Device and method for growing gallium oxide crystal by multi-step method

Abstract

The invention discloses a device and a method for growing gallium oxide crystals by a multi-step method. The device comprises a crucible; the temperature control structure comprises a heating element arranged on the periphery of the crucible and a plurality of sets of heat insulation baffles, the heat insulation baffles are located below the heating element, and a gap is formed between every two sets of heat insulation baffles; the lifting structure comprises a crucible bottom support for supporting the crucible and a lifting device which is connected to the crucible bottom support and enables the crucible to move up and down; and the atmosphere control structure is used for controlling the atmosphere in the furnace through a gap between the lifting device and the heat insulation baffle. The device disclosed by the invention is used for growing the gallium oxide crystal through a multi-step method, the growth condition is accurately controlled, and the fine management of the crystal growth process is realized. By adjusting position parameters in multiple steps and adopting a temperature drop method, the crystal grows in a more stable environment, and the defect density in the crystal can be effectively reduced, so that the purity and integrity of the crystal are improved.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor material preparation, and in particular to a device and method for growing gallium oxide crystals in a multi-step process. Background Art

[0002] Gallium oxide (Ga2O3) is an excellent ultra-wide bandgap semiconductor material with a bandgap width of 4.2-5.3eV (a manifestation of anisotropy of different crystal structures), and the most stable phase is the monoclinic β-Ga2O3 structure. Compared with other mainstream semiconductor materials, β-Ga2O3 (hereinafter referred to as Ga2O3) has unique physical properties. In addition to excellent chemical and thermal stability, it also has a high ultraviolet visible light transmittance. At the same time, the material can easily obtain excellent N-type conductivity, which can simultaneously meet the requirements of good conductivity and high optical transmittance required for transparent conductive electrodes. In addition, due to the large band gap of the material, it has a large breakdown electric field strength, which is more than 1 times higher than that of common wide bandgap semiconductors SiC and GaN. In addition to its high-voltage resistance, the theoretical value of the on-resistance of Ga2O3 is very low, which makes the conduction loss of Ga2O3-based unipolar devices at the same voltage more than one order of magnitude lower than that of SiC and GaN devices, thereby significantly improving the working efficiency of devices such as MOSFET. The above advantages make Ga2O3-based devices have broad research and development prospects in the field of high-voltage electronic devices.

[0003] The guided-mold method is currently the mainstream commercial technology for growing gallium oxide crystals, but given the shortcomings of this technical route, such as large investment, high cost, and low yield, the industry has begun to explore new technical paths. In recent years, the descent method has gradually emerged in the growth of gallium oxide crystals, and it has shown great potential in reducing costs and increasing yields. However, the traditional descent method achieves crystal growth by lowering the position of the crucible. Since the speed of downward movement remains unchanged, as the crystal continues to grow, the downward thermal conductivity will deteriorate, resulting in changes in the crystal growth temperature gradient, which affects the quality of the crystal. In addition, the traditional descent method requires the equipment to remain at the highest temperature (above 1805°C) for dozens or even hundreds of hours, which is a great challenge for high-temperature heating elements.

[0004] High-temperature heating elements in oxygen atmosphere are generally made of silicon-molybdenum materials. Silicon-molybdenum rod electric heating elements are high-temperature resistant and oxidation-resistant resistance heating elements made based on molybdenum disilicide. They can be used for a long time at 1750°C. Once their own temperature exceeds 1800°C, their life will be significantly reduced. The furnace temperature of the molten gallium oxide material needs to be higher than 1805°C. At this time, the temperature of the heating element itself needs to be 1810°C or even higher (related to the size of the furnace and the number of heating elements). Therefore, developing new process paths to extend the service life of crystal furnace heating elements as much as possible while ensuring the quality of the crystal has become the main research direction of the descent method in the future. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the art, the present application aims to provide a device and method for growing gallium oxide crystals in a multi-step process. By precisely controlling the growth conditions, refined management of the crystal growth process is achieved.

[0006] According to one aspect of the present application, a device for growing gallium oxide crystals by a multi-step method is provided, comprising:

[0007] Crucible;

[0008] The temperature control structure includes a heating element and a plurality of heat-insulating baffles arranged around the crucible, wherein the heat-insulating baffles are located below the heating element, and each group of heat-insulating baffles has a spacing therebetween;

[0009] A lifting structure, comprising a crucible bottom support for supporting the crucible and a lifting device connected to the crucible bottom support to move the crucible up and down; and

[0010] The atmosphere control structure controls the atmosphere in the furnace through the gap between the lifting device and the insulation baffle.

[0011] According to some embodiments of the present application, the device further includes a furnace cover, which covers the outside of the crucible, the temperature control structure and the lifting structure;

[0012] According to some embodiments of the present application, a heat insulating material is provided inside the furnace hood;

[0013] According to some embodiments of the present application, the thermal insulation material is a lightweight zirconium oxide heat-resistant material.

[0014] According to some embodiments of the present application, the heat insulation baffle material is hollow alumina sphere material.

[0015] According to some embodiments of the present application, a seed crystal groove is provided at the bottom of the crucible, and a crucible cover is provided at the top.

[0016] According to some embodiments of the present application, the material of the crucible cover is alumina fiber;

[0017] According to some embodiments of the present application, the material of the crucible bottom support is aluminum oxide material.

[0018] According to some embodiments of the present application, the lifting speed of the lifting device is 0.1-100 mm / h.

[0019] According to another aspect of the present application, a method for growing gallium oxide crystals using the above-mentioned device in a multi-step method is also provided, comprising:

[0020] Place seed crystals and gallium oxide filler into the crucible, start the lifting device to move the crucible into the heating element, and close the lifting device;

[0021] Start the heating element to raise the temperature in the furnace so that all the gallium oxide filler melts;

[0022] Start the lifting device to move the crucible downward and control the cooling rate until the gallium oxide melt is completely crystallized;

[0023] The crystals are cooled and annealed to obtain gallium oxide crystals.

[0024] According to some embodiments of the present application, starting the lifting device to move the crucible downward and controlling the cooling rate until the gallium oxide melt is completely crystallized includes:

[0025] Step 1: Keep the furnace temperature at 1800℃, control the crucible to drop 5-10mm at a speed of 1-2mm / h, and then cool it down at a rate of 1-2℃ / h for 5-10h;

[0026] Step 2: Keep the furnace temperature unchanged at the end of the first step, control the crucible to drop 5-10mm at a speed of 2-5mm / h, and then cool it down at a rate of 2-10℃ / h for 2-5h;

[0027] Repeat the second step, so that the crucible is lowered by more than 30 mm and the furnace temperature is lower than 1775° C., until the gallium oxide melt is completely crystallized.

[0028] According to some embodiments of the present application, cooling the crystallization comprises: cooling to 1200° C. at 30-60° C. / h and then cooling in the furnace.

[0029] According to some embodiments of the present application, gallium oxide crystals are grown in an atmosphere of oxygen and argon;

[0030] According to some embodiments of the present application, the partial pressure ratio of oxygen to argon is 1:4;

[0031] According to some embodiments of the present application, the annealing is performed at 1200-1300° C. for 2-3 hours.

[0032] Compared with the prior art, this application has at least the following beneficial effects:

[0033] The present application provides a device for growing gallium oxide crystals by a multi-step method. The device is provided with heat-insulating baffles on both sides of the crucible and the lifting device, which can precisely control the cooling of the crystals.

[0034] The device of the present application is used to grow gallium oxide crystals through a multi-step method, accurately control the growth conditions, and achieve refined management of the crystal growth process. By adjusting the position parameters in multiple steps and using the temperature drop method to grow the crystal in a more stable environment, the defect density inside the crystal can be effectively reduced, thereby improving the purity and integrity of the crystal.

[0035] The multi-step method of the present application reduces the operating time of the equipment at high temperature by optimizing the growth conditions, increases the life of the heating element (heating body), and also reduces energy consumption. The multi-step method also has stronger adaptability and can flexibly adjust the growth parameters to produce gallium oxide crystals that meet specific requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the structure of an apparatus for growing gallium oxide crystals using a multi-step method according to an exemplary embodiment of the present application.

[0037] Figure 2 This is a single crystal photograph of Example 1 of the present application.

[0038] Figure 3 This is a single crystal photo of Example 4 of this application

[0039] Figure 4 This is a polycrystalline photo of Comparative Example 1 of this application.

[0040] Figure 5 This is a polycrystalline photo of comparative example 5 of this application. DETAILED DESCRIPTION

[0041] The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0042] It is particularly important to point out that similar substitutions and modifications made to the present application are obvious to those skilled in the art, and they are all deemed to be included in the present application. Relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application to implement and apply the technology of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0043] If no specific conditions are specified in this application, the preparation shall be carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, for which the manufacturers are not specified, are all conventional products that can be obtained commercially.

[0044] The application is described in detail below.

[0045] The device for growing gallium oxide crystals by a multi-step method of the present application is mainly composed of a crucible, a temperature control structure, a lifting structure and an atmosphere control structure. The heating elements of the temperature control structure are placed around the crucible, and the movement of the crucible is achieved by a lifting mechanism. Optionally, as Figure 1 As shown, the device of the present application includes:

[0046] Crucible;

[0047] The temperature control structure includes a heating element and a plurality of heat-insulating baffles arranged around the crucible, wherein the heat-insulating baffles are located below the heating element, and each group of heat-insulating baffles has a spacing therebetween;

[0048] A lifting structure, comprising a crucible bottom support for supporting the crucible and a lifting device connected to the crucible bottom support for moving the crucible up and down;

[0049] The atmosphere control structure controls the atmosphere in the furnace through the gap between the lifting device and the heat insulation baffle;

[0050] A furnace cover, covering the outside of the crucible, the temperature control structure and the lifting structure;

[0051] The furnace hood is provided with heat-insulating material; and

[0052] A seed crystal groove is provided at the bottom of the crucible, and a crucible cover is provided at the top.

[0053] The device of the present application generally places a crucible containing gallium oxide raw materials in a heating environment. After the temperature is raised to a certain level and the raw materials are melted, the crucible is first lowered to a certain position and kept stationary, and then the temperature is controlled to be lowered. After that, the crucible is lowered to a certain position and kept stationary, and then the temperature is lowered again. After multiple steps, the highest temperature in the crucible is reduced to below the solidification point of the melt and all the crystals are crystallized.

[0054] In some examples, the apparatus for growing gallium oxide crystals in a multi-step process of the present application includes:

[0055] Crucible: The lower part is provided with a seed crystal groove, and its physical properties are oxidation resistance, a melting point higher than that of gallium oxide, a thermal expansion coefficient close to or slightly smaller than that of gallium oxide, and no obvious diffusion reaction with gallium oxide melt at high temperature. Optionally, the crucible height Hc is greater than the crucible diameter Dc, and the preferred ratio is 2.5<Hc / Dc<5. Its thickness tc ranges from 3-8mm, and the preferred size is tc=5mm. In order to facilitate the nucleation and growth of the crystal, the bottom of the crucible is designed to form a shoulder area with a certain angle θ with the plane, and the angle range is 0-60°.

[0056] Seed crystal: length 8-12mm, diameter 5-8mm, the diameter should be 0.1-0.2mm smaller than the seed crystal groove.

[0057] Crucible cover: It plays a role of heat preservation and forms an axial temperature gradient that is conducive to crystal growth during the cooling growth process. The selected material is alumina fiber (thermal conductivity is 0.001W / (cm·K)).

[0058] Crucible bottom support: It plays the role of fixing the crucible. The selected material is alumina material with high thermal conductivity (thermal conductivity is 0.4W / (cm·K)).

[0059] Heating element: Silicon molybdenum rod heater. The specific number is arranged according to the size of the furnace and the crucible. If the crucible size is 2 inches, 6-10 silicon molybdenum rods need to be arranged at equal distances around the crucible.

[0060] Lifting device: used to control the lifting and lowering of the crucible position, with a speed control range of 0.1-100mm / h.

[0061] Thermal insulation material: The material used is lightweight zirconium oxide heat-resistant material (thermal conductivity is 0.001W / (cm·K)).

[0062] Heat insulation baffle: It blocks the heat loss in the furnace. The material used is hollow alumina ball material (thermal conductivity is 0.01W / (cm·K)).

[0063] In some examples, the multi-step method for growing gallium oxide crystals of the present application includes:

[0064] Raw material loading: first load a round seed crystal of a certain crystal orientation into the seed crystal slot of the crucible, and then load 5N grade gallium oxide sintered block into the crucible, with the loading volume being about 95% of the crucible volume;

[0065] Atmosphere control: The atmosphere in the furnace is controlled to be oxygen and argon (partial pressure ratio is 1:4);

[0066] Raw material melting: Start the heating device to raise the temperature in the furnace to above the melting point (1805-1810°C) and maintain it for 1-2 hours until the gallium oxide sintered block is completely melted;

[0067] Directed nucleation: lower the temperature to near the melting point of gallium oxide (1800±2℃), maintain for 1-2h, and control the bottom of the melt to perform directed nucleation on the partially melted seed crystal according to the crystallographic orientation of the seed crystal;

[0068] Solidification and crystallization: Control the crucible to be lowered to a certain position at a certain speed (1-2mm / h), and then slowly cool down (1-2℃ / h). After reaching a certain temperature, lower the crucible to the next position at a certain speed (2-5mm / h), and then slowly cool down (2-10℃ / h). Repeat this process until all the melt in the crucible is crystallized. Then control the cooling rate to 30-60℃ / h to cool down to 1200℃, and finally cool down to room temperature with the furnace.

[0069] The technical solution of the present application is further described below in conjunction with specific embodiments.

[0070] Example 1

[0071] Charging and melting: Load a Φ5.8×10mm round seed crystal into the seed crystal slot of the crucible, and then load the sintered gallium oxide block with a purity of 99.999% into the crucible, and the charging volume is 95% of the volume of the crucible; install the charged crucible concentrically in the crucible bottom support, and cover it with an alumina fiber insulation cover; after evacuating to 0.1Pa, open the gas valve and fill it with 99.99% high-purity oxygen and high-purity argon (partial pressure of 1:4). When the pressure in the furnace reaches 0.15MPa, start the silicon-molybdenum rod heating power supply, first heat to 1200℃ at a speed of 10℃ / min, then heat to 1600℃ at a speed of 5℃ / min, then heat to 1750℃ at a speed of 2℃ / min, and finally heat to 1810℃ at a speed of 1℃ / min. Keep warm for 1h to melt all the raw materials; reduce the heating power to reduce the melt temperature to 1800℃, keep the temperature constant for 1h to stabilize the melt temperature.

[0072] Multi-step crystal growth: The furnace temperature remains unchanged at 1800℃, the crucible is lowered 5mm from the 0 position at a speed of 2mm / h, the crucible is kept stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 5h. The crucible is then lowered 10mm at a speed of 5mm / h, the crucible is kept stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 5℃ / h for 2h. The crucible is then lowered 10mm at a speed of 5mm / h, the crucible is kept stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2.5℃ / h for 2h. At this time, the furnace temperature is 1775℃, and then the cooling rate is controlled to be 30℃ / h to cool to 1200℃, and finally cooled to room temperature with the furnace, and the crystal growth is completed.

[0073] Example 2

[0074] The charging and melting steps are the same as in Example 1.

[0075] Multi-step crystal growth: The furnace temperature remains unchanged at 1800℃, and the crucible is lowered by 5mm from the 0 position at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 1℃ / h for 10h. Then the crucible is lowered by 10mm at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 5h. Then the crucible is lowered by 10mm at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 2.5h. At this time, the furnace temperature has dropped to 1775℃, and then the cooling rate is controlled to be 50℃ / h to cool to 1200℃, and finally cooled to room temperature with the furnace.

[0076] Example 3

[0077] Charging and melting: Load a Φ5.8×10mm round seed crystal into the seed crystal slot of the crucible, and then load the sintered gallium oxide block with a purity of 99.999% into the crucible, and the charging volume is 95% of the volume of the crucible; install the charged crucible concentrically in the crucible bottom support, and cover it with an alumina fiber insulation cover; then evacuate to 0.1Pa, open the gas valve, and fill in 99.99% high-purity oxygen and high-purity argon (partial pressure of 1:4). When the pressure in the furnace reaches 0.12MPa, start the silicon-molybdenum rod heating power supply, first heat to 1200℃ at a speed of 10℃ / min, then heat to 1600℃ at a speed of 5℃ / min, then heat to 1750℃ at a speed of 2℃ / min, and finally heat to 1805℃ at a speed of 1℃ / min. Keep warm for 2h to melt all the raw materials; reduce the heating power to reduce the melt temperature to 1800℃, keep the temperature constant for 1.5h to stabilize the melt temperature.

[0078] Multi-step crystal growth: The furnace temperature is kept at 1800℃, and the crucible is lowered 10mm from the 0 position at a speed of 1mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 5h. Then the crucible is lowered 10mm at a speed of 5mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 5h. Then the crucible is lowered 5mm at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 5℃ / h for 1h. At this time, the furnace temperature has dropped to 1775℃, and then the cooling rate is controlled to be 30℃ / h to cool to 1200℃, and finally cooled to room temperature with the furnace.

[0079] Example 4

[0080] The charging and melting steps are the same as those in Example 3.

[0081] Multi-step crystal growth: The furnace temperature is kept at 1800℃, and the crucible is lowered by 5mm from the 0 position at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 1℃ / h for 5h. Then the crucible is lowered by 5mm at a speed of 5mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 2℃ / h for 5h. Then the crucible is lowered by 15mm at a speed of 2mm / h. At this time, the crucible remains stationary, the heating power is reduced, and the furnace temperature is slowly cooled at a rate of 5℃ / h for 2h. At this time, the furnace temperature has dropped to 1775℃, and then the cooling rate is controlled to be 60℃ / h to cool to 1200℃, and finally cooled to room temperature with the furnace.

[0082] Comparative Example 1

[0083] The preparation steps are the same as those in Example 1, except that: in the first step, the crucible is lowered at a speed of 8 mm / h for 0.5 h, and the crystals grown at the end are polycrystalline (such as Figure 3 ).

[0084] Comparative Example 2

[0085] The preparation steps are the same as those in Example 1, except that the cooling rate in the first step is 10° C. / h, and the crystals finally grown are in a polycrystalline form.

[0086] Comparative Example 3

[0087] The preparation steps are the same as those in Example 2, except that the descending speed in the second step is 12 mm / h, and the grown crystals are mostly polycrystalline.

[0088] Comparative Example 4

[0089] The preparation steps are the same as those in Example 3, except that the cooling rate in the second step is 15° C. / h, and the grown crystals are mostly polycrystalline.

[0090] Comparative Example 5

[0091] The preparation steps are the same as those in Example 4, except that the last step of slow cooling is eliminated (the step of slowly cooling the furnace temperature at a rate of 5°C / h for 2h is eliminated), the furnace temperature is directly cooled from 1785°C to 1200°C at a rate of 60°C / h, and finally cooled to room temperature with the furnace, and the grown crystals are polycrystalline (such as Figure 4 ).

[0092] According to the above comparative examples and embodiments, the device and method of the present application can reduce the operating time of the equipment at high temperature by optimizing the growth conditions of gallium oxide crystals, increase the life of the heating element (heating body), and reduce energy consumption. At the same time, the present application also realizes the temperature gradient control of the crystal growth area by reasonably designing the temperature field distribution, and can guide the crystal to grow under more stable conditions by adjusting the position parameters in multiple steps.

[0093] The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A device for growing gallium oxide crystals by a multi-step method, characterized in that: include: Crucible; A temperature control structure, comprising a heating element and a plurality of groups of heat-insulating baffles arranged around the crucible, wherein the heat-insulating baffles are located below the heating element, and there is a spacing between each group of the heat-insulating baffles; A lifting structure, comprising a crucible bottom support for supporting the crucible and a lifting device connected to the crucible bottom support for moving the crucible up and down; as well as The atmosphere control structure controls the atmosphere in the furnace through the gap between the lifting device and the heat insulation baffle.

2. The device according to claim 1, characterized in that It also includes a furnace cover, which covers the outside of the crucible, the temperature control structure and the lifting structure; Optionally, a heat insulating material is provided inside the furnace cover; Further optionally, the thermal insulation material is a lightweight zirconium oxide heat-resistant material.

3. The device according to claim 2, characterized in that The heat insulation baffle material is hollow alumina ball material.

4. The device according to claim 1, characterized in that The bottom of the crucible is provided with a seed crystal groove, and the top of the crucible is provided with a crucible cover.

5. The device according to claim 4, characterized in that The material of the crucible cover is alumina fiber; the material of the crucible bottom support is alumina material.

6. The device according to claim 1, characterized in that The lifting speed of the lifting device is 0.1-100 mm / h.

7. A method for growing gallium oxide crystals by a multi-step method using the apparatus described in any one of claims 1 to 6, characterized in that: include: Loading seed crystals and gallium oxide fillers into the crucible, starting the lifting device to move the crucible into the heating element, and closing the lifting device; Starting the heating element to increase the temperature in the furnace so that all the gallium oxide filler is melted; Starting the lifting device to move the crucible downward and controlling the cooling rate until the gallium oxide melt is completely crystallized; The crystallized material is cooled and annealed to obtain the gallium oxide crystal.

8. The method according to claim 7, characterized in that Starting the lifting device to move the crucible downward and controlling the cooling rate until the gallium oxide melt is completely crystallized includes: Step 1: Keep the furnace temperature at 1800℃, control the crucible to drop 5-10mm at a speed of 1-2mm / h, and then cool it down at a rate of 1-2℃ / h for 5-10h; Step 2: Keep the furnace temperature unchanged at the end of the first step, control the crucible to drop 5-10mm at a speed of 2-5mm / h, and then cool it down at a rate of 2-10℃ / h for 2-5h; Repeat the second step, so that the crucible is lowered by more than 30 mm and the furnace temperature is lower than 1775° C., until the gallium oxide melt is completely crystallized.

9. The method according to claim 7, characterized in that: The cooling of the crystallization comprises: cooling the temperature to 1200° C. at 30-60° C. / h and then cooling along with the furnace.

10. The method according to any one of claims 7 to 9, characterized in that: growing the gallium oxide crystal in an atmosphere of oxygen and argon; Optionally, the partial pressure ratio of oxygen to argon is 1:4; Further optionally, the annealing is performed at 1200-1300° C. for 2-3 hours.

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