A power device gallium oxide material prepared based on phase inversion and a preparation method thereof

Abstract

The application relates to the technical field of semiconductor devices, in particular to a method for preparing a gallium oxide material for a power device based on phase conversion and application thereof. The method comprises the following steps: depositing a polycrystalline Ga2O3 film on a substrate and heavily doping the same as a substrate material for subsequent device preparation; bonding a light-doped beta-Ga2O3 film with a preset thickness on the polycrystalline Ga2O3 film through bonding, and using the lattice arrangement of the beta-Ga2O3 as a traction for the subsequent polycrystalline Ga2O3 phase conversion process; converting the polycrystalline Ga2O3 into beta-Ga2O3 under preset conditions, and repairing the damage of the film interface during bonding; and removing the substrate, thereby completing the material preparation of the device. The method utilizes the property that the metastable phase of gallium oxide isomers can be converted into beta-phase isomers under certain conditions, converts the polycrystalline Ga2O3 film into a high-quality beta-Ga2O3 substrate, eliminates the lattice mismatch between different phases, and finally obtains a low-cost high-quality beta-Ga2O3 film which can realize a large power device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and specifically to a gallium oxide material for power devices prepared based on phase transformation and its preparation method. Background Technology

[0002] A wider bandgap semiconductor means lower power loss and higher conversion efficiency in power device applications, enabling superior and more ideal power electronics. Among wide bandgap semiconductor materials, Ga2O3 boasts a bandgap of 4.8 eV, an ideal breakdown electric field strength of 8 MV / cm, and a BFOM value as high as 3400, approximately four times that of GaN and ten times that of SiC. Therefore, in today's power electronics applications demanding higher power density and lower power consumption, Ga2O3 materials have significant research value and broader market application prospects. For Ga2O3 applications in devices, the growth and preparation of large-size, high-quality, low-defect single-crystal epitaxial films is currently a key research focus.

[0003] Gallium oxide has five isomers: α, β, γ, ε, and δ. β-Ga₂O₃ (β-phase gallium oxide) is the stable phase, while the α and ε phases are metastable, and the γ and δ phases are less stable. Under certain conditions, the other four phases can transform into β-Ga₂O₃. In the field of power device research, β-Ga₂O₃ is the preferred choice among various gallium oxide types due to its superior thermal stability. Current research methods for growing β-Ga₂O₃ substrates mainly focus on the Czochralski method, the casting method, and the optical floating zone method. However, growing large-size, low-cost, high-quality β-Ga₂O₃ wafers is very difficult. This is because gallium oxide single crystals have a melting point of 1820℃, and they are prone to decomposition and volatilization during high-temperature growth, easily generating a large number of oxygen vacancies, leading to defects such as twins, damascene structures, and spiral dislocations. Furthermore, the GaO, Ga₂O, and Ga gases generated during high-temperature decomposition severely corrode the iridium crucible, increasing crucible maintenance costs. This makes the fabrication of high-quality, low-cost β-Ga2O3 substrates a challenge, which in turn limits the development of gallium oxide power devices. Summary of the Invention

[0004] Based on this, the present invention provides a new preparation method, which is based on the property that the metastable phase isomer of gallium oxide can be converted into the β phase isomer under certain conditions, transforming the polycrystalline Ga2O3 film into a high-quality β-Ga2O3 substrate and eliminating the lattice mismatch between different phases, and finally obtaining a low-cost, high-quality β-Ga2O3 film that can realize the needs of high-power devices.

[0005] The present invention adopts the following technical solution to achieve the above technical objectives: This invention provides a method for preparing gallium oxide materials for power devices based on phase transformation, comprising the following steps: Polycrystalline Ga2O3 thin films were deposited on the substrate and heavily doped to serve as substrate materials for subsequent device fabrication. A lightly doped β-Ga2O3 film of a predetermined thickness is bonded to a polycrystalline Ga2O3 film by bonding, and the lattice arrangement of β-Ga2O3 is used to guide the subsequent polycrystalline Ga2O3 phase transformation process. Under preset conditions, polycrystalline Ga2O3 is converted into β-Ga2O3, while repairing the damage to the thin film interface during bonding. Removing the substrate completes the material preparation of the device.

[0006] As a preferred embodiment, the bonding method is as follows: First, the two surfaces to be bonded are treated with argon plasma at 20~25℃ to activate their surface atoms. Then, they are placed in a bonding device and the bonding is completed at 1000~1400℃ and 2000~4000mbar.

[0007] In a preferred embodiment, the thickness of the bonded lightly doped β-Ga2O3 film is 5~10 μm.

[0008] As a preferred embodiment, the preset conditions for converting polycrystalline Ga2O3 into β-Ga2O3 are: annealing at 600~1500℃ for 8~24h.

[0009] As a preferred embodiment, the preset condition for converting polycrystalline Ga2O3 into β-Ga2O3 is: wet heating to above 300°C.

[0010] As a preferred embodiment, the method for depositing polycrystalline Ga2O3 thin films on the substrate is molecular beam epitaxy, metal-organic chemical vapor deposition, magnetron sputtering, pulsed laser deposition, or fog chemical vapor deposition.

[0011] As a preferred embodiment, the method for depositing polycrystalline Ga2O3 thin films on the substrate is fog chemical vapor deposition.

[0012] In a preferred embodiment, the bonded lightly doped β-Ga2O3 thin film is obtained by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0013] In a preferred embodiment, the electron concentration of the polycrystalline Ga2O3 thin film is 2~3×10⁻⁶. 18 cm -3 The electron concentration of lightly doped β-Ga2O3 thin films is 1.0~10×10⁻⁶. 16 cm -3 .

[0014] The present invention also provides a gallium oxide material prepared by the above method and a power device prepared using the material.

[0015] This invention is based on the property that metastable gallium oxide isomers can be converted into β-phase isomers under certain conditions. Lightly doped β-Ga2O3 is bonded onto a polycrystalline Ga2O3 film, and then the polycrystalline Ga2O3 film is transformed into a high-quality β-Ga2O3 substrate, thus eliminating the lattice mismatch problem between different phases. Finally, a low-cost, high-quality β-Ga2O3 film required for high-power devices is obtained. This method is simple to operate, low in cost, and easy to implement. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for preparing gallium oxide materials for power devices based on phase transformation according to the present invention; Figure 2 This is a schematic diagram of the structure of the substrate material prepared in Example 1; Figure 3 This is a schematic diagram of the structure after lightly doped β-Ga2O3 is bonded to a polycrystalline Ga2O3 thin film in Example 1; Figure 4 This is a schematic diagram of the bonded material in Example 1; Figure 5 This is a schematic diagram of the structure of the gallium oxide material finally prepared in Example 1; Figure 6 These are schematic diagrams of the lattice arrangement before and after repair in Examples 1 and 2, where a is the schematic diagram of the lattice arrangement before repair and b is the schematic diagram of the lattice arrangement after repair.

[0017] In the picture: 1 Substrate, 2 Polycrystalline Ga2O3 thin film, 3 Lightly doped β-Ga2O3 thin film. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0019] To address the current inability to grow low-cost, high-quality β-Ga2O3 substrates, researchers in this field have begun to explore heteroepitaxial growth, using cheaper and less defective materials such as silicon and sapphire as substrates, and growing gallium oxide epitaxy on them. Ultimately, the resulting heteroepitaxial layer structure is used to fabricate power devices.

[0020] While heteroepitaxial growth can address wafer size limitations, it introduces lattice mismatch at the heteroepitaxial interface, leading to numerous epitaxial defects and limiting its application in high-power devices. Furthermore, due to differing crystal orientations, gallium oxide epitaxial layers heterogenously grown on substrates such as silicon and sapphire are generally not β-phase; therefore, heteroepitaxial growth also results in β-Ga2O3 epitaxial defects and poor thermal stability.

[0021] Based on the aforementioned problems, in order to obtain high-quality, low-cost β-Ga2O3 substrates and epitaxial growth methods, it is necessary to study new material growth schemes or substrate epitaxial construction methods to achieve low-cost, high-quality β-Ga2O3 thin films suitable for device fabrication, laying the foundation for the fabrication of high-power, high-voltage, and high-reliability gallium oxide devices. The technical concept of this application lies in using readily available high-quality lightly doped thin films to guide low-quality substrates through phase transitions, thereby obtaining high-quality heavily doped substrates. Specifically, the method utilizes the property that metastable gallium oxide isomers can be converted into β-phase isomers under certain conditions. Under the guidance of high-quality lightly doped thin films, the prepared polycrystalline Ga2O3 thin film is transformed into β-Ga2O3, achieving low-cost, high-quality β-Ga2O3 film fabrication and eliminating the lattice mismatch problem between different phases, enabling the fabrication of high-power devices.

[0022] This invention provides a method for preparing gallium oxide materials for power devices based on phase transformation, comprising the following steps: A polycrystalline Ga2O3 thin film 2 is deposited on substrate 1 and heavily doped as a substrate material for subsequent device fabrication; it is understood that the substrates used include, but are not limited to, sapphire substrates, silicon substrates, silicon carbide substrates, and diamond substrates, and are not limited by the size, price, etc. of Ga2O3 single crystal substrates. A high-quality, lightly doped β-Ga₂O₃ thin film of a predetermined thickness is bonded onto a polycrystalline Ga₂O₃ thin film. The lattice arrangement of β-Ga₂O₃ serves as a guide for the subsequent polycrystalline Ga₂O₃ phase transformation process. It is important to note that bonding a high-quality, lightly doped β-Ga₂O₃ thin film onto a polycrystalline Ga₂O₃ thin film is fundamental for fabricating high-reliability devices. Fewer epitaxial defects allow for the fabrication of high-current devices, avoiding device failure caused by defect damage. Furthermore, high-quality, lightly doped β-Ga₂O₃ thin films are readily available, and currently, only bonding can achieve good crystal quality. If traditional epitaxial growth methods are used, the epitaxial layer grows on a substrate with poor crystal quality, resulting in polymorphism and low yield of power devices fabricated from the entire material system.

[0023] Under preset conditions, polycrystalline Ga2O3 is converted into β-Ga2O3, while the thin film interface is repaired during bonding. Removing the substrate completes the material preparation of the device.

[0024] The bonding method is as follows: First, the two surfaces to be bonded are treated with argon plasma at 20~25℃ to activate the surface atoms. Then, they are placed in a bonding device and brought into contact with each other at 1000~1400℃ and 2000~4000mbar. Finally, due to the mutual attraction between molecules, the bonding is completed.

[0025] The bonded lightly doped β-Ga2O3 films have a thickness of 5~10 μm and can be obtained by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0026] The preset conditions for converting polycrystalline Ga2O3 into β-Ga2O3 are: annealing at 600~1500℃ for 8~24h or by wet heating to above 300℃.

[0027] Furthermore, it is understood that the method of depositing polycrystalline Ga2O3 thin films on the substrate does not significantly affect the final material properties. This can be achieved using molecular beam epitaxy, metal-organic chemical vapor deposition, magnetron sputtering, pulsed laser deposition, or fog chemical vapor deposition. Fog chemical vapor deposition is preferred.

[0028] In practical applications, to ensure that the prepared material meets the requirements for device fabrication, the electron concentration of lightly doped β-Ga₂O₃ films needs to be lower than that of polycrystalline Ga₂O₃ films. For example, the electron concentration of polycrystalline Ga₂O₃ films is typically 2~3×10⁻⁶. 18 cm -3 The electron concentration of lightly doped β-Ga2O3 thin films is typically 1.0~10×10⁻⁶. 16 cm -3 .

[0029] In this invention, the gallium oxide deposited on the substrate will be used as a conductive layer, and high doping can reduce the forward conduction resistance; the lightly doped bonded layer will be used as a breakdown layer, and light doping is beneficial to improving the breakdown voltage.

[0030] The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the specific embodiments of the invention without inventive effort are within the protection scope of the invention.

[0031] Example 1 This invention provides a method for preparing gallium oxide materials for power devices based on phase transformation, comprising the following steps: Polycrystalline Ga2O3 thin films were deposited on sapphire substrates using fog chemical vapor deposition (CVD) and heavily doped, serving as substrate materials for subsequent device fabrication. (See [link to documentation]). Figure 2 ; A high-quality 10 μm thick lightly doped β-Ga₂O₃ film was bonded to a polycrystalline Ga₂O₃ film via bonding. The lattice arrangement of β-Ga₂O₃ facilitated the subsequent phase transformation process of the polycrystalline Ga₂O₃. The bonding conditions were as follows: first, the two surfaces to be bonded were treated with argon plasma at 20–25 °C to activate their surface atoms; then, they were placed in a bonding device and brought into contact at 1200 °C and 3000 mbar pressure. Finally, due to intermolecular attraction, bonding was completed. (See [link to documentation]). Figure 3 ; Polycrystalline Ga₂O₃ was converted to β-Ga₂O₃ by high-temperature annealing at 800℃ for 12 hours, simultaneously repairing damage at the bonding film interface. Since both the substrate and the epitaxial layer are β-phase, lattice mismatch at the interface can be eliminated. (See [link to documentation]). Figure 4 ; Removing the sapphire substrate completes the material fabrication of the device. See [link to documentation]. Figure 5 .

[0032] Example 2 This invention provides a method for preparing gallium oxide materials for power devices based on phase transformation, comprising the following steps: Polycrystalline Ga2O3 thin films were deposited on sapphire substrates using magnetron sputtering and heavily doped, serving as the substrate material for subsequent device fabrication. See details in [link to documentation]. Figure 2 ; A high-quality 8μm thick lightly doped β-Ga2O3 film was bonded onto a polycrystalline Ga2O3 film by bonding. The lattice arrangement of β-Ga2O3 was used to guide the subsequent phase transformation process of polycrystalline Ga2O3. The bonding conditions were as follows: first, the two surfaces to be bonded were treated with argon plasma at 25°C to activate their surface atoms. Then, they were placed in a bonding device and brought into contact with each other under a pressure of 1100°C and 3500mbar. Finally, the bonding was completed due to the mutual attraction between molecules. Polycrystalline Ga2O3 is converted to β-Ga2O3 by heating it to above 300℃ under hydrothermal conditions, while repairing the damage at the bonding film interface. Since both the substrate and the epitaxial layer are β phase, lattice mismatch at the interface can be eliminated. Removing the sapphire substrate completes the material fabrication of the device.

[0033] It should be noted that the above embodiments are only for further elaboration and explanation of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention. The method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing gallium oxide materials for power devices based on phase transformation, characterized in that, Includes the following steps: Polycrystalline Ga2O3 thin films were deposited on the substrate and heavily doped to serve as substrate materials for subsequent device fabrication. A lightly doped β-Ga2O3 film of a predetermined thickness is bonded to a polycrystalline Ga2O3 film by bonding, and the lattice arrangement of β-Ga2O3 is used to guide the subsequent polycrystalline Ga2O3 phase transformation process. Under preset conditions, polycrystalline Ga2O3 is converted into β-Ga2O3, while repairing the damage to the thin film interface during bonding. Removing the substrate completes the material preparation of the device.

2. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, The bonding method is as follows: First, the two surfaces to be bonded are treated with argon plasma at 20~25℃ to activate the surface atoms. Then, they are placed in a bonding device and the bonding is completed at 1000~1400℃ and 2000~4000mbar.

3. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, The thickness of the bonded lightly doped β-Ga2O3 film is 5~10 μm.

4. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, The preset conditions for converting polycrystalline Ga2O3 into β-Ga2O3 are: annealing at 600~1500℃ for 8~24h.

5. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, The preset condition for converting polycrystalline Ga2O3 into β-Ga2O3 is: wet heating to above 300℃.

6. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, Methods for depositing polycrystalline Ga2O3 thin films on substrates include molecular beam epitaxy, metal-organic chemical vapor deposition, magnetron sputtering, pulsed laser deposition, and fog chemical vapor deposition.

7. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 6, characterized in that, The method for depositing polycrystalline Ga2O3 thin films on a substrate is fog chemical vapor deposition.

8. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, Bonded lightly doped β-Ga2O3 thin films were obtained by metal-organic chemical vapor deposition or molecular beam epitaxy.

9. The method for preparing gallium oxide materials for power devices based on phase transformation according to claim 1, characterized in that, The electron concentration of polycrystalline Ga2O3 thin films is 2~3×10⁻⁶. 18 cm -3 The electron concentration of lightly doped β-Ga2O3 thin films is 1.0~10×10⁻⁶. 16 cm -3 .

10. Gallium oxide material prepared by the method according to any one of claims 1 to 9.

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