【発明の詳細な説明】[Detailed description of the invention]
〔発明の技術分野〕
本発明は窒化アルミニウム焼結体に関する。
〔発明の技術的背景とその問題点〕
窒化アルミニウム（AlN）は常温から高温ま
での強度が高く（焼結体の曲げ強さは通常40Kg／
ml以上）、化学的耐性にも優れているため、耐熱
材料として用いられる一方、その高熱伝導性、高
電気絶縁性を利用して半導体装置の放熱板材料と
しても有望視されている。こうしたAlNは通常、
融点を持たず、2200℃以上の高温で分解するた
め、薄膜などの用途を除いては焼結体として用い
られる。
ところで、AlN焼結体は従来より常圧焼結法、
ホツトプレス法により製造されている。常圧焼結
法では高密度化の目的でアルカリ土類金属酸化物
又は希土類酸化物などの化合物を焼結助剤として
添加することが多い。ホツトプレス法では、
AlN単独又は助剤が添加されたAlNを用い、高
温高圧下にて焼結する。
しかしながら、ホツトプレス法では複雑な形状
の焼結体の製造が難しく、しかも生産性が低く、
高コストとなるという問題がある。一方、常圧焼
結法ではホツトプレス法のような問題を解消でき
るものの、得られたAlN焼結体の熱伝導率は
AlNの理論熱伝導率が320W／ｍ・ｋであるのに
対し、高々40W／ｍ・ｋと低い。又、ホツトプレ
ス法で造られたAlN焼結体のうち助剤が添加さ
れたAlNを原料とするものも、熱伝導率が
40W／ｍ・ｋ程度と低い。
〔発明の目的〕
本発明は熱伝導率が著しく改善されかつ、高密
度なAlN焼結体を提供しようとするものである。
〔発明の概要〕
本発明者らは、各種助剤が添加されたAlN焼
結体の焼結性および熱伝導率について種々、実験
検討した結果、希土類のフツ化物が高密度化及び
高熱伝導率化用助剤として最適であることを見い
出した。
従来、希土類の酸化物が高密度化に対して有効
であることはよく知られていたが、フツ化物にお
いても同等又はそれ以上の高密度化が可能であ
り、しかも熱伝導率が大幅に上昇することを見い
出したものである。
そこで、本発明者らは上記究明結果を踏えて更
に鋭意研究したところ、希土類のフツ化物を0.01
〜20重量％を添加して焼結したAlN焼結体にお
いて熱伝導率が著しく改善され、かつ高密度化す
ることを確認した。
なお希土類元素のフツ化物が上述の如き効果を
有することは、これまで全く知られておらずその
メカニズムに関しては現在、まだ不明の点が多
い。
本発明者がＸ線回折により焼結体の構成相を調
査したところ、明らかに酸化物を助剤として用い
た場合と異なつていることが判明した。すなわち
希土類としてＹ（イツトリウム）を例にして述べ
ると、YF3とY2O3とを各々添加した焼結体の構
成相を調査したところ、Y2O3ではAlN相の他に
3Y2O3・5Al2O3が生成されるが、YF3ではY2O3
の場合と全く異なる未知相が検出された。
しかしながら熱伝導率の相異が上記構成相の差
に起因するものであるか否かは必ずしも明らかで
はない。またAlNは合成過程そして粉砕過程な
どで酸素を混入しやすいが、本発明においては、
不純物酸素量が20重量％以内であれば何ら発明の
効果を防げるものではない。
以上述べた如く、本発明はAlNを主成分とし
て、これに希土類のフツ化物を0.01〜20重量％添
加して焼結することを特徴とするものである。
添加する範囲を上記の如く限定した理由は、そ
の量が0.01重量％未満では所期の効果が得られ
ず、かといつてその量が20重量％を超えると耐熱
性・高強度性が損なわれるばかりか、熱伝導性も
低下する。
次に、本発明のAlN焼結体を得るための一製
造方法を説明する。
まず、AlN粉末に所定量の希土類フツ化物を
添加し、ボールミル等を用いて混合した後、常圧
焼結の場合はバインダーを加え、混練、造粒、整
粒を行ない、金型、静水圧プレス或いはシート成
形により成形を行なう。つづいて、成形体をN2
ガス気流中で700℃前後で加熱してバインダーを
除去する。次いで、成形体を黒鉛又は窒化アルミ
ニウムの容器にセツトし、N2ガス雰囲気中にて
1600〜1850℃で常圧焼結を行なう。
一方、ホツトプレス焼結の場合は前記ボールミ
ル等で混合した原料を1600〜1800℃でホツトプレ
スする。
〔発明の実施例〕
次に、本発明の実施例を説明する。
実施例 １
まず、平均粒径1μｍのAlN粉末に、同じく平
均粒径1μｍのYF3粉末３重量％を添加し、ボール
ミルを用いて粉砕・混合を行なつて原料を調整し
た。
つづいて、この原料を直径10mmのカーボン型に
充てんし、圧力400Kg／cm3、温度1800℃の条件で
１時間ホツトプレスを行なつてAlN焼結体を製
造した。
比較例 １
実施例１で用いたAlN粉末のみを、実施例１
と同様な方法によりAlN焼結体を製造した。
しかして、上記実施例１及び比較例１により得
たAlN焼結体を夫々約3.5mmの厚さに研摩した後、
レーザフラツシユ法によつて室温での熱伝導率を
測定した。その結果、実施例１のAlN焼結体で
は82W／ｍ・ｋであつたのに対し、比較例−１の
AlN焼結体では32W／ｍ・ｋであつた。
又、Ｘ線回折で各焼結体の構成相を調査したと
ころ、実施例−１のAlN焼結体ではAlN相及び
上述した未知相が比較例−１ではAlN相以外に
かなりな量の酸窒化物相が夫々検出された。
実施例 ２
実施例−１で用いたAlN粉末にYF33重量％を
添加し、ボールミルを用いて粉砕・混合した。つ
づいて、これらの原料に夫々パラフインを７重量
％添加し、造粒した後、300Kg／cm3の圧力でプレ
ス成形して30×30×３mm圧粉体とした。これを、
窒素ガス雰囲気で最高700℃まで加熱してパラフ
インを除去した。
次にカーボン型中にセツトし、窒素ガス雰囲気
下で1800℃、２時間加熱して常圧焼結した。
比較例 ２
実施例−２で用いたAlN粉末のみを、実施例
１と同様な方法によりAlN焼結体を製造した。
しかして、上記実施例２及び比較例２により得
たAlN焼結体を夫々約3.5mmの厚さに研摩した後、
レーザフラツシユ法によつて室温での熱伝導率を
測定した。その結果、実施例２のAlN焼結体で
は80W／ｍ・ｋであつたのに対し、比較例−２の
AlN焼結体では15W／ｍ・ｋであつた。
又、各々の焼結体の密度を測定したところ、実
施例２の焼結体は3.28ｇ／cm3、比較例−２の焼結
体は2.88ｇ／cm3であつた。
実施例 ３
実施例−２と同様な方法でYF3の代りに各々種
の希土類元素のフツ化物を３重量％ずつ加えた
AlN焼結体を製造した。
得られた各AlN焼結体の密度、並びに熱伝導
率を調べた。
その結果を第１表に示した。
[Technical Field of the Invention] The present invention relates to an aluminum nitride sintered body. [Technical background of the invention and its problems] Aluminum nitride (AlN) has high strength from room temperature to high temperature (the bending strength of a sintered body is usually 40 kg/
ml or more), and has excellent chemical resistance, so it is used as a heat-resistant material, and its high thermal conductivity and high electrical insulation properties make it a promising material for heat sinks in semiconductor devices. These AlNs are typically
Since it has no melting point and decomposes at high temperatures of 2200°C or higher, it is used as a sintered body except for applications such as thin films. By the way, AlN sintered bodies have traditionally been produced by pressureless sintering,
Manufactured using the hot press method. In the pressureless sintering method, compounds such as alkaline earth metal oxides or rare earth oxides are often added as sintering aids for the purpose of increasing density. In the hot press method,
Sintering is performed under high temperature and pressure using AlN alone or AlN with additives added. However, with the hot press method, it is difficult to manufacture sintered bodies with complex shapes, and productivity is low.
There is a problem of high cost. On the other hand, although the pressureless sintering method can solve the problems of the hot pressing method, the thermal conductivity of the obtained AlN sintered body is
The theoretical thermal conductivity of AlN is 320W/m・k, while it is low at 40W/m・k. Also, among the AlN sintered bodies made by the hot pressing method, those made from AlN with additives added have low thermal conductivity.
Low at around 40W/m・k. [Object of the Invention] The present invention aims to provide an AlN sintered body with significantly improved thermal conductivity and high density. [Summary of the Invention] As a result of various experimental studies on the sinterability and thermal conductivity of AlN sintered bodies to which various auxiliary agents have been added, the present inventors have found that rare earth fluorides have high density and high thermal conductivity. It has been found that it is most suitable as a chemical auxiliary agent. It has been well known that rare earth oxides are effective for increasing density, but fluorides can also achieve the same or higher density, and have significantly increased thermal conductivity. This is what I discovered. Therefore, the present inventors conducted further intensive research based on the above investigation results, and found that 0.01
It was confirmed that the thermal conductivity of the AlN sintered body sintered with ~20% by weight was significantly improved and the density increased. It should be noted that it has not been known until now that rare earth element fluorides have the above-mentioned effects, and there are currently many points that are still unclear regarding the mechanism. When the present inventor investigated the constituent phases of the sintered body by X-ray diffraction, it was found that the phase was clearly different from that when an oxide was used as an auxiliary agent. In other words, using Y (yttrium) as an example of a rare earth element, when we investigated the constituent phases of a sintered body to which YF 3 and Y 2 O 3 were added, we found that in Y 2 O 3 , in addition to the AlN phase,
3Y 2 O 3・5Al 2 O 3 is generated, but YF 3 produces Y 2 O 3
An unknown phase completely different from that in the case was detected. However, it is not necessarily clear whether the difference in thermal conductivity is due to the difference in the constituent phases. In addition, AlN is easily mixed with oxygen during the synthesis process and pulverization process, but in the present invention,
If the amount of impurity oxygen is within 20% by weight, the effects of the invention will not be prevented in any way. As described above, the present invention is characterized in that 0.01 to 20% by weight of a rare earth fluoride is added to AlN as a main component and then sintered. The reason for limiting the range of addition as described above is that if the amount is less than 0.01% by weight, the desired effect will not be obtained, whereas if the amount exceeds 20% by weight, heat resistance and high strength will be impaired. Not only that, but thermal conductivity also decreases. Next, one manufacturing method for obtaining the AlN sintered body of the present invention will be explained. First, a predetermined amount of rare earth fluoride is added to AlN powder, mixed using a ball mill, etc. In the case of pressureless sintering, a binder is added, kneading, granulation, and sizing are performed, followed by molding, isostatic pressure Molding is performed by press or sheet molding. Next, the molded body was heated with N2
The binder is removed by heating at around 700℃ in a gas stream. Next, the compact was placed in a graphite or aluminum nitride container and heated in an N2 gas atmosphere.
Pressureless sintering is performed at 1600-1850℃. On the other hand, in the case of hot press sintering, the raw materials mixed in the ball mill or the like are hot pressed at 1600 to 1800°C. [Embodiments of the Invention] Next, embodiments of the present invention will be described. Example 1 First, 3% by weight of YF 3 powder having an average particle size of 1 μm was added to AlN powder having an average particle size of 1 μm, and the mixture was ground and mixed using a ball mill to prepare a raw material. Subsequently, this raw material was filled into a carbon mold with a diameter of 10 mm, and hot-pressed for 1 hour at a pressure of 400 Kg/cm 3 and a temperature of 1800° C. to produce an AlN sintered body. Comparative Example 1 Only the AlN powder used in Example 1 was used in Example 1.
An AlN sintered body was manufactured using the same method as described above. After polishing the AlN sintered bodies obtained in Example 1 and Comparative Example 1 to a thickness of about 3.5 mm,
Thermal conductivity at room temperature was measured by the laser flash method. As a result, the AlN sintered body of Example 1 had a power of 82 W/m・k, while that of Comparative Example-1.
In the case of the AlN sintered body, it was 32 W/m·k. In addition, when the constituent phases of each sintered body were investigated by X-ray diffraction, it was found that the AlN sintered body of Example 1 contained the AlN phase and the above-mentioned unknown phase, while the comparative example 1 contained a considerable amount of acid in addition to the AlN phase. Nitride phases were detected respectively. Example 2 3% by weight of YF 3 was added to the AlN powder used in Example-1, and the mixture was ground and mixed using a ball mill. Subsequently, 7% by weight of paraffin was added to each of these raw materials, granulated, and then press-molded at a pressure of 300 Kg/cm 3 to obtain a compact of 30×30×3 mm. this,
Paraffin was removed by heating to a maximum of 700°C in a nitrogen gas atmosphere. Next, it was set in a carbon mold and heated at 1800° C. for 2 hours in a nitrogen gas atmosphere to perform normal pressure sintering. Comparative Example 2 An AlN sintered body was manufactured in the same manner as in Example 1 using only the AlN powder used in Example-2. After polishing the AlN sintered bodies obtained in Example 2 and Comparative Example 2 to a thickness of about 3.5 mm,
Thermal conductivity at room temperature was measured by the laser flash method. As a result, the AlN sintered body of Example 2 had a power of 80 W/m・k, while that of Comparative Example-2.
In the case of the AlN sintered body, it was 15 W/m·k. Further, when the density of each sintered body was measured, the density of the sintered body of Example 2 was 3.28 g/cm 3 , and the density of the sintered body of Comparative Example 2 was 2.88 g/cm 3 . Example 3 In the same manner as in Example 2, 3% by weight of each type of rare earth element fluoride was added in place of YF3 .
An AlN sintered body was manufactured. The density and thermal conductivity of each AlN sintered body obtained were investigated. The results are shown in Table 1.
【表】
実施例 ４
YF3を各々0.1，0.5，１，５，10，20重量％添
加した各混合物から、実施例−１と同様な方法に
より、ホツトプレス焼結体を６ケ製造した。
同じく、上記の各混合物から実施例−２と同様
な方法により、常圧焼結体を６ケ製造した。
得られた各AlN焼結体の密度、並びに熱伝導
率を調べた。その結果を第２表に示した。[Table] Example 4 Six hot-pressed sintered bodies were produced from each mixture to which 0.1, 0.5, 1, 5, 10, and 20% by weight of YF 3 were added in the same manner as in Example-1. Similarly, six pressureless sintered bodies were manufactured from each of the above mixtures in the same manner as in Example-2. The density and thermal conductivity of each AlN sintered body obtained were investigated. The results are shown in Table 2.
〔発明の効果〕〔Effect of the invention〕
以上詳述した如く、本発明によれば熱伝導率が
40W／ｍ・ｋ以上を半導体装置の放熱板等に有効
な高熱伝導性高密度窒化アルミニウム焼結体を提
供できる。
As detailed above, according to the present invention, the thermal conductivity is
It is possible to provide a highly thermally conductive, high-density aluminum nitride sintered body that is effective for heat dissipation plates of semiconductor devices of 40 W/m·k or more.