JP3851393B2 - Method for producing porous silicon oxide film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a porous silicon oxide film.
[0002]
[Prior art]
Conventionally, silicon oxide or silicon oxide into which fluorine or an organic group is introduced has been used for an interlayer insulating film used for LSI multilayer wiring. However, the relative permittivity values of these materials are relatively large, and problems such as wiring delays arise due to the use of these materials as interlayer insulating films as LSI wiring becomes finer in the future. For this reason, attempts have been made to lower the dielectric constant by making silicon oxide porous and making it a composite with air having a relative dielectric constant of about 1, both of which involve complicated processes, A simple method for producing a high-quality silicon oxide film has not been established.
[0003]
According to a report by Saegusa et al. (Journal of Macromolecular Science-Chemistry, Vol. 27, 13-14, P. 1603-1612 (1990)) When the decomposition and dehydration condensation reactions are performed, the carbonyl group of the amide bond and the silanol group on the silicon are hydrogen-bonded in the resulting silicon oxide gel and are stably dispersed at the molecular level. When the polymer content is burned out, a porous silicon oxide in which very small pores at the molecular level are uniformly dispersed can be obtained.
[0004]
However, in the method described in the above report, the time required for hydrolysis and dehydration condensation is long, and when the gel shape is a film, the evaporation of the solvent preferentially occurs, so a good film cannot be obtained. It was.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for easily and rapidly producing a uniform and high-quality porous silicon oxide film free from the formation of large particles.
[0006]
[Means for Solving the Problems]
In the present invention, an alkoxysilane and an organic polymer containing an amide bond are dissolved in a solvent, an acid is added to partially hydrolyze, a base catalyst is added, and the resulting solution is applied in a film form on a substrate for hydrolysis. And a method for producing a porous silicon oxide film, characterized in that the organic polymer is removed from the dried gel obtained by performing dehydration condensation and then evaporating the solvent.
[0007]
Hereinafter, the present invention will be described in detail.
In the method for producing a porous silicon oxide film of the present invention, first, an organic polymer containing an amide bond and an alkoxysilane are dissolved in a solvent, and a catalyst acid and water are added and stirred to partially add water. The process of decomposing is performed. As a result, the alkoxysilane partially becomes a silicon hydroxide and partially undergoes a dehydration condensation reaction, but does not gel immediately.
[0008]
Specific examples of the alkoxysilane used in the present invention include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetra (i-propyl) silane, tetra (t-butyl) silane, and mixtures thereof. Moreover, the partial hydrolyzate of said tetraalkoxysilane can also be used. In order to further improve the porous film, an alkoxysilane having one alkyl group or aryl group on a silicon atom is used, or an alkoxysilane having 1 to 3 alkyl groups or aryl groups on a silicon atom is used as described above. It is also possible to mix with tetraalkoxysilane.
[0009]
Specific examples of the organic polymer containing an amide bond used in the present invention include poly (N-vinylpyrrolidone), poly (N-vinylcaprolactone), polyacrylamide derivative, polymethacrylamide derivative, polyoxazoline derivative, polyimide derivative, Examples include polyurethane derivatives, polyurea derivatives, nylon derivatives, and mixtures thereof. Moreover, you may use the copolymer of the monomers which are the structural components of these polymers, and a copolymer with another arbitrary monomer. The amide bond in the polymer effectively forms a hydrogen bond with the silanol group produced by hydrolysis of the alkoxysilane during the course of the gelation of the alkoxysilane, thereby preventing phase separation. Therefore, the amide bond content in the polymer needs to have a molecular weight of 5,000 or less per amide residue.
[0010]
The amount of the amide bond-containing organic polymer added is 1 to 10,000 parts by weight, preferably 10 to 1000 parts by weight, based on 100 parts by weight of the alkoxysilane. The porosity of the porous film obtained in the present invention is mainly determined by the amount of the amide bond-containing organic polymer added. Therefore, when the addition amount of the amide bond-containing organic polymer is less than 1 part by weight, the porosity is small and the characteristics of the porous film do not appear. On the other hand, when the amount is more than 10,000 parts by weight, the strength of the obtained porous film is reduced and the practicality is poor.
[0011]
The solvent is preferably a solvent in which both the alkoxysilane used and the amide bond-containing organic polymer are dissolved, and C1-C4 monohydric alcohol, dimethylformamide, formamide, dimethylacetamide and the like are preferably used. These solvents may be mixed, or any other solvent or additive may be mixed.
[0012]
Specific examples of the acid as the catalyst include hydrochloric acid, nitric acid, sulfuric acid, acetic acid and the like. The amount of these acids added is suitably 10 ^-5 to 1 mol, preferably 10 ^-4 to 10 ^-1 mol, per mol of alkoxysilane. If the amount of the catalyst added is less than 10 ⁻⁵ mol, hydrolysis does not proceed sufficiently, and gelation may not occur in the next step. On the other hand, when the amount is more than 1 mol, a precipitate is formed and a uniform porous film cannot be obtained, or gelation occurs before the next step.
[0013]
Hydrolysis of the alkoxysilane that occurs in this step is caused by the solvent water when the catalyst acid is an aqueous solution, and additional water is added if necessary. An appropriate amount of water is 0.3 to 100 mol, preferably 1 to 10 mol, based on 1 mol of alkoxysilane, although it depends on the type of raw material alkoxysilane. If the amount is less than 0.3 mol, hydrolysis does not proceed sufficiently, and gelation does not occur rapidly in the next step, so that a good quality film cannot be obtained. On the other hand, when the amount is more than 100 mol, the homogeneity of the porous membrane is lowered.
[0014]
The temperature of the partial hydrolysis reaction using an acid catalyst is 0 to 100 ° C, preferably 20 to 60 ° C. If it is less than 0 ° C., the reaction rate is low, and it takes a long time for the hydrolysis to proceed sufficiently, and if it exceeds 100 ° C., it may gel before the next step. The time required for gelation varies depending on the temperature of gelation and the amount of catalyst, but is usually in the range of several hours to several days.
[0015]
In the method for producing a porous silicon oxide film of the present invention, a base as a catalyst and water as required are added to the solution of the partially hydrolyzed alkoxysilane obtained by the above method, and the film is formed on the substrate. After the coating is applied, the hydrolysis and dehydration condensation of the alkoxysilane is terminated.
Specific examples of the base used here include aqueous ammonia, potassium hydroxide, sodium hydroxide, triethylamine, triethanolamine and the like. It is important that these bases are added to a certain extent in excess of the acid added in the previous step. If the amount of the base added is too small, it will not gel, or it will take a long time for gelation. I can't get it. The amount of the base added is suitably 10 ^-5 to 1 mol, preferably 10 ^-4 to 10 ^-1 mol in excess of the acid added in the previous step with respect to 1 mol of the raw material alkoxysilane. When the excess amount of the base is more than 1 mol, a rapid increase in viscosity occurs, making it difficult to apply a film or gelling instantaneously.
[0016]
The amount of water added depends on the type of raw material alkoxysilane, but the total amount of water added in the previous step and this step is 1 to 100 mol, preferably 2 to 10 mol per mol of alkoxysilane. It is. When the amount is less than 1 mol, hydrolysis and gelation do not occur sufficiently and a porous membrane cannot be obtained. On the other hand, when the amount is more than 100 mol, the homogeneity of the porous membrane is lowered. If a sufficient amount of water has already been added in the previous step, it is not necessary to add new water in this step.
[0017]
The film coating is performed by a known method such as casting, dipping, spraying, or spin coating. The film thickness is not particularly limited, but is preferably 0.1 μm or more. If the thickness is less than 0.1 μm, the effect of the porous film cannot be sufficiently obtained. Furthermore, it is preferable that the film thickness is 1 mm or less because the gel can be dried in a short time. It is also possible to create a film having a film thickness exceeding 1 mm by taking sufficient time to dry the gel.
[0018]
In order to obtain a film having excellent adhesion, homogeneity, crack resistance, and peel resistance, the substrate may be treated with an adhesion improver in advance. As the adhesion improver in this case, those used as so-called silane coupling agents can be used. As preferred ones, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3- Aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropylmethyldiethoxysilane , 3-chloropropylmethyldichlorosilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (2-methoxyethoxy) silane, etc., among others 3-aminopropyltrimethoxysilane 3-aminopropyltriethoxysilane, N- (2- aminoethyl) -3-aminopropyltrimethoxysilane, N- (2- aminoethyl) -3-aminopropyl methyl dimethoxy silane is particularly preferably used. In applying these adhesion improvers, other additives may be added as necessary, or diluted with a solvent such as alcohol or water. The adhesion improving agent is applied by a known method such as casting, dipping, spraying, or spin coating. After coating, the excess adhesion improver is removed by washing with a common organic solvent such as alcohol. A few minutes is usually sufficient from application to washing. Thereafter, the cleaning solvent is dried to obtain a processed substrate. If the time from application to cleaning is short, the effect of the adhesion improving agent cannot be obtained. Conversely, if the time is too long, the adhesion improving agent may be cured on the substrate.
[0019]
The temperature of the gelation reaction of the applied film is in the range of 0 to 100 ° C, and preferably 20 to 60 ° C. If it is less than 0 ° C., the reaction rate is low, and it takes a long time to cause sufficient crosslinking, and if the temperature exceeds 100 ° C., voids are likely to be generated, and the homogeneity of the resulting porous film is lowered. The time required for gelation varies depending on the gelation temperature and the amount of catalyst, but is usually in the range of several minutes to several days.
[0020]
After allowing the gelation to proceed sufficiently, it is dried to remove the solvent. Although drying temperature naturally changes with kinds of solvent, it is normally performed in the range of 20-200 degreeC. In order to control the generation of voids and obtain a homogeneous dry gel film, a method of gradually raising the temperature during the drying process is also preferred.
A desired porous silicon oxide film can be obtained by removing only the organic polymer from the dried gel film. Examples of the method for removing the organic polymer include heating and baking, solvent extraction, and plasma treatment. The simplest is a method of heating for about 1 to 24 hours at a temperature higher than the thermal decomposition temperature of the amide bond-containing organic polymer.
[0021]
In the method of the present invention, since the hydrolysis and dehydration condensation of the tetraalkoxysilane are completed quickly, deterioration of the film quality due to evaporation of the solvent can be prevented, and a uniform porous film can be obtained quickly.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the present invention are shown below. The silicon oxide films obtained in the examples were evaluated as follows.
1. Surface area (N2 BET)
Measurement was performed using a nitrogen adsorption surface area measuring device manufactured by Shimadzu Corporation.
2. Scanning electron microscope (SEM)
The sample was cut into approximately 5 mm squares, placed on a sample table with a conductive tape, and secured with carbon paste. Further, about 1 nm of platinum-palladium was deposited and measured with a scanning electron microscope manufactured by Hitachi, Ltd. . The electron acceleration voltage was set to 1 kV.
[0023]
[Example 1]
0.6 g of tetraethoxysilane and 0.5 g of poly (N-vinylpyrrolidone) are dissolved in 0.8 g of ethanol and 1.2 g of dimethylformamide, 0.05 g of 0.1N hydrochloric acid is added to this solution, and the mixture is stirred at room temperature for 5 hours. Stir. After adding 0.5 ml of 0.1N aqueous ammonia solution to this solution and stirring, it was cast on a glass substrate promptly so as to have a film thickness of 1 mm, and then allowed to stand at room temperature for 1 hour in a sealed container. The membrane lost fluidity. It was allowed to stand overnight, dried at 60 ° C. to 150 ° C. over 5 hours, and heated at 600 ° C. for 12 hours in nitrogen. It was found by the nitrogen adsorption method that the obtained silicon oxide film had a surface area of 760 m ² / g.
[0024]
[Example 2]
3-Aminopropyltriethoxysilane was cast on a silicon substrate, allowed to stand for 3 minutes, washed with methanol, and dried at 60 ° C. for 10 minutes. In a 10 ml container, 1.2 g of tetraethoxysilane and 1.0 g of poly (N-vinylpyrrolidone) are dissolved in 1.6 g of ethanol and 2.4 g of dimethylformamide, and 0.1 g of 0.1N hydrochloric acid is added to this solution. For 3 hours. To this solution, 0.5 ml of 0.1N aqueous ammonia solution was added and stirred, and the solution was spin-coated on the above silicon substrate for 10 seconds at a speed of 1500 rpm so that the film thickness became 1 μm, and then at room temperature in a sealed container. Left for 1 hour. The mixture was allowed to stand overnight, dried at 60 ° C. to 160 ° C. over 4 hours, and heated at 600 ° C. for 8 hours in nitrogen. When the surface of the obtained silicon oxide film was observed with a scanning electron microscope, it was very uniform and no cracks or giant particles were observed.
[0025]
[Comparative Example 1]
Dissolve 5.2 g of tetraethoxysilane and 1.5 g of poly (N-vinylpyrrolidone) in 2.5 g of ethanol and 3.5 g of dimethylformamide, add 3.5 g of 0.08N hydrochloric acid to this solution, and stir at room temperature for 3 hours. did. This solution was cast on a glass substrate so as to have a film thickness of 1 mm, and then left overnight in a sealed container at room temperature. However, the coating film was viscous and did not lose its fluidity.
[0026]
【The invention's effect】
The porous silicon oxide thin film obtained in the present invention is of a high quality despite the extremely simple and rapid production method compared with the conventional method. Further, since the pore diameter is small and the porosity can be increased, the dielectric constant can be lowered, so that it can be used for an insulating film for LSI multilayer wiring. In addition, since it can be used as a catalyst carrier, it is very useful industrially.

Claims (3)

A coating composition for forming a film, comprising a partial hydrolyzate of alkoxysilane with an alkoxysilane and an acid, a base, and an organic polymer containing an amide bond . 1 × 10 ⁻⁵ to 1 mol of acid with respect to 1 mol of the alkoxysilane, 0.3 to 100 mol of water with respect to 1 mol of the alkoxysilane, and 100 parts by weight of the alkoxysilane 1 to 10000 parts by weight of the organic polymer containing the amide bond at 0 to 100 ° C. to partially acid hydrolyze the alkoxysilane, and subsequently to 1 mol of the alkoxysilane. The method for producing a coating composition for forming a film according to claim 1, which is obtained through a step of adding 2 × 10 ^{−5 to} 2 mol of a base. After the coating composition according to claim 1 or the coating composition obtained by the production method according to claim 2 is coated on a substrate in a film shape, the alkoxysilane and its partial hydrolyzate are further hydrolyzed. A method for producing a porous silicon oxide, which is obtained by dehydrating condensation to obtain a silicon oxide and subsequently removing the organic polymer containing the amide bond .