Film formation method

Abstract

The method for forming a film of the present invention includes: a first step of coating a first solution containing polysilazane on the surface (2a) of a metal substrate (2), and subjecting the first solution to silica conversion by heating to form a first film (1) having an opening defect portion (3) on the surface (2a) of the metal substrate (2); and a second step of coating a second solution containing polysilazane on the surface (1a) of the first film (1) to fill the opening defect portion (3), and subjecting the second solution to silica conversion by heating at a temperature lower than the heating temperature in the first step to form a second film (5) on the surface (1a) of the first film (1).

Description

Technical Field

[0001] The present invention relates to a method for forming a film having corrosion resistance. Background Art

[0002] Among the structural members of manufacturing apparatuses such as semiconductor or flat panel display, or apparatuses based on these, there are members exposed to corrosive gases or plasmas of corrosive gases.

[0003] These structural members are usually formed of metal materials such as aluminum alloy or stainless steel. However, metal materials such as aluminum alloy or stainless steel have low corrosion resistance to halogen-based corrosive gases or plasmas of these gases. Therefore, in order to impart corrosion resistance to these members, for example, sometimes a silica-based film using perhydropolysilazane is applied. The silica-based film is very dense and has high corrosion resistance to halogen-based corrosive gases or plasmas. Therefore, by forming a silica-based film on the surface of the structural member, the surface of the structural member can be separated from the external environment, and corrosion of the structural member can be suppressed.

[0004] In addition, the silica-based film formed using perhydropolysilazane is dense but fragile, and has a very small coefficient of linear expansion compared to metal materials. Therefore, cracks are generated in the film during the film formation process. In addition, in order to suppress the generation of the cracks, it is formed into a thin film and cannot sufficiently cover the structural member, and the effect of separating the structural member from the external environment is reduced, resulting in a problem of reduced anti-corrosion effect of the structural member.

[0005] In view of such a problem, Patent Document 1 discloses a method for forming a silica-based film using a solution containing perhydropolysilazane and polyorganosilazane.

[0006] In Patent Document 1, by making the solution contain polyorganosilazane, a film having higher flexibility than a silica-based film formed using only perhydropolysilazane is formed, thereby preventing cracks from being generated in the film (for example, refer to Patent Document 1).

[0007] [Prior Art Documents]

[0008] [Patent Documents]

[0009] Patent Document 1: Japanese Patent Laid-Open No. 2002-105676 Summary of the Invention

[0010] [Problems to be Solved by the Invention]

[0011] In Reference Document 1, since the heat treatment temperature after coating the solution is set to a relatively low temperature (around 300°C), in the film, in addition to the silica obtained by the conversion of polysilazane, unconverted substances are also included. The inclusion of unconverted substances in the film contributes to the flexibility of the film, but reduces the density of the film. Therefore, a sufficiently dense silica-based film cannot be obtained. In addition, since the heat treatment temperature is 300°C, it is difficult to obtain a film with sufficient corrosion resistance for raw materials with a large coefficient of linear expansion, especially aluminum alloys.

[0012] Thus, in the silica-based film described in Reference Document 1, although cracks generated on the film can be prevented, a sufficiently dense film cannot be obtained, and sometimes the corrosion resistance is poor.

[0013] Furthermore, the silica-based film formed in this way sometimes has pores. In the case where the pores connect the surface side and the structural member side for some reason, the anti-corrosion effect sometimes decreases.

[0014] The present invention is made in view of such a situation, and its object is to provide a technique that can prevent the reduction of the anti-corrosion effect caused by open defect parts such as cracks and pores, can obtain a sufficiently dense film, and can form a film with high corrosion resistance.

[0015] [Technical means for solving the problem]

[0016] (1) The film forming method of the present invention includes:

[0017] A first step of coating a first solution containing polysilazane on the surface of a metal substrate, and forming a first film having open defect parts on the surface of the metal substrate by heating the first solution to cause silica conversion; and

[0018] A second step of coating a second solution containing polysilazane on the surface of the first film to fill the open defect parts, and forming a second film on the surface of the first film by heating the second solution at a temperature lower than the heating temperature of the first step to cause silica conversion.

[0019] According to the film forming method having the above structure, the first film has open defect parts, but in the second step, the second solution is coated on the surface of the first film to fill the open defect parts. After that, by causing the polysilazane contained in the second solution to undergo silica conversion, a second film can be formed in the open defect parts. As a result, the second film can seal at least the open parts of the open defect parts, thereby preventing the reduction of the corrosion resistance caused by the open defect parts.

[0020] Therefore, the polysilazane of the first solution can be converted into silica at a sufficiently high temperature to form a dense first film, without worrying about cracks appearing in the film during the first process.

[0021] In addition, by heating at a temperature lower than that of the first process in the second process, a second film covering the opening defect portion of the first film can be formed without generating new cracks in the first film.

[0022] Thus, according to the present invention, a reduction in the anticorrosion effect caused by the opening defect portion can be prevented, and a sufficiently dense film can be obtained, so that a film with high corrosion resistance can be formed.

[0023] (2) The silica-based film formed using a solution containing polysilazane contains organosilica having an organic component such as methyl. If such a silica-based film containing organosilica is exposed to a halogen-based gas, the organic part is selectively corroded, and sometimes the corrosion resistance is poor.

[0024] Therefore, in the film forming method, it is preferable that the polysilazane contained in the second solution is perhydropolysilazane.

[0025] More preferably, both the polysilazane contained in the first solution and the polysilazane contained in the second solution are perhydropolysilazane.

[0026] In this case, a dense film can be obtained, and a film with higher corrosion resistance can be formed.

[0027] (3) In the film forming method, it is preferable that the concentration ratio of the polysilazane content in the second solution to the polysilazane content in the first solution is 0.001 or more and less than 1.

[0028] When the concentration ratio is 1 or more, the viscosity of the second solution becomes relatively high, and when the second solution is coated on the surface of the first film in the second process, the second solution may not be able to fill the opening defect portion.

[0029] When the concentration ratio is less than 0.001, even if the second solution fills the opening defect portion, a film cannot be sufficiently formed within the opening defect portion, and it may not be possible to seal the pores.

[0030] By making the concentration ratio 0.001 or more and less than 1, a second solution with a viscosity that can fill the opening defect portion and a concentration that can sufficiently form a film in the opening defect portion can be obtained.

[0031] The concentration ratio of the polysilazane content in the second solution to the polysilazane content in the first solution is more preferably 0.01 or more and less than 0.6.

[0032] (4) The second solution contains at least one of an organometal, a metal compound, and an amine compound.

[0033] The total amount of the organometal, the metal compound, and the amine compound is preferably 0.0001 or more and 1 or less with respect to the weight ratio of the polysilazane.

[0034] The organometal, the metal compound, and the amine compound are catalysts for reducing the silica conversion temperature of the polysilazane. By including these in the second solution, the silica conversion temperature of the polysilazane can be reduced, so that the heating temperature can be a lower temperature.

[0035] In addition, when the weight ratio is less than 0.0001, it may not be possible to sufficiently obtain the effect as a catalyst.

[0036] In addition, if the weight ratio exceeds 1, the thickening (gelation) of the second solution becomes significant, and it may not be possible to fill the opening defects of the first film.

[0037] By making the weight ratio 0.0001 or more and 1 or less, the second solution can be filled into the opening defects of the first film and can function properly as a catalyst.

[0038] In addition, if the weight ratio exceeds 0.2, a tendency of thickening (gelation) of the second solution can be seen. Therefore, the total amount of the organometal, the metal compound, and the amine compound is more preferably 0.001 or more and 0.2 or less with respect to the weight ratio of the polysilazane.

[0039] (5) In the film forming method, it is preferable that the total film thickness of the first film and the second film is 0.01 μm or more and 10.0 μm or less.

[0040] When the film thickness is less than 0.01 μm, it may not be possible to sufficiently shield the surface of the metal substrate from the external environment.

[0041] When the film thickness exceeds 10.0 μm, the stress acting on the first film due to the difference in the linear expansion coefficient between the metal substrate and the first film becomes large, and peeling may occur in the first film, or film peeling, film breakage, etc. may occur due to the internal stress of the first film.

[0042] By making the total film thickness of the first film and the second film 0.01 μm or more and 10.0 μm or less, a film capable of appropriately shielding the surface of the metal substrate from the external environment can be obtained.

[0043] The total film thickness of the first film and the second film is more preferably 0.05 μm or more and 3.0 μm or less.

[0044] (6) In the film forming method, the first step may form the first film by repeatedly performing the step of coating the first solution on the metal substrate and the step of heating the first solution to cause silica conversion a specified number of times.

[0045] In this case, thickening of the first film can be achieved, so that the surface of the metal substrate can be sufficiently covered.

[0046] (7) In the film forming method, the second step may form the second film by repeatedly performing the step of coating the second solution on the first film and the step of heating the second solution to cause silica conversion at a temperature lower than the heating temperature of the first step a specified number of times.

[0047] In this case, sealing of the opening portion of the opening defect portion can be more effectively performed.

[0048] [Advantages of the Invention]

[0049] According to the present invention, a film having high corrosion resistance can be formed. Description of the Drawings

[0050] Figure 1 It is a partial cross-sectional view of the metal substrate and the film after forming the first film by the first step.

[0051] Figure 2 It is a partial cross-sectional view of the metal substrate and the film after coating the second solution on the surface of the first film by the second step.

[0052] Figure 3 It is a partial cross-sectional view of the metal substrate and the film after forming the second film by the second step.

[0053] Figure 4 It is an electron micrograph of the film cross-section of the comparative example.

[0054] Figure 5 It is an electron micrograph of the film surface of the comparative example.

[0055] Figure 6 It is an electron micrograph of the film cross-section of Example 1.

[0056] Figure 7 It is an electron micrograph of the film surface of Example 1.

[0057] Figure 8 It is an electron micrograph of the film cross-section of Example 2.

[0058] Figure 9It is an electron micrograph of the film surface of Example 2.

[0059] [Explanation of symbols]

[0060] 1: First film

[0061] 1a: Surface

[0062] 2: Metal substrate

[0063] 2a: Surface

[0064] 3: Opening defect part

[0065] 3a: Crack

[0066] 3b: Open pore part

[0067] 4: Second solution

[0068] 5: Second film

[0069] 6: Non-defect part Detailed implementation manners

[0070] Hereinafter, a film formation method according to an embodiment of the present invention will be described.

[0071] The film formation method of the present embodiment is a method for forming a silica-based film using polysilazane.

[0072] The silica-based film obtained by the present embodiment is formed on a structural member such as a chamber or a pipe exposed to a halogen-based corrosive gas or a plasma of a corrosive gas in an etching apparatus used in the manufacture of semiconductors or flat panel displays, or a film formation apparatus such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0073] The film formation method of the present embodiment includes: a first step of coating a first solution containing polysilazane on the surface of a metal substrate, and forming a first film having an opening defect part on the surface of the metal substrate by heating the first solution to cause silica conversion; and a second step of coating a second solution containing polysilazane on the surface of the first film to fill the opening defect part, and forming a second film on the surface of the first film by heating the second solution at a temperature lower than the heating temperature of the first step to cause silica conversion.

[0074] Hereinafter, each step will be described.

[0075] (1) Regarding the first step

[0076] (1-1) Coating of the first solution

[0077] In the first step, as described above, the first solution is coated on the surface of the metal substrate.

[0078] The first solution is a polysilazane-containing solution obtained by dissolving polysilazane in an organic solvent.

[0079] Regarding polysilazane, as a chain polysilazane, perhydropolysilazane, polymethylhydrosilazane, poly(N-methylsilazane), poly-N-(triethylsilyl)allylsilazane, poly-N-(dimethylamino)cyclohexylsilazane, phenylpolysilazane, etc. can be used. Among these, perhydropolysilazane having an average molecular weight of 300 to 5000 is particularly preferred.

[0080] Examples of the organic solvent include ethers (diethyl ether, isopropyl ether, ethyl butyl ether, dibutyl ether, 1,2-dioxoethane, dioxane, dimethyldioxane, tetrahydrofuran, tetrahydropyran, etc.), or hydrocarbons (pentane, hexane, isohexane, methylpentane, heptane, isoheptane, octane, isooctane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, ethylbenzene, etc.). One or a mixture of two or more of these ethers and hydrocarbons can be used as the organic solvent.

[0081] The content concentration of polysilazane in the first solution is preferably 0.05% by mass or more and 40% by mass or less. If the concentration of polysilazane is less than 0.05% by mass, it may not be possible to obtain a first film with a sufficient film thickness. If the concentration of polysilazane exceeds 40% by mass, the viscosity of the first solution becomes high, and the film thickness of the first film may become uneven. The content concentration of polysilazane is more preferably 1% by mass or more and 25% by mass or less.

[0082] The first solution may also contain a catalyst in addition to polysilazane. The catalyst has the effect of relatively reducing the temperature for the conversion of polysilazane to silica or accelerating the silica conversion rate.

[0083] Examples of the catalyst include metal catalysts (organometals or metal compounds), amine-based catalysts (amine compounds).

[0084] Examples of the metal catalyst include organometals or metal compounds containing at least one metal selected from nickel, titanium, platinum, rhodium, cobalt, iron, ruthenium, osmium, palladium, iridium, and aluminum. From the viewpoints of solubility, stability, and reactivity in the polysilazane-containing solution, metal carboxylates are particularly preferred.

[0085] Examples of the amine-based catalyst include amine compounds such as monoamines, diamines, triamines, tetraamines, hydroxy compounds containing a chain amine residue, and hydroxy compounds containing a cyclic amine residue.

[0086] In addition, a hydroxyl compound containing an amine residue reacts with a polysilazane to be modified into a polysilazane containing an amine residue.

[0087] When the first solution contains a catalyst (at least one of an organometal, a metal compound, and an amine compound), the weight ratio of the catalyst (total amount thereof) to the polysilazane is preferably 0.0001 or more and 1 or less. If the weight ratio of the catalyst to the polysilazane is less than 0.0001, the effect as a catalyst may not be obtained sufficiently. If the weight ratio of the catalyst to the polysilazane exceeds 1, the thickening (gelation) of the first solution becomes remarkable, and the film thickness of the first film may become uneven. The weight ratio of the catalyst to the polysilazane is more preferably 0.001 or more and 0.2 or less. By setting the weight ratio of the catalyst to the polysilazane to 0.2 or less, the thickening of the first solution can be effectively suppressed.

[0088] Here, the conditions for converting the polysilazane contained in the first solution and the second solution into silica (silica conversion conditions) include parameters such as the heating temperature, heating time, heating environment, the presence or absence of the catalyst, or the type of the catalyst.

[0089] The heating temperature (silica conversion temperature) is determined according to other parameters included in the silica conversion conditions, that is, the presence or absence of the catalyst, or the type of the catalyst, heating time, and heating environment.

[0090] In addition, in the following description, the conditions for converting the polysilazane in the first solution into silica are also referred to as the first silica conversion conditions, and the silica conversion temperature of the polysilazane in the first solution is also referred to as the first silica conversion temperature. Further, the conditions for converting the polysilazane in the second solution into silica are also referred to as the second silica conversion conditions, and the silica conversion temperature of the polysilazane in the second solution is also referred to as the second silica conversion temperature.

[0091] In addition, in the present embodiment, the conversion of the polysilazane into silica means that the film density of the film obtained by heating the solution containing the polysilazane is 2.0 g / cm 3 or more.

[0092] Therefore, the silica conversion conditions are heating conditions under which the film density of the first film or the second film becomes 2.0 g / cm 3 or more.

[0093] When the first solution does not contain a catalyst, the first silica conversion temperature is, for example, 300°C to 550°C.

[0094] When the first solution contains a metal catalyst, the first silica conversion temperature is, for example, 120°C to 350°C.

[0095] When the first solution contains an amine-based catalyst, the first silica conversion temperature is, for example, room temperature to 250°C.

[0096] The first silica conversion conditions including the first silica conversion temperature can be determined by measuring the first solution using the following method.

[0097] The measurement of the first silica conversion conditions is carried out by forming a film using the first solution on a silicon wafer.

[0098] First, measure the weight of the silicon wafer using an electronic balance or the like. After coating the first solution on the silicon wafer by spin coating, heat it in the atmosphere at a specified heating temperature and for a specified heating time to form a silica-based film, and measure the weight of the silicon wafer with the silica-based film formed thereon. Then, find the difference in weight of the silicon wafer before and after the formation of the silica-based film, and use this value as the film weight. Next, measure the film thickness using a known method, preferably by measuring from the film cross-section using a field emission-scanning electron microscope (FE-SEM) device or the like to obtain a more accurate film thickness. Using the obtained film weight and film thickness, calculate the film density according to the following formula.

[0099] In this method, set multiple combinations of heating temperature and heating time, and find the film density for each combination. In each combination, use the combination with a film density of 2.0 g / cm 3 or more as the first silica conversion conditions.

[0100] Film density [g / cm 3 =

[0101] Film weight [g] / (Film thickness [μm] × Silicon wafer surface area [cm 2 × 0.0001)

[0102] The silica-based film obtained by heating polysilazane under conditions that do not satisfy the silica conversion conditions (heating at a temperature lower than the silica conversion temperature or for a heating time shorter than the silica conversion conditions) contains unreacted substances and is not a dense silica film. The unreacted substances are intermediate substances that are converted from polysilazane to silica.

[0103] The silica-based film obtained by heating the first solution under the first silica conversion conditions does not contain unconverted substances. That is, the first silica conversion conditions represent the heating conditions for completely converting polysilazane containing the first solution into silica, and a sufficiently dense silica film can be obtained.

[0104] As the metal substrate for coating the first solution, as described above, an etching device, or a chamber or pipe of a film-forming device can be cited. These chambers or pipes are formed of stainless steel or aluminum alloy.

[0105] The surface of the metal substrate formed of stainless steel or aluminum alloy is cleaned and degreased. Then, the first solution is coated on the surface of the metal substrate.

[0106] In addition, as a pretreatment for coating the first solution, a known method such as irradiation with an ultraviolet (UV) lamp, an excimer lamp, or plasma can also be used to modify the surface of the metal substrate.

[0107] The coating of the first solution is carried out by a known coating method such as spin coating, roll coating, flow coating, spray coating, or dip coating.

[0108] (1-2) Formation of the first film

[0109] Furthermore, in the first step, the first solution coated on the metal substrate is heated in the atmosphere or an environment containing water vapor to convert the polysilazane contained in the first solution into silica, forming the first film. The first film is a silica-based film (inorganic silica film) obtained by converting the polysilazane contained in the first solution into silica. The first solution coated on the metal substrate is heated based on the specified first silica conversion conditions.

[0110] The heating temperature in the first step is set to be equal to or higher than the first silica conversion temperature under the specified first silica conversion conditions. For example, when the specified first silica conversion conditions are a heating time of 1 hour and a first silica conversion temperature T (T is a certain value), when the heating time of the first step is set to 1 hour, the heating temperature of the first step is set to be equal to or higher than the first silica conversion temperature T.

[0111] In addition, the heating temperature in the first step only needs to be equal to or higher than the first silica conversion temperature, but is preferably 10°C or more higher than the first silica conversion temperature, and more preferably 30°C or more higher. When the heating temperature is lower than the value obtained by adding 30°C to the first silica conversion temperature, it is possible that the entire first solution applied may not reach a temperature equal to or higher than the first silica conversion temperature. By making the heating temperature 30°C or more higher than the first silica conversion temperature, the entire first solution can be at a temperature equal to or higher than the first silica conversion temperature, so that the polysilazane in the first solution can be appropriately converted into silica.

[0112] As a result, a sufficiently dense first film without unreacted substances can be obtained, and thus a silica-based film with excellent corrosion resistance can be obtained.

[0113] Regarding the heating time in the first step, as long as the first solution on the metal substrate is sufficiently heated and the polysilazane in the first solution is converted into silica, for example, it is preferably 0.5 hours or more and 10 hours or less. If it is shorter than 0.5 hours, the conversion of polysilazane in the first solution into silica may become insufficient. If it exceeds 10 hours, time is unnecessarily spent, resulting in an increase in cost.

[0114] In addition, the first step can form the first film by repeating the step of applying the first solution and the step of heating the first solution to cause silica conversion a specified number of times.

[0115] In this case, thickening of the first film can be achieved, and thus the surface of the metal substrate can be sufficiently covered.

[0116] Figure 1 It is a partial cross-sectional view of the metal substrate and the film after forming the first film through the first step.

[0117] Figure 1 In [figure], the first film 1 is formed on the surface 2a of the metal substrate 2. The surface 1a of the first film 1 has a non-defective portion 6 and a plurality of open defect portions 3. The open defect portion 3 is a defect that opens on the surface 2a. The open defect portion 3 includes a crack 3a and an open pore portion 3b.

[0118] The crack 3a is mainly caused by the difference in the linear expansion coefficient between the first film 1 and the metal substrate 2. The crack 3a includes a crack that remains within the first film 1 or a crack that reaches the surface 2a of the metal substrate 2.

[0119] The open pore portion 3b is generated due to bubbles contained in the first solution during the film formation process of the first film 1.

[0120] The first film 1 is formed by converting polysilazane in the first solution into silicon dioxide and is mainly composed of silicon dioxide. Therefore, the linear expansion coefficient of the first film is an intermediate value between that of inorganic silica glass and quartz, which is about 0.6 to 6 (×10 -6 / °C).

[0121] On the other hand, the metal substrate 2 is made of stainless steel or aluminum alloy. As an example, the linear expansion coefficient of Japanese Industrial Standards (JIS) SUS316L, which is a type of stainless steel, is 16.0 (×10 -6 / °C), and that of JIS A6061, which is an aluminum alloy, is 23.6 (×10 -6 / °C).

[0122] In the first step, the metal substrate 2 coated with the first solution is heated to a temperature above the silicon dioxide conversion temperature of the polysilazane in the first solution to form the first film 1. Therefore, when cooled to room temperature after heating, stress acts on the first film 1 due to the difference in the linear expansion coefficients between the first film 1 and the metal substrate 2. Due to this stress, cracks 3a are generated on the first film 1.

[0123] (2) Regarding the second step

[0124] (2-1) Coating of the second solution

[0125] In the second step, the second solution is coated on the surface of the first film.

[0126] Figure 2 is a partial sectional view of the metal substrate and the film after the second solution is coated on the surface of the first film through the second step.

[0127] As Figure 2 shown, by coating the second solution 4 on the surface 1a of the first film 1, the second solution 4 is filled into the opening defect part 3.

[0128] The second solution is a polysilazane-containing solution obtained by dissolving polysilazane in an organic solvent.

[0129] Regarding polysilazane, as chain polysilazane, perhydropolysilazane, polymethylhydrosilazane, poly(N-methylsilazane), poly-N-(triethylsilyl)allylsilazane, poly-N-(dimethylamino)cyclohexylsilazane, phenylpolysilazane, etc. can be used. Among these, perhydropolysilazane with an average molecular weight of 300 to 5000 is particularly preferred.

[0130] As the organic solvent, the same type of organic solvent as that of the first solution can be used. Specific examples thereof include: ethers (such as diethyl ether, isopropyl ether, ethyl butyl ether, dibutyl ether, 1,2-dichloroethane, dioxane, dimethyl dioxane, tetrahydrofuran, tetrahydropyran, etc.), or hydrocarbons (such as pentane, hexane, isohexane, methyl pentane, heptane, isoheptane, octane, isooctane, cyclopentane, methyl cyclopentane, cyclohexane, methyl cyclohexane, benzene, toluene, xylene, ethylbenzene, etc.). A mixture of one or more of these ethers and hydrocarbons can also be used as the organic solvent.

[0131] The content concentration of polysilazane in the second solution is preferably 0.05% by mass or more and 40% by mass or less. If the concentration of polysilazane is less than 0.05% by mass, it may not be possible to obtain the second film with the minimum required film thickness. If the concentration of polysilazane exceeds 40% by mass, the viscosity of the second solution becomes high, and the film thickness of the second film may become uneven.

[0132] The content concentration of polysilazane is more preferably 1% by mass or more and 25% by mass or less.

[0133] In addition, the concentration ratio of the content concentration of polysilazane in the second solution to the content concentration of polysilazane in the first solution is preferably 0.001 or more and less than 1.

[0134] When the concentration ratio is 1 or more, the viscosity of the second solution becomes relatively high, and when the second solution is coated on the surface of the first film in the second step, the second solution may not fill into the opening defect portion 3.

[0135] In addition, when the concentration ratio is less than 0.001, even if the second solution is filled into the opening defect portion 3, a film cannot be sufficiently formed in the opening defect portion 3, and it may not be possible to seal the holes.

[0136] By making the concentration ratio 0.001 or more and less than 1, a second solution with a viscosity that can fill into the opening defect portion 3 and a concentration that can sufficiently form a film in the opening defect portion 3 can be obtained.

[0137] The concentration ratio of the content concentration of polysilazane in the second solution to the content concentration of polysilazane in the first solution is more preferably 0.01 or more and less than 0.6.

[0138] In addition, the concentration ratio of the content concentration of polysilazane in the second solution to the content concentration of polysilazane in the first solution can also be 1 or more and 200 or less.

[0139] When the concentration ratio is greater than 200, the viscosity of the second solution becomes high, and the second solution cannot be uniformly coated, so the film thickness of the second film may become uneven.

[0140] In addition, when the concentration ratio is less than 1, it may not be possible to obtain a second film with a sufficient thickness.

[0141] By setting the concentration ratio to 1 or more and 200 or less, even if the first film is an extremely thin film (for example, less than 0.01 μm), a second film that supplements the first film and can sufficiently cover the metal substrate can be obtained.

[0142] The second solution preferably contains a catalyst in addition to the polysilazane. By the second solution containing a catalyst, it is easy to set the heating temperature for the silica conversion conditions in the second step to a temperature lower than the heating temperature for the silica conversion conditions in the first step.

[0143] As the catalyst, the same type of catalyst as that in the first solution can be used, and examples include metal catalysts (organometals or metal compounds) and amine-based catalysts (amine compounds).

[0144] As the metal catalyst, examples include organometals or metal compounds containing at least one metal selected from nickel, titanium, platinum, rhodium, cobalt, iron, ruthenium, osmium, palladium, iridium, and aluminum. From the viewpoints of solubility, stability, and reactivity in the solution containing polysilazane, metal carboxylates are particularly preferred.

[0145] Examples of the amine-based catalyst include amine compounds such as monoamines, diamines, triamines, tetraamines, hydroxy compounds containing a chain-like amine residue, and hydroxy compounds containing a cyclic amine residue.

[0146] When the second solution contains a catalyst (at least one of an organometal, a metal compound, and an amine compound), the weight ratio of the catalyst (total amount) to the polysilazane is preferably 0.0001 or more and 1 or less. If the weight ratio of the catalyst to the polysilazane is less than 0.0001, it may not be possible to sufficiently obtain the effect of the catalyst. If the weight ratio of the catalyst to the polysilazane exceeds 1, the viscosity increase (gelation) of the second solution becomes significant, not only making the film thickness uneven, but also possibly unable to fill the opening defect portion 3 on the surface of the first film. The weight ratio of the catalyst to the polysilazane is more preferably 0.001 or more and 0.2 or less. By setting the weight ratio of the catalyst to the polysilazane to 0.2 or less, the viscosity increase of the second solution can be effectively suppressed.

[0147] When the second solution does not contain a catalyst, the second silica conversion temperature is, for example, 300°C to 550°C.

[0148] When the second solution contains a metal catalyst, the second silica conversion temperature is, for example, 120°C to 350°C.

[0149] When the second solution contains an amine-based catalyst, the second silica conversion temperature is, for example, room temperature to 250°C.

[0150] For example, when the first solution does not contain a catalyst, the first silica conversion temperature is 300°C to 550°C. As long as the heating temperature of the second process is lower than that of the first process, the second solution may or may not contain a catalyst.

[0151] When the first solution contains palladium as a metal catalyst, the first silica conversion temperature is 120°C to 350°C. In this case, it is preferable to contain a catalyst in the second solution. When no catalyst is contained, the second silica conversion temperature is 300°C to 550°C, and it is difficult to satisfy the condition that the heating temperature of the second process is lower than that of the first process.

[0152] The second silica conversion condition including the second silica conversion temperature can be determined by measuring the second solution in the same way as the measurement method of the first silica conversion condition.

[0153] In the present embodiment, the second silica conversion condition is set as a condition including the second silica conversion temperature, and the second silica conversion temperature is a value equal to or lower than the first silica conversion temperature included in the specified first silica conversion condition.

[0154] The second solution is applied by a known coating method such as a spin coating method, a roll coating method, a flow coating method, a spraying method, or a dipping method.

[0155] (2-2) Formation of the second film

[0156] Furthermore, in the second process, the second solution coated on the surface of the first film is heated in the air or an environment containing water vapor to cause the polysilazane contained in the second solution to undergo silica conversion, thereby forming a second film. The second film is a silica-based film (inorganic silica film) obtained by converting the polysilazane contained in the second solution into silica.

[0157] The heating temperature in the second process is set to a temperature lower than the heating temperature in the first process and equal to or higher than the second silica conversion temperature.

[0158] If the heating temperature is equal to or higher than the heating temperature in the first process, when the first film is heated to a temperature higher than that at the time of forming the first film and then cooled to room temperature, new cracks may occur in the first film due to the difference in the linear expansion coefficients between the metal substrate and the first film.

[0159] If the heating temperature is lower than the second silica conversion temperature, the silica conversion of the polysilazane contained in the second solution may not proceed sufficiently.

[0160] By setting the heating temperature to a temperature that is lower than the heating temperature of the first step and equal to or higher than the second silica conversion temperature, the polysilazane in the second solution can be appropriately converted into silica without applying pressure to the first film.

[0161] Regarding the heating time in the second step, as long as the second solution on the first film is sufficiently heated and the polysilazane in the second solution is converted into silica, it is preferably 0.5 hours or more and 10 hours or less, for example. If it is shorter than 0.5 hours, the silica conversion of the polysilazane in the second solution may become insufficient. If it exceeds 10 hours, time is unnecessarily spent, resulting in an increase in cost.

[0162] In addition, the second film can be formed by repeating the step of coating the second solution and the step of heating the second solution at a temperature lower than the heating temperature of the first step to convert it into silica a predetermined number of times.

[0163] Figure 3 It is a partial cross-sectional view of the metal substrate and the film after the second film is formed by the second step.

[0164] If the metal substrate coated with the second solution is heated in the second step, the polysilazane contained in the second solution filled in the opening defect portion 3 is converted into silica. Therefore, as Figure 3 shown, a second film 5 is formed in the opening defect portion 3.

[0165] As a result, the opening defect portion 3 on the surface 1a of the first film 1 is sealed with the second film.

[0166] The second film 5 only needs to be formed at least in the opening defect portion 3 in the surface 1a and the opening defect portion 3 is sealed, but it can also be formed in a portion other than the opening defect portion 3 (for example, on the non-defect portion 6).

[0167] Thus, according to the film forming method having the above structure, the first film has an opening defect portion 3, but in the second step, the second solution is filled into the opening defect portion 3 by coating the second solution on the surface of the first film. After that, by converting the polysilazane contained in the second solution into silica, a second film can be formed in the opening defect portion 3. As a result, the opening defect portion 3 can be sealed with the second film, thereby preventing a decrease in corrosion resistance caused by the opening defect portion 3.

[0168] Therefore, the polysilazane of the first solution can be converted into silica at a sufficiently high temperature to form a dense first film, without worrying about cracks appearing on the film in the first process.

[0169] In addition, by heating at a temperature lower than that of the first process in the second process, a second film covering the opening defect part of the first film can be formed without generating new cracks in the first film.

[0170] Thus, according to the present embodiment, a reduction in the anti-corrosion effect caused by the opening defect part 3 can be prevented, and a sufficiently dense film can be obtained, so that a film with high corrosion resistance can be formed.

[0171] Furthermore, as long as the second process is a process of forming the second film by repeatedly performing the process of coating the second solution and heating the second solution at a temperature lower than the heating temperature of the first process to cause silica conversion a specified number of times, the sealing of the opening defect part 3 can be carried out more effectively.

[0172] In addition, as the polysilazane contained in the second solution, as described above, perhydropolysilazane is particularly preferred.

[0173] If the polysilazane contained in the second solution is perhydropolysilazane, a dense second film can be obtained, so that a film with higher corrosion resistance can be formed.

[0174] In addition, in the above embodiment, the total film thickness of the first film and the second film is preferably 0.01 μm or more and 10.0 μm or less.

[0175] When the film thickness is less than 0.01 μm, it may not be possible to sufficiently shield the surface of the metal substrate from the external environment.

[0176] When the film thickness exceeds 10.0 μm, the stress acting on the first film due to the difference in the linear expansion coefficient between the metal substrate and the first film becomes large, and peeling may occur in the first film, or film peeling, film breakage, etc. may occur due to the internal stress of the first film.

[0177] By making the total film thickness of the first film and the second film 0.01 μm or more and 10.0 μm or less, a film that can appropriately shield the surface of the metal substrate from the external environment can be obtained.

[0178] The total film thickness of the first film and the second film is more preferably 0.05 μm or more and 3.0 μm or less.

[0179] [Examples]

[0180] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0181] (Example 1)

[0182] As the first solution, a dibutyl ether solution (manufactured by Merck Performance Materials, trade name Durazane 2400) containing a metal catalyst (palladium) and having a concentration of 20% by mass of perhydropolysilazane was used. In the first silica conversion conditions in the first solution, the values obtained by the above measurement method were used, the heating time was 1 hour, and the first silica conversion temperature was determined to be 150°C.

[0183] As the second solution, a solution was prepared by preparing a dibutyl ether solution (manufactured by Merck Performance Materials, trade name Durazane 2400) containing a metal catalyst (palladium) and having a concentration of 20% by mass of perhydropolysilazane so that the concentration of perhydropolysilazane became 10% by mass. Therefore, the concentration ratio of the perhydropolysilazane content in the second solution to the perhydropolysilazane content in the first solution was 0.5.

[0184] In the second silica conversion conditions in the second solution, the values obtained by the above measurement method were used, the heating time was 1 hour, and the second silica conversion temperature was determined to be 150°C.

[0185] As the metal substrate, a stainless steel (JIS SUS316L) plate of 50 mm × 50 mm and a thickness of 5 mm was prepared.

[0186] The surface of the metal substrate was degreased and cleaned, the first solution was coated by spin coating, heated at 250°C for 1 hour, and after 1 hour, it was taken out from the heating furnace and cooled in the atmosphere. Thus, a first film having an opening defect portion was formed on the surface of the metal substrate.

[0187] After that, the second solution was coated on the surface of the first film by spin coating and heated at the second silica conversion temperature of 150°C for 1 hour. Thus, a second film was formed on the surface of the first film, and a test piece having the first film and the second film (total film thickness 1.7 μm to 1.8 μm) formed on the metal substrate was obtained.

[0188] In addition, the density of the first film at this time was 2.31 g / cm 3 , and the density of the second film was 2.14 g / cm 3 . Therefore, both the first film and the second film were subjected to silica conversion. The densities of these films were obtained by measuring the densities of the films heated under the same conditions using the above measurement method.

[0189] (Example 2)

[0190] As the first solution, a dibutyl ether solution (manufactured by Merck Performance Materials, trade name Durazane 2400) containing a metal catalyst (palladium) and having a concentration of 20% by mass of perhydropolysilazane was used. In the first silica conversion conditions in the first solution, the value obtained by the measurement method was used, the heating time was 1 hour, and the first silica conversion temperature was determined to be 150 °C.

[0191] As the second solution, a solution prepared by preparing a dibutyl ether solution (manufactured by Merck Performance Materials, trade name Durazane 2400) containing a metal catalyst (palladium) and having a concentration of 20% by mass of perhydropolysilazane so that the concentration of perhydropolysilazane becomes 5% by mass was used. Therefore, the concentration ratio of the perhydropolysilazane content in the second solution to the perhydropolysilazane content in the first solution is 0.25.

[0192] In the second silica conversion conditions in the second solution, the value obtained by the measurement method was used, the heating time was 2 hours, and the second silica conversion temperature was determined to be 130 °C.

[0193] As the metal substrate, a plate of aluminum alloy (JIS A6061) with a size of 50 mm × 50 mm and a thickness of 5 mm was prepared.

[0194] The surface of the metal substrate was degreased and cleaned, the first solution was coated by spin coating, heated at 250 °C for 1 hour, and after 1 hour, it was taken out of the heating furnace and cooled in the air. Thus, a first film having an opening defect portion was formed on the surface of the metal substrate.

[0195] After that, the second solution was coated on the surface of the first film by spin coating and heated at the second silica conversion temperature of 130 °C for 2 hours. Thus, a second film was formed on the surface of the first film, and a test piece having the first film and the second film (total film thickness: 1.4 μm to 1.5 μm) formed on the metal substrate was obtained.

[0196] In addition, the density of the first film at this time was 2.31 g / cm 3 , and the density of the second film was 2.21 g / cm 3 . Therefore, both the first film and the second film were subjected to silica conversion.

[0197] (Comparative Example)

[0198] As the first solution, a dibutyl ether solution containing a metal catalyst (palladium) and having a concentration of 20% by mass of perhydropolysilazane (manufactured by Merck Performance Materials, trade name Durazane 2400) was used. The first silica conversion conditions in the first solution were based on the manufacturer's published data, with a heating time of 1 hour and the first silica conversion temperature determined to be 250°C.

[0199] As the metal substrate, a stainless steel (JIS SUS316L) plate with dimensions of 50 mm × 50 mm and a thickness of 5 mm was prepared.

[0200] The surface of the metal substrate was degreased and cleaned, and the first solution was applied by spin coating, followed by heating at the first silica conversion temperature of 250°C for 1 hour. Thus, test pieces having a first film (film thickness 1.2 μm to 1.3 μm) formed on the surface of the metal substrate were obtained.

[0201] 〔Observation of film cross-section and surface〕

[0202] Each of the test pieces obtained in Example 1, Example 2, and the Comparative Example was cut with a high-speed cutter, and the obtained cut pieces were embedded in resin and then ion milled (IM400 manufactured by Hitachi High-tech), and the film cross-section was observed using an FE-SEM device (SU8020 manufactured by Hitachi High-tech). In addition, the surface of the film of each of the test pieces obtained in Example 1, Example 2, and the Comparative Example was observed using an FE-SEM device.

[0203] Figure 4 is an electron micrograph of the film cross-section of the Comparative Example, Figure 5 is an electron micrograph of the film surface of the Comparative Example.

[0204] As Figure 4 and Figure 5 shown, it can be seen that there are a plurality of cracks on the surface of the first film.

[0205] Figure 6 is an electron micrograph of the film cross-section of Example 1, Figure 7 is an electron micrograph of the film surface of Example 1.

[0206] Figure 8 is an electron micrograph of the film cross-section of Example 2, Figure 9 is an electron micrograph of the film surface of Example 2.

[0207] As Figures 6 to 9As shown, it can be seen that in Example 1 and Example 2, the cracks seen in the comparative example were sealed.

[0208] [Hydrochloric acid corrosion resistance test]

[0209] In a manner that only exposes the surface on which the film is formed, each test piece obtained in Example 1, Example 2, and the comparative example was masked, and each masked test piece was immersed in a 10% hydrochloric acid solution at room temperature for 24 hours, and the corrosion state of the surface on which the film was formed was observed.

[0210] The results are shown in Table 1 below.

[0211] [Table 1]

[0212] With or without corrosion Example 1 None Example 2 None Comparative example Yes

[0213] As shown in Table 1, in the comparative example with the first film on which the second film was not formed, corrosion was observed and a part of peeling occurred, but in Example 1 and Example 2 in which the second film was formed, no corrosion was observed.

[0214] From this, it can be known that the cracks in the first film were sealed, and a reduction in the anti-corrosion effect caused by the cracks can be prevented.

[0215] In addition, it can be known that the first film and the second film have high corrosion resistance in the hydrochloric acid solution.

Claims

1. A method for forming a film, comprising: a first step of coating a first solution containing only perhydropolysilazane as a polysilazane on the surface of a metal substrate, and heating the first solution at a temperature exceeding the silica conversion temperature of the polysilazane in the first solution to cause silica conversion, thereby forming a first film having open defect portions on the surface of the metal substrate; and a second step of coating a second solution containing only perhydropolysilazane as a polysilazane on the surface of the first film to fill the open defect portions, and heating the second solution at a temperature equal to or higher than the silica conversion temperature of the polysilazane in the second solution and lower than the heating temperature in the first step to cause silica conversion, thereby forming a second film of dense silica on the surface of the first film and at least the open defect portions on the surface; when the first solution does not contain a catalyst, the silica conversion temperature of the polysilazane in the first solution is 300°C to 550°C; when the first solution contains a metal catalyst, the silica conversion temperature of the polysilazane in the first solution is 120°C to 350°C; when the first solution contains an amine-based catalyst, the silica conversion temperature of the polysilazane in the first solution is room temperature to 250°C; when the second solution does not contain a catalyst, the silica conversion temperature of the polysilazane in the second solution is 300°C to 550°C; when the second solution contains a metal catalyst, the silica conversion temperature of the polysilazane in the second solution is 120°C to 350°C; when the second solution contains an amine-based catalyst, the silica conversion temperature of the polysilazane in the second solution is room temperature to 250°C.

2. The film forming method according to claim 1, wherein the concentration ratio of the polysilazane content in the second solution to the polysilazane content in the first solution is 0.001 or more and less than 1.

3. The film forming method according to claim 1 or 2, wherein the second solution contains at least one of an organometal, a metal compound, and an amine compound, and the total amount of the organometal, the metal compound, and the amine compound is 0.0001 or more and 1 or less with respect to the weight ratio of the polysilazane.

4. The film forming method according to claim 1 or 2, wherein the total film thickness of the first film and the second film is 0.01 μm or more and 10.0 μm or less.

5. The film forming method according to claim 1 or 2, wherein the first step forms the first film by repeating the step of coating the first solution on the metal substrate and the step of heating the first solution to cause silica conversion a predetermined number of times.

6. The film forming method according to claim 1 or 2, wherein The second process forms the second film by repeating a process of coating the second solution on the first film and a process of heating the second solution at a temperature lower than the heating temperature of the first process to cause silica conversion a predetermined number of times.

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