Method for growing gallium oxide single crystal by cold crucible method and czochralski method

Abstract

The invention belongs to the technical field of semiconductor wafer manufacturing, and particularly relates to a method for growing a gallium oxide single crystal by a cold crucible method and a czochralski method, which comprises the following steps of: heating a gallium oxide raw material in a crucible at high frequency for the first time, keeping the temperature for a certain time, increasing the heating frequency to completely melt gallium oxide, and adjusting the pressure of cooling water to obtain the gallium oxide single crystal. The molten gallium oxide forms a gallium oxide solid layer on the inner wall of the crucible to isolate the contact between the gallium oxide at the center and the inner wall of the crucible, then crystal pulling is carried out, and the heating frequency is gradually reduced while crystal pulling is carried out. According to the technical scheme, through the design of the crucible structure and the adjustment of the heating frequency of the high-frequency heating device, a solid gallium oxide layer is formed between gallium oxide melt and the inner surface of the crucible in the crystal pulling process, the gallium oxide solid layer can completely isolate the contact between internal gallium oxide and a crucible body material, and the crystal pulling quality is improved. And the produced gallium oxide crystal is prevented from being polluted.

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 by a cold crucible method and a Czochralski method. Background Art

[0002] Gallium oxide has excellent material properties, and its energy saving effect is 3,400 times that of silicon and 10 times that of silicon carbide. Gallium oxide, like silicon, can be grown from liquid crystals by dissolving raw materials, but the current crystallization method uses very expensive metal iridium in the crucible that holds the molten liquid, making it difficult to reduce costs.

[0003] The currently reported growth methods of β-Ga2O3 crystals include the Czochralski method, the guided mold method, the Bridgman method, the floating zone method, etc. Among them, the crucibles used are mostly made of precious metals, mainly iridium and platinum-rhodium alloys. However, because the melting point of gallium oxide is 1793°C, and gallium oxide will volatilize and decompose at high temperatures, there is a problem that the metal gallium is enriched in the melt and corrodes the iridium crucible, affecting the growth process and crystal quality of the crystal; and the platinum-rhodium alloy crucible has a melting point very close to that of gallium oxide, so the temperature control needs to be extremely accurate, and there are problems such as rhodium pollution; in addition, because a large amount of precious metals are required for growth, the cost of crystal growth investment is high, and the cost of crucible corrosion maintenance after growth is very high; the optical floating zone method does not require precious metal crucibles for growing crystals, and its commonly used heating light sources are high-pressure xenon lamps and laser heating; ordinary optical floating zone furnaces are limited by the size of the heating heat source, and the floating zone method can only obtain φ5-10mm crystal rods. Although the crystal quality is good, it cannot meet the industrial needs of large quantities and large sizes.

[0004] Due to the high volatility of raw materials in the Czochralski method, the gallium oxide crystal growth process has gradually evolved from the Czochralski method to the guided mold method with an iridium cover and mold. Both methods require the use of an iridium crucible. Currently, the guided mold method has become the mainstream gallium oxide crystal growth method. However, due to the high cost and loss of iridium crucibles, they will be corroded and worn out after dozens of furnaces of growth, requiring re-smelting and processing. In addition, during the crystal growth process, iridium will form impurities and enter the crystal. The industry has a strong demand for the development of iridium-free methods.

[0005] In April 2022, the Nihon Keizai Shimbun reported that Japan's C&A company used the direct pulling technology of the copper crucible of Tohoku University to grow 2-inch gallium oxide single crystals, which can reduce the cost to 1 / 100 of the guided mold method. Its working principle is to fill the gallium oxide raw material in a crucible with a gap, and the high-frequency coil generates a magnetic field to directly heat the gallium oxide raw material. Then, by further increasing the output of the high-frequency magnetic field, the gallium oxide raw material will melt. At this time, a temperature zone suitable for sintering will be generated between the raw material melt and the water-cooled crucible, where the raw material solidifies, replacing the crucible that holds the melt. The center part is in a molten state, and the sintered state is maintained near the cold crucible wall. Although the direct pulling method reduces costs, it still cannot grow large-size (6-10 inch) gallium oxide single crystals, cannot meet industrial needs, and cannot be produced continuously, and production efficiency is limited. 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, and the vacuum degree reaches the set value, and then inject argon mixed with oxygen into the device to make the pressure in the device reach 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°C at a uniform rate and keep it warm for 1-3 hours; while heating, introduce 80-100°C cooling water into the cooling chamber of the crucible, and the pressure of the cooling water 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°C, 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] Further, in step S1, the device includes a crucible, the crucible includes a crucible body, and connected cooling chambers are provided at the bottom and side walls of the crucible body, namely a bottom cooling chamber and a side cooling chamber, and cooling water inlets and cooling water outlets are provided on the bottom cooling chamber and the side cooling chamber;

[0015] The overall shape of the side cooling cavity is cylindrical, the overall shape of the bottom cooling cavity is disc-shaped, and the ratio of the radial dimension 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 comprises 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 dimension 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 coil in the middle 1 / 3-1 / 2 of the 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 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 by designing the crucible structure and adjusting the heating frequency of the high-frequency heating device. The solid gallium oxide layer can completely isolate the internal gallium oxide from contact with the crucible body material, thereby 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 out by the direct pulling method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the device structure used in the present invention.

[0027] Description of reference numerals:

[0028] 1. Shell; 2. Crucible; 3. Lifting device; 4. Insulation layer; 5. High-frequency heating device; 6. Control system; 7. Crystal rising and rotating mechanism; 8. Suspension line; 9. Isolation valve; 10. Feed inlet; 11. 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 solution of the present invention is described in detail below through examples. The following examples are merely exemplary and can only be used to explain and illustrate the technical solution of the present invention, but cannot be construed as limiting the technical solution 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, extract the air in the device, and the vacuum degree reaches the 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 the existing technology, which is usually to clean the gallium oxide raw material, crush it into gallium oxide particles of corresponding sizes, usually D50 is less than 5mm, and then use dilute nitric acid to clean it to remove oxide impurities on the surface, etc., by starting the vacuum pump, the vacuum degree in the device is less than 1000, and then fill the device with a mixed gas of 2.5-3MPa 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, with 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 balance the temperature of the gallium oxide raw materials in the crucible; while heating, 80-100°C cooling water is introduced into the cooling chamber of the crucible, and the pressure of the cooling water is 0.1-0.3MPa; in other embodiments of the present application, it is better to select 0.1-0.3MPa of steam to be filled. In this step, the high temperature in the crucible is avoided from leaking out and wasting energy.

[0033] S3, adjust the heating frequency of the high frequency heating device to 2×10 7 , increase the heating frequency, and use the characteristics of high-step heating 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, and the gallium oxide is heated to 1820-1850°C. This temperature refers to the temperature in the central area of ​​the crucible, and the temperature near the inner wall of the crucible is about 10°C lower. Then increase the pressure of the cooling water to 1.0-1.5MPa. By increasing the cooling water pressure, the cooling capacity is enhanced at this time, and the temperature of the gallium oxide near the inner wall of the crucible can be reduced by 300-500°C, so that it is lower than the melting point of gallium oxide and solidified to form a gallium oxide solid layer. In this technical solution, the thickness of the gallium oxide solid layer is 0.5-1mm as the best. Of course, it is adjusted by the temperature and pressure of the cooling water introduced and 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 cannot play a barrier role. The insulation for 3-5 hours in this step is to make the internal structure of gallium oxide tend to be 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 purpose is to reduce the heating step so that the solid gallium oxide layer melts and enters the bottom of the crucible, and can be pulled out together with the crystal. This part of the gallium oxide single crystal is used for low-quality applications. During the crystal pulling process, the rotation speed of the seed crystal is 2.5-10rmp.

[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, both of which 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 due to the consideration of the production site, and does not involve 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. It is used to evacuate the shell when heating after feeding to avoid impurities in gallium oxide. This technology is also a conventional technology for producing gallium oxide crystals by the Czochralski method. The vacuum pump is connected to the control system by electrical signals.

[0038] A diameter control sensor 13 is provided on the upper end surface of the shell body. The diameter control sensor is electrically connected to the control system 6 for monitoring the crystal diameter during the crystal pulling process. The single crystal silicon pulling assembly includes a crystal rising and rotating mechanism 7, a hanging wire 8, a seed crystal chuck 14 and a seed crystal 15. The crystal rising and rotating mechanism 7 is provided on the top outer side of the shell. The rotating shaft of the crystal rising and rotating mechanism passes through the shell and is connected to the upper end of the hanging wire. The lower end of the hanging wire is connected to the seed crystal chuck, and the seed crystal chuck is connected to the seed crystal. An isolation valve 9 is provided at the connection between the shell body 11 and the neck 12. The seed crystal, the seed crystal chuck and the hanging wire can all pass through the isolation valve. Before the high-frequency heating device heats the gallium oxide raw material to pull the crystal, the isolation valve remains closed. When pulling the crystal, the isolation valve is opened, and the crystal rising and rotating mechanism is started, so that the seed crystal passes through the isolation valve and enters the shell 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 CZT device and can be designed by a person skilled in the art according to actual needs.

[0040] The housing also includes a lifting device 3 disposed below the housing body. The lifting device 3 passes through the bottom of the housing and is connected to the bottom of the crucible 2. 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 it has a high thermal conductivity and 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 a bottom cooling chamber and a side cooling chamber, respectively. 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 it is installed in a sleeve-connected manner with the crucible rotating device to avoid interference with the crucible rotation.

[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 commonly used insulating materials 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 lateral 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 gallium oxide layer formed will be too thick, wasting gallium oxide and reducing 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 cavity is greater than the thickness of the side cooling cavity (here, the thickness of the side cooling cavity is measured along the radial direction of the crucible), and the ratio of the thickness of the bottom cooling cavity to the thickness of the side cooling cavity is 1.2-2: 1. If the ratio is too large, cooling water will accumulate in the bottom cooling cavity, and the temperature of the cooling water will be too high, and the gallium oxide crucible layer cannot be realized at this time. If the ratio is too small, the cooling water temperature of the side cooling cavity may be too low, so that the thickness of the gallium oxide crucible layer increases, thereby affecting the yield. In this ratio range of the present application, it can basically ensure that the temperature difference between the cooling water and the molten gallium oxide in the crucible is about 300-500°C, so as to realize the cold crucible method technology of the present application.

[0045] In other embodiments of the present application, shallow grooves in the upper and lower directions are evenly arranged 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 outer side 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 coils of the same layer of high-frequency heating coils are not equal. In the technical solution of the present application, the number of layers of the high-frequency heating coil 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 the high-frequency heating coil 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 2×10 6 Up to 2×10 7 The conversion is specifically realized by the control system. Such frequency modulation control is already a prior art. The specific control module can be obtained by those skilled in the art through commercial channels as needed.

[0047] The high-frequency heating coil of the present application extends from the upper and lower ends to the middle, and the distance between two adjacent coils gradually decreases. The key is that when the cold crucible method is used, the temperature at the middle position of the inner diameter of the crucible increases, while the temperature at other positions is slightly different. In other embodiments of the present application, the cross-section of the coil in 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. The technical design of this part takes into account the heating direction of electromagnetic induction heating to facilitate the subsequent realization of the direct pulling method.

[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 shell body, a feed pipe is movably inserted into the feed port and extends into the cavity of the crucible body, and the outer end of the feed pipe is connected to the feed system. This structure allows feeding into the crucible in the later stage of crystal pulling, thereby solving the problem that after each straight pulling of the existing straight pulling method, the device needs to be cooled down and then heated up, which not only prolongs the production cycle but also leads to energy waste.

[0050] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present 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, and the vacuum degree reaches the set value, and then inject argon mixed with oxygen into the device to make the pressure in the device reach 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°C at a uniform rate and keep it warm for 1-3 hours; while heating, introduce 80-100°C cooling water into the cooling chamber of the crucible, and the pressure of the cooling water 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°C, 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 .

2. The method for growing gallium oxide single crystals by 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 cold crucible Czochralski method according to claim 1, characterized in that: In step S1, the device includes a crucible, the crucible includes a crucible body, and connected cooling chambers are provided at the bottom and side walls of the crucible body, namely, a bottom cooling chamber and a side cooling chamber, and a cooling water inlet and a cooling water outlet are provided on the bottom cooling chamber and the side cooling chamber; The overall shape of the side cooling cavity is cylindrical, the overall shape of the bottom cooling cavity is disc-shaped, and the ratio of the radial dimension of the side cooling cavity to the inner diameter of the crucible is 1:20-100.

4. The method for growing gallium oxide single crystals by cold crucible Czochralski method according to claim 3, 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.

5. The method for growing gallium oxide single crystals by cold crucible Czochralski method according to claim 3, 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; The high-frequency heating device comprises high-frequency heating coils, and the distances between two adjacent high-frequency heating coils in the same layer are not equal.

6. The method for growing gallium oxide single crystals by cold crucible Czochralski method according to claim 5, characterized in that: The high-frequency heating coil extends from the upper and lower ends to the middle, and the distance between two adjacent coils gradually decreases.

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

8. The method for growing gallium oxide single crystals by 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.

9. The method for growing gallium oxide single crystals by 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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