JP2007044870A - Method of detecting disconnection of wire saw, method of inspection quality, and method of manufacturing cut product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin bond wire saw to be used in slicing a silicon wafer, which is electrically conductive by itself, and has a high retention force of abrasive grains and excellent sharpness. <P>SOLUTION: One end of a metal coated abrasive grain is brought into contact with a metallic core wire 1 and part of it is exposed from a bonded surface, thereby providing electric conductivity to the core wire from the external surface of the wire saw so as to detect disconnection during processing. In addition, bonding strength with a resin 3 serving as a bond is improved through the use of the metal coated abrasive grain 2, and further increased by plating the core wire 1 with copper or copper alloy, to thereby prevent the abrasive grain from missing or the bond from peeling. Two conductive rolls are used to inspect the disconnection of the wire saw. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention mainly relates to a wire saw used for slicing a semiconductor from a silicon ingot or a silicon wafer for solar cells, or slicing a difficult-to-cut material such as crystal.

  In slicing processing of silicon ingots, multi-wire cutting using loose abrasive grains is often used from cutting with a diamond inner peripheral cutting wheel due to the increase in diameter of the ingot. However, since this cutting method is a problem of environmental hygiene, the cleaning process takes time, and the processing efficiency and processing accuracy are poor, a fixed abrasive type wire saw has begun to be proposed.

  This includes a wire saw in which superabrasive grains such as diamond and CBN are electrodeposited on a steel wire, but a multi-cutting process of a silicon ingot requires a length of at least several hundred meters. Electrodeposition of abrasive grains on such a long steel wire requires a very long time and is not practically used due to manufacturing problems.

  Therefore, a wire saw in which abrasive grains are fixed to a core wire with a synthetic resin has been proposed as a method that can be easily manufactured in a short time. However, when the abrasive grains are fixed to the core with the synthetic resin, the holding power of the abrasive grains is weak and the abrasive grains are likely to fall off as compared with the case of electrodeposition. For this reason, it is necessary to make the amount of protrusion of the abrasive grains small. As a result, the chip pocket becomes small, the water and chips are not easily removed, and the wire saw has poor sharpness.

  In the multi-cutting of a silicon wafer, a single wire is spirally wound between a plurality of main rollers to run, and usually about 400 pieces are cut at a time. The length of the wire used for this is as much as 200 to 300 km. For this reason, when there is a disconnection in the wire being cut, it is necessary to detect it and stop the apparatus promptly. As a means for detecting this abnormality, the most commonly used method is to detect disconnection using the electrical conductivity of the outer surface of the wire, and it is necessary that the outer surface of the wire has electrical conductivity. It is. However, in resin bond wire saws, even if the core wire is electrically conductive, the surface is covered with synthetic resin as an insulator and abrasive grains, so there is no electrical conductivity between the outer surface and the core wire. With this method, disconnection cannot be detected.

  Since the present invention is a resin bond wire saw, it has a structure that allows the core wire to have electrical conductivity from the outer surface, and since the bond is formed along the abrasive grains from the beginning of manufacture, the abrasive grains It has excellent holding power and enables formation of a large chip pocket.

  In the wire saw disconnection detection method, in a wire saw in which superabrasive particles coated with metal on the outer peripheral surface of a conductive core wire are fixed by a resin bond, one end of the abrasive particle is brought into contact with the core wire, and a part thereof By making the abrasive grains projecting from the resin bond layer present, a wire saw having electrical conductivity was prepared, the wire saw was brought into contact with two conductive rolls, and the electrical resistance between the rolls was reduced. The wire saw is detected by measuring the change continuously.

  In the method for manufacturing a cut object, the disconnection is detected using the above-described disconnection detection method, and at the same time, the workpiece is cut with a wire saw to manufacture the cut object.

  In the quality inspection method of the wire saw, in a wire saw in which superabrasive particles coated with metal on the outer peripheral surface of a conductive core wire are fixed with a resin bond, one end of the abrasive particle is brought into contact with the core wire, and partly By making the abrasive grains projecting from the resin bond layer present, a wire saw having electrical conductivity was prepared, the wire saw was brought into contact with two conductive rolls, and the electrical resistance between the rolls was reduced. Inspect the quality of wire saws by measuring changes continuously.

  In the method of manufacturing a cut product, the quality is inspected using the quality inspection method, and at the same time, the workpiece is cut with a wire saw to manufacture a cut product.

The wire saw according to the present invention will be described below with reference to the drawings.
In FIG. 1, 2 is a metal-coated superabrasive grain. As described above, when the molten resin is dried and solidified, it rises along the abrasive grains. However, when metal-coated abrasive grains are used, the wettability and bondability with the resin are several times better than bare abrasive grains. Therefore, a large swell 5 along the abrasive grains can be formed, and the resin bond layer between the abrasive grains can be protruded greatly. For this reason, even if the thickness t of the bond layer is 1/3 to 2/3 of the abrasive grain size, there is sufficient holding power.

  The coating metal is not particularly limited, such as Cu, Ni, Ti, TiC, and W. However, Cu has good wettability and bonding properties with the resin and is excellent in electrical conductivity. Ni is good in terms of strength. In order to improve the wettability and bondability with the bond, it is sufficient if the coated metal thickness of the abrasive grains is 1 μm. However, if it is too thin, the effect of increasing the abrasive grain holding force is small, and if it is too thick, so-called biting becomes worse due to contact between the coated metal and the work material at the start of cutting. Further, even if the coated metal on the top of the abrasive grains is worn and the abrasive grains are exposed, 1 μm or more is required to generate an energizing circuit around them. From these relationships, it is preferably 1 to 10 μm. If the superabrasive grains are too fine, the cutting ability is inferior. If the superabrasive grains are too large, the diameter of the wire saw itself becomes large, which increases the margin of the work material, which is not preferable. Therefore, depending on cutting conditions, the range of 10 to 100 μm is preferable.

  1 is a core wire and may not be a metal wire as long as it has high strength and conductivity, but steel wire such as piano wire or copper or copper alloy wire is strong in strength, wettability with resin, bondability, and availability. It is preferable in terms of ease and price. In the case of a steel wire such as a piano wire, the bondability with the resin can be further improved by plating with Cu or Cu alloy.

  3 is a resin bond, and a bond layer is formed by, for example, applying abrasive grains in a solution obtained by dissolving a resin in a solvent as disclosed in JP-A-8-126953, JP-A-9-155631, JP-A-10-315029, and the like. A method in which the mixed paint is applied and baked onto the above core wire, or abrasive grains are mixed in a heated molten resin, this mixed melt is filled into an extruder, and the core wire is passed through to coat the mixed solution around the core wire. Alternatively, a solution obtained by mixing abrasive grains may be attached to the core wire by electrostatic coating. However, in order to bring as much metal-coated abrasive grains as possible into contact with the core wire, it is preferable that the abrasive-containing molten resin applied to the core wire is passed through a required die hole diameter (core wire diameter + double abrasive diameter + α). As a result, it is impossible to bring all the abrasive grains into contact with the core wire due to variations in the abrasive grain diameter, but many abrasive grains can be brought into contact and fixed.

  The resin used as a bond is phenol resin, polyimide resin, polyurethane resin, polyamideimide resin, polyester resin, epoxy resin, melamine resin, urea resin, alkyd resin, etc. from the viewpoint of moldability, physical properties during processing, grindability during processing, etc. It is preferable to select from these.

By mixing the filler 4 in the resin bond, it is possible to improve the strength and abrasion resistance of the bond and further improve the performance of the wire saw. Hard particles such as diamond, SiC, Al ₂ O ₃ , SiO ₂ , CrO ₂ are preferable. In particular, fine diamond is most suitable because of its excellent abrasion resistance and thermal conductivity. In addition, the same effect can be obtained by filling metal powder such as Cu or Ag. If a lubricant such as hBN or carbon is filled, the cutting resistance can be reduced. Furthermore, these can be mixed and a synergistic effect can also be aimed at.

  From the manufacturing method described above, it is predicted that the metal-coated abrasive grains 2 are slightly covered with resin on the upper surface, thereby causing a concern that the conductivity is lost. However, there is practically no worry about this. If the conductivity is lost for this reason, the covering resin is thin and does not contain filler, so it can be easily removed by, for example, light contact with loose abrasive grains. The In addition, since there is no fear of disconnection at the beginning of cutting use, it is removed naturally at the very beginning of this use and does not cause any practical problems.

  However, in general, the conductivity is maintained even if a small amount of resin remains for the following reason. The superabrasive is coated with metal by electroplating, electroless plating, chemical vapor deposition (CVD), or physical vapor deposition (PVD). At this time, the unevenness on the surface of the metal coating becomes extremely large. Especially in the case of electroplating, it is large. This unevenness is also useful for improving the adhesion to the resin, but in the case of the present invention, the convex portion is not covered with the resin and is effective for maintaining conductivity.

  As described above, the fact that the electrical conductivity between the surface of the wire and the core wire is necessary for detecting the disconnection at the time of cutting has the following effects. As described above, the standard method for making this product is to disperse the abrasive grains in a resin dissolved in a solvent, immerse the core wire in the resin, pass through a die, and then bake. At this time, it is necessary to inspect whether the abrasive grains are uniformly or uniformly applied, but no suitable method has been found so far. According to the present invention, since it was possible to provide conductivity, a means for detecting this was obtained. That is, when the product of the present invention is brought into contact with two or two pairs of two rolls having electrical conductivity and moderate elasticity and the distance between the rolls is about 100 mm, the electrical resistance value between them is the number of abrasive grains. It depends on. It has become possible to inspect quickly by continuously measuring the change in electrical resistance.

Example 1 A phenol resin was dissolved in cresol, and Ni-coated diamond abrasive grains having an average particle diameter of 25 μm were mixed so as to have a ratio of 2.2 ct / cm ³ . This was applied to a brass-plated piano wire having an outer diameter of 0.18 mm, passed through a floating die having a hole diameter of 0.24 mm, and then baked at a furnace temperature of 300 ° C. to obtain a wire saw. The wire saw diameter was 0.22 mm, and the thickness of the resin bond layer was about 15 μm. This wire saw 5 km was wound around a reel having a width of 100 mm and an outer diameter of 50 mm. When the resin bond layer at the beginning of winding was peeled off and several places on the surface of the wire saw wound around this reel were subjected to a current test using a tester, it was confirmed that there was sufficient conductivity.

  (Comparative Example 1) The abrasive grains in Example 1 were replaced with diamond grains having the same average particle diameter not coated with metal, and the core wire was a piano wire having the same diameter to obtain a wire saw in exactly the same manner. It was. The same energization test as in the example was performed, but no energization was performed.

(Comparative Test Result 1) A single crystal Si having a thickness of 100 mm □ x30 mm and having a cutting area of 100 × 30 mm was used. The wire saw used was 30 m, and the processing conditions were a reciprocating speed of 500 mm / min, a wire tension of 2 and 5 kgf. In the wire saw of Example 1, the cutting width was 0.25 mm, and the cutting at a cutting speed of 1 mm / min was stably performed over the cutting process of 1500 cm ² . On the other hand, in the wire saw of Comparative Example 1, the cutting speed decreased from around 1000 cm ² , and the dropping of the abrasive grains was severe and the cutting was interrupted.

  (Example 2) Cu powder and Cu-coated diamond abrasive grains having an average particle size of 30 μm are mixed with polyimide resin so that the respective solid content ratios are 60 V%, 20 V%, and 20 V%, and cresol is further added as a solvent to add paint. The amount of the solvent was 50 V%. The paint is applied to a Cu-plated piano wire with an outer diameter of 0.18 mm, passed through a die with an inner diameter of 0.28 mm, and then baked and cured in a baking furnace at a furnace temperature of 300 ° C. to obtain a wire saw with an outer diameter of 0.24 mm. Obtained. The resin bond layer had a thickness of about 20 μm. In Example 1, when conducting an energization test by the same method, it was confirmed that there was good electrical conductivity.

  (Comparative Example 2) The abrasive grains in Example 1 were replaced with diamond grains having the same average particle diameter without metal coating, and the core wire was made the same diameter piano wire to obtain a wire saw in exactly the same manner. The current test for the wire saw was conducted in the same manner as described above, but there was no electrical conductivity at all.

  (Comparative Test 2) Using the wire saw of Example 2, a single crystal silicon having a length of 150 mm was subjected to a cutting test for 1 hour at a wire speed of 800 m / min and a pressing pressure of 2.5 kgf. It was 0 mm / min. On the other hand, in the wire saw of the comparative example 2, it was 0.3 mm / min.

  As described in the above sections, according to the present invention, in place of conventional slicing processing of silicon wafers with loose abrasive grains, resin bond superabrasives with excellent abrasive grain holding power, large chip pockets and good sharpness and long life Since it is a grain wire saw and the wire saw itself has a conductive structure, it is possible to detect disconnection during processing in the same way as conventional wire cutting, and also to assure the quality of products.

  The present invention is characterized in that metal-coated abrasive grains are used, and the abrasive grains are brought into contact with a metal core wire and fixed to a resin bond, thereby obtaining a conductive wire saw. Thereby, even if it was a resin bond wire saw, it enabled it to use the disconnection detection means employ | adopted by the wire cutting of a loose abrasive system as it is.

  Furthermore, the resin bond mixes abrasive grains in a solution in which a resin is dissolved in a solvent, and is applied to a metal core wire, dried by heating to evaporate the solvent, and the resin bond becomes wettable with the coated metal in the process of solidifying the resin. Because it has good bondability, it solidifies in a form that rises along the abrasive grains. For this reason, it acts as a holding force of the abrasive grains, and the protrusion of the abrasive grains can be increased, and a chip pocket between the abrasive grains is also formed large.

Sectional view of the wire saw of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core wire 2 Metal-coated superabrasive grain 3 Resin bond 4 Filler 5 Bond layer rise t Bond layer thickness

Claims (4)

In a wire saw in which superabrasive particles coated with metal on the outer peripheral surface of an electrically conductive core wire are fixed by a resin bond, one end of the abrasive particle is brought into contact with the core wire, and a part of the abrasive protrudes from the resin bond layer. Prepare a wire saw with electrical conductivity by making grains present,
The wire saw is brought into contact with two conductive rolls,
A wire saw breakage detection method for detecting breakage of the wire saw by continuously measuring a change in electrical resistance between the rolls.   The manufacturing method of the cut article which cuts a workpiece | work with the said wire saw and manufactures a cut article simultaneously with detecting a disconnection using the disconnection detection method of Claim 1. In a wire saw in which superabrasive particles coated with metal on the outer peripheral surface of a conductive core wire are fixed with a resin bond, one end of the abrasive particle is in contact with the core wire, and a part of the abrasive protrudes from the resin bond layer Prepare a wire saw with electrical conductivity by making grains present,
The wire saw is brought into contact with two conductive rolls,
A quality inspection method for a wire saw, in which the quality of the wire saw is inspected by continuously measuring a change in electrical resistance between the rolls.   A method for manufacturing a cut article, wherein the quality is inspected using the quality inspection method according to claim 3 and at the same time the workpiece is cut with the wire saw to produce a cut article.

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