Near-normal-pressure MPCVD system and application thereof

Abstract

The invention provides a near-normal-pressure MPCVD system and application thereof.The system comprises a deposition module, the deposition module comprises a resonant cavity, a base table used for containing a substrate is arranged in the center of the lower end of the resonant cavity, and the deposition module deposits a thin film on the surface of the substrate located in the resonant cavity through a microwave plasma chemical vapor deposition method; the resonant cavity comprises a first gathering cavity and a second tuning cavity which are connected from top to bottom, and the aperture of the first gathering cavity is increased from top to bottom. The aperture of the first gathering cavity is increased from top to bottom, energy in the cavity is concentrated, the second tuning cavity tunes distribution of a standing wave electric field of the cavity, so that the resonant cavity can form a microwave plasma chemical vapor deposition system with stable plasma under near normal pressure (30-80kPa), high-speed diamond deposition is realized, and meanwhile, the high-speed diamond deposition is realized. Nitrogen doping formed by leakage of a cavity in a traditional negative pressure environment can be avoided through a near-normal-pressure film growth environment, and production of a high-purity film is better facilitated.

Description

Technical Field

[0001] The present invention relates to the field of MPCVD technology, and in particular to a near-normal pressure MPCVD system and applications thereof. Background Art

[0002] Diamond has many excellent properties, such as extremely high hardness, ultra-high thermal conductivity, low thermal expansion coefficient, high light transmittance, etc., so it has a wide range of uses in industry, such as making wear-resistant tools, acoustic diaphragms, optical windows, chip heat sinks, etc. In addition, when traditional silicon-based semiconductors are approaching their physical limits, diamond has become a popular choice for the next generation of new semiconductors with its ultra-wide bandgap and extremely high carrier mobility. However, to achieve the above applications, in addition to high requirements for the quality of diamond, it also requires a large area. However, natural diamonds are formed under high temperatures and high pressures generated by meteorite impacts or crustal movement. The harsh formation conditions lead to limited reserves of diamonds, and large areas of high-quality diamonds are even rarer and more expensive. Therefore, the artificial synthesis of high-quality diamond films has always been a hot topic of research.

[0003] Conventional artificial diamond synthesis mostly adopts high temperature and high pressure method (HTHP) and chemical vapor deposition method (CVD). Diamond synthesized by HTHP method is powdered crystal and contains many impurities, which cannot meet the practical application. Chemical vapor deposition method uses mixed gas containing elements required for thin film deposition as source gas, carries out a series of complex elementary reactions in the reaction chamber, and carries out a series of surface reactions on the substrate surface, and finally produces a thin film on the substrate surface. However, in the early stage of research, it was found that a large amount of intergrown graphite would be produced during the reaction process, and the deposition rate was extremely low, which lacked practical application value. It was not until a study found that high concentration of hydrogen atoms can suppress the graphite phase that CVD method became a practical method, and in principle there is no limit on the size of diamond.

[0004] At present, the main methods for synthesizing diamonds by CVD include hot wire chemical vapor deposition (HFCVD), direct current arc plasma jet chemical vapor deposition (DC-PJCVD) and microwave plasma chemical vapor deposition (MPCVD). These methods have their own advantages in different fields due to their different principles. HFCVD belongs to ohmic thermal excitation, and hot wire vaporization at high temperature will reduce the quality of the film; DC-PJCVD belongs to strong electric field excitation, and high-energy particles impacting the electrode will cause metal contamination of the electrode material; compared with the first two, MPCVD is a microwave-excited discharge without electrodes to avoid metal doping, and has the advantages of high plasma density and good controllability. It is the preferred method for preparing high-quality diamonds. However, the MPCVD method also has problems such as low diamond growth rate and poor production quality.

[0005] In an MPCVD system, by increasing the growth pressure, the concentration of plasma active substances can be increased, thereby achieving a deposition rate of up to dozens of micrometers per hour. However, an excessively high growth pressure will cause the plasma to discharge and contract, so the upper limit of the diamond growth pressure is restricted by plasma instability. At the same time, negative pressure reaction conditions are likely to cause leakage in the microwave reaction cavity, resulting in gas nitrogen doping, which becomes the main source of nitrogen impurities in the production of high-purity diamonds. Summary of the Invention

[0006] The purpose of the present invention is to overcome the disadvantages and deficiencies existing in the prior art, and to provide a near-atmospheric-pressure MPCVD system and its application.

[0007] The technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a near-atmospheric-pressure MPCVD system, including a deposition module. The deposition module includes a resonant cavity, and a substrate stage for placing a substrate is provided at the center of the lower end of the resonant cavity. The deposition module deposits a thin film on the surface of the substrate located in the resonant cavity by microwave plasma chemical vapor deposition.

[0008] The resonant cavity includes a connected first focusing cavity and a second tuning cavity from top to bottom, and the diameter of the first focusing cavity becomes larger from top to bottom.

[0009] Preferably, the second tuning cavity has a uniform diameter from top to bottom.

[0010] Preferably, the first focusing cavity is frustum-shaped, and the second tuning cavity is cylindrical.

[0011] Preferably, the system further includes a microwave source and a microwave transmission module.

[0012] The microwave transmission module includes a waveguide and a coaxial converter. The microwave generated by the microwave source is transmitted through the waveguide and then coupled into the resonant cavity through the coaxial converter.

[0013] The coaxial converter extends from above the resonant cavity into the resonant cavity.

[0014] Preferably, the microwave transmission module further includes a circulator for restricting the microwave transmission direction.

[0015] Preferably, the system further includes:

[0016] A vacuum module for creating a vacuum environment in the resonant cavity;

[0017] A gas feeding module for feeding reaction gases into the resonant cavity;

[0018] A temperature control module for detecting the real-time temperature of the substrate surface and adjusting the substrate stage temperature by controlling the flow rate of the cooling fluid.

[0019] Preferably, an observation window is hermetically arranged on the resonant cavity.

[0020] Preferably, a lifting module is connected to the bottom of the base.

[0021] The second aspect of the present invention provides an application of the near-atmospheric-pressure MPCVD system as described above in thin film deposition.

[0022] Preferably, it includes the following steps:

[0023] (1) Place the substrate on the base. After evacuating the resonant cavity, introduce the first reaction gas to increase the air pressure in the resonant cavity to 500 - 1500 Pa.

[0024] (2) Feed the microwave generated by the microwave source into the resonant cavity through the microwave transmission module, act on the first reaction gas injected above the base, and generate a hydrogen plasma sphere above the substrate.

[0025] (3) Adjust the air pressure in the resonant cavity to the thin film growth pressure of 30 - 80 kPa, adjust the microwave power in the resonant cavity, introduce the second reaction gas and deposit the thin film.

[0026] The beneficial effects of the present invention are as follows: By designing a novel resonant cavity structure, the diameter of the first focusing cavity becomes larger from top to bottom, concentrating the internal energy of the cavity. The second tuning cavity tunes the standing wave electric field distribution of the cavity, enabling this resonant cavity to form a microwave plasma chemical vapor deposition system with stable plasma under near-atmospheric pressure (30 - 80 kPa), achieving high-speed diamond deposition. At the same time, the near-atmospheric-pressure thin film growth environment can avoid nitrogen doping caused by cavity leakage in the traditional negative-pressure environment, which is more conducive to the production of high-purity thin films. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, obtaining other drawings based on these drawings still belongs to the scope of the present invention.

[0028] Figure 1 It is a schematic diagram of the system structure of Embodiment 1 of the present invention;

[0029] Figure 2 It is a front view of the electromagnetic field simulation result of the MPCVD resonant cavity in Embodiment 1 of the present invention;

[0030] In the figure, 1 is a resonant cavity; 2 is a microwave source; 3 is a circulator; 4 is a waveguide; 5 is a coaxial converter; 6 is a vacuum module; 7 is a gas feeding module; 8 is a temperature control module; 11 is a first focusing cavity; 12 is a second tuning cavity; 91 is a base; 92 is a pedestal; 93 is an observation window. Detailed implementation mode

[0031] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] This embodiment provides a near-atmospheric-pressure MPCVD system, including:

[0034] A deposition module, the deposition module includes a resonant cavity 1, and a base 91 for placing a substrate is provided at the center of the lower end of the resonant cavity 1. The deposition module deposits a film on the surface of the substrate located in the resonant cavity 1 by microwave plasma chemical vapor deposition.

[0035] A microwave source 2;

[0036] A microwave transmission module, including a circulator 3, a waveguide 4 and a coaxial converter 5. The microwave generated by the microwave source 2 is transmitted through the circulator 3 to constrain the microwave transmission direction, and then through the waveguide 4 and coupled into the resonant cavity 1 through the coaxial converter 5. The coaxial converter 5 extends from above the resonant cavity 1 into the resonant cavity 1. The coaxial converter 5 is specifically a coaxial antenna.

[0037] A vacuum module 6, used to form a vacuum environment in the resonant cavity 1, including a vacuum pump, a control valve, a vacuum detection device and a connecting device, and the internal gas of the resonant cavity 1 is pumped out through an air extraction port provided on the resonant cavity 1.

[0038] A gas feeding module 7, used to feed reaction gas into the resonant cavity 1, including reaction gas, a control valve, a flow meter, a gas mixing chamber and a connecting device. The reaction gas is uniformly mixed in the gas mixing chamber and then fed into the resonant cavity 1 through an air inlet provided on the resonant cavity 1.

[0039] The temperature control module 8 is used to detect the real-time temperature of the substrate surface and adjust the temperature of the base 91 by controlling the flow rate of the cooling fluid. Since the gas discharge is concentrated directly above the base 91, to control the temperature of the base 91 stably, a pedestal 92 can be specifically arranged below the base 91, and a water channel is arranged inside the pedestal 92. The temperature of the pedestal 92 is adjusted by the flow rate of the cooling water, and then the temperature of the base 91 is adjusted. The water-cooled pedestal 92 is made of copper, and the base 91 is located at the center above the pedestal 92 and is specifically made of molybdenum. A lifting module is arranged between the pedestal 92 and the base 91 to ensure that during the deposition process, the deposition surface is always at the same height position of the plasma in the resonance cavity 1. The specific form of the lifting module can be a bag-type adjustable bracket.

[0040] The resonance cavity 1 includes a connected first focusing cavity 11 and a second tuning cavity 12 from top to bottom. The first focusing cavity 11 has an increasing diameter from top to bottom to facilitate the concentration of energy inside the cavity, and the second tuning cavity 12 has a uniform diameter from top to bottom to tune the standing wave electric field distribution of the cavity. Specifically, the first focusing cavity 11 is frustum-shaped, and the second tuning cavity 12 is cylindrical to further optimize the energy distribution inside the cavity.

[0041] The material of the cavity wall of the resonance cavity 1 is selected as stainless steel. To ensure the microwave performance, a copper plating process can be further adopted. An observation window 93 is hermetically arranged on the cavity wall of the resonance cavity 1, and the temperature of the base 91 and the thickness of the deposited sample are monitored through the observation window 93.

[0042] As Figure 2 (a) shows the front view of the electromagnetic field simulation result of the MPCVD resonance cavity of this embodiment. Only a unique and stable standing wave electric field is formed at the bottom of the cavity of the resonance cavity. Figure 2 (b) shows the electron density distribution in the resonance cavity. A stable plasma sphere is formed in the standing wave electric field region. With the power set unchanged, the pressure inside the cavity is gradually increased, and the change of the electron density is as Figure 2 (c) shows. As the pressure increases, the axial radius of the plasma sphere gradually decreases, the intensity gradually increases, and it still remains stable.

[0043] Example 2

[0044] The diamond film is deposited using the near-atmospheric-pressure MPCVD system of Example 1. In the MPCVD system, the microwave frequency is set to 2.45 GHz.

[0045] For the homoepitaxial substrate, Ib-type HPHT and CVD diamond wafers with a (100) orientation are selected, having dimensions of approximately 4×4 mm to 5.3×5.3 mm and a thickness of 0.4 - 1.0 mm. Before depositing diamond, the substrate is subjected to standard pretreatment in a 2% O2 / H2 microwave plasma (70 Torr, 2500 W, 20 minutes) to etch away surface defects such as dislocations and defects caused by polishing. The epitaxial growth is carried out using a methane-H2 mixture with a methane content of 2.5–4.1%, a total flow rate of 417 - 520 sccm, and a microwave power of 2.7 kW. The source gas purity of H2 is 99.999%, and the purity of CH4 is 99.999%. The substrate temperature is measured using a pyrometer, and the dependence of the SCD growth rate on pressure is measured in-situ using low-coherence interferometry.

[0046] For the heteroepitaxial substrate, a polished single-crystalline silicon (100) wafer with a diameter of 50 mm and a thickness of 3 mm is used as the deposition substrate. Before depositing the diamond film, the surface of the substrate is ground with diamond powder having a particle size of 10 μm to increase the diamond nucleation density; then the substrate is ultrasonically cleaned with acetone and dried with hot air. To detect the change in substrate temperature during the deposition of the diamond film, an infrared thermometer is used for temperature monitoring, and a vacuum gauge is used to monitor the gas pressure inside the cavity. During deposition, H2 with a purity of 99.999% and CH4 with a purity of 99.999% are used as reaction gases.

[0047] The specific preparation steps are as follows:

[0048] First, evacuate the gas pressure inside the cavity to below 0.1 Pa, introduce H2, and gradually increase the gas pressure inside the cavity to about 800 Pa; then turn on the microwave source power supply, input about 2 kW of microwave power into the device to excite the plasma above the substrate; then, adjust the vacuum pump and the vacuum control valve to slowly increase the gas pressure to about 80 kPa (growth pressure), and at the same time slowly increase the microwave input power. At this time, introduce CH4 and start the deposition timing; after deposition is completed, close the gas valve of CH4, adjust the vacuum pump and the vacuum control valve to gradually reduce the gas pressure, and at the same time slowly reduce the microwave input power until the power is below 800 W, then turn off the microwave power supply; then close the gas valve of H2, evacuate to below 0.1 Pa; finally, turn off the vacuum pump, slowly open the vacuum valve of the cavity to balance the gas pressure inside and outside the cavity; at this time, the deposition substrate stage can be lowered to take out the diamond film.

[0049] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A near-atmospheric-pressure MPCVD system, characterized in that: It includes a deposition module, and the deposition module includes a resonant cavity. At the center of the lower end of the resonant cavity, there is a substrate stage for placing a substrate. The deposition module deposits a thin film on the surface of the substrate located in the resonant cavity by microwave plasma chemical vapor deposition method. The resonant cavity includes a connected first focusing cavity and second tuning cavity from top to bottom, and the diameter of the first focusing cavity increases from top to bottom.

2. The near-atmospheric-pressure MPCVD system according to claim 1, wherein: The diameter of the second tuning cavity is uniform from top to bottom.

3. The near-atmospheric-pressure MPCVD system according to claim 2, characterized in that: The first focusing cavity is frustum-shaped, and the second tuning cavity is cylindrical.

4. The near-atmospheric-pressure MPCVD system according to claim 1, wherein: The system further includes a microwave source and a microwave transmission module. The microwave transmission module includes a waveguide and a coaxial converter. The microwave generated by the microwave source is transmitted through the waveguide and then coupled into the resonant cavity through the coaxial converter. The coaxial converter extends from above the resonant cavity into the resonant cavity.

5. The near-atmospheric-pressure MPCVD system according to claim 1, wherein: The microwave transmission module further includes a circulator for restricting the microwave transmission direction.

6. The near-atmospheric-pressure MPCVD system according to claim 1, wherein The system further includes: A vacuum module for creating a vacuum environment in the resonant cavity; A gas feeding module for feeding reaction gas into the resonant cavity; A temperature control module for detecting the real-time temperature of the substrate surface and adjusting the temperature of the substrate stage by controlling the flow rate of the cooling fluid.

7. The near-atmospheric-pressure MPCVD system according to claim 1, characterized in that: An observation window is hermetically arranged on the resonant cavity.

8. The near-atmospheric-pressure MPCVD system according to claim 1, wherein: The bottom of the substrate stage is connected with a lifting module.

9. Application of a near-atmospheric-pressure MPCVD system according to any one of claims 1-8 in thin film deposition.

10. The application according to claim 9, wherein It includes the following steps: (1) Place the substrate on the substrate stage. After evacuating the resonant cavity, introduce a first reaction gas to increase the gas pressure in the resonant cavity to 500-1500 Pa; (2) Feed the microwave generated by the microwave source into the resonant cavity through the microwave transmission module, act on the first reaction gas injected above the substrate stage, and generate a hydrogen plasma sphere above the substrate; (3) Adjust the gas pressure in the resonant cavity to the thin film growth pressure of 30-80 kPa, adjust the microwave power in the resonant cavity, introduce a second reaction gas and deposit the thin film.

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