JP2018158871A - Silicon carbide powder, method for producing the same, and method for producing silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: silicon carbide powder that is capable of giving a silicon carbide single crystal in which impurity elements are not unevenly distributed and that serves as a raw material for producing the single crystal; a method for producing the same; and a method for producing the silicon carbide single crystal.SOLUTION: An inorganic siliceous raw material, a carbon raw material and a boron compound are mixed with one another to give a raw material for producing silicon carbide. The raw material for producing silicon carbide is calcined at 2,200°C or higher to form a lump material composed of silicon carbide. The lump material is crushed, and the crushed material is classified to give silicon carbide powder containing silicon carbide particles with a particle diameter of 100 μm or more. In the silicon carbide powder, not just particles with a particle diameter of 100 μm or less but also the particles with a particle diameter of more than 100 μm contain boron in an entirety of the particles. The silicon carbide powder is to be used as a raw material for producing a silicon carbide single crystal by a sublimation-recrystallization method.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a silicon carbide powder suitable as a raw material for producing a silicon carbide single crystal containing a certain amount of boron, a method for producing the same, and a method for producing a silicon carbide single crystal.

  In recent years, silicon carbide has been adopted as a constituent substrate of devices in order to enable devices to have higher breakdown voltage, lower loss, and use in high temperature environments. Silicon carbide is a wide band gap semiconductor having a large band gap as compared with silicon that has been widely used as a constituent substrate of conventional devices. Therefore, by using silicon carbide, it is possible to achieve a high breakdown voltage and a reduction in on-resistance of the device, and there is an advantage that the deterioration of characteristics when used in a high temperature environment is small.

  Silicon carbide used as a material for a semiconductor substrate is obtained by slicing a single crystal of silicon carbide. Conventionally, a sublimation recrystallization method has been widely used as a method for growing a silicon carbide single crystal. In this sublimation recrystallization method, a seed crystal is joined to a graphite pedestal placed in a graphite crucible, and the silicon carbide raw material disposed on the bottom of the crucible is heated and sublimated, and the sublimation gas is supplied to the seed crystal. A silicon carbide single crystal is grown on the crystal.

  The silicon carbide single crystal needs to be managed so as to contain an impurity element that can be a donor or an acceptor at a certain concentration. The following method has been proposed as a method for producing a silicon carbide single crystal containing an impurity element.

  Patent Document 1 listed below describes a method of growing a silicon carbide single crystal using a material heated by mixing impurities (Al) with silicon carbide.

  In Patent Document 2 below, impurities are placed in a separate heating system in addition to silicon carbide as a raw material, and while the silicon carbide single crystal is grown, the impurities are fed into the growth chamber of the silicon carbide crystal to obtain the silicon carbide single crystal. A growth method is described.

  Patent Document 3 listed below describes a method of growing a silicon carbide single crystal using silicon carbide to which boron carbide is added (mixed).

JP-A-63-85097 JP2013-133234A JP 2009-256155 A

  In the method described in Patent Document 1, Al contained as an impurity is not unevenly distributed when viewed macroscopically, but when viewed in units of silicon carbide particles, the Al concentration increases near the surface of the silicon carbide particles. As a result, a difference in concentration tends to occur in the impurity element in the silicon carbide single crystal between the initial stage and the late stage of the single crystal growth.

  In the method described in Patent Document 2, the manufacturing conditions are easy to touch and the manufacturing is difficult. For this reason, the concentration of the impurity element is likely to be uneven in the silicon carbide single crystal.

  In both Patent Documents 1 and 2, the process is complicated and complicated as compared with the case of growing a high-purity silicon carbide single crystal.

  In the method described in Patent Document 3, the composition of raw materials must be changed slightly by a growth furnace, which is complicated in the mass production process.

  Accordingly, an object of the present invention is to obtain a silicon carbide single crystal having a uniform distribution of impurity elements, a silicon carbide powder as a raw material for producing the single crystal, a method for producing the same, and a production of the silicon carbide single crystal It is to provide a method.

  In order to achieve the above object, the silicon carbide powder of the present invention comprises silicon carbide particles containing boron as an impurity, contains particles having a particle size exceeding 100 μm in the particle size distribution, and is limited to particles having a particle size of 100 μm or less. In addition, the boron is contained in the entire silicon carbide particles even in particles having a particle diameter exceeding 100 μm.

  Since the silicon carbide powder of the present invention contains boron in the entire silicon carbide particles constituting the silicon carbide powder, a silicon carbide single crystal is grown by sublimation recrystallization using the silicon carbide powder as a raw material. Thus, a silicon carbide single crystal in which boron as an impurity element is uniformly contained in the silicon carbide single crystal can be obtained.

  In the silicon carbide powder of the present invention, it is preferable that 98% by mass or more of the silicon carbide powder has a particle size range of 45 to 1400 μm depending on the opening size of the sieve. According to this, when manufacturing a silicon carbide single crystal by the sublimation recrystallization method, it is possible to obtain silicon carbide powder in which carbon inclusion and silicon droplets are hardly generated.

  The method for producing silicon carbide powder according to the present invention comprises a raw material production step of obtaining a raw material for producing silicon carbide by mixing an inorganic siliceous raw material, a carbonaceous raw material, and a boron compound; It includes a firing step of forming a mass composed of boron carbide-containing silicon carbide by firing at a temperature of not lower than ° C, and a powder formation step of obtaining a silicon carbide powder by pulverizing the mass. .

  According to the method for producing silicon carbide powder of the present invention, it is possible to obtain a silicon carbide powder containing boron in the entire silicon carbide particles constituting the silicon carbide powder, and sublimation recrystallization using the silicon carbide powder as a raw material. By growing a silicon carbide single crystal by the method, a silicon carbide single crystal in which boron as an impurity element is uniformly contained in the silicon carbide single crystal can be obtained.

  In the method for producing silicon carbide powder of the present invention, it is preferable to use boron carbide and / or boron nitride as the boron compound. According to this, since both boron carbide and boron nitride have a high melting point, the boron compound is hardly volatilized in the firing step, and boron can be effectively contained in the silicon carbide particles formed by firing.

  Moreover, in the said powder formation process, after grind | pulverizing the said lump, it is preferable to classify so that a particle size may contain the particle | grains exceeding 100 micrometers. According to this, the particle size distribution contains particles having a particle size exceeding 100 μm, and not only particles having a particle size of 100 μm or less but also particles having a particle size exceeding 100 μm contain boron in the entire silicon carbide particles. Silicon carbide powder can be obtained.

  Moreover, in the said powder formation process, after grind | pulverizing the said lump, it is preferable to classify so that 98 mass% or more of the said silicon carbide powder may become the particle size range of 45-1400 micrometers by the opening dimension of a sieve. According to this, when manufacturing a silicon carbide single crystal by the sublimation recrystallization method, it is possible to obtain silicon carbide powder in which carbon inclusion and silicon droplets are hardly generated.

  Moreover, it is preferable to perform the said baking process by the Atchison method. According to this, silicon carbide powder of several tens to several hundreds μm or more suitable for the sublimation recrystallization method can be easily obtained.

  The method for producing a silicon carbide single crystal of the present invention is characterized in that a single crystal of silicon carbide containing boron as an impurity is grown by a sublimation recrystallization method using a raw material containing the silicon carbide powder of the present invention described above. And

  According to the method for producing a silicon carbide single crystal of the present invention, a single crystal of silicon carbide is grown by a sublimation recrystallization method using silicon carbide powder composed of silicon carbide particles containing boron in the interior as a raw material. A single crystal in which boron as an impurity is uniformly contained inside the crystal can be obtained.

According to the present invention, since the silicon carbide powder is composed of silicon carbide particles containing boron as a whole, by producing a silicon carbide single crystal by a sublimation recrystallization method using a raw material containing the silicon carbide powder. A silicon carbide single crystal in which boron as an impurity element is uniformly contained in the silicon carbide single crystal can be obtained.

It is explanatory drawing which shows an example of the method of manufacturing the silicon carbide single crystal by the sublimation recrystallization method. It is explanatory drawing which shows each cross-sectional structure of the silicon carbide particle which comprises the silicon carbide powder of the present invention, and the silicon carbide particle which comprises the silicon carbide powder of a comparative example.

  Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention.

  First, a method for producing silicon carbide powder will be described. Although a method using a solid phase reaction will be described here, a method using a liquid phase reaction or the like may be used.

  The method for producing silicon carbide powder according to the present invention comprises a raw material production step of obtaining a raw material for producing silicon carbide by mixing an inorganic siliceous raw material, a carbonaceous raw material, and a boron compound; It includes a firing step of forming a lump made of silicon carbide by firing at a temperature of at least ° C and a powder forming step of obtaining a silicon carbide powder by pulverizing the lump.

  Examples of the inorganic siliceous material include crystalline silica such as silica, silica fume, amorphous silica such as silica gel, and granular metal silicon. These may be used alone or in combination of two or more. The average particle size of the inorganic siliceous raw material is appropriately selected depending on the environment during firing, the state of the raw material (crystalline or amorphous), the reactivity with the carbonaceous raw material, and the like. However, it is preferable to use amorphous silica as the inorganic siliceous raw material because the reactivity during firing is good and the furnace is easily controlled.

  Examples of the carbonaceous raw material include crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon such as carbon black, coke, and activated carbon. These may be used alone or in combination of two or more. The average particle size of the carbonaceous raw material is appropriately selected depending on the environment during firing, the state of the raw material (crystalline or amorphous), the reactivity with the inorganic siliceous raw material, and the like.

  In order to obtain the silicon carbide powder of the present invention, it is necessary to add a boron compound raw material in addition to the inorganic siliceous raw material and the carbonaceous raw material.

As the boron compound raw material, boron carbide or boron nitride is preferable. Although it is possible to use boric acid, it volatilizes at 1000 ° C. or lower, which is not preferable from the viewpoint of controlling the amount of boron in silicon carbide. On the other hand, a metal boride such as TiB ₂ is not preferable because the metal remains as an impurity in silicon carbide. Boron carbide and boron nitride have a high melting point, and the constituent elements are carbon and nitrogen in addition to boron, respectively, so that the purity of silicon carbide is not lowered. In order to use as a raw material for silicon carbide single crystal for devices, high purity is desired.

  An inorganic siliceous raw material, a carbonaceous raw material, and a boron compound raw material are mixed to prepare a mixed powder serving as a raw material for silicon carbide powder. The mixing method at this time is arbitrary, and may be either wet mixing or dry mixing.

  The mixing molar ratio (C / Si) between the carbonaceous raw material and the inorganic siliceous raw material during mixing is optimal in consideration of the environment during firing, the particle size of the silicon carbide powder raw material, the reactivity, etc. Select. The term “optimum” as used herein means improving the yield of silicon carbide obtained by firing and reducing the unreacted residual amount of the inorganic siliceous raw material and carbonaceous raw material.

  Moreover, what is necessary is just to set the addition amount of a boron compound raw material suitably with the density | concentration made into the desired boron contained as an impurity. The higher the concentration of boron contained in the silicon carbide powder, the higher the concentration of boron in the single crystal when a silicon carbide single crystal is produced by the sublimation recrystallization method using it as a raw material. However, since a part of boron volatilizes in the firing step described later, the concentration of boron contained in the silicon carbide powder as a raw material and a silicon carbide single crystal formed by sublimation recrystallization using the concentration as a raw material It is not the same as the concentration of boron in it.

  The obtained mixed powder (raw material for producing silicon carbide) is fired at 2200 ° C. or higher, preferably 2500 ° C. or higher to obtain lump silicon carbide.

  The firing method is not particularly limited, and examples thereof include a method using external heating and a method using current heating. Examples of the external heating method include a method using a fluidized bed furnace, a batch type furnace, and the like. An example of a method using electric heating is an Atchison method using an Atchison furnace. The Atchison method is preferably employed because silicon carbide powder of several tens to several hundreds μm or more suitable for the sublimation recrystallization method can be easily obtained.

  The firing atmosphere is preferably a reducing atmosphere. This is because the yield of silicon carbide decreases when fired in an atmosphere with low reducing ability. At this time, if amorphous silica is used as one of the inorganic siliceous raw materials, the control of the furnace becomes easy because of the good reactivity. It is preferable to use a mixture partially containing amorphous silica.

  In the present specification, the “Atchison furnace” refers to a box-type indirect resistance heating furnace having an open top. Here, indirect resistance heating is to obtain silicon carbide by a heating element that generates heat by flowing an electric current, instead of flowing an electric current directly through an object to be heated. An example of a specific configuration of such an Atchison furnace is described in Japanese Patent Laid-Open No. 2013-112544.

  The type of the heating element of the Atchison furnace is not particularly limited as long as it can conduct electricity, and examples thereof include graphite powder and carbon rod.

  The form of the substance constituting the heating element is not particularly limited, and examples thereof include powder and lump. The heating element is provided so as to have a rod-like shape as a whole so as to connect the electrode cores provided at both ends in the energizing direction of the Atchison furnace. Examples of the rod shape here include a columnar shape and a prismatic shape.

By using such a furnace, the reaction shown in the following formula (1) occurs, and a lump made of silicon carbide (SiC) is obtained.
SiO ₂ + 3C → SiC + 2CO (1)

On the other hand, it is estimated that a part of SiO ₂ reacts with a boron compound (for example, B ₄ C) near 1600 ° C. and boron is incorporated, so that a silicon carbide crystal in which boron is uniformly incorporated grows. Yeah. Since the silicon carbide particles are often aggregates of crystallites, the tendency becomes stronger as the particles become coarser.

  After energization, a lump of silicon carbide is generated in the furnace. And it cools until the inside of a furnace becomes normal temperature.

  And the lump (ingot) which consists of obtained silicon carbide is grind | pulverized. Examples of the pulverization method include a pulverization method using a top grinder, a disk grinder, a jet mill, a ball mill and the like.

  Thereafter, it is preferable to classify the pulverized product so as to obtain a desired particle size range. For classification, a method using a sieve is the simplest and preferable. However, classification is not limited to a method using a sieve, and may be either dry or wet. Further, as a dry classification, for example, a centrifugal classification method using an air flow can be used.

  The classification is preferably performed so that particles with a particle size exceeding 100 μm are included, and further, 98 mass% or more of the silicon carbide powder is performed so that the particle size range depending on the sieve opening size is 45 to 1400 μm. More preferably, it is most preferable to carry out so that the particle size range is 100 to 1000 μm. Fine particles tend to cause carbon inclusion due to fine carbon powder, and coarse particles tend to have low sublimation speed due to a small specific surface area, and silicon droplets tend to occur.

  Further, contamination by pulverization may be removed by appropriately washing the pulverized product with hydrochloric acid or the like.

  The silicon carbide powder of the present invention thus obtained is composed of silicon carbide particles containing boron as an impurity. The silicon carbide particles are not limited to those having a particle size of 100 μm or less, and those having a particle size of more than 100 μm Contains boron. Here, “the whole contains boron” means that boron is contained from the surface layer to the center of the particle. In addition, those having a particle size exceeding 100 μm do not include those having a particle size exceeding 1400 μm. For example, in a powder in which 98% by mass or more of the silicon carbide powder has a particle size range of 45 to 1400 μm depending on the opening size of the sieve, boron is contained from the surface layer to the center of the particle at least in the particle size distribution. It should just be contained.

  In a preferred embodiment of the silicon carbide powder of the present invention, boron is contained almost uniformly from the surface layer to the center of the silicon carbide particles constituting the silicon carbide powder. Here, “substantially uniform” means that the difference between the highest density portion and the lowest density portion is within 70% with respect to the higher density portion.

  The method for producing a silicon carbide single crystal of the present invention is a method of growing a silicon carbide single crystal by a sublimation recrystallization method using the silicon carbide powder of the present invention as a raw material. A method for producing a silicon carbide single crystal by a sublimation recrystallization method may be performed according to a conventional method, and is not particularly limited, but an example thereof is as follows.

  As shown in FIG. 1, the raw material silicon carbide powder 5 is filled in a crucible 1 made of graphite, for example, and the crucible 1 is disposed in a heating device. However, the container in which the silicon carbide powder 5 is filled is not limited to the graphite crucible 1, and any container that can be used when producing single-crystal silicon carbide by the sublimation recrystallization method may be used. The crucible 1 is covered with a graphite plate 11 having a pedestal 2 in the center and a silicon carbide single crystal (seed crystal) 4 bonded thereto, and the periphery is covered with a heat insulating material. The crucible 1 is filled with argon gas. The silicon carbide powder 5 in the crucible 1 is heated to 2000 to 2500 ° C. under a reduced pressure such as an inert gas atmosphere. However, the temperature at which the silicon carbide single crystal 4 on the lower surface of the lid of the crucible 1 grows is about 100 ° C. lower than this.

  This heating is continued for several hours to several tens of hours. As a result, the silicon carbide powder 5 as a raw material is sublimated to become a sublimation gas, reaches the lower surface of the lid and becomes a single crystal, and this single crystal grows, whereby a lump of silicon carbide single crystal can be obtained.

  As described above, since the silicon carbide powder of the present invention contains boron in the entire silicon carbide particles constituting the silicon carbide powder, the concentration of boron taken into the single crystal as the single crystal grows. Is constant, and a single crystal having a uniform boron concentration as an impurity can be obtained.

  Hereinafter, examples and comparative examples of the present invention will be described. However, the present invention is not limited to these examples.

<Examples 1 and 2>
The following materials were used.
Inorganic siliceous raw material: Amorphous silica Average particle size 2 mm or less Carbonaceous raw material: Carbon black Average granule diameter 2 mm or less Boron compound: Boron carbide powder Particle size range Several to 20 μm
Boron carbide powder was mixed at a weight ratio of amorphous silica: carbon black = 2: 1 so as to be 0.8% by mass (Example 1) and 6% by mass (Example 2), respectively. These were used as raw materials.

  Each raw material was fired at 2500 ° C. for 6 hours in an Atchison furnace to obtain a silicon carbide ingot.

  The silicon carbide ingot was pulverized using a jaw crusher and a ball mill to obtain silicon carbide powders of Examples 1 and 2.

<Comparative Examples 1 and 2>
The following materials were used.
Inorganic siliceous raw material: Amorphous silica Average particle diameter 2 mm or less Carbonaceous raw material: Carbon black Average granule diameter 2 mm or less Boron compound: Boron carbide powder Particle size range 3-20 μm
Amorphous silica: carbon black = 2: 1 was mixed in a weight ratio and baked in an Atchison furnace at 2500 ° C. for 6 hours to obtain a silicon carbide ingot.

  The silicon carbide ingot was pulverized using a jaw crusher and a ball mill and sieved to obtain silicon carbide powder having a particle size range of 45 to 1400 μm.

  The silicon carbide powder was mixed with the boron carbide powder so as to be 0.8% by mass (Comparative Example 1) and 6% by mass (Comparative Example 2), respectively. The silicon carbide powder of Comparative Examples 1 and 2 was obtained by firing for a period of time.

<Test Example 1>
From the silicon carbide powders of Examples 1 and 2 and Comparative Examples 1 and 2, sieve classifications having a particle size range of 45 to 500 μm and 500 to 1400 μm were taken out.

  These were pulverized to 10 μm or less with a disc grinder. The pulverized product was molded, and the amount of boron was measured using fluorescent X-ray analysis (XRF). The results are shown in Table 1.

  As shown in Table 1, in Examples 1 and 2, the amount of boron was constant regardless of the particle size range. From this, it is presumed that the particles of the silicon carbide powders of Examples 1 and 2 uniformly contain boron up to the inside.

  On the other hand, in Comparative Examples 1 and 2, the boron amount was different in the particle size range, and the larger the particle size, the smaller the boron amount than the smaller particle size. The reason why the amount of boron differs depending on the particle size range is presumed to be because the amount of boron in the particles is uneven.

<Test Example 2>
In order to confirm the results of Test Example 1, the boron distribution in the particles was measured with an electron beam microanalyzer (EPMA) for each of the silicon carbide powders of Examples 1 and 2 and Comparative Examples 1 and 2. The silicon carbide powder was embedded in an acrylic resin and polished so that a cross section of the particles of the silicon carbide powder was obtained. In the measurement, particles having a particle diameter close to 45, 100, 500, 1400 μm were selected.

  As a result, it was found that the area where boron was detected in the cross section of the particle was divided into the type of FIG. 2A or the type of FIG. 2B. Note that the grayed out portion in FIG. 2 is an area where boron is detected.

  Table 2 shows the results of determining whether each of the silicon carbide powders is the A type or the B type.

  As shown in Table 2, in Examples 1 and 2, it was all A, and it was confirmed that boron was contained from the surface layer to the center of the particle regardless of the particle diameter.

  On the other hand, in Comparative Examples 1 and 2, the particle having a small particle size was A, but the particle having a large particle size was B. In Comparative Example 1 with a small amount of boron carbide, A was only A with a particle size of 45 μm, and with Comparative Example 2 with a large amount of Compound A, A was up to a particle size of 100 μm.

  On the other hand, even in coarse particles such as the particle size of 1400 μm in Example 1 in which the amount of boron carbide was small, boron was present in the center.

  In Comparative Examples 1 and 2, the depth from the surface containing boron does not change even when the particle diameter increases. For this reason, since the amount of boron per particle decreases as the particle diameter increases, when a silicon carbide single crystal containing boron is produced using the silicon carbide powder as in Comparative Examples 1 and 2, the single crystal It is estimated that the distribution of boron in it will vary.

Claims (8)

  The silicon carbide is composed of silicon carbide particles containing boron as an impurity, contains particles having a particle size exceeding 100 μm in the particle size distribution, and is not limited to particles having a particle size of 100 μm or less. A silicon carbide powder characterized in that the boron is contained in the whole of the particles.   2. The silicon carbide powder according to claim 1, wherein 98% by mass or more of the silicon carbide powder has a particle size range of 45 to 1400 μm according to a sieve opening size. A raw material production process for obtaining a raw material for producing silicon carbide by mixing an inorganic siliceous raw material, a carbonaceous raw material, and a boron compound;
A firing step of forming a lump of silicon carbide containing boron by firing the raw material for producing silicon carbide at 2,200 ° C. or higher;
A powder forming step of obtaining a silicon carbide powder by pulverizing the lump.   The method for producing silicon carbide powder according to claim 3, wherein boron carbide and / or boron nitride is used as the boron compound.   5. The method for producing silicon carbide powder according to claim 3, wherein, in the powder forming step, classification is performed so as to include particles having a particle size exceeding 100 μm after the lump is pulverized.   In the powder forming step, after the lump is pulverized, 98 mass% or more of the silicon carbide powder is classified so that the particle size range according to the sieve opening size is 45 to 1400 µm. The manufacturing method of the silicon carbide powder of any one of these.   The manufacturing method of the silicon carbide powder of any one of Claims 3-6 which performs the said baking process by an Atchison method.   A method for producing a silicon carbide single crystal comprising growing a silicon carbide single crystal containing boron as an impurity by a sublimation recrystallization method using a raw material containing the silicon carbide powder according to claim 1 or 2. .