JP4660715B2 - Si purification method, Si purification apparatus, and Si purification film production apparatus - Google Patents

Description

  The present invention uses, for example, atmospheric pressure hydrogen plasma, and removes impurities (especially boron (B)) contained in low-purity Si such as metal grade Si with high efficiency to purify high-purity Si. The present invention relates to a purification method, a Si purification apparatus, and a Si purification film manufacturing apparatus.

  With the recent interest in energy and environmental issues, the solar cell market is experiencing explosive growth worldwide. In 2015, global solar cell production is going to reach 6 GW (gigawatts) annually, and bulk silicon (Si) (hereinafter “silicon (Si)”), which is currently mainstream, is simply referred to as “Si”. .) If solar cells occupy the mainstream of solar cell products in 2015, about 60 kton of solar cell grade Si (SOG-Si: Solar grade Si) raw material is required per year. In addition, solar cell grade Si means Si which has the purity which satisfies the quality of a solar cell.

  Against this background, various efforts have been made to save resources and reduce costs of solar cells. In particular, the thin-film Si solar cell can greatly reduce the high value-added Si raw material to be used, and therefore has great expectations as a device that replaces bulk Si that is currently mainstream.

  However, the crystalline Si thin film has a very small light absorption coefficient. Therefore, when the photocurrent related to the conversion efficiency is increased, the film structure is inevitably thickened or the surface structure aimed at the light confinement effect is intentionally used. However, conversion efficiency equivalent to that of bulk Si solar cells has not been obtained yet, and there are many problems. In addition, plasma CVD (Chemical Vapor Deposition), which is a general method for forming a thin film for solar cells, requires only about 20% of purified source gas that requires a lot of energy and time. There is a problem that it cannot contribute to the formation of a thin film.

  Here, the production amount of high-purity Si raw material in 2007 is about 7 kton including the LSI (Large Scale Integrated circuit) grade, so the raw material of solar cell grade Si of 60 kton in 2015 You can see how big the consumption is.

  While the demand for solar cell grade Si is increasing and the price of solar cell grade Si is screaming as the demand for solar cell increases at this stage, maintaining the production of 10 times more solar cell grade Si It can be said that this is a major issue for the popularization of low prices.

  Originally, solar cell grade Si is manufactured by refining metal grade Si (MG-Si: Metallurgical Grade Si). Metal grade Si refers to Si containing impurities at a level that does not reach the level of solar cell grade Si. Specifically, metal grade Si has an impurity concentration of 1000 ppmwt or more, and solar cell grade Si has an impurity concentration of 1 ppmwt or less.

  This raw material, metal grade Si, maintains imports of 242 kton annually from countries with low power costs, such as China and Brazil, and the material supply stability is a major concern in the span of 5 years. It is thought that there is not. Therefore, if these inexpensive metal-grade Si can be refined at low cost, it can be said that a solution to the tight supply of raw materials for solar cell-grade Si can be obtained.

In view of such circumstances, various efforts have been made with the aim of producing inexpensive bulk Si solar cell raw materials, and various applications have been made. Basically, iron (Fe), aluminum (Al), titanium ( Metallurgical methods and acid cleaning are performed on metals such as Ti), tungsten (W), and chromium (Cr), and oxygen (O), phosphorus (P), arsenic (As), calcium (Ca), etc. Evaporation removal is adopted. On the other hand, carbon (C), boron (B), and the like are exposed to an oxidizing atmosphere (water vapor, oxidized slag, oxidized plasma), so that carbon dioxide (CO ₂ ), which is an oxide having a high vapor pressure, is oxidized. It is modified and removed to carbon (CO), boric anhydride (B ₂ O ₃ ) or the like.

  As described above, in producing solar cell grade Si from metal grade Si, a multi-step impurity removal process is essential at present. Of these, boron (B) is an element that is very difficult to remove from metallic grade Si. That is, since boron (B) has a small segregation coefficient at the solid-liquid interface, it cannot be removed by a solidification method, and it cannot be removed by an evaporation method because its vapor pressure is very low. Moreover, when it remains in Si, it has a big influence on an electrical property, Furthermore, it forms the cause of deteriorating a solar cell characteristic by forming the boron (B) complex with the oxygen in Si.

  In boron (B) removal by an oxidation method that has been reported in the past, generally, boron (B) that can be removed in one purification step is about ½, and the same process is repeated in multiple stages. Therefore, the present situation is that Si having a target boron (B) concentration is produced.

  In contrast, as disclosed in Patent Document 1, the present inventors have adopted an impurity removal method that employs a hydrogenation reaction between atmospheric-pressure hydrogen plasma and metal grade Si, rather than an oxidation method. A film manufacturing method, a purified film manufacturing method and an apparatus using atmospheric pressure hydrogen plasma are proposed.

  In this film manufacturing method, as shown in FIG. 12, a hydrogenation reaction between atmospheric hydrogen plasma and metal grade Si is used. Specifically, one upper electrode 101 is water-cooled and a Si target 102 made of metal-grade Si is mounted, the other lower electrode 103 is heated and an arbitrary substrate 104 is mounted, and an atmospheric pressure is interposed between them. When the hydrogen plasma is generated, Si is vaporized as a hydride from the Si target 102 on the low temperature side, and Si can be deposited on the high temperature side substrate 104 using the Si hydride as a raw material. .

  That is, in this film manufacturing method, when metal grade Si is exposed to atmospheric pressure hydrogen plasma, metal impurities such as iron (Fe), aluminum (Al), titanium (Ti), tungsten (W), chromium (Cr), etc. Since it does not volatilize even when hydrogenated by atmospheric hydrogen plasma, it utilizes the phenomenon that it tends to remain on the surface of the metal grade Si.

And by this method, it became possible to reduce boron (B) to 1/10 per process by examining various conditions about boron (B) which is the most difficult to remove. ing.
International Publication No. WO2007 / 049402 (published on May 3, 2007) Japanese Patent Laid-Open No. 4-275914 (published on October 1, 1992) Japanese Patent Laid-Open No. 5-279008 (released on October 26, 1993)

  However, even in the film manufacturing method and apparatus using atmospheric pressure hydrogen plasma described in the above-mentioned conventional patent document 1, the above process must be repeated in multiple stages when general metal grade Si is used. For example, there is a problem that the Si deposited on the substrate 104 cannot be at the level of solar cell grade Si.

For example, in Patent Document 2 and Patent Document 3, in order to remove B ₂ H ₆ from SiH ₄ gas, a treatment agent mainly composed of a mixture of copper oxide and zinc oxide is used. Specifically, B ₂ H ₆ is adsorbed and removed after first being adsorbed and saturated with SiH ₄ .

  In this regard, since the technique of Patent Document 1 is efficient, it is possible to reduce the number of repetitions in multiple stages as compared with the conventional technique. However, if the process does not go through at least two stages, the solar cell There is a problem that it cannot be reduced to a desired boron (B) concentration in grade Si.

  The present invention has been made in view of the above-described conventional problems, and its purpose is to efficiently purify low-purity Si to high-purity Si, for example, to produce solar-grade Si from metal-grade Si. An object of the present invention is to provide a Si purification method, a Si purification apparatus, and a Si purification film production apparatus.

  In order to solve the above-described problems, the Si purification method of the present invention chemically reacts low-purity Si as a raw material with atomic hydrogen to obtain a hydrogenated gas composed of an element to be removed and a hydrogenated gas composed of Si. A step of generating a hydrogenated gas population including the temperature of the hydrogenated gas population within a range not less than the decomposition temperature of the hydrogenated gas composed of the element to be removed and not more than the decomposition temperature of the hydrogenated gas composed of Si. A step of causing the element to be removed to adhere to the surface of the heated object by removing it from the hydrogenated gas population by colliding with the surface of the heated object to obtain high purity Si having a purity higher than that of the low purity Si. It is characterized by including.

  In order to solve the above-described problems, the Si purification apparatus of the present invention chemically reacts low-purity Si as a raw material with atomic hydrogen to obtain a hydrogenated gas composed of an element to be removed and a hydrogenated gas composed of Si. Hydrogen gas population generating means for generating a hydrogen gas population including the hydrogen gas population generation means, and the hydrogen gas population above the decomposition temperature of the hydrogen gas consisting of the element to be removed and below the decomposition temperature of the hydrogen gas consisting of Si Impurity hydrogen gas removal means for fixing an element to be removed to the surface of the heated object by removing it from the hydrogenated gas population by colliding with the surface of the heated object whose temperature is controlled within a range of It is a feature.

  According to the above invention, a low-purity Si as a raw material is chemically reacted with atomic hydrogen to generate a hydrogenated gas population including a hydrogenated gas composed of an element to be removed and a hydrogenated gas composed of Si. .

That is, by chemically reacting low purity Si as a raw material with atomic hydrogen, a hydrogenated gas population in which hydrogenated gases such as SiH ₄ and B ₂ H ₆ are mixed is generated. At this time, for example, metals such as iron (Fe), aluminum (Al), titanium (Ti), tungsten (W), and chromium (Cr) do not volatilize even when hydrogenated by chemical reaction with atomic hydrogen. Therefore, it remains on the surface of the low-purity Si as a raw material and does not come out from the low-purity Si.

Here, SiH _4, and the hydrogenation gas population became mixed state such as B ₂ H _6, to collect only the high purity Si is a hydrogenated gas consisting of elements to be removed B ₂ H ₆ It is necessary to remove the hydrogenated gas.

  Therefore, in the present invention, the hydrogenated gas population collides with the surface of a heated object whose temperature is controlled within a range that is higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and lower than the decomposition temperature of the hydrogenated gas composed of Si. Thus, the element to be removed is fixed to the surface of the heated object and removed from the hydrogenated gas population.

In other words, in the present invention, the element to be removed is removed from the hydrogenated gas population by utilizing the difference in thermal decomposition temperatures exhibited by various hydrogenated gases. That is, in the present invention, for example, in order to remove hydrogen gas other than SiH ₄ from a hydrogen gas population in a mixed state such as SiH ₄ and B ₂ H ₆ , the temperature dependence of the thermal decomposition reaction Is actively used.

  As a result, conventionally, for example, boron (B) contained in low-purity Si could be removed only from 1/2 to 1/10 in a single step. In the process, for example, boron (B) contained in low-purity Si can be removed to 1/1000 or less.

  Therefore, for example, in order to produce solar cell grade Si from metal grade Si, it is possible to provide an Si purification method and an Si purification apparatus that can efficiently purify from low purity Si to high purity Si.

  In the Si purification method of the present invention, the low purity Si is preferably metal grade Si.

  In the Si purification apparatus of the present invention, the low purity Si is preferably metal grade Si.

  Thereby, for example, solar cell grade Si having an impurity concentration of 1 ppmwt or less can be efficiently produced from inexpensive metal grade Si having an impurity concentration of 1000 ppmwt or more.

In the Si purification method of the present invention, it is preferable that the hydrogenation gas composed of the element to be removed is B ₂ H ₆ and the hydrogenation gas composed of Si is SiH ₄ .

In the Si purification apparatus of the present invention, it is preferable that the hydrogenation gas composed of the element to be removed is B ₂ H ₆ and the hydrogenation gas composed of Si is SiH ₄ .

  Thereby, since there exists a difference in thermal decomposition temperature among various hydrogenation gases contained in the hydrogenation gas population, it is possible to specifically form solar cell grade Si.

  In the Si purification method of the present invention, it is preferable that the temperature-controlled heating object is made of a porous body. In addition, it is preferable to use an insulator, a metal, or a semimetal for a porous body, for example.

  In the Si purification apparatus of the present invention, it is preferable that the temperature-controlled heating object is made of a porous body. In addition, it is more preferable that the heating object to be temperature controlled is made of a conductive porous body.

  As a result, the hydrogenation gas consisting of the element to be removed and the hydrogenation gas consisting of Si pass through the inside of the porous body having a large specific surface area, so that the number of collisions with the solid surface can be sufficiently secured in a small volume. can do. In addition, when the heating object is a conductive porous body, it can be heated directly by energization and the porous body itself can be used as a heating element, and the temperature can be kept constant with high accuracy even in the inside. . Therefore, the temperature of the hydrogenated gas population can be controlled easily and accurately within a range that is equal to or higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and equal to or lower than the decomposition temperature of the hydrogenated gas composed of Si. Can be made compact.

  In the Si purification method of the present invention, the porous body is preferably made of a carbon porous body.

  In the Si purification apparatus of the present invention, the porous body is preferably made of a carbon porous body.

  Thereby, since the carbon porous body has electrical conductivity, it is easy to adjust the temperature as a heated object by directly applying a voltage to the carbon porous body.

  In addition, since the carbon porous body does not have a catalytic action on the decomposition of the hydrogenated gas composed of Si and has high chemical resistance, even when an element to be removed adheres to the carbon porous body, Playback processing is possible.

  In the Si purification method of the present invention, it is preferable that the temperature-controlled heating object is made of piping.

  In the Si purification apparatus of the present invention, it is preferable that the temperature-controlled heating object is a pipe.

  That is, when the porous body is not used as the heating object, it is not easy to efficiently contact the heating object with the mixture of the hydrogenation gas composed of the element to be removed and the hydrogenation gas composed of Si. In this case, since the solid surface area with respect to the gas passage channel volume can be increased by using the piping as the heating object, the number of collisions can be maintained, so that the apparatus volume can be made compact.

  Further, in the Si purification method of the present invention, it is preferable to control the temperature by directly heating the porous body with electricity by using a conductive substance as the porous body.

  In the Si purification apparatus of the present invention, it is preferable that the porous body is made of a conductive material and provided with temperature control means for controlling the temperature by energizing and heating the porous body.

  Thereby, since the porous body has electrical conductivity, it is easy to adjust the temperature as a heated object by directly applying a voltage to the porous body.

  In addition, in the Si purification method of the present invention, by using an electromagnetic wave absorbing material as the porous body, it is possible to control the temperature using a heating action by electromagnetic wave absorption.

  This method also makes it possible to easily and accurately control the temperature of the hydrogenated gas population within a range that is higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and lower than the decomposition temperature of the hydrogenated gas composed of Si. It becomes.

  Moreover, in the Si purification method of the present invention, it is preferable to use a chemical solution with hydrofluoric acid as a method for regenerating the clogging of the element attached to the porous body to be removed.

  Thereby, even when the element to be removed is fixed to the carbon porous body, the regenerating process can be easily performed by using the chemical solution with hydrofluoric acid.

  In the Si purification method of the present invention, it is preferable that the porous body has a filter function for trapping fine particles contained in the hydrogenated gas population.

  That is, when a low-purity Si as a raw material is chemically reacted with atomic hydrogen to generate a hydrogenated gas population including a hydrogenated gas composed of an element to be removed and a hydrogenated gas composed of Si, it is removed. In addition to the hydrogenated gas composed of the element desired and the hydrogenated gas composed of Si, fine particles such as metal and silicon aggregates may be contained.

  In this regard, in the present invention, since the porous body has a filter function for trapping fine particles contained in the hydrogenated gas population, by adjusting the pore diameter of the porous body, a desired size can be obtained. The fine particles can be removed by the porous body.

  In the Si purification method of the present invention, it is preferable to use plasma generated in an atmosphere containing hydrogen and having a total pressure of 10 to 1520 Torr as the method for generating atomic hydrogen.

  In the Si purification apparatus of the present invention, it is preferable that the hydrogenated gas population generation means includes a plasma means for generating plasma.

  Thereby, a hydrogen gas population can be easily generated.

  Further, in the Si purification method of the present invention, as a method for generating the atomic hydrogen, a heated medium is installed in an atmosphere containing hydrogen at a total pressure of 10 to 1520 Torr, and a catalytic decomposition reaction generated on the surface of the medium is utilized. It is possible to generate atomic hydrogen.

  That is, in the present invention, the method for generating atomic hydrogen is not limited to the method using plasma, and catalytic decomposition that occurs on the surface of the medium is performed by installing a heated medium in an atmosphere containing hydrogen and having a total pressure of 10 to 1520 Torr. It is also possible to generate atomic hydrogen using a reaction.

  In the Si purification method of the present invention, it is preferable that the temperature of the heated object is 150 ° C. to 650 ° C.

  In this way, the temperature of the hydrogenated gas population can be specifically controlled in a range that is not less than the decomposition temperature of the hydrogenated gas composed of the element to be removed and not more than the decomposition temperature of the hydrogenated gas composed of Si.

  In the Si purification method of the present invention, it is preferable to adjust the amount of the element to be removed fixed to the surface of the heated object by controlling the temperature of the heated object.

  In the Si purification apparatus of the present invention, it is preferable that the porous body is made of a conductive material and provided with temperature control means for controlling the temperature by energizing and heating the porous body.

  This makes it possible to control the temperature of the hydrogenated gas population within a range that is higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and lower than the decomposition temperature of the hydrogenated gas composed of Si, and facilitates the reaction rate. Can be adjusted.

  In the Si purification method of the present invention, it is preferable that after removing the element to be removed from the hydrogenated gas population, the hydrogenated gas comprising Si is decomposed and attached to the substrate to form solid Si.

  In order to solve the above-mentioned problem, the Si purified film manufacturing apparatus of the present invention is a Si purified film manufacturing apparatus equipped with the Si purification apparatus described above, after the element to be removed is removed from the hydrogenated gas population. And a Si film forming means for decomposing and adhering the hydrogenated gas composed of Si to the substrate to form solid Si.

Thus, for example, a high purity Si film such as a solar cell grade Si raw material can be formed by depositing Si using high purity SiH ₄ purified from low purity Si such as metal grade Si. it can.

  In the Si purified film manufacturing apparatus of the present invention, it is preferable that the apparatus includes a circulating unit that returns the hydrogen gas discharged from the Si film forming unit to the inlet side of the hydrogenated gas population generating unit.

  As a result, the hydrogen gas discharged from the Si film forming means is returned to the inlet side of the hydrogenated gas population generating means by the circulating means, so that the hydrogenated gas population generating means converts the hydrogen gas into atomic form. Can be reused for hydrogen.

  As described above, the Si purification method of the present invention includes a hydrogenation gas comprising an element to be removed and a hydrogenation gas comprising Si by chemically reacting low-purity Si as a raw material with atomic hydrogen. A step of generating a gas population, and heating the hydrogenated gas population to a temperature that is higher than a decomposition temperature of a hydrogenated gas composed of an element to be removed and lower than a decomposition temperature of a hydrogenated gas composed of Si And a step of fixing the element to be removed to the heated object surface by colliding with the object surface and removing it from the hydrogenated gas population to obtain high purity Si having a purity higher than that of the low purity Si. is there.

  As described above, the Si purification apparatus of the present invention includes a hydrogenation gas comprising an element to be removed and a hydrogenation gas comprising Si by chemically reacting low-purity Si as a raw material with atomic hydrogen. Hydrogen gas population generating means for generating a gas population and a range in which the hydrogen gas population is equal to or higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and equal to or lower than the decomposition temperature of the hydrogenated gas composed of Si. Impurity hydrogenated gas removing means for fixing the element to be removed to the surface of the heated object and removing it from the hydrogenated gas population by making it collide with the temperature-controlled heated object surface.

  As described above, the Si purified film manufacturing apparatus of the present invention is a Si purified film manufacturing apparatus including the Si purifying apparatus described above, and the Si after the element to be removed is removed from the hydrogenated gas population. And a Si film forming means for forming solid Si by decomposing and adhering a hydrogenation gas comprising

  Therefore, there is an effect of providing an Si purification method, an Si purification apparatus, and an Si purified film manufacturing apparatus that can efficiently purify from low purity Si to high purity Si.

[Embodiment 1]
An embodiment of the present invention will be described with reference to FIGS. 1 to 8 as follows.

  The silicon (Si) refining method described in the present embodiment is a solar cell grade by removing impurities such as boron (B) contained in metal grade Si (MG-Si: Metallurgical Grade Si) with high efficiency. This is a method for purifying silicon (Si) (hereinafter simply referred to as “Si”), which is reduced to the boron (B) concentration of Si (SOG-Si: Solar grade Si). Metal grade Si refers to Si having an impurity concentration of 1000 ppmwt or more. Solar cell grade Si refers to Si having an impurity concentration of 1 ppmwt or less.

  First, the principle of the Si purification method of the present embodiment will be described.

  In order to purify metal-grade Si with higher efficiency, what is important is a hydrogenation reaction between atmospheric hydrogen plasma and metal-grade Si. In the Si purification method of the present embodiment, when metal grade Si is exposed to atmospheric pressure hydrogen plasma, iron (Fe), aluminum (Al), titanium (Ti), tungsten (W), chromium (Cr), etc. Since metal impurities do not volatilize even when hydrogenated by atmospheric pressure hydrogen plasma, the fact that they easily remain on the surface of metal grade Si is utilized.

When the metal grade Si is exposed to atmospheric pressure hydrogen plasma, silicon (Si) constituting the metal grade Si is a silane (SiH ₄ ) (hereinafter simply referred to as “SiH ₄ ”) hydride. At the same time, boron (B) is vaporized as a hydride of diborane (B ₂ H ₆ ) (hereinafter simply referred to as “B ₂ H ₆ ”) with a probability different from that of Si. To do.

Here, it can be seen that the activation energies in the decomposition reaction of SiH ₄ and B ₂ H ₆ are 2 eV and 1.11 eV, respectively, and the activation energy of B ₂ H ₆ is about 0.9 eV lower. This means that B ₂ H ₆ is easily decomposed at a lower temperature. For example, consider a case where a mixed gas of SiH ₄ and B ₂ H ₆ is in contact with the surface of a substance kept at a certain temperature.

First, as shown in FIG. 1A, if the temperature of the material surface is sufficiently low, both SiH ₄ and B ₂ H ₆ are re-scattered from the material surface without being decomposed. On the other hand, as shown in FIG. 1B, when the temperature of the material surface is very high, both SiH ₄ and B ₂ H ₆ are decomposed and fixed on the material surface. Then, neither SiH ₄ nor B ₂ H ₆ is contained in the gas after contacting the object. Therefore, by utilizing the fact that SiH ₄ and B ₂ H ₆ have different decomposition activation energies, the object surface temperature is set to a temperature in a region where SiH ₄ is not significantly decomposed and B ₂ H ₆ is efficiently decomposed. Set. In this case, in the SiH ₄ and B ₂ H ₆ mixed gas that has reached a certain mixing ratio, B ₂ H ₆ is easily decomposed and fixed as compared with SiH ₄ .

Therefore, in the mixed gas after Solid surface collision, as shown in FIG. 1 (c), the ratio of SiH ₄ is increased. Here, the fixation rate constant r at which one molecule is fixed to the solid surface by the thermal decomposition reaction is given by the following Arrhenius equation (1).

r = A · exp (−Ea / k · T) (1)
However, A is a frequency factor, T is an absolute temperature, and k is a Boltzmann constant.

  By substituting the activation energy of each gas listed above into this equation, the fixing rate constant r at each temperature was determined, and the ratio of the rate constants was calculated, so that quantitative estimation was performed.

  Strictly speaking, the coefficient A is a function of temperature. However, since the coefficient A shows only a very gradual change compared to the change of the exponential function term, it is assumed to be constant here.

When Ax of each gas is given as ASiH ₄ and AB ₂ H ₆ ,
AB ₂ H ₆ = (200, 1, 0.2, 0.0002) × ASiH ₄
It calculated in four ways. Here, ASiH ₄ = 1 is set for standardization. The results are shown in FIG.

  As shown in FIG. 2, it can be seen that when the temperature of the object surface becomes low, the ratio of the fixing rate constant r, which is the reaction rate (hereinafter simply referred to as “reaction rate ratio”), increases significantly.

In a general thermal CVD experiment, the thermal decomposition and fixing phenomenon of SiH ₄ becomes prominent at a temperature of 550 ° C. or higher, but at a temperature of 550 ° C., the reaction rate ratio between SiH ₄ and B ₂ H ₆ is when having the same frequency factor, 100,000 times or more, B ₂ H ₆ it can be seen that easily decomposes secured. Further, as shown in FIG. _2, also the frequency factor of B 2 _{H 6} becomes 1/5000 of SiH _4, 100 times or _more, B 2 _{H 6} is fixed to a solid surface easily. This is because thermal decomposition of B ₂ H ₆ is likely to occur, and by bringing a mixed gas of SiH ₄ and B ₂ H ₆ into contact with an object surface appropriately set as a temperature at which SiH ₄ does not substantially decompose, B ₂ H ₆ Since only adheres to the solid surface at a selection ratio of 100 times or more, the SiH ₄ concentration in the mixed gas relatively increases.

This phenomenon is nothing but the removal of boron (B) component from the mixed gas, that is, the purification of SiH ₄ , and the removal of boron (B) hydride in the gas by the technique utilizing fixation by such thermal decomposition. Is possible.

  Therefore, by applying this principle to a hydrogenated mixed gas containing silicon (Si) and boron (B) generated by exposing metal grade Si to atmospheric pressure hydrogen plasma, boron (B) in the gas is obtained. Concentration can be dramatically reduced.

  If the Si film is formed by a general film forming method such as thermal CVD using the mixed gas in which boron (B) is dramatically reduced, the initial boron (B) concentration in the metal grade Si is reduced. Thus, Si having an extremely reduced boron (B) concentration can be formed. In other words, metal removal from metal grade Si (selectivity of hydrogenation reaction) and boron (B) removal (selectivity of thermal decomposition reaction) are possible.

  In order to demonstrate the boron (B) removal effect based on the above principle, a verification experiment using the Si purifying apparatus 10 shown in FIG. 3 was conducted, which will be described below.

  As shown in FIG. 3, the Si purification apparatus 10 includes, for example, a vacuum chamber 1 having a volume of 400 L, a mass flow controller 2 that controls the flow rate of each gas, and a sintering that generates plasma and supplies gas into the plasma. Porous carbon electrode 3 made of glassy carbon, gas supply chamber 4 for supplying gas to porous carbon electrode 3, substrate heater 6 on which Si substrate 5 is placed, and matching for supplying electric power It consists of a box 7 and a power source 8 for plasma. In the present embodiment, a Si (001) substrate is used as the substrate.

In the Si purification apparatus 10, first, the substrate temperature is 570 ° C., the power density is 40 W / cm ² , the SiH ₄ flow rate is constant at 35 sccm, and the B ₂ H ₆ flow rate is 0.01, 0.03, 0.1 sccm. The Si film was manufactured by plasma decomposition. Here, the thickness of the porous carbon electrode 3 was 5 mm. The porous carbon electrode 3 is heated by radiant heat when the Si substrate 5 is heated to 570 ° C. and by heat from the generated plasma. The distance between the Si substrate 5 and the surface of the porous carbon electrode 3, that is, the gap in which plasma is generated is 0.7 mm.

  The boron (B) concentration in the Si film produced by atmospheric pressure plasma CVD using the source gas that has passed through such a heated porous body is measured by SIMS (Secondary Ion-microprobe Mass Spectrometer). did. The produced Si film was single crystallized. Therefore, the ratio (Γfilm = (CB / CSi)) of the boron (B) atomic number density in the Si film to the atomic number density of crystalline silicon (Si) is calculated, and the raw material gas before passing through the porous body is calculated. The ratio of the number of boron (B) atoms to the number of Si atoms contained in (Γgas = (CB / CSi)) was also calculated, and the relationship between Γgas and Γfilm was examined. The result is shown in FIG.

  As shown in FIG. 4, it can be seen that Γgas and Γfilm have a linear relationship. The fitted straight line is also shown in the figure.

Here, the slope of the straight line obtained by the fitting was 0.001. This is because the ratio of boron (B) in the produced film is compared to the ratio of boron (B) to Si contained in the gas by forming a film using the gas that has passed through the porous body. It shows that it becomes 1/1000. That is, since the gas component containing the boron (B) element is removed by passing the raw material gas through the porous body, the boron (B) concentration is significantly reduced from the boron (B) concentration of the supplied raw material gas. This shows that a Si film can be formed. Also. As described above, since Γgas and Γfilm show a good linear relationship in any Γgas, even when the initial boron concentration in the supply gas is reduced below this condition,
Γfilm = 1/1000 × Γgas
From the relational expression, it can be seen that the concentration of boron (B) in the film can be reduced.

Therefore, in order to investigate what physical phenomenon this proportionality factor 1/1000 is determined, the SiH ₄ flow rate is 35 sccm, the B ₂ H ₆ flow rate is 0.1 sccm, and the input power density is constant at 40 W / cm ^2. The substrate temperature was changed to 370 ° C., 470 ° C., and 570 ° C., and the change in the slope of the linear function indicated by Γfilm and Γgas was examined. The result is shown in FIG. FIG. 5 is represented by an Arrhenius plot.

  As can be seen from FIG. 5, the slope determined by Γfilm / Γgas decreases exponentially with increasing temperature. When the substrate temperature was 570 ° C., it was about 1/1000, when it was 470 ° C., about 1/300, and when it was 370 ° C., it was about 1/10.

This is because the substrate temperature is raised, that is, the temperature of the porous body is raised, so that the B ₂ H ₆ gas is decomposed and fixed with a higher probability, and the incorporation of boron (B) into the Si film is suppressed. It shows that it is made. This is none other than the fact that Si with higher purity could be produced from a B ₂ H ₆ and SiH ₄ mixed gas using a heated porous body. Therefore, in order to identify the main cause of this B ₂ H ₆ removal phenomenon, the activation energy of the boron (B) removal phenomenon was calculated from the slope of the Arrhenius plot obtained in FIG. As a result, about 1.04 ± 0.009 eV was obtained. This value is very close to the above-described decomposition activation energy of B ₂ H ₆ of 1.11 eV in the error range. This indicates that the observed boron (B) removal phenomenon is dominated by the thermal decomposition of B ₂ H ₆ .

  From the above examination results, it can be said that the effectiveness of the impurity removal method using the difference in the thermal decomposition behavior of various hydrogenation gases described in the explanation of the principle described above has been proved.

Based on the principle proposed in the present embodiment, by using the Si purification apparatus 10, only SiH ₄ is preferentially extracted from a hydrogenated mixed gas such as B ₂ H ₆ and SiH ₄ to produce high-purity solid Si. It became clear that we could do it.

Here, in order to increase the removal rate of B ₂ H ₆ using the principle of the Si purification method of the present embodiment, it is preferable to increase the contact probability between B ₂ H ₆ and the solid surface. In order to satisfy this condition, in practice, for example, as shown in FIG. 6, a mixed gas is passed through a long pipe 11 to increase the surface area, or as shown in FIG. A method of passing through the heated porous body 12 is conceivable.

In particular, the porous body 12 is considered optimal because it can secure a large surface area with a small volume. For example, if the surface reaction probabilities due to collisions with the porous body surface of AH ₃ and BH ₄ per time are x and y, and the respective initial concentrations are C _A0 and C _B0 , the porous body is Z times of collisions. When the gas collides with the inner wall of the internal microhole constituting 12 and the gas passes through the porous body 12, the concentrations C _A and C _B after passing are respectively
C _A = C _A0 (1-x) ^z
C _B = C _B0 (1-y) ^z
Can be described.

The above expression means that when x ≠ y, the density ratio between the density C _A and the density C _B after passing can be amplified by the number of times of collision Z (exponential amplification).

Therefore, when the gas concentration ratio C _A / C _B after N collisions is taken, it is as shown in FIG. Here, the initial density was C _A0 = C _B0 .

As shown in FIG. 8, the dependence of the concentration ratio on the number of collisions is very sensitive to the reaction probability of the element A, and even if the reaction probability of the gas containing the element B fluctuates by about 1 to 2 digits, there is not much influence. . Further, as shown in FIG. 8, the reaction probability of the element A is sufficiently high (about 10% in FIG. 8) in order to increase the concentration ratio of the concentration C _{B to} the concentration C _A with a relatively low collision probability. It can be seen that the temperature needs to be set. When the reaction probability of the gas related to the element A is 10%, even if the reaction probability of the gas related to the element B is 1/100 of that of the element A, the element of the element B is repeated by repeating collisions only 50 times. It can be seen that the concentration ratio to A can be increased up to 100 times.

As a result, it can be seen that B ₂ H ₆ can be removed from the mixed gas of SiH ₄ and B ₂ H ₆ by utilizing the difference in temperature dependence of the thermal decomposition behavior.

Thus, the Si purification method of the present embodiment is a method of collecting only SiH ₄ from a hydrogenated mixed gas such as SiH ₄ and B ₂ H ₆ . More specifically, B ₂ H ₆ is decomposed and fixed using temperature dependence, SiH ₄ is allowed to pass through without being decomposed, and B ₂ H ₆ is removed from the gas. A gas contact part appropriately controlled in temperature is provided in the path of the SiH ₄ gas containing the gas B ₂ H _6, and the contact part for the decomposition and fixation reaction of the gas molecules is in the form of an intended long pipe or porous body. Is used.

  This makes it possible to easily remove boron (B) contained in metal-grade Si to 1/1000 or less in just one step, using this method for a mixture of hydrogenated gases made from metal-grade Si. can do.

Here, in the conventional method (oxidation removal method), it is about 1/2 at most in one step, and it can be seen that this method has a purification capacity of 500 times or more when compared with this value. Moreover, the boron (B) removal capability by this method works effectively also to the mixed gas of the hydrogenation gas produced | generated by the general Siemens method etc. Furthermore, if metal grade Si is used for the hydrogenated mixed gas produced from the raw material by, for example, APECT method (Atmospheric-pressure Plasma Enhanced Chemical Transport), the metal grade Si is similarly used. Boron (B) and metal elements can be removed. This is because not only can the boron (B) removal in the solar cell grade Si manufacturing process, which was not easy in the past, be made easy by using the APECT method and this method together, but also refinement and manufacturing through the Siemens method and the like. This means that a high-purity Si film can be produced without using SiH ₄ . That is, since it is possible to produce a solar cell grade Si bulk substrate and a thin film Si using inexpensive metal grade Si as a raw material, the solar cell manufacturing field has an advantage that does not depend on the supply of Si raw materials.

In the present embodiment, a porous body that can be controlled by heating is used for the boron removing device in order to efficiently generate a thermal decomposition reaction. The porous body is preferably a carbon sintered body from the viewpoint that it has no catalytic action against SiH ₄ decomposition, high chemical resistance, and electrical conductivity.

  By using a porous body made of the above material, not only temperature adjustment by electric heating is possible, but also regeneration processing with a chemical solution or the like is possible when the porous body is clogged with a removal substance.

  Furthermore, the porous body plays a major role in removing particles, that is, fine particles generated in the hydrogenation process of metal grade Si, in addition to the role of removing unnecessary hydrides. Such a pyrolytic porous filter with a filter function used in the present embodiment is, for example, sintered glassy carbon spheres having a diameter of about 80 μm, a gas passage thickness of 5 mm, and a porosity of about 30%. Can be. However, the present invention is not necessarily limited to this, and the combination of these numerical values may be appropriately changed under actual operation conditions. However, if the porosity is reduced, the pressure loss due to the porous material will increase, the frequency of clogging will increase, and the regeneration time during the regeneration process is expected to be long. Porosity is not desirable. From the above viewpoint, it can be said that the porosity is preferably about 5% to 70%.

Further, although depending on the decomposition temperature of the hydride to be removed, the temperature of the thermal decomposition type porous filter is a temperature at which decomposition of SiH ₄ becomes remarkable under the condition of a particle size of 80 μm and a porosity of 30%. 650 ° C. or lower is desirable. Further, when removing B ₂ H ₆ mixed in the hydrogenated gas population, it is necessary to set the temperature to 150 ° C. or higher. In the above temperature range, when the pyrolytic porous filter is set to a temperature close to the upper limit temperature, it is necessary to shorten the length of the porous body through which the gas passes. This is because an increase in the length of the porous body also hinders the passage of SiH ₄ to be purified. On the other hand, when the temperature is set close to the lower limit temperature, it is necessary to ensure a long porous body.

In the present invention, if there is a difference in thermal decomposition reaction temperature with SiH ₄ , the technique is not limited to B ₂ H ₆ .

  In addition, the hydrogenation method of metal grade Si is not limited to the one using plasma (for example, use of atomic hydrogen by a high-temperature metal heater), but a remarkable region (10 Torr or more) in which the gas exhibits viscous flow properties. It is desirable to operate in

Furthermore, conventional, in the manufacture of a typical high purity SiH _4, although the production of SiH ₄ by disproportionation reaction using SiHCl ₃ as the starting material takes place, in this case, requires a large cost to reprocess SiCl ₄ is generated as a reaction byproduct. On the other hand, according to the Si purification method of the present embodiment, SiH ₄ can be directly produced, so that the problem of the by-product treatment can be avoided. In other words, it is an environmentally conscious process.

As described above, in the Si purification method of the present embodiment, for example, hydrogenated gases such as SiH ₄ and B ₂ H ₆ are mixed by reacting metallic grade Si as a raw material with atomic hydrogen. The resulting hydrogen gas population is generated. At this time, for example, metals such as iron (Fe), aluminum (Al), titanium (Ti), tungsten (W), and chromium (Cr) do not volatilize even when hydrogenated by chemical reaction with atomic hydrogen. Therefore, it remains on the surface of the metal grade Si as a raw material and does not come out from the metal grade Si.

Here, from SiH _4, and hydrogenation gas population became mixed state such as _B 2 _{H 6,} in order to collect only the solar-grade Si consists boron (B) to be removed of the _B 2 _{H 6} It is necessary to remove the hydrogenation gas.

Therefore, in this embodiment, the hydrogenation gas population is equal to or higher than the decomposition temperature of the hydrogenation gas B ₂ H ₆ made of boron (B), which is the element to be removed, and the decomposition temperature of the hydrogenation gas SiH ₄ made of Si. The boron (B) to be removed is fixed to the surface of the heated object by colliding with the surface of the porous carbon electrode 3, the pipe 11 or the porous body 12, which is a heated object whose temperature is controlled in the following range. Remove from the chemical gas population.

That is, in this embodiment, boron (B) to be removed is removed from the hydrogenated gas population by utilizing the difference in thermal decomposition temperatures exhibited by various hydrogenated gases. That is, in this embodiment, for example, in order to remove the hydrogenated gas of B ₂ H ₆ from a hydrogenated gas population in a mixed state such as SiH ₄ and B ₂ H ₆ , a thermal decomposition reaction is performed. We are actively using temperature dependence.

As a result, conventionally, for example, boron (B) contained in low-purity Si could be removed only up to 1/2 to 1/10 in one step, but in the present embodiment, In one step, for example, boron (B) contained in low-purity Si can be removed to 1/1000 or less. In this way, B ₂ H ₆ contained in the hydrogenation gas population can be particularly efficiently removed.

  Therefore, for example, in order to efficiently purify solar cell grade Si from metal grade Si, it is possible to provide a Si purification method and Si purification apparatus 10 that can efficiently purify from low purity Si to high purity Si. That is, it is possible to purify solar cell grade Si from metal grade Si without requiring any chemical solution, high temperature melting treatment, and oxidizing atmosphere.

  Further, in the Si purification method and the Si purification apparatus 10 of the present embodiment, the low purity Si is preferably metal grade Si.

  Thereby, for example, solar cell grade Si having an impurity concentration of 1 ppmwt or less can be efficiently produced from inexpensive metal grade Si having an impurity concentration of 1000 ppmwt or more.

Further, in the Si purification method and the Si purification apparatus 10 of the present embodiment, after removing boron (B) to be removed from the hydrogenated gas population, the hydrogenated gas SiH ₄ made of Si is decomposed and attached to the Si substrate 5. Thus, it is preferable to form solid Si.

Thereby, for example, a film of high purity Si such as solar cell grade Si can be formed by depositing Si using high purity SiH ₄ purified from low purity Si such as metal grade Si. .

Further, in the Si purification method and the Si purification apparatus 10 of the present embodiment, it is preferable that the hydrogenated gas composed of boron (B) to be removed is B ₂ H ₆ and the hydrogenated gas composed of Si is SiH _4. .

  Thereby, since the difference in thermal decomposition temperature exists in various hydrogenation gas contained in a hydrogenation gas population, a solar cell grade Si raw material can be specifically formed.

  In the Si purification method and the Si purification apparatus 10 of the present embodiment, the temperature-controlled heating object is preferably composed of the porous body 12. In addition, the porous body 12 can use an insulator, a metal, or a semimetal, for example.

As a result, the hydrogenated gas B ₂ H ₆ made of boron (B) to be removed and the hydrogenated gas SiH ₄ made of Si pass through the inside of the porous body 12, so that the temperature is kept constant with high accuracy. Can be kept in. Accordingly, the hydrogenated gas population is easily and accurately within a range that is higher than the decomposition temperature of the hydrogenated gas B ₂ H ₆ made of boron (B) to be removed and lower than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si. The temperature can be controlled.

  Moreover, in the Si purification method and the Si purification apparatus 10 of the present embodiment, the porous body 12 is preferably made of a carbon porous body such as the porous carbon electrode 3.

  Thereby, since the carbon porous body has electrical conductivity, it is easy to adjust the temperature as a heated object by directly applying a voltage to the carbon porous body.

Further, since the carbon porous body has no catalytic action on the decomposition of the hydrogenated gas SiH ₄ made of Si and has high chemical resistance, the boron (B) to be removed is fixed to the carbon porous body. Also, the regeneration process with a chemical solution or the like becomes possible.

  Further, in the Si purification method and the Si purification apparatus 10 of the present embodiment, the heated object whose temperature is controlled can be assumed to be composed of the pipe 11.

That is, when a porous body is not used as the heating object, a mixture of the hydrogenated gas B ₂ H ₆ made of boron (B) and the hydrogenated gas SiH ₄ made of Si to be removed is efficiently brought into contact with the heated object. It is not easy. In this case, since the solid surface area with respect to the gas passage channel volume can be increased by using the pipe 11 as the heating object, a large number of collisions can be maintained, so that the apparatus volume can be made compact.

  Further, in the Si purification method of the present embodiment, it is preferable to control the temperature by directly energizing and heating the porous body 12 by using a conductive material as the porous body.

  Further, in the Si purification apparatus 10 of the present embodiment, the porous body is composed of the porous carbon electrode 3 which is a conductive substance, and as temperature control means for controlling the temperature by energizing and heating the porous body. A plasma power source 8 is provided.

  Thereby, since the porous body has electrical conductivity, it is easy to adjust the temperature as a heated object by directly applying a voltage to the porous body.

  In addition, in the Si purification method of the present embodiment, by using an electromagnetic wave absorbing material ranging from radio waves to ultraviolet rays as the porous body, it is possible to control the temperature using the heating action by electromagnetic wave absorption.

Also by this method, the hydrogenated gas population is easily within a range that is higher than the decomposition temperature of the hydrogenated gas B ₂ H ₆ made of boron (B) to be removed and lower than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si. In addition, temperature control can be performed with high accuracy.

  In addition, in the Si purification method of the present embodiment, a chemical solution using hydrofluoric acid can be used as a method for regenerating clogging of elements attached to the porous body to be removed.

  Thereby, even when boron (B) to be removed adheres to the carbon porous body, the regenerating process can be easily performed by using the chemical solution of hydrofluoric acid.

  In the Si purification method of the present embodiment, the porous body preferably has a filter function for trapping fine particles contained in the hydrogenated gas population.

That is, a hydrogenated gas mother containing a hydrogenated gas B ₂ H ₆ made of boron (B) and a hydrogenated gas SiH ₄ made of Si to be removed by chemically reacting metal grade Si as a raw material with atomic hydrogen. In the case of generating a group, in addition to the hydrogenated gas B ₂ H ₆ made of boron (B) to be removed and the hydrogenated gas SiH ₄ made of Si, fine particles such as metals and silicon aggregates may be contained. .

  In this respect, the present embodiment has a filter function for trapping fine particles contained in the hydrogenated gas population of the porous body. Therefore, by adjusting the pore diameter of the porous body, a desired size can be obtained. Fine particles such as metal and silicon aggregates can also be removed by the porous body.

  In the Si purification method of the present embodiment, it is preferable to use generated plasma in an atmosphere containing hydrogen at a total pressure of 10 to 1520 Torr as a method for generating atomic hydrogen.

  Furthermore, in the Si purification apparatus 10 of the present embodiment, it is preferable that the hydrogen gas population generating means includes a plasma power source 8 as plasma means for generating plasma.

  Thereby, a hydrogen gas population can be easily generated.

  Further, in the Si purification method of the present embodiment, as a method for generating atomic hydrogen, a heated medium (not shown) is placed in an atmosphere containing hydrogen at a total pressure of 10 to 1520 Torr, and a catalytic decomposition reaction that occurs on the surface of the medium is performed. It can be used to generate atomic hydrogen.

  That is, in the present embodiment, the method for generating atomic hydrogen is not limited to a method using plasma, and a catalyst that is generated on the surface of the medium by installing a heated medium in an atmosphere containing hydrogen and having a total pressure of 10 to 1520 Torr. It is also possible to generate atomic hydrogen using a decomposition reaction.

  Further, in the Si purification method of the present embodiment, it is preferable that the temperature of the heated object is 150 ° C. to 650 ° C.

Thus, specifically, a range in which the hydrogenation gas population is equal to or higher than the decomposition temperature of the hydrogenated gas B ₂ H ₆ made of boron (B) and lower than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si to be removed. The temperature can be controlled.

  In the Si purification method of the present embodiment, the amount of the element to be removed fixed on the surface of the heated object can be adjusted by controlling the temperature of the heated object.

  Furthermore, in the Si purification apparatus 10 of the present embodiment, the porous body is composed of the porous carbon electrode 3 that is a conductive substance, and temperature control means for controlling the temperature by energizing and heating the porous body is provided. It is preferable that

  This makes it possible to control the temperature of the hydrogenated gas population within a range that is higher than the decomposition temperature of the hydrogenated gas composed of the element to be removed and lower than the decomposition temperature of the hydrogenated gas composed of Si, and facilitates the reaction rate. Can be adjusted.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIG. The configurations other than those described in the present embodiment are the same as those in the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and explanation thereof is omitted.

  As shown in FIG. 9, the Si purification apparatus 20 of the present embodiment has a low-purity Si 22 installed on a water-cooled electrode 21 cooled by means such as water, and hydrogen between the grounded porous electrode. Plasma is generated. That is, the Si purification apparatus 20 is different from the Si purification apparatus 10 of the first embodiment in that low-purity Si22 is used.

  Specifically, as shown in FIG. 9, the Si purification apparatus 20 includes, for example, a water-cooled electrode 21 that can be cooled by installing low-purity Si 22 such as metal grade Si, and a grounded impurity removing porous body 23. A gas suction negative pressure chamber 24 for sucking gas with a pump (not shown) through the impurity removing porous body 23, a thermocouple 25 for controlling the temperature of the impurity removing porous body 23, and the porous body temperature. A conditioning power supply 26 and a gas supply system 27 for supplying hydrogen at a constant flow rate are provided.

  A general method may be used to generate plasma in the Si purification apparatus 20. For example, a direct current method may be used, a high frequency method via a matching box 7 or a microwave method may be used.

  In addition, the cooling method of the water-cooled electrode 21 is not limited to water, but water is preferable from an economical viewpoint. The water cooling temperature is, for example, 0 to 40 ° C.

In the Si purification apparatus 20 of the present embodiment, as shown in FIG. 9, plasma is generated between the impurity removing porous body 23 and the low-purity Si 22, and the gas generated by hydrogenation from the low-purity Si 22 is generated. Suction is performed through the porous body 23 for removing impurities. At this time, the temperature of the impurity removing porous body 23 is set to a temperature at which thermal decomposition of the hydride composed of the element to be removed becomes remarkable. Specifically, for example, when SiH ₄ and B ₂ H ₆ are contained in the generated hydrogenated gas, the temperature is set to, for example, 150 ° C. to 650 ° C., which is a temperature at which B ₂ H ₆ is easily decomposed. .

In Si purifying apparatus 20 of the present embodiment, the B ₂ H ₆ concentration in the gas flowing into the gas suction negative pressure chamber 24 is a considerably reduced state compared to the B ₂ H ₆ concentration in the plasma. Since the gas flowing into the gas suction negative pressure chamber 24 contains a large amount of Si hydride gas SiH ₄ , film formation is performed using the gas after passing through the impurity removing porous body 23. For example, it is possible to form a Si film having a significantly reduced boron (B) concentration compared to the boron (B) concentration of low-purity Si22 used in the initial stage.

  In addition, when plasma is generated at a high pressure of 50 Torr or more, the mean free path of atoms, molecules, and ions is significantly reduced, so that the kinetic energy of ions generated in the plasma is reduced. . As a result, the physical sputtering phenomenon is suppressed, and the hydrogenation and vaporization reaction between hydrogen and raw material silicon becomes remarkable. From the element selectivity of this hydrogenation reaction, the metal contained in the low purity Si22 is left behind in the low purity Si. In this way, since it is removed from the hydrogenation gas mixture, it is possible to form a Si film in which not only boron (B) but also other metal impurity concentrations are reduced. That is, metals such as iron (Fe), aluminum (Al), titanium (Ti), tungsten (W), and chromium (Cr), which are metals contained in low-purity Si22, chemically react with atomic hydrogen. Since it does not volatilize even when hydrogenated, it remains on the surface of low-purity Si as a raw material and does not come out from the low-purity Si22.

As described above, in the Si purification method and the Si purification apparatus 20 of the present embodiment, the temperature of the heated object is set to 150 ° C. to 650 ° C. Thus, specifically, a range in which the hydrogenation gas population is equal to or higher than the decomposition temperature of the hydrogenated gas B ₂ H ₆ made of boron (B) and lower than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si to be removed. The temperature can be controlled.

  Further, in the Si purification method of the present embodiment, the amount of boron (B) to be removed fixed on the heated object surface can be adjusted by controlling the temperature of the impurity removing porous body 23 as the heated object. It can be done.

  That is, in the Si purification apparatus 20 of the present embodiment, the porous body is made of the impurity removing porous body 23 that is a conductive substance, and the temperature control means for controlling the temperature by energizing and heating the porous body. As a porous body temperature control power source 26 is provided.

As a result, the temperature of the hydrogenated gas population is controlled in a range that is equal to or higher than the decomposition temperature of the hydrogenated gas B ₂ H ₆ made of boron (B) to be removed and lower than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si. And the reaction rate can be easily adjusted.

  That is, by adopting a method of adjusting the amount of boron (B) to be removed to be fixed to the heated object surface by controlling the temperature of the porous body 23 for removing impurities as the heated object in this way, It becomes possible to arbitrarily control the boron (B) concentration of solid Si formed by decomposing and adhering to the top. Here, boron (B) is also an important dopant element in forming p-type silicon.

[Embodiment 3]
The following will describe still another embodiment of the present invention with reference to FIG. The configurations other than those described in the present embodiment are the same as those in the first embodiment and the second embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiment 1 and Embodiment 2 are given the same reference numerals, and explanation thereof is omitted.

  As shown in FIG. 10, the Si purification apparatus 30 of the present embodiment is configured such that the porous body for removing impurities does not directly contact the plasma.

  That is, as shown in FIG. 10, the Si refining device 30 includes water-cooled electrodes 31 and 31 cooled by water or the like on both the electrode side and the ground side, and low-purity Si 32 and 32 respectively installed on the electrode side and the ground side. A gas supply system 33 capable of supplying hydrogen at a constant flow rate, an impurity removing porous body 34 for removing impurities, and a porous body temperature adjusting power source 35.

  In the Si purification apparatus 30 having the above-described configuration, a general technique may be used to generate plasma, as in the Si purification apparatus 20 shown in FIG. 9 of the second embodiment.

In the Si purification apparatus 30, as shown in FIG. 10, for example, a hydrogenated mixed gas generated from low-purity Si 32 such as metal grade Si is heated on the downstream side, and is a porous body 34 for removing impurities. By passing through, B ₂ H ₆ contained in the gas can be removed. If a film is formed using the gas after passing through the porous body 34 for removing impurities, Si having a higher purity than that of the low-purity Si 32 used can be produced.

  Here, the gas used in the present embodiment does not need to be pure hydrogen gas, and can be implemented using a mixture with an inert rare gas mainly composed of hydrogen. As the rare gas, for example, helium (He), neon (Ne), or argon (Ar) can be used.

[Embodiment 4]
The following will describe still another embodiment of the present invention with reference to FIG. The configurations other than those described in the present embodiment are the same as those in the first to third embodiments. For convenience of explanation, members having the same functions as those shown in the drawings of Embodiments 1 to 3 are given the same reference numerals, and descriptions thereof are omitted.

As shown in FIG. 11, the Si refined film manufacturing apparatus 40 of the present embodiment uses the Si refinement apparatuses 10, 20, and 30 shown in the first to third embodiments and is desired to be removed. Si as a Si film forming means for forming solid Si by decomposing and adhering SiH ₄ , which is a hydrogenated gas composed of Si, after removing boron (B) as an element from the hydrogenated gas population to Si substrate 5. A film forming unit 43 is provided.

  Moreover, in the Si refined film manufacturing apparatus 40 of this Embodiment, in order to save the usage-amount of hydrogen gas, as shown in FIG. 11, the circulation refinement | purification system is comprised.

That is, as shown in FIG. 11, the Si refined film manufacturing apparatus 40 according to the present embodiment removes the hydrogenated gas generator 41 and B ₂ H ₆ that generate a hydrogenated gas from low-purity Si 32 such as metal grade Si. For example, a porous part 42, a Si film forming part 43, and a circulation pump 44.

In the Si refined film manufacturing apparatus 40, the hydrogen gas generated from the low-purity Si 32 once removes impurities such as B ₂ H ₆ in the porous part 42 and then the Si film forming part 43 installed in the subsequent stage. SiH ₄ is decomposed by heat or the like to produce a high-purity Si film. In this case, since the composition of the gas after passing through the film forming region is substantially only hydrogen, the circulation pump 44 circulates and supplies the hydrogen gas again to the inlet side of the hydrogenated gas generator 41. This makes it possible to purify the Si film without wasting hydrogen (H) permanently.

Thus, in the Si purification method of the present embodiment, boron (B), which is an element to be removed, is removed from the hydrogenated gas population, and then the hydrogenated gas SiH ₄ made of Si is decomposed and attached to the Si substrate 5. Thus, solid Si is formed.

Further, the Si refined film manufacturing apparatus 40 of the present embodiment chemically reacts low-purity Si as a raw material with atomic hydrogen, thereby hydrogenating gas B ₂ H ₆ made of boron (B), which is an element to be removed. And hydrogen gas generating section 41 as a hydrogen gas population generating means for generating a hydrogen gas population including a hydrogen gas SiH ₄ made of Si, and boron (B) to be removed from the hydrogen gas population The surface and pores of the porous body 34 for removing impurities as a heated object whose temperature is controlled in a range of not less than the decomposition temperature of the hydrogenated gas B ₂ H _{6 made} of and not more than the decomposition temperature of the hydrogenated gas SiH ₄ made of Si Impurity hydrogen gas removing means for removing boron (B) to be removed from the hydrogen gas population by fixing the boron (B) to be removed to the surface of the impurity removing porous body 34 and the inner surface of the hole by colliding with the inner surface. The porous portion 42 of Te, the hydrogenation gas SiH ₄ consisting of Si after boron (B) to be removed is removed from the hydrogenated gas population by decomposition adhere to the Si substrate 5, Si formed to form a solid Si A Si film forming unit 43 is provided as a film means.

  Therefore, for example, in order to efficiently purify solar cell grade Si from metal grade Si, it is possible to provide a Si purification method and Si refined film manufacturing apparatus 40 capable of efficiently purifying from low purity Si32 to high purity Si. it can.

  That is, by using the Si purification method and the Si purified film manufacturing apparatus 40 of the present embodiment, it is possible to purify solar cell grade Si from metal grade Si without requiring any chemical solution, high temperature melting treatment, and oxidizing atmosphere. It becomes possible.

  Further, the Si purified film manufacturing apparatus 40 according to the present embodiment includes a circulation pump 44 as a circulation means for returning the hydrogen gas discharged from the Si film forming unit 43 to the entrance side of the hydrogenated gas generation unit 41. .

  As a result, the hydrogen gas discharged from the Si film forming unit 43 is returned to the entrance side of the hydrogenated gas generating unit 41 by the circulation pump 44. Therefore, the hydrogenated gas generating unit 41 converts the hydrogen gas into atomic hydrogen. Can be reused for.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Such embodiments are also included in the technical scope of the present invention.

  The present invention uses, for example, atmospheric pressure hydrogen plasma, and removes impurities (especially boron (B)) contained in low-purity Si such as metal grade Si with high efficiency to purify high-purity Si. The present invention can be applied to a purification method, a Si purification apparatus, and a Si purification film manufacturing apparatus.

(A), (b), (c) shows one embodiment of the Si purification method in the present invention, and is a diagram showing the temperature of the material surface and the decomposition state of SiH ₄ and B ₂ H ₆ . . It is a graph which shows the relationship between the temperature of an object surface, and reaction rate ratio. It is a block diagram which shows the structure of the Si refinement | purification apparatus for verifying the said Si refinement | purification method. Ratio of boron (B) atom number density in Si film to atom number density of crystalline silicon (Si) (Γfilm = (CB / CSi)) and Si atoms contained in source gas before passing through porous body It is a graph which shows the relationship with the ratio (Γgas = (CB / CSi)) of the number of boron (B) atoms to the number. It is a graph which shows the temperature dependence of the ratio of the said Γfilm and Γgas. It is a perspective view which shows the structure in the case of using piping as a heating object by which the temperature control in the said Si refinement | purification apparatus was carried out. It is sectional drawing which shows a structure in the case of using a porous body as a heating object by which the temperature control in the said Si refinement | purification apparatus was carried out. It is a graph which shows the solid surface collision frequency dependence of gas concentration ratio. The other embodiment of Si refinement | purification apparatus in this invention is shown, and it is sectional drawing which shows the structure of Si refinement | purification apparatus. The further another embodiment of Si refinement | purification apparatus in this invention is shown, and it is sectional drawing which shows the structure of Si refinement | purification apparatus. FIG. 14 is a sectional view showing still another embodiment of the present invention and showing a configuration of a Si purified film manufacturing apparatus. It is sectional drawing which shows the structure of the conventional Si refinement | purification film manufacturing apparatus.

Explanation of symbols

1 Vacuum chamber 3 Porous carbon electrode (heating object, porous body, carbon porous body)
5 Si substrate (substrate)
8 Power supply for plasma (plasma means)
10 Si purification equipment 11 Piping (Heating object)
12 Porous body (Heating object)
20 Si refiner 22 Low purity Si (metal grade Si)
23 Porous material for removing impurities (heating object, porous material)
25 Thermocouple (Temperature control means)
26 Power source for temperature control of porous body (temperature control means)
30 Si refiner 32 Low purity Si (metal grade Si)
33 Gas supply system 34 Porous body for removing impurities 35 Power source for temperature control of porous body (temperature control means)
40 Si refined film production apparatus 41 Hydrogenation gas generation part (hydrogenation gas population generation means)
42 Porous part (impurity hydrogen gas removal means)
43 Si film forming part (Si film forming means)
44 Circulation pump (circulation means)

Claims (25)

Generating a hydrogenated gas population including a hydrogenated gas composed of an element to be removed and a hydrogenated gas composed of Si by chemically reacting low-purity Si as a raw material with atomic hydrogen;
The hydrogenated gas population is removed by colliding with the surface of a heated object whose temperature is controlled to be within the range of the decomposition temperature of the hydrogenation gas composed of the element to be removed and the decomposition temperature of the hydrogenation gas composed of Si or less. And a step of fixing a desired element on the surface of the heated object and removing it from the hydrogenation gas population to obtain high purity Si having a purity higher than that of the low purity Si.   2. The Si purification method according to claim 1, wherein the low purity Si is metal grade Si.   3. The Si purification method according to claim 1, wherein the element to be removed is removed from the hydrogenation gas population, and then the hydrogenation gas comprising Si is decomposed and attached to a substrate to form solid Si. . The Si purification method according to claim 1, 2 or 3, wherein the hydrogenation gas composed of the element to be removed is B ₂ H ₆ and the hydrogenation gas composed of Si is SiH ₄ .   The Si purification method according to any one of claims 1 to 4, wherein the temperature-controlled heating object is made of a porous body.   The Si purification method according to claim 5, wherein the porous body is made of a carbon porous body.   The Si purification method according to any one of claims 1 to 4, wherein the temperature-controlled heating object is made of piping. The Si purification method according to claim 5 or 6, wherein the temperature is controlled by directly energizing and heating the porous body by using a conductive substance as the porous body. The method for purifying Si according to claim 5 or 6, wherein an electromagnetic wave absorbing substance is used as the porous body, and the temperature is controlled using a heating action by electromagnetic wave absorption.   The Si purification method according to claim 6, wherein a chemical solution using hydrofluoric acid is used as a method for regenerating clogging of an element to be removed attached to the porous body.   The Si purification method according to claim 6, wherein the porous body has a filter function of trapping fine particles contained in the hydrogenated gas population.   The Si purification method according to any one of claims 1 to 11, wherein plasma generated in an atmosphere containing hydrogen and having a total pressure of 10 to 1520 Torr is used as the method for generating atomic hydrogen.   The method for producing atomic hydrogen is characterized in that a heated medium is placed in an atmosphere containing hydrogen at a total pressure of 10 to 1520 Torr, and atomic hydrogen is generated using a catalytic decomposition reaction generated on the surface of the medium. The Si purification method according to any one of claims 1 to 11.   The temperature of the said heating object shall be 150 degreeC-650 degreeC, The Si refinement | purification method of any one of Claims 1-13 characterized by the above-mentioned. Wherein by controlling the temperature of the heating object, Si purifying method according to any one of claims 1 to 14, characterized in that adjusting the amount to be fixed to the heating surface of the object element to be removed. Hydrogen gas population generating means for generating a hydrogen gas population including a hydrogen gas consisting of an element to be removed and a hydrogen gas consisting of Si by chemically reacting low purity Si as a raw material with atomic hydrogen When,
The hydrogenated gas population is removed by colliding with the surface of a heated object whose temperature is controlled to be within the range of the decomposition temperature of the hydrogenation gas composed of the element to be removed and the decomposition temperature of the hydrogenation gas composed of Si or less. An Si refining apparatus, comprising: an impurity hydrogenated gas removing means for fixing an element desired to be heated to the surface of the heated object and removing the element from the hydrogenated gas population.   17. The Si purifier according to claim 16, wherein the low purity Si is metal grade Si. 18. The Si purifier according to claim 16, wherein the hydrogenated gas composed of an element to be removed is B ₂ H ₆ and the hydrogenated gas composed of Si is SiH ₄ .   The Si purifier according to claim 16, 17 or 18, wherein the temperature-controlled heating object is made of a porous material.   The Si purifier according to claim 19, wherein the porous body is made of a carbon porous body.   The Si purifier according to claim 16, 17 or 18, wherein the temperature-controlled heating object is a pipe. The porous body is made of a conductive material,
21. The Si purifier according to claim 19 or 20, further comprising temperature control means for controlling the temperature by energizing and heating the porous body.   The Si purification apparatus according to any one of claims 16 to 22, wherein the hydrogen gas population generating means includes plasma means for generating plasma. A Si refined film manufacturing apparatus comprising the Si refiner according to any one of claims 16 to 23,
Si purification means comprising Si film forming means for forming a solid Si by decomposing and adhering the hydrogenated gas comprising Si after removing the element to be removed from the hydrogenated gas population. Membrane manufacturing equipment.   25. The Si refined film manufacturing apparatus according to claim 24, further comprising a circulating means for returning the hydrogen gas discharged from the Si film forming means to the inlet side of the hydrogenated gas population generating means.

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