A PVT growth device for large-size silicon carbide single crystal

Abstract

The present invention provides a PVT growth device for large-sized silicon carbide single crystals, comprising a growth furnace, an X-ray in-situ imaging module and a control system. The growth furnace comprises a furnace wall, a heat preservation felt, a plate-type resistance heater and a crucible from outside to inside. The X-ray in-situ imaging module comprises an X-ray source and an X-ray imaging receiver respectively arranged on opposite sides of the radial direction of the single crystal growth of the growth furnace; the furnace wall has non-metal windows for X-ray transmission on both sides of the radial direction, and the heat preservation felt, the plate-type resistance heater and the crucible are all made of non-metallic materials; the control system receives the imaging signal of the X-ray imaging receiver and controls the operation of the X-ray source and the plate-type resistance heater. The growth device can meet the small radial temperature gradient and the necessary axial temperature gradient required for the growth of large-sized silicon carbide PVT single crystals, and utilizes the information feedback of in-situ monitoring, which is of great significance for the regulation of the PVT growth process of high-quality, large-sized silicon carbide single crystal substrates.

Description

Technical Field

[0001] The invention relates to a semiconductor single crystal PVT growth device, in particular to a silicon carbide single crystal PVT growth device based on resistance heating and capable of in-situ monitoring and crystal growth regulation by X-rays. Background Art

[0002] Silicon carbide is a compound formed by C and Si. Among them, the hexagonal 4H-SiC (4H-SiC) has the advantages of high critical breakdown electric field and high electron mobility. It is an excellent semiconductor material for manufacturing high-voltage, high-temperature, and radiation-resistant power semiconductor devices. It is also the third-generation semiconductor material with the best comprehensive performance, the highest degree of commercialization, and the most mature technology. Compared with traditional silicon materials, its excellent physical properties are mainly manifested in the following: (1) critical breakdown electric field strength is nearly 10 times that of silicon; (2) high thermal conductivity, which is 3 times that of silicon materials; (3) high saturated electron drift velocity, which is 2 times that of silicon materials; (4) excellent radiation resistance and chemical stability; (5) like silicon materials, a silicon dioxide insulating layer can be directly grown on the surface by thermal oxidation process. Therefore, silicon carbide materials are considered to be the most ideal semiconductor devices to replace silicon-based power devices and have achieved rapid development in recent years.

[0003] At present, silicon carbide single crystal substrates are mainly prepared using physical vapor transport (PVT) growth technology, which has the characteristics of high growth temperature, complex chemical reactions involved, and the inability to observe the crystal growth process in real time and obtain growth information in a timely manner. In addition, the long growth cycle easily leads to reduced crystal growth quality and waste of raw materials. In addition, due to the control of the temperature field and the uniformity of vapor phase transport, the diameter of the silicon carbide single crystals currently prepared is generally small and the thickness is also limited, which leads to the relatively high cost of silicon carbide single crystal substrates, especially high-quality single crystal substrates with low defect density, which limits the large-scale application of the device. In order to further reduce the cost of the substrate, the preparation of large-size (≥6 inches) and high-quality single crystals is particularly important. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a PVT growth device for large-sized silicon carbide single crystals, which uses a plate-type resistance heater as the basis for the construction of a growth chamber to achieve the uniform radial thermal field distribution and axial gradient field required for the growth of ≥6-inch single crystals, and uses an in-situ X-ray imaging device to implement in-situ monitoring of the growth process and crystal growth parameter regulation, thereby meeting the thermal field and crystal growth process regulation required for the growth of large-sized single crystals. To achieve the above functions, the resistance heater is composed of a combined heater, combined with a graphite crucible, insulation felt, and an auxiliary system, which is used to construct the thermal field required for the growth of large-sized (6-8 inches) single crystals; the material selection and setting of the chamber components can meet the effective penetration of X-rays; the light source of the X-ray in-situ imaging module sequentially reaches the opposite side of the furnace body through the furnace wall, insulation felt, crucible and other media, and the imaging detector realizes imaging in the crucible, thereby realizing in-situ monitoring of the growth process and growth regulation. In addition, by utilizing the axial up and down translation of the X-ray emitting end / receiving imaging end and combining it with computer image processing, it is also possible to scan the entire crucible growth area in two-dimensional and three-dimensional imaging, and realize dynamic monitoring of reaction processes such as crystal morphology, powder consumption, and crucible carbonization during the growth process, thereby providing a basis for growth regulation.

[0005] In order to achieve the above purpose, the technical solution of the present invention is:

[0006] A PVT growth device for large-size silicon carbide single crystals, comprising a growth furnace, an X-ray in-situ imaging module arranged outside the growth furnace, and a control system; the growth furnace comprises a furnace wall, a thermal insulation felt, a plate-type resistance heater, and a crucible from the outside to the inside; the X-ray in-situ imaging module comprises an X-ray source and an X-ray imaging receiver, and the X-ray source and the X-ray imaging receiver are respectively arranged on opposite sides of the radial direction of the single crystal growth of the growth furnace; the furnace wall has non-metallic windows on both sides of the radial direction for X-ray transmission, and the thermal insulation felt, the plate-type resistance heater and the crucible are all made of non-metallic materials; the control system is connected to the X-ray source, the X-ray imaging receiver and the plate-type resistance heater, the control system receives the signal imaging of the X-ray imaging receiver, and controls the operation of the X-ray source and the plate-type resistance heater.

[0007] Optionally, the plate-type resistance heater is made of a graphite plate with a thickness of 5 to 30 mm.

[0008] Optionally, the plate-type resistance heater includes one or more side wall barrel-shaped arc plate heaters and a bottom flat plate heater arranged outside the crucible, and the one or more side wall barrel-shaped arc plate heaters and the bottom flat plate heater are respectively connected to the control system, and the control system independently controls the heating of each heater.

[0009] Optionally, the X-ray in-situ imaging module also includes a driving device; the driving device is connected to the control system, and drives the X-ray source to translate along the longitudinal and transverse directions of the growth furnace under the control of the control system.

[0010] Optionally, the X-ray source is a point light source, a line light source or a surface light source, and the light source acceleration voltage is 50 to 350 KV.

[0011] Optionally, the non-metallic window is made of quartz or alumina.

[0012] Optionally, the insulation felt and the crucible are made of graphite.

[0013] Optionally, the furnace wall is a double-layer hollow structure, and the hollow part is used to form a cooling water channel.

[0014] Optionally, the non-metallic window, thermal insulation felt, plate-type resistance heater and crucible have uniform thickness distribution in the direction of X-ray penetration.

[0015] Optionally, the size of the large-size silicon carbide single crystal is ≥ 6 inches.

[0016] The beneficial effects of the present invention are:

[0017] The main function of the PVT growth device of the present invention is to use resistive heating, combined with supporting crucibles and other components, to meet the temperature field required for the growth of large-sized silicon carbide; it can also realize in-situ monitoring of single crystal growth changes, powder consumption and other crucible structure and morphology information during long-term single crystal growth through auxiliary X-ray in-situ monitoring modules and matching structures, thereby realizing timely adjustment of growth parameters to meet the preparation of high-quality, large-sized single crystals. To achieve the above functions, the growth device adopts an improved non-metallic resistive heating module. On the one hand, the non-metallic resistive heating method adopted can significantly improve the thermal field distribution in the crucible of the large-sized PVT growth furnace, and realize a slightly convex or near-zero radial temperature field distribution in the single crystal growth area, which is conducive to the preparation of large-sized single crystals of more than 6 inches; on the other hand, the supporting X-ray imaging module and the corresponding structural setting can truly realize in-situ monitoring of the growth process, overcoming the disadvantages of the traditional inductive heating equipment that cannot realize in-situ imaging or low imaging resolution due to the strong absorption of X-rays by the metal inductor coil. In addition, in terms of imaging function, the X-ray light source proposed in this case that can move in the lateral and axial directions can ensure effective imaging of the entire crucible. This large-size silicon carbide single crystal growth device plays an important guiding role in constructing a high-quality temperature field suitable for large-size single crystals, and timely adjusting growth parameters by obtaining the growth of silicon carbide single crystals and the consumption of raw materials in the crucible in real time. It can be used for high-quality PVT preparation of high-quality, large-size silicon carbide (6 inches and above) single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The schematic diagram of the structure of a large-size silicon carbide single crystal growth device according to an embodiment, wherein 1-silicon carbide single crystal growth crucible, 2-silicon carbide seed crystal, 3-plate-type resistance heater, 4-silicon carbide powder, 5-insulation felt, 6-furnace wall, 7-crucible axis and temperature measuring hole, 8-non-metallic window, 9-X-ray source, 10-X-ray imaging receiver;

[0019] Figure 2 A schematic diagram of a control system of a large-size silicon carbide single crystal growth device according to an embodiment;

[0020] Figure 3 for Figure 1 Schematic diagram of the principle of X-ray scanning and imaging in the X-axis and Z-axis; Based on the growth furnace and in-situ X-ray monitoring principle, the X-ray in-situ imaging of the entire silicon carbide growth crucible can be further satisfied by scanning in the X-axis and Z-axis;

[0021] Figure 4 for Figure 1 The thermal field distribution diagram obtained by graphite resistance heating; From the figure, it can be seen that the resistance electric heating can achieve a radial temperature gradient of nearly zero (≤1°C) in the seed crystal growth area in a large-sized crystal growth furnace (8 inches), which can meet the high-quality preparation of large-sized silicon carbide single crystals;

[0022] Figure 5 The structure of a silicon carbide single crystal PVT growth furnace using an induction coil for heating is shown in the comparative example (existing technology), wherein 1-silicon carbide single crystal growth crucible, 2-silicon carbide seed crystal, 3-silicon carbide powder, 4-furnace wall, 5-coil, 6-crucible axis and temperature measuring hole; it can be seen from the figure that during the single crystal growth process, the metal coil is wrapped around the periphery of the growth crucible, resulting in the inability to achieve the X-ray imaging required for single crystal growth directly on the inside of the crucible;

[0023] Figure 6 for Figure 5 The thermal field distribution diagram of the inductor coil in a large-sized (8-inch) crystal growth crucible; it can be seen from the figure that the inductor coil has a bottleneck in the uniformity of the radial temperature field distribution of the crucible, and a small or near-zero radial temperature distribution cannot be achieved in the area where the silicon carbide single crystal grows (seed crystal substrate area), which is not conducive to the growth of large-sized silicon carbide single crystals. DETAILED DESCRIPTION

[0024] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The accompanying drawings of the present invention are only for illustration to make it easier to understand the present invention, and the specific proportions thereof can be adjusted according to design requirements.

[0025] The present invention provides a large-size silicon carbide single crystal growth device, including a thermal field structure using a non-metallic plate-type resistance heater as a heating path, an X-ray imaging module capable of realizing in-situ monitoring of the silicon carbide single crystal growth process, and a furnace structure that meets the above functions. The growth device can meet the small radial temperature gradient and necessary axial temperature gradient required for the growth of large-size silicon carbide PVT single crystals, and utilizes the information feedback of in-situ monitoring to be used for the PVT preparation of large silicon carbide single crystals of 6 inches and above.

[0026] refer to Figure 1 , a PVT growth device for large-size silicon carbide single crystals according to one embodiment includes a growth furnace, an X-ray in-situ imaging module and a control system arranged outside the growth furnace. The growth furnace includes a furnace wall 6, a thermal insulation felt 5, a plate-type resistance heater 3 and a silicon carbide single crystal growth crucible 1 from the outside to the inside. Silicon carbide seed crystals 2 and silicon carbide powder 4 are placed in the silicon carbide single crystal growth crucible 1. The crucible 1 is also connected to a crucible shaft and a temperature measuring hole 7. A non-metallic window 8 for X-rays to pass through is provided on the furnace wall 6. The X-ray in-situ imaging module includes an X-ray source 9 and an X-ray imaging receiver 10. Combined with Figure 1 and Figure 2 The PVT growth device for large-size silicon carbide single crystals mainly includes the following features and achievable functions:

[0027] S1: The heating unit of the device is composed of a plate-shaped resistance heater 3 made of non-metallic material, the shape and thickness of which are evenly distributed along the axial direction of the single crystal growth, preferably composed of a plate-like structure, and has high and uniform penetration of X-rays;

[0028] S2: The heating unit of the device adopts a combined resistance heater of multiple heater units, which is typically arranged around the outside of the crucible 1 in the form of a combination of a side wall cylindrical plate heater and a bottom flat plate heater. The supporting crucible 1, insulation felt 5, furnace wall 6, cooling water circulation system, vacuum system and other functional components form the thermal field and chamber environment required for the growth of large-size single crystals;

[0029] S3: The growth device has an X-ray in-situ monitoring module. In the radial direction of the single crystal growth, the X-rays emitted by the X-ray source 9 are sequentially transmitted through the non-metallic window 8 of the external furnace wall, the vacuum layer in the growth furnace, the insulation felt 5, the crucible 1, the powder material (or the single crystal growth area) and other symmetrical structures to the opposite X-ray imaging receiver 10, thereby forming an image of the inside of the growth crucible;

[0030] S4: To achieve the above-mentioned in-situ imaging and monitoring effects, the non-metallic window 8, the thermal insulation felt 5, and the crucible 1 area through which the X-rays pass are all made of non-metallic materials, and the thickness is uniformly distributed in the radial direction;

[0031] S5: The X-ray imaging function is realized by an imaging module composed of an X-ray source 9, an X-ray imaging receiver 10, and an auxiliary computer control system;

[0032] S6: Based on the feedback of X-ray in-situ imaging and monitoring inside the crucible, the control system can control the adjustment of the power of the plate-type resistance heater 3 and the relative position of the crucible to meet the growth surface temperature field distribution and mass transfer process required for the continuous growth of large-size, high-quality single crystals; the crucible position is achieved by moving up and down in the vertical direction through the guide rail and drive device connected to the crucible to change the relative position between the crucible and the heater.

[0033] The plate-type resistance heater 3 made of non-metallic material is preferably made of graphite material with a thickness of 5 to 30 mm. The thickness in the traditional transverse direction of X-rays is kept uniform to facilitate the uniform penetration of X-rays; the side wall barrel-shaped plate-type heater and the bottom flat plate heater can be driven and controlled by independent power by the control system, including but not limited to DC constant voltage heating, and its heating power value can be linearly adjusted. The metal electrode terminals of the plate-type resistance heater 3 can be distributed at the top or bottom of the barrel-shaped heater and the bottom of the disc-shaped heater to avoid the area where X-rays pass through and reduce the potential imaging interference inside the crucible caused by the electrode absorbing X-rays. Further, the large-size single crystal growth chamber formed by the S2 is composed of the crucible 1, the plate-type resistance heater 3 and the insulation felt 5 to form the thermal field temperature required for the growth of the furnace body; the basic vacuum furnace body structure of the growth furnace is composed of the known support parts, furnace walls, etc., as well as operations such as crucible lifting; the cooling water circulation system is used to ensure the low temperature and low temperature deformation of the furnace body shell. The large-size single crystal growth chamber formed can achieve a radial growth surface temperature difference of ≤2°C for large-size single crystals ≥6 inches, and the center temperature of the formed temperature field is slightly lower and the edge temperature is slightly higher.

[0034] The furnace wall 6 can be composed of a non-metallic or non-metallic-metal composite structure, wherein the non-metallic part (non-metallic window 8) is used for the passage of X-rays, and the non-metallic material is preferably a material with high mechanical strength and high penetration of X-rays, such as quartz and alumina; in order to improve the mechanical stability of the furnace wall, the furnace wall can be a double-layer hollow structure for forming a cooling water channel to achieve water cooling; considering that high temperature may affect the X-ray surface detector, the non-metallic material close to the imaging detector side can also be a double-layer water-cooled structure or an additional water-cooling channel can be added near it. In order to reduce thermal stress and enhance wall strength, cooling water can be introduced around the window or in the interlayer of the furnace wall. Similar to the conventional PVT growth device, the enclosed space formed by the entire furnace wall has good vacuum tightness, which can meet the vacuum environment required for silicon carbide PVT growth.

[0035] The relative distance between the X-ray source 9 and the X-ray imaging receiver 10 (planar imaging detector) is fixed. The X-ray point light source irradiates the growth chamber through the quartz window at a certain divergence angle. The emission angle is 0 to 30°. The acceleration voltage of the X-ray light source is 50 to 350 kV. The structural information in the growth chamber is projected to the planar imaging unit on the opposite side. The X-ray absorption rate of different materials in the chamber is used for corresponding contrast imaging.

[0036] The X-ray source 9 can be driven to translate along the longitudinal or lateral direction of the growth furnace by a driving device such as a linear module. The driving device is controlled by a control system to complete full coverage scanning imaging of the growth crucible or imaging of a specific area. In order to improve the clarity of the imaging, it can be achieved by adjusting the power of the X-ray source and the image processing function, and virtual three-dimensional imaging can be achieved. Based on the design of the above-mentioned furnace body, the X-rays can effectively pass through the single crystal growth area in the lateral direction and form an image on the opposite imaging detector. Typical information obtained includes the evolution of the single crystal growth process, the position of the growth surface, the formation of polycrystalline by-products, the consumption of powder, the surface morphology of powder, the consumption of the crucible and other information. In order to achieve imaging of the entire crucible, the provided X-ray light source can translate along the Z-axis and X-axis directions to achieve scanning of the entire crucible area; combined with the image processing function of the imaging device, such as the image stitching function, imaging of the entire crucible can be achieved, such as Figure 3 As shown. The X-ray imaging module can be processed into a structural module that is easy to disassemble and install quickly to meet the needs of multiple sets of imaging devices. The feedback of X-ray in-situ imaging and monitoring in the crucible includes but is not limited to the evolution of single crystal morphology, growth rate, powder consumption, changes in powder morphology, evolution of amorphous areas, consumption of C in the crucible and other information.

[0037] When in use, the silicon carbide seed crystal 2 and the silicon carbide powder 4 are placed in the crucible 1, and the conventional PVT growth process is used for single crystal growth. During the growth process, the control system controls the X-ray source to emit X-rays, and controls the X-ray source to translate for scanning through the driving device. The X-ray imaging receiver detects the signal after the X-ray passes through the growth furnace to form an image in the crucible, and transmits the imaging signal to the control system. By monitoring the real-time status of the single crystal growth in the crucible, the control system can control the power adjustment of each unit of the plate-type resistance heater to change the growth conditions, so as to meet the growth surface temperature field distribution and mass transfer process required for the continuous growth of large-size, high-quality single crystals. Among them, the control system can be a single-chip microcomputer, a computer, etc., and includes equipment units such as position sensors as needed.

[0038] The above-mentioned resistance heating method can significantly improve the radial temperature gradient of the single crystal growth interface, achieve a near-zero radial temperature difference, and meet the high-quality preparation of large-size single crystals (≥6 inches). Figure 4As shown, the temperature field distribution is achieved by combining a typical barrel-type side heater with a bottom disk-type graphite resistance heater, wherein the crucible can meet the growth of single crystals with a maximum size of 200 mm (8 inches).

[0039] Through the arrangement of the non-metallic window of the furnace wall, the plate-type resistance heater made of non-metallic material, the thermal insulation felt made of graphite material, etc., it can be understood that by using an X-ray imaging device to irradiate the silicon carbide single crystal growth crucible on the physical structure, a clear structure of the crucible can be seen, especially the morphology of the silicon carbide seed crystal (growth zone).

[0040] As a comparative example, Figure 5 The figure shows a conventional silicon carbide PVT single crystal furnace using induction heating, including the same silicon carbide single crystal growth crucible 1, silicon carbide seed crystal 2, silicon carbide powder 3, furnace wall 4 made of conventional materials, crucible shaft and temperature measuring hole 6, and metal coil 5 wound outside the growth furnace. It can be seen from the simulation that the adhesion heat effect of induction heating itself leads to a large radial thermal field distribution gradient at the crystal growth interface in the furnace body ( Figure 6 ), which is easy to produce large stress in the crystal, which is not conducive to the growth of large-sized single crystals with uniform quality. In addition, it can be seen that the peripheral induction metal coil is not conducive to the transmission and imaging of X-rays.

[0041] The large-size silicon carbide single crystal PVT growth device of the present invention can also be used for in-situ monitoring of other PVT material growth systems, such as in-situ monitoring of PVT growth of semiconductor materials such as aluminum nitride.

[0042] The above embodiments are only used to further illustrate a PVT growth device for large-size silicon carbide single crystals of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the technical solution of the present invention.

Claims

1. A PVT growth device for large-size silicon carbide single crystals, characterized in that: The size of the large-size silicon carbide single crystal is ≥6 inches; the growth device includes a growth furnace, an X-ray in-situ imaging module and a control system arranged outside the growth furnace; the growth furnace includes a furnace wall, a thermal insulation felt, a plate-type resistance heater and a crucible from the outside to the inside; the X-ray in-situ imaging module includes an X-ray source and an X-ray imaging receiver, and the X-ray source and the X-ray imaging receiver are respectively arranged on opposite sides of the radial direction of the single crystal growth of the growth furnace; the furnace wall has non-metallic windows for X-ray transmission on both sides of the radial direction, and the thermal insulation felt, the plate-type resistance heater and the crucible are all made of non-metallic materials; the control system is connected to the X-ray source, the X-ray imaging receiver and the plate-type resistance heater, the control system receives the signal imaging of the X-ray imaging receiver, and controls the operation of the X-ray source and the plate-type resistance heater; the plate-type resistance heater is composed of a graphite plate with a thickness of 5~30 mm; the plate-type resistance heater includes one or more side wall barrel-shaped arc plate heaters and a bottom flat plate heater arranged outside the crucible, and the one or more side wall barrel-shaped arc plate heaters and the bottom flat plate heater are respectively connected to the control system, and the control system independently controls the heating of each heater.

2. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The X-ray in-situ imaging module also includes a driving device; the driving device is connected to the control system and drives the X-ray source to translate along the longitudinal and transverse directions of the growth furnace under the control of the control system.

3. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The X-ray source is a point light source, a line light source or a surface light source, and the light source acceleration voltage is 50-350 KV.

4. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The non-metal window is made of quartz or alumina.

5. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The insulation felt and the crucible are made of graphite.

6. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The furnace wall is a double-layer hollow structure, and the hollow part is used to form a cooling water channel.

7. The PVT growth device for large-size silicon carbide single crystal according to claim 1, characterized in that: The thickness of the non-metallic window, the thermal insulation felt, the plate-type resistance heater and the crucible is evenly distributed in the direction in which the X-ray penetrates.

Images