A method for producing a nitride thin film

Abstract

This invention discloses a method for preparing nitride thin films, belonging to the field of advanced functional thin film material preparation technology. The method employs pulsed laser deposition technology and includes the following steps: placing an alloy target material prepared according to the stoichiometric ratio of the target thin film in a deposition chamber, evacuating to a background vacuum ≤, heating a single-crystal substrate to 400-1000℃, turning on a 13.56MHz radio frequency ion source and adjusting the power to 50-500W for ionizing nitrogen gas; injecting ammonia or nitrogen gas with a purity ≥99.999% into the chamber through a high-speed pulse valve with a response delay ≤50μs and an opening / closing time ≤200μs, precisely synchronized with the laser pulse electronic signal; the high-energy metallic plasma plume generated by the laser pulse ablation of the alloy target material undergoes an instantaneous gas-phase reaction with the synchronously injected reactive gas, while simultaneously bombarding the substrate surface with a high-energy nitrogen ion beam, controlling the deposition parameters to deposit a nitride thin film on the substrate, which can be cooled after in-situ annealing.

Description

Technical Field

[0001] This invention belongs to the field of advanced functional thin film material preparation technology, specifically relating to a method for preparing nitride thin films, and more particularly to a method for preparing nitride thin films based on pulsed laser deposition (PLD) technology, through precise alloy target proportioning, synchronous gas intake with a high-speed pulse valve and laser pulse, and synergistic effect of radio frequency ion source-assisted nitriding. The prepared thin films can be applied to passivation layers of semiconductor chips, electrode layers of electronic devices, wear-resistant coatings of mechanical parts, catalyst layers of fuel cells, functional layers of photovoltaic cells, and photosensitive layers of photodetectors, belonging to a strategic emerging industry technology at the intersection of new materials and next-generation information technology. Background Technology

[0002] Nitride thin films, due to their excellent electrical, optical, mechanical, and catalytic properties, have become a core research direction in advanced functional thin film materials, with irreplaceable application prospects in semiconductors, optoelectronics, new energy, and high-end equipment manufacturing. Currently, the mainstream technology for preparing nitride thin films is physical vapor deposition (PVD), among which pulsed laser deposition (PLD) is widely used due to its advantages such as controllable deposition rate, strong film-substrate adhesion, and ability to prepare films with complex compositions. However, existing PLD technologies for preparing nitride thin films consistently face three core challenges: efficient nitriding, oxygen impurity suppression, and precise composition control. Furthermore, the poor crystallinity quality and low batch-to-batch repeatability of the films severely limit their industrial application.

[0003] Existing PLD-based nitride thin film preparation technologies mainly suffer from the following drawbacks:

[0004] 1) Regarding the target material, either ceramic targets with harsh preparation conditions are used, or single metal targets are used. The precise proportioning and stable ablation of alloy targets according to stoichiometry are not achieved, resulting in large deviations in metal component transfer and poor uniformity of film composition.

[0005] 2) Regarding the atmosphere supply, continuous nitrogen / argon gas supply is used, which fails to achieve precise synchronization between the reaction gas and the laser pulse. The gas utilization rate is low (usually ≤30%), the active nitrogen concentration in the local reaction zone is insufficient, and the nitriding efficiency is low. 3) Regarding the auxiliary deposition, ion source assistance is rarely introduced, or the ion source is only used for the ionization of other gases. The radio frequency ionization of nitrogen and the precise bombardment of the high-energy nitrogen ion beam are not achieved, which cannot effectively fill nitrogen vacancies and remove oxygen-containing impurities. The oxygen impurity content of the film is usually ≥6at%, and the full width at half maximum (FWHM) of the XRD diffraction peak is ≥0.35°.

[0006] 4) The core features lack synergy. Existing technologies only disclose the individual applications of alloy targets, ion sources, and pulse valves, without designing the three as a whole, making it impossible to achieve the timing linkage of process parameters and the synergistic improvement of performance.

[0007] Among the existing publicly available technologies in China, CN109830429A discloses a method for depositing InGaN nitride thin films using a dual-path pulsed laser. This method employs a continuous nitrogen / argon atmosphere, a single InGaN target, and no ion source assistance. The prepared thin films have oxygen impurities ≥7.5 at%, and a compositional deviation ≥±5%. CN119685935A discloses a method for remote epitaxial deposition of nitride thin films using ammonia. Although ammonia is used as the nitrogen source, this is an epitaxial process, fundamentally different from PLD processes, and lacks synchronous gas inlet and ion source assistance. CN112259673A discloses a method for preparing superconducting thin films using radio frequency ion source-assisted PLD. This method only uses the ion source for oxygen ionization and does not involve nitrogen ionization or synchronous gas inlet. CN119233549A discloses a method for preparing thin films using pulse valve-assisted PLD. This method only uses the pulse valve for instantaneous oxygen supply and lacks laser pulse synchronization control and ion source assistance. None of the above technologies disclose the inseparable synergistic effect of the three core features of the present invention: precise alloy target material ratio, synchronous gas intake with high-speed pulse valve, and RF ion source-assisted nitriding. Nor do they achieve the preparation of nitride films with high purity, high crystallinity, and high uniformity.

[0008] The publicly available technologies in China are shown in Table 1:

[0009]

[0010] Existing technologies abroad also have significant shortcomings:

[0011] 1. The gas supply method is either a continuous gas flow or only a single synchronization valve, which lacks a gas pulse that can provide an extremely short and precise dose during each laser pulse, resulting in low gas utilization and uneven thin film nitriding;

[0012] 2. The ion source is only used for ionizing oxygen or ordinary nitrogen, and it does not work in conjunction with the synchronous gas intake. The coupling between the ion source power and frequency and the PLD plasma has not been systematically studied.

[0013] 3. The stoichiometric ratio of the alloy target material is not directly related to nitride deposition, nor does it resolve the compositional deviation caused by multi-target co-sputtering;

[0014] 4. Currently, no literature has fully combined the three key elements of alloy target material, synchronous ammonia / ionized nitrogen gas, and radio frequency ion source, so achieving simultaneous and precise control of film composition, structure, and purity remains a technological gap.

[0015] The existing publicly available technologies abroad are shown in Table 2:

[0016]

[0017] None of the aforementioned domestic and international technologies disclose the synergistic effect of the three core features of this invention: precise alloy target material proportioning, synchronous gas intake via high-speed pulse valve, and RF ion source-assisted nitriding. Nor have they achieved the preparation of nitride films with high purity, high crystallinity, and high uniformity. Therefore, it is urgent to develop a novel method for preparing nitride films to address the shortcomings of existing technologies. Summary of the Invention

[0018] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for preparing nitride thin films. This method utilizes the synergistic effects of precise alloy target proportioning, synchronous gas intake via a high-speed pulse valve and laser pulse, and RF ion source-assisted nitriding to solve the technical problems of low nitriding efficiency, easy introduction of oxygen impurities, difficulty in composition control, and poor film crystallization quality in existing technologies. It achieves stable ablation transfer of alloy targets at 0.05-0.2 μm / pulse, producing nitride thin films with low oxygen impurities, high crystallization quality, and uniform composition. Furthermore, through precise limitation of process parameters and integrated equipment modification, the process window and batch repeatability are improved, meeting the needs of industrial production.

[0019] To achieve the above-mentioned objective, the present invention provides a method for preparing nitride thin films, specifically comprising the following steps:

[0020] 1. Precise preparation of substrate and target: Provide a clean single-crystal substrate, which may be a single-crystal silicon, sapphire, magnesium oxide, strontium titanate, lanthanum aluminate, strontium tantalum lanthanum aluminate, dysprosium scandate, or samarium scandate substrate; ultrasonically clean the single-crystal substrate sequentially with acetone, anhydrous ethanol, and deionized water for 10-20 minutes, rinsing it three times with deionized water after each cleaning, and finally drying it with nitrogen gas with a purity ≥99.999%. Then, it is placed on the substrate holder of the pulsed laser deposition cavity and fixed firmly. Simultaneously, an alloy target is provided, which is made of metal A and metal B according to the stoichiometric ratio of the target nitride film. Metal A is one of titanium or a rare earth element, and metal B is one of molybdenum, tungsten, niobium, tantalum, rhenium, and silicon. The target density is ≥95%, and the grain size is 5-20 μm, ensuring uniform composition and no segregation. Through precise control of laser energy density and pulse frequency, the ablation rate of the alloy target is controlled to 0.05-0.2 μm / pulse (this ablation rate range is a key parameter to ensure stable transfer of metal components to the substrate according to stoichiometric ratio; below 0.05 μm / pulse, the ablation rate is significantly reduced). The deposition efficiency is too low when the laser energy density is below 0.2 μm / pulse, and it is prone to target spatter and compositional deviation when it is above 0.2 μm / pulse. Specifically, laser energy density is positively correlated with ablation rate; for every 0.5 J / cm² increase in laser energy density within the range of 1.5-2.5 J / cm², the ablation rate increases by approximately 0.03-0.05 μm / pulse. Pulse frequency is negatively correlated with ablation rate; for every 5 Hz increase in pulse frequency within the range of 5-15 Hz, the ablation rate decreases by approximately 0.02-0.04 μm / pulse. In actual control, adjusting the energy density is the primary means, with the pulse frequency used as an auxiliary adjustment parameter. The alloy target is fixed at the target position within the pulsed laser deposition cavity, and the distance between the target and the single-crystal substrate is adjusted to 3-8 cm.

[0021] 2. High-vacuum pretreatment of the cavity: Start the vacuum pump unit to evacuate the pulsed laser deposition cavity until the background vacuum is no higher than [previous value]. Hold for 20-40 minutes to thoroughly remove water vapor, oxygen, and other impurities from the cavity, preventing these impurities from participating in the deposition reaction and affecting the purity of the film.

[0022] 3. Substrate Heating and RF Ion Source Activation: The single-crystal substrate is heated to a preset temperature of 400-1000℃ using a resistance heating device within the pulsed laser deposition cavity, with a heating rate of 5-10℃ / min. Simultaneously, an RF ion source operating at 13.56MHz is activated, with its RF power adjusted to 50-500W, ionizing auxiliary nitrogen gas (purity ≥99.999%) to form a plasma with an energy of 100-500eV and a plasma density of 1×10¹. 0 A high-energy nitrogen ion beam of -1×10¹² cm⁻³ is continuously applied to the single-crystal substrate region. The high-energy nitrogen ion beam can clean the substrate surface and provide a highly active nitrogen source for subsequent nitriding reactions.

[0023] 4. Establishment of a synchronous reaction atmosphere using a high-speed pulse valve: A reactive gas, specifically ammonia or nitrogen with a purity ≥99.999%, is introduced into the pulsed laser deposition cavity. The ammonia flow rate is controlled at 5-100 sccm, and the nitrogen flow rate is also 5-100 sccm. The reactive gas is injected into the cavity through a high-speed pulse valve synchronized with the laser pulse electronic signal. This high-speed pulse valve is an electromagnetic type with a response delay ≤50μs, an opening and closing time of 50-200μs, and a synchronization error with the laser pulse ≤±10μs. Its control logic is linked to the laser's pulse control module: when the laser emits a laser pulse to ablate the target, the high-speed pulse valve opens synchronously and closes synchronously when the laser pulse ends. This ensures precise temporal and spatial matching between the gas injection and the plasma plume generated by the laser pulse ablation of the target, improving gas utilization and nitriding reaction efficiency. By adjusting the reactive gas flow rate, the reactive gas pressure within the pulsed laser deposition cavity is controlled to 0.5-2.0 Pa.

[0024] 5. Pulsed Laser Deposition and Simultaneous Nitriding Reaction: The KrF laser is activated, and the laser wavelength is adjusted to 248 nm, the laser energy density to 0.5-3 J / cm², and the laser pulse frequency to 1-20 Hz. After being focused by the optical system, the laser pulse vertically ablates the alloy target. At the instant the laser pulse ablates the alloy target, the high-speed pulse valve opens synchronously. The high-energy metal plasma plume generated by the laser ablation reacts with the synchronously injected reactive gas in the gas phase as it travels towards the single-crystal substrate. Simultaneously, the high-energy nitrogen ion beam generated by the radio frequency ion source continuously bombards the substrate surface, achieving dual nitriding of the gas phase and the surface, thereby improving the degree of nitriding and crystal quality of the thin film.

[0025] 6. Thin film growth control: Based on the thickness requirements of the target nitride film, the laser deposition time is controlled to be 3-120 min to deposit a nitride film of the target thickness on a single crystal substrate. By precisely controlling the deposition time, the film thickness can be precisely controlled.

[0026] 7. Post-treatment of thin films: After deposition, post-treatment is performed according to the material properties of the target nitride film. If the film needs to improve crystal quality, under the protection of ammonia or nitrogen with a purity ≥99.999%, the film is heated to 500-800℃ at a heating rate of 5-10℃ / min and annealed in situ for 10-60min. During annealing, the chamber pressure is maintained at 0.5-2.0Pa. Then, it is slowly cooled to room temperature at a rate of 3-10℃ / min. In-situ annealing can eliminate internal stress in the film and improve crystal integrity. If the film has low requirements for crystal quality, in-situ annealing is not necessary, and it can be directly cooled to room temperature slowly at a rate of 3-10℃ / min.

[0027] The pulsed laser deposition cavity used in this invention is an improved cavity, which integrates the following into the traditional pulsed laser deposition cavity: a high-speed pulse valve synchronized with the laser's electronic signal, a 13.56MHz radio frequency ion source, and a directional gas tube. The high-speed pulse valve, radio frequency ion source, and laser control module are linked to achieve timing synchronization (synchronization error ≤ ±10μs). The directional gas tube is made of stainless steel, and its outlet is directly facing the plasma plume region between the alloy target and the substrate, so that the ejected reaction gas directly reacts with the plasma plume, further improving the reaction efficiency.

[0028] The specific parameters of the experimental apparatus used in the implementation of this invention are shown in Table 3:

[0029]

[0030] The relevant test methods of this invention:

[0031] 1. XRD Test: Cu Kα (λ=1.5406Å) was used, scanning 2θ=20°-80° with a step size of 0.01°. For nitride films with different crystal structures, corresponding characteristic diffraction peaks were selected for crystal quality characterization: the full width at half maximum (FWHM) of cubic phase films (such as TiAlN and TaSiN) was calculated using the (002) diffraction peak; the FWHM of hexagonal phase films was calculated using the (001) diffraction peak. The FWHM of the characteristic peak is the core indicator reflecting the integrity of the film crystallization. The smaller the FWHM, the higher the crystal quality. The crystallinity of films with different crystal structures was compared laterally. The Scherrer formula D=Kλ / βcosθ (where D is the grain size, K is the Scherrer constant (taken as 0.89), λ is the X-ray wavelength, β is the FWHM of the diffraction peak after deducting instrument broadening, and θ is the diffraction angle) was used to calculate the grain size for comparison.

[0032] 2. XPS Testing: Using an Al Kα (1486.6 eV) light source, photoelectron spectral peaks of the O1s and N1s core energy levels were acquired. The O1s peak corresponds to the 1s energy level photoelectrons of oxygen, and the N1s peak corresponds to the 1s energy level photoelectrons of nitrogen. The peak intensities (corrected for relative sensitivity factors) were used to calculate the atomic percentages of oxygen and nitrogen in the film. The oxygen impurity content was expressed as the atomic percentage of the integrated intensity of the O1s peak to the total intensity of (O1s + N1s); the nitrogen content was expressed as the N / (N + O) molar ratio, i.e., the proportion of the integrated intensity of the N1s peak to the total intensity of (O1s + N1s).

[0033] 3. Resistivity test: The four-probe method is used, with metal probes placed at the four corners of the substrate to measure the IV curve, and the thin film resistivity is calculated based on the curve.

[0034] 4. Surface roughness test: A 5µm×5µm area was scanned using an atomic force microscope (AFM) and the root mean square roughness (RMS) was calculated.

[0035] 5. Gas utilization rate test: By accurately measuring the total flow rate of the reactant gas (Q_total) and the flow rate of the unreacted tail gas (Q_tail) into the cavity, and using a mass flow controller to monitor the flow rates at the inlet and outlet in real time, the gas utilization rate is calculated as (Q_total - Q_tail) / Q_total × 100%. After multiple tests, the gas utilization rate of the method of this invention is consistently ≥80%.

[0036] 6. Batch Repeatability Test: Ten batches of nitride films were continuously prepared using the same process parameters. The oxygen impurity content, XRD characteristic peak full width at half maximum (FWHM), and composition ratio of each batch were tested. The relative standard deviation (σ = standard deviation / average) of each indicator was calculated. Batch repeatability = (1 - average relative standard deviation) × 100%. In the table, "±5%, ±4%, ±2%" represent the maximum relative standard deviation of the three indicators for each method. These correspond to batch repeatability ≥95% (1-2%) for this invention, ≥96% (1-4%) for ion source PLD only, and ≥95% (1-5%) for traditional continuous gas flow PLD. The data are consistent and reproducible.

[0037] This invention achieves significant technical advantages over existing technologies through the synergistic effects of precise alloy target material proportioning, synchronous gas intake with high-speed pulse valve and laser pulse, and RF ion source-assisted nitriding. Table 4 shows a comparison of the film properties prepared by this invention with those prepared by traditional continuous gas flow PLD and ion source-only PLD.

[0038] Table 4 shows a comparison of the relevant data and effects between the present invention and traditional methods:

[0039] Table 4 Comparison of thin film properties prepared by different methods

[0040]

[0041] Note:

[0042] 1. The nitrogen percentage is the nitrogen percentage at the anion sites, calculated using the N / (N+O) molar ratio, where the atomic percentages of N and O are calculated from the N1s and O1s peak intensities measured by XPS (after sensitivity factor correction);

[0043] 2. XRD characteristic peaks are selected based on the thin film crystal structure: cubic phase thin films (such as TiAlN, TaSiN) are characterized by (002) diffraction peaks, and hexagonal phase thin films are characterized by (001) diffraction peaks. The full width at half maximum (FWHM) value is only used for comparing the crystal quality of thin films with the same crystal structure; for lateral comparison of thin films with different crystal structures, the Scherrer formula is used to calculate the grain size.

[0044] The specific technical effects are reflected in the following aspects:

[0045] 1. Improved nitriding efficiency and superior film crystal quality: By simultaneously supplying ammonia / nitrogen (increasing gas utilization to ≥80%), combined with the assistance of a high-energy nitrogen ion beam generated by a radio frequency ion source, dual nitriding of the gas phase and the surface was achieved. The prepared nitride films showed a half-width at half-maximum (WHM) of ≤0.30° for the characteristic diffraction peaks of their respective crystal structures ((002) peak for cubic phase and (001) peak for hexagonal phase), indicating that the films have excellent crystal quality.

[0046] 2. Effective suppression of oxygen impurities and improved film purity: Through multi-step synergy of high vacuum pretreatment in the cavity, suppression of oxygen adsorption by the reducing atmosphere of ammonia, and removal of oxygen-containing impurities by high-energy nitrogen ion beam bombardment, the prepared film has an oxygen impurity atomic percentage of ≤3at%, which is ≥70% lower than that of traditional PLD technology, and the film purity is greatly improved.

[0047] 3. Uniform composition control and excellent batch repeatability: Using alloy targets with a density of ≥95% and a grain size of 5-20μm, a stable ablation rate of 0.05-0.2μm / pulse is achieved. The compositional deviation of the film between different batches is ≤±2%, and the batch repeatability is ≥95%, which meets the requirements of large-scale industrial production.

[0048] 4. Simplified and practical process with low modification cost: It abandons the difficult-to-prepare nitride ceramic target and the complex multi-target co-sputtering process, and can achieve precise transfer of metal components by using a single alloy target; the improved equipment can be obtained by modifying the traditional PLD equipment, only requiring the addition of a high-speed pulse valve, a 13.56MHz radio frequency ion source and linkage control module. The modification cost is as low as 10%-20% of the traditional equipment, and the modification does not affect the use of the traditional PLD process, realizing one machine for multiple uses and easy to scale up production. Attached Figure Description

[0049] Figure 1 This is a process flow diagram of the method for preparing nitride thin films according to the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of the improved pulsed laser deposition equipment used in this invention;

[0051] Figure 3The timing waveform diagram of the PLD synchronous air intake and laser sputtering system used in this invention is shown.

[0052] Figure 4 This is a PLD-assisted ion source plasma spectral analysis diagram during the preparation of TiAlN thin films in Example 1 of the present invention.

[0053] Figure 1 Explanation: The process flow is as follows: substrate and target preparation, cavity pretreatment, substrate heating, introduction of reactive gas, pulsed laser deposition, in-situ treatment and cooling, sampling characterization and result analysis. Each step is connected in an orderly manner to form a complete preparation process.

[0054] Figure 2 Explanation: The improved pulsed laser deposition equipment includes core components such as an air inlet (controlled by a pulse valve), an ion source, a laser, an observation window, a vacuum pump (air outlet), a deposition chamber, a substrate holder, and a target. These components work together to achieve the deposition of nitride thin films.

[0055] Figure 3 illustrates the timing waveforms of the PLD synchronous gas intake and laser sputtering system. The pulse valve signal and the laser signal are precisely synchronized. The pulse valve opening time is 0.02s, the stopping interval is 0.18s, and the period is 0.2s. The laser pulse starts at the same time as the valve closes, ensuring precise matching between the gas and the plasma plume.

[0056] Figure 4 Explanation: This figure corresponds to the plasma spectral test results of Example 1 (preparation of TiAlN thin film), comparing the spectral differences between no ion source (Scenario A) and with ion source (Scenario B): In Scenario A, only neutral atomic lines of TiⅠ and AlⅠ appear, and the nitrogen-related feature lines are extremely weak, indicating low plasma activity; In Scenario B, the TiⅡ and AlⅡ ion lines are enhanced by 10 times (target ionization is improved), and obvious NiⅠ atomic lines (enhanced by 5 times) and NiⅡ ion lines appear, proving that the radio frequency ion source effectively ionizes nitrogen gas to form highly active nitrogen species, which, together with the synchronous gas inlet, improves the nitriding reaction efficiency and directly supports the technical effect of the present invention. Detailed Implementation

[0057] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. All embodiments have been verified by repeated experiments, the process parameters are stable, and the technical effects can be repeatedly achieved. The embodiments of the present invention are only used to illustrate the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] The equipment used in this embodiment of the invention is an improved pulsed laser deposition equipment, modified from a traditional KrF pulsed laser deposition equipment. It integrates a high-speed pulse valve (response delay 40μs, opening / closing time 100μs), a 13.56MHz radio frequency ion source, a directional gas tube, and a linkage control module. The linkage control module is implemented as follows: the synchronous output signal of the laser is used as the trigger source. This signal is isolated by an optocoupler and then input to the FPGA (Field Programmable Gate Array) control unit. The FPGA outputs a control signal to drive the high-speed pulse valve to open according to a preset delay parameter (adjustable range 0-100μs). The laser pulse end signal controls the pulse valve to close via the same path, achieving precise synchronization between the valve opening / closing and the laser pulse, with a synchronization error ≤ ±5μs. The high-purity ammonia and nitrogen used are both 99.9999% pure; the alloy targets used are prepared according to stoichiometry, with a density ≥96%, a grain size of 8-15μm, and a stable ablation rate of 0.08-0.15μm / pulse.

[0059] Example 1: Preparation of TiAlN Nitride Thin Films

[0060] 1. Select single-crystal silicon as the single-crystal substrate, and ultrasonically clean it sequentially with acetone, anhydrous ethanol, and deionized water for 15 min each. After rinsing with deionized water three times, dry it with 99.9999% nitrogen gas and place it on the substrate holder of the improved pulsed laser deposition cavity. Prepare Ti-Al alloy target material according to the stoichiometric ratio of Ti:Al=1:1, with a density of 97%, a grain size of 10 μm, and an ablation rate controlled at 0.1 μm / pulse. Fix it in the cavity with a distance of 6 cm from the substrate.

[0061] 2. Start the vacuum pump unit to evacuate the chamber to a base vacuum of 3.0 × 10⁻⁻⁻⁶. 5 Pa, maintain for 30 minutes;

[0062] 3. Heat the single-crystal silicon substrate to 600℃ at a heating rate of 8℃ / min; turn on the 13.56MHz radio frequency ion source and adjust the radio frequency power to 300W to ionize nitrogen gas to form a plasma with an energy of 250eV and a plasma density of 5×10¹. 0 A high-energy nitrogen ion beam of cm⁻³ acts on the substrate surface;

[0063] 4. Introduce 99.9999% high-purity ammonia gas into the cavity at a flow rate of 20 sccm. The injection is controlled by a high-speed pulse valve with an opening and closing time of 150 μs and a synchronization error of ±5 μs with the laser pulse. The reaction gas pressure in the cavity is kept stable at 1.0 Pa.

[0064] 5. Start the KrF laser, adjust the laser wavelength to 248nm, energy density to 2J / cm², and pulse frequency to 10Hz. The laser pulse ablates the Ti-Al alloy target and reacts with the synchronously injected ammonia gas in the gas phase. At the same time, the high-energy nitrogen ion beam continuously bombards the substrate surface.

[0065] 6. By controlling the deposition time to 60 min, a TiAlN nitride film with a thickness of 1.2 μm was deposited on a single-crystal silicon substrate;

[0066] 7. After deposition, under the protection of ammonia atmosphere, the temperature is raised to 700℃ at 8℃ / min and annealed in situ for 30 min, and then slowly cooled to room temperature at a rate of 5℃ / min.

[0067] Performance characterization results: The percentage of oxygen impurities in the TiAlN film is 2.2 at%, the full width at half maximum (FWHM) of the XRD (002) diffraction peak is 0.26°, the Ti / Al / N atomic ratio deviation is ±0.8%, the nitrogen content of anion sites is N / (N+O)≥92%, the surface roughness (RMS) is 2.1 nm, the resistivity is 1.8×10⁻³Ω·cm, the gas utilization rate is 85%, and the batch repeatability is 96%.

[0068] Example 2 Preparation of TaSiN Nitride Thin Films

[0069] 1. Magnesium oxide was selected as the single crystal substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 20 min each. After rinsing with deionized water three times, it was dried with 99.9999% nitrogen and placed on the substrate holder of the improved pulsed laser deposition cavity. A Ta-Si alloy target was prepared according to the stoichiometric ratio of Ta:Si=1:1, with a density of 98%, a grain size of 8 μm, and an ablation rate controlled at 0.08 μm / pulse. The target was fixed in the cavity with a distance of 7 cm from the substrate.

[0070] 2. Start the vacuum pump unit to evacuate the chamber to a base vacuum of 2.0 × 10⁻⁻⁻⁶. 5 Pa, maintain for 40 minutes;

[0071] 3. Heat the magnesium oxide substrate to 700℃ at a heating rate of 10℃ / min; turn on the 13.56MHz radio frequency ion source and adjust the radio frequency power to 350W to ionize nitrogen gas to form a plasma with an energy of 300eV and a plasma density of 8×10¹. 0 A high-energy nitrogen ion beam of cm⁻³ acts on the substrate surface;

[0072] 4. Introduce 99.9999% high-purity ammonia gas into the cavity at a flow rate of 15 sccm. The injection is controlled by a high-speed pulse valve with an opening and closing time of 100 μs and a synchronization error with the laser pulse of ±3 μs. The reaction gas pressure in the cavity is kept stable at 0.8 Pa.

[0073] 5. Start the KrF laser, adjust the laser wavelength to 248nm, energy density to 2.5J / cm², and pulse frequency to 15Hz. The laser pulse ablates the Ta-Si alloy target material and reacts with the synchronously injected ammonia gas in the gas phase. At the same time, the high-energy nitrogen ion beam continuously bombards the substrate surface.

[0074] 6. By controlling the deposition time to 90 min, a TaSiN nitride film with a thickness of 1.08 μm was deposited on a magnesium oxide substrate;

[0075] 7. After deposition, under the protection of ammonia atmosphere, the temperature is raised to 650℃ at 10℃ / min and annealed in situ for 40 min, and then slowly cooled to room temperature at a rate of 4℃ / min.

[0076] Performance characterization results: The percentage of oxygen impurities in the TaSiN thin film is 0.2 at%, the full width at half maximum (FWHM) of the XRD (002) diffraction peak is 0.18°, the Ta / Si / N atomic ratio deviation is ±0.5%, the nitrogen content of anion sites is N / (N+O)≥95.8%, the surface roughness (RMS) is 1.8 nm, the resistivity is 1.5×10⁻³Ω·cm, the gas utilization rate is 85%, and the batch repeatability is 98%.

[0077] Example 3: Preparation of TiAlN nitride films without in-situ annealing

[0078] 1. Sapphire was selected as the single crystal substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 min each. After rinsing with deionized water three times, it was dried with 99.9999% nitrogen and placed on the substrate holder of the improved pulsed laser deposition cavity. Ti-Al alloy target material was prepared according to the stoichiometric ratio of Ti:Al=1:1, with a density of 96%, a grain size of 15 μm, and an ablation rate controlled at 0.15 μm / pulse. It was fixed in the cavity with a distance of 5 cm from the substrate.

[0079] 2. Start the vacuum pump unit to evacuate the chamber to a base vacuum of 4.0 × 10⁻⁻⁻⁶. 5 Pa, maintain for 20 minutes;

[0080] 3. Heat the sapphire substrate to 550℃ at a heating rate of 5℃ / min; turn on the 13.56MHz radio frequency ion source and adjust the radio frequency power to 400W to ionize nitrogen gas and form a high-energy nitrogen ion beam with an energy of 350eV and a plasma density of 1×10¹¹ cm⁻³, which acts on the substrate surface.

[0081] 4. Introduce 99.9999% high-purity nitrogen gas into the cavity at a flow rate of 10 sccm. Control the injection through a high-speed pulse valve with an opening and closing time of 200 μs and a synchronization error of ±8 μs with the laser pulse. Maintain a stable cavity reaction pressure of 1.5 Pa.

[0082] 5. Start the KrF laser, adjust the laser wavelength to 248nm, energy density to 1.5J / cm², and pulse frequency to 8Hz. The laser pulse ablates the Ti-Al alloy target and reacts with the synchronously injected nitrogen gas in the gas phase. At the same time, the high-energy nitrogen ion beam continuously bombards the substrate surface.

[0083] 6. By controlling the deposition time to 80 min, a TiAlN nitride film with a thickness of 1.2 μm was deposited on the sapphire substrate;

[0084] 7. After deposition, the material is slowly cooled to room temperature at a rate of 8°C / min without in-situ annealing.

[0085] Performance characterization results: Compared with Example 1 (with in-situ annealing), the TiAlN thin film prepared in this example has an oxygen impurity atomic percentage of 0.5 at% (slightly lower than Example 1, as the lack of annealing reduces the chance of oxygen adsorption), an XRD (001) diffraction peak full width at half maximum (FWHM) of 0.25° (slightly higher than Example 1, as the lack of annealing eliminates internal stress and results in slightly poorer crystal integrity), a Ti / Al / N atomic ratio deviation of ±1.2% (slightly higher than Example 1), an anion site nitrogen ratio N / (N+O) ≥ 93.2%, a surface roughness (RMS) of 2.3 nm (slightly higher than Example 1), a resistivity of 2.0 × 10⁻³ Ω・cm (slightly higher than Example 1), a gas utilization rate of 82%, and a batch repeatability of 95%. Overall, the crystal quality and electrical properties of the film without in-situ annealing are slightly inferior to those of the film with in-situ annealing, but are still far superior to the film prepared by traditional PLD technology. It can meet the application scenarios with lower requirements for crystal quality, and has a shorter preparation cycle and lower cost.

[0086] Comparative Experiment Example: TiAlN Thin Film Preparation Using Traditional PLD Technology

[0087] Explanation of target material differences: This comparative experimental example uses a Ti-Al ceramic target, while the embodiments of this invention use a Ti-Al alloy target. Ceramic targets and alloy targets differ significantly in terms of compositional uniformity (ceramic targets exhibit micro-regional compositional fluctuations), density (ceramic targets are typically ≤90%, while alloy targets are ≥96%), and laser ablation behavior (ceramic targets are prone to spatter and segregation). This invention, by employing a high-density, compositionally uniform alloy target, ensures stable transfer of metal components from the source, which is a crucial component of the technical effectiveness of this invention.

[0088] For fair comparison, this comparative experiment is identical to Example 1 except for the target type and the absence of simultaneous gas inlet and ion source assistance. The specific steps are as follows: using the method described in the prior art CN109830429A, dual-path pulsed laser deposition is performed with a Ti-Al ceramic target, continuous nitrogen supply (flow rate 30 sccm), no ion source assistance, no simultaneous gas inlet, and other parameters are identical to Example 1 to prepare a TiAlN thin film.

[0089] Performance characterization results: oxygen impurity atomic percentage of thin film 7.8 at%, XRD (002) diffraction peak full width at half maximum 0.42°, Ti / Al / N atomic ratio deviation ±5.5%, nitrogen content of anion sites N / (N+O)≥81%, surface roughness (RMS) 3.5 nm, resistivity 4.5×10⁻³Ω・cm, gas utilization 25%, batch repeatability 82%.

[0090] Comparative conclusion: Compared with traditional PLD technology, the preparation method of the present invention reduces oxygen impurities in the thin film by ≥70%, reduces the full width at half maximum (FWHM) of XRD diffraction peaks by ≥38%, reduces compositional deviation by ≥78%, increases gas utilization by ≥200%, and improves batch repeatability by ≥16%. All performance indicators have been significantly improved, which fully demonstrates the advanced nature and superiority of the technical solution of the present invention.

[0091] The core parameters defined in this invention are all based on extensive experimental verification:

[0092] 1. Substrate heating temperature 400-1000℃: The nitriding reaction is insufficient below 400℃, and interdiffusion between the substrate and the thin film is likely to occur above 1000℃;

[0093] 2. RF power 50-500W: Below 50W, nitrogen cannot be effectively ionized; above 500W, it will cause thin film sputtering damage.

[0094] 3. Pulse valve opening and closing time: 50-200μs: less than 50μs results in insufficient gas supply, and more than 200μs results in decreased gas utilization.

[0095] 4. Ablation rate 0.05-0.2μm / pulse: Balances deposition efficiency and compositional uniformity; exceeding this range may lead to splashing or excessively low efficiency.

[0096] The various parameters work together to achieve the preparation of high-purity, highly crystalline thin films.

[0097] The present invention provides a method for preparing nitride thin films, which features clear process steps, controllable parameters, and good repeatability, demonstrating significant industrial applicability and industrialization prospects. Specifically, it includes the following:

[0098] 1. Low equipment modification cost and strong compatibility: The improved pulsed laser deposition equipment used can be obtained by modifying traditional industrial-grade PLD equipment. Only a high-speed pulse valve, a 13.56MHz radio frequency ion source and linkage control module need to be added. The modification cost is 10%-20% of that of traditional equipment. Moreover, the modification does not affect the use of traditional PLD processes, realizing multiple uses of one machine and making it suitable for enterprises of all sizes to upgrade their technology.

[0099] 2. Strong process controllability and wide process window: The precise transfer of metal components can be achieved by using a single alloy target. All process parameters are industrially mature and controllable parameters. High-quality thin films can be obtained within a pressure window of 0.5-2.0 Pa and a temperature window of 400-800℃. The process is highly adaptable and parameters can be flexibly adjusted according to different product requirements.

[0100] 3. High raw material utilization and low preparation cost: Through synchronous gas intake via high-speed pulse valve, the utilization rate of reaction gas is increased from the traditional ≤30% to ≥80%, significantly reducing raw material consumption; batch repeatability ≥95% reduces product scrap due to process fluctuations, reduces production losses, and effectively controls preparation costs.

[0101] 4. Excellent product performance and wide range of applications: The prepared nitride films have high purity, excellent crystallinity and uniform composition, and can be widely used in many fields such as semiconductor chips, electronic devices, new energy electrodes, wear-resistant coatings, and photoelectric detectors. There is a large market demand and broad industrialization prospects.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing nitride thin films, characterized in that, Includes the following steps: a. Provide a clean single-crystal substrate, which is ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10-20 minutes, and then dried with nitrogen gas of ≥99.999% purity, and then placed into a pulsed laser deposition cavity; at the same time, provide an alloy target material made of metal A and metal B according to the stoichiometric ratio of the target nitride film. The alloy target material has uniform composition, no segregation, density ≥95%, and grain size of 5-20μm. Fix it in the pulsed laser deposition cavity with a distance of 3-8cm between it and the single-crystal substrate; b. Evacuate the pulsed laser deposition cavity to a background vacuum level not exceeding [a certain value]. Keep it on for 20-40 minutes; c. Heat the single-crystal substrate to a preset temperature of 400-1000℃ at a heating rate of 5-10℃ / min, turn on the radio frequency ion source with an operating frequency of 13.56MHz, and adjust its radio frequency power to 50-500W, so that the auxiliary nitrogen ionization forms an energy of 100-500eV and a plasma density of 1×10¹. 0 A high-energy nitrogen ion beam of -1×10¹² cm⁻³ is continuously applied to the single-crystal substrate region; d. Introduce a reactive gas into the pulsed laser deposition cavity. The reactive gas is ammonia or nitrogen with a purity ≥99.999%, wherein the ammonia flow rate is 5-100 sccm and the nitrogen flow rate is 5-100 sccm. The reactive gas is injected through a high-speed pulse valve synchronized with the laser pulse electronic signal. The high-speed pulse valve has a response delay ≤50μs, an opening and closing time of 50-200μs, and a synchronization error with the laser pulse ≤±10μs, so that the gas injection and the plasma plume generated by the laser pulse ablation of the target material are matched in time and space. The reactive gas pressure in the cavity is controlled to be 0.5-2.0 Pa. e. Start the KrF laser, adjust the laser wavelength to 248nm, the laser energy density to 0.5-3J / cm², and the pulse frequency to 1-20Hz. The laser pulse ablates the alloy target material. The high-energy metal plasma plume generated by the ablation reacts with the synchronously injected reactive gas in a gas phase. At the same time, the high-energy nitrogen ion beam continuously bombards the substrate surface. The ablation rate of the alloy target material is controlled to be 0.05-0.2μm / pulse. f. Control the deposition time of the laser to 3-120 min, and deposit a nitride film of the target thickness on the single crystal substrate; g. After deposition, under the protection of ammonia or nitrogen with a purity ≥99.999%, the film is heated to 400-800℃ at a heating rate of 5-10℃ / min and annealed in situ for 10-60 min. During the annealing process, the chamber pressure is maintained at 0.5-2.0 Pa. Then, it is slowly cooled to room temperature at a rate of 3-10℃ / min; or, it is directly cooled to room temperature at a rate of 3-10℃ / min.

2. The method for preparing nitride thin films according to claim 1, characterized in that, In step a, metal A is one of titanium or rare earth elements, and metal B is one of molybdenum, tungsten, niobium, tantalum, rhenium, and silicon; the single crystal substrate is one of single crystal silicon, sapphire, magnesium oxide, strontium titanate, lanthanum aluminate, strontium tantalum lanthanum aluminate, dysprosium scandate, and samarium scandate.

3. The method for preparing nitride thin films according to claim 1, characterized in that, The pulsed laser deposition cavity is an improved cavity that integrates: a high-speed pulse valve synchronized with the laser's electronic signal, a 13.56MHz radio frequency ion source, and a directional gas tube. The directional gas tube allows the ejected reaction gas to directly react with the plasma plume in the gas phase. Furthermore, the high-speed pulse valve, the radio frequency ion source, and the laser's control module are linked to achieve time synchronization with a synchronization error of ≤±10μs.

4. The method for preparing nitride thin films according to claim 1, characterized in that, In step e, the laser energy density is positively correlated with the ablation rate. Within the range of 1.5-2.5 J / cm², for every 0.5 J / cm² increase in laser energy density, the ablation rate increases by approximately 0.03-0.05 μm / pulse. The pulse frequency is negatively correlated with the ablation rate. Within the range of 5-15 Hz in pulse frequency, for every 5 Hz increase, the ablation rate decreases by approximately 0.02-0.04 μm / pulse.

5. The method for preparing nitride thin films according to claim 1, characterized in that, The prepared nitride thin film has an oxygen impurity atomic percentage of ≤3at%, an XRD characteristic diffraction peak full width at half maximum (FWHM) of ≤0.30°, batch repeatability of ≥95%, and reaction gas utilization rate of ≥80%.

6. The method for preparing nitride thin films according to claim 1, characterized in that, In step a, the single crystal substrate is rinsed with deionized water three times after each cleaning, and the ablation rate of the alloy target is stably controlled by precise regulation of laser energy density and pulse frequency.

7. The method for preparing nitride thin films according to claim 1, characterized in that, The high-speed pulse valve is an electromagnetic high-speed pulse valve, and its control logic is linked with the laser's pulse control module: when the laser emits a laser pulse to ablate the target material, the high-speed pulse valve opens synchronously, and closes synchronously when the laser pulse ends.

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