JP2008024526A - Method for forming silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming silicon by which an environmental load can be sufficiently reduced without requiring the use of combustible gas and toxic gas, and the silicon can efficiently be formed with a sufficiently reduced energy without applying high heat. <P>SOLUTION: In the method for forming the silicon, a silicon-containing material containing silicon of 30 to 99.9 atomic% and a reducing metallic element of 0.1 to 50 atomic% is irradiated with laser light having a wavelength of 192 to 1,064 nm, a pulse width of 100 nanoseconds to 10 femtoseconds and an irradiation intensity of 10<SP>8</SP>to 10<SP>15</SP>W/cm<SP>2</SP>in a vacuum atmosphere under the oxygen partial pressure of ≤10<SP>-2</SP>Pa, so as to obtain silicon. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for forming silicon.

  At present, polycrystalline silicon solar cells are mainly used as solar cells. Such silicon for solar cells has been provided mainly by the reuse of non-standard products for semiconductor silicon used in large-scale integrated circuits. For this reason, there is a concern that the silicon for solar cells will be insufficient in the future when solar cells are widely used at the current pace. In order to solve such a problem, a method for producing a silicon for solar cells by purifying low-purity silicon (hereinafter simply referred to as “metal silicon”) whose production amount is larger than that of semiconductor silicon. Has been studied.

  For example, in Japanese Patent Laid-Open No. 11-60228 (Patent Document 1), silicon tetrachloride, which is a silicon raw material, is reduced with molten zinc collected by distilling and condensing zinc gas to recover polycrystalline silicon. Is described. In Japanese Patent Laid-Open No. 10-287413 (Patent Document 2), gasified chlorinated silicon is used as a raw material, and unconsumed chlorinated silicon is recovered from exhaust gas. A silicon forming method is described in which polycrystalline silicon is manufactured by CVD or the like while being recycled by being charged. Furthermore, in JP-A-11-49508 (Patent Document 3), a step of reacting metal silicon, hydrogen and silicon tetrachloride to produce a reaction product containing trichlorosilane, and distilling the reaction product into distillation. And a method for forming silicon, which includes a step of separating purified trichlorosilane and purified silicon tetrachloride and a step of reacting the purified trichlorosilane with hydrogen to produce high-purity silicon.

However, in the method for forming silicon as described in Patent Documents 1 to 3, since a temperature of about 1500 ° C. to 2000 ° C. is necessary to produce metallic silicon, a great deal of energy is required for producing metallic silicon. (Refer to Fumio Shimura, “Semiconductor Silicon Crystal Optics”, published by Maruzen, 1993, page 16 (Non-patent Document 1)). In addition, the silicon forming methods described in Patent Documents 1 to 3 have a problem that the environmental load is large because a flammable gas such as hydrogen or a toxic gas such as silicon tetrachloride is used.
Japanese Patent Laid-Open No. 11-60228 JP-A-10-287413 Japanese Patent Laid-Open No. 11-49508 Fumio Shimura, “Semiconductor Silicon Crystal Optics”, Maruzen, 1993, 16 pages

  The present invention has been made in view of the above-described problems of the prior art, and it is not necessary to use a flammable gas or a toxic gas, so that it is possible to sufficiently reduce the environmental load, and it is not necessary to apply high heat. It is an object of the present invention to provide a method for forming silicon, which can sufficiently reduce energy and can efficiently form silicon.

As a result of intensive studies to achieve the above object, the inventors of the present invention have applied a specific silicon-containing raw material to a wavelength of 192 to 1064 nm and a pulse width of 100 nanometers in a vacuum atmosphere having an oxygen partial pressure of 10 ⁻² Pa or less. By irradiating a laser beam with a second to 10 femtoseconds and an irradiation intensity of 10 ⁸ to 10 ¹⁵ W / cm ² to obtain silicon, it is not necessary to use a flammable gas or a toxic gas, thereby sufficiently reducing the environmental load. As a result, the inventors have found that the energy to be input can be sufficiently reduced without applying high heat and silicon can be formed efficiently, and the present invention has been completed.

That is, the silicon forming method of the present invention is applied to a silicon-containing material containing 30 to 99.9 atomic% of silicon and 0.1 to 50 atomic% of a reducing metal element at a pressure of 10 ⁻² Pa or less. In a vacuum atmosphere, silicon is obtained by irradiating a laser beam having a wavelength of 192 to 1064 nm, a pulse width of 100 nanoseconds to 10 femtoseconds, and an irradiation intensity of 10 ⁸ to 10 ¹⁵ W / cm ² .

  In the silicon forming method of the present invention, the Gibbs free energy change value for producing the oxide of the reducing metal element is greater than the Gibbs free energy change value for producing the silicon oxide. A small value is preferred.

  In the silicon formation method of the present invention, it is preferable that the silicon-containing material is irradiated with the laser light in an atmosphere in which reducing metal atoms are scattered.

In the method for forming silicon of the present invention, a step of covering at least a part of the outer surface of the silicon-containing material with a reducing metal layer,
Irradiating the reducing metal layer with the laser light in the vacuum atmosphere to scatter the reducing metal atoms in advance;
It is preferable that it is further included.

  In addition, the silicon formation method of the present invention may further include a step of irradiating a target made of a reducing metal element with a laser beam to scatter the reducing metal atoms in advance.

  The reason why the above object is achieved by the silicon formation method of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, when a material containing silicon is irradiated with laser light as described above, the material is first decomposed, and silicon atoms and other atoms or molecules other than silicon constituting the material are scattered. In the case where the substrate is used as a recovery device for recovering scattered silicon atoms, the scattered silicon atoms collide with oxygen molecules before reaching the substrate. It becomes a silicon molecule (hereinafter, the silicon monoxide molecule and the silicon dioxide molecule are collectively referred to as “silicon oxide molecule”). Further, even if silicon atoms can reach the substrate for recovering them, silicon and oxygen molecules collide with each other on the substrate to become silicon oxide molecules. Therefore, silicon cannot be formed efficiently even if a method of simply irradiating laser light is employed.

Therefore, in the present invention, first, such laser irradiation is performed in a vacuum atmosphere having an oxygen partial pressure of 10 ⁻² Pa or less, thereby reducing the abundance of oxygen molecules and suppressing the generation of silicon oxide molecules. However, even under such a vacuum atmosphere, the number of oxygen molecules corresponding to the pressure exists, and thus generation of silicon oxide molecules cannot be sufficiently suppressed. Therefore, in the present invention, in addition to irradiating laser light in the vacuum atmosphere as described above, generation of silicon oxide molecules is sufficiently suppressed by using a silicon-containing material further containing a reducing metal element. To do. That is, when a silicon-containing material is irradiated with laser light, reducing metal atoms are scattered in addition to silicon. Such a reducible metal element is more easily oxidized than silicon (for example, a value of change in Gibbs free energy (ΔG ₁ : negative value) for generating an oxide of the reducible metal element is silicon). A value (ΔG ₁ <ΔG ₂ ) that is smaller than the value of change in Gibbs free energy (ΔG ₂ : negative value) for producing the oxide is preferably used. Therefore, even when a silicon oxide molecule is generated by collision between a silicon atom and an oxygen molecule, the oxygen atom is more stably bonded to the reducing metal atom than the silicon atom, and the silicon oxide molecule and the reduced oxygen molecule are reduced. When contact is made with the reducible metal atom, the silicon oxide molecules are reduced to silicon atoms, and the reducible metal is oxidized to become oxides. Alternatively, the reducing metal atom can be bonded to the oxygen molecule and the number of oxygen molecules in contact with the silicon atom can be reduced. Since generation of silicon oxide molecules can be sufficiently suppressed in this way, in the present invention, silicon atoms can efficiently reach the substrate, and silicon can be obtained efficiently. In addition, in this invention, since the method of irradiating a laser beam is employ | adopted as mentioned above, when forming silicon, it is not necessary to use a combustible gas or a toxic gas, and can reduce environmental impact fully. In addition, in the present invention, it is not necessary to apply high heat when forming silicon, and since a method of irradiating laser light is adopted, it is possible to efficiently form silicon while reducing input energy. It is.

  Further, when at least a part of the outer surface of the silicon-containing material is covered with a reducing metal layer and the reducing metal layer is irradiated with the laser light, atoms of the reducing metal are scattered. When such reducible metal atoms are scattered, oxygen in the vacuum atmosphere and reducible metal atoms are combined to further reduce the oxygen partial pressure in the vacuum atmosphere. That is, the number of oxygen molecules contained in the unit volume in the vacuum atmosphere can be reduced by previously scattering the reducing metal atoms in this way. Therefore, in the method for forming silicon of the present invention, a step of covering at least a part of the outer surface of the silicon-containing material with a reducing metal layer, and irradiating the reducing metal layer with the laser light in the vacuum atmosphere. And the step of previously scattering the reducing metal atom, the number of oxygen molecules per unit volume in the vacuum atmosphere can be reduced by the reducing metal atom in advance, so that it is scattered from the silicon-containing material. The chance of collision between silicon atoms and oxygen molecules can be further reduced, and more silicon atoms can reach the substrate for recovering silicon atoms, thereby depositing in silicon size or unit time The present inventors speculate that the silicon tends to be increased.

  According to the present invention, it is not necessary to use a flammable gas or a toxic gas, and it is possible to sufficiently reduce the environmental load, and it is not necessary to apply high heat. It is possible to provide a method for forming silicon that can be efficiently formed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

In the silicon forming method of the present invention, an oxygen partial pressure of 10 ⁻² Pa or less is applied to a silicon-containing material containing 30 to 99.9 atomic% of silicon and 0.1 to 50 atomic% of a reducing metal element. In this vacuum atmosphere, silicon is obtained by irradiating a laser beam having a wavelength of 192 to 1064 nm, a pulse width of 100 nanoseconds to 10 femtoseconds, and an irradiation intensity of 10 ⁸ to 10 ¹⁵ W / cm ^2. .

  FIG. 1 is a schematic diagram showing a basic configuration of a preferred embodiment of a silicon forming apparatus suitable for carrying out the silicon forming method of the present invention. That is, the silicon forming apparatus shown in FIG. 1 includes a laser light source 1, an optical system 2, and a vacuum chamber 3 into which laser light L emitted from the laser light source 1 is collected and introduced by the optical system 1. Yes. In addition, a silicon-containing material 4 to which the laser beam L is irradiated and a recovery device 5 for recovering scattered silicon atoms are disposed inside the vacuum chamber 3.

The laser light L applied to the silicon-containing material 4 has a wavelength of 192 to 1064 nm (more preferably 192 to 532 nm), a pulse width of 1 microsecond to 1 femtosecond (more preferably 100 nanoseconds to 10 femtoseconds), and an irradiation intensity. The laser beam is 10 ⁷ to 10 ¹⁶ W / cm ² (more preferably 10 ⁸ to 10 ¹⁵ W / cm ² ). When the wavelength of such laser light L exceeds the upper limit, the silicon-containing material 4 is not sufficiently decomposed and a sufficient amount of Si atoms tends not to be generated.

  When the pulse width of the laser beam L is less than the lower limit, the silicon-containing material 4 tends to evaporate, dissipate, and does not accumulate. On the other hand, when the pulse width exceeds the upper limit, the power supplied to the silicon-containing material 4 is not sufficient. Therefore, there is a tendency that a sufficient amount of Si atoms is not efficiently generated. Furthermore, when the irradiation intensity of the laser beam L is less than the lower limit, the power supplied to the silicon-containing material 4 is not sufficient, and a sufficient amount of Si atoms tends not to be generated efficiently. The contained material 4 tends to evaporate, dissipate and do not accumulate.

The laser light source 1 that emits the laser light L is not particularly limited, and may be any laser light generator that can irradiate laser light having a wavelength of 192 to 1064 nm and a pulse width of 100 nanoseconds to 10 femtoseconds. For example, a laser device having a pulse width of nanoseconds such as an excimer laser device or a YAG laser device; a laser device having a pulse width of picoseconds to femtoseconds such as a titanium sapphire laser can be appropriately configured. Further, the laser light source 1 is disposed at a position where the laser light L is irradiated toward the silicon-containing material 4 disposed inside the vacuum chamber 3. Furthermore, in the present embodiment, when the silicon-containing material 4 is irradiated with the laser light L, particles (such as silicon atoms 6 and reducing metal atoms 7) scattered from the surface of the silicon-containing material 4 are efficiently generated. In addition, an optical system (for example, a condensing lens, a mirror, etc.) 2 is disposed in the middle of the optical path of the laser light L. Then, the energy density, irradiation angle, and the like of the laser light L are adjusted by the optical system 2. In the present invention, the irradiation intensity of the laser beam L is adjusted to 10 ⁸ to 10 ¹⁵ W / cm ² .

The vacuum chamber 3 is composed of a container (for example, a stainless steel container) for accommodating at least the silicon-containing material 4 and the recovery device 5 therein, and the laser beam L is irradiated with the silicon-containing material 4 disposed in the vacuum chamber 3. A window (for example, a quartz window) for introduction into the surface is provided. In addition, a vacuum pump (not shown) is connected to the vacuum chamber 3, and the inside of the vacuum chamber 3 is maintained in a vacuum atmosphere state with an oxygen partial pressure of 10 ⁻² Pa (more preferably 10 ⁻³ Pa) or less. It is possible to do. Thus, by setting the internal pressure to 10 ⁻² Pa or less, when silicon atoms 6 are generated by the irradiation of the laser beam 3, the chance of coming into contact with oxygen in the air is reduced, and the surface of the recovery device 5 is efficiently provided. It becomes possible to recover silicon atoms.

  The silicon-containing material 4 contains 30 to 99.9 atomic% of silicon and 0.1 to 50 atomic% (more preferably 1 to 30 atomic%) of a reducing metal element. If the content of silicon is less than the lower limit, the amount of silicon is too small to make it difficult to form silicon efficiently. On the other hand, if the upper limit is exceeded, the price of the silicon-containing material increases and the cost increases. Soars. Further, if the content of the reducing metal element is less than the lower limit, the oxygen partial pressure cannot be sufficiently reduced, and generation of silicon oxide molecules cannot be sufficiently suppressed, making it difficult to efficiently form silicon, When the upper limit is exceeded, the frequency of bonding of silicon atoms and reducing metal atoms increases in the plasma P formed on the surface of the silicon-containing material by laser irradiation or during the scattering of silicon atoms, and silicon is efficiently formed. It becomes difficult. The silicon contained in the silicon-containing material 4 may be contained as a simple substance of silicon, may be contained as a simple substance of silicide such as silicon dioxide, silicon nitride, silicon carbide, or the like. It may be contained as a mixture.

In addition, as such a reducible metal element, the value of change in Gibbs free energy (ΔG ₁ : negative value) for producing 1 mol of the oxide of the reducible metal element is 1 mol of silicon. A value (ΔG ₁ <ΔG ₂ ) smaller than the value of change in Gibbs free energy (ΔG ₂ : negative value) for generating an oxide can be suitably used. That is, such a reducing metal element is preferably one that is more easily oxidized than silicon. In the present invention, since the silicon-containing material 4 contains such a reducing metal element, when the silicon-containing material 4 is irradiated with the laser beam L, it is oxidized together with the silicon atoms 6 rather than the silicon atoms 6. Even when the reducible metal atom 7 is easily scattered and a silicon oxide molecule is generated by collision between the silicon atom 6 and oxygen, the oxygen atom 8 is more preferably bonded to the reducible metal atom than to be bonded to silicon. Since it is stable, when the silicon oxide molecule and the reducing metal atom 7 come into contact with each other, the silicon oxide molecule is reduced to become a silicon atom, and the reducing metal atom 7 is oxidized to become an oxide, thereby generating the silicon oxide molecule. The silicon atoms 6 can efficiently reach the recovery device 5 with sufficient suppression, and the silicon can be prevented from being oxidized even after reaching the recovery device 5.

  Although it does not restrict | limit especially as such a reducible metal element, For example, aluminum and magnesium are mentioned. For example, the values of change in Gibbs free energy (ΔG) when 1 mol of silicon, aluminum, and magnesium are oxidized at room temperature are −199 kcal, −243 kcal, and −275 kcal, respectively. Yes (see Chemical Society of Japan, “Chemical Handbook Application”, 3rd edition, page 243). Among these reducing metal elements, aluminum is particularly preferable from the viewpoint that it is a p-type impurity with respect to silicon and does not cause any particular inconvenience in the semiconductor electrical characteristics of silicon. The reducing metal element may be contained as a simple substance of these metals or as a compound such as an oxide, nitride, or carbide of the reducing metal element.

  The silicon-containing material 4 is not particularly limited as long as it contains 30 to 99.9 atomic percent silicon and 0.1 to 50 atomic percent reducing metal element. In addition to silicon-containing materials made in the natural world, minerals that contain reducing metals such as feldspar, biotite, amphibole, jadeite, and feldspar, etc. that exist in nature, and whose main component is silicon or silicide, and these minerals Rocks such as black granite, granite, diorite, gabbro, crystalline schist, gneiss and the like.

  The recovery device 5 is not particularly limited as long as it can recover silicon atoms 6 scattered when the silicon-containing material 4 is irradiated with the laser beam L. For example, a known substrate ( An alumina substrate or the like can be used as appropriate. Furthermore, the positional relationship (distance, angle, etc.) between the silicon-containing material 4 and the recovery device 5 is not particularly limited, and can be appropriately disposed at a position where the scattered silicon atoms 6 can be efficiently recovered.

Then, using such a silicon forming apparatus shown in FIG. 1, the silicon-containing material 4 is subjected to a wavelength of 192 to 1064 nm, a pulse width of 100 nanoseconds to 10 femtoseconds in a vacuum atmosphere having an oxygen partial pressure of 10 ⁻² Pa or less. Silicon can be obtained by irradiating the laser beam L with an irradiation intensity of 10 ⁸ to 10 ¹⁵ W / cm ² . That is, when the silicon-containing material 4 is irradiated with the laser beam L, plasma P is generated on the surface of the silicon-containing material 4 and the silicon-containing material 4 is decomposed, and silicon atoms 6 and reducing metal atoms 7 are scattered. And since such a reducible metal atom 7 is scattered with the silicon atom 6, even if oxygen 8 exists in a vacuum atmosphere, the reductive metal atom 7 is preferentially oxidized, so that the silicon atom 6 Is sufficiently prevented from being oxidized. Therefore, the silicon atoms 6 can be efficiently reached on the surface of the recovery device 5 and silicon can be prevented from being oxidized even after reaching the recovery device 5, and the recovery device ( The silicon film 9 can be efficiently formed on the substrate 5.

  The preferred embodiment of the silicon forming method of the present invention has been described above, but the silicon forming method of the present invention is not limited to the above embodiment. For example, the silicon formation method of the present invention preferably further includes the following steps. That is, in the method for forming silicon according to the present invention, a step of forming a reducing metal layer on at least a part of the outer surface of the silicon-containing material 4 and irradiating the reducing metal layer with the laser light in the vacuum atmosphere. It is preferable to further include a step of previously scattering the reducing metal atom. As described above, in the present invention, silicon can be more efficiently formed by irradiating the silicon-containing material with laser light in an atmosphere in which reducing metal atoms are scattered.

  FIG. 2 is a schematic diagram showing a basic configuration of a preferred embodiment of a silicon forming apparatus suitable for carrying out a method suitable as the silicon forming method of the present invention.

  2 includes a laser light source 1, an optical system 2, and a vacuum chamber 3 into which laser light L emitted from the laser light source 1 is collected and introduced by the optical system 1. . In addition, a silicon-containing material 4 irradiated with laser light L, a reducing metal layer 10 covering the silicon-containing material 4, and a recovery device 5 for recovering scattered silicon atoms are disposed inside the vacuum chamber 3. Has been.

  The method for covering at least a part of the outer surface of the silicon-containing material 4 with the reducing metal layer 10 is not particularly limited. For example, the reducing metal layer 10 is formed by a known method such as a vacuum deposition method or a sputtering method. A method of forming a film may be employed, or the film may be simply covered with a reducing metal foil, or may be covered by affixing it. As a material for forming such a reducible metal layer, the aforementioned reducible metal element can be suitably used.

  In a preferred embodiment of the present invention, at least a part of the outer surface of the silicon-containing material 4 is covered with the reducing metal layer 10, and then the reducing metal layer 10 is irradiated with the laser light L in the vacuum atmosphere. Then, the reducing metal atoms 7 are scattered in advance. In this way, the reducing metal atoms 7 are scattered in advance, whereby the oxygen existing in the vacuum atmosphere and the reducing metal atoms 7 are combined to reduce the oxygen partial pressure in the vacuum atmosphere. That is, the number of oxygen molecules contained in the unit volume in the vacuum atmosphere can be reduced by scattering the reducing metal atoms 7 in advance. When the irradiation with the laser beam L is continued, the reducing metal layer 10 disappears and the surface of the silicon-containing material 4 appears, and the silicon-containing material 4 is irradiated with the laser beam L to form a silicon film 9. It becomes possible to do. At this time, since the reducing metal atoms are previously scattered, the number of oxygen molecules per unit volume existing in the vacuum atmosphere is smaller as described above, and the silicon atoms scattered from the silicon-containing material 4 are reduced. Opportunities to collide with oxygen molecules are decreasing. Therefore, more silicon atoms can reach the substrate, and the size of silicon obtained or the amount of silicon deposited per unit time increases.

  Further, the thickness of the reducible metal layer 10 is not particularly limited because the thickness suitable for sufficiently reducing the oxygen partial pressure varies depending on the kind of reducible metal, the implementation conditions, and the like. A thickness of 15 μm is preferred. When the thickness is less than 3 μm, it tends to be difficult to sufficiently reduce the oxygen partial pressure. On the other hand, it is preferable that the thickness of the reducing metal layer 10 is larger because the oxygen partial pressure decreases. However, when the thickness exceeds 15 μm, silicon atoms are scattered from the silicon-containing material 4. There is a tendency that the time required to make it long becomes inefficient.

  In the present embodiment, a reducing metal film 11 formed on the surface of the recovery device 5 is formed by the reducing metal atoms 7 scattered in advance, but the reducing metal atoms 7 are scattered in advance to form oxygen. While the molecules are being reduced, the recovery device 5 may be covered with a shutter or the like so that the reducing metal film 11 is not formed.

  According to the present invention, since it is not necessary to use a flammable gas or a toxic gas, it is possible to sufficiently reduce the environmental load, and furthermore, since it is not necessary to apply high heat during the formation of silicon, the energy to be input can be reduced, Silicon can be formed efficiently. Moreover, since natural materials such as feldspar, biotite, and amphibolite can be used as raw materials, there is no worry of shortage of raw materials. And the silicon obtained in this way can be used suitably as silicon for solar cells, for example.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Test Example 1)
Using the silicon forming apparatus shown in FIG. 1, the oxygen partial pressure in the vacuum chamber 3 was measured when the silicon-containing material 4 in which various concentrations of aluminum were contained in silicon dioxide was used. In such measurement, the vacuum chamber 3 was previously set to an oxygen partial pressure of 10 ⁻² Pa by a vacuum pump. A graph showing the relationship between the oxygen partial pressure and the aluminum content obtained as a result of the measurement is shown in FIG.

  As is clear from the results shown in FIG. 3, when the aluminum concentration in silicon dioxide is 0.1 atomic% or more, the oxygen partial pressure is sufficiently reduced. When the aluminum concentration is 1 atomic% or more, only silicon dioxide is present. It was confirmed that the oxygen partial pressure was one order of magnitude lower than the oxygen partial pressure when the laser was irradiated. From these results, in order to prevent silicon from being oxidized while the silicon atoms scattered from the surface of the silicon-containing material are scattered or after reaching the substrate, a reducing metal contained in the silicon-containing material is used. It was necessary to make the concentration of 0.1 atomic% or more, and it was confirmed that it is more preferably 1 atomic% or more.

(Example 1)
Silicon was formed using the silicon forming apparatus shown in FIG. That is, first, as the silicon-containing material 4, black granite containing 5.6 atomic% of aluminum, 2.3 atomic% of magnesium and 16 atomic% of silicon as a reducing metal element was used. Table 1 shows the result of analyzing the concentration of elements contained in the black granite used as the silicon-containing material 4 by X-ray photoelectron spectroscopy.

Further, as the laser light source 1, a YAG laser device (trade name “Quanta Ray” manufactured by SpectraPhysic Co., Ltd.) is used, and the inside of the vacuum chamber 3 is a vacuum atmosphere with an oxygen partial pressure of 9 × 10 ⁻³ Pa by a vacuum pump. It was. Further, an alumina substrate was used as the recovery device 5. Then, with such an apparatus, the silicon-containing material 4 (black granite) is subjected to a wavelength of 532 nm, a pulse width of 7 ns, and an irradiation intensity of 9 × 10 ⁸ W / cm in a vacuum atmosphere having an oxygen partial pressure of 9 × 10 ⁻³ Pa. No. ² YAG laser beam L was irradiated, and the particles scattered from the black granite were deposited on the alumina substrate and collected to obtain a deposit. In this embodiment, heating other than laser irradiation is not performed. FIG. 4 shows the Raman spectrum of the deposit thus obtained.

  As is clear from the results shown in FIG. 4, a peak of silicon (crystal) was observed in the deposit thus obtained, and it was confirmed that silicon can be obtained efficiently.

(Example 2)
Silicon was formed using the silicon forming apparatus shown in FIG. That is, first, a black granite equivalent to the black granite used in Example 1 was used as the silicon-containing material 4. Further, the silicon-containing material 4 was covered with an aluminum foil (reducible metal layer 10) having a thickness of 15 μm. Further, as the laser light source 1, a YAG laser device (trade name “Quanta Ray” manufactured by SpectraPhysic Co., Ltd.) is used, and the inside of the vacuum chamber 3 is a vacuum atmosphere with an oxygen partial pressure of 9 × 10 ⁻³ Pa by a vacuum pump. It was. Further, an alumina substrate was used as the recovery device 5.

With such an apparatus, first, the reducing metal layer 10 is applied to the reducing metal layer 10 in a vacuum atmosphere having an oxygen partial pressure of 9 × 10 ⁻³ Pa, a wavelength of 532 nm, a pulse width of 7 ns, and an irradiation intensity of 9 × 10 ⁸ W / cm ^2. The YAG laser beam L is irradiated to scatter reducing metal atoms from the reducing metal layer 10, and then the silicon-containing material 4 is irradiated with the laser beam to deposit particles on the alumina substrate. Collected to obtain a deposit. In addition, after about 3 minutes have passed since the laser beam irradiation, the aluminum foil (reducing metal layer 10) is etched by 3 μm, and the oxygen partial pressure in the vacuum chamber 3 is reduced to 6 × 10 ⁻⁴ Pa. Was. Further, after about 10 minutes from the first laser irradiation, the aluminum foil (reducing metal layer 10) was completely removed, and the surface of black granite (silicon-containing material 4) was exposed. In this embodiment, heating other than laser irradiation is not performed. FIG. 5 shows the Raman spectrum of the deposit thus obtained.

  As is clear from the results shown in FIG. 5, a peak of silicon (crystal) was observed in the deposit thus obtained, and it was confirmed that silicon can be obtained efficiently according to the present invention. . Compared with the Raman spectrum shown in FIG. 4, the Raman peak intensity of silicon (crystal) was increased in the Raman spectrum shown in FIG. From these results, it was confirmed that silicon can be formed more efficiently when it is further covered with a reducing metal layer 10 and further irradiated with laser light.

(Comparative Example 1)
A deposit was obtained in the same manner as in Example 1 except that quartz (silicon compound containing no reducing metal) was used instead of black granite (silicon-containing material 4). FIG. 6 shows the Raman spectrum of the deposit thus obtained.

From the results shown in FIG. 6, when a silicon compound (quartz) containing no reducing metal is irradiated with laser, silicon oxide is formed even in a vacuum atmosphere with an oxygen partial pressure of 9 × 10 ⁻³ Pa. It was confirmed that no silicon was obtained.

  As described above, according to the present invention, it is not necessary to use a flammable gas or a toxic gas, and it is possible to sufficiently reduce the environmental load, and it is not necessary to apply high heat, and the input energy is sufficiently reduced. Therefore, it is possible to provide a silicon formation method capable of efficiently forming silicon.

  Therefore, the silicon formation method of the present invention is particularly useful as a method for forming silicon for use in fuel cells.

It is a schematic diagram which shows the basic composition of suitable one Embodiment of the silicon formation apparatus suitable for enforcing the formation method of the silicon | silicone of this invention. It is a schematic diagram which shows the basic composition of other suitable embodiment of the silicon forming apparatus suitable for enforcing the silicon formation method of this invention. It is a graph which shows the relationship between oxygen partial pressure and aluminum content. 2 is a graph showing a Raman spectrum of the deposit obtained in Example 1. FIG. 4 is a graph showing a Raman spectrum of the deposit obtained in Example 2. FIG. 5 is a graph showing a Raman spectrum of the deposit obtained in Comparative Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Optical system, 3 ... Vacuum chamber, 4 ... Silicon-containing material, 5 ... Recovery apparatus, 6 ... Silicon atom, 7 ... Reducing metal atom, 8 ... Oxygen, 9 ... Silicon film, 10 ... Reducing metal layer, 11 ... reducing metal film, L ... laser beam, P ... plasma.

Claims (4)

In a silicon-containing material containing 30 to 99.9 atomic% silicon and 0.1 to 50 atomic% of a reducing metal element, under a vacuum atmosphere having an oxygen partial pressure of 10 ⁻² Pa or less, a wavelength of 192 A method for forming silicon, characterized in that silicon is obtained by irradiation with a laser beam of 1064 nm, a pulse width of 100 nanoseconds to 10 femtoseconds, and an irradiation intensity of 10 ⁸ to 10 ¹⁵ W / cm ² .   The Gibbs free energy change value for producing the oxide of the reducing metal element is smaller than the Gibbs free energy change value for producing the silicon oxide. 2. The method for forming silicon according to 1.   3. The method for forming silicon according to claim 1, wherein the silicon-containing material is irradiated with the laser beam in an atmosphere in which reducing metal atoms are scattered. Covering at least part of the outer surface of the silicon-containing material with a reducing metal layer;
Irradiating the reducing metal layer with the laser light in the vacuum atmosphere to scatter the reducing metal atoms in advance;
The method of forming silicon according to claim 3, further comprising: