Method of producing nitride ceramic substrate and nitride ceramic metalized substrate, and nitride ceramic substrate and nitride ceramic metalized substrate

Abstract

To provide a method of producing a nitride ceramic substrate by aligning and defatting / sintering nitride ceramic substrates without using a mold release agent.SOLUTION: The method of producing a nitride ceramic substrate having plane faces and side faces, according to an embodiment of the present invention, comprises three steps. The first step is an alignment step of placing a plurality of molded bodies of the nitride ceramic substrate so that the side faces of the molded bodies are in contact with a ceramic setter. The second step is a degreasing step of degreasing the molded body installed on the ceramic setter to obtain a degreased body. The third step is a sintering step of sintering the degreased body installed on the ceramic setter to obtain a sintered body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments described below relate to methods for manufacturing a nitride ceramic substrate and a metallized nitride ceramic substrate, as well as to a nitride ceramic substrate and a metallized nitride ceramic substrate. [Background technology]

[0002] In recent years, the demand for ceramic substrates has been increasing year by year with the development of semiconductor devices that require large currents, such as power ICs and high-frequency transistors. In particular, nitride ceramic substrates, such as aluminum nitride (AlN) substrates and silicon nitride (Si3N4) substrates, have attracted attention as substrates that can handle the increasing amount of heat dissipation from semiconductor devices due to their high thermal conductivity and excellent heat dissipation properties. However, nitride ceramic substrates are difficult to sinter and require high sintering temperatures. For this reason, when sintering nitride ceramic substrates by laminating them, a bedding powder that acts as a mold release agent is used (Patent Document 1). Patent Document 1 discloses an aluminum nitride substrate that is laminated and sintered using boron nitride powder as the bedding powder.

[0003] Although these powders act as release agents, there is a problem in that some of them adhere to the sintered body and remain. For this reason, they are removed by grinding with a grinding wheel, belt grinding, wet or dry honing, etc. (Patent Document 2). According to Patent Document 2, release agents can be efficiently removed by using a brush with diamond powder attached. [Prior art documents] [Patent documents]

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-131491 Patent document 2: Japanese Patent Application Laid-Open No. 07-082030 Summary of the Invention [Problem to be solved by the invention]

[0005] Release agents are useful for efficiently stacking (laminarizing) nitride ceramic substrates. However, processes for applying and removing the release agent are required. Furthermore, a process for confirming that the release agent has been removed is required. Furthermore, if the release agent is not completely removed and remains on the surface of the nitride ceramic substrate, there is a problem of poor metallization properties.

[0006] The present invention solves these problems and provides a method for manufacturing a nitride ceramic substrate in which nitride ceramic substrates are aligned, degreased, and sintered without using a mold release agent. [Means for solving the problem]

[0007] The method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment includes the following three steps. The first step is an alignment step in which a plurality of molded bodies of the nitride ceramic substrate are placed on a ceramic setter so that their side portions contact a ceramic setter. The second step is a degreasing step in which the molded bodies placed on the ceramic setter are degreased to obtain a degreased body. The third step is a sintering step in which the degreased body placed on the ceramic setter is sintered to obtain a sintered body. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an example of a nitride ceramic substrate according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing an example of an installation state of the nitride ceramic substrate according to the embodiment. [Figure 3] 1 is a diagram showing an example of a metallized nitride ceramic substrate according to an embodiment. [Figure 4] FIG. 10 is a perspective view showing an installation state of a nitride ceramic substrate of a comparative example. [Figure 5] FIG. 1 shows a surface analysis of a nitride ceramic substrate. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, with reference to the drawings, a method for manufacturing a nitride ceramic substrate and a metallized nitride ceramic substrate, as well as the nitride ceramic substrate and the metallized nitride ceramic substrate will be described in detail.

[0010] The method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment includes the following three steps. The first step is an alignment step in which a plurality of molded bodies of the nitride ceramic substrate are placed on a ceramic setter so that their side portions contact a ceramic setter. The second step is a degreasing step in which the molded bodies placed on the ceramic setter are degreased to obtain a degreased body. The third step is a sintering step in which the degreased body placed on the ceramic setter is sintered to obtain a sintered body.

[0011] FIG. 1 shows a perspective view of an example of a nitride ceramic substrate according to an embodiment. 1 denotes a nitride ceramic substrate, 11 denotes a rectangular planar portion, 12 denotes a side portion, 13 denotes a long side of planar portion 11, 14 denotes a short side of planar portion 11, and 15 denotes the height (substrate thickness). 121 denotes a long side portion (hereinafter abbreviated as "long side portion") on the long side 13 side of planar portion 11. 122 denotes a short side portion (hereinafter abbreviated as "short side portion") on the short side 14 side of planar portion 11. As long as the nitride ceramic substrate is composed of planar portion 11 and side portion 12, the planar portion does not have to be rectangular; planar portion 11 may be square, polygonal, circular, or elliptical. The nitride ceramic substrate includes not only the substrate state before metallization, but also a molded body, a degreased body, and a sintered body, as described below.

[0012] Fig. 2 is a perspective view showing an example of an installation state of nitride ceramic substrates according to an embodiment. 2 is a frame setter, and 3 is a bottom plate setter. In Fig. 2, the nitride ceramic substrates are aligned and arranged so that the short side surface portions 122 contact the bottom plate setter 3 and the flat surfaces 11 overlap. In this case, the nitride ceramic substrates may also be aligned and arranged so that the long side surface portions 121 contact the bottom plate setter 3. Note that Fig. 2 only shows the front three rows of nitride ceramic substrates.

[0013] The first step in the method for manufacturing a nitride ceramic substrate according to the embodiment is an alignment step in which a plurality of compacts of the nitride ceramic substrate are placed so that their side surfaces come into contact with a ceramic setter.

[0014] The manufacturing method for nitride ceramic substrate compacts (hereinafter referred to as "compacts") can be any method for manufacturing ceramic substrates, such as powder press molding, sheet molding, or extrusion molding. Powder press molding, also known as uniaxial pressing, is a method in which ceramic powder is placed in a mold and pressed to form a shape. Sheet molding, also known as the doctor blade method, is a method in which a slurry containing a mixture of ceramic raw materials and an organic agent is poured onto a carrier sheet, the thickness is adjusted by the gap between the carrier sheet and a blade (doctor blade), and the sheet is peeled off from the carrier sheet after a drying process, thereby continuously obtaining sheets of a consistent thickness. In the sheet molding method, the obtained sheet can be divided into individual sizes by punching using a mold press or the like.

[0015] The compacts are preferably aligned so that the flat surfaces 11 overlap, as shown in Figure 2. It is also possible to place the compacts randomly rather than aligning them in one direction, but this may result in a decrease in the number of compacts that can be stored in the same setter, which could lower productivity. Also, it is not necessary to align all the compacts in the same direction; depending on the size and shape of the setter, it is possible to arrange compacts aligned in a gap and compacts aligned in a different direction.

[0016] 2, the setter can be divided into a bottom plate setter 3 and a frame setter 2, but the bottom plate setter 3 and the frame setter 2 can also be integrated. Furthermore, the frame setter 2 can be divided.

[0017] The second step in the method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment is a degreasing step in which the compact placed on the ceramic setter is degreased to obtain a degreased body.

[0018] Because ceramic raw materials are in powder form, it is difficult to mold them into a substrate shape by themselves. For this reason, organic substances such as resins called binders (adhesives) are added to make it easier to mold them into a substrate shape. The debinding process is the process of removing this binder after molding, and if debinding is insufficient, the binder may burn during firing, causing holes or deformation in the molded body. For this reason, in the first process, the molded body placed in the setter is heated to remove the binder, resulting in a debound nitride ceramic substrate (hereinafter referred to as the "debound body"). The obtained debound body has almost no change in volume because the binder has been removed from the molded body. For this reason, the debound body is placed in the setter in the same state as when the molded body was placed therein.

[0019] The debinding process involves heating the compact to remove the binder, and the process varies depending on the thermal decomposition temperature and content of the binder. For binders used in nitride ceramic substrates, the process is preferably carried out at a temperature in the range of 300 to 800°C in air or a non-oxidizing atmosphere. A batch furnace or continuous furnace is used for heating.

[0020] The third step in the method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment is a sintering step in which the degreased body placed on a ceramic setter is sintered to obtain a sintered body.

[0021] Sintering is a process in which the degreased body is heated at a high temperature to bond the raw material particles together and increase the density. The degreased nitride ceramic substrate becomes a sintered nitride ceramic substrate (hereinafter abbreviated as "sintered body"). The sintering process for the nitride ceramic substrate is preferably carried out in a nitrogen atmosphere at a temperature in the range of 1600°C to 1900°C.

[0022] In the method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment, the material of the ceramic setter is the same as that of the nitride ceramic substrate.

[0023] When a nitride ceramic substrate compact is degreased in a degreasing process to obtain a degreased body, the organic binder of the compact is simply removed, and there is almost no change in the external dimensions of the compact and the degreased body. In contrast, when a sintered body is obtained by sintering the degreased body in a sintering process, the sintered body shrinks by approximately 15-25% of the compact. This is because adjacent raw material particles in the ceramic compact gradually bond together, reducing the gaps between the particles. In this way, ceramics become more dense as they are sintered, and densified ceramics shrink when the temperature drops. When a setter with a different thermal expansion is used, the difference in thermal expansion causes the ceramic to be subjected to force at the contact point of the setter, causing deformation.

[0024] For this reason, it is preferable to make the thermal expansion coefficients of the ceramic setter and the nitride ceramic substrate similar. For this reason, it is preferable that the ceramic setter be a common material for the nitride ceramic substrate. A common material refers to a material of the same type as the material to be sintered. Furthermore, the same material means that the main raw material contains 85% by mass or more. For example, if the nitride ceramic substrate is aluminum nitride, the ceramic setter will either have the same composition as the aluminum nitride substrate, or be aluminum nitride containing 85% by mass or more of aluminum nitride but with a different type and ratio of auxiliary components. Since the thermal expansion coefficients of ceramics are similar or close depending on the main raw material, using a common ceramic setter can prevent deformation due to differences in thermal expansion.

[0025] Furthermore, even when using a co-material with the same composition as a nitride ceramic substrate, it is effective to over-sinter the ceramic setter by increasing the sintering temperature or lengthening the sintering time compared to the sintering conditions for the nitride ceramic substrate. An over-sintered ceramic setter can be used for a long life under normal sintering conditions for a nitride ceramic substrate. For co-materials with nitride ceramic substrates, it is also effective to reduce the amount of sintering aid compared to the composition of the nitride ceramic substrate. By reducing the amount of sintering aid in the ceramic setter, it is possible to suppress the formation of a glass phase and reduce reaction with the nitride ceramic substrate. Furthermore, to suppress the formation of a glass phase, it is possible to sinter it at a higher temperature than the nitride ceramic substrate, resulting in a long life.

[0026] In the method for manufacturing a nitride ceramic substrate according to the embodiment, the nitride ceramic substrate is an aluminum nitride substrate or a silicon nitride substrate.

[0027] Aluminum nitride substrates can achieve a high thermal conductivity of 170 to 230 W / m·k, making them suitable for applications where heat dissipation is required, or where a high withstand voltage is required and a certain degree of substrate thickness is required. In addition, the thermal expansion coefficient is 4.6×10 ―6 / k, which is similar to semiconductor chips made of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and gallium arsenide (GaAs), it can be used in semiconductor packaging. Silicon nitride substrates have a thermal conductivity of 70 to 130 W / m·k, which is lower than that of aluminum nitride substrates, but they have higher heat dissipation than the widely used alumina (aluminum oxide) substrate, which has a thermal conductivity of 20 W / m·k. In addition, silicon nitride ceramic substrates have a high three-point bending strength of 600 to 700 MPa, which allows for the substrate to be made thinner.

[0028] Because aluminum nitride and silicon nitride substrates are difficult to sinter, they are typically sintered at high temperatures in a gas-pressure atmosphere. Sintering aids are often added to lower the sintering temperature and facilitate sintering. The addition of sintering aids generates a liquid phase composed of low-melting-point oxides, lowering the sintering temperature. However, the liquid phase can react with the setter, potentially resulting in adhesion. Furthermore, when nitride ceramic substrates are stacked for efficient production, the substrates may react with each other and bond. To prevent this adhesion, boron nitride (BN), which does not readily react with aluminum nitride or silicon nitride, is used as a setter or mold release agent. However, if boron nitride remains on the substrate surface, it can interfere with the formation of metal circuits on the substrate surface. For this reason, it is preferable to manufacture aluminum nitride and silicon nitride substrates using the nitride ceramic substrate manufacturing method described above.

[0029] In the method for manufacturing a nitride ceramic substrate according to the embodiment, the ratio (W / H) of the width (W) of the side surface of the placed compact to the height (H) of the flat surface of the compact is 20 or less.

[0030] In FIG. 1, if the distance of height 15 is defined as height (H) and the distance of the side surface of long side 13 or short side 14 is defined as width (W), the ratio (W / H) of the width (W) of the side surface of the molded body to the height (H) of the flat surface of the installed molded body is 20 or less. In FIG. 2, since short side surface 122 is installed on bottom plate setter 3, the distance of long side 13 is defined as the width (W) of the side surface. If long side surface 121 is installed on bottom plate setter 3, the distance of short side 14 is defined as the width (W) of the side surface. Furthermore, if the shape of flat surface 11 is square, the width (W) of the side surface, which is the distance between long side 13 and short side 14, is the same.

[0031] In the manufacturing method of a nitride ceramic substrate, if the ratio (W / H) of the width (W) of the side portion of the placed molded body to the height (H) of the flat portion of the placed molded body is large, exceeding 20, warping may occur. That is, when the side portion 12 of the nitride ceramic substrate 1 is placed on a setter and sintered, warping may occur due to its own weight. That is, if the width (W) is large, warping is likely to occur due to the large weight of the molded body. On the other hand, if the height (H) is small, the nitride ceramic substrate becomes thin and warping is likely to occur during sintering. For this reason, the ratio (W / H) of the width (W) of the side portion of the placed molded body to the height (H) of the flat portion of the placed molded body is more preferably 15 or less, and even more preferably 10 or less.

[0032] In the method for producing a metallized nitride ceramic substrate, a metallization is formed on the surface of the nitride ceramic substrate produced by the above-mentioned production method.

[0033] One application of nitride ceramic substrates is circuit boards. Circuit boards are substrates in which primarily conductive circuits are formed on the surface of a ceramic substrate. Taking advantage of the insulating properties of ceramics, electrical circuits are formed while insulating the front and back of the ceramic substrate and between circuits. Metallization is the process of forming a metal layer on the surface of a ceramic substrate to form a circuit. Metallization of ceramic substrates can be performed using thin films, thick films, high-melting-point metals, or DBC. Figure 3 shows an example of a nitride ceramic metallized substrate according to an embodiment. Figure 3(a) is a perspective view of a nitride ceramic metallized substrate, with 5 representing the metallization. The short side surface portion 122 is the surface that was in contact with the bottom plate setter 3 in Figure 2. Figure 3(b) is a cross-sectional view of portion A in Figure 3(a). 111 denotes the metallized portion of the ceramic substrate where metallization is performed (hereinafter abbreviated as "metallized portion"). 112 denotes the non-metallized portion of the flat surface portion 11 where metallization is not performed (hereinafter abbreviated as "non-metallized portion").

[0034] Thin-film circuits have a metallization thickness of 10 μm or less, and mainly a few μm or less. A barrier layer of platinum (Pt) or palladium (Pd) is formed on a bonding layer such as titanium (Ti), and gold (Au), nickel (Ni), copper (Cu), etc. is formed on the top surface to improve bonding. Methods for forming thin-film circuits include evaporation, ion plating, sputtering, chemical vapor deposition, and atomic layer deposition. Thin-film circuits have a thin metallization layer, making it possible to form fine circuits. Thin-film circuits are used in optical storage, optical communications, and other applications.

[0035] Thick film circuits have a metallization thickness of 10 to 30 μm. Copper, silver-palladium, gold, etc. are screen-printed and heated at 1000°C or less to form the circuit. The bonding strength of the metallization is not high, but it can be manufactured using a simple process as it does not require processes such as plating or etching. In addition to the metal circuits mentioned above, resistors and insulators can also be printed on thick film substrates. Thick film circuits are used for radio frequency (RF) circuit applications, etc.

[0036] Refractory metal circuits have a metallization thickness of 10 to 30 μm, the same as thick film circuits. High-melting metals such as molybdenum (Mo) and tungsten (W) are screen-printed and then heated at 1400 to 1700°C to form the circuit. The high temperature heating results in high bonding strength, but since soldering and other bonding methods cannot be used on the surface of refractory metals, nickel (Ni) plating is required. Refractory metal circuits are used in semiconductor circuits and other applications.

[0037] DBC (Direct Bond Copper) circuits bond copper circuits directly to ceramic substrates. The copper circuit is thick, ranging from 0.1 to 1 mm, and it is also possible to bond copper plates thicker than 1 mm. Copper circuits are formed by etching after the copper plate is bonded to the ceramic. Because the circuit is thick, DBC circuits can carry large currents and are used in high-output semiconductor substrates such as power modules. Types of DBC circuits include AMC (Active Metal Copper) circuits, in which copper plates are bonded with active metals, and DBA (Direct Bond Aluminum) circuits, in which aluminum (Al) is used as the circuit.

[0038] In all of the above-mentioned metallization processes, the nitride ceramic reacts with the metal to form a bonding layer. Therefore, if the metallization is formed while the release agent used during manufacturing remains on the surface of the nitride ceramic substrate, the bonding strength may decrease. In particular, the release agent tends to remain on the surface to prevent adhesion of the nitride ceramic substrate at high temperatures, so a process is required to thoroughly remove it. In the method for manufacturing a nitride ceramic substrate according to the above-mentioned embodiment, no release agent is used, so the process of removing the release agent is not necessary.

[0039] In the nitride ceramic substrate manufactured by the above-described method for manufacturing a nitride ceramic substrate, boron nitride is not present on the surface of the flat portion.

[0040] Boron nitride has excellent release properties even at high temperatures, so it is used as a release agent for nitride ceramic substrates. When sintering a nitride ceramic substrate, boron nitride powder is applied between the ceramic setter and the nitride ceramic substrate, or between nitride ceramic substrates themselves, to prevent adhesion due to a reaction. It is also possible to use a boron nitride setter shaped like a setter, and sinter the nitride ceramic substrate inside the boron nitride setter.

[0041] 4 is a perspective view showing the installed state of nitride ceramic substrates of a comparative example, which will be described later. The nitride ceramic substrates 1 are aligned so that the flat surfaces 11 of the nitride ceramic substrates 1 are in contact with the bottom plate setter 3. The nitride ceramic substrates 1 are also stacked so that the flat surfaces 11 of the nitride ceramic substrates 1 are in contact with each other. For this reason, a release agent 4 is applied to prevent reaction and adhesion between the bottom plate setter 3 and the nitride ceramic substrate 1, and between the nitride ceramic substrates 1.

[0042] In the method for manufacturing a nitride ceramic substrate according to the embodiment described above, boron nitride is not used, and therefore boron nitride is not detected from the nitride ceramic substrate. If no boron nitride is detected, it can be said that the substrate is in a state where it does not interfere with the metallization described above.

[0043] The absence of boron nitride can be confirmed by X-ray mass analysis. When the surface of a nitride ceramic substrate is measured for boron (B) using an energy dispersive X-ray fluorescence analyzer (EDX), if the result is ND (not detected) or below the detection limit, it means that boron is not present.

[0044] Furthermore, it is preferable that boron nitride is not detected throughout the nitride ceramic substrate. However, if boron nitride is not detected in the metallized portion 111, it will not affect the metallization. Therefore, it is possible for boron nitride not to be detected on the metallized substrate surface. This means that even if boron nitride is detected in the non-metallized portion 112 or side portion 12 of the flat portion 11 where no metallization is performed, it will not affect the metallization. However, if boron nitride is present even in a small area, there is a possibility that boron nitride will remain on the metallized substrate surface due to contact or the like. Therefore, it is preferable that boron nitride is not detected in the metallized portion 111. Furthermore, it is more preferable that boron nitride is not detected in the flat portion 11 of the nitride ceramic substrate, and even more preferable that it is not detected throughout the nitride ceramic substrate 1.

[0045] An example of when boron nitride is present in non-metallized portions is when a boron nitride setter is used. For example, if the bottom plate setter 3 is made of boron nitride, even when the nitride ceramic substrates are aligned as shown in Figure 2, boron nitride will only be present on the side surface 12 that comes into contact with the ground surface. Furthermore, if the frame setter 2 is also made of boron nitride, in addition to the bottom plate setter 3, boron nitride may be present on the flat surface 11 and side surface 12 due to contact or other reasons. For this reason, it is preferable to install a dummy between the nitride ceramic substrate and the frame setter 2 to prevent any influence from the frame setter 2.

[0046] When boron nitride is detected in the side surface portion 12, the absence of boron nitride in the metallized portion 111 can also be confirmed using an energy dispersive X-ray fluorescence analyzer (EDX). Figure 5 shows a surface analysis (EDX) of a nitride ceramic substrate. Figure 5(a) shows the state before metallization 5 in Figure 3(a). Analysis is performed on the flat surface portion 11 in the direction of arrow D. Figure 5(b) is a cross-sectional view of B in Figure 5(a). The boron mass percentage is measured from the side surface (outside) toward the metallized substrate surface (inside). The point where the mass percentage reaches 1% or less is considered to be a point where boron element is not present, i.e., where boron nitride is not present. The mass percentage is set to 1% or less because even if the measurement range is narrowed, there is a possibility of influence from the surroundings and the possibility of picking up noise.

[0047] The metallized nitride ceramic substrate according to the embodiment has metallization formed on a nitride ceramic substrate in which no boron nitride exists on the flat surface portion.

[0048] As mentioned above, if there is no boron nitride on the surface of a nitride ceramic substrate, it is possible to form a metallization with high bonding strength. Types of metallization that can be formed include thin films, thick films, high-melting-point metals, and DBC. These bonding methods make it possible to bond nitride ceramics and metals without being affected by boron nitride.

[0049] Next, a method for efficiently manufacturing a nitride ceramic substrate and a metallized nitride ceramic substrate according to the embodiment will be described using an aluminum nitride substrate and a metallized aluminum nitride substrate as examples.

[0050] First, appropriate amounts of sintering aid powder, additives, solvent, binder, etc. are added to the raw material aluminum nitride powder, mixed and crushed, and then granulated using a spray dryer. Furthermore, when the total of the aluminum nitride powder and sintering aid powder is taken as 100 mass%, it is preferable that the aluminum nitride powder account for 90 mass% or more. Furthermore, the additive is a plasticizer. The solvent is water or an organic solvent. Examples of organic solvents include alcohol, ketone, and benzene. Furthermore, the binder is an organic substance. The amount of binder added is within the range of 3 to 20 mass parts when the total of the aluminum nitride powder and sintering aid powder is taken as 100 mass parts.

[0051] Next, the adjusted granulated powder is subjected to press molding. Press molding is a molding method that uses a die press molding device with a rectangular punch at the tip and a die with a rectangular cross-section hole. By filling the granulated powder and applying pressure vertically to the upper and lower punches, a substrate-shaped molded body with rectangular surface and side surfaces is obtained.

[0052] Next, an alignment process is carried out in which the compacts are lined up inside the setter. In this process, a rectangular, flat bottom plate setter and a square, cylindrical frame setter that matches the outer dimensions of the bottom plate setter are prepared. The bottom plate setter and frame setter are made of aluminum nitride. In this alignment process, the compacts are stacked and aligned in an upright position with their side surfaces in contact with the bottom plate setter. The flat surface of the compacts has long and short sides, and when aligned so that the short side surfaces are in contact with the bottom setter, they are aligned without any gaps, as shown in Figure 2. In this case, if the compacts are aligned by being pressed into the frame setter, there is a risk that they will react during sintering and stick together. For this reason, a gap is provided that prevents the degreased bodies from becoming tilted when the setter is shaken.

[0053] Next, a degreasing step is performed to degrease the compact. The degreasing step is a step in which the compact is heated to a temperature equal to or higher than the decomposition temperature of organic components such as binders to remove the organic components. The degreasing step may be performed in a nitrogen atmosphere or an air atmosphere. A degreased body can be obtained by the degreasing step.

[0054] Next, the degreased body is sintered in a sintering process. The sintering process is preferably carried out at 1600 to 2000°C in a nitrogen atmosphere. The sintering pressure is preferably in the range of atmospheric pressure to 300 MPa. Note that atmospheric pressure is 0.10133 MPa (=1 atm). After the sintering process, the sintered bodies in the setter are in a shrunk state, so they are either lined up with gaps between them or tilted and stacked due to vibrations during transport.

[0055] The sintered body undergoes barrel processing to remove any foreign matter adhering during press molding, resulting in an aluminum nitride substrate. Barrel processing includes wet barrel processing and dry barrel processing. In wet barrel processing, the sintered body, media such as abrasive stones and abrasives, and a polishing aid compound are placed in a barrel tank along with a solution such as water, and the barrel tank is rotated, stirred, vibrated, etc., causing the sintered body to rub against the media, removing foreign matter through friction. In dry barrel processing, polishing is performed in barrel processing without using a solution such as water.

[0056] Aluminum nitride metallized substrates are produced by applying various metallization processes to the surface of an aluminum nitride substrate. In thin-film metallization, a triple layer of titanium, platinum, and gold is deposited on the aluminum nitride substrate using, for example, an electron beam evaporation system. An example of thick-film metallization is printing and heating a copper thick-film paste. In high-melting-point metal metallization, for example, printing and heating a molybdenum-titanium nitride (TiN) paste. In DBC metallization, for example, an active metal method is used, where an active metal brazing paste is printed, a copper plate is placed on top, and then heated.

[0057] (Examples 1 to 5, Comparative Examples 1 to 5) For Examples 1-2, 4-5 and Comparative Examples 1-3, 5, press-molded bodies were prepared. Sintering aid powder, additives, solvents, binders, etc. were added to the raw ceramic powder, which was then mixed and crushed, and granulated powder was obtained using a spray dryer. The obtained granulated powder was then press-molded to obtain a molded body with the dimensions shown in Table 1. The length of the short side of the molded body was 10 mm. For Example 3 and Comparative Example 4, sheet-molded bodies were prepared. Sintering aids, additives, solvents, binders, etc. were added to the raw ceramic powder, which was then mixed and crushed, and sheets were obtained using a sheet molding machine. The obtained sheets were punched using a mold to obtain molded bodies with the dimensions shown in Table 1. The length of the short side of the molded body was 10 mm.

[0058] Next, we prepared a setter made of aluminum nitride and a setter made of boron nitride. The setter consisted of a bottom plate setter and a frame setter. The bottom plate setter measured 100 mm x 100 mm x 5 mm, and the frame setter was a square tube with external dimensions of 100 mm x 100 mm x 20 mm and a thickness of 5 mm.

[0059] Next, the compacts were aligned and placed in the setter. In Examples 1 to 5 and Comparative Examples 3 and 4, the compacts were aligned and placed so that the short side surfaces were in contact with the bottom plate setter, as shown in Figure 2. When a boron nitride setter was used, a dummy substrate made of the same material as the ceramic substrate was placed between the compacts and the frame setter to prevent contact between the compacts and the frame setter. In Comparative Examples 1 to 5 and 5, the compacts were aligned so that the flat surfaces were in contact with the bottom plate setter, as shown in Figure 4. When a boron nitride setter was used, a dummy substrate made of the same material as the ceramic substrate was placed between the compacts and the frame setter to prevent contact between the compacts and the frame setter. In Comparative Examples 2 and 5, boron nitride powder was applied as a release agent to the surfaces of the compacts before alignment.

[0060] Next, the aluminum nitride molded body and the silicon nitride molded body were subjected to a debinding process and a sintering process using separate furnaces. The debinding process was carried out at 450°C in a nitrogen atmosphere. A sintering process was also carried out. The sintering process was carried out at 1800°C in a nitrogen atmosphere. In the sintering process, a bottom plate setter was placed on top of the frame setter to serve as a lid. The manufacturing conditions for the examples and comparative examples are shown in Table 1. In Table 1, aluminum nitride is AlN, silicon nitride is SiN, and boron nitride is BN, and the alignment state shown in Figure 2 is referred to as vertical placement, while the alignment state shown in Figure 4 is referred to as horizontal placement.

[0061] [Table 1]

[0062] As can be seen from Table 1, in the Examples, the ratio of width W to height H (W / H) and the combination of alignment state and use of release agent are within the preferred ranges. On the other hand, in Comparative Examples 3 and 4, the combinations of W / H, alignment state and use of release agent are outside the preferred ranges.

[0063] Next, after the sintering process, the ceramic sintered bodies were removed from the setter and 500 samples were sampled and inspected. Those in which the ceramic sintered bodies were bonded together and could not be easily separated after vibration were judged to be defective in sintering. Next, the peeled ceramic substrates were polished with plastic media at 20,000 cm 3 , 250cm of white alundum as abrasive 3 , water 20,000cm 3 The ceramic sintered body was then rotated at 100 rpm for 15 minutes for barrel processing. After barrel processing, the ceramic sintered body was washed with water and dried to obtain a ceramic substrate. The warpage of the obtained ceramic substrate was measured, and those with a warpage of 2 μm / mm or more were deemed defective. Table 2 shows the sintering defect rate and warpage defect rate.

[0064] Next, boron nitride was detected in the areas to be metallized, as described below. As shown in Figure 5(a), the areas to be metallized were set inside the boundary between the flat portion 11 and the short side surface portion 122 of the ceramic substrate. As shown in Figure 5(b), the distance L112 from the short side 14 to the non-metallized portion 112 was set to 1 mm, and boron (B) mass % analysis was performed using EDX from the non-metallized portion 112 toward the metallized portion 111. When the distance from the edge of the metallized portion 111 to the EDX measurement data point is Lm, the mass % of boron at a point where Lm is 1 mm is shown in Table 2 as the amount of boron detected.

[0065] Next, the ceramic substrate was metallized and the bonding strength was measured. For the thin film, 0.1 μm of titanium, 0.2 μm of platinum, and 0.3 μm of gold were deposited in this order using an electron beam deposition device, and then a pattern was formed by etching. For the high-melting-point metal, a high-melting-point metal paste made of molybdenum with titanium nitride added was pattern-printed to a thickness of 25 μm and heated at 1650°C in a nitrogen atmosphere to form a circuit. The surface of the circuit was plated with 2 μm of nickel. For the thin film and high-melting-point metal, a copper plate measuring 50 mm long, 3 mm wide, and 0.3 mm thick was soldered so that a portion of the copper plate for bonding strength measurement was bonded to the metallized layer.

[0066] For DBC (AMC), the active metal paste was pattern printed to a thickness of 25 μm, and then the copper plate for measuring the bonding strength described above was laminated on top of it, and the bonding was carried out by heating at 850°C in a vacuum.

[0067] The copper plate for measuring the strength of each metallized substrate was bent upward at a right angle and pulled upward at a speed of 50 mm / min using an Instron tensile tester to measure the bonding strength (peel strength). The bonding strength measurement results are shown in Table 2.

[0068] [Table 2]

[0069] As can be seen from Table 2, no sintering defects occurred in the Examples. In contrast, many sintering defects occurred in Comparative Example 1. This is because the green compacts were stacked and sintered horizontally without using a release agent, causing them to react with each other and adhere to each other.

[0070] Furthermore, as can be seen from Table 2, in the examples, the warpage defect rate was either non-existent or small, within a desirable range. This is because the ratio of width W to height H (W / H) was small, and even when aligned vertically, deformation did not occur, and the amount of warpage was small. On the other hand, in comparative examples 3 and 4, many warpage defects occurred. This is because the ratio of width W to height H (W / H) was large, and deformation occurred even when aligned vertically, resulting in a large amount of warpage.

[0071] Furthermore, as can be seen from Table 2, in the Examples, the detected amount of boron was below the measurement limit or a low value of 2 mass% or less. On the other hand, in Comparative Examples 2 and 5, the detected amount was high. Under the alignment conditions of the Examples, a boron nitride setter was not used, or even if a boron nitride setter was used, no release agent was used, resulting in a small detected amount. In contrast, in Comparative Examples 2 and 5, a release agent was used, so boron nitride remained and was detected as boron.

[0072] Furthermore, as can be seen from Table 2, the bonding strength in the Examples was within the preferred range. On the other hand, the bonding strength in Comparative Examples 2 and 5 was outside the preferred range. This is because the Examples did not use boron nitride as a release agent, so no boron nitride remained in the metallized portion, and a good metallization reaction occurred. In contrast, in Comparative Examples 2 and 5, boron nitride remained in the metallized portion on the nitride ceramic substrate surface, inhibiting the metallization reaction and reducing the bonding strength.

[0073] As is clear from the results shown above, it was recognized that the Examples had less deformation such as warping and had better metallization properties than the Comparative Examples.

[0074] As described above, the method for manufacturing a nitride ceramic substrate allows the nitride ceramic substrate to be aligned, degreased, and sintered without using a mold release agent. Furthermore, by metallizing the obtained nitride ceramic substrate, a metallized nitride ceramic substrate with excellent metallization properties can be obtained.

[0075] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. [Explanation of symbols]

[0076] 1...Nitride ceramic substrate 11...flat portion, 111...metallized portion, 112...non-metallized portion 12...side surface portion, 121...long side surface portion, 122...short side surface portion 13...long side 14...short side 15…Height 2...Bottom plate setter 3...Frame setter 4...Release agent 5...Metallized

Claims

1. A method for manufacturing a nitride ceramic substrate having a flat portion and a side portion, comprising: an alignment step of placing the plurality of nitride ceramic substrate compacts so that their side surfaces are in contact with a ceramic setter; a degreasing step of degreasing the green body placed on the ceramic setter to obtain a degreased body; a sintering step of sintering the degreased body placed on a ceramic setter to obtain a sintered body; A method for manufacturing a nitride ceramic substrate, comprising:

2. 2. The method for manufacturing a nitride ceramic substrate according to claim 1, wherein the material of the ceramic setter is the same as that of the nitride ceramic substrate.

3. 3. The method for producing a nitride ceramic substrate according to claim 1, wherein the nitride ceramic substrate is an aluminum nitride substrate or a silicon nitride substrate.

4. 3. The method for manufacturing a nitride ceramic substrate according to claim 1, wherein the ratio (W / H) of the width (W) of the side surface of the molded body to the height (H) of the planar surface of the placed molded body is 20 or less.

5. 3. A method for producing a metallized nitride ceramic substrate, comprising forming a metallization on the surface of a nitride ceramic substrate produced by the method for producing a nitride ceramic substrate according to claim 1 or 2.

6. 4. A method for producing a metallized nitride ceramic substrate, comprising forming a metallization on the surface of a nitride ceramic substrate produced by the method for producing a nitride ceramic substrate according to claim 3.

7. 3. A nitride ceramic substrate manufactured by the method for manufacturing a nitride ceramic substrate according to claim 1 or 2, characterized in that no boron nitride is present on the surface.

8. 4. A nitride ceramic substrate manufactured by the method for manufacturing a nitride ceramic substrate according to claim 3, wherein no boron nitride is present on the surface.

9. A metallized nitride ceramic substrate, comprising the nitride ceramic substrate according to claim 7 and a metallized layer formed on the nitride ceramic substrate.

10. A metallized nitride ceramic substrate, comprising the nitride ceramic substrate according to claim 8 and a metallized layer formed on the nitride ceramic substrate.

Images