WO2016051761A1 - Method for evaluating cleanness of surface of polycrystalline silicon and method for guaranteeing quality - Google Patents
Method for evaluating cleanness of surface of polycrystalline silicon and method for guaranteeing quality Download PDFInfo
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- WO2016051761A1 WO2016051761A1 PCT/JP2015/004919 JP2015004919W WO2016051761A1 WO 2016051761 A1 WO2016051761 A1 WO 2016051761A1 JP 2015004919 W JP2015004919 W JP 2015004919W WO 2016051761 A1 WO2016051761 A1 WO 2016051761A1
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- the present invention relates to a method for evaluating the surface cleanliness of polycrystalline silicon, and a quality assurance method for polycrystalline silicon using the same.
- Single crystal silicon which is indispensable for manufacturing semiconductor devices, is crystal-grown by the CZ method or FZ method, and a polycrystalline silicon rod or a polycrystalline silicon lump is used as a raw material at that time.
- Such polycrystalline silicon materials are often manufactured by the Siemens method (see Patent Document 1 (Japanese Patent Publication No. 37-18861) and the like).
- the Siemens method is a process in which polycrystalline silicon is vapor-phase grown (deposited) by CVD (Chemical Vapor Deposition) method by bringing a silane source gas such as trichlorosilane or monosilane into contact with a heated silicon core wire. It is a method to make it.
- polycrystalline silicon requires extremely high surface cleanliness.
- polycrystalline silicon obtained by crushing a polycrystalline silicon rod is used.
- chemical cleaning with fluorinated nitric acid or the like is performed, and then packing is performed for final production.
- An object of the present invention is to provide a technique that contributes to surface cleaning of polycrystalline silicon, and in particular, to provide a technique for lowering the lower limit of measurement of the surface concentration of phosphorus (P) and metal impurities. There is to do.
- the surface cleanliness evaluation method for polycrystalline silicon according to the first aspect of the present invention is based on the condition that the extract obtained by dissolving the surface of polycrystalline silicon with an acid is at 90 ° C. or lower.
- a first step of evaporating to dryness a second step of adding hydrofluoric acid to the residue after evaporating to dryness and evaporating to dryness under a condition of 90 ° C. or less, and a residue after the evaporating to dryness again
- a fourth step is provided, and the surface cleanliness of the polycrystalline silicon is evaluated by quantifying the phosphorus (P) concentration on the surface of the polycrystalline silicon based on the mass analysis result of the test solution.
- the method for evaluating the surface cleanliness of polycrystalline silicon uses the extract obtained by dissolving the surface of polycrystalline silicon with an acid with a machining allowance of 10 ⁇ m or more as a test solution, and the test Based on the mass analysis result of the liquid, the surface metal concentration of the polycrystalline silicon is quantified to evaluate the surface cleanliness of the polycrystalline silicon.
- the quality assurance method for polycrystalline silicon according to the present invention guarantees the cleanliness of the surface of the polycrystalline silicon based on the result evaluated by the above method.
- the lower limit of measurement of phosphorus (P) and metal impurity concentrations on the surface of polycrystalline silicon is lower than in the prior art, and a technique that contributes to surface cleaning of polycrystalline silicon is provided.
- ICP-MS method ICP mass spectrometry method capable of simultaneously measuring multiple elements with high sensitivity.
- a decomposition solution (test solution) of a sample to be measured (specimen) is sprayed into plasma, and ion species of the element to be measured generated in this plasma are separated by a mass spectrometer. A quantification is made.
- an ICP-MS apparatus having two mass analysis units is used, and all the generated ions other than P are exhausted in the first mass analysis unit, and only the P ions that are measurement target elements are exhausted. It is also conceivable to introduce the amount into the second mass spectrometer and quantify it.
- the present inventors examined desiliconization conditions for significantly reducing the Si concentration in the test solution used for analysis. As a result, it was confirmed that the P concentration could be quantified at a level of 1 pptw by using a test solution obtained by the following method.
- FIG. 1 is a flowchart showing an outline of a procedure for obtaining a test solution used in the method for evaluating the surface cleanliness of polycrystalline silicon (P surface concentration measuring method) according to the present invention.
- an extract obtained by dissolving the surface of polycrystalline silicon with an acid is obtained (S100).
- HF is 50 wt%
- HNO 3 is 70 wt%, both of which are of the electronic industry grade.
- this extract is evaporated to dryness under the condition of 90 ° C. or less (S101).
- the reason why the temperature of distillation to dryness is set to 90 ° C. or less is that, when evaporated to dryness at a temperature exceeding 90 ° C., the recovery rate of P is significantly reduced.
- Fluoric acid is added to the residue after evaporation to dryness obtained in step S101, and again evaporated to dryness under a condition of 90 ° C. or less (S102).
- 0.5 ml of 50 wt% HF was added to the residue.
- hydrofluoric acid is added to the residue obtained after the evaporation to dryness obtained in step S102 again, and evaporated to dryness again at a temperature of 90 ° C. or less (S103). Again, 0.5 ml of 50 wt% HF was added to the residue.
- step S104 ultrapure water was added to the residue obtained by evaporation to dryness in step S103 to obtain a test solution (S104).
- 1.0 ml of ultrapure water was added to the residue.
- the test solution is an aqueous nitric acid solution of about 0.5 to 1 wt%.
- the above-mentioned insoluble matter is dissolved, resulting in the test solution.
- 30 SiH + is generated therein, which hinders the determination of P.
- the test solution is obtained by the above-described method, such inconvenience does not occur.
- Mass spectrometry is performed using the test solution thus obtained, and the surface cleanliness is evaluated by quantifying the phosphorus (P) concentration on the surface of the polycrystalline silicon based on the result (S105).
- Patent Document 2 in analyzing the metal concentration on the silicon surface, chemical removal of the silicon surface by dissolution is performed according to ASTM F 1724-96, and the obtained removal is performed. There is a statement that the solution is analyzed by ICP-MS.
- the mixed acid that etches the silicon surface has a hydrofluoric acid concentration of 0.91 wt%, a nitric acid concentration of 1.2 wt%, and a hydrogen peroxide concentration of 0.57 wt%. Dilute acid concentration. Therefore, the silicon surface layer to be dissolved is as small as about 1 ⁇ m, and there is a possibility that not all of the surface contamination impurities can be collected in the removal solution.
- the present inventors examined the extent of machining allowance to collect almost all surface impurities.
- a polycrystalline silicon lump for CZ single crystal production was crushed with a WC hammer, and then etched with a mixed acid of hydrofluoric acid and nitric acid to collect impurities on the surface in the removal solution.
- the liquid temperature during etching was controlled between room temperature and 39 ° C. As the etching progresses, the liquid temperature rises, but the etchant is made to flow with a circulation pump, and a heat exchanger is installed in the middle of the piping to remove the heat generated.
- the volume of the etching tank is 40 liters, and the circulation flow rate is 40 liters / minute.
- the etching time was 5 to 10 minutes, and the machining allowance was about 10 ⁇ m by setting the etching time.
- rinsing was performed sufficiently with ultrapure water.
- the electrical conductivity in the final rinse tank is 3 M ⁇ -cm or more.
- drying was performed with a ventilator. Ventilation air passed through a HEPA filter. The drying temperature is 85 ° C. and the drying time is 7 minutes.
- the impurity concentration detected from the test solution B greatly exceeds the impurity concentration detected from the test solution A.
- almost no impurities are detected from the test solution A under the analysis condition II.
- Polycrystalline silicon with B concentration on the surface of 1pptw level Polycrystalline silicon with B concentration on the surface of 1pptw level.
- Polycrystalline silicon with a surface Al concentration of 1pptw or less Polycrystalline silicon with a surface Al concentration of 1pptw or less.
- the lower limit of measurement of phosphorus (P) and metal impurity concentrations on the surface of polycrystalline silicon is lower than that in the prior art, and a technique that contributes to surface cleaning of polycrystalline silicon is provided.
Abstract
A method for evaluating the cleanness of a surface of polycrystalline silicon, the method comprising: a step (S100) in which an extract is obtained by dissolving the surface of polycrystalline silicon with an acid; a step (S101) in which the extract is evaporated to dryness under the conditions of 90°C or lower; a step (S102) in which hydrofluoric acid is added to the residue remaining after the evaporation to dryness obtained in step S101 and the mixture is again evaporated to dryness under the conditions of 90°C or lower; a step (S103) in which hydrofluoric acid is subsequently added to the residue remaining after the second evaporation to dryness obtained in step S102 and the mixture is once again evaporated to dryness under the conditions of 90°C or lower; a step (S104) in which ultrapure water is added to the residue obtained by the evaporation to dryness in step S103, thereby obtaining a test liquid; and a step (S105) in which the test liquid thus obtained is examined by mass analysis and the concentration of phosphorus (P) present in the surface of the polycrystalline silicon is determined on the basis of the results thereof, thereby evaluating the surface cleanness.
Description
本発明は、多結晶シリコンの表面清浄度を評価方法、および、これを用いた多結晶シリコンの品質保証方法に関する。
The present invention relates to a method for evaluating the surface cleanliness of polycrystalline silicon, and a quality assurance method for polycrystalline silicon using the same.
半導体デバイス等の製造に不可欠な単結晶シリコンは、ＣＺ法やＦＺ法により結晶育成され、その際の原料として多結晶シリコン棒や多結晶シリコン塊が用いられる。このような多結晶シリコン材料は、多くの場合、シーメンス法により製造される（特許文献１（特公昭３７－１８８６１号公報）等参照）。シーメンス法とは、トリクロロシランやモノシラン等のシラン原料ガスを加熱されたシリコン芯線に接触させることにより、該シリコン芯線の表面に多結晶シリコンをＣＶＤ（Chemical Vapor Deposition）法により気相成長（析出）させる方法である。
Single crystal silicon, which is indispensable for manufacturing semiconductor devices, is crystal-grown by the CZ method or FZ method, and a polycrystalline silicon rod or a polycrystalline silicon lump is used as a raw material at that time. Such polycrystalline silicon materials are often manufactured by the Siemens method (see Patent Document 1 (Japanese Patent Publication No. 37-18861) and the like). The Siemens method is a process in which polycrystalline silicon is vapor-phase grown (deposited) by CVD (Chemical Vapor Deposition) method by bringing a silane source gas such as trichlorosilane or monosilane into contact with a heated silicon core wire. It is a method to make it.
言うまでもなく、このような多結晶シリコンには、極めて高い表面清浄度が求められるため、例えば、多結晶シリコン塊を製品化する際には、多結晶シリコン棒を破砕して得られた多結晶シリコン塊（ナゲット）の表面に付着した汚染物を取り除くために、フッ硝酸等による薬液洗浄が行われ、その後、最終製品化のために梱包が行われる。
Needless to say, such polycrystalline silicon requires extremely high surface cleanliness. For example, when commercializing a polycrystalline silicon lump, polycrystalline silicon obtained by crushing a polycrystalline silicon rod is used. In order to remove contaminants adhering to the surface of the lump (nugget), chemical cleaning with fluorinated nitric acid or the like is performed, and then packing is performed for final production.
多結晶シリコンの更なる表面清浄化のためには、特に、シリコン結晶中で電気的に活性化してドナーやアクセプタとなるリン（Ｐ）やボロン（Ｂ）などのドーパントや結晶欠陥等の原因となるＦｅやＣｕなどの金属不純物の検出下限を、更に低くしてゆく必要がある。
In order to further clean the surface of polycrystalline silicon, in particular, it is caused by dopants such as phosphorus (P) and boron (B), which are electrically activated in silicon crystals to become donors and acceptors, and crystal defects. It is necessary to further lower the lower limit of detection of metal impurities such as Fe and Cu.
本発明の目的は、多結晶シリコンの表面清浄化に寄与する技術を提供すること、特に、リン（Ｐ）および金属不純物の表面濃度の測定下限を従来よりも低いものとするための技術を提供することにある。
An object of the present invention is to provide a technique that contributes to surface cleaning of polycrystalline silicon, and in particular, to provide a technique for lowering the lower limit of measurement of the surface concentration of phosphorus (P) and metal impurities. There is to do.
上記課題を解決するために、本発明に係る第１の態様の多結晶シリコンの表面清浄度評価方法は、多結晶シリコンの表面を酸で溶解して得た抽出液を９０℃以下の条件で蒸発乾固させる第１ステップと、該蒸発乾固後の残留物にフッ酸を添加して９０℃以下の条件で再び蒸発乾固させる第２ステップと、該再度の蒸発乾固後の残留物にフッ酸を添加して９０℃以下の条件でもう一度蒸発乾固させる第３のステップと、前記第３のステップの蒸発乾固で得られた残留物に超純水を加えて試験液とする第４のステップを備え、前記試験液の質量分析結果に基づいて前記多結晶シリコンの表面のリン（Ｐ）濃度を定量して該多結晶シリコンの表面清浄度を評価する。
In order to solve the above-mentioned problem, the surface cleanliness evaluation method for polycrystalline silicon according to the first aspect of the present invention is based on the condition that the extract obtained by dissolving the surface of polycrystalline silicon with an acid is at 90 ° C. or lower. A first step of evaporating to dryness, a second step of adding hydrofluoric acid to the residue after evaporating to dryness and evaporating to dryness under a condition of 90 ° C. or less, and a residue after the evaporating to dryness again A third step of adding hydrofluoric acid to the mixture and evaporating to dryness again at a temperature of 90 ° C. or less, and adding ultrapure water to the residue obtained by evaporating to dryness in the third step to obtain a test solution. A fourth step is provided, and the surface cleanliness of the polycrystalline silicon is evaluated by quantifying the phosphorus (P) concentration on the surface of the polycrystalline silicon based on the mass analysis result of the test solution.
また、本発明に係る第２の態様の多結晶シリコンの表面清浄度評価方法は、多結晶シリコンの表面を１０μｍ以上の取り代で酸で溶解して得た抽出液を試験液とし、該試験液の質量分析結果に基づいて前記多結晶シリコンの表面金属濃度を定量して該多結晶シリコンの表面清浄度を評価する。
In addition, the method for evaluating the surface cleanliness of polycrystalline silicon according to the second aspect of the present invention uses the extract obtained by dissolving the surface of polycrystalline silicon with an acid with a machining allowance of 10 μm or more as a test solution, and the test Based on the mass analysis result of the liquid, the surface metal concentration of the polycrystalline silicon is quantified to evaluate the surface cleanliness of the polycrystalline silicon.
さらに、本発明に係る多結晶シリコンの品質保証方法は、上記方法で評価した結果に基づき、前記多結晶シリコン表面の清浄度を保証する。
Furthermore, the quality assurance method for polycrystalline silicon according to the present invention guarantees the cleanliness of the surface of the polycrystalline silicon based on the result evaluated by the above method.
本発明によれば、多結晶シリコン表面のリン（Ｐ）および金属不純物の濃度の測定下限が、従来よりも低いものとなり、多結晶シリコンの表面清浄化に寄与する技術が提供される。
According to the present invention, the lower limit of measurement of phosphorus (P) and metal impurity concentrations on the surface of polycrystalline silicon is lower than in the prior art, and a technique that contributes to surface cleaning of polycrystalline silicon is provided.
以下に、図面を参照して、本発明に係る多結晶シリコンの表面清浄度評価方法について説明する。
Hereinafter, a method for evaluating the surface cleanliness of polycrystalline silicon according to the present invention will be described with reference to the drawings.
［多結晶シリコン表面のリン（Ｐ）濃度の評価方法］
無機元素の分析方法として、多元素を同時に且つ高感度で測定可能なＩＣＰ質量分析法（ＩＣＰ－ＭＳ法）が広く用いられる。一般的なＩＣＰ－ＭＳ装置では、測定対象試料（検体）の分解溶液（試験液）をプラズマ中に噴霧し、このプラズマ中で生成する測定対象元素のイオン種を、質量分析計で分離して定量がなされる。 [Method for evaluating phosphorus (P) concentration on polycrystalline silicon surface]
As an inorganic element analysis method, an ICP mass spectrometry method (ICP-MS method) capable of simultaneously measuring multiple elements with high sensitivity is widely used. In a general ICP-MS apparatus, a decomposition solution (test solution) of a sample to be measured (specimen) is sprayed into plasma, and ion species of the element to be measured generated in this plasma are separated by a mass spectrometer. A quantification is made.
無機元素の分析方法として、多元素を同時に且つ高感度で測定可能なＩＣＰ質量分析法（ＩＣＰ－ＭＳ法）が広く用いられる。一般的なＩＣＰ－ＭＳ装置では、測定対象試料（検体）の分解溶液（試験液）をプラズマ中に噴霧し、このプラズマ中で生成する測定対象元素のイオン種を、質量分析計で分離して定量がなされる。 [Method for evaluating phosphorus (P) concentration on polycrystalline silicon surface]
As an inorganic element analysis method, an ICP mass spectrometry method (ICP-MS method) capable of simultaneously measuring multiple elements with high sensitivity is widely used. In a general ICP-MS apparatus, a decomposition solution (test solution) of a sample to be measured (specimen) is sprayed into plasma, and ion species of the element to be measured generated in this plasma are separated by a mass spectrometer. A quantification is made.
しかし、測定対象元素がｍ／ｚ＝３１のリン（３１Ｐ＋）の場合、同じくプラズマ中に生成した各種の分子イオンが妨害因子となり、特に、試験液中に４０ｐｐｂｗ程度存在するｍ／ｚ＝３０のＳｉ（３０ＳｉＨ＋）が妨害因子となって超微量のＰ濃度を定量化する際の大きな障害となる。
However, when the measurement target element is phosphorus ( 31 P + ) with m / z = 31, various molecular ions generated in the plasma are interference factors, and in particular, m / z = about 40 ppbw is present in the test solution. 30 Si ( 30 SiH + ) acts as a disturbing factor, which is a great obstacle when quantifying an extremely small amount of P concentration.
このような問題に対する対策として試験液中のＳｉを除去するための脱珪処理があるが、フッ酸（ＨＦ）を多量に使用してＳｉをＳｉＦ４に変化させ、これを加熱により揮散除去した場合にはＰの回収率が半分以下になってしまうから、試験液中の測定対象元素であるＰを損失させずに液中のＳｉを除去することは事実上不可能である。
As a countermeasure against such a problem, there is a desiliconization treatment for removing Si in the test solution, but a large amount of hydrofluoric acid (HF) is used to change Si to SiF 4 , which is volatilized and removed by heating. In some cases, since the recovery rate of P is less than half, it is practically impossible to remove Si in the liquid without losing P as a measurement target element in the test liquid.
妨害因子を除去する手法としては、質量分析部を２式備えたＩＣＰ－ＭＳ装置を用い、第１の質量分析部にてＰ以外の生成イオンを全て排気し、測定対象元素であるＰイオンのみを第２の質量分析部に導入して定量するという方法も考えられる。
As a method for removing the interfering factor, an ICP-MS apparatus having two mass analysis units is used, and all the generated ions other than P are exhausted in the first mass analysis unit, and only the P ions that are measurement target elements are exhausted. It is also conceivable to introduce the amount into the second mass spectrometer and quantify it.
しかし、本発明者らがこのような「ＭＳ／ＭＳ分離モード」での測定を試みたところ、試験液中のＳｉ濃度が４０ｐｐｂｗ程度の場合のＰの検出下限は精々２０ｐｐｔｗであり、１ｐｐｔｗレベルまで検出下限を下げることは困難であるとの結論に至った。
However, when the present inventors tried the measurement in such “MS / MS separation mode”, the detection limit of P when the Si concentration in the test solution is about 40 ppbw is 20 pptw at most, up to the level of 1 pptw. It was concluded that it was difficult to lower the detection limit.
そこで、本発明者らは、分析に用いる試験液中のＳｉの濃度を顕著に低下させるための脱珪処理条件について検討を行った。その結果、以下の方法により得た試験液を用いることで、Ｐ濃度を１ｐｐｔｗのレベルで定量できることを確認した。
Therefore, the present inventors examined desiliconization conditions for significantly reducing the Si concentration in the test solution used for analysis. As a result, it was confirmed that the P concentration could be quantified at a level of 1 pptw by using a test solution obtained by the following method.
図１は、本発明に係る多結晶シリコンの表面清浄度の評価方法（Ｐの表面濃度測定方法）で用いる試験液を得る手順の概要を示すフローチャートである。
FIG. 1 is a flowchart showing an outline of a procedure for obtaining a test solution used in the method for evaluating the surface cleanliness of polycrystalline silicon (P surface concentration measuring method) according to the present invention.
先ず、多結晶シリコンの表面を酸で溶解して得た抽出液を得る（Ｓ１００）。抽出液は、多結晶シリコンを、ＨＦ：ＨＮＯ３＝１：９（体積比）の混合液でエッチングして得たもので、例えば５ｍｌ程度の量である。ここでは、ＨＦは５０ｗｔ％のもの、ＨＮＯ３は７０ｗｔ％のもので、何れも、電子産業用グレードのものである。そして、この抽出液を９０℃以下の条件で蒸発乾固させる（Ｓ１０１）。蒸留乾固の温度を９０℃以下とするのは、９０℃を超える温度で蒸発乾固した場合には、Ｐの回収率が著しく低下するためである。
First, an extract obtained by dissolving the surface of polycrystalline silicon with an acid is obtained (S100). The extract is obtained by etching polycrystalline silicon with a mixed solution of HF: HNO 3 = 1: 9 (volume ratio), and has an amount of about 5 ml, for example. Here, HF is 50 wt% and HNO 3 is 70 wt%, both of which are of the electronic industry grade. Then, this extract is evaporated to dryness under the condition of 90 ° C. or less (S101). The reason why the temperature of distillation to dryness is set to 90 ° C. or less is that, when evaporated to dryness at a temperature exceeding 90 ° C., the recovery rate of P is significantly reduced.
ステップＳ１０１で得られた蒸発乾固後の残留物に、フッ酸を添加して９０℃以下の条件で再び蒸発乾固させる（Ｓ１０２）。ここでは、上記残留物に５０ｗｔ％のＨＦを０．５ｍｌ添加した。
Fluoric acid is added to the residue after evaporation to dryness obtained in step S101, and again evaporated to dryness under a condition of 90 ° C. or less (S102). Here, 0.5 ml of 50 wt% HF was added to the residue.
これに続き、ステップＳ１０２で得られた再度の蒸発乾固後の残留物にフッ酸を添加して９０℃以下の条件でもう一度蒸発乾固させる（Ｓ１０３）。ここでも、上記残留物に５０ｗｔ％のＨＦを０．５ｍｌ添加した。
Subsequently, hydrofluoric acid is added to the residue obtained after the evaporation to dryness obtained in step S102 again, and evaporated to dryness again at a temperature of 90 ° C. or less (S103). Again, 0.5 ml of 50 wt% HF was added to the residue.
そして、ステップＳ１０３の蒸発乾固で得られた残留物に超純水を加えて試験液とした（Ｓ１０４）。ここでは、上記残留物に超純水を１．０ｍｌ加えた。
Then, ultrapure water was added to the residue obtained by evaporation to dryness in step S103 to obtain a test solution (S104). Here, 1.0 ml of ultrapure water was added to the residue.
この際に不溶解物が生成するが、これはＳｉ若しくはＳｉＯ２であり、液中に溶解していたものが不溶解なものに変わったものである。一般的なＩＣＰ－ＭＳ測定では、試験液は０．５～１ｗｔ％程度の硝酸水溶液とするが、このような硝酸水溶液中では上述の不溶解物が溶解してしまい、結果的に、試験液中に３０ＳｉＨ＋が生成してしまいＰの定量を妨害してしまうが、上述の手法で試験液を得た場合には、斯かる不都合が生じない。
At this time, an insoluble material is generated. This is Si or SiO 2 , and the material dissolved in the liquid is changed to an insoluble material. In general ICP-MS measurement, the test solution is an aqueous nitric acid solution of about 0.5 to 1 wt%. In such an aqueous nitric acid solution, the above-mentioned insoluble matter is dissolved, resulting in the test solution. 30 SiH + is generated therein, which hinders the determination of P. However, when the test solution is obtained by the above-described method, such inconvenience does not occur.
このようにして得た試験液を用いて質量分析を行い、その結果に基づいて多結晶シリコンの表面のリン（Ｐ）濃度を定量して表面清浄度を評価する（Ｓ１０５）。
Mass spectrometry is performed using the test solution thus obtained, and the surface cleanliness is evaluated by quantifying the phosphorus (P) concentration on the surface of the polycrystalline silicon based on the result (S105).
なお、Ｐ以外の主要なドーパンと元素であるボロン（Ｂ）について検討したところ、１１Ｂの近傍には多原子イオンによる妨害は比較的少ないため相対的に低い定量下限での測定が可能であるが、装置内でのメモリ効果（ボロン成分の吸着や付着）が１ｐｐｔｗの濃度レベルで認められた。この問題は、試験液の導入系（ネブライザ）を０．１～０．５ｗｔ％のＨＮＯ３にて２～３時間程度クリーニングすることにより解決する。
In addition, when the main dopan other than P and boron (B), which is an element, were studied, the interference with polyatomic ions is relatively small in the vicinity of 11 B, so that measurement with a relatively low lower limit of quantification is possible. However, a memory effect (adsorption and adhesion of boron components) in the apparatus was observed at a concentration level of 1 pptw. This problem can be solved by cleaning the test liquid introduction system (nebulizer) with 0.1 to 0.5 wt% HNO 3 for about 2 to 3 hours.
また、バックグラウンドの低減のためには、Ｆｅ以下の原子量の金属元素についてはＨ２を、Ｃｏ以上の原子量の金属元素についてはＨｅを導入することが効果的であり、定量下限を１ｐｐｔｗまで下げることができる。
In order to reduce the background, it is effective to introduce H 2 for a metal element having an atomic weight of Fe or less and He for a metal element having an atomic weight of Co or more, and lower the lower limit of quantification to 1pptw. be able to.
［多結晶シリコン表面の金属不純物濃度の評価方法］
従来、多結晶シリコン表面の汚染物は、例えばフッ硝酸混合液により表面を数μｍ程度エッチングで取り除けば、十分に除去できるものと考えられてきた。 [Evaluation method of metal impurity concentration on the surface of polycrystalline silicon]
Conventionally, it has been considered that contaminants on the surface of polycrystalline silicon can be sufficiently removed if the surface is removed by etching with a hydrofluoric acid mixed solution of about several μm.
従来、多結晶シリコン表面の汚染物は、例えばフッ硝酸混合液により表面を数μｍ程度エッチングで取り除けば、十分に除去できるものと考えられてきた。 [Evaluation method of metal impurity concentration on the surface of polycrystalline silicon]
Conventionally, it has been considered that contaminants on the surface of polycrystalline silicon can be sufficiently removed if the surface is removed by etching with a hydrofluoric acid mixed solution of about several μm.
例えば、特開２０１３－１５１４１３号公報（特許文献２）には、シリコン表面の金属濃度を分析するに際し、ASTM F 1724-96に則り、溶解によるシリコン表面の化学的除去を行い、得られた除去溶液をＩＣＰ－ＭＳ分析する旨の記載がある。
For example, in Japanese Patent Laid-Open No. 2013-151413 (Patent Document 2), in analyzing the metal concentration on the silicon surface, chemical removal of the silicon surface by dissolution is performed according to ASTM F 1724-96, and the obtained removal is performed. There is a statement that the solution is analyzed by ICP-MS.
上記ASTM F 1724-96の溶解条件の場合、シリコン表面をエッチングする混酸は、フッ酸濃度が０．９１ｗｔ％、硝酸濃度が１．２ｗｔ％、過酸化水素濃度が０．５７ｗｔ％であり、極めて希薄な酸濃度である。従って、溶解するシリコン表面層は精々１μｍ程度と僅かであり、表面の汚染不純物の全てが除去溶液に捕集できていない可能性がある。
In the above ASTM F 1724-96 dissolution conditions, the mixed acid that etches the silicon surface has a hydrofluoric acid concentration of 0.91 wt%, a nitric acid concentration of 1.2 wt%, and a hydrogen peroxide concentration of 0.57 wt%. Dilute acid concentration. Therefore, the silicon surface layer to be dissolved is as small as about 1 μm, and there is a possibility that not all of the surface contamination impurities can be collected in the removal solution.
そこで、本発明者らは、どの程度の取り代であればほぼ全ての表面不純物を捕集できるのかという点につき検討を行った。
Therefore, the present inventors examined the extent of machining allowance to collect almost all surface impurities.
ＣＺ単結晶製造用途の多結晶シリコン塊をＷＣ製のハンマにて破砕した後に、フッ酸と硝酸の混酸でエッチングして、表面の汚染不純物を除去溶液に捕集した。混酸は、ＨＦ：ＨＮＯ３＝１：９（体積比）とし、ＨＦは５０ｗｔ％、ＨＮＯ３は７０ｗｔ％の、電子産業用グレードのものである。
A polycrystalline silicon lump for CZ single crystal production was crushed with a WC hammer, and then etched with a mixed acid of hydrofluoric acid and nitric acid to collect impurities on the surface in the removal solution. The mixed acid is HF: HNO 3 = 1: 9 (volume ratio), HF is 50 wt%, HNO 3 is 70 wt%, and the grade for electronic industry.
エッチングの際の液温は、常温から３９℃の間に制御した。エッチングの進行に伴い液温は上昇するが、エッチャントを循環ポンプにより流動させ、その配管途中に熱交換器を設置し発熱量の除熱を行った。エッチング槽の容積は４０リットル、循環流量は４０リットル／分である。
The liquid temperature during etching was controlled between room temperature and 39 ° C. As the etching progresses, the liquid temperature rises, but the etchant is made to flow with a circulation pump, and a heat exchanger is installed in the middle of the piping to remove the heat generated. The volume of the etching tank is 40 liters, and the circulation flow rate is 40 liters / minute.
エッチング時間は５分～１０分とし、エッチング時間の設定により、取り代を１０μｍ程度とした。エッチング終了後に超純水にてリンスを十分に行った。なお、最終リンス槽での電気伝導度は３ＭΩ－ｃｍ以上である。その後に通風乾燥器による乾燥を行った。通風空気はＨＥＰＡフィルタを介した。乾燥温度は８５℃、乾燥時間は７分である。
The etching time was 5 to 10 minutes, and the machining allowance was about 10 μm by setting the etching time. After the etching was completed, rinsing was performed sufficiently with ultrapure water. The electrical conductivity in the final rinse tank is 3 MΩ-cm or more. Thereafter, drying was performed with a ventilator. Ventilation air passed through a HEPA filter. The drying temperature is 85 ° C. and the drying time is 7 minutes.
上述したASTM F 1724-96に則ったエッチングで得た除去溶液（試験液Ａ）と、取り代を１０μｍ程度としたエッチングで得た除去溶液（試験液Ｂ）による、表面不純物の捕集レベルを比較するために、（ｉ）試験液Ａを得た後の多結晶シリコン塊をエッチングして試験液Ｂを得る条件（分析条件Ｉ）と、（ｉｉ）試験液Ｂを得た後の多結晶シリコン塊をエッチングして試験液Ａを得る条件（分析条件ＩＩ）の２条件で、ＩＣＰ－ＭＳ分析の結果を比較した。その分析結果を表１及び表２に纏めた。なお、不純物濃度の単位はｐｐｔｗである。
The collection level of surface impurities by the removal solution (test solution A) obtained by etching according to ASTM F 1724-96 described above and the removal solution (test solution B) obtained by etching with a removal allowance of about 10 μm. For comparison, (i) the condition (analysis condition I) for obtaining the test solution B by etching the polycrystalline silicon lump after obtaining the test solution A, and (ii) the polycrystal after obtaining the test solution B The results of ICP-MS analysis were compared under the two conditions (analysis condition II) for etching the silicon mass to obtain test solution A. The analysis results are summarized in Tables 1 and 2. The unit of impurity concentration is pptw.
これらの結果によれば、分析条件Ｉでは、試験液Ｂから検知される不純物濃度は試験液Ａで検知された不純物濃度を大きく上回っている。これに対し、分析条件ＩＩでは、試験液Ａからは不純物は殆ど検知されていない。
According to these results, under the analysis condition I, the impurity concentration detected from the test solution B greatly exceeds the impurity concentration detected from the test solution A. On the other hand, almost no impurities are detected from the test solution A under the analysis condition II.
この事実は、ASTM F 1724-96の溶解条件では表面の汚染不純物の全てが除去溶液に捕集できていないこと、表面を１０μｍ以上の取り代で酸で溶解すれば表面汚染不純物のほぼ全てを除去溶液に捕集できることを意味している。
This fact indicates that all of the surface contamination impurities cannot be collected in the removal solution under the dissolution conditions of ASTM F 1724-96, and if the surface is dissolved with an acid with a removal allowance of 10 μm or more, almost all of the surface contamination impurities are removed. It means that it can be collected in the removal solution.
つまり、多結晶シリコンの表面を１０μｍ以上の取り代で酸で溶解して得た抽出液を試験液とし、この試験液の質量分析結果に基づいて多結晶シリコンの表面金属濃度を定量すれば、多結晶シリコンの表面清浄度を評価することができる。
That is, if an extract obtained by dissolving the surface of polycrystalline silicon with an acid with a machining allowance of 10 μm or more is used as a test solution, and the surface metal concentration of polycrystalline silicon is quantified based on the mass analysis result of this test solution, The surface cleanliness of polycrystalline silicon can be evaluated.
これまで説明してきた本発明に係る多結晶シリコンの表面清浄度評価手法を用いることにより、例えば、下記のような表面清浄度を有する多結晶シリコンの品質保証が可能となる。
By using the polycrystalline silicon surface cleanliness evaluation method according to the present invention described so far, for example, the quality of polycrystalline silicon having the following surface cleanliness can be assured.
表面のＰ濃度が１ｐｐｔｗレベルの多結晶シリコン。
Polycrystalline silicon whose surface P concentration is 1pptw level.
表面のＢ濃度が１ｐｐｔｗレベルの多結晶シリコン。
Polycrystalline silicon with B concentration on the surface of 1pptw level.
表面のＡｓ濃度が０．１ｐｐｔｗレベルの多結晶シリコン。
Polycrystalline silicon with a surface As concentration of 0.1 pptw.
表面のＡｌ濃度が１ｐｐｔｗ以下レベルの多結晶シリコン。
Polycrystalline silicon with a surface Al concentration of 1pptw or less.
表面のＦｅ、Ｃｒ、Ｎｉ、Ｃｕ、Ｎａ、Ｚｎの６元素の合計濃度が１ｐｐｔｗレベルの多結晶シリコン。
Polycrystalline silicon with a total concentration of 6 elements of Fe, Cr, Ni, Cu, Na and Zn on the surface being 1pptw level.
表面のＬｉ、Ｍｇ、Ｋ、Ｃａ、Ｔｉ、Ｍｎ、Ｃｏ、Ｍｏ、Ｓｎ、Ｗ、Ｐｂの１１元素の合計濃度が１ｐｐｔｗレベルの多結晶シリコン。
Polycrystalline silicon with a total concentration of 11 elements of Li, Mg, K, Ca, Ti, Mn, Co, Mo, Sn, W, and Pb on the surface of 1 ptw level.
本発明により、多結晶シリコン表面のリン（Ｐ）および金属不純物の濃度の測定下限が、従来よりも低いものとなり、多結晶シリコンの表面清浄化に寄与する技術が提供される。
According to the present invention, the lower limit of measurement of phosphorus (P) and metal impurity concentrations on the surface of polycrystalline silicon is lower than that in the prior art, and a technique that contributes to surface cleaning of polycrystalline silicon is provided.
According to the present invention, the lower limit of measurement of phosphorus (P) and metal impurity concentrations on the surface of polycrystalline silicon is lower than that in the prior art, and a technique that contributes to surface cleaning of polycrystalline silicon is provided.
Claims (3)
- 多結晶シリコンの表面清浄度評価方法であって、
多結晶シリコンの表面を酸で溶解して得た抽出液を９０℃以下の条件で蒸発乾固させる第１ステップと、
該蒸発乾固後の残留物にフッ酸を添加して９０℃以下の条件で再び蒸発乾固させる第２ステップと、
該再度の蒸発乾固後の残留物にフッ酸を添加して９０℃以下の条件でもう一度蒸発乾固させる第３のステップと、
前記第３のステップの蒸発乾固で得られた残留物に超純水を加えて試験液とする第４のステップを備え、
前記試験液の質量分析結果に基づいて前記多結晶シリコンの表面のリン（Ｐ）濃度を定量して該多結晶シリコンの表面清浄度を評価する方法。 A method for evaluating the surface cleanliness of polycrystalline silicon,
A first step of evaporating and drying an extract obtained by dissolving the surface of polycrystalline silicon with an acid at a temperature of 90 ° C. or lower;
A second step of adding hydrofluoric acid to the residue after the evaporation to dryness and evaporating to dryness again at a temperature of 90 ° C. or lower;
A third step of adding hydrofluoric acid to the residue after the re-evaporation to dryness and evaporating to dryness again at a temperature of 90 ° C. or lower;
A fourth step of adding ultrapure water to the residue obtained by evaporation to dryness in the third step to obtain a test solution;
A method for evaluating the surface cleanliness of the polycrystalline silicon by quantifying the phosphorus (P) concentration on the surface of the polycrystalline silicon based on a mass analysis result of the test solution. - 多結晶シリコンの表面清浄度評価方法であって、
多結晶シリコンの表面を１０μｍ以上の取り代で酸で溶解して得た抽出液を試験液とし、該試験液の質量分析結果に基づいて前記多結晶シリコンの表面金属濃度を定量して該多結晶シリコンの表面清浄度を評価する方法。 A method for evaluating the surface cleanliness of polycrystalline silicon,
An extract obtained by dissolving the surface of polycrystalline silicon with an acid with an allowance of 10 μm or more is used as a test solution, and the surface metal concentration of the polycrystalline silicon is quantified based on the mass analysis result of the test solution. A method for evaluating the surface cleanliness of crystalline silicon. - 請求項１または２に記載の方法で評価した結果に基づき、前記多結晶シリコン表面の清浄度を保証する、多結晶シリコンの品質保証方法。
A quality assurance method for polycrystalline silicon, which guarantees the cleanliness of the surface of the polycrystalline silicon based on the result of evaluation by the method according to claim 1.
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