JP2008195575A - Method for manufacturing aluminum oxide single crystal and aluminum oxide single crystal obtained by using the method - Google Patents

Method for manufacturing aluminum oxide single crystal and aluminum oxide single crystal obtained by using the method Download PDF

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JP2008195575A
JP2008195575A JP2007033231A JP2007033231A JP2008195575A JP 2008195575 A JP2008195575 A JP 2008195575A JP 2007033231 A JP2007033231 A JP 2007033231A JP 2007033231 A JP2007033231 A JP 2007033231A JP 2008195575 A JP2008195575 A JP 2008195575A
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single crystal
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aluminum oxide
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JP4905171B2 (en
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Toshiyuki Komi
利行 小見
Akira Terajima
彰 寺島
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Sumitomo Metal Mining Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently manufacturing an aluminum oxide single crystal having a high quality and suitable for an electronic component material or an optical component material by suppressing the occurrence of micro-bubbles. <P>SOLUTION: In the method for manufacturing the aluminum oxide single crystal by a melting/solidifying process, by which a raw material for the single crystal is charged into a crucible provided in a furnace of a single crystal manufacturing apparatus and is heated and melted, and a growing crystal is pulled from a melt of the raw material, when the raw material for the single crystal in heated and melted, the raw material for the single crystal is melted under conditions sufficient to remove the gas produced from the raw material for the single crystal by heating, in a nitrogen or inert gas atmosphere and at a furnace pressure of ≥0.1 MPa, then after introducing oxygen into the furnace, the melt of the raw material is further heated for at least 5 h under a mixed gas atmosphere comprising oxygen and nitrogen or an inert gas, thereafter pulling of a growing crystal is started, and the mixed gas atmosphere comprising oxygen and nitrogen or the inert gas is successively maintained even during crystal growth. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、酸化アルミニウム単結晶の製造方法及びこの方法を用いて得られる酸化アルミニウム単結晶に関し、より詳しくは、単結晶育成時のピットとマイクロバブルの発生を抑制して高品質な酸化アルミニウム単結晶を効率的に製造する方法及びこの方法を用いて得られる酸化アルミニウム単結晶に関するものである。   The present invention relates to a method for producing an aluminum oxide single crystal and an aluminum oxide single crystal obtained by using this method. More specifically, the present invention relates to a high-quality aluminum oxide single crystal by suppressing generation of pits and microbubbles during single crystal growth. The present invention relates to a method for efficiently producing a crystal and an aluminum oxide single crystal obtained by using this method.

酸化アルミニウム単結晶は、青色LEDや白色LEDを作製する際のエピ成長基板として多く利用されている。これらのLEDは、省エネルギーの観点で照明分野への普及が拡大することが予想されており多方面から注目されている。   Aluminum oxide single crystals are widely used as an epi growth substrate for producing blue LEDs and white LEDs. These LEDs are expected to spread in the lighting field from the viewpoint of energy saving, and are attracting attention from various fields.

酸化物単結晶の育成方法は様々あるが、LN、LT、YAGや酸化アルミニウムなどの酸化物単結晶材料の大部分は、その結晶特性や大口径の結晶が得られることから溶融固化法で育成されており、特にチョクラルスキー法(Cz法)は、技術的完成度が高いことから最も広く用いられている。
上記チョクラルスキー法による酸化物単結晶製造方法は、まずルツボに酸化物原料を充填し、高周波誘導加熱法や抵抗加熱法によりルツボを加熱し原料を溶融し、その後、所定の結晶方位に切り出した種結晶を原料融液表面に接触させ、種結晶を所定の回転速度で回転させながら所定の速度で上方に引き上げて単結晶を成長させる。
There are various methods for growing oxide single crystals, but the majority of oxide single crystal materials such as LN, LT, YAG and aluminum oxide are grown by melt solidification because their crystal characteristics and large diameter crystals can be obtained. In particular, the Czochralski method (Cz method) is most widely used because of its high technical perfection.
The oxide single crystal manufacturing method by the Czochralski method is as follows. First, the crucible is filled with an oxide raw material, and the crucible is heated by a high frequency induction heating method or a resistance heating method to melt the raw material, and then cut into a predetermined crystal orientation. The seed crystal is brought into contact with the surface of the raw material melt, and the seed crystal is pulled up at a predetermined speed while rotating the seed crystal at a predetermined rotation speed to grow a single crystal.

酸化アルミニウム単結晶をチョクラルスキー法で成長させると、結晶中に無数の微小な気泡が発生しやすい。この微小な気泡には、エピ成長基板となるウエハーをポリッシュ研磨したときに、ピットと呼ばれる直径数μmの微小な窪みを発現させる相対的に大きな気泡と光散乱レーザートモグラフ法(非特許文献1参照)によって、レーザー光を照射したときに雲状に確認できる相対的に小さな気泡であってマイクロバブルと呼ばれるものがある。これらの中でマイクロバブルの影響は、未だ確定されていないものの、ピットと共にLED特性に悪影響を与えると言われている。   When an aluminum oxide single crystal is grown by the Czochralski method, innumerable minute bubbles are likely to be generated in the crystal. These fine bubbles include a relatively large bubble that expresses a minute pit called a pit having a diameter of several μm when a wafer serving as an epitaxial growth substrate is polished, and a light scattering laser tomography method (see Non-Patent Document 1). ), There are relatively small bubbles called microbubbles which can be confirmed in a cloud shape when irradiated with laser light. Among these, although the influence of microbubbles has not been determined yet, it is said that the LED characteristics are adversely affected together with the pits.

結晶中の微細な気泡の原因は酸化アルミニウム単結晶を育成する際に、高温で原料が分解して生成した酸素原子(O)や酸素分子(O)が融液中に過飽和に存在し、これが育成した単結晶に取り込まれ、単結晶中の気泡となることが知られている。
そして、気泡の取り込みを回避するために、水素ガスや一酸化炭素ガスなどの還元性雰囲気で単結晶を育成することが提案されている(特許文献1参照)。
The cause of the fine bubbles in the crystal is that when the aluminum oxide single crystal is grown, oxygen atoms (O) and oxygen molecules (O 2 ) generated by decomposition of the raw material at high temperature are supersaturated in the melt, It is known that this is taken into the grown single crystal and becomes bubbles in the single crystal.
In order to avoid entrapment of bubbles, it has been proposed to grow a single crystal in a reducing atmosphere such as hydrogen gas or carbon monoxide gas (see Patent Document 1).

これにより融液中に存在する酸素原子(O)や酸素分子(O)が水素ガスや一酸化炭素ガスと反応して除去されるため、育成した単結晶中への気泡の取り込み量は確かに減少するが、育成された単結晶からウエハーを切り出し、ポリッシュ研磨したときに、ウエハー表面には多数のピットが存在しており、前記気泡の取り込みを十分に抑制することはできていなかった。 As a result, oxygen atoms (O) and oxygen molecules (O 2 ) present in the melt are removed by reaction with hydrogen gas or carbon monoxide gas, so the amount of bubbles taken into the grown single crystal is certain. However, when the wafer was cut out from the grown single crystal and polished and polished, a large number of pits were present on the surface of the wafer, so that the introduction of the bubbles could not be sufficiently suppressed.

また、融液に平衡固溶しているガス成分は、結晶化する固液界面で融液より排出される傾向にあり、界面近傍の融液は、ガス成分が過飽和となって気泡が生成されやすい。しかし、融液の対流を強化することによって界面付近で生じるガス成分の過飽和を抑制でき、結晶内へのガス成分の取り込み量を減少させられることが開示されている(非特許文献2参照)。
したがって、まず、原料に含まれるガス成分を融解前にできるだけ除去して融液中に存在する過飽和のガス成分を減少させ、融解後は対流を強化し攪拌の効果を増加させることで、単結晶育成時に結晶内に取り込まれる微小な気泡の量を少なくすれば、ピットやマイクロバブルの発生を抑えることができるものと考えられる。
In addition, gas components that are in equilibrium with the melt tend to be discharged from the melt at the solid-liquid interface where crystallization occurs, and in the melt near the interface, gas components become supersaturated and bubbles are generated. Cheap. However, it is disclosed that supersaturation of the gas component generated near the interface can be suppressed by enhancing the convection of the melt, and the amount of the gas component taken into the crystal can be reduced (see Non-Patent Document 2).
Therefore, first, the gas component contained in the raw material is removed as much as possible before melting, the supersaturated gas component present in the melt is reduced, and after melting, the convection is strengthened and the effect of stirring is increased. It is considered that the generation of pits and microbubbles can be suppressed by reducing the amount of minute bubbles taken into the crystal during growth.

そして、チタンが含まれる酸化アルミニウム単結晶の製造方法ではあるが、低酸素濃度雰囲気下で単結晶を育成すると、融液の対流が強化でき攪拌の効果を増加しうることが報告されている(特許文献2参照)。
ここには、酸素分圧が10−2〜10−7気圧というような低酸素濃度雰囲気下でチタンを含む酸化アルミニウム単結晶を育成すると、融液が融液表面において還元され、それに伴い表面張力の変化が生じ、表面張力流が誘起された結果、融液の自然対流と同方向の流れが著しく促進され攪拌の効果が増すと考えることができる。
And although it is a manufacturing method of the aluminum oxide single crystal containing titanium, when the single crystal is grown in a low oxygen concentration atmosphere, it is reported that the convection of the melt can be strengthened and the effect of stirring can be increased ( Patent Document 2).
Here, when an aluminum oxide single crystal containing titanium is grown in a low oxygen concentration atmosphere where the oxygen partial pressure is 10 −2 to 10 −7 atm, the melt is reduced on the surface of the melt, and accordingly the surface tension is increased. As a result of this change and the surface tension flow being induced, it can be considered that the flow in the same direction as the natural convection of the melt is remarkably accelerated and the effect of stirring is increased.

ところが、低酸素濃度雰囲気下で酸化アルミニウム単結晶を育成すると、成長界面は融液側に著しく凸形状となる傾向がある。このような状況の中で結晶育成を行った場合、結晶成長によってルツボ内の融液高さがある程度低下すると、成長界面の先端とルツボ底面とが接触し、それ以上は結晶成長を継続することが不可能となり、ルツボに充填した原料の量に対して得られる結晶をそれほど大きくできないという不具合が生じる。また、融液の自然対流と同方向の流れが著しく促進された結果、融液中の単結晶成長速度が早くなり、得られた結晶に結晶欠陥が発生しやすいという問題も生じる。
融液の過剰な対流を抑制する方法として、特許文献2では、成長結晶の回転数を、例えば、20回転/分以上、特に30〜120回転/分に上昇させることを提案している。しかしながら、このような手段では、結晶収率をあげることはできても、単結晶中への微細な気泡の発生を十分に抑制できない。
However, when an aluminum oxide single crystal is grown in a low oxygen concentration atmosphere, the growth interface tends to be significantly convex on the melt side. When crystal growth is performed in such a situation, if the melt height in the crucible decreases to some extent due to crystal growth, the tip of the growth interface and the bottom of the crucible come into contact with each other, and crystal growth continues beyond that. Is impossible, and there is a problem that the crystals obtained cannot be made so large with respect to the amount of raw material filled in the crucible. In addition, as a result of remarkably accelerating the flow in the same direction as the natural convection of the melt, the single crystal growth rate in the melt is increased, and there is a problem that crystal defects are likely to occur in the obtained crystal.
As a method for suppressing excessive convection of the melt, Patent Document 2 proposes increasing the rotational speed of the grown crystal to, for example, 20 revolutions / minute or more, particularly 30 to 120 revolutions / minute. However, with such means, although the crystal yield can be increased, the generation of fine bubbles in the single crystal cannot be sufficiently suppressed.

こうした問題を解決するために、本発明者等は高周波誘導加熱方式のチョクラルスキー法による酸化物単結晶の製造において、単結晶用原料(以下、単に原料ともいう)をルツボ内で加熱中および溶融中に炉体内を減圧し、原料に吸着または内包しているガスを強制的に排除すると単結晶へのガス成分の取り込み量が抑えられ、ピットやマイクロバブルの発生量を低減できることを見出している。   In order to solve such a problem, the present inventors in the production of an oxide single crystal by a high-frequency induction heating type Czochralski method, heating a raw material for a single crystal (hereinafter also simply referred to as a raw material) in a crucible and We found that if the pressure inside the furnace is reduced during melting and the gas adsorbed or contained in the raw material is forcibly removed, the amount of gas components taken into the single crystal can be suppressed, and the amount of pits and microbubbles generated can be reduced. Yes.

しかしながら、高周波誘導加熱方式のチョクラルスキー法による酸化物単結晶の製造において、特に発振周波数が10kHz以上の高周波発振機を用いた場合に、炉体内の圧力が0.01MPaよりも低くなると、ルツボの温度が1000℃に達したところで放電現象が発生し、電源の供給が不安定となり、原料溶解、更には結晶育成を行うことが出来なくなる。減圧によるガス成分の強制的な排除は、ピットやマイクロバブルの抑制に最も効果的な方法であるが、発振周波数が10kHz以上の誘導加熱単結晶製造装置に対しては提供できるものではなかった。
特開平04−132695号 特開平09−278592号 応用物理 第55巻 第6号 1986 P542−569 第28回結晶成長国内会議予稿集,22Pa2 1997 P15
However, in the production of an oxide single crystal by the Czochralski method using a high frequency induction heating method, particularly when a high frequency oscillator having an oscillation frequency of 10 kHz or more is used, if the pressure in the furnace is lower than 0.01 MPa, When the temperature reaches 1000 ° C., a discharge phenomenon occurs, the power supply becomes unstable, and it becomes impossible to melt the raw material and further grow the crystal. Forcibly removing gas components by depressurization is the most effective method for suppressing pits and microbubbles, but it cannot be provided for an induction heating single crystal manufacturing apparatus having an oscillation frequency of 10 kHz or more.
Japanese Patent Laid-Open No. 04-132695 JP 09-278592 A Applied Physics Vol.55 No.6 1986 P542-569 Proceedings of the 28th National Conference on Crystal Growth, 22Pa2 1997 P15

本発明の目的は、上記従来技術の課題に鑑み、単結晶育成時のピットとマイクロバブルの発生を抑制して高品質な酸化アルミニウム単結晶を効率的に製造する方法及びこの方法を用いて得られる酸化アルミニウム単結晶を提供することにある。   An object of the present invention is to provide a method for efficiently producing a high-quality aluminum oxide single crystal by suppressing the generation of pits and microbubbles during single crystal growth in view of the above-mentioned problems of the prior art, and this method. It is to provide an aluminum oxide single crystal.

本発明者らは、上記課題を解決するために鋭意研究を重ねた結果、原料加熱中は窒素または不活性ガスの雰囲気として特定圧力下で原料を溶融し、原料溶融と同時に酸素を導入し、酸素および窒素または不活性ガスとの混合雰囲気にして融液を一定時間維持することにより、減圧によるガス成分の強制的な排除を行うことができない誘導加熱単結晶製造装置や発振周波数が10kHz以上の誘導加熱単結晶製造装置を用いた場合でも、原料に吸着または内包されたガス成分が融液から放出され、ピットやマイクロバブルの発生量を低減できること、さらには、融液中における単結晶の成長速度を制御することによって成長界面が融液側に著しく凸となる現象を抑制して結晶欠陥を低減させ、原料からの固化率を向上させ効率的に単結晶を製造できることを見出し、本発明を完成するに至った。   As a result of intensive research to solve the above problems, the present inventors have melted the raw material under a specific pressure as an atmosphere of nitrogen or an inert gas during heating of the raw material, introduced oxygen simultaneously with the melting of the raw material, By maintaining the melt in a mixed atmosphere with oxygen and nitrogen or an inert gas for a certain period of time, an induction heating single crystal manufacturing apparatus that cannot forcibly eliminate gas components by decompression or an oscillation frequency of 10 kHz or more Even when an induction heating single crystal manufacturing device is used, the gas component adsorbed or contained in the raw material can be released from the melt, reducing the amount of pits and microbubbles generated, and further, the growth of the single crystal in the melt By controlling the speed, the phenomenon that the growth interface becomes significantly convex toward the melt side is suppressed, crystal defects are reduced, the solidification rate from the raw material is improved, and single crystals are efficiently produced. It found that kill, which resulted in the completion of the present invention.

すなわち、本発明の第1の発明によれば、単結晶製造装置の炉体内のルツボに単結晶用原料を入れて加熱溶融し、原料融液から成長結晶を引き上げる溶融固化法により酸化アルミニウム単結晶を製造する方法において、単結晶用原料を加熱溶融する際に、まず窒素または不活性ガス雰囲気下、炉内圧力0.1MPa以上において、加熱によって単結晶用原料から発生するガスを除去するに十分な条件で単結晶用原料を溶融し、次に炉内に酸素を導入し、酸素および窒素または不活性ガスからなる混合ガス雰囲気下、引き続き原料融液を5時間以上加熱してから成長結晶の引き上げを開始し、結晶成長中も引き続き酸素および窒素または不活性ガスの混合雰囲気で維持することを特徴とする酸化アルミニウム単結晶の製造方法が提供される。   That is, according to the first invention of the present invention, an aluminum oxide single crystal is obtained by a melt solidification method in which a raw material for a single crystal is placed in a crucible in a furnace of a single crystal manufacturing apparatus and heated and melted, and a grown crystal is pulled up from the raw material melt. When the single crystal raw material is heated and melted in the method for producing the first, it is sufficient to first remove the gas generated from the single crystal raw material by heating in a nitrogen or inert gas atmosphere at a furnace pressure of 0.1 MPa or more. The raw material for single crystal is melted under various conditions, oxygen is then introduced into the furnace, and the raw material melt is subsequently heated for 5 hours or more in a mixed gas atmosphere consisting of oxygen and nitrogen or an inert gas. There is provided a method for producing an aluminum oxide single crystal, characterized in that pulling is started and maintained in a mixed atmosphere of oxygen and nitrogen or an inert gas during crystal growth.

また、本発明の第2の発明によれば、第1の発明において、単結晶製造装置が、発振周波数10kHz以上の高周波誘導加熱方式の装置であることを特徴とする酸化アルミニウム単結晶の製造方法が提供される。
また、本発明の第3の発明によれば、第1の発明において、前記ルツボの材料がイリジウムであることを特徴とする酸化アルミニウム単結晶の製造方法が提供される。
また、本発明の第4の発明によれば、第1の発明において、単結晶用原料が、融点に達するまで10時間以上かけて加熱溶融されることを特徴とする酸化アルミニウム単結晶の製造方法が提供される。
さらに、本発明の第5の発明によれば、第1の発明において、混合雰囲気の酸素濃度が、0.01〜0.5容積%であることを特徴とする酸化アルミニウム単結晶の製造方法が提供される。
According to the second invention of the present invention, in the first invention, the single crystal manufacturing apparatus is a high frequency induction heating type apparatus having an oscillation frequency of 10 kHz or more. Is provided.
According to a third aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the first aspect, wherein the material of the crucible is iridium.
According to the fourth invention of the present invention, in the first invention, the single crystal raw material is heated and melted for 10 hours or more until the melting point reaches the melting point. Is provided.
Furthermore, according to the fifth aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the first aspect, wherein the oxygen concentration in the mixed atmosphere is 0.01 to 0.5% by volume. Provided.

一方、本発明の第6の発明によれば、第1〜5のいずれかの発明に係り、その製造方法によって得られる酸化アルミニウム単結晶が提供される。
また、本発明の第7の発明によれば、第6の発明において、散乱光強度(酸化アルミニウム単結晶の側面にレーザー光を照射して、入射するレーザー光に対して90゜の方向に放射される散乱光をCCDカメラに取り込み、画像処理装置で算出)が、130以下であることを特徴とする酸化アルミニウム単結晶が提供される。
On the other hand, according to the sixth invention of the present invention, there is provided an aluminum oxide single crystal obtained by the manufacturing method according to any one of the first to fifth inventions.
According to the seventh invention of the present invention, in the sixth invention, the scattered light intensity (irradiates the side surface of the aluminum oxide single crystal with laser light and emits it in the direction of 90 ° with respect to the incident laser light. The aluminum oxide single crystal is provided in which the scattered light is taken into a CCD camera and calculated by an image processing apparatus) is 130 or less.

本発明によれば、減圧によるガス成分の強制的な排除を行うことができない誘導加熱単結晶製造装置や発振周波数が10kHz以上の誘導加熱単結晶製造装置においてもピットやマイクロバブルの発生を抑制して効率的に高品質な酸化アルミニウム単結晶を製造することができる。
原料をルツボ内で加熱する際、窒素または不活性ガスのみの雰囲気とすることで、原料に吸着または内包しているガス成分は排除されるが、僅かに原料から融液中へのガス成分の取り込みが発生するが、原料溶融と同時に酸素および窒素または不活性ガスとの混合雰囲気にして、一定時間融液を維持することにより、残留したガス成分を排除でき、また、酸化アルミニウムの分解によるガス成分の生成が抑えられ、融液中での微小な気泡の発生を抑制できる。
また、融液中における単結晶の成長速度を制御することによって成長界面が融液側に著しく凸となる現象を抑制して結晶欠陥を低減させ、さらに凸度を低減させた結果、原料からの固化率を向上させ効率的に単結晶を製造することができる。
こうして得られた単結晶は、微小な気泡に起因するピット、マイクロバブル、結晶欠陥等が低減しており、さらにルツボ材料からのインクルージョン(内包物)がなくなるために、高品質なものとなり、この単結晶を用いれば優れた特性を有する電子部品材料、光学用部品材料を提供できる。
According to the present invention, the generation of pits and microbubbles can be suppressed even in an induction heating single crystal manufacturing apparatus that cannot forcibly exclude gas components due to reduced pressure or in an induction heating single crystal manufacturing apparatus with an oscillation frequency of 10 kHz or more. Thus, a high quality aluminum oxide single crystal can be produced efficiently.
When the raw material is heated in the crucible, the gas component adsorbed or contained in the raw material is eliminated by making the atmosphere of only nitrogen or inert gas, but the gas component from the raw material into the melt is slightly removed. Incorporation occurs, but when the raw material is melted and mixed with oxygen and nitrogen or an inert gas and the melt is maintained for a certain period of time, residual gas components can be eliminated, and gas generated by decomposition of aluminum oxide Generation of components is suppressed, and generation of minute bubbles in the melt can be suppressed.
In addition, by controlling the growth rate of the single crystal in the melt, the phenomenon that the growth interface becomes significantly convex toward the melt side is suppressed, crystal defects are reduced, and the degree of convexity is further reduced. A solid crystal can be improved and a single crystal can be produced efficiently.
The single crystal thus obtained has reduced pits, microbubbles, crystal defects, and the like due to minute bubbles, and further has no inclusion (inclusion) from the crucible material. If a single crystal is used, electronic component materials and optical component materials having excellent characteristics can be provided.

以下、本発明の酸化アルミニウム単結晶及びその製造方法について、図面を用いて詳細に説明する。   Hereinafter, the aluminum oxide single crystal of the present invention and the production method thereof will be described in detail with reference to the drawings.

1.酸化アルミニウム単結晶の製造方法
本発明の酸化アルミニウム単結晶の製造方法は、単結晶製造装置の炉体内のルツボに単結晶用原料を入れて加熱溶融し、原料融液から成長結晶を引き上げる溶融固化法により酸化アルミニウム単結晶を製造する方法において、単結晶用原料を加熱溶融する際に、まず窒素または不活性ガス雰囲気下、炉内圧力0.1MPa以上において、加熱によって単結晶用原料から発生するガスを除去するに十分な条件で単結晶用原料を溶融し、次に炉内に酸素を導入し、酸素および窒素または不活性ガスからなる混合ガス雰囲気下、引き続き原料融液を5時間以上加熱してから成長結晶の引き上げを開始し、結晶成長中も引き続き酸素および窒素または不活性ガスの混合雰囲気で維持することを特徴とする。
1. Method for Producing Aluminum Oxide Single Crystal The method for producing an aluminum oxide single crystal of the present invention comprises melting and solidifying a raw material for single crystal in a crucible in a furnace of a single crystal production apparatus, heating and melting, and pulling a growth crystal from the raw material melt. In the method of producing an aluminum oxide single crystal by the method, when the raw material for single crystal is heated and melted, it is first generated from the raw material for single crystal by heating in a nitrogen or inert gas atmosphere at a furnace pressure of 0.1 MPa or more. The raw material for single crystal is melted under conditions sufficient to remove the gas, oxygen is then introduced into the furnace, and the raw material melt is subsequently heated for 5 hours or longer in a mixed gas atmosphere consisting of oxygen and nitrogen or an inert gas. Thereafter, the growth crystal is started to be pulled up, and is maintained in a mixed atmosphere of oxygen and nitrogen or an inert gas during the crystal growth.

本発明においては、融液固化法により、単結晶製造装置の炉体内のルツボに原料を入れて加熱溶融し、原料融液から成長結晶を引き上げて酸化アルミニウム単結晶を製造するにあたり、単結晶製造装置の炉体内の酸素濃度をモニターする手段を設け、原料を加熱溶融した際に発生するガス成分の放出量を酸素濃度の挙動により確認し、原料溶融後の炉体内の雰囲気を酸素濃度0.01〜0.5容積%の範囲となるよう調整し、融液を維持する作業を行う。   In the present invention, when a raw material is put into a crucible in a furnace of a single crystal manufacturing apparatus and heated and melted by the melt solidification method, the grown crystal is pulled up from the raw material melt to produce an aluminum oxide single crystal. A means for monitoring the oxygen concentration in the furnace body of the apparatus is provided, and the amount of gas components released when the raw material is heated and melted is confirmed by the behavior of the oxygen concentration. Adjustment is made to be in the range of 01 to 0.5% by volume, and the work of maintaining the melt is performed.

酸化アルミニウム単結晶を育成するには、従来のチョクラルスキー法による酸化物単結晶育成装置を使用できる。例えば、貴金属で形成されたルツボと、ルツボの周囲に保温材としてアルミナなどで形成された炉材と、炉材の外側に加熱装置として発振周波数10kHz以上の高周波コイルが配置された高周波誘導加熱方式の装置が挙げられる。装置には、炉体内の酸素濃度をモニターする手段と、炉体内に酸素および窒素または不活性ガスの混合ガスを供給する手段と、必要により炉体内を減圧する手段が設けられる。   In order to grow an aluminum oxide single crystal, a conventional oxide single crystal growing apparatus based on the Czochralski method can be used. For example, a high-frequency induction heating method in which a crucible formed of a noble metal, a furnace material formed of alumina or the like as a heat insulating material around the crucible, and a high-frequency coil having an oscillation frequency of 10 kHz or more as a heating device outside the furnace material Apparatus. The apparatus is provided with means for monitoring the oxygen concentration in the furnace body, means for supplying a mixed gas of oxygen and nitrogen or an inert gas into the furnace body, and means for reducing the pressure inside the furnace body as necessary.

原料であるアルミナの融点は2000℃強であるため、ルツボとしてイリジウム製のものを用いることが好ましい。保温材としては、発泡ジルコニア等の断熱材を充填してもよい。ルツボの上方には、材料融液から単結晶を回転させながら引き上げるための引き上げ装置が設けられ、炉材の上方は遮蔽板で遮蔽されている。   Since the melting point of alumina as a raw material is slightly higher than 2000 ° C., it is preferable to use an iridium-made crucible. As the heat insulating material, a heat insulating material such as foamed zirconia may be filled. Above the crucible, a pulling device for pulling up the single crystal from the material melt is provided, and the furnace material is shielded by a shielding plate.

まず、ルツボに前記した原料を入れ、次に高周波コイルによってルツボを加熱し、原料を溶融して原料融液を得る。
炉体内の酸化アルミニウム原料を常圧状態で加熱溶融し、チョクラルスキー法で成長させると、結晶中に無数の微小な気泡が発生しやすい。酸化アルミニウム気泡の原因となるガスは、酸化アルミニウムの分解によっても発生するが、原料に吸着または内包しているガスが原料の溶融前に完全に除去されず融液内に残り、これが結晶に取り込まれて気泡となっているものが多い。そこで、原料をルツボ内で加熱中および溶融中に炉体内の雰囲気を窒素または不活性ガスのみとし、原料に吸着または内包しているガスを排除する。溶融した際に殆どのガス成分が放出されるが、一部のガス成分は融液に取り残される。このため、原料溶融と同時に酸素および窒素または不活性ガスとの混合雰囲気にして融液を維持させ、融液中の残留したガス成分を排除する。この工程では、融液を維持させる時間が短いと残留したガス成分の排除が不十分となるので、混合雰囲気下で5時間以上は融液を放置させる必要がある。
First, the raw material described above is put into a crucible, and then the crucible is heated by a high frequency coil to melt the raw material to obtain a raw material melt.
When the aluminum oxide raw material in the furnace body is heated and melted at normal pressure and grown by the Czochralski method, innumerable fine bubbles are likely to be generated in the crystal. The gas that causes aluminum oxide bubbles is also generated by the decomposition of aluminum oxide, but the gas adsorbed or contained in the raw material is not completely removed before melting of the raw material and remains in the melt, which is taken into the crystal Many of them are bubbles. Therefore, during heating and melting of the raw material in the crucible, the atmosphere in the furnace body is limited to nitrogen or an inert gas, and the gas adsorbed or contained in the raw material is excluded. Most gas components are released when melted, but some gas components are left behind in the melt. For this reason, the melt is maintained in a mixed atmosphere of oxygen and nitrogen or an inert gas simultaneously with melting of the raw material, and the remaining gas components in the melt are eliminated. In this step, if the time for maintaining the melt is short, the remaining gas components are not sufficiently removed. Therefore, it is necessary to leave the melt for 5 hours or longer in a mixed atmosphere.

本発明においては、単結晶用原料として通常の酸化アルミニウム粉末を用いる。酸化アルミニウム粉末は、実質的にAlとOの2元素からなる酸化アルミニウムである。また、目的とする酸化アルミニウム単結晶の種類に合わせて、AlとOのほかに、Ti、Cr、Si、Ca、Mgなどを含んでいてもよい。このうちSi、Ca、Mgなどは、焼結助剤の成分として不可避的に含まれうるが、その含有量は極力少ないことが望ましい。また、酸化アルミニウムの直径や密度は、特に制限されないが、取り扱い上、例えば、直径は、10mm以下、好ましくは5mm以下であるものがよく、密度は、5g/cm以下、好ましくは3g/cm以下であるものがよい。 In the present invention, an ordinary aluminum oxide powder is used as a raw material for a single crystal. The aluminum oxide powder is aluminum oxide substantially composed of two elements of Al and O. In addition to Al and O, Ti, Cr, Si, Ca, Mg, and the like may be included in accordance with the type of target aluminum oxide single crystal. Among these, Si, Ca, Mg and the like can be inevitably contained as components of the sintering aid, but the content is desirably as small as possible. The diameter and density of aluminum oxide are not particularly limited, but for handling, for example, the diameter is preferably 10 mm or less, preferably 5 mm or less, and the density is 5 g / cm 3 or less, preferably 3 g / cm. What is 3 or less is good.

通常の酸化アルミニウム粉末は、比表面積が5〜10m/g程度と大きいので、多くのガス成分が吸着または内包されているが、原料の融解後の融液放置により多くのガス成分が除去される。これは、比表面積が0.1〜10m/gの酸化アルミニウム焼結体である場合により効果的である。 Since normal aluminum oxide powder has a large specific surface area of about 5 to 10 m 2 / g, many gas components are adsorbed or encapsulated, but many gas components are removed by leaving the melt after the raw material is melted. The This is more effective when the aluminum oxide sintered body has a specific surface area of 0.1 to 10 m 2 / g.

クラックル原料は、ベルヌーイ法で製造された酸化アルミニウム単結晶原料を直径20mm以下に粉砕して得ているが、比表面積が0.1m/g未満と非常に小さく吸着ガスは少ない。しかし、酸化アルミニウム粉末を溶解し、得られた融液より作製された単結晶を粉砕しているため、その内部に無数の泡を内包することが多い。クラックル原料では、酸化アルミニウム融液の粘性が高く表面張力が大きいにも拘らず、加熱溶融後に融液放置することで、微小な気泡となって融液に溶解したガス成分もほとんど除去される。クラックル原料は、密度が高いので、酸化アルミニウム粉末など他の原料形態と比べると育成前の原料投入回数が少なくてすむ利点がある。 The crackle raw material is obtained by pulverizing an aluminum oxide single crystal raw material produced by the Bernoulli method to a diameter of 20 mm or less. However, the specific surface area is as small as less than 0.1 m 2 / g and the adsorbed gas is small. However, since the aluminum oxide powder is dissolved and the single crystal produced from the obtained melt is pulverized, innumerable bubbles are often included therein. In the crackle raw material, although the viscosity of the aluminum oxide melt is high and the surface tension is large, by leaving the melt after heating and melting, the gas components dissolved in the melt as microbubbles are almost removed. Since the crackle raw material has a high density, there is an advantage that the number of raw material inputs before the growth can be reduced as compared with other raw material forms such as aluminum oxide powder.

次に、本発明において好ましい原料溶融工程の態様を示す。原料溶融工程は、原料の加熱溶融段階と、融液の単結晶育成段階からなる。
原料の加熱溶融段階では、前記した通り、炉体内のルツボに原料を入れて、原料を加熱する際に、炉体内の雰囲気を窒素または不活性ガスのみとし、加熱によって原料から発生するガスを排除しながら溶融する。窒素または不活性ガス雰囲気下、炉内圧力0.1MPa以上において、加熱によって単結晶用原料から発生するガスを除去するに十分な条件に設定される。炉内圧力0.1MPa以上とは、炉内をことさら減圧することはしない、ということである。原料を融点に達するまで10時間以上、好ましくは12時間以上かけて徐々に加熱することが望ましい。原料が融点に達するまでの加熱速度は、特に制限されるわけではないが、急速に加熱せずに長時間かけて徐々に加熱するほうが、融液へのガスの取り込みを抑えることができる。
Next, a preferred embodiment of the raw material melting step in the present invention will be shown. The raw material melting step includes a raw material heating and melting stage and a melt single crystal growing stage.
In the heating and melting stage of the raw material, as described above, when the raw material is put in the crucible in the furnace and the raw material is heated, the atmosphere in the furnace is limited to nitrogen or an inert gas, and the gas generated from the raw material by heating is eliminated. While melting. Under a nitrogen or inert gas atmosphere, at a furnace pressure of 0.1 MPa or more, conditions are set sufficient to remove gas generated from the single crystal raw material by heating. The furnace pressure of 0.1 MPa or more means that the furnace is not further depressurized. It is desirable that the raw material is gradually heated over 10 hours or more, preferably 12 hours or more until reaching the melting point. The heating rate until the raw material reaches the melting point is not particularly limited, but it is possible to suppress gas incorporation into the melt by heating gradually over a long time without rapidly heating.

炉体内の原料温度が1000℃以上になると、原料に吸着しているガス成分が排出されるため炉体内の酸素濃度は徐々に増加していく。原料溶融時になると炉体内の酸素濃度が一時的に100〜1000ppmと増加するが、融液中の微小なガス成分は残留するために炉体内の酸素濃度は徐々に低下していく。
原料溶融後、2050〜2150℃において加熱を続けると、融液中の微小なガス成分は融液の自然対流により徐々に排出されていくが、炉体内の酸素濃度が100ppm以下になると原料である酸化アルミニウムの分解により新たなガス成分の発生を引き起こす。一方、炉体内の酸素濃度が0.5容積%以上の雰囲気では、融液の自然対流が弱まり、融液中の微小なガス成分が排出され難くなるばかりでなく、雰囲気中の酸素とルツボ材であるイリジウムとの反応が発生し、イリジウムインクルージョンの原因となる。そのため、炉体内の酸素濃度は0.01〜0.5容積%の範囲となるよう調整し、5時間以上融液を維持させると残留した微小なガス成分を排除することができる。溶融から5時間以上、好ましくは8時間以上、より好ましくは10時間以上経過後、種子結晶を融液表面に接触させて回転させながら結晶成長を開始させる。単結晶育成中もこの酸素濃度を維持することにより、酸化アルミニウムの分解も抑制できる。5時間未満では融液中に残留した微小なガス成分を十分に排除することができない。
When the temperature of the raw material in the furnace becomes 1000 ° C. or higher, the gas component adsorbed on the raw material is discharged, so that the oxygen concentration in the furnace gradually increases. When the raw material is melted, the oxygen concentration in the furnace body temporarily increases to 100 to 1000 ppm. However, since minute gas components in the melt remain, the oxygen concentration in the furnace body gradually decreases.
If the heating is continued at 2050 to 2150 ° C. after the raw material is melted, minute gas components in the melt are gradually discharged by natural convection of the melt, but it is a raw material when the oxygen concentration in the furnace body becomes 100 ppm or less. The decomposition of aluminum oxide causes the generation of new gas components. On the other hand, in an atmosphere where the oxygen concentration in the furnace body is 0.5% by volume or more, the natural convection of the melt is weakened, and not only the minute gas components in the melt are hardly discharged, but also the oxygen in the atmosphere and the crucible material Reaction with iridium, which is a cause of iridium inclusion. Therefore, if the oxygen concentration in the furnace body is adjusted to be in the range of 0.01 to 0.5% by volume and the melt is maintained for 5 hours or more, the remaining minute gas components can be eliminated. After elapse of 5 hours or more, preferably 8 hours or more, more preferably 10 hours or more after melting, crystal growth is started while rotating the seed crystal in contact with the melt surface. By maintaining this oxygen concentration even during single crystal growth, decomposition of aluminum oxide can be suppressed. If it is less than 5 hours, minute gas components remaining in the melt cannot be sufficiently removed.

単結晶の育成は、原料溶融工程で炉体内の雰囲気を下記のように調整する以外は常法に従い、回転数や引き上げ速度を調整してネック部および肩部を形成し、引き続き直胴部を形成する。このとき、放射温度計などを用いて単結晶と原料融液との界面近傍における融液表面の温度を測定することが好ましい。結晶形状の調節は、育成中の結晶重量を測定し直径や育成速度などを計算によって導き出し、回転速度や引き上げ速度を調整して行う。また、結晶重量の変化を高周波誘導コイル投入電力にフィードバックして融液温度をコントロールできる。   Single crystal growth is carried out by adjusting the rotation speed and pulling speed to form the neck and shoulders according to the usual method, except that the atmosphere in the furnace is adjusted as follows in the raw material melting process. Form. At this time, it is preferable to measure the temperature of the melt surface in the vicinity of the interface between the single crystal and the raw material melt using a radiation thermometer or the like. The crystal shape is adjusted by measuring the weight of the crystal during growth, deriving the diameter, growth speed, and the like by calculation, and adjusting the rotation speed and pulling speed. Also, the melt temperature can be controlled by feeding back the change in crystal weight to the power applied to the high frequency induction coil.

融液中に含まれる過剰なガス成分が減少した結果、単結晶育成時に結晶内に析出する気泡がなくなる。なお、単結晶の育成時も、酸素濃度を0.01〜0.5容積%、好ましくは0.1〜0.3容積%の範囲に調整することで、融液中における単結晶の成長速度を制御し結晶欠陥を低減させ、また、成長界面が融液側に著しく凸とならず、原料に対して得られる結晶がそれほど大きくできないという不具合は解消される。   As a result of the reduction of excess gas components contained in the melt, there are no bubbles that precipitate in the crystal during single crystal growth. Even during the growth of the single crystal, the growth rate of the single crystal in the melt is adjusted by adjusting the oxygen concentration to a range of 0.01 to 0.5% by volume, preferably 0.1 to 0.3% by volume. This reduces the defect that the crystal defects are reduced by controlling the crystal defects, and the growth interface is not significantly convex on the melt side, so that the crystal obtained with respect to the raw material cannot be made so large.

このようにして、特定の酸素濃度雰囲気下で原料を溶融、融液放置させたのち単結晶を育成することで、原料の形態を問わず、また、減圧によるガス成分の強制的な排除を行うことができない安価な誘導加熱単結晶製造装置や発振周波数が10kHz以上の誘導加熱単結晶製造装置であっても、一定時間以上の融液放置を行うという簡単な操作で、融液の表面に吸着あるいは内包しているガス成分が容易に排除できる。その結果、融液中に含まれる過剰なガスが減少し、単結晶育成時に結晶内に取り込まれる微小な気泡を少なくなくすることができ、得られる単結晶中のピットやマイクロバルブを少なくすることができる。   In this way, a raw material is melted and allowed to stand in a specific oxygen concentration atmosphere, and then a single crystal is grown, thereby forcibly eliminating gas components regardless of the form of the raw material and by decompression. Even if it is an inexpensive induction heating single crystal manufacturing device that cannot be used or an induction heating single crystal manufacturing device with an oscillation frequency of 10 kHz or more, it can be adsorbed on the surface of the melt by a simple operation of leaving the melt for a certain period of time. Alternatively, the contained gas component can be easily removed. As a result, excess gas contained in the melt is reduced, so that the number of minute bubbles taken into the crystal during single crystal growth can be reduced, and the number of pits and microvalves in the resulting single crystal can be reduced. Can do.

育成した単結晶に取り込まれた微小な気泡の度合いは、前記非特許文献1に示されている光散乱レーザートモグラフ法に従って、レーザー光を結晶に照射し、その散乱光を観察できる。図1に光散乱を測定する光学系を示す。円筒状に加工した酸化アルミニウム単結晶1に波長532nm、出力500mWのレーザー光2を照射し、照射したレーザー光2の入射方向に対して90°の方向に放射される散乱光3をCCDカメラ4に取り込み、画像処理装置5で強度を0〜255までの256階調に処理し、画像中の結晶部分40mm四方の強度平均を散乱光強度として算出する。このとき、レーザー光の偏光方向は、CCDカメラの方向に対して90°となる直線偏光とする。
次に、育成された単結晶を切断し、例えば直径3インチ程度のウエハーを得、研磨してピットの発生状況を確認する。前記非表面積が異なるいずれの原料を用いた場合でも、ピットの発生状況は平均数十個、あるいはそれ以下となる。
The degree of minute bubbles taken into the grown single crystal can be observed by irradiating the crystal with laser light and observing the scattered light according to the light scattering laser tomography method disclosed in Non-Patent Document 1. FIG. 1 shows an optical system for measuring light scattering. The aluminum oxide single crystal 1 processed into a cylindrical shape is irradiated with a laser beam 2 having a wavelength of 532 nm and an output of 500 mW, and scattered light 3 emitted in a direction of 90 ° with respect to the incident direction of the irradiated laser beam 2 is emitted from the CCD camera 4. The image processing apparatus 5 processes the intensity to 256 gradations from 0 to 255, and calculates the average intensity of the 40 mm square of the crystal portion in the image as the scattered light intensity. At this time, the polarization direction of the laser light is linearly polarized light that is 90 ° with respect to the direction of the CCD camera.
Next, the grown single crystal is cut to obtain a wafer having a diameter of about 3 inches, for example, and polished to check the occurrence of pits. When any raw material having a different non-surface area is used, the average number of pits generated is tens or less.

2.酸化アルミニウム単結晶
本発明の酸化アルミニウム単結晶は、上記の製造方法により得られるアルミニウム及び酸素の2元素を含む単結晶である。
2. Aluminum oxide single crystal The aluminum oxide single crystal of the present invention is a single crystal containing two elements of aluminum and oxygen obtained by the above production method.

更には、前記の光散乱レーザートモグラフ法によって求められる散乱光強度が130以下まで減少した単結晶である。散乱光強度は、円筒状に加工された酸化アルミニウム単結晶の側面にレーザー光を照射して、入射するレーザー光に対して90゜の方向に放射される散乱光をCCDカメラに取り込み、画像処理装置で算出する。   Furthermore, it is a single crystal in which the scattered light intensity obtained by the light scattering laser tomography method is reduced to 130 or less. The scattered light intensity is measured by irradiating the side surface of the aluminum oxide single crystal processed into a cylindrical shape with laser light and capturing the scattered light emitted in the direction of 90 ° with respect to the incident laser light into the CCD camera. Calculate with the device.

この単結晶からウエハーをスライスし、ポリッシュ研磨することで、エピ結晶基板とすることができる。単結晶中には微小な気泡が極めて少ないので、ピット数もマイクロバブルも少なくなり優れた特性を有する電子部品材料、光学用部品材料を提供できる。   By slicing a wafer from this single crystal and polishing it, an epicrystal substrate can be obtained. Since there are very few microbubbles in the single crystal, the number of pits and microbubbles is reduced, and electronic component materials and optical component materials having excellent characteristics can be provided.

以下に、実施例を用いて、本発明をさらに詳細に説明するが、本発明は、これら実施例によって限定されるものではない。   Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

〔微小な気泡の測定〕
育成した単結晶に取り込まれた微小な気泡は、光散乱レーザートモグラフ法に従って観察した。具体的には、図1に示したように、円筒状に加工した酸化アルミニウム単結晶の側面にレーザー光を照射して、酸化アルミニウム単結晶端面より射出される散乱光をCCDカメラに取り込み、画像処理装置で散乱光強度を算出した。すなわち、円筒状に加工した酸化アルミニウム単結晶1に波長532nm、出力500mWのレーザー光2を照射し、照射したレーザー光2の入射方向に対して90°の方向に放射される散乱光3をCCDカメラ4に取り込み、画像処理装置5で強度を0〜255までの256階調に処理し、画像中の結晶部分40mm四方の強度平均を散乱光強度として算出した。この結果、散乱光強度が130以下であれば、育成した単結晶中のマイクロバブル量は少ないと判断される。
[Measurement of minute bubbles]
Microscopic bubbles taken into the grown single crystal were observed according to the light scattering laser tomography method. Specifically, as shown in FIG. 1, the side surface of the cylindrically processed aluminum oxide single crystal is irradiated with laser light, and the scattered light emitted from the end surface of the aluminum oxide single crystal is taken into the CCD camera, and an image is obtained. The scattered light intensity was calculated by the processing apparatus. That is, the aluminum oxide single crystal 1 processed into a cylindrical shape is irradiated with a laser beam 2 having a wavelength of 532 nm and an output of 500 mW, and the scattered light 3 emitted in the direction of 90 ° with respect to the incident direction of the irradiated laser beam 2 is converted into a CCD. The image was taken into the camera 4 and processed by the image processing apparatus 5 into 256 gradations from 0 to 255, and the intensity average of the 40 mm square of the crystal portion in the image was calculated as the scattered light intensity. As a result, if the scattered light intensity is 130 or less, it is determined that the amount of microbubbles in the grown single crystal is small.

〔ピットの評価〕
育成した単結晶から50枚のウエハーをスライスし、ポリッシュ研磨して、ピットがどの程度あるか測定した。ピット数は少ないほど良好な単結晶が育成されていることを示している。
[Evaluation of pits]
Fifty wafers were sliced from the grown single crystal and polished to measure how many pits there were. The smaller the number of pits, the better the single crystal is grown.

〔実施例1〕
発振周波数12kHz、出力40kWの高周波誘導加熱方式の育成炉を用い、イリジウム製ルツボに4N(99.99%)のAl原料を10kg投入した。装置には、炉体内を減圧する手段、減圧度をモニターする手段、および酸素および窒素または不活性ガスの混合ガス供給手段を設けている。Al原料はクラックルとよばれるもので、これはベルヌーイ法で育成した酸化アルミニウム単結晶を20mm角程度の大きさに粉砕したものである。
原料を加熱する前に真空引きを開始し、炉内の圧力が20Paまで減圧したところで真空引きを停止して窒素ガスを導入した。炉内の圧力が0.1MPaに達した後は、窒素ガスのみ毎分3リットルの流量でフローさせ、原料の加熱を開始した。この時の炉内の酸素濃度は0.1ppmであった。この原料が融点に達するまで12時間かけて徐々に加熱し、原料が1000℃以上となったところで酸素濃度の上昇が始まり、原料溶融時、炉内の酸素濃度は200ppmから400ppmに急上昇した。原料溶融から30分後、酸素濃度が300ppmまで減少したところで炉内に酸素ガスを導入し、酸素および窒素の混合雰囲気とし、炉内の酸素濃度が0.3容積%となるよう調整した。
原料溶融から5時間後、a軸方向に切り出した酸化アルミニウム単結晶を種結晶として用い、種結晶を融液近くまで降下させた。この種結晶を毎分2回転の速度で回転させながら徐々に降下させ、種結晶の先端を融液に接触させて温度を徐々に降下させながら引上速度2mm/hで種結晶を上昇させて結晶成長を行った。
その結果、直径101mm、直胴部の長さ136mmで目視では気泡が観察されない結晶を得た。また、結晶底部の成長界面を測定したところ、51mm凸であった。さらに、この結晶に波長532nmのレーザーを照射し、結晶内部の散乱光を観察したところ、ほとんど散乱はなく(散乱光強度112)、結晶内部に微小な気泡が少ないことがわかった。また、この結晶をウエハーにし、ポリッシュ研磨したところ微小な窪みは確認できなかった。
[Example 1]
Using a high-frequency induction heating type growth furnace with an oscillation frequency of 12 kHz and an output of 40 kW, 10 kg of 4N (99.99%) Al 2 O 3 raw material was charged into an iridium crucible. The apparatus includes means for reducing the pressure inside the furnace, means for monitoring the degree of pressure reduction, and means for supplying a mixed gas of oxygen and nitrogen or an inert gas. The Al 2 O 3 raw material is called crackle, which is obtained by grinding an aluminum oxide single crystal grown by Bernoulli method to a size of about 20 mm square.
Vacuuming was started before the raw material was heated, and when the pressure in the furnace was reduced to 20 Pa, the vacuuming was stopped and nitrogen gas was introduced. After the pressure in the furnace reached 0.1 MPa, only nitrogen gas was allowed to flow at a flow rate of 3 liters per minute to start heating the raw material. At this time, the oxygen concentration in the furnace was 0.1 ppm. The raw material was gradually heated over 12 hours until the raw material reached the melting point, and when the raw material reached 1000 ° C. or higher, the oxygen concentration started to increase. When the raw material melted, the oxygen concentration in the furnace rapidly increased from 200 ppm to 400 ppm. Thirty minutes after the melting of the raw material, when the oxygen concentration decreased to 300 ppm, oxygen gas was introduced into the furnace to prepare a mixed atmosphere of oxygen and nitrogen, and the oxygen concentration in the furnace was adjusted to 0.3% by volume.
Five hours after melting the raw material, the aluminum oxide single crystal cut in the a-axis direction was used as a seed crystal, and the seed crystal was lowered to near the melt. The seed crystal is gradually lowered while rotating at a speed of 2 revolutions per minute, and the seed crystal is raised at a pulling speed of 2 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. Crystal growth was performed.
As a result, a crystal having a diameter of 101 mm and a length of the straight body portion of 136 mm, in which bubbles were not observed visually, was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 51 mm convex. Furthermore, when this crystal was irradiated with a laser having a wavelength of 532 nm and the scattered light inside the crystal was observed, it was found that there was almost no scattering (scattered light intensity 112), and there were few fine bubbles inside the crystal. Further, when this crystal was made into a wafer and polished, no minute depressions could be confirmed.

〔実施例2〕
原料として粉末の酸化アルミニウム原料を用いた以外は実施例1と同様にして行った。その結果、直径99mm、直胴部の長さ118mmで目視では気泡が観察されない結晶が得られた。また、結晶底部の成長界面を測定したところ、41mm凸であった。さらに、この結晶に波長532nmのレーザーを照射し結晶内部の散乱光を観察したところ、ほとんど散乱はなく(散乱光強度126)、結晶内部に微小な気泡が少ないことがわかった。また、この結晶をウエハーにしポリッシュ研磨したところ微小な窪みは確認できなかった。
[Example 2]
This was carried out in the same manner as in Example 1 except that powdered aluminum oxide raw material was used as the raw material. As a result, a crystal having a diameter of 99 mm and a length of the straight body portion of 118 mm, in which no bubbles were observed visually, was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 41 mm convex. Furthermore, when this crystal was irradiated with a laser having a wavelength of 532 nm and the scattered light inside the crystal was observed, it was found that there was almost no scattering (scattered light intensity 126), and there were few fine bubbles inside the crystal. Further, when this crystal was polished on a wafer and fine polishing was not confirmed.

〔実施例3〕
粉末の酸化アルミニウム原料を用い、原料溶融後、炉内の酸素濃度が0.1容積%となるよう調整した以外は実施例1と同様にして行った。
その結果、直径99mm、直胴部の長さ123mmで目視では気泡が観察されない結晶が得られた。また、結晶底部の成長界面を測定したところ、60mm凸であった。さらに、この結晶に波長532nmのレーザーを照射し、結晶内部の散乱光を観察したところ、ほとんど散乱はなく(散乱光強度59)、結晶内部に微小な気泡が少ないことがわかった。また、この結晶をウエハーにしポリッシュ研磨したところ微小な窪みは確認できなかった。
Example 3
This was carried out in the same manner as in Example 1 except that a powdered aluminum oxide raw material was used and the oxygen concentration in the furnace was adjusted to 0.1% by volume after melting the raw material.
As a result, a crystal having a diameter of 99 mm and a length of the straight body portion of 123 mm, in which no bubbles were observed visually, was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 60 mm convex. Further, when this crystal was irradiated with a laser having a wavelength of 532 nm and the scattered light inside the crystal was observed, it was found that there was almost no scattering (scattered light intensity 59), and there were few fine bubbles inside the crystal. Further, when this crystal was polished on a wafer and fine polishing was not confirmed.

〔比較例1〕
比較のために、原料を加熱溶融する際、加熱開始から炉内に酸素を導入して酸素および窒素の混合雰囲気とし、炉内の酸素濃度が0.3容積%となるよう調整した以外は実施例1と同様にして行った。
その結果、得られた結晶は、直径119mm、直胴部の長さ120mm、結晶底部の成長界面は49mm凸であった。この結晶に波長532nmのレーザーを照射し結晶内部の散乱光を観察したところ、散乱光強度が強く(散乱光強度140)、結晶内部に微小な気泡が多いことがわかった。また、この結晶をウエハーにしポリッシュ研磨したところ微小な窪みが数多く観察された。
[Comparative Example 1]
For comparison, when the raw material was heated and melted, it was implemented except that oxygen was introduced into the furnace from the start of heating to create a mixed atmosphere of oxygen and nitrogen, and the oxygen concentration in the furnace was adjusted to 0.3% by volume. Performed as in Example 1.
As a result, the obtained crystal had a diameter of 119 mm, a straight body length of 120 mm, and a growth interface at the bottom of the crystal was 49 mm convex. When this crystal was irradiated with a laser having a wavelength of 532 nm and the scattered light inside the crystal was observed, it was found that the scattered light intensity was strong (scattered light intensity 140) and that there were many fine bubbles inside the crystal. Further, when this crystal was polished on a wafer, many fine dents were observed.

〔比較例2〕
比較のために、加熱開始から結晶育成終了まで、炉内に酸素を導入せずに窒素のみの低酸素濃度雰囲気とした以外は実施例1と同様にして行った。
その結果、直径99mm、直胴部の長さ121mmの結晶を得たところで、ルツボ底に結晶底部が接触したので育成を中止した。結晶底部の成長界面を測定したところ、73mm凸と大きかった。この結晶に波長532nmのレーザーを照射し、結晶内部の散乱光を観察した。微小な散乱はほとんど観察されなかったが(散乱光強度49)、比較的大きな散乱体が観測され、結晶内部に微小な気泡が少ないがインクルージョン(内包物)が存在する可能性があることがわかった。
また、この結晶をウエハーにしポリッシュ研磨したところ、微小な窪みは確認できなかったが、どのウエハーにも差し渡し数μmの大きさの突起状異物が数個程度ウエハー上に観測された。これをEPMAで分析したところイリジウムであった。低酸素分圧下で育成すると、アレキサンドライトやGGGではイリジウムのインクルージョンが発生することが報告されているが、酸化アルミニウムでも同様に観測されることがわかった。
[Comparative Example 2]
For comparison, the same procedure as in Example 1 was performed from the start of heating to the end of crystal growth except that a low oxygen concentration atmosphere containing only nitrogen was used without introducing oxygen into the furnace.
As a result, when a crystal having a diameter of 99 mm and a length of the straight body portion of 121 mm was obtained, the growth was stopped because the crystal bottom contacted the crucible bottom. When the growth interface at the bottom of the crystal was measured, it was as large as 73 mm convex. The crystal was irradiated with a laser having a wavelength of 532 nm, and the scattered light inside the crystal was observed. Although very little scatter was observed (scattered light intensity 49), a relatively large scatterer was observed, and it was found that there might be inclusions (inclusions) although there are few fine bubbles inside the crystal. It was.
Further, when this crystal was polished and polished on a wafer, minute dents could not be confirmed, but several protruding foreign matters having a size of several μm were observed on the wafer. When this was analyzed by EPMA, it was iridium. It has been reported that when grown under a low oxygen partial pressure, iridium and GGG generate iridium inclusions, but aluminum oxide is also observed in the same manner.

〔比較例3〕
比較のために、原料溶融後の融液放置を3時間で行った以外は実施例1と同様にして行った。
その結果、得られた結晶は、直径104mm、直胴部の長さ126mm、結晶底部の成長界面は44mm凸であった。この結晶に波長532nmのレーザーを照射し結晶内部の散乱光を観察したところ、散乱光強度が強く(散乱光強度138)、結晶内部に微小な気泡が多いことがわかった。また、この結晶をウエハーにしポリッシュ研磨したところ微小な窪みが数多く観察された。
[Comparative Example 3]
For comparison, the same procedure as in Example 1 was performed except that the melt was allowed to stand after melting for 3 hours.
As a result, the obtained crystal had a diameter of 104 mm, a length of the straight body portion of 126 mm, and a growth interface at the bottom of the crystal having a convexity of 44 mm. When this crystal was irradiated with a laser having a wavelength of 532 nm and the scattered light inside the crystal was observed, the scattered light intensity was high (scattered light intensity 138), and it was found that there were many fine bubbles inside the crystal. Further, when this crystal was polished on a wafer, many fine dents were observed.

以上説明したように、実施例では、原料をルツボ内で加熱し溶融するまでは炉体内の雰囲気を窒素または不活性ガスのみとし、原料溶融後は酸素濃度が0.01〜0.5容積%となるような酸素および窒素または不活性ガスとの混合雰囲気にして一定時間融液を維持することにより、原料に吸着または内包しているガスを排除することができ、結晶成長開始後も引き続き酸素および窒素または不活性ガスとの混合雰囲気で行うことで、融液に含まれる過剰なガスが減少した。その結果、単結晶へのガスの取り込みを抑えることができ、また、低酸素濃度下での育成ではないためインクルージョンの発生を抑制することができた。さらには成長界面が融液側に著しく凸となる現象を抑制して結晶欠陥を低減させ、また、凸度を低減させたことで原料からの固化率を増加でき、効率的に単結晶を製造することができた。
これに対して、比較例では、原料加熱、結晶育成を通して酸素を含む雰囲気で行った場合、原料に吸着または内包しているガスを十分に排除することができなかった。また、加熱中は窒素または不活性ガスのみとし、原料溶融後は酸素を含む混合雰囲気で結晶育成を行った場合でも、融液の放置時間が短いと融液内のガスを十分に排除することができなかった。炉体内の雰囲気を原料加熱から結晶育成を通して窒素または不活性ガスのみの低酸素濃度下で行った場合、イリジウムのインクルージョンが発生した。
As described above, in the examples, until the raw material is heated and melted in the crucible, the atmosphere in the furnace body is only nitrogen or inert gas, and after the raw material is melted, the oxygen concentration is 0.01 to 0.5% by volume. By maintaining the melt in a mixed atmosphere with oxygen and nitrogen or an inert gas for a certain period of time, it is possible to eliminate the gas adsorbed or contained in the raw material, and continue to oxygen after the start of crystal growth. Further, the excess gas contained in the melt was reduced by carrying out in a mixed atmosphere with nitrogen or an inert gas. As a result, it was possible to suppress gas uptake into the single crystal and to suppress inclusion because it was not grown under a low oxygen concentration. Furthermore, the phenomenon that the growth interface becomes extremely convex toward the melt side is suppressed to reduce crystal defects, and the degree of solidification from the raw material can be increased by reducing the degree of convexity, thereby efficiently producing a single crystal. We were able to.
On the other hand, in the comparative example, when it was performed in an atmosphere containing oxygen through raw material heating and crystal growth, the gas adsorbed or contained in the raw material could not be sufficiently eliminated. In addition, only nitrogen or inert gas should be used during heating, and even if the crystal growth is performed in a mixed atmosphere containing oxygen after melting the raw material, the gas in the melt should be sufficiently eliminated if the melt is left for a short time. I could not. When the atmosphere inside the furnace was heated from the raw material to crystal growth under a low oxygen concentration of only nitrogen or inert gas, iridium inclusions were generated.

育成された単結晶にレーザー光を照射し、光散乱を測定する光学系を用いて結晶中の微小気泡(マイクロバルブ)を調べる手段を示す説明図である。It is explanatory drawing which shows the means to investigate the micro bubble (micro valve | bulb) in a crystal | crystallization using the optical system which irradiates a laser beam to the grown single crystal and measures light scattering.

符号の説明Explanation of symbols

1 育成された単結晶
2 レーザー光
3 散乱光
4 CCDカメラ
5 画像処理装置
DESCRIPTION OF SYMBOLS 1 Grown single crystal 2 Laser light 3 Scattered light 4 CCD camera 5 Image processing device

Claims (7)

単結晶製造装置の炉体内のルツボに単結晶用原料を入れて加熱溶融し、原料融液から成長結晶を引き上げる溶融固化法により酸化アルミニウム単結晶を製造する方法において、
単結晶用原料を加熱溶融する際に、まず窒素または不活性ガス雰囲気下、炉内圧力0.1MPa以上において、加熱によって単結晶用原料から発生するガスを除去するに十分な条件で単結晶用原料を溶融し、次に炉内に酸素を導入し、酸素および窒素または不活性ガスからなる混合ガス雰囲気下、引き続き原料融液を5時間以上加熱してから成長結晶の引き上げを開始し、結晶成長中も引き続き酸素および窒素または不活性ガスの混合雰囲気で維持することを特徴とする酸化アルミニウム単結晶の製造方法。
In a method for producing an aluminum oxide single crystal by a melt solidification method in which a raw material for a single crystal is put into a crucible in a furnace of a single crystal production apparatus and heated and melted, and a growth crystal is pulled up from the raw material melt.
When the single crystal raw material is heated and melted, first, in a nitrogen or inert gas atmosphere, at a furnace pressure of 0.1 MPa or higher, the single crystal raw material is heated under conditions sufficient to remove the gas generated from the single crystal raw material by heating. The raw material is melted, oxygen is then introduced into the furnace, the raw material melt is subsequently heated for 5 hours or longer in a mixed gas atmosphere consisting of oxygen and nitrogen or an inert gas, and then the growth crystal is pulled up. A method for producing an aluminum oxide single crystal, which is continuously maintained in a mixed atmosphere of oxygen and nitrogen or an inert gas during growth.
単結晶製造装置が、発振周波数10kHz以上の高周波誘導加熱方式の装置であることを特徴とする請求項1に記載の酸化アルミニウム単結晶の製造方法。   2. The method for producing an aluminum oxide single crystal according to claim 1, wherein the single crystal production apparatus is a high frequency induction heating type apparatus having an oscillation frequency of 10 kHz or more. 前記ルツボの材料がイリジウムであることを特徴とする請求項1に記載の酸化アルミニウム単結晶の製造方法。   The method for producing an aluminum oxide single crystal according to claim 1, wherein the material of the crucible is iridium. 単結晶用原料が、融点に達するまで10時間以上かけて加熱溶融されることを特徴とする請求項1に記載の酸化アルミニウム単結晶の製造方法。   The method for producing an aluminum oxide single crystal according to claim 1, wherein the single crystal raw material is heated and melted for 10 hours or more until the melting point reaches the melting point. 混合雰囲気の酸素濃度が、0.01〜0.5容積%であることを特徴とする請求項1に記載の酸化アルミニウム単結晶の製造方法。   The method for producing an aluminum oxide single crystal according to claim 1, wherein the oxygen concentration in the mixed atmosphere is 0.01 to 0.5% by volume. 請求項1〜5のいずれかの製造方法によって得られる酸化アルミニウム単結晶。   The aluminum oxide single crystal obtained by the manufacturing method in any one of Claims 1-5. 散乱光強度(酸化アルミニウム単結晶の側面にレーザー光を照射して、入射するレーザー光に対して90゜の方向に放射される散乱光をCCDカメラに取り込み、画像処理装置で算出)が、130以下であることを特徴とする請求項6に記載の酸化アルミニウム単結晶。   Scattered light intensity (irradiated with laser light on the side surface of the aluminum oxide single crystal, and the scattered light emitted in the direction of 90 ° with respect to the incident laser light is taken into the CCD camera and calculated by the image processing apparatus) is 130. The aluminum oxide single crystal according to claim 6, wherein:
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