JP2016222470A - Polycrystal silicon piece - Google Patents
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本発明は多結晶シリコン片の製造技術に関する。 The present invention relates to a technique for manufacturing a polycrystalline silicon piece.
ＣＺ法による単結晶シリコンの製造原料となる多結晶シリコン塊は、シーメンス法により合成された多結晶シリコンロッドを反応炉から取り出した後に、それを２０〜８０ｍｍ程度のサイズに粉砕して得られる。粉砕作業後には、表面を清浄化するために、フッ硝酸等による薬液エッチングを行って製品化される。 A polycrystalline silicon lump as a raw material for producing single crystal silicon by the CZ method is obtained by removing a polycrystalline silicon rod synthesized by the Siemens method from a reaction furnace and then pulverizing it to a size of about 20 to 80 mm. After the pulverization operation, the product is manufactured by performing chemical etching with hydrofluoric acid or the like in order to clean the surface.
多結晶シリコン塊にハンマーで衝撃破壊力を加えて粉砕する際、上記サイズを下回る破砕片が生じることは避けられない。このような破砕片の比率は、多結晶シリコン塊の硬さや粉砕条件にもよるが、基の多結晶シリコン塊の概ね５〜１０％程度に及ぶ。 When a polycrystalline silicon lump is crushed by applying an impact destructive force with a hammer, it is inevitable that crushed pieces having a size smaller than the above size are generated. The ratio of such crushed pieces depends on the hardness and pulverization conditions of the polycrystalline silicon lump, but ranges from about 5 to 10% of the base polycrystalline silicon lump.
このような多結晶シリコン片は、その小さなサイズ故に比表面積が大きく、表面の金属不純物や有機物の濃度が高くなり、最早、半導体グレードのシリコン結晶育成用の原料としては利用できず、太陽電池や鉄鋼の製造原料として利用せざるを得ない。 Such a polycrystalline silicon piece has a large specific surface area due to its small size and a high concentration of metal impurities and organic matter on the surface, which can no longer be used as a raw material for semiconductor-grade silicon crystal growth. It must be used as a raw material for steel production.
一方、連続ＣＺ法（ＣＣＺ法）による単結晶シリコン成長技術の提案の後、高純度の粒状多結晶シリコンを得る試みも進められてきた（例えば、特許文献１を参照）。 On the other hand, after proposing a single crystal silicon growth technique by a continuous CZ method (CCZ method), attempts have been made to obtain high-purity granular polycrystalline silicon (see, for example, Patent Document 1).
このような粒状多結晶シリコンをはじめとする小サイズの多結晶シリコン（以下では「多結晶シリコン片」と総称する）を半導体製造用原料として使用するためには、表面不純物を除去することが必須である。しかし、このような多結晶シリコン片を、多結晶シリコン塊の清浄化工程と同様の条件でエッチングしてしまうと、その比表面積の大きさ故に、エッチングにより除去されるシリコン量（溶解量）の体積比が顕著に大きくなり収率は顕著に低くなる。 In order to use small-sized polycrystalline silicon (hereinafter collectively referred to as “polycrystalline silicon piece”) including such granular polycrystalline silicon, it is essential to remove surface impurities. It is. However, if such a piece of polycrystalline silicon is etched under the same conditions as the step of cleaning the polycrystalline silicon lump, the amount of silicon removed by the etching (dissolved amount) due to the large specific surface area. The volume ratio is significantly increased and the yield is significantly reduced.
従って、多結晶シリコン片の清浄化に際し、なるべく表面を溶解させずに、表面に付着した異物や不純物（金属不純物や有機不純物）を除去し得る条件の検討が求められるところであり、これに基づき、半導体製造用原料として利用し得るレベルの清浄度を有する多結晶シリコン片の提供が求められる。 Therefore, when cleaning the polycrystalline silicon piece, it is necessary to study conditions that can remove foreign matters and impurities (metal impurities and organic impurities) adhering to the surface without dissolving the surface as much as possible. There is a need to provide a polycrystalline silicon piece having a level of cleanliness that can be used as a raw material for semiconductor manufacturing.
上記課題を解決するために、本発明に係る多結晶シリコン片は、表面をエッチングして得られた抽出液を質量分析法で分析して評価した際の表面不純物濃度が、金属元素の１元素につき１００ｐｐｔｗ以下であり、有機物につき１００ｐｐｔｗ未満である、長径が３０ｍｍ以下で短径が５ｍｍ以上のサイズの多結晶シリコン片である。 In order to solve the above problems, a polycrystalline silicon piece according to the present invention has a surface impurity concentration of one element of a metal element when an extract obtained by etching a surface is analyzed and evaluated by mass spectrometry. It is a piece of polycrystalline silicon having a major axis of 30 mm or less and a minor axis of 5 mm or more, which is less than 100 pptw per one and less than 100 pptw per organic matter.
例えば、前記金属元素は、Ｌｉ、Ｂ、Ｍｇ、Ａｌ、Ｋ、Ｃａ、Ｍｎ、Ｃｏ、Ｃｕ、Ａｓ、Ｍｏ、Ｓｎ、Ｗ、Ｐｂの何れかである。 For example, the metal element is any one of Li, B, Mg, Al, K, Ca, Mn, Co, Cu, As, Mo, Sn, W, and Pb.
また、例えば、前記金属元素は、Ｎａ、Ｃｒ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎの６種のうちの何れかであり、該６種の金属元素の合計濃度が１００ｐｐｔｗ以下である。 Further, for example, the metal element is any one of six kinds of Na, Cr, Fe, Ni, Cu, and Zn, and the total concentration of the six kinds of metal elements is 100 pptw or less.
前記多結晶シリコン片は、多結晶シリコン塊の破砕片を混酸で洗浄して得られたものである。 The polycrystalline silicon piece is obtained by washing a fragment of a polycrystalline silicon lump with a mixed acid.
好ましくは、前記混酸は、フッ酸濃度が１〜１０ｗｔ％であり、過酸化水素濃度または硝酸濃度が２％以下である混合液である。 Preferably, the mixed acid is a mixed solution having a hydrofluoric acid concentration of 1 to 10 wt% and a hydrogen peroxide concentration or nitric acid concentration of 2% or less.
本発明によれば、多結晶シリコン片の清浄化に際し、なるべく表面を溶解させずに、表面に付着した異物や不純物（金属不純物や有機不純物）を除去し得る。その結果、半導体製造用原料として利用し得るレベルの清浄度を有する多結晶シリコン片の提供が可能となる。 According to the present invention, when cleaning a polycrystalline silicon piece, foreign substances and impurities (metal impurities and organic impurities) attached to the surface can be removed without dissolving the surface as much as possible. As a result, it is possible to provide a polycrystalline silicon piece having a level of cleanliness that can be used as a raw material for semiconductor manufacturing.
本発明者らは、多結晶シリコン塊を破砕した際に生じる多結晶シリコン片の清浄化を検討するに際し、先ず、超純水のみで多結晶シリコン片を洗浄してみた。なお、このような多結晶シリコン片の形状は個々に異なるが、本発明では、長径が３０ｍｍ以下で短径が５ｍｍ以上のサイズの多結晶シリコン片を対象としている。その結果、目視のレベルでは、微粒子の付着等は認められなかった。しかし、電子顕微鏡によりミクロレベルの観察を行うと、表面の付着物は完全に除去されてはいないことが確認された。 When examining the cleaning of the polycrystalline silicon piece generated when the polycrystalline silicon lump is crushed, the inventors first cleaned the polycrystalline silicon piece with only ultrapure water. In addition, although the shape of such a polycrystalline silicon piece differs individually, the present invention is intended for a polycrystalline silicon piece having a major axis of 30 mm or less and a minor axis of 5 mm or more. As a result, no adhesion of fine particles or the like was observed at the visual level. However, when microscopic observation was performed with an electron microscope, it was confirmed that the surface deposits were not completely removed.
そこで、多結晶シリコン塊の洗浄工程における一般的な条件（エッチャントはＨＦ（５０ｗｔ％）：ＨＮＯ3（７０ｗｔ％）の体積比が１：９前後の混酸液）でエッチングを行ったところ、エッチングの進行が速く多結晶シリコン片の重量が５〜１５％程度も減少してしまうことに加え、表面にエッチャントが残存してしまいその除去のためのリンスに長時間を要する、という問題があることが分かった。このような問題は、混酸として、硝酸の代わりに過酸化水素水とした場合でも同様であった。 Therefore, etching was performed under the general conditions in the polycrystalline silicon lump cleaning process (the etchant is a mixed acid solution having a volume ratio of HF (50 wt%): HNO 3 (70 wt%) of about 1: 9). In addition to the rapid progress, the weight of the polycrystalline silicon piece is reduced by about 5 to 15%, and there is a problem that the etchant remains on the surface and it takes a long time to rinse it. I understood. Such a problem is the same even when the mixed acid is a hydrogen peroxide solution instead of nitric acid.
本発明者らは、これらの結果を踏まえ、多結晶シリコン片の清浄化に好適な液組成について抜本的な検討を進めた結果、フッ酸の組成比を高くし且つ硝酸の組成比を低くした場合に、上記問題を回避しつつ、多結晶シリコン片の表面金属濃度を顕著に低下させ得るとの知見を得た。また、混酸として硝酸の代わりに過酸化水素水を用いた場合でも同様の効果を得ることができた。 Based on these results, the present inventors have made a fundamental study on a liquid composition suitable for cleaning a polycrystalline silicon piece. As a result, the composition ratio of hydrofluoric acid was increased and the composition ratio of nitric acid was decreased. In some cases, the inventors have found that the surface metal concentration of the polycrystalline silicon piece can be significantly reduced while avoiding the above problem. The same effect could be obtained even when hydrogen peroxide was used instead of nitric acid as a mixed acid.
具体的には、フッ酸濃度が１〜１０ｗｔ％であり、過酸化水素濃度または硝酸濃度が２％以下である混合液（混酸）を処理液として用いる。 Specifically, a mixed solution (mixed acid) having a hydrofluoric acid concentration of 1 to 10 wt% and a hydrogen peroxide concentration or nitric acid concentration of 2% or less is used as the treatment liquid.
上記処理液で清浄化された多結晶シリコン片の表面をエッチングし、得られた抽出液を質量分析法で分析して表面不純物濃度を評価すると、金属元素については１元素につき１００ｐｐｔｗ以下（ＩＣＰ−ＭＳ法で分析）であり、有機物については１００ｐｐｔｗ未満（ＧＣ−ＭＳ法で分析）の値が得られた。 When the surface of the polycrystalline silicon piece cleaned with the above treatment liquid is etched, and the resulting extract is analyzed by mass spectrometry to evaluate the surface impurity concentration, the metal element is 100 pptw or less per element (ICP- The value of the organic substance was less than 100 pptw (analyzed by the GC-MS method).
なお、上述の金属元素は、例えば、Ｌｉ、Ｂ、Ｍｇ、Ａｌ、Ｋ、Ｃａ、Ｍｎ、Ｃｏ、Ｃｕ、Ａｓ、Ｍｏ、Ｓｎ、Ｗ、Ｐｂの何れかであり、これらは何れも半導体製造用のシリコン結晶中に取り込まれると、単結晶シリコンの品質を低下させる不純物となる金属元素である。 The above-described metal element is, for example, any one of Li, B, Mg, Al, K, Ca, Mn, Co, Cu, As, Mo, Sn, W, and Pb, and these are all for semiconductor manufacturing. It is a metal element that becomes an impurity that degrades the quality of single crystal silicon when incorporated into the silicon crystal.
また、上記条件で表面処理した場合には、金属元素は、Ｎａ、Ｃｒ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎの６種のうちの何れかであり、該６種の金属元素の合計濃度が１００ｐｐｔｗ以下である多結晶シリコン片を得ることもできる。 Further, when the surface treatment is performed under the above conditions, the metal element is any one of six kinds of Na, Cr, Fe, Ni, Cu, and Zn, and the total concentration of the six kinds of metal elements is 100 pptw or less. It is also possible to obtain a polycrystalline silicon piece.
上述のとおり、フッ酸濃度が１〜１０ｗｔ％であり、過酸化水素濃度または硝酸濃度が２％以下である処理液（混酸）は、多結晶シリコン塊の洗浄工程で一般的に用いられるエッチャントに比較して著しく硝酸濃度が低く、その結果、エッチング効果は低い。しかし、液組成がフッ酸を主とするため、除去対象となる金属不純物は、フッ酸と錯化合物を形成し、その結果、効率良く除去されるものと考えられる。つまり、いわゆるエッチングによる清浄化とは異なるメカニズムにより不純物除去が行われるものと理解される。 As described above, a treatment liquid (mixed acid) having a hydrofluoric acid concentration of 1 to 10 wt% and a hydrogen peroxide concentration or nitric acid concentration of 2% or less is used as an etchant generally used in a polycrystalline silicon lump cleaning process. Compared with the concentration of nitric acid, the etching effect is low. However, since the liquid composition is mainly hydrofluoric acid, it is considered that the metal impurities to be removed form a complex compound with hydrofluoric acid, and as a result, are efficiently removed. That is, it is understood that impurities are removed by a mechanism different from so-called cleaning by etching.
このような混酸で多結晶シリコン片の表面処理を行うと、エッチング効果が著しく低いために処理後の収率は高く、重量損失は０．２〜１％程度である。しかも、酸濃度が低いために多結晶シリコン片に残存する薬液成分も少量であるという利点がある。なお、処理後の多結晶シリコン片の表面を電子顕微鏡で観察しても、微粉等の付着も認められない。 When the surface treatment of the polycrystalline silicon piece is performed with such a mixed acid, the etching effect is remarkably low, so the yield after the treatment is high and the weight loss is about 0.2 to 1%. In addition, since the acid concentration is low, there is an advantage that a small amount of chemical components remain in the polycrystalline silicon piece. In addition, even if the surface of the polycrystal silicon piece after a process is observed with an electron microscope, adhesion of fine powder etc. is not recognized.
なお、実際の清浄化工程においては多量の多結晶シリコン片を同バッチで処理するため、多結晶シリコン片同士の擦れ合い等により微粒子等が発生し得る。これらの除去のためには、槽内で処理液を循環させ、配管途中に設けたフィルタでこれを捕捉回収することが好ましい。 Since a large amount of polycrystalline silicon pieces are processed in the same batch in the actual cleaning process, fine particles and the like may be generated due to rubbing of the polycrystalline silicon pieces. In order to remove these, it is preferable to circulate the treatment liquid in the tank and capture and collect it with a filter provided in the middle of the piping.
シーメンス法による合成で得られた多結晶シリコンロッドを破砕して多結晶シリコン塊を製造した。その際の破砕には、ＷＣ製のハンマーを使用した。この破砕時に生じた多結晶シリコン片のうち、長径が３０ｍｍ以下で短径が５ｍｍ以上のサイズの多結晶シリコン片を蒐集した。 The polycrystalline silicon rod obtained by the synthesis by the Siemens method was crushed to produce a polycrystalline silicon lump. A WC hammer was used for crushing at that time. Among the polycrystalline silicon pieces generated during the crushing, polycrystalline silicon pieces having a major axis of 30 mm or less and a minor axis of 5 mm or more were collected.
上記蒐集した多結晶シリコン片（総計７ｋｇ）をＰＰ製の洗浄用籠に収納し、処理液（混酸）が、フッ酸５ｗｔ％、硝酸２ｗｔ％の混合溶液（処理液（混酸））に浸して洗浄を行った（後述の実施例1-3に当たる）。なお、ＨＦは５０ｗｔ％水溶液の電子産業用もの、硝酸は７０ｗｔ％、過酸化水素は３０％の水溶液の電子産業用ものを用いた。 The collected polycrystalline silicon pieces (total 7 kg) are stored in a PP cleaning basket, and the treatment liquid (mixed acid) is immersed in a mixed solution of 5 wt% hydrofluoric acid and 2 wt% nitric acid (treatment liquid (mixed acid)). Washing was performed (corresponding to Example 1-3 described later). In addition, HF used the thing for electronic industries of 50 wt% aqueous solution, the nitric acid used 70 wt%, and the hydrogen peroxide used the electronic industry thing of 30% aqueous solution.
洗浄槽は内槽容積が６０リットルで外槽容積が３０リットルのものを用い、これに上記処理液１１８リットルを充填し、ポンプによる循環を行い、槽上部においてオーバーフローさせた。なお、処理液の温度は常温であり、エッチング反応による温度上昇は認められなかった。 The washing tank having an inner tank volume of 60 liters and an outer tank volume of 30 liters was filled with 118 liters of the above processing solution, and circulated by a pump to overflow the upper part of the tank. Note that the temperature of the treatment liquid was room temperature, and no temperature increase due to the etching reaction was observed.
表面金属不純物の低減効果を確認するため、最初のバッチと最終のバッチで清浄化した多結晶シリコン片を評価した。金属不純物の評価と有機不純物の評価条件は下記のとおりであり、一連の分析操作はクラス１００のクリーンルームに設置されたクラス１０のクリーンベンチ内で行った。 In order to confirm the effect of reducing surface metal impurities, the polycrystalline silicon pieces cleaned in the first batch and the final batch were evaluated. The evaluation conditions of metal impurities and organic impurities are as follows, and a series of analysis operations were performed in a class 10 clean bench installed in a class 100 clean room.
［金属不純物］
サンプル１５０ｇを５００ｍｌの清浄なテフロン（登録商標）ビーカに移し、溶解液２００ｍｌ（５０ｗｔ％−ＨＦ：１００ｍｌ、超純水：９９ｍｌ、３０ｗｔ％−過酸化水素：１ｍｌ）を加えて１０分間の抽出を行った。これにより得られた抽出液５．０ｍｌを清浄なテフロン容器に分取し８５±５℃の温度範囲にて蒸発乾固させ、１ｗｔ％−硝酸水溶液１．０ｍｌを加え定容化しＩＣＰ―ＭＳ測定を行った。なお、ＩＣＰ−ＭＳの測定装置は、Agilent 社製、7500 CS を使用した。
[Metal impurities]
Transfer 150 g of sample to 500 ml of clean Teflon (registered trademark) beaker, add 200 ml of lysis solution (50 wt% -HF: 100 ml, ultrapure water: 99 ml, 30 wt% -hydrogen peroxide: 1 ml) and extract for 10 minutes. went. 5.0 ml of the extract thus obtained was dispensed into a clean Teflon container, evaporated to dryness in a temperature range of 85 ± 5 ° C., added with 1.0 ml of 1 wt% -nitric acid aqueous solution, made constant volume, and ICP-MS measurement. Went. Note that 7500 CS manufactured by Agilent was used as an ICP-MS measurement apparatus.
［有機不純物］
サンプル５ｇを密閉容器内に移し、不活性ガス（ヘリウム、５０ｍｌ/分）を通気しながら加熱温度を３５０℃に上げ、多結晶シリコン片の表面に付着した有機物を追い出し、吸着剤に吸着させた。その後、吸着剤を加熱（２５０℃×１０分）し成分を脱着させ、ＧＣ−ＭＳに導入し成分の定性および定量を行った。
[Organic impurities]
5 g of the sample was transferred into a sealed container, the heating temperature was raised to 350 ° C. while venting inert gas (helium, 50 ml / min), the organic matter adhering to the surface of the polycrystalline silicon piece was driven off, and adsorbed by the adsorbent. . Thereafter, the adsorbent was heated (250 ° C. × 10 minutes) to desorb components and introduced into GC-MS for qualitative and quantitative determination of the components.
上記吸着は、放出成分の捕捉を−６０℃（液体窒素）で行い、２５０℃までの昇温時間は２５秒とした。なお、用いた吸着剤は、Ｔｅｎａｘ−ＴＡ（２，６−ジフェニル−ｐ−フェニレンオキサイドをベースにした弱極性のポーラスポリマービーズであり、表面積が３５ｍ2/ｇ、ポア面積２．４ｃｍ2/ｇ、平均ポアサイズ２００ｎｍ、比重は０．２５ｇ/ｃｍ3）である。 In the adsorption, the released component was captured at −60 ° C. (liquid nitrogen), and the temperature rising time to 250 ° C. was 25 seconds. The adsorbent used was Tenax-TA (a weakly polar porous polymer bead based on 2,6-diphenyl-p-phenylene oxide, having a surface area of 35 m 2 / g and a pore area of 2.4 cm 2 / g. The average pore size is 200 nm, and the specific gravity is 0.25 g / cm 3 ).
また、ＧＣ−ＭＳ測定に用いた装置はアジレント社製の５９７５Ｃ−ＭＳＤであり、分離カラムはアジレント社製のＨＰ−５ＭＳ（長さ２５ｍｍ、口径０．２ｍｍ、厚み０．３３μｍ）であり、５０℃で５分間保持後に１０℃／分で３００℃まで昇温した。なお、注入口のスプリット比は２０：１、キャリアーガス（ヘリウム）の流量は１ｍｌ／分、質量分析検出モードはＥＩ（電子衝撃イオン化）モードである。 The apparatus used for the GC-MS measurement was 5975C-MSD manufactured by Agilent, and the separation column was HP-5MS manufactured by Agilent (length 25 mm, diameter 0.2 mm, thickness 0.33 μm), 50 After holding at 5 ° C. for 5 minutes, the temperature was raised to 300 ° C. at 10 ° C./min. The split ratio of the injection port is 20: 1, the flow rate of the carrier gas (helium) is 1 ml / min, and the mass spectrometry detection mode is the EI (electron impact ionization) mode.
上述の条件下で清浄化処理した多結晶シリコン片を原料としてＣＺ法で単結晶シリコンの育成を行った。成長中の単結晶シリコンの外周には晶癖線が現れるが、有転位化するとこの晶癖線は消滅する。 Single crystal silicon was grown by CZ method using a polycrystalline silicon piece cleaned under the above conditions as a raw material. Although the habit line appears on the outer periphery of the growing single crystal silicon, the habit line disappears when dislocation occurs.
この現象を利用して、フッ酸と硝酸の混合溶液（処理液（混酸））の濃度を変えたときのＣＺ単結晶シリコンの結晶性を定性的に評価した。また、同様にフッ酸と過酸化水素水の混合溶液（処理液（混酸））の濃度を変えたときのＣＺ単結晶シリコンの結晶性を定性的に評価した。 Using this phenomenon, the crystallinity of CZ single crystal silicon when the concentration of a mixed solution of hydrofluoric acid and nitric acid (treatment liquid (mixed acid)) was changed was qualitatively evaluated. Similarly, the crystallinity of CZ single crystal silicon when the concentration of a mixed solution of hydrofluoric acid and hydrogen peroxide solution (treatment liquid (mixed acid)) was changed was qualitatively evaluated.
表１に、実施例１−１〜１−４および比較例１−１〜１−２それぞれの、処理液（混酸）のフッ酸濃度および硝酸濃度上記手順で測定した金属不純物および有機不純物の濃度、異物および付着微粉の有無、そして、上記晶癖線で評価した際のＣＺ単結晶シリコンの結晶性の評価結果を纏めた。 Table 1 shows the hydrofluoric acid concentration and nitric acid concentration of the treatment liquid (mixed acid) in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-2. The results of evaluating the crystallinity of CZ single crystal silicon when evaluated with the presence of foreign matter and adhering fine powder and the crystal habit line were summarized.
同様に、表２には、実施例２−１〜２−４および比較例２−１〜２−２それぞれの、処理液（混酸）のフッ酸濃度および過酸化水素水濃度、上記したのと同様の手順で測定した金属不純物および有機不純物の濃度、異物および付着微粉の有無、そして、上記晶癖線で評価した際のＣＺ単結晶シリコンの結晶性の評価結果を纏めた。 Similarly, Table 2 shows the hydrofluoric acid concentration and hydrogen peroxide solution concentration of the treatment liquid (mixed acid) in Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-2. The concentrations of metal impurities and organic impurities, the presence or absence of foreign matters and adhering fine powders measured in the same procedure, and the evaluation results of the crystallinity of CZ single crystal silicon when evaluated by the crystal habit line were summarized.
なお、これらの表中の「表面金属１元素」とは、Ｌｉ、Ｂ、Ｍｇ、Ａｌ、Ｋ、Ｃａ、Ｍｎ、Ｃｏ、Ｃｕ、Ａｓ、Ｍｏ、Ｓｎ、Ｗ、Ｐｂの１４元素群に含まれる何れかの元素であり、実施例においては何れも、上記１４元素の何れについても１００ｐｐｔｗ以下となっている。 In addition, “surface metal 1 element” in these tables is included in the 14 element group of Li, B, Mg, Al, K, Ca, Mn, Co, Cu, As, Mo, Sn, W, and Pb. Any element, and in the examples, any of the above 14 elements is 100 pptw or less.
また、「表面金属６元素」とは、Ｎａ、Ｃｒ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎの群に含まれる６元素であり、実施例においては何れも、これら６種の金属元素の合計濃度が１００ｐｐｔｗ以下となっている。 The “surface metal 6 elements” are 6 elements included in the group of Na, Cr, Fe, Ni, Cu, and Zn. In the examples, the total concentration of these 6 metal elements is 100 pptw. It is as follows.
表１および表２に示したように、本発明によれば、表面をエッチングして得られた抽出液を質量分析法で分析して評価した際の表面不純物濃度が、金属元素の１元素につき１００ｐｐｔｗ以下であり、有機物につき１００ｐｐｔｗ未満である、長径が３０ｍｍ以下で短径が５ｍｍ以上のサイズの多結晶シリコン片が得られる。そして、この多結晶シリコン片を原料としてＣＺ単結晶シリコンの育成を行うと、良質の単結晶が得られる。 As shown in Table 1 and Table 2, according to the present invention, the surface impurity concentration when the extract obtained by etching the surface was analyzed and evaluated by mass spectrometry was 1 element per metal element. A polycrystalline silicon piece having a major axis of 30 mm or less and a minor axis of 5 mm or more, which is 100 pptw or less and less than 100 pptw per organic substance, is obtained. Then, when CZ single crystal silicon is grown using this polycrystalline silicon piece as a raw material, a high quality single crystal can be obtained.
表３には、ＣＺ単結晶シリコンの育成に際して原料をルツボにチャージする際の多結晶シリコンの形状と仕込み時間、並びに、リチャージの可否を纏めている。 Table 3 summarizes the shape and charging time of the polycrystalline silicon when the raw material is charged to the crucible when CZ single crystal silicon is grown, and whether or not recharging is possible.
ここで、「仕込み時間」は、比較的大きなサイズの多結晶シリコン塊（ナゲット）の仕込み時間を１としたときの相対値で評価している。 Here, the “preparation time” is evaluated as a relative value when the preparation time of a relatively large size polycrystalline silicon lump (nugget) is 1.
以上説明したように、本発明によれば、多結晶シリコン片の清浄化に際し、なるべく表面を溶解させずに、表面に付着した異物や不純物（金属不純物や有機不純物）を除去し得る。その結果、半導体製造用原料として利用し得るレベルの清浄度を有する多結晶シリコン片の提供が可能となる。 As described above, according to the present invention, when cleaning a polycrystalline silicon piece, foreign substances and impurities (metal impurities and organic impurities) attached to the surface can be removed without dissolving the surface as much as possible. As a result, it is possible to provide a polycrystalline silicon piece having a level of cleanliness that can be used as a raw material for semiconductor manufacturing.
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