A diamond thin film, its preparation method and application

Abstract

A diamond thin film, its preparation method, and its applications are disclosed. The preparation method includes: using a substrate material with a lattice constant matching that of the diamond thin film material as a substrate, and performing surface treatment on the substrate; introducing a mixed reaction gas comprising 80%-95% hydrogen, 3%-8% methane, and 2%-12% auxiliary gas, wherein the auxiliary gas includes at least one of argon, chlorine, hydrogen fluoride, and hydrogen chloride; performing controlled chemical vapor deposition at 850℃-1000℃ and a pressure of not less than 21 kPa to grow a diamond thin film on the substrate surface; and annealing the diamond thin film. This invention utilizes the synergistic effect of auxiliary gas and temperature-pressure gradient controlled chemical vapor deposition to achieve corrosion-free, high-speed growth of high-purity single-crystal diamond thin films; combined with dynamic annealing, it effectively repairs lattice defects, optimizes overall performance, and significantly improves the reliability of the thin film in applications such as heat dissipation components.

Description

Technical Field

[0001] This invention belongs to the field of diamond preparation technology, specifically relating to a diamond thin film, its preparation method, and its application. Background Technology

[0002] Diamond not only possesses high Mohs hardness, but also boasts numerous superior properties such as high thermal conductivity, high carrier mobility, wide bandgap, and breakdown resistance. These characteristics have gradually given it unique natural advantages in national defense and cutting-edge technology fields, particularly in 5G communication high-frequency filters, semiconductor circuit heat dissipation substrates, and heat dissipation packaging for ultra-high-power electronic components, demonstrating irreplaceable application potential and attracting great research enthusiasm from scientists. Compared with other semiconductor materials, the preparation of single-crystal diamond films, which combine large size, low defects, and high purity, has always been a hot topic of widespread interest.

[0003] Currently, high-quality diamond thin films are typically fabricated using homoepitaxial mosaic stitching and heteroepitaxial methods. However, the mosaic stitching method suffers from a surge in interfacial resistance due to grain orientation deviations, while heteroepitaxial methods result in polycrystalline dominance due to lattice mismatch. More seriously, polycrystalline diamond thin films exhibit carrier mobility less than 1 / 10 that of single-crystal diamond due to carrier scattering at grain boundaries, failing to meet the stringent requirements for interfacial conductivity in high-precision electrical storage devices. Therefore, achieving controllable fabrication of large-size single-crystal diamond thin films remains a core problem that urgently needs to be solved in this field.

[0004] Chinese patent application CN1928151A discloses a method for preparing a three-layer diamond film with controllable thickness, belonging to the field of inorganic non-metallic material chemical vapor deposition technology. This invention uses existing hot-wire chemical vapor deposition experimental equipment to adjust and control parameters such as carbon source concentration, deposition temperature, reaction gas pressure, and applied bias voltage to deposit a three-layer diamond film on a silicon wafer. However, this preparation method, due to the use of a lattice-mismatched silicon substrate and acetone carbon source, results in high interface defect density, polycrystalline predominance, and insufficient purity in the film; the three-stage low-pressure deposition process is too time-consuming and lacks an annealing repair mechanism, leading to high residual stress and poor thermal stability in the film, making it difficult to meet the performance requirements of high-power devices for single-crystal diamond.

[0005] Meanwhile, diamond thin film materials grow slowly and require high power consumption. Therefore, from the perspective of process optimization, achieving rapid growth of single-crystal diamond thin film materials with low energy consumption is also one of the hot issues of concern in the industry.

[0006] Traditional manufacturing processes, such as the one described in Chinese patent CN110724930B, involve the following steps: placing a pretreated porous metal substrate in the reaction chamber of a hot-wire chemical vapor deposition apparatus; introducing a reactive gas into the reaction chamber to allow the reactive gas to grow a diamond / silicon carbide / metal composite film on the surface of the porous metal substrate; etching the obtained diamond / silicon carbide / metal composite film to remove the metal and silicon carbide phases, thus obtaining a diamond film; and calcining the diamond film in an oxygen-containing atmosphere to obtain a finished diamond film with a hierarchical porous structure. However, the manufacturing method disclosed in this invention requires indirect film formation through a porous metal substrate and relies on multi-step acid etching to remove the metal / silicon carbide phases, resulting in a prolonged process cycle; the growth rate is limited under low-pressure deposition conditions, requiring a significant extension of deposition time to achieve the target film thickness, thus significantly increasing power consumption.

[0007] Therefore, how to overcome the limitations of large-size growth of single-crystal diamond films without multi-step acid corrosion and heterogeneous substrates, while achieving high-rate, low-energy preparation through deposition process optimization and ensuring the thermodynamic stability of the diamond phase in subsequent processing, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, this invention provides a diamond thin film, its preparation method, and its applications. By utilizing the synergistic effect of in-situ purification with an optimized auxiliary gas ratio and crystal plane control, and through the dynamic etching-growth balance of a chlorine / fluorine-containing auxiliary gas and a hydrogen-methane system under high pressure, the simultaneous removal of amorphous carbon impurities and the integrated formation of single-crystal directional epitaxy are achieved. This completely eliminates the damage to the thin film structure caused by multi-step acid etching processes. At the same time, combined with a gradient temperature-controlled deposition strategy, the growth rate and interface integrity of the single-crystal diamond thin film are significantly improved.

[0009] In a first aspect, the present invention provides a method for preparing a diamond thin film, comprising the following steps:

[0010] S1. A substrate material matching the lattice constant of the diamond thin film material is used as the substrate, and the substrate is surface treated.

[0011] S2. By volume percentage, a mixed reaction gas comprising 80%-95% hydrogen, 3%-8% methane, and 2%-12% auxiliary gas is introduced; the auxiliary gas includes at least one of argon, chlorine, hydrogen fluoride, and hydrogen chloride.

[0012] S3. A diamond film is grown on the substrate surface by controlled chemical vapor deposition at 850℃-1000℃ and a pressure of not less than 21kPa.

[0013] S4. Anneal the diamond film.

[0014] Among them, lattice constant matching means that the absolute value of the difference between the lattice constant of the substrate material and the lattice constant of the diamond thin film material is less than 5% of the lattice constant of the diamond thin film material.

[0015] The mixed reaction gas in step S2 can be limited to the combination of the aforementioned gases, that is, by volume percentage, it consists of 80%-95% hydrogen, 3%-8% methane and 2%-12% auxiliary gas. Preferably, it consists of 85%-91% hydrogen, 3%-5% methane and 6%-10% auxiliary gas.

[0016] In step S3, under the same temperature and pressure conditions, the deposition thickness is basically proportional to the deposition time. The film thickness can be controlled by adjusting the process parameters according to the application requirements of the thin film.

[0017] Preferably, the substrate material is selected from natural diamond single crystal, HPHT diamond single crystal, or CVD diamond single crystal, and the surface of the seed crystal has undergone (100) or (111) crystal plane orientation cutting treatment. Selecting a suitable substrate material is beneficial for rapid matching and ensuring the matching degree between its lattice constant and the lattice constant of the diamond thin film material.

[0018] Preferably, the auxiliary gas is composed of argon, chlorine, and hydrogen fluoride in a volume ratio of 1:(0.5-1.5):(0.3-1).

[0019] In the conventional chemical vapor deposition (CVD) process for preparing diamond films, hydrogen and methane are usually used as the basic reaction gases. Such systems are prone to the generation of amorphous carbon and graphite phase impurities due to insufficient carbon source decomposition or local supersaturation. The lack of an effective in-situ purification mechanism causes the film growth interface to be gradually contaminated by non-diamond phases, eventually forcing the introduction of additional post-processing steps (such as acid etching or plasma etching) to remove impurities. This not only significantly increases the process complexity, but may also cause lattice damage or surface roughening problems due to secondary processing.

[0020] To address this technical bottleneck, this invention innovatively introduces auxiliary gas components, particularly a combination of argon, chlorine, and hydrogen fluoride. Through the synergistic effect of the active components (Cl2 / HF) and the dilution gas (Ar), dynamic etching and preferential crystal growth are simultaneously achieved during the deposition process. The active free radicals (Cl· / F·) released by chlorine and hydrogen fluoride at high temperatures preferentially etch amorphous carbon and grain boundary defects. Their etching products (such as CCl4 and CF4) escape from the reaction system in gaseous form, thereby forming a self-cleaning effect at the growth interface. Argon, as a dilution carrier, suppresses the disordered deposition of byproducts such as carbon black by regulating the plasma density and the partial pressure of the reactant gases, maintaining a stable gas-phase reaction kinetic environment.

[0021] Specifically, the auxiliary gas is prepared at a volume ratio of argon:chlorine:hydrogen fluoride = 1:(0.5-1.5):(0.3-1), which precisely balances the dynamic relationship between etching rate and deposition rate. An excessively high chlorine content may lead to over-etching of the single crystal surface, while an insufficient hydrogen fluoride content weakens the purification effect on edge defects. Argon, as the main dilution medium, ensures the controllability of the reaction atmosphere. This composite gas system enables continuous epitaxial growth of high-purity single crystals without relying on post-processing steps, fundamentally solving the dual problems of impurity phase accumulation and process redundancy in traditional processes.

[0022] Preferably, the controlled chemical vapor deposition in step S3 includes:

[0023] 1) High-temperature pre-growth: High-temperature pre-growth is carried out at a pre-growth temperature T0 of 950℃-1000℃, maintaining a chamber pressure P0≥25kPa, preferably a chamber pressure P0≥27kPa, and the duration of high-temperature pre-growth is 25%-55% of the total controlled chemical vapor deposition time;

[0024] 2) Cooling deposition: The temperature is gradually reduced from the pre-growth temperature T0 to the end temperature T1 for deposition. The end temperature T1 is from T0-100℃ to T0-50℃. The chamber pressure is maintained at P1≥P0-3kPa, preferably P1≥24kPa.

[0025] Preferably, controlled chemical vapor deposition includes at least one of the following conditions:

[0026] 1) During the high-temperature pre-growth process, a boron-containing doping gas is periodically introduced, with a boron doping concentration of 1×10⁻⁶. 18 Up to 5×10 20 cm -3 Preferably, the on / off cycle is controlled between 5 and 15 minutes to make the boron distribution more uniform.

[0027] Periodically introducing borane-containing dopant gas during the high-temperature pre-growth stage allows for the introduction of appropriate amounts of boron atoms into the diamond lattice. Boron atoms, acting as acceptor dopant sources, can modulate the band structure and surface electronic state distribution of diamond, thereby influencing the lattice defect formation mechanism and promoting stable crystal plane expansion. Specifically, the core role of the borane-containing dopant gas is to impart specific semiconductor properties to the diamond film through a controllable atomic substitution mechanism. Boron atoms generated from the decomposition of borane at high temperatures preferentially occupy carbon atom sites in the diamond lattice, forming acceptor energy levels and introducing hole carriers, thanks to the highly reactive carbon-based atmosphere during chemical vapor deposition. This periodic doping strategy achieves a gradient distribution of boron atoms along the crystal growth direction through intermittent gas introduction, avoiding excessive lattice stress accumulation caused by continuous doping while ensuring controllable adjustment of carrier concentration in the depth direction of the film. During the doping process, the covalent bonding between boron atoms and carbon atoms is strengthened at high temperatures, effectively suppressing the precipitation of impurity atom clusters. At the same time, the active surface mobility during the pre-growth stage promotes the uniform embedding of boron atoms into the lattice, ultimately forming a diamond film with stable p-type semiconductor properties, laying the electrical performance foundation for subsequent device functionalization applications.

[0028] 2) Gradually reducing the temperature from the pre-growth temperature T0 to the final temperature T1 includes: gradually cooling at a rate of 3-8℃ / min;

[0029] Using gradual cooling instead of isothermal temperature during deposition helps to create a dynamic thermodynamic deposition equilibrium environment, gradually controlling surface diffusion behavior during growth and reducing thermal stress concentration. Simultaneously, the cooling rate can regulate the adsorption and nucleation rates of carbon sources on the crystal surface, promoting the expansion of single-crystal regions.

[0030] 3) During the cooling deposition stage, the growth rate of the diamond film shall not be less than 30 μm / h.

[0031] Maintaining a growth rate of no less than 30 μm / h during the cooling phase helps to maintain the stability of deposition kinetics and avoids the growth of amorphous regions or voids caused by the low nucleation rate during the cooling process of the crystal surface.

[0032] This invention employs a gradient cooling strategy, gradually decreasing the pre-growth temperature to the final temperature. Its core function is to achieve a balance between crystal growth quality and process efficiency through dynamic adjustment of the thermodynamic environment. During the high-temperature pre-growth stage, a dense single-crystal substrate is formed by enhanced carbon source decomposition. Subsequent gradient cooling effectively alleviates lattice stress caused by sudden temperature changes, promoting the orderly migration and arrangement of carbon atoms on the substrate surface. During cooling, carbon atoms maintain appropriate migration capacity under a controllable temperature field, preventing rapid defect proliferation caused by high temperatures and avoiding amorphous phase deposition due to insufficient atomic kinetic energy at low temperatures. Simultaneously applied auxiliary gas continuously purifies the growth interface through selective etching, and under high pressure, synergistic gradient temperature control suppresses impurity phase formation, ultimately achieving high-speed epitaxial growth of single-crystal thin films while ensuring the integrity of the crystal structure and surface flatness.

[0033] After employing the above-mentioned optimized process, the obtained diamond thin film material exhibits an infrared transmittance of no less than 80%, preferably no less than 82%, and displays a large-size single-crystal quality crystal structure with a highly uniform lattice arrangement at both the edges and the center, meeting the application requirements for areas larger than 2.5 inches. This superior performance is particularly suitable for substrate materials of infrared windows, heat sinks for power devices, and high-frequency microwave devices.

[0034] Preferably, the surface treatment in step S1 includes at least one of the following conditions:

[0035] 1) Pickling treatment: The substrate surface is pickled using an acid solution with a concentration of 55%-75%;

[0036] 2) Physical sputtering: Small molecule gas is used to perform physical sputtering on the substrate surface for 10-20 seconds to form high-density uniform nucleation sites.

[0037] In addition to selecting a suitable substrate material, surface treatment is also an important guarantee for the high-quality and high-efficiency generation of diamond films. The present invention can form high-density and uniformly distributed nucleation sites through the aforementioned pretreatment, which serve as the preferred growth sites for diamond film atoms. Small molecule gas treatment is used to ensure the number density of nucleation sites. The small molecule gas is argon or nitrogen, and the physical sputtering power is 200-500W.

[0038] Preferably, in step S4, the annealing temperature T of the annealing treatment satisfies:

[0039] T∈[max(0.9T 高 1.05T 低 ), min(1050℃, 1.1T) 高 )];

[0040] Among them, T 高 The pre-growth temperature is T0±50℃, T 低The final temperature is T1±25℃. This formula indicates that the lower limit of the annealing temperature range T is the larger of 0.9 times T0±50℃ and 1.05 times T1±25℃, and the upper limit of T is the smaller of 1050℃ and 1.1 times T0±50℃.

[0041] Preferably, the annealing process includes at least one of conditions (1) and (2):

[0042] Condition (1) Step annealing treatment for 2-5 hours, including:

[0043] First-order annealing: at (T 高 +T 低 ) / 2 to T 高 Annealing at a temperature range of 1-2 hours;

[0044] Second-order annealing: at T 低 to less than (T) 高 +T 低 Annealing at a temperature range of 1-3 hours (2 / 2).

[0045] Condition (2): Alternately introduce hydrogen and argon, with a hydrogen flow rate to argon flow rate ratio of 1:(1-3), and each switching cycle is 10-30 min.

[0046] In chemical vapor deposition (CVD), temperature is a crucial factor influencing reaction kinetics. Higher temperatures typically increase the decomposition and diffusion rates of reactants, promoting crystal growth. However, the rate of temperature change affects crystal structure formation; rapid cooling can lead to internal stress, while slow cooling promotes the formation of ordered structures. Furthermore, maintaining a certain growth rate may require optimizing parameters such as gas flow rate, pressure, and temperature to ensure sufficient carbon source supply and appropriate deposition conditions.

[0047] Conventional annealing processes use heating to give atoms within diamond films the kinetic energy to migrate. This is mainly used to eliminate residual stress caused by temperature gradients or lattice mismatches during deposition and to repair point and line defects. At high temperatures, atomic rearrangement can partially restore lattice integrity. However, traditional methods often use fixed-temperature annealing, which does not consider the thermal history matching of the deposition process, easily leading to incomplete repair or localized overheating.

[0048] The annealing process of this invention dynamically matches the temperature history of the deposition stage, ensuring that the annealing temperature is sufficient to activate the repair mechanism of bulk defects while avoiding exceeding the thermodynamic stability threshold of diamond, which could lead to sp³ bond breakage. Based on this, a stepped annealing strategy is implemented in two stages: a first-stage high-temperature annealing targets the deep dislocation network formed during the pre-growth stage, achieving dislocation climb and annihilation through high-temperature atomic migration; a second-stage low-temperature annealing focuses on the interfacial stress and surface microcracks accumulated during the cooling deposition stage, filling microdefects through vacancy diffusion and releasing residual stress. Furthermore, the introduction of alternating hydrogen / argon atmospheres creates a dynamic surface reconstruction mechanism: hydrogen passivates surface dangling bonds and inhibits amorphous carbon formation, while argon inhibits excessive etching by hydrogen plasma. Periodic switching causes surface atoms to rearrange to low-energy states, ultimately achieving full-dimensional defect repair and interface optimization from the bulk to the surface, overcoming the limitations of traditional processes.

[0049] Secondly, the present invention also provides a diamond film prepared by the aforementioned method for preparing diamond films.

[0050] Preferably, the infrared transmittance of the diamond film is not less than 80%, and more preferably not less than 82%.

[0051] Preferably, the crystal structure in the diamond film includes a large-size single crystal structure of not less than 2.5 inches.

[0052] Preferably, large-size single-crystal structures of not less than 2.5 inches account for at least 90% of the total crystal volume.

[0053] Preferably, the diamond film material can achieve gem-quality color.

[0054] Thirdly, the present invention also provides an application of the diamond film as a heat dissipation component.

[0055] Preferably, the diamond film is used as a heat dissipation component in electronic components such as integrated circuits. The diamond film prepared by this invention has large-scale single-crystal characteristics and high thermal conductivity, and can be used as a heat dissipation accessory for electronic components such as large-scale integrated circuits, thereby improving the heat dissipation capability of integrated circuits.

[0056] Furthermore, the diamond film of the present invention can also be used in high-frequency power devices, electrical sensing chips, and infrared optical window materials.

[0057] The technical solution of the present invention has at least the following beneficial effects:

[0058] (1) This invention achieves simultaneous vapor-phase etching of amorphous carbon impurities and preferential growth of single crystals during chemical vapor deposition through the synergistic effect of an optimally proportioned auxiliary gas. The Cl / F active component preferentially etches grain boundary defects and non-diamond phases, while argon dilution regulates the stability of the reaction atmosphere. Combined with a high-pressure and high-temperature environment, this enhances the carbon source decomposition efficiency, enabling high-speed epitaxial growth of single-crystal thin films. Compared to traditional impurity removal methods that rely on multi-step acid etching, this invention reduces impurity generation from the source through an in-situ auxiliary gas etching mechanism, avoids lattice damage, significantly improves film transmittance and structural integrity, and lays a structural foundation for subsequent functional applications.

[0059] (2) The controlled chemical vapor deposition of the present invention includes two processes: high-temperature pre-growth and cooling deposition, each with temperature and pressure control. By dynamically adjusting the thermodynamic environment, a balance between crystal growth quality and process efficiency is achieved. The high-temperature pre-growth process forms a dense single-crystal substrate by strengthening the decomposition of the carbon source. The subsequent gradient cooling effectively alleviates the lattice stress caused by the sudden temperature change and promotes the orderly migration and arrangement of carbon atoms on the substrate surface. During the cooling deposition process, carbon atoms maintain a moderate migration ability under a controllable temperature field, which avoids the rapid proliferation of defects caused by high temperature and prevents the deposition of amorphous phases caused by insufficient atomic kinetic energy at low temperature. The simultaneously applied auxiliary gas continuously purifies the growth interface through selective etching and, under high pressure, synergistically suppresses the generation of impurity phases through gradient temperature control, ultimately achieving high-speed epitaxial growth of single-crystal thin films while ensuring the integrity of the crystal structure and surface flatness.

[0060] (3) Based on the dynamic design of the annealing temperature range and the step / alternating atmosphere strategy of the thermal history of the deposition stage, this invention achieves full-dimensional defect repair from the bulk phase to the surface. Step annealing eliminates deep dislocation networks and interfacial micro-stresses through high-temperature-low-temperature step-by-step treatment; the alternating hydrogen / argon atmosphere dynamically balances surface reconstruction and etching loss, resulting in an atomically smooth interface. This process forms a closed loop with the aforementioned auxiliary gas deposition system: the high-purity single-crystal substrate in the deposition stage reduces the initial defect density, and the annealing stage specifically repairs residual micro-defects. The two work together to give the film both high crystal quality and excellent electrical properties.

[0061] (4) The diamond film prepared by the method of the present invention has the triple characteristics of high infrared transmittance, large-size single crystal structure, and low defect density. It is particularly suitable for applications in multiple scenarios such as high-frequency power devices, electrical sensing chips, and infrared optical windows, and has a good industrialization foundation. According to actual measurements, the large-size single crystal structure of the film is above 90vt%, the thermal conductivity is above 1800 W / (m·K), the refractive index is above 2.41, and the transmittance in the infrared region (3-5μm) is above 80%. It can be directly applied to fields with extremely high requirements for material uniformity and structural integrity, such as power-intensive packaging, microwave windows, and heat dissipation substrates. Attached Figure Description

[0062] Figure 1 This is a flowchart of the diamond thin film preparation method of the present invention;

[0063] Figure 2 The image shows a color comparison of the diamond film samples of Example 9 and Comparative Example 1, where a is the sample of Example 9 and b is the sample of Comparative Example 1.

[0064] Figure 3 The image shows a comparison of the crystal structures of diamond film samples from Example 9 and Comparative Example 2, where a is the sample from Example 9 and b is the sample from Comparative Example 2. Detailed Implementation

[0065] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0066] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0067] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0068] This invention provides a method for preparing a diamond thin film, which specifically includes the following steps:

[0069] S1. A substrate material with a lattice constant matching that of the diamond thin film material is used as the substrate, and the substrate undergoes surface treatment:

[0070] 1.1) Substrate preparation: A substrate material with a lattice constant matching that of the diamond film is selected as the substrate. The substrate is preferably a natural diamond single crystal, a diamond single crystal prepared by the HPHT method, or a diamond single crystal prepared by CVD. The crystal plane orientation of the substrate is preferably (100) or (111), and a highly oriented surface structure is obtained by crystal plane orientation cutting.

[0071] 1.2) Surface treatment: including pickling and / or physical sputtering, preferably pickling and physical sputtering are performed sequentially.

[0072] 1.2.1) Pickling treatment: Use a mixed acid solution with a concentration of 55%-75% to remove surface impurities. The mixed acid can be a combination of concentrated hydrochloric acid and hydrofluoric acid with a volume ratio of (5-10):1, a combination of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of (3-5):1, or a combination of three acids: concentrated hydrochloric acid, hydrofluoric acid and concentrated nitric acid.

[0073] 1.2.2) Physical sputtering: Small molecule gases such as argon and hydrogen are introduced and low-pressure plasma with a power of 200-500W is applied for excitation for 10-20s, generating a large number of high-density nucleation sites. These nucleation sites serve as preferential growth sites for subsequent carbon deposition, which helps to improve the nucleation uniformity and orientation consistency of the single crystal structure.

[0074] S2. A suitable gas-phase reaction atmosphere is established by introducing a mixed reaction gas with a specific ratio into the deposition chamber. The mixed gas composition, by volume percentage, includes 80%-95% hydrogen, 3%-8% methane, and 2%-12% auxiliary gas, preferably consisting of 85%-91% hydrogen, 3%-5% methane, and 6%-10% auxiliary gas.

[0075] The auxiliary gas includes at least one of argon, chlorine, hydrogen fluoride and hydrogen chloride, with a preferred combination of argon:chlorine:hydrogen fluoride = 1:(0.5-1.5):(0.3-1).

[0076] Hydrogen and methane provide the carbon source and reducing atmosphere, while the Cl· and F· free radicals released by chlorine and hydrogen fluoride at high temperatures can preferentially react with amorphous carbon or impurity phases to generate volatile byproducts (such as CCl4 and CF4) which are removed from the gas phase, thereby achieving in-situ etching and purification at the growth interface. Argon, as an inert diluent component, helps to control plasma density and atmosphere stability, thereby improving the overall interface quality and crystal selectivity of epitaxial growth.

[0077] S3. Controlled chemical vapor deposition to grow diamond films, including at 850℃-1000℃ and a chamber pressure of not less than 21 kPa, preferably 24-30 kPa, using a two-stage temperature control strategy to optimize deposition kinetics:

[0078] 3.1) High-Temperature Pre-Growth: Maintain a chamber pressure P0 ≥ 25 kPa, preferably not lower than 27 kPa, and control the pre-growth temperature T0 at 950℃-1000℃. This stage accounts for 25%-55% of the total controlled chemical vapor deposition time and is mainly used to form a dense, highly oriented single-crystal initial layer. Optionally, a boron-containing dopant gas can be introduced for boron doping control. It is preferred to periodically introduce boron-based gases, with the doping concentration controlled at 1×10⁻⁶. 18 Up to 5×10 20 cm -3 Between these intervals, the doping cycle is 5-15 minutes;

[0079] 3.2) Cooling Deposition: Maintain a chamber pressure P1 ≥ P0 - 3 kPa, preferably P1 not lower than 24 kPa. Gradually reduce the temperature from the pre-growth temperature T0 to the final temperature T1, which is approximately 50℃-100℃ lower than the pre-growth temperature T0. The cooling rate should be controlled between 3-8℃ / min to help stabilize the diffusion path of carbon atoms on the surface, improve lattice integrity, and reduce stress concentration. Throughout the cooling deposition process, the film growth rate is preferably not lower than 30 μm / h to ensure process efficiency and flexibility in thickness control.

[0080] S4. Annealing treatment: After deposition, the resulting diamond film needs to be thermally annealed to release internal stress, repair defects, and improve crystal quality.

[0081] Annealing temperature T∈[max(0.9T)] 高 1.05T 低 ),min(1050℃, 1.1T) 高 )];

[0082] Among them, T 高 The pre-growth temperature is T0±50℃, T 低 The final temperature is T1±25℃. The lower limit of the annealing temperature range T is the larger of 0.9 times T0±50℃ and 1.05 times T1±25℃, and the upper limit of T is the smaller of 1050℃ and 1.1 times T0±50℃.

[0083] Preferably, the annealing treatment specifically includes the following process conditions:

[0084] Condition (1) Step annealing treatment for 2-5 hours, including:

[0085] First-order annealing: at (T 高 +T 低 ) / 2 to T 高 Annealing at a temperature range of 1-2 hours;

[0086] Second-order annealing: at T 低 to less than (T)高 +T 低 Annealing at a temperature range of 1-3 hours (2 / 2).

[0087] Condition (2): During the annealing process, hydrogen and argon are periodically alternately introduced, with a hydrogen / argon volume flow rate ratio of 1:(1-3) and a switching cycle of 10-30 min.

[0088] The diamond thin film material prepared by the above method possesses multiple characteristics such as high infrared transmittance, large-size single-crystal structure, and low defect density. Specifically, the infrared transmittance is not less than 80%, preferably not less than 82%, and the crystal structure exhibits large-size single-crystal quality with a highly uniform lattice arrangement at both the edges and center, meeting the application requirements for areas larger than 2.5 inches. Furthermore, the thickness of the diamond thin film can be controlled by adjusting process parameters according to requirements. These superior properties enable the diamond thin film to be used as a heat dissipation component in various fields such as electronic components, for example, as a heat sink for integrated circuits and power devices, and it is also suitable as an infrared window material and high-frequency microwave device.

[0089] Example 1

[0090] Example 1 describes the preparation of a diamond thin film sample using the following steps:

[0091] S1. Natural diamond single crystal is used as the substrate, and the substrate undergoes surface treatment:

[0092] 1) Pickling treatment: 65wt% mixed acid solution is used to remove surface impurities. The mixed acid is concentrated hydrochloric acid and hydrofluoric acid with a volume ratio of 8:1.

[0093] 2) Physical sputtering: Argon and hydrogen gas with a volume ratio of 4:1 are introduced and low-pressure plasma excitation with a power of 350W is applied for 15s to generate a large number of high-density nucleation sites.

[0094] S2. Introduce mixed reaction gas into the deposition chamber to establish a suitable gaseous reaction atmosphere: by volume percentage, it contains 80% hydrogen, 8% methane and 12% auxiliary gas, wherein the auxiliary gas is argon, chlorine, hydrogen fluoride and hydrogen chloride premixed in a volume ratio of 1:1:1:1.

[0095] S3. Controlled chemical vapor deposition for growing diamond films, employing a two-stage temperature and pressure controlled deposition strategy:

[0096] 1) High-temperature pre-growth: Maintain the chamber pressure P0 at 25 kPa and control the pre-growth temperature T0 at 975 ± 5℃. This stage accounts for 40% of the total controlled chemical vapor deposition time.

[0097] 2) Cooling deposition: Maintain the chamber pressure P1 at 22 kPa, and gradually reduce the temperature from the pre-growth temperature T0 to the end temperature T1. The end temperature T1 is 900±5℃, and the cooling rate is controlled at about 5℃ / min. During the entire cooling deposition process, the film growth rate is preferably not less than 30 μm / h.

[0098] S4. Annealing Treatment: After deposition, the resulting diamond film needs to be thermally annealed. During the annealing process, hydrogen and argon are periodically alternately introduced at a hydrogen / argon volume flow rate ratio of 1:2, with a switching cycle of 30 minutes. A stepped annealing method is adopted, including:

[0099] First-stage annealing: Anneal at 945±5℃ for 1.5h;

[0100] Second-stage annealing: Anneal at 925±℃ for 1.5h.

[0101] Example 2-18

[0102] The process conditions for Examples 2-18 are the same as those for Example 1, except that the composition of the mixed reaction gas is different, as shown in Table 1.

[0103] Table 1. Composition of Mixed Reaction Gases in Examples 1-18

[0104]

[0105] Examples 19-25

[0106] Examples 19-25 are based on the mixed reaction gas composition of Example 9, and the difference from Example 9 is the adjustment of process parameters in the preparation method, as shown in Table 2.

[0107] Table 2. List of partial process parameters for Examples 9 and 19-25

[0108]

[0109] Comparative Example 1

[0110] Compared with Example 9, Comparative Example 1 did not use an auxiliary gas, and its mixed reaction gas contained only 90% hydrogen and 10% methane by volume.

[0111] Comparative Example 2

[0112] Compared to Example 9, Comparative Example 2 used an auxiliary gas, but in a lower amount. The volume percentage of the mixed reaction gas was:

[0113] 90.5% hydrogen, 8% methane and 1.5% auxiliary gas, wherein the auxiliary gas is argon (0.6%), chlorine (0.6%) and hydrogen fluoride (0.3%) premixed in a volume ratio of 1:1:0.5.

[0114] Comparative Example 3

[0115] The difference between Comparative Example 3 and Example 9 lies in the controlled chemical vapor deposition conditions. Comparative Example 3 used a single deposition condition: deposition at 900±5℃ and a pressure of 23 kPa for 25 min.

[0116] Comparative Example 4

[0117] Compared with Example 9, Comparative Example 4 differs in that only argon gas is introduced during the annealing stage, and a single annealing method is used, namely annealing at 925±5℃ for 3 hours.

[0118] Tests and Results

[0119] The following tests were performed on the samples of Examples 1-25 and Comparative Examples 1-4. Three samples were prepared for each group and the average value was taken. The test results are shown in Table 3.

[0120] 1. Test the film's color, refractive index, and infrared transmittance.

[0121] Each sample was irradiated with cathode rays, and the different colors of fluorescence emitted by each sample were observed.

[0122] (1) The diamond film samples of Examples 1-25 were white, transparent and without fluorescence;

[0123] (2) The sample of Comparative Example 1 did not use an auxiliary gas and showed obvious yellow-green fluorescence. Comparative Example 2 also showed a lighter yellow-green fluorescence due to the smaller amount of auxiliary gas used.

[0124] (3) The samples of Comparative Examples 3 and 4 showed no fluorescence, but their chromaticity and transparency were significantly lower than those of the Examples.

[0125] 2. Crystal structure testing, using Raman spectroscopy (XRD can also be used).

[0126] 3. Thermal conductivity test: laser flash method.

[0127] Table 3 Test results of Examples 1-25 and Comparative Examples 1-4

[0128]

[0129] By comparing the test results and referring to... Figure 2-3As can be seen, the sample of the embodiment of the present invention is white, transparent and non-fluorescent, with a refractive index of 2.41 or higher, preferably 2.42 or higher, an infrared transmittance of 80% or higher, preferably 82% or higher, a large-size single crystal structure ratio of 90% or higher, preferably 91% or higher, and a thermal conductivity of 1800 W / (m·K) or higher, preferably 2000 W / (m·K) or higher, more preferably 2010 W / (m·K) or higher.

[0130] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing a diamond thin film, characterized in that, Includes the following steps: S1. A substrate material matching the lattice constant of the diamond thin film material is used as the substrate, and the substrate is surface treated. S2. By volume percentage, a mixed reaction gas comprising 80%-95% hydrogen, 3%-8% methane, and 2%-12% auxiliary gas is introduced; the auxiliary gas includes at least one of argon, chlorine, hydrogen fluoride, and hydrogen chloride. S3. A diamond film is grown on the substrate surface by controlled chemical vapor deposition at 850℃-1000℃ and a pressure of not less than 21kPa. S4. Anneal the diamond film; The controlled chemical vapor deposition in step S3 includes: 1) High-temperature pre-growth: High-temperature pre-growth is carried out at a pre-growth temperature T0 of 950℃-1000℃, while maintaining a chamber pressure P0≥25kPa. The duration of high-temperature pre-growth is 25%-55% of the total controlled chemical vapor deposition time. 2) Cooling deposition: The temperature is gradually reduced from the pre-growth temperature T0 to the end temperature T1 for deposition. The end temperature T1 is from T0-100℃ to T0-50℃, and the chamber pressure P1 is maintained at P0-3kPa.

2. The preparation method according to claim 1, characterized in that, The substrate material is selected from natural diamond single crystal, HPHT diamond single crystal or CVD diamond single crystal, and the surface of the seed crystal is subjected to (100) or (111) crystal plane orientation cutting treatment.

3. The preparation method according to claim 1 or 2, characterized in that, In step S2, the auxiliary gas is composed of argon, chlorine, and hydrogen fluoride in a volume ratio of 1:(0.5-1.5):(0.3-1).

4. The preparation method according to claim 1, characterized in that, Controlled chemical vapor deposition includes at least one of the following conditions: 1) During the high-temperature pre-growth process, a boron-containing doping gas is periodically introduced, with a boron doping concentration of 1×10⁻⁶. 18 Up to 5×10 20 cm -3 ; 2) Gradually reducing the temperature from the pre-growth temperature T0 to the final temperature T1 includes: gradually cooling at a rate of 3-8℃ / min; 3) During the cooling deposition process, the growth rate of the diamond film is not less than 30 μm / h.

5. The preparation method according to claim 1 or 4, characterized in that, The surface treatment in step S1 includes at least one of the following conditions: 1) Pickling treatment: The substrate surface is pickled using an acid solution with a concentration of 55%-75%; 2) Physical sputtering: Small molecule gas is used to perform physical sputtering on the substrate surface for 10-20 seconds to form high-density uniform nucleation sites.

6. The preparation method according to claim 1 or 4, characterized in that, In step S4, the annealing temperature T of the annealing process satisfies: T∈[max(0.9T 高 1.05T 低 (min(1050℃, 1.1T)) 高 )]; Among them, T 高 The pre-growth temperature is T0±50℃, T 低 The final temperature is T1 ± 25℃.

7. The preparation method according to claim 6, characterized in that, The annealing process includes at least one of conditions (1) and (2): Condition (1) Step annealing treatment for 2-5 hours, including the following: First-order annealing: at (T 高 +T 低 ) / 2 to T 高 Annealing at a temperature range of 1-2 hours; Second-order annealing: at T 低 to less than (T) 高 +T 低 Annealing at a temperature range of 1-3 hours (2 / 2). Condition (2) Alternately introduce hydrogen and argon, with a hydrogen flow rate to argon flow rate ratio of 1:(1-3), and each switching cycle is 10-30 min.

8. A diamond film, characterized in that, Prepared by the method for preparing diamond films according to any one of claims 1-7.

9. An application of the diamond film of claim 8 as a heat dissipation component.

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