JP2004002085A

JP2004002085A - Method for purifying carbon/graphite member

Info

Publication number: JP2004002085A
Application number: JP2002157391A
Authority: JP
Inventors: Sanji Ochiai; 落合　三二
Original assignee: Osaka Titanium Technologies Co Ltd
Current assignee: Osaka Titanium Technologies Co Ltd
Priority date: 2002-05-30
Filing date: 2002-05-30
Publication date: 2004-01-08

Abstract

<P>PROBLEM TO BE SOLVED: To improve the purity of a carbon/graphite member for use in a process for producing a semiconductor-class polycrystalline silicon and to improve the quality of the same by suppressing the contamination of the polycrystalline silicon to be produced. <P>SOLUTION: The carbon/graphite member is subjected to high-temperature halogen treatment in a treatment furnace. After the high-temperature halogen treatment, when the temperature of the carbon/graphite member is reduced to 50°C or less, the member is taken out of the treatment furnace and packaged immediately. The carbon/graphite member is forced to be cooled in an inert gas atmosphere. A polyethylene bag using no release agent is used as a material for packaging the carbon/graphite member taken out of the treatment furnace. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、半導体級多結晶シリコンの製造プロセスに使用される高純度の炭素・黒鉛部材の製造等に好適に用いられる炭素・黒鉛部材の精製方法に関し、より具体的には、高温ハロゲン処理による炭素・黒鉛部材の精製方法に関する。
【０００２】
【従来の技術】
半導体級多結晶シリコンの製造プロセスでは、シリコン芯棒の支持・通電に使用される黒鉛電極、予熱用の黒鉛ヒータを始めとして、多くの炭素・黒鉛部材が使用されている。これらの炭素・黒鉛部材には、不純物による製品汚染を防止するために高い純度が要求される。このため、これらの炭素・黒鉛部材は、通常は加工後、部材メーカーの側で高温ハロゲン処理による精製処理を施されてユーザーに出荷される。また、加工後の部材に対する精製処理に代えて、或いはこの精製処理と共に、加工前の素材段階の炭素・黒鉛部材に対して高温ハロゲン処理による精製処理が行われることもある。
【０００３】
ここにおける高温ハロゲン処理は、炭素・黒鉛部材を処理炉内で高温（２４００〜３０００℃）で且つハロゲンガス又はハロゲンを含むガス雰囲気中で所定時間処理するものであり、処理過程で炭素・黒鉛部材に含まれる金属及びその酸化物が除去される。そして、炭素・黒鉛部材のハンドリングが可能になる２００〜１００℃程度に部材温度が低下した段階で処理炉を開放し、炭素・黒鉛部材を取り出している。処理炉から取り出された炭素・黒鉛部材は、表面の再汚染を防止するために、ナイロンフィルムなどにより包装されて取り扱われ、また保管される。
【０００４】
ナイロンフィルムによる包装に代え、ガス不透過製フィルムにより真空包装するとか不活性ガスを封じ込んで包装するといった新しい汚染防止技術も特許第２７２５０４２号公報に記載されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、従来の高温ハロゲン処理では、精製度が不十分である。このため、特許第２６４９１６６号公報に記載されるような低温ハロゲン処理が、部材ユーザー（多結晶シリコンメーカー）の側で実施されている。低温ハロゲン処理では、炭素・黒鉛部材が８００〜１１００℃の比較的低い温度に加熱された状態でハロゲンガス又はハロゲンを含むガス雰囲気中で処理される。
【０００６】
部材メーカー側で実施される高温ハロゲン処理と、部材ユーザー側で実施される低温ハロゲン処理との組み合わせにより、旧来から多結晶シリコンに要求されている純度レベル（０．１ｐｐｂａオーダー，１０００Ωｃｍ）は満足されていたが、近年益々高まる多結晶シリコンの高い純度要求に対応することは困難になってきた。即ち、最近の半導体級多結晶シリコンに要求される純度は、高い場合、リン濃度で０．０３ｐｐｂａ以下、ボロン濃度で０．０２ｐｐｂａ以下であるが、炭素・黒鉛部材の包装技術等に如何に工夫を講じても、このような高い要求を満足させるレベルに炭素・黒鉛部材の汚染度を低下させることは困難になってきた。
【０００７】
本発明の目的は、簡単な手法で炭素・黒鉛部材の純度を従来よりも大幅に高めることができる炭素・黒鉛部材の精製方法を提供することにある。
【０００８】
【課題を解決するための手段】
ところで、多結晶シリコン製品の汚染経路は複雑であり、原料ガス品質、炉体からの汚染、炉体に使用されているパッキンなどが考えられている。いずれの経路にしても、汚染源の汚染度は、現在の如何なる分析手段を用いても測定下限未満の不純物レベルであるため、定量的に汚染源を特定することは不可能である。製品を分析して始めて汚染の事実を知ることができるに過ぎないのである。そして黒鉛電極、黒鉛ヒータなどの炭素・黒鉛部材については、部材メーカー側で実施される高温ハロゲン処理と、部材ユーザー側で実施される低温ハロゲン処理との組み合わせにより、問題ないと考えられていた。
【０００９】
このような状況下で、本発明者らは、部材メーカー側で実施される高温ハロゲン処理条件、とりわけ、その処理後に処理炉から炭素・黒鉛部材を取り出すときの部材温度に着目した。この取り出し温度は、処理温度が２４００〜３０００℃と高いことに伴い、処理能率優先の観点から相当に高く設定され、部材のハンドリングが可能になる２００〜１００℃程度とされていた。ところが、このような高温で部材を処理炉から取り出すと、部材を包装するまでの間に部材の表面が再汚染されてしまい、この取り出し温度の高さに起因する再汚染が、部材の高純度化を阻害し、ひいては製品を汚染する大きな原因であると推定し、部材取り出し温度を５０℃以下に下げた。その結果、部品ユーザー側で実施される低温ハロゲン処理を省略しても、低温ハロゲン処理を組み合わせた場合よりも更に高い製品純度が得られることがことを知見した。
【００１０】
本発明の炭素・黒鉛部材の精製方法は、かかる知見に基づいて開発されたものであり、炭素・黒鉛部材に処理炉内で２４００〜３０００℃の高温ハロゲン処理を実施した後、その炭素・黒鉛部材を温度が５０℃以下に低下した後に前記処理炉から取り出すものである。
【００１１】
炭素・黒鉛部材を高温ハロゲン処理した後、処理炉から取り出すときの温度を５０℃以下に下げることにより、部材表面の活性度が下がり、且つ取り出し直後に炭素・黒鉛部材を包装することが可能になる。これらにより、部材表面の再汚染が抑制され、低温ハロゲン処理なしにもかかわらず、多結晶シリコン製品の純度として、リン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下が可能になる。
【００１２】
処理炉から取り出すときの部材温度を下げることにより部材表面の再汚染が抑制される理由としては、炭素・黒鉛部材を取り出し後、直ちに包装することが可能で、大気雰囲気に暴露する時間を短くできることなどが考えられる。大気雰囲気で冷却が進むと、大気中の汚染物質が吸着し再汚染されるのである。この温度が５０℃を超えると、包装に工夫を講じてもその包装までの間に部材表面の再汚染が進み、その部材を半導体級多結晶シリコンの製造に使用したときの多結晶シリコン製品の純度としてリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を実現できない。処理炉から取り出された炭素・黒鉛部材をクリーンルームで保管し冷却する方法も考えられるが、設備が大掛かりになり、コスト面で現実的でない。低温ハロゲン処理を省略することによる処理コスト面でのコストメリットが大きいことも当然である。
【００１３】
処理炉から取り出すときの部材温度の下限については、再汚染を防止する点からは室温まで冷却することが望ましいが、作業能率上は冷却時間が長くなり、処理炉の占有時間が長くなって生産性が低下するので、４０℃程度が最も好ましい。取り出しから包装までの時間としては４時間以下が好ましい。高温ハロゲン処理における処理温度を２４００〜３０００℃としたのは、高純度を要求される半導体プロセスの炭素・黒鉛部材は高温下（２４００〜３０００℃）で処理する必要があるからであり，特許第２７２５０４２号公報に説明されているとおりである。
【００１４】
処理炉から取り出すときの部材温度を下げると処理能率が低下する。高温ハロゲン処理の後、炭素・黒鉛部材を処理炉内で不活性ガスの流通により冷却することにより、この能率低下が回避される。不活性ガスとしては窒素ガスが安価で一般的であるが、アルゴンガスなどでもよい。
【００１５】
また、本発明者は処理炉内から取り出した炭素・黒鉛部材を包装する材料についても調査した。その結果、剥離材を使用しないポリエチレンフィルムが包装材として好ましいとの結論に達した。その理由は、剥離材を使用した包装材料は、剥離材に含まれる汚染物質が炭素・黒鉛部材に付着することにより、半導体級多結晶シリコンの品質に影響がでる点にある。
【００１６】
【発明の実施の形態】
以下に本発明の実施形態を図面に基づいて説明する。図１は本発明の一実施形態に使用される処理炉の構造説明図である。
【００１７】
処理炉は、高純度黒鉛からなる炉体１と、炉体１内にセットされた被処理物３を周囲から加熱する電気ヒータ２とを備えている。炉体１は一端側から他端側へ処理ガスを流通させる構成になっている。電気ヒータ２は、炉体１内に処理ガスの流通方向に沿って配置されている。
【００１８】
操業では、まず、半導体級多結晶シリコンの製造に使用される黒鉛電極、黒鉛ヒータなどの炭素・黒鉛部材を処理炉内にセットする。次いで、高温ハロゲン処理として、処理炉内を不活性ガスにて置換した後、被処理物を２４００〜３０００℃に加熱し、この状態で処理炉内にハロゲンガス又はハロゲンを含むをガスを流通させる。数十時間この状態を保つことにより、被処理物中の不純物が除去される。
【００１９】
高温ハロゲン処理工程が終わると、処理炉内に不活性ガスを流通させて炉内の被処理物を強制的に冷却する。被処理物が５０℃以下に冷却された段階で処理炉を開放し、処理炉から被処理物を取り出し、その後、直ちに包装する。高温ハロゲン処理工程自体は従来と同じである。高温ハロゲン処理工程終了後の被処理物取り出し温度が相違する。これにより、被処理物の純度が上がる。処理炉内の被処理物の温度は放射温度計により監視される。低温ハロゲン処理による精製工程は不必要になる。
【００２０】
実施例１として、半導体級多結晶シリコンの製造に使用される黒鉛部材を上記方法で実際に精製した。具体的には、黒鉛部材を２５００℃の温度下で塩化水素（ＨＣｌ）ガスにより２０時間処理し、不純物を除去した後、その黒鉛部材を窒素ガス雰囲気中で４０℃まで冷却し、処理炉から取り出した。処理炉から取り出した黒鉛部材を包装せずに直ちに半導体級多結晶シリコン製造装置に組み込み、多結晶シリコンを製造した。製造された多結晶シリコンの純度はリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足するリン濃度０．０２５ｐｐｂａ、ボロン濃度０．０１０ｐｐｂａであった。
【００２１】
従来例１として、実施例１と同じ条件で高温ハロゲン処理を行い、不純物を除去した後、その黒鉛部材を２００℃で処理炉から取り出し、大気中で常温まで冷却した。この黒鉛部材を使用して半導体級多結晶シリコンを製造したところ、製造された多結晶シリコンの純度はリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足しないリン濃度０．０９５ｐｐｂａ、ボロン濃度０．０３５ｐｐｂａであった。
【００２２】
従来例２として、実施例１と同じ条件で高温ハロゲン処理を行い、不純物を除去した後、その黒鉛部材を１００℃で処理炉から取り出し、大気中で常温まで冷却した。この黒鉛部材を使用して半導体級多結晶シリコンを製造した。製造された多結晶シリコンの純度はリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足しないリン濃度０．０６０ｐｐｂａ、ボロン濃度０．０３３ｐｐｂａであった。
【００２３】
従来例３として、実施例１と同じ条件で高温ハロゲン処理を行い、不純物を除去した後、その黒鉛部材を２００℃で処理炉から取り出し、大気中で常温まで冷却した。更に９００℃で１０時間、塩化水素（ＨＣｌ）ガスにより低温ハロゲン処理した。低温ハロゲン処理での部材取り出し温度は常温とした。この黒鉛部材を使用して半導体級多結晶シリコンを製造したところ、低温ハロゲン処理を併用し、且つ常温取り出しを行ったにもかかわらず、製造された多結晶シリコンの純度は、リン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足しないリン濃度０．０５５ｐｐｂａ、ボロン濃度０．０３２ｐｐｂａであった。
【００２４】
従来例４として、実施例１と同じ条件で高温ハロゲン処理を行い、不純物を除去した後、その黒鉛部材を１００℃で処理炉から取り出し、大気中で常温まで冷却した。更に９００℃で１０時間、塩化水素（ＨＣｌ）ガスにより低温ハロゲン処理した。低温ハロゲン処理での部材取り出し温度は常温とした。この黒鉛部材を使用して半導体級多結晶シリコンを製造した。低温ハロゲン処理を併用し、且つ常温取り出しを行ったにもかかわらず、製造された多結晶シリコンの純度は、リン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足しないリン濃度０．０４５ｐｐｂａ、ボロン濃度０．０２８ｐｐｂａであった。
【００２５】
実施例２として、実施例１と同じ条件で高温ハロゲン処理を行い、窒素ガスで４０℃まで冷却した後、処理炉から黒鉛部材を取り出した。取り出した黒鉛部材を、剥離材を使用しないポリエチレンフィルム（東和化工株式会社製　クリーンＬＤＰＥフィルム）の袋で直ちに包装し保管した。そして１０日目、５０日目、１２０日目に包装を取り除いて半導体級多結晶シリコン製造装置に組み込み、多結晶シリコンの製造に使用した。製造された多結晶シリコンの純度を、処理炉から取り出した直後の未包装の黒鉛部材を使用した場合の結果と合わせて表１に示す。
【００２６】
処理炉から取り出した黒鉛部材の包装材に、剥離材を使用しないポリエチレンフィルムを使用すると、長期間経過しても汚染が進まず、処理炉から取り出した直後の黒鉛部材を使用する場合と同等の製品純度が得られる。
【００２７】
実施例３として、包装材を、剥離材を使用しないポリエチレンフィルムから、通常に使用されているナイロンフィルムに変更した。結果を表１に併記する。
【００２８】
【表１】

【００２９】
処理炉から取り出した直後の未包装の黒鉛部材を使用した場合は、製造された多結晶シリコンの純度はリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足する。しかし、処理炉から取り出した黒鉛部材を時間をおいて使用した場合、包装されているにもかかわらず汚染が進みり、製造された多結晶シリコンの純度はリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下を満足できなくなる。
【００３０】
上記実施例では、黒鉛電極、黒鉛ヒータなどの黒鉛部材を精製したが、多結晶シリコンの製造には原料ガス供給ノズル等の炭素部材も使用されるので、これらの炭素部材の精製にも本発明を適用することが可能である。
【００３１】
また、これらの炭素・黒鉛部材は、多結晶シリコンの製造に使用される完成された部材（完成品）であるが、その完成品を加工製造する際の素材となる炭素・黒鉛部材に対しても本発明を適用することが可能である。
【００３２】
【発明の効果】
以上に説明したとおり、本発明の炭素・黒鉛部材の精製方法は、炭素・黒鉛部材を処理炉内で高温ハロゲン処理した後、その炭素・黒鉛部材を温度が５０℃以下に低下した後に前記処理炉から取り出すという簡単な手法により、炭素・黒鉛部材の純度を従来よりも大幅に高めることができ、これにより、これまでは実操業レベルでは容易には実現できなったリン濃度０．０３ｐｐｂａ以下、ボロン濃度０．０２ｐｐｂａ以下という高純度の多結晶シリコンの経済的な製造を可能にする。また、低温ハロゲン処理を不要にし、処理コストの低減を可能にする。
【図面の簡単な説明】
【図１】本発明の一実施形態に使用される処理炉の構造説明図である。
【符号の説明】
１　炉体
２　電気ヒータ
３　被処理物[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of purifying a carbon / graphite member suitably used for the production of a high-purity carbon / graphite member used in a production process of a semiconductor grade polycrystalline silicon, and more specifically, by a high-temperature halogen treatment. The present invention relates to a method for refining carbon / graphite members.
[0002]
[Prior art]
In the manufacturing process of semiconductor-grade polycrystalline silicon, many carbon and graphite members are used, including a graphite electrode used for supporting and energizing a silicon core rod and a graphite heater for preheating. These carbon and graphite members are required to have high purity in order to prevent product contamination by impurities. For this reason, these carbon / graphite members are usually processed, refined by high-temperature halogen treatment on the member manufacturer's side, and shipped to users. In addition, instead of, or in addition to, the refining process on the member after processing, a refining process by a high-temperature halogen treatment may be performed on the carbon / graphite member in the material stage before processing.
[0003]
Here, the high-temperature halogen treatment is a treatment in which a carbon / graphite member is treated in a treatment furnace at a high temperature (2400 to 3000 ° C.) for a predetermined time in a halogen gas or a gas atmosphere containing halogen. Is removed. Then, when the temperature of the member is lowered to about 200 to 100 ° C. at which the carbon / graphite member can be handled, the processing furnace is opened to take out the carbon / graphite member. The carbon / graphite member taken out of the processing furnace is handled and stored after being wrapped with a nylon film or the like in order to prevent recontamination of the surface.
[0004]
Japanese Patent No. 2725042 discloses a new pollution control technique, such as vacuum packaging with a gas-impermeable film or sealing with an inert gas, instead of packaging with a nylon film.
[0005]
[Problems to be solved by the invention]
However, the conventional high-temperature halogen treatment has an insufficient degree of purification. For this reason, a low-temperature halogen treatment as described in Japanese Patent No. 2649166 is performed on the part user (polycrystalline silicon maker) side. In the low-temperature halogen treatment, the carbon / graphite member is treated in a halogen gas or a gas atmosphere containing halogen while being heated to a relatively low temperature of 800 to 1100 ° C.
[0006]
By combining the high-temperature halogen treatment performed by the component manufacturer and the low-temperature halogen treatment performed by the component user, the purity level (0.1 ppba order, 1000 Ωcm) conventionally required for polycrystalline silicon is satisfied. However, it has become difficult to meet the demand for higher purity of polycrystalline silicon, which has been increasing in recent years. That is, in recent years, the purity required for semiconductor grade polycrystalline silicon is 0.03 ppba or less in terms of phosphorus concentration and 0.02 ppba or less in terms of boron concentration in the case of high purity. However, it has become difficult to reduce the degree of contamination of the carbon / graphite member to a level that satisfies such high requirements.
[0007]
An object of the present invention is to provide a method for purifying a carbon / graphite member that can greatly increase the purity of a carbon / graphite member by a simple method as compared with the conventional method.
[0008]
[Means for Solving the Problems]
Incidentally, the contamination route of the polycrystalline silicon product is complicated, and the quality of the raw material gas, contamination from the furnace body, packing used in the furnace body, and the like are considered. In any route, the contamination level of the contamination source is an impurity level below the lower limit of measurement using any current analysis means, so that it is impossible to quantitatively identify the contamination source. Only by analyzing the product can the fact of contamination be known. For carbon / graphite members such as graphite electrodes and graphite heaters, it was considered that there was no problem due to the combination of the high-temperature halogen treatment performed by the member manufacturer and the low-temperature halogen treatment performed by the member user.
[0009]
Under such circumstances, the present inventors have paid attention to the high-temperature halogen treatment conditions performed on the member manufacturer side, in particular, the member temperature when the carbon / graphite member is taken out of the processing furnace after the treatment. This take-out temperature is set to be considerably high from the viewpoint of processing efficiency priority as the processing temperature is as high as 2400 to 3000 ° C., and is set to about 200 to 100 ° C. at which handling of the member becomes possible. However, if the member is taken out of the processing furnace at such a high temperature, the surface of the member is re-contaminated until the member is packed, and the re-contamination caused by the high temperature at which the member is taken out causes a high purity of the member. It was presumed that this was a major cause of inhibiting product formation and eventually contaminating the product. As a result, it has been found that even when the low-temperature halogen treatment performed on the part user side is omitted, a higher product purity can be obtained than when the low-temperature halogen treatment is combined.
[0010]
The method for purifying a carbon / graphite member of the present invention has been developed based on such knowledge. After a carbon / graphite member is subjected to a high-temperature halogen treatment of 2400 to 3000 ° C. in a processing furnace, the carbon / graphite is purified. The member is taken out of the processing furnace after the temperature has dropped to 50 ° C. or less.
[0011]
After the carbon / graphite member is treated with high-temperature halogen, the temperature at the time of removal from the processing furnace is reduced to 50 ° C or less, so that the activity of the member surface is reduced and the carbon / graphite member can be packaged immediately after removal. Become. As a result, recontamination of the member surface is suppressed, and the polycrystalline silicon product can have a phosphorus concentration of 0.03 ppba or less and a boron concentration of 0.02 ppba or less, even without the low-temperature halogen treatment.
[0012]
The reason why the re-contamination of the member surface is suppressed by lowering the temperature of the member when removing it from the processing furnace is that the carbon / graphite member can be immediately packaged after being removed, and the time for exposure to the atmosphere can be shortened. And so on. As the cooling proceeds in the atmosphere, the pollutants in the atmosphere are adsorbed and recontaminated. If this temperature exceeds 50 ° C., even if the packaging is devised, recontamination of the surface of the member proceeds before the packaging, and the polycrystalline silicon product when the member is used for the production of semiconductor-grade polycrystalline silicon. As a purity, a phosphorus concentration of 0.03 ppba or less and a boron concentration of 0.02 ppba or less cannot be realized. A method of storing and cooling the carbon / graphite member taken out of the processing furnace in a clean room is also conceivable, but the equipment becomes large-sized and is not realistic in cost. It is natural that the cost merit in terms of processing cost by omitting the low-temperature halogen treatment is great.
[0013]
Regarding the lower limit of the temperature of the members when they are taken out of the processing furnace, it is desirable to cool them down to room temperature in order to prevent re-contamination. A temperature of about 40 ° C. is most preferable because the properties are reduced. The time from removal to packaging is preferably 4 hours or less. The reason why the treatment temperature in the high-temperature halogen treatment is set to 2400 to 3000 ° C. is that the carbon / graphite member of the semiconductor process requiring high purity needs to be treated at a high temperature (2400 to 3000 ° C.). As described in Japanese Patent No. 2725042.
[0014]
If the temperature of the member when taken out of the processing furnace is lowered, the processing efficiency is lowered. After the high-temperature halogen treatment, the efficiency is avoided by cooling the carbon / graphite member in the treatment furnace by flowing an inert gas. As the inert gas, nitrogen gas is generally used at a low cost, but argon gas or the like may be used.
[0015]
The inventor also investigated materials for packaging the carbon / graphite member taken out of the processing furnace. As a result, they came to the conclusion that a polyethylene film not using a release material is preferable as a packaging material. The reason is that the packaging material using the release material has an effect on the quality of semiconductor-grade polycrystalline silicon due to the contaminants contained in the release material adhering to the carbon / graphite member.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a structural explanatory view of a processing furnace used in one embodiment of the present invention.
[0017]
The processing furnace includes a furnace body 1 made of high-purity graphite, and an electric heater 2 for heating an object 3 set in the furnace body 1 from the surroundings. The furnace body 1 is configured to flow a processing gas from one end to the other end. The electric heater 2 is arranged in the furnace body 1 along the flow direction of the processing gas.
[0018]
In operation, first, a carbon / graphite member such as a graphite electrode and a graphite heater used for manufacturing semiconductor-grade polycrystalline silicon is set in a processing furnace. Next, as a high-temperature halogen treatment, after the inside of the processing furnace is replaced with an inert gas, the object to be processed is heated to 2400 to 3000 ° C., and a halogen gas or a gas containing halogen is passed through the processing furnace in this state. . By maintaining this state for several tens of hours, impurities in the object to be processed are removed.
[0019]
After the high-temperature halogen treatment step, an inert gas is circulated in the treatment furnace to forcibly cool the object in the furnace. When the object is cooled to 50 ° C. or lower, the processing furnace is opened, the object is taken out of the processing furnace, and then immediately packed. The high-temperature halogen treatment process itself is the same as the conventional one. The temperature at which the workpiece is taken out after the high-temperature halogen treatment step is different. Thereby, the purity of the object to be processed is increased. The temperature of the object in the processing furnace is monitored by a radiation thermometer. A purification step by low-temperature halogen treatment becomes unnecessary.
[0020]
Example 1 As Example 1, a graphite member used for producing semiconductor-grade polycrystalline silicon was actually purified by the above method. Specifically, the graphite member is treated with hydrogen chloride (HCl) gas at a temperature of 2500 ° C. for 20 hours to remove impurities, and then the graphite member is cooled to 40 ° C. in a nitrogen gas atmosphere, and is then discharged from a processing furnace. I took it out. The graphite member removed from the processing furnace was immediately incorporated into a semiconductor-grade polycrystalline silicon manufacturing apparatus without packaging, and polycrystalline silicon was manufactured. The purity of the produced polycrystalline silicon was 0.025 ppba for phosphorus concentration and 0.010 ppba for boron concentration which satisfied the phosphorus concentration of 0.03 ppba or less and the boron concentration of 0.02 ppba or less.
[0021]
As Conventional Example 1, a high-temperature halogen treatment was performed under the same conditions as in Example 1, and after removing impurities, the graphite member was taken out of the processing furnace at 200 ° C. and cooled to room temperature in the atmosphere. When a semiconductor-grade polycrystalline silicon was manufactured using this graphite member, the purity of the manufactured polycrystalline silicon was 0.03 ppba or less, and the phosphorus concentration was 0.095 ppba and the boron concentration which did not satisfy the boron concentration of 0.02 ppba or less. 0.035 ppba.
[0022]
As Conventional Example 2, a high-temperature halogen treatment was performed under the same conditions as in Example 1 to remove impurities, and then the graphite member was taken out of the processing furnace at 100 ° C. and cooled to room temperature in the atmosphere. Semiconductor graphite polycrystalline silicon was manufactured using this graphite member. The purity of the produced polycrystalline silicon was 0.03 ppba or less, and the phosphorus concentration was 0.060 ppba or 0.033 ppba, which does not satisfy the boron concentration of 0.02 ppba or less.
[0023]
As Conventional Example 3, a high-temperature halogen treatment was performed under the same conditions as in Example 1 to remove impurities, and then the graphite member was taken out of the processing furnace at 200 ° C. and cooled to room temperature in the atmosphere. Further, a low-temperature halogen treatment was performed with hydrogen chloride (HCl) gas at 900 ° C. for 10 hours. The temperature at which the members were taken out during the low-temperature halogen treatment was set to room temperature. When semiconductor-grade polycrystalline silicon was manufactured using this graphite member, the purity of the manufactured polycrystalline silicon was 0.03 ppba with a phosphorus concentration of 0.03 ppba despite the use of low-temperature halogen treatment and extraction at room temperature. Hereinafter, the phosphorus concentration was 0.055 ppba and the boron concentration was 0.032 ppba, which did not satisfy the boron concentration of 0.02 ppba or less.
[0024]
As Conventional Example 4, a high-temperature halogen treatment was performed under the same conditions as in Example 1 to remove impurities, and then the graphite member was taken out of the processing furnace at 100 ° C. and cooled to room temperature in the atmosphere. Further, a low-temperature halogen treatment was performed with hydrogen chloride (HCl) gas at 900 ° C. for 10 hours. The temperature at which the members were taken out during the low-temperature halogen treatment was set to room temperature. Semiconductor graphite polycrystalline silicon was manufactured using this graphite member. Despite using a low-temperature halogen treatment and taking out at room temperature, the purity of the produced polycrystalline silicon is 0.045 ppba or less, which does not satisfy the phosphorus concentration of 0.03 ppba or less and the boron concentration of 0.02 ppba or less. The boron concentration was 0.028 ppba.
[0025]
In Example 2, a high-temperature halogen treatment was performed under the same conditions as in Example 1, and after cooling to 40 ° C. with nitrogen gas, the graphite member was taken out of the processing furnace. The removed graphite member was immediately packaged and stored in a polyethylene film bag (Clean LDPE film manufactured by Towa Kako Co., Ltd.) without using a release material. Then, on days 10, 50, and 120, the packaging was removed and incorporated into a semiconductor-grade polycrystalline silicon production apparatus, and used for producing polycrystalline silicon. The purity of the produced polycrystalline silicon is shown in Table 1 together with the results obtained when an unpackaged graphite member immediately after being taken out of the processing furnace was used.
[0026]
If a polyethylene film that does not use a release material is used for the packaging material of the graphite member taken out of the processing furnace, contamination does not progress even after a long period of time, and the same level as when using a graphite member just taken out of the processing furnace is used. Product purity is obtained.
[0027]
In Example 3, the packaging material was changed from a polyethylene film not using a release material to a commonly used nylon film. The results are also shown in Table 1.
[0028]
[Table 1]

[0029]
When an unpackaged graphite member immediately after being taken out of the processing furnace is used, the purity of the produced polycrystalline silicon satisfies the phosphorus concentration of 0.03 ppba or less and the boron concentration of 0.02 ppba or less. However, when the graphite member taken out of the processing furnace is used with a certain time, contamination proceeds even though it is packaged, and the purity of the produced polycrystalline silicon is 0.03 ppba or less in phosphorus concentration and 0 in boron concentration. .02 ppba or less cannot be satisfied.
[0030]
In the above embodiment, graphite members such as graphite electrodes and graphite heaters were purified. However, since carbon members such as a raw material gas supply nozzle are used in the production of polycrystalline silicon, the present invention is also used for purification of these carbon members. It is possible to apply
[0031]
In addition, these carbon / graphite members are completed members (finished products) used in the production of polycrystalline silicon. However, the carbon / graphite members used as materials for processing and producing the completed products are not included. The present invention can also be applied to the present invention.
[0032]
【The invention's effect】
As described above, the method for purifying a carbon / graphite member of the present invention comprises the steps of: subjecting the carbon / graphite member to a high-temperature halogen treatment in a treatment furnace; By a simple method of taking out from the furnace, the purity of the carbon / graphite member can be greatly increased compared to the conventional method, and as a result, the phosphorus concentration of 0.03 ppba or less, which was not easily realized in the actual operation level, This enables economical production of high-purity polycrystalline silicon having a boron concentration of 0.02 ppba or less. In addition, the low-temperature halogen treatment is not required, and the processing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a structural explanatory view of a processing furnace used in an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Furnace body 2 Electric heater 3 Workpiece

Claims

A carbon / graphite member which is subjected to a high-temperature halogen treatment at 2400 to 3000 ° C. in a processing furnace, and then the carbon / graphite member is taken out of the processing furnace after the temperature is lowered to 50 ° C. or lower. A method for refining components.

The method for purifying a carbon / graphite member according to claim 1, wherein the carbon / graphite member is cooled in an inert gas atmosphere after the high-temperature halogen treatment.

The method for refining a carbon / graphite member according to claim 1, wherein a polyethylene sheet without using a release material is used as a material for packaging the carbon / graphite member taken out of the processing furnace.

The method for refining a carbon / graphite member according to claim 1, wherein the carbon / graphite member is a member used in a manufacturing process of semiconductor-grade polycrystalline silicon or a member used as a material for manufacturing the member.