JP2002012475A - Method of manufacturing highly thermo conductive silicon nitride material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a silicon nitride material that high thermal conductivity is realized by forming with pressure in any direction including isotropic pressure. SOLUTION: The formed body containing the silicon nitride powder is fired in the gaseous nitrogen atmosphere of 9-9.9 atm and 1850-1950 deg.C for 4-8 hr (the first firing), then is gas-pressure-fired in the gaseous nitrogen atmosphere of 100-1000 atm and 2000-2200 deg.C for 4-48 hr (the second firing). Relative density after the first firing and the second firing are 91-95 vol.% and 98.5-99.9 vol.%, respectively, Further heat treatment by gas-pressure firing under the condition of 2000-2400 deg.C and 100-1100 atm is available. A substrate for a semiconductor, a gas turbine cylinder and a bushing of an OA appliance are made from the above material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon nitride material having a high thermal conductivity.
The present invention relates to a method for producing a silicon nitride fired body that can realize high thermal conductivity without being restricted by a pressing direction at the time of molding.

[0002]

2. Description of the Related Art
When trying to achieve high thermal conductivity in silicon nitride materials, a nucleating substance such as silicon nitride single crystal is added to silicon nitride powder and a certain directionality is applied to the pressing direction such as extrusion molding or sheet molding. A method of improving the thermal conductivity has been performed in which a molding having (one direction) is performed and then firing is performed (Japanese Patent Application Laid-Open No. Hei 9-165265). However,
If the above-mentioned extrusion molding or the like is not performed, the silicon nitride powder and crystals in the molded body are randomly oriented, and the direction of each crystal is not one direction. Since crystal growth interferes with each other and hinders the oriented growth, crystal growth that is advantageous for improving thermal conductivity cannot be expected.

Further, the thermal conductivity is improved by a conventional method.
Includes the type of silicon nitride powder (α-type, β-type, etc.)
Types of sintering aids (MgO, CaO, Al
₂O ₃, Y₂O₃, Nd₂O₃, Yb₂O₃, HfO,
Sc₂O₃, CeO₂, ZrO₂, SiO₂, Cr₂O
₃, AlN, etc.) as appropriate, and 1 atm.
Firing at 1700-2200 ° C in a nitrogen atmosphere with high pressure
Or two-stage firing using hot gas pressure firing
However, when the crystal is randomly oriented as described above,
Means that the thermal conductivity obtained is limited to 120-130 w / mk
It is.

Further, addition of a silicon nitride crystal or a single crystal whisker has been conventionally performed (Japanese Patent Laid-Open No.
However, conventional silicon nitride crystals and single crystal whiskers cannot sufficiently improve the thermal conductivity because crystal defects are present inside the crystals.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object the purpose of the present invention is not limited to the pressing direction at the time of molding, and the pressure is almost isotropic. An object of the present invention is to provide a method for producing a silicon nitride material that can achieve high thermal conductivity even in molding.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have divided the firing process into predetermined two-stage processes and controlled the crystal growth.
The inventors have found that the above-mentioned object is achieved, and have completed the present invention.

That is, according to the method for producing a silicon nitride material having high thermal conductivity of the present invention, a raw material powder containing silicon nitride powder is molded to obtain a molded product.
Low-pressure sintering at 1850 to 1950 ° C. for 4 to 8 hours in a nitrogen atmosphere of 9 to 9.9 atm.
2000 to 2200 ° C in a nitrogen atmosphere of 0 to 1000 atm
And hot gas pressure firing for 4 to 48 hours.

A preferred embodiment of the method for producing a silicon nitride material having high thermal conductivity according to the present invention is (volume of fired body / volume of molded body)
When x100 is defined as a firing density ratio (vol%), the firing density ratio after the first firing is 91 to 95 vol%, and the firing density ratio after the second firing is 98.5 to 99.9.
vol%.

Further, in another preferred embodiment of the production method of the present invention, after the second baking, a temperature higher than the firing temperature of the second firing by 200 ° C. and a pressure higher by the same pressure to 100 atm higher, It is characterized by performing heat treatment by hot gas pressure firing.

[0010] Still another preferred embodiment of the production method of the present invention is characterized in that a high-purity silicon nitride single crystal having few internal defects produced by a reaction between molten silicon and nitrogen gas is added to the raw material powder. In this case, it is desirable to add the high-purity silicon nitride single crystal at a ratio of 3.0% or less.

Further, the heat generating component of the present invention is characterized by using a high thermal conductive silicon nitride material obtained by the above-described manufacturing method.

[0012]

In the present invention, the firing process is divided into two stages, a first firing relating to low pressure firing and a second firing relating to hot gas pressure firing. Therefore, the silicon nitride crystal does not grow at once, and the crystal initially generated in the first baking grows preferentially in the second baking, so that selective grain growth effective for improving the thermal conductivity can be easily realized. can do.

It is also possible to add a predetermined heat treatment step after the second baking, whereby the selective grain growth can be further promoted. The thermal conductivity of the silicon material can be improved. Further, in the present invention, it is possible to use a silicon nitride single crystal having a small number of defects as a nucleus for further promoting selective grain growth, so that a silicon nitride crystal generated based on such a nucleus has no defects. Therefore, a significant improvement in thermal conductivity can be realized. In addition, since crystals grow faster by the action of nuclei, collision (interference) between the crystals is reduced, and the firing density is improved.

In general, a silicon nitride material is stable under environmental conditions, has no toxicity, and has higher strength and toughness than alumina (Al ₂ O ₃ ) and aluminum nitride (AlN). The silicon nitride material obtained by the method is further excellent in thermal conductivity, so that it is a member or component that requires strength and toughness using Al ₂ O ₃ or AlN, and also requires high thermal conductivity. It is effectively used for heat conduction parts and heat generation parts.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production method of the present invention will be described below in detail. In addition, in this specification, "%" represents a mass percentage unless otherwise specified. As described above, in the method for producing high thermal conductive silicon nitride of the present invention, a raw material powder containing silicon nitride powder is formed, and the formed body is fired in predetermined first firing and second firing, and further, if necessary. By performing a predetermined heat treatment, a silicon nitride material having a high thermal conductivity, specifically, a silicon nitride fired body is obtained.

Here, the silicon nitride powder is particularly limited.
Although not specified, thermal conductivity and strength / toughness
It is preferable to use β-type silicon nitride powder from
In addition, high purity of 99.9% or more is used.
It is desirable to do. As the raw material powder, as described above
It is sufficient to contain silicon nitride powder.
Metal oxides such as magnesia (MgO), cal
Shea (CaO), alumina (Al₂O₃), Yttria
(Y₂O₃), Neodymium oxide (Nd ₂O₃), Oxidation
Ytterbium (Yb₂O₃), Hafnium oxide (Hf
O), scandium oxide (Sc₂O₃), Ceria (Ce)
O₂), Zirconia (ZrO)₂), Silica (Si
O₂), Chromium oxide (Cr₂O₃) Or aluminum nitride
(AlN) and sintering aids such as any mixture thereof
Agents can be added. In the present invention,
Y₂O₃-Nd₂O₃System, Y₂O₃-Nd₂O₃-Mg
O-based and Mg₂O₄-ZrO₂-Yb₂O₃System sintering aid
An agent can be suitably used.

In the present invention, a high-purity silicon nitride single crystal having few internal defects can be added to the raw material powder as a nucleus for crystal growth. Since the crystal grows quickly during the firing by the action of the nucleus, interference (collision) between the crystals is reduced, a homogeneous fired body is obtained, and the firing density is improved. Furthermore, since the silicon nitride crystal generated from the nucleus has almost no defects, the thermal conductivity is further improved. The addition ratio of such a high-purity silicon nitride single crystal is preferably 3.0% or less with respect to the raw material powder, and if it exceeds 3.0%, interference between the crystals becomes severe, and the thermal conductivity of the obtained silicon nitride material becomes high. The rate may decrease. The high-purity silicon nitride having few internal defects described above can be obtained, for example, by reacting molten silicon with nitrogen gas.

The method for molding the raw material powder is not particularly limited, and a method of pressing in one direction, such as extrusion molding or sheet molding, may be employed. It is preferable to adopt a molding method by isotropic pressure as described above. In the present invention, since the two-stage firing described below is employed, the thermal conductivity of the obtained silicon nitride material can be significantly improved without aligning the crystal or powder in a certain direction. Further, according to the forming method by the isotropic pressing, a fired body having a uniform and high density can be obtained, and as a result, the thermal conductivity can be further improved.

Next, the firing step will be described. In the present invention, the compact obtained from the raw material powder is formed by a first baking related to low pressure baking and a second baking related to hot gas pressure baking.
It is subjected to a stage firing. First, in the first firing, the obtained molded body was placed in a nitrogen atmosphere of 9 to 9.9 atm for 1850 to 19 atm.
This is carried out by firing at 50 ° C. for 4 to 8 hours, mainly performing the function of initially generating silicon nitride crystals in the molded body, and adding the core of high-purity silicon nitride single crystal as described above. Plays a role in triggering rapid crystal growth based on this nucleus.

If the firing pressure in the first firing deviates from the above-mentioned range, sufficient initial grain growth does not proceed, or the entire grains become coarse. When the firing temperature is 1
If the temperature is lower than 850 ° C., the initial grain growth does not proceed,
If it exceeds, the fine particles are also coarsened and the strength is reduced. Furthermore, if the firing time is less than 4 hours, the initial grain growth does not proceed, and if it exceeds 8 hours, the fine particles are coarsened and the strength is reduced.

Although the compact is shrunk by the first baking, if the ratio of (calcined body volume / molded body volume) × 100 = calcined density ratio (vol%) is defined in the present invention,
It is preferable that the firing density ratio after firing be 91 to 95 vol%. If the sintering density ratio deviates from the above range, the initial grain growth does not grow sufficiently, and the thermal conductivity may not be improved, which is not preferable.

Next, the second firing is performed by hot gas pressure firing (HIP) at 2000 to 2200 ° C. for 4 to 48 hours in a nitrogen atmosphere of 100 to 1000 atm. Crystal grown preferentially,
It functions to easily realize selective grain growth effective for improving thermal conductivity.

If the firing pressure in the second firing is less than 100 atm, the sintering may not proceed sufficiently,
When the pressure exceeds the atmospheric pressure, the fine particles are also coarsened, so that the strength is reduced. If the sintering temperature is lower than 2000 ° C., the selective grain growth proceeds excessively, and the thermal conductivity decreases due to the interference between crystals. If the firing temperature exceeds 2200 ° C., the fine particles are coarsened. Invite. Furthermore, if the sintering time is less than 4 hours, sintering may not proceed sufficiently. If the sintering time exceeds 48 hours, the selective grain growth proceeds too much and the thermal conductivity decreases due to interference between crystals. . . Further, in the present invention, the firing density ratio after the second firing is preferably 98.5 to 99.9 vol%. If the firing density ratio deviates from the above range, the number of pores becomes too large, and the strength increases. In addition, thermal conductivity may be reduced, which is not preferable.

In the manufacturing method of the present invention, the desired effect can be obtained by performing the two-stage firing as described above. However, after the second firing, a temperature higher than the firing temperature of the second firing by 200 ° C. Further, it is possible to perform heat treatment by hot gas pressure firing at a pressure higher by an equivalent pressure to 100 atm. By adding such a heat treatment step, the above-described selective grain growth can be further promoted.
The thermal conductivity of the obtained silicon nitride material can be improved as compared with the case of only two-stage firing. However, when the grain growth is sufficiently advanced at the end of the two-stage firing due to the selection of the firing conditions, the firing aid, and the like, there is no effect and the thermal conductivity may be rather lowered.

FIG. 1 is a firing pattern diagram showing an example of the above firing process. In the figure, in the first firing, 1
Target 1 at a heating rate of 400 to 800 ° C per hour
In the course of raising the temperature to 900 ° C. (symbol (a)), the heating rate is changed in three stages. Then, after reaching the target temperature, it is heated and held in a 9 atm N ₂ gas atmosphere for 4 hours,
Then cool down. In the second baking, the temperature is raised at a stretch at a rate of 400 to 600 ° C. per hour to the target 2000 ° C. (sign (b)), and N 2 at 300 atm is applied.
After heating and holding in a _two- gas atmosphere for 4 hours, it is cooled. Further, the heat treatment step subsequent to the second baking is a step of promoting selective grain growth of silicon nitride crystals, and is 400 to 400 hours / hour.
The temperature is raised at a stretch of 600 ° C. to 2200 ° C. (symbol (c)), followed by heating and holding in an N ₂ gas atmosphere at 300 atm for 4 to 48 hours, followed by cooling.

In the firing pattern of FIG. 1, it is effective to change the heating rate of the first firing (symbol (a)) in terms of controlling the initial grain growth, but it is an essential requirement of the manufacturing method of the present invention. Needless to say, there is nothing. In the firing pattern of FIG. 1, cooling is performed after the first firing and the second firing. However, such cooling is not an essential requirement of the present manufacturing method. For example, after the second firing, the same HIP firing is performed. It is also possible to shift to the heat treatment step without cooling in the furnace.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 β-type silicon nitride powder;
A sintering aid of 0 mol% Y ₂ O ₃ -1.0 mol% Nd ₂ O ₃ and a solvent (such as ethanol) are mixed and pulverized by a ball mill for 48 hours, and then separately prepared by a Si molten N ₂ gas synthesis method. About 0.1% of the obtained high-purity silicon nitride single crystal was added, mixed and pulverized again with a ball mill for 48 hours, dried and sieved to prepare a raw material powder. Then, the raw material powder obtained by molding into a predetermined shape, after solidified by isostatic pressing, in accordance with firing patterns shown in FIG 1, N ₂ atmosphere 1900 ° C. As a first firing for 4 hours at 9 atm And then cooled, followed by hot gas pressure firing and holding for 4 hours at 2000 ° C. and 300 atm in N ₂ atmosphere as a second firing, and after cooling, in the same hot gas pressure firing furnace. After heat treatment at 2200 ° C. and 300 atm for 12 hours, the sample was cooled and a test piece of the silicon nitride material of this example was taken out. The firing density ratio after the first firing was 93.2 vol%.
And the firing density ratio after the second firing was 99.2 vol%.

Using the obtained test piece, the thermal conductivity was measured at three points by a laser flash method. The minimum value of the thermal conductivity was 144 w / mk, the maximum value was 149 w / mk, and the average value was 147 w / mk. / Mk. Table 1 shows the obtained results together with the firing conditions and the like.

Example 2 The same operation as in Example 1 was repeated, except that the heat treatment time after the second baking was extended, to obtain a silicon nitride material of this example. The firing density ratio after the first firing was 92.5 vol%, and the firing density ratio after the second firing was 99.4 vol%. Table 1 shows the results of the thermal conductivity measurement and the firing conditions.

Example 3 The same operation as in Example 1 was repeated except that the high-purity silicon nitride single crystal was not added and the heat treatment time after the second baking was extended to obtain the silicon nitride material of this example. Was. The firing density ratio after the first firing was 92.4 vo.
1%, and the firing density ratio after the second firing is 98.4 vol.
%Met. Table 1 shows the results of thermal conductivity measurement and firing conditions.
Shown in

Example 4 The same operation as in Example 1 was repeated except that the high-purity silicon nitride single crystal was not added, to obtain a silicon nitride material of this example. The firing density ratio after the first firing was 92.6 vol%, and the firing density ratio after the second firing was 99.0 vol%. Table 1 shows the results of the thermal conductivity measurement and the firing conditions.

Example 5 As shown in Table 1, Y ₂ O ₃
Increasing the amount of -nd ₂ O ₃ based fired aid, without the addition of high-purity silicon nitride single crystal, extending the first firing time, except for shortening the heat treatment time, the same procedure as in Example 1, A silicon nitride material of this example was obtained. The firing density ratio after the first firing is 92.4 vol%, and the firing density ratio after the second firing is 9
It was 9.4 vol%. Table 1 also shows the results of the thermal conductivity measurement.

Example 6 The same operation as in Example 5 was repeated except that the amount of the Y ₂ O ₃ —Nd ₂ O ₃ based sintering aid was reduced and a high-purity silicon nitride single crystal was added. A silicon nitride material was obtained. The firing density ratio after the first firing is 94.2 vo
1%, and the firing density ratio after the second firing is 99.3 vol.
%Met. Table 1 shows the results of thermal conductivity measurement and firing conditions.
Shown in

Example 7 Example 5 was repeated except that the amount of the Y ₂ O ₃ —Nd ₂ O ₃ based sintering aid was reduced and the heat treatment time was extended.
The same operation as described above was repeated to obtain the silicon nitride material of this example. The firing density ratio after the first firing was 91.4 vol%, and the firing density ratio after the second firing was 98.9 vol%. Table 1 shows the results of the thermal conductivity measurement and the firing conditions.

Example 8 The same operation as in Example 7 was repeated, except that the high-purity silicon nitride single crystal was added and the first firing temperature was raised, to obtain a silicon nitride material of this example. First
The firing density ratio after the firing was 94.9 vol%, and the firing density ratio after the second firing was 99.9 vol%. Table 1 shows the results of the thermal conductivity measurement and the firing conditions.

Example 9 The same operation as in Example 8 was repeated, except that the first firing time was extended, to obtain a silicon nitride material of this example. The firing density ratio after the first firing is 94.8 vo
1%, and the firing density ratio after the second firing is 99.9 vol.
%Met. Table 1 shows the results of thermal conductivity measurement and firing conditions.
Shown in

Comparative Example 1 0.5 mol% of Y ₂ O ₃ -0.5 mol instead of Y ₂ O ₃ —Nd ₂ O ₃ -based sintering aid
% Nd ₂ O ₃ -2.0 mol% MgO, high purity silicon nitride single crystal was not added, and as shown in Table 1, the sintering process was changed to only one stage, and the second sintering and heat treatment were performed. The same operation as in Example 1 was repeated except that was not performed, to obtain a silicon nitride material of this example. The firing density ratio after the first firing was 97.0 vol%. Table 1 also shows the results of the thermal conductivity measurement.

Comparative Example 2 0.5 mol% Y ₂ O ₃ −
Instead of 0.5 mol% Nd ₂ O ₃ -2.0 mol% MgO-based sintering aid, 0.5% Mg ₂ O ₄ -0.9% ZrO
With ₂ -4.0% Yb ₂ O _3, except that the addition of silicon of high purity nitride single crystal, repeating the same operation as in Comparative Example 1, to obtain a silicon nitride material of the present embodiment. The firing density ratio after the first firing was 97.4 vol%. Table 1 shows the results of the thermal conductivity measurement and the firing conditions.

Comparative Example 3 0.5 mol% of Y ₂ O ₃ -0.5 mol instead of Y ₂ O ₃ —Nd ₂ O ₃ type sintering aid
% Nd ₂ O ₃ -2.0 mol% MgO, and as shown in Table 1, the same operation as in Example 1 was repeated except that the sintering process was changed to one step under different sintering conditions. A silicon material was obtained. The firing density ratio after the first firing is 97.2v
ol%. Table 1 also shows the results of the thermal conductivity measurement.

(Comparative Examples 4 to 6) In Comparative Examples 4 to 6, the second firing was not performed, and the hot gas pressure firing conditions of the conventional silicon nitride material firing process were employed. Is 0.5 mol% Y ₂ O ₃ -0.5 mol% Nd
₂ O ₃ was used. In Comparative Examples 4 and 5, no silicon nitride crystal was added. In Comparative Example 6, a commercially available silicon nitride crystal was added. Table 1 shows the firing conditions and the like of each example, and Table 1 also shows the results of measuring the thermal conductivity of the obtained silicon nitride material of each example. The firing density ratio after the first firing was 96.0 vol in Comparative Example 4.
%, 97.4 vol% in Comparative Example 5, 9% in Comparative Example 6.
6.2 vol%. In addition, the measurement result of the thermal conductivity in Comparative Examples 4 to 6 shows not the average value but the maximum value.

[0042]

[Table 1]

Example 10 A flat plate of silicon nitride material (thermal conductivity 110) manufactured by the method of the present invention as described above was used.
w / mk, 128 w / mk and 146 w / mk, see FIG. 2), and a flat plate (49 w / m
For k), as shown in Table 2, a # 600 abrasive grain finish was performed, and under a load of 490 N, a speed of 0.5 m / s, and an engine oil of 5W30SJ, dynamic friction was measured with a pin-on type friction / wear tester. The test was performed. FIG. 2 shows the obtained results.

[0044]

[Table 2]

As is clear from FIG. 2, a decrease in the coefficient of kinetic friction was observed as the thermal conductivity increased. Thus, it is presumed that the silicon nitride material having excellent thermal conductivity obtained by the production method of the present invention has an oil film retaining effect due to removal of heat generated during friction. From this, regarding the high thermal conductivity silicon nitride material of the present invention, a heat generating component, specifically, a component that dissipates the generated heat, for example, an automobile engine component, a semiconductor substrate, a gas turbine combustion cylinder, etc. Utilization is also conceivable, and it is also conceivable to use components that generate heat, for example, bushings of OA equipment that generates dry friction.

[0046]

As described above, according to the present invention, the firing step is divided into predetermined two-step steps to control the crystal growth. It is possible to provide a method for producing a silicon nitride material, which can realize high thermal conductivity even by molding by substantially isotropic pressure.

[Brief description of the drawings]

FIG. 1 is a firing pattern diagram showing an example of a firing step in a manufacturing method of the present invention.

FIG. 2 is a graph showing the relationship between the thermal conductivity of silicon nitride material and the coefficient of dynamic friction.

Claims (7)

[Claims] 1. A molded body is obtained by molding a raw material powder containing silicon nitride powder. As a first firing, the obtained molded body is heated at 1850 to 1950 ° C. in a nitrogen atmosphere of 9 to 9.9 atm. Low-pressure sintering for 8 to 8 hours, followed by hot gas pressure sintering at 2000 to 2200 ° C. for 4 to 48 hours in a nitrogen atmosphere of 100 to 1000 atm as a second sintering, producing a silicon nitride material having high thermal conductivity. Method. 2. When (volume of fired body / volume of molded body) × 100 is defined as a fired density ratio (vol%), the fired density ratio after the first firing is 91 to 95 vol%, and the fired density ratio is 91 to 95 vol%.
The method for producing a silicon nitride material having a high thermal conductivity according to claim 1, wherein a firing density ratio after firing is 98.5 to 99.9 vol%. 3. After the second baking, a temperature higher by 200 ° C. and a pressure equal to 200 ° C.
3. The method for producing a silicon nitride material having a high thermal conductivity according to claim 1, wherein the heat treatment is performed by hot gas pressure firing at a pressure higher by 00 atm. 4. The method according to claim 1, wherein a high-purity silicon nitride single crystal having few internal defects produced by a reaction between molten silicon and nitrogen gas is added to the raw material powder. A method for producing a high thermal conductive silicon nitride material as described above. 5. The high-purity silicon nitride single crystal is 3.0%
The method for producing a silicon nitride material having a high thermal conductivity according to claim 4, wherein the silicon nitride material is added in the following ratio. 6. The method for producing a silicon nitride material having high thermal conductivity according to claim 1, wherein the molding is performed by isotropic pressing. 7. A heat-generating component comprising a high thermal conductive silicon nitride material obtained by the method according to claim 1. Description: