Surface treatment method for boron nitride plate, manufacturing method for ceramic sintered body, and manufacturing method for boron nitride plate

Abstract

A boron nitride plate surface treatment method according to an embodiment comprises a first polishing step and a second polishing step. In the first polishing step, a surface of a boron nitride plate is polished using a first polishing member having a grit in the range of F120 to F220 inclusive, or #240 to #320 inclusive. In the second polishing step, said surface of the boron nitride plate is polished using a second polishing member having a grit in the range of #360 to #1000 inclusive. The second polishing step is performed after the first polishing step. The boron nitride plate is suitable for a method for manufacturing a silicon nitride substrate. In the first polishing step, a pressing amount of the first polishing member preferably lies in the range of 0.2 mm to 1.0 mm inclusive, and a processing point speed preferably lies in the range of 80 mm / s to 180 mm / s inclusive.

Description

[Technical Field]

[0001] The embodiments described below generally relate to a surface treatment method for a boron nitride plate, a manufacturing method for a ceramic sintered body, and a manufacturing method for a boron nitride plate. [Background technology]

[0002] Ceramic substrates are used for circuit boards on which semiconductor elements are mounted. Various ceramic substrates are used, including silicon nitride substrates, aluminum nitride substrates, aluminum oxide substrates, zirconium oxide substrates, and aluzirconia substrates. Aluzirconia substrates are substrates made by mixing zirconium oxide and aluminum oxide.

[0003] The manufacturing process of a ceramic substrate includes a raw material mixing step, a molding step, a debinding step, and a sintering step. The raw material mixing step is a step of mixing raw material powder with an organic binder to prepare a raw material paste. The molding step is a step of preparing a sheet-shaped compact from the raw material paste. The debinding step is a step of removing the binder from the sheet-shaped compact. The sintering step is a step of sintering the sheet-shaped compact after debinding.

[0004] In the degreasing and sintering processes, the sheet-shaped compact is placed on a mounting plate. In International Publication No. 2013 / 146789 (Patent Document 1), a boron nitride plate is used as the mounting plate. In the sintering process of a ceramic substrate, the temperature generally reaches a high temperature of about 1600 to 2000°C. A boron nitride plate is used for the mounting plate because of its excellent durability at high temperatures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 146789 Summary of the Invention [Problem to be solved by the invention]

[0006] When boron nitride plates used as mounting plates are used repeatedly, foreign matter adheres to the surface. The foreign matter adheres from the ceramic sintered body to the boron nitride plate. The presence of foreign matter on the boron nitride plate deteriorates the surface flatness of the ceramic substrate placed on the boron nitride plate. For this reason, a process of periodically removing foreign matter from the surface of the boron nitride plate has been performed. Honing has been used as a surface treatment method for boron nitride plates. Honing is a polishing method using abrasive grains. While this method was successful in removing foreign matter, it increased the surface irregularities of the boron nitride plate. As the surface irregularities of the boron nitride plate increased, the surface irregularities of the ceramic substrate also increased. For this reason, a surface treatment method for boron nitride plates that can suppress the increase in surface irregularities was needed. [Means for solving the problem]

[0007] The surface treatment method for a boron nitride plate according to the embodiment includes a first polishing step and a second polishing step. In the first polishing step, the surface of the boron nitride plate is polished using a first polishing member having a grit size in the range of F120 to F220 or #240 to #320. In the second polishing step, the surface of the boron nitride plate is polished using a second polishing member having a grit size in the range of #360 to #1000. The second polishing step is performed after the first polishing step. [Brief explanation of the drawings]

[0008] [Figure 1] 1A to 1C are diagrams showing an example of a surface treatment method for a boron nitride plate according to an embodiment. [Figure 2] FIG. 10 is a diagram showing an example in which a ceramic compact is placed on a boron nitride plate. [Figure 3] FIG. 10 is a view showing another example in which a ceramic compact is placed on a boron nitride plate. [Figure 4] FIG. 2 is a diagram showing an example of black whiskers on the surface of a boron nitride plate. [Figure 5] 1 is a flowchart showing a processing method according to an embodiment. [Figure 6] 3 is a flowchart showing a method for manufacturing a ceramic sintered body according to an embodiment. [Figure 7] 3 is a flowchart showing a surface treatment method for a boron nitride plate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The surface treatment method for a boron nitride plate according to the embodiment includes a first polishing step and a second polishing step. In the first polishing step, the surface of the boron nitride plate is polished using a first polishing member having a grit size in the range of F120 to F220 or #240 to #320. In the second polishing step, the surface of the boron nitride plate is polished using a second polishing member having a grit size in the range of #360 to #1000. The second polishing step is performed after the first polishing step.

[0010] An example of a surface treatment method for a boron nitride plate is shown in Figure 1. In Figure 1, 1 is a boron nitride plate and 2 is abrasive paper. The boron nitride plate 1 is made of a boron nitride sintered body. FIG. 1 shows a square boron nitride plate 1. The shape of the boron nitride plate 1 is not limited to the example shown in the figure. The shape of the boron nitride plate 1 may be a square, rectangle, triangle, pentagon, hexagon, circle, ellipse, or the like. The shape of the boron nitride plate 1 is arbitrary as long as it is a shape in which a ceramic molded body can be placed. The length and width of the boron nitride plate 1 are selected appropriately depending on the size and number of the ceramic molded bodies to be placed.

[0011] The thickness of the boron nitride plate 1 is preferably 0.5 mm or more. If the thickness is less than 0.5 mm, the strength of the boron nitride plate 1 may decrease. There is no particular upper limit to the thickness of the boron nitride plate 1, but it is preferably 10 mm or less. If the boron nitride plate 1 is thicker than 10 mm, the space available for placing the ceramic molded body in the processing chamber for the degreasing or sintering step may become small. For this reason, the thickness of the boron nitride plate 1 is preferably in the range of 0.5 mm to 10 mm, and more preferably in the range of 0.8 mm to 5 mm.

[0012] Examples of abrasive members include abrasive paper, abrasive cloth, abrasive resin film, and grinding stone. Abrasive paper is a member in which an abrasive material is fixed to the surface of paper. Abrasive cloth is a member in which an abrasive material is fixed to the surface of cloth. Abrasive resin film is a member in which an abrasive material is fixed to the surface of resin film. A grinding stone is a member in which abrasive materials are bonded together with a binder. Abrasive materials are used in all of these abrasive members.

[0013] The size of abrasives is expressed by grit. The grit is indicated by a number followed by either "F" or "#." The smaller the grit number, the coarser the abrasive. The grit is determined by the particle size of the abrasive. Grits are specified in JIS-R-6001-1 (2017) and JIS-R-6001-2 (2017). For abrasive paper, JIS-R-6252 (2006), JIS-R-6253 (2006), JIS-R-6111 (2020), JIS-R-6010 (2020), and JIS-R-6004 (2020) are referenced. These JIS standards correspond to ISO3366 (1999), ISO21948 (2001), ISO21950 (2001), etc.

[0014] The JIS standard distinguishes between coarse grain abrasives used for grits of F220 and below, and fine grain abrasives used for grits of #240 and above. The particle size of abrasives (abrasive grains) between F120 and F220 is determined by sieving. Furthermore, the particle size of abrasives (grains) between #240 and #1000 is determined by the sedimentation tube test method.

[0015] For example, the nominal opening of the first test sieve of F120, which allows all abrasive material to pass through, is defined as 180 μm. The nominal opening of the fifth test sieve is defined as 63 μm. The nominal opening of the fifth test sieve is also defined as the nominal opening at which the maximum mass fraction of abrasive material passing through the fifth sieve is 3%.

[0016] The nominal opening of the first test sieve of F220, through which all abrasives pass, is defined as 106 μm. The nominal opening of the third test sieve is defined as 53 μm. The nominal opening of the fourth test sieve is defined as 43 μm. The minimum mass fraction of abrasives that must be retained on the third and fourth sieves combined is defined as 60%.

[0017] For #240 to #1000, the particle size is determined by the sedimentation tube test method. For example, for #240, the particle size at a cumulative height fraction of 50% (d 50 ) is defined as 60 μm ± 4.0 μm. For #320, the particle diameter at 50% cumulative height fraction (d 50 ) is defined as 46 μm ± 2.5 μm. For #360, the particle diameter at 50% cumulative height fraction (d 50 ) is defined as 40 μm ± 2.0 μm. For #1000, the particle diameter at 50% cumulative height fraction (d 50 ) is defined as 15.5 μm ± 1.0 μm.

[0018] The abrasive material used is aluminum oxide, zirconium oxide, silicon carbide, etc. When the ceramic molded body is an oxide-based ceramic, the abrasive material is preferably aluminum oxide or zirconium oxide. When the ceramic molded body is a nitride-based ceramic, the abrasive material is preferably silicon carbide.

[0019] The abrasive member is preferably abrasive paper. Abrasive paper is also called sandpaper or emery paper. Abrasive paper uses paper as the base material. In the process of pressing an abrasive member against the boron nitride plate 1 to polish it, if the base material is paper, the polished surface of the boron nitride plate 1 is less affected by the unevenness of the base material. This makes it easier to obtain a flat surface for the boron nitride plate 1. If the base material is cloth, the polished surface of the boron nitride plate 1 is affected by the thickness of the cloth fibers. Furthermore, abrasive paper is cheaper than abrasive cloth. Abrasive resin films or grinding wheels are even more expensive than abrasive cloth.

[0020] When polishing with a certain pressure, the abrasive paper and abrasive cloth may break. The frequency of replacing the abrasive paper and the abrasive cloth is about the same. For this reason, it is preferable to use abrasive paper. 、 An example will be described in which abrasive paper is used as the abrasive member. When an abrasive cloth, an abrasive resin film, or a grindstone is used, the abrasive paper in the following description can be read as these abrasive members.

[0021] FIG. 1 shows an example in which the abrasive paper 2 is attached to a roller. In addition to a roller, the abrasive paper 2 may be attached to a rotating disk. By performing the polishing process mechanically using a mounting jig such as a roller or rotating disk, it is possible to suppress uneven polishing. It is more preferable to attach the abrasive paper 2 to a roller rather than a rotating disk. By matching the length of the roller to the length of the boron nitride plate 1, it is possible to further suppress uneven polishing. Furthermore, a polishing belt may be formed using multiple rollers.

[0022] The surface treatment method for a boron nitride plate according to the embodiment includes a first polishing step and a second polishing step. The first polishing step is a step of polishing the surface of the boron nitride plate using a first polishing paper. First, the surface is polished with a first polishing paper having a grit size in the range of F120 to F220 or #240 to #320. The first polishing paper is an example of a first polishing member. If the grit size is smaller than F120, the abrasive grain is coarse, and polishing marks are likely to be formed on the surface of the boron nitride plate 1. If the grit size is larger than #320, the abrasive grain is fine, and polishing the surface of the boron nitride plate 1 takes time. For this reason, the grit size of the first polishing paper used in the first polishing step is preferably in the range of F120 to F220 or #240 to #320. More preferably, the grit size of the first polishing paper is in the range of #220 to #280.

[0023] The second polishing step is a step of polishing the surface of the boron nitride plate 1 using a second abrasive paper. After the first polishing step, the surface is polished with a second abrasive paper having a grit size in the range of #360 to #1000. The second abrasive paper is an example of a second abrasive member. If the grit size is smaller than #360, the second polishing step will be the same as the first polishing step. If the grit size is larger than #1000, the abrasive grain will be finer, and it will take a long time to polish the surface of the boron nitride plate 1. For this reason, the grit size of the second abrasive paper used in the second polishing step is preferably in the range of #360 to #1000, and more preferably in the range of #400 to #800.

[0024] The second polishing step is a step in which the surface that has been subjected to the first polishing step is further polished. In other words, the surface of the boron nitride plate 1 is subjected to two polishing steps, the first polishing step and the second polishing step. The grit size of the abrasive paper used in the second polishing step is larger than that of the abrasive paper used in the first polishing step. After the first polishing step using coarse abrasive paper, the second polishing step using fine abrasive paper is performed. This makes it possible to improve the flatness of the boron nitride plate 1.

[0025] In the first polishing step, the pressing amount of the first abrasive paper is preferably in the range of 0.2 mm to 1.0 mm, and the processing point speed is preferably in the range of 80 mm / s to 180 mm / s. The pressing amount of the abrasive paper refers to the force pressing the abrasive paper 2 perpendicularly against the boron nitride plate 1. The roller around which the abrasive paper 2 is wrapped is called the polishing roller. The pressing amount refers to the distance the polishing roller is pressed against the boron nitride plate 1 when placed on top of it. When the pressing amount is in the range of 0.2 mm to 1.0 mm, both flatness and polishing efficiency can be achieved. When the pressing amount is less than 0.2 mm, the pressing force is insufficient, which may reduce polishing efficiency. When the pressing amount exceeds 1.0 mm, over-polishing may occur, resulting in large unevenness on the polished surface. For this reason, in the first polishing step, the pressing amount of the abrasive paper is preferably in the range of 0.2 mm to 1.0 mm, and more preferably in the range of 0.3 mm to 0.7 mm.

[0026] The amount of pressure can be adjusted by the hardness of the roller body of the polishing roller and the pressure applied. The roller body refers to the roller body to which the abrasive paper is attached. The roller body can be made of various materials, such as rubber, metal, and ceramics. The roller body is preferably made of rubber. A rubber roller body can prevent damage to the ceramic substrate. If the roller body is made of rubber, its hardness is preferably within the range of 10° to 90°. The method for measuring rubber hardness is specified in JIS-K-6253-3 (2012). JIS-K-6253-3 corresponds to ISO7619-1 (2010). The pressure applied is preferably within the range of 10 N (Newton) to 200 N.

[0027] The processing point speed is the distance the abrasive paper moves per unit time. The unit "mm / s" indicates the distance (mm) the abrasive paper moves per second. For example, if the abrasive paper is wound around a roller, the unit "mm / s" indicates the rotational speed of the roller. If the abrasive paper is attached to a rotating disk, the unit "mm / s" indicates the rotational speed of the rotating disk. The processing point speed is a parameter for controlling the stress when the abrasive paper 2 contacts the boron nitride plate 1. If the processing point speed is in the range of 80 mm / s or more and 180 mm / s or less, the processing efficiency can be improved. If the processing point speed is less than 80 mm / s, the processing efficiency may decrease. If the processing point speed is too fast and exceeds 180 mm / s, processing variations may occur, and the unevenness of the surface of the boron nitride plate 1 may become large. For this reason, the processing point speed is preferably in the range of 80 mm / s or more and 180 mm / s or less, and more preferably in the range of 100 mm / s or more and 150 mm / s or less. point By adjusting the speed and the amount of pressure of the abrasive paper in combination, a synergistic effect can be obtained.

[0028] In the second polishing step, the pressing amount of the abrasive paper is preferably in the range of 0.2 mm to 1.0 mm, and the processing point speed is preferably in the range of 20 mm / s to 100 mm / s. The pressing amount in the second polishing step is preferably in the range of 0.2 mm to 1.0 mm, and more preferably in the range of 0.3 mm to 0.7 mm. The processing point speed in the second polishing step is preferably in the range of 20 mm / s to 100 mm / s, and more preferably in the range of 30 mm / s to 80 mm / s. In the second polishing step, too, the processing efficiency can be improved by controlling the pressing amount and the processing point speed.

[0029] The processing point speed in the first polishing step is preferably faster than the processing point speed in the second polishing step. The grit size of the abrasive paper used in the first polishing step is smaller than that of the abrasive paper used in the second polishing step. Therefore, the first polishing step results in a rougher finish than the second polishing step. By increasing the processing point speed in the first polishing step, the surface can be roughly processed in a shorter time while reducing the unevenness of the surface of the boron nitride plate. Furthermore, if the surface is roughly processed in the first polishing step, it becomes easier to finish the surface with abrasive paper of a larger grit size in the second polishing step. In this case, by slowing the processing point speed, a flatter surface can be obtained.

[0030] By subjecting the boron nitride plate 1 to the above-described polishing process, a flat surface can be obtained. A "flat surface" means that there are no recesses with a depth of 40 μm or more. Furthermore, a flat surface free of acicular silicon nitride crystal particles can be obtained on the surface of the boron nitride plate 1. Furthermore, a third polishing process may be performed as necessary after the second polishing process. In the third polishing process, a polishing member with a larger grit size is used compared to the second polishing process.

[0031] The boron nitride plate 1 is used during the debinding or sintering process of a ceramic compact. During these processes, the ceramic compact is placed on top of the boron nitride plate 1. The debinding and sintering processes are also heating processes. Applying heat to the ceramic compact causes grain growth of the ceramic raw powder and shrinkage of the compact. If the surface of the boron nitride plate 1 has a recessed portion with a depth of 40 μm or more, it is likely that a protrusion of 40 μm or more will form in the resulting ceramic sintered body. When the ceramic sintered body is plate-shaped, it is undesirable for a protrusion of 40 μm or more to form. A plate-shaped ceramic sintered body is known as a ceramic substrate. Ceramic substrates can be bonded to metal plates to form ceramic circuit boards. Furthermore, a pressure-welded module structure can be formed by pressure-welding semiconductor devices to the ceramic substrate. The ceramic substrate used in a pressure-welded module structure is a single plate without a metal plate.

[0032] In a ceramic circuit board, a brazing material layer is used to bond the ceramic substrate and the metal plate. Large protrusions on the surface of the ceramic substrate can adversely affect the bonding between the ceramic substrate and the metal plate. Furthermore, large protrusions on the surface of a ceramic substrate used in a pressure-welded structure module can adversely affect the adhesion between the ceramic substrate and the semiconductor element. For this reason, it is preferable that the surface of the ceramic substrate does not have protrusions of 40 μm or more. In other words, the boron nitride plate 1 according to the embodiment is suitable for use in a process for obtaining a ceramic substrate.

[0033] For this reason, it is preferable that there are no recesses on the surface of the boron nitride plate that are 40 μm or deeper. Recesses that are 40 μm or deeper are mainly formed by the polishing process. For this reason, recesses that are 40 μm or deeper on the surface of the boron nitride plate 1 are sometimes called polishing marks. Recesses that are 40 μm or deeper on the surface of the boron nitride plate 1 are measured using a three-dimensional shape measuring machine. The entire surface of the boron nitride plate 1 on which the ceramic compact is placed is measured. The three-dimensional shape measuring machine used is a Keyence One-Shot 3D Shape Measuring Machine VR Series or an equivalent device.

[0034] The absence of recesses of 40 μm or more in depth on the surface of the boron nitride plate means that there are no recesses of 40 μm or more in depth in the locations where the ceramic molded body is to be placed. In other words, recesses of 40 μm or more in depth may exist in the locations where the ceramic molded body is not to be placed. Furthermore, it is most preferable that there are no recesses of 40 μm or more in depth on the entire surface of the boron nitride plate. This eliminates restrictions on the location where the ceramic molded body can be placed.

[0035] It is preferable that the surface of the boron nitride plate 1 be free of acicular silicon nitride crystal particles. During the sintering process of a ceramic molded body, the ceramic raw material powder undergoes grain growth. In particular, in the case of a silicon nitride molded body, round silicon nitride powder transforms into elongated silicon nitride crystal particles. These elongated silicon nitride crystal particles grow to an aspect ratio of 2 or greater. Silicon nitride crystal particles with an aspect ratio of 2 or greater are called acicular silicon nitride crystal particles. The elongated silicon nitride crystal particles are primarily composed of beta-type silicon nitride crystal particles. The acicular silicon nitride crystal particles that grow during the sintering process form convex portions on the surface of the silicon nitride sintered body. These convex portions pierce the boron nitride plate 1, resulting in the presence of acicular silicon nitride crystal particles on the surface of the boron nitride plate 1. Acicular silicon nitride crystal particles are a hard substance. The first and second polishing processes are also effective in removing acicular silicon nitride crystal particles from the surface of the boron nitride plate 1. In particular, by using abrasive paper containing a silicon carbide abrasive, acicular silicon nitride crystal particles can be efficiently removed. In other words, the surface treatment method for a boron nitride plate according to the embodiment is suitable for a boron nitride plate used in the degreasing process or sintering process of a silicon nitride molded body.

[0036] The presence or absence of acicular silicon nitride crystal particles on the surface of the boron nitride plate 1 can be analyzed by energy dispersive X-ray analysis (EDX). The presence or absence of silicon on the surface of the boron nitride plate 1 can be determined. The presence or absence of acicular silicon nitride crystal particles can also be confirmed by observing the areas where silicon is detected with a scanning electron microscope (SEM). For example, if the boron nitride plate does not contain a sintering aid, the presence or absence of acicular silicon nitride crystal particles can be confirmed by EDX analysis alone. If the boron nitride plate contains a sintering aid, the presence or absence of acicular silicon nitride crystal particles can be confirmed by a combination of EDX and SEM. The entire surface of the boron nitride plate on which the ceramic compact is placed is analyzed to confirm the presence or absence of acicular silicon nitride crystal particles.

[0037] For SEM-EDX, a Keyence VE9800 or equivalent device is used. During observation, the magnification is set to 200x and the applied voltage is set to 12kV. Furthermore, in areas where the silicon nitride content is determined to be below the detection limit by SEM-EDX, it is determined that no acicular silicon nitride crystal particles are present. For simplicity, this determination can also be made based on the amount of silicon. Acicular nitride silicon It is effective that crystal grains do not exist in the area where the ceramic molded body is placed. silicon The absence of crystal grains increases the degree of freedom in the placement of the ceramic molded body. silicon Preferably, no crystalline particles are present.

[0038] Figure 4 shows an example of acicular silicon nitride crystal particles and polishing marks. In Figure 4, 4 is an acicular silicon nitride crystal particle, and 5 is a polishing mark. When a surface measured with a 3D shape measuring instrument is color-mapped, the acicular silicon nitride crystal particles 4 and polishing marks 5 appear to have different colors due to the difference in elevation from other parts. For example, when measured with the default settings of a Keyence One-Shot 3D Shape Measuring Instrument VR Series, the acicular silicon nitride crystal particles 4 appear red because they are convex. Furthermore, the polishing marks 5 appear blue because they are concave.

[0039] By applying the surface treatment method according to the embodiment to a boron nitride plate 1, the amount of warpage of the boron nitride plate 1 can be reduced to 0.1 mm or less. Furthermore, by applying the surface treatment method according to the embodiment to a boron nitride plate 1, the maximum height roughness Rz of the boron nitride plate 1 can be reduced to 40 μm or less. The amount of warpage of the boron nitride plate 1 is the flatness defined in JIS-B-0621 (1984). The maximum height roughness Rz is defined in JIS-B-0601 (2013). The amount of warpage and the maximum height roughness Rz are also measured using a three-dimensional shape measuring instrument. JIS-B-0601 (2013) corresponds to ISO 4287 (2009).

[0040] When the warpage of the boron nitride plate 1 is 0.1 mm or less, the warpage of the resulting ceramic sintered body can be reduced. Furthermore, when the maximum height roughness Rz of the boron nitride plate 1 is 40 μm or less, the maximum number of surface protrusions of the resulting ceramic sintered body can be reduced to 20 μm or less. By controlling the warpage and maximum height roughness Rz of the boron nitride plate 1, the warpage and surface protrusions of the resulting ceramic sintered body can be reduced. Reducing the warpage and reducing the surface protrusions is effective for producing ceramic substrates with a thickness of 1 mm or less. In other words, the surface treatment method according to the embodiment is suitable for boron nitride plates 1 for producing ceramic substrates with a thickness of 1 mm or less. Furthermore, by setting the maximum height roughness Rz of the boron nitride plate 1 to 40 μm or less, acicular silicon nitride crystal particles can be made less likely to be stuck. Therefore, the warpage of the boron nitride plate is preferably 0.1 mm or less, and more preferably 0.06 mm or less. The maximum height roughness Rz of the boron nitride plate is preferably 40 μm or less, and more preferably 20 μm or less. Furthermore, when a boron nitride plate is subjected to a degreasing process or a sintering process, the surface of the boron nitride plate 1 deteriorates. The surface treatment method according to the embodiment is effective when applied after the boron nitride plate 1 has deteriorated or before any signs of deterioration appear. This can improve the yield of ceramic substrates.

[0041] A boron nitride plate that has been subjected to the above-described surface treatment method can be used in a method for manufacturing a sintered ceramic body. The manufacturing process for a sintered ceramic body includes a raw material mixing step, a molding step, a degreasing step, and a sintering step. The raw material mixing step is a step of preparing a raw material paste by mixing raw material powder with an organic binder. The molding step is a step of preparing a ceramic molded body from the raw material paste. The degreasing step is a step of removing the binder from the ceramic molded body. The sintering step is a step of sintering the degreased ceramic molded body. The degreasing and sintering steps are performed by placing the ceramic molded body on a boron nitride plate 1. Figures 2 and 3 show an example of a ceramic molded body placed on a boron nitride plate.

[0042] In Figures 2 and 3, 1 denotes a boron nitride plate and 3 denotes a ceramic molded body. Figure 2 shows an example in which a single-layer ceramic molded body is placed on a boron nitride plate. Figure 3 shows an example in which ceramic molded bodies are stacked on top of a boron nitride plate. A weight plate (not shown) may be placed on the ceramic molded body 3. A boron nitride plate may also be used as the weight plate. A structure in which boron nitride plates 1 and ceramic molded bodies 3 are alternately stacked, such as boron nitride plate 1 / ceramic molded body 3 / boron nitride plate 1 / ceramic molded body 3, may also be used. When ceramic molded bodies 3 are stacked on top of each other, a bedding powder may be placed between the ceramic molded bodies 3. The use of a weight plate also has the effect of suppressing warping of the ceramic sintered body. Similarly, alternate stacking of boron nitride plates 1 and ceramic molded bodies 3 also has the effect of suppressing warping of the ceramic sintered body. Suppressing warpage is suitable for producing a plate-shaped ceramic sintered body, which is referred to herein as a ceramic substrate.

[0043] Ceramic substrates include silicon nitride substrates, aluminum nitride substrates, aluminum oxide substrates, zirconium oxide substrates, and alu-zir substrates. Silicon nitride substrates and aluminum nitride substrates are called nitride-based ceramic substrates. Aluminum oxide substrates, zirconium oxide substrates, and alu-zir substrates are called oxide-based ceramic substrates. They are classified according to the component content of 50% by mass or more. The component content of 50% by mass or more is the main component. For example, a ceramic substrate containing 50% by mass or more of silicon nitride is called a silicon nitride substrate.

[0044] A method for manufacturing a ceramic substrate will be described below by way of example. The manufacturing process for a ceramic substrate includes a raw material mixing step, a molding step, a degreasing step, and a sintering step. In the raw material mixing step, a raw material powder is prepared by mixing ceramic powder, which is the main component, with sintering aid powder. An organic binder is mixed with the raw material powder to prepare a raw material paste. In the molding step, a sheet-shaped ceramic molded body is prepared from the raw material paste. Methods for preparing the sheet-shaped ceramic molded body include the doctor blade method, mold molding method, and injection molding method. When manufacturing a ceramic substrate with a thickness of 1 mm or less, it is preferable to use the doctor blade method. If necessary, the sheet-shaped ceramic molded body is cut.

[0045] The boron nitride plate subjected to the surface treatment method according to the embodiment can be used as a member for placing a ceramic molded body in the degreasing step or the sintering step. The boron nitride plate may be used in both the degreasing step and the sintering step. In other words, after placing a ceramic molded body on the boron nitride plate and performing the degreasing step, the sintering step can be performed directly.

[0046] The degreasing step is a step of removing the binder from the sheet-shaped ceramic compact. Here, the sheet-shaped ceramic compact is simply referred to as the ceramic compact 3. The ceramic compact 3 is placed on the boron nitride plate 1. The degreasing step is preferably carried out at a temperature in the range of 350°C to 600°C. The organic binder is removed by the degreasing step.

[0047] The sintering process is a process in which the degreased ceramic compact 3 is sintered. The sintering process is preferably carried out within a temperature range of 1600°C to 2000°C. The sintering process may be carried out in a vacuum, in air, or in an inert atmosphere. The pressure during the sintering process may be normal pressure or pressurized. During the sintering process, the ceramic powder undergoes grain growth. When producing a silicon nitride substrate, round silicon nitride powder grains grow into elongated silicon nitride crystal particles. The aspect ratio of these elongated silicon nitride crystal particles is 1.5 or more, or even 2 or more. Here, silicon nitride crystal particles with an aspect ratio of 1.5 or more are referred to as acicular silicon nitride crystal particles.

[0048] The acicular silicon nitride crystal particles that grow during the sintering process become convex portions on the surface of the silicon nitride sintered body. These convex portions pierce the boron nitride plate 1, resulting in the presence of acicular silicon nitride crystal particles on the surface of the boron nitride plate. Placing a weight plate on the silicon nitride molded body improves adhesion between the boron nitride plate 1 and the silicon nitride molded body. Improved adhesion is effective in preventing warping of the silicon nitride substrate. However, it also makes it easier for acicular silicon nitride crystal particles to pierce the boron nitride plate 1. The presence of acicular silicon nitride crystal particles on the surface of the boron nitride plate 1 can adversely affect the resulting silicon nitride substrate and potentially reduce yield. Improved adhesion can also be achieved by stacking silicon nitride molded bodies together or by using a layered structure of the boron nitride plate 1 and the ceramic molded body 3. However, it also makes it easier for acicular silicon nitride crystal particles to pierce the boron nitride plate.

[0049] By subjecting a boron nitride plate to the surface treatment according to the embodiment, it is possible to obtain a surface on the boron nitride plate 1 that is less susceptible to penetration by acicular silicon nitride crystal particles. If there are recesses on the surface of the boron nitride plate 1, these regions are more likely to be penetrated by acicular silicon nitride crystal particles. By setting the maximum height roughness Rz of the boron nitride plate to 40 μm or less, it is possible to obtain a surface that is less susceptible to penetration by acicular silicon nitride crystal particles. If the surface is less susceptible to penetration by acicular silicon nitride particles, the boron nitride plate 1 can be used repeatedly. This reduces the frequency of surface treatment of the boron nitride plate, leading to improved efficiency and reduced costs.

[0050] In the production of aluminum nitride substrates, aluminum oxide substrates, and zirconium oxide substrates, crystal grain growth occurs, similar to the production of silicon nitride substrates. However, these substrates mainly consist of crystal grains with an aspect ratio of less than 2. Therefore, compared to silicon nitride substrates, there is a lower possibility that needle-shaped crystal grains will pierce the boron nitride substrate 1. In other words, the surface treatment method according to the embodiment and the method for producing a ceramic sintered body using the same are suitable for producing silicon nitride substrates.

[0051] The obtained ceramic sintered body is preferably plate-shaped, with a warpage of 0.1 mm or less and a maximum surface projection of 20 μm or less. According to the method for producing a ceramic sintered body described above, the warpage of the plate-shaped ceramic sintered body can be reduced to 0.1 mm or less. Furthermore, the maximum surface projection of the plate-shaped ceramic sintered body can be reduced to 20 μm or less. The plate-shaped ceramic sintered body is a ceramic substrate. Most ceramic substrates have a thickness of 1 mm or less. When a silicon nitride substrate is used as the ceramic substrate, the thickness of the silicon nitride substrate can be further reduced to 0.1 mm or more and 0.4 mm or less. According to the method for producing a ceramic sintered body according to the embodiment, ceramic substrates with a thickness of 1 mm or less, or even 0.4 mm or less, can be used, thereby reducing the warpage and surface projection. This improves yield. Furthermore, the frequency of surface treatment of the boron nitride plate 1 can be reduced, thereby reducing costs.

[0052] The amount of warpage and maximum value of the surface convexity of the silicon nitride substrate are also measured using a three-dimensional shape measuring device. Although the manufacturing method for a silicon nitride substrate has been exemplified above, the manufacturing method described can also be applied to other ceramic substrates in the same way.

[0053] FIG. 5 is a flowchart showing a processing method according to an embodiment. As shown in FIG. 5, first, a boron nitride plate is prepared (step S1). The boron nitride plate can be obtained, for example, by sintering a molded body containing boron nitride powder. Commercially available boron nitride plates may also be used. Next, a ceramic sintered body is manufactured using the boron nitride plate (step S2). After manufacturing the ceramic sintered body, the boron nitride plate is surface-treated (step S3). Thereafter, a ceramic sintered body is manufactured again using the treated boron nitride plate (step S2).

[0054] Fig. 6 is a flowchart showing a method for manufacturing a ceramic sintered body according to an embodiment. As shown in Fig. 6, in manufacturing the ceramic sintered body (step S2), a ceramic molded body is placed on a boron nitride plate (step S2a). The ceramic molded body is subjected to a degreasing step and a sintering step (steps S2b and S2c). As a result, a ceramic sintered body is obtained.

[0055] FIG. 7 is a flowchart showing a surface treatment method for a boron nitride plate according to an embodiment. As shown in FIG. 7, a first polishing step (step S3a) is performed on a boron nitride plate used in the production of a ceramic sintered body. Next, a second polishing step (step S3b) is performed on the boron nitride plate. In the production of the ceramic sintered body (step S2), acicular silicon nitride crystal particles are stuck into the surface of the boron nitride plate. These acicular silicon nitride crystal particles can be effectively removed by the first polishing step and the second polishing step. The first polishing step and the second polishing step can reduce the maximum height roughness Rz of the boron nitride plate, thereby reducing the amount of warpage.

[0056] In the flowchart shown in FIG. 5, the production of the ceramic sintered body (step S2) is repeated multiple times as needed. The production of the ceramic sintered body and the surface treatment of the boron nitride plate may be repeated multiple times alternately. By subjecting the boron nitride plate to a surface treatment, the yield of the ceramic sintered body produced thereafter can be improved. Furthermore, if necessary, surface treatment of the boron nitride plate (step S3) may be performed between the preparation of the boron nitride plate (step S1) and the production of the ceramic sintered body (step S2).

[0057] It should be noted that when treating the surface of the boron nitride plate 1, it is not necessary to treat the entire surface. As long as at least the area of ​​the surface of the boron nitride plate 1 where the ceramic molded body will be placed is treated, the area to which the surface treatment is applied can be changed as appropriate. Furthermore, when the boron nitride plate 1 is placed on the ceramic molded body in the production of a ceramic sintered body, there is a possibility that the acicular silicon nitride crystal particles will also prick the back surface of the boron nitride plate 1. For this reason, when the boron nitride plate 1 is placed on the ceramic molded body, it is preferable that the surface treatment method according to the embodiment be applied to the back surface of the boron nitride plate 1 as well.

[0058] (Example) (Examples 1 to 5, Comparative Examples 1 to 3) First, a boron nitride plate was prepared. The boron nitride plate had a length of 240 mm, a width of 180 mm, and a thickness of 1.5 mm. A silicon nitride molded body was prepared as a ceramic molded body. The silicon nitride molded body was formed into a sheet using the doctor blade method. The silicon nitride molded body was placed on the boron nitride plate and subjected to a degreasing process and a sintering process. The degreasing process was carried out at a temperature between 350°C and 600°C. The sintering process was carried out at a temperature between 1600°C and 2000°C. The obtained silicon nitride sintered body was then moved, and another silicon nitride molded body was placed on the same boron nitride plate and subjected to a degreasing process and a sintering process. Each degreasing and sintering process was considered one set and these processes were repeated five times. As a result, several areas where acicular silicon nitride crystal particles had penetrated the surface of the boron nitride plate were observed.

[0059] The boron nitride plate with acicular silicon nitride crystal particles stuck in it was subjected to the surface treatment shown in Table 1. In Examples 1 to 4 and Comparative Examples 2 and 3, abrasive paper was used. The abrasive material was made of silicon carbide. In Example 5, abrasive cloth was used. The abrasive material was made of silicon carbide. The abrasive paper or abrasive cloth was wrapped around the roller body for surface treatment. In Table 1, the symbol F for grit sizes 120 to 220 and the symbol # for grit sizes 240 to 1000 are omitted. In Comparative Example 1, no surface treatment was performed. A rubber roller with a hardness of 10° to 90° was used for the roller body. The pressing amount was adjusted by setting the pressing pressure within the range of 10 N to 200 N.

[0060] [Table 1]

[0061] The surface treatment conditions for Examples 1 to 5 were set within a range that satisfied the conditions of the surface treatment method for boron nitride plates according to the embodiment. In Comparative Example 1, no surface treatment was performed. In Comparative Examples 2 and 3, the polishing step was performed only once. In other words, in Comparative Examples 2 and 3, the second polishing step was not performed.

[0062] After surface treatment, the presence of acicular silicon nitride crystal particles on the surface of the boron nitride plate was confirmed, the amount of warpage of the boron nitride plate was measured, and the presence of any areas with a maximum height roughness Rz exceeding 40 μm was confirmed. The amount of warpage of the boron nitride plate was measured using the flatness standard specified in JIS-B-0621 (1984). The maximum height roughness Rz was measured according to JIS-B-0601 (2013). The amount of warpage and maximum height roughness Rz of the boron nitride plate were measured using a 3D shape measuring instrument. A Keyence VR series one-shot 3D shape measuring instrument was used. The entire surface on which the ceramic compact will be placed was measured using the 3D shape measuring instrument. The presence of acicular silicon nitride crystal particles on the surface of the boron nitride plate was measured using EDX and SEM. For these measurements, the entire surface on which the ceramic compact will be placed was also measured. A Keyence VE9800 SEM-EDX instrument was used. The results are shown in Table 2.

[0063] [Table 2]

[0064] In Examples 1 to 3 and Example 5, the amount of warpage of the boron nitride plates was 0.1 mm or less. No acicular silicon nitride crystal particles or locations where the maximum height roughness Rz exceeded 40 μm were observed. This indicates that the boron nitride plates according to Examples 1 to 3 and Example 5 have a maximum height roughness Rz of 40 μm or less. In Example 4, two recesses with a maximum height roughness Rz exceeding 40 μm were observed. This is thought to be due to the machining point speed being outside the preferred range in Example 4.

[0065] In Comparative Example 1, no surface treatment was performed, and therefore all of the characteristics were poor. In Comparative Examples 2 and 3, only one polishing step was performed. As a result, although the amount of warping could be reduced, there were still acicular silicon nitride crystal grains and portions where the maximum height roughness Rz exceeded 40 μm. Therefore, it was found that performing both the first polishing step and the second polishing step is an effective surface treatment for boron nitride plates.

[0066] Next, silicon nitride substrates were produced using the boron nitride plates of the Example and Comparative Examples. The thickness of the resulting silicon nitride substrates was set to 0.32 mm. A silicon nitride sheet was placed on each of the Example and Comparative Examples. Ten silicon nitride sheet plates were placed on each boron nitride plate, and a weight plate was placed on top of them. A degreasing step at 400°C and a sintering step at 1800°C were performed. After repeating the set of placing the silicon nitride sheet, the degreasing step, and the sintering step five times, the amount of warping of the boron nitride plate was measured, and the presence or absence of acicular silicon nitride crystal particles and the presence or absence of areas where the maximum height roughness Rz exceeded 40 μm were confirmed. Furthermore, after repeating the set eight times, the amount of warping of the boron nitride plate was measured, and the presence or absence of acicular silicon nitride crystal particles and the presence or absence of areas where the maximum height roughness Rz exceeded 40 μm were confirmed. The results are shown in Table 3.

[0067] [Table 3]

[0068] As can be seen from Table 3, for the boron nitride plates subjected to the surface treatment according to the examples, surface deterioration was reduced even when the degreasing process and sintering process were repeated. In particular, for the boron nitride plates according to Examples 1 to 3 and Example 5, surface deterioration was significantly reduced, thereby demonstrating excellent durability. Therefore, the frequency of surface treatment of the boron nitride plates can be reduced.

[0069] Next, the amount of warpage and maximum height roughness Rz of the silicon nitride substrates were examined. Silicon nitride substrates with an amount of warpage of 0.1 mm or less and a maximum height roughness Rz of 20 μm or less were considered "good products." The amount of warpage and maximum height roughness Rz of the silicon nitride substrates were also measured using a three-dimensional shape measuring instrument (Keyence One-Shot 3D Shape Measuring Instrument VR Series). 1,000 silicon nitride substrates were produced for each example and comparative example, and the proportion of good products was examined. The results are shown in Table 4.

[0070] [Table 4]

[0071] As can be seen from Table 4, the silicon nitride substrate manufacturing method according to the example resulted in a high yield of silicon nitride substrates. It was also found that the boron nitride plates were not significantly deteriorated even when used repeatedly. This also contributes to cost reduction.

[0072] Embodiments of the invention include the following features. (Appendix 1) a first polishing step of polishing the surface of the boron nitride plate using a first polishing member having a grit size within the range of F120 to F220 or #240 to #320; a second polishing step of polishing the surface using a second polishing member having a grit size within a range of #360 to #1000 after the first polishing step; A surface treatment method for a boron nitride plate comprising: (Appendix 2) 2. The surface treatment method according to claim 1, wherein the first abrasive member and the second abrasive member are abrasive paper. (Appendix 3) 3. The surface treatment method for a boron nitride plate according to claim 1, wherein in the first polishing step, the pressing amount of the first polishing member is 0.2 mm or more and 1.0 mm or less, and the processing point speed is 80 mm / s or more and 180 mm / s or less. (Appendix 4) 4. The surface treatment method for a boron nitride plate according to claim 1, wherein in the second polishing step, the pressing amount of the second polishing member is 0.2 mm or more and 1.0 mm or less, and the processing point speed is 20 mm / s or more and 100 mm / s or less. (Appendix 5) 5. The surface treatment method for a boron nitride plate according to any one of claims 2 to 4, wherein a processing point speed in the first polishing step is faster than a processing point speed in the second polishing step. (Appendix 6) 6. The surface treatment method for a boron nitride plate according to any one of claims 1 to 5, wherein the surface after the second polishing step is free of acicular silicon nitride crystal particles and free of recesses having a depth of 40 μm or more. (Appendix 7) 7. The surface treatment method for a boron nitride plate according to any one of claims 1 to 6, wherein the amount of warpage of the boron nitride plate after the second polishing step is 0.1 mm or less and the maximum height roughness Rz is 40 μm or less. (Appendix 8) placing a ceramic formed body on the surface treated by the surface treatment method according to any one of Supplementary Note 1 to Supplementary Note 7; degreasing the ceramic compact; sintering the degreased ceramic compact; A method for manufacturing a ceramic sintered body comprising: (Appendix 9) 9. The method for producing a ceramic sintered body according to claim 8, wherein the obtained ceramic sintered body has a plate shape. (Appendix 10) The obtained ceramic sintered body has a plate shape. the amount of warping of the ceramic sintered body is 0.1 mm or less, 10. The method for producing a ceramic sintered body according to any one of claims 8 to 9, wherein the ceramic sintered body has a maximum height roughness Rz of 20 μm or less. (Appendix 11) 11. The method for producing a ceramic sintered body according to any one of claims 8 to 10, wherein the ceramic sintered body is a silicon nitride sintered body. (Appendix 12) A step of preparing a boron nitride plate made of a boron nitride sintered body; a first polishing step of polishing the surface of the boron nitride plate using a first polishing member having a polishing surface roughness of F120 or more and F220 or #240 or more and #320 or less; a second polishing step of polishing the surface using a second polishing member having a polishing surface ... A method for manufacturing a boron nitride plate comprising the steps of:

[0073] 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. These embodiments and their modifications 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]

[0074] 1...Boron nitride plate 2…Abrasive paper 3...Ceramic molding 4...Needle-shaped silicon nitride crystal particles 5...Polishing marks

Claims

1. A surface treatment method for a boron nitride plate used in sintering a ceramic substrate, comprising: a first polishing step of polishing the surface of the boron nitride plate using a first polishing member having a grit size within the range of F120 to F220 or #240 to #320; a second polishing step of polishing the surface using a second polishing member having a grit size within a range of #360 to #1000 after the first polishing step, a processing point speed in the first polishing step is 80 mm / s or more and 180 mm / s or less; a processing point speed in the second polishing step is 20 mm / s or more and 100 mm / s or less; the processing point speed in the first polishing step is faster than the processing point speed in the second polishing step; A surface treatment method for a boron nitride plate, wherein the pressing amount in the first polishing step and the second polishing step is 0.2 mm or more and 1.00 mm or less.

2. 2. The method for treating the surface of a boron nitride plate according to claim 1, wherein said first abrasive member and said second abrasive member are abrasive papers.

3. 3. The surface treatment method for a boron nitride plate according to claim 1, wherein the surface after the second polishing step is free of acicular silicon nitride crystal particles and free of recesses having a depth of 40 μm or more.

4. 3. The surface treatment method for a boron nitride plate according to claim 1, wherein the amount of warpage of the boron nitride plate after the second polishing step is 0.1 mm or less and the maximum height roughness Rz is 40 μm or less.

5. a step of placing a ceramic formed body on the surface treated by the surface treatment method according to any one of claims 1 and 2; degreasing the ceramic compact; sintering the degreased ceramic compact; A method for manufacturing a ceramic sintered body comprising:

6. The amount of warping of the ceramic sintered body is 0.1 mm or less, The method for producing a ceramic sintered body according to claim 5, wherein the maximum height roughness Rz of the ceramic sintered body is 20 μm or less.

7. 6. The method for producing a ceramic sintered body according to claim 5, wherein the ceramic sintered body is a silicon nitride sintered body.

8. A method for manufacturing a boron nitride plate used in sintering a ceramic substrate, comprising: A step of preparing a boron nitride plate made of a boron nitride sintered body; a first polishing step of polishing the surface of the boron nitride plate using a first polishing member having a polishing surface diameter of F120 or more and F220 or less, or a polishing surface diameter of #240 or more and #320 or less; a second polishing step of polishing the surface using a second polishing member having a grit size in the range of #360 to #1000 after the first polishing step, a processing point speed in the first polishing step is 80 mm / s or more and 180 mm / s or less; a processing point speed in the second polishing step is 20 mm / s or more and 100 mm / s or less; the processing point speed in the first polishing step is faster than the processing point speed in the second polishing step; A method for manufacturing a boron nitride plate, wherein the pressing amount in the first polishing step and the second polishing step is 0.2 mm or more and 1.00 mm or less.

9. A surface treatment method for a boron nitride plate for use in manufacturing a ceramic sintered body having a plate shape, a warpage of 0.1 mm or less, and a maximum height roughness Rz of 20 μm or less, comprising: a first polishing step of polishing the surface of the boron nitride plate using a first polishing member having a grit size within the range of F120 to F220 or #240 to #320; a second polishing step of polishing the surface using a second polishing member having a grit size within a range of #360 to #1000 after the first polishing step, a processing point speed in the first polishing step is 80 mm / s or more and 180 mm / s or less; a processing point speed in the second polishing step is 20 mm / s or more and 100 mm / s or less; the processing point speed in the first polishing step is faster than the processing point speed in the second polishing step; A surface treatment method for a boron nitride plate, wherein the pressing amount in the first polishing step and the second polishing step is 0.2 mm or more and 1.00 mm or less.

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