Key method for realizing beta-Ga2O3 two-dimensional step flow growth on MOCVD (Metal Organic Chemical Vapor Deposition)

Abstract

The invention belongs to the technical field of semiconductor material epitaxial growth, and particularly relates to a key method for realizing beta-Ga2O3 two-dimensional step flow growth on MOCVD (Metal Organic Chemical Vapor Deposition). According to the method, on the MOCVD equipment originally used for growing the GaN material, the downward detection type spraying head is used for replacing an original spraying head, and the distance between the spraying head and the substrate is accurately controlled, so that the instability problem in the MOCVD epitaxial process is successfully solved, the pre-reaction phenomenon existing in the beta-Ga2O3 epitaxial process is effectively inhibited, and the yield of the epitaxial wafer is improved. And meanwhile, the good uniformity of the beta-Ga2O3 epitaxial layer is ensured. According to the scheme of the invention, the occurrence of pre-reaction can be effectively avoided, and the quality and uniformity of the beta-Ga2O3 epitaxial film are ensured. Meanwhile, the airflow mixing can be effectively controlled, so that the airflow can be fully mixed before reaching the surface of the substrate, and the step flow two-dimensional growth mode of the beta-Ga2O3 epitaxial layer can be better realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of epitaxial growth of semiconductor materials, and particularly relates to a key method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD. Background Art

[0002] β-Ga2O3 is a promising new semiconductor material with many outstanding properties, such as excellent heat resistance, an ultra-wide bandgap of 4.85 eV, etc. These properties make the β-Ga2O3 material have great potential in the fields of manufacturing high-power devices, sensors, infrared photodetectors, deep ultraviolet solar-blind detectors, radio frequency devices, etc. In various application scenarios of β-Ga2O3, the crystal quality of the epitaxial layer faces strict requirements, after all, the quality of the epitaxial layer directly determines the upper limit of the performance of gallium oxide devices. Among many epitaxial technologies, the MOCVD technology is highly recognized in the industry because it can grow high-quality epitaxial layers and can precisely control the thickness and carrier concentration of the epitaxial layer. Compound semiconductor materials represented by GaN have achieved large-scale industrial production by means of the MOCVD technology, providing a reference idea for the future realization of related applications of β-Ga2O3 through the MOCVD technology.

[0003] An important reason for the stagnation in the research and development of high-quality epitaxial layers is that there is currently no MOCVD equipment specifically developed for β-Ga2O3. Most of the MOCVD equipment used at present is designed for growing GaN. However, the MOCVD epitaxy of oxide semiconductors is more complex than that of traditional nitrides. The key lies in suppressing the pre-reaction and maintaining the two-dimensional growth of the epitaxial layer. To achieve high-quality two-dimensional growth, the key lies in controlling the location where the epitaxial reaction occurs. We expect that after the reactants reach the substrate, they can react normally and produce the target product only under the driving of the high-temperature conditions provided by the substrate. However, the problem currently plaguing the epitaxial growth of β-Ga2O3 is the difficulty in controlling the location where the reaction occurs. Especially when using reactants such as TMGa and O2 that can achieve high growth rates, after being irradiated by the thermal radiation of the substrate, the reactants are prone to react before reaching the substrate, that is, pre-reaction. The powder generated by this pre-reaction falling on the surface of the substrate can serve as new nucleation points, promoting the three-dimensional growth of the epitaxial layer, thus seriously deteriorating the quality of the epitaxial layer. For this reason, the foreign IKZ and Agnitron research groups have adopted two different ideas for epitaxial growth. Among them, IKZ uses TEGa and O2 with a low reaction dimension, and the consequence of this solution is that the lateral thermal diffusion rate of atoms on the substrate is low. Therefore, the substrate bevel cutting technology needs to be used. By artificially creating a bevel angle, the width of the step is shortened. This approach not only has a high cost and great processing difficulty, but more importantly, it is not universal. That is, since the actual temperature required during the epitaxy process of each MOCVD epitaxial equipment is different, beveled substrates with different angles are required, so this technology has limitations. And Agnitron uses N2O with a higher cracking temperature as the oxygen source (Alema F, Zhang Y, Osinsky A, et al. Low 1014 cm-3 free carrier concentration in epitaxial β-Ga2O3 grown by MOCVD. APL Mater. 2020, 8(2), 021110.), so that TMGa and N2O are only activated to react when they are close to the substrate. However, in fact, the ultra-high-temperature epitaxial growth of oxides is itself a difficult problem for MOCVD equipment, and there are many technical difficulties to be overcome in terms of equipment service life and epitaxial layer uniformity. Therefore, how to control the location where the reaction occurs is the key to achieving step-flow two-dimensional growth of β-Ga2O3. Summary of the Invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention replaces the original shower head with a downward-probing shower head and optimizes the reaction distance between the shower head and the substrate, so as to effectively suppress the "pre-reaction" existing in β-Ga2O3 during the MOCVD epitaxy process and prepare a uniform and high-quality β-Ga2O3 epitaxial layer.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a key method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD, that is, replacing the original showerhead with a downward-probing showerhead on the MOCVD equipment, controlling the distance between the showerhead and the substrate to be 16 - 24 mm, and then using it for the growth of β-Ga2O3 epitaxial wafers.

[0007] The present invention improves the distance between the MOCVD showerhead and the substrate, and successfully suppresses the pre-reaction problem existing in the MOCVD epitaxial process. When epitaxially growing β-Ga2O3, the present invention finds through research that the distance between the showerhead and the substrate is not the closer the better. When the reaction distance is too close, the surface thickness of the epitaxial wafer will be uneven. When the distance is too far, serious pre-reaction will occur, and serious powdery particles will appear on the epitaxial wafer. The reaction distance plays a more important role in the adjustment of the process. It can not only optimize the gas flow and avoid the occurrence of turbulence, but more importantly, it can broaden the process window to a certain extent. This is crucial for β-Ga2O3 with a narrow epitaxial process window. At present, the mature MOCVD epitaxial equipment is basically developed for GaN, and there is no MOCVD equipment designed for β-Ga2O3. Therefore, the present invention is a key technology capable of realizing high-quality epitaxy of β-Ga2O3.

[0008] Preferably, the downward-probing showerhead is a downward-probing showerhead with a forced water cooling function.

[0009] Preferably, the MOCVD equipment is the MOCVD equipment originally used for growing GaN materials.

[0010] Preferably, for the MOCVD equipment originally used for growing GaN materials, the distance between the showerhead and the substrate is 20 cm.

[0011] Preferably, the process parameters for growing β-Ga2O3 epitaxial wafers are: growth temperature 1000 - 1300 °C, pressure 150 - 300 mbar, TMGa flow rate of gallium source 50 - 70 sccm, and O2 flow rate 5000 - 6000 sccm.

[0012] The present invention also provides a β-Ga2O3 epitaxial wafer grown by the above method. The surface of the β-Ga2O3 epitaxial wafer has no dust particles and is bright and flat.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] The present invention discloses a key method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD. On the MOCVD equipment originally used for growing GaN materials, by using a downward-probing showerhead to replace the original showerhead and precisely controlling the distance between the showerhead and the substrate, the instability problem in the MOCVD epitaxial process is successfully improved, providing a feasible optimization scheme for the growth of β-Ga2O3. On the one hand, the present invention effectively suppresses the pre-reaction phenomenon existing in the β-Ga2O3 epitaxial process, while ensuring that the β-Ga2O3 epitaxial layer has good uniformity. Therefore, the solution of the present invention can effectively avoid the occurrence of pre-reaction and ensure the quality and uniformity of the β-Ga2O3 epitaxial film. At the same time, the gas flow mixing can also be effectively controlled, enabling the gas flow to be fully mixed before reaching the substrate surface, and better realizing the two-dimensional growth mode of the step-flow of the β-Ga2O3 epitaxial layer. Description of the Drawings

[0015] Figure 1 Schematic diagram of the transformation of the MOCVD chamber;

[0016] Figure 2 β-Ga2O3 epitaxial layers grown when the distance between the showerhead and the substrate is too close (left) and too far (right) (the growth conditions of β-Ga2O3 when less than 16 mm and greater than 24 mm are presented respectively with 12 mm and 30 mm as examples);

[0017] Figure 3 β-Ga2O3 epitaxial wafers prepared by using the improved MOCVD at reaction distances of 16 mm and 24 mm.

[0018] Figure 4 β-Ga2O3 epitaxial wafer prepared at a reaction distance of 20 mm and its atomic force microscope (AFM) image. Detailed Embodiments

[0019] The following further describes the detailed embodiments of the present invention. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the test materials used in the following embodiments are all commercially available through conventional channels unless otherwise specified.

[0021] The present invention is based on the transformation of a MOCVD device originally used for growing GaN materials. The core of the transformation lies in the design and optimization of the reaction chamber, mainly adjusting the showerhead part of the device (the original one belongs to a long-distance showerhead). By adopting the design of a down-dip showerhead with forced water cooling function, the distance between the showerhead and the substrate is greatly reduced, and good heat dissipation can be ensured during the epitaxial growth process. At the same time, in order to optimize the growth process of the β-Ga2O3 thin film, the distance between the showerhead and the substrate is also optimized (the original distance between the showerhead and the substrate is 20 cm), so that the distance between the showerhead and the substrate is 16 - 24 mm, to ensure that the pre-reaction can be effectively inhibited while the gas flow can be evenly mixed before reaching the substrate surface.

[0022] The following further details the key methods for realizing the two-dimensional step-flow growth of β-Ga2O3 on MOCVD in combination with specific embodiments.

[0023] As Figure 1 shown, the original showerhead is removed and a down-dip showerhead with forced water cooling function (purchased from Shenzhen Shengda Vacuum Brazing Technology Co., Ltd., model number W2*1-gz03-02-00) is installed to ensure good heat dissipation during the epitaxial growth process. Among them, the MOCVD device originally used for growing GaN materials is Jason W120 MOCVD. For details, see the literature: Chen, B.; Zhang, X.; Fan, A. J.; et al. Impacts of hydrogen flow and growth pressure on characteristics of semipolar (1122) plane AlInGaN quaternary epilayers. Micro Nanostructures 2022, 170, 207363.

[0024] At the same time, by further improving the distance between the MOCVD showerhead and the substrate, the pre-reaction problem existing in the MOCVD epitaxial process is successfully solved. The experimental results show that during the epitaxial growth of β-Ga2O3, the reaction distance, as an important parameter, cannot be ignored in its influence on the quality of the β-Ga2O3 epitaxial layer. The distance between the showerhead and the substrate is not the closer the better. When the reaction distance is too close, it will cause problems such as uneven surface thickness of the epitaxial wafer. As Figure 2 shown by the experimental results, being too close or too far is not conducive to the epitaxial growth of β-Ga2O3. In the case of too close distance, the epitaxial layer will face problems such as uneven mixing of reactants, uneven film thickness, turbulence in the cavity, and low quality of the epitaxial layer. When the distance is too far, the pre-reaction will be more serious, and at the same time, problems such as powdery particles will appear on the surface of the epitaxial wafer.

[0025] Among them, the specific process of epitaxial growth of β-Ga2O3 is as follows:

[0026] (1) Open the chamber and carefully clean the contaminants inside the chamber.

[0027] (2) Place the required gallium oxide single crystal substrate on the graphite tray.

[0028] (3) Carefully wipe the spray head seal ring with a lint-free cloth dipped in alcohol twice to ensure that there is no dust on the seal ring.

[0029] (4) Close the reaction chamber to ensure good airtightness of the chamber.

[0030] (5) Write the program menu according to the process requirements and run the program. During the program operation, closely monitor the current, voltage, gas flow rate, temperature change, and valve opening and closing. When the gas parameter box turns red, it indicates that there is a large difference between the set value and the actual value, and the valve status and parameter settings need to be checked. The specific process parameters are: growth temperature is 1100 °C, pressure is 200 mbar, the flow rate of TMGa (gallium source) is 60 sccm, the flow rate of O2 is 5400 sccm, the growth time is 1 hour, and the expected thickness is 900 nm.

[0031] (6) After the process operation is completed, when the temperature drops below 150 °C, open the chamber lid, turn on the light, and use clean tweezers to take out the gallium oxide wafer.

[0032] Through a large number of experimental tests, it is finally determined that during the epitaxial growth process of β-Ga2O3, we found that when the distance between the spray head and the substrate is 16 - 24 mm, β-Ga2O3 epitaxy can prepare a β-Ga2O3 homoepitaxial wafer with uniform thickness and extremely smooth surface. Within this distance range, the occurrence of pre-reaction can be effectively avoided, ensuring the quality and uniformity of the epitaxial film. At the same time, the gas flow mixing within this distance range can also be effectively controlled, enabling the gas flow to be fully mixed before reaching the substrate surface and obtaining a better reaction. Thus, the present invention designs a feasible β-Ga2O3 solution, which successfully improves the instability problem in the MOCVD epitaxial process by precisely controlling the distance between the spray head and the substrate, providing a feasible optimization scheme for the growth of β-Ga2O3. The spray head used in the solution of the present invention can effectively inhibit the occurrence of pre-reaction and make the gas flow mix evenly before reaching the substrate surface. As Figure 3 shown by the experimental results, there are no dust particles, etc. on the surface of the β-Ga2O3 epitaxial wafer prepared within the reaction distance of 16 - 24 mm, and it is bright and flat. At the same time, Figure 4The AFM test results in [reference] show that the regulation of the reaction distance can achieve the step-flow growth mode of the epitaxial layer. Previously, only the Leibniz Institute for Crystal Growth (IKZ) in Germany prepared a β-Ga2O3 epitaxial layer with a surface roughness of 0.2 nm based on a large-angle inclined gallium oxide substrate. However, through the re-design of the MOCVD chamber in this invention, a gallium oxide homoepitaxial layer with a step-flow morphology and a surface roughness of 0.147 nm can be prepared on a common gallium oxide substrate, and the result reaches the international advanced level (refer to the literature: Bin Anooz, S.; Grueneberg, R.; Wouters, C.; et al. Step flow growth of β-Ga2O3 thin films on vicinal (100) β-Ga2O3 substrates grown by MOVPE. Appl. Phys. Lett. 2020, 116(18), 182106.).

[0033] In summary, this invention designs an MOCVD reaction chamber specifically for growing β-Ga2O3. On the MOCVD equipment originally used for growing GaN materials, by using a downward-probing showerhead to replace the original showerhead and optimizing the reaction distance between the showerhead and the substrate, the β-Ga2O3 epitaxial layer can grow in a step-flow mode. This invention effectively suppresses the pre-reaction phenomenon existing in the epitaxial process (the surface of the β-Ga2O3 epitaxial wafer prepared within the reaction distance of 16 - 24 mm is smooth, and AFM shows that it is step-flow growth, indicating that only two-dimensional growth of the epitaxial layer occurs during the growth process), and at the same time ensures that the epitaxial layer has good uniformity. The method for realizing two-dimensional step-flow growth of β-Ga2O3 in this invention has stronger universality and promotion compared with the method of realizing step-flow growth through substrate beveling technology.

[0034] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions, and variations made to these embodiments still fall within the protection scope of the present invention.

Claims

1. A method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD, characterized in that, Replace the original showerhead with a downward-probing showerhead on the MOCVD equipment, control the distance between the showerhead and the substrate to be 16 - 24 mm, and then use it for the growth of β-Ga2O3 epitaxial wafers.

2. A method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD according to claim 1, characterized in that, The downward-probing showerhead is a downward-probing showerhead with forced water cooling function.

3. A method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD according to claim 1, characterized in that, The MOCVD equipment is the MOCVD equipment originally used for growing GaN materials.

4. A method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD according to claim 3, characterized in that, For the MOCVD equipment originally used for growing GaN materials, the distance between the showerhead and the substrate is 20 cm.

5. A method for realizing two-dimensional step-flow growth of β-Ga2O3 on MOCVD according to claim 1, characterized in that, The process parameters for growing β-Ga2O3 epitaxial wafers are: growth temperature 1000 - 1300 °C, pressure 150 - 300 mbar, TMGa flow rate of gallium source 50 - 70 sccm, and O2 flow rate 5000 - 6000 sccm.

6. The β-Ga2O3 epitaxial wafer grown by the method according to any one of claims 1-5, characterized in that, The surface of the β-Ga2O3 epitaxial wafer has no dust particles and is bright and flat.

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