JP5244007B2 - Method for producing 3C-SiC single crystal - Google Patents

Method for producing 3C-SiC single crystal Download PDF

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JP5244007B2
JP5244007B2 JP2009075974A JP2009075974A JP5244007B2 JP 5244007 B2 JP5244007 B2 JP 5244007B2 JP 2009075974 A JP2009075974 A JP 2009075974A JP 2009075974 A JP2009075974 A JP 2009075974A JP 5244007 B2 JP5244007 B2 JP 5244007B2
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徹 宇治原
亮 田中
和明 関
美和 竹田
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Nagoya University NUC
Tokai National Higher Education and Research System NUC
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本発明は、立方晶炭化珪素(3C−SiC)単結晶の製造方法に関するものである。   The present invention relates to a method for producing a cubic silicon carbide (3C—SiC) single crystal.

炭化珪素(SiC)は、熱的および化学的に非常に安定な半導体材料である。SiCは、電子デバイスなどの基板材料として現在広く用いられている珪素(Si)と比較して、禁制帯幅が2〜3倍程度、絶縁破壊電圧が約10倍である。そのため、SiC単結晶は、珪素を用いたデバイスを超えるパワーデバイスの基板材料などとしての応用が期待されている。   Silicon carbide (SiC) is a highly thermally and chemically stable semiconductor material. SiC has a forbidden band width of about 2 to 3 times and a breakdown voltage of about 10 times that of silicon (Si), which is currently widely used as a substrate material for electronic devices and the like. Therefore, the SiC single crystal is expected to be applied as a substrate material for power devices exceeding the devices using silicon.

SiCは200種類以上の多くの結晶多形をもつと言われている。結晶多形とは、化学量論的には同じ組成でありながら、Si−C結合をもつ正四面体構造からなる正四面体構造層の積層順序が異なるものである。代表的な多形として、3C−SiC、6H−SiC、4H−SiC、15R−SiCが挙げられる。ここで、Cは立方晶、Hは六方晶、Rは菱面体構造、数字は積層方向の一周期中に含まれる正四面体構造層の数を表す。なかでも、4H−SiC単結晶は、他の多形よりも禁制帯幅および電子移動度の点で優れるため、各種デバイスの基板材料として有望視されている。   SiC is said to have many crystal polymorphs of over 200 types. The crystal polymorph is a composition having the same stoichiometric composition but a different stacking order of a regular tetrahedral structure layer composed of a regular tetrahedral structure having a Si—C bond. Typical polymorphs include 3C—SiC, 6H—SiC, 4H—SiC, and 15R—SiC. Here, C represents a cubic crystal, H represents a hexagonal crystal, R represents a rhombohedral structure, and a number represents the number of regular tetrahedral structure layers included in one cycle in the stacking direction. Among these, 4H—SiC single crystal is promising as a substrate material for various devices because it is superior to other polymorphs in terms of forbidden band width and electron mobility.

ところで、集積化に適した回路素子として、MOS素子がある。MOS素子は、金属と半導体との間にSiOなどの酸化物が挟まれた構造をもつ。MOS素子においては、半導体/酸化物の界面状態を改善する、具体的には、界面準位密度を減少させて電子移動度を向上させることが重要である。MOS素子において、酸化物としてSiO、半導体として3C−SiC単結晶を用いると、半導体として4H−SiC単結晶を用いた場合よりも界面準位密度が減少し電子移動度が向上することが知られている。つまり、MOS素子、MOS構造をゲートに用いた電界効果トランジスタ(MOSFET)等には、3C−SiC単結晶の使用が有効である。 Incidentally, there is a MOS element as a circuit element suitable for integration. The MOS element has a structure in which an oxide such as SiO 2 is sandwiched between a metal and a semiconductor. In a MOS device, it is important to improve the semiconductor / oxide interface state, specifically, to reduce the interface state density and improve the electron mobility. In a MOS device, it is known that the use of SiO 2 as an oxide and 3C—SiC single crystal as a semiconductor reduces the interface state density and improves the electron mobility as compared with the case of using 4H—SiC single crystal as a semiconductor. It has been. That is, it is effective to use a 3C-SiC single crystal for a MOS element, a field effect transistor (MOSFET) using a MOS structure as a gate, or the like.

さらに、3C−SiC単結晶は、窒化物系材料の無極性成長用の基板としても注目されている。たとえば、窒化ガリウム(GaN)などは、電子デバイス、LEDなどに使用されるが、ピエゾ効果による特性の低下が問題となる。この特性の低下は、GaNを無極性方向へ成長させることで抑制されることが知られている。3C−SiC単結晶は、窒化物系材料に対する格子不整合が他の化合物半導体に比べて小さいため、窒化物系材料のエピタキシャル成長に好適な無極性面が得られる。   Further, the 3C—SiC single crystal has attracted attention as a substrate for nonpolar growth of nitride-based materials. For example, gallium nitride (GaN) or the like is used for electronic devices, LEDs, and the like, but the deterioration of characteristics due to the piezoelectric effect is a problem. It is known that this deterioration in characteristics is suppressed by growing GaN in a nonpolar direction. The 3C—SiC single crystal has a small lattice mismatch with respect to the nitride-based material as compared with other compound semiconductors, so that a nonpolar plane suitable for epitaxial growth of the nitride-based material can be obtained.

現在、3C−SiCなどのSiC単結晶の製造方法としては、気相成長法(化学蒸着(CVD)法または昇華法)と液相成長法とがある。3C−SiC単結晶は、シランガスおよび炭化水素系ガスを原料ガスとして用いたCVD法により、Si基板表面に形成することができる。しかし、CVD法では、3C−SiCとSiとの格子定数の差が大きいため、Si基板表面に成長する3C−SiCに欠陥が生じやすく積層欠陥密度が5000cm−1以上となるため、高品質な3C−SiC単結晶が得られるとは言い難い。 Currently, there are a vapor phase growth method (chemical vapor deposition (CVD) method or a sublimation method) and a liquid phase growth method as a method for producing a SiC single crystal such as 3C-SiC. The 3C—SiC single crystal can be formed on the surface of the Si substrate by a CVD method using silane gas and hydrocarbon-based gas as source gases. However, since the difference in lattice constant between 3C-SiC and Si is large in the CVD method, defects are likely to occur in 3C-SiC grown on the surface of the Si substrate, and the stacking fault density becomes 5000 cm -1 or higher. It is difficult to say that a 3C—SiC single crystal is obtained.

昇華法は、SiC粉末を原料とし、2000℃以上の高温で原料を昇華させ、SiとCとからなる蒸気を低温にした種結晶基板上で過飽和にし、SiC単結晶を析出させる方法である。この方法によれば、種結晶基板としても使用可能な比較的大型のSiC基板を製造することが可能となる。しかし、SiCが安定に存在する温度域は、6H−SiC→4H−SiC→3C−SiCの順で低くなり、2000℃以上の高温では3C−SiCの存在確率は、格段に低くなる。つまり、昇華法により6H−SiCおよび4H−SiCの単結晶を製造することは容易であるが、3C−SiC単結晶を製造することは困難である。   The sublimation method is a method in which SiC powder is used as a raw material, the raw material is sublimed at a high temperature of 2000 ° C. or higher, supersaturated on a seed crystal substrate at a low temperature of Si and C, and a SiC single crystal is precipitated. According to this method, it is possible to manufacture a relatively large SiC substrate that can also be used as a seed crystal substrate. However, the temperature range where SiC exists stably decreases in the order of 6H—SiC → 4H—SiC → 3C—SiC, and the existence probability of 3C—SiC is significantly reduced at a high temperature of 2000 ° C. or higher. That is, it is easy to produce 6H—SiC and 4H—SiC single crystals by the sublimation method, but it is difficult to produce 3C—SiC single crystals.

液相成長法では、SiまたはSi合金の融液中に炭素を溶解させて、原料融液を調製する。このSiC溶液に種結晶基板を浸漬し、少なくとも基板近傍の溶液を過冷却状態にすることで過飽和状態を作り出し、SiC単結晶を種結晶基板上にエピタキシャル成長させる。液相成長法では、熱平衡状態に近い環境で結晶成長が行われるため、積層欠陥などの欠陥密度の低い良質なSiC単結晶が得られる。また、比較的低温での結晶成長が可能であることから、3C−SiC単結晶であっても製造可能である。   In the liquid phase growth method, carbon is dissolved in a melt of Si or a Si alloy to prepare a raw material melt. A seed crystal substrate is immersed in this SiC solution, and a supersaturated state is created by bringing the solution in the vicinity of the substrate into a supercooled state, and an SiC single crystal is epitaxially grown on the seed crystal substrate. In the liquid phase growth method, since crystal growth is performed in an environment close to a thermal equilibrium state, a high-quality SiC single crystal having a low defect density such as stacking faults can be obtained. Further, since crystal growth at a relatively low temperature is possible, even a 3C—SiC single crystal can be manufactured.

以上より、3C−SiC単結晶の製造方法として好適なのは、低欠陥密度の結晶が得られる液相成長法である。3C−SiC単結晶を製造可能な液相成長法の具体例として、以下の特許文献1〜3がある。   From the above, the preferred method for producing a 3C—SiC single crystal is a liquid phase growth method that yields crystals with a low defect density. As specific examples of the liquid phase growth method capable of producing a 3C—SiC single crystal, there are the following Patent Documents 1 to 3.

特許文献1では、1670〜1900℃の温度範囲で、SiとCと第三の元素を含む原料融液を用い、SiC単結晶基板の表面に第三の元素の種類に応じた種々のSiC単結晶を成長させることが記載されている。たとえば、スカンジウム(Sc)を2重量%含む1680℃のSiC溶液を用い、6H−または15R−SiC単結晶基板の表面にSiC単結晶を成長させると、3C−SiC単結晶が成長すると記載されている。その一方で、Scを含むSiC溶液を1860℃とすると、基板と同様の構造をもつSiCが得られることが記載されている。   In Patent Document 1, a raw material melt containing Si, C, and a third element is used in a temperature range of 1670 to 1900 ° C., and various SiC single crystals corresponding to the type of the third element are formed on the surface of the SiC single crystal substrate. It is described to grow crystals. For example, it is described that when a SiC single crystal is grown on the surface of a 6H- or 15R-SiC single crystal substrate using a 1680 ° C SiC solution containing 2% by weight of scandium (Sc), a 3C-SiC single crystal grows. Yes. On the other hand, it is described that when the SiC solution containing Sc is 1860 ° C., SiC having the same structure as the substrate can be obtained.

特許文献2では、SiとCとを含む原料融液に、15R−SiC単結晶基板を接触させ、基板の周囲に所定の温度勾配を生じさせて、基板の(000−1)炭素面に3C−SiC単結晶を成長させている。このとき、種結晶基板の温度を1700〜1900℃とし、原料融液内部から種結晶基板と接触する表面に向かう温度勾配を5〜50℃/mmの範囲内としている。   In Patent Document 2, a 15R-SiC single crystal substrate is brought into contact with a raw material melt containing Si and C, a predetermined temperature gradient is generated around the substrate, and 3C is formed on the (000-1) carbon surface of the substrate. -Growing SiC single crystal. At this time, the temperature of the seed crystal substrate is set to 1700 to 1900 ° C., and the temperature gradient from the inside of the raw material melt toward the surface in contact with the seed crystal substrate is set in the range of 5 to 50 ° C./mm.

特許文献3では、Si−Al合金を溶媒とするSiC溶液を原料融液とし、サファイアと原料融液とを反応させて、サファイア結晶の(0001)面に3C−SiC単結晶を成長させている。このとき、サファイア結晶が溶解しないように、原料融液の温度を1500℃以下としている。また、サファイアと原料融液との反応生成物がアルミナ(Al)となるように、原料融液としてアルミニウム(Al)を含む溶媒を用いている。 In Patent Document 3, a SiC solution using a Si—Al alloy as a solvent is used as a raw material melt, and sapphire and the raw material melt are reacted to grow a 3C—SiC single crystal on the (0001) plane of the sapphire crystal. . At this time, the temperature of the raw material melt is set to 1500 ° C. or less so that the sapphire crystal does not dissolve. Further, a solvent containing aluminum (Al) is used as the raw material melt so that the reaction product of sapphire and the raw material melt becomes alumina (Al 2 O 3 ).

特開2006−321681号公報JP 2006-321681 A 特開2007−197274号公報JP 2007-197274 A 特開2008−100890号公報JP 2008-1000089 A

液相成長法により作製される3C−SiC単結晶は、CVD法に比べ、欠陥密度が低減される。しかしながら、液相成長法により基板の表面に3C−SiC単結晶を成長させても、さらに成長させる過程において結晶構造が変化しやすく、3C−SiCの構造を保ったままで大きく成長させることは困難である。これは、SiCの結晶構造が多形現象を示し、結晶成長過程で正四面体構造層の積層順序が僅かに変わるだけで、その構造が容易に変化するためである。つまり、引用文献1〜3に記載のような方法を用いても、大型の3C−SiC単結晶は得られていないのが実状である。   The defect density of the 3C—SiC single crystal produced by the liquid phase growth method is reduced as compared with the CVD method. However, even if a 3C-SiC single crystal is grown on the surface of the substrate by the liquid phase growth method, the crystal structure is likely to change during the further growth process, and it is difficult to grow large while maintaining the 3C-SiC structure. is there. This is because the crystal structure of SiC exhibits a polymorphism, and the structure easily changes even if the stacking order of the tetrahedral structure layers slightly changes during the crystal growth process. That is, even if the methods described in the cited documents 1 to 3 are used, a large 3C-SiC single crystal is not actually obtained.

また、種結晶基板として3C−SiC単結晶を用いれば、3C−SiC単結晶を容易に製造できる可能性はある。しかし、種結晶基板として3C−SiC単結晶を使用できない。これは、種結晶基板として好適な大型の3C−SiC単結晶が存在しないためである。大型のSiC単結晶は昇華法により作製が可能であるが、既に述べたように、昇華法では、3C−SiC単結晶は得られない。また、CVD法により得られる3C−SiC単結晶は欠陥密度が高い。欠陥密度の高い基板を液相成長法に用いても、基板の表面に成長する結晶に欠陥が伝搬するため、良質な3C−SiC単結晶は得られない。   Further, if a 3C—SiC single crystal is used as the seed crystal substrate, there is a possibility that the 3C—SiC single crystal can be easily manufactured. However, a 3C—SiC single crystal cannot be used as a seed crystal substrate. This is because there is no large 3C—SiC single crystal suitable as a seed crystal substrate. A large SiC single crystal can be manufactured by a sublimation method, but as already described, a 3C-SiC single crystal cannot be obtained by a sublimation method. In addition, a 3C—SiC single crystal obtained by a CVD method has a high defect density. Even when a substrate having a high defect density is used in the liquid phase growth method, defects propagate to the crystal growing on the surface of the substrate, and thus a high-quality 3C—SiC single crystal cannot be obtained.

なお、引用文献3のように、サファイアのような異種材料を種結晶基板として用いると、サファイア結晶と3C−SiC単結晶との界面には欠陥が生じやすい。この欠陥は、3C−SiC単結晶の厚みの増加に伴い減少するが、欠陥の少ない高品質な3C−SiC単結晶は、表面から数ミクロン厚程度である。さらに、3C−SiC単結晶を厚く成長させる程、多形変化を起こして3C構造以外の構造に変化する可能性は高まる。   Note that when a different material such as sapphire is used as a seed crystal substrate as in the cited document 3, defects are likely to occur at the interface between the sapphire crystal and the 3C-SiC single crystal. This defect decreases as the thickness of the 3C-SiC single crystal increases, but a high-quality 3C-SiC single crystal with few defects is about several microns thick from the surface. Furthermore, as the 3C-SiC single crystal grows thicker, the possibility of causing a polymorphic change and changing to a structure other than the 3C structure increases.

本発明は、上記問題点に鑑み、低欠陥密度で種結晶基板としても使用可能な程度に大型である3C−SiC単結晶を容易に成長させることができる3C−SiC単結晶の製造方法を提供することを目的とする。   In view of the above problems, the present invention provides a method for producing a 3C-SiC single crystal capable of easily growing a 3C-SiC single crystal that has a low defect density and is large enough to be used as a seed crystal substrate. The purpose is to do.

3C−SiC単結晶の製造においては、成長過程の多形変化を抑制することが重要である。たとえば、昇華法による単結晶の成長においては、種結晶基板がもつ“らせん転位”により形成されるステップからの結晶成長(ステップフロー成長)により種結晶の積層順序を継承させることで、多形変化を抑制している。また、CVD法による単結晶の成長においては、種結晶基板のオフ角を利用した、いわゆる「ステップ制御エピタキシー法」による基板のステップからの結晶成長により種結晶の積層順序を継承させることで、多形変化を抑制している。液相成長法においても、成長速度が十分に遅い場合は同様にして種結晶の結晶構造を継承させることができるが、テラス上に形成された結晶核が「二次元核成長」して多形変化が生じることがある。そこで、本発明者等は発想を転換し、種結晶基板の積層順序の継承という方法ではなく、二次元核成長する結晶構造を常に熱力学的に安定化させることで、多形変化を抑制する方法を見出した。そして、結晶成長における種結晶基板と原料融液との固液界面エネルギーを制御することによって3C−SiC単結晶を安定に二次元核成長させることに成功した。そして本発明者は、この成果を発展させることで、以降に述べる発明を完成させるに至った。   In the production of 3C—SiC single crystal, it is important to suppress polymorphic changes in the growth process. For example, in the growth of single crystals by the sublimation method, polymorphic changes are made by inheriting the stacking order of the seed crystals by crystal growth (step flow growth) from the steps formed by the “screw dislocations” of the seed crystal substrate. Is suppressed. In addition, in the growth of a single crystal by the CVD method, the seed crystal stacking order is inherited by crystal growth from the step of the substrate by the so-called “step control epitaxy method” using the off-angle of the seed crystal substrate. The shape change is suppressed. Even in the liquid phase growth method, if the growth rate is sufficiently slow, the crystal structure of the seed crystal can be inherited in the same way, but the crystal nuclei formed on the terrace are “two-dimensional nuclei growth” and polymorphic Changes may occur. Therefore, the inventors changed the way of thinking and suppressed polymorphic change by always thermodynamically stabilizing the crystal structure that grows two-dimensional nuclei, not the method of inheriting the stacking order of the seed crystal substrate. I found a way. Then, by controlling the solid-liquid interface energy between the seed crystal substrate and the raw material melt during crystal growth, the 3C-SiC single crystal was successfully grown in a two-dimensional nucleus. The present inventor has developed this result and completed the invention described below.

すなわち、本発明の3C−SiC単結晶の製造方法は、液相成長法を用いた3C−SiC単結晶の製造方法であって、
Si−Sc系溶媒に炭素が溶解している原料融液を1350℃未満とし、該原料溶液を6H−SiC単結晶基板の少なくとも(0001)炭素面に接触させて該面に3C−SiC単結晶を二次元核成長させることを特徴とする。
That is, the 3C-SiC single crystal manufacturing method of the present invention is a 3C-SiC single crystal manufacturing method using a liquid phase growth method,
The raw material melt in which carbon is dissolved in the Si—Sc solvent is set to less than 1350 ° C., and the raw material solution is brought into contact with at least the (0001) carbon surface of the 6H—SiC single crystal substrate to form a 3C—SiC single crystal on the surface. Is characterized by two-dimensional nuclear growth.

結晶成長における固液界面エネルギーを考慮すると、二次元核成長における多形変化を抑制することが可能である。図4は本発明者等が作成した、安定なSiC多形の成長条件を示すダイアグラムである。6H−SiC結晶基板に3C−SiC単結晶を成長させる場合、3C−SiCの固液界面エネルギーσが6H−SiCの固液界面エネルギーσよりも小さく、かつ、その差(σ−σ)が大きくなるほど3C−SiCの安定な領域が広くなり、3C−SiCが成長しやすい。また、3C−SiCの固液界面エネルギーσが小さいほど3C−SiCが成長しやすいとも言える。しかし、3C−SiCの固液界面エネルギーσが小さくても、高温域に6H−SiCが安定な領域が存在する。つまり、低温かつ低σのもとで、6H−SiC結晶基板に3C−SiCの単結晶を安定に二次元核成長させることができる。なお、図4のダイアグラムは下記の式に基づき作成された。 Considering the solid-liquid interface energy in crystal growth, it is possible to suppress polymorphic changes in two-dimensional nucleus growth. FIG. 4 is a diagram showing the growth conditions of a stable SiC polymorph prepared by the present inventors. When a 3C-SiC single crystal is grown on a 6H-SiC crystal substrate, the solid-liquid interface energy σ B of 3C-SiC is smaller than the solid-liquid interface energy σ A of 6H-SiC, and the difference (σ AAs B ) increases, the stable region of 3C—SiC increases and 3C—SiC is likely to grow. It can also be said that 3C-SiC grows easier as the solid-liquid interface energy σ B of 3C-SiC is smaller. However, even if the solid-liquid interface energy σ B of 3C—SiC is small, there is a region where 6H—SiC is stable in the high temperature region. That is, a 3C—SiC single crystal can be stably grown in a two-dimensional nucleus on a 6H—SiC crystal substrate at low temperature and low σ B. The diagram in FIG. 4 was created based on the following formula.

ここで、ΔGは結晶構造Aの結晶に結晶構造Bの結晶が二次元核成長するときの自由エネルギー変化、Δμは結晶構造Bの結晶化の駆動力、χは二次元核のエッジエネルギー、Sは分子の占める面積、σは結晶構造Aの固液界面エネルギー、σは結晶構造Bの固液界面エネルギー、σは結晶構造Aの結晶と結晶構造Bの結晶との界面エネルギー、である。ΔGの値が小さい程、二次元核形成が生じやすい。 Here, ΔG * is a change in free energy when the crystal of the crystal structure B grows in the crystal of the crystal structure A, Δμ B is the driving force for crystallization of the crystal structure B, and χ B is the edge of the two-dimensional nucleus energy, S C is the area occupied by the molecules, sigma a solid-liquid interfacial energy of the crystal structure a, sigma B is the solid-liquid interfacial energy of the crystal structure B, sigma i is the crystal of the crystal structure B with crystals of crystal structure a Interfacial energy. As the value of ΔG * is smaller, two-dimensional nucleation is more likely to occur.

原料融液の溶媒については、これまでにも多くの試みがなされているが、そのほとんどは試行錯誤であり、溶媒組成と多形変化との関連は全く解明されていなかった。本発明の3C−SiC単結晶の製造方法では、従来のSi系溶媒にScを添加したSi−Sc系溶媒を用いることで、6H−SiCと3C−SiCとの固液界面エネルギー差を大きくでき、SiC単結晶の3C構造を安定化させる。また、Si−Sc系合金は、Si−Sc二元合金の状態図(省略)から明らかなように、Scの添加量に応じて融点が1155℃まで低下する。そのため、3C−SiC単結晶の二次元核成長に望ましい1350℃未満の原料融液温度を実現することができる。   Many attempts have been made for the solvent of the raw material melt, but most of them have been trial and error, and the relationship between the solvent composition and the polymorphic change has not been elucidated at all. In the method for producing a 3C-SiC single crystal according to the present invention, the difference in solid-liquid interface energy between 6H-SiC and 3C-SiC can be increased by using a Si-Sc solvent obtained by adding Sc to a conventional Si solvent. , Stabilize the 3C structure of the SiC single crystal. Further, as is clear from the phase diagram (omitted) of the Si—Sc binary alloy, the melting point of the Si—Sc alloy decreases to 1155 ° C. depending on the amount of Sc added. Therefore, it is possible to realize a raw material melt temperature of less than 1350 ° C. desirable for two-dimensional nucleus growth of 3C—SiC single crystal.

また、本発明の3C−SiC単結晶の製造方法では、3C−SiC単結晶を、6H−SiC単結晶基板の(0001)炭素面に二次元核成長させる。(0001)面は、正四面体構造層の積層方向である[0001]方向に垂直な面である。つまり、この(0001)面は、積層される正四面体構造層の積層順序によって結晶構造が変化する面である。そのため、種結晶基板として6H−SiC単結晶を用いても、(0001)面にSiC単結晶を成長させれば、6H−SiC単結晶とは積層順序の異なる3C−SiC単結晶であっても安定に成長する。さらに、6H−SiC単結晶基板の(0001)炭素面であれば、6H−SiC単結晶基板の(000−1)珪素面よりも、二次元核成長における6H−SiCと3C−SiCとの固液界面エネルギー差を大きくできる。   In the 3C—SiC single crystal manufacturing method of the present invention, the 3C—SiC single crystal is grown two-dimensionally on the (0001) carbon surface of the 6H—SiC single crystal substrate. The (0001) plane is a plane perpendicular to the [0001] direction, which is the stacking direction of the regular tetrahedral structure layer. That is, the (0001) plane is a plane in which the crystal structure changes depending on the stacking order of the stacked tetrahedral structure layers. Therefore, even if a 6H—SiC single crystal is used as the seed crystal substrate, even if a SiC single crystal is grown on the (0001) plane, a 3C—SiC single crystal having a different stacking order from the 6H—SiC single crystal may be used. Stable growth. Furthermore, if the (0001) carbon surface of the 6H—SiC single crystal substrate is used, the solid state of 6H—SiC and 3C—SiC in two-dimensional nuclear growth is higher than that of the (000-1) silicon surface of the 6H—SiC single crystal substrate. The liquid interface energy difference can be increased.

すなわち、本発明の3C−SiC単結晶の製造方法によれば、十分に低温な原料融液を用いるとともに、6H−SiC単結晶基板の表面に固液界面エネルギー差が大きい状態で3C−SiC単結晶を二次元核成長させるため、結晶の成長過程での多形変化が抑制され、大型の3C−SiC単結晶であっても容易に作製できる。なお、本明細書において「大型の3C−SiC単結晶」とは、種結晶基板の表面からの単結晶の成長量(厚さ)、および、単結晶の成長面積(口径)が大型なものを意味する。本発明の3C−SiC単結晶の製造方法では、6H−SiC単結晶基板は大口径のものが入手しやすく、かつ3C−SiC単結晶を大きく成長させることが可能である。   That is, according to the 3C-SiC single crystal manufacturing method of the present invention, a sufficiently low temperature raw material melt is used, and a 3C-SiC single crystal is formed on the surface of the 6H-SiC single crystal substrate with a large solid-liquid interface energy difference. Since the crystal is grown two-dimensionally, polymorphic changes during the crystal growth process are suppressed, and even a large 3C-SiC single crystal can be easily manufactured. In the present specification, the term “large 3C-SiC single crystal” means that the single crystal growth amount (thickness) from the surface of the seed crystal substrate and the single crystal growth area (caliber) are large. means. In the method for producing a 3C—SiC single crystal of the present invention, a 6H—SiC single crystal substrate having a large diameter is easily available, and a 3C—SiC single crystal can be grown greatly.

また、本発明の3C−SiC単結晶の製造方法により得られる3C−SiC単結晶を種結晶基板とし、該基板上にさらに3C−SiC単結晶を成長させてもよい。また、本発明の3C−SiC単結晶の製造方法により得られる3C−SiC単結晶は、3C−SiC単結晶のみならず窒化物系半導体材料を成長させる種結晶基板としても有用である。   Alternatively, a 3C-SiC single crystal obtained by the 3C-SiC single crystal manufacturing method of the present invention may be used as a seed crystal substrate, and a 3C-SiC single crystal may be further grown on the substrate. Moreover, the 3C-SiC single crystal obtained by the 3C-SiC single crystal production method of the present invention is useful not only as a 3C-SiC single crystal but also as a seed crystal substrate for growing a nitride-based semiconductor material.

本発明の3C−SiC単結晶の製造方法に用いられる単結晶成長装置の一例を模式的に示す断面図である。It is sectional drawing which shows typically an example of the single-crystal growth apparatus used for the manufacturing method of the 3C-SiC single crystal of this invention. 本発明の3C−SiC単結晶の製造方法により得られる単結晶の断面を示す図面代用写真である。It is a drawing substitute photograph which shows the cross section of the single crystal obtained by the manufacturing method of the 3C-SiC single crystal of this invention. 図2に示す成長層または種結晶基板から得られるラマン分光分析の結果を示す。The result of the Raman spectroscopic analysis obtained from the growth layer or seed crystal substrate shown in FIG. 2 is shown. 横軸を6H−SiCと3C−SiCとの固液界面エネルギー差、縦軸を結晶成長温度としたとき、安定なSiC結晶多形の成長条件を示すダイアグラムである。It is a diagram which shows the growth conditions of stable SiC crystal polymorphism, where the horizontal axis represents the solid-liquid interface energy difference between 6H—SiC and 3C—SiC and the vertical axis represents the crystal growth temperature.

以下に、本発明の3C−SiC単結晶の製造方法を実施するための最良の形態を説明する。なお、特に断らない限り、本明細書に記載された数値範囲「x〜y」は、下限xおよび上限yをその範囲に含む。   Below, the best form for implementing the manufacturing method of the 3C-SiC single crystal of this invention is demonstrated. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y.

本発明の3C−SiC単結晶の製造方法は、液相成長法を用いる。SiC単結晶の液相成長法とは、SiおよびCを含む原料融液を用い、少なくとも種結晶基板周辺で原料融液を過飽和状態とすることにより、種結晶基板の表面にSiC単結晶をエピタキシャル成長させる方法である。原料融液を過飽和状態とする手段は、一般的な液相成長法で採られている手段であれば特に限定はない。たとえば、少なくとも種結晶基板と接触する原料融液を低温にして過飽和状態とすることで、連続的に結晶成長させることができる。この方法によれば、大型の3C−SiC単結晶が得られやすいため、本発明の3C−SiC単結晶の製造方法に好適である。具体的には、原料融液と種結晶基板とを接触させ、種結晶基板を冷却する。たとえば、種結晶基板を原料融液中に保持する保持具を冷却することで、保持具から種結晶基板を介して周辺の原料融液が冷却され、過飽和状態が形成される。あるいは、原料融液を収容する坩堝の周囲に配した加熱手段を制御する、原料融液と接する雰囲気ガスからの冷却によって溶液の上下方向に温度差を作る、などの方法によっても、過飽和状態を形成することができる。なお、本発明の3C−SiC単結晶の製造方法に用いられる単結晶成長装置の一例を図1に模式的に示すが、使用可能な装置はこれに限られるものではない。以下に、本発明の3C−SiC単結晶の製造方法に用いられる原料融液、種結晶基板、等について詳説する。   The method for producing a 3C—SiC single crystal of the present invention uses a liquid phase growth method. The SiC single crystal liquid phase growth method is an epitaxial growth of a SiC single crystal on the surface of a seed crystal substrate by using a raw material melt containing Si and C and making the raw material melt supersaturated at least around the seed crystal substrate. It is a method to make it. The means for bringing the raw material melt into a supersaturated state is not particularly limited as long as it is a means adopted in a general liquid phase growth method. For example, the crystal can be continuously grown by setting the raw material melt in contact with at least the seed crystal substrate to a low temperature and being in a supersaturated state. According to this method, since a large 3C—SiC single crystal can be easily obtained, it is suitable for the method for producing a 3C—SiC single crystal of the present invention. Specifically, the raw material melt is brought into contact with the seed crystal substrate, and the seed crystal substrate is cooled. For example, by cooling a holder that holds the seed crystal substrate in the raw material melt, the surrounding raw material melt is cooled through the seed crystal substrate from the holder, and a supersaturated state is formed. Alternatively, a supersaturated state can also be achieved by controlling the heating means disposed around the crucible containing the raw material melt, or creating a temperature difference in the vertical direction of the solution by cooling from the atmospheric gas in contact with the raw material melt. Can be formed. In addition, although an example of the single crystal growth apparatus used for the manufacturing method of the 3C-SiC single crystal of this invention is typically shown in FIG. 1, the apparatus which can be used is not restricted to this. Hereinafter, the raw material melt, the seed crystal substrate, and the like used in the method for producing a 3C—SiC single crystal of the present invention will be described in detail.

<原料融液>
原料融液は、Si−Sc系溶媒に炭素を溶解してなる。固液界面エネルギーの観点からSiにScを添加した溶媒を用いることは、前述の通りである。なお、Si−Sc系溶媒とは、Siを主成分とし少なくともScを含む溶媒であればよい。そのため、溶媒の調製は、それぞれの純金属、Si系合金またはSc系合金を所定の割合で混合してから高温にして溶融させて行ってもよいし、Si−Sc系合金を高温にして溶融させて行ってもよい。このとき、溶媒の調製と同時に炭素含有材料も混合し、その後加熱して炭素をも溶解させて原料融液を得てもよい。本発明の3C−SiC単結晶の製造方法では1350℃未満で結晶を成長させることから、Si−Sc系溶媒は、Si−Sc系溶媒全体を100原子%としたときに、15原子%以上32原子%以下のScを含み残部がSiと不可避不純物からなるのが好ましい。さらに好ましいScの含有量は、20原子%以上25原子%以下である。なお、原料融液の融点を1350℃以上に上昇させない限り、他の合金元素を含んでもよい。他の合金元素として、たとえば、Si−Sc系溶媒への炭素の溶解度を大きくする効果がある希土類元素および遷移金属元素が挙げられ、これらの元素から選ばれる1種あるいは2種以上であるのが好ましい。
<Raw material melt>
The raw material melt is formed by dissolving carbon in a Si—Sc solvent. As described above, using a solvent obtained by adding Sc to Si from the viewpoint of solid-liquid interface energy. Note that the Si—Sc solvent may be any solvent containing Si as a main component and containing at least Sc. Therefore, the solvent may be prepared by mixing each pure metal, Si-based alloy or Sc-based alloy at a predetermined ratio and then melting it at a high temperature, or melting the Si-Sc-based alloy at a high temperature. You may do it. At this time, the carbon-containing material may be mixed simultaneously with the preparation of the solvent, and then heated to dissolve the carbon to obtain a raw material melt. Since the method for producing a 3C—SiC single crystal of the present invention grows crystals at less than 1350 ° C., the Si—Sc solvent is 15 atom% or more and 32 when the entire Si—Sc solvent is 100 atom%. It is preferable that it contains Sc of atomic% or less and the balance is made of Si and inevitable impurities. A more preferable Sc content is 20 atomic% or more and 25 atomic% or less. Note that other alloy elements may be included as long as the melting point of the raw material melt is not raised to 1350 ° C. or higher. Other alloy elements include, for example, rare earth elements and transition metal elements that have the effect of increasing the solubility of carbon in Si—Sc solvents, and one or more selected from these elements may be used. preferable.

原料融液は、上記のSi−Sc系溶媒に炭素を溶解させることにより得られる。黒鉛、ダイアモンド、アモルファスカーボン、フラーレン、カーボンナノチューブ、などの純炭素材料およびSiCなどの炭素と珪素とを含む化合物のような炭素含有材料のうちの1種以上をSi−Sc系溶媒に溶解させると、原料融液への不純物の混入を回避できるため好ましい。ただし、炭素含有材料が珪素を含む場合には、Si−Sc系溶媒に過剰に溶解すると、原料融液全体としてSi含有量が多くなり原料融液の融点が1350℃以上となることがあるため、溶解量が限られる。炭素含有材料は、Si−Sc系溶媒に直接投入してもよいが、原料融液を収容する坩堝の少なくとも一部を炭素含有材料から構成してもよい。炭素含有材料が坩堝から原料融液に溶出することで、Si−Sc系溶媒あるいは原料融液に炭素が供給されるため、3C−SiC単結晶を成長させている間にも炭素の供給が可能となる。   The raw material melt can be obtained by dissolving carbon in the above Si—Sc solvent. When one or more of carbon-containing materials such as graphite, diamond, amorphous carbon, fullerene, carbon nanotubes, and other pure carbon materials, and SiC and other compounds containing silicon and silicon are dissolved in a Si-Sc solvent. It is preferable because impurities can be prevented from being mixed into the raw material melt. However, when the carbon-containing material contains silicon, if it is excessively dissolved in the Si—Sc solvent, the Si content in the entire raw material melt increases, and the melting point of the raw material melt may be 1350 ° C. or higher. The amount of dissolution is limited. The carbon-containing material may be directly charged into the Si—Sc solvent, but at least a part of the crucible containing the raw material melt may be composed of the carbon-containing material. The carbon-containing material elutes from the crucible into the raw material melt, so that carbon is supplied to the Si-Sc solvent or the raw material melt, so that carbon can be supplied even while the 3C-SiC single crystal is grown. It becomes.

原料融液の温度は、1350℃未満とする。1350℃以上では、主として6H構造が安定となり3C−SiCが安定に成長しにくいからである。融液温度は、1325℃以下が好ましく、さらに好ましくは1300℃以下である。原料融液の温度の下限が原料融液の融点以上であることは言うまでもない。しかし、原料融液の温度が低すぎると3C−SiC単結晶の成長速度が遅くなるため、原料融液は1000℃以上1350℃未満が好適である。   The temperature of the raw material melt is less than 1350 ° C. This is because at 1350 ° C. or higher, the 6H structure is mainly stable and 3C—SiC hardly grows stably. The melt temperature is preferably 1325 ° C. or lower, more preferably 1300 ° C. or lower. Needless to say, the lower limit of the temperature of the raw material melt is equal to or higher than the melting point of the raw material melt. However, if the temperature of the raw material melt is too low, the growth rate of the 3C—SiC single crystal is slowed, and therefore the raw material melt is preferably 1000 ° C. or higher and lower than 1350 ° C.

<種結晶基板>
本発明の3C−SiC単結晶の製造方法では、種結晶基板として6H−SiC単結晶基板を用いる。特に、昇華法により作製された6H−SiC単結晶であれば、大口径の基板の入手が容易であり、欠陥密度が小さいため、種結晶基板として好適である。
<Seed crystal substrate>
In the 3C—SiC single crystal manufacturing method of the present invention, a 6H—SiC single crystal substrate is used as a seed crystal substrate. In particular, a 6H—SiC single crystal manufactured by a sublimation method is suitable as a seed crystal substrate because it is easy to obtain a large-diameter substrate and the defect density is small.

本発明の3C−SiC単結晶の製造方法では、6H−SiC単結晶基板の少なくとも(0001)炭素面に前述の原料融液を接触させて、その面に3C−SiC単結晶を二次元核成長させる。このとき、6H−SiC単結晶基板は、3C−SiC単結晶を成長させる主表面のオフ角が(0001)炭素面から8°未満であるのが好ましい。オフ角が8°以上になると、ステップフロー成長しやすくなるので3C−SiC単結晶が得られない。最も好ましいのは、オフ角0°(±0.2°を許容する)のジャスト面であるが、(0001)炭素面から4°以下、2°以下さらには1.25°以下のオフ角で使用するのが好ましい。オフ角が0°に近い程、種結晶基板に存在する積層欠陥が、3C−SiC単結晶中に伝搬しにくくなる。   In the method for producing a 3C-SiC single crystal of the present invention, the above-mentioned raw material melt is brought into contact with at least the (0001) carbon surface of the 6H-SiC single crystal substrate, and the 3C-SiC single crystal is grown on the surface in two-dimensional nucleus Let At this time, the 6H—SiC single crystal substrate preferably has an off angle of a main surface on which the 3C—SiC single crystal is grown of less than 8 ° from the (0001) carbon plane. If the off-angle is 8 ° or more, step flow growth is likely to occur, and a 3C—SiC single crystal cannot be obtained. Most preferred is a just surface with an off angle of 0 ° (allows ± 0.2 °), but with an off angle of 4 ° or less, 2 ° or less, or even 1.25 ° or less from the (0001) carbon surface. It is preferred to use. As the off angle is closer to 0 °, stacking faults present in the seed crystal substrate are less likely to propagate into the 3C—SiC single crystal.

<3C−SiC単結晶の種結晶基板としての使用>
本発明の3C−SiC単結晶の製造方法により得られた3C−SiC単結晶は、種結晶基板として使用可能である。この種結晶基板(以下「3C−SiC単結晶基板」と記載)に、3C−SiC単結晶のみならず、窒化物系半導体材料をも良好に成長させることが可能である。窒化物系半導体材料としては、GaN、AlN、InN、InGaN、InAlN、InGaAlNなどのIII族元素窒化物が挙げられる。3C−SiC単結晶および窒化物系半導体材料の製造方法に特に限定はなく、一般的な方法を用いればよい。ただし3C−SiC単結晶を成長させるのであれば、液相成長法を用いるとよい。液相成長法であれば、少なくともSiおよびCを含む1800℃以下の原料融液を3C−SiC単結晶基板に接触させて3C−SiC単結晶を成長させるとよい。さらに好ましくは、上記の原料融液を1350℃未満とし、その原料融液を3C−SiC単結晶基板に接触させて3C−SiC単結晶を成長させるとよい。3C−SiC単結晶基板は、その表面に3C−SiC単結晶が成長して、さらに大きな3C−SiC単結晶となる。このとき、3C−SiC単結晶を、3C−SiC単結晶基板の(111)炭素面および/または(111)珪素面に成長させるのが望ましい。また、3C−SiC単結晶基板を使用する場合には、これらの(111)面からある程度のオフ角を有する表面に3C−SiC単結晶を成長させると、十分な厚さにまで成長させ易く、大型化が可能となる。オフ角としては、(111)面から0.2〜8°が望ましい。
<Use of 3C-SiC single crystal as a seed crystal substrate>
The 3C-SiC single crystal obtained by the 3C-SiC single crystal production method of the present invention can be used as a seed crystal substrate. On this seed crystal substrate (hereinafter referred to as “3C—SiC single crystal substrate”), not only 3C—SiC single crystals but also nitride-based semiconductor materials can be favorably grown. Examples of the nitride-based semiconductor material include group III element nitrides such as GaN, AlN, InN, InGaN, InAlN, and InGaAlN. There are no particular limitations on the method of manufacturing the 3C—SiC single crystal and the nitride-based semiconductor material, and a general method may be used. However, if a 3C—SiC single crystal is grown, a liquid phase growth method may be used. In the case of the liquid phase growth method, a 3C—SiC single crystal is preferably grown by bringing a raw material melt containing at least Si and C at 1800 ° C. or less into contact with a 3C—SiC single crystal substrate. More preferably, the above-mentioned raw material melt is set to less than 1350 ° C., and the raw material melt is brought into contact with the 3C—SiC single crystal substrate to grow a 3C—SiC single crystal. The 3C—SiC single crystal substrate has a 3C—SiC single crystal grown on its surface to become a larger 3C—SiC single crystal. At this time, it is desirable to grow the 3C—SiC single crystal on the (111) carbon surface and / or the (111) silicon surface of the 3C—SiC single crystal substrate. In addition, when using a 3C-SiC single crystal substrate, if a 3C-SiC single crystal is grown on a surface having a certain degree of off-angle from these (111) planes, it is easy to grow to a sufficient thickness, Larger size is possible. The off angle is preferably 0.2 to 8 ° from the (111) plane.

<3C−SiC単結晶>
本発明の3C−SiC単結晶の製造方法により得られた3C−SiC単結晶は、積層欠陥密度が30cm−1以下かつ厚さが30μm以上である。積層欠陥密度が小さいほど高品質な単結晶であるため、さらに好ましい積層欠陥密度は20cm−1以下さらには10cm−1以下であり、5〜20cm−1程度の積層欠陥密度をもつ3C−SiC単結晶であれば容易に製造可能である。なお、本明細書において3C−SiC単結晶の厚さは、種結晶基板の表面から、その表面に成長してなる3C−SiC単結晶の成長層の表面までの最短距離を測定した値とする。本製造方法によれば、50μm以上、100μm以上さらには1mm以上であっても成長させることができるが、厚さの上限を敢えて規定するのであれば300mm以下である。
<3C-SiC single crystal>
The 3C—SiC single crystal obtained by the 3C—SiC single crystal production method of the present invention has a stacking fault density of 30 cm −1 or less and a thickness of 30 μm or more. For more stacking fault density lower is a high quality single crystal, more preferably the stacking fault density is more 20 cm -1 below are 10 cm -1 or less, 3C-SiC single with stacking fault densities of the order of 5 to 20 cm -1 If it is a crystal | crystallization, it can manufacture easily. Note that in this specification, the thickness of the 3C—SiC single crystal is a value obtained by measuring the shortest distance from the surface of the seed crystal substrate to the surface of the growth layer of the 3C—SiC single crystal grown on the surface. . According to this production method, growth can be achieved even when the thickness is 50 μm or more, 100 μm or more, and even 1 mm or more. However, if the upper limit of the thickness is specified, it is 300 mm or less.

<その他の形態>
本発明の3C−SiC単結晶の製造方法によれば、低欠陥密度の3C−SiC単結晶を実用的な速度で成長させることができる。結晶成長中の原料融液に含まれるSiC濃度にもよるが、0.5μm/hr以上さらには1.0μm/hr以上の速度で結晶を成長させられる。
<Other forms>
According to the method for producing a 3C—SiC single crystal of the present invention, a 3C—SiC single crystal having a low defect density can be grown at a practical rate. Although depending on the SiC concentration contained in the raw material melt during crystal growth, the crystal can be grown at a rate of 0.5 μm / hr or more, further 1.0 μm / hr or more.

以上、本発明の3C−SiC単結晶の製造方法の実施形態を説明したが、本発明は、上記実施形態に限定されるものではない。本発明の要旨を逸脱しない範囲において、当業者が行い得る変更、改良等を施した種々の形態にて実施することができる。   As mentioned above, although embodiment of the manufacturing method of the 3C-SiC single crystal of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

以下に、本発明の3C−SiC単結晶の製造方法の実施例を挙げて、本発明を具体的に説明する。   Hereinafter, the present invention will be specifically described with reference to examples of the method for producing a 3C—SiC single crystal of the present invention.

[実施例1]
<3C−SiC単結晶の製造>
図1に示す単結晶成長装置を用いて、3C−SiC単結晶を製造した。単結晶成長装置1は、原料融液Mを収容する坩堝11と、種結晶基板Sを保持する結晶保持具16と、を備える。坩堝11は、高純度の黒鉛からなる。坩堝11は略有底円筒形状で、その収容空間の直径はφ23mm、高さは50mmである。なお、原料融液Mの液面は、底面から25mm程度とする。結晶保持具16は、φ10mmの円柱形状の本体部17と、本体部17よりも大径の円柱形状の冷却部18と、からなる。本体部17は、坩堝16と同じく黒鉛からなる。また、冷却部18は、ステンレス鋼からなり、その一端面と本体部17の一端面とが互いに同軸的に接続されている。結晶保持具16は、坩堝11の開口部上方に、坩堝11と同軸的に配設される。坩堝11および結晶保持具16は、軸方向へ結晶保持具16を昇降可能、軸を中心として坩堝11を回転可能な移動機構(図示せず)をもつ。
[Example 1]
<Production of 3C-SiC single crystal>
A single crystal growth apparatus shown in FIG. 1 was used to manufacture a 3C—SiC single crystal. The single crystal growth apparatus 1 includes a crucible 11 that contains a raw material melt M, and a crystal holder 16 that holds a seed crystal substrate S. The crucible 11 is made of high purity graphite. The crucible 11 has a substantially bottomed cylindrical shape, and its accommodation space has a diameter of 23 mm and a height of 50 mm. The liquid level of the raw material melt M is about 25 mm from the bottom surface. The crystal holder 16 includes a cylindrical main body portion 17 having a diameter of 10 mm and a cylindrical cooling portion 18 having a larger diameter than the main body portion 17. The main body portion 17 is made of graphite like the crucible 16. The cooling unit 18 is made of stainless steel, and one end surface of the cooling unit 18 and one end surface of the main body unit 17 are coaxially connected to each other. The crystal holder 16 is disposed coaxially with the crucible 11 above the opening of the crucible 11. The crucible 11 and the crystal holder 16 have a moving mechanism (not shown) capable of moving the crystal holder 16 in the axial direction and rotating the crucible 11 around the axis.

単結晶を成長させる際には、結晶保持具16の本体部17の他端面に種結晶基板Sを固定し、図示しない冷却手段により冷却部18ひいては結晶保持具16を冷却することにより、基板Sを介して基板Sの周辺の原料融液Mを冷却する。   When growing a single crystal, the seed crystal substrate S is fixed to the other end surface of the main body portion 17 of the crystal holder 16, and the cooling unit 18 and then the crystal holder 16 are cooled by a cooling means (not shown). Then, the raw material melt M around the substrate S is cooled.

本実施例では、まず、Si−23原子%Sc合金および黒鉛を坩堝11に投入した。また、結晶保持具16の端面に、種結晶基板Sを固定した。なお、この種結晶基板Sには、昇華法で製造された市販のバルク6H−SiC単結晶(20mm×20mm×厚さ250μm)を用いた。結晶を成長させる主表面として、(0001)炭素面のジャスト面を使用した。種結晶基板Sを結晶保持具16に固定する際には、主表面となる(0001)炭素面が坩堝11の底面と対向するようにした。図示しない移動機構により結晶保持具16を下降させて、種結晶基板Sを坩堝11の内部に配置させた。   In this example, first, an Si-23 atomic% Sc alloy and graphite were put into the crucible 11. The seed crystal substrate S was fixed to the end face of the crystal holder 16. As the seed crystal substrate S, a commercially available bulk 6H—SiC single crystal (20 mm × 20 mm × 250 μm thick) manufactured by a sublimation method was used. A (0001) carbon plane just face was used as the main surface for crystal growth. When the seed crystal substrate S was fixed to the crystal holder 16, the (0001) carbon surface serving as the main surface was made to face the bottom surface of the crucible 11. The crystal holder 16 was lowered by a moving mechanism (not shown), and the seed crystal substrate S was placed inside the crucible 11.

次に、図示しない加熱手段により坩堝11を加熱して、Si−Sc合金を溶融させて炭素を溶解させるとともに坩堝11から炭素を溶出させて、原料融液MのSiC濃度を飽和濃度付近とした。そして、原料融液Mの温度を1300℃で一定となるように加熱手段を制御した。このとき、種結晶基板Sは、移動機構により原料融液Mと接触させた。冷却手段により結晶保持具16の冷却を開始すると、種結晶基板Sと接触している原料融液Mは、冷却されている結晶保持具16からの抜熱により冷却され、基板Sの周辺を低温域とする温度勾配が原料融液Mに形成されて、基板周辺の融液は過冷却状態となり、SiC濃度が過飽和となって、結晶成長が開始された。なお、結晶成長中は、坩堝11を回転させた。   Next, the crucible 11 is heated by a heating means (not shown) to melt the Si—Sc alloy to dissolve the carbon and to elute the carbon from the crucible 11 so that the SiC concentration of the raw material melt M is close to the saturation concentration. . Then, the heating means was controlled so that the temperature of the raw material melt M was constant at 1300 ° C. At this time, the seed crystal substrate S was brought into contact with the raw material melt M by a moving mechanism. When the cooling of the crystal holder 16 is started by the cooling means, the raw material melt M that is in contact with the seed crystal substrate S is cooled by heat removal from the crystal holder 16 being cooled, and the periphery of the substrate S is cooled to a low temperature. A temperature gradient as a region was formed in the raw material melt M, the melt around the substrate became supercooled, the SiC concentration became supersaturated, and crystal growth was started. Note that the crucible 11 was rotated during crystal growth.

成長開始から50時間後、結晶保持具16を結晶の成長速度以上の速度で引き上げて、種結晶基板Sに形成された成長層を原料融液Mから分離した。得られた成長層の軸方向断面を光学顕微鏡により観察した結果を図2に示す。種結晶基板Sの主表面には、3C−SiC単結晶と思われる黄色い成長層が形成された。この黄色い成長層全体から成長層の厚さを画像処理により算出した結果、最大厚さが91μm、最小厚さが40μmであった。また、[0001]方向に垂直な方向には緑色の成長層が形成された。そして、厚さから算出した最大成長速度は、1.8μm/hrであった。なお、引き続き結晶を成長させることで、黄色い成長層は1mm程度の厚さまで成長した。   After 50 hours from the start of growth, the crystal holder 16 was pulled up at a rate higher than the crystal growth rate, and the growth layer formed on the seed crystal substrate S was separated from the raw material melt M. The result of having observed the axial direction cross section of the obtained growth layer with the optical microscope is shown in FIG. On the main surface of the seed crystal substrate S, a yellow growth layer thought to be a 3C—SiC single crystal was formed. As a result of calculating the thickness of the growth layer from the entire yellow growth layer by image processing, the maximum thickness was 91 μm and the minimum thickness was 40 μm. In addition, a green growth layer was formed in a direction perpendicular to the [0001] direction. The maximum growth rate calculated from the thickness was 1.8 μm / hr. By continuing to grow crystals, the yellow growth layer grew to a thickness of about 1 mm.

<成長層のラマン分光分析>
ラマン分光分析により得られるラマンシフトのピーク値から、成長層の結晶構造を確認した。測定結果を図3に示す。[0001]方向に成長した黄色い成長層からは、図3に◇で示されるSiC単結晶の3C構造を示すピークが得られた。この黄色い成長層のいずれの位置で測定しても、同様の結果が得られたため、この成長層は、3C−SiC単結晶のみからなることがわかった。また、[0001]方向と垂直な方向に成長した緑色の成長層からは、図3に◆で示されるSiC単結晶の6H構造を示すピークが得られた。この緑色の成長層のいずれの位置で測定しても、同様の結果が得られた。なお、6H−SiC単結晶からなる種結晶基板からは、言うまでもなく図3に◆で示されるSiC単結晶の6H構造を示すピークが得られた。
<Raman spectroscopic analysis of the growth layer>
The crystal structure of the growth layer was confirmed from the peak value of Raman shift obtained by Raman spectroscopy. The measurement results are shown in FIG. From the yellow growth layer grown in the [0001] direction, a peak indicating the 3C structure of the SiC single crystal indicated by ◇ in FIG. 3 was obtained. Since the same result was obtained even if it measured in any position of this yellow growth layer, it turned out that this growth layer consists only of 3C-SiC single crystal. Further, from the green growth layer grown in the direction perpendicular to the [0001] direction, a peak indicating the 6H structure of the SiC single crystal indicated by ♦ in FIG. 3 was obtained. Similar results were obtained regardless of the position of the green growth layer. Needless to say, a peak indicating the 6H structure of the SiC single crystal indicated by ♦ in FIG. 3 was obtained from the seed crystal substrate made of 6H—SiC single crystal.

<3C−SiC単結晶の積層欠陥密度>
[0001]方向に成長した黄色い成長層、すなわち成長した3C−SiC単結晶の積層欠陥密度を、X線トポグラフィーを用いて測定した。その結果、3C−SiC単結晶からなる成長層の積層欠陥密度は、10cm−1であった。CVD法によりSi基板表面に成長させた3C−SiC単結晶の積層欠陥密度は、少ないものでも5000cm−1程度であることから、本実施例で得られた3C−SiC単結晶は従来にない低欠陥密度をもつ大型単結晶であることがわかった。
<Stacking defect density of 3C-SiC single crystal>
The stacking fault density of the yellow growth layer grown in the [0001] direction, that is, the grown 3C—SiC single crystal was measured using X-ray topography. As a result, the stacking fault density of the growth layer made of 3C—SiC single crystal was 10 cm −1 . Since the stacking fault density of the 3C-SiC single crystal grown on the Si substrate surface by the CVD method is about 5000 cm -1 even if it is small, the 3C-SiC single crystal obtained in this example has an unprecedented low density. It was found to be a large single crystal with defect density.

<比較例>
原料融液の温度、種結晶基板およびオフ角のうちのいずれかを変更して、実施例1と同様の手順でSiC単結晶を成長させた。その後、主表面に形成された成長層に対してラマン分光分析を行い、結晶構造を確認した。
<Comparative example>
A SiC single crystal was grown in the same procedure as in Example 1 by changing any of the temperature of the raw material melt, the seed crystal substrate, and the off angle. Thereafter, Raman spectroscopic analysis was performed on the growth layer formed on the main surface to confirm the crystal structure.

[比較例1]
原料融液の温度を1350℃とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが120μm、最小厚さが70μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の6H構造を示すピークが得られた。すなわち、得られた成長層は、6H−SiC単結晶であった。
[Comparative Example 1]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the temperature of the raw material melt was 1350 ° C. The growth layer grown on the main surface had a maximum thickness of 120 μm and a minimum thickness of 70 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 6H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 6H—SiC single crystal.

[比較例2]
原料融液の温度を1600℃とし、結晶の成長開始から終了までを5時間とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが227μm、最小厚さが110μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った。測定は、成長層の厚さ方向において主表面からの距離が異なる複数の位置において行った。その結果、SiC単結晶の4H構造と6H構造を示すピークが厚さ方向に交互に得られた。すなわち、得られた成長層は、結晶成長の過程で多形変化し、4H−SiC単結晶と6H−SiC単結晶とが交互に積層してなることがわかった。
[Comparative Example 2]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the temperature of the raw material melt was 1600 ° C. and the time from the start to the end of crystal growth was 5 hours. The maximum thickness of the growth layer grown on the main surface was 227 μm and the minimum thickness was 110 μm. In addition, Raman spectroscopic analysis was performed on the growth layer grown on the main surface. The measurement was performed at a plurality of positions at different distances from the main surface in the thickness direction of the growth layer. As a result, peaks indicating the 4H structure and 6H structure of the SiC single crystal were alternately obtained in the thickness direction. That is, it was found that the obtained growth layer was polymorphically changed during the crystal growth process, and 4H—SiC single crystals and 6H—SiC single crystals were alternately stacked.

[比較例3]
種結晶基板の主表面を(0001)珪素面のジャスト面とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層には、黄色い部分と緑色の部分とが観察された。主表面に成長した成長層の最大厚さが91μm、最小厚さが40μmであった。また、それぞれの部分に対してラマン分光分析を行った。その結果、緑色の部分からはSiC単結晶の6H構造を示すピークが、黄色の部分からは3C構造を示すピークが得られた。すなわち、得られた成長層は、結晶成長の過程で多形変化し、3C−SiC単結晶と6H−SiC単結晶とからなることがわかった。
[Comparative Example 3]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the main surface of the seed crystal substrate was a (0001) silicon surface just surface. A yellow portion and a green portion were observed in the growth layer grown on the main surface. The growth layer grown on the main surface had a maximum thickness of 91 μm and a minimum thickness of 40 μm. Further, Raman spectroscopic analysis was performed on each part. As a result, a peak indicating the 6H structure of the SiC single crystal was obtained from the green portion, and a peak indicating the 3C structure was obtained from the yellow portion. That is, it was found that the obtained growth layer was polymorphically changed in the course of crystal growth and consisted of 3C—SiC single crystal and 6H—SiC single crystal.

[比較例4]
主表面のオフ角を(0001)炭素面から8°とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが57μm、最小厚さが0μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の6H構造を示すピークが得られた。すなわち、得られた成長層は、6H−SiC単結晶であった。
[Comparative Example 4]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the off angle of the main surface was set to 8 ° from the (0001) carbon plane. The growth layer grown on the main surface had a maximum thickness of 57 μm and a minimum thickness of 0 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 6H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 6H—SiC single crystal.

[比較例5]
6H−SiC結晶基板の(0001)珪素面を主表面とし、主表面のオフ角を(0001)珪素面から8°とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが52μm、最小厚さが15μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の6H構造を示すピークが得られた。すなわち、得られた成長層は、6H−SiC単結晶であった。
[Comparative Example 5]
The SiC single crystal was formed on the seed crystal substrate in the same manner as in Example 1 except that the (0001) silicon surface of the 6H-SiC crystal substrate was the main surface and the off angle of the main surface was 8 ° from the (0001) silicon surface. Grown up. The growth layer grown on the main surface had a maximum thickness of 52 μm and a minimum thickness of 15 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 6H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 6H—SiC single crystal.

[比較例6]
種結晶基板を4H−SiC単結晶基板とし、主表面を(0001)炭素面のジャスト面とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが22μm、最小厚さが20μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の4H構造を示すピークが得られた。すなわち、得られた成長層は、4H−SiC単結晶であった。
[Comparative Example 6]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the seed crystal substrate was a 4H-SiC single crystal substrate and the main surface was a (0001) carbon plane just surface. The maximum thickness of the growth layer grown on the main surface was 22 μm, and the minimum thickness was 20 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 4H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 4H—SiC single crystal.

[比較例7]
種結晶基板を4H−SiC単結晶基板とし、主表面を(0001)珪素面のジャスト面とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが70μm、最小厚さが15μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の6H構造を示すピークが得られた。すなわち、得られた成長層は、6H−SiC単結晶であった。
[Comparative Example 7]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the seed crystal substrate was a 4H-SiC single crystal substrate and the main surface was a (0001) silicon surface just surface. The growth layer grown on the main surface had a maximum thickness of 70 μm and a minimum thickness of 15 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 6H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 6H—SiC single crystal.

[比較例8]
種結晶基板を4H−SiC単結晶基板とし、主表面を(11−20)のジャスト面とした他は、実施例1と同様にして種結晶基板にSiC単結晶を成長させた。主表面に成長した成長層の最大厚さが98μm、最小厚さが41μmであった。また、主表面に成長した成長層に対してラマン分光分析を行った結果、厚さ方向のいずれの位置においてもSiC単結晶の4H構造を示すピークが得られた。すなわち、得られた成長層は、4H−SiC単結晶であった。
[Comparative Example 8]
A SiC single crystal was grown on the seed crystal substrate in the same manner as in Example 1 except that the seed crystal substrate was a 4H—SiC single crystal substrate and the main surface was a (11-20) just surface. The maximum thickness of the growth layer grown on the main surface was 98 μm, and the minimum thickness was 41 μm. Further, as a result of performing Raman spectroscopic analysis on the growth layer grown on the main surface, a peak indicating the 4H structure of the SiC single crystal was obtained at any position in the thickness direction. That is, the obtained growth layer was a 4H—SiC single crystal.

Claims (6)

液相成長法を用いた3C−SiC単結晶の製造方法であって、
Si−Sc系溶媒に炭素が溶解している原料融液を1350℃未満とし、該原料溶液を6H−SiC単結晶基板の少なくとも(0001)炭素面に接触させて該面に3C−SiC単結晶を二次元核成長させることを特徴とする3C−SiC単結晶の製造方法。
A method for producing a 3C-SiC single crystal using a liquid phase growth method,
The raw material melt in which carbon is dissolved in the Si—Sc solvent is set to less than 1350 ° C., and the raw material solution is brought into contact with at least the (0001) carbon surface of the 6H—SiC single crystal substrate to form a 3C—SiC single crystal on the surface. A method for producing a 3C-SiC single crystal, characterized in that a two-dimensional nucleus is grown.
前記6H−SiC単結晶基板は、3C−SiC単結晶を成長させる主表面のオフ角が(0001)炭素面から8°未満である請求項1記載の3C−SiC単結晶の製造方法。   2. The method for producing a 3C—SiC single crystal according to claim 1, wherein the 6H—SiC single crystal substrate has an off angle of a main surface on which a 3C—SiC single crystal is grown of less than 8 ° from a (0001) carbon plane. 前記Si−Sc系溶媒は、該溶媒全体を100原子%としたときに、15原子%以上32原子%以下のScを含み残部がSiと不可避不純物からなる請求項1または2記載の3C−SiC単結晶の製造方法。   The 3C-SiC according to claim 1 or 2, wherein the Si-Sc-based solvent contains 15 atomic percent or more and 32 atomic percent or less of Sc, with the balance being Si and inevitable impurities when the total amount of the solvent is 100 atomic percent. A method for producing a single crystal. 前記6H−SiC単結晶基板は、昇華法により作製されたものである請求項1〜3のいずれかに記載の3C−SiC単結晶の製造方法。   The method for producing a 3C-SiC single crystal according to any one of claims 1 to 3, wherein the 6H-SiC single crystal substrate is produced by a sublimation method. 請求項1〜4のいずれかに記載の方法により得られた3C−SiC単結晶を種結晶基板とし、該基板上にさらに3C−SiC単結晶を成長させることを特徴とする3C−SiC単結晶の製造方法。   A 3C-SiC single crystal obtained by using the 3C-SiC single crystal obtained by the method according to any one of claims 1 to 4 as a seed crystal substrate and further growing a 3C-SiC single crystal on the substrate. Manufacturing method. 1350℃未満の前記原料融液を前記種結晶基板に接触させて3C−SiC単結晶を液相成長法により成長させる請求項5記載の3C−SiC単結晶の製造方法。   The method for producing a 3C-SiC single crystal according to claim 5, wherein the 3C-SiC single crystal is grown by a liquid phase growth method by bringing the raw material melt of less than 1350 ° C into contact with the seed crystal substrate.
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