A crystal growth apparatus

Abstract

The application provides a crystal growth device, comprising a crucible with a cavity, a tray structure and a seed crystal arranged in the cavity, the tray structure is arranged between the inner surface of the top wall of the crucible and the seed crystal, the tray structure comprises a first tray area and a second tray area with different thicknesses, the thickness of the second tray area is smaller than that of the first tray area, and the side of the first tray area and the second tray area close to the seed crystal is coplanar, and the spatial position of the second tray area corresponds to the facet growth area of the seed crystal. The application reduces the thickness of the part of the tray structure corresponding to the facet growth area, changes the local thermal conductivity of the thickness-thinned part of the tray structure, makes the local temperature gradient on one side of the facet growth area greater than that of other areas, makes the growth interface at the facet growth area steeper, inhibits the expansion of the facet growth area to the center of the crystal, and thus reduces the area growth of the facet growth area.

Description

Technical Field

[0001] This application relates to the field of semiconductor processing technology, and in particular to a crystal growth apparatus. Background Technology

[0002] Silicon carbide (SiC) crystals, as representatives of third-generation semiconductor materials, possess superior physicochemical properties, offering advantages over silicon-based semiconductors in high-temperature, high-frequency, and high-power applications. Currently, physical vapor transport (PVT) is widely used for the commercial preparation of SiC single crystals, and 6-inch SiC substrates are already in mass production. With the increasing prevalence of SiC power devices, the market demand for cost reduction is becoming more urgent. Larger SiC substrates offer higher effective chip processing area, which helps reduce the cost per SiC chip. Therefore, the development and large-scale production of 8-inch to 12-inch large-diameter SiC single crystal fabrication processes have become a current research hotspot.

[0003] However, the growth of larger-sized silicon carbide single crystals also faces many technical bottlenecks that need to be addressed. For example, the PVT method for growing silicon carbide single crystals requires high uniformity of temperature gradients, and larger sizes mean that the temperature field is more difficult to control, leading to problems such as uneven doping, polymorphism, dislocation multiplication, and cracking. In particular, for the preparation of conductive 4H silicon carbide single crystals, N doping is crucial for reducing resistivity, and larger sizes mean that N doping uniformity is more difficult to guarantee. Especially for the facets of 4H silicon carbide single crystal growth, due to their unique spiral growth mechanism, higher N doping concentrations are often required, causing resistivity differences between the facet and non-facet regions, which is detrimental to the uniformity of in-plane resistivity of the silicon carbide substrate. At the same time, the growth steps in the facet regions are wider, making it easier to generate two-dimensional nucleation sites, thus inducing crystal defects such as impurities and polymorphism. Therefore, controlling the area of ​​the facets and minimizing the facet growth area is beneficial to improving the N doping uniformity of the silicon carbide single crystal substrate, reducing defect levels, and improving yield. Existing technical solutions mostly focus on improving a certain defect or technical indicator in silicon carbide crystal growth, lacking a complete technical solution for controlling small facet area. Summary of the Invention

[0004] In view of this, this application proposes a crystal growth apparatus designed to effectively reduce the area of ​​small facet growth in silicon carbide crystals grown by the PVT method.

[0005] This application provides a crystal growth apparatus, including:

[0006] A crucible with a cavity;

[0007] The tray structure and seed crystal are disposed within the cavity;

[0008] in:

[0009] The tray structure is disposed between the inner surface of the top wall of the crucible and the seed crystal;

[0010] The tray structure includes a first tray area and a second tray area with different thicknesses. The thickness of the second tray area is less than the thickness of the first tray area, and the first tray area and the second tray area are coplanar on the side closest to the seed crystal.

[0011] The spatial position of the second tray area corresponds to the facet growth area of ​​the seed crystal.

[0012] In one embodiment, the tray structure includes:

[0013] The first tray portion has its first surface connected to the inner surface of the top wall of the crucible;

[0014] The second tray portion is stacked on the second surface of the first tray portion and connected to the seed crystal;

[0015] in:

[0016] The cross-sectional area of ​​the second tray portion is larger than that of the first tray portion;

[0017] The first tray area is formed by the overlapping area of ​​the first tray portion and the second tray portion;

[0018] The second tray area is formed by the non-overlapping area of ​​the second tray portion that extends beyond the first tray portion.

[0019] In one embodiment, the circumferential side of the first tray portion includes a first side and a second side, the first side facing the second tray area, and the second side being coplanar with the circumferential side of the second tray portion.

[0020] In one embodiment, both the first tray portion and the second tray portion are circular, the diameter of the first tray portion is smaller than the diameter of the second tray portion, the first tray portion is eccentrically positioned relative to the second tray portion, and there exists a reference straight line that is tangent to both the first tray portion and the second tray portion.

[0021] In one embodiment, the diameter of the seed crystal is the same as the diameter of the second tray portion.

[0022] In one embodiment, the diameter ratio of the second tray portion to the first tray portion is 1.02 to 1.1.

[0023] In one embodiment, the thickness ratio of the second tray portion to the first tray portion is 1 to 2.

[0024] In one embodiment, the seed crystal is a 4H-type silicon carbide seed crystal, and the side of the silicon carbide seed crystal facing away from the tray structure is a carbon surface (000-1). The side of the first tray portion facing the second tray area has a central cross-section. The direction is perpendicular to the central tangent.

[0025] In one embodiment, the first tray portion and the second tray portion are integrally formed or separately connected.

[0026] In one embodiment, the cavity is provided with an inner liner assembly, which includes a sleeve, a support ring, and a flow guide tube. The sleeve is attached to the inner surface of the side wall of the crucible and supported on the inner surface of the bottom wall of the crucible. One end of the support ring is connected to the top end of the sleeve and the other end is connected to the bottom end of the flow guide tube. The top end of the flow guide tube is located close to the seed crystal and surrounds the periphery of the seed crystal, and the diameter of the top end of the flow guide tube is smaller than the diameter of the bottom end of the flow guide tube.

[0027] And / or, the crucible includes a crucible body and a crucible lid, the crucible lid is connected to the top of the crucible body, the crucible lid and the crucible body enclose the cavity, the tray structure is connected to the side of the crucible lid facing the crucible body, and the central axis of the second tray portion coincides with the central axis of the crucible;

[0028] And / or, the crystal growth apparatus further includes a heating coil, which is arranged around the periphery of the crucible for heating the crucible, and the heating coil is configured to be movable along the central axis of the crucible.

[0029] In summary, this application provides a crystal growth apparatus, including a crucible with a cavity, a tray structure disposed within the cavity, and a seed crystal. The tray structure is disposed between the inner surface of the top wall of the crucible and the seed crystal. The tray structure includes a first tray region and a second tray region with different thicknesses. The thickness of the second tray region is less than the thickness of the first tray region, and the first and second tray regions are coplanar on the side closest to the seed crystal. The spatial position of the second tray region corresponds to the facet growth region of the seed crystal. This application reduces the thickness of the portion of the tray structure corresponding to the facet growth region to change the local thermal conductivity of the thinned portion, making the local temperature gradient on the facet growth region side greater than other areas. This results in a steeper growth interface at the facet growth region, inhibiting the expansion of the facet growth region towards the crystal center, thereby achieving the effect of reducing the area growth of the facet growth region. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of a crystal growth apparatus in one embodiment of this application.

[0031] Figure 2 for Figure 1 A top view of the tray of the crystal growth apparatus.

[0032] Figure 3 for Figure 1 A cross-sectional view of the tray of the crystal growth apparatus.

[0033] Figure 4 This is a top view of the tray in another embodiment.

[0034] Figure 5 This is a top view of the tray in yet another embodiment.

[0035] Figure 6 for Figure 1 A schematic diagram showing the relative positions of the seed crystal and the tray in the medium crystal growth apparatus.

[0036] Reference numerals: x-axial direction; a-central axis; y-central section; 10-crystal growth apparatus; 12-crucible; 14-tray structure; 14a-first tray area; 14b-second tray area; 16-seed crystal; 18-cavity; 20-first tray section; 22-second tray section; 24-top surface of crucible; 26-upper surface of second tray section; 28-powder; 30-vacancy section; 32-small facet growth area; 36-first collinear edge; 38-second collinear edge; 40-first side surface; 41-median line; 42-sleeve; 44-support ring; 46-guide tube; 48-inner wall of crucible; 50-bottom surface of crucible; 52-body of crucible; 54-crucible lid. Detailed Implementation

[0037] Before describing the embodiments in detail, it should be understood that this application is not limited to the detailed structures or element arrangements described below or in the accompanying drawings. This application can be implemented in other ways. Furthermore, it should be understood that the wording and terminology used herein are for descriptive purposes only and should not be construed as limiting. The terms "comprising," "including," "having," and similar expressions used herein mean to include the items listed thereafter, their equivalents, and other additional items. In particular, when describing "an element," this application does not limit the number of elements to one, but may include multiple elements.

[0038] Please refer to Figures 1 to 3As shown, one embodiment of this application provides a crystal growth apparatus 10, which can grow crystals by physical vapor transport (PVT). The crystal growth apparatus 10 includes a crucible 12 with a cavity 18, a tray structure 14 disposed within the cavity 18, and a seed crystal 16. The tray structure 14 is disposed between the inner surface of the top wall of the crucible 12 and the seed crystal 16. The tray structure 14 includes a first tray region 14a and a second tray region 14b with different thicknesses. The thickness of the second tray region 14b is less than the thickness of the first tray region 14a. The first tray region 14a and the second tray region 14b are coplanar on the side closest to the seed crystal 16. The spatial position of the second tray region 14b corresponds to the facet growth region 32 of the seed crystal 16. This application reduces the thickness of the portion of the tray structure 14 corresponding to the facet growth region 32, thereby changing the local thermal conductivity of the thinned portion of the tray structure 14. This results in a larger local temperature gradient on one side of the facet growth region 32 compared to other areas, making the growth interface at the facet growth region 32 steeper and inhibiting the expansion of the facet growth region 32 toward the crystal center, thus achieving the effect of reducing the area growth of the facet growth region 32.

[0039] Furthermore, the tray structure 14 includes a first tray portion 20 and a second tray portion 22 stacked and connected. The first surface of the first tray portion 20 facing away from the second tray portion 22 is connected to the inner surface of the top wall of the crucible 12. The inner surface of the top wall of the crucible 12 is the top surface 24 of the crucible 12 located in the cavity 18. The second tray portion 22 is stacked on the second surface of the first tray portion 20 and connected to the seed crystal 16. The second surface is the surface of the first tray portion 20 opposite to its first surface. The seed crystal 16 is connected to the side of the second tray portion 22 facing away from the first tray portion 20.

[0040] In this configuration, the vertical projection of the first tray portion 20 relative to the second tray portion 22 falls on the upper surface 26 of the second tray portion 22. This means the cross-sectional area of ​​the second tray portion 22 is greater than the cross-sectional area of ​​the first tray portion 20. The cross-sectional area refers to the area of ​​the portion where a plane intersects the first tray portion 20 or the second tray portion 22 after being cut along a direction perpendicular to the circumferential side of either the first tray portion 20 or the second tray portion 22. For example, when both the first tray portion 20 and the second tray portion 22 are circular, a diameter greater than the diameter of the first tray portion 20 will result in a larger cross-sectional area of ​​the second tray portion 22 than that of the first tray portion 20. The first tray area 14a is formed by the overlapping area of ​​the first tray portion 20 and the second tray portion 22, and the second tray area 14b is formed by the non-overlapping area of ​​the second tray portion 22 extending beyond the first tray portion 20.

[0041] From another perspective, a gap 30 is formed between the circumferential side of the first tray portion 20 and the upper surface 26 of the second tray portion 22. Due to the setting of the gap 30, the thickness of the second tray region 14b is less than the thickness of the first tray region 14a, and the gap 30 corresponds to the position of the facet growth region 32 of the seed crystal 16.

[0042] In this embodiment, as Figure 1 As shown, the crucible 12 is placed vertically and has an axial direction x. The crucible 12, the tray structure 14, and the seed crystal 16 are all circular. The central axis a of the crucible 12 is parallel to the axial direction x, and the central axes of the tray structure 14 and the seed crystal 16 coincide with the central axis a of the crucible 12. The central axis of the tray structure 14 is also the central axis of the second tray portion 22, meaning that the central axis of the second tray portion 22 coincides with the central axis a of the crucible 12. The tray structure 14 and the seed crystal 16 are both disposed within the cavity 18 and are placed along the axial direction x. The side of the first tray portion 20 facing away from the second tray portion 22 is the upper surface of the first tray portion 20, and the side of the second tray portion 22 facing away from the first tray portion 20 is the lower surface of the second tray portion 22. The vertical projection of the first tray portion 20 relative to the second tray portion 22 falls on the upper surface 26 of the second tray portion 22, that is, the projection of the first tray portion 20 in the axial direction x falls on the upper surface 26 of the second tray portion 22. The circumferential side of the first tray portion 20 refers to the side connecting the upper surface and the lower surface of the first tray portion 20. The position of the vacancy portion 30 corresponding to the facet growth area 32 of the seed crystal 16 means that the vacancy portion 30 and the facet growth area 32 correspond in the axial direction x.

[0043] In such Figure 2 and Figure 3In the illustrated embodiment, both the first tray portion 20 and the second tray portion 22 are cylindrical. The diameter of the first tray portion 20 is smaller than the diameter of the second tray portion 22. The first tray portion 20 is eccentrically positioned relative to the second tray portion 22, and a reference straight line exists that is tangent to both the first tray portion 20 and the second tray portion 22. Further, the circumferential side surface of the first tray portion 20 includes a first side surface 40 and a first collinear edge 36 in the axial direction x. The first side surface 40 faces the second tray area 14b, or the first side surface 40 is a portion corresponding to a missing portion 30, which is formed between the first side surface 40 and the upper surface 26 of the second tray portion 22. The circumferential side surface of the second tray portion 22 includes a second collinear edge 38 in the axial direction x. The circumferential side surface of the second tray portion 22 refers to the side surface connecting the upper and lower surfaces of the second tray portion 22. The circumferential side of the first tray portion 20 and the circumferential side of the second tray portion 22 have an intersection point, that is, the lower end point of the first collinear side 36 and the upper end point of the second collinear side 38 are the intersection point mentioned above, or in other words, the first collinear side 36 and the second collinear side 38 intersect and share the intersection point mentioned above, and the first collinear side 36 and the second collinear side 38 are on the same straight line.

[0044] In the illustrated embodiment, the vacancy 30 is a curved arc shape that is small at both ends and large in the middle. In other embodiments, the vacancy 30 can also be designed in other shapes, as long as it can meet the requirement of increasing the radial temperature gradient of the small surface area.

[0045] In such Figure 4 In the illustrated embodiment, the circumferential side surface of the first tray portion 20 includes a first side surface 40 and a second side surface. The first side surface 40 faces the second tray area 14b, or the first side surface 40 is a portion corresponding to the missing portion 30. Therefore, the missing portion 30 is formed between the first side surface 40 and the upper surface 26 of the second tray portion 22, and the second side surface is coplanar with the circumferential side surface of the second tray portion 22. More specifically, the second tray portion 22 is cylindrical, and the first tray portion 20 can be configured as an asymmetrical cylinder. For example, because the outer periphery of the first tray portion 20 is provided with the missing portion 30, the first tray portion 20 has an asymmetrical structure. The central axes of the first tray portion 20 and the second tray portion 22 coincide, meaning the diameter of the first tray portion 20 is the same as the diameter of the second tray portion 22. Therefore, the second side surface of the first tray portion 20 is coplanar with the circumferential side surface of the second tray portion 22.

[0046] In such Figure 5In the illustrated embodiment, the first tray portion 20 and the second tray portion 22 can be configured such that their sides do not intersect. In this case, the circumferential side surface of the first tray portion 20 is not limited to a first side surface and a second side surface, and the gap 30 is formed between the circumferential side surface of the first tray portion 20 and the upper surface 26 of the second tray portion 22. Further, both the first tray portion 20 and the second tray portion 22 are cylindrical, the diameter of the first tray portion 20 is set to be smaller than the diameter of the second tray portion 22, and the first tray portion 20 is eccentrically disposed relative to the second tray portion 22.

[0047] Please refer to Figure 1 As shown, the diameter of the seed crystal 16 is set to be the same as the diameter of the second tray portion 22, so that the seed crystal 16 just completely covers the lower surface of the second tray portion 22.

[0048] Preferably, the diameter ratio of the second tray portion 22 to the first tray portion 20 is 1.02 to 1.1. Based on experimental results, setting the diameter ratio of the second tray portion 22 to the first tray portion 20 within the range of 1.02 to 1.1 is the optimal and reasonable setting range. Within this range, a large radial temperature gradient can be effectively achieved at the corresponding seed crystal facet growth region 32, thereby achieving a steeper facet growth region 32 and further controlling the area of ​​the facet growth region 32 to be smaller.

[0049] Preferably, the thickness ratio of the second tray portion 22 to the first tray portion 20 is 1 to 2. Based on experimental results, setting the thickness ratio of the second tray portion 22 to the first tray portion 20 within the range of 1 to 2 is the optimal and reasonable setting range. Within this range, the thickness of the tray structure 14 corresponding to the seed crystal facet region is less than the thickness of other regions, changing the local thermal conductivity of the thinned portion of the tray structure, thereby creating a large temperature gradient. This makes the local temperature gradient on one side of the facet growth region 32 greater than other regions, thus making the growth interface at the facet growth region 32 more "steep" and inhibiting the expansion of the facet growth region 32 towards the crystal center.

[0050] Furthermore, please also refer to Figure 6 As shown, seed crystal 16 is a 4H-type silicon carbide seed crystal, therefore, seed crystal 16 belongs to the hexagonal crystal system. The hexagonal crystal system uses four indices, namely (hkil), to represent the crystal orientation and crystal plane. The indices are calibrated using a four-axis system of c, a1, a2, and a3, with an angle of 120 degrees between a1, a2, and a3, and the c-axis is perpendicular to a1, a2, and a3. In this application, seed crystal 16 has two crystal planes, (0001) and (000-1), and... Two directions, where (0001) is the silicon surface of seed crystal 16 and (000-1) is the carbon surface of seed crystal 16. The direction indicates moving 1 unit length along the a1 axis, 1 unit length along the a2 axis, -2 units length along the a3 axis, and not moving along the c axis (i.e., l = 0). The direction represents a family of crystal directions along the c-axis (six-fold symmetry axis), which consists of all crystal directions parallel to the c-axis and arranged at a 120-degree angle in the a1-a2-a3 plane. The side of the silicon carbide seed crystal facing away from the tray structure 14 is used to grow silicon carbide ingots. Preferably, the side of the silicon carbide seed crystal facing away from the tray structure 14 is the carbon surface (000-1), and the side of the first tray portion 20 facing the second tray area 14b has a central sectional plane y, which is parallel to the

[1100] direction of the silicon carbide seed crystal. The central sectional plane y passes through the middle edge 41 of the first side surface 40 along the axial direction x and is tangent to the first side surface 40. The

[1120] direction of the silicon carbide seed crystal is perpendicular to the central sectional plane y of the first side surface 40.

[0051] like Figure 1 As shown, the cavity 18 is equipped with an inner liner assembly, which includes a sleeve 42, a support ring 44, and a flow guide cylinder 46. The cross-sections of the sleeve 42, the support ring 44, and the flow guide cylinder 46 are, for example, circular. The sleeve 42 is a cylindrical structure with openings at both the top and bottom. The sleeve 42 is disposed against the inner surface of the side wall of the crucible 12, which is the inner side wall 48 of the cavity 18 where the crucible 12 is located. The bottom end of the sleeve 42 is supported on the inner surface of the bottom wall of the crucible 12, which is the bottom surface 50 of the cavity 18 where the crucible 12 is located. The bottom surface 50 of the cavity 18 where the crucible 12 is located is used to place the powder 28 to be grown, such as silicon carbide powder. The support ring 44 is a flat, annular structure. One end (radially outer end) of the support ring 44 is connected to the top end of the sleeve 42, and the other end (radially inner end) is connected to the bottom end of the guide tube 46. The guide tube 46 is an annular cylindrical structure with openings at both the top and bottom. The guide tube 46 is located below the seed crystal 16, with its top end positioned close to the seed crystal 16 and surrounding its periphery. Preferably, the diameter of the top end of the guide tube 46 is smaller than the diameter of its bottom end; for example, the diameter of the guide tube 46 gradually decreases from its bottom end to its top end. Preferably, the sleeve 42, the support ring 44, and the guide tube 46 are detachably connected, for example, by means of snap-fit ​​connections, to facilitate assembly and disassembly.

[0052] Furthermore, the crucible 12 includes a crucible body 52 and a crucible lid 54. The crucible body 52 has an open top structure, and the crucible lid 54 is connected to the top of the crucible body 52. ​​The crucible lid 54 and the crucible body 52 are detachably connected, for example, by means of snap-fit, to facilitate assembly and disassembly. The crucible lid 54 and the crucible body 52 enclose a cavity 18. A tray structure 14 is connected to the side of the crucible lid 54 facing the crucible body 52, i.e., the top surface 24. The top surface 24 of the crucible 12 located inside the cavity 18 is the bottom surface of the crucible lid 54.

[0053] In the illustrated embodiment, the crystal growth apparatus 10 further includes a heating coil (not shown), which is arranged around the periphery of the crucible 12 for heating the crucible 12, and the heating coil is configured to move up and down along the central axis a of the crucible 12.

[0054] Preferably, the crucible 12, the tray structure 14, and the inner liner assembly are all made of graphite. The tray structure 14 and the crucible 12 can be bonded together with an adhesive, and the seed crystal 16 and the tray structure 14 can be bonded together with an adhesive, including but not limited to organic adhesives, carbon glue, resin, etc.

[0055] In the embodiments of this application, the first tray portion 20 and the second tray portion 22 can be configured as an integrally molded structure. For example, the tray structure 14 is made of a single graphite disc, and a gap 30 is machined out, thereby making the tray structure 14 form an asymmetrical structure. Alternatively, the first tray portion 20 and the second tray portion 22 can also be configured as separate structures, with the first tray portion 20 and the second tray portion 22 connected separately. For example, two graphite discs are bonded together with an adhesive, thereby forming a gap 30 between the first tray portion 20 and the second tray portion 22. The adhesive includes, but is not limited to, organic adhesives, carbon adhesives, resins, etc.

[0056] The following describes the assembly process and technology flow of the crystal growth apparatus 10 of this application for growing crystals using the physical vapor transport (PVT) method, for example, growing 4H-type silicon carbide ingots using the crystal growth apparatus 10. The crucible 12, tray structure 14, and inner liner components are all made of graphite, and the seed crystal 16 is a silicon carbide seed crystal.

[0057] Seed crystal 16 is adhered to the lower surface of the second tray portion 22, with the carbon surface (000-1) facing downwards. Simultaneously, the small facet growth area 32 of the seed crystal 16 must be adhered to the side corresponding to the vacancy portion 30 in the axial direction x, i.e., the small facet of the seed crystal is tightly attached to the side where the thickness of the tray structure 14 is reduced, and the

[1120] direction of the seed crystal 16 is perpendicular to the tangent direction of the center portion of the first side surface 40. After the seed crystal 16 is adhered to the tray structure 14, it undergoes high-temperature curing treatment. The high-temperature curing temperature is set between 500 and 1000°C to form a sufficient and firm connection between the first tray portion 20, the second tray portion 22, and the seed crystal 16.

[0058] The tray structure 14 with the seed crystal 16 attached is aligned and attached to the bottom surface of the crucible cover 54, so that the central axis of the second tray part 22 coincides with the central axis a of the crucible 12. The sleeve 42 is placed inside the crucible body 52, the silicon carbide powder is placed at the bottom of the crucible body 52, and then the support ring 44 is placed inside the crucible body 52, with its outer edge locked onto the sleeve 42. The guide tube 46 is locked onto the inner edge of the support ring 44. Finally, the crucible cover 54 is placed on the crucible body 52.

[0059] The assembled crucible 12 was placed inside the insulation felt of the crystal growth furnace, and a vacuum was drawn to 100°C. -3 After introducing argon and nitrogen gas to 1–5 mbar, the temperature is raised to 2100–2300 °C at the center to begin crystal growth. Simultaneously, the heating coil is moved downwards, preferably at a speed of 0.1–0.3 mm / h. Crystal growth ends after 100–300 hours. Once cooled to room temperature, the grown silicon carbide ingot is removed.

[0060] Through experiments, the researchers of this application discovered that in the early stages of silicon carbide growth, the step growth pattern on one side of the facet region is significantly different from that on the non-facet region. The facet side exhibits a spiral growth pattern and wide growth steps. If the radial temperature gradient of the facet region is small and the growth interface is flat, the facet will rapidly expand towards the center via a spiral growth mechanism, leading to a rapid increase in the facet area. According to the paper "Study on the Mechanism of Facet Formation Based on the Shape of Temperature Field" published by Hongyu Shao et al. in Crystal Growth & Design, the position of facet growth depends on the tangent position between the growth interface and the base plane. As the convexity of the growth interface increases, the tangent position moves from the edge of the ingot towards the center. Therefore, controlling the change in convexity during growth, so that the growth interface always maintains a near-flat, slightly convex state, can suppress the expansion of the facet towards the center region, thereby reducing the area of ​​the facet. Meanwhile, the morphology of the facets depends on the change of the local temperature field. The facet morphology can be controlled by adjusting the local temperature gradient of the seed crystal facets. Thermodynamic simulation results show that the width of the facets is inversely proportional to the radial temperature gradient of the ingot. A large local radial temperature gradient can form a relatively steep growth interface, thereby inhibiting the increase of the facet width and thus reducing the facet area.

[0061] Graphite possesses excellent thermal conductivity, and the graphite liner assembly inside the crucible can regulate the temperature gradient. The local temperature gradient can be altered through the structural design of the graphite liner assembly. Based on experimental research and literature, this application utilizes an asymmetric graphite tray design (the tray's thickness corresponding to the seed crystal facet region is less than the thickness of other regions) to change the local thermal conductivity of the thinned portion of the tray, thereby creating a larger temperature gradient. This results in a greater local temperature gradient on one side of the facet compared to other regions, making the growth interface at the facet more "steep" and inhibiting the expansion of the facet towards the crystal center.

[0062] Furthermore, the position of the facets depends on the convexity change of the crystal growth interface. As the crystal thickness increases during growth, the growth interface gets closer and closer to the high-temperature zone of the powder, and the radial temperature gradient increases continuously, leading to a continuous increase in crystal convexity. This causes the facets to continuously move towards the crystal center during growth, resulting in an increase in the facet area. Lower convexity can suppress the movement of the position where the growth interface is tangent to the base plane towards the crystal center, thereby controlling the expansion of the facet area. Therefore, one embodiment of this application also includes a heating coil movement process during growth. By matching the position of the heating coil with the crystal growth thickness, i.e., the position of the heating coil slowly decreases as the crystal growth thickness increases, the crystal maintains a low convexity throughout the growth process, thereby suppressing the displacement of the facets and preventing them from continuously moving towards the crystal center during growth, thus reducing the area of ​​the silicon carbide crystal facet growth.

[0063] The radial direction mentioned above refers to the direction perpendicular to the axial direction x.

[0064] Therefore, this application combines the structural design of the asymmetric tray with the crystal growth process of moving the heating coil to simultaneously achieve a large local temperature gradient on the small facet and a flat growth interface, thereby suppressing the expansion of the small facet area and keeping its position always at the edge of the ingot.

[0065] The following are specific examples of crystal growth process flow.

[0066] Example 1:

[0067] The second tray portion 22, with a thickness ratio of 1:2, is pressed together with the first tray portion 20 as follows: Figure 2 and Figure 3 Adhere the components together as shown, ensuring that air bubbles are completely eliminated during the adhesion process. Then, attach the seed crystal 16, which has the same diameter as the second tray 22, to the bottom surface of the second tray 22. Place the tray structure 14 with the seed crystal 16 attached into a curing oven for high-temperature curing, with a maximum curing temperature in the range of 800–1000°C. Finally, attach the cured tray structure 14 to the center of the bottom surface of the crucible lid 54, as shown. Figure 1 The crystal growth apparatus 10 shown is now assembled. The assembled crucible 12 is placed inside the insulation felt of the crystal growth furnace, and a vacuum is drawn to 10... -3 After introducing argon and nitrogen to 2 mbar, the temperature is raised to 2100℃. The heating coil is then moved downwards at a rate of 0.1 mm / h. After 150 h of growth, the crystal growth is stopped. After cooling to room temperature, the ingot 1 is removed.

[0068] Example 2:

[0069] The second tray portion 22, with a thickness ratio of 1:1.5, is pressed together with the first tray portion 20 as follows: Figure 2 and Figure 3 Adhere the components together as shown, ensuring that air bubbles are completely eliminated during the adhesion process. Then, attach the seed crystal 16, which has the same diameter as the second tray 22, to the bottom surface of the second tray 22. Place the tray structure 14 with the seed crystal 16 attached into a curing oven for high-temperature curing, with a maximum curing temperature in the range of 800–1000°C. Finally, attach the cured tray structure 14 to the center of the bottom surface of the crucible lid 54, as shown. Figure 1 The crystal growth apparatus 10 shown is now assembled. The assembled crucible 12 is placed inside the insulation felt of the crystal growth furnace, and a vacuum is drawn to 10... -3 After introducing argon and nitrogen to 2 mbar, the temperature is raised to 2100℃. The heating coil is then moved downwards at a rate of 0.15 mm / h. After 150 h of growth, the crystal growth is stopped. After cooling to room temperature, the ingot 2 is removed.

[0070] Example 3:

[0071] The second tray portion 22, with a thickness ratio of 1:1, is pressed together with the first tray portion 20 as follows: Figure 2 and Figure 3 Adhere the components together as shown, ensuring that air bubbles are completely eliminated during the adhesion process. Then, attach the seed crystal 16, which has the same diameter as the second tray 22, to the bottom surface of the second tray 22. Place the tray structure 14 with the seed crystal 16 attached into a curing oven for high-temperature curing, with a maximum curing temperature in the range of 800–1000°C. Finally, attach the cured tray structure 14 to the center of the bottom surface of the crucible lid 54, as shown. Figure 1 The crystal growth apparatus 10 shown is now assembled. The assembled crucible 12 is placed inside the insulation felt of the crystal growth furnace, and a vacuum is drawn to 10... -3 After introducing argon and nitrogen to 2 mbar, the temperature is raised to 2100℃. The heating coil is then moved downwards at a rate of 0.2 mm / h. After 150 h of growth, the crystal growth is stopped. After cooling to room temperature, the ingot is removed.

[0072] Comparative Example 1:

[0073] The seed crystal is attached to a tray, which is a single-layer graphite disk of uniform diameter, and assembled according to the normal furnace loading sequence described above. The assembled crucible is placed inside the insulation felt of the crystal growth furnace, and a vacuum of 100°C is applied. -3 After passing through mbar, argon and nitrogen are introduced to 2 mbar and the temperature is raised to 2100℃. After growing for 150 hours, the crystal growth is stopped. After cooling to room temperature, the ingot 4 is removed.

[0074] As shown in Table 1, the facet area ratio of the crystals produced in Examples 1-3 is less than 10% of the ingot cross-sectional area. Comparative Example 1, which did not use the asymmetric tray structure and heating coil moving process, exhibits a significantly larger facet area. This indicates that the technical solution of this application generates a large local radial temperature gradient at the seed crystal facet, effectively suppressing the expansion of the facet from the edge to the crystal center. Simultaneously, by moving the heating coil, the high-temperature line continuously moves downwards as the crystal thickness increases, thus maintaining a small temperature gradient at the growth interface and a small crystal convexity. This ensures that the facet remains on one side of the ingot and does not move towards the center. Combining these two technical advantages, the facet area growth during silicon carbide crystal growth can be effectively suppressed, resulting in silicon carbide ingots with smaller facet areas. This is beneficial for improving the N-doping uniformity of silicon carbide single-crystal substrates, reducing defect levels, and improving overall yield.

[0075] Table 1

[0076]

[0077]

[0078] In one technical solution provided in this application, the combination of an asymmetric tray structure and a crystal growth process involving moving heating coils achieves a large local temperature gradient on the facets, thereby suppressing the expansion of the facets towards the crystal center. The heating coils, which move downwards with the increasing ingot thickness during crystal growth, achieve a smaller radial temperature gradient at the growth interface, thus maintaining a small ingot convexity and suppressing the displacement of the facets towards the crystal center. Simultaneously, the large local temperature gradient on the facets and the flatness of the growth interface are achieved, thereby suppressing the expansion of the facet area and ensuring its position remains at the edge of the ingot. The prepared ingots have facet areas accounting for less than 10% of the ingot cross-sectional area, the ingots are free of polymorphic defects, and the maximum difference in in-plane resistivity is less than 1 mΩ·cm.

[0079] In summary, this application provides a crystal growth apparatus, including a crucible with a cavity, a tray structure disposed within the cavity, and a seed crystal. The tray structure is disposed between the inner surface of the top wall of the crucible and the seed crystal. The tray structure includes a first tray region and a second tray region with different thicknesses. The thickness of the second tray region is less than the thickness of the first tray region, and the first and second tray regions are coplanar on the side closest to the seed crystal. The spatial position of the second tray region corresponds to the facet growth region of the seed crystal. This application reduces the thickness of the portion of the tray structure corresponding to the facet growth region to change the local thermal conductivity of the thinned portion, making the local temperature gradient on the facet growth region side greater than other areas. This results in a steeper growth interface at the facet growth region, inhibiting the expansion of the facet growth region towards the crystal center, thereby achieving the effect of reducing the area growth of the facet growth region. The crystal growth apparatus of this application can effectively reduce the area of ​​the small facet growth region in silicon carbide crystals grown by PVT method, which is beneficial to reduce the defect level of silicon carbide single crystal growth, improve the uniformity of N doping, improve the yield of silicon carbide single crystal growth, and facilitate the growth and mass production of higher quality silicon carbide crystals.

[0080] The concepts described herein may be implemented in other forms without departing from their spirit and characteristics. The specific embodiments disclosed should be considered illustrative rather than restrictive. Therefore, the scope of this application is determined by the appended claims, and not by the preceding description. Any changes within the literal meaning and equivalent scope of the claims should fall within the scope of those claims.

Claims

1. A crystal growth apparatus, characterized in that, include: A crucible with a cavity; The tray structure and seed crystal are disposed within the cavity; in: The tray structure is disposed between the inner surface of the top wall of the crucible and the seed crystal; The tray structure includes a first tray area and a second tray area with different thicknesses. The thickness of the second tray area is less than the thickness of the first tray area, and the first tray area and the second tray area are coplanar on the side closest to the seed crystal. The spatial position of the second tray area corresponds to the facet growth area of ​​the seed crystal.

2. The crystal growth apparatus as described in claim 1, characterized in that, The tray structure includes: The first tray portion has its first surface connected to the inner surface of the top wall of the crucible; The second tray portion is stacked on the second surface of the first tray portion and connected to the seed crystal; in: The cross-sectional area of ​​the second tray portion is larger than that of the first tray portion; The first tray area is formed by the overlapping area of ​​the first tray portion and the second tray portion; The second tray area is formed by the non-overlapping area of ​​the second tray portion that extends beyond the first tray portion.

3. The crystal growth apparatus as described in claim 2, characterized in that, The circumferential side of the first tray portion includes a first side and a second side, the first side is disposed facing the second tray area, and the second side is coplanar with the circumferential side of the second tray portion.

4. The crystal growth apparatus as described in claim 2, characterized in that, Both the first tray portion and the second tray portion are circular. The diameter of the first tray portion is smaller than the diameter of the second tray portion. The first tray portion is eccentrically positioned relative to the second tray portion, and there exists a reference straight line that is tangent to both the first tray portion and the second tray portion.

5. The crystal growth apparatus as described in claim 4, characterized in that, The diameter of the seed crystal is the same as the diameter of the second tray portion.

6. The crystal growth apparatus as described in claim 3 or 4, characterized in that, The diameter ratio of the second tray portion to the first tray portion is 1.02 to 1.

1.

7. The crystal growth apparatus as described in claim 3 or 4, characterized in that, The thickness ratio of the second tray portion to the first tray portion is 1 to 2.

8. The crystal growth apparatus as described in claim 3 or 4, characterized in that, The seed crystal is a 4H type silicon carbide seed crystal. The side of the silicon carbide seed crystal facing away from the tray structure is a carbon surface. The side of the first tray portion facing the second tray area has a central cross-section. The silicon carbide seed crystal [11] 0] The direction is perpendicular to the central tangent.

9. The crystal growth apparatus according to any one of claims 2-5, characterized in that, The first tray portion and the second tray portion are integrally formed or separately connected.

10. The crystal growth apparatus according to any one of claims 2-5, characterized in that, The cavity is provided with an inner liner assembly, which includes a sleeve, a support ring, and a flow guide tube. The sleeve is attached to the inner surface of the side wall of the crucible and supported on the inner surface of the bottom wall of the crucible. One end of the support ring is connected to the top end of the sleeve and the other end is connected to the bottom end of the flow guide tube. The top end of the flow guide tube is located close to the seed crystal and surrounds the periphery of the seed crystal, and the diameter of the top end of the flow guide tube is smaller than the diameter of the bottom end of the flow guide tube. And / or, the crucible includes a crucible body and a crucible lid, the crucible lid is connected to the top of the crucible body, the crucible lid and the crucible body enclose the cavity, the tray structure is connected to the side of the crucible lid facing the crucible body, and the central axis of the second tray portion coincides with the central axis of the crucible; And / or, the crystal growth apparatus further includes a heating coil, which is arranged around the periphery of the crucible for heating the crucible, and the heating coil is configured to be movable along the central axis of the crucible.

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