JP6128588B2 - SiC single crystal, manufacturing method thereof and surface cleaning method thereof - Google Patents
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Description
本発明は、溶液法によるＳｉＣ（炭化珪素）単結晶の成長方法による製造方法に関し、溶液引き上げ成長法による成長結晶の成長速度を、種結晶の結晶成長面とＳｉおよびＣを含む溶液との界面に電流を通ずることにより、成長炉内の温度勾配や坩堝内の溶液の流れを特別に変更することなく、増大もしくは減少することを実現し、かつ電流量を調整することで種結晶の溶解も実現し、成長速度高速化、表面のモフォロジーの向上、種結晶の結晶多形と異なる結晶多形の発生や多結晶化の抑制を実現するＳｉＣ単結晶の製造方法およびこれにより得られる高品質なＳｉＣ単結晶に関するものである。 The present invention relates to a method for producing a SiC (silicon carbide) single crystal by a solution method, and relates to a growth rate of a grown crystal by a solution pulling growth method, and an interface between a crystal growth surface of a seed crystal and a solution containing Si and C. By passing an electric current, the temperature gradient in the growth furnace and the flow of the solution in the crucible can be increased or decreased without any special change, and the seed crystal can be dissolved by adjusting the current amount. Realize and increase the growth rate, improve the surface morphology, generate a polymorphism different from the crystal polymorph of the seed crystal, and suppress the polycrystallization, and the high quality obtained thereby It relates to a SiC single crystal.
熱的・化学的安定性に優れたＳｉＣ単結晶は、Ｓｉ（珪素）と比較してバンドギャップエネルギーが約３倍、絶縁破壊電界が７倍、熱伝導率が３倍と大きく、かつ不純物の添加によって伝導型（ｐ型、ｎ型）制御が容易であり、熱酸化膜の形成がＳｉと同様に可能であることから、Ｓｉやガリウムヒ素などの既存技術では達成できない高温、高耐圧、高周波、高耐環境性を有する次世代の電力変換用素子への応用が強く期待されている。 SiC single crystal with excellent thermal and chemical stability has a band gap energy of about 3 times, a dielectric breakdown electric field of 7 times, and a thermal conductivity of 3 times that of Si (silicon). Addition makes it easy to control the conduction type (p-type and n-type) and allows the formation of a thermal oxide film as well as Si. Application to next-generation power conversion elements having high environmental resistance is strongly expected.
ＳｉＣ単結晶の成長法としては、アチソン法、気相法（昇華法、化学気相法）、溶液法が知られている。アチソン法ではＳｉ原料である硅砂とＣ（炭素）原料となるコークスを黒鉛電極周囲に配置し、黒鉛電極を通電加熱することにより不定形板状ＳｉＣ結晶を得る。この際、不純物制御や形状制御が困難であり、半導体基板の作製には向いていない。気相法の代表例である昇華法はインチサイズの単結晶基板が作製可能であるが、結晶中の欠陥密度が大きいという問題がある。化学気相（ＣＶＤ）法はガスによる原料供給を行うため、一般的には薄膜結晶成長の方法であり、バルク単結晶成長法としては多くの課題を残している。 As an SiC single crystal growth method, an Atchison method, a vapor phase method (sublimation method, chemical vapor phase method), or a solution method is known. In the Atchison method, cinnabar sand, which is a Si raw material, and coke, which is a C (carbon) raw material, are arranged around a graphite electrode, and an amorphous plate-like SiC crystal is obtained by energizing and heating the graphite electrode. At this time, impurity control and shape control are difficult and are not suitable for manufacturing a semiconductor substrate. The sublimation method, which is a typical example of the vapor phase method, can produce an inch-size single crystal substrate, but has a problem that the defect density in the crystal is large. The chemical vapor deposition (CVD) method is generally a thin film crystal growth method because it supplies a raw material by gas, and many problems remain as a bulk single crystal growth method.
溶液法は、黒鉛坩堝中でＳｉまたはＳｉ含有合金を融解し、その融液中に黒鉛坩堝もしくは炭化水素ガス供給によって気相からＣを溶解させ、低温部に設置した単結晶基板上にＳｉＣ結晶層を溶液析出によって成長させる方法である。なかでも溶液引き上げ成長法では、溶液表面付近に保持されたＳｉＣ種結晶を、ＳｉＣ結晶層の析出による厚み増大に伴い、ＳｉＣ種結晶を上方へ引き上げながらＳｉＣ単結晶を製造する方法であり、製造される単結晶の長尺化に適している。溶液法は気相法に比べ比較的熱平衡状態に近い条件で結晶成長が進行すると考えられることから、一般的には高品質な単結晶を得る方法としては好都合であることが知られている。上述の理由から、近年、溶液法によるＳｉＣ単結晶の成長方法について、成長速度や結晶品質を高める検討がなされている。 In the solution method, Si or a Si-containing alloy is melted in a graphite crucible, C is dissolved from the gas phase by supplying the graphite crucible or hydrocarbon gas into the melt, and a SiC crystal is formed on a single crystal substrate placed in a low temperature part. It is a method of growing a layer by solution deposition. In particular, the solution pulling growth method is a method of manufacturing a SiC single crystal while pulling the SiC seed crystal upward while the SiC seed crystal held near the surface of the solution is increased in thickness due to precipitation of the SiC crystal layer. Suitable for lengthening single crystals. It is known that the solution method is generally advantageous as a method for obtaining a high-quality single crystal because crystal growth is considered to proceed under conditions that are relatively close to a thermal equilibrium state as compared with a gas phase method. For the reasons described above, in recent years, studies have been made on increasing the growth rate and crystal quality of a method for growing a SiC single crystal by a solution method.
特許文献１には、上下いずれかの位置に配置した種結晶と原料結晶の間を、当該種結晶と同一格子定数の固層を析出するごとき溶液で満たした状態で加熱し、種結晶、原料結晶、および溶液の温度をある温度幅で周期的に上下に変化させるとともに、当該原料結晶と溶液間に電流を通ずることによって原料結晶側から溶解させた溶液を種結晶側へ輸送させ、その溶質を種結晶に析出させる結晶の製造方法が提案されている。
該特許文献によれば、原料結晶の固液界面に電流を通ずることによって、溶質の供給速度を高め、高速成長が可能になると記述されている。
In
According to the patent document, it is described that by passing an electric current through a solid-liquid interface of a raw material crystal, a supply speed of a solute is increased and high-speed growth is possible.
しかしながら、ＳｉおよびＣを含む溶液を用い、１６００〜２４００℃でＳｉＣ単結晶の溶液引き上げ成長法を行うためには、電気伝導率の大きい黒鉛坩堝を溶液容器として用いる以外の手段がなく、該特許文献に記載されている電気絶縁が可能な容器の利用は、現実的には実質的に不可能である。ＳｉＣ単結晶の溶液引き上げ成長法では原料とするＳｉＣ原料結晶は用いないが、仮にＳｉＣ原料結晶をＳｉおよびＣを含む溶液とともに用いたとしても、１６００〜２４００℃で利用可能な黒鉛坩堝を用いた場合には、原料結晶の固液界面にのみ電流を通じるように、電流経路を制限することは不可能である。 However, there is no means other than using a graphite crucible with high electrical conductivity as a solution container in order to perform a solution pulling growth method of a SiC single crystal at 1600 to 2400 ° C. using a solution containing Si and C. The use of containers that can be electrically insulated as described in the literature is practically impossible. The SiC single crystal solution pulling growth method does not use the SiC raw material crystal as a raw material, but even if the SiC raw material crystal is used together with a solution containing Si and C, a graphite crucible usable at 1600 to 2400 ° C. is used. In some cases, it is impossible to limit the current path so that current flows only through the solid-liquid interface of the raw crystal.
非特許文献１には、成長温度１１００〜１３００℃の条件において、ガリウムおよびイットリビウムを溶媒として用いた溶液成長における直流電流に対する通電効果が述べられている。該非特許文献では、ガリウムおよびイットリビウムを挟んだｎ型６Ｈ−ＳｉＣ種結晶と６Ｈ−ＳｉＣ原料結晶との間に電流を通ずることによって、結晶成長速度が増大することが記述されている。しかしながら、工業的に利用される１６００〜２４００℃の成長温度での結晶成長に関しては記述がなく、しかも種結晶の溶解に関する記述もなされていない。
特許文献２には、温度勾配を増加させることなく成長速度を向上させ、同時に、安定して平坦な成長表面を維持できるＳｉＣ単結晶の製造方法が提案されている。黒鉛坩堝内のＳｉ融液内に、内部から融液面に向けて温度低下する温度勾配を維持しつつ、該融液面の直下に保持したＳｉＣ種結晶を起点としてＳｉＣ単結晶を成長させる方法において、Ｓｉ融液に希土類元素の少なくとも１種と、Ｓｎ、Ａｌ、Ｇｅのうちいずれか１種を添加した融液を用いることによって成長速度を増しつつも、Ｓｎ、Ａｌ、Ｇｅの表面活性剤としての働きから、成長表面が荒れる多結晶化を抑制し、平坦な成長表面が安定して維持されることが述べられている。
しかしながら、成長速度を制御する上で、結晶成長中に融液組成を変化させることは安定した結晶成長面を維持する上で好ましくなく、しかも技術的にも容易ではない。該特許文献の技術を用いても、成長速度を結晶成長中に変化させるためには坩堝の温度勾配を変化させなくてはならない。加えて、融液組成が限定されており、該特許文献に記載の融液組成以外を用いた場合には、ＳｉＣ単結晶の溶液成長に対して汎用的に効果を発揮するとは限らない。 However, in controlling the growth rate, changing the melt composition during crystal growth is not preferable for maintaining a stable crystal growth surface, and is not technically easy. Even using the technique of this patent document, the temperature gradient of the crucible must be changed in order to change the growth rate during crystal growth. In addition, the melt composition is limited. When a melt composition other than the melt composition described in the patent document is used, the melt composition is not always effective for the solution growth of the SiC single crystal.
以上のように、公知文献に記載の溶液法による半導体成長法は、溶液を保持し得る絶縁性の容器が利用可能であることが前提である比較的低温における溶液引き上げ成長法でない成長法であるか、あるいは、溶液引き上げ成長法であっても、温度勾配のみによって成長速度が調整される方法であり、実用面での課題が多い。
ただし、本発明による溶液引き上げ成長法と比較し、溶液を保持し得る絶縁性の容器が利用可能であることが前提である溶液引き上げ成長法でない成長法を用いた場合には、比較的低温で電流制御型の結晶成長を実施できることは有利点であるが、逆に低温であることによって、溶液中に存在するＣ成分が少なくなり、大きな単結晶を得るためには厳しい条件となる。例えば、Ｓｉ溶液へのＣ（炭素）成分の溶解度は１５００℃では約０．０１％以下であり、一方、２０５０℃では約０．４５％程度まで増加する。このため、大きな単結晶を得るには、より高温にして、溶液中のＣ成分の溶解度を増すことが重要となる。
一方、溶液を保持する容器に絶縁性容器を使用する場合、高温にすると容器の素材がＳｉを含む溶液に溶融するため、高温化に対する限界がある。
しかも、更なる高純度高品質のＳｉＣ単結晶、大きな単結晶、連続的に製造できる方法が望まれる。
As described above, the semiconductor growth method based on the solution method described in the publicly known literature is a growth method that is not a solution pull-up growth method at a relatively low temperature on the premise that an insulating container capable of holding the solution is available. Alternatively, even the solution pulling growth method is a method in which the growth rate is adjusted only by the temperature gradient, and there are many practical problems.
However, in comparison with the solution pulling growth method according to the present invention, when a growth method other than the solution pulling growth method, which is based on the premise that an insulating container capable of holding a solution is used, is used at a relatively low temperature. The ability to carry out current-controlled crystal growth is an advantage, but conversely, the low temperature reduces the C component present in the solution, which is a severe condition for obtaining a large single crystal. For example, the solubility of the C (carbon) component in the Si solution is about 0.01% or less at 1500 ° C., and increases to about 0.45% at 2050 ° C. For this reason, in order to obtain a large single crystal, it is important to increase the solubility of the C component in the solution at a higher temperature.
On the other hand, when an insulating container is used as a container for holding a solution, since the material of the container melts into a solution containing Si at a high temperature, there is a limit to the increase in temperature.
In addition, a further high purity and high quality SiC single crystal, a large single crystal, and a method capable of continuous production are desired.
従って、本発明は、可能な限り高純度・高品質で、大きな単結晶が得られ、これが簡便に達成できるＳｉＣ単結晶の製造方法、該製造方法で得られた高純度・高品質なＳｉＣ単結晶および結晶表面の浄化方法を提供することを課題とする。 Therefore, the present invention provides a method for producing a SiC single crystal that can be easily achieved by obtaining a large single crystal with the highest possible purity and quality, and the high purity and quality SiC single crystal obtained by the production method. It is an object of the present invention to provide a purification method for a crystal and a crystal surface.
本発明者らは、溶液の高温度化が可能な容器が使用でき、連続的な結晶成長が可能な溶液引き上げ成長法をさらに改善することで、かつ簡便な手段で高純度・高品質を達成すべく検討を行った。
種々検討するなかで、高純度・高品質の達成には、使用する種結晶の少なくとも結晶成長させる側の結晶表面を不純物や凹凸ができるだけ少ないものにすること、非特許文献１のように、ガリウムやイットリビウム溶液を使用した場合、高純度・高品質の達成が厳しくなることから、溶液に存在する成分を、Ｓｉを主成分とすること、が重要であることがわかった。
The present inventors can use a container capable of raising the temperature of the solution, further improve the solution pulling growth method capable of continuous crystal growth, and achieve high purity and high quality by simple means. We examined as much as possible.
In various studies, in order to achieve high purity and high quality, at least the crystal surface on the crystal growth side of the seed crystal to be used should have as few impurities and irregularities as possible. When using a yttrium solution or yttrium solution, it becomes difficult to achieve high purity and high quality. Therefore, it was found that it is important to use Si as a main component in the solution.
このことを達成するために、具体的手段をさらに検討した結果、ＳｉＣの種結晶のうち、結晶成長させる結晶表面と、ＳｉとＣを含む溶液の界面に通電することが有効であることを見出した。
具体的には、ＳｉＣ単結晶の成長速度増大にはペルチェ効果およびエレクトロマイグレーションによる溶質輸送効果が寄与しており、また、成長速度減少には、電流の流れる方向を反転させた場合のペルチェ効果およびエレクトロマイグレーションによる溶質輸送効果とともに、種結晶、該溶液も含む通電経路中の電気抵抗によるジュール発熱が寄与していることを見出し、結晶成長時の任意の局面で成長速度を変化させる方法について検討を行った結果、本発明の完成に至った。
In order to achieve this, as a result of further investigation of specific means, it has been found that it is effective to supply current to the crystal surface of the SiC seed crystal and the interface between the solution containing Si and C. It was.
Specifically, the Peltier effect and the solute transport effect by electromigration contribute to the increase in the growth rate of the SiC single crystal, and the decrease in the growth rate includes the Peltier effect when the direction of current flow is reversed and We found that the Joule heating due to the electrical resistance in the energization path including the seed crystal and the solution contributed together with the solute transport effect due to electromigration, and examined the method of changing the growth rate at any stage during crystal growth. As a result, the present invention was completed.
すなわち、本発明の課題は、以下の手段によって達成された。 That is, the subject of this invention was achieved by the following means.
（１）ＳｉおよびＣを含む溶液中に、ＳｉＣの種結晶を浸漬し、ＳｉＣを連続的に析出・成長させる溶液引き上げ成長法によるＳｉＣ単結晶の製造方法であって、
前記ＳｉＣの種結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶成長面に、結晶が成長する間、直流もしくは交流電流を流し続け、
電流密度が１〜５０Ａ／ｃｍ２の範囲内で、かつ前記電流を流さない場合の結晶成長速度より遅い結晶成長速度となる電流密度で結晶成長を行うことを特徴とするＳｉＣ単結晶の製造方法。
（２）前記結晶成長面に流す電流が、直流電流であって、前記ＳｉＣの種結晶に直流電源のプラス極を接続することを特徴とする（１）に記載のＳｉＣ単結晶の製造方法。
（３）前記結晶成長面に流す電流が、直流電流であって、前記ＳｉＣの種結晶に直流電源のマイナス極を接続することを特徴とする（１）に記載のＳｉＣ単結晶の製造方法。
（４）前記結晶成長面に流す電流が、周波数１０〜１，０００，０００Ｈｚの交流電流であることを特徴とする（１）に記載のＳｉＣ単結晶の製造方法。
（５）前記結晶成長面での前記１〜５０Ａ／ｃｍ２の電流密度分布が、前記ＳｉＣの種結晶を保持する導電性ロッドの形状と、該ＳｉＣの種結晶と該導電性ロッドとの接着領域の変更により調整することを特徴とする（１）〜（４）のいずれか１項に記載のＳｉＣ単結晶の製造方法。
（６）前記溶液中に遷移金属元素および／または希土類元素を含むことを特徴とする（１）〜（５）のいずれか１項に記載のＳｉＣ単結晶の製造方法。
（７）結晶成長温度が、１６００〜２４００℃であることを特徴とする（１）〜（６）のいずれか１項に記載のＳｉＣ単結晶の製造方法。
（８）ＳｉおよびＣを含む溶液中に、ＳｉＣの種結晶を浸漬し、ＳｉＣを連続的に析出・成長させる溶液引き上げ成長法によるＳｉＣ単結晶の製造方法であって、
前記種結晶を、前記溶液中に浸漬した後、該種結晶をマイナス極として、１５Ａ／ｃｍ２以上の直流電流を流すか、または、２２Ａ／ｃｍ２以上の交流電流を流して、単結晶表面を溶解させて単結晶の表面清浄化を行った後、
前記ＳｉＣの種結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶成長面に、直流もしくは交流電流を１〜５０Ａ／ｃｍ２流すことを特徴とするＳｉＣ単結晶の製造方法。
（９）ＳｉおよびＣを含む溶液中に、ＳｉＣの単結晶を浸漬し、ＳｉＣを連続的に析出・成長させる溶液引き上げによるＳｉＣ単結晶の表面清浄化方法であって、
前記ＳｉＣの単結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶面に、直流もしくは交流電流を流し、
前記電流を流さない場合の結晶成長速度より遅い結晶成長速度となるように電流密度を設定し、該単結晶表面を溶解させることを特徴とするＳｉＣ単結晶の表面清浄化方法。
（１０）前記電流が直流の場合、前記単結晶をマイナス極として、１５Ａ／ｃｍ２以上の直流電流を流し、前記電流が交流の場合、２２Ａ／ｃｍ２以上の直流電流を流して、前記単結晶表面を溶解させることを特徴とする（９）に記載のＳｉＣ単結晶の表面清浄化方法。
(1) A method for producing a SiC single crystal by a solution pulling growth method in which a SiC seed crystal is immersed in a solution containing Si and C, and SiC is continuously precipitated and grown.
While the crystal grows on the crystal growth surface, which is a contact surface between the SiC seed crystal and the solution held by the graphite crucible, a direct current or an alternating current continues to flow,
A method for producing a SiC single crystal, characterized in that crystal growth is performed at a current density within a range of 1-50 A / cm 2 and a crystal growth rate slower than the crystal growth rate when no current is passed. .
(2) The method for producing a SiC single crystal according to (1), wherein a current flowing through the crystal growth surface is a direct current, and a positive electrode of a direct current power source is connected to the SiC seed crystal.
(3) The method for producing a SiC single crystal according to (1), wherein a current flowing through the crystal growth surface is a direct current, and a negative electrode of a direct current power source is connected to the SiC seed crystal.
(4) The method for producing an SiC single crystal according to (1 ), wherein the current flowing through the crystal growth surface is an alternating current having a frequency of 10 to 1,000,000 Hz.
(5) The current density distribution of 1 to 50 A / cm 2 on the crystal growth surface is such that the shape of the conductive rod holding the SiC seed crystal and the adhesion between the SiC seed crystal and the conductive rod. The method for producing a SiC single crystal according to any one of (1) to (4), wherein the adjustment is performed by changing the region.
(6) The method for producing an SiC single crystal according to any one of (1) to (5), wherein the solution contains a transition metal element and / or a rare earth element.
(7) The method for producing an SiC single crystal according to any one of (1) to (6), wherein the crystal growth temperature is 1600 to 2400 ° C.
(8) A method for producing a SiC single crystal by a solution pulling growth method in which a SiC seed crystal is immersed in a solution containing Si and C, and SiC is continuously precipitated and grown.
After immersing the seed crystal in the solution, using the seed crystal as a negative electrode, a direct current of 15 A / cm 2 or more is passed, or an alternating current of 22 A / cm 2 or more is passed, After dissolving the surface and cleaning the surface of the single crystal,
A method for producing a SiC single crystal, wherein a direct current or an alternating current of 1 to 50 A / cm 2 is passed through a crystal growth surface, which is a contact surface between the SiC seed crystal and the solution held by a graphite crucible.
(9) A method of cleaning a surface of a SiC single crystal by immersing the SiC single crystal in a solution containing Si and C, and pulling the solution continuously to precipitate and grow SiC.
A direct current or an alternating current is passed through a crystal plane which is a contact surface between the SiC single crystal and the solution held by a graphite crucible,
A method for cleaning the surface of a SiC single crystal, wherein the current density is set so that the crystal growth rate is slower than the crystal growth rate when no current is passed, and the surface of the single crystal is dissolved.
(10) if said current is direct current, the single crystal as a minus pole, 15A / cm 2 flowed more DC current, when the current is AC, by flowing 22A / cm 2 or more DC current, the single The method for cleaning the surface of a SiC single crystal according to (9), wherein the crystal surface is dissolved.
本発明により、成長炉内の温度勾配や坩堝内の溶液の流れを特別に変更することなく簡便な方法で、結晶成長速度を調節でき、結晶成長速度の増大、減少だけでなく、種結晶の表面溶解による表面清浄化ができるＳｉＣ単結晶、その製造方法およびその表面清浄化方法が提供できる。 According to the present invention, the crystal growth rate can be adjusted by a simple method without specially changing the temperature gradient in the growth furnace and the flow of the solution in the crucible. An SiC single crystal capable of surface cleaning by surface dissolution, a method for manufacturing the same, and a method for cleaning the surface can be provided.
本発明のＳｉＣ単結晶の製造方法は、ＳｉおよびＣを含む溶液中に、ＳｉＣの種結晶を浸漬し、ＳｉＣを連続的に析出・成長させる溶液引き上げ成長法であって、該ＳｉＣの種結晶と黒鉛坩堝により保持された該溶液との接触面である結晶成長面に、直流もしくは交流電流を通じて、結晶成長速度を増大または減少、さらには該ＳｉＣの種結晶の表面溶解による表面清浄化する製造方法である。 The method for producing a SiC single crystal according to the present invention is a solution pulling growth method in which a SiC seed crystal is immersed in a solution containing Si and C, and SiC is continuously precipitated and grown. The crystal growth surface, which is the contact surface between the solution and the solution held by the graphite crucible, is increased or decreased through direct current or alternating current, and further the surface is cleaned by dissolving the surface of the SiC seed crystal. Is the method.
本発明の製造方法は、連続的な結晶成長が可能な溶液引き上げ成長法であり、ＳｉＣ単結晶を成長させる際、種結晶と溶液が接する結晶成長面に直流あるいは交流の電流を通ずることにより、１６００〜２４００℃の高い結晶成長温度であっても、成長炉内の温度勾配や坩堝内の溶液の流れを特別に変更することなく、または特別な装置を用いることなく、電流量の調整や種結晶と溶液が接する結晶成長面を通ずる電流の流れの方向の変更で、ＳｉＣ結晶の成長速度を温度制御によらず増大あるいは減少することができる。 The production method of the present invention is a solution pulling growth method capable of continuous crystal growth. When growing a SiC single crystal, a direct current or an alternating current is passed through the crystal growth surface where the seed crystal and the solution are in contact with each other, Even at a high crystal growth temperature of 1600 to 2400 ° C., adjustment of the amount of electric current and seeds without specially changing the temperature gradient in the growth furnace or the flow of the solution in the crucible, or without using a special device. By changing the direction of current flow through the crystal growth surface where the crystal and the solution are in contact, the growth rate of the SiC crystal can be increased or decreased without temperature control.
最初に、本発明のＳｉＣ単結晶の製造方法を図１により説明する。
図１において、ＳｉＣ単結晶成長は、加熱装置である高周波コイル４によって加熱された溶液８に、ＳｉＣ単結晶基板を支持する機構の一部である種結晶保持棒２の先端に、ＳｉＣからなる単結晶基板を接着または機械的固定により、ＳｉＣ種結晶７を保持し、これを溶液内に浸漬させて単結晶成長させる。種結晶保持棒２は、ＳｉＣ種結晶を保持している先端とは反対側の端で、直流あるいは交流の電流源１に接続され、必要により接地１０されている。一方、黒鉛坩堝５は種結晶保持棒２が直流あるいは交流の電流源１に接続されている場合には接地１０されており、種結晶保持棒２が接地１０されている場合には、黒鉛坩堝５は直流あるいは交流の電流源１に接続できる。種結晶保持棒２と黒鉛坩堝５はおのおの独立に回転する機構を備えたものである。黒鉛坩堝５の外側底面の温度は、放射温度計９のような高温温度計により直接測温する。高周波コイル４による黒鉛坩堝５の加熱は、黒鉛坩堝５の外側底面の測定温度をもとに制御される。
Initially, the manufacturing method of the SiC single crystal of this invention is demonstrated with reference to FIG.
In FIG. 1, the SiC single crystal growth is made of SiC at the tip of the seed
電流は直流でも交流でも構わないが、交流電流では選択的にジュール効果のみを発現させて成長速度を減少させ、直流電流では種結晶側をプラス極とした場合には成長速度が増大し、反対に、種結晶をマイナス極とした場合には成長速度が減少する。
ただし、種結晶側をプラス極とした場合でも、電流密度が大きくなり、成長速度の増大に寄与するペルチェ効果およびエレクトロマイグレーション効果よりも、ジュール効果が大きくなった場合には、結晶成長速度は低下する。また、交流電流を通じた場合、または種結晶側をマイナス極とした場合、もしくはプラス極とした場合であって、成長速度の増大に寄与するペルチェ効果およびエレクトロマイグレーション効果よりも、ジュール効果が大きくなる電流密度では、結晶成長が完全に抑制され、種結晶のエッチングが生じ、結晶成長表面の溶解による表面クリーニングを実施するに適正である。
The current may be direct current or alternating current, but the alternating current selectively causes only the Joule effect to decrease the growth rate, while the direct current increases the growth rate when the seed crystal side is a positive pole, and the opposite. In addition, when the seed crystal is a negative electrode, the growth rate decreases.
However, even when the seed crystal side is a positive electrode, the current density increases, and if the Joule effect becomes larger than the Peltier effect and the electromigration effect that contribute to the growth rate increase, the crystal growth rate decreases. To do. In addition, when an alternating current is passed, or when the seed crystal side is a negative pole or a positive pole, the Joule effect is larger than the Peltier effect and the electromigration effect that contribute to the growth rate increase. With the current density, crystal growth is completely suppressed, seed crystal etching occurs, and it is appropriate to perform surface cleaning by dissolving the crystal growth surface.
これらの成長速度の制御を行う電流量は、用いる種結晶の電気抵抗率に依存して、効果の発現が異なるが、一般的には成長速度を増大させるためには種結晶をプラス極として、１０Ａ／ｃｍ２以下程度の直流電流が適している。また、成長速度を減少させ、種結晶の表面を溶解させることによる表面クリーニングに用いるためには、種結晶をマイナス極として、１５Ａ／ｃｍ２以上程度の直流電流が適している。 The amount of current for controlling the growth rate depends on the electrical resistivity of the seed crystal to be used. However, in general, the seed crystal is used as a positive electrode in order to increase the growth rate. A direct current of about 10 A / cm 2 or less is suitable. Further, a direct current of about 15 A / cm 2 or more is suitable with the seed crystal as a negative electrode in order to use it for surface cleaning by reducing the growth rate and dissolving the surface of the seed crystal.
溶液との接触面である結晶成長面に流す直流もしくは交流電流は電流密度１〜５０Ａ／ｃｍ２が好ましく、交流の場合、周波数は１０〜１，０００，０００Ｈｚが好ましい。 The direct current or alternating current flowing through the crystal growth surface, which is the contact surface with the solution, preferably has a current density of 1 to 50 A / cm 2. In the case of alternating current, the frequency is preferably 10 to 1,000,000 Hz.
結晶成長面の電流密度の調整は、ＳｉＣの種結晶を保持する導電性ロッド（黒鉛のロッド）の形状と、ＳｉＣ種結晶と該導電性ロッドとの接着領域の変更により調整することが好ましい。
具体的には、ＳｉＣの種結晶と導電性ロッドとの接着領域を、ＳｉＣの種結晶に接する溶液面で、溶液中より比較的温度が低くなりやすく、この結果、多結晶の発生などにより表面荒れの原因となり得るＳｉＣの種結晶の端、隅部分とすることで、この部分が集中的に通電されて、溶質輸送効果やジュール発熱によって、多結晶の発生を抑えることが可能となり、ＳｉＣの種結晶の結晶成長面の局部的な成長、溶解を行うことが可能となる。
The current density on the crystal growth surface is preferably adjusted by changing the shape of the conductive rod (graphite rod) holding the SiC seed crystal and the adhesion region between the SiC seed crystal and the conductive rod.
Specifically, the adhesion region between the SiC seed crystal and the conductive rod is likely to be relatively lower in the solution surface in contact with the SiC seed crystal than in the solution. By making the edges and corners of the SiC seed crystal that can cause roughness, this portion is energized intensively, and it is possible to suppress the occurrence of polycrystals due to the solute transport effect and Joule heat generation. It becomes possible to perform local growth and dissolution of the crystal growth surface of the seed crystal.
ＳｉＣの結晶は、六方晶（２Ｈ、４Ｈ、６Ｈ、８Ｈ、１０Ｈ）、立方晶（３Ｃ）、菱面体晶（１５Ｒ）等が知られているが、いずれの結晶においてもＳｉＣの種結晶の形状は円盤、六角形平板、四角形平板等の板状でも、立方体でもよいが、円盤、六角形平板、四角形平板等の板状が好ましい。種結晶の大きさは、どのような大きさでもよく、その目的にもよるが、直径０．１ｃｍ以上が好ましく、０．５ｃｍ以上がより好ましく、１ｃｍ以上がさらに好ましい。直径の好ましい上限は特に限定されるものでなく、結晶成長装置の容量に合わせて調製すればよく、例えば１０ｃｍでも構わない。 As the crystal of SiC, hexagonal crystal (2H, 4H, 6H, 8H, 10H), cubic crystal (3C), rhombohedral crystal (15R), and the like are known. The plate may be a plate such as a disk, a hexagonal flat plate, a rectangular flat plate, or a cube, but a plate shape such as a disk, a hexagonal flat plate, or a square flat plate is preferred. The size of the seed crystal may be any size, and depending on the purpose, the diameter is preferably 0.1 cm or more, more preferably 0.5 cm or more, and even more preferably 1 cm or more. The upper limit of the diameter is not particularly limited, and may be adjusted according to the capacity of the crystal growth apparatus, and may be 10 cm, for example.
本発明のＳｉＣ単結晶を得る方法において、溶液成長に用いる溶液の組成に関しては、少なくともＳｉとＣが含まれているならば特に制限はない。本発明においては、溶液成長に用いる溶液には遷移金属元素（好ましくはＴｉ、Ｃｒ等の第一遷移元素）または／および希土類元素（例えば、スカンジウム、イットリウム等）を含んでもよい。
これらの元素は、高純度・高品質を得るためには、原子組成で５０％未満が好ましく、例えば、Ｃｒの場合は最大でも４０％であり、これより多いと、温度にもよるが溶解しているＣ成分がグラファイトとして析出する。
In the method for obtaining the SiC single crystal of the present invention, the composition of the solution used for solution growth is not particularly limited as long as at least Si and C are contained. In the present invention, the solution used for solution growth may contain a transition metal element (preferably a first transition element such as Ti or Cr) and / or a rare earth element (for example, scandium or yttrium).
In order to obtain high purity and high quality, these elements preferably have an atomic composition of less than 50%. For example, in the case of Cr, the maximum is 40%. C component is deposited as graphite.
特に、Ｓｉ−Ｃ溶液、Ｓｉ−Ｃ−Ｔｉ溶液、Ｓｉ−Ｃ−Ｃｒ溶液が好ましく、溶液に遷移金属元素（好ましくはＴｉ、Ｃｒ等の第一遷移元素）または／および希土類元素を含んだ場合においても、種結晶を溶液に浸漬する際に、種結晶と溶液が接する結晶成長面に直流あるいは交流の電流を通じて電流印加を付与した場合にはＳｉＣ単結晶の成長速度は電流量と結晶成長面を通ずる電流の流れの方向に依存して増減される。
ここで、Ｓｉ−Ｃ溶液、Ｓｉ−Ｃ−Ｔｉ溶液、Ｓｉ−Ｃ−Ｃｒ溶液におけるＣの少なくとも一部は黒鉛坩堝から溶液中に溶解させたものである。
また、Ｃの一部はＣＨ４などの炭化水素ガスを溶液中に吹き込む、または雰囲気ガスに混入することにより溶液中にＣを供給する方法もある。
In particular, a Si-C solution, a Si-C-Ti solution, or a Si-C-Cr solution is preferable, and the solution contains a transition metal element (preferably a first transition element such as Ti or Cr) or / and a rare earth element. However, when the seed crystal is immersed in the solution and a current is applied to the crystal growth surface where the seed crystal is in contact with the solution through a direct current or alternating current, the growth rate of the SiC single crystal is determined by the amount of current and the crystal growth surface. It is increased or decreased depending on the direction of current flow through it.
Here, at least a part of C in the Si-C solution, Si-C-Ti solution, and Si-C-Cr solution is dissolved in the solution from the graphite crucible.
In addition, there is a method in which a part of C is supplied into the solution by injecting a hydrocarbon gas such as CH 4 into the solution or mixing it with an atmospheric gas.
雰囲気ガスは、ＳｉＣ単結晶成長時に、ＳｉＣ結晶および溶液の酸化を防止するために、Ｈｅ、Ｎｅ、Ａｒ等の不活性希ガスを用い、またＮ２のような不活性ガス、ＣＨ４などのガスを混合してもよい。
ＳｉＣ結晶成長は、Ｓｉの融点（１４１４℃）以上の１６００〜２４００℃の高温が好ましく、このような高温で実施するため、雰囲気ガス圧力が０．１ＭＰａよりも低いと溶液の蒸発が激しいので、加圧条件でＳｉＣ単結晶成長を実施することが望ましい。雰囲気ガス圧力は０．１ＭＰａ以上が好ましい。
As the atmospheric gas, an inert rare gas such as He, Ne, or Ar is used to prevent oxidation of the SiC crystal and the solution during the growth of the SiC single crystal, and an inert gas such as N 2 , CH 4, or the like is used. Gas may be mixed.
The SiC crystal growth is preferably performed at a high temperature of 1600 to 2400 ° C., which is higher than the melting point of Si (1414 ° C.), and since it is performed at such a high temperature, the evaporation of the solution is severe when the atmospheric gas pressure is lower than 0.1 MPa. It is desirable to carry out SiC single crystal growth under pressure conditions. The atmospheric gas pressure is preferably 0.1 MPa or more.
ＳｉＣ単結晶成長時の温度は、１６００〜２４００℃の範囲内で設定可能であるが、溶液組成によって最適な温度条件を１６００〜２４００℃の範囲内で任意に設定すればよい。ただし成長温度によっては溶液の蒸発が激しくなるので、雰囲気ガスの圧力としては、１６００〜１９００℃の成長温度の場合には０．１ＭＰａ〜１ＭＰａ、１９００〜２４００℃の範囲の成長温度では１ＭＰａ〜１０ＭＰａが好適である。
前記の本発明における溶液法によるＳｉＣ単結晶成長によって、高温で長時間、例えば１２時間以上、成長するＳｉＣ単結晶中の成長速度を電流により制御しながらＳｉＣ単結晶を成長させることができる。
The temperature during SiC single crystal growth can be set within a range of 1600 to 2400 ° C., but an optimal temperature condition may be arbitrarily set within a range of 1600 to 2400 ° C. depending on the solution composition. However, since the evaporation of the solution becomes intense depending on the growth temperature, the atmospheric gas pressure is 0.1 MPa to 1 MPa at a growth temperature of 1600 to 1900 ° C., and 1 MPa to 10 MPa at a growth temperature in the range of 1900 to 2400 ° C. Is preferred.
By the SiC single crystal growth by the solution method in the present invention described above, the SiC single crystal can be grown while controlling the growth rate in the SiC single crystal growing at a high temperature for a long time, for example, 12 hours or more, by the current.
以下に実施例に基づき、本発明について更に詳細に説明するが、本発明はこれらに限定して解釈されるものではない。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not construed as being limited thereto.
以下の実施例では、いずれも図１に示すＳｉＣ単結晶成長の実施形態と同様の装置を用いて、ＳｉＣ単結晶成長を行った。種結晶は、ｎ型の約４ｍｍ２角の０°オフ４Ｈ−ＳｉＣ（０００−１）基板を使用した。実施例４以外は、溶液にはＳｉを用い、成長温度は実施例１、２、４で１８７０℃、実施例３で２０５０℃であり、雰囲気ガスにＨｅ、該雰囲気ガスの圧力０．４ＭＰａで３時間の成長を行った。種結晶を溶液に浸漬する際に、種結晶と溶液が接する結晶成長面に、種結晶をプラス極またはマイナス極とし、０〜２Ａの直流電流および５０Ｈｚの交流電流を０〜１Ａ通ずる電流印加を付与した。 In the following examples, SiC single crystal growth was performed using the same apparatus as that of the SiC single crystal growth embodiment shown in FIG. Seed crystal, 0 ° off 4H-SiC n-type about 4 mm 2 square of (000-1) was used substrate. Except for Example 4, Si was used as the solution, the growth temperature was 1870 ° C. in Examples 1, 2, and 4, 2050 ° C. in Example 3, He was the atmospheric gas, and the pressure of the atmospheric gas was 0.4 MPa. Growing for 3 hours. When the seed crystal is immersed in the solution, the seed crystal is applied to the crystal growth surface where the seed crystal is in contact with the positive electrode or the negative electrode, and 0 to 2 A direct current and 50 Hz alternating current are passed through 0 to 1 A. Granted.
実施例では、黒鉛坩堝にＳｉまたはＳｉとＣｒを充填し、減圧下でＳｉの融点以下の温度に保持し吸着ガスを脱気した後、雰囲気ガスとしてＨｅガスを０．４ＭＰａの圧力で充填し、黒鉛坩堝の底面が所定の温度になるように加熱し、溶媒原料を融解させた。黒鉛坩堝の内壁からＳｉ溶液へＣが飽和濃度まで十分に供給されるように、一定時間保持した。その後、図１に例示した種結晶保持機構と同様な構造によって保持されたＳｉＣ種結晶を溶液に浸漬するとともに、種結晶と溶液が接する結晶成長面に種結晶をプラス極またはマイナス極とし、０〜２Ａの直流電流および５０Ｈｚの交流電流を０〜１Ａ通じながら３時間の浸漬を行った。浸漬時間が経過した後、種結晶保持機構を保持している種結晶保持棒を上昇させ、種結晶を溶液から引き上げた。結晶成長中は種結晶保持棒と黒鉛坩堝を互いに逆方向に回転させた。 In this example, a graphite crucible was filled with Si or Si and Cr, held at a temperature lower than the melting point of Si under reduced pressure, and the adsorbed gas was deaerated, and then helium gas was filled as an atmospheric gas at a pressure of 0.4 MPa. Then, the bottom surface of the graphite crucible was heated to a predetermined temperature to melt the solvent raw material. It was held for a certain time so that C was sufficiently supplied from the inner wall of the graphite crucible to the Si solution to the saturation concentration. Thereafter, the SiC seed crystal held by the same structure as the seed crystal holding mechanism illustrated in FIG. 1 is immersed in the solution, and the seed crystal is set as a positive electrode or a negative electrode on the crystal growth surface in contact with the seed crystal. The immersion was performed for 3 hours while passing a direct current of ˜2 A and an alternating current of 50 Hz through 0 to 1 A. After the immersion time, the seed crystal holding rod holding the seed crystal holding mechanism was raised, and the seed crystal was pulled up from the solution. During crystal growth, the seed crystal holding rod and the graphite crucible were rotated in opposite directions.
炉内の温度を室温まで冷却させた後、ＳｉＣ種結晶を回収し、フッ硝酸を用いて洗浄を行い、ＳｉＣ結晶表面に付着している溶液の凝固物を取り除いた。種結晶上に溶液法により成長したＳｉＣ単結晶の断面に対して、透過照明を用いた顕微鏡観察を実施し、成長結晶膜厚の計測値から成長速度を算出した。 After the temperature in the furnace was cooled to room temperature, the SiC seed crystal was recovered and washed with hydrofluoric acid to remove the solidified product of the solution adhering to the SiC crystal surface. The cross section of the SiC single crystal grown by the solution method on the seed crystal was observed with a microscope using transmitted illumination, and the growth rate was calculated from the measured value of the grown crystal film thickness.
実施例１
黒鉛坩堝にＳｉを充填し、１Ｐａ以下の減圧下で黒鉛坩堝およびＳｉ原料を１１００℃程度の温度に保持し、吸着ガスを脱気した後、雰囲気ガスとしてＨｅガスを０．４ＭＰａの圧力になるように充填し、黒鉛坩堝の底面が１８７０℃になるように加熱し、Ｓｉ原料を融解させた。その後、図１に例示した種結晶保持機構と同様な構造によって保持されたＳｉＣ種結晶を溶液に浸漬するとともに、種結晶と溶液が接する結晶表面に種結晶をプラス極またはマイナス極とし、０〜２Ａの直流電流を通じながら３時間の浸漬を行った。浸漬時間が経過した後、種結晶保持機構を保持している種結晶保持棒を上昇させ、種結晶を溶液から引き上げた。結晶成長中は種結晶保持棒と黒鉛坩堝を互いに逆方向に回転させた。
実施例１で実施した結晶成長時の溶液温度の時間変化を図２に示した。図２に示した溶液温度の時間変化を示すグラフの中で、（１）部は減圧下での吸着ガス脱気過程、（２）は成長温度（１８７０℃）までの加熱過程、（３）はＳｉＣ種結晶浸漬過程、（４）は溶液からの種結晶引き上げ後の冷却過程を示している。実施例１で実施した直流電流を通じた溶液引き上げ結晶成長の成長速度と直流電流量および結晶成長面を流れる電流の方向に関する依存性を図３と図４に示した。
Example 1
The graphite crucible is filled with Si, the graphite crucible and the Si raw material are kept at a temperature of about 1100 ° C. under a reduced pressure of 1 Pa or less, the adsorbed gas is degassed, and He gas is brought to a pressure of 0.4 MPa as the atmospheric gas. Then, the bottom surface of the graphite crucible was heated to 1870 ° C. to melt the Si raw material. Thereafter, the SiC seed crystal held by the same structure as the seed crystal holding mechanism illustrated in FIG. 1 is immersed in the solution, and the seed crystal is set as a positive electrode or a negative electrode on the crystal surface in contact with the seed crystal. The immersion was performed for 3 hours while passing a direct current of 2A. After the immersion time, the seed crystal holding rod holding the seed crystal holding mechanism was raised, and the seed crystal was pulled up from the solution. During crystal growth, the seed crystal holding rod and the graphite crucible were rotated in opposite directions.
The time change of the solution temperature during the crystal growth carried out in Example 1 is shown in FIG. In the graph showing the change over time of the solution temperature shown in FIG. 2, (1) is the adsorption gas degassing process under reduced pressure, (2) is the heating process up to the growth temperature (1870 ° C.), (3) Indicates the SiC seed crystal immersion process, and (4) indicates the cooling process after pulling the seed crystal from the solution. 3 and 4 show the dependency of the growth rate of the solution pulling crystal growth through the direct current performed in Example 1, the amount of direct current, and the direction of the current flowing on the crystal growth surface.
実施例２
実験では、黒鉛坩堝にＳｉを充填し、1Ｐａ以下の減圧下で黒鉛坩堝およびＳｉ原料を１１００℃程度の温度に保持し、吸着ガスを脱気した後、雰囲気ガスとしてＨｅガスを０．４ＭＰａの圧力になるように充填し、黒鉛坩堝の底面が１８７０℃になるように加熱し、Ｓｉ原料を融解させた。その後、図１に例示した種結晶保持機構と同様な構造によって保持されたＳｉＣ種結晶を溶液に浸漬するとともに、種結晶と溶液が接する結晶表面に５０Ｈｚの交流電流を０〜１Ａ通じながら３時間の浸漬を行った。浸漬時間が経過した後、種結晶保持機構を保持している種結晶保持棒を上昇させ、種結晶を溶液から引き上げた。結晶成長中は種結晶保持棒と黒鉛坩堝を互いに逆方向に回転させた。
実施例２で実施した結晶成長時の溶液温度の時間変化を図２に示した。図２に示した溶液温度の時間変化を示すグラフの中で、（１）部は減圧下での吸着ガス脱気過程、（２）は成長温度（１８７０℃）までの加熱過程、（３）はＳｉＣ種結晶浸漬過程、（４）は溶液からの種結晶引き上げ後の冷却過程を示している。実施例２で実施した交流電流を通じた溶液引き上げ結晶成長の成長速度と交流電流量に対する依存性を図５に示した。
Example 2
In the experiment, the graphite crucible was filled with Si, the graphite crucible and the Si raw material were kept at a temperature of about 1100 ° C. under a reduced pressure of 1 Pa or less, the adsorbed gas was degassed, and then He gas as an atmospheric gas was 0.4 MPa. Filled to a pressure and heated so that the bottom surface of the graphite crucible was 1870 ° C. to melt the Si raw material. Thereafter, the SiC seed crystal held by the same structure as the seed crystal holding mechanism illustrated in FIG. 1 is immersed in the solution, and the alternating current of 50 Hz is passed through 0 to 1 A on the crystal surface where the seed crystal and the solution are in contact for 3 hours. Was immersed. After the immersion time, the seed crystal holding rod holding the seed crystal holding mechanism was raised, and the seed crystal was pulled up from the solution. During crystal growth, the seed crystal holding rod and the graphite crucible were rotated in opposite directions.
The time change of the solution temperature during the crystal growth carried out in Example 2 is shown in FIG. In the graph showing the change over time of the solution temperature shown in FIG. 2, (1) is the adsorption gas degassing process under reduced pressure, (2) is the heating process up to the growth temperature (1870 ° C.), (3) Indicates the SiC seed crystal immersion process, and (4) indicates the cooling process after pulling the seed crystal from the solution. FIG. 5 shows the dependency of the solution pulling crystal growth through alternating current performed in Example 2 on the growth rate and the amount of alternating current.
実施例３
黒鉛坩堝にＳｉを充填し、１Ｐａ以下の減圧下で黒鉛坩堝およびＳｉ原料を１１００℃程度の温度に保持し、吸着ガスを脱気した後、雰囲気ガスとしてＨｅガスを０．４ＭＰａの圧力になるように充填し、黒鉛坩堝の底面が２０５０℃になるように加熱し、Ｓｉ原料を融解させた。その後すぐに、図１に例示した種結晶保持機構と同様な構造によって保持されたＳｉＣ種結晶を溶液に浸漬するとともに、種結晶と溶液が接する結晶成長面に種結晶をプラス極またはマイナス極とし、０．５Ａの直流電流を通じながら１時間の浸漬を行った。浸漬時間が経過した後、種結晶保持機構を保持している種結晶保持棒を上昇させ、種結晶を溶液から引き上げた。結晶成長中は種結晶保持棒と黒鉛坩堝を互いに逆方向に回転させた。実施例３で実施した結晶成長時の成長速度と直流電流量および結晶成長面を流れる電流の方向に関する依存性を図６に示した。
Example 3
The graphite crucible is filled with Si, the graphite crucible and the Si raw material are kept at a temperature of about 1100 ° C. under a reduced pressure of 1 Pa or less, the adsorbed gas is degassed, and He gas is brought to a pressure of 0.4 MPa as the atmospheric gas. Then, the bottom surface of the graphite crucible was heated to 2050 ° C. to melt the Si raw material. Immediately thereafter, the SiC seed crystal held by the same structure as the seed crystal holding mechanism illustrated in FIG. 1 is immersed in the solution, and the seed crystal is set as a positive electrode or a negative electrode on the crystal growth surface where the seed crystal contacts the solution. And immersion for 1 hour while passing a direct current of 0.5 A. After the immersion time, the seed crystal holding rod holding the seed crystal holding mechanism was raised, and the seed crystal was pulled up from the solution. During crystal growth, the seed crystal holding rod and the graphite crucible were rotated in opposite directions. FIG. 6 shows the dependency on the growth rate, the amount of direct current, and the direction of the current flowing through the crystal growth surface during the crystal growth performed in Example 3.
実施例４
ＳｉおよびＣｒを原子組成で７０％−Ｓｉ、３０％−Ｃｒとした原料と、６０％−Ｓｉ、４０％−Ｃｒとした原料と、１００％−Ｓｉ、０％−Ｃｒとした原料を溶媒として用いた。上記３種類の溶媒原料の各々に対して、黒鉛坩堝に溶媒原料を充填し、１Ｐａ以下の減圧下で黒鉛坩堝およびＳｉ原料を１１００℃程度の温度に保持し、吸着ガスを脱気した後、雰囲気ガスとしてＨｅガスを０．４ＭＰａの圧力になるように充填し、黒鉛坩堝の底面が１８７０℃になるように加熱し、溶媒原料を融解させた。その後すぐに、図１に例示した種結晶保持機構と同様な構造によって保持されたＳｉＣ種結晶を溶液に浸漬するとともに、種結晶と溶液が接する結晶成長面に種結晶をプラス極およびマイナス極とし、０．５Ａの直流電流を通じながら３時間の浸漬を行った。浸漬時間が経過した後、種結晶保持機構を保持している種結晶保持棒を上昇させ、種結晶を溶液から引き上げた。結晶成長中は種結晶保持棒と黒鉛坩堝を互いに逆方向に回転させた。実施例４で実施した結晶成長時の成長速度と直流電流量および結晶成長面を流れる電流の方向に関する依存性を図７に示した。
Example 4
A raw material with Si and Cr as atomic composition of 70% -Si, 30% -Cr, a raw material with 60% -Si, 40% -Cr, and a raw material with 100% -Si, 0% -Cr as solvents Using. For each of the three types of solvent raw materials, the graphite crucible is filled with the solvent raw material, the graphite crucible and the Si raw material are kept at a temperature of about 1100 ° C. under a reduced pressure of 1 Pa or less, and the adsorbed gas is degassed. He gas was filled as an atmospheric gas to a pressure of 0.4 MPa, and the bottom surface of the graphite crucible was heated to 1870 ° C. to melt the solvent raw material. Immediately thereafter, the SiC seed crystal held by the same structure as the seed crystal holding mechanism illustrated in FIG. 1 is immersed in the solution, and the seed crystal is set as a positive electrode and a negative electrode on the crystal growth surface where the seed crystal contacts the solution. And soaking for 3 hours while passing a direct current of 0.5 A. After the immersion time, the seed crystal holding rod holding the seed crystal holding mechanism was raised, and the seed crystal was pulled up from the solution. During crystal growth, the seed crystal holding rod and the graphite crucible were rotated in opposite directions. FIG. 7 shows the dependence on the growth rate, the amount of direct current, and the direction of the current flowing through the crystal growth surface during the crystal growth performed in Example 4.
実施例１で行った方法によって成長したＳｉＣ結晶のうち、０．８Ａの直流電流を、種結晶をマイナス極とした場合、プラス極とした場合と、電流を通じなかった場合の３種類のＳｉＣ結晶に対して、成長面に垂直な断面の透過画像を示す光学顕微鏡写真を図３に示した。図３によれば、実施例１で行った方法によるＳｉＣ単結晶成長では、直流電流の付与と電流の流れの方向によって、成長速度を増大もしくは減少することが可能である。この方法による成長速度の増大に関しては、種結晶をプラス極とした場合には成長速度が増大することから、溶液中からＳｉＣ種結晶へと移動する電子と、溶液中に存在する炭素（溶質）との間の運動量交換により、溶質である炭素が溶液の中で結晶成長面へ向けて移動するエレクトロマイグレーションと、ＳｉＣ種結晶と溶液の間で生じるペルチェ冷却による過飽和度の増大が寄与していると考えられる。一方、この方法による成長速度の減少に関しては、種結晶をマイナス極とした場合には成長速度が減少することから、ＳｉＣ種結晶から溶液へと移動する電子と、溶液中に存在する炭素（溶質）との間の運動量交換により、溶質である炭素が溶液の中で結晶成長面から離れる方向へ移動するエレクトロマイグレーションと、ＳｉＣ種結晶と溶液の間で生じるペルチェ発熱による過飽和度の減少、および電流が流れる経路中の電気抵抗によるジュール発熱に起因する過飽和度の減少が寄与していると考えられる。 Among the SiC crystals grown by the method performed in Example 1, three types of SiC crystals were obtained when a direct current of 0.8 A was used when the seed crystal was a negative electrode, a positive electrode, and a case where no current was passed. On the other hand, an optical micrograph showing a transmission image of a cross section perpendicular to the growth surface is shown in FIG. According to FIG. 3, in the SiC single crystal growth by the method performed in Example 1, it is possible to increase or decrease the growth rate depending on the direction of direct current application and current flow. Regarding the increase of the growth rate by this method, the growth rate increases when the seed crystal is a positive electrode, so the electrons moving from the solution to the SiC seed crystal and the carbon (solute) present in the solution. Exchange of momentum between the solute and carbon contributes to the electromigration in which the solute carbon moves toward the crystal growth surface in the solution and the increase in supersaturation due to Peltier cooling that occurs between the SiC seed crystal and the solution. it is conceivable that. On the other hand, regarding the reduction of the growth rate by this method, when the seed crystal is a negative pole, the growth rate is reduced. Therefore, the electrons moving from the SiC seed crystal to the solution and the carbon present in the solution (solute) ), The electromigration in which the solute carbon moves away from the crystal growth plane in the solution, the decrease in supersaturation due to the Peltier heat generation between the SiC seed crystal and the solution, and the current It is thought that the decrease in the degree of supersaturation due to Joule heat generation due to the electrical resistance in the path through which the current flows contributes.
実施例１で行った方法によって成長したＳｉＣ結晶の成長速度と直流電流に対する依存性を図４に示した。図４によれば、種結晶をプラス極とした場合、直流電流密度で１２〜１３Ａ／ｃｍ２程度まで成長速度を増大することが可能であった。これ以上の直流電流では、ジュール熱が大きくなるため成長速度が減少傾向に転ずる。この傾向は、実施例１で用いたＳｉＣ種結晶の電気抵抗に依存して変わるため、成長速度を増大させるに適した直流電流密度の上限を制限するものではない。加えて、種結晶をプラス極とした場合、さらに電流密度を増大していくと、実施例１で用いたＳｉＣ種結晶を用いた場合には、４０Ａ／ｃｍ２程度の電流密度で直流電流を通じた場合に、種結晶の成長表面の溶解が認められた。これ以上の電流密度では、結晶表面の溶解による表面清浄化の効果を得ることができる。また、反対に、種結晶をマイナス極とした場合、成長速度は直流電流密度の増大とともに減少する。実施例１で用いたＳｉＣ種結晶を用いた場合には、−２０Ａ／ｃｍ２程度の電流密度で直流電流を通じた場合に、種結晶の成長表面の溶解が認められた。これ以上の電流密度では、結晶表面の溶解による表面清浄化の効果を得ることができる。 The dependence of the SiC crystal grown by the method performed in Example 1 on the growth rate and DC current is shown in FIG. According to FIG. 4, when the seed crystal is a positive electrode, the growth rate can be increased to about 12 to 13 A / cm 2 in terms of direct current density. At higher direct current, the Joule heat increases and the growth rate starts to decrease. Since this tendency changes depending on the electrical resistance of the SiC seed crystal used in Example 1, it does not limit the upper limit of the direct current density suitable for increasing the growth rate. In addition, when the seed crystal is a positive electrode, if the current density is further increased, when the SiC seed crystal used in Example 1 is used, a direct current is passed at a current density of about 40 A / cm 2. In this case, dissolution of the seed crystal growth surface was observed. When the current density is higher than this, the effect of surface cleaning by melting the crystal surface can be obtained. On the other hand, when the seed crystal is a negative electrode, the growth rate decreases as the direct current density increases. When the SiC seed crystal used in Example 1 was used, dissolution of the seed crystal growth surface was observed when a direct current was passed at a current density of about −20 A / cm 2 . When the current density is higher than this, the effect of surface cleaning by melting the crystal surface can be obtained.
実施例２で行った方法によって成長したＳｉＣ結晶の成長速度と交流電流に対する依存性を図５に示した。図５によれば、いずれの交流電流密度でも成長速度を減少することが可能であった。交流電流を流した場合には、直流電流を流した場合と異なり、エレクトロマイグレーションとペルチェ効果は消失し、ジュール発熱の効果のみが結晶成長速度の増減に寄与すると考えられる。したがって、交流電流を流した場合には、成長速度は減少するのみであり、実施例２で行った方法では、およそ２２Ａ／ｃｍ２以上の電流密度で交流電流を通じた場合に、種結晶の成長表面の溶解が認められる。これ以上の電流密度では、結晶表面の溶解による表面清浄化の効果を得ることができる。なお、この傾向は、実施例２で用いたＳｉＣ種結晶の電気抵抗に依存して変わるため、成長速度の減少、種結晶の成長表面の溶解を実施するに適した交流電流密度の範囲を制限するものではない。 The dependence of the SiC crystal grown by the method performed in Example 2 on the growth rate and the alternating current is shown in FIG. According to FIG. 5, it was possible to reduce the growth rate at any alternating current density. When an alternating current is applied, unlike the case where a direct current is applied, the electromigration and the Peltier effect disappear, and only the effect of Joule heating is considered to contribute to the increase and decrease of the crystal growth rate. Therefore, when an alternating current is passed, the growth rate only decreases. In the method performed in Example 2, the seed crystal grows when the alternating current is passed at a current density of about 22 A / cm 2 or more. Dissolution of the surface is observed. When the current density is higher than this, the effect of surface cleaning by melting the crystal surface can be obtained. Since this tendency changes depending on the electric resistance of the SiC seed crystal used in Example 2, the range of alternating current density suitable for carrying out the reduction of the growth rate and the dissolution of the growth surface of the seed crystal is limited. Not what you want.
実施例３で行った方法によって成長したＳｉＣ結晶の成長速度と直流電流に対する依存性を図６に示した。図６によれば、実施例３で行った方法によるＳｉＣ単結晶成長では、実施例１と同様に直流電流の付与と電流の流れの方向によって、成長速度を増大もしくは減少することが可能である。しかも成長温度が高温であることに起因して、直流電流を通ずることによる成長速度の増大・減少が１８７０℃での成長である実施例１で行った方法で得られる結晶成長よりも２０５０℃での成長である実施例３の方が大きくなっている。このことはＳｉ−Ｃ溶液中のＣの量が熱力学的平衡炭素溶解度の上昇によって大きくなっていることに起因して、溶液中を流れる電子と、溶液中の炭素との運動量交換である衝突の頻度が大きくなったことにより、エレクトロマイグレーション効果が増大したものと考えられる。 The dependence of the SiC crystal grown by the method performed in Example 3 on the growth rate and direct current is shown in FIG. According to FIG. 6, in the SiC single crystal growth by the method performed in Example 3, the growth rate can be increased or decreased depending on the application of direct current and the direction of current flow as in Example 1. . Moreover, because the growth temperature is high, the growth rate increase / decrease by passing a direct current is 2050 ° C. higher than the crystal growth obtained by the method performed in Example 1 in which growth is performed at 1870 ° C. The growth of Example 3, which is the growth of, is larger. This is due to the momentum exchange between the electrons flowing in the solution and the carbon in the solution due to the increase in the amount of C in the Si-C solution due to the increase in thermodynamic equilibrium carbon solubility. It is considered that the electromigration effect increased due to the increase in the frequency of.
実施例４で行った方法によって成長したＳｉＣ結晶の成長速度と直流電流に対する依存性を図７に示した。図７によれば、実施例４で行った方法によるＳｉＣ単結晶成長では、実施例１と同様に直流電流の付与と電流の流れの方向によって、成長速度を増大もしくは減少することが可能である。しかもＳｉ−Ｃｒ−Ｃ溶媒を用いた場合でも、Ｓｉ−Ｃ溶媒を用いた場合と同様に、直流電流の付与と電流の流れの方向によって、成長速度を増大もしくは減少することが可能である。加えて、Ｓｉ−Ｃｒ−Ｃ溶媒中のＣｒ濃度が大きくなるにつれて、直流電流を通ずることによる成長速度の増大・減少がＳｉ−Ｃ溶媒を用いた結晶成長よりも大きくなっている。このことはＳｉ−Ｃｒ−Ｃ溶液中のＣの量が溶媒中へのＣｒ添加量の増大とともに大きくなっていることに起因して、溶液中を流れる電子と、溶液中の炭素との運動量交換である衝突の頻度が大きくなったことにより、エレクトロマイグレーション効果が増大したものと考えられる。 FIG. 7 shows the growth rate of the SiC crystal grown by the method performed in Example 4 and the dependence on the direct current. According to FIG. 7, in the SiC single crystal growth by the method performed in the fourth embodiment, the growth rate can be increased or decreased depending on the application of a direct current and the direction of the current flow as in the first embodiment. . Moreover, even when the Si—Cr—C solvent is used, the growth rate can be increased or decreased depending on the application of direct current and the direction of current flow, as in the case of using the Si—C solvent. In addition, as the Cr concentration in the Si—Cr—C solvent increases, the increase / decrease in the growth rate due to passing a direct current is greater than the crystal growth using the Si—C solvent. This is because the amount of C in the Si-Cr-C solution increases as the amount of Cr added to the solvent increases, and the momentum exchange between the electrons flowing in the solution and the carbon in the solution occurs. It is considered that the electromigration effect increased due to the increased frequency of collisions.
以上のように、ＳｉＣ溶液成長が実施可能な１６００〜２４００℃の高温で、溶液引き上げ成長法によるＳｉＣ単結晶製造おいて、成長炉内の温度勾配や坩堝内の溶液の流れを特別に変更することなく、結晶成長速度を増大、減少させることができ、または種結晶の表面溶解による表面清浄化も実現し、良好な表面モフォロジーを維持し、大きい成長速度にてＳｉＣ単結晶を製造することが可能となる。また、このような方法で製造することで、得られるＳｉＣの単結晶は高品質で、他の方法よりも大きな単結晶を得ることが可能となった。 As described above, the temperature gradient in the growth furnace and the flow of the solution in the crucible are specially changed in the production of the SiC single crystal by the solution pulling growth method at a high temperature of 1600 to 2400 ° C. at which SiC solution growth can be performed. Without increasing the crystal growth rate, it can also achieve surface cleaning by surface dissolution of the seed crystal, maintain good surface morphology, and produce SiC single crystal at a high growth rate It becomes possible. Further, by producing by such a method, the obtained SiC single crystal is of high quality, and a single crystal larger than other methods can be obtained.
１ 直流または交流電流源
２ 種結晶保持棒
３ 断熱材
４ 高周波加熱コイル
５ 黒鉛坩堝
６ 放射温度計
７ ＳｉＣ種結晶
８ 溶液
９ 放射温度計
DESCRIPTION OF
Claims (10)
前記ＳｉＣの種結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶成長面に、結晶が成長する間、直流もしくは交流電流を流し続け、
電流密度が１〜５０Ａ／ｃｍ２の範囲内で、かつ前記電流を流さない場合の結晶成長速度より遅い結晶成長速度となる電流密度で結晶成長を行うことを特徴とするＳｉＣ単結晶の製造方法。 A method for producing a SiC single crystal by a solution pulling growth method in which a SiC seed crystal is immersed in a solution containing Si and C, and SiC is continuously precipitated and grown.
While the crystal grows on the crystal growth surface, which is a contact surface between the SiC seed crystal and the solution held by the graphite crucible, a direct current or an alternating current continues to flow,
A method for producing a SiC single crystal, characterized in that crystal growth is performed at a current density within a range of 1-50 A / cm 2 and a crystal growth rate slower than the crystal growth rate when no current is passed. .
前記種結晶を、前記溶液中に浸漬した後、該種結晶をマイナス極として、１５Ａ／ｃｍ２以上の直流電流を流すか、または、２２Ａ／ｃｍ２以上の交流電流を流して、単結晶表面を溶解させて単結晶の表面清浄化を行った後、
前記ＳｉＣの種結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶成長面に、直流もしくは交流電流を１〜５０Ａ／ｃｍ２流すことを特徴とするＳｉＣ単結晶の製造方法。 A method for producing a SiC single crystal by a solution pulling growth method in which a SiC seed crystal is immersed in a solution containing Si and C, and SiC is continuously precipitated and grown.
After immersing the seed crystal in the solution, using the seed crystal as a negative electrode, a direct current of 15 A / cm 2 or more is passed, or an alternating current of 22 A / cm 2 or more is passed, After dissolving the surface and cleaning the surface of the single crystal,
A method for producing a SiC single crystal, wherein a direct current or an alternating current of 1 to 50 A / cm 2 is passed through a crystal growth surface, which is a contact surface between the SiC seed crystal and the solution held by a graphite crucible.
前記ＳｉＣの単結晶と黒鉛坩堝により保持された前記溶液との接触面である結晶面に、直流もしくは交流電流を流し、
前記電流を流さない場合の結晶成長速度より遅い結晶成長速度となるように電流密度を設定し、該単結晶表面を溶解させることを特徴とするＳｉＣ単結晶の表面清浄化方法。 A method for cleaning the surface of a SiC single crystal by immersing the SiC single crystal in a solution containing Si and C, and continuously raising and precipitating and growing SiC.
A direct current or an alternating current is passed through a crystal plane which is a contact surface between the SiC single crystal and the solution held by a graphite crucible,
A method for cleaning the surface of a SiC single crystal, wherein the current density is set so that the crystal growth rate is slower than the crystal growth rate when no current is passed, and the surface of the single crystal is dissolved.
If the current is direct current, the single crystal as a minus pole, 15A / cm 2 flowed more DC current, when the current is AC, by flowing 22A / cm 2 or more DC current, the single crystal surface The method for cleaning the surface of a SiC single crystal according to claim 9, wherein melting is performed.
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