An automatic cleaning MPCVD apparatus and a cleaning method of the apparatus

Abstract

The application discloses an MPCVD device capable of automatic cleaning and a cleaning method of the device, and the device comprises a cavity (1) provided with a wave-transparent window (5), a substrate table (2) located in the cavity (1), a microwave source (3) located above the cavity (1) and a conductive coil (4) uniformly wound around the cavity (1), the conductive coil (4) is connected with a power supply to form a magnetic field coaxial with the cavity (1) in the cavity (1), and the power supply is a current-adjustable power supply. By introducing an external magnetic field, the distribution of plasma in the MPCVD cavity is changed, the plasma is guided to the edge of the inner wall of the cavity, and then the impurities in the MPCVD cavity are quickly and effectively removed.

Description

Technical Field

[0001] This invention relates to MPCVD equipment, and more specifically, to an automatically cleaning MPCVD equipment and a cleaning method for the equipment. Background Technology

[0002] High-quality diamonds possess a wide bandgap, broad optical transmittance, extremely high hardness and thermal conductivity, excellent insulation, and superior physicochemical properties such as resistance to acids, heat, and radiation. Furthermore, diamond devices are more suitable for high-temperature operation than silicon-based devices without the need for external cooling systems and are less prone to damage. Therefore, diamonds have wide applications in precision machining, grown gemstones, optical windows, heat sinks, and semiconductor devices. However, natural diamond reserves are limited, leading to the development of various methods for diamond synthesis, such as high-temperature high-pressure (HPHT), hot-filament chemical vapor deposition (HFCVD), direct-current arc plasma jet chemical vapor deposition (DC Arc Plasma Jet CVD), and microwave plasma chemical vapor deposition (MPCVD). Among these, MPCVD, due to the absence of impurities, can synthesize high-quality, large-area diamonds, making it the most ideal method for producing large-area, high-quality diamonds currently available.

[0003] The quality of diamond synthesized by MPCVD is related to various process parameters, including carbon source concentration, gas flow rate, substrate stage height, microwave power, and synthesis temperature. Furthermore, during diamond synthesis, a thin film of yellow carbon-related solid impurities deposits on the inner wall of the MPCVD equipment. The formation of these impurities is highly detrimental to the synthesis of high-quality diamond products. The growth temperature for synthesizing high-quality diamond by MPCVD is 700℃–1300℃. During the heating process, due to the increased temperature and plasma etching, these impurities decompose, releasing carbon source particles and thus disrupting the stability of the growth process parameters. During growth, these impurities, due to poor thermal stress matching with the inner wall of the chamber, may peel off, leading to a decrease in the clarity of the grown diamond product and even a severe decline in diamond quality, forming polycrystalline particle impurities on the growth surface. Therefore, effectively cleaning the impurities on the inner wall of the MPCVD chamber is crucial for producing high-quality diamond products.

[0004] Chinese patent application CN111560599A discloses a process for removing the thin film from the inner wall of an MPCVD cavity. The method includes the following steps: sealing the MPCVD cavity and evacuating it; then closing all evacuation valves; gradually introducing etching gas into the MPCVD cavity; when the gas pressure reaches 0.6-1.5 kPa, turning on the microwave source to form plasma; continuing to gradually introduce etching gas, increasing the gas pressure and microwave source power, so that the temperature of the substrate stage reaches a certain value and is maintained, while the corresponding cavity pressure remains constant within a certain range; gradually increasing the microwave source power to a certain value and maintaining a stable state under these process conditions for 25-40 minutes; finally, performing a shutdown operation, thus completing the process of removing the thin film from the inner wall of the cavity and the impurity film on the surface of the substrate stage. This method thoroughly removes the impurity film from the inner wall of the MPCVD cavity, the surface of the substrate stage, and the quartz observation window, reducing impurities that contaminate the diamond product and improving the quality of the synthesized product. However, in actual operation, this method requires a relatively long etching time, resulting in a long production cycle. Moreover, this etching method cannot effectively etch edges far from the plasma, meaning its etching ability is insufficient, resulting in an unsatisfactory cleaning effect that still requires manual auxiliary cleaning.

[0005] Chinese patent application CN111441034A discloses a substrate stage and a method for in-situ plasma cleaning. The substrate stage includes an axisymmetric cylindrical vacuum cavity, and a metal base with a metal wire is placed in the center of the vacuum cavity. During the surface cleaning of the inner wall of the vacuum cavity, after microwaves are fed into the vacuum cavity, the needle-like structure of the metal wire near the vacuum cavity wall easily generates a "point discharge" effect at the metal tip due to the microwave electric field. This excites the gas in the vacuum cavity to generate plasma. The plasma approaches the vacuum cavity wall, thus performing plasma cleaning on the inner wall of the vacuum cavity. The generated byproducts are removed by the vacuum system. The metal wire moves up and down with the rotation and movement of the substrate stage, so that the tip discharge end of the metal wire can effectively clean the inner wall of the vacuum cavity. However, in actual use, this solution has the following disadvantages: ① The metal wire that generates plasma generates extremely high temperatures, while the metal base has a very low temperature. Due to the temperature gradient, the metal wire is very easy to bend; ② The plasma generated by the point discharge is far from the resonance region, so the plasma intensity is very low, resulting in extremely slow cleaning efficiency. Summary of the Invention

[0006] To address the problems of poor cleaning effect and slow efficiency of impurities on the inner wall of the MPCVD cavity, the present invention provides an automatically cleaning MPCVD device and a cleaning method for the device. The device introduces an external magnetic field to change the distribution of plasma inside the MPCVD vacuum cavity, guiding the plasma to the edge of the inner wall of the cavity, thereby quickly and effectively removing impurities inside the MPCVD cavity.

[0007] To achieve the above objectives, the present invention provides an automatically cleaning MPCVD device, which includes a cavity with a wave-transparent window, a substrate stage located inside the cavity, a microwave source located above the wave-transparent window, and a conductive coil uniformly wound around the cavity. The conductive coil is connected to a power supply to form a magnetic field coaxial with the cavity inside the cavity. The power supply is an adjustable current power supply.

[0008] Preferably, the conductive coil is wound around the outside of the cavity; or

[0009] The cavity has grooves formed inside to accommodate the conductive coil.

[0010] Preferably, the conductive coil has 2 turns. <n<100。

[0011] Preferably, the magnetic induction intensity of the magnetic field is adjustable in the range of 80 to 120 mT.

[0012] More preferably, the conductive coil contains an iron core, or

[0013] The cavity is provided with permanent magnets symmetrically arranged outside the cavity.

[0014] Furthermore, the number of permanent magnets is 6 to 12.

[0015] A second aspect of the present invention provides a cleaning method for an MPCVD device, the cleaning method comprising the following steps:

[0016] S1. Vacuum treatment is performed on the cavity (1) of the MPCVD equipment;

[0017] S2. Etching gas is introduced into the vacuum cavity (1) until the internal pressure is 0.5KPa to 1KPa, and then microwaves are fed in to cover the substrate stage (2) with plasma.

[0018] S3. Turn on the power to generate a stable magnetic field in the cavity (1);

[0019] S4. Adjust the power supply current to adjust the magnetic induction intensity, thereby changing the shape of the plasma and then precisely cleaning different positions on the inner wall of the cavity (1).

[0020] Preferably, in step S2, the etching gas is hydrogen, or a hydrogen / argon mixture, or a hydrogen / chlorine mixture, or a hydrogen / argon / chlorine mixture. In the mixture, hydrogen is the main gas, and the volume of secondary mixed gases such as argon and chlorine accounts for less than 10% of the volume of hydrogen.

[0021] Preferably, in step S2, the power of the microwave is 1500W to 3500W.

[0022] Through the above technical solution, the present invention achieves the following beneficial effects:

[0023] 1. This invention introduces an external magnetic field through a power supply and a conductive coil, and changes the plasma distribution inside the MPCVD equipment cavity by adjusting the current, guiding the plasma to the edge of the cavity wall, thereby quickly and effectively removing impurities inside the MPCVD cavity.

[0024] 2. In a preferred embodiment of the present invention, the magnetic induction intensity is adjusted within the range of 80 to 120 mT, so that charged particles in the plasma can move at high speed and collide with the inner wall of the cavity, thereby effectively cleaning the inner wall of the cavity. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the automatically cleaning MPCVD equipment described in this invention.

[0026] Explanation of reference numerals in the attached figures

[0027] 1. Cavity, 2. Substrate stage, 3. Microwave source, 4. Conductive coil, 5. Wave-transparent window. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] First, it should be noted that some directional terms used in the following description to clearly illustrate the technical solution of the present invention, such as "outer" and "inner," are used by analogy to the normal orientation of components in an MPCVD device. For example, the part through which the plasma passes is the interior, and the opposite part is the exterior. These terms are used only for the convenience of describing the present invention and for simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0030] In the description of the present invention, it should be noted that the terms "mounting" and "connection" should be understood in a broad sense unless otherwise expressly specified and limited. For example, the connection may be a fixed connection, a detachable connection, or an integrated connection; it may be a direct connection, or an indirect connection through an intermediate medium, and it may be the internal communication between two elements or the interaction relationship between the two elements. Those skilled in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

[0031] As Figure 1 shows, the automatically cleaned MPCVD device of the present invention comprises a cavity 1 with a wave-transmitting window 5, a substrate stage 2 located inside the cavity 1, a microwave source 3 located above the wave-transmitting window 5, and a conductive coil 4 uniformly wound around the cavity 1, the conductive coil 4 is connected to a power supply to form a magnetic field coaxial with the cavity 1 inside the cavity 1, and the power supply is a current-adjustable power supply. The wave-transmitting window 5 is made of a material with good wave-transmitting performance, such as quartz.

[0032] In a plasma system, although the whole is electrically neutral, the interior of the plasma contains electrons and positively charged ions. When an external magnetic field is applied, electrons and positive ions moving perpendicular to the direction of the magnetic field perform Larmor gyration under the action of Lorentz force. By gradually adjusting the magnitude of the magnetic induction intensity B, the shape of the plasma can be gradually changed, so that the plasma fireball inside the vacuum cavity 1 is close to the inner wall of the vacuum cavity 1, which significantly increases the cleaning efficiency. The plasma fireball in the present invention emits visible light, so the change of the fireball can be visually observed by naked eyes. When no magnetic field is applied, the plasma fireball gathers at the center; when the magnetic field is increased, the shape of the fireball changes and gets close to the inner wall of the cavity.

[0033] The present invention introduces an external magnetic field through a power supply and a conductive coil 4, changes the distribution of plasma inside the cavity 1 of the MPCVD device by adjusting the current, guides the plasma to the edge of the inner wall of the cavity 1, thereby quickly and effectively removing impurities inside the MPCVD cavity. The magnitude of the current is adjustable, and the specific magnitude of the current is determined according to the effect of the magnetic field changing the shape of the plasma, as long as it can effectively ensure that the shape of the plasma contacts the inner wall of the cavity.

[0034] As some preferred embodiments of the present invention, the conductive coil 4 can be wound outside the cavity 1; since the cavity 1 has a certain wall thickness, a wire slot for accommodating the conductive coil 4 can also be processed inside the cavity 1, and the conductive coil 4 is embedded inside the cavity 1.

[0035] Preferably, the number of turns of the conductive coil 4 satisfies 2<n<100. According to Biot-Savart law, when the magnitude of the current in the conductive coil 4 is changed, the magnitude of the uniform magnetic induction intensity B generated inside the coil is:

[0036] B=μ0nI

[0037] Where μ0 is the free permeability, and its magnitude is 4π × 10⁻⁶. -7 Newton / Ampere 2 n is the number of turns of the conductive coil 4, and I is the magnitude of the current. When a constant current is passed through the conductive coil 4, the plasma inside the cavity 1 will move due to the Lorentz force, and the radius of motion is related to the magnitude of the magnetic induction intensity.

[0038] When the magnetic induction intensity is within a suitable range, the charged particles in the plasma will move at high speed and collide with the inner wall of cavity 1, thereby effectively cleaning the inner wall of cavity 1. Specifically, the adjustment range of the magnetic induction intensity is 80 to 120 mT.

[0039] To increase the magnetic induction intensity, an iron core can be placed inside the conductive coil 4, or permanent magnets can be placed outside the cavity 1. The number of permanent magnets is 6 to 12, and they are symmetrically placed outside the cavity 1.

[0040] The process of growing diamond using the above-mentioned MPCVD equipment is as follows:

[0041] 1) Ignition process: Turn on the vacuum pump to evacuate the cavity 1 of the MPCVD equipment to a vacuum, and then introduce H2. When the pressure inside the cavity 1 is 0.5KPa to 1KPa, turn on the microwave source 3 to feed microwave power into the vacuum cavity 1. Due to the introduction of microwave power, the gas inside discharges under low pressure to form plasma, and the shape of the plasma just covers the top of the substrate stage 2.

[0042] 2) Heating process: Gradually increase the pressure of vacuum chamber 1 to 15-30 kPa and microwave power to 3000-6000 W. When the single crystal temperature rises to 700℃~1300℃, stabilize for 10~30 minutes.

[0043] 3) Stabilizing the growth process: Stabilize the temperature inside chamber 1 at 800-1000℃ for 15-60 minutes, then introduce carbon source gas to start diamond growth, which takes 40-400 hours (the growth time depends on the target thickness).

[0044] 4) Cooling process: After growth is complete, gradually reduce the pressure to below 5 kPa and the microwave power to below 1500 W, turn off microwave source 3, and remove the diamond product.

[0045] The cleaning process for the MPCVD equipment described above is as follows:

[0046] 1) After growth is complete, remove the diamond product and then perform the ignition operation according to the diamond growth process. That is, turn on the vacuum pump to evacuate the cavity 1 of the MPCVD equipment to a vacuum, and then introduce H2 gas. When the pressure inside the cavity 1 is 0.5KPa to 1KPa, turn on the microwave source 3 and feed the microwave power into the vacuum cavity 1. The microwave power range is 1500W to 3500W. The gas discharges under low pressure to form plasma, which just covers the top of the substrate stage 2.

[0047] 2) Turn on the power to generate a stable magnetic field inside the vacuum chamber 1. The direction of the magnetic induction intensity is distributed along the axial direction of the vacuum chamber.

[0048] 3) By adjusting the magnitude of the current, the magnetic induction intensity B is gradually adjusted to gradually change the shape of the plasma, so that the plasma fireball inside the vacuum chamber 1 approaches the inner wall of the vacuum chamber 1 for efficient cleaning.

[0049] When cleaning is not performed using this method, manual wiping is typically employed. This requires removing the inner wall or the top quartz translucent window for thorough cleaning, which is labor-intensive and time-consuming, and carries the risk of incomplete cleaning and the introduction of external contamination. The method of this invention allows for rapid cleaning, typically completing the process in 15-20 minutes, without the possibility of external contamination.

[0050] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0052] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A cleaning method for an MPCVD device, characterized in that, The MPCVD equipment includes a cavity (1) with a wave-transparent window (5), a substrate stage (2) located inside the cavity (1), a microwave source (3) located above the wave-transparent window (5), and a conductive coil (4) uniformly wound around the cavity (1). The conductive coil (4) is connected to a power source to form a magnetic field coaxial with the cavity (1) inside the cavity (1). The power source is an adjustable current power source. The cleaning method includes the following steps: S1. Vacuum treatment is performed on the cavity (1) of the MPCVD equipment; S2. Etching gas is introduced into the vacuum cavity (1) until the internal pressure is 0.5kPa~1kPa, and then microwaves are fed in to cover the substrate stage (2) with plasma. S3. Turn on the power to generate a stable magnetic field in the cavity (1); S4. Adjust the power supply current to achieve the adjustment of magnetic induction intensity from 80 to 120 mT, so as to change the shape of the plasma and then precisely clean different positions on the inner wall of the cavity (1).

2. The cleaning method according to claim 1, characterized in that, The conductive coil (4) is wound around the outside of the cavity (1); or The cavity (1) has a groove inside for accommodating the conductive coil (4).

3. The cleaning method according to claim 1, characterized in that, The conductive coil (4) has 2 turns. <n<100。 4. The cleaning method according to any one of claims 1 to 3, characterized in that, The conductive coil (4) is equipped with an iron core, or The cavity (1) is provided with a permanent magnet outside the cavity (1), and the permanent magnet is symmetrically arranged outside the cavity (1).

5. The cleaning method according to claim 4, characterized in that, The number of permanent magnets is 6 to 12.

6. The cleaning method according to claim 1, characterized in that, In step S2, the etching gas is hydrogen, or a mixture of hydrogen and argon, or a mixture of hydrogen and chlorine, or a mixture of hydrogen, argon, and chlorine.

7. The cleaning method according to claim 1, characterized in that, In step S2, the power of the microwave is 1500W~3500W.

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