Device and method for growing gallium oxide crystal by cooling method

Abstract

The invention discloses a device and method for growing gallium oxide crystals by a cooling method, and the device comprises a crucible heating unit which is arranged at the periphery of a crucible; the lifting unit is used for supporting the crucible; the air cooling unit is positioned below the crucible and is used for adjusting the temperature of the lower part of the crucible; wherein the crucible can enter or move out of the heating unit under the action of the lifting unit, and the temperature gradient of the crucible can be adjusted by adjusting the air flow of the air cooling unit and the power of the heating unit. According to the device and the temperature drop method for crystal growth, a water cooling system required by an edge-defined film-fed crystal growth method is not required, so that the dependence on complex equipment and a high-temperature environment is reduced. Therefore, not only is the energy consumption reduced, but also the equipment maintenance cost is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of crystal growth, and in particular to a device and method for growing gallium oxide crystals by a cooling method. Background Art

[0002] Semiconductor materials are the cornerstone of the semiconductor industry and an important engine driving the development of modern information technology. 2 O 3 As a new generation of ultra-wide bandgap semiconductor materials, Ga has the advantages of large bandgap width (4.9eV), wide transmission range (260nm-2500nm), high breakdown electric field strength (8MV / cm), large Baliga quality factor and stable physical and chemical properties. It is the preferred material for preparing short-wavelength optoelectronic devices, high-efficiency power electronic devices and high-precision sensors. Under the same voltage resistance, Ga 2 O 3 The on-resistance of GaC-based power electronic devices can theoretically be reduced to 1 / 10 of that of SiC-based devices. In addition to the excellent properties of the material, low preparation cost is also a major factor. 2 O 3 Another advantage of semiconductor materials is that they use mature crystal growth methods similar to those used to prepare sapphire single crystals, which can achieve low-cost, high-quality single crystal material mass production. Compared with SiC and GaN crystals, which can only be mass-produced using the vapor phase method (growth rate of about 0.1 mm / h), gallium oxide crystals can be prepared using the melt method (growth rate of about 1-10 mm / h), which can effectively reduce the material preparation cost. 2 O 3 It is expected that high-voltage, low-loss semiconductor power electronic devices with the same or even better performance can be developed at a lower cost. Therefore, the growth of gallium oxide crystals has very obvious industrial advantages.

[0003] Gallium oxide ultra-wide bandgap semiconductor materials have many applications in information, energy, transportation, manufacturing, national defense and other fields. It has become one of the key areas of high-tech competition among countries in the world today, and is also one of the key areas for the development of my country's high-tech and strategic emerging industries.

[0004] β-Ga 2 O 3It belongs to the monoclinic system and has two main cleavage planes (100) and (001). The crystal symmetry is low and it shows strong anisotropy during the growth of different main crystals. Compared with the crystal surface substrates with crystal orientations such as (100) and (001), the (010) crystal surface substrate has the best thermal conductivity. The thermal performance figure of merit of the

[010] direction perpendicular to the (010) plane is 528. It is very suitable for high current, high power and ultra-high temperature application scenarios. It is the best choice for power electronic devices, high temperature working devices and other fields. At the same time, the epitaxial film growth rate of the (010) crystal surface substrate is the fastest among substrates with different crystal orientations, and the preparation cost of epitaxial materials is low. Therefore, there is a large overall demand for (010) crystal surface substrates in the frontier research and development and market application of gallium oxide crystal materials. However, the mature size of the (010) crystal surface substrate grown by the current guided mode method is only 25mm. The main reason is that the (010) crystal surface is the growth cross section, and its size is limited by the size of the mold, which makes it difficult to grow. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the art, the present application aims to provide a growth device for growing gallium oxide crystals by a cooling method and a method for growing gallium oxide crystals.

[0006] The present application provides a growth device for growing gallium oxide crystals by a cooling method, comprising:

[0007] Crucible;

[0008] A heating unit is placed around the crucible;

[0009] A lifting unit, used for supporting the crucible;

[0010] An air cooling unit, located below the crucible, for adjusting the temperature of the lower part of the crucible;

[0011] Wherein, the crucible can enter or move out of the heating unit under the action of the lifting unit, and the temperature gradient of the crucible can be adjusted by adjusting the flow rate of the air in the air cooling unit and the power of the heating unit.

[0012] In some examples, a heat-insulating material is further included between the crucible and the heating unit;

[0013] In some examples, the thermal insulation material includes two or more materials having different thermal conductivities;

[0014] In some examples, the thermal conductivity of the insulation material decreases gradually from bottom to top;

[0015] In some examples, the insulation material includes, from bottom to top, a high thermal conductivity crucible base, a low thermal conductivity crucible sleeve, and a low thermal conductivity crucible cover;

[0016] In some examples, the material of the low thermal conductivity crucible sleeve and the low thermal conductivity crucible cover is alumina fiber; the material of the high thermal conductivity crucible base is alumina air ball material;

[0017] In some examples, the heating unit is a silicon molybdenum rod heater.

[0018] On the other hand, the present application also provides a method for growing gallium oxide crystals by cooling, and the above-mentioned growth device is used to grow gallium oxide crystals.

[0019] In some examples, the growing method includes:

[0020] Place the crucible on the lifting unit, add seed crystals and gallium oxide fillers into the crucible, and start the lifting unit to move it into the furnace;

[0021] The heating unit is started to melt all the gallium oxide filler;

[0022] Lower the temperature of the heating unit and turn on the air cooling unit to cool down the temperature at a rate of 1-3℃ / h;

[0023] After the crystal growth is completed, it is cooled and annealed to obtain gallium oxide crystals.

[0024] In some examples, the gallium oxide crystals are grown under an atmosphere of oxygen and argon;

[0025] In some examples, the partial pressure ratio of oxygen to argon is 1:4.

[0026] In some examples, turning on the air cooling unit to reduce the temperature at a rate of 1-3°C / h includes: when the temperature is 1790-1800°C, the air flow rate is set to 1-5L / min, when the temperature is 1780-1790°C, the air flow rate is set to 10-20L / min;

[0027] In some examples, after the crystal growth is completed, the cooling rate is 30-60°C / h to 1200-1300°C, and then cooled to 20-40°C.

[0028] In some examples, the annealing is performed at 1200-1300° C. for 2-3 hours.

[0029] Compared with the prior art, this application has at least the following beneficial effects:

[0030] The present application provides a growth device for growing gallium oxide crystals by a cooling method, comprising a crucible, a heating unit, a lifting unit and an air cooling unit; in particular, by controlling the air flow of the air cooling unit and the power of the heating unit, the temperature gradient of the growing crystal is controlled to achieve directional solidification of gallium oxide.

[0031] The growth device of the present application can accurately control the temperature gradient of crystal growth, thereby improving the stability of the solid-liquid interface, reducing the potential impact of the reverse temperature gradient on the crystal quality, and alleviating problems such as crystal cracking. The growth device of the present application can be used to grow gallium oxide crystals with (010) main faces, and can better control the growth rate and direction of (010) and other main face crystals, thereby obtaining a more regular and uniform crystal structure. The crucible diameter can be enlarged as needed, thereby improving the flexibility of crystal growth.

[0032] The crystal growth by the device and temperature drop method of the present application does not need to rely on the water cooling system required by the guided mold method, thereby reducing the dependence on complex equipment and high temperature environment. This not only reduces energy consumption, but also reduces the cost of equipment maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of a growth device for growing gallium oxide crystals using a cooling method according to an exemplary embodiment of the present application.

[0034] Figure 2 The single wafer is a (010) crystal plane single wafer after being cut according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The application is described in detail below.

[0039] The present application provides a device and method for growing gallium oxide crystals by cooling method, which are particularly suitable for the device and method for growing gallium oxide crystals with (010) main surface. The growth device consists of three parts: a heating unit, a lifting unit and an air cooling unit. Among them, the heating elements of the heating unit are all placed around the crucible, and the movement of the crucible is achieved by a lifting mechanism. The growth method mainly includes: first placing the raw material in a heating environment, heating it to a certain temperature and melting it, the crucible remains stationary, and the temperature gradient of the crystal growth is controlled by controlling the flow rate of the wind at the bottom of the crucible and the power of the heating element, thereby achieving directional solidification of gallium oxide.

[0040] The growth device of the present application actually uses a unique temperature drop method to realize the growth process of gallium oxide crystals. Compared with the currently widely used guided mode method, it has significant advantages. The temperature drop method of the present application gradually reduces the temperature of the growth environment, so that gallium oxide crystals can be gradually formed under more stable and controllable conditions. It can not only effectively reduce the defects and impurities that may appear during the crystal growth process, but also improve the overall quality and uniformity of the crystal.

[0041] In addition, the temperature drop method of the present application shows many advantages in the process of gallium oxide crystal growth, including improving crystal quality, reducing production costs and simplifying operation procedures, etc. These advantages make the present application have broad application prospects and market potential in the field of gallium oxide crystal growth.

[0042] Combine the following Figure 1 The schematic diagram of the growth device structure is used to introduce the technical solution of growing gallium oxide crystals by the cooling method of the present application.

[0043] Crucible 1: 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. In some examples, the optional crucible parameters include: 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, preferably 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°.

[0044] Seed crystal 4: The optional length is 8-12mm, the diameter is 5-8mm, and the growth direction is

[010] (generally, the diameter of the seed crystal is 0.1-0.2mm smaller than the seed crystal groove).

[0045] Crucible cover 5: plays a role in heat preservation. It forms an axial temperature gradient that is beneficial to crystal growth during the cooling growth process. The optional material is alumina fiber (thermal conductivity is 0.001W / (cm·K)).

[0046] Crucible sleeve 6: plays a role of heat preservation, which is beneficial to the control of temperature gradient during the cooling growth process. The optional material is alumina fiber (thermal conductivity is 0.001W / (cm·K)).

[0047] Heating element 7: can be a silicon-molybdenum rod heater, the specific number of which is arranged according to the size of the furnace and the crucible. In some examples, a 2-inch crucible can be arranged with more than 10 silicon-molybdenum rods at equal distances around the crucible.

[0048] Crucible bottom support 8: Optionally, an alumina air ball material (thermal conductivity is 0.01 W / (cm·K)) with higher thermal conductivity than the crucible cover is used to form an axial temperature gradient with the upper part of the crucible.

[0049] Furthermore, the temperature drop method or device of the present application is used to grow a (010)-plane gallium oxide single crystal, and the steps include:

[0050] Raw material filling: first, load the cylindrical seed crystal with the crystal orientation of

[010] into the seed crystal slot of the crucible, and then load the 5N grade gallium oxide sintered block into the crucible, and the loading volume is 90%-95% of the crucible volume;

[0051] Atmosphere control: The atmosphere in the furnace is controlled to be oxygen and argon (partial pressure ratio is 1:4);

[0052] 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 all the gallium oxide sintered blocks are melted;

[0053] Nucleation solidification: lower the temperature to near the melting point of gallium oxide (1800±2℃), maintain for 1-2h, slowly cool down at a rate of 1-3℃ / h, and control the bottom of the crucible to air cool while cooling. When the furnace temperature is in the range of 1790-1800℃, the air flow rate is set to 1-5L / min, and when the furnace temperature is in the range of 1780-1790℃, the air flow rate is set to 10-20L / min. The purpose of air cooling is to make the melt form a crystal nucleus at the seed crystal and gradually grow along the direction of the temperature gradient until the crystal growth is completed, and then control the cooling rate to 30-60℃ / h to cool to 1200℃, and then cool to room temperature with the furnace.

[0054] Subsequent treatment: The single crystal is taken out from the crucible, and then annealed at 1200°C for 2-3 hours. After orientation, a gallium oxide single crystal with (010) as the main surface can be cut out in the direction perpendicular to the axial direction.

[0055] The technical solution of the present application is further described below in conjunction with specific embodiments.

[0056] Example 1

[0057] A

[010] cylindrical seed crystal (with a diameter 0.1 mm smaller than the inner diameter of the seed crystal slot) is loaded into the seed crystal slot, and a sintered gallium oxide block with a purity of 99.999% is loaded, and the loading volume is 90% of the crucible volume; the loaded crucible is concentrically installed in the crucible bottom support, and an insulation sleeve is put on, and an alumina fiber insulation cover is covered.

[0058] Turn on the mechanical pump to evacuate the furnace to 0.1Pa, then turn on the molecular pump to evacuate the furnace to 0.01Pa, open the gas valve, and fill in 99.99% high-purity oxygen and high-purity argon (partial pressure of 1:4).

[0059] When the pressure in the furnace reaches 0.15MPa, start the silicon-molybdenum rod heating power supply, heat to 1200℃ at 10℃ / min, then heat to 1600℃ at 5℃ / min, then heat to 1750℃ at 2℃ / min, and finally heat to 1810℃ at 1℃ / min. Keep warm for 1h to melt all the raw materials and partially melt the seed crystal.

[0060] Reduce the heating power to lower the melt temperature to 1800℃, keep the temperature constant for 1h, and stabilize the melt temperature; reduce the heating power, slowly cool down at a rate of 1℃ / h, and control the bottom of the crucible with air cooling. When the temperature is higher than 1790℃, the air flow rate is 1L / min, and when the temperature is in the range of 1780-1790℃, the air flow rate is 10L / min. After the temperature drops to 1780℃, the crystal growth is completed. Continue to reduce the heating power, cool down at a rate of 30℃ / h, and after reaching 1200℃, slowly cool to room temperature with the furnace. The grown gallium oxide is a single crystal, and the crystal plane perpendicular to the growth direction is the (010) plane.

[0061] Example 2

[0062] A

[010] cylindrical seed crystal (with a diameter 0.2 mm smaller than the inner diameter of the seed crystal slot) is loaded into the seed crystal slot, and a sintered gallium oxide block with a purity of 99.999% is loaded, and the loading volume is 95% of the crucible volume; the loaded crucible is concentrically installed in the crucible bottom support, covered with an insulation sleeve, and covered with an alumina fiber insulation cover.

[0063] Turn on the mechanical pump to evacuate the furnace to 0.1Pa, turn on the molecular pump to evacuate the furnace to 0.01Pa, open the gas valve, and fill in 99.99% high-purity oxygen and high-purity argon (partial pressure of 1:4).

[0064] When the pressure in the furnace reaches 0.15MPa, start the silicon-molybdenum rod heating power supply, heat to 1200℃ at 10℃ / min, heat to 1600℃ at 5℃ / min, then heat to 1750℃ at 2℃ / min, and finally heat to 1810℃ at 1℃ / min. Keep warm for 1.5h to melt all the raw materials and partially melt the seed crystal.

[0065] Reduce the heating power to lower the melt temperature to 1800℃, keep the temperature constant for 1h, and stabilize the melt temperature; reduce the heating power, slowly cool down at a rate of 3℃ / h, and control the bottom of the crucible with air cooling. When the temperature is higher than 1790℃, the air flow rate is 2L / min, and when the temperature is in the range of 1780-1790℃, the air flow rate is 10L / min. After the temperature drops to 1780℃, the crystal growth is completed. Then continue to reduce the heating power, cool down at a rate of 40℃ / h, and after reaching 1200℃, slowly cool to room temperature with the furnace. The grown gallium oxide is a single crystal, and the crystal plane perpendicular to the growth direction is the (010) plane.

[0066] Example 3

[0067] A

[010] cylindrical seed crystal (with a diameter 0.2 mm smaller than the inner diameter of the seed crystal slot) is loaded into the seed crystal slot, and a sintered gallium oxide block with a purity of 99.999% is loaded, and the loading volume is 95% of the crucible volume; the loaded crucible is concentrically installed in the crucible bottom support, covered with an insulation sleeve, and covered with an alumina fiber insulation cover.

[0068] Turn on the mechanical pump to evacuate the furnace to 0.1Pa, then turn on the molecular pump to evacuate the furnace to 0.01Pa, open the gas valve, and fill in 99.99% high-purity oxygen and high-purity argon (partial pressure of 1:4).

[0069] When the pressure in the furnace reaches 0.15MPa, start the silicon-molybdenum rod heating power supply, heat to 1200℃ at 10℃ / min, heat to 1600℃ at 5℃ / min, then heat to 1750℃ at 2℃ / min, and finally heat to 1810℃ at 1℃ / min. Keep warm for 1.5h to melt all the raw materials and partially melt the seed crystal.

[0070] Reduce the heating power to reduce the melt temperature to 1800℃, keep the temperature constant for 1h, and stabilize the melt temperature; reduce the heating power, slowly cool down at a rate of 3℃ / h, and control the bottom of the crucible with air cooling. When the temperature is higher than 1790℃, the air flow rate is 5L / min, and when the temperature is in the range of 1780-1790℃, the air flow rate is 20L / min. After the temperature drops to 1780℃, the crystal growth is completed. Then continue to reduce the heating power, cool down at a rate of 50℃ / h, and after reaching 1200℃, slowly cool to room temperature with the furnace. The grown gallium oxide is a single crystal, and the crystal plane perpendicular to the growth direction is the (010) plane.

[0071] Comparative Example 1

[0072] The gallium oxide crystals were grown in the same manner as in Example 1, except that during the temperature drop, no air cooling was used at the bottom (the air flow rate was 0). After the growth was completed, the gallium oxide crystals were in a dendrite-like form, indicating that the temperature gradient required for crystal growth was not formed in the axial direction, and the crystal growth requirements were not met.

[0073] Comparative Example 2

[0074] The gallium oxide crystal was grown in the same manner as in Example 1, except that the diameter of the seed crystal was 0.4 mm thinner than the seed crystal groove. After the growth was completed, the gallium oxide crystal was in a polycrystalline form. After the crystal was removed, it was found that the (010) seed crystal in the seed crystal groove had completely melted.

[0075] Comparative Example 3

[0076] The gallium oxide crystals were grown in the same manner as in Example 2, except that the temperature was lowered at a faster rate (not at a rate of 3°C / h in the example, but at a rate of 10°C / h). Due to the large degree of supercooling, the gallium oxide was in a polycrystalline state.

[0077] Comparative Example 4

[0078] The gallium oxide crystals were grown in the same manner as in Example 3, except that the end temperature of the slow temperature drop was not 1780° C., but 1790° C. After the growth was completed, the crystals near the bottom of the crucible were in a single crystal form, and then due to the fast cooling rate and large undercooling, the unsolidified melt subsequently grew in a polycrystalline form.

[0079] like Figure 2 The figure shows a single crystal sheet of the (010) crystal plane cut out of Examples 1, 2 and 3. The diameter of the original crystal blank is 30 mm, and the size after cutting is 10×10 mm. Different from the technical solution of the present application, when the existing technology uses the guided mode method to grow the (010) crystal plane, it grows in the form of a thin slice through capillary phenomenon. Since the (010) crystal plane is perpendicular to the two cleavage planes (100) and (001), the growth cross section is prone to accumulate stress during the crystal growth process, and the growth is difficult. The interface free energy of the (100) or (001) crystal plane is relatively low, so the (010) or (001) crystal plane is relatively low. <100> and <001> The non-dominant growth crystal orientation as the growth seed crystal has relatively poor solid-liquid growth interface stability and tends to be rough. If the external temperature gradient cannot meet the interface stability requirements, it is very likely to promote the occurrence of dendrite growth. Therefore, the largest commercially available size of the (010) crystal plane substrate is only 25mm.

[0080] According to the above embodiments and comparative examples, the present application provides a growth device and a growth method for growing gallium oxide crystals by a cooling method, and in particular provides a method for growing gallium oxide crystals with a (010) primary surface, which at least includes the following beneficial effects:

[0081] The temperature drop method of the present application can more accurately control the temperature gradient of crystal growth by controlling the temperature drop rate, thereby improving the stability of the solid-liquid interface and well controlling the growth rate and direction of the main surface crystals such as (010), thereby obtaining gallium oxide single crystals with the desired crystal surface.

[0082] The present application realizes an axial temperature distribution with low temperature at the bottom and high temperature at the top through cooling control of the bottom of the crucible, thereby ensuring that the crystal grows from the bottom to the top from the seed crystal.

[0083] The temperature drop method of the present application does not need to rely on the water cooling system required by the guided mold method, nor does it need to introduce a complex lifting control system, thereby reducing dependence on complex equipment. This not only reduces energy consumption, but also reduces equipment maintenance costs, making it more suitable for large-scale industrial production.

[0084] 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 cooling method, characterized in that: include: Crucible; A heating unit is placed around the crucible; A lifting unit, used for supporting the crucible; An air cooling unit, located below the crucible, for adjusting the temperature of the lower part of the crucible; Wherein, the crucible can enter or move out of the heating unit under the action of the lifting unit, and the temperature gradient of the crucible can be adjusted by adjusting the flow rate of the air in the air cooling unit and the power of the heating unit.

2. The device according to claim 1, characterized in that A heat-insulating material is also included between the crucible and the heating unit.

3. The device according to claim 2, characterized in that The thermal insulation material includes two or more materials with different thermal conductivities; Optionally, the thermal conductivity of the thermal insulation material decreases gradually from bottom to top.

4. The device according to claim 2, characterized in that The heat-insulating material comprises, from bottom to top, a high-thermal-conductivity crucible bottom support, a low-thermal-conductivity crucible sleeve, and a low-thermal-conductivity crucible cover.

5. The device according to claim 4, characterized in that The low thermal conductivity crucible sleeve and the low thermal conductivity crucible cover are made of alumina fiber; the high thermal conductivity crucible base is made of alumina air ball material.

6. The device according to claim 1, characterized in that The heating unit is a silicon-molybdenum rod heater.

7. A method for growing gallium oxide crystals using the device according to any one of claims 1 to 6, characterized in that: include: Loading seed crystals and gallium oxide fillers into the crucible, and starting the lifting unit to move into the heating unit; Starting the heating unit to completely melt the gallium oxide filler; Lowering the temperature of the heating unit and turning on the air cooling unit to lower the temperature at a rate of 1-3°C / h; After the crystal growth is completed, it is cooled and annealed to obtain the gallium oxide crystal.

8. The method according to claim 7, 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.

9. The method according to claim 7, characterized in that: Turning on the air cooling unit to reduce the temperature at a rate of 1-3°C / h includes: when the temperature is 1790-1800°C, the air flow rate is set to 1-5L / min; when the temperature is 1780-1790°C, the air flow rate is set to 10-20L / min; Optionally, after the crystal growth is completed, the cooling rate is 30-60°C / h to cool to 1200-1300°C, and then cooled to 20-40°C.

10. The method according to claim 7, characterized in that The annealing is performed at 1200-1300° C. for 2-3 hours.

Images