A method of characterizing a temperature field during crystal growth

Abstract

This invention relates to a method for characterizing the temperature field during crystal growth. The method, by observing the position and shape of facet regions—natural features on the surface of a SiC substrate—inversely characterizes the temperature field distribution during growth, providing a novel method for indirect inference and optimization of the temperature field. This method achieves temperature field optimization without damaging the crystal or disrupting production schedules. Furthermore, it eliminates the need for any measuring equipment or complex calculations, enabling low-cost characterization and control of the temperature field. This optimizes the SiC single crystal growth process, achieves precise growth control, reduces defects, improves crystal quality, lowers costs, and shortens the experimental cycle.

Description

Technical Field

[0001] This invention relates to a method for characterizing the temperature field during crystal growth, belonging to the field of silicon carbide (SiC) single crystal growth technology. Background Technology

[0002] Silicon carbide (SiC) is an advanced third-generation semiconductor material. Its wide bandgap, high thermal conductivity, high electric field breakdown strength, and high electron saturation drift velocity make it crucial for applications in high-power, high-frequency, and high-temperature electronic devices. Due to its superior performance in power electronic devices, SiC single crystals are gradually replacing traditional silicon-based materials, becoming a core material in fields such as electric vehicles, photovoltaic inverters, and high-temperature avionics. However, the growth process of SiC single crystals is highly complex, with the distribution and stability of the temperature field playing a decisive role in the crystal's growth quality and performance. During SiC single crystal growth, the temperature field directly affects the crystal's morphology, lattice quality, and defect formation. SiC single crystals are typically grown using the physical vapor transport (PVT) method, which relies on sublimation and recrystallization processes at high temperatures to build up a single crystal structure layer by layer. However, in actual growth, local temperature field inhomogeneities or temperature fluctuations can lead to inconsistent crystal growth rates, thus affecting the crystal's quality and structure. Specifically, the non-uniformity of the growth temperature field will affect the lattice structure of SiC single crystals, thereby causing the following problems: 1) Increased crystal defects: Temperature field inhomogeneity may cause stress concentration or distortion in the crystal, forming dislocations, vacancies and other crystal defects. These defects will directly affect the electronic properties of the crystal and reduce the stability and reliability of the device.

[0003] 2) Unstable growth front: The uneven temperature distribution makes the morphology of the crystal growth front unstable, which may form irregular crystal shapes, causing interference to the subsequent growth process and further affecting the quality of the final crystal.

[0004] 3) Impurity enrichment and uneven distribution: During the growth of SiC single crystals, temperature field inhomogeneity can also lead to uneven distribution of dopants within the crystal. Regions of impurity enrichment typically result in localized decreases in resistivity or deterioration of crystal performance, affecting the electrical characteristics of the final device.

[0005] Traditional temperature field optimization methods typically use pyrometers to directly monitor the top and bottom center temperatures of the crucible, or calculate the internal boundary temperature distribution by setting multiple blind holes on the crucible surface. These methods require cumbersome calculations and cannot accurately determine the temperature field shape. Other methods use X-rays for direct temperature field detection, but this technology requires complex sensors and equipment, resulting in high costs and complex procedures, and its current maturity is insufficient for stable production. Modulated nitrogen-doped growth technology refers to growing undoped SiC single crystals for a period of time, followed by the introduction of high-purity nitrogen gas into the growth chamber to grow nitrogen-doped SiC single crystals in another period of time, alternating between undoped and nitrogen-doped growth. The grown crystal is cut along the growth direction to obtain longitudinal slices. Nitrogen-doped stripes can show the shape of the crystal growth front and the evolution of defects at different stages. The shape of the growth front at different stages can reflect the temperature field during the growth process. However, this method has a significant impact on crystal stability. Controlling other growth parameters requires a high level of experience from technicians. Furthermore, even slight deviations during the growth process can lead to a significant decrease in crystal quality. Therefore, this growth technique is very difficult. In addition, this method requires destroying the crystal, and each experiment requires multiple iterations for debugging and optimization, resulting in high experimental costs.

[0006] Therefore, how to characterize the temperature field through other means without directly measuring the temperature field, and further optimize and control the growth temperature field, has always been an unsolved problem in the field of SiC single crystal growth. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for characterizing the temperature field during crystal growth.

[0008] This invention provides a novel method for indirectly inferring and optimizing the temperature field by observing the location and shape of facet regions—natural features on the surface of SiC substrates—and inversely characterizing the temperature field distribution during growth. This method achieves temperature field optimization without damaging the crystal or disrupting production schedules. Furthermore, it eliminates the need for any measuring equipment or complex calculations, enabling low-cost characterization and control of the temperature field. This optimizes the SiC single crystal growth process, achieves precise growth control, reduces defects, improves crystal quality, lowers costs, and shortens the experimental cycle.

[0009] This invention is achieved through the following technical solution: A method for characterizing the temperature field during crystal growth includes the following steps: (1) SiC single crystal growth was carried out by physical vapor transport (PVT) under the set growth temperature, pressure and time conditions; (2) Adjust the growth conditions, process the crystal ingot into slices, obtain SiC substrate wafers, and after growth, use a wafer scanner to scan the substrate wafers to obtain the position and shape of the facet regions. Record the position and shape characteristics of the facet regions under different growth conditions, obtain facet region morphology data under different temperature field conditions, and establish an experimental database. (3) The obtained facet region morphology is correlated with the temperature field map output by the temperature field simulation software. The relationship between facet region morphology and temperature field distribution is analyzed, and a quantitative mapping relationship between facet morphology and temperature field distribution is constructed. (4) Check whether the established quantitative mapping relationship model can accurately reflect the morphological changes of small facet regions under different temperature field conditions through cross-validation, and further revise and optimize the model to ensure its accuracy and reliability; (5) Combine multiple sets of experimental data to analyze the distribution pattern of small facet regions under different temperature field conditions.

[0010] According to a preferred embodiment of the present invention, in step (2), adjusting the growth conditions includes adjusting the position of the heating coil and adjusting the layout of the insulation material.

[0011] According to a preferred embodiment of the present invention, in step (2), the crystal ingot is processed into slices including early growth SiC substrate slices and late growth SiC substrate slices. The first 10 slices are early growth slices, and the 20 slices and later slices are late growth slices. During scanning, one slice is selected from the first 10 slices and the last 20 slices to represent the early growth SiC substrate slice and the late growth SiC substrate slice, respectively.

[0012] According to a preferred embodiment of the present invention, in step (2), the experimental database includes growth condition data information, facet region location data information, and facet region shape feature data information.

[0013] According to a preferred embodiment of the present invention, in step (3), the temperature field simulation software is VR-PVT software.

[0014] According to a preferred embodiment of the present invention, in step (3), for different temperature field shapes that are uniform or non-uniform, a quantitative mapping relationship between the facet shape and the temperature field distribution is constructed by comparing experimental data and simulation results.

[0015] According to a preferred embodiment of the present invention, in step (3), the uniform temperature field shape includes flat, slightly convex, nearly flat, and slightly concave temperature field shapes, and the non-uniform temperature field shape includes convex and concave temperature field shapes.

[0016] According to a preferred embodiment of the present invention, in step (5), the formation mechanism of the facet region is as follows: when the normal direction of the growth front is perpendicular to

[000] When the crystal orientations coincide, (000) When the crystal plane is tangent to the growth interface, a cross section of a certain size, i.e. a facet, is formed at a specific location. Obviously, the change in the shape of the facet can reflect the change in the shape of the temperature field.

[0017] According to a preferred embodiment of the present invention, in step (5), the distribution pattern of the small facet region under different temperature field conditions is as follows: Small facets located near the edge: When the area of ​​a small facet region is close to the edge, it reflects a uniform radial temperature field and a relatively small overall convexity of the crystal; Facets located near the center: When the area of ​​a facet region is close to the center, it reflects an overall non-uniform radial temperature field and a larger crystal convexity; Narrow strip-shaped facets with small areas: If the facet area is small and has a narrow width, it indicates that the central temperature field is uniform and the crystal center is slightly concave.

[0018] Technical features and advantages of the present invention: 1. A key innovation of this invention is the introduction of a feedback mechanism. By monitoring the morphological changes of small facet regions at different growth stages, the temperature field distribution during the growth process is continuously inferred in reverse, thereby dynamically adjusting growth conditions and forming a closed-loop feedback system. This enables continuous optimization of the temperature field distribution during the actual production process, improving the overall quality of SiC single crystals.

[0019] 2. The characterization method of this invention does not require damaging the crystal, thus optimizing the temperature field without delaying production. Furthermore, it eliminates the need for any measuring equipment or complex calculations, achieving temperature field control at low cost.

[0020] 3. The method of the present invention can achieve precise control of the temperature field without direct measurement and at low cost, thereby optimizing the growth process of SiC single crystal, achieving precise growth control, reducing defects, improving crystal quality, reducing costs and shortening the experimental cycle. Attached Figure Description

[0021] Figure 1 The model shows the facet position when the crystal has a large convexity. The left figure is a cross-sectional view of the crystal ingot, and the right figure is a crystal wafer after the crystal ingot is cut. It is used to describe the relationship between the facet formation position and shape and the growth front (temperature field shape). Figure 2 The model shows the facet position when the crystal has a low convexity. The left figure is a cross-sectional view of the crystal ingot, and the right figure is a wafer image after the crystal ingot is cut. It is used to describe the relationship between the facet formation position and shape and the growth front (temperature field shape). Figure 3 The left image is a cross-sectional view of the crystal ingot, and the right image is a crystal wafer after the crystal ingot is cut. It is used to describe the relationship between the location and shape of the facet formation and the growth front (temperature field shape). Figure 4A schematic diagram of the simulated temperature field during the growth process of the crystal's overall frontal shape changing from flat to convex; Figure 5 A schematic diagram of the simulated temperature field during the growth process where the shape of the local front edge at the center of the crystal changes from slightly concave to slightly convex; Figure 6 A schematic diagram of the simulated temperature field for maintaining near-flat crystal growth; Figure 7 The actual position of the facet during the growth process of the crystal's overall frontal shape changing from flat to convex; Figure 8 The actual shape of the facet during the growth process of the local frontal shape of the crystal center changing from slightly concave to slightly convex; Figure 9 To preserve the actual shape of the facets during the near-flat growth process of the crystal. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] The method for characterizing the temperature field during crystal growth in this invention is a method based on the position and shape of facet regions in a silicon carbide (SiC) single crystal. When the normal direction of the growth front is perpendicular to [000...] When crystal orientations coincide, facets are formed. By observing and analyzing the morphological characteristics of the facet regions, the temperature field distribution during crystal growth can be inferred in reverse. This achieves control over the SiC single crystal growth process without damaging the crystal, is simple and easy to understand, low-cost, and does not delay production schedules. The following is a detailed description of the specific implementation method: Example 1 A method for characterizing the temperature field during crystal growth includes the following steps: (1) SiC single crystal growth was carried out by physical vapor transport (PVT) under the set growth temperature, pressure and time conditions; The growth temperature was set at 2400℃, the growth pressure at 10mbar, and the initial position of the induction heating coil was 550mm from the top of the furnace cavity. (2) By adjusting the position of the initial induction heating coil, ensure that the temperature field is as uniform as possible in the early stage of crystal growth and maintain a small crystal convexity; after growing for a period of time, move the induction heating coil 60mm to 610mm away from the top of the furnace cavity, so that the temperature field is as non-uniform as possible in the later stage of crystal growth and maintain a large crystal convexity. (3) The ingot is processed into slices to obtain SiC substrate wafers. One wafer is selected from the first 10 wafers and one wafer from the last 20 wafers to represent the early growth stage and the late growth stage. The first 10 wafers are the early growth stage and the wafers after the last 20 wafers are the late growth stage. After the growth is completed, a wafer scanner is used to scan and record the position and shape characteristics of the facet region under different growth conditions. Facet morphology data under different temperature field conditions are obtained and an experimental database is established. It is found that the facet position of the wafer in the early growth stage is close to the crystal edge, and the facet position of the wafer in the late growth stage is close to the crystal center. (4) The obtained facet region morphology is correlated with the temperature field map output by the temperature field simulation software VR-PVT to analyze the relationship between the facet region morphology and the temperature field distribution, and to construct a quantitative mapping relationship between the facet region morphology and the temperature field distribution. The temperature field map calculated by the temperature field simulation software VR-PVT shows that the overall temperature field distribution is uniform in the early stage of growth and the crystal convexity is small. At this time, the facet region is located at the edge of the wafer in the actual growth process. In the later stage of growth, the overall temperature field distribution is uneven and the crystal convexity is large. At this time, the facet region moves towards the center of the wafer in the actual growth process. Simulated temperature field during the growth process of the crystal's overall frontal shape changing from planar to convex, such as Figure 4 As shown, the simulated temperature field during the growth process of the local frontal shape of the crystal center changing from slightly concave to slightly convex is as follows: Figure 5 As shown, the simulated temperature field during the near-flat growth process of the crystal is as follows: Figure 6 As shown.

[0024] The actual positions of the facets during the crystal's overall frontal shape change from planar to convex are shown in the figure. Figure 7 The actual shape of the facets during the growth process, where the shape of the local front edge at the crystal center changes from slightly concave to slightly convex, is shown in the figure. Figure 8 The actual shape of the facets during the near-flat growth process of the crystal is shown in the figure. Figure 9 .

[0025] (5) Check whether the established quantitative mapping relationship model can accurately reflect the morphological changes of small facet regions under different temperature field conditions through cross-validation, and further revise and optimize the model to ensure its accuracy and reliability; (6) Based on multiple sets of experimental data, analyze the distribution pattern of small facet regions under different temperature field conditions.

[0026] The distribution patterns of small facet regions under different temperature conditions are as follows: Small facets located near the edge: When the area of ​​a small facet region is close to the edge, it reflects a uniform radial temperature field and a relatively small overall convexity of the crystal; Facets located near the center: When the area of ​​a facet region is close to the center, it reflects an overall non-uniform radial temperature field and a larger crystal convexity; Narrow strip-shaped facets with small areas: If the facet area is small and has a narrow width, it indicates that the central temperature field is uniform and the crystal center is slightly concave.

[0027] When the crystal convexity is large, the facet position model is shown below. Figure 1 When the crystal convexity is small, the facet position model is shown below. Figure 2 When the crystal front is flat, see the facet shape model. Figure 3 .

[0028] Example 2 A method for characterizing the temperature field during crystal growth includes the following steps: (1) Under the set growth temperature, pressure and time conditions, SiC single crystals are grown by physical vapor transport (PVT); the growth process is a SiC single crystal growth process in which the shape of the local front edge of the crystal center changes from slightly concave to slightly convex. The growth temperature was set at 2400℃, the growth pressure at 10mbar, and the initial position of the induction heating coil was 550mm from the top of the furnace cavity. (2) A 5mm thick, 50mm diameter heat-insulating material was added to the back of the seed crystal to ensure that the central temperature field was slightly uneven in the early stage of crystal growth, and the crystal center was slightly concave. After adding the heat-insulating material to the back of the seed crystal, SiC single crystal growth experiments were conducted. Due to the presence of the heat-insulating material, the temperature at the crystal center was too high, the uniformity of the central temperature field was slightly worse, the growth rate at the crystal center was slower, and the morphology was slightly concave. In the later stage of growth, the crystal growth front was too far away from the heat-insulating material on the back of the seed crystal, and the temperature field was almost unaffected by it. The uniformity of the central temperature field at the crystal growth front changed, the central growth rate was faster, and the central morphology became slightly convex. For the experiment of adding heat-insulating material to the crystal center, it was found that the shape of the facet region became narrow strip in the early stage of growth, and the width of the facet increased in the later stage of growth.

[0029] (3) The ingot is processed into slices to obtain SiC substrate wafers. One wafer is selected from the first 10 wafers and one wafer from the last 20 wafers to represent the early growth stage and the late growth stage. The first 10 wafers are the early growth stage and the last 20 wafers are the late growth stage. After the growth is completed, a wafer scanner is used to scan and record the position and shape characteristics of the facet region under different growth conditions. Facet morphology data under different temperature field conditions are obtained and an experimental database is established. (4) The obtained facet morphology was correlated with the temperature field map output by the temperature field simulation software VR-PVT to analyze the relationship between the facet morphology and the temperature field distribution, and to construct a quantitative mapping relationship between the facet morphology and the temperature field distribution. The temperature field map calculated by the temperature field simulation software VR-PVT shows that the central temperature field distribution is uniform in the early stage of growth, and the crystal center is slightly concave. At this time, the facet region in the actual growth process is narrow and has a small width. In the later stage of growth, the central temperature field distribution is uniform, and the crystal is slightly convex. At this time, the facet width in the actual growth process increases significantly.

[0030] (5) Check whether the established quantitative mapping relationship model can accurately reflect the morphological changes of small facet regions under different temperature field conditions through cross-validation, and further revise and optimize the model to ensure its accuracy and reliability; (6) Based on multiple sets of experimental data, analyze the distribution pattern of small facet regions under different temperature field conditions.

[0031] Example 3 A method for characterizing the temperature field during crystal growth includes the following steps: (1) SiC single crystal growth was carried out by physical vapor transport (PVT) under the set growth temperature, pressure and time conditions; The growth temperature was set at 2400℃, the growth pressure at 10mbar, and the initial position of the induction heating coil was 550mm from the top of the furnace cavity. (2) By adjusting the position of the initial induction heating coil, the temperature field is made as uniform as possible in the early stage of crystal growth, maintaining a small crystal convexity. Throughout the growth process, the coil is continuously moved downwards, a total of 60 mm, to ensure that the temperature field remains uniform throughout the entire crystal growth process, maintaining a small crystal convexity. (3) The crystal ingot is processed into slices to obtain SiC substrate wafers. One wafer is selected from the first 10 wafers and one wafer from the last 20 wafers to represent the early growth stage and the late growth stage. The first 10 wafers are the early growth stage and the last 20 wafers are the late growth stage. After the growth is completed, a wafer scanner is used to scan and record the position and shape characteristics of the facet region under different growth conditions. Facet morphology data under different temperature field conditions are obtained and an experimental database is established. It is found that the facet position of the wafer in the early and late growth stages is close to the crystal edge. (4) The obtained facet region morphology was correlated with the temperature field map output by the temperature field simulation software VR-PVT to analyze the relationship between the facet region morphology and the temperature field distribution, and to construct a quantitative mapping relationship between the facet region morphology and the temperature field distribution. The temperature field map calculated by the temperature field simulation software VR-PVT shows that the overall temperature field distribution is uniform in the early and late stages of growth, and the crystal convexity is small. At this time, the facet regions are all located at the edge of the wafer in the actual growth process. (5) Check whether the established quantitative mapping relationship model can accurately reflect the morphological changes of small facet regions under different temperature field conditions through cross-validation, and further revise and optimize the model to ensure its accuracy and reliability.

Claims

1. A method for characterizing the temperature field during crystal growth, comprising the following steps: (1) SiC single crystal growth was carried out by physical vapor transport (PVT) under the set growth temperature, pressure and time conditions; (2) Adjust the growth conditions, process the crystal ingot into slices, obtain SiC substrate wafers, and after growth, use a wafer scanner to scan the substrate wafers to obtain the position and shape of the facet regions. Record the position and shape characteristics of the facet regions under different growth conditions, obtain facet region morphology data under different temperature field conditions, and establish an experimental database. (3) The obtained facet region morphology is correlated with the temperature field map output by the temperature field simulation software. The relationship between facet region morphology and temperature field distribution is analyzed, and a quantitative mapping relationship between facet morphology and temperature field distribution is constructed. (4) Check whether the established quantitative mapping relationship model can accurately reflect the morphological changes of small facet regions under different temperature field conditions through cross-validation, and further revise and optimize the model to ensure its accuracy and reliability; (5) Combine multiple sets of experimental data to analyze the distribution pattern of small facet regions under different temperature field conditions.

2. The method of claim 1, wherein, In step (2), adjusting the growth conditions includes adjusting the position of the heating coil and adjusting the layout of the insulation material.

3. The method of claim 1, wherein, In step (2), the crystal ingot is processed into slices including early growth SiC substrate slices and late growth SiC substrate slices. The first 10 slices are early growth slices, and the 20 slices and later slices are late growth slices. During scanning, one slice is selected from the first 10 slices and the last 20 slices to represent the early growth SiC substrate slice and the late growth SiC substrate slice, respectively.

4. The method of claim 1, wherein, In step (3), the temperature field simulation software is VR-PVT software.

5. The method of claim 1, wherein, In step (3), for different temperature field shapes that are uniform or non-uniform, a quantitative mapping relationship between the facet shape and the temperature field distribution is constructed by comparing experimental data and simulation results.

6. The method of claim 1, wherein, In step (3), the uniform temperature field shape includes flat, slightly convex, nearly flat, and slightly concave temperature field shapes, and the non-uniform temperature field shape includes convex and concave temperature field shapes.

7. The method of claim 1, wherein, In step (5), the distribution pattern of the small area under different temperature field conditions is as follows: Small facets located near the edge: When the area of ​​a small facet region is close to the edge, it reflects a uniform radial temperature field and a relatively small overall convexity of the crystal; Facets located near the center: When the area of ​​a facet region is close to the center, it reflects an overall non-uniform radial temperature field and a larger crystal convexity; Narrow strip-shaped facets with small areas: If the facet area is small and has a narrow width, it indicates that the central temperature field is uniform and the crystal center is slightly concave.

Images