the laser beam 24. The efficiency for generating the laser beam 24 can be described as the ratio of the electrical power supplied to the laser beam source 22 for generating the laser beam 24 to the power of the laser beam 24.

[0097] The laser-active medium 30 extends along an X, Y, and Z direction. The X, Y, and Z directions are orthogonal to each other. The Z direction runs parallel to an emission direction 36 in which the laser beam source 22 emits the laser beam 24. The emission direction 36 is orthogonal to the output coupler mirror 28.

[0098] The thickness of the laser-active medium 30 in the Z-direction is less than its length in the X-direction and its width in the Y-direction. The length and width are each more than six times the thickness. The thickness of the laser-active medium 30 is 500 pm.

[0099] The laser-active medium 30 has a first broadside 38 and a second broadside 40. The two broadsides 38, 40 are parallel to each other. Each of the two broadsides 38, 40 is parallel to a plane spanned by the X and Y directions. The two broadsides 38, 40 are opposite sides of the laser-active medium 30. Each broadside 38, 40 is planar; in particular, each broadside 38, 40 is formed by a planar surface section of the laser-active medium 30. The two broadsides 38, 40 are each oriented orthogonally to the Z direction.

[0100] The mirror 26 is arranged on the first broad side 38 in contact with the laser-active medium 30. This means that the mirror 26, in particular a mirror surface 42 of the mirror 26, faces the first broad side 38.

[0101] On the second broad side 40, the photonic element 32 is arranged in contact with the laser-active medium 30.

[0102] The photonic element 32 is made of quartz glass. The photonic element 32, in particular the photonic structure 34, is separated from the laser-active medium 30. The photonic structure 34 of the photonic element 32 is configured to determine at least one beam parameter of the laser beam 24. The photonic structure 34 is a two-dimensional photonic structure. The photonic structure 34 is a photonic crystal lattice. The photonic structure 34 is formed from a regular arrangement of holes in the photonic element 32. The regular arrangement of the holes results in a regular change in the refractive index within the photonic element 32, which causes the photonic structure 34 to determine at least one beam parameter of the laser beam 24.

[0103] In the illustrated embodiment, the beam parameter is the degree of collimation of the laser beam 24, which the laser beam exhibits when the laser beam 24 leaves the laser beam source 22. The photonic structure 34 causes the laser beam source 22 to emit the laser beam 24 in a collimated state.

[0104] The output coupling mirror 28 is arranged on the photonic element 32. As a result, the photonic structure 34, in particular its entirety, is arranged between the laser-active medium 30 and the output coupling mirror 28. Consequently, the output coupling mirror 28, in particular a mirror surface 44 of the output coupling mirror 28, faces the second broad side 40.

[0105] The laser beam source 22 has a heat sink 46 for dissipating heat from the laser-active medium 30. Typically, the laser-active medium 30 heats up during the generation of the laser beam 24, and this heat is dissipated by means of the heat sink 46 to prevent damage to the laser beam source 22.

[0106] The heat sink 46 is made of copper. A cooling fluid can flow through the heat sink 46. The cooling fluid is water.

[0107] The heat sink 46 is arranged on the mirror 26. This allows the heat generated in the laser-active medium 30 to be transferred through the mirror 26 into the heat sink 46. The heat can then be dissipated by the water flowing through the heat sink 46.

[0108] The laser beam source 22 has a first electrode 48 and a second electrode 52. The two electrodes 48 and 52 are designed to be connected to a power source, so that the laser beam source can be supplied with electrical energy via the two electrodes 48 and 52. When the laser beam source 22 is supplied with electrical energy via the two electrodes 48 and 52, the laser-active medium 30 will convert the electrical energy into optical energy by generating the laser beam 24.

[0109] The heat sink 46 is designed to be conductive. This allows the heat sink 46 to act as the first electrode 48. Therefore, the heat sink 46 has a dual function: conducting electrical current and dissipating heat. In other words, the heat sink 46 and the electrode 48 can be formed as a single unit. However, it is also conceivable that the laser beam source 22 has a first electrode 48 that is separate from the heat sink 46.

[0110] The second electrode 52 is made of copper. The second electrode 52 is arranged at the output coupling mirror 28. This places the output coupling mirror 28 between the laser-active medium 30 and the second electrode 52. The second electrode 52 is annular in shape. The second electrode 52 has a hole 54, which forms an exit aperture for the laser beam 24. When the laser beam source 22 generates the laser beam 24, the laser beam 24 exits through the hole 54.

[0111] The heat sink 46, the mirror 26, the laser-active medium 30, the photonic element 32, the output coupling mirror 28, and the second electrode 52 are permanently joined together, in particular, attached to one another. Thus, the heat sink 46, the mirror 26, the laser-active medium 30, the photonic element 32, the output coupling mirror 28, and the second electrode 52 are formed as a single component.

[0112] Fig. 1 shows that the laser beam sources 22 are attached to a carrier unit 56 of the EUV driver laser 10. The laser beam sources 22 are arranged on a flat surface 58 of the carrier unit 56, which is a plate. The carrier unit 56 is a plate.

[0113] The carrier unit 56 is detachably attached to a base plate 60 of the EUV driver laser 10. If one or more of the laser beam sources 22 are defective, the carrier unit 56 simplifies their replacement, thereby minimizing downtime of the EUV driver laser 10. The laser beam sources 22 can be replaced by swapping the carrier unit 56 with another carrier unit to which functional laser beam sources are attached. For this purpose, the carrier unit 56 can be detached from the base plate 60. After removing the carrier unit 56, the new carrier unit can be placed in its position and attached to the base plate 60. This allows all laser beam sources 22 to be replaced simultaneously.

[0114] The additional carrier unit and the functional laser beam sources can each be identical in construction to the carrier unit 56 and the laser beam sources 22.

[0115] Due to the photonic structures, the functional laser beam sources emit the laser beams in a collimated state, which simplifies the adjustment of the EUV driver laser 10 after a replacement of the laser beam sources.

[0116] The removed carrier unit 56 with the laser beam sources 22 can be inspected in a separate setup, and those laser beam sources 22 that are defective can be repaired or replaced without increasing the downtime of the EUV driver laser 10. The carrier unit 56 enables a modular design of the EUV driver laser 10.

[0117] The EUV driver laser 10 has a combination unit 62. The combination unit 62 is attached to the base plate 60. The combination unit 62 combines the laser beams 24 from the laser beam sources 22 into a single excitation beam 64. The combination unit 62 is configured to combine the laser beams 24 into the excitation beam 64 by means of a non-coherent beam combination. However, it is also conceivable that the combination unit 62 is configured to combine the laser beams 24 into the excitation beam 64 by means of a coherent beam combination.

[0118] In the illustrated embodiment, the laser beams 24 are combined to form the excitation beam 64 by spatial beam combination using the combination device 62. It is also conceivable that the laser beams 24 are combined to form the excitation beam 64 by spectral beam combination or polarization beam combination using the combination device 62.

[0119] The excitation beam 64 has an average power of over 180 W and a diffraction coefficient M 2 of less than 1.4. The excitation beam 64 has a wavelength in the range of 1900 to 2100 nm.

[0120] The EUV driver laser 10 has a focusing device 66. The focusing device 66 is designed to focus the excitation beam 64 onto a target material. The focusing device 66 is a mirror. The focusing device 66 is arranged in the target chamber 12.

[0121] Target chamber 12 is designed as a vacuum chamber. A vacuum is maintained within the interior of target chamber 12.

[0122] In the target chamber 12, a target material 68 is arranged in the form of a tin droplet.

[0123] The excitation beam 64 is focused onto the target material 68 by means of the focusing device 66. The excitation beam 64 strikes the target material 68 and brings the target material 68 into a plasma state such that the EUV light beam 18 is emitted by the target material 68.

[0124] In this example, the EUV driver laser 10 does not have an optical amplifier for amplifying the laser beams 24 or the excitation beam 64. In other words, the laser beams 24 leave the laser beam sources 22 and do not undergo any optical amplification after leaving them. Similarly, in this embodiment, the excitation beam 64 leaves the combination device 62 and does not undergo any optical amplification. Specifically, the power of the laser beams 24 and the power of the excitation beam 64 are not amplified. In other words, the EUV driver laser 10 does not have an optical amplifier between the laser beam sources 22 and the target material 68.In embodiments not specifically shown, the EUV driver laser 10 thus has optical amplifiers, wherein the optical amplifiers can each be assigned to at least one or more laser beam sources 22 and can thus optically amplify the laser beam 24 of at least one laser beam source 22 or of several laser beam sources 22.

[0125] The EUV driver laser 10 may include a beam guidance device not shown in Fig. 1. The beam guidance device may be configured to guide the laser beams 24 from the laser beam sources 22 to the combination device 62 and / or to guide the excitation beam 64 from the combination device 62 to the focusing device 66. The beam guidance device may include a plurality of optical components, in particular lenses and / or mirrors. Consequently, the EUV driver laser 10 and the system 500 comprising the EUV driver laser 10 are used to expose the photosensitive coating 16, which is supported by the semiconductor substrate 14.

[0126] Fig. 3 shows a further embodiment of the laser beam source 22 of Figs. 1 and 2, wherein identical and functionally equivalent elements are represented by the same reference numerals, and in this respect reference is made to the above descriptions of the embodiment of Fig.

[0127] Reference can be made to sections 1 and 2, so that essentially only the existing differences will be addressed.

[0128] The laser beam source 22 of Fig. 3 has no photonic element 32. The laser-active medium 30 has the photonic structure 34.

[0129] The output coupling mirror 28 is arranged on the second broad side 40, forming a contact with the laser-active medium 30. This allows the laser-active medium 30 to extend from the mirror 26 to the output coupling mirror 28.

Claims

Patent claims 1. EUV driver laser (10) for generating an EUV light beam (18) emitting plasma state of a target material (68), comprising: a plurality of laser beam sources (22) for generating a plurality of laser beams (24), a combination device (62) for combining the plurality of laser beams (24) into an excitation beam (64) for generating the plasma state, and a focusing device (66) for focusing the excitation beam (64) onto the target material (68) for generating the plasma state, wherein each laser beam source (22) has: a mirror (26), a coupling mirror (28), a laser-active medium (30) arranged between the mirror (26) and the output coupler mirror (28), and a photonic structure (34) designed to determine at least one beam parameter of the laser beam (24), wherein the mirror (26) faces a first broadside (38) of the laser-active medium (30), wherein the output coupling mirror (28) faces a second broadside (40) of the laser-active medium (30).

2. EUV driver laser (10) according to claim 1, wherein the photonic structure (34) of each laser beam source (22) is arranged at least sectionally between the laser-active medium (30) and the output coupler mirror (28), and / or wherein the photonic structure (34) of each laser beam source (22) is arranged at least sectionally between the laser-active medium (30) and the mirror (26), and / or wherein the laser-active medium (30) of each laser beam source (22) has the photonic structure (34) at least section by section.

3. EUV driver laser (10) according to one of the preceding claims, wherein each laser beam source (22) is configured by the photonic structure (34) to emit the laser beam (24) in a collimated state.

4. EUV driver laser (10) according to any one of the preceding claims, wherein in each laser beam source (22) the mirror (26), the output coupling mirror (28), the laser-active medium (30) and the photonic structure (34) are inextricably joined together.

5. EUV driver laser (10) according to any one of the preceding claims, wherein each laser beam source (22) has a heat sink (46) for dissipating heat generated during the generation of the laser beam (24), wherein the heat sink (46) is arranged on the mirror (26), in particular attached to it.

6. EUV driver laser (10) according to any one of the preceding claims, wherein the laser-active medium (30) has a plurality of thin layers.

7. EUV driver laser (10) according to any one of the preceding claims, the EUV driver laser (10) is amplifierless.

8. EUV driver laser (10) according to one of the preceding claims, wherein the combination device (62) is configured to to combine the laser beams (24) to form the excitation beam (64) by means of a coherent beam combination and / or a non-coherent beam combination, and / or to combine the laser beams (24) to form the excitation beam (64) by means of a spectral beam combination, a polarization beam combination, an intensity beam combination and / or a spatial beam combination.

9. EUV driver laser (10) according to any one of the preceding claims, wherein the EUV driver laser (10) has a carrier unit (56), wherein the majority of laser beam sources (22) are attached to the carrier unit (56).

10. EU VT reiberlaser (10) according to one of the preceding claims, wherein a number of the laser beam sources (22) has a value in the range of 2 to 1000.

11. EU VT friction laser (10) according to one of the preceding claims, wherein the excitation beam (64) has a wavelength in a range of 1600 nm to 4000 nm, in particular 1800 nm to 3000 nm, preferably 1800 nm to 2400 nm.

12. Device (500) for exposing a photosensitive coating (16) by means of an EUV light beam (18), wherein the photosensitive coating (16) is supported by a semiconductor substrate (14), comprising: an EUV driver laser (10) according to any one of claims 1 to 11, and a target chamber (12) in which the target material (68) is arranged for generating the EUV light beam (18).

13. Use of an EU driver laser (10) according to one of claims 1 to 11 or a device (500) according to claim 12 for exposing a photosensitive coating (16) arranged on a semiconductor substrate (14), in particular supported by the semiconductor substrate (14).

14. Method for generating an EUV light beam (18) emitting plasma state of a target material (68), wherein the method comprises: Generating a plurality of laser beams (24) by means of a plurality of laser beam sources (22), wherein each laser beam source (22) comprises a mirror (26), an output coupler (28), a laser-active medium (30) arranged between the mirror (26) and the output coupler (28), and a photonic structure (34) configured to determine at least one beam parameter of the laser beam (24), wherein the mirror (26) faces a first broadside (38) of the laser-active medium (30), wherein the output coupler (28) faces a second broadside (40) of the laser-active medium (30), combining the plurality of laser beams (24) into an excitation beam (64) for generating the plasma state, and Generating the plasma state by irradiating the target material (68) with the excitation beam (64).

15. Method for irradiating a photosensitive coating (16) supported by a semiconductor substrate (14), the method comprising: Generating a plurality of laser beams (24) by means of a plurality of laser beam sources (22), wherein each laser beam source (22) comprises a mirror (26), an output coupler (28), a laser-active medium (30) arranged between the mirror (26) and the output coupler (28), and a photonic structure (34) configured to determine at least one beam parameter of the laser beam (24), wherein the mirror (26) faces a first broadside (38) of the laser-active medium (30), wherein the output coupler (28) faces a second broadside (40) of the laser-active medium (30), combining the plurality of laser beams (24) into an excitation beam (64) for generating the plasma state, Generating the EUV light beam (18) by irradiating the target material (68) with the excitation beam (64), and - Exposure of the photosensitive coating (16) by directing the EUV light beam (18) onto the photosensitive coating (16).

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