JP2024026590A - Silicon nitride substrate and its manufacturing method - Google Patents

Abstract

The present invention provides a silicon nitride substrate with excellent thermal conductivity in the thickness direction. [Solution method] The silicon nitride substrate of the present invention has an X-ray diffraction peak of β-Si3N4 when the substrate surface is irradiated with X-rays, and the silicon nitride substrate has β-Si3N4 particles oriented in the thickness direction. The degree of orientation fa, which indicates the ratio of the long axis (c-axis), is in the range of 0 to 0.3, and the thermal conductivity in the thickness direction is 80 W/m·K or more. [Selection diagram] Figure 2

Description

The present invention relates to a silicon nitride substrate having excellent thermal conductivity in the thickness direction and a method for manufacturing the same.

In recent years, attempts have been made to apply silicon nitride (Si3N4) substrates to semiconductor circuit boards such as power semiconductors. As semiconductor circuit boards, alumina (Al2O3) substrates and aluminum nitride (AlN) substrates are used. Although the alumina substrate has a thermal conductivity of about 30 W/m·K, cost reduction is possible. In addition, the aluminum nitride substrate has a thermal conductivity of 160W.
It is possible to achieve high thermal conductivity of /m·K or more. On the other hand, as silicon nitride substrates, substrates with thermal conductivity of 50 W/m·K or more have been developed.

A silicon nitride substrate has a lower thermal conductivity than an aluminum nitride substrate, but has an excellent three-point bending strength of 500 MPa or more. The three-point bending strength of aluminum nitride substrates is usually 300 to 4
00 MPa, and the higher the thermal conductivity, the lower the strength tends to be. Silicon nitride substrates can be made thinner by taking advantage of their high strength. By making the substrate thinner, it is possible to lower thermal resistance, which improves heat dissipation.

Taking advantage of these characteristics, silicon nitride substrates are widely used as circuit boards provided with circuit parts such as metal plates. There is also a method of using it as a circuit board for a press-contact structure as shown in the pamphlet of International Publication No. WO2011/010597 (Patent Document 1).

International publication number WO2011/010597 pamphlet

However, as mentioned above, silicon nitride substrates have lower thermal conductivity than aluminum nitride, etc., so when used in semiconductor circuit boards, they cannot efficiently dissipate heat generated by semiconductor chips to heat sinks. Moreover, the power that can be input to the semiconductor circuit board is also limited.
Therefore, silicon nitride substrates are required to have higher thermal conductivity, especially in the thickness direction.

An object of the present invention is to provide a silicon nitride substrate with excellent thermal conductivity in the thickness direction.

In order to solve the above problems, the present invention provides that when the substrate surface is irradiated with X-rays,
The degree of orientation fa, which indicates the proportion of the long axis (c-axis) of β-Si3N4 particles that have a line diffraction peak and are oriented in the thickness direction in the silicon nitride substrate, is in the range of 0 to 0.3, and The present invention relates to a silicon nitride substrate having a thermal conductivity of 80 W/m·K or more.

fa=(P-P0)/(1-P0) (1).

In formula (1), P is represented by formula (2), and P is (10°
All X-ray diffraction line intensity ratios related to the c-axis (specifically (101
) plane, (111) plane, (201) plane, (121) plane, (301) plane, (221) plane, (1
31) plane, (002) plane, (401) plane, (102) plane, (112) plane, (231) plane,
(202) plane, (141) plane, (212) plane, (302) plane, (501) plane) In powder (10°≦2θ≦
80°) related to the c-axis (specifically, the (101) plane, (
111) plane, (201) plane, (121) plane, (301) plane, (221) plane, (131) plane, (002) plane, (401) plane, (102) plane, (112) plane, ( 231) plane, (202
) plane, (141) plane, (212) plane, (302) plane, (501) plane).

P=(I(101)+I(111)+I(201)+I(121)+I(301)+I
(221)+I(131)+I(002)+I(401)+I(102)+I(112)
+I(231)+I(202)+I(141)+I(212)+I(302)+I(50
1))/(I(100)+I(110)+I(200)+I(101)+I(120)+
I (111) + I (300) + I (201) + I (220) + I (121) + I (130
)+I(301)+I(400)+I(221)+I(131)+I(230)+I(0
02)+I(140)+I(401)+I(102)+I(112)+I(231)+I
(202)+I(500)+I(141)+I(330)+I(212)+I(240)
+I(302)+I(501))...(2).

P0=(I0(101)+I0(111)+I0(201)+I0(121)+I0(
301) + I0 (221) + I0 (131) + I0 (002) + I0 (401) + I0 (
102) + I0 (112) + I0 (231) + I0 (202) + I0 (141) + I0 (
212)+I0(302)+I0(501))/(I0(100)+I0(110)+I
0 (200) + I0 (101) + I0 (120) + I0 (111) + I0 (300) + I
0 (201) + I0 (220) + I0 (121) + I0 (130) + I0 (301) + I
0 (400) + I0 (221) + I0 (131) + I0 (230) + I0 (002) + I
0 (140) + I0 (401) + I0 (102) + I0 (112) + I0 (231) + I
0 (202) + I0 (500) + I0 (141) + I0 (330) + I0 (212) + I
0(240)+I0(302)+I0(501))...(3).

The present invention also includes a step of preparing a slurry by mixing silicon powder, a sintering aid, and a dispersion medium, a step of forming a sheet body from the slurry, and a step of heat-treating the sheet body in a nitrogen-containing atmosphere. , a step of nitriding silicon in the sheet body to form silicon nitride, and a step of manufacturing a silicon nitride substrate by sintering the sheet body containing the silicon nitride, the step of nitriding the silicon in the sheet body to form silicon nitride; The present invention relates to a method for manufacturing a silicon nitride substrate, characterized in that in the forming step, volatilization of a sintering aid is controlled and silicon nitride particles are oriented in the thickness direction, which is the direction of movement of the sintering aid.

According to the present invention, when obtaining a silicon nitride substrate from silicon through a nitriding step and further through a sintering step, volatilization of the sintering aid is promoted at least when obtaining silicon nitride.
Therefore, due to the diffusion movement caused by the volatilization of the sintering aid, the generated silicon nitride β particles become oriented in the thickness direction.

As a result, when the substrate surface is irradiated with X-rays, it has an X-ray diffraction peak of β-Si3N4,
A silicon nitride substrate can be obtained in which the degree of orientation fa, which indicates the proportion of the long axis (c-axis) of β-Si3N4 particles oriented in the thickness direction, is in the range of 0 to 0.3. Since this substrate has a thermal conductivity in the thickness direction of 80 W/m·K or more, it has a higher thermal conductivity than a conventional silicon nitride substrate.

Therefore, even when used in a semiconductor circuit board, the heat generated in the semiconductor chip can be efficiently dissipated to the heat sink, and the power that can be input to the semiconductor circuit board can be improved. That is, in combination with the excellent strength of the silicon nitride substrate, it can be applied to various semiconductor circuit boards including power semiconductors.

In the silicon nitride substrate and the manufacturing method thereof of the present invention, the sintering aid is preferably at least one of a rare earth oxide and a magnesium compound. As a result, the movement of the liquid phase generated from the sintering aid described above in the thickness direction is promoted, so that the above-mentioned effects can be more prominently achieved.

Further, it is preferable that the silicon nitride substrate of the present invention has a bending strength of 500 MPa or more by a three-point method and a thickness of 0.1 to 1.2 mm. As a result, a silicon nitride substrate having a strength sufficient for practical use can be obtained.

Furthermore, in the silicon nitride substrate of the present invention, the main surface has a size of 400 to 40,000 mm2.
It is preferable that the density is 3.15 to 3.40 g/cm 3 and the dielectric strength voltage is 20 kV/mm or more. In this case, a silicon nitride substrate having a dielectric strength sufficient for practical use can be obtained.

As described above, according to the present invention, it is possible to provide a silicon nitride substrate with excellent thermal conductivity in the thickness direction.

FIG. 2 is a schematic diagram showing the crystal system of β-Si3N4. FIG. 1 is a schematic cross-sectional view of a silicon nitride substrate in an embodiment of the present invention.

FIG. 1 is a schematic diagram showing the crystal system of β-Si3N4, and FIG. 2 is a schematic cross-sectional diagram of a silicon nitride substrate in an embodiment of the present invention.

The silicon nitride substrate of the present invention preferably has a silicon nitride content of 85% by mass or more,
More preferably, it is 87% by mass or more. As a result, as explained below, the thermal conductivity in the thickness direction of the silicon nitride substrate is improved due to the crystal system (crystal structure) of silicon nitride. If the content of silicon nitride is less than 85% by mass, the proportion of silicon nitride will be small, resulting in insufficient improvement in the thermal conductivity in the thickness direction of the silicon nitride substrate.

Further, the content of silicon nitride is preferably 95% by mass or less, more preferably 93% by mass or less.
mass% or less. When the content of silicon nitride exceeds 95% by mass, the content of the sintering aid contained in the silicon nitride substrate decreases, so the amount of liquid phase decreases, and the vertical direction toward the separating agent layer decreases. Since the movement of the liquid phase is reduced, it becomes difficult to orient the generated silicon nitride in the thickness direction of the silicon nitride substrate, making it impossible to improve the thermal conductivity of the silicon nitride substrate in the thickness direction.

In the silicon nitride substrate of the present invention, the content of the sintering aid is preferably 5% by mass or more, more preferably 7% by mass or more. By including the sintering aid in a proportion of 5% by mass or more, as explained below, the proportion of the liquid phase during sintering and manufacturing the silicon nitride substrate is optimized, and the silicon nitride particles become thicker. In addition to being oriented perpendicular to the direction, the proportion of silicon nitride is optimized,
Thermal conductivity in the thickness direction of the silicon nitride substrate is improved.

On the other hand, in the silicon nitride substrate of the present invention, the content of the sintering aid needs to be 15% by mass or less. When the sintering aid is contained in an amount exceeding 15% by mass, the proportion of silicon nitride decreases, so that the thermal conductivity in the thickness direction of the silicon nitride substrate derived from silicon nitride decreases.

Note that the silicon nitride substrate of the present invention contains inevitable impurities in addition to the above-mentioned silicon nitride and sintering aid. These unavoidable impurities include, for example, organic solvents used as dispersion media, binders, additives such as plasticizers, etc. used in the manufacturing process of silicon nitride substrates.

The silicon nitride substrate of the present invention has an X-ray diffraction peak of β-Si3N4 when the substrate surface is irradiated with X-rays, and the long axis (c It is preferable that the degree of orientation fa, which indicates the ratio of the axis), is in the range of 0 to 0.3.

As shown in Figure 1, the crystal system (crystal structure) of β-Si3N4 has (200) plane and (1
It has a hexagonal prism shape with multiple faces including a 20) face on its side faces and a (002) face on its end faces. Therefore, when the substrate surface is irradiated with X-rays, β-S oriented in the thickness direction of the silicon nitride substrate
The fact that the degree of orientation fa, which indicates the proportion of i3N4 particles, is in the range of 0 to 0.3 means that β-Si3N4 particles are preferentially oriented in the thickness direction of the silicon nitride substrate, resulting in the morphology shown in FIG. This means that most of the columnar β-Si3N4 particles 11 in the silicon nitride substrate 10 are oriented in the thickness direction. Note that reference numeral 12 indicates a grain boundary phase caused by a sintering aid or the like.

Originally, the thermal conductivity of silicon nitride particles is higher in the length direction of the hexagonal prism than in other directions. That is, in the present invention, as shown in FIG. 2, for example, hexagonal columnar silicon nitride (β-
Si3N4) is more likely to be oriented along the thickness direction of the silicon nitride substrate. therefore,
The present invention can exhibit high thermal conductivity in the thickness direction.

Note that when the degree of orientation fa, which indicates the proportion of β-Si3N4 particles oriented in the thickness direction in the silicon nitride substrate, is less than 0, that is, in a negative range, the orientation in the plane direction becomes strong, and the above-mentioned effects are sufficiently exerted. Therefore, high thermal conductivity cannot be obtained in the thickness direction of the silicon nitride substrate. Further, the upper limit of the degree of orientation fa is currently 0.3, but from the viewpoint of thermal conductivity, the higher the degree is, the more preferable it is. However, if this ratio becomes too high, mechanical strength such as breaking strength in the thickness direction will decrease.

In the silicon nitride substrate of the present invention, the thermal conductivity in the thickness direction is 80 W/m·K or more,
Preferably it is 85 W/m·K or more. As a result, even when the silicon nitride substrate of the present invention is used in a semiconductor circuit board, the heat generated in the semiconductor chip can be efficiently dissipated to the heat sink, and the power that can be input to the semiconductor circuit board can be improved. It becomes like this. That is, in combination with the excellent strength of the silicon nitride substrate, it can be applied to various semiconductor circuit boards including power semiconductors.

Note that the above thermal conductivity can be obtained when the silicon nitride substrate of the present invention satisfies the above-mentioned contents of silicon nitride and sintering aid, as well as the requirements for X-ray diffraction.

Further, it is preferable that the silicon nitride substrate of the present invention has a bending strength of 500 MPa or more by a three-point method and a thickness of 0.1 to 1.2 mm. As a result, a silicon nitride substrate having a strength sufficient for practical use can be obtained. Further, as shown in Table 1 below, the silicon nitride substrate of the present invention has a bending strength of 650 MPa or more, preferably 700 MPa or more by the three-point method.
a or more.

Furthermore, in the silicon nitride substrate of the present invention, the main surface has a size of 400 to 40,000 mm2.
It is preferable that the density is 3.15 to 3.40 g/cm 3 and the dielectric strength voltage is 20 kV/mm or more. In this case, a silicon nitride substrate having a dielectric strength sufficient for practical use can be obtained.

Next, a method for manufacturing a silicon nitride substrate according to the present invention will be explained.

First, silicon powder and sintering aid powder are prepared as raw materials. It is preferable that the silicon powder has a median diameter D50 of, for example, 50 μm or less, and an impurity oxygen content of 0.6% by mass or less. Note that the amount of the sintering aid is preferably 15 parts by mass based on 100 parts by mass of silicon powder.

The sintering aid is preferably a metal compound powder having a median diameter D50 of 10 μm or less, for example. Examples of the metal compound powder include oxides of rare earth elements, magnesium, titanium, hafnium, etc., but rare earth element oxides and magnesium compounds (magnesia etc.) are more preferred. Since these sintering aids have excellent fluidity, they exhibit fluid behavior as described below, and facilitate orientation of silicon nitride (particles) in the thickness direction.

Next, a dispersion medium is added to the silicon powder and the sintering aid, and the mixture is dispersed in a media using, for example, a ball mill, and pulverized and mixed to prepare a slurry. As the dispersion medium, organic solvents such as toluene, ethanol, butanol, etc. can be used.

Next, a binder, a plasticizer, etc. are added to the slurry as necessary, and the slurry is further defoamed in vacuum to adjust the viscosity of the slurry. As the binder, organic binders such as butyl methacrylate, polyvinyl butyral, polymethyl methacrylate, etc. can be used.

Next, the viscosity-adjusted slurry is formed into a sheet by a sheet forming method such as a doctor blade method or a roll method to form a sheet having a thickness of, for example, 0.2 to 1.5 mm. Note that the sheet body is obtained, for example, by coating a slurry on a film to form it, and then removing the film after drying.

Next, if necessary, a slurry made of ceramic powder and a dispersion medium is applied onto the main surface of the sheet to form a separating agent layer. Note that as the dispersion medium, organic solvents such as toluene, ethanol, butanol, etc. can be used, as described above. Further, as a coating method, a spray method, a bar coating method, a screen printing method, etc. can be used.

Then, if necessary, the sheet body is degreased, for example, in a non-oxidizing atmosphere at a temperature of 600° C. or lower for several hours. Thereafter, the sheet body is held in a nitrogen-containing atmosphere at a temperature of 1200 to 1500° C. for 2 to 8 hours, thereby nitriding the silicon constituting the sheet body to form silicon nitride. Note that the nitrogen partial pressure in the nitrogen-containing atmosphere is, for example, 0.05 to 0.5 MPa.

Next, the silicon nitride is sintered by holding it at a temperature of 1800 to 1950° C. for 6 to 24 hours in the same nitrogen-containing atmosphere.

In addition, in the present invention, a weight plate is used in the nitriding and sintering process, but (1) during nitriding of silicon, the top surface is left free without using a weight plate, and the weight plate is used only during sintering. (2) A method using a porous plate as a weight plate and applying a load to the formed body in succession with silicon nitriding and sintering of silicon nitride; (3) Or a method using a dense plate as a weight plate and forming There are methods such as providing a separating agent layer between the body and the dense plate.

The separating agent layer is made of ceramic powder, but is not particularly limited as long as it is thermally stable during nitriding and sintering and can separate the dense plate after sintering is completed, but boron nitride may be used. preferable.

Further, when boron nitride is used as the ceramic powder, its purity is preferably 95% or more, and its average particle size is preferably 5 to 20 μm. Further, the thickness of the separating agent layer is preferably 10 to 60 μm, or 20 to 60 μm.

A plurality of sheet bodies each having a separating agent layer formed on the main surface may be stacked with the separating agent layer interposed therebetween. In this case, a plurality of silicon nitride substrates can be manufactured simultaneously through the nitriding and sintering steps described above.

As a result, when the substrate surface is irradiated with X-rays, it has an X-ray diffraction peak of β-Si3N4,
A silicon nitride substrate can be obtained in which the degree of orientation fa, which indicates the proportion of the long axis (c-axis) of β-Si3N4 particles oriented in the thickness direction, is in the range of 0 to 0.3.

(Example)

(Example 1)
The metal Si powder, sintering aid (rare earth oxide and magnesium compound), dispersant (polyoxyalkylene type dispersant), and dispersion medium (ethanol, butanol) were mixed for 35 hours using a ball mill. The metal Si powder and the sintering aid were adjusted so that the mass ratio of the silicon nitride content to the sintering aid content after sintering was 0.89:0.11. Thereafter, a dispersion medium (ethanol, methyl ethyl ketone), an organic binder (acrylic resin), and a plasticizer were added to the mixture and mixed again to prepare a slurry. continue,
The produced slurry was taken out of the ball mill and transferred to a defoaming machine, and then the viscosity of the slurry was adjusted by vacuum defoaming, and the slurry was molded into a sheet shape to produce a sheet molded body of 100 x 100 x t0.38 mm. The doctor blade method was adopted as the sheet forming method.

Thereafter, a 10 μm thick separating agent layer was formed on the surface of the sheet molded body by applying a ceramic slurry made of boron nitride to the sheet molded body, and then the sheet molded body was heated at 550°C in a non-oxidizing atmosphere. Performed degreasing treatment.

Next, the sheet molded body having a separating agent layer made of boron nitride formed on its main surface was subjected to a nitriding treatment at 1400° C. for 2 hours in a nitrogen-containing atmosphere with a nitrogen partial pressure of 0.2 MPa.
Furthermore, sintering was performed at 1820° C. for 9 hours in a nitrogen-containing atmosphere with a nitrogen partial pressure of 0.7 MPa to produce the silicon nitride substrate of Example 1.

(Example 2)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 895:0.105, a separating agent layer with a thickness of 20 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 2 was fabricated under the same fabrication conditions.

(Example 3)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 878:0.122, a separating agent layer with a thickness of 25 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 3 was fabricated under the same fabrication conditions.

(Example 4)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 885:0.115, a separating agent layer with a thickness of 35 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 4 was manufactured under the same manufacturing conditions as described above.

(Example 5)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 883:0.117, a separating agent layer with a thickness of 35 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 5 was manufactured under the same manufacturing conditions as described above.

(Example 6)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 885:0.115, a separating agent layer with a thickness of 50 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 6 was manufactured under the same manufacturing conditions.

(Example 7)
Degreasing treatment is performed on the sheet molded body without a separation agent layer on the surface of the sheet molded body,
A silicon nitride substrate of Example 7 was manufactured under the same manufacturing conditions as Example 1, except that the sheet molded body was sintered without a weight plate.

(Example 8)
The manufacturing conditions were the same as in Example 1, except that a porous plate with a porosity of 40% was formed on the surface of the sheet molded body instead of the separating agent layer, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 8 was manufactured in accordance with the following.

(Example 9)
Production was performed in the same manner as in Example 1, except that a semi-dense plate with a porosity of 15% was formed on the surface of the sheet molded body instead of the separating agent layer, and the sheet molded body was degreased in that state. A silicon nitride substrate of Example 8 was produced according to the conditions.

(Example 10)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 921:0.079, a sheet molded body of 240 x 180 x t0.29 mm was produced, a separating agent layer with a thickness of 20 μm was formed on the surface of the sheet molded body, and in that state, the sheet molded body The silicon nitride substrate of Example 10 was fabricated under the same manufacturing conditions as Example 1, except that it was degreased and sintered at 1840° C. for 12 hours in a nitrogen-containing atmosphere with a nitrogen partial pressure of 0.7 MPa. was created.

(Example 11)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 92:0.08 and sintered at 1830° C. for 12 hours in a nitrogen-containing atmosphere with a nitrogen partial pressure of 0.7 MPa. A silicon substrate was fabricated.

(Example 12)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 926:0.074, a 240 x 180 x t0.38 mm sheet molded body was produced, a separating agent layer with a thickness of 10 μm was formed on the surface of the sheet molded body, and in that state, the sheet molded body A silicon nitride substrate of Example 12 was manufactured under the same manufacturing conditions as Example 11, except that the silicon nitride substrate was subjected to degreasing treatment.

(Example 13)
The mass ratio of silicon nitride content to sintering aid content after sintering of metal Si powder and sintering aid is 0.
．． 927:0.073, a separating agent layer with a thickness of 20 μm was formed on the surface of the sheet molded body, and the sheet molded body was subjected to degreasing treatment in that state. A silicon nitride substrate of Example 13 was fabricated under the same fabrication conditions.

(Comparative example)

(Comparative example 1)
The metal Si powder, the silicon nitride powder, and the sintering aid were adjusted so that the mass ratio of the silicon nitride content and the sintering aid content after sintering was 0.909:0.091, and the mass ratio was 100×100×t0. 38m
m sheet molded body was produced, a separating agent layer with a thickness of 35 μm was formed on the surface of the sheet molded body, and in that state, the sheet molded body was subjected to a degreasing treatment, and nitrogen gas with a nitrogen partial pressure of 0.7 MPa was applied. A silicon nitride substrate was produced by sintering at 1820° C. for 9 hours in a containing atmosphere. A silicon nitride substrate of Comparative Example 1 was manufactured under the same manufacturing conditions as Example 1 except for the following.

(Comparative example 2)
Comparative Example 1 except that the metal Si powder, silicon nitride powder, and sintering aid were adjusted so that the mass ratio of silicon nitride content to sintering aid content after sintering was 0.904:0.096. A silicon nitride substrate of Comparative Example 2 was manufactured under the same manufacturing conditions as described above.

(Evaluation method)
The characteristics of the silicon nitride substrates of each Example and each Comparative Example were evaluated as follows.

(Orientation degree based on X-ray diffraction peak intensity)
For X-ray diffraction, scanning was performed using the θ-2θ method using Cu-Kα rays excited at 40 kV and 15 mA, with a step width of 0.01°.

(Elemental analysis)
Quantitative analysis of Si, N, Mg, and rare earth elements was performed using ZSX Primu manufactured by Rigaku.
This was carried out by fluorescent X-ray analysis using sII. On the other hand, the analysis of O was carried out using HORIBA's E
This was carried out using an inert gas fusion non-dispersive infrared absorption (NDIR) method using MGA-920. The content of SiN was calculated from the amounts and ratios of Si and N, and the amount of sintering aid was calculated from the amounts and ratios of Mg and O, and the amounts and ratios of rare earth elements and O.

(Thermal conductivity)
Thermal diffusivity was measured by the flash method using LFA 467 Hyp manufactured by NETZSCH.
This was done using an erFlash device. With this device, by irradiating xenon flash light with a pulse width of 20 μsec, the AC temperature response was measured with an IR detector, and the thermal diffusivity was calculated from the amplitude of the temperature response and the attenuation rate with respect to position. The measurement was performed after blackening treatment was performed on the surface of a test piece with a size of 10 mm x 10 mm.

(density measurement)
The density was measured using the Archimedes method.

(Deflection strength by 3-point method)
The three-point bending strength is based on JIS R1601:2008 for a 4mm x 35mm test piece.
According to value.

Table 1 summarizes some of the manufacturing conditions for the silicon nitride substrates of each Example and each Comparative Example and the evaluation results.

In Examples 1 to 5, 10 to 13 in which a separating agent layer was formed on one principal surface of the sheet body, and Examples 6 to 9 in which a porous plate was formed, the separation agent layer was oriented in the thickness direction on the silicon nitride substrate. β
It was found that the degree of orientation fa, which indicates the proportion of -Si ₃ N ₄ particles, was in the range of 0 to 0.3, and the thermal conductivity in the thickness direction was 80 W/m·K or more.

10 Silicon nitride substrate 11 Silicon nitride particles 12 Grain boundary phase

Claims (1)

When the substrate surface is irradiated with X-rays, it has an X-ray diffraction peak of β-Si ₃ N ₄ ,
The degree of orientation fa, which indicates the proportion of the long axis (c-axis) of β-Si ₃ N ₄ particles oriented in the thickness direction in the silicon nitride substrate, is within the range of 0 to 0.3,
A silicon nitride substrate having a thermal conductivity in the thickness direction of 80 W/m·K or more.

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