Method for manufacturing high melting point member having interface

Abstract

A high melting point member having an interface can be easily manufactured. [Solution] Powder of a material such as silicon carbide is sealed in a tantalum container or tantalum foil, ensuring sufficient contact of the tantalum with the material. The material is then sintered at 1100-2680°C in a heating furnace suitable for high-temperature heating, such as a carbon furnace. This process produces a high-melting-point component made of cubic silicon carbide. Furthermore, by adjusting the sintering temperature and time, the outer region becomes a region rich in p-type elements, while the inner region becomes a region rich in n-type elements, forming a PN junction at the interface between the two. The ratio of the p-type element-rich and n-type element-rich regions can be changed by adjusting the sintering time, making it possible to make the entire region a region rich in p-type elements or a region rich in n-type elements. As described above, according to the manufacturing method of the present invention, it is possible to relatively easily manufacture a high-melting-point member having an interface.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a high melting point member having an interface. [Background technology]

[0002] A member made of a material selected from the group consisting of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina, or a combination thereof (hereinafter referred to as a "high-melting-point member") has characteristics such as a high melting point and high strength, and is expected to have a variety of applications. When a high-melting-point member has an interface in its cross section where the properties change discontinuously, even more useful applications are expected. One example of such an interface is a pn junction. Patent Document 1 discloses a technique for realizing a pn junction using silicon carbide, which is one of the above-mentioned materials, in which an n-type silicon carbide layer is formed by liquid phase epitaxy and a p-type silicon carbide layer is formed by vapor phase epitaxy, thereby forming both layers continuously to realize a pn junction. Although not an interface, Patent Document 2 discloses a technique for relatively easily forming a gradient composition, in which a carbon layer and a metal tantalum layer are formed on one surface of a silicon carbide substrate, and then heated to form a tantalum carbide layer having a gradient composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-7017 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-187420 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 is a technology in which an n-type layer and a p-type layer are formed separately, and there is a problem that it is not easy to do. Furthermore, the technology of Patent Document 2 is not able to form an interface. The object of the present invention is to provide a technology that allows for relatively easy formation of an interface in a high-melting-point material. [Means for solving the problem]

[0005] The present invention provides A method for manufacturing a high-melting-point member having an interface, comprising: (a) contacting tantalum with a material selected from the group consisting of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina, or a combination thereof; (b) heating the materials while they are in contact at a sintering temperature determined depending on the materials until an interface is formed in the materials.

[0006] Experiments by the inventors have confirmed that an interface is formed within the high-melting-point member using the above-mentioned manufacturing method. Although the mechanism by which the interface is formed is not entirely clear, it is speculated that the diffusion of the redox effect that occurs between the tantalum and the material due to heating at the contact surface between the tantalum and the material has an effect on the interior of the high-melting-point member. As a result of the experiment, it was confirmed that the position where the interface is formed varies depending on the heating time. Therefore, in the present invention, it is preferable to determine the heating time analytically or experimentally so that the interface is formed at a desired position depending on the material and shape of the high-melting-point member. Based on this result, for example, as a pretreatment for the step (b), A step of determining in advance the relationship between heating time and the position where an interface is formed; a step of setting a heating time based on the relationship in accordance with the position where the desired interface is to be formed; The above configuration may be adopted.

[0007] Here, the raw material may be in a molded state or in a state of powder before being molded, etc. Contact with tantalum may also be carried out by an appropriate method depending on the state of the raw material. The sintering temperature is the temperature used to sinter the material, and can be determined depending on the material. It is in the range below the melting point of tantalum (3020°C) and the melting point of the material.

[0008] In the present invention, Preferably, the material is silicon carbide.

[0009] Experimental results confirmed that when silicon carbide is used, cubic silicon carbide (3C-SiC) with an interface is formed. Cubic silicon carbide (3C-SiC) can be used as a semiconductor material and is known for its excellent properties, such as high dielectric breakdown field strength, wide band gap, excellent chemical stability, and high thermal conductivity of 500 W / m·K. Conventionally, methods for growing cubic silicon carbide (3C-SiC) crystals have often been used on substrates such as 4H-SiC and 6H-SiC, but the present invention makes it relatively easy to obtain cubic silicon carbide (3C-SiC).

[0010] In the present invention, Step (a) may be a step of contacting a tantalum container or tantalum foil with the material and sealing it.

[0011] Because the sintering temperature is very high, it is preferable to use a carbon furnace for heating, but in this case, carbonization of the high-melting-point material may occur. In contrast, carbonization can be avoided by sealing with tantalum as in the above embodiment.

[0012] When sealed with a tantalum container or tantalum foil, In the step (a), the raw material is a powder, In the step (b), the heating may be carried out so as to sinter the powder.

[0013] By doing so, it is possible to form a high melting point member of any shape by sintering the material from powder, while forming an interface. As explained above, the position where the interface is formed varies depending on the heating time, and therefore the heating time may be longer than the time required for sintering the powder. Here, the time required for sintering the powder refers to the time required for the entire powder to solidify to the extent that it can maintain its shape as a single solid. In the case of a heating profile in which the temperature is raised to a predetermined temperature and then maintained at that temperature, if the entire powder solidifies to a certain density during the heating process, the time required to achieve that state is the "time required for sintering the powder," and does not refer to the time required to reach the predetermined temperature or the time required to complete maintaining the predetermined temperature.

[0014] In the present invention, The interface may be a PN junction surface.

[0015] In this way, the high melting point material obtained by the method of the present invention can be used as a semiconductor. The interface of the present invention is not limited to a PN junction surface. For example, when using oxide materials such as yttria, zirconia, or alumina, it is possible to form an interface in which the metal is on the surface side and the oxide is on the inside. In this way, various interfaces can be formed in the present invention.

[0016] The various features of the present invention described above do not necessarily have to be provided in their entirety, and some of them may be omitted or combined as appropriate. The present invention also includes a high-melting-point member manufactured by the above-mentioned manufacturing method. [Brief explanation of the drawings]

[0017] [Figure 1] 1A to 1C are process diagrams showing a method for manufacturing a high-melting-point member according to an embodiment of the present invention. [Figure 2] 1 is a photograph showing an example of a cross section of a high-melting-point member. [Figure 3] 10 is a graph showing an example of a spectral analysis result of a high-melting-point member. [Figure 4] 1 is a graph showing an example of a Raman spectrum of a high-melting-point member. [Figure 5] 10 is a graph showing an example of a Raman spectrum when sintered for 3 hours. DETAILED DESCRIPTION OF THE INVENTION

[0018] Examples of the present invention will be described below. FIG. 1 is a process diagram showing a manufacturing method of a high-melting-point member according to an embodiment. In this manufacturing method, first, a powder of a material is prepared (step S10). The material can be one or a combination of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina. These materials are generally known to have high melting points and are difficult to sinter. The purity of each material is preferably 95% or higher, and more preferably 99% or higher, but is not limited to such high purities.

[0019] Then, the prepared material is sealed in a tantalum container or foil (step S11). The figure shows an example in which the material is sealed in a cylindrical container. After the material is filled into the container, it can be sealed with a tantalum lid. The shape of the container is not limited to a cylindrical shape. Alternatively, the material may be wrapped in tantalum foil instead of a container. For example, the material may be wrapped in tantalum foil to form a cylindrical shape, and the openings at both ends may be crushed and sealed. Any other shape or wrapping method is also possible. The thickness of the tantalum can be determined arbitrarily for both the tantalum container and the tantalum foil. It should be determined taking into consideration the ability to maintain the shape of the high-melting-point material and sufficient heat conduction inside. In this example, the thickness was set to approximately 50 μm.

[0020] In step S11, it is important to ensure sufficient contact between the raw material and the tantalum container or tantalum foil. The particle size of the raw material powder, the shape of the container, the method of wrapping with foil, etc. can be determined to ensure sufficient contact.

[0021] Next, the material sealed with tantalum is heated at a sintering temperature (step S12). The sintering temperature can be set to a temperature equal to or lower than the melting point of tantalum (3020° C.) and lower than the melting point of the material. in particular, In the case of boron, the melting point is preferably 1400 to 2280°C, which is lower than the melting point of 2300°C. In the case of silicon carbide, the melting point is preferably 1100 to 2680°C, which is lower than the melting point of 2700°C. In the case of yttria, the temperature is preferably 1400 to 2400°C, which is lower than the melting point of 2425°C. In the case of boron nitride, the melting point is preferably 1200 to 2680°C, which is lower than the melting point of 2700°C. In the case of zirconia, the temperature is preferably 1100 to 2700°C, which is lower than the melting point of 2715°C. In the case of boron carbide, the melting point is preferably 1400 to 2400°C, which is lower than the melting point of 2427°C. In the case of tungsten carbide, the temperature is preferably 1400 to 2850°C, which is lower than the melting point of 2870°C. In the case of titanium nitride, the temperature is preferably 1400 to 2680°C, which is lower than the melting point of 2700°C. In the case of titanium carbide, the temperature is preferably 1000 to 3000°C, which is lower than the melting point of 3160°C. In the case of molybdenum, the melting point is preferably 1400 to 2580°C, which is lower than the melting point of 2600°C. In the case of tungsten, the temperature is preferably 1400 to 3000°C, which is lower than the melting point of 3422°C. In the case of alumina, the temperature is preferably 1100 to 2050°C, which is lower than the melting point of 2072°C.

[0022] Any suitable heating furnace can be used. For example, a carbon furnace can be used to heat the material to such a high temperature. The sintering time can be determined depending on the material, the thickness and shape of the tantalum container or tantalum foil, etc. For example, it is preferably in the range of 1 hour to 10 hours. Sintering may be carried out at atmospheric pressure or in a vacuum. When sintering is carried out at atmospheric pressure, it may be carried out in either an air gas atmosphere or an inert gas atmosphere such as argon. When the sintering is completed in this manner, a high melting point member is completed.

[0023] Figure 2 is a photograph showing an example of a cross section of a high-melting-point material. A cylindrical member with a diameter of about 6 mm was manufactured using silicon carbide, and the cross section is shown. Figure 2(a) shows the state before sintering, where the powder shape of the material is still visible. Figure 2(b) shows a sample sintered at 1800°C for one hour. The cross section shows that the surrounding region P1 and the inner region N1 are different colors. However, there is no remaining powder material in either region P1 or N1, and sintering is complete. Visually, it can be seen that the interiors of regions P1 and N1 are homogeneous, and that the boundary between regions P1 and N1, i.e., the interface, is clearly present. In other words, the high-melting-point material in Figure 2(b) does not have properties that are graded from the outside to the inside, but rather is manufactured with a clear interface within. Figure 2(c) shows the results of sintering at 1800°C for 3 hours. The cross section shows that the entire area is uniform, as seen in region P3. The color of region P3 appears to be the same as region P1 after sintering for 1 hour (Figure 2(b)). This suggests that as the sintering time is increased, region P1 expands inward, and by sintering for 3 hours, it has expanded to cover the entire area. This shows that in order to manufacture a high-melting-point component with an interface, it is necessary to limit the sintering time to below a specified upper limit, depending on the material, shape, sintering temperature, etc.

[0024] Although the mechanism behind the formation of the interface shown in Figure 2(b) is not fully understood, it is speculated that the diffusion of the redox effect that occurs between tantalum and the material due to heating at the contact surface between tantalum and the material may have an effect on the interior of the high-melting-point material. Tantalum's extremely high affinity with carbon may also have some influence. In this sense, it can be said that it is preferable to use a material containing carbon, such as silicon carbide, to form the interface.

[0025] Figure 3 is a graph showing an example of the results of a spectroscopic analysis of a high-melting-point material. The horizontal axis shows wavenumber, and the vertical axis shows the measured light intensity. Since each is in an arbitrary unit derived from the measuring instrument, it shows relative characteristics. In the figure, curve S-0H shows the results for the raw material before sintering (corresponding to Fig. 2(a)). Curve S-1H shows the results for sintering for 1 hour (corresponding to Fig. 2(b)), and curve S-3H shows the results for sintering for 3 hours (corresponding to Fig. 2(c)). In regions A1, A2, and A3, the peak value of curve S-0H is significantly smaller than the peak values ​​of curves S-1H and S-3H. The appearance of such peak values ​​in curves S-1H and S-3H is characteristic of cubic silicon carbide (3C—SiC), and it is confirmed that cubic silicon carbide, which was almost nonexistent before sintering, was produced by sintering. On the other hand, when comparing curves S-1H and S-3H, we can see that while there is a slight difference in the peak value for the wavenumber in region A1, there is almost no difference for the wavenumbers in regions A2 and A3. Since there is an interface in curve S-1H (corresponding to Figure 2(b)) and no interface in curve S-3H (corresponding to Figure 2(c)), if regions P1 and N1 in Figure 2(b) have different compositions, we should see a more significant difference between curves S-1H and S-3H. In other words, the graph in Figure 3 indicates that both regions P1 and N1 in Figure 2(b) are likely cubic silicon carbide (3C-SiC).

[0026] Figure 4 is a graph showing an example of a Raman spectrum of a high-melting-point material. A Raman spectrum is the result of detecting, with a spectrometer, what is called Raman scattering, which is a type of light scattered when a monochromatic laser is used as a light source. Raman spectra are sometimes used to detect the ratio of holes (p-type elements) and electrons (n-type elements) within a substance, and it is known that the peak value of the spectrum tends to decrease as the p-type elements increase.

[0027] Figure 4(a) shows the results for sintering for 1 hour (corresponding to Figure 2(b)). Curve Cp is the measurement result for the outer region P1, and curve Cn is the measurement result for the inner region N1. In the region B1 near wavenumber 800, no significant difference was confirmed between the peak values ​​of both, but in the regions B2 and B3, a significant difference was confirmed between the peak values ​​of both. 4(b) is an enlarged view of region B2. As indicated by the arrow in the figure, it can be seen that the peak value of curve Cp is significantly lower than that of curve Cn. 4(c) is an enlarged view of region B3. As indicated by the arrow in the figure, it can be seen that the peak value of curve Cp is significantly lower than that of curve Cn, to the extent that the peak is barely identifiable. These results confirm that the p-type element is more abundant in region P1 than in region N1. In other words, the interface shown in Figure 2(b) is the interface between the outer region P1, which has a high p-type element content, and the inner region N1, which has a high n-type element content, i.e., a PN junction surface.

[0028] Figure 5 is a graph showing an example of a Raman spectrum obtained after sintering for three hours. As shown in Figure 2(c), the entire area is region P3 (corresponding to region P1 in Figure 2(b)), so it is not possible to compare regions with different appearances as in Figure 4. However, as shown in Figure 5, peaks can be confirmed in three locations, regions C1 to C3, which are considered qualitatively equivalent to regions B1 to B3 in Figure 4. In Fig. 4, curve Cn shows no significant difference between the peak values ​​in region B2 and region B3, whereas curve Cp shows that the peak value in region B3 is significantly lower than that in region B2. In Fig. 5, the peak in region C3 is also significantly lower than that in region C2. Therefore, when comparing Figs. 4 and 5 based on the above-mentioned characteristics, the results in Fig. 5 can be considered to correspond to curve Cp in Fig. 4. In other words, region P3 obtained after sintering for 3 hours can be considered to be a region with a high concentration of p-type elements. As a result, it can be seen that as the sintering time increases, the region (region P1) with a large number of p-type elements shown in FIG. 2(b) expands toward the center, eventually reaching the entire region.

[0029] As explained above, it was confirmed that the manufacturing method of this example can manufacture a high-melting-point component having an interface when silicon carbide is used as the material. It was also confirmed that the interface is a PN junction surface. That is, the manufacturing method of this example has the effect of manufacturing a PN junction surface in a relatively simple manner. It was also confirmed that when silicon carbide is used as the material, cubic silicon carbide, a highly useful high-melting-point material, can be obtained relatively easily.

[0030] It is not necessary to provide all of the various features described above, and some may be omitted or combined as appropriate. Furthermore, the present invention is not limited to the embodiments, and various modifications may be made. For example, in the examples, a method of sintering powder of the material was shown, but a method may also be used in which a member formed from the material into a predetermined shape is used from the beginning, and tantalum is brought into contact with this and then sintered. In addition, although silicon carbide is used as the material in the examples, other materials can also be used. Furthermore, it has been confirmed that the interface, i.e., the position of the PN junction, explained in the examples spreads toward the center by increasing the sintering time. By adjusting the sintering time, it is possible to adjust the overall region to be one with a high n-type element or one with a high p-type element. [Industrial Applicability]

[0031] The present invention can be used as a method for manufacturing a high-melting-point member having an interface.

Claims

1. A method for manufacturing a high-melting-point member having a PN junction surface, comprising: (a) contacting tantalum with silicon carbide or a combination of silicon carbide with any of boron, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina; (b) heating the materials while they are in contact at a sintering temperature determined depending on the materials until a PN junction surface is formed in the materials.

2. The manufacturing method according to claim 1, The method of manufacturing wherein the material is silicon carbide.

3. The manufacturing method according to claim 1, The manufacturing method in which step (a) is a step of bringing a tantalum container or tantalum foil into contact with the material and sealing it.

4. The manufacturing method according to claim 3, In the step (a), the raw material is a powder, In the step (b), the heating is carried out so as to sinter the powder.

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