EP4331326A1

EP4331326A1 - Euv light source having a separation device

Info

Publication number: EP4331326A1
Application number: EP21722173.8A
Authority: EP
Inventors: Oliver SCHLOSSER; Stefan PIEHLER
Original assignee: Trumpf Lasersystems for Semiconductor Manufacturing GmbH
Current assignee: Trumpf Lasersystems For Semiconductormanufacturing Se
Priority date: 2021-04-26
Filing date: 2021-04-26
Publication date: 2024-03-06
Also published as: US11968767B2; WO2022228646A1; TW202314362A; CN117280874A; KR20240004590A; US20240057243A1

Abstract

The invention relates to an EUV light source (1), comprising a supply device (3) for supplying a target material (4), a pre-pulse laser source (5) for emitting at least one pre-pulse laser beam (9) at at least one pre-pulse wavelength (λ_V), a main pulse laser source (6) for emitting a main pulse laser beam (10) at a main pulse wavelength (λH) different from the at least one pre-pulse wavelength (λ_V), a pre-pulse beam guiding device (7) for delivering the at least one pre-pulse laser beam (9) from the pre-pulse laser source (5) into a beam generation chamber (2) and for focused irradiation of the target material (4) inside the beam generation chamber (2) with in each case at least one pre-pulse (11) of the at least one pre-pulse laser beam (9), and a main pulse beam guiding device (8) for delivering the main pulse laser beam (10) from the main pulse laser source (6) into the beam generation chamber (2) and for focused irradiation of the target material (4) inside the beam generation chamber (2) with in each case a main pulse (12) of the main pulse laser beam (10). The target material (4) is designed to emit EUV radiation (19) following the irradiation. The pre-pulse beam guiding device (7) has at least one separation device (22) which is designed to reflect interfering radiation (21) entering the pre-pulse beam guiding device (7) from the beam generation chamber (2), in at least one wavelength range which does not include the at least one pre-pulse wavelength (λ_V), in a focused manner back into the beam generation chamber (2) or in a focused manner into at least one beam dump (24).

Description

EUV light source with a separation device

Background of the Invention

The invention relates to an EUV light source, comprising: a supply device for supplying a target material, a pre-pulse laser source for emitting at least one pre-pulse laser beam at at least one pre-pulse wavelength, a main pulse laser source for emitting a main-pulse laser beam at a main pulse wavelength that differs from the at least one pre-pulse wavelength, a pre-pulse beam guiding device for supplying the at least one pre-pulsed laser beam from the pre-pulsed laser source into a radiation generation chamber and for focused irradiation of the target material within the radiation generation chamber with at least one pre-pulse of the at least one pre-pulsed laser beam, and a main pulse beam guiding device for feeding the main pulsed laser beam from the main pulsed laser source into the radiation generation chamber and for focused irradiation of the target material within the radiation generation chamber each with a main pulse of the main pulse laser beam, wherein the target material is designed to emit EUV radiation as a result of the irradiation. An EUV light source is a radiation source that serves to emit EUV radiation. EUV radiation refers to electromagnetic radiation with a wavelength between 5 nm and 30 nm. EUV radiation is used in particular in the semiconductor industry. Compared to currently widespread lithography systems that are operated with wavelengths in the UV wavelength range, the use of EUV radiation for microlithographic production allows the reliable production of components with significantly smaller structure sizes and thus leads to a corresponding increase in performance.

The EUV light source is suitable for generating EUV radiation using an LPP (“Laser Produced Plasma”) process. The target material, which is typically a metal, in particular tin, is preferably provided in droplet form by means of the delivery device. A respective droplet is first irradiated with one, two or possibly more than two pre-pulses. The pre-pulse or the pre-pulses serve to prepare the droplet for the irradiation with the main pulse, in particular to heat up the droplet, to expand it, to vaporize it and/or to generate a plasma. The subsequent irradiation of a respective droplet with a main pulse in each case serves to convert the target material into the plasma state, as a result of which EUV radiation is emitted.

The pre-pulses are laser pulses of the at least one pre-pulsed laser beam, and the main pulses are laser pulses of the main pulsed laser beam. The wavelength of the or a respective pre-pulse laser beam and thus the pre-pulse is referred to as the pre-pulse wavelength, the wavelength of the main pulse laser beam and thus the main pulse is referred to as the main pulse wavelength. The main pulsed laser source is a CO2 laser, for example, and the pre-pulsed laser source is a solid-state laser, for example. The use of a pre-pulsed laser source in the form of a solid-state laser has the advantage of a higher conversion efficiency compared to the use of a pre-pulsed laser source in the form of a further CO 2 laser. As a rule, the pre-pulse beam guidance device and the main pulse beam guidance device each have a large number of optical elements, for example lenses and/or mirrors.

The pre-pulse laser source can have precisely one laser source for generating a pre-pulse laser beam at a pre-pulse laser wavelength. the However, the pre-pulse laser source can also have two or more laser sources for generating two or more pre-pulse laser beams, which can have the same or different pre-pulse laser wavelengths, as is described, for example, in US Pat. No. 10,932,350 B2. If two different pre-pulse laser wavelengths are used, they typically do not deviate greatly from one another in order to enable the pre-pulse laser beams to be guided together via the optical elements of the pre-pulsed beam guide device. In the event that the pre-pulse laser source has two or more laser sources for generating two or more pre-pulse laser beams, the pre-pulse laser beams are usually combined in the pre-pulse laser source and jointly directed via the optical elements of the pre-pulse beam guiding device. The pre-pulse laser beams can pass through the optical elements of the pre-pulse beam guiding device collinearly, but this is not absolutely necessary, see US Pat. No. 10,932,250 B2.

When the target material is irradiated in the form of droplets, a portion of the main pulses is scattered on the target material. In addition, the target material emits broadband electromagnetic radiation as a result of the irradiation. Part of this scattered or emitted radiation reaches the pre-pulse beam guidance device as electromagnetic interference radiation, where it leads to undesirable effects, in particular to heating of optical elements of the pre-pulse beam guidance device and the associated thermal lens effects. A particular challenge also arises from the fact that, due to the use of two separate beam guidance devices for the pre-pulses and the main pulses, typically only little space is available for structural adjustments to the EUV light source.

WO 2015/036024 A1 and WO 2015/036025 A1 describe EUV beam generating devices with two beam sources for emitting two laser beams (pre-pulsed laser beam and main pulsed laser beam) with different wavelengths, which each enter a vacuum chamber via an opening. In WO 2015/036024 A1, in one example, the openings in the vacuum chamber are sealed gas-tight with a window that transmits the respective laser beam (pre-pulse or main pulse laser beam). The window that transmits the main pulsed laser beam has a den on its vacuum-side surface Pre-pulsed laser beam reflective coating. This serves to superimpose the pre-pulse and main pulse laser beams and guide the beam together within the vacuum chamber onto the target material. Superposition in the opposite way is also described.

object of the invention

In contrast, the object of the invention was to provide an EUV light source of the type mentioned at the outset in which the disadvantageous effects of interference radiation entering the pre-pulse beam path are avoided, in particular in a space-saving manner.

subject of the invention

This object is achieved by an EUV light source of the type mentioned at the beginning, in which the pre-pulse beam guidance device has at least one separation device that is designed to focus interference radiation entering the pre-pulse beam guidance device from the radiation generation chamber in at least one wavelength range that does not include the at least one pre-pulse wavelength reflecting the radiation generating chamber back or focused into at least one beam trap.

The separation device comprises one or more optical elements and forms part of the pre-pulse beam guidance device. It is arranged in the beam path of the pre-pulsed laser beam before it enters the radiation-generating chamber. The separation device, more precisely at least a part of the separation device, shows a wavelength-dependent behavior, as a result of which the pre-pulses and the interference radiation are influenced differently. This wavelength dependency can be the result of interference effects, for example. For this purpose, the separation device can have, for example, a diffraction grating or a dichroic mirror. A dichroic mirror is an optical element that has a stack of layers made of at least two dielectric materials with different refractive indices and therefore reflects or transmits radiation depending on the wavelength. Due to the wavelength-dependent behavior of the separation device, the pre-pulses can be fed into the radiation generation chamber and focused on the target material while the electromagnetic interference radiation is reflected in at least one wavelength range that does not include the at least one pre-pulse wavelength, focused back into the radiation generation chamber or focused into at least one beam trap. As a result, the further

Pre-pulse beam guidance device, ie the part of the pre-pulse beam guidance device which is in the beam path of the pre-pulses before the separation device is not further affected by the electromagnetic interference radiation.

If the interference radiation is reflected back into the radiation generation chamber, this has the advantage of being particularly space-saving, since no additional installation space is required for a beam trap. This is particularly advantageous in the present case of two separate beam guidance devices, since the space conditions are severely restricted. Focusing the back into the

Radiation generation chamber reflected interfering radiation has the consequence that this can pass an opening in the radiation generation chamber unhindered and re-enter the radiation generation chamber. The radiation divergent behind the focus is then absorbed within the radiation generating chamber.

In the case of reflection in the at least one beam trap, the electromagnetic interference radiation is absorbed in the beam trap. Due to the focussing in the beam trap, installation space can also be saved in this case. In order to absorb high powers, the beam trap typically has a suitable cooling device.

Instead of one separation device, a plurality of separation devices can also be used, for example in order to reflect the interfering radiation in different wavelength ranges in a focused manner back into the radiation generating chamber or in a focused manner in at least one beam trap. The individual separation devices can also be constructed differently.

In one embodiment, the separation device is designed to reflect interfering radiation in the form of a portion of the main pulses backscattered on the target material in a focused manner back into the radiation generation chamber or in a focused manner into the at least one beam trap. Since the main pulsed laser beam used to transfer the Target material in the plasma state has a high power of typically more than about 30-40 kW, it is particularly important to reduce the influence of the backscattered portion of the main pulses on the pre-pulse beam guidance device. For this purpose, the wavelength dependency of the separation device is specifically adapted to the main pulse wavelength.

In a further embodiment, the separation device is designed to reflect interfering radiation in the form of radiation emitted as a result of the irradiation of the target material in at least one wavelength range that does not include the at least one pre-pulse wavelength, focused back into the radiation generation chamber or focused into the at least one beam trap. The irradiation of the target material leads to a typically broadband emission of radiation, which also includes parts in the UVA/IS range, corresponding to wavelengths from 100 nm to 780 nm, and has a disadvantageous effect when it enters the pre-pulse beam guidance device.

In one embodiment, the separation device is designed to reflect the pre-pulses. In this case, the separation device can be used, for example, as a (planar) deflection mirror for the pre-pulses.

In a development of this embodiment, the separation device comprises a dichroic mirror and a curved deflection mirror, with the dichroic mirror serving as a deflection mirror for reflecting the pre-pulses and being designed to transmit and transmit the interference radiation in at least one wavelength range that does not include the at least one pre-pulse wavelength wherein the curved deflection mirror is designed to reflect the interfering radiation transmitted by the dichroic mirror, preferably through the dichroic mirror, focussed back into the radiation generation chamber or focused into the at least one beam trap. The curvature of the deflection mirror serves to focus the interference radiation. The orientation of the curved deflection mirror is selected in such a way that the interfering radiation is reflected in the desired direction.

In order to avoid adverse effects of the interference radiation on the pre-pulse beam guidance device, it does not necessarily have to be focused back into the radiation generation chamber or focused into the at least one Beam trap are reflected. Alternatively, a dichroic mirror can also serve as a deflection mirror for reflecting the pre-pulses and can be designed to transmit the interference radiation in at least one wavelength range that does not include the at least one pre-pulse wavelength. In this case, a beam trap is arranged in such a way that the interference radiation transmitted by the dichroic mirror is absorbed in the beam trap. A disadvantage of this solution is that there is typically not enough space available for it.

In a development of this embodiment, the separation device has a base body that transmits the interfering radiation, the dichroic mirror being formed as a coating on a front side of the base body and the deflection mirror as a coating on a rear side of the base body. In this case, the dichroic mirror and the deflection mirror are not two separate optical elements, rather they form a common separation element. An advantage of this embodiment is the particularly small space requirement. The optical separation element is based on a dielectric base body that transmits the interfering radiation and consists of zinc selenide (ZnSe), diamond or SiC, for example. The coating on the front side of the base body should have the highest possible degree of reflection at the at least one pre-pulse wavelength and the highest possible degree of transmission in the at least one wavelength range that does not include the at least one pre-pulse wavelength, in particular at the main pulse wavelength. The coating on the back of the base body should have the highest possible degree of reflection for the interference radiation transmitted by the dichroic mirror, in particular at the main pulse wavelength. For this purpose, the coatings on the front and the back comprise, for example, a multiplicity of dielectric thin layers of at least two materials with different refractive indices, which are applied to the base body of the optical separation element by means of a suitable deposition process. The coating on the back of the base body can also have a highly reflective metallic layer or coating instead of a dielectric coating.

In a further embodiment, the separation device is designed to transmit the pre-pulses. In a development of this embodiment, the separation device comprises a base body that transmits the pre-pulses and has an entry surface through which the pre-pulses enter the base body and a curved exit surface through which the pre-pulses exit the base body, with the curved exit surface having a coating , which is designed to transmit the pre-pulses and to reflect the interference radiation in at least one wavelength range that does not include the at least one pre-pulse wavelength, focussed back into the radiation-generating chamber or focused into the at least one beam trap. In this case, too, the separation device forms a single optical separation element. In this case, the optical separation element is based on a dielectric base body, which consists, for example, of quartz glass or sapphire. The curved exit surface typically has a concave shape to focus the interference radiation. The reflectance of the coating of the exit surface should be as high as possible in the at least one wavelength range that does not include the at least one pre-pulse wavelength, in particular at the main pulse wavelength, while the transmittance should be as high as possible for the at least one pre-pulse wavelength. The coating of the curved exit surface can preferably also be designed as a bandpass filter, which transmits the pre-pulses as well as possible and reflects all other wavelengths as well as possible. The coating of the curved exit surface can comprise a multiplicity of dielectric thin layers which are applied to the base body by means of a suitable vapor deposition method, for example by means of a method based on the principle of physical vapor deposition.

In a further development of this embodiment, the entry surface and the exit surface are curved in such a way that the optical separation element serves as a focusing lens for the pre-pulses. Considered in itself, a concave shape of the exit surface of the optical separation device leads to a scattering of the exiting pre-pulses. However, if the entrance surface is convex and more curved than the exit surface, ie if the radius of curvature of the entrance surface is smaller than the radius of curvature of the exit surface, the optical separation element as a whole acts as a focusing lens for the pre-pulses. There are other configurations of the curvature of the entrance surface or the Exit surface possible, which lead to the fact that the optical separation element serves as a focusing lens for the pre-pulses.

In a further embodiment, the entry surface has an antireflection coating to increase the transmission of the pre-pulses. This avoids back reflections of the pre-pulses when they enter the optical separation element and the associated problems, and increases the efficiency of the EUV light source. The transmittance at the at least one pre-pulse wavelength should therefore be as high as possible. In this case, too, the antireflection coating can be configured, for example, in the form of a layer stack made of dielectric thin layers

In a further embodiment, the separation device is designed to reflect the interfering radiation in at least one wavelength range that does not include the at least one pre-pulse wavelength in a focused manner back into the radiation generation chamber, with a focus of the reflected interfering radiation being offset in relation to the target material and in particular a focal plane of the back-reflected interfering radiation being in front a target level. This has the advantage that as a result the plasma generation is not or only slightly influenced by the back-reflected interfering radiation.

The focal plane of the back-reflected interfering radiation, in which the focus of the back-reflected interfering radiation lies, and the target plane, in which the target material is irradiated in a focused manner, are planes perpendicular to the beam axis of the pre-pulsed laser beam. The further the focal plane of the interfering radiation reflected back into the radiation generation chamber is in front of the target plane, the more the back-reflected interfering radiation is expanded in the target plane and the smaller the influence on the plasma generation. Alternatively or additionally, the focus of the back-reflected interfering radiation may not lie on the beam axis of the pre-pulsed laser beam, but rather have a slight angular offset. As a result, the back-reflected electromagnetic interference radiation does not hit the target material directly after its focus.

The focus of the spurious radiation reflected back into the radiation generating chamber is not necessarily an ideal focus. Rather, it can be advantageous to spatially allocate the corresponding power density distribution smudge In this case, the rays of the interference radiation reflected back into the vacuum chamber do not intersect at one point. This can be achieved, for example, by appropriately designing the curved exit surface or the curved deflection mirror.

In another embodiment, the at least one pre-pulse wavelength is less than 1.5 pm and the main pulse wavelength is greater than 10 pm. Compared to conventional pre-pulse wavelengths of around 10 pm, the use of correspondingly short pre-pulse wavelengths leads to higher conversion efficiencies. This is due, among other things, to the fact that short pulse durations and sharp focussing of the pre-pulses on the target material are achieved, and that the pre-pulses have a different absorption behavior than the main pulses. For example, the pre-pulse wavelength can be 1030 nm when a Yb:YAG laser is used as the pre-pulse laser source.

In a further embodiment, the EUV light source has a vacuum chamber in which the radiation generation chamber is arranged, the vacuum chamber having a first opening with a first window for the passage of the at least one pre-pulsed laser beam and a second opening with a second window for the passage of the main pulse laser beam. The vacuum that prevails in the radiation generation chamber is sealed off from the environment typically not at one or more openings in the radiation generation chamber itself, but at a vacuum chamber in which the radiation generation chamber is arranged. In this way, a sufficient distance can be produced between the windows and the target material, so that contamination of the windows by the target material can be avoided or at least greatly reduced. Due to the different pre-pulse wavelength(s) and the main pulse wavelength, two windows are typically required for the vacuum seal, which windows consist of a different material that is transmissive for the pre-pulse wavelength(s) and for the main pulse wavelength. With the aid of the separation device described above, optical elements that are located in the section of the beam path of the pre-pulse beam guidance device that is inside the vacuum chamber (ie in the vacuum) can also be protected from interfering radiation. Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can each be implemented individually or together in any combination in a variant of the invention.

drawing

Exemplary embodiments are shown in the schematic drawing and are explained in the following description. Show it

Fig. 1 is a schematic representation of an EUV light source with a

Pre-pulse beam guidance device, which has a separation device in order to reflect interfering radiation entering the pre-pulse beam guidance device from a radiation generation chamber back into the radiation generation chamber in a focused manner,

FIG. 2 is a simplified schematic detail view of that shown in FIG. 1. FIG

EUV light source, in which the separation device is designed to reflect a pre-pulsed laser beam and

3 shows a schematic detailed view of an EUV light source with a

Separation device designed to transmit a pre-pulsed laser beam.

In Fig. 1, an EUV light source 1 is shown, the one

Radiation generation chamber 2, a supply device 3 for supplying a target material 4, a pre-pulse laser source 5, a low-pulse laser source 6, a pre-pulse beam guide device 7 and a low-pulse beam guide device 8. The target material 4 is tin, which is provided in the form of droplets 4 by the provision device 3 within the radiation generation chamber 2 . The droplets 4 that emerge from the supply device 3 move within the radiation-generating chamber 2 along a predetermined path of movement, which runs approximately in a straight line. In principle, however, the target material 4 can also be a different material, for example a different material trade metal. Also, the supply by means of the supply device 3 does not have to be in the form of droplets.

The pre-pulsed laser source 5 emits a pulsed laser beam, referred to below as the pre-pulsed laser beam 9 , while the main pulsed laser source 6 emits a pulsed laser beam, referred to below as the main pulsed laser beam 10 . The laser pulses of the pre-pulsed laser beam 9 are referred to as pre-pulses 11, and the laser pulses of the main-pulsed laser beam 10 are referred to as main pulses 12. The main pulsed laser source 6 shown is a CO2 laser. The wavelength of the main pulse laser beam 10, referred to as the main pulse wavelength AH, is approximately 10.6 pm. However, the main pulsed laser source 6 can also be another laser. The pre-pulse laser source 5 shown is a Yb:YAG laser. The wavelength of the pre-pulse laser beam 9, referred to as the pre-pulse wavelength Av, is 1030 nm. The pre-pulse laser source 5 can also be another laser, for example another solid-state laser, a fiber laser, etc.

The pre-pulse laser source 5 can also have two or possibly more than two laser sources, which are each designed to generate a pre-pulse laser beam 9 . In this case, the pre-pulsed laser beams are combined in the pre-pulsed laser source 5 . The pre-pulse laser beams 9 generated by the pre-pulse laser source 5 can have the same pre-pulse wavelength Av, but it is also possible for the pre-pulse laser beams to have different pre-pulse wavelengths Av, which usually differ only slightly, so that they can be guided using the common pre-pulse beam guidance device 7.

The pre-pulse laser beam 9 is fed from the pre-pulse laser source 5 to the radiation generation chamber 2 by means of the pre-pulse beam guiding device 7 . The pre-pulsed laser beam 9 passes through a first opening 13 in a vacuum chamber 14 in which the radiation-generating chamber 2 is arranged. In addition, the pre-pulse laser beam 9 is focused onto the tin droplets 4 by means of the pre-pulse beam guidance device 7 . For these purposes, the pre-pulse beam guidance device 7 shown comprises a number of optical elements in the form of lenses and mirrors. However, the pre-pulse beam guidance device 7 can also have other transmissive and/or reflective optical elements for these purposes. The main pulsed laser beam 10 is fed from the main pulsed laser source 6 to the beam guidance chamber 2 by means of the main pulsed beam guidance device 8 . The main pulsed laser beam 10 passes through a second opening 15 in the vacuum chamber 14. In addition, the main pulsed laser beam 10 is focused by the main pulsed beam guidance device 8 onto the target material 4, more precisely onto one of the tin droplets. For these purposes, the main pulse beam guidance device 8 shown comprises a plurality of optical elements in the form of mirrors. Deviating from this, the main pulse beam guidance device 8 can also have other reflective and/or transmissive optical elements.

In particular, within the vacuum chamber 14, the pre-pulse beam guidance device 7 and the main pulse beam guidance device 8 can also coincide at least in sections. The pre-pulsed laser beam 9 and the main pulsed laser beam 10 are then guided over the same optical elements in a respective section and form a common beam guiding device. In the example shown, the pre-pulsed laser beam 9 and the main pulsed laser beam 10 are guided into the radiation generation chamber 2 via separate openings 16, 16'. However, it goes without saying that the pre-pulsed laser beam 9 and the main pulsed laser beam 10 can alternatively be guided into the radiation generation chamber 2 via a common opening.

Since the pressure inside the vacuum chamber 14 is typically significantly lower than outside the vacuum chamber 14, the openings 13, 15 are gas-tight, in the example shown by means of a window 17, 18. The first window 17 consists of quartz glass and has a high transmission the pre-pulse wavelength ln. The second window 18 is a diamond window that has a high transmission at the main pulse wavelength AH. The two windows 17,18 can also consist of other materials. The openings 16, 16' through which the pre-pulsed laser beam 9 or the main pulsed laser beam 10 enter the radiation-generating chamber 2 have no windows.

The tin droplets are first irradiated with two pre-pulses 11 and then with a main pulse 12 each in a focused manner. A respective focus position of the pre-pulses 11 or of the main pulse 12 during the focused irradiation does not necessarily correspond to the position of the tin droplet. The respective focus position Rather, the pre-pulse 11 or the main pulse 12 can lie in front of or behind the tin droplet in the beam path. A higher conversion efficiency is thus achieved in comparison to irradiation with only one main pulse 12 . As a result of the irradiation, the tin droplets are converted into the plasma state and EUV radiation 19 is emitted, which is collected by means of a collector mirror 20 which is arranged in the radiation generation chamber 2 . The radiation generation chamber 2 serves as a holder or as a support frame for the collector mirror 20. The collector mirror 20 has an opening through which the pre-pulses 11 and the main pulse 12 pass. The supply device 3 is attached to the radiation generation chamber 2 and is used to supply the target material 4 inside the radiation generation chamber 2.

During the irradiation, a proportion 21 of the main pulses 12 is backscattered by the tin droplets and reaches the pre-pulse beam guidance device 7 as interference radiation 21. The tin droplets can essentially be assumed to be a point light source. The pre-pulse beam guidance device 7 has a separation device 22 in order to reflect the interfering radiation 21 in the form of the backscattered portion of the main pulses 12 back into the radiation generation chamber 2 in a focused manner. The interference radiation 2T reflected back into the radiation generation chamber 2 is absorbed within the radiation generation chamber 2 .

This serves to avoid disadvantageous effects, in particular thermal effects, for example thermal lens effects, which the interfering radiation 21 can cause in the pre-pulse beam guidance device 7 . The separation device 22 shown in FIG. 1 acts as a deflection mirror for the pre-pulses 11 . There is also an additional deflection mirror 23 between the separation device 22 and the radiation generation chamber 2. Deviating from this, one or more other optical elements or no additional optical element can also be located between the separation device 22 and the radiation generation chamber 2.

Alternatively, as also shown in FIG. 1, the separation device 2 can be designed to reflect the interfering radiation 21 in a focused manner into a beam trap 24 or, in contrast to what is shown in FIG. 1, to reflect it in a focused manner into more than one beam trap 24 . The interference radiation 21 is not limited to the backscattered portion 21 of the main pulses 12 . For example, as a result of the irradiation of the target material 4 , radiation 25 is emitted, which is typically very broadband and also reaches the pre-pulse beam guidance device 7 as interference radiation 21 . In this case, too, the target material 4 can essentially be described as a point light source. The interfering radiation 21 can also be reflected back into the vacuum chamber 2 in a focused manner or into at least one beam trap 24 in a focused manner in more than one wavelength range that does not include the at least one pre-pulse wavelength ln by means of the separation device 22 .

In the example shown, the additional deflection mirror 23 serves to absorb the radiation 25 emitted by the target material 4 as a result of the irradiation and entering the pre-pulse beam guidance device 7 as interference radiation 21, primarily in the UVA/IS range. The additional deflection mirror 23 is suitably cooled for this purpose. Alternatively, the additional deflection mirror 23 can transmit the interference radiation 21 so that it can be absorbed by a suitably arranged beam trap.

In addition to the separation device 22, further separation devices 22 can also be arranged in the pre-pulse beam guidance device 7, for example in order to reflect the interfering radiation 21 in different wavelength ranges in a focused manner back into the radiation generation chamber 2 or in a focused manner in at least one beam trap 24.

Alternatively, the additional deflection mirror 23 can also absorb the interference radiation 21 as completely as possible, while the pre-pulses 11 are reflected as completely as possible. For this purpose, the additional deflection mirror 23 can have a coating which acts as a bandpass filter and which is highly reflective only for the pre-pulse wavelength ln, while the coating transmits or absorbs all other wavelengths. In the event that the substrate material of the additional deflection mirror 23 is absorbent for the wavelengths deviating from the pre-pulse wavelength ln, the interfering radiation 21 is absorbed—with appropriate cooling of the additional deflection mirror 23. The rear side of the additional deflection mirror 23 can also have an absorption layer, which can also be used as a “beam sump” with appropriate cooling of the additional deflection mirror 23 . A disadvantage of this solution is one thermal deformation of the additional deflection mirror 23 caused by the absorption and an associated impairment of the quality of the pre-pulse beam guidance device 7.

FIG. 2 shows the EUV light source 1 shown in FIG. 1 in a detailed view. For reasons of simplification, the additional deflection mirror 23 between the separation device 22 and the first opening 13 in the radiation generation chamber 2 is not shown, among other things.

In the example shown, the separation device is a single optical separation element 22. The optical separation element 22 has a dielectric base body 25, which consists of quartz glass in the example shown. A coating 26 in the form of a stack of dielectric layers on a front side 27 of the optical separation element 22 serves as a dichroic mirror 26. A coating 28 in the form of a metal layer on a rear side 29 of the optical separation element 28 serves as a curved deflection mirror 28. The coatings 26,28 do not have to be implemented as a stack of dielectric layers or as a thin metal layer.

The dichroic mirror 26 serves as a deflection mirror for reflecting the pre-pulses 11. The dichroic mirror 26 also transmits the interference radiation 21 entering the pre-pulse beam guidance device 7 from the radiation-generating chamber 2 in at least one wavelength range that does not include the pre-pulse wavelength ln. The transmitted interfering radiation 21 impinges on the curved deflection mirror 28 and is reflected back into the radiation generation chamber 2 in a focused manner through the dichroic mirror 26 .

In contrast to what is shown in FIG. 2 , the interference radiation 21 ′ reflected by the curved deflection mirror 28 does not have to pass through the dichroic mirror 26 again. The transmitted interference radiation 21 can also be reflected by the curved deflection mirror 28 onto at least one beam trap 24 . Furthermore, the separation device 22 does not have to be a single optical separation element 22 . Rather, the separation device 22 can also consist of a plurality of optical elements over which their function is distributed. For example, the dichroic mirror 26 and the curved turning mirror 28 can be separate optical elements.

FIG. 3 shows an EUV light source 1 in a detailed view, which essentially corresponds to the EUV light source 1 already shown in FIG. 1 . Deviating from the EUV light source 1 shown in FIG. 1 , the EUV light source 1 shown here has a pre-pulse beam guidance device 7 with a separation device 22 which is designed to transmit the pre-pulses 11 .

In the example shown, the separation device is a single optical separation element 22. The optical separation element 22 has a dielectric base body 25, which consists of quartz glass in the example shown. The pre-pulses 11 enter the optical separation element 22 through an entry surface 30 and exit again through a curved exit surface 31 . The curved exit surface 31 has a coating 32 which, in the example shown, but not necessarily, is a stack of dielectric layers of two materials with different refractive indices. The coating 32 of the curved exit surface 31 is designed to transmit the pre-pulses 11 and reflect the interfering radiation 21 in at least one wavelength range, which does not include the pre-pulse wavelength ln, back into the radiation generation chamber 2 in a focused manner. In particular, the coating 32 of the curved exit surface 31 can be designed such that, in addition to the pre-pulse wavelength AH, other wavelength ranges, for example in the UVA/IS range, which do not include the pre-pulse wavelength Av, are also reflected.

The curvature of the entry surface 30 of the optical separation element 22 shown in FIG. For this purpose, in the example shown, the entry surface 30 has a convex shape and is more curved than the exit surface 31. The entry surface 30 of the optical separation element 22 also has an antireflection coating 33 to increase the transmittance at the pre-pulse wavelength Av. Deviating from the illustration in FIG. 3, the optical separation element 22 does not have to serve as a focusing lens for the pre-pulses 11 and the entry surface does not have to have an anti-reflection coating 33. The separation device is not necessarily a single optical separation element 22, but can also comprise a plurality of optical elements.

In FIGS. 1-3, a focus 34 of the interference radiation 21 ′ reflected back into the radiation generation chamber 2 is offset relative to the target material 4 . More precisely, a focal plane 35 of the interfering radiation 21' reflected back into the radiation generation chamber 2 is clearly in front of a target plane 36 in which the target material 4 is provided. Both the pre-pulses 11 and the

The pre-pulsed laser beam 9 and the main pulses 12 or the main pulsed laser beam 10 are focused onto the target plane 36 . Due to the offset between the focal plane 34 of the back-reflected interfering radiation 2T and the target plane 36, the back-reflected interfering radiation 2T in the target plane 36 is expanded to such an extent that the plasma generation is not affected. Deviating from this, the focus 34 of the back-reflected interfering radiation 2T cannot lie on the beam axis of the pre-pulse laser beam 9 or the pre-pulses 11, but rather be arranged laterally offset to the beam axis, i.e. the beam axis of the back-reflected interfering radiation 2T can be at a (small) angle to the beam axis of the pre-pulse laser beam 9 must be aligned in order to prevent the back-reflected interfering radiation 2T from hitting the site of the irradiation of the target material 4 in the radiation-generating chamber 2 directly.

Claims

patent claims

1. EUV light source (1) comprising:

- A supply device (3) for supplying a target material

(4),

- a pre-pulse laser source (5) for emitting at least one pre-pulse laser beam (9) at at least one pre-pulse wavelength (ln),

- a main pulse laser source (6) for emitting a main pulse laser beam (10) at a main pulse wavelength (AH) that differs from the at least one pre-pulse wavelength (ln),

- a pre-pulse beam guidance device (7) for feeding the at least one pre-pulse laser beam (9) from the pre-pulse laser source (5) into a radiation generation chamber (2) and for focused irradiation of the target material (4) within the radiation generation chamber (2) with at least one pre-pulse (11) each time the at least one pre-pulsed laser beam (9) and

- A main pulse beam guiding device (8) for feeding the main pulsed laser beam (10) from the main pulsed laser source (6) into the radiation generation chamber (2) and for the focused irradiation of the target material (4) within the radiation generation chamber (2) with one main pulse (12) of the main pulsed laser beam ( 10), wherein the target material (4) is designed to emit EUV radiation (19) as a result of the irradiation, characterized in that the pre-pulse beam guidance device (7) has at least one separation device (22) which is designed to separate from the radiation generation chamber ( 2) interfering radiation (21) entering the pre-pulse beam guidance device (7) in at least one wavelength range that does not include the at least one pre-pulse wavelength (Av), focused back into the radiation generation chamber (2) or focused into at least one beam trap (24).

2. EUV light source (1) according to claim 1, characterized in that the separation device (22) is designed to focus interfering radiation (21) in the form of a portion (21) of the main pulses (12) backscattered on the target material (4) into the Radiation generating chamber (2) to reflect back or focused in the at least one beam trap (24).

3. EUV light source (1) according to one of the preceding claims, characterized in that the separation device (22) is designed to absorb interfering radiation (21) in the form of radiation (25) emitted as a result of the irradiation of the target material (4) in at least one Wavelength range that does not include the at least one pre-pulse wavelength (ln) focuses back into the radiation generating chamber (2) or focuses into at least one beam trap (24).

4. EUV light source (1) according to one of the preceding claims, characterized in that the separation device (22) is designed to reflect the pre-pulses (11).

5. EUV light source (1) according to claim 4, characterized in that the separation device (22) comprises a dichroic mirror (26) and a curved deflection mirror (28), the dichroic mirror (26) as a deflection mirror for reflecting the pre-pulses ( 11) is used and is designed to transmit the interfering radiation (21) in at least one wavelength range that does not include the at least one pre-pulse wavelength (ln), and the curved deflection mirror (28) is designed to transmit the interfering radiation transmitted by the dichroic mirror (26). (21), preferably through the dichroic mirror (26), focused back into the radiation generating chamber (2) or focused into the at least one beam trap (24).

6. EUV light source (1) according to claim 5, characterized in that the separation device (22) transmits the interfering radiation (21). Base body (25), the dichroic mirror (26) as a coating (26) on a front side (27) of the base body (25) and the deflection mirror (28) as a coating (28) on a rear side (29) of the base body (25 ) are trained.

7. EUV light source (1) according to any one of claims 1 to 3, characterized in that the separation device (22) is designed to transmit the pre-pulses (11).

8. EUV light source (1) according to claim 7, characterized in that the separation device (22) comprises a pre-pulse (11) transmitting base body (25) having an entrance surface (30) through which the pre-pulse (11) in the entering the base body (25) and having a curved exit surface (31) through which the pre-pulses (11) exit the base body (25), the curved exit surface (31) having a coating (32) which is formed which to transmit pre-pulses (11) and to reflect the interfering radiation (21) in at least one wavelength range that does not include the at least one pre-pulse wavelength (ln), focussed back into the radiation-generating chamber (2) or focused into the at least one beam trap (24).

9. EUV light source (1) according to claim 8, characterized in that the entry surface (30) and the exit surface (31) are curved such that the optical separation device (22) serves as a focusing lens for the pre-pulses (11).

10. EUV light source (1) according to claim 8 or 9, characterized in that the entry surface (30) has an anti-reflection coating (33) to increase the transmission of the pre-pulses (11).

11. EUV light source (1) according to one of the preceding claims, characterized in that the separation device (22) is designed to focus the interfering radiation (21) in at least one wavelength range that does not include the at least one pre-pulse wavelength (ln) into the radiation generating chamber (2), a focus (34) of the back-reflected interference radiation (21 ') being offset in relation to the target material (4) and in particular a focal plane (35) of the back-reflected interference radiation (2T) being arranged in front of a target plane (36). .

12. EUV light source (1) according to one of the preceding claims, characterized in that the at least one pre-pulse wavelength (ln) is less than 1.5 pm and the main pulse wavelength (AH) is more than 10 pm.

13. EUV light source (1) according to one of the preceding claims, characterized by a vacuum chamber (14) in which the radiation generating chamber (2) is arranged, the vacuum chamber (14) having a first opening (13) with a first window (17 ) for the passage of the at least one pre-pulsed laser beam (9) and a second opening (15) with a second window (18) for the passage of the main pulsed laser beam (10).