JP2002316875A - Silicon nitride sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride sintered compact which has excellent dielectric strength and heat radia bility, and is suitable as ceramics, e.g. used for an insulated substrate for a semiconductor. SOLUTION: The silicon nitride sintered compact contains at least one kind of element selected from light rare earth elements in 3 to 14 mass% by an amount expressed in terms of oxide, and alkaline-earth metal elements in 4 to 10 mass% by an amount expressed in terms of oxides. The sintered compact further contains alkali metal elements by <=0.5 pts.mass, and a cobalt element or/and a nickel element in 0.05 to 2.0 mass% by an amount expressed in terms of oxides to 100 pts.mass of the balance obtained by removing the amount of the cobalt element or/and the nickel element expressed in terms of oxides and the amount of the alkali metal elements expressed in terms of oxides from the total amount of the components in the silicon nitride sintered compact. Also, its dielectric strength in a thickness of 0.3 mm is >=10 kV, and its thermal conductivity at a room temperature is >=54 W/m.K. The volume fraction of the above silicon nitride in the sintered compact is 90 to 95 vol.

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, and more particularly, to a silicon nitride sintered body having excellent dielectric strength and heat dissipation and suitable as a ceramic used for an insulating substrate for semiconductors.

[0002]

2. Description of the Related Art Sintered silicon nitride has excellent properties such as mechanical properties, heat resistance, abrasion resistance and corrosion resistance. Therefore, sliding members such as bearing balls and tappets and cutting tools have been conventionally used. Practical application to engine members such as wear-resistant members such as turbocharger rotors, engine valves, and ceramic glow plugs is being studied. Conventionally, the use of aluminum nitride sintered bodies as an insulating substrate for semiconductors in inverters that control motors of hybrid electric vehicles has been considered, but the mechanical strength of aluminum nitride sintered bodies is insufficient. ,in recent years,
Focusing on the excellent mechanical properties of the silicon nitride sintered body, application to an insulating substrate for a semiconductor has been studied.

When a sintered body is used as an insulating substrate for a semiconductor, it is important to efficiently release the heat generated in the semiconductor element to the outside. However, compared with a conventionally used aluminum nitride sintered body, It has been pointed out that the silicon nitride sintered body is inferior in heat conduction characteristics, which has been a factor hindering its application as an insulating substrate for semiconductors. Therefore, conventionally, many attempts have been made to improve the thermal conductivity of a silicon nitride sintered body, and most of them have realized high thermal conductivity by growing silicon nitride particles.

However, when the grain growth of silicon nitride particles is promoted, a needle-like structure having a high aspect ratio is formed, and steric hindrance occurs at a microstructure level, so that it becomes difficult to obtain a dense sintered body. There is a problem. On the other hand, conventionally, gas pressure sintering (G
Pressure sintering methods such as PS), hot isostatic pressing sintering (HIP) of about 10 to 300 MPa, and hot press sintering (HP) sintering while applying mechanical uniaxial pressure are known. Have been. According to these sintering methods, a relatively dense sintered body can be obtained. However, since the production cost is generally high, it is not suitable as a production process of industrial materials requiring low cost. In addition, it is difficult to obtain a high-density sintered body by a normal-pressure sintering method in a nitrogen atmosphere pressure of less than 1 MPa.

Further, when a silicon nitride sintered body is used as an insulating substrate for a semiconductor, a high dielectric strength voltage is required as a characteristic of the sintered body. However, as described above, particles of silicon nitride are required to improve thermal conductivity. When the growth is promoted, there is a problem that the dielectric strength and the withstand voltage decrease. Therefore, conventionally, there has been a demand for the development of a silicon nitride sintered body that can be densified by an economical method while improving the thermal conductivity and that has excellent dielectric strength.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has excellent dielectric strength and heat dissipation.
It is an object of the present invention to provide a silicon nitride sintered body suitable as a ceramic used for an insulating substrate for a semiconductor or the like.

[0007]

Means for Solving the Problems The inventors of the present invention have studied in detail the cause of a decrease in dielectric strength when silicon nitride grain growth is promoted in a silicon nitride sintered body. As a result, it was found that residual pores were generated at the grain boundary triple point, and the electric field was concentrated on these pores. The present inventors have found that by including a predetermined amount of a light rare earth element and an alkaline earth metal element in a silicon nitride sintered body, residual pores are removed or reduced, and thermal conductivity and dielectric strength are improved. The present inventors have found that a finer sintered body can be obtained, and have completed the present invention.

In order to achieve the above object, a silicon nitride sintered body provided by the present invention contains at least one element selected from light rare earth elements in an amount of 3 to 14% by mass in terms of oxide and an alkaline earth metal. The element contains 3 to 10% by mass in terms of oxide and has a withstand voltage of 10 kV at a thickness of 0.3 mm.
It is characterized by the above.

The above-mentioned "light rare earth element" in the silicon nitride sintered body of the present invention is a general term for elements from La of atomic number 57 to Nd of atomic number 60 among lanthanoid elements. The “alkaline earth metal element” in the silicon nitride sintered body of the present invention includes, for example, Be, M
g, Ca, Sr, Ba and the like. In the silicon nitride sintered body of the present invention, two or more different light rare earth elements and alkali metals are contained as long as at least one of each of the above “light rare earth elements” and “alkaline earth metal elements” is included. It may contain an earth metal element. Further, a rare earth element other than the light rare earth element may be further contained.

In the silicon nitride sintered body of the present invention, the content of the “light rare earth element” is at least one element component in an amount of 3 to 14% by mass, preferably 5 to 14% by mass in terms of oxide.
To 10% by mass. The content of the “alkaline earth metal element” is 3 to 10% by mass, preferably 5 to 8% by mass in terms of oxide. If the amount of the light rare earth element in terms of oxide is less than 3% by mass or the amount of the alkaline earth metal element in terms of oxide is less than 3% by mass, the amount of the grain boundary phase in the sintered body is reduced and the residual It is not preferable because the number of pores increases and the dielectric breakdown voltage decreases. On the other hand, if the oxide equivalent of the light rare earth element exceeds 14% by mass or the oxide equivalent of the alkaline earth metal element exceeds 10% by mass, the amount of the grain boundary phase increases, Since the needle-like structure is excessively developed, steric hindrance occurs as described above, and as a result, residual pores are generated at the triple point of the grain boundary, and the dielectric breakdown voltage is similarly lowered, which is not preferable.

The light rare earth element and the alkaline earth metal element contained in the silicon nitride sintered body of the present invention are usually used as compounds such as oxides and carbonates in the step of producing the silicon nitride sintered body. It is mixed with silicon nitride raw material powder. Then, during the firing process, it reacts with an oxide film present on the surface of the silicon nitride raw material powder particles to generate a liquid phase, and has a function as a sintering aid for obtaining a silicon nitride sintered body. Also,
After sintering, it exists as a component of a grain boundary glass phase or a grain boundary crystal phase between silicon nitride particles.

The silicon nitride sintered body of the present invention has a thickness of 0.3 m
m has a high value of 10 kV or more. Here, the value of the withstand voltage at a specific thickness is defined because it is difficult to uniquely define the correlation between the withstand voltage and the thickness. For example,
The withstand voltage characteristics of a relatively thin plate-like sintered body such as a silicon nitride insulating substrate can be obtained by directly applying the value of the withstand voltage measured using a relatively thick sintered body exceeding 2 to 3 mm. In many cases, the desired performance cannot be obtained. Therefore, in order to obtain an insulating substrate having a truly excellent dielectric strength, it is necessary to use the value of the dielectric strength when the sintered body has a specific thickness. The thickness of the silicon nitride sintered body of the present invention when expressing the dielectric strength is based on the above 0.3 mm, but may be in the range of 0.3 ± 0.02 mm. However, the present invention is not limited to this. For example, if the substrate is thicker than 0.32 mm, 0.3 ± 0.02
Any substrate can be used as long as it exhibits a dielectric breakdown voltage of 10 kV or more when ground to a thickness of 0.3 mm. On the other hand, for a substrate thinner than 0.28 mm, a thickness of 0.3 ± 0.2 mm is obtained by the same manufacturing method. A substrate of 02 mm is manufactured and the withstand voltage is evaluated. The surface state of the sample is not particularly limited, and may be a burnt surface or a ground surface. As a guide for the grinding surface, a surface obtained by finishing a fine grinding amount (finish grinding amount) of 10 μm in 1 μm increments using a grindstone of # 170 or more.

Further, the silicon nitride sintered body of the present invention may contain a cobalt element and / or a nickel element in addition to the light rare earth element and the alkaline earth metal element. By containing the cobalt element or the nickel element, it is possible to suppress the grain growth in the major axis direction of the silicon nitride particles. For this reason, it is possible to further suppress the residual pores at the grain boundary triple point due to steric hindrance. In this case, the cobalt element and / or the nickel element can be included in the sintered body in the form of a compound, and examples of such a compound include an oxide, a nitride, and an oxynitride. The content of the cobalt element or / and the nickel element is expressed in terms of an oxide conversion amount with respect to the remaining 100 parts by mass excluding the oxide conversion amount of the cobalt element and / or nickel element from the total component amount of the silicon nitride sintered body. 0.05 to 2.0 parts by mass, preferably 0.05 to 0.5
Parts by mass, more preferably 0.05 to 0.1 part by mass. Incidentally, by containing the cobalt element or the nickel element, it is also possible to obtain a secondary effect of making the coloration of the sintered body uniform.

[0014] The silicon nitride sintered body of the present invention may contain at least one element component selected from alkali metal elements. Examples of the “alkali metal element” include Li, Na, K, and the like. If at least one of these elements is included, two or more different alkali metal elements may be included. By containing such an alkali metal element, the viscosity of the liquid phase generated at the grain boundary can be reduced, and as a result, the densification of the sintered body can be promoted, which is preferable. The content of the “alkali metal element” is not particularly limited, but is usually oxidized with respect to the remaining 100 parts by mass of the total content of the silicon nitride sintered body excluding the equivalent amount of the alkali metal element as oxide. 0.5 parts by mass or less (however, 0 parts by mass is not included), preferably 0.01 to 0.5 parts by mass, more preferably 0.01 to 0.3 parts by mass, particularly preferably 0.
It can be from 0.1 to 0.1 part by mass. By setting the amount of the above “alkali metal element” in terms of oxide to the above range, while promoting the densification of the sintered body, suppressing the expression of ionic conductivity in the grain boundary phase, and preventing a decrease in insulation properties. It is preferable because excellent insulating properties can be maintained. The content of the above-mentioned “alkali metal element” in the case of containing the cobalt element and / or the nickel element is calculated from the total amount of the components of the silicon nitride sintered body in terms of the oxide equivalent of the cobalt element and / or the nickel element and the alkali element. With respect to the remaining 100 parts by mass excluding the oxide equivalent amount of the metal element, the equivalent amount of the oxide is 0.1%.
5 parts by mass or less (however, 0 parts by mass is not included), preferably 0.01 to 0.5 parts by mass, more preferably 0.01 parts by mass.
To 0.3 part by mass, particularly preferably 0.01 to 0.1 part by mass.

In the silicon nitride sintered body of the present invention, the volume fraction of silicon nitride in the sintered body can be 90 to 95 vol%, preferably 91 to 94 vol%. By setting the volume fraction of the silicon nitride to 90 vol% or more, a grain boundary phase component having a low thermal conductivity of usually 1 W / m · K or less, which is a rare earth element-silicon-oxygen-nitrogen as a basic component, that is, Generation of glass components can be suppressed. As a result, a decrease in the thermal conductivity of the sintered body can be prevented, and the sintered body can be suitably used as an insulating substrate for a semiconductor that requires high heat dissipation. On the other hand, the silicon nitride has a volume fraction of 9
By setting the content to 5 vol% or less, the grain boundary phase is not insufficient for the silicon nitride component, so that it is possible to prevent a large number of residual pores from being generated and lowering the thermal conductivity.
It is preferable because a decrease in AC withstand voltage is also prevented and a withstand voltage characteristic of 10 kV or more can be obtained at a thickness of 0.3 mm.
In the present invention, the volume fraction of silicon nitride is determined as follows. After an arbitrary cross section of the silicon nitride sintered body is mirror-polished, a photograph of the polished surface is taken with a scanning electron microscope at a magnification of 3000 times at a high resolution. The obtained photograph image is binarized, the area occupied by the silicon nitride particles is specified, the ratio of the area area of the silicon nitride particles to the entire viewing area (area ratio) is calculated, and this is calculated as the volume fraction of silicon nitride. I do.

By providing the silicon nitride sintered body of the present invention with the above-described structure, the silicon nitride sintered body can have both excellent withstand voltage and high thermal conductivity as compared with a conventional silicon nitride sintered body. it can. In addition, the thermal conductivity at room temperature was 54 W /
m · K or more, preferably 60 W / m · K or more, more preferably 65 W / m · K or more. When the thermal conductivity at room temperature is in the above range, it is preferable to use it as a semiconductor insulating substrate or the like that needs to release generated heat, because heat can be efficiently promoted.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to experimental examples.
This will be described more specifically. (1) Preparation of sintered body As raw material powder, Si_ThreeN_FourPowder (average particle size 1.0 μm,
α rate 99%, impurity oxygen content 1.2 mass%) and rare earth element
Elemental compound (CeO_Two, La_TwoO_Three, Nd_TwoO_ThreeAnd Pr₆O₁₁
[Average particle size 1-3 μm]) and SrCO_Three(Average particle size 1
μm) and an alkali metal oxide (Li_TwoCO_Three, Na_TwoC
O_ThreeAnd K_TwoCO_Three[Average particle size 0.5-2 μm]),
Co_ThreeO_Four(Average particle size 1 μm) and NiO (average particle size 1 μm).
m) was used. These have the composition ratios shown in Table 1.
Thus, a raw material powder mixture was prepared. In Table 1,
Si_ThreeN_Four, Rare earth element compound and SrO amount are mass
%. Also, a Co compound, a Ni compound and an alkali
The value of the amount of metal oxide is Si _ThreeN_Four, Rare earth element compounds and
And 100 parts by mass of the total amount of SrO and SrO.
Then, using the raw material powder mixture as a dispersion medium with ethanol
In a resin pot, mixed and crushed with a resin ball for 16 hours
Thereafter, the slurry was dried in hot water to obtain a mixed powder. Then,
Pellet of φ40mm × t5mm by pressing the mixed powder
After the shape, the pressure is 150MPa by CIP device
The molded product was obtained by molding. Thereafter, a release agent is added to the molded body.
After applying boron nitride, baking silicon nitride
8 hours in a case, according to the conditions shown in Table 1 below
After sintering, sintering of each of Examples 1 to 7 and Comparative Examples 1 to 3
I got a body.

[0018]

[Table 1]

(2) Performance evaluation Examples 1 to 7 and Comparative examples 1 to 3 obtained by the above method.
The performance of each sintered body was evaluated by the following method. The theoretical density ratio (%) was determined by measuring the density of the sintered body by the Archimedes method and expressing the ratio with respect to the theoretical density calculated by the mixing rule. The withstand voltage value (kV) is
Examples 1 to 7 and Comparative Examples 1 to 3 obtained by the above method
After polishing each sintered body to a thickness of 0.3 mm,
It was determined by performing a withstand voltage measurement in normal oil based on SC2110 “Test method for dielectric strength of solid electrical insulating material”. Here, the shape of the electrodes used in measuring the breakdown voltage is as shown in FIG. The sample thickness according to the JIS standard is 2 mm or 3 mm. However, in the case of application to an insulating substrate for a semiconductor, since an actual substrate is often used with a thickness of about 0.3 mm, the test was conducted in this test. Was 0.3 mm in thickness. Furthermore, the thermal conductivity (W / m · K) at room temperature (25 ° C.) was determined by separately using φ10 mm for each of the sintered bodies of Examples 1 to 7 and Comparative Examples 1 to 3 obtained by the above method. XT2mm to produce a sample polished,
It was measured according to JLS R1611 "Test method for thermal diffusivity, specific ripening capacity and thermal conductivity of fine ceramics by laser flash method". The results of these evaluations are shown in Table 2 below.

[0020]

[Table 2]

(3) Effects of Experimental Examples From Table 2, all the sintered bodies of Examples 1 to 7, which are within the scope of the present invention, have a high thermal conductivity of 54 to 75 W / m · K. At the same time, the theoretical density ratio is 98.0-99.0.
% To achieve high densification, and further 0.3%
It shows high withstand voltage with a withstand voltage value of 10 kV or more at a sample thickness of mm. From these results, Examples 1 to 7
It can be seen that each of the sintered bodies has excellent thermal conductivity and dielectric strength, and is a dense sintered body in which residual pores are removed or reduced. In particular, each of the sintered bodies of Examples 3 and 5 to 7 containing an alkali metal element has a withstand voltage of 11 to 13 kV.
Which is slightly higher than the sintered bodies of Examples 1, 2 and 4. From these results, it can be seen that by containing an alkali metal element, it is possible to obtain a sintered body having high denseness and excellent withstand voltage. Also,
In each of the sintered bodies of Examples 1, 3, 5 to 7 in which the volume fraction of silicon nitride is 90 vol% or more, the thermal conductivity is 57 to 75.
It shows a high value of W / m · K. In particular, in Examples 3 and 5 to 7 in which the volume fraction of silicon nitride is large, 65 to 75 W / m
-It shows K and a more excellent value. From this result, it is understood that when the volume fraction of silicon nitride is 90 vol% or more, the thermal conductivity can be improved.

On the other hand, in the sintered body of Comparative Example 1, the content of the light rare earth element in the sintered body was as low as 2% by mass.
The theoretical density ratio is as small as 90.1%, and the withstand voltage value is as low as 3 kV. From this result, it can be seen that the sintered body of Comparative Example 1 is a sintered body in which the densification of the sintered body has not progressed and the dielectric strength is inferior. The sintered body of Comparative Example 2 has a theoretical density ratio of 95.0%, which is slightly improved as compared with Comparative Example 1. However, the light rare earth element in the sintered body is as large as 15% by mass. It can be seen that the withstand voltage value is as low as 7 kV and the sintered body is still inferior in the withstand voltage. It is considered that the cause is that a large amount of the light rare earth element is added, so that the grain growth of silicon nitride excessively progresses and residual pores remain at the grain boundary triple point. Further, the sintered body of Comparative Example 3 had a light rare earth element content within the range of the present invention, but had a small SrO content of 2% by mass. The voltage value also shows a low value of 5 kV. From these results, in the sintered body of Comparative Example 3,
It can be seen that the densification of the sintered body has not progressed and the sintered body is inferior in dielectric strength.

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.

[0024]

According to the silicon nitride sintered body of the present invention, by including a predetermined amount of a light rare earth element and an alkaline earth metal element in the silicon nitride sintered body, excellent thermal conductivity and dielectric strength can be obtained. In addition, a dense sintered body in which residual pores are removed or reduced can be obtained by a more economical method. And, since the silicon nitride sintered body of the present invention is excellent in thermal conductivity and dielectric strength, it is suitable as a ceramic used for various parts such as semiconductor devices such as insulating substrates for semiconductors and OA equipment, for example. Can be used.

[Brief description of the drawings]

FIG. 1 shows the shape of an electrode used for measuring a breakdown voltage in an experimental example.

[Explanation of symbols]

 1: sample, 2: upper electrode, 3: lower electrode.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masaya Ito 14-18 Takatsuji-cho, Mizuho-ku, Nagoya F-term in Japan Special Ceramics Co., Ltd. 4G001 BA01 BA05 BA08 BA10 BA32 BB01 BB05 BB08 BB10 BB32 BC23 BD03 BD23 BD38

Claims (5)

[Claims] At least one selected from light rare earth elements
Containing 3 to 14% by mass of an element as an oxide and 3 to 10% by mass of an alkaline earth metal element in terms of an oxide;
A silicon nitride sintered body having a withstand voltage of 10 kV or more at a thickness of 0.3 mm. 2. An alkali metal element is contained in an amount of 0.5 parts by mass or less in terms of an oxide with respect to 100 parts by mass of the total content of the silicon nitride sintered body excluding the amount of the alkali metal element in terms of oxide. The silicon nitride sintered body according to claim 1, wherein 3. The amount of cobalt element and / or nickel element in terms of oxide relative to the remaining 100 parts by mass excluding the amount of cobalt element and / or nickel element in terms of oxide from the total amount of components of the silicon nitride sintered body. The silicon nitride sintered body according to claim 1, which contains 0.05 to 2.0 parts by mass. 4. An alkali metal element is added to the remaining 100 parts by mass of the total content of the silicon nitride sintered body excluding the oxide equivalent of the cobalt element and / or nickel and the oxide equivalent of the alkali metal element. In terms of oxide
The silicon nitride sintered body according to claim 1, which contains not more than parts by mass. 5. The sintered body according to claim 1, wherein a volume fraction of silicon nitride in the sintered body is 90 to 95 vol%, and a thermal conductivity at room temperature is 54 W / m · K or more. Silicon nitride sintered body.