JP7751672B2 - Methods for manufacturing nitride ceramic substrates and metallized nitride ceramic substrates, and nitride ceramic substrates and metallized nitride ceramic substrates - Google Patents

Description

The embodiments described below relate to methods for manufacturing nitride ceramic substrates and metallized nitride ceramic substrates, as well as nitride ceramic substrates and metallized nitride ceramic substrates.

In recent years, the demand for ceramic substrates has been increasing year by year with the development of semiconductor devices requiring large currents, such as power ICs and high-frequency transistors. In particular, nitride ceramic substrates, such as aluminum nitride (AlN) substrates and silicon nitride (Si ₃ N ₄ ) substrates, have attracted attention as substrates that can accommodate 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.

Although these powders act as release agents, there is an issue that some of them adhere to the sintered body and remain. For this reason, they are removed by grinding with a grindstone, 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.

Patent Document 1: Japanese Patent Application Laid-Open No. 2007-131491 Patent Document 2: Japanese Patent Application Laid-Open No. 07-082030

Release agents are useful for efficiently manufacturing nitride ceramic substrates by stacking (laminarizing). 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 the issue of poor metallization properties.

The present invention solves these problems by providing a method for manufacturing nitride ceramic substrates in which nitride ceramic substrates are aligned, degreased, and sintered without using a mold release agent.

The method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment comprises the following three steps. The first step is an alignment step in which multiple molded bodies of the nitride ceramic substrate are placed 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.

FIG. 1 is a perspective view showing an example of a nitride ceramic substrate according to an embodiment. FIG. 2 is a perspective view showing an example of an installation state of the nitride ceramic substrate according to the embodiment. 1 is a diagram showing an example of a metallized nitride ceramic substrate according to an embodiment. FIG. 10 is a perspective view showing an installation state of a nitride ceramic substrate of a comparative example. FIG. 1 shows a surface analysis of a nitride ceramic substrate.

Below, with reference to the drawings, we will explain in detail the manufacturing methods for nitride ceramic substrates and nitride ceramic metallized substrates, as well as the nitride ceramic substrates and nitride ceramic metallized substrates.

The method for manufacturing a nitride ceramic substrate having a flat portion and a side portion according to the embodiment comprises the following three steps. The first step is an alignment step in which multiple molded bodies of the nitride ceramic substrate are placed 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.

Figure 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 the long side of planar portion 11, 14 denotes the short side of planar portion 11, and 15 denotes the height (substrate thickness). 121 denotes the long side portion (hereinafter abbreviated as "long side portion") on the long side 13 side of planar portion 11. 122 denotes the 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 the molded body, degreased body, and sintered body described below.

Figure 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 Figure 2, the nitride ceramic substrates are aligned 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 so that the long side surface portions 121 contact the bottom plate setter 3. Note that Figure 2 only shows the front three rows of nitride ceramic substrates.

The first step in the method for manufacturing a nitride ceramic substrate according to this embodiment is an alignment step in which multiple molded bodies of the nitride ceramic substrate are placed so that their side surfaces contact the ceramic setter.

The manufacturing method of a nitride ceramic substrate compact (hereinafter referred to as "compact") can be any method for manufacturing a ceramic substrate, 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 the powder. 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 resulting material is peeled off from the carrier sheet after a drying process, continuously obtaining sheets of a consistent thickness. In the sheet molding method, the resulting sheet can be divided into individual sizes by punching using a mold press or the like.

As shown in Figure 2, it is preferable to align the molded bodies so that the flat surfaces 11 overlap. It is also possible to place the molded bodies randomly rather than aligning them in one direction, but this may result in a decrease in the number of molded bodies that can be stored in the same setter, resulting in lower productivity. Also, it is not necessary to align all molded bodies in the same direction; depending on the size and shape of the setter, it is possible to arrange molded bodies aligned in gaps and molded bodies aligned in a different direction.

Furthermore, the setter can be separated into a bottom plate setter 3 and a frame setter 2 as shown in Figure 2, but the bottom plate setter 3 and frame setter 2 can also be integrated. Furthermore, the frame setter 2 may be separated.

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

Because ceramic raw materials are in powder form, it is difficult to form them into a substrate shape by themselves. For this reason, organic substances such as resins called binders are added to make it easier to form them into a substrate shape. The debinding process is the process of removing this binder after forming; if debinding is insufficient, the binder may burn during firing, causing holes or deformation in the formed body. For this reason, in the first process, the formed 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, as the binder has been removed from the formed body. For this reason, the debound body is placed in the setter in the same state as when the formed body was placed therein.

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.

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

Sintering is a process in which the degreased body is heated at high temperatures to bond the raw material particles together and increase density. Sintering the degreased nitride ceramic substrate body results in a sintered nitride ceramic substrate (hereafter abbreviated as "sintered body"). The sintering process for nitride ceramic substrates is preferably carried out in a nitrogen atmosphere at temperatures between 1600°C and 1900°C.

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.

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 degreased body. In contrast, when the degreased body is sintered in a sintering process to obtain a sintered body, 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 cooled. 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 point of contact with the setter, causing deformation.

For this reason, it is preferable to make the thermal expansion coefficients of the ceramic setter and the nitride ceramic substrate similar. Therefore, 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 refers to a material containing 85% or more by mass of the main raw material. For example, if the nitride ceramic substrate is aluminum nitride, the ceramic setter is either the same composition as the aluminum nitride substrate, or aluminum nitride containing 85% or more by mass of aluminum nitride but with a different type or 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.

Furthermore, even when using a co-material with the same composition as the 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 with a long life under normal sintering conditions for the nitride ceramic substrate. Furthermore, when using a co-material for the nitride ceramic substrate, 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.

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

Aluminum nitride substrates can achieve a high thermal conductivity of 170 to 230 W/m·k, making them suitable for applications requiring heat dissipation or where high voltage resistance requires a thicker substrate. Furthermore, their thermal expansion coefficient of 4.6 x ^10-6 /k is similar to that of semiconductor chips made from silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and gallium arsenide (GaAs), making them suitable for semiconductor packaging. Silicon nitride substrates have a lower thermal conductivity of 70 to 130 W/m·k than aluminum nitride substrates, but offer higher heat dissipation than the widely used alumina (aluminum oxide) substrates, which have a 20 W/m·k. Furthermore, silicon nitride ceramic substrates have a high three-point bending strength of 600 to 700 MPa, allowing for thinner substrates.

Because aluminum nitride and silicon nitride substrates are difficult to sinter, they are typically sintered at high temperatures in a gas-pressure atmosphere. To lower the sintering temperature and facilitate sintering, sintering aids are added. 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 is less reactive with aluminum nitride and silicon nitride, is used as a setter or mold release agent. However, if boron nitride remains on the substrate surface, it inhibits reaction with metals, hindering 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.

In the manufacturing method of the nitride ceramic substrate according to the embodiment, the ratio (W/H) of the width (W) of the side surface of the placed molded body to the height (H) of the planar surface of the molded body is 20 or less.

In Figure 1, if the distance of height 15 is the height (H) and the distance of the side surface of the long side 13 or short side 14 is the 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 Figure 2, the short side surface 122 is installed on the bottom plate setter 3, so the distance of the long side 13 is the width (W) of the side surface. If the long side surface 121 is installed on the bottom plate setter 3, the distance of the short side 14 is the width (W) of the side surface. Furthermore, if the shape of the flat surface 11 is square, the width (W) of the side surface, which is the distance between the long side 13 and the short side 14, is the same.

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 greater than 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 more likely to occur due to the heavy weight. On the other hand, if the height (H) is small, the nitride ceramic substrate becomes thinner and warping is more 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.

In the method for manufacturing a nitride ceramic metallized substrate, metallization is formed on the surface of the nitride ceramic substrate manufactured by the aforementioned manufacturing method.

One application of nitride ceramic substrates is as a circuit board. 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").

Thin-film circuits have a metallization thickness of 10 μm or less, typically 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), or the like is formed on the top surface to improve bonding. Methods for forming thin-film circuits include vapor deposition, 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.

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 a circuit. Thick film circuits do not have high bonding strength, but they can be manufactured using a simple process because they do not require processes such as plating or etching. Furthermore, thick film circuits can be printed with resistors and insulators in addition to the metal circuits mentioned above. Thick film circuits are used for radio frequency (RF) circuits, etc.

High-melting-point metal circuits have a metallization thickness of 10 to 30 μm, the same as thick-film circuits. High-melting-point metals such as molybdenum (Mo) and tungsten (W) are screen-printed and then heated at 1400 to 1700°C to form the circuit. Because they are heated at high temperatures, the bonding strength is high, but since soldering or other bonding is not possible on the surface of high-melting-point metals, nickel (Ni) plating or other methods are required. High-melting-point metal circuits are used in semiconductor circuits, etc.

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 bonding the copper plate 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.

In all of the above-mentioned metallization processes, the nitride ceramic and the metal react 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.

In nitride ceramic substrates manufactured using the aforementioned nitride ceramic substrate manufacturing method, boron nitride is not present on the flat surface.

Boron nitride has excellent release properties even at high temperatures, so it is used as a release agent for nitride ceramic substrates. When sintering nitride ceramic substrates, 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 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.

Figure 4 is a perspective view showing the installation 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 thereof contact the bottom plate setter 3. The nitride ceramic substrates 1 are stacked so that the flat surfaces 11 thereof contact 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 themselves. Note that Figure 4 shows only the top three rows of nitride ceramic substrates.

The method for manufacturing a nitride ceramic substrate according to the embodiment described above does not use boron nitride, so boron nitride is not detected in the nitride ceramic substrate. If no boron nitride is detected, it can be said that it does not interfere with the metallization described above.

The absence of boron nitride can be confirmed by X-ray mass analysis. When the surface of the 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, as will be described later, 1 mass % or less, this indicates that boron is not present.

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 does 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 the side portion 12 of the flat portion 11 where no metallization is performed, it does 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 portion 111 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.

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, etc. For this reason, it is preferable to place a dummy between the nitride ceramic substrate and the frame setter 2 to prevent any influence from the frame setter 2.

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 by 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 the metallization 5 in Figure 3(a) is applied. 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 portion 111 (inside) , and any point below 1 mass % is considered to be a point where boron element is not present, i.e., where boron nitride is not present . The reason for setting the measurement range to 1 mass% or less is that even if the measurement range is narrowed, there is a possibility of influence from the surroundings and that noise may be picked up.

The metallized nitride ceramic substrate according to this embodiment has metallization formed on a nitride ceramic substrate that does not contain boron nitride on the flat surface.

As mentioned above, if there is no boron nitride on the surface of a nitride ceramic substrate, it is possible to form 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.

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

First, appropriate amounts of sintering aid powder, additives, solvent, binder, etc. are added to the raw material aluminum nitride powder, which is then mixed and crushed, and 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.

Next, the adjusted granulated powder is used for 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 mold with 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.

Next, an alignment process is performed in which the compacts are arranged 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. When the flat surface of the compacts has long and short sides and they are 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. If the compacts are aligned by being pressed into the frame setter, they may react during sintering and stick together. For this reason, a gap is provided large enough to prevent the degreased bodies from becoming slanted when the setter is shaken.

Next, a degreasing process is carried out to degrease the compact. In this process, the compact is heated to a temperature above the decomposition temperature of organic components such as binders to remove the organic components. The degreasing process may be carried out in a nitrogen atmosphere or in the air. A degreased body can be obtained by the degreasing process.

Next , a sintering process is carried out to sinter the degreased body. The sintering process is preferably carried out at 1600 to 2000°C in a nitrogen atmosphere. The pressure during sintering 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 lined up with gaps between them, or tilted and stacked due to vibrations during movement.

The sintered body is subjected to 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.

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 device. 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 in which an active metal brazing paste is printed, a copper plate is placed on top, and then heated.

(Examples 1 to 5, Comparative Examples 1 to 5)
For Examples 1-2, 4-5 and Comparative Examples 1-3, and 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 short side length 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 short side length of the molded body was 10 mm.

Next, aluminum nitride setters and boron nitride setters were prepared. The setters consisted of a bottom plate setter and several stages of frame setters. The bottom plate setter had dimensions of 100 mm × 100 mm × 5 mm, and the frame setter had a rectangular cylindrical shape with outer dimensions of 100 mm × 100 mm × 20 mm and a thickness of 5 mm.

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 so that their 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 compact and the frame setter to prevent contact between the compact and the frame setter. In Comparative Examples 1 to 5, the compacts were aligned so that their 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 compact and the frame setter to prevent contact between the compact and the frame setter. In Comparative Examples 2 and 5, boron nitride powder was applied to the surface of the compact as a release agent before alignment.

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 form 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.

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 and use of release agent are within the preferred ranges. On the other hand, in the Comparative Examples , the ratio of W/H and the combination of alignment and use of release agent are outside the preferred ranges.

Next, after the sintering process, the ceramic sintered bodies were removed from the setter, and 500 samples were sampled and inspected. Ceramic sintered bodies that were bonded together and could not be easily peeled off after vibration were deemed defective. The peeled ceramic substrates were then subjected to barrel processing by adding 20,000 ^cm3 of plastic media as abrasive stones, 250 ^{cm3 of} white alundum as abrasive, and 20,000 ^cm3 of water, and rotating at 100 rpm for 15 minutes. After barrel processing, the ceramic sintered bodies were washed with water and dried to obtain ceramic substrates. The warpage of the obtained ceramic substrates was measured, and those with a warpage of 2 μm/mm or more were deemed defective. Table 2 shows the sintering failure rate and warpage failure rate.

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 EDX was used to analyze the mass % of boron (B) 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.

Next, the ceramic substrate was metallized, and the bonding strength was measured. For the thin film, titanium 0.1 μm, platinum 0.2 μm, and gold 0.3 μm were deposited in this order using an electron beam deposition device, and a pattern was formed by etching. For the high-melting-point metal, a high-melting-point metal paste containing molybdenum and titanium nitride 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 for bonding strength measurement, measuring 50 mm long, 3 mm wide, and 0.3 mm thick, was soldered so that a portion of the copper plate was bonded to the metallized layer.

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

The copper plate used to measure the strength of each metallized substrate was bent upward at a right angle and pulled upward at a rate 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.

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 compacts were stacked horizontally and sintered without using a release agent, causing them to react with each other and adhere to each other.

Furthermore, as can be seen from Table 2, in the examples, there was no warpage defect rate, or even if there was, it was small and within a desirable range. This is because the ratio of width W to height H (W/H) was small, so even when aligned vertically there was no deformation and the amount of warpage was small. On the other hand, in comparative examples 3 and 4, there was a lot of warpage defect. This is because the ratio of width W to height H (W/H) was large, so deformation occurred even when aligned vertically, resulting in a large amount of warpage.

Furthermore, as can be seen from Table 2, in the Examples, the amount of boron detected was either below the measurement limit or was a low value of 2 mass% or less. On the other hand, in Comparative Examples 2 and 5, the values were high. Under the alignment conditions in the Examples, a boron nitride setter was not used, or even if one was used, no release agent was used, resulting in a small amount of detection. In contrast, in Comparative Examples 2 and 5, a release agent was used, which resulted in residual boron nitride being detected as boron.

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 surface of the nitride ceramic substrate, inhibiting the metallization reaction and reducing the bonding strength.

As is clear from the results shown above, the examples showed less deformation such as warping and better metallization properties than the comparative examples.

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

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.

1... nitride ceramic substrate 11... flat portion, 111... metallized portion, 112... non-metallized portion 12... side portion, 121... long side portion, 122... short side portion 13... long side 14... short side 15... height 2... frame setter 3... bottom plate setter 4... mold release agent 5... metallized

Claims (10)

A method for manufacturing a nitride ceramic substrate having a flat portion on at least one surface of which a metallization is formed and a side portion formed substantially perpendicular to the flat portion , comprising:
an aligning step of placing the plurality of nitride ceramic substrate compacts so that their side surfaces are in contact with a ceramic setter without using a mold release agent ;
a degreasing step of degreasing the compact placed on the ceramic setter at 800°C or less to obtain a degreased body;
a sintering step of sintering the degreased body placed in a ceramic setter at 1600°C or higher to obtain a sintered body;
Equipped with
A method for manufacturing a nitride ceramic substrate, characterized in that the ratio (W/H) of the width (W), which is the distance from the installation surface of the side surface of the molded body to the end furthest vertically, to the height (H) of the planar portion of the installed molded body is 20 or less . 2. The method for manufacturing a nitride ceramic substrate according to claim 1, wherein the ceramic setter is made of a common material having a reduced amount of sintering aid compared to the composition of the nitride ceramic substrate. A method for manufacturing a nitride ceramic substrate according to claim 1 or 2, characterized in that the nitride ceramic substrate is an aluminum nitride substrate or a silicon nitride substrate. 3. The method for producing a nitride ceramic substrate according to claim 1, wherein the mold release agent is boron nitride. A method for manufacturing a nitride ceramic metallized substrate, characterized in that metallization is formed on the surface of a nitride ceramic substrate produced by the method for manufacturing a nitride ceramic substrate described in claim 1 or 2. A method for manufacturing a nitride ceramic metallized substrate, characterized in that metallization is formed on the surface of a nitride ceramic substrate produced by the nitride ceramic substrate manufacturing method described in claim 3. 3. A method for producing a nitride ceramic substrate according to claim 1 , wherein boron nitride diffused from a setter is not present on the surface of the nitride ceramic substrate on which metallization is formed. 4. A method for producing a nitride ceramic substrate according to claim 3 , wherein boron nitride diffused from the setter is not present on the surface of the nitride ceramic substrate on which metallization is to be formed . A method for producing a metallized nitride ceramic substrate, comprising forming a metallization on the nitride ceramic substrate according to claim 7. A method for producing a metallized nitride ceramic substrate, comprising forming a metallization on the nitride ceramic substrate according to claim 8.