KR20090113091A - Method of Refining Silicon By Compression - Google Patents

Abstract

PURPOSE: A method for purifying silicon through compression is provided to effectively remove impurity and reduce production cost. CONSTITUTION: A method for purifying silicon through compression comprises: a step of pulverizing silicon of metal level; a step of dipping the silicon with chemical; a step of compressing in pellet form; a step of coagulating the compressed silicon; a step of mixing the silicon with binder; and a step of drying the silicon.

Description

Method of Refining Silicon by Compression {Method of Refining Silicon By Compression}

The present invention relates to a method of purifying silicone. More specifically, the present invention relates to a silicon purification method for removing impurities contained in silicon used for photovoltaic power generation and the like.

In order to easily manufacture silicon used for solar cells and the like, it is economical to purify (or refine) silicon of metallurgical grade (purity 95 to 99%). By refining metal grade silicon of 2N or less (more than 99% purity), in order to make silicon of grade suitable for solar cell, various kinds such as Al (aluminum), Fe (iron), Ca (calcium), Ti (titanium) Impurities must be removed.

In the conventional method of removing impurities from metal silicon to produce high purity solar cell grade silicon, a method of melting silicon and treating it with slag is used. After melting the slag metal grade, the directional solidification removes most of the metal impurities by the partition coefficient between the liquid and the solid state in the silicon.

However, some impurities such as iron are very difficult to remove by slag treatment. Therefore, a method of treating silicon with chemicals is used to effectively remove iron components from impurities contained in silicon. In other words, after pulverizing metal grade silicon, treating the pulverized silicon with chemicals such as hydrochloric acid, hydrofluoric acid, and nitric acid is called leaching. In order to further remove impurities from the leached silicon, directional solidification must be performed, and the leached silicon must be melted to perform such directional solidification. However, since the silicon pulverized for the leaching treatment has a disadvantage in that the surface area thereof is increased and melting becomes difficult under the condition that ordinary silicon is melted, it is very difficult to continuously remove impurities in the pulverized state.

U. S. Patent No. 6,861, 040 also discloses a method in which two directional solidifications are used. The patent first solidifies molten silicon using a kind of directional solidification and then grows grain significantly in metal grade silicon. At this time, due to the distribution coefficient between the liquid and the solid state in the silicon, impurities such as iron are collected at the grain boundary surface, and after the leaching process, which is pulverized and treated with a chemical, impurities such as iron are removed. Furthermore, the impurities are further removed by going through the directional solidification and leaching process once again.

However, directional solidification for crystal growth of silicon is a very slow process, and the cost is very expensive. Therefore, when the directional solidification is performed two or more times, impurities such as iron can be effectively removed, but there is a problem that the cost is inevitably increased.

It is an object of the present invention to provide a method for purifying silicon which reduces and easily removes various kinds of impurities by reducing the reaction surface area.

Another object of the present invention is to provide a method for purifying silicon, which reduces the production cost by shortening the reaction time.

The above and other objects of the present invention can be achieved by the present invention described in detail.

The present invention relates to a method for purifying silicon containing impurities, comprising the steps of pulverizing metal grade silicon, leaching the pulverized silicon with chemicals, and leaching the leached silicon into pellets. Compacting, and melting the compacted silicon and then solidifying the compacted silicon.

The present invention may mix the leached silicon with a binder and then compress the mixed silicon before pressing the leached silicon. In addition, the impurities may be first removed by a slag method and then solidified.

The silicon purified by the process according to the invention is at least 99% pure.

The present invention has the effect of reducing the production cost by reducing the reaction surface area to easily and efficiently remove various kinds of impurities, and shorten the reaction time.

The present invention relates to a method for purifying silicon containing impurities, comprising the steps of pulverizing a metal grade silicon, leaching the pulverized silicon with a chemical, compressing the leached silicon in pellet form, and And solidifying the melted compressed silicon.

The step of removing impurities such as iron by grinding the metal grade silicon and leaching the pulverized silicon with chemicals such as hydrochloric acid, hydrofluoric acid, nitric acid, ferric oxide, etc. is already known, so it is easy for those skilled in the art. Can be done. The present invention has a technical feature in that the step of compressing silicon, which has already been treated with chemicals, into pellets, in order to increase the reaction efficiency by increasing the contact surface area of silicon when removing impurities.

Also, in general, after the silicon is ground, the method itself of melting and solidifying the ground silicon is a known technique. Therefore, the method itself of melting and solidifying silicon can be easily carried out by those skilled in the art. However, the present invention is characterized in that the silicon compressed in the form of pellets is treated in a conventional melting and directional solidification method. At this time, the impurities such as Al, Ca, etc. may be first removed by a slag method that is already known, and then solidified.

In the present invention, the step of melting and then solidifying the compressed silicon refers to purifying silicon formed by metallurgical routes using a material such as quartz or carbon black. The detailed metallurgical method is AFB Braga et al (AFB Braga, SP Moreira, PR Zampieri, JMG Bacchin, PR Mei, "New processes for the production of solar-grade polycrystalline silicon: A review," Solar Energy Materials & Solar Cells 92 (2008) 418-424) It is well shown on the back.

Further, before squeezing the leached silicon, the leached silicon may be mixed with a binder, and then the mixed silicon may be squeezed. In this case, the binder is PVA (Poly vynyl Alcohol), starch, cellulose, HEC (Hydro Ethyl Celluose), water glass and the like, these may be used in combination of one or more. It is preferable that the mixing reaction of the present invention proceeds at room temperature. In addition, water or the like may be appropriately used as the reaction solvent.

In addition, in order to prevent contamination of the binder itself, the compressed silicon may be dried before melting the compressed silicon. At this time, it is preferable to advance drying at 30-1000 degreeC. At this time, the higher the drying temperature is shorter drying time, it is possible to further prevent contamination due to the binder itself. For example, it can be dried for 4 to 5 hours at a temperature of about 50 ℃, it can be dried for 20 to 30 minutes at a temperature of about 400 ℃.

The pressing according to the present invention uses a conventional pressing machine, the silicon mixed with the binder may be put in the press, or the silicon without the binder may be put in the press. The method of using the compactor itself is a known technique. However, in the present invention, the pressure of the compactor is preferably 0.5 to 150 ton · m 2 / cm 2, more preferably 1 to 100 ton · m 2 / cm 2. When passing through the compactor, pelleted silicon is discharged.

The compressed silicon of the pellet form according to the present invention is melted and then solidified, wherein the melting method is a resistance heating method, an induction method, a plasma method, an electron beam method, and the like. In particular, it is not limited to this. The above-mentioned melting method itself is a known technique.

Therefore, the present invention is to remove impurities twice, and to proceed once with chemicals, and once again by using the directional solidification method according to the present invention once purified silicon made in pellet form to reduce the reaction surface area. It is to remove impurities. As a result, the use of the directional solidification method only once to reduce the purification process time, while purifying the metal grade silicon to have a purity of 99% or more.

The invention can be better understood by the following examples, which are intended for the purpose of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

Example

Example  One

Silicon having a purity of 99.0% or less was pulverized with a grinder and leached with hydrofluoric acid and hydrochloric acid. The leached silicon was pressed using a compactor at a pressure of 20 ton · middle / cm 2 to produce pellet-type silicon. After the pellet-type silicon was melted using a resistance heating method, the silicon used for the solar cell was manufactured by directional solidification. At this time, the purity of silicon was more than 99.9%.

Example  2

Silicon having a purity of 99.0% or less was pulverized with a grinder and leached with hydrofluoric acid and hydrochloric acid. PVA was added to the leached silicon and stirred at room temperature, and then the stirred silicon was pressed at a pressure of 20 ton. After the thus-obtained pellet-type silicon was dried at 400 ° C, the pellet-type silicon was melted using a resistance heating method and then directionally solidified to prepare silicon used in the solar cell. At this time, the purity of silicon was more than 99.9%.

Example  3

Silicon having a purity of 99.0% or less was pulverized with a grinder and leached with hydrofluoric acid and hydrochloric acid. PVA was added to the leached silicon and stirred at room temperature, and then the stirred silicon was pressed at a pressure of 20 ton. After the thus-obtained pellet-type silicon was dried at 400 ° C, the pellet-type silicon was melted using a resistance heating method, slag-treated, and then directionally solidified, thereby preparing silicon used in the solar cell. At this time, the purity of silicon was more than 99.9%.

Simple modifications and variations of the present invention can be readily made by those skilled in the art, and such variations or modifications can be considered to be included within the scope of the present invention.

Claims (7)

In the method for purifying silicon containing impurities, Grinding the metal grade silicon; Leaching the pulverized silicon with a chemical; Pressing the leached silicon into pellets; And Melting and then solidifying the compressed silicon; Silicon purification method comprising a. The method of claim 1, wherein the leached silicon is mixed with a binder and then compressed into pellets. The method of claim 1, wherein the compressed silicon is dried and then melted. The method of claim 2, wherein the binder is polyvinyl alcohol (PVA), starch, cellulose, hydro ethyl cellulose (HEC), water glass, or combinations thereof. 5. The method of claim 1, wherein the pressing is performed at 0.5 to 150 ton · m 2 / cm 2. 6. The method of claim 1, wherein the compacted silicon is melted and solidified after applying a slag method to the molten silicon. The method of claim 1, wherein the compressed silicon is melted by any one of a resistive heating method, an induction method, a plasma method, and an electron beam method. Silicon purification method, characterized in that.