JP2014188655A - Wire tool for polycrystalline silicon cutting and polycrystalline silicon cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire tool for polycrystalline silicon cutting and a polycrystalline silicon cutting method which has high cutting efficiency, is excellent in surface finishing without giving big damages to a cut wafer, and can cut with sufficient wafer strength in polycrystalline silicon cutting processing.SOLUTION: A wire tool 7 is constituted mainly by a core wire 11, abrasive grains 13 and a plating layer 15. The core wire 11 is a metallic wire which is of high strength and is conductive, or a non-metallic wire which is of high strength and includes a conductive coating layer. The abrasive grains 13 and the plating layer 15 are mounted in the outer periphery of the core wire 11. The plating layer 15 functions as a holding layer of the abrasive grains 13. The abrasive grains 13 shall be harder than the article to be polished, without any additional requirement. Although copper, zinc, silver and the like can be used for the plating layer, copper is most desirable. As for Vickers hardness of the plating layer 15, a range of 60 HV to 200 HV is desirable and a range of 80 HV to 180 HV is more desirable.

Description

  The present invention relates to a polycrystalline silicon cutting wire tool for cutting polycrystalline silicon and a method for cutting polycrystalline silicon using the same.

  Conventionally, wire tools have been used to cut hard and brittle materials such as polycrystalline silicon. For example, there has been a method of slicing a processing target (free abrasive processing) while supplying a slurry containing abrasive grains using a steel wire.

  However, in such a method, grinding waste liquid containing a large amount of abrasive grains and cutting waste of the workpiece is generated. Therefore, there is a problem that this processing is necessary and the environmental load is large. Further, since the processing is performed only when the abrasive grains exist between the steel wire and the workpiece, the amount of wire used for cutting out one wafer becomes very large, and the cutting efficiency is extremely poor. was there.

  On the other hand, the wire tool which fixed the abrasive grain beforehand to the core wire with high intensity | strength like a piano wire may be used. In this case, for example, there is a method of holding the abrasive grains on the outer periphery of a core wire or the like with a thermosetting resin or a photocurable resin (Patent Document 1).

  There is also a method using a wire tool in which abrasive grains are held by nickel plating on the outer periphery of a metal core wire (Patent Document 2). In addition, when holding the abrasive grains by nickel plating, in order to expose the tip of the abrasive grains or to align the tips of the abrasive grains, the plating layer on the abrasive grains is dressed using a grindstone or the like A wire tool may be used.

  As described above, in order to cut hard and brittle materials, in consideration of reduction of environmental load and improvement of cutting efficiency, fixed abrasive processing in which abrasive grains are fixed to the core wire is preferable to free abrasive processing.

Japanese Patent No. 3078020 Japanese Patent No. 4139810

  However, although the method of Patent Document 1 does not require treatment of a large amount of waste liquid, the holding power of abrasive grains is not necessarily high. For this reason, abrasive grains may fall off during the cutting process, and cutting efficiency may deteriorate. Therefore, in order to efficiently cut the workpiece, it is necessary to increase the amount of wire used.

  Furthermore, since the wire tool travels at a high speed when the workpiece is being machined, high frictional heat is generated even though the grinding part (cooling liquid) is applied to the machined portion. The frictional heat may soften the resin holding the abrasive grains. When the resin is softened, the holding power of the abrasive grains is weakened, and the cutting efficiency is further deteriorated. For this reason, the amount of wire used must be increased, and the cost of cutting out one wafer may increase.

  Moreover, since the method of patent document 2 has fixed the abrasive grain by nickel plating, since the plating layer holding an abrasive grain is hard and the holding power of an abrasive grain is very high, it prevents the fall of the abrasive grain during a process. it can. For this reason, the amount of wire used for cutting out the wafer can be reduced. However, when cutting polycrystalline silicon, especially when processing at the interface of the crystal, when a heavy load is applied between the workpiece and the wire tool (abrasive grains), the abrasive grains do not fall off Processing proceeds to the workpiece. At that time, there is a possibility that a large scratch or a peeling scratch may be applied to the workpiece. When such a scratch is made on the workpiece, not only the surface accuracy of the cut wafer is lowered, but also the strength of the wafer is lowered. For this reason, there is a possibility that the wafer cannot be used as a product.

  Furthermore, the abrasive grains are firmly fixed on the core wire with a particle size distribution and a certain variation in the particle diameter, and the most protruding abrasive grains among the fixed abrasive grains are processed. When a load is applied to a single abrasive grain in this way, the sharpness is good, but the surface roughness of the cut wafer is deteriorated, and the strength of the cut wafer may be reduced.

  In the case of a wire tool in which abrasive grains are held on the outer periphery of a metal core wire by a nickel plating layer, it is common to use abrasive grains in which metal such as nickel or titanium is present on the surface. When such an abrasive grain is used, conductivity is imparted to the abrasive grain surface, so that a plating layer is formed on the abrasive grain and the abrasive grain can be firmly fixed. However, if the wire tool is used as it is, it takes time until the abrasive tip is worn and the abrasive is exposed, and it takes time until the abrasive exhibits its cutting ability. Further, while the plating is worn, the original sharpness of the wire tool cannot be exhibited, and slip occurs with the workpiece at the start of cutting. For this reason, there exists a possibility that the thickness variation of a to-be-cut object and a curvature may generate | occur | produce.

  On the other hand, there is a method of performing dressing using a grindstone before cutting of a hard and brittle material in order to expose the tip of the abrasive and align the tip of the abrasive. However, when dressing is performed for nickel plating on the abrasive grains, the nickel plating is hard and the dressing takes time, so the productivity is lowered. In addition, an excessive load is applied to the abrasive grains during dressing, which may cause the abrasive grains to fall off and the fixing strength to decrease. If the abrasive grains fall off or the fixing strength is reduced, the original sharpness cannot be exhibited, cutting efficiency is deteriorated, and cutting accuracy is also deteriorated. Moreover, in order to align the front-end | tip part of an abrasive grain, it is necessary to grind an abrasive grain further, and productivity will fall since it requires very long time.

  Thus, in the cutting of polycrystalline silicon, if a wire tool in which abrasive grains are fixed by nickel plating is used, the cut wafer will be damaged greatly, and the surface roughness of the cut wafer will increase. This is a cause of inferior wafer strength due to surface scratches. For this reason, at present, the free abrasive processing is most frequently used for cutting polycrystalline silicon.

  However, free abrasive grain processing has a small surface roughness of the wafer, and it is possible to cut out the wafer while maintaining the wafer strength. However, as described above, it contains a large amount of abrasive grains and cutting waste. There is a problem that grinding waste liquid is generated and the environmental load and work load increase. In addition, since the cutting method involves processing when abrasive grains exist between the workpiece and the core wire, the amount of steel wire and abrasive grains used is increased, and the cutting efficiency is very poor. Therefore, the productivity is poor, and the total cost may increase if the amount and time of wire used for one wafer and the treatment of the cutting waste liquid are included.

  The present invention has been made in view of such problems. In the cutting process of polycrystalline silicon, while having high cutting efficiency, it has excellent surface finish without causing large scratches on the cut wafer. An object of the present invention is to provide a polycrystalline silicon wire tool and a polycrystalline silicon cutting method capable of cutting with sufficient strength.

  In order to achieve the above-described object, the first invention provides a core wire having conductivity at least on the surface, abrasive grains provided on the outer periphery of the core wire, and a plating layer formed on the outer periphery of the core wire and holding the abrasive grains And the plating layer is formed by any one of copper plating, zinc plating, and silver plating, and the plating layer has a Vickers hardness in the range of 60 HV to 200 HV. It is a wire tool.

  The plating layer is preferably copper plating, and the plating layer preferably has a Vickers hardness of 80 HV or more and 200 HV or less.

  The abrasive grains are composed of any of diamond abrasive grains, aluminum oxide-based abrasive grains, or silicon carbide-based abrasive grains in which palladium adheres to a part of the surface of the abrasive grains, and the average grain diameter of the abrasive grains is 20 μm. The following is desirable.

  It is desirable that the thickness of the plating layer is not less than 1/4 and not more than 3/4 of the average particle diameter of the abrasive grains. It is more preferable that the thickness of the plating layer is 1/3 or more and 3/5 or less of the average grain size of the abrasive grains in terms of the holding power of the abrasive grains and the cutting accuracy.

  According to the first invention, since metal plating is used as the abrasive grain holding means for fixing the abrasive grains to the core wire, the abrasive grains can be firmly fixed as compared with the case where the abrasive grains are fixed with resin. . In addition, since the abrasive grains are firmly fixed, the abrasive grains are not dropped during processing, the cutting efficiency is increased, the processing time is short, and the amount of wire used can be reduced. Furthermore, compared to resin, metal plating is extremely excellent in heat resistance, and the holding power of abrasive grains is not reduced by heat.

  In addition, the hardness of the plating layer of the present invention is lower than that of nickel plating used as a conventional plating layer. For this reason, when the abrasive grains are pressed against the processed part while cutting the polycrystalline silicon, the abrasive grains themselves follow the elastic deformation of the plating layer within the plating layer due to the elastic deformation of the plating layer. Can move on. For this reason, the protruding abrasive grains are pushed into the plating layer and the tips of the abrasive grains are easily aligned. Therefore, a large number of abrasive grains can contribute to the machining at the same time, and the surface accuracy of the workpiece can be improved by reducing the force applied to one abrasive grain.

  Further, when cutting a portion having different hardness, such as an interface of polycrystalline silicon, a large load may be applied between the workpiece and the wire tool (abrasive grain). At that time, by removing the abrasive grains first without forcibly cutting, it becomes possible to process the cut wafer without causing large scratches or bruises, and the strength as a wafer is maintained. The wafer can be cut out as it is. Such an effect can be more reliably obtained when the Vickers hardness of the plating layer is in the range of 60 HV to 200 HV, particularly when the plating layer is copper plating and in the range of 80 HV to 200 HV.

  Moreover, since the potential of palladium is noble by attaching palladium to the surface of the abrasive grains, the adhesion between the copper plating and the abrasive grains can be improved.

  Moreover, the holding | maintenance force of an abrasive grain can fully be ensured by making thickness of a plating layer into 1/4 or more and 3/4 or less of the average particle diameter of an abrasive grain. Moreover, since the protrusion amount of an abrasive grain can be ensured appropriately, the tool life is extended and it is not necessary to make the plating layer excessively thick. It is more preferable that the thickness of the plating layer is 1/3 or more and 3/5 or less of the average grain size of the abrasive grains in terms of the holding power of the abrasive grains and the cutting accuracy.

  According to a second aspect of the present invention, there is provided a core wire having conductivity on at least a surface thereof, an abrasive having an average particle diameter of 20 μm or less provided on an outer periphery of the core wire, a metal having a Vickers hardness of 60 HV or more and 200 HV or less. Using a wire tool having a plating layer, the polycrystalline silicon is cut, the surface roughness Ra of the wafer cut from the polycrystalline silicon is 0.5 μm or less, and the strength of the wafer by a three-point bending test is 100 MPa or more. This is a method for cutting polycrystalline silicon.

It is preferable that the thickness of the plating layer is not less than 1/4 and not more than 3/4 of the average particle diameter of the abrasive grains.

  It is desirable to use a wire tool in which palladium is attached to a part of the surface of the abrasive grains and the plating layer for holding the abrasive grains is copper plating.

  According to the second invention, since the hardness of the plating layer holding the abrasive grains is appropriate, it is possible to prevent the abrasive grains from falling off. In particular, the presence of palladium on part of the surface of the abrasive grains can improve the adhesion between the abrasive grains and the copper plating.

  In addition, since the abrasive grains themselves can move elastically in the plating layer during cutting, the abrasive grains can be processed without causing large scratches or peeling scratches on the wafer. For this reason, the surface roughness Ra of the cut wafer is set to 0.5 μm or less, and it becomes possible to ensure the wafer strength of 100 MPa or more in the three-point bending test. If the surface roughness Ra of the cut wafer is 0.4 μm or less, it is preferable because it is possible to ensure a wafer strength of 100 MPa or more in a three-point bending test.

  According to the present invention, in the cutting process of polycrystalline silicon, while having high cutting efficiency, the surface finish is excellent without damaging the cut wafer, and the wafer can be cut with sufficient strength. A wire tool for crystalline silicon and a method for cutting polycrystalline silicon can be provided.

The figure which shows the cutting device 1. FIG. Sectional drawing of the wire tool 7. FIG. (A) is sectional drawing which shows the state which provided the metal layer 17 in the whole outer peripheral surface of the abrasive grain 13, (b) shows the state which provided the metal layer 17 in a part of outer peripheral surface of the abrasive grain 13. FIG. Sectional drawing. Schematic which shows the wire tool manufacturing apparatus 20. FIG. The figure which shows the method of measuring the intensity | strength of the wafer.

(Cutting device)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a cutting device 1. The cutting device 1 is for slicing an ingot 3 that is a cutting object. The cutting device 1 includes a holding unit 5 that holds the ingot 3, a roller 9 having a multi-groove for moving the wire tool 7, a motor (not shown) for driving the holding unit 5 and the roller 9, and the like. Composed.

  In the cutting device 1, the wire tool 7 is wound many times around the outer periphery of the roller 9 with a predetermined tension applied. The wire tool 7 is fed from one side (in the direction of arrow A in the figure) and wound up from the other side (in the direction of arrow B in the figure). The wire tool 7 can be reciprocated between the rollers 9 by reversibly rotating the rollers 9 by the drive motor.

  In a state where the polycrystalline silicon ingot 3 is held by the holding portion 5, the polycrystalline silicon ingot 3 is moved perpendicularly to the moving direction of the wire tool 7 (in the direction of arrow C in the figure). The wire tool 7 cuts the ingot 3 by applying a predetermined load to the holding unit 5 and bringing the ingot 3 into contact with the wire tool 7. That is, the ingot 3 can be sliced into a large number of workpieces at a time. The cutting method of the present invention is not limited to the illustrated example, and can be applied to all cutting processes performed using the wire tool according to the present invention.

(Wire tool)
Next, the wire tool 7 will be described. FIG. 2 is a view showing a cross section of the wire tool 7 in a direction perpendicular to the axial direction. The wire tool 7 is mainly composed of a core wire 11, abrasive grains 13, a plating layer 15, and the like.

  The core wire 11 is a metal wire having high strength and conductivity, or a non-metal wire having a high strength and conductive coating layer. Examples of the metal wire include a piano wire, a stainless steel wire, a tungsten wire, and a molybdenum wire. Glass fiber, aramid fiber, carbon fiber, alumina fiber, boron fiber, or the like can be used as the material for the non-metallic wire having the conductive coating layer.

  Here, when using a non-metallic wire as the core wire, in order to impart conductivity to the outer peripheral surface of the core wire, the surface conductive layer of the core wire is formed by performing metal plating on the glass fiber or polymer fiber by electroless plating. Can be formed. Alternatively, a conductive polymer can be used on the outer peripheral surface of the core wire, or a conductive material can be included in the polymer to impart conductivity.

  Of these, the piano wire is most preferable. The wire diameter of the core wire 11 can be appropriately selected depending on the workpiece. The surface of the core wire 11 is preferably plated with thin brass or copper for rust prevention.

Abrasive grains 13 and a plating layer 15 are provided on the outer periphery of the core wire 11. The plating layer 15 functions as a holding layer for the abrasive grains 13. The abrasive grain 13 is not particularly limited as long as it has a higher hardness than the workpiece, but as a polycrystalline silicon cutting wire tool, in addition to diamond, an aluminum oxide (Al ₂ O ₃ ) system (for example, A : Brown alumina, WA: white alumina), silicon carbide (SiC) (for example, GC: green silicon carbide, C: black silicon carbide), and the like. The hardness is diamond> silicon carbide (SiC)> aluminum oxide (Al ₂ O ₃ ).

  The type of the abrasive grain 13 can be properly used depending on the balance between cutting efficiency and cutting accuracy. As the hardness of the abrasive grains 13 is higher, the wear of the abrasive grains 13 is reduced and the amount of wire used can be reduced. On the other hand, the lower the hardness of the abrasive grains, the less the load is applied to the workpiece, so that the cutting accuracy is improved.

  Further, the average particle diameter of the abrasive grains 13 is appropriately changed depending on the workpiece or the core wire 11. However, when the average particle size of the abrasive grains 13 is increased, there is a possibility that a large scratch is generated on the workpiece. For example, in order to set the surface roughness Ra of the cut wafer to 0.5 μm, the average particle size of the abrasive grains 13 is desirably 20 μm or less. For use as a wire tool, the average grain size of the abrasive grains 13 is desirably 3 μm or more. It is because cutting efficiency will fall if the average particle diameter of the abrasive grain 13 is too small.

  The average particle size of the abrasive grains 13 in the present invention is the average particle size (arithmetic average particle size) of the distribution measured by a general laser diffraction type particle size distribution measuring device (for example, SALD-2300 manufactured by Shimadzu Corporation). To do.

  FIG. 3A is a conceptual cross-sectional view showing the abrasive grains 13. As shown in FIG. 3A, a metal layer 17 is preferably provided on the surface of the abrasive grain 13. The metal layer 17 is for strengthening the adhesion between the core wire 11 and the abrasive grains 13. The metal layer 17 may be any metal, such as nickel, titanium, or palladium. Since the metal layer 17 is present on the surface of the abrasive grain 13, the plating layer 15 is formed on the abrasive grain 13, so that the adhesion between the abrasive grain 13 and the core wire 11 is improved.

  In addition, since nickel and titanium form a passive film on the surface, when the plating layer 15 is copper, adhesiveness with copper is weak, and the holding power of the abrasive grains 13 may be insufficient. On the other hand, since palladium does not form a passive film, it has good adhesion with copper. Therefore, palladium, which has better compatibility with copper plating than nickel or titanium, is most preferable.

  The method for forming the metal layer 17 on the abrasive grains 13 is not particularly limited, and examples include electroless plating and sputtering. For example, as a method for depositing palladium, a general pretreatment for electroless plating may be used, and examples include a catalyst accelerator method. The metal layer 17 may completely cover the outer peripheral surface of the abrasive grains 13 as shown in FIG. 3 (a), but the abrasive grains 13 are completely covered as shown in FIG. 3 (b). It does not need to be coated, and it only needs to be formed on at least a part thereof. For example, the metal layer 17 may be distributed in an island shape or partially in a film shape, and preferably covers more than 50% of the surface area of the abrasive grains 13.

  The plating layer 15 can be made of metal such as copper, zinc, and silver, but copper is most preferable. The plating layer 15 preferably has a Vickers hardness of 60 HV or more and 200 HV or less, and more preferably 80 HV or more and 180 HV or less. When the hardness of the plating layer 15 is less than 60 HV, the holding force of the abrasive grains 13 becomes insufficient, and the abrasive grains that fall off during processing increase. If the hardness of the plating layer 15 is greater than 200 HV, the holding force of the abrasive grains 13 is sufficient, but the metal of the plating layer 15 is hard and the risk of damaging the wafer increases. Moreover, it is more preferable that it is 80HV or more because the abrasive grains can be held more reliably than when the hardness of the plating layer is 60HV.

  In addition, the value measured according to JISZ2244 is employ | adopted for the measuring method of the Vickers hardness of the plating layer 15. FIG. The plating bath for plating each metal is not particularly limited. For example, in the case of copper plating, a copper sulfate bath containing copper sulfate, sulfuric acid, and a brightener may be used.

  The hardness of plating can be changed depending on the type of plating bath, the type and amount of brightener, and plating conditions. The thickness of the plating layer 15 is preferably not less than 1/4 and not more than 3/4 of the average particle diameter of the abrasive grains 13. If the thickness of the plating layer 15 is smaller than ¼ of the average grain size of the abrasive grains 13, the holding power of the abrasive grains 13 becomes insufficient, the abrasive grains fall off during processing, and the amount of wire used is increased. I must. When the thickness of the plating layer 15 is larger than 3/4 of the average particle diameter of the abrasive grains 13, the amount of protrusion of the abrasive grains 13 from the plating layer 15 decreases, so that the tool life is shortened and the plating layer 15 It takes time to form and productivity decreases. More preferably, it is 1/3 or more and 3/5 or less of the average particle diameter. If the average particle diameter is 1/3 or more and 3/5 or less, the protrusion amount on the surface of the abrasive grains can be ensured while sufficiently securing the retention force, and the balance between retention force and cutting accuracy is excellent.

  Although it is desirable that the plating layer 15 completely covers the abrasive grains 13, it is also possible to form the plating layer 15 with the tips of the abrasive grains 13 protruding. When the abrasive grains 13 are completely covered with the plating layer 15, even if the wire tool 7 is used as it is, the plating layer 15 is not hard, so that the tip of the abrasive grains 13 is immediately exposed and the original sharpness of the tool can be exhibited. In addition, it is also possible to exclude the plating of the front-end | tip part of the abrasive grain 13 by the dressing using a grindstone before a process. In that case, since the plating layer 15 is not hard, the time required for dressing is short, and therefore, the wire tool 7 can be manufactured without reducing productivity. As a dressing method, there is a method of cutting a dummy grindstone such as alumina with respect to a wire tool once wound.

(Production method)
Next, the manufacturing process of the wire tool 7 will be described. FIG. 4 is a schematic view showing the wire tool manufacturing apparatus 20. First, the core wire 11 is manufactured. If the core wire 11 is a metal wire such as a piano wire, it can be used as it is. In the case of a non-metallic wire such as a glass wire, a conductive coating layer is provided on the outer peripheral surface in advance. In addition, also when using a piano wire, it is desirable to form copper plating etc. in an outer peripheral surface as mentioned above.

  Next, the core wire 11 is sent to the degreasing tank 21 (in the direction of arrow F in the figure). The degreasing tank 21 is a tank in which, for example, an aqueous sodium hydroxide solution is stored, and dirt such as oil adhering to the outer surface of the core wire 11 is removed. In the water rinsing tank 23, the chemical solution or the like in the degreasing tank 21 attached to the surface is washed.

  The plating tank 25 is a tank for performing electrolytic plating on the core wire 11 and electrodepositing the abrasive grains 13. The plating tank 25 is a copper bath in which abrasive grains 13 are dispersed in a solution in which copper is dissolved, for example. A metal layer 17 is formed on the abrasive grains 13 in advance. A cathode 29 is connected to the core wire 11 passing through the plating tank 25. An anode 31 is immersed in the plating tank 25. The cathode 29 and the anode 31 are connected to a power source (not shown). Thus, the plating layer 15 having a desired thickness is formed.

  In a state where the abrasive grains 13 are held by the plating layer 15, excess chemicals and the like are washed in the water washing tank 27 and wound up by the winding device 33 (in the direction of arrow G in the figure), whereby the wire tool 7 is manufactured. .

  As described above, according to the present embodiment, metal plating is used as the abrasive grain holding means for fixing the abrasive grains 13 to the core wire 11, and the Vickers hardness of the plating layer 15 is 60 HV or higher. The abrasive grains 13 can be held firmly as compared with the case where they are fixed with resin. For this reason, there is little omission of abrasive grain 13 during processing. Therefore, the cutting efficiency of the work material is increased, the processing time is short, and the amount of wire used can be reduced. Furthermore, the metal plating layer 15 is very excellent in heat resistance compared to the resin, and the holding power of the abrasive grains 13 is not reduced by heat.

  Moreover, since the Vickers hardness of the plating layer 15 is 200 HV or less, the hardness is lower than, for example, conventional nickel plating. Therefore, when the abrasive grains 13 are pressed against the processed portion during cutting of the work material, the abrasive grains 13 themselves follow the elastic deformation of the plating layer in the plating layer 15 due to the elastic deformation of the plating layer. Move slightly. For this reason, the protruding abrasive grains 13 are pushed into the plating layer 15 and the tips of the abrasive grains 13 are easily aligned. For this reason, a plurality of abrasive grains 13 can simultaneously contribute to the processing, and the force applied to one abrasive grain 13 can be reduced. In particular, polycrystalline silicon is easily damaged due to the presence of a crystal interface, and the effect obtained by reducing the Vickers hardness of the plating layer 15 to 200 HV or less is great. That is, the wire tool 7 of the present invention is particularly suitable for cutting polycrystalline silicon.

  Further, by forming a metal layer 17 such as palladium on the surface of the abrasive grain 13, the adhesion between the plating layer 15 and the abrasive grain 13 can be improved.

  Moreover, since the thickness of the plating layer 15 is 1/4 or more of the average particle diameter of the abrasive grains 13, a sufficient holding power of the abrasive grains 13 can be obtained. For this reason, dropping of the abrasive grains 13 during cutting can be suppressed. In addition, since the thickness of the plating layer 15 is 3/4 or less of the average particle diameter of the abrasive grains 13, it is possible to ensure the allowance for the abrasive grains 13 to protrude from the plating layer 15. For this reason, tool life can be secured. Moreover, since it is not necessary to make the plating layer 15 excessively thick, productivity is good. Here, desirably, the thickness of the plating layer is more preferably 1/3 or more and 3/5 or less of the average particle diameter in terms of the holding power of the abrasive grains and the cutting accuracy.

  Using a wire tool according to the present invention, a conventional wire tool in which abrasive grains are fixed with a nickel plating layer, and a wire tool in which abrasive grains are fixed with a resin, the amount of wire used, The surface roughness Ra and the wafer strength were compared.

Example 1
The wire tool according to the present invention was manufactured as follows. A diamond wire having an average particle size of 9.6 μm was formed on a core wire in which a copper wire was coated on a piano wire having a diameter of 120 μm with a thickness of 1 μm, and fixed to a copper plating layer having a thickness of 5.0 μm. Diamond was supported by palladium on the surface by the catalyst accelerator method. The diamond was added to a plating bath composed of copper sulfate, sulfuric acid, and a brightener, and composite plating was performed to form a plating layer while incorporating diamond abrasive grains. When the Vickers hardness of the plating layer of this wire tool was measured, it was 80 HV.

(Examples 2-3)
Examples 2 and 3 were produced in the same manner as in Example 1 except that the hardness was adjusted by changing the amount of the brightener. It was 142HV and 196HV when the Vickers hardness of each plating layer of Example 2 and Example 3 was measured. In the present invention, the sulfate bath is used in Example 2, but it is also possible to use a cyanide bath instead of the sulfate bath.

(Examples 4 to 5)
Examples 4 and 5 were produced in the same manner as Example 1 except that the plating layers were zinc and silver (Vickers hardness: 91 HV, 109 HV), respectively.

(Examples 6 to 7)
In Examples 6 and 7, the abrasive grains were changed from diamond to alumina (WA) and silicon carbide (GC), and the others were produced in the same manner as in Example 2.

(Examples 8 to 9)
Examples 8 and 9 were the same as Example 2 except that nickel and titanium were used instead of palladium on the diamond surface. A metal layer was formed on the diamond surface by electroless plating of nickel and sputtering by titanium.

(Examples 10 to 11)
Example 10 and Example 11 were manufactured in the same manner as Example 2 except that the thickness of the plating layer was 3.5 μm and 6.5 μm.

(Comparative Examples 1-2)
Moreover, the comparative example 1 and the comparative example 2 were manufactured similarly to Example 1 except having formed the plating layer with nickel. Each Vickers hardness was 261HV and 412HV. The plating bath used was a sulfamic acid bath composed of nickel sulfamate, nickel chloride, boric acid and additives. In Comparative Example 1 and Comparative Example 2, the Vickers hardness was changed by changing the amount of the additive.

(Comparative Example 3)
Comparative Example 3 had the same configuration as Example 1 except that the plating layer was a resin (phenolic resin). In addition, because it was formed with resin, the hardness was too low, Vickers hardness could not be measured under the same conditions,

(Comparative Examples 4-5)
Comparative Example 4 and Comparative Example 5 were manufactured in the same manner as Example 2 except that the plating thickness was 2.0 μm and 8.0 μm.

  The polycrystalline silicon was cut using the wire tool of the present invention (Example) and a conventional wire tool (Comparative Example). Polycrystalline silicon used was a 156 mm square rectangular ingot of 60 mm. As cutting conditions, a wire tool was wound around a groove having a cutting pitch of 0.35 mm, and a polycrystalline silicon ingot was cut at a linear velocity of 800 m / min while moving the reciprocating cycle at 1 minute / cycle. During cutting, a tension of 25 N was applied to the wire tool. In addition, the processing was performed while applying a grinding liquid to the processing portion for discharging chips and cooling the processing portion. The pressing speed of the workpiece was fixed, the supply amount of the wire was adjusted by deflection, and the amount of wire used per sheet was calculated from the amount of the wire tool used.

  Further, for the cut wafers, a total of 20 wafers were selected, 10 on each of the cutting start side and cutting end side, and the surface roughness Ra and wafer strength were measured, and the average value was calculated. For the surface roughness, the surface roughness Ra in the cutting direction (direction in which the wire saw bites in) was measured with a stylus type surface roughness measuring instrument, and the average value was taken as Ra. FIG. 5 is a diagram showing a method for measuring the wafer strength. Wafer strength was evaluated by three-point bending of the wafer. A wafer 35 as a test body was placed on a fulcrum 37, and a load was applied to the center (arrow I in the figure). The distance between the fulcrums 37 (H in the figure) was 120 mm. A load was applied to the center of the wafer 35 at a speed of 20 mm / min, and the load when the wafer 35 was cracked was measured. The measurement was performed on all 20 sheets whose surface roughness was measured, and the average value was adopted. These results are shown in Tables 1 to 4 below.

  From Table 1, although Example 1-Example 5 compared with Comparative Example 1 and Comparative Example 2, the result was that the amount of wire used was equal or slightly higher, but the surface roughness of the obtained wafers was significantly improved. . Compared to nickel plating, the abrasive grains move in an elastic region in the plating layer during processing, and the abrasive grains are aligned when a large load is applied. It is thought that the effect was not attached. In Examples 1 to 5, the wafer surface roughness was improved, and as a result, the wafer strength was improved by 40% or more compared to Comparative Examples 1 and 2. From this, it can be seen that the wafer was able to be cut without being severely damaged.

  On the other hand, Comparative Example 3 had the same surface roughness and wafer strength as those of Examples 1 to 5, but the abrasive grains were fixed with resin, so that the abrasive grains dropped off and the amount of wire used was 1 to 3 to 4 times that of Example 6 were necessary.

  In addition, when Example 1 to Example 5 are compared, copper plating is the most excellent in both surface roughness and wafer strength in the difference in metal of the plating layer, and galvanization and silver plating also have good results. . Thus, in the present invention, a wafer having a wafer surface roughness of 0.5 μm or less and a wafer strength of 100 MPa or more in a three-point bending test could be obtained.

  Next, Table 2 shows the evaluation results based on the difference in abrasive grains. Looking at the results due to the difference in abrasive grains, compared to diamond (Example 2), when using alumina and silicon carbide, the surface roughness and wafer strength were the same or better, although the amount of wire used was slightly increased. It was. The increase in the amount of wire used is thought to be due to faster wear due to the reduced hardness of the abrasive grains. The reason why the surface roughness and the wafer strength were satisfactory was considered to be because the load during cutting was reduced with respect to polycrystalline silicon. Thus, the abrasive grains may be appropriately selected from diamond, alumina, and silicon carbide as necessary.

  Next, in Table 3, the evaluation result about the metal of the metal layer of the abrasive grain surface is shown. When the cutting result when the metal of the metal layer on the abrasive grain surface is nickel or titanium is seen, the amount of wire used is slightly increased as compared with the case of using palladium (Example 2), and the surface of the obtained wafer As a result, the roughness and wafer strength also deteriorated slightly. However, it was possible to obtain a result that both the wafer surface roughness and the wafer strength were above a certain level (the wafer surface roughness was 0.5 μm or less, and the wafer strength in the three-point bending test was 100 MPa or more). This is thought to be because the holding power of the abrasive grains was slightly reduced when nickel or titanium was used, compared to when palladium was used.

  Next, Table 4 shows the evaluation results based on the plating thickness. Examples 10 and 11 with plating thicknesses of 3.5 μm and 8.5 μm showed good results, but Comparative Example 4 with a plating thickness of 2.0 μm increased the amount of wire used and increased the surface roughness. It got worse. This is presumably because the holding power of the abrasive grains decreased and the amount of wires had to be increased, and the dropped abrasive grains damaged the wafer. Further, Comparative Example 5 in which the thickness of the plating layer is 8.0 μm shows good results in terms of surface roughness and wafer strength, but because most of the abrasive grains are buried, the life as a wire tool is short. As a result, the amount of wire used increased.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs.

DESCRIPTION OF SYMBOLS 1 ......... Cutting device 3 ......... Ingot 5 ......... Holding part 7 ......... Wire tool 9 ......... Roller 11 ......... Core wire 13 ...... Abrasive grain 15 ...... Plating layer 17 ......... Metal Layer 20 ......... Wire tool manufacturing apparatus 21 ......... Degreasing tank 23 ......... Washing tank 25 ......... Plating tank 27 ......... Washing tank 29 ......... Cathode 31 ......... Anode 33 ......... Winding device

Claims (7)

A core wire having conductivity on at least the surface, abrasive grains provided on the outer periphery of the core wire, and a plating layer formed on the outer periphery of the core wire and holding the abrasive grains,
A wire tool for cutting polycrystalline silicon, wherein the plating layer is formed by any one of copper plating, zinc plating, and silver plating, and the plating layer has a Vickers hardness in a range of 60 HV to 200 HV.   The polycrystalline silicon cutting wire tool according to claim 1, wherein the plating layer is copper plating.   The abrasive grains are composed of any of diamond abrasive grains, aluminum oxide-based abrasive grains, or silicon carbide-based abrasive grains in which palladium adheres to a part of the surface of the abrasive grains, and the average grain diameter of the abrasive grains is 20 μm. The wire tool for cutting polycrystalline silicon according to claim 1 or 2, wherein:   The wire tool for cutting polycrystalline silicon according to any one of claims 1 to 3, wherein the thickness of the plating layer is not less than 1/4 and not more than 3/4 of the average particle diameter of the abrasive grains. .   A wire comprising an electrically conductive core wire at least on the surface, an abrasive having an average particle diameter of 20 μm or less provided on the outer periphery of the core wire, and a metal plating layer holding the abrasive and having a Vickers hardness of 60 HV to 200 HV Using a tool, the polycrystalline silicon is cut, the surface roughness Ra of the wafer cut from the polycrystalline silicon is 0.5 μm or less, and the strength of the wafer by a three-point bending test is 100 MPa or more. A method for cutting polycrystalline silicon. 6. The method for cutting polycrystalline silicon according to claim 5, wherein the thickness of the plating layer is not less than 1/4 and not more than 3/4 of the average grain size of the abrasive grains.   7. The polycrystalline silicon according to claim 5, wherein palladium is attached to a part of the surface of the abrasive grains, and a wire tool in which the plating layer for holding the abrasive grains is copper plating is used. Cutting method.

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