KR20100032964A - Separation of silicon with high purity from backgrinding silicon wastes - Google Patents

Abstract

PURPOSE: A method for separating high purity silicon from backgrinding silicon waste is provided to recycle high purity silicon from silicon waste, and to inexpensively recycle the silicon as a silicon raw material for a solar battery etc. CONSTITUTION: A method for separating high purity silicon from backgrinding silicon waste comprises the following steps: producing solids by centrifuging and precipitating backgrinding silicon waste liquid from the waste(S1); drying the solids to remove moisture in the solids(S2); adding heavy liquid to the dried solids; pulverizing the solids with a ultrasonic homogenizer; separating silicon, silicon carbide and the heavy liquid in the solids through a centrifuge(S3); and drying the heavy liquid by drying the solids(S4).

Description

SEPARATION OF SILICON WITH HIGH PURITY FROM BACKGRINDING SILICON WASTES

      Recently, the development of new energy sources is important due to the environmental pollution and the continuous increase in the price of oil, and it is known that oil, which is the most used energy source, is almost depleted after decades. Accordingly, many investments are being made at each industrial site to develop alternative energy. Among them, solar cells, which are infinite energy sources, are continuously researched with the recognition that they are the only solution to this problem. However, solar cells that generate energy using the electron and hole movement of semiconductors as a principle use silicon to obtain energy. However, the manufacturing cost of silicon itself is high, and the investment cost is not enough. In addition, the price of silicon substrates is gradually increasing due to the shortage of raw materials of silicon itself. As a result, silicon substrates with low cost and high purity are needed, and research is being continued in various fields to reduce the cost of generating solar cells. Therefore, attempts have been made to recycle high-purity silicon by using waste silicon sludge generated in the backgrinding process.

      Accordingly, the recycling of the silicon substrate is indeed a lot of research in this field, the purity of the silicon itself is very important in order to reuse the silicon contained in the back grinding silicon waste as a raw material for the solar cell substrate. In order to recycle the silicon, it is known that the purity should be at least 99.5%. The main solids in the backgrinding silicon waste are silicon and carbon mixtures, most of which are silicon and the remainder is contained within a few percent as a major impurity. In order to recycle, only silicon powder should be separated from the silicon and carbon mixture separately. In particular, it is most important to separate and recover high purity silicon powder having a purity of 99.5% or more.

      The present invention relates to the separation and recovery of silicon contained in the waste which is a by-product generated in the rear processing process of the silicon wafer, and more particularly, the specific gravity separation method from the backgrinding silicon waste generated in the process of processing the rear surface of the silicon wafer. The present invention relates to a method for separating and recovering silicon of high purity.

      Among the processes for processing the silicon wafer, there is a backgrinding process, which refers to a process of grinding the back surface of the silicon wafer into a diamond grindstone. The solids in the backgrinding silicon waste from this process are mostly silicon powder, but also a small amount of carbon powder from diamond grindstones. The backgrinding silicon waste is mainly obtained in the liquid phase because the silicon and carbon powder generated in the backgrinding process are washed out with water and discharged in a suspended or precipitated state in water. Generally, liquid backgrinding silicon waste contains more than 99.9% by weight of water and less than 0.1% by weight of solids of silicon and carbon mixtures. In addition, most of the silicon and carbon mixture contains silicon, and carbon is contained in about 1% by weight.

     In order to separate and recover high-purity silicon from the backgrinding silicon waste, it is necessary to first separate and remove the carbon powder as an impurity. However, the density of silicon is 2.33 while the density of diamond carbon is 3.51, which has a density value of at least one greater than that of silicon. Therefore, it was judged that the most effective method was to separate these two materials using specific gravity difference using liquid of appropriate density. In other words, a liquid having a medium density between these materials is used to subside diamond carbon heavier than this liquid and lighter silicon than this liquid.

     Conventionally, there has been no method for separating and recovering high purity silicon of 99.5% or more from the above-mentioned backgrinding silicon waste.

     Accordingly, the inventors of the present invention devised the present invention for the purpose of separating and obtaining only high-purity silicon of 99.5% or more from expensive back-grinding silicon waste and recycling it as a silicon raw material for solar cells.

      In order to achieve the present invention, high-purity silicon is separated from the silicon and carbon mixture, which is a solid in the backgrinding silicon waste generated in the backside processing of the silicon wafer, using a heavy liquid having a density between the density of silicon and carbon. I found out that I can retrieve it.

     That is, an object of the present invention is to apply a method for separating and recovering high purity silicon by heavy liquid specific gravity separation method from backgrinding silicon waste which is not currently recycled and discarded.

     In addition, the present invention is to remove and remove the carbon from the backgrinding silicon waste through the high-purity silicon recovery method, and to require a high cost for the backgrinding silicon waste solid mixed with conventional silicon and carbon that is not easy to separate and remove It is an object of the present invention to recover high purity silicon of 99.5% or more that can be reused as a silicon raw material for solar cells at low cost by simply separating silicon and carbon without using a chemical reaction.

      In order to achieve the above object, the present invention provides a high-purity silicon of 99.5% or more that can be used as a silicon raw material for solar cells by separating and recovering only silicon from the backgrinding silicon waste generated in the process of processing the back surface of the silicon wafer. In order to provide a high-purity silicon separation method using the backgrinding silicon waste, the high-purity silicon separation method is a centrifugation step (S1) for separating only the solid content and the first drying step for drying to remove the moisture of the solid content ( S2), the solid-liquid separation step (S3) of separating silicon and carbon of the solid content to obtain silicon, and the secondary drying step (S4) of removing and recovering the heavy liquid.

     In other words, the high-purity silicon separation method using the backgrinding silicon waste of the present invention comprises the centrifugation step (S1) of centrifuging the backgrinding silicon waste stock solution to obtain a solid content; The first drying step (S2) and dried to remove the moisture of the solid content passed through the centrifugation step (S1); The heavy liquid separation step of obtaining a silicon by adding a heavy solution to the solids subjected to the first drying step (S2), ultrasonic grinding through an ultrasonic mill, and separating silicon and silicon carbide and solids of the solid component through a centrifuge (S3). )Wow; It characterized in that it consists of a secondary drying step (S4) to remove the heavy liquid by drying the solid content passed through the heavy liquid separation step (S3).

In addition, the heavy liquid of the high-purity silicon separation method using the backgrinding silicon waste of the present invention is dibrominated methane (CH ₂ Br ₂ ), bromoform (CHBr ₃ ), tetrabromoethane (Br ₂ CHCHBr ₂ ), as a halogenated organic matter. It is characterized by consisting of any one or more of carbon tetrabromide (CBr ₄ ).

      In addition, the heavy-liquid separation step of the high-purity silicon separation method using the backgrinding silicon waste of the present invention is characterized by separating diamond carbon and silicon by non-differential separation method.

      The present invention configured as described above, water is removed from the backgrinding silicon waste consisting of water, carbon, silicon, and the like, and carbon and silicon are separated from the solids mixed with carbon and silicon by specific gravity separation method, so that only silicon having a purity of 99.5% or more By obtaining it, there is an effect that can be recycled to silicon materials for solar cells at low cost.

      Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

      1 is an overall process diagram for implementing the present invention.

      In order to separate the high purity silicon of the present invention, the centrifugation step (S1) of centrifuging the liquid backgrinding silicon waste stock solution held by most solids is performed to recover the backgrinding silicon waste solids. The centrifugation step (S1) is a step of removing water on the backgrinding silicon waste stock solution by performing several times.

      Thereafter, the step is performed, the first drying step (S2) for removing the water contained in the solid content such as silicon and carbon passed through the centrifugation step (S1). This is because the remaining water may affect the specific gravity separation using the next step, the heavy liquid, and it is preferable to remove it in advance.

Next, a solid solution having a density of 2.34 to 3.50 is added to the solids such as silicon and carbon that have undergone the first drying step (S2), so as to ultrasonically grind through an ultrasonic grinder, and the silicon, carbon, and solid liquid of solids through a centrifuge. Separation is carried out a heavy liquid separation step (S3) to obtain only silicon. In the heavy liquid separation step, the heavy liquid penetrates between the silicon and the carbon particles of the solids subjected to the first drying step (S2) by ultrasonic vibration by a specific gravity separation method, and the silicon, carbon, and heavy liquid are separated by the centrifuge. Has a configuration. The heavy liquid used in the separation method is any one of dibrominated methane (CH ₂ Br ₂ ), bromoform (CHBr ₃ ), tetrabromoethane (Br ₂ CHCHBr ₂ ) and carbon tetrabromide (CBr ₄ ) as halogenated organics. One or more may be optionally used, preferably dibromine methethane (CH ₂ Br ₂ ). The heavy solution is not necessarily a pure compound, dibrominated methane (CH ₂ Br ₂ ) and bromoform (CHBr ₃ ) may be mixed and used, and in some cases solid carbon tetrabromide (CBr) at room temperature ₄ ) may be substituted with dissolved in carbon tetrachloride.

      After that, the final step is to perform a secondary drying step (S4) to completely remove the volatile substances such as the remaining heavy liquid by inputting the solid silicon passed through the heavy liquid separation step (S3) to the drying furnace. Through this configuration, volatile substances such as the heavy liquid used in the above process are evaporated, so that only silicon having a purity of 99.5% or more remains.

     As a high-purity silicon separation method using the backgrinding silicon waste of the present invention configured as described above, water is removed from the backgrinding silicon waste stock solution consisting of water, silicon, and carbon, and carbon is separated from the solids mixed with silicon and carbon. By separating, high purity silicon with a purity of 99.5% or more can be obtained.

     Figure 2 is a view showing the particle size analysis results of high purity silicon separated from the backgrinding silicon waste by the present invention.

     As shown, the particle size of the high-purity silicon separated is about 0.2 micrometer.

Hereinafter, the present invention will be described with reference to Examples.

Example

      The backgrinding silicon waste solids are first separated from the backgrinding silicon waste stock solution 36L by centrifugation. Centrifugation is carried out under the condition of 10 minutes at 3000rpm. Thereafter, 22.54 g of backgrinding silicon waste solids are separated by removing water using an oven or a vacuum drying furnace to remove water remaining in the solids separated from the backgrinding silicon waste stock solution.

Then, for convenience, 5.0 g of the solid is taken and 25 mL of dibrominated methane (CH ₂ Br ₂ ) is used as the backgrinding silicon waste solid, and ultrasonic grinding is performed for 15 minutes in the heavy liquid separation process, and the centrifugation is performed at 3000 rpm for 30 minutes. Do it for a minute. The heavy liquid separation step is carried out several times.

      Next, high purity silicon powder can be obtained by drying the separated silicon, and carbon analysis by carbon / sulfur analyzer, elemental analysis by ICP-AES, and particle size analyzer by the carbon / sulfur analyzer The results are shown in the following Table 1 and Figure 2, it can be seen that the high purity silicon powder of 99.5% or more can be obtained.

<Carbon Analysis and Elemental Analysis of Silicon Powder>  element  C  Fe  Al  Cu  Mn  Ca  Content (ppm)  2300  21.9  104.9  283.7  ND  412.1

* ND: No Detection

As shown in the above table, impurities contained in the separated silicon include 2300 ppm of carbon as the main impurity and metal impurities such as Ca as other impurities. The total content of these impurities is 5000 ppm or less, and the purity of silicon is 99.5. It tells you more than%.

The present invention can be used to recycle the waste silicon generated during the backgrinding process to silicon used as a solar cell substrate raw material.

      BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the flowchart of the process of isolate | separating and collect | recovering high purity silicon from backgrinding silicon waste by this invention.

Figure 2 is a view showing the particle size analysis results of high purity silicon separated from the backgrinding silicon waste by the present invention.

Claims (3)

      In the high purity silicon separation method using backgrinding silicon waste to recycle silicon,      A centrifugation step (S1) of centrifuging the backgrinding silicon waste stock solution to obtain solids;     The first drying step (S2) and dried to remove the moisture of the solid content passed through the centrifugation step (S1);      The solid solution is added to the solids subjected to the first drying step (S2), the ultrasonic grinding is performed by an ultrasonic mill, and the heavy liquid separation step of obtaining silicon by separating the silicon, silicon carbide and the solid of the solids through a centrifuge (S3). )Wow;       High purity silicon separation method using the back-grinding silicon waste, characterized in that consisting of a secondary drying step (S4) for removing the heavy liquid by drying the solid content passed through the heavy liquid separation step (S3).        The method of claim 1, The heavy liquid may be a halogenated organic substance having any one or more of dibromine methane (CH ₂ Br ₂ ), bromoform (CHBr ₃ ), tetrabromoethane (Br ₂ CHCHBr ₂ ), and carbon tetrabromide (CBr ₄ ). Separation method of high purity silicon using backgrinding silicon waste, characterized in that the configuration. The method of claim 1, The heavy liquid separation step is a high-purity silicon separation method using the back grinding silicon waste, characterized in that the separation of diamond carbon and silicon by a specific gravity separation method.

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