JP2014034506A - Method of selecting polycrystalline silicon rod, method of manufacturing polycrystalline silicon bulk, and method of manufacturing single crystal silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique contributing to stable manufacture of single crystal silicon by selecting polycrystalline silicon which is suitable as a raw material for single crystal silicon manufacture with high quantitativity and reproducibility.SOLUTION: A method of selecting a polycrystalline silicon rod includes: sampling a plate-like sample having a main plane in a section perpendicular to a radial direction of a polycrystalline silicon rod grown by deposition in a chemical growth method; measuring and comparing a thermal diffusivity α(T) of the plate-like sample with a thermal diffusivity α(T) of a standard sample; and selecting a polycrystalline silicon rod which is suitable as a raw material for single crystal silicon manufacture based upon the ratio (α(T)/α(T))) of the thermal diffusivities. As a standard sample for standardization, single crystal silicon is suitable and a single crystal silicon plate-like sample having a <100> plane as a main plane is specially suitable. When single crystal silicon is grown using the polycrystalline silicon rod, a crystal line is not lost. Consequently, single crystal silicon can be stably manufactured.

Description

  The present invention relates to a method for selecting a polycrystalline silicon rod used as a raw material for producing single crystal silicon, and more specifically to a method for selecting a polycrystalline silicon rod suitable for stably producing single crystal silicon.

  Single crystal silicon indispensable for manufacturing a semiconductor device or the like 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). Siemens method is a process of vapor deposition (precipitation) of polycrystalline silicon on the surface of silicon core wire by CVD (Chemical Vapor Deposition) method by contacting silane source gas such as trichlorosilane and monosilane with heated silicon core wire. It is a method to make it.

  For example, when single crystal silicon is grown by the CZ method, a polycrystalline silicon lump is charged in a quartz crucible, and a seed crystal is immersed in a silicon melt obtained by heating and melting this to eliminate dislocation lines. Crystals are pulled by gradually expanding the diameter until a predetermined diameter is obtained after the dislocation. At this time, if unmelted polycrystalline silicon remains in the silicon melt, this unmelted polycrystalline piece drifts in the vicinity of the solid-liquid interface by convection, causing dislocation generation and disappearing crystal lines. Cause.

  Further, Patent Document 2 discloses that needle-like crystals may be precipitated in a rod during the process of manufacturing a polycrystalline silicon rod (polycrystalline silicon rod) by the Siemens method. When single crystal silicon is grown by the above method, the individual crystallites do not melt uniformly according to their size due to the above-mentioned inhomogeneous microstructure, and the unmelted crystallites become solid particles as single particles through the melting zone. It has been reported that it passes through the crystal rod and is incorporated into the solidified surface of the single crystal as unmelted particles, which causes defect formation, but in single crystallization by the FZ method, the single crystal is formed by one FZ operation. There is a demand for highly productive polycrystalline silicon.

  With respect to this problem, in Patent Document 2, the sample surface cut perpendicularly to the long axis direction of the polycrystalline silicon rod is polished or polished, and after etching, the microcrystals of the structure are contrasted to such an extent that they can be visually recognized under an optical microscope. Has been proposed to measure the size and area ratio of needle-like crystals and determine the quality as a raw material for growing FZ single crystal silicon based on the measurement results.

Japanese Patent Publication No. 37-18861 JP 2008-285403 A

  However, the quality judgment by visual recognition under the optical microscope as in the method disclosed in Patent Document 2 is likely to cause a difference in results depending on the degree of etching of the observation sample surface, the observation technician's observation skill, and the like. In addition, it has poor quantitativeness and reproducibility. For this reason, from the standpoint of increasing the production yield of single crystal silicon, it is necessary to set a higher standard for quality determination, and as a result, the defective rate of polycrystalline silicon rods is increased.

  Further, according to the study by the present inventors, even when a polycrystalline silicon rod determined to be a non-defective product by the method disclosed in Patent Document 2 is used, a single crystal silicon rod growing step by the FZ method is used. It was also found that dislocations occurred and the crystal line disappeared.

  Furthermore, even in the crystal growth of single crystal silicon by the CZ method, if the degree of crystal orientation of the polycrystalline silicon lump used as a raw material is high, unmelted crystallites drift in the silicon melt in the quartz crucible, which is solidified. There is a possibility that the liquid crystal interface is reached and the crystal line disappears.

  Therefore, in order to stably produce single crystal silicon at a high yield, a technique for selecting polycrystalline silicon suitable as a raw material for producing single crystal silicon with high quantitativeness and reproducibility is required.

  The present invention has been made in view of such problems, and the object of the present invention is to select polycrystalline silicon suitable as a raw material for producing single crystal silicon with high quantitativeness and reproducibility. It is to provide a technology that contributes to stable manufacturing.

In order to solve the above problems, a method for selecting a polycrystalline silicon rod according to the present invention is a method for selecting a polycrystalline silicon rod used as a raw material for producing single crystal silicon, wherein the polycrystalline silicon rod is chemically A plate-like sample grown by precipitation by a growth method and having a cross section perpendicular to the radial direction of the polycrystalline silicon rod as a main surface is collected, and the plate-like sample is obtained at a temperature T (° C.) of 1100 ° C. or less. And the ratio (α (T) / α _R (T)) between the thermal diffusivity α (T) and the thermal diffusivity α _R (T) of the standard sample is determined, A polycrystalline silicon rod for producing single crystal silicon is selected based on the thermal diffusivity ratio (α (T) / α _R (T)).

  Preferably, the standard sample is a single crystal silicon plate sample having a <100> plane as a main surface.

In this case, in the first aspect, a polycrystalline silicon rod whose thermal diffusivity α (T) satisfies the following formula (1) is selected as a raw material for producing single crystal silicon.
α (T) / α _R (T) ≧ 0.10 × 10 ⁻³ T + 0.80 (1)

In the second aspect, a polycrystalline silicon rod having the measurement temperature T of 25 ° C. and the thermal diffusivity α (25 ° C.) satisfying the following formula (2) is selected as a raw material for producing single crystal silicon.
α (25 ° C.) / α _R (25 ° C.) ≧ 0.80 (2)

In a third aspect, a polycrystalline silicon rod having the measurement temperature T of 900 ° C. and the thermal diffusivity α (900 ° C.) satisfying the following formula (3) is selected as a raw material for producing single crystal silicon.
α (900 ° C.) / α _R (900 ° C.) ≧ 0.90 (3)

In the fourth aspect, a polycrystalline silicon rod having the measurement temperature T of 1000 ° C. and the thermal diffusivity α (1000 ° C.) satisfying the following formula (4) is selected as a raw material for producing single crystal silicon.
α (1000 ° C.) / α _R (1000 ° C.) ≧ 0.91 (4)

  The method for producing a polycrystalline silicon lump according to the present invention includes a step of crushing a polycrystalline silicon rod selected by the above-described method.

  In the method for producing single crystal silicon according to the present invention, the polycrystalline silicon rod selected by the above method is used as the silicon raw material, or the polycrystalline silicon lump obtained by the above method is used as the raw material.

  By using a polycrystalline silicon rod selected by the method of the present invention or a polycrystalline silicon lump obtained by pulverizing it as a raw material, the crystal line disappears in the growth process of single crystal silicon in both the FZ method and the CZ method. Is less likely to occur, and single crystal silicon can be obtained stably.

Single crystal silicon plate sample with a main surface of <100> plane used as standard sample and thermal diffusivity α (T) of plate sample obtained from polycrystalline silicon rod successfully single crystallized by one FZ treatment the ratio of the thermal diffusivity of the _{α R (T) (α (} T) / α R (T)) is a diagram plotting the measurement temperature. It is a figure for demonstrating the collection example of the plate-shaped sample for thermal diffusivity measurement from the polycrystalline-silicon stick | rod grown by the chemical vapor deposition method. It is a figure for demonstrating the collection example of the plate-shaped sample for thermal diffusivity measurement from the polycrystalline-silicon stick | rod grown by the chemical vapor deposition method.

  The method for selecting a polycrystalline silicon rod according to the present invention will be described below with reference to the drawings. In the following description, a case where the polycrystalline silicon rod selected by the method of the present invention is used for the production of single crystal silicon by the FZ method will be described as an example. It goes without saying that a polycrystalline silicon lump having low properties may be obtained and used as a raw material for producing single crystal silicon by the CZ method.

In the method for selecting a polycrystalline silicon rod for a raw material for producing single crystal silicon according to the present invention, a main surface is a cross section perpendicular to the radial direction of the polycrystalline silicon rod from a polycrystalline silicon rod grown by precipitation by a chemical growth method. A plate sample is taken and the thermal diffusivity α (T) of the plate sample is measured. Then, this thermal diffusivity α (T) is compared with the thermal diffusivity α _R (T) of the standard sample, and based on the ratio of thermal diffusivity (α (T) / α _R (T)), a single crystal A polycrystalline silicon rod suitable as a raw material for silicon production is selected.

  The thermal diffusivity measurement is not limited to the stationary method, but may be a non-stationary method such as a pulse heating method, a periodic heating method, or a hot wire method, but the pulse heating method (flash heating method) that excels in ease and accuracy of measurement should be used. Is preferred.

  In the pulse heating method, a sample to be measured is formed into a plate shape (generally a disk shape), and the thermal diffusivity is measured by the following procedure.

  First, a plate-like sample is fixed to an apparatus, and the surface of the plate-like sample is irradiated with pulsed light (usually a laser pulse) and heated instantaneously. By this heating, heat is transferred from the front surface to the back surface of the plate-like sample, and the temperature of the back surface rises. The thermal diffusivity α (T) is calculated by observing the change in the back surface temperature. . The temperature for measuring the thermal diffusivity can be arbitrarily set by heating from an electric furnace installed in the apparatus.

In the present invention, the calculated thermal diffusivity α (T) is normalized by the thermal diffusivity α _R (T) of the standard sample for the purpose of improving the reproducibility of the measurement result. Specifically, the ratio (α (T) / α _R (T)) between the thermal diffusivity α (T) and the thermal diffusivity α _R (T) is obtained.

  As a standard sample for standardization, single crystal silicon is preferable, and a single crystal silicon plate sample having a <100> plane as a main surface is particularly preferable.

Such a measurement is possible in principle if the temperature is lower than the melting temperature of the silicon crystal. However, according to the study by the present inventors, the value of α (T) / α _R (T) tends to decrease as the measurement temperature increases. That is, not only the difference in α (T) / α _R (T) value among a plurality of samples obtained from one polycrystalline silicon rod is reduced, but the polycrystalline grains that should originally have different crystal grain states The difference in α (T) / α _R (T) value between samples obtained from silicon rods also tends to be small. In such a case, a polycrystalline silicon rod suitable as a raw material for producing single crystal silicon is used. Selection (sorting) becomes difficult.

Therefore, the present inventors prepared a plurality of polycrystalline silicon rods having different crystal grain states for the purpose of clarifying a suitable measurement temperature range, and cross-sections perpendicular to the radial direction from each polycrystalline silicon rod. A plate-like sample as the main surface is collected, and the thermal diffusivity of these plate-like samples is measured at each temperature of 25 ± 0.5 ° C., 900 ± 1 ° C., 1000 ± 1 ° C., 1100 ± 1 ° C. The ratio of thermal diffusivity (α (T) / α _R (T)) was determined, and single crystal crystallization of these polycrystalline silicon rods by the FZ method was conducted to examine whether or not crystal lines disappeared.

As a result, there was a relationship between the thermal diffusivity and the presence or absence of crystal line disappearance in one FZ operation, and a polycrystalline silicon rod successfully crystallized by one FZ operation (crystal line disappearance). None) was found to have a higher thermal diffusivity than the unsuccessful polycrystalline silicon rod (with crystal line disappearance). That is, if the measurement temperature is 1100 ° C. or lower, a polycrystalline silicon rod suitable as a raw material for producing single crystal silicon can be selected based on the thermal diffusivity ratio (α (T) / α _R (T)). And gained knowledge. For this reason, in the present invention, the measurement temperature for measuring the thermal diffusivity is set to 1100 ° C. or lower.

Specifically, a polycrystalline silicon rod having a thermal diffusivity α (T) satisfying α (T) / α _R (T) ≧ 0.10 × 10 ⁻³ T + 0.80 is used as a raw material for producing single crystal silicon. select.

FIG. 1 shows a single crystal whose principal surface is a thermal diffusivity α (T) of a plate-like sample obtained from a polycrystalline silicon rod successfully single-crystallized by one FZ treatment and a <100> plane used as a standard sample. the minimum value of the ratio _{(α (T) / α R} (T)) the thermal diffusivity of the silicon plate-shaped sample alpha _R (T) is plotted with respect to the measured temperature.

From this result, as the first-order correlation, the above equation α (T) / α _R (T) ≧ 0.10 × 10 ⁻³ T + 0.80 is obtained, and the correlation coefficient R ² is extremely high, 0.9997. High linearity. Therefore, if the above equation is used as a discriminant, a polycrystalline silicon rod suitable as a raw material for producing single crystal silicon can be selected based on the result of thermal diffusivity measurement performed at an arbitrary temperature of 1100 ° C. or lower. .

The above formula α (T) / α _R (T) ≧ 0.10 × 10 ⁻³ T + 0.80 is obtained when a single crystal silicon plate sample having a <100> plane as a main surface is used as a standard sample. It is a discriminant.

  In addition, if the measurement temperature is less than 1100 ° C., even if the difference in thermal diffusivity between a plurality of samples obtained from one polycrystalline silicon rod is taken into consideration, the polycrystalline silicon rod and the single crystal having a high single crystallization success rate It was estimated that a reference value for distinguishing polycrystalline silicon rods having a relatively low conversion success rate could be set. For these reasons, in the present invention, the reference for selecting a polycrystalline silicon rod suitable as a raw material for producing single crystal silicon for each of the measurement temperatures of thermal diffusivity measurement of 25 ° C., 900 ° C., and 1000 ° C. Value (value of thermal diffusivity ratio) is set.

Specifically, when the measurement temperature T is 25 ° C., a polycrystalline silicon rod having a thermal diffusivity α (25 ° C.) satisfying α (25 ° C.) / Α _R (25 ° C.) ≧ 0.80. Select as raw material for single crystal silicon production.

When the measurement temperature T is 900 ° C., a polycrystalline silicon rod having a thermal diffusivity α (900 ° C.) satisfying α (900 ° C.) / Α _R (900 ° C.) ≧ 0.90 is produced as single crystal silicon. Select as raw material.

Furthermore, when the measurement temperature T is 1000 ° C., a polycrystalline silicon rod having a thermal diffusivity α (1000 ° C.) satisfying α (1000 ° C.) / Α _R (1000 ° C.) ≧ 0.91 is produced as single crystal silicon. Select as raw material.

  In addition, the reference value (the value of the thermal diffusivity ratio) for selecting the above polycrystalline silicon rod is any case where a single crystal silicon plate sample having a <100> plane as a main surface is used as a standard sample. Is the value of

  In the method for selecting a polycrystalline silicon rod of the present invention, a plate-like sample is collected from the polycrystalline silicon rod in order to measure the thermal diffusivity. The plate-like sample is not particularly limited as long as it is suitable for measuring the thermal diffusivity, but the polycrystalline silicon rod often has crystal grains growing in the radial direction. This is because the diameter of the polycrystalline silicon rod is increased due to the progress of the CVD reaction on the surface of the silicon core wire. Therefore, in order to suppress variations in measurement values depending on the sampling position of the plate-like sample, it is preferable to use a plate-like test sample whose main surface is a cross section perpendicular to the radial direction of the polycrystalline silicon rod.

  2A and 2B are diagrams for explaining an example of collecting a plate-like sample 20 for measuring thermal diffusivity from a polycrystalline silicon rod 10 grown by chemical vapor deposition (Siemens method). is there. In the figure, reference numeral 1 denotes a silicon core wire for depositing polycrystalline silicon on the surface to form a silicon rod. In this example, three parts (CTR: part close to the silicon core wire 1, EDG: polycrystalline silicon) are used to confirm whether or not the crystal state (orientation, grain size, etc.) of the polycrystalline silicon rod 10 is dependent on the radial direction. The plate-like sample 20 is collected from a portion close to the side surface of the rod 10 (R / 2: an intermediate portion between CTR and EGD), but is not limited to collection from such a portion.

  The diameter of the polycrystalline silicon rod 10 illustrated in FIG. 2A is approximately 120 mm, and the three portions (CTR: the portion close to the silicon core wire 1, EDG: many) from the side surface side of the polycrystalline silicon rod 10 to the silicon core wire 1 side. A rod 11 having a diameter of approximately 20 mm and a length of approximately 60 mm is cut out from a portion close to the side surface of the crystalline silicon rod 10 (R / 2: an intermediate portion between CTR and EGD). In the example shown in this figure, the rod 11 is a columnar sample whose bottom is a cross section perpendicular to the radial direction of the polycrystalline silicon rod 10.

  Then, as shown in FIG. 2B, a plate-like sample 20 having a cross section perpendicular to the major axis direction of these rods 11 as a main surface is sliced and collected with a thickness of approximately 2 mm. Therefore, in this case, the plate-like sample 20 is collected so that the main surface is a cross section perpendicular to the radial direction of the polycrystalline silicon rod 10.

  It should be noted that the part and diameter from which the rod 11 is collected need not be limited to the above example, and any part can be used as long as the properties of the polycrystalline silicon rod 10 can be reasonably estimated and the measurement of the thermal diffusivity is not hindered. It may be collected and the diameter may be determined appropriately. The diameter may be determined in consideration of the diameter of the polycrystalline silicon rod 10, the diameter of the rod 11 to be hollowed out, the length of the rod 11 to be hollowed out, or the like. Further, the plate-like sample 20 may be collected from an appropriate portion of the rod 11.

  The plate-like sample 20 may be collected so that the main surface is a cross section perpendicular to the major axis direction of the polycrystalline silicon rod 10. For example, a plate-like sample having a thickness of about 2 mm and having a principal surface perpendicular to the major axis direction of the polycrystalline silicon rod 10 is obtained by slicing, and a portion (CTR) near the silicon core wire 1 of this plate-like sample is obtained. You may make it extract the plate-shaped sample 20 about 20 mm in diameter from the site | part (EDG) near the side surface of the stick | rod 10, and the intermediate | middle site | part (R / 2) of CTR and EGD.

  It is preferable that the flatness of the surface of the sampled plate sample 20 is increased by polishing prior to the measurement of the thermal diffusivity. Various methods are known for polishing silicon crystals, and any method may be used. For example, a vibration polishing apparatus can be used.

Four polycrystalline silicon rods (A to D) grown by chemical growth under different deposition conditions were prepared. A plate-like sample (20 _CTR , 20 _EDG , 20 _{R / 2} ) having a thickness of about 2 mm and a diameter of about 20 mm was obtained for each of these polycrystalline silicon rods by the sampling method shown in FIGS. 2A and 2B. .

  The thermal diffusivity of each of these plate-like samples was measured at each temperature of 25 ± 0.5 ° C., 900 ± 1 ° C., 1000 ± 1 ° C., and 1100 ± 1 ° C. Further, a thermal diffusivity measurement was performed under the same conditions for a single crystal silicon plate sample having a <100> plane as a main surface as a standard sample. The thermal diffusivity is measured by the laser flash method, which is an unsteady method, and the conditions are as shown in Table 1.

A single crystal silicon plate sample having a <100> plane as a standard sample as a main surface is
A single crystal silicon ingot (diameter: 12 mm × length: 170 cm) grown by the FZ method was sampled at a thickness of 2 mm by circular cutting.

Thermal diffusivity α (T) of a standardized plate sample when the thermal diffusivity α _R (T) of a standard sample (single crystal silicon plate sample having a <100> plane as a main surface) is 1.00 ), That is, the thermal diffusivity ratio α (T) / α _R (T) is summarized in Table 2.

  Further, single crystal crystallization of these polycrystalline silicon rods A to D by the FZ method was performed to examine the presence or absence of crystal line disappearance. Table 2 also shows the presence or absence of the disappearance of the crystal line in one FZ operation.

From the results summarized in Table 2, the polycrystalline silicon rods A and B having a value of α (25 ° C.) / Α _R (25 ° C.) at a measurement temperature of 25 ° C. of 0.80 or more are 1 Successful single crystallization by FZ treatment.

Further, the polycrystalline silicon rods A and B having a value of α (900 ° C.) / Α _R (900 ° C.) of 0.90 or more at a measurement temperature of 900 ° C. can be obtained by a single FZ treatment without disappearance of crystal lines. Successful crystallization.

Furthermore, polycrystalline silicon rods A and B having a value of α (1000 ° C.) / Α _R (1000 ° C.) at a measurement temperature of 1000 ° C. of 0.91 or more can be obtained by a single FZ treatment without loss of crystal lines. Successful crystallization.

Note that the polycrystalline silicon rods A and B having a value of α (1100 ° C.) / Α _R (1100 ° C.) of 0.92 or higher at a measurement temperature of 1100 ° C. can be obtained by single FZ treatment without disappearance of crystal lines. Although the crystallization was successful, the disappearance of the crystal line was observed once for the polycrystalline silicon rod C in which some α (1100 ° C.) / Α _R (1100 ° C.) was 0.92 or more. Single crystallization in FZ treatment has failed.

  FIG. 1 shows the lowest standardization among the six plate-like samples taken from the polycrystalline silicon rods A and B that were successfully single-crystallized by one FZ treatment among the thermal diffusivities shown in Table 2. The thermal diffusivity (25 ° C .: 0.80, 900 ° C .: 0.90, 1000 ° C .: 0.91, 1100 ° C .: 0.92) is plotted against the measured temperature. Here, in order to see the correlation with the measured temperature, 0.92 which is the minimum value at 1100 ° C. is also taken into consideration.

  The present invention provides a technique that contributes to stable production of single crystal silicon by selecting polycrystalline silicon suitable as a raw material for producing single crystal silicon with high quantitativeness and reproducibility.

1 Silicon core wire 10 Polycrystalline silicon rod 11 Rod 20 Plate sample

Claims (9)

A method for selecting a polycrystalline silicon rod used as a raw material for producing single crystal silicon,
The polycrystalline silicon rod is grown by precipitation by a chemical growth method, and a plate-like sample having a cross section perpendicular to the radial direction of the polycrystalline silicon rod as a main surface is collected, and a temperature T ( ), The thermal diffusivity α (T) of the plate sample is measured, and the ratio of the thermal diffusivity α (T) to the thermal diffusivity α _R (T) of the standard sample (α (T) / α _R (T)), and a polycrystalline silicon rod for producing single crystal silicon is selected based on the thermal diffusivity ratio (α (T) / α _R (T)). How to select a bar.   The method for selecting a polycrystalline silicon rod according to claim 1, wherein the standard sample is a single crystal silicon plate sample having a <100> plane as a main surface. The method for selecting a polycrystalline silicon rod according to claim 2, wherein a polycrystalline silicon rod whose thermal diffusivity α (T) satisfies the following formula (1) is selected as a raw material for producing single crystal silicon.
α (T) / α _R (T) ≧ 0.10 × 10 ⁻³ T + 0.80 (1) 3. The polycrystal according to claim 2, wherein a polycrystalline silicon rod having the measurement temperature T of 25 ° C. and the thermal diffusivity α (25 ° C.) satisfying the following formula (2) is selected as a raw material for producing single crystal silicon. How to select a crystalline silicon rod.
α (25 ° C.) / α _R (25 ° C.) ≧ 0.80 (2) The polycrystal silicon rod according to claim 2, wherein a polycrystalline silicon rod having the measurement temperature T of 900 ° C and the thermal diffusivity α (900 ° C) satisfying the following formula (3) is selected as a raw material for producing single crystal silicon. How to select a crystalline silicon rod.
α (900 ° C.) / α _R (900 ° C.) ≧ 0.90 (3) The polycrystal silicon rod according to claim 2, wherein the polycrystalline silicon rod having the measurement temperature T of 1000 ° C and the thermal diffusivity α (1000 ° C) satisfying the following formula (4) is selected as a raw material for producing single crystal silicon. How to select a crystalline silicon rod.
α (1000 ° C.) / α _R (1000 ° C.) ≧ 0.91 (4)   A method for producing a polycrystalline silicon lump comprising a step of crushing a polycrystalline silicon rod selected by the method according to any one of claims 1 to 6.   A method for producing single crystal silicon using a polycrystalline silicon rod selected by the method according to any one of claims 1 to 6 as a silicon raw material.   The manufacturing method of the single crystal silicon which uses the polycrystal silicon lump obtained by the method of Claim 7 as a raw material.