Preparation method of self-supporting polycrystalline diamond film

Abstract

The invention discloses a preparation method of a self-supporting polycrystalline diamond film, which comprises the following steps: a, by taking a molybdenum table subjected to ultrasonic cleaning and plasma cleaning as a substrate, depositing an amorphous carbon thin layer with the thickness of about 0.1-2 mu m on the surface of the substrate through an MPCVD (Micro Plasma Chemical Vapor Deposition) technology; b, adjusting the gas proportion, and depositing the polycrystalline diamond in situ; c, after deposition is completed, slow cooling is conducted, and automatic demolding is conducted in the cooling process. The molybdenum substrate with the diamond peeled off can be repeatedly used. According to the method, the amorphous carbon thin layer is added on the surface of the grown molybdenum substrate in situ, so that the defects that the polycrystalline diamond film is broken and cannot be demolded in the cooling process are overcome, and meanwhile, the problems of high pollution, high cost, long period, difficulty in reutilization of the substrate and the like caused by stripping the substrate are solved.

Description

Technical Field

[0001] This invention belongs to the field of diamond preparation technology, specifically relating to a method for preparing a self-supporting polycrystalline diamond film. Background Technology

[0002] Diamond is a material that combines many excellent properties, with a hardness of up to 10,000 kg / mm². 2 With a thermal conductivity as high as 2000 W / (m·K) at room temperature and a bandgap of 5.47 eV, polycrystalline diamond is transparent across almost the entire wavelength range from ultraviolet (>227 nm) to far-infrared, except for the mid-infrared band. Its excellent mechanical, thermal, electrical, and optical properties make it a promising candidate for applications in machining and protection, heat sinks, optical windows, and semiconductors. Currently, heteroepitaxial single-crystal diamond is still in the research and development stage. Industrialized single-crystal diamond is mostly produced using heteroepitaxial growth, leading to difficulties and high costs in manufacturing inch-scale single-crystal diamond, thus limiting its application scope. In contrast, polycrystalline diamond can be grown via heteroepitaxial growth, with fewer substrate size limitations. MPCVD polycrystalline diamond substrates can reach sizes of 8 inches and above, making it widely applicable in semiconductors, heat sinks, and optical windows.

[0003] Currently, the mainstream method for fabricating self-supporting polycrystalline diamond films typically uses single-crystal silicon wafers as the substrate material for epitaxial growth. After the epitaxial layer is grown, the self-supporting epitaxial layer is peeled off by etching the silicon substrate with acid or alkali. This approach has several problems, such as the silicon substrate material not being reusable, the large amount of acid or alkali used for etching causing severe pollution, and the long substrate peeling time. The significant difference in thermal expansion coefficients between the substrate and the grown layer makes it prone to cracking or splitting during the cooling process after growth. An excessively thin substrate can lead to increased warping of the polycrystalline film after demolding. All of these problems ultimately result in increased costs, environmental pollution, and resource waste.

[0004] Several improvement measures have been proposed, such as improving the substrate stage structure. CN119465396B adopts a novel substrate stage design combining an inner molybdenum disk and an outer stainless steel ring, directly depositing polycrystalline diamond films on the substrate stage. This avoids the growth of polycrystalline diamonds on the side edges of the molybdenum disk, reducing the possibility of breakage of polycrystalline diamonds grown on the molybdenum disk during the removal stage. However, it still cannot avoid the risk of cracking caused by differences in thermal expansion coefficients. Another approach is to add an intermediate layer. CN112430803B uses a polished diamond film substrate, first depositing a 100-3000nm ultra-nano diamond thin layer as an intermediate layer, then depositing a polycrystalline diamond film, followed by heat treatment to carbonize the ultra-nano diamond thin layer for demolding. However, this method involves substrates that are not readily available, and the post-processing is still relatively complex. CN117051475A involves transferring multiple layers of graphene films as intermediate layers layer by layer on the growth surface of the growth substrate. After the polycrystalline diamond sheet is grown, the diamond sheet is peeled off using a purely mechanical method. However, the high price of graphene itself is not conducive to cost reduction. Therefore, there is an urgent need to research and develop a low-cost, low-pollution, and short-time preparation process for polycrystalline diamond films. Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing a self-supporting polycrystalline diamond film. This method solves many problems such as high pollution, high cost, long time consumption and resource waste caused by substrate separation after the polycrystalline diamond film is grown.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a self-supporting polycrystalline diamond film includes the following steps: (1) A flat molybdenum stage is used as the substrate, which is cleaned before use; (2) An amorphous carbon thin layer with a thickness of 0.1-2 μm was deposited on the substrate surface using MPCVD technology; (3) Then the gas ratio was quickly adjusted and polycrystalline diamond was deposited in situ; (4) After deposition, demolding is completed during the slow cooling process.

[0007] Specifically, in step (1), the flatness of the molybdenum flattening table is required to be ≤0.5mm; preferably, the molybdenum flattening table is obtained by turning or milling and then grinding.

[0008] Specifically, in step (2), the thickness of the amorphous carbon thin layer is 0.1-2 μm, and deposition is performed directly after switching gas parameters following plasma cleaning; the preferred deposition parameters for the amorphous carbon thin layer are: hydrogen flow rate 50-100 Sccm; methane flow rate 40-50 Sccm; volume ratio V 甲烷 / V 氢气The concentration is 40-100%; the cavity pressure is 100-120 Torr; the microwave power is 5500-9500W; and the deposition time is 0.5-2h.

[0009] Furthermore, in step (3), after the amorphous carbon thin layer is deposited, the gas parameters are quickly adjusted, and the preferred adjustment time is 5~20 min.

[0010] Specifically, in step (3), the deposition parameters for polycrystalline diamond are: hydrogen flow rate 400~500 Sccm; methane flow rate 5~50 Sccm; oxygen flow rate 0~8 Sccm; nitrogen flow rate 0~3 Sccm; cavity pressure 90~130 Torr; microwave power 4500~9500W; growth temperature 930~1150℃; and deposition time 20~300h.

[0011] A further preferred embodiment has a gas volume ratio of: V for optical thin films used in optical windows and other applications. 甲烷 / V 氢气 It is 1~3%, V 氮气 / V 氢气 0%; heat sink films used for heat dissipation and other purposes. 甲烷 / V 氢气 It is 9~12%, V 氮气 / V 氢气 It ranges from 1% to 5%.

[0012] Specifically, in step (4), the cooling rate during the cooling process is 4-10℃ / min, and the cooling time is 120±30min.

[0013] Furthermore, in step (1), the molybdenum stage can be reused. Before reuse, any possible diamond particles and carbon residues on the surface must be removed. Preferably, surface residues are removed by methods such as sandblasting, laser ablation, or oxygen plasma calcination.

[0014] Furthermore, in step (1), the molybdenum stage is ultrasonically cleaned before use; preferably, it is ultrasonically cleaned with deionized water and alcohol in sequence, and then dried with compressed air (CDA).

[0015] Further preferably, the molybdenum stage, after ultrasonic cleaning, needs to undergo plasma cleaning before use; preferably, the plasma cleaning is performed by in-furnace etching within the MPCVD deposition chamber; preferably, the parameters for the plasma etching cleaning are: hydrogen flow rate 100~400 Sccm; oxygen flow rate 2~10 Sccm; volume ratio V 氧气 / V 氢气 The etching rate is 2-4%; the cavity pressure is 100-120 Torr; the microwave power is 5500-9500W; and the etching time is 5-20min.

[0016] This invention provides a self-supporting polycrystalline diamond film prepared by the above method.

[0017] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: 1) This invention introduces an amorphous carbon thin layer between a molybdenum substrate and polycrystalline diamond. Since the bonding force inside the amorphous carbon thin layer is relatively weak, during the cooling process, the thermal stress generated between the molybdenum substrate and polycrystalline diamond due to the difference in thermal expansion coefficients will first cause the amorphous carbon thin layer to disintegrate, thereby releasing the stress and avoiding the problem of cracking and splitting. 2) This invention achieves the demolding of polycrystalline diamond film while disintegrating amorphous carbon thin film, eliminating the substrate peeling process, greatly reducing environmental pollution and saving time and costs; 3) The molybdenum substrate after demolding can be reused after simple processing, which greatly reduces resource waste and lowers production costs. Attached Figure Description

[0018] To more clearly illustrate the implementation of this solution, the accompanying drawings used in the description of the embodiments will be briefly introduced. It should be stated that the drawings are used to provide a further understanding of the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the structure of a self-supporting polycrystalline diamond film before demolding after growth is complete. Among them, 1-polycrystalline diamond; 2-amorphous carbon thin layer; 3-molybdenum substrate; Figure 3 This is a photograph of the results of growing polycrystalline diamond in Comparative Example 1 without the introduction of amorphous carbon thin film after 32 hours. Figure 4 The overall optical photograph (left) and optical micrograph (right) of polycrystalline diamond grown on an amorphous carbon thin layer for 32 hours in Example 1. Figure 5 The image shows an overall optical photograph (left) and an optical micrograph (right) of polycrystalline diamond grown on an amorphous carbon thin layer for 200 hours in Example 2. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] In the following embodiments, the substrate planarization molybdenum stage used was obtained through the following treatment: 1) The molybdenum stage should be ultrasonically cleaned before use; at room temperature, it should be ultrasonically cleaned with deionized water and alcohol for 10 minutes each, and then dried with CDA. 2) The molybdenum stage undergoes plasma cleaning after ultrasonic cleaning; the plasma cleaning is performed by in-furnace etching within the MPCVD deposition chamber; the parameters for the plasma etching cleaning are: hydrogen flow rate 200 Sccm; oxygen flow rate 4 Sccm; volume ratio V 氧气 / V 氢气 The etching rate was 2%; the cavity pressure was 120 Torr; the microwave power was 6500W; and the etching time was 20min.

[0022] Comparative Example 1 A method for preparing a polycrystalline diamond film, comprising the following steps:

[0023] Polycrystalline diamond was deposited directly on a 2-inch flat molybdenum substrate. 甲烷 / V 氢气 The diamond growth reaction was carried out at 1050℃ under microwave excitation at 6KW and 2.45GHz with a pressure of 110 Torr and a concentration of 10%.

[0024] Under the above conditions, after continuous growth for 32 hours, the methane gas was disconnected, and the power and gas pressure were gradually reduced to 600W and 10Torr within 2 hours. The microwave input was stopped, a vacuum was drawn, and then the vacuum was broken to open the cavity.

[0025] Figure 3 The following images show the results of growing polycrystalline diamond in a thin film without the introduction of amorphous carbon for 32 hours in this comparative example; Figure 3 As shown, the polycrystalline diamond film is completely shattered. Example 1

[0026] A method for preparing a self-supporting polycrystalline diamond film (flowchart shown) Figure 1 As shown), it includes the following steps: First, an amorphous carbon thin layer with a thickness of approximately 1.5 μm was deposited on a 2-inch flat molybdenum substrate using MPCVD technology, with a hydrogen flow rate of 100 Sccm and a methane flow rate of 50 Sccm. 甲烷 / V 氢气 The deposition growth reaction was carried out under microwave excitation at 6000W and 2.45GHz with a pressure of 110 Torr and a concentration of 50%.

[0027] After continuous growth for 1 hour, the reaction gases were switched to carry out the diamond growth reaction. The deposition parameters for polycrystalline diamond were: hydrogen flow rate 400 Sccm, methane flow rate 40 Sccm, V 甲烷 / V 氢气 The value is 10%, the nitrogen flow rate is 5 Sccm, and the V氮气 / V 氢气 The growth rate is 1.25%, the pressure is 110 Torr, and the temperature is maintained at 1050℃ (heat sink film).

[0028] Under the above conditions, after 32 hours of continuous growth (see structural diagram), Figure 2 As shown), disconnect the methane and nitrogen gases, gradually reduce the power and pressure to 600W and 10Torr at a cooling rate of 6℃ / min for 2 hours, stop the microwave input, disconnect the hydrogen gas, evacuate the vacuum, and then break the vacuum to open the cavity.

[0029] Figure 4 The following images are provided: an overall optical photograph (left) and an optical micrograph (right) of polycrystalline diamond grown on an amorphous carbon thin layer after 32 hours in this embodiment. Figure 4 As shown, the polycrystalline film has been automatically demolded and is intact without cracks, obvious warping, and uniform grain size. Example 2

[0030] A method for preparing a self-supporting polycrystalline diamond film includes the following steps: First, an amorphous carbon thin layer with a thickness of approximately 2 μm was deposited on a 2-inch flat molybdenum substrate using MPCVD technology, with a hydrogen flow rate of 100 Sccm and a methane flow rate of 50 Sccm. 甲烷 / V 氢气 The deposition growth reaction was carried out under microwave excitation at 6000W and 2.45GHz with a pressure of 110 Torr and a concentration of 50%.

[0031] After continuous growth for 1.5 hours, the reaction gas was switched to carry out the diamond growth reaction. The deposition parameters for polycrystalline diamond were: hydrogen flow rate 400 Sccm, methane flow rate 10 Sccm, V 甲烷 / V 氢气 The concentration is 2.5%, the nitrogen flow rate is 0 Sccm, and the V 氮气 / V 氢气 The temperature is 0%, the pressure is 110 Torr, and the growth (optical thin film) is carried out at 1100℃.

[0032] Under the above conditions, after continuous growth for 200 hours, the methane gas was disconnected, and the power and gas pressure were gradually reduced to 600W and 10Torr at a cooling rate of 6℃ / min for 2 hours. The microwave input was stopped, the hydrogen gas was disconnected, a vacuum was drawn, and then the vacuum was broken to open the cavity, thus obtaining the product.

[0033] Figure 5 The following images are provided: an overall optical photograph (left) and an optical micrograph (right) of polycrystalline diamond grown on an amorphous carbon thin layer after 200 hours in this embodiment. Figure 5As shown, the polycrystalline film has been automatically demolded and is intact without cracks, obvious warping, and uniform grain size.

[0034] In summary, this invention overcomes the shortcomings of polycrystalline diamond film cracking and inability to be demolded during the cooling process by adding an amorphous carbon thin layer in situ on the surface of the growing molybdenum substrate. At the same time, it solves the problems of high pollution, high cost, long cycle and difficulty in substrate reuse caused by substrate peeling.

[0035] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting polycrystalline diamond film, characterized in that, Includes the following steps: (1) A flat molybdenum stage is used as the substrate, which is cleaned before use; (2) An amorphous carbon thin layer with a thickness of 0.1-2 μm was deposited on the substrate surface using MPCVD technology; (3) Then the gas ratio was adjusted and polycrystalline diamond was deposited in situ; (4) After deposition, demolding is completed during the cooling process.

2. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (1), the flatness requirement of the flat molybdenum stage is ≤0.5mm; the flat molybdenum stage is obtained by turning or milling and then grinding.

3. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (2), the deposition parameters for the amorphous carbon thin layer are: hydrogen flow rate 50~100 Sccm; methane flow rate 40~50 Sccm; volume ratio V 甲烷 / V 氢气 The concentration is 40-100%; the cavity pressure is 100-120 Torr; the microwave power is 5500-9500W; and the deposition time is 0.5-2h.

4. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (3), the deposition parameters for polycrystalline diamond are: hydrogen flow rate 400~500 Sccm; methane flow rate 5~50 Sccm; oxygen flow rate 0~8 Sccm; nitrogen flow rate 0~3 Sccm; cavity pressure 90~130 Torr; microwave power 4500~9500W; growth temperature 930~1150℃; deposition time 20~300h.

5. The method for preparing a self-supporting polycrystalline diamond film as described in claim 4, characterized in that, The gas volume ratio is: optical thin film V 甲烷 / V 氢气 It is 1~3%, V 氮气 / V 氢气 It is 0%; heat sink film V 甲烷 / V 氢气 It is 9~12%, V 氮气 / V 氢气 It ranges from 1% to 5%.

6. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (4), the cooling rate is 4-10℃ / min and the cooling time is 120±30min.

7. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (1), the molybdenum stage can be reused. Before reuse, surface residues are removed by sandblasting, laser ablation, or oxygen plasma calcination.

8. The method for preparing a self-supporting polycrystalline diamond film as described in claim 1, characterized in that, In step (1), the molybdenum stage is ultrasonically cleaned before use; it is then ultrasonically cleaned with deionized water and alcohol in sequence, and finally dried with compressed air.

9. The method for preparing a self-supporting polycrystalline diamond film as described in claim 8, characterized in that, The molybdenum stage is subjected to plasma cleaning after ultrasonic cleaning; the plasma cleaning is performed by in-furnace etching within the MPCVD deposition chamber; the parameters for the plasma etching cleaning are: hydrogen flow rate 100~400 Sccm; oxygen flow rate 2~10 Sccm; chamber pressure 100~120 Torr; microwave power 5500~9500W; etching time 5~20min.

10. A self-supporting polycrystalline diamond film prepared by any one of the methods described in claims 1 to 9.

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