【０００１】
【発明の属する技術分野】
本発明は、液体封止引き上げ法（Ｌｉｑｕｉｄ Ｅｎｃａｐｓｕｌａｔｅｄ Ｃｚｏｃｈｒａｌｓｋｉ法：ＬＥＣ法）による化合物半導体単結晶の製造方法、特に引上軸の回転技術に関するものである。
【０００２】
【従来の技術】
化合物半導体はその単結晶の高品質化により、高速集積回路、光−電子集積回路やその他の電子素子に広く用いられるようになってきた。なかでも、ＩＩＩ−Ｖ族化合物半導体の砒化ガリウム（ＧａＡｓ）は電子移動度がシリコンに比べて早く、１０７Ω・ｃｍ以上の比抵抗のウエハが製造容易という特徴がある。現在では上記ＧａＡｓの単結晶は、主に液体封止引き上げ法（ＬＥＣ法）により製造されている。
【０００３】
ＧａＡｓ単結晶成長方法を図１によって説明する。
【０００４】
ＬＥＣ法によるＧａＡｓ単結晶の製造装置は、圧力容器であるチャンバー９と、結晶を引き上げる為の引上軸１、原料の容器であるＰｙｒｏｌｉｔｉｃ Ｂｏｒｏｎ Ｎｉｔｒｉｄｅ（略称：ＰＢＮ）製のルツボ７、このＰＢＮルツボを受ける為のルツボ軸８を有する構造となっている。
【０００５】
結晶製造方法については、先ず原料の容器となるＰＢＮルツボ７にＧａとＡｓ及びＡｓの揮発防止材である液体封止剤として三酸化硼素を入れ、これをチャンバー９内にセットする。又、引上軸１の先端に結晶の元となる種結晶２を取りつける。この種結晶２はＧａＡｓ融液と接する面を（１００）面としているのが一般的である。
【０００６】
チャンバー９に原料をセットした後、チャンバー９内を真空にし、不活性ガスを充填する。その後、チャンバー９内に設置してあるカーボン製ヒータ５に通電し、チャンバー９内の温度を昇温させ、三酸化硼素を軟化、融解して融液化させ三酸化硼素融液４とする。更に昇温させＧａとＡｓを合成しＧａＡｓを作製し、その後、更に昇温させＧａＡｓを融液化させ、ＧａＡｓ融液６とする。
【０００７】
続いて、引上軸１、ルツボ軸８を相対的に回転させる。この状態で、引上軸１を先端に取り付けてある種結晶２がＧａＡｓ融液６に接触するまで下降させる。
【０００８】
続いて、カーボン製ヒータ５の設定温度を徐々に下げつつ引上軸１を一定の速度で上昇させることで、種結晶２（種付け部３１）から徐々に結晶径を太らせながら定径部３３までの増径部（結晶肩部）３２を形成する。肩部形成後、目標とする結晶外径となったならば、外径を一定に保つ為、外形を制御しつつＧａＡｓ単結晶３の製造を行う。
【０００９】
しかし、ＬＥＣ法で化合物半導体単結晶を成長する技術は非常に難しく、加熱手段のヒータ及び、熱遮蔽筒等の部材（ホットゾーンと呼ばれる。以下ＨＺと記す）の配置、形状、材質等により、より細かく影響を受けるため、再現性の良い化合物半導体単結晶の成長条件を得るのが難しい。化合物半導体単結晶を再現性よく得るための要因は、ＨＺの配置、形状、材質などＨＺに係わるものと考えてきたが、根本的には固化した単結晶と融液の界面（以下、「固液界面」と記す）の形状を如何に制御するかが、単結晶を得るための大きな要因であることが明確になってきた。
【００１０】
固液界面形状と単結晶収率の関係は、固液界面が融液側に凹形状の場合は、成長過程全般、または成長のある一定期間に係わらず、結晶欠陥であるリネージ、亜粒界が集積され易く多結晶化し易い。当然ながら単結晶収率も低くなる。単結晶収率を向上させるためには、固液界面を成長過程全般に渡り、融液側に凸形状に制御することが重要である。
【００１１】
そこで、融液の温度勾配をもとに、３ｒｐｍ、６ｒｐｍ、１０ｒｐｍといった固定値の集まりから成る臨界回転数テーブルを作製し、回転引き上げ最適制御が臨界回転数テーブルを参照して臨界回転数を取り出し、この臨界回転数か、少し遅い回転数に回転引き上げ機構を制御する方法（例えば、特許文献１参照。）や、ルツボ側壁付近で上昇してから成長結晶に向かって流れる自然対流と、結晶の回転により固液界面付近で渦巻く強制対流が発生するとの認識の下で、成長結晶の周囲に円筒体を配設して先端を原料融液中に浸漬し、ルツボ、成長結晶、円筒体のいずれかの回転数を適宜設定して固液界面形状の凹化を防止しながら結晶を引き上げる方法（例えば、特許文献２参照。）、などが提案されている。
【００１２】
しかし、これらの制御の下でも、従来のＬＥＣ法による化合物半導体単結晶製造時の引上軸回転数は、種付け部、増径部、定径部といった育成する結晶の部位に係わらず、一定とするのが一般的である。
【００１３】
化合物半導体の一種である砒化ガリウム（以下ＧａＡｓと記す）を例に説明する。直径が２８０ｍｍであるＰＢＮ製のルツボ、断面１０ｍｍ角の種結晶を用い、定径部結晶直径１１０ｍｍ、結晶長さ４００ｍｍの砒化ガリウムの単結晶成長を、引上軸の回転数８ｒｐｍで５０回行った。その結果、結晶の種付けから結晶成長最終部まで全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）は５０％以下であった。
【００１４】
【特許文献１】
特開平６−１８３８７７号公報（段落番号００１５、図４（ｂ））
【００１５】
【特許文献２】
特開平８−３１０８９３号公報（段落番号００２９、００１３、図２）
【００１６】
【発明が解決しようとする課題】
上記のように、ＬＥＣ法による化合物半導体単結晶の製造において、単結晶収率を向上させることは、なかなか困難である。
【００１７】
単結晶収率を向上させるための大きな要点は、固液界面を成長過程全般に渡り、融液側に凸形状に制御することである。特に、結晶欠陥であるリネージ、亜粒界の集積は、種付け部から定径部までの成長初期の段階で発生している場合が多く、従って種付け部から定径部までの成長初期段階での固液界面形状を再現性良く制御することが特に必要である。
【００１８】
現状では、固液界面形状を再現性良く制御すること、特に固液界面を融液側に凸形状に制御することは困難であり、化合物半導体単結晶の収率が低下する原因となっていた。
【００１９】
そこで、本発明の目的は、上記課題を解決し、ＬＥＣ法での化合物半導体単結晶の成長において、成長過程、特に種付け部から定径部までの成長初期段階での固液界面形状を再現性良く融液側に凸形状に制御することが可能で、化合物半導体単結晶の収率を大幅に向上させることができる化合物半導体単結晶の製造方法を提供することにある。
【００２０】
【課題を解決するための手段】
上記目的を達成するため、本発明は、次のように構成したものである。
【００２１】
請求項１に記載の発明は、不活性ガスを充填した耐圧容器内に収容され加熱されたルツボに、原料融液、液体封止剤を収納し、引上軸に取り付けた種結晶を原料融液に接触させつつ種結晶とルツボとを相対的に移動させて化合物半導体単結晶を成長させるＬＥＣ法による化合物半導体単結晶の製造方法において、種付け部からある成長時点までの引上軸の回転数を、それ以降の回転数以下とすることを特徴とする。
【００２２】
請求項２に記載の発明は、請求項１記載の化合物半導体単結晶の製造方法において、種付け部からある成長時点までの引上軸の回転数を一定の割合で増加させることを特徴とする。
請求項３に記載の発明は、不活性ガスを充填した耐圧容器内に収容され加熱されたルツボに、原料融液、液体封止剤を収納し、引上軸に取り付けた種結晶を原料融液に接触させつつ種結晶とルツボとを相対的に移動させて化合物半導体単結晶を成長させるＬＥＣ法による化合物半導体単結晶の製造方法において、種付け部から定径部までの増径部、及び定径部初期の段階の引上軸の回転数を、それ以降の回転数以下とすることを特徴とする。
【００２３】
請求項４の発明は、請求項３記載の化合物半導体単結晶の製造方法において、種付け部から定径部までの増径部、及び定径部初期の段階の完了時点を、種付け部が液体封止剤の界面を過ぎた時点とすることを特徴とする。
【００２４】
請求項５の発明は、請求項３又は４記載の化合物半導体単結晶の製造方法において、種付け部から定径部までの増径部、及び定径部の初期までの引上軸の回転数を一定の割合で増加させることを特徴とする。
【００２５】
＜発明の要点＞
本発明の要点は、ＬＥＣ法での化合物半導体単結晶を製造する方法において、種付け部からある一定部位迄の引上軸の回転数を、その部位以降の引上軸回転数より遅くすることにあり、これにより、成長過程、特に種付け部からある一定部位までの成長初期段階での固液界面形状を再現性良く融液側に凸形状に制御することを可能とし、化合物半導体単結晶の収率を大幅に向上させるようにしたものである。
【００２６】
ＬＥＣ法ではコストの面から、種結晶の断面積を目標とする結晶断面積よりも小さい結晶を用い、種付け部、増径部、定径部、尾部と結晶成長を行うのが一般的である。また、引上軸の回転数は、種付け部、増径部、定径部、尾部に係わらず、一定とするのが一般的である。
【００２７】
また、固液界面形状は、融液の径方向の温度分布によってほぼ決定されるが、融液内の対流も固液界面形状に大きな影響を及ぼす。一般に、引上軸の回転数が小さいほど、固液界面形状は融液側に凸形状になることが知られている。
【００２８】
また、成長完了部（固化部）の断面積が小さい種付け部から結晶増径部までは、固化部からの放熱が少ないため、定径部に対し相対的に融液の対流の影響が大きくなり、よって固液界面形状に対する引上軸の回転数の影響が大きくなる。
【００２９】
そこで、本発明では、種付け部から定径部までの増径部、及び定径部初期の段階までの引上軸の回転数を、それ以降の部位の引上軸回転数より遅くすることにより、これらの成長初期段階での固液界面形状を再現性良く融液側に凸形状にすることを可能とし、化合物半導体単結晶の収率を大幅に向上させる。
【００３０】
【発明の実施の形態】
本発明の実施例について、以下に記す。
【００３１】
前提となる製造装置には上記した図１のものを用いた。すなわち、不活性ガスを充填した耐圧容器たるチャンバー９内に収容され加熱されたＰＢＮルツボ７に原料のＧａＡｓ融液９、液体封止剤の三酸化硼素融液４を収納し、種結晶２をＧａＡｓ融液９に接触させつつ種結晶２とルツボ７とを相対的に移動させて、ＬＥＣ法により化合物半導体単結晶を成長した。その際、ＰＢＮルツボ７と引上軸１は相対的に回転させた。
【００３２】
＜実施例＞
従来技術と同様に、直径が２８０ｍｍであるＰＢＮ製のルツボ７、断面１０ｍｍ角の種結晶２を用い、定径部３３の結晶直径１１０ｍｍ、結晶長さ４００ｍｍのＧａＡｓ単結晶３の成長を５０回行った。なお、この場合の引上軸１の回転数は、種付け部３１で２ｒｐｍ、定径部２０ｍｍ（定径部初期の段階）経過時点で８ｒｐｍとし、種付け部３１から定径部２０ｍｍ経過時点までの間の引上軸１の回転数は、一定の割合で増加することとした。
【００３３】
その結果、結晶の種付け部３１から結晶成長の最終部まで、全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）が９５％以上の確率で得られた。なお、この５０回の成長において、定径部２０ｍｍ経過時点では、種付け部３１は三酸化硼素融液４の界面を過ぎていた。
【００３４】
また、成長完了後の結晶の固液界面の形状を確認したところ、従来技術で成長した結晶の固液界面形状に比較し、融液側への凸の度合いが大きくなっていた。特に、結晶増径部３２での固液界面の融液側への凸の度合いが、定径部３３の凸の度合いに比較して相対的に大きかった。
【００３５】
また、種付け部３１からある成長時点（定径部２０ｍｍ経過時点）までの引上軸１の回転数が、それ以降の回転数以下である条件を満たす条件で、単結晶成長を５０回実施した。その結果、結晶の種付けから結晶成長最終部まで全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）は８０％以上の確率で得られた。なお、この５０回の成長においてのある成長時点では、種付け部は三酸化硼素融液４の界面を過ぎていた。
【００３６】
＜比較例＞
実施例と同様に、直径が２８０ｍｍであるＰＢＮ製のルツボ７、断面１０ｍｍ角の種結晶２を用い、定径部３３の結晶直径１１０ｍｍ、結晶長さ４００ｍｍのＧａＡｓ単結晶３の成長を５０回行った。なお、実施例と同様に引上軸１の回転数は、種付け部３１で２ｒｐｍ、定径部２０ｍｍ（定径部初期の段階）経過時点で８ｒｐｍとし、種付け部３１から定径部２０ｍｍ経過時点までの間の引上軸１の回転数は、一定の割合で増加することとした。但し、この５０回の成長において、定径部２０ｍｍ経過時点では、種付け部３１は三酸化硼素４の界面を過ぎていなかった。
【００３７】
この比較例の結果は、結晶の種付け部３１から結晶成長の最終部まで、全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）が８０％以下の確率であった。
【００３８】
本実施例の方法で得られる化合物半導体単結晶は、従来法よりも全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）の確率が高いだけではなく、従来法で得られた化合物半導体単結晶に比べ、転位の集積部が少ない傾向にある。これは、従来法の場合には、全域単結晶（Ａｌｌ Ｓｉｎｇｌｅ）であっても、リネージ、亜粒界には発展しないまでも転位が集積していることを示している。
【００３９】
本実施例で得られる化合物半導体ウェハは、これを用いて素子を形成した場合、転位に基づく素子歩留の低下を防止することができる。従って、本発明の工業生産における経済的効果は多大なものがある。
【００４０】
上記実施例では、ＧａＡｓ単結晶の成長方法の場合について記載したが、ＩｎＰ、ＧａＰ、ＩｎＡｓ等のＬＥＣ法で結晶成長を行う化合物半導体単結晶の成長方法についても、同様の効果が得られる。
【００４１】
【発明の効果】
以上説明したように本発明によれば、種付け部から定径部までの増径部、及び定径部初期の段階までの引上軸の回転数を、それ以降の部位の引上軸回転数より遅くしているので、成長過程、特に種付け部から定径部までの成長初期段階での固液界面形状を融液側に凸形状に再現性良く制御し、これにより化合物半導体単結晶の収率を大幅に向上させることができる。
【図面の簡単な説明】
【図１】本発明の化合物半導体単結晶の製造方法に用いた装置の概略図である。
【符号の説明】
１ 引上軸
２ 種結晶
３ 単結晶
４ 三酸化硼素融液
５ カーボン製ヒータ
６ ＧａＡｓ融液
７ ＰＢＮルツボ
８ ルツボ軸
９ チャンバー
３１ 種付け部
３２ 増径部（結晶肩部）
３３ 定径部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a compound semiconductor single crystal by a liquid encapsulating and pulling method (Liquid Encapsulated Czochralski method: LEC method), and more particularly to a technique for rotating a pulling shaft.
[0002]
[Prior art]
Compound semiconductors have been widely used in high-speed integrated circuits, opto-electronic integrated circuits, and other electronic devices due to the high quality of single crystals. Above all, gallium arsenide (GaAs), a III-V compound semiconductor, has a feature that electron mobility is faster than that of silicon and that a wafer having a specific resistance of 10 7 Ω · cm or more can be easily manufactured. At present, the GaAs single crystal is mainly manufactured by a liquid sealing and pulling method (LEC method).
[0003]
The GaAs single crystal growth method will be described with reference to FIG.
[0004]
An apparatus for producing a GaAs single crystal by the LEC method includes a chamber 9 as a pressure vessel, a pulling shaft 1 for pulling up a crystal, a crucible 7 made of Pyrolytic Boron Nitride (abbreviation: PBN) as a vessel for raw materials, and a PBN crucible. Having a crucible shaft 8 for receiving the heat.
[0005]
Regarding the crystal production method, first, Ga, As, and boron trioxide as a liquid sealant, which is a volatilization inhibitor of As, are put into a PBN crucible 7 serving as a raw material container, and this is set in a chamber 9. At the tip of the pulling shaft 1, a seed crystal 2 serving as a crystal is attached. The seed crystal 2 generally has a (100) plane in contact with the GaAs melt.
[0006]
After setting the raw material in the chamber 9, the inside of the chamber 9 is evacuated and filled with an inert gas. Thereafter, the carbon heater 5 installed in the chamber 9 is energized to increase the temperature in the chamber 9, and the boron trioxide is softened, melted and melted to obtain a boron trioxide melt 4. The temperature is further raised to synthesize Ga and As to produce GaAs, and then the temperature is further raised to melt the GaAs to obtain a GaAs melt 6.
[0007]
Subsequently, the pulling shaft 1 and the crucible shaft 8 are relatively rotated. In this state, the pulling shaft 1 is attached to the tip, and the seed crystal 2 is lowered until it comes into contact with the GaAs melt 6.
[0008]
Subsequently, the pull-up shaft 1 is raised at a constant speed while the set temperature of the carbon heater 5 is gradually lowered, so that the crystal diameter is gradually increased from the seed crystal 2 (seed portion 31) while the constant diameter portion 33 is gradually increased. The diameter increasing portion (crystal shoulder portion) 32 is formed. After the formation of the shoulder portion, when the target crystal outer diameter is reached, the GaAs single crystal 3 is manufactured while controlling the outer shape in order to keep the outer diameter constant.
[0009]
However, the technique of growing a compound semiconductor single crystal by the LEC method is very difficult, and depends on the arrangement, shape, material, and the like of a heater (heating zone) and other members (called a hot zone; hereinafter, referred to as HZ) such as a heating means. Since it is more minutely affected, it is difficult to obtain a condition for growing a compound semiconductor single crystal with good reproducibility. Although it has been considered that the factors for obtaining a compound semiconductor single crystal with good reproducibility are related to the HZ, such as the arrangement, shape, and material of the HZ, the interface between the solidified single crystal and the melt (hereinafter, referred to as the “solid It has become clear that how to control the shape of the “liquid interface” is a major factor in obtaining a single crystal.
[0010]
The relationship between the solid-liquid interface shape and the yield of single crystal is such that when the solid-liquid interface is concave on the melt side, regardless of the overall growth process or a certain period of growth, lineage and sub-grain boundaries are crystal defects. Are easily accumulated and polycrystalline. Naturally, the single crystal yield also decreases. In order to improve the single crystal yield, it is important to control the solid-liquid interface to be convex toward the melt over the entire growth process.
[0011]
Therefore, based on the temperature gradient of the melt, a critical rotation speed table composed of a set of fixed values such as 3 rpm, 6 rpm, and 10 rpm is prepared, and the rotational pull-up optimal control refers to the critical rotation speed table to extract the critical rotation speed. A method of controlling the rotation pulling mechanism to the critical rotation speed or a slightly lower rotation speed (for example, see Patent Document 1), a natural convection flowing near the crucible side wall and flowing toward the grown crystal, Recognizing that swirling forced convection occurs near the solid-liquid interface due to rotation, a cylindrical body is arranged around the growing crystal and the tip is immersed in the raw material melt, and any of the crucible, growing crystal, and cylindrical body A method has been proposed in which the crystal is pulled up while appropriately setting the number of revolutions to prevent the solid-liquid interface shape from being depressed (for example, see Patent Document 2).
[0012]
However, even under these controls, the number of rotations of the pulling shaft during the production of the compound semiconductor single crystal by the conventional LEC method is constant irrespective of the part of the crystal to be grown such as the seeding part, the diameter increasing part, and the constant diameter part. It is common to do.
[0013]
Gallium arsenide (hereinafter referred to as GaAs), which is a kind of compound semiconductor, will be described as an example. Using a PBN crucible having a diameter of 280 mm and a seed crystal having a cross section of 10 mm square, single crystal growth of gallium arsenide having a crystal diameter of a fixed diameter portion of 110 mm and a crystal length of 400 mm was performed 50 times at a rotation speed of a pulling shaft of 8 rpm. Was. As a result, the entire single crystal (All Single) from the seeding of the crystal to the final part of the crystal growth was 50% or less.
[0014]
[Patent Document 1]
JP-A-6-183877 (paragraph number 0015, FIG. 4B)
[0015]
[Patent Document 2]
JP-A-8-310893 (paragraph numbers 0029 and 0013, FIG. 2)
[0016]
[Problems to be solved by the invention]
As described above, it is very difficult to improve the single crystal yield in the production of a compound semiconductor single crystal by the LEC method.
[0017]
A major point for improving the single crystal yield is to control the solid-liquid interface to be convex toward the melt over the entire growth process. In particular, lineage, which is a crystal defect, and accumulation of sub-grain boundaries often occur at the initial stage of growth from the seeded portion to the constant diameter portion, and therefore, at the initial growth stage from the seeded portion to the constant diameter portion. It is particularly necessary to control the solid-liquid interface shape with good reproducibility.
[0018]
At present, it is difficult to control the solid-liquid interface shape with good reproducibility, especially to control the solid-liquid interface to have a convex shape toward the melt, causing a decrease in the yield of the compound semiconductor single crystal. .
[0019]
In view of the above, an object of the present invention is to solve the above-mentioned problems and to reproduce the solid-liquid interface shape at the initial stage of growth from the seeding portion to the constant diameter portion in the growth of the compound semiconductor single crystal by the LEC method. An object of the present invention is to provide a method for producing a compound semiconductor single crystal, which can be controlled to have a shape that is well convex toward the melt and can significantly improve the yield of the compound semiconductor single crystal.
[0020]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0021]
According to the first aspect of the present invention, a raw material melt and a liquid sealant are stored in a heated crucible housed in a pressure-resistant container filled with an inert gas, and the seed crystal attached to the pulling shaft is melted. In a method of manufacturing a compound semiconductor single crystal by the LEC method in which a compound semiconductor single crystal is grown by relatively moving a seed crystal and a crucible while being in contact with a liquid, the number of rotations of a pulling shaft from a seeding portion to a certain growth point Is set to be equal to or less than the rotation speed thereafter.
[0022]
According to a second aspect of the present invention, in the method of manufacturing a compound semiconductor single crystal according to the first aspect, the rotation speed of the pulling shaft from the seeding portion to a certain growth point is increased at a constant rate.
According to a third aspect of the present invention, a raw material melt and a liquid sealant are stored in a heated crucible housed in a pressure-resistant container filled with an inert gas, and the seed crystal attached to the pulling shaft is melted. In a method for producing a compound semiconductor single crystal by the LEC method of growing a compound semiconductor single crystal by relatively moving a seed crystal and a crucible while being in contact with a liquid, a diameter increasing portion from a seeding portion to a constant diameter portion, and a constant diameter portion. The rotation speed of the pulling shaft in the initial stage of the diameter portion is set to be equal to or less than the rotation speed thereafter.
[0023]
According to a fourth aspect of the present invention, in the method for manufacturing a compound semiconductor single crystal according to the third aspect, the seeding section is configured to perform liquid sealing with respect to completion of the diameter increasing section from the seeding section to the constant diameter section and the initial stage of the constant diameter section. It is characterized by the point in time after passing through the interface of the blocking agent.
[0024]
According to a fifth aspect of the present invention, in the method for manufacturing a compound semiconductor single crystal according to the third or fourth aspect, the number of rotations of the pulling shaft from the seeding portion to the constant diameter portion and the initial diameter of the constant diameter portion is reduced. It is characterized in that it is increased at a constant rate.
[0025]
<The gist of the invention>
The gist of the present invention is that, in the method of manufacturing a compound semiconductor single crystal by the LEC method, the rotation speed of the pulling shaft from a seeding portion to a certain portion is made slower than the pulling shaft rotation speed after that portion. This makes it possible to control the shape of the solid-liquid interface in the growth process, particularly at the initial stage of growth from the seeding portion to a certain site, to a shape that is convex toward the melt with good reproducibility, and the yield of the compound semiconductor single crystal is improved. The rate is greatly improved.
[0026]
In the LEC method, from the viewpoint of cost, it is common to use a crystal whose cross-sectional area of a seed crystal is smaller than a target crystal cross-sectional area and grow a seed, a diameter-increased portion, a constant-diameter portion, and a tail portion. . In addition, the rotation speed of the pulling shaft is generally constant regardless of the seeding portion, the increased diameter portion, the fixed diameter portion, and the tail portion.
[0027]
Further, the shape of the solid-liquid interface is substantially determined by the temperature distribution in the radial direction of the melt, but convection in the melt also has a large effect on the shape of the solid-liquid interface. In general, it is known that the lower the rotation speed of the pulling shaft, the more the solid-liquid interface shape becomes convex toward the melt.
[0028]
In addition, from the seeded part where the cross-sectional area of the growth completed part (solidified part) is small to the crystal diameter-increased part, the heat radiation from the solidified part is small, so the influence of the convection of the melt becomes relatively large with respect to the constant diameter part. Therefore, the influence of the rotation speed of the pulling shaft on the solid-liquid interface shape becomes large.
[0029]
Therefore, in the present invention, by increasing the rotation speed of the raising shaft from the seeding portion to the constant diameter portion, and the initial stage of the constant diameter portion to the initial stage, by lowering the rotation speed of the pulling shaft of the subsequent portions. In addition, it is possible to make the solid-liquid interface shape at the initial stage of the growth a convex shape toward the melt with good reproducibility, and to greatly improve the yield of the compound semiconductor single crystal.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below.
[0031]
The manufacturing apparatus used as the premise was the one shown in FIG. That is, a GaAs melt 9 as a raw material and a boron trioxide melt 4 as a liquid sealant are housed in a heated PBN crucible 7 housed in a chamber 9 which is a pressure-resistant container filled with an inert gas, and the seed crystal 2 is cooled. The seed crystal 2 and the crucible 7 were relatively moved while being brought into contact with the GaAs melt 9 to grow a compound semiconductor single crystal by the LEC method. At that time, the PBN crucible 7 and the pulling shaft 1 were relatively rotated.
[0032]
<Example>
As in the prior art, using a PBN crucible 7 having a diameter of 280 mm and a seed crystal 2 having a cross section of 10 mm square, the GaAs single crystal 3 having a crystal diameter of 110 mm of the constant diameter portion 33 and a crystal length of 400 mm was grown 50 times. went. In this case, the rotation speed of the pull-up shaft 1 is 2 rpm at the seeding portion 31 and 8 rpm at the time when the constant diameter portion 20 mm (the initial stage of the constant diameter portion) has passed. The number of rotations of the pulling shaft 1 between them is increased at a constant rate.
[0033]
As a result, an entire single crystal (All Single) was obtained with a probability of 95% or more from the seeding portion 31 of the crystal to the final portion of the crystal growth. In the 50 growths, the seeding portion 31 had passed the interface of the boron trioxide melt 4 at the time when the constant diameter portion had passed 20 mm.
[0034]
Further, when the shape of the solid-liquid interface of the crystal after the completion of the growth was confirmed, the degree of protrusion toward the melt was larger than that of the crystal grown by the conventional technique. In particular, the degree of protrusion of the solid-liquid interface toward the melt at the crystal diameter increasing part 32 was relatively larger than the degree of protrusion of the constant diameter part 33.
[0035]
In addition, the single crystal was grown 50 times under the condition that the rotation speed of the pull-up shaft 1 from the seeding portion 31 to a certain growth time (elapse of 20 mm of the constant diameter portion) is equal to or less than the rotation speed thereafter. . As a result, an entire single crystal (All Single) was obtained with a probability of 80% or more from the seeding of the crystal to the final part of the crystal growth. At some point during the 50 growths, the seeding portion had passed the interface of the boron trioxide melt 4.
[0036]
<Comparative example>
As in the embodiment, a GaAs single crystal 3 having a crystal diameter of 110 mm and a crystal length of 400 mm was grown 50 times using a PBN crucible 7 having a diameter of 280 mm and a seed crystal 2 having a cross section of 10 mm square. went. As in the embodiment, the rotation speed of the pulling shaft 1 is 2 rpm at the seeding portion 31 and 8 rpm at the time when the constant diameter portion 20 mm (the initial stage of the constant diameter portion) has passed, and at the time when the constant diameter portion 20 mm has passed from the seeding portion 31. The rotation speed of the pulling shaft 1 during this period is to be increased at a constant rate. However, in the 50 growths, the seeding portion 31 had not passed the interface of the boron trioxide 4 at the time when the constant diameter portion had passed 20 mm.
[0037]
As a result of this comparative example, from the seeding part 31 of the crystal to the final part of the crystal growth, the probability of the whole area single crystal (All Single) being 80% or less.
[0038]
The compound semiconductor single crystal obtained by the method of the present embodiment not only has a higher probability of an all single crystal (All Single) than the conventional method, but also has a higher dislocation accumulation portion than the compound semiconductor single crystal obtained by the conventional method. Tend to be less. This indicates that in the case of the conventional method, even in the case of an all single crystal, dislocations accumulate even if they do not develop into lineage and sub-grain boundaries.
[0039]
When the compound semiconductor wafer obtained in this example is used to form an element, it is possible to prevent a decrease in element yield due to dislocation. Therefore, the economic effects of the present invention in industrial production are significant.
[0040]
In the above embodiment, the case of the method of growing a GaAs single crystal has been described. However, a similar effect can be obtained also in the case of a method of growing a compound semiconductor single crystal in which crystal growth is performed by an LEC method such as InP, GaP, and InAs.
[0041]
【The invention's effect】
As described above, according to the present invention, the diameter of the diameter increasing portion from the seeding portion to the constant diameter portion, and the number of rotations of the pulling shaft up to the initial stage of the constant diameter portion, the number of rotations of the raising shaft of the subsequent portions. Since it is slower, the shape of the solid-liquid interface in the growth process, especially in the initial stage of growth from the seeding portion to the constant diameter portion, is controlled to be convex toward the melt with good reproducibility, thereby obtaining the compound semiconductor single crystal. The rate can be greatly improved.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus used for a method for producing a compound semiconductor single crystal of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pull-up shaft 2 Seed crystal 3 Single crystal 4 Boron trioxide melt 5 Carbon heater 6 GaAs melt 7 PBN crucible 8 Crucible shaft 9 Chamber 31 Seeding part 32 Increased diameter part (crystal shoulder part)
33 constant diameter part
