Structure, substrate, heat dissipation substrate, joint body and power module

Abstract

To provide a structure, a substrate, a heat dissipation substrate, a joined body, and a power module that have both high thermal conductivity and high strength.SOLUTION: According to an embodiment, a structure of the present invention has a grain and a grain boundary, the grain contains a β-type silicon nitride phase, the unit cell volume of the grain is between 145.45 Å3 and 145.60 Å3, and the average grin size of the grain is between 3.5 μm and 10 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a structure, a substrate, a heat dissipation substrate, a bonded body, and a power module. [Background technology]

[0002] The chemical formula of beta-type silicon nitride is Si3N4, which is supposed to be a highly covalent compound composed only of silicon and nitrogen, but in reality it contains impurity oxygen. It is known that the thermal conductivity of silicon nitride increases as the impurity oxygen within the silicon nitride crystal grains is reduced. One method for reducing the impurity oxygen within silicon nitride crystal grains is reaction sintering. Conventionally, silicon nitride has been used as the starting material for fabricating silicon nitride structures. However, this method oxidizes the silicon nitride during the milling and mixing of silicon nitride and sintering additives. This impurity oxygen is then incorporated into the silicon nitride crystal grains after sintering, reducing thermal conductivity. In reaction sintering, silicon is used instead of silicon nitride. After milling and mixing the silicon and additives, the silicon is nitrided before sintering. Therefore, the nitriding process reduces the silicon oxidation that occurs during milling and mixing of the raw materials.

[0003] Furthermore, a method for reducing the impurity oxygen is to subject the silicon nitride to a long heat treatment in the reaction sintering method. However, in this case, the long heat treatment causes grain growth of the silicon nitride, resulting in large grain sizes and a decrease in bending strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5836522 [Non-patent literature]

[0005] [Non-Patent Document 1] You Zhou et al., Adv. Mater., 23 (2011) 4563-4567. [Non-patent document 2] RE Fryxell and BA Chandler: J. Am. Ceram.Soc., 47 (1964), 283 Summary of the Invention [Problem to be solved by the invention]

[0006] Embodiments of the present invention provide a structure, a substrate, a heat dissipation substrate, a bonded body, and a power module that combine high thermal conductivity and high strength. [Means for solving the problem]

[0007] According to an embodiment, the crystal grains include a β-type silicon nitride phase, and the unit cell volume of the crystal grains is 145.45 Å. 3 Over 145.60Å 3 or less, and the average grain size of the crystal grains is 3.5 μm or more and 10 μm or less, and the structure is produced by a reaction sintering method. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are schematic cross-sectional views illustrating structures according to an embodiment. [Figure 2] Graph showing the results of X-ray diffraction analysis of Examples 1 and 2 and Comparative Example 4. [Figure 3] FIG. 1 is a perspective view illustrating a structure according to an embodiment. [Figure 4] FIG. 10 is a perspective view illustrating another example of the structure according to the embodiment. [Figure 5] 1A and 1B are schematic cross-sectional views illustrating a bonded body according to an embodiment. [Figure 6] 3 is a cross-sectional view of the structure according to Example 1, illustrating the results of observation of the structure by a scanning electron microscope. FIG. [Figure 7] 10 is a cross-sectional view of the structure according to Example 2, illustrating the results of observation of the structure by a scanning electron microscope. FIG. [Figure 8] FIG. 10 is a cross-sectional view of a structure illustrating the results of observation of the structure according to Comparative Example 4 with a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. In the following description, components that perform the same or similar functions are designated by the same reference numerals throughout the drawings, and duplicate descriptions will be omitted. Each drawing is a schematic diagram for explaining and facilitating understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from those of an actual device. However, these may be appropriately modified in design, taking into consideration the following description and known techniques.

[0010] [First embodiment] The structure according to the embodiment has crystal grains and grain boundaries, the crystal grains contain a β-type silicon nitride phase, and the unit cell volume of the crystal grains is 145.45 Å. 3 Over 145.60Å 3 The average grain size of the crystal grains is 3.5 μm or more and 10.0 μm or less, and the material is produced by a reaction sintering method.

[0011] FIG. 1 is a schematic cross-sectional view illustrating a structure according to an embodiment.

[0012] As shown in FIG. 1 , the structure 110 according to the embodiment includes a plurality of crystal grains 10 and grain boundaries 20 provided around the crystal grains 10. Each crystal grain 10 exists within the grain boundary 20. The plurality of crystal grains 10 within the grain boundary 20 may be separated from one another or may be partially in contact with one another. Some of the plurality of crystal grains 10 may be separated from one another, and other parts of the plurality of crystal grains 10 may be partially in contact with one another.

[0013] The crystal grains 10 contain a β-type silicon nitride (β-Si3N4) phase. The grain boundaries 20 contain at least silicon, oxygen, and nitrogen, as well as ytterbium or yttrium, and may further contain magnesium. For example, the grain boundaries 20 may contain a Yb4Si2O7N2-type crystal phase or a Y2Si3O3N4-type crystal phase. The Yb4Si2O7N2-type crystal phase refers to a crystal having the same crystal structure as that of Yb4Si2O7N2. Similarly, the Y2Si3O3N4-type crystal phase refers to a crystal having the same crystal structure as that of Y2Si3O3N4. Here, the term "same crystal structure" refers to the crystal system, space group, and positional relationship of the constituent atoms being the same, but the interatomic distances or lattice constants are not necessarily the same. Furthermore, the elements contained in the crystal phases are not important. That is, the composition of the Yb4Si2O7N2 type crystal phase may be the same as or different from the composition of the Yb4Si2O7N2 crystal. The grain boundary 20 may be crystalline, amorphous, or may contain both crystalline and amorphous. The same applies to the Y2Si3O3N4 type crystal phase.

[0014] The structure according to the embodiment may be a structure containing a β-type silicon nitride phase and a Yb4Si2O7N2-type crystalline phase, or a structure containing a β-type silicon nitride phase and a Y2Si3O3N4-type crystalline phase, and may also contain other crystalline phases. By forming a structure using only a β-type silicon nitride phase and a Yb4Si2O7N2-type crystalline phase, or a structure using only a β-type silicon nitride phase and a Y2Si3O3N4-type crystalline phase, the thermal conductivity and strength can be further improved. This is because by forming a structure using only a β-type silicon nitride phase and a Yb4Si2O7N2-type crystalline phase or a β-type silicon nitride phase and a Y2Si3O3N4-type crystalline phase, the strength of the grain boundaries 20 is improved and the adhesion between the β-type silicon nitride crystal grains 10 is also improved.

[0015] The strength is measured, for example, by three-point bending strength according to JIS-R-1601. JIS-R-1601 corresponds to ISO14704 (2000). First, a structure is peeled from a bonded assembly containing semiconductor elements, etc., and three structural pieces are prepared from this structure, each measuring 36 mm or more but less than 45 mm in total length, 4.0±0.1 mm in width, and 3.0±0.1 mm in thickness. Alternatively, three structural pieces measuring 45 mm or more in total length, 4.0±0.1 mm in width, and 3.0±0.1 mm in thickness are prepared. Next, the three-point bending strength is measured at room temperature (5 to 35°C) using, for example, an Autograph AG-X (100 kN) manufactured by Shimadzu Corporation, with a load cell set to 1 kN, a test speed of 0.5 mm / min, an indenter radius and a support base radius both set to R2, and a support distance of 30 mm. The three-point bending strength measurement is performed once for each of the three structural pieces. The strength of the structure is the average of the test results thus obtained.

[0016] The thermal conductivity can be measured, for example, by preparing multiple, for example, two, cut structures, coating their surfaces with Au and C, and then using the laser flash method (in accordance with JIS R1611). For the measurement, for example, a Netzsch flash analyzer LFA 467 HyperFlash is used to measure the thermal diffusivity α, and the specific heat capacity Cp is set to 0.68 J / g / K, and the thermal conductivity κ can be calculated from the following formula (1). The measurement is performed multiple times, for example, three times, for each structure. The average value of the values ​​thus obtained is used as the thermal conductivity of the structure. κ = ρ·Cp·α (1)

[0017] Furthermore, in order to achieve high strength, it is also important that the average grain size of the β-type silicon nitride phase is small, because a small average grain size of the β-type silicon nitride phase makes it possible to maintain high strength.

[0018] The average grain size of the crystal grains 10 containing the β-type silicon nitride phase is preferably 3.5 μm or more and 10.0 μm or less. If the average grain size is less than 3.5 μm, the number of grain boundaries between the crystal grains 10 increases. Since the thermal conductivity of the grain boundaries is lower than the thermal conductivity of the crystal grains 10, an increase in the number of grain boundaries between the crystal grains 10 reduces the thermal conductivity of the entire structure. On the other hand, if the average grain size of the crystal grains 10 is greater than 10.0 μm, the strength of the structure 110 decreases. It is more preferable that the average grain size of the crystal grains 10 of the β-type silicon nitride phase is 4.0 μm or more and 9.0 μm or less, since this allows for both high thermal conductivity and high strength. Even more preferably, the average grain size of the crystal grains 10 is 5 μm or more and 7.5 μm or less.

[0019] The average grain size of the crystal grains 10 is measured as follows. For example, a cross section of the structure obtained by the method described for measuring strength, where the crystal grains 10 can be seen, such as a fractured surface, cut surface, or plasma-etched surface, is imaged with a scanning electron microscope (SEM), and then the average grain size can be calculated by converting the image into a sphere. For example, an SU8020 SEM, manufactured by Hitachi High-Technologies Corporation, is used to image the fractured surface of the structure, and the average grain size of the structure imaged with the SEM can be calculated in terms of a sphere using the theoretical formula of the intercept method.

[0020] The accelerating voltage during SEM observation is set to around 5 to 20 kV. A magnification of around 500 to 3000 times is desirable during imaging, but this is not limited to the above as long as the grain boundaries can be confirmed. On the imaged cross section, two diagonal lines L2 are drawn across the cross section, crossing 20 or more crystal grains 10, and the number Ln of crystal grains 10 crossed by these lines L2 is calculated for each length of line L2. The number of crystal grains 10 whose ends lie within the line L2 is counted as (1 / 2). From this Ln value, the average crystal grain size (average intercept length) L1 is calculated for each line L2 using the following formula (2). L1 = L2 / Ln (2)

[0021] In this method, the straight line does not necessarily cross the center of the crystal grain 10, so it is thought that the intercept length gives a value that is smaller than the grain size. Therefore, after calculating L1 using the above formula (2), L1 is substituted into the following formula (3) (Non-Patent Document 2) to calculate the grain size D1 for each straight line L2. As shown in the following formula (3), taking into account the relationship between the diameter of the circle in the two-dimensional cross-sectional structure and the intercept length, the value obtained by multiplying L1 by a constant is taken as the grain size D1. D1 = (4 / π)×L1 = 1.27×L1 (3)

[0022] The process of imaging the cross section and calculating D1 by the intercept method is repeated three times, and the six D1 values ​​obtained are averaged, and this average value is defined as the average particle diameter D2.

[0023] Furthermore, reducing the oxygen concentration within crystal grains is also important for achieving high thermal conductivity. In crystals, molecular vibrations called "phonons" are responsible for thermal conduction. Because phonons are molecular vibrations derived from lattice structures, the regularity of the medium through which phonons travel—in this case, the material itself—is crucial for their propagation. Where the regularity is disrupted, phonons are scattered, attenuating their vibrational energy. For example, the thermal conductivity of silicon dioxide (SiO2) is 10 W / m / K for crystalline quartz and 0.5 W / m / K for glass, more than an order of magnitude higher. This is because the regularity of the arrangement of silicon and oxygen atoms affects thermal conductivity. The more regular a material is, the more phonon vibrations can propagate without attenuation of their vibrational energy. Therefore, when oxygen is introduced as an impurity into silicon nitride crystals, which are composed solely of silicon and nitrogen and have a high degree of regularity, the oxygen replaces the nitrogen, impairing the regularity of the silicon and nitrogen arrangement, i.e., the crystallinity. Therefore, by reducing the oxygen concentration in the silicon nitride crystal, the crystallinity of the silicon nitride can be prevented from deteriorating and phonon vibrations can be transmitted more smoothly. In addition to the above, by reducing the oxygen concentration in the silicon nitride crystal, the structure according to this embodiment can achieve both high thermal conductivity and high strength.

[0024] In order to reduce the oxygen concentration in the silicon nitride crystals, the present invention adjusts the ratio of the Yb4Si2O7N2 type crystal phase or Y2Si3O3N4 type crystal phase, which are the grain boundaries, to the β-type silicon nitride phase, and sets the average grain size of the β-type silicon nitride phase to 3.5 μm or more and 10.0 μm or less, thereby achieving both high thermal conductivity and strength.

[0025] To achieve the above-described adjustment, a reaction sintering method can be used, and a non-oxide auxiliary can also be used. Examples of the non-oxide auxiliary include ytterbium nitride, ytterbium silicon nitride, ytterbium oxynitride, ytterbium silicon oxynitride, ytterbium chloride, ytterbium silicon chloride, ytterbium fluoride, yttrium nitride, yttrium silicon nitride, yttrium oxynitride, yttrium silicon oxynitride, yttrium fluoride, and yttrium chloride. The use of these non-oxide auxiliary agents can reduce the intragranular oxygen concentration in the silicon nitride crystals.

[0026] In theory, β-type silicon nitride, represented by Si3N4, should be a highly covalent compound consisting only of silicon and nitrogen, but in reality it contains impurity oxygen, which affects the unit lattice of silicon nitride. In particular, it is thought that the impurity oxygen mainly substitutes for nitrogen in a solid solution. Also, since the covalent bond radius of oxygen is smaller than that of nitrogen, the more impurity oxygen there is, the smaller the unit lattice of silicon nitride becomes, and the smaller the lattice constant becomes. As a result, the unit lattice volume of the crystal grains in the structure calculated from the lattice constant is 145.45 Å. 3 Over 145.60Å 3 or less, it can be seen that the oxygen concentration of the crystal grains in the structure is low.

[0027] The lattice constant of the crystal grains for calculating the unit lattice volume of the crystal grains can be measured by, for example, X-ray diffraction (XRD) measurement under the following conditions.

[0028] First, the surface of the structure obtained by the method described in the strength measurement is polished so that the surface roughness Ra is 0.05 μm or less. For the measurement, for example, an XRD device, such as a Rigaku Smart-Lab, is used, and XRD is performed using the focusing method (reflection method, Bragg-Brendano method). A Cu target (Cu-Kα) is used, and the tube voltage is set to 45 kV, the tube current to 200 mA, the scan speed to 2.0° / min, the entrance parallel slit to 0.1°, the longitudinal limiting slit to 10 mm, the receiving slit to 20 mm, and the receiving parallel slit to 5°. The scan range (2θ) is set to 10° to 140°, and measurements are taken in 0.01° increments. The obtained XRD pattern was used with Rigaku's structural analysis software PDXLII to identify the main phase and grain boundaries, and then the lattice constants (a-axis length and c-axis length) of the crystal grains of the main phase, β-type silicon nitride phase (space group p63), were analyzed and determined using the software's full pattern analysis. The unit cell volume could be calculated from the a-axis length and c-axis length obtained in this way.

[0029] The unit cell volume of the β-type silicon nitride phase (crystal grain 10) calculated by the above method is 145.45 Å. 3 Over 145.60Å 3 It is preferable that the unit cell volume is 145.45 Å or less. 3 Over 145.60Å 3 When the oxygen concentration in the silicon nitride crystals and grain boundaries is sufficiently low, the thermal conductivity of the structure can be increased. 3 Over 145.55Å 3 It is more preferable that the thickness is not more than 100 nm, since phonon scattering due to impurity oxygen in the crystal can be further suppressed.

[0030] Furthermore, when the relative density of the structure according to this embodiment is close to 100%, for example, 95% or more, both high strength and high thermal conductivity can be achieved. In this embodiment, the relative density refers to the ratio of the density of the structure to the density of silicon nitride single crystal without grain boundaries. The theoretical density of silicon nitride single crystal is calculated as 3.203 g / cc (Source: Boulay et al., Acta Cryst., B60 (2004) 388-405). That is, a relative density of 95% or more means that the density of the structure is equal to that of silicon nitride single crystal and that the structure has a dense structure. In contrast, as the relative density decreases below 95%, the structure becomes less dense than silicon nitride single crystal due to the presence of many grain boundaries and pores between the crystal grains. This results in poor adhesion between the crystal grains and reduced strength. Furthermore, when many grain boundaries exist within the structure, the thermal conductivity also decreases for the reasons mentioned above. Furthermore, since thermal conductivity is expressed as the product of thermal diffusivity and density, a decrease in relative density also results in a decrease in thermal conductivity.

[0031] The ratio of the intensity of the (-122) peak of the Yb4Si2O7N2-type crystalline phase to the intensity of the (200) peak of the β-type silicon nitride phase, as determined by XRD measurement, should be 0.1 or more and 0.2 or less. That is, if the intensity of the (-122) peak of the Yb4Si2O7N2-type crystalline phase is A and the intensity of the (200) peak of the β-type silicon nitride phase is B, then it is preferable that 0.1≦A / B≦0.2. By ensuring that the ratio A / B falls within this range, the relative density of the structure according to this embodiment can be increased. If the aforementioned A / B ratio is less than 0.1, the number of grain boundaries within the structure is small, and a sufficient density such that the relative density is 95% or more cannot be obtained. On the other hand, if the A / B ratio is greater than 0.2, the number of grain boundaries within the structure increases, resulting in a decrease in thermal conductivity for the reasons described above.

[0032] For the measurement, an XRD device, such as a Rigaku Smart-Lab, is used, and XRD is performed using the focusing method (reflection method, Bragg-Brendano method). A Cu target (Cu-Kα) is used, with a tube voltage of 45 kV, a tube current of 200 mA, a scan speed of 2.0° / min, an incident parallel slit of 5°, a longitudinal limiting slit of 10 mm, a receiving slit of 20 mm, and a receiving parallel slit of 5°. The scan range (2θ) is set to 10° to 80°, and measurements are taken in 0.01° increments.

[0033] 3 and 4 are perspective views illustrating the structure according to the first embodiment.

[0034] The structure according to the embodiment serves as a substrate, and in the cases of FIGS. 3 and 4, the shape of the substrate is rectangular or disc-shaped, but the shape is not critical. As described above, the structure according to the embodiment has high thermal conductivity and high bending strength. Therefore, the structure according to the embodiment can be suitably used as a substrate. Alternatively, the structure according to the embodiment may be a bearing or the like.

[0035] The structure according to the first embodiment described above has crystal grains and grain boundaries, the crystal grains contain a β-type silicon nitride phase, and the unit cell volume of the crystal grains is 145.45 Å. 3 Over 145.60Å 3 The average grain size of the crystal grains is 3.5 μm or more and 10.0 μm or less, and the structure is produced by a reaction sintering method. This allows the structure to achieve both high thermal conductivity and high strength.

[0036] [Second embodiment] FIG. 5 is a schematic cross-sectional view illustrating a bonded body according to the second embodiment.

[0037] As shown in Fig. 5, the joined body 210 according to the embodiment includes a first metal part 31 and the structure 110 according to the first embodiment. In this example, the joined body 210 is a power module, and the structure 110 is used as a substrate, for example, a heat dissipation substrate. The power module shown in Fig. 5 can be used for EV / HEV.

[0038] The first metal part 31 is joined to the structure 110 via a joint 41. The first metal part 31 may be joined directly to the structure 110 without the joint 41. The first metal part 31 is, for example, a Cu frame.

[0039] In the example shown in FIG. 5, the bonded body 210 further includes a second metal portion 32 and a semiconductor element 50. The semiconductor element 50 is bonded to the first metal portion 31, for example, via a bonding portion 42. The first metal portion 31 is located between the structure 110 and the semiconductor element 50. The semiconductor element 50 may be bonded directly to the first metal portion 31 without via the bonding portion 42. The semiconductor element 50 is, for example, a semiconductor chip. The components from the structure 110 to the semiconductor element 50 in FIG. 5 are collectively called a semiconductor package.

[0040] The second metal part 32 is joined to the structure 110, for example, via a joint 43. The structure 110 is located between the first metal part 31 and the second metal part 32. The second metal part 32 may be joined directly to the structure 110 without the joint 43. The second metal part 32 is, for example, a heat sink. The first joint is the joint 41.

[0041] The first metal portion 31 and the second metal portion 32 include, for example, at least one selected from the group consisting of copper and aluminum. The bonding portions 41 to 43 include, for example, at least one selected from the group consisting of silver and copper. The bonding portions 41 to 43 may further include at least one selected from the group consisting of titanium, hafnium, zirconium, niobium, silicon, magnesium, indium, tin, and carbon. The semiconductor element 50 includes, for example, a diode, a MOSFET, or an IGBT.

[0042] The bonding portions 41 to 43 preferably contain an active metal. For example, when the first metal portion 31 and the second metal portion 32 contain copper, the active metal is at least one selected from the group consisting of titanium, hafnium, zirconium, and niobium. The bonding portions 41 to 43 preferably contain silver, copper, and at least one selected from the group consisting of titanium, hafnium, zirconium, and niobium.

[0043] When the first metal portion 31 and the second metal portion 32 contain aluminum, the active metal is at least one selected from the group consisting of silicon and magnesium. Preferably, the bonding portions 41 to 43 contain at least one selected from the group consisting of silver, copper, silicon, and magnesium.

[0044] When the first metal portion 31 and the second metal portion 32 contain copper, titanium is particularly preferable as the active metal. Titanium reacts with silicon nitride to form titanium nitride, thereby increasing the bonding strength.

[0045] By using the structure 110 according to the first embodiment for the bonded body 210, the thermal conductivity and bending strength of the bonded body 210 can be improved. Furthermore, by using the structure 110 having excellent thermal conductivity for a substrate, for example, the heat dissipation performance of the substrate can be improved. In addition, the structure 110 has excellent bending strength. Therefore, the substrate can be made thinner while maintaining its strength. This can further improve the heat dissipation performance of the substrate.

[0046] The bonded body according to the second embodiment includes the structure according to the first embodiment. Therefore, the bonded body according to the second embodiment can also achieve both high thermal conductivity and high strength. In addition, it can cope with increased heat generation from semiconductor chips and contribute to higher output of power modules.

[0047] [Example] Examples will be described below, but the embodiments are not limited to the examples described below.

[0048] Example 1 Si, YbF3, and MgO were weighed out to a molar ratio of Si3N4 / YbF3 / MgO = 93 / 4 / 5. These materials were crushed and mixed in a planetary ball mill for 1 hour, and the resulting mixture was dried, and then granulated with polyvinyl alcohol in an amount of 5 mass% of the total amount of the mixture.

[0049] Then, this granulated powder is mixed with 1t / cm 2 The obtained molded body was degreased at 500°C in the air, and then heat-treated in a nitrogen atmosphere at 1 atmosphere pressure and 1420°C for 11 hours, and further sintered under conditions of 10 atmosphere pressure and 1900°C for 12 hours to obtain a structure according to the embodiment.

[0050] Example 2 A structure was fabricated in the same manner as in Example 1, except that the molar ratio of Si, YbF3, and MgO was changed to Si3N4 / YbF3 / MgO=92 / 6 / 5.

[0051] Example 3 Si, YO, and MgO were weighed to give a molar ratio of SiN / YO / MgO = 93 / 2 / 5. These materials were crushed and mixed in a planetary ball mill for 1 hour, and the resulting mixture was dried and then granulated with polyvinyl alcohol in an amount of 5% by mass of the total mixture.

[0052] Then, this granulated powder is mixed with 1t / cm 2 The obtained molded body was degreased at 500°C in the air, and then heat-treated in a nitrogen atmosphere at 1 atmosphere pressure and 1350°C for 8 hours, and further sintered under conditions of 10 atmosphere pressure and 1900°C for 24 hours to obtain a structure according to the embodiment.

[0053] (Comparative Example 1) A structure was produced in the same manner as in Example 3, except that the sintering temperature at 10 atmospheres was changed to 1800°C.

[0054] (Comparative Example 2) A structure was produced in the same manner as in Example 3, except that the sintering temperature at 10 atmospheres was changed to 1850°C.

[0055] (Comparative Example 3) A structure was fabricated in the same manner as in Example 1, except that the molar ratio of Si, Y2O3, and MgO was changed to Si3N4 / Y2O3 / MgO=93 / 2 / 5.

[0056] Comparative Example 4 A structure was fabricated in the same manner as in Example 1, except that the molar ratio of Si, YbF3, and MgO was changed to Si3N4 / YbF3 / MgO=94 / 2 / 5.

[0057] <Measurement of average grain size> The average grain size of the crystal grains 10 in the structures according to Examples 1-3 and Comparative Examples 1-3 was measured using an SEM. Here, the results of the measurements performed on the structures according to Examples 1-2 and Comparative Example 4 are shown. FIG. 6 shows an observation image of the fracture surface of the structure according to Example 1, FIG. 7 shows an observation image of Example 2, and FIG. 8 shows an observation image of the fracture surface of the structure according to Comparative Example 4. In FIGS. 6-8, grain boundaries 20 are white portions present at the boundaries between the crystal grains 10.

[0058] The observation was performed under conditions of an accelerating voltage of 10 kV and a magnification of 1500. From the images obtained by the above-mentioned method, the average grain size of the crystal grains 10 in the structures according to Comparative Example 4 and Examples 1 and 2, measured using a sectioning method, was calculated. The results are shown in Table 1.

[0059] <Measurement of lattice constant> The lattice constant of the crystal grains was measured as follows.

[0060] The structure surface was polished to a surface roughness Ra of 0.05 μm or less. Measurements were performed using a Rigaku Corporation Smart-Lab XRD instrument using the focusing method (reflection, Bragg-Brendano method). A Cu target (Cu-Kα) was used, with a tube voltage of 45 kV, a tube current of 200 mA, a scan rate of 2.0° / min, an incident parallel slit of 0.1°, a longitudinal limiting slit of 10 mm, a receiving slit of 20 mm, and a receiving parallel slit of 5°. The scan range (2θ) was set from 10° to 140°, measured in 0.01° increments. The obtained XRD patterns were analyzed using Rigaku Corporation's structural analysis software PDXLII to identify the main phase and grain boundaries. The lattice constants (a-axis length and c-axis length) of the crystal grains of the main phase, β-type silicon nitride phase (space group p63), were then determined by analyzing the entire pattern using the software. The unit cell volume was calculated from the obtained a-axis length and c-axis length.

[0061] Table 1 shows the unit lattice volumes in Examples 1 to 3 and Comparative Examples 1 to 3, which were determined from the lattice constants of the crystal grains calculated by the above method.

[0062] <Measurement of Intragranular Oxygen Concentration in Comparative Examples 1 and 2 and Example 3> The oxygen concentration in the grains was measured by the hot gas extraction method in Comparative Examples 1 and 2 and Example 3. The measurement of the oxygen concentration in the grains was carried out by the following procedure.

[0063] First, the structure was pretreated to remove the grain boundaries and extract only the silicon nitride crystal grains as follows: The structure was pulverized and sieved through a #200 mesh sieve, then immersed in 50% hydrofluoric acid at 60°C for 3 hours, then in 50% sulfuric acid at 120°C for 2 hours, and then washed with pure water. After drying at 110°C, the structure was sieved through a #100 mesh sieve to obtain silicon nitride crystal grains.

[0064] 0.02 g of these silicon nitride crystal grains were mixed with 0.2 g of carbon, and the oxygen concentration was measured by temperature-programmed analysis (room temperature to 2500°C) using an inert gas fusion-infrared absorption method using a LECO ONH836 oxygen / nitrogen analyzer (manufactured by LECO Corporation). The measurement was repeated three times for each sample, and the median value of the three measurements was used. The results of the intragranular oxygen concentration measurements for Comparative Examples 1 and 2 and Example 3 are shown in Table 1.

[0065] <Bending strength measurement> The bending strength of the structures of the examples was measured by the method and under the conditions described below.

[0066] To measure the bending strength, three structures were first cut to 4 mm x 3 mm x 37 mm and prepared, and the three-point bending strength was measured in accordance with JIS-R-1601. JIS-R-1601 corresponds to ISO14704 (2000). The three-point bending strength test was performed using an Autograph AG-X (100 kN) manufactured by Shimadzu Corporation. The load cell was set to 1 kN, the test speed was 0.5 mm / min, the indenter radius and support base radius were both R2, and the distance between supports was 30 mm, and the test was performed at 23°C. The measured value was the average of the test results for the three structures described above.

[0067] The results of measurements under the above conditions are shown in Table 1.

[0068] <Method for measuring thermal conductivity> The thermal conductivity of the structure of the example was measured by the method and under the conditions described below.

[0069] First, the structure was cut into 10 mm squares and 2 mm thick pieces, and the surfaces were coated with Au and C, after which measurements were made using the laser flash method (compliant with JIS R1611). For the measurements, a Netzsch flash analyzer LFA 467 HyperFlash was used to measure the thermal diffusivity α, and the specific heat capacity Cp was set to 0.68 J / g / K, and the thermal conductivity κ was calculated from the following formula (1). The measurement was performed three times for each structure, and the average value was used. Here, ρ in the following formula (1) is the density of the structure. κ = ρ·Cp·α (1)

[0070] The results of the thermal conductivity measured and calculated by the above method are shown in Table 1.

Table 1

[0071] <Measurement of Peak Intensity by XRD> For the measurement, an XRD apparatus, for example, Smart-Lab manufactured by Rigaku Corporation, is used to perform XRD by the convergent beam method (reflection method, Bragg-Brendano method). A Cu target (Cu-Kα) is used, the tube voltage is 45 kV, the tube current is 200 mA, the scanning speed is 2.0° / min, the incident parallel slit is set to 5 degrees, the longitudinal limiting slit is set to 10 mm, the receiving slit is set to 20 mm, and the receiving parallel slit is set to 5 degrees. The scanning range (2θ) is set to 10° to 80° and measured at 0.01° intervals.

[0072] Figure 2 is a graph showing the analysis results of the structures of Comparative Example 4 and Examples 1 to 2, and is an XRD pattern by the θ-2θ method. The horizontal axis represents 2θ, and the vertical axis represents the normalized intensity.

[0073] In Figure 2, which shows the analysis results, the peak indicated by ▼ is the (200) peak of the β-type silicon nitride phase, the peak indicated by ▽ is the (-122) peak of the Yb4Si2O7N2 phase, ◆ is the β-type silicon nitride phase, and ◇ is the JCPDS card data for the Yb4Si2O7N2 phase. Comparison with these card data revealed that the main phase in all of Comparative Example 4 and Examples 1 and 2 was the β-type silicon nitride crystalline phase, and that the XRD pattern of Comparative Example 4 contained very small peaks corresponding to the peak positions of the Yb4Si2O7N2 crystalline phase, while the XRD patterns of Examples 1 and 2 contained peaks corresponding to the peak positions of the Yb4Si2O7N2 crystalline phase. This indicates that the structures of Examples 1 and 2 contained the Yb4Si2O7N2 crystalline phase. The ratios of the (-122) peak intensity of the Yb4Si2O7N2 crystalline phase to the (200) peak intensity of the β-silicon nitride crystalline phase in the XRD patterns of Comparative Example 4 and Examples 1 and 2 are shown in Table 2, along with the relative density measurement results. The density of the structures from which the surface layer was removed by cutting was measured by the Archimedes method. The relative density was calculated based on the theoretical density of silicon nitride of 3.203 g / cc.

[0074] Table 2 shows the ratio of the intensity at the (-122) peak of the Yb4Si2O7N2 phase to the intensity at the (200) peak of the β-type silicon nitride phase obtained by XRD measurement, as well as the calculated relative density. [Table 2]

[0075] A comparison of Examples 1 and 2 with Comparative Examples 3 and 4 reveals that the relative density can be increased by 95% or more by adjusting the ratio of the intensity at the (-122) peak of the Yb4Si2O7N2 phase to the intensity at the (200) peak of the β-type silicon nitride phase, as determined by XRD measurement, to 0.1 or more and 0.2 or less. Furthermore, since the thermal conductivity of a silicon nitride structure is expressed as the product of thermal diffusivity and density, a decrease in relative density also results in a decrease in thermal conductivity. For this reason, Comparative Examples 3 and 4, which have a relative density of less than 95%, had lower thermal conductivity and bending strength than Examples 1 and 2, which have a relative density of 100%.

[0076] Comparison of Example 3 with Comparative Examples 1 and 2 reveals that the unit cell volume of the structure according to Example 3 is 145.45 Å 3 Over 145.60Å 3 It was found that the intragranular oxygen concentration was low because the unit cell volume was within the above range. It was also found that the bending strength and thermal conductivity of Example 3 were both higher than those of Comparative Examples 1 and 2 because the unit cell volume was within the above range. This also indicates that the unit cell volume for Examples 1 and 2 was 145.45 Å 3 Over 145.60Å 3 Since the oxygen concentration in the grains was lower than that in the comparative example, it can be inferred that the oxygen concentration in the grains was able to be made lower than that in the comparative example, and in fact both the bending strength and the thermal conductivity were higher than those in the comparative example.

[0077] Comparison of Examples 1 to 3 with Comparative Examples 1 to 3 reveals that both bending strength and thermal conductivity can be increased in Examples 1 to 3 by setting the average grain size of the crystal grains to 3.5 μm or more and 10.0 μm or less.

[0078] The structure according to this embodiment has crystal grains and grain boundaries, and the crystal grains contain a β-type silicon nitride phase. 3 Over 145.60Å 3 The average grain size is 3.5 μm or more and 10.0 μm or less, which achieves both the intragranular oxygen concentration required for high thermal conductivity of the structure and the small grain size required for high strength.

[0079] The embodiments of the present invention have been described above with reference to specific examples. However, the embodiments of the present invention are not limited to these specific examples. For example, the specific configurations of each element, such as the structure, metal part, joint, and semiconductor element, are within the scope of the present invention as long as a person skilled in the art can implement the present invention in a similar manner and obtain similar effects by appropriately selecting them from known ranges.

[0080] Furthermore, any combination of two or more elements of each specific example within the scope of technical feasibility is also included within the scope of the present invention as long as it includes the gist of the present invention.

[0081] In addition, all structures and joined bodies that can be implemented by a person skilled in the art by appropriately modifying the design based on the structures and joined bodies described above as embodiments of the present invention also fall within the scope of the present invention, as long as they include the gist of the present invention.

[0082] In addition, within the scope of the concept of the present invention, a person skilled in the art may come up with various modifications and alterations, and it will be understood that these modifications and alterations also fall within the scope of the present invention.

[0083] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0084] 10...crystal grain, 20...grain boundary, 31...first metal portion, 32...second metal portion, 41-43...joint portion, 50...semiconductor element, 110...structure, 210...joint

Claims

1. The crystal grains and grain boundaries, the crystal grains contain a β-type silicon nitride phase, The unit cell volume of the crystal grain is 145.45 Å ３ Over 145.60 Å ３ is less than or equal to: The average grain size of the crystal grains is 3.5 μm or more and 10.0 μm or less, The grain boundary is Yb ４ Si ２ O ７ N ２ Type crystalline phase or Y ２ Si ３ O ３ N ４ containing a crystalline phase, A structure in which the ratio of the intensity at the (-122) peak of the Yb 4 Si 2 O 7 N 2 type crystal phase to the intensity at the (200) peak of the β type silicon nitride phase is 0.1 or more and 0.2 or less.

2. The unit cell volume of the crystal grain is 145.47 Å ３ More than 145.55 Å ３ 2. The structure of claim 1, wherein:

3. 3. The structure according to claim 1, wherein the average grain size of the crystal grains is 4.0 μm or more and 9.0 μm or less.

4. A substrate having the structure according to any one of claims 1 to 3.

5. A heat dissipation substrate comprising the substrate according to claim 4.

6. The substrate according to claim 4; A bonded body comprising a first metal part bonded to the substrate.

7. the substrate and the first metal portion are joined via a first joining portion, the first metal portion includes copper, The bonded body according to claim 6 , wherein the first bonding portion contains at least one selected from the group consisting of silver, copper, titanium, hafnium, zirconium, niobium, silicon, magnesium, indium, tin, and carbon.

8. Further comprising a second metal part bonded to the substrate; The bonded body according to claim 6 or 7, wherein the substrate is located between the first metal part and the second metal part.

9. further comprising a semiconductor element bonded to the first metal portion; The bonded body according to claim 6 , wherein the first metal portion is located between the substrate and the semiconductor element.

10. A power module comprising the bonded body according to claim 9, wherein the substrate is a heat dissipation substrate.

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