JP4867102B2 - Method for forming polycrystalline silicon film and composition therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for crystallizing amorphous silicon, a method for forming polycrystalline silicon, and a composition for use therein.
[0002]
[Prior art]
As a method for producing a polycrystalline silicon film for use in a solar cell or the like, a thermal CVD method using monosilane gas or disilane gas as a raw material (J. Vac. Sci. Technology., Vol. 14, p. 1082 (1977), etc.) Alternatively, an amorphous silicon film is first formed by a plasma CVD method (Solid State Com., 17: 1193 (1975), etc.), and then converted to a polycrystalline silicon film by laser annealing, hydrogen plasma treatment, or the like. Mainstream. In the formation of a silicon film using such a CVD method, (1) since a gas phase reaction is used, silicon particles are generated in the gas phase, resulting in a low production yield due to contamination of the apparatus and generation of foreign matter. ▼ Because the raw material is gaseous, it is difficult to obtain a uniform film thickness on a substrate with an uneven surface. (3) Productivity is low due to slow film formation rate. (4) In plasma CVD method Due to problems such as the need for complicated and expensive high-frequency generators and vacuum devices, further improvements have been awaited.
[0003]
In recent years, a method has been reported in which, when amorphous silicon is converted to polycrystalline silicon, a dissimilar metal or metal silicide thin film layer is provided on the surface of amorphous silicon and heat treatment is performed. For example, J. et al. Appl. Phy. 69 , 6394 (1991), J. MoI. Appl. Phy. 70 , 5153 (1991), JPn. J. et al. Appl. Phys. , Part 1, 29 , 729 (1990), J. Am. Appl. Phy. , 87 , 609 (2000), etc., it is reported that a thin film layer of aluminum, copper, nickel or the like is provided on amorphous silicon and can be converted to polycrystalline silicon by heat treatment at about 500 ° C.
However, according to this method, since a relatively high temperature is required for the heat treatment, there is a disadvantage that the material of the substrate that can be used is limited. In the first place, the CVD method is adopted when forming amorphous silicon. Also have.
In recent years, it has been reported that NiSi ₂ can be deposited on a part of the surface of amorphous silicon and converted to polycrystalline silicon by heat treatment at about 380 ° C. According to this method, since polycrystallization can be performed at a relatively low temperature, the degree of freedom of the material of the substrate that can be used is large. However, since the CVD method is necessary when forming amorphous silicon, it has the same problems. Yes.
[0004]
By the way, when using a polycrystalline silicon film for a solar cell, it is preferable to have a (220) crystal plane on the surface. However, all of the polycrystalline silicon formed by the above method has a (111) plane, and a (220) plane could not be selectively formed.
A technique capable of forming a polycrystalline silicon film having a (220) plane on the surface, which can be suitably used for a solar cell, by a simple method is desired.
[0005]
[Problems to be solved by the invention]
The object of the present invention is different from a method requiring a complicated and expensive vacuum system such as a CVD method or a sputtering method, and a polycrystalline silicon film having a (220) surface on a substrate with a simple operation and device. And a composition for the same.
[0006]
According to the present invention, the object is firstly at least one compound selected from the following formulas (1) to (3):
Ni (CO) ₄ . . . (1)
Ni (CO) ₃ (SiF ₃ ) ₂ . . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a composition for use in polycrystallizing amorphous silicon (hereinafter sometimes referred to as “first composition”).
[0007]
Secondly, the object is secondly at least one compound selected from the following formulas (1) to (3):
Ni (CO) ₄ . . . (1)
Ni (CO) ₃ (SiF ₃ ) ₂ . . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a compound represented by the following formula (4) Si _n R _m . . . (4)
(Here, a plurality of R's independently represent a hydrogen atom, an alkyl group, a phenyl group or a halogen atom, n is an integer of 3 or more, and m is an integer of n to 2n + 2.)
It is achieved by a composition containing the following (hereinafter sometimes referred to as “second composition”).
[0008]
The object of the present invention is also achieved by a method for polycrystallizing amorphous silicon, characterized in that thirdly, the first or second composition is applied onto amorphous silicon and then heat-treated.
Further, the object of the present invention is achieved by a method for forming polycrystalline silicon, characterized in that fourth, the second composition is applied onto a substrate and then heat-treated.
Hereinafter, each component of the composition of this invention is demonstrated in detail.
[0009]
First composition The first composition of the present invention comprises at least one compound selected from the following formulas (1) to (3):
Ni (CO) ₄ . . . (1)
Ni (CO) ₃ (SiF ₃ ) ₂ . . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a solvent.
Methods for synthesizing the compounds of the above formulas (1) to (3) are known. The compound of the formula (1) can be synthesized according to, for example, Inorg. Synth., 2 , 234 (1946), Z. Anorg. Allg. Chem., 269 , 308 (1952).
The compound of the formula (2) is, for example, J. Org. Metal. Chem. , 259 , 337 (1983) and the like.
The compound of formula (3) is described in, for example, Inorg. Chem. , 4 , 651 (1965) or the like.
The above compounds (1) to (3) can be used alone or in admixture of two or more.
[0010]
The solvent used in the first composition of the present invention is not particularly limited as long as it dissolves the compounds of the above formulas (1) to (3) and does not substantially react with them. Are aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, decane, cyclopentane, benzene, toluene, xylene, durene, indene, tetrahydronaphthalene, decahydronaphthalene, squalane, etc. Solvent or aromatic hydrocarbon type medium: diethyl ether, dipropyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether Ether solvents such as tetrahydrofuran, tetrahydropyran, 1,2-dimethoxyethane, p-dioxane, tetrahydrofuran; and propylene carbonate, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, dimethyl sulfoxide, methylene chloride, Mention may be made of polar solvents such as chloroform. Of these, aromatic hydrocarbon solvents are preferable from the viewpoint of the stability of the solution, and benzene, toluene, xylene and durene are particularly preferable.
These solvents can be used singly or as a mixture of two or more.
[0011]
The content of the compounds represented by the above formulas (1) to (3) in the first composition of the present invention can be set to an appropriate value depending on the desired film thickness and purpose, but is usually 0.00001. -1.0% by weight, preferably 0.0001-0.5% by weight, particularly preferably 0.0005-0.1% by weight.
[0012]
Second composition The second composition of the present invention comprises at least one compound selected from the following formulas (1) to (3):
Ni (CO) ₄ . . . (1)
Ni (CO) ₃ (SiF ₃ ) ₂ . . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a compound represented by the following formula (4) Si _n R _m . . . (4)
Here, a plurality of R's independently represent a hydrogen atom, an alkyl group, a phenyl group or a halogen atom, n is an integer of 3 or more, and m is an integer of n to 2n + 2. .
[0013]
The compounds represented by the above formulas (1) to (3) are the same as the first composition described above.
When there are a plurality of Rs in the above formula (4), they are each independently a hydrogen atom, an alkyl group, a phenyl group or a halogen atom. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, and neopentyl group. C1-C10 alkyl groups such as n-hexyl group, cyclohexyl group, n-heptyl group, n-octyl group, n-nonyl group and n-decyl group can be mentioned as preferable examples.
n is an integer of 3 or more, and m is an integer of n to 2n + 2. n is preferably from 3 to 8, particularly preferably from 3 to 6.
[0014]
The compound represented by the above formula (4) can be a chain, a ring, or a cage.
Of the compounds represented by the above formula (4), compounds in which all of R are hydrogen atoms are preferably used. As such a compound, a chain compound represented by the formula Si _n H _{2n + 2} , a cyclic compound represented by the formula Si _n H _2n , and a cage compound represented by the formula Si _n H _n are preferably used. Particularly preferred is a cyclic compound represented by the formula Si _n H _2n . The “cage shape” means a structure including a Prisman skeleton, a Cuban skeleton, a pentagonal skeleton, and the like. In the above formula, n is an integer of 3 or more, preferably 3 to 8, particularly preferably 3 to 6.
Among the compounds represented by the above formula (4), particularly preferred are cyclopentasilane, silylcyclopentasilane, and cyclohexasilane.
[0015]
The addition amount of at least one compound among the compounds represented by the above formulas (1) to (3) in the second composition of the present invention is appropriately set depending on the purpose of use of the second composition of the present invention. it can.
When the second composition of the present invention is used for polycrystallizing amorphous silicon, the amount of at least one compound among the compounds represented by the above formulas (1) to (3) is the above formula (4). ) Is usually 0.0001 to 10% by weight, preferably 0.001 to 5% by weight, and particularly preferably 0.002 to 1% by weight.
On the other hand, when the second composition of the present invention is used for forming polycrystalline silicon on a substrate, the addition amount of at least one compound among the compounds represented by the above formulas (1) to (3) Is usually 0.0001 to 10% by weight, preferably 0.001 to 5% by weight, particularly preferably 0.002 to 1%, based on the total of the compound represented by the above formula (4). % By weight.
[0016]
The 2nd composition of this invention can contain the solvent similar to what was illustrated in the 1st composition.
When the second composition of the present invention contains a solvent, the total of the compound represented by the above formulas (1) to (3) and at least one compound represented by the above formula (4) The proportion of the amount in the solution is usually 0.01% by weight or more, preferably 0.05 to 80% by weight, more preferably 0.1 to 50% by weight.
[0017]
Next, a method for polycrystallizing amorphous silicon using the first or second composition of the present invention will be described.
When polycrystallizing amorphous silicon by the method of the present invention, the amorphous silicon is preferably in the form of a film formed on a substrate.
The substrate used at this time is not particularly limited. The substrate on which the coating film is formed may be flat or non-planar with a step, and the form is not particularly limited. When the polysilane compound coating film is oxidized by heat treatment, the substrate material is preferably one that can withstand the processing temperature.
Specific examples of such a substrate material include glass, metal, plastic, ceramics, and the like. Examples of the glass that can be used include quartz glass, borosilicate glass, soda glass, lead glass, and lanthanum glass. As the metal, for example, gold, silver, copper, nickel, silicon, aluminum, iron, and stainless steel can be used. As the plastic, for example, polyimide, polyethersulfone, norbornene-based ring-opening polymer and hydrogenated product thereof can be used. Furthermore, the shape of these substrates is not particularly limited by a lump shape, a plate shape, a film shape, or the like.
[0018]
An appropriate method can be used to form amorphous silicon on the substrate. For example, a plasma CVD method or the like may be used, or a solution-like composition may be formed by the method described in WO 00/58409.
The film thickness of the amorphous silicon film may be an appropriate value depending on the purpose, but is usually 0.01 to 20 μm, preferably 0.02 to 10 μm, and more preferably 0.03 to 5 μm.
[0019]
In order to polycrystallize amorphous silicon by the method of the present invention, the first or second composition of the present invention is applied to the above amorphous silicon, for example, spray method, roll coating method, curtain coating method, spin coating method, The film is applied by an appropriate method such as a screen printing method, an offset printing method, or an ink jet method so that the film thickness is preferably about 0.00001 to 1.0 μm, particularly preferably about 0.0001 to 0.1 μm. In addition, when a composition contains a solvent, the said film thickness should be understood as a film thickness after solvent removal.
The film forming step is preferably performed in a non-oxidizing atmosphere. In order to realize such an atmosphere, an atmosphere that does not substantially contain an oxidizing substance such as oxygen and carbon dioxide may be used. Specifically, nitrogen, hydrogen, a rare gas, and a mixed gas thereof can be used. An atmosphere can be preferably used.
[0020]
After forming a coating film of the composition of the present invention on amorphous silicon, the amorphous silicon film is converted into a polycrystalline silicon film by heat treatment in an appropriate atmosphere. The heat treatment is preferably performed in a non-oxidizing atmosphere, usually in an argon atmosphere or argon containing hydrogen. As processing temperature, it is about 200-1000 degreeC, Preferably it is about 200-850 degreeC, More preferably, it is about 300-500 degreeC.
The heat treatment time is usually 1 to 180 minutes, preferably 5 to 120 minutes.
[0021]
Next, a method for forming polycrystalline silicon on a substrate using the second composition of the present invention will be described.
The film thickness of the second composition of the present invention is adjusted on a substrate by an appropriate method such as a spray method, a roll coating method, a curtain coating method, a spin coating method, a screen printing method, an offset printing method, or an ink jet method. The coating is preferably performed to 0.005 to 10 μm, particularly preferably about 0.01 to 5 μm. In addition, when a composition contains a solvent, the said film thickness should be understood as a film thickness after solvent removal. The same substrate as described above can be used.
The film forming step is preferably performed in a non-oxidizing atmosphere. Such an atmosphere can be realized in the same manner as described above.
[0022]
Further, in order to form a coating film of the second composition of the present invention on the substrate with good adhesion and denseness, it is preferable to perform a light irradiation treatment at least once before and after coating.
In such light irradiation treatment, in addition to visible light, ultraviolet light, far ultraviolet light, low pressure or high pressure mercury lamp, deuterium lamp, or discharge light of rare gas such as argon, krypton, xenon, YAG laser, argon laser An excimer laser such as carbon dioxide laser, XeF, XeCl, XeBr, KrF, KrCl, ArF, ArCl, or the like can be used as a light source. As these light sources, those having an output of 10 to 5000 W are generally used, but 100 to 1000 W is usually sufficient. Although the wavelength of these light sources will not be specifically limited if the polysilane compound in a composition or a coating film absorbs to some extent, 170 nm-600 nm are preferable.
The temperature at the time of performing the light irradiation treatment is usually room temperature to 300 ° C., and the treatment time is about 0.1 to 30 minutes. These light irradiation processes are preferably performed in a non-oxidizing atmosphere similar to the polysilane compound film forming step.
[0023]
The coating film of the second composition of the present invention formed as described above is converted into a polycrystalline silicon film by heat treatment in an appropriate atmosphere.
The coating film of the composition of the present invention formed as described above is preferably at a temperature of about 100 to 1000 ° C., preferably about 200 to 850 ° C. in a non-oxidizing atmosphere, usually an argon atmosphere or argon containing hydrogen. More preferably, it is heat-treated at about 300 ° C. to 500 ° C. to obtain a polycrystalline silicon film.
[0024]
According to the method of the present invention, the polycrystalline silicon film is formed as described above. The method of the present invention can form a dense polycrystalline silicon film regardless of the area and shape of the substrate, and can be suitably used for manufacturing a device that requires high reliability. Further, the method of the present invention is low in cost because an expensive apparatus such as a vacuum apparatus is not necessary.
In addition, the polycrystalline silicon film formed by the method of the present invention has a (220) plane as the main surface, and can be suitably used for the production of solar cells.
[0025]
【Example】
EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.
Synthesis Example 1 (Synthesis of Ni (CO) ₃ (SiF ₃ ) ₂ )
In a 200 mL eggplant flask, 6.4 g (0.11 g / atm) of nickel, 40 g (0.44 mol) of toluene, and 68.1 g (0.4 mol) of hexafluorodisilane were weighed and cooled at −196 ° C. for 2 hours. The precipitated reddish-brown solid was heated and melted, excess toluene and hexafluorodisilane were removed under reduced pressure, and the resulting black powder was washed twice with 40 ml of toluene. Further, the filter was filtered under nitrogen to obtain a pale yellow filtrate. The solvent of the pale yellow solution was removed under reduced pressure to obtain 0.2 g of a pale yellow solid. The melting point of this product was 95 ° C., and ¹ H-NMR measured in deuterated chloroform solvent showed peaks at 2.5 (s, 3H) and 6.8 ppm (s, 5H), and the product was (η ⁶ − It was shown to be C ₆ H ₅ CH ₃ ) Ni (SiF ₃ ) ₂ .
Next, 0.05 g of (η ⁶ -C ₆ H ₅ CH ₃ ) Ni (SiF ₃ ) ₂ was weighed into a 100 mL two-necked eggplant flask, and the inside of the container was replaced with carbon monoxide to be filled. For 1 hour. Further, toluene produced as a by-product under reduced pressure was removed to obtain a white product. The IR spectrum of the product showed absorption of C = O stretching vibration at 2100 cm ^-1 , indicating that the product was Ni (CO) ₃ (SiF ₃ ) ₂ .
[0026]
Synthesis Example 2 (Synthesis of cyclosilane)
After replacing the inside of a 2 L 4-neck flask equipped with a thermometer, a condenser, a dropping funnel and a stirrer with argon gas, 1.5 L of dry tetrahydrofuran and 27.4 g of lithium metal were charged and bubbled with argon gas. . To this solution, 500 g of diphenyldichlorosilane was added from a dropping funnel while stirring under ice cooling. The reaction was continued until the lithium metal completely disappeared, and then the reaction mixture was poured into ice water to precipitate the reaction product. The precipitate was filtered off, washed well with water, and then washed with cyclohexane to obtain 208 g of product. When this product was analyzed by high performance liquid chromatography, it was a mixture of decaphenylcyclopentasilane and undecaphenylcyclohexasilane, and the mixing ratio was 10/1 (weight ratio).
Next, 190 g of the above product and 2000 mL of toluene were charged into a 3 L flask substituted with argon, 15 g of aluminum chloride was added, and hydrogen chloride gas was introduced. After confirming that the phenyl group was substituted with chlorine by ¹ H-NMR, 1 equivalent of lithium aluminum hydride was added to one chlorine atom in an argon atmosphere under cooling to carry out a reduction reaction. By removing the aluminum compound produced by the reaction, 16 g of a reduced silane compound was obtained. This was found to be a mixture of Si ₅ H ₁₀ and Si ₆ H ₁₂ (weight ratio 10/1) by ²⁹ Si-NMR, IR spectrum and gas chromatographic analysis.
[0027]
Example 1
(1) Formation of Amorphous Silicon 4 g of cyclosilane obtained in Synthesis Example 1 above was dissolved in 10 g of toluene, filtered through a 0.2 micron membrane filter to prepare a cyclosilane coating solution, and dip coated in an argon atmosphere. Thus, a cyclosilane coating film was formed on the quartz substrate. The coated substrate was evaporated in an argon atmosphere and then heated at 500 ° C. for 5 minutes to form a silicon film having a metallic luster on the substrate. The thickness of this silicon film was 1500 mm. When the ESCA spectrum of this silicon film was measured, a peak was observed at 99 eV. This peak is attributed to the 2p orbit of Si.
The Raman scattering spectrum of this silicon film showed 100% amorphous silicon.
(2) Conversion of amorphous silicon into polycrystalline silicon After dissolving 10 mg of Ni (CO) ₃ (SiF ₃ ) ₂ synthesized in Synthesis Example 1 in 200 mL of toluene in a 300 mL eggplant flask substituted with nitrogen, 0.05 μm The Ni (CO) ₃ (SiF ₃ ) ₂ solution was prepared by filtering through a membrane filter.
The Ni (CO) ₃ (SiF ₃ ) ₂ solution was spin-coated under nitrogen on the amorphous silicon prepared in the above (1) to form a coating film having a thickness of 5 mm. Subsequently, it baked at 450 degreeC for 1 hour.
The Raman scattering spectrum of the silicon film thus obtained showed a sharp peak at 520 cm ⁻¹ , indicating that amorphous silicon was converted to polycrystalline silicon.
[0028]
Example 2
(1) Preparation of Ni (CO) ₃ (SiF ₃ ) ₂ / cyclosilane composition 50 mg of Ni (CO) ₃ (SiF ₃ ) ₂ synthesized in Synthesis Example 1 and 10 g of cyclosilane synthesized in Synthesis Example 2 were added to 90 g of toluene. After dissolution, the mixture was filtered through a 0.2 micrometer membrane filter to prepare a mixed solution of Ni (CO) ₃ (SiF ₃ ) ₂ and cyclosilane.
(2) Formation of polycrystalline silicon The mixed solution of Ni (CO) ₃ (SiF ₃ ) ₂ and cyclosilane prepared in (1) above was applied to a quartz substrate by spin coating in an argon atmosphere. The coated substrate was evaporated in an argon atmosphere and then heated at 450 ° C. for 1 hour to form a silicon film having a metallic luster on the substrate. The thickness of this silicon film was 1.0 μm.
When the ESCA spectrum of this silicon film was measured, a peak attributed to the 2p orbit of Si was observed at 99 eV.
The Raman scattering spectrum of this silicon film showed a sharp peak at 520 cm ⁻¹ , indicating that a polycrystalline silicon film was formed.
[0029]
【Effect of the invention】
According to the present invention, unlike a method that requires a complicated and expensive vacuum system such as a CVD method or a sputtering method, a method for forming a polycrystalline silicon film on a substrate with a simple operation or device, and a method therefor A composition is provided.

Claims (6)

At least one compound selected from the following formulas (2) and (3) :
_{N i (CO) 3 (SiF} 3) 2. . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a composition for use in the crystallization of amorphous silicon. At least one compound selected from the following formulas (1) to (3);
Ni (CO) ₄ . . . (1)
Ni (CO) ₃ (SiF ₃ ) ₂ . . . (2)
Ni (CO) (PF ₃ ) ₃ . . . (3)
And a compound represented by the following formula (4) Si _n R _m . . . (4)
Here, a plurality of R's independently represent a hydrogen atom, an alkyl group, a phenyl group or a halogen atom, n is an integer of 3 or more, and m is an integer of n to 2n + 2. Composition. The composition according to claim 1 , wherein the composition is for use in crystallization of amorphous silicon.   The composition according to claim 2, wherein the composition is for forming polycrystalline silicon on a substrate.   A method for polycrystallizing amorphous silicon, wherein the composition according to claim 1 or 3 is applied onto amorphous silicon and then heat-treated.   A method for forming polycrystalline silicon, wherein the composition according to claim 4 is applied on a substrate and then heat-treated.