A method for growing gallium oxide single crystals using a cold crucible method and a Czochralski method

Abstract

The present invention belongs to the field of semiconductor wafer manufacturing technology, and specifically relates to a method for growing gallium oxide single crystals using a cold crucible Czochralski method. The method involves first applying high-frequency heating to the gallium oxide raw material in a crucible, then maintaining the temperature for a certain period of time, and then increasing the heating frequency to completely melt the gallium oxide. The pressure of the cooling water is then adjusted to form a solid gallium oxide layer on the inner wall of the crucible, isolating the gallium oxide at the center from contact with the inner wall of the crucible. Crystal pulling is then performed, and the heating frequency is gradually reduced during crystal pulling. This technical solution, through the design of the crucible structure and the adjustment of the heating frequency of the high-frequency heating device, achieves the formation of a solid gallium oxide layer between the gallium oxide melt and the inner surface of the crucible during the crystal pulling process. This solid gallium oxide layer can completely isolate the gallium oxide inside from contact with the crucible material, preventing contamination of the produced gallium oxide crystals.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor wafer manufacturing, and in particular relates to a method for growing gallium oxide single crystals using a cold crucible method and a Czochralski method. Background Art

[0002] Gallium oxide, due to its excellent material properties, offers 3,400 times the energy efficiency of silicon and 10 times that of silicon carbide. Gallium oxide, like silicon, can be grown by dissolving raw materials and crystallizing them from a liquid. However, current crystallization methods use the very expensive metal iridium in the crucible that holds the molten liquid, making it difficult to reduce costs.

[0003] Currently reported β-Ga2O3 crystal growth methods include the Czochralski method, the guided mold method, the Bridgman method, and the float zone method. Crucibles used in these methods are often made of precious metals, primarily iridium and platinum-rhodium alloys. However, because gallium oxide melts at 1793°C and volatilizes and decomposes at high temperatures, metallic gallium accumulates in the melt, corroding the iridium crucible and affecting crystal growth and quality. Platinum-rhodium alloy crucibles, however, have a melting point very close to that of gallium oxide, requiring extremely precise temperature control and subjecting them to rhodium contamination. Furthermore, the large amount of precious metals required for growth increases the cost of crystal growth, and post-growth crucible corrosion and maintenance are very expensive. The optical float zone method does not require a precious metal crucible for crystal growth. High-pressure xenon lamps and laser heating are commonly used as heating sources. Conventional optical float zone furnaces are limited by the size of the heating source, and the float zone method can only produce crystal ingots 5-10 mm in diameter. While the crystal quality is good, it cannot meet the industrial demand for large-scale, high-volume crystals.

[0004] Due to the high volatility of raw materials in the Czochralski method, the gallium oxide growth process has gradually evolved from the Czochralski method to the guided mold method using an iridium cap and mold. Both methods require the use of an iridium crucible, and the guided mold method has become the mainstream gallium oxide growth method. However, due to the high cost and wear of iridium crucibles, they corrode and wear out after just a few dozen growth cycles, requiring remelting. Furthermore, iridium can form impurities and enter the crystal during the growth process, leading to a strong demand in the industry for the development of iridium-free methods.

[0005] In April 2022, the Nikkei reported that C&A, a Japanese company, had grown 2-inch gallium oxide single crystals using the Czochralski method, a copper crucible developed by Tohoku University. This method reduces costs to 1 / 100 of the guided-mold method. Gallium oxide raw material is placed in a crucible with a gap. A high-frequency coil generates a magnetic field, directly heating the gallium oxide raw material. Then, by further increasing the output of the high-frequency magnetic field, the gallium oxide raw material melts. At this point, a temperature zone suitable for sintering is created between the raw material melt and the water-cooled crucible, where the raw material solidifies, replacing the crucible holding the melt. The center remains molten, while the sintered state remains near the cold crucible wall. While this Czochralski method reduces costs, it still cannot grow large gallium oxide single crystals (6-10 inches), failing to meet industrial needs. Furthermore, it cannot be produced continuously, limiting production efficiency. Summary of the Invention

[0006] The object of the present invention is to provide a method for growing gallium oxide single crystals by a cold crucible Czochralski method to solve the problems existing in the above-mentioned background technology.

[0007] To achieve the above objectives, this application is implemented through the following technical solutions:

[0008] A method for growing gallium oxide single crystals by a cold crucible Czochralski method comprises the following steps:

[0009] S1. Add the pre-treated gallium oxide raw material into the crucible, start the vacuum pump, extract the air in the device until the vacuum reaches the set value, and then inject argon mixed with oxygen into the device until the pressure in the device reaches the set pressure;

[0010] S2, start the high-frequency heating device to heat the gallium oxide raw material in the crucible, the heating frequency is 3×10 6 , keep the gallium oxide raw material heated to 1750℃ at a constant speed and keep it at that temperature for 1-3 hours; while heating, introduce 80-100℃ cooling water into the cooling chamber of the crucible, and the cooling water pressure is 0.1-0.3MPa;

[0011] S3, adjust the heating frequency of the high frequency heating device to 2×10 7 , heat gallium oxide to 1820-1850℃, then increase the pressure of cooling water to 1.0-1.5MPa and keep warm for 3-5 hours;

[0012] S4, start the gallium oxide crystal pulling assembly to pull the crystal, and in the process of pulling the crystal, the lifting device drives the crucible to lift synchronously, and in the process of lifting the crucible, the heating frequency of the high-frequency heating device is increased from 2×10 7 Down to 3×10 6 .

[0013] Furthermore, in step S1, the partial pressure ratio of oxygen and argon is 1:5, and the set pressure is 2.5-3 MPa.

[0014] Furthermore, in step S1, the device includes a crucible, the crucible includes a crucible body, and connected cooling cavities are provided in the bottom and side walls of the crucible body, namely a bottom cooling cavity and a side cooling cavity, and a cooling water inlet and a cooling water outlet are provided on the bottom cooling cavity and the side cooling cavity;

[0015] The overall shape of the side cooling cavity is cylindrical, the overall shape of the bottom cooling cavity is circular plate-shaped, and the ratio of the radial size of the side cooling cavity to the inner diameter of the crucible is 1:20-100.

[0016] Furthermore, a high-frequency heating device is wound around the outer side of the side wall of the crucible body, and the high-frequency heating device is connected to a power source;

[0017] The high-frequency heating device includes high-frequency heating coils, and the distances between two adjacent high-frequency heating coils in the same layer are not equal.

[0018] Furthermore, the ratio of the radial size of the side cooling cavity to the inner diameter of the crucible is 1:30-60.

[0019] Furthermore, the high-frequency heating coil extends from the upper and lower ends to the middle, and the distance between two adjacent coils gradually decreases.

[0020] Furthermore, the cross-section of the middle 1 / 3-1 / 2 axial length of the high-frequency heating coil is rectangular, and the cross-section of the remaining coils is circular.

[0021] Furthermore, in step S3, a solid gallium oxide layer with a thickness of 0.5-1 mm is formed on the inner surface of the crucible.

[0022] Furthermore, in step S4, during the crystal pulling process, the rotation speed of the seed crystal is 2.5-10 rpm.

[0023] The beneficial effects of the present invention are:

[0024] This technical solution, through the design of the crucible structure and the adjustment of the heating frequency of the high-frequency heating device, realizes the formation of a solid gallium oxide layer between the gallium oxide melt and the inner surface of the crucible during the crystal pulling process. This solid gallium oxide layer can completely isolate the internal gallium oxide from contact with the crucible body material, preventing the produced gallium oxide crystals from being contaminated.

[0025] This technical solution achieves comprehensive heating of the gallium oxide raw material in the crucible and concentrated heating in the center by adjusting the heating frequency of the high-frequency heating device, so that a solid gallium oxide layer is formed between the gallium oxide melt and the inner surface of the crucible, and a 6-10 inch gallium oxide single crystal is stretched using the Czochralski method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the device structure used in the present invention.

[0027] Description of reference numerals:

[0028] 1. Outer shell; 2. Crucible; 3. Lifting device; 4. Insulation layer; 5. High-frequency heating device; 6. Control system; 7. Crystal rising and rotating mechanism; 8. Hanging wire; 9. Isolation valve; 10. Feed port; 11. Outer shell body; 12. Neck; 13. Diameter control sensor; 14. Seed crystal chuck; 15. Seed crystal; 16. Vacuum outlet; 17. Filling gas inlet. DETAILED DESCRIPTION

[0029] The technical solutions of the present invention are described in detail below through examples. The following examples are merely exemplary and can only be used to explain and illustrate the technical solutions of the present invention, and cannot be interpreted as limiting the technical solutions of the present invention.

[0030] The present application provides a method for growing gallium oxide single crystals by a cold crucible Czochralski method, comprising the following steps:

[0031] S1. Add the pre-treated gallium oxide raw material into the crucible, start the vacuum pump, evacuate the air in the device until the vacuum reaches a set value, and then inject argon mixed with oxygen into the device to make the pressure in the device reach the set pressure. In this embodiment, the pre-treatment of the gallium oxide raw material is based on existing technology, which generally involves cleaning the gallium oxide raw material, crushing it into gallium oxide particles of corresponding size, usually with a D50 of less than 5 mm, and then washing it with dilute nitric acid to remove oxide impurities on the surface. By starting the vacuum pump, the vacuum degree in the device is reduced to below 1000, and then the device is filled with a mixed gas of 2.5-3 MPa of oxygen and argon with a partial pressure ratio of 1:5.

[0032] S2, start the high-frequency heating device to heat the gallium oxide raw material in the crucible, the heating frequency is 3×10 6Under this heating frequency, all the gallium oxide raw materials in the crucible can be heated, and the gallium oxide raw materials are kept at a uniform temperature of 1750°C at a heating rate of 10-15°C / min, and kept warm for 1-3 hours. During this process, the gallium oxide raw materials are on the verge of melting. The main purpose of keeping warm is to ensure that the temperature of the gallium oxide raw materials in the crucible is balanced; while heating, 80-100°C cooling water is introduced into the cooling chamber of the crucible, and the pressure of the cooling water is 0.1-0.3 MPa; in other embodiments of the present application, the effect of filling with steam at 0.1-0.3 MPa is better. In this step, the high temperature in the crucible is prevented from escaping and wasting energy.

[0033] S3, adjust the heating frequency of the high frequency heating device to 2×10 7 The heating frequency is increased, and the characteristics of high-step heating are utilized to concentrate the heating on the central area of ​​the gallium oxide in the crucible, while the temperature of the gallium oxide in the outer area, that is, near the inner wall of the crucible, rises slowly. The gallium oxide is heated to 1820-1850°C. This temperature refers to the temperature in the central area of ​​the crucible, while the temperature near the inner wall of the crucible is about 10°C lower. The cooling water pressure is then increased to 1.0-1.5 MPa. By increasing the cooling water pressure, the cooling capacity is enhanced, and the temperature of the gallium oxide near the inner wall of the crucible can be reduced by 300-500°C, thereby solidifying below the melting point of gallium oxide and forming a gallium oxide solid layer. In this technical solution, the thickness of the gallium oxide solid layer is optimally 0.5-1 mm. Of course, the thickness of the gallium oxide solid layer is adjusted by the temperature and pressure of the cooling water in combination with the heating frequency. If the solid layer is too thick, too much gallium oxide cannot be pulled, resulting in waste. If it is too thin, it will not serve as a barrier. The 3-5 hours of holding temperature in this step is to make the internal structure of the gallium oxide more stable.

[0034] S4, start the gallium oxide crystal pulling assembly to pull the crystal, and in the process of pulling the crystal, the lifting device drives the crucible to lift synchronously, and in the process of lifting the crucible, the heating frequency of the high-frequency heating device is increased from 2×10 7 Down to 3×10 6 The goal is to reduce the heating step so that the solid gallium oxide layer melts and enters the bottom of the crucible, where it can be pulled out along with the crystal. This portion of the gallium oxide single crystal is used for low-quality applications. During the crystal pulling process, the seed crystal rotates at a speed of 2.5-10 rpm.

[0035] like Figure 1As shown, the present application provides a device for the method of growing gallium oxide single crystals by the above-mentioned cold crucible method and the Czochralski method, including a shell 1. The shell 1 of the present device is basically the same as the shell of the existing device for producing gallium oxide by the Czochralski method, and both include a shell body and a neck 12 arranged on the upper part of the shell body 11. The outer shape of the shell body of the present application is cylindrical, with a bottom cover at the bottom and an upper cover at the top. In other embodiments of the present application or the existing technology, a structure with a square tube cross-section is also used, which also has a bottom cover at the bottom and an upper cover at the top. The selection of the specific shape is more based on the consideration of the production site rather than technical reasons.

[0036] The neck of the present application is also cylindrical, and the ratio of the outer diameter of the neck to the outer diameter of the shell body is between 1:4-8, which is determined according to actual needs.

[0037] A vacuum outlet 16 is provided at the lower side of the shell body and is connected to a vacuum pump through a pipeline. This is used to evacuate the shell during heating after feeding to prevent impurities from being generated in gallium oxide. This technology is also a conventional technology for producing gallium oxide crystals by the Czochralski method. The vacuum pump is electrically connected to the control system.

[0038] A diameter control sensor 13 is provided on the upper end surface of the housing body. This diameter control sensor is electrically connected to the control system 6 and is used to monitor the crystal diameter during the crystal pulling process. The single crystal silicon pulling assembly includes a crystal lifting and rotating mechanism 7, a suspension wire 8, a seed crystal chuck 14, and a seed crystal 15. The crystal lifting and rotating mechanism 7 is located on the top exterior of the housing. The rotating shaft of the crystal lifting and rotating mechanism passes through the housing and connects to the upper end of the suspension wire. The lower end of the suspension wire is connected to the seed crystal chuck, which in turn is connected to the seed crystal. An isolation valve 9 is provided at the junction of the housing body 11 and the neck 12. The seed crystal, seed crystal chuck, and suspension wire can all pass through the isolation valve. While the high-frequency heating device heats the gallium oxide raw material until crystal pulling is complete, the isolation valve remains closed. During crystal pulling, the isolation valve opens, and the crystal lifting and rotating mechanism is activated, allowing the seed crystal to pass through the isolation valve and into the housing body.

[0039] A filling gas inlet 17 is provided on the upper side of the neck 12 and is connected to a filling gas supply device through a pipeline. This part is a conventional component of an existing Czochralski device and can be designed by those skilled in the art according to actual needs.

[0040] The housing further comprises a lifting device 3 provided below the housing body, the lifting device 3 passing through the bottom of the housing and connected to the bottom of the crucible 2 , and the lifting device 3 is electrically connected to the control system 6 for moving the crucible up and down in the housing.

[0041] The crucible 2 of the present application includes a crucible body. In the technical solution of the present application, the material of the crucible is copper, that is, a copper crucible is used. The advantage of using a copper crucible is that the thermal conductivity is high and it is easy to process and manufacture. The bottom and side walls of the crucible body of the present application are provided with connected cooling chambers, which are respectively a bottom cooling chamber and a side cooling chamber. 2-6 cooling water inlets and cooling water outlets are provided on the bottom cooling chamber and the side cooling chamber. In the device of the present application, during the crystal pulling process, the crucible is only lifted accordingly according to the pulling speed, and does not rotate. Therefore, the crucible rotating device is not included in the present device. In other embodiments of the present application, a crucible rotating device can be added. In this case, a cooling water inlet is not provided on the side wall of the crucible, and a cooling water inlet is only provided at the bottom of the crucible body, and is installed in a sleeve-type manner with the crucible rotating device to avoid interference with the rotation of the crucible.

[0042] In the technical solution of the present application, an insulating layer 4 is provided between the inside of the shell 1 and the crucible 2 to prevent the high temperature outside the shell from affecting the production site. This structure is a conventional technology in the field. The specific insulating material used is not required in this application, and the insulating materials commonly used in the field can be used as needed.

[0043] The overall shape of the side cooling cavity of the present application is cylindrical, and the transverse thickness is the same, and the overall shape of the bottom cooling cavity is a circular plate. The ratio of the radial dimension of the side cooling cavity of the present application to the inner diameter of the crucible is 1:20-100. Preferably, the ratio of the radial dimension of the side cooling cavity to the inner diameter of the crucible is 1:30-60. This part of the technical features is the key to the present application. Only within this range can the cold crucible technology be realized. Within this range, the cooling water entering the side of the crucible can partially cool the gallium oxide in the crucible to below the melting point of gallium oxide, forming a gallium oxide crucible shape. If the ratio is too large, the thickness of the formed gallium oxide layer will be too large, which will waste gallium oxide and reduce the yield of gallium oxide single crystals. If the ratio is too small, the gallium oxide crucible layer cannot be formed.

[0044] In the technical solution of the present application, the thickness of the bottom cooling chamber is greater than that of the side cooling chamber (here, the thickness of the side cooling chamber is measured along the radial direction of the crucible), and the ratio of the bottom cooling chamber thickness to the side cooling chamber thickness is 1.2-2:1. If the ratio is too large, cooling water will accumulate in the bottom cooling chamber, resulting in excessively high cooling water temperature, making it impossible to form a gallium oxide crucible layer. If the ratio is too small, the cooling water temperature in the side cooling chamber may be too low, increasing the thickness of the gallium oxide crucible layer and thus affecting the yield. Within this ratio range of the present application, the temperature difference between the cooling water and the molten gallium oxide in the crucible is generally maintained at approximately 300-500°C, which is required for the cold crucible method of the present application.

[0045] In other embodiments of the present application, shallow grooves are evenly arranged in the upper and lower directions on the inner wall of the crucible, and the cross-section of the shallow grooves is an isosceles triangle. Such a structural design is to increase the cooling area, further improve the appearance of the cold crucible layer, and avoid the gallium oxide crucible layer from rotating and melting during the rotating crystal pulling process, thereby affecting the quality of the gallium oxide single crystal.

[0046] In the technical solution of the present application, a high-frequency heating device 5 is wound around the outside of the side wall of the crucible body, and the high-frequency heating device 5 is connected to a power source; the high-frequency heating device includes a high-frequency heating coil, and the distances between two adjacent high-frequency heating coils in the same layer are not equal. In the technical solution of the present application, the number of layers of high-frequency heating coils is between 1 and 3 layers, which is specifically determined by the inner diameter of the crucible. The larger the inner diameter of the crucible, the higher the number of layers of high-frequency heating coils required. In this embodiment, one layer of high-frequency heating coil is used as an example for explanation. The high-frequency heating coil of the present application can be used in a 2×10 6 to 2×10 7 The conversion is specifically realized by the control system. Such frequency modulation control is already an existing technology. The specific control module can be obtained by those skilled in the art through commercial channels as needed.

[0047] The high-frequency heating coils of the present application extend from the upper and lower ends toward the center, with the spacing between adjacent coils gradually decreasing. The key is that when the cold crucible method is used, the temperature at the center of the crucible's inner diameter increases, while the temperatures at other locations vary slightly. In other embodiments of the present application, the cross-section of the coils in the middle 1 / 3-1 / 2 of the axial length of the high-frequency heating coil is rectangular, while the cross-section of the remaining coils is circular. The technical design of this part takes into account the heating direction of electromagnetic induction heating to facilitate the subsequent implementation of the Czochralski method for crystallization.

[0048] As for other auxiliary components for realizing the operation of this device, they are the same as those of the existing devices and will not be described one by one here.

[0049] In other embodiments of the present application, a feed port 10 is provided at the top of the housing. A feed tube is movably inserted into the port and extends into the cavity of the crucible body. The outer end of the feed tube is connected to a feed system. This structure allows for feeding of material into the crucible during the later stages of crystal pulling, thereby resolving the problem of the existing Czochralski method, which requires cooling and then reheating the device after each pull. This not only prolongs the production cycle but also wastes energy.

[0050] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for growing gallium oxide single crystals by a cold crucible Czochralski method, characterized in that: The following steps are involved: S1. Add the pre-treated gallium oxide raw material into the crucible, start the vacuum pump, extract the air in the device until the vacuum reaches the set value, and then inject argon mixed with oxygen into the device until the pressure in the device reaches the set pressure; S2, start the high-frequency heating device to heat the gallium oxide raw material in the crucible, the heating frequency is 3×10 6 , keep the gallium oxide raw material heated to 1750℃ at a constant speed and keep it at that temperature for 1-3 hours; while heating, introduce 80-100℃ cooling water into the cooling chamber of the crucible, and the cooling water pressure is 0.1-0.3MPa; S3, adjust the heating frequency of the high frequency heating device to 2×10 7 , heat gallium oxide to 1820-1850℃, then increase the pressure of cooling water to 1.0-1.5MPa and keep warm for 3-5 hours; S4, start the gallium oxide crystal pulling assembly to pull the crystal, and in the process of pulling the crystal, the lifting device drives the crucible to lift synchronously, and in the process of lifting the crucible, the heating frequency of the high-frequency heating device is increased from 2×10 7 Down to 3×10 6 ; In step S1, the device includes a crucible, the crucible includes a crucible body, and connected cooling cavities are provided in the bottom and side walls of the crucible body, namely a bottom cooling cavity and a side cooling cavity, and a cooling water inlet and a cooling water outlet are provided on the bottom cooling cavity and the side cooling cavity; The overall shape of the side cooling cavity is cylindrical, the overall shape of the bottom cooling cavity is circular plate-shaped, and the ratio of the radial size of the side cooling cavity to the inner diameter of the crucible is 1:20-100; The high-frequency heating device includes high-frequency heating coils, and the distances between two adjacent high-frequency heating coils in the same layer are not equal; The high-frequency heating coils extend from the upper and lower ends to the middle, and the distance between two adjacent coils gradually decreases.

2. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: In step S1, the partial pressure ratio of oxygen and argon is 1:5, and the set pressure is 2.5-3 MPa.

3. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: The ratio of the radial dimension of the side cooling cavity to the inner diameter of the crucible is 1:30-60.

4. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: A high-frequency heating device is wound around the outer side of the side wall of the crucible body, and the high-frequency heating device is connected to a power source.

5. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: The cross section of the middle 1 / 3-1 / 2 axial length of the high-frequency heating coil is rectangular, and the cross section of the remaining coils is circular.

6. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: In step S3, a solid gallium oxide layer with a thickness of 0.5-1 mm is formed on the inner surface of the crucible.

7. The method for growing gallium oxide single crystals by the cold crucible Czochralski method according to claim 1, characterized in that: In step S1, during the crystal pulling process, the rotation speed of the seed crystal is 2.5-10 rpm.

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