JP2001089250A - Sintering case for highly thermal-conductive silicon nitride sintered body and production process of highly thermal-conductive silicon nitride sintered body using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintering case which is particularly suitable for sintering a highly thermal-conductive silicon nitride sintered body and can also be used for sintering at a >=1,800 deg.C high temperature, irrespective of the composition of an unsintered body to be sintered and also to provide a process for producing the silicon nitride sintered body by using the sintering case. SOLUTION: The manufacturing process of this sintering case comprises, mixing a powdery silicon nitride raw material or powdery silicon carbide raw material, various sintering aids and a binder to prepare a raw material for a sintering case then forming the sintering case raw material into a green body and thereafter, sintering the green body in an nitrogen atmosphere when the green body consists essentially of silicon nitride, or in an argon atmosphere when the green body consists essentially of silicon carbide, to manufacture the objective sintering case having a <=3.5 wt.% Al content. Also, the objective highly thermal-conductive silicon nitride sintered body is produced by sintering a corresponding green body at >=1,800 deg.C in a nitrogen-containing atmosphere by using the sintering case.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a firing case for a silicon nitride sintered body having a high thermal conductivity and a method for producing a silicon nitride sintered body having a high thermal conductivity using the same. More specifically, 180
A firing case for a high thermal conductive silicon nitride sintered body capable of obtaining a silicon nitride sintered body having high thermal conductivity even when fired at a high temperature of 0 ° C. or higher, and a high thermal conductive silicon nitride using the same The present invention relates to a method for manufacturing a porous sintered body. The high thermal conductive silicon nitride sintered body obtained by the production method of the present invention can be suitably used for an insulating substrate for a semiconductor or the like that requires high heat dissipation and insulation.

[0002]

2. Description of the Related Art As is well known, a silicon nitride sintered body is excellent in mechanical properties such as strength and fracture toughness, heat resistance, corrosion resistance and the like. Further, in recent years, attention has been paid to its excellent high insulation properties and high heat conduction properties, and application to insulating substrates for semiconductors and the like has been attempted. Since silicon nitride has a high covalent bond property, it is difficult to sinter a molded body using the same. For this reason, various sintering methods have been studied so far. Among them, a liquid phase sintering method in which a specific sintering aid is added and sintering is performed through a liquid phase generated by reaction melting at a high temperature has been widely used.

In this method, alumina, magnesia, silica and the like used as a sintering aid are easily volatilized at a high temperature in a liquid phase sintering method. For this reason, a firing case is required as a means for maintaining the atmosphere. As this firing case, Japanese Patent Publication No. 49-40123 and Japanese Patent Publication No. 6-668 are used.
However, the publication does not aim at obtaining a high thermal conductive silicon nitride based sintered body. Until now, there has been no known firing case particularly suitable for obtaining a silicon nitride sintered body having high thermal conductivity.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and at a high temperature of 1800 ° C. or more,
An object of the present invention is to provide a fired case for a high-thermal-conductivity silicon nitride-based sintered body that can be used for firing an unsintered body to be a high-thermal-conductivity silicon nitride-based sintered body (hereinafter, also simply referred to as an “unfired body”). And It is another object of the present invention to provide a method for manufacturing a high thermal conductive silicon nitride based sintered body using the firing case.

[0005]

The fired case for a high thermal conductive silicon nitride based sintered body according to the first aspect of the present invention is a sintered body for a high thermal conductive silicon nitride based sintered body used for manufacturing a high thermal conductive silicon nitride based sintered body. The case is characterized in that the content of the Al component is 3.5% by weight or less in terms of oxide, and has a different composition to be the high thermal conductive silicon nitride based sintered body.

The above-mentioned "high thermal conductive silicon nitride sintered body" (hereinafter also simply referred to as "high thermal conductive sintered body") has a thermal conductivity of 50 W / m · K or more (more preferably 55 W / m · K).
K or more), and refers to a sintered body containing at least 80% by weight of silicon nitride. The “Al component” includes:
It includes a simple substance of aluminum and a compound containing an Al element. The above “content of Al” can be measured by X-ray fluorescence analysis, and the content is the content when converted to oxide (Al ₂ O ₃ ).

When the Al component is contained in the sintering case in an amount exceeding 3.5% by weight, particularly at 1800 ° C. (further 1900 ° C.)
Under the above high temperatures, it may volatilize from the firing case. The volatilized Al component may migrate into the unfired body, and may further form a solid solution. Sialon is formed by the solid solution of the Al component, and the thermal conductivity of the silicon nitride sintered body on which sialon is formed is significantly reduced. Therefore, the content of the Al component is preferably 3.5% by weight or less, more preferably 3% by weight or less, particularly preferably 2% by weight or less, and particularly preferably 1% by weight or less. Is preferred.

The above-mentioned "different compositions" means that they are composed of the same element, differ in the content ratio, and contain different elements. These elements are intentionally added and exclude unavoidable impurities and elements below the measurement limit. A firing case for a high thermal conductive silicon nitride sintered body fired from the same main component and sintering agent as the unfired body (hereinafter, also simply referred to as “fired case”).
In the case where is used, the transfer of the element between the element in the unfired body and the firing case can be eliminated or reduced. In particular, in the fired case of the present invention, since the contained elements may be different, it is not necessary to manufacture a fired case composed of the same element as the unfired body for each unfired body containing a different element.

The above-mentioned "fired case for a silicon nitride sintered body having a high thermal conductivity" has an Al content of 3.5% by weight or less in terms of oxide, and is heated at 1800 ° C. in an inert atmosphere containing nitrogen.
Any composition may be used as long as the composition is stable at the above high temperature. For example, a sintered body containing silicon nitride as a main component, a sintered body containing silicon carbide as a main component, or a composite sintered body thereof can be given.

Particularly, as in the second invention, a raw material powder containing silicon nitride as a main component, a rare earth element component and one of a Mg component and a Si component as a sintering aid is formed, and then fired. What is obtained is preferred. With such a firing case, a silicon nitride sintered body having particularly high thermal conductivity can be obtained. The above “rare earth element components”, “M
The “g component” and “Si component” represent each simple substance and a compound containing each element. As rare earth oxides,
Yttrium oxide, lanthanum oxide, cerium oxide, erbium oxide, ytterbium oxide, and the like can be used. As the Mg component, magnesium oxide powder, magnesium carbonate powder that becomes magnesium oxide by calcination, or the like can be used. In addition, silica powder can be used as the Si component.

Further, the maximum temperature at the time of firing the green body is 18
By setting the temperature to be lower than 00 ° C., the volatilization amount of the Al component can be reduced. However, in a high-thermal-conductivity sintered body in which the formation of a single crystal having a larger grain size realizes a high thermal conductivity, if this temperature is low, the grain growth is not sufficient and it becomes difficult to obtain a high-thermal-conductivity sintered body. Therefore, the firing temperature is 1
800 ° C. or higher (more preferably 1900 ° C. or higher, usually 2
200 ° C. or less).

[0012] A method for producing a silicon nitride sintered body having high thermal conductivity according to the third invention uses the firing case according to the first invention or the second invention,
The method is characterized in that the method comprises a step of firing an unfired body to be a highly thermally conductive silicon nitride sintered body at a temperature of 1800 ° C. or higher in an inert atmosphere containing nitrogen.

The firing temperature is preferably 1800 ° C. or higher (more preferably 1900 ° C. or higher, usually 2200 ° C. or lower). As in the first invention, firing at a temperature lower than 1800 ° C. is not preferable. In addition, although firing may be performed at a temperature exceeding 2200 ° C., the energy required for firing is unnecessarily large, which is not preferable. Thereby, as described above, the grain growth of silicon nitride is promoted, and a high heat conductive sintered body having higher heat conductivity can be obtained.

When the firing cases of the first and second inventions are used, the thermal conductivity is 55 W / m · K or more (furthermore, 60 W / m · K or more).
W / m · K or more, particularly 70 W / m · K or more). In particular, as a green body, 91% by weight of silicon nitride raw material powder and 5.0% of cerium oxide powder were used.
The green body molded from the mixed powder containing 0.2% by weight of magnesium oxide powder, 3.0% by weight of zirconium oxide powder and 1.0% by weight of zirconium oxide powder under nitrogen pressure of 0.2 to 200 MPa as in the third invention In an inert atmosphere containing
When fired at 800 ° C. or higher, the thermal conductivity is 55 W / m ·
K or more (furthermore, 60 W / m · K or more, especially 70 W / m ·
K or more).

Furthermore, when silicon nitride is used as a main component and yttrium oxide and 3% by weight or less of alumina are used as sintering aids, 65 W / m · K or more, and when this alumina is 2% by weight or less, 70 W / m · K is used. m · K or more, this alumina is 1
When the content is less than 75% by weight, a high thermal conductive sintered body having a thermal conductivity of 75 W / m · K or more can be obtained. The outer surface of the high heat conductive sintered body can be made smoother in the case where the fired case mainly containing silicon nitride is used than in the case where the fired case mainly containing silicon carbide is used.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. (1) A firing case (K1 to K
5) Preparation of Raw Material The following powders were mixed at the ratio shown in Table 1, and a binder of 8% by weight was added to each of the mixed powders to prepare raw material powder for a firing case. In addition, * shows that it is out of the range of 1st invention. Si ₃ N ₄ : silicon nitride raw material powder (average particle size: 1.0 μm, impurity Al content: 700 ppm) Y ₂ O ₃ : yttrium oxide powder (average particle size: 2.0 μm) Yb ₂ O ₃ : ytterbium oxide powder (average particle size) 2.2μ diameter
m) SiO ₂ : silica powder (average particle size 0.2 μm) Al ₂ O ₃ : alumina powder (average particle size 0.6 μm) MgO: magnesia powder (average particle size 0.3 μm)

(2) Preparation of Raw Materials for Fired Cases (K6 to K8) Mainly Containing Silicon Carbide The following powders were mixed in the proportions shown in Table 1, and a binder of 8% by weight was added to each of the mixed powders. Raw material powder for the firing case was prepared. In addition, * shows that it is out of the range of 1st invention. SiC: silicon carbide raw material powder (average particle diameter 0.5 μm, impurity Al content 300 ppm) Al ₂ O ₃ : alumina powder (average particle diameter 0.6 μm) B: boron powder (average particle diameter 0.3 μm) C: pitch

[0018]

[Table 1]

(3) Firing of each firing case and firing case The raw material for the firing case prepared in (1) is subjected to CIP molding, and a cylindrical body having an outer diameter of 70 mm, a height of 50 mm, and a thickness of 7 mm, both ends being open; A molded body for a firing case composed of a disc having a diameter of 70 mm and a thickness of 10 mm was formed and degreased. Thereafter, the molded body for a firing case was fired at 1800 ° C. for 6 hours under a nitrogen atmosphere while applying a pressure of 0.2 MPa to obtain a cylindrical body and a disk body as firing cases K1 to K5.

Further, the raw material powder for the firing case prepared in (2) was subjected to CIP molding to form a green body for the firing case having the same shape as above. It was fired in an argon atmosphere to obtain a cylinder and a disk. Note that K6 and K7 are 10
K8 was fired at 2000 ° C. for 30 minutes. Among the obtained sintered bodies, a cylinder is placed on one disk so that its opening surface is closed, and another disk is placed so as to cover another opening surface of the cylinder. By doing so, it becomes a firing case.

(4) Production of High Thermal Conductive Sintered Body 91.0% by weight of silicon nitride raw material powder (average particle size 1.0 μm)
m, α rate 97%, impurity oxygen content 0.6% by weight)
5.0% by weight of cerium oxide powder (average particle size 3.0 μm)
m), 3.0% by weight of magnesium oxide powder (average particle size 0.3 μm) and 1.0% by weight of zirconium oxide powder (average particle size 0.5 μm)
Using 0 mm silicon nitride spheres, mixing and grinding were performed for 24 hours using ethanol as a dispersion medium. After the obtained slurry was dried in hot water, it was press-formed into a disk having a diameter of 15 mm and a thickness of 5 mm, and then subjected to a CIP treatment at 100 MPa to prepare an unfired body for a firing test. Next, this green body was fired at 1950 ° C. for 6 hours under a nitrogen atmosphere by applying a pressure of 1 MPa using a firing case shown in Table 1.

(5) Evaluation of properties of high thermal conductive sintered body The density of the high thermal conductive sintered body obtained in (4) was measured by the Archimedes method, and the relative density was calculated. Further, the obtained high thermal conductive sintered body was processed into a diameter of 10 mm and a thickness of 2 mm,
The thermal conductivity at room temperature (23 ° C.) was measured by a laser flash method (using a thermal constant measuring device, model “TC-7000” manufactured by Vacuum Riko Co., Ltd.). Furthermore, fluorescent X
X-ray analysis (using a wavelength-dispersive X-ray fluorescence spectrometer manufactured by Rigaku Co., Ltd., model "RIX-3000").
The contents of the components were measured and converted to oxides. Table 2 shows the results. In addition, * shows that it is out of the range of 1st invention.

[0023]

[Table 2]

In Experimental Examples 1 to 4, 6, 7, and 9 in Table 2, since a sintering case having an Al content of 3.5% by weight or less was used, a component different from that of the unsintered body was contained. In any of the firing cases, a thermal conductivity of 55 to 82 W / mK can be obtained. The main component is silicon nitride,
In Experimental Example 4 using a firing case in which the content of the Al component was 3% by weight, a high-thermal-conductivity sintered body of 67 W / mK
In Experimental Examples 1 and 2 using the firing case in which the content of the 1 component is 1% by weight, it can be seen that a high heat conductive sintered body of 72 to 79 W / m · K can be obtained.

In particular, in Experimental Example 6 using a firing case in which the main component is silicon nitride and the content of the Al component is below the measurement limit, a high thermal conductive sintered body of 82 W / m · K was obtained. Table 2 shows that the higher the content of the Al component contained in the firing case, the more the Al component contained in the obtained high thermal conductive silicon nitride sintered body.

Further, in order to obtain a sintered body having a high thermal conductivity of silicon nitride, even if a firing case containing silicon carbide as a main component without using silicon nitride as a main component is used, the firing case is 64 to 68 W / watt.
Experimental examples 7 and 8 show that a high thermal conductive silicon nitride based sintered body having a high thermal conductivity of m · K can be obtained.

On the other hand, in Experimental Example 5, the firing case having an Al component content of 5% by weight was used.
It can be seen from Table 2 that a large amount of the l component migrated to the green body. Therefore, although the relative density is high and the sintered body is well sintered, a high heat conductive sintered body of 55 W / m · K or more has not been obtained. Similar results were obtained in Experimental Example 8.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention in accordance with the purpose and application. That is, in this embodiment, since the unsintered body having the composition described above was used, the thermal conductivity was 57 to 82 W / m · K. However, the firing case of the present invention is not only for firing an unfired body having the above composition. Therefore,
For example, by firing an unfired body having another known composition using the firing case of the present invention, a fired body having a higher thermal conductivity can be obtained.

[0029]

According to the firing case for a silicon nitride sintered body having high thermal conductivity according to the first aspect of the present invention, the firing case is particularly suitable for use in the production of silicon nitride having high thermal conductivity. A conductive sintered body can be obtained. Further, it can be used regardless of the components of the unfired body to be fired. According to the third aspect of the present invention, a silicon nitride sintered body having high thermal conductivity can be easily obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaya Ito 14-18 Takatsuji-cho, Mizuho-ku, Nagoya F-term in Japan Special Ceramics Co., Ltd. 4G001 BA03 BA04 BA06 BA08 BA09 BA11 BA14 BA22 BA32 BA60 BA68 BB03 BB04 BB06 BB08 BB09 BB11 BB14 BB22 BB23 BB32 BC13 BC46 BC52 BC54 BC62 BD03 BD07

Claims (3)

[Claims] 1. A fired case for a highly thermally conductive silicon nitride based sintered body used for producing a highly thermally conductive silicon nitride based sintered body, wherein the content of Al component is 3.5% by weight or less in terms of oxide. A firing case for a high thermal conductive silicon nitride based sintered body, characterized by having a different composition to provide the high thermal conductive silicon nitride based sintered body. 2. The method according to claim 1, wherein a raw material powder containing silicon nitride as a main component, a rare earth oxide and one of a Mg component and a Si component as a sintering aid is molded, and then calcined. Fired case for high thermal conductive silicon nitride sintered body. 3. A step of using the firing case according to claim 1 and firing an unfired body to be a high thermal conductive silicon nitride sintered body at a temperature of 1800 ° C. or more in an inert atmosphere containing nitrogen. A method for producing a silicon nitride sintered body having high thermal conductivity, characterized in that: