JP5657949B2 - Low nitrogen concentration graphite material and storage method thereof - Google Patents
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本発明は、炭化ケイ素（以下、ＳｉＣという。）のエピタキシャル成長膜製造用治具又はＳｉＣ単結晶の製造用治具に用いられる、低窒素濃度黒鉛材料、及び、その保管方法に関する。 The present invention relates to a low nitrogen concentration graphite material used for a jig for manufacturing an epitaxial growth film of silicon carbide (hereinafter referred to as SiC) or a jig for manufacturing a SiC single crystal, and a storage method thereof.
近年、ＳｉＣ或いはガリウムヒ素、インジウムリン等の軽元素で構成された化合物系半導体の開発が活発に行われている。かかる化合物系半導体は、エネルギーのバンドギャップ、絶縁破壊電界、熱伝導度が大きいことが特徴である。そして、この特徴を活かして、高効率・高耐圧パワーデバイス、高周波パワーデバイス、高温動作デバイス、あるいは青色から紫外発光デバイス用の材料として注目を集めている。しかしながら、結合エネルギーが強いため、これらの化合物は、大気圧では高温にしても融解せず、シリコン（以下、Ｓｉという。）半導体で用いられる場合のごとくＳｉ融液を再結晶化してバルク結晶とすることが困難である。 In recent years, compound semiconductors composed of light elements such as SiC, gallium arsenide, and indium phosphide have been actively developed. Such a compound semiconductor is characterized by a large energy band gap, dielectric breakdown electric field, and thermal conductivity. And taking advantage of this feature, it has attracted attention as a material for high efficiency and high withstand voltage power devices, high frequency power devices, high temperature operation devices, or blue to ultraviolet light emitting devices. However, since the binding energy is strong, these compounds do not melt even at high temperatures at atmospheric pressure, and recrystallize the Si melt as used in silicon (hereinafter referred to as Si) semiconductors to form bulk crystals. Difficult to do.
例えば、ＳｉＣを半導体材料として使用するためには、ある程度の大きさを有する高品質な単結晶を得る必要がある。このため従来は、アチェソン法と呼ばれる化学反応を利用する方法、レーリー法と呼ばれる昇華再結晶法を利用する方法によりＳｉＣ単結晶の小片を得ていた。最近は、これらの方法によって製造されたＳｉＣの単結晶を種結晶として用い、この上に昇華再結晶化させる改良レーリー法によってＳｉＣインゴットを育成し、このＳｉＣインゴットをスライス、鏡面研磨したＳｉＣ基板が製造されるようになった。そして、その基板上に気相エピタキシャル成長法または液相エピタキシャル成長法によって目的規模のＳｉＣ単結晶を成長させることにより、不純物密度と膜厚を制御した活性層が形成され、これを用いてｐｎ接合ダイオード、ショットキーダイオードや各種のトランジスタ等のＳｉＣ半導体デバイスが製造されている。これらの方法には、ハロゲンガス雰囲気下で高純度処理した黒鉛材料や、該黒鉛材料表面にＳｉＣを被覆したＳｉＣ被覆黒鉛材料が使用されている。 For example, in order to use SiC as a semiconductor material, it is necessary to obtain a high-quality single crystal having a certain size. For this reason, conventionally, SiC single crystal pieces have been obtained by a method using a chemical reaction called the Acheson method and a method using a sublimation recrystallization method called the Rayleigh method. Recently, a SiC ingot is grown by an improved Rayleigh method in which a single crystal of SiC produced by these methods is used as a seed crystal and is sublimated and recrystallized thereon, and this SiC ingot is sliced and mirror polished. It came to be manufactured. Then, an active layer with a controlled impurity density and film thickness is formed by growing a SiC single crystal of a target scale on the substrate by vapor phase epitaxy or liquid phase epitaxy, and using this, a pn junction diode, SiC semiconductor devices such as Schottky diodes and various transistors are manufactured. In these methods, a graphite material subjected to high-purity treatment in a halogen gas atmosphere and a SiC-coated graphite material in which SiC is coated on the surface of the graphite material are used.
しかしながら、ハロゲンガス雰囲気下で高純度処理を行った黒鉛材料中であっても、約１０００ｐｐｍの窒素が含まれている。この窒素は、黒鉛材料の気孔中に存在しているものではなく、例えば、黒鉛の層間にトラップされたり、炭素原子と置換された状態で存在している。また、黒鉛材料中に微量に含まれる金属不純物と結合して窒素化合物を形成している。これら黒鉛材料中に含まれる窒素は、従来、特に注目されていなかったが、化合物系半導体、特にＳｉＣデバイスの製造用治具として用いた場合、前述のＳｉＣ単結晶や、ＳｉＣエピタキシャル成長時に、ＳｉＣ中に侵入し、ＳｉＣ単結晶や、ＳｉＣウェハー中等の窒素濃度を上昇させ、結晶中の欠陥の一因となることが最近になって見出された。例えば、ＳｉＣウェハー中には、１０ １７ ａｔｏｍｓ／ｃｍ３以上、ＳｉＣエピタキシャル成長膜中には、１０ １６ ａｔｏｍｓ／ｃｍ３以上の窒素が含有される。この窒素は、ＳｉＣ半導体等の化合物系半導体に対してドーパントとなり、製造されるＳｉＣデバイスの特性を著しく劣化させている。また、低窒素化した場合、これを一定期間保持する必要がある。 However, even in a graphite material that has been subjected to high-purity treatment in a halogen gas atmosphere, about 1000 ppm of nitrogen is contained. This nitrogen is not present in the pores of the graphite material, but is present, for example, in a state where it is trapped between graphite layers or substituted with carbon atoms. Moreover, it combines with metal impurities contained in a trace amount in the graphite material to form a nitrogen compound. Conventionally, nitrogen contained in these graphite materials has not been particularly noticed. However, when used as a jig for manufacturing a compound semiconductor, particularly a SiC device, the above-mentioned SiC single crystal or SiC during epitaxial growth can be contained in SiC. Recently, it has been found that the nitrogen concentration in SiC single crystals and SiC wafers increases and contributes to defects in the crystals. For example, the SiC wafer contains 10 17 atoms / cm 3 or more of nitrogen, and the SiC epitaxial growth film contains 10 16 atoms / cm 3 or more of nitrogen. This nitrogen serves as a dopant for compound semiconductors such as SiC semiconductors, and significantly deteriorates the characteristics of the manufactured SiC device. In addition, when the nitrogen is lowered, it is necessary to maintain this for a certain period.
本発明は、ＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いる場合に、ＳｉＣへの窒素の侵入を抑制可能な、低窒素濃度黒鉛材料、及び、その保管方法を提供することを目的とする。 The present invention provides a low nitrogen concentration graphite material capable of suppressing nitrogen intrusion into SiC and a storage method thereof when used in a jig for SiC epitaxial growth film production or a jig for SiC single crystal production. With the goal.
本願発明者は、窒素濃度を低減させた低窒素濃度黒鉛材料をＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具として使用することで、製造される製品（ＳｉＣ半導体デバイス等）における結晶中の欠陥の発生を抑制できることを見出し、本発明を完成した。すなわち、前記課題を解決するための本発明は、ＧＤＭＳによる窒素濃度が９８ｐｐｍ以下（ただし、０．８〜３６ｐｐｍを除く）であり、大気と遮断した状態で保管された、ＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いられる、低窒素濃度黒鉛材料である。また、本発明は、ＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いられる、グロー放電質量分析法による窒素濃度が９８ｐｐｍ以下（ただし、０．８〜３６ｐｐｍを除く）である低窒素濃度黒鉛材料を、樹脂フィルムからなる袋内に真空パックするか又は希ガスと共に封入して、大気と遮断した状態で保管する方法である。 The inventor of the present application uses a low nitrogen concentration graphite material with a reduced nitrogen concentration as a jig for manufacturing an SiC epitaxial growth film or a jig for manufacturing a SiC single crystal, so that a crystal in a manufactured product (such as a SiC semiconductor device) is obtained. The present inventors have found that the occurrence of defects inside can be suppressed and completed the present invention. That is, the present invention for solving the above problems is for producing an SiC epitaxial growth film having a nitrogen concentration by GDMS of 98 ppm or less (excluding 0.8 to 36 ppm) and stored in a state of being cut off from the atmosphere. It is a low nitrogen concentration graphite material used for jigs or jigs for producing SiC single crystals. Further, according to the present invention, the nitrogen concentration by glow discharge mass spectrometry used in a jig for producing an SiC epitaxial growth film or a jig for producing a SiC single crystal is 98 ppm or less (except for 0.8 to 36 ppm). In this method, the low nitrogen concentration graphite material is vacuum packed in a bag made of a resin film or sealed together with a rare gas, and stored in a state where it is cut off from the atmosphere.
黒鉛材料中の窒素濃度を、好ましくは１０ｐｐｍ以下、さらに好ましくは５ｐｐｍ以下とする。これにより、本発明に係る黒鉛材料をＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いた場合、ＳｉＣへの窒素の侵入を抑制することができ、従来よりも１桁以上窒素濃度が少ない製品（ＳｉＣ半導体デバイス等）を製造することが可能となる。 The nitrogen concentration in the graphite material is preferably 10 ppm or less, more preferably 5 ppm or less. As a result, when the graphite material according to the present invention is used in a jig for producing an SiC epitaxial growth film or a jig for producing an SiC single crystal, nitrogen can be prevented from entering the SiC, and the nitrogen content can be reduced by one digit or more than before. A product (SiC semiconductor device or the like) having a low concentration can be manufactured.
また、本発明でいうＳｉＣ単結晶製造用治具は、例えば、ＳｉＣ単結晶の引上げ等に使用される、ルツボやヒーター等の炉内部品を含む。また、ＳｉＣエピタキシャル成長膜製造用治具としては、例えば、ＳｉＣ膜のエピタキシャル成長用サセプター等が例示できる。その他には、断熱材や加熱用ヒーター等の炉内部品も、治具に含まれるものとする。 The SiC single crystal manufacturing jig referred to in the present invention includes in-furnace parts such as a crucible and a heater used for pulling up a SiC single crystal, for example. Examples of the SiC epitaxial growth film manufacturing jig include a susceptor for epitaxial growth of an SiC film. In addition, in-furnace parts such as a heat insulating material and a heater are also included in the jig.
なお、本発明において、黒鉛材料は、高純度処理後、又は、黒鉛材料中の窒素等を除去する熱処理を行った後に、大気と遮断した状態で保管される。これによって、より確実に黒鉛材料中の窒素濃度を低い状態で維持することができる。ここで、大気と遮断した状態とは、例えば、いわゆる真空パックと呼ばれる樹脂フィルム等の機密性に優れた袋内を大気圧よりも減圧状態にして黒鉛材料を密封した状態とする。又は、ガスパックと呼ばれる樹脂フィルム等の機密性に優れた袋内に希ガス雰囲気とともに黒鉛材料を密封した状態としたものをいう。ここで、樹脂フィルムとしては、塩化ビニルフィルム、ポリエチレンフィルム等を使用することができる。 In the present invention, the graphite material is stored in a state of being cut off from the atmosphere after high-purity treatment or after heat treatment for removing nitrogen or the like in the graphite material. As a result, the nitrogen concentration in the graphite material can be more reliably maintained in a low state. Here, the state cut off from the atmosphere is, for example, a state in which the graphite material is sealed by making the inside of a bag excellent in confidentiality, such as a resin film called a so-called vacuum pack, in a reduced pressure state from atmospheric pressure. Or the thing which made the state which sealed the graphite material with the noble gas atmosphere in the bag excellent in confidentiality, such as a resin film called a gas pack. Here, a vinyl chloride film, a polyethylene film, etc. can be used as a resin film.
本発明によれば、当該黒鉛材料をＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いる場合に、ＳｉＣへの窒素の侵入を抑制することができる。 According to the present invention, when the graphite material is used for a jig for manufacturing an SiC epitaxial growth film or a jig for manufacturing a SiC single crystal, nitrogen can be prevented from entering the SiC.
以下に、本発明に係る黒鉛材料の一実施形態について説明する。 Hereinafter, an embodiment of the graphite material according to the present invention will be described.
本実施形態に係る黒鉛材料は、一般的な製法で製造されたものを使用することができる。一般的な製法の一例として、先ず炭素成形体を焼成炉内において８００乃至１０００℃に加熱し、バインダー等に含まれる易揮発成分を、分散、蒸散させて焼成する工程（工程Ａ）、次に焼成体を取り出し、黒鉛化炉、例えばアチェソン式炉、カストナー式炉又は誘導加熱炉（例えば特開昭５７−１６６３０５号、１６６３０６号、１６６３０７号、１６６３０８号）にて３０００℃に加熱して黒鉛化する工程（工程Ｂ）、更に、このようにして得られた黒鉛材料を、別の反応器中でハロゲンガス雰囲気中で加熱し、黒鉛材料中の不純物を蒸気圧の高い物質に変化せしめて母材から揮散させ、黒鉛材料の高純度化を行う工程（工程Ｃ）から成る工程を経て製造する。 The graphite material which concerns on this embodiment can use what was manufactured by the general manufacturing method. As an example of a general production method, first, a carbon molded body is heated to 800 to 1000 ° C. in a firing furnace, and a readily volatile component contained in a binder or the like is dispersed and evaporated to be fired (step A), then The fired body is taken out and graphitized by heating to 3000 ° C. in a graphitization furnace such as an Acheson furnace, a Kaston furnace, or an induction heating furnace (for example, JP-A 57-166305, 166306, 166307, 166308). Further, the graphite material thus obtained is heated in a halogen gas atmosphere in a separate reactor to change the impurities in the graphite material into a substance having a high vapor pressure. It is produced through a process consisting of a process (process C) which is volatilized from the material and purifies the graphite material.
これら黒鉛化、高純度化処理時には、加熱に要するヒーター等の周りに窒素ガスを流し、ヒーター等の酸化を防止することが一般的に行われている。この窒素ガスが、黒鉛化及び高純度化処理の時に、黒鉛の層間にトラップされたり、炭素原子と置換したり、あるいは、黒鉛材料中に僅かに残った金属不純物と反応し、窒素化合物を形成し、黒鉛材料中に残存してしまう。 At the time of these graphitization and high-purification treatments, it is generally performed to flow a nitrogen gas around a heater or the like required for heating to prevent oxidation of the heater or the like. This nitrogen gas is trapped between the graphite layers during the graphitization and high-purification treatment, is replaced with carbon atoms, or reacts with metal impurities slightly remaining in the graphite material to form nitrogen compounds. And remain in the graphite material.
また、一般に、高純度化処理及び黒鉛化処理後の冷却時には、冷却速度を高めるとともに、黒鉛材料の酸化を防止するために、窒素雰囲気下での冷却が行われている。この冷却時に炉内に導入される窒素ガスも、黒鉛材料の層間にトラップされたり、炭素原子と置換したり、あるいは、黒鉛材料中に僅かに残った金属不純物と反応し、窒素化合物を形成する。 In general, at the time of cooling after the high-purification treatment and the graphitization treatment, cooling in a nitrogen atmosphere is performed in order to increase the cooling rate and prevent oxidation of the graphite material. Nitrogen gas introduced into the furnace during this cooling is also trapped between the layers of the graphite material, replaced with carbon atoms, or reacts with metal impurities slightly remaining in the graphite material to form nitrogen compounds. .
このように、黒鉛材料中に残存した窒素は、当該黒鉛材料をＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具として使用した場合、ＳｉＣ中に侵入し、ＳｉＣ中の窒素濃度を高めることになる。これらＳｉＣ中の窒素は、結晶内の欠陥の一因になると考えられている。 As described above, when the graphite material is used as a SiC epitaxial growth film manufacturing jig or a SiC single crystal manufacturing jig, the nitrogen remaining in the graphite material enters the SiC and increases the nitrogen concentration in the SiC. It will be. Nitrogen in these SiC is thought to contribute to defects in the crystal.
そこで、本実施形態に係る黒鉛材料は、黒鉛化処理及び高純度化処理時あるいは高純度処理後に、極力窒素（大気）に晒されないようにするか若しくは後処理で窒素を放出させる。これにより、黒鉛材料の黒鉛層間にトラップされる窒素、炭素原子と置換する窒素原子及び黒鉛材料中に僅かに残る金属不純物と反応する窒素を低減させるものである。 Therefore, the graphite material according to the present embodiment is prevented from being exposed to nitrogen (atmosphere) as much as possible during or after the graphitization treatment and the high-purity treatment, or releases nitrogen in the post-treatment. As a result, nitrogen trapped between the graphite layers of the graphite material, nitrogen atoms replacing carbon atoms, and nitrogen reacting with metal impurities slightly remaining in the graphite material are reduced.
すなわち、本実施形態に係る黒鉛材料の製造にあたっては、黒鉛化若しくは高純度化処理の時のヒーター周りに流す窒素ガスに代えて、アルゴンガスやヘリウムガス等の希ガスを用いることもできる。さらには、黒鉛化処理(工程Ｂ)の時に、雰囲気ガスとしてアルゴンガスやヘリウムガス等の希ガスを用いることが好ましい。また、高純度化処理(工程Ｃ)時においては、ハロゲンガスによる処理の後、圧力１００Ｐａ以下、好ましくは１Ｐａ以下、若しくはアルゴンガスやヘリウムガス等の希ガス雰囲気下で、１８００℃以上、好ましくは２０００℃以上で熱処理を行い、黒鉛材料中に何らかの状態で存在する窒素を放出させる。さらに、冷却時においても、できるだけ、窒素ガスを使用せずに、圧力１００Ｐａ以下、好ましくは１Ｐａ以下、若しくはアルゴンガスやヘリウムガス等の希ガス雰囲気下で冷却処理を行う。この一連の工程は、同一炉で連続的に行うことも、また、各工程を夫々別の炉で行うこともできる。また、高純度処理(工程Ｃ)時におけるヒーター周りに流すガスは、ハロゲンガスによる高純度化処理時には、窒素ガスを流し、ハロゲンガスによる高純度化処理終了時にアルゴンガスやヘリウムガス等の希ガスを導入し、熱処理及び冷却処理を行い、窒素ガスを放出させてもよい。 That is, in producing the graphite material according to the present embodiment, a rare gas such as argon gas or helium gas can be used instead of the nitrogen gas flowing around the heater during the graphitization or high-purification treatment. Furthermore, it is preferable to use a rare gas such as argon gas or helium gas as the atmospheric gas during the graphitization treatment (step B). Further, at the time of the high-purification treatment (step C), after the treatment with the halogen gas, the pressure is 100 Pa or less, preferably 1 Pa or less, or 1800 ° C. or more, preferably in a rare gas atmosphere such as argon gas or helium gas. Heat treatment is performed at 2000 ° C. or higher to release nitrogen existing in some state in the graphite material. Further, at the time of cooling, the cooling treatment is performed under a pressure of 100 Pa or less, preferably 1 Pa or less, or a rare gas atmosphere such as argon gas or helium gas without using nitrogen gas as much as possible. This series of steps can be performed continuously in the same furnace, or each step can be performed in a separate furnace. In addition, the gas that flows around the heater during the high-purity treatment (Step C) is a nitrogen gas during the high-purity treatment with the halogen gas, and a rare gas such as argon gas or helium gas at the end of the high-purity treatment with the halogen gas. May be introduced to perform heat treatment and cooling treatment to release nitrogen gas.
また、従来の方法で、黒鉛化処理、高純度化処理を行った黒鉛材料も、後工程として圧力１００Ｐａ以下、好ましくは１Ｐａ以下、あるいはアルゴンガスやヘリウムガス等の希ガス雰囲気下で、１８００℃以上、好ましくは２０００℃以上に再加熱することにより、黒鉛材料中の窒素濃度を低減させることができる。 Further, a graphite material subjected to graphitization treatment and high-purity treatment by a conventional method is also subjected to a pressure of 100 Pa or less, preferably 1 Pa or less, or 1800 ° C. in a rare gas atmosphere such as argon gas or helium gas. As described above, the nitrogen concentration in the graphite material can be reduced by reheating to 2000 ° C. or higher.
このようにして、黒鉛化処理時や高純度化処理時に、窒素ガスに代えてアルゴンガスやヘリウムガス等の希ガスを用いる。あるいは、窒素を使うのであれば、黒鉛材料をできるだけ窒素が黒鉛材料中に残存しないようにする。若しくは、黒鉛化処理、高純度化処理を経て製造された黒鉛材料を、別途圧力１００Ｐａ以下、好ましくは１Ｐａ以下、若しくはアルゴンガスやヘリウムガス等の希ガス雰囲気下で１８００℃以上、好ましくは２０００℃以上で加熱処理を行うことにより、黒鉛材料中の窒素濃度を低減でき、ＧＤＭＳによる窒素濃度が９８ｐｐｍ以下、好ましくは１０ｐｐｍ以下、さらに好ましくは５ｐｐｍ以下（ただし、１．０〜１．２ｐｐｍを除く）の黒鉛材料とすることができる。
ここで、ＧＤＭＳによる窒素濃度の測定は、グロー放電質量分析装置（ＶＧ９０００、ＶＧ Ｅｌｅｍｅｎｔａｌ社製）を用い、到達圧力が１０ −４ Ｐａ以下に保たれた容器内で、黒鉛材料の表面や気孔中に含まれる窒素ガスを十分に排気した後に行った。
In this way, a rare gas such as argon gas or helium gas is used in place of nitrogen gas during the graphitization process or the purification process. Alternatively, if nitrogen is used, the graphite material should be kept as little as possible in the graphite material. Alternatively, a graphite material produced through graphitization treatment or high-purification treatment is separately used at a pressure of 100 Pa or less, preferably 1 Pa or less, or 1800 ° C. or more, preferably 2000 ° C. in a rare gas atmosphere such as argon gas or helium gas. By performing the heat treatment as described above, the nitrogen concentration in the graphite material can be reduced, and the nitrogen concentration by GDMS is 98 ppm or less, preferably 10 ppm or less, more preferably 5 ppm or less (excluding 1.0 to 1.2 ppm). Graphite material.
Here, the measurement of the nitrogen concentration by GDMS is performed using a glow discharge mass spectrometer (VG9000, manufactured by VG Elemental) in a vessel in which the ultimate pressure is maintained at 10 −4 Pa or less, in the surface of the graphite material or in the pores. The nitrogen gas contained in was exhausted sufficiently.
なお、本実施形態に係る黒鉛材料は、このままであっても、或いは、ＳｉＣ被覆黒鉛材の基材としても、ＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いることができる。例えば、本実施形態に係る黒鉛材料を基材とするＳｉＣ被覆黒鉛材をＳｉＣのエピタキシャル成長膜製造用治具として使用した場合であっても、ＳｉＣウェハー中への窒素の侵入を抑制することができる。 Note that the graphite material according to the present embodiment can be used as it is or as a base material for a SiC-coated graphite material in a SiC epitaxial growth film manufacturing jig or a SiC single crystal manufacturing jig. For example, even when the SiC-coated graphite material based on the graphite material according to the present embodiment is used as a jig for producing an epitaxial growth film of SiC, nitrogen can be prevented from entering the SiC wafer. .
次に、実施例により本発明を具体的に説明する。 Next, the present invention will be described specifically by way of examples.
（実施例１）
以下に順を追って本発明を説明する。先ず、炉内に炭素材を設置する。次に、炉内に窒素ガスを導入し、容器内部の空気を窒素ガスで置換したのち、炉内を減圧する。そして、ヒーターに徐々に電圧を印加して炉内を加熱し、その輻射熱により被加熱炭素材を８００〜１０００℃に約５時間保ったのち（焼成工程）、徐々に昇温を続け、２４５０〜２５００℃に調節しながら１５時間保持した（黒鉛化工程）。容器内は加熱を始めた時点から０．１Ｐａ程度に保たれているので、この段階で僅かに揮散してくる脱ガスの排出には好都合である。そして、黒鉛化の際、最初から或いは、黒鉛化が若干進んだ段階で、減圧状態（約０．１Ｐａ程度）のままハロゲン又はその化合物のガス、例えばジクロルジフルオルメタンを（流量は容器内に充填する被加熱炭素材の量により増減されるが、例えば１〜７ｌNTP/ｋg程度で）８時間程度供給する。なお、前記工程中は、ヒーターを保護することを目的としてヒーター周りに常時アルゴンガスを流しておく。上記方法によって黒鉛化、高純度化工程を完了する。そして、引き続き、連続的に黒鉛化した材料を、２２００℃で保持するとともに、容器内圧力を０．１Ｐａに強減圧したまま５時間熱処理を行う（脱窒素ガス工程）。このとき、ヒーター周りのガスもアルゴンガスを使用し、窒素ガスが黒鉛材料へ侵入するのを防止する。これにより、低窒素濃度黒鉛材料を得ることができる。そして、所定時間熱処理を行うと、容器内圧力を０．１Ｐａに保持したまま、黒鉛材料を２００℃まで冷却する。２００℃に到達した時点で、容器内に希ガスとしてアルゴンガスを導入し、黒鉛材料を室温まで冷却する。室温まで冷却した後、黒鉛材料を、大気に晒されないように、樹脂フィルムからなる袋内にアルゴンガスと共に封入して保管した。
Example 1
The present invention will be described below step by step. First, a carbon material is installed in the furnace. Next, nitrogen gas is introduced into the furnace, the air inside the container is replaced with nitrogen gas, and then the pressure in the furnace is reduced. And after applying a voltage gradually to a heater and heating the inside of a furnace and keeping the to-be-heated carbon material at 800-1000 degreeC for about 5 hours by the radiant heat (baking process), temperature rising is continued gradually, 2450- The temperature was maintained at 2500 ° C. for 15 hours (graphitization step). Since the inside of the container is maintained at about 0.1 Pa from the start of heating, it is convenient for discharging degass that slightly volatilizes at this stage. During graphitization, or at the stage where graphitization has progressed slightly, a halogen or its compound gas, such as dichlorodifluoromethane (flow rate is in the vessel) in a reduced pressure state (about 0.1 Pa). It is increased or decreased depending on the amount of the carbon material to be heated, but is supplied for about 8 hours (for example, about 1 to 7 lNTP / kg). During the process, argon gas is always flowed around the heater for the purpose of protecting the heater. The graphitization and purification steps are completed by the above method. Subsequently, the continuously graphitized material is maintained at 2200 ° C., and heat treatment is performed for 5 hours while the internal pressure of the container is strongly reduced to 0.1 Pa (denitrification gas process). At this time, argon gas is also used as the gas around the heater to prevent nitrogen gas from entering the graphite material. Thereby, a low nitrogen concentration graphite material can be obtained. When heat treatment is performed for a predetermined time, the graphite material is cooled to 200 ° C. while maintaining the internal pressure of the container at 0.1 Pa. When the temperature reaches 200 ° C., argon gas is introduced as a rare gas into the container, and the graphite material is cooled to room temperature. After cooling to room temperature, the graphite material was sealed and stored with argon gas in a bag made of a resin film so as not to be exposed to the atmosphere.
（実施例２）
実施例１と同様の方法により、黒鉛化、高純度化工程を経た黒鉛材料を、一旦、処理炉から取り出した。このとき、黒鉛材料を、できるだけ、大気に晒されないように樹脂フィルムからなる袋内にアルゴンガスと共に封入して保管した。そして、この黒鉛材料を樹脂フィルムからなる袋から取り出し、再度、炉内に設置し、２２００℃に再加熱するとともに、容器内圧力を０．１Ｐａに強減圧し、５時間熱処理を行う（脱窒素ガス工程）。そして、所定時間熱処理を行うと、容器内圧力を０．１Ｐａに保持したまま、黒鉛材料を２００℃まで冷却する。２００℃に到達した時点で、容器内に希ガスとしてアルゴンガスを導入し、黒鉛材料を室温まで冷却する。室温まで冷却した後、黒鉛材料を、大気に晒されないように、樹脂フィルムからなる袋内にアルゴンガスと共に封入して保管した。
(Example 2)
By the same method as in Example 1, the graphite material that had undergone the graphitization and purification steps was once taken out of the processing furnace. At this time, the graphite material was stored with argon gas in a bag made of a resin film so as not to be exposed to the atmosphere as much as possible. Then, the graphite material is taken out from the bag made of a resin film, placed in the furnace again, reheated to 2200 ° C., and the pressure in the container is strongly reduced to 0.1 Pa, followed by heat treatment for 5 hours (denitrogenation). Gas process). When heat treatment is performed for a predetermined time, the graphite material is cooled to 200 ° C. while maintaining the internal pressure of the container at 0.1 Pa. When the temperature reaches 200 ° C., argon gas is introduced as a rare gas into the container, and the graphite material is cooled to room temperature. After cooling to room temperature, the graphite material was sealed and stored with argon gas in a bag made of a resin film so as not to be exposed to the atmosphere.
（実施例３）
実施例１と同様の方法により、黒鉛化、高純度化工程を経た黒鉛材料を、２２００℃に再加熱するとともに、容器内圧力を０．１Ｐａに強減圧し、５時間熱処理を行う（脱窒素ガス工程）。そして、所定時間熱処理を行うと、容器内に希ガスとしてアルゴンガスを導入し、黒鉛材料を室温まで冷却する。室温まで冷却した後、黒鉛材料を、大気に晒されないように、樹脂フィルムからなる袋内にアルゴンガスと共に封入して保管した。
Example 3
By the same method as in Example 1, the graphite material that has undergone the graphitization and purification step is reheated to 2200 ° C., and the internal pressure of the container is strongly reduced to 0.1 Pa, followed by heat treatment for 5 hours (denitrogenation). Gas process). Then, when heat treatment is performed for a predetermined time, argon gas is introduced into the container as a rare gas, and the graphite material is cooled to room temperature. After cooling to room temperature, the graphite material was sealed and stored with argon gas in a bag made of a resin film so as not to be exposed to the atmosphere.
（実施例４）
脱窒素ガス工程として、容器内圧力を０．１Ｐａに強減圧することなく、常圧、２０００℃でアルゴンガス雰囲気としたことを除き、実施例１と同様な操作を行うことで得られた材料を、実施例４の試料とした。
Example 4
Materials obtained by performing the same operation as in Example 1 except that the pressure inside the container was reduced to 0.1 Pa and the argon gas atmosphere was used at 2000 ° C. without depressurizing the inner pressure of the vessel as a denitrification gas step. Was used as a sample of Example 4.
（比較例１）
実施例１と同様の方法によって、黒鉛化、高純度化処理を完了した黒鉛材料を脱窒素ガス工程を行うことなく、窒素ガスで冷却し、大気中で保管しておいた材料を比較例１の試料とした。
(Comparative Example 1)
A graphite material that has been graphitized and highly purified by the same method as in Example 1 was cooled with nitrogen gas without performing a denitrification gas step, and a material stored in the atmosphere was compared with Comparative Example 1. It was set as the sample of this.
（比較例２）
脱窒素ガス工程として、容器内圧力を０．１Ｐａに強減圧することなく、常圧、１８００℃でアルゴンガス雰囲気としたことを除き、実施例１と同様な操作を行うことで得られた材料を、比較例２の試料とした。
(Comparative Example 2)
Materials obtained by performing the same operation as in Example 1 except that the denitrification gas step was performed under normal pressure and 1800 ° C. in an argon gas atmosphere without strongly reducing the internal pressure to 0.1 Pa. Was used as a sample of Comparative Example 2.
以下（１）乃至（３）の状態の試料について、夫々ＧＤＭＳにより、含有する窒素濃度を測定した。
（１）実施例１乃至４及び比較例１，２の黒鉛材料中の窒素濃度、
（２）実施例１乃至４及び比較例１，２の黒鉛材料を基材として用い、これら黒鉛材料の表面にＣＶＤ−ＳｉＣを形成したときのＣＶＤ−ＳｉＣ中の窒素濃度、
（３）上記(２)に係るＣＶＤ−ＳｉＣ被覆黒鉛材をサセプターとして用い、ＳｉＣウェハー上にエピタキシャル成長膜を形成する際の治具として用いた場合のエピタキシャル成長膜中の窒素濃度。
In the following samples (1) to (3), the nitrogen concentration contained was measured by GDMS.
(1) Nitrogen concentration in the graphite materials of Examples 1 to 4 and Comparative Examples 1 and 2,
(2) Using the graphite materials of Examples 1 to 4 and Comparative Examples 1 and 2 as a base material, the nitrogen concentration in CVD-SiC when CVD-SiC was formed on the surface of these graphite materials,
(3) Nitrogen concentration in the epitaxially grown film when the CVD-SiC coated graphite material according to (2) is used as a susceptor and used as a jig when an epitaxially grown film is formed on a SiC wafer.
各試料の窒素濃度について表１にまとめて示す。 Table 1 summarizes the nitrogen concentration of each sample.
表１より、脱窒素ガス工程を経た黒鉛材料は、各段階での含有窒素濃度が低いことがわかる。また、これに伴って、実施例１乃至４に係る低窒素濃度黒鉛材料をＳｉＣエピタキシャル成長膜製造用治具として用いることによって、製造される製品（ＳｉＣ半導体デバイス等）の結晶欠陥の発生を抑制できる。 From Table 1, it can be seen that the graphite material that has undergone the denitrification gas process has a low nitrogen concentration at each stage. Accordingly, by using the low nitrogen concentration graphite material according to Examples 1 to 4 as a jig for manufacturing an SiC epitaxial growth film, generation of crystal defects in a manufactured product (SiC semiconductor device or the like) can be suppressed. .
以上に述べたように、黒鉛化処理若しくは高純度化処理時に希ガスを用いること、又は、高純度処理後に脱窒素ガス工程を経ることによって、低窒素濃度黒鉛材料が得られる。そしてこれらの低窒素濃度黒鉛材料を、樹脂を用いていわゆる真空パック等し、大気と遮断した状態で保管する。そして現場で樹脂を除去してクリーンな状態とした低窒素濃度黒鉛材料を、ＳｉＣエピタキシャル成長膜製造用治具又はＳｉＣ単結晶製造用治具に用いることにより、ＳｉＣへの窒素の侵入を抑制でき、製造される製品（ＳｉＣ半導体デバイス等）の結晶欠陥を抑制できる効果を奏する。 As described above, a low nitrogen concentration graphite material can be obtained by using a rare gas during the graphitization treatment or the high-purification treatment, or by performing a denitrification gas step after the high-purity treatment. These low-nitrogen concentration graphite materials are stored in a state where they are cut off from the atmosphere by using a resin, such as a so-called vacuum pack. And, by using a low nitrogen concentration graphite material that is made clean by removing the resin on site, it is possible to suppress the penetration of nitrogen into SiC by using it as a jig for SiC epitaxial growth film production or a jig for SiC single crystal production, This has the effect of suppressing crystal defects in manufactured products (such as SiC semiconductor devices).
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| JPH11157989A (en) * | 1997-11-25 | 1999-06-15 | Toyo Tanso Kk | Susceptor for gas phase growth and its production |
| JPH11310459A (en) * | 1998-04-28 | 1999-11-09 | Tokai Carbon Co Ltd | Glass-like carbon material excellent in plasma resistance |
| JP4238450B2 (en) * | 2000-02-18 | 2009-03-18 | 株式会社デンソー | Method and apparatus for producing silicon carbide single crystal |
| JP3845563B2 (en) * | 2001-09-10 | 2006-11-15 | 株式会社東芝 | Silicon carbide film CVD method, CVD apparatus, and susceptor for CVD apparatus |
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2010
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