JP2002265276A - Silicon nitride powder and silicon nitride sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride sintered compact having high strength, high toughness and excellent heat dissipating properties. SOLUTION: A silicon nitride powder is characterized in that the particle diameters (d10 ), (d50 ) and (d90 ) corresponding to accumulated frequencies of 10%, 50% and 90% by volume, respectively, have particle diameter distribution of 0.5 to 0.8 μm, 2.5 to 4.5 μm and 7.5 to 10.0 μm, respectively, and the content of oxygen is 0.01 to 0.5 wt.%. The silicon nitride sintered compact is obtained by using this silicon nitride power, and has a thermal conductivity of >=80 W/m.K, a three-point bending strength at room temperature of >=600 MPa and fracture toughness of >=5 MPa.m<1/2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body having high strength, high toughness and excellent heat dissipation, and a silicon nitride powder capable of obtaining the silicon nitride sintered body and having excellent sheet formability. About.

[0002]

2. Description of the Related Art Sintered silicon nitride has excellent mechanical properties such as high-temperature strength and abrasion resistance, as well as excellent heat resistance, low thermal expansion, thermal shock resistance, and corrosion resistance to metals. It is used for various structural members such as members for gas turbines, members for engines, mechanical members for steelmaking, and melt-resistant members of molten metal. In addition, it is used as an electrical insulating material by utilizing high insulating properties.

[0003] In recent years, with the practical use of semiconductor elements having a large amount of heat, such as high-frequency transistors and power ICs, there has been a demand for ceramic substrates having high thermal conductivity so as to obtain good heat dissipation characteristics in addition to electric insulation. It has increased. As such a ceramic substrate, an aluminum nitride substrate is used. However, the mechanical strength and the fracture toughness are low, and the substrate may be cracked by tightening during the assembly process of the substrate unit, or a circuit on which a Si semiconductor element is mounted. In the substrate, since the thermal expansion difference between the Si metal and the substrate is large, there is a problem that cracks and cracks are generated in the aluminum nitride substrate due to the thermal cycle and the mounting reliability is reduced.

[0004] Therefore, a substrate made of a high thermal conductive silicon nitride sintered body having a lower thermal conductivity than an aluminum nitride substrate but having a coefficient of thermal expansion close to that of Si and having excellent mechanical strength, fracture toughness, and thermal fatigue resistance is used. Attention has been paid.

As a raw material silicon nitride powder for producing a silicon nitride sintered body having high strength and high thermal conductivity, a specific surface area, an average particle diameter, and a particle size distribution are taken into consideration in consideration of sinterability and the above-mentioned properties to be obtained. Studies on powder characteristics such as the ratio of β-type silicon nitride particles (β fraction) and the like have been actively conducted.

For example, Japanese Patent Application Laid-Open No. 2000-72552 discloses a silicon nitride heat radiating member having a thermal conductivity of 50 W / m · K or more and a three-point bending strength at room temperature of 700 MPa or more, and a heat radiating member. The average particle diameter of the silicon nitride powder used as a raw material is 0.4 to 0.7 μm,
There is a description that 60 to 80% of the particles having a particle size of μm or less are accumulated, and 90% of the particles have a particle size distribution of 2 to 5 μm.

Further, Japanese Patent No. 3002462 discloses α
Silicon nitride powder having a particle size of 70 to 98% by weight, containing 2 to 15% by weight of β-type silicon nitride particles having a particle diameter of 0.6 μm or less, and β-type silicon nitride particles contained in the silicon nitride powder. Characterized in that β-type silicon nitride particles having a particle size of 1.0 to 3.0 μm are contained in an amount of 2 to 5% by weight based on the total amount. A powder is described.

The silicon nitride sintered body using the silicon nitride powder as a raw material has a four-point bending strength of 1000 MPa.
a, a fracture toughness of 7.0 MPa · m ^1/2 or more, a thermal conductivity of 30 W / m · K or more, and high strength, high toughness, and excellent heat dissipation.

[0009]

Problems to be Solved by the Invention
The silicon nitride heat-dissipating member described in Japanese Patent No. 72552 is made of a sintered body having a relative density of 95% or more mainly composed of silicon nitride columnar crystals, and a major axis of silicon nitride particles on a cut surface of the sintered body. The average particle diameter is 1 to 3 μm, and 50 to 70% of crystal particles having a particle diameter of 1 μm or less are accumulated.
Having a thermal conductivity of 50 W / m · K or more and a three-point bending strength at room temperature of 700 MPa or more,
It has the advantage of having both high heat dissipation and high strength.

[0010] Further, in the method of manufacturing the silicon nitride heat radiating member, the sheet moldability is improved by using the silicon nitride raw material powder having a specific particle size distribution as described above, and the silicon nitride in the sintered body is concomitantly improved. By controlling the particle size distribution of the particles to a specific range, there is an advantage that a thin heat-dissipating member having a single-layer or laminated structure can be provided without cutting or polishing.

Further, the aforementioned Japanese Patent No. 3002462 discloses that the particle size of β-type silicon nitride particles contained in raw material powder together with α-type silicon nitride particles is adjusted.
It has the advantage that a sintered body having excellent strength and toughness and having a thermal conductivity of 30 W / m · K or more can be produced.

However, Japanese Patent Application Laid-Open No. 2000-72552
In the heat dissipating member described in Japanese Patent Application Laid-Open No. H10-209, the heat conductivity of the semiconductor element cannot be quickly dissipated to the outside due to low thermal conductivity in order to use it as a high-power, high-current, high-output power semiconductor substrate. There's a problem.

In the method described in Japanese Patent No. 3002462, the average particle diameter of the silicon nitride powder used as a raw material is 0.4 μm to 0.7 μm, and a total 90% diameter (d
₉₀ ) is as small as 2.0 to 5.0 μm.
When producing a sheet molded body having a thickness of 5 to 2.0 mm,
There is a problem that the moldability is remarkably inferior, for example, the degree of filling of particles and the density of the compact are low, and cracks are generated during drying.

[0014] Further, with respect to a sintered body obtained by using the raw material powder, there is a description that silicon nitride particles in a microstructure can distinguish a central portion from a peripheral portion.
This suggests that the added β particles act as growth nuclei, but on the other hand, indicates that the composition is different between the central part and the peripheral part. This is because there is a difference in the etching rate in plasma etching, that is,
This indicates that auxiliary components and the like are dissolved in the peripheral portion during the grain growth process. The impurities in the particles serve as a scattering source of phonons, which are a heat conduction medium, and lower the thermal conductivity of the sintered body. Therefore, as described in the examples, the thermal conductivity of the sintered body is at most 70 W / m · K. Therefore, similarly to the sintered body disclosed in the above-mentioned Japanese Patent No. 3002462, there is a drawback in that the sintered body has poor heat dissipation when used as a high-voltage, high-current, high-output power semiconductor substrate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a silicon nitride powder having a particle size distribution excellent in sheet formability and a high-strength,
An object is to provide a sintered body having high toughness and excellent heat dissipation.

[0016]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have specified powder characteristics such as the particle size distribution of silicon nitride powder to be used, the ratio and shape of β-type silicon nitride particles, and the oxygen content. As a result, the present inventors have found that a silicon nitride-based sintered body having a thermal conductivity of 80 W / m · K or more and sufficient bending strength and fracture toughness can be stably obtained, thereby leading to the present invention.

That is, the silicon nitride powder of the present invention that has solved the above-mentioned problems has an integration frequency of 10% and 50% in volume ratio.
And the particle size (d ₁₀ ) at 90% (d ₅₀ ) and (d ₅₀ )
₉₀ ) are 0.5-0.8 μm and 2.5-4.
Having a particle size distribution of 5 μm and 7.5 to 10.0 μm,
In addition, the oxygen content is 0.01 to 0.5 wt%.

The particle size distribution of the raw material powder greatly affects the sheet formability and the density of the sintered body. Particle size (d ₁₀ ) at cumulative frequency of 10%, 50% and 90% in volume ratio
(D _{5 0)} and is (d _90), respectively, when outside the above range is not appropriate particle packing degree obtained, it becomes impossible to obtain sufficient green density, by force sintering Problems such as a decrease in body density occur. In particular, when (d ₅₀ ) is less than 2.5 μm, the particle diameter of the cumulative particles of the total silicon nitride powder is small, the degree of particle filling is reduced, and defects such as cracks occur in the molded sheet after sheet molding.

When (d ₉₀ ) is less than 7.5 μm, the difference in particle diameter of the silicon nitride powder, which is a driving force for grain growth, becomes small, the firing temperature is 1850 ° C. to 1950 ° C., and the holding time is relatively short. If the firing is performed for 10 hours or less, a microstructure in which the degree of grain growth is small and columnar particles are developed cannot be obtained, and the thermal conductivity is less than 80 W / m · K.

When (d ₉₀ ) is more than 10 μm, the sheet formability is good, but the ratio of the excessively large particle size increases, so that the reaction with the sintering aid powder is hindered and sintering is difficult. And becomes a low-density sintered body. Therefore, sufficient strength and thermal conductivity cannot be obtained. Therefore,
(D ₁₀ ), (d ₅₀ ) and (d ₉₀ ) are each 0.
5-0.8 μm, 2.5-4.5 μm and 7.5-1
It is desirable to have a particle size distribution of 0.0 μm.

When the oxygen content is less than 0.01% by weight, the amount of SiO ₂ component which reacts with the sintering aid becomes extremely small, so that a sufficient liquid phase cannot be obtained and the sintering becomes difficult. on the other hand,
When the content is more than 0.5 wt%, a sufficient sintered body density can be obtained due to the presence of a sufficient SiO ₂ component, but the amount of the grain boundary phase having a low thermal conductivity, which is the second microstructure component of the sintered body. Becomes excessive, and in addition, the amount of oxygen remaining in the silicon nitride particles increases, and the thermal conductivity of the sintered body becomes 80 W
/ M · K. Therefore, the oxygen content is 0.0
It is preferably 1 to 0.5 wt%.

Further, the silicon nitride powder of the present invention is characterized in that the ratio of β-type silicon nitride particles present in particles having an average particle diameter (d ₅₀ ) or more is 1 to 50%. β
When the percentage of silicon nitride particles is less than 1%, the effect as growth nuclei is effective, but the content is small, so the number of acting nuclei is small, abnormal grain growth occurs, and large particles are uniformly dispersed in the microstructure. And the bending strength decreases. On the other hand, if it exceeds 50%, the number of nuclei of growth nuclei increases, and the particles collide with each other in the course of grain growth. As a result, the grain growth is inhibited, and the strength can be maintained. Since a microstructure cannot be obtained, it becomes difficult to achieve a higher thermal conductivity than in the past.

The β-type silicon nitride particles have a particle size of 0.5
.About.5 .mu.m, an aspect ratio of 2 to 10, and an oxygen content as an impurity of 0.5 wt% or less. β
If the particle size of the silicon nitride particles is less than 0.5 μm, it will form a solid solution in the liquid phase during the liquid phase generation process, lose its effect as a growth nucleus, and cannot obtain a microstructure composed of developed columnar particles, Both thermal conductivity and toughness are significantly reduced.
On the other hand, if it exceeds 5 μm, although it acts as a growth nucleus, selective grain growth is promoted, and the frequency of collision of particles with each other increases, thereby inhibiting grain growth. As a result, pores are formed at the grain boundary triple point in the vicinity of the collision of the columnar particles, causing a decrease in density, and dislocations are easily formed in the particles. As a result, the mechanical properties of strength and toughness decrease, and A decrease in thermal conductivity occurs. Therefore, the particle size of the β-type silicon nitride particles is preferably 0.5 to 5 μm.

The aspect ratio of β-type silicon nitride particles is 10
If it is more than that, the densification of the silicon nitride sintered body is hindered, and as a result, the three-point bending strength at room temperature becomes less than 600 MPa. Therefore, the aspect ratio of the β-type silicon nitride particles is desirably 10 or less, preferably 2 to 10.

When the amount of oxygen contained in the β-type silicon nitride particles exceeds 0.5 wt%, the amount of oxygen remaining in the silicon nitride particles constituting the microstructure increases. Oxygen contained in the silicon nitride particles causes phonons, which are a heat conductive medium, to be scattered, thereby lowering the thermal conductivity of the silicon nitride sintered body.
Therefore, the oxygen content of the β-type silicon nitride particles is 0.5
Desirably, it is not more than wt%.

The silicon nitride sintered body made of the silicon nitride powder has a thermal conductivity of 80 W / m · K or more, a three-point bending strength at room temperature of 600 MPa or more, and a fracture toughness of 5M or more.
Pa · m ^1/2 or more, rich in high strength, high toughness and high thermal conductivity. A metal circuit board using the sintered body as an insulating substrate is excellent in impact resistance and cold-heat cycle resistance.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a method of adjusting the particle size distribution of the silicon nitride powder of the present invention, for example, a method of mixing powders having different particle size distributions, or a method of mixing silicon diimide and amorphous nitride of a precursor obtained by an imide decomposition method A method of controlling the heat treatment conditions including the temperature, time, and rate of temperature rise for crystallizing silicon, and a method of sequentially classifying bulk silicon nitride obtained by silicon direct nitridation or silicon oxide reduction nitridation can be applied.

[0028] When a mixture of different powder particle size distribution to adjust the particle size distribution, for example, is _{(d 1 0) (d 50} ) and _{(d 90), 1) 0.2μm} , 0.5μm and 1 .0
μm, 2) 0.75 μm, 2.5 μm and 7.5 μm,
3) Three kinds of silicon nitride powders having a particle size distribution of 0.75 μm, 2.5 μm and 7.5 μm are mixed to have volume fractions of 12%, 70% and 22%, respectively.

In addition, for adjusting the amount of β-type silicon nitride particles,
(D ₅₀ ) in a powder of 2.5-4.5 μm, wherein (d ₅₀ )
Addition and mixing are performed so that the ratio of the particles contained above becomes 1 to 50%. As described above, it is important to determine the shape and oxygen content of the β-type silicon nitride particles for controlling the microstructure and obtaining high strength, high toughness and high thermal conductivity as described above.

The β-type silicon nitride particles used here can be produced, for example, by subjecting silicon nitride powder to heat treatment at 1400 ° C. to 1950 ° C. × 5 to 20 hours in a nitrogen or nitrogen / hydrogen mixed atmosphere. In order to realize a high β fraction and low oxygen content, the heat treatment conditions are set to 1800 ° C. to 1900 ° C.
C. × 5 to 20 hours is more preferable. In order to reduce the oxygen content after the heat treatment to 0.5 wt% or less, it is preferable that the initial oxygen content be less than 2 wt% in terms of SiO ₂ . From the viewpoint of minimizing the amount of impurities such as Fe and Al, it is more preferable to use a high-purity raw material silicon nitride powder by an imide decomposition method.

Further, according to the method for preparing a silicon nitride powder having a particle size distribution of the present invention by a method of crystallizing a precursor of silicon nitride such as silicon diimide and amorphous silicon nitride, the method comprises the steps of: A heat treatment is performed at a temperature of from 1500C to 1500C to generate α-type silicon nitride particles. Subsequently, the amount, shape and content of β-type silicon nitride particles are adjusted by a heat treatment at 1500 ° C. or higher. The particle size of the α-type particles depends on the particle sizes of the silicon nitride precursor and the amorphous silicon nitride. In addition, the particle size is easily affected by the temperature rise time, and the particle size can be small when the temperature rise time is short and large when the temperature rise time is slow. The shape of the β-type silicon nitride particles depends on the heat treatment temperature, and the particle size increases as the temperature increases. Further, the aspect ratio also increases as the heat treatment temperature increases. Therefore, it is important to control the heat treatment conditions so that the particle size distribution is obtained.

In the method of sequentially classifying the bulk silicon nitride obtained by the silicon direct nitridation method or the silicon oxide reduction nitridation method, the amount of impurities such as Fe, Al and Ca in the obtained silicon nitride powder depends on the amount of metallic silicon and Since it largely depends on the purity of the silicon oxide, and the bulk silicon nitride requires a pulverizing / classifying step, these impurity elements from the equipment to be used are often mixed.
In order to improve the thermal conductivity of the sintered body, it is important to suppress the incorporation of these impurities that cause an obstacle.

The substrate made of the silicon nitride sintered body of the present invention is characterized by high strength, high toughness and high thermal conductivity, and various substrates such as a substrate for a power semiconductor or a substrate for a multi-chip module, and a Peltier. It is suitable for electronic component members such as a heat transfer plate for an element or a heat sink for various heating elements.

When a substrate for a semiconductor device is constituted by the silicon nitride substrate of the present invention, the occurrence of cracks in the substrate due to the repetitive cooling / heating cycles accompanying the operation of the semiconductor device is suppressed, and the thermal shock resistance and the cooling / cooling / heat cycling resistance are remarkably improved. In addition, a product excellent in durability and reliability can be provided. Further, even when a semiconductor element for high output and high integration is mounted, deterioration of thermal resistance characteristics is small and excellent heat radiation characteristics are exhibited. In addition, since the silicon nitride substrate of the present invention can also serve as a structural member by reflecting the excellent mechanical properties of the silicon nitride substrate, it has a practical advantage that the circuit board structure can be simplified.

Further, the silicon nitride sintered body of the present invention can be widely used for materials requiring heat resistance characteristics such as thermal shock and thermal fatigue, in addition to the above-mentioned members for electronic parts. Structural members include various heat exchanger parts and heat engine parts, heater tubes used in the field of melting metals such as aluminum and zinc, Stokes, die-cast sleeves, propellers for molten metal agitation, ladles, thermocouple protection tubes, etc. Applicable to Further, by applying the present invention to a sink roll, a support roll, a bearing, a shaft, or the like used in a hot-dip metal plating line for aluminum, zinc, or the like, a member having excellent crack resistance against rapid heating and cooling can be obtained. Also,
In the field of steel or non-ferrous processing, when used for rolling rolls, squeeze rolls, guide rollers, drawing dies, or tool tips, etc., it has good heat dissipation when it comes into contact with the workpiece, so it can withstand heat fatigue and heat resistance. The impact resistance can be improved, thereby reducing abrasion and making thermal stress cracking less likely to occur.

Further, the present invention can be applied to a sputter target member, for example, for forming an electric insulating film used for an MR head, a GMR head or a TMR head of a magnetic recording apparatus, and for abrasion resistance used for a thermal head of a thermal transfer printer. Suitable for forming a film. The film obtained by sputtering has inherently high thermal conductivity, a sufficiently high sputter rate, and a high electric breakdown voltage of the film. Therefore, an MR head, GMR head, or TM
Since the electrical insulating film for the R head has characteristics of high thermal conductivity and high withstand voltage, it is possible to increase the heat generation density of the element and to reduce the thickness of the insulating film. In addition, the wear-resistant coating for a thermal head formed with this sputter target has not only good wear resistance due to the inherent characteristics of silicon nitride but also high thermal conductivity, so that thermal resistance can be reduced. Can be enhanced.

[0037]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 (d ₁₀ ), (d ₅₀ ) and (d ₉₀ )
1) 0.2 μm, 0.5 μm and 1.0 μm, 2) 0.
75 μm, 2.5 μm and 7.5 μm, 3) 0.75 μm
Three types of silicon nitride powders having different particle size distributions of m, 2.5 μm, and 7.5 μm were respectively obtained by a volume fraction of 12%,
The silicon nitride powder was adjusted to 70% and 22%. In addition, to adjust the amount of β-type silicon nitride particles,
The ratio of particles having (d ₅₀ ) of 2.5 μm or more is 30
% And mixed. Here, the β-type silicon nitride particles used were those produced by the above-described production method.

The particle size distribution of the obtained silicon nitride powder was measured using a laser diffraction scattering type particle size distribution analyzer (LA, manufactured by Horiba, Ltd.).
-920) by the wet method. The solvent used was distilled water, the dispersant used was a 2 wt% aqueous solution of sodium methacrylate, and the refractive index of silicon nitride in water was 1.65 real parts.
Since the imaginary part is 0.2, a real part 1.70 and an imaginary part 0.1 which are close to these numerical values are selected from the refractive index selection menu of the device. The oxygen content was measured using a simultaneous nitrogen / oxygen analyzer (TC436, manufactured by LECO).

The ratio (β fraction) of β-type silicon nitride particles present in particles having an average particle diameter (d ₅₀ ) or more was determined by the following method. That is, 500 g of the obtained silicon nitride powder was inserted into a 2 L resin pot, and 1.0 L of ethanol to which 2 wt% of a dispersant (Leoguard GP) was added based on the amount of the powder was added. Using a ball, ball mill mixing was performed for 5 hours to obtain a silicon nitride slurry. The obtained silicon nitride slurry was subjected to wet classification with a centrifugal classifier under predetermined classification conditions such that the classification point was (d ₅₀ ) determined by particle size distribution measurement. The adjustment of the classification point was controlled by the rotation speed of the apparatus. This operation was repeated three times to further increase the accuracy. The obtained silicon nitride classified slurry was dried, and then granulated using a sieve having an opening of 150 μm.
-It was determined from the X-ray diffraction intensity ratio using Kα radiation according to the formula (1). beta fraction _{(%) = {(I β} (101) + I β (210)) / (I β (101) + I β (210) + I α (102) + I α (20 1))} × _{100 ...... (1) I β (} 101): β -type _Si 3 _{N 4} in (101) plane diffraction peak intensity I _{beta (210):} beta-type _Si 3 of _{N 4} (210) plane diffraction peak intensity I _{alpha (102 ):} alpha-type _Si 3 (102 of _{N 4)} plane diffraction peak intensity I _{α (210): (210} of alpha-type _Si 3 _{N 4)} plane diffraction peak intensity

The particle diameter and the aspect ratio of the β-type silicon nitride particles were determined by a scanning electron microscope (FE-SEM S4 manufactured by Hitachi, Ltd.).
500), direct observation magnification x 2000 times, observation visual field 20
500 powders in 0 μm × 500 μm were evaluated, columnar silicon nitride particles having an aspect ratio of 2 or more were randomly selected, the minimum and maximum diameters were measured by an image analyzer, and the average value was determined. Was evaluated. The amount of oxygen in the β-type silicon nitride particles was determined by multiplying the ratio of the β-type particles in all the powders obtained by using the formula (1) and the oxygen content in the entire powders. FIG. 1 shows the particle size distribution evaluation results of the obtained silicon nitride powder, and FIG. 2 shows the observed shape image of the adjusted silicon nitride powder. 10%, 50% and 9 of the powder
The 0% cumulative diameters (d ₁₀ , d ₅₀ and d ₉₀ ) are 0.72 μm, 3.1 μm and 8.6 μm, respectively,
The oxygen content is 0.45 wt%. Further, the proportion of β-type silicon nitride particles contained in (d ₅₀ ) or more is 30%, the particle size is 3.5 μm, the aspect ratio is 8.5, and the oxygen content is 0.2 wt%.

Next, using the silicon nitride powder, 3 wt% of MgO powder having an average particle diameter of 0.2 μm as a sintering aid,
And 1 wt% of Y ₂ O ₃ powder having an average particle diameter of 0.4 μm, and then mixed powder prepared in a resin pot of a ball mill filled with a toluene / butanol solution containing 2 wt% of an amine-based dispersant; A ball made of silicon nitride as a pulverizing medium was charged and wet-mixed for 48 hours. Next, 15 parts by weight of a polyvinyl-based organic binder and 5 parts by weight of a plasticizer (dimethyl phthalate) were added to 100 parts by weight of the mixed powder in the pot, and then wet-mixed for 48 hours to obtain a sheet forming slurry. . After adjusting the amount of the solvent by vacuum degassing so that the viscosity of the molding slurry becomes 100 poise, the thickness is 0.7 mm to
A molded sheet having a size of 1.5 mm was formed. An appearance inspection was performed on the produced molded body sheet to check for cracks. Then, this molded body sheet is 60 mm × 70
mm, and the dimensions, average thickness and weight were measured to calculate the density of the compact. Further, the molded sheet is laminated and pressed at a temperature of 120 ° C. and a press pressure of 100 kgf / cm ² ,
A laminated molded product of 60 mm × 70 mm × 6 t was obtained.

Next, the laminated molded product was placed in air at 400 to
By heating at 600 ° C. for 2 to 5 hours, the organic binder component added in advance was sufficiently degreased (removed). Next, the degreased body was cooled to 18 MPa in a nitrogen atmosphere of 0.9 MPa (9 atm).
Firing was performed at 50 ° C. × 5 to 10 hours, and then cooled to room temperature to obtain a silicon nitride sintered body. Furthermore, 100W / m · K
In order to increase the thermal conductivity as described above, firing was performed at a high temperature of 1900 ° C. × 10 hours and 1950 ° C. × 5 hours, or heat treatment was performed at 1900 ° C. × 20 hours in the same nitrogen atmosphere.

Next, from the obtained silicon nitride sintered body, a test piece of 10 mm in diameter × 3 mm in thickness for measuring thermal conductivity and density and a bending test piece of 3 mm in length × 4 mm in width × 40 mm in length were collected. did. The density was calculated by measuring the size with a micrometer and measuring the weight. The relative density (ratio to the theoretical density) was also determined. The thermal conductivity was calculated by measuring the specific heat and the thermal diffusivity at room temperature by a laser flash method. The three-point bending strength and fracture toughness were measured at room temperature according to JIS R1606 and JIS, respectively.
The measurement was performed according to R1607. The outlines of the above manufacturing conditions and the evaluation results are shown in Samples 1 to 8 of Tables 1 and 2.

Comparative Example 1 The particle diameter (d ₁₀ ) was the same as in Example 1 except that the production conditions described in Table 1 were used.
(D ₅₀ ) and (d ₉₀ ) and those having different silicon nitride powder characteristics in terms of oxygen content, the ratio of β-type silicon nitride particles present in particles having an average particle diameter (d ₅₀ ) or more, the particle size of the particles Silicon nitride powders having different powder characteristics such as diameter, aspect ratio, and oxygen content were prepared. Then, a silicon nitride slurry using the obtained silicon nitride-based powder was adjusted to obtain a molded body sheet, and the presence or absence of cracks and the sheet moldability of the molded body density were evaluated.
For the sample from which a better molded sheet was obtained,
The material properties of the sintered body were also evaluated. The outline of the above manufacturing conditions and the evaluation results are shown in Samples Nos. 11 to 24 of Tables 1 and 2. In addition, No. 11 to 1 in which the sheet formability had a problem
For No. 5, material property evaluation was not performed.

[0045]

[Table 1]

[0046]

[Table 2]

From the sample Nos. 1 to 8 in Tables 1 and 2,
The following findings were obtained. 10% integration frequency by volume ratio, 5
Particle size at 0% and 90% (d₁₀) (D₅₀)and
(D ₉₀) Are 0.5-0.8 μm, 2.5-
Has particle size distribution of 4.5 μm and 7.5 to 10.0 μm
And the oxygen content is 0.01 to 0.5 wt%,
Uniform particle size (d₅₀) Β-type nitride existing in the above particles
The ratio of the i-particles is 1 to 50%, and the particle size of the particles is
0.5-5 μm, aspect ratio 2-10, impurities
Nitride powder containing less than 0.5 wt% oxygen
The silicon nitride sintered body obtained from
Thermal conductivity of 80 W / m · K or more and at room temperature
Flexural toughness is 600MPa or more and fracture toughness is 5M
Pa ・ m^{1 / 2}That is all. On the other hand, nitriding by the prior art
The thermal conductivity of the silicon-based sintered body is about 40 W / m · K.
Was.

On the other hand, Sample N of Comparative Example 1 in Tables 1 and 2
o. The following findings were obtained from 11 to 24. Regarding the compact density in Table 1, "poor compact density" means 1.4 g / cm ^3.
Below this value, the sintered body density after firing was 90% or less in each case.

In No. 11, the (d ₁₀ ) of the silicon nitride particles was less than 0.5 μm, the proportion of fine particles increased, the moldability deteriorated, and cracks occurred in the molded sheet. No.1
In No. 2, (d ₁₀ ) was more than 0.8 μm, which was out of the range of the particle size distribution at which a high packing density was obtained, so that the moldability was deteriorated and the molded article density was poor. In No.13,
The (d ₅₀ ) of the silicon nitride particles was less than 2.5 μm, the proportion of fine particles increased, the moldability deteriorated, and cracks occurred in the molded sheet. In No. 14, (d ₅₀ ) is 4.5
Since it was more than μm and was out of the range of the particle size distribution at which a high packing density was obtained, the moldability was deteriorated and a molded article density defect occurred.

In No. 15, the silicon nitride particles (d₉₀)
Is less than 7.5 μm, and
Baking for a relatively short time with a holding time of 10 hours or less
The thermal conductivity of the sintered body was less than 80 W / m · K. N
In o.16, (d₉₀) Is larger than 10.0 μm,
And the density of the sintered body is 8
9.1%, so thermal conductivity, strength and fracture toughness
Remarkably deteriorated. In No. 17, in silicon nitride particles
Oxygen content of less than 0.01 wt%, sintering aid component
To form a liquid phase by reacting with₂Ingredients are extremely
Due to the decrease, the density of the obtained sintered body is 80.0%
And extremely low, thus thermal conductivity, bending strength and fracture
The toughness deteriorated significantly. In No. 18, silicon nitride particles
Oxygen content is more than 0.5wt% and reacts with auxiliary components
To produce a liquid phase ₂Excessive ingredients
Therefore, the particles of the low thermal conductive phase, which is the second component in the microstructure,
Good density of sintered body is obtained because the ratio of interphase increases.
However, the thermal conductivity was less than 80 W / m · K.

In No. 19, the ratio of β-type silicon nitride particles in (d ₅₀ ) or more was less than 1%, and coarse columnar particles were generated in the microstructure of the sintered body due to abnormal grain growth. The value was as low as 520 MPa. In No. 20, the ratio of β-type silicon nitride particles in (d ₅₀ ) or more was more than 50%, and β acting as a growth nucleus
Since the number of silicon nitride particles was large, grain growth was inhibited during the grain growth process, and a microstructure in which columnar grains were sufficiently developed could not be obtained, the thermal conductivity was less than 80 W / m · K. No.
In No. 21, since the particle size of β-type silicon nitride particles is as small as less than 0.5 μm and does not act as a growth nucleus, a microstructure in which columnar particles are sufficiently developed cannot be obtained. , Respectively, and became 60 W / m · K and 4.5 MPa · m ^1/2 , respectively.

In Nos. 22 and 23, the β-type silicon nitride particles have a particle size of more than 5 μm and an aspect ratio of more than 10, and coarse β-type particles serve as growth nuclei. It becomes sinterable and 3 of columnar particles grown from the core
Residual pores were formed at the points and the density was significantly reduced. Therefore, the thermal conductivity, bending strength, and fracture toughness of the sintered body were all low values. In No. 24, the amount of oxygen in the β-type silicon nitride particles exceeds 0.5 wt%, and the amount of oxygen dissolved in the silicon nitride particles in the microstructure increases,
Thermal conductivity dropped to 70 W / mK.

(Example 2) The thickness 0.8 m obtained in Example 1
m was heated in air at 400 to 600 ° C. for 2 to 5 hours to sufficiently add and degrease (remove) the organic binder component in advance. Next, the degreased body is 0.9MP
A firing was performed at 1850 ° C. × 5 hours in a nitrogen atmosphere of a (9 atm), then a heat treatment was performed at 1900 ° C. × 20 hours in the same nitrogen atmosphere, and then cooled to room temperature to obtain a sintered body. The obtained silicon nitride sintered body sheet was machined to produce a semiconductor device substrate having a length of 50 mm, a width of 50 mm and a thickness of 0.6 mm.

A circuit board shown in FIG. 3 was manufactured using the silicon nitride sintered body. The silicon nitride substrate 32
Flexural strength 750 MPa shown in No. 3 of Table 1 and Table 2,
Fracture toughness of 6.4 MPa · m ^1/2 and thermal conductivity of 10
5 W / m · K.

Referring to FIG. 3, a circuit board 30 is provided with a copper circuit board 31 on the surface of a silicon nitride sintered body 32 having dimensions of 50 mm × 50 mm × 0.6 mm. And a copper plate 33 joined by a brazing material 34. For this circuit board 30, 3
Evaluation of point bending strength and 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 cracks due to tightening cracks in the mounting process of the circuit board 30 and thermal stress in the soldering process is almost not observed, and the semiconductor device using the circuit board It has been proved that the production yield can be greatly improved.
In the heat cycle test, cooling at −40 ° C.
A heating / cooling cycle in which holding at room temperature for 10 minutes and heating at 180 ° C. for 20 minutes are one cycle,
This was repeatedly applied, and the number of cycles until cracks or the like occurred in the substrate portion was measured. As a result, even after the lapse of 1000 cycles, there was no cracking of the silicon nitride sintered body substrate 32 or peeling of the copper circuit board 31 and the copper plate 33,
It was confirmed that it had both excellent durability and reliability. Also, even after 1000 cycles, the withstand voltage characteristics did not decrease.

[0056]

As described above, the silicon nitride powder of the present invention has excellent sheet moldability without causing cracks during sheet molding and lowering of the compact density, and has a relatively short time of 10 hours or less. Also during firing, it is possible to uniformly disperse the columnar particles developed in the microstructure of the sintered body.
Furthermore, the silicon nitride sintered body of the present invention to which the powder is applied has a high thermal conductivity in addition to the inherent high strength / high toughness. The occurrence of cracks in the substrate due to repeated cooling / heating cycles can be suppressed, and the thermal shock resistance and the cooling / heating cycle resistance can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a typical particle size distribution evaluation diagram of a silicon nitride powder of the present invention.

FIG. 2 is a photograph taken by a typical scanning electron microscope of the silicon nitride powder of the present invention.

FIG. 3 is a sectional view of a main part showing an example of a circuit board of the present invention.

[Explanation of symbols]

30: circuit board, 31: copper circuit board, 32: silicon nitride substrate, 33: copper circuit board, 34: brazing material.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G001 BA06 BA09 BA32 BB06 BB09 BB32 BB73 BC13 BC14 BC17 BC22 BC31 BC34 BC42 BC54 BC71 BD01 BD03 BD04 BD11 BD12 BD14 BD16 BD37 BE03 BE22 BE23 BE32

Claims (4)

[Claims] 1. Particle diameters (d ₁₀ ), (d ₅₀ ) and (d ₅₀ ) at an integration frequency of 10%, 50% and 90% in volume ratio
₉₀ ) are 0.5-0.8 μm and 2.5-4.
Having a particle size distribution of 5 μm and 7.5 to 10.0 μm,
A silicon nitride powder having an oxygen content of 0.01 to 0.5% by weight. 2. The silicon nitride powder according to claim 1, wherein the proportion of β-type silicon nitride particles present in the particles having an average particle diameter (d ₅₀ ) or more is 1 to 50%. 3. The particle size of the β-type silicon nitride particles is 0.5 to 0.5.
3. The composition according to claim 1, wherein the content is 5 μm, the aspect ratio is 2 to 10, and the content of oxygen as an impurity is 0.5 wt% or less. 4.
3. The silicon nitride powder according to item 1. 4. The silicon nitride powder according to claim 1, having a thermal conductivity of 80 W / m · K or more, a three-point bending strength at room temperature of 600 MPa or more, and a fracture toughness of 5 MPa · A silicon nitride sintered body characterized by having a m ^1/2 or more.