Patent Publication Number: US-2022219287-A1

Title: Method for cutting polycrystalline silicon rod, method for manufacturing cut rod of polycrystalline silicon rod, method for manufacturing nugget of polycrystalline silicon rod, and polycrystalline silicon rod cutting device

Description:
TECHNICAL FIELD 
     The present invention relates to a method for cutting a polycrystalline silicon rod, a method for manufacturing a cut rod of a polycrystalline silicon rod, a method for manufacturing a nugget of a polycrystalline silicon rod, and a polycrystalline silicon rod cutting device. 
     BACKGROUND ART 
     A polycrystalline silicon rod, when manufactured by the Siemens process, is typically substantially cylindrical and elongated. In order to manufacture, by a pulling process or the like, a monocrystalline silicon ingot by using such a polycrystalline silicon rod as a raw material, the polycrystalline silicon rod needs to be cut to an appropriate length in some cases. 
     When a polycrystalline silicon rod is cut by using a typical rotating blade, a medium serving as a cooler and a lubricant, such as water and oil, is blown to a portion of the polycrystalline silicon rod while the portion is being cut. This is intended to prevent, for example, detachment of abrasive particles due to frictional heat generated between the blade and a material or attrition of the abrasive particles, and distortion of the blade. This process is known as a wet cutting process. 
     Problems connected with cutting of a polycrystalline silicon rod by using a blade in the wet cutting process or other cutting processes include contamination of the polycrystalline silicon rod not only due to powdery cutting chips of silicon but also due to dust generated from a metal component of the blade. The cause of this is explained as follows. The abrasive particles firmly fixed to the blade wear during cutting of the polycrystalline silicon rod. As a result, the metal component used as a binder for the abrasive particles comes into direct contact with the polycrystalline silicon rod and generates dust. 
     As an example of a solution to this problem, Patent Literature 1 proposes cutting a polycrystalline silicon rod by using an inner diameter blade which has abrasive particles firmly fixed to its inner circumferential part by electrodeposition, not by using an outer diameter blade which has the abrasive particles firmly fixed to its outer circumferential part with use of a metal bond. Patent Literature 2 proposes removing contaminants by subjecting, to a special etching process, the surface of the polycrystalline silicon rod which has undergone machining such as crushing. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] 
       
    
     Japanese Patent Application Publication Tokukai No. 2005-288891
     [Patent Literature 2]   

     Japanese Patent Application Publication Tokukaihei No. 08-067510 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the cutting by using the inner diameter blade proposed in Patent Literature 1 may damage the blade under high load because a typical inner diameter blade has a thin edge. Further, even if the special etching process proposed in Patent Literature 2 is carried out, it may be impossible to completely remove contaminants from the surface of the polycrystalline silicon rod and thus impossible to sufficiently reduce impurity contamination of a monocrystalline silicon ingot. In addition, the etching process leads to an increased number of steps and increased costs in manufacture of a polycrystalline silicon rod. 
     An object of an aspect of the present invention is to provide a method for effectively preventing impurity contamination, in particular, metal contamination, during cutting of a polycrystalline silicon rod. 
     Solution to Problem 
     In order to solve the above problem, a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod includes the step of cutting the polycrystalline silicon rod by using a cutting tool, the step of cutting including: delivering a liquid to a cutting position of the polycrystalline silicon rod through a first nozzle; and delivering a liquid to a surface of the polycrystalline silicon rod through a second nozzle. 
     A method, in accordance with an aspect of the present invention, for manufacturing a cut rod of a polycrystalline silicon rod, includes the step of cutting the polycrystalline silicon rod by using a cutting tool, the step of cutting including: delivering a liquid to a cutting position of the polycrystalline silicon rod through a first nozzle; and delivering a liquid to a surface of the polycrystalline silicon rod through a second nozzle. 
     A polycrystalline silicon rod cutting device in accordance with an aspect of the present invention includes: a cutting tool for cutting a polycrystalline silicon rod; a first nozzle for delivering a liquid to a cutting position of the polycrystalline silicon rod; and a second nozzle for delivering a liquid to a surface of the polycrystalline silicon rod. 
     Advantageous Effects of Invention 
     An aspect of the present invention makes it possible to effectively prevent impurity contamination, in particular, metal contamination, during cutting of a polycrystalline silicon rod. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a polycrystalline silicon rod cutting device in accordance with Embodiment 1 of the present invention. 
         FIG. 2  is a schematic view of aspects in which abrasive particles are firmly fixed in a diamond blade. 
         FIG. 3  is a schematic view of a polycrystalline silicon rod cutting device in accordance with Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     The following will describe an Embodiment of the present invention in detail with reference to drawings. 
     &lt;Polycrystalline Silicon Rod Cutting Device&gt; 
     As illustrated in  FIG. 1 , a cutting device  10  for cutting a polycrystalline silicon rod S includes a proximal end-side support  11 , a distal-side support  12 , a cutting section  13 , a first nozzle  14 , and a second nozzle  15 . 
     The polycrystalline silicon rod S to be cut in the present invention is prepared by, for example, the Siemens process. According to the Siemens process, a silicon core wire is set substantially upright in a bell jar reactor, and is heated by feeding electrical current and kept at approximately 1100° C. The silicon core wire has, for example, an inverted-U shape and has a diameter of several millimeters and a length of 1000 mm to 3000 mm. In the above condition, a silicon-containing compound, such as monosilane or trichlorosilane, is supplied to the reactor together with hydrogen gas, and caused to react together on a surface of the silicon core wire so that silicon is deposited on the surface of the silicon core wire. The polycrystalline silicon rod S is thus obtained. This polycrystalline silicon rod S is typically elongated and substantially cylindrical and has a diameter of 50 mm to 200 mm and a length of 1000 mm to 3000 mm. 
     The proximal end-side support  11  is a member for rotatably supporting one end portion (hereinafter, the one end is referred to as a proximal end) of the polycrystalline silicon rod S. The distal-side support  12  is a member for rotatably supporting another end portion (hereinafter, the other end is referred to as a distal end) of the polycrystalline silicon rod S. 
     The proximal end-side support  11  includes: a cylinder wall  111  having a cylindrical shape; chucks  111   a  protruding radially inward from the vicinity of the axially central part of the cylinder wall  111 ; a cylinder bottom wall  112  for covering a proximal end-side edge face of the cylinder wall  111 ; and a shaft member  113  extending from the cylinder bottom wall  112  in a direction away from the distal end and disposed coaxially with the cylinder wall  111 . The proximal end-side support  11  is arranged to coaxially receive and support, in a cavity of the cylinder wall  111 , a proximal end-side portion of the polycrystalline silicon rod S to be cut. The shaft member  113  is connected, via a power transmission member  114  such as a chain, to a rotation drive source  115  which drives the shaft member  113  so as to rotate the shaft member  113 . 
     The distal-side support  12  includes a set of three rollers  121  which are used together and which are spaced 120° apart from each other along a circumference direction of the polycrystalline silicon rod S. The three rollers have a rotation axis parallel to the rotation axis of the cylinder wall  111  of the proximal end-side support  11 . 
     The cutting section  13  is a member for cutting the polycrystalline silicon rod S at a position that is closer to the proximal end than the distal-side support  12  is. The cutting section  13  includes: a rotation drive source  131 ; a rotation shaft  132  connected to an output shaft of the rotation drive source  131 ; and a blade (a cutting tool)  133  attached to the rotation shaft  132 . In the present embodiment, the blade  133  is an outer diameter diamond blade in which diamond abrasive particles are firmly fixed to an outer circumferential part of a substrate of the blade  133 . However, the cutting tool of the present invention is not limited to this, and can be, for example, an inner diameter blade, a band saw, or a wire saw. Cutting the polycrystalline silicon rod S prepared by the Siemens process requires cutting, into two pieces, in a direction substantially perpendicular to an extending direction of the polycrystalline silicon rod S in several minutes, the polycrystalline silicon rod S having a diameter of 50 mm to 200 mm. The cutting tool of the present invention is therefore preferably an outer diameter blade in terms of productivity and facility costs. Although the blade  133  has dimensions that are not limited to any particular dimensions, the blade  133  has, for example, a diameter of 250 mm to 450 mm and a thickness of 1 mm to 3 mm. 
     Examples of the type of the outer diameter diamond blade include a metal bond blade  133   a  and an electrodeposition blade  133   b  which are illustrated in  FIG. 2 . The metal bond blade  133   a  is prepared by mixing and packing together diamond abrasive particles and several kinds of metal powder which are to serve as a binder, and then sintering a resultant mixture. Examples of the metal powder to be used include cobalt, iron, steel, tungsten, bronze (Cu—Sn), and nickel. 
     The electrodeposition blade  133   b  is prepared, with use of a metal plating solution (electrolyte solution) in which diamond abrasive particles are suspended, by (i) causing metal to be deposited on a surface of the substrate by an electrolytic plating process and (ii) causing the diamond abrasive particles to be adsorbed and incorporated on a surface of the metal. A typical plated layer serving as the binder is based on nickel. 
     Besides these blades, usable examples of the type of the outer diameter diamond blade include a resin bond blade (not illustrated) in which diamond abrasive particles are firmly fixed by using a resin bond. The resin bond to be used is not limited to any particular bond, and can be a commercially available one. 
     In the electrodeposition blade  133   b , since the abrasive particles are densely packed on the surface of the substrate, the binder has a small exposed area. Further, in the electrodeposition blade  133   b , a metal component of the binder is limited primarily to nickel. This makes a contaminant coming from the blade  133  less likely to be scattered during cutting of the polycrystalline silicon rod S with use of the electrodeposition blade  133   b , and also makes it possible to identify the type of the contaminant that is scattered. The blade  133  is therefore preferably the electrodeposition blade  133   b  in order to more effectively reduce contamination of the polycrystalline silicon rod S due to the contaminant coming from the blade  133 . 
     Note that, unless otherwise specified herein, the phrase “contamination during cutting of the polycrystalline silicon rod” in the present invention refers to contamination through attachment to the surface of the polycrystalline silicon rod S and contamination through diffusion into the polycrystalline silicon rod S, and includes, in particular, metal contamination. The contamination through diffusion into the polycrystalline silicon rod S means contamination which remains even after a surface is dissolved with use of a chemical(s) and removed by several micrometers by dissolution using a chemical(s), from a cut rod of a polycrystalline silicon rod obtained by cutting the polycrystalline silicon rod S or a nugget obtained by crushing the cut rod. 
     Reference is made to  FIG. 1  again. The first nozzle  14  is a member for delivering a liquid L 1  to the cutting position of the polycrystalline silicon rod S. The first nozzle  14  is disposed above the blade  133  and the cutting position of the polycrystalline silicon rod S, and has an opening facing downward. The liquid L 1  delivered through the first nozzle  14  serves not only as a lubricating medium for reducing friction between the blade  133  and the polycrystalline silicon rod S but also as a cooling medium for absorbing heat generated by the friction. In addition, the liquid L 1  serves to remove abrasive particles and metal powder coming from the blade  133  and powdery cutting chips from the polycrystalline silicon rod S, when blown and delivered to the blade  133  and the cutting position of the polycrystalline silicon rod S during cutting of the polycrystalline silicon rod S. 
     The first nozzle  14  is connected to a pipe (not illustrated) through which the liquid L 1  is supplied. This makes it possible to deliver the liquid L 1  at any flow rate to the cutting position, during cutting of the polycrystalline silicon rod S. 
     The first nozzle  14  can have an end of any shape. Usable examples of the first nozzle  14  include, but not limited to, a flared nozzle. The opening at the end of the first nozzle  14  has a size which is not limited to any particular size. The opening preferably has a size which allows for delivery of the liquid enough for cutting depending on, for example, a size of the polycrystalline silicon rod S and an amount of the liquid to be delivered to the cutting position of the polycrystalline silicon rod S. Specifically, the opening preferably has a width in the range of approximately 0.5 mm to 15 mm. 
     The liquid L 1  is of a type that is not limited to any particular type, provided that the liquid serves as a lubricating medium and a cooling medium. The liquid L 1  can be, for example, water or oil, or can be a liquid in which an additive such as a cleaning ingredient is further added. In order to minimize contamination of the polycrystalline silicon rod S, the liquid L 1  is preferably pure water, and particularly preferably pure water having a resistivity of not less than 1 MS/cm (mega-ohm centimeter). 
     The liquid L 1  flows at a flow rate that is not limited to any particular flow rate. The flow rate can be a rate at which, when blown toward an upper surface of the polycrystalline silicon rod S through the first nozzle  14 , the liquid L 1  flows so as to spread, on the upper surface of the polycrystalline silicon rod S, over a region corresponding to an area of diameter× diameter, where the diameter is the diameter of the polycrystalline silicon rod S. For example, the flow rate can be 5 L/min to 20 L/min. 
     As described later, during cutting of the polycrystalline silicon rod S, the liquid L 1  may be scattered together with the powdery cutting chips from the polycrystalline silicon rod S and contaminants coming from the blade  133 . Scattered substances include one or more of (i) the liquid L 1 , (ii) the powdery cutting chips of the polycrystalline silicon rod S, and (iii) the contaminants coming from the blade  133 . The contaminants coming from the blade  133  include, for example, some of the abrasive particles and the binder. Diligent study by the present inventors has revealed the following: a region where the liquid L 1  flows on the surface of the polycrystalline silicon rod S extends for a width substantially the same as the diameter of the polycrystalline silicon rod S, independently of the flow rate of the liquid L 1 , but a region where the scattered substances adhere to the surface of the polycrystalline silicon rod S extends, in the extending direction of the polycrystalline silicon rod S, to a position which is three to five times the diameter of the polycrystalline silicon rod S away from the cutting position of the polycrystalline silicon rod S, depending on the flow rate of the liquid L 1 . 
     The second nozzle  15  is disposed so as to be closer to the proximal end than the first nozzle  14  is, and is a member for delivering a liquid L 2  to be used for removal of the contaminants on the surface of the polycrystalline silicon rod S. The second nozzle  15  is disposed in a manner that allows the liquid L 2  to be delivered to a region of the surface of the polycrystalline silicon rod S, the region extending, toward the proximal end, from the cutting position to a position which is at least not less than two times the diameter of the polycrystalline silicon rod S away from the cutting position, for example, a position 1000 mm away from the cutting position toward the proximal end. The second nozzle  15  has an opening facing downward. The liquid L 2  delivered through the second nozzle  15  serves to remove, from the surface of the polycrystalline silicon rod S, the scattered substances scattered during cutting of the polycrystalline silicon rod S. 
     In order to more effectively remove the scattered substances generated during cutting of the polycrystalline silicon rod S, it is preferable to deliver the liquid L 2  delivered through the second nozzle  15 , to a region on the surface of the polycrystalline silicon rod S, the region extending to a position where the liquid L 1  delivered through the first nozzle  14  does not flow but the scattered substances adhere. 
     The second nozzle  15  is connected to a pipe (not illustrated) through which the liquid L 2  is supplied. The second nozzle  15  can have an end of any shape. Usable examples of the second nozzle  15  include, but not limited to, a flared nozzle, as with the first nozzle  14 . Although the opening at the end of the second nozzle  15  has a size which is not limited to any particular size, the opening preferably has a size which allows delivery of the liquid enough for cutting, depending on, for example, a size of the polycrystalline silicon rod S and an amount of the liquid to be delivered to the cutting position of the polycrystalline silicon rod S. Specifically, the opening preferably has a width in the range of approximately 0.5 mm to 15 mm. 
     The liquid L 2  is of a type not limited to any particular type, provided that the liquid can serve to remove the scattered substances generated during cutting of the polycrystalline silicon rod S. The liquid L 2  can be, for example, pure water, or water containing an additive such as a cleaning ingredient. In order to minimize contamination of the polycrystalline silicon rod S, the liquid L 2  is preferably pure water, and particularly preferably pure water having a resistivity of not less than 1 MΩcm. 
     The liquid L 2  and the liquid L 1  can be the same or different in composition. In order to simplify a piping arrangement for the liquids L 1  and L 2 , the liquid L 2  and the liquid L 1  are preferably the same in composition. 
     The liquid L 2  flows at a flow rate that is not limited to any particular flow rate. The flow rate may be a rate at which, when blown toward the upper surface of the polycrystalline silicon rod S through the second nozzle  15 , the liquid L 2  flows so as to spread, on the upper surface of the polycrystalline silicon rod S, over a region corresponding to an area of diameter× diameter, where the diameter is the diameter of the polycrystalline silicon rod S. For example, the flow rate of the liquid L 2  is preferably larger than the flow rate of the liquid L 1  in terms of more effectively removing impurities. Specifically, the flow rate of the liquid L 2  can be 20 L/min to 40 L/min. 
     According to the present embodiment, the second nozzle  15  is disposed so as to be closer to the proximal end than the first nozzle  14  is and so as to be above the polycrystalline silicon rod S, and the number of the second nozzle  15  is one. However, the position and number of the second nozzle  15  are not limited to the above. The second nozzle  15  can be disposed at a position that is not limited to a particular position. For example, the second nozzle  15  can be disposed at a position where it is possible to deliver the liquid L 2  to a region of the surface of the polycrystalline silicon rod S through the second nozzle  15 , the region extending, toward at least one end (i.e., at least one of the proximal end and the distal end) of the polycrystalline silicon rod S in the extending direction of the polycrystalline silicon rod S, from the cutting position to a position which is at least not less than two times the diameter of the polycrystalline silicon rod S away from the cutting position. Accordingly, one or more second nozzle  15  can be disposed so as to be closer to the proximal end than the first nozzle  14  is, can be disposed so as to be closer to the distal end than the first nozzle  14  is, or can be disposed on both sides of the first nozzle  14 . 
     The upper limit of the number of the second nozzles  15  is not limited to any particular number. The number of the second nozzles  15  is preferably not more than ten, in order to simplify an arrangement of the cutting device  10 , or to reduce costs for the cutting work. 
     Further, the second nozzle  15  can be positionally fixed, or can be movable in the extending direction of the polycrystalline silicon rod S. In a case where the second nozzle  15  is movable, it is possible to deliver the liquid L 2  to a wider region and thus more effectively remove contaminants than in a case where the second nozzle  15  is fixed. 
     According to the present embodiment, the second nozzle  15  is disposed at a position above the polycrystalline silicon rod S. However, the position of the second nozzle  15  is not limited to this, and can be disposed at a position lateral to or below the polycrystalline silicon rod S. The second nozzle  15  is preferably disposed above the polycrystalline silicon rod S in order that the liquid delivered through the second nozzle  15  can flow downward to fall off together with contaminants scattered during cutting of the polycrystalline silicon rod S. 
     &lt;Method for Cutting Polycrystalline Silicon Rod&gt; 
     When the polycrystalline silicon rod S is cut by using the blade  133 , the rotation drive source  115  connected to the proximal end-side support  11  is rotated first. This causes, via the power transmission member  114 , rotation of the shaft member  113 , the cylinder bottom wall  112 , and the cylinder wall  111  of the proximal end-side support  11 , and thus causes rotation of the polycrystalline silicon rod S fixed to the cylinder wall  111  by the chucks  111   a . While the polycrystalline silicon rod S rotates, the three rollers  121  of the distal-side support  12  also rotate. This allows the distal-side support  12  to support the polycrystalline silicon rod S without causing interference with the rotation of the polycrystalline silicon rod S. 
     In addition, the liquid L 1  is delivered, through the first nozzle  14 , to the blade  133  and to the cutting position of the polycrystalline silicon rod S, while the liquid L 2  is delivered to the surface of the polycrystalline silicon rod S through the second nozzle  15 . 
     Then, the blade  133  is pushed against the polycrystalline silicon rod S at the cutting position so as to be substantially perpendicular to the extending direction of the polycrystalline silicon rod S, while the rotation shaft  132  and the blade  133  are rotated in a direction opposite to the rotation direction of the polycrystalline silicon rod S by rotating the rotation drive source  131  of the cutting section  13 . When the diamond abrasive particles of the blade  133  come in contact with the surface of the polycrystalline silicon rod S and grind the polycrystalline silicon rod S, the polycrystalline silicon rod S is cut from the outer circumference toward the center. 
     By appropriately repeating this cutting step at different positions in the extending direction of the polycrystalline silicon rod S, cut rods of the polycrystalline silicon rod S are manufactured. In other words, the method for manufacturing a cut rod of the polycrystalline silicon rod S includes the above cutting step. In addition, by carrying out a crushing step of crushing the cut rod by using, for example, a hammer or a crushing device, a nugget of the polycrystalline silicon rod S is manufactured. In other words, the method for manufacturing a nugget of the polycrystalline silicon rod S includes the above crushing step. 
     With such an arrangement, it is possible to remove contaminants from the cutting position of the polycrystalline silicon rod S by using the liquid L 1  delivered through the first nozzle  14 , the contaminants coming from the blade  133 . Further, it is also possible to remove scattered substances from the surface of the polycrystalline silicon rod S by using the liquid L 2  delivered through the second nozzle  15 , the scattered substances being scattered during the cutting of the polycrystalline silicon rod S and including the contaminants coming from the blade  133 . This makes it possible to effectively reduce contamination of the polycrystalline silicon rod S due to the contaminants coming from the blade  133 . 
     The method in accordance with an embodiment of the present invention makes it possible to effectively reduce not only contaminants which are simply adhered to the surface of the polycrystalline silicon rod S but also metal contaminants which are difficult to remove by an etching process in which the surface of the polycrystalline silicon rod S is removed by several micrometers by dissolution. 
     More specifically, according to conventional methods, a scattered cutting liquid do not flow so as to fall off during the cutting, and thus adheres to the polycrystalline silicon rod and dries. The metal contaminants contained in the cutting liquid then diffuse on the surface of and into the subsurface portion of the polycrystalline silicon rod S. It may be therefore impossible to sufficiently reduce such metal contaminants even by etching. Contrarily, the method in accordance with an embodiment of the present invention makes it possible to more efficiently reduce the metal contaminants. The polycrystalline silicon rod S obtained by etching is therefore suitable for use in manufacture of a monocrystalline silicon ingot in which metal contaminants are sufficiently reduced. 
     The liquid delivered through the second nozzle  15  can be delivered to a region extending from the cutting position to a position which is at least not less than two times the diameter of the polycrystalline silicon rod S away from the cutting position. This makes it possible to deliver the liquid to a region where most of the scattered substances generated during the cutting of the polycrystalline silicon rod S reach, the region being on the surface of the polycrystalline silicon rod S. This consequently makes it possible to more effectively reduce contamination on the surface. 
     Further, the liquid is delivered through the second nozzle  15  from above the polycrystalline silicon rod S. This can cause the liquid including the contaminants scattered during the cutting of the polycrystalline silicon rod S to move on the surface of the polycrystalline silicon rod S and then flow downward so as to fall off the polycrystalline silicon rod S. This arrangement makes it possible to efficiently remove the liquid including the contaminants from the polycrystalline silicon rod. 
     The polycrystalline silicon rod S can be cut by using the electrodeposition blade  133   b  in which the diamond abrasive particles have been firmly fixed by electrolytic plating that primarily uses only nickel as a metal component, not by using a binder which contains a number of metal components. This makes the contaminants coming from the blade  133  less likely to be scattered during the cutting of the polycrystalline silicon rod S, and also makes it possible to identify the type of contaminants that are scattered. It is therefore possible to more effectively reduce contamination of the polycrystalline silicon rod S due to the contaminants coming from the blade  133 . Further, since the polycrystalline silicon rod S rotates in a direction opposite to the rotation direction of the blade  133 , it is possible to prevent the polycrystalline silicon rod from breaking at a position other than the cutting position in the cutting step. 
     Embodiment 2 
     The following will describe another embodiment of the present invention. For convenience of description, the same reference sign is assigned to a member having the same function as the member described in the above embodiment, and the description of such a member is omitted. 
     As illustrated in  FIG. 3 , a cutting device  20  has the same configuration as the cutting device  10  in accordance with Embodiment 1, except that the cutting device  20  further includes a suction opening  26  for sucking and removing an air including scattered substances having been scattered due to cutting of the polycrystalline silicon rod S. 
     The suction opening  26  is located at a position that is not limited to any particular position. For example, the suction opening  26  can be disposed between the first nozzle  14  and the second nozzle  15  in the extending direction of the polycrystalline silicon rod S. The suction opening  26  is preferably disposed in this way on a first nozzle  14  side of the second nozzle  15  in order to more effectively suck and remove the scattered substances generated during the cutting of the polycrystalline silicon rod S. Further, the suction opening  26  has a height that is not limited to any particular height. The suction opening  26  can be at substantially the same height as the polycrystalline silicon rod S. The suction opening  26  is preferably disposed at a position that does not interfere with an operation of a worker. 
     In a case where the blade  133  is an outer diameter blade, the suction opening  26  is preferably disposed at a position ahead of a portion of the blade  133  in a direction in which after the portion has come in contact with the polycrystalline silicon rod S, the portion moves by rotation. For example, when viewed from the proximal end of the polycrystalline silicon rod S, the suction opening  26  is preferably disposed on the left side of the polycrystalline silicon rod S in a case where the blade  133  rotates to the right. This arrangement makes it possible to effectively suck, through the suction opening  26 , the scattered substances having been scattered from the blade  133 , and thus makes it possible to more effectively reduce contamination of the polycrystalline silicon rod S with contaminants coming from the blade  133 . 
     The suction opening  26  sucks the contaminants at a suction rate that is not limited to any particular rate, provided that the suction rate makes it possible to sufficiently suck the scattered substances generated during cutting of the polycrystalline silicon rod S. The suction opening  26  preferably sucks the air including the scattered substances at a suction rate of, for example, 10 m 3 /min to 30 m 3 /min. 
     More than one suction opening  26  can be provided so as to more effectively suck and remove the scattered substances generated during cutting of the polycrystalline silicon rod S. 
     Such an arrangement makes it possible to suck and remove scattered substances having been scattered due to cutting of the polycrystalline silicon rod S, before the scattered substances reach the surface of the polycrystalline silicon rod S. This makes it possible to reduce the amount of scattered substances which reach the surface of the polycrystalline silicon rod S, and thus to more effectively remove, by using the liquid L 2  delivered through the second nozzle  15 , the scattered substances from the surface of the polycrystalline silicon rod S. 
     Aspects of the present invention can also be expressed as follows: 
     In order to solve the above problem, a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod, includes the step of cutting the polycrystalline silicon rod by using a cutting tool, the step of cutting including: delivering a liquid to a cutting position of the polycrystalline silicon rod through a first nozzle; and delivering a liquid to a surface of the polycrystalline silicon rod through a second nozzle. 
     Such an arrangement makes it possible to remove contaminants from the cutting position of the polycrystalline silicon rod by using the liquid delivered through the first nozzle, the contaminants coming from the cutting tool. In addition, the arrangement makes it possible to remove scattered substances from the surface of the polycrystalline silicon rod by using the liquid delivered through the second nozzle, the scattered substances being scattered during cutting of the polycrystalline silicon rod and including the contaminants coming from the cutting tool. This makes it possible to effectively reduce contamination of the polycrystalline silicon rod with the contaminants coming from the cutting tool. 
     According to a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod, the liquid can be delivered to a region of the surface through the second nozzle, the region extending, toward at least one end in an extending direction of the polycrystalline silicon rod, from the cutting position to a position which is at least not less than two times a diameter of the polycrystalline silicon rod away from the cutting position. 
     Such an arrangement causes the liquid delivered through the second nozzle to be delivered to the region extending from the cutting position to the position which is at least not less than two times the diameter of the polycrystalline silicon rod away from the cutting position. This makes it possible to deliver the liquid to a region where most of the scattered substances scattered during the cutting of the polycrystalline silicon rod reach, the region being on the surface of the polycrystalline silicon. This consequently makes it possible to more effectively reduce contamination of the surface. 
     According to a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod, the liquid can be delivered through the second nozzle from above the polycrystalline silicon rod so that the liquid delivered through the second nozzle moves on the surface of the polycrystalline silicon rod and then flows downward so as to fall off the polycrystalline silicon rod. 
     With this arrangement, the liquid is delivered from above the polycrystalline silicon rod through the second nozzle. Accordingly, the liquid including contaminants scattered during cutting of the polycrystalline silicon rod flows downward so as to fall off the polycrystalline silicon rod. This makes it possible to efficiently remove, from the polycrystalline silicon rod, the liquid including the contaminants. 
     According to a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod, the step of cutting can further include sucking and removing an air including a scattered substance having been scattered due to the cutting. 
     This arrangement makes it possible to suck and remove the scattered substances having been scattered due to cutting of the polycrystalline silicon rod before the scattered substances reach the surface of the polycrystalline silicon rod. This makes it possible to reduce the amount of scattered substances which reach the surface of the polycrystalline silicon rod, and thus to more effectively remove, by using the liquid delivered through the second nozzle, the scattered substances from the surface of the polycrystalline silicon rod. 
     According to a method, in accordance with an aspect of the present invention, for cutting a polycrystalline silicon rod, the cutting tool is an outer diameter blade in which diamond abrasive particles are firmly fixed, and the step of cutting further includes rotating the polycrystalline silicon rod in a direction opposite to a rotation direction of the outer diameter blade. 
     In a case where the diamond abrasive particles are firmly fixed in the outer diameter blade, the polycrystalline silicon rod may be contaminated with contaminants coming from a binder (for example, a resin bond, a metal bond, or the like) used for such firm fixation. Consequently, this may adversely affect the quality of a monocrystalline silicon ingot manufactured from the polycrystalline silicon rod. Contrarily, the above-described arrangement makes it possible to reduce or prevent the adverse effect from these contaminants. 
     In a case of using, among other outer diameter blades, an outer diameter blade in which diamond abrasive particles are electrodeposited, the following effects are produced. A polycrystalline silicon rod is cut by using a blade in which diamond abrasive particles are firmly fixed by electrolytic plating that primarily uses only nickel as a metal component, but not by using a binder which contains a number of metal components. This makes contaminants coming from such a cutting tool less likely to be scattered during cutting of the polycrystalline silicon rod, and also makes it possible to identify the type of contaminants that are scattered. It is therefore possible to more effectively reduce contamination of the polycrystalline silicon rod with the contaminants coming from the cutting tool. 
     In addition, it is possible to prevent the polycrystalline silicon rod from breaking at a position other than the cutting position in the cutting step. 
     A method, in accordance with an aspect of the present invention, for manufacturing a cut rod of a polycrystalline silicon rod, includes the step of cutting the polycrystalline silicon rod by using a cutting tool, the step of cutting including: delivering a liquid to a cutting position of the polycrystalline silicon rod through a first nozzle; and delivering a liquid to a surface of the polycrystalline silicon rod through a second nozzle. 
     A method, in accordance with an aspect of the present invention, for manufacturing a nugget of a polycrystalline silicon rod, can include the step of crushing the cut rod obtained by the method for manufacturing the cut rod of the polycrystalline silicon rod. 
     A polycrystalline silicon rod cutting device in accordance with an aspect of the present invention includes: a cutting tool for cutting a polycrystalline silicon rod; a first nozzle for delivering a liquid to a cutting position of the polycrystalline silicon rod; and a second nozzle for delivering a liquid to a surface of the polycrystalline silicon rod. 
     The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. The present invention also encompasses, in its technical scope, any embodiment derived by combining technical means disclosed in differing embodiments. 
     EXAMPLES 
     The following will describe examples of the present invention. 
     [Preparation of Cleaned Nugget] 
     Example 1 
     A polycrystalline silicon rod (diameter: approximately 100 mm) was cut by using the cutting device  10  in accordance with Embodiment 1. The polycrystalline silicon S was cut with use of a diamond electrodeposition blade manufactured by Asahi Diamond Industrial Co., Ltd. During this cutting, the polycrystalline silicon S was rotated at approximately 50 rpm, while the blade  133  was rotated at approximately 2000 rpm in a direction opposite to a rotation direction of the polycrystalline silicon rod S. During the cutting, pure water was delivered as the liquid L 1  at a flow rate of 10 L/min through the first nozzle  14  and pure water was delivered as the liquid L 2  at a flow rate of 30 L/min through the second nozzle  15 . A cut rod which is approximately 500 mm long was prepared by carrying out the cutting two times. 
     A nugget of the polycrystalline silicon rod S in accordance with Example 1 was prepared by crushing, with use of a tungsten carbide hammer, the above cut rod of the polycrystalline silicon rod until the maximum dimension of the nugget became approximately 100 mm. The nugget thus prepared was immersed in a bath of fluonitric acid (a mixture of nitric acid and hydrofluoric acid) so that a surface of the nugget was removed by several micrometers by dissolution. Subsequently, the nugget was washed with water and dried, so that a cleaned nugget was prepared. 
     Example 2 
     A cleaned nugget of a polycrystalline silicon rod S in accordance with Example 2 was prepared as in Example 1, except that a metal bond blade was used instead of the diamond electrodeposition blade. The metal bond blade is a blade in which diamond abrasive particles are firmly fixed by using a metal bond. 
     Comparative Example 1 
     A cleaned nugget of a polycrystalline silicon rod S in accordance with Comparative Example 1 was prepared as in Example 1, except that the polycrystalline silicon rod was cut without delivery of the liquid L 2  through the second nozzle  15 . 
     Comparative Example 2 
     A cleaned nugget of a polycrystalline silicon rod S in accordance with Comparative Example 1 was prepared as in Example 2, except that the polycrystalline silicon rod was cut without delivery of the liquid L 2  through the second nozzle  15 . 
     Reference Example 
     A cleaned nugget was prepared as a Reference Example, by: (i) immersing a nugget obtained by crushing a polycrystalline silicon rod S which had not been cut, as in Example 1, in a bath of fluonitric acid so that a surface of the nugget was removed by several micrometers by dissolution; and then (ii) washing with water and drying the nugget. 
     [Surface Heavy Metal Concentration] 
     The cleaned nuggets prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured for respective surface heavy metal concentrations, by the method as follows. 
     First, each of the cleaned nuggets was immersed in a bath of fluonitric acid at room temperature, and a surface of the nugget was dissolved by a depth of approximately 20 micrometers, so that a resultant solution was obtained. Next, the mass of each of heavy metal components included in the resultant solution was measured by ICP-MS. Lastly, the surface heavy metal concentration was calculated by dividing the mass of the heavy metal component by the mass of the cleaned nugget (unit: parts per billion weight (ppbw)). Table 1 shows results of such calculations. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Surface heavy metal 
               
               
                   
                 concentration (ppbw) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Fe 
                 Ni 
                 Cr 
                 Co 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 Electrodeposition blade 
                 0.08 
                 0.02 
                 0.07 
                 0.01 
               
               
                   
                 used 
               
               
                 Example 2 
                 Metal bond blade used 
                 0.09 
                 0.02 
                 0.08 
                 0.01 
               
               
                 Comparative 
                 Cutting by using 
                 0.12 
                 2.7 
                 0.07 
                 0.01 
               
               
                 Example 1 
                 electrodeposition blade 
               
               
                   
                 without delivery of 
               
               
                   
                 liquid L2 
               
               
                 Comparative 
                 Cutting by using metal 
                 0.11 
                 0.92 
                 1.6 
                 0.84 
               
               
                 Example 2 
                 bond blade without 
               
               
                   
                 delivery of liquid L2 
               
               
                 Reference 
                 (Non-cut product) 
                 0.08 
                 0.02 
                 0.06 
                 0.01 
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     The heavy metal concentrations in Examples were lower than the heavy metal concentrations in Comparative Examples, and were substantially equal to those of the non-cut product in Reference Example. 
     REFERENCE SIGNS LIST 
     
         
           10 : Cutting device 
           13 : Cutting section 
           14 : First nozzle 
           15 : Second nozzle 
           20 : Cutting device 
           26 : Suction opening 
           133 : Blade 
           133   b : Electrodeposition blade 
         L 1 : Liquid 
         L 2 : Liquid