JP2010173916A - Method of manufacturing silicon carbide from silicon waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of economically manufacturing silicon carbide of suitable property for industrial use with a cutting waste of silicon or the like as a raw material which generates in large quantity in the manufacturing process of silicon wafer etc. <P>SOLUTION: This method of manufacturing silicon carbide is a method of manufacturing silicon carbide in which silicon waste is mixed with carbon powder equivalent to or more than an amount of the silicon waste and the mixed powder is heated in a non-oxidative atmosphere at 1,000-1,400°C for 6-24 hours to react the silicon waste with the carbon powder to manufacture silicon carbide, and after cooling it is acid-washed to remove impurities, then dried, and favorably, the silicon cutting waste generated in the manufacturing process of silicon wafer is used, and the silicon cutting waste is mixed with the carbon powder after defatting treatment or dewatering treatment, then the product is acid-lixiviated after heat treatment, and impurities are removed by washing with water or alcohol. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing silicon carbide using silicon scrap as a raw material. More specifically, the present invention relates to a method for economically producing silicon carbide having a quality suitable for industrial materials, using as a raw material a large amount of silicon cutting waste or the like generated in the production process of a silicon wafer.

  In the manufacturing process of a silicon wafer used as a semiconductor material, when the wafer is cut out from a single crystal silicon rod, silicon cutting waste is generated in an amount substantially equal to the number of wafers. As silicon wafers become thinner and the number of wafers increases, silicon scraps also increase. Since single crystal silicon used for a silicon wafer is extremely high in purity, there is a great industrial advantage if a large amount of generated silicon cutting waste can be recovered and reused effectively.

  Since this silicon cutting scrap contains iron and the like, it is necessary to economically remove these impurities for reuse. Specifically, in order to manufacture a silicon wafer, a high-purity single crystal silicon rod is generally sliced thinly using a wire saw. A high hardness silicon carbide powder is adhered to the wire saw, and the silicon carbide powder serves as a grindstone to cut the silicon rod, thereby cutting out a thin wafer. For this reason, silicon carbide powder and iron powder resulting from the wire are mixed in the silicon cutting waste. For this reason, it is necessary to remove these impurities in order to reuse the silicon cutting scrap, but since silicon carbide has similar properties to silicon, it is difficult to economically remove silicon carbide from the silicon cutting scrap. There is a problem.

  On the other hand, silicon carbide has been widely used as a polishing material and a refractory material, and in recent years, its use as a raw material for engineer ceramics has increased due to high purity and high densification. As industrially established methods for producing silicon carbide, the Atchison method and the direct reduction method of silica are known.

  In the Atchison method, coke is mixed with silica, heated to around 2000 ° C., and sintered to produce α-type silicon carbide. In the direct reduction method of silica, carbon powder is mixed with silica powder, pelletized, heated to around 2000 ° C. and sintered to produce β-type silicon carbide.

Both the Atchison method and the direct silica reduction method have the advantage that silicon carbide can be produced using inexpensive silica, silica, and coke. However, since silica and silica (SiO ₂ ) are used as starting materials, Requires heat treatment. Further, since impurities are easily mixed, there is a problem that it is not suitable for a high-purity semiconductor material. Specifically, since the silicon carbide powder produced by the Atchison method is bulky, it must be pulverized. In this pulverization step, impurities are likely to be mixed, and the particle size of the silicon carbide powder is difficult to control.

  On the other hand, a direct synthesis method for producing silicon carbide by reacting carbon with metal silicon (Si) as a raw material has been studied (see Japanese Patent Application Laid-Open No. 2002-316812). However, since the raw material silicon metal is expensive and requires fine pulverization, there is a problem that it is not suitable for industrial production.

  Further, as a method for producing silicon carbide using metal silicon as a raw material, a high-purity silicon carbide film is formed by a gas phase reaction on the inner peripheral surface of the kneading vessel and the outer peripheral surface of the mixing rod, and silicon powder and carbon powder are formed in the kneading vessel. And a method of producing silicon carbide powder by mixing under a pressure of 5 to 10 Pascal at a temperature of 50 ° C. to 100 ° C. is known (see Japanese Patent Application Laid-Open No. 2000-44223). However, this method has a problem that the kneading container is manufactured in advance, so that the process is complicated and mass production cannot be performed. A general method for producing silicon carbide is described in “Ceramic”, No. 22 (published in 1987), pages 46-50.

JP 2002-316812 A JP 2000-44223 A

Ceramic, No.22 (issued in 1987), p.46-50

  The present invention provides a method for producing silicon carbide that effectively utilizes silicon chips generated in the production process of a silicon wafer and solves the above-mentioned problems in conventional methods for producing silicon carbide. That is, the present invention can effectively use silicon cutting waste generated in the manufacturing process of a silicon wafer, and since silicon powder (Si) is used as a raw material, heat treatment at about 1000 ° C. to 1400 ° C. is sufficient. A production method that does not require high-temperature treatment at around 2000 ° C., can efficiently remove impurities such as iron, and can economically produce high-quality silicon carbide that can be used industrially. provide.

The present invention is a method for producing silicon carbide that solves the above-described problems by the following technical configuration.
[1] Carbon dust is mixed with silicon scrap in an equivalent amount or more, and this mixed powder is heated at 1000 ° C. to 1400 ° C. for 6 hours to 24 hours in a non-oxidizing atmosphere to react silicon scrap with carbon powder. A method for producing silicon carbide, comprising: producing silicon carbide, cooling, removing acid by washing with an acid, and drying.
[2] The method for producing silicon carbide as described in [1] above, wherein the silicon scrap is silicon sludge generated in the cutting process of the silicon wafer.
[3] The method for producing silicon carbide according to [1] or [2] above, wherein the silicon waste is degreased or dehydrated and then mixed with carbon powder, and the mixed powder is pelletized and heat-treated.
[4] Any one of the above [1] to [3], wherein the mixed powder obtained by mixing carbon powder with an equivalent amount or more with silicon waste is pelletized and heated in an inert gas, a reducing gas or a vacuum during sealing. A method for producing silicon carbide as described.
[5] The method for producing silicon carbide as described in any one of [1] to [4] above, wherein after leaching the product after the heat treatment, the impurities are removed by washing with water or alcohol.

  Since the manufacturing method of this invention uses the silicon | silicone cutting waste etc. which occurred in the manufacturing process of a silicon wafer as a raw material, it can manufacture silicon carbide at low cost. These silicon cutting scraps have no effective recycling means when trying to recover metal silicon, and are currently disposed of as waste. However, the manufacturing method of the present invention recovers silicon cutting scraps as silicon carbide. It is not necessary to remove the silicon carbide powder mixed in the scrap, and the silicon cutting scrap that has been treated as a waste can be effectively reused.

The manufacturing method of the present invention, since the silicon swarf is metal silicon as a raw material, silica (SiO ₂₎ to produce a low reaction temperature, silicon carbide at about 1000 ° C. to 1400 ° C. than the method using as a raw material Can be economically advantageous.

  Furthermore, in the manufacturing method of the present invention, silicon carbide produced by the heat treatment is lightly crushed into powder, so that a pulverization step as in the conventional manufacturing method is not required. Generally, the average particle diameter of silicon cutting scraps is approximately 0.5 to 20 μm, and silicon carbide produced by reacting this with heat and carbon powder has a reaction temperature of about 1000 ° C. to 1400 ° C. The sintered state of the powder is loose, and it becomes a powder similar to the raw silicon cutting scraps just by lightly crushing. Therefore, a pulverization step is not required after the reaction, and there is no problem that impurities such as iron are mixed from the pulverizer, and high-purity silicon carbide can be obtained.

Process drawing which shows the outline of the manufacturing method which concerns on this invention

  Hereinafter, the present invention will be specifically described based on embodiments. An outline of the production method of the present invention is shown in FIG. As shown in the figure, in the production method of the present invention, carbon powder is mixed in an equivalent amount or more with respect to silicon scraps, and this mixed powder is preferably pelletized, and in a non-oxidizing atmosphere at 1000 ° C. to 140 ° C. for 6 hours. It is a method for producing silicon carbide, characterized in that silicon carbide is produced by reacting silicon scrap and carbon powder by heating for -24 hours, and after cooling, acid cleaning is performed to remove impurities and drying.

  As the raw silicon scrap, silicon cutting scrap (called silicon sludge) generated in the cutting process of the silicon wafer, processed slurry, or the like can be used. Silicon sludge is preferably used after dehydration and degreasing and removing iron by magnetic sorting. The degreasing treatment may be performed by acid cleaning, alkali cleaning, or alcohol cleaning. After washing, dry and mix with carbon powder.

  As the carbon powder, pure carbon powder can be used for producing high-purity silicon carbide, and coke powder or the like can be used for producing silicon carbide used for refractory materials, abrasives, engineer ceramics, and the like.

  Carbon powder is mixed in an equivalent amount or more with respect to silicon waste. Specifically, 0.4 kg to 0.8 kg of carbon powder is preferably mixed with 1 kg of degreased and dried silicon sludge. When the carbon powder is less than the equivalent, unreacted silicon scrap increases. Too much carbon powder is wasted because the amount of unreacted carbon increases.

  The mixed powder of silicon scrap and carbon powder is pelletized, put into a heating furnace, and heat-treated in a non-oxidizing atmosphere. In order to make the inside of the heating furnace a non-oxidizing atmosphere, the furnace may be hermetically shut off, or an inert gas or a reducing gas may be introduced into the furnace, or a vacuum atmosphere may be used.

  The heat treatment temperature is suitably 1000 ° C. to 1400 ° C., and the heating is performed for 6 hours to 24 hours. By this heat treatment, silicon scrap and carbon powder react to produce silicon carbide. The produced silicon carbide powder has a loose sintered state, and becomes a powder equivalent to the raw silicon cutting scraps only by light pulverization.

  The crushed silicon carbide powder is immersed in hydrofluoric acid or the like, and acid leaching is performed, or acid cleaning is performed using hydrofluoric acid or the like, and iron or the like remaining in the silicon carbide powder is dissolved and removed. Since silicon carbide does not dissolve in hydrofluoric acid or the like, iron or the like is selectively dissolved and removed. Subsequently, it is washed with water or alcohol to wash away hydrofluoric acid and the like and then dried to obtain a fine high-quality silicon carbide powder from which impurities such as iron are removed.

Examples of the present invention will be described below.
[Example 1]
Silicon sludge (average particle size: 7 to 8 μm) generated in the silicon wafer cutting step was washed with alcohol, degreased, dried, and magnetically sorted to remove iron and used as a raw material. 115 g of carbon black was mixed with 500 g of this silicon sludge to form pellets. The mixed powder pellets were charged into a reaction furnace, the inside of the furnace was adjusted to a nitrogen gas atmosphere, and heated at a temperature of 1380 ° C. for 6 hours. After heating, the product was gradually cooled, and the product was lightly crushed and then immersed in hydrofluoric acid for 1 hour, then pulled up, filtered, washed with water and dried to obtain a synthetic silicon carbide powder (average particle size 10 μm to 15 μm). The results are shown in Table 1. The product was confirmed to be silicon carbide (SiC) by X-ray diffraction.

[Examples 2 to 5]
Using the same silicon sludge and carbon powder as in Example 1, silicon carbide powder was produced by the same production process as in Example 1 according to the production conditions shown in Table 2. The results are shown in Table 2.

Claims (5)

Carbon carbide is mixed with silicon scrap in an equivalent amount or more, and the mixed powder is heated at 1000 ° C. to 1400 ° C. for 6 hours to 24 hours in a non-oxidizing atmosphere to react silicon scrap with carbon powder to form silicon carbide. A method for producing silicon carbide, comprising: after cooling, washing with acid to remove impurities and drying. The method for producing silicon carbide according to claim 1, wherein the silicon scrap is silicon sludge generated in a cutting process of a silicon wafer. 3. The method for producing silicon carbide according to claim 1, wherein the silicon waste is degreased or dehydrated and then mixed with carbon powder, and the mixed powder is pelletized and heat-treated. The silicon carbide according to any one of claims 1 to 3, wherein a mixed powder obtained by mixing carbon powder with an equivalent amount of silicon scrap is pelletized and heated in an inert gas, a reducing gas or a vacuum during sealing. Production method. The method for producing silicon carbide according to any one of claims 1 to 4, wherein impurities are removed by washing with water or alcohol after acid leaching of the product after the heat treatment.

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