WO2007013644A1

WO2007013644A1 - Process for producing polycrystalline silicon

Info

Publication number: WO2007013644A1
Application number: PCT/JP2006/315088
Authority: WO
Inventors: Toshiharu Yamabayashi
Original assignee: Sumitomo Chemical Company, Limited
Priority date: 2005-07-28
Filing date: 2006-07-25
Publication date: 2007-02-01

Abstract

A process for producing polycrystalline silicon which comprises reacting a metal whose chloride has a lower free energy of formation than silicon and whose melting point is lower than that of silicon with a gaseous chlorosilane represented by the following formula (1): SiHnCl4-n (1) (wherein n is an integer of 0-3). In the process, the gaseous chlorosilane is bubbled into a melt of the metal while keeping the molten metal at a temperature which is not lower than 1.03 times the melting point of the metal, in terms of absolute temperature, and is lower than 1.79 times the melting point thereof and which is lower than the melting point of silicon. The chlorosilane is fed at such a rate that the number of moles of the chlorosilane being fed per minute is less than 1.0 percent of the moles of the metal.

Description

Method for producing polycrystalline silicon

Technical field

The present invention relates to a method for producing polycrystalline silicon. Specifically, the present invention relates to a method for producing polycrystalline silicon with a high yield. Memorandum

Background art

As environmental issues are highlighted, solar cells are attracting attention as a clean energy source, and demand in Japan is rapidly increasing, especially for residential use. Since silicon solar cells are excellent in reliability and conversion efficiency, they account for about 80% of solar power generation. In addition, it is desired to secure low-priced silicon raw materials in order to increase demand and reduce the unit price of power generation. Currently, most manufacturers use a method of pyrolyzing trichlorosilane (Siemens method) as a method for producing high-purity silicon. However, this method has a limit in the power consumption, and it is said that further cost reduction is difficult.

As a production method that can replace the pyrolysis method, a method of producing silicon by reducing chlorosilane using zinc or aluminum has been proposed. As a method of reducing using aluminum, a method is known in which silicon is obtained by reacting fine aluminum particles in a tetrachlorosilane gas. In general formula _{_{_{S i H n X 4 _ n}}} ( wherein, X is halogen, n represents 0 to 3.) A method for producing a silicon by reacting silicon compounds of the gases with aluminum A finely dispersed molten surface of pure aluminum or A 1—Si alloy is in close contact with the gaseous silicon compound. There is known a method of bringing it into contact (Japanese Patent Laid-Open No. 2-6400).

However, since conventional methods cannot produce silicon with a sufficient yield, none of the methods has been put to practical use. An object of the present invention is to provide a method for producing polycrystalline silicon with a high yield.

In order to solve the above problems, the present inventor has intensively studied a method for producing polycrystalline silicon, and as a result, has completed the present invention.

That is, the present invention provides: [1] a metal having a lower free energy of formation of metal chloride than silicon and a metal having a melting point lower than that of silicon;

_{_{S i HC l 4. N (}} 1)

(In the formula, n represents an integer of 0 to 3.)

A method for producing silicon by reacting with a gaseous chlorosilane represented by the formula (1), wherein when the gaseous chlorosilane is blown into the molten metal, the temperature of the molten metal is expressed by the melting point represented by the absolute temperature of the metal. 1.0 3 times or more and less than 1.7 times, and kept below the melting point of silicon, and the number of moles of chlorosilane supplied per minute is less than 1.0 percent with respect to the number of moles of metal. A method for producing polycrystalline silicon is provided.

The present invention also provides [2] a method for producing polycrystalline silicon including steps (i) and (ii), (i) a metal chloride free energy of formation lower than that of silicon, and a metal melting point lower than that of silicon. A step of reacting the gaseous chlorosilane represented by the formula (1) to obtain silicon,

(i i) a step of directionally solidifying the obtained silicon,

In the step (i), when the gaseous chlorosilane is blown into the molten metal, The temperature of the genus is 1.03 times or more and less than 1.79 times the melting point of the metal expressed in absolute temperature, the temperature is kept below the melting point of silicon, and the number of moles of chlorosilane supplied per minute is Less than 1.0 percent of the number of moles of

[3] The method according to [1] or [2], wherein the gas blown into the metal is chlorosilane alone or a mixed gas of chlorosilane and an inert gas,

[4] The method according to [3] above, wherein the concentration of chlorosilane in the gas blown into the metal is 10% by volume or more,

[5] The metal according to any one of [1] to [4], wherein the metal is at least one selected from the group consisting of potassium, cesium, rubidium, strontium, lithium, sodium, magnesium, aluminum, zinc, and manganese. Method,

[6] The method according to any one of [1] to [5], wherein the metal is aluminum, [7] at least selected from the group consisting of silicon tetrachloride, trichlorosilane, dichlorosilane, and monochlorosilane. The method according to any one of the above [1] to [6], which is one kind,

[8] The method according to any one of [1] to [7], wherein boron and phosphorus contained in chlorosilane and metal are each less than 1 ppm.

[9] A solar cell comprising polycrystalline silicon obtained by the method according to any one of [1] to [8] is provided. Brief Description of Drawings

Figure 1 shows an overview of the reactor.

Figure 2 shows the gas supply system.

Figure 3 represents the yield of S i C 1 ₄ / A 1 molar ratio and S i.

Explanation of symbols Vertical annular furnace 1

Gas introduction pipe 2

Alumina container 3

Alumina Tanman tube · · 4

Aluminum 5

S i C 1 ₄ / A r

Dilution gas 7

Carrier gas 8

S i C 1 ₄ 9

Thermostatic bath 10 Best mode for carrying out the invention

In the method for producing polycrystalline silicon according to the present invention, a metal chloride generation free energy is lower than that of silicon and a metal melting point is lower than that of silicon, and a gaseous chlorosilane represented by the above formula (1) is reacted. Is the method.

In the production method of the present invention, a gas containing chlorosilane is blown into a molten metal to react the metal with gaseous chlorosilane. When a gas containing chlorosilane is blown into the molten metal, the temperature of the molten metal is 1.0 3 times or more, preferably 1.10 times or more, more preferably 1. 20 times or more, 1. Less than 79 times, preferably less than 1.50 times, more preferably less than 1.40 times, below the melting point of silicon.

In the production method of the present invention, the number of moles of chlorosilane supplied per minute is less than 1.0 percent, preferably 0.5 percent or less, relative to the number of moles of metal. On the other hand, the number of moles of chlorosilane supplied is usually 0.01 to the number of moles of metal. % Or more, preferably 0.1% or more.

The gas blown into the molten metal may be chlorosilane alone or a mixed gas of chlorosilane and inert gas. In the case of a mixed gas, the gas concentration of chlorosilane in the mixed gas is preferably 10% by volume or more.

Examples of the inert gas include nitrogen gas, argon gas, helium gas, and neon gas, and argon gas is preferable from the viewpoint of reducing the reaction with chlorosilane and the availability.

Metals have lower free energy and melting point for metal chlorides than silicon. Examples of the metal include potassium, cesium, rubidium, strontium, lithium, sodium, magnesium, aluminum, zinc, and manganese.

. These may be used alone or in combination. Of these, even if metal remains in the silicon or on its surface, it can be easily removed by segregation if it is dissolved and removed by acid or alkali, and further, it does not corrode the structural members of the reactor. As the metal, aluminum is preferably used. The higher the purity of the metal, the higher the purity of the silicon produced, so boron (B) and phosphorus (P) are less than l p p m

It is preferable to use a metal having a purity of 99.98% or more.

As chlorosilanes, silicon tetrachloride, trichlorosilane, dichlorosilane, and monochlorosilane can be used, but hydrogen-containing trichlorosilane, dichlorosilane, and monochlorosilane generate hydrogen chloride by reaction. Induces corrosion of piping. For this reason, it is preferable to use tetrachlorosilane alone. The purity of chlorosilane is that B and P are less than l p p m, 99.9

It is preferable to use one having a purity of 9% or more.

In the present invention, a metal chloride produced as a by-product by reacting with a metal (for example,

Aluminum chloride, aluminum dichloride, aluminum chloride, silicon dichloride, If the silicon trichloride) and the raw material chlorosilane gas are collected separately and unreacted chlorosilane gas is circulated to the reaction side, the cost can be reduced.

According to the present invention, usually, silicon can be obtained in an amount of more than 40% of the weight of the metal used, so that the yield of the obtained silicon is high, which is economically advantageous. The material for holding the metal and the gas introduction pipe for introducing chlorosilane usually does not react with the metal used, and examples thereof include oxides, nitrides, and carbides. Examples of the oxide include silica, alumina, zirconia, titania, zinc oxide, magnesia, and tin oxide. Examples of the nitride include silicon nitride and aluminum nitride. These constituent elements may be partially substituted with other elements, for example, compounds such as sialon composed of silicon, aluminum, oxygen and nitrogen may be used. Examples of the carbide include SiC, graphite, and the like, and these constituent elements may be partially substituted with other elements.

For gaseous chlorosilane, for example, at least one gas inlet tube is installed on the top or side of the molten metal and blown from there, or the molten metal does not leak due to surface tension at the bottom of the container holding the molten metal It is only necessary to install many holes of the same size and blow from there. Even when a large number of holes for introducing gas are provided, the number of moles of chlorosilane supplied per minute is within the above range.

The obtained polycrystalline silicon has a high purity and is suitably used as a raw material for solar cell silicon.

If necessary, the obtained polycrystalline silicon can be treated with acid or alkali to remove the unreacted metal component residue, segregation such as directional solidification, dissolution at high vacuum, etc. May be applied. By such operations, particularly directional solidification, the impurity elements contained in silicon are further reduced and highly purified.

In the present invention, the metal and silicon used for the reduction are in a molten state, or the metal and silicon. In addition to the above method, the temperature of the system can be reduced by lowering the temperature of the system below the reaction temperature or cooling a specific part of the reactor. Silicon deposits corresponding to the lowered amount are obtained. If a metal having the same weight as the deposited silicon is added and the temperature is raised to the reaction temperature, and then chlorosilane is added, the silicon concentration rises to a predetermined concentration. If this operation is repeated, silicon can be obtained continuously.

The obtained silicon is usually formed by a casting method or an electromagnetic forging method to obtain an ingot.

The conductivity type of the substrate is generally p-type, and can be achieved, for example, by adding boron or leaving aluminum as a dopant.

Ingots are usually sliced by cutting the inner peripheral edge, etc., then both sides are lapped with loose abrasive grains, and further immersed in an etching solution such as hydrofluoric acid to remove the damaged layer. Is obtained.

In order to reduce light reflection loss on the surface of a polycrystalline substrate, a V-groove is mechanically formed using a dicing machine, or a texture structure is formed by reactive ion etching or isotropic etching using acid. It is formed.

Subsequently, a diffusion layer of an n-type dopant such as phosphorus or arsenic is formed on the light receiving surface to obtain a pn junction. Further, with the electrodes on each side of the oxide film layer, such as a T I_〇 ₂ after forming on the surface, it forms the shape of the anti-reflection film such as M g F ₂ for reducing the loss of light energy due to reflection, solar A battery cell is produced.

Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is defined by the terms of the claims, and also includes all modifications within the meaning and scope equivalent to the terms of the claims. is there.

Example

The following examples illustrate the invention. However, the present invention is not limited to this.

Example 1

Figure 1 shows an outline of the reactor.

Alumina Tanman tube 4 (Nitsukato SSA—S, T 5 (inner diameter Φ 30)) containing aluminum 5 is held in alumina container 3 and held in vertical annular furnace 1, 1273K (melting point of aluminum tetrachloride Kei-containing gas (mixture gas of _{S i C 1 4 / Ar)} 6 was reacted by introducing into the molten aluminum 1. 36x) of.

The aluminum used has a purity of 99.999 wt% [impurity concentration Fe 0.73 ppm, Si 2. 7 ppm, Cu 1.9 ppm, Mg O. 45 ppm, B 0.05 ppm, P 0.27 p pm (according to the results of glow discharge mass spectrometry (GDMS analysis))), and its weight was 25 g (0.93 mol).

In the present invention, the purity of aluminum is obtained by subtracting the total weight% of impurities Fe, Si, Cu, and Mg from 100%.

The tetrachlorosilane is manufactured by Trichemical Laboratories with a purity of 99.9999% by weight (6) [impurity concentration: Fe 5.2 ppb, A 1 0.8 ppb, Cu 0.9 9 pp b, Mg 0. 8 p pb, Na 2.4 ppb, Ca 5.5 ppb (P and B are less than l ppm)].

In order to perform gas publishing, the distance between the tip of the gas inlet tube 2 [Nichikato SSA-S, (outer diameter Φ 6, inner diameter Φ4)] and the bottom of the Tamman tube was 5 mm.

Figure 2 shows the gas supply system.

The transport of the tetrachlorobenzene is Argon gas (made by Japan AG) (purity 99 · 9 995%) was supplied as 0. IMP a and used as a carrier gas. At that time, the stainless steel container containing the tetrachloride cage 9 was held in a constant temperature bath 10 at 20 ° C. Since the vapor pressure of silicon tetrachloride at the same temperature is 193 mmHg, the concentration of the gas is 25.4% by volume.

Through the carrier gas control valve 8, 240 SCCM (flow rate: 24 OmLZm i n., 0 ° C, 101.3 kPa) of argon gas is allowed to flow into the tetrachlorosilane gas container and evaporate. The resulting gas was further diluted by flowing 200 SCCM of argon gas through the dilution gas control valve 7.

As a result, the concentration of carbon tetrachloride gas charged into the reactor is 13.9% by volume. The amount of supply of tetrachlorosilane per minute is 0.431 g, which is 0.0025 mol. Therefore, the number of moles of chlorosilane supplied is 0.27% with respect to the number of moles of aluminum.

The gas was allowed to flow for 16 hours and 30 minutes, and then cooled to recover a 14 g sample. When the sample was dissolved in hydrochloric acid and the silicon weight in the sample was determined, it was found to be 82% by weight. The weight of silicon obtained for the input aluminum is

46%.

In addition, impurity concentration of dissolved and extracted silicon was measured by GDSMS analysis. Fe 0.88 ppm, Cu 0.41 ppm, Mg 0.3 ppm, B

It was 0.05 ppm and P 0.667 ppm.

Impurity elements contained in silicon can be further reduced by unidirectionally solidifying the obtained silicon.

This silicon is considered suitable as a raw material for solar cells. Example 2 An alumina protective tube containing aluminum (SSA-S, No.9 (inner diameter Φ 16) manufactured by Nikato) is held in an alumina container and held in a vertical annular furnace, 1273K (the melting point of aluminum) 1.36 times the same), and tetrachloromethane gas was introduced into the molten aluminum for 5 hours to react. The same aluminum and tetrachlorosilane as in Example 1 were used. The weight of aluminum was 12 g (0.44 mol).

In order to perform gas bubbling, the distance between the tip of the gas inlet pipe [Nichikato SSA-S, (outer diameter Φ 6, inner diameter 4)] and the bottom of the alumina protective tube was 5 mm.

The transfer of silicon tetrachloride was carried out as a carrier gas by supplying argon gas (manufactured by Japan AG) (purity 99.9 995%) at 0. IMP a.

In the carbon tetrachloride gas container, 104SCCM (flow rate 104 mLZmin, 0 ° C, 101.3 kPa) of argon gas is allowed to flow as the carrier gas, and the gas obtained by evaporation is directly used as the carrier. It was introduced into the reactor along with the gas. The supply of silicon tetrachloride per minute is 0.595 g, which is 3.5X 10-3 moles. Therefore, the moles of silicon tetrachloride supplied is 0.8% of the moles of aluminum.

The stainless steel container containing silicon tetrachloride is held in a thermostatic chamber of 318 K, and the vapor pressure of silicon tetrachloride at the same temperature is 50 OmmHg (66.6 kPa). The concentration of the gas is 66% by volume.

Upon cooling, a 8.27 g sample was collected. The sample was dissolved in hydrochloric acid and the silicon weight in the sample was determined to be 61% by weight. Therefore, the weight of silicon obtained for the input albumin is 42%.

Impurity elements contained in silicon can be further reduced by unidirectionally solidifying the obtained silicon. In addition, after a predetermined amount of reaction, the temperature is cooled to, for example, 1073 K, and silicon is deposited and taken out at a specific site. If the same weight of aluminum as recon is added and kept at 1273 K, further addition of silicon tetrachloride will increase the silicon concentration to 61%. By repeating this operation, silicon can be obtained continuously. The obtained silicon is considered suitable as a raw material for solar cells.

The results of the example are shown in FIG. While maintaining the temperature of the molten metal at 1.03 times or more and less than 1.79 times the melting point represented by the absolute temperature of the metal and below the melting point of silicon, the supply moles of chlorosilane per minute By making it less than 1.0 percent with respect to the number of moles, the silicon yield is considered to be greater than 40% by weight with respect to the metal weight. Comparative Example 1

The same experiment as in Example 1 was performed, except that the reaction temperature was 1673 K (1.79 times the melting point of aluminum).

After flowing gas for 16 hours and 30 minutes, the alumina container was opened by cooling, but the sample disappeared and did not remain. High temperature may cause the formation of silicon dichloride. Comparative Example 2

The same experiment as in Example 1 was performed, except that the reaction temperature was 683 K (1.02 times the melting point of aluminum).

The gas was allowed to flow for 16 hours and 30 minutes, and then cooled to recover a 24 g sample. The sample was dissolved in hydrochloric acid, and the silicon weight% in the sample was determined to be 0.5% by weight. Comparative Example 3

The weight of aluminum is 6.0 g (0.22 mol), and argon is 334 SCCM (flow rate 334 mL / min, 0 ° C, 101.3 kPa) as the carrier gas in the tetrachlorosilane gas container. The gas obtained by flowing and evaporating the gas was introduced into the reactor together with the carrier gas. The supply amount of silicon tetrachloride per minute is 1.912 g, which is 0.011 mol. Therefore, the number of moles of silicon tetrachloride supplied is 5% of the number of moles of aluminum. Hydrogen tetrachloride gas was introduced into the molten aluminum for 2 hours to react. Other than that, the examination was performed in the same manner as in Example 2.

Upon cooling, a 3.71 g sample was collected. The sample was dissolved in hydrochloric acid and the silicon weight in the sample was determined to be 50% by weight. Therefore, the weight of silicon obtained for the input albumin is 31%. Comparative Example 4

The weight of aluminum is 6.0 g (0.22 mol), and argon is 174 S CCM (flow rate 174 mL Zm i n., 0 ° C, 101.3 kPa) as the carrier gas in the tetrachlorosilane gas container. The gas obtained by flowing and evaporating the gas was introduced into the reactor together with the carrier gas as it was. Supply amount tetrachloride Kei containing per minute is 0. 996 g, a 5. 9Χ 10- ³ moles. (The number of moles of silicon tetrachloride supplied is 2.7% of the number of moles of aluminum.) Carbon tetrachloride gas was introduced into molten aluminum for 2 hours to react. Other than that, the examination was performed in the same manner as in Example 2.

On cooling, a 4.14 g sample was collected. The sample was dissolved in hydrochloric acid and the silicon weight in the sample was determined to be 49% by weight. Therefore, Industrial applicability

According to the production method of the present invention, polycrystalline silicon can be produced with high yield.

Claims

The scope of the claims

1. A metal chloride has a lower free energy of formation than silicon and a metal melting point lower than that of silicon.

_{_{S i H n C l 4.}} N (1)

(In the formula, η represents an integer of 0 to 3.)

A method for producing silicon by reacting with a gaseous chlorosilane represented by the above, wherein when the gaseous chlorosilane is blown into the molten metal, the melting point of the temperature of the molten metal is expressed by the absolute temperature of the metal. 1.0 3 times or more and less than 1.7 9 times, and kept below the melting point of silicon, and the number of moles of chlorosilane supplied per minute is less than 1.0 percent of the number of moles of metal. A method for producing polycrystalline silicon.

2. a process for producing polycrystalline silicon comprising steps (i) and (i i),

(0 The step of obtaining silicon by reacting a metal having a free energy of formation of metal chloride lower than that of silicon and having a metal melting point lower than that of silicon with gaseous chlorosilane represented by the above formula (1),

(i i) a step of directionally solidifying the obtained silicon,

In step (i), when gaseous chlorosilane is blown into the molten metal, the temperature of the molten metal is not less than 1.03 times and less than 1.79 times the melting point of the metal expressed in absolute temperature, Keep the temperature below the melting point of silicon and supply less than 1.0 percent moles of chlorosilane per minute with respect to the number of moles of metal.

3. The method according to [1] or [2], wherein the gas blown into the metal is chlorosilane alone or a mixed gas of chlorosilane and inert gas.

4. The concentration of chlorosilane in the gas blown into the metal is 10% by volume or more [3] The method described.

5. The method according to any one of [1] to [4], wherein the metal is at least one selected from the group consisting of potassium, cesium, rubidium, strontium, lithium, sodium, magnesium, aluminum, zinc and manganese. .

6. The method according to any one of [1] to [5] above, wherein the metal is aluminum.

7. The method according to any one of [1] to [6], wherein the chlorosilane is at least one selected from the group consisting of silicon tetrachloride, trichlorosilane, dichlorosilane, and monochlorosilane.

8. The method according to any one of [1] to [7], wherein boron and phosphorus contained in chlorosilane and metal are each less than 1 ppm.

9. A solar cell containing polycrystalline silicon obtained by the method according to any one of [1] to [8].