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Researchers Submit Patent Application, "Method for Selecting Polycrystalline Silicon Rod, and Method for Producing Single-Crystalline Silicon", for...

February 27, 2014



Researchers Submit Patent Application, "Method for Selecting Polycrystalline Silicon Rod, and Method for Producing Single-Crystalline Silicon", for Approval

By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Miyao, Shuichi (Niigata, JP); Okada, Junichi (Niigata, JP); Netsu, Shigeyoshi (Niigata, JP), filed on April 4, 2012, was made available online on February 13, 2014.

The patent's assignee is Shin-Etsu Chemical Co., Ltd.

News editors obtained the following quote from the background information supplied by the inventors: "Single-crystalline silicon essential for the production of devices such as semiconductor devices is grown as a crystal by the CZ method and the FZ method, and a polycrystalline silicon rod or a polycrystalline silicon block is used as the raw materials in such a case. Such a polycrystalline silicon material is produced in many cases by the Siemens method (see, for example, Patent Literature 1). The Siemens method is a method in which by bringing a gas of a silane raw material such as trichlorosilane or monosilane into contact with a heated silicon core wire, polycrystalline silicon is grown in the vapor phase (deposited) on the surface of the silicon core wire by the CVD (Chemical Vapor Deposition) method.

"For example, when single-crystalline silicon is crystal-grown by the CZ method, a polycrystalline silicon block is charged in a quartz crucible and heated to be melted, a seed crystal is dipped in the resulting silicon melt to extinguish dislocation lines to be made free from dislocation, and then the crystal pulling up is performed while the crystal diameter is being slowly expanded until the diameter of the crystal reaches a predetermined diameter. In this case, when unmelted polycrystalline silicon remains in the silicon melt, the unmelted polycrystalline pieces drift in the vicinity of the solid-liquid interface by convection to induce the generation of dislocation, and thus the polycrystalline silicon remaining unmelted causes the crystal line to be extinguished."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Technical Problem

"The present inventors have obtained, in the course of the investigation of the quality improvement of polycrystalline silicon for the purpose of stably performing the production of single-crystalline silicon, findings such that, depending on the conditions at the time of the deposition of polycrystalline silicon, differences occur in the randomness of the orientation of the crystal grains in the polycrystalline silicon rod. In contrast to single-crystalline silicon, a polycrystalline silicon block includes a large number of crystal grains, and such a large number of crystal grains tend to be regarded as independently randomly oriented. However, according to the investigation performed by the present inventors, the crystal grains included in a polycrystalline silicon block are not necessarily completely randomly oriented.

"In a powder sample obtained by pulverizing a polycrystalline silicon block, the individual crystal grains can be handled as completely randomly oriented. In fact, in an X-ray diffraction measurement performed with a powder sample, even when the powder sample is rotated arbitrarily in relation to the incident X-ray, no change is found in the chart obtained.

"On the contrary, according to the results of the X-ray diffraction measurement performed by the present inventors by sampling plate-like samples, each having as a principal plane thereof a cross section perpendicular to the long axis direction of a polycrystalline silicon rod, from many different polycrystalline silicon rods grown by the deposition using a chemical vapor deposition method, and by performing X-ray diffraction measurement omnidirectionally in the plane of each of the plate-like samples, it has been revealed that a remarkable dependence on the X-ray incident direction is sometimes found in the diffraction intensity of any of the X-ray diffraction peaks from the crystal planes having the Miller indices of , , and .

"Such a remarkable dependence on the X-ray incident direction means that the crystal grains included in the polycrystalline silicon block are not randomly oriented, and the crystal grains tend to align in the direction of the crystal plane having a specific Miller index.

"It has also been revealed that when a polycrystalline silicon rod or a polycrystalline silicon block including crystal grains oriented in the direction of the crystal plane having a specific Miller index is used as a raw material for use in the production of single-crystalline silicon, portions remaining unmelted are sometimes locally caused, and such portions remaining unmelted induce the occurrence of the dislocations and can be a cause for the extinguishment of the crystal line.

"The present invention has been achieved on the basis of a novel finding that differences are caused in the orientation randomness of the crystal grains in the polycrystalline silicon depending on the various conditions at the time of the deposition in the growth of the polycrystalline silicon rod by using a chemical vapor deposition method; and an object of the present invention is to provide a polycrystalline silicon material having a high random orientation property, namely, a non-oriented polycrystalline silicon rod and a non-oriented polycrystalline silicon block so as to contribute to the stable production of single-crystalline silicon.

"Solution to Problem

"In order to solve the foregoing technical problem, the 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 use in the production of single-crystalline silicon, wherein the polycrystalline silicon rod is a product grown by the deposition using a chemical vapor deposition method; and plate-like samples each having as a principal plane thereof a cross section perpendicular to the long axis direction of the polycrystalline silicon rod are sampled; an X-ray diffraction measurement is performed omnidirectionally in the plane of each of the plate-like samples; and when none of the plate-like samples has any X-ray diffraction peak with a diffraction intensity deviating from the average value .+-.2.times.standard deviation (.mu..+-.2.sigma.) found for any one of the Miller indices , , and , the polycrystalline silicon rod is selected as the raw material for use in the production of single-crystalline silicon.

"The polycrystalline silicon rod thus selected or the polycrystalline silicon block obtained by pulverizing the polycrystalline silicon rod thus selected for any one of the Miller indices , , and is polycrystalline silicon having an orientation property such that no X-ray diffraction peak having a diffraction intensity deviating from the average value .+-.2.times.standard deviation (.mu..+-.2.sigma.) is shown; and in the method for producing single-crystalline silicon according to the present invention, the polycrystalline silicon rod thus selected or the polycrystalline silicon block obtained by pulverizing the polycrystalline silicon rod thus selected is used as a raw material for use in the production of single-crystalline silicon.

"Advantageous Effects of Invention

"The crystal growth performed with the polycrystalline silicon rod according to the present invention by the FZ method, or the crystal growth performed by the CZ method with the polycrystalline silicon block obtained by crushing the polycrystalline silicon rod suppresses the local occurrence of the portions remaining unmelted, and can contribute to the stable production of single-crystalline silicon.

BRIEF DESCRIPTION OF DRAWINGS

"FIG. 1A is a diagram for illustrating an example of the sampling of a plate-like sample for use in an X-ray diffraction measurement from a polycrystalline silicon rod grown by the deposition using a chemical vapor deposition method.

"FIG. 1B is another diagram for illustrating an example of the sampling of a plate-like sample for use in an X-ray diffraction measurement from a polycrystalline silicon rod grown by the deposition using a chemical vapor deposition method.

"FIG. 1C is a diagram for illustrating another example of the sampling of a plate-like sample for use in an X-ray diffraction measurement from a polycrystalline silicon rod grown by the deposition using a chemical vapor deposition method.

"FIG. 1D is still a diagram for illustrating another example of the sampling of a plate-like sample for use in an X-ray diffraction measurement from a polycrystalline silicon rod grown by the deposition using a chemical vapor deposition method.

"FIG. 2 is a diagram for illustrating the measurement of the X-ray diffraction from the plate-like sample sampled from a polycrystalline silicon rod.

"FIG. 3 is an example of the X-ray diffraction chart of a sample as a powder prepared by pulverizing polycrystalline silicon.

"FIG. 4A is an example of the X-ray diffraction chart obtained from the sample A.

"FIG. 4B is a radar chart prepared from the rotation angle .phi. and the diffraction intensity cps of the sample A.

"FIG. 5A is an example of the X-ray diffraction chart obtained from the sample h: (a) .phi.=0.degree. and (b) .phi.=45.degree.

"FIG. 5B is a radar chart prepared from the rotation angle .phi. and the diffraction intensity cps of the sample h.

"FIG. 6A is an example of the X-ray diffraction chart obtained from the sample g: (a) .phi.=0.degree. and (b) .phi.=270.degree.

"FIG. 6B is a radar chart prepared from the rotation angle .phi. and the diffraction intensity cps from the lattice plane having a Miller index of ."

For additional information on this patent application, see: Miyao, Shuichi; Okada, Junichi; Netsu, Shigeyoshi. Method for Selecting Polycrystalline Silicon Rod, and Method for Producing Single-Crystalline Silicon. Filed April 4, 2012 and posted February 13, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=7125&p=143&f=G&l=50&d=PG01&S1=20140206.PD.&OS=PD/20140206&RS=PD/20140206

Keywords for this news article include: Silicon, Nanotechnology, Emerging Technologies, Chemical Vapor Deposition, Shin-Etsu Chemical Co. Ltd..

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Source: Politics & Government Week


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