A plasma generator for molecular beam epitaxy equipment

Abstract

This invention discloses a plasma generating device for molecular beam epitaxy (MBE) equipment, comprising: a gas ionization chamber, a gas ionization unit, and a heating unit; wherein the gas ionization unit and the heating unit are disposed within the gas ionization chamber; the gas ionization chamber is disposed within and connected to the reaction chamber of the MBE equipment; the gas ionization unit is a capacitively coupled plasma source, including a grounded upper electrode and a lower electrode connected to a radio frequency power supply; a plasma generation region is located between the upper and lower electrodes; the gas ionization chamber surrounds the plasma generation region, reducing plasma leakage into the reaction chamber of the MBE equipment; the heating unit heats the gas ionization chamber, ensuring that the temperature and pressure of the gas ionization chamber are higher than those of the reaction chamber of the MBE equipment. The plasma generating device of this invention has advantages such as good shielding, high plasma concentration, and excellent uniformity.

Description

Technical Field

[0001] This invention relates to the field of semiconductor thin film epitaxial growth technology, and more specifically to a plasma generating device for molecular beam epitaxy equipment. Background Technology

[0002] III-V group materials are widely used in semiconductor light-emitting devices, electronic devices, photodetectors, solar cells, and other fields due to their excellent properties. Currently used thin film growth methods such as metal-organic chemical vapor deposition (MOCVD), sputtering deposition, atomic layer deposition (ALD), and hydride vapor phase epitaxy (HVPE) all have their own shortcomings for the preparation of InN materials and high-In-content InGaN materials. For example, the high ammonia decomposition temperature in MOCVD contradicts the low InN decomposition temperature, and the use of organic sources introduces carbon and other elemental contamination problems; sputtering deposition is difficult to control particle energy, leading to etching issues in the thin film material; ALD technology has a slow growth rate, while hydride epitaxy is mainly used for bulk materials, and the grown thin films have a high background electron concentration, making it difficult to achieve p-type doping.

[0003] Molecular beam epitaxy (MBE) is considered a good choice for growing InN materials and high-In-content InGaN materials. To solve the problem of low ammonia and nitrogen cracking rates at low temperatures, plasma generators are introduced to provide an active nitrogen source for ionization gas. For example, the epitaxial device disclosed in CN107675141A uses a radio frequency ion gun as the ionization source. However, due to the small plasma emission area, the radio frequency ion gun is difficult to form a large-area uniform nitrogen plasma, making it difficult to apply in MBE equipment for mass production of high-quality nitride films. In order to mass produce high-quality, high-In-content InGaN thin film materials, a new plasma generator needs to be introduced.

[0004] The molecular beam epitaxy (MBE) device disclosed in CN114855270A introduces a capacitively coupled plasma (CCP) generator to provide an active nitrogen source for ionization gas and spatially separates the metal evaporation region from the plasma generation region. However, simply separating the two sources does not effectively isolate the metal source and the plasma source, and pre-reaction still occurs. Furthermore, due to the influence of the mean free path during metal diffusion to the substrate, the growth process requires maintaining a low gas pressure, making it impossible to maintain a high gas concentration. Increasing the ionization rate by increasing the RF power of the CCP device may introduce etching damage.

[0005] To address the aforementioned issues, it is necessary to design a plasma generator with good shielding, high plasma concentration, and excellent uniformity for growing InN materials and InGaN materials with high In content at lower temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a plasma generator for molecular beam epitaxy (MBE) equipment. It utilizes a self-designed gas ionization chamber to separate the plasma generation region from the reaction chamber of the MBE equipment, reducing pre-reaction. Under high vacuum conditions, the gas ionization rate of the plasma generator is increased, and the plasma concentration is improved by semi-enclosing the gas ionization chamber and adding a heating device. A spray-head type lower electrode plate is used to improve the uniformity of plasma generation. This further enhances the plasma concentration and improves the uniformity of plasma distribution.

[0007] The objective of this invention is achieved as follows: A plasma generating device for molecular beam epitaxy equipment, characterized by comprising a gas ionization chamber, a gas ionization device, and a heating device, wherein: The gas ionization device and the heating device are installed inside the gas ionization chamber; The gas ionization chamber is located within the reaction chamber of the molecular beam epitaxy (MBE) equipment and is connected to the reaction chamber of the MBE equipment. The gas ionization device is a capacitively coupled plasma source, including an upper electrode plate and a lower electrode plate that are grounded and connected to a radio frequency power supply; There is a plasma generation region between the upper and lower electrodes; The gas ionization chamber surrounds the plasma generation region, reducing the escape of plasma into the reaction chamber of the molecular beam epitaxy device; The heating device heats the gas ionization chamber, making its temperature and pressure higher than those of the reaction chamber in the molecular beam epitaxy equipment.

[0008] Furthermore, an air inlet is provided at the bottom of the gas ionization chamber, located directly below the lower electrode plate.

[0009] Furthermore, the lower electrode plate has several evenly distributed holes that penetrate the upper and lower surfaces of the lower electrode plate.

[0010] Furthermore, the upper and lower electrode plates are hollow metal plates.

[0011] Furthermore, a cooling substance is provided inside the metal plate to cool the upper and lower electrode plates.

[0012] The beneficial effects of the present invention are as follows: The plasma generating device for molecular beam epitaxy equipment provided by the present invention introduces a gas ionization chamber to prevent plasma from escaping outward, thereby isolating the plasma generation area from the metal source area and reducing the probability of pre-reaction during thin film deposition. At the same time, the introduction of a heating device in the ionization chamber enables the temperature and pressure inside the ionization chamber to be higher than those in the reaction chamber, which can improve the gas ionization rate of the gas ionization device to a certain extent, that is, increase the plasma concentration, without affecting the crossing of the metal source outside the ionization chamber.

[0013] By making uniform openings in the lower electrode plate, the ionized gas is uniformly injected between the upper and lower electrodes through the small holes in the lower electrode plate and is confined in the ionization chamber. This increases the gas concentration and produces more uniform plasma after gas ionization.

[0014] The upper and lower metal plates of the plasma generator are equipped with cooling materials, which allows the device to operate at higher temperatures for longer periods of time, thus improving the stability and service life of the plasma generator. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the molecular beam epitaxy device of the present invention.

[0016] Figure 2 This is a schematic diagram of the side structure of the gas ionization chamber of the present invention.

[0017] Figure 3 This is a schematic diagram of the upper electrode structure of the gas ionization device of the present invention.

[0018] Figure 4 This is a schematic diagram of the lower electrode structure of the gas ionization device of the present invention.

[0019] Figure 5 This is a structural diagram of the lower electrode plate of the gas ionization device of the present invention, with arrows indicating the direction of gas flow.

[0020] Figure 6 This is a schematic diagram of the electrical connections of the gas ionization device of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be further described below with reference to the accompanying drawings. Furthermore, the accompanying drawings of the present invention are all simplified and not precisely to scale, and are only used to facilitate and clarify the explanation of the present invention.

[0022] like Figure 1-6 As shown, a capacitively coupled plasma generator for a molecular beam epitaxy (MBE) device includes a gas ionization chamber 2, a gas ionization device 3, and a heating device 6. The gas ionization chamber 2, the gas ionization device 3, and the heating device 6 are disposed within the reaction chamber 1 of the MBE device. The gas ionization chamber 2 is hollow and semi-open, and is connected to the reaction chamber 1 of the MBE device. The bottom of the gas ionization chamber 2 is in contact with the bottom of the reaction chamber 1 of the MBE device. The gas ionization device 3 and the heating device 6 are disposed within the gas ionization chamber 2.

[0023] The gas ionization device 3 is a capacitively coupled plasma generator, including an upper electrode 31 and a lower electrode 32 connected to a radio frequency power supply, and a plasma generation region between the upper electrode 31 and the lower electrode 32.

[0024] The gas ionization chamber 2 surrounds the plasma generation region, reducing the escape of plasma into the reaction chamber 1 of the molecular beam epitaxy device.

[0025] The upper electrode plate 31 of the gas ionization device 3 is placed in the gas ionization chamber 2 through the support plate 21, and partially contacts the side wall of the gas ionization chamber 2 through the insulating material 22; the electrode wire is connected to the upper electrode plate 31 from the opening 211 of the support plate 21 to ground the upper electrode plate 31.

[0026] The lower electrode plate 32 of the gas ionization device 3 is located directly below the upper electrode plate 31. The lower electrode plate 32 has evenly spaced holes except in the area of ​​the cooling pipe 321. The holes penetrate the upper and lower surfaces of the lower electrode plate 32 to allow for uniform gas flow. The lower electrode plate 32 is placed in the gas ionization chamber 2 via a support plate 21 and partially contacts the side wall of the gas ionization chamber 2 via an insulating material 22. The electrode wire is connected to the lower electrode plate 32 from the opening 211 of the support plate 21, thus connecting the lower electrode plate 32 to the matching device and the radio frequency power supply.

[0027] The upper electrode plate 31 and the lower electrode plate 32 are hollow structures. Cooling pipes 3111, 3121, and 321 are provided between the inner and outer surfaces of the electrode plates. The cooling pipes are introduced from the side wall of the gas ionization chamber 2 (the side without openings) to the perforated water inlet 221 of the insulating material 22. 221 is connected to the cooling pipes of the electrode plates, and a waterproof sealing ring 223 is provided at the connection. Cooling liquid flows out from the outlet 222. By controlling the cooling medium and flow rate in the cooling pipes, the temperature of the gas ionization chamber 2 can be controlled below 30°C.

[0028] Heating device 6 is located on both sides of gas ionization chamber 2. Heating device 6 heats gas ionization chamber 2 by thermal radiation, so that the temperature and pressure of gas ionization chamber 2 are higher than the temperature and pressure of reaction chamber 1 of molecular beam epitaxy equipment.

[0029] The air inlet 4 is located below the lower electrode plate 32 and in the central area at the bottom of the gas ionization chamber 2, and is used to introduce the gas that needs to be ionized. Example 1

[0030] The molecular beam epitaxy apparatus of this embodiment uses the plasma generator of the present invention to generate ionized gas to provide the nitrogen source required for growth. Its structural schematic diagram is shown below. Figure 1Several beam source furnaces 81, located at the bottom of the reaction chamber 1, are used to provide the metal source required for growth. Each beam source furnace 81 has a corresponding shield 82 to prevent the metal source from escaping. Several substrate trays 52 are connected to the rotating mechanism at the top of the chamber via tray connecting rods 51 and are located on the same circumference. The substrate trays 52 can revolve around this circumference, passing between the upper electrode plate 31 and the lower electrode plate 32 of the plasma generator during their revolution. The gas ionization chamber 2 and the upper electrode plate 31 provide reserved positions for the rotation of the substrate trays 52 and the tray connecting rods 51. The heating device 6 of the gas ionization chamber 2 is located on both sides of the unopened gas ionization chamber 2. The height of the heating device 6 is flush with the substrate trays 52. A heating device 7 is installed at the bottom of the reaction chamber 1 outside the gas ionization chamber 2, using thermal radiation to heat the reaction chamber 1. The vacuum system 9 for evacuating the reaction chamber 1 includes a mechanical pump 92 and a molecular pump 91. The input end of the molecular pump 91 is located on the middle side wall of the reaction chamber 1 to connect to the reaction chamber 1. The mechanical pump 92 serves as the pre-pump for the molecular pump 91, and the input end of the mechanical pump 92 is connected to the output end of the molecular pump 91.

[0031] Before material growth, several substrates are mounted on several substrate trays 52. Heating devices 6 and 7 are turned on, and vacuum system 9 is turned on to bake reaction chamber 1 and gas ionization chamber 2 at a temperature higher than the material growth temperature. This removes volatile substances from the substrate surface and removes impurity gases adsorbed in reaction chamber 1, increasing the base vacuum of reaction chamber 1. During this process, the substrates rotate at a low speed. During material growth, vacuum system 9 is kept running, heating devices 6 and 7 are turned on, and beam source furnace 81 is turned on for heating. The crucible lid of beam source furnace 81 is kept closed, and the substrates rotate at a low speed. Before reaching the set temperature, etching gases such as H2 and Ar are introduced. Gas ionization device 3 is turned on to remove oxides and other impurities from the substrate surface. After this process, gas introduction is stopped, and gas ionization device 3 is turned off. After the substrate temperature and beam source furnace temperature reach the set temperature, the required ionization gas is introduced, the substrate rotation speed is set, gas ionization device 3 is turned on, and the crucible lid of beam source furnace 81 is opened to introduce a metal source, starting material growth. Throughout the above process, the cooling systems of upper electrode plate 31 and lower electrode plate 32 remain on. After the material growth is completed, the metal source is stopped, the beam source furnace 81 is turned off, the plasma generator 3 is turned off, and the heating devices 6 and 7 of the reaction chamber 1 and the gas ionization chamber 2 are turned off. The substrate rotates at a low speed. After the temperature of the reaction chamber 1 drops, the ionization gas is stopped and the substrate rotation is stopped.

[0032] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A plasma generating device for molecular beam epitaxy equipment, characterized in that, include: Gas ionization chamber, gas ionization device, heating device; The gas ionization device and the heating device are disposed inside the gas ionization chamber; The gas ionization chamber is disposed within the reaction chamber of the molecular beam epitaxy apparatus and is connected to the reaction chamber of the molecular beam epitaxy apparatus. The gas ionization device is a capacitively coupled plasma source, comprising a grounded upper electrode and a lower electrode connected to a radio frequency power supply; A plasma generation region is located between the upper electrode plate and the lower electrode plate; The gas ionization cavity surrounds the plasma generation region, reducing the escape of plasma into the reaction chamber of the molecular beam epitaxy device; The heating device heats the gas ionization chamber, so that the temperature and pressure of the gas ionization chamber are higher than the temperature and pressure of the reaction chamber of the molecular beam epitaxy equipment. Several substrate trays are connected to the top rotating mechanism of the reaction chamber of the molecular beam epitaxy equipment via tray connecting rods and are located on the same circumference. The substrate trays can revolve around the circumference. During the revolve, the substrate trays pass between the upper and lower electrodes of the gas ionization device. The gas ionization chamber and the upper electrode provide reserved positions for the rotation of the substrate trays and tray connecting rods.

2. The plasma generating device for molecular beam epitaxy equipment according to claim 1, characterized in that: The bottom of the gas ionization chamber is provided with an air inlet, which is located directly below the lower electrode plate.

3. The plasma generating device for molecular beam epitaxy equipment according to claim 1, characterized in that: The lower electrode plate has several evenly distributed holes that penetrate the upper and lower surfaces of the lower electrode plate.

4. The plasma generating apparatus for molecular beam epitaxy equipment according to claim 1 or 3, characterized in that: The upper and lower electrode plates are hollow metal plates.

5. The plasma generator for molecular beam epitaxy equipment according to claim 4, characterized in that: The metal plate contains a cooling substance to cool the upper and lower electrode plates.

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