JP6850982B2 - Vacuum drying method for crushed silicon - Google Patents
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- 238000001291 vacuum drying Methods 0.000 title claims description 18
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- 238000001035 drying Methods 0.000 claims description 56
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Description
本発明は、高純度の多結晶シリコンの破砕片又は塊状片（以下、単にシリコン破砕片という。）を洗浄した後に真空乾燥する方法に関するものである。 The present invention relates to a method for cleaning crushed pieces or lumpy pieces of high-purity polycrystalline silicon (hereinafter, simply referred to as crushed silicon pieces) and then vacuum-drying them.
高純度の多結晶シリコンは、チョクラルスキー法（以下、ＣＺ法という。）で製造される単結晶シリコンの原料に使用される場合、坩堝に充填する作業を円滑にするために、通常１００ｍｍ以下の破砕片に加工される。この多結晶シリコンから単結晶シリコンをＣＺ法等により製造する場合、不純物の取り込みを極力低く抑える観点から、多結晶シリコンには極めて高い純度が要求される。 When high-purity polycrystalline silicon is used as a raw material for single-crystal silicon produced by the Czochralski method (hereinafter referred to as the CZ method), it is usually 100 mm or less in order to facilitate the filling operation in the crucible. It is processed into crushed pieces. When single crystal silicon is produced from this polycrystalline silicon by the CZ method or the like, extremely high purity is required for the polycrystalline silicon from the viewpoint of suppressing the uptake of impurities as low as possible.
このため、通常は多結晶シリコンの破砕時や破砕後にその表面に付着した金属などの汚染を除去するために、多結晶シリコンを酸液により洗浄して、金属を含む表面不純物を多結晶シリコンから除去している。この洗浄工程及び洗浄工程以降の乾燥工程では、乾燥した不活性ガス等を流す温風乾燥又は真空乾燥が行われる。温風乾燥ではシリコン表面の水分に熱を与え、気化した水分を排出しているが、シリコン表面に境膜を形成して乾燥効率が低下するという欠点がある。一方、真空乾燥では、シリコン表面に境膜を形成しにくく、平衡蒸気圧が系内圧力を上回る限り水分は気化し続け、真空ポンプにより排出されるが、気相の伝熱性が悪く、気化熱を与える工夫が必要になるという欠点がある。そこで特許文献１には、合成樹脂製の容器に収容した多数のシリコン破砕片が洗浄後、乾燥室内に配置されて、７０〜７５℃の温度に保持しながら、真空乾燥工程と乾燥した窒素ガスを導入して真空圧力より高いパージ圧力に保持するパージ工程とを交互に繰り返すことにより、上記欠点を克服し、シリコンの乾燥を促進できたことが示されている。シリコンを真空乾燥する場合、シリコン破砕片が新たに金属で汚染されないように、シリコンと金属との接触を避けるために、容器として、非金属製の保持部材が用いられる。 For this reason, in order to remove contamination such as metals adhering to the surface of polycrystalline silicon at the time of crushing or after crushing, polycrystalline silicon is usually washed with an acid solution to remove surface impurities containing metals from polycrystalline silicon. It is being removed. In the washing step and the drying step after the washing step, warm air drying or vacuum drying in which a dried inert gas or the like is passed is performed. In warm air drying, heat is applied to the moisture on the silicon surface and vaporized moisture is discharged, but there is a drawback that a boundary film is formed on the silicon surface and the drying efficiency is lowered. On the other hand, in vacuum drying, it is difficult to form a boundary film on the silicon surface, and as long as the equilibrium vapor pressure exceeds the internal pressure, moisture continues to vaporize and is discharged by a vacuum pump. There is a drawback that it is necessary to devise a way to give. Therefore, in Patent Document 1, a large number of crushed silicon pieces contained in a container made of synthetic resin are washed and then placed in a drying chamber, and while being maintained at a temperature of 70 to 75 ° C., a vacuum drying step and dried nitrogen gas are provided. It has been shown that the above-mentioned drawbacks could be overcome and the drying of the silicon could be promoted by alternately repeating the purging step of introducing the above-mentioned and holding the purging pressure higher than the vacuum pressure. When vacuum-drying silicon, a non-metal holding member is used as the container to prevent contact between the silicon and the metal so that the silicon debris is not newly contaminated with metal.
上述の多結晶シリコンの高純度化への要求が高まるにつれて、多結晶シリコンの表面に
付着する有機物に起因した炭素汚染が問題となり、熱処理などによってその汚染を除去し、表面炭素濃度を２０ｐｐｂｗ未満に低減する方法が開示されている（例えば、特許文献２及び特許文献３参照。）。
As the above-mentioned demand for high purification of polycrystalline silicon increases, carbon contamination caused by organic substances adhering to the surface of polycrystalline silicon becomes a problem, and the contamination is removed by heat treatment or the like to reduce the surface carbon concentration to less than 20 ppbw. Methods for reduction are disclosed (see, for example, Patent Document 2 and Patent Document 3).
特許文献２では、多結晶シリコンの表面における炭素による汚染を除去するための改善が提案されている。具体的には、特許文献２には、多結晶シリコン破砕片を酸素を排除した雰囲気中において、不活性ガス（例えば、窒素やアルゴンガス）によるパージを３５０〜６００℃の温度下で、一定時間熱処理を行う方法が示されている。この方法では、熱処理後には、不活性ガスをパージしながらほぼ室温まで冷却することで、例えば接触により表面に付着したポリエチレンやポリプロピレンの除去が実質的に可能とされている。これらのポリエチレンやポリプロピレンなどのいわゆるポリマーは、有機化合物であり、多結晶シリコン製品の表面不純物としては、炭素不純物として扱われるが、酸素を排除した雰囲気での加熱処理により、表面の炭素濃度が低減された多結晶シリコンが得られるとされている。 Patent Document 2 proposes an improvement for removing carbon contamination on the surface of polycrystalline silicon. Specifically, Patent Document 2 states that a polycrystalline silicon fragment is purged with an inert gas (for example, nitrogen or argon gas) in an oxygen-free atmosphere at a temperature of 350 to 600 ° C. for a certain period of time. A method of performing the heat treatment is shown. In this method, after the heat treatment, the inert gas is purged and cooled to about room temperature, so that polyethylene or polypropylene adhering to the surface by contact, for example, can be substantially removed. These so-called polymers such as polyethylene and polypropylene are organic compounds and are treated as carbon impurities as surface impurities in polycrystalline silicon products, but the carbon concentration on the surface is reduced by heat treatment in an oxygen-free atmosphere. It is said that the obtained polycrystalline silicon can be obtained.
また特許文献３では、特許文献２と同様に多結晶シリコンの表面洗浄化方法として、多結晶シリコンを不活性ガスを流しながら、その雰囲気中で１８０〜３５０℃の範囲で熱処理することで、多結晶シリコンの表面に付着した炭素による汚染を低コストで効果的に除去することができるとされている。特許文献３には、このような多結晶シリコン表面の炭素不純物は、金属汚染を防止するために合成樹脂コーティングされた治具や部品、プラスチック製の手袋でシリコン表面を触るなどのシリコンとの接触で生じるおそれがあることが記載されている。 Further, in Patent Document 3, as in Patent Document 2, as a method for cleaning the surface of polycrystalline silicon, the polycrystalline silicon is heat-treated in the atmosphere in the range of 180 to 350 ° C. while flowing an inert gas. It is said that carbon contamination adhering to the surface of crystalline silicon can be effectively removed at low cost. According to Patent Document 3, such carbon impurities on the surface of polycrystalline silicon come into contact with silicon, such as by touching the silicon surface with a jig or part coated with synthetic resin to prevent metal contamination, or with plastic gloves. It is stated that it may occur in.
特許文献１に示されるように、シリコン破砕片を合成樹脂製洗浄籠に収容して７０〜７５℃で真空乾燥する場合、金属汚染を抑制できるが、有機物汚染の低減について考慮されていない。特許文献２及び特許文献３に示されているのはシリコンの表面炭素汚染を除去する方法であり、炭素汚染の原因については、有機ポリマー又はプラスチックとの機械的接触で完全に回避することはできないとしている。 As shown in Patent Document 1, when the silicon crushed pieces are housed in a synthetic resin washing basket and vacuum dried at 70 to 75 ° C., metal contamination can be suppressed, but reduction of organic matter contamination is not considered. Patent Document 2 and Patent Document 3 show a method for removing surface carbon contamination of silicon, and the cause of carbon contamination cannot be completely avoided by mechanical contact with an organic polymer or plastic. It is supposed to be.
本発明の目的は、シリコン破砕片を保持部材に収容して保持部材の耐熱温度未満の温度にて真空乾燥する場合に、乾燥時の保持部材から発生する有機性ガスを低減してシリコン破砕片の表面への炭素による汚染を低減するシリコン破砕片の真空乾燥方法を提供することにある。 An object of the present invention is to reduce the amount of organic gas generated from the holding member during drying when the silicon crushed piece is housed in the holding member and vacuum dried at a temperature lower than the heat resistant temperature of the holding member to reduce the silicon crushed piece. It is an object of the present invention to provide a vacuum drying method for silicon debris, which reduces carbon contamination of the surface of silicon.
本発明者らは、炭素汚染源を排除するべく、酸洗浄以降の工程において、多結晶シリコンを破砕した後の有機物の付着する工程を鋭意調査した結果、意外にも、酸洗浄後の水分を蒸発させるために加熱する乾燥工程において保持部材等を構成する樹脂材料からの有機性ガス発生が顕著であることを確認し、ポリエチレン等の合成樹脂製保持部材を用いた場合、真空乾燥中に発生した樹脂添加剤等の有機性ガスがシリコン破砕片表面に付着することが炭素汚染を生じる極めて大きな要因であることを突き止めた。更に、本発明者らは、乾燥工程において樹脂材料からの有害な有機性ガスの発生を抑制することで、シリコン破砕片の表面炭素汚染を低減できることを確認し、本発明に到達した。 As a result of diligent investigation of the process of adhering organic substances after crushing the polycrystalline silicon in the process after the acid cleaning in order to eliminate the carbon contamination source, the present inventors unexpectedly evaporate the water content after the acid cleaning. It was confirmed that the generation of organic gas from the resin material constituting the holding member etc. was remarkable in the drying step of heating to make it, and when a synthetic resin holding member such as polyethylene was used, it was generated during vacuum drying. It was found that the adhesion of organic gas such as resin additives to the surface of crushed silicon is an extremely large factor that causes carbon contamination. Furthermore, the present inventors have confirmed that the surface carbon contamination of silicon crushed pieces can be reduced by suppressing the generation of harmful organic gas from the resin material in the drying step, and arrived at the present invention.
本発明の第１の観点は、保持部材に収容して洗浄した後のシリコン破砕片を乾燥室内に収容し、前記乾燥室内を減圧して乾燥することにより前記シリコン破砕片を乾燥する方法において、前記保持部材が合成樹脂製保持部材であって、上記乾燥の温度が５０℃以下であり、上記乾燥の時間が５時間以上であることを特徴とするシリコン破砕片の真空乾燥方法である。 A first aspect of the present invention is a method in which a silicon crushed piece after being housed in a holding member and washed is housed in a drying chamber, and the silicon crushed piece is dried by depressurizing and drying the drying chamber. wherein a holding member is made of synthetic resin holding member, the temperature of the drying Ri der 50 ° C. or less, is in a vacuum drying method of a silicon fragments, characterized in der Rukoto time more than 5 hours of the drying ..
本発明の第１の観点のシリコン破砕片の真空乾燥方法では、保持部材がポリエチレン等の合成樹脂製であっても、乾燥温度を５０℃以下に設定することにより、乾燥中に、合成樹脂製保持部材から樹脂添加剤等の有機性ガスの発生を抑えるため、シリコン破砕片の炭素による汚染を低減することができる。 In the vacuum drying method of crushed silicon pieces according to the first aspect of the present invention, even if the holding member is made of synthetic resin such as polyethylene, by setting the drying temperature to 50 ° C. or lower, it is made of synthetic resin during drying. Since the generation of organic gas such as a resin additive is suppressed from the holding member, contamination of silicon crushed pieces by carbon can be reduced.
＜第１の実施形態＞
先ず本発明を実施するための第１の実施形態を図面に基づいて説明する。図１に示すように、保持部材１０の中には多数のシリコン破砕片１１が収容される。これらのシリコン破砕片１１は、シーメンス法等により得られた柱状の多結晶シリコンを破砕して得られ、１００ｍｍ以下のサイズを有する。この実施の形態で用いるかご状の保持部材１０は、上部を開放したポリエチレン製の直方体の箱状容器である。保持部材１０の貫通孔１０ａの形状とサイズは、収容したシリコン破砕片が貫通孔から抜け出ないように、シリコン破砕片の形状とサイズに合わせて任意に設定される。これらのシリコン破砕片１１を保持部材１０に所定量収容した後、フッ化水素酸と硝酸との混合液のような酸液に保持部材１０を浸漬させることで、酸液が貫通孔１０ａから保持部材内に浸入してシリコン破砕片と接触する。これにより、シリコン破砕片の表面に付着した異物や酸化膜が除去される。
<First Embodiment>
First, a first embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, a large number of silicon crushed
この実施形態の特徴ある構成は、純水でシリコン破砕片が洗浄された後の乾燥方法にある。シリコン破砕片が純水で洗浄され、保持部材１０内の純水が流下して水切りがなされた後、シリコン破砕片を収容した保持部材１０は、図２に示すように、乾燥機の乾燥室２０内に配置される。この実施の形態では、乾燥室２０内には複数の棚２１が設けられ、それぞれの棚２１の上にシリコン破砕片を収容した複数の保持部材１０が配置される。乾燥室２０には図示しない配管を介して真空ポンプが接続される。また乾燥室２０の周囲に温水浴が設けられ、乾燥室内を周囲から加熱することができるようになっている。
A characteristic configuration of this embodiment is a drying method after the silicon debris has been washed with pure water. After the silicon crushed pieces were washed with pure water and the pure water in the
第１の実施形態のシリコン破砕片の真空乾燥方法では、ポリエチレン製の保持部材１０に収容されたシリコン破砕片１１が、上述したように、保持部材１０内の純水の水切りを行った後、乾燥室２０の棚２１の上に配置される。乾燥室２０を密閉状態にした後、温水浴を作動させ、５０℃に維持する。乾燥機の真空ポンプを作動させ、乾燥室２０内の圧力を減圧し、この圧力で一定時間保持する。到達圧力としては、水の平衡蒸気圧以下であることが必要で、５０℃では１０ｋＰａ以下が好ましい。ただし、１ｋＰａ程度の残圧がある方が、熱伝導に寄与して望ましい場合がある。また保持時間は５時間以上である。この保持時間は、乾燥室内真空圧力及び温度に依存する。
In the method of vacuum-drying the silicon crushed pieces of the first embodiment, the silicon crushed
乾燥室内の温度を５０℃以下にするのは、ポリエチレン製保持部材から発生する樹脂添加剤等の有機性ガス量を減少させるためである。一般論として、樹脂材料からのガス発生量Ｖと温度Ｔ（絶対温度）には、ｌｏｇＶ＝−Ｃ１／Ｔ＋Ｃ２（Ｃ１、Ｃ２は材料固有の係数）という相関があるとされており、非特許文献１によれば、５０℃でのガスの発生量は７０℃の１／１０程度まで低減できると考えられる。好ましい乾燥室内の乾燥温度は３０℃以上５０℃以下である。好ましい乾燥温度の下限値を３０℃にするのは、乾燥速度はおよそ水の平衡蒸気圧に比例すると考えられ、３０℃では５０℃の１／３となり、これ以上温度を低下させた場合に乾燥に要する時間が実用的とは言えなくなるためである。ただし、炭素汚染低減という観点からは、温度は低い方が望ましく、３０℃以下で乾燥した場合に本発明の効果が得られなくなるわけではない。 The temperature in the drying chamber is set to 50 ° C. or lower in order to reduce the amount of organic gas such as resin additives generated from the polyethylene holding member. As a general theory, it is said that there is a correlation between the amount of gas generated from the resin material V and the temperature T (absolute temperature) as logV = -C1 / T + C2 (C1 and C2 are coefficient peculiar to the material). According to No. 1, it is considered that the amount of gas generated at 50 ° C. can be reduced to about 1/10 of 70 ° C. The drying temperature in the drying chamber is preferably 30 ° C. or higher and 50 ° C. or lower. The reason why the lower limit of the preferable drying temperature is set to 30 ° C. is that the drying rate is considered to be approximately proportional to the equilibrium vapor pressure of water. This is because the time required for this is not practical. However, from the viewpoint of reducing carbon pollution, it is desirable that the temperature is low, and the effect of the present invention is not lost when the product is dried at 30 ° C. or lower.
＜第２の実施形態＞
次に本発明を実施するための第２の実施形態のシリコン破砕片の真空乾燥方法について説明する。この実施の形態のシリコン破砕片の乾燥方法では、石英製保持部材又は保持部材表面をシリカコーティングした合成樹脂製かごを保持部材に用いる。これは、有機性ガスを発生する表面をなくすためであり、石英製部材を用いた場合には加熱温度によらず有機性ガスの発生は原理的には全く生じない。しかしながら、石英は樹脂と比較して高価な材質である上に、脆性材料であり取り扱いに多大な注意が必要になる。シリカコーティングは、現実的には完全に樹脂表面を覆い切ることは難しく、有機性ガスの多少の透過性も残ることから、石英部材を用いる場合よりは汚染防止の効果は落ちるが、簡便で実用的である。シリカコーティングされる合成樹脂は特に限定されず、ポリエチレン、ポリプロピレン、ポリカーボネート等が例示される。シリカコーティングの手法としては、溶射などが知られているが、樹脂材料へのシリカ溶射は困難であり、実用的にはポリシラザンを使用したコーティングが有用である。
<Second embodiment>
Next, a method for vacuum-drying the crushed silicon piece of the second embodiment for carrying out the present invention will be described. In the method for drying the crushed silicon pieces of this embodiment, a quartz holding member or a synthetic resin basket whose surface is silica-coated on the surface of the holding member is used as the holding member. This is to eliminate the surface that generates organic gas, and when a quartz member is used, organic gas is not generated at all regardless of the heating temperature in principle. However, quartz is a material that is more expensive than resin and is a brittle material, so great care must be taken in handling it. In reality, it is difficult for silica coating to completely cover the resin surface, and some organic gas permeability remains. Therefore, the effect of preventing contamination is lower than when using a quartz member, but it is simple and practical. Is the target. The synthetic resin coated with silica is not particularly limited, and polyethylene, polypropylene, polycarbonate and the like are exemplified. As a method of silica coating, thermal spraying or the like is known, but it is difficult to spray silica on a resin material, and a coating using polysilazane is practically useful.
第２の実施形態のシリコン破砕片の真空乾燥方法では、石英製保持部材又は保持部材表面をシリカコーティングした合成樹脂製保持部材に収容されたシリコン破砕片が、第１の実施形態と同様に、乾燥室内に配置され、乾燥室を密閉状態にして、真空乾燥される。樹脂材料にシリカコーティングした場合には、乾燥室内の温度を樹脂の耐熱温度より低い温度に保持する。それ以外は第１の実施形態と同様にシリコン破砕片を真空乾燥する。上記条件により、乾燥室内を減圧状態にすると、第１の実施形態で述べたように、シリコン破砕片表面に付着した水分が蒸発しやすくなる。これにより、シリコン破砕片から十分に水分を除去できるとともに、保持部材からの樹脂添加剤等の有機性ガスの発生がなく、シリコン破砕片の表面への汚染をより一層低減することができる。 In the vacuum drying method of the silicon crushed piece of the second embodiment, the silicon crushed piece housed in the quartz holding member or the synthetic resin holding member whose surface is coated with silica is similar to that of the first embodiment. It is placed in a drying chamber, and the drying chamber is sealed and vacuum dried. When the resin material is coated with silica, the temperature in the drying chamber is kept lower than the heat resistant temperature of the resin. Other than that, the silicon crushed pieces are vacuum dried in the same manner as in the first embodiment. When the drying chamber is depressurized under the above conditions, as described in the first embodiment, the moisture adhering to the surface of the crushed silicon pieces tends to evaporate. As a result, water can be sufficiently removed from the crushed silicon pieces, no organic gas such as a resin additive is generated from the holding member, and contamination of the surface of the crushed silicon pieces can be further reduced.
＜第３の実施形態＞
次に本発明を実施するための第３の実施形態のシリコン破砕片の真空乾燥方法について説明する。この実施の形態のシリコン破砕片の乾燥方法では、ポリプロピレン、ポリカーボネート、シリコーン合成樹脂、エチレン・四フッ化エチレン共重合体、ＰＥＥＫ、ＰＴＦＥ、ＰＦＡ、ＦＥＰ及びＰＶＤＦからなる群より選ばれた１種又は２種以上の合成樹脂からなる保持部材を用いる。そしてシリコン破砕片の乾燥温度を樹脂の種類に応じて適切に定めるが、例えばポリプロピレンでは７０℃以下が望ましい。それ以外は、第１の実施形態と同様にシリコン破砕片を真空乾燥する。
<Third embodiment>
Next, a method for vacuum-drying the crushed silicon pieces of the third embodiment for carrying out the present invention will be described. In the method for drying the shattered silicon of this embodiment, one selected from the group consisting of polypropylene, polycarbonate, silicone synthetic resin, ethylene / tetrafluoroethylene copolymer, PEEK, PTFE, PFA, FEP and PVDF or A holding member made of two or more kinds of synthetic resins is used. The drying temperature of the crushed silicon pieces is appropriately determined according to the type of resin, but for polypropylene, for example, 70 ° C. or lower is desirable. Other than that, the silicon crushed pieces are vacuum dried in the same manner as in the first embodiment.
第３の実施形態のシリコン破砕片の真空乾燥方法では、ポリプロピレン、ポリカーボネート、シリコーン合成樹脂、エチレン・四フッ化エチレン共重合体、ＰＥＥＫ、ＰＴＦＥ、ＰＦＡ、ＦＥＰ及びＰＶＤＦからなる群より選ばれた１種又は２種以上の合成樹脂からなる保持部材に収容されたシリコン破砕片が、第１の実施形態と同様に、乾燥室内に配置され、乾燥室を密閉状態にして、真空乾燥される。第３の実施形態では、乾燥室内の温度を樹脂の種類に応じて適切な温度以下に保持する。それ以外は第１の実施形態と同様にシリコン破砕片を真空乾燥する。上記条件により、乾燥室内を減圧状態にすると、第１の実施形態で述べたように、シリコン破砕片表面に付着した水分が蒸発しやすくなる。これにより、シリコン破砕片表面から十分に水分を除去できるとともに、保持部材からの樹脂添加剤等の有機性ガスの発生を抑制し、シリコン破砕片の表面への汚染をより一層低減することができる。 In the vacuum drying method of the silicon crushed pieces of the third embodiment, one selected from the group consisting of polypropylene, polycarbonate, silicone synthetic resin, ethylene / tetrafluoroethylene copolymer, PEEK, PTFE, PFA, FEP and PVDF1 Silicon crushed pieces contained in a holding member made of seeds or two or more kinds of synthetic resins are arranged in a drying chamber, and the drying chamber is sealed and vacuum-dried, as in the first embodiment. In the third embodiment, the temperature in the drying chamber is maintained below an appropriate temperature depending on the type of resin. Other than that, the silicon crushed pieces are vacuum dried in the same manner as in the first embodiment. When the drying chamber is depressurized under the above conditions, as described in the first embodiment, the moisture adhering to the surface of the crushed silicon pieces tends to evaporate. As a result, it is possible to sufficiently remove water from the surface of the crushed silicon piece, suppress the generation of organic gas such as a resin additive from the holding member, and further reduce the contamination of the surface of the crushed silicon piece. ..
＜第４の実施形態＞
第１の実施の形態及び第３の実施の形態において、合成樹脂製保持部材を乾燥温度以上の温度であって、前記合成樹脂製保持部材の耐熱温度未満の温度で、予めベーキング処理することが好ましい。ここで「耐熱温度」とは、樹脂の物理的性状を保持できる上限の温度（例えば樹脂材料に軟化・変形が生じる温度、或いは樹脂材料に熱分解が生じる温度等）である。具体的には、耐熱温度とは、物理的耐熱性の観点では軟化温度やガラス転移点等の温度であり、化学的耐熱性の観点では、加熱時の重量減少等が生じる温度である。ベーキング処理の方法としては、第１、第２、第３の実施の形態と同様の乾燥室内に合成樹脂製保持部材をシリコン破砕片を収容しない状態で設置し、窒素等不活性ガス雰囲気下で乾燥室内の温度を設置している合成樹脂の耐熱温度未満に保持しながら、１０分以上保持する。ベーキング処理した保持部材にシリコン破砕片が収容されるのは、シリコンの破砕後、洗浄工程の前であることが好ましい。このようなベーキング処理をすることにより、真空乾燥中に発生する樹脂添加剤等の有機性ガスの発生を更に抑制し、シリコン破砕片の炭素による汚染をより一層低減することができる。
<Fourth Embodiment>
In the first embodiment and the third embodiment, the synthetic resin holding member may be pre-baked at a temperature equal to or higher than the drying temperature and lower than the heat resistant temperature of the synthetic resin holding member. preferable. Here, the "heat-resistant temperature" is an upper limit temperature at which the physical properties of the resin can be maintained (for example, a temperature at which the resin material is softened or deformed, a temperature at which the resin material is thermally decomposed, or the like). Specifically, the heat-resistant temperature is a temperature such as a softening temperature or a glass transition point from the viewpoint of physical heat resistance, and is a temperature at which weight loss or the like occurs during heating from the viewpoint of chemical heat resistance. As a method of baking treatment, a synthetic resin holding member is installed in the same drying chamber as in the first, second, and third embodiments in a state where silicon debris is not contained, and under an atmosphere of an inert gas such as nitrogen. The temperature in the drying chamber is kept below the heat-resistant temperature of the installed synthetic resin for 10 minutes or more. It is preferable that the silicon crushed pieces are contained in the baking-treated holding member after the silicon is crushed and before the cleaning step. By performing such a baking treatment, it is possible to further suppress the generation of organic gas such as a resin additive generated during vacuum drying, and further reduce the contamination of silicon crushed pieces with carbon.
次に本発明の実施例を比較例とともに詳しく説明する。 Next, examples of the present invention will be described in detail together with comparative examples.
＜比較例１＞
保持部材として底面がたて２０ｃｍ、よこ２０ｃｍで高さが２５ｃｍのポリエチレン製のカゴ（すべての側板部と底板部に縦方向５ｍｍ、横方向５ｍｍの角孔の貫通孔が格子状に配列される）を用意し、長辺の長さが１０〜３０ｍｍの高純度シリコン破砕片を約５ｋｇ投入し、フッ酸、硝酸によるエッチングと純水による洗浄を行った後に内寸約３０ｃｍ角のＳＵＳ３０４製の真空乾燥機にて乾燥を行った。乾燥温度は、この真空乾燥機自体を温水に浸漬し、温水の温度を調整することで調整した。真空度はおよそ１ｋＰａまで到達するが、１ｋＰａ程度で保持した場合、伝熱性が悪く乾燥が進まないため、１時間毎に窒素ガスを投入して約２５ｋＰａで３０分間保持することで、内部のシリコン破砕片まで熱が伝わるようにした。温水温度を７０℃に設定し、５．５時間後に乾燥機から取り出すと、シリコン破砕片は十分に乾燥された状態であった。
<Comparative example 1>
As a holding member, a polyethylene basket with a bottom surface of 20 cm, a width of 20 cm, and a height of 25 cm (through holes of 5 mm in the vertical direction and 5 mm in the horizontal direction are arranged in a grid pattern on all side plates and bottom plates. ), And about 5 kg of high-purity silicon crushed pieces with a long side length of 10 to 30 mm are put in, etched with hydrofluoric acid and nitric acid, and washed with pure water. It was dried in a vacuum dryer. The drying temperature was adjusted by immersing the vacuum dryer itself in hot water and adjusting the temperature of the hot water. The degree of vacuum reaches about 1 kPa, but if it is held at about 1 kPa, the heat transfer property is poor and drying does not proceed. Therefore, by adding nitrogen gas every hour and holding it at about 25 kPa for 30 minutes, the silicon inside Heat was transferred to the crushed pieces. When the hot water temperature was set to 70 ° C. and the silicon crushed pieces were taken out from the dryer after 5.5 hours, the silicon crushed pieces were in a sufficiently dried state.
＜実施例１＞
温水温度を５０℃に設定し、比較例１と同様に乾燥を行った。５．５時間乾燥を行ったところ、乾燥が不十分であり、１０時間後に乾燥機から取り出すと、シリコン破砕片は十分に乾燥された状態であった。
<Example 1>
The hot water temperature was set to 50 ° C., and drying was carried out in the same manner as in Comparative Example 1. When it was dried for 5.5 hours, the drying was insufficient, and when it was taken out from the dryer after 10 hours, the silicon crushed pieces were in a sufficiently dried state.
＜実施例２＞
温水温度を３０℃に設定し、実施例１と同様に１０時間乾燥を行ったところ、乾燥が不十分であり、１５．５時間後に乾燥機から取り出すと、シリコン破砕片は十分に乾燥された状態であった。
<Example 2>
When the hot water temperature was set to 30 ° C. and the drying was carried out for 10 hours in the same manner as in Example 1, the drying was insufficient, and when it was taken out from the dryer after 15.5 hours, the silicon debris was sufficiently dried. It was in a state.
上記比較例１、実施例１、２で乾燥されたシリコン破砕片を試料として、３００℃に加熱燃焼させ、この燃焼により発生するＣＯ及びＣＯ2についてＩＲ（Infrared spectroscopic analysis）測定を行って試料に含まれる炭素濃度を分析した。表１に示すように、実施例１、２で得られた試料は、比較例１で得られた試料に対して、表面炭素濃度が大幅に低下していることを確認できた。 Using the silicon crushed pieces dried in Comparative Examples 1 and 1 and 2 as a sample, they are heated and burned at 300 ° C., and IR (Infrared spectroscopic analysis) measurement is performed on CO and CO 2 generated by this combustion to prepare a sample. The carbon concentration contained was analyzed. As shown in Table 1, it was confirmed that the surface carbon concentration of the samples obtained in Examples 1 and 2 was significantly lower than that of the samples obtained in Comparative Example 1.
＜比較例２、実施例３〜９＞
次に、ポリエチレン、ポリプロピレン、シリコーン樹脂、ポリカーボネート、ＥＴＦＥ、ＰＥＥＫ、ＰＴＦＥ、市販のポリシラザンコーティング剤にてシリカコーティングしたシリカコートポリエチレンを材質とする８種類の板（寸法２０ｃｍ×２０ｃｍ×２ｍｍ）を用意した。ポリエチレンの板を比較例２とし、ポリプロピレンの板を実施例３とし、シリコーン合成樹脂の板を実施例４とし、ポリカーボネートの板を実施例５とし、ＥＴＦＥの板を実施例６とし、ＰＥＥＫの板を実施例７とし、ＰＴＦＥの板を実施例８とし、シリカコートポリエチレンの板を実施例９とした。
<Comparative Example 2, Examples 3 to 9>
Next, eight types of plates (
これら８種類の板の上に、目開き７ｍｍと３ｍｍの篩で分級し、それらの中間から回収して水洗したシリコン破砕片を濡れたままの状態で、それぞれ約１０ｇずつ載せて、それぞれ異なる真空乾燥機に投入した。７０℃の温水に全ての真空乾燥機を浸漬させて２時間真空引き（到達圧力約１ｋＰａ）したところ、水分は無くなっていた。得られたシリコン破砕片を上記実施例１、２、比較例１と同じ方法で１回目の分析試験を行った。 On these eight types of plates, about 10 g of each of the silicon crushed pieces collected from the middle of them and washed with water, which was classified by a sieve with a mesh size of 7 mm and 3 mm, was placed in a wet state, and each vacuum was different. It was put into a dryer. When all the vacuum dryers were immersed in warm water at 70 ° C. and evacuated for 2 hours (reaching pressure of about 1 kPa), the water content was lost. The obtained crushed silicon pieces were subjected to the first analytical test in the same manner as in Examples 1 and 2 and Comparative Example 1.
続いて、８種類の板をそのまま使用して、１回目の分析試験で使用したシリコン破砕片と同一ロットから新たに採取したシリコン破砕片を、８種類の板の上にそれぞれ載せて、上記と同じ分析試験を２回実施した（２回目及び３回目の試験を実施した）。その後、ポリエチレン、シリカコートポリエチレン以外の６種類の板を、シリコン破砕片を載せない状態でまとめて、同じ真空乾燥機を用いて８０℃の温水に浸漬させて１時間窒素ガス雰囲気にて真空引きせずに保持することで、ベーキング処理を行った。続いて、ポリエチレン、シリカコートポリエチレン以外の６種類の板の上に、上記と同じく目開き７ｍｍと３ｍｍの篩で回収して水洗したシリコン破砕片を約１０ｇずつ載せて、それぞれ異なる真空乾燥機に投入し、７０℃の温水に真空乾燥機を浸漬させて２時間真空引きし、得られたシリコン破砕片の４回目の分析試験を行った。 Subsequently, using the eight types of plates as they are, the silicon crushed pieces newly collected from the same lot as the silicon crushed pieces used in the first analysis test were placed on the eight types of plates, respectively, as described above. The same analytical test was performed twice (second and third tests were performed). After that, 6 types of plates other than polyethylene and silica-coated polyethylene were put together without silicon crushed pieces, immersed in warm water at 80 ° C. using the same vacuum dryer, and evacuated in a nitrogen gas atmosphere for 1 hour. The baking process was performed by holding the mixture without using it. Next, on 6 types of plates other than polyethylene and silica-coated polyethylene, about 10 g of crushed silicon collected and washed with water using a sieve with a mesh size of 7 mm and 3 mm as described above was placed in different vacuum dryers. The material was charged, and the vacuum dryer was immersed in warm water at 70 ° C. and evacuated for 2 hours, and the obtained silicon crushed pieces were subjected to the fourth analytical test.
上記２回目、３回目及び４回目の試験の結果、表２に示すように材質によって表面炭素量の相違が確認された。比較例２、実施例３〜９に示す試験で用いたシリコン破砕片は実施例１、２、比較例１に示す試験で用いたシリコン破砕片に比べ、長辺が短いため、比表面積が大きく、表面炭素濃度が高めであった。表２に示す結果より、ポリエチレンとその他の材質を板として用いた場合の差異がはっきりと確認できた。１回目の試験では、ＰＴＦＥ、シリカコートポリエチレン以外について、樹脂添加剤等有機物が残留していたため、ポリエチレンとの表面炭素濃度の差異が小さかったが、２回目以降回数を重ねるごとに表面炭素濃度が低下していき、３回目の試験で表面炭素濃度の高かったポリプロピレン、シリコーン合成樹脂、ＰＥＥＫについて、４回目の試験で表面炭素濃度が大きく低減した。なお、上記材質を２種類以上組み合わせたものを用いた場合も同様の効果が得られる。 As a result of the second, third and fourth tests, it was confirmed that the surface carbon content was different depending on the material as shown in Table 2. The silicon crushed pieces used in the tests shown in Comparative Examples 2 and 3 to 9 have a shorter long side than the silicon crushed pieces used in the tests shown in Examples 1 and 2, and therefore have a large specific surface area. , The surface carbon concentration was high. From the results shown in Table 2, the difference when polyethylene and other materials were used as the plate was clearly confirmed. In the first test, organic substances such as resin additives remained except for PTFE and silica-coated polyethylene, so the difference in surface carbon concentration from polyethylene was small, but the surface carbon concentration increased as the number of times increased from the second time onward. The surface carbon concentration of polypropylene, silicone synthetic resin, and PEEK, which had high surface carbon concentrations in the third test, decreased significantly in the fourth test. The same effect can be obtained when a combination of two or more of the above materials is used.
本発明のシリコン破砕片の真空乾燥方法は、ＣＺ法で製造される単結晶シリコンの原料である高純度の多結晶シリコン破砕片を洗浄後、乾燥するのに利用することができる。 The method for vacuum drying silicon crushed pieces of the present invention can be used to wash and then dry high-purity polycrystalline silicon crushed pieces, which are raw materials for single crystal silicon produced by the CZ method.
１０ 保持部材
１１ シリコン破砕片
２０ 乾燥室
２１ 棚
10 Retaining
Claims (1)
前記保持部材が合成樹脂製保持部材であって、
前記乾燥の温度が５０℃以下であり、前記乾燥の時間が５時間以上である
ことを特徴とするシリコン破砕片の真空乾燥方法。 In a method in which a silicon crushed piece after being housed in a holding member and washed is housed in a drying chamber, and the silicon crushed piece is dried by reducing the pressure in the drying chamber and drying the silicon crushed piece.
The holding member is a synthetic resin holding member.
The temperature of the drying Ri der 50 ° C. or less, vacuum drying method of a silicon fragments, characterized in that the drying time is Ru der least 5 hours.
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