Device and method for preparing diamond film through liquid-phase pulse glow discharge

Abstract

The invention belongs to the technical field of diamond film preparation, and relates to a liquid-phase pulse glow discharge device for improving the deposition rate of a diamond film, comprising: a microwave resonant reaction chamber, the left and right ends of which are respectively connected with an air inlet, a pressure gauge and an air outlet, and a vacuum pump; a high-power bipolar pulse glow discharge power supply is arranged at the upper part of the cavity, two poles are respectively connected with a cathode lifting rod and an anode lifting rod, and the cathode and the anode are controlled to move up and down through an insulating lifting system; and a microwave electrode is arranged at the bottom of the container and is connected with a microwave generation system at the lower end of the cavity. Compared with a traditional gas reaction cavity, a liquid-phase reaction precursor has higher plasma density, the quality of a deposited film is better, the deposition rate is higher, a high-density plasma area is generated by applying cathode and anode of a pulse power supply and auxiliary microwave electrode glow discharge, the movement speed and the collision ionization efficiency of molecules in liquid are increased, and the deposition efficiency is improved. And high-speed deposition of the diamond film can be effectively realized.

Description

Technical Field

[0001] The invention belongs to the technical field of diamond film preparation, and in particular relates to a device and a method for improving the deposition rate of diamond film by liquid phase pulse glow discharge. Background Art

[0002] Diamond has excellent physical and chemical properties, and exhibits excellent characteristics in mechanics, electricity, optics, and heat. In particular, diamond films have shown broad application prospects in many fields due to their unique properties. In the early days of the development of diamond film deposition technology, people began to realize that its disadvantage was the low efficiency of diamond film deposition. Since the 1980s, improving diamond film deposition equipment to enhance the deposition rate of films has been the core topic of diamond film deposition technology research.

[0003] At present, the widely used method for preparing diamond thin films is to use gas as raw material and generate plasma through direct current, microwave and other methods to deposit thin films. However, since the raw material supply is in gas state and the material density is low, it is difficult to improve the film formation rate of diamond thin films, resulting in low film deposition rate and difficult to meet application requirements. Therefore, the method of depositing thin films by generating plasma through liquid phase discharge has attracted people's attention. This method uses liquid as raw material and has a higher plasma density.

[0004] Especially for some doped diamond films, their growth rate is slow and often cannot meet the requirements of practical applications, so a technology to grow high-quality diamond at a higher rate is needed. In addition, the previous chemical vapor deposition equipment will release heat when plasma is generated, causing the substrate to melt, and often requires complex cooling equipment.

[0005] Liquid plasma deposition of diamond thin film technology is an emerging plasma technology, and there is little research at home and abroad. In 1938, MATHESON LORNE et al. in the United States proposed an arc device in the patent (US2263443A) for the pyrolysis of liquid hydrocarbons to produce acetylene gas, which effectively increased the production rate of acetylene, but did not explain the mechanism by which the gas substance was decomposed. From the perspective of the method principle, there are many unclear points.

[0006] In 2006, Japanese Hitotoshi Murase et al. creatively proposed in their patent (US8653404B2) to use microwave glow discharge as a source of liquid phase plasma, which can effectively increase the plasma density in the liquid phase, but did not specifically explain the application of liquid phase plasma in the preparation of thin films or other materials.

[0007] In 2017, Japanese researchers HARADA YOHEI et al. published a device for growing diamond film on a substrate by generating plasma in a liquid phase containing a carbon source (JP2017251689A). According to this liquid phase plasma method, the diamond film deposition rate can be increased by more than 100 times compared with gas phase microwave equipment. This method solves the problem of low diamond film deposition rate to a certain extent, but compared with pulsed glow discharge, the film deposition rate is still relatively low. Unlike using microwave electrodes as a discharge power source, pulsed discharge plasma has a higher density and more complete ionization. Summary of the invention

[0008] In order to solve the above problems, the present invention proposes a device for increasing the deposition rate of diamond film in liquid phase through pulse and microwave assisted glow discharge equipment. The device can effectively increase the deposition rate of the film and ensure the stability and continuity of the deposition of diamond film in liquid phase.

[0009] The present invention is achieved through the following technical solutions:

[0010] A device for preparing diamond film by liquid phase pulse glow discharge, characterized in that: a high-power bipolar pulse glow discharge power supply is arranged in the device, and the pulse glow discharge power supply is arranged in the upper area of ​​a microwave resonant reaction cavity; a microwave generating system and a liquid phase reaction container for depositing diamond film connected thereto are arranged at the lower end of the reaction cavity.

[0011] Furthermore, the two poles of the pulse glow discharge power supply are respectively connected to the cathode lifting rod and the anode lifting rod, and an insulating lifting system is arranged between the two rods.

[0012] Furthermore, a gas inlet is provided at the left end of the microwave resonance reaction cavity and is connected to a pressure gauge; a gas outlet is provided at the right end of the cavity and is connected to a vacuum pump.

[0013] Furthermore, a microwave electrode is arranged at the lower end of the liquid phase reaction container, and a cathode lifting rod, an anode lifting rod, a cathode and an anode are placed in the middle position, the cathode lifting rod is connected to the cathode, and the anode lifting rod is connected to the substrate holder and the anode; a sample fixing molybdenum sheet is installed on the surface of the substrate holder, and a plasma ball generated by glow discharge is between the cathode and the substrate holder.

[0014] Furthermore, the lower end of the microwave electrode is connected to a microwave generating system to provide microwaves for the electrode, and the system includes a mode converter, a three-screw impedance adjuster, a waveguide and a microwave power supply.

[0015] Furthermore, four vacuum observation windows are arranged on the upper cover of the microwave resonance reaction cavity. The device also includes a liquid phase thermometer, which is connected to the liquid phase reaction container.

[0016] Furthermore, the entire liquid phase reaction container is made of quartz, the interior of the liquid phase reaction container is coated with nano-ferrite absorbing material, the substrate support material is tungsten, niobium or molybdenum, the anode and cathode system is composed of a tantalum cathode and a copper anode, and the microwave electrode material is tungsten.

[0017] A method for preparing a diamond film by liquid phase pulse glow discharge using the above-mentioned device, characterized in that the method is to generate plasma in a container containing a diamond liquid phase carbon source by glow discharge in the liquid phase through microwave electrodes and anodes and cathodes, the plasma excites the liquid phase diamond solution to form high-density chemically active groups, and deposits the diamond film on the substrate. The liquid in the container includes: diamond carbon source methanol or ethanol and H2O, and a diamond film is formed on the substrate. A boron source B2O3 can also be added to the liquid to form a boron-doped diamond film.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Compared with the method of depositing diamond film by plasma generated by gas phase DC glow discharge, the liquid phase precursor has a higher ionization rate and a higher plasma density, which can take into account both the deposition rate and quality of the film. In addition, gas phase DC equipment often causes severe thermal shock to the substrate due to high temperature and high speed airflow, causing the substrate to melt, and often requires the installation of complex cooling equipment. The present invention uses the liquid phase as a carbon source and can naturally cool the substrate, without causing thermal damage to the equipment, and has a simple equipment configuration.

[0020] 2. Compared with the method of depositing diamond film by generating plasma through gas or liquid phase microwave glow discharge, the efficiency of anode and cathode glow discharge under pulse power supply is higher, the electron temperature and liquid temperature are relatively high, and the plasma is more fully ionized, so that the diamond film deposition has a higher deposition rate and quality.

[0021] 3. The present invention adds microwave electrodes to the preparation of diamond thin films by liquid phase pulse glow discharge, which can effectively prevent the extinction problem caused by the sudden failure of the anode and cathode, and ensure the continuity and stability of thin film deposition. In addition, the plasma zone generated by the microwave electrode overlaps with the plasma zone generated by the anode and cathode, so that the area has a higher plasma density, thereby improving the deposition rate and quality of the thin film.

[0022] 4. The present invention has many advantages in structural setting: using a high-power bipolar pulse glow discharge power supply, it can achieve high-precision voltage and current control and has high power density, which can meet the high load requirements of deposition equipment; adding a molybdenum sheet on the surface of the substrate holder to fix the sample solves the problem that the sample is easily displaced when it is fixed only by gravity in the liquid phase; coating the inside of the cavity with nano-ferrite absorbing material can eliminate the interference of electromagnetic waves emitted by microwave discharge on anode and cathode discharges, and improve the cavity effect; four vacuum observation windows are set on the upper cover of the cavity, which can be used to observe the plasma state at various positions during the thin film growth process.

[0023] In summary, the present invention has a simple configuration and a reasonable design. By applying pulse voltage to the anode and cathode and glow discharge of the microwave electrode in the liquid phase to form a high-density plasma zone, the high-speed growth of the diamond film can be achieved, which solves the problems of low thermal stability of DC equipment and the need to increase microwave power to increase the deposition rate of the diamond film in microwave equipment. At the same time, the substrate can be naturally cooled in the liquid phase and is not prone to melting, and no additional cooling equipment is required, which greatly improves the stability of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 This is a schematic diagram of the upper cover of the reaction chamber of the present invention;

[0026] Figure 3 It is a method for fixing the molybdenum sheet on the surface of the substrate holder.

[0027] The meanings of the symbols in the figure are as follows:

[0028] 1. Gas inlet; 2. Vacuum pump; 3. Pressure gauge; 4. Microwave resonant cavity; 5. Cathode lifting rod; 6. Insulation lifting system; 7. Anode lifting rod; 8. High-power bipolar pulse glow discharge power supply; 9. Gas outlet; 10. Liquid phase reaction vessel; 11. Cathode; 12. Microwave electrode; 13. Plasma ball; 14. Substrate holder; 15. Anode; 16. Liquid phase thermometer; 17. Microwave generation system; 18. Vacuum observation window; 19. Sample fixing molybdenum sheet; 20. Mode converter; 21. Three-screw impedance adapter; 22. Waveguide; 23. Microwave power supply. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] Example 1

[0031] This exemplary embodiment provides a method and apparatus for preparing a diamond film by liquid phase pulse glow discharge. Figure 1 , Figure 2 and Figure 3 As shown, the deposition device includes: a vacuum reaction chamber 4, a high-power bipolar pulse glow discharge power supply 8 with an output power of 1 KW, and a 2.45 GHz microwave generation system 17. The left and right ends of the cavity are connected to a vacuum delivery system, the left end is a gas inlet 1 connected to a pressure gauge 3, and the right end is a gas outlet 9 connected to a vacuum pump 2;

[0032] Specifically, a liquid phase reaction vessel 10 is provided inside the vacuum reaction chamber, where the diamond film deposition process occurs, and the plasma zone is mainly formed in two ways: one is a cathode 11 and an anode 15 connected to a pulse glow discharge power supply, which are located at the left and right ends of the liquid phase reaction vessel. By applying a pulse voltage (1 KV to 50 KV) to the two electrodes, as the voltage increases, the liquid around the electrodes is electrolyzed at the beginning and the Joule heat generated causes the liquid to vaporize to form a gas sheath layer, and then the gas sheath layer breaks down to form a plasma zone; the other is a microwave electrode 12 at the lower end of the liquid phase reaction vessel, and the microwave generating device 17 connected thereto generates microwaves and transmits them to the electrode, and the electrode obtains sufficient energy to excite and ionize atoms to produce a plasma zone.

[0033] Furthermore, the substrate holder 14 for thin film deposition is connected to the anode 15, and the generated plasma excites the liquid reaction solution to produce chemically active groups, which diffuse to the surface of the sample fixed by the molybdenum sheet 19 and are deposited as a diamond film; the upper cover of the vacuum reaction chamber is provided with four circular observation windows 18, which are located in four directions of the plasma generation area for observing the plasma state; a liquid phase thermometer 16 is arranged outside the cavity and connected to the inside of the liquid phase reaction container to monitor the liquid temperature.

[0034] Furthermore, the order of opening the electrodes is: first open the anode and cathode, and after the plasma zone is stable, open the microwave electrode to overlap with the microwave plasma zone; the inside of the liquid phase reaction container is coated with ferrite absorbing material, which has a high magnetic permeability and is used to eliminate the interference of electromagnetic waves emitted by microwave discharge on the anode and cathode discharges and improve the cavity effect; if there is serious interference between the glow discharge and the microwave discharge, the two discharges are carried out alternately and periodically.

[0035] Furthermore, each layer of the reaction chamber is fastened with bolts, and each layer is glued with non-water-soluble glue to ensure the airtightness of the container.

[0036] Example 2

[0037] Depositing a diamond film using the liquid phase pulse device as described in Example 1 comprises the following steps:

[0038] (1) 50 mm single crystal silicon substrate nucleation pretreatment: The substrate uses a single crystal silicon wafer (100), which is placed in a diamond nucleation liquid for ultrasonic treatment for 30 min, then rinsed with distilled water and dried with high-purity nitrogen.

[0039] (2) Fix the pretreated substrate between the substrate holder 14 and the molybdenum sheet 19, open the upper cover of the reaction chamber, install the fixed anode and cathode, add an organic solvent (MeOH / EtOH / H2O=17.1:66.7:16.2) into the liquid phase container, and then close the upper cover of the reaction chamber.

[0040] (3) Evacuate the chamber to 1.0×10 -1 Pa, and after the vacuum reaches a predetermined value, Ar gas is introduced into the reaction chamber, and the chamber pressure is adjusted to 20 kPa.

[0041] (4) Lower the cathode, anode and substrate through the lifting system 6, and adjust the lowest horizontal line of the substrate to be 1.5 mm away from the microwave electrode; turn on the pulse glow discharge power supply, and the discharge voltage is between 1 KV and 50 KV. Gradually increase the voltage, and at the same time, the chamber pressure rises to 60 kPa until glow discharge occurs between the cathode and the anode to form plasma.

[0042] (5) When the cathode and anode begin to glow discharge and generate plasma, turn on the 2.45 GHz microwave power supply, gradually increase the power to 550 W, and adjust the three-screw impedance adjuster to minimize the microwave reflection coefficient. As the microwave power increases, the microwave electrode generates glow discharge to form plasma, which overlaps with the plasma zone generated by the cathode and anode. The generated plasma excites the liquid phase reaction solution to produce chemically active groups, which are deposited on the substrate surface to form a diamond film.

[0043] (6) After the film deposition is completed, turn off the power supply, lift the cathode, anode and substrate through the lifting system, continue to introduce argon gas to dry the substrate, then turn off the gas, take out the substrate and evacuate to the ultimate vacuum and turn off the power.

[0044] The above shows and describes the thin film deposition principle, equipment features and advantages of the present invention, but it is only a preferred implementation case described in the present invention and cannot be used to limit the present invention. Under the premise of not departing from the scope and essence of the present invention, the corresponding modifications and improvements of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for preparing diamond film by liquid phase pulse glow discharge, characterized in that: A high-power bipolar pulse glow discharge power supply is arranged on the upper part of the device, and the pulse glow discharge power supply is arranged in the upper area of ​​the microwave resonance reaction cavity; a microwave generating system and a liquid phase reaction container for depositing diamond film connected thereto are arranged at the lower end of the reaction cavity.

2. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1, characterized in that: The two poles of the pulse glow discharge power supply are respectively connected to the cathode lifting rod and the anode lifting rod, and an insulating lifting system is arranged between the two rods.

3. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1, characterized in that: A gas inlet is provided at the left end of the microwave resonance reaction cavity and is connected to a pressure gauge; a gas outlet is provided at the right end of the cavity and is connected to a vacuum pump.

4. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1, characterized in that: An auxiliary microwave electrode is arranged at the lower end of the liquid phase reaction container, and a cathode lifting rod, an anode lifting rod, a cathode and an anode are placed in the middle position. The cathode lifting rod is connected to the cathode, and the anode lifting rod is connected to the substrate support and the anode; a sample fixing molybdenum sheet is installed on the surface of the substrate support, and a plasma ball generated by glow discharge is between the cathode and the substrate support.

5. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1, characterized in that: The lower end of the microwave electrode is connected to a microwave generating system, which includes a mode converter, a three-screw impedance adjuster, a waveguide and a microwave power supply.

6. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1, characterized in that: Four vacuum observation windows are arranged at the upper cover of the microwave resonance reaction cavity; the device also includes a liquid phase thermometer, which is connected to the liquid phase reaction container.

7. The device for preparing diamond film by liquid phase pulse glow discharge according to claim 1 or 4, characterized in that: The entire liquid phase reaction container is made of quartz, the interior of the liquid phase reaction container is coated with nano-ferrite absorbing material, the substrate support material is tungsten, niobium or molybdenum, the anode and cathode system is composed of a tantalum cathode and a copper anode, and the microwave electrode material is tungsten.

8. A method for preparing a diamond film by liquid phase pulse glow discharge using the device of claim 1, characterized in that: In a container containing a diamond liquid carbon source, plasma is generated by glow discharge in the liquid phase by applying a pulse power supply to the cathode and a microwave electrode. The plasma excites the liquid diamond solution to form a high-density chemically active group, which is deposited on the substrate to form a diamond film. The liquid in the container includes: diamond carbon source methanol or ethanol and H2O. A diamond film is formed on the substrate. Boron source B2O3 can also be added to the liquid to form a boron-doped diamond film.

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