EUV driver laser, system having an EUV driver laser, use, method for generating an amplified light beam, method for exposing semiconductor substrates coated with a photosensitive coating to EUV light, and method for producing microchips or semiconductor intermediate products

Abstract

The invention relates to an EUV driver laser (16) for generating a plasma of a target material (20) emitting EUV light (14). The EUV driver laser (16) has a beam source arrangement (30) having at least one beam source (32), which is designed to generate a light beam (34) having a first wavelength λ1. Furthermore, the EUV driver laser (16) has an amplifier arrangement (36) having at least one optical amplifier (38) which has a first active medium (48), wherein the optical amplifier (38) is designed to optically amplify at least a portion of the light beam (34) passing through the optical amplifier (38) to form an amplified light beam (18). A pump source arrangement (40) is provided, which has at least one optical pump source unit (42) which has a second active medium (50), wherein the optical pump source unit (42) is designed to generate a pump beam (44) having a second wavelength λ2 and to supply the optical amplifier (38) with optical pump energy.

Description

[0001] EUV driver laser, system with an EUV driver laser, use, method for generating an amplified light beam, method for irradiating semiconductor substrates coated with a photosensitive coating with EUV light and method for manufacturing microchips or semiconductor intermediates

[0002] BACKGROUND OF THE INVENTION

[0003] 1. Field of the invention

[0004] The invention relates to an EUV driver laser for generating an EUV light-emitting plasma of a target material, with

[0005] a) a beam source arrangement with at least one beam source configured to produce a beam of light with a first wavelength Ai,

[0006] b) an amplifier arrangement with at least one optical amplifier comprising a first active medium, wherein the optical amplifier is configured to optically amplify at least a portion of the light beam passing through the optical amplifier to become an amplified light beam,

[0007] c) a pump source arrangement comprising at least one optical pump source unit comprising a second active medium, wherein the optical pump source unit is configured to generate a pump beam with a second wavelength X2 and to supply the optical amplifier with optical pump energy, and

[0008] d) a focusing unit designed to focus the amplified light beam into a target chamber for the target material and onto the target material to generate the EUV light-emitting plasma.

[0009] The invention also relates to a system for exposing semiconductor substrates coated with a photosensitive coating to EUV light.

[0010] Furthermore, the invention relates to the use of such an EUV driver laser or such a system for irradiating semiconductor substrates coated with a photosensitive coating with EUV light. The invention further relates to a method for generating an amplified light beam for generating an EUV light-emitting plasma of a target material, comprising the steps of:

[0011] a) Generating at least one light beam with a first wavelength Ai by means of a beam source arrangement which has at least one beam source for this purpose;

[0012] b) Amplifying at least a portion of the light beam to produce an amplified light beam by means of an amplifier arrangement comprising at least one optical amplifier for this purpose with a first active medium;

[0013] c) Generating a pump beam with a second wavelength X2 and supplying the optical amplifier with pump energy, wherein the generation of the pump beam is carried out by means of a pump source arrangement which has at least one optical pump source unit for this purpose with a second active medium;

[0014] d) Guiding the amplified light beam towards a focusing unit designed to focus the amplified light beam into a target chamber for the target material and onto the target material to generate the EUV light-emitting plasma.

[0015] Furthermore, the invention relates to a method for exposing semiconductor substrates coated with a photosensitive coating to EUV light, as well as a method for manufacturing microchips or semiconductor intermediates for manufacturing microchips.

[0016] 2. State of the art

[0017] In the production of integrated circuits, so-called microchips, semiconductor substrates (hereinafter referred to as "wafers"), which are often monocrystalline, are coated with a layer in a relatively early manufacturing step. This layer is then structured in subsequent manufacturing steps. Such structuring acts as a mask in further downstream manufacturing steps, enabling the functional layer beneath the coating to be etched, doped with foreign atoms (e.g., by ion implantation), or introduced into the structure by foreign materials (e.g., by LIGA and lift-off).

[0018] The aim of these process steps is, among other things, to fabricate transistors and conductive areas that connect the transistors on the wafers. The structuring can be introduced into the coating using various methods.

[0019] In photolithography, for example, the coating is a photosensitive coating, specifically a photoresist. Here, the photoresist is exposed to light of a specific wavelength, to which it is sensitive, in a particular pattern. This allows the chemical properties of the exposed areas of the photoresist, such as its solubility in a developer solution, to be influenced. Some photoresists polymerize the exposed areas, meaning their solubility increases compared to the unexposed areas (so-called negative resists). Others become less soluble in the exposed areas compared to the unexposed areas (so-called positive resists).In any case, to form the structure in the photoresist and thus the mask for the functional layer located under the photoresist, the more soluble areas of the photoresist are removed using the developer solution.

[0020] To introduce the specific pattern into the photoresist, a masking element (hereinafter referred to as "photomask") is usually placed between the light source and the wafer, which, depending on the photoresist used (negative or positive), is designed as a negative or positive of the structure to be formed on the photoresist.

[0021] In conventional photolithography, the photomask either lies directly on the photoresist or is positioned just above it, i.e., spaced apart from it, resulting in a 1:1 relationship between the photomask and the resulting pattern on the photoresist. Since photomasks can only be scaled to a finite size, this method is essentially limited to feature sizes of a few hundred nanometers. Because smaller patterns enable microchips with significantly higher performance per unit area or volume (since more transistors can be implemented on the same small area), there is a general drive to reduce the size of the pattern to its absolute physical limits.

[0022] For this reason, projection exposure systems are generally used nowadays, in which a focusing optic is usually positioned between the photomask and the photoresist. This allows the photomask to be drastically reduced in size and projected onto the photoresist. This enables the photomasks to be manufactured more cheaply, as the structures of the photomask do not need to be as small. Furthermore, it allows for significantly smaller structures to be imaged onto the wafers compared to conventional photolithography. The photomask and the resulting structure on the photoresist can then be present in a ratio of, for example, 5:1 or greater. The photomask itself can be designed as an absorptive or a reflective photomask.

[0023] Since the reduced image size of the photomask on the photoresist does not allow the entire wafer to be covered, prior art methods often employ a so-called "step-and-repeat" process: the wafer is exposed at a first exposure position, moved a certain distance, and then exposed again at a second exposure position. This process is repeated until the wafer is largely covered with instances of the same pattern.

[0024] After the areas of the photoresist that are more soluble than the developer solution have been removed and the underlying functional layer has been treated, for example by etching, the photoresist is often removed from the functional layer by a process called "stripping".

[0025] For multi-layered microchips, the projection exposure method described above can be performed up to one hundred times for the same microchip.

[0026] EUV lighting system and EUV generation

[0027] Besides reducing the size of the photomask and using focusing optics, another way to reduce the size of the pattern on the wafers is to use light with a shorter wavelength for exposure.

[0028] In methods known from the prior art, extreme ultraviolet light (EUV light) with a wavelength in a range of about 8 nm to about 15 nm is generated, with a main proportion of the EUV light being at 13.5 nm, which is directed onto the photoresist by means of an EUV projection optic and an EUV focusing optic of the projection exposure system.

[0029] A system used for this purpose, to expose photosensitive semiconductor substrates to EUV light, essentially comprises an EUV driver laser, which can generate at least one light beam, a target material generator, and a target chamber. Typically, a pulsed high-power laser is used as the EUV driver laser, and a target material generator is used to supply units of the target material to the target chamber. In particular, a droplet generator is frequently used as the target material generator, which can inject droplets, representing units of the target material, into the target chamber.To avoid damage to the system due to particle contamination, a high vacuum can prevail within the target chamber under a process gas atmosphere in conversions known from the prior art, whereby hydrogen (H2) or helium (He) are particularly suitable as the process gas.

[0030] In prior art processes, a tin (Sn) target material is frequently used. However, in addition to tin (Sn), target materials containing xenon (Xe), gold (Au), and / or lithium (Li) are also possible. To increase the amount of emitted EUV light, the droplets generated by the droplet generator can be excited in very rapid succession, for example, first with a pre-pulse and then with a main pulse. The two beams can be independent or generated by splitting a single beam and delaying one of them. In principle, EUV light can be generated with only a single excitation beam; a second beam is therefore not strictly necessary.By using a second light beam, the conversion efficiency—i.e., the ratio of input laser power to generated EUV power—increases significantly in prior art methods where EUV driver lasers with CO2 as the active medium are used in an optical amplifier. In these known methods, the light beam has a wavelength of approximately 10.6 pm.

[0031] This is because, in these known methods, the pre-pulse excitation causes a preconditioning of the target material droplet. Currently, this preconditioning involves the target material droplet forming an approximately disk-like shape due to the energy input from the pre-pulse, thereby comparatively increasing the surface area of ​​the target material droplet that can be excited by the main pulse. The main pulse then strikes the preconditioned target material droplet, thereby exciting it. In the known methods, this excitation includes the generation of an ionized gas of the target material—if the target material contains tin (Sn), this generates a tin plasma. This tin plasma then emits, as part of a so-called "plasma glow," the EUV light required for the formation of the structure in the photoresist.

[0032] In another known method, a third light beam, in the form of a so-called rarefaction pulse, can be used for further preconditioning. This pulse strikes the target material droplet between the pre-pulse and the main pulse. In this known method, the rarefaction pulse causes a density dilution or volume increase of the target material droplet, which has been shaped into a disk by the pre-pulse, towards a target material cloud. The term "cloud" here is not to be equated with a gaseous or vapor state of the target material. The use of such a rarefaction pulse further increases the conversion efficiency of the methods known from the prior art.

[0033] The dilution pulse can be generated by splitting the first light beam into the pre-pulse and the dilution pulse. However, it is also possible to use a separate light source for the dilution pulse or even to split a single light beam into the pre-pulse, the dilution pulse, and the main pulse. Furthermore, the dilution pulse can also be designed as a temporally preceding segment of the main pulse, with a distinct intensity distribution over time. In this case, it is often referred to as a "pedestal."

[0034] In each of the above cases, the main pulse hits the target material droplet with an average power in the range of 20 kW to 50 kW.

[0035] Problem arising from the state of the art

[0036] A disadvantage of EUV driver lasers known from the prior art is that the conversion efficiency of the total electrical power input to the EUV driver laser to generate an amplified light beam for illuminating the target material, to the optical power of the generated amplified light beam (so-called "wall-plug efficiency"), is comparatively low. In known devices and methods, a significant portion of the total electrical power input to the EUV driver laser is therefore not converted into optical power, but remains as heat loss within the EUV driver laser, particularly in an optical amplifier. This severely limits the achievable power of the amplified light beam, since the optical amplification efficiency decreases with increasing temperature in the active medium of the optical amplifier.On the other hand, this also limits the scalability of a number of EUV driver lasers, for example in semiconductor factories, due to the high energy consumption, especially with regard to modern efforts toward sustainable production. Accordingly, there is a need to increase the overall wall-plug efficiency of the EUV driver laser and thus achieve higher power levels of the amplified light beam while simultaneously reducing the electrical power required relative to the generated optical power. SUMMARY OF THE INVENTION.

[0037] The object of the invention is therefore to provide an EUV driver laser, a system, a use of the EUV driver laser or the system, a method for generating an enhanced light beam for generating an EUV light-emitting plasma of a target material, a method for irradiating semiconductor substrates coated with a photosensitive coating with EUV light and a method for manufacturing microchips or semiconductor intermediates for manufacturing microchips, which overcome the aforementioned disadvantages of the prior art.

[0038] This problem is solved according to the invention by the EUV driver laser mentioned at the outset, in which

[0039] e) the first active medium has a plurality of laser bands No to N2, each comprising one or more quantum states, wherein the quantum states have at least a lower laser level Eo, an upper laser level Ei and a high level E2, wherein Eo < Ei < E2, wherein the pump source arrangement is configured to supply the first active medium of the optical amplifier with optical pump energy by means of the optical pump source unit such that the first active medium transitions directly from a lower laser band No to an upper laser band Ni.

[0040] In this context, an active medium is understood to be a medium in which particles of the medium can be brought into a state of population inversion by an input of electrical or optical energy, i.e., a state in which more particles are in an energetically higher quantum state than in an energetically lower quantum state, in particular in an energetically higher laser band than in an energetically lower laser band, which is the basis for the generation of stimulated emission of photons.

[0041] In this context, quantum states are understood to be distinct quantum mechanical levels that particles of the active medium can occupy. The upper laser level Ei is understood here as the quantum state that defines an upper limit of a laser transition; similarly, the lower laser level Eo is understood as the quantum state that defines a lower limit of the laser transition. When a particle of an active medium transitions from the upper laser level Ei to the lower laser level Eo, a photon can be emitted whose wavelength corresponds to the energy difference between the upper laser level Ei and the lower laser level Eo. The high level E2 is understood to be a quantum state that is energetically higher than the upper laser level Ei and into which particles of an active medium briefly transition during the pumping process before falling back to the upper laser level Ei.

[0042] Preferably, the lower laser level Eo and the upper laser level Ei are located in different laser bands. Particularly preferably, the lower laser level Eo is located in the lower laser band No, and the upper laser level Ei is located in the upper laser band Ni, which is different from the lower laser band No and has a higher energy. Preferably, the high level E2 is located together with the upper laser level Ei in the upper laser band Ni. In this case, the active medium would fall back from the high level E2, into which it is pumped, within the upper laser band Ni, and then into the upper laser level Ei. Preferably, the optical pump source unit is configured to supply the first active medium with pump energy such that the first active medium transitions directly into the high level E2 located in the upper laser band Ni.

[0043] In other words, the laser bands No, Ni, and N2 each comprise one or more quantum states that, while distinguishable from one another, are at the same or very similar energy levels and, in this case, can typically follow a statistical and thermal population distribution (Bolzmann distribution). Conversely, this means that a two-band system, as defined above, is not equivalent to a two-level system.

[0044] In the solution proposed by the invention, the first active medium of the optical amplifier is supplied with optical pump energy in such a way that it transitions directly into the upper laser band Ni, i.e., without first transitioning into the high band N2, which is energetically above the upper laser band Ni, or into further laser bands located above the high band N2, as is known, for example, from conventional pumping processes, in which a relaxation process of the active medium is generally utilized. According to the invention, this prevents energy released during a transition from the high level E2 or further quantum states, possibly located above the high level E2, but especially in the high band N2, into the upper laser level Ei from remaining as power loss, particularly as heat, in the optical amplifier and thus impairing the amplification efficiency of the optical amplifier or the Wal I-Plug efficiency of the EUV driver laser.The solution according to the invention therefore provides a particularly energy-efficient EUV driver laser, in which particularly high power levels of the amplified light beam can be achieved at the same time.

[0045] When it is stated that the first active medium transitions from one quantum state to another, this is to be understood as meaning that a majority of particles in the active medium change the quantum state in the described manner. This applies equally when the first active medium transitions from one laser band to another. A wavelength is understood here as the average wavelength of any emission spectrum that may be present.

[0046] Preferably, the quantum states of the first active medium have a ground level Eo', wherein the ground level Eo' and the lower laser level Eo lie in a lower laser band No. In particular, the lower laser level Eo and the ground level Eo' are different from each other. This further prevents power loss in the form of heat from remaining in the system, since the first active medium cannot then transition from the lower laser band No to an even lower-energy laser band No'.

[0047] Preferably, the first active medium transitions directly from the ground level Eo', which is particularly different from the laser level Eo, to the upper laser level Ei, which is advantageously arranged in the upper laser band Ei, when it is supplied with optical pump energy by the optical pump source unit.

[0048] Preferably, the first active medium between an upper laser band Ni and a high band N2 has at least two further laser bands in the form of a first intermediate band Hi and a second intermediate band H2.

[0049] It is particularly advantageous if the value of the second wavelength X2 of the pump beam is smaller than the value of the first wavelength Ai of the light beam by a factor in the range of 0.7 to 0.97, especially in the range of 0.725 to 0.95, particularly in the range of 0.75 to 0.95, and particularly in the range of 0.775 to 0.85. This allows the amplification efficiency of the EUV driver laser to be increased even further, since the energy difference between the wavelength X2 of the optical pump beam and the wavelength Ai of the light beam is comparatively small in such a configuration.

[0050] Preferably, the first active medium has an emission spectrum for the light beam and an absorption spectrum for the pump beam, wherein the emission and absorption spectra overlap at least partially. This further facilitates the transition of the first active medium directly into the upper laser band Ni when it is supplied with optical pump energy by the optical pump source unit.

[0051] Advantageously, the emission spectrum of the first active medium includes the first wavelength Ai of the light beam and the second wavelength X2 of the pump jet.

[0052] As with the emission spectrum, the absorption spectrum of the active medium of the optical amplifier can additionally or alternatively include the first wavelength Ai of the light beam and the second wavelength X2 of the pump beam. To further increase the wall-plug efficiency and thus further reduce the power loss remaining as heat in the EUV driver laser, it is advantageous if a quantum defect is present in the first active medium between the first wavelength Ai of the light beam and the second wavelength X2 of the pump beam when the optical amplifier amplifies the light beam and the pump beam supplies the optical amplifier with optical pump energy. The quantum defect has a value in the range of 1.5% to 30%, particularly in the range of 5% to 25%, and especially in the range of 7.5% to 22.5%, and particularly in the range of 12.5% ​​to 20%. The quantum defect is thus comparatively small.

[0053] In a beneficial further development of the EUV driver laser, the first and second active media are identical. When the first and second active media are the same, the first wavelength Ai of the light beam and the second wavelength X2 of the pump beam can be particularly close together. It is advantageous if the upper laser level Ei of the first active media and the upper laser level Ei of the second active media are different. This allows for a particularly simple design of the EUV driver laser, since the first and second active media can, for example, be produced using the same process, which can significantly reduce the manufacturing costs of the EUV driver laser.

[0054] Additionally or alternatively, in an advantageous further development of the EUV driver laser, the beam source comprises a third active medium, wherein the first and third active media and / or the second and third active media are identical. Preferably, the first and third active media are identical. If the first and third active media are identical, it is advantageous if the upper laser level Ei of the first active media and the upper laser level Ei of the third active media are identical. If the second and third active media are identical, it is advantageous if the upper laser level Ei of the second active media and the upper laser level Ei of the third active media are different.

[0055] Preferably, the first active medium comprises thulium (Tm) or holmium (Ho). Furthermore, in a further development of the EUV driver laser according to the invention, the second active medium preferably comprises thulium (Tm), holmium (Ho), or erbium (Er). In addition, the third active medium preferably comprises thulium (Tm) or holmium (Ho).

[0056] In an alternative advantageous further development of the EUV driver laser, the second active medium comprises an III-V compound semiconductor selected from a group of III-V compound semiconductors including: GaN, AIN, InN, BN, ScN, GaP, AIP, InP, InGaP, BP, GaAs, AlAs, InAs, BAs, GaSb, AlSb, InSb, InGaAsP. In particular, the second active medium comprises InP or InGaAsP. The second active medium can then advantageously be comprised of a photonic structure. Furthermore, the second active medium can then be supplied with electrical pumping energy by an applied electric field.

[0057] For example, the first, second, and third active medium may include the following advantageous material combinations in the order they are immediately mentioned:

[0058] i) Thulium (Tm), InP, Thulium (Tm);

[0059] ii) Thulium (Tm), InP, Holmium (Ho);

[0060] iii) Holmium (Ho), InP, Thulium (Tm);

[0061] iv) Holmium (Ho), InP, Holmium (Ho);

[0062] v) Thulium (Tm), InGaAsP, Thulium (Tm);

[0063] vi) Thulium (Tm), InGaAsP, Holmium (Ho);

[0064] vii) Holmium (Ho), InGaAsP, Thulium (Tm);

[0065] viii) Holmium (Ho), InGaAsP, Holmium (Ho);

[0066] ix) Thulium (Tm), Erbium (Er), Thulium (Tm);

[0067] x) Thulium (Tm), Erbium (Er), Holmium (Ho);

[0068] xi) Holmium (Ho), Erbium (Er), Thulium (Tm);

[0069] xii) Holmium (Ho), Erbium (Er), Holmium (Ho);

[0070] xiii) Sulfur (Tm), Sulfur (Tm), Sulfur (Tm);

[0071] xiv) Sulfur (Tm), Sulfur (Tm), Holmium (Ho);

[0072] xv) Holmium (Ho), Sulfur (Tm), Sulfur (Tm); xvi) Holmium (Ho), Thulium (Tm), Holmium (Ho);

[0073] xvii) Sulfur (Tm), Holmium (Ho), Sulfur (Tm);

[0074] xviii) Sulfur (Tm), Holmium (Ho), Holmium (Ho);

[0075] xix) Holmium (Ho), Holmium (Ho), Thulium (Tm);

[0076] xx) Holmium (Ho), Holmium (Ho), Holmium (Ho).

[0077] Advantageously, the optical pump source unit comprises a non-linear optical element. In this context, a non-linear optical element is defined as one in which, starting from an excitation with light of a first frequency, light with a second frequency different from this first frequency is generated within the non-linear optical element. Such a non-linear optical process can, for example, be the inelastic scattering of light by particles of the non-linear optical element. Advantageously, such inelastic scattering can generate light with a lower energy and / or frequency and / or wavelength.

[0078] In an advantageous further development, the non-linear optical element comprises the second active medium of the optical pump source unit.

[0079] Preferably, the pump beam of the optical pump source unit is a signal beam that can be generated within the non-linear optical element by means of inelastic scattering, in particular Raman scattering.

[0080] Advantageously, the optical pump source unit has an electrical or optical pump source designed to supply the second active medium of the optical pump source unit with pumping energy.

[0081] In an advantageous embodiment of the EUV driver laser according to the invention, the pump source is an optical pump source configured to generate a second pump beam with a third wavelength A3. This is particularly advantageous when the first pump beam of the optical pump source unit is a signal beam. In an advantageous embodiment of the EUV driver laser, the optical pump source unit comprises several non-linear optical elements and a beam splitter arrangement for the second pump beam of the optical pump source, which can generate the second pump beam with wavelength A3. By means of the beam splitter arrangement, two or more partial beams of the second pump beam can be generated, which can then be coupled into correspondingly assigned non-linear optical elements.

[0082] Advantageously, with respect to the first wavelength Ai of the light beam, the second wavelength X2 of the first pump beam, and the third wavelength X3 of the second pump beam, which can supply the second active medium of the optical pump source unit with optical pump energy, the following holds: X3 < X2 < Ai. In other words, a value of the third wavelength X3 of the second pump beam is advantageously smaller than a value of the second wavelength X2 of the first pump beam, which in turn is smaller than a value of the first wavelength Ai of the light beam.

[0083] In an advantageous embodiment of the EUV driver laser, the second pump beam is an idler beam when it exits the non-linear optical element, wherein a value of the second wavelength X2 of the signal beam corresponds to a value of the third wavelength X3 that is frequency-shifted by n Stokes orders, where n > 1, in particular n > 1, where n is an integer multiple of 1 when n > 1. It is particularly advantageous in this context if a value of the second wavelength X2 is greater than a value of the third wavelength X3. This embodiment of the EUV driver laser according to the invention makes it possible to use a particularly advantageous optical pump source for the optical pump source unit.

[0084] Preferably, the pump source arrangement comprises a plurality of optical pump source units, each optical pump source unit being configured to emit a pump beam i with a second wavelength X2 1to generate the second wavelengths X2 1 The pump jets can be the same. The second wavelengths X2 1 However, they can also differ from each other, with the second wavelengths being X2. 1 They can differ from each other according to an increment j. The second wavelength X2 1 A second optical pump source unit can therefore be expanded by the increment j of a second wavelength X2 1 a first optical pump source unit may differ, whereby the second wavelength of the second optical pump source unit is equal to Ä2 l+jto be designated, and so on. The increment j is preferably a factor with a value in the range of 0.73 • Ai to 0.9 • Ai. Preferably, the increment j lies in the range of 0.5 nm to 400 nm, in particular 2.5 nm to 200 nm, and in particular 5 nm to 100 nm. A particular advantage of these possible embodiments is that a comparatively higher optical pump source arrangement can provide a comparatively higher optical pump energy for the optical amplifier.

[0085] Preferably, a plurality of pump source arrangements and a plurality of optical amplifiers are provided, wherein each pump source arrangement is assigned to exactly one optical amplifier, and wherein the optical amplifiers are each configured to optically amplify at least a portion of the light beam passing through the respective optical amplifier to produce an amplified light beam. A portion of the light beam passing through one of the optical amplifiers can, for example, be understood to be a partial beam that is generated by splitting the light beam in the propagation direction upstream of the corresponding optical amplifier using a beam splitter.

[0086] In a further advantageous embodiment of the EUV driver laser according to the invention, each pump source arrangement has a beam combination unit by means of which the pump beams i of the optical pump source units of the respective pump source arrangement can be combined to form a combined pump beam. The combined pump beam can then supply the corresponding optical amplifier with optical pump energy.

[0087] Preferably, each pump source arrangement is configured to combine the pump beams i by means of spatial beam combination, spectral beam combination, coherent beam combination, or polarization beam combination. To achieve particularly high pumping efficiency, it is advantageous to combine the pump beams spectrally or coherently, or by polarization, since a purely spatial beam combination generally does not increase the brightness of the combined pump beam.

[0088] Preferably, the pump beams of the optical pump source units can be combined with each other in such a way that

[0089] a) they propagate essentially without superposition, parallel to each other and side by side along a propagation direction,

[0090] or

[0091] b) they overlap spatially and especially temporally, such that the pump jets interfere with each other in a substantially constructive manner.

[0092] The pump jets can be combined, for example, "side-by-side" as described in the preceding feature a). This means that the pump jets do not overlap spatially, or only to a negligible extent, but propagate parallel to each other and alongside each other along the propagation direction. The pump jets can preferably be combined in such a way that they are in phase with each other.

[0093] Furthermore, in accordance with the immediately preceding feature b), it is also possible that the pump jets are combined in a particularly coherent manner by means of a so-called filled aperture.

[0094] Such a filled aperture can be generated, for example, by a mirror arrangement comprising multiple mirror zones, each with a different reflectivity, ranging from nearly completely transmissive to nearly completely reflective. Ideally, a first mirror zone has a reflectivity of nearly 0% and is coated with an anti-reflective coating, while a final mirror zone ideally has a reflectivity adapted to the power of the pump jet, which has already been combined coherently up to this mirror zone. Advantageously, the number of mirror zones can correspond to the number of pump jets to be combined.Furthermore, the reflectivities of one or more mirror zones arranged between the first mirror zone and the last mirror zone can also be adapted to the power of the pump jets already combined up to the corresponding mirror zones and, in particular, be smaller than the reflectivity of the last mirror zone.

[0095] However, such a filled aperture can also be realized by at least one, preferably several, diffractive optical elements (DOEs), for example diffraction gratings or diffraction lenses, wherein a first or several first diffractive optical elements can diffract the pump beams in such a way that they propagate onto at least a second diffractive optical element, through which the pump beams can be diffracted in such a way that they are combined in a single combined pump beam, in particular coherently.

[0096] When coherently combining pump beams, it is advantageous to arrange one or more phase modulation units within a beam path of one, several, or all pump beams in order to compensate for possible differences in the propagation time of the pump beams by means of phase modulation, for example, a temporal delay. This advantageously ensures that the pump beams interfere constructively with each other—destructive interference, which would lead to at least partial mutual cancellation of at least two pump beams, would be detrimental in this respect.

[0097] However, the pump jets do not necessarily have to be coherent with each other, but can, for example, have different polarizations with the same or different phases.

[0098] In a further advantageous development of the EUV driver laser, each pump source assembly can have a support structure to which the majority of optical pump source units, in particular all optical pump source units of the respective pump source assembly, are attached. Specifically, a common support structure carries all optical pump source units of the respective pump source assembly. This allows the pump source assembly(s) to be designed modularly and, in case of maintenance, to be easily removed and reattached, for example, for replacement purposes.

[0099] With advantageous further development of the EUV driver laser, the EUV driver laser exhibits the following additional features:

[0100] a) a beam source pump source which is configured to supply the beam source with beam source pumping energy such that the light beam is generated, in particular without scattering, by converting the beam source pumping energy,

[0101] b) a beam splitter arrangement designed to split the light beam, particularly in the propagation direction, into several partial beams in front of the amplifier arrangement,

[0102] where

[0103] c) the amplifier arrangement comprises several optical amplifiers, each of which is configured to amplify at least one of the partial beams to form an amplified partial beam.

[0104] An advantageous further development of the EUV driver laser according to the invention further comprises a combination unit which is configured to combine the amplified partial beams to form the amplified light beam.

[0105] Preferably, the light beam and / or the amplified light beam has a wavelength in the range of 1200 nm to 5000 nm, in particular 1500 nm to 4500 nm, in particular 1650 nm to 3500 nm, in particular 1800 nm to 2400 nm.

[0106] In an EUV driver laser that generates a light beam and / or an amplified light beam with a wavelength in the range specified above, the conversion efficiency can be significantly lower compared to the CC-EUV driver lasers known from the prior art and described at the beginning, due to a wavelength-specific increase in the self-absorption of the generated plasma towards EUV light. In other words, for the same power input, comparatively less net EUV light can be provided for the exposure of semiconductor substrates when the target material is excited with light of lower wavelengths, including in the range from 1200 nm to 5000 nm. With the known CC-EUV driver lasers, it was therefore necessary to precondition the target material accordingly in order to achieve this comparatively high conversion efficiency.

[0107] The target materials commonly used can exhibit higher absorptivity at these lower wavelengths than at the longer wavelengths known from the prior art. It is therefore particularly advantageous to split the light beam into several partial beams, amplify these individually in optical amplifiers, and subsequently combine the amplified partial beams into a single amplified light beam. This advantageously compensates for the comparatively lower overall conversion efficiency compared to known CC-EUV driver lasers and allows significantly more power to be delivered to the target material through the amplified light beam than with previously known CO2-EUV driver lasers and corresponding methods, without necessarily requiring preconditioning of the target material.

[0108] Similarly, an amplified light beam with a wavelength in the range specified above can have a significantly higher conversion efficiency than a light beam with a wavelength in the range of, for example, 900 nm to 1100 nm, because in this range the self-absorption of the generated plasma for the generated EUV light is comparatively too high and therefore particularly difficult to compensate for by a higher power of the amplified light beam. Consequently, the wavelength range of 1200 nm to 5000 nm can offer an advantageous compromise between EUV conversion efficiency and energy efficiency.

[0109] If multiple optical amplifiers are present, they are preferably connected in parallel.

[0110] It is particularly advantageous if the optical amplifier(s) include at least one solid-state amplifier, especially a rod or fiber amplifier. The technical distinction between what is referred to as "fiber" and what is referred to as "rod" is fluid. Fiber amplifiers typically exhibit a certain degree of flexibility, meaning they can be bent around a certain radius without being damaged, whereas rod amplifiers have a ratio of transverse to longitudinal dimensions such that they are essentially rigid and therefore inflexible. Since the classification as a rod or fiber amplifier ultimately depends on the ratio of transverse to longitudinal dimensions, both conceivable variants are encompassed here by the term rod or fiber amplifier.If the EUV driver laser includes at least one optical amplifier designed as a solid-state amplifier, the maximum achievable power for the light beam can theoretically be scaled arbitrarily, since the effort required to include further optical amplifiers in the amplifier arrangement is comparatively low. Consequently, the power output of generated EUV light can also theoretically be scaled arbitrarily.

[0111] The term "scatter-free," used above in relation to the conversion of the beam source pump energy to the light beam, means that a major portion of the light beam, when the EUV driver laser is operating, is generated by stimulated emission. In other words, when the EUV driver laser is operating, a major portion of the light beam is generated by the production of photons with wavelengths in the range of 1200 nm to 5000 nm, either through the stimulation of excited atoms and / or molecules and / or through spontaneous emission that triggers a chain reaction in excited atoms and / or molecules, in a population inversion state within the third active medium of the beam source.

[0112] The term "scatter-free" does not, however, refer to a situation where a significant portion of the light beam, when the EUV driver laser is operating, is generated directly or indirectly by inelastic scattering of light by atoms and / or molecules. In other words, a light beam is not considered "scatter-free" if a significant portion of the light beam is generated solely or predominantly by Raman scattering when the EUV driver laser is operating.

[0113] Preferably, the light beam can be generated directly by converting the energy of the beam source pump. By eliminating possible intermediate steps in the generation of the light beam, power losses, e.g., due to elastic scattering, can be reduced.

[0114] Advantageously, the optical amplifier(s) comprise at least one amorphous material transparent to the light beam from the following group of amorphous materials: SiC>2, Al2O3, MgO, B2O3, CaO, Na2CO3. An optical amplifier designed as a rod or fiber amplifier can therefore be configured as a Tm:SiO2-, TnrcAlOs-, Tm:MgO-, Tm:B2O3-, Tm:CaO-, Tm:Na2CO3-, Ho:SiO2-, Ho:Al2O3-, Ho:MgO-, Ho:B2O3-, Ho:CaO- or Ho:Na2CO3- rod or fiber amplifier.

[0115] If the light beam is split into several partial beams by means of a beam splitter arrangement, the combination unit can be designed to combine the partial beams coherently, spectrally, depending on polarization, or spatially.According to a further aspect of the invention, the aforementioned problem is also solved by a system for exposing semiconductor substrates coated with a photosensitive coating to EUV light, wherein the system comprises an EUV driver laser with some or all of the features mentioned above for the EUV driver laser, wherein the system also comprises a target chamber in which the target material for generating the EUV light can be provided, a target material generator for generating units of the target material, an EUV light collection device for collecting the EUV light that can be generated from the target material, and an EUV light guidance device for guiding the EUV light onto a semiconductor substrate coated with the photosensitive coating.

[0116] The target material can comprise tin (Sn), gold (Au), xenon (Xe), or lithium (Li), advantageously comprising tin (Sn). The target material can be provided in delineable units that can be individually excited with the amplified light beam, thereby generating individual EUV light-emitting plasmas. The target material can be provided as a fluid, particularly in a liquid state. Advantageously, the target material can be provided in droplet form. The target material generator can accordingly be designed as a droplet generator capable of providing the target material units in the form of target material droplets.The EUV light collecting device can be an EUV light collecting optic, in particular an EUV light collecting mirror, through which significant portions of the EUV light emitted in all spatial directions from the excited unit of the target material can be directed in a main propagation direction into the EUV light guiding device.

[0117] According to a further aspect of the invention, the aforementioned problem is also solved by using an EUV driver laser with some or all of the features mentioned above for the EUV driver laser or a system with some or all of the features mentioned above for the system for exposing semiconductor substrates coated with a photosensitive coating with EUV light.

[0118] According to a further aspect of the invention, the aforementioned problem is also solved by the aforementioned method for generating an enhanced light beam for generating an EUV light-emitting plasma of a target material, which comprises the following process step:

[0119] e) Supplying the first active medium of the optical amplifier with optical pump energy by means of the optical pump source unit, such that the first active medium transitions directly from a lower laser band No to an upper laser band Ni, wherein the first active medium has a plurality of laser bands No to N2, which in turn comprise several quantum states, wherein the quantum states have the lower laser level Eo, the upper laser level Ei and a high level E2, where Eo < Ei < E2.

[0120] In an advantageous further development of the process, an EUV driver laser with some or all of the features mentioned above for the EUV driver laser is used to carry out the process steps.

[0121] According to a further aspect of the invention, the aforementioned problem is solved by a method for exposing semiconductor substrates coated with a photosensitive coating to EUV light, which comprises the steps of the method for generating an amplified light beam for generating an EUV light-emitting plasma and further the following steps:

[0122] a) Providing the target material in the target chamber;

[0123] b) Focusing the amplified light beam onto the target material and thereby generating the EUV light-emitting plasma;

[0124] c) Collecting EUV light using an EUV light collection device;

[0125] d) Guiding the collected EUV light by means of an EUV light guiding device onto a semiconductor substrate coated with a photosensitive coating.

[0126] According to a further aspect of the invention, the aforementioned problem is solved by a method for manufacturing microchips or semiconductor intermediates for manufacturing microchips, in which an EUV driver laser with some or all of the features mentioned above for the EUV driver laser is used and / or in which some or all of the process steps of the method for generating an EUV light-emitting plasma of a target material or some or all of the process steps of the method for irradiating semiconductor substrates coated with a photosensitive coating with EUV light are carried out, wherein the method further comprises the following steps:

[0127] a) Exposure of the semiconductor substrates coated with a photosensitive coating with EUV light;

[0128] b) Further processing of the semiconductor substrates exposed with EUV light into microchips or semiconductor intermediates for the manufacture of microchips. List of figures

[0129] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. These show:

[0130] Fig. 1 shows an embodiment of a system for exposing semiconductor substrates coated with a photosensitive coating, comprising an EUV driver laser;

[0131] Fig. 2 shows a first embodiment of the EUV driver laser;

[0132] Fig. 3 shows a second embodiment of the EUV driver laser;

[0133] Fig. 4 shows a third embodiment of the EUV driver laser;

[0134] Fig. 5 shows a fourth embodiment of the EUV driver laser;

[0135] Fig. 6 shows a fifth embodiment of the EUV driver laser;

[0136] Fig. 7 shows a sixth embodiment of the EUV driver laser;

[0137] Fig. 8 shows an emission spectrum for a light beam and an absorption spectrum for the pump beam of a first active medium of an optical amplifier;

[0138] Fig. 9a-b shows a plurality of laser bands, each comprising one or more quantum states, in EUV driver lasers known from the prior art;

[0139] Fig. 9c shows a plurality of laser bands, each comprising one or more quantum states, in the EUV driver laser according to the invention;

[0140] Fig. 10 schematically shows the steps of a first method for generating an amplified light beam to generate an EUV light-emitting plasma of a target material;

[0141] Fig. 11 schematically shows the steps of a second method for exposing semiconductor substrates coated with a photosensitive coating to EUV light; Fig. 12 schematically shows the steps of a third method for manufacturing microchips or semiconductor intermediates for manufacturing microchips.

[0142] The invention is, of course, not limited to the embodiments shown. The embodiments shown in the figures merely represent specific examples of the invention. Within the scope of their expert knowledge, a person skilled in the art can recognize embodiments of the invention that are not explicitly shown. List of reference numerals

[0143] 10 Annex

[0144] 12 Semiconductor substrate

[0145] 14 EUV light

[0146] 16 EUV driver lasers

[0147] 18 amplified light beam

[0148] 20 Target material

[0149] 22 Target chamber

[0150] 24 Target material generator

[0151] 26 EUV light collection device

[0152] 28 EUV light guidance device

[0153] 30 beam source arrangement

[0154] 32 Beam source

[0155] 34 Light beam

[0156] 36 Amplifier arrangement

[0157] 38 optical amplifiers

[0158] 40 Pump source arrangement

[0159] 42 optical pump source unit

[0160] 44 Pump jet

[0161] 46 Focusing unit

[0162] 48 first active medium

[0163] 50 second active medium

[0164] 51a Beam splitter arrangement

[0165] 51b Beam combination unit

[0166] 52 Emission spectrum for the light beam

[0167] 54 Absorption spectrum for the pump jet

[0168] 56 first end face

[0169] 58 second end face

[0170] 60 dichroic beam splitters

[0171] 62 non-linear optical element

[0172] 64 Pumping station

[0173] 65 Beam combination unit

[0174] 65a combined pump jet

[0175] 66 Oscillator

[0176] 68 second pump jet

[0177] 70 optical fibers

[0178] 72 diffractive optical element 74 common support structure

[0179] 76 reflective element

[0180] 78 fiber couplers

[0181] M1 first procedure

[0182] M2 second procedure

[0183] M3 third procedure

[0184] 51 first procedural step first procedure 52 second procedural step first procedure 53 third procedural step first procedure 54 fourth procedural step first procedure 55 fifth procedural step first procedure 56 first procedural step second procedure 57 second procedural step second procedure 58 third procedural step second procedure 59 fourth procedural step second procedure 510 first procedural step third procedure 511 second procedural step third procedure

[0185] AI first wavelength

[0186] X2 second wavelength

[0187] Ä2 S second (total) wavelength

[0188] X2 1 incremental wavelength

[0189] X3 third wavelength

[0190] AEI first exemplary wavelength

[0191] XE2 second example wavelength

[0192] Eo' basic level

[0193] Eo lower laser level

[0194] Egg upper laser level

[0195] E2 High Level

[0196] No' Basic band

[0197] No lower laser band

[0198] Ni upper laser band

[0199] N2 High Band

[0200] Hi, first interim volume

[0201] H2 Second Intermediate Volume DESCRIPTION OF PREFERRED EXAMPLES

[0202] Figure 1 schematically shows an embodiment of a system designated 10 for irradiating semiconductor substrates 12 coated with a photosensitive coating with EUV light 14, the photosensitive coating not being specifically identified by a reference numeral. The system 10 includes an EUV driver laser 16, which is configured to generate an amplified light beam 18 for producing an EUV light 14-emitting plasma of a target material 20. For clarity, the plasma of the target material 20 is not shown in detail in the figures. In the literature, the plasma of the target material 20 that can be generated in this way is sometimes referred to as LPP (laser-produced plasma).

[0203] The system 10 includes a target chamber 22 in which the target material 20 can be provided for generating the EUV light 14. Furthermore, the system 10 includes a target material generator 24 for generating units of the target material 20. The units of the target material 20 are in the form of droplets; accordingly, the target material 20 is provided in a liquid state in the target chamber 22. The system 10 also includes an EUV light collection device 26 for collecting the EUV light 14 generated from the target material 20, and an EUV light guidance device 28 for guiding the EUV light 14 onto the semiconductor substrate coated with the photosensitive coating.

[0204] The EUV driver laser 16 comprises a beam source arrangement 30 with a beam source 32. In an embodiment not shown, the EUV driver laser 16 comprises a beam source arrangement 30 with a plurality of beam sources 32. The beam source 32 is configured to generate a light beam 34 with a first wavelength Ai. Furthermore, the EUV driver laser 16 comprises an amplifier arrangement 36 with several optical amplifiers 38. Each optical amplifier 38 is configured to optically amplify at least a portion of the light beam 34 passing through the respective optical amplifier 38 to produce the amplified light beam 18 or a partially amplified beam not specifically designated with a reference numeral. The EUV driver laser 16 also comprises several pump source arrangements 40, each of which includes at least one optical pump source unit 42 (shown in Figures 3 to 7).In embodiments not specifically shown, the EUV driver laser 16 may also have only one optical amplifier 38 and only one pump source arrangement 40. The at least one optical pump source unit 42 is configured to generate a pump beam 44 with a second wavelength X2. Furthermore, each pump source arrangement 40 is configured, by means of at least one optical pump source unit 42, to supply an associated optical amplifier 38 with optical pump energy.

[0205] The embodiment of the EUV driver laser 16 shown here also has a focusing unit 46 which is designed to focus the amplified light beam 18 into the target chamber 22 for the target material 20 of the system 10 to generate the EUV light 14 emitting plasma.

[0206] The optical amplifiers 38 each have a first active medium 48, which is only identified by a reference numeral in Fig. 1. Each optical pump source unit 42 of each pump source arrangement 40 has a second active medium 50, which is also only identified by a reference numeral in Fig. 1. The optical amplifier 38 according to Fig. 1 is shown here as an example configured as a multimode fiber. In embodiments not specifically shown, the optical amplifier 38 can also be part of an amplifier arrangement 36 configured as a multicore fiber, which thus comprises a plurality of optical amplifiers 38. Furthermore, the EUV driver laser 16 according to the illustrated embodiment has a beam splitter arrangement 51a, which is configured to divide the light beam 34 into several partial beams not specifically identified by a reference numeral.The beam splitter arrangement 51a can comprise one or more beam splitters (not shown). Furthermore, the embodiment of the EUV driver laser 16 includes a beam combination unit 51b, which is arranged downstream of the optical amplifier 38 in the propagation direction of the partial beams and by means of which the partial beams can be combined to form a common amplified light beam 18.

[0207] The first active medium 48 of the optical amplifiers 38 has a plurality of laser bands No to N2. Each laser band No to N2 comprises one or more quantum states. Reference is made to Fig. 9c. The quantum states have a lower laser level Eo, an upper laser level Ei, and a high level E2. Furthermore, in EUV driver lasers known from the prior art (see Figs. 9a and 9b), the quantum states of the first active medium 48 have a ground level Eo'. For the quantum states, Eo < Ei < E2. Eo' < Eo also holds. Between the upper laser level Ei and the high level E2, further quantum states are arranged in EUV driver lasers known from the prior art, in individual laser bands designated as the first intermediate band Hi and the second intermediate band H2.In EUV driver lasers known from the prior art, the active medium has the lower laser level Eo, the upper laser level Ei, and the high level E2 in different laser bands, namely Eo in a lower laser band No, Ei in an upper laser band Ni, and E2 in a high band N2. The pump source arrangements 40 according to the EUV driver laser 16 according to the invention are configured to supply the first active medium 48 of the optical amplifiers 38 with optical pump energy by means of the optical pump source units 42 such that the first active medium 48 transitions directly from the lower laser band No to the upper laser band Ni. "Directly" in this context means that the first active medium 48 transitions directly to the upper laser band Ni without intermediate steps, without first transitioning to the high band N2, when the first active medium 48 is supplied with the optical pump energy of the optical pump source units 42.

[0208] In the active medium 48 of the optical amplifiers 38 according to the present invention, the ground level Eo' and the lower laser level Eo are arranged in the same laser band, namely in the lower laser band No.

[0209] In EUV driver lasers known from the prior art (see Fig. 9a), the ground level Eo' is energetically lower than the lower laser level Eo and is also located in a ground band No' that is energetically lower than the lower laser band No. Furthermore, in EUV driver lasers known from the prior art, the first active medium of the optical amplifiers is initially pumped into the high level E2 located in the high band N2. Particles of the first active medium of the optical amplifiers must therefore first fall back from the high level E2 in the high band N2 to the energetically lower quantum state of the upper laser level Ei in the upper laser band Ni before they can enter a laser transition between the quantum state of the upper laser level Ei and the lower laser level Eo in the lower laser band No.Then, when the laser falls back to the more energetically stable lower laser level Eo, a photon is emitted in EUV driver lasers known from the prior art. When falling back from the high level E2 to the upper laser level Ei, power loss occurs in EUV driver lasers known from the prior art, which remains as heat in the EUV driver laser, more precisely in the optical amplifiers. The heat generated in the optical amplifiers 38 thus negatively affects the wall-plug efficiency of the EUV driver laser, since the power loss remaining as heat in the optical amplifiers can no longer be used to amplify the light beam. Furthermore, excessively high temperatures in the optical amplifiers negatively affect the amplification efficiency of the optical amplifiers.When the laser falls back from the lower laser level Eo to the more stable state of the ground level Eo' in the ground band No', the EUV driver lasers known from the prior art also generate power loss, which remains in the optical amplifiers in the form of heat.

[0210] As can be seen in Fig. 9b, prior art EUV driver lasers employ approaches to increase amplification efficiency by exciting two particles of the first active medium of the optical amplifiers for each incident pump photon. This is achieved via a process called cross-relaxation, in which, upon decay from the high level E2 to the upper laser level Ei, another particle of the first active medium 48 is excited to transition from the ground level Eo', located in the base band No', to the upper laser level Ei. While this generates two photons per incident pump photon, contributing to the amplified light beam, the wall-plug efficiency remains comparatively low, especially at the high laser powers achievable in the multi-kilowatt range, because the power dissipation in the optical amplifiers in the form of heat is comparatively too high.

[0211] According to the invention, the optical pump source units 42, as illustrated by way of example in Fig. 9c, are therefore configured to pump the first active medium 48 of the optical amplifiers 38 directly into the upper laser band Ni. In the present embodiment of the EUV driver laser 16, the first active medium 48 is pumped directly into the high level E2, which is located in the upper laser band Ni. Here, the first active medium 48 is configured such that the lower laser level Eo and the ground level Eo' are different from each other, but are located in the same laser band, namely the lower laser band No. This means that the first active medium 48 transitions directly from the lower laser band No. into the upper laser band Ni when it is supplied with optical pump energy from an optical pump source unit 42. Consequently, the lower laser band No. also forms the stable ground band No'.

[0212] In the present embodiment of the EUV driver laser 16, the value of the second wavelength X2 of the pump beam 44 is smaller by a factor in the range of 0.7 to 0.97 than the value of the first wavelength Ai of the light beam 34. The light beam 34 and the amplified light beam 18 have the same wavelength.

[0213] Figure 8 schematically shows an emission spectrum 52 of the first active medium 48 of the optical amplifiers 38 and an absorption spectrum 54 of the first active medium 48 for the pump beam 44 at a specific wavelength. Figure 5 shows that, in an embodiment of the EUV driver laser 16, the emission spectrum 52 for the light beam 34 and the absorption spectrum 54 for the pump beam 44 of the optical pump source unit 42 overlap in an overlap region not specifically labeled with a reference numeral. The emission spectrum 52 of the first active medium 48 for the light beam 34 includes both the first wavelength Ai of the light beam 34 and the second wavelength X2 of the pump beam 44. Similarly, the absorption spectrum 54 includes the first wavelength Ai and the second wavelength X2. Exemplary wavelengths that meet this criterion are labeled AEI and AE2 in Figure 9.In the present case, a quantum defect exists between the first wavelength Ai and the second wavelength X2, which has a value in the range of 1.5% to 30% when the first active medium 48 of the optical amplifier 38 amplifies the light beam 34 and the pump beam 44 supplies the optical amplifier 38 with optical pump energy.

[0214] Figures 2 to 7, which illustrate different configurations of the EUV driver laser 16 with respect to the pump source arrangements 40, will now be discussed. Only one pump source arrangement 40 is shown in each figure as an example. It will be self-evident to those skilled in the art that the configurations shown also apply to EUV driver lasers 16 with more than one or a plurality of pump source arrangements 40.

[0215] In the embodiment of the EUV driver laser 16 shown in Fig. 2, the first active medium 48 of the optical amplifier 38 and the second active medium 50 of the optical pump source unit 42 are, for example, identical. In this specific, albeit exemplary, case, this means that the active media 48 and 50 have the same dopant. The dopant can be, for example, thulium (Tm) or holmium (Ho). In this configuration of the EUV driver laser 16, the light beam 34 is coupled into the optical amplifier 38 at a first end face 56, wherein the optical amplifier 38 is, in this example and also in all other illustrated embodiments, designed as a rod or fiber amplifier. The pump beam 44, on the other hand, is coupled into the optical amplifier 38 at a second end face 58 opposite the first end face 56.Dichroic beam splitters 60 are arranged at each end face 56, 58, by means of which either the amplified light beam 34 or the pump beam 44 can be deflected or pass through in a wavelength-selective manner.

[0216] In the embodiment of the EUV driver laser 16 shown in Fig. 3, the optical pump source unit 42 comprises a non-linear optical element 62, which is implemented here as a Raman conversion module. The pump source unit also includes a pump source 64 and an oscillator 66. In embodiments not shown specifically, a pump source amplifier may be used instead of an oscillator 66, in which case the optical pump source unit 42 is in a MOPA configuration. In the embodiment illustrated in Fig. 4, a second pump beam 68 emitted by the pump source beam 64 has a third wavelength X3 that differs from the first wavelength Ai of the light beam 34 and from the second wavelength X2 of the first pump beam 44.The second pump beam 68 oscillates in the oscillator 66 after emission and is then, after exiting the oscillator 66 and entering the Raman conversion module 62, frequency-shifted by one Stokes order due to Raman scattering taking place in the Raman conversion module 62, so that the second wavelength X2 results at an unspecified output of the Raman conversion module 62 and the second pump beam 68 transitions into the first pump beam 44 to supply the optical amplifier 38 with optical pump energy. In embodiments not specifically shown, the Raman conversion module 62 can be configured as a cascaded Raman conversion module, whereby the third wavelength A3 can be frequency-shifted by n Stokes orders, where n > 1. In this embodiment, the pump beam 44 is coupled into the optical amplifier 38 by means of a waveguide, which in this case is configured as an optical fiber 70.In this embodiment, the second pump jet 68 is an idler jet when it leaves the Raman conversion module 62, and the first pump jet 44 is a signal jet. With respect to the wavelengths Xi, A2, and X3, in the embodiment of Fig. 4: X3 < X2 < Ai.

[0217] The embodiment of the EUV driver laser 16 according to Fig. 4 has, by way of example, three optical pump source units 42, each emitting a pump beam 44. In the embodiment of Fig. 5, the pump beams 44 are directed onto a diffractive optical element 72, by means of which the pump beams 44 can be coherently combined. The optical pump source units 42 each have a non-linear optical element 62, which can, for example, be designed as a Raman amplifier. In this embodiment, the optical pump source units 42 are only by way of example designed as Raman lasers.

[0218] In the embodiments of the EUV driver laser 16 shown in Figures 5 to 7, the pump source arrangement 40 comprises several optical pump source units 42, in which the second active medium 50 comprises an 13-V compound semiconductor. This 13-V compound semiconductor can be, for example, InP or InGaAsP. In this embodiment, the optical pump source units 42 are pumped with electrical pump energy; therefore, in this embodiment, the pump source 64 is designed as an electric field generator. Specifically, in this embodiment, an electric field is applied to the second active medium 50 of the optical pump source units 42, so that released electrons recombine with holes in a photonic structure (not specifically designated), thereby generating photons. The optical pump source units 42 in the embodiments shown in Figures 5 to 7 can be configured as follows:Figures 5 to 7 can be configured as edge-emitting or surface-emitting laser diodes. The embodiments shown in Figures 5 to 7 differ only in the type of beam combination and the further transport of the generated first pump beams 44 into the optical amplifier 38. The embodiments shown in Figures 5 to 7 each have a beam combination unit 65 by means of which the pump beams 44 of the optical pump source units 42 can be combined to form a combined pump beam 65a, which can then be coupled into the optical amplifier 38. In the embodiment shown in Figure 5, a reflecting element 76, which can be designed, for example, as a mirror, prism, or optical wedge, is arranged on a common support structure 74 for each optical pump source unit 42.The pump jets 44 are combined in the present case as free jets in the manner of a filled aperture, before being coupled into the optical amplifier 38. In the embodiment of Fig. 6 and also in the embodiments of Figs. 7 and 8, the pump jets 44 can also be combined in the manner of a tiled aperture. The pump jets 44 can be combined coherently or incoherently, for example, depending on polarization.

[0219] The embodiment according to Fig. 6 differs from the embodiment shown in Fig. 6 only in that the optical pump source units 42 each emit pump beams 44 with different second wavelengths. The wavelengths X2 1differ from each other by an increment j. This means, for example, that a first optical pump source unit 42 has a second wavelength X2. 1 can emit a second optical pump source unit 42 a second wavelength Ä2 l+j , a third optical pump source unit 42 a second wavelength Ä2 l+2j , etc. The pump jets 42 combined spectrally result in a pump jet 44 with a second (total) wavelength Ä2 S , where the second (total) wavelength Ä2 S from proportions of the incrementally different second wavelengths X2 1 The optical pump source units result in 42.

[0220] The embodiment of Fig. 7 differs from the embodiment of Fig. 6 only in that the pump jets 44 generated by the optical pump source units 42 do not propagate as a free jet through the pump source arrangement 40, but are supplied to a fiber coupler 78 by means of optical fibers 70.

[0221] In all illustrated embodiments, the light beam 34 and the amplified light beam 18 have a first wavelength Ai in the range of 1200 nm to 5000 nm. Conventional EUV driver lasers have a CC gas mixture as their first active medium and emit a light beam 34 with a wavelength of approximately 10.6 pm.

[0222] Figure 10 schematically shows a method M1 for generating an amplified light beam 18 to generate an EUV light-emitting plasma 14 of a target material. Method M1 comprises the following steps:

[0223] S1 Generating at least one light beam with a first wavelength Ai using a beam source arrangement comprising at least one beam source for this purpose. 52 Amplifying at least one component of the light beam to produce an amplified light beam using an amplifier arrangement comprising at least one optical amplifier for this purpose with a first active medium.

[0224] 53 Generating a pump beam with a second wavelength X2 and supplying the optical amplifier with pump energy, wherein the generation of the pump beam is carried out by means of a pump source arrangement which has at least one optical pump source unit for this purpose with a second active medium.

[0225] 54 Guiding the amplified light beam towards a focusing unit designed to focus the amplified light beam into a target chamber for the target material and onto the target material to generate the EUV light-emitting plasma.

[0226] According to the invention, the method M1 comprises the following step:

[0227] 55 Supplying the first active medium of the optical amplifier with optical pump energy by means of the optical pump source unit, such that the first active medium transitions directly from a lower laser band No to an upper laser band N2, wherein the first active medium has a plurality of laser bands No to N2, each of which in turn comprises several quantum states, wherein the quantum states have the lower laser level Eo, the upper laser level Ei and a high level E2, wherein Eo < Ei < E2.

[0228] Figure 11 schematically illustrates a second method, M2, which is implemented as a method for exposing semiconductor substrates coated with a photosensitive coating to EUV light. Method M2 comprises the steps of method M1 and, in addition, the following steps:

[0229] 56. Providing the target material in the target chamber using a target material generator.

[0230] 57 Focusing the amplified light beam onto the target material and thereby generating the EUV light-emitting plasma.

[0231] 58 Collecting EUV light using an EUV light collection device.

[0232] 59 Guiding the collected EUV light by means of an EUV light guiding device onto a semiconductor substrate coated with a photosensitive coating. Fig. 12 shows a method M3, which is designed as a method for manufacturing microchips or semiconductor intermediates for manufacturing microchips. In method M3, an EUV driver laser 16 with some or all of the features described above for the EUV driver laser 16 is used and / or process steps S1 to S5 of method M1 or process steps S6 to S9 of method M2 are performed. In addition, method M3 in each case comprises the following steps:

[0233] 510 Exposure of the semiconductor substrates coated with a photosensitive coating with EUV light.

[0234] 511 Further processing of the semiconductor substrates exposed with EUV light into microchips or semiconductor intermediates for the manufacture of microchips.

Claims

Claims 1. EUV driver laser (16) for generating an EUV light (14) emitting plasma of a target material (20), with a) a beam source arrangement (30) with at least one beam source (32) configured to generate a light beam (34) with a first wavelength Ai, b) an amplifier arrangement (36) with at least one optical amplifier (38) comprising a first active medium (48), wherein the optical amplifier (38) is configured to optically amplify at least a portion of the light beam (34) passing through the optical amplifier (38) to an amplified light beam (18), c) a pump source arrangement (40) comprising at least one optical pump source unit (42) comprising a second active medium (50), wherein the optical pump source unit (42) is configured to generate a pump jet (44) with a second wavelength X2 and to supply the optical amplifier (38) with optical pump energy, d) a focusing unit (46) designed to focus the amplified light beam (18) into a target chamber (22) for the target material (20) and onto the target material (20) to generate the EUV light (14) emitting plasma, characterized by the fact that e) the first active medium (48) has a plurality of laser bands No to N2, each comprising one or more quantum states, wherein the quantum states have at least a lower laser level Eo, an upper laser level Ei and a high level E2, wherein Eo < Ei < E2, wherein the pump source arrangement (40) is configured to supply the first active medium (48) of the optical amplifier (38) with optical pump energy by means of the optical pump source unit (42) such that the first active medium (48) transitions directly from a lower laser band No to an upper laser band Ni.

2. EUV driver laser according to claim 1, characterized in that the quantum states of the first active medium (48) have a ground level Eo', wherein the ground level Eo' and the lower laser level Eo are located in a lower laser band No.

3. EUV driver laser according to claim 1 or 2, characterized in that the first active medium (48) between an upper laser band Ni and a high band N2 has at least two further laser bands in the form of a first intermediate band Hi and a second intermediate band H2.

4. EUV driver laser according to one of the preceding claims, characterized in that a value of the second wavelength X2 of the pump beam (44) is smaller by a factor in a range of 0.7 to 0.97 than a value of the first wavelength Ai of the light beam.

5. EUV driver laser according to one of the preceding claims, characterized in that the first active medium (48) has an emission spectrum (52) for the light beam (34) and an absorption spectrum (54) for the pump beam (44), wherein the emission spectrum (52) and the absorption spectrum (54) overlap at least partially.

6. EUV driver laser according to claim 5, characterized in that the emission spectrum (52) of the first active medium (48) comprises the first wavelength Ai of the light beam (34) and the second wavelength X2 of the pump beam (44).

7. EUV driver laser according to claim 5 or 6, characterized in that the absorption spectrum (54) of the first active medium (48) of the optical amplifier (38) comprises the first wavelength Ai of the light beam and the second wavelength X2 of the pump beam (44).

8. EUV driver laser according to one of the preceding claims, characterized in that a quantum defect is present between the first wavelength Ai of the light beam (34) and the second wavelength X2 of the pump beam (44) in the first active medium (48) when the optical amplifier (38) amplifies the light beam (34) and the pump beam (44) supplies the optical amplifier (38) with optical pump energy, wherein the quantum defect has a value in the range of 1.5% to 30%.

9. EUV driver laser according to one of the preceding claims, characterized in that the first active medium (48) and the second active medium (50) are identical.

10. EUV driver laser according to any one of claims 1 to 8, characterized in that the second active medium (50) comprises an Ill-V compound semiconductor selected from a group of Ill-V compound semiconductors comprising: GaN, AIN, InN, BN, ScN, GaP, AIP, InP, InGaP, BP, GaAs, AlAs, InAs, BAs, GaSb, AlSb, InSb, InGaAsP.

11. EUV driver laser according to one of claims 1 to 8 or 10, characterized in that the optical pump source unit (42) comprises a non-linear optical element (62).

12. EUV driver laser according to claim 11, characterized in that the pump beam (44) of the optical pump source unit (42) is a signal beam which can be generated within the non-linear optical element (62) by means of inelastic scattering, in particular Raman scattering.

13. EUV driver laser according to one of the preceding claims, characterized in that the optical pump source unit (42) has an electrical or an optical pump source (64) configured to supply the second active medium (50) of the optical pump source unit (42) with pump energy.

14. EUV driver laser according to claim 13, characterized in that the pump source (64) is an optical pump source configured to generate a second pump beam (68) with a third wavelength X3.

15. EUV driver laser according to claim 14, characterized in that with respect to the first wavelength Ai of the light beam (34), the second wavelength X2 of the first pump beam (44) and the third wavelength A3 of the second pump beam (68) the following applies: X3 < A2 < Ai.

16. EUV driver laser according to claim 15 with reference to claim 12, characterized in that the second pump beam (68) is an idler beam when it leaves the nonlinear optical element (62), wherein a value of the second wavelength X2 of the signal beam corresponds to a value of the third wavelength X3 frequency-shifted by n Stokes orders, wherein n > 1, in particular n > 1, where n is an integer multiple of 1 when n > 1.

17. EUV driver laser according to one of the preceding claims, characterized in that the pump source arrangement (40) has a plurality of optical pump source units (42), each optical pump source unit (42) being configured to emit a pump beam (44) with a second wavelength X2 1 to produce.

18. EUV driver laser according to claim 17, characterized in that a plurality of pump source arrangements (40) and a plurality of optical amplifiers (38) are provided, wherein each pump source arrangement (40) is assigned to exactly one optical amplifier (38) and wherein the optical amplifiers (38) are each configured to optically amplify at least a portion of the light beam (34) passing through the respective optical amplifier (38) to an amplified light beam (18).

19. EUV driver laser according to claim 17 or 18, characterized in that the or Each pump source arrangement (40) has a beam combination unit (65) by means of which the pump beams (44) of the optical pump source units (42) of the respective pump source arrangement (40) can be combined to form a combined pump beam (65a).

20. EUV driver laser according to claim 19, characterized in that the pump source arrangement (40) or each pump source arrangement is configured to combine the pump beams (44) by means of spatial beam combination, spectral beam combination, coherent beam combination or polarization beam combination.

21. EUV driver laser according to one of claims 17 to 20, characterized in that the pump source arrangement (40) has a support structure (74) to which the plurality of optical pump source units (42) are attached.

22. System (10) for exposing semiconductor substrates (12) coated with a photosensitive coating with EUV light (14), characterized in that the system (10) has an EUV driver laser (16) according to one of claims 1 to 21, wherein the system (10) also has a target chamber (22) in which the target material (20) can be provided for generating the EUV light (14), a target material generator (24) for generating units of the target material (20), an EUV light collection device (26) for collecting the EUV light (14) that can be generated from the target material (20), and an EUV light guidance device (28) for guiding the EUV light (14) onto a semiconductor substrate (12) coated with the photosensitive coating.

23. Use of an EUV driver laser (16) according to one of claims 1 to 21 or a device (10) according to claim 22 for exposing semiconductor substrates (12) coated with a photosensitive coating with EUV light (14).

24. Method for generating an enhanced light beam (18) for generating an EUV- light (14) emitting plasma of a target material (20), wherein the method (M1) comprises the following steps: a) Generating at least one light beam with a first wavelength Ai using a beam source arrangement which includes at least one beam source for this purpose (S1); b) Amplifying at least a portion of the light beam to an amplified light beam by means of an amplifier arrangement which has at least one optical amplifier for this purpose with a first active medium (S2); c) Generating a pump beam with a second wavelength X2 and supplying the optical amplifier with pump energy, wherein the generation of the pump beam is carried out by means of a pump source arrangement which has at least one optical pump source unit for this purpose with a second active medium (S3); d) Guiding the amplified light beam towards a focusing unit designed to focus the amplified light beam into a target chamber for the target material and onto the target material to generate the EUV light-emitting plasma (S4), where the procedure (M1) is characterized by the following step: e) Supplying the first active medium of the optical amplifier with optical pump energy by means of the optical pump source unit, such that the first active medium transitions directly from a lower laser band No to an upper laser band Ni, wherein the first active medium has a plurality of laser bands No to N2, each of which in turn comprises several quantum states, wherein the quantum states have the lower laser level Eo, the upper laser level Ei and a high level E2, wherein Eo < Ei < E2 (S5).

25. Method according to claim 24, characterized in that an EUV driver laser (16) according to one of claims 1 to 21 is used to carry out the method steps.

26. Method for exposing semiconductor substrates (12) coated with a photosensitive coating with EUV light (14), characterized in that the method (M2) comprises the steps of the method (M1) for generating an amplified light beam (18) for generating an EUV light (14) emitting plasma according to claim 24 and further includes the following steps: a) Providing the target material in the target chamber using a target material generator (S6); b) Focusing the amplified light beam onto the target material and thereby generating the EUV light-emitting plasma (S7); c) Collection of EUV light by means of an EUV light collection device (S8); d) Guiding the collected EUV light by means of an EUV light guiding device onto a semiconductor substrate coated with a photosensitive coating (S9).

27. A method for manufacturing microchips or semiconductor intermediates for manufacturing microchips, characterized in that the method (M3) uses an EUV driver laser (16) according to one of claims 1 to 21 or a device (10) according to claim 22 and / or the method (M3) comprises the process steps of the method (M1) according to one of claims 24 or 25 or the process steps of the method (M2) according to claim 26 and further comprises the following steps: a) Exposure of the semiconductor substrates coated with a photosensitive coating with EUV light (S10); b) Further processing of the semiconductor substrates exposed with EUV light into microchips or semiconductor intermediates for the manufacture of microchips (S11).

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