JP2005187657A - Coating liquid for forming silica-based coating film and method for producing the same, method for forming coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for forming a silica-based coating film good in both preserving stability and applicability, capable of coping with various coating processes developed currently. <P>SOLUTION: This coating liquid for forming the silica-based coating film is produced through steps including a step of proceeding a hydrolysis reaction of a trialkoxysilane in a reaction solvent mainly comprising an alkylene glycol dialkyl ether to obtain a homogeneous dispersion of the reaction product in the reaction solvent as a dispersant; a step of further adding another organic solvent having a boiling point higher than that of the alkylene glycol dialkyl ether to the dispersion; and a step of removing the alkylene glycol dialkyl ether from the dispersion obtained by adding the other organic solvent through fractional distillation to obtain a homogeneous dispersion of the reaction product in the other organic solvent as a dispersant instead of the alkylene glycol dialkyl ether. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating liquid for forming a silica-based film and a method for producing the same.

  Conventionally, as a method for forming a silica-based film such as a silicon oxide film, a coating liquid made of an organic solvent containing a coating film raw material or a precursor thereof is prepared along with a chemical vapor deposition method (CVD method). A so-called coating method in which a film is formed on a substrate by coating, drying, and baking the coating on the substrate is actively performed.

  The coating method makes it possible to form a film at a relatively low temperature and to easily form a film with excellent flatness, and in particular, to form a planarization film or an interlayer insulating film of a semiconductor device. Therefore, it is one of the methods for forming a silica-based film that is indispensable in the manufacture of today's semiconductor devices. In particular, if a coating solution containing a hydrolyzate of alkoxysilane is used, it is possible to form an insulating film having a dielectric constant as low as that of a silicon dioxide film. In recent years, it has become an indispensable method for forming a coating film in combination with the demand for an improved coating.

  By the way, various improvements have also been made with respect to the method of applying the coating liquid, and various methods have been devised and devised in recent years in addition to the conventional dipping method and the central dropping method.

  For example, in Japanese Patent Application Laid-Open No. 2001-168021, a single or a plurality of supply nozzles are moved relative to each other in a row and column direction on a substrate to be processed, and a coating material raw material liquid is supplied at regular intervals from the supply nozzles. Disclosed is a method for forming a film by disposing droplets of a coating film on a substrate to be processed by performing droplet discharge, followed by drying to volatilize a solvent component and performing heat treatment (Patent Document 1). . According to the description, this method is not limited to the formation of an interlayer insulating film in a semiconductor device, but can be applied to the formation of various coatings such as the formation of resists, antireflection films, dielectric films, and wiring materials.

  Japanese Patent Laid-Open No. 2002-110664 discloses that a liquid raw material obtained by dissolving polymethylsiloxane as a film raw material in a solvent is discharged from a nozzle, and the nozzle is reciprocated on a substrate having a diameter of 200 mm. Is moved in a direction perpendicular to this motion to scan and apply the liquid raw material to form a liquid film on the entire surface of the substrate, and then rotate the substrate at a rotation speed at which the liquid film liquid does not scatter outside the substrate, so that the film quality is uniform. And then a method of forming an insulating film made of polymethylsiloxane by volatilizing the solvent and then performing heat treatment (Patent Document 2).

  Further, as a means for effectively realizing such a coating method, Japanese Patent Application Laid-Open No. 2002-151485 discloses a conventional spin coating method or discharges a liquid insulating film material onto a semiconductor wafer as a substrate to be processed. Equipped with a system that can carry out multiple heat treatment operations such as baking, curing, and post-treatment, which can be performed even by a scan coating method in which an insulating film material is applied to the entire surface of the wafer by scanning the nozzle in the X and Y directions on the wafer. An integrated substrate processing apparatus is disclosed (Patent Document 3).

  As described in these documents, a relative movement is performed with respect to the substrate to be treated, and a coating film is intermittently discharged onto the substrate surface to realize a coating film on the substrate, and then heated. In recent methods of film formation, which achieves film formation by solvent drying and baking by methods such as rotation of the base material, etc., it is generally necessary to shake off the coating liquid compared to the conventional coating method by central dropping spin coating No. For this reason, it is possible to avoid the problem of waste of chemical solution, which has been said to be 90% or more, and environmental pollution caused by the waste solution, which is an excellent coating method in this respect.

  Many studies have been made on the composition and manufacturing method of the coating liquid from various aspects such as film quality, industrialization, and environment.

  In Japanese Patent Laid-Open No. 4-216827, a soluble hydrolyzate solution is obtained by mixing and heating a hydridosilane such as triethoxysilane, an oxygen-containing polar organic solvent, preferably an alcohol such as ethanol, a small amount of water and an acid. It is disclosed that this solution is applied to an electronic device substrate such as an aluminum panel and heated to form a coating film (Patent Document 7).

  Inorganic SOG (spin-on-glass) using trialkoxysilane as a film raw material is a particularly preferable material among silane-based film raw materials in that trouble caused by gas generation does not occur during heat treatment. However, in the method for producing a coating liquid in which a hydrolysis reaction is carried out using an alcohol such as ethanol as a solvent, there is a reaction in which an H-Si bond in a trialkoxysilane molecule is decomposed or an intermediate hydroxyl group of silanol is substituted with an alkoxy group. Prone to progress secondary. For this reason, there has been a problem in the stability of the coating solution over time, such as the gelation in the manufactured coating solution is easily caused.

  Japanese Patent Laid-Open No. 9-137121 discloses a method for producing a coating solution for forming a silica-based film by causing a hydrolysis reaction of triethoxysilane using ethylene glycol dimethyl ether as a solvent, and the method thus produced. A coating solution is disclosed (Patent Document 4, and for example, Patent Documents 5 and 6).

When an application liquid is produced using an alkylene glycol dialkyl ether such as ethylene glycol dimethyl ether as a solvent, changes in properties of the coating liquid over time, such as changes in molecular weight of coating film components in the coating liquid, are small after production. If it is such a method, the coating liquid excellent in storage stability can be manufactured.
JP 2001-168021 A JP 2002-110664 A JP 2002-151485 A JP-A-9-137121 Japanese Patent Laid-Open No. 10-31002 JP 7-97548 A Japanese Patent Laid-Open No. 4-216827

  However, in a recent new coating method not particularly based on the spin coating method, a coating solution using an alkylene glycol dialkyl ether as a solvent has a new problem.

In recent years, the coating method by the so-called “scanning coating method” is that a coating film raw material or a precursor thereof is arranged on a substrate to be treated in units of droplets, if position scanning is performed.
This is a system that achieves continuous application of the coating film, and is fundamentally different from the conventional coating system by one-point dropping and coating expansion by centrifugal force.

  In the scan coating method, a significant time elapses from the start to the end of application of the coating liquid to the substrate to be processed. For this reason, when a coating film formation is attempted using a conventional coating solution by a scan coating method, the solvent of the coating solution is volatilized before the coating is completed. As a result, the film having excellent film quality uniformity cannot be formed.

  In addition, in the scan coating method, a continuous coating film is formed on the substrate to be treated, and thus a certain amount of self-expansion that does not depend on rotational centrifugal force or the like is required for the dropped coating droplets at each point. If the viscosity of the coating solution and the wettability to the base material are inappropriate, this is not quickly performed in an appropriate amount, and efficient film production cannot be realized.

  As described above, when a silica-based film is formed by the scan coating method which has been adopted recently, various disadvantages occur in the coating liquids typically used so far, and efficient film formation cannot be expected.

  The present invention has been completed as a result of intensive studies and researches by the inventor as to whether or not a coating liquid that can be adapted to various coating methods can be manufactured in view of the present situation of silica-based coating production as described above.

  The present invention includes a step of obtaining a uniform dispersion of a reaction product using a reaction solvent as a dispersion medium by allowing a hydrolysis reaction of trialkoxysilane to proceed in a reaction solvent containing an alkylene glycol dialkyl ether as a main component, And further adding another organic solvent having a boiling point higher than that of the alkylene glycol dialkyl ether, and removing the alkylene glycol dialkyl ether from the dispersion to which the other organic solvent has been added by fractional distillation operation. And a step of obtaining a uniform dispersion of a reaction product using as a dispersion medium. A method for producing a coating liquid for forming a silica-based film.

  ADVANTAGE OF THE INVENTION According to this invention, the coating liquid for silica type film formation with the favorable storage stability of a coating liquid and favorable applicability | paintability is provided. Since the coating solution according to the present invention is easy to handle, that is, easy to use, it can be effectively used in various coating methods such as a central dropping spin coating method and a scan coating method.

  Hereinafter, specific embodiments of the present invention will be described in more detail.

  In the embodiment of the present invention, a dialkyl ether of alkylene glycol is used as a reaction solvent (reaction solution) for hydrolysis and condensation polymerization reaction of trialkoxysilane. Specifically, for example, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl Mention may be made of ether, propylene glycol dipropyl ether, propylene glycol dibutyl ether. Of these, particularly preferred are dialkyl ethers of ethylene glycol or propylene glycol, especially dimethyl ether. These alkylene glycol dialkyl ethers may be used alone or in combination of two or more.

  In an embodiment of the present invention, trialkoxysilane is used as a coating film precursor. Specifically, for example, trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, diethoxymonomethoxysilane, monomethoxydipropoxysilane, dibutoxymonomethoxysilane, ethoxymethoxypropoxysilane, monoethoxydimethoxysilane And monoethoxydipropoxysilane, butoxyethoxypropoxysilane, dimethoxymonopropoxysilane, diethoxymonopropoxysilane, and monobutoxydimethoxysilane. Among these, preferred compounds for practical use are trimethoxysilane, triethoxysilane, tripropoxysilane, and tributoxysilane, and trimethoxysilane and triethoxysilane are particularly preferable. These trialkoxysilanes may be used alone or in combination of two or more.

In order to produce a coating solution using trialkoxysilane as a starting material,
The trialkoxysilane is about 1 to 5% by weight, more preferably 2 to 4% by weight, in terms of the amount of SiO ₂ when converted to SiO ₂ at a reaction rate of 100%. It is preferably used in a concentration. When the trialkoxysilane is used in an amount exceeding 5% by weight, gelation of the coating solution is likely to occur with the passage of time after the coating solution is produced, and the storage stability of the coating solution is reduced. Detailed investigation of the chemical cause must wait for further research in the future, but the storage stability of the coating solution prepared under a high concentration of trialkoxysilane is low when the amount of trialkoxysilane is small. This is probably because the progress of the hydrolysis reaction becomes slow, the Si—H bond is hardly decomposed, and a stable ladder structure is easily constructed in the produced polymer molecule.

  In order to obtain a coating solution, water must be reacted with trialkoxysilane as a starting material to cause hydrolysis and further condensation reaction. The alkylene glycol dialkyl ether used as the reaction solvent works as a compatible solvent that dissolves both the trialkoxysilane and water. The trialkoxysilane and water are not directly miscible, but they can initiate a substantial hydrolysis reaction in the reaction solvent due to their compatibilizing action.

  Water is preferably used in an amount in the range of 2.5 to 3.0 mol, more preferably 2.8 to 3.0 mol, relative to 1 mol of trialkoxysilane. If the amount of water used at the time of manufacture is less than 2.5 mol, the coating solution finally produced has high storage stability over time, but the hydrolysis degree is low, and many organic substances are present in the hydrolyzate. The group will remain. For this reason, if a coating film is formed using this coating solution, gas generation due to decomposed organic components becomes remarkable, which is not preferable. Conversely, if the amount of water during production exceeds 3.0 mol, the storage stability of the produced coating solution is lowered, which is also not preferable.

  The reaction is carried out in the presence of an acid catalyst. As the acid catalyst, an organic acid or an inorganic acid conventionally used for producing a coating liquid for forming this kind of silane-based film can be used. Examples of the organic acid include acetic acid, propionic acid, and butyric acid. Examples of inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. Nitric acid is particularly preferred from the viewpoints of being easily available industrially and inexpensive and having little adverse effect on the other layers from the formed silica-based coating.

  The hydrolysis reaction is typically initiated by a method in which pure water containing an acid catalyst is added to a mixture of trialkoxysilane and alkylene glycol dialkyl ether. However, the order of addition of each reagent is generally arbitrary. There is no limitation unless a technical inconvenience is expected.

  It is preferable to add the acid catalyst so that the acid concentration in the reaction solution is 1 to 200 ppm. When the addition amount is 1 ppm or less, the storage stability of the reaction solution is low, and the change over time in the molecular weight of the hydrolyzed product after the reaction increases. Similarly, even if it is 200 ppm or more, the storage stability of the reaction solution is low, and the change over time in the molecular weight of the hydrolyzed product after the reaction is unfavorable. From such a viewpoint, the addition amount is more preferably in the range of 1 to 40 ppm.

  If trialkoxysilane and water are mixed in the presence of an alkylene glycol dialkyl ether, the reaction is substantially carried out at room temperature, typically about 5 to 100 hours, under reaction rate control by an acid catalyst. finish. Alternatively, the hydrolysis reaction and the polymerization reaction may be performed in a shorter time by proceeding the reaction at a temperature not exceeding 60 ° C. to 70 ° C.

  In the hydrolysis reaction and polymerization reaction, an alcohol corresponding to the alkoxy group of trialkoxysilane is generated. In order to obtain a final coating solution, it is more desirable to remove the generated alcohol from the reaction solution. As a result, in the coating solution finally prepared, the alcohol content is preferably 15% by weight or less. More preferably, it is 8 wt% or less. If the alcohol content exceeds 15% by weight, the storage stability of the coating solution is lowered, and the problem of an increase in molecular weight tends to occur, which is not preferable.

  As a method for removing the alcohol content, a method of vacuum distillation at a degree of vacuum of 10 to 300 mmHg, more preferably 20 to 150 mmHg and a temperature of 20 to 50 ° C. is suitable.

  In the embodiment of the present invention, after completion of the trialkoxysilane reaction, solvent replacement is performed to obtain a final coating solution. In the course of the synthesis reaction from trialkoxysilane, a good dispersion state of trialkoxysilane and / or its hydrolyzate or condensation polymer with the reaction solvent as it is as a dispersion medium has already been realized. In the conventional coating solution, this “sol” is used as the coating solution substantially as it is and is used for spin coating and the like.

  In the embodiment of the present invention, it is based on the difference in boiling point based on the recognition that the proper reaction liquid or dispersion medium and the coating liquid solvent exist in the synthesis for the synthesis and the coating liquid in the final coating liquid. By the fractional distillation method, the solvent is replaced while maintaining this dispersed state without substantially impairing, thereby obtaining a final coating liquid in which the dispersed state is well maintained.

  As a method of solvent replacement according to the embodiment of the present invention, the uniform dispersion obtained after completion of hydrolysis and polymerization reaction is used as it is, and another organic solvent having a higher boiling point compared to the used reaction solvent is used. Further blend. The mixture is distilled at an appropriate intermediate temperature such that fractional distillation efficiently proceeds under reduced pressure, for example, and the reaction solvent is selectively separated and removed from the dispersoid mainly composed of a silica-based polymer. .

  According to such a method, the dispersion medium is replaced while substantially maintaining the dispersion state of the dispersoid without passing through the aggregation process. Therefore, it is possible to prepare a coating solution that matches a new coating method such as a scan coating method without substantially impairing the good dispersion state of the silica-based polymer formed during the polymerization reaction. Of course, for this purpose, it is needless to say that another organic solvent which is a solvent for the coating solution must be appropriately selected and used from various viewpoints of using the coating solution.

  As other organic solvents that serve as solvents for such coating solutions, for example, methyl-3-methoxypropionate (MMP, boiling point 145 ° C.), propylene glycol monomethyl ether acetate (MMP, boiling point: 145 ° C.) PGMEA, boiling point 146 ° C.), propylene glycol monomethyl ether (PGME, boiling point 121 ° C.), and propylene glycol monopropyl ether (PGP, boiling point 150 ° C.) can be exemplified. A plurality of these can be used simultaneously as a mixture in the coating solution.

  In addition, when adding another organic solvent to the uniform dispersion of the reaction solvent and the polymer, the uniform dispersion is concentrated in advance to the extent that the dispersion state of the uniform dispersion is not impaired. May be provided. In this way, the fractionation process could be completed more quickly. In the present invention, trialkoxysilane is used as a starting material for the production of the coating liquid. In this case, the upper limit of the concentration that can be concentrated after the hydrolysis and condensation reaction is uniform within the range studied by the inventors so far. It is about 20% by weight with respect to the total amount of the dispersion. When the concentration exceeds 20% by weight, a phenomenon of increase in molecular weight tends to occur with time during concentration.

  Further, depending on how to use the produced coating solution, the alkylene glycol dialkyl ether used as the reaction solvent does not necessarily need to be completely removed from the coating solution, and the dispersion medium constituting the coating solution is the solvent used as the reaction solvent. And a mixture of other solvents. In this case, the uniform dispersion of the reaction solvent and the polymer is concentrated in the above range, and then another organic solvent to be mixed is blended to form a coating solution. However, also in this case, the miscibility of the reaction solvent with the other organic solvent to be blended is carefully examined, and a sufficient compositional design is performed in advance so that an appropriate coating solution can be obtained.

  Although it depends on the purpose of use of the coating solution, the solid content concentration (approximately SiO2 equivalent concentration in the coating solution) is usually adjusted to about 1 to 20% by weight by concentration or dilution, and various coatings are used. Used for forming coating solution.

[Example 1]
73.9 g of 3% by weight of triethoxysilane in terms of SiO ₂ concentration was dissolved in 799.0 g of propylene glycol dimethyl ether and stirred. Next, 24.2 g of pure water mixed with 5 ppm of nitric acid was added dropwise thereto while stirring slowly, and then allowed to stand at room temperature for 6 days to obtain a solution.

  Further, this solution was distilled under reduced pressure at 120 mmHg and 40 ° C. for 1 hour to obtain a concentrated solution having a solid content concentration of 10 wt%, an ethanol concentration of 3 wt%, and a solid content molecular weight (weight average) of 1700.

Next, 400 g of methyl-3-methoxypropionate (MMP) was blended into the concentrated solution obtained, and distilled under reduced pressure at 20 mmHg and 60 ° C. for 1 hour, so that the MMP was finally replaced with MMP as a SiO ₂ equivalent concentration As a result, a coating solution 1 for forming a silica-based film having a content of 9 wt% was obtained.

[Example 2]
After performing hydrolysis reaction and concentration in the same manner as in Example 1, solvent replacement was performed using the same amount of propylene glycol monomethyl ether acetate (PGMEA) instead of MMP to obtain a coating solution 2 for forming a silica-based film. It was.

Example 3
After performing hydrolysis and concentration in the same manner as in Example 1, solvent replacement was performed using the same amount of propylene glycol monomethyl ether (PGME) instead of MMP to obtain a coating solution 3 for forming a silica-based film. .

Example 4
Hydrolysis reaction and concentration were carried out in the same manner as in Example 1, followed by solvent substitution using the same amount of propylene glycol monopropyl ether (PGP) instead of MMP, to obtain a coating solution 4 for forming a silica-based film. It was.

Example 5
In the same manner as in Example 1, a concentrated solution having a solid content molecular weight of 1700 was obtained.

Next, MMP was added to the obtained concentrated solution to obtain a coating solution 5 for forming a silica-based film having a SiO ₂ equivalent concentration of 5% by weight.

Example 6
A silica-based coating-forming coating solution 6 was obtained in the same manner as in Example 5 except that PGMEA was used instead of MMP.

Example 7
A silica-based coating-forming coating solution 7 was obtained in the same manner as in Example 5 except that PGME was used instead of MMP.

Example 8
A coating solution 8 for forming a silica-based film was obtained in the same manner as in Example 5 except that PGP was used instead of MMP.

[Comparative Example 1]
73.9 g of 3% by weight of triethoxysilane in terms of SiO ₂ concentration was dissolved in 799.0 g of propylene glycol dimethyl ether and stirred. Subsequently, 24.2 g of pure water mixed with 5 ppm nitric acid was added dropwise thereto while slowly stirring, and then allowed to stand at room temperature for 6 days to obtain a solution.

This solution was distilled under reduced pressure at 120 mmHg and 40 ° C. for 1 hour to obtain a coating solution 1C having a SiO ₂ equivalent concentration of 9% by mass using the reaction solvent propylene glycol dimethyl ether as a dispersion medium.

[Comparative Example 2]
A coating solution 2C was obtained in the same manner as in Comparative Example 1 except that propylene glycol monomethyl ether acetate (PGMEA) was used instead of propylene glycol dimethyl ether.

  The following tests were conducted on the coating solutions of the Examples and Comparative Examples produced as described above, and the evaluations were performed.

[Storage stability test]
The molecular weight of the hydrolysis polymer contained in the coating solution immediately after preparation was measured. The prepared coating solution was placed in a container and allowed to stand at 25 ° C. for 6 days. Then, the molecular weight of the decomposition polymer present in the coating solution was measured again, and the change in molecular weight before and after standing for 6 days was observed. The results are shown in Table 1.

[Handling test]
After the preparation, a handling test was performed as follows using a coating solution that was placed in a container and allowed to stand at 25 ° C. for 6 days. The results are shown in Table 1.

In a 25 ° C. atmosphere, 1 cc of the coating solution was dropped on the glass substrate, and after 30 minutes, the presence or absence of precipitates was confirmed.

Claims (6)

A step of proceeding a hydrolysis reaction of trialkoxysilane in a reaction solvent containing an alkylene glycol dialkyl ether as a main component to obtain a uniform dispersion of a reaction product using the reaction solvent as a dispersion medium; A step of adding another organic solvent having a boiling point higher than that of the alkylene glycol dialkyl ether, and the alkylene glycol dialkyl ether is removed from the dispersion to which the other organic solvent has been added by fractional distillation, and the other organic solvent is used instead. A method for producing a coating liquid for forming a silica-based film, comprising a step of obtaining a uniform dispersion of the reaction product using as a dispersion medium. Before the step of adding another organic solvent and after the step of proceeding with the hydrolysis reaction, the method further comprises a step of concentrating the uniform dispersion of the reaction product in a range not exceeding 20% by weight by distillation operation. The manufacturing method of the coating liquid for forming the silica type coating film of Claim 1. A step of proceeding hydrolysis reaction of trialkoxysilane in a reaction solvent mainly comprising an alkylene glycol dialkyl ether to obtain a uniform dispersion of a reaction product using the reaction solvent as a dispersion medium; and the reaction by distillation operation. A coating solution for forming a silica-based film, comprising a step of concentrating a uniform dispersion of a product to a concentration not exceeding 20% by weight and a step of further adding another organic solvent to the concentrated dispersion. Manufacturing method. The other organic solvent is methyl-3-methoxypropionate (MMP), propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), and propylene glycol monopropyl ether (PGP) and mixtures thereof. The method for producing a coating solution for forming a silica-based film according to any one of claims 1 to 3, wherein the solvent is a solvent selected from the group consisting of: Coating solution for forming ladder-type hydrogen silsesquioxane type silica-based coatings. A method for forming a silica-based coating, wherein the coating is formed by a scan spray method using the coating solution produced according to the method according to claim 1.