Production method for silicon nitride substrate

Abstract

To conveniently obtain a silicon nitride substrate with high uniformity.SOLUTION: A production method for a silicon nitride substrate comprises a firing step, in which a green sheet containing silicon nitride powder and sintering aid powder, along with an atmosphere conditioning agent, is placed in a firing container having two or more corners at a connecting portion of the container part and a lid part, and is fired at 1700°C to 1900°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silicon nitride substrate.

Background Art

[0002] Silicon nitride is excellent in mechanical strength, thermal conductivity, and electrical insulation, and is therefore used for substrates for semiconductor modules and the like. Generally, a silicon nitride substrate is manufactured by storing a plate-shaped green sheet containing silicon nitride powder and sintering aid powder in a firing container and firing it at about 1700 to 1900°C. Conventionally, containers as shown in FIGS. 3 and 4 have been widely used as the firing container.

[0003] When firing at a high temperature such as silicon nitride, there has been a problem that the uniformity of the obtained silicon nitride substrate deteriorates due to the volatilization of the sintering aid during firing. In order to suppress the volatilization of the sintering aid against such a problem, a sintering aid component (atmosphere regulator) is arranged separately from the green sheet in the firing container, and this is volatilized to adjust the atmosphere in the container to prevent the volatilization of the sintering aid. A technique is known.

[0004] For example, in Patent Document 1, in order to solve the problems that the amount of the auxiliary agent is different between the central part and the end part of the silicon nitride substrate, and the physical properties differ between the central part and the end part, or the substrate warps, a degreased body (green sheet) is placed in the container. It is disclosed that a silicon nitride substrate for atmosphere preparation is installed together. As a result, a silicon nitride substrate can be manufactured in which the difference between the amount of magnesium at the center of the substrate and the amount of magnesium at the end of the substrate is 20% or less, and as a result, the warping of the silicon nitride substrate can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, it is disclosed to use an atmosphere conditioner to suppress the volatilization of a sintering aid. However, in order to obtain a silicon nitride substrate with high uniformity, simply using an atmosphere conditioner is not sufficient. In Patent Document 1, it is also necessary to control the firing temperature, firing time, and cooling rate, which imposes restrictions on the manufacturing conditions. Therefore, an object of the present invention is to provide a method capable of easily obtaining a silicon nitride substrate with high uniformity.

Means for Solving the Problems

[0007] To solve the above problems, the present inventors conducted intensive research. In order to suppress the volatilization of the sintering aid from the green sheet by the atmosphere conditioner, it is important that the volatilized atmosphere conditioner remains in the container. By devising the shape of the connection portion between the container part and the lid part of the firing container, it becomes possible to efficiently keep the atmosphere conditioner in the container, efficiently suppress the volatilization of the sintering aid from the green sheet, and it has been found that a highly uniform silicon nitride substrate can be easily obtained.

[0008] That is, the present invention is a method for manufacturing a silicon nitride substrate, including a firing step of disposing a green sheet containing silicon nitride powder and a sintering aid powder and an atmosphere conditioner in a firing container having two or more corners at the connection portion between the container part and the lid part, and firing at 1700°C to 1900°C.

Effects of the Invention

[0009] By the manufacturing method of the present invention, a highly uniform silicon nitride substrate can be easily manufactured without precisely controlling the firing conditions.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] The method for manufacturing a silicon nitride substrate of the present invention includes a step of disposing a green sheet containing silicon nitride powder and a sintering aid powder and an atmosphere adjuster in a firing container having two corners at a connection portion between a container portion and a lid portion, and firing at 1700°C to 1900°C.

[0012] The green sheet is not particularly limited as long as it contains silicon nitride powder and a sintering aid powder, and a known green sheet can be used. The green sheet can be obtained by a method including a raw material mixing step of mixing the silicon nitride powder and the sintering aid powder to obtain a raw material mixture, and a molding step of molding the raw material mixture into a desired shape.

[0013] The method of mixing the silicon nitride powder and the sintering aid powder in the raw material mixing step is not particularly limited. For example, each component can be weighed out in a predetermined blending amount and mixed dry, or mixed wet using a dispersion medium. Examples of the mixing device for dry mixing include a dry bead mill, an attritor, etc. Examples of the mixing device for wet mixing include an ultrasonic dispersion device, a bead mill, a ball mill, a roll mill, a homomixer, an ultramixer, a disperser mixer, a penetration type high-pressure dispersion device, a collision type high-pressure dispersion device, a porous type high-pressure dispersion device, a damato type high-pressure dispersion device, a (collision + penetration) type high-pressure dispersion device, an ultra-high pressure homogenizer, etc. Examples of the dispersion medium for wet mixing include water, alcohol, toluene, etc.

[0014] The silicon nitride powder is not particularly limited, and known silicon nitride powders can be used. The silicon nitride powder may be composed of α-type silicon nitride, β-type silicon nitride, or a mixture thereof. Since β powder is less likely to undergo grain growth during sintering and is easier to control uniformity compared to α powder, it is preferable to include β-type silicon nitride when emphasizing the uniformity of the silicon nitride substrate. In that case, the β-phase ratio of the silicon nitride powder is preferably 80% or more, more preferably 90% or more, and even more preferably 99% or more. The β-phase ratio of the silicon nitride powder means the peak intensity ratio of the β-phase to the total of the α-phase and β-phase in the silicon nitride powder [100×(peak intensity of the β-phase) / (peak intensity of the α-phase + peak intensity of the β-phase)], and is determined by powder X-ray diffraction (XRD) measurement using CuKα radiation. More specifically, it is determined by calculating the weight ratio of the α-phase and β-phase of the silicon nitride powder by the method described in C.P. Gazzara and D.R. Messier: Ceram. Bull., 56(1977), 777-780.

[0015] The particle size of the silicon nitride powder is not particularly limited, but the average particle size D50 is preferably 0.5 to 3.0 μm, and more preferably 1.0 to 2.0 μm. Also, the specific surface area of the silicon nitride powder is preferably 7 to 20 m 2 / g, and more preferably 12 to 15 m 2 / g. In the present invention, the average particle size D50 means the value at the 50% volume basis measured by the laser diffraction scattering method, and the specific surface area means the BET specific surface area measured using the BET one-point method by nitrogen gas adsorption.

[0016] Known sintering aid powders can be used without particular limitation, and examples include oxides such as yttria, magnesia, ceria, and calcia, and oxygen-free compounds such as carbonitride-based compounds and nitride-based compounds. Examples of carbonitride-based compounds include Y2Si4N6C, Yb2Si4N6C, Ce2Si4N6C, and MgSi4N6C. Examples of nitride-based compounds include MgSiN2.

[0017] Among these, magnesium-based compounds have a low boiling point and tend to cause volatilization of the sintering aid during the firing process. Therefore, when using a sintering aid containing magnesium, the effect of the present invention is particularly great, which is preferable. In particular, the ratio of magnesium atoms in the total amount of the sintering aid is preferably 10% by mass or more, and more preferably 15% by mass or more. The upper limit of the ratio of magnesium atoms in the total amount of the sintering aid is not particularly limited, but for example, it may be 65% by mass or less, particularly 50% by mass or less.

[0018] The raw material mixture may contain other components in addition to the silicon nitride powder and the sintering aid powder. Examples of other components include, in addition to the dispersion medium, binders, dispersants, plasticizers, antifoaming agents, and the like.

[0019] Examples of the binder include polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, acrylic resins, polyacrylamide, urethane resins, polyesters, polyethers, melamine, epoxy resins, cellulose-based resins, starch, and the like. These binders can be used alone or in combination of two or more. The amount of the binder can be appropriately selected. For example, it can be selected from the range of usually 1 to 30 parts by mass, particularly 10 to 25 parts by mass, based on 100 parts by mass of the total amount of the silicon nitride powder and the sintering aid powder.

[0020] The dispersant is used to enhance the dispersibility of silicon nitride powder and sintering aid powder. Generally, surfactants can be preferably used. Known surfactants can be used without any limitation. Specific examples of surfactants that can be preferably used in the present invention include carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, tetraglycerin monooleate, hexaglycerin monooleate, sorbitan laurate, sorbitan oleate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, and the like. These surfactants may be used alone or in combination of two or more. The amount of the dispersant can be appropriately selected. For example, it can usually be selected from the range of 0.1 to 5 parts by mass based on 100 parts by mass of the total amount of the silicon nitride powder and the sintering aid powder. Among this range, the upper limit value of the amount of the dispersant is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less.

[0021] In the molding step, a molded body having a desired shape is obtained from the raw material mixture obtained in the mixing step. The molding method for obtaining the molded body is not particularly limited. For example, it can be molded by press molding from the raw material mixture, or press molding can be carried out using granules obtained by drying a slurry of the raw material mixture containing a dispersion medium with a spray dryer or the like, or sheet molding can be performed on the slurry of the raw material mixture containing a dispersion medium by the doctor blade method or the like. Among these, sheet molding by the doctor blade method is preferable because it can be manufactured simply.

[0022] When the formed body obtained in the forming process contains an organic component such as a dispersion medium, a binder, a dispersant, a plasticizer, and an antifoaming agent, in order to facilitate firing, before the firing process, drying to remove the dispersion medium and degreasing to remove the binder, etc. may be performed to obtain a green sheet. The conditions for the drying are not particularly limited. For example, when the dispersion medium is water, it may be performed by heating the formed body to about 30°C to 150°C. The degreasing conditions are not particularly limited. For example, it may be performed by heating the formed body to 450 to 650°C in air or an inert atmosphere such as nitrogen or argon.

[0023] In the firing process, the green sheet and the atmosphere conditioner are placed in a firing container having two corners at the connection part between the container part and the lid part, and fired at 1700°C to 1900°C. The atmosphere conditioner is used to prevent the volatilization of the auxiliary agent component. Specifically, those having the same chemical composition as the sintering aid powder or compounds of the metal elements contained in the sintering aid are used. As the compounds of the metal elements contained in the sintering aid, oxides of the metal elements contained in the sintering aid are preferably used. For example, when magnesia is used as the sintering aid, magnesia is used as the atmosphere conditioner, and when MgSiN2 is used as the sintering aid, it is preferable to use MgSiN2 or magnesia as the atmosphere conditioner.

[0024] When a plurality of compounds are used as the sintering aid powder, the abundance ratio of the metal elements contained in the atmosphere conditioner may be adjusted so that the difference from the abundance ratio with the sintering aid powder is within 20%. In that case, those having the same chemical composition as the sintering aid powder or oxides of the metal elements contained in the sintering aid may be mixed and used in a desired abundance ratio, or each may be placed in the firing container so as to have a desired abundance ratio.

[0025] The amount of the atmosphere regulator placed in the firing container in the firing process is preferably 5.0 g or more, more preferably 7.0 g or more per 100 g of the green sheet. By setting the amount of the atmosphere regulator within the above range, the volatilization of the sintering aid from the green sheet can be efficiently suppressed. The upper limit of the amount of the atmosphere regulator is not particularly limited, but if it is too much, the production efficiency will be poor. Therefore, it is preferably 15.0 g or less, more preferably 10.0 g or less per 100 g of the green sheet.

[0026] The atmosphere regulator may be in powder form or in bulk form. However, since it can efficiently volatilize and easily fill the firing container, it is preferably in powder form. When the atmosphere regulator is in powder form, from the viewpoint of efficiently filling the firing container, the particle size is preferably 1.0 μm to 2.0 μm.

[0027] The firing container has two corners at the connection part between the container part and the lid part. By increasing the number of corners of the connection part in this way, it becomes difficult for the gas inside the firing container to be released to the outside of the firing container through the connection part, and the airtightness of the firing container is improved. As a result, it is highly prevented that the atmosphere regulator volatilized during firing is discharged outside the container and fills the inside of the firing container. By highly suppressing the volatilization of the sintering aid from the green sheet, it is presumed that the uniformity of the silicon nitride substrate can be easily enhanced.

[0028] As such a firing container having two corners at the connection part between the container part and the lid part, for example, a firing container as shown in FIGS. 1 and 2 in the cross-sectional view can be used. The firing container shown in FIG. 1 has a container part 1 and a lid part 2, and has two corners at the connection part 3 between the container part 1 and the lid part 2. The firing container shown in FIG. 2 has the same two corners although the structure of the connection part 3 is different from that of FIG. 1.

[0029] On the one hand, the firing container shown in FIG. 3, which has been widely used in the past, has only one corner at the connection part between the container part and the lid part, and the firing container shown in FIG. 4 has no corner at the connection part between the container part and the lid part. In such a firing container, the airtightness is not high enough to highly prevent the atmosphere regulator volatilized during firing from being discharged outside the container, and since it does not fill the firing container sufficiently, it is necessary to control the firing conditions and the like in detail in order to highly enhance the uniformity of the silicon nitride substrate.

[0030] In the firing container, there may be three or more corners, but as the number of corners increases, it becomes troublesome to manufacture and maintain the firing container. Therefore, the number of corners is preferably five or less, and more preferably three or less. The angle of the corner may be an acute angle or an obtuse angle rather than 90°, but from the viewpoints of ensuring airtightness and ease of manufacturing and maintenance of the firing container, it is preferably 45° to 135°, and more preferably 80° to 100°. Since the shape on the container part side and the shape on the lid part side at the connection part are the same due to the necessity of sealing, the sum of the angle on the container part side and the angle on the lid part side is 360°. However, the angle of the corner is the smaller value of the angle on the container body side and the angle on the lid side.

[0031] In the firing container, the length of the connection part 3 is preferably 2 mm or more, and more preferably 4 mm or more. By increasing the length of the connection part, it becomes difficult for the gas inside the firing container to be released to the outside of the firing container through the connection part, and it becomes easy to improve the airtightness. The upper limit of the length of the connection part 3 is not particularly limited, but if it is made long, the firing container becomes large and difficult to manufacture and handle. Therefore, it is usually 50 mm or less, and particularly 45 mm or less. The length of the connection part is the shortest length from the inside to the outside of the firing container at the part where the container part 1 and the lid part 2 of the firing container are in contact. Since the shape on the container part side and the shape on the lid part side at the connection part are the same as described above, the length of the connection part may be measured on the container part side.

[0032] The volume of the firing container is not particularly limited, but in order to easily fill the firing container sufficiently with the volatilized atmosphere regulator, the volume of the firing container per 100 g of the atmosphere regulator is 5250 m3 Hereinafter, particularly 5000 m 3 or less is preferable. The lower limit of the volume of the firing container is not particularly limited, but if it is too small, the internal pressure will increase due to the volatilized atmosphere regulator, making it difficult to handle. Therefore, the volume of the firing container per 100 g of the atmosphere regulator is 2500 m 3 or more, particularly preferably 2600 m 3 or more.

[0033] The shape of the firing container in the previous stage is not particularly limited. For example, it may be a rectangular parallelepiped shape or a cylindrical shape. The material of the firing container in the previous stage is not particularly limited and may be a known material used as a firing container for a silicon nitride substrate.

[0034] Only one green sheet may be placed in the firing container, or a plurality of green sheets may be placed. When a plurality of green sheets are placed, they may be stacked.

[0035] The firing temperature is 1700°C to 1900°C, preferably 1820°C to 1880°C. The firing time is not particularly limited, but it is preferably 1 to 30 hours, particularly preferably 3 to 20 hours. The firing atmosphere is preferably carried out under an inert atmosphere. The firing pressure may be carried out at normal pressure or under pressure.

Examples

[0036] Hereinafter, in order to specifically explain the present invention, examples will be described, but the present invention is not limited to these examples. The measurement of each item in the examples and comparative examples was carried out by the following methods.

[0037] (1) Evaluation of uniformity by measuring the hardness distribution by nanoindentation test A silicon nitride substrate was cut into 10 mm × 10 mm to obtain test pieces. Subsequently, mirror finishing was performed on the main surface, and the surface roughness of the main surface of the test body was processed to 0.2 μm or less. The surface roughness of the test body was measured at five locations for the surface roughness Ra of an arbitrary 1000 μm × 1000 μm test area of the test body using a non-contact three-dimensional measuring device (manufactured by Keyence Corporation: VR-5000), and it was confirmed that Ra was 0.2 μm or less in all the test areas. A nanoindentation test was performed by pressing a indenter into 3600 locations at equal intervals in a range of 30 μm × 30 μm on the mirror-finished surface of the test body under the conditions of a load of 0.5 mN in an air atmosphere to obtain the microhardness. The nanoindentation test was performed at five points near the center and near the four corners of the main surface of the test piece, and the hardness distribution in the micro region was obtained from the results. The nanoindentation test measures the indentation hardness using a small indenter and enables the evaluation of a micro region. The hardness reflects the properties of silicon nitride particles or the auxiliary phase at each measurement location. If the hardness distribution is sharp, it can be said that the uniformity is high. The hardness distribution is evaluated by the ratio of the hardness at 10% cumulative and the hardness at 90% cumulative (the value obtained by dividing the hardness at 10% cumulative by the hardness at 90% cumulative). The closer this value is to 1, which is the theoretically maximum value, the sharper and more uniform the hardness distribution. Generally, the silicon nitride particles and the auxiliary phase have different hardnesses, and the silicon nitride particles show a higher hardness. In this evaluation, the properties of the silicon nitride particles were evaluated by the region with a hardness of 15.00 or more, and the properties of the auxiliary phase were evaluated by the region with a hardness of less than 15.00. In Table 1, HA10 represents the hardness at 10% cumulative in the region with a hardness of less than 15.00, HA90 represents the hardness at 90% cumulative in the region with a hardness of less than 15.00, HS10 represents the hardness at 10% cumulative in the region with a hardness of 15.00 or more, and HS90 represents the hardness at 90% cumulative in the region with a hardness of 15.00 or more, respectively.

[0038] (2) Evaluation of uniformity by measuring the Young's modulus distribution by nanoindentation test A silicon nitride substrate was cut into 10 mm × 10 mm to obtain test pieces. Next, mirror finishing was performed on the main surface, and the surface roughness of the main surface of the test body was processed to 0.2 μm or less. The surface roughness of the test body was measured at five locations for the surface roughness Ra of an arbitrary 1000 μm × 1000 μm test area of the test body using a non-contact three-dimensional measuring device (Keyence Corporation: VR-5000), and it was confirmed that Ra was 0.2 μm or less in all the test areas. A nanoindentation test was performed by pressing a indenter into 3600 locations at equal intervals in a range of 30 μm × 30 μm on the mirror-finished surface of the test body under the conditions of a load of 0.5 mN in an air atmosphere to obtain the Young's modulus in a minute region. The nanoindentation test was performed at five points near the center and near the four corners of the main surface of the test piece, and the Young's modulus distribution in the minute region was obtained from the results. As described above, the nanoindentation test enables evaluation of a minute region. The Young's modulus reflects the properties of silicon nitride particles or the auxiliary agent phase at each measurement location. If the Young's modulus distribution is sharp, it can be said that the uniformity is high. The Young's modulus distribution is evaluated by the ratio of the hardness at 10% cumulative and the hardness at 90% cumulative (the value obtained by dividing the hardness at 10% cumulative by the hardness at 90% cumulative), and the closer this value is to 1, which is the theoretical maximum value, the sharper the hardness distribution and the higher the uniformity. Generally, the silicon nitride particles and the auxiliary agent phase have different hardnesses, and the silicon nitride particles exhibit a higher Young's modulus. In this evaluation, the properties of the silicon nitride particles were evaluated by the region with a Young's modulus of 225 GPa or more, and the properties of the auxiliary agent phase were evaluated by the region with a Young's modulus of less than 225 GPa. In Table 2, EA10 represents the hardness at 10% cumulative in the region with a hardness of less than 225 GPa, EA90 represents the hardness at 90% cumulative in the region with a hardness of less than 225 GPa, ES10 represents the hardness at 10% cumulative in the region with a hardness of 225 GPa or more, and ES10 represents the hardness at 90% cumulative in the region with a hardness of 225 GPa or more, respectively.

[0039] For the production of the silicon nitride substrate, raw materials containing the following silicon nitride powder and sintering aid were used.

[0040] <Silicon nitride powder> ·Silicon nitride powder Y that was subjected to steam heat treatment by placing a silicon nitride powder produced in the same manner as silicon nitride powder A described in the examples of WO2021 / 107021 and a vat containing twice the amount of water of the silicon nitride powder in a thermostatic bath, heating to 500°C, and allowing to stand for 1 hour. The β-phase conversion rate was 99%. The average particle size D50 was 1.8 μm. ·Silicon nitride powder produced in the same manner as silicon nitride powder A described in the examples of WO2021 / 107021 was acid-treated at 60°C for 2 hours using a 1:1 mixed aqueous solution of 35% hydrochloric acid and 55% hydrofluoric acid, then filtered, washed with water, vacuum-dried at 200°C, and pulverized with a vibration ball mill for 4 hours. Thereafter, silicon nitride powder Z that was subjected to steam heat treatment by placing a vat containing twice the amount of water of the silicon nitride powder in a thermostatic bath, heating to 500°C, and allowing to stand for 1 hour. The β-phase conversion rate was 99%. The average particle size D50 was 1.8 μm.

[0041] <Sintering aid> ·Yttria (manufactured by Shin-Etsu Chemical Co., Ltd.) ·Magnesia (manufactured by Ube Materials Co., Ltd.)

[0042] <Binder and dispersant> ·Binder: Acrylic resin (manufactured by Fujikura Kasei Co., Ltd.) ·Dispersant: Cerna D735 (manufactured by Chukyo Yushi Co., Ltd.)

[0043] <Example 1> 100 parts by mass of silicon nitride powder, 5 parts by mass of yttria, 3 parts by mass of magnesia, and 0.5 parts by mass of a dispersant were weighed. Using water as a solvent, a resin pot and silicon nitride balls, mixing was carried out in a ball mill for 24 hours. Incidentally, water was previously weighed so that the concentration of the slurry was 60% by mass and put into the resin pot. After the mixing, 22 parts by mass of a binder was added and mixing was further carried out for 12 hours to obtain a slurry-like molding composition. Next, defoaming of the molding composition was carried out using a vacuum degassing machine (manufactured by Sayama Riken Co., Ltd.) and the viscosity was adjusted to prepare a coating slurry. Thereafter, using this viscosity-adjusted coating slurry, sheet forming was carried out by the doctor blade method, and drying was carried out at 100 ° C in air to vaporize the solvent, and a green sheet having a width of 750 mm and a thickness of 420 μm was obtained. The green sheet obtained as described above was subjected to a debinding treatment at a temperature of 550 ° C in dry air to obtain a debound green sheet. Thereafter, the debound green sheet was cut into 100 mm × 100 mm, put into a firing container, and fired at 1880 ° C for 9 hours under a nitrogen atmosphere and a pressure of 0.9 MPa·G to obtain a silicon nitride substrate. As the firing container, a container having two corners at the connection part and a connection part length of 4.0 mm as shown in FIG. 1 was used. Further, as an atmosphere regulator, 5 g of yttria and 3 g of magnesia per 100 g of the green sheet (molded body) were present in the firing container. The evaluation results of the obtained silicon nitride substrate are shown in Table 1.

[0044] <Example 2> A silicon nitride substrate was obtained in the same manner as in Example 1 except that a container having two corners at the connection part and a connection part length of 4.0 mm as shown in FIG. 2 was used as the firing container. The evaluation results of the obtained silicon nitride substrate are shown in Table 1.

[0045] <Comparative Example 1> A silicon nitride substrate was obtained in the same manner as in Example 1 except that a container having one corner at the connection part and a connection part length of 3.0 mm as shown in FIG. 3 was used as the firing container. The evaluation results of the obtained silicon nitride substrate are shown in Table 1.

[0046] <Comparative Example 2> As the fired container, a container shown in Fig. 4 having no corner at the connection portion and a connection portion length of 2.0 mm was used, and a silicon nitride substrate was obtained in the same manner as in Example 1. The evaluation results of the obtained silicon nitride substrate are shown in Table 1.

[0047] <Example 3> A silicon nitride substrate was obtained in the same manner as in Example 1, except that silicon nitride powder Z was used as the silicon nitride powder. The evaluation results of the obtained silicon nitride substrate are shown in Table 2.

[0048] <Example 4> A silicon nitride substrate was obtained in the same manner as in Example 2, except that silicon nitride powder Z was used as the silicon nitride powder. The evaluation results of the obtained silicon nitride substrate are shown in Table 2.

[0049] <Comparative Example 3> A silicon nitride substrate was obtained in the same manner as in Comparative Example 1, except that silicon nitride powder Z was used as the silicon nitride powder. The evaluation results of the obtained silicon nitride substrate are shown in Table 2.

[0050] <Comparative Example 4> A silicon nitride substrate was obtained in the same manner as in Comparative Example 2, except that silicon nitride powder Z was used as the silicon nitride powder. The evaluation results of the obtained silicon nitride substrate are shown in Table 2.

[0051]

Table 1

[0052]

Table 2

[0053] As shown in Tables 1 and 2, when using the same green sheet and performing firing while only changing the firing container, when using a firing container having two or more corners at the connection part between the container part and the lid part, the uniformity of the obtained silicon nitride substrate was higher compared to the case of using a firing container having one or less corners at the connection part. Usually, since the auxiliary agent volatilizes disorderly from the green sheet during firing, unevenness occurs in the progress of sintering, and it is difficult to highly enhance the uniformity of the obtained silicon nitride substrate. However, by using a firing container having two or more corners at the connection part between the container part and the lid part as the firing container and using an atmosphere adjuster, the volatilization of the sintering aid from the green sheet is suppressed, and as a result, even without highly controlling the firing conditions, sintering proceeds uniformly, and it is considered that a silicon nitride substrate with high uniformity could be easily obtained. Thereby, it was shown that a silicon nitride substrate with high uniformity can be easily obtained by the manufacturing method of the present invention.

Explanation of Signs

[0054] 1 Container part 2 Lid part 3 Connection part

Claims

1. A method for manufacturing a silicon nitride substrate, comprising a firing step of disposing a green sheet containing silicon nitride powder and a sintering aid powder and an atmosphere conditioner in a firing container having two or more corners at a connection portion between a container part and a lid part, and firing at 1700°C to 1900°C.

2. The method for manufacturing a silicon nitride substrate according to claim 1, wherein the sintering aid powder contains a compound containing magnesium.

3. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, wherein the amount of the atmosphere conditioner disposed in the firing container is 5.0 g or more and 15.0 g or less per 100 g of the green sheet.

4. A firing container having two or more corners at a connection portion between a container part and a lid part.

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