JP5712176B2 - Method for selecting polycrystalline silicon rod, method for producing polycrystalline silicon lump, and method for producing single crystal silicon - Google Patents

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, a non-oriented polycrystalline silicon rod suitable for stably producing single crystal silicon. Relates to the method of selection.

  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 let

  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

2006 IEEE / SEMI Advanced Semiconductor Manufacturing Conference Proceedings pp. 244-246

  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.

  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 to be used as a raw material for producing single crystal silicon, which is collected from the polycrystalline silicon rod. Analyzing a backscattered diffraction image obtained by irradiating an electron beam onto the principal surface of the plate-like sample, and selecting a polycrystalline silicon rod that simultaneously satisfies the following two conditions as a raw material for producing single crystal silicon; It is characterized by.
Condition 1: The total area of the regions where crystal grains having a grain size of 0.5 μm or more are not detected is 10% or less of the entire area irradiated with the electron beam.
Condition 2: The number of crystal grains having a grain size in the range of 0.5 μm or more and less than 3 μm is 45% or more of the entire detected crystal grains.

  Preferably, the plate-like sample is collected so that the main surface is a cross section perpendicular to the radial direction of the polycrystalline silicon rod.

  For example, the plate-like sample is collected by slicing from a columnar sample whose bottom is a cross section perpendicular to the radial direction of the polycrystalline silicon rod.

  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.

  The degree of crystal orientation of polycrystalline silicon is evaluated by the method according to the present invention, and crystal growth is carried out by the FZ method using a polycrystalline silicon rod selected as a non-defective product, or a lump obtained from a polycrystalline silicon block is obtained. By using and growing the crystal by the CZ method, it is possible to contribute to stable production of single crystal silicon.

It is a block diagram for demonstrating the outline | summary of the apparatus structure for obtaining an electron backscattering diffraction image. It is a figure for demonstrating the collection example of the plate-shaped sample for an electron backscattering diffraction 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 an electron backscattering diffraction measurement from the polycrystalline-silicon stick | rod grown by the chemical vapor deposition method. It is an example of an analysis result about the particle size distribution of the crystal grain obtained from the plate-shaped sample, and is an orientation mapping image (IPF map) and (001) pole figure of the crystal grain having a grain size of 0.5 μm or more and less than 3 μm. It is an example of the analysis result about the particle size distribution of the crystal grain obtained from the plate-shaped sample, and is an orientation mapping image (IPF map) and a (001) pole figure of the crystal grain having a grain size of 3 μm or more and less than 5 μm. It is an example of the analysis result about the particle size distribution of the crystal grain obtained from the plate-shaped sample, and is an orientation mapping image (IPF map) and (001) pole figure of the crystal grain having a particle size of 5 μm or more and less than 10 μm. It is an example of an analysis result about the particle size distribution of the crystal grain obtained from the plate-shaped sample, and is an orientation mapping image (IPF map) and (001) pole figure of the crystal grain having a particle size of 10 μm or more and less than 30 μm.

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, 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.
Needless to say, the selected polycrystalline silicon rod may be crushed to obtain a polycrystalline silicon lump having a low crystal orientation and used as a raw material for producing single crystal silicon by the CZ method.

  First, the electron backscattering diffraction measurement method (EBSD method) will be briefly described. An electron backscatter diffraction image (EBSP) obtained by the EBSD method is generated on the same principle as the Kikuchi line observed with a transmission electron microscope. Multiple bands are obtained when a crystal sample is irradiated with an electron beam, but each band is generated by diffraction from one crystal plane, and the band width and intensity depend on the crystal structure including the lattice constant. . The angle at which the bands intersect and the position at which they appear are uniquely determined by the crystal orientation. Therefore, by analyzing the pattern appearing in EBSP, the substance can be identified and the crystal orientation can be known.

  In recent electron microscopes, from measurement to data analysis has been automated, the time required for analysis has been greatly reduced compared to conventional methods, and in addition to crystal orientation, information such as crystal grain size and second phase separation has also been rapidly obtained. It can be acquired. Therefore, by analyzing EBSP obtained from a polycrystalline sample with such an apparatus system, information on each crystal grain can be obtained quickly.

  FIG. 1 is a block diagram for explaining an outline of an apparatus configuration for obtaining an electron backscattered diffraction image. A scanning microscope (SEM) 100 includes an irradiation system control unit 101, a sample stage control unit 102, and a camera control unit 103, and these control units are controlled by a computer 109.

  When the sample 105 set on the sample stage 104 provided in the lens barrel is irradiated with the electron beam 106, diffraction from the crystal plane is generated to obtain a plurality of bands, which are projected on the screen 107 as EBSP, The image is taken by the high-sensitivity camera 108, and this EBSP is taken into the computer 109 as image information and analyzed.

  The computer 109 includes a processing unit 109a for controlling the main body of the SEM 100, a processing unit 109b for controlling image capturing or capturing, a computing unit 109c for analyzing a crystal structure based on the captured image, and a recording for storing data. The EBSP is subjected to image analysis by the calculation unit 109c, and crystal orientation is determined by pattern comparison with an image obtained by simulation for a sample having a known crystal structure. The determined crystal orientation is recorded as numerical data in angle notation along with the position coordinates (x, y), etc., and various analyzes such as mapping the crystal orientation and displaying the crystal grain boundary based on these data It can be performed.

  An example in which such an EBSD method is applied to the evaluation of a silicon material has already been reported. For example, in Non-Patent Document 1, the EBSD method is used as a tool for studying single crystallization of amorphous silicon. EBSP such as single crystal silicon and polycrystalline silicon obtained by the EBSD method and the analysis result thereof are shown.

  As described above, the quality judgment by visual recognition under the optical microscope as in the method disclosed in Patent Document 2 has a difference in the result depending on the degree of etching of the observation sample surface, the observation technician's observation skill, and the like. In addition to being easy, it has poor quantitativeness and reproducibility. Moreover, according to the study by the present inventors, there is also a problem that the result of the quality determination by microscopic observation does not necessarily match the single crystallization rate of silicon. Therefore, the present inventors tried to apply the EBSD method as a method for selecting (selecting) a polycrystalline silicon rod suitable as a raw material for producing single crystal silicon, and the results of evaluation and analysis by the EBSD method And the correlation between the single crystallization rate and the single crystallization rate were investigated.

  When the evaluation by the EBSD method is performed, if the pixel size of the EBSP is, for example, 0.5 μm, crystal grains having a grain size of approximately 0.5 μm or more can be confirmed. It is also possible to perform particle size mapping of all sample surfaces that contribute to the formation of EBSP.

  Patent Document 2 discloses that as a raw material for producing single crystal silicon by the FZ method, a polycrystalline silicon rod that contains as little crystal grains as possible is preferable. Under such circumstances, when the present inventors started evaluation / analysis by the EBSD method, initially, a polycrystalline silicon rod containing as many crystal grains as small as possible is a raw material for producing single crystal silicon. It was thought that it was suitable as.

  However, as the study progresses, when single crystal silicon is grown by the FZ method using a polycrystalline silicon rod containing a large number of fine grains having a grain size of less than 0.5 μm, the process can be performed in a single process. It has become clear that the probability of single crystallization (one pass) is not necessarily high.

  Specifically, as an analysis result of an electron backscatter diffraction image of a plate-like sample collected from a polycrystalline silicon rod, the total area of a region where a crystal grain having a grain size of 0.5 μm or more is not detected is an area irradiated with an electron beam. It has been found that when a polycrystalline silicon rod that is 10% or less of the total is used, the crystal line does not disappear, whereas in the case of a polycrystalline silicon rod that does not satisfy the above conditions, the crystal line is likely to disappear.

  In addition, when a polycrystalline silicon rod having a grain size of at least 45 μm and less than 3 μm is 45% or more of the detected crystal grains, the crystal line does not disappear. It has also been found that in the case of a polycrystalline silicon rod that does not satisfy the above conditions, the crystal line tends to disappear.

  Therefore, in the method for selecting a polycrystalline silicon rod according to the present invention, an electron backscatter diffraction image obtained by irradiating an electron beam onto the principal surface of a plate sample collected from the polycrystalline silicon rod is analyzed, and the particle size is determined. The total area of the regions where crystal grains of 0.5 μm or more are not detected is 10% or less of the entire area irradiated with the electron beam (condition 1), and the grain size is 0.5 μm or more and less than 3 μm. A polycrystalline silicon rod simultaneously satisfying that the number of crystal grains is 45% or more of the total number of detected crystal grains (condition 2) is selected as a raw material for producing single crystal silicon.

  Here, the “particle diameter” is defined by the diameter of a circle having the area obtained by obtaining the area of each crystal grain detected by the analysis of the electron backscatter diffraction image.

  2A and 2B are diagrams for explaining an example of collecting a plate-like sample 20 for electron backscatter diffraction measurement from a polycrystalline silicon rod 10 grown by chemical vapor deposition (Siemens method). It is. 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: close to the side surface of the polycrystalline silicon stick 10) are used to confirm whether or not the crystal grain size of the polycrystalline silicon stick 10 is dependent on the radial direction. The plate-like sample 20 is collected from the part, R / 2: the intermediate part between CTR and EGD, but is not limited to the collection from such a part.

  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 may be taken from any part as long as the properties of the entire polycrystalline silicon rod 10 can be reasonably estimated. 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.

  Further, 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 collected plate-like sample 20 is increased by polishing prior to the EBSD measurement. Various methods are known for polishing silicon crystals, and any method may be used. For example, a vibration polishing apparatus can be used.

First, five polycrystalline silicon rods (A to E) grown under different precipitation 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. . For the polycrystalline silicon rod E, acquisition of 20 _CTR and 20 _{R / 2} failed and only 20 _EDG was obtained.

  These plate samples were analyzed by the EBSD method. The apparatus used was an ultra-low acceleration scanning electron microscope (ZEISS, SUPRA40VP) and an EBSD apparatus (EDAX (TSL), Hikari High Speed EBSD Detector). The electron beam irradiation conditions were an acceleration voltage of 5 kV during electron microscope observation and an acceleration voltage of 20 kV during EBSD. The image thus obtained was analyzed, and the area of the region not including crystal grains having a grain size of 0.5 μm or more and the grain size distribution and number distribution were determined for the crystal grains having a grain size of 0.5 μm or more.

  FIGS. 3A to 3D are analysis result examples (left figure: orientation mapping image (IPF map), right figure: (001) pole figure) regarding the grain size distribution of the crystal grains obtained from the plate-like sample. Crystal grains having a particle size of 5 μm or more and less than 3 μm (FIG. 3A) Crystal grains having a particle size of 3 μm or more and less than 5 μm (FIG. 3B) Crystal grains having a particle size of 5 μm or more and less than 10 μm (FIG. 3C) 10 μm or more but less than 30 μm It is about the grain size (FIG. 3D).

  Table 1 summarizes the crystal grain size distribution for each plate-like sample obtained from these polycrystalline silicon rods and the presence or absence of the disappearance of the crystal line in one FZ operation. In this table, the crystal grain size distributions I to V are less than 0.5 μm (I), 0.5 μm or more and less than 3 μm (II), 3 μm or more and less than 5 μm (III), and 5 μm or more and less than 10 μm. (IV) 10 μm or more and less than 30 μm (V).

In addition, regarding the distribution I (less than 0.5 μm), the entire area (S ₀ ) of the distribution area (the area in which crystal grains having a grain size of 0.5 μm or more are not detected) of the total area (S _I ) irradiated ) (S _I / S ₀ ), and for other distributions II to V, the number of crystal grains (N) counted in each distribution is 0.5 μm or more. The ratio (N / N _tot ) to the total number (N _tot ) is shown.

  As shown in Table 1, the total area of the regions where crystal grains having a grain size of 0.5 μm or more are not detected is 10% or less of the entire area irradiated with the electron beam (Condition 1), and the grain size is In polycrystalline silicon rods C and D that simultaneously satisfy that the number of crystal grains in the range of 0.5 μm or more and less than 3 μm is 45% or more of the total number of detected crystal grains (Condition 2), The disappearance of the line has not occurred. On the other hand, in the polycrystalline silicon rods A, B, and E that do not satisfy at least one of the two conditions, the disappearance of the crystal line was observed.

  As described above, when the polycrystalline silicon rod selected by the method according to the present invention is used as a silicon raw material, it becomes possible to stably produce single crystal silicon.

  Also, it is possible to stably produce single crystal silicon by crushing a polycrystalline silicon rod selected by the method to obtain a polycrystalline silicon lump and using this as a raw material.

  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.

DESCRIPTION OF SYMBOLS 1 Silicon core wire 10 Polycrystalline silicon rod 11 Rod 20 Plate sample 100 Scanning microscope 101 Irradiation system control unit 102 Sample stage control unit 103 Camera control unit 104 Sample stage 105 Sample 106 Electron beam 107 Screen 108 High sensitivity camera 109 Computer 109a SEM Processing unit 109b for controlling the main body of the image processing unit 109c for controlling the photographing or capturing of the image Calculation unit 109d Recording unit

Claims (6)

An electron backscatter diffraction image obtained by irradiating an electron beam onto a main surface of a plate-like sample collected from a polycrystalline silicon rod, for selecting a polycrystalline silicon rod used as a raw material for producing single crystal silicon And selecting a polycrystalline silicon rod that simultaneously satisfies the following two conditions as a raw material for producing single crystal silicon.
Condition 1: The total area of the regions where crystal grains having a grain size of 0.5 μm or more are not detected is 10% or less of the entire area irradiated with the electron beam.
Condition 2: The number of crystal grains having a grain size in the range of 0.5 μm to 3 μm is 45% or more of the entire detected crystal grains.   2. The method for selecting a polycrystalline silicon rod according to claim 1, wherein the plate sample is collected so that a cross section perpendicular to a radial direction of the polycrystalline silicon rod is a main surface.   The method for selecting a polycrystalline silicon rod according to claim 2, wherein the plate-like sample is collected by slicing from a columnar sample having a bottom surface in a cross section perpendicular to the radial direction of the polycrystalline silicon rod.   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 3.   A method for producing single crystal silicon using a polycrystalline silicon rod selected by the method according to claim 1 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 4 as a raw material.