JP2019119663A - SiC POWDER, AND MANUFACTURING METHOD OF SiC SINGLE CRYSTAL USING THE SAME - Google Patents

Abstract

To provide SiC powder capable of uniformizing an obtained SiC single crystal, when being used as a raw material in a sublimation recrystallization method; and to provide a manufacturing method of a SiC single crystal using the same.SOLUTION: SiC powder contains particles having the degree of sphericity of 0.85 or less as much as 60 mass% or more. A manufacturing method of a SiC single crystal includes a filling step S1 for filling a container with SiC powder containing particles having the degree of sphericity of 0.85 or less as much as 60 mass% or more, an installation step S2 for moving the container filled with SiC powder and installing it in a heating apparatus, and a SiC single crystal generation step S3 for obtaining a SiC single crystal by sublimating SiC powder by being heated in the heating apparatus.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a SiC (silicon carbide) powder and a method for producing an SiC single crystal using the same.

  SiC single crystals have excellent electrical characteristics, and are attracting attention as materials for power semiconductor substrates to replace Si (silicon) in recent years, where the energy saving intention is increasing.

  As a method of producing a SiC single crystal, a sublimation recrystallization method (a modified Lely method) is well known, in which a raw material SiC powder is sublimed under high temperature conditions of 2000 ° C. or more to grow SiC single crystal. It is widely used.

  In the sublimation recrystallization method, a container such as a crucible made of graphite is filled with SiC powder, and the container is heated in a heating device such as a heating furnace. Here, in general, the amount of charging the SiC powder into the container is controlled by weight, and the surface of the charged SiC powder is leveled by the worker.

  Patent Document 1 discloses that a SiC powder having a high flowability index is used to uniformly fill a container. This is because when the packing density is nonuniform, different polytypes other than the target polytype are mixed, and crystal defects are easily generated.

JP, 2016-147790, A

  However, if the flowability of the SiC powder is high, the SiC in the container is subjected to vibration, impact, etc. when moving from the place where the operator filled the container to the SiC powder to place in the heating apparatus. The height of the powder changes. Also, if the filling method such as the pouring height from the spout to the container in filling the SiC is different, the height of the SiC powder in the container changes even if the same amount of SiC powder is filled. The change in height of the SiC powder in the container that occurs in this way depends on the individual differences of the workers.

  Such a change in the height of the SiC powder is accompanied by a change in the gap between the SiC powders and affects the sublimation characteristics. Therefore, as a result, there is a problem that the uniformity of the obtained SiC single crystal can not be secured.

  An object of the present invention is to provide a SiC powder capable of achieving uniformization of the obtained SiC single crystal when used as a raw material in a sublimation recrystallization method, and a method of producing a SiC single crystal using the same. I assume.

  The SiC powder of the present invention is characterized by containing 60% by mass or more of particles having a sphericity of 0.85 or less.

  When the SiC powder of the present invention is used as a raw material powder for producing a SiC single crystal by a sublimation recrystallization method, as will be understood from the examples described later, the height of the SiC powder when the SiC powder is filled in the container; When the container filled with the SiC powder is installed in the heating apparatus, the difference in height of the SiC powder and the variation in the height thereof are small, including the individual differences among workers.

  Thereby, it is possible to suppress the variation of the gap between the SiC powders in the container, so that the variation of the sublimation characteristics is suppressed, and as a result, it is possible to achieve the uniformity of the quality of single crystal SiC obtained.

  In the method of producing an SiC single crystal according to the present invention, a step of filling a container with an SiC powder containing 60 mass% or more of particles having a sphericity of 0.85 or less, and moving the container filled with the SiC powder The method further comprises the steps of: installing in a heating device; and heating the inside of the heating device to sublime the SiC powder to obtain a SiC single crystal.

  According to the method of manufacturing an SiC single crystal of the present invention, since the SiC powder of the present invention is used as a raw material, it is possible to achieve uniformity in the quality of single crystal SiC obtained.

The flowchart which shows the manufacturing method of the SiC single crystal which concerns on embodiment of this invention.

  The SiC powder according to the embodiment of the present invention will be described. The present SiC powder is used as a raw material when producing a SiC single crystal by a sublimation recrystallization method.

  Here, a method of producing a SiC single crystal by a sublimation recrystallization method will be described with reference to FIG.

  First, a filling step S1 of filling a container with SiC powder which is a raw material powder is performed. The container is, for example, a crucible made of graphite, but the container is not limited thereto, and may be any container as long as it is used when producing a SiC single crystal by a sublimation recrystallization method.

  Generally, the amount of SiC powder introduced into the container is controlled by weight, and the surface of the introduced SiC powder is leveled by the worker.

  Next, the container filled with the SiC powder is moved to perform the installation step S2 of installing in the heating device. The container filled with the SiC powder may be moved as it is and placed in the heating device, or may be placed in the heating device after being stored in a storage location.

  Next, the inside of the heating device is heated to sublime the SiC powder, and an SiC single crystal production step S3 for obtaining a SiC single crystal is performed. Specifically, for example, the SiC powder in the container is heated to 2000 to 2500 ° C. under a reduced pressure in which the atmosphere in the heating device is an inert gas atmosphere such as argon gas. However, it is preferable that the temperature at which the portion of the lower surface of the lid of the container on which the SiC single crystal grows grow be about 100 ° C. lower.

  This heating is continued for several hours to several tens of hours. Thereby, the SiC powder is sublimed to become a sublimation gas, and reaches the lower surface of the lid to be single-crystallized, and a single-crystal is grown, whereby a lump of SiC single crystal can be obtained.

  In the present embodiment, the SiC powder as the raw material contains 60% by mass or more of particles having a sphericity Sp of 0.85 or less, more preferably 80 mass of particles having a sphericity Sp of 0.85 or less % Or more is included.

The sphericity Sp is defined by the following equation (1).
Sp = 4πS / L ² (1)

  Here, S is the projected cross-sectional area of the observation image of the particle, and L is the outer peripheral length (peripheral length) of the observation image of the particle. The observation image of the particles is a two-dimensional image obtained by observing the particles observed by SEM (scanning electron microscope) or an optical microscope. The sphericity Sp of a true circle is 1, and the closer the sphericity Sp is to 1, the closer it is to a perfect circle.

  As long as 60 mass% or more of particles having a sphericity Sp of 0.85 or less are contained in the raw material SiC powder, as will be understood from the examples described later, the SiC powder when filled with the SiC powder The height, the difference in height of the SiC powder when the container filled with the SiC powder is installed in the heating apparatus, and the variation in the height are small, including individual differences among workers.

  Thereby, it is possible to suppress the variation of the gap between the SiC powders in the container, so that the variation of the sublimation characteristics is suppressed, and as a result, it is possible to achieve the uniformity of the quality of single crystal SiC obtained.

  On the other hand, if less than 60% by mass of particles having a sphericity Sp of 0.85 or less is contained in the raw material SiC powder, as can be seen from a comparative example described later, when the SiC powder is filled in the container The difference between the height of the SiC powder and the height of the SiC powder when installed in a container heating apparatus filled with the SiC powder, and the variation in the height are large including the individual differences among workers.

  As a result, the change in the gap between the SiC powders in the container becomes large, so that the influence of the fluctuation of the sublimation characteristic occurs, and as a result, it becomes difficult to achieve the uniformity of the quality of the obtained single crystal SiC.

  The SiC powder having a sphericity Sp of 0.85 or less is preferably obtained by grinding large particles or a lump of SiC. In particular, it is preferable to obtain by grinding a block of SiC obtained by the Achison method.

  The purity, particle size, and specific surface area of the SiC powder may be the same as conventional SiC powder used as a raw material powder when producing a SiC single crystal by a sublimation recrystallization method.

  Hereinafter, an example of a method of manufacturing SiC powder concerning an embodiment of the present invention is explained. This manufacturing method comprises a raw material preparation step, a lump preparation step, a grinding step, a classification step, a measurement step and a mixing step.

  First, a raw material preparation step of obtaining a raw material for SiC production by mixing an inorganic siliceous raw material containing Si (silicon) and a carbonaceous raw material is performed. Examples of the inorganic siliceous material include crystalline silica such as silica stone, non-crystalline silica such as silica fume and silica gel. You may use these individually by 1 type or in combination of 2 or more types. The average particle diameter of the inorganic siliceous raw material is appropriately selected depending on the environment at the time of firing, the state of the raw material (crystalline and non-crystalline), the reactivity with the carbonaceous material, and the like.

  Examples of the carbonaceous material include crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon such as carbon black, coke and activated carbon. You may use these individually by 1 type or in combination of 2 or more types. The average particle size of the carbonaceous raw material is appropriately selected depending on the environment at the time of firing, the state of the raw material (crystalline and non-crystalline), the reactivity with the carbonaceous material, and the like.

  The inorganic siliceous raw material and the carbonaceous raw material are mixed to prepare a raw material for SiC powder. The mixing method in this case is arbitrary, and may be either wet mixing or dry mixing, and for example, it may be mixed by a twin screw mixer or the like.

  The mixing molar ratio (C / Si) of the inorganic siliceous material and the carbonaceous material at the time of mixing is selected in consideration of the environment at the time of firing, the particle size of the raw material for SiC powder, reactivity, etc. . The term "optimal" as used herein means to improve the yield of SiC obtained by firing and to reduce the unreacted residual amount of the inorganic siliceous material and the carbonaceous material.

  Next, a mass forming step is performed to obtain a mass of SiC by the Atchison method. In the lump formation step, the raw material for SiC production obtained in the raw material formation step is fired at 2200 ° C. or higher in an Acheson furnace to obtain a lump consisting of SiC. The Acheson furnace may be a general one.

  In the present specification, the "Acheson furnace" refers to a box-shaped indirect resistance heating furnace whose upper side is opened. Here, indirect resistance heating is to obtain SiC by means of a heating element that generates heat by flowing a current, instead of flowing the current directly to the object to be heated. Moreover, an example of a specific structure of such an Atchison furnace is described in Unexamined-Japanese-Patent No. 2013-112544.

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

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

  The form of the substance constituting the heating element is not particularly limited, and examples thereof include powdery, massive and the like. The heating element is provided in a bar-like shape as a whole so as to connect the electrode cores provided at both ends of the Acheson furnace in the current supply direction. Examples of the rod-like shape here include a cylindrical shape and a prismatic shape.

  After energization, a lump of SiC is formed in the furnace. Then, an inert gas such as argon gas is introduced to perform air cooling until the inside of the furnace reaches a normal temperature. After cooling, the SiC lump is taken out from the furnace.

  Next, the mass of SiC obtained in the mass forming step is pulverized to obtain an SiC powder. The grinding method is not limited, and for example, grinding may be performed using a jaw crusher, a roller mill, a disc grinder, a ball mill, a jet mill, and the like. However, in general, it is often crushed using a jaw crusher or a roller mill so that abrasion is less likely to occur during crushing. However, in pulverization using these pulverizers, it is difficult to adjust the particle size distribution, and few fall within the particle size range suitable for the SiC powder that is the raw material for obtaining SiC single crystals by the sublimation recrystallization method. Poor in yield.

  Then, it is preferable to grind | pulverize using the ball mill or jet mill which can adjust particle size distribution. However, in a ball mill, if grinding is performed for a long time under weak crushing power, the ends of the SiC particles are rounded during grinding, approaching a spherical shape, and the sphericity Sp becomes too large.

  Therefore, it is preferable to carry out grinding for a short time under conditions of high grinding power so that the sphericity Sp does not become too large. The strength of the pulverizing force can be adjusted by the ball diameter, the number of balls, the material of the balls, the amount of lumps fed to the mill, the rotational speed of the mill, and the like.

  Next, a classification step of classifying the SiC powder ground in the grinding step is performed. In the classification step, the SiC powder is limited to a predetermined particle size range. Classification is most conveniently and preferably a method using a sieve according to the desired particle size. However, classification is not limited to the method using a sieve, and may be performed either dry or wet. Further, as a dry classification, for example, a centrifugal classification method using an air flow can also be used.

  Next, in the SiC powder obtained in the classification step, a measurement step of measuring the proportion of particles having a sphericity Sp of 0.85 or less is performed. The sphericity Sp may be obtained by the above equation (1) for an image obtained by observing particles observed with an SEM or an optical microscope. However, since this is complicated, the sphericity Sp may be measured using an image analysis device such as particle image analysis device Mophorogi G3 manufactured by Malvern.

  Next, if necessary, different grinding modes in the grinding step are different, and plural types of SiC powders having different proportions of particles having a sphericity Sp of 0.85 or less measured in the measurement step are mixed to obtain a spherical shape. The mixing step is performed to obtain a SiC powder in which the proportion of particles having a degree Sp of 0.85 or less is 60% by mass or more.

  That is, in order to obtain a SiC powder having a proportion of particles having a sphericity Sp of 0.85 or less at 60 mass% or more, a plurality of types of SiC powders are appropriately selected in consideration of the content ratio measured in the measurement step. Mix at a certain ratio. The mixing method is not limited, but for example, a twin screw mixer can be used to uniformly mix without crushing the SiC powder. In the SiC powder measured in the measurement step, the mixing step may be omitted if the proportion of particles which are particles having a sphericity Sp of 0.85 or less is 60% by mass or more.

  Note that the above is an explanation of the case where the block of SiC obtained by the Acheson method is manufactured by grinding, but not a block of SiC but a sintered body or single crystal of SiC, etc. Classification, mixing, etc. may be performed.

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

(Preparation of SiC powder)
First, silica (amorphous silica) was prepared as an inorganic siliceous material in the material preparation step, and carbon black (amorphous carbon) was prepared as a carbonaceous material. Then, these raw materials by using a biaxial mixer, the molar ratio of carbon and silicon (C / SiO ₂₎ is mixed so that 3.0 to obtain a material for SiC powder production.

  Next, in the lump formation process, the raw material obtained in the raw material preparation process was fired for 12 hours in an Acheson furnace with a center temperature of 2500 ° C. or higher. Thereby, a lump of SiC was obtained.

  Next, in the pulverizing step, the obtained lump of SiC is pulverized with a jaw crusher, and sifted into a SiC powder of 3 mm or less. And this SiC powder was grind | pulverized using a ball mill, and SiC powder was obtained.

  When the processing amount in a normal ball mill is 1, and the ball amount is 1, the SiC powder of A is obtained by grinding the processing amount at 1.4 and the ball amount at 0.8. The B powder was obtained by grinding with a treatment amount of 0.6 and a ball amount of 1.2.

  Next, in the classification step, the particle size range of the A and B SiC powders was made 150 μm or more and 500 μm or less using a sieve.

  Next, in the measurement step, the sphericity Sp of the SiC powders of A and B classified in the classification step was measured 1000 by 1000 using a particle image analyzer Mophorogi G3 manufactured by Malvern. In the SiC powder of A, the proportion of particles having a sphericity Sp of 0.85 or less was 81% by mass. On the other hand, in the SiC powder of B, the proportion of particles having a sphericity Sp of 0.85 or less was 12% by mass.

  Next, in Example 2 and Comparative Examples 1 and 2, SiC powders of A and B were mixed using a twin-screw mixer at a ratio shown in Table 1 below as a mixing step. As a result, the ratio of the sphericity Sp of 0.85 or less was calculated from the mass average and was as shown in Table 1.

(Filling of SiC powder and installation of crucible
The workers A, S or S and A, in Example 1, work the SiC powder of A, and in Example 2 and Comparative Examples 1 and 2, work 1500 g of each of the SiC powder processed in the mixing step. It was filled in a crucible made of graphite which was placed on a table. The weir had a cylindrical shape with an inner diameter of 100 mm and a height of 150 mm. At the time of filling, the operator charged the SiC powder into the crucible using a funnel, filled the entire amount, then slightly shaken the crucible and smoothed the surface with a spatula. Then, after filling, the height from the bottom of the crucible to the top of the SiC powder was measured.

  Then, each worker who filled the SiC powder in the crucible moved 20 m on foot while holding the crucible with both hands, and installed the crucible on the table in the heating furnace. Then, in this furnace, the height from the bottom of the crucible to the top of the SiC powder was measured. The ratio of this height to the height immediately after filling was determined. The results are shown in Table 1. Each of Examples 1 and 2 and Comparative Examples 1 and 2 was performed three times.

(Discussion)
In Example 1, as can be seen from Table 1, the change in height was as small as 2% or less, and the variation was also as small as 1%.

  In Example 2, as can be seen from Table 1, the change in height was as small as 4% or less, and the variation was also as small as 1%. Furthermore, the variation in height due to the difference in workers was also small, less than 1%.

  On the other hand, in Comparative Example 1, as can be seen from Table 1, the change in height was as large as 9% at the maximum, and the variation was as large as 4% as the maximum. In addition, the variation in height due to differences in workers was as large as 4%.

  In Comparative Example 2, as can be seen from Table 1, the change in height was as large as 13% at maximum, and the variation was also as large as 6%.

From the above, in the case of the SiC powder in which the ratio of particles having a sphericity Sp of 0.85 or less is 60 mass% or more as in Examples 1 and 2, the height of the SiC powder when the SiC powder is filled in the crucible and , The difference in height of the SiC powder when the crucible filled with the SiC powder was installed in the heating apparatus, and further, the variation in the height was small, including the individual difference among workers.
On the other hand, in the case of the SiC powder in which the proportion of particles having a sphericity Sp of 0.85 or less is less than 60 mass% as in Comparative Examples 1 and 2, the height of the SiC powder when the SiC powder is filled in the crucible; When the crucible filled with the SiC powder was placed in the heating apparatus, the height difference of the SiC powder and the dispersion of the height were large including the individual differences among workers.

Claims (2)

  60 mass% or more of particle | grains whose sphericity is 0.85 or less are contained, SiC powder characterized by the above-mentioned. Filling a container with an SiC powder containing 60% by mass or more of particles having a sphericity of 0.85 or less;
Moving the container filled with the SiC powder for installation in a heating device;
And d) heating the inside of the heating device to sublime the SiC powder to obtain a SiC single crystal.