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Method of removing impurities from metallurgical grade silicon to produce solar grade silicon

A metallurgical-grade silicon and solar-grade technology, applied in chemical instruments and methods, silicon compounds, non-metallic elements, etc., can solve problems such as practical damage and ratio drop

Inactive Publication Date: 2007-01-03
DOW CORNING CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0004] In addition, when scaled up to larger quantities, the surface area to mass ratio does not change significantly according to the method of the present invention, whereas it drops significantly according to existing methods using molten silicon unless at least one Scale increases to a point where practicality is compromised

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0025]According to this example, several operations involving the removal of phosphorus from silicon were carried out using the method according to the invention, summarized below and given in Table 1. The data presented are the results obtained using different treatment atmospheres. Column 1 of Table 1 presents the analysis performed on the silica fume used as the starting material for the samples treated in columns 2-4. When the method is maintained at about 1370° C. for 36 hours, the removal efficiency of phosphorus from silicon is about 23% under an argon atmosphere of 760 Torr (101325 Pa), that is, as shown in column 2 of Table 1, at a pressure of 0.5 Torr ( 66.66Pa) is about 76%, which is shown in the third column of Table 1. The lower the total pressure conditions, the better the phosphorus removal efficiency obtained. Table 1 also shows that impurities such as calcium, copper, magnesium, manganese, sodium, tin and zinc were also significantly removed. The increase i...

Embodiment 2

[0029] This example shows how the choice of crucible composition affects the level of impurities in the product. Columns 2 and 3 of Table 2 show the impurities that exist after the powder described in Column 1 of Table 2 is treated in an alumina or fused silica crucible at a pressure of 0.5 Torr (66.66 Pa) at 1330°C for 36 hours content. The samples treated in alumina, Table 2, column 2, showed substantial removal of calcium, copper, manganese, phosphorus and zinc, but increased aluminum content. In contrast, the samples treated in fused silica, Table 2, column 3, showed a large reduction in aluminum, while reductions in other elements were similar to those seen with alumina crucibles. This shows that when suitable structural materials are used, the method of the present invention can also effectively remove aluminum in silicon. In column 4 of Table 2 for copper, the symbol <DL indicates that the content is below the measurement limit, below which the quantification of the c...

Embodiment 3

[0032] This example shows the effect of shorter processing times on impurity removal efficiency. Column 1 of Table 3 presents the analysis performed on the silicon powder used as the starting material for the samples in column 2 with a particle size of less than 180 microns. It was treated at 1370° C. for 7 hours under a pressure of 0.5 Torr (66.66 Pa). Column 3 of Table 3 presents the analysis performed on the silicon powder used as the starting material for the samples in column 4 having a particle size of less than 300 microns. It was treated at 1370° C. for 20 hours under a pressure of 0.5 Torr (66.66 Pa). Compared with the 36-hour treatment shown in the third column of Table 1, the removal efficiency of phosphorus decreased gradually with the decrease of treatment time. However, even 7 hours of treatment reduced the phosphorus content by approximately 42%.

[0033] condition

[0034] Table 3 shows that in the 20-hour treatment, the removal efficiency of phos...

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Abstract

Metallurgical grade silicon is purified by removing metallic impurities and non-metallic impurities. The object is to produce a silicon species that is suitable for use as solar grade silicon. The process involves grinding metallurgical grade silicon containing metallic and non-metallic impurities to a silicon powder consisting of particles of silicon having a diameter of less than about 5 millimeter. While maintaining the ground silicon powder in the solid state, the ground silicon powder is heated to a temperature less than the melting point of silicon (1410 DEG C) under reduced pressure. The heated ground silicon powder is maintained at that temperature for a period of time sufficient to enable at least one metallic or non-metallic impurity to be removed from the metallurgical grade silicon.

Description

field of invention [0001] The present invention relates to a process for the removal of impurities, especially phosphorus, from metallurgical grade (MG) silicon to produce solar grade (SG) silicon. Specifically, according to the present invention, when metallurgical grade silicon is processed, it is in a solid state and not in a molten state as is commonly practiced in prior art methods. Metallurgical grade silicon remains solid throughout the process. Background of the invention [0002] In US Patent 5,182,091 (January 26, 1993), phosphorus is removed by melting silicon under vacuum with an electron beam, followed by boron removal using a plasma process. Each step is followed by directional solidification to remove metal. In US Patent 6090361 (July 18, 2000) a method is described for the purification of metallurgical grade silicon for use in solar cell applications by evaporation of phosphorus from molten silicon under vacuum followed by directional solidification to remo...

Claims

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Application Information

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IPC IPC(8): C01B33/037
CPCC01B33/037
Inventor G·伯恩斯J·拉博S·伊尔麦茨
Owner DOW CORNING CORP
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