An efficient composite thin film target for an extreme ultraviolet lithography light source and a preparation method thereof

Abstract

The present invention relates to the field of plasma technology, and specifically provides a high-efficiency composite thin film target for an extreme ultraviolet lithography light source and a preparation method thereof. Using the laser thin film deposition technology, an Sn thin film is deposited on the surface of a substrate C target to obtain a C-Sn thin film target; the plasma extreme ultraviolet emission spectrum generated by the C-Sn thin film target under laser irradiation is collected by using the plasma spectroscopy measurement technology to obtain a first efficiency calculation value, and the pulsed laser deposition parameters are optimized to determine the optimal thickness of the Sn thin film; a C thin film is deposited again on the surface of the optimized C-Sn thin film target by using the laser thin film deposition technology to obtain a C-Sn-C composite thin film target; the plasma emission spectrum of the C-Sn-C composite thin film target under laser irradiation is continuously collected to obtain a second efficiency calculation value, and the thickness of the C thin film is optimized. The present invention has the advantages of simple preparation process, low preparation cost, high extreme ultraviolet light conversion efficiency and stable output.

Description

Technical Field

[0001] The present invention relates to the field of plasma technology, and particularly to a high-efficiency composite thin film target for an extreme ultraviolet lithography light source and a preparation method thereof. Background Art

[0002] The laser plasma generated by irradiating a target with a pulsed laser has been regarded as an ideal short-wave light source and is widely used in extreme ultraviolet (EUV) lithography. An efficient and stable extreme ultraviolet light source is crucial for semiconductor nanolithography technology to produce finer linewidth semiconductors. To meet the requirements of large-scale production, the laser plasma light source should have the properties of high and stable EUV light power collected at the central focus, low pollution, and low maintenance cost.

[0003] The EUV light power at the central focus of the laser plasma light source is jointly determined by the incident laser power, EUV light conversion efficiency, overall transmission efficiency, and light source power stability. Among them, how to effectively improve the conversion efficiency of the EUV light source has become a key research direction in the international EUVL field and is also a problem that must be overcome when developing domestic EUV light sources.

[0004] Currently, the Sn droplet target used for the laser plasma light source has problems such as high cost, difficult preparation, difficult alignment of the laser with the droplet, and limited room for improving the conversion efficiency. Summary of the Invention

[0005] The present invention provides a high-efficiency composite thin film target for an extreme ultraviolet lithography light source and a preparation method thereof, which have the advantages of simple preparation process, low preparation cost, high and stable extreme ultraviolet light conversion efficiency, and can solve the problems existing in the above Sn droplets.

[0006] The present invention provides a method for preparing a high-efficiency composite thin film target for an extreme ultraviolet lithography light source, including: depositing a Sn thin film on a substrate C target by using laser thin film deposition technology to obtain a C-Sn thin film target; collecting a first plasma extreme ultraviolet emission spectrum generated by the C-Sn thin film target under laser irradiation by using plasma spectroscopy measurement technology, and calculating the extreme ultraviolet light conversion efficiency according to the first plasma spectrum to obtain a first efficiency calculation value; optimizing the parameters of pulsed laser deposition according to the first efficiency calculation value, and adjusting the thickness of the Sn thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn thin film target meets the predetermined requirements; continuously depositing a C thin film on the C-Sn thin film target by using laser thin film deposition technology to obtain a "sandwich"-type C-Sn-C composite thin film target; collecting a second plasma extreme ultraviolet emission spectrum generated by the C-Sn-C composite thin film target under laser irradiation by using plasma spectroscopy measurement technology, and calculating the extreme ultraviolet light conversion efficiency according to the second plasma extreme ultraviolet emission spectrum to obtain a second efficiency calculation value; further optimizing the parameters of pulsed laser deposition according to the second efficiency calculation value, and adjusting the thickness of the uppermost C thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn-C composite thin film target meets the predetermined requirements.

[0007] According to a method for preparing a high-efficiency composite thin film target for an extreme ultraviolet lithography light source provided by the present invention, the preparation of the high-efficiency composite thin film target for the extreme ultraviolet lithography light source is carried out by using a pulsed laser deposition-plasma spectroscopy measurement integration device; the pulsed laser deposition-plasma spectroscopy measurement integration device includes a pulsed laser deposition part and a plasma spectroscopy measurement part; the pulsed laser deposition-plasma spectroscopy measurement integration device synchronizes laser triggering, target movement, and spectrum acquisition through timing control; the lasers used in the pulsed laser deposition part and the plasma spectroscopy measurement part are Nd:YAG lasers.

[0008] According to a method for preparing a high-efficiency composite thin film target for an extreme ultraviolet lithography light source provided by the present invention, the laser power density required for the preparation of the C-Sn thin film target is 6×10 10 W / cm², the frequency is 10 Hz, and the substrate temperature is 25 °C.

[0009] According to a method for preparing a high-efficiency composite thin film target for an extreme ultraviolet lithography light source provided by the present invention, the laser power density required for the preparation of the C-Sn-C composite thin film target is 10 11 W / cm², the frequency is 10 Hz, and the substrate temperature is 25 °C.

[0010] A method for preparing an efficient composite thin film target for an extreme ultraviolet lithography light source according to the present invention. When preparing the C-Sn thin film target, the distance between the substrate C target and the Sn target for coating is 5 cm, the pulsed laser deposition time is 30 minutes, and the plasma plume is monitored in real time.

[0011] A method for preparing an efficient composite thin film target for an extreme ultraviolet lithography light source according to the present invention. When preparing the C-Sn-C composite thin film target, the distance between the C-Sn thin film target and the C target for coating is 6.5 cm, the pulsed laser deposition time is 10 minutes, and the plasma plume is monitored in real time.

[0012] The present invention also provides an efficient composite thin film target for an extreme ultraviolet lithography light source, which is prepared by using the above-mentioned method for preparing an efficient composite thin film target for an extreme ultraviolet lithography light source.

[0013] The present invention also provides a laser plasma extreme ultraviolet lithography light source system, including the above-mentioned efficient composite thin film target for an extreme ultraviolet lithography light source.

[0014] The present invention also provides an extreme ultraviolet lithography machine, including the above-mentioned laser plasma extreme ultraviolet lithography light source system.

[0015] An efficient composite thin film target for an extreme ultraviolet lithography light source and a preparation method thereof provided by the present invention. The Sn thin film is deposited on the substrate C target by using the laser thin film deposition technology to obtain the C-Sn thin film target; the plasma extreme ultraviolet emission spectrum generated by the C-Sn thin film target under laser irradiation is collected by using the plasma spectroscopy measurement technology, and the extreme ultraviolet light conversion efficiency is calculated according to the plasma spectrum to obtain the first efficiency calculation value; the parameters of the pulsed laser deposition are optimized according to the first efficiency calculation value, and the thickness of the Sn thin film is continuously adjusted until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn thin film target meets the efficiency requirement; the C thin film is deposited on the optimized C-Sn thin film target by using the laser thin film deposition technology to obtain the "sandwich"-type C-Sn-C composite thin film target; the plasma extreme ultraviolet emission spectrum generated by the C-Sn-C composite thin film target under laser irradiation is collected by using the plasma spectroscopy measurement technology, and the extreme ultraviolet light conversion efficiency is calculated according to the plasma extreme ultraviolet emission spectrum to obtain the second efficiency calculation value; the parameters of the pulsed laser deposition are optimized according to the second efficiency calculation value, and the thickness of the uppermost C thin film is continuously adjusted until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn-C composite thin film target meets the efficiency requirement, and the extreme ultraviolet light conversion efficiency beyond the existing process level can be achieved. The present invention has the advantages of simple preparation process, low preparation cost, high extreme ultraviolet light conversion efficiency and stable output, and further improves the process stability and film formation consistency by introducing data-driven optimization means, and is applicable to high-performance laser plasma extreme ultraviolet light source systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic flow chart of a method for preparing a highly efficient composite thin film target for an extreme ultraviolet lithography light source provided by the present invention.

[0018] Figure 2 It is a schematic structural diagram of a pulsed laser deposition - plasma spectroscopy measurement integration device provided by the present invention.

[0019] Figure 3 It is a plasma extreme ultraviolet emission spectrum diagram generated by irradiating a C - Sn - C composite thin film target with different laser energies provided by the present invention.

[0020] Figure 4 It is an XRD pattern of a C - Sn thin film target provided by the present invention.

[0021] Figure 5 It is an XRD pattern of a C - Sn - C composite thin film target provided by the present invention.

[0022] Figure 6 It is a plasma extreme ultraviolet emission spectrum diagram generated by irradiating a C - Sn thin film target and a pure Sn target with a laser of 250 mJ energy under different deposition times provided by the present invention.

[0023] Figure 7 It is a plasma extreme ultraviolet emission spectrum diagram generated by irradiating a C - Sn - C composite thin film target, a C - Sn thin film target and a pure Sn target with a laser of 350 mJ energy provided by the present invention.

[0024] Reference numerals:

[0025] 1: First trigger; 2: First laser; 3: First laser reflection lens; 4: Second laser reflection lens; 5: First laser focusing lens; 6: Vacuum transparent window; 7: Vacuum chamber; 8: First target holder; 9: First moving platform; 10: First controller; 11: Second target holder; 12: Vacuum gate valve; 13: Second moving platform; 14: Second controller; 15: Second laser; 16: Third laser mirror; 17: Fourth laser mirror; 18: Second laser focusing lens; 19: Spectrometer entrance slit; 20: Extreme ultraviolet spectrometer; 21: CCD camera; 22: Second trigger. DETAILED DESCRIPTION OF THE INVENTION

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the scope of protection of the present invention.

[0027] With the rapid development of information technology, the demand for advanced semiconductor chips with faster processing speeds, lower power consumption, and finer line widths in the fields of high-speed large-capacity data communication, high-performance computing, and artificial intelligence continues to grow. Extreme ultraviolet (EUV) lithography technology, especially EUV lithography machines based on laser-produced plasma (LPP) light sources, has become an indispensable key equipment for large-scale mass production of advanced chips and the continuation of the process. Currently, commercial EUV lithography machines generally use EUV radiation with a wavelength of 13.5 nm and a bandwidth of about 2% as the exposure light source, and this radiation is generated by laser plasma radiation.

[0028] To meet the requirements of large-scale wafer manufacturing, the laser plasma EUV light source system must have the following performances: output high-power and high-stability EUV light at the intermediate focus (IF), have low-pollution characteristics, and relatively low operation and maintenance costs. Among them, the output of high-power and low-fluctuation EUV light at the IF point is one of the core indicators determining the performance of the entire EUV lithography system.

[0029] The EUV light power of the laser plasma light source at the IF point depends on multiple factors such as the incident laser power, the EUV light conversion efficiency (CE), the transmission efficiency of the overall optical system, and the source-end power stability. Among them, how to significantly improve the conversion efficiency of laser energy to EUV radiation has become an important research direction in the global EUV lithography field and is also a technical bottleneck that must be focused on to achieve domestic EUV light sources.

[0030] In current commercial EUV lithography machines, Sn droplets are generally used as the plasma target for the laser plasma light source. Liquid tin has become the preferred target form for achieving high conversion efficiency (CE) and sustainable high-power output due to its high intrinsic radiation ability at the 13.5 nm wavelength, stable physical and chemical properties, and moderate evaporation temperature (about 2602 K). The droplet target technology continuously generates tin droplets with diameters in the order of dozens of micrometers by means of high-speed jetting. Subsequently, a high-energy pulsed laser irradiates a single droplet to trigger the formation of local plasma, thereby generating intense 13.5 nm extreme ultraviolet radiation.

[0031] However, although the Sn droplet target technology has been widely applied in current EUV lithography light sources, there are still several key technical challenges and deficiencies:

[0032] Firstly, the problem of spatter debris contamination remains prominent. During the interaction between the laser and the tin droplet, a large number of high-energy particles, incompletely ionized tin clusters, and tiny droplets are generated. These spatter materials may deposit on the surfaces of optical components such as the main reflector, resulting in a decrease in reflectivity, affecting the long-term stable operation of the system, and increasing the maintenance frequency and cost.

[0033] Secondly, there are limitations in the controllability of droplet morphology and spatial positioning. Due to minute fluctuations in factors such as droplet diameter, velocity, and trajectory jitter, it is difficult to maintain the optimal targeting position and incident angle of the laser on the droplet, thus affecting the plasma generation efficiency and the power stability of the EUV light source.

[0034] Thirdly, the energy utilization efficiency is limited. Only a part of the laser pulse energy effectively participates in the excitation and radiation processes of tin plasma. The low CE has become an important constraint for further improving the overall efficiency of the EUV light source and reducing the energy consumption per unit exposure.

[0035] In addition, the complexity of the droplet preparation and supply system is also an issue that cannot be ignored. It requires a nozzle structure with highly precise control, stable hydrodynamic conditions of liquid tin, and droplet generation technology with a high frequency (above dozens of kilohertz), which poses high requirements for the overall reliability and engineering integration of the light source system.

[0036] In response to the above challenges, current research is focused on the following directions: including improving the droplet pretreatment and plasma generation processes by optimizing the pre-pulse and main-pulse laser parameters; developing more advanced droplet detection and tracking technologies to improve the targeting accuracy; studying low-pollution target configurations (such as cluster targets, double-droplet targets, or aerosol targets) to reduce mirror contamination; and exploring alternative materials or composite target systems to further enhance the EUV radiation efficiency and system stability.

[0037] To address the key technical challenges such as sputtering contamination, insufficient stability, and low energy utilization efficiency in the application of traditional Sn droplet targets in laser-produced plasma extreme ultraviolet (LPP-EUV) light sources, the present invention proposes a high-efficiency composite thin film target for extreme ultraviolet lithography light sources and provides a specific preparation method. This composite thin film target can be applied to the EUV lithography machine light source system, and is expected to significantly improve the conversion efficiency of extreme ultraviolet light and the system reliability.

[0038] The preparation method process of the high-efficiency composite thin film target for extreme ultraviolet lithography light sources is as follows (in combination with the attached Figure 1 description):

[0039] Step 101: Deposit a Sn thin film on a substrate C target using laser thin film deposition technology to obtain a C-Sn thin film target.

[0040] Adopt the Pulsed Laser Deposition (PLD) technology to deposit a Sn thin film on a substrate C target to form a C-Sn thin film target. The basic principle of PLD is to use a high-power density laser pulse to irradiate a solid target, inducing ablation of the material surface and generating a high-temperature and high-density plasma plume. The atoms, ions, and molecules rich in the plume move at high speed and deposit on the substrate surface, finally forming a dense, uniform, and compositionally controllable thin film. Compared with other deposition technologies, PLD has the following advantages: it can achieve precise transfer of thin film composition, can prepare high-purity thin films, has excellent microstructure regulation ability, and is applicable to a variety of complex substrates.

[0041] The PLD process is particularly suitable for preparing high-quality Sn thin films. By precisely controlling the laser energy, pulse frequency, background atmosphere, and substrate temperature, it can ensure that the Sn thin film has excellent crystallinity, high purity, and good adhesion performance. In addition, PLD can prepare multi-layer composite structures through multi-target switching or staged deposition, providing a process basis for optimizing energy absorption and transfer during subsequent laser ablation.

[0042] During the thin film deposition process, the selection of the substrate material is crucial for the performance of the final C-Sn thin film target. The substrate needs to meet the following conditions:

[0043] Thermal stability: It can withstand the high temperature during deposition and subsequent laser action;

[0044] Lattice matching: If epitaxial growth is required, the lattice constant matching needs to be considered;

[0045] Chemical compatibility: Avoid reacting with Sn or the deposition environment to prevent interface contamination or diffusion;

[0046] Surface quality: Lower surface roughness helps to improve thin film uniformity and adhesion;

[0047] Application adaptability: Selected according to the target application requirements, such as optical transparency, electrical conductivity, etc.;

[0048] Economy: Comprehensively consider the material cost and processing feasibility.

[0049] Commonly available substrates include single-crystal materials, oxide materials, metal materials, and flexible materials, etc. However, based on the requirements of laser-induced breakdown spectroscopy (LIBS) in the present invention (especially for accurate spectral analysis of Sn element), a single-element substrate is preferred to reduce spectral interference, improve the signal-to-noise ratio, and ensure the repeatability and accuracy of the experiment.

[0050] After systematic comparison, the present invention preferably selects carbon (C) element as the substrate, and the specific reasons are as follows:

[0051] High melting point and thermal stability: The melting point of C element is as high as about 3550 °C, showing excellent thermal stability in the high-energy laser ablation environment, which can effectively withstand the high-temperature impact of deposition and subsequent laser action, and prevent substrate damage;

[0052] Excellent thermal conductivity: The thermal conductivity of C material is about 2000 W / m·K, much higher than that of silicon (~150 W / m·K) and germanium (~60 W / m·K), which helps to dissipate heat quickly, maintain plasma stability and improve ablation efficiency;

[0053] Chemical inertness: C material has good chemical inertness, with almost no chemical reaction with the Sn film, which can ensure the chemical purity of the film and avoid the formation of interface diffusion or reaction layer;

[0054] Excellent surface quality: High-quality C substrate can provide a surface with extremely low roughness, promote the uniformity and compactness of Sn film deposition, improve film adhesion and reduce defect density;

[0055] Thermal expansion coefficient matching: The thermal expansion coefficient of C material is relatively low, close to that of the Sn film, which helps to reduce the interfacial thermal stress caused by temperature changes and reduce the failure risks such as film cracking and peeling;

[0056] Advantages in electrical and optical properties: C material has both good thermal conductivity and electrical conductivity, and also has good optical transparency (in the visible-infrared band), which is convenient for subsequent application expansion in multiple fields;

[0057] Advantages in plasma ablation: Under the action of high-energy laser, the laser first ablates the Sn film to form a high-density Sn plasma. When the laser continues to act on the C substrate, due to its extremely high melting point, the laser energy is mainly deposited on the substrate surface, inhibiting the conversion of energy into the thermal kinetic energy of the plasma, further enhancing the density and ablation rate of the Sn plasma, and enhancing the plasma radiation performance;

[0058] Preparation structure optimization: A 10 Hz pulsed deposition frequency is adopted. After each deposition, the Sn atoms on the substrate surface are allowed to rearrange to form a nanoscale transition layer, which improves the film density and plasma ablation efficiency, helps to form a good gradient interface structure, and further optimizes the spectral characteristics and conversion efficiency.

[0059] Spectral background is clean: Element C does not have strong characteristic spontaneous emission spectral lines in the extreme ultraviolet band (especially at 13.5 nm ±2%). Compared with elements such as Si and Ge, its own plasma excitation will not introduce additional spectral line interference, significantly improving the signal-to-noise ratio of the Sn plasma spectral lines, which is crucial for the measurement of EUV radiation intensity and spectral purity.

[0060] Compared with other main group elements, such as substrate materials like silicon (Si), germanium (Ge), and lead (Pb), carbon (C) exhibits the best comprehensive performance in terms of thermal stability, spectral background interference control, processing cost, reliability, etc. Among them, although the Si substrate has a relatively high melting point, its rich spontaneous emission spectral lines are prone to introduce spectral line interference in the EUV band; the Ge substrate has a low melting point and is easily oxidized, making it unsuitable for high-temperature laser deposition environments; the Pb substrate has a high density but an extremely low melting point and is toxic, unable to meet the requirements of high stability and safety. Therefore, the present invention preferably uses a C substrate as the carrier of the composite thin film target.

[0061] Step 102: Use plasma spectroscopy measurement technology to collect the extreme ultraviolet emission spectrum of the C-Sn thin film target generated under laser irradiation, and calculate the extreme ultraviolet light conversion efficiency based on the plasma spectrum to obtain the first efficiency calculation value.

[0062] After the C-Sn thin film target is prepared, use a high-resolution extreme ultraviolet spectrometer to perform real-time spectroscopy measurement on the plasma generated by laser irradiation of the C-Sn thin film target, and focus on monitoring the extreme ultraviolet emission intensity within the 13.5 nm band.

[0063] Through spectral data analysis, calculate the extreme ultraviolet light conversion efficiency in the first stage (the first efficiency calculation value).

[0064] Step 103: Optimize the parameters of pulsed laser deposition according to the first efficiency calculation value, and adjust the thickness of the Sn thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn thin film target meets the predetermined requirements.

[0065] According to the first efficiency calculation value, machine learning algorithms (such as Bayesian optimization, genetic algorithms, or reinforcement learning) can be used to intelligently optimize the pulsed laser deposition parameters, including but not limited to laser power density, pulse frequency, background gas pressure, deposition time, and substrate temperature.

[0066] The machine learning model establishes a training set through historical deposition data and real-time spectral feedback data, and automatically adjusts the parameter combination to quickly converge to the deposition conditions that optimize the extreme ultraviolet light conversion efficiency.

[0067] Finally, an optimized C-Sn thin film target is obtained, and the corresponding extreme ultraviolet light conversion efficiency meets or exceeds the design index.

[0068] In this embodiment, the thickness of the optimized Sn thin film is about 400 nm, and in this case, the extreme ultraviolet light conversion efficiency can reach more than 2%.

[0069] Step 104: Continuously deposit a C thin film on the C-Sn thin film target by using the laser thin film deposition technology to obtain a "sandwich"-type C-Sn-C composite thin film target.

[0070] Based on the C-Sn thin film target optimized in the first stage, continue to use the pulsed laser deposition technology to deposit a layer of C thin film on the surface of the Sn thin film to form a C-Sn-C composite thin film target.

[0071] The functions of the top C thin film include:

[0072] 1. The splash suppression effect. The top C film acts as a buffer barrier, which can absorb and disperse part of the energy pulse when the laser is initially incident, avoiding the direct impact of the laser on the surface of the Sn layer, thereby weakening the formation of local superheated regions; the top C film can reduce the material rupture and ejection caused by the rapid expansion of the local high-temperature and high-pressure region; at the same time, the C film has high thermal stability and strong interfacial bonding force, and can withstand the initial pulse of the laser-induced shock wave, thereby suppressing the non-uniform expansion and particle escape of the Sn layer. The effect is manifested as a significant reduction in Sn particle and debris contamination, and an improvement in the life and cleanliness of the system optical components.

[0073] 2. The energy redistribution and coupling optimization effect. The partial absorption and scattering of the laser by the top C film can form an energy slow-release layer, which delays the laser energy delivery rate longitudinally, making the absorption of the Sn layer more uniform and gentle; when the thickness of the top C film is appropriate (such as 150 nm), the laser still has enough intensity to excite the Sn layer to form a high-density plasma after penetration, while avoiding the concentration of the laser energy peak at a single surface point; this energy redistribution mechanism significantly improves the coupling efficiency of the laser energy and the Sn plasma, weakens the optical thickness of the Sn plasma, and thus improves the EUV photon output efficiency. The effect is manifested as an increase in the EUV emission intensity corresponding to a single laser energy, the spectral peak concentrating near 13.5 nm, and an improvement in the spectral purity SP value.

[0074] 3. Enhancement of plume stability and spatial uniformity. The top C film can promote the melting and vaporization of Sn to form a stable evaporation interface on the surface, avoiding local plume instability in the high-speed vaporization region; the spatial confinement effect of the film structure on the plasma plume can reduce the asymmetric plume expansion, promote the formation of axisymmetric plasma, and improve the stability of the light source focus. The effect is manifested as more uniform output light intensity, facilitating the light collection of the EUV focusing system and long-term repeated operation.

[0075] 4. Repetitive process control and enhancement of solid target stability. Compared with the liquid instability and landing point drift of droplet targets, the composite film target is mechanically fixed and thermally stable, which is conducive to process repetitive control; the top C film has good mechanical strength and thermal shock resistance, which can avoid the structure spalling or deformation during the repeated laser action. The effect is manifested as an increase in the target life, a reduction in the replacement frequency, and is conducive to industrial mass production operation.

[0076] 5. Spectroscopic background advantage. Element C does not produce obvious spontaneous emission spectral lines in the extreme ultraviolet band of 13.5nm ± 2%. This spectral characteristic enables the top C film, even if it is partially broken through or excited under laser ablation, not to cause background interference or peak position superposition to the EUV main emission spectral lines of Sn plasma (such as the spectral band corresponding to Sn 10+ –Sn 14+ ). Therefore, the introduction of the C film not only does not affect the spectral purity (Spectral Purity, SP) of the EUV emission measurement signal, but instead improves the signal-to-noise ratio of the spectral line and the quality of the light source focus by improving the plasma spatial stability and energy transport behavior. This characteristic also makes the C-Sn-C structure have higher reliability and application adaptability in EUV radiation spectroscopy diagnosis and radiation modeling.

[0077] Step 105: Use plasma spectroscopy measurement technology to collect the extreme ultraviolet emission spectrum of the plasma generated by the C-Sn-C composite film target under laser irradiation, and calculate the extreme ultraviolet light conversion efficiency according to the plasma emission spectrum to obtain the second efficiency calculation value.

[0078] Using plasma spectroscopy measurement technology, analyze the plasma plume generated by laser irradiation of the C-Sn-C composite film target, collect the extreme ultraviolet emission spectrum and calculate the extreme ultraviolet light conversion efficiency in the second stage (the second efficiency calculation value).

[0079] Step 106: Further optimize the parameters of pulsed laser deposition according to the second efficiency calculation value, and adjust the thickness of the top C thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn-C composite film target meets the predetermined requirements.

[0080] Similarly, a machine learning optimization strategy is adopted to intelligently optimize the deposition thickness and laser conditions of the topmost C film. Through continuous iteration with extreme ultraviolet spectroscopy feedback, the thickness of the C layer is adjusted to the optimal state, thereby further improving the overall extreme ultraviolet light conversion efficiency and stability of the final C-Sn-C composite film target.

[0081] In this embodiment, the optimized thickness of the C film is about 150 nm, and in this case, the extreme ultraviolet light conversion efficiency can reach more than 6%.

[0082] In this embodiment, by real-time monitoring the emission spectrum of the laser plasma in the extreme ultraviolet band, the pulsed laser deposition parameters are dynamically adjusted to improve the quality of the deposited film and the extreme ultraviolet light conversion efficiency. The system can automatically complete data acquisition, CE calculation, and closed-loop feedback optimization of the deposition parameters, effectively improving the process stability and the consistency and controllability of the film performance.

[0083] There are multiple core points to note in the process of preparing the composite target and measuring the extreme ultraviolet light, which are as follows:

[0084] 1. Plasma generation and target breakdown control: To ensure that the C-Sn-C composite film target can be effectively broken down and excited to produce distinct characteristic spectral lines near 13.5 nm of Sn plasma, the power density of the laser pulse is adjusted to ensure stable breakdown under single-shot pulse conditions. The power density is estimated according to the following formula:

[0085]

[0086] On the premise of determining the laser pulse width and focal spot (the laser focal spot radius in this embodiment remains 50 μm), the laser energy is gradually increased from zero until plasma flash (the simultaneous appearance of white light continuum and characteristic spectral lines) is observed to confirm the occurrence of breakdown. The power density at this time is set as the breakdown threshold, and the laser power density for generating Sn plasma EUV radiation subsequently needs to be higher than this threshold to avoid insufficient energy for breakdown.

[0087] To determine whether the top C film in the C-Sn-C composite film target has been effectively broken down by the laser and the middle Sn layer has been excited, the present invention establishes the following criterion system:

[0088] EUV spectral line feature recognition: When the laser is excited, if a strong and sharp emission peak first appears in the 13.5 nm ±2% band, and its peak intensity is significantly higher than the continuum background, it indicates that the laser has penetrated the top C film and excited the Sn layer to undergo effective ionization. In this embodiment, as shown in the appendix Figure 3As shown, in the EUV spectrum in the non-breakdown state, there is only a weak continuous spectrum generated by C plasma, and there are no obvious spectral lines near 13.5 nm; when the laser energy reaches the breakdown threshold, clear Sn plasma emission peaks appear in the same wavelength band, indicating that the breakdown of the C film and the excitation of Sn have been completed.

[0089] Relationship between excitation energy and thickness: Taking the C-Sn-C composite thin film target with a top C film thickness of 40 nm as an example, single-pulse excitation experiments were carried out at different laser energies, and the appearance threshold and intensity response of the Sn spectral line were analyzed in combination with the EUV spectrum measurement results (as shown in the appendix). Figure 3 As shown), the results show that when the laser energy reaches about 60 mJ, a significant emission peak is first observed in the 13.5 nm wavelength band. Laser stable penetration can be achieved under this thickness condition, and the excitation repeatability is good.

[0090] Through the comprehensive verification of the above criteria, it is possible to effectively judge whether the laser has achieved complete breakdown of the C film and effective excitation of the Sn layer, thus laying a foundation for subsequent improvement of EUV radiation efficiency and optimization of spectral line purity.

[0091] 2. Optimization of the spectral measurement system and resolution guarantee: To ensure the accurate identification of elemental spectral lines, according to the emission characteristics of the Sn target in the EUV band, a grating with a grating density of 1200 g / mm is selected for extreme ultraviolet radiation spectroscopy, and the spectral resolution is improved by reducing the spectrometer slit width to 50 μm. Since the high-resolution configuration (narrow slit and high-grating grating) may lead to signal attenuation, compensation is carried out by increasing the laser energy or accumulating the signal multiple times. At the same time, a high-pixel density CCD detector is used to ensure that the spectral line spans multiple pixels and improve the measurement accuracy.

[0092] 3. Synergistic timing control and spatial coupling strategy for thin film deposition and extreme ultraviolet spectroscopy measurement: To achieve the synergistic optimization of the thin film target preparation process and its extreme ultraviolet emission performance characterization, the present invention constructs a set of timing control and spatial coupling strategies based on laser deposition - plasma excitation - spectroscopy measurement integration.

[0093] In terms of timing control, the entire system is uniformly managed by the first trigger in the appendix. Figure 2 It mainly includes three core modules: pulsed laser deposition module, target movement / conversion module, and EUV spectrum measurement module. The system coordinates the operation timing of each module through a high-speed digital delay pulse controller (Stanford DG535), so that: after each round of thin film deposition is completed, the laser excitation program can be automatically started; the trigger synchronization accuracy between the laser pulse and the spectral exposure can be better than 10 ns; there is a clear time locking relationship between laser deposition - laser excitation - spectroscopy acquisition, avoiding system jitter or measurement drift.

[0094] In terms of spatial coupling design, the thin film deposition area, the laser ablation area and the EUV signal acquisition path are designed in a unified manner through precise beam and target geometry arrangements. The laser deposition uses a 45° incident angle to control the deposition film thickness and uniformity. The laser excitation and spectral line acquisition path is set to a structure with a 90° angle to the target surface normal, and is supplemented by: an adjustable beam collimation module to ensure that the laser focus spot stably covers the deposition area; a high-precision 4D moving sample stage to achieve in-plane deposition uniformity correction and avoid overlapping of ablation areas.

[0095] In addition, to further improve the time resolution ability of spectral line data, the spectral acquisition system supports linkage with the layer-by-layer thin film deposition steps of the laser deposition system to form a closed-loop control process of "deposition - excitation - measurement - feedback - re-deposition", which is suitable for optimizing the thickness of the Sn thin film and the top C film buffer layer.

[0096] 4. Wavelength calibration and measurement accuracy improvement: To ensure the wavelength and intensity accuracy of the measurement system, absolute calibration is carried out using a standard metal target in the NIST database. By adjusting the focal length, energy and spot size, the spectral acquisition parameters are optimized. After calibration, the wavelength error is controlled within 0.2 nm, and the relative intensity error is less than 5%.

[0097] 5. Laser plasma emission spectrum acquisition of the C-Sn thin film target and calculation of the first efficiency value: In this embodiment, laser pulses generated by a Nd:YAG laser with a frequency of 10 Hz, a wavelength of 1064 nm and a pulse width of 10 ns are focused on the surface of the C-Sn thin film target in a vacuum chamber to excite a high-temperature and high-density plasma. The plasma emission light enters a grazing incidence extreme ultraviolet spectrometer through a 50 μm slit, and after being dispersed by a grating, it is collected by an absolutely calibrated back-illuminated CCD detector, covering a wavelength range of 11 - 16 nm.

[0098] According to the collected plasma emission spectrum, the extreme ultraviolet light conversion efficiency is calculated to obtain the first efficiency calculation value of the C-Sn thin film target. The extreme ultraviolet light conversion efficiency CE can be calculated by the following formula:

[0099] ,

[0100] where, is the laser absorption rate, which depends on the electron density distribution of the plasma, especially strong absorption occurs near the critical density; is the radiation conversion ratio, which represents the proportion of the absorbed laser energy converted into radiation energy and emitted in the solid angle towards the laser incident side; is the spectral purity, which represents the proportion of the radiation energy within a 13.5 nm bandwidth in the total radiation energy. The laser absorption rate and the radiation conversion ratio are obtained by simulation with a two-dimensional radiation hydrodynamics program, and the spectral purity is obtained by observing spectral line analysis.

[0101] 6. Process Optimization and Feedback Control of C-Sn Thin Film Targets: The first calculated efficiency value of the C-Sn thin film target provides crucial real-time feedback information for optimizing the deposition parameters of the Sn film. To further improve the response speed and accuracy of thin film deposition and spectral measurement, an intelligent parameter optimization module based on machine learning (ML) is introduced in the invention. Through the training of historical data sets and the dynamic input of real-time monitoring data, methods such as Bayesian optimization, genetic algorithms, or reinforcement learning are used to quickly deduce the optimal combination of key parameters such as laser energy density, pulse frequency, and target-substrate distance, thereby automatically guiding the iteration of deposition conditions and significantly improving the optimization efficiency.

[0102] In the preparation and optimization of the C-Sn thin film target, the influence of laser power density, the distance between the Sn target and the C substrate for coating on the film quality also needs to be considered. In terms of laser power density, if the power density is too low, the ablation is insufficient, resulting in a decrease in deposition rate and deterioration of film quality. If the power density is too high, sputtering is likely to increase, reducing the conversion efficiency and film quality. Therefore, the power density should be kept slightly higher than the ablation threshold. In this embodiment, the laser power density is set to 6×10 10 W / cm 2 . In terms of the distance between the Sn target and the C substrate for coating, if the distance is set too small, particle splash contamination will occur, and if the distance is set too large, the deposition efficiency will be reduced. In this embodiment, the distance is set to 5 cm.

[0103] During the preparation and optimization of the C-Sn thin film target, the thickness of the Sn thin film needs to be evaluated based on the characteristic spectral line intensity of Sn within the wavelength range of 13.5 nm (±2% bandwidth). At the same time, the C element spectral line is monitored synchronously during the experiment to avoid the C spectral line signal being too strong and masking the Sn signal. The optimal experimental conditions are determined according to the change in the peak value of the Sn spectral line intensity. Combining the pulse frequency and the single-pulse deposition rate, the total deposition time is determined according to the following formula:

[0104] ,

[0105] In this embodiment, the optimal thickness of the Sn film of the C-Sn thin film target is about 400 nm, and the corresponding Sn film deposition time is 30 minutes.

[0106] 7. Design of C-Sn-C Composite Film Target and Optimization of Sandwich Structure: As a preferred embodiment, after preparing the C-Sn film target, a C film is further deposited on its surface by laser thin film deposition technology to form a sandwich-type C-Sn-C composite structure. Subsequently, the C-Sn-C composite film target is irradiated with a laser, and its plasma emission spectrum is collected to obtain a second efficiency calculation value. According to this value, the deposition parameters are continuously optimized using machine learning methods until an optimized composite film target with an extreme ultraviolet light source efficiency greater than 6% is obtained. During the preparation and optimization of the C-Sn-C composite film target, attention should still be paid to the influence of laser energy density and target spacing on the film quality. In this embodiment, the laser power density for generating the top C film is set to 10 11 W / cm 2 ; the distance between the C target for film coating and the C-Sn film target is set to 6.5 cm. In this embodiment, the optimal thickness of the C film in the C-Sn-C composite film target is about 150 nm, and the corresponding C film deposition time is 10 minutes. The sandwich-type target structure realizes the efficient absorption and utilization of laser energy through the functional collaborative design of different material layers, significantly improves the plasma uniformity and film stability, and enhances the spectral purity and conversion efficiency.

[0107] In the present invention, the preparation of the C-Sn-C composite film target for the extreme ultraviolet lithography light source and the corresponding extreme ultraviolet spectrum measurement are carried out by the pulsed laser deposition-plasma spectrum measurement integration device shown in the appendix Figure 2 . This integration device includes a pulsed laser deposition module and a plasma spectrum measurement module, and realizes synchronous operation by timing control of laser triggering, target movement, and spectrum acquisition. The pulsed laser deposition module and the spectrum measurement module share a Nd: YAG laser to form a closed-loop and highly efficient integrated operation process. Refer to Figure 2 Figure 2 shows the structural schematic diagram of the pulsed laser deposition-plasma spectrum measurement integration device provided by the present invention. Through this integrated design, the problems existing in the traditional spectrum measurement device, such as inability to diagnose in real time, inconsistent repeated measurement conditions, and cumbersome data processing, are effectively overcome, and the experimental efficiency and result reliability in the deposition preparation process are further improved.

[0108] The pulsed laser deposition module mainly includes a first trigger 1, a first laser 2, a first laser reflection lens 3, a second laser reflection lens 4, a first laser focusing lens 5, a vacuum transparent window 6, a vacuum chamber 7, a first target holder 8, a first moving platform 9, a first controller 10, a second target holder 11, a vacuum gate valve 12, a second moving platform 13 and a second controller 14. The first trigger 1 is used to simultaneously trigger the first laser 2 and the first controller 10. The first laser 2 outputs an ablation laser beam with a wavelength of 1064 nm and a pulse width of 10 ns. The ablation laser is vertically reflected by the first laser reflection lens 3 (the included angle between the incident and reflected light beams is 90 degrees) to the second laser reflection lens 4. After further reflection by the second laser reflection lens 4, it is focused and incident on the first target holder 8 in the vacuum chamber 7 through the first laser focusing lens 5 and the vacuum transparent window 6. The first laser focusing lens 5 is a quartz lens with a focal length of 300 mm. A solid Sn or C target is placed on the first target holder 8, and after the laser beam is focused, high-energy density ablation is induced to form a high-temperature Sn or C plasma plume. The first target holder 8 is installed on the first moving platform 9 and is controlled by the first controller 10 to achieve precise displacement and collimation in the two-dimensional plane direction. The second target holder 11 is connected to the second moving platform 13 and is used to carry a C substrate target or a C-Sn thin film target and receive Sn or C plasma sputtering materials to form a C-Sn thin film target or a C-Sn-C composite thin film target. The second moving platform 13 is controlled by the second controller 14 to achieve precise two-dimensional position adjustment. The vacuum chamber 7 provides the required vacuum environment for the entire deposition and measurement process. The vacuum gate valve 12 is set in the vacuum system and is used to control the chamber partition or deflation during target replacement to ensure independent adjustment and stable maintenance of the system vacuum degree.

[0109] The plasma spectroscopy measurement module includes a vacuum chamber 7, a second target holder 11, a vacuum gate valve 12, a second moving platform 13, a second controller 14, a second laser 15, a third laser mirror 16, a fourth laser mirror 17, a second laser focusing lens 18, a spectrometer entrance slit 19, an extreme ultraviolet spectrometer 20, a CCD camera 21 and a second trigger 22. The second trigger 22 is used to coordinately control the timing trigger of the second laser 15, the CCD camera 21 and the second controller 14. The second laser 15 also outputs a laser beam with a wavelength of 1064 nm and a pulse width of 10 ns. This laser beam is first reflected by 90 degrees by the third laser mirror 16, then deflected by the fourth laser mirror 17, and finally focused on the deposition target surface on the second target holder 11 by the second laser focusing lens 18. The second laser focusing lens 18 is a quartz lens with a focal length of 150 mm, and the focusing angle is designed to be 45 degrees.

[0110] The extreme ultraviolet (EUV) emission light of the plasma formed under the action of the laser enters the EUV spectrometer 20 through the entrance slit 19 of the spectrometer for spectral splitting. The EUV spectrometer 20 is used to receive the EUV light of the plasma and perform spectral splitting processing. The CCD camera 21 is connected to the rear end of the EUV spectrometer 20 and is used to enhance and detect the split optical signal.

[0111] The first trigger 1 and the second trigger 22 are connected through a synchronous control circuit to realize the timing coupling of the laser ablation and spectral measurement processes, ensuring that after each pulsed laser action, the plasma emission signal can be accurately collected and recorded within the optimal time window, thereby significantly improving the repeatability of the data and the reliability of the analysis.

[0112] In this embodiment, both the first laser 2 and the second laser 15 can be selected as Nd:YAG lasers (neodymium-doped yttrium aluminum garnet lasers). Nd:YAG lasers have the characteristics of high energy output and multiple wavelength options, and are particularly suitable for interacting with solid targets to generate high-temperature and high-density plasmas. By reasonably regulating parameters such as the laser wavelength and single-pulse energy, the dynamic behavior of the plasma plume can be effectively controlled, thereby realizing the deposition of a thin film with uniform thickness and pure composition on the surface of the substrate target. In addition, Nd:YAG lasers have good stability and adaptability, and can continuously and efficiently generate high-temperature and high-density plasmas under different laser parameter configurations, which is an ideal laser source for laser plasma generation and thin film deposition in the present invention.

[0113] During multiple plasma measurement processes, to ensure the stability of the laser plasma and avoid excessive local ablation of the target, in the design of the present invention, the first moving platform 9 is used to control the movement of the first target holder 8 in a two-dimensional plane to achieve uniform laser irradiation of different regions on the surface of the target, preventing damage to the target caused by the continuous action of laser pulses on the same point. At the same time, by controlling the movement of the second target holder 11 in a two-dimensional plane through the second moving platform 13, laser ablation measurement can be carried out on the deposited C-Sn thin film target or C-Sn-C composite thin film target at different positions, and then the corresponding EUV emission spectral data of the C-Sn thin film target or C-Sn-C composite thin film target under different experimental conditions can be obtained. The EUV spectrometer 20 receives the EUV light signal of the plasma incident through the entrance slit 19 of the spectrometer and outputs the corresponding EUV band emission spectrum.

[0114] In each set of spectral measurements, usually six independent plasma extreme ultraviolet spectrograms are collected. To improve the data accuracy, it is necessary to preprocess the spectral data collected in each group, that is, first screen out the abnormal spectral curves, and then perform summation and averaging on the screened spectral signals, so as to obtain a high-quality plasma spectrogram after removing the outliers. Through the above data processing steps, the systematic fluctuations and random errors in the measurement process are effectively eliminated, the representativeness and repeatability of the plasma spectral data are improved, and a reliable basis is provided for the accurate calculation of the subsequent extreme ultraviolet light conversion efficiency (CE) and the evaluation of the thin film performance.

[0115] Through the above integrated device for pulsed laser deposition - plasma spectral measurement, the preparation of composite thin film targets and real-time spectral measurement can be efficiently completed on the same platform, realizing closed-loop process control from deposition to diagnosis, greatly improving the process development efficiency and the consistency of target preparation, and providing important technical support for the efficient development of the light source system of extreme ultraviolet lithography machines.

[0116] In this embodiment, the preparation process of the composite thin film target needs to comprehensively consider key details such as material characteristics, process parameters, and environmental control. By finely regulating environmental variables, laser parameters, substrate state, and post-treatment processes, the quality and performance of the thin film are optimized. The specific process steps are as follows:

[0117] First, chamber preparation is carried out. Since Sn is extremely easy to oxidize to form SnO2, once exposed to air or an oxygen-containing atmosphere, it will significantly increase the resistivity of the thin film and reduce the performance. Therefore, it is necessary to operate in a high vacuum or an environment filled with inert gases (such as argon, nitrogen) to avoid oxidation reactions to the greatest extent. In this embodiment, the chamber is pumped to a vacuum state with a pressure lower than 10 -5 Pa.

[0118] In the substrate pre-treatment stage, the Sn target is first ultrasonically cleaned and dried, and then mechanically polished or ion sputtered to remove the surface oxide layer and adsorbed pollutants to ensure a clean surface. The substrate temperature also needs to be precisely controlled to regulate the crystallinity and density of the deposited thin film. In this embodiment, the substrate temperature is maintained at 25°C.

[0119] The target installation steps are divided into two stages. The first stage is the preparation of the C-Sn thin film target and extreme ultraviolet spectral measurement. In this stage, the high-purity Sn target for coating is fixed on the first target holder 8. A C substrate is placed on the second target holder 11 to produce the C-Sn thin film target. The second stage is the preparation of the C-Sn-C composite thin film target and extreme ultraviolet spectral measurement. In this stage, the high-purity C target for coating is fixed on the first target holder 8. The prepared C-Sn substrate is placed on the second target holder 11 to produce the C-Sn-C composite thin film target.

[0120] In the laser parameter setting step, an Nd:YAG laser is selected to output a laser with a wavelength of 1064 nm, and an appropriate laser power density is set to ensure effective ablation of the Sn target while avoiding the generation of large-sized particles. As a preferred embodiment, when preparing the C-Sn thin film target, the laser power density is set to 6×10 10 W / cm 2 in this embodiment, the frequency is set to 10 Hz, and the substrate temperature is 25 °C. When preparing the C-Sn-C composite thin film target, the laser power density is increased to 10 11 W / cm 2 in this embodiment, the frequency is also 10 Hz, and the substrate temperature remains at 25 °C.

[0121] During the deposition process, it is necessary to optimize the target-substrate distance and deposition time to balance the film thickness, deposition rate, and film uniformity. If the target-substrate distance is too small, the plasma plume causes local heat accumulation in the substrate area, easily leading to non-uniform film layers or microstructural defects; if the distance is too large, the plume density significantly decays, resulting in reduced target utilization and insufficient film thickness. At the same time, the choice of deposition time plays a key role in the final film thickness and film formation quality. Under fixed laser energy and frequency conditions, the film thickness basically increases linearly, so the deposition time needs to be comprehensively determined according to the target film thickness, deposition rate, and adhesion matching relationship. In addition, too short deposition time may lead to discontinuous film layers or insufficient nucleation, while too long may result in adverse effects such as thermal stress accumulation and loose structure, which need to be reasonably set in combination with plasma plume monitoring and pre-experiment data. In this embodiment, when preparing the C-Sn thin film target, the distance between the substrate C target and the Sn target is set to 5 cm, the pulsed laser deposition time is 30 minutes, and the plasma plume is monitored in real time; when preparing the C-Sn-C composite thin film target, the distance between the C-Sn substrate and the C target is set to 6.5 cm, the pulsed laser deposition time is 10 minutes, and the plasma plume is also monitored in real time.

[0122] After the C-Sn thin film target and the C-Sn-C composite thin film target are prepared, thin film characterization is required. In the present invention, structural characterization and emission spectrum diagnosis methods are comprehensively used to evaluate the structural quality and radiation performance of the C-Sn thin film target and the C-Sn-C composite thin film target.

[0123] First, X-ray diffraction (XRD) is used to analyze the crystallization state of the thin film sample. In this embodiment, through attachment Figure 4 and attachment Figure 5 show the XRD patterns of the C-Sn thin film target and the C-Sn-C composite thin film target.

[0124] The XRD pattern of the C-Sn thin film target (attachment Figure 4)The results show that the sample uses highly crystalline graphite (Graphite-2H, PDF#41-1487) as the substrate, and a metallic Sn thin film is successfully deposited on its surface. In the figure, the strong (002) diffraction peak at 2θ ≈ 26.5° comes from the graphite substrate, indicating its highly preferred orientation. Multiple diffraction peaks of β-Sn in the film layer (corresponding to PDF#04-0673) appear in the range of 30°–70°, indicating that the deposited tin film is polycrystalline but has weak crystallinity. No impurity phase peaks such as SnO2 or SnC are seen in the spectrum, indicating that no significant chemical reaction occurred during the laser deposition process, and a relatively pure C / Sn layered structure was obtained.

[0125] XRD pattern of the C-Sn-C composite thin film target (attached Figure 5 ) shows that after sequentially depositing Sn and C thin films on the graphite substrate by the laser deposition process, the bottom graphite exhibits a typical (002) diffraction peak (2θ ≈ 26.5°), with a high and sharp peak intensity, indicating that the graphite substrate has excellent crystallization orientation. The polycrystalline structure of the intermediate Sn film is retained, and its characteristic peaks match those of PDF#04-0673 β-Sn. Although the intensity is relatively weak, it is still clearly distinguishable. No impurity phase peaks such as SnO2 or SnC are seen in the spectrum, indicating that no significant reaction occurred during the deposition process, and a pure C / Sn / C composite structure was obtained. There are no obvious diffraction peaks in the top C film of the composite thin film target. The main reasons are as follows: 1. The penetration depth of XRD (usually on the order of µm) is much larger than the film thickness (in this example, the thickness of the top C film is about 150 nm). For X-rays, the diffraction signals generated by such thin films are extremely weak and are often overwhelmed by the substrate signals or masked by the instrument background noise. 2. The (002) peak of the bottom C substrate is extremely strong, and the middle Sn film also contributes to diffraction. Even if there is weak diffraction in the top C film, it is easily masked by the main peak of the substrate or difficult to distinguish.

[0126] In addition, the extreme ultraviolet emission characteristics of the target under excited conditions are diagnosed and analyzed by laser-induced plasma emission spectroscopy measurement. Under the standard single-pulse laser excitation conditions, the EUV emission spectrum is collected, and the emission line intensity, spectral purity SP, and background continuum are analyzed. This spectroscopic response characteristic can be used as a feedback basis for the target structure design and film formation optimization. Attached Figure 6 Shown are the EUV emission spectra of the C-Sn thin film target after excitation under different deposition conditions, attached Figure 7 And the spectral line response comparison of the corresponding C-Sn-C composite thin film target and C-Sn thin film target. Attached Figure 6The results in [specific context] show that in the case of a laser energy of 250 mJ, the emission intensity of the C-Sn thin film target with a Sn film deposition time of 30 minutes in the 13.5 nm band is significantly enhanced, the spectral purity is improved, and the continuous spectrum interference is reduced, indicating that it has better energy coupling efficiency and radiation stability. Attached Figure 7 The results in [specific context] show that in the case of a laser energy of 350 mJ, an obvious emission peak from Sn appears in the EUV spectrum of the C-Sn-C composite thin film target, indicating that the top C film has been completely broken through, and enough laser energy has reached the middle Sn layer and ablated to generate high-temperature and high-density Sn plasma.

[0127] In the process of analyzing and inversing the data of the EUV spectrum of laser plasma, spectral wavelength calibration is required first. By measuring the characteristic spectral lines of low-Z elements (such as Al, Si) plasmas, the spectral data of high-Z element Sn plasmas are accurately calibrated to determine the corresponding relationship between the Pixel points of the spectral abscissa and the wavelength. In the spectral line identification step, the measured spectrum is compared with the standard spectral line data in the NIST database to clarify the transition energy levels and ionization states corresponding to each spectral peak, and the spectral line interference caused by the C substrate target is identified and excluded.

[0128] The diagnosis of plasma temperature and density parameters is jointly deduced by the Boltzmann plot method and the Stark broadening method, and at the same time, the Cowan program is combined to calculate and analyze the energy level structure and transition information of Sn ions, and the key physical quantities such as the temperature, density and charge state distribution of the plasma are accurately extracted. The configurations considered in the Cowan program calculation include Sn 6+ - Sn 14+ The ground state, double-excited state, triple-excited state and higher multiple-excited states of ions.

[0129] The present invention further prepares C-Sn thin film targets with different Sn film deposition times (20 / 30 / 40 minutes). Through the measurement and analysis of the laser plasma spectrum, the influence of the deposition time on the extreme ultraviolet emission performance of Sn plasma is systematically studied. Figure 6 shows the EUV spectra of different C-Sn thin film targets and pure Sn targets when the laser energy is 250 mJ. The results of the figure show that the C-Sn thin film target prepared with a Sn film deposition time of 30 minutes improves the spectral purity SP value while maintaining good spectral intensity and reduces the background noise.

[0130] In this embodiment, the laser absorption rate f of the C-Sn thin film target with a Sn film deposition time of 30 minutes calculated by the radiative hydrodynamics program L is 0.4, and the radiation conversion ratio C R is 0.5, and the spectral purity SP is 0.12. The conversion efficiency CE is comprehensively obtained as 2.4%. It shows that the C-Sn / 30-minute thin film target achieves the predetermined CE target.

[0131] Based on the C-Sn thin film target, a C layer is further deposited to form a C-Sn-C composite thin film target, which can further improve the plasma emission intensity, spectral purity and conversion efficiency. Figure 7 shows the EUV spectra of the C-Sn / 30 min-C / 10 min composite thin film target, the C-Sn / 30 min thin film target and the pure Sn target under a laser energy of 350 mJ. The results in the figure show that the EUV spectral line intensity, spectral purity and CE value of the C-Sn-C composite thin film target are further improved compared with those of the C-Sn thin film target. Among them, the peak spectral line intensity is enhanced by about 2 times, the spectral purity SP is increased by about 2.3 times, and the conversion efficiency CE is increased by about 3 times to reach 6%. It shows that the C-Sn / 30 min-C / 10 min composite thin film target has achieved the predetermined CE target.

[0132] The present invention proposes a preparation method of an efficient composite thin film target for an extreme ultraviolet lithography light source and a supporting laser deposition-plasma spectroscopy integrated system, which is specifically applied to the light source system of a laser plasma extreme ultraviolet (LPP-EUV) lithography machine, and has the following remarkable technical advantages:

[0133] The present invention adopts device integration and automatic control design to construct a cooperative working mode of a dual-laser system. The first laser is used for pulsed laser deposition (PLD) to prepare a C-based Sn thin film, and the second laser is dedicated to plasma spectroscopy excitation and real-time diagnosis. The two optical paths are independently and parallelly designed, effectively avoiding optical cross-interference and improving the system stability. Through a high-precision timing controller (such as Stanford Research Systems DG535), precise synchronization of the triggering of the two lasers, the movement of the target and the acquisition of spectral data is realized, ensuring good repeatability and controllability of the experimental process.

[0134] Real-time spectral feedback and process closed-loop optimization are the highlights of this system. An integrated grazing incidence extreme ultraviolet (EUV) spectrometer and a high-time-resolution CCD camera are integrated to capture the evolution process of plasma emission on a nanosecond time scale and monitor the 8+ –Sn 14+ transition characteristic spectral lines of highly charged ions of Sn (near 13.5 nm), and the extreme ultraviolet light conversion efficiency (CE) is calculated in real time based on the change of spectral line intensity. Combining the built-in algorithm, the system can dynamically adjust key parameters such as laser energy and target-substrate distance to form an intelligent closed-loop control of "measurement-optimization-deposition" integration.

[0135] To avoid local damage caused by single-point laser ablation, the target is installed on a high-precision four-dimensional moving platform (step accuracy ≤ 1 µm), which supports programmed path planning (such as a spiral scanning trajectory), effectively extending the service life of the target and improving the uniformity and density of the deposited thin film.

[0136] In terms of thin film design, the present invention innovatively proposes a multi-layer film structure strategy. By alternately depositing Sn thin films and C buffer layers, a C-Sn-C composite thin film target is formed. The top C film is used to achieve the suppression of Sn particle sputtering and a significant improvement in spectral purity and conversion efficiency. In this embodiment, the radiation intensity of the C-Sn / 30 minutes-C / 10 minutes composite thin film target in the 13.5 nm band is increased by 2 times compared with that of the single-layer Sn thin film, the improvement of spectral purity SP reaches about 2.3 times, and the conversion efficiency CE is increased by about 3 times. It proves the great application prospect of the C-Sn-C composite thin film target prepared by the present invention in extreme ultraviolet lithography.

[0137] For CE calculation, the present invention introduces a CE inversion framework based on two-dimensional radiative hydrodynamics simulation, and combines experimental measured spectra for parameter inversion and correction. By combining the laser absorption rate f L , the radiation conversion ratio C R and spectral purity SP, the CE value of the C-Sn-C composite thin film target can reach 6%, which is significantly better than the level of about 5% of the droplet Sn target and much higher than the level of 2% of the solid Sn target.

[0138] In terms of technical compatibility and scalability, the present invention has carried out a comprehensive optimization design. The target holder adopts a modular structure, supports the rapid replacement of different targets (such as Sn, Mo, Si, etc.), and combined with the PLD process, the preparation of Sn-Mo / Si multi-layer film structure can be realized, supporting the development needs of new EUV mirror materials. The spectral database (based on NIST standard data) is integrated inside the system, and supplemented with machine learning algorithms for spectral line identification, parameter inversion and automatic generation of process optimization suggestions, which can quickly match the Sn ion transition characteristics. In addition, the system design is compatible with CO2 lasers (10.6 µm) and 2 µm solid-state lasers, adapting to the experimental requirements of different bands, providing a broad space for the future research on high-efficiency CE processes of short-wave lasers.

[0139] In terms of economic benefits and industrialization potential, the present invention also has significant advantages. By using the pulsed laser deposition (PLD) technology to replace the traditional micro-droplet injection target system, the complex droplet generator is eliminated, and the overall cost can be greatly reduced. At the same time, since the utilization rate of the solid Sn target material is increased to more than 90%, the material consumption and operation cost are greatly reduced. The system adopts a modular vacuum chamber design (such as an integrated gate valve structure), supports rapid target replacement and chamber cleaning operations, and shortens the maintenance cycle from 48 hours of the traditional system to 4 hours, greatly improving the equipment availability and industrial mass production adaptation ability.

[0140] In summary, through the innovation of the target structure, real-time spectral diagnosis, data-driven process optimization, and system integration design, the present invention significantly improves the conversion efficiency, stability, and reliability of the target in the laser plasma extreme ultraviolet lithography light source system. It has the comprehensive advantages of high efficiency, low cost, and easy expansion, providing strong support for the independent breakthrough of domestic high-end EUV lithography technology.

[0141] The present invention also provides a high-efficiency composite thin film target for an extreme ultraviolet lithography light source. The high-efficiency composite thin film target for the extreme ultraviolet lithography light source is prepared by using the preparation method of the high-efficiency composite thin film target for the extreme ultraviolet lithography light source described above. The high-efficiency composite thin film target for the extreme ultraviolet lithography light source has a stable structure, uniform composition, and excellent adhesion. It has the characteristics of high purity, high conversion efficiency, and good processability, and can be effectively applied to the laser plasma extreme ultraviolet (LPP-EUV) lithography light source system, significantly improving the extreme ultraviolet radiation output efficiency and system operation stability.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an efficient composite thin film target for an extreme ultraviolet lithography light source, characterized in that, Including: Depositing a Sn thin film on a substrate C target by using pulsed laser deposition technology to obtain a C-Sn thin film target; Collecting the plasma extreme ultraviolet emission spectrum generated by the C-Sn thin film target under laser irradiation by using plasma spectroscopy measurement technology, and calculating the extreme ultraviolet light conversion efficiency according to the plasma spectrum to obtain a first efficiency calculation value; Optimizing the parameters of pulsed laser deposition according to the first efficiency calculation value, and adjusting the thickness of the Sn thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn thin film target meets the predetermined requirements; Continuously depositing a C thin film on the C-Sn thin film target by using pulsed laser deposition technology to obtain a "sandwich"-type C-Sn-C composite thin film target; Collecting the plasma extreme ultraviolet emission spectrum generated by the C-Sn-C composite thin film target under laser irradiation by using plasma spectroscopy measurement technology, and calculating the extreme ultraviolet light conversion efficiency according to the plasma emission spectrum to obtain a second efficiency calculation value; Further optimizing the parameters of pulsed laser deposition according to the second efficiency calculation value, and adjusting the thickness of the top C thin film until the extreme ultraviolet light conversion efficiency corresponding to the optimized C-Sn-C composite thin film target meets the predetermined requirements.

2. The preparation method of the high-efficiency composite thin film target for the extreme ultraviolet lithography light source according to claim 1, characterized in that Preparing the high-efficiency composite thin film target for the extreme ultraviolet lithography light source by using a pulsed laser deposition-plasma spectroscopy measurement integration device; the pulsed laser deposition-plasma spectroscopy measurement integration device includes a pulsed laser deposition part and a plasma spectroscopy measurement part; the pulsed laser deposition-plasma spectroscopy measurement integration device synchronizes laser triggering, target movement and spectrum acquisition through timing control; the lasers used in the pulsed laser deposition part and the plasma spectroscopy measurement part are Nd:YAG lasers.

3. The preparation method of the high-efficiency composite thin film target for an extreme ultraviolet lithography light source according to claim 1, wherein The required laser power density for the preparation of the C-Sn thin film target is 6×10 10 W / cm², the frequency is 10 Hz, and the substrate temperature is 25°C.

4. The preparation method of the high-efficiency composite thin film target for an extreme ultraviolet lithography light source according to claim 2, characterized in that, The laser power density required for the preparation of the C-Sn-C composite thin film target is 10 11 W / cm², the frequency is 10 Hz, and the substrate temperature is 25°C.

5. The preparation method of the high-efficiency composite thin film target for an extreme ultraviolet lithography light source according to claim 1, characterized in that When preparing the C-Sn thin film target, the distance between the substrate C target and the Sn target for coating is 5 cm, pulsed laser deposition is carried out for 30 minutes, and the plasma plume is monitored in real time.

6. The preparation method of the high-efficiency composite thin-film target for an extreme ultraviolet lithography light source according to claim 2, wherein When preparing the C-Sn-C composite thin film target, the distance between the C-Sn thin film target and the C target for coating is 6.5 cm, pulsed laser deposition is carried out for 10 minutes, and the plasma plume is monitored in real time.

7. An efficient composite thin film target for an extreme ultraviolet lithography light source, characterized in that, Preparing by using the preparation method of the high-efficiency composite thin film target for the extreme ultraviolet lithography light source according to any one of claims 1 to 6.

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