Metal carbide sintered body and method for producing same

Abstract

The present invention addresses the problem of providing a metal carbide sintered body in which occurrence of cracks is suppressed. Also provided is a method for producing a metal carbide sintered body in which the occurrence of cracks is suppressed. The problem is solved by a metal carbide sintered body of at least one metal selected from the group consisting of Group 4 and Group 5 elements of the periodic table, wherein the average particle diameter of particles in a first region is 3.5-9.5 μm, and the ratio of the average particle diameter of particles in a second region to the average particle diameter of the particles in the first region is 0.75-1.0. The problem is also solved by a method for producing a carbide sintered body, the method involving a step for adding carbon powder to a powder mixture of SiO2 powder and a metal carbide of at least one metal selected from the group consisting of Group 4 and Group 5 elements of the periodic table, and a step for sintering the mixture to which the carbon powder is added, wherein the amount of the carbon powder added is 0.30-3.00 parts by mass based on 100 parts by mass of the powder mixture.

Description

Metal carbide sintered body and its manufacturing method

[0001] The present invention relates to a metal carbide sintered body, and more specifically to a metal carbide sintered body with reduced crack generation.

[0002] Silicon carbide (SiC) semiconductors have not only higher heat resistance than silicon (Si) semiconductors, but also a wide band gap and high breakdown field strength. Therefore, they have attracted attention as semiconductor materials for low-power-loss power devices, and are particularly expected to be a core material for automotive electronic components. Because SiC does not melt under normal pressure and sublimes at temperatures of approximately 2000°C, the CZ method and FZ method used to manufacture Si single crystals cannot be employed for the production of SiC single crystals. Therefore, sublimation methods such as the modified Lely process are primarily used for mass production of SiC single crystals. In recent years, there has been a demand for larger-diameter SiC single crystal wafers, and methods for efficiently obtaining low-defect, high-quality SiC single crystals have been sought, and manufacturing methods other than sublimation (e.g., solution method and gas growth method) have also attracted attention.

[0003] In all of the above methods, raw materials (powder, gas, etc.) are supplied to a heat-resistant container (crucible, furnace tube, etc.) made of graphite or the like, and the raw materials are heated from outside the container by means of high-frequency heating or the like, and SiC single crystal growth is carried out in an ultra-high temperature range of 2000°C or higher. Although graphite is known to be a material that can withstand heat of 2500°C or higher, in the above-mentioned SiC single crystal growth method, SiC that has been sublimated by high-temperature heating is generated. ２ C and SiC ２ Sublimation gases such as SiH ４ , H ２ In this process, the surface of the graphite container is exposed to reactive gases derived from the raw material gas, such as hydrocarbons. In the presence of such reactive gases, graphite sublimes, significantly reducing the heat resistance of the container. Therefore, instead of graphite containers, it is necessary to use containers made of metal carbides (e.g., tantalum carbide or niobium carbide) that have much higher melting points than graphite.

[0004] Furthermore, SiC semiconductor devices are manufactured by using wafers cut from bulk single crystal SiC and growing SiC epitaxial films on the wafers by chemical vapor deposition (CVD), physical vapor deposition (PVD), etc. In the film-forming apparatus used to manufacture such SiC semiconductor devices, it is necessary to heat the substrate SiC single crystal wafer to a high temperature and maintain that temperature by means of high-frequency induction heating or the like, and therefore it has been proposed to use highly heat-resistant metal carbide materials as heat-resistant members in the film-forming apparatus as well (e.g., Patent Documents 1 and 2).

[0005] JP-T-2015-514673 A JP-A-2016-4933

[0006] However, these metal carbide sintered bodies have the disadvantage that cracks tend to occur on the surface. Therefore, the cracked surface areas must be removed by polishing. As a result, it has been necessary to prepare large sintered bodies in advance, taking into account the removal by polishing.

[0007] Therefore, the problem to be solved by the present invention is to provide a metal carbide sintered body that eliminates the above-mentioned inconvenience, i.e., that is ...

[0008] As a result of intensive research, the present inventors have found that the occurrence of cracks can be suppressed by making the particle size of the particles constituting the metal carbide sintered body uniform throughout the sintered body, that is, by reducing the variation in the average particle size of the particles throughout the sintered body. Furthermore, they have found that by adding a carbon component to the metal carbide sintered body in an amount that would conventionally be excessive, the particle size of the particles constituting the obtained metal carbide sintered body can be made uniform throughout the sintered body, and have completed the present invention.

[0009] A typical embodiment of the present invention is as follows: A metal carbide sintered body of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table, wherein a cross-sectional photograph is taken of one continuous cross section of the metal carbide sintered body, the cross-sectional photograph being a plane perpendicular to a parallel projection of the metal carbide sintered body and passing through the center of an inscribed circle inscribed in the parallel projection and having the largest area, the direction parallel to the parallel projection being the horizontal direction, the horizontal direction being 2.0 mm, and the cross-sectional photograph of the metal carbide sintered body is obtained so that both ends of a surface portion of the metal carbide sintered body are included in the vertical direction of the cross-sectional photograph, provided that when a plurality of continuous cross sections of the metal carbide sintered body are included in the plane perpendicular to the parallel projection, the cross-sectional photograph is obtained for one continuous cross section of the metal carbide sintered body having the largest cross-sectional area, a portion cut out in the center of the cross-sectional photograph measuring 260 μm in length x 360 μm in width is defined as a first region, a second region obtained by further cutting out a portion of the metal carbide sintered body from the first region toward the surface side of the metal carbide sintered body, measuring 260 μm in length and 360 μm in width, in the cross-sectional photograph, and when a side portion of the second region on the surface side of the metal sintered body is located 40 μm toward the center of the cross-sectional photograph in the vertical direction from a point on the surface portion of the metal carbide sintered body that is closest to the center of the cross-sectional photograph, the average grain size of grains in the first region is 3.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of grains in the second region to the average grain size of grains in the first region is 0.75 or more and 1.0 or less.

[0010] Another typical embodiment of the present invention is as follows: A metal carbide of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table, and SiO ２ a step of adding carbon powder to a powder mixture of powders, and a step of sintering the mixture to which the carbon powder has been added, wherein the amount of the carbon powder added is 0.30 parts by mass or more and 3.00 parts by mass or less per 100 parts by mass of the powder mixture.

[0011] The metal carbide sintered body of the present invention (hereinafter sometimes simply referred to as "sintered body") has grains with uniform grain size throughout. More specifically, if the interior of the sintered body is designated as a first region and the surface area is designated as a second region, the metal carbide sintered body of the present invention has a grain size in the first region of 3.5 μm to 9.5 μm, and the ratio of the grain size in the second region to the grain size in the first region is 0.75 to 1.0. This makes the metal carbide sintered body of the present invention less susceptible to cracks on the surface. Therefore, it is possible to suppress the removal of the surface portion by polishing, which is required in conventional sintered bodies, and thereby obtain excellent advantages such as reduced raw material usage, improved yield, shorter delivery time, and reduced initial defect rate.

[0012] Fig. 1 shows a schematic diagram illustrating a method for obtaining a cross-sectional photograph of a sintered body according to one embodiment of the present invention. Fig. 2 shows a schematic diagram illustrating a cross-sectional photograph of a sintered body according to one embodiment of the present invention. However, for convenience of explanation, the actual length ratios may differ. Fig. 3 shows a reference diagram illustrating a method for measuring the average particle size of particles from a cross-sectional photograph of a sintered body according to one embodiment of the present invention by the intercept method.

[0013] Metal Carbide Sintered Body The sintered body of the present invention is a metal carbide sintered body of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table, and the grain size of the grains constituting the sintered body is uniform throughout. More specifically, in the sintered body of the present invention, the average grain size of the grains in the first region is 3.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the grains in the second region to the average grain size of the grains in the first region is 0.75 or more and 1.0 or less. In general metal carbide sintered bodies, the grain size of the grains constituting the sintered body becomes larger toward the center of the sintered body and becomes smaller toward the surface of the sintered body.

[0014] The sintered body of the present invention is a carbide sintered body of at least one metal selected from the group consisting of Group 4 and Group 5 elements of the periodic table. Carbides of metals such as titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta), which are Group 4 and Group 5 elements of the periodic table, are known as metal carbides with high melting points. For example, the melting point (Tm) of titanium carbide is 3530°C, that of zirconium carbide is 3803°C, that of hafnium carbide is 3887°C, that of niobium carbide is 3800°C, and that of tantalum carbide is 3880°C. Therefore, the above-mentioned metal carbide sintered body is suitable as a material for heat-resistant containers, etc.

[0015] As the metal carbide used in the sintered body of the present invention, among carbides of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table, carbides of Ta, Nb, Ti, and Zr are preferred from the viewpoint of heat resistance, etc., and carbides of Ta and Nb are particularly preferred. These metal carbides may be used alone or in combination of two or more. Note that metal carbide is a general term for compounds composed of metal elements and carbon, and the composition ratio of metal elements to carbon is not limited as long as it exists stably. For example, tantalum carbide can be TaC, Ta ２ The sintered body contains both TaC particles and TaC particles. ２ In addition, in the case of niobium carbide, both NbC and NbC particles may be contained. ２ C, Nb ６ C ５ The sintered body contains NbC particles, Nb ２ C particles and Nb ６ C ５ From the viewpoint of preventing cracks by making the lattice constant constant as described later, the niobium carbide is preferably NbC particles, the tantalum carbide is preferably TaC particles, the titanium carbide is preferably TiC particles, and the zirconium carbide is preferably ZrC particles.

[0016] The above-mentioned metal carbides can be obtained by known methods, for example, by mixing an oxide of a metal (titanium, zirconia, hafnium, niobium, tantalum, tungsten, etc.) with carbon and heating the mixture in a hydrogen reducing atmosphere. Alternatively, metal carbides can be obtained by heat-treating a mixed solution in an oxygen-free atmosphere, in which an organic substance having a functional group capable of coordinating with the metal (e.g., an OH group or a COOH group) is added as a carbon source to a metal alkoxide.

[0017] The metal carbide used to obtain the sintered body of the present invention may be in granular form. When granular metal carbide is used, the average particle size of the granular metal carbide may preferably be 0.05 μm or more and 20.0 μm or less, more preferably 0.1 μm or more and 10.0 μm or less. By using the average particle size of the granular metal carbide within the above range, a denser sintered body can be obtained. Note that the average particle size of the granular metal carbide refers to the average particle size (Fischer diameter) measured by the air permeability method using a Fischer subsieve sizer. The average particle size of the carbide can be appropriately adjusted by the average particle size of the raw material (metal oxide) and the grinding conditions when grinding (disintegrating) the obtained carbide. Note that a short grinding time tends to result in a large particle size of the ground product, while a long grinding time tends to result in a small particle size of the ground product.

[0018] Here, a cross-sectional photograph for defining the "first region" and the "second region" in the sintered body of the present invention will be described.

[0019] The cross-sectional photograph in the present invention is a photograph of one continuous cross section of the metal carbide sintered body, which is a plane perpendicular to the parallel projection of the metal carbide sintered body and which passes through the center of the inscribed circle inscribed in the parallel projection and has the largest area, with the direction parallel to the parallel projection being the horizontal direction, the horizontal direction being 2.0 mm, and both ends of the surface portion of the metal carbide sintered body being included in the vertical direction of the cross-sectional photograph. However, when a plurality of cross sections of the metal carbide sintered body are included in the plane perpendicular to the parallel projection, the cross-sectional photograph is taken for one continuous cross section of the metal carbide sintered body having the largest cross-sectional area.

[0020] The method for obtaining a cross-sectional photograph in the present invention will be described with reference to the drawings. However, the sintered body and the direction of obtaining the cross section in the drawings are merely examples, and the shape of the sintered body of the present invention, the direction of the cross section to be obtained, etc. are not limited thereto.

[0021] First, a parallel projection of the sintered body of the present invention from an arbitrary direction is assumed. For example, in Fig. 1, a plate-shaped sintered body 101 is placed so that its surface is approximately horizontal, and a parallel projection 102 is assumed to be directed vertically downward. The parallel projection 102 in the present invention refers to a drawing drawn with the line of sight from the viewpoint to the target sintered body 101 parallel, and is assumed to be a silhouette of the target sintered body 101.

[0022] Next, as shown in Fig. 1, an inscribed circle 103 is assumed to be inscribed in the parallel projection 102 and to have the largest area. The inscribed circle 103 is the circle inscribed in the parallel projection 102 and to have the largest area, and it touches the outer edge of the parallel projection 102 at at least two points. In Fig. 1, the parallel projection 102 of the plate-like sintered body 101 has a rectangular shape, so the inscribed circle 103 is the circle that touches the outer edge of the parallel projection 102 at at least three points and has the largest area.

[0023] Next, as shown in Fig. 1, a plane 104 is assumed to be perpendicular to the parallel projection 102 and to pass through the center of the inscribed circle 103. The cross-sectional photograph in the present invention is a photograph of the cross-section of the sintered body 101 obtained along the plane 104. When obtaining the cross-sectional photograph, the cross-section of the sintered body is mirror-polished and etched to facilitate observation of the cross-section of the sintered body.

[0024] The cross-sectional photograph in the present invention is a cutout of the cross section of the sintered body, with the direction parallel to the parallel projection (shown as A-A' in FIGS. 1 and 2) being the horizontal direction, with a dimension of 2.0 mm in the horizontal direction and both ends of the surface portion of the metal carbide sintered body being included in the vertical direction. That is, as shown in FIG. 2, the upper and lower sides of the cross-sectional photograph are parallel to the parallel projection 102 in FIG. 1, and the horizontal length of the cross-sectional photograph corresponds to 2.0 mm of the actual sintered body 101. The vertical length of the cross-sectional photograph is determined so that the uppermost part 201 and the lowermost part 202 of the surface of the sintered body fit vertically in the cross section of the sintered body. Therefore, as shown in FIG. 2, the uppermost part 201 of the surface of the sintered body is located on the upper side of the cross-sectional photograph, and the lowermost part 202 of the surface of the sintered body is located on the lower side of the cross-sectional photograph.

[0025] In the above-described method for obtaining a cross-sectional photograph, multiple cross sections of the sintered body may be obtained depending on the three-dimensional shape of the sintered body, the viewpoint setting for assuming a parallel projection view, etc. In such a case, in the present invention, a cross-sectional photograph is obtained for one continuous cross section having the largest cross-sectional area among the multiple cross sections. One continuous cross section means that the cross section of the sintered body is not divided by any part other than the sintered body. By obtaining a cross-sectional photograph of the cross section, a cross-sectional photograph can be obtained in which the entire cross section of the sintered body can be observed, as shown in FIG. 2.

[0026] In the present invention, the "first region" refers to a portion cut out from the center of the cross-sectional photograph obtained by the above-mentioned method, measuring 260 μm in length and 360 μm in width. That is, in Fig. 2, the first region is a portion 203 cut out from the center of the cross-sectional photograph. Note that, since the cross-sectional photograph is rectangular, the center of the cross-sectional photograph coincides with the intersection of two diagonal lines, and is indicated by a black dot in Fig. 2.

[0027] In the present invention, the second region refers to a portion of the cross-sectional photograph obtained by the above-mentioned method, which is further cut out from the first region toward the surface of the sintered body, measuring 260 μm in length and 360 μm in width, and the side of the second region on the surface side of the sintered body is located 40 μm toward the center of the cross-sectional photograph in the vertical direction from the point closest to the center of the surface portion of the sintered body. That is, in the example of the cross-sectional photograph of the sintered body shown in Figure 2, the second region is the cut-out portion 204 of the cross-sectional photograph, and is located 40 μm below the point 205 closest to the center of the surface portion of the sintered body.

[0028] In the above cross-sectional photograph and the definitions of the first and second regions, the lengths indicated correspond to the lengths of the actual sintered body. For example, when the cross-sectional photograph is enlarged, the cutout ranges of the first and second regions are also enlarged according to the magnification. Also, in order to explain the first and second regions and the cross-sectional photograph of the present invention, the scale and magnification of Figure 2 differ from those of the actual cross-sectional photograph.

[0029] In the sintered body of the present invention, the average grain size of the grains in the first region is 3.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the grains in the second region to the average grain size of the grains in the first region is 0.75 or more and 1.0 or less.

[0030] The average grain size of the first and second regions can be measured by the intercept method. The intercept method involves drawing lines at regular intervals in a grid pattern on a cross-sectional photograph and calculating the grain size based on the distance between the intersections of the lines and the grains. The intercept method for measuring grain size is described below with reference to Figure 3. (1) A tentative SEM image (Figure 3) is obtained within the first and second regions of the metal carbide sintered body at a magnification of 1000x. (2) As shown in Figure 3, lines are drawn in a grid pattern across the entire SEM image, with each side measuring 20 μm. The average grain size is calculated from the intersections of all the lines and the grains. When counting the intersections of a line and a grain, the number of intersections is "1" when the line touches or intersects the outer edge of the grain, and "1.5" when the line intersects a triple junction of the grain. (3) Depending on the grain size observed in the SEM image, the number of intersections of the line and the grid is set to approximately 200. If the number of intersections between the lines and the particles in the SEM image is insufficient or excessive with respect to 200, the magnification of the SEM image is adjusted, and the average particle size is calculated again, so that the number of intersections between the lines and the particles in the SEM image is approximately 200. For example, if the particle size is large, the magnification may be adjusted to about 500 times, and if the particle size is small, the magnification may be adjusted to about 2000 times.

[0031] The average particle size of the particles in the first region varies depending on the type of metal carbide, as described below. The average particle size of the particles in the first region may be preferably 3.5 μm or more and 9.4 μm or less, more preferably 3.5 μm or more and 9.3 μm or less, even more preferably 3.5 μm or more and 9.2 μm or less, even more preferably 3.5 μm or more and 9.1 μm or less, even more preferably 3.5 μm or more and 9.0 μm or less, even more preferably 3.5 μm or more and 8.9 μm or less, even more preferably 3.5 μm or more and 8.8 μm or less, even more preferably 3.5 μm or more and 8.7 μm or less, and particularly preferably 3.5 μm or more and 8.6 μm or less. Generally, the average particle size of the particles constituting the sintered body is larger toward the interior of the sintered body and smaller toward the surface of the sintered body. The greater the variation in the average particle size, the more likely cracks are to occur. Therefore, a small average particle size in the first region may be preferable.

[0032] The ratio of the average particle size of the particles in the second region to the average particle size of the particles in the first region may be preferably 0.76 to 1.0, more preferably 0.77 to 1.0, even more preferably 0.78 to 1.0, still more preferably 0.79 to 1.0, even more preferably 0.80 to 1.0, still more preferably 0.81 to 1.0, even more preferably 0.82 to 1.0, still more preferably 0.83 to 1.0, and particularly preferably 0.84 to 1.0. The closer the ratio of average particle sizes is to 1.0, the smaller the difference between the average particle size of the particles in the first region and the average particle size of the particles in the second region is, and the more uniform the particle size is throughout the sintered body, which preferably results in a sintered body in which the occurrence of cracks is significantly suppressed.

[0033] While not wishing to be bound by theory, it is believed that in conventional sintered bodies, grain growth is caused by a lack of carbon components inside the sintered body during the sintering process. Therefore, as mentioned above, in general metal carbide sintered bodies, the grain size of the grains constituting the sintered body becomes larger toward the inside of the sintered body and becomes smaller toward the surface of the sintered body. The inventors focused on this empirical rule in conventional sintered bodies and discovered that the occurrence of cracks can be suppressed by controlling the grain growth inside the sintered body to be suppressed and making the grain size of the grains constituting the sintered body uniform throughout, thereby completing the present invention.

[0034] The average particle size of the particles constituting the sintered body of the present invention is approximately the same in the first and second regions. The average particle size of the particles constituting the sintered body is preferably 1 μm or more and 100 μm or less, more preferably 1 μm or more and 10 μm or less. In the present invention, the added carbon forms a compound with a metal element, thereby uniforming the degree of grain growth between the center and the surface layer, thereby preventing stress caused by partial coarsening of particles. As a result, a sintered body without cracks can be obtained, exhibiting excellent mechanical strength and corrosion resistance. The particle size can be calculated by mirror-polishing the cross section of the sintered body, etching it, observing the cross section, and performing image analysis. Here, excessive etching at high temperatures and / or for long periods of time can promote grain growth of the particles constituting the sintered body. Therefore, it is desirable to minimize the influence of etching when calculating the average particle size of the particles constituting the sintered body of the present invention. Examples of such etching conditions include: (1) The sintered body is heated from room temperature to 2400°C at a rate of 200°C / hr over 12 hours in an argon atmosphere (0.098 MPa). (2) After the temperature is increased, the temperature is maintained at 2400° C. for 4 hours. (3) After the temperature is maintained for 4 hours, the temperature is naturally decreased from 2400° C. to room temperature.

[0035] In one aspect of the present invention, as described above, the metal is preferably selected from the group consisting of Nb, Ta, Ti, and Zr. More preferably, the metal is Nb or Ta. As described above, metal carbides of these metals have particularly high melting points and are therefore suitable as materials for heat-resistant containers and the like used in ultra-high temperature regions of 2000°C or higher.

[0036] The average particle size of the particles constituting the metal carbide sintered body varies depending on the type of metal.

[0037] In one embodiment of the present invention, the metal may be Nb. In this case, the average grain size of the particles in the first region of the sintered body may be 5.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the particles in the second region to the average grain size of the particles in the first region may be 0.75 or more and 1.0 or less. The average grain size of the particles in the first region of the sintered body may be preferably 5.6 μm or more and 9.4 μm or less, more preferably 5.7 μm or more and 9.3 μm or less, even more preferably 5.8 μm or more and 9.2 μm or less, even more preferably 5.9 μm or more and 9.1 μm or less, even more preferably 6.0 μm or more and 9.0 μm or less, even more preferably 6.1 μm or more and 8.9 μm or less, even more preferably 6.2 μm or more and 8.8 μm or less, even more preferably 6.3 μm or more and 8.7 μm or less, and particularly preferably 6.4 μm or more and 8.6 μm or less. The ratio of the average particle size of the particles in the second region to the average particle size of the particles in the first region may be preferably 0.76 or more and 1.0 or less, more preferably 0.77 or more and 1.0 or less, even more preferably 0.78 or more and 1.0 or less, still more preferably 0.79 or more and 1.0 or less, even more preferably 0.80 or more and 1.0 or less, still more preferably 0.81 or more and 1.0 or less, even more preferably 0.82 or more and 1.0 or less, still more preferably 0.83 or more and 1.0 or less, and particularly preferably 0.84 or more and 1.0 or less.

[0038] In one embodiment of the present invention, the metal may be Ta. In this case, the average grain size of the particles in the first region of the sintered body may be 3.5 μm or more and 7.5 μm or less, and the ratio of the average grain size of the particles in the second region to the average grain size of the particles in the first region may be 0.75 or more and 1.0 or less. The average grain size of the particles in the first region of the sintered body may be preferably 3.6 μm or more and 7.4 μm or less, more preferably 3.7 μm or more and 7.3 μm or less, even more preferably 3.8 μm or more and 7.2 μm or less, even more preferably 3.9 μm or more and 7.1 μm or less, even more preferably 4.0 μm or more and 7.0 μm or less, even more preferably 4.1 μm or more and 6.9 μm or less, even more preferably 4.2 μm or more and 6.8 μm or less, even more preferably 4.3 μm or more and 6.7 μm or less, and particularly preferably 4.4 μm or more and 6.6 μm or less. The ratio of the average particle size of the particles in the second region to the average particle size of the particles in the first region may be preferably 0.76 or more and 1.0 or less, more preferably 0.77 or more and 1.0 or less, even more preferably 0.78 or more and 1.0 or less, still more preferably 0.79 or more and 1.0 or less, even more preferably 0.80 or more and 1.0 or less, still more preferably 0.81 or more and 1.0 or less, even more preferably 0.82 or more and 1.0 or less, still more preferably 0.83 or more and 1.0 or less, and particularly preferably 0.84 or more and 1.0 or less.

[0039] In one embodiment of the present invention, the metal may be Ti. In this case, the average grain size of the particles in the first region of the sintered body may be 3.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the particles in the second region to the average grain size of the particles in the first region may be 0.75 or more and 1.0 or less. The average grain size of the particles in the first region of the sintered body may be preferably 3.6 μm or more and 9.4 μm or less, more preferably 3.7 μm or more and 9.3 μm or less, even more preferably 3.8 μm or more and 9.2 μm or less, even more preferably 3.9 μm or more and 9.1 μm or less, even more preferably 4.0 μm or more and 9.0 μm or less, even more preferably 4.1 μm or more and 8.9 μm or less, even more preferably 4.2 μm or more and 8.8 μm or less, even more preferably 4.3 μm or more and 8.7 μm or less, and particularly preferably 4.4 μm or more and 8.6 μm or less. The ratio of the average particle size of the particles in the second region to the average particle size of the particles in the first region may be preferably 0.76 or more and 1.0 or less, more preferably 0.77 or more and 1.0 or less, even more preferably 0.78 or more and 1.0 or less, still more preferably 0.79 or more and 1.0 or less, even more preferably 0.80 or more and 1.0 or less, still more preferably 0.81 or more and 1.0 or less, even more preferably 0.82 or more and 1.0 or less, still more preferably 0.83 or more and 1.0 or less, and particularly preferably 0.84 or more and 1.0 or less.

[0040] In one embodiment of the present invention, the metal may be Zr. In this case, the average grain size of the particles in the first region of the sintered body may be 3.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the particles in the second region to the average grain size of the particles in the first region may be 0.75 or more and 1.0 or less. The average grain size of the particles in the first region of the sintered body may be preferably 3.6 μm or more and 9.4 μm or less, more preferably 3.7 μm or more and 9.3 μm or less, even more preferably 3.8 μm or more and 9.2 μm or less, even more preferably 3.9 μm or more and 9.1 μm or less, even more preferably 4.0 μm or more and 9.0 μm or less, even more preferably 4.1 μm or more and 8.9 μm or less, even more preferably 4.2 μm or more and 8.8 μm or less, even more preferably 4.3 μm or more and 8.7 μm or less, and particularly preferably 4.4 μm or more and 8.6 μm or less. The ratio of the average particle size of the particles in the second region to the average particle size of the particles in the first region may be preferably 0.76 or more and 1.0 or less, more preferably 0.77 or more and 1.0 or less, even more preferably 0.78 or more and 1.0 or less, still more preferably 0.79 or more and 1.0 or less, even more preferably 0.80 or more and 1.0 or less, still more preferably 0.81 or more and 1.0 or less, even more preferably 0.82 or more and 1.0 or less, still more preferably 0.83 or more and 1.0 or less, and particularly preferably 0.84 or more and 1.0 or less.

[0041] The average particle size of the particles in the first region is determined by the ratio of the metal carbide and SiO ２ This can be adjusted by adding carbon powder to the mixed powder of metal carbide and SiO ２ This is thought to be because the addition of carbon powder to the mixed powder effectively suppresses grain growth caused by a lack of carbon components.

[0042] Metal carbides and SiO ２ The amount of carbon powder added to the mixed powder of metal carbide and SiO may vary depending on the shape of the sintered body to be finally obtained, particularly the thickness of the sintered body. ２The amount of carbon powder to be added may be 0.30 parts by mass or more and 3.00 parts by mass or less with respect to 100 parts by mass of the mixed powder of metal carbide and SiO ２ The amount of carbon powder to be added may be preferably 0.50 parts by mass or more and 2.75 parts by mass or less, and more preferably 0.75 parts by mass or more and 2.00 parts by mass or less, relative to 100 parts by mass of the mixed powder of metal carbide and SiO ２ By adding 0.30 parts by mass or more of the carbon powder to 100 parts by mass of the mixed powder, it is possible to supply a sufficient amount of carbon component to suppress grain growth caused by a deficiency of the carbon component. Therefore, grain growth within the sintered body is suppressed, and a sintered body consisting of particles with a uniform particle size as a whole can be obtained, and the occurrence of cracks in the sintered body can be reduced or prevented. On the other hand, when the amount of carbon powder added is equal to or greater than the amount of the metal carbide and SiO ２ When the amount of the sintered body is 3.00 parts by mass or less relative to 100 parts by mass of the mixed powder, a sintered body having a high relative density can be obtained, and therefore a sintered body having excellent mechanical strength can be obtained.

[0043] In one embodiment of the present invention, the ratio of the lattice constant of the metal carbide in the second region to the lattice constant of the metal carbide in the first region may be 0.9999 or more and 1.0001 or less. When the ratio of the lattice constant of the metal carbide in the second region to the lattice constant of the metal carbide in the first region is within the above range, the size of the grains constituting the sintered body is uniform throughout the sintered body, and a sintered body in which the occurrence of cracks is suppressed can be obtained.

[0044] In one aspect of the present invention, the difference between the lattice constant of the metal carbide in the first region and the lattice constant of the metal carbide in the second region may be 0.0005 Å or less. When the difference between the lattice constant of the metal carbide in the first region and the lattice constant of the metal carbide in the second region is within the above range, the size of the grains constituting the sintered body is uniform throughout the sintered body, and a sintered body in which the occurrence of cracks is suppressed can be obtained.

[0045] In one aspect of the present invention, the values ​​of the lattice constant of the metal carbide in the first region and the lattice constant of the metal carbide in the second region may be 99.98% or more and 100.02% or less of the theoretical value of the lattice constant of the metal carbide. That is, the value of the lattice constant of the metal carbide in the first region is 99.98% or more and 100.02% or less of the theoretical value of the lattice constant of the metal carbide, and the value of the lattice constant of the metal carbide in the second region is also 99.98% or more and 100.02% or less of the theoretical value of the lattice constant of the metal carbide. When the values ​​of the lattice constant of the metal carbide in the first region and the lattice constant of the metal carbide in the second region are within the above ranges, the size of the grains constituting the sintered body as a whole is uniform, and the sintered body can be one in which the occurrence of cracks is suppressed.

[0046] The lattice constant can be calculated using the WPPF (Whole Powder Pattern Fitting) method based on the diffraction peaks derived from the components of the sintered body obtained by X-ray diffraction measurement.

[0047] In a sintered carbide of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table, the abundance ratio of the metal element forming the metal carbide to the carbon element is ideally 1: 1. In this specification and the like, the value of the lattice constant in this state is taken as the theoretical value of the lattice constant of the metal carbide.

[0048] Specific theoretical values ​​of lattice constants for preferred examples of carbides of metal elements in Groups 4 and 5 of the periodic table are described below. When the metal is Nb, the theoretical value of the lattice constant of niobium carbide (NbC) is 4.4704. When the metal is Ta, the theoretical value of the lattice constant of tantalum carbide (TaC) is 4.4564. When the metal is Ti, the theoretical value of the lattice constant of titanium carbide (TiC) is 4.32. When the metal is Zr, the theoretical value of the lattice constant of zirconium carbide (ZrC) is 4.689.

[0049] The lattice constant of the metal carbide in the second region can be adjusted by the carbon content of the raw material, the type of jig on which the carbide is placed during firing, and whether or not there is contact with carbon components present in the furnace (e.g., components derived from furnace internal parts such as heaters and insulation materials).

[0050] The lattice constant of the metal carbide in the first region can be adjusted by the carbon content of the raw material.

[0051] The sintered body of the present invention can contain a trace amount of silicon (Si). Examples of the Si element source contained in the sintered body include SiO ２ For example, a metal carbide powder containing an appropriate amount of SiO ２ Powder is added to metal carbide and SiO ２ A sintered body can be obtained by preparing a mixed powder of the above, adding carbon powder or the like to the mixed powder, forming the sintering slurry, and sintering the slurry. ２ By controlling the content, it is possible to adjust the Si element content in the sintered body. Although it depends on the contents of other components in the mixed powder and the sintering conditions, the content of metal carbides and SiO ２ SiO ２ is preferably in the range of 0.01 parts by mass or more and 12 parts by mass or less, more preferably in the range of 0.06 parts by mass or more and 3 parts by mass or less, and particularly preferably in the range of 0.2 parts by mass or more and 0.9 parts by mass or less.

[0052] Metal carbides and SiO ２ In the mixed powder ２ From the viewpoint of uniformly dispersing SiO ２ Preferably, SiO may be supplied in the form of particles having a small average particle size, or in the form of a dispersion in which the particles are dispersed in a dispersion medium such as water. ２ When SiO is granular, ２ The average particle size of SiO may be preferably 0.05 μm or more and 10.0 μm or less, more preferably 0.1 μm or more and 5.0 μm or less, and even more preferably 0.2 μm or more and 0.5 μm or less. ２ When the compound is supplied in the form of a dispersion, SiO dispersed in the dispersion medium ２ The average particle size of the particles may be preferably 0.001 μm or more and 0.5 μm or less, and more preferably 0.005 μm or more and 0.1 μm or less. ２The average particle size of the particles means the average particle size (Fischer diameter) measured by the air permeability method using a Fischer sub-sieve sizer, as in the case of granular metal carbides.

[0053] When obtaining the sintered body of the present invention, metal carbide and SiO ２ A binder resin may be further added to the mixed powder. By adding the binder resin, the metal carbide and SiO ２ When preparing a sintering slurry containing the mixed powder, the viscosity of the sintering slurry can be easily adjusted and handled, and the moldability of the sintered body can be improved when the sintering slurry is sintered. The binder resin is not particularly limited as long as it can achieve the above-mentioned effects, and examples thereof include polyvinyl alcohol resin, acrylic resin, polyvinyl butyral resin, methyl cellulose resin, ethyl cellulose resin, acetyl cellulose resin, phenol resin, urea resin, and melamine resin. Two or more of these binder resins may be mixed and used. A preferred binder resin is polyvinyl alcohol resin.

[0054] The amount of binder resin added affects the viscosity of the sintering slurry, and can be adjusted appropriately depending on the application of the sintered body. For example, when the sintered body is used as a heat-resistant member, the amount of binder resin added may vary depending on whether it is used as a base material for the heat-resistant member or as a coating material for the base material. The amount of binder resin added can be adjusted, for example, depending on the amount of metal carbide and SiO ２ The amount of the binder resin added may be 0.01 parts by mass or more and 5.0 parts by mass or less, preferably 0.03 parts by mass or more and 3.0 parts by mass or less, and more preferably 0.05 parts by mass or more and 2.0 parts by mass or less, relative to 100 parts by mass of the mixed powder. By setting the amount of the binder resin added within this range, distortion of the obtained metal carbide sintered body can be suppressed, and the generation of carbon deposits derived from the binder resin can be suppressed.

[0055] Metal carbides and SiO ２ When the mixed powder is made into a sintering slurry, metal carbides and SiO ２In order to improve the dispersibility of the metal carbide and SiO, additives may be further added in addition to the binder resin. Examples of additives include polyethyleneimine-based polymer dispersants, polyurethane-based polymer dispersants, and polyallylamine-based polymer dispersants. The amount of additive to be added depends on the amount of metal carbide and SiO. ２ The amount of the mixed powder may be 0.03 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the mixed powder.

[0056] Metal carbides and SiO ２ In addition to the binder resin and additives, a solvent may be added to the mixed powder. Examples of the solvent include organic solvents such as ethanol, benzyl alcohol, toluene, dimethylacetamide, and methyl ethyl ketone, and water. One type of solvent may be used, or two or more types may be mixed and used. The amount of solvent added affects the viscosity of the sintering slurry, so it can be adjusted appropriately depending on the application of the sintered body. The amount of solvent added is determined based on the viscosity of the metal carbide and SiO ２ The amount of the inorganic filler may be 5.0 parts by mass or more and 30.0 parts by mass or less relative to 100 parts by mass of the mixed powder.

[0057] In one aspect of the present invention, even when sintered under normal pressure, the sintered body may have a relative density of 94% or more. From the viewpoint of mechanical strength, the relative density of the sintered body may be preferably 97.5% or more, and particularly preferably 99% or more. The relative density is defined as the ratio of the sintered body density (bulk density) to the theoretical density expressed as a percentage, and can be measured in accordance with JIS-R1634. For example, when the density of TaC is 14.3 g / cm ３ The density of NbC is 7.76 g / cm ３ The density of TiC is 4.90 g / cm ３ The density of ZrC is 6.9 g / cm ３ As SiO ２ The density is 2.65 g / cm ３The density calculated by the weighted average of the above is the theoretical density, and the closer the bulk density calculated by the Archimedes' method is to 100% of the theoretical density, the more dense the structure of the sintered body, with no defects such as voids inside. In this embodiment, a sintered body with a high relative density can be obtained without sintering under pressure. Therefore, there is no need to perform sintering under pressure, such as hot pressing or HIP, which has conventionally been required to obtain a sintered body with a high relative density. Even if the molded body has a relatively complex shape, a sintered body with a high relative density and excellent mechanical strength can be obtained by sintering at normal pressure.

[0058] In the sintered body of the present invention, the purity of the sintered body (the mass ratio of metal carbide to the entire sintered body) is preferably 97.5% or more. By increasing the purity of the sintered body, when the sintered body is used as a heat-resistant member for SiC semiconductor manufacturing equipment, the corrosion resistance (resistance to reactive gases) of the heat-resistant member can be improved. Note that a sintered body having a purity of 97.5% or more is a sintered body having a high purity of metal carbide and SiO ２ The mass ratio of the metal carbide in the sintered body can be measured by inductively coupled plasma emission spectroscopy (ICP), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), or the like.

[0059] In one aspect of the present invention, pores may be present in the sintered body. In this case, the open porosity is preferably 1% or less, and more preferably 0.5% or less. The closed porosity is preferably 5% or less, and more preferably 3% or less. The open porosity (%) can be calculated by Archimedes' method in accordance with JIS-R1634. The closed porosity (%) is the value (%) obtained by subtracting the ratio of the apparent density to the theoretical density described above from 1, expressed as a percentage. The apparent density refers to the value measured in accordance with JIS-R1634. Generally, the smaller the open porosity and closed porosity, the higher the mechanical strength of the sintered body.

[0060] The ratio of open porosity to closed porosity may preferably be 0 or more and 0.5 or less. The smaller the open porosity to closed porosity, the fewer pores that are likely to become a source of fracture on the outer surface of the sintered body, and therefore the higher the mechanical strength of the sintered body can generally be. Furthermore, by using such a sintered body as a heat-resistant member for SiC semiconductor manufacturing equipment, the surface area in contact with atmospheric gas is reduced, and therefore the corrosion resistance of the heat-resistant member can be improved.

[0061] Furthermore, even if pores are present in the sintered body, the smaller the pores, the better from the viewpoint of the corrosion resistance of the heat-resistant member. The average pore diameter is preferably 50 μm or less, more preferably 10 μm or less. The average pore diameter can be calculated by mirror-polishing a cross section of the sintered body, observing the cross section with an electron microscope, observing the image at an arbitrary magnification, and performing image analysis. Specifically, an arbitrary observation area of ​​the cross section is divided into two regions: a sintered body portion (matrix region) and a pore portion (non-matrix region), and the diameters of the pores present in a predetermined range of the cross section (e.g., a 1 mm × 1 mm range) are measured, and the average diameter can be calculated. The maximum pore diameter is preferably 100 μm or less, more preferably 50 μm or less.

[0062] Moreover, from the viewpoint of increasing strength and improving corrosion resistance, the shape of the pores is preferably approximately circular, and the aspect ratio of the pores is preferably in the range of 1 to 2. The aspect ratio of the pores here is defined as the value obtained by approximating the pores to ellipsoids from image analysis by electron microscope observation of the cross section of the sintered body, measuring the major axis and minor axis, and then dividing the minor axis by the major axis.

[0063] The sintered body of the present invention has a bending strength of 150 MPa or more. The bending strength is preferably 200 MPa or more, and more preferably 300 MPa or more. The bending strength means the three-point bending strength at room temperature (25°C) measured in accordance with JIS-R1601. Since the sintered body of the present invention has a bending strength of 150 MPa or more, when the sintered body of the present invention is used as a heat-resistant member of semiconductor manufacturing equipment, the durability of the equipment can be improved.

[0064] The sintered body of the present invention is a sintered body of a metal carbide having a very high melting point, a high relative density, and excellent mechanical strength, and is therefore suitable for use as a heat-resistant member in a manufacturing apparatus for silicon carbide (SiC) bulk single crystals and a heat-resistant member in a film-forming apparatus for manufacturing silicon carbide semiconductor wafers.

[0065] The sintered body of the present invention is less susceptible to cracks on the surface, which makes it possible to avoid the need for polishing the surface, which is required for conventional sintered bodies, and therefore offers the following excellent advantages: reduced raw material usage, improved yield, shorter delivery time, and reduced initial defect rate.

[0066] According to one aspect of the present invention, a method for producing a sintered carbide is provided, comprising the steps of: forming a sintered carbide of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table; ２ and sintering the mixture to which the carbon powder has been added, wherein the amount of the carbon powder added is such that the amount of the metal carbide and SiO ２ The amount of the carbide sintered body is 0.30 parts by mass or more and 3.00 parts by mass or less per 100 parts by mass of the mixed powder.

[0067] The metal carbide of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the periodic table is preferably a carbide of Ta, Nb, Ti, or Zr, with Ta and Nb carbides being particularly preferred. These metal carbides may be used alone or in combination of two or more. Metal carbides can be obtained by known methods. For example, a metal carbide can be obtained by mixing an oxide of a metal (titanium, zirconia, hafnium, niobium, tantalum, tungsten, etc.) with carbon and heating the mixture under a hydrogen reducing atmosphere. Alternatively, a metal carbide can be obtained by heat-treating a mixed solution in an oxygen-free atmosphere in which a metal alkoxide is added as a carbon source to an organic substance having a functional group capable of coordinating with the metal (e.g., an OH group or a COOH group). Alternatively, commercially available metal carbides may be used.

[0068] The metal carbide used to produce the sintered body is preferably in granular form. The average particle size of the granular metal carbide is preferably 0.05 μm or more and 20.0 μm or less, more preferably 0.1 μm or more and 10.0 μm or less. To adjust the granular metal carbide to the above average particle size, the metal oxide or the like that serves as the raw material for the metal carbide or the metal carbide itself may be crushed (disintegrated) in advance. In this case, there are no particular restrictions on the crushing conditions, but the longer the crushing time, the smaller the particle size of the metal carbide. Note that the average particle size of the granular metal carbide means the average particle size (Fischer diameter) measured by the air permeability method using a Fischer subsieve sizer, as described above.

[0069] SiO used ２ The powder is not particularly limited, but its particle size is preferably 0.05 μm or more and 10.0 μm or less, more preferably 0.1 μm or more and 5.0 μm or less, and even more preferably 0.2 μm or more and 0.5 μm or less.

[0070] Metal carbides and SiO ２ The powders are mixed to obtain metal carbide and SiO ２ There is no particular limitation on the method for obtaining the mixed powder of the metal carbide and SiO. For example, they can be mixed using a ball mill, a kneader, a mixer, a high-speed stirrer, etc. ２ The mixing ratio of the powders is metal carbide and SiO ２ SiO ２ It is preferable to mix in a range of 0.01 parts by mass or more and 12 parts by mass or less, more preferably 0.06 parts by mass or more and 3 parts by mass or less, and particularly preferably 0.2 parts by mass or more and 0.9 parts by mass or less.

[0071] The method for producing a sintered body of the present invention is a method for producing a sintered body by sintering a metal carbide and SiO ２ The method includes a step of adding carbon powder to the mixed powder of the above. There is no particular limitation on the carbon powder used, but the particle size is preferably 5 nm or more and 100 nm or less, more preferably 10 nm or more and 50 nm or less, and particularly preferably about 40 nm. The amount of carbon powder added is determined by the amount of the metal carbide and SiO ２The amount of carbon powder added is 0.30 parts by mass or more and 3.00 parts by mass or less with respect to 100 parts by mass of the mixed powder of metal carbide and SiO ２ The amount of the mixed powder may be preferably 0.50 parts by mass or more and 2.75 parts by mass or less, and more preferably 0.75 parts by mass or more and 2.00 parts by mass or less, relative to 100 parts by mass of the mixed powder.

[0072] In the method for producing a sintered body of the present invention, metal carbide and SiO ２ When adding the carbon powder to the mixed powder, other additives such as a binder resin, a dispersant, and / or a solvent may be further added.

[0073] The binder resin is not particularly limited as long as it can achieve the above-mentioned effects, and examples thereof include polyvinyl alcohol resin, acrylic resin, polyvinyl butyral resin, methyl cellulose resin, ethyl cellulose resin, acetyl cellulose resin, phenol resin, urea resin, melamine resin, etc. Two or more of these binder resins may be mixed and used. A preferred binder resin is polyvinyl alcohol resin. The amount of binder resin added may be, for example, based on the amount of metal carbide and SiO ２ The amount of the mixed powder may be 0.01 parts by mass or more and 5.0 parts by mass or less, preferably 0.03 parts by mass or more and 3.0 parts by mass or less, and more preferably 0.05 parts by mass or more and 2.0 parts by mass or less, relative to 100 parts by mass of the mixed powder.

[0074] As the dispersant, for example, polyethyleneimine-based polymer dispersants, polyurethane-based polymer dispersants, polyallylamine-based polymer dispersants, etc. can be used. The amount of dispersant to be added is determined based on the amount of metal carbide and SiO ２ The amount of the mixed powder may be 0.03 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the mixed powder.

[0075] Examples of the solvent include water and organic solvents such as ethanol, benzyl alcohol, toluene, dimethylacetamide, and methyl ethyl ketone. One type of solvent may be used, or two or more types may be mixed and used. The amount of solvent to be added may vary depending on, for example, the amount of metal carbide and SiO ２The amount of the inorganic filler may be 5.0 parts by mass or more and 30.0 parts by mass or less relative to 100 parts by mass of the mixed powder.

[0076] Metal carbides and SiO ２ There is no particular limitation on the method for adding and mixing the carbon powder to the mixed powder, but examples include kneading for 1 to 6 hours using a ball mill, kneader, mixer, high-speed stirrer, or the like.

[0077] The method for producing a sintered body of the present invention is a method for producing a sintered body by sintering a metal carbide and SiO ２ The method includes a step of sintering a mixture obtained by adding carbon powder to the mixed powder of the above. The mixture to which the carbon powder has been added is molded into a desired shape and sintered to obtain a sintered body. For example, the above components are mixed to prepare a sintering slurry, the slurry is molded into a desired shape, and the obtained molded body is sintered to obtain a metal carbide sintered body. Alternatively, the slurry may be made into granules by means of a spray dryer or the like, and the granules may be molded into a desired shape and the obtained molded body may be sintered. The molding method for molding the mixture into a desired shape is not particularly limited, and conventionally known molding methods such as press molding, extrusion molding, and slip casting can be used.

[0078] After obtaining the green body as described above, the green body can be sintered to obtain a sintered body of the desired shape. Sintering can be carried out at a temperature of 2200°C or higher and 2600°C or lower. Sintering can be preferably carried out at a temperature of 2250°C or higher and 2450°C or lower. SiO2 can be formed at a temperature lower than the sintering start temperature (approximately 1600 to 1700°C). ２ When melted, it acts as a sintering aid, making the sintered body denser. Sintering is preferably carried out in an inert gas atmosphere such as argon or helium. Sintering may be carried out under normal pressure or under pressure.

[0079] Next, the embodiments of the present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0080] The following metal carbides were used: Tantalum carbide (manufactured by Mitsui Mining & Smelting Co., Ltd., Fischer diameter 1 μm, purity 99.9%) Niobium carbide (manufactured by Mitsui Mining & Smelting Co., Ltd., Fischer diameter 1 μm, purity 99.9%)

[0081] SiO ２ The powder used was: Elkem Silica 971U (manufactured by Elkem Japan Co., Ltd.) From the SEM image, the particle size was determined to be about 0.05 to 0.5 μm.

[0082] The following carbon powders were used: Mitsubishi (registered trademark) Carbon Black MA14 (manufactured by Mitsubishi Chemical Corporation, particle size 40 nm)

[0083] Preparation of sintered body Metal carbide and SiO were mixed to obtain the composition shown in Table 1. ２ The powders are mixed to form metal carbides and SiO ２ A polyethyleneimine-based polymer dispersion was added as a dispersant to the mixture to disperse the metal carbide and SiO ２ 0.5 parts by mass of polyvinyl alcohol as a resin binder for 100 parts by mass of the mixed powder of metal carbide and SiO ２ and water as a solvent, with respect to 100 parts by mass of the mixed powder of metal carbide and SiO ２ The resulting mixture was mixed in a ball mill for 4 hours to prepare a sintering slurry. The resulting sintering slurry was used to fabricate a circular plate-shaped compact having a thickness shown in Table 1 and a diameter of 50 mm.

[0084] The plate-shaped compact was sintered in an argon atmosphere at a temperature of 2300° C. for 10 hours under normal pressure to obtain a circular plate-shaped sintered body.

[0085] Measurement of the average particle size of particles constituting the sintered body The obtained sintered body was divided so as to pass through approximately the center of the circular plane of the obtained circular plate-shaped sintered body. The cross section of the divided sintered body was mirror-polished and etched, and then the cross section was photographed. The photographed cross section was trimmed so that the width corresponded to 2 mm of the sintered body and the vertical width included both ends of the surface portion of the sintered body, thereby obtaining a cross-sectional photograph for observation. The approximate center of the cross-sectional photograph for observation was trimmed to a range equivalent to 260 μm in length x 360 μm in width of the sintered body, to obtain a cross-sectional photograph of the first region. The sintered body was trimmed to a range equivalent to 260 μm in length x 360 μm in width of the sintered body, so that the upper edge of the trimmed range was 40 μm below the point of the upper surface portion of the sintered body closest to the first region in the cross-sectional photograph for observation (i.e., the lowest part of the upper surface portion of the sintered body), to obtain a cross-sectional photograph of the second region. The etching conditions were as follows. (1) The sintered body was heated in an argon atmosphere (0.098 MPa) from room temperature to 2400°C at a rate of 200°C / hr over 12 hours. (2) After heating, it was held at 2400°C for 4 hours. (3) After holding for 4 hours, the temperature was allowed to drop naturally from 2400°C to room temperature.

[0086] The average grain size of the grains constituting the sintered body was calculated by the intercept method using cross-sectional photographs of the first and second regions. The intercept method was performed as follows: (1) SEM images were obtained within the first and second regions of the metal carbide sintered body at a provisional magnification of 1000x. (2) Lines were drawn in a grid pattern across the entire SEM image, with each side corresponding to 20 μm of the sintered body. The average grain size was calculated by dividing the length of all the lines by the number of intersections with the grains. When counting the intersections between the lines and the grains, the number of intersections was set to "1" when the line touched the outer edge of the grain or when it intersected, and "1.5" when the line intersected the triple junction of the grain. (3) Depending on the grain size of the grains observed in the SEM image, the number of intersections between the line and the grid was set to approximately 200. When the number of intersections between the lines and the particles in the SEM image was insufficient or excessive with respect to 200, the magnification of the SEM image was adjusted, and the average particle size was calculated again, so that the number of intersections between the lines and the particles in the SEM image was approximately 200. For example, when the particle size was large, the magnification was adjusted to about 500 times, and when the particle size was small, the magnification was adjusted to about 2000 times.

[0087] Measurement of Lattice Constant The sintered powder to be measured was spread on a measurement holder and smoothed using a glass plate to prepare an X-ray diffraction sample. X-ray diffraction measurements were performed using the X-ray diffraction sample. The lattice constant was calculated using the WPPF method by analyzing the diffraction peaks derived from NbC or TaC obtained by X-ray diffraction measurement. In analyzing the diffraction peaks, correction was performed using data obtained from a silicon powder sample (640c series), a standard material provided by the National Institute of Standards and Technology (NIST).

[0088] The conditions for the X-ray diffraction measurement and the analysis of the measurement data were as follows. Device name: SmartLab (9 kW): manufactured by Rigaku Corporation <Device configuration> Wavelength ・Target: Cu ・Wavelength type: Ka1 ・Kα1: 1.54059 (Å) ・Horizontal polarization rate: 0.500 Diffraction device ・Goniometer: SmartLab studio II ver 4.6.358.0 ・Attachment base: Z stage alone ・Attachment: ASC6-reflection ・Kα1 focusing Beam optical system: Johansson crystal <Measurement conditions> ・Optical system attribute: Focusing method ・CBO selection slit: BB ・Incidence parallel slit: Soller_slit_5.0deg ・Incidence slit: 2 / 3deg ・Length limiting slit: 10.0 mm ・Receiving slit 1: Open ・Receiving parallel slit: Soller_slit_5.0deg <Measurement data analysis conditions> - Analysis software: Rigaku PDXL2 ver. 2.8.4 - Analysis method: WPPF method - Data processing: Automatic profile processing (see Rigaku PDXL user manual, p. 305)

[0089] Measurement of relative density The bulk density of the sintered body was calculated by Archimedes' method in accordance with JIS-R1634. Specifically, the sintered body was placed in distilled water and kept under reduced pressure using a diaphragm-type vacuum pump for 1 hour, after which the weight in water W2 (g) was measured. Excess water was removed with a wet cloth, and the weight in water W3 (g) was measured. Thereafter, the sintered body was placed in a dryer to thoroughly dry it, and the dry weight W1 (g) was measured. The bulk density ρb (g / cm) was calculated using the following formula: ３ ) was calculated. ρb = {W1 / (W3-W2)} × ρ1 In the formula, ρ1 (g / cm ３) is the density of distilled water. From the density of metal carbide, the theoretical density ρc (g / cm ３ The relative density [RD] (%) was calculated using the obtained bulk density ρb and the theoretical density according to the following formula: RD = (ρb / ρc) × 100

[0090] Evaluation of crack occurrence The surface of the obtained sintered body was sprayed with 70% ethanol to visually check for the presence of cracks. Since ethanol evaporates quickly in the cracked area, the presence or absence of cracks was judged by the appearance of white in the cracked area. In addition, since it can be difficult to judge by ethanol spraying, the surface of the sintered body for which it was judged that no cracks had occurred after ethanol spraying was roughly ground to about 50 to 100 μm, and further visually checked for the presence or absence of cracks. In this case, the cracks appear as streaks, allowing for a more reliable determination of the presence or absence of cracks. In both visual tests, a sample in which no cracks were found was evaluated as "no cracks," and a sample in which cracks were found in either test was evaluated as "cracks present."

[0091] Measurement of bending strength: A rectangular plate-shaped sintered body measuring 4 mm x 36 mm was cut out from the circular flat surface of the sintered body. For sintered bodies with a thickness of 3 mm, the three-point bending strength was measured as is in accordance with JIS-R1601:2008. For sintered bodies with a thickness of more than 3 mm, the front and back surfaces of the sintered body were polished to the same extent so that the thickness was 3 mm, and then the three-point bending strength was measured in accordance with JIS-R1601:2008.

[0092] Calculation of Weight Change Rate The weight of the rectangular sintered plate of 4 mm x 36 mm x 3 mm used in the bending strength measurement was measured at room temperature (25°C). Thereafter, a carbon sheet was attached inside a carbon crucible, and the sintered plate was placed on the carbon sheet. Using a vacuum sintering furnace, the temperature was raised to 2400°C at a rate of 80°C / hr in an Ar atmosphere, and then sintered at 2400°C for 6 hours. After sintering, the sintered plate was cooled to room temperature (25°C), and its weight was measured. The weight change rate was calculated using the following formula: Weight change rate (%) = ((weight after sintering - weight before sintering) / weight before sintering) x 100

[0093] Types of metal carbides, metal carbides and SiO in Examples and Comparative Examples ２ Table 1 shows the mixing ratio of the mixed powders, the amount of carbon powder added, the thickness of the sintered body, the average particle size, the lattice constant, the relative density, the presence or absence of cracks, the bending strength, and the weight change rate.

[0094] The sintered body of the present invention is less susceptible to cracking on the surface, thereby reducing the need for surface polishing, which is required for conventional sintered bodies. This results in excellent advantages, such as reduced raw material usage, improved yield, shorter delivery times, and reduced initial defect rates. The sintered body of the present invention is a sintered body of a metal carbide with a very high melting point, has a high relative density, and excellent mechanical strength. Therefore, it can be suitably used as a heat-resistant component in manufacturing equipment for silicon carbide (SiC) bulk single crystals and in film-forming equipment for manufacturing silicon carbide semiconductor wafers. Therefore, it has high applicability not only in the ceramics industry, where such sintered bodies are required, but also in many other industries, such as the semiconductor and electronic component industries.

[0095] 101 Sintered body 102 Parallel projection 103 Inscribed circle inscribed in the parallel projection and having the largest area 104 Plane 201 Uppermost part of the surface of the sintered body 202 Lowermost part of the surface of the sintered body 203 First region 204 Second region 205 Point of the surface of the sintered body closest to the center of the cross-sectional photograph

Claims

1. A metal carbide sintered body of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the Periodic Table, wherein a cross-sectional photograph is taken of one continuous cross section of the metal carbide sintered body, the cross-sectional photograph being a plane perpendicular to a parallel projection of the metal carbide sintered body and passing through the center of an inscribed circle inscribed in the parallel projection and having a maximum area, the direction parallel to the parallel projection being the horizontal direction, the horizontal dimension being 2.0 mm, and both ends of a surface portion of the metal carbide sintered body being included in the vertical direction of the cross-sectional photograph, provided that when a plurality of continuous cross sections of the metal carbide sintered body are included in the plane perpendicular to the parallel projection, the cross-sectional photograph is taken of one continuous cross section of the metal carbide sintered body having a maximum cross-sectional area, a portion cut out of the center of the cross-sectional photograph, measuring 260 μm in length and 360 μm in width, is defined as a first region, a second region is a portion obtained by further cutting out a size of 260 μm vertically and 360 μm horizontally from the first region on the surface side of the metal carbide sintered body in the cross-sectional photograph, and an edge portion of the surface side of the metal sintered body in the second region is located 40 μm vertically toward the center of the cross-sectional photograph from a point on the surface portion of the metal carbide sintered body that is closest to the center of the cross-sectional photograph; an average grain size of grains in the first region is 3.5 μm or more and 9.5 μm or less; and a ratio of the average grain size of grains in the second region to the average grain size of grains in the first region is 0.75 or more and 1.0 or less.

2. The metal carbide sintered body according to claim 1, wherein the metal is selected from the group consisting of Nb, Ta, Ti, and Zr.

3. The metal carbide sintered body according to claim 1, wherein the metal is Nb, the average grain size of the grains in the first region is 5.5 μm or more and 9.5 μm or less, and the ratio of the average grain size of the grains in the second region to the average grain size of the grains in the first region is 0.75 or more and 1.0 or less.

4. The metal carbide sintered body according to claim 1, wherein the metal is Ta, the average grain size of the grains in the first region is 3.5 μm or more and 7.5 μm or less, and the ratio of the average grain size of the grains in the second region to the average grain size of the grains in the first region is 0.75 or more and 1.0 or less.

5. A metal carbide sintered body according to claim 1, wherein the ratio of the lattice constant of the metal carbide in the second region to the lattice constant of the metal carbide in the first region is 0.9999 or more and 1.0001 or less.

6. The metal carbide sintered body according to claim 1, wherein the difference between the lattice constant of the metal carbide in the first region and the lattice constant of the metal carbide in the second region is 0.0005 Å or less.

7. A metal carbide sintered body according to claim 1, wherein the value of the lattice constant of the metal carbide in the first region and the value of the lattice constant of the metal carbide in the second region are 99.98% or more and 100.02% or less of the theoretical value of the lattice constant of the metal carbide.

8. A metal carbide of at least one metal selected from the group consisting of elements of Groups 4 and 5 of the Periodic Table, and SiO ２ A method for producing a sintered carbide body, comprising: adding carbon powder to a mixed powder of powders; and sintering the mixture to which the carbon powder has been added, wherein an amount of the carbon powder added is 0.30 parts by mass or more and 3.00 parts by mass or less per 100 parts by mass of the mixed powder.

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