Ceramic substrate, ceramic circuit substrate, semiconductor device, method for producing slurry, and method for applying release agent

Abstract

A ceramic substrate having a first surface and a second surface on the front and back surfaces is characterized in that when a midpoint of a line segment connecting a center portion P1 of the first surface and a center portion P2 of the second surface is defined as a midpoint portion C1, the component amount of a mold release agent measured at the center portion P1 or the center portion P2 is at least five times the component amount of the mold release agent measured at the midpoint portion C1. In addition, it is preferable that the ratio P1 / P2 of the component amount of the release agent measured at the central portion P1 of the first surface to the component amount of the release agent measured at the central portion P2 of the second surface is 0.5 < = P1 / P2 < = 2.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate generally to a ceramic substrate, a ceramic circuit substrate, a semiconductor device, a manufacturing method of a paste, and a release agent coating method. BACKGROUND

[0002] A ceramic substrate is manufactured by mixing raw materials such as ceramic powder and a binder, forming a sheet-shaped ceramic formed body by sheeting, and sintering a plate-shaped ceramic formed body obtained by cutting the sheet-shaped ceramic formed body. In this manufacturing method, a plurality of plate-shaped ceramic formed bodies coated with a release agent are stacked and sintered with the aim of sintering the plate-shaped ceramic formed body in one step. By coating the surface of the green sheet with a release agent, sticking of the resulting ceramic substrate (plate-shaped ceramic sintered body) to each other can be prevented.

[0003] For example, Patent Document 1 describes a method in which a release agent layer obtained by coating a sheet-shaped ceramic formed body with a boron nitride paste is sintered by controlling the composition thereof, thereby obtaining a plate-shaped ceramic sintered body, i.e., a ceramic substrate, having little unevenness.

[0004] On the other hand, in the conventional manufacturing process of a ceramic substrate, scraps generated when a sheet-shaped ceramic formed body coated with a release agent is cut to a target size, sheet-shaped ceramic formed bodies and plate-shaped ceramic formed bodies having defects such as holes, cracks, and excess or insufficient amount of release agent coating observed after the release agent is coated, and the like are discarded as end materials.

[0005] It is preferable to recycle the end materials such as scraps of sheet-shaped ceramic formed bodies and plate-shaped ceramic formed bodies as raw materials for a ceramic substrate for improvement of yield and reduction of waste. However, it is difficult to completely separate the release agent from the end materials generated after the release agent is coated, and the remaining release agent component at the time of recycling becomes a major cause of performance reduction of the ceramic substrate. Such performance reduction has not been understood based on the distribution of the release agent component. For these reasons, recycling of the end materials generated after the release agent is coated is hindered.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent No. 5673847 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] The present application provides a ceramic substrate, a ceramic circuit substrate, a semiconductor device, a manufacturing method of a paste, and a release agent coating method, which are excellent in yield even when containing a release agent component.

[0011] Means for solving the problem

[0012] The ceramic substrate of the embodiment is characterized in that, when a midpoint of a line segment connecting a central portion P1 of the first surface and a central portion P2 of the second surface is set as a midpoint portion C1, a component of the release agent measured at the central portion P1 of the first surface or the central portion P2 of the second surface is 5 times or more of a component of the release agent measured at the midpoint portion C1. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic cross-sectional view showing an example of the ceramic substrate of the embodiment.

[0014] Figure 2 is a schematic view showing an example of the ceramic circuit substrate of the embodiment.

[0015] Figure 3 is a schematic view showing an example of the semiconductor device.

[0016] Figure 4 is a view showing an example of the sheet-shaped ceramic formed body.

[0017] Figure 5 is a view showing an example of a cutting step of cutting the sheet-shaped ceramic formed body.

[0018] Figure 6 is a flowchart showing an example of the manufacturing method of the ceramic sintered body of the embodiment. DETAILED DESCRIPTION

[0019] REFERENCE Figures 1-6 The ceramic substrate, the ceramic circuit substrate, the semiconductor device, the manufacturing method of the paste, and the release agent application method of the embodiment are described.

[0020] The ceramic substrate of the embodiment is preferably used for the ceramic circuit substrate, the semiconductor device, and the like to which a conductor portion is joined.

[0021] USAGES Figures 1-6 The ceramic substrate, the ceramic circuit substrate, and the semiconductor device of the embodiment are described. Figure 1 is a schematic cross-sectional (orthogonal surface of the front and back surfaces) view showing an example of the ceramic substrate to which the release agent is applied. In the ceramic substrate of the embodiment, the symbol S1 is a first surface (front surface). Furthermore, a center of the first surface S1 is set as a central portion P1. In addition, the symbol S2 is a second surface (back surface). Furthermore, a center of the second surface S2 is set as a central portion P2. Figure 2 is a ceramic circuit substrate in which a front copper plate and a back copper plate are arranged via a joining layer on both surfaces of the ceramic substrate. Figure 3 is a semiconductor device. Figure 4An example of a sheet-shaped ceramic formed body is shown. In addition, Figure 5 An example of a cutting step of cutting the sheet-shaped ceramic formed body is shown.

[0022] Figure 6 A manufacturing method of a ceramic sintered body according to the embodiment is shown. Figure 5 In the figure, the symbol ST1 is a mixing step, the symbol ST2 is a forming step, the symbol ST3 is a release agent application step, the symbol ST4 is a cutting step, the symbol ST5 is a sintering step, and the symbol ST6 is a cleaning step.

[0023] In the figure, the symbol 1 indicates a ceramic circuit substrate (for example, a ceramic copper circuit substrate), the symbol 2 indicates a ceramic substrate, the symbol 3 indicates a copper plate (a surface copper plate) that is a conductor portion, the symbol 4 indicates a copper plate (a back copper plate) that is a conductor portion, the symbol 5 indicates a bonding layer (an active metal brazing layer), the symbol 6 indicates a bonding layer of a copper plate and a semiconductor element, the symbol 7 indicates a semiconductor element, the symbol 8 indicates a semiconductor device, the symbol 11 indicates a sheet-shaped ceramic formed body that does not contain an applied release agent (a dusting powder), the symbol 12 indicates a plate-shaped ceramic formed body that does not contain an applied release agent (a dusting powder), the symbol 13 indicates a terminal that does not contain an applied release agent (a dusting powder), the symbol 14 indicates a release agent, the symbol 15 indicates a release agent layer, the symbol 16 indicates a sheet-shaped ceramic formed body that contains the sheet-shaped ceramic formed body 11 and a release agent applied thereto, the symbol 17 indicates a cutting jig, the symbol 22 indicates a plate-shaped ceramic formed body that contains the plate-shaped ceramic formed body 12 and a release agent applied thereto, the symbol 23 indicates a terminal before cleaning, and the symbol 24 indicates a terminal after cleaning.

[0024] Figure 2 The ceramic circuit substrate 1 shown is a structure in which the copper plate 3 of one face of the surface and back is given a circuit shape, and the other copper plate 4 is used as a heat dissipation plate. For convenience, the copper plate 3 is referred to as a surface copper plate, and the copper plate 4 is referred to as a back copper plate. Figure 2 The ceramic circuit substrate 1 shown is provided with two surface copper plates 3 on the ceramic substrate 2. The ceramic circuit substrate 1 according to the embodiment is not limited to this manner, and can be a structure in which three or more surface copper plates 3 are provided on the ceramic substrate 2, or a structure in which one surface copper plate 3 is provided. In addition, it can be a structure in which the back copper plate 4 is given a circuit shape. In addition, it can be a structure in which the back copper plate 4 is not provided on the ceramic substrate 2, and only the surface copper plate 3 is provided.

[0025] Figure 3 The semiconductor device 8 shown is provided with the semiconductor element 7 at only one place, but the semiconductor device 8 according to the embodiment is not limited to this manner, and can be provided with the semiconductor element 7 at a plurality of places. A plurality of semiconductor elements 7 can be provided on one surface copper plate 3 that is a circuit portion.

[0026] In Figure 2、 Figure 3 The ceramic substrate 2 and the semiconductor device 8 are each shown as being provided with a copper plate on both surfaces, but the ceramic substrate 2 and the semiconductor device 8 according to the embodiment are not limited to such a configuration. For example, an aluminum plate can be provided instead of the back copper plate 4 as a heat dissipation plate. Also, the ceramic substrate 2 and the semiconductor device 8 are each shown as having a bonding layer, but the ceramic substrate 2 and the semiconductor device 8 according to the embodiment can have a bonding layer 6 or can not have one (can be directly bonded). Figure 2 、 Figure 3 The ceramic substrate 2 and the semiconductor device 8 are each shown as having a bonding layer, but the ceramic substrate 2 and the semiconductor device 8 according to the embodiment can have a bonding layer 6 or can not have one (can be directly bonded).

[0027] The thickness of the ceramic substrate 2 according to the embodiment is preferably 0.1 mm or more and 3 mm or less. If the thickness of the ceramic substrate 2 is less than 0.1 mm, the strength can be insufficient. Also, if the thickness is more than 3 mm, the ceramic substrate 2 becomes a thermal resistance body, which can reduce the heat dissipation performance of the ceramic circuit board 1. It is preferable that the thickness of the ceramic substrate 2 be more preferably 0.15 mm or more and 2 mm or less.

[0028] The shape of the front and back surfaces of the ceramic substrate 2 according to the embodiment is not particularly limited, and can be, for example, rectangular (including square) or substantially circular. In the case where the shape of the front and back surfaces of the ceramic substrate 2 is rectangular, the center portions P1 and P2 are the intersection points of the two diagonal lines. In the case where the shape of the front and back surfaces of the ceramic substrate 2 is circular, the center portions P1 and P2 are the center of the circle. In either case, the length of the diagonal or the diameter is preferably 100 mm or more.

[0029] Specific examples of the material of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, an Alusil substrate, and the like.

[0030] The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. By increasing the strength of the substrate, the thickness of the substrate can be reduced. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The silicon nitride substrate can be reduced in thickness to 0.40 mm or less, and more preferably to 0.30 mm or less. Also, the thermal conductivity is preferably 80 W / m K or more. As the silicon nitride substrate having a thermal conductivity of 80 W / m K or more, for example, a 90 W / m K or 130 W / m K substrate can be used.

[0031] The three-point bending strength of the aluminum nitride substrate is generally around 300 MPa to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is generally 160 W / m K or more. The strength of the aluminum nitride substrate is low, and thus the thickness of the substrate is preferably 0.60 mm or more.

[0032] Alumina substrates generally have a three-point bending strength of around 300-450 MPa, but are inexpensive. Alusil high-silicon heat-resistant aluminum alloy substrates typically have a three-point bending strength of around 550 MPa, but a thermal conductivity of around 30-50 W / m·K. It should be noted that Alusil high-silicon heat-resistant aluminum alloy substrates are formed from a sintered body of a mixture of alumina and zirconia.

[0033] The ceramic substrate 2 of the embodiment is more preferably a nitride-based ceramic. From the viewpoint of thermal and mechanical properties, it is more preferred that the ceramic substrate 2 be a silicon nitride substrate or an aluminum nitride substrate among nitride-based ceramics. When an active metal brazing filler metal is used to join a metal component to a ceramic substrate, the nitride-based ceramic forms a reactant at the interface with the brazing filler metal that contributes to the strength of the joint. For example, when an active metal brazing filler metal containing Ti is used for joining, the nitride-based ceramic reacts with the Ti in the brazing filler metal to form titanium nitride. Since such a reactant strengthens the joint, it is possible to improve the strength of the joint between the metal component, in particular, the copper plate.

[0034] The ceramic substrate 2 of the embodiment contains a component of a release agent 14. The release agent 14 contained in the ceramic substrate 2 is obtained by coating the ceramic substrate 2 with a release agent in the release agent coating step ST3 ( Figure 6 The release agent applied to the sheet-like ceramic formed body 11 in the figure) and the release agent contained in the end material 24 which is the raw material of the recycled slurry described later. The amount of the release agent 14 at the center P1 or the center P2 of the ceramic substrate 2 of the preferred embodiment is 5 times or more the amount of the release agent 14 at the midpoint C1 which is the midpoint of the line segment connecting the center P1 and the center P2. Preferably, in addition to the above, it is more preferred that the ratio P1 / P2 of the amount of the release agent 14 at the center P1 to the amount of the release agent 14 at the center P2 is 0.5≤P1 / P2≤2. In addition to the above, the amount of the release agent 14 at the midpoint C1 is more preferably greater than 0 mass ppm and is 50 mass ppm or less. By controlling the composition of the release agent 14 of the ceramic substrate 2 as described above, excellent voltage resistance and mechanical properties are exhibited. During the manufacturing process of the ceramic substrate 2, the amount of release agent 14 applied to the sheet-like ceramic compact 11 (described later) can be adjusted to control the amount of release agent 14 at the center portions P1 and P2. Furthermore, the amount of release agent 14 at the midpoint portion C1 can be controlled by adjusting the degree of cleaning of the end material 23 produced after applying the release agent 14 to the sheet-like ceramic compact 11 in the slurry manufacturing method described later, and by adjusting the amount of cleaned end material 24 added to the slurry.

[0035] Note that, in the case where the ceramic substrate 2 has, as an auxiliary agent, a component that is the same as a component of the release agent 14 in the raw material composition, in the case where the amount of the component measured at the midpoint portion Cl is very small, for example, 300 mass ppm or less, the effect of the auxiliary agent as the component does not substantially occur, and thus the component is regarded as a component of the release agent 14.

[0036] In the case where the ceramic substrate 2 is used for the ceramic circuit substrate 1, at least one conductor portion is preferably provided on both or one of the front surface and the back surface of the ceramic substrate 2. In the ceramic circuit substrate 1 of the embodiment, the conductor portion can be directly provided on the ceramic substrate 2 or can be provided via the solder layer 5. In addition, the ceramic circuit substrate 1 of the embodiment can be one in which the conductor portion is joined after the circuit shape is imparted by cutting, punching, or the like, or can be one in which the circuit shape is imparted by etching after joining. In the case where the conductor portion is provided on the front surface and the back surface of the ceramic substrate 2, the thickness of the conductor portion provided on the front surface and the thickness of the conductor portion provided on the back surface can be the same or different.

[0037] In the circuit substrate 1 of the embodiment, the conductor portion is preferably any one or more of copper, a copper alloy, aluminum, or an aluminum alloy. More preferably, the conductor portion is copper or a copper alloy. Copper or a copper alloy is superior in thermal conductivity to aluminum or an aluminum alloy. In general, the thermal conductivity of copper is as high as about 400 W / m K, and thus the heat dissipation of the ceramic circuit substrate 1 can be improved. More preferably, the conductor portion that is copper or a copper alloy preferably has a graphite layer in an oxygen-free copper or copper layer. Aluminum or an aluminum alloy is inexpensive compared to copper, and thus is preferred in the case where cost is valued.

[0038] In addition, in the case where the conductor portion is copper or a copper alloy, the thickness of the conductor portion can be 0.3 mm or more and further can be 0.6 mm or more. The conductor portion that is copper or a copper alloy and that is 0.6 mm or more can be, for example, a 1-mm copper plate or a 2-mm copper plate, or the like. By thickening the conductor portion, the heat dissipation of the joined body can be improved.

[0039] As described above, the ceramic circuit substrate 1 of the embodiment is preferably a ceramic copper circuit substrate. Here, the ceramic copper circuit substrate refers to a circuit substrate having a conductor portion formed of copper or a copper alloy as a circuit.

[0040] The ceramic circuit substrate 1 of the embodiment can also have a heat dissipation member as the conductor portion. The heat dissipation member can be a shape that protrudes from the ceramic substrate (for example, a shape in which a heat dissipation plate is integrated with a lead frame), or can have a groove shape. Further, a recessed portion can also be provided on the surface.

[0041] In the case where the ceramic circuit substrate 1 of the embodiment has a solder, the kind of the solder constituting the solder layer 5 can be changed depending on the kind of the ceramic constituting the ceramic circuit substrate 1 and the kind of the conductor portion, for example, in the case where the kind of the ceramic is a nitride-based ceramic and the conductor portion is copper or a copper alloy, it is preferable to contain any one or more of silver, copper and an active metal. It is more preferable that the active metal be at least one or more kinds of metal selected from Ti, Zr, Nb and Hf. The solder can be, for example, a solder composed of only two kinds (in components other than inevitable impurities) of metal components, such as an Al-Ti alloy, a Cu-Mg alloy, a Cu-Ti alloy, an Ag-Ti alloy and the like, or a solder composed of three or more kinds (in components other than inevitable impurities) of metal components, such as an Ag-Cu-Ti alloy, a Cu-Sn (or In or Mn)-Ti alloy, an Ag-Cu-Sn (or In or Mn)-Ti alloy. Note that "Sn (or In or Mn)" herein means at least one or more kinds (may be two or three kinds) of metal selected from Sn, In and Mn.

[0042] In the above-described solder composition, it is more preferable that the solder composition particularly contain an active metal. It is more preferable that any one or more of Ag (silver) or Cu (copper) be contained in a total amount of 50 wt% or more and 99 wt% or less. It is more preferable that Sn (or In or Mn) be contained in a proportion of 0.5 wt% or more and 35 wt% or less. It is more preferable that the active metal be contained in a total amount of 0.5 wt% or more and 25 wt% or less.

[0043] In addition, the thickness of the solder layer 5 is preferably 5 μm or more and 45 μm or less. The thickness of the solder layer 5 is more preferably 10 μm or more and 25 μm or less. If the thickness of the solder layer 5 is less than 5 μm, it can be impossible to maintain sufficient strength. On the other hand, if the thickness of the solder layer 5 exceeds 45 μm, it can be possible to cause problems such as cracks in the interface of the joint, warping of the ceramic circuit substrate 1 and the like caused by the difference in the thermal expansion rate of the ceramic substrate 2 and the joint layer 6.

[0044] The solder layer 5 is formed by brazing the ceramic substrate 2 and the conductor portion. When brazing the ceramic substrate 2 and the conductor portion, a solder paste can be used, or a solder foil can be used. In the case where a solder paste is used, the solder paste can be applied multiple times, or the composition can be changed and applied multiple times.

[0045] In a semiconductor device 8 of the embodiment, a semiconductor element 7 is provided on a conductor portion of a circuit board 1 of the embodiment, for example, via a bonding layer 6. The bonding layer 6 is formed by bonding the conductor portion and the semiconductor element 7, for example, using solder or a conductive adhesive. When bonding the conductor portion and the semiconductor element 7 using a conductive adhesive, silver paste containing silver as a primary component or copper paste containing copper as a primary component can be used as the conductive adhesive. Silver paste is preferred because it is less susceptible to oxidation. Copper paste is less expensive than silver paste and is therefore preferred when cost is a concern.

[0046] Examples of the semiconductor element 7 include silicon carbide (SiC) power semiconductors and gallium nitride (GaN) power semiconductors.

[0047] The method for producing the slurry according to the embodiment will be described.

[0048] The method for producing the slurry according to the embodiment includes the following steps: a cleaning step ST6 ( Figure 6 ), cleaning the end material 23 obtained by cutting the sheet-like ceramic formed body 16 coated with the release agent 14; and mixing step ST1, adding the end material 24 after a part of the release agent 14 is separated by the cleaning step ST6 to a new slurry composed of ceramic powder, adhesive and sintering aid and mixing, thereby obtaining a regenerated slurry.

[0049] First, an end material 23 is prepared that can be cut into the sheet-like ceramic compact 16 coated with the release agent 14. The end material 23 is produced through steps ST1 to ST4. Alternatively, the end material 23 prepared here may be an end material to which no recycled raw materials such as the end material 24 are added in the mixing step ST1, that is, an end material produced solely from new slurry.

[0050] In the mixing step ST1 ( Figure 6 In the figure), ceramic powder, adhesive and sintering aid are mixed to obtain a slurry. As the ceramic powder, a powder whose main component is one selected from silicon nitride, aluminum nitride, aluminum oxide, zirconium oxide and silicon carbide can be mentioned. The type of ceramic powder is selected according to the main component of the target ceramic substrate (plate-shaped ceramic sintered body). Here, the main component of the sheet-shaped ceramic formed body 11, the plate-shaped ceramic formed body 22, and the plate-shaped ceramic sintered body generated by sintering them is the component with the largest mass ratio among the sheet-shaped ceramic formed body 11, the plate-shaped ceramic formed body 22, and the components constituting the plate-shaped ceramic sintered body. The sheet-shaped ceramic formed body 11 with silicon nitride as the main component becomes a silicon nitride sintered body after sintering. In addition, the sheet-shaped ceramic formed body 11 with aluminum oxide as the main component becomes an aluminum oxide sintered body after sintering.

[0051] In the forming process ST2 ( Figure 6In the forming step ST2 (illustrated in FIG. 1), the sheet-shaped ceramic formed body 11 is formed from the slurry by a doctor blade method, a mold forming, a cold isostatic press (CIP), an injection molding method, or the like. The doctor blade method is preferable in the production of the ceramic substrate. The doctor blade method can produce a long sheet-shaped ceramic formed body 11. Thereby, the mass productivity of the ceramic substrate (the sheet-shaped ceramic sintered body) can be improved. Hereinafter, the case where the sheet-shaped ceramic formed body 11 is obtained by the doctor blade method will be described.

[0052] In the forming step ST2 (illustrated in FIG. 1), the sheet-shaped ceramic formed body 11 is formed from the slurry by a doctor blade method, a mold forming, a cold isostatic press (CIP), an injection molding method, or the like. The doctor blade method is preferable in the production of the ceramic substrate. The doctor blade method can produce a long sheet-shaped ceramic formed body 11. Thereby, the mass productivity of the ceramic substrate (the sheet-shaped ceramic sintered body) can be improved. Hereinafter, the case where the sheet-shaped ceramic formed body 11 is obtained by the doctor blade method will be described. Figure 6 In the forming step ST2 (illustrated in FIG. 1), the sheet-shaped ceramic formed body 11 is formed from the slurry by a doctor blade method, a mold forming, a cold isostatic press (CIP), an injection molding method, or the like. The doctor blade method is preferable in the production of the ceramic substrate. The doctor blade method can produce a long sheet-shaped ceramic formed body 11. Thereby, the mass productivity of the ceramic substrate (the sheet-shaped ceramic sintered body) can be improved. Hereinafter, the case where the sheet-shaped ceramic formed body 11 is obtained by the doctor blade method will be described.

[0053] Figure 6 Next, in the release agent application step ST3 (illustrated in FIG. 1), the release agent 14 is applied to the sheet-shaped ceramic formed body 11, and the release agent layer 15 is provided. The method of applying the release agent 14 to the sheet-shaped ceramic formed body 11 can be, for example, a method using a spray, a method passing through a solution containing the release agent 4, a method using a brush, a method using static electricity, a method using a gravure, a method of dipping in a solution containing the release agent 4, or the like. Next, in the cutting step ST4 (illustrated in FIG. 1), the sheet-shaped ceramic formed body 16 to which the release agent 14 is attached is cut to the target size. Figure 6

[0054] In addition, in the production of the ceramic substrate 2, the sheet-shaped ceramic formed body 16 is generally cut to the target size (illustrated in FIG. 1) using, for example, a cutting jig 17 or the like. Here, the formed body before such release agent application and cutting is referred to as the sheet-shaped ceramic formed body 11 (illustrated in FIG. 1), the formed body before cutting to which the release agent 14 is applied to the sheet-shaped ceramic formed body 11 is referred to as the sheet-shaped ceramic formed body 16 (illustrated in FIG. 1), and each formed body obtained by cutting the sheet-shaped ceramic formed body 16 is referred to as the sheet-shaped ceramic formed body 22 (illustrated in FIG. 1). The sheet-shaped ceramic formed body 16 is formed by applying the release agent 14 to the sheet-shaped ceramic formed body 11 to form the release agent layer 15 on the sheet-shaped ceramic formed body 11. The sheet-shaped ceramic formed body 22 is formed by forming the release agent layer 15 on the sheet-shaped ceramic formed body 12. Figure 5 Figure 4 Figure 4 Figure 5 In addition, in the production of the ceramic substrate 2, the sheet-shaped ceramic formed body 16 is generally cut to the target size (illustrated in FIG. 1) using, for example, a cutting jig 17 or the like. Here, the formed body before such release agent application and cutting is referred to as the sheet-shaped ceramic formed body 11 (illustrated in FIG. 1), the formed body before cutting to which the release agent 14 is applied to the sheet-shaped ceramic formed body 11 is referred to as the sheet-shaped ceramic formed body 16 (illustrated in FIG. 1), and each formed body obtained by cutting the sheet-shaped ceramic formed body 16 is referred to as the sheet-shaped ceramic formed body 22 (illustrated in FIG. 1). The sheet-shaped ceramic formed body 16 is formed by applying the release agent 14 to the sheet-shaped ceramic formed body 11 to form the release agent layer 15 on the sheet-shaped ceramic formed body 11. The sheet-shaped ceramic formed body 22 is formed by forming the release agent layer 15 on the sheet-shaped ceramic formed body 12.​​​​​

[0055] Here, the end material 23 refers to a scrap generated when the sheet-shaped ceramic formed body 16 is cut to a target size. Further, the end material 23 refers to a defective product in which a hole, a breakage, an excess or a deficiency in thickness, an excess or a deficiency in the amount of release agent applied, and the like are observed. Further, the end material 23 refers to a constituent part of the sheet-shaped ceramic formed body 16, the sheet-shaped ceramic formed body 22, or the sheet-shaped ceramic formed body 16, the sheet-shaped ceramic formed body 22 in the form of a cutting chip or the like, which is reused as a raw material of the slurry. Hereafter, the end material of the sheet-shaped ceramic formed body 16 or the sheet-shaped ceramic formed body 22 to which the release agent 14 is applied is sometimes simply referred to as an "end material".

[0056] In the present embodiment, the release agent 14 is, for example, one or two or more selected from boron nitride, zirconium oxide, aluminum oxide, and aluminum nitride. The release agent 14 has a function of preventing the sheet-shaped ceramic formed bodies 22 from adhering to each other when the sheet-shaped ceramic formed bodies 22 are laminated and sintered. The average particle diameter of the release agent 14 is preferably 20 μm or less. If the average particle diameter is excessively large, the amount of application becomes uneven, and it is likely to adversely affect the surface properties of the sintered body. The average particle diameter of the release agent 14 is preferably 10 μm or less, and further preferably 6 μm or less. The lower limit of the average particle diameter of the release agent 14 is not particularly limited, and is preferably 2 μm or more. If the average particle diameter is less than 2 μm, the handleability is likely to be poor.

[0057] Next, a cleaning step is performed, and the release agent 14 is separated from the end material 23 by cleaning, and the end material 24 from which a part of the release agent 14 is separated is recovered.

[0058] It is preferable to make the sizes of the end materials 23 uniform before the end materials 23 are cleaned. Therefore, in the case where the sizes of the plurality of end materials 23 are different, it is preferable to cut the plurality of end materials 23 so that the sizes of the plurality of end materials 23 are substantially the same. In addition, substantially the same here means that the average of the areas of the front and back surfaces of the plurality of end materials 23 is 1 / 3 or more of the maximum value. The closer the areas of the front and back surfaces of the plurality of end materials 23 are to each other, the less likely uneven removal of the release agent 14 is to occur. In addition, when reused as a raw material of the slurry, the dispersion of the components of the release agent 14 into the slurry is easily homogenized, and even the end material 23 in which the amount of the components of the release agent 14 adhered is about 50 mass ppm can be reused without problems.

[0059] In addition, the areas of the front and back surfaces of the end material 23 are preferably 2 cm 2 The above. If the areas of the front and back surfaces of the end material 23 are less than 2 cm 2 in a small shape, the amount of the cleaning liquid adhered to the end material 23 increases, and drying can take time. The upper limit of the areas of the front and back surfaces of the end material 23 is not particularly limited, but in order to improve the efficiency of cleaning, it is preferable that the areas of the front and back surfaces of the end material 23 be 100 cm 2The following. In addition, in the case where the end material 23 is not in a sheet shape or a plate shape, a proper reference such as a surface area, an apparent surface area, or the like can be used instead of the area of the front and back surfaces.

[0060] The cleaning of the end material 23 in the cleaning step ST6 Figure 6 The cleaning of the end material 23 in the cleaning step ST6

[0061] The cleaning liquid for the cleaning of the end material 23 is not particularly limited, but a solution in which a water-soluble additive is added to water is preferred. As the water-soluble additive, for example, an organic compound having a hydrophilic group such as a carboxyl group, an alcohol group, an amino group, a thiol group, a sulfo group, a phosphoric acid group, a ketone group, or the like, or a salt thereof, or the like can be given. The cleaning of the end material 23 can be performed using a plurality of cleaning liquids.

[0062] In order to prevent the reattachment of the components of the releasing agent 14, a surfactant can also be added to the cleaning liquid for the cleaning of the end material 23. The added surfactant can be any one of a nonionic or ionic surfactant. In the case where an ionic surfactant is added, any one of an anionic surfactant, a cationic surfactant, an amphoteric surfactant can be used, but an amphoteric surfactant is preferably used.

[0063] In the case where the anionic surfactant and the cationic surfactant remain in the cleaned end material 24, if the cleaned end material 24 described later is used as a slurry raw material, it can be possible to affect the sinterability of the formed plate-shaped ceramic molded body 22.

[0064] As the anionic surfactant, a carboxylic acid type substance, a sulfonic acid type substance, a sulfate type substance, a phosphate type substance can be given. As the cationic surfactant, an alkyl amine salt type surfactant, a quaternary ammonium salt type surfactant and the like can be given. As the amphoteric surfactant, a carboxybetaine type substance, a derivative of 2-alkylimidazoline type, a glycine type, an amine oxide type substance can be given. Further, the surfactant used is preferably a nonionic surfactant. As the nonionic surfactant, an ester type, an ether type, an ester ether type, an alkanolamide type surfactant and the like can be given. In the case of using a nonionic surfactant, a polyol type surfactant can be used, or a polyoxyethylene type surfactant can be used. In the case of using a nonionic surfactant as the surfactant, the nonionic surfactant does not remain as ions in the end material 24 after cleaning. Therefore, it is possible to suppress the decrease in sinterability at the time of reuse.

[0065] As described above, the cleaning liquid used for cleaning of the end material 23 is a cleaning liquid in which a water-soluble additive is added to water as a solvent, and the water-soluble additive is particularly preferably an amphoteric surfactant or a nonionic surfactant having 3 or more types of atoms selected from carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) as main components, and not containing other atoms. In the case where the end material 24 after cleaning is used as a raw material of slurry, if the components of the release agent 14 remain in the end material 24 after cleaning and are mixed into the slurry, it is less likely to have an influence on sinterability.

[0066] Further, in the case where the surfactant has a straight chain portion, the number of carbon atoms of the straight chain portion is preferably 25 or less. If the number of carbon atoms of the straight chain portion is small, it is possible to prevent the binder contained in the end material 23 from dissolving in the cleaning liquid. Further, if the number of carbon atoms is too large, it can be difficult to sufficiently dissolve in the cleaning liquid, and it can be difficult to separate the components of the release agent 14 from the end material 23. By controlling the number of carbon atoms as described above, it is easy to separate the components of the release agent 14 from the end material 23.

[0067] Further, the cleaning liquid can be an inorganic compound solution. The inorganic compound solution can be a solution in which carbon dioxide, nitrogen, oxygen, argon, or the like is a solute. In the case of using a gas, when a bubble formed of the gas breaks in water, it is possible to expect an effect of removing the components of the release agent 14 adhering to the end material 23. Further, in the case of using the above-mentioned gas component, it is further preferable to control the temperature of the cleaning liquid to be 5°C or higher. If the temperature of the cleaning liquid is 5°C or higher, the solubility of the gas component in water is sufficiently increased, and thus it is possible to reduce the variation in cleaning effect.

[0068] The number of times of washing of the end material 23 and the amount of additive added to the washing liquid can be freely selected according to the purpose. Therefore, the number of times of washing of the end material 23 and the amount of additive are not particularly limited. The washed end material 24 can be taken out from the washing liquid together using a skimmer or the like, or can be taken out one by one. In addition, in the case of using an instrument in the shape of a skimmer at the time of taking out, an instrument having a mesh size that allows the washing liquid, the release agent 14, and the like to sufficiently pass through is preferably used.

[0069] The release agent 14 contained in the solution generated by washing of the end material 23 in the washing step ST6 Figure 6 may be separated from the solution component by a method such as a method of standing and precipitating, filtration, centrifugal separation, or the like, and the solution component can be reused as a washing liquid. The component of the release agent 14 separated from the end material 23 can also be used again as the release agent 14 to be applied to a new sheet-shaped ceramic formed body 11. In addition, the content of the component of the release agent 14 or other components can be adjusted, and used as a solution for application of the release agent 14.

[0070] Next, a mixing step ST1 Figure 6 in which a regenerated slurry is obtained by adding the washed end material 24 to a new slurry and mixing is performed. When the washed end material 24 is added to the new slurry, the amount of the washed end material 24 to be added is preferably 25% by mass or less, based on 100% by mass of the powder raw material of the new slurry. More preferably, it is 5% by mass or more and 20% by mass or less. If the amount of the washed end material 24 to be added is less than 5% by mass, based on 100% by mass of the powder raw material of the slurry, it can be difficult to sufficiently obtain the advantage of recycling. On the other hand, if it exceeds 25% by mass, more careful washing needs to be performed by increasing the number of times or the like, and the cost of washing can increase.

[0071] When the end material 24 is added to the new slurry, wet mixing is preferably performed using a bead mill or a ball mill or the like. At the time of the wet mixing, a larger amount of the binder component than usual is preferably added. In addition, as described above, after the predetermined amount of the binder component is added, a solvent is preferably added until a predetermined viscosity is reached.

[0072] The component ratio of the cleaned end material 24 is different from the component ratio preferred as the slurry due to volatilization during the manufacturing process. As described above, by adjusting the binder component and the solvent component, the various components that are insufficient due to the addition of the cleaned end material 24 can be supplemented to obtain a regenerated slurry with a preferred component ratio. In addition, during the above mixing, substances that cause cracking, poor thickness, etc. can also be added together in the drying process before the application of the release agent 14. As described above, by further mixing the substances before the application of the components of the release agent 14, the number of ceramic sintered bodies that can be produced in the same raw material powder can be increased, and the yield relative to the same amount of raw material can be further improved. At this time, it is preferred that the powder raw material of the slurry is set to 100% by mass, and the total amount of the added amount of the cleaned end material 24 and the added amount of the sheet-like ceramic formed body 11 before the application of the release agent 14 is set to 25% by mass or less. It is preferred that the total amount be set to 5% by mass or more and 20% by mass or less.

[0073] In addition, when using the method of the embodiment to manufacture a slurry of a ceramic sintered body using alumina as the raw material, if the alumina sintered body is used in the medium of a bead mill or a ball mill, the amount of alumina added to the raw material can also be controlled by considering the alumina mixed in due to the wear of the medium.

[0074] It should be noted that after using new slurry through steps ST1 to ST4, and after using recycled slurry (based on the end material 24) through steps ST1 to ST4, in the sintering step ST5 ( Figure 6 In the sintering step ST5, the plate-shaped ceramic formed body 22 is sintered to produce a plate-shaped ceramic sintered body, i.e., a ceramic substrate. The sintering step ST5 involves heat treatment at normal pressure or under pressure, typically at 1600°C to 2000°C, to achieve sintering. Alternatively, the sintering step ST5 may be performed in two stages, with varying temperature ranges.

[0075] In addition, in the release agent coating step ST3 ( Figure 6In the embodiment shown in the figure, a reused release agent 14 may be applied. In this case, the release agent component application method includes, for example, the following steps: a cleaning step ST6 of cleaning the end material 23 to obtain a ceramic sintered body sheet from which a portion of the release agent 14 is separated; an adjustment step of adjusting the content of the separated release agent 14 to prepare a solution containing the release agent 14; a dispersion step of uniformly dispersing the concentration of the release agent 14 contained in the solution adjusted by the adjustment step; and a coating step of coating the solution that has undergone the dispersion step on the sheet-like ceramic formed body 11. The release agent coating step ST3, for example, includes the coating step of coating the solution that has undergone the dispersion step on the sheet-like ceramic formed body 11. In the coating step, the release agent 14 is preferably attached to the sheet-like ceramic formed body 11 by spraying. If the spraying method is used, the spraying amount of the release agent 14 can be stabilized. In addition, by providing a plurality of spray nozzles, the release agent 14 can be applied over a wide range. Alternatively, in the case of a spray method, a long sheet-like ceramic compact 11 may be arranged and the mold release agent 14 may be applied while being conveyed. Alternatively, in the case of a spray method, a solution containing the mold release agent 14 may be sprayed.

[0076] (Example)

[0077] A sheet-like ceramic compact 11 mainly composed of silicon nitride and aluminum nitride is prepared, and boron nitride is applied as a release agent 14. Then, the sheet-like ceramic compact 16 coated with the release agent 14 is placed with the area of ​​the front and back less than 15 cm 2 The plate-shaped ceramic formed body (hereinafter referred to as "ceramic formed body sheet") is cut in a manner to make a simulated product of the end material 23. Then, in the cleaning step ST6 ( Figure 6 In the figure, the ceramic compact sheet was cleaned using an initial cleaning solution (cleaning solution 1), a second cleaning solution (cleaning solution 2), and a third cleaning solution (cleaning solution 3). Table 1 shows the materials of the sheet-like ceramic compacts 11 constituting the ceramic compact sheets of Examples 1 to 5 and Comparative Examples 1 and 2, the causes of ceramic compact sheet failure, and the cleaning methods.

[0078] The composition formulas listed in the "Sheet" column of Table 1 indicate the types of materials constituting the sheet-shaped ceramic compacts 11 of Examples 1 to 5 and Comparative Examples 1 and 2 as the types of ceramic substrates after sintering. Here, Si3N4 is a ceramic substrate primarily composed of silicon nitride (50% by mass or greater), and similarly, AlN is a ceramic substrate primarily composed of aluminum nitride (50% by mass or greater).

[0079] The ceramic formed body sheet described as "small" in the column of the cause of the defect in Table 1 was smaller than the required size, although the amount of application and the presence or absence of the shape defect of the release agent 14 were normal. In addition, the ceramic formed body sheet described as "crack" in the column of the cause of the defect in Table 1 had a shape defect (crack, break, or hole) although the amount of application and the size of the release agent 14 were normal. The ceramic formed body sheet described as "uneven" in the column of the cause of the defect in Table 1 had an unevenly large amount of application of the release agent 14, a small amount of application on a single surface, or the like, and was defective in the amount of application, although the size and the presence or absence of the shape defect of the release agent 14 were normal.

[0080] In the item section of the first cleaning step and the second cleaning step in Table 1, the cleaning described as "cleaning 1" is rough cleaning, the cleaning described as "cleaning 2" is formal cleaning, and the cleaning described as "cleaning 3" is final cleaning. In the rough cleaning, the formal cleaning, and the final cleaning, different types of cleaning liquids are used, respectively.

[0081] In Example 1 and Example 3, ultrasonic cleaning was performed in all of the cleanings. On the other hand, in other Examples 2, 4, and 5 and Comparative Examples 1 and 2, ultrasonic cleaning was not performed.

[0082] Table 1

[0083]

[0084] Next, the amount of the release agent 14 adhered to the surface of the ceramic formed body sheet was measured before and after the cleaning step.

[0085] The ceramic formed body sheet in which the surface adhered amount (proportion) of the release agent 14 after cleaning was greater than 0 mass ppm and 25 mass ppm or less was set to "A", the ceramic formed body sheet in which the surface adhered amount was greater than 25 mass ppm and 50 mass ppm or less was set to "B", and the ceramic formed body sheet in which the surface adhered amount was greater than 50 mass ppm was set to "D", and is shown in Table 2.

[0086] Next, the surface adhered amount of the release agent 14 before cleaning was compared with the surface adhered amount of the release agent 14 after cleaning. The surface adhered amount of the release agent 14 before cleaning with respect to the surface adhered amount of the release agent 14 after cleaning (before / after removal) is shown in Table 2. This ratio becomes a value indicating the cleaning efficiency. The cleaning efficiency of the ceramic formed body sheet of Examples 1 to 5 was in the preferable range (40% or more).

[0087] [Table 2]

[0088]

[0089] Next, in step ST1, the washed ceramic formed body sheet is mixed with new slurry raw material powder of the ceramic substrate, and a regenerated slurry is produced. The mass ratio (%) of the washed ceramic formed body sheet to the raw material powder in Examples 1 to 5 and Comparative Examples 1 and 2 is shown in Table 3.

[0090] The obtained slurry is formed into a sheet-shaped ceramic formed body 11, and a release agent 14 is applied to the sheet-shaped ceramic formed body 11. Then, the ceramic formed body sheet to which the release agent 14 is applied is subjected to debinding sintering and main sintering, and a ceramic substrate is obtained. Boron nitride is used as the release agent 14. In the release agent application step ST3, the release agent 14 is applied to the sheet-shaped ceramic formed body 11 by spraying a mixture of boron nitride powder and water.

[0091] The ceramic substrate obtained by sintering is subjected to a pressure resistance test and a bending strength test. In addition, in order to make a comparison, a ceramic substrate for comparison (hereinafter referred to as a standard ceramic substrate) is produced under the same conditions from a new slurry instead of a regenerated slurry, and the same tests are performed.

[0092] In the pressure resistance test, a voltage of a constant pressure is applied to the ceramic substrate based on the regenerated slurry of the ceramic formed body sheet from Examples 1 to 5 and Comparative Examples 1 and 2 and the standard ceramic substrate based on the new slurry, and the current value of the leakage current is compared. Regarding the results of the pressure resistance test of the ceramic substrate of Examples 1 to 5 and Comparative Examples 1 and 2, a case where the current value is increased by 0% or more and less than 0.5% compared to the standard ceramic substrate is set as "A", a case where the current value is increased by 0.5% or more and less than 0.75% is set as "B", a case where the current value is increased by 0.75% or more and less than 1.0% is set as "C", and a case where the current value is grounded is set as "D", and is shown in Table 3.

[0093] In the bending strength test, the three-point bending strength of the ceramic substrate based on the regenerated slurry of the ceramic formed body sheet from Examples 1 to 5 and Comparative Examples 1 and 2 and the standard ceramic substrate based on the new slurry is measured based on JIS R1601. Regarding the bending strength test of the ceramic substrate of Examples 1 to 5 and Comparative Examples 1 and 2, a case where the bending strength is 99% or more of the standard ceramic substrate is set as "A", a case where the bending strength is 96% or more and less than 99% is set as "B", a case where the bending strength is 94% or more and less than 96% is set as "C", and a case where the bending strength is less than 94% is set as "D", and is shown in Table 3.

[0094] [Table 3]

[0095]

[0096] In addition, the ceramic substrate of each of Examples 1 to 5 controls the amount of the component of the release agent 14 at the midpoint portion C1 in the cleaning process and the manufacturing process of the slurry. The amount of the component of the release agent 14 at the center portion P1 of the first surface S1, the center portion P2 of the second surface S2, and the midpoint portion C1 of each of the ceramic substrates of Examples 1 to 5 and Comparative Examples 1 and 2 was measured using an ICP emission spectrometer.

[0097] The ratio (mP1) / (mC1) of the amount of the component of the release agent 14 measured at the center portion P1 (or the center portion P2) (mP1) to the amount of the component of the release agent 14 measured at the midpoint portion C1 (mC1) was calculated for each of the ceramic substrates of Examples 1 to 5 and Comparative Examples 1 and 2. The results are shown in Table 4. The ratio (mP1) / (mC1) in each of the ceramic substrates of Examples 1 to 5 was 5 or more. In addition, the amount of the component of the release agent 14 measured at the midpoint portion C1 (mC1) was less than 30 mass ppm in Examples 1 and 3, 30 mass ppm or more and less than 40 mass ppm in Example 2, 40 mass ppm or more and 50 mass ppm or less in Examples 4 and 5. On the other hand, in Comparative Examples 1 and 2, the amount of the component of the release agent 14 was as much as more than 50 mass ppm, and the amount of the component of the release agent 14 in Comparative Example 1 was more than that in Comparative Example 2.

[0098] [Table 4]

[0099]

[0100] In addition, the ratio P1 / P2 of the amount of the component of the release agent 14 at the center portion P1 of the first surface S1 to the amount of the component of the release agent 14 at the center portion P2 of the second surface S2 opposite to the first surface S1 was 0.5 ≤ P1 / P2 ≤ 2 in each of Examples 1 to 5. In addition, the amount of the component of the release agent 14 at the midpoint portion C1 was more than 0 mass ppm and 50 mass ppm or less in each of Examples 1 to 5.

[0101] Therefore, the ceramic substrate that has excellent voltage resistance and mechanical strength (for example, bending strength) in Table 3 has the amount of the component of the release agent 14 measured at the center portion P1 (or the center portion P2) that is five times or more the amount of the component of the release agent 14 measured at the midpoint portion C1 when the midpoint of the line segment connecting the center portion P1 of the first surface S1 and the center portion P2 of the second surface S2 is set as the midpoint portion C1.

[0102] According to at least one embodiment described above, even if the component of the release agent 14 is contained, it is possible to provide a ceramic substrate, a ceramic circuit substrate, a semiconductor device, a manufacturing method of a slurry, and a release agent application method with good yield.

[0103] Several embodiments of the present application have been described, but these embodiments are presented by way of example only and are not intended to limit the scope of the application. These new embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the application. These embodiments and variations thereof are included in the scope or spirit of the application, and are included in the scope of the application as recited in the claims and equivalents thereof.

Claims

1. A ceramic substrate, characterized in that It is a ceramic substrate having a first surface and a second surface. In which, when the midpoint of the line segment connecting the center portion P1 of the first surface and the center portion P2 of the second surface is set as the midpoint portion C1, the component amount of the release agent measured at the center portion P1 of the first surface or the center portion P2 of the second surface is more than 5 times the component amount of the release agent measured at the midpoint portion C1.

2. The ceramic substrate according to claim 1, wherein A ratio P1 / P2 of the amount of the release agent component measured at the center P1 of the first surface to the amount of the release agent component measured at the center P2 of the second surface is 0.5≤P1 / P2≤2.

3. The ceramic substrate according to claim 1, wherein The amount of the release agent component measured at the midpoint portion C1 is greater than 0 mass ppm and is 50 mass ppm or less.

4. The ceramic substrate according to claim 2, wherein: The amount of the release agent component measured at the midpoint portion C1 is greater than 0 mass ppm and is 50 mass ppm or less.

5. The ceramic substrate according to claim 1, wherein The component of the release agent is boron nitride.

6. The ceramic substrate according to claim 4, characterized in that The component of the release agent is boron nitride.

7. The ceramic substrate according to claim 1, wherein The ceramic substrate contains nitride-based ceramics as a main component.

8. The ceramic substrate according to claim 4, wherein The ceramic substrate contains nitride-based ceramics as a main component.

9. The ceramic substrate according to claim 6, wherein: The ceramic substrate contains nitride-based ceramics as a main component.

10. A ceramic circuit substrate, characterized in that: The ceramic substrate according to claim 1 is used. At least one conductor portion is bonded to at least one of the first surface and the second surface of the ceramic substrate.

11. A ceramic circuit substrate, characterized in that: The ceramic substrate according to claim 4 is used. At least one conductor portion is bonded to at least one of the first surface and the second surface of the ceramic substrate.

12. A ceramic circuit substrate, characterized in that: The ceramic substrate according to claim 9 is used. At least one conductor portion is bonded to at least one of the first surface and the second surface of the ceramic substrate.

13. The ceramic circuit substrate according to claim 10, wherein: The ceramic substrate and the conductor portion are bonded via a brazing material. The brazing filler metal contains at least an active metal, The brazing filler metal contains at least one selected from Ag, Al, Cu, Sn, In, and Mn as a metal component other than the active metal.

14. The ceramic circuit substrate according to claim 12, wherein: The ceramic substrate and the conductor portion are bonded via a brazing material. The brazing filler metal contains at least an active metal, The brazing filler metal contains at least one selected from Ag, Al, Cu, Sn, In, and Mn as a metal component other than the active metal.

15. The ceramic circuit substrate according to claim 14, wherein: The active metal is at least one selected from Ti, Zr, Nb, and Hf.

16. A semiconductor device, characterized in that: A semiconductor element is arranged on the ceramic circuit substrate according to claim 10 .

17. A method for producing a slurry, characterized in that: It has the following steps: a cleaning step of cleaning the ceramic sintered body sheet to obtain a ceramic sintered body sheet from which a portion of the release agent has been separated; as well as In the mixing step, when the powder raw material of the new slurry is set to 100 mass %, 25 mass % or less of the ceramic sintered body pieces from which a part of the release agent has been separated are added to the new slurry and mixed to obtain a regenerated slurry.

18. A method for applying a release agent, characterized in that: It has the following steps: a cleaning step of cleaning the ceramic sintered body sheet to obtain a ceramic sintered body sheet from which a portion of the release agent has been separated; an adjustment step of adjusting the content of the release agent after separation to prepare a solution containing the release agent; a dispersing step of uniformly dispersing the concentration of the release agent contained in the solution adjusted in the adjusting step; as well as The coating step is to coat the solution that has undergone the dispersion step on a sheet-like ceramic compact.

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