A method for preparing a filter layer and a crystal growth device

Abstract

The present application provides a preparation method of a filter layer and a crystal growth device, the crystal growth device includes a crucible and a filter layer, the crucible has a growth cavity; the filter layer is arranged in the growth cavity, and the growth cavity is separated into a raw material cavity and a crystal cavity that are interconnected; wherein the filter layer includes a loose layer and a plurality of spherical structures embedded in the loose layer, the material of the loose layer is metal carbide, and the loose layer has micropores that connect the raw material cavity and the crystal cavity. Specifically, the filter layer is not corroded by the growth atmosphere before, during and after the crystal growth, and its components are metal carbides, the structure is stable at high temperature, and no carbon particles are generated, so that the use of the filter layer for crystal growth can effectively reduce the carbon inclusions on the crystal and improve the product yield.

Description

Technical Field

[0001] The invention relates to the field of semiconductors, and in particular to a preparation method of a filter layer and a crystal growth device. Background Art

[0002] Silicon carbide (SiC) crystal materials have the characteristics of wide bandgap, high thermal conductivity, high breakdown electric field, high radiation resistance, etc., and semiconductor devices made from them can meet today's demand for high-power and strong radiation devices. They are ideal substrate materials for preparing high-temperature, high-frequency, high-power and radiation-resistant devices, and are emerging in the fields of hybrid vehicles, high-voltage power transmission, LED lighting, aerospace, etc.

[0003] At present, the main production methods of silicon carbide crystals include physical vapor transport, high-temperature chemical vapor deposition, liquid phase epitaxy, etc.

[0004] However, the silicon carbide crystals produced by the existing process have a high density of carbon inclusions in the silicon carbide crystals, resulting in a low product yield. Summary of the invention

[0005] The present application provides a method for preparing a filter layer and a crystal growth device, which can solve the problem of high density of carbon inclusions in silicon carbide crystals, resulting in low product yield.

[0006] In order to solve the above technical problems, a technical solution adopted in the present application is: to provide a crystal growth device, comprising: a crucible and a filter layer, the crucible having a growth chamber; the filter layer is arranged in the growth chamber, and divides the growth chamber into a raw material chamber and a crystal chamber that are interconnected; wherein the filter layer comprises a loose layer and a plurality of spherical structures embedded in the loose layer, the material of the loose layer is metal carbide, and the loose layer has micropores that connect the raw material chamber and the crystal chamber.

[0007] In one embodiment, the spherical structure is a metal ball and / or a graphite ball.

[0008] In one embodiment, the diameter of the spherical structure is 0.1mm-3mm, and the thickness of the loose layer is 5mm-20mm; and / or the spherical structure is a metal ball, or the spherical structure is a metal ball and a graphite ball, and the material of the metal ball is one or more of tantalum, niobium, molybdenum and tungsten.

[0009] In one embodiment, the arrangement of the plurality of spherical structures in the loose layer is multi-layer stacking.

[0010] In one embodiment, the height of the plurality of spherical structures stacked in multiple layers is the same as the thickness of the loose layer.

[0011] In one embodiment, at least one balance adjustment ring is further included, which is stacked on one side of the filter layer close to the crystal cavity. The balance adjustment ring has a plurality of evenly distributed through holes, and the radius of the plurality of through holes gradually decreases along the direction from the center of the balance adjustment ring to the edge of the circle.

[0012] In one embodiment, one of the plurality of through holes is disposed at the center of the balance adjustment ring, and the other through holes are distributed on the balance adjustment ring to form a plurality of concentric rings, and the plurality of through holes in the same ring have the same radius.

[0013] In one embodiment, the number of the balancing adjustment rings is 2 and they are stacked; wherein the number of through holes on the two balancing adjustment rings is the same and they are arranged in a one-to-one correspondence.

[0014] In one embodiment, the crucible includes a crucible body and a crucible cover, and the crucible body and the crucible cover cooperate to define the growth chamber; a seed crystal layer is provided on the crucible cover, and the seed crystal layer is located in the crystal chamber; the crystal growth device also includes a guide ring, which is arranged in the crystal chamber and close to the crucible cover, and the guide ring has an air guide channel, and the air guide channel is used to guide the growth atmosphere generated in the raw material chamber to the growth surface of the seed crystal layer.

[0015] In order to solve the above technical problems, a technical solution adopted in the present application is: to provide a method for preparing a filter layer for use in a crystal growth device, comprising: filling a mixed slurry formed by mixing metal oxide powder, carbon source and slurry into a first mold, baking and curing it to form a prefabricated filter layer; and sintering the prefabricated filter layer.

[0016] In one embodiment, a plurality of spherical structures are arranged in the first mold; the mixed slurry formed by mixing the metal oxide powder, the carbon source and the slurry is filled in the gaps between the plurality of spherical structures in the first mold and covers the plurality of metal spherical structures; the upper surface of the mixed slurry is flattened; the mixed slurry and the plurality of spherical structures in the first mold are baked and solidified to form the prefabricated filter layer.

[0017] In one embodiment, the step of sintering the prefabricated filter layers includes: transferring several of the prefabricated filter layers to a second mold; placing the second mold into a growth chamber of a crystal growth furnace; evacuating the growth chamber of the crystal growth furnace to a vacuum state and then introducing an inert gas; sintering several of the prefabricated filter layers for a first preset time under conditions of a preset temperature and a first preset pressure; and sintering several of the prefabricated filter layers for a second preset time under conditions of gradually decreasing the preset temperature to room temperature and a second preset pressure.

[0018] In one embodiment, the ratio of metal ions to carbon sources in the mixed slurry is 1:1-1:2; and the concentration of the metal ions is 0.1 mol-3 mol.

[0019] In one embodiment, the metal oxide powder includes at least one of tantalum oxide powder, niobium oxide powder, molybdenum oxide powder and tungsten oxide powder, the carbon source is carbon powder and / or graphite, and the slurry includes polyvinyl butyral, acetylacetone and phenolic resin.

[0020] In one embodiment, the preset temperature is 2000° C.-2500° C., the first preset pressure is 1 mbar-10 mbar, the second preset pressure is 500 mbar-900 mbar, the first preset time is 0.1 h-10 h, and the second preset time is 5 h-20 h.

[0021] Different from the prior art, the present application provides a preparation method of the filter layer of the present application and a crystal growth device, the crystal growth device includes a crucible and a filter layer, the crucible has a growth cavity; the filter layer is arranged in the growth cavity, and the growth cavity is separated into a raw material cavity and a crystal cavity that are interconnected; wherein the filter layer includes a loose layer and a plurality of spherical structures embedded in the loose layer, the material of the loose layer is metal carbide, and the loose layer has micropores that connect the raw material cavity and the crystal cavity. Specifically, the filter layer is not corroded by the growth atmosphere before, during and after the crystal growth, and its components are metal carbides, the structure is stable at high temperature, and no carbon particles are generated, so that the use of the filter layer for crystal growth can effectively reduce the carbon inclusions on the crystal and improve the product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0023] Figure 1 A schematic structural diagram of an embodiment of a crystal growth device provided in the present application;

[0024] Figure 2 A schematic structural diagram of an embodiment of a filter layer in a crystal growth device provided in the present application;

[0025] Figure 3 A schematic structural diagram of an embodiment of a balance adjustment ring in a crystal growth device provided by the present application;

[0026] Figure 4 for Figure 3The cross-sectional view of the balance adjustment ring along line AA is shown;

[0027] Figure 5 A schematic structural diagram of an embodiment of a guide ring in a crystal growth device provided in the present application;

[0028] Figure 6 for Figure 5 The cross-sectional view of the guide ring along line BB is shown;

[0029] Figure 7 A schematic flow chart of an embodiment of a method for preparing a filter layer provided in the present application;

[0030] Figure 8 for Figure 7 A schematic diagram of a specific process of step S1 in the method for preparing the filter layer shown;

[0031] Fig. 9 for Figure 7 The specific flow chart of step S2 in the method for preparing the filter layer is shown. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] The terms "first", "second", "third" in this application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", "third" can expressly or implicitly include at least one of the features. In the description of this application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of this application, all directional indications (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the steps or units listed, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] The present application is described in detail below with reference to the accompanying drawings and embodiments.

[0036] Among the production methods of silicon carbide crystals, the physical vapor transport method is the most mature, and this method is adopted by most research institutions and companies in the world. The physical vapor transport method uses medium-frequency induction heating, a high-density graphite crucible as a heating element, silicon carbide raw materials are placed at the bottom of the crucible, and the silicon carbide seed crystal layer is at the top of the crucible. The growth of 4H-SiC generally uses the C surface as the growth surface for crystal growth. By adjusting the insulation layer outside the crucible (usually using insulation carbon felt), the temperature in the SiC raw material area is higher, while the temperature at the top crucible cover seed crystal is lower. Then the silicon carbide raw material must be directly sublimated into Si, Si2C, SiC2 and other gases at a temperature above 2100°C and a low-pressure environment, and transferred from the high-temperature area to the seed crystal layer in the lower temperature area along the temperature gradient to deposit and crystallize into silicon carbide crystals. Among them, in the physical vapor deposition method, the growth atmosphere in the crucible is mainly advection in the vertical direction, the axial temperature gradient dominates the transmission rate of the atmosphere, and the concentration gradient dominates the flow direction of the gas.

[0037] During the growth of silicon carbide crystals, the average particle size of the silicon carbide raw material used is about 200um, but the particle size distribution range of the silicon carbide raw material is relatively wide, with the finest particle diameter being only a few microns, and the coarse particles being up to several hundred microns or even millimeters. In the early stage of silicon carbide crystal growth, since the growth temperature is relatively low at this time, the gas phase vapor pressure in the growth chamber is low, so the growth rate is slow, and the raw material graphitization has not yet begun. As the growth proceeds, the gas phase vapor pressure in the growth chamber gradually increases, and the fine particles of the raw material gradually begin to graphitize. The graphitized fine particles may be brought to the growth surface of the seed layer under the convection of the gas phase vapor in the growth chamber, thereby starting to produce carbon inclusions in the growing silicon carbide crystals. However, since the growth has just begun, the silicon carbide raw material has just begun to graphitize, and there are fewer graphite particles, and the density of the carbon inclusions is low at this time. As the growth progresses, the silicon carbide raw material is severely graphitized and a large number of graphite particles are produced. These fine graphite particles are easily driven to the growth surface of the silicon carbide crystal by the sublimated airflow and the convection of the gas phase vapor, thereby forming carbon inclusions in the silicon carbide crystal, affecting the product yield.

[0038] Research has found that microtubes are "killer-type" defects in silicon carbide crystals. The presence of this defect will seriously affect the performance of silicon carbide devices. Microtube density has become one of the most important indicator parameters of silicon carbide wafers. Carbon inclusions are a source of microtubes in crystals. Observations have found that carbon inclusions can both terminate microtubes and induce the generation of microtubes. Therefore, in order to reduce the density of microtubes, in addition to selecting high-quality seed crystals and suppressing the occurrence of polymorphic phase transitions, it is also necessary to suppress the generation of carbon inclusions in silicon carbide crystals.

[0039] The applicant of this application has discovered that the existing technology places porous graphite on the surface of the raw material to filter the carbon particles in the growth atmosphere. After slicing the silicon carbide crystals grown by this measure, it was found that the carbon inclusions in the substrate in the early stage of growth were significantly reduced and improved a lot, but the quality of the substrate in the later stage of growth was significantly deteriorated, and more carbon inclusions were produced in the substrate. This is mainly because the porous graphite is constantly eroded by the atmosphere during the crystal growth process, resulting in continuous pulverization of the porous graphite. The pulverized carbon particles are still brought to the crystal growth surface with the growth atmosphere and then enter the crystal to form carbon inclusions, affecting the product yield.

[0040] For this purpose, see Figure 1 and Figure 2 , Figure 1 A schematic structural diagram of an embodiment of a crystal growth device provided in the present application; Figure 2 A schematic diagram of the structure of an embodiment of a filter layer in a crystal growth device provided by the present application. The present application provides a crystal growth device 100, comprising a crucible 10 and a filter layer 20, wherein the crucible 10 has a growth chamber 11; the filter layer 20 is disposed in the growth chamber 11, and separates the growth chamber 11 into a raw material chamber 111 and a crystal chamber 112 that are interconnected; wherein the filter layer 20 comprises metal carbides, which are structurally stable at high temperatures, do not generate carbon particles, and can filter fine particles after graphitization of the raw material, so that the use of the filter layer 20 for crystal growth can effectively reduce the carbon inclusions on the silicon carbide crystals and improve the product yield.

[0041] In one embodiment, the crucible 10 includes a crucible body 12 and a crucible cover 13, and the crucible body 12 and the crucible cover 13 cooperate to define a growth chamber 11; a seed crystal layer 14 is provided on the crucible cover 13, and the seed crystal layer 14 is located in the crystal cavity 112, and the growth atmosphere is deposited and crystallized into silicon carbide crystals at the growth surface of the seed crystal layer 14.

[0042] In one embodiment, the filter layer 20 includes a loose layer 21 and a plurality of spherical structures 22 embedded in the loose layer 21. The metal carbide forms the loose layer 21, and the loose layer 21 has micropores (not shown) connecting the raw material cavity 111 and the crystal cavity 112. The arrangement of the plurality of spherical structures 22 in the loose layer 21 is a single-layer arrangement or a multi-layer stacking, and the height of the plurality of spherical structures 22 in a single-layer arrangement or a multi-layer stacking arrangement is the same as the thickness of the loose layer 21. During the preparation of the filter layer 20, the surfaces of the plurality of adjacent spherical structures are slightly melted and connected. Therefore, the plurality of spherical structures 22 can improve the structural stability of the filter layer 20, so that the diameter of the filter layer 20 can be made larger.

[0043] The plurality of spherical structures 22 may be metal balls or graphite balls, or may be partially metal balls and partially graphite balls, which is not limited here. Specifically, the raw material cost of graphite balls is low, while the structural stability of metal balls is good. Therefore, the ratio of the plurality of spherical structures 22 may be selected according to actual conditions, as long as the structural stability of the filter layer 20 can be ensured.

[0044] The metal ball is made of one or more of tantalum, niobium, molybdenum and tungsten. The metal ball can react with carbon atoms in the growth atmosphere at high temperature to form high temperature resistant carbide metals, which slightly reduces the partial pressure of carbon atoms in the growth atmosphere, slightly lower than the saturation partial pressure in the growth atmosphere, making it difficult for graphite particles of a few microns to tens of microns to survive in a silicon-rich atmosphere. The main reactions are Si2C+C=2SiC and Si+C=SiC; and because tungsten, molybdenum, tantalum, niobium and other materials are also heating elements in eddy current heating, the mesh will not be blocked due to the recrystallization of the atmosphere on its surface.

[0045] In one embodiment, in order to improve the filtering ability of graphite particles in the growth atmosphere, the arrangement of the plurality of spherical structures 22 in the loose layer 21 is a multi-layer stacking, specifically, the diameter of the spherical structure 22 is 0.1mm-3mm, and the thickness of the loose layer 21 is 5mm-20mm. For example, the diameter of the spherical structure 22 is 2.5mm, the thickness of the loose layer 21 is 5mm, and the arrangement of the plurality of spherical structures 22 in the loose layer 21 is a double-layer stacking; for example, the diameter of the spherical structure 22 is 2mm, the thickness of the loose layer 21 is 10mm, and the arrangement of the plurality of spherical structures 22 in the loose layer 21 is a five-layer stacking.

[0046] Among them, in the physical vapor transport method, in the gas phase area on the silicon carbide raw material, and on the same cross section of the crucible 10, the temperature at the center is the lowest and the temperature at the edge is the highest, which will cause the growth atmosphere to flow along the inner wall to flow faster, while the growth atmosphere sublimated in the middle of the silicon carbide raw material will rise more slowly. And because the electromagnetic coil is a spiral rising structure, the magnetic flux passing through the crucible 10 at different directions is different, and the induced current density is also different, so the concentration of the atmosphere sublimated at different directions of the inner wall of the crucible 10 is also different, and the growth atmosphere may produce clockwise and counterclockwise flow directions.

[0047] In addition, in order to reduce production costs during the production process, the crucible 10 and the thermal insulation carbon felt are basically reused, and the silicon atoms in the growth atmosphere will continuously erode the crucible 10 and the thermal insulation carbon felt, seize carbon atoms, and cause mass loss, making the crucible 10 and the thermal insulation carbon felt asymmetric in geometry. The asymmetric temperature field during crystal growth causes uneven direction and rate of growth atmosphere delivery, resulting in asymmetric geometry of the growing silicon carbide crystal, uneven stress distribution inside the crystal, and increased defect density in the single crystal. Especially as the crystal growth size increases, the impact of this uneven temperature field becomes more obvious.

[0048] See also Figure 1 , Figure 3 and Figure 4 , Figure 3 A schematic structural diagram of an embodiment of a balance adjustment ring in a crystal growth device provided by the present application; Figure 4 for Figure 3 The cross-sectional view of the balance adjustment ring along the AA line is shown. In order to solve the problem of uneven temperature field in the crucible 10, the crystal growth device 100 also includes at least one balance adjustment ring 30, which is stacked on the side of the filter layer 20 close to the crystal cavity 112 and abuts against the inner wall of the crucible 10. The balance adjustment ring 30 has a plurality of evenly distributed through holes 31, and the plurality of through holes 31 are used to transmit the production atmosphere in the raw material cavity 111 to the crystal cavity 112, and along the direction from the center of the balance adjustment ring 30 to the edge of the circle, the radius of the plurality of through holes 31 gradually decreases, thereby effectively solving the problem of uneven transmission of the growth atmosphere.

[0049] Specifically, the balance adjustment ring 30 is arranged in the growth chamber 11 and its edge is in contact with the side wall of the crucible 10. The growth atmosphere filtered by the filter layer 20 needs to be transmitted from the multiple through holes 31 on the balance adjustment ring 30 to the crystal chamber 112. The porous design of the balance adjustment ring 30 can disperse the resistance, reduce the friction of eddy current and turbulent flow, greatly reduce the loss of kinetic energy of the growth atmosphere, and effectively solve the problem of uneven transportation of the growth atmosphere. In addition, the present application sets the through hole 31 at the edge of the balance adjustment ring 30 with a small radius and the through hole 31 at the center with a large radius, so as to reduce the transmission rate of the growth atmosphere near the inner wall of the crucible 10 and increase the transmission rate of the growth atmosphere in the center area of ​​the crucible 10, thereby realizing balanced rectification of the growth atmosphere and solving the influence of uneven temperature field on the growth of silicon carbide crystals.

[0050] In one embodiment, please continue to see Figure 3 and Figure 4 The balance adjustment ring 30 is a porous conical graphite part, similar to a lampshade structure. One of the multiple through holes 31 is set at the center of the balance adjustment ring 30, and the other through holes 31 are distributed on the balance adjustment ring 30 to form multiple concentric rings. The radius of multiple through holes 31 in the same ring is the same. It should be noted that the size and distribution of each through hole 31 are formulated based on a special formula and continuous test data, which is called a function hole; the radius of the through hole 31 in the concentric ring close to the inner wall of the crucible 10 is the smallest, and increases row by row inward, and the ratio of the radius of the through hole 31 in two adjacent concentric rings is 1:1-2:1. When the growth atmosphere passes through the through hole 31, the growth atmosphere is balanced and rectified; the porous symmetrical design of the balance adjustment ring 30 can disperse the resistance, so that both eddy current and turbulent friction are minimized, further reducing the loss of kinetic energy of the growth atmosphere, and solving the problem of uneven transmission of the growth atmosphere.

[0051] In some preferred embodiments, the number of the plurality of concentric rings is 2 to 5. In this embodiment, the number of the plurality of concentric rings is 3.

[0052] The number of the balance adjustment rings 30 can be 2, 3 or 4, which can be selected according to the actual situation, as long as the problem of uneven atmosphere transmission can be better solved. Specifically, multiple balance adjustment rings 30 are stacked, and the number of through holes 31 on the multiple balance adjustment rings 30 is the same and is arranged one by one.

[0053] Among them, due to the condensation and deposition of silicon and carbon atoms in the growth atmosphere and the release of latent heat of crystallization, the concentration of silicon and carbon atoms in the growth atmosphere around the growth surface of the silicon carbide crystal is relatively small, causing the airflow to move upward, and the growth atmosphere slightly away from the growth surface flows toward the growth surface, thereby forming a cyclone on the side of the silicon carbide crystal. The cyclone makes the material supply of the growing silicon carbide crystal uneven.

[0054] For this purpose, see Figure 1 , Figure 5 and Figure 6 , Figure 5 A schematic structural diagram of an embodiment of a guide ring in a crystal growth device provided in the present application; Figure 6 for Figure 5 The guide ring shown is a cross-sectional view along line BB. The crystal growth device 100 provided in the present application also includes a guide ring 40, which is arranged in the crystal cavity 112 and close to the crucible cover 13. The side wall of the guide ring 40 abuts against the side wall of the crucible 10. The guide ring 40 has an air guide channel 41, and the air guide channel 41 is used to guide the growth atmosphere generated in the raw material cavity 111 to the growth surface of the seed crystal layer 14. Specifically, the guide ring 40 can guide the airflow, and the growth atmosphere diffuses upward along the air guide channel 41 and continuously adjusts the diffusion direction under the support force of the side wall of the air guide channel 41, and continuously gathers the growth atmosphere together and finally flows out from the air guide channel 41, flows to the growth surface, reaches the crystal growth surface in a relatively uniform manner, and continuously transmits the growth atmosphere to the growth surface, maintains the supersaturation of the atmosphere near the growth surface, and avoids the generation of cyclones.

[0055] Specifically, the guide ring 40 includes an outer guide ring 42 and a guide ring 43. The outer guide ring 42 is a hollow tubular structure, which abuts against the side wall of the crucible 10. The two ends of the side wall of the guide ring 43 are the upper edge 431 and the lower edge 432 of the guide ring 43. The side wall of the guide ring 43 is inclined toward the center of the guide ring 43, and the lower edge 432 of the guide ring 43 is connected to the inner wall of the outer guide ring 42. The side wall of the guide ring 43 defines a gas guide channel 41, and the upper edge 431 of the guide ring 43 is arranged toward the seed crystal layer 14.

[0056] Furthermore, the guide ring 43 has the same height as the outer guide ring 42, and the guide ring 43 is arranged concentrically with the outer guide ring 42. Specifically, the lower edge 432 of the guide ring 43 is flush with the bottom end of the outer guide ring 42, and the upper edge 431 of the guide ring 43 is flush with the top end of the outer guide ring 42.

[0057] Specifically, the crystal growth device 100 provided in the present application includes a filter layer 20 stacked in sequence in a growth chamber 11, at least one balance adjustment ring 30, and a guide ring 40. It can solve the problem that the asymmetric temperature field during the growth of silicon carbide crystals causes uneven growth atmosphere delivery direction and delivery rate (the local atmosphere concentration on the growth surface is high while the concentration in other directions is low), resulting in asymmetric geometric structure of the grown silicon carbide crystals and uneven stress distribution inside the silicon carbide crystals; and it can solve the problem that the density of carbon inclusions in the silicon carbide crystals is high and the defect density in the silicon carbide crystals is increased, thereby ensuring the production yield of silicon carbide crystals and achieving stable mass production.

[0058] See also Figure 7 , Figure 7This is a schematic flow chart of an embodiment of a method for preparing a filter layer provided in the present application; the present application also provides a method for preparing a filter layer 20, comprising:

[0059] Step S1: Filling a mixed slurry formed by mixing metal oxide powder, carbon source and slurry into a first mold, baking and curing the mixture to form a prefabricated filter layer.

[0060] The metal oxide powder includes at least one of tantalum oxide powder, niobium oxide powder, molybdenum oxide powder and tungsten oxide powder, the carbon source is carbon powder and / or graphite, and the slurry includes polyvinyl butyral, acetylacetone and phenolic resin. Specifically, the particle size of the metal oxide powder is 0.1-5um, the purity is 99.99%, the slurry uses polyvinyl butyral (analytical grade) as a dispersant, and adds acetylacetone (analytical grade), phenolic resin (analytical grade), high-purity carbon powder (purity 99.99%) or graphite as a carbon source, the metal ion source / carbon source = 1:1-1:2, and anhydrous ethanol (analytical grade) is added as a solvent, and the metal ion concentration in the prepared mixed slurry is 0.1mol / l-3mol / l.

[0061] The first mold may be a graphite box, and the first mold has a receiving cavity, and the cross section of the receiving cavity is greater than or equal to the cross section area of ​​the filter layer. After the mixed slurry is filled into the first mold, the first mold is placed on a heating device for baking and curing to form a prefabricated filter layer.

[0062] Step S2: sintering the prefabricated filter layer.

[0063] Specifically, the prefabricated filter layer is transferred to a crystal growth furnace for sintering. During the sintering process, a carbon thermal reduction reaction occurs between the metal oxide powder, the slurry and the carbon source, and metal carbides are generated in situ on the carbon. The metal carbides condense together at high temperatures, and small molecular gases are generated during the reaction, so that a large number of micropores are generated between the metal carbides, so that the prepared filter layer can play the role of filtering graphite particles like porous graphite. For example, when the metal oxide powder is tantalum powder, the main reaction is: Ta2O5+7C=2TaC+5CO↑.

[0064] See also Figure 8 , Figure 8 for Figure 7 The specific flow diagram of step S1 in the method for preparing the filter layer is shown; in one embodiment, step S1 includes:

[0065] Step S11: Arrange a plurality of spherical structures in a first mold.

[0066] Specifically, a spherical structure formed by a plurality of metal balls and / or graphite balls is placed in the first mold, and the arrangement of the plurality of spherical structures can be a single-layer arrangement or a multi-layer stacking. When the plurality of spherical structures are arranged in a multi-layer stacking, the plurality of spherical structures are stacked layer by layer to form a densest stacking state. In this embodiment, the diameter of the spherical structure is 0.1 mm-3 mm, and the stacking height of the spherical structure is 5 mm-20 mm.

[0067] Step S12: Filling the mixed slurry formed by mixing the metal oxide powder, the carbon source and the slurry into the gaps between the multiple spherical structures in the first mold and covering the multiple metal spherical structures; Step S13: Flattening the upper surface of the mixed slurry.

[0068] Specifically, after the mixed slurry covers the metal ball, a brush is used to smooth the material surface, and then a press is used to flatten the material surface of the mixed slurry.

[0069] Step S14: baking and curing the mixed slurry and the plurality of spherical structures in the first mold to form a prefabricated filter layer.

[0070] Specifically, the first mold is placed on a heating device to bake and solidify the mixed slurry and the multiple spherical structures in the first mold to form a prefabricated filter layer.

[0071] See also Fig. 9 , Fig. 9 for Figure 7 The specific flow diagram of step S2 in the method for preparing the filter layer is shown; in one embodiment, step S2 includes:

[0072] Step S21: transferring a plurality of prefabricated filter layers to a second mold.

[0073] Specifically, the prefabricated filter layer is transferred from the first mold to the second mold. The second mold may be a graphite crucible. The second mold may accommodate several prefabricated filter layers at the same time, for example, one, two, four, etc., to improve the preparation efficiency.

[0074] Step S22: placing the second mold into the growth chamber of the crystal growth furnace.

[0075] Step S23: evacuate the growth chamber of the crystal growth furnace to a vacuum state and then introduce an inert gas.

[0076] Specifically, after the second mold equipped with a single or multiple prefabricated filter layers is loaded into the growth chamber of the crystal growth furnace, the growth chamber of the crystal growth furnace is evacuated to a vacuum state and a leak test is performed. After the leak test is normal, an inert gas is introduced into the growth chamber, and the inert gas is argon or helium.

[0077] Step S24: sintering a plurality of prefabricated filter layers for a first preset time at a preset temperature and a first preset pressure.

[0078] The pressure in the growth chamber of the crystal growth furnace is maintained at a first preset pressure. After the pressure stabilizes, the power supply is started to gradually increase the temperature of the growth chamber of the crystal growth furnace from room temperature to a preset temperature. After the temperature in the growth chamber of the crystal growth furnace rises to the preset temperature, the preset temperature and the first preset pressure are maintained for stable sintering for a first preset time.

[0079] Among them, the preset temperature is 2000°C-2500°C, the first preset pressure is 1mbar-10mbar, and the first preset time is 0.1h-10h.

[0080] As shown in Table 1, Table 1 is a correspondence table of the preset temperature, the first preset pressure and the first preset time in step S24 of the present application.

[0081] Table 1

[0082]

[0083] Step S25: Sintering the plurality of prefabricated filter layers for a second preset time under the conditions of gradually decreasing the preset temperature to room temperature and a second preset pressure.

[0084] Specifically, after the first preset time, the temperature of the crystal growth furnace growth chamber begins to be cooled, and the current is slowly reduced to 0A in 0.1-5h, so that the temperature in the crystal growth furnace growth chamber gradually decreases from the preset temperature to room temperature, and inert gas is continuously introduced during this process to slowly increase the pressure in the crystal growth chamber to the second preset pressure (cooling and pressure increase are carried out simultaneously). After reaching the second preset pressure, the hot field is placed in the crystal growth chamber and taken out after the second preset time.

[0085] Among them, the second preset pressure is 500mbar-900mbar, and the second preset time is 5h-20h.

[0086] As shown in Table 2, Table 2 is a correspondence table of the preset temperature, the second preset pressure and the second preset time in step S25 of the present application.

[0087] Table 2

[0088]

[0089] Among them, when the spherical structure is a metal ball, it will react with the carbon source during the sintering process to form a metal carbide. During the reaction, the joints between the metal balls will melt slightly and connect with each other, which can improve the structural stability of the filter layer. On the other hand, the metal ball is also a heating element in eddy current heating, which can increase the growth rate of silicon carbide crystals.

[0090] Among them, when the spherical structure is a graphite ball, the joints between multiple graphite balls will melt slightly and connect during the sintering process, which can improve the structural stability of the filter layer; on the other hand, the cost of graphite ball raw materials is relatively low, and it can be used as a carbon source.

[0091] After step S2, the prefabricated filter layer has reacted completely to become a loose and porous filter layer, and after the filter layer is pickled, washed, and dried, it can be stored for use. The filter layer provided in the present application is not corroded by the growth atmosphere before, during, and after the crystal growth, and its components are metal carbides, which are structurally stable at high temperatures and do not produce carbon particles, so that the use of the filter layer for crystal growth can effectively reduce the carbon inclusions on the crystal and improve the product yield.

[0092] The present application also provides a method for growing silicon carbide crystals:

[0093] The silicon carbide raw material is loaded into the graphite crucible and then loaded into the machine for sintering. After the sintering process is completed and the sintering test is completed, the filter plate, two balance adjustment rings and a guide ring are loaded in sequence. Finally, the crucible cover with the seed crystal layer bonded is sealed with the crucible with the heat field placed inside. The outer wall, top and bottom of the crucible will be wrapped with 1 to 4 layers of 5 to 10 mm thick graphite soft felt insulation layer. Then the crucible is placed in the crystal growth furnace and first evacuated to a pressure of 5x10 -2 mbar, argon is filled to control the pressure in the environment of 1-50mbar, and a water-cooled induction coil is energized to heat the crucible by the principle of electromagnetic induction. When the heating temperature reaches above 2100℃, the silicon carbide powder begins to sublimate into Si, Si2C, SiC2 and other gases, and is transmitted along the temperature gradient from the high temperature area to the seed crystal layer in the lower temperature area to deposit and crystallize to form silicon carbide crystals. After 5-10 days of deposition and crystallization time, the growth of silicon carbide crystals is completed.

[0094] Through testing, it was found that the 4-inch N-doped 4H-SiC crystal grown by this growth method was a single crystal type 4H, and there were no macroscopic defects such as impurities and dense microtubes on the surface of the crystal. The thickness of the crystal was measured in four directions, and the thickness difference was less than 1mm (maximum value-minimum value), and the crystal convexity was less than 2mm. After the crystal was cut, ground and polished, a wafer was obtained. The crystal was placed under an optical microscope for observation, and it can be seen that there is basically no carbon inclusion in the crystal, and the density of carbon inclusions is less than 0.1 / cm 2 The number of base plane dislocations (BPD) is at the same level as that of mass-produced crystals of the same period. The number of through screw dislocations (TSD) and candela micropipe defect density (MPD) has improved, decreasing by 20%-40%, indicating that the use of this filter layer for crystal growth can not only effectively reduce the density of carbon inclusions from the original 5-10 / cm 2 Reduced to <0.1 / cm 2It can also effectively solve the problem of uneven crystal growth thickness, reducing the thickness difference from the original 3mm-10mm to <1mm, and increasing production capacity by 50%-100%.

[0095] The above description is only an implementation method of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A crystal growth device, characterized in that: include: a crucible having a growth chamber; A filter layer is disposed in the growth chamber and separates the growth chamber into a raw material chamber and a crystal chamber that are interconnected; The filter layer includes a loose layer and a plurality of spherical structures embedded in the loose layer. The material of the loose layer is metal carbide. The loose layer has micropores connecting the raw material cavity and the crystal cavity. A plurality of adjacent spherical structures are connected. Wherein, the spherical structure is a metal ball, or the spherical structure is a metal ball and a graphite ball.

2. The crystal growth device according to claim 1, characterized in that: The diameter of the spherical structure is 0.1 mm to 3 mm, and the thickness of the loose layer is 5 mm to 20 mm; And / or, the material of the metal ball is one or more of tantalum, niobium, molybdenum and tungsten.

3. The crystal growth device according to any one of claims 1 to 2, characterized in that: The arrangement of the plurality of spherical structures in the loose layer is multi-layer stacking.

4. The crystal growth device according to claim 3, characterized in that: The height of the plurality of spherical structures stacked in multiple layers is the same as the thickness of the loose layer.

5. The crystal growth device according to claim 1, characterized in that: Also includes: At least one balance adjustment ring is stacked on one side of the filter layer close to the crystal cavity, and the balance adjustment ring has a plurality of evenly distributed through holes, and the radius of the plurality of through holes gradually decreases along the direction from the center to the edge of the balance adjustment ring.

6. The crystal growth device according to claim 5, characterized in that: One of the plurality of through holes is disposed at the center of the balance adjustment ring, and the other through holes are distributed on the balance adjustment ring to form a plurality of concentric rings, and the radii of the plurality of through holes in the same ring are the same.

7. The crystal growth device according to claim 6, characterized in that: The number of the balance adjustment rings is 2 and they are stacked; wherein the number of through holes on the two balance adjustment rings is the same and they are arranged in a one-to-one correspondence.

8. The crystal growth device according to claim 1, characterized in that: The crucible comprises a crucible body and a crucible cover, wherein the crucible body and the crucible cover cooperate to define and form the growth cavity; a seed crystal layer is arranged on the crucible cover, and the seed crystal layer is located in the crystal cavity; The crystal growth apparatus further comprises: A guide ring is arranged in the crystal cavity and close to the crucible cover. The guide ring has an air guide channel, and the air guide channel is used to guide the growth atmosphere generated in the raw material cavity to the growth surface of the seed crystal layer.

9. A method for preparing a filter layer, used in the crystal growth device according to any one of claims 1 to 8, characterized in that: include: Arranging a plurality of spherical structures in a first mold; Filling the mixed slurry formed by mixing metal oxide powder, carbon source and slurry into the gaps between the plurality of spherical structures in the first mold and covering the plurality of spherical structures; The mixed slurry and the plurality of spherical structures in the first mold are baked and solidified to form a prefabricated filter layer; The prefabricated filter layer is sintered; wherein the connection between the spherical structures is slightly melted and connected; Wherein, the step of sintering the prefabricated filter layer comprises: transferring a plurality of the prefabricated filter layers to a second mold; placing the second mold into the growth chamber of the crystal growth furnace; The growth chamber of the crystal growth furnace is evacuated to a vacuum state and then an inert gas is introduced; Sintering the plurality of prefabricated filter layers for a first preset time at a preset temperature and a first preset pressure; The plurality of prefabricated filter layers are sintered for a second preset time under the conditions that the preset temperature is gradually reduced to room temperature and the second preset pressure is applied.

10. The preparation method according to claim 9, characterized in that: The upper surface of the mixed slurry is planarized.

11. The preparation method according to claim 9, characterized in that: The ratio of metal ions to carbon sources in the mixed slurry is 1:1-1:2; the concentration of metal ions is 0.1 mol-3 mol.

12. The preparation method according to claim 9, characterized in that: The metal oxide powder includes at least one of tantalum oxide powder, niobium oxide powder, molybdenum oxide powder and tungsten oxide powder, the carbon source is carbon powder and / or graphite, and the slurry includes polyvinyl butyral, acetylacetone and phenolic resin.

13. The preparation method according to claim 9, characterized in that: The preset temperature is 2000° C.-2500° C., the first preset pressure is 0.11 mbar-10 mbar, the second preset pressure is 500 mbar-900 mbar, the first preset time is 0.1 h-10 h, and the second preset time is 5 h-20 h.

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