JP2018135228A - METHOD FOR GROWING LiTaO3 SINGLE CRYSTAL AND METHOD FOR PROCESSING LiTaO3 SINGLE CRYSTAL - Google Patents

METHOD FOR GROWING LiTaO3 SINGLE CRYSTAL AND METHOD FOR PROCESSING LiTaO3 SINGLE CRYSTAL Download PDF

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JP2018135228A
JP2018135228A JP2017029683A JP2017029683A JP2018135228A JP 2018135228 A JP2018135228 A JP 2018135228A JP 2017029683 A JP2017029683 A JP 2017029683A JP 2017029683 A JP2017029683 A JP 2017029683A JP 2018135228 A JP2018135228 A JP 2018135228A
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litao
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single crystal
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platinum crucible
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英一郎 西村
Eiichiro Nishimura
英一郎 西村
圭吾 干川
Keigo Hoshikawa
圭吾 干川
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Sumitomo Metal Mining Co Ltd
Shinshu University NUC
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Shinshu University NUC
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Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a LiTaOsingle crystal, using a LiTaOcrystal raw material (melting point of 1650°C) having a congruent composition and a platinum crucible (melting point of 1760°C), having melting points close to each other.SOLUTION: A LiTaOsingle crystal is grown by a unidirectional solidification crystal growth method of charging a LiTaOseed crystal 7 into a lower portion in a platinum crucible 1, charging a LiTaOcrystal raw material 8 having a congruent composition on the LiTaOseed crystal, forming a temperature gradient in the vertical direction in the platinum crucible by a carbon resistance heater 3 and dissolving an upper portion of the LiTaOseed crystal and the LiTaOcrystal raw material to solidify the melt. Since the carbon resistance heater 3 excellent in temperature control is used, the platinum crucible having a melting point close to that of the LiTaOcrystal raw material having a congruent composition can be applied.SELECTED DRAWING: Figure 1

Description

本発明は、ＬｉＴａＯ3単結晶の育成方法とこの方法により育成されたＬｉＴａＯ3単結晶の処理方法に係り、特に、白金製坩堝を用いてＬｉＴａＯ3単結晶を育成する方法の改良に関するものである。 The present invention relates to a processing method of LiTaO 3 single crystal growing method as LiTaO 3 single crystal grown by this method, more particularly, to an improvement of a method for growing a LiTaO 3 single crystal using a platinum crucible .

ＬｉＴａＯ3単結晶は強誘電体単結晶として知られ、携帯電話の表面弾性波（Surface Acoustic Wave、以下ＳＡＷと略記する）デバイス用の圧電基板や、焦電センサー、圧電センサー、振動アクチュエーター等に幅広く使用されており、近年、携帯電話の高機能化や、周波数バンド数の増加等により、益々、需要が増加している。また、ＬｉＴａＯ3単結晶は、非線形光学結晶として、大容量高速通信網用の光変調器や波長変換素子等の光応用製品にも使用されている。 LiTaO 3 single crystal is known as a ferroelectric single crystal and is widely used in piezoelectric substrates for surface acoustic wave (hereinafter abbreviated as SAW) devices for mobile phones, pyroelectric sensors, piezoelectric sensors, vibration actuators, etc. In recent years, demand has been increasing more and more due to the high functionality of mobile phones and the increase in the number of frequency bands. LiTaO 3 single crystals are also used as nonlinear optical crystals in optical application products such as optical modulators and wavelength conversion elements for large-capacity high-speed communication networks.

ＬｉＴａＯ3単結晶は、一般的にチョクラルスキー法（以後、ＣＺ法と略称する場合がある）を用いて育成されている。ＣＺ法は、坩堝内の原料融液に種結晶を接触させ、種結晶を回転させながらゆっくりと上昇させることで種結晶と同一方位の単結晶を育成する方法である。 The LiTaO 3 single crystal is generally grown using the Czochralski method (hereinafter sometimes abbreviated as CZ method). The CZ method is a method for growing a single crystal having the same orientation as the seed crystal by bringing the seed crystal into contact with the raw material melt in the crucible and slowly raising the seed crystal while rotating the seed crystal.

ところで、ＣＺ法を用いた従来のＬｉＴａＯ3単結晶の育成方法は、多結晶化、熱歪によるクラック発生、転位列の発生による結晶性低下等の問題があるため、高収率で安定して高品質単結晶を育成するための種々の提案がなされている。 By the way, the conventional LiTaO 3 single crystal growth method using the CZ method has problems such as polycrystallization, crack generation due to thermal strain, and crystallinity degradation due to the generation of dislocation arrays, so that it is stable at a high yield. Various proposals for growing high quality single crystals have been made.

例えば、特許文献１では、育成される結晶の直胴部直径（ｄ）と坩堝の内径（Ｄ）の比（ｄ／Ｄ）を０．８〜０．９として育成する方法が提案されている。しかし、この方法による単結晶育成の成功率は９０％程度であり、９０％を越える高収率で安定して高品質のＬｉＴａＯ3単結晶を育成することは困難であった。 For example, Patent Document 1 proposes a method for growing a crystal body to be grown with a ratio (d / D) of a straight body diameter (d) of a crystal to be grown and an inner diameter (D) of a crucible being 0.8 to 0.9. . However, the success rate of single crystal growth by this method is about 90%, and it has been difficult to stably grow a high quality LiTaO 3 single crystal at a high yield exceeding 90%.

また、ＣＺ法による単結晶の育成方法では育成炉内の温度勾配を高く保つ必要があることから、タンタル酸リチウム（ＬｉＴａＯ3；融点１６５０℃）とその融点が近い白金製坩堝（Ｐｔ：融点１７６０℃）の使用が難しいため、特許文献１〜２に記載されているようにイリジウム（Ｉｒ：融点２４１０℃）製坩堝が利用される。しかし、白金製の坩堝に較べ高価となる問題が存在した。 Further, in the method for growing a single crystal by the CZ method, it is necessary to maintain a high temperature gradient in the growth furnace, so that a platinum crucible (Pt: melting point 1760) having a melting point close to that of lithium tantalate (LiTaO 3 ; melting point 1650 ° C.). Since the use of iridium (Ir: melting point: 2410 ° C.) is used, as described in Patent Documents 1 and 2, it is difficult to use. However, there is a problem that it is more expensive than a platinum crucible.

一方、特許文献３においては、イリジウム製の坩堝より安価な白金製坩堝を用いて垂直ブリッジマン（ＶＢ）法によりＬｉＴａＯ3単結晶を育成する方法が提案されている。しかし、この方法では、ストイキオメトリ組成［酸化リチウム：酸化タンタル＝０．５０：０．５０（モル比）］の結晶原料が適用され、かつ、原料融液が収容される白金製の上方坩堝と種結晶が配置される白金製の下方坩堝を用いてＬｉＴａＯ3単結晶を育成する必要があり、ストイキオメトリ組成の原料融液を上方坩堝から下方坩堝に逐次補給する作業を要する分、ＬｉＴａＯ3単結晶の育成作業が煩雑となる問題が存在した。 On the other hand, Patent Document 3 proposes a method of growing a LiTaO 3 single crystal by a vertical Bridgman (VB) method using a platinum crucible that is cheaper than an iridium crucible. However, in this method, a platinum upper crucible in which a crystal raw material having a stoichiometric composition [lithium oxide: tantalum oxide = 0.50: 0.50 (molar ratio)] is applied and a raw material melt is accommodated. LiTaO 3 single crystal must be grown using a platinum lower crucible in which a seed crystal is placed, and LiTaO 3 is required to sequentially replenish a raw melt of stoichiometric composition from the upper crucible to the lower crucible. There was a problem that the growth of three single crystals was complicated.

また、特許文献４でも、イリジウム製の坩堝より安価な白金製坩堝を用いて垂直ブリッジマン（ＶＢ）法によりニオブ酸リチウム単結晶（ＬｉＮｂＯ3；融点１２５０℃）を育成する方法が提案されている。この方法では、上記ストイキオメトリ組成とは異なるコングルエント組成［Ｌｉ2Ｏ/Ｎｂ2Ｏ5＝４８．５/５１．５］の結晶原料が適用されているため、白金製坩堝内の下部にＬｉＮｂＯ3種結晶を充填し、該ＬｉＮｂＯ3種結晶上にＬｉＮｂＯ3結晶原料を充填して結晶原料を融解させることでＬｉＮｂＯ3種結晶上にＬｉＮｂＯ3単結晶を育成することが可能となる。そして、ストイキオメトリ組成の原料融液を上方坩堝から下方坩堝に逐次補給する作業を必要とする特許文献３の方法に較べ、特許文献４の方法は、育成作業の簡便化が図れる顕著な利点を有している。 Patent Document 4 also proposes a method of growing lithium niobate single crystal (LiNbO 3 ; melting point 1250 ° C.) by a vertical Bridgman (VB) method using a platinum crucible that is cheaper than an iridium crucible. . In this method, since a crystal material having a congruent composition [Li 2 O / Nb 2 O 5 = 48.5 / 51.5] different from the stoichiometric composition is applied, LiNbO is formed in the lower part of the platinum crucible. the three crystals are filled, it is possible to grow a LiNbO 3 single crystal on LiNbO 3 seed crystal by melting the crystal raw material filling the LiNbO 3 crystal material on said LiNbO 3 seed crystal. And compared with the method of patent document 3 which requires the operation | work which replenishes the raw material melt of stoichiometric composition from an upper crucible to a lower crucible sequentially, the method of patent document 4 is a remarkable advantage which can attain simplification of a cultivation operation | work. have.

そこで、ＬｉＮｂＯ3単結晶の育成方法に係る特許文献４を応用してＬｉＴａＯ3単結晶を育成する方法が考えられる。すなわち、コングルエント組成のＬｉＴａＯ3結晶原料を適用し、かつ、白金製坩堝内の下部にＬｉＴａＯ3種結晶を充填し、該ＬｉＴａＯ3種結晶上にＬｉＴａＯ3結晶原料を充填してＬｉＴａＯ3単結晶を育成する方法が考えられる。 Therefore, a method of growing a LiTaO 3 single crystal by applying Patent Document 4 relating to a method of growing a LiNbO 3 single crystal is conceivable. That is, by applying the LiTaO 3 crystal raw material of congruent composition, and, filling the lower part LiTaO 3 or crystal platinum crucible, a LiTaO 3 single crystal by filling a LiTaO 3 crystal material onto the LiTaO 3 or crystal A method of training is conceivable.

しかし、特許文献３で用いられるストイキオメトリ組成の場合には、ＬｉＴａＯ3結晶原料の融点が１５５０℃程度と低いため、白金（Ｐｔ：融点１７６０℃）製坩堝を利用することができるが、ＬｉＴａＯ3結晶原料がコングルエント組成の場合には、結晶原料の融点が約１６５０℃と上昇してしまうため、特許文献４の方法を応用してＬｉＴａＯ3単結晶を育成しようとした場合、白金製坩堝の融点（１７６０℃）とコングルエント組成を有するＬｉＴａＯ3結晶原料の融点（約１６５０℃）が接近する問題を考慮した改善策が必要となる新たな課題が存在した。 However, in the case of the stoichiometric composition used in Patent Document 3, since the melting point of the LiTaO 3 crystal raw material is as low as about 1550 ° C., a crucible made of platinum (Pt: melting point 1760 ° C.) can be used. 3 When the crystal raw material has a congruent composition, the melting point of the crystal raw material rises to about 1650 ° C. Therefore, when applying the method of Patent Document 4 to grow a LiTaO 3 single crystal, There has been a new problem that requires an improvement measure that takes into account the problem that the melting point (1760 ° C.) and the melting point (about 1650 ° C.) of a LiTaO 3 crystal raw material having a congruent composition approach.

特開２００８−２６０６６３号公報（請求項１、実施例６参照）Japanese Patent Laying-Open No. 2008-260663 (refer to claim 1, embodiment 6) 特開２０１４−０１２６１３号公報（請求項１参照）JP 2014-012613 A (refer to claim 1) 特開平０３−２９０３８９号公報（実施例１参照）Japanese Patent Laid-Open No. 03-290389 (see Example 1) 特開２０１１−１２６７１９号公報（段落0033-0036参照）Japanese Patent Laying-Open No. 2011-126719 (see paragraphs 0033-0036)

本発明はこのような問題点に着目してなされたもので、その課題とするところは、特許文献３の方法に較べて作業の簡便化が図れると共に、融点が互いに接近するコングルエント組成のＬｉＴａＯ3結晶原料と白金製坩堝を用いてＬｉＴａＯ3単結晶を育成する方法を提供し、かつ、育成されたＬｉＴａＯ3単結晶の処理方法を提供することにある。 The present invention has been made paying attention to such problems, and the problem is that the work can be simplified as compared with the method of Patent Document 3, and the LiTaO 3 having a congruent composition whose melting points are close to each other. An object is to provide a method for growing a LiTaO 3 single crystal using a crystal raw material and a platinum crucible, and to provide a method for processing the grown LiTaO 3 single crystal.

そこで、上記課題を解決すべく本発明者等が鋭意研究し、試行錯誤を重ねた結果、ＣＺ法に較べて融液中の温度勾配が小さいため、多結晶化、熱歪によるクラック発生、転位列の発生による結晶性低下等が起こり難いとされる垂直ブリッジマン（ＶＢ）法等「一方向凝固結晶成長法」を採用し、かつ、坩堝周囲に配置される加熱手段として高周波誘導加熱に較べて温度制御に優れる「カーボン製の抵抗加熱ヒータ」を採用した場合、融点が互いに接近するコングルエント組成のＬｉＴａＯ3結晶原料と白金製坩堝を用いて高品質のＬｉＴａＯ3単結晶が安定して育成される方法を見出すに至った。 Therefore, the inventors of the present invention diligently researched to solve the above problems, and as a result of repeated trial and error, the temperature gradient in the melt is small compared to the CZ method. Compared with high-frequency induction heating as a heating means that uses a “unidirectional solidification crystal growth method” such as the vertical Bridgman (VB) method, which is unlikely to cause a decrease in crystallinity due to the occurrence of a row. When a “carbon resistance heater” with excellent temperature control is used, a high-quality LiTaO 3 single crystal is stably grown using a congruent composition LiTaO 3 crystal material and a platinum crucible with melting points close to each other. I came to find a way.

すなわち、本発明に係る第１の発明は、
白金製坩堝を用いてＬｉＴａＯ3単結晶を育成する方法において、
白金製坩堝内の下部にＬｉＴａＯ3種結晶を充填し、かつ、ＬｉＴａＯ3種結晶上にＬｉとＴａ比率が化学量論比でコングルエント組成に調製されたＬｉＴａＯ3結晶原料を充填すると共に、坩堝周囲に配置されたカーボン製の抵抗加熱ヒータにより上記白金製坩堝内に垂直方向の温度勾配を形成させて、ＬｉＴａＯ3種結晶の上部とＬｉＴａＯ3結晶原料を融解させた後に凝固させる一方向凝固結晶成長法によりＬｉＴａＯ3単結晶を育成することを特徴とする。 That is, the first invention according to the present invention is:
In a method for growing a LiTaO 3 single crystal using a platinum crucible,
Filling the LiTaO 3 or crystal at the bottom of the platinum crucible, and, together with Li and Ta ratio on LiTaO 3 or crystal fills the LiTaO 3 crystal raw material which is prepared to congruent composition in a stoichiometric ratio, the crucible periphery Unidirectional solidification crystal growth in which a temperature gradient in the vertical direction is formed in the platinum crucible by the carbon resistance heater arranged in the above, and the upper part of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material are melted and then solidified. A LiTaO 3 single crystal is grown by the method.

次に、本発明に係る第２の発明は、
第１の発明に記載のＬｉＴａＯ3単結晶の育成方法において、
上記白金製坩堝がモリブデン製またはタングステン製の耐熱性外側容器内に収容された状態でＬｉＴａＯ3単結晶を育成することを特徴とし、
第３の発明は、
第２の発明に記載のＬｉＴａＯ3単結晶の育成方法において、
ジルコニアバブル、アルミナ粉末、サファイア粉末、カーボンシート、ジルコニアシートから選ばれる一種以上の緩衝材が上記白金製坩堝と耐熱性外側容器間に介在された状態でＬｉＴａＯ3単結晶を育成することを特徴とし、
第４の発明は、
第１の発明〜第３の発明のいずれかに記載のＬｉＴａＯ3単結晶の育成方法において、
上記ＬｉＴａＯ3単結晶が、Ｆｅ、Ｃｕ、Ｃｏ、Ｎｉ、Ｍｎ、Ｙ、Ｔｉから選ばれる一種以上の添加元素を３０ｐｐｍ〜１０００ｐｐｍ含んでいることを特徴とし、
第５の発明は、
第１の発明〜第４の発明のいずれかに記載のＬｉＴａＯ3単結晶の育成方法において、
育成炉内の雰囲気ガスとして不活性ガスを導入することを特徴とし、
第６の発明は、
第１の発明〜第５の発明のいずれかに記載のＬｉＴａＯ3単結晶の育成方法において、
育成炉内の酸素分圧が１ｋＰａ以下となる雰囲気に設定することを特徴とし、
また、第７の発明は、
ＬｉＴａＯ3単結晶の処理方法において、
第１の発明〜第６の発明のいずれかに記載の方法により育成されたＬｉＴａＯ3単結晶を、当該単結晶育成後において酸素を含有する雰囲気でアニール処理することを特徴とするものである。 Next, the second invention according to the present invention is as follows.
In the method for growing a LiTaO 3 single crystal according to the first invention,
The platinum crucible is grown in a heat-resistant outer container made of molybdenum or tungsten, and the LiTaO 3 single crystal is grown.
The third invention is
In the method for growing a LiTaO 3 single crystal according to the second invention,
One or more kinds of buffer materials selected from zirconia bubble, alumina powder, sapphire powder, carbon sheet, and zirconia sheet are grown between the platinum crucible and the heat-resistant outer container to grow a LiTaO 3 single crystal. ,
The fourth invention is:
In the method for growing a LiTaO 3 single crystal according to any one of the first to third inventions,
The LiTaO 3 single crystal contains 30 ppm to 1000 ppm of one or more additive elements selected from Fe, Cu, Co, Ni, Mn, Y, Ti,
The fifth invention is:
In the method for growing a LiTaO 3 single crystal according to any one of the first to fourth inventions,
It is characterized by introducing an inert gas as an atmospheric gas in the growth furnace,
The sixth invention is:
In the method for growing a LiTaO 3 single crystal according to any one of the first to fifth inventions,
It is characterized by setting an atmosphere in which the oxygen partial pressure in the growth furnace is 1 kPa or less,
In addition, the seventh invention,
In the processing method of LiTaO 3 single crystal,
The LiTaO 3 single crystal grown by the method according to any one of the first to sixth inventions is annealed in an atmosphere containing oxygen after the single crystal growth.

本発明に係るＬｉＴａＯ3単結晶の育成方法によれば、
融液中の温度勾配が小さいため、多結晶化、熱歪によるクラック発生、転位列の発生による結晶性低下等が起こり難い「一方向凝固結晶成長法」を採用し、かつ、坩堝周囲に配置される加熱手段として温度制御に優れる「カーボン製の抵抗加熱ヒータ」を採用しているため、ＬｉとＴａ比率が化学量論比でコングルエント組成に調製されたＬｉＴａＯ3結晶原料と白金製坩堝を用いて高品質なＬｉＴａＯ3単結晶を安定して育成することが可能となる。 According to the method for growing a LiTaO 3 single crystal according to the present invention,
Since the temperature gradient in the melt is small, the unidirectional solidification crystal growth method, which is unlikely to cause crystallization, cracking due to thermal strain, or crystallinity degradation due to the generation of dislocation arrays, is placed around the crucible. As a heating means, a “resistive heater made of carbon” with excellent temperature control is used, so a LiTaO 3 crystal raw material and a platinum crucible, in which the Li and Ta ratios are stoichiometrically adjusted to a congruent composition, are used. High quality LiTaO 3 single crystal can be stably grown.

白金製坩堝を用いたＬｉＴａＯ3単結晶の育成方法に利用される育成炉の概略構成断面図。1 is a schematic cross-sectional view of a growth furnace used in a method for growing a LiTaO 3 single crystal using a platinum crucible.

以下、本発明の実施の形態について詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail.

（１）育成炉
図１は、白金製坩堝を用いて「一方向凝固結晶成長法」によりＬｉＴａＯ3単結晶を育成する方法に利用される育成炉の一例を示す概略構成断面図である。 (1) Growth furnace FIG. 1 is a schematic sectional view showing an example of a growth furnace used in a method of growing a LiTaO 3 single crystal by a “unidirectional solidification crystal growth method” using a platinum crucible.

まず、上記育成炉は、筒状チャンバ（図示せず）の内側に設けられた断熱材２と、チャンバ内にアルゴンや窒素等の不活性ガスが給排される給排孔（図示せず）を備えた構造を有している。尚、ＬｉＴａＯ3単結晶の育成を可能とする温度勾配が、炉内の垂直方向に形成できることを条件に公知の育成炉を使用することができる。 First, the growth furnace includes a heat insulating material 2 provided inside a cylindrical chamber (not shown), and a supply / discharge hole (not shown) through which an inert gas such as argon or nitrogen is supplied / exhausted in the chamber. It has the structure provided with. A known growth furnace can be used on the condition that a temperature gradient capable of growing a LiTaO 3 single crystal can be formed in the vertical direction in the furnace.

また、断熱材２の内側にはカーボン製の抵抗加熱ヒータ３が配置され、ＬｉＴａＯ3単結晶の育成時に上記抵抗加熱ヒータ３によりホットゾーンが形成される。また、カーボン製の抵抗加熱ヒータ３は、上段ヒータ３ａ、中段ヒータ３ｂおよび下段ヒータ３ｃとで構成され、これ等ヒータへの投入電力を調整することにより上記ホットゾーン内の温度勾配を制御することが可能となっている。 Further, a resistance heater 3 made of carbon is disposed inside the heat insulating material 2, and a hot zone is formed by the resistance heater 3 when the LiTaO 3 single crystal is grown. The resistance heater 3 made of carbon is composed of an upper heater 3a, a middle heater 3b, and a lower heater 3c, and the temperature gradient in the hot zone is controlled by adjusting the input power to these heaters. Is possible.

また、カーボン製の抵抗加熱ヒータ３の内側にはモリブデン製またはタングステン製の耐熱性外側容器９に収容された白金製坩堝１が配置され、上下方向に移動可能な可動用ロッド４が設けられた坩堝受け５に載置されている。また、上記耐熱性外側容器９と白金製坩堝１との間には、ジルコニアバブル、アルミナ粉末、サファイア粉末、カーボンシート、ジルコニアシートから選ばれた緩衝材１０が介在されている。更に、白金製坩堝１内の下部にＬｉＴａＯ3種結晶７が充填され、該ＬｉＴａＯ3種結晶７上にＬｉとＴａ比率が化学量論比でコングルエント組成に調製されたＬｉＴａＯ3結晶原料８が充填される。 Further, a platinum crucible 1 housed in a heat-resistant outer container 9 made of molybdenum or tungsten is disposed inside the resistance heater 3 made of carbon, and a movable rod 4 movable in the vertical direction is provided. It is placed on the crucible receptacle 5. A buffer material 10 selected from zirconia bubbles, alumina powder, sapphire powder, carbon sheets, and zirconia sheets is interposed between the heat-resistant outer container 9 and the platinum crucible 1. Furthermore, the lower the filling LiTaO 3 or crystal 7 is platinum crucible 1, Li and Ta ratio on the LiTaO 3 or crystal 7 is LiTaO 3 crystal material 8 which is prepared to congruent composition in a stoichiometric ratio filler Is done.

尚、モリブデン製またはタングステン製の耐熱性外側容器９内に上記白金製坩堝１が収容される理由は、育成されたＬｉＴａＯ3単結晶インゴットを取り出す際に白金製坩堝１を破壊する必要があるため、作業の簡便性と経済的理由による。また、耐熱性外側容器９にモリブデンまたはタングステンが選択された理由は、耐衝撃性が高く割れ難いことから繰り返し使用でき、熱伝導率が高いため坩堝１内のＬｉＴａＯ3結晶原料を効率的に加熱できると共に、上記原料融液との反応性が非常に低いことから融液が漏れ出たとしても外側容器９に孔が開くことがないためである。 The reason why the platinum crucible 1 is housed in the heat-resistant outer container 9 made of molybdenum or tungsten is that the platinum crucible 1 needs to be broken when the grown LiTaO 3 single crystal ingot is taken out. Due to the simplicity of work and economic reasons. The reason why molybdenum or tungsten is selected for the heat-resistant outer container 9 is that it can be used repeatedly because of its high impact resistance and resistance to cracking, and since the thermal conductivity is high, the LiTaO 3 crystal material in the crucible 1 is efficiently heated. This is because, since the reactivity with the raw material melt is very low, no hole is opened in the outer container 9 even if the melt leaks.

また、上方側が開放された白金製坩堝１にはゴミ落下防止用蓋材（図示せず）を被せてもよい。更に、白金製坩堝１は、上述したように育成炉内で可動用ロッド４が設けられた坩堝受け５上に載置され、該ロッド４を上下させることにより白金製坩堝１を育成炉内で上下させることができる。また、上記坩堝１が収容される耐熱性外側容器９の上方側も開放されている。尚、符号６は、白金製坩堝１に取り付けられた熱電対を示している。   The platinum crucible 1 whose upper side is opened may be covered with a dust fall prevention lid (not shown). Furthermore, the platinum crucible 1 is placed on the crucible receiver 5 provided with the movable rod 4 in the growth furnace as described above, and the platinum crucible 1 is moved in the growth furnace by moving the rod 4 up and down. Can be moved up and down. The upper side of the heat-resistant outer container 9 in which the crucible 1 is accommodated is also opened. Reference numeral 6 denotes a thermocouple attached to the platinum crucible 1.

また、「一方向凝固結晶成長法」において、白金製坩堝１を垂直に移動させて単結晶が育成される方式を垂直ブリッジマン法（Vertical Bridgman：ＶＢ法）と称し、また、白金製坩堝１を固定した状態で垂直方向の温度勾配により単結晶が育成される方式を垂直温度勾配凝固法（Vertical Gradient Freeze：ＶＧＦ法）と称している。   In the “unidirectional solidified crystal growth method”, a method in which the platinum crucible 1 is moved vertically to grow a single crystal is referred to as a vertical Bridgman method (Vertical Bridgman: VB method). A method in which a single crystal is grown by a temperature gradient in the vertical direction in a state in which is fixed is called a vertical temperature gradient solidification method (Vertical Gradient Freeze: VGF method).

（２）ＬｉＴａＯ3単結晶の育成方法
ＬｉＴａＯ3単結晶の育成方法で用いられるＬｉＴａＯ3結晶原料は、炭酸リチウム（Ｌｉ2ＣＯ3）粉末と酸化タンタル（Ｔａ2Ｏ5）粉末を混合し、仮焼して調製される。このときの温度は８００〜１６５０℃であることが好ましい。８００℃以上とすることで炭酸リチウムの炭酸を分解することが可能となり、１６５０℃以下とすることで混合粉の融解を防止することができる。 (2) LiTaO 3 LiTaO 3 crystal raw material used in the growing method LiTaO 3 single crystal growing method of a single crystal is lithium carbonate (Li 2 CO 3) powder and tantalum oxide (Ta 2 O 5) powder were mixed, tentative Prepared by baking. The temperature at this time is preferably 800 to 1650 ° C. It becomes possible to decompose | disassemble the carbonate of lithium carbonate by setting it as 800 degreeC or more, and it can prevent melting of mixed powder by setting it as 1650 degreeC or less.

また、ＬｉＴａＯ3結晶原料には、Ｆｅ、Ｃｕ、Ｃｏ、Ｎｉ、Ｍｎ、Ｙ、Ｔｉから選ばれる少なくとも一種以上の添加元素の濃度が３０〜１０００ｐｐｍとなるように、酸化鉄、酸化銅、酸化コバルト、酸化ニッケル、酸化マンガン、酸化イットリウム、酸化チタンから選ばれる少なくとも一種以上の酸化物を混合してもよい。Ｆｅ、Ｃｕ、Ｃｏ、Ｎｉ、Ｍｎ、Ｙ、Ｔｉから選ばれる少なくとも一種以上の添加元素を３０ｐｐｍ以上含むことで、育成後における単結晶切断時の切断境界に生ずるチッピングの発生を抑制する効果が得られる。他方、添加元素の濃度が１０００ｐｐｍ越えた場合、結晶中の添加元素の偏析や結晶欠陥の増加に繋がることがある。 In addition, the LiTaO 3 crystal raw material includes iron oxide, copper oxide, and cobalt oxide so that the concentration of at least one additive element selected from Fe, Cu, Co, Ni, Mn, Y, and Ti is 30 to 1000 ppm. In addition, at least one oxide selected from nickel oxide, manganese oxide, yttrium oxide, and titanium oxide may be mixed. By containing 30 ppm or more of at least one additional element selected from Fe, Cu, Co, Ni, Mn, Y, and Ti, an effect of suppressing the occurrence of chipping that occurs at the cutting boundary during single crystal cutting after growth is obtained. It is done. On the other hand, if the concentration of the additive element exceeds 1000 ppm, it may lead to segregation of the additive element in the crystal and an increase in crystal defects.

尚、ＬｉＴａＯ3単結晶を育成する際の育成炉内における雰囲気は、真空またはアルゴンや窒素等の不活性ガス雰囲気である。尚、育成炉内に酸素は存在しない方が好ましいが、配管、チャンバ、耐火材、原料の脱ガス等に起因する酸素の存在は避けられない。この場合、酸素分圧が３ｋＰａ以下であることが好ましく、１ｋＰａ以下であることがより好ましい。酸素分圧が１ｋＰａを越えてしまうとカーボン製の抵抗加熱式ヒータの蒸発量が大きくなり、結晶中へのカーボンのコンタミネーション（contamination：混入）の増加やヒータ厚みの減少に繋がることがある。 The atmosphere in the growth furnace when growing the LiTaO 3 single crystal is a vacuum or an inert gas atmosphere such as argon or nitrogen. Although it is preferable that no oxygen exists in the growth furnace, the presence of oxygen due to piping, chambers, refractory materials, degassing of raw materials, etc. is unavoidable. In this case, the oxygen partial pressure is preferably 3 kPa or less, and more preferably 1 kPa or less. If the oxygen partial pressure exceeds 1 kPa, the evaporation amount of the resistance heating heater made of carbon increases, which may lead to an increase in carbon contamination (contamination) in the crystal and a decrease in heater thickness.

更に、ＬｉＴａＯ3単結晶の育成開始前における白金製坩堝内の昇温速度は１００℃／ｈｒ以下であることが好ましい。昇温速度を１００℃／ｈｒ以下にすることにより、ＬｉＴａＯ3種結晶の熱歪みによるクラック発生を抑制することが可能となる。 Furthermore, it is preferable that the temperature increase rate in the platinum crucible before starting the growth of the LiTaO 3 single crystal is 100 ° C./hr or less. By setting the temperature increase rate to 100 ° C./hr or less, it is possible to suppress the generation of cracks due to thermal distortion of the LiTaO 3 seed crystal.

ＬｉＴａＯ3単結晶を育成するためのシーディングは、ＬｉＴａＯ3種結晶の上部とＬｉＴａＯ3結晶原料とを融解させて安定した固液界面を形成させることにより行われるが、上記固液界面の温度およびその温度での保持時間がシーディングにおいて重要な要素となる。これは、ＬｉＴａＯ3種結晶の表面近傍に、種結晶の加工時に形成された破砕層を有しており、この破砕層を融解させておく必要があるためである。また、ＬｉＴａＯ3種結晶が全て融解してしまう前に、固液界面を形成させておく必要があるためでもある。 The seeding for growing the LiTaO 3 single crystal is performed by melting the upper part of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material to form a stable solid-liquid interface. The holding time at that temperature is an important factor in seeding. This is because it has a crushed layer formed at the time of processing the seed crystal in the vicinity of the surface of the LiTaO 3 seed crystal, and it is necessary to melt this crushed layer. This is also because it is necessary to form a solid-liquid interface before all the LiTaO 3 seed crystals are melted.

上記要件を満足させるため、ＬｉＴａＯ3種結晶とＬｉＴａＯ3結晶原料との境界面の温度が、ＬｉＴａＯ3単結晶の融点プラス２０℃以下になるような位置に白金製坩堝１をセットする。境界面の温度は、ＬｉＴａＯ3単結晶の融点プラス１０℃以下であることが更に好ましい。上記温度で所定時間（後述するように１時間以上、好ましくは４時間〜６時間）保持し、ＬｉＴａＯ3種結晶の上部とＬｉＴａＯ3結晶原料とを融解させてシーディングを行う。ＬｉＴａＯ3種結晶は、結晶育成の核となるものであり、ＬｉＴａＯ3種結晶は、ＬｉＴａＯ3結晶原料と一体化させるために一部を融解させるが、ＬｉＴａＯ3種結晶の全部を融解させないようにしなければならない。 In order to satisfy the above requirements, the platinum crucible 1 is set at a position where the temperature of the interface between the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material becomes the melting point of the LiTaO 3 single crystal plus 20 ° C. or less. The interface temperature is more preferably the melting point of the LiTaO 3 single crystal plus 10 ° C. or less. Holding at the above temperature for a predetermined time (1 hour or more as described later, preferably 4 to 6 hours), the upper part of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material are melted to perform seeding. The LiTaO 3 seed crystal is a nucleus for crystal growth. The LiTaO 3 seed crystal is partially melted so as to be integrated with the LiTaO 3 crystal raw material, but the entire LiTaO 3 seed crystal is not melted. There must be.

シーディングが終了した後、白金製坩堝１を徐々に降下させてホットゾーン内の温度勾配を通過させる。このようにして、ＬｉＴａＯ3種結晶の結晶方位に従い、ＬｉＴａＯ3結晶原料を冷却固化させることでＬｉＴａＯ3単結晶が育成される。 After the seeding is completed, the platinum crucible 1 is gradually lowered to pass the temperature gradient in the hot zone. Thus, the LiTaO 3 single crystal is grown by cooling and solidifying the LiTaO 3 crystal raw material according to the crystal orientation of the LiTaO 3 seed crystal.

尚、結晶育成後は、急激な降温を行わない方が好ましい。急激な降温を行うと、単結晶にストレスが生じるため、クラックを生ずる場合がある。   In addition, it is preferable not to perform a rapid temperature drop after crystal growth. When the temperature is rapidly lowered, a stress is generated in the single crystal, which may cause a crack.

本実施の形態に係るＬｉＴａＯ3単結晶の育成方法は、上述したようにＬｉＴａＯ3単結晶の融点に対して、ＬｉＴａＯ3種結晶とＬｉＴａＯ3結晶原料との界面温度を上記融点プラス２０℃以下にして溶融を行っているため、ＬｉＴａＯ3種結晶の上部数ミリ程の部分とＬｉＴａＯ3結晶原料とが融解し、ＬｉＴａＯ3種結晶とＬｉＴａＯ3結晶原料とを一体にすることができる。尚、ＬｉＴａＯ3種結晶とＬｉＴａＯ3結晶原料との界面温度が上記融点プラス２０℃を超えると、ＬｉＴａＯ3種結晶の底面部まで融解してしまう場合がある。 As described above, the method for growing a LiTaO 3 single crystal according to the present embodiment sets the interface temperature between the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material to the melting point plus 20 ° C. or lower with respect to the melting point of the LiTaO 3 single crystal. Therefore, the upper part of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material are melted and the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material can be integrated. When the interface temperature between the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material exceeds the melting point plus 20 ° C., the bottom surface of the LiTaO 3 seed crystal may be melted.

また、ＬｉＴａＯ3種結晶の上部とＬｉＴａＯ3結晶原料を融解させる保持時間は上述したように１時間以上とすることが好ましい。この時間保持することにより、ＬｉＴａＯ3種結晶とＬｉＴａＯ3結晶原料との固液界面を安定化させることができるため、品質の高い単結晶を育成することができる。また、４〜６時間保持することは更に好ましい。すなわち、４時間以上保持すれば、概ねシーディングに関する反応は進行しており、６時間以下で概ね反応は終了している。従って、４〜６時間保持することにより生産性を低下させずにシーディングを安定して行うことが可能となる。 The holding time for melting the upper portion of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material is preferably 1 hour or longer as described above. By holding for this time, the solid-liquid interface between the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material can be stabilized, so that a high-quality single crystal can be grown. Further, it is more preferable to hold for 4 to 6 hours. That is, if it is kept for 4 hours or more, the reaction related to seeding is generally progressing, and the reaction is almost completed in 6 hours or less. Therefore, by holding for 4 to 6 hours, it is possible to stably perform seeding without reducing productivity.

次に、ＬｉＴａＯ3単結晶の育成後におけるアニール処理は、空気中若しくは酸素雰囲気等酸素を含有する雰囲気で行うことが好ましい。雰囲気中に酸素を含有させることで、上記ＬｉＴａＯ3単結晶の育成時に生じた酸素欠陥の低減が期待できる。このときの温度は、１６５０℃未満とすることが好ましい。１６５０℃未満とすることでＬｉＴａＯ3単結晶の融解を防止することができる。 Next, the annealing treatment after the growth of the LiTaO 3 single crystal is preferably performed in air or an atmosphere containing oxygen such as an oxygen atmosphere. By containing oxygen in the atmosphere, reduction of oxygen defects generated during the growth of the LiTaO 3 single crystal can be expected. The temperature at this time is preferably less than 1650 ° C. By making the temperature lower than 1650 ° C., melting of the LiTaO 3 single crystal can be prevented.

以上、本発明に係る実施の形態について説明したが、本発明は上記実施の形態に記載された内容に限定されるものでなく、本発明の要旨を逸脱しない範囲において、育成方法や装置構成等の変更を行なってもよい。   As mentioned above, although embodiment which concerns on this invention was described, this invention is not limited to the content described in the said embodiment, In the range which does not deviate from the summary of this invention, a growth method, an apparatus structure, etc. Changes may be made.

以下、本発明の実施例について比較例を挙げて具体的に説明する。   Examples of the present invention will be specifically described below with reference to comparative examples.

［実施例１］
まず、化学量論比でＬｉとＴａ比率が４８．４：５１．６（コングルエント組成）になるように炭酸リチウム（Ｌｉ2ＣＯ3）粉末と酸化タンタル（Ｔａ2Ｏ5）粉末を秤量し、これ等粉末を混合機によって十分に混合した後、この混合粉末を８００〜１６５０℃で１０時間仮焼してＬｉＴａＯ3結晶原料を得た。 [Example 1]
First, the lithium carbonate (Li 2 CO 3 ) powder and the tantalum oxide (Ta 2 O 5 ) powder are weighed so that the Li / Ta ratio in the stoichiometric ratio is 48.4: 51.6 (congruent composition). After these powders were sufficiently mixed by a mixer, the mixed powder was calcined at 800 to 1650 ° C. for 10 hours to obtain a LiTaO 3 crystal raw material.

そして、図１に示す厚さ０．５ｍｍ、内径５２ｍｍ、高さ３００ｍｍの白金製坩堝１内の下部に予め調製しておいたＬｉＴａＯ3種結晶７を充填し、かつ、当該ＬｉＴａＯ3種結晶７上に上記ＬｉＴａＯ3結晶原料８を充填した。 Then, the prepared LiTaO 3 seed crystal 7 is filled in the lower part of the platinum crucible 1 having a thickness of 0.5 mm, an inner diameter of 52 mm, and a height of 300 mm shown in FIG. 1, and the LiTaO 3 seed crystal 7 The above LiTaO 3 crystal raw material 8 was filled thereon.

次に、ＬｉＴａＯ3種結晶７とＬｉＴａＯ3結晶原料８が充填された白金製坩堝１を、図１に示すようにモリブデン（Ｍｏ）製の耐熱性外側容器９内に収容し、かつ、白金製坩堝１と耐熱性外側容器９との間にジルコニアシートから成る緩衝材１０を介在させた。 Next, the platinum crucible 1 filled with the LiTaO 3 seed crystal 7 and the LiTaO 3 crystal raw material 8 is housed in a heat-resistant outer container 9 made of molybdenum (Mo) as shown in FIG. A cushioning material 10 made of a zirconia sheet was interposed between the crucible 1 and the heat resistant outer container 9.

そして、上記白金製坩堝１と緩衝材１０と耐熱性外側容器９とで構成される坩堝構造体を、図１に示す多孔質アルミナ製の坩堝受け５上に載置し、かつ、耐熱性外側容器９と緩衝材１０を貫通させた熱電対６の先端部を白金製坩堝１の側面に接触させた。   And the crucible structure comprised by the said platinum crucible 1, the buffer material 10, and the heat resistant outer container 9 is mounted on the crucible holder 5 made of porous alumina shown in FIG. The tip of the thermocouple 6 that penetrates the container 9 and the buffer material 10 was brought into contact with the side surface of the platinum crucible 1.

尚、上記熱電対６の接触点はＬｉＴａＯ3種結晶７の底面から１５ｍｍの高さ位置になるよう設定した。 The contact point of the thermocouple 6 was set to be 15 mm high from the bottom surface of the LiTaO 3 seed crystal 7.

次に、上記坩堝構造体を育成炉内の最下部にセットした後、不活性ガスであるアルゴン（純度９９．９９％）を育成炉９内に流した。   Next, after the crucible structure was set at the lowermost part in the growth furnace, argon (purity 99.99%) as an inert gas was allowed to flow into the growth furnace 9.

尚、育成炉内の酸素分圧は５００Ｐａであった。   The oxygen partial pressure in the growth furnace was 500 Pa.

また、カーボン製の抵抗加熱ヒータ３における上段ヒータ３ａ、中段ヒータ３ｂおよび下段ヒータ３ｃについては独立に制御可能で、かつ、各ヒータ３ａ〜３ｃの長さは２００ｍｍであった。   Further, the upper heater 3a, the middle heater 3b, and the lower heater 3c in the resistance heater 3 made of carbon can be controlled independently, and the lengths of the heaters 3a to 3c were 200 mm.

そして、上段ヒータ３ａの温度を１７５０℃、中段ヒータ３ｂの温度を１７５０℃、下段ヒータ３ｃの温度を１６５０℃の温度幅で設定し、昇温を行った。昇温が終了して育成炉内の温度が安定した後、白金製坩堝１を緩やかな速度で上昇させた。育成炉内には上部の温度が高く、下部の温度が低い温度勾配がつくられているので、育成炉の上部に移動するに従って白金製坩堝１内の温度が上昇し、ＬｉＴａＯ3結晶原料８が融解してその融液が形成された。 The temperature of the upper heater 3a was set to 1750 ° C., the temperature of the middle heater 3b was set to 1750 ° C., and the temperature of the lower heater 3c was set to a temperature range of 1650 ° C. to raise the temperature. After the temperature increase was completed and the temperature in the growth furnace was stabilized, the platinum crucible 1 was raised at a moderate speed. Since a temperature gradient is created in the growth furnace where the temperature at the top is high and the temperature at the bottom is low, the temperature in the platinum crucible 1 rises as it moves to the top of the growth furnace, and the LiTaO 3 crystal raw material 8 becomes The melt formed upon melting.

上記融液が形成された白金製坩堝１の位置付近で、上記熱電対６の接触点位置の温度をモニターしながら、白金製坩堝１の位置を数ｍｍ上昇させて温度を安定させた。この工程を繰り返して、熱電対６の温度が安定した状態で１６３５〜１６６５℃の範囲になるよう白金製坩堝１を上昇させた。数時間の保持を行った後、２ｍｍ／ｈで白金製坩堝１を降下させ、ＬｉＴａＯ3単結晶の育成を開始した。白金製坩堝１の降下距離は２２０ｍｍであり、約５日間で育成が終了した。 While monitoring the temperature at the contact point position of the thermocouple 6 near the position of the platinum crucible 1 where the melt was formed, the position of the platinum crucible 1 was raised by several mm to stabilize the temperature. This process was repeated, and the platinum crucible 1 was raised so that the temperature of the thermocouple 6 was in the range of 1635 to 1665 ° C. in a stable state. After holding for several hours, the platinum crucible 1 was lowered at 2 mm / h to start growing a LiTaO 3 single crystal. The descending distance of the platinum crucible 1 was 220 mm, and the growth was completed in about 5 days.

上記単結晶の育成終了後、白金製坩堝１を破壊してＬｉＴａＯ3単結晶のインゴットを取り出したところ、インゴットの長さは２００ｍｍであり、黒色のＬｉＴａＯ3単結晶が得られた。 After the growth of the single crystal, the platinum crucible 1 was broken and the LiTaO 3 single crystal ingot was taken out. The length of the ingot was 200 mm, and a black LiTaO 3 single crystal was obtained.

そして、取り出したＬｉＴａＯ3単結晶を、大気雰囲気下、１４００℃で１０時間のアニール処理を行ったが、アニール処理後もクラック等を発生することなく、良質な透明単結晶が得られた。 The extracted LiTaO 3 single crystal was subjected to an annealing treatment at 1400 ° C. for 10 hours in an air atmosphere, and a high-quality transparent single crystal was obtained without generating cracks after the annealing treatment.

［実施例２］
化学量論比でＬｉとＴａ比率が４８．４：５１．６（コングルエント組成）になるように炭酸リチウム（Ｌｉ2ＣＯ3）粉末と酸化タンタル（Ｔａ2Ｏ5）粉末を秤量し、かつ、Ｆｅ濃度が１００ｐｐｍとなるように酸化鉄（Ｆｅ2Ｏ3）粉末を秤量した。 [Example 2]
Lithium carbonate (Li 2 CO 3 ) powder and tantalum oxide (Ta 2 O 5 ) powder are weighed so that the Li / Ta ratio is 48.4: 51.6 (congruent composition) in stoichiometric ratio, and Iron oxide (Fe 2 O 3 ) powder was weighed so that the Fe concentration was 100 ppm.

これ等の粉末を混合機によって十分に混合した後、この混合粉末を８００〜１６５０℃で１０時間仮焼してＦｅドープＬｉＴａＯ3結晶原料を得た。 After these powders were sufficiently mixed by a mixer, the mixed powder was calcined at 800 to 1650 ° C. for 10 hours to obtain a Fe-doped LiTaO 3 crystal raw material.

そして、このＦｅドープＬｉＴａＯ3結晶原料を使用した以外は実施例１と同様にしてＦｅドープＬｉＴａＯ3単結晶の育成を行った。 Then, an Fe-doped LiTaO 3 single crystal was grown in the same manner as in Example 1 except that this Fe-doped LiTaO 3 crystal raw material was used.

次に、単結晶の育成終了後、白金製坩堝１を破壊してＦｅドープＬｉＴａＯ3単結晶のインゴットを取り出したところ、インゴットの長さは２００ｍｍであり、黒色のＦｅドープＬｉＴａＯ3単結晶が得られた。 Next, after the growth of the single crystal was completed, the platinum crucible 1 was broken and the Fe-doped LiTaO 3 single crystal ingot was taken out. The length of the ingot was 200 mm, and a black Fe-doped LiTaO 3 single crystal was obtained. It was.

そして、取り出したＦｅドープＬｉＴａＯ3単結晶を、大気雰囲気下、１４００℃で１０時間のアニール処理を行ったが、アニール処理後もクラック等を発生することなく、良質な透明単結晶が得られた。 The extracted Fe-doped LiTaO 3 single crystal was subjected to an annealing treatment at 1400 ° C. for 10 hours in an air atmosphere, and a high-quality transparent single crystal was obtained without generating cracks after the annealing treatment. .

［比較例１］
実施例１と同様、原料粉末の秤量、混合および仮焼を行ってＬｉＴａＯ3結晶原料を調製した。 [Comparative Example 1]
As in Example 1, raw material powder was weighed, mixed and calcined to prepare a LiTaO 3 crystal raw material.

次に、ＬｉＴａＯ3結晶原料を白金製坩堝内に投入し、かつ、不活性ガスであるアルゴン（純度９９．９９％）を炉内に流し、カーボン製の抵抗加熱ヒータにより投入した全てのＬｉＴａＯ3結晶原料を融解させた。坩堝底の温度は１６５０℃であった。 Next, the LiTaO 3 crystal raw material was put into a platinum crucible, and argon (purity 99.99%), which is an inert gas, was allowed to flow into the furnace, and all the LiTaO 3 charged with a resistance heater made of carbon. The crystal raw material was melted. The temperature at the bottom of the crucible was 1650 ° C.

この原料融液の中に、所定の方位に切り出したＬｉＴａＯ3単結晶を浸し、回転数１０ｒｐｍ、引き上げ速度２ｍｍ／ｈｒで引き上げるチョクラルスキー法によりＬｉＴａＯ3単結晶の育成を試みようとしたが、ＬｉＴａＯ3結晶原料の融解途中に白金製坩堝の一部が融解してしまい、単結晶の育成を行うことができなかった。 An attempt was made to grow a LiTaO 3 single crystal by the Czochralski method in which a LiTaO 3 single crystal cut out in a predetermined orientation was immersed in this raw material melt and pulled at a rotation speed of 10 rpm and a pulling speed of 2 mm / hr. A part of the platinum crucible melted during the melting of the LiTaO 3 crystal raw material, and the single crystal could not be grown.

［比較例２］
図１に示すカーボン製の抵抗加熱ヒータ３に代えて高周波誘導加熱ヒータが組み込まれた育成炉を用いてＬｉＴａＯ3単結晶の育成を試みた。 [Comparative Example 2]
An attempt was made to grow a LiTaO 3 single crystal using a growth furnace in which a high-frequency induction heater was incorporated instead of the carbon resistance heater 3 shown in FIG.

すなわち、実施例１と同様、原料粉末の秤量、混合および仮焼を行ってＬｉＴａＯ3結晶原料を調製した後、ＬｉＴａＯ3種結晶が充填された白金製坩堝の種結晶上にＬｉＴａＯ3結晶原料を充填した後、実施例１と同様にしてＬｉＴａＯ3単結晶の育成を行った。 That is, the first embodiment similarly weighed raw material powders, was prepared mixing and LiTaO 3 crystal raw material by performing a calcination, an LiTaO 3 crystal raw material in three crystal on a seed crystal of the filled platinum crucible LiTaO After filling, a LiTaO 3 single crystal was grown in the same manner as in Example 1.

しかし、ＬｉＴａＯ3結晶原料の融解を温度制御に劣る高周波誘導加熱ヒータを用いて行ったため、比較例１と同様、原料融解途中に白金製坩堝の一部が融解してしまい、単結晶の育成を行うことができなかった。 However, since the melting of the LiTaO 3 crystal raw material was performed using a high-frequency induction heater that is inferior in temperature control, as in Comparative Example 1, a part of the platinum crucible melted during the raw material melting, and the growth of the single crystal was performed. Could not do.

本発明に係る育成方法によれば、融液中の温度勾配が小さいために多結晶化、熱歪によるクラック発生、転位列の発生による結晶性低下等が起こり難い一方向凝固結晶成長法を採用し、かつ、坩堝周囲に配置される加熱手段として温度制御に優れるカーボン製の抵抗加熱ヒータを採用していることから、コングルエント組成に調製されたＬｉＴａＯ3結晶原料と白金製坩堝を用いたＬｉＴａＯ3単結晶の育成が可能になるため、ＳＡＷデバイス用圧電基板として好適な形状制御された高品質ＬｉＴａＯ3単結晶の製造に適用される産業上の利用可能性を有している。 The growth method according to the present invention employs a unidirectionally solidified crystal growth method in which polycrystallization, crack generation due to thermal strain, and crystallinity degradation due to dislocation arrays are unlikely to occur due to a small temperature gradient in the melt. and, and, since it adopts a carbon-made resistance heater which is excellent in temperature control as a heating means disposed in a crucible periphery, LiTaO 3 using LiTaO 3 crystal material and a platinum crucible was prepared congruent composition Since single crystals can be grown, the present invention has industrial applicability applied to the production of high-quality LiTaO 3 single crystals having a shape control suitable as piezoelectric substrates for SAW devices.

１ 白金製坩堝
２ 断熱材
３ カーボン製の抵抗加熱ヒータ
３ａ 上段ヒーター
３ｂ 中段ヒーター
３ｃ 下段ヒーター
４ 可動用ロッド
５ 坩堝受け
６ 熱電対
７ ＬｉＴａＯ3種結晶
８ ＬｉＴａＯ3結晶原料
９ 耐熱性外側容器
１０ 緩衝材 DESCRIPTION OF SYMBOLS 1 Platinum crucible 2 Heat insulating material 3 Carbon resistance heater 3a Upper heater 3b Middle heater 3c Lower heater 4 Movable rod 5 Crucible receptacle 6 Thermocouple 7 LiTaO 3 seed crystal 8 LiTaO 3 crystal raw material 9 Heat resistant outer container 10 Buffer Material

Claims (7)

白金製坩堝を用いてＬｉＴａＯ3単結晶を育成する方法において、
白金製坩堝内の下部にＬｉＴａＯ3種結晶を充填し、かつ、ＬｉＴａＯ3種結晶上にＬｉとＴａ比率が化学量論比でコングルエント組成に調製されたＬｉＴａＯ3結晶原料を充填すると共に、坩堝周囲に配置されたカーボン製の抵抗加熱ヒータにより上記白金製坩堝内に垂直方向の温度勾配を形成させて、ＬｉＴａＯ3種結晶の上部とＬｉＴａＯ3結晶原料を融解させた後に凝固させる一方向凝固結晶成長法によりＬｉＴａＯ3単結晶を育成することを特徴とするＬｉＴａＯ3単結晶の育成方法。 In a method for growing a LiTaO 3 single crystal using a platinum crucible,
Filling the LiTaO 3 or crystal at the bottom of the platinum crucible, and, together with Li and Ta ratio on LiTaO 3 or crystal fills the LiTaO 3 crystal raw material which is prepared to congruent composition in a stoichiometric ratio, the crucible periphery Unidirectional solidification crystal growth in which a temperature gradient in the vertical direction is formed in the platinum crucible by the carbon resistance heater arranged in the above, and the upper part of the LiTaO 3 seed crystal and the LiTaO 3 crystal raw material are melted and then solidified. LiTaO 3 method for growing single crystals, which comprises growing a LiTaO 3 single crystal by law. 上記白金製坩堝がモリブデン製またはタングステン製の耐熱性外側容器内に収容された状態でＬｉＴａＯ3単結晶を育成することを特徴とする請求項１に記載のＬｉＴａＯ3単結晶の育成方法。 LiTaO 3 method for growing single crystals according to claim 1 in which the platinum crucible is characterized by growing a LiTaO 3 single crystal in a state of being accommodated in molybdenum or tungsten refractory outer container. ジルコニアバブル、アルミナ粉末、サファイア粉末、カーボンシート、ジルコニアシートから選ばれる一種以上の緩衝材が上記白金製坩堝と耐熱性外側容器間に介在された状態でＬｉＴａＯ3単結晶を育成することを特徴とする請求項２に記載のＬｉＴａＯ3単結晶の育成方法。 One or more kinds of buffer materials selected from zirconia bubble, alumina powder, sapphire powder, carbon sheet, zirconia sheet are grown between the platinum crucible and the heat-resistant outer container to grow a LiTaO 3 single crystal. The method for growing a LiTaO 3 single crystal according to claim 2. 上記ＬｉＴａＯ3単結晶が、Ｆｅ、Ｃｕ、Ｃｏ、Ｎｉ、Ｍｎ、Ｙ、Ｔｉから選ばれる一種以上の添加元素を３０ｐｐｍ〜１０００ｐｐｍ含んでいることを特徴とする請求項１〜３のいずれかに記載のＬｉＴａＯ3単結晶の育成方法。 The LiTaO 3 single crystal contains 30 ppm to 1000 ppm of one or more additive elements selected from Fe, Cu, Co, Ni, Mn, Y, and Ti. Method for growing LiTaO 3 single crystal. 育成炉内の雰囲気ガスとして不活性ガスを導入することを特徴とする請求項１〜４のいずれかに記載のＬｉＴａＯ3単結晶の育成方法。 The method for growing a LiTaO 3 single crystal according to any one of claims 1 to 4, wherein an inert gas is introduced as an atmospheric gas in the growth furnace. 育成炉内の酸素分圧が１ｋＰａ以下となる雰囲気に設定することを特徴とする請求項１〜５のいずれかに記載のＬｉＴａＯ3単結晶の育成方法。 The method for growing a LiTaO 3 single crystal according to any one of claims 1 to 5, wherein an atmosphere in which a partial pressure of oxygen in the growth furnace is 1 kPa or less is set. 請求項１〜６のいずれかに記載の方法により育成されたＬｉＴａＯ3単結晶を、当該単結晶育成後において酸素を含有する雰囲気でアニール処理することを特徴とするＬｉＴａＯ3単結晶の処理方法。 A method for treating a LiTaO 3 single crystal, comprising subjecting the LiTaO 3 single crystal grown by the method according to claim 1 to an annealing treatment in an atmosphere containing oxygen after the single crystal growth.
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