JP4987784B2 - Method for producing silicon carbide single crystal ingot - Google Patents
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Description
本発明は、欠陥密度が小さく、かつ結晶性の良い炭化珪素単結晶の製造方法に関するものである。特に限定されるものではないが、本発明の製造方法で得られる炭化珪素単結晶は、各種半導体電子デバイスを構成する基板材料として特に好適に用いられる。 The present invention relates to a method for producing a silicon carbide single crystal having a low defect density and good crystallinity. Although not particularly limited, the silicon carbide single crystal obtained by the production method of the present invention is particularly preferably used as a substrate material constituting various semiconductor electronic devices.
炭化珪素（SiC）は、半導体材料として優れた物理特性、耐熱性及び機械的強度等を有することから、電力用パワーデバイスを含む各種デバイス用の基板ウェハ向け材料として注目されている。SiC単結晶は、昇華再結晶法によって製造されることが一般的であるが、半導体デバイスとしての使用に耐え得る十分な大きさを持った、結晶欠陥の少ない高品質のSiC単結晶を得ることが困難であったために、長年、その実用化が阻まれてきた経緯がある。 Silicon carbide (SiC) has attracted attention as a material for substrate wafers for various devices including power devices for electric power because it has excellent physical properties, heat resistance, mechanical strength and the like as a semiconductor material. SiC single crystals are generally manufactured by sublimation recrystallization, but to obtain high-quality SiC single crystals that are large enough to withstand use as semiconductor devices and have few crystal defects Because of its difficulty, its practical application has been hindered for many years.
近年、従来の昇華再結晶法を改善した、改良レーリー法(非特許文献１)が提案され、単結晶インゴットの高品質化及び大型化に飛躍的進捗がもたらされた。近年では、GaN系青色あるいは白色発光ダイオードや、ショットキーバリアダイオード等の各種デバイスの製品化に向けた応用開発が加速度的に進められると同時に、SiC単結晶基板開発においても、直径１００mmに及ぶ大口径の単結晶ウェハが市販されるに至っている(非特許文献２)。 In recent years, an improved Rayleigh method (Non-Patent Document 1), which is an improvement over the conventional sublimation recrystallization method, has been proposed, and a dramatic progress has been made in improving the quality and size of single crystal ingots. In recent years, application development for commercialization of various devices such as GaN-based blue or white light-emitting diodes and Schottky barrier diodes has been accelerated, and at the same time, SiC single crystal substrates have a large diameter of 100 mm. A single crystal wafer having a diameter has been commercially available (Non-patent Document 2).
改良レーリー法では、主として黒鉛製の坩堝等々の耐熱容器を用い、高温におけるSiC物質の昇華・再結晶現象を応用して単結晶を製造する。即ち、主としてSiCからなる原料粉末を加熱して昇華分解させ、坩堝内の比較的低温部に予め設置しておいたSiC単結晶からなる種結晶上に昇華ガスを移動させて再結晶させることにより、SiC単結晶インゴットが得られる。このような単結晶化プロセスは、約２０００℃以上に及ぶ高温環境下で行う必要がある。そして、このような超高温域で、かつ結晶欠陥等々の発生の無い良質なSiC単結晶インゴットを得るためには、坩堝内温度分布や昇華SiCガス分布、あるいは昇華ガス組成等々を制御して単結晶成長が安定化する最適成長条件を保ち、かつその条件を全成長時間に亘って維持することが必要である。 In the modified Rayleigh method, a single crystal is produced by applying a sublimation / recrystallization phenomenon of SiC material at high temperature, mainly using a heat-resistant container such as a graphite crucible. That is, the raw material powder mainly composed of SiC is heated to be sublimated and decomposed, and the sublimation gas is moved and recrystallized on a seed crystal composed of a SiC single crystal previously set in a relatively low temperature portion in the crucible. A SiC single crystal ingot is obtained. Such a single crystallization process needs to be performed in a high temperature environment of about 2000 ° C. or more. In order to obtain a high-quality SiC single crystal ingot that is free from crystal defects and the like in such an ultra-high temperature range, the temperature distribution in the crucible, the sublimation SiC gas distribution, the sublimation gas composition, and the like are controlled. It is necessary to maintain optimum growth conditions that stabilize crystal growth and to maintain those conditions over the entire growth time.
しかしながら、このような超高温域でのプロセス条件制御は、高度な技術を要する上に、坩堝内部の様子をリアルタイムでモニタリングすることが困難であることから、坩堝の外表面温度を測定して得られた情報等々から推測して行う以外に工業的に有効な方法がなく、かような制御技術に関係する制約から、現時点においても結晶成長条件に未解明な制御因子を抱えており、安定な結晶成長条件を完全に確立するには至っていないのが実情である。 However, such control of process conditions in the ultra-high temperature range requires advanced techniques and it is difficult to monitor the inside of the crucible in real time, so it is obtained by measuring the outer surface temperature of the crucible. There is no industrially effective method other than inferring from the estimated information, etc., and due to constraints related to such control technology, there are still unclear control factors in crystal growth conditions at present, and stable The fact is that the crystal growth conditions have not been completely established.
このため、昇華再結晶法によるSiC単結晶の製造時に、成長結晶の一部に乱れが発生して多結晶化したり、また、異種ポリタイプが発生する等々の現象が頻発し、単結晶インゴットの製造歩留まりが低下するのみならず、マイクロパイプ等々の結晶欠陥が新たに発生して結晶品質を劣化させてしまう等の問題が残されていた。 For this reason, during the production of SiC single crystals by the sublimation recrystallization method, phenomena such as turbulence occur in part of the grown crystal and polycrystallization, and the occurrence of different types of polytypes frequently occur. In addition to a decrease in manufacturing yield, there still remains a problem that crystal defects such as micropipes are newly generated to deteriorate the crystal quality.
ところで、種結晶を用いた昇華再結晶法によってSiC単結晶インゴットを製造する場合、その結晶成長時の昇温過程においては、比較的低温域で生成し易いSiCポリタイプが存在することが知られている(非特許文献３)。例えば、３Ｃと称されるSiCポリタイプは、成長装置にもよるが、２０００℃以下の比較的低温域で、特に非平衡条件下で生成し易いと言われている。しかるに、半導体物性に関係する諸特性の観点から、デバイス応用として現在最も注目されているSiCポリタイプは、４Ｈ及び６Ｈである。そして、昇華再結晶法では、これらのポリタイプからなる単結晶インゴットが安定的して晶出する温度域が概ね約２０００℃以上の高温域であるため、４Ｈ及び６Ｈポリタイプ単結晶を製造する場合には、種結晶付近の温度が前記の温度範囲に入るように、坩堝を含めた成長系全体の温度を制御しなければならない。 By the way, when producing a SiC single crystal ingot by sublimation recrystallization using a seed crystal, it is known that there are SiC polytypes that are likely to form at relatively low temperatures in the temperature rising process during crystal growth. (Non-patent Document 3). For example, an SiC polytype called 3C is said to be easily formed in a relatively low temperature range of 2000 ° C. or lower, particularly under non-equilibrium conditions, depending on the growth apparatus. However, from the viewpoint of various properties related to semiconductor physical properties, SiC polytypes that are currently attracting the most attention as device applications are 4H and 6H. In the sublimation recrystallization method, since the temperature range in which the single crystal ingot composed of these polytypes stably crystallizes is a high temperature range of about 2000 ° C. or higher, 4H and 6H polytype single crystals are produced. In some cases, the temperature of the entire growth system including the crucible must be controlled so that the temperature in the vicinity of the seed crystal falls within the above temperature range.
このため、原料純化や脱ガス処理、即ち、原料表面に吸着している不純物を低圧下で加熱処理して除去する場合等々のような、別途異なる目的で熱処理を行う場合を除き、基本的には低温域での異種SiCポリタイプの晶出を抑制する目的から、雰囲気圧力を高くした状態で昇温し、所望の成長温度近傍に到達後に圧力を低下して、成長を開始させる手法が一般的に行われている(非特許文献４、特許文献１)。所望の成長温度近傍に到達するまで昇温時の雰囲気圧力を高くすると、SiC昇華ガスの坩堝内での拡散輸送が抑制されることから、種結晶上での結晶成長を抑制することができ、これが本法の基本原理となっている。しかしながら、かような雰囲気圧力制御を行っても、依然として成長結晶が多結晶化したり、異種SiCポリタイプが混入したりする等の現象が頻発しており、必ずしも有効に結晶製造の歩留まりが向上しているとは言い難い状況にある。 For this reason, basically, except for the case where heat treatment is performed for different purposes such as raw material purification and degassing treatment, that is, when impurities adsorbed on the raw material surface are removed by heat treatment under low pressure, etc. For the purpose of suppressing crystallization of different SiC polytypes in the low temperature range, a general method is to start the growth by raising the temperature while increasing the atmospheric pressure and reducing the pressure after reaching the vicinity of the desired growth temperature. (Non-patent document 4, Patent document 1). If the atmospheric pressure at the time of raising the temperature is increased until reaching the vicinity of the desired growth temperature, diffusion transport in the crucible of the SiC sublimation gas is suppressed, so that crystal growth on the seed crystal can be suppressed, This is the basic principle of this method. However, even if such atmospheric pressure control is performed, there are still frequent occurrences such as polycrystal growth and mixing of different types of SiC polytypes, which effectively improves the yield of crystal production. It is difficult to say that it is.
そこで、発明者らは、昇華再結晶法における雰囲気圧力制御の問題点を解明するために昇温時の坩堝温度に関する詳細な調査を行った結果、例えば、黒鉛坩堝内で結晶成長を行う場合、圧力降下速度にもよるが、雰囲気圧力低下時に、坩堝の発熱部分付近でも約５０〜１００℃温度が上昇することを見出した。雰囲気圧力を低下させる場合、坩堝を含めた系全体の温度分布を決定している輻射や熱伝導等の熱流支配要因の中で、雰囲気ガスによる熱伝導の寄与分が寡少になり、結果として一時的に断熱性が向上するために、坩堝内の温度分布が上昇するものと推測される。 Therefore, the inventors conducted a detailed investigation on the temperature of the crucible at the time of raising the temperature in order to elucidate the problem of atmospheric pressure control in the sublimation recrystallization method.For example, when performing crystal growth in a graphite crucible, Although it depends on the pressure drop rate, it has been found that the temperature rises by about 50 to 100 ° C. even in the vicinity of the heat generating portion of the crucible when the atmospheric pressure drops. When the atmospheric pressure is lowered, the contribution of heat conduction by the atmosphere gas is reduced among the factors governing heat flow such as radiation and heat conduction that determine the temperature distribution of the entire system including the crucible. In order to improve heat insulation, the temperature distribution in the crucible is estimated to increase.
このような温度変化が発生する場合、結晶成長速度が雰囲気圧力低下時の温度変動に誘発されて安定せず、成長結晶の結晶性に乱れが発生し易くなり、場合によっては結晶方位の異なる結晶粒が生成して多結晶化してしまう。あるいは、原料昇華温度が大きく変化すると、原料から発生する昇華ガスの組成が揺らぐことになり、成長前に意図しなかった他の異種ポリタイプが生成し易い成長条件へ変移して、所望の単一ポリタイプ単結晶を得ることができなくなってしまう。これらのような状況が起こると、例えば、異種ポリタイプとの界面付近等からマイクロパイプと呼ばれる中空状微小欠陥が生じ、結果として結晶品質の劣化を引き起こすことになる(非特許文献５)。 When such a temperature change occurs, the crystal growth rate is not stabilized due to the temperature fluctuation at the time of the atmospheric pressure drop, and the crystallinity of the grown crystal is likely to be disturbed. Grains are formed and polycrystallized. Alternatively, when the raw material sublimation temperature changes greatly, the composition of the sublimation gas generated from the raw material fluctuates, and changes to growth conditions where other different polytypes that were not intended before the growth are likely to be produced, and the desired single unit. One polytype single crystal cannot be obtained. When such a situation occurs, for example, hollow micro-defects called micropipes are generated near the interface with different polytypes and the like, resulting in deterioration of crystal quality (Non-Patent Document 5).
一方、前述のような昇温時の圧力降下による結晶成長擾乱を回避する目的から、雰囲気圧力を結晶成長が起こる以前から下げておく方法が開示されている(特許文献２)。この方法によれば、圧力降下による結晶成長の擾乱は回避できるものの、必然的に低温域から結晶成長が開始することが避けられず、３Ｃポリタイプ等のような、目的とするポリタイプ以外のポリタイプが発生して結晶品質を劣化させる等の問題が生ずることは避けられない。 On the other hand, for the purpose of avoiding the crystal growth disturbance due to the pressure drop at the time of temperature increase as described above, a method of lowering the atmospheric pressure before crystal growth occurs is disclosed (Patent Document 2). According to this method, although disturbance of crystal growth due to pressure drop can be avoided, it is unavoidable that crystal growth starts from a low temperature region, and other than the target polytype such as 3C polytype. It is inevitable that problems such as generation of polytypes and deterioration of crystal quality occur.
以上のようなことから、従来の昇華再結晶法においては、いずれにしても、高品質SiC単結晶インゴットの製造歩留まりの低下が避けられず、安定結晶成長を実現する成長プロセスを提案することが強く望まれていた。 As described above, in any case, in the conventional sublimation recrystallization method, a decrease in the production yield of high-quality SiC single crystal ingots cannot be avoided, and a growth process that realizes stable crystal growth can be proposed. It was strongly desired.
そこで、本発明者らは、SiC物質の熱分解現象に与える雰囲気ガスの影響を詳細に調査したところ、プロパンやエチレンのような炭素及び水素からなる炭化水素系ガス雰囲気中では、２０００℃超の高温域で処理した後でも、SiCインゴットあるいはウェハ表面は目視レベルで全く変化せず、SiC自身の熱分解による表面炭化がほぼ生じないことを見出した。 Therefore, the present inventors investigated in detail the influence of the atmospheric gas on the thermal decomposition phenomenon of the SiC substance. In a hydrocarbon-based gas atmosphere composed of carbon and hydrogen such as propane and ethylene, the present inventors exceeded 2000 ° C. It was found that the SiC ingot or the wafer surface did not change at the visual level at all even after processing in a high temperature range, and surface carbonization due to thermal decomposition of SiC itself hardly occurred.
そして、本発明者らは、上記知見に基づいて、種結晶を用いる昇華再結晶法において、その雰囲気ガスとして炭化水素系ガスを用いることを鋭意検討した結果、特に、昇温過程における結晶成長の擾乱を抑制し、成長安定性を画期的に改善できる新しい単結晶製造プロセスを発明するに至った。 Based on the above findings, the present inventors have intensively studied the use of a hydrocarbon-based gas as the atmosphere gas in the sublimation recrystallization method using a seed crystal. The inventors have invented a new single crystal manufacturing process that can suppress disturbance and dramatically improve growth stability.
本発明は、上記事情に鑑みてなされたものであり、結晶性の良い単結晶ウェハの安定製造を可能にするSiC単結晶インゴットの製造方法を提供するものである。 The present invention has been made in view of the above circumstances, and provides a method for producing a SiC single crystal ingot that enables stable production of a single crystal wafer having good crystallinity.
本発明は、種結晶を用いる昇華再結晶法によるSiC単結晶の製造方法であって、以下の構成を趣旨とする。 The present invention is a method for producing a SiC single crystal by a sublimation recrystallization method using a seed crystal and has the following structure.
(1) 昇華再結晶法により種結晶上に炭化珪素単結晶を成長させる工程を含む炭化珪素単結晶インゴットの製造方法であって、結晶成長炉内に配置した成長用坩堝内の炭化珪素原料及び種結晶の温度が結晶成長開始温度に達するまでの昇温時には、結晶成長炉内の炉内雰囲気を、炭化水素系ガスとアルゴン、ヘリウム及び窒素から選ばれた少なくとも1種の不活性ガスとの混合ガスからなるガス雰囲気にすると共に、０．８×１０ 5 Pa以上の高圧雰囲気とし、坩堝内の炭化珪素原料及び種結晶が結晶成長開始温度に達した後には、前記結晶成長炉内の炉内雰囲気を、結晶成長条件の低圧雰囲気に降下させると共に、結晶成長炉内の圧力及び温度が安定した後に前記炭化水素系ガスの導入を停止して不活性ガスからなるガス雰囲気とし、この不活性ガスからなるガス雰囲気中で昇華再結晶による結晶成長を行うことを特徴とする炭化珪素単結晶インゴットの製造方法。 (1) A method for producing a silicon carbide single crystal ingot including a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, comprising: a silicon carbide raw material in a growth crucible disposed in a crystal growth furnace; At the time of temperature rise until the temperature of the seed crystal reaches the crystal growth start temperature , the atmosphere in the crystal growth furnace is composed of a hydrocarbon-based gas and at least one inert gas selected from argon, helium and nitrogen. A gas atmosphere composed of a mixed gas and a high-pressure atmosphere of 0.8 × 10 5 Pa or more are used, and after the silicon carbide raw material and the seed crystal in the crucible reach the crystal growth start temperature , the furnace in the crystal growth furnace The inner atmosphere is lowered to a low-pressure atmosphere under crystal growth conditions, and after the pressure and temperature in the crystal growth furnace are stabilized, the introduction of the hydrocarbon gas is stopped to form a gas atmosphere composed of an inert gas. Ga Method of manufacturing a silicon carbide single crystal ingot and performing crystal growth by sublimation recrystallization in a gas atmosphere consisting of.
(2) 前記混合ガスが、体積比で０．５%以上の炭化水素系ガスを含有する(1)に記載の炭化珪素単結晶インゴットの製造方法。 (2) The method for producing a silicon carbide single crystal ingot according to (1), wherein the mixed gas contains a hydrocarbon gas having a volume ratio of 0.5% or more.
(3) 前記混合ガスが、体積比で１%以上の炭化水素系ガスを含有する(1)に記載の炭化珪素単結晶インゴットの製造方法。 (3) The method for producing a silicon carbide single crystal ingot according to (1), wherein the mixed gas contains a hydrocarbon-based gas having a volume ratio of 1% or more.
(4) 前記混合ガスが、体積比で５%以上の炭化水素系ガスを含有する(1)に記載の炭化珪素単結晶インゴットの製造方法。 (4) The method for producing a silicon carbide single crystal ingot according to (1), wherein the mixed gas contains a hydrocarbon gas having a volume ratio of 5% or more.
(5) 前記炭化水素系ガスが、メタン、エタン、プロパン又はエチレンの少なくとも１種である(1)〜(4)の何れかに記載の炭化珪素単結晶インゴットの製造方法。 (5) The method for producing a silicon carbide single crystal ingot according to any one of (1) to (4), wherein the hydrocarbon gas is at least one of methane, ethane, propane, and ethylene.
本発明のSiC単結晶インゴットの製造法により、圧力変動に起因する成長環境不安定性や成長初期における異種ポリタイプ結晶の生成に起因する結晶成長擾乱が皆無になる。その結果、結晶性の良いSiC単結晶インゴットの安定製造が可能になり、高品質SiC単結晶ウェハを安定に製造できるようになる。 According to the method for producing a SiC single crystal ingot of the present invention, there is no growth environment instability caused by pressure fluctuations and no crystal growth disturbance caused by the formation of different polytype crystals in the early stage of growth. As a result, a SiC single crystal ingot with good crystallinity can be stably manufactured, and a high quality SiC single crystal wafer can be stably manufactured.
以下に、本発明の詳細について述べる。
まず、本発明のSiC単結晶製造方法において採用される雰囲気ガスについては、炭素及び水素からなると共に種結晶等のSiC単結晶に対して腐食やエッチング等々の影響を及ぼさない炭化水素系ガスであり、望ましくはメタン、エタン、プロパン、及びエチレンから選ばれた少なくとも1種からなるガスである。
Details of the present invention will be described below.
First, the atmospheric gas employed in the method for producing a SiC single crystal of the present invention is a hydrocarbon-based gas that is composed of carbon and hydrogen and does not affect the SiC single crystal such as a seed crystal by corrosion or etching . a gas preferably consisting of methane, ethane, of at least one species selected propane, and ethylene.
さらに、この雰囲気ガスについては、上記炭化水素系ガスと、アルゴン、ヘリウム、及び窒素から選ばれた１種又は２種以上の不活性ガスとの混合ガスであってもよい。また、特に電気抵抗率等のSiC単結晶の電気的特性を制御する必要性がある場合には、上記雰囲気ガス中に窒素を適当量混合しても良い。雰囲気ガスとして混合ガス、即ち不活性ガスで希釈された炭化水素系ガスを用いる場合には、炭化水素系ガスが０．５体積%以上、好ましくは１体積%以上、さらに好ましくは５体積%以上存在していることが望ましい。雰囲気ガス中の炭化水素系ガス濃度が０．５体積%未満の場合には、焼鈍処理時の表面炭化抑制効果が得られないおそれがあり、また、炭化水素系ガス濃度の上限については、高温での焼鈍処理時の防爆等々に対する安全性が確保されれば、特に制限されるものでは無いが、通常は５０体積%程度までの混合ガスであるのがよい。 Further, the atmosphere gas may be a mixed gas of the hydrocarbon gas and one or more inert gases selected from argon, helium and nitrogen. Further, when there is a need to control the electrical characteristics of the SiC single crystal such as the electrical resistivity, an appropriate amount of nitrogen may be mixed in the above atmospheric gas. When a mixed gas, that is, a hydrocarbon gas diluted with an inert gas is used as the atmospheric gas, the hydrocarbon gas is 0.5 volume% or more, preferably 1 volume% or more, more preferably 5 volume% or more. It is desirable to exist. If the hydrocarbon gas concentration in the atmospheric gas is less than 0.5% by volume, the surface carbonization suppression effect during the annealing process may not be obtained, and the upper limit of the hydrocarbon gas concentration is high. Although there is no particular limitation as long as safety against explosion proofing during annealing is ensured, it is usually preferable to use a mixed gas of up to about 50% by volume.
また、本発明において、結晶成長炉の圧力については、結晶成長温度に達するまでの昇温時には所定の圧力より高く維持し、これによって昇温時における低温域での異種SiCポリタイプの晶出を可及的に抑制すると共に、結晶成長温度に到達した後には圧力を所定の圧力にまで低下させ、その後に所定の温度及び圧力に維持して昇華再結晶により結晶成長を行う。本発明方法により圧力変動に起因する成長環境不安定性が解消されるので、上記の昇華再結晶工程での雰囲気圧力制御による効果を可及的に引き出すことができる。 Further, in the present invention, the pressure of the crystal growth furnace is maintained higher than a predetermined pressure at the time of temperature rise until reaching the crystal growth temperature , thereby crystallization of different SiC polytypes in a low temperature region at the time of temperature rise. thereby reduced as much as possible, after reaching the crystal growth temperature reduces the pressure to a predetermined pressure, crystal growth by subsequently maintained at a predetermined temperature and pressure sublimation recrystallization. Since the growth environment instability caused by pressure fluctuation is eliminated by the method of the present invention, the effect of atmospheric pressure control in the sublimation recrystallization step can be brought out as much as possible.
本発明において昇温過程での結晶成長擾乱の抑制や成長安定性の改善が達成されるメカニズムについては、上記ガスを構成する元素の中で、特に炭素が昇華及び再結晶化の反応速度を規定する系全体の自由エネルギーに影響を与え、この炭素の増加により昇華分解速度を低下させている可能性が高いと推察している。しかしながら、水素を始めとする雰囲気ガス中の他の元素の影響まで勘案したメカニズムの詳細については、依然不明な点が残されており、現時点では必ずしも明らかではない。 In the present invention, regarding the mechanism by which the suppression of crystal growth disturbance and the improvement of growth stability in the temperature rising process are achieved, among the elements constituting the above gas, in particular, carbon defines the reaction rate of sublimation and recrystallization. It is presumed that there is a high possibility that the free energy of the entire system is affected and that the sublimation decomposition rate is lowered by the increase of carbon. However, the details of the mechanism that takes into account the influence of other elements in the atmospheric gas such as hydrogen remain unclear and are not necessarily clear at this time.
図1に、本発明者らが提案する好適な成長処理パターンの一例を示す。なお、本パターンは発明の一例を示すものであり、本発明がこれに限定されるものでは無い。 FIG. 1 shows an example of a suitable growth processing pattern proposed by the present inventors. In addition, this pattern shows an example of invention and this invention is not limited to this.
先ず、昇温前に、雰囲気ガスの組成を、本発明が提案する炭素及び水素からなる炭化水素系ガスと不活性ガスとの混合ガスで予め構成しておく。また、昇温時には、雰囲気圧力を大きくして（高圧雰囲気）、比較的低温で発生し易い異種SiCポリタイプの生成を更に抑えている。なお、昇温過程時の圧力は０．８×１０5Pa以上であれば十分である。 First, before heated, the composition of the atmosphere gas in advance constituted by a mixed gas of hydrocarbon gas and inert gas present invention is composed of carbon and hydrogen proposed. In addition, when the temperature is raised, the atmospheric pressure is increased (high pressure atmosphere) to further suppress the generation of different types of SiC polytypes that are likely to occur at relatively low temperatures. It is sufficient that the pressure during the temperature raising process is 0.8 × 10 5 Pa or more.
所定の成長温度、例えば、２０００℃に到達した後、雰囲気圧力の減圧を開始し、所定の成長圧力、例えば１．３×１０4Paへ雰囲気圧力を降下させる（低圧雰囲気）。雰囲気圧力及び坩堝の表面温度から推測される坩堝内温度（結晶成長炉内の圧力及び温度）が十分に安定した後に、上記炭化水素系ガスの導入を停止し、窒素を適当量混合したアルゴンガスのみを成長炉に導入する（アルゴン等の不活性雰囲気）。これにより、成長処理パターンの初期昇温過程時の異種SiCポリタイプ生成を完全に抑制すると同時に、雰囲気圧力減圧時に発生する温度変化や圧力変動等々による成長不安定性を回避でき、温度や雰囲気圧力が十分安定した成長条件下で、所望の単結晶成長を開始することができる。 After reaching a predetermined growth temperature, for example, 2000 ° C., pressure reduction of the atmospheric pressure is started, and the atmospheric pressure is lowered to a predetermined growth pressure, for example, 1.3 × 10 4 Pa (low pressure atmosphere). After the temperature in the crucible (pressure and temperature in the crystal growth furnace) estimated from the atmospheric pressure and the surface temperature of the crucible is sufficiently stabilized, the introduction of the hydrocarbon-based gas is stopped, and an argon gas mixed with an appropriate amount of nitrogen Is introduced into the growth furnace (inert atmosphere such as argon). This completely suppresses the generation of heterogeneous SiC polytypes during the initial heating process of the growth process pattern, while avoiding growth instability due to temperature changes and pressure fluctuations that occur when the atmospheric pressure is reduced. The desired single crystal growth can be started under sufficiently stable growth conditions.
また、本発明の製造方法を採用することで、炭化水素系ガスそれ自体により、不要な異種SiCポリタイプの初期生成を抑制する効果が得られることになり、昇温時に雰囲気圧力を大きくする必要も無い。この場合、所望の結晶成長開始温度に到達し、温度が十分に安定した後に、上記の炭化水素系ガスの導入を遮断し、アルゴンやヘリウム、もしくは窒素等々の不活性ガスに切り替えることで、従来問題になっていた圧力降下時の圧力変動による成長環境擾乱起因の結晶成長不安定化を回避できると共に、特に上記の結晶成長開始温度よりも低温域側で生成してしまう異種ポリタイプの結晶生成核の発生を抑え、目的とする所望のポリタイプから構成される高品質SiC単結晶を得ることができるようになる。 In addition, by adopting the production method of the present invention, the hydrocarbon gas itself has the effect of suppressing the initial generation of unnecessary different SiC polytypes, and it is necessary to increase the atmospheric pressure at the time of temperature rise. There is no. In this case, after reaching the desired crystal growth start temperature and the temperature is sufficiently stabilized, the introduction of the hydrocarbon gas is cut off and switched to an inert gas such as argon, helium, or nitrogen. It is possible to avoid crystal growth instability caused by disturbance of the growth environment due to pressure fluctuation at the time of pressure drop, which is a problem, and crystal formation of different polytypes that are generated at a lower temperature range than the above-mentioned crystal growth start temperature Nucleation is suppressed, and a high-quality SiC single crystal composed of a desired polytype of interest can be obtained.
以下に、本発明の実施例について説明する。
〔実施例１〕
図２に、本発明で用いた、種結晶を用いる昇華再結晶法の製造装置の概略図を示す。
Examples of the present invention will be described below.
[Example 1]
FIG. 2 shows a schematic diagram of a production apparatus of the sublimation recrystallization method using a seed crystal used in the present invention.
図２において、黒鉛製坩堝中にSiC原料粉末を充填し、その上部対向面に６Ｈポリタイプの単結晶種結晶ウェハを据え付けた後、水冷式二重石英炉心管の内部に静置した。坩堝内径は約２５．４mmである。SiC原料粉末の不純物を除去する目的から、約１０-3Pa以下の高真空下で高周波加熱方式により約５００℃に加熱、保持し、脱ガス処理を行った。 In FIG. 2, a SiC crucible was filled in a graphite crucible, and a 6H polytype single crystal seed crystal wafer was installed on the upper facing surface, and then placed in a water-cooled double quartz furnace core tube. The inner diameter of the crucible is about 25.4 mm. For the purpose of removing impurities from the SiC raw material powder, degassing was performed by heating and holding at about 500 ° C. by a high-frequency heating method under a high vacuum of about 10 −3 Pa or less.
しかる後に、プロパンガスを１体積%混合したアルゴンガスを二重石英管内の圧力が１．０×１０5Paになるまで充填し、その後２２００℃まで約１時間かけて昇温した。なお、坩堝温度の測温方法であるが、坩堝上部の断熱材中央部分に直径２〜４mmの光路を設け、二重石英炉心管の外に設置した二色温度計にて測定した。 Thereafter, argon gas mixed with 1% by volume of propane gas was charged until the pressure in the double quartz tube became 1.0 × 10 5 Pa, and then the temperature was raised to 2200 ° C. over about 1 hour. In addition, although it is a temperature measuring method of the crucible temperature, an optical path having a diameter of 2 to 4 mm was provided in the central portion of the heat insulating material at the upper part of the crucible, and the temperature was measured with a two-color thermometer installed outside the double quartz furnace core tube.
引き続いて、二重石英管内圧力の減圧を開始し、圧力１．３×１０3Paへ約５分で到達した。その状態で約１時間保持し、温度が平衡状態に達するのを待った。１時間後、約２２００℃の温度で安定になることを確認し、その後、炉内に導入する雰囲気ガスを純アルゴンガス(純度99.999%)に切り替えた。
この状態で約２０時間保持して結晶成長を行った。
Subsequently, pressure reduction in the double quartz tube was started, and the pressure reached 1.3 × 10 3 Pa in about 5 minutes. The state was kept for about 1 hour and waited for the temperature to reach equilibrium. After 1 hour, it was confirmed that the temperature became stable at a temperature of about 2200 ° C., and then the atmospheric gas introduced into the furnace was switched to pure argon gas (purity 99.999%).
In this state, the crystal was grown for about 20 hours.
成長完了後に成長結晶を取り出し、透過光線照射による観察を行ったところ、この実施例１で作製した結晶は、完全な６Ｈポリタイプの単結晶インゴットであり、異種ポリタイプの混入は全く見られず、用いた種結晶とほぼ同等のマイクロパイプ密度を持っていることを確認した。なお、確認のために、マルチワイヤーソーを用いて、成長方向に垂直に切り出して厚さ約１mmのスライス基板を作製し、得られた全ての基板についてポリタイプを目視にて確認したが、全て６Ｈのシングルポリタイプであった。 After the growth was completed, the grown crystal was taken out and observed by transmission light irradiation. As a result, the crystal produced in Example 1 was a complete 6H polytype single crystal ingot, and no contamination of different polytypes was observed. It was confirmed that the micropipe density was almost equal to the seed crystal used. For confirmation, a multi-wire saw was used to cut slices perpendicular to the growth direction to produce sliced substrates with a thickness of about 1 mm, and polytypes were visually confirmed for all the obtained substrates. It was a 6H single polytype.
〔比較例１〕
上記実施例１の比較実験として、全プロセスに亘って雰囲気ガスを純アルゴンガス(純度99.999%)とした以外は、上記実施例１とほぼ完全に同一の条件下で結晶成長実験を行った。
[Comparative Example 1]
As a comparative experiment of Example 1, a crystal growth experiment was performed under almost the same conditions as in Example 1 except that the atmosphere gas was changed to pure argon gas (purity 99.999%) throughout the entire process.
この比較例１の場合には、大傾角の結晶粒界は皆無であり、かつ単結晶状態は維持されているもの、成長結晶の内部、特に種結晶直上近傍に４Ｈポリタイプ領域及び３Ｃポリタイプ結晶核が混入しており、６Ｈポリタイプ部分との界面付近よりマイクロパイプ欠陥が多数発生して、インゴットの結晶性が著しく劣化していた。 In the case of this comparative example 1, there is no crystal grain boundary with a large inclination and the single crystal state is maintained, and the 4H polytype region and the 3C polytype are present inside the grown crystal, particularly in the immediate vicinity of the seed crystal. Crystal nuclei were mixed, many micropipe defects were generated near the interface with the 6H polytype portion, and the crystallinity of the ingot was significantly deteriorated.
〔実施例２〕
実施例１とほぼ同様な成長条件にて、６Ｈポリタイプの単結晶インゴット成長実験を実施した。但し、種結晶の口径は７６mm、坩堝内径は７６．５mmであり、使用したプロパンガス混合アルゴンガス中のプロパン濃度は０．５体積%であること以外は、実施例１とほぼ同じ条件で成長を行っている。
[Example 2 ]
A 6H polytype single crystal ingot growth experiment was conducted under the growth conditions almost the same as in Example 1. However, the diameter of the seed crystal is 76 mm, the inner diameter of the crucible is 76.5 mm, and the propane concentration in the used propane gas mixed argon gas is 0.5% by volume, and the growth is performed under substantially the same conditions as in Example 1. It is carried out.
この条件での結晶成長を２０回繰り返して行い、得られた成長結晶について、外周刃切断機を用いて成長方向に平行に切断し、透過光線照射による観察を行ったところ、得られた結晶中の１個について、成長結晶の周辺端部の極近傍に、直径約１mm程度の微小４Ｈポリタイプが混入しており、この部分を起点としてマイクロパイプ欠陥が新たに発生していることを確認した。他の１９個については、全てほぼ完全な６Ｈポリタイプの単結晶インゴットであり、異種ポリタイプの混入は全く見られなかった。 Crystal growth under these conditions was repeated 20 times, and the obtained grown crystal was cut in parallel to the growth direction using an outer cutter and observed by transmission light irradiation. For one of these, a very small 4H polytype with a diameter of about 1 mm was mixed in the very vicinity of the peripheral edge of the grown crystal, and it was confirmed that a micropipe defect was newly generated starting from this part. . The other 19 were all almost single crystal ingots of 6H polytype, and no contamination of different polytypes was observed.
〔実施例３〕
上記実施例２の成長実験について、プロパンガス混合アルゴンガス中のプロパン濃度を５体積%とした以外は全く同様の条件にて成長実験を行い、同様な透過光線照射による観察を行った。その結果、２０個全ての結晶について、完全な６Ｈポリタイプの単結晶インゴットであり、異種ポリタイプの混入は全く見られなかった。
[Example 3 ]
Regarding the growth experiment of Example 2, the growth experiment was performed under exactly the same conditions except that the propane concentration in the propane gas mixed argon gas was changed to 5% by volume, and the same observation by transmitted light irradiation was performed. As a result, all of the 20 crystals were complete 6H polytype single crystal ingots, and no mixing of different polytypes was observed.
上記実施例２及び３の結果から明らかなように、プロパン濃度０．５体積%及び５体積%のアルゴンガスを用いた場合は、共に高品質な単結晶が得られる有効な方法であるが、濃度５体積%の条件下で実施することにより、より大きな効果が得られることが判明した。 As is apparent from the results of Examples 2 and 3 , when argon gas having a propane concentration of 0.5% by volume and 5% by volume is used, both are effective methods for obtaining a high-quality single crystal. It has been found that a greater effect can be obtained by carrying out under the condition of a concentration of 5% by volume.
１…種結晶（SiC単結晶）、２…SiC粉末原料、３…黒鉛坩堝、４…二重石英炉心管（水冷式）、５…断熱材、６…真空排気装置、７…高周波加熱コイル。
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