A high-efficiency extreme ultraviolet radiation generation method and system

Abstract

The present invention discloses a high-efficiency extreme ultraviolet radiation generation method, wherein extreme ultraviolet radiation is generated by hitting a solid target with a laser, the laser is focused, and the focused laser acts on a target material. The laser source before focusing is a femtosecond laser source; the target material is a material having an average density between that of a conventional solid and a conventional gas, a uniform distribution at a micron size, and a steep boundary. The present invention also discloses a high-efficiency extreme ultraviolet radiation generation system, comprising a laser source (1) and a target (2), an off-axis parabolic mirror focusing device (4) being provided between the laser source (1) and the target (2), and a plasma mirror device (5) being provided between the laser source (1) and the off-axis parabolic mirror focusing device (4). The high-efficiency extreme ultraviolet radiation generation method and device according to the present invention have many advantages, such as high efficiency in generating extreme ultraviolet radiation, spectral bandwidth, and tunable spectrum.

Description

Technical Field

[0001] The present invention relates to a method and system for generating extreme ultraviolet radiation, and in particular to a method and system for generating extreme ultraviolet radiation with high efficiency, belonging to the field of extreme ultraviolet (EUV) technology. Background Art

[0002] The energy of extreme ultraviolet radiation is moderate, corresponding to photon energies of approximately tens of eV, which corresponds exactly to the transition energy levels of the outer or middle-shell electrons of atoms. Therefore, the coupling of extreme ultraviolet radiation with outer or middle-shell electrons can be used to probe the electronic energy level structure and chemical bond composition at the atomic level, providing a new method for studying microscopic matter and helping to understand the physical reasons behind the properties of macroscopic matter. Due to the short wavelength of extreme ultraviolet radiation and the relatively small diffraction limit, if used for microscopic imaging, it can achieve a resolution of tens of nanometers, better analyzing the structure of matter. For the same reason, extreme ultraviolet radiation is suitable for nanofabrication and high-precision lithography.

[0003] At present, the methods for generating extreme ultraviolet light sources include electron synchrotron radiation (ECR), laser plasma source (LPP) and discharge plasma source (DPP). Among them, DPP earlier used the method of discharging high-temperature and high-density xenon (Xe) gas. Later studies found that the EUV conversion efficiency of tin (Sn) is higher than that of Xe. However, tin is solid at room temperature, so laser bombardment is used to generate Sn vapor on the surface of a solid Sn target and then discharge it, which is called laser-induced tin target discharge plasma (LDP).

[0004] Electron synchrotron radiation (ECR) sources are large in size and high in cost, making them difficult to apply to manufacturing.

[0005] Laser plasma technology (LPP) sprays tin droplets through a nozzle. High-energy lasers are focused on the tin droplets to vaporize and ionize them to produce plasma, radiating 13.5nm extreme ultraviolet light. However, due to the instability of the tin droplets sprayed by the nozzle, there are disadvantages such as the tin droplets swinging in the air and difficult to position, the laser and the tin droplets are difficult to synchronize, and the electrical energy is first converted into laser and then into extreme ultraviolet light, resulting in low efficiency.

[0006] Laser-induced discharge plasma (LDP) technology uses two disks partially immersed in liquid tin. When the disks rotate, a layer of tin film is adsorbed on their surface by surface tension and friction. Laser radiation generates pre-plasma on the tin film. High voltage is applied between the two disks, which breaks down the pre-plasma to generate electricity. The main plasma generated by power generation radiates 13.5nm extreme ultraviolet light. Although it can directly convert electrical energy into extreme ultraviolet light with higher efficiency, tin droplets may detach from the surface of the disks when they rotate at high speed, causing contamination. There are also disadvantages such as the centrifugal force generated by high-speed rotation causing uneven thickness of the tin film, the need to heat the disks to prevent the tin film from solidifying, damage caused by the laser acting on the disks, and changes in their surface properties, and a complex mechanical structure.

[0007] Therefore, it is necessary to study a new method and system for generating extreme ultraviolet radiation to solve the above problems. Summary of the Invention

[0008] In order to overcome the above problems, the inventors have conducted intensive research and, on the one hand, provided a high-efficiency method for generating extreme ultraviolet radiation by laser-hitting a solid target.

[0009] The extreme ultraviolet radiation is broad-spectrum extreme ultraviolet radiation with a wavelength range of 3-50 nm. The spectrum peak of the extreme ultraviolet radiation within the wavelength range is adjustable.

[0010] Specifically, the laser is focused and acts on the target. Preferably, the peak power of the focused laser is not less than 10 15 W / cm 2 .

[0011] Furthermore, the laser source before focusing is a femtosecond laser source, preferably a laser source with a single-shot laser energy of 0.001 to 100 joules and a pulse width of 1 to 100 femtoseconds;

[0012] The diameter of the laser focal spot after focusing is no more than 10 microns, and the energy concentration within 10 microns after focusing is no less than 50%.

[0013] According to the present invention, the target material is a material that satisfies the characteristics of average density between conventional solids and conventional gases, uniform distribution under micron size, and steep boundaries. Preferably, the average density of the target material is 1 to 100 mg / cm 3 .

[0014] In a preferred embodiment, the target material of the target is a nanotube foam material. The nanotube foam material refers to a material in which atoms are randomly arranged in space to form a nanoscale framework structure, which has a large number of nanoscale pore structures.

[0015] More preferably, the target material is carbon nanotube foam material.

[0016] According to the present invention, metal atoms are loaded on the framework structure formed by the nanotubes.

[0017] In a preferred embodiment, before laser focusing, the laser contrast is not less than 10 30 picoseconds before the main pulse. 10 .

[0018] On the other hand, the present invention also provides a high-efficiency extreme ultraviolet radiation generation system, comprising a laser source 1 and a solid target 2.

[0019] The laser source 1 is a femtosecond laser source;

[0020] The target material is a material having an average density between that of a solid and a gas, a uniform distribution in a micron size, and a steep boundary.

[0021] Furthermore, an off-axis parabolic mirror focusing device 4 is provided between the laser source 1 and the solid target 2.

[0022] Preferably, a plasma mirror device 5 is provided between the laser source 1 and the off-axis parabolic mirror focusing device 4;

[0023] Preferably, the system further includes a beam-target coupling device 6 and an extreme ultraviolet radiation monitoring device 7 .

[0024] The beneficial effects of the present invention include:

[0025] (1) According to the high-efficiency extreme ultraviolet radiation generation method and device of the present invention, extreme ultraviolet radiation can be generated by laser targeting;

[0026] (2) The high-efficiency EUV radiation generation method and device according to the present invention can generate a wider EUV spectrum compared to laser plasma sources (LPP) and discharge plasma sources (DPP);

[0027] (3) According to the high-efficiency extreme ultraviolet radiation generation method and device of the present invention, the obtained extreme ultraviolet radiation efficiency is higher;

[0028] (4) According to the high-efficiency extreme ultraviolet radiation generation method and device described in the present invention, the spectrum of the generated extreme ultraviolet radiation is adjustable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 An electron microscope photograph of a carbon nanotube foam target material according to a preferred embodiment of the present invention is shown;

[0030] Figure 2 A schematic structural diagram of a high-efficiency extreme ultraviolet radiation generating system according to a preferred embodiment of the present invention is shown;

[0031] Figure 3A schematic structural diagram of a beam-target coupling device of a high-efficiency extreme ultraviolet radiation generation system according to a preferred embodiment of the present invention is shown;

[0032] Figure 4 The extreme ultraviolet radiation spectra generated by different target materials in Experimental Example 1 are shown;

[0033] Figure 5 FIG2 shows the spectrum of extreme ultraviolet radiation detected in Experimental Example 2;

[0034] Figure 6 The energy angular distribution of extreme ultraviolet radiation generated by different target materials in Experimental Example 3 is shown.

[0035] Description of Figure Numbers:

[0036] 1-Laser source;

[0037] 2-target;

[0038] 3- Vacuum chamber;

[0039] 31-vacuum pump;

[0040] 4-Off-axis parabolic mirror focusing device;

[0041] 5-ion body mirror device;

[0042] 6-beam target coupling device;

[0043] 61-Long working distance microscope objective lens;

[0044] 62-beam splitter;

[0045] 63-imaging lens;

[0046] 64-CCD;

[0047] 65-LED light source;

[0048] 7-Extreme ultraviolet radiation monitoring device. DETAILED DESCRIPTION

[0049] The present invention will be described in further detail below with reference to the accompanying drawings and examples, through which the features and advantages of the present invention will become more clearly understood.

[0050] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0051] On the one hand, the present invention provides a high-efficiency method for generating extreme ultraviolet radiation, which generates extreme ultraviolet radiation through a laser solid target. In the present invention, the laser target shooting refers to bombarding the target with a laser, and the generation of extreme ultraviolet radiation refers to generating radiation between soft X-rays and deep ultraviolet radiation, with a radiation wavelength range of 3-50nm.

[0052] Preferably, during the process of laser drilling of a solid target, the laser is first focused, and the focused laser acts on the target material.

[0053] More preferably, continuous targeting is achieved by moving the target or the laser so that the focus of the laser acts on different positions of the target material or on different target materials.

[0054] Furthermore, since air will affect the focusing and targeting effect of the laser, and extreme ultraviolet radiation (EUV) is easily absorbed in air, the light source targeting is carried out in a vacuum. In the present invention, the laser targeting is carried out in a vacuum environment, preferably, the vacuum degree is less than 10 -3 Pa.

[0055] The interaction between femtosecond lasers and target materials offers significant advantages in generating EUV light. In this case, photoionization dominates, directly ionizing atoms in the target and effectively increasing the power of EUV radiation.

[0056] In the present invention, the peak power of the laser after focusing is not less than 10 15 W / cm 2 More preferably, the peak power of the laser after focusing is not less than 10 18 W / cm 2 , which meets the field ionization threshold of carbon in carbon nanotubes and can improve the conversion efficiency.

[0057] Preferably, the diameter of the focal spot after focusing is no greater than 10 microns, and the energy concentration within 10 microns after focusing is no less than 50%.

[0058] Preferably, the laser source before focusing is a femtosecond laser source, preferably a laser source with a single-shot laser energy of 0.001 to 100 joules and a pulse width of 1 to 100 femtoseconds, which bombards the target material after focusing.

[0059] The laser source parameters and the parameters of the focal spot after focusing ensure that the light intensity after focusing is greater than 10 18 W / cm 2 , so that carbon atoms can be directly and quickly ionized to pentavalent and hexavalent atoms by the light field, and the field ionization mechanism is dominant, which can quickly ionize the target material and produce high-intensity, short-pulse extreme ultraviolet radiation; if the parameters of the focal spot and the light intensity parameters are low, the collision ionization mechanism is dominant, and the intensity of the extreme ultraviolet radiation produced will be weaker.

[0060] Since femtosecond lasers have pre-pulses, which can damage the target material, in a preferred embodiment, the contrast of the laser is increased before the laser is focused, thereby protecting the target material.

[0061] The contrast refers to the ratio of the laser main pulse to the laser pre-pulse intensity. Further, before the laser is focused, the laser contrast is not less than 10 30 picoseconds before the main pulse. 10 In the present invention, the laser contrast can be improved by the plasma mirror system.

[0062] The target material of a conventional target will mainly realize particle acceleration and generate X-ray radiation under laser conditions. What kind of target material can realize the excitation of extreme ultraviolet radiation is the key to the present invention.

[0063] According to the present invention, the solid target material is a material that meets the characteristics of low average density, uniform distribution at micron size and steep boundary.

[0064] Furthermore, the low average density means that the average density of the solid target is between that of conventional solids and conventional gases, preferably 1 to 100 mg / cm 3 ;

[0065] The interaction between femtosecond laser and this low-density target material can obtain critical density plasma, and the strong coupling between laser and plasma in the critical density plasma can significantly improve the laser absorption rate, thereby improving the efficiency of generating the final extreme ultraviolet radiation.

[0066] The high boundary steepness means that when the material forms a plasma state and interacts with the laser, the density gradient of the plasma is very large and there is a sharp boundary, thereby suppressing instabilities such as filamentation caused by the laser propagating in the plasma with slowly changing density.

[0067] In a preferred embodiment, the target material is a nanotube foam material, which is formed by disorderly arrangement of atoms in space to form a nanoscale framework structure and has a large number of nanoscale pore structures, so it is called a foam material.

[0068] The foam-shaped material greatly improves the target material's absorption efficiency of laser, and its absorption efficiency of laser is much greater than that of the target material with ordinary structure.

[0069] More preferably, the target material is a carbon nanotube foam material, such as Figure 1 As shown, compared with other critical density targets, carbon nanotube foam has a relatively steep boundary, and the diameter of the carbon nanotube filament is tens of nanometers. Therefore, it is relatively uniform on the micron scale corresponding to the focal spot. It is easy to form a tubular structure, has low manufacturing difficulty and low cost, and has many advantages. It is especially suitable as a target material for generating extreme ultraviolet radiation.

[0070] The carbon nanotube foam material can be single-walled or multi-walled carbon nanotubes, preferably single-walled carbon nanotubes.

[0071] A typical example of a carbon nanotube foam material target is the self-supporting carbon nanotube film target obtained through Chinese patent application 2020107630093.

[0072] In a preferred embodiment, the thickness of the target material is 5 to 200 microns, more preferably 10 to 100 microns. The inventors found that the mechanical strength of the target material of this thickness can support the formation of a self-supporting structure on a hole with a diameter of millimeters. After laser ionization, a plasma is formed with an electron density of 10 21 / cm 3 Magnitude.

[0073] In a more preferred embodiment, the framework structure formed by the nanotubes can be loaded with different metal atoms, so that the spectral peak of the extreme ultraviolet radiation formed after laser targeting can be adjusted within the wavelength range. For example, when photolithography is required to generate extreme ultraviolet radiation with an energy peak at 13.5nm, metal tin can be used to modify carbon nanotubes to form a tin-loaded carbon nanotube foam material; for another example, gold (Au) can be used to modify carbon nanotubes, and the peak of the obtained extreme ultraviolet radiation is 4 to 5nm.

[0074] Preferably, the metal atoms are supported on the framework formed by carbon nanotubes by vapor deposition, which can be achieved by using a floating catalytic method or by modifying the carbon nanotubes, which will not be described in detail in the present invention.

[0075] In a preferred embodiment, before laser targeting, the focus of the laser and the position of the target are monitored to ensure that the laser focus is located on the target.

[0076] In a preferred embodiment, after laser targeting, the spectrum and energy of the generated extreme ultraviolet radiation are detected to monitor the laser targeting process.

[0077] On the other hand, the present invention also provides a high-efficiency extreme ultraviolet radiation generation system, including a laser source 1 and a solid target 2.

[0078] The laser source 1 is a device capable of providing laser light. The laser light generated by the laser source acts on the target, thereby generating extreme ultraviolet radiation.

[0079] Furthermore, the laser source 1 is a femtosecond laser source, preferably a device that can provide a laser beam with a single shot energy of 0.001 to 100 joules and a pulse width of 1 to 100 femtoseconds.

[0080] The solid target 2 has a target material, and the target material of the solid target is a material that satisfies the conditions of average density between conventional solids and conventional gases, uniform distribution in micron size, and steep boundaries.

[0081] Preferably, the average density of the target material is 1 to 100 mg / cm 3 .

[0082] In a preferred embodiment, the target material is a nanotube foam material.

[0083] More preferably, the target material is a carbon nanotube foam material, and the carbon nanotube foam material can be a single-walled carbon nanotube or a multi-walled carbon nanotube, preferably a single-walled carbon nanotube material.

[0084] Since carbon nanotube foam material has the characteristics of self-support, when it is used as a target material, no other support structure is required for the target material, which not only simplifies the structural complexity of the target 2, but also reduces the impact of the target material support structure on target shooting, thereby improving the stability of the system.

[0085] In a preferred embodiment, the nanotube foam material is loaded with different metal atoms, so that the spectrum of the extreme ultraviolet radiation generated after laser targeting is adjustable.

[0086] Preferably, the target 2 also includes a target moving device, which has a translation stage connected to a motor. A plurality of target materials are mounted on the translation stage. The translation stage is driven by the motor to move the target moving device, thereby enabling the laser to act on different target materials, thereby continuously generating extreme ultraviolet radiation.

[0087] In a more preferred embodiment, the translation stage of the target moving device is a six-dimensional translation stage, which can move and rotate up and down, left and right, and front and back respectively, so that the position of the target material can be accurately adjusted, thereby achieving the precise movement of the target material at different positions to the laser targeting position.

[0088] In the present invention, there is no particular limitation on the specific structure of the translation stage, as long as it can meet the above functions, such as the six-dimensional translation stage produced by Wuhan Hongxingyang Technology Co., Ltd., Beijing Zhuoli Hanguang Instrument Co., Ltd., etc.

[0089] According to the present invention, the target 2 is installed in a vacuum chamber 3 , and a vacuum pump 31 is provided on the vacuum chamber 3 .

[0090] In a preferred embodiment, an off-axis parabolic mirror focusing device 4 is further provided between the laser source 1 and the target 2 to focus the laser beam provided by the laser source 1 . Furthermore, the off-axis parabolic mirror focusing device 4 is also provided in the vacuum chamber 3 .

[0091] Furthermore, the diameter of the laser spot after being focused by the off-axis parabolic mirror focusing device 4 is no more than 10 microns, and the energy concentration within 10 microns is no less than 50%.

[0092] Furthermore, the peak power of the laser after focusing by the off-axis parabolic mirror focusing device 4 is not less than 10 15 W / cm 2 , preferably, the peak power of the laser after focusing is not less than 10 18 W / cm 2 , which meets the field ionization threshold of carbon in carbon nanotubes and can improve the conversion efficiency.

[0093] In the present invention, the specific structure of the off-axis parabolic mirror focusing device 4 is not particularly limited, as long as it can meet the above requirements, such as the off-axis parabolic reflector of Thorlabs in the United States.

[0094] In a preferred embodiment, a plasma mirror device 5 is further provided between the laser source 1 and the off-axis parabolic mirror focusing device 4 to remove pre-pulses in the femtosecond laser and improve the laser contrast. Preferably, the plasma mirror device 5 is provided in the vacuum chamber 3.

[0095] In the present invention, there is no particular restriction on the specific manufacturer or model of the plasma mirror device 5. As long as the laser source 1 can be processed and the laser contrast before the laser main pulse 30ps is not less than 10 10 That's it.

[0096] In a preferred embodiment, the plasma mirror device includes a plasma mirror. The plasma mirror (PM) is a transparent material coated with an antireflection film. When the pre-pulse of the main laser reaches the surface of the plasma mirror, the high-transmittance film material will reflect only one thousandth of the pre-pulse, while the majority of the pre-pulse is transmitted. When the main pulse is about to arrive, the laser intensity increases over time, and the pulse front will continuously generate plasma on the surface of the plasma mirror. When the density of this plasma exceeds the critical density, the plasma mirror will no longer be transparent, and most of the main laser will be reflected. The final result in the time domain is that the pre-pulse intensity of the laser is reduced by three orders of magnitude, while the main pulse intensity does not change much, so the laser contrast is improved by more than two orders of magnitude.

[0097] The use of a plasma mirror system will result in a partial loss of laser energy, and its reflectivity is related to the energy of the incident laser. The inventors have found that s-polarized laser light is weakly absorbed on the plasma surface and generally has a higher reflectivity.

[0098] In a more preferred embodiment, a half-wave plate is further provided in front of the plasma mirror to change the polarization of the main laser to achieve s-polarization incidence on the plasma mirror.

[0099] In a preferred embodiment, the system further comprises a beam-target coupling device 6 , which is a microscopic imaging system that can be used to observe laser light and target materials.

[0100] Furthermore, the depth of field of the beam-target coupling device 6 is no more than 10 microns, so that the laser and the target material can be observed clearly.

[0101] In the present invention, any existing beam-target coupling device can be used. Preferably, the beam-target coupling device includes a long working distance microscope objective lens 61, a beam splitter 62, an imaging lens 63, two CCDs 64 and an LED light source 65, such as Figure 3 As shown, an LED light source 65 is arranged in front of the target 2, and the light emitted by the LED light source 65 provides illumination for transmission imaging of the target body. A long working distance microscope objective lens 65 and a beam splitter 62 are sequentially arranged behind the target 2. Two CCDs 64 are respectively arranged on the reflection light path and the transmission light path of the beam splitter 62 to provide target point images with different magnification speeds. The imaging lens 63 is arranged on the transmission light path of the beam splitter 62, and is located between the beam splitter 62 and the CCD 64.

[0102] Through the above settings, the two CCDs can simultaneously achieve 50x and 10x magnification imaging, among which 50x magnification imaging is used for precise positioning of the laser spot and target material, and 10x magnification imaging is used for adjusting the target angle and determining the center point.

[0103] Furthermore, the long working distance microscope objective lens 61, beam splitter 62, imaging lens 63 and CCD 64 are mounted on a three-dimensional electric translation stage, by which the target 2 is adjusted to achieve a target material repeatability accuracy of 0.5 μm.

[0104] In a preferred embodiment, the system further has an extreme ultraviolet radiation monitoring device 7, which includes a flat-field grating spectrometer and an AXUV diode. The flat-field grating spectrometer is used to measure the extreme ultraviolet radiation spectrum, and the AXUV diode is used in conjunction with a specific extreme ultraviolet filter to measure the absolute energy of the extreme ultraviolet radiation, and the feedback signal obtained from the measurement is transmitted to the target moving device to adjust the target position.

[0105] The flat-field grating may have multiple pieces, respectively measuring extreme ultraviolet radiation of different wavelength bands. Preferably, there are two pieces, whose line pairs are 1200 and 300 respectively, corresponding to the measurement spectral ranges of 3.3-30nm and 20-80nm.

[0106] The AXUV diode is a photodiode developed by IRD for the extreme ultraviolet radiation band. It is also one of the standard measurement elements recommended by NIST and is widely used in laser plasma light sources and synchrotron radiation devices.

[0107] Example

[0108] Example 1

[0109] Experiments were conducted to generate extreme ultraviolet radiation by hitting a target with a laser source.

[0110] During the experiment, the target position was adjusted by the beam-target coupling device, so that the laser generated by the laser source passed through the plasma mirror and the off-axis parabolic mirror focusing device in sequence before hitting the target. The generated extreme ultraviolet radiation was detected by the extreme ultraviolet radiation monitoring device. The plasma mirror, off-axis parabolic mirror focusing device, target and beam-target coupling device were all set in a vacuum chamber. The vacuum environment of the vacuum chamber was less than 10 -3 pa.

[0111] The laser source is a 200TW commercial laser produced by THALES, France, which can generate 30 femtosecond pulses of laser light with an output energy of 5 joules per shot. The full width at half maximum of the laser focal spot measured by the beam-target coupling device is 5.5μm, and the 1 / e 2 The energy concentration is 60%, and the power density of the available laser is estimated to be 6.6×10 19 W / cm 2 , the corresponding normalized light intensity is a0 = 5.5;

[0112] The target material used is carbon nanotube foam, which is prepared by chemical vapor deposition (CVD) method. Its thickness is 40 microns and its density is 4 mg / cm 3 , its electron microscope photos are as follows Figure 1 As shown;

[0113] The target moving device is a device with a six-dimensional translation stage, and its repeatability accuracy is not less than 10 microns. The target moving platform is adjusted so that the laser incident angle on the target is within 1°.

[0114] The extreme ultraviolet radiation monitoring device includes two flat-field grating spectrometers and AXUV diodes. The line pairs of the two flat-field grating spectrometers are 1200 and 300 respectively, and the AXUV diode model is AXUV100AL.

[0115] Example 2

[0116] The same experiment as in Example 1 was performed, except that the thickness of the target material was 60 μm.

[0117] Example 3

[0118] The same experiment as in Example 1 was performed, except that the thickness of the target material was 80 μm.

[0119] Comparative Example 1

[0120] The same experiment as in Example 1 was conducted, except that the target material was a plastic target with a thickness of 120 μm.

[0121] Experimental Example 1

[0122] The extreme ultraviolet radiation spectra generated by comparative example 1 and examples 1 and 2 were detected. Figure 4 As shown in the figure, it can be clearly seen that no extreme ultraviolet radiation is observed when the laser interacts with the plastic target, as shown in figure a);

[0123] The interaction between the laser and the carbon nanotube foam target can generate broad-spectrum extreme ultraviolet radiation. The extreme ultraviolet radiation in Figures b) and c) appears as many discrete line radiations and a quasi-continuous background radiation. It is worth noting that due to the different diffraction efficiencies and spectral resolutions of the 1200-line and 300-line gratings, there is a discontinuity at 25nm in the spliced ​​spectrum.

[0124] Experimental Example 2

[0125] The spectrum was inversely analyzed from the data collected by the flat-field grating spectrometer in Example 2. The results are as follows: Figure 5 As shown, the inset in the upper left corner is the radiation energy signal measured by the AXUV diode in the direction of 15 degrees in the experiment.

[0126] From the solved spectrum, we can see that in the radiation segment with a wavelength less than 10nm, the characteristics of line radiation are very obvious, while in the radiation segment with a wavelength greater than 10nm, the relatively flat quasi-continuous radiation is dominant.

[0127] Experimental Example 3

[0128] The energy angular distribution of the extreme ultraviolet radiation measured by the AXUV diode in Examples 1 to 3 is observed. Figure 6 As shown, the points with * represent the actual measured values ​​of the AXUV diode, the radiation energy at other angles is estimated by linear interpolation and symmetry, and the radial value represents the radiation yield in mJ / Sr.

[0129] It can be seen that the interaction between the laser and the carbon nanotube foam target in Examples 1-3 all produces EUV radiation, and the generated EUV radiation has a certain forward orientation. Taking into account the radiation distribution, the estimated total solid angle of radiation is 3π, corresponding to a total EUV radiation output of 240 mJ and a corresponding conversion efficiency of 22%.

[0130] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear" and the like, indicating positions or locations, are based on the operating state of the present invention and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0131] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific contexts.

[0132] The present invention has been described above with reference to preferred embodiments, but these embodiments are merely exemplary and serve only as illustrations. On this basis, various replacements and improvements can be made to the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A high-efficiency extreme ultraviolet radiation generation method, characterized in that: The target material of the solid target is a material having an average density of 1 to 100 mg / cm 3 , materials with steep boundaries; The laser is focused and acts on the target. Before the laser is focused, the laser contrast is not less than 10 30 picoseconds before the main pulse. 10 ; The target material is a nanotube foam material. The nanotube foam material refers to a material in which atoms are randomly arranged in space to form a nanoscale framework structure. The nanotube foam material has a large number of nanoscale pore structures. The framework structure formed by the nanotubes is loaded with metal atoms. The peak power of the laser after focusing is not less than 10 15 W / cm 2 .

2. The high-efficiency extreme ultraviolet radiation generation method according to claim 1, characterized in that: The extreme ultraviolet radiation is broad-spectrum extreme ultraviolet radiation with a wavelength range of 3-50 nm.

3. The high-efficiency extreme ultraviolet radiation generation method according to claim 1, characterized in that: The spectrum peak of the extreme ultraviolet radiation is adjustable within a wavelength range.

4. The high-efficiency extreme ultraviolet radiation generation method according to claim 1, characterized in that: The single-shot laser energy of the femtosecond laser source before focusing is 0.001 to 100 joules, and the pulse width is 1 to 100 femtoseconds; The diameter of the laser focal spot after focusing is no more than 10 microns, and the energy concentration within 10 microns after focusing is no less than 50%.

5. A high-efficiency extreme ultraviolet radiation generation system, comprising a laser source (1) and a solid target (2), The laser source (1) is a femtosecond laser source; The target material of the solid target satisfies the average density of 1 to 100 mg / cm 3 , a material with uniform distribution and steep boundaries at micron size, which is a nanotube foam material. The nanotube foam material refers to a material in which atoms are randomly arranged in space to form a nanoscale framework structure, which has a large number of nanoscale pore structures, and the framework structure formed by the nanotubes is loaded with metal atoms; An off-axis parabolic mirror focusing device (4) is also provided between the laser source (1) and the target (2); A plasma mirror device (5) is provided between the laser source (1) and the off-axis parabolic mirror focusing device (4) for removing pre-pulses in the femtosecond laser and improving the laser contrast so that the laser contrast is not less than 10 30 picoseconds before the main pulse before the laser is focused. 10 , the laser peak power after focusing is not less than 10 15 W / cm 2 .

6. The high-efficiency extreme ultraviolet radiation generation system according to claim 5, characterized in that: The system further comprises a beam-target coupling device (6), which is a microscopic imaging system for observing laser light and target materials.

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