KR102802111B1 - Shortwave radiation source with multi-section collector module - Google Patents

Abstract

The radiation source comprises a collector module comprising an optical collector positioned within a vacuum chamber having an emitting plasma, and further comprises debris reduction means comprising at least two casings arranged to output a fragment-free hollow beam of shortwave radiation towards the optical collector, preferably comprising a plurality of identical mirrors. Outside each casing are permanent magnets which generate a magnetic field within the casing to reduce the charged fraction of the debris particles and provide a fragment-free hollow beam of shortwave radiation. Other debris reduction techniques are additionally used. Preferably the plasma is a laser-generated plasma of a liquid metal target supplied by a rotating target assembly into the focal region of the laser beam. The technical result of the present invention is the production of a high intensity, high brightness, fragment-free source of shortwave radiation having a large collection solid angle, preferably greater than 0.25 sr.

Description

Shortwave radiation source with multi-section collector module

[0001] The present invention relates to a high brightness radiation source and radiation collection method designed to generate soft X-rays, extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) radiation at wavelengths of about 0.4 to 200 nm, which provides very effective debris mitigation at large collection angles to ensure long-term operation of the high brightness light source and its integrated equipment.

[0002] High-intensity soft X-ray, extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) range radiation sources are used in many fields such as microscopy, biomedicine, medical diagnostics, materials testing, nanostructure analysis, atomic physics and lithography.

[0003] Plasmas that are efficiently radiated in the soft X-ray (0.4-10 nm), EUV (10-20 nm) and VUV (20-120 nm) ranges can be obtained by focusing radiation from high-power lasers onto a target and by discharges.

[0004] International patent application РСТЕР, published on August 22, 2013 under the international publication number WO 2014/001071, discloses a laser-produced plasma (LPP) EUV light source having a collector module for collecting and directing radiation generated by a radiation-producing plasma, and further comprising means for suppressing infrared laser radiation from the plasma radiation beam.

[0005] The LPP EUV light source is characterized by high brightness. However, there is a problem of protecting the optical collector from debris to ensure a long life of the LPP EUV light source.

[0006] During the operation of the radiation source, debris generated as a by-product of the plasma may be in the form of high-energy ions, neutral atoms, or vapors and clusters of the plasma fuel material. The debris particles damage the collector optical device, which may consist of one or more collector mirrors located near the radiation source. In addition to the fact that the microdroplets and particles accumulating on the collector mirror reduce the reflection coefficient of the collector mirror, the high-velocity particles may damage the collector mirror and other components of the optical system that may be located behind the collector mirror. Therefore, there is an urgent need to develop a high-brightness light source of short-wavelength radiation without debris.

[0007] In international patent application PCT/RU2012/000701, published on August 22, 2013 as international publication number WO/2013/122505, a laser-triggered discharge plasma EUV source is known. A focused laser beam is directed onto one of the electrodes such that the laser-triggered discharge has an asymmetrical and mostly curved banana shape. The inherent magnetic field of this discharge has a gradient which determines the predominant movement of the discharge plasma towards the region of weaker magnetic field. The direction of the plasma flow is significantly different from the direction of the optical collector. In order to obtain high radiation powers, the discharge is generated at a high pulse repetition rate. The invention provides a simple and very effective reduction of charged particles.

[0008] However, suppression of neutral particles and clusters requires the use of more sophisticated fragmentation reduction techniques.

[0009] Photogeneration in the soft X-ray, EUV and VUV ranges is most effective using laser-generated plasmas. In recent years, the development of LPP radiation sources has been greatly stimulated by the development of projection extreme ultraviolet lithography for high-volume manufacturing of integrated circuits (ICs) down to the 7 nm node.

[0010] A debris reduction technique based on the use of an auxiliary plasma generated along the path of a short wavelength radiation beam in a specially injected gas is disclosed in US Patent No. 9268031, published on February 23, 2016. The debris, which acquires a charge as a result of exposure to the auxiliary plasma, is deflected by a pulsed electric field. This method is effective in protecting optical collectors from the ion/vapor fraction of the debris, for example in sources using xenon as plasma fuel.

[0011] However, in sources using metals as plasma forming agents, the main threat to the elements of the optical collector is the fine droplet fraction of debris particles, against which the above method is powerless.

[0012] U.S. Patent No. 8,519,366, published on August 27, 2013, discloses a method for fragment reduction in an LPP EUV radiation source using a Sn droplet target. The method includes using magnetic reduction of the charged portion of the fragment particles. In addition, the fragmentation technique includes a foil trap and ports for supplying a protective flow of buffer gas, which provides sufficiently effective capture of neutral atoms and clusters of the liquid metal target material.

[0013] However, additional and somewhat complex means are required to reduce the fine droplet fraction of the fragment particles.

[0014] A method for debris reduction disclosed in U.S. Patent No. 7,302,043, published November 27, 2007, partially avoids these drawbacks. The method provides for the use of a high-speed rotating shutter capable of transmitting short-wave radiation through at least one aperture during one rotation period and preventing the passage of debris during other rotation periods of the shutter.

[0015] However, the use of these means for fragmentation reduction in compact radiation sources is technically very challenging to implement.

[0016] These drawbacks are substantially eliminated by the shortwave radiation sources disclosed in U.S. Pat. No. 1,063,8588, published April 28, 2020, U.S. Pat. No. 1,058,8210, published March 10, 2020, and U.S. Patent Application No. 20200163197, published May 5, 2020, which are herein incorporated by reference in their entireties. The sources disclosed in these patents comprise a vacuum chamber having a rotating target assembly that delivers a target in the form of a molten metal layer into an interaction region with the focused laser beam. The complex of means for debris reduction comprises rotating the target at a high linear speed of greater than 80 m/s. A foil trap, a magnetic field, and a directional flow of a protective buffer gas are used to suppress the ion/vapor fraction of the debris. In an embodiment of the radiation source, a replaceable membrane of carbon nanotubes (CNT membrane) is installed in the path of the shortwave radiation beam. Additionally, a debris shield surrounding the region of the emission plasma is provided which is fixedly installed to direct the laser beam into the region of the pulsed emission plasma and to divert the short wavelength radiation beam therefrom. It is also proposed to use a laser pre-pulse to suppress the ion fraction of the debris. Another proposed debris reduction mechanism is to use high repetition rate laser pulses, for example, of the order of 1 MHz, to ensure vaporization of microdroplets of up to 0.1 μm in size resulting from the plasma of the previous laser pulse and of the subsequent pulse by radiation.

[0017] Although these methods have sufficiently high fragmentation efficiency, they are directed to the collection of short-wavelength plasma radiation over a relatively small spatial angle, and as a result, the average power in the short-wavelength radiation beam is not sufficient for many applications.

[0018] Therefore, there is a need to eliminate at least some of the above-mentioned drawbacks. In particular, there is a need for an improved optical source which is compact, has high power, has a large collection angle and provides virtually complete debris reduction in the path of the output beam of short-wave radiation.

[0019] The present invention aims to solve the technical problems associated with the multiple amplification of the average power of pure high-brilliance sources of soft X-rays, EUV and VUV radiation, while ensuring commercial availability and economic operation.

[0020] The technical result of the present invention is the production of a high-power, high-brightness source of short-wave radiation with very effective fragmentation reduction in a short-wave radiation beam propagating over a large solid angle, preferably greater than 0.25 sr.

[0021] This objective is achieved by using a plasma short-wave radiation source having a collector module including an optical collector positioned within a vacuum chamber having a plasma emitting short-wave radiation, and further including means for reducing debris in the path of the short-wave radiation toward the optical collector.

[0022] The source comprises at least two casings arranged such that the debris reduction means outputs a fragment-free hollow beam of short-wave radiation to an optical collector, each casing having a permanent magnet on the outside thereof that generates a magnetic field inside the casing, the magnetic field formed by the permanent magnets being characterized in that it removes charged portions of debris particles from the hollow beam to provide a fragment-free hollow beam.

[0023] Preferably, the outer surface of each casing comprises two first faces extending substantially parallel to the direction of propagation of short-wave radiation from the plasma and parallel to the vertical direction or other selected direction.

[0024] Preferably, each casing includes two second faces extending substantially parallel to the direction of propagation of short-wave radiation from the plasma and substantially perpendicular to the two first faces of the casing.

[0025] An embodiment of the present invention is characterized in that the area of the first surface of each casing is larger than the area of the remaining portion of the casing surface, and the permanent magnet is in substantial contact with the first surface of each casing.

[0026] An embodiment of the invention is characterized in that the area of the first face of each casing is smaller than the area of the remainder of the casing surface, and the permanent magnets are positioned on the surface of the casing outside their first face.

[0027] An embodiment of the present invention is wherein the angle between the two first faces of each casing is less than 30 degrees.

[0028] In an embodiment of the present invention, the angle between adjacent faces of two adjacent casings is 3 to 10 degrees.

[0029] In an embodiment of the present invention, the permanent magnets are positioned farthest from each other and from each other's most distant parts of the different casings and are connected by a magnetic core.

[0030] In an embodiment of the present invention, the optical collector comprises a plurality of mirrors each installed in the path of a fragment-free hollow beam of short-wave radiation.

[0031] Preferably, the reflecting surfaces of all mirrors form a spheroid of revolution, one focus of which is the plasma and the other focus is the focal point of all mirrors of the optical collector.

[0032] Preferably, the debris reduction means comprises a membrane based on carbon nanotubes (CNT) installed between each casing and the optical collector in the path of the short-wave radiation beam.

[0033] In an embodiment of the present invention, the debris reduction means comprises a shielding gas flow directed towards the plasma within each casing, while each CNT membrane simultaneously functions as a casing window for the exit of a fragment-free hollow beam of short-wave radiation and a gas shutter to prevent the escape of the shielding gas therethrough.

[0034] In an embodiment of the present invention, the permanent magnets are positioned along the entire length of the casing.

[0035] Preferably, the debris reduction means comprises a foil plate (22) positioned in each casing and oriented radially with respect to the plasma and substantially perpendicular to the magnetic field lines.

[0036] In an embodiment of the present invention, the plasma can be selected from the group consisting of laser generated plasma, z-pinch plasma, plasma focus, discharge generated plasma, and laser triggered discharge plasma.

[0037] Preferably, the plasma is a laser-generated plasma of a liquid metal target supplied by a rotating target assembly into the focal region of the laser beam.

[0038] Preferably, the target is installed in a rotating target assembly and is a molten metal layer formed by centrifugal force on a surface facing the rotation axis of the annular groove.

[0039] In another aspect, the present invention relates to a method of collecting radiation, comprising the steps of collecting radiation emitted by a plasma at a plasma generation location with an optical collector, and directing at least a portion of the radiation to a focal point, wherein the radiation emitted by the plasma is guided through at least two casings equipped with debris reduction means and arranged to form a debris-free hollow beam of short-wavelength radiation emanating from the casings to the optical collector.

[0040] Preferably, each casing has a permanent magnet outside the casing that generates a magnetic field inside the casing, the magnetic field formed by the permanent magnet reduces the charged portion of the debris particles, and other debris reduction technologies including shielding gas flow, foil traps, CNT membranes are also used in each casing to provide a debris-free hollow beam.

[0041] Preferably, the optical collector comprises several mirrors installed in the path of each of the fragment-free hollow beams, the reflecting surfaces of all the mirrors lying on the surface of an ellipsoid or a modified ellipsoid, one of the focal points being the plasma and the other focal points being the focal points of all the mirrors of the optical collector.

[0042] The above and other objects, advantages and features of the present invention will become more apparent from the following non-limiting description of embodiments, which are provided by way of example only, with reference to the accompanying drawings.

[0043] The essence of the present invention is illustrated by the following drawings:
[0044] Figures 1 and 2 are schematic diagrams of a short wavelength radiation source having a multi-section collector module according to the present invention.
[0045] Figures 3 and 4 are schematic diagrams of a laser-generated plasma radiation source with a rotating target assembly.
[0046] The above drawings do not encompass or limit the entire range of options for implementing the present technical solution, but rather represent only exemplary material for specific cases of its implementation.

[0047] According to an example embodiment of the present invention, which is illustrated in various scales in FIG. 1, the plasma radiation source comprises a vacuum chamber (1) having a region of a pulsed high temperature plasma (2) emitting short-wave radiation. As by-products, debris particles including vapor, ions and clusters of plasma forming material are generated in the plasma region. The plasma radiation source further comprises a collector module comprising an optical collector (3) and debris reduction means (4) arranged in the path of a short-wave radiation beam (5) from the plasma (2) to the optical collector (3). The optical collector redirects the short-wave radiation to an intermediate focus and then to an optical system operating with short-wave radiation.

[0048] According to the invention, the debris reduction means (4) preferably comprises at least two casings (6) arranged to output a fragment-free hollow beam (7) of short-wave radiation to an optical collector (3) consisting of several mirrors (8). Since the characteristic plasma size is about 0.1 mm (measured as the FWHM of the free electron density or the FWHM of the brightness profile of the luminous plasma region), the plasma radiation source can be considered as quasi-point and the radiation beams emanating therefrom can be considered as homocentric.

[0049] Outside of each casing (6), there is a permanent magnet (9) which generates a magnetic field inside the casing (6), and the magnetic field formed by the permanent magnet (9) removes the charged portion of the debris particles from the hollow beams (7) to provide debris-free hollow beams.

[0050] The outer surface of each casing (6) includes two first faces (10) extending substantially parallel to the direction of propagation of short-wave radiation from the plasma (2) and perpendicular or parallel to another selected direction.

[0051] There is a permanent magnet (9) outside each casing (6), and the permanent magnet (9) generates a magnetic field inside the casing (6), and the magnetic induction vector of the magnetic field is directed substantially perpendicular to the optical axis of the casing.

[0052] Preferably, the permanent magnet (9) is positioned along the entire length of the casing (6).

[0053] In contrast to known solutions, the fragment reduction means (4) according to the present invention is a multi-section system which allows a significant increase in the collection solid angle of the short-wavelength plasma radiation while maintaining a high efficiency of fragment reduction. The increase in the collection solid angle allows a significant (several times) increase in the collected power of the short-wavelength radiation, which can increase the efficiency of using this type of radiation source in almost all applications.

[0054] In a single-section system, a simple increase in the transverse dimensions of the housing leads to a sharp decrease in the magnetic shielding effect for charged particles. This is because the larger the casing size along the lines of force of the magnetic field, the lower the magnetic induction in the volume of the casing, which leads to a decrease in the transverse velocity of charged particles propagating through the casing from the plasma region emitting short-wave radiation (3) to the collector mirror (8). Therefore, during the flight of the section, the particles cannot be deflected a sufficient distance to avoid hitting the mirror. Experiments have shown that for effective operation of the magnetic shielding, the magnetic induction in the center of the casing at a distance of about 40 mm from the plasma region emitting short-wave radiation must be at least 0.5 T. It has also been experimentally established that the flat angle between the sides of the casing, where the magnets are located, must not exceed 30 degrees.

[0055] Therefore, the use of a multi-section debris reduction system in which the plane angle between the faces of the casings does not exceed 30 degrees allows for the generation of a constant magnetic field of sufficient magnitude for highly efficient magnetic mitigation of charged particles in each casing.

[0056] According to a preferred embodiment of the present invention, permanent magnets (9) located farthest from different first faces (10) located farthest from each other of different casings (6) are connected by a magnetic core (11). The magnetic core (11) is preferably made of soft magnetic steel, and can reduce the loss of the magnetic field due to scattering by concentrating the magnetic field in the magnetic core, thereby increasing the volume of each casing and increasing the efficiency of reducing magnetic debris.

[0057] In an embodiment of the present invention, each casing (6) includes two second faces (12) extending substantially parallel to the direction of propagation of short-wave radiation from the plasma (2) and substantially perpendicular to the two first faces (10) of the casing.

[0058] The orientation of the first and second faces (10, 12) in the radial direction relative to the plasma (2) provides a high geometrical transparency of the multi-section debris reduction system. The same purpose is achieved in embodiments of the present invention by the fact that the angle between the adjacent faces of two adjacent casings (6) is in the range of 3 to 10 degrees.

[0059] In a preferred embodiment of the present invention, the area of the first surface (10) of each casing (6) is larger than the area of the remaining portion of the surface of the casing (6), and the permanent magnet (9) is in substantial contact with the first surface (10) of each casing (6).

[0060] In another embodiment (not shown), the area of the first face (10) of each casing (6) may be smaller than the area of the remaining surface of the casing, and the permanent magnets (9) may be positioned on a surface of the casing (6) outside the first face (10), for example, on a large second face (12) of each casing (6).

[0061] The debris reduction means (4) is preferably installed between each casing (6) and the mirror (8) of the optical collector (3) in the path of the hollow beams (7) and comprises a membrane (13) formed of carbon nanotubes. The CNT membrane preferably has a thickness in the range of 20 to 100 nm, which ensures high intensity and high transparency in the range of wavelengths shorter than 20 nm. Thus, the CNT membrane (13) provides an exit for the hollow beams (7) due to its high transparency in the range of wavelengths shorter than 20 nm. At the same time, the CNT membrane (13) prevents the passage of debris particles therethrough, thereby providing a hollow beam (7) free of debris of short-wavelength radiation.

[0062] In addition, the debris reduction means comprises a shielding gas flow directed towards the plasma inside each casing (6), while each CNT membrane (13) simultaneously functions as a casing window for the exit of fragment-free hollow beams (7) of short-wave radiation and as a gas shutter preventing the outflow of shielding gas therethrough.

[0063] Providing an average vacuum in the casing at a shielding gas pressure of about 20 Pa increases the number of collisions between gas molecules and scattered debris particles from the plasma region, thereby deflecting them from a rectilinear motion. At the same time, the use of the CNT membrane as a gas seal allows the use of an increased pressure only within the casing, and not along the entire path along which the hollow beam (7) propagates to the user optics. This reduces losses of short-wave radiation due to absorption in the gas.

[0064] To obtain radiation in a wavelength range greater than 20 nm, a CNT membrane (13) is not used because the transparency in that range rapidly decreases with increasing radiation wavelength.

[0065] In a preferred embodiment as shown in Fig. 2, the optical collector (3) comprises several mirrors (8), while the reflecting surfaces of all mirrors belong to an ellipsoid of revolution, or in other words a spheroid of revolution (15), wherein one focus of the spheroid of revolution is the region of the pulsed emission plasma (2), and the other focus is the focus point (16) of the mirror (8) of the optical collector (3). The manufacture of such mirrors is very expensive, since the roughness of the collector mirror substrate is only 0.2-0.3 nm, and the cost of such mirrors, especially mirrors having an aspherical profile, tends to increase by a factor of 2-3 more than the increase in area. Therefore, the use of several identical mirrors (8) significantly reduces the cost of the optical collector.

[0066] The pulse emission plasma can be selected from the group consisting of laser generated plasma, z-pinch plasma, plasma focus, discharge generated plasma, and laser triggered discharge plasma.

[0067] In a preferred embodiment, the pulsed high temperature plasma is a laser plasma of a liquid metal target material delivered to the focal region of the laser beam by a rotating target assembly, as described in U.S. Patent Application No. 20200163197, published on May 21, 2020, which is incorporated herein by reference in its entirety.

[0068] According to a preferred embodiment of the present invention, which is schematically illustrated in FIG. 3, the target (17) is a molten metal layer formed by centrifugal force on the surface of an annular groove (19) of a rotating target assembly (20) facing the rotation axis (18). An isometric view of a preferred embodiment of the present invention is schematically illustrated in FIG. 4.

[0069] In a preferred embodiment using laser-generated plasma of a liquid metal target as exemplified in FIGS. 3 and 4, the operation of the high-brightness short-wave radiation source is performed as follows. The vacuum chamber (1) is pumped to a pressure of 10 ^-5 ... 10 ^-8 mbar or less by an oil-free pumping system to remove gaseous components such as nitrogen, oxygen, carbon, etc., which may interact with the liquid metal target material.

[0070] The target (17) belongs to the group of non-toxic low melting point metals including Sn, Li, In, Ga, Pb, Bi, Zn and alloys thereof and is transferred by the rotating target assembly into the interaction region with the focused laser beam (21). The target is exposed to the focused pulsed laser beam (21) having a high pulse repetition rate in the range of 1 kHz to 1 MHz. Depending on the target material and the laser power density on the target, short wavelength radiation of the laser plasma is generated in the soft X-ray and/or EUV and/or VUV spectral range.

[0071] A beam (5) of short-wave radiation emitted by the plasma (2) passes through the casing (6) and preferably through a CNT membrane (13) and is converted into a fragment-free hollow beam directed to a mirror (8) of the optical collector (3). Here, a permanent magnet (9, FIG. 4) generates a magnetic field which is directed at a constant, preferably perpendicular to the axis of the hollow beam. Under the action of the Lorentz force, the charged part of the fragment particles (mainly ions) deviates from the linear motion along the axis of the hollow beam (7) and collides with the inner wall of the casing (6) or with plates (22) specially arranged within the casing (FIG. 3) and is trapped by them. The plates (22) mounted on the casing (6) are directed radially to the plasma (2) and preferably perpendicular to the lines of the magnetic field generated by the magnet (9). The plates (22) allow for more efficient capture of the fast charged particles, since the higher the particle velocity, the smaller the distance through which it is deflected under the influence of the magnetic field. In addition, the shielding gas flow prevents the migration of the ion/vapor fraction of the debris particles, causing them to deposit on the walls of the casing (6) and the plates (22), thereby protecting the CNT membrane (13) from debris. Due to their high transparency in the wavelength range shorter than 20 nm, the CNT membranes provide an exit for the short-wavelength beam to the mirrors (8) of the optical collector (3). At the same time, the CNT membranes (13) prevent the passage of debris through them, thereby providing reliable protection for the individual mirrors (8). In addition, an effective debris reduction within the casing (6) is ensured by configuring a directional flow of the shielding gas supplied via the gas inlets (14). The shielding gas stream protects the CNT membrane (13) from the ion/vapor fraction of the debris, thereby increasing its service life.

[0072] Similar means for fragment reduction are also used along the path of the laser beam (21).

[0073] The above-described devices realize specific embodiments of the present invention relating to one of the aspects relating to a method for collecting radiation. The method comprises the steps of collecting short-wave radiation emitted by a plasma (2) at a plasma formation site by means of an optical collector (3) and directing at least a portion of the radiation to a focus (16, FIG. 2). A beam of radiation (5) emitted by the plasma (2) is guided through at least two casings (6) integrated with debris reduction means (4) and arranged to form fragment-free hollow beams (7) of short-wave radiation emanating from the casings (6) and directed towards the optical collector (3).

[0074] Permanent magnets (9) that generate a magnetic field inside the casing (6) from outside each casing are used to reduce the charged portion of the debris particles, and other debris reduction technologies including shielding gas flow, foil traps, and CNT membranes are also used in each casing to provide debris-free hollow beams (7).

[0075] The optical collector (3) preferably comprises several mirrors (8) mounted in the path of each of the fragment-free isocenter beams (7), the reflecting surfaces of all mirrors lying on the surface of an ellipsoid (15) or a modified ellipsoid, one focus of which is the plasma (2) and the other focus (16) being the focal points of all mirrors (8) of the optical collector (3). The modified ellipsoid shape can be used to provide improved intensity uniformity of the radiation collected at a distance compared to a perfect ellipsoid shape.

[0076] Thus, the present invention enables the generation of sources of soft X-rays, EUV and VUV radiation which are long-lasting, easy-to-use, fragment-free, powerful and high-brightness.

[0077] The proposed device is intended for several applications including microscopy, materials science, X-ray diagnostics of materials, biomedical and medical diagnostics, and nano- and microstructural inspection including actinic mask defect inspection for EUV lithography.

Claims (19)

As a plasma short-wave radiation source having a collector module,
An optical collector (3) positioned within a vibration chamber (1) having a plasma (2) emitting short-wave radiation; further comprising a means (4) for reducing debris on the path of the short-wave radiation toward the optical collector (3);
The above debris reduction means (4) comprises at least two casings (6) arranged to output debris-free homocentric beams (7) of short-wave radiation directed to the optical collector (3),
The outer surface of each casing comprises two first faces (10) extending substantially parallel to the direction of propagation of short-wave radiation from said plasma (2), said two first faces being parallel to the vertical direction or parallel to another selected direction,
A plasma short-wave radiation source, wherein outside of each casing (6) there are permanent magnets (9) which generate a magnetic field inside the casings (6), and the magnetic field formed by the permanent magnets (9) removes the charged portion of the debris particles from the hollow beams (7) to provide the debris-free hollow beams. In the first aspect, each casing (6) comprises two second faces (12) extending substantially parallel to the direction of propagation of short-wave radiation from the plasma (2) and substantially perpendicular to the two first faces (10) of the casing, a plasma short-wave radiation source. In the first paragraph, the area of the first faces (10) of each casing (6) is larger than the area of the remaining surface of the casing (6), and the permanent magnets (9) are in substantial contact with the first faces (10) of each casing (6). A plasma short-wave radiation source. In the first paragraph, the area of the first faces (10) of each casing (6) is smaller than the area of the remaining surface of the casing (6), and the permanent magnets (9) are positioned on the surface of the casing (6) outside the first faces (10). A plasma short-wave radiation source. In the first paragraph, a plasma short-wave radiation source, wherein the angle between the two first faces (10) of each casing (6) is less than 30 degrees. A plasma short-wave radiation source, wherein in the first paragraph, the angle between adjacent faces of two adjacent casings (6) is 3 to 10 degrees. In the first paragraph, the permanent magnets (9) located farthest from the different parts located farthest from the different casings (6) are connected by a magnetic core (11), a plasma short-wave radiation source. A plasma short-wave radiation source, wherein in the first aspect, the optical collector (3) comprises a plurality of mirrors (8) installed in the path of each of the fragment-free hollow beams (7). In the 8th paragraph, the reflecting surfaces of all mirrors (9) form a rotating ellipsoid (15), one focus of the rotating ellipsoid (15) is the plasma (2), and the other focus (16) is the focus point of all mirrors of the optical collector, a plasma short-wave radiation source. In the first aspect, the fragment reduction means (4) is a plasma short-wave radiation source including a membrane (13) based on carbon nanotubes (CNT) installed between each casing (6) and the optical collector (3). In the 10th paragraph, the fragment reduction means (4) comprises shielding gas flows directed towards the plasma inside each casing (6), and each CNT membrane (13) functions simultaneously as a casing window for the exit of the fragment-free hollow beam (7) of the short-wave radiation and as a gas shutter preventing the outflow of the shielding gas passing therethrough. In the first paragraph, the permanent magnets (9) are positioned along the entire length of the casings, a plasma short-wave radiation source. In the first aspect, the fragment reduction means (4) is a plasma short-wave radiation source comprising a foil plate (22) positioned in each of the casings (6) and oriented in radial directions with respect to the plasma (2) and substantially perpendicular to the magnetic field lines. A plasma short wavelength radiation source, wherein the plasma in the first aspect can be selected from the group consisting of laser generated plasma, z-pinch plasma, plasma focus, discharge generated plasma, and laser triggered discharge plasma. In the first aspect, the plasma is a short-wavelength radiation source, wherein the plasma is a laser-generated plasma of a liquid metal target (17) supplied by a rotating target assembly (20) to a focal area of a laser beam (21). In the 15th paragraph, the target (17) is a plasma short-wave radiation source, which is a molten metal layer formed by centrifugal force on a surface facing the rotation axis (18) of an annular groove (19) implemented in a rotating target assembly (20). As a method of collecting radiation,
A step of collecting radiation emitted by plasma (2) at a plasma generation location by an optical collector (3), and a step of directing at least a portion of the radiation emitted by plasma (2) to a focal point,
The radiation emitted by the plasma (2) is guided through at least two casings, which are equipped with fragment reduction means (4) and arranged to form fragment-free hollow beams (7) of short-wave radiation emanating from the casings (6) and directed to the optical collector,
The outer surface of each of the at least two casings comprises two first faces (10) extending parallel to the direction of propagation of short-wave radiation from the plasma (2), the two first faces (10) being parallel to the vertical direction or parallel to another selected direction,
A method of collecting radiation, wherein at least one permanent magnet (9) is used to generate a magnetic field inside each casing (6) to reduce the charged portion of the debris particles, outside each casing (6) of the at least two casings. A method for collecting radiation, wherein in claim 17, the debris reduction means further comprises at least one of a shielding gas flow, a foil trap, and a CNT membrane debris reduction element. A method for collecting radiation, wherein in claim 17, the optical collector comprises a plurality of mirrors installed on the path of each of the fragment-free hollow beams, and the reflective surfaces of all the mirrors are located on the surface of an ellipsoid or a modified ellipsoid having one focus as plasma.