JP4842701B2 - Method for separating silicon carbide from silicon and apparatus used therefor - Google Patents

Description

  The present invention relates to a method for separating silicon carbide and silicon from a mixture containing silicon carbide grains and silicon grains, and an apparatus used therefor.

Silicon materials for semiconductor integrated circuits are expensive, and many of the silicon materials for solar cells have been used with scraps produced in the manufacturing process (single crystal pulling process) of silicon materials for semiconductor integrated circuits.
A technique for manufacturing a silicon material at low cost has also been proposed.
For example, in Japanese Patent Laid-Open No. 2000-34116 (Patent Document 1), a mixture of silicon carbide and silicon is produced from steel slag, melted at about 1410 to 1600 ° C., and melted using a ceramic filter or the like. Discloses a method of obtaining silicon by filtering off silicon carbide that does not melt at the above temperature.

Japanese Patent Laid-Open No. 11-228280 (Patent Document 2) discloses a method of directly scooping impurities such as silicon carbide floating on a molten silicon surface when purifying low-purity metal grade silicon, It is described that a method of removing by filtering, a method of removing a portion near the hot water surface after solidifying the floating surface of the hot water once, and the like.
However, none of the above-mentioned patent documents describes specific methods, and techniques using these methods have not been put into practical use. Moreover, even if it removes impurities, such as silicon carbide, in said patent document, it does not describe utilizing it.

  Many silicon wafers for solar cells are produced by slicing a silicon ingot using a multi-wire saw. As one means for obtaining a solar cell at a low price, a technique for slicing a silicon wafer as a substrate as thinly as possible has been developed. For example, in a silicon wafer having a thickness of 200 μm, since the thickness and the wire diameter for slicing are approximately the same, a silicon ingot that is approximately the same as the processed silicon becomes a mixture with silicon carbide particles that are abrasive grains. Was discarded.

Japanese Patent Laying-Open No. 2005-313030 (Patent Document 3) describes a method of recovering abrasive grains from a used slurry containing silicon, abrasive grains (silicon carbide), etc. by centrifugation or the like. However, the above patent document does not describe the use of silicon.
JP-A-2001-278612 (Patent Document 4) discloses a dispersant obtained by washing a solid obtained by solid-liquid separation of used slurry containing silicon and abrasive grains (silicon carbide) with an organic solvent. And a method of recovering silicon by removing silicon oxide and abrasive grains from a solid content obtained using an air classifier or the like. However, sufficiently pure silicon has not been obtained, and a technique using this method has not been put into practical use.
Further, JP-A-7-172998 (Patent Document 5) describes a method of growing a silicon carbide single crystal from silicon melted in a crucible containing carbon as a constituent element.

  Japanese Unexamined Patent Publication No. 2001-172729 (Patent Document 6) discloses a purification apparatus and a purification method for obtaining a high-purity metal from a metal such as metal silicon or aluminum containing impurities by using segregation solidification.

JP 2000-34116 A Japanese Patent Laid-Open No. 11-228280 JP-A-2005-313030 JP 2001-278612 A JP-A-7-172998 JP 2001-172729 A

  An object of the present invention is to provide a method of separating and extracting silicon and silicon carbide from a used slurry containing silicon and silicon carbide abrasive grains, and recovering both of them, and an apparatus used therefor.

  Thus, according to the present invention, a mixture containing silicon carbide particles and silicon particles is heated to a first temperature in a container in an inert gas atmosphere to melt the silicon particles, and then the obtained molten silicon containing molten silicon is melted. The liquid is maintained at the second temperature, and then a take-out jig is immersed in the upper layer portion of the melt to deposit silicon carbide on the take-out jig, the precipitated silicon carbide is collected, and the purified molten silicon is removed from the container. A method for separating silicon carbide and silicon is provided, wherein the silicon carbide and silicon are separated by recovery.

  In addition, according to the present invention, there is provided an apparatus for use in the above-described method for separating silicon carbide and silicon, the first container for heating and melting the scrap silicon generated in the cutting process of the silicon ingot to the first temperature, and the first container 1 heating means, a first charging passage for supplying milled silicon to the first container, a second container for melting the silicon grains and holding the melt containing the molten silicon at the second temperature, and the second heating means, A first passage for allowing the liquid to overflow from the first container to the second container, a second introduction passage for supplying a mixture containing silicon carbide grains and silicon grains to the second container, and immersing silicon carbide in the upper layer portion of the melt. A take-out jig for precipitation, a third container for recovering purified molten silicon, a second passage for allowing purified molten silicon to overflow from the second container to the third container, and a seal for sealing the entire apparatus And separating apparatus as silicon carbide and silicon with a gas supply means for the inside shield inert gas atmosphere is provided.

  According to the present invention, silicon and silicon carbide can be recovered from used slurry generated in the cutting process of a silicon ingot. The recovered silicon carbide has a large particle size and can be reused as abrasive grains. The recovered silicon has a high purity and can be used as a raw material for silicon wafers for solar cells.

The method for separating silicon carbide and silicon of the present invention (hereinafter referred to as “separation method”)
Under inert gas atmosphere,
(A) A mixture containing silicon carbide grains and silicon grains in a container is heated to a first temperature to melt the silicon grains,
(B) Next, the obtained melt containing molten silicon is kept at the second temperature,
(C) Next, silicon carbide is immersed in the upper layer portion of the melt, silicon carbide is deposited on the take-out jig, the precipitated silicon carbide is recovered, and the refined molten silicon is recovered from the container. And silicon are separated.

In the separation method of the present invention, the steps up to the recovery of silicon carbide in step (A), step (B) and step (C) may be carried out in one container, but the steps (A) and (B ) And in the step (C), the container used for the recovery of the molten silicon is provided separately, and a passage is provided for overflowing the molten silicon-containing molten liquid and the purified molten silicon into another container in the next process, respectively. It is preferable to carry out continuously by continuously feeding a mixture containing material silicon or silicon carbide grains and silicon grains.
In addition, in the inert gas atmosphere, the end material silicon generated in the cutting process of the silicon ingot in the container in advance is heated to the first temperature and melted, and the mixture is added to the obtained molten silicon melt, It is preferable to melt the silicon grains by heating to the second temperature.

  That is, the container is heated to the first temperature, the first container for melting the silicon grains, or the silicon grains and the end material silicon, the second container for holding the melt containing the molten silicon at the second temperature, and the melt in the first temperature. A first passage that overflows from one container to a second container, a third container that collects purified molten silicon, and a second passage that overflows purified molten silicon from the second container to the third container. It is preferable that the separation is continuously performed by continuously adding the scrap silicon to the container and continuously adding the mixture to the second container.

  The separation method of the present invention will be described in detail with reference to the drawings based on the above preferred embodiments, but the present invention is not limited thereby.

FIG. 1 is a schematic diagram of a separation apparatus for explaining the separation method of the present invention.
The separation apparatus includes a first container (2) and a first heating means (3) installed on the first stage (1), a second container (5) and a second container (5) installed on the second stage (4). 2 A heating means (6), a third container (7), a first charging passage (9) for charging silicon scraps (8) into the first container (2), and a melt (10) containing molten silicon. A first passage (11) for overflowing the first container (2) to the second container (5), and a second introduction passage for introducing the mixture (12) containing silicon carbide particles and silicon particles into the second container (5) (13) A take-out jig (15) immersed in the upper layer portion of the melt (14) containing the molten silicon in the second container (5), and the purified molten silicon (16) from the second container (5) to the second container (5). It consists of the 2nd channel | path (17) made to overflow into 3 containers (7). The take-out jig (15) has a precipitation portion (18), rotates in the arrow direction by a rotation mechanism (not shown), and moves in the arrow direction by a movement mechanism (not shown).
The separation method of the present invention is performed in an inert gas atmosphere, and includes a shield for sealing the entire apparatus (not shown) and a gas supply means for making the inside of the shield an inert gas atmosphere.

  The first container (2), the second container (5), and the third container (7) are materials capable of holding the melt (10), (14) and purified molten silicon (16) containing molten silicon, respectively. And a crucible having an open upper surface made of a material used in the field. Specific examples include crucibles made of quartz, boron nitride, and graphite carbon. Among these, crucibles made of graphite carbon, particularly high-purity graphite carbon are preferred. Thereby, it is considered that carbon of silicon carbide is supplied from each container, in particular, the first container (2) and the second container (5), and the recovered amount of silicon carbide is increased.

  The shape of the first container (2), the second container (5) and the third container (7) is not particularly limited, but the first container (2) can be heated uniformly, the processing of the container is ready, etc. The second container (5) preferably has a horizontally long long cylindrical shape because it requires a space for the take-out jig (15). The third container (7) is preferably cylindrical in that it can be heated uniformly, the container is ready for processing, and the like.

The first stage (1) and the second stage (4) are made of materials capable of holding the first container (2) and the second container (5), respectively, and the materials include quartz, boron nitride, and graphite carbon. Is mentioned.
The first heating means (3) and the second heating means (6) are capable of melting silicon grains in the first container (2) and the second container (5), or silicon grains and scrap silicon, respectively. If it does not specifically limit, a resistance heating body and a heater are mentioned.

  The first charging path (9) and the second charging path (13) are respectively a charging path for charging the scrap silicon (8) into the first container (2), and a mixture containing silicon carbide particles and silicon particles. This is an introduction passage for introducing (12) into the second container (5), and examples of the material include quartz, boron nitride, and graphite carbon. Among these, graphite carbon, particularly high purity graphite carbon is preferable.

  The first passage (11) and the second passage (17) are respectively a passage through which the melt (10) containing molten silicon overflows from the first container (2) to the second container (5), and purified molten silicon. (16) is a passage for overflowing the second container (5) to the third container (7). Examples of the material include quartz, boron nitride, and graphite carbon. Among these, graphite carbon, particularly high purity. Of these, graphite carbon is preferred.

  The material and shape of the take-out jig (15) are not particularly limited as long as the take-out jig (15) can be immersed in the upper layer portion of the melt to precipitate silicon carbide efficiently. Examples of the material include quartz, boron nitride, and graphite carbon. Among these, graphite carbon, particularly high purity graphite carbon is preferable.

  The shape of the take-out jig (15) is preferably one having a plurality of (about 3 to 10) precipitation portions (projections) (18) as shown in FIG. If it is such a shape, a some precipitation part (18) will be continuously immersed in the upper layer site | part of a melt, silicon carbide will be deposited on each precipitation part, and the deposited silicon carbide can be efficiently collect | recovered.

In order to continuously immerse the plurality of precipitation portions in the upper layer portion of the melt, the take-out jig (15) is provided with a rotation mechanism (not shown) that rotates in the direction of the arrow. That is, by rotating the take-out jig (15), the respective precipitation portions (18) are sequentially immersed in the upper layer portion of the melt, and the pulling up of the silicon carbide precipitate is repeated.
The take-out jig (15) is provided with a moving mechanism (not shown) for moving in the direction of the arrow. That is, the precipitated silicon carbide can be recovered by the vertical movement of the take-out jig (15).

The take-out jig (15) is preferably composed of a plurality (about 2 to 3). Thereby, a plurality of extraction jigs (15) can be continuously immersed in the upper layer portion of the melt to deposit silicon carbide on each extraction jig, and the precipitated silicon carbide can be efficiently recovered.
When using a graphite carbon crucible as the first container (2) and the second container (5), when the carbon constituting the crucible is melted in the melt and the precipitation portion (18) is immersed, As described in Kaihei 7-172998, precipitation of silicon carbide occurs from the melt (14) containing molten silicon starting from the precipitation portion (18), and the silicon carbide particles that are suspended are It is considered that the mixture (12) containing silicon grains precipitates around the silicon carbide grains, and these aggregate into large particles. The particle size is considered to change depending on the conditions.

In the separation method of the present invention, first, in an inert gas atmosphere, in step (A), a mixture containing silicon carbide grains and silicon grains is heated to a first temperature in a container to melt the silicon grains.
The first temperature is a temperature at which silicon (melting point: 1414 ° C.) can be melted, and is usually about 1500 to 1700 ° C., preferably about 1650 ° C.
In the case of the separation apparatus shown in FIG. 1, the scrap silicon (8) generated in the cutting process of the silicon ingot in the first container (2) is heated to the first temperature and melted in advance in the first container (2). The additional material silicon (8) is additionally charged into the first container (2) through the first charging passage (9) and the molten silicon silicon (8) is melted, and the melt is melted through the first passage (11). Is overflowed from the first container to the second container. And the mixture (12) containing a silicon carbide grain and a silicon grain is thrown into the melt of a 2nd container (5), and it heats to 2nd temperature and fuse | melts a silicon grain.

End material silicon is an end material generated in the cutting process of a silicon ingot.
Further, the mixture containing silicon carbide grains and silicon grains is a used slurry obtained by cutting silicon grains mixed in a slurry composed of silicon carbide grains as abrasive grains and a dispersion medium thereof, which is generated in a cutting process of a silicon ingot. It is preferable that the mixture is purified by at least a centrifugal separation process, that is, a powdery substance obtained by solid-liquid separation, purification, and drying of cutting waste liquid generated when a silicon ingot is cut into a wafer by cutting with a multi-wire saw. As such a powdery substance, Japanese Patent Laid-Open No. 2001-278612 describes a powder made of silicon and abrasive grains.

Next, the melt containing the molten silicon obtained in the step (B) is held at the second temperature.
The second temperature is a temperature at which suspended matter can be formed in the melt, and is usually about 1430 to 1500 ° C., preferably about 1450 ° C.
In the case of the separation apparatus of FIG. 1, a mixture (12) containing silicon carbide particles and silicon particles is additionally charged to the melt maintained at the second temperature. Thereby, silicon carbide (stable up to about 1600 ° C.) is deposited.

Next, in step (C), a takeout jig is immersed in the upper layer portion of the melt to deposit silicon carbide on the takeout jig, the precipitated silicon carbide is collected, and purified molten silicon is collected from the container.
In order to precipitate silicon carbide efficiently, it is preferable to use a plurality of extraction jigs having a plurality of precipitation portions as described above.

  The separation method of the present invention is performed in an inert gas atmosphere. The inert gas is not particularly limited as long as it does not react with silicon. Examples of the inert gas include helium, neon, and argon, and argon is preferable. Thereby, generation of silicon oxide can be suppressed and high-purity silicon can be recovered.

Further, the step of heating the first temperature in the step (A) to melt the silicon grains, or the silicon grains and the edge silicon, or a part of the step is performed by supplying a hydrocarbon gas to the inert gas atmosphere. Is preferred. Examples of the hydrocarbon gas include methane, ethane, propane, propylene, butylene and the like, and preferably methane.
The ratio of hydrocarbon gas is about 0.1 to 1%.
Thereby, the recovery amount of silicon carbide increases, and the recovered silicon carbide becomes strong particles. This is considered because carbon decomposed from methane participates in the formation of silicon carbide.
In order to control the gas atmosphere as described above in the separation apparatus of FIG. 1, the apparatus further includes a shield and a gas supply means for making the molten silicon in the first container a mixed gas atmosphere of an inert gas and a hydrocarbon gas. That's fine.

  The recovered silicon carbide has a large particle size and can be reused as abrasive grains for cutting (slicing) silicon ingots. The recovered silicon is highly pure and is a raw material for silicon wafers for solar cells. Available to:

  From the above, under the inert gas atmosphere, the scrap silicon generated in the cutting process of the silicon ingot in the container in advance is heated to the first temperature and melted, and the mixture is added to the obtained molten silicon melt. In addition, as an apparatus used in the separation method of the present invention in which the silicon particles are melted by heating to the second temperature, a first container for heating and melting the scrap silicon generated in the cutting process of the silicon ingot to the first temperature and its A first heating means, a first charging passage for supplying scrap silicon to the first container, a second container for melting the silicon grains and holding the melt containing the molten silicon at the second temperature, and the second heating means; A first passage for allowing the melt to overflow from the first container to the second container; a second charging passage for supplying a mixture containing silicon carbide grains and silicon grains to the second container; and an upper layer portion of the melt A take-out jig for precipitating silicon carbide by immersing in a second container, a third container for recovering purified molten silicon, a second passage for allowing purified molten silicon to overflow from the second container to the third container, and sealing the entire apparatus. An apparatus for separating silicon carbide and silicon is provided, which includes a shield and gas supply means for making the inside of the shield an inert gas atmosphere.

(Example)
The present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

Example 1
Silicon carbide and silicon were separated using the separation apparatus shown in FIG.
First, the whole apparatus was sealed with a shield (not shown), and the inside of the shield was made an argon gas atmosphere.
The first container (2), which is installed on the first stage (1) made of graphite carbon and made of a graphite carbon crucible having an inner diameter of 185 mm and a height of 250 mm, passes through the first input passage (9) made of graphite carbon. 7 kg of the end material silicon (8) is charged, and the end material silicon (8) is heated to 1650 ° C. by the first heating means (3) made of a resistance heating body to be completely melted, and a melt containing molten silicon (10) was obtained. After melting, the molten state was maintained at the same temperature. At this time, it is considered that carbon is dissolved from the first container (2) in the melt (10) containing molten silicon.

  When the scrap silicon (8) is additionally charged into the first container (2) through the first charging passage (9) and the melting is continued, the melt (10) containing the molten silicon becomes the first made of graphite carbon. It overflowed through the passage (11) and overflowed into a second container (5) made of a graphite carbon crucible having a major axis of 400 mm and a height of 200 mm installed on the second stage (4) made of graphite carbon. The melt (14) containing molten silicon overflowed was heated and held at 1450 ° C. by the second heating means (6) made of a resistance heating body. When the melt (14) containing molten silicon is sufficiently accumulated in the second container (5), a second charging passage (13) made of graphite carbon is provided in the vicinity of the first passage (11) of the second container (5). Then, a mixture (12) containing silicon carbide grains and silicon grains was introduced to melt the silicon grains. This mixture (12) containing silicon carbide grains and silicon grains is a powdery substance obtained by solid-liquid separation, purification, and drying of cutting waste liquid generated when a silicon ingot is cut into a wafer by a multi-wire saw. , Si was included at a ratio of 80% and SiC at a ratio of 20%, and the particle size was about 5 μm.

  It is confirmed that there is a suspended matter in the melt (14) containing the molten silicon, and has a precipitation portion (18) composed of a plurality of protrusions in the upper layer portion of the melt (14) containing the molten silicon. And a graphite carbon take-out jig (15) equipped with a moving mechanism (not shown) was immersed to allow floating matter to adhere. The take-out jig (15) was gear-shaped and had an outer diameter of 60 mm, a maximum protruding length of 20 mm and 10 depositing portions. Then, rotation and movement of the take-out jig (15) and collection of deposits, that is, silicon carbide grains were repeated. When the component of this deposit was analyzed, it was found to be silicon carbide. The particle size was about 15 μm.

By repeatedly collecting the adhering matter (floating matter), the floating matter decreased, and the floating matter was not observed near the second passage (17) of the second container (5).
By repeating the above steps, the refined molten silicon (16) overflows through the second passage (17), and a third container made of a graphite carbon crucible having an inner diameter of 185 mm and a height of 150 mm ( 7) Overflowed. When this overflowed silicon was analyzed, it was silicon with a purity of 99% or more, and most of the impurities were iron powder.
The impurity iron powder is considered to be contained in a mixture (slurry refined product) containing silicon carbide grains and silicon grains, and this iron powder can be easily removed by a known purification method.

Since the recovered silicon carbide has a large particle size of 15 μm, it was found that it can be reused as abrasive grains.
It was also found that the recovered silicon can be used as a raw material for polycrystalline silicon silicon wafers for solar cells, etc., by purifying it by a known method, for example, the method described in JP-A-2001-172729.

(Example 2)
The first container (2) is separated from the entire apparatus including the second container (5) other than the first container (2) by a partition wall (not shown) that prevents mixing of atmospheric gas. The separation apparatus shown in FIG. 1 was prepared in the same manner as in Example 1 except that the side was a mixed gas atmosphere of argon gas and methane gas (0.5%) and the second container (5) side was an argon gas atmosphere. Used to separate silicon carbide and silicon.
There was no difference in the recovered silicon, but the recovered amount of silicon carbide was increased, and the recovered silicon carbide was strong particles.

It is a schematic diagram of the separation apparatus for demonstrating the separation method of this invention.

Explanation of symbols

1 First Stage 2 First Container (Crucible)
3 First heating means 4 Second stage 5 Second container (crucible)
6 Second heating means 7 Third container (crucible)
8 End material silicon 9 First input passage 10, 14 Melt containing molten silicon (molten metal)
DESCRIPTION OF SYMBOLS 11 1st channel | path 12 The mixture containing a silicon carbide grain and a silicon grain 13 2nd injection | throw-in channel | path 15 Taking-out jig | tool 16 Purified molten silicon (molten metal)
17 Second passage 18 Precipitation part

Claims (14)

  In an inert gas atmosphere, a mixture containing silicon carbide grains and silicon grains is heated to a first temperature in a container to melt the silicon grains, and then the obtained melt containing molten silicon is held at the second temperature. Then, the silicon carbide and silicon are obtained by immersing the take-out jig in the upper layer part of the melt and precipitating silicon carbide in the take-out jig, collecting the precipitated silicon carbide, and collecting the purified molten silicon from the container. And separating silicon carbide from silicon.   In an inert gas atmosphere, the scrap silicon generated in the cutting process of the silicon ingot in the container in advance is heated to the first temperature to be melted, and the mixture is added to the obtained molten silicon melt, and the second The separation method according to claim 1, wherein the silicon particles are melted by heating to a temperature.   The mixture is a mixture obtained by cutting at least a used slurry in which silicon particles cut into a slurry composed of silicon carbide particles as abrasive grains and a dispersion medium thereof, which are generated in a cutting process of a silicon ingot, are mixed by a centrifugal separation process. The separation method according to claim 1 or 2.   The separation method according to claim 1, wherein the container and the take-out jig are made of graphite carbon.   The take-out jig has a plurality of precipitation portions, the plurality of precipitation portions are continuously immersed in an upper layer portion of the melt, silicon carbide is precipitated in each precipitation portion, and the precipitated silicon carbide is recovered. 5. The separation method according to any one of 4.   The said taking-out jig | tool has two or more, The some taking-out jig is continuously immersed in the upper layer part of a melt, silicon carbide is deposited on each taking-out jig, and the deposited silicon carbide is collect | recovered. The separation method according to any one of the above.   The process of heating the first temperature to melt the silicon grains, or the silicon grains and the off-chip silicon, or a part of the process is performed by supplying a hydrocarbon gas to an inert gas atmosphere. The separation method according to any one of the above.   The container is heated to a first temperature to melt silicon grains, or silicon grains and end material silicon, a second container for holding a melt containing molten silicon at a second temperature, and the melt to the first temperature. The first container includes a first passage for overflowing from the container to the second container, a third container for recovering the purified molten silicon, and a second passage for allowing the purified molten silicon to overflow from the second container to the third container. The separation method according to any one of claims 2 to 7, wherein the separation is continuously performed by continuously adding the silicon scrap material to the second container and continuously adding the mixture to the second container.   The separation method according to any one of claims 1 to 8, wherein the recovered silicon carbide is used as abrasive grains for cutting a silicon ingot.   A device for use in the method for separating silicon carbide and silicon according to any one of claims 2 to 9, wherein the first container that heats and melts the offcut silicon generated in the cutting process of the silicon ingot to a first temperature. And the first heating means, the first charging passage for supplying the silicon scrap to the first container, the second container for melting the silicon grains and holding the melt containing the molten silicon at the second temperature, and the second heating thereof. Means, a first passage for overflowing the melt from the first container to the second container, a second input passage for supplying a mixture containing silicon carbide grains and silicon grains to the second container, and immersing in an upper layer portion of the melt. A take-out jig for depositing silicon carbide, a third container for recovering purified molten silicon, a second passage for allowing purified molten silicon to overflow from the second container to the third container, and sealing the entire apparatus. Rudo, and separation device between silicon carbide and silicon with a gas supply means for inert gas atmosphere inside the shield.   The separation apparatus according to claim 10, wherein the first container, the second container, and the take-out jig are made of graphite carbon.   The separation device according to claim 10 or 11, wherein the take-out jig has a plurality of precipitation portions for continuously immersing in an upper layer portion of the melt.   The separation device according to any one of claims 10 to 12, wherein the take-out jig is plurally provided so as to be continuously immersed in an upper layer portion of the melt.   The separation apparatus according to any one of claims 10 to 13, further comprising a shield and a gas supply unit that make the molten silicon in the first container a mixed gas atmosphere of an inert gas and a hydrocarbon gas.

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