JP3100892B2 - High thermal conductive silicon nitride sintered body and method for producing the same - Google Patents

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 thermal conductivity and a method for producing the same. In particular, in addition to the inherent high strength characteristics of silicon nitride, it has high thermal conductivity and excellent heat dissipation. The present invention relates to a high thermal conductive silicon nitride sintered body suitable as a semiconductor substrate or various heat sinks, and a method for producing the same.

[0002]

2. Description of the Related Art A ceramic sintered body containing silicon nitride as a main component has excellent heat resistance even in a high temperature environment of 1000 ° C. or more, and has excellent thermal shock resistance due to a low coefficient of thermal expansion. Therefore, application to various high-strength heat-resistant parts such as parts for gas turbines, parts for engines, and mechanical parts for steelmaking has been attempted as a high-temperature structural material replacing conventional heat-resistant superalloys. In addition, because of its excellent corrosion resistance to metals, application of molten metal as a melting-resistant material has been attempted, and because of its excellent wear resistance, it has been put to practical use in sliding members such as bearings and cutting tools. ing.

Conventionally, the sintered composition of a silicon nitride ceramic sintered body has been silicon nitride-yttrium oxide-aluminum oxide, silicon nitride-yttrium oxide-aluminum oxide-aluminum nitride, silicon nitride-yttrium oxide. Aluminum oxide-titanium, magnesium or zirconium oxides are known.

An oxide of a rare earth element such as yttrium oxide (Y ₂ O ₃ ) in the above-mentioned sintering composition has been generally used as a sintering aid in the past. It is added to increase the strength.

[0005] A conventional silicon nitride sintered body is formed by adding the above-mentioned sintering aid as an additive to silicon nitride powder and molding the obtained molded body at a high temperature of about 1600 to 1900 ° C. It is mass-produced by a method of baking in a furnace for a predetermined time and then cooling the furnace.

[0006]

However, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent functional strength such as toughness, it has a problem in terms of heat conduction characteristics. AlN) sintered bodies, beryllium oxide (BeO) sintered bodies, silicon carbide (SiC) sintered bodies, and the like are extremely low, so they are particularly suitable for electronic materials such as semiconductor substrates that require heat dissipation. It has not been put to practical use and has a drawback in that its application range is narrow.

On the other hand, since the aluminum nitride sintered body has characteristics of high thermal conductivity and low coefficient of thermal expansion as compared with other ceramic sintered bodies, high speed, high output, multifunctionality,
Although they have become widespread as semiconductor circuit board materials and package materials, which have been increasing in size, none of them have been sufficiently satisfactory in terms of mechanical strength. Therefore, there is a demand for the development of a ceramic sintered body having high strength and high thermal conductivity.

SUMMARY OF THE INVENTION The present invention has been made in order to address the above-mentioned demands. In addition to the high strength characteristics inherent in a silicon nitride sintered body, the present invention has a particularly high heat conductivity and excellent heat dissipation. An object is to provide a silicon sintered body and a method for manufacturing the same.

[0009]

Means for Solving the Problems To achieve the above object, the present inventor has proposed a method for manufacturing a conventional silicon nitride sintered body.
By changing the types of commonly used silicon nitride powder, the types and amounts of sintering aids and additives, and the sintering conditions, these factors can change the characteristics of the sintered body as the final product. The effect was confirmed by experiments.

As a result, a rare earth element, if necessary, aluminum nitride,
Alumina, Ti, Zr, Hf, V, Nb, Ta, Cr,
A raw material mixture to which at least one selected from the group consisting of oxides, carbides, nitrides, silicides, and borides of Mo and W are added by a predetermined amount is molded and degreased, and the obtained molded body is heated at a predetermined temperature. After carrying out densification sintering by heating and holding for a certain period of time, it was found that when gradually cooled at a predetermined cooling rate, the thermal conductivity greatly improved, and a silicon nitride sintered body having high strength was obtained. .

Further, by using a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements, setting the thickness of the silicon nitride compact to a small value, and sintering the compact.
The formation of a glass phase (amorphous phase) in the grain boundary phase can be effectively prevented, and silicon nitride firing having a high thermal conductivity of 80 W / m · K or more even when only a rare earth element oxide is added to the raw material powder. We obtained the knowledge that a solid body could be obtained.

Conventionally, when the sintered body was cooled with the heating power supply turned off after the sintering operation, the cooling rate was as fast as 400 to 800 ° C. per hour. According to the experiment of the inventor, in particular, the cooling rate was set to 10
By slowly controlling the temperature to 0 ° C. or less, the grain boundary phase of the silicon nitride sintered body structure changes from an amorphous state to a phase containing a crystalline phase, and high strength characteristics and high heat transfer characteristics are simultaneously achieved. Turned out to be.

A part of such a highly thermally conductive silicon nitride sintered body itself has already been applied for a patent by the present inventor, and further filed in Japanese Patent Application Laid-Open Nos. 6-135977 and 7-48174. It has been published. And the silicon nitride sintered body described in these patent applications converts rare earth elements into oxides of 2.0 to 2.0.
It contains 7.5% by weight. However, as a result of further improvement research, the present inventor has found that when the content of the rare earth element exceeds 7.5% by weight in terms of oxide, the sintered body has higher thermal conductivity, and The inventors have found that they have good binding properties and completed the present invention. In particular, when the rare earth element is a lanthanoid element, the effect is remarkable. Incidentally, even when the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 60 to 70%, the sintered body can achieve a high thermal conductivity of 110 to 120 W / m · K or more.

The present invention has been completed based on the above findings. That is, the high thermal conductivity silicon nitride sintered body according to the present invention has a rare earth element converted to oxide of 7.5% by weight.
Over 17.5% by weight, Li, Na, K, Fe, Ca, Mg, Sr, Ba, M as impurity cation elements
n and B in total of 0.3% by weight or less, comprising silicon nitride crystal and grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase is 50% or more; It is characterized in that the point bending strength is 650 MPa or more at room temperature, the thermal conductivity is 80 W / m · K or more, and the porosity is 2.5% or less in volume ratio.

In another embodiment, the rare earth element is contained in an amount of more than 7.5% by weight and not more than 17.5% by weight in terms of oxide, and is composed of silicon nitride crystals and a grain boundary phase and contained in the grain boundary phase. The ratio of the crystalline compound phase to the whole grain boundary phase is 50% or more, and the three-point bending strength is 650 M at room temperature.
Pa or more, thermal conductivity is 80 W / m · K or more, and porosity is 2.5% or less in terms of volume ratio.

Further, as the rare earth element, a lanthanoid series element is particularly preferred for improving the thermal conductivity.

Further, aluminum nitride or alumina may be added in an amount of 1.0% by weight or less. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used in combination.

Further, the high thermal conductive silicon nitride sintered body of the present invention comprises Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,
It is preferable that at least one selected from the group consisting of W is contained in an amount of 0.1 to 3.0% by weight in terms of oxide. This Ti, Zr, Hf, V, Nb, Ta, Cr, M
At least one selected from the group consisting of o and W can be contained as an oxide, carbide, nitride, silicide, or boride by adding to silicon nitride powder.

Further, according to the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention, oxygen is not more than 1.7% by weight, and Li, Na, K, Fe, Ca, M as impurity cation elements are contained.
g, Sr, Ba, Mn and B in total of 0.3% by weight or less;
In silicon nitride powder containing at least 90% by weight of α-phase silicon nitride and having an average particle diameter of 1.0 μm or less, a rare earth element is converted into an oxide and exceeds 7.5% by weight to 17.5% by weight or less. And a raw material mixture to which at least one of alumina and aluminum nitride is added in an amount of 1.0% by weight or less as needed to prepare a molded body. Atmospheric pressure sintering, the cooling rate of the sintered body from the sintering temperature to the temperature at which the liquid phase formed during sintering by the rare earth element solidifies is 1 hour
It is characterized by gradually cooling to a temperature of not more than 00 ° C.

In the above method, at least one of alumina and aluminum nitride may be further added to the silicon nitride powder in an amount of 1.0% by weight or less.

Further, Ti, Z are added to the silicon nitride powder.
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W;
At least one selected from the group consisting of carbides, nitrides, silicides, and borides may be added in an amount of 0.1 to 3.0% by weight.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 80 W / m · K or more, A silicon nitride sintered body having a point bending strength of 650 MPa or more at room temperature and excellent in both mechanical properties and heat conduction properties is obtained.

The silicon nitride powder used in the method of the present invention and serving as a main component of the sintered body has an oxygen content of 1.7% by weight or less in consideration of sinterability, strength and thermal conductivity. Preferably 0.5-1.5% by weight, Li, Na,
Α-phase silicon nitride in which the total content of impurity cation elements such as K, Fe, Mg, Ca, Sr, Ba, Mn, and B is suppressed to 0.3% by weight or less, preferably 0.2% by weight or less. Containing 90% by weight or more, preferably 93% by weight or more, and having an average particle size of 1.0 μm or less, preferably 0.4 to
A fine silicon nitride powder of about 0.8 μm can be used.

By using a fine raw material powder having an average particle size of 1.0 μm or less, a dense sintered body having a porosity of 2.5% or less can be formed even with a small amount of a sintering aid. Is also possible, and the possibility that the sintering aid impairs the heat transfer properties is reduced.

Also, Li, Na, K, Fe, Ca, Mg,
Since the impurity cation elements of Sr, Ba, Mn, and B are also substances that inhibit the thermal conductivity, the content of the impurity cation element must be at least 80 W / m · K to ensure the thermal conductivity of 80 W / m · K or more. This can be achieved by making the total 0.3% by weight or less. Particularly for the same reason, the content of the impurity cation element is set to 0.2% by weight or less in total.
More preferred. Here, the silicon nitride powder used for obtaining a normal silicon nitride sintered body includes, in particular, Fe, C
a, Mg are contained in a relatively large amount, so that Fe, C
The total amount of a and Mg is a measure of the total content of the impurity cation element.

Further, a high-density sintered body can be produced by using a silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride which is superior in sinterability as compared with β-phase type. can do.

Rare earth elements added as a sintering aid to the silicon nitride raw material powder include Ho, Er, Yb, Y,
Oxides such as La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or substances that become these oxides by sintering operation alone or in combination of two or more oxides are included. Good, but especially holmium oxide (Ho ₂ O
₃ ), erbium oxide (Er ₂ O ₃ ) is preferred. In particular, Ho, which is a lanthanoid element as a rare earth element,
By using Er and Yb, sinterability is improved, and a sufficiently dense sintered body can be obtained even in a low temperature range of about 1850 ° C. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids react with the silicon nitride raw material powder to generate a liquid phase and function as sintering accelerators.

The amount of the sintering aid added is in the range of more than 7.5% by weight and not more than 17.5% by weight based on the raw material powder in terms of oxide. When the addition amount is 7.5% by weight or less, the density of the sintered body or the high thermal conductivity is insufficient, and particularly when the rare earth element is an element having a large atomic weight such as a lanthanoid element, A sintered body having relatively low strength and relatively low thermal conductivity is formed. On the other hand, the addition amount is 17.
If the amount exceeds 5% by weight, an excessive amount of the grain boundary phase is generated, and the thermal conductivity and strength begin to decrease. Particularly, for the same reason, it is desirable to set the content to 8 to 15% by weight.

In the present invention, Ti, Zr, Hf, V, Nb, Ta, C
The oxides, carbides, nitrides, silicides, and borides of r, Mo, and W promote the function of the sintering accelerator for the rare earth element, and also have the function of strengthening the dispersion of Si _{3 in the} crystal structure.
It is intended to improve the mechanical strength of the N ₄ sintered body, and particularly, a compound of Hf and Ti is preferable. When the added amount of these compounds is less than 0.1% by weight, the effect of the addition is insufficient, while when the added amount exceeds 3.0% by weight, the thermal conductivity and mechanical strength and electric breakdown are caused. Since the strength is reduced, the amount of addition is in the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The compounds such as Ti, Zr, and Hf also function as a light-shielding agent that imparts opacity by coloring the silicon nitride sintered body to a black color. Therefore, in particular, when manufacturing a circuit board on which an integrated circuit or the like which easily malfunctions due to light is mounted, it is desirable to appropriately add the compound such as Ti and the like to obtain a silicon nitride substrate excellent in light shielding properties.

Furthermore, in the present invention, alumina (Al ₂ O ₃ ) as another optional additive component plays a role of promoting the function of the rare earth element sintering accelerator, and particularly, pressure sintering. This has a remarkable effect when knotting is performed. When the addition amount of Al ₂ O ₃ is less than 0.1% by weight, sintering at a higher temperature is required. On the other hand, when the addition amount exceeds 1.0% by weight, an excessive grain boundary is used. Phase or begin to dissolve in silicon nitride,
Since the heat conduction is reduced, the addition amount is 1% by weight or less, preferably in the range of 0.1 to 0.75% by weight. In particular, in order to ensure good performance in both strength and thermal conductivity, it is desirable that the amount of addition be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, the total amount thereof is desirably 1.0% by weight or less.

Aluminum nitride (AlN) as another additive component serves to suppress the evaporation of silicon nitride during the sintering process and to further promote the function of the rare earth element as a sintering accelerator. It is.

When the amount of AlN added is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required, while
If the amount exceeds 0% by weight, an excessive amount of the grain boundary phase is generated, or the solid solution starts to be dissolved in silicon nitride to cause a decrease in thermal conductivity. % By weight. In particular, in order to ensure good performance in sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferable.

Since the porosity of the sintered body greatly affects the thermal conductivity and the strength, the sintered body is manufactured to be 2.5% or less. If the porosity exceeds 2.5%, it hinders heat conduction,
As the thermal conductivity of the sintered body decreases, the strength of the sintered body decreases.

The silicon nitride sintered body is systematically composed of silicon nitride crystals and a grain boundary phase. The proportion of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the sintered body according to the present invention, it is necessary that the crystal phase accounts for 50% or more of the grain boundary phase, more preferably 60% or more. If the crystal phase is less than 50%, it becomes difficult to obtain a sintered body having high thermal conductivity, excellent heat dissipation characteristics, and excellent high-temperature strength.

Further, as described above, the porosity of the silicon nitride sintered body is set to 2.5% or less, and the crystal phase accounts for 50% or more of the grain boundary phase formed in the silicon nitride crystal structure. The silicon nitride compact was heated to a temperature of 1800 to 210
It is important to perform pressure sintering at 0 ° C. for about 2 to 10 hours and gradually cool the sintered body immediately after completion of the sintering operation at a cooling rate of 100 ° C. or less per hour.

When the sintering temperature is lower than 1800 ° C., the density of the sintered body is insufficient and the porosity is 2.5 vol%.
As a result, both the mechanical strength and the thermal conductivity decrease. On the other hand, when the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to be vaporized and decomposed. In particular, when normal pressure sintering is performed instead of pressure sintering, decomposition and evaporation of silicon nitride starts at about 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when a rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. Is that the grain boundary phase of the sintered body structure becomes non-crystalline (glass phase), the ratio of the liquid phase generated in the sintered body as a crystalline phase to the grain boundary phase is less than 20%, and the strength and thermal conductivity are reduced. Both will fall.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to a temperature at which a liquid phase produced by the reaction of the sintering aid solidifies. Is enough. Incidentally, the liquidus freezing point when using the sintering aid as described above is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body at least from the sintering temperature to the above-mentioned liquid phase solidification temperature is set to 10
0 ° C. or lower, preferably 50 ° C. or lower, more preferably 2 ° C.
By controlling the temperature to 5 ° C. or less, 50% or more of the grain boundary phase becomes a crystalline phase, and a sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The silicon nitride sintered body according to the present invention is manufactured through, for example, the following process. That is, a predetermined amount of a sintering aid, a necessary additive such as an organic binder, and optionally Al ₂ O are added to the fine silicon nitride powder having the predetermined fine particle size and a small impurity content. ₃ or an AlN or Ti compound is added to adjust the raw material mixture, and then the obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a forming method of the raw material mixture, a general-purpose mold pressing method, a sheet forming method such as a doctor blade method, or the like can be applied. Subsequent to the above molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours so that the organic binder component added in advance is sufficiently cooled. And degrease. Next, the degreased compact is placed in an atmosphere of an inert gas such as nitrogen gas, hydrogen gas or argon gas in an atmosphere of 1800-2100.
Atmospheric pressure sintering is performed at a temperature of ° C for a predetermined time.

The silicon nitride sintered body manufactured by the above method has a porosity of 2.5% or less and 80 W / m · K (25
° C) or more, and has excellent three-point bending strength of 650 MPa or more at room temperature.

It should be noted that the silicon nitride sintered body of which the thermal conductivity as a whole is 80 W / m · K or more by adding high thermal conductivity SiC or the like to low thermal conductivity silicon nitride is the present invention. Not included in range. However, the thermal conductivity is 80W
/ M · K or higher silicon nitride sintered body with high thermal conductivity S
It goes without saying that a silicon nitride-based sintered body in which iC or the like is compounded is included in the scope of the present invention.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples.

Examples 1-2 and Reference Example 1 1.3% by weight of oxygen, Li, as impurity cation element
Na, K, Fe, Ca, Mg, Sr, Ba, Mn, and B are contained in a total of 0.15% by weight, and α-phase silicon nitride is 97%.
Is added to a raw material powder of silicon nitride having an average particle size of 0.55 μm and Ho ₂ O _{3 having} an average particle size of 0.9 μm as a sintering aid.
(Holmium oxide) powder (12.5% by weight) was added, and the mixture was wet-mixed in ethyl alcohol using silicon nitride balls for 72 hours and then dried to prepare a raw material powder mixture.
Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed. The mixture is press-formed at a forming pressure of 1000 kg / cm ² to obtain a formed body having a length of 50 mm × a width of 50 mm × a thickness of 5 mm. Made many. Next, the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, and then this degreased body was subjected to 1950 at 9 atm in a nitrogen gas atmosphere.
C. for 6 hours, and after performing the densification sintering, control the amount of electricity to the heating device attached to the sintering furnace to control the sintered body until the temperature in the sintering furnace drops to 1500 ° C. At a cooling rate of 100 ° C./hr (Reference Example 1) and 50 ° C., respectively.
/ Hr (Example 1) and 25 ° C./hr (Example 2), and the sintered body was gradually cooled to prepare silicon nitride ceramic sintered bodies according to Examples and Reference Examples, respectively. .

Comparative Example 1 On the other hand, immediately after completion of the densification sintering, the power of the heating device was turned off and the sintered body was cooled at a conventional cooling rate by furnace cooling (about 500 ° C./hr). Sintering was performed under the same conditions as in Example 1 to prepare a silicon nitride sintered body according to Comparative Example 1.

Comparative Example 2 Silicon nitride containing 1.5% by weight of oxygen and a total of 0.6% by weight of the impurity cation element and containing 93% of α-phase type silicon nitride and having an average particle diameter of 0.60 μm Processing was performed under the same conditions as in Reference Example 1 except that the raw material powder was used, to prepare a silicon nitride ceramics sintered body according to Comparative Example 2.

COMPARATIVE EXAMPLE 3 Silicon nitride containing 1.7% by weight of oxygen and 0.7% by weight of the impurity cation element in total and containing 91% of α-phase type silicon nitride and having an average particle size of 1.2 μm Except for using the raw material powder, treatment was performed under the same conditions as in Reference Example 1 to prepare a silicon nitride sintered body according to Comparative Example 3.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature of the silicon nitride sintered bodies according to Examples 1 to 2, Reference Example 1 and Comparative Examples 1 to 3 thus obtained. Was measured. Furthermore, the ratio (area ratio) of the crystal phase to the grain boundary phase of each sintered body was measured by X-ray diffraction, and the results shown in Table 1 below were obtained.

[0050]

[Table 1]

As is clear from the results shown in Table 1, in the silicon nitride ceramic sintered bodies according to the examples and the reference examples, compared with the comparative example 1, the cooling rate of the sintered body immediately after the completion of the densification sintering Is set lower than before,
The crystal phase is included in the grain boundary phase, and the higher the proportion of the crystal phase,
A high-strength sintered body having high heat conductivity and high heat dissipation was obtained.

On the other hand, when the cooling rate of the sintered body was set to a high value as in Comparative Example 1 and the cooling was performed rapidly, the proportion of the crystal phase in the grain boundary phase was as small as 10% or less, and the thermal conductivity was lowered. Further, when a silicon nitride powder containing as much as 0.6% by weight of the total amount of the impurity cation elements as in Comparative Example 2 was used, the cooling rate of the sintered body was the same as in Example 1. Most of the grain boundary phase was formed in an amorphous state, and the thermal conductivity was lowered.

Further, as in Comparative Example 3, the average particle size was 1.2.
When silicon nitride powder as coarse as μm was used, densification was insufficient in sintering, and both strength and thermal conductivity were reduced.

Examples 3 to 7, Reference Examples 2 to 10 and Comparison
Examples 4 to 7 The silicon nitride powder and the Ho ₂ O ₃ powder used in Reference Example 1 as Examples 3 to 7 and Reference Examples 2 to 10 were blended so as to have the composition ratios shown in Table 2, and a raw material mixture was prepared. Was prepared respectively.

Next, each raw material mixture obtained was molded and degreased under the same conditions as in Reference Example 1, and then sintered under the conditions shown in Table 2 to give Examples 3 to 7 and Reference Examples 2 to 10, respectively. Such a silicon nitride ceramic sintered body was manufactured.

Meanwhile those added to excess of _Ho 2 _{O 3} as shown in Table 2 as Comparative Examples 4 to 6 (Comparative Example 4), Ho ₂
O ₃ added in an excessively small amount (Comparative Example 5), Ho ₂ O ₃
Of the raw materials (Comparative Example 6) in which excessive amounts were added, and sintering operations were performed from the raw material mixture under the same conditions as in Reference Example 1 to produce sintered bodies according to Comparative Examples 4 to 6, respectively. did.

As a comparative example 7, the sintering temperature was 1750
A sintering operation was performed from the raw material mixture under the same conditions as in Reference Example 1 except that the temperature was changed to ° C., thereby producing a sintered body according to Comparative Example 7.

Examples 3 to 7 thus produced and Reference Example 2
Porosity, thermal conductivity (25 ° C.), average value of three-point bending strength at room temperature, and X-rays for the silicon nitride ceramics sintered bodies according to Comparative Examples 4 to 7 and Comparative Examples 4 to 7 under the same conditions as in Reference Example 1. The ratio of the crystal phase to the grain boundary phase was measured by a diffraction method, and the results shown in Table 2 below were obtained.

[0059]

[Table 2]

As is clear from the results shown in Table 2, Ho
_The sintered bodies according to Examples and Reference Examples which contain a predetermined amount of ₂ O _{3 and} have a predetermined cooling rate after sintering have a high thermal conductivity and a high strength value. On the other hand, as shown in Comparative Examples 4 to 6, when the Ho ₂ O ₃ component is excessively small or excessively added, the densification is insufficient or the crystal in which the grain boundary phase is excessive or occupies the grain boundary phase. It was confirmed that the bending strength was lowered or the thermal conductivity was inferior because the proportion of the phase was too low. The sintered body according to Comparative Example 7 in which the sintering temperature was set to 1750 ° C. was insufficiently densified, and both the strength and the thermal conductivity were reduced.

Examples 8 to 14 and Reference Examples 11 to 34 H used in Examples and Reference Example 1 as Reference Examples
According to Examples 8 to 14 and Reference Examples 11 to 34 under the same conditions as in Reference Example 1 except that the rare earth oxides shown in Table 3 were blended so as to have the composition ratios shown in Table 3 instead of the o ₂ O ₃ powder. A silicon nitride ceramic sintered body was manufactured.

The porosity, thermal conductivity (25 ° C.),
The average value of the three-point bending strength at room temperature and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured, and the results shown in Table 3 below were obtained.

[0063]

[Table 3]

As is clear from the results shown in Table 3, Ho ₂
Sintered bodies replaced with O ₃ according to Examples and Reference Examples using other rare earth elements was confirmed to have a similar performance to that of Ho ₂ O ₃ added.

Example 15, Reference Examples 35 to 45 and Comparison
Examples 8 to 11 The silicon nitride powder used in Reference Example 1 and Ho ₂ O ₃
The powder and the Al ₂ O ₃ powder were blended so as to have the composition ratios shown in Table 4 to prepare raw material mixtures.

Next, each raw material mixture obtained was subjected to molding and degreasing under the same conditions as in Reference Example 1, and then subjected to sintering treatment under the conditions shown in Table 4 to obtain nitriding products according to Example 15 and Reference Examples 35 to 45, respectively. A silicon ceramic sintered body was manufactured.

On the other hand, as shown in Table 4, Comparative Examples 8 to 11 each containing Ho ₂ O ₃ in an excessive amount (Comparative Example 8)
_{One in} which a small amount of ₂ O ₃ was added (Comparative Example 9), Al ₂ O
₃ (Comparative Example 10) and a raw material mixture of Ho ₂ O ₃ (Comparative Example 11) were added, and the sintering operation was performed from the raw material mixture under the same conditions as in Reference Example 1. Was performed to produce sintered bodies according to Comparative Examples 8 to 11, respectively.

The porosity, thermal conductivity (25 ° C.), and three-point bending at room temperature of the silicon nitride ceramics sintered bodies according to Examples, Reference Examples, and Comparative Examples manufactured in this manner were the same as in Example 1. The average value of the strength and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured, and the results shown in Table 4 below were obtained.

[0069]

[Table 4]

As is clear from the results shown in Table 4, Ho
_The sintered bodies according to the examples and the reference examples in which ₂ O ₃ and Al ₂ O ₃ are contained in predetermined amounts and the cooling rate after sintering is set to predetermined,
All have a high thermal conductivity and a high strength value. On the other hand, as shown in Comparative Examples 8 to 11, when at least one component of Ho ₂ O ₃ and Al ₂ O ₃ is excessively small or excessively added, the densification is insufficient or the grain boundary is insufficient. Because the phase is excessive or the proportion of the crystal phase in the grain boundary phase is too low,
It was confirmed that the bending strength was lowered or the thermal conductivity was inferior.

Reference Examples 46 to 69 H used in Reference Example 39 as Reference Examples 46 to 69
Reference Example 39 except that the rare earth oxides shown in Table 5 were blended so as to have the composition ratios shown in Table 5 instead of the o ₂ O ₃ powder.
The same conditions were used to produce silicon nitride ceramics sintered bodies according to Reference Examples.

The porosity and thermal conductivity (25%) of the thus obtained sintered bodies according to Reference Examples were obtained under the same conditions as in Reference Example 39.
C), the average value of the three-point bending strength at room temperature, and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured, and the results shown in Table 5 below were obtained.

[0073]

[Table 5]

As is clear from the results shown in Table 5, Ho ₂
Sintered bodies replaced with O ₃ according to the reference example using the other rare earth elements was confirmed to have a similar performance to that of Ho ₂ O ₃ added.

Next, aluminum nitride (Al
The case where N) is used will be specifically described with reference to the following examples.

Example 16 and Reference Examples 70 to 71 An average particle diameter of 1.3% by weight of oxygen, 0.15% by weight of the above-mentioned impurity cation element in total, and 97% of α-phase silicon nitride. .55 μm silicon nitride raw material powder
12.5% by weight of Ho ₂ O ₃ (holmium oxide) powder having an average particle diameter of 0.9 μm as a sintering aid, and an average particle diameter of 0.8 μm
0.25% by weight of AlN (aluminum nitride) powder was added, wet-mixed in ethyl alcohol using a silicon nitride ball for 72 hours, and then dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed.
Press molding with a molding pressure of cm ² , length 50 mm × width 5
A large number of compacts having a size of 0 mm and a thickness of 5 mm were produced. Next, after the obtained compact was degreased in an atmosphere gas at 700 ° C. for 2 hours, the degreased body was held at 1900 ° C. for 6 hours at 9 atm in a nitrogen gas atmosphere, and after densifying and sintering, The cooling rate of the sintered body was 100 ° C./hr until the temperature in the sintering furnace dropped to 1500 ° C. by controlling the amount of electricity to the heating device attached to the sintering furnace (Reference Example 7).
0), 50 ° C./hr (Reference Example 71), and 25 ° C./hr (Example 16), and the sintered body was gradually cooled, and sintered silicon nitride ceramics according to Examples and Reference Examples, respectively. A body was prepared.

Comparative Example 12 On the other hand, immediately after completion of the densification sintering, the power of the heating device was turned off and the sintered body was cooled at the conventional cooling rate by furnace cooling (about 500 ° C./hr). Sintering was performed under the same conditions as in Example 1 to prepare a silicon nitride sintered body according to Comparative Example 12.

Comparative Example 13 Silicon nitride containing 1.5% by weight of oxygen and a total of 0.6% by weight of the impurity cation element and containing 93% of α-phase silicon nitride and having an average particle diameter of 0.60 μm A treatment was performed under the same conditions as in Reference Example 70 except that the raw material powder was used, to prepare a silicon nitride ceramics sintered body according to Comparative Example 13.

Comparative Example 14 Silicon nitride containing 1.7% by weight of oxygen and 0.7% by weight of the above-mentioned impurity cation element in total and containing 91% of α-phase type silicon nitride and having an average particle diameter of 1.2 μm Processing was performed under the same conditions as in Reference Example 70 except that the raw material powder was used, to thereby prepare a silicon nitride sintered body according to Comparative Example 14.

The porosity, the thermal conductivity (25 ° C.), and the average value of the three-point bending strength at room temperature of the silicon nitride sintered bodies according to the respective Examples, Reference Examples and Comparative Examples thus obtained were measured. Furthermore, the ratio (area ratio) of the crystal phase to the grain boundary phase of each sintered body was measured by X-ray diffraction, and the results shown in Table 6 below were obtained.

[0081]

[Table 6]

As is clear from the results shown in Table 6, in the silicon nitride ceramics sintered bodies according to Example 16 and Reference Examples 70 to 71, compared with Comparative Example 12, the sintering immediately after the completion of densification sintering was performed. Since the cooling rate of the body was set lower than before, the crystal phase was included in the grain boundary phase, and the higher the proportion of the crystal phase, the higher the heat-radiating high-strength sintered body having high thermal conductivity was obtained. .

On the other hand, when the cooling rate of the sintered body was set to a high value as in Comparative Example 12, and the crystal was rapidly cooled, the proportion of the crystal phase in the grain boundary phase was small and the thermal conductivity was lowered. Further, when a silicon nitride powder containing as much as 0.6% by weight of the impurity cation element as in Comparative Example 13 was used, even if the cooling rate of the sintered body was the same as that of Reference Example 70, Most of them were formed in an amorphous state, and the thermal conductivity was lowered.

Further, as in Comparative Example 14, the average particle size was 1.
When silicon nitride powder having a coarse particle diameter of 2 μm was used, densification was insufficient in sintering, and both strength and thermal conductivity were reduced.

Reference Examples 72 to 86 and Comparative Examples 15 to 21 Silicon nitride powder, Ho ₂ O ₃ powder, AlN powder and Al ₂ O having an average particle diameter of 0.5 μm used in Reference Example 70 as Reference Examples 72 to 86. _{The three} powders were blended so as to have the composition ratios shown in Table 7 to prepare raw material mixtures.

Next, each of the obtained raw material mixtures was subjected to molding and degreasing under the same conditions as in Reference Example 70, and then sintered under the conditions shown in Table 7 to obtain the silicon nitride ceramics according to Reference Examples 72 to 86, respectively. A compact was produced.

On the other hand, as shown in Table 7, Comparative Examples 15 to 21 in which Ho ₂ O ₃ was added in an excessive amount (Comparative Example 15)
A sample in which Ho ₂ O ₃ was added in an excessively small amount (Comparative Example 16), A
One with excessive addition of 1N (Comparative Example 17), Ho ₂ O ₃
(Comparative Example 18), AlN and Al ₂
The total amount added with O ₃ was set to an excessive amount (Comparative Example 19)
And 20), a raw material mixture in which the total addition amount was set to be too small (Comparative Example 21) was prepared, and the sintering operation was performed from the raw material mixture under the same conditions as in Reference Example 70. 21 was produced.

The porosity, the thermal conductivity (25 ° C.), and the porosity of the silicon nitride ceramics sintered bodies according to Examples, Reference Examples, and Comparative Examples manufactured in the same manner as in Reference Example 70 were obtained.
The average value of the three-point bending strength at room temperature and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured, and the results shown in Table 7 below were obtained.

[0089]

[Table 7]

As is clear from the results shown in Table 7, Ho
_{2 O 3,} optionally AlN, the Al ₂ O ₃ contains a predetermined amount, the sintered body according to the reference example 72 to 86 set the cooling rate after sintering a predetermined low speed are both high thermal conductivity It has a high strength value in percent. On the other hand, as shown in Comparative Examples 15 to 21, when at least one component of Ho ₂ O ₃ and AlN or the total amount of AlN and Al ₂ O ₃ components is too small or too large, densification is not achieved. It was confirmed that the bending strength was lowered or the thermal conductivity was inferior due to insufficiency, an excessive amount of the grain boundary phase or an excessively low proportion of the crystal phase in the grain boundary phase.

Reference Examples 87 to 101 The same conditions as in Reference Example 70, except that the rare earth oxides shown in Table 8 were blended so as to have the composition ratios shown in Table 8 instead of the Ho ₂ O ₃ powder used in Reference Example 70. To produce silicon nitride ceramics sintered bodies according to Reference Examples 87 to 101.

The porosity and thermal conductivity (25%) of the thus obtained sintered bodies according to Reference Examples were obtained under the same conditions as Reference Example 70.
C), the average value of the three-point bending strength at room temperature, and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured, and the results shown in Table 8 below were obtained.

[0093]

[Table 8]

As is clear from the results shown in Table 8, Ho ₂
Reference Example 87 Using Another Rare Earth Element Instead of O ₃
It was confirmed that the sintered bodies according to Nos. 101 to 101 had the same performance as that of the sintered body to which Ho ₂ O _{3 was} added.

Next, a Si ₃ N ₄ sintered body to which an Hf compound or the like is added will be specifically described with reference to the following examples.

Examples 17 to 18 and Reference Example 102 An average particle diameter of 1.3% by weight of oxygen, 0.15% by weight of the impurity cation element in total, and 97% of α-phase silicon nitride. .55 μm silicon nitride raw material powder
As a sintering aid, 12.5% by weight of Ho ₂ O ₃ (holmium oxide) powder having an average particle size of 0.9 μm and H having an average particle size of 1 μm
1.5% by weight of fO ₂ (hafnium oxide) powder is added,
Using silicon nitride balls in ethyl alcohol
After wet-mixing for hours, the mixture was dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture and uniformly mixed, and then 1000 kg / cm ²
Press molding at a molding pressure of 50 mm long x 50 mm wide
× Many molded bodies having a thickness of 5 mm were manufactured. Next, after the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, the degreased body was heated in a nitrogen gas atmosphere at 9 atm for 190 hours.
After maintaining at 0 ° C. for 6 hours and performing densification sintering, sintering is performed until the temperature in the sintering furnace falls to 1500 ° C. by controlling the amount of electricity to a heating device attached to the sintering furnace. The cooling rate of the body is 100 ° C./hr (Reference Example 102),
50 ° C./hr (Example 17), 25 ° C./hr (Example 1)
The sintered body was gradually cooled by adjusting to 8) to prepare silicon nitride ceramics sintered bodies according to the example and the reference example, respectively.

Comparative Example 22 On the other hand, immediately after the completion of the densification sintering, the heating apparatus was turned off and the sintered body was cooled at the conventional cooling rate of furnace cooling (about 500 ° C./hr). By performing sintering treatment under the same conditions as in the above, a silicon nitride sintered body according to Comparative Example 22 was prepared.

Comparative Example 23 Silicon nitride containing 1.5% by weight of oxygen and 0.6% by weight of the impurity cation element in total and containing 93% of α-phase type silicon nitride and having an average particle diameter of 0.60 μm A treatment was performed under the same conditions as in Reference Example 102 except that the raw material powder was used, to prepare a silicon nitride ceramics sintered body according to Comparative Example 23.

Comparative Example 24 Silicon nitride having an average particle diameter of 1.2 μm containing 1.7% by weight of oxygen and 0.7% by weight of the impurity cation element in total and containing 91% of α-phase type silicon nitride A treatment was performed under the same conditions as in Reference Example 102 except that the raw material powder was used, to prepare a silicon nitride sintered body according to Comparative Example 24.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature of the silicon nitride sintered bodies according to the respective Examples, Reference Examples and Comparative Examples thus obtained were measured. Further, the ratio (area ratio) of the crystal phase to the grain boundary phase of each sintered body was measured by an X-ray diffraction method, and the results shown in Table 9 below were obtained.

[0101]

[Table 9]

As is clear from the results shown in Table 9, in the silicon nitride ceramic sintered bodies according to the examples and the reference examples, the cooling rate of the sintered bodies immediately after the completion of the densification sintering was lower than that in the comparative example 22. Is set lower than in the prior art, so that a high-strength sintered body having a high heat conductivity and a high thermal conductivity was obtained as the grain boundary phase contained a crystal phase and the proportion occupied by the crystal phase was higher.

On the other hand, when the cooling rate of the sintered body was set to a high value as in Comparative Example 22, and the crystal was rapidly cooled, the proportion of the crystal phase in the grain boundary phase was small and the thermal conductivity was lowered. When a silicon nitride powder containing a large amount of the impurity cation element as much as 0.6% by weight as in Comparative Example 23 was used, even if the cooling rate of the sintered body was the same as that of Reference Example 102, Most of the boundary phase was formed in an amorphous state, and the thermal conductivity decreased.

Further, as in Comparative Example 24, the average particle size was 1.
When silicon nitride powder having a coarse particle diameter of 2 μm was used, densification was insufficient in sintering, and both strength and thermal conductivity were reduced.

Examples 19 to 39 and Reference Examples 103 to 138
And Comparative Examples 25 to 31 The silicon nitride powder used in Reference Example 102 and Ho
₂ O ₃ powder, various rare earth oxide powders and various metal compound powders shown in Tables 10 to 12 in addition to the HfO ₂ powder,
Further, the Al ₂ O ₃ powder and the AlN powder are shown in Tables 10 to 1
The raw material mixtures were respectively prepared so as to have the composition ratios shown in FIG.

Next, each of the obtained raw material mixtures was used in Reference Example 102.
After performing the molding and degreasing treatment under the same conditions as described above, sintering treatment was performed under the conditions shown in Tables 10 to 12 to produce silicon nitride ceramics sintered bodies according to Examples and Reference Examples, respectively.

On the other hand, as shown in Table 12, Comparative Examples 25 to 31 in which HfO ₂ was added in an excessively small amount (Comparative Example 2)
5) A sample to which Ho ₂ O ₃ was added in an excessively small amount (Comparative Example 2)
6), one containing HfO ₂ in an excessive amount (Comparative Example 27),
Excessive addition of Ho ₂ O ₃ (Comparative Example 28), Ti
A raw material mixture was prepared by adding an excessive amount of O ₂ (Comparative Example 29), by adding an excessive amount of AlN (Comparative Example 30), and by adding an excessive amount of alumina (Comparative Example 31). The sintering operation was performed from the raw material mixture under the same conditions as in Example 118 to produce sintered bodies according to Comparative Examples 25 to 31, respectively.

The porosity and thermal conductivity (25%) of the silicon nitride ceramics sintered bodies according to Examples, Reference Examples and Comparative Examples manufactured in this manner under the same conditions as in Reference Example 102.
° C), the average value of the three-point bending strength at room temperature, and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured.
The results shown in Table 12 were obtained.

[0109]

[Table 10]

[0110]

[Table 11]

[0111]

[Table 12]

As is clear from the results shown in Tables 10 to 12, various metal compounds such as Ho ₂ O ₃ , rare earth oxides and HfO ₂ , and if necessary, Al ₂ O ₃ and AlN are contained in predetermined amounts. Each of the sintered bodies according to the examples and the reference examples in which the cooling rate after sintering is set to a predetermined value has a high thermal conductivity and a high strength value. On the other hand, as shown in Comparative Examples _{25~31, Ho 2 O 3, HfO} 2, TiO 2, Al 2 O 3, A
If at least one component of 1N is added in an excessively small amount or an excessive amount, the densification is insufficient or the grain boundary phase is excessive or the proportion of the crystal phase occupying the grain boundary phase is too low. It was confirmed that the strength was reduced or the thermal conductivity was inferior.

In addition to the above examples, 12.5% by weight of Ho ₂ O ₃ powder was added to silicon nitride powder, and ZrC, VC, N
bC, TaC, Cr ₃ C ₂ , Mo ₂ C, TiN, Zr
_{N, VN, TaN, CrN,} Mo 2 N, W 2 N, HfS
i ₂ , TiSi ₂ , ZrSi ₂ , VSi ₂ , NbS
i ₂ , TaSi ₂ , CrSi ₂ , MoSi ₂ , WS
i ₂ , ZrB ₂ , VB ₂ , NbB ₂ , TaB ₂ , CrB
A raw material mixture having a composition containing 1% by weight of at least one selected from the group consisting of ₂ , MoB ₂ and WB ₂ was treated under the same conditions as in Reference Example 102 to produce various Si ₃ N ₄ sintered bodies. . The porosity, the thermal conductivity (25 ° C.), the average value of the three-point bending strength at room temperature, and the ratio of the crystal phase to the grain boundary phase by X-ray diffraction were measured on these sintered bodies under the same conditions as in Reference Example 102. However, almost the same results as in Reference Examples 102 to 138 and Examples 19 to 39 were obtained.

[0114]

As described above, according to the high thermal conductivity silicon nitride sintered body and the method of manufacturing the same of the present invention, a silicon nitride sintered body having high strength and high thermal conductivity can be obtained. Therefore, the silicon nitride sintered body is extremely useful as a substrate for a semiconductor or a substrate such as a heat sink.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-48174 (JP, A) JP-A-7-187793 (JP, A) JP-A-3-199166 (JP, A) JP-A-3-1991 218975 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/584

Claims (9)

(57) [Claims] 1. The method according to claim 1, wherein the rare earth element is converted to an oxide in an amount exceeding 7.5% by weight and not more than 17.5% by weight, and Li, Na, K, Fe, Ca, Mg, Sr, B as impurity cation elements.
a, Mn, and B in total of 0.3% by weight or less, comprising silicon nitride crystals and a grain boundary phase, and a ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase is 50% or more; And a high thermal conductivity silicon nitride baked material having a three-point bending strength of at least 650 MPa at room temperature, a thermal conductivity of at least 80 W / m · K, and a porosity of at most 2.5% by volume. Union. 2. An oxide containing a rare earth element in an amount of more than 7.5% by weight and not more than 17.5% by weight in terms of oxide, comprising a silicon nitride crystal and a grain boundary phase and a crystalline compound phase in the grain boundary phase. The ratio to the entire grain boundary phase is 50% or more;
And a high thermal conductivity silicon nitride baked material having a three-point bending strength of at least 650 MPa at room temperature, a thermal conductivity of at least 80 W / m · K, and a porosity of at most 2.5% by volume. Union. 3. The high thermal conductive silicon nitride sintered body according to claim 1, wherein the rare earth element is a lanthanoid series element. 4. The high thermal conductive silicon nitride sintered body according to claim 1, wherein the high thermal conductive silicon nitride sintered body contains 1.0% by weight or less of aluminum in terms of alumina. . 5. The high thermal conductive silicon nitride sintered body according to claim 1, wherein the high thermal conductive silicon nitride sintered body contains 1.0% by weight or less of aluminum nitride. 6. The high thermal conductivity silicon nitride sintered body is Ti,
The composition according to claim 1, wherein at least one selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo and W is contained in an amount of 0.1 to 3.0% by weight in terms of oxide. 3. The high thermal conductive silicon nitride sintered body according to 1 or 2. 7. Oxygen content of 1.7% by weight or less, Li, Na, K, Fe, Ca, Mg, S as impurity cation element
r, Ba, Mn, B in total of 0.3% by weight or less, α-phase type silicon nitride of 90% by weight or more, and an average particle size of 1.0 μm
m or less, and a raw material mixture in which a rare earth element is added in an amount of more than 7.5% by weight and converted to oxide in an amount of 17.5% by weight or less in terms of oxide to form a molded body. After degreasing the body, the body is sintered under pressure at a temperature of 1800 to 2100 ° C., and the cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed at the time of sintering by the rare earth element solidifies is reduced. By slow cooling at a temperature of 100 ° C. or less per hour, the ratio of the crystalline compound phase to the entire grain boundary phase in the grain boundary phase of the sintered body is 50% or more, and the thermal conductivity is 80 W / m ·.
A method for producing a highly thermally conductive silicon nitride sintered body, wherein the sintered body has a porosity of not less than K and a porosity of 2.5% or less in volume ratio. 8. The method according to claim 7, wherein at least one of alumina and aluminum nitride is added to the silicon nitride powder in an amount of 1.0% by weight or less. 9. Ti, Zr, Hf,
At least one selected from the group consisting of V, Nb, Ta, Cr, Mo, and W is converted into an oxide to form 0.1 to 3.0.
The method for producing a silicon nitride sintered body having high thermal conductivity according to claim 7, wherein the addition is performed by weight percent.