A low-defect gallium oxide seed crystal and a method for cultivating the same

Abstract

The application provides a low-defect gallium oxide seed crystal and a cultivation method thereof, and belongs to the technical field of gallium oxide seed crystal cultivation. The method is characterized in that the [010] crystal direction of the defective seed crystal is deviated from the axis of a guide mold furnace in a clockwise direction by an inclination angle of 3-8 degrees, and through the processes of crystal drawing, necking, shoulder opening and lifting, a first newly-generated crystal is obtained; the first newly-generated crystal is cut into a size of a seed crystal to serve as a new seed crystal required for secondary growth; the new seed crystal is used to continue growing the crystal according to the foregoing method to obtain a second newly-generated crystal, except that the [010] crystal direction of the new seed crystal is deviated from the axis of the guide mold furnace in a counterclockwise direction by an inclination angle of 3-8 degrees; and the second newly-generated crystal is cut into a size of a seed crystal, which is the low-defect gallium oxide seed crystal. After the two symmetrical seed crystal deflections, crystal drawing and necking, the defects of the newly-generated seed crystal are greatly reduced. The newly-generated seed crystal can be used to prepare high-quality gallium oxide single crystals.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gallium oxide single crystal growth, in particular to the technical field of gallium oxide seed crystal cultivation, and specifically relates to a low-defect gallium oxide seed crystal and a cultivation method thereof. BACKGROUND

[0002] Gallium oxide has a relatively low melting point (less than 1800℃), and can be efficiently and rapidly grown on a large scale by a melt method, breaking the restriction of slow growth rate caused by the gas phase transmission growth technology due to the high melting point of compound semiconductors. With the increasing demand for large-size, low-defect gallium oxide single crystal substrates, the process of gallium oxide grown by the melt method is gradually improved. The traditional melt method process can successfully prepare single crystal wafers suitable for industrial production. With the rapid development of device manufacturing, higher performance gallium oxide devices require better quality homogeneous substrates to achieve high lattice matching. Therefore, process improvement and modification based on the traditional melt method are an important part of the current research on gallium oxide substrate preparation.

[0003] The main factor affecting the quality of gallium oxide single crystal is the defects introduced during crystal growth. The process of gallium oxide grown by the melt method includes four processes: seeding, necking, shoulder, and main body growth. Seeding is the first step of crystal growth, in which a specific crystal seed is in contact with the melt, and the crystal is precipitated during the cooling process. Therefore, the original dislocation defects in the seed crystal can be transmitted to the newly formed crystal, and then extended into cracks, voids or even through dislocations, which form the main leakage current channel in actual device preparation, seriously degrading device performance. Existing research results show that the seeding temperature and necking width are the most critical factors for controlling the crystalline quality of the melt-grown crystal. Therefore, the seed necking should be thin and the necking stage should be long to reduce the dislocations in the crystal; the seeding process can also affect the occurrence of new dislocations, and a higher seeding temperature can not only inhibit the occurrence of new dislocations, but also play an important role in promoting the reconstruction of atomic arrangement. According to this improved crystal growth technology, most of the dislocations in the seed crystal can be effectively stopped, but the dislocations extending in the direction parallel to the growth axis can still be transmitted to the crystal interior.

[0004] The prior art effective way to inhibit the generation of seed crystal dislocation is to increase the setting temperature of the seeding, and to bake the seed crystal for a certain time before the seed crystal contacts with the melt, so as to reduce the formation and propagation of dislocations in the seed crystal by a process similar to high-temperature annealing. In addition, the driving force of melt growth is proportional to the supercooling degree, and there is only growth driving force near the solid-liquid interface, and the rest of the melt is superheated melt. When the seeding temperature is high enough, only the center of the melt above the mold shows a certain supercooling degree, so there is no other crystal nucleus generated in the seeding stage. Although a higher seeding temperature can inhibit the formation and extension of dislocations, a high seeding temperature also means a decrease in the axial temperature gradient and a decrease in the supercooling degree, resulting in a decrease in the driving force for the crystal to transfer from the liquid phase melt to the solid phase single crystal, thereby affecting the pulling rate and causing slow crystal growth. In addition, high seeding temperature has a very high inhibitory effect on the generation of new dislocations, but it does not have effective filtering capacity for the original dislocations.

[0005] In the process of growing single crystals by the melt method, the seed crystal is contacted with the melt and pulled upward to obtain sufficient supercooling degree as the growth driving force. The melt gradually moves to the low temperature zone under the traction of the seed crystal, and the atoms in the melt can form a periodic ordered arrangement according to the arrangement of the atoms in the seed crystal, and then grow into a crystal with long-range ordered structure. Due to the close contact of the seed crystal with the melt and the newly grown crystal, the dislocations in the seed crystal can extend into the newly grown crystal. The proposal of the necking technique can effectively stop most of the dislocations in the seed crystal in the neck, thereby effectively reducing the dislocation density in the crystal. In the pulling process, a narrow neck is formed by controlling the pulling rate, and most of the dislocations in the seed crystal cannot extend into the newly grown crystal in the process of axial growth due to the influence of the neck width, so the necking stage has a good stopping and filtering effect on dislocations, and the narrow neck width has a positive promoting effect on the reduction of dislocations and the growth of single crystals. However, the dislocations extending along the axial direction or approximately parallel to the axial direction can still enter the newly grown crystal through the narrow neck, and even form through dislocations, which can form the main leakage current channel in the subsequent device preparation, and seriously degrade the device performance. SUMMARY

[0006] In order to solve the above problems, the present application provides a method for cultivating low-defect gallium oxide seed crystal. The method is based on the growth platform of the guided mode method, and combines the existing seeding and necking technology to optimize the quality of the seed crystal, eliminate the axial dislocations in the seed crystal, and significantly improve the crystal quality in the crystal growth of the newly grown seed crystal, reduce the leakage current channel in the preparation of gallium oxide devices, and improve the application potential of gallium oxide devices.

[0007] Specifically, in order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] A method for cultivating low-defect gallium oxide seed crystal based on the guided mode method, comprising the following steps:

[0009] S1, placing gallium oxide powder with purity ≥ 99.999% in a crucible of a die mold furnace, fixing a seed crystal with defects on a pulling rod, rotating the seed crystal counterclockwise so that the

[010] crystal orientation of the seed crystal forms a first tilt angle of 3°-8° with the axial direction of the die mold furnace;

[0010] S2, heating the gallium oxide powder into a melt, baking the seed crystal, vertically lowering the seed crystal to contact the melt, and pulling the pulling rod upward to form a narrow neck, then reducing the pulling rate to a second pulling rate, shoulder-joining and gradually pulling to obtain a first newly grown crystal, and cutting the first newly grown crystal into a seed crystal size as a new seed crystal required for secondary growth;

[0011] S3, placing gallium oxide powder with purity ≥ 99.999% in a crucible of a die mold furnace, fixing the new seed crystal obtained in step S2 on a pulling rod, rotating the seed crystal clockwise so that the

[010] crystal orientation of the seed crystal forms a second tilt angle of 3°-8° with the axial direction of the die mold furnace;

[0012] S4, continuing to grow a second newly grown crystal according to the method in step S2, and cutting the obtained second newly grown crystal into a seed crystal size to obtain a low-defect gallium oxide seed crystal.

[0013] In a preferred embodiment, the second tilt angle is mirror-symmetric to the first tilt angle along the axial direction of the die mold furnace.

[0014] In the above method, due to the special fixing direction of the seed crystal, the dislocations remaining in step S1, which are nearly parallel to the

[010] crystal orientation, can be effectively stopped at the secondary necking position, thereby avoiding the shortcoming that the axial dislocations in the traditional die mold method extend to the newly grown crystal. A suitable seed crystal deflection angle ensures effective stopping of the dislocations and does not affect the crystallization rate of the crystal. After two symmetrical seed crystal deflections, seed crystal pulling, and two necking, the second newly grown seed crystal has high crystal quality and can be used for growing low-defect high-quality gallium oxide single crystals in combination with the growth scheme of the traditional die mold method.

[0015] In a preferred embodiment, step S1 includes the step of placing 3-5 g of gallium oxide powder above the mold, and in step S2, the seed crystal is vertically lowered to contact the melt when the gallium oxide powder begins to melt.

[0016] In a preferred embodiment, the amount of the seed crystal with defects used in step S1 is 8-12 g.

[0017] In a preferred embodiment, the length of the narrow neck in step S2 is 18-22 mm, and the cross-sectional area is 1-2 mm 2 .

[0018] The narrow neck formed by changing the pulling rate in the present application is thinner and longer, with a length of 18-22 mm and a cross-sectional area of 1-2 mm 2 The formation of the elongated narrow neck can effectively inhibit the extension of more dislocations, further optimizing the quality of the newly born crystal.

[0019] In a preferred embodiment, the temperature at which the gallium oxide powder is heated to a melt in step S2 is 1900-2100℃, and the baking time of the seed crystal is 10-20 min.

[0020] When the gallium oxide powder is heated to a melt and the temperature reaches above 1900℃, the superheated melt can avoid the formation of new crystal nuclei in the melt during crystal growth, effectively inhibiting the formation of polycrystals.

[0021] In a preferred embodiment, the first pulling rate in step S2 is 6-8 mm / h.

[0022] In a preferred embodiment, the second pulling rate in step S2 is 2-3 mm / h. The low-defect gallium oxide seed crystal cultivated by the method according to any one of the above embodiments of the present application for growing a gallium oxide single crystal can significantly improve the quality of the gallium oxide single crystal and reduce the leakage current path in the preparation of gallium oxide devices.

[0023] Compared with the prior art, the present application has the following advantages: (1) From the perspective of substrate preparation, the low-defect seed crystal cultivated by the present application has the characteristics of few defects and no axial dislocations, greatly reducing the defects from the seed crystal in the newly born crystal during crystal growth. (2) From the perspective of the complexity of the implementation scheme, the cultivation method of the low-defect seed crystal in the present application is based on the guided mode method device used for crystal growth, which has very similar operation procedures and parameter settings as crystal growth, without the need to introduce new equipment and materials, and without the need to add new complex processes and components. (3) From the perspective of cost control, the low-defect seed crystal cultivation method of the present application can cultivate high-quality seed crystals for subsequent crystal growth, saving the procurement cost of seed crystals, reducing the external dependence of high-quality gallium oxide single crystal preparation, improving the quality and yield of single crystals, reducing the cost problems such as raw material loss, precious metal loss, and energy loss caused by deteriorated crystal quality. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure A is a schematic diagram of counterclockwise deflection, and Figure B is a schematic diagram of clockwise deflection. DETAILED DESCRIPTION

[0025] The technical solutions of the present application are clearly and completely described below in combination with the embodiments, so that those skilled in the art can fully understand the present application. Obviously, the described embodiments are only a part of the preferred embodiments of the present application, rather than all the embodiments. Any equivalent transformation or replacement of the following embodiments made by those skilled in the art without creative labor is within the protection scope of the present application.

[0026] Embodiment 1

[0027] This embodiment adopts the method of combining seed crystal deflection and secondary necking to inhibit the extension of dislocations in the seed crystal, and the specific method comprises the following steps:

[0028] S1, using a conventional die mold furnace, high-purity (5N) gallium oxide powder is placed in an iridium crucible, and 4g of gallium oxide powder is placed above the mold for judging the temperature of the upper surface of the mold. 10g of a seed crystal with defects is fixed on a pulling rod, as shown in FIG. A of the drawings, the seed crystal is rotated counterclockwise, so that the

[010] crystal direction of the seed crystal presents a first inclination angle of 3° with the axial direction of the die mold furnace. Figure 1

[0029] S2, the iridium crucible is heated to 2000°C by medium frequency induction, when the gallium oxide powder above the mold begins to melt, the seed crystal is baked for 15 minutes, then the transmission device of the pulling rod is used to make the seed crystal which has been inclined clockwise vertically descend and contact with the melt, and then it is pulled upward at a rate of 8mm / h to form a narrow neck with a length of 20mm and a cross-sectional area of 1mm 2 . Then the pulling rate is reduced to 3mm / h, the shoulder is released, and the first newly grown crystal is gradually pulled. This step can inhibit the transmission of part of the dislocations in the seed crystal. The first newly grown crystal is cut into a seed crystal size as a new seed crystal required for secondary growth.

[0030] S3, high-purity (5N) gallium oxide powder is again placed in the crucible of the die mold furnace, and the new seed crystal obtained in step S2 is fixed on the pulling rod, as shown in FIG. B of the drawings, the new seed crystal is rotated clockwise, so that the

[010] crystal direction of the new seed crystal presents a second inclination angle of 3° counterclockwise deviated from the axial direction of the furnace body. The second inclination angle and the first inclination angle are mirror-symmetric along the axial direction of the die mold furnace. Figure 1

[0031] S4, repeat the same die mold process flow as step S2 to perform the process of seeding, necking, releasing the shoulder and pulling the crystal to grow the second newly grown crystal. The second newly grown crystal obtained is cut into a seed crystal size, which is a low-defect gallium oxide seed crystal.

[0032] Embodiment 2

[0033] ​​The embodiment adopts the combination of seed crystal deflection and secondary necking to inhibit the dislocation extension in the seed crystal, and the specific method comprises the following steps:

[0034] S1, using a conventional mold furnace, high purity (6N) gallium oxide powder is put into an iridium crucible, 3g of gallium oxide powder is placed above the mold for judging the temperature of the upper surface of the mold. 8g of the seed crystal with defects is fixed on the pulling rod, as shown in FIG. A of the drawings, the seed crystal is rotated counterclockwise, and the

[010] crystal direction of the seed crystal is presented with a first inclination angle of 5° with the axial direction of the mold furnace. Figure 1

[0035] S2, the iridium crucible is heated to 1900°C by using intermediate frequency induction, when the gallium oxide powder above the mold begins to melt, the seed crystal is baked for 20 minutes, the transmission device of the pulling rod is used to make the seed crystal which has been inclined clockwise vertically descend and contact with the melt, and is pulled upward at a rate of 7mm / h to form a narrow neck with a length of 18mm and a cross-sectional area of 1mm 2 Then the pulling rate is reduced to 2mm / h, the shoulder is released, and the first newly grown crystal is gradually pulled. This step can inhibit the transmission of part of the dislocations in the seed crystal. The first newly grown crystal is cut into a seed crystal size as a new seed crystal required for secondary growth.

[0036] S3, high purity (6N) gallium oxide powder is again put into the crucible of the mold furnace, the new seed crystal obtained in step S2 is fixed on the pulling rod, as shown in FIG. B of the drawings, the seed crystal is rotated clockwise, and the

[010] crystal direction of the new seed crystal is presented with a second inclination angle of 5° counterclockwise deviated from the axial direction of the furnace body. The second inclination angle and the first inclination angle are mirror-symmetric along the axial direction of the mold furnace. Figure 1

[0037] S4, the same mold method process flow as step S2 is repeated, and the processes of seeding, necking, releasing the shoulder and pulling the crystal are performed to grow the second newly grown crystal. The second newly grown crystal obtained is cut into a seed crystal size, which is a low-defect gallium oxide seed crystal.

[0038] Example 3

[0039] The embodiment adopts the combination of seed crystal deflection and secondary necking to inhibit the dislocation extension in the seed crystal, and the specific method comprises the following steps:

[0040] S1, using a conventional mold furnace, high purity (5N) gallium oxide powder is put into an iridium crucible, 5g of gallium oxide powder is placed above the mold for judging the temperature of the upper surface of the mold. 12g of the seed crystal with defects is fixed on the pulling rod, as shown in FIG. A of the drawings, the seed crystal is rotated counterclockwise, and the

[010] crystal direction of the seed crystal is presented with a first inclination angle of 8° with the axial direction of the mold furnace. Figure 1

[0041] ​​​S2. The iridium crucible is heated to 2100℃ using medium-frequency induction heating. When the gallium oxide powder above the mold begins to melt, the seed crystal is baked for 10 minutes. Using the lifting rod transmission device, the seed crystal, which has been tilted clockwise, is vertically lowered to contact the melt, and then pulled upwards at a rate of 6mm / h to form a length of 22mm and a cross-sectional area of ​​2mm². 2 The narrow neck is then formed. The pulling rate is reduced to 2.5 mm / h, the shoulder is formed, and the crystal is gradually pulled to obtain the first nascent crystal. This step suppresses the propagation of some dislocations in the seed crystal. The first nascent crystal is then cut to seed crystal size to serve as the new seed crystal for secondary growth.

[0042] S3. Place high-purity (5N) gallium oxide powder again into the crucible of the mold furnace, and fix the new seed crystal obtained in step S2 onto the lifting rod, as shown. Figure 1 As shown in Figure B, rotating the seed crystal clockwise causes the

[010] crystal orientation of the new seed crystal to deviate counterclockwise from the axial direction of the furnace body, presenting a second tilt angle of 8°. The second tilt angle is mirror-symmetrical to the first tilt angle along the axial direction of the furnace body.

[0043] S4. Repeat the same mold-guided process as in step S2, performing the processes of crystal pulling, necking, shoulder formation, and crystal lifting to grow a second nascent crystal. Cut the resulting second nascent crystal into seed crystal size, which is the low-defect gallium oxide seed crystal.

[0044] During the mode-guided growth of gallium oxide single crystals, dislocations in the seed crystal and new dislocations generated upon contact with the melt can extend into the newly formed crystal along their fixed directions, resulting in a high number of dislocations in the newly formed crystal. According to... Figure 1 It is known that while a single necking can stop the propagation of most dislocations, it cannot effectively intercept axial dislocations. A small number of dislocations can still enter the nascent crystal through the narrow neck, leading to the growth of fatal defects that can form leakage current channels. Therefore, the present invention employs two mirror-image deflection necking techniques to address the propagation of axial dislocations. The first necking technique stops dislocation defects other than axial dislocations at the narrow neck, thereby obtaining a nascent crystal III (e.g., axial dislocations) that is only affected by the propagation of axial dislocations. Figure 1 (As shown in Figure A). Subsequently, using this newly formed crystal III as a seed crystal, a second crystal necking was performed in a mirror-symmetric manner with the first deflection. This effectively stopped the axial dislocations left over from the previous step at the narrow neck, thus achieving effective suppression of all dislocations and obtaining a nearly defect-free seed crystal V (as shown in Figure A). Figure 1 (As shown in Figure B).

[0045] The above merely provides the preferred embodiments of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement or improvement made by any person skilled in the art based on the present application should be included in the protection scope of the present application.

Claims

1. A method for growing low-defect gallium oxide seed crystals based on the edge- mode method, characterized by, The method comprises the following steps: S1, placing gallium oxide powder with purity ≥99.999% in a crucible of a mold guiding furnace, fixing a seed crystal with defects on a pulling rod, rotating the seed crystal counterclockwise so that the [010] crystal orientation of the seed crystal forms a first inclination angle of 3°-8° with the axial direction of the mold guiding furnace; S2, heating the gallium oxide powder into a melt, baking a seed crystal; vertically lowering the seed crystal into contact with the melt and pulling the pulling rod upward at a first pulling rate to form a narrow neck; subsequently reducing the pulling rate to a second pulling rate, shoulder-on and gradually pulling a first newly born crystal; cutting the first newly born crystal into a size of the seed crystal as a new seed crystal required for secondary growth; the length of the narrow neck is 18-22 mm, and the cross-sectional area is 1 mm 2 ; S3, placing gallium oxide powder with purity ≥99.999% in the crucible of the mold guiding furnace, fixing the new seed crystal obtained in step S2 on the pulling rod, rotating the seed crystal clockwise so that the [010] crystal orientation of the seed crystal forms a second inclination angle of 3°-8° with the axial direction of the mold guiding furnace; the second inclination angle is mirror-symmetrical to the first inclination angle along the axial direction of the mold guiding furnace; S4, continuing to grow a second new crystal according to the method in step S2; cutting the obtained second new crystal into the size of a seed crystal to obtain a low-defect gallium oxide seed crystal.

2. The method for growing low-defect gallium oxide seed crystal based on the guided mode method according to claim 1, characterized by, In step S1, the step of placing 3-5 g of gallium oxide powder above the mold is included, and in step S2, the seed crystal is vertically lowered to contact the melt when the gallium oxide powder starts to melt.

3. The method for growing low-defect gallium oxide seed crystal based on the guided-mode method according to claim 1, characterized by, In step S1, the amount of the seed crystal with defects is 8-12 g.

4. The method for growing low-defect gallium oxide seed crystal based on the guided-mode method according to claim 1, characterized by, In step S2, the temperature for heating the gallium oxide powder into a melt is 1900-2100 °C, and the baking time of the seed crystal is 10-20 min.

5. The method for growing low-defect gallium oxide seed crystal based on the guided-mode method according to claim 1, characterized by, In step S2, the first pulling rate is 6-8 mm / h.

6. The method for growing low-defect gallium oxide seed crystal based on the guided-mode method according to claim 1, characterized by, In step S2, the second pulling rate is 2-3 mm / h.

7. A low-defect gallium oxide seed crystal cultivated by the method according to any one of claims 1-6.

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