Method for manufacturing functional membranes

Abstract

To provide a method for manufacturing a functional film that uses a stable functional film-forming composition, can form a thick film in a single application, and requires a low heat treatment temperature during film formation. [Solution] A method for producing a functional film, comprising the steps of: mixing an alcohol-containing solvent, an oxalic acid compound, and an amine compound to obtain a mixture A; adding a silicon compound to mixture A to obtain a mixture B; refluxing the mixture B under conditions where the liquid temperature of mixture B is above the boiling point of mixture B for 1 to 8 hours to generate an anionic silicon complex with oxalic acid as a ligand to produce a functional film-forming composition; applying the functional film-forming composition onto a substrate to form a composition layer; and heating the composition layer to 150°C to 400°C to obtain a functional film containing amorphous silicon oxide, wherein the amount of oxalic acid compound contained in the functional film-forming composition is 2.5 mol or more per 1 mol of silicon atoms contained in the silicon compound.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a functional film.

Background Art

[0002] Conventionally, a silicon oxide film has attracted attention as a functional film useful for an interlayer insulating film of semiconductor elements such as integrated circuits and large-scale integrated circuits. As a method for manufacturing a silicon oxide film, a method of applying a coating solution for forming a silicon oxide film on a substrate and forming a film by a sol-gel method is generally applied (see, for example, Non-Patent Document 1). On the other hand, as a method for manufacturing an amorphous silicon oxide film, a molecular precursor method is known, in which a solvent containing alcohol, at least one selected from oxalic acid compounds, and a titanium compound or a silicon oxide compound are mixed to obtain a mixture, water or hydrogen peroxide is added to the mixture and refluxed to obtain an anionic silicon complex, which is applied to a substrate and irradiated with ultraviolet rays, thereby proposing a method for manufacturing a functional film useful for forming a conductive film (see Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One of the problems with forming films using the sol-gel method described in Non-Patent Document 1 is the large shrinkage stress generated during film formation. For example, in sol-gel film formation, when the amount of silicon oxide film-forming coating solution is increased and film formation is completed in a single step, cracks due to shrinkage stress may occur when forming films with a thickness exceeding 0.3 μm. Therefore, when forming a silicon oxide film as an interlayer insulating film on a device substrate with irregularities exceeding 0.3 μm, it is difficult to fill the steps in a single process, and the manufacturing process becomes complicated, requiring multiple coats. Furthermore, the sol-gel method, which involves the polymerization of components in the silicon oxide film-forming coating solution, uses unstable complexes that are prone to hydrolysis as raw materials, resulting in a problem of insufficient storage time for the solution. In addition, the formation of the silicon oxide film-forming coating solution applied to the device substrate requires heat treatment at around 500°C, making it difficult to apply to devices with low heat resistance.

[0006] According to the manufacturing method described in Patent Document 1, a highly transparent silicon oxide film can be formed on a substrate made of any material and having any shape. However, the resulting silicon oxide film has a high oxygen content relative to silicon, and there is no interest in its use as an interlayer insulating film. Furthermore, Patent Document 1 does not address the storage stability of the coating solution for forming the silicon oxide film or the insulating properties of the formed silicon oxide film.

[0007] The object of one embodiment of this disclosure is to provide a method for manufacturing a functional film that can form a thick film in a single application by using a stable functional film-forming composition, and can form a functional film with a lower heat treatment temperature during film formation compared to conventional methods. [Means for solving the problem]

[0008] The means for solving the above problem include the following embodiments. <1> A step of obtaining mixture A by mixing an alcohol-containing solvent, at least one oxalic acid compound selected from oxalic acid compounds, and an amine compound. The process involves adding at least one silicon compound selected from the silicon compounds to the obtained mixture A to obtain mixture B, refluxing the mixture B under conditions where the liquid temperature of mixture B is above the boiling point of mixture B for 1 to 8 hours to generate an anionic silicon complex with oxalic acid as a ligand, and thereby producing a functional film-forming composition. The steps include applying the obtained functional film-forming composition to a substrate to form a functional film-forming composition layer, and The process includes heating the above-mentioned functional film-forming composition layer formed on a substrate to 150°C to 400°C to obtain a functional film containing amorphous silicon oxide. A method for producing a functional film, wherein the amount of the oxalic acid compound contained in the functional film-forming composition is 2.5 moles or more per mole of silicon atoms contained in the silicon compound.

[0009] <2> The amount of oxalic acid compound contained in the above mixture A is 3 moles or more to 4 moles per mole of silicon atoms contained in the silicon compound. <1> A method for producing a functional membrane as described above. <3> The thickness of the functional film obtained by performing the above-mentioned step of forming the functional film-forming composition layer and the step of heating the above-mentioned functional film-forming composition layer to obtain a functional film once each is 0.3 μm or more. <1> or <2> A method for producing a functional membrane as described above. <4> The above functional film is an interlayer insulating film. <1> ~ <3> A method for producing a functional membrane as described in any one of the following.

[0010] [Effects of the Invention]

[0011] According to one embodiment of the present invention, by using a stable functional film-forming composition, it is possible to provide a method for producing a functional film in which a thick film can be formed in a single application and the heat treatment temperature during film formation is lower than that of conventional methods. [Brief explanation of the drawing]

[0012] [Figure 1]It is a graph showing the absorbance from immediately after the production of the composition for forming a functional film obtained by the production method of Example 1 of the present disclosure to 19 weeks after the production. [Figure 2] It is a graph showing the FT-IR spectrum of the functional film obtained by the production method of Example 1 of the present disclosure. [Figure 3] It is a graph showing the current-voltage characteristics of the functional film obtained by the production method of Example 1 of the present disclosure.

Mode for Carrying Out the Invention

[0013] Hereinafter, the method for producing a functional film of the present disclosure will be described in detail with specific embodiments. The production method of the present disclosure is not limited to the following embodiments, and can be implemented by various modifications as long as it does not contradict the gist thereof.

[0014] In the present disclosure, a numerical range described using "~" represents a numerical range including the numerical values before and after "~" as the lower limit value and the upper limit value. In the present disclosure, the term "step" includes not only an independent step but also this term as long as the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps. In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. Also, in the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, unless otherwise specified, room temperature and normal temperature mean 25°C. In the present disclosure, "thick film" means a film having a thickness of 0.3 μm or more.

[0015] <Method for manufacturing functional membranes> The method for producing a functional film according to the present disclosure (hereinafter sometimes simply referred to as "the method for producing the functional film according to the present disclosure") includes the steps of: getting a mixture A by mixing an alcohol-containing solvent with at least one oxalic acid compound selected from oxalic acid compounds and an amine compound; getting a mixture B by adding at least one silicon compound selected from silicon compounds to the obtained mixture A; refluxing the mixture B under conditions where the liquid temperature of the mixture B is above the boiling point of the mixture B for 1 to 8 hours to generate an anionic silicon complex with oxalic acid as a ligand to produce a functional film-forming composition (step b); applying the obtained functional film-forming composition onto a substrate to form a functional film-forming composition layer (step c); and heating the functional film-forming composition layer formed on the substrate to 150°C to 400°C to obtain a functional film containing amorphous silicon oxide (step d), wherein the amount of oxalic acid compound contained in the functional film-forming composition is 2.5 mol or more per 1 mol of silicon atoms contained in the silicon compound.

[0016] (Step a) Step a in the manufacturing method of the present disclosure is a step of mixing a solvent containing an alcohol, at least one selected from oxalic acid compounds, and an amine compound to obtain a mixture A. Examples of alcohol-containing solvents in step a include monohydric alcohols and mixed solvents of alcohol and water, with monohydric alcohols being preferred. When the solvent contains water, it is preferable that the water contains few impurities. From this viewpoint, it is preferable to use purified water, ion-exchanged water, or pure water.

[0017] Examples of monohydric alcohols that can be used as solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and other C1-C5 alcohols. Ethanol is preferred from the viewpoint of providing better coatability of the resulting functional film-forming composition. Mixture A may contain only one type of alcohol, or it may contain two or more types of alcohol. The content of the alcohol-containing solvent relative to the total mass of mixture A can be 10% by mass or more, preferably 30% to 75% by mass, and more preferably 60% to 70% by mass.

[0018] Examples of oxalic acid compounds used in the preparation of mixture A include oxalic acid, oxalic acid hydrate, ammonium salt of oxalic acid, hydrate of ammonium salt of oxalic acid, amine salt of oxalic acid, and hydrate of amine salt of oxalic acid. More specifically, examples of oxalic acid hydrate include oxalic acid dihydrate, examples of hydrate of ammonium salt of oxalic acid include ammonium oxalate monohydrate, and examples of amines in amine salts of oxalic acid include salts of amines having 1 to 5 carbon atoms of oxalic acid. Among these, oxalic acid is preferred. Mixture A may contain only one oxalic acid compound, or it may contain two or more. The content of the oxalic acid compound relative to the total mass of mixture A is preferably 15% to 30% by mass, and more preferably 20% to 25% by mass.

[0019] Examples of amine compounds include alkylamines, aminocarboxylic acids, and monoamines. From the viewpoint of improving the temporal stability of the functional film-forming composition, alkylamines are more preferred, and specifically, n-butylamine is preferred. Mixture A may contain only one amine compound or two or more. The content of the amine compound relative to the total mass of mixture A is preferably 8% to 20% by mass, and more preferably 10% to 15% by mass.

[0020] Mixture A can be obtained by placing each of the above components in a container and stirring and mixing them thoroughly at room temperature. Stirring can be performed, for example, in a container equipped with stirring blades, at a speed of 300 rpm (revolutions per minute: the same applies hereafter) to 6000 rpm, preferably 400 rpm to 500 rpm. From the viewpoint of homogeneity of mixture A, it is preferable to continue stirring for 10 minutes or more, and more preferable to continue stirring for 15 to 30 minutes.

[0021] (Step b) Step b is a process to produce a functional film-forming composition by adding at least one silicon compound selected from among silicon compounds to the mixture A obtained in step a to obtain mixture B, and refluxing the mixture B under conditions where the liquid temperature of mixture B is above the boiling point of mixture B for 1 to 8 hours to generate an anionic silicon complex with oxalic acid as a ligand. The functional film-forming composition obtained in step b contains a silicon complex with oxalic acid as a ligand, which serves as a precursor for the functional film.

[0022] Examples of silicon compounds include silicon alkoxides, such as tetraethoxysilane (TEOS: also known as tetraethyl orthosilicate) and methyltriethoxysilane. From the viewpoint of being able to form stable complexes, TEOS is preferred as the silicon compound. The silicon compound used in step b may be a single type or a mixture of two or more types. The silicon compound may be added to mixture A as is, or it may be added to mixture A after being dissolved in a solvent containing alcohol or the like. When added as a solution, from the viewpoint of handling, the concentration of the silicon compound in the solution is preferably 10% to 20% by mass. As the alcohol used to prepare the silicon compound solution, the monohydric alcohols listed above as solvents that can be used to prepare mixture A can be used in the same way.

[0023] In step b, the amount of silicon compound added to the oxalic acid compound in mixture A is important. When adding the silicon compound to mixture A in step b, a stable functional film-forming composition can be obtained by adding the silicon compound in an amount such that the oxalic acid compound is 2.5 moles or more for every 1 mole of silicon atoms contained in the silicon compound in the resulting functional film-forming composition. There is no particular upper limit on the content of the oxalic acid compound, but from the viewpoint of the stability of the composition, the upper limit can be set to 5 moles. In particular, from the viewpoint of the stability of the functional film-forming composition and the uniformity of the resulting film, it is preferable that the amount of oxalic acid compound in the functional film-forming composition be such that there are 3 to 4 moles of oxalic acid compound per 1 mole of silicon atoms contained in the silicon compound. If the amount of oxalic acid compound in the functional film-forming composition obtained in step b is less than 2.5 mol per 1 mol of silicon compound, it is undesirable because a functional film-forming composition with a uniform composition cannot be obtained, or the shelf life of the functional film-forming composition deteriorates.

[0024] When adding a silicon compound to mixture A, the addition can be done dropwise while stirring mixture A. By adding the entire amount of silicon compound to mixture A and then refluxing, a functional film-forming composition can be obtained. Reflux is continued for 1 to 8 hours while heating under conditions that maintain the temperature of mixture B (hereinafter also simply referred to as "liquid temperature"), obtained by adding a silicon compound to mixture A, at a temperature above the boiling point of mixture B. The boiling point of mixture B to be refluxed can be determined by measuring the boiling point of mixture B beforehand and setting the heating conditions accordingly. Alternatively, it can be confirmed that the liquid temperature of mixture B is above its boiling point by observing that reflux of mixture B is progressing and continuing due to heating. In step b, the mixture B is heated under conditions that maintain its temperature above its boiling point. There are no particular restrictions on the heating method as long as the heating can be performed under conditions that maintain the temperature within the above temperature range. One heating method involves heating mixture B on a heating device (e.g., a hot plate) controlled to a predetermined temperature range. Any known heating device can be used as the heating device without any particular limitations. Heating methods include heating on a hot plate or other heating device while observing the continued reflux of mixture B, and controlling the ambient temperature using a heating device.

[0025] The heating of mixture B will be explained in more detail using Example 1 described below as an example, but the method is not limited to this. When heating and refluxing mixture B, the liquid temperature of mixture B described in Example 1 should be 80°C or higher, and it is preferable to maintain it in the range of 100°C to 120°C. As a heating method to maintain the liquid temperature of mixture B at 100°C to 120°C, a method of heating mixture B on a hot plate controlled to a predetermined temperature range, for example, 150°C to 200°C, is used. Heating of mixture B may also be carried out in a space where the ambient temperature is adjusted to 150°C to 200°C. A hot plate temperature or ambient temperature of 150°C to 190°C is more preferable. In Example 1, it was confirmed that reflux of mixture B continued by heating to the set temperature.

[0026] The reflux time in step b is 1 to 8 hours, preferably 2 to 7 hours.

[0027] By thoroughly heating under reflux, a silicon complex with oxalic acid as a ligand is formed in the solution. At this time, if the content of oxalic acid compound is 2.5 mol or more per mol of silicon compound, a stable silicon complex is formed in which oxalic acid is coordinated to the silicon atoms. If the content of oxalic acid compound is less than 2.5 mol, unreacted sites remain on the silicon atoms, which is thought to reduce the stability of the silicon complex with oxalic acid as a ligand, making it easier for the viscosity of the composition to increase and precipitates to form. For example, a functional film-forming composition prepared with a content of 3 mol of oxalic acid compound per 1 mol of silicon compound used in the examples described later showed no change in absorbance over time even after 19 weeks of storage in a refrigerator (Panasonic Corporation, MPR-312DCN) at a set temperature of 7°C, confirming its good stability over time.

[0028] (Step c) Step c is a step in which the functional film-forming composition obtained in step b is applied to a substrate to form a functional film-forming composition layer. There are no particular restrictions on the method of applying the functional film-forming composition to the substrate. Depending on the material and shape of the substrate, various methods can be applied, such as applying the functional film-forming composition to the substrate using a known coating method, or immersing the substrate in the functional film-forming composition. In particular, from the viewpoint of easy film thickness control, a method of applying a functional film-forming composition to a substrate is preferred.

[0029] Methods for applying the functional film-forming composition to a substrate include, for example, dip coating, spray coating, spin coating, blade coating, bar coating, roll coating, die coating, and flow coating. Alternatively, the functional film-forming composition may be applied to the substrate by casting. By applying printing methods such as screen printing and inkjet printing to the substrate, the functional film-forming composition can be locally applied to a desired area of ​​the substrate. In particular, from the viewpoint of uniformity of the functional film-forming composition layer, the spin coating method is preferred. The amount of the functional film-forming composition applied to the substrate can be appropriately selected depending on the thickness of the functional film to be formed. In one embodiment, the application amount can be in the range of 3 μm to 150 μm in terms of wet film thickness.

[0030] (Step d) Step d is a step in which the functional film-forming composition layer formed on the substrate in step c is heated to 150°C to 400°C to obtain a functional film containing amorphous silicon oxide. The functional film-forming composition used in the manufacturing method of this disclosure has good stability and contains a stable silicon complex with oxalic acid as a ligand, so it is possible to form a functional film that is stable at low temperatures compared to known methods for forming functional films. The heating temperature of the functional film-forming composition layer can be 150°C to 400°C, with a range of 150°C to 300°C being preferred. Therefore, since a functional film can be formed on a substrate with relatively low heat resistance using the manufacturing method of this disclosure, there is a high degree of freedom in selecting the substrate on which the functional film is formed. The heating time is selected appropriately depending on the purpose, but generally it can be 10 to 60 minutes, and from the viewpoint of the properties of the functional membrane and productivity, it is preferable to heat it for 20 to 40 minutes.

[0031] There are no particular restrictions on the heating method for the functional film-forming composition layer. Known heating methods can be used. Examples of heating methods include heating in an electric furnace with a temperature controlled within a predetermined range, and heating in a combustion furnace with a temperature controlled within a predetermined range. Heating can be performed under atmospheric pressure. Furthermore, prior to heating, a preheating step may be performed in which the functional film-forming composition layer is heated to approximately 50°C to 80°C, for purposes such as volatilizing the solvent in the functional film-forming composition layer. The preheating time can be 5 to 20 minutes. Furthermore, when the solvent in the functional film-forming composition layer is evaporated by heating, it is not always necessary to remove all of the solvent; reducing the amount of solvent contained in the functional film-forming composition layer by evaporation is also included in the preheating process.

[0032] According to the manufacturing method of this disclosure, the thickness of the functional film obtained by performing the steps of forming a functional film-forming composition layer and heating the functional film-forming composition layer to obtain a functional film once each can be 0.3 μm or more. In other words, the thickness of the functional film formed by performing steps c and d only once each can be 0.3 μm or more, and since a functional film with a thickness of 0.3 μm or more can be easily formed, its applications are wide-ranging. There is no particular upper limit to the thickness of the functional film formed in a single step, and it can be appropriately selected depending on the application of the functional film. For example, according to the manufacturing method of this disclosure, a functional film of 1.0 μm (1000 nm) or more can be formed in a single coating. It goes without saying that when forming a functional film with even greater thickness, the formation of the functional film-forming composition layer by coating can be repeated multiple times.

[0033] According to step d, a stable functional film is formed at a heating temperature of 400°C or lower. For this reason, the functional film obtained by the manufacturing method of this disclosure is preferably an interlayer insulating film. The functional film obtained by the manufacturing method of this disclosure is suitably used as an interlayer insulating film such as a circuit board on which wiring has already been formed. This is because, when forming an interlayer insulating film on a circuit board that already has wiring, it is known that heating to, for example, 450°C or higher causes rapid deterioration of the wiring made of aluminum, copper, etc., resulting in the formation of voids and protrusions within the wiring. By applying a method that can form a stable functional film even at low heating temperatures, as described in the manufacturing method of this disclosure, it can be suitably used as an interlayer insulating film on a substrate that already has wiring.

[0034] For example, in the sol-gel method described in Non-Patent Document 1, it is difficult to completely remove hydroxyl groups, silanol groups, etc. remaining in the coating solution from the formed film with low-temperature heat treatment of around 300°C, and the dielectric constant tends to be high. For example, it has been reported that the dielectric constant of a functional film containing silicon dioxide formed by the sol-gel method is 3.47 after heat treatment at 300°C (Jung-Kyun Hong et al., Thin Solid Films, 332, 1-2, pp.449-454 (1998)). A relative permittivity of 3.47 is considered insufficient for function as an interlayer insulating film. On the other hand, according to the manufacturing method of the present disclosure, as shown in Example 1 described later, the relative permittivity of the silicon oxide film obtained by heat treatment at 300°C is 2.3, and from this point as well, it can be seen that a functional film suitable as an interlayer insulating film can be obtained according to the manufacturing method of the present disclosure.

[0035] The manufacturing method disclosed herein provides a method for producing a functional film that allows for the formation of a thick functional film in a single application by using a stable functional film-forming composition, and that enables the formation of a functional film with a lower heat treatment temperature during film formation compared to conventional methods. Furthermore, since the manufacturing method of this disclosure allows for the formation of a low dielectric constant functional film at low temperatures, it can be applied to substrates with existing wiring to easily form interlayer insulating films with low dielectric constants, thus offering a wide range of applications. [Examples]

[0036] The manufacturing method of this disclosure will be described in detail below with reference to examples, but this disclosure is not limited to the following examples and can be implemented in various modified forms as long as it does not exceed the spirit of the disclosure.

[0037] [Example 1] (Manufacturing of functional membranes) In a 200 mL flask, 17.3 g of oxalic acid, 50 g of ethanol, and 9.39 g of butylamine were added and stirred at 500 rpm for 15 minutes at room temperature to obtain mixture A. (Step a) The stirring of the obtained mixture A was stopped, and 13.1 g of tetraethoxysilane was added dropwise using a Pasteur pipette to obtain mixture B. The obtained mixture B was heated under reflux on a hot plate at a set temperature of 180°C for 5 hours to prepare a silicon oxide film-forming coating solution, which is a functional film-forming composition. It was confirmed that reflux of mixture B was continuing by heating at the above set temperature. (Step b) The amount of oxalic acid per mole of silicon in the silicon oxide film-forming coating solution was 3 moles.

[0038] The obtained silicon dioxide film-forming coating solution was used as the test subject, and its absorbance was measured using a visible-ultraviolet spectrophotometer (Shimadzu Corporation, UV-1900i) under the following conditions. (Measurement conditions) Cell: Disposable acrylic resin cell with an optical path length of 10 mm. Measurement wavelength range: 200nm~1100nm Measurement interval: 0.5nm Measurement speed: 9nm / s Reference: Air Scan speed 200nm / min

[0039] Subsequently, the samples were stored in a refrigerator (Panasonic Corporation, MPR-312DCN) at a set temperature of 7°C, and the absorbance was measured every four weeks, with the final measurement taken after 19 weeks. This method was used to observe whether or not there was a change in absorbance over time. The results are shown in Figure 1. Figure 1 is a graph showing the absorbance of the functional film-forming composition obtained by the manufacturing method of Example 1 of this disclosure from immediately after manufacturing to 19 weeks after manufacturing. As shown in Figure 1, the absorption curve of the silicon dioxide film-forming coating solution immediately after preparation and the absorption curves every four weeks up to 19 weeks later overlap as shown in Figure 1, indicating almost no change. From the results in Figure 1, it was confirmed that the absorbance of the silicon dioxide film-forming coating solution remained almost unchanged from immediately after preparation to 19 weeks after manufacturing, demonstrating its stability as a coating solution.

[0040] The silicon oxide film-forming coating solution obtained in step b was dropped onto a 20 mm × 20 mm × 1.5 mm cleaned quartz glass surface at a rate of 100 μL, and then coated by spin coating. The spin coating was performed in two steps: the first step at 500 rpm for 5 seconds, and the second step at 2000 rpm for 30 seconds, to form a silicon oxide film-forming coating layer on the quartz glass. (Step c) The formed silicon oxide film-forming coating layer was preheated in a 70°C dryer for 10 minutes, and then heat-treated in an electric furnace (muffle furnace: FUW210PB, manufactured by ADVANTEC) at 300°C under air for 30 minutes to obtain a functional film (silicon oxide film). (Step d)

[0041] (Evaluation of functional membranes) 1. Film thickness The obtained functional film was measured using a stylus profiler (Bruker, DEKTAK XT) with a diamond probe having a tip radius of 2.5 μm, scanning 3000 μm for 30 seconds. The film thickness was found to be 970 ± 10 nm. The film thickness was determined by measuring the step height at five points on the substrate surface prepared by partial masking for each sample, and calculating the average and standard deviation of the three points excluding the maximum and minimum values. According to the manufacturing method of Example 1, it was confirmed that a functional film of 1.14 μm (1140 ± 20 nm) was formed with a single coating.

[0042] 2. Relative permittivity of functional films The relative permittivity εr of a functional film is given by εr = n from the measured refractive index n. 2 It was calculated as follows. The refractive index was measured at five points using an ellipsometer (A MARY-102) manufactured by FIBLAB, Inc., with an incident angle of 70.19° and a wavelength of 632.8 nm. The refractive index was defined as the average of the three values ​​excluding the maximum and minimum values ​​from the five measurements. The refractive index of the functional film obtained by the manufacturing method of Example 1 was 1.5. As a result, the relative permittivity was 2.3, confirming that the obtained functional film had good dielectric properties.

[0043] 3. Confirmation of peaks caused by silanol groups in functional films FT-IR measurements were performed on the functional film. A Fourier transform infrared spectrophotometer (FT / IR-4600) manufactured by JASCO Corporation was used for the FT-IR measurements. The KBr tablet method was used, with measurement wavenumbers of 400–4000 cm⁻¹. -1 The measurement was performed with a cumulative count of 128 times. The results are shown in Figure 2. Figure 2 is a graph showing the FT-IR spectrum of the functional film obtained by the manufacturing method of Example 1. As shown in Figure 2, the FT-IR spectrum shows a peak (3750 cm⁻¹) attributable to the silanol group that degrades the dielectric properties. -1No silanol groups were observed. The FT-IR spectrum shown in Figure 2 also confirmed that the peaks attributable to silanol groups disappeared after heat treatment at 300°C, indicating that the resulting functional film exhibits good dielectric properties.

[0044] 4. Dielectric breakdown strength To evaluate its performance as an interlayer insulating film, a functional film was formed on a Si substrate on which Cr had been deposited, and this was used as the subject of evaluation. The Si substrate coated with Cr used in the dielectric breakdown test was prepared by dropping dicing resist (Tokyo Ohka Kogyo Co., Ltd., PMER N-CA3000 PM) onto a 100 mm diameter double-sided polished Si wafer (Shin-Etsu Chemical Co., Ltd.), and then spin-coating it using a spin coater (Mikasa Corporation, 1H-DX2) (slope up: increasing rpm by 300 rpm over 5 seconds, 1st step: 300 rpm for 10 seconds, slope up: increasing rpm by 4000 rpm over 10 seconds, 2nd step: 4300 rpm for 20 seconds, slope down: stopping after 10 seconds). Afterwards, it was baked for 5 minutes using a 120°C hot plate (AS ONE Corporation, NINOS ND-1) and then cut into 15 × 15 mm pieces using a fine glass cutter (Crystal Base Co., Ltd., FU-100). 2 The substrate was then cut. Next, ultrasonic cleaning was performed using acetone (Fujifilm Wako Pure Chemical Industries, Ltd.) for 10 minutes, followed by ultrasonic cleaning with IPA (Fujifilm Wako Pure Chemical Industries, Ltd.) for 10 minutes. The IPA was removed with dry air, and carbon-derived dust was removed with ozone generated using a UV irradiation device (Ushio Inc.). Subsequently, Cr (High Purity Chemical Laboratory Co., Ltd.) was deposited to a thickness of 50 nm using an electron beam deposition apparatus (JEOL Ltd., JBS-Z0501EVC) at a deposition rate of 0.10 nm / s. The Si substrate with the resulting deposited Cr was used as the lower electrode.

[0045] The silicon oxide film-forming coating solution obtained in Example 1 was dropped onto a Si substrate on which Cr had been deposited, at a rate of 100 μL, and then coated by spin coating. The spin coating was performed in two steps: the first step at 500 rpm for 5 seconds, and the second step at 2000 rpm for 30 seconds. After preheating in a 70°C dryer for 10 minutes, the material was heat-treated in the aforementioned electric furnace at 300°C under air for 30 minutes to form a functional film. A Cu electrode was formed as the upper electrode of the functional film. Using a semiconductor parameter analyzer (KEITHLEY, 4200), the current (I)-voltage (V) characteristics were measured at one point for each sample by linearly sweeping the voltage range from -2V to 200V. In all measurements, the speed setting was set to Quiet. A manual prober (MJC, 708ft) was used to connect the sample to the power supply, and the power supply was connected to the upper electrode (Cu) and lower electrode (Cr electrode formed on Si) of the functional film being measured, respectively. The results are shown in Figure 3.

[0046] Figure 3 is a graph showing the measurement results of the current-voltage characteristics of the functional film obtained by the manufacturing method of Example 1. From the measurement results shown in Figure 3, the current-voltage characteristics of the functional film obtained by the manufacturing method of Example 1 show that when a voltage of approximately 114V to 116V is applied, the current is 3.9 × 10⁻¹⁰. -7 ~1.0×10 -2 The voltage increased rapidly to approximately V. As a result, a discontinuity was observed in the graph showing the current value against the applied voltage. According to the Iwanami Dictionary of Physics and Chemistry, 5th Edition (5th printing, 2001, Iwanami Shoten), dielectric breakdown is described as "a phenomenon in which an insulator almost discontinuously loses its insulating properties and becomes capable of conducting large currents when the electric field acting on it exceeds a certain level," and it states that "the minimum voltage required for dielectric breakdown is called the breakdown voltage." From this, the discontinuity in the graph showing the current value against the applied voltage in the current-voltage characteristic graph shown in Figure 3 indicates that dielectric breakdown occurred in the functional film, and a voltage of approximately 114V to 116V can be said to be the breakdown voltage of the functional film obtained by the manufacturing method of Example 1. The power supply voltage for current large-scale integrated circuits (LSIs) is becoming increasingly low, with LSIs operating at 1.8V and 1.5V being widely used. Therefore, it can be seen that the functional film obtained by the manufacturing method of Example 1 has sufficient dielectric breakdown strength as an interlayer insulating film.

[0047] [Example 2] A functional film was formed in the same manner as in Example 1, except that the reflux time was changed from 5 hours to 1 hour in step a of Example 1. The thickness of the obtained functional film was measured in the same manner as in Example 1 and was found to be 350 ± 20 nm. This confirmed that a functional film of 0.3 μm or more can be obtained in a single coating, even when the reflux time is changed.

[0048] [Example 3] A functional film was formed in the same manner as in Example 1, except that the reflux time was changed from 5 hours to 3 hours in step a of Example 1. The thickness of the obtained functional film was measured in the same manner as in Example 1 and was found to be 680 ± 170 nm. This confirmed that a functional film of 0.3 μm or more can be obtained in a single coating, even when the reflux time is changed.

[0049] [Example 4] A functional film was formed in the same manner as in Example 1, except that the reflux time was changed from 5 hours to 7 hours in step a of Example 1. The thickness of the obtained functional film was measured in the same manner as in Example 1 and was found to be 1000 ± 10 nm. This confirmed that a functional film of 0.3 μm or more could be obtained in a single coating, even when the reflux time was changed.

[0050] Based on the results from Examples 1 to 4, it is estimated that there is a correlation between the increase in reflux time and the thickness of the resulting functional film.

[0051] [Comparative Example 1] In step a of Example 1, the amount of ethanol was changed from 50 g to 10 g, the amount of oxalic acid from 17.3 g to 2.07 g, and the amount of butylamine from 9.39 g to 1.68 g. In step b, the amount of tetraethoxysilane added was changed from 13.1 g to 2.35 g. When the amount of oxalic acid was set to 2 moles per mole of silicon atoms in the silicon compound, a coating solution for forming a silicon oxide film was prepared, but the solute did not dissolve sufficiently in the solvent, and a uniform coating solution for forming a silicon oxide film could not be obtained.

[0052] According to the manufacturing methods of Examples 1 to 4, a stable functional film-forming composition can be obtained, and a functional film with a thickness of 0.3 μm or more can be formed in a single application using this functional film-forming composition. Furthermore, it can be seen that a functional film with good insulating properties can be formed under conditions where the heat treatment temperature during film formation is lower than conventional conditions. On the other hand, in Comparative Example 1, where the amount of oxalic acid per 1 mol of silicon atoms in the silicon compound was less than 2.5 mol, a stable functional film-forming composition could not be obtained.

Claims

1. A step of obtaining mixture A by mixing an alcohol-containing solvent, at least one oxalic acid compound selected from oxalic acid compounds, and an amine compound. The process involves adding at least one silicon compound selected from the obtained mixture A to obtain mixture B, refluxing the mixture B under conditions where the liquid temperature of mixture B is above the boiling point of mixture B for 1 to 8 hours to generate an anionic silicon complex with oxalic acid as a ligand, and thereby producing a functional film-forming composition. The steps include applying the obtained functional film-forming composition onto a substrate to form a functional film-forming composition layer, and The process includes heating the functional film-forming composition layer formed on a substrate to 150°C to 400°C to obtain a functional film containing amorphous silicon oxide. A method for producing a functional film, wherein the amount of the oxalic acid compound contained in the functional film-forming composition is 2.5 mol or more per mol of silicon atoms contained in the silicon compound.

2. The method for producing a functional film according to claim 1, wherein the amount of the oxalic acid compound contained in the functional film-forming composition is 3 mol or more to 4 mol per mol of silicon atoms contained in the silicon compound.

3. A method for producing a functional film according to claim 1 or claim 2, wherein the thickness of the functional film obtained by performing the steps of forming the functional film-forming composition layer and heating the functional film-forming composition layer to obtain a functional film once each is 0.3 μm or more.

4. The method for manufacturing a functional film according to claim 1 or claim 2, wherein the functional film is an interlayer insulating film.

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