JPH11304791A - Method for analyzing impurity of polycrystal silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a concentration of impurities of a granular polycrystal silicon that cannot be turned to a single crystal by the FZ method, by forming the granular polycrystal silicon of a small shape to a columnar sintered silicon by a method not contaminating the silicon, turning the columnar body to a single crystal by the FZ method, and measuring a quantity of impurities of a finally solidified part. SOLUTION: A granular polycrystal silicon of an average particle size of 1000 μm is induction heated to be formed into a rod formation body without impurities mixed. The formed columnar silicon 8 of a diameter of 15 mm is induction heated and, a seed crystal 9 is moved from below to dip and melt an upper end in a melt liquid generated at a lower end of the columnar silicon 8. A single crystal is grown at the upper end of the seed crystal 9. After the single crystal 10 is grown to 10-300 mm, the movement is stopped and the melt liquid between the columnar silicon 8 and the single crystal 10 is cut. Immediately before being cut, the melt liquid is held at an upper end of the single crystal and solidified, whereby a final solidified part 11 is obtained. After a weight of the single crystal is measured, impurities of the cut final solidified part are analyzed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the impurity concentration of polycrystalline silicon having a small shape. In particular, the present invention relates to a method for quantifying the impurity concentration of small-sized granular polycrystalline silicon.

[0002]

2. Description of the Related Art Conventionally, chemical analysis and activation analysis have been known as methods for quantifying the impurity concentration of granular polycrystalline silicon having a small shape. However, in the case of polycrystalline silicon having an extremely small impurity content, it has been difficult to quantify the impurity content therein. Further, utilizing the fact that the segregation coefficient of impurities is smaller than 1, focusing on the fact that impurities are concentrated in the final solidified portion after growing polycrystalline silicon into a single crystal by the FZ method, (Japanese Patent Application Laid-Open No. 6-26803), it has been reported that granular silicon has an extremely small shape and cannot be directly single-crystallized by the FZ method. Could not be adopted.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and cannot be quantitatively determined by direct chemical analysis or activation analysis or the like and has an extremely small shape due to an extremely small impurity content. It is an object of the present invention to provide a novel method capable of quantifying the impurity concentration of granular polycrystalline silicon which cannot be single-crystallized by the FZ method because of its small size.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above technical problems, and as a result, have been proposed to reduce the size of granular polycrystalline silicon by a method that does not cause contamination first. Is formed, and the formed body is formed as F
A single crystal is formed by the Z method, and the amount of impurities in the final solidified portion is measured. As a result, the amount of impurities is extremely small, so that it cannot be directly quantified by chemical analysis or activation analysis, and the shape is extremely small. The present inventors have found a method for accurately quantifying the impurity concentration of granular polycrystalline silicon that cannot be single-crystallized by the method, and have completed the present invention.

According to the present invention, there is provided a method for measuring the concentration of impurities contained in granular polycrystalline silicon having a particle size of 200 to 15000 μm.
m in a non-conductive cylinder, and the cylinder filled with the granular polycrystalline silicon is set up vertically, and heated in a belt shape from the circumferential direction. By melting and sintering silicon and integrating it,
By separating from the surface of the cylinder, forming a constricted part in the polycrystalline silicon in the cylinder, and sequentially moving the heating zone upward or downward, the constricted part is continuously expanded to form a columnar body of sintered silicon. Using the columnar body obtained as a sample as a sample, a single crystal is formed by the FZ method, and the final solidified portion is 5% by weight to 10% by weight of the entire single crystal.
This is a method for measuring the impurity concentration of granular polycrystalline silicon, wherein the impurity content is determined to be less than 10% by weight, and the impurity in the final solidified portion is measured and converted into the concentration in the sample.

The polycrystalline silicon to be analyzed in the present invention can be used without particular limitation as long as it has a particle size of about 200 to 15000 μm.
It can be applied to granular polycrystalline silicon grown by depositing silicon on seed particles by utilizing thermal decomposition or reduction reaction of silanes such as dichlorosilane and trichlorosilane, and a bell jar type reactor Thus, silicon may be deposited on a silicon core wire by utilizing thermal decomposition or reduction reaction of silanes such as monosilane, dichlorosilane, trichlorosilane and the like, grown into a rod shape, and then crushed into a granular polycrystal. In the present invention, the impurity element that can be measured in the present invention is more preferably as the segregation coefficient is smaller, for example, an element having a segregation coefficient smaller than 1 is particularly preferable. These elements include Li, Cu, Ag, Au, Zn, Cd, Cr, A
1, Ga, In, Th, Sn, As, Bi, Mg, F
e, Co, Ni, Ta and the like. The method of converting granular polycrystalline silicon into columnar sintered silicon is particularly important in the present invention and forms the basis. That is,
In order to convert the granular polycrystalline silicon into a columnar sintered silicon without being contaminated by impurities in the cylindrical body filled with the granular polycrystalline silicon, first, the granular polycrystalline silicon has an inner diameter of 10 to 50 mm and a length of 100 to 50 mm. Fill a non-conductive cylinder with a bottom of 1000 mm, preferably 200-300 mm. If the inner diameter of the cylindrical body is smaller than 10 mm, the diameter of the columnar sintered silicon obtained is too small and it is difficult to single crystallize it by the FZ method. It will be difficult. The thickness of the cylindrical body is about 2 to 10 mm, and preferably about 3 to 8 mm in consideration of strength and heat conduction. The material of the cylindrical body may be non-conductive, but usually, ceramics such as alumina, silica and silicon nitride are used. In particular, transparent quartz glass is preferably used because the inside can be seen through.
Next, the cylindrical body filled with granular polycrystalline silicon is set up vertically, heated in a belt shape from the circumferential direction, and at least a part of the granular polycrystalline silicon is integrated by fusion sintering in the cross section inside the cylindrical body. Let it. If the cylinder does not stand upright,
The silicon melt generated by heating is likely to come into contact with the inner surface of the cylindrical body, and if it does, it is not preferable because impurities are contaminated from the cylindrical body.

As a heating method, when heating is not performed in a belt shape from the circumferential direction, the whole silicon filled in the cylinder is melted, and the granular polycrystalline silicon which forms the basis of the present invention is converted into columnar sintered silicon. This is not preferable because it is not possible to do so. Therefore, if the heating means can heat the polycrystalline silicon as a content to 1400 ° C. to 1450 ° C.,
Any means can be used as long as heating can be performed in a belt shape from the circumferential direction. For example, a method such as high-frequency induction heating, infrared heating, or microwave heating can be adopted. By heating in such a manner, at least a part of the sintered portion and the fused portion of the granular polycrystalline silicon are formed in the cross section inside the cylinder. At this time, if the heating is excessive, the melted portion becomes too large, the portion integrated by melt sintering is not separated from the surface of the cylinder, and furthermore, the portion confined to the polycrystalline silicon in the cylinder is not formed, It is not preferable because the molten silicon flows out or the molten silicon comes into contact with the surface of the cylinder and is contaminated with impurities from the cylinder. Therefore, it is necessary to adjust the degree of heating so that the fusion zone does not become too large. Generally, the length of the silicon melted portion in the height direction has an appropriate length according to the inner diameter of the non-conductive cylinder, and is generally set to be equal to or less than the length of the inner diameter. For example, when using a non-conductive cylinder having a diameter of 30 mm, it is preferable to adjust the degree of heating so as to be 1 mm to 20 mm. The constricted portion of the polycrystalline silicon formed in this manner is sequentially moved upward or downward in the heating zone, so that the constricted portion is continuously enlarged to form a columnar body of sintered silicon. The moving speed of the heating zone has an appropriate speed according to the diameter of the non-conductive cylinder. For example, when a non-conductive cylinder having an inner diameter of 30 mm is used, a speed of 10 to 30 mm / min is employed. Is preferred. The method of converting the compact into a single crystal by the FZ method is a method that does not cause contamination of impurities when the FZ method is performed, and that the final solidified portion is less than 5% by weight to 10% by weight of the entire single crystal. The method is not particularly limited as long as it is a method, but it is preferable to carry out the method so that the final solidified portion is 6% by weight to 8% by weight. 5% by weight of the final solidified part of the whole single crystal
If the content is less than 10% by weight, the concentration of the impurities in the portion becomes insufficient. It is not preferable to determine the amount of impurities in an extremely small amount of polycrystal. The method for measuring the amount of impurities in the final solidified portion is not particularly limited, but general methods include chemical analysis and activation analysis, and in particular, dissolving the final solidified portion in a solution to measure each element in the solution. The concentration is determined by atomic absorption or ICP-
A method of measuring by MS or the like may be used. The calculation of the impurity concentration in the granular polycrystalline silicon as the raw material from the measurement result of the impurity amount in the final solidified portion can be performed by dividing the impurity amount in the final solidified portion by the weight of the entire FZ single crystal.

Next, details of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of a method of forming granular polycrystalline silicon grown by a fluidized bed method into a rod-shaped formed body without being contaminated by an impurity component. Particle size 500
Granular polycrystalline silicon 1 having an average particle diameter of 1000 μm in the range of ~ 1200 μm has an inner diameter of 20 mm, a length of 500 mm,
Fill a transparent quartz cylinder 2 with a thickness of 5 mm and output 5 to 50
A high frequency induction heating device of about kilowatts applies high frequency to the coil 6 to inductively heat the carbon plate 7 provided for preheating, and a temperature sufficient to perform induction heating of the granular silicon 1 by radiant heat from the carbon plate 7. Heat until As the carbon plate, an annular or divided annular having a diameter approximately 3 to 10 mm larger than the outer diameter of the cylindrical body is used. When the high frequency is applied to the granular silicon 1, a part of the granular silicon near the high frequency induction heating coil 6 is melted to form a sintered portion and a fused portion of polycrystalline silicon. At this time, the output of the high frequency is adjusted so that the length of the fusion zone in the height direction is 5 mm to 10 mm. As shown in FIG. 2, after this state is formed, the entire cylinder is moved downward at a speed of 10 mm / min to bring the molten silicon 3 into contact with the inner wall 5 of the cylindrical body by the surface tension of the molten silicon 3. In this way, the columnar silicon 4 is formed without any impurities, and the rod-shaped formed body 4 free of impurities from the inner wall 5 of the cylindrical body is formed. FIG. 3 is a schematic view showing an embodiment in which the columnar silicon thus produced is made into a single crystal by the FZ method. The columnar silicon 8 having a diameter of 15 mm prepared by the method of FIG. 1 is set so that its lower end is near the high-frequency induction heating coil 6. A high frequency is applied to the high frequency induction heating coil 6 to inductively heat the carbon plate 7, and the lower end of the columnar silicon 8 is heated by the radiant heat from the carbon plate 7 to a temperature sufficient to perform induction heating. When high frequency is applied to the lower end of the columnar silicon 8, it melts. After this state is formed, the seed crystal 9 is moved from below, and the upper end of the seed crystal 9 is immersed and melted in the molten liquid formed at the lower end of the columnar silicon 8. After the upper end of the seed crystal 9 is melted, the columnar silicon 8 and the seed crystal 9 are simultaneously moved downward at a predetermined speed, generally 1 to
By moving the columnar silicon 8 at a rate of 5 mm / min, the columnar silicon 8 melts sequentially from the lower end, and a single crystal grows sequentially on the upper end of the seed crystal 9. As shown in FIG. 4, a predetermined length, for example, 10
After the single crystal 10 has grown to 0 to 300 mm, the downward movement of the columnar silicon 8 is stopped to cut off the melt formed between the columnar silicon 8 and the single crystal 10,
The melt formed between the columnar silicon and the single crystal immediately before cutting is held at the upper end of the single crystal and then solidified to obtain a so-called final solidified portion 11. Immediately before the cutting, the amount of the melt formed between the columnar silicon and the single crystal is set to a predetermined amount, generally a triangular pyramid having a height substantially the same as the diameter. The output of the high frequency is adjusted before cutting the melt formed in the above. After measuring the weight of the thus prepared single crystal by the FZ method, the final solidified portion is separated from the single crystal with a cutter or the like, and the amount of impurities in the separated final solidified portion is measured by chemical analysis. By dividing the measured amount by the weight of the entire FZ single crystal, the impurity concentration in the raw material granular polycrystalline silicon is calculated.

[0009]

According to the method of the present invention, since the impurity content is extremely small, it cannot be quantified by direct chemical analysis or activation analysis or the like, and since the shape is extremely small, it is directly crystallized by the FZ method. It is easy to quantify the impurity concentration of the granular polycrystalline silicon that cannot be performed.

[0010]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Granular polycrystalline silicon having a mean particle size of 1200 μm, which was grown by depositing silicon on seed particles using a thermal decomposition reaction of monosilane in a fluidized bed reactor.
A cylinder with a bottom made of transparent quartz glass having a length of 20 cm, an inner diameter of 20 mm, and a thickness of 5 mm was installed vertically, and 80 g of granular polycrystalline silicon was filled therein. In the initial stage of heating using an apparatus as shown in FIG. 1, a carbon plate is heated by a high-frequency induction heating coil at an output of 7 KW (frequency is 2 MHz), and granular polycrystalline silicon is subjected to induction heating by radiant heat from the carbon plate. The cylinder was radiantly heated to a temperature sufficient to perform. After confirming that the high frequency was applied to the granular polycrystalline silicon, the carbon plate was removed, and at the same time, the high frequency output was reduced from 7 KW to 5 KW, and a portion of the granular polycrystalline silicon near the high frequency induction heating coil was melted,
The upper part of the molten silicon was in a sintered state. At this time, the high-frequency output was adjusted so that the length of the fusion zone in the height direction was 12 mm. After the above state was made, the entire cylinder was lowered at a moving speed of 10 mm / min, and the heating area was relatively raised. During the movement of the heating zone, the high frequency output was maintained at 3 KW so that the state of sintering, melting and solidification did not change. Thus, a rod-shaped silicon having a diameter of 15 mm and a length of 170 mm was produced. The obtained bar-shaped silicon was set so that its lower end was in the plane of the high-frequency induction heating coil. In the initial stage of heating, the carbon plate is heated by a high-frequency induction heating coil at an output of 7 KW (frequency is 2 MHz), and the radiant heat from the carbon plate causes the bar-shaped silicon to reach a temperature sufficient for induction heating. Was radiatively heated. After confirming that high frequency was applied to the bar-shaped silicon, the carbon plate was removed, and at the same time, the high frequency output was reduced to 7 KW.
To 4 KW, so that the lower end of the bar-shaped silicon 10 mm was in a molten state. A seed single crystal having a length of 80 mm and a side of 5 mm square is moved from below, and its upper end is immersed and melted in a molten liquid formed at the lower end of the rod-shaped silicon. It was connected. After the above-mentioned state was formed, the rod-shaped silicon and the seed crystal were simultaneously moved downward at a speed of 2 mm / min and 2 mm / min, respectively, and the heating area was relatively raised. During the movement of the heating zone, the high-frequency output is set to 4 so that the amount of melt does not change.
KW was maintained. Thus, a length of 100 above the seed crystal
After growing a single crystal of 1 mm, the high-frequency output was lowered from 4 KW to 2.5 KW, the amount of the melt was reduced, and the downward movement of the rod-shaped silicon was stopped to form between the columnar silicon and the single crystal. The melt was cut off, and the melt formed between the rod-shaped silicon and the single crystal was held at the upper end of the single crystal immediately before cutting, and then solidified to form a so-called final solidified portion. Thus, a single crystal of 40 g was prepared. The final solidified portion was separated from the single crystal with a diamond cutter to obtain 2.8 g of the final solidified portion. This final solidified portion was 7% by weight of the entire single crystal. After cleaning the surface with nitric acid, the whole was dissolved in a mixed solution of hydrofluoric acid and nitric acid, and the contents of the elements in the solution were measured by ICP-MS. The measured amount was divided by the single crystal weight of 40 g to obtain the impurity concentration in the raw material granular polycrystalline silicon. The results are shown in Table 1. For comparison, after the surface of the granular polycrystalline silicon was washed with nitric acid, the whole was dissolved in a mixed solution of hydrofluoric acid and nitric acid, and the contents of the elements in the solution were measured by ICP-MS. As shown in Table 1, the method of directly dissolving granular polycrystalline silicon could not be quantified because the content of each element in the granular polycrystalline silicon was below the detection limit of each element in ICP-MS. . On the other hand, in the method of obtaining the impurity concentration in the raw material granular polycrystalline silicon based on the analysis result of the final solidified portion, the impurity is concentrated 14 times in the final solidified portion, so that the concentration exceeds the detection limit of each element in ICP-MS, and the amount is determined. did it.

[0012]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a perspective view of a typical method of forming granular polycrystalline silicon into a rod-shaped body without being contaminated by an impurity component according to the present invention.

FIG. 2 is a schematic view of a method of forming a representative granular polycrystalline silicon into a rod-shaped body without being contaminated by an impurity component according to the present invention.

FIG. 3 shows a typical columnar silicon of the present invention in FZ.
FIG. 3 is a perspective view of a method of forming a single crystal by a method.

FIG. 4 is a schematic diagram of a method for forming a final solidified portion of a typical single crystal of the present invention.

[Description of Signs] 1, granular polycrystalline silicon 2, non-conductive cylinder 3, molten silicon 4, solidified columnar silicon 5, non-conductive cylindrical inner wall 6, high-frequency induction heating coil 7, carbon plate 8 , Sintered columnar silicon 9, seed crystal 10, silicon single crystal 11, final solidification of single crystal

Claims (1)

[Claims] 1. A method for measuring the concentration of impurities contained in granular polycrystalline silicon having a particle size of 200 to 15000 μm, wherein said granular polycrystalline silicon is filled in a non-conductive cylinder having an inner diameter of 10 to 50 mm, and The cylinder filled with silicon is set up vertically, heated in a belt shape from the circumferential direction, and at least a part of the granular polycrystalline silicon is integrated by fusion sintering in the cross section of the cylinder, thereby obtaining the surface of the cylinder. To form a constricted portion in the polycrystalline silicon in the cylindrical body, and by sequentially moving the heating zone upward or downward, the constricted portion is continuously expanded to form a columnar body of sintered silicon. Using the obtained columnar body as a sample, a single crystal was formed by the FZ method,
The final solidified portion is 5% to 10% by weight of the entire single crystal
A method of measuring impurities in a granular polycrystalline silicon, wherein impurities in a final solidified portion are measured and converted into a concentration in a sample.