JPH0788256B2 - Method for manufacturing aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing an aluminum nitride sintered body, and particularly to an aluminum nitride sintered body having high density and high thermal conductivity. It is an object of the present invention to provide a manufacturing method of.

(Prior Art) Aluminum nitride (AlN) has many excellent properties such as high strength from normal temperature to high temperature, high wettability to molten metal, high electric insulation and high thermal conductivity. It is attracting attention as a new material.

In recent years, application research on semiconductor substrates has been actively conducted, and the thermal conductivity of mass-produced AlN sintered bodies was 40 to 60 W / mk until a few years ago, but it will be improved to ~ 200 W / mk. Arrived

Regarding the achievement of high thermal conductivity of the aluminum nitride sintered body, the first factor is that mass production of high-purity AlN raw material, particularly AlN powder having a low oxygen content, has become possible.

AlN powder with low oxygen content was the main component, and by optimizing the sintering aid, it became possible to obtain an AlN sintered body with high thermal conductivity, but on the other hand, the oxygen content decreased and sinterability increased. However, in order to obtain a dense sintered body, it has become necessary to sinter at a higher temperature than in the past.

That is, it can be said that the AlN powder having a large amount of oxygen in the past was excellent in sinterability although the sintered body obtained from the powder had a low thermal conductivity. When considering application to semiconductor mounting boards, it is possible to substitute for alumina substrates that are widely used at present, but when considering such applications, it is necessary to thoroughly reduce the cost and increase the sintering temperature. Was unfavorable because it increased the manufacturing cost.

(Problems to be Solved by the Invention) The present invention uses AlN with high purity and low oxygen content to improve sinterability without impairing its high thermal conductivity, and enables sintering at low temperature. To do.

[Structure of Invention]

(Means and Actions for Solving Problems) The present inventors have conducted various studies on sinterability and thermal conductivity of AlN sintered bodies to which various additives are added, and as a result, alkaline earth compounds and It has also been found that by adding an additive consisting of a rare earth compound and a transition metal element or a compound thereof, and an aluminum oxide, the sinterability is improved without dealing with the high thermal conductivity inherent in the high-purity AlN raw material.

That is, the present invention contains AlN as a main component, to which an additive consisting of an alkaline earth metal compound and / or a rare earth compound and a transition metal compound and an aluminum oxide is added in an amount of 0.05 to 20% by weight in terms of each oxide. It is characterized by being sintered.

In the present invention, as the alkaline earth metal element, Ca, Ba, Sr
However, Y, La, and Ce as rare earth elements and Zr, Ti, Hf, Ni, Cr, Mn, Fe, Co, Ta, Nb, W and V are particularly effective as transition metal elements. It is desirable to add and sinter as a compound consisting of, that is, an oxide, a nitride, a carbide, or the like. Furthermore, the total amount of alkaline earth compounds and / or rare earth compounds is 0.02 to 15 in terms of each oxide.
% By weight, transition metal compound is 0.02 to 3 in terms of oxide
It is desirable to add 0.02 to 3% by weight of aluminum oxide and sinter.

In general, alkaline earth metal compounds and rare earth compounds are effective for densification as sintering aids because they mainly react with impurity oxygen in AlN raw material at the sintering temperature to form a liquid phase,
It is believed that the liquid phase sintering of is promoted. In such a sintering mechanism, in the low oxygen content AlN raw material, the sinterability decreases because the amount of liquid phase generated during the sintering due to the reaction with the sintering aid as described above decreases. It is presumed that this may be because it is difficult for the marriage to proceed. That is, low oxygen content
In the AlN raw material, by adding aluminum oxide and an alkaline earth metal and / or a rare earth compound, a liquid phase 1 sufficient for sintering is generated, and the added aluminum oxide reacts with AlN to form an oxynitride of Al. , Spinel or α-Al ₂ O ₃ etc. are not formed, and since they are formed as alkaline earth metal aluminate compounds or rare earth aluminate compounds, it is presumed that the thermal conductivity will not be reduced. It

Furthermore, in the AlN sintered body according to the present invention, a transition metal element or a compound thereof, especially Group IV of the periodic table, that is, Zr, Tr, Hf, in addition to high thermal conductivity, extremely high strength Other transition metal elements such as Ni and C
The thermal conductivity of r, Mn, Fe, Co, Ta, Nb, W, V or a compound thereof is similar to that of the Zr compound.

AlN is a compound of alkaline earth metals and rare earths
It has been known that it is effective as a sintering aid of and for increasing the thermal conductivity. These additives react with impurity oxygen unavoidably contained in AlN.For example, when the additive is CaO of alkaline earth metal compound, CaO.2Al ₂ after sintering is used.
It is considered that it becomes a sub-phase of O ₃ , CaO / Al ₂ O _3, etc., and becomes a product in which impurity oxygen is taken in, thereby increasing the thermal conductivity of the sintered body. Also, without such additives at all
When sintered with AlN alone, the impurity oxygen reacts with AlN and oxynitride of Al (Al (8/3 + x / 3) O _4-X N _X ) or spinel (Al ₉ O
It is known that even if ₃ N ₇ ) is converted into α-Al ₂ O ₃ or the like and densified by hot press sintering, the thermal conductivity is significantly reduced.

In general, in order to obtain an AlN sintered body having high thermal conductivity, it is a normal idea to prevent aluminum oxide from being mixed as a harmful impurity as much as possible. However, the research results of the inventors of the present invention show that addition of an aluminum oxide together with an alkaline earth metal compound and / or a rare earth compound and a transition metal compound does not impair the thermal conductivity at all,
On the contrary, it was found to improve the sinterability.

Further, the sintered body of the present invention is colored by containing the transition element which is the second additive, and its color tone can be variously changed depending on the kind of the additive element, its addition amount and combination. It is possible. That is, in general, the AlN raw material does not always have an Al / N molar ratio of 1 and is often Al-rich, and with such a raw material, the color of the sintered body is gray or black. Further, as the raw material is richer in Al, blackening progresses, while the thermal conductivity is usually lowered. Therefore, in the AlN raw material, the more the AlN molar ratio is as close as possible to 1 and the smaller the amount of impurities contained, the more the thermal conductivity is improved, and a white or translucent sintered body can be obtained. In other words, in the past, when trying to obtain a material with high thermal conductivity, the color of the sintered body was inevitably white or translucent, while when trying to obtain a colored material, the thermal conductivity decreased. Resulting in. On the other hand, in the present invention, by simultaneously adding the alkaline earth element and / or the rare earth element and the transition metal element, the Al / N molar ratio is close to 1, and the AlN raw material containing a small amount of impurities is used to obtain high heat. It is possible to obtain variously colored sintered bodies by appropriately selecting the type or combination of additive elements while ensuring the conductivity. For example, when Cr ₂ O ₃ or the like is added, it is colored dark gray, and when TiO ₂ is added, it is colored brown. On the other hand, Eu
Addition of ₂ O ₃ , Sm ₂ O _3, etc. gives a pale red color, and simultaneous addition of TiO ₂ and Cr ₂ O ₃ gives a dark gray to black color. Therefore, according to the present invention, it is possible to manufacture an AlN sintered body exhibiting a desired color tone. The AlN sintered body colored in this way has a higher emissivity of heat, so that the heat dissipation is further improved, and it blocks the light that causes malfunction of the semiconductor circuit, and coloring causes uneven sintering. It is possible to avoid such problems and to enhance the aesthetic appearance of the product.

In the present invention, the total amount of the alkaline earth metal compound and / or the rare earth compound and the aluminum oxide is 0.05 to
20% by weight is because if less than 0.05% by weight, the intended effect cannot be obtained, and if it exceeds 20% by weight, not only the heat resistance and mechanical strength are impaired, but also the thermal conductivity decreases. This is because there is a possibility that Further, the alkaline earth metal compound and the rare earth compound are preferably oxides, fluorides, nitrides and carbides, but there is no problem even if they become these compounds during firing. Further, as the aluminum oxide, it is possible to use Al ₂ O ₃ such as α-Al ₂ O ₃ and γ-Al ₂ O _3, or those which become these oxides during firing.

Next, one manufacturing method for obtaining the AlN sintered body of the present invention will be described.

First, after adding a predetermined amount of additives to the AlN powder and mixing using a ball mill or the like, in the case of pressureless sintering, a binder is added, and kneading, granulation and sizing are performed, and a mold, a hydrostatic press or Molding is performed by sheet molding. Next, the molded body is N ₂
The binder is removed by heating at around 700 ° C in a gas stream. Next, the molded body is set in a container of graphite or aluminum nitride, and pressureless sintering is performed at 1600 to 1850 ° C. in a N ₂ gas atmosphere.

On the other hand, in the case of hot press sintering, the raw materials mixed by the ball mill or the like are hot pressed at 1600 to 1800 ° C.

Example of Invention

Example 1 1.4% by weight of oxygen as an impurity was contained and the average particle size was 2.2.
3% by weight of Y ₂ O ₃ having an average particle size of 2.5 μm and 0.5% by weight of ZrO ₂ having an average particle size of 3 μm were added to 0.2 μ% of α-Al ₂ O _{3 having an} average particle size of 1.0 μm, The raw material was prepared by crushing and mixing using a ball mill. Then, 7% by weight of paraffin was added as a binder to this raw material, and the mixture was granulated, and then press-molded at a pressure of 300 kg / cm ² to obtain a green compact of 50 × 50 × 8 mm. This green compact was heated to 700 ° C in a nitrogen gas atmosphere.
To remove paraffin. Further, it was housed in a carbon container and sintered under atmospheric pressure at 1800 ° C. for 2 hours in a nitrogen gas atmosphere. The density of the obtained AlN sintered body was measured. Further, a disk having a diameter of 10 mm and a thickness of 2.5 mm was ground from the sintered body, and this was used as a test piece to measure the thermal conductivity by the laser flash method.

In addition, 6 square bars with a width of 4 mm, a thickness of 3 mm, and a length of 40 mm were ground from the obtained sintered body, and this was used as a test piece for bending strength measurement.
Three-point bending strength was measured under the conditions of a fulcrum distance of 20 mm and a crosshead speed of 0.5 mm / min. The results are shown in Table 1.

Examples 2 to 24, Comparative Examples 1 to 5 AlN sintered bodies were manufactured in the same manner as in the above-mentioned Examples by changing the types of AlN powder and the types of additives in various ways. Three-point bending strength was measured. The results are shown in Table 1 together with the particle size of each AlN powder, the oxygen content, the type of sintering additive, and the amount added.

Example 25 AlN powder having an average particle size of 2.8 μm and an impurity oxygen content of 1.8% by weight, Y ₂ O ₃ 5% by weight having an average particle size of 2.5 μm, and an average particle size of 1.0
0.2% by weight of γ-Al ₂ O ₃ and Ti having an average particle size of 2.1 μm
0.5% by weight of O ₂ was added, and the raw material was adjusted by grinding and mixing with a ball mill.

Then, 7% by weight of paraffin was added as a binder to this raw material, and the mixture was granulated and then press-molded under a pressure of 500 kg / cm ² to obtain a 30 × 30 × 8 mm green compact. The green compact was heated to a maximum temperature of 700 ° C. in a nitrogen stream to remove paraffin.

Next, set it in a carbon container, and in a nitrogen gas atmosphere
It was heated at each temperature of 1650, 1700, 1750, 1800, 1850, 1900 ° C. for 2 hours and sintered under normal pressure. The density of each obtained sintered body was measured. Further, a disk having a diameter of 10 mm and a thickness of 2.5 mm was cut out from each sintered body, and a thermal conductivity was measured by a laser flash method using this as a test piece. The results are shown in Table 2 and Table 1.
Shown as A in the figure.

Comparative Example 6 The AlN powder used in Example 25 was the same as Y used in Example 25.
₆ % normal pressure sintered bodies were manufactured in the same manner as in Example 25 by adding 5% by weight of ₂ O ₃ . The density of each sintered body was measured, and
The thermal conductivity was measured in the same manner as 25. Examples of these results
The results of 25 are also shown in Table 2 and FIG. 1B.

Example 26 3% by weight of Y ₂ O ₃ powder used in Example 25, 0.5% by weight of TiO ₂ used in Example 25 and γ− used in Example 25 were added to the AlN powder used in Example 22. Al ₂ O ₃ 0.2 wt%
Was added, and the raw materials were adjusted by crushing and mixing using a ball mill. This raw material powder was press-molded at a pressure of 500 kg / cm ² to obtain a green compact having a diameter of 12 mm and a pressure of 10 mm. Then, this pressure powder was put into a carbon mold, and hot press sintering was carried out in a nitrogen gas atmosphere at a temperature of 1700 ° C. under a pressure of 400 kg / cm ² . The density and thermal conductivity of the obtained sintered body were measured in the same manner as in Example 25, and the results are shown in the third element.

Examples 27-33, Comparative Examples 7-11 The above-mentioned Example 2 was carried out by changing the types of AlN powder and additives.
An AlN sintered body was manufactured by hot press sintering in the same manner as in 6. The density and thermal conductivity of each of the obtained sintered bodies were measured, and the results are shown in Table 3.

Example 34 Y (NO ₃ ) ₃ .6H ₂ O in the AlN powder used in Example 1 was 5% by weight in terms of Y ₂ O ₃ , and Ca (NO ₃ ) ₂ 4H ₂ O was 2 in terms of CaO.
0.5% by weight of Ti powder having an average particle size of 1.5 μm and 0.3% by weight of γ-Al ₂ O ₃ having an average particle size of 1.0 μm were added and pulverized and mixed using a ball mill to prepare a raw material powder.
In this _{case, Y (NO 3) 3 ·} 6H 2 O and _{Ca (NO 3) 2 · 4H} 2 O
Was dissolved in n-butanol and mixed with other powders.
Then, in the same manner as in Example 25, a green compact was formed, paraffin was removed, and the mixture was placed in a carbon container under a nitrogen gas atmosphere.
It was heated at 00 ° C for 1 hour to obtain a normal pressure sintered body. The density and thermal conductivity of the obtained sintered body were measured, and the results are shown in Table-3.

[Effects of the Invention] As described above, according to the present invention, it is possible to suppress the decrease in sinterability when using a low oxygen content AlN half, without impairing the original high thermal conductivity. Is.

Further, according to the present invention, AlN having high strength and high thermal conductivity
Sintered body and AlN with high strength, high thermal conductivity and light shielding property
It is also possible to manufacture a sintered body. Such a sintered body is suitable for applications such as a heat dissipation substrate for semiconductors, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in density and thermal conductivity of a sintered body with respect to each sintering temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Ueno 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research Institute Co., Ltd. (56) References JP-A-58-55376 (JP, A) JP-A-61-39918 (JP, A)

Claims (3)

[Claims] 1. An aluminum nitride having an oxygen content of 2% by weight or less and an average particle diameter of 5 μm or less as a main component, and 0.02 to 15 of a compound of (i) an alkaline earth element and / or a rare earth element in terms of oxide. weight%. (Ii) 0.02 to 3% by weight of at least one transition metal element selected from Ti, Hf, Ni, Cr, Mn, Fe, Co, Ta, Nb, W and V or a compound thereof. (Iii) 0.02 to 3% by weight of aluminum oxide. A method for producing an aluminum nitride sintered body having a thermal conductivity of 90 w / m · k or more, which comprises adding 0.06 to 15% by weight as an additive and sintering the mixture. 2. The method for producing an aluminum nitride sintered body according to claim 1, wherein the alkaline earth element is at least one of Ca, Ba and Sr. 3. The method for producing an aluminum nitride sintered body according to claim 1, wherein the rare earth element is at least one of Y, La and Ce.