JP2003313079A - Silicon nitride-based sintered compact, method of producing the same, and circuit board using the sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride-based sintered compact having a high thermal conductivity in addition to high strength and high toughness, and to provide a method of producing the same. <P>SOLUTION: In the silicon nitride-based sintered compact, fine particles having diameters of ≤100 nm, which are composed of Mg or at least one rare earth element selected from La, Y, Gd and Yb and oxygen, and which are each composed of an amorphous nucleus part and an amorphous peripheral part, are contained in an amount of ≥5 pieces/μm<SP>2</SP>in silicon nitride particles. The method of producing the silicon nitride-based sintered compact comprises blending 1 to 50 parts by weight of silicon nitride-based powder containing β-fraction in an amount of 30 to 100% and oxygen in amount of ≤0.5 wt.% and having an average diameter of 0.2 to 10 μm and an aspect ratio of ≤10, 99 to 50 parts by weight of an α-type silicon nitride powder having an average diameter of 0.2 to 4 μm, and a sintering aid including Mg and at least one kind of element selected from the group of Y and rare earth elements (RE), then keeping the blend for 1 to 10 h at 1,400 to 1,600°C under a nitrogen atmosphere of 0.5 MPa, thereafter, raising the temperature to 1,800 to 1,950°C with a temperature rising speed of ≤5.0°C/min, and sintering for 5 to 40 h at a temperature of 1,800 to 1,950°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member for electronic parts such as a semiconductor substrate and a heat sink for a heat generating element, or a member for general machinery, a member for molten metal, a member for a heat engine and the like. The present invention relates to a silicon nitride sintered body having high strength and high thermal conductivity, a method for manufacturing the same, and a circuit board formed by using the silicon nitride sintered body.

[0002]

2. Description of the Related Art Silicon nitride sintered bodies are excellent in heat resistance, low thermal expansion, thermal shock resistance, and corrosion resistance against metals in addition to mechanical characteristics such as high temperature strength characteristics and wear resistance. Are used for various structural members such as members for gas turbines, members for engines, machine members for steelmaking, and members for melting molten metal. Further, it is used as an electric insulating material by utilizing its high insulating property.

With the recent development of semiconductor devices such as high-frequency transistors and power ICs that generate a large amount of heat, there is an increasing demand for ceramic substrates having high thermal conductivity in order to obtain good heat dissipation characteristics in addition to electrical insulation. ing. Although an aluminum nitride substrate is used as such a ceramic substrate, there is a problem that mechanical strength, fracture toughness, and the like are low, and cracks occur due to tightening in a substrate unit assembling process. Further, in a circuit board in which a Si semiconductor element is mounted on an aluminum nitride substrate, since the thermal expansion difference between Si and the aluminum nitride substrate is large, cracks or breaks occur in the aluminum nitride substrate due to thermal cycles, and mounting reliability is reduced. There's a problem.

Therefore, although the thermal conductivity is inferior to that of the aluminum nitride substrate, a substrate made of a high thermal conductive silicon nitride sintered body having a thermal expansion coefficient close to that of Si and excellent in mechanical strength, fracture toughness and thermal fatigue resistance is noted. And various proposals have been made.

For example, Japanese Patent Laid-Open No. 175268/1992 discloses that silicon nitride is substantially used, Al and oxygen contained as impurities are both 3.5 wt% or less, and the density is
A silicon nitride sintered body having a thermal conductivity of 3.15 Mg / m3 (3.15 g / cm3) or more and 40 W / (m · K) or more is described.

Further, Japanese Patent Laid-Open No. 9-30866 discloses that
It is composed of 85 to 99% by weight of β-type silicon nitride grains and the balance of the grain boundary phase of oxide or oxynitride, and Mg, Ca, S are contained in the grain boundary phase.
r, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er and
0.5-10 at least one element selected from Yb
% By weight, the Al element content in the grain boundary phase is 1% by weight or less, the porosity is 5% or less, and the proportion of β-type silicon nitride particles having a minor axis diameter of 5 μm or more is 10-60
A silicon nitride sintered body is described which is a volume percentage.

The Proceedings 1G11 and 1G12 of the 1996 Annual Meeting of the Ceramic Society of Japan and JP-A-10-19484.
In Japanese Patent Laid-Open No. 2 (1994), columnar silicon nitride particles or whiskers are added in advance to a raw material powder, and a doctor blade method or an extrusion molding method is used to form a molded body in which the particles are two-dimensionally oriented and sintered. By doing so, anisotropy is imparted to the heat conduction to increase the thermal conductivity in a specific direction, and a silicon nitride sintered body is described.

Further, in Japanese Patent Laid-Open No. 2001-19557, by controlling the total amount of impurities of oxygen, Al, Ca, Fe in the silicon nitride grains to be 1500 ppm or less and the minor axis diameter to be 2 μm or more, A silicon nitride sintered body having improved thermal conductivity and mechanical properties and a method for producing the same are described.

Further, in Japanese Patent Laid-Open No. 2002-29848, columnar whiskers are added to the raw material powder in advance, and a microstructure is formed by selectively growing grains by using the whiskers as nuclei in the firing process. A silicon nitride sintered body having improved conductivity and a method for manufacturing the whiskers are described.

[0010] The Ceramic Society of Japan 1998 Annual Meeting Proceedings 2B04 shows that a compact of silicon nitride powder is sintered in nitrogen gas of 1.0 MPa at 2000 ° C. for 4 hours, and then 2200 ° C. in nitrogen gas of 30 MPa. It is described that a silicon nitride sintered body having a high thermal conductivity of 100 w / (m · K) or more can be produced by performing heat treatment at a high temperature and high pressure of × 4 hr. It is described that the development of high thermal conductivity involves not only the growth of silicon nitride particles in a sintered body but also the hexagonal precipitation phase in the silicon nitride particles by the high temperature heat treatment.

[0011]

The problems of the above-mentioned prior art will be described below step by step. First, in Japanese Patent Application Laid-Open No. 4-175268, a thermal conductivity of 40 W / (m · K) or more is obtained, but recently, the thermal conductivity is further increased.
A material having excellent mechanical strength is desired. Further, according to the methods described in JP-A-9-30866 and JP-A-10-194842, seed crystals or whiskers to serve as growth nuclei are obtained in order to obtain huge columnar particles in a silicon nitride sintered body. Was added in advance, and the temperature was 2000 ° C or higher and 10.1 MPa (100
Baking under a nitrogen atmosphere above atmospheric pressure is essential. Therefore, special high temperature such as hot press or HIP
High-voltage equipment is required, resulting in higher costs. Also,
Since the molding process for obtaining the molded product in which the silicon nitride particles are oriented is complicated, there is a problem that the productivity is significantly reduced.

Further, the silicon nitride sintered body described in Japanese Patent Laid-Open No. 2001-19557 reduces the amount of impurities in the silicon nitride grains (expressed as a purification effect) to improve the thermal conductivity of the grains themselves. It is characterized by improving the thermal conductivity of the sintered body. In addition, Zr and / or Hf is selected as an additive useful for promoting the purification effect, and 0.5 wt% to 3.0 wt% of these are added in terms of oxide. However, when the oxides of Zr and Hf are added, they easily react with N in Si3N4 during the sintering process to produce electrically conductive ZrN and HfN in the grain boundary phase.
Therefore, there is a problem that the electrical insulation that is essentially required for the ceramics substrate cannot be maintained, and it is difficult to use it as an insulating substrate for a power semiconductor module that operates at high frequency.

Further, in the manufacturing method described in JP-A-2002-29848, the average circularity of the constituent silicon nitride particles is 0.8 or more, the β conversion rate is 10% or more and less than 80%, and the oxygen content is 0.5%. 〜1.8% by mass, specific surface area 12〜22m ² / g
1 or more selected from the group consisting of rare earth oxides, silicon oxides, and magnesium oxides are added to the silicon nitride powder, which is 2.5 to 14 mass%, and a silicon nitride whisker is further added. After adding 0.1-8.5% by mass,
They are mixed, molded, and sintered in a nitriding atmosphere. Further, in order to improve the sinterability, the silicon nitride whiskers are characterized in that they are previously hydrothermally treated at a boiling point of water or higher (for example, in a temperature range of 110 ° C. to 140 ° C.). However, the hydrothermal treatment of the silicon nitride whiskers used in this example can improve the sinterability by oxidizing the surface and increasing the SiO ₂ component that acts as an auxiliary agent, but on the other hand,
As described in the examples, hydrothermal treatment for obtaining a dense sintered body requires treatment at 120 ° C. for 96 hours, which complicates the process. Moreover, although the sinterability can be improved by hydrothermal treatment, the oxygen content of the sintered body, and hence the oxygen content in the silicon nitride particles, cannot be reduced, and it is difficult to obtain a high thermal conductive material. .

Next, the sintered body described in the above-mentioned proceedings 2B04 of the 1998 Annual Meeting of the Ceramic Society of Japan was prepared in a nitrogen gas of 1 MPa.
There is an advantage that a high thermal conductivity of 100 W / (m · K) or more can be obtained by further performing high-temperature and high-pressure heat treatment at 2200 ° C. in 30 MPa nitrogen gas after firing at 2000 ° C. Furthermore, it is explained that the mechanism of manifestation of high thermal conductivity is related to the growth of silicon nitride particles in the sintered body and the hexagonal precipitation phase in the silicon nitride particles due to the high temperature heat treatment. That is, during sintering and grain growth, the auxiliary component composed of Y-Nd-Si-O is incorporated into the silicon nitride particles to form a solid solution, and the Y-Nd-Si-O composition during heat treatment and cooling at high temperature. It is considered that the amorphous phase is precipitated in the silicon nitride particles, and a part of the precipitate is crystallized, which is considered to be one of the purification effects of the silicon nitride particles. From the above, in order to obtain the above-mentioned sintered body, special high temperature and high pressure equipment is required, which causes an increase in cost. Further, there is a problem that productivity is markedly reduced because heat treatment is applied after sintering. Further, detailed composition analysis and observation of the precipitated phase in the silicon nitride particles in the above-mentioned sintered body have not been carried out, and the relationship with the improvement of thermal conductivity has not been clarified.

The present invention has been made in view of the above conventional problems, and does not require a costly firing method such as high temperature / high pressure firing of 2000 ° C. or higher and 10.1 MPa (100 atm) or higher, and mechanical It is an object of the present invention to provide a high thermal conductivity type silicon nitride sintered material which is excellent in strength, has no anisotropy in the direction of thermal conduction, and has higher thermal conductivity than conventional ones. Another object of the present invention is to provide a high thermal conductivity type silicon nitride sintered material having a high thermal conductivity by investigating in detail the composition and morphology of fine particles precipitated in silicon nitride particles. Further, the present invention, β fraction of the silicon nitride powder, oxygen content,
A silicon nitride sintered body having high thermal conductivity and high strength and a method for producing the same are provided by defining a sintering process and the like including an impurity amount, a mixing ratio with an α-type silicon nitride powder, and a holding process. The purpose is to It is another object of the present invention to provide a circuit board having a good heat dissipation property, which is formed by using the above-mentioned silicon nitride sintered body rich in high strength and high thermal conductivity.

[0016]

In order to achieve the above object, the inventors of the present invention intentionally deposit fine particles containing at least oxygen and a sintering aid component in the composition in silicon nitride particles to achieve nitriding. It has been found that the thermal conductivity of the silicon particles themselves is improved, and a silicon nitride sintered body having a thermal conductivity of 100 W / (m · K) or more and a sufficient bending strength can be stably obtained. Further, at this time, it is effective that the sintering aid component is made MgO-based to improve the sinterability, and that MgO and (RE _x O _y ) are contained in a specific amount and specific ratio. I found out. Further, in the method for producing a silicon nitride-based sintered body, a sintering step including powder characteristics such as β-fraction of silicon nitride-based powder to be used, oxygen content, impurities and mixing ratio with α powder, and a holding process. It was found that it is essential to specify such rules. The present invention has been completed as described above.

That is, in the silicon nitride sintered material of the present invention, Mg or Y and rare earth element (R
At least one element selected from the group consisting of E),
It is characterized by the presence of fine particles containing an O element and having a particle size of 100 nm or less. Further, the silicon nitride sintered body of the present invention,
What is claimed is: 1. A silicon nitride sintered body comprising Mg, and at least one element selected from the group consisting of Y and a rare earth element (RE) added as a sintering aid.
Alternatively, a grain size of 10 including at least one rare earth element selected from the group consisting of La, Y, Gd and Yb and an O element is provided.
It is characterized by the presence of fine particles of 0 nm or less.
The fine particles are those in which the auxiliary component taken in the particles in the grain growth of the silicon nitride particles during the firing process is re-precipitated in the silicon nitride particles, although the trace amount is extremely small, and the high thermal conductivity of the silicon nitride particles themselves. Contribute to At this time, in the observation image at a direct magnification of 10,000 times or more by a transmission electron microscope (TEM), it is desirable that the fine particles having a particle size of 100 nm or less be present in an amount of 5 particles / μm ² or more. The thermal conductivity of the sintered body is improved by the precipitation phenomenon and the ratio.

Further, in the silicon nitride sintered body of the present invention, the fine particles have at least a Si-N-O-Mg-RE composition, and are composed of a core and a peripheral portion having different composition ratios. Is characterized by. This core has a high Si component and a small amount of components (for example, Mg and rare earth elements) added as an auxiliary component. On the other hand, it is desirable that the peripheral portion, on the contrary, has a small Si component and a large amount of auxiliary component. Further, it is desirable that the fine particles are entirely in an amorphous phase.

In the silicon nitride sintered body of the present invention, Mg contained in the silicon nitride sintered body is converted into magnesium oxide (Mg
Converted to O) and also contained La, Y, Gd and Yb
When a rare earth element containing is converted to a rare earth oxide (RE _x O _y ), the total oxide content converted to these oxides is
It is characterized by being 0.6 to 10 wt% and (RE _x O _y ) / (MgO)> 1. The total amount of oxide conversion is 0.6 wt%
If less than 100%, the densification effect during sintering is insufficient and the relative density is 95%.
If the content exceeds 10 wt%, the amount of the grain boundary phase having low thermal conductivity, which is the second microstructure component of the silicon nitride sintered body, becomes excessive, and the thermal conductivity of the sintered body becomes 100 W / (m ・Less than K). The total content of these oxides is more preferably 0.6 to 6 wt%. Further, it is desirable that (RE _x O _y ) / (MgO)> 1, and in this case, particularly high strength and high thermal conductivity are improved. Although this will be described later, the ionic radius of the rare earth oxide (RE _x O _y ) is larger than the ionic radius of magnesium oxide (MgO), and it may be more stable when precipitated than in solid solution in the silicon nitride particles. This is due to new findings. Further, the silicon nitride sintered body of the present invention has a thermal conductivity of 100 to 300 W / (m · K) at room temperature and a three-point bending strength of 600 to 1500 MPa at room temperature, which provides high strength and high thermal conductivity. Rich

The method for producing a silicon nitride sintered body of the present invention has a β fraction of 30 to 100% and an oxygen content of 0.5 w.
1% to 50% of the first silicon nitride powder having an average particle size of 0.2 to 10 μm and an aspect ratio of 10 or less.
Parts by weight, 99 to 50 parts by weight of the second α-type silicon nitride powder having an average particle size of 0.2 to 4 μm, Mg, and at least one element selected from the group consisting of Y and rare earth elements (RE). Blended with a sintering aid containing a temperature of 1800 ° C. or higher and 0.
It is characterized in that it is sintered in a nitrogen pressure atmosphere of 5 MPa or more. Here, in the sintering step, the temperature rises from 1400 ° C to 16 ° C.
It is preferable to have at least one holding step at a temperature of 00 ° C for 1 to 10 hours, and to raise the temperature rising rate from the holding temperature to the sintering temperature at 5.0 ° C / min or less, more preferably 2.5 ° C. / min or less.

When the β fraction of the silicon nitride powder is less than 30%, it has an effect as a growth nucleus but partially acts as a nucleus, so that abnormal grain growth occurs and the finally obtained silicon nitride sintered material is obtained. Large particles cannot be uniformly dispersed in the microstructure of the body, and bending strength decreases. Therefore, the β fraction of the silicon nitride powder is preferably 30% or more. Further, if the average particle diameter of the silicon nitride powder is less than 0.2 μm, it is not possible to obtain a silicon nitride sintered body having a microstructure in which columnar particles are uniformly developed similarly to the above, and it is possible to increase the thermal conductivity and bending strength. Have difficulty. If the average particle size of the silicon nitride powder is larger than 10 μm, the densification of the silicon nitride in the sintered body is hindered. Therefore, the average particle diameter of the silicon nitride powder is preferably 0.2 to 10 μm. Further, if the aspect ratio exceeds 10, the densification of the silicon nitride sintered body is hindered, and as a result, the three-point bending strength at room temperature is 60.
It will be less than 0 MPa. Therefore, it is preferable to set the aspect ratio of the silicon nitride powder to 10 or less.

In the sintering process, the temperature is raised from 1400 ° C. to 16 ° C.
The inclusion of a holding step at a temperature of 00 ° C for 1 to 10 hours, and the rate of temperature increase from this holding temperature to the sintering temperature of 5.0 ° C / min or less, are necessary for the density (sinterability) ) And the final microstructure and the amount of solid solution of the auxiliary component and the oxygen component in the silicon nitride particles. Ie
In the temperature range of 1400 ° C to 1600 ° C, the auxiliary component and the SiO2 component on the surface of the Si3N4 powder react to form a liquid phase, a phase transition from α to β occurs, and then grain growth starts. Holding in this temperature range has the effect of homogenizing the shape of β particles that are growth nuclei, and can suppress abnormal grain growth in the subsequent temperature raising step. Further, the advantage of adding the Mg component together with the rare earth oxide as an auxiliary component is that the liquidus formation temperature can be lowered and the sinterability can be improved. However, since the Mg component has a high vapor pressure, diffusion of the Mg component from the inside of the sintered body to the surface portion progresses during the sintering process. Therefore, there is a difference in composition between the inside and the surface,
In particular, when a thick product is sintered, there is a problem that a difference in color tone is exhibited between the two and that the density and strength inside the sintered body are significantly reduced. In this respect, the addition of the holding step in the temperature range of 1400 ° C to 1600 ° C has the effect of suppressing this tendency, and is a desirable step for obtaining a dense and high-strength sintered body.

Next, when the temperature rising rate from the holding temperature to the sintering temperature is set to 5.0 ° C./min or less, rapid evaporation of the Mg component out of the system can be suppressed. Especially when it is 2.5 ° C / min or less, it becomes easy to control the amount of Mg in the final sintered body, and in particular, there is no difference in composition of the amount of Mg between the samples for the thin sheet sintered body. In addition, there is no difference in various characteristics such as density and strength, and product yield and quality can be stabilized. Therefore, it is possible to efficiently reduce the grain boundary phase having low heat conduction without generating pores in the sintered body, which contributes to the improvement of the thermal conductivity of the sintered body. Further, in the grain growth process in which dissolution and reprecipitation are repeated, it is possible to reduce the amount of auxiliary components and the amount of oxygen taken into the silicon nitride particles, and this effect also leads to an improvement in the thermal conductivity of the sintered body. Therefore, holding in the step of raising the temperature, and the temperature rising rate from the holding temperature to the sintering temperature is 5.0 ° C./min or less is desirable in order to achieve both thermal conductivity and strength of the sintered body. It is a process.

If the compact is pre-fired at a sintering temperature of 1650 to 1850 ° C. and then heat-treated at 1850 to 1900 ° C., high thermal conductivity becomes remarkable, and the silicon nitride having a conductivity of more than 120 w / (m · K) is obtained. It is particularly preferable because an elemental sintered body can be obtained. The high thermal conductivity due to this heat treatment is due to the combined effect of the growth of silicon nitride particles and the efficient vaporization of MgO-based grain boundary phase components with high vapor pressure outside the silicon nitride sintered body. By extending the firing time at a firing temperature of 1850 ° C. to 1950 ° C., the same effect of high thermal conductivity as described above can be achieved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In the silicon nitride-based sintered body of the present invention, the thermal conductivity of the sintered body is improved by the high temperature heat treatment and the extension of the firing time, which is due to the grain growth of silicon nitride particles and the volatilization of the sintering additive component. In addition to the effect, the precipitation of fine particles in the silicon nitride particles affects the increase in the thermal conductivity of the silicon nitride particles themselves. Therefore, 10
In order to obtain a thermal conductivity of 0 w / (m · K) or more, the effect of precipitating fine particles in silicon nitride particles is effective. Further, in order to achieve both strength and thermal conductivity, it is important to make the size of the silicon nitride particles that act as the starting point of fracture constant and to apply the purifying action within the particles.

Mg and Y are useful as sintering aids.
It is effective for densifying the silicon nitride raw material powder. this
These elements are the 1st micro group that constitutes the silicon nitride sintered body
Small solid solubility for silicon nitride particles that are woven components
Therefore, the silicon nitride particles, and thus the silicon nitride sintered body
The thermal conductivity can be kept at a high level. Also, the same as Y
Similarly, the solid solubility in silicon nitride particles is small,
As elements useful as agents, La, Ce, Pr, Nd,
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
at least one selected from the group consisting of m, Yb and Lu
Rare earth elements are listed. Of which, temperature and pressure
La, Ce, G in that it can be fired without the temperature becoming too high
at least one selected from the group of d, Dy and Yb
Rare earth elements are preferred. The fine particles are ionic half
Mainly composed of elements with a large diameter, and as a sintering aid
Convert the added Mg to magnesium oxide (MgO),
Rare earth elements containing La, Y, Gd and Yb
Oxide of at least one element selected from (RE)
(RE_xO_y) When converted, RE_xO _y/ MgO> 1
When it is, fine particles are likely to be deposited. In other words
If the amount of MgO added as a sintering aid is large,
It becomes difficult to deposit particles.

The reason for this is that the fine particles are
Comprised of auxiliary component and Si, O and N
Elemental ion radius (Mg²⁺) Radius: 0.07nm is silicon nitride
Ion radius of Si element composing (Si3N4): 0.04nm
Form that is relatively close and forms a solid solution with silicon nitride particles together with oxygen
The condition is stable. On the other hand, rare earth element oxide (RE
_xO _y) When the amount is large, the amount of rare earth elements of Yb or more
ON radius (RE^{x +}) Is 0.09 nm and is an ion of Si element
Radius: more than twice as large as 0.04 nm, and Mg element ion
Radius (Mg²⁺) Radius: Larger than 0.07 nm,
The precipitated form is more stable than solid solution in the silicon particles.
Therefore, in order to precipitate fine particles,
To the extent that densification can be achieved, rare earth element oxides
(RE_xO_y) Group is desirable. Where the fine
If the particle size of the particles exceeds 100 nm, the nitriding
The number of fine particles of more than 100 nm deposited in the silicon particles is remarkable.
To increase. Fine particles are glass composed of Si-N-O-Mg-R
It is composed of phases, and its own thermal conductivity is low. this
Therefore, if the number of fine particles larger than 100 nm increases, the
It is possible to achieve the desired improvement in the thermal conductivity of the silicon nitride particles themselves.
Absent. Therefore, fine particles should be controlled to a particle size of 100 nm or less.
It is essential that

The thermal conductivity of the silicon nitride sintered body is closely related to the microstructure, and is governed by the thermal conductivity of the silicon nitride particles and the grain boundary phase constituting them. The latter exists mainly as a glass phase, and their thermal conductivity is at most about 3 W / (mK). Even when the grain boundary glass phase is crystallized by a predetermined heat treatment or a slow cooling rate after sintering, it is about 30 W / (m · K). The thermal conductivity of the former is estimated to be 300 W / (m ・ K), which is close to the theoretical value of 319 W / (m ・ K) of AlN, and the measured value is 180 W / (m ・ K). . Therefore, the high thermal conductivity of the sintered body is largely related to the thermal conductivity of the silicon nitride particles themselves. Here, intragranular dislocations and solid solution elements are factors that inhibit the thermal conductivity of the silicon nitride particles themselves. These impeding factors cause scattering of phonons, which are heat carriers, and significantly reduce heat transfer. Therefore, in order to improve the thermal conductivity of the silicon nitride particles, and thus the thermal conductivity of the sintered body, it is important to suppress these inhibiting factors. Among these inhibiting factors, the solid solution element in the grain is Si-NO-Mg-R composed of Si, N and auxiliary components in the liquid phase formation stage in the sintering process.
E is generated, and relatively small particles are dissolved in this liquid phase at the grain growth stage, and subsequently, Si and N are re-precipitated on the surface of the large particles, and grain growth proceeds. At this time, Mg, an auxiliary component of RE and oxygen (O) mixed with Si and N are also taken into the particle surface. As mentioned above, the smaller the ionic radius of the element, the greater this tendency.

Therefore, in the silicon nitride particles constituting the final microstructure after sintering, a very small amount of auxiliary component and oxygen are present in the fine particles. This solid solution element is, for example, Mg,
Rare earth elements such as Y, La, Gd, and Yb. If these are finely precipitated in the particles, the surroundings of the fine particles are highly purified, and the thermal conductivity of the particles themselves is increased. The presence of such a solid solution element is a characteristic point of the present invention, whereby a high thermal conductivity of the sintered body can be achieved. The precipitation of the solid solution element can be adjusted by sintering including the above-mentioned holding process, extension of sintering time, or heat treatment. However, if the amount of solid solution elements in the silicon nitride particles after sintering is large, the effect of purifying the particles by fine particle precipitation does not occur, so select an appropriate sintering aid and apply the sintering method. Is essential.

Next, in the method for producing a silicon nitride sintered body, the ratio of the first silicon nitride powder having a β fraction of 30 to 100% and the second α-type silicon nitride powder is 1 to 50 wt%. : 99
~ 50 wt% is preferred. If the β fraction of the silicon nitride powder having a β fraction of 30 to 100% is less than 1 wt%, it has an effect as growth nuclei, but since the amount of addition is small, the number of growth nuclei acting is small and abnormal grain growth occurs. Large particles cannot be uniformly dispersed in the microstructure, and bending strength decreases. If it exceeds 50 wt%, the number of growth nuclei will increase, and particles will collide with each other during the grain growth process, resulting in growth inhibition and maintaining strength, but a silicon nitride sintered body composed of developed columnar particles. However, it is difficult to obtain a higher thermal conductivity than the conventional one. The oxygen content of the silicon nitride powder is set to 0.5 wt% or less. When the silicon nitride powder acts as a growth nucleus to form a silicon nitride sintered body, it constitutes a silicon nitride sintered body. The amount of oxygen solid-dissolved in the silicon nitride particles strongly depends on the amount of oxygen in the silicon nitride powder used as a growth nucleus. The higher the amount of oxygen in the silicon nitride powder, the more oxygen dissolved in the silicon nitride particles. Higher quantity. Then, the oxygen contained in the silicon nitride particles causes scattering of phonons, which are the heat conductive medium, and the thermal conductivity of the silicon nitride sintered body decreases. In order to develop a high thermal conductivity of 100 W / (mK) or higher, which was not possible with conventional silicon nitride sintered bodies, the oxygen content of silicon nitride powder should be kept below 0.5 wt% It is indispensable to reduce the amount of oxygen in the silicon nitride sintered body that is obtained as a result.

Fe content and A in the silicon nitride powder
If the content of l is more than 100 ppm, F will be contained in the silicon nitride particles.
e or Al is remarkably solid-dissolved, and phonons, which are the heat-conducting medium, are scattered in this solid-solution portion, and the thermal conductivity of the silicon nitride sintered body is lowered. Therefore, in order to obtain a thermal conductivity of 100 W / mK or more, it is important to control the Fe content and the Al content in the silicon nitride powder to 100 ppm or less.

The substrate made of the silicon nitride sintered body of the present invention makes use of the characteristics of high strength, high toughness, and high thermal conductivity, and is used for various substrates such as substrates for power semiconductors or substrates for multi-chip modules, or It is suitable as a member for electronic parts such as a heat transfer plate for a Peltier element or a heat sink for various heating elements. For example, when a silicon nitride sintered body is used as a substrate for a semiconductor element, the occurrence of cracks in the substrate when subjected to repeated thermal cycles associated with the operation of the semiconductor element is suppressed, and thermal shock resistance and thermal cycle resistance are significantly improved. It is improved and has excellent reliability. Further, even when a semiconductor element directed to high output and high integration is mounted, thermal resistance characteristics are less deteriorated and excellent heat dissipation characteristics are exhibited. Furthermore, because of its excellent mechanical properties, it can function not only as an original substrate material but also as a structural member, so that the structure of the substrate unit itself can be simplified.

Alternatively, when the silicon nitride sintered body of the present invention is used as a heat transfer plate for a Peltier device, cracks in the substrate when subjected to repeated heat cycles accompanied by switching of the polarity of the applied voltage of the Peltier device. Is suppressed, the thermal cycle resistance is remarkably improved, and the reliability is improved. Further, when used as a Seebeck element heat transfer plate, the heat absorption side has a high temperature of around 600 ° C., and therefore, thermal cycle resistance and thermal shock resistance are also required here. When it is used, these life characteristics are greatly improved and the reliability becomes excellent.

Further, the silicon nitride sintered body of the present invention can be widely used for materials other than the above-mentioned members for electronic parts, which are required to have thermal shock resistance and thermal fatigue resistance. As structural members, various heat exchanger parts, heat engine parts, heater tubes used in the field of melting metals such as aluminum and zinc, Stokes, die casting sleeves, molten metal stirring propellers, ladles, or thermocouple protection tubes. Applicable to Further, by applying it to a sink roll, a support roll, a bearing, a shaft, or the like used in a molten metal plating line for aluminum, zinc, etc., it can be a member having excellent crack resistance against rapid heating and cooling. Also,
In the field of steel or non-ferrous metal processing, if it is used for rolling rolls, squeeze rolls, guide rollers, wire drawing dies, tool tips, etc., it has good heat dissipation when it comes into contact with the work piece, so it has good heat resistance Impact resistance can be improved, which results in less wear and less thermal stress cracking.

Further, it can be applied to a sputter target member, for example, it is used to form an electrically insulating film used in MR heads, GMR heads, TMR heads of magnetic recording devices, and wear resistance used in thermal heads of thermal transfer printers. Suitable for forming a film. The coating film obtained by sputtering essentially has a high thermal conductivity property, and the sputtering rate can be sufficiently high, so that the coating film has a high electrical withstand voltage. Therefore, the MR head, GMR head, or TM formed by this sputter target
Since the electrically insulating coating for the R head has the characteristics of high heat conduction and high withstand voltage, it is possible to increase the heat generation density of the element and thin the insulating coating. Further, the wear-resistant coating for the thermal head formed by this sputter target has good wear resistance due to the inherent characteristics of silicon nitride, and since it has high thermal conductivity, it can reduce the heat resistance, so that the printing speed can be reduced. Can be increased.

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. (Example 1) 1-50 wt% of the first silicon nitride powder having a β-conversion rate of 30% or more, an average particle size of 0.7-1.2 μm, and an oxygen content of 0.5
~ 2.0wt% α-type second silicon nitride powder, 1.0wt% or 2.0wt% MgO, and 3wt% or 6.0wt% Gd ₂ O ₃ or sintering aid shown in Table 1 is added. The mixed powder was prepared. The ratio of the second silicon nitride powder was a balance between the second silicon nitride powder and the sintering aid powder. Further, 2 wt% of a dispersant (trade name: Rheogade GP) was blended, charged into a ball mill container filled with ethanol, and then mixed. The obtained mixture was vacuum dried, and then granulated through a sieve having an opening of 150 μm. Next, with a press machine, diameter 20 mm × thickness
A disk-shaped compact having a diameter of 10 mm and a diameter of 100 mm and a thickness of 15 mm was obtained by CIP molding under a pressure of 3 tons. Then 1850 ℃ ~ 1950
5 to 5 in a nitrogen gas atmosphere of 0.7 to 0.9 MPa (7 to 9 atm)
It was baked for 40 hours. In the sintering process, the temperature rises to 1400
A holding step was performed at a temperature of ℃ to 1600 ℃ for 1 to 10 hours, and the temperature rising rate from the holding temperature to the sintering temperature was 5.0 ℃ / min or less. Table 1 shows the manufacturing conditions for each sample.
Sample No. 1 to 15 are shown.

The fine particles in the silicon nitride particles of the obtained silicon nitride sintered material were observed with a transmission electron microscope (HF2000 manufactured by Hitachi, Ltd.) at an observation magnification of 10,000 to 600,000 times. Further, the composition analysis of fine particles was evaluated by an attached energy dispersive analyzer. Figure 1
FIG. 4 is a photograph of a TEM observation image of the silicon nitride sintered body of the present invention (samples No. 1 to No. 4 in Table 1). Also,
FIG. 5 is a photograph of a TEM observation image of the comparative example (sample No. 31 in Table 3). 6 to 9 are photographs of high-resolution observation images of fine particles (samples No. 1 to No. 4 in Table 1), and FIG.
0 (No. 1 sample in Table 1) and FIG. 11 (No. 2 sample in Table 1) are photographs of STEM observation images of the nuclei and peripheral portions of the fine particles.

Next, a test piece for measuring thermal conductivity and density having a diameter of 10 mm and a thickness of 3 mm, and a bending test piece having a length of 3 mm, a width of 4 mm and a length of 40 mm were collected from the obtained silicon nitride sintered body. did. The density was calculated by measuring the dimensions by a micrometer and measuring the weight. The thermal conductivity was calculated by measuring the specific heat and the thermal diffusivity at room temperature by the laser flash method. 3-point bending strength is JIS R1 at room temperature
The measurement was performed according to 606. The outline of the above manufacturing conditions and the evaluation results are shown in Sample Nos. 1 to 15 of Table 1 and Table 2.

(Comparative Example 1) Evaluation was made in the same manner as in Example 1 except that the manufacturing conditions of Sample Nos. 31 to 42 shown in Table 1 were used.
The outline of the above manufacturing conditions and the evaluation results are shown in Sample Nos. 31 to 42 of Table 1 and Table 2.

[0040]

[Table 1]

[0041]

[Table 2]

As shown in Tables 1 and 2, the sintered bodies in which fine particles were found in the silicon nitride particles had a thermal conductivity of 100 W / (m · K) or more and a bending strength of 600 MPa or more. was gotten. Moreover, it was confirmed that the thermal conductivity tends to improve as the proportion of the fine particles increases. The RExOy / MgO ratio of the sintering aid component used for the sintered body in which fine particles were recognized was 1 or more. On the other hand, 100 W / (mK) for all sintered bodies where fine particles are not found in the silicon nitride particles.
The thermal conductivity was less than. In addition to this, sample No. 37 ~ 4
For 2, the temperature rises from 1400 ℃ to 1600 ℃ in the sintering process.
If the temperature is not maintained at this temperature, or if the rate of temperature increase from this holding temperature to the sintering temperature is more than 5.0 ° C / min,
Both the thermal conductivity and the strength were significantly reduced.

TEM observation images of FIGS. 1 to 5, high resolution electron microscope (HREM) observation images of fine particles of FIGS. 6 to 9 and FIG.
0, the STEM observation image of the nuclei of fine particles and the peripheral portion thereof will be considered. 1 to 4 show that Gd2O3 is used as a sintering aid.
(Fig. 1), Yb2O3 (Fig. 2), Y2O3 (Fig. 3) and La2O3
Transmission electron microscope (TEM) of the present invention using (FIG. 4)
Show the image. Further, FIG. 5 shows a TEM observation image of the comparative example. From FIG. 1 to FIG. 4, fine particles are present in the silicon nitride particles in all cases. In Fig. 1, the lower right portion is scattered in the range of 8 to 45 nm, in Fig. 2, the central right portion is scattered in the 10 to 60 nm range, in Fig. 3, the central left and right portions are scattered in the 8 to 60 nm range nm, and in Fig. 4, the upper right portion. It was found that the particles were scattered in the range of 4 to 85 nm, and the particle size of these fine particles was 100 nm or less. On the other hand, in the comparative example of FIG. 5, such fine particles were not observed. In addition, it was not confirmed in another observation visual field. Here, when the particle diameter of the fine particles is more than 100 nm, the number of fine particles of more than 100 nm precipitated in the silicon nitride particles is significantly increased, and does not contribute to the improvement of the thermal conductivity of the desired silicon nitride particles themselves. .

Next, as shown in FIGS. 6 to 9, Gd2O3 was used as a sintering aid.
(Fig. 6), Yb2O3 (Fig. 7), Y2O3 (Fig. 8) and La2O3
The high-resolution observation (HREM) image of the example of the present invention using (FIG. 9) is shown. 6 to 9 are observation images of the fine particles observed in FIGS. 1 to 4, respectively. From FIGS. 6 to 9, it was found that the fine particles precipitated in the silicon nitride particles consisted of an amorphous phase because the random lattice image and the electron diffraction image showed the halo pattern peculiar to the glass phase. Furthermore,
In the HREM image of FIG. 7, it was confirmed that the nucleus 7 and the peripheral portion 8 had different compositions. From the results of TEM-EDX analysis,
The core had a high Si component, a low Mg and RE components (Yb corresponds in the present invention), and the composition of the peripheral portion was the opposite evaluation result. In the HREM image, when observing a very small area for a long period of time, it is difficult to observe the nucleus and the peripheral part separately due to damage by the electron beam.
The image is excellent in that it can be referred to separation of constituents of fine particles and quantification of composition. 10 and 1
1 is a scanning transmission electron microscope (STE) of the example of the present invention using Gd2O3 (FIG. 10) and Yb2O3 (FIG. 11) as sintering aids.
M) Shows the image. These figures are STEM images of the fine particles observed in FIGS. 1 and 2, respectively. ST
EM images are especially useful when observing nano-level microscopic regions.
This is an effective observation method for expressing a slight difference in composition or component amount as image contrast. As shown in FIG. 10 and FIG. 11, it can be confirmed that each fine particle is composed of a nucleus and a peripheral portion. The nucleus has a high Si component, and Mg and
It was found that RE (Gd and Yb correspond in the present invention) is low, while the peripheral portion has a composition opposite to this.

(Example 2) 1 to 50 wt% of the second silicon nitride powder having a β-conversion rate of 30% or more, an oxygen content of 0.5 wt% or less, an average particle size of 1 μm to 10 μm, and an aspect ratio of 10 or less. %, An average particle size of 0.7 to 1.2 μm, and an oxygen content of 0.5 to 2.0 wt% α-type second silicon nitride powder with 1 wt% MgO and 3 wt% Gd ₂ O ₃ sintering aid added. The mixed powder was prepared. Then, the mixed powder prepared in a resin pot of a ball mill filled with a toluene-butanol solution added with 2 wt% of an amine-based dispersant and a silicon nitride ball of a grinding medium are charged,
Wet mixed for 48 hours. Then, the mixed powder in the pot
15 parts by weight of a polyvinyl organic binder and 5 parts by weight of a plasticizer (dimethyl phthalate) were added to 100 parts by weight, and the mixture was wet mixed for 48 hours to obtain a sheet forming slurry. After adjusting this forming slurry, a green sheet was formed by a doctor blade method. Then, the molded green sheet was heated in air at 400 to 600 ° C. for 2 to 5 hours to sufficiently degrease (remove) the organic binder component added in advance. Next, the degreased body was fired at 1900 ° C. for 10 hours in a nitrogen atmosphere of 0.9 MPa (9 atm), and then cooled to room temperature. In the sintering process, the temperature rises from 1400 ℃ to 1600 ℃
At a temperature of 1 to 10 hours, and the temperature rising rate from this holding temperature to the sintering temperature is 2.0 ° C / min.
And The obtained silicon nitride sintered body sheet was machined to produce a substrate for a semiconductor module having a length of 50 mm, a width of 50 mm and a thickness of 0.6 mm.

A circuit board shown in FIG. 12 was produced using this silicon nitride sintered body substrate. In FIG. 12, the circuit board 11 is provided with a copper circuit board 13 on the front surface of the silicon nitride sintered body substrate 12 having dimensions of 50 mm in length × 50 mm in width × 0.6 mm in thickness, and a copper plate on the back surface of the substrate 12. 14 is joined by a brazing material 15. This circuit board 11
On the other hand, a three-point bending strength evaluation and a heat cycle test were performed. As a result, the bending strength is as large as 600 MPa or more, and the frequency of occurrence of tightening cracks in the mounting process of the circuit board 11 and cracks caused by thermal stress in the soldering process is hardly seen. It was demonstrated that the manufacturing yield can be significantly improved. In the heat resistance cycle test, cooling at -40 ° C
For 10 minutes at room temperature and 20 minutes at 180 ° C.
The cycle of temperature increase / decrease for one minute was set as one cycle, and this cycle was repeatedly applied, and the number of cycles until cracks and the like occurred in the substrate part was measured. As a result, it was confirmed that, even after 1000 cycles, the silicon nitride sintered body substrate 12 was not cracked and the copper circuit board 13 was not peeled off, and it had excellent durability and reliability. In addition, the withstand voltage characteristics did not deteriorate even after 1000 cycles.

Finally, the β fraction used in Examples 1 and 2 was
The silicon nitride powder of 30% or more has an oxygen content of less than 2.0 wt% in terms of SiO ₂ and an average particle diameter of 0.2 to
A BN crucible was filled with a silicon nitride powder by an imide decomposition method of 2.0 μm, and then N _{2 at} atmospheric pressure to 1.0 MPa (10 atm).
Heat treatment was performed by heating in an atmosphere at 1400 ° C to 1950 ° C for 1 to 20 hours, and then cooled to room temperature. The obtained silicon nitride powder has a β fraction of 90 to 100% and an oxygen content of 0.2.
It was ~ 0.4 wt%. FIG. 13 shows an SEM observation image of the obtained silicon nitride powder example. Β fraction of the powder is 100
%, The amount of oxygen was 0.2 wt%, and the amounts of Fe and Al were 50 ppm and 40 ppm, respectively. Grooves are formed in the powder in parallel with the major axis direction of the particles, which is a characteristic when grain growth occurs through the gas phase, and becomes more remarkable as the amount of oxygen is very small. F of the obtained silicon nitride powder
The impurities of e and Al were analyzed by plasma emission spectrometry (ICP). The oxygen content was measured by the infrared heating absorption method.

Further, the β fraction of the obtained silicon nitride powder was obtained from the formula (1) from the X-ray diffraction intensity ratio using Cu-Kα ray. β fraction (%) = {(I _{β (101)} + I _{β (210)} ) / (I _{β (101)} + I _{β (210)} + I _{α (102)} + I _{α (201)} )} × 100 _{(1) I β (101)} : β -type _Si 3 of _{N 4} (101) plane diffraction peak - click intensity, I β _(210): β-type _Si 3 of _{N 4} (210) plane diffraction peak - click intensity, I _{alpha (102):} the alpha-type _Si 3 _{N 4} (102) plane diffraction peak - click intensity, I _{α (210):} the alpha-type _Si 3 _{N 4} (210) plane diffraction peak - click strength.

The average particle size and the average aspect ratio of the obtained silicon nitride powder were 500 in total in the visual field area of 200 μm × 500 μm, using the SEM photograph obtained by SEM observation at an observation magnification of × 2000. Randomly select silicon nitride particles and measure the minimum and maximum diameters with an image analyzer.
The average value was calculated and evaluated. The obtained silicon nitride powder has a β fraction of 30% or more, an average particle diameter of 0.5 to 10 μm, an aspect ratio of 10 or less, and Fe and Al contents of both.
The oxygen content was 100 ppm or less, and the oxygen content was 0.5 wt% or less.

[0050]

As described above, the silicon nitride-based sintered body of the present invention is characterized in that at least one element of Mg or rare earth elements such as Y, La, Gd, and Yb is contained in the silicon nitride particles and the oxygen element. The presence of fine particles having a particle size of 100 nm or less containing and provides high thermal conductivity in addition to the original high strength / high toughness. This can be manufactured without the need for a costly firing method such as high temperature / high pressure sintering, and a firing apparatus. When this is used as a substrate for a semiconductor element, cracks are less likely to occur in the substrate due to repeated thermal cycles associated with the operation of the semiconductor element, and thermal shock resistance and thermal cycle resistance can be remarkably improved.

[Brief description of drawings]

FIG. 1 shows a transmission electron microscope (TEM) observation photograph of a silicon oxynitride sintered body when Gd2O3 was used as the rare earth oxide of the present invention.

FIG. 2 shows a transmission electron microscope (TEM) observation photograph of a silicon nitride sintered body when Yb2O3 is used as the rare earth oxide of the present invention example.

FIG. 3 shows a transmission electron microscope (TEM) observation photograph of a silicon nitride sintered body when Y2O3 is used as the rare earth oxide of the present invention.

FIG. 4 shows a transmission electron microscope (TEM) observation photograph of a silicon nitride sintered body when La2O3 is used as the rare earth oxide of the present invention.

FIG. 5 shows a transmission electron microscope (TEM) observation photograph of a silicon nitride sintered body of a comparative example.

FIG. 6 shows a high-resolution observation photograph (HREM) of fine particles precipitated in silicon nitride particles in a silicon nitride sintered body when Gd2O3 is used as the rare earth oxide of the present invention.

FIG. 7 shows a high-resolution observation photograph (HREM) of fine particles deposited in silicon nitride particles in a silicon nitride sintered body in which Yb2O3 is used as the rare earth oxide of the present invention example.

FIG. 8 is a high-resolution observation photograph (HREM) of fine particles precipitated in silicon nitride particles in a silicon nitride sintered body in which Y2O3 is used as the rare earth oxide of the present invention example.

FIG. 9 is a high-resolution observation photograph (HREM) of fine particles precipitated in silicon nitride particles in a silicon nitride sintered body in which La2O3 is used as the rare earth oxide of the present invention example.

FIG. 10 is a scanning transmission electron micrograph (STEM) of fine particles precipitated in silicon nitride particles in a silicon nitride sintered body using Gd2O3 as the rare earth oxide of the present invention.
Indicates.

FIG. 11 is a scanning transmission electron micrograph (STEM) of fine particles precipitated in silicon nitride particles in a silicon nitride nitride sintered body using Yb2O3 as the rare earth oxide of the present invention.
Indicates.

FIG. 12 is a cross-sectional view of a main part of a circuit board using the silicon nitride sintered body of the present invention.

FIG. 13 shows an SEM observation image photograph of the silicon nitride powder used for manufacturing the silicon nitride sintered body of the example of the present invention.

[Explanation of symbols]

11: Circuit board 12: substrate 13: Copper circuit board 14: Copper plate 15: Brazing material.

[Procedure amendment]

[Submission date] January 10, 2003 (2003.1.1
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

That is, the silicon nitride sintered body of the present invention is at least selected from the group consisting of Mg or Y and rare earth elements (RE) in silicon nitride particles in a transmission micrograph at a magnification of 10,000 or more. It is characterized by the presence of fine particles having an average particle diameter of 100 nm or less containing one kind of element and O element. The silicon nitride sintered body of the present invention is a silicon nitride sintered body to which Mg and at least one element selected from the group consisting of Y and rare earth elements (RE) are added as a sintering aid. Therefore, in a transmission type micrograph with a magnification of 10,000 times or more, in the silicon nitride particles, M
It is characterized by the presence of fine particles having an average particle size of 100 nm or less, which contains g or at least one element selected from the group consisting of La, Y, Gd and Yb, and O element. The fine particles are those in which the auxiliary component taken in the particles in the grain growth of the silicon nitride particles during the firing process is re-precipitated in the silicon nitride particles, although the trace amount is extremely small, and the high thermal conductivity of the silicon nitride particles themselves. Contribute to At this time, in a transmission electron micrograph with a magnification of 10,000 times or more, it is desirable that 5 / μm ² or more of fine particles having an average particle diameter of 100 nm or less are present in the silicon nitride particles. The thermal conductivity of the sintered body is improved by the ratio.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

Further, the silicon nitride sintered body of the present invention is characterized in that the fine particles are composed of different nuclei and peripheral portions. The fine particles are at least Si-N-
It has an O-Mg-RE composition, and the composition ratio is such that the Si component is high in the core portion and the amount of the component (for example, Mg and rare earth element) added as an auxiliary component is small. On the other hand, in the peripheral portion, on the contrary, it is desirable that the Si component is small and the amount of the auxiliary component is large. Further, it is desirable that the fine particles are entirely in an amorphous phase.

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Claims (10)

[Claims] 1. Fine particles having a particle size of 100 nm or less containing at least one element selected from the group consisting of Mg or Y and a rare earth element (RE) and an O element in the silicon nitride particles. A silicon nitride sintered body characterized by: 2. A silicon nitride sintered body to which at least one element selected from the group consisting of Mg, Y and a rare earth element (RE) is added as a sintering aid, wherein the silicon nitride particles are Inside, Mg or La, Y, Gd and Yb
A silicon nitride sintered body, characterized in that fine particles having a particle size of 100 nm or less containing at least one element selected from the group consisting of and O element are present. 3. An observation image with a direct magnification of 10,000 times or more by a transmission electron microscope (TEM), characterized in that the fine particles having a particle size of 100 nm or less are present in an amount of 5 particles / μm ² or more. The silicon nitride sintered body according to claim 1. 4. The fine particles are at least Si—N—O.
The silicon nitride sintered body according to any one of claims 1 to 3, which has a -Mg-RE composition and is composed of a core and a peripheral portion having different composition ratios. 5. The silicon nitride sintered body according to claim 1, wherein the fine particles have an amorphous phase. 6. The Mg contained in the silicon nitride sintered body.
Is converted to magnesium oxide (MgO), and the rare earth elements containing La, Y, Gd, and Yb which are also contained are converted to rare earth oxides (RE _x O _y ), the oxide content converted to these oxides total at 0.6~10wt%, and _{(RE x O y) / (} MgO)> 1 a silicon nitride sintered body according to any one of claims 1 to 5, characterized in that. 7. The high thermal conductivity at room temperature is 100 W / (m · K) or more, and the three-point bending strength at room temperature is 600 MPa or more, which is rich in high strength and high thermal conductivity. The silicon nitride sintered body according to. 8. A method for producing a silicon nitride sintered body having high strength and high thermal conductivity, wherein the β fraction is 30 to 100%, the oxygen content is 0.5 wt% or less, and the average. Particle size is
0.2 to 10 μm, 1 to 50 parts by weight of a first silicon nitride powder having an aspect ratio of 10 or less, and an average particle size of 0.2 to 4
99-50 parts by weight of the second α-type silicon nitride powder of μm, and Mg
And a sintering aid containing Y and at least one element selected from the group consisting of rare earth elements (RE), 18
A method for producing a silicon nitride sintered body, comprising sintering at a temperature of 00 ° C. or higher and a nitrogen pressure atmosphere of 0.5 MPa or higher. 9. In the sintering step, the temperature rises from 1400 ° C. to
9. A holding step at least once for 1 to 10 hours at a temperature of 1600 ° C., and a temperature rising rate from the holding temperature to the sintering temperature is 5.0 ° C./min or less. 1. A method for manufacturing a silicon nitride sintered body according to claim 1. 10. A circuit board having a high strength and a high thermal conductivity, which is constituted by using the silicon nitride sintered body according to any one of claims 1 to 9.