Silicon nitride substrate

Abstract

To provide a silicon nitride substrate having few microcracks and high uniformity at the microstructure level when the substrate is cut using laser scribing.SOLUTION: A silicon nitride substrate is configured such that, in a Young's modulus distribution obtained from nanoindentation testing under a load of 0.5 mN, a ratio R1 (EA10 / EA90) of a cumulative 10% Young's modulus EA10 in a region having a Young's modulus of less than 225 GPa and a cumulative 90% Young's modulus EA90 in a region having a Young's modulus of less than 225 GPa is 0.46 or more, and a ratio R2 (ES10 / ES90) of a cumulative 10% Young's modulus ES10 in a region having a Young's modulus of 225 GPa or more and a cumulative 90% Young's modulus ES90 in a region having a Young's modulus of 225 GPa or more is 0.71 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to silicon nitride substrates. [Background technology]

[0002] Silicon nitride is used for semiconductor module substrates and the like because of its excellent mechanical strength, thermal conductivity, and electrical insulation (for example, Patent Document 1). When using such a silicon nitride substrate, the silicon nitride substrate is often cut to an appropriate size. When cutting a silicon nitride substrate, cutting by applying pressure as is may cause cracks or uneven cut surfaces, so cutting using laser scribing is widely used. Laser scribing is a method of forming shallow grooves on the surface of a silicon nitride substrate along the cut location using a laser, and then by applying bending pressure to the silicon nitride substrate, it is possible to easily cut along the grooves, making it easy to prevent cracks and uneven cut surfaces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2020 / 203787 issue Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, by utilizing laser scribing, it is possible to suppress appearance problems such as cracks and uneven cut surfaces when cutting a silicon nitride substrate. However, the inventors' investigations have revealed that even when laser scribing is utilized to cut a silicon nitride substrate, microcracks may occur starting from the cut site. Furthermore, such microcracks may become the starting point for fracture of the silicon nitride substrate when mechanical and thermal loads are applied during use of the silicon nitride substrate, and may cause a decrease in reliability when the silicon nitride substrate is used for a long period of time.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicon nitride substrate in which microcracks are less likely to occur when cut. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors have conducted extensive research and have concluded that in order to control the occurrence of microcracks, it is effective to prevent large localized strains from occurring during cutting, and that this can be prevented by increasing the uniformity of the silicon nitride substrate at the microstructure level. Incidentally, Patent Document 1 discloses a silicon nitride substrate in which the amounts of magnesium, yttrium, and oxygen are measured at the center and near the edges of the substrate surface, and there is little difference between the center and the edges. As such, it discloses that the distribution of the auxiliary agent is made uniform from a macroscopic point of view. However, it was thought that with regard to the occurrence of microcracks, it is not uniformity from such a macroscopic point of view, but uniformity at the microstructural level that is important.

[0007] After further investigation, the inventors discovered that by controlling the raw material silicon nitride powder and sintering conditions, it is possible to obtain a silicon nitride substrate with a highly uniform Young's modulus at the microstructural level, and that such a silicon nitride substrate can suppress the occurrence of microcracks, which led to the completion of the present invention.

[0008] That is, the present invention is a silicon nitride substrate in which, in a Young's modulus distribution obtained by a nanoindentation test under a load of 0.5 mN, the ratio R1 (EA10 / EA90) of the cumulative 10% Young's modulus EA10 in the region where the Young's modulus is less than 225 GPa to the cumulative 90% Young's modulus EA90 in the region where the Young's modulus is less than 225 GPa is 0.46 or more, and the ratio R2 (ES10 / ES90) of the cumulative 10% Young's modulus ES10 in the region where the Young's modulus is 225 GPa or more to the cumulative 90% Young's modulus ES90 in the region where the Young's modulus is 225 GPa or more is 0.71 or more. Effect of the Invention

[0009] The silicon nitride substrate of the present invention makes it possible to suppress the occurrence of microcracks when cut, and thus makes it possible to provide a highly reliable silicon nitride substrate that is less likely to break due to mechanical or thermal loads during use. [Brief description of the drawings]

[0010]

Figure 1

Figure 2

Figure 3

[0011] In the silicon nitride substrate of the present invention, in a Young's modulus distribution obtained by a nanoindentation test under a load of 0.5 mN, the ratio R1 (EA10 / EA90) of the cumulative 10% Young's modulus EA10 in the region where the Young's modulus is less than 225 GPa to the cumulative 90% Young's modulus EA90 in the region where the Young's modulus is less than 225 GPa is 0.46 or more, and the ratio R2 (ES10 / ES90) of the cumulative 10% Young's modulus ES10 in the region where the Young's modulus is 225 GPa or more to the cumulative 90% Young's modulus ES90 in the region where the Young's modulus is 225 GPa or more is 0.71 or more.

[0012] The nanoindentation test performs a pressing test using a minute indenter and enables evaluation of a minute region. Usually, a silicon nitride substrate has silicon nitride particles and an auxiliary phase derived from a sintering aid. If each of the silicon nitride particles and the auxiliary phase is homogeneous, it can be said that they have high uniformity at the microstructural level. Note that in the nanoindentation test, in order to prevent the influence of surface irregularities, it is necessary to perform the test with the surface roughness of the test piece being 0.2 μm or less. If the surface roughness is 0.2 μm or less, evaluation can be performed with almost no influence from surface irregularities. The surface roughness of the test piece can be made 0.2 μm or less by mirror finishing.

[0013] As a result of investigations by the present inventors, it has been found that the uniformity of each of the silicon nitride particles and the auxiliary phase can be evaluated by a nanoindentation test. That is, by performing a nanoindentation test under the condition of a load of 0.5 mN, a Young's modulus distribution in a minute region can be obtained. The Young's modulus reflects the properties of the silicon nitride particles or the auxiliary phase at each measurement location, and if the Young's modulus distribution is sharp, it can be said that the uniformity is high. Generally, the Young's modulus of the silicon nitride particles and the auxiliary phase is different, and the silicon nitride particles exhibit a higher Young's modulus. In the nanoindentation test under the above conditions, it was considered that the properties of the silicon nitride particles can be evaluated by the region with a Young's modulus of 225 GPa or more, and the properties of the auxiliary phase can be evaluated by the region with a Young's modulus of less than 225 GPa. And if the Young's modulus distribution is sharp, that is, if the ratio of the cumulative 10% Young's modulus to the cumulative 90% Young's modulus (the value obtained by dividing the cumulative 10% Young's modulus by the cumulative 90% Young's modulus) is large, it can be said that the uniformity is high.

[0014] In the present invention, the Young's modulus of 10% cumulative is the Young's modulus of 10% cumulative from the smallest when the measurement data of Young's modulus obtained in the range of Young's modulus, i.e., Young's modulus of 225 GPa or more and Young's modulus of less than 225 GPa, are rearranged in ascending order of Young's modulus. Similarly, the Young's modulus of 90% cumulative is the Young's modulus of 90% cumulative from the smallest when the measurement data obtained are rearranged in ascending order of Young's modulus. Specifically, when n pieces of measurement data are obtained, the Young's modulus of the 0.1nth Young's modulus is the Young's modulus of 10% cumulative, and the Young's modulus of the 0.9nth Young's modulus is the Young's modulus of 90% cumulative. In addition, when 0.1n and 0.9n are not integers, the cumulative Young's modulus of 10% and the cumulative Young's modulus of 90% may be obtained by rounding them to integers.

[0015] As described above, the properties of the auxiliary phase can be evaluated by the region where the Young's modulus is less than 225 GPa, and therefore, in the Young's modulus distribution obtained by the nanoindentation test, the Young's modulus is evaluated by calculating the ratio R1 (EA10 / EA90) of the cumulative 10% Young's modulus (EA10) in the region where the Young's modulus is less than 225 GPa to the cumulative 90% Young's modulus (EA90) in the region where the Young's modulus is less than 225 GPa. In the silicon nitride substrate of the present invention, R1 is 0.46 or more, preferably 0.47 or more, and more preferably 0.48 or more. The upper limit of R1 is not particularly limited, and may be any value less than 1.00, which is the theoretical maximum value, but is usually 0.90 or less, particularly 0.80 or less, and further 0.60 or less.

[0016] In addition, since the properties of the silicon nitride particles can be evaluated by the region with a Young's modulus of 225 GPa or more, in the Young's modulus distribution obtained by the nanoindentation test, the ratio R2 (ES10 / ES90) of the cumulative 10% Young's modulus (ES10) in the region with a Young's modulus of 225 GPa or more to the cumulative 90% Young's modulus (ES90) in the region with a Young's modulus of 225 GPa or more is calculated for evaluation. The silicon nitride substrate of the present invention has an R2 of 0.71 or more, preferably 0.72 or more. The upper limit of R2 is not particularly limited and may be any value equal to or less than the theoretical maximum value of 1.00, but is usually 0.90 or less, particularly 0.80 or less.

[0017] If R1 and R2 are within the above ranges, it can be said that the silicon nitride substrate has high uniformity at the microstructural level for each of the silicon nitride particles and the auxiliary phase. And the silicon nitride substrate can suppress the generation of microcracks. The reason for this is not clear, but the inventors of the present invention consider it as follows.

[0018] When a force is applied to cut the silicon nitride substrate, stress is applied to the silicon nitride substrate, and due to this stress, strain is unevenly generated in the silicon nitride substrate, resulting in a locally large load being generated in the silicon nitride substrate and microcracks being generated. And since microcracks are cracks generated in a micro region, it is presumed that the non-uniformity at the microstructural level causes microcracks. Here, the Young's modulus is an index indicating the relationship between stress and strain. If the Young's modulus is uniform at the microstructural level, the strain will also be generated uniformly. Therefore, it is presumed that a locally large load at the microstructural level in the silicon nitride substrate can be suppressed, and the generation of microcracks can be suppressed. Note that the silicon nitride substrate contains both the silicon nitride particles and the auxiliary phase as described above, and since their Young's moduli are different, it is difficult to make them completely uniform. However, by enhancing the uniformity of the Young's modulus at the microstructural level for each of the silicon nitride grains and the auxiliary phase, it is presumed that the non-uniformity of strain generation can be reduced, and the generation of microcracks can be suppressed.

[0019] The silicon nitride substrate has silicon nitride particles and an auxiliary phase as described above. The auxiliary phase is composed of components derived from a sintering auxiliary. The blending ratio of the silicon nitride particles and the auxiliary phase is not particularly limited, but if the auxiliary phase is too little, sintering may be insufficient and mechanical properties such as strength may be insufficient, and if the auxiliary phase is too much, the advantages of the silicon nitride substrate may not be fully exhibited. Therefore, in the Young's modulus distribution obtained by the nanoindentation test, the points with a Young's modulus of 225 GPa or more are preferably 60% or more, more preferably 70% or more, and preferably 95% or less, and more preferably 90% or less.

[0020] The silicon nitride substrate of the present invention is preferably plate-shaped. The size of the main surface is not particularly limited, but if the size is too large, it becomes difficult to improve uniformity, so the main surface is preferably rectangular and is 200 mm x 200 mm or less, more preferably 100 mm x 100 mm or less. The lower limit of the size of the main surface is preferably 10 mm x 10 mm or more, which is easy to process for nanoindentation measurement. In addition, the ratio of the length of the long side to the short side of the main surface is not particularly limited. The thickness of the silicon nitride substrate of the present invention is not particularly limited, but is generally 0.1 mm to 2.0 mm.

[0021] The silicon nitride substrate of the present invention preferably has a three-point bending strength of 600 MPa or more. 1 / 2 It is preferable that the EA10 is 80 GPa or more, and preferably 90 GPa or more, and the ES90 is 400 GPa or less, and more preferably 380 GPa or less. Furthermore, the silicon nitride substrate of the present invention preferably has an iron content of 20 ppm or less, and the total amount of iron and metal impurities other than iron is preferably 25 ppm or less.

[0022] The silicon nitride substrate of the present invention can be easily obtained by a method for producing a silicon nitride substrate including at least the following steps: a water vapor heat treatment step of exposing silicon nitride powder having an iron content of 20 ppm or less to water vapor under heating and an oxygen-containing atmosphere; a mixing step of mixing the silicon nitride powder obtained in the water vapor heat treatment step with a sintering aid powder having an iron content of 20 ppm or less to obtain a raw material mixture; a molding step of obtaining a molded body of a desired shape from the raw material mixture; and a firing step of firing the molded body at 1700°C to 1900°C in the presence of 5.0 g or more of an atmospheric adjuster per 100 g of molded body.

[0023] The steam heating process is a process in which silicon nitride powder is exposed to steam under heating and oxygen-containing atmosphere. It is believed that this process adjusts the surface of the silicon nitride powder to a stable and uniform state, thereby making it possible to obtain a silicon nitride substrate with high uniformity at the microstructure level. Although the reason is unclear, the present inventors speculate as follows. That is, oxygen is required for sintering silicon nitride, and the auxiliary component reacts with oxygen to generate a liquid phase, which is then densified by liquid phase sintering. Therefore, it is believed that if there is variation in the surface oxidation state of the silicon nitride powder, there will be variation in the sintering reaction, and the uniformity at the microstructure level will decrease. The oxidation of silicon nitride powder also progresses due to thermal and mechanical loads during the manufacturing process of the silicon nitride substrate, such as mixing with sintering auxiliary powder, molding, and firing. Oxidation due to loads in such manufacturing processes is difficult to control, and surface oxidation state is likely to vary. Here, by performing a steam heating process in advance before firing, the oxidation of the surface of the silicon nitride powder will progress sufficiently. This makes it difficult for oxygen to reach the silicon nitride portion, making it less likely for oxidation due to stress during the manufacturing process to occur and less likely for the oxidation to vary in progress. As a result, it is believed that variation in the sintering reaction is suppressed, making it possible to obtain a silicon nitride substrate with high uniformity at the microstructural level.

[0024] The steam heat treatment only needs to expose the silicon nitride powder to steam under heating. Specifically, the silicon nitride powder and water may be placed in a container with a lid, and heating may be performed to a temperature above the temperature at which steam is generated in an oxygen-containing atmosphere. The amount of water placed in the sealed container may be equal to or more than the amount of the silicon nitride powder. The heating temperature may be 100°C or higher at which steam is generated, but from the viewpoints of ensuring and efficiently performing the treatment, it is preferably 250°C to 700°C, more preferably 400°C to 600°C. From the viewpoints of ensuring and efficiently performing the treatment, the time of the steam heat treatment is preferably 10 minutes to 200 minutes, more preferably 30 minutes to 100 minutes. The atmosphere during the steam heat treatment may be an oxygen-containing atmosphere and may be under the atmosphere. The container with a lid only needs to be filled with steam inside the container and does not necessarily have to be completely sealed. The silicon nitride powder and water may be placed in a container with an open top such as a vat and then placed inside the container with a lid.

[0025] Furthermore, in the manufacturing method, it is important that the silicon nitride powder has an iron content of 20 ppm or less. When iron is present, it is a small amount itself, so the effect on the overall mechanical properties of the silicon nitride substrate is minor, but it is not negligible when viewed locally, and is important for the uniformity at the microstructure level of the present invention. The presence of such impurities locally increases the Young's modulus and makes stress concentration more likely to occur, so it is presumed that the iron content is important. The iron content of the silicon nitride powder is preferably 15 ppm or less, more preferably 10 ppm or less. In addition, the silicon nitride powder preferably has a small amount of metal impurities other than iron, and the total amount of iron and metal impurities other than iron (hereinafter simply referred to as the "metal impurity content") is preferably 25 ppm or less, more preferably 20 ppm or less, and even more preferably 15 ppm or less. In addition, the metal impurities in the present invention refer to metal elements that are unintentionally contained in the silicon nitride substrate when manufacturing the silicon nitride substrate, and metal elements contained in the sintering aid used are not included in the metal impurities. For example, when yttria is used as a sintering aid, the amount of metal elements other than yttrium is the content of metal impurities in the present invention, and when yttria and magnesia are used, the amount of metal elements other than yttrium and magnesium is the content of metal impurities in the present invention.

[0026] In the present invention, the content of metal impurities in the silicon nitride powder, the sintering aid powder and the silicon nitride substrate can be measured by fluorescent X-ray analysis.

[0027] The content of metal impurities in silicon nitride powder can be reduced by washing (particularly, acid washing) or magnetic separation of silicon nitride powder. For example, acid washing may be performed using a mixed aqueous solution of hydrochloric acid and hydrofluoric acid at 10°C to 80°C for 0.5 to 5 hours. Commercially available hydrochloric acid with a concentration of 35% may be used, or it may be appropriately diluted before use. Commercially available hydrofluoric acid with a concentration of 55% may be used, or it may be appropriately diluted before use. The mixing ratio of hydrochloric acid and hydrofluoric acid may be, for example, 1:5 to 5:1.

[0028] The silicon nitride powder may be made of α-type silicon nitride, β-type silicon nitride, or a mixture of these. However, since β-powder is less susceptible to grain growth during sintering than α-powder and is easier to control uniformity, it is preferable to include β-type silicon nitride. The β-phase ratio of the silicon nitride powder is preferably 80% or more, more preferably 90% or more, and 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 x (peak intensity of β-phase) / (peak intensity of α-phase + peak intensity of β-phase)], and is obtained by powder X-ray diffraction (XRD) measurement using CuKα rays. More specifically, it is obtained by calculating the weight ratio of the α-phase and β-phase in the silicon nitride powder by the method described in C.P. Gazzara and D.R. Messier: Ceram. Bull., 56 (1977), 777-780.

[0029] 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, more preferably 1.0 to 2.0 μm. The specific surface area of ​​the silicon nitride powder is preferably 7 to 20 m. 2 / g, and 12 to 15m 2 In the present invention, the specific surface area refers to a BET specific surface area measured by a BET single point method using nitrogen gas adsorption.

[0030] For the same reason as for silicon nitride powder, it is important that the sintering aid powder has an iron content of 20 ppm or less. Any known sintering aid powder can be used without any particular limitation as long as the iron content is within the above range. Examples of such sintering aid powder include oxides such as yttria, magnesia, ceria, and calcia, as well as compounds that do not contain oxygen, such as carbonitride compounds and nitride compounds. Examples of carbonitride compounds include Y 2 S 4 N 6 C, Yb 2 S 4 N 6 C, Ce 2S 4 N 6 C, MgSi 4 N 6 C. Examples of nitride compounds include MgSiN 2 etc.

[0031] The sintering aid powder also preferably contains small amounts of metal impurities other than iron, and the content of metal impurities is preferably 25 ppm or less, more preferably 20 ppm or less, and even more preferably 15 ppm or less.

[0032] The silicon nitride powder and the sintering aid powder are mixed to obtain a raw material mixture. The mixing method is not particularly limited, and for example, each component may be weighed out in a predetermined blending amount and mixed in a dry state, or mixed in a wet state using a dispersion medium. Examples of mixing devices for dry mixing include a dry bead mill and an attritor. Examples of mixing devices for wet mixing include an ultrasonic dispersion device, a bead mill, a ball mill, a roll mill, a homomixer, an ultramixer, a dispersing mixer, a penetrating type high-pressure dispersion device, a collision type high-pressure dispersion device, a multi-hole type high-pressure dispersion device, a trapping type high-pressure dispersion device, a (collision + penetrating) type high-pressure dispersion device, and an ultra-high-pressure homogenizer. For example, when mixing with a ball mill, it is preferable to select and use a material that can suppress the inclusion of metal impurities such as iron, such as using a resin pot and a silicon nitride ball. Examples of dispersion media for wet mixing include water, alcohol, toluene, and the like.

[0033] The raw material mixture may contain other components in addition to the silicon nitride powder and the sintering aid powder. Examples of the other components include the dispersion medium, a binder, a dispersant, a plasticizer, and an antifoaming agent.

[0034] Examples of the binder include polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, acrylic resin, polyacrylamide, urethane resin, polyester, polyether, melamine, epoxy resin, cellulose resin, and starch. These binders can be used alone or in combination of two or more. The amount of the binder can be appropriately selected, and can be selected from the range of, for example, usually 1 to 30 parts by mass, particularly 10 to 25 parts by mass, relative to 100 parts by mass of the total amount of the silicon nitride powder and the sintering aid powder.

[0035] The dispersant is used to enhance the dispersibility of the total amount of silicon nitride powder and sintering aid powder in the molding composition, and generally, a surfactant can be suitably used. As the surfactant, any known surfactant can be used without any restrictions. Specific examples of surfactants that can be suitably used in the present invention include carboxylated trioxyethylene tridecyl ether, diglycerol monooleate, diglycerol monostearate, carboxylated heptaoxyethylene tridecyl ether, tetraglycerol monooleate, hexaglycerol 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, and can be selected, for example, from the range of 0.1 to 5 parts by mass per 100 parts by mass of the total amount of the silicon nitride powder and the sintering aid powder. Within this range, the upper limit of the amount of 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.

[0036] 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, and for example, the raw material mixture is molded by press molding, a slurry of the raw material mixture containing a dispersion medium is dried with a spray dryer or the like to obtain granules, or a slurry of the raw material mixture containing a dispersion medium is molded into a sheet by a doctor blade method or the like. Among these, the sheet molding by the doctor blade method is preferred because it can be easily produced.

[0037] When the molded body obtained in the molding step contains organic components such as a dispersion medium, a binder, a dispersant, a plasticizer, and an antifoaming agent, drying to remove the dispersion medium and degreasing to remove the binder, etc., may be performed before the firing step in order to facilitate firing. The drying conditions are not particularly limited, but for example, when the dispersion medium is water, the molded body may be heated to about 30°C to 150°C. The degreasing conditions are not particularly limited, but for example, the molded body may be heated to 450°C to 650°C in air or in an inert atmosphere such as nitrogen or argon.

[0038] In the firing step of the present invention, the green body is fired at 1700°C to 1900°C in the presence of 5.0 g or more of an atmosphere adjusting agent per 100 g of the green body. The atmosphere adjusting agent is used to prevent the volatilization of the sintering aid components, and specifically, an atmosphere adjusting agent having the same chemical composition as the sintering aid or an oxide of a metal element contained in the sintering aid is used. For example, when yttria is used as the sintering aid, yttria is used as the atmosphere adjusting agent, and Y is used as the sintering aid. 2 S 4 N 6 When C is used, Y is used as an atmosphere adjuster. 2 S 4 N 6 C or yttria is used.

[0039] When multiple compounds are used as the sintering aid powder, the difference between the abundance ratio of the metal elements contained in the atmosphere adjuster and that of the sintering aid powder may be adjusted to within 20%. In this case, a compound having the same chemical composition as the sintering aid powder or an oxide of the metal elements contained in the sintering aid may be mixed in a desired abundance ratio and used, or each may be placed in the firing vessel to achieve the desired abundance ratio.

[0040] In general, volatilization of sintering aids occurs randomly during the firing process. In order to improve the uniformity of silicon nitride substrates, it is necessary to control the volatilization of sintering aids. It is presumed that by using an atmosphere adjuster, the atmosphere adjuster volatilizes during firing and fills the firing vessel, suppressing the volatilization of sintering aids and improving the uniformity of silicon nitride substrates.

[0041] It is important that the firing step is carried out in the presence of 5.0 g or more of an atmosphere adjusting agent per 100 g of the molded body. If the amount of the atmosphere adjusting agent is small, the volatilization of the sintering aid cannot be sufficiently controlled, and uniformity at the microstructure level cannot be obtained. The amount of the atmosphere adjusting agent is preferably 5.0 g or more per 100 g of the molded body, and more preferably 7.0 g or more. There is no particular upper limit to the amount of the atmosphere adjusting agent, but if it is too much, the manufacturing efficiency is poor, so it is preferably 15.0 g or less, more preferably 10.0 g or less per 100 g of the molded body.

[0042] The atmosphere control agent may be in the form of a powder or a bulk material, but is preferably in the form of a powder, since it volatilizes efficiently and fills the firing vessel easily. When the atmosphere control agent is in the form of a powder, the particle size is preferably 1.0 μm to 2.0 μm, from the viewpoint of efficiently filling the firing vessel.

[0043] In the firing process of the present invention, it is also important to increase the airtightness of the firing vessel. If the firing vessel is not airtight, the volatilized atmosphere control agent will not sufficiently fill the firing vessel, resulting in a decrease in the uniformity of the silicon nitride substrate.

[0044] As the firing container, for example, a firing container having a cross-sectional view as shown in FIG. 1 or FIG. 2 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 a connection part 3 between the container part 1 and the lid part 2. The firing container shown in FIG. 2 has a different structure of the connection part 3 from that shown in FIG. 1, but also has two corners. A firing container that has been widely used in the past (FIG. 3) has only one corner at the connection part between the container part and the lid part. By increasing the number of corners at the connection part, it becomes difficult for gas inside the firing container to be released to the outside of the firing container through the connection part, improving airtightness.

[0045] The firing container may have three or more corners, but since the manufacturing and maintenance of the firing container becomes time-consuming when the number of corners is large, the number of corners is preferably 5 or less, and more preferably 3 or less. The angle of the corner may be more acute or obtuse than 90°, but from the viewpoint 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°. In addition, since the shape of the container side and the shape of the lid side at the connection part are the same due to the need for sealing, the angle of the container side and the angle of the lid side are summed to 360°, but the angle of the corner is the smaller value of the angle of the container body side and the angle of the lid side.

[0046] In the firing container, the length of the connection part 3 is preferably 2.0 mm or more, more preferably 4.0 mm or more. By lengthening 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. There is no particular limit to the upper limit of the length of the connection part 3, but if it is made longer, the firing container becomes large and manufacturing and handling become difficult, so it is usually 5.0 mm or less, particularly 4.5 mm or less. The length of the connection part is the shortest length from the inside to the outside of the container at the part where the container part 1 and the lid part 2 of the firing container are in contact. As described above, the shape of the container part side and the shape of the lid part side of the connection part are the same, so the length of the connection part may be measured on the container part side.

[0047] The volume of the firing container is not particularly limited. However, 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 m 3 Hereinafter, particularly 5000 m 3 or less is preferably used. The lower limit of the volume of the firing container is not particularly limited. However, 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.

[0048] 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 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

[0049] Hereinafter, in order to specifically describe the present invention, examples will be described. However, 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.

[0050] (1) Measurement of Young's modulus distribution by nanoindentation test A silicon nitride substrate was cut into 10 mm x 10 mm to obtain a test piece. Next, the main surface was mirror-finished, and the surface roughness of the main surface of the test piece was processed to 0.2 μm or less. The surface roughness of the test piece was measured at five points in an arbitrary 1000 μm x 1000 μm test area of ​​the test piece 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 test areas. A nanoindentation test was performed on the mirror-finished surface of the test piece by pressing an indenter at equal intervals at 3600 points in a range of 30 μm x 30 μm under a load of 0.5 mN in air, to obtain the Young's modulus of the micro-area. 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 of the micro-area was obtained from the results.

[0051] (2) Check for the presence of microcracks A silicon nitride substrate was cut along the groove by applying force by hand after forming a groove on it using a laser scriber. The cut surface was observed under a microscope to evaluate the presence or absence of microcracks.

[0052] The silicon nitride substrate was manufactured using the following raw materials containing silicon nitride powder and a sintering aid. <Silicon nitride powder> Silicon nitride powder X was obtained by treating silicon nitride powder produced in the same manner as silicon nitride powder A described in the examples of WO2021 / 107021 with an acid treatment using a 1:1 mixed aqueous solution of 35% hydrochloric acid and 55% hydrofluoric acid at 60°C for 2 hours, filtering, washing with water, drying in vacuum at 200°C, and pulverizing in a vibrating ball mill for 4 hours. ·Betaization rate: 99% ·Average particle size D50: 1.8μm Metal impurity content: 10ppm or less <Sintering aid> Yttria (manufactured by Shin-Etsu Chemical Co., Ltd., metal impurity content: 20 ppm or less) Magnesia (manufactured by Ube Materials, metal impurity content: 20ppm or less) <Binders and dispersants> Binder: Acrylic resin (manufactured by Fujikura Kasei Co., Ltd.) Dispersant: Cerna D735 (manufactured by Chukyo Yushi Co., Ltd.) <Example 1> A vat containing silicon nitride powder X and a vat containing water twice the amount of silicon nitride powder were placed in a thermostatic chamber, heated to 500°C, and left to stand for 1 hour, whereby a steam heating treatment was performed to obtain silicon nitride powder Y. Next, 100 parts by mass of silicon nitride powder Y, 5 parts by mass of yttria, 3 parts by mass of magnesia, and 0.5 parts by mass of dispersant were weighed, and mixed in a ball mill for 24 hours using water as a solvent and a resin pot and silicon nitride balls. The water was weighed in advance so that the concentration of the slurry was 60% by mass, and was poured into the resin pot. After the mixing, 22 parts by mass of binder was added, and mixing was performed for another 12 hours to obtain a slurry-like molding composition. Next, the molding composition was defoamed using a vacuum defoamer (manufactured by Sayama Riken Co., Ltd.), and the viscosity was adjusted to prepare a coating slurry. Thereafter, the viscosity-adjusted coating slurry was used to form a sheet by a doctor blade method, and the sheet was dried in air at 100° C. to evaporate the solvent, yielding a green sheet having a width of 750 mm and a thickness of 420 μm. The green sheet obtained as described above was subjected to a degreasing treatment at a temperature of 550° C. in dry air to obtain a degreased green sheet. The degreased green sheet was then cut into a 100 mm x 100 mm piece, placed in a sintering vessel, and sintered at 1880°C for 9 hours in a nitrogen atmosphere under a pressure of 0.9 MPa·G to obtain a silicon nitride substrate. The firing vessel used was the one shown in FIG. 1, which had two corners at the connection portion and had a length of 4.0 mm. Furthermore, 5 g of yttria and 3 g of magnesia were present in the firing vessel as atmospheric adjusters per 100 g of green sheet (molded body). The evaluation results of the obtained silicon nitride substrate are shown in Table 1. In the nanoindentation test, 4915 locations had a Young's modulus of less than 225 GPa, and 13085 locations had a Young's modulus of 225 GPa or more. The content of metal impurities in the silicon nitride substrate was 25 ppm or less.

[0053] <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 portion, the length of which was 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. In the nanoindentation test, there were 5811 locations with a Young's modulus of less than 225 GPa, and 12189 locations with a Young's modulus of 225 GPa or more. The content of metal impurities in the silicon nitride substrate was 25 ppm or less.

[0054] <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 portion and a length of 2.0 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. In the nanoindentation test, there were 6395 locations with a Young's modulus of less than 225 GPa and 11605 locations with a Young's modulus of 225 GPa or more.

[0055] <Comparative Example 2> A silicon nitride substrate was obtained in the same manner as in Example 1, except that no water vapor heating treatment was performed and silicon nitride powder X was used. The evaluation results of the obtained silicon nitride substrate are shown in Table 1. In the nanoindentation test, there were 5284 locations with a Young's modulus of less than 225 GPa and 12716 locations with a Young's modulus of 225 GPa or more.

[0056] [Table 1] [Explanation of symbols]

[0057] 1 Container part 2 Lid 3 Connection part

Claims

[Claim 1] A silicon nitride substrate, in which, in a Young's modulus distribution obtained by a nanoindentation test under a load of 0.5 mN, the ratio R1 (EA10 / EA90) of the cumulative 10% Young's modulus EA10 in an area where the Young's modulus is less than 225 GPa to the cumulative 90% Young's modulus EA90 in an area where the Young's modulus is less than 225 GPa is 0.46 or more, and the ratio R2 (ES10 / ES90) of the cumulative 10% Young's modulus ES10 in an area where the Young's modulus is 225 GPa or more to the cumulative 90% Young's modulus ES90 in an area where the Young's modulus is 225 GPa or more is 0.71 or more.

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