JP2007313454A - Method for washing polycrystalline silicon with pure water and apparatus for washing polycrystalline silicon with pure water - Google Patents

Method for washing polycrystalline silicon with pure water and apparatus for washing polycrystalline silicon with pure water Download PDF

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JP2007313454A
JP2007313454A JP2006147167A JP2006147167A JP2007313454A JP 2007313454 A JP2007313454 A JP 2007313454A JP 2006147167 A JP2006147167 A JP 2006147167A JP 2006147167 A JP2006147167 A JP 2006147167A JP 2007313454 A JP2007313454 A JP 2007313454A
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pure water
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JP4377393B2 (en
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Kenji Yamawaki
健治 山脇
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Osaka Titanium Technologies Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a pure water washing method which enables a reduction in Fe contamination and suppression in supply amount of pure water at the time of washing polycrystalline silicon with pure water and an apparatus for the method. <P>SOLUTION: The pure water washing method is a method for washing polycrystalline silicon, which is an ingot type crystal and treated by pickling, by successively immersing the polycrystalline silicon in a plurality of water-washing tanks and involves continuously or intermittently discharging pure washing water out of the water-washing tanks and turning the water back to the water-washing tanks after Fe concentration in the pure water as the pure washing water is decreased. The pure water washing apparatus employs the method. In the pure water washing method and the pure water washing apparatus, it is preferable to install pure water circulation and regeneration means in a tank at pH4 to decrease the Fe concentration in the pure washing water to 5 ng/ml or lower. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、多結晶シリコンの純水洗浄方法およびそれを適用する純水洗浄装置に関し、さらに詳しくは、半導体用単結晶シリコンの製造に用いられるチョクラルスキー法（以下、「ＣＺ法」という。）における、製造原料として供される多結晶シリコンの酸洗処理後の純水洗浄方法および純水洗浄装置に関する。   The present invention relates to a pure water cleaning method for polycrystalline silicon and a pure water cleaning apparatus to which the method is applied. More specifically, the Czochralski method (hereinafter referred to as “CZ method”) used for manufacturing single crystal silicon for semiconductors. ), A pure water cleaning method and a pure water cleaning apparatus after the pickling treatment of polycrystalline silicon provided as a manufacturing raw material.

半導体用単結晶シリコンの製造には、ＣＺ法による回転引上げ法が多用されている。このＣＺ法は、るつぼ内で多結晶シリコンを溶融し、その融液にシリコンの種結晶を浸漬し、種結晶を回転させながら引上げることによって、半導体デバイスの素材として使用される単結晶シリコンを育成する方法である。   In the production of single crystal silicon for semiconductors, the rotational pulling method by the CZ method is frequently used. In this CZ method, polycrystalline silicon is melted in a crucible, a silicon seed crystal is immersed in the melt, and the seed crystal is pulled up while being rotated, whereby single crystal silicon used as a material for a semiconductor device is obtained. It is a method of training.

上記ＣＺ法の原料となるシリコン原料には、一般にシーメンス法により製造された棒状の多結晶シリコンが用いられる。前記シーメンス法で製造された棒状の多結晶シリコンは、タングステンカーバイドなどの超硬工具を用いて適当な大きさの塊状に破砕され、表面をフッ硝酸等でエッチング（以下、「酸洗処理」という。）し、純水洗浄した後乾燥され、ＣＺ法の原料として供される。   In general, rod-shaped polycrystalline silicon produced by the Siemens method is used as the silicon material that is the material of the CZ method. The rod-shaped polycrystalline silicon produced by the Siemens method is crushed into a lump of appropriate size using a carbide tool such as tungsten carbide, and the surface is etched with hydrofluoric acid or the like (hereinafter referred to as “pickling treatment”). ), Washed with pure water, dried, and used as a raw material for the CZ method.

ＣＺ法の原料として供される多結晶シリコンの品質は、それを原料として製造される単結晶シリコンの品質に直接影響を及ぼすため、高純度であることが要求される。したがって、多結晶シリコンを破砕した後の酸洗処理や純水による洗浄工程が単結晶シリコンの品質に重要な役割を担う。   Since the quality of polycrystalline silicon provided as a raw material for the CZ method directly affects the quality of single crystal silicon produced using the raw material as a raw material, high purity is required. Therefore, the pickling treatment after crushing the polycrystalline silicon and the cleaning step with pure water play an important role in the quality of the single crystal silicon.

多結晶シリコンは重金属と接触すると、重金属が不純物として表面に付着することから、不純物付着を防止するため、多結晶シリコンを洗浄工程に搬入する際は、樹脂製のコンテナに多結晶シリコンを充填し、多結晶シリコンが重金属に接触することがないように配慮されている。   When polycrystalline silicon comes into contact with heavy metals, the heavy metals adhere to the surface as impurities, so to prevent the adhesion of impurities, when bringing polycrystalline silicon into the cleaning process, fill the resin container with polycrystalline silicon. Care is taken so that the polycrystalline silicon does not come into contact with the heavy metal.

しかし、酸洗処理槽から水洗槽へ多結晶シリコンを充填したコンテナを搬入する際に、酸洗処理後の水洗槽、特に酸洗処理の直後に多結晶シリコンを浸漬する水洗槽には、酸洗処理槽から汚染された酸が多結晶シリコンとともに大量に持ち込まれる。このため、水洗槽内の純水洗浄水中における重金属の濃度は、半導体用単結晶シリコンの原料として供される多結晶シリコンの重金属の濃度に比べ、極めて高い状態になる。   However, when carrying a container filled with polycrystalline silicon from the pickling tank to the washing tank, the washing tank after the pickling process, particularly a washing tank in which polycrystalline silicon is immersed immediately after the pickling process, A large amount of contaminated acid is brought together with the polycrystalline silicon from the washing tank. For this reason, the density | concentration of the heavy metal in the pure water wash water in a water washing tank will be in a very high state compared with the density | concentration of the heavy metal of the polycrystalline silicon provided as a raw material of the single crystal silicon for semiconductors.

従来は、水洗槽内に大量となる必要量の純水を供給することによって、水洗槽中の不純物となる重金属の濃度を低下させていた。しかし、供給される純水は高価であるため、多結晶シリコンの製造コストが大幅に上昇することとなり、純水の供給量を極力抑制する純水洗浄方法が望まれている。   Conventionally, the concentration of heavy metals that become impurities in the washing tank has been lowered by supplying a large amount of pure water in the washing tank. However, since the supplied pure water is expensive, the manufacturing cost of the polycrystalline silicon greatly increases, and a pure water cleaning method that suppresses the supply amount of pure water as much as possible is desired.

純水の供給量を低減するには、水洗槽内の純水洗浄水にコンテナを搬入する際に、酸洗処理槽から水洗槽内へ多量の重金属不純物を含有した酸が持ち込まれることを防止する方法がある。すなわち、酸洗処理槽内の酸洗液中の重金属不純物濃度を低下させることにより、酸の持ち込みによる純水洗浄水中の重金属不純物の濃度を低下させることも考えられる。   In order to reduce the amount of pure water supplied, when a container is brought into the pure water washing water in the washing tank, the acid containing a large amount of heavy metal impurities is prevented from being brought into the washing tank from the pickling tank. There is a way to do it. That is, by reducing the concentration of heavy metal impurities in the pickling solution in the pickling treatment tank, it is also conceivable to reduce the concentration of heavy metal impurities in the pure water cleaning water by bringing acid.

酸洗液中の重金属不純物濃度を低下させるために、酸洗処理槽に酸洗液を連続供給すればよいが、酸洗液の購入費用、また酸を含む液の廃棄費用が多大になることから、洗浄槽に純水を供給する場合と同様に、酸洗液を連続供給する方法は効果的ではない。   In order to reduce the concentration of heavy metal impurities in the pickling solution, it is only necessary to continuously supply the pickling solution to the pickling treatment tank. However, the purchase cost of the pickling solution and the disposal cost of the acid-containing solution increase. Thus, as in the case of supplying pure water to the cleaning tank, the method of continuously supplying the pickling solution is not effective.

酸洗液中の重金属不純物の濃度は、多結晶シリコンの洗浄量とともに増加し、通常、酸洗液を更新する前の酸洗処理槽の酸洗液に含有される重金属不純物の濃度は、水洗槽の約１０4倍にも達することがある。従来は、下記の図１に示す多結晶シリコンの純水洗浄装置、いわゆる「カスケード式の純水洗浄装置」を用いて水洗槽へ必要量の純水を供給し、水洗槽中の重金属の濃度を低下させる方法も採用されていた。 The concentration of heavy metal impurities in the pickling solution increases with the amount of polycrystalline silicon washed. Normally, the concentration of heavy metal impurities contained in the pickling solution in the pickling bath before renewing the pickling solution is It can be as high as about 104 times that of the bath. Conventionally, a necessary amount of pure water is supplied to a washing tank using a polycrystalline silicon pure water washing apparatus shown in FIG. 1 below, that is, a so-called “cascade-type pure water washing apparatus”, and the concentration of heavy metals in the washing tank. A method of lowering was also adopted.

図１は、従来から使用されている多結晶シリコンの純水洗浄装置の構成例を示す図である。図１に示すように、純水洗浄装置１の構成例では、酸洗処理槽２、第一水洗槽３、第二水洗槽４、第三水洗槽５、第四水洗槽６および第五水洗槽７が設けられており、塊状に処理された多結晶シリコン１０は、酸洗処理槽２において樹脂製のコンテナ９に充填された状態で酸洗処理される。   FIG. 1 is a diagram showing a configuration example of a conventionally used polycrystalline silicon pure water cleaning apparatus. As shown in FIG. 1, in the configuration example of the pure water cleaning apparatus 1, the pickling treatment tank 2, the first water washing tank 3, the second water washing tank 4, the third water washing tank 5, the fourth water washing tank 6, and the fifth water washing. A tank 7 is provided, and the polycrystalline silicon 10 processed in a lump shape is pickled in a state where the resin container 9 is filled in the pickling tank 2.

酸洗処理された多結晶シリコン１０は、図１では省略した搬送機によって酸洗処理槽２から引き上げられ、黒抜き矢印で示すように第一水洗槽３から第五水洗槽７まで、順次、浸漬することによって純水洗浄が行われる。   The pickled polycrystalline silicon 10 is pulled up from the pickling tank 2 by the transport machine omitted in FIG. 1 and sequentially from the first washing tank 3 to the fifth washing tank 7 as indicated by the black arrows, Pure water cleaning is performed by dipping.

その際、純水は白抜き矢印で示すように第五水洗槽７に供給され、第五水洗槽７でオーバーフローした純水洗浄水をリザーブ槽８へ供給し、前記リザーブ槽８からポンプＰを用いて第四水洗槽６へ供給し、第四水洗槽６でオーバーフローした純水洗浄水をリザーブ槽８へ供給し、前記リザーブ槽８からポンプＰを用いて第三水洗槽５へ供給される。   At that time, the pure water is supplied to the fifth water washing tank 7 as indicated by the white arrow, the pure water washing water overflowed in the fifth water washing tank 7 is supplied to the reserve tank 8, and the pump P is turned off from the reserve tank 8. The pure water washing water overflowed in the fourth water washing tank 6 is supplied to the reserve tank 8 and supplied from the reserve tank 8 to the third water washing tank 5 using the pump P. .

同様の操作を第一水洗槽３まで繰り返すことによって、重金属不純物の濃度が低い水洗槽の純水洗浄水を重金属不純物の濃度が高い水洗槽へ供給することができ、図１に示すようなカスケード式の純水洗浄装置を採用することによって、純水洗浄水を繰り返し使用し、純水の供給量の低減を図っていた。   By repeating the same operation up to the first washing tank 3, the pure water washing water in the washing tank having a low concentration of heavy metal impurities can be supplied to the washing tank having a high concentration of heavy metal impurities, and a cascade as shown in FIG. By adopting a pure water cleaning device of the type, pure water cleaning water was repeatedly used to reduce the supply amount of pure water.

ところが、カスケード式の純水洗浄装置では、数多くの水洗槽を設置できる場合には効果的に純水の供給量をある程度低減できるが、純水洗浄装置が大型になると、広い設置スペースを確保する必要があり、それぞれの水洗槽に純水洗浄水のリザーブ槽やポンプを設けることを要し、多大な設備費用が必要になる。このため、水洗槽の設置に制限が生じ、カスケード式の純水洗浄装置においても、純水の供給量を充分に低減させることができなかった。   However, in the cascade type pure water cleaning apparatus, when a large number of water washing tanks can be installed, the supply amount of pure water can be effectively reduced to some extent, but when the pure water cleaning apparatus becomes large, a large installation space is secured. Therefore, it is necessary to provide a pure water washing water reserve tank and a pump in each water washing tank, and a large amount of equipment costs are required. For this reason, the installation of the washing tank is limited, and the supply amount of pure water cannot be reduced sufficiently even in the cascade type pure water washing apparatus.

前述の通り、ＣＺ法の原料として供される多結晶シリコンの製造においては、多結晶シリコンの洗浄方法が重要であることから、種々の洗浄方法が提案されており、特許文献１には、洗浄液の劣化や変色が無く、かつ温度コントロールを容易とし、生産性が高く安全にシリコン酸化膜および不純物を除去することができる多結晶シリコンの洗浄方法が開示されている。   As described above, in the production of polycrystalline silicon used as a raw material for the CZ method, a washing method for polycrystalline silicon is important, and therefore various washing methods have been proposed. There is disclosed a method for cleaning polycrystalline silicon that is free from deterioration and discoloration, that is easy to control temperature, that is highly productive and that can safely remove a silicon oxide film and impurities.

また、特許文献２には、多結晶シリコンの表面を王水、水およびフッ硝酸で洗浄することによって表面を清浄にした多結晶シリコンの製造方法が開示されている。しかし、特許文献２の方法では、酸洗浄で表面の金属汚染を除去しても、次の水洗槽に汚れを持ち込み、純水を大量に流さなければ再び汚染されることになる。   Patent Document 2 discloses a method for producing polycrystalline silicon in which the surface of the polycrystalline silicon is cleaned by washing with aqua regia, water and hydrofluoric acid. However, in the method of Patent Document 2, even if the metal contamination on the surface is removed by the acid cleaning, the contamination is brought into the next water washing tank unless it is contaminated and a large amount of pure water is not flowed.

このように、特許文献１、２の方法は、多結晶シリコンの表面を酸洗処理することによって多結晶シリコン表面の重金属汚染を除去することを目的するに留まっており、酸洗処理後の純水洗浄での重金属汚染を低減することを意図するものではない。   As described above, the methods of Patent Documents 1 and 2 are only intended to remove heavy metal contamination on the surface of polycrystalline silicon by pickling the surface of polycrystalline silicon. It is not intended to reduce heavy metal contamination in water washing.

一方、特許文献３では、多結晶シリコン塊の酸洗浄後の純水洗浄工程において、逆浸透による精製処理を行うＲＯ装置とイオン交換による精製処理を行うＥＸ装置とを備え、両処理を行った純水を用いて多結晶シリコン塊の表面に残留する重金属を低減する洗浄方法が開示されている。   On the other hand, in patent document 3, in the pure water washing | cleaning process after the acid washing of the polycrystal silicon lump, it equipped with the RO apparatus which performs the refinement | purification process by reverse osmosis, and the EX apparatus which performs the refinement | purification process by ion exchange, and performed both processes. A cleaning method for reducing heavy metals remaining on the surface of a polycrystalline silicon lump using pure water is disclosed.

特許文献３で用いられる純水洗浄槽は、その底から洗浄排水を抜き出してフィルター処理した後に洗浄槽に戻す循環路が設けられているが、この循環路にはプレフィルター、ポンプ、フィルターが設けられ粒子の除去を行うが、液中に溶解している重金属の低減は行われない。そこで、重金属の濃度を低下させるには、純水洗浄槽へ精製処理装置からＲＯおよびＥＸの両処理された純水が供給されるようになっている。このため、特許文献３で開示される洗浄方法は、純水洗浄槽に供給される純水供給量の低減を図るものではない。   The pure water cleaning tank used in Patent Document 3 is provided with a circulation path for extracting the cleaning waste water from the bottom and filtering it, and then returning it to the cleaning tank. This circulation path is provided with a prefilter, a pump, and a filter. The particles are removed, but the heavy metals dissolved in the liquid are not reduced. Therefore, in order to reduce the concentration of heavy metals, pure water that has been subjected to both RO and EX treatments is supplied from a purification treatment apparatus to a pure water washing tank. For this reason, the cleaning method disclosed in Patent Document 3 does not attempt to reduce the supply amount of pure water supplied to the pure water cleaning tank.

特開平５−００４８１１号公報JP-A-5-004811 特開平８−０６７５１１号公報JP-A-8-067511 特開２００６−６２９４８号公報JP 2006-62948 A

前述の通り、ＣＺ法の原料として供される多結晶シリコンは高純度であることが要求されることから、酸洗処理後の純水洗浄の際に、純水洗浄水中の重金属不純物として、特にＦｅの濃度を低減すること、同時に、効率的な純水洗浄を行うために、高価な純水洗浄水の供給量を削減することが望まれる。   As described above, since polycrystalline silicon provided as a raw material for the CZ method is required to have high purity, in the pure water cleaning after the pickling treatment, particularly as heavy metal impurities in the pure water cleaning water, In order to reduce the concentration of Fe and at the same time perform efficient pure water cleaning, it is desired to reduce the supply amount of expensive pure water cleaning water.

本発明は、上述した状況に鑑みてなされたものであり、酸洗処理された塊状の多結晶シリコンを複数設けた水洗槽に順次浸漬し、純水洗浄する際に、水洗槽内の純水洗浄水を連続的または断続的に抜き取り、純水洗浄水に含有されるＦｅ濃度を低下させて循環利用することによって、高価な純水の供給量を削減しつつ、多結晶シリコン表面に付着するＦｅ濃度を半導体レベルまで低減できる多結晶シリコンの純水洗浄方法およびその純水洗浄方法を用いた多結晶シリコンの純水洗浄装置を提供することを目的とする。   The present invention has been made in view of the above-described situation, and when pure water cleaning is performed by sequentially immersing and washing pure water into a plurality of pickled lump-like polycrystalline silicon, By removing the cleaning water continuously or intermittently and reducing the Fe concentration contained in the pure water cleaning water and recycling it, the amount of expensive pure water can be reduced while adhering to the polycrystalline silicon surface. It is an object of the present invention to provide a pure water cleaning method for polycrystalline silicon capable of reducing the Fe concentration to a semiconductor level and a pure water cleaning device for polycrystalline silicon using the pure water cleaning method.

本発明者は、上述した問題を解決するため、酸洗処理後の純水洗浄の洗浄効率を向上させつつ、純水の供給量を低減させる方法に関して種々の検討を加えた。その結果、純水洗浄水中の重金属、例えばＦｅは、ｐＨ値が４未満の場合は、純水洗浄水中に金属イオンとして存在するが、ｐＨ値が４以上になると、純水洗浄水中で水酸化物等を形成し、重金属は水酸化物として表面に付着する。   In order to solve the above-described problem, the present inventor has made various studies on a method for reducing the supply amount of pure water while improving the cleaning efficiency of the pure water cleaning after the pickling treatment. As a result, heavy metals, such as Fe, in pure water washing water exist as metal ions in the pure water washing water when the pH value is less than 4, but when the pH value becomes 4 or more, they are hydroxylated in the pure water washing water. The heavy metal adheres to the surface as a hydroxide.

そして、水酸化物として付着した重金属は、多結晶シリコンを浸漬洗浄した後、水洗槽から引き上げる際に純水洗浄水とともに多結晶シリコンの表面に付着するが、水酸化物が付着した状態で多結晶シリコンが空気と接触すると、表面に付着した重金属が不純物として酸化膜内に取り込まれ、多結晶シリコンの表面を金属汚染する。   The heavy metal adhering as a hydroxide adheres to the surface of the polycrystalline silicon together with pure water washing water when the polycrystalline silicon is immersed and washed and then pulled up from the washing tank. When the crystalline silicon comes into contact with air, heavy metal adhering to the surface is taken into the oxide film as an impurity, and the surface of the polycrystalline silicon is contaminated with metal.

一旦、不純物として重金属が多結晶シリコン中に取り込まれた場合は、その後の純水洗浄によってはこの重金属不純物を多結晶シリコン中から除去することは困難であり、再度、酸洗処理することが必要となり、酸洗処理の作業効率が極端に悪化する。   Once heavy metal is incorporated into polycrystalline silicon as an impurity, it is difficult to remove the heavy metal impurity from the polycrystalline silicon by subsequent pure water cleaning, and it is necessary to perform pickling treatment again. Thus, the work efficiency of the pickling process is extremely deteriorated.

このように、水洗槽内の純水洗浄水中の重金属不純物の濃度が高い場合は、純水洗浄水中の重金属が、多結晶シリコンの表面に生じる酸化膜に不純物として取り込まれ、多結晶シリコンの表面を金属汚染するため、十分な洗浄効果が得られない。そこで、本発明者の検討によれば、従来試みられたことがないが、水洗槽内の純水洗浄水中の重金属不純物の濃度を低減するために、イオン交換系フィルター等を用いて除去することが有効であることが分かった。   Thus, when the concentration of heavy metal impurities in the pure water cleaning water in the water rinsing tank is high, heavy metals in the pure water cleaning water are incorporated as impurities into the oxide film generated on the surface of the polycrystalline silicon, and the surface of the polycrystalline silicon As a result of metal contamination, a sufficient cleaning effect cannot be obtained. Therefore, according to the study of the present inventor, there has never been attempted before, but in order to reduce the concentration of heavy metal impurities in the pure water washing water in the washing tank, it is removed using an ion exchange filter or the like. Was found to be effective.

本発明者は、酸洗処理槽にイオン交換系フィルターを設けることも検討した。しかし、 前述の通り、酸洗液中の重金属不純物の濃度は、多結晶シリコンの洗浄量とともに増加し、酸洗処理槽の酸洗液に含有される重金属不純物の濃度は、水洗槽の約１０4倍にも達するため、多くのイオン交換系フィルターを設けることが必要になるだけでなく、イオン交換系フィルターの寿命は短期間となり、イオン交換系フィルターの交換頻度は非常に高くなり、多大な設置費用が必要になる。 The present inventor also considered providing an ion exchange filter in the pickling tank. However, as described above, the concentration of heavy metal impurities in the pickling solution increases with the amount of polycrystalline silicon washed, and the concentration of heavy metal impurities contained in the pickling solution in the pickling bath is about 10 times that in the washing bath. Because it reaches 4 times, it is not only necessary to install many ion exchange filters, but the life of the ion exchange filters is short and the exchange frequency of the ion exchange filters is very high. Installation costs are required.

さらに、酸洗処理槽にイオン交換系フィルターを設ける場合に、多結晶シリコンの酸洗処理に用いられる酸洗液は、強酸であるためイオン交換系フィルターの材質は高価なフッ素樹脂系に限定されることから、さらにコストアップの要因となる。   Furthermore, when an ion exchange filter is provided in the pickling tank, the pickling solution used for the pickling treatment of polycrystalline silicon is a strong acid, so the material of the ion exchange filter is limited to an expensive fluororesin system. Therefore, it becomes a factor of further cost increase.

上述した検討を重ねた結果、酸洗処理された多結晶シリコンを浸漬して水洗する水洗槽を複数設け、そのうち所定の水洗槽から純水洗浄水を連続的または断続的に抜き取り、純水洗浄水中の重金属不純物のうち、Ｆｅ濃度を低下させて、純水洗浄水を抜き取った水洗槽へ戻し、純水洗浄水を循環して利用することによって、多結晶シリコン表面に付着するＦｅ濃度の低減とともに、水洗槽への純水供給量の低減を効率的に達成できることを知見した。   As a result of repeating the above-described studies, a plurality of water washing tanks for immersing and washing the pickled polycrystalline silicon are provided, and pure water washing water is continuously or intermittently extracted from a predetermined water washing tank, and pure water washing is performed. Among heavy metal impurities in water, Fe concentration is reduced, returned to the water washing tank from which pure water washing water has been extracted, and the concentration of Fe adhering to the polycrystalline silicon surface is reduced by circulating and using pure water washing water. At the same time, it was found that a reduction in the amount of pure water supplied to the washing tank can be achieved efficiently.

本発明は、上記の知見に基づいて完成したものであり、下記（１）〜（５）の多結晶シリコンの純水洗浄方法、および（６）に示す純水洗浄装置を要旨とする。
（１）塊状結晶で酸洗処理された多結晶シリコンを複数設けた水洗槽に順次浸漬しながら純水洗浄する方法であって、前記水洗槽内の純水洗浄水を連続的または断続的に抜き取り、前記純水洗浄水に含有されるＦｅ濃度を低下させた後に前記水洗槽へ戻すことを特徴とする多結晶シリコンの純水洗浄方法である。
（２）上記（１）の純水洗浄方法では、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽（以下、「ｐＨ４槽」という。）を含めてその前段に設けられた水洗槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すこと、または、最初に純水洗浄水のｐＨ値が２以上となった水洗槽（以下、「ｐＨ２槽」という。）乃至最初に純水洗浄水のｐＨ値が４以上となった水洗槽、すなわちｐＨ４槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことが望ましい。
（３）さらに、上記（１）の純水洗浄方法では、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽、すなわちｐＨ４槽、またはその前段に設けられた水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すこと、さらに、ｐＨ４槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことが望ましい。
（４）上記（１）の純水洗浄方法では、ｐＨ４槽の純水洗浄水が含有するＦｅ濃度に比べ、その後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が低いこと、または、ｐＨ４槽およびその後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が５ｎｇ／ｍｌ以下であることが望ましい。
（５）上記（１）〜（３）の純水洗浄方法では、前記水洗槽から抜き取られた純水洗浄水に含有されるＦｅ濃度をイオン交換系フィルターを用いて低下させるのが望ましい。
（６）塊状結晶を酸洗処理する酸洗処理槽と、酸洗処理された多結晶シリコンを純水洗浄水を用いて浸漬水洗する水洗槽を複数設け、前記水洗槽への順次浸漬する純水洗浄装置であって、前記水洗槽には、純水洗浄水に含有されるＦｅ濃度を低下させて連続的または断続的に循環させる純水循環再生手段を設置することを特徴とする多結晶シリコンの純水洗浄装置である。 The present invention has been completed on the basis of the above knowledge, and the gist thereof is the following pure water cleaning method for polycrystalline silicon (1) to (5) and the pure water cleaning apparatus shown in (6).
(1) A method of performing pure water cleaning while sequentially immersing in a water washing tank provided with a plurality of polycrystalline silicons pickled with bulk crystals, wherein the pure water washing water in the water washing tank is continuously or intermittently used. The polycrystalline silicon pure water cleaning method is characterized in that it is extracted and returned to the water washing tank after reducing the Fe concentration contained in the pure water washing water.
(2) In the pure water cleaning method of (1) above, among the water washing tanks in which the pH value of the pure water washing water changes, the water washing tank (hereinafter, The pure water washing water is extracted from at least one of the water washing tanks provided in the preceding stage including the “pH 4 tank”) and returned after reducing the Fe concentration, or first the pure water washing water From a water washing tank (hereinafter referred to as “pH 2 tank”) having a pH value of 2 or more from a water washing tank having a pH value of 4 or more initially, that is, from at least one water washing tank of pH 4 tank. It is desirable to extract pure water washing water and return it after reducing the Fe concentration.
(3) Furthermore, in the pure water cleaning method according to (1) above, the water washing tank in which the pH value of the pure water washing water is initially 4 or more among the washing tanks in which the pH value of the pure water washing water changes, That is, after removing pure water washing water from the pH 4 tank or the water washing tank provided in the preceding stage and returning it after reducing the Fe concentration, after removing pure water washing water from the pH 4 tank and reducing the Fe concentration It is desirable to return.
(4) In the pure water cleaning method of (1) above, the Fe concentration contained in the pure water cleaning water in the subsequent water washing tank is lower than the Fe concentration contained in the pure water cleaning water in the pH 4 tank. Alternatively, it is desirable that the Fe concentration contained in the pure water washing water in the pH 4 tank and the water washing tank provided in the subsequent stage is 5 ng / ml or less.
(5) In the pure water cleaning methods (1) to (3) above, it is desirable to reduce the Fe concentration contained in the pure water cleaning water extracted from the water cleaning tank using an ion exchange filter.
(6) A pickling treatment tank for pickling bulk crystals, and a plurality of washing tanks for immersing and washing the pickled polycrystalline silicon using pure water washing water, and sequentially immersing into the washing tank A polycrystal which is a water washing apparatus, wherein the water washing tank is provided with pure water circulation regenerating means for continuously or intermittently circulating the Fe concentration contained in the pure water washing water. This is a pure water cleaning device for silicon.

本発明が対象とする「塊状結晶」は、例えば、ＣＺ法の原料として供される多結晶シリコン塊であって、１ｍｍ以上の粒状から棒状（破砕しない）までの結晶塊を含むものである。   The “bulk crystal” targeted by the present invention is, for example, a polycrystalline silicon lump provided as a raw material of the CZ method, and includes a lump of crystal of 1 mm or more in size to a rod shape (not crushed).

また、本発明で規定する「水洗槽に順次浸漬しながら」とは、単に純水洗浄水を供給する純水洗浄に限定されず、途中工程においてシャワー洗浄を追加する場合も含まれる。   In addition, the phrase “while sequentially immersing in a water-washing tank” defined in the present invention is not limited to pure water cleaning in which pure water cleaning water is supplied, and includes a case where shower cleaning is added in an intermediate process.

本発明の多結晶シリコンの純水洗浄方法および純水洗浄装置によれば、水洗槽内の純水洗浄水を抜き取り、純水洗浄水中のＦｅ濃度を低下させ、その純水洗浄水を循環利用していることから、高価な純水の供給量を抑制させ効率的な純水洗浄を行うとともに、多結晶シリコン表面に付着するＦｅ濃度を半導体レベルまで低減させることができる。   According to the pure water cleaning method and the pure water cleaning apparatus of the present invention, the pure water cleaning water in the water cleaning tank is extracted, the Fe concentration in the pure water cleaning water is reduced, and the pure water cleaning water is circulated and used. Therefore, it is possible to suppress the supply amount of expensive pure water and perform efficient pure water cleaning, and to reduce the concentration of Fe adhering to the polycrystalline silicon surface to the semiconductor level.

図２は、本発明の純水洗浄方法を用いた多結晶シリコンの純水洗浄装置の構成例を示す図である。本発明の純水洗浄装置１は、塊状結晶を酸洗処理する酸洗処理槽２と、酸洗処理された多結晶シリコンを純水洗浄水を用いて浸漬水洗する水洗槽を複数設け、前記水洗槽への順次浸漬する純水洗浄装置であって、前記水洗槽には、純水洗浄水に含有されるＦｅ濃度を低下させて連続的または断続的に循環させる純水循環再生手段１１を設置することを特徴としている。   FIG. 2 is a diagram showing a configuration example of a pure water cleaning apparatus for polycrystalline silicon using the pure water cleaning method of the present invention. The pure water cleaning apparatus 1 of the present invention is provided with a plurality of pickling treatment tanks 2 for pickling bulk crystals, and a plurality of washing tanks for immersing and washing pickled polycrystalline silicon using pure water washing water, A pure water cleaning apparatus for sequentially immersing in a water washing tank, wherein the water washing tank is provided with pure water circulation and regeneration means 11 that continuously or intermittently circulates by reducing the Fe concentration contained in the pure water washing water. It is characterized by installation.

図２に示す純水洗浄装置１では、複数の水洗槽として、第一水洗槽３、第二水洗槽４、第三水洗槽５、第四水洗槽６および第五水洗槽７が設けられ、純水循環再生手段１１は、リザーブ槽８、イオン交換フィルター１２およびポンプＰで構成される。   In the pure water washing apparatus 1 shown in FIG. 2, the 1st water washing tank 3, the 2nd water washing tank 4, the 3rd water washing tank 5, the 4th water washing tank 6, and the 5th water washing tank 7 are provided as a some water washing tank, The pure water circulation / regeneration means 11 includes a reserve tank 8, an ion exchange filter 12, and a pump P.

本発明の純水洗浄装置１は、図２では省略した搬送機によって、黒抜き矢印で示すように、コンテナ９に充填した塊状の多結晶シリコン１０を酸洗処理槽２および各水洗槽に順次、浸漬する構成である。酸洗処理された多結晶シリコンを各水洗槽へ順次浸漬するのにともない、純水洗浄水のｐＨ値が、例えば酸洗処理槽側から高められるように変化する。また、必要に応じて、いずれかの水洗槽において純水洗浄水のｐＨ値を低めることもできる。   The pure water cleaning apparatus 1 according to the present invention sequentially transfers the bulk polycrystalline silicon 10 filled in the container 9 to the pickling tank 2 and each water tank as shown by the black arrow by a transport machine omitted in FIG. It is the structure to immerse. As the pickled polycrystalline silicon is sequentially immersed in each washing tank, the pH value of the pure water washing water changes so as to be increased from the pickling tank side, for example. Moreover, the pH value of the pure water washing water can be lowered in any of the water washing tanks as necessary.

本発明の純水洗浄方法は、上記の純水洗浄装置で適用され、塊状結晶で酸洗処理された多結晶シリコンを複数設けた水洗槽に順次浸漬しながら純水洗浄する方法であり、前記水洗槽内の純水洗浄水を連続的または断続的に抜き取り、前記純水洗浄水に含有されるＦｅ濃度を低下させた後に前記水洗槽へ戻すことを特徴とする。   The pure water cleaning method of the present invention is a method of cleaning with pure water while being sequentially immersed in a water rinsing tank provided with a plurality of polycrystalline silicon pickled with lump crystals, which is applied in the above pure water cleaning apparatus, The pure water washing water in the water washing tank is continuously or intermittently extracted, and the Fe concentration contained in the pure water washing water is lowered and then returned to the water washing tank.

本発明の純水洗浄方法では、純水洗浄水に含有される重金属不純物のうち、Ｆｅ濃度の低減に顕著な効果を発揮することができる。純水洗浄水に含有されるＦｅは、ｐＨ値に応じて含有形態が異なり、ｐＨ値を調整しつつＦｅ濃度を低下させることにより、多結晶シリコン塊の表面に付着するＦｅ量を低減できることによる。   In the pure water cleaning method of the present invention, among the heavy metal impurities contained in the pure water cleaning water, a remarkable effect can be exhibited in reducing the Fe concentration. Fe contained in pure water washing water has different forms depending on the pH value, and by reducing the Fe concentration while adjusting the pH value, the amount of Fe adhering to the surface of the polycrystalline silicon lump can be reduced. .

本発明の純水洗浄方法では、複数設けた水洗槽のうち、ｐＨ４槽を含めてその前段に設けられた水洗槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことが望ましい。純水洗浄水のｐＨ値が４未満の場合は、純水洗浄水中に金属イオンとして存在するが、ｐＨ値が４以上になると、純水洗浄水中で水酸化物等を形成する。   In the pure water cleaning method of the present invention, the pure water cleaning water was extracted from at least one of the water cleaning tanks provided in the preceding stage including the pH 4 tank among the plurality of water cleaning tanks to reduce the Fe concentration. It is desirable to return later. When the pH value of the pure water washing water is less than 4, it exists as metal ions in the pure water washing water, but when the pH value becomes 4 or more, hydroxides and the like are formed in the pure water washing water.

したがって、純水洗浄水のｐＨ値が４以上になると、純水洗浄の際に多結晶シリコンの表面に付着し易くなる。このため、純水洗浄水中のＦｅが多結晶シリコンの表面に付着し易くなるｐＨ４槽を含め、その前段に設けられた１または２以上の水洗槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、多結晶シリコン表面への付着を低減する。   Therefore, when the pH value of the pure water cleaning water is 4 or more, it easily adheres to the surface of the polycrystalline silicon during the pure water cleaning. For this reason, pure water washing water is supplied from at least one washing tank of one or two or more washing tanks provided in the preceding stage, including a pH 4 tank in which Fe in pure water washing water easily adheres to the surface of polycrystalline silicon. Extract and reduce adhesion to the polycrystalline silicon surface.

本発明の純水洗浄方法では、複数設けた水洗槽のうち、ｐＨ２槽乃至ｐＨ４槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことが望ましい。ｐＨ２槽より前段の水洗槽は、純水洗浄水が強酸性となっており、純水洗浄水中のＦｅ濃度を低下させるためには、例えば、高価なフッ素樹脂系のイオン交換フィルター等が必要になる。さらに、ｐＨ２槽より前段の水洗槽には、酸洗処理槽から大量のＦｅを含有した酸溶液が持ち込まれることから、純水洗浄水中のＦｅ濃度は高く、ｐＨ２槽より前段の水洗槽において、イオン交換系フィルターを用い、Ｆｅ濃度を低下させる場合、イオン交換系フィルターの設置台数が増えるとともに、イオン交換系フィルターの交換頻度が極めて高くなる。   In the pure water cleaning method of the present invention, it is desirable to extract pure water washing water from at least one of the pH 2 tank to pH 4 tank among the plurality of water washing tanks, and return it after reducing the Fe concentration. In the water washing tank preceding the pH 2 tank, the pure water washing water is strongly acidic, and in order to reduce the Fe concentration in the pure water washing water, for example, an expensive fluororesin ion exchange filter is required. Become. Furthermore, since the acid solution containing a large amount of Fe is brought from the pickling tank into the water tank before the pH 2 tank, the Fe concentration in the pure water cleaning water is high, and in the water tank before the pH 2 tank, When an ion exchange filter is used and the Fe concentration is decreased, the number of ion exchange filters installed is increased and the exchange frequency of the ion exchange filter is extremely increased.

一方、ｐＨ４槽より後段の水洗槽になると、純水洗浄水中のＦｅは水酸化物等を形成し、純水洗浄の際に多結晶シリコンの表面に多量に付着するおそれがある。このため、対象をｐＨ４槽より前段の水洗槽として、Ｆｅは金属イオンとして純水洗浄水中に存在している状態で循環利用することとした。   On the other hand, when it becomes a washing tank of the latter stage from pH4 tank, Fe in pure water washing water forms a hydroxide etc., and there is a possibility of adhering in large quantities on the surface of polycrystalline silicon at the time of pure water washing. For this reason, it was decided to circulate and use Fe as a metal ion in the pure water washing water as a water washing tank before the pH 4 tank.

本発明の純水洗浄方法では、複数設けた水洗槽のうち、ｐＨ４槽、またはその前段に設けられた水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことが望ましい。さらに望ましくは、ｐＨ４槽の純水洗浄水を抜き取り循環利用することである。   In the pure water cleaning method of the present invention, it is desirable to remove pure water cleaning water from a pH 4 tank or a water washing tank provided in the preceding stage among a plurality of water washing tanks, and then to return after reducing the Fe concentration. More desirably, the pure water washing water in the pH 4 tank is extracted and recycled.

ｐＨ４槽、またはｐＨ４槽の前段の水洗槽における純水洗浄水中のＦｅ濃度が低く、特にｐＨ４槽では、ｐＨ２槽に比べ、純水洗浄水中のＦｅ濃度は１０-1〜１０-2程度にまで低下しており、最も効率よく純水洗浄水中のＦｅ濃度を低下させることができる。 The Fe concentration in the pure water washing water in the pH 4 tank or the preceding water washing tank of the pH 4 tank is low. In particular, in the pH 4 tank, the Fe concentration in the pure water washing water is about 10 −1 to 10 −2 compared to the pH 2 tank. The Fe concentration in the pure water washing water can be reduced most efficiently.

このため、ｐＨ４槽、またはｐＨ４槽の前段の水洗槽における純水洗浄水中のＦｅ濃度を低下させるイオン交換系フィルターを用いた場合には、イオン交換系フィルターの設置台数を大幅に削減でき、さらに、イオン交換系フィルターの交換頻度も低くなることから、安価に純水洗浄水中のＦｅ濃度を低下できる。   For this reason, when using an ion exchange filter that reduces the Fe concentration in the pure water washing water in the pH 4 tank or the preceding water washing tank of the pH 4 tank, the number of installed ion exchange filters can be greatly reduced. Since the exchange frequency of the ion exchange filter is also reduced, the Fe concentration in the pure water washing water can be reduced at a low cost.

さらに、ｐＨ４槽内の純水洗浄水中のＦｅ濃度を低下させるために用いるフィルターの材質には、ポリエチレン（ＰＥ）またはポリプロピレン（ＰＰ）等の安価な樹脂が使用できることから、フィルター素材のコスト面でも有利となる。   Furthermore, since the filter material used for reducing the Fe concentration in the pure water washing water in the pH 4 tank can be made of an inexpensive resin such as polyethylene (PE) or polypropylene (PP), the cost of the filter material can be reduced. It will be advantageous.

また、ｐＨ４槽に加え、ｐＨ４槽の前段の水洗槽も対象にしたのは、ｐＨ４槽における純水洗浄水のｐＨ値が５に近く（例えば、ｐＨ＝４．８）、ｐＨ４槽の前段の水洗槽における純水洗浄水のｐＨ値が４に近い（例えば、ｐＨ＝３．９）場合には、ｐＨ４槽の前段の槽でもｐＨ４槽と同等の洗浄効率を確保できる場合があるからである。   In addition to the pH 4 tank, the water washing tank before the pH 4 tank was also targeted because the pH value of the pure water washing water in the pH 4 tank is close to 5 (for example, pH = 4.8), This is because when the pH value of the pure water washing water in the water washing tank is close to 4 (for example, pH = 3.9), the washing efficiency equivalent to that of the pH 4 tank may be secured even in the previous stage of the pH 4 tank. .

本発明の純水洗浄方法は、ｐＨ４槽の純水洗浄水が含有するＦｅ濃度に比べ、その後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が低いのが望ましい。本発明ではｐＨ４槽かそれより前段の水洗槽においてＦｅ濃度を低下させているが、その後の水洗槽でよりＦｅ濃度が高い純水洗浄水で洗浄することは合理性がないことから、確認的な規定を設けている。   In the pure water cleaning method of the present invention, it is desirable that the Fe concentration contained in the pure water washing water in the water washing tank provided in the subsequent stage is lower than the Fe concentration contained in the pure water washing water of pH 4 tank. In the present invention, the Fe concentration is lowered in the pH 4 tank or the preceding water washing tank, but it is not reasonable to wash with pure water washing water having a higher Fe concentration in the subsequent water washing tank. Provisions are in place.

本発明の純水洗浄方法は、ｐＨ４槽およびその後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が５ｎｇ／ｍｌ以下であることが望ましい。本発明ではｐＨ４槽においてＦｅ濃度を低下させることができるが、それ以降の水洗槽においても純水洗浄水中のＦｅ濃度を５ｎｇ／ｍｌ以下とすることによって、純水洗浄後の多結晶シリコンの表面におけるＦｅ濃度を０．０２ｐｐｂｗ未満とすることが可能になる。このように多結晶シリコン塊の表面に残留するＦｅ濃度を低減することによって、ＣＺ法に供すること原料として優れた品質を確保できる。   In the pure water cleaning method of the present invention, it is desirable that the Fe concentration contained in the pure water cleaning water in the pH 4 tank and the water cleaning tank provided in the subsequent stage is 5 ng / ml or less. In the present invention, the Fe concentration can be lowered in the pH 4 tank, but in the subsequent water washing tank, the Fe concentration in the pure water washing water is set to 5 ng / ml or less, so that the surface of the polycrystalline silicon after the pure water washing is reduced. It becomes possible to make Fe density | concentration in less than 0.02 ppbw. Thus, by reducing the Fe concentration remaining on the surface of the polycrystalline silicon lump, it is possible to ensure excellent quality as a raw material to be subjected to the CZ method.

さらに、ｐＨ値が４以上となる全ての水洗槽における純水洗浄水中のＦｅ濃度を５ｎｇ／ｍｌ以下とする条件を達成する手段としては、例えば、ｐＨ４槽より後段に設けられた水洗槽を前述した「カスケード式の純水洗浄装置」の構成とする方法、または、ｐＨ４槽よりも後段に設けられた全ての水洗槽の純水洗浄水を抜き取りＦｅ濃度を低下させる方法等がある。   Further, as a means for achieving the condition that the Fe concentration in the pure water washing water in all the water washing tanks having a pH value of 4 or more is 5 ng / ml or less, for example, the water washing tank provided in the subsequent stage from the pH 4 tank is described above. There is a method of configuring the “cascade type pure water cleaning apparatus” or a method of reducing the Fe concentration by extracting pure water cleaning water from all the water cleaning tanks provided at a stage subsequent to the pH 4 tank.

本発明の純水洗浄方法では、前記水洗槽から抜き取られた純水洗浄水に含有されるＦｅ濃度をイオン交換系フィルターを用いて低下させるのが望ましい。具体的な構成は、例えば、前述した図２に示すように、ポンプＰを用いてリザーブ槽８へ純水洗浄水を供給し、イオン交換フィルター１２を介し、純水洗浄水中のＦｅ濃度を低下させてリザーブ槽８から水洗槽５へ供給する構成である。   In the pure water cleaning method of the present invention, it is desirable to reduce the Fe concentration contained in the pure water cleaning water extracted from the water cleaning tank using an ion exchange filter. Specifically, for example, as shown in FIG. 2 described above, pure water cleaning water is supplied to the reserve tank 8 using the pump P, and the Fe concentration in the pure water cleaning water is reduced via the ion exchange filter 12. In this configuration, the water is supplied from the reserve tank 8 to the washing tank 5.

さらに、本発明の純水洗浄方法では、前記図２に示さないが、各水洗槽にｐＨ測定器を設け、各水洗槽のｐＨ値を管理するのがよい。複数設けた水洗槽において、純水洗浄される多結晶シリコンの量、大きさおよび表面形状によって、洗浄液の持ち出し量（すなわち水洗槽への持ち込み量）が変化する。したがって、最も効率よくＦｅ濃度を低下させることができる水洗槽、すなわちｐＨ４槽が洗浄の際に異なる位置となる可能性があることによる。   Furthermore, in the pure water cleaning method of the present invention, although not shown in FIG. 2, it is preferable to provide a pH measuring device in each washing tank and manage the pH value of each washing tank. In a plurality of water washing tanks, the amount of cleaning liquid taken out (that is, the amount brought into the water washing tank) varies depending on the amount, size and surface shape of polycrystalline silicon to be cleaned with pure water. Therefore, it is because the water washing tank which can reduce an Fe density | concentration most efficiently, ie, pH4 tank, may become a different position in the case of washing | cleaning.

本発明の純水洗浄方法において、前記図２に示す純水循環再生手段１１を設ける水洗槽の切り替えは手動バルブを用いてもよいが、自動バルブ等を用いてｐＨ測定器と連動させ、自動で切り替える構造を採用するのが望ましい。ｐＨ測定器と自動バルブを連動させることによって、常にｐＨ４槽に純水循環再生手段１１を設けることが可能になる。   In the pure water cleaning method of the present invention, switching of the water washing tank provided with the pure water circulation and regeneration means 11 shown in FIG. 2 may be performed by a manual valve, but an automatic valve or the like is used in conjunction with a pH measuring device to automatically It is desirable to adopt a structure that switches between. By linking the pH measuring instrument and the automatic valve, it is possible to always provide the pure water circulation and regeneration means 11 in the pH 4 tank.

前記図２に示す多結晶シリコンの純水洗浄装置を用い、最も効果的に純水洗浄水中のＦｅを除去し、かつ純水の供給量を低減させることが可能な水洗槽を選定するためのＦｅ除去試験（実施例１）、および純水洗浄後の多結晶シリコン塊表面のＦｅ濃度を半導体レベルにできる必要供給量を求める純水供給試験（実施例２）を行った。
（実施例１）
供試材には、同一還元反応によって得られた同一ロッドの棒状の多結晶シリコンを、タングステンカーバイド製のハンマーを用いて、粒径が５ｍｍ〜３０ｍｍとなるように破砕した。破砕した１０ｋｇの多結晶シリコン１０を樹脂製のコンテナ９に充填して酸洗処理を行った。酸洗処理にはフッ硝酸溶液を用い、沸酸と硝酸の混合比を１：４０、酸洗処理時間２００ｓｅｃおよび液温は３０℃とした。 Using the polycrystalline silicon pure water cleaning apparatus shown in FIG. 2 to select a water washing tank that can most effectively remove Fe in pure water cleaning water and reduce the amount of pure water supplied. An Fe removal test (Example 1) and a pure water supply test (Example 2) for obtaining a necessary supply amount capable of bringing the Fe concentration on the surface of the polycrystalline silicon lump after cleaning with pure water to a semiconductor level were conducted.
Example 1
For the test material, rod-shaped polycrystalline silicon of the same rod obtained by the same reduction reaction was crushed using a tungsten carbide hammer so that the particle size would be 5 mm to 30 mm. The crushed 10 kg of polycrystalline silicon 10 was filled in a resin container 9 and pickled. A hydrofluoric acid solution was used for the pickling treatment, the mixing ratio of boiling acid and nitric acid was 1:40, the pickling treatment time was 200 sec, and the liquid temperature was 30 ° C.

また、全ての水洗槽には常に４ｌ／ｍｉｎの純水を供給し、純水洗浄工程におけるサイクルタイム（浸漬時間および搬送時間）は一定とした。試験条件は、純水循環再生手段１１を設けてＦｅ除去を行う槽を第一水洗槽３、第二水洗槽４、第三水洗槽５、第四水洗槽６および第五水洗槽７とし、さらにいずれの水洗槽からもＦｅ除去を行わない条件とした。   In addition, 4 l / min of pure water was always supplied to all water washing tanks, and the cycle time (immersion time and transport time) in the pure water washing process was constant. The test condition is that the tank for performing Fe removal by providing the pure water circulation and regeneration means 11 is the first water washing tank 3, the second water washing tank 4, the third water washing tank 5, the fourth water washing tank 6 and the fifth water washing tank 7, Furthermore, it was set as the conditions which do not remove Fe from any washing tank.

Ｆｅ除去の際に、水洗槽から抜き取った純水洗浄水の量は２０ｌ／ｍｉｎとし、すなわち、３分で水洗槽内の純水洗浄水が完全に入れ替わる量とした。   When removing Fe, the amount of pure water washing water extracted from the water washing tank was 20 l / min, that is, the amount of pure water washing water in the washing tank completely replaced in 3 minutes.

上記の純水洗浄によって得られた塊状の多結晶シリコン１０をコンテナ９から５個で２０ｇとなるように採取し、フッ硝酸でその表面を０．６００±０．０５０ｇ溶解し、溶解したフッ硝酸中のＦｅ濃度を測定した。Ｆｅ濃度の測定手段は、ＪＩＳ Ｋ ０１２０に規定されている原子吸光法によった。   The bulk polycrystalline silicon 10 obtained by the above pure water cleaning is collected from the container 9 so as to be 20 g, and its surface is dissolved with hydrofluoric acid at 0.600 ± 0.050 g. The Fe concentration in the medium was measured. The means for measuring the Fe concentration was based on the atomic absorption method defined in JIS K 0120.

Ｆｅ濃度の評価は、最もＦｅ濃度が低い場合を１とし、その何倍に該当するかを求めて行った。また、そのときの純水洗浄水のｐＨ値をｐＨ測定器を用いて測定した。それらの結果を表１に示した。純水循環再生手段１１を設けた水洗槽を循環槽と表記する。   The evaluation of the Fe concentration was performed by obtaining 1 when the Fe concentration is the lowest and determining how many times the Fe concentration falls. Moreover, the pH value of the pure water washing water at that time was measured using a pH meter. The results are shown in Table 1. The washing tank provided with the pure water circulation regeneration means 11 is referred to as a circulation tank.

Figure 2007313454
Figure 2007313454

表１に示すように、純水洗浄水のｐＨ値が４．１である第三水洗槽５、すなわちｐＨ４槽の純水洗浄水中のＦｅ濃度を低下させることによって、純水洗浄後の多結晶シリコン１０の表面におけるＦｅ濃度を最も低下させることができる。これは、Ｆｅ濃度を低下させない場合と比較すると、純水洗浄後の多結晶シリコン１０の表面に残留するＦｅ濃度は１８分の１になることが確認できた。   As shown in Table 1, by reducing the Fe concentration in the third water washing tank 5 having a pH value of 4.1, that is, pure water washing water in the pH 4 tank, the polycrystal after washing with pure water is obtained. The Fe concentration on the surface of the silicon 10 can be reduced most. It was confirmed that the Fe concentration remaining on the surface of the polycrystalline silicon 10 after the pure water cleaning was 1/18 compared to the case where the Fe concentration was not lowered.

また、Ｆｅの除去は、ｐＨ４槽（第三水洗槽５）より後段の第四水洗槽６または第五水洗槽７で行ってもＦｅ除去を行わない場合よりも多結晶シリコン１０の表面におけるＦｅ濃度を低下することが可能となるが、ｐＨ４槽（第三水洗槽５）までに行う方がより一層、洗浄効率の向上が図れることが確認できた。   In addition, Fe removal on the surface of the polycrystalline silicon 10 is performed in the fourth water washing tank 6 or the fifth water washing tank 7 subsequent to the pH 4 tank (third water washing tank 5) than in the case where Fe removal is not performed. Although the concentration can be lowered, it has been confirmed that the cleaning efficiency can be further improved by performing the treatment up to pH 4 tank (third water washing tank 5).

また、循環量を変えて同様に多結晶シリコン表面のＦｅ濃度を確認するとｐＨ４槽（第三水洗槽５）の純水洗浄水中のＦｅ濃度が、５ｎｇ／ｍｌ以下であれば、純水洗浄後の多結晶シリコン１０表面のＦｅ濃度が、半導体レベルである０．０２ｐｐｂｗ未満となり、ＣＺ法の原料として供することが可能であることが確認できた。
（実施例２）
各水洗槽への純水供給量を変えて、純水洗浄後の多結晶シリコン１０表面のＦｅ濃度が０．０２ｐｐｂｗ未満となる純水供給量を確認した。ここで、洗浄におけるサイクルタイム、純水洗浄水の循環量、酸洗処理の条件およびＦｅ濃度測定は、実施例１の場合と同条件とした。純水供給量試験の結果を表２に示す。 Further, when the Fe concentration on the surface of the polycrystalline silicon is similarly confirmed by changing the circulation amount, if the Fe concentration in the pure water washing water in the pH 4 tank (third water washing tank 5) is 5 ng / ml or less, after the pure water washing It was confirmed that the Fe concentration on the surface of polycrystalline silicon 10 was less than 0.02 ppbw, which is a semiconductor level, and could be used as a raw material for the CZ method.
(Example 2)
The pure water supply amount to each water washing tank was changed, and the pure water supply amount at which the Fe concentration on the surface of the polycrystalline silicon 10 after the pure water cleaning was less than 0.02 ppbw was confirmed. Here, the cycle time in washing, the circulation amount of pure water washing water, the conditions for pickling treatment, and the Fe concentration measurement were the same as those in Example 1. Table 2 shows the results of the pure water supply amount test.

Figure 2007313454
Figure 2007313454

表２に示すように、水洗槽内の純水洗浄水におけるＦｅ濃度を低下させることによって、純水の供給量を低減することができる。また、ｐＨ４槽（第三水洗槽５）を含め、ｐＨ４槽より前段の第二水洗槽４および第一水洗槽３における純水洗浄水のＦｅ濃度を低下させて純水洗浄水を循環利用することによって、純水の供給量は従来の純水洗浄方法の約５分の一以下となり、純水洗浄水を循環利用することによって純水の供給量が大幅に低減できることが確認できた。   As shown in Table 2, the supply amount of pure water can be reduced by reducing the Fe concentration in the pure water washing water in the washing tank. In addition, the pure water washing water is circulated and used by reducing the Fe concentration of the pure water washing water in the second water washing tank 4 and the first water washing tank 3 preceding the pH 4 tank, including the pH 4 tank (third water washing tank 5). As a result, the supply amount of pure water was about one-fifth or less than that of the conventional pure water cleaning method, and it was confirmed that the supply amount of pure water can be significantly reduced by circulating the pure water cleaning water.

さらに、ｐＨ４槽（第三水洗槽５）の純水洗浄水中のＦｅ濃度を低下させて純水洗浄水を循環利用することによって、純水の供給量を最も低減することができ、従来の循環槽を設けない純水洗浄方法と比較すると、純水の供給量が１／２０になることが確認できた。   Further, by reducing the Fe concentration in the pure water washing water in the pH 4 tank (third water washing tank 5) and circulating the pure water washing water, the supply amount of pure water can be reduced most, and the conventional circulation It was confirmed that the supply amount of pure water was 1/20 compared with the pure water cleaning method without a tank.

本発明の多結晶シリコンの純水洗浄方法および純水洗浄装置によれば、水洗槽内の純水洗浄水を抜き取り、純水洗浄水中のＦｅ濃度を低下させ、その純水洗浄水を循環利用していることから、高価な純水の供給量を抑制させ効率的な純水洗浄とともに、多結晶シリコン表面に残留するＦｅ濃度を低減させることができる。これにより、半導体用単結晶シリコンの製造に用いられるＣＺ法に用いる製造原料として供される多結晶シリコンの純水洗浄手段として、高い信頼性を持って適用できる。   According to the pure water cleaning method and the pure water cleaning apparatus of the present invention, the pure water cleaning water in the water cleaning tank is extracted, the Fe concentration in the pure water cleaning water is reduced, and the pure water cleaning water is circulated and used. Therefore, it is possible to reduce the concentration of Fe remaining on the surface of the polycrystalline silicon, while suppressing the supply amount of expensive pure water and performing efficient pure water cleaning. Thus, it can be applied with high reliability as a pure water cleaning means for polycrystalline silicon provided as a manufacturing raw material used in the CZ method used for manufacturing single crystal silicon for semiconductors.

従来から使用されている多結晶シリコンの純水洗浄装置の構成例を示す図である。It is a figure which shows the structural example of the pure water washing | cleaning apparatus of the polycrystalline silicon used conventionally. 本発明の純水洗浄方法を用いた多結晶シリコンの純水洗浄装置の構成例を示す図である。It is a figure which shows the structural example of the pure water cleaning apparatus of the polycrystalline silicon using the pure water cleaning method of this invention.

符号の説明Explanation of symbols

１：純水洗浄装置、 ２：酸洗処理槽、
３：第一水洗槽、 ４：第二水洗槽、
５：第三水洗槽、 ６：第四水洗槽、
７：第五水洗槽、 ８：リザーブ槽、
９：コンテナ、 １０：多結晶シリコン、
１１：純水循環再生手段、 １２：イオン交換フィルター、
Ｐ：ポンプ
1: pure water cleaning device, 2: pickling treatment tank,
3: First water washing tank, 4: Second water washing tank,
5: Third washing tank, 6: Fourth washing tank,
7: Fifth water washing tank, 8: Reserve tank,
9: Container, 10: Polycrystalline silicon,
11: Pure water circulation regeneration means, 12: Ion exchange filter,
P: Pump

Claims (16)

塊状結晶で酸洗処理された多結晶シリコンを複数設けた水洗槽に順次浸漬しながら純水洗浄する方法であって、
前記水洗槽内の純水洗浄水を連続的または断続的に抜き取り、前記純水洗浄水に含有されるＦｅ濃度を低下させた後に前記水洗槽へ戻すことを特徴とする多結晶シリコンの純水洗浄方法。 A method of washing with pure water while sequentially immersing in a washing tank provided with a plurality of polycrystalline silicon pickled with lump crystals,
Pure water of polycrystalline silicon, wherein the pure water washing water in the water washing tank is continuously or intermittently extracted and returned to the water washing tank after reducing the Fe concentration contained in the pure water washing water Cleaning method. 純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽を含めてその前段に設けられた水洗槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことを特徴とする請求項１に記載の多結晶シリコンの純水洗浄方法。   Among the washing tanks in which the pH value of the pure water washing water is changed, at least one of the washing tanks provided in the preceding stage including the washing tank in which the pH value of the pure water washing water is initially 4 or more. 2. The method for pure water cleaning of polycrystalline silicon according to claim 1, wherein pure water cleaning water is extracted from the water and returned after the Fe concentration is lowered. 純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が２以上となった水洗槽乃至最初に純水洗浄水のｐＨ値が４以上となった水洗槽の少なくとも１の水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことを特徴とする請求項１または２に記載の多結晶シリコンの純水洗浄方法。   Among the washing tanks in which the pH value of the pure water washing water changes, the water washing tank in which the pH value of the pure water washing water first becomes 2 or more, or the water washing in which the pH value of the pure water washing water first becomes 4 or more. 3. The pure water cleaning method for polycrystalline silicon according to claim 1 or 2, wherein pure water cleaning water is extracted from at least one water cleaning tank of the tank and returned after the Fe concentration is lowered. 純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽、またはその前段に設けられた水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことを特徴とする請求項１または２に記載の多結晶シリコンの純水洗浄方法。   Among the washing tanks that change the pH value of the pure water washing water, the pure water washing water is first extracted from the washing tank in which the pH value of the pure water washing water is 4 or more, or the washing tank provided in the preceding stage. 3. The method for pure water cleaning of polycrystalline silicon according to claim 1 or 2, wherein the Fe concentration is lowered and then returned. 純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽から純水洗浄水を抜き取り、Ｆｅ濃度を低下させた後に戻すことを特徴とする請求項１または２に記載の多結晶シリコンの純水洗浄方法。   Among the washing tanks in which the pH value of the pure water washing water changes, the pure water washing water is first extracted from the washing tank in which the pH value of the pure water washing water is 4 or more, and returned after the Fe concentration is lowered. The pure water cleaning method for polycrystalline silicon according to claim 1 or 2. 最初に純水洗浄水のｐＨ値が４以上となった水洗槽の純水洗浄水が含有するＦｅ濃度に比べ、その後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が低いことを特徴とする請求項１または２に記載の多結晶シリコンの純水洗浄方法。   Compared to the Fe concentration contained in the pure water cleaning water in the water washing tank whose pH value was 4 or more at first, the Fe concentration contained in the pure water washing water in the subsequent water washing tank is lower. The method for cleaning pure water of polycrystalline silicon according to claim 1 or 2. 最初に純水洗浄水のｐＨ値が４以上となった水洗槽、およびその後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が５ｎｇ／ｍｌ以下であることを特徴とする請求項１または２に記載の多結晶シリコンの純水洗浄方法。   The Fe concentration contained in the pure water washing water of the water washing tank in which the pH value of the pure water washing water is initially 4 or more and the water washing tank provided in the subsequent stage is 5 ng / ml or less. Item 3. The pure water cleaning method for polycrystalline silicon according to Item 1 or 2. 前記水洗槽から抜き取られた純水洗浄水に含有されるＦｅ濃度をイオン交換系フィルターを用いて低下させることを特徴とする請求項１〜７のいずれかに記載の多結晶シリコンの純水洗浄方法。   The pure water washing of polycrystalline silicon according to any one of claims 1 to 7, wherein the Fe concentration contained in the pure water washing water extracted from the water washing tank is reduced using an ion exchange filter. Method. 塊状結晶を酸洗処理する酸洗処理槽と、酸洗処理された多結晶シリコンを純水洗浄水を用いて浸漬水洗する水洗槽を複数設け、前記水洗槽へ順次浸漬する純水洗浄装置であって、
前記水洗槽には、純水洗浄水に含有されるＦｅ濃度を低下させて連続的または断続的に循環させる純水循環再生手段を設置することを特徴とする多結晶シリコンの純水洗浄装置。 In a pure water cleaning apparatus that includes a pickling treatment tank for pickling bulk crystals, and a plurality of water washing tanks for immersing and washing pickled polycrystalline silicon using pure water washing water, and sequentially immersing in the washing tank. There,
A pure water cleaning apparatus for polycrystalline silicon, wherein pure water circulation regeneration means for reducing the concentration of Fe contained in pure water cleaning water and circulating continuously or intermittently is installed in the water washing tank. 前記純水循環再生手段が、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、純水洗浄水のｐＨ値が５未満である少なくとも１の水洗槽に設けられていることを特徴とする請求項９に記載の多結晶シリコンの純水洗浄装置。   The pure water circulation regeneration means is provided in at least one washing tank having a pH value of less than 5 in the washing tank in which the pH value of the pure water washing water changes. The pure water cleaning apparatus for polycrystalline silicon according to claim 9. 前記純水循環再生手段が、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が２以上となった水洗槽乃至最初に純水洗浄水のｐＨ値が４以上となった水洗槽の少なくとも１の水洗槽に設けられていることを特徴とする請求項９または１０に記載の多結晶シリコンの純水洗浄装置。   The pure water circulation and regeneration means is configured such that the pH value of the pure water cleaning water first becomes a pH value of 2 or more from the water cleaning tank in which the pH value of the pure water cleaning water changes to the pH value of the pure water cleaning water. 11. The pure water cleaning apparatus for polycrystalline silicon according to claim 9, wherein the cleaning apparatus is provided in at least one of the water cleaning tanks having a value of 4 or more. 前記純水循環再生手段が、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽、またはその前段に設けられた水洗槽に設けられていることを特徴とする請求項９または１０に記載の多結晶シリコンの純水洗浄装置。   The pure water circulation and regeneration means is a water washing tank in which the pH value of the pure water washing water is initially 4 or more among the washing tanks in which the pH value of the pure water washing water changes, or the water washing provided in the preceding stage. The pure water cleaning apparatus for polycrystalline silicon according to claim 9 or 10, wherein the apparatus is provided in a tank. 前記純水循環再生手段が、純水洗浄水のｐＨ値が変化する前記水洗槽のうち、最初に純水洗浄水のｐＨ値が４以上となった水洗槽に設けられていることを特徴とする請求項９または１０に記載の多結晶シリコンの純水洗浄装置。   The pure water circulation / regeneration means is provided in a water washing tank in which the pH value of the pure water washing water is initially 4 or more among the washing tanks in which the pH value of the pure water washing water is changed. The pure water cleaning apparatus for polycrystalline silicon according to claim 9 or 10. 最初に純水洗浄水のｐＨ値が４以上となった水洗槽の純水洗浄水が含有するＦｅ濃度に比べ、その後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が低いことを特徴とする請求項９または１０に記載の多結晶シリコンの純水洗浄装置。   Compared to the Fe concentration contained in the pure water cleaning water in the water washing tank whose pH value was 4 or more at first, the Fe concentration contained in the pure water washing water in the subsequent water washing tank is lower. The pure water cleaning apparatus for polycrystalline silicon according to claim 9 or 10. 最初に純水洗浄水のｐＨ値が４以上となった水洗槽、およびその後段に設けられた水洗槽の純水洗浄水が含有するＦｅ濃度が５ｎｇ／ｍｌ以下であることを特徴とする請求項９または１０に記載の多結晶シリコンの純水洗浄装置。   The Fe concentration contained in the pure water washing water of the water washing tank in which the pH value of the pure water washing water is initially 4 or more and the water washing tank provided in the subsequent stage is 5 ng / ml or less. Item 11. The pure water cleaning apparatus for polycrystalline silicon according to Item 9 or 10. 前記純水循環再生手段がイオン交換系フィルターを用いてＦｅ濃度を低下させる構造であることを特徴とする請求項９〜１５のいずれかに記載の多結晶シリコンの純水洗浄装置。
The pure water cleaning apparatus for polycrystalline silicon according to any one of claims 9 to 15, wherein the pure water circulation and regeneration means has a structure for reducing the Fe concentration by using an ion exchange filter.
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