JP3508167B2 - Silicon purification method and silicon pretreatment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for producing high-purity silicon that can be used as a raw material for solar cells and the like.
Before the removal, pre-treatment mainly includes boron removal.
The present invention relates to a method for purifying silicon and a pretreatment device for silicon .

[0002]

2. Description of the Related Art For example, silicon used for solar cells has a specific resistance of 0.1 Ωcm or more. In such silicon, impurities contained in the silicon are ppm.
The order must be removed. On the other hand, various methods have been conventionally studied, and it is known that boron and carbon are the most difficult elements to remove as impurities.

Japanese Patent Application Laid-Open No. H4-228414 discloses a method in which molten silicon is held in a container containing silica or silica as a main component, and a plasma jet is jetted onto the container to remove boron and carbon in the silicon. I have. In Japanese Patent Application Laid-Open No. 4-193706, silicon is dissolved in a silica-based container having a gas injection tuyere at the bottom, and boron and carbon in the silicon are similarly removed by blowing gas from the tuyere. A method for doing so is disclosed.

[0004]

SUMMARY OF THE INVENTION
In the method disclosed in Japanese Patent Application Laid-Open No. 4-228414, the reduction of the processing time is limited because the removal reaction of boron and carbon proceeds in the plasma jet irradiation part of the silicon bath. Also,
In the method disclosed in Japanese Patent Application Laid-Open No. 4-193706, boron and carbon are removed by blowing gas from a tuyere provided at the bottom of the container, so that it is necessary to remove these from molten silicon in a very short time. It is necessary to increase the amount of gas blown. As a result, the stirring of the silicon bath is strengthened and the tuyere is significantly damaged, shortening the life of the furnace. Therefore, there is a limit to the reduction of the processing time in order to perform the treatment while suppressing the damage to the tuyere.

[0005] In order to solve the above-mentioned problems, the present invention provides a method for purifying silicon by removing boron, which is suitable as a pretreatment before the above-mentioned treatment, and a method for preparating silicon.
It is an object to provide a processing device . That is, by using the silicon pretreatment apparatus provided by the present invention and performing the silicon purification method, the burden of the above treatment is reduced, and the time for finally removing boron is shortened.

[0006]

That is, according to the present invention, there is provided:
The silicon purification method is a reaction vessel that purifies silicon
In inner, while introducing Ar gas, dissolved material silicon
・ Dissolved in a holding vessel to form molten silicon
Ar gas containing water vapor is introduced, and the dissolution / holding volume is introduced.
Ar containing 1 vol % or more and 40 vol % or less water vapor below the vessel
Forming a gas atmosphere layer, and dissolving and holding the gas atmosphere layer in the gas atmosphere layer;
Drop molten silicon from the container and receive the dropped silicon.
While receiving in a container, the boron in the drip silicon and the water
Oxidizing gas generated by the reaction with steam and gas after use
Perform gas emissions scan, Ru purification methods der silicon characterized that you purifying the raw material silicon. Alternatively a further method for purifying silicon which is characterized that you irradiated water droplets toward the dropping silicon, more preferably,
A method for purifying silicon, wherein the average diameter of the droplets of the dropped silicon is 30 mm or less. Further, the silicon according to the present invention
Is a reaction vessel for purifying silicon.
Dissolve and hold raw silicon in the upper part of the chamber
The melting / holding container is provided with a molten silicon.
Is configured to allow dripping of the
A receiving container for receiving silicon after dripping is installed in the lower part of the chamber.
The chamber is further provided with an Ar gas
And a dissolving / holding vessel
In the height direction intermediate position directly below the vessel H ₂ O - Ar mixed gas
Gas inlet, and a gas outlet underneath.
A silicon pretreatment device characterized in that
You.

[0007]

First, an embodiment of the method for purifying silicon of the present invention will be described. The inert gas referred to below is Ar gas
That is. Silicon purification method according to the present invention,
The raw material silicon in the reaction vessel, quality introducing Ar gas
First, melt in the melting and holding vessel provided at the top of the chamber.
Dissolve and hold the raw silicon to be melted and held
Ar gas containing a certain amount of water vapor is introduced and used for dissolution and holding
In the Ar gas atmosphere layer containing water vapor formed below
Purification through the dropping process of molten silicon
I am trying to do it. (I) Dissolution and Retention in Dissolution and Retention Process) Silicon as a raw material is dissolved and retained in a container mainly composed of silica or a container mainly composed of graphite. Here, the holding temperature of the molten silicon is not particularly limited.

(Ii) Including the step of dropping molten silicon
In the process of descent, dropping of molten silicon is performed by discharging molten silicon at a predetermined speed from a discharge port provided at the bottom and / or the side wall of the container or from the top of the container by tilting the container. Can be done by Under the container holding the molten silicon, a layer of an inert gas containing water vapor is formed, and the dropped molten silicon passes through this gas layer and is passed through another container installed below the gas layer. Can be received. As a result, the concentration of boron contained in the silicon that has been dropped and entered into the container is lower than the concentration of boron contained in the molten silicon before the addition.

It is considered that boron in silicon reacts with water vapor in a gas phase and is removed as an oxidizing gas. Therefore, in order to efficiently remove boron, it is necessary to increase the boundary area of the molten silicon dropped. Therefore, it is preferable that the average diameter of the molten silicon droplet to be dropped is as small as possible and desirably 30 mm or less. If the flow becomes larger or continuous, the boron concentration of silicon after dropping is almost equal to the boron concentration of molten silicon before dropping, and the effect of removing boron is lost.

If the concentration of water vapor in the inert gas layer through which the molten silicon drops passes is less than 1 vol%, there is almost no effect on removing boron, so that a water vapor concentration of 1 vol% or more is required. If the concentration of the water vapor in the inert gas layer is too high, oxidation of the dripped silicon also becomes remarkable, and the yield of silicon decreases. Therefore, the water vapor concentration is 40 vol%
The content is more preferably 20 vol% or less.

In the present invention, water droplets are directed toward the drip silicon.
By Rukoto be irradiated, it can make removal of boron more efficiently.

[0012]

FIG. 1 is an example of a longitudinal sectional view of an apparatus used in carrying out the present invention. (I) In the melting and holding process, the silicon 1 is heated and melted by the resistance heater 3 in the silica crucible 2 and held.
Ar is flowed from Ar inlet 4 installed in the chamber 11 of the crucible above how to prevent oxidation of the silicon. A drip hole provided at the bottom of the crucible 2 is closed by a stopper 5. (Ii) In the subsequent steps including the dropping step of molten silicon,
When starting the dropping of silicon, the stopper 5 is lifted upward, the distance between the dropping hole and the tip of the stopper 5 is appropriately adjusted, and the size of the dropping silicon 6 is adjusted.

The dripped silicon 6 is used as a dissolving / holding container.
Is received and accumulated in a silica receiving crucible 8 on a crucible table 7 installed below the silica crucible 2 . From a gas inlet 9 which had been <br/> placed in the height direction intermediate position of the chamber 11 directly below the silica crucible 2 flowing H ₂ O -Ar gas mixture. Gas introduced from the gas inlet 4 and 9 finally Ji
The gas is exhausted from the chamber 11 through a gas exhaust port 10 provided at a lower portion of the chamber 11. In addition, a water droplet 13 is irradiated from a water droplet generator 12, and the dropping silicon passes therethrough.

(Comparative Example) [0014] 2 kg of silicon was obtained by the apparatus schematically shown in FIG.
It was heated and melted by a resistance heater 3 in a silica crucible 2 having an inner diameter of 150 mm and a depth of 150 mm. Ar flows into the chamber 11 at a rate of 25 l / min to prevent oxidation of silicon from the Ar inlet 4 provided at the top of the crucible. Next, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, the average diameter of the silicon being dropped was 20 mm. Table 1 shows the boron concentration of silicon before dropping and the boron concentration of silicon dropped and collected.

Example 1 2 kg of silicon was heated and melted by the same apparatus as in the comparative example. Ar is introduced from the Ar inlet 4 located above the crucible.
The mixture was flowed into the chamber 11 at a flow rate of 10 l / min, and a mixed gas of 1 vol% H ₂ O—Ar was flowed at a flow rate of 15 l / min from a gas inlet 9 provided immediately below the melting crucible 2. In this state, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, the average diameter of the silicon being dropped was 20 mm. Table 1 shows the boron concentration of silicon before dropping and the boron concentration of silicon recovered after dropping.

Example 2 2 kg of silicon was melted by heating using the same apparatus as in the comparative example. Ar is introduced from the Ar inlet 4 located above the crucible.
The mixture was supplied into the chamber 11 at a flow rate of 10 l / min, and a mixed gas of 5 vol% H ₂ O—Ar was supplied at a flow rate of 15 l / min from a gas inlet 9 provided immediately below the melting crucible 2. In this state, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, the average diameter of the silicon being dropped was 15 mm. Table 1 shows the boron concentration of silicon before dropping and the boron concentration of silicon recovered after dropping.

Example 3 2 kg of silicon was heated and melted using the same apparatus as in the comparative example. Ar is introduced from the Ar inlet 4 located above the crucible.
The mixture was supplied into the chamber 11 at a flow rate of 10 l / min, and a mixed gas of 5 vol% H ₂ O—Ar was supplied at a flow rate of 15 l / min from a gas inlet 9 provided immediately below the melting crucible 2. In this state, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, a water droplet 13 of about 50 μm was irradiated from the water droplet generator 12, and the silicon dripped there passed. At this time, the average diameter of the silicon being dropped was 10 mm. Table 1 shows the boron concentration of silicon before dropping and the boron concentration of silicon dropped and collected.

Example 4 2 kg of silicon was heated and melted using the same apparatus as in the comparative example. Ar is introduced from the Ar inlet 4 located above the crucible.
10 l / min Flow into the chamber 11, and adjust the water vapor concentration from 1 to 60 vol through the gas inlet 9 installed immediately below the melting crucible 2.
% Of H ₂ O—Ar mixed gas was flowed at 15 l / min.
In this state, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, the average diameter of the silicon being dropped was 25 mm. Ratio relationship H ₂ O -Ar boron concentration in the silicon before and after dropping the water vapor concentration in the mixed gas, as well as the relationship between the H ₂ O -Ar water vapor concentration in the mixed gas and yield of silicon to remove oxide As shown in FIG.

Example 5 2 kg of silicon was heated and melted using the same apparatus as in the comparative example. Ar is introduced from the Ar inlet 4 located above the crucible.
The mixture was supplied into the chamber 11 at a flow rate of 10 l / min, and a mixed gas of 5 vol% H ₂ O—Ar was supplied at a flow rate of 15 l / min from a gas inlet 9 provided immediately below the melting crucible 2. In this state, the stopper 5 was lifted and molten silicon was dropped, and was collected in the receiving crucible 8. At this time, the distance between the dropping hole and the tip of the stopper 5 was adjusted to change the average particle size of the dropping silicon 6 from 5 to 50 mm. FIG. 3 shows the relationship between the size of silicon during dropping and the ratio of the boron concentration in silicon before and after dropping.

In the examples of the present invention, as can be seen from Table 1, boron in silicon is not always reduced to a sufficient amount for solar cells, but sufficient results can be obtained by using the above-mentioned prior art together. Obtainable.

[0021]

[Table 1]

[0022]

According to the present invention, boron which is difficult to remove from silicon can be easily reduced in advance.
The burden of the boron removal processing disclosed in the above-mentioned Japanese Patent Application Laid-Open Nos. 4-284414 and 4-193706 is reduced, and the time for finally removing boron is reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of an apparatus used when carrying out the present invention.

[Figure 2] and the yield of H ₂ O -Ar relationship and H ₂ O -Ar water vapor concentration in the gas mixture the ratio of boron concentration in the silicon before and after dropping the water vapor concentration in the mixed gas and the silicon removal of the oxide The graph which shows the relationship.

FIG. 3 is a graph showing the relationship between the size of silicon dropped and the ratio of the concentration of boron in silicon before and after dropping.

[Explanation of symbols]

1 silicon 2 silica crucible (container dissolution and retention) 3 resistive heater 4 Ar inlet 5 stopper 6 dropping silicon 6 'after dropping silicon 7 crucible base 8 receiving crucible (receiving container) 9 H ₂ O -Ar mixed gas inlet Reference Signs List 10 Gas outlet 11 Chamber (reaction vessel) 12 Water drop generator 13 Water drop

──────────────────────────────────────────────────の Continuing on the front page (72) Koji Nishikawa, Inventor 1 at Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (56) References UK Patent 897730 (GB, B) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 33/037

Claims (4)

(57) [Claims] 1. A method for purifying silicon in a reaction vessel.
For dissolving and holding raw silicon while introducing Ar gas
Dissolved in a container to form molten silicon, and a predetermined amount of steam
While introducing Ar gas containing, lower container the dissolution and retention
1 vol% or more, Ar gas containing 40 vol% or less of water vapor Kiri囲
A vapor layer is formed, and molten silicon is dropped into the atmosphere layer from the melting / holding container , and the dropped silicon is received in the container.
At the same time, the boron in the drip silicon and the water vapor
Oxidizing gas generated by reaction and used gas
Evacuate method for purifying silicon which is characterized that you purifying the raw material silicon. 2. The method for purifying silicon according to claim 1, wherein a water droplet is irradiated to the silicon drop. 3. The method according to claim 1, wherein the average diameter of the silicon droplets is 30.
The method for purifying silicon according to claim 1 or 2, wherein the diameter is not more than mm. 4. A reaction vessel for purifying silicon,
In the upper part of the chamber, a vessel for melting and holding the raw material silicon
Vessel is provided, and the melting and holding vessel
The chamber is configured to allow dripping, while the chamber
In the lower part of the inside, a receiving container for receiving silicon after dripping is provided.
The chamber is further provided with the Ar gas
An inlet is installed and the dissolution / holding vessel is
H ₂ O in a height direction intermediate position directly below - Ar mixed gas guide
There is an inlet and a gas outlet below it.
A silicon pre-processing apparatus.