Composite material

Abstract

To provide a composite material having sufficient strength and thermal conductivity.SOLUTION: A composite material 10 includes silicon and silicon carbide. When the composite material is cut along a plain surface, a cross section SA thus obtained includes a plurality of first areas S1 each being a section of particles of silicon carbide with a particle diameter 20 μm or longer; and a second area S2 being an entire area excluding the plurality of first areas S1 in the cross section SA, and including a section of silicon and a section of silicon carbide. In the cross section SA, the plurality of first areas S1 account for 70% or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to composite materials comprising silicon and silicon carbide. [Background technology]

[0002] A composite material containing silicon and silicon carbide is also called "SiSiC" and is known as a material having high corrosion resistance, heat resistance, etc. As described in Patent Document 1 below, the composite material can be obtained, for example, by reactive sintering a molded body made of powdered carbon and silicon carbide while impregnating it with molten silicon.

[0003] The composite material is relatively lightweight yet highly rigid, and also has high thermal conductivity, making it promising for use in a variety of fields, including semiconductor manufacturing equipment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-348288 Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in the figures etc. in the above patent documents, when a composite material containing silicon and silicon carbide is cut, the cut surface shows cross sections of multiple silicon carbide particles and cross sections of silicon arranged in a matrix so as to fill the spaces between each silicon carbide particle.

[0006] It is known that the smaller the particle size of each silicon carbide particle, the higher the strength (e.g., three-point bending strength) of the composite material. For this reason, in conventional composite materials, it has been desirable to make the particle size of the silicon carbide particles as small as possible. However, while reducing the particle size of the silicon carbide particles increases the strength of the composite material as described above, it also creates the problem of decreasing the thermal conductivity of the composite material.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a composite material having sufficient strength and thermal conductivity. [Means for solving the problem]

[0008] The composite material according to the present invention is a composite material containing silicon and silicon carbide. When the composite material is cut along a plane, the cut surface has a plurality of first regions, which are cross sections of silicon carbide particles with a particle diameter of 20 μm or more, and a second region, which is the entire area of ​​the cut surface excluding the first regions and includes cross sections of silicon and silicon carbide. Furthermore, the first regions account for 70% or more of the cut surface.

[0009] The first region is a cross section of a relatively large silicon carbide particle with a particle diameter of 20 μm or more. Because there are no grain boundaries inside this first region that would cause thermal resistance, it can be said to be the part that contributes to the thermal conductivity of the composite material.

[0010] The second region is a portion that includes both a relatively small silicon carbide cross section that is not included in the first region and a silicon cross section. Since the absence of large particles makes it difficult for cracks to propagate in the second region, it can be said that this second region contributes to the strength of the composite material.

[0011] In the composite material having the above configuration, the first region that contributes to thermal conductivity occupies 70% or more of the cut surface. This makes it possible to ensure sufficient thermal conductivity of the composite material. Furthermore, the portion of the cut surface other than the first region is made into a second region that contributes to strength. The presence of the second region prevents the strength of the composite material from decreasing too much. In this way, in the composite material having the above configuration, by making the first region occupy 70% or more of the cut surface and making the remaining portion into the second region, it is possible to ensure both thermal conductivity and strength of the composite material. [Effects of the Invention]

[0012] According to the present invention, a composite material having sufficient strength and thermal conductivity can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a cross section of a composite material according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing a cross section of a composite material according to an embodiment of the present invention. [Figure 3] 10A to 10C are diagrams showing evaluation results of composite materials, etc. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0015] The composite material 10 according to this embodiment is a solid material containing silicon and silicon carbide, and is also known as "SiSiC," etc. The composite material 10 is used, for example, as a material for components constituting semiconductor manufacturing equipment, but its specific use, final shape, etc. are not particularly limited.

[0016] As will be explained later, composite material 10 is a molded body made of powdered carbon and silicon carbide that is impregnated with molten silicon and then reactively sintered. In this respect, it is similar to conventional SiSiC. However, composite material 10 according to this embodiment differs from conventional SiSiC in the shape and distribution of each region that appears on the cut surface when cut.

[0017] The image shown in Figure 1 was obtained by observing a cross section SA that appeared when a composite material 10 was cut along a plane using a scanning electron microscope (SEM). The area of ​​the cross section SA was 500 µm x 350 µm, and the magnification was 500 times. It has been confirmed that the black areas in the image of Figure 1 are cross sections of silicon carbide (SiC), and the white areas are cross sections of silicon (Si).

[0018] The black regions in the image of Figure 1, i.e., the cross section of the silicon carbide, include multiple regions that are cross sections of relatively large silicon carbide particles with particle diameters of 20 μm or more. These regions are also referred to as "first regions S1" below. The entire region of the cross section SA excluding the first regions S1 is also referred to as "second regions S2" below. The "particle diameter" here refers to the diameter of the smallest imaginary circle that can contain a single silicon carbide particle appearing on the cross section SA.

[0019] In Figure 2(A), a plurality of first regions S1 included in the cross section SA are schematically depicted as hatched regions for the same cross section SA as shown in Figure 1. In addition, in the region of Figure 2(A) excluding the first region S1 (i.e., the second region S2), the image of Figure 1 is subjected to binarization processing, so that the cross section of silicon carbide appears white and the cross section of silicon appears black.

[0020] FIG. 2(B) is a schematic redrawing of an enlarged portion of FIG. 2(A). In the second region S2, the cross section of silicon carbide shown in white in FIG. 2(A) is depicted as "S21" in FIG. 2(B). In addition, in the second region S2, the cross section of silicon shown in black in FIG. 2(A) is depicted as "S22" in FIG. 2(B). In this way, the second region S2, which is the entire region of the cross section SA excluding the first region S1, includes the silicon cross section (S22) and the silicon carbide cross section (S21).

[0021] The second region S2 may include only a silicon carbide cross section (S21) and a silicon cross section (S22), or may further include a cross section made of a material other than these. Such a cross section may be, for example, a cross section of carbon particles, which is one of the raw materials used in molding.

[0022] In this embodiment, the proportion of the first region S1 in the cut surface SA is 73%. In addition, the proportion of the total silicon cross section (S22) in the cut surface SA is 1%. In this embodiment, the proportion of the silicon carbide cross section (S21) in the second region S2 is 96%.

[0023] As shown in Figure 2(B), at least a portion of the silicon cross section (S22) included in the second region S2 is surrounded from the outside and all around by the silicon carbide cross section (S21). Furthermore, in at least the range of the second region S2 shown in Figure 2(B), the silicon carbide cross section (S21) appears to be a continuous single cross section without any intervening grain boundaries. In other words, in an image obtained by observation at a magnification of 500x or less, as in Figure 1, the silicon carbide cross section (S21) shown in Figure 2(B) does not appear to have any grain boundaries that divide it into multiple pieces.

[0024] As will be described later, in this embodiment, granulated powder having higher sphericity and improved flowability than conventional powders is used as the raw material in manufacturing the composite material 10. It is believed that silicon carbide, carbon, and the like in the raw material are dispersed more evenly than conventional powders, resulting in grain growth of the silicon carbide, and the continuous silicon carbide cross section (S21) as shown in FIG. 2(B) is formed.

[0025] The silicon carbide cross-section (S21) surrounding the silicon cross-section (S22) from the outside over the entire circumference is a continuous single region without any grain boundaries as described above, but it does not need to be a continuous single region over the entire cross-section SA shown in FIG. 1. For example, the cross-section SA shown in FIG. 1 may have a plurality of continuous silicon carbide cross-sections (S21) without any grain boundaries, and these plurality of silicon carbide cross-sections (S21) may be adjacent to each other via grain boundaries. In this case, it is sufficient that a silicon cross-section (S22) completely surrounds at least one silicon carbide cross-section (S21) inside.

[0026] The cross section (S21) of silicon carbide can be observed as a "single continuous region without grain boundaries" at least when observed with a scanning electron microscope at a magnification of 500x or less. When the cross section (S21) of silicon carbide surrounding the cross section (S22) of silicon from the outside is observed in detail at a magnification of more than 500x, grain boundaries dividing the cross section (S21) or boundaries equivalent thereto may be observed.

[0027] As described above, the composite material 10 according to this embodiment has, at a cross section SA when cut along a plane, a plurality of first regions S1, which are cross sections of silicon carbide particles having a particle diameter of 20 μm or more, and a second region S2, which is the entire area of ​​the cross section SA excluding the first regions S1 and includes cross sections of silicon (S22) and cross sections of silicon carbide (S21). The proportion of the first regions S1 in the cross section SA is 73%. The proportion of the total cross sections of silicon (S22) in the cross section SA is 1%.

[0028] The reason for adopting such a configuration will be explained. It is generally known that for composite materials containing silicon and silicon carbide, the smaller the particle diameter of each silicon carbide particle that appears on the cut surface, the higher the strength (e.g., three-point bending strength) of the composite material. For this reason, in conventional composite materials, it has been desired to make the particle diameter of the silicon carbide particles as small as possible. However, when the particle diameter of the silicon carbide particles is reduced, while the strength of the composite material increases as described above, a problem arises in that the thermal conductivity of the composite material decreases.

[0029] Therefore, in the composite material 10 according to this embodiment, the particle size of the silicon carbide particles appearing on the cross section SA is adjusted to achieve both high thermal conductivity and high strength.

[0030] As described above, the first region S1 is a cross section of a silicon carbide particle having a relatively large particle diameter of 20 μm or more. Since the first region does not have a grain boundary that would cause thermal resistance inside, it can be said to be a portion that contributes to the thermal conductivity of the composite material 10.

[0031] The second region S2 is a portion that includes both a relatively small silicon carbide cross section (S21) that is not included in the first region S1 and a silicon cross section (S22). Since the absence of large particles makes it difficult for cracks to propagate in the second region S2, it can be said that this portion contributes to the strength of the composite material 10.

[0032] In the composite material 10 according to this embodiment, the proportion of the cross section SA occupied by the first region S1 that contributes to thermal conductivity is 73%, as described above, which is a relatively large proportion. This ensures sufficient thermal conductivity of the composite material 10. Furthermore, the portion of the cross section SA that is the first region S1 is made into the second region S2 that contributes to strength. The presence of the second region S2 also ensures sufficient strength of the composite material 10.

[0033] 1 and 2, the proportion of the total silicon cross section (S22) in the cross section SA is 1%, which is a very small proportion, as described above. Furthermore, as a result of reducing the proportion of silicon, the proportion of the silicon carbide cross section (S21) in the second region S2 is 96%, which is a very large proportion in this embodiment.

[0034] In this embodiment, while the second region S2 is configured to contain both silicon carbide and silicon, the strength of the composite material 10 is further increased by keeping the proportion of silicon occupying the entire cut surface SA small.

[0035] As is generally known, silicon has lower strength than silicon carbide. In composite material 10, the proportion of the silicon cross section (S22), which is the weaker part, is reduced, which prevents localized "overcutting" during processing, enabling more precise processing than conventional methods.

[0036] Furthermore, the silicon carbide cross section (S21) surrounding the silicon cross section (S22) is not a collection of multiple particles, but a single continuous region without any intervening grain boundaries. The continuous silicon carbide, which has relatively high strength, further suppresses localized "over-cutting" during processing. Another effect is that particles are less likely to fall off during processing.

[0037] FIG. 3 shows the results of an experiment comparing the composite material 10 according to this embodiment with two composite materials according to comparative examples that were prepared separately.

[0038] In the table of Figure 3, "First region [%]" indicates the proportion of the first region S1 in the cut surface SA of each sample, expressed as a percentage. "Second region [%]" indicates the proportion of the second region S2 in the cut surface SA of each sample, expressed as a percentage. The definitions of "first region S1" and "second region S2" are the same as those explained above.

[0039] "Strength [MPa]" in the table in Figure 3 indicates the results, in units of MPa, obtained by conducting a three-point bending strength test on each sample. The test method used was the method specified in Japanese Industrial Standards (JIS) R1601:2008.

[0040] The "Thermal conductivity [W / (m K)]" in the table in Figure 3 is the result of measuring the thermal conductivity of each sample using the laser flash method, and is shown in units of W / (m K).

[0041] The "machinability" in the table of Figure 3 shows the results of observing the smoothness of the surface after grinding the cut surface of each sample under the same conditions. If the root mean square height (Sq) of the processed surface was less than 10 nm, it was marked "Good." If Sq was 10 nm or more but less than 50 nm, it was marked "Average." If Sq was 50 nm or more, it was marked "Poor."

[0042] In both samples of Comparative Examples 1 and 2, the proportion of the first region S1 in the cross section SA is smaller than that of this embodiment, being less than 70% in both cases. Also, the proportion of the silicon cross section (S22) in the cross section SA is larger than that of this embodiment, being more than 10% in both cases.

[0043] As shown in FIG. 3, it was confirmed that the composite material 10 according to this embodiment has a significantly higher strength than Comparative Examples 1 and 2, while maintaining a thermal conductivity roughly equivalent to that of Comparative Examples 1 and 2.

[0044] In addition, in Comparative Examples 1 and 2, the Sq after processing was large, so the processability was evaluated as "×" and "△", respectively. In contrast, in this embodiment, the proportion of the silicon cross section (S22) was small at 1%, so the processability was evaluated as "◯", which was good. In other words, the average processing depth was kept small compared to Comparative Examples 1 and 2, and it was confirmed that this material is easier to process precisely.

[0045] In addition to the present embodiment shown in FIG. 1 and other figures, the inventors have prepared multiple types of composite material 10 under different manufacturing conditions, and measured the parameters shown in the table in FIG. 3 for each sample. These measurements have revealed that if the proportion of the first region S1 in the cross-section SA of composite material 10 is 70% or more, and the remaining portion is the second region S2 containing silicon and silicon carbide, composite material 10 can ensure both sufficient thermal conductivity and sufficient strength required for a component of semiconductor manufacturing equipment, etc. Furthermore, it has been confirmed that if the proportion of the total silicon cross-sections (S22) in the cross-section SA is 10% or less, more preferably 5% or less, the strength of composite material 10 is further increased and its processability is significantly improved. Furthermore, it has been confirmed that it is preferable to have the proportion of the silicon carbide cross-sections (S21) in the second region S2 be at least 70% or more from the standpoints of strength, processability, etc.

[0046] Assuming that the particle size of the silicon carbide particles appearing on the cross section SA is approximately uniform, the relationship between the particle size of the silicon carbide particles and the fracture strength of the composite material can be calculated using the Griffith equation or the Knudsen equation, etc. Similarly, the relationship between the particle size of the silicon carbide particles and the thermal conductivity of the composite material can also be theoretically calculated.

[0047] For example, assuming that the particle size of the silicon carbide particles is approximately uniform, if the particle size is increased to such an extent that the thermal conductivity of the composite material becomes 180 W / (m K), the same as in this embodiment, the fracture strength is calculated to be approximately 307 MPa. In contrast, the fracture strength of the composite material 10 according to this embodiment is 450 MPa, which is significantly higher than 307 MPa, as shown in FIG.

[0048] In this way, the composite material 10 of this embodiment was able to achieve a sufficiently high breaking strength while maintaining a thermal conductivity similar to that of the comparative example, which is thought to be due to the effects of increasing the proportion of the first region S1 in the cut surface SA to 70% or more and reducing the proportion occupied by the total silicon cross section (S22) to 10% or less.

[0049] A method for manufacturing the composite material 10 will be described below. In the following, the description of well-known aspects of the manufacturing method for SiSiC will be simplified or omitted as appropriate.

[0050] First, predetermined amounts of raw materials, carbon powder and silicon carbide powder, are weighed out and dispersed in pure water together with a binder and a dispersant to create a slurry. The silicon carbide powder has an average particle size of 20 μm or more. The powder may contain silicon carbide powder with a particle size of 5 μm or less. The silicon carbide powder with a particle size of 20 μm or more becomes the silicon carbide in the first region S1. The carbon powder has an average particle size of 20 μm or less, more preferably 5 μm or less.

[0051] The resulting slurry is then spray-dried using a spray dryer to produce granulated powder (granules) containing carbon and silicon carbide. The sphericity of the resulting granulated powder can be increased by appropriately selecting a binder and dispersant. The target sphericity value is preferably set to a value higher than the sphericity of granulated powders used in conventional SiSiC materials.

[0052] The purpose of increasing the sphericity of the granulated powder is to provide the granulated powder with sufficient fluidity. It is preferable to increase the fluidity of the granulated powder to a level that would have been considered excessive in the past. The fluidity of the granulated powder varies not only depending on the sphericity of the granulated powder but also on the size of the granulated powder. For this reason, for example, when spray-drying a slurry, it is preferable to control the size of the granulated powder by adjusting the flow rate of the supplied air to obtain granulated powder with optimal fluidity.

[0053] At this stage, the obtained granulated powder contains granules of various sizes. These granules are classified into a first granulated powder containing only granules with a diameter of 100 to 200 μm, and a second granulated powder containing only granules with a diameter of 30 to 70 μm. Next, the first granulated powder and the second granulated powder are mixed in a predetermined ratio. At this time, the blending amount of the first granulated powder is set to 60 to 80% by weight. In other words, the blending amount of the second granulated powder is set to 20 to 40% by weight. It is preferable to mix the whole mixture well so that the first granulated powder and the second granulated powder are sufficiently dispersed.

[0054] The granulated powder thus mixed is then placed in a predetermined mold and subjected to dry uniaxial press molding to obtain a molded body. By increasing the fluidity of the granulated powder in advance as described above, the granulated powder is packed sufficiently densely into the mold. As a result, a molded body with a small pore size can be obtained.

[0055] Furthermore, by setting the mixing ratio of the first granulated powder to the second granulated powder at the above ratio, the second granulated powder fills the gaps between the densely arranged first granulated powder particles, making it easier to pack the granulated powder closely throughout the mold. As a result, the porosity of the molded body becomes even smaller.

[0056] As a molding method, methods other than the dry uniaxial pressing described above may be used as long as they can pack the highly fluid granulated powder sufficiently densely. For example, molding may be performed using cold isostatic pressing (CIP), or a method of forming the shape by laying the powder using a 3D printer may be used.

[0057] After molding is complete, metal silicon is placed on the resulting molded body and sintered under reduced pressure. Molten silicon is impregnated into the molded body, and reactive sintering with carbon powder occurs. The silicon carbide produced by reactive sintering becomes part of the silicon carbide (S21) in the second region S2. Through these steps, the composite material 10 shown in FIG. 1 etc. can be obtained.

[0058] In this embodiment, as described above, the fluidity of the granulated powder is increased compared to conventional methods, and the molded body is obtained by sufficiently densely packing the granulated powder into the mold. As a result, the reaction between silicon and carbon powder occurs more uniformly throughout the second region S2, and it is believed that the single silicon carbide cross section (S21) that is continuous over a relatively wide area is formed, as described above.

[0059] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-described specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-described specific examples can be combined in various ways as appropriate, as long as no technical contradictions arise. [Explanation of symbols]

[0060] 10: Composite material SA: Cutting surface S1: 1st area S2:Second area

Claims

1. A composite material comprising silicon and silicon carbide, When the composite material is cut along a plane, the cut surface is A plurality of first regions each being a cross section of a silicon carbide particle having a particle diameter of 20 μm or more; a second region that is the entire region of the cut surface excluding the first region and includes a cross section of silicon and a cross section of silicon carbide; A composite material characterized in that the first region accounts for 70% or more of the cut surface.

2. 2. The composite material according to claim 1, wherein the proportion of the total cross section of silicon in the cut surface is 10% or less.

3. In at least a portion of the second region, 2. The composite material according to claim 1, wherein a single continuous silicon carbide cross section without grain boundaries completely surrounds the outside of one silicon cross section.

4. 2. The composite material according to claim 1, wherein the proportion of silicon carbide in the cross section of the second region is 70% or more.

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