A method for synthesizing single crystal diamond based on microwave plasma chemical vapor deposition technology

Abstract

The application belongs to the field of diamond preparation, and particularly relates to a method for synthesizing single crystal diamond based on a microwave plasma chemical vapor deposition technology. Hydrogen is introduced into straw for etching by using the microwave plasma chemical deposition method, high-concentration carbon source gas is generated as a carbon source for synthesizing diamond, and a small amount of oxygen source gas and nitrogen source gas are carried, so that the macroscopic surface of the synthesized diamond is more smooth, the growth defects of the growth surface are reduced, the crystal quality of the diamond is improved, and meanwhile, the special structure design of the support frame in the microwave plasma chemical deposition device can make the microwave electric field provided by the support frame concentrated on the single crystal diamond substrate, so that the high-speed growth of the diamond is effectively promoted.

Description

Technical Field

[0001] This invention belongs to the field of diamond preparation, specifically relating to a method for synthesizing single-crystal diamond based on microwave plasma chemical vapor deposition technology. Background Technology

[0002] Diamond is valued for its unique physicochemical properties, such as a high breakdown field (10 MV / cm) at room temperature and extremely high carrier mobility (holes: 3800 cm⁻¹). 2 ·V -1 ·S -1 Electron: 4500cm 2 ·V -1 ·S -1 Diamond has attracted much attention due to its excellent properties, such as high thermal conductivity (2000 W / (m·K)) and a band gap of 5.5 eV. Therefore, diamond is considered an important material in fields such as radiation detectors, neutron detectors, magnetic field sensing, quantum computing, quantum applications, and electronic applications.

[0003] Due to the scarcity and quality of natural diamonds, they cannot be widely used in cutting-edge fields. Therefore, the artificial synthesis of diamonds has attracted much attention. Currently, the main methods for synthesizing diamonds are high-temperature high-pressure (HTHP) and chemical vapor deposition (CVD). However, due to limitations in equipment and process conditions, HTHP is not as advantageous as CVD in controlling impurities and dimensions, and cannot meet the stringent requirements of cutting-edge fields. The principle of existing microwave plasma CVD for diamond synthesis involves a microwave generator producing microwaves, which are then introduced into a vacuum cavity through a waveguide. This plasma ionizes reactive gases such as methane and hydrogen, which are then deposited onto a substrate as diamond.

[0004] Chinese patent application number 202210072423.9 discloses a method for MPCVD single-crystal diamond splicing growth. Multiple single-crystal diamond seed crystals are placed on square seed crystal pads in a seed crystal tray to obtain a tray with arranged seed crystals. This tray is then placed in the reaction chamber of an MPCVD diamond growth apparatus. The chamber door is closed, a vacuum is drawn, hydrogen is introduced, and a microwave generator is activated to produce plasma. Oxygen and argon are introduced into the reaction chamber for etching. The pre-etched single-crystal diamond seed crystals are placed with their etched surfaces facing upwards on a growth sample tray, with adjacent single-crystal diamond seed crystals closely arranged, resulting in a growth sample tray with arranged seed crystals. This tray is then placed in the MPCVD diamond growth apparatus, the chamber door is closed, a vacuum is drawn, hydrogen is introduced, and a microwave generator is activated to produce plasma. Methane and nitrogen are introduced into the reaction chamber to promote lateral growth and connection in the etched step areas at the edges of the diamond seed crystals. Then, the methane content is increased to promote vertical diamond growth, completing the MPCVD single-crystal diamond splicing growth. However, this method has a low carbon source utilization rate and also results in a large waste of high-purity hydrogen. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for synthesizing single-crystal diamond based on microwave plasma chemical vapor deposition (MPCVD). The method utilizes MPC to etch straw with hydrogen gas, generating a high-concentration carbon source gas that serves as the carbon source for diamond synthesis, thereby growing single-crystal diamond.

[0006] The technical solution of the present invention to solve the above problems is as follows:

[0007] A method for synthesizing single-crystal diamond based on microwave plasma chemical vapor deposition technology includes the following steps:

[0008] S1. Prepare a microwave plasma chemical vapor deposition reactor and cleaned and dried straw. The microwave plasma chemical vapor deposition reactor includes a conveying device, an upper substrate stage, a lower substrate stage and a reaction chamber. The lower substrate stage is provided with a first groove and a support frame is placed there. The upper surface of the support frame is provided with a second groove and a single crystal diamond substrate is placed there.

[0009] S2. Place the cleaned and dried straw in the central circular hole of the upper substrate stage, introduce hydrogen gas into the reaction chamber of the microwave plasma chemical vapor deposition reactor, use microwave to excite gas discharge to generate plasma, adjust the process parameters of the deposition device, and use a conveying device to extend the straw into the plasma and be etched to generate carbon source gas for the growth of single crystal diamond.

[0010] S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate.

[0011] Furthermore, the reaction chamber is spherical; and the single-crystal diamond is located at the center of the spherical reaction chamber, which makes it easier to concentrate the electric field.

[0012] Furthermore, the lower half of the support frame is cylindrical and the upper half is frustum-shaped, with the diameter of the upper base being smaller than the diameter of the lower base. The purpose of this arrangement is to concentrate the microwave electric field at the tip of the upper surface of the frustum, i.e., at the single-crystal diamond substrate, where it is easy to accumulate and form a high-density plasma, thereby promoting diamond growth.

[0013] Furthermore, the depth of the second groove is less than the thickness of the single-crystal diamond substrate; the single-crystal diamond substrate is located in the second groove, which can effectively prevent the single-crystal diamond substrate from falling off the support frame when subjected to impact force.

[0014] Furthermore, the straw is broken down into thin strips with a width of 1.2-1.8 mm.

[0015] Furthermore, in step S2, the straw is inserted into the plasma at a speed of 0.1-0.3 m / h and etched by a conveying device.

[0016] The beneficial effects of this invention are:

[0017] During the synthesis process, hydrogen gas is introduced through microwave plasma chemical vapor deposition to etch the straw, generating a high concentration of carbon source gas, along with small amounts of oxygen and nitrogen source gas. This results in a smoother macroscopic surface of the synthesized diamond, reduces growth defects on the growth surface, and improves the crystal quality of the diamond. In the microwave plasma chemical vapor deposition apparatus, the support frame forms an upwardly tapered conical structure, which concentrates the provided microwave electric field on the single-crystal diamond substrate on the support frame, effectively promoting the high-speed growth of diamond. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the microwave plasma chemical deposition reactor of the present invention;

[0019] Figure 2 The diagram shows the diamond growth rate during the synthesis process in the embodiments and comparative examples of this invention.

[0020] In the picture:

[0021] 1. Conveying device; 2. Reaction chamber; 3. Upper substrate stage; 4. Lower substrate stage; 5. Plasma; 6. First groove; 7. Support frame; 8. Second groove; 9. Single crystal diamond substrate. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Example 1

[0024] Before the experiment, the single-crystal diamond substrate 9 needs to be pretreated: the single-crystal diamond substrate 9 is cleaned by ultrasonic cleaning, which involves sequentially ultrasonic cleaning in deionized water, acetone, and alcohol for 15 minutes each. The pretreated single-crystal diamond substrate 9 is then subjected to O2 / H2 plasma etching at a volume ratio of 2%, an etching temperature of 800℃, and an etching time of 30 minutes. After etching, it is ready for use.

[0025] The synthesis of single-crystal diamond specifically includes the following steps:

[0026] S1. Prepare the microwave plasma chemical vapor deposition reactor and clean, dried straw, such as... Figure 1 As shown, the microwave plasma chemical vapor deposition (PCCVD) apparatus includes a transfer device 1, an upper substrate stage 3, a lower substrate stage 4, and a reaction chamber 2. The lower substrate stage has a first groove 6 on which a support frame 7 is placed. During the synthesis process, the upper surface of the support frame 7 has a second groove 8 on which a single-crystal diamond substrate 9 is placed. The reaction chamber 2 is spherical. The lower half of the support frame 7 is cylindrical, and the upper half is frustum-shaped, with the diameter of the upper base being smaller than the diameter of the lower base. The depth of the second groove 8 is less than the thickness of the single-crystal diamond substrate 9. The upper substrate stage 3 has a through-hole with a diameter of 2-3 mm at its center.

[0027] S2. The cleaned and dried straw is broken down into thin strips with a width of 1.5 mm and placed in the central circular hole of the upper substrate stage. Hydrogen gas is introduced into the reaction chamber of the microwave plasma chemical vapor deposition reactor. Plasma is generated by microwave-induced gas discharge. The process parameters of the deposition device are adjusted, with the growth power set to 2000 W, pressure 25 kPa, growth temperature 1000 ℃, and growth time 6 h. The straw is extended into the plasma at a speed of 0.2 m / h through a conveying device and etched to generate carbon source gas for the growth of single crystal diamond.

[0028] S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate.

[0029] The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 4.32 cm. -1 .

[0030] Example 2

[0031] Before the experiment, the single-crystal diamond substrate 9 needs to be pretreated: the single-crystal diamond substrate 9 is cleaned by ultrasonic cleaning, which involves sequentially ultrasonic cleaning in deionized water, acetone, and alcohol for 10 minutes each. The pretreated single-crystal diamond substrate 9 is then subjected to O2 / H2 plasma etching at a volume ratio of 2%, an etching temperature of 800℃, and an etching time of 25 minutes. After etching, it is ready for use.

[0032] The synthesis of single-crystal diamond specifically includes the following steps:

[0033] S1. Prepare the microwave plasma chemical vapor deposition reactor and clean, dried straw, such as... Figure 1 As shown, the microwave plasma chemical vapor deposition (PCCVD) apparatus includes a transfer device 1, an upper substrate stage 3, a lower substrate stage 4, and a reaction chamber 2. The lower substrate stage has a first groove 6 on which a support frame 7 is placed. During the synthesis process, a second groove 8 is provided on the surface of the support frame 5, and a single-crystal diamond substrate 9 is placed there. The reaction chamber 2 is spherical. The lower half of the support frame 7 is cylindrical, and the upper half is frustum-shaped, with the diameter of the upper base being smaller than the diameter of the lower base. The depth of the second groove 8 is less than the thickness of the single-crystal diamond substrate 9. The upper substrate stage 3 has a through-hole with a diameter of 2-3 mm at its center.

[0034] S2. The cleaned and dried straw is broken down into thin strips with a width of 1.2 mm and placed in the central circular hole of the upper substrate stage. Hydrogen gas is introduced into the reaction chamber of the microwave plasma chemical vapor deposition reactor. Plasma is generated by microwave-induced gas discharge. The process parameters of the deposition device are adjusted, with the growth power set to 1500 W, pressure 20 kPa, growth temperature 800 ℃, and growth time 5 h. The straw is extended into the plasma at a speed of 0.1 m / h through a conveying device and etched to generate carbon source gas for the growth of single crystal diamond.

[0035] S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate.

[0036] The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 4.57 cm. -1 .

[0037] Example 3

[0038] Before the experiment, the single-crystal diamond substrate 9 needs to be pretreated: the single-crystal diamond substrate 9 is cleaned by ultrasonic cleaning, which involves sequentially ultrasonic cleaning in deionized water, acetone, and alcohol for 20 minutes each. The pretreated single-crystal diamond substrate 9 is then subjected to O2 / H2 plasma etching at a volume ratio of 2%, an etching temperature of 800℃, and an etching time of 40 minutes. After etching, it is ready for use.

[0039] The synthesis of single-crystal diamond specifically includes the following steps:

[0040] S1. Prepare the microwave plasma chemical vapor deposition reactor and clean, dried straw, such as... Figure 1 As shown, the microwave plasma chemical vapor deposition (PCCVD) apparatus includes a transfer device 1, an upper substrate stage 3, a lower substrate stage 4, and a reaction chamber 2. The lower substrate stage has a first groove 6 on which a support frame 7 is placed. During the synthesis process, a second groove 8 is provided on the surface of the support frame 5, and a single-crystal diamond substrate 9 is placed there. The reaction chamber 2 is spherical. The lower half of the support frame 7 is cylindrical, and the upper half is frustum-shaped, with the diameter of the upper base being smaller than the diameter of the lower base. The depth of the second groove 8 is less than the thickness of the single-crystal diamond substrate 9. The upper substrate stage 3 has a through-hole with a diameter of 2-3 mm at its center.

[0041] S2. The cleaned and dried straw is broken down into thin strips with a width of 1.8 mm and placed in the central circular hole of the upper substrate stage. Hydrogen gas is introduced into the reaction chamber of the microwave plasma chemical vapor deposition reactor. Plasma is generated by microwave-excited gas discharge. The process parameters of the deposition device are adjusted, with the growth power set to 2500 W, pressure 30 kPa, growth temperature 1500 ℃, and growth time 6 h. The straw is extended into the plasma at a speed of 0.3 m / h through a conveying device and etched to generate carbon source gas for the growth of single crystal diamond.

[0042] S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate.

[0043] The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 5.12 cm. -1 .

[0044] Example 4

[0045] Before the experiment, the single-crystal diamond substrate 9 needs to be pretreated: the single-crystal diamond substrate 9 is cleaned by ultrasonic cleaning, which involves sequentially ultrasonic cleaning in deionized water, acetone, and alcohol for 25 minutes each. The pretreated single-crystal diamond substrate 9 is then subjected to O2 / H2 plasma etching at a volume ratio of 2%, an etching temperature of 800℃, and an etching time of 35 minutes. After etching, it is ready for use.

[0046] The synthesis of single-crystal diamond specifically includes the following steps:

[0047] S1. Prepare the microwave plasma chemical vapor deposition reactor and clean, dried straw, such as... Figure 1 As shown, the microwave plasma chemical vapor deposition (PCCVD) apparatus includes a transfer device 1, an upper substrate stage 3, a lower substrate stage 4, and a reaction chamber 2. The lower substrate stage has a first groove 6 on which a support frame 7 is placed. During the synthesis process, the upper surface of the support frame 7 has a second groove 8 on which a single-crystal diamond substrate 9 is placed. The reaction chamber 2 is spherical. The lower half of the support frame 7 is cylindrical, and the upper half is frustum-shaped, with the diameter of the upper base being smaller than the diameter of the lower base. The depth of the second groove 8 is less than the thickness of the single-crystal diamond substrate 9. The upper substrate stage 3 has a through-hole with a diameter of 2-3 mm at its center.

[0048] S2. The cleaned and dried straw is broken down into thin strips with a width of 1.4 mm and placed in the central circular hole of the upper substrate stage. Hydrogen gas is introduced into the reaction chamber of the microwave plasma chemical vapor deposition reactor. Plasma is generated by microwave-induced gas discharge. The process parameters of the deposition device are adjusted, with the growth power set to 2200 W, pressure 32 kPa, growth temperature 1200 ℃, and growth time 5 h. The straw is extended into the plasma at a speed of 0.2 m / h through a conveying device and etched to generate carbon source gas for the growth of single crystal diamond.

[0049] S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate.

[0050] The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 4.82 cm. -1 .

[0051] Comparative Example

[0052] Compared with Example 1, this comparative example does not introduce straw as a carbon source, but instead introduces methane and nitrogen as carbon sources, wherein methane accounts for 6% of the total gas volume in the reaction chamber and nitrogen accounts for 0.01% of the total gas volume in the reaction chamber. The rest of the process is the same as in Example 1.

[0053] The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 5.76 cm. -1 .

[0054] Figure 2 This diagram shows the diamond growth rate during the synthesis process of Examples 1-4 and the comparative examples. (Source: [Diagram showing diamond growth rate during synthesis]) Figure 2It can be seen that the diamond growth rate during the synthesis process of Examples 1-4 is higher than that of the comparative examples, especially the diamond growth rate under the preparation conditions of Example 1.

[0055] Existing technologies often use carbon-containing gases such as methane, ethanol, and carbon dioxide as carbon sources. However, this method not only has low carbon source utilization but also wastes a large amount of high-purity hydrogen. Therefore, this application uses clean straw as the carbon source. The main component of straw is cellulose-based carbohydrates, and it also includes a small amount of crude protein and crude fat. It is mainly composed of carbon, hydrogen, and oxygen, and the crude protein also contains nitrogen. During the synthesis process, hydrogen gas is introduced to etch the straw using microwave plasma chemical vapor deposition, generating a high concentration of carbon source gas, along with small amounts of oxygen and nitrogen source gas. The introduction of nitrogen source gas can make the macroscopic surface of the synthesized diamond smoother and reduce dislocations inside the epitaxial diamond crystal. The introduction of oxygen source gas can promote diamond deposition, and the O-containing groups formed in the plasma can more effectively etch away SP. 2 Carbon reduces growth defects on the growth surface, thereby improving the crystal quality of diamond. In a microwave plasma chemical vapor deposition apparatus, a support frame 7 with a frustum-shaped upper part is placed in the first groove 6 of the lower substrate stage 4, and the radius of the upper base of the frustum is smaller than the radius of the lower base, forming an upwardly tapered structure. The single-crystal diamond substrate is located in the second groove 8 of the upper base. Due to the existence of the tip effect, the sharper the object, the greater the force and the stronger the physical effect. Compared with the smooth part, the surface charge density of the tip is larger, and the electric field intensity near the tip is stronger. The electric field provided by this can be concentrated on the upper surface of the support frame 7, that is, at the single-crystal diamond substrate 9, where a high-density plasma can be generated, effectively promoting the high-speed growth of diamond. In addition, setting the reaction chamber 2 to be spherical and placing the single-crystal diamond substrate at its center is more conducive to the concentration of the electric field. Furthermore, the radiated microwaves can be reflected by the spherical reaction chamber and returned to the support frame 7 located at the center, further enhancing the plasma density near the single-crystal diamond substrate 9 and ensuring the high-speed growth of diamond.

[0056] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0057] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing single-crystal diamond based on microwave plasma chemical vapor deposition technology, characterized in that, Includes the following steps: S1. Prepare a microwave plasma chemical vapor deposition (MPCVD) reactor and cleaned and dried straw. The MPCVD reactor includes a conveying device, an upper substrate stage, a lower substrate stage, and a reaction chamber. The lower substrate stage has a first groove for placing a support frame. The upper surface of the support frame has a second groove for placing a single-crystal diamond substrate. The reaction chamber is spherical, and the single-crystal diamond substrate is located at its center. The lower half of the support frame is cylindrical, and the upper half is frustum-shaped, with the diameter of the upper base smaller than the diameter of the lower base. The depth of the second groove is less than the thickness of the single-crystal diamond substrate. The upper substrate stage has a through hole with a diameter of 2-3 mm at its center. Before the experiment begins, the single-crystal diamond substrate needs to be pretreated: the single-crystal diamond substrate is cleaned by ultrasonic cleaning; the cleaning method is to ultrasonically clean it in deionized water, acetone and alcohol for 15 minutes in sequence. The pretreated single-crystal diamond substrate is then subjected to O2 / H2 plasma etching with a volume ratio of 2%, an etching temperature of 800℃ and an etching time of 30 minutes. After etching, it is ready for use. S2. The cleaned and dried straw is broken down into thin strips with a width of 1.5 mm and placed in the central circular hole of the upper substrate stage. Hydrogen gas is introduced into the reaction chamber of the microwave plasma chemical vapor deposition device. Plasma is generated by microwave-excited gas discharge. The process parameters of the deposition device are adjusted, with the growth power set to 2000 W, the pressure to 25 kPa, the growth temperature to 1000 ℃, and the growth time to 6 h. The straw is extended into the plasma at a speed of 0.2 m / h through a conveying device and etched to generate carbon source gas for the growth of single crystal diamond. S3. Single-crystal diamond prepared from straw as a carbon source is obtained by laser ablation of the single-crystal substrate. The deposited diamond was characterized using Raman spectroscopy, yielding a thickness of 1332.151 cm⁻¹. -1 The full width at half maximum (FWHM) of the characteristic peak is 4.32 cm. -1 .

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