JP6405199B2 - Electrodeposition electrolyte and method for producing metal film - Google Patents

Description

  The present invention relates to an electrolyte for electrodeposition and a method for producing a metal film.

  A silicon film used as a solar cell is produced by producing a silicon ingot by the Siemens method, slicing the silicon ingot to a thickness of about 1 mm, producing a silicon wafer, and forming a pn junction on the silicon wafer. (Non-Patent Document 1). At that time, the content of metal impurities in the silicon film must be suppressed to 0.1 mass ppm or less, and the boron content must be suppressed to 0.3 mass ppm or less.

  Further, a high melting point metal film such as tungsten, molybdenum and titanium having high hardness and wear resistance is formed by a thermal spraying method (Patent Document 1) or a chemical vapor deposition (CVD) method (Patent Document 2). . However, when a refractory metal film is formed by a thermal spraying method, there is a drawback that the substrate on which the refractory metal film is deposited is subjected to great thermal damage. In addition, when a refractory metal film is formed by a CVD method, there is a drawback that the film forming speed of the refractory metal film is slow. Note that the silicide film can also be formed by the CVD method (Patent Document 3), but has the same drawback as the case of forming the refractory metal film by the CVD method.

  Therefore, conventionally, an electrolyte for electrodeposition is prepared by containing a metal that is an object of electrodeposition in the molten salt, and a film is formed on the substrate by electrodeposition of the electrodepositing electrolyte, or electrodeposition. A method of directly forming a film such as a silicon film, a refractory metal film, a silicide film, or an alloy film on the substrate by an electrodeposition method in which an alloy phase is formed by reacting a metal contained in the substrate with a metal contained in the substrate has been studied I came.

  For example, in Non-Patent Document 2 and Non-Patent Document 3, lithium fluoride (LiF) -sodium fluoride (NaF) -potassium fluoride (KF) mixed molten salt (hereinafter sometimes referred to as “FLINAK”). Alternatively, it has been proposed to form a silicon film by an electrodeposition method using an electrodeposition electrolyte prepared using a lithium fluoride (LiF) -potassium fluoride (KF) mixed molten salt.

  However, according to the electrodeposition methods described in Non-Patent Document 2 and Non-Patent Document 3, a silicon film having a relatively smooth surface and a high purity can be obtained. Since the solubility is low, it is difficult to wash and remove the electrodepositing electrolyte attached to the surface of the silicon film.

  When a high melting point metal film such as tungsten or molybdenum is formed by electrodeposition, a molten salt made of a metal fluoride such as FLINAK has a relatively smooth surface and high purity. Although a melting point metal film can be obtained, it is difficult to remove the electrodeposition electrolyte by washing with water because the electrodeposition electrolyte has low solubility in water (Non-patent Document 4).

  On the other hand, it is possible to deposit a refractory metal film using a molten salt made of a metal chloride that can be easily washed away with water, but in this case, the surface is not smooth and the content of impurities is high. Only a melting point metal film was obtained (Non-Patent Document 5).

JP 2006-249578 A JP 2001-011628 A JP 2008-187190 A

Semiconductor Fundamental Technology Study Group, Silicon Science, Realization Science and Technology Center, 1992 Gopalakrishna M. Rao et al., “Electrowinning of Silicon from K2SiF6-Molten Fluoride Systems”, Journal of The Electrochemical Society, 1980, Vol.127, No.9, pp.1940-1944 Geir Martin Haarberg et al., “Electrodeposition of silicon from fluoride melts”, Electrochemica Acta, 100 (2013), pp.226-228 S. Senderoff and G. W. Mellors et al., “Electrodeposition of Coherent Deposits of Refractory Metals”, Journal of The Electrochemical Society, 1967, Vol.114, No.6, pp.586-587 M. Masuda et al., “Electrodeposition of Tungsten and Related Voltammetric Study in a Basic ZnCl2-NaCl (40-60 mol%) Melt”, Journal of The Electrochemical Society, 2001, vol.148, No.1, pp.C59 -C64

  When forming a silicon film, a refractory metal film, a silicide film and an alloy film by the electrodeposition method, a film having a smooth surface is required unless a metal fluoride is added to the molten salt used in the preparation of the electrolyte for electrodeposition. Could not be formed. On the other hand, since metal fluorides other than KF have low solubility in water, it has been difficult to wash and remove the electrodeposition electrolyte after film formation. Furthermore, in the electrodeposition method, it is desired to reduce the thermal damage to the substrate on which the film is formed by electrodeposition at as low a temperature as possible, and to suppress the peeling of the film from the substrate.

  In view of the above circumstances, the following embodiment is capable of forming a metal film having a smooth surface at a relatively low temperature by electrodeposition, and is easy to remove with water after the metal film is formed. And it aims at providing the manufacturing method of a metal film.

  According to the 1st aspect of this invention, the electrolyte for electrodeposition containing a potassium ion, a fluoride ion, a chloride ion, and a metal ion can be provided.

  According to the second aspect of the present invention, a step of producing an electrodepositing electrolyte from potassium fluoride, potassium chloride, at least one of a metal compound and a metal, and immersing the substrate in the electrodepositing electrolyte Forming a metal film on the substrate by electrolyzing the electrodepositing electrolyte using the substrate as a cathode, and washing the electrodepositing electrolyte adhering on the surface of the metal film with water And a step of removing the metal film.

  According to the above aspect, a metal film having a smooth surface at a relatively low temperature can be formed by electrodeposition, and the electrodeposition electrolyte and metal film can be easily washed and removed after the metal film is formed. A method can be provided.

It is a flowchart of the manufacturing method of the metal film of embodiment. It is typical sectional drawing illustrating an example of the process of immersing a board | substrate in the electrolyte for electrodeposition in the manufacturing method of the metal film of embodiment. It is typical sectional drawing illustrating an example of the process of forming a metal film on the board | substrate in the manufacturing method of the metal film of embodiment. It is typical sectional drawing illustrating an example of the process of producing the electrolyte for electrodeposition by metal anodic dissolution in the manufacturing method of the metal film of embodiment. 2 is a scanning electron microscope (SEM) image of a cross section of a Si film formed in Experimental Example 1. FIG. 3 is an X-ray diffraction (XRD) pattern of the Si film formed in Experimental Example 1. FIG. (A)-(c) are the XRD patterns of the Fe-Ti film | membrane formed in Experimental example 21. FIG. 22 is a SEM image of a cross section of a Si film formed in Experimental Example 22. 24 is a SEM image of a cross section of a Si film formed in Experimental Example 23. 24 is a SEM image of a cross section of a Si film formed in Experimental Example 24. 22 is a SEM image of a cross section of a Si film formed in Experimental Example 25. 27 is a SEM image of a cross section of a Si film formed in Experimental Example 26. 42 is a SEM image of a cross section of a Si film formed in Experimental Example 27. 42 is a SEM image of a cross section of a Si film formed in Experimental Example 28. 42 is a SEM image of a cross section of a Si film formed in Experimental Example 29. 4 is a SEM image of a cross section of a Si film formed in Experimental Example 30. 4 is a SEM image of a cross section of a Si film formed in Experimental Example 31. 32 is a SEM image of a cross section of a Si film formed in Experimental Example 32. It is a SEM image of the section of the Si film formed in example 33 of an experiment. 24 is an enlarged view of an SEM image of a cross section of a Si film formed in Experimental Example 24. FIG. 29 is an enlarged view of an SEM image of a cross section of a Si film formed in Experimental Example 25. FIG. 14 is a SEM photograph of the surface of the metal film of Experimental Example 34. 14 is a SEM photograph of the surface of a metal film in Experimental Example 36. 14 is a low-acceleration scanning electron micrograph of a cross section of a metal film of Experimental Example 34. 4 is a low acceleration scanning electron micrograph of a cross section of a metal film of Experimental Example 36. It is an EDX analysis result of the analysis point shown in FIG. It is an EDX analysis result of the analysis point shown in FIG.

[Description of Embodiment of the Present Invention]
(1) According to the 1st aspect of this invention, the electrolyte for electrodeposition containing a potassium ion, a fluoride ion, a chloride ion, and a metal ion can be provided. By adopting such a configuration, a metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and an electrolyte for electrodeposition that can be easily washed and removed after the metal film is formed. Can do.

  (2) In the first aspect of the present invention, the metal ion preferably has a cation fraction of 0.12 or less. In this case, the electrolyte for electrodeposition tends to be easily removed by washing with water after forming the metal film.

  (3) In the 1st aspect of this invention, it is preferable that the anion fraction of the said fluoride ion is 0.1-0.9. In this case, the electrolyte for electrodeposition tends to be easily removed by washing with water after forming the metal film.

  (4) In the first aspect of the present invention, the metal ions preferably include at least one selected from the group consisting of silicon ions, tungsten ions, molybdenum ions, titanium ions, nickel ions, and cobalt ions. . In this case, the metal film can be a film suitable for various applications.

  (5) According to the second aspect of the present invention, a step of producing an electrodepositing electrolyte from potassium fluoride, potassium chloride, at least one of a metal compound and a metal, and a substrate on the electrodepositing electrolyte , A step of forming a metal film on the substrate by electrolyzing the electrodepositing electrolyte using the substrate as a cathode, and the electrodepositing electrolyte adhering on the surface of the metal film The method of manufacturing a metal film including the process of removing by water washing can be provided. By adopting such a configuration, a metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and an electrolyte for electrodeposition that can be easily washed and removed after the metal film is formed. Can do. In the present specification, the “metal film” includes metal films such as a silicon film, a refractory metal film, a silicide film, and an alloy film.

  (6) In the second aspect of the present invention, in the step of producing the electrodeposition electrolyte, the total mass of the potassium fluoride and the potassium chloride is 70% by mass or more of the electrodeposition electrolyte. Is preferred. In this case, a metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and the electrodeposition electrolyte can be easily washed away after the metal film is formed.

  (7) In the second aspect of the present invention, the step of preparing the electrodeposition electrolyte includes a step of preparing a molten salt by mixing potassium fluoride and potassium chloride and then melting the molten salt, and the molten salt. At least one of the step of adding at least one of the metal compounds and the step of anodic dissolution of the metal may be included. Also in this case, a metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and the electrodeposition electrolyte can be easily washed away after the metal film is formed.

  (8) In the second aspect of the present invention, the metal compound may contain a metal chloride gas. Also in this case, a metal film having a smooth surface can be formed by electrodeposition at a relatively low temperature, and the electrodeposition electrolyte can be easily washed away after the metal film is formed.

  (9) In the second aspect of the present invention, the molar ratio of the potassium chloride to the potassium fluoride in the molten salt is preferably 0.2 or more and 5 or less. In this case, since electrodeposition is possible at a relatively low temperature, thermal damage to the substrate on which the metal film is formed can be suppressed, and as a result, the electrodeposition electrolyte can be removed by washing with water after the metal film is formed. The metal film can be prevented from peeling from the substrate.

(10) In the second aspect of the present invention, in the step of forming a metal film on the substrate, a current having an absolute value of a current density of 1 mA / cm ² or more and 500 mA / cm ² or less is passed, so that the electrodeposition electrolyte It is preferable to perform the electrolysis. In this case, a metal film can be formed on the surface of the substrate in a shorter time, and a metal film with improved surface smoothness can be formed.

  (11) In the second aspect of the present invention, the surface of the substrate preferably contains at least one selected from the group consisting of iron, silver, carbon, copper and molybdenum. In this case, the adhesion between the substrate and the metal film formed on the surface of the substrate can be improved.

  (12) In the second aspect of the present invention, the substrate preferably has a columnar shape or a pipe shape. In this case, when a concentrating solar cell is fabricated using a Si film formed on the surface of the substrate, light incidence from all directions can be used, so the light utilization efficiency per unit area Can be improved.

[Details of the embodiment of the present invention]
Hereinafter, an embodiment which is an example of the present invention will be described. Note that in the drawings used to describe the embodiments, the same reference numerals represent the same or corresponding parts.

<Configuration of electrolyte for electrodeposition>
The electrodeposition electrolyte according to the embodiment includes potassium ions (K ⁺ ), fluoride ions (F ⁻ ), chloride ions (Cl ⁻ ), and metal ions (M ^{n +} ; n is a natural number). Yes. The electrolyte for electrodeposition according to the embodiment is prepared by, for example, dissolving a metal compound containing metal (M) to be electrodeposited in a molten salt of potassium fluoride (KF) and potassium chloride (KCl). be able to.

In the molten salt of KF and KCl, KF and KCl are ionized and exist in the state of K ⁺ , F ⁻ and Cl ⁻ , respectively, and when the metal compound containing M deposited therein is dissolved. , And the metal compound containing M is ionized and M is deposited as a metal ion (M ^{n +} ).

That is, in the electrodepositing electrolyte of the embodiment, the metal compounds containing KF, KCl, and M are ionized and exist in an ionic state. Therefore, the electrodepositing electrolyte of the embodiment is K ⁺ , F ⁻ , Cl ⁻ and M ^{n +} .

As for K ⁺ , F ⁻ , Cl ⁻ and M ^{n + in} the electrodepositing electrolyte of the embodiment, for example, ICP emission spectroscopic analysis is performed after dissolving the electrodepositing electrolyte in a mixed solution of nitric acid and hydrofluoric acid. (Inductively Coupled Plasma Spectrometry). As the ICP emission spectroscopic analyzer, for example, iCAP6200 manufactured by Thermo Fisher Scientific Co., Ltd. can be used.

In addition, K ⁺ , F ⁻ , Cl ⁻ and M ^{n + in} the electrodeposition electrolyte according to the embodiment may be confirmed by ion chromatography after dissolving the electrodeposition electrolyte in a large amount of water, for example. it can. As the ion chromatography device, for example, HIC-SP manufactured by Shimadzu Corporation can be used.

The cation fraction of M ^{n +} in the electrodeposition electrolyte of the embodiment is preferably 0.12 or less, and more preferably 0.1 or less. When the cation fraction of M ^{n +} is 0.12 or less, particularly when it is 0.1 or less, the electrolyte for electrodeposition tends to be easily removed by washing with water after forming the metal film. In addition, the cation fraction of M ^{n +} in the electrodeposition electrolyte of the embodiment is more preferably 0.05 or less, and particularly preferably 0.01 or more and 0.04 or less. When the cation fraction of M ^{n +} is 0.05 or less, particularly when it is 0.01 or more and 0.04 or less, the removal of the electrolyte for electrodeposition by washing with water after the formation of the metal film tends to be easier. It is in.

Here, the cation fraction of M ^{n +} in the electrodeposition electrolyte of the embodiment can be calculated by the following formula (I).

Cation fraction of M ^{n +} = (Amount of M ^{n + in} the electrodeposition electrolyte) / (Total amount of cations in the electrodeposition electrolyte) (I)

The anion fraction of F ⁻ in the electrodeposition electrolyte of the embodiment is preferably 0.1 or more and 0.9 or less, and more preferably 0.25 or more and 0.75 or less. When the anion fraction of F ⁻ is 0.1 or more and 0.9 or less, particularly when it is 0.25 or more and 0.75 or less, it is easy to remove the electrolyte for electrodeposition by washing with water after forming the metal film. It tends to be.

Here, the anion fraction of F ⁻ in the electrodeposition electrolyte of the embodiment can be calculated by the following formula (II).

F ⁻ anion fraction = (amount of F ^{− in} the electrodeposition electrolyte) / (total amount of anion in the electrodeposition electrolyte) (II)

M ^{n +} is at least one selected from the group consisting of silicon (Si) ions, tungsten (W) ions, molybdenum (Mo) ions, titanium (Ti) ions, nickel (Ni) ions, and cobalt (Co) ions. It is preferable to include. For example, when the electrodepositing electrolyte of the embodiment contains Si ions, and depositing Si on the substrate by electrodepositing the electrodepositing electrolyte, the Si film is formed as a solar cell. The Si film used can be used. In addition, when a film containing W, Mo, Ti and at least two kinds of these alloys is formed on the substrate by electrodepositing the electrolyte for electrodeposition according to the embodiment, the film has, for example, a high hardness. In addition, it can be used as a protective film having a wear resistance function. Further, when a film containing Ni, Co, and an alloy of Ni and Co is formed on the substrate by electrodepositing the electrolyte for electrodeposition according to the embodiment, the film is used as, for example, a corrosion-resistant film. be able to. Moreover, a film containing at least one silicide (compound with silicon) selected from the group consisting of W, Mo, Ti, Ni and Co on the substrate by electrodepositing the electrolyte for electrodeposition according to the embodiment When formed, the film can be used, for example, as a low-resistance electrode to a semiconductor substrate, enabling a low-voltage operation of the semiconductor device. Furthermore, when an alloy film in which the deposited metal and the metal contained in the substrate are alloyed is formed by electrodeposition from the electrodeposition electrolyte according to the embodiment, the alloy film is, for example, wear resistant. It can be used for a protective film or a hydrogen storage alloy film.

<Method for producing metal film>
FIG. 1 shows a flowchart of an example of a metal film manufacturing method using the electrodeposition electrolyte of the embodiment (metal film manufacturing method of the embodiment). The manufacturing method of the metal film of the embodiment includes a step of producing an electrodeposition electrolyte (S10), a step of immersing the substrate in the electrodeposition electrolyte (S20), and a step of forming a metal film on the substrate (S30). ) And a step (S40) of removing the electrolyte for electrodeposition by washing with water. In addition, it cannot be overemphasized that processes other than S10, S20, S30, and S40 may be included in the manufacturing method of the metal film of embodiment, and the order of a process is not specifically limited.

[Process for producing electrolyte for electrodeposition]
The step (S10) of preparing the electrodepositing electrolyte is performed by preparing an electrodepositing electrolyte from KF, KCl, and a metal compound containing M. The step (S10) of preparing the electrodepositing electrolyte includes, for example, a step of preparing a molten salt by melting a mixture of KF and KCl, and adding an M compound to the molten salt of KF and KCl. Producing an electrolyte for electrodeposition.

Molar ratio of KCl to KF in the molten salt of KF and KCl ((substance quantity of KCl in the molten salt of KF and KCl n _KCl ) / (substance quantity of KF in the molten salt of KF and KCl n _KF ) ) Is preferably 0.2 or more and 5 or less, and more preferably 0.5 or more and 2 or less. When the molar ratio of KCl to KF in the molten salt of KF and KCl is 1.2, the melting point of the molten salt is 871 K, which is the lowest, but in the molten salt of KF and KCl, KCl to KF. When the molar ratio is 0.2 or more and 5 or less, particularly when the molar ratio is 0.5 or more and 2 or less, the melting point of the molten salt should be sufficiently lower than the melting point of the KF single salt (1133K). Therefore, electrodeposition can be performed at a relatively low temperature. Thereby, the thermal damage to the board | substrate with which a metal film is formed can be suppressed, and also it can suppress that a metal film peels from a board | substrate at the time of removal of the electrodeposition electrolyte by the water washing after formation of a metal film.

  The M compound added to the molten salt of KF and KCl includes at least one solid M compound, at least one gaseous M compound, or at least one solid M compound and a gaseous compound. Both with at least one of the compounds of M can be added.

As the solid M compound, for example, a silicon compound such as K ₂ SiF ₆ can be added when an Si film is formed on the substrate by electrodeposition of the electrolyte for electrodeposition according to the embodiment. When forming a W film, for example, a tungsten compound such as KWF ₆ , WO _2, or WO ₃ can be added. In the case of forming a Mo film, for example, it can be added to the molybdenum compound such KMoF _6, MoO ₂ or MoO _3. When forming a Ti film, for example, a titanium compound such as K ₂ TiF ₆ or TiO ₂ can be added. Further, when forming the Ni film, for example, a nickel compound such as NiCl ₂ can be added. Furthermore, when forming a Co film, for example, a cobalt compound such as CoCl ₂ can be added.

As the gaseous M compound, when forming a Si film on the substrate by electrodeposition of the electrodeposition electrolyte according to the embodiment, for example, a silicon compound gas such as SiCl _{4 is used} as a molten salt of KF and KCl. It can be added by blowing. When forming a W film, for example, at least one tungsten compound gas selected from the group consisting of WCl ₄ , WCl ₅ and WCl ₆ is added by blowing it into a molten salt of KF and KCl. be able to. When forming a Mo film, for example, at least one selected from the group consisting of MoF ₆ , MoCl ₄ , MoCl ₅ and MoCl ₆ is blown into a molten salt of KF and KCl. Can be added. When forming a Ti film, for example, a titanium compound gas such as TiCl ₄ can be added by blowing it into a molten salt of KF and KCl.

  The method of blowing the gaseous M compound into the molten salt of KF and KCl is not particularly limited, but for example, a blowing method using a pipe can be used.

  In addition, each of the solid M compound and the gaseous M compound may be added alone or in combination.

  In addition, the electrodeposition electrolyte according to the embodiment is preferably manufactured so that the total mass of KF and KCl is 70% by mass or more of the electrodeposition electrolyte. In the case where a metal film is formed by performing electrodeposition using an electrolyte for electrodeposition in which the total mass of KF and KCl is 70% by mass or more of the electrolyte for electrodeposition, electrolysis by washing after forming the metal film is performed. It tends to be easy to remove the electrolyte for deposition. That is, when a molten salt containing a molten salt component other than KF and KCl in an amount of more than 30% by mass of the electrodeposition electrolyte is used, a metal salt having low solubility in water is generated by ion exchange. It tends to be difficult to remove the electrolyte for washing with water (for example, LiF obtained by the reaction formula of KF + LiCl → LiF + KCl is hardly soluble in water). In addition, even when the metal to be electrodeposited is contained in an amount of more than 30% by mass of the electrolyte for electrodeposition, the metal to be electrodeposited is hardly soluble in water. It tends to be difficult to remove the electrolyte for electrodeposition by washing with water.

[Step of immersing substrate in electrolyte for electrodeposition]
In the step of immersing the substrate in the electrodeposition electrolyte (S20), for example, as shown in the schematic cross-sectional view of FIG. 2, the electrodepositing electrolyte 2 prepared in the step of preparing the electrodeposition electrolyte (S10) is the container 1. It can be performed by immersing the anode 3 and the substrate 4 as the cathode in the electrolyte 2 for electrodeposition.

  Here, as the substrate 4, a substrate whose surface includes at least one selected from the group consisting of iron (Fe), silver (Ag), carbon (C), copper (Cu), and Mo is used. It is preferable. When the surface of the substrate 4 contains at least one of Ag and C, the adhesion between the Si film formed on the surface of the substrate 4 and the substrate 4 can be improved. Further, when the surface of the substrate 4 contains at least one of Cu and Mo, the adhesion between the W film formed on the surface of the substrate 4 and the substrate 4 can be improved.

  The shape of the substrate 4 is not particularly limited, but is preferably a columnar shape or a pipe shape. When the shape of the substrate 4 is a columnar shape or a pipe shape, when a concentrating solar cell is manufactured using a Si film formed on the surface of the substrate 4, light incidence from all directions is caused to occur on the surface of the substrate 4. Therefore, it is possible to improve the light utilization efficiency per unit area.

  In the present specification, the “columnar shape” means a shape extending in an arbitrary direction, and examples thereof include a shape of a cylinder or a prism.

  Further, in this specification, the “pipe shape” is provided inside the outer shell portion so as to extend in the same direction as the outer shell portion extending in an arbitrary direction and the extending direction of the outer shell portion. For example, a shape having a hollow portion extending in the same direction as the extending direction of the prism may be included inside the prism.

[Process of forming metal film on substrate]
In the step of forming a metal film on the substrate (S30), a voltage is applied between the anode 3 immersed in the electrodeposition electrolyte 2 and the substrate 4 as the cathode, and the electrodeposition electrolyte 2 is electrolyzed. To be implemented. Thereby, as shown in the schematic cross-sectional view of FIG. 3, the metal M is deposited on the surface of the substrate 4 according to the following formula (III), and the metal film 5 is formed on the surface of the substrate 4.

M ^{n +} + ne ⁻ → M (III)

Here, it is preferable to perform the electrolysis of the electrodeposition electrolyte 2 by setting the absolute value of the current density of the current flowing between the anode 3 and the substrate 4 on the substrate 4 to 1 mA / cm ² or more and 500 mA / cm ² or less. More preferably, the electrodeposition electrolyte 2 is electrolyzed at 1 mA / cm ² or more and 300 mA / cm ² or less. When the electrodepositing electrolyte 2 is electrolyzed with the absolute value of the current density of the current flowing between the anode 3 and the substrate 4 being 1 mA / cm ² or more, the metal film 5 is formed on the surface of the substrate 4. This can be done in a shorter time. Further, when electrolysis of the electrodepositing electrolyte 2 is carried out with the absolute value of the current density of the current flowing between the anode 3 and the substrate 4 being 500 mA / cm ² or less, particularly 300 mA / cm ² or less, the surface is smooth. The metal film 5 with improved properties can be formed. In addition, it is more preferable to carry out absolute value electrolytic electrodeposition析用electrolyte 2 as a 50 mA / cm ² or more 250 mA / cm ² or less of the current density of the current flowing between the anode 3 and the substrate 4. When electrolysis of the electrodepositing electrolyte 2 is performed with the absolute value of the current density of the current flowing between the anode 3 and the substrate 4 set to 50 mA / cm ² or more, the electrolysis of the electrodepositing electrolyte 2 is performed at a practical speed. And the metal film 5 is less likely to be peeled off from the surface of the substrate 4. In addition, when electrolysis of the electrodepositing electrolyte 2 is performed with the absolute value of the current density of the current flowing between the anode 3 and the substrate 4 being 250 mA / cm ² or less, the metal film having improved surface smoothness. 5 can be formed.

[Step of removing electrolyte for electrodeposition by washing with water]
The step of removing the electrodepositing electrolyte by washing (S40) is performed by washing the electrodepositing electrolyte 2 adhering to the surface of the metal film 5 with water after the step of depositing the metal film 5 on the substrate 4 (S30). This is done by removing.

In the present embodiment, a molten salt prepared from KF and KCl and containing K ⁺ , F ⁻ and Cl ⁻ is used as a molten salt for dissolving the M compound as an electrodeposition target. Compared with a molten salt prepared using a metal fluoride other than KF, the solubility in water can be increased, so that it adheres to the surface of the metal film 5 formed by electrodeposition of M on the substrate 4. The electrolyte for electrodeposition can be easily removed by washing with water.

[Metal film]
The ratio (100 × (Ra / R)) of the surface average roughness Ra of the metal film 5 to the average thickness R of the metal film 5 manufactured by the metal film manufacturing method of the embodiment is 10% or less. Is preferable, and it is more preferable that it is 5% or less. In this case, the surface of the metal film 5 can be made smoother.

  The surface average roughness Ra and the average thickness R of the metal film 5 were respectively determined by polishing paper (grain size: 240, 400) attached to a rotary polishing machine after the metal film 5 was embedded in the resin and the resin was dried. No. 600, 1000 and 2000), the resin is polished to expose the cross section of the metal film 5. And the surface average roughness Ra and average thickness R of the metal film 5 can be measured by observing the exposed cross section of the metal film 5 using SEM (for example, VE-8800 made by Keyence Corporation). .

  The thickness of the metal film 5 is perpendicular to the surface of the substrate 4 in the SEM cross section between the substrate 4 and the metal film 5, and from the surface on the metal film 5 side of the substrate 4 to the side opposite to the substrate 4 of the metal film 5. This means the length of the perpendicular to the surface. The surface average roughness Ra of the metal film 5 means the arithmetic average roughness Ra defined in JIS B 0601 (2001). Further, the average thickness R of the metal film 5 means an arithmetic average of the thickness of the metal film 5.

  The purity of the metal film 5 manufactured by the metal film manufacturing method of the embodiment is preferably 99.9% by mass or more. When the purity of the metal film 5 is 99.9% by mass or more, a silicon film is deposited as the metal film 5 and the conversion efficiency of the solar cell tends to be improved when this is used as a solar cell. In addition, a film containing W, Mo, Ti and at least two kinds of these alloys is deposited as the metal film 5, and the function of the film is improved when it is used as a protective film having a function of high hardness and wear resistance. Can be made.

  The purity of the metal film 5 is the ratio of the mass obtained by subtracting the total mass of impurities from the total mass of the metal film 5 with respect to the total mass of the metal film 5, and can be calculated by the following formula (IV).

  Purity [%] of metal film 5 = 100 × (mass obtained by subtracting the total mass of impurities from the total mass of metal film 5) / (total mass of metal film 5) (IV)

  In the present specification, the “impurity” of the metal film 5 means a component other than M that becomes an electrodeposition target in, for example, boron, phosphorus, iron, aluminum, lithium, potassium, magnesium, and calcium.

  The purity of the metal film 5 can be measured by glow discharge mass spectrometry (GD-MS). As a measuring device, for example, VG9000 manufactured by Thermo Electron Co., Ltd. can be used. The purity of the metal film 5 by glow discharge mass spectrometry is determined by, for example, determining the content of impurity components other than the M component constituting the sputtered metal film 5 by sputtering the metal film 5 to a thickness of 1 to 5 μm from the surface. This can be done by measuring.

  The metal film 5 may be an alloy of a metal electrodeposited from the electrodeposition electrolyte 3 and a metal contained in the substrate 4. Also in this case, the metal film 5 having a smooth surface at a relatively low temperature can be formed.

[Preferred Form of Metal Film Manufacturing Method]
In the case where a Si film is formed as a metal film 5 on the substrate 4 by electrodeposition of the electrolyte 2 for electrodeposition according to the embodiment, SiCl ₄ is blown into a molten salt of KF and KCl, so that KF and KCl It is preferable to produce the electrodeposition electrolyte 2 of the embodiment by adding a Si compound to the molten salt.

That is, by blowing SiCl ₄ into a molten salt of KF and KCl, an ion exchange reaction represented by the following formula (V) can be caused.

SiCl ₄ + 6F ⁻ → SiF ₆ ²⁻ + 4Cl ⁻ (V)

Then, as shown in FIG. 2, the anode 3 and the substrate 4 as the cathode are immersed in the electrodeposition electrolyte ² containing SiF ₆ ²⁻ , and a current flows between the anode 3 and the substrate 4. Thus, when electrolysis of the electrodeposition electrolyte 2 is performed, a reaction represented by the following formula (VI) occurs at the anode 3, and a reaction represented by the following formula (VII) occurs at the substrate 4 as the cathode. Get up.

(Anode) 4Cl ⁻ → 2Cl ₂ + 4e ⁻ (VI)

(Cathode) SiF ₆ ²⁻ + 4e ⁻ → Si + 6F ⁻ (VII)

  Therefore, when the reaction formulas (V) to (VII) are collected, a reaction formula represented by the following formula (VIII) is obtained.

SiCl ₄ → Si + 2Cl ₂ (VIII)

Therefore, in the preferred embodiment of the method for producing a metal film described above, the electrodepositing electrolyte 2 can be electrolyzed without changing the composition of the electrodepositing electrolyte 2, so that the metal film 5 is formed on the substrate 4. The Si film can be formed continuously and efficiently. In a preferred embodiment of the above-described method for producing a metal film, chlorine gas (Cl ₂ ) that is a by-product of the Si film as the metal film 5 produces SiCl ₄ that is blown into a molten salt of KF and KCl. Can be reused. From these viewpoints, after SiCl ₄ is blown into the molten salt of KF and KCl, the electrodeposition electrolyte 2 in which the Si component is added to the molten salt of KF and KCl is electrolyzed to thereby form Si as the metal film 5. It is preferable to form a film.

[Other forms of metal film manufacturing method]
In the above description, the case where the electrolyte 2 for electrodeposition is prepared by adding an M compound as an electrodeposition target to a molten salt of KF and KCl has been described. The electrodepositing electrolyte 2 can also be produced.

  FIG. 4 is a schematic cross-sectional view illustrating an example of a process for producing the electrodeposition electrolyte 2 by anodic dissolution of M. As shown in FIG. 4, when the electrodepositing electrolyte 2 is prepared by dissolving the anode of M, first, the M substrate 3a, which is the object of electrodeposition, is immersed in the molten salt 2a of KF and KCl as the anode. . And by flowing an electric current between the board | substrate 3a as an anode and the board | substrate 4 as a cathode, M elutes from the board | substrate 3a to the molten salt 2a, and the electrolyte 2 for electrodeposition can be produced.

[Function and effect]
When an electrodeposition electrodepositing electrolyte is produced using a molten salt made of a metal chloride, a metal film having a smooth surface cannot be formed. On the other hand, when an electrodeposition electrodeposited electrolyte is produced from a molten salt prepared using a metal fluoride other than KF, a metal film having a smooth surface can be formed. It is difficult to wash and remove the electrodeposition electrolyte adhering to the surface of the metal film. Furthermore, when an electrodeposition electrodeposited electrolyte is prepared using a molten salt of KF single salt, a metal film having a smooth surface can be formed, but the melting point of KF single salt is high. Electrodeposition cannot be performed at a low temperature, the substrate on which the metal film is formed is thermally damaged, and the metal film is peeled off from the substrate.

Therefore, in the present embodiment, a molten salt that is prepared from KF and KCl and contains K ⁺ , F ^−, and Cl ⁻ is used as a molten salt for dissolving the M compound that is an electrodeposition target. Therefore, the solubility in water can be increased as compared with the case where a metal fluoride other than the conventional KF is used, and therefore, the electrode attached to the surface of the metal film 5 formed by the electrodeposition of M on the substrate 4. The electrolyte for deposition can be easily removed by washing with water.

  In this embodiment, since a binary molten salt of KF and KCl is used, electrodeposition can be performed at a lower temperature than when a KF single salt is used, and a smooth surface can be obtained. A metal film can be formed.

[Experimental Examples 1 to 21]
<Preparation of electrolyte for electrodeposition>
A molten salt made of the material shown in the column of molten salt in Table 1 was prepared, and K ₂ SiF ₆ powder, SiCl ₄ gas, or K ₂ TiF ₆ powder shown in the column of metal compound in Table 1 was added to 100 mol of molten salt. by dissolving at a rate of 0.5Mol～15mol, the total mass ratio between KF and KCl shown in Table 1, Si ⁴⁺ cation fraction and F ^- electrodeposition of example 1 to experiment example 21 having an anion fraction An electrolyte was prepared. The Si ⁴⁺ cation fraction shown in Table 1 is calculated by the following formula (IX), the Ti ⁴⁺ cation fraction is calculated by the following formula (X), and the F ⁻ anion fraction is: (XI). The molar mass of KF was 58.1, the molar mass of KCl was 74.6, and the molar mass of K ₂ SiF ₆ was 220.3.

Si ⁴⁺ cation fraction = (amount of substance of Si ^{4+ in} the electrolyte for electrodeposition) / ((amount of substance of Si ^{4+ in} the electrolyte for electrodeposition) + (amount of substance of K ^{+ in} the electrolyte for electrodeposition) )) ... (IX)

Ti ⁴⁺ cation fraction = (amount of substance of Ti ^{4+ in} the electrolyte for electrodeposition) / ((amount of substance of Ti ^{4+ in} the electrolyte for electrodeposition) + (amount of substance of K ^{+ in} the electrolyte for electrodeposition) ))… (X)

F ⁻ anion fraction = (amount of F ^{− in} the electrodepositing electrolyte) / ((amount of F ^{− in} the electrodepositing electrolyte) + (amount of Cl ⁻ in the electrodepositing electrolyte)) (XI)

Specifically, in Experimental Example 1, Experimental Example 6 to Experimental Example 11, and Experimental Example 16 to Experimental Example 20, KF (manufactured by Wako Pure Chemical Industries, Ltd.) and KCl (manufactured by Wako Pure Chemical Industries, Ltd.) are used. KF: KCl = 45: by melting the mixture were mixed in a molar ratio of 55, the molar ratio of KCl for KF (KF ratio of amount of substance n _KF of KCl to a substance amount n _KCl of (n _KCl / n _KF)) Was a KF-KCl molten salt having a melting point of 871K. Thereafter, K ₂ SiF ₆ powder (manufactured by Wako Pure Chemical Industries, Ltd.) was added (Experimental Example 1, Experimental Example 6 to Experimental Example 11 and Experimental Example) so as to have a ratio of 2 mol to 100 mol of KF-KCl molten salt. 17 to Experimental Example 20) or by blowing SiCl ₄ gas (Experimental Example 16), the electrolytes for electrodeposition of Experimental Example 1, Experimental Example 6 to Experimental Example 11 and Experimental Example 16 to Experimental Example 20 were produced. . The SiCl ₄ gas was blown by a method using a pipe.

  In Experimental Example 2, a KF molten salt having a melting point of 1133K is produced by melting KF, and in Experimental Example 3, a KCl molten salt having a melting point of 1043K is produced by melting KCl. did. In Experimental Example 4, a mixture obtained by mixing LiF (lithium fluoride), NaF (sodium fluoride), and KF at a molar ratio of LiF: NaF: KF = 46.5: 11.5: 42 was melted. As a result, a LiF-NaF-KF molten salt having a melting point of 727K was produced. Furthermore, in Experimental Example 5, a LiF-KF molten salt having a melting point of 765K was prepared by melting a mixture obtained by mixing LiF and KF at a molar ratio of LiF: KF = 50: 50. Thereafter, the electrodeposition electrolytes of Experimental Examples 2 to 5 were produced in the same manner as Experimental Example 1, Experimental Examples 6 to 11, and Experimental Examples 17 to 20.

In Experimental Example 12, the mixture of KF and KCl mixed at a molar ratio of KF: KCl = 87: 13 was melted, so that the molar ratio of KCl to KF (n _KCl / n _KF ) was 0.15. A KF-KCl molten salt having a melting point of 1093K was prepared. In Experimental Example 13, the molar ratio of KCl to KF (n _KCl / n _KF ) was obtained by melting a mixture obtained by mixing KF and KCl at a molar ratio of KF: KCl = 62.5: 37.5. A KF-KCl molten salt having a melting point of 973K and a melting point of 973K was prepared. Thereafter, the electrodeposition electrolytes of Experimental Example 12 and Experimental Example 13 were produced in the same manner as Experimental Example 1, Experimental Example 6 to Experimental Example 11, and Experimental Example 17 to Experimental Example 20.

In Experimental Example 14, the molar ratio of KCl to KF (n _KCl / n _KF ) was obtained by melting a mixture obtained by mixing KF and KCl at a molar ratio of KF: KCl = 29.4: 70.6. A KF-KCl molten salt having a melting point of 933K and a melting point of 933K was prepared. In Experimental Example 15, the molar ratio of KCl to KF (n _KCl / n _KF ) was obtained by melting a mixture obtained by mixing KF and KCl at a molar ratio of KF: KCl = 15.4: 84.6. A KF-KCl molten salt having a melting point of 998K was prepared. Thereafter, the electrodeposition electrolytes of Experimental Example 14 and Experimental Example 15 were produced in the same manner as Experimental Example 1, Experimental Example 6 to Experimental Example 11, and Experimental Example 17 to Experimental Example 20.

In Experimental Example 21, K ₂ TiF ₆ (manufactured by Wako Pure Chemical Industries, Ltd.) was added instead of K ₂ SiF ₆ powder at a rate of 0.5 mol with respect to 100 mol of KF-KCl molten salt. In the same manner as in Experimental Example 1, Experimental Example 6 to Experimental Example 11, and Experimental Example 17 to Experimental Example 20, the electrodeposition electrolyte of Experimental Example 21 was produced.

<Electrodeposition of electrolyte for electrodeposition>
A glassy carbon crucible was filled with the electrodeposition electrolytes of Experimental Examples 1 to 21 prepared as described above, and was placed on the bottom of a quartz inner holder installed in an airtight container composed of a cantal cylindrical container and a stainless steel lid. The glassy carbon crucible after filling with the electrolyte for electrodeposition of Experimental Examples 1 to 21 was allowed to stand. And Ar (argon) gas was flowed in the airtight container by the flow volume of 300 ml / min, and the atmosphere in an airtight container was made into Ar atmosphere. Then, a cylindrical glassy carbon rod having a circular surface with a diameter of 5 mm as an anode serving as a counter electrode is immersed in each of the electrodeposition electrolytes of Experimental Examples 1 to 21 as a cathode. (Tokai Carbon Co., Ltd.) was immersed. Then, using the electrochemical measuring apparatus (HZ-3000 manufactured by Hokuto Denko Co., Ltd.), the conditions for the temperature, current density, and electrodeposition time shown in Table 2 were used. Constant current electrolysis was performed to form a metal film on the surface of the cathode.

Specifically, in Experimental Example 1, Experimental Example 6 to Experimental Example 8, and Experimental Example 16 to Experimental Example 20, the temperature of the electrodeposition electrolyte was 923 K, the current density was −193 mA / cm ² , and the electrodeposition time was 15 minutes. Constant current electrolysis was performed under the conditions. At this time, in Experimental Example 1, Experimental Examples 6 to 8, and Experimental Examples 16 to 20, the anode was a glassy carbon rod. However, in Experimental Example 1, Experimental Example 6 to Experimental Example 8 and Experimental Example 16, the cathode is a cylindrical Ag wire (manufactured by Niraco Co., Ltd.) having a circular surface with a diameter of 1 mm, and Experimental Example 17 to Experimental Example 20 The cathode was a carbon rod, a cylindrical Mo wire (manufactured by Niraco Co., Ltd.) having a circular surface with a diameter of 1 mm, a W wire and an Ag plate.

In Experimental Examples 2 to 5, the current density was −193 mA / cm ² , the electrodeposition time was 15 minutes, the anode was a glassy carbon rod, and the cathode was Ag wire. Moreover, the temperature of the electrolyte for electrodeposition at the time of electrodeposition of Experimental Example 2 to Experimental Example 5 was set to 1173K, 1073K, 873K, and 873K, respectively.

In Experimental Examples 6 to 8, the current density was −193 mA / cm ² , the electrodeposition time was 15 minutes, the anode was a glassy carbon rod, and the cathode was Ag wire. K ₂ SiF ₆ added to the electrolyte for electrodeposition was dissolved at a ratio of 5 mol, 10 mol and 15 mol, respectively, with respect to 100 mol of the molten salt.

In Experimental Examples 9 to 11, constant current electrolysis was performed at a temperature of 923K. However, the current densities of Experimental Example 9 to Experimental Example 11 were −97 mA / cm ² , −386 mA / cm ² and −772 mA / cm ² , respectively, and the electrodeposition times of Experimental Example 9 to Experimental Example 11 were respectively 30 minutes, 7.5 minutes and 3.75 minutes. At this time, in Experimental Examples 9 to 11, the anode was a glassy carbon rod and the cathode was an Ag wire.

Furthermore, in Experimental Examples 12 to 15, the current density was −193 mA / cm ² , the electrodeposition time was 15 minutes, the anode was a glassy carbon rod, and the cathode was Ag wire. Moreover, the temperature of the electrolyte for electrodeposition at the time of electrodeposition of Experimental Example 12 to Experimental Example 15 was set to 1123K, 1023K, 973K, and 1073K, respectively.

In Experimental Example 21, an electrodepositing electrolyte to which K ₂ TiF ₆ was added at a ratio of 0.5 mol with respect to 100 mol of the molten salt was used. The anode was a glassy carbon rod, the cathode was an Fe wire, the pseudo reference electrode was a platinum (Pt) wire, and constant potential electrolysis was performed at a temperature of 923 K at a potential of +0.25 V for 30 minutes. The current density during electrolysis was an average of −156 mA / cm ² .

<Evaluation of metal film>
As described above, the thickness of the experimental examples 1 to 21 of the materials shown in Table 3 on the surface of the cathode shown in Table 2 by performing electrodeposition of the electrolyte for electrodeposition of Experimental Examples 1 to 21. A metal film of about 100 μm was formed. Specifically, in Experimental Examples 1 to 17 and Experimental Example 20, a Si film was formed, in Experimental Example 18, a Mo silicide film was formed, and in Experimental Example 19, a W silicide film was formed. Furthermore, in Experimental Example 21, an Fe—Ti film that is an alloy film of Fe and Ti was formed.

  And about the metal film of Experimental example 1-Experimental example 21 formed as mentioned above, it evaluated from the viewpoint of water washing removal, peeling at the time of water washing, and Ra / R, and integrated these. A comprehensive evaluation was performed. The results are shown in Table 3. Experimental Example 1 and Experimental Examples 6 to 21 are Examples, and Experimental Examples 2 to 5 are Comparative Examples.

[Evaluation of water removal]
(Evaluation method for water removal)
Evaluation of water washing removal in Experimental Examples 1 to 21 was carried out by immersing the metal film formed on the cathode in 333K distilled water for 20 hours, and then drying the XRD device (Ultima IV manufactured by Rigaku Corporation; CuKα line). , Λ = 0.15418 nm, 40 kV, 40 mA) was subjected to XRD analysis of the components remaining on the surface of the dried metal film, and evaluated according to the following evaluation criteria.

(Evaluation criteria for water washing removal)
A: No X-ray diffraction peak attributed to the electrolyte component for electrodeposition remaining on the surface of the metal film B: Slight X-ray diffraction peak attributed to the electrolyte component for electrodeposition remaining on the surface of the metal film C: Metal There is a clear X-ray diffraction peak due to the electrolyte component for electrodeposition remaining on the surface of the film [Evaluation of peeling during washing with water]
(Evaluation method for peeling during washing with water)
As described above, the evaluation of peeling of the metal film in Experimental Example 1 to Experimental Example 21 when washed with water was performed by immersing the metal film formed on the cathode in 333K distilled water for 20 hours and lifting the cathode. The presence or absence of peeling of the metal film from was evaluated according to the following evaluation criteria.

(Evaluation criteria for peeling during washing with water)
A: No peeling of metal film from cathode B: Slight peeling of metal film from cathode C: Complete peeling of metal film from cathode [Ra / R evaluation]
The Ra / R of the metal film of Experimental Example 1 to Experimental Example 21 is determined by polishing paper (grain size) attached to a rotary polishing machine after the metal film of Experimental Example 1 to Experimental Example 21 was embedded in the resin and the resin was dried. : No. 240, No. 400, No. 600, No. 1000 and No. 2000) By observing the cross section of the metal film exposed by polishing the resin with SEM, the average surface roughness Ra and the average thickness of the metal film R was measured and calculated by multiplying the value obtained by dividing the surface average roughness Ra of the metal film by the average thickness R by 100. Note that the lower the value of Ra / R in Table 3, the smoother the surface of the metal film.

<Evaluation results>
(Experimental example 1)
As shown in Table 3, in Experimental Example 1, since the molten salt used for the preparation of the electrodepositing electrolyte is made using KF, a Si film having a smooth surface can be formed. It was easy to remove the electrodeposition electrolyte deposited on the surface of the Si film by washing with water. Furthermore, in Experimental Example 1, the molten salt used for the preparation of the electrodeposition electrolyte is prepared using both KF and KCl, and is not prepared using a metal fluoride other than KF. Since electrodeposition could be performed at a relatively low temperature and thermal damage to the cathode could be kept low, the occurrence of peeling of the Si film during washing with water could be suppressed.

  FIG. 5 shows an SEM image of a cross section exposed in the experimental example 1 after the Si film 12 formed on the surface of the Ag wire 11 is embedded in the resin 13 and then polished by polishing paper attached to a rotary polishing machine. Show. As shown in FIG. 5, it can be seen that the Si film 12 formed in Experimental Example 1 is densely formed.

  FIG. 6 shows an XRD pattern of the Si film 12 formed on the surface of the Ag line 11 in Experimental Example 1. As shown in FIG. 6, a peak corresponding to Si was confirmed in the XRD pattern of the Si film 12 formed in Experimental Example 1.

(Experimental example 2)
As shown in Table 3, in Experimental Example 2, since the molten salt used in the preparation of the electrodeposition electrolyte was prepared using KF, a high-purity Si film with a smooth surface was formed. It was. However, in Experimental Example 2, since the temperature of the electrolyte for electrodeposition during electrodeposition was very high, the thermal damage of the cathode was large, and the Si film was completely peeled off when washed with water.

(Experimental example 3)
As shown in Table 3, in Experimental Example 3, since the molten salt used in the preparation of the electrodeposition electrolyte was not prepared using KF, a Si film having a non-smooth surface was formed. Further, since the temperature of the electrolyte for electrodeposition during electrodeposition was very high, thermal damage to the cathode was great, and the Si film was completely peeled off during washing with water.

(Experimental example 4)
As shown in Table 3, in Experimental Example 4, since the electrolyte for electrodeposition was prepared using a ternary molten salt of metal fluoride, a Si film having a smooth surface was formed. However, since the electrolyte for electrodeposition was produced using a metal fluoride other than KF, the peak of the XRD pattern caused by the residue of the electrolyte for electrodeposition was clearly confirmed on the surface of the Si film after washing with water.

(Experimental example 5)
As shown in Table 3, in Experimental Example 5, since the electrolyte for electrodeposition was prepared using a binary molten salt of metal fluoride, a Si film having a smooth surface was formed. However, since the electrolyte for electrodeposition was produced using a metal fluoride other than KF, the peak of the XRD pattern caused by the residue of the electrolyte for electrodeposition was clearly confirmed on the surface of the Si film after washing with water.

(Experimental Example 1 and Experimental Examples 6-8)
In Experimental Example 1, Experimental Example 6 and Experimental Example 7, the electrodepositing electrolyte was prepared using a molten salt composed of KF and KCl, and thus the electrodepositing electrolyte adhered to the surface of the Si film was washed with water. Removal was confirmed. However, in Experimental Example 8 in which the amount of K ₂ SiF ₆ powder added was large, a slight XRD pattern peak of the electrodeposition electrolyte residue was confirmed on the surface of the Si film after water washing.

(Experimental Example 1 and Experimental Examples 9-11)
In Experimental Example 1, Experimental Example 9, and Experimental Example 10, since the absolute value of the current density during electrodeposition is in the range of 1 mA / cm ^{2 to} 500 mA / cm ^2, a Si film having a smooth surface is formed. It was. However, in Experimental Example 11 in which the absolute value of the current density during electrodeposition exceeds the range, it was confirmed that the smoothness of the surface of the Si film was inferior compared with Experimental Example 1, Experimental Example 9 and Experimental Example 10. It was done.

(Experimental Examples 12-15)
In Experimental Example 12, a Si film having a smooth surface can be obtained because the molar ratio of KCl to KF is less than 0.2. However, since the temperature of the electrolyte for electrodeposition during electrodeposition is high, The Si film peeled slightly.

  In Experimental Example 13 and Experimental Example 14, since the molar ratio of KCl to KF is included in the range of 0.2 or more and 5 or less, it is possible to obtain a Si film having a smooth surface, and after washing with water. Although peeling of the Si film did not occur, the value of Ra / R was higher in Experimental Example 14 having a higher molar ratio, resulting in a lack of surface smoothness of the Si film.

  In Experimental Example 15, since the molar ratio of KCl to KF is larger than 0.5, the result is that the surface of the Si film lacks smoothness compared with Experimental Examples 12 to 14, and for the electrodeposition during the electrodeposition. Since the temperature of the electrolyte was high, the Si film slightly peeled off after washing with water.

(Experimental Examples 16 to 20)
In Experimental Example 16, a Si film was formed in the same manner as in Experimental Example 1 except that SiCl ₄ gas was blown in place of adding the K ₂ SiF ₆ powder. Results were obtained.

  In Experimental Example 17, the Si film was formed in the same manner as in Experimental Example 1 except that a carbon rod was used instead of the Ag wire, but the same good results as in Experimental Example 1 were obtained. .

  In Experimental Example 18, a metal film was formed in the same manner as in Experimental Example 1 except that Mo wire was used instead of Ag wire. In Experimental Example 19, W wire was used instead of Ag wire. In the same manner as in Experimental Example 1, metal films were formed, but a Mo silicide film and a W silicide film were formed instead of pure metal.

  In Experimental Example 20, the Si film was formed in the same manner as in Experimental Example 1 except that an Ag plate was used instead of the Ag wire, but good results similar to those in Experimental Example 1 were obtained. .

In Experimental Example 21, electrolysis was performed at an average current density of −156 mA / cm ² using K ₂ TiF ₆ instead of K ₂ SiF ₆ and using Fe wire instead of Ag wire as a cathode. The molten salt used in the preparation of the electrolyte for electrodeposition is prepared using both KF and KCl, and is not prepared using a metal fluoride other than KF, so electrodeposition is performed at a relatively low temperature. In addition, it was possible to suppress the occurrence of peeling of the Fe—Ti film, and there was no residue when washed with water. FIGS. 7A to 7C show XRD patterns of the Fe—Ti film formed on the surface of the Fe wire in Experimental Example 21. FIG. As shown in FIG. 7A to FIG. 7C, an XRD pattern of an FeTi phase that is an alloy of Ti as an electrodeposited material and Fe in the Fe wire is confirmed on the surface of the Fe wire as the cathode. It was.

[Experimental Examples 22 to 33]
<Preparation of electrolyte for electrodeposition>
A molten salt made of the material shown in the column of the molten salt in Table 4 was prepared, and K ₂ SiF ₆ powder was dissolved at a ratio of 0.5 mol to 5 mol with respect to 100 mol of the molten salt, whereby KF shown in Table 4 and the total weight ratio of the KCl, Si ⁴⁺ cation fraction and F ^- to produce the electrostatic析用electrolyte of example 22 to experiment 33 having an anionic fraction. The Si ⁴⁺ cation fraction shown in Table 4 was calculated by the above formula (IX), and the F ⁻ anion fraction was calculated by the above formula (XI).

Specifically, in Experimental Example 22 to Experimental Example 33, KF (manufactured by Wako Pure Chemical Industries, Ltd.) and KCl (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed at a molar ratio of KF: KCl = 45: 55. by melting the mixture, the mole ratio of KCl for KF (ratio of amount of substance n _KF of KCl to a substance amount n _KCl of _{KF (n KCl / n KF)} ) is 1.2, a melting point of 871K A KF-KCl molten salt was made. Then, 0.5 mol (Experimental example 22), 2 mol (Experimental example 23 to Experimental example 26), 3.5 mol (Experimental example 27 to Experimental example 30) and 5 mol (Experimental example 31) were each used for 100 mol of KF-KCl molten salt. The electrolyte for electrodeposition of Experimental Example 22 to Experimental Example 33 was prepared by adding K ₂ SiF ₆ powder (manufactured by Wako Pure Chemical Industries, Ltd.) so as to have a ratio of ˜Experimental Example 33).

<Electrodeposition of electrolyte for electrodeposition>
The electrodepositing electrolytes of Experimental Examples 22 to 33 prepared as described above were filled in a glassy carbon crucible and placed on the bottom of a quartz inner holder installed in an airtight container consisting of a cantal cylindrical container and a stainless steel lid. The glassy carbon crucible after filling with the electrolyte for electrodeposition of Experimental Examples 22 to 33 was allowed to stand. Then, the atmosphere in the hermetic container was changed to an Ar atmosphere by flowing Ar gas into the hermetic container at a flow rate of 300 ml / min. Each of the electrodeposition electrolytes of Experimental Examples 22 to 33 is immersed with Ag wire as a cathode, and a cylindrical glassy carbon rod (Tokai Carbon) having a circular surface with a diameter of 5 mm as an anode as a counter electrode. Soaked). Then, using the electrochemical measuring device (HZ-3000 manufactured by Hokuto Denko Co., Ltd.), the conditions for the temperature, current density, and electrodeposition time shown in Table 5 were used. Constant current electrolysis was performed to form a Si film on the surface of the Ag wire as the cathode.

Specifically, in Experimental Example 22, Experimental Example 23, and Experimental Example 27, constant-current electrolysis was performed under the conditions of an electrolyte electrodeposition temperature of 923 K, a current density of −39 mA / cm ² , and an electrodeposition time of 80 minutes. .

Further, in Experimental Example 24, Experimental Example 28, and Experimental Example 31, constant current electrolysis was performed under the conditions of an electrodeposition electrolyte temperature of 923 K, a current density of −78 mA / cm ² , and an electrodeposition time of 40 minutes.

Further, in Experimental Example 25, Experimental Example 29, and Experimental Example 32, constant current electrolysis was performed under the conditions of the temperature of the electrodeposition electrolyte 923K, the current density of −155 mA / cm ² , and the electrodeposition time of 20 minutes.

Furthermore, in Experimental Example 26, Experimental Example 30 and Experimental Example 33, constant-current electrolysis was performed under the conditions of an electrodeposition electrolyte temperature of 923 K, a current density of -310 mA / cm ² , and an electrodeposition time of 10 minutes.

<Evaluation of Si film>
As described above, by performing electrodeposition of the electrolyte for electrodeposition of Experimental Examples 22 to 33, the thicknesses of Experimental Examples 22 to 33 of the materials shown in Table 6 on the surface of the Ag wire are about 60 μm. A Si film was formed.

  And about Si film | membrane of Experimental Example 22-Experimental Example 33 formed as mentioned above, it evaluated from the viewpoint of water washing removal, peeling at the time of water washing, and Ra / R, and integrated these. A comprehensive evaluation was performed. The results are shown in Table 6. Experimental Examples 22 to 33 are examples.

[Evaluation of water removal]
(Evaluation method for water removal)
Evaluation of water washing removal in Experimental Example 22 to Experimental Example 33 was conducted by immersing the Si film formed on the Ag wire in 333K distilled water for 20 hours and then drying the XRD device (Ultima IV manufactured by Rigaku Corporation; CuKα wire). , Λ = 0.15418 nm, 40 kV, 40 mA) was subjected to XRD analysis of components remaining on the surface of the Si film after drying, and evaluation was performed according to the following evaluation criteria.

(Evaluation criteria for water washing removal)
A: No X-ray diffraction peak due to the electrodeposition electrolyte component remaining on the surface of the Si film B: There is a slight X-ray diffraction peak due to the electrodeposition electrolyte component remaining on the surface of the Si film C: Si There is a clear X-ray diffraction peak due to the electrolyte component for electrodeposition remaining on the surface of the film [Evaluation of peeling during washing with water]
(Evaluation method for peeling during washing with water)
As described above, the evaluation of peeling of the Si films in Experimental Examples 22 to 33 at the time of washing was performed when the Si film formed on the Ag line was immersed in 333K distilled water for 20 hours and the Ag line was pulled up. The presence or absence of peeling of the Si film from the Ag line was evaluated according to the following evaluation criteria.

(Evaluation criteria for peeling during washing with water)
A: No peeling of Si film from Ag line B: Slight peeling of Si film from Ag line C: Complete peeling of Si film from Ag line [Ra / R evaluation]
The Ra / R of the Si films of Experimental Examples 22 to 33 is determined by polishing paper (grain size) attached to a rotary polishing machine after the Si films of Experimental Examples 22 to 33 were embedded in the resin and the resin was dried. : No. 240, No. 400, No. 600, No. 1000 and No. 2000) By observing the cross section of the Si film exposed by polishing the resin with SEM, the surface average roughness Ra and the average thickness of the Si film R was measured and calculated by multiplying the value obtained by dividing the surface average roughness Ra of the Si film by the average thickness R by 100. Note that the lower the value of Ra / R in Table 6, the smoother the surface of the Si film. 8 to 19 show SEM images of cross sections of the Si films formed in Experimental Examples 22 to 33, respectively. 20 is an enlarged view of the SEM image of the cross section of the Si film formed in Experimental Example 24, and FIG. 21 is an enlarged view of the SEM image of the cross section of the Si film formed in Experimental Example 25.

<Evaluation results>
As shown in Table 6, in Experimental Example 22 to Experimental Example 33 in which the Si ⁴⁺ cation fraction is 0.05 or less, it is easy to remove the electrodepositing electrolyte by washing with water after the formation of the Si film. As a result, no peeling of the Si film was observed.

In particular, Experimental Example 24 (Si ⁴⁺ cation fraction: 0.019) prepared by adding K ₂ SiF ₆ powder to a ratio of 2 mol and 3.5 mol with respect to 100 mol of KF-KCl molten salt, Electrodeposition of Experimental Example 25 (Si ^{4 +} cation fraction: 0.019), Experimental Example 28 (Si ^{4 +} cation fraction: 0.032) and Experimental Example 29 (Si ^{4 +} cation fraction: 0.032) for use electrolyte, the absolute value of the current density at Ag line of the current flowing between the glassy carbon rod and an Ag wire as an anode 50 mA / cm ² or more 250 mA / cm ² or less (experimental examples 24 and experimental example 28: 78mA / cm ^2; experiment 25 and experiment example 29: 155mA / cm ²⁾ as a Si film obtained by performing electrolysis, no peeling of the Si film from the Ag line, had a surface of the Si film is also smooth Results were seen.

[Experimental Examples 34 to 37]
<Preparation of electrolyte for electrodeposition>
A molten salt made of the material shown in the column of molten salt in Table 7 was prepared, and the WCl ₄ powder shown in the column of the amount of metal compound when the molten salt in Table 7 was 100 mol was added to the molten salt in an amount of 0.00. dissolved at a rate of 1 mol (experimental examples 34 and experimental example 35), or WCl ₄ powder and WO ₃ powder and is dissolved in a proportion of one by 0.1mol to the molten salt 100mol respectively (experimental examples 36 and experimental example 37 Thus, electrolytes for electrodeposition of Experimental Example 34 to Experimental Example 37 were produced.

Specifically, by melting a mixture of KF (manufactured by Wako Pure Chemical Industries, Ltd.) and KCl (manufactured by Wako Pure Chemical Industries, Ltd.) at a molar ratio of KF: KCl = 45: 55, a KCl molar ratio (ratio of KF substance amount n _KCl to KCl amount of substance _{n KF (n KCl / n KF} )) is 1.2, to prepare a KF-KCl molten salt having a melting point of 871K. Thereafter, WCl ₄ powder is added so that the ratio is 0.1 mol with respect to 100 mol of KF-KCl molten salt (Experimental Example 34 and Experimental Example 35), or WCl ₄ powder and WO ₃ powder are each added to 100 mol of molten salt. On the other hand, the electrolyte for electrodeposition of Experimental Example 34 to Experimental Example 37 was produced by adding 0.1 mol (Experimental Example 36 and Experimental Example 37).

<Electrodeposition of electrolyte for electrodeposition>
A glassy carbon crucible was filled with the electrodepositing electrolytes of Experimental Examples 34 to 37 prepared as described above, and placed on the bottom of the quartz inner holder installed in an airtight container composed of a cylindrical container made of Kanthal and a stainless steel lid. The glassy carbon crucible after filling with the electrolyte for electrodeposition of Experimental Examples 34 to 37 was allowed to stand. And Ar (argon) gas was flowed in the airtight container by the flow volume of 300 ml / min, and the atmosphere in an airtight container was made into Ar atmosphere. In each of the electrolytes for electrodeposition of Experimental Examples 34 to 37, a Mo substrate was immersed as a cathode, and cylindrical graphite having a circular surface with a diameter of 5 mm was immersed as an anode serving as a counter electrode. Then, using an electrochemical measurement device (HZ-3000 manufactured by Hokuto Denko Co., Ltd.), the temperature, potential (potential with respect to K ⁺ / K) and time (deposition time) shown in the column of electrodeposition conditions in Table 7 The electrodepositing electrolytes of Experimental Examples 34 to 37 were subjected to constant potential electrolysis under the conditions, and the metal films of Experimental Examples 34 to 37 were formed on the surface of the cathode.

<Evaluation of the surface of the metal film>
The surface of each metal film of Experimental Example 34 to Experimental Example 37 formed as described above was observed using a scanning electron microscope (SEM; VE-8800 manufactured by Keyence Corporation) under the condition of an acceleration voltage of 20 kV. Typically, FIG. 22 shows an SEM photograph of the surface of the metal film of Experimental Example 34, and FIG. 23 shows an SEM photograph of the surface of the metal film of Experimental Example 36.

  Further, the surface of each metal film of Experimental Examples 34 to 37 formed as described above was subjected to an acceleration voltage of 20 kV using an energy dispersive X-ray (EDX) analyzer (Genesis manufactured by EDAX Inc.). EDX analysis was performed. The results are shown in the column of W precipitation in the evaluation of Table 7. As shown in the column of W precipitation in the evaluation of Table 7, it was confirmed that there was W precipitation on the surfaces of all the metal films of Experimental Example 34 to Experimental Example 37. Also, from the results of EDX analysis, the surface of the metal film of Experimental Example 34 is typically made of Mo (14.0 atomic%), W (46.3 atomic%), and oxygen (39.7 atomic%). And the surface of the metal film of Experimental Example 36 was confirmed to be composed of Mo (19.5 atomic%), W (63.0 atomic%), and oxygen (17.5 atomic%). .

<Evaluation of cross section of metal film>
Each of the metal films of Experimental Examples 34 to 37 formed as described above is cut using a focused ion beam (FIB) device to expose the cross section, and each of the metal films of Experimental Examples 34 to 37 is exposed. The cross section was observed under the condition of an acceleration voltage of 2 kV using a low acceleration scanning electron microscope (ULTRA55), and the film thickness of the metal film on the Mo substrate was measured. The result is shown in the column of the film thickness in the evaluation of Table 7. As shown in the column of the film thickness of the evaluation in Table 7, the film thicknesses of the metal films of Experimental Example 34 to Experimental Example 37 are 0.3 μm, 0.2 μm, 0.5 μm, and 0.2 μm, respectively. confirmed. Typically, FIG. 24 shows a low acceleration scanning electron micrograph of the cross section of the metal film of Experimental Example 34, and FIG. 25 shows a low acceleration scanning electron micrograph of the cross section of the metal film of Experimental Example 36. 24 and 25 corresponds to the layer in which W is deposited.

  Further, EDX analysis was performed on the analysis point of the low acceleration scanning electron micrograph of the cross section of the metal film of Experimental Example 34 shown in FIG. 24 under the condition that the acceleration voltage was 30 kV using the same EDX analyzer. The result is shown in FIG. From the result of the EDX analysis, the cross section of the metal film at the analysis point in Experimental Example 34 is Mo (11.3 atomic%), W (69.9 atomic%), oxygen (2.1 atomic%), and carbon (16 .7 atomic%).

  Further, EDX analysis was performed on the analysis point of the low acceleration scanning electron micrograph of the cross section of the metal film of Experimental Example 36 shown in FIG. 25 under the condition that the acceleration voltage was 30 kV using the same EDX analyzer. The result is shown in FIG. From the result of EDX analysis, the cross section of the metal film at the above analysis point in Experimental Example 36 is Mo (13.4 atomic%), W (77.9 atomic%), oxygen (2.1 atomic%), carbon (3 .7 atomic%) and calcium (2.9 atomic%).

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The embodiment of the present invention can be used for an electrodeposition electrolyte and a method for manufacturing a metal film, and particularly preferably used for a silicon solar cell manufacturing process, a wear-resistant surface processing process, and a semiconductor manufacturing process. it can.

DESCRIPTION OF SYMBOLS 1 Container 2 Electrode for electrodeposition 2a Molten salt 3 Anode 3a Substrate 4 Substrate 5 Metal film 11 Ag wire 12 Si film 13 Resin

Claims (11)

And potassium ions, and fluoride ions, and chloride ions, and metal ions seen including,
The electrolyte for electrodeposition whose anion fraction of the said fluoride ion is 0.1-0.9.   The electrolyte for electrodeposition of Claim 1 whose cation fraction of the said metal ion is 0.12 or less. The electrolyte for electrodeposition according to claim 1 or 2 , wherein the metal ions include at least one selected from the group consisting of silicon ions, tungsten ions, molybdenum ions, titanium ions, nickel ions, and cobalt ions. Producing an electrolyte for electrodeposition from potassium fluoride, potassium chloride, and at least one of a metal compound and a metal;
Immersing the substrate in the electrodeposition electrolyte;
Forming a metal film on the substrate by electrolyzing the electrodeposition electrolyte using the substrate as a cathode;
See containing and removing by washing the electrostatic析用electrolyte adhering to the surface of the metal film,
The method for producing a metal film, wherein the anion fraction of fluoride ions in the electrolyte for electrodeposition is 0.1 or more and 0.9 or less . 5. The method for producing a metal film according to claim 4 , wherein in the step of producing the electrodeposition electrolyte, a total mass of the potassium fluoride and the potassium chloride is 70 mass% or more of the electrodeposition electrolyte. The step of preparing the electrolyte for electrodeposition includes
A step of preparing a molten salt by melting after obtained by mixing the potassium chloride and the potassium fluoride,
The method for producing a metal film according to claim 4 or 5 , comprising at least one of a step of adding at least one metal compound to the molten salt and an anodic dissolution of the metal. The method of manufacturing a metal film according to claim 6 , wherein the metal compound includes a metal chloride gas. The manufacturing method of the metal film of Claim 6 or Claim 7 whose molar ratio of the said potassium chloride with respect to the said potassium fluoride in the said molten salt is 0.2-5. In the step of forming a metal film on the substrate, performing electrolysis of said conductive析用electrolyte absolute value of the current density flowing a 1 mA / cm ² or more 500mA / cm ² or less of the current, of Claims 4 to 8 The manufacturing method of the metal film of any one of these. The method for producing a metal film according to any one of claims 4 to 9 , wherein the surface of the substrate contains at least one selected from the group consisting of iron, silver, carbon, copper, and molybdenum. The shape of the substrate, a columnar or tubular, method for producing a metal film according to any one of claims 4 to claim 10.