CN114735703A

CN114735703A - Synthesis method and application of silicon carbide fiber

Info

Publication number: CN114735703A
Application number: CN202210458294.7A
Authority: CN
Inventors: 陈豆; 马远; 潘尧波
Original assignee: Clc Semiconductor Co ltd
Current assignee: Clc Semiconductor Co ltd
Priority date: 2022-04-28
Filing date: 2022-04-28
Publication date: 2022-07-12

Abstract

The invention provides a synthetic method and application of silicon carbide fibers, wherein the synthetic method at least comprises the following steps: placing a silicon source in a crucible; placing a graphite plate in the crucible, wherein the bottom of the graphite plate is a preset distance away from the silicon source; placing carbon fibers on the surface of the graphite plate; putting the crucible into a furnace cavity, and heating; and cooling the crucible to obtain the silicon carbide fiber. The synthesis method and the application of the silicon carbide fiber provided by the invention can effectively improve the quality of silicon carbide crystals.

Description

Synthetic method and application of silicon carbide fiber

Technical Field

The invention relates to the technical field of silicon carbide single crystal growth, in particular to a synthetic method and application of silicon carbide fibers.

Background

In the process of growing a silicon carbide (SiC) crystal by using a physical vapor transport process (PVT process), the crucible is enlarged along with the enlargement of the diameter of the crystal, and the longitudinal distance between a raw material and a seed crystal face does not need to be enlarged in equal proportion, so that the heat resistance of heat transfer from outside to inside is increased, and the transverse temperature difference of the crystal caused by the reduction of the central temperature of the crystal and the raw material is enlarged, thereby increasing the defects of crystal polytype, Basal Plane Dislocation (BPD) and even cracking. Because the temperature distribution of the raw material zone has the characteristics of external cooling and internal heating, the low temperature of the middle area of the raw material and the high temperature of the side surface of the raw material cause the decomposition speed of the raw material to be slow in the center and the side surface to be fast, so that the gas flow near the wall surface is large, the growth speed of the outer edge of the crystal is accelerated, and even the transverse decomposition and crystallization processes are generated.

On the other hand, impurity elements in the raw material induce the generation of defects, which affect the crystal quality, and nitrogen elements are difficult to completely remove, resulting in low purity of the silicon carbide powder.

Disclosure of Invention

The invention provides a synthetic method and application of silicon carbide fiber, which takes the synthesized porous silicon carbide fiber as a silicon carbide crystal growth raw material, and solves the problem that the quality of crystals is reduced due to the generation of defects in the crystals caused by the unbalance of the ratio of silicon to carbon in the gas phase of the crystal growth caused by the uneven sintering of the raw material under heating. Meanwhile, in the synthesis of the silicon carbide fiber, the content of nitrogen element in the synthesized silicon carbide fiber is reduced and the purity of the synthesized silicon carbide fiber is improved by modifying the silicon source material.

In order to solve the technical problems, the invention is realized by the following technical scheme:

the invention provides a synthetic method of silicon carbide fiber, which at least comprises the following steps:

placing a silicon source in a crucible;

placing a graphite plate in the crucible, wherein the bottom of the graphite plate is a preset distance away from the silicon source;

placing carbon fibers on the surface of the graphite plate;

putting the crucible into a furnace cavity, and heating; and

and cooling the crucible to obtain the silicon carbide fiber.

In an embodiment of the present invention, the graphite sheet is a porous graphite sheet, and the opening ratio of the graphite sheet is 30 to 60%.

In an embodiment of the present invention, the silicon source is one or more of pure silicon, silicon monoxide, silicon tetrafluoride, or organosilane.

In an embodiment of the present invention, the organosilane is one or more of polysilane, polycarbosilane, chlorosilane, or polysiloxane.

In an embodiment of the present invention, the carbon fiber is one or more of a pitch-based fiber, a glue (cellulose) -based fiber, a polyacrylonitrile-based fiber, or an activated carbon fiber.

In an embodiment of the present invention, the method for obtaining the activated carbon fiber includes subjecting the carbon fiber to a high temperature activation process to generate a nano-scale pore size on the surface of the carbon fiber.

In an embodiment of the present invention, the predetermined distance is in a range of 10-60 mm.

The invention also provides a growth method of the silicon carbide crystal, which comprises the following steps of using the following substances as raw materials and carrying out silicon carbide crystal growth by using a physical vapor transport method:

the silicon carbide fiber synthesized by any of the above methods.

In one embodiment of the invention, the method for growing silicon carbide crystals comprises:

and placing the silicon carbide fibers in a crucible according to a preset arrangement mode, and growing silicon carbide crystals.

In an embodiment of the present invention, the preset arrangement manner is one of a layering manner, an orthogonal manner, and a vertical manner.

The invention provides a synthetic method and application of silicon carbide fiber, which takes the synthesized porous silicon carbide fiber as a raw material for growing silicon carbide crystals, and reduces the generation of defects in the crystals caused by unbalance of silicon/carbon ratio of crystal growth gas phase due to nonuniform sintering of the raw material when the raw material is heated. Meanwhile, the silicon source material is modified, so that the content of nitrogen element in the synthetic material is reduced, and the purity of the synthetic material is improved.

Drawings

FIG. 1 is a flow chart of a process for synthesizing silicon carbide fibers according to the present invention.

FIG. 2 is a schematic view of a crucible according to an embodiment of the present invention.

FIG. 3 is a schematic structural diagram of a crystal growth system using PVT method.

Fig. 4 is a schematic diagram of a crystal growth process using granular silicon carbide as a raw material.

FIG. 5 is a schematic diagram of a crystal growth process using porous silicon carbide fiber as a raw material.

FIG. 6 is a schematic view showing the structure of a crucible in example 2 of the present invention.

Description of reference numerals:

1, a crucible; 101 a crucible cover; 102, presetting a position; 2 carbon fibers; 3, graphite plates; 4, silicon source; 5 a first heat dissipation hole; 6, heat insulation material; 7 seed crystals; 8 an induction coil; 9, silicon carbide raw material; 901 silicon carbide particles; 902 silicon carbide; 903 silicon carbide fiber; 10 a second heat dissipation hole; 11 air inlet.

Detailed Description

The following embodiments of the present invention are provided by way of specific examples, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

The technical solutions of the present invention are further described in detail below with reference to several embodiments and the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Silicon carbide is a wide bandgap semiconductor material, and has incomparably excellent properties such as high thermal conductivity, high saturation electron mobility, high breakdown field strength and the like, so that it is used in the preparation of various semiconductor devices. The silicon carbide semiconductor device mainly comprises a power diode and a power switch tube, has the characteristics of high frequency, high efficiency and high temperature, can be applied to the field with strict requirements on efficiency or temperature, and can be applied to the fields of solar inverters, vehicle-mounted power supplies, new energy automobile motor controllers, UPS (uninterrupted power supply), charging piles, power supplies and the like.

Referring to FIG. 1, the present invention provides a method for synthesizing silicon carbide fiber, including but not limited to the following steps S1-S5.

And S1, placing a silicon source in the crucible.

S2, placing a graphite plate in the crucible, wherein the bottom of the graphite plate is a preset distance away from the silicon source.

And S3, placing the carbon fibers on the surface of the graphite plate.

And S4, placing the crucible into the furnace cavity, and heating.

And S5, cooling the crucible to obtain the silicon carbide fiber.

Referring to fig. 1-2, in step S1, the crucible 1 is not limited in kind, and may be, for example, an isostatic graphite crucible in one embodiment of the present invention, or a tantalum carbide crucible in another embodiment. In one embodiment of the invention, the crucible 1 may have a cylindrical shape, for example, and a height of 40 to 140mm, for example. In an embodiment of the present invention, the silicon source 4 may be placed at a predetermined position 102 in the crucible 1, and the predetermined position 102 is located at the bottom center of the crucible 1, and the diameter of the predetermined position 102 may be, for example, 10-30 mm.

Referring to fig. 1-2, in step S1, the type of the silicon source 4 is not limited in the present invention, and the silicon source 4 may be one or more of pure silicon, silicon monoxide (SiO), silicon tetrafluoride (ptfe), or organosilane, for example. Further, optionally, in some embodiments of the present invention, the silicon source 4 may be, for example, an organosilane, which may be any one or more of polysilane, polycarbosilane, chlorosilane, and polysiloxane. When organosilane is used as a silicon source, the organosilane is cracked along with the increase of temperature, for example, polycarbosilane is decomposed to generate hydrogen, methane, silicon-containing micromolecules and the like, and the hydrogen reacts with adsorbed nitrogen, so that the content of nitrogen in the synthetic material is reduced. The silicon-containing small molecules can be adsorbed by the activated carbon fibers and react to form silicon carbide, and on the other hand, undecomposed polycarbosilane is cracked to form silicon carbide particles. In another embodiment of the present invention, the silicon source 4 may be, for example, pure silicon, and the purity may be, for example, greater than 99.999%.

Referring to fig. 1-2, in step S2, in an embodiment of the present invention, the graphite plate 3 is not in direct contact with the silicon source 4, and the graphite plate 3 is suspended above the silicon source 4 to serve as a substrate for supporting the carbon fibers 2. In an embodiment of the present invention, a predetermined distance d is left between the bottom of the graphite plate 3 and the silicon source 4, and the predetermined distance d may be, for example, in a range of 10-60 mm. The shape and size of the graphite sheet 3 are not limited in the present invention, and in the present embodiment, the graphite sheet 3 may be, for example, disposed in a disk shape, and the thickness of the graphite sheet 3 may be, for example, 1 to 10 mm. In other embodiments, the shape and size of the graphite plates 3 can be flexibly set. In an embodiment of the present invention, the graphite sheet 3 may be a porous graphite sheet, and the opening ratio may be 30 to 60%. At high temperature, the silicon source 4 is heated and sublimated, and the gas-phase silicon source permeates the carbon fiber 2 to react with the carbon fiber through the hole on the graphite plate 3.

Referring to fig. 1-2, in step S3, in one embodiment of the present invention, carbon fiber 2 is present as a carbon source. The present invention is not limited to the kind of the carbon fiber 2, and the carbon fiber 2 may be one or more of pitch-based fiber, glue (cellulose) -based fiber, Polyacrylonitrile (PAN) -based fiber, and activated carbon fiber. Further, alternatively, the carbon fiber 2 may be, for example, an activated carbon fiber. In the invention, the active carbon fiber is obtained by activating the carbon fiber at high temperature to generate nano-scale aperture on the surface of the carbon fiber. In the process of synthesizing the silicon carbide fiber, the carbon fiber is used as an aggregate, the specific surface area of the carbon fiber is large, more reaction sites are provided for forming silicon carbide through reaction, a large-particle silicon carbide raw material is obtained, the influence of the silicon/carbon ratio in the atmosphere on the silicon carbide in the crystal growth process is reduced, and therefore the generation of point defects and line defects in the silicon carbide crystal growth process is avoided.

Referring to fig. 1-2, in step S4, before heating the crucible 1, a vacuum-purge operation is performed on the furnace chamber. When heating the crucible 1, a protective atmosphere needs to be introduced, and in an embodiment of the present invention, the protective atmosphere may be, for example, argon, and may also be, for example, helium. Further, the flow rate of the protective atmosphere can be set within the range of 100 to 1000sccm, for example. In an embodiment of the present invention, the temperature for the temperature raising heating may be set in a range of, for example, 1400 ℃ to 2200 ℃.

Referring to fig. 1-2, in step S5, in an embodiment of the present invention, the crucible 1 is cooled to 10-30 ℃, the furnace chamber is opened, and the composite material at the predetermined position 102 of the bottom of the crucible 1 and on the graphite plate 3 is collected to obtain the porous silicon carbide fiber 903. According to the method for synthesizing the silicon carbide fiber, carbon fiber is used as a carbon source, pure silicon or organosilane is used as a silicon source, silicon powder is sublimated into gas phase silicon at high temperature under the protection of inert gas, and the gas phase silicon permeates from holes of a graphite plate 3 and reacts with active carbon fiber to generate the porous silicon carbide fiber. In the process, the carbon fiber exists as the aggregate, and the activated carbon fiber has the advantages of large specific surface area, moderate aperture, uniform distribution, high adsorption speed, large adsorption capacity, less impurities and the like. The gas phase silicon can be fully absorbed by the active carbon fiber, the high temperature reaction forms large-grain silicon carbide which takes the carbon fiber as a framework, and the grain growth of the silicon carbide is not limited because the bulk density of the carbon fiber is less than that of the powder. On the other hand, compared with the method that silicon powder and carbon powder are directly subjected to solid-phase reaction, the synthesis method of the silicon carbide fiber provided by the invention has the advantages of more sufficient and more uniform reaction.

Referring to fig. 3, the present invention further provides a method for growing silicon carbide crystals, in one embodiment, the silicon carbide fiber 903 obtained by the above synthesis method is used as a raw material for crystal growth, and the silicon carbide fiber 903 is placed in a crucible in a predetermined arrangement to grow silicon carbide crystals. The preset arrangement of the silicon carbide fibers is not limited in the present invention, and in some embodiments, the preset arrangement may be, for example, one of a layering manner, an orthogonal manner, and a vertical manner. The method of growing a silicon carbide crystal according to the present invention is not limited, and in the present embodiment, for example, the silicon carbide crystal can be grown by a physical vapor transport method. In an embodiment of the present invention, for example, silicon carbide fiber 903 and silicon carbide particles 901 may be mixed to be used as a growth raw material of silicon carbide crystals. Silicon carbide fibers 903 and silicon carbide particles 901 are used as crystal growth raw materials, the silicon carbide particles 901 are dispersed among the silicon carbide fibers 903 arranged in a layering mode, the extremely high length-diameter ratio of the silicon carbide fibers realizes a heat conduction effect, and the silicon carbide particles 901 are used as fillers for providing a proper silicon/carbon ratio in a crystal growth process and a gas phase. The good mechanical properties of silicon carbide fiber 903 can maintain the fiber form at high temperature, and surface layer silicon carbide fiber 903 plays a role in isolating carbon powder, so that the carbon powder is prevented from passing through and entering crystals, and the formation and aggregation of impurity wrappings are prevented.

Referring to FIG. 3, FIG. 3 is a schematic view of a system for growing silicon carbide crystals by PVT. In one embodiment of the invention, the bottom of the crucible 1 contains silicon carbide raw material 9, the crucible cover 101 is positioned at the side opposite to the silicon carbide raw material 9, and the crucible cover 101 carries the silicon carbide seed crystal 7. The crucible 1 is coated with a heat insulation material 6, the heat insulation material 6 is provided with heat dissipation holes, the first heat dissipation hole 5 is located on one side close to the crucible cover 101, and the second heat dissipation hole 10 is located on one side opposite to the crucible cover 101. An induction coil 8 is arranged around the heat insulating material 6 to heat the crucible 1.

Referring to FIG. 6, in one embodiment of the present invention, the bottom of the silicon carbide crystal growth crucible 1 may be provided with a gas inlet 11 for introducing silicon tetrafluoride gas during the reaction. In an embodiment of the present invention, the obtained porous silicon carbide fiber 903 is placed in a crystal growth crucible 1 in a layered manner to grow a silicon carbide crystal. Polysilane is used as a silicon source assisted by the introduction of silicon tetrafluoride gas. The raw materials are put into a graphite crucible and then are put into a furnace chamber, polysilane is cracked to generate silicon-containing gas, hydrogen and the like along with the rise of temperature, silicon tetrafluoride gas is introduced as auxiliary gas and reacts to generate fluorine-containing gas, the fluorine-containing gas reacts with impurity elements, and the hydrogen reacts with adsorbed nitrogen, so that the aim of reducing the content of the impurity elements in the synthetic raw materials is fulfilled. Hereinafter, the present invention will be more specifically explained by referring to examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, and all of them fall within the technical scope of the present invention.

Example 1

And placing the powdery pure silicon at a preset position at the bottom of the graphite crucible.

And a porous graphite plate is placed in the middle of the graphite crucible, the aperture ratio of the graphite plate is 35%, and the preset distance between the bottom of the graphite plate and the silicon powder is 30 mm.

Active PAN-based carbon fibers were placed on the surface of the graphite plate.

And putting the graphite crucible into a furnace cavity, and heating under the protection of inert gas after vacuum-gas washing operation.

And cooling the graphite crucible to obtain the porous silicon carbide fiber.

Referring to FIG. 5, the obtained porous silicon carbide fiber 903 is placed in a crucible 1 for silicon carbide crystal growth in a layered manner, and silicon carbide crystal growth is carried out by a physical vapor transport method.

Comparative example 1

Referring to FIG. 4, silicon carbide particles 901 are placed in a silicon carbide crystal growth crucible 1 and silicon carbide crystal growth is carried out by physical vapor transport.

Referring to fig. 4, silicon carbide particles 901 are used as the raw material for silicon carbide crystal growth, after a certain period of reaction, the raw material is heated unevenly, so that the edge portion of the raw material is carbonized to form silicon carbide 902, while the raw material in the middle area is still silicon carbide particles 901. The temperature difference in the raw materials is not suitable for matching with the temperature difference between the surface of the raw materials and the long grain boundary surface, so that silicon carbide gas-phase components are accumulated and crystallized on the surface of the raw materials, the temperature of the top of the raw materials is low, the consumption rate of the raw materials in the area is low, the flow rate of the raw materials is low, the edge area of the raw materials is carbonized, the partial pressure of the internal gas-phase products is increased, the decomposition reaction of the raw materials is balanced, and the consumption of the raw materials is stopped.

TABLE 1 comparison of thermal conductivities of silicon carbide fibers and silicon carbide particles

Referring to fig. 4-5, compared to the silicon carbide particles 901, the porous silicon carbide fiber 903 horizontally disposed has better thermal conductivity to avoid non-uniform heating inside the raw material. The silicon carbide fiber raw materials have extremely high length-diameter ratio, and the more the silicon carbide fiber raw materials are, the easier the raw materials are mutually contacted to form a continuous heat conduction path in the matrix, so that the silicon carbide fiber raw materials are more easily lapped to realize the heat conduction effect. As can be seen from Table 1, the silicon carbide fiber has higher thermal conductivity than the silicon carbide particle in the same raw material filling amount, and the silicon carbide fiber has higher thermal conductivity than the silicon carbide particle by more than 20% when the mass fraction of the filler is 40%, so that the influence on the crystal growth rate and the growth cost caused by local heating and sintering of the raw material into blocks is reduced.

In summary, the invention provides a synthesis method and application of silicon carbide fiber, wherein carbon fiber is used as a carbon source, pure silicon or organosilane is used as a silicon source, and porous silicon carbide fiber is obtained by reaction at high temperature. Porous carborundum fibre that obtains with the synthesis is as carborundum crystal raw materials for growth, and porous carborundum fibre material has good heat transfer nature, and inside is heated more evenly, has reduced the raw materials and has heated the inequality and the caking leads to the problem that the raw materials utilization ratio is low, promotes that the holistic homogeneity of raw materials volatilizees, reduces the production of parcel defect in the crystal to a certain extent. On the other hand, in the process of synthesizing the silicon carbide fiber, organosilane is cracked, and the generated hydrogen can react with the adsorbed nitrogen, so that the content of nitrogen elements in the synthetic material is reduced, the generation of defects is reduced, and the purity of the silicon carbide fiber is improved.

The above description is only a preferred embodiment of the present application and a description of the applied technical principle, and it should be understood by those skilled in the art that the scope of the present invention related to the present application is not limited to the technical solution of the specific combination of the above technical features, and also covers other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, for example, the technical solutions formed by mutually replacing the above features with (but not limited to) technical features having similar functions disclosed in the present application.

Other technical features than those described in the specification are known to those skilled in the art, and are not described herein in detail in order to highlight the innovative features of the present invention.

Claims

1. A method for synthesizing silicon carbide fiber is characterized by at least comprising the following steps:

placing a silicon source in a crucible;

placing carbon fibers on the surface of the graphite plate;

putting the crucible into a furnace cavity, and heating; and

and cooling the crucible to obtain the silicon carbide fiber.

2. The method for synthesizing silicon carbide fiber according to claim 1, wherein the graphite sheet is a porous graphite sheet, and the opening ratio of the graphite sheet is 30 to 60%.

3. The method for synthesizing silicon carbide fiber according to claim 1, wherein the silicon source is one or more of pure silicon, silicon monoxide, silicon tetrafluoride or organosilane.

4. The method for synthesizing silicon carbide fiber according to claim 3, wherein the organosilane is one or more of polysilane, polycarbosilane, chlorosilane or polysiloxane.

5. The method for synthesizing silicon carbide fiber according to claim 1, wherein the carbon fiber is one or more of pitch-based fiber, glue (cellulose) -based fiber, polyacrylonitrile-based fiber, or activated carbon fiber.

6. The method of claim 5, wherein the activated carbon fiber is obtained by subjecting the carbon fiber to a high temperature activation treatment to generate a nano-scale pore size on the surface of the carbon fiber.

7. A method of synthesizing silicon carbide fiber according to claim 1, wherein the predetermined distance is in the range of 10 to 60 mm.

8. A method for growing silicon carbide crystals, which comprises growing silicon carbide crystals by a physical vapor transport method using the silicon carbide fibers obtained by the method according to any one of claims 1 to 7 as a starting material.

9. A method according to claim 8, comprising:

10. The method for growing silicon carbide crystals according to claim 9, wherein the predetermined arrangement is one of a layer arrangement, an orthogonal arrangement and a vertical arrangement.