JPH11310464A - Heat dissipating component made of silicon nitride and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat dissipating component made of silicon nitride at a low cost, capable of being produced through calcining at a temperature of <=1800 deg.C and normal pressure, and having high thermal conductivity, and to provide a method for producing the same component. SOLUTION: This heat dissipating component made of silicon nitride is obtained by calcining a molded product which contains 70-95 mol.% Si3 N4 , 4-30 mol.% [rare earth metals (RE)+Mg] in terms of their oxides and in a mol ratio (RE2 O3 /MgO) of 0.1-15 in terms of RE2 O3 and MgO and <=1.0 mol.% Al in terms of its oxides in a non-oxidizing atmosphere at 1,650-1,800 deg.C and then by the heat treatment of the product at 1,100-1,600 deg.C for >=1 h. The resultant product has a relative density of >=90%, a surface roughness (Rmax) of <=10 μm on the calcined face and a thermal conductivity of >=50 W/(m.K), and contains crystalline phases comprising MgSiO3 , MgSiN2 in grain boundary layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride heat radiation member suitable for radiating heat generated from semiconductor elements and heat generated from various heat-generating elements in a semiconductor element housing package material, and a method of manufacturing the same. Things.

[0002]

2. Description of the Related Art In recent years, power modules using power devices such as MOSFETs and IGBTs have been applied to control boards in electric vehicles such as electric trains and electric vehicles. Since the current used for these power devices exceeds several tens to several hundreds of amperes and the voltage is very high at several hundred volts, the heat generated from the power devices increases. This prevents the device from malfunctioning,
A major problem is how to release the generated heat out of the system.

Conventionally, ceramics such as silicon carbide, beryllium, and aluminum nitride have been used as a suitable material for radiating heat generated from the device. However, aluminum nitride is preferred in terms of safety and mass productivity. Ceramics are most frequently used.

However, in order to be used as a module substrate in an electric vehicle, it is necessary to have not only high thermal conductivity but also high durability. However, aluminum nitride ceramics have low strength and fracture toughness. It is unsuitable as a substrate material for electric vehicles and the like used under severe conditions.

Therefore, silicon nitride sintered bodies have recently been receiving attention as a material that meets the requirements of high thermal conductivity, high strength and high reliability. BACKGROUND ART Conventionally, silicon nitride-based sintered bodies have been actively studied and developed as high-temperature structural materials for gas turbines and the like. In general, a rare earth element oxide is added as a sintering aid to a temperature of 1800 ° C. to 2000 ° C. It is manufactured by firing at a very high temperature and in a pressurized nitrogen atmosphere of several to 100 atm in order to suppress the decomposition reaction of silicon nitride at a high temperature.

On the other hand, when heat resistance is not so required, it is manufactured by adding alumina, magnesia or the like as a sintering aid and firing at a relatively low temperature of 1700 to 1800 ° C.

[0007]

Although silicon nitride is predicted to have high thermal conductivity based on its constituent elements and crystal structure, much less research has been done on a heat dissipating member than research on structural materials. Recently, attention has been paid to the fact that silicon nitride as a high-temperature structural material has a considerably high thermal conductivity, and studies on heat dissipation members have begun.

[0008] From such circumstances, most of the research as a heat dissipating member is based on the premise of sintering at a high temperature.
There is not much research on the technology of manufacturing heat dissipating members under low temperature and low pressure. For example, Japanese Unexamined Patent Application Publication No.
No. 71 and JP-A-7-149588, a silicon nitride sintered body mainly containing a rare earth element oxide as an auxiliary agent and having a thermal conductivity of 60 W / m · K or more by pressurizing with nitrogen at 1800 to 2000 ° C. Is obtained.

[0009] However, high temperature and pressure sintering requires the use of a high pressure nitrogen gas, so that a special sintering furnace is required and the cost is increased.

Further, decomposition of silicon nitride itself is inevitable during firing, and the burning surface of the sintered body is very rough. Therefore, in order to actually use such a material, processing such as polishing is required, which is troublesome and contributes to an increase in cost.

On the other hand, a silicon nitride sintered body fired at a low temperature of 1700 to 1800 ° C. has a reduced thermal conductivity of 20 to 30 W / m · K, while the roughness of the burning surface of the sintered body is reduced. Was low.

The present inventors have heretofore added a rare earth element compound and a magnesium compound together as sintering aids, and controlled the amount of Al in the sintered body to reduce the silicon nitride sintered body to a low temperature. It was proposed that it could be fired at normal pressure and improve the thermal conductivity. However, its thermal conductivity is at most 30-40 W / m · K
And it was practically insufficient.

[0013]

The present inventors have solved the above-mentioned problem by adding both a rare earth element compound and a magnesium compound as sintering aids,
The silicon nitride-based heat radiating member having a high thermal conductivity is obtained by subjecting the silicon nitride-based heat radiating member whose amount is controlled to heat treatment after firing, thereby precipitating Mg present at the grain boundaries as a specific crystal phase. And found that the present invention was achieved.

That is, the silicon nitride heat dissipation member of the present invention comprises a main crystal phase made of silicon nitride, at least a rare earth element,
a sintered body consisting of a grain boundary phase containing g and Si, wherein the grain boundary phase contains a crystal phase consisting of MgSiO ₃ or MgSiN ₂ and the content of Al in terms of oxide is 1.0 mol% or less; The relative density is 90% or more, the surface roughness (Rmax) of the burnt surface is 10 μm or less, and the thermal conductivity is 50
W / m · K or more.

In the silicon nitride heat dissipation member of the present invention, 70 to 95 mol% of silicon nitride, and 4 to 30 mol% of rare earth metal (RE) and Mg in total in terms of RE ₂ O ₃ and MgO. And the rare earth element metal (RE) and Mg
Molar ratio of an oxide converted (RE ₂ O ₃ / MgO) may be desirable to include a proportion of a 0.1 to 15.

As a method of manufacturing the same, silicon nitride (Si ₃
N ₄₎ 70-95 mol%, the rare earth element (RE) and M
g in a total amount of 4 to 30 in terms of RE ₂ O ₃ and MgO.
Mol%, and the molar ratio represented by RE ₂ O ₃ / MgO in terms of oxide of the rare earth element (RE) and Mg is 0.1 to 1
5 in a non-oxidizing atmosphere.
After firing at a temperature of 0 to 1800 ° C, 1100 to 160
The heat treatment is performed in a temperature range of 0 ° C. for 1 hour or more.

According to the present invention, according to the silicon nitride heat radiation member and the method of manufacturing the same, the presence of the rare earth element (RE) added as a sintering aid promotes the crystallization of the crystal phase. Rare earth elements (RE) exist in the liquid phase,
Finally, RE ₂ Si ₃ O ₃ N ₄ and RE ₂ Si
As a result of reducing the amorphous phase having low thermal conductivity that precipitates as a crystal phase such as O ₅ and RE ₂ Si ₂ O ₇ and remains at the grain boundary, a sintered body having high thermal conductivity can be obtained. Further, the rare earth element (RE) has an effect of increasing the aspect ratio of the columnar crystal accompanying the α-β transition of silicon nitride and improving the fracture toughness of the obtained sintered body.

According to the silicon nitride heat dissipation member and the method of manufacturing the same of the present invention, the rare earth element (RE) component and the Mg component of the sintering aid react with impurity oxygen in the silicon nitride raw material to form a liquid phase. By generating, the sintering at a low temperature can be promoted and the sintering of silicon nitride can be sintered at a relatively low temperature of 1800 ° C. or less. A sintered body with less roughness can be obtained.

According to the present invention, a heat treatment is performed after the sintering so that the amorphous phase mainly containing Mg remaining at the grain boundary is MgSi.
By crystallizing as O ₃ or MgSiN ₂ , the low thermal conductivity amorphous phase remaining at the grain boundary is reduced,
The thermal conductivity of the sintered body can be further improved.

Further, the Al component forms a liquid phase at a low temperature and enhances the low-temperature sinterability similarly to the rare earth element (RE) component and the Mg component, but if present in a large amount, it may form a solid solution in silicon nitride grains or form sialon. In order to reduce the thermal conductivity by, for example, forming Al, by setting the Al content to 1.0 mol% or less, high thermal conductivity can be imparted.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a heat radiating member of the present invention and a method of manufacturing the same will be described in detail. First, the silicon nitride heat radiating member of the present invention has a β-silicon nitride phase as a main component, and the silicon nitride crystal has an average aspect ratio of 1.5 to 5 short as determined from an electron micrograph of a cross section of the sintered body. It is composed of a crystal having a shaft diameter of 0.1 μm to 1 μm. The sintered body contains a rare earth element and Mg as essential components.

As the rare earth element (RE), Y, La, C
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
Any of y, Ho, Er, Tm, Yb, and Lu can be suitably used, and among these, Y, Ce,
Sm, Dy, Er, Yb, and Lu, especially Y and Er, are desirable in terms of characteristics and cost.

The rare earth element (RE) and Mg are contained in a total amount of 4 to 30 mol%, particularly 5 to 25 mol% in terms of oxide. However, it is desirable that the molar ratio (RE ₂ O ₃ / MgO) of the rare earth element and Mg in terms of oxide be in the range of 0.1 to 15, particularly 0.5 to 13.

This is because when the total amount is less than 4 mol%,
It is difficult to fire the sintered body at a temperature of 1800 ° C. or less to sufficiently densify the sintered body, and if it exceeds 30 mol%, the absolute amount of the grain boundary phase in the sintered body increases. This is because the thermal conductivity of the aluminum alloy decreases. If the ratio of RE ₂ O ₃ / MgO exceeds 15 or is smaller than 0.1, the absolute amount of Mg or the rare earth element (RE) decreases, so that a liquid phase is not sufficiently generated during firing, and In this case, the densification becomes insufficient, and the thermal conductivity decreases. The compounding of an Al compound such as Al ₂ O ₃ greatly contributes to the improvement of the sinterability, but results in a solid solution in the Si ₃ N ₄ crystal to generate defects in the crystal and inhibit the propagation of phonons. In order to significantly lower the thermal conductivity of the sintered body, it is desirable that the sintered body does not exist in a large amount for high thermal conductivity. Specifically, Al is 1.0 mol% or less in terms of oxide, preferably 0 mol%. 0.5 mol% or less,
More desirably, the content is 0.1 mol% or less, further preferably 0.01 mol% or less.

The sintered body contains T as a coloring component.
i, Hf, Zr, V, Nb, Ta, Cr, Mo, W and at least one of metals belonging to Groups 4a, 5a and 6a of the Periodic Table.
The seed may be contained at a ratio of 0.05 to 1% by weight in terms of oxide.

The silicon nitride heat radiation member of the present invention is composed of the above-mentioned respective component compositions. The relative density of the heat radiation member is preferably at least 90%, especially at least 95% in order to achieve high thermal conductivity. Importantly, if the relative density is lower than 90%, it is difficult to achieve a thermal conductivity of 50 W / m · K or more.

In the silicon nitride heat dissipation member of the present invention, MgSiO ₃ or MgS
It contains a crystal phase of iN ₂ , and further contains RE ₂ Si
R such as ₃ O ₃ N ₄ , RE ₂ SiO ₅ , RE ₂ Si ₂ O ₇
It contains an E-containing crystal phase. By precipitation of these crystal phases, the low thermal conductivity amorphous phase present in the grain boundaries can be reduced, and high thermal conductivity can be achieved.

The silicon nitride heat radiation member of the present invention has a surface roughness (Rmax) of 10 μm or less, especially 7 μm,
m is also a major feature, whereby the product can be provided to the product without necessarily polishing the surface.

In order to manufacture the silicon nitride heat radiation member of the present invention, a rare earth element compound, a Mg compound, and in some cases, an Al compound are added to silicon nitride powder in the above-described ratio as a sintering aid.

The silicon nitride powder used preferably has an impurity oxygen content of 0.5 to 3.0% by weight. This is because if the amount of impurity oxygen is more than 3.0% by weight, the surface of the sintered body may be roughened and the strength may be degraded. If the amount is less than 0.5% by weight, the sinterability is deteriorated. The average particle size is
0.1 to 1.5 μm, and the α ratio is desirably 90% or more. The compound serving as a sintering aid is preferably a compound capable of forming an oxide by firing, such as an oxide, a carbonate, and an acetate.

Next, an organic binder and a solvent are added to the mixed powder to prepare the mixture. For example, a press molding method, a CIP molding method, a doctor blade method, a rolling method, a tape molding method, an extrusion molding method, an injection molding method A molded body is produced by a known molding method such as that described above. Thereafter, the molded body is subjected to a binder removal treatment in a weakly oxidizing atmosphere at a predetermined temperature, and then in a non-oxidizing atmosphere such as nitrogen at 1650 to 1800 ° C., particularly 1700 to 1700 ° C.
Baking at a temperature of 1800 ° C.

Thereafter, according to the present invention, after the sintering,
Heat treatment is performed in the range of 1100 to 1600 ° C. for 1 hour or more, particularly 3 hours or more. Heat treatment temperature 1100-1600 ° C
The reason is that the crystallization temperature of the grain boundary phase is about 1200 ° C., and even if heat treatment is performed at a temperature lower than 1100 ° C., a desired crystal phase cannot be obtained and a large amount of the amorphous grain boundary phase remains. Thermal conductivity decreases. Further, when the heat treatment is performed at a temperature higher than 1600 ° C., it becomes the same as normal firing, and the desired crystal phase does not precipitate.

If the heat treatment is shorter than one hour, the crystallization of the grain boundary phase is insufficient, so that the thermal conductivity decreases. In order to improve the thermal conductivity, a heat treatment of at least 3 hours is particularly effective.

In the heat treatment, the temperature is once cooled to room temperature after firing and then raised to 1100 to 1600 ° C. again and held for one hour or more.
Hold at a temperature of 0 to 1600 ° C. for 1 hour or more or 1
For example, there is a method in which the temperature is slowly cooled in a temperature range of 100 to 1600 ° C over 5 hours or more. If the temperature range of 1100 ° C. to 1600 ° C. is quenched, a desired crystal phase cannot be obtained, and the thermal conductivity similarly decreases. The silicon nitride heat dissipation member of the present invention can be used, for example, as a heat sink member in a package on which a semiconductor element is mounted, and also as an insulating substrate of a wiring board on which the semiconductor element is mounted. In that case, a wiring layer may be formed on the surface or inside of the insulating substrate. In such a case, Cu, W, Mo-Mn, Mo, Pd
It can be produced by printing and applying a conductive paste made of a high melting point metal such as -Ag and baking it in a non-oxidizing atmosphere, or by applying the paste on the surface of the molded body and firing it simultaneously.

It is also possible to form a wiring layer by bonding a copper foil to the surface of the heat radiating member after firing, directly or via a metallizing layer for connection, and in some cases, etching.

[0036]

EXAMPLE A rare earth element oxide, MgCO ₃ , Al ₂ O _{3 was} added to a silicon nitride raw material powder having an average particle diameter of 1.2 μm, an oxygen content of 1.3% by weight and an α rate of 93% by a direct nitriding method.
Is added and mixed so as to obtain a molded body composition as shown in Tables 1 and 2, paraffin wax is added as a molding binder to the mixed powder, isopropyl alcohol is added as a solvent, kneaded and dried, and then passed through a sieve. Obtain granules,
The granules were pressed by a mold press at a molding pressure of 1 ton / cm ² ,
It was formed into a disk having a diameter of 12 mm and a thickness of 5 mm.

After debinding the thus obtained molded body at a predetermined temperature, it is fired at a temperature shown in Tables 1 and 2 for 3 hours under a normal pressure (atmospheric pressure) and a nitrogen atmosphere. To produce a silicon nitride-based sintered body
The sample was used for evaluation.

Using the obtained evaluation sample, the density of the silicon nitride sintered body was first measured by the Archimedes method, and the relative density (%) as a ratio to the theoretical density was calculated. Next, the thermal conductivity of the sample having a thickness of 3 mm was measured by a laser flash method. For a sample having a relative density of 90% or more, X-ray diffraction measurement was performed on the surface of the sintered body, and it was considered that a crystal phase other than silicon nitride was present at the grain boundary,
The grain boundary crystal phase was identified. Furthermore, JISR1601
, The three-point bending strength of the burnt skin surface at room temperature was measured. Further, the surface roughness Rmax of the burnt skin surface was measured. The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

As is clear from the results in Tables 1 and 2, Sample No. For 1 to 13, the amount of silicon nitride, RE ₂ O ₃ + M
The sample No. whose gO amount and the ratio of RE ₂ O ₃ / MgO deviated from the scope of the present invention. In 1, 7, 8, and 13, the relative density decreased or the thermal conductivity decreased, and a thermal conductivity of 50 W / m · K or more was not obtained. The content of Al is 1.0 mol% including the impurity Al contained in the raw material powder.
Sample no. In No. 18, although densification was performed, the thermal conductivity was significantly reduced.

Further, the same sintering behavior and high thermal conductivity were exhibited in other rare earth elements of Y as the rare earth element.

Sample No. which was not subjected to any heat treatment 27
Sample No. with a heat treatment time of 0.5 hour. 32 for M
No g-containing crystal phase was observed, and the thermal conductivity decreased. In the sample having a heat treatment time of 1 hour or more, a grain boundary crystal phase was precipitated, and the thermal conductivity was significantly improved. However, Sample No. 3 in which the heat treatment time was extended by 3 hours or more. For 34, the thermal conductivity did not change.

Sample No. 1 which was heat-treated at a temperature lower than 1100 ° C. Sample No. 28 which was subjected to a heat treatment at a temperature higher than In Sample No. 31, no Mg-containing crystal phase was observed, and the thermal conductivity of Sample No. 31 was not heat-treated. It was not different from the thermal conductivity of 27.

Further, Sample No. 2 was fired at a temperature lower than 1650 ° C. At 35, the relative density decreases, and
Sample No. baked at a temperature higher than 800 ° C. 38
In the table, the surface roughness (Rmax) was increased. On the other hand, those having a relative density of 90% or more and a three-point bending strength of 700 MPa or more and a surface roughness (Rma
x) A sintered body having 10 μm or less and a thermal conductivity of 50 W / m · K or more was obtained.

[0046]

As described above in detail, according to the silicon nitride heat radiation member and the method of manufacturing the same of the present invention, normal pressure firing at a temperature of 1800 ° C. or less is possible and thermal conductivity is 50 W / m.
・ Because it can achieve K or more, it can be applied to a wide range of fields as various heat dissipating members with low cost.

Claims (3)

[Claims] 1. A sintered body comprising a main crystal phase made of silicon nitride and a grain boundary phase containing at least a rare earth element, Mg and Si, wherein said grain boundary phase is made of MgSiO ₃ or MgS
It contains a crystalline phase composed of iN _2, has an Al content of 1.0 mol% or less in terms of oxide, and a relative density of 90%.
As described above, the surface roughness (Rmax) of the burnt surface is 10 μm or less,
A silicon nitride heat radiation member having a thermal conductivity of 50 W / m · K or more. 2. A silicon nitride of 70 to 95 mol%, a rare earth element (RE) and Mg of 4 to 30 mol% in total in terms of RE ₂ O ₃ and MgO, said rare earth element (RE) and Mg
RE ₂ O ₃ / claim 1 silicon nitride radiator member according to the molar ratio comprising a ratio to be 0.1 to 15 represented by MgO of an oxide converted. 3. A silicon nitride of 70 to 95 mol%, a rare earth element (RE) and Mg of 4 to 30 mol% in total in terms of RE ₂ O ₃ and MgO, said rare earth element (RE) and Mg
Of a compact having a molar ratio expressed as RE ₂ O ₃ / MgO in terms of oxide of 0.1 to 15 and containing Al of 1.0 mol% or less in terms of oxide. After firing at a temperature of 1650 to 1800 ° C. in a neutral atmosphere,
A method for producing a silicon nitride heat radiating member, wherein a heat treatment is performed in a temperature range of 100 to 1600 ° C. for 1 hour or more.