Film formation method

Abstract

A coating film formation method according to the present invention includes: a first step in which a polysilazane-containing first solution is applied to a surface 2a of a metal substrate 2, and the first solution is heated to cause silica conversion and form a first coating film 1 having open defects 3 on the surface 2a of the metal substrate 2; and a second step in which a polysilazane-containing second solution is applied to a surface 1a of the first coating film 1 to fill the open defects 3, and the second solution is heated at a lower temperature than the heating temperature at the first step to cause silica conversion and form a second coating film 5 on the surface 1a of the first coating film 1.

Description

Technical Field

[0001] The present invention relates to a method for forming a corrosion-resistant film.

Background Art

[0002] Some manufacturing apparatuses such as semiconductor and flat panel display devices, or constituent members of apparatuses similar thereto, are exposed to corrosive gases or plasmas of corrosive gases. These constituent members are usually formed using metal materials such as aluminum alloys and stainless steels. However, metal materials such as aluminum alloys and stainless steels have low corrosion resistance against halogen-based corrosive gases or their plasmas. Therefore, in order to impart corrosion resistance to these members, for example, coating with a silica-based film using perhydropolysilazane may be performed. The silica-based film is very dense and has high corrosion resistance against halogen-based corrosive gases and plasmas. Therefore, by forming a silica-based film on the surface of the above-described constituent member, the surface of the constituent member can be shielded from the external environment, and corrosion of the constituent member can be suppressed.

[0003] By the way, a silica-based film formed using perhydropolysilazane is dense, but on the other hand, it is fragile and has a very small linear expansion coefficient compared to metal materials. For this reason, cracks occur in the film during the process of forming the film, and in order to suppress the occurrence of these cracks, by making the film thin, the constituent member cannot be sufficiently coated, and the anticorrosion effect of the constituent member is reduced due to a decrease in the effect of shielding the constituent member from the external environment.

[0004] In response to such problems, Patent Document 1 discloses forming a silica-based film using a solution containing perhydropolysilazane and polyorganosilazane. In Patent Document 1, by including polyorganosilazane in the solution, a film having higher flexibility than a silica-based film formed using only perhydropolysilazane is formed, and the occurrence of cracks in the film is prevented (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Reference Document 1, since the heat treatment temperature after applying the solution is set to a relatively low temperature (around 300°C), the film contains, in addition to silica obtained by silica conversion, unconverted substances. The inclusion of unconverted substances in the film contributes to the flexibility of the film, but since it reduces the density of the film, a sufficiently dense silica-based film cannot be obtained. Further, since the heat treatment temperature is 300°C, it is difficult to obtain a film having sufficient corrosion resistance for a material having a large coefficient of linear expansion, particularly an aluminum alloy.

[0007] Thus, in the silica-based film described in Reference Document 1, cracks generated in the film can be prevented, but a sufficiently dense film cannot be obtained, and the corrosion resistance may be inferior.

[0008] Furthermore, the silica-based film formed in this way may have pores, and if these pores communicate between the surface side and the component side for some reason, the anticorrosion effect may decrease. The present invention has been made in view of such circumstances, and an object thereof is to provide a technique capable of forming a film having high corrosion resistance, while preventing a decrease in the anticorrosion effect caused by opening defects such as cracks and pores and obtaining a sufficiently dense film.

Means for Solving the Problems

[0009] (1) The film forming method according to the present invention is Apply a first solution containing polysilazane to the surface of a metal substrate, heat the first solution to cause silica conversion, and form a first film having opening defects on the surface of the metal substrate in a first step. Apply a second solution containing polysilazane to the surface of the first film to fill the opening defects, heat the second solution at a temperature lower than the heating temperature in the first step to cause silica conversion, and form a second film on the surface of the first film in a second step.

[0010] According to the film formation method having the above configuration, although the first film has opening defects, the opening defects are filled with the second solution by applying the second solution to the surface of the first film in the second step. Then, by subjecting the polysilazane contained in the second solution to silica conversion, a second film can be formed in the opening defects. As a result, at least the opening portion of the opening defects can be sealed by the second film, and a decrease in corrosion resistance due to the opening defects can be prevented. Therefore, without worrying about cracks in the film in the first step, the polysilazane in the first solution can be subjected to silica conversion at a sufficiently high temperature, and a dense first film can be formed. Also, by heating at a temperature lower than that in the first step in the second step, a second film covering the opening defects of the first film can be formed without generating new cracks in the first film. Thus, according to the present invention, it is possible to obtain a sufficiently dense film while preventing a decrease in the anticorrosion effect due to the opening defects, and to form a film having high corrosion resistance.

[0011] (2) The silica-based film formed using a solution containing polyorganosilazane contains organosilica having an organic component such as a methyl group. When such a silica-based film containing organosilica is exposed to a halogen-based gas, the organic portion is selectively corroded, and the corrosion resistance may be inferior. Therefore, in the film formation method, the polysilazane contained in the second solution is preferably perhydro Ropo silazane. More preferably, both the polysilazane contained in the first solution and the polysilazane contained in the second solution are perhydro Ropo polysilazane. In this case, a dense film can be obtained, and a film with higher corrosion resistance can be formed.

[0012] (3) In the above film formation method, it is preferable that the concentration ratio of the polysilazane content concentration in the second solution to the polysilazane content concentration in the first solution is 0.001 or more and less than 1. When the concentration ratio is 1 or more, the viscosity of the second solution becomes relatively high, and when the second solution is applied to the surface of the first film in the second step, the second solution may not be able to fill the opening defect portion. When the concentration ratio is less than 0.001, even if the second solution fills the opening defect portion, a film may not be sufficiently formed in the opening defect portion, and there is a risk that the hole cannot be sealed. By setting the concentration ratio to 0.001 or more and less than 1, a second solution having a viscosity that can fill the opening defect portion and having a concentration at which a film is sufficiently formed in the opening defect portion can be obtained. The concentration ratio of the polysilazane content concentration in the second solution to the polysilazane content concentration in the first solution is more preferably 0.01 or more and less than 0.6.

[0013] (4) The second solution contains at least one of an organometal, a metal compound, and an amine compound. The weight ratio of the total amount of the organometal, the metal compound, and the amine compound to the polysilazane is preferably 0.0001 or more and 1 or less. The organometal, the metal compound, and the amine compound are catalysts for lowering the silica conversion temperature of the polysilazane. By containing these in the second solution, the silica conversion temperature of the polysilazane can be lowered, and the heating temperature can be made lower. Also, when the weight ratio is less than 0.0001, there is a risk that the effect as a catalyst cannot be sufficiently obtained. In addition, when the weight ratio exceeds 1, the thickening (gelation) of the second solution becomes remarkable, and there is a risk that it may not be possible to fill the opening defects of the first film. By setting the weight ratio to 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 appropriately as a catalyst. In addition, when the weight ratio exceeds 0.2, a tendency of thickening (gelation) of the second solution is observed. Therefore, the weight ratio of the total amount of the organometal, the metal compound, and the amine compound to the polysilazane is more preferably 0.001 or more and 0.2 or less.

[0014] (5) In the above film forming method, 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. When the above film thickness is less than 0.01 μm, there is a risk that the surface of the metal substrate may not be sufficiently shielded from the external environment. When the above film thickness exceeds 10.0 μm, the stress acting on the first film increases due to the difference in the linear expansion coefficient between the metal substrate and the first film, and there is a risk that peeling may occur in the first film, or film peeling, film breakage, etc. may occur due to the internal stress of the first film. By setting the total film thickness of the first film and the second film to 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. 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.

[0015] (6) In the above film forming method, the first step may be to form the first film by repeating a step of applying the first solution to the metal substrate and a step of converting it to silica by heating the first solution a predetermined number of times. In this case, it becomes possible to increase the thickness of the first film, and the surface of the metal substrate can be sufficiently covered.

[0016] (7) In the above-described film formation method, the second step may be a step of applying the second solution to the first film, and a step of forming silica by heating the second solution at a temperature lower than the heating temperature in the first step a predetermined number of times to form the second film. In this case, the sealing of the opening portion in the opening defect portion can be performed more effectively.

Effects of the Invention

[0017] According to the present invention, a film having high corrosion resistance can be formed.

Brief Description of the Drawings

[0018]

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Modes for Carrying Out the Invention

[0019] Hereinafter, a film formation method according to an embodiment of the present invention will be described. The film formation method according to this embodiment is a method for forming a silica-based film using polysilazane. The silica-based film obtained according to this embodiment is formed on components such as chambers and pipes that are exposed to halogen-based corrosive gases or plasmas of corrosive gases in etching apparatuses used in the manufacture of semiconductors and flat panel displays, and film formation apparatuses such as CVD and PVD.

[0020] The film formation method according to this embodiment includes a first step of applying a first solution containing polysilazane to the surface of a metal substrate, heating the first solution to cause silica conversion, and forming a first film having opening defect portions on the surface of the metal substrate; and a second step of applying a second solution containing polysilazane to the surface of the first film to fill the opening defect portions, heating the second solution at a temperature lower than the heating temperature of the first step to cause silica conversion, and forming a second film on the surface of the first film. Hereinafter, each step will be described.

[0021] (1) Regarding the first step (1-1) Application of the first solution In the first step, as described above, the first solution is applied to the surface of the metal substrate. The first solution is a polysilazane-containing solution obtained by dissolving polysilazane in an organic solvent. As the 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 preferable.

[0022] Examples of the organic solvent include ethers (ethyl ether, isopropyl ether, ethyl butyl ether, dibutyl ether, 1,2-dioxyethane, 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 may be used as the organic solvent.

[0023] 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 may increase, and the film thickness of the first film may become non-uniform. The content concentration of polysilazane is more preferably 1% by mass or more and 25% by mass or less.

[0024] The first solution may contain a catalyst in addition to polysilazane. This catalyst has the effect of relatively lowering the temperature at which polysilazane is converted to silica or accelerating the silica conversion rate. Examples of the catalyst include metal catalysts (organometals or metal compounds) and amine-based catalysts (amine compounds). Examples of the metal catalyst include organometals or metal compounds containing at least one kind of metal selected from nickel, titanium, platinum, rhodium, cobalt, iron, ruthenium, osmium, palladium, iridium, and aluminum. In particular, metal carboxylates are preferred from the viewpoints of solubility, stability, and reactivity in the polysilazane-containing solution. Examples of the amine-based catalyst include amine compounds such as monoamines, diamines, triamines, tetraamines, hydroxyl compounds containing a chain amine residue, and hydroxyl compounds containing a cyclic amine residue. Incidentally, the amine residue-containing hydroxyl compound reacts with the polysilazane and is modified into an amine residue-containing polysilazane.

[0025] When the first solution contains a catalyst (at least one of an organometallic compound, 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, the effect as a catalyst may not be sufficiently obtained. If the weight ratio of the catalyst to the polysilazane exceeds 1, thickening (gelation) of the first solution becomes remarkable, and the film thickness of the first film may become non-uniform. 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, thickening of the first solution can be effectively suppressed.

[0026] 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 heating temperature, heating time, heating atmosphere, presence or absence of the above catalyst, and type of the above catalyst. The above heating temperature (silica conversion temperature) is determined according to the presence or absence of the above catalyst, the type of the above catalyst, heating time, and heating atmosphere, which are other parameters included in the silica conversion conditions. In the following description, the silica conversion conditions of the polysilazane in the first solution 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. Also, the silica conversion conditions of the polysilazane in the second solution 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.

[0027] In the present embodiment, the conversion of polysilazane into silica means that the film density of the film obtained by heating the solution containing polysilazane is 2.0 g / cm 3 or more. Therefore, the silica conversion conditions are heating conditions under which the film density of the first film or the second film is 2.0 g / cm 3 or more.

[0028] When the first solution does not contain a catalyst, the first silica conversion temperature is, for example, 300°C to 550°C. When the first solution contains a metal catalyst, the first silica conversion temperature is, for example, 120°C to 350°C. When the first solution contains an amine-based catalyst, the first silica conversion temperature is, for example, room temperature to 250°C. The first silica conversion conditions including the first silica conversion temperature can be determined by measuring the first solution in the following manner.

[0029] The measurement of the first silica conversion conditions is performed by forming a film using the first solution on a silicon wafer. First, measure the weight of the silicon wafer using an electronic balance or the like. After applying the first solution on this silicon wafer by the spin coating method, heat it in the air at a predetermined heating temperature and for a predetermined heating time to form a silica-based film, and measure the weight of the silicon wafer on which the silica-based film is formed. Next, obtain 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 with an FE-SEM apparatus 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. In the above method, set a plurality of combinations of heating temperature and heating time, and obtain the film density for each combination. Among each combination, the combination with a film density of 2.0 g / cm 3 or more is taken as the first silica conversion conditions. Film density [g / cm3] = Film weight [g] / (film thickness [μm] × silicon wafer surface area [cm 2 × 0.0001)

[0030] The silica-based film obtained by heating polysilazane under conditions that do not meet the silica conversion conditions (heating below 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 until polysilazane is converted to silica. The silica-based film obtained by heating the first solution under the first silica conversion conditions does not contain unreacted substances. That is, the first silica conversion conditions indicate heating conditions under which the polysilazane contained in the first solution is completely converted to silica, and a sufficiently dense silica film can be obtained.

[0031] Examples of the metal substrate on which the first solution is applied include, as described above, an etching apparatus, a chamber or piping of a film-forming apparatus, etc. These chambers and piping are formed of stainless steel or an aluminum alloy.

[0032] The surface of the metal substrate formed of stainless steel or an aluminum alloy is cleaned and degreased. Thereafter, the first solution is applied to the surface of the metal substrate. Note that, as a pretreatment before applying the first solution, the surface of the metal substrate may be modified by a known method such as irradiation with a UV lamp, an excimer lamp, or plasma. The application of the first solution is performed using a known coating method such as a spin coating method, a roll coating method, a flow coating method, a spray coating method, or a dip coating method.

[0033] (1-2) Formation of the first film Furthermore, in the first step, the first solution applied on the metal substrate is heated in the air or in an atmosphere containing water vapor to convert the polysilazane contained in the first solution to silica and form the first film. The first film is a silica-based film (inorganic silica film) obtained by the conversion of the polysilazane contained in the first solution to silica. The first solution applied on the metal substrate is heated based on predetermined first silica conversion conditions.

[0034] The heating temperature in the first step is set to be equal to or higher than the first silica conversion temperature under predetermined first silica conversion conditions. For example, when the predetermined first silica conversion conditions are a heating time of 1 hour and a first silica conversion temperature T (where T is a certain value), when the heating time of the first step is 1 hour, the heating temperature of the first step is set to be equal to or higher than the first silica conversion temperature T. Also, the heating temperature in the first step only needs to be equal to or higher than the first silica conversion temperature, but it is preferably 10°C or more higher than the first silica conversion temperature, and more preferably 30°C or more higher. If the heating temperature is less than the value obtained by adding 30°C to the first silica conversion temperature, there is a possibility that the entire applied first solution will not reach the first silica conversion temperature or higher. By setting the heating temperature to be 30°C or more higher than the first silica conversion temperature, the entire first solution can be made to reach the first silica conversion temperature or higher, and the polysilazane in the first solution can be appropriately converted into silica. As a result, a sufficiently dense first film that does not contain unreacted substances can be obtained, and a silica-based film with excellent corrosion resistance can be obtained.

[0035] The heating time in the first step only needs to be such that 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, there is a possibility that the conversion of polysilazane in the first solution into silica will be insufficient. If it exceeds 10 hours, it will waste time unnecessarily and increase costs.

[0036] Note that in the first step, the first film may be formed by repeating a predetermined number of times the step of applying the above-mentioned first solution and the step of converting the first solution into silica by heating. In this case, the thickness of the first film can be increased, and the surface of the metal substrate can be sufficiently covered.

[0037] FIG. 1 is a partial cross-sectional view of the metal substrate and the film after forming the first film by the first step. In FIG. 1, 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 opening defects 3. The opening defect 3 is a defect that opens to the surface 2a. The opening defect 3 includes a crack 3a and an opening pore portion 3b. The crack 3a is mainly caused by the difference between the linear expansion coefficient of the first film 1 and the linear expansion coefficient of the metal substrate 2. The crack 3a includes those that remain within the first film 1 and those that reach the surface 2a of the metal substrate 2. The opening pore portion 3b is caused by bubbles or the like contained in the first solution during the film formation process of the first film 1. The first film 1 is formed by the conversion of polysilazane in the first solution into silica, and is mainly formed of silica. Therefore, the linear expansion coefficient of the first film is a value intermediate between that of inorganic silica glass and quartz, and is about 0.6 to 6 (×10 -6 / °C). On the other hand, the metal substrate 2 is made of stainless steel or an aluminum alloy. As an example, JIS SUS316L, which is stainless steel, is 16.0 (×10 -6 / °C), and JIS A6061, which is an aluminum alloy, is 23.6 (×10 -6 / °C). In the first step, since the metal substrate 2 coated with the first solution is heated to a temperature equal to or higher than the silica conversion temperature of polysilazane in the first solution to form the first film 1, when cooled to room temperature after heating, stress acts on the first film 1 due to the difference in linear expansion coefficient between the first film 1 and the metal substrate 2. Due to this stress, cracks 3a are generated in the first film 1.

[0038] (2) Regarding the second step (2-1) Application of the second solution In the second step, the second solution is applied to the surface of the first film. FIG. 2 is a partial cross-sectional view of the metal substrate and the film after applying the second solution to the surface of the first film in the second step. As shown in FIG. 2, by applying the second solution 4 to the surface 1a of the first film 1, the opening defect 3 is filled with the second solution 4.

[0039] The second solution is a polysilazane-containing solution obtained by dissolving polysilazane in an organic solvent. As the 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.

[0040] As the organic solvent, the same kind as the first solution can be adopted. Specific examples thereof include ethers (ethyl ether, isopropyl ether, ethyl butyl ether, dibutyl ether, 1,2-dioxyethane, 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 kind or a mixture of two or more kinds of these ethers and hydrocarbons may be used as the organic solvent.

[0041] 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, there is a possibility that the second film with the required minimum film thickness cannot be obtained. 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 non-uniform. The content concentration of polysilazane is more preferably 1% by mass or more and 25% by mass or less.

[0042] Also, 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. When the concentration ratio is 1 or more, the viscosity of the second solution becomes relatively high, and when the second solution is applied to the surface of the first film in the second step, there is a possibility that the second solution may not be filled in the opening defect portion 3. Further, when the concentration ratio is less than 0.001, even if the second solution is filled in the opening defect portion 3, there is a possibility that a sufficient film may not be formed in the opening defect portion 3 and the sealing may not be achieved. By setting the concentration ratio to 0.001 or more and less than 1, it is possible to obtain a second solution having a viscosity capable of filling the opening defect portion 3 and having a concentration at which a sufficient film is formed in the opening defect portion 3. The concentration ratio of the polysilazane content concentration in the second solution to the polysilazane content concentration in the first solution is more preferably 0.01 or more and less than 0.6.

[0043] Also, the concentration ratio of the polysilazane content concentration in the second solution to the polysilazane content concentration in the first solution may be 1 or more and 200 or less. When the concentration ratio is greater than 200, the viscosity of the second solution becomes high, the second solution cannot be uniformly applied, and the film thickness of the second film may become non-uniform. Also, when the concentration ratio is less than 1, there is a possibility that a second film having a sufficient thickness cannot be obtained. By setting the concentration ratio to 1 or more and within 200, even if the first film is an extremely thin film (for example, less than 0.01 μm), it is possible to obtain a second film that can complement the first film and sufficiently coat the metal substrate.

[0044] The second solution preferably contains a catalyst in addition to polysilazane. When the second solution contains a catalyst, it becomes easier to set the heating temperature of the silica conversion conditions in the second step to a temperature lower than the heating temperature of the silica conversion conditions in the first step. As the catalyst, the same type as the first solution can be adopted, and examples thereof include a metal catalyst (organic metal or metal compound) and an amine-based catalyst (amine compound). Examples of the metal catalyst include an organometal or a metal compound containing at least one kind of metal selected from nickel, titanium, platinum, rhodium, cobalt, iron, ruthenium, osmium, palladium, iridium, and aluminum. In particular, metal carboxylates are preferable from the viewpoints of solubility, stability, and reactivity in the polysilazane-containing solution. Examples of the amine-based catalyst include amine compounds such as monoamines, diamines, triamines, tetraamines, hydroxyl compounds containing a chain amine residue, and hydroxyl compounds containing a cyclic amine residue.

[0045] 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, the effect as a catalyst may not be sufficiently obtained. When the weight ratio of the catalyst to the polysilazane exceeds 1, the thickening (gelation) of the second solution becomes remarkable, and not only the film thickness becomes non-uniform but also there is a possibility that the opening defect portion 3 on the surface of the first film cannot be filled. 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 second solution can be effectively suppressed.

[0046] When the second solution does not contain a catalyst, the second silica conversion temperature is, for example, 300°C to 550°C. When the second solution contains a metal catalyst, the second silica conversion temperature is, for example, 120°C to 350°C. When the second solution contains an amine-based catalyst, the second silica conversion temperature is, for example, room temperature to 250°C. For example, when the first solution does not contain a catalyst, the first silica conversion temperature is 300°C to 550°C, and the second solution may or may not contain a catalyst as long as the heating temperature in the second step satisfies the condition that it is lower than the heating temperature in the first step. When the first solution contains palladium which is 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 not containing a catalyst, the second silica conversion temperature becomes 300°C to 550°C, and it becomes difficult to satisfy the condition that the heating temperature in the second step is lower than the heating temperature in the first step. The second silica conversion condition including the second silica conversion temperature can be obtained by measuring in the same method as the measurement method of the first silica conversion condition for the second solution.

[0047] In this embodiment, the second silica conversion condition is a condition including a second silica conversion temperature having a value equal to or lower than the first silica conversion temperature included in a predetermined first silica conversion condition.

[0048] The application of the second solution is performed using a known application method such as a spin coating method, a roll coating method, a flow coating method, a spray coating method, or a dip coating method.

[0049] (2-2) Formation of the second film Furthermore, in the second step, the second solution applied to the surface of the first film is heated in the air or in an atmosphere containing water vapor to convert the polysilazane contained in the second solution into silica, 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.

[0050] The heating temperature in the second step is set to a temperature lower than the heating temperature in the first step and equal to or higher than the second silica conversion temperature. If the heating temperature is equal to or higher than the heating temperature in the first step, the first film will be heated to a temperature higher than when the first film was formed, and when cooled to room temperature thereafter, there is a risk of generating new cracks in the first film due to the difference in the linear expansion coefficient between the metal substrate and the first film. If the heating temperature is lower than the second silica conversion temperature, there is a possibility that the conversion of the polysilazane contained in the second solution into silica may not be sufficiently performed. By setting the heating temperature to be lower than the heating temperature in the first step and equal to or higher than the second silica conversion temperature, polysilazane in the second solution can be appropriately converted into silica without applying stress to the first film. The heating time in the second step only needs to be such that the second solution on the first film is sufficiently heated and the polysilazane in the second 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 second solution into silica may be insufficient. If it exceeds 10 hours, it will unnecessarily consume time and increase costs.

[0051] Note that the second step may form the second film by repeating a process of applying the above-mentioned second solution and a process of converting the second solution into silica by heating it at a temperature lower than the heating temperature in the first step a predetermined number of times.

[0052] Figure 3 is a partial cross-sectional view of the metal substrate and the film after forming the second film by the second step. When 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 shown in Figure 3, the second film 5 is formed in the opening defect portion 3. As a result, the opening defect portion 3 on the surface 1a of the first film 1 is sealed by the second film. The second film 5 only needs to be formed at least in the opening defect portion 3 on the surface 1a and seal the opening defect portion 3, but it may also be formed in a portion other than the opening defect portion 3 (for example, on the non-defect portion 6).

[0053] Thus, according to the film formation method having the above configuration, although the first film has the opening defect portion 3, the second solution is filled in the opening defect portion 3 by applying the second solution to the surface of the first film in the second step. Then, by converting the polysilazane contained in the second solution into silica, the second film can be formed in the opening defect portion 3. As a result, the opening defect portion 3 can be sealed by the second film, and a decrease in corrosion resistance due to the opening defect portion 3 can be prevented. Therefore, without worrying about cracks forming in the film in the first step, the polysilazane of the first solution can be converted into silica at a sufficiently high temperature to form a dense first film. Also, by heating at a temperature lower than that in the first step in the second step, a second film that covers the opening defects of the first film can be formed without generating new cracks in the first film. Thus, according to the present embodiment, it is possible to obtain a sufficiently dense film while preventing a decrease in the corrosion protection effect caused by the opening defects 3, and to form a film having high corrosion resistance. Furthermore, if the second step is a step of applying a second solution and a step of forming the second film by repeating the step of subjecting the second solution to silica conversion by heating at a temperature lower than the heating temperature of the first step a predetermined number of times, the sealing of the opening defects 3 can be performed more effectively.

[0054] As the polysilazane contained in the second solution, perhydropolysilazane is particularly preferable as described above. If the polysilazane contained in the second solution is perhydropolysilazane, a dense second film can be obtained, and a film having higher corrosion resistance can be formed.

[0055] Also, 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. When the above film thickness is less than 0.01 μm, there is a possibility that the surface of the metal substrate cannot be sufficiently shielded from the external environment. When the above film thickness exceeds 10.0 μm, the stress acting on the first film increases due to the difference in the linear expansion coefficient between the metal substrate and the first film, 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. By setting the total film thickness of the first film and the second film to be 0.01 μm or more and 10.0 μm or less, it is possible to obtain a film that can appropriately shield the surface of the metal substrate from the external environment. 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.

Examples

[0056] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. (Example 1) 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 perhydropolysilazane content concentration of 20% by mass was used. The first silica conversion conditions in the first solution were determined using the values obtained by the above measurement method, and the first silica conversion temperature was set to 150 °C with a heating time of 1 hour. As the second solution, a dibutyl ether solution (manufactured by Merck Performance Materials, trade name Durazane 2400) containing a metal catalyst (palladium) and having a perhydropolysilazane content concentration of 20% by mass was prepared so that the perhydropolysilazane content concentration became 10% by mass. Therefore, the concentration ratio of the perhydropolysilazane content concentration in the second solution to the perhydropolysilazane content concentration in the first solution is 0.5. The second silica conversion conditions in the second solution were determined using the values obtained by the above measurement method, and the second silica conversion temperature was set to 150 °C with a heating time of 1 hour.

[0057] 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. The surface of this metal substrate was degreased and washed, the first solution was applied by the spin coating method, heated at 250 °C for 1 hour, taken out of the heating furnace after 1 hour, and cooled in the air. As a result, a first film having an opening defect portion was formed on the surface of the metal substrate. Thereafter, a second solution was spin-coated on the surface of the first film and heated at 150 °C, which is the second silica conversion temperature, for 1 hour. As a result, 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 to 1.8 μm) formed on the metal substrate was obtained. Note that 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 silica-converted. The densities of these films were obtained by measuring the density of the films heated under the same conditions by the above-described measuring method.

[0058] (Example 2) 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 perhydropolysilazane content concentration of 20% by mass was used. For the first silica conversion conditions in the first solution, the value obtained by the above-described measuring method was used, and the first silica conversion temperature was set to 150 °C with a heating time of 1 hour. As the second solution, a dibutyl ether solution (manufactured by Merck Performance Materials, trade name: Durazane 2400) containing a metal catalyst (palladium) and having a perhydropolysilazane content concentration of 20% by mass was prepared so that the perhydropolysilazane content concentration became a 5% by mass solution. Therefore, the concentration ratio of the perhydropolysilazane content concentration in the second solution to the perhydropolysilazane content concentration in the first solution is 0.25. For the second silica conversion conditions in the second solution, the value obtained by the above-described measuring method was used, and the second silica conversion temperature was set to 130 °C with a heating time of 2 hours.

[0059] As the metal substrate, a plate material of an aluminum alloy (JIS A6061) having a size of 50 mm × 50 mm and a thickness of 5 mm was prepared. The surface of this metal substrate was degreased and cleaned, the first solution was applied by spin coating, heated at 250°C for 1 hour, taken out of the heating furnace after 1 hour, and cooled in the air. As a result, a first film having an opening defect portion was formed on the surface of the metal substrate. Thereafter, the second solution was applied to the surface of the first film by spin coating and heated at 130°C, which is the second silica conversion temperature, for 2 hours. As a result, 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 to 1.5 μm) formed on the metal substrate was obtained. 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 silica-converted.

[0060] (Comparative Example) 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 content concentration of perhydropolysilazane of 20% by mass was used. Based on the manufacturer's disclosure data, the first silica conversion conditions in the first solution were set such that the first silica conversion temperature was 250°C with a heating time of 1 hour.

[0061] As the metal substrate, a stainless steel (JIS SUS316L) plate having a size of 50 mm × 50 mm and a thickness of 5 mm was prepared. The surface of this metal substrate was degreased and cleaned, the first solution was applied by spin coating, and heated at 250°C, which is the first silica conversion temperature, for 1 hour. As a result, a test piece having a first film (film thickness: 1.2 to 1.3 μm) formed on the surface of the metal substrate was obtained.

[0062] 〔Observation of Film Cross-Section and Surface〕 Each test piece obtained in Example 1, 2 and the Comparative Example was cut with a high-speed cutter, and the obtained cut piece was embedded in resin and then ion milled (IM400 manufactured by Hitachi High-Technologies Corporation), and the cross section of the film was observed using an FE-SEM apparatus (SU8020 manufactured by Hitachi High-Technologies Corporation). Further, the surface of the film of each test piece obtained in Example 1, 2 and the Comparative Example was observed using an FE-SEM apparatus.

[0063] Figure 4 is an electron micrograph of the cross section of the film according to the Comparative Example, and Figure 5 is an electron micrograph of the surface of the film according to the Comparative Example. As shown in FIGS. 4 and 5, it can be seen that a large number of cracks exist on the surface of the first film.

[0064] Figure 6 is an electron micrograph of the cross section of the film according to Example 1, and Figure 7 is an electron micrograph of the surface of the film according to Example 1. Figure 8 is an electron micrograph of the cross section of the film according to Example 2, and Figure 9 is an electron micrograph of the surface of the film according to Example 2. As shown in FIGS. 6 to 9, it can be seen that in Example 1 and Example 2, the cracks found in the Comparative Example are sealed.

[0065] 〔Hydrochloric acid corrosion resistance test〕 Each test piece obtained in Example 1, 2 and the Comparative Example was masked so that only the surface on which the film was formed was exposed, 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. The results are shown in Table 1 below.

[0066]

Table 1

[0067] As shown in Table 1, in the Comparative Example having the first film on which the second film was not formed, corrosion was observed and partial peeling occurred, but in Example 1 and Example 2 in which the second film was formed, no corrosion was observed. From this, it can be seen that the cracks in the first film are sealed, and a decrease in the corrosion prevention effect due to the cracks can be prevented. Also, it can be seen that the first film and the second film have high corrosion resistance in a hydrochloric acid solution.

Explanation of symbols

[0068] 1 First film 1a Surface 2 Metal substrate 2a Surface 3 Opening defect part 3a Crack 3b Opening pore part 4 Second solution 5 Second film 6 Non-defect part

Claims

1. A first step of applying a first solution containing only perhydropolysilazane as a polysilazane onto the surface of a metal substrate, heating the first solution to cause silica conversion, and forming a first film having opening defects on the surface and a film density of 2.0 g / cm3 or more on the surface of the metal substrate; A second solution containing only perhydropolysilazane as the polysilazane is applied to the surface of the first film to fill the opening defect portion, and the second solution is heated at a temperature lower than the heating temperature in the first step to cause silica conversion, and at least the opening defect portion of the first film has a film density of 2.0 g / cm ３ or more to form a second film, and a second step, including Film forming method.

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

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

4. The total film thickness of the first film and the second film is 0.01 μm or more and 10.0 μm or less. The film forming method according to any one of Claims 1 to 3.

5. The first step forms the first film by repeating a step of applying the first solution to the metal substrate and a step of causing silica conversion by heating the first solution a predetermined number of times. The film forming method according to any one of Claims 1 to 4.

6. The second step forms the second film by repeating a step of applying the second solution to the first film and a step of causing silica conversion by heating the second solution at a temperature lower than the heating temperature of the first step a predetermined number of times. The film forming method according to any one of Claims 1 to 5.

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