Evaporation of Phosphorus in Molten Silicon by an Electron Beam Irradiation Method

Hanazawa, Kazuhiro; Yuge, Noriyoshi; Kato, Yoshiei

doi:10.2320/matertrans.45.844

Cited by 76 publications

(34 citation statements)

References 14 publications

(18 reference statements)

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“…Figure 11 shows a schematic representation of the metallurgical process used to produce high-purity SOG-Si from MG-Si. 1) This comprises two sequential processes: 1) evaporation of phosphorus 3) and elimination of metallic impurities by first directional solidification 2) in the electron beam melting furnace, followed by 2) boron oxidation with steam-added plasma, as described here, and elimination of metallic elements by second directional solidification. …”

Section: Kinetics Of Boron Oxidation In Molten Siliconmentioning

confidence: 99%

“…However, to obtain the properties required in solar grade silicon (SOG-Si), which includes p-type, 0.005-0.01 m and a conversion efficiency of 14-15%, the content of impurities such as boron, phosphorus, iron, aluminum, and titanium in the silicon must be reduced to below the permissible levels shown in Table 1. [1][2][3] With the metallurgical purification method, metallic elements with a low equilibrium partition coefficient are eliminated by directional solidification, 1,2) and phosphorus is removed by evaporation, taking advantage of its high vapor pressure. [3][4][5] On the other hand, boron is difficult to remove by either of these two methods because it has an equilibrium partition coefficient of 0.8 6) and a low vapor pressure similar to that of iron and titanium.…”

Section: Introductionmentioning

confidence: 99%

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Boron Removal in Molten Silicon by a Steam-Added Plasma Melting Method

Nakamura¹,

Baba²,

Sakaguchi³

et al. 2004

Mater. Trans.

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Oxidation and removal of boron from molten silicon by a steam-added plasma melting method was investigated as an important part of a sequential metallurgical process for producing high-purity solar grade silicon (SOG-Si) from commercially available metallurgical grade silicon (MG-Si). Experiments were carried out with the mass of silicon per charge varied in the range from 0.6 to 300 kg, corresponding to the laboratory scale to industrial scale. Boron was removed to ½B < 0:1 mass ppm, which is the permissible boron content for SOG-Si. The deboronization rate was proportional to the steam content, 3.2th power of the hydrogen content of the plasma gas, boron content of the molten silicon, and area of the dimple formed by the plasma gas jet, and was inversely proportional to the mass of the molten silicon. A thermodynamic study showed that preferential oxidation of boron in molten silicon is positively related to higher temperatures, supporting the conclusion that this plasma method, which causes a local increase in the temperature of the reaction surface, is in principle advantageous.

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Section: Kinetics Of Boron Oxidation In Molten Siliconmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Boron Removal in Molten Silicon by a Steam-Added Plasma Melting Method

Nakamura¹,

Baba²,

Sakaguchi³

et al. 2004

Mater. Trans.

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“…Table 1 shows experimental conditions such as the silicon feed rate, EB power, chamber pressure, and mold size in the laboratory scale and industrial scale experiments. Silicon melted by the EB flows from the silicon melting and dephosphorization hearth 7) to the water-cooled copper mold used for directional solidification through an overflow gate. The EB is irradiated on the surface of the molten silicon in the water-cooled copper mold as well as in the de-P hearth.…”

Section: Introductionmentioning

confidence: 99%

“…Metallic impurities such as iron, aluminum, and titanium are removed from molten silicon in the EB melting furnace after dephosphorization. 7) The EB melting furnace consists of a vacuum chamber, EB gun, vacuum pump system, raw material feed system, hearth for phosphorous evaporation, and water-cooled copper mold for directional solidification. The mold can turn in both the normal and reverse directions with respect to the central axis.…”

Section: Introductionmentioning

confidence: 99%

Removal of Metal Impurities in Molten Silicon by Directional Solidification with Electron Beam Heating

Yuge¹,

Hanazawa²,

Kato³

2004

Mater. Trans.

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An industrial-scale pyrometallurgical method of removing metallic impurities from metallurgical grade silicon (MG-Si) was developed as an element technology in a sequential purification process for manufacturing high-purity silicon for solar grade silicon (SOG-Si) by segregation of metallic impurities during solidification. Metallic impurities were removed from MG-Si using an electron beam heating equipment. Molten silicon was supplied continuously at a constant mass to a water-cooled copper mold and was allowed to solidify gradually in an unidirectional manner from the bottom upward. This process is termed directional solidification. The iron concentration after solidification can be expressed by Pfann's and Burton's equations, and was reduced from an initial 1500 mass ppm to below 10 mass ppm. Aluminum removal was excessive, presumably due to vaporization to the gas phase. Above a certain height in the ingot, it became impossible to remove metallic impurities by partition during directional solidification. This phenomenon showed a correlation with the concentration of enriched iron in the silicon pool. The mechanism of metallic impurity removal was estimated based on visual examination of the solidified structure and EPMA. The iron concentration profile of ingots and critical purification height were estimated experimentally using a 20 kg scale device and verified as being applicable on an industrial scale in experiments with 150 kg scale equipment. Solar grade silicon was test-produced by this process and showed satisfactory quality for solar cell use.

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“…The purification of MG-Si through metallurgical routes such as directional solidification [1,2], slag refining [3][4][5], oxidation with plasma melting [6][7][8][9], and vacuum melting [10,11] has been investigated. The individual process has its own limitations and does not allow removal of all impurities.…”

Section: Introductionmentioning

confidence: 99%

Effect of solidification conditions on the silicon growth and refining using Si–Sn melt

Lei

Yoshikawa

et al. 2015

Journal of Crystal Growth

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Effect of solidification conditions on the silicon growth and refining using si-Sn melt, Journal of Crystal Growth, http://dx.doi.org/10.1016/j. jcrysgro. 2015.08.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Institute of Industrial Science, The University of Tokyo, Tokyo, Japan. AbstractThe solidification refining of Si using a Si-Sn solvent was investigated under various cooling conditions: (1) slow cooling, (2) slow cooling with electromagnetic stirring, and (3) directional solidification with the aim of developing a novel low-cost route for solar-grade Si production. The separation efficiency of refined Si achieved by combining slow cooling and electromagnetic stirring was much higher than that achieved using directional solidification; in addition, the purification efficiency of the refined Si in both methods was similar. The separation mechanism of refined Si from a Si-Sn melt is also discussed. Purification testing of the refined Si revealed that more than 96% of the metallic impurities, approximately 60% B, and over 70% P were removed.

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Evaporation of Phosphorus in Molten Silicon by an Electron Beam Irradiation Method

Cited by 76 publications

References 14 publications

Boron Removal in Molten Silicon by a Steam-Added Plasma Melting Method

Boron Removal in Molten Silicon by a Steam-Added Plasma Melting Method

Removal of Metal Impurities in Molten Silicon by Directional Solidification with Electron Beam Heating

Effect of solidification conditions on the silicon growth and refining using Si–Sn melt

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