Method for improving thickness and quality uniformity of crystal growth, repair method, and crystal

Abstract

The application discloses a method for improving the thickness and quality uniformity of crystal growth, a repairing method and a crystal. The method comprises the following steps: providing a growth system required for growing a group III nitride crystal by a flux method liquid phase epitaxy, forming a temperature gradient between a top layer part and a bottom layer part of a molten growth material, so as to form a closed circulation flow field of the molten growth material and a nitrogen source in the molten growth material; and in an initial stage of the growth of the group III nitride crystal, adjusting the temperature gradient to a positive temperature gradient, and then alternately switching the temperature gradient between the positive temperature gradient and a negative temperature gradient, so as to change the nitrogen source concentration distribution and the growth rate of different regions of a growth interface of the group III nitride crystal, until the growth interface of the group III nitride crystal presents as a flat surface. The method provided by the application is simple in operation and wide in application range, and can reduce the production cost and improve the yield of the crystal.

Description

Technical Field

[0001] This invention specifically relates to a method, repair method, and crystal for improving the thickness and uniformity of crystal growth, belonging to the field of semiconductor crystal growth technology. Background Technology

[0002] Gallium nitride (GaN) materials, with their excellent properties such as wide bandgap, high electron mobility, and high breakdown electric field, have extremely broad application prospects in optoelectronics and power devices. The flux method has shown significant advantages in the preparation of large-size, extremely low dislocation density GaN single crystals.

[0003] However, current methods for growing gallium nitride using flux methods often encounter issues with uneven crystal growth thickness and mass. This inhomogeneity can lead to unbalanced stress distribution within the crystal, inducing crack formation and promoting the propagation and accumulation of crystal defects such as dislocations, thereby degrading the overall crystal quality. As crystal size continues to increase, the problem of growth uniformity will become more prominent, becoming a key bottleneck restricting improvements in crystal quality and size, and directly affecting the performance and reliability of devices based on this type of substrate. Therefore, ensuring the uniformity of crystal growth thickness and mass is extremely important.

[0004] However, current technologies are mainly designed for crystal growth of a single melt, controlling a uniform temperature gradient to achieve a relatively uniform growth rate. That is, they can only regulate the overall growth rate, but cannot control the local growth rate of the crystal. The uniformity of crystal thickness cannot be specifically corrected and regulated during the growth process according to the actual growth situation. This is mainly because current technologies can maintain a consistent horizontal temperature gradient, but cannot detect the number and state of internal eddy currents. The growth conditions in the melt are like a black box, and the internal melt flow and mass transfer cannot be controlled. Summary of the Invention

[0005] The main objective of this invention is to provide a method, repair method, and crystal for improving the uniformity of crystal growth thickness and quality. By utilizing the heat source inherent in the liquid phase epitaxial growth system to form a specific temperature gradient, the number and morphology of eddies within the liquid phase epitaxial growth system can be effectively controlled, thereby obtaining a specific mass transfer trajectory / mode. Combined with real-time monitoring of crystal thickness, the local growth rate, thickness, and quality of the crystal can be effectively controlled during the growth process. It can also perform secondary growth on crystals with uneven thickness, optimize their flatness, improve crystal quality, and reduce production costs, thereby overcoming the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] The first aspect of this invention provides a method for improving the thickness and uniformity of group III nitride crystal growth, comprising:

[0008] A growth system is provided for the flux-assisted liquid phase epitaxial growth of group III nitride crystals, in which the top layer of the molten growth material is in a first temperature zone formed by heating by a first heat source, and the bottom layer is in a second temperature zone formed by heating by a second heat source. The temperature difference between the first heat source and the second heat source is ΔT∈(50~250)℃, so as to form a temperature gradient between the top and bottom layers of the molten growth material, and to form a closed-loop flow field of the molten growth material and the nitrogen source within the molten growth material.

[0009] Furthermore, in the initial stage of group III nitride crystal growth, the temperature gradient is adjusted to a positive temperature gradient, and then the temperature gradient is alternately switched between a positive temperature gradient and a negative temperature gradient to change the nitrogen source concentration distribution and growth rate in different regions of the growth interface of the group III nitride crystal until the growth interface of the group III nitride crystal presents a flat surface.

[0010] When the temperature gradient is positive, the trajectory of the closed-loop flow field is: edge region of the top layer → middle region of the top layer → middle region of the bottom layer → edge region of the bottom layer → edge region of the top layer. The nitrogen source concentration on the surface of the seed crystal in the molten growth material decreases in the direction gradient from the middle region to the edge region. When the temperature gradient is negative, the trajectory of the closed-loop flow field is: edge region of the bottom layer → middle region of the bottom layer → middle region of the top layer → edge region of the top layer → edge region of the bottom layer. The nitrogen source concentration on the surface of the seed crystal in the molten growth material increases in the direction gradient from the middle region to the edge region.

[0011] Wherein, the temperature gradient = temperature of the top part - temperature of the bottom part, the liquid surface of the molten growth material is located in the top part, the seed crystal required for crystal growth is located in the bottom part of the molten growth material, and the second heat source keeps the temperature of the bottom part at the crystal growth temperature.

[0012] Furthermore, the method for improving the uniformity of crystal growth thickness and quality includes: keeping the temperature of the bottom layer of the molten growth material constant, and changing the temperature of the top layer so that the temperature gradient alternates between a positive temperature gradient and a negative temperature gradient.

[0013] In a preferred embodiment, the method for improving the uniformity of the growth thickness and quality of group III nitride crystals includes: periodically alternating the temperature gradient between a positive temperature gradient and a negative temperature gradient, wherein one complete alternation cycle of the positive and negative temperature gradients constitutes a growth cycle, and the positive and negative temperature gradients are maintained for the same time in each growth cycle.

[0014] Furthermore, within each growth cycle, the holding time of the positive or negative temperature gradient is 3 to 5 hours. The holding time of the positive or negative temperature gradient is usually determined according to the growth rate. For example, when the crystal growth rate is high, a shorter holding time can be selected, and when the growth rate is low, a longer holding time can be selected. However, the holding time should not be too long, otherwise the increased thickness difference will affect the generation of internal stress in the crystal, causing the crystal to crack.

[0015] Furthermore, the method for improving the uniformity of crystal growth thickness and quality includes: gradually decreasing the holding time of the growth cycle in a linear trend. For example, the holding time of the positive or negative temperature gradient in each growth cycle is Y = 5-0.5X hours, where X represents the number of growth cycle changes.

[0016] Furthermore, the growth container containing the molten growth material and the seed crystal is placed in a growth chamber with a first space and a second space that have independent heat exchange. The top of the growth container and the top layer of the molten growth material are located in the first space, and the bottom of the growth container and the bottom layer of the molten growth material are located in the second space.

[0017] A first heat source is provided in the first space, which forms a first temperature zone in the first space. A second heat source is provided in the second space, which forms a second temperature zone in the second space. The second heat source keeps the temperature of the bottom layer at the temperature required for the growth of group III nitride crystals. By adjusting the temperature of the first heat source, the temperature gradient is alternately switched between a positive temperature gradient and a negative temperature gradient.

[0018] A second aspect of this invention provides a method for repairing group III nitride crystals with uneven thickness, comprising:

[0019] A growth system is provided for the flux-assisted liquid phase epitaxial growth of group III nitride crystals. A group III nitride crystal with uneven thickness is placed in a molten growth material. The top part of the molten growth material is in a first temperature zone formed by heating by a first heat source, and the bottom part is in a second temperature zone formed by heating by a second heat source. The temperature difference between the first heat source and the second heat source is ΔT∈(50~250)℃, so as to form a temperature gradient between the top part and the bottom part of the molten growth material. A closed-loop flow field of molten growth material and nitrogen source is formed in the molten growth material.

[0020] Furthermore, based on the thickness distribution of the growth interface of the group III nitride crystal, the temperature gradient is adjusted to a positive or negative temperature gradient to change the nitrogen source concentration distribution and growth rate in different regions of the growth interface of the group III nitride crystal, and to make the growth interface of the group III nitride crystal with uneven thickness distribution appear as a flat surface.

[0021] When the growth interface of the group III nitride crystal is a convex interface, the temperature gradient is adjusted to a negative temperature gradient. At this time, the trajectory of the closed loop flow field is: the edge region of the bottom part → the middle region of the bottom part → the middle region of the top part → the edge region of the top part → the edge region of the bottom part. The nitrogen source concentration on the crystal surface in the molten growth material increases in a gradient from the middle region to the edge region.

[0022] When the growth interface of the group III nitride crystal is a concave interface, the temperature gradient is adjusted to a positive temperature gradient. At this time, the trajectory of the closed loop flow field is: edge region of the top part → middle region of the top part → middle region of the bottom part → edge region of the bottom part → edge region of the top part. The nitrogen source concentration on the crystal surface in the molten growth material decreases in the direction gradient from the middle region to the edge region.

[0023] Wherein, the temperature gradient = temperature of the top part - temperature of the bottom part, the liquid surface of the molten growth material is located in the top part, the uneven thickness of the group III nitride crystal is located in the bottom part of the molten growth material, and the temperature of the bottom part is maintained at the crystal growth temperature.

[0024] Furthermore, the method for repairing the unevenly thick Group III nitride crystal includes: keeping the temperature of the second heat source constant, and adjusting the temperature of the first heat source to adjust the temperature gradient to a positive or negative temperature gradient.

[0025] In a preferred embodiment, the method for repairing the uneven thickness of the group III nitride crystal includes: alternating the temperature gradient between a positive temperature gradient and a negative temperature gradient until the growth interface of the group III nitride crystal becomes a flat surface.

[0026] Furthermore, the method for repairing the uneven thickness of the group III nitride crystal includes: periodically alternating the temperature gradient between a positive temperature gradient and a negative temperature gradient, with one complete alternation cycle of the positive and negative temperature gradients constituting one growth cycle, and the positive and negative temperature gradients being maintained for the same time.

[0027] Furthermore, within each growth cycle, the holding time for the positive or negative temperature gradient is 3 to 5 hours. The holding time for the positive or negative temperature gradient is usually determined by the growth rate. For example, when the crystal growth rate is high, a shorter holding time can be chosen, and when the growth rate is low, a longer holding time can be chosen. However, the holding time should not be too long, otherwise the increased thickness difference will affect the generation of internal stress in the crystal, leading to crystal cracking. It should be noted that the crystal growth rate can be obtained by monitoring changes in crystal thickness.

[0028] Furthermore, the method for repairing the uneven thickness of the group III nitride crystal includes: reducing the holding time of the growth cycle in stages with a linear trend, for example, the holding time of the positive or negative temperature gradient of each growth cycle is Y = 5-0.5X hours, where X represents the number of changes in the growth cycle.

[0029] Furthermore, in the initial stage of group III nitride crystal growth, the temperature gradient is adjusted to a positive temperature gradient.

[0030] A third aspect of the present invention provides a group III nitride crystal obtained by the method for improving the uniformity of thickness and quality of group III nitride crystal growth, or by the method for repairing group III nitride crystals with non-uniform thickness.

[0031] Compared with the prior art, the advantages of the present invention include:

[0032] The present invention provides a method for improving the uniformity of crystal growth thickness and quality, and a crystal repair method. By controlling the alternation of positive and negative temperature gradients, the uniformity of crystal growth thickness can be regulated. Furthermore, monitoring the crystal thickness during the growth process makes the growth process more controllable. This method is applicable to all flux-based or liquid-phase methods of different sizes.

[0033] This invention provides a method for improving the uniformity of crystal growth thickness and quality, as well as a crystal repair method. By changing the temperature gradient of the heat source, the local growth rate of the crystal can be effectively controlled, thereby improving the uniformity of crystal growth thickness and crystal quality. Furthermore, by alternating the local high and low growth rates, this invention can further improve the flatness of the crystal surface and reduce crystal warping and cracking.

[0034] The present invention provides a method for improving the uniformity of crystal growth thickness and quality, as well as a crystal repair method. It can also perform secondary growth compensation on obtained crystals with uneven thickness distribution to obtain relatively flat crystals.

[0035] The present invention provides a method for improving the uniformity of crystal growth thickness and quality, as well as a crystal repair method. The operation method is simple, the application range is wide, and it can reduce production costs and improve crystal yield. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a flux-based liquid phase epitaxial growth apparatus.

[0037] Figure 2 This is a typical embodiment of the present invention, showing the internal closed-loop flow field and nitrogen concentration distribution of gallium-sodium molten metal under a positive temperature gradient.

[0038] Figure 3 This is a typical embodiment of the present invention, which provides the morphology of gallium nitride crystals obtained by growing gallium-sodium metal melt under positive temperature gradient conditions;

[0039] Figure 4 This is a typical embodiment of the present invention, showing the internal closed-loop flow field and nitrogen concentration distribution of gallium-sodium molten metal under a negative temperature gradient.

[0040] Figure 5 This is a typical embodiment of the present invention, which provides the morphology of gallium nitride crystals obtained by growing gallium-sodium metal melt under negative temperature gradient conditions;

[0041] Figure 6 This is a typical embodiment of the present invention, which provides a schematic diagram of the growth principle of gallium nitride crystal. Detailed Implementation

[0042] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate the technical solution, its implementation process, and principles in conjunction with the accompanying drawings and specific embodiments. Unless otherwise specified, the growth system (including growth equipment and growth raw materials, etc.) required for flux-driven liquid phase epitaxial growth of group III nitride crystals, and the monitoring device for detecting the thickness distribution of the crystal growth interface during crystal growth, involved in the embodiments of this invention, are known in the art and will not be explained redundantly here.

[0043] The following section will take gallium nitride (GaN) crystal, a typical group III nitride crystal, as an example to provide a detailed introduction and explanation of its growth process.

[0044] The flux-assisted gallium nitride crystal growth apparatus used in this embodiment of the invention is a conventional apparatus structure in the art, such as... Figure 1As shown, it mainly includes: a growth furnace, a first heat source, a second heat source, a heat insulation mechanism, a crucible (i.e., a typical growth container), and an in-situ monitoring mechanism. The growth furnace and the in-situ monitoring mechanism are mounted on a support frame. The growth furnace has a growth chamber that provides the growth environment. The inner wall of the growth furnace is provided with a heat insulation layer. The first heat source, the second heat source, the heat insulation mechanism, and the crucible are all located in the growth chamber. The heat insulation mechanism divides the growth chamber into a first space and a second space with independent heat exchange. The first space is located above the second space along the axial direction of the growth chamber. The first heat source is located in the first space and forms a first temperature zone with a first temperature in the first space. The second heat source is located in the second space and forms a second temperature zone with a second temperature in the second space. The top of the crucible is located in the first space, the bottom is located in the second space, and the mouth of the crucible is located at the top. The top of the growth furnace has an observation window. The in-situ monitoring mechanism corresponds to the observation window and is used to measure the thickness distribution of the crystal growth interface in the crucible.

[0045] The growth furnace, first heat source, second heat source, and insulation layer are all cylindrical structures. The growth furnace with insulation layer is a known structure in the art, and the specific structure and equipment model of the growth furnace are not limited here. The first heat source and second heat source can be conventional electrothermal heating mechanisms or other heating mechanisms, and the insulation mechanism can be made of known organic or inorganic insulation materials, such as ceramic fiber materials.

[0046] Preferably, the flux-based gallium nitride crystal growth apparatus further includes a growth material supply mechanism for adding molten growth material to the crucible and a nitrogen source supply mechanism for introducing a nitrogen source into the growth furnace. As known to those skilled in the art, the molten growth material required for flux-based liquid-phase epitaxial growth of gallium nitride crystals can be a gallium-sodium metal melt containing fluxes such as metallic gallium and metallic sodium, and optional additives such as carbon. The specific composition of this liquid-phase growth material is not a direction of improvement of the present invention, and therefore will not be specifically described. It can adopt the proportions and compositions known in the art. The gas-phase growth material can be nitrogen or ammonia, etc.

[0047] In a typical implementation, the method for growing gallium nitride crystals specifically includes: placing gallium-sodium metal melt and seed crystal in a crucible (i.e., a typical growth container), forming a high-pressure nitrogen atmosphere in the growth chamber, and providing other conditions required for growing gallium nitride crystals in the growth chamber (the conventional growth conditions for flux-driven liquid phase epitaxial growth of gallium nitride are known in the art and will not be described in detail here), thereby achieving flux-driven liquid phase epitaxial growth of gallium nitride crystals.

[0048] The present invention places the top layer of the gallium-sodium metal melt in a first temperature zone formed by heating by a first heat source, and the bottom layer in a second temperature zone formed by heating by a second heat source. The temperature difference between the first heat source and the second heat source is ΔT∈(50~250)℃, forming a temperature gradient (i.e., temperature gradient, the same below) between the top layer and the bottom layer of the gallium-sodium metal melt. A closed-loop flow field of gallium-sodium metal melt and nitrogen source is formed in the gallium-sodium metal melt.

[0049] Furthermore, in the initial stage of gallium nitride crystal growth, the temperature gradient is adjusted to a positive temperature gradient, and then the temperature gradient is periodically switched between a positive temperature gradient (i.e., a positive temperature gradient) and a negative temperature gradient (i.e., a negative temperature gradient) to change the nitrogen source concentration distribution and growth rate in different regions of the gallium nitride crystal growth interface until the gallium nitride crystal growth interface presents a flat surface.

[0050] In this embodiment of the invention, the temperature gradient of the gallium-sodium molten metal is mainly achieved by controlling the temperatures of the first and second heat sources. The temperature of the crucible wall cannot be precisely controlled; the temperature gradient between the first and second heat sources can reach hundreds of degrees Celsius, but the temperature gradient transferred to the crucible is usually very small, only about 10°C. Therefore, the controlled temperature gradient between the first and second heat sources must be greater than 50°C; otherwise, the temperature difference transferred to the crucible surface will not be significant. That is, the temperature difference or temperature gradient involved in this invention is 50°C to 250°C, excluding 50°C, and must be greater than 50°C.

[0051] It should be noted that the flux-based liquid phase epitaxial growth apparatus for gallium nitride crystals based on this invention is known in the art. There is heat loss between the first heat source, the second heat source and the molten gallium-sodium metal and other molten growth materials. However, once the growth apparatus is determined, the heat loss is generally relatively stable. This invention does not discuss heat loss and heat transfer efficiency.

[0052] Specifically, when preparing gallium-sodium metal melt, too low sodium content will reduce the overall growth rate, while too high sodium content may cause C-axis growth to be too fast, resulting in incomplete merging between crystal islands, which in turn leads to the formation of voids and reduces the growth quality of the crystal. Therefore, it is necessary to control the sodium content between 60wt% and 80wt% to improve the overall growth rate of the crystal.

[0053] Specifically, a higher temperature on the upper surface (i.e., the liquid surface) of the gallium-sodium molten metal in the crucible facilitates the dissolution of the nitrogen source, while a lower temperature at the bottom of the seed crystal helps the nitrogen source to be transported downwards to the seed crystal, preventing the seed crystal from dissolving back and promoting crystal growth. In the initial stage of gallium nitride crystal growth, the temperature T1 of the first heat source needs to be controlled to be higher than the temperature T2 of the second heat source. The crystal growth region is always within the second temperature range; therefore, the temperature of the second heat source needs to be maintained at T2 ∈ (700℃~900℃). For each complete growth cycle, the temperature of the second heat source must remain constant to maintain stable gallium nitride crystal growth.

[0054] It should be noted that the temperature of the first temperature zone can be approximated as the temperature of the first heat source, and the temperature of the second temperature zone can be approximated as the temperature of the second heat source. The temperature gradient between the top and bottom parts of the gallium-sodium molten metal is consistent with the temperature gradient trend between the first and second temperature zones. That is, when there is a positive temperature gradient between the top and bottom parts of the gallium-sodium molten metal, the temperature of the first heat source is greater than the temperature of the second heat source, and the first and second heat sources also have a positive temperature gradient. When there is a negative temperature gradient between the top and bottom parts of the gallium-sodium molten metal, the temperature of the first heat source is less than the temperature of the second heat source, and the first and second heat sources also have a negative temperature gradient. Here, the temperature gradient between the first and second heat sources is the temperature of the first heat source minus the temperature of the second heat source.

[0055] For details, please refer to Figure 6 In this embodiment of the invention, each growth cycle of the gallium nitride crystal includes two growth stages: a first growth stage (i.e., stage one) and a second growth stage (i.e., stage two).

[0056] First growth stage: To avoid seed crystal remelting, the temperature gradient between the first and second heat sources must be set to a positive temperature gradient: T1 > T2, T2 ∈ (700℃~900℃), so that the seed crystal is in the optimal growth temperature range. It should be noted that the temperature T1 of the first heat source must be greater than the temperature T2 of the second heat source. The larger the difference between T1 and T2, the faster the nitrogen source transfer rate and the greater the growth rate. This invention requires that the temperature gradient (i.e., temperature difference) between the first and second heat sources be greater than 50℃. Preferably, the temperature gradient (i.e., the aforementioned temperature difference ΔT, the same below) between the first and second heat sources is 50℃~250℃. Research has found that if the temperature difference between the first and second heat sources is too small, it is difficult to provide sufficient driving force for the gallium-sodium metal melt in the crucible to effectively transfer the melt, and it is also difficult to effectively promote the generation of eddies in the gallium-sodium metal melt. On the other hand, if the temperature gradient is too large, the equipment cannot meet the temperature gradient requirement. Furthermore, conventional temperature gradients are difficult to form a controllable flow field in the gallium-sodium metal melt.

[0057] like Figure 2As shown, the transport paths of the components in the gallium-sodium metal melt are as follows: converging from the edge region near the crucible wall of the gallium-sodium metal melt surface to the middle region along the central axis of the crucible, transporting downward along the central axis of the crucible to the surface of the seed crystal, then moving radially outward along the seed crystal to the edge region, and flowing along the edge region close to the crucible wall to the gallium-sodium metal melt surface, finally forming a closed circulation flow field (the movement paths / trajectories of each component are shown by the arrows in Figure 2 ). Under the action of this convection mechanism, the nitrogen source dissolved from the upper surface of the gallium-sodium metal melt is transported along with the fluid and first concentrated in the central region of the seed crystal. The nitrogen source concentration distribution is as shown in Figure 2 . The redder the color, the higher the nitrogen concentration. Maintaining this temperature distribution state, the growth thickness of the gallium nitride crystal will gradually change. The growth rate in the middle is fast, and the growth rate at the edge is slow, forming a convex interface growth thickness distribution trend as shown in Figure 3 . Maintaining this growth time for 5 hours, the growth thickness of the gallium nitride crystal can be measured by using an in-situ monitoring mechanism during the growth process.

[0058] The second growth stage: change the temperature of the first heat source to make the temperature gradient between the first heat source and the second heat source a negative temperature gradient, that is, T1 < T2, and make the temperature gradient between the first heat source and the second heat source 50°C to 250°C, T2 ∈ (700°C to 900°C). Keep the temperature of the second heat source in the second growth stage the same as that of the second heat source in the first growth stage. Since the temperature of the second heat source remains unchanged, the growth of the gallium nitride crystal will not cause excessive growth fluctuations due to temperature changes. At the same time, the positive temperature gradient becomes a negative temperature gradient, the eddy current state and the nitrogen transport path change. Under the condition of the negative temperature gradient, the flow direction of the gallium-sodium metal melt is opposite to that under the positive temperature gradient. Its flow path and nitrogen concentration distribution are as shown in Figure 4 . The edge growth rate of the gallium nitride crystal is greater than the middle growth rate (the concave interface growth thickness distribution formed by the negative temperature gradient is as shown in Figure 5 ), making the convex interface of the gallium nitride crystal grown in the first growth stage gradually become flat, and also growing for 5 hours.

[0059] Specifically, the first growth stage and the second growth stage are alternately carried out as a growth cycle. And it should be noted that the priority order of the first growth stage should be avoided to prevent the seed crystal from redissolving. In the later stage of growth, it is preferred to gradually shorten the time of the growth cycle. For example, the holding time of the positive temperature gradient / negative temperature gradient in the growth cycle is gradually shortened from 5h to 1h. This can gradually reduce the difference in the crystal thickness grown in each growth cycle until the growth ends, so as to improve the flatness of the growth interface of the gallium nitride crystal.

[0060] The inventors of this invention discovered that the composition of molten growth materials (i.e., melts or liquids, such as gallium-sodium metal melts) is affected by temperature gradients and thus moves. In flux-assisted liquid-phase epitaxial growth of nitride crystals, the radius of the growth container, such as the crucible, is generally larger than the height of the molten growth material. Taking a positive temperature gradient as an example, the temperature of the upper wall of the crucible is higher than that of the lower wall, but the temperature difference is small due to heat conduction. The temperature of the upper surface of the melt at the center of the crucible is the lowest, causing the vortex flow direction. Conventional studies have not considered controlling the positive or negative temperature gradient to control the flow direction; instead, they almost always aim to minimize the temperature gradient to achieve uniform growth. However, the disordered and unpredictable melt flow cannot regulate the crystal thickness distribution, growth rate, or crystal quality. This invention influences the temperature gradient within the molten growth material by controlling the temperature difference / temperature gradient between the first and second heat sources, thereby controlling the vortex motion state and trajectory of the molten growth material. This, in turn, regulates the distribution of components in the molten growth material, achieving adjustments to the crystal thickness distribution, growth rate, and crystal quality, ultimately obtaining a crystal with a uniform thickness distribution.

[0061] This invention, through specific temperature gradient control, can alter the distribution of components within the molten growth material, thereby enabling control over the component concentration at different locations within the crystal and allowing for the regulation of local crystal growth rate / thickness. Of course, this invention is not limited to the flux-driven growth of gallium nitride crystals; it can also be extended to liquid-phase crystal growth methods similar to gas pressure methods.

[0062] In a typical implementation, the present invention can also repair existing crystals with uneven thickness distribution, so as to achieve local growth of the crystal, complete the thickness compensation and optimization of the crystal, and obtain a crystal with uniform thickness distribution.

[0063] For example, when there is a crystal with a convex interface, it can be placed in the crucible of a flux growth apparatus, and the temperature gradient between the first heat source and the second heat source can be controlled to be a negative temperature gradient. Before growth, the crystal thickness is measured by a monitoring device, and then crystal growth is carried out. At regular intervals, the crystal thickness is checked by the monitoring device until the growth surface becomes smooth.

[0064] In a typical implementation, when the existing gallium nitride crystal has a convex growth interface, the gallium nitride crystal is placed in the crucible of the aforementioned growth system, the temperature gradient in the growth chamber is adjusted to a negative temperature gradient, and liquid phase epitaxial growth of the gallium nitride crystal is performed. Alternatively, in the initial stage, the temperature gradient is adjusted to a negative temperature gradient, and then the temperature gradient is periodically switched between negative and positive temperature gradients until the growth interface of the gallium nitride crystal becomes a flat surface.

[0065] In a typical implementation, when the existing gallium nitride crystal has a concave growth interface, the gallium nitride crystal is placed in the crucible of the aforementioned growth system, the temperature gradient in the growth chamber is adjusted to a positive temperature gradient, and liquid phase epitaxial growth of the gallium nitride crystal is performed. Alternatively, in the initial stage, the temperature gradient is adjusted to a positive temperature gradient, and then the temperature gradient is periodically switched between positive and negative temperature gradients until the growth interface of the gallium nitride crystal becomes a flat surface.

[0066] The present invention provides a method for improving the uniformity of crystal growth thickness and quality, and a crystal repair method. By controlling the alternation of positive and negative temperature gradients, the uniformity of crystal growth thickness can be regulated. Furthermore, monitoring the crystal thickness during the growth process makes the growth process more controllable. This method is applicable to all flux-based or liquid-phase methods of different sizes.

[0067] This invention provides a method for improving the uniformity of crystal growth thickness and quality, as well as a crystal repair method. By changing the temperature gradient of the heat source, the local growth rate of the crystal can be effectively controlled, thereby improving the uniformity of crystal thickness and crystal quality. Furthermore, by alternating between high and low local growth rates, this invention can further improve the flatness of the crystal surface and reduce crystal warping and cracking.

[0068] The present invention provides a method for improving the uniformity of crystal growth thickness and quality, as well as a crystal repair method. This method can not only achieve the original growth of crystals, but also perform secondary growth compensation on crystals with uneven thickness distribution to obtain relatively flat crystals. Alternatively, the present invention can use the current scheme to control the concentration of doped elements at different positions of the same crystal, with the concentration of doped elements consistent with the concentration distribution of nitrogen source. Under a positive temperature gradient, the concentration of doped elements at the center of the crystal is higher than that at the edge, and under a negative temperature gradient, the concentration of doped elements at the center of the crystal is lower than that at the edge. This method is conducive to achieving industrialized, low-cost, and high-quality crystal production.

[0069] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the thickness and quality uniformity of Group III nitride crystal growth, comprising: The method comprises the following steps: providing a growth system required for growing III-nitride crystals by flux method liquid phase epitaxy, so that the top part of the molten growth material is in a first temperature zone formed by a first heat source, and the bottom part of the molten growth material is in a second temperature zone formed by a second heat source, the temperature difference ΔT between the first heat source and the second heat source is (50~250) ℃, so as to form a temperature gradient between the top part and the bottom part of the molten growth material, and a closed circulation flow field of the molten growth material and a nitrogen source is formed in the molten growth material; and, in the initial stage of growing III-nitride crystals, the temperature gradient is adjusted to be a positive temperature gradient, and then the temperature gradient is alternately switched between the positive temperature gradient and a negative temperature gradient, so as to change the nitrogen source concentration distribution and the growth rate of different regions of the growth interface of the III-nitride crystals, until the growth interface of the III-nitride crystals presents a flat surface; when the temperature gradient is the positive temperature gradient, the trajectory of the closed circulation flow field is: the edge region of the top part→the middle region of the top part→the middle region of the bottom part→the edge region of the bottom part→the edge region of the top part, and the directional gradient of the nitrogen source concentration on the seed crystal surface in the molten growth material decreases from the middle region to the edge region; when the temperature gradient is the negative temperature gradient, the trajectory of the closed circulation flow field is: the edge region of the bottom part→the middle region of the bottom part→the middle region of the top part→the edge region of the top part→the edge region of the bottom part, and the directional gradient of the nitrogen source concentration on the seed crystal surface in the molten growth material increases from the middle region to the edge region; wherein, the temperature gradient = the temperature of the top part - the temperature of the bottom part, the liquid surface of the molten growth material is located in the top part, and the seed crystal required for crystal growth is located in the bottom part of the molten growth material, and the second heat source keeps the temperature of the bottom part at the crystal growth temperature.

2. The method of claim 1, wherein the method further comprises: The method comprises the following steps: keeping the temperature of the second heat source constant, and adjusting the temperature of the first heat source to alternately switch the temperature gradient between the positive temperature gradient and the negative temperature gradient.

3. The method of claim 1 or 2, wherein the method further comprises: The method comprises the following steps: periodically alternately switching the temperature gradient between the positive temperature gradient and the negative temperature gradient, and one complete alternating cycle of the positive temperature gradient and the negative temperature gradient is one growth period, and in each growth period, the keeping time of the positive temperature gradient and the negative temperature gradient is the same; and / or, in each growth period, the keeping time of the positive temperature gradient or the negative temperature gradient is 3 hours to 5 hours; and / or, the keeping time of the growth period is phasedly reduced in a linear trend.

4. The method for improving the thickness and quality uniformity of III-nitride crystals according to claim 1 or 2, wherein: the growth container containing the molten growth material and the seed crystal is placed in a growth chamber having a first space and a second space with independent heat exchange, the top of the growth container and the top part of the molten growth material are located in the first space, and the bottom of the growth container and the bottom part of the molten growth material are located in the second space. The first space is provided with a first heat source, which forms a first temperature zone for the first space. The second space is provided with a second heat source, which forms a second temperature zone for the second space. The second heat source keeps the temperature of the bottom part at a temperature required for growing the group III nitride crystal. The temperature gradient is adjusted between a positive temperature gradient and a negative temperature gradient by adjusting the temperature of the first heat source.

5. A method of repairing a III-nitride crystal having a thickness that is not uniform, the method comprising: The application comprises: A growth system for growing a group III nitride crystal by a flux method liquid phase epitaxy is provided. A group III nitride crystal with uneven thickness is placed in a molten growth material. A top part of the molten growth material is in a first temperature zone heated by a first heat source, and a bottom part of the molten growth material is in a second temperature zone heated by a second heat source. A temperature difference ΔT between the first heat source and the second heat source is (50-250) °C, so as to form a temperature gradient between the top part and the bottom part of the molten growth material. A closed circulation flow field of the molten growth material and a nitrogen source is formed in the molten growth material. The temperature gradient is adjusted to be a positive temperature gradient or a negative temperature gradient according to the thickness distribution of a growth interface of the group III nitride crystal, so as to change the nitrogen source concentration distribution and the growth rate of different regions of the growth interface of the group III nitride crystal, and make the growth interface of the group III nitride crystal with uneven thickness appear to be a flat surface. When the growth interface of the group III nitride crystal is a convex interface, the temperature gradient is adjusted to be a negative temperature gradient. At this time, the trajectory of the closed circulation flow field is: an edge region of the bottom part→a middle region of the bottom part→a middle region of the top part→an edge region of the top part→the edge region of the bottom part. The directional gradient of the nitrogen source concentration on the crystal surface in the molten growth material increases from the middle region to the edge region. When the growth interface of the group III nitride crystal is a concave interface, the temperature gradient is adjusted to be a positive temperature gradient. At this time, the trajectory of the closed circulation flow field is: an edge region of the top part→a middle region of the top part→a middle region of the bottom part→an edge region of the bottom part→the edge region of the top part. The directional gradient of the nitrogen source concentration on the crystal surface in the molten growth material decreases from the middle region to the edge region. The temperature gradient is equal to the temperature of the top part minus the temperature of the bottom part. The liquid surface of the molten growth material is located in the top part. The group III nitride crystal with uneven thickness is located in the bottom part. The second heat source keeps the temperature of the bottom part at a crystal growth temperature.

6. The method for repairing group III nitride crystals with uneven thickness according to claim 5, characterized in that, The application comprises: The temperature of the second heat source is kept constant. The temperature of the first heat source is adjusted to adjust the temperature gradient to be a positive temperature gradient or a negative temperature gradient.

7. The method for repairing group III nitride crystals with uneven thickness according to claim 5, characterized in that, The application comprises: The temperature gradient is adjusted between a positive temperature gradient and a negative temperature gradient until the growth interface of the group III nitride crystal appears to be a flat surface.

8. The method for repairing group III nitride crystals with uneven thickness according to claim 7, characterized in that, The application comprises: the temperature gradient is periodically switched between a positive temperature gradient and a negative temperature gradient, one complete cycle of the positive temperature gradient and the negative temperature gradient is one growth cycle, and in each growth cycle, the positive temperature gradient and the negative temperature gradient are maintained for the same time period; and / or, in each growth cycle, the positive temperature gradient or the negative temperature gradient is maintained for a time period of 3 hours to 5 hours; and / or, the time period of each growth cycle is linearly and periodically decreased.

9. The method of claim 7 or 8, wherein the thickness non-uniformity of the Ill-nitride crystal is repaired by: In the initial stage of the growth of the III-nitride crystal, the temperature gradient is adjusted to be a positive temperature gradient.

10. A III-nitride crystal obtained by the method for improving the thickness and quality uniformity of the growth of a III-nitride crystal according to any one of claims 1 to 4, or the method for repairing a III-nitride crystal with non-uniform thickness according to any one of claims 5 to 9.

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