Gallium nitride in-situ stripping equipment and method for preparing gallium nitride single crystal

Abstract

The invention relates to gallium nitride in-situ stripping equipment and a method for preparing gallium nitride single crystal, the gallium nitride in-situ stripping equipment comprises a reaction cavity with a gas inlet and a gas outlet, and the reaction cavity is provided with a heater capable of controlling the temperature in the reaction cavity. An optical-grade quartz support and an epitaxial substrate which is placed on the optical-grade quartz support and used for epitaxial growth of gallium nitride are installed in the reaction cavity, an optical-grade quartz plate is arranged on the lower portion of the reaction cavity, a laser is arranged below the reaction cavity, the laser emits laser towards the epitaxial substrate, and the optical-grade quartz plate is arranged on the lower portion of the reaction cavity. According to the method, the phenomenon of cracking caused by too large difference of thermal expansion coefficients of gallium nitride and sapphire in the cooling process is avoided, the gallium nitride single crystal after epitaxy can be directly used for grinding and polishing, and the method is suitable for large-scale production. And epitaxy does not need to be performed again, so that working procedures and time are saved.

Description

Technical Field

[0002] The invention belongs to the technical field of hydride vapor phase epitaxy (HVPE), and in particular relates to a gallium nitride in-situ stripping device and a method for preparing a gallium nitride single crystal. Background Art

[0004] When growing GaN on a template using HVPE technology, the problem of separating the sapphire template and GaN after growing to a certain thickness is faced. Usually, cooling is used to achieve self-separation or laser stripping is performed after cooling to room temperature. Since self-separation growth requires complex structural design and the separation is unstable, and laser stripping requires cooling down before heating for stripping, there are certain restrictions on the thickness of GaN growth. If it is too thick, it will cause cracking after cooling due to the large difference in thermal expansion coefficients between GaN and sapphire. However, since subsequent grinding and polishing have requirements for GaN thickness, multiple epitaxy is generally used to increase the thickness of GaN, and the process is cumbersome and inefficient. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a gallium nitride in-situ stripping device and a method for preparing a gallium nitride single crystal. The gallium nitride in-situ stripping device and the method for preparing a gallium nitride single crystal avoid the cracking phenomenon caused by the large difference in thermal expansion coefficients between gallium nitride and sapphire during the cooling process. The gallium nitride single crystal after epitaxy can be directly used for grinding and polishing without the need for further epitaxy, thereby saving processes and time.

[0007] To achieve the above object, the present invention adopts the following technical solution: The invention discloses an in-situ stripping device for gallium nitride, which is characterized by comprising a reaction chamber with a gas inlet and a gas outlet, the reaction chamber being provided with a heater capable of controlling the temperature inside the reaction chamber, an optical-grade quartz holder and an epitaxial substrate placed on the optical-grade quartz holder for epitaxially growing gallium nitride installed in the reaction chamber, an optical-grade quartz plate being provided at the lower part of the reaction chamber, a laser being provided below the reaction chamber, the laser emitting laser in the direction of the epitaxial substrate, so that the laser passes through the optical-grade quartz plate, the optical-grade quartz holder and the epitaxial substrate in sequence to reach the interface between the epitaxial substrate and gallium nitride, the temperature of gallium nitride at the interface rises and thermal decomposition occurs, thereby realizing in-situ separation of the epitaxial substrate and gallium nitride, and obtaining the epitaxially grown gallium nitride single crystal.

[0008] Preferably, there are multiple gas inlets for introducing different gases or fluids into the reaction chamber.

[0009] Preferably, the gas inlet includes an NH3 inlet, an isolation gas inlet and a GaCl inlet.

[0010] Preferably, the bottom surface of the optical grade quartz tray is flat, and the upper surface of the optical grade quartz tray has a sink for placing the epitaxial substrate.

[0011] Preferably, the epitaxial substrate is a double-polished sapphire flat wafer substrate.

[0012] Preferably, the isolation gas is N2, H2 or a mixture of N2 and H2.

[0013] Preferably, the epitaxial growth of gallium nitride is carried out by HVPE epitaxial growth of gallium nitride, the epitaxial growth temperature is controlled above 1000° C., and the epitaxial growth thickness is controlled within a range of 100-2000 μm.

[0014] Preferably, the laser has a wavelength less than 365 nm.

[0015] Method for preparing gallium nitride single crystal using the aforementioned gallium nitride in-situ stripping equipment: Step 1, epitaxially growing gallium nitride on the epitaxial substrate: various gases or fluids are introduced into the reaction chamber through the NH3 inlet, the isolation gas inlet and the GaCl inlet to achieve epitaxial growth of gallium nitride on the epitaxial substrate.

[0016] Step 2, stripping of the epitaxially grown gallium nitride on the epitaxial substrate 107: after the epitaxial growth of the gallium nitride single crystal is completed, the input of GaCl and H2 is stopped, leaving only N2 and a small amount of NH3, wherein NH3 is used to prevent the grown gallium nitride single crystal from decomposing during the stripping process; at the same time, the temperature in the reaction chamber is controlled to control the stripping temperature within the range of 100-1000° C., and the lifting and lowering of the laser or the reaction chamber is adjusted to make the gallium nitride single crystal on the epitaxial substrate at the laser focus position. The laser passes through the optical grade quartz plate, the optical grade quartz support and the epitaxial substrate in sequence to reach the interface between the epitaxial substrate and the gallium nitride. At the interface, the gallium nitride temperature rises and thermal decomposition occurs, thereby realizing the in-situ separation of the epitaxial substrate and the gallium nitride.

[0017] In addition, the laser's galvanometer controls the path to gradually incident from the periphery to the center, so that the N2 produced by the peeling can overflow and will not accumulate in the wafer, thus avoiding high pressure and rupture.

[0018] The beneficial effects of the present invention are as follows: a thicker gallium nitride single crystal can be grown in one step, and then the temperature can be lowered after in-situ stripping, so there is no need to worry about the large difference in thermal expansion coefficients between the sapphire and gallium nitride of the epitaxial substrate, which may cause the chip to bend greatly due to the thermal stress caused by the cracks and the resulting thermal stress, thus affecting subsequent processing. The gallium nitride single crystal obtained by the method of the present invention can be directly used for grinding and polishing, and no further thickening is required, thus saving processes and time. If in-situ stripping is not adopted, the gallium nitride and sapphire composite substrate will crack after cooling due to the large thermal mismatch, and the critical growth thickness is about 400um. After stripping the sapphire, due to the thin thickness of gallium nitride, the gallium nitride single crystal substrate cannot be prepared, and secondary thickening is required, which makes the process more complicated and has a low yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a preparation method for obtaining a thicker gallium nitride single crystal in one step by using gallium nitride in-situ stripping technology according to a preferred embodiment of the present invention.

[0020] In the figure, 101: heater, used for heating the reaction chamber; 102: reaction chamber, used for GaN epitaxial growth; 103: optical grade quartz plate, used for transmitting laser; 104: laser, mainly with 355 nm or 266 nm wavelength, providing laser energy required for stripping; 105: optical grade quartz support, used for epitaxial growth and back-transmitting laser; 106: gas outflow port; 107: epitaxial substrate, used as epitaxial growth template; 108: NH3 inlet; 109: isolation gas inlet; 110: GaCl inlet; gas inlet 111. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0025] The gallium nitride in-situ stripping device of the present invention comprises a reaction chamber 102 having a gas inlet 111 and a gas outlet 106 . The reaction chamber 102 is provided with a heater 101 capable of controlling the temperature inside the reaction chamber.

[0026] The above-mentioned gas inlet 111 has multiple ones for introducing different gases or fluids into the reaction chamber. The gas inlet includes an NH3 inlet, an isolation gas inlet and a GaCl inlet. The isolation gas is N2, H2 or a mixture of N2 and H2. The gas outlet 106 is used for gas discharge.

[0027] An optical grade quartz holder 105 (made of optical grade quartz material, the bottom of the optical grade quartz holder is flat, and the upper surface of the optical grade quartz holder has a sink for placing the epitaxial substrate) and an epitaxial substrate 107 for epitaxial growth of gallium nitride placed on the optical grade quartz holder (the epitaxial substrate 107 is a double-polished sapphire flat plate substrate, that is, both surfaces of the sapphire flat plate are polished; or epitaxial growth of 2-10 nanometers is performed on the double-polished sapphire flat plate substrate in advance by metal chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) and other methods) are installed in the reaction chamber. μm thick gallium nitride single crystal template layer), when epitaxially growing gallium nitride on the epitaxial substrate 107, the temperature of the reaction chamber is controlled by a heater, and corresponding gases or fluids are introduced through the NH3 inlet, the isolation gas inlet and the GaCl inlet, and the reaction gas is epitaxially grown on the epitaxial substrate 107 to form a gallium nitride single crystal (the above-mentioned epitaxial growth of gallium nitride uses the hydride vapor phase epitaxy HVPE technology to epitaxially grow gallium nitride, the epitaxial growth temperature is controlled at more than 1000°C, and the epitaxial growth thickness is controlled at 100-2000μm).

[0028] An optical-grade quartz plate 103 is provided at the lower part of the reaction chamber, and a laser 104 is provided below the reaction chamber. The laser emits laser light (laser wavelength is less than 365 nm, and 355 nm, 266 nm or 248 nm wavelength can be selected) in the direction of the epitaxial substrate, so that the laser light passes through the optical-grade quartz plate 103, the optical-grade quartz support 105 and the epitaxial substrate 107 in sequence to reach the interface between the epitaxial substrate and gallium nitride. The temperature of gallium nitride at the interface rises and thermal decomposition occurs, thereby realizing in-situ separation of the epitaxial substrate and gallium nitride, and obtaining the epitaxially grown gallium nitride single crystal.

[0029] Specifically, after the epitaxial growth of the gallium nitride single crystal is completed, the input of GaCl and H2 is stopped, and only N2 and a small amount of NH3 are left, wherein NH3 is used to prevent the grown gallium nitride single crystal from decomposing during the stripping process. The temperature in the reaction chamber is controlled, and the stripping temperature can be controlled within the range of 100-1000°C. For example, the stripping is performed after being controlled to be stable at 1000°C. The laser 104 or the reaction chamber 102 is adjusted to move up and down so that the epitaxial wafer on the epitaxial substrate 107 is at the laser focus position, that is, the laser passes through the optical grade quartz wafer 103, the optical grade quartz support 105 and the epitaxial substrate 107 in sequence to reach the interface between the epitaxial substrate and gallium nitride. At the interface, the gallium nitride temperature rises and thermal decomposition occurs (generating Ga and N2), thereby realizing the in-situ separation of the epitaxial substrate and gallium nitride. The laser can adjust the galvanometer to control the laser path range. The diameter is 10 larger than the diameter of the epitaxial substrate 107. mm, ensuring that the laser scanning area covers the entire epitaxial wafer. After the stripping is completed, the wafer can be directly taken out at a temperature below 150°C to obtain the epitaxially grown gallium nitride single crystal.

[0030] In addition, in order to prevent the N2 produced by peeling from accumulating in the chip, the laser galvanometer can be used to control the path to gradually incident from the periphery to the center. This will allow the N2 produced by peeling to overflow and will not accumulate in the chip, thus avoiding high pressure and rupture.

[0031] The present invention uses the gallium nitride in-situ stripping technology, which does not require complex structural design before growth, can directly perform epitaxial growth on the epitaxial substrate, and can grow a thicker gallium nitride film in one step. The in-situ stripping and then cooling are performed to avoid the cracking phenomenon caused by the large difference in thermal expansion coefficients between gallium nitride and sapphire during the cooling process.

[0032] Implementation examples: 1. Place the GaN single crystal template into the HVPE chamber to grow GaN thick film; 2. Introduce GaCl gas at a flow rate of 150 sccm, NH3 gas at a flow rate of 7500 sccm, nitrogen gas at a flow rate of 15000 sccm, H2 at a flow rate of 8000 sccm, set the growth temperature to 1010°C, and the growth pressure to 600 torr; 3. After 5 hours of growth, stop the introduction of GaCl and H2, and keep the introduction of NH3 at a flow rate of 2000sccm to prevent the decomposition of GaN. Keep the introduction of N2 at a flow rate of 15000sccm. At this time, the thickness of GaN is about 250um. 4. Turn on the laser, the laser wavelength is 355nm, adjust the focus distance, the focus is set to 150m, set The laser power is set to 5W, the scanning line speed is set to 3000mm / s, and the line spacing is set to 20um; 5. Select the drawn scanning pattern, spiral scanning, and scan the scanning path from the outer circle of the wafer to the inner circle. After scanning, the in-situ separation of sapphire and gallium nitride is achieved. 6. After separation, continue to introduce GaCl gas at a flow rate of 150 sccm, introduce NH3 gas at a flow rate of 7500 sccm, introduce nitrogen at a flow rate of 15000 sccm, introduce H2 at a flow rate of 8000 sccm, set the growth temperature to 1010°C, and the growth pressure to 600 torr; 7. After 10 hours of growth, stop the introduction of GaCl and H2, and keep the introduction of NH3 at a flow rate of 2000sccm to prevent the decomposition of GaN. Keep the introduction of N2 at a flow rate of 15000sccm. At this time, the thickness of GaN is about 750um. 8. After cooling down, take out the gallium nitride single crystal, which can be directly subjected to the grinding and polishing process. Once the processing is completed, the output of the gallium nitride single crystal substrate is completed.

[0033] The beneficial effects of the present invention are as follows: a thicker gallium nitride single crystal can be grown in one step, and then the temperature can be lowered after in-situ stripping, so there is no need to worry about the large difference in thermal expansion coefficients between the sapphire and gallium nitride of the epitaxial substrate, which may cause the chip to bend greatly due to the thermal stress caused by the cracks and the resulting thermal stress, thus affecting subsequent processing. The gallium nitride single crystal obtained by the method of the present invention can be directly used for grinding and polishing, and no further thickening is required, thus saving processes and time. If in-situ stripping is not adopted, the gallium nitride and sapphire composite substrate will crack after cooling due to the large thermal mismatch, and the critical growth thickness is about 400um. After stripping the sapphire, due to the thin thickness of gallium nitride, the gallium nitride single crystal substrate cannot be prepared, and secondary thickening is required, which makes the process more complicated and has a low yield.

[0034] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A gallium nitride in-situ stripping device, characterized in that: The invention comprises a reaction chamber with a gas inlet and a gas outlet, wherein the reaction chamber is provided with a heater capable of controlling the temperature inside the reaction chamber, wherein an optical-grade quartz holder and an epitaxial substrate placed on the optical-grade quartz holder for epitaxially growing gallium nitride are installed in the reaction chamber, wherein an optical-grade quartz plate is provided at the lower part of the reaction chamber, and a laser is provided below the reaction chamber, wherein the laser emits laser light in the direction of the epitaxial substrate, so that the laser light passes through the optical-grade quartz plate, the optical-grade quartz holder and the epitaxial substrate in sequence to reach the interface between the epitaxial substrate and gallium nitride, wherein the temperature of gallium nitride at the interface rises and thermal decomposition occurs, thereby realizing in-situ separation of the epitaxial substrate and gallium nitride, and obtaining a gallium nitride single crystal after epitaxial growth.

2. The gallium nitride in-situ stripping device according to claim 1, characterized in that: There are multiple gas inlets for introducing different gases or fluids into the reaction chamber.

3. The gallium nitride in-situ stripping device according to claim 1, characterized in that: The gas inlet includes an NH3 inlet, an isolation gas inlet and a GaCl inlet.

4. The gallium nitride in-situ stripping device according to claim 1, characterized in that: The bottom surface of the optical grade quartz tray is flat, and the upper surface of the optical grade quartz tray is provided with a sink for placing an epitaxial substrate.

5. The gallium nitride in-situ stripping device according to claim 1, characterized in that: The epitaxial substrate is a double-polished sapphire flat wafer substrate.

6. The gallium nitride in-situ stripping device according to claim 3, characterized in that: The isolation gas is N2, H2 or a mixture of N2 and H2.

7. The gallium nitride in-situ stripping device according to claim 1, characterized in that: The epitaxial growth of gallium nitride is to use HVPE to epitaxially grow gallium nitride, the epitaxial growth temperature is controlled at above 1000° C., and the epitaxial growth thickness is controlled at 100-2000 μm.

8. The gallium nitride in-situ stripping device according to claim 1, characterized in that: The laser has a wavelength less than 365 nm.

9. A method for preparing a gallium nitride single crystal using the gallium nitride in-situ stripping device according to any one of claims 1 to 8: Step 1, epitaxially growing gallium nitride on the epitaxial substrate: various gases or fluids are introduced into the reaction chamber through the NH3 inlet, the isolation gas inlet and the GaCl inlet to achieve epitaxial growth of gallium nitride on the epitaxial substrate; Step 2, stripping of the epitaxially grown gallium nitride on the epitaxial substrate 107: after the epitaxial growth of the gallium nitride single crystal is completed, the input of GaCl and H2 is stopped, leaving only N2 and a small amount of NH3, wherein NH3 is used to prevent the grown gallium nitride single crystal from decomposing during the stripping process; at the same time, the temperature in the reaction chamber is controlled to control the stripping temperature within the range of 100-1000° C., and the lifting and lowering of the laser or the reaction chamber is adjusted to make the gallium nitride single crystal on the epitaxial substrate at the laser focus position. The laser passes through the optical grade quartz plate, the optical grade quartz support and the epitaxial substrate in sequence to reach the interface between the epitaxial substrate and the gallium nitride. At the interface, the gallium nitride temperature rises and thermal decomposition occurs, thereby realizing the in-situ separation of the epitaxial substrate and the gallium nitride.

10. The method for preparing a gallium nitride single crystal according to claim 9, characterized in that: The laser's galvanometer controls the path to gradually incident from the periphery to the center, so that the N2 produced by the peeling can overflow and will not accumulate in the wafer, avoiding high pressure and rupture.

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