JPH10158012A - Production of porous silicon dioxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform porous silicon dioxide film free from the formation of coarse grains by dissolving alkoxysilane and an amido bond-contg. org. polymer in a solvent, adding an acid, carrying out partial hydrolysis, adding a base, filmily coating the top of a substrate with the resultant soln., carrying out hydrolysis and dehydration condensation, removing the solvent and then removing the org. polymer from the resultant dry gel. SOLUTION: Alkoxysilane and an amido bond-contg. org. polymer such as poly(N-vinylcaprolactone) or a polyurethane deriv. are dissolved in a solvent, an acid is added and partial hydrolysis is carried out. A base catalyst is further added, the top of a substrate is filmily coated with the resultant soln. and hydrolysis and dehydration condensation are carried out. The solvent is evaporated and the org. polymer is removed from the resultant dry gel to obtain the objective porous silicon dioxide film. The org. polymer is removed from the dry gel film by firing by heating, solvent extraction or other method but it is easily removed by heating at a temp. above the thermal decomposition temp. of the polymer for about 1-24hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a porous silicon oxide film.

[0002]

2. Description of the Related Art Conventionally, a silicon oxide or a silicon oxide into which fluorine or an organic group is introduced has been used for an interlayer insulating film used for an LSI multilayer wiring. However, the relative permittivity of these materials is relatively large, and as LSI wiring becomes finer in the future, the use of these materials as interlayer insulating films causes various problems such as wiring delay. For this reason, attempts have been made to make the silicon oxide porous and to reduce the relative permittivity by forming a composite with air having a relative permittivity of about 1, but all of them involve a complicated process. A simple method for producing a high-quality silicon oxide film has not been established.

A report by Saegusa et al. (Journal of M)
acromolecular Science-Che
mystry, A27, 13-14 Merger No. 16
According to 03-1612 (1990), when the hydrolysis and dehydration condensation reaction of tetraalkoxysilane is performed using an acid catalyst in the presence of a polymer containing an amide bond, the amide bond of the generated silicon oxide gel is The carbonyl group and the silanol group on silicon are hydrogen-bonded and are stably dispersed at the molecular level. Therefore, when the organic polymer component is burned off, very small pores at the molecular level are uniformly dispersed. A porous silicon oxide is 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 is a film, evaporation of the solvent takes precedence. Could not.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for easily and quickly producing a uniform and high-quality porous silicon oxide film without generation of giant particles.

[0006]

According to the present invention, there is provided a method of dissolving an alkoxysilane and an organic polymer containing an amide bond in a solvent, adding an acid, partially hydrolyzing the solution, and then adding a base catalyst to the substrate. This is a method for producing a porous silicon oxide film, which comprises applying a film thereon, performing hydrolysis and dehydration condensation, and then removing an organic polymer from a dried gel obtained by evaporating a solvent.

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 an acid and water as a catalyst are added and stirred to partially hydrolyze. Perform a decomposition step. As a result, the alkoxysilane partially becomes a silicon hydroxide,
Although a partial dehydration reaction occurs, it 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 and tetra (t-butyl) silane.
And mixtures thereof. Further, a partial hydrolyzate of the above tetraalkoxysilane can also be used. In order to further improve the porous film, an alkoxysilane having one alkyl group or an aryl group on a silicon atom or an alkoxysilane having one to three alkyl groups or an aryl group on a silicon atom is used. It is also possible to mix with tetraalkoxysilane.

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, Examples include polyimide derivatives, polyurethane derivatives, polyurea derivatives, nylon derivatives, and mixtures thereof. Further, a copolymer of monomers which are constituent components of these polymers or a copolymer with any other monomer may be used. The amide bond in the polymer effectively forms a hydrogen bond with a silanol group generated by hydrolysis of the alkoxysilane during the process of gelation of the alkoxysilane, thereby preventing phase separation. For this purpose, the amide bond content in the polymer needs to be 5000 or less in molecular weight per amide residue.

The amount of the amide bond-containing organic polymer is from 1 to 10 parts by weight per 100 parts by weight of the alkoxysilane.
000 parts by weight, preferably 10 to 1000 parts by weight. The porosity of the porous film obtained by the present invention is mainly determined by the amount of the amide bond-containing organic polymer. Therefore, if the 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. Also one
If the amount is more than 0000 parts by weight, the strength of the obtained porous membrane becomes small, and the practicability is poor.

The solvent is preferably a solvent in which both the alkoxysilane and the amide bond-containing organic polymer are dissolved, and a monohydric alcohol of C1 to C4,
Dimethylformamide, formamide, dimethylacetamide and the like are preferably used. These solvents may be mixed, or any other solvent or additive may be mixed.

Specific examples of the acid serving as a catalyst include hydrochloric acid, nitric acid, sulfuric acid, and acetic acid. The addition amount of these acids is 10 ^-5 to 1 mol, preferably 10 ^-4 to 10 ^-1 mol, per 1 mol of the alkoxysilane. If the amount of the catalyst is less than 10 ^-5 mol, hydrolysis does not proceed sufficiently and gelation may not occur in the next step. On the other hand, if it is more than 1 mol, precipitation or the like occurs, and a uniform porous film cannot be obtained, or gelation occurs before the next step is performed.

[0013] The hydrolysis of the alkoxysilane which occurs in this step is caused by water as a solvent when the acid serving as the catalyst is an aqueous solution, and if necessary, water is added separately. The appropriate amount of water depends on the type of the alkoxysilane as a raw material, but is preferably from 0.3 to 1 mol per mol of the alkoxysilane.
It is 100 moles, preferably 1 to 10 moles. 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 high quality film cannot be obtained. If the amount is more than 100 mol, the uniformity of the porous film is reduced.

[0014] The temperature of the partial hydrolysis reaction using an acid catalyst is 0 to 100 ° C, preferably 20 to 60 ° C. If the temperature is lower than 0 ° C., the reaction rate is low, and it takes a long time for hydrolysis to proceed sufficiently. If the temperature exceeds 100 ° C., gelation may occur before the next step is performed. The time required for gelling varies depending on the gelling temperature, the amount of catalyst, and the like, but is usually in the range of several hours to several days.

In the method for producing a porous silicon oxide film of the present invention, a base as a catalyst and, if necessary, water are added to a solution of the partial hydrolyzate of alkoxysilane obtained by the above method, After being coated on the film, hydrolysis and dehydration condensation of the alkoxysilane are terminated. Specific examples of the base used here include aqueous ammonia, potassium hydroxide, sodium hydroxide, triethylamine, and triethanolamine. It is important that these bases are added to some extent in excess of the acid added in the previous step, and if the amount of the base added is too small, gelation does not occur or gelation takes a long time, so a good quality film is formed. I can't get it. The base is added in an amount of 10 ^-5 to 1 mol, preferably 1 to 1 mol of the acid added in the previous step, per mol of the starting alkoxysilane.
It is appropriate to have a molar excess of 0 ^-4 to 10 ^-1 . If the excess amount of the base is more than 1 mol, a sharp increase in viscosity occurs, making it difficult to apply a film-like coating or gelling instantly.

The amount of water to be added depends on the type of the 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 1 mol per mol of alkoxysilane. 10 to 10 mol. If the amount is less than 1 mol, hydrolysis and gelation do not sufficiently occur, and a porous membrane cannot be obtained. If the amount is more than 100 mol, the uniformity of the porous film is reduced. If a sufficient amount of water has already been added in the previous step, it is not necessary to newly add water in this step.

The film-form coating is performed by a known method such as casting, dipping, spraying, and spin coating. The thickness is not particularly limited, but is preferably 0.1 μm or more. 0.1 μm
If it is less than 3, the effect of the porous membrane cannot be sufficiently obtained. Further, the thickness is preferably 1 mm or less because the gel can be dried in a short time. It is also possible to prepare a film having a thickness of more than 1 mm by taking sufficient time for drying the gel.

In order to obtain a film excellent in adhesion, homogeneity, crack resistance and peeling resistance, the substrate may be treated in advance with an adhesion improver. As the adhesion improver in this case, those used as a so-called silane coupling agent can be used. 3- is preferably used.
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, among which 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N-
(2-Aminoethyl) -3-aminopropylmethyldimethoxysilane is particularly preferably used. When applying these adhesion improvers, other additives may be added as necessary, or they may be diluted with a solvent such as alcohol or water before use. The adhesion improver is applied by casting, dipping, spraying,
This is performed by a known method such as a spin coating method. After the application, the excess adhesion improver is removed by washing with a general organic solvent such as alcohol. A few minutes from application to washing is usually sufficient. Thereafter, the cleaning solvent is dried to obtain a processing substrate. If the time from application to washing is short, the effect of the adhesion improver cannot be obtained, and if too long, the adhesion improver may be cured on the substrate.

The temperature of the gelation reaction of the applied film is from 0 to 10
The temperature is in the range of 0 ° C, particularly preferably 20 to 60 ° C. If the temperature is lower than 0 ° C., the reaction rate is low, and it takes a long time to cause sufficient crosslinking. If the temperature is higher than 100 ° C., voids are easily formed, and the homogeneity of the obtained porous membrane is reduced. The time required for gelation varies depending on the gelling temperature, the amount of catalyst, and the like, but is usually in the range of several minutes to several days.

After the gelling has sufficiently proceeded, drying is performed to remove the solvent. The drying temperature depends on the type of the solvent, but is usually in the range of 20 to 200 ° C. In order to control the generation of voids and obtain a uniform dried gel film, a method of gradually increasing the temperature during the drying step is also preferable. The target porous silicon oxide film can be obtained by removing only the organic polymer from the dried gel film. As a method for removing the organic polymer, heat baking, solvent extraction,
Plasma treatment and the like can be mentioned. The simplest method is 1 to 24 at or above the thermal decomposition temperature of the amide bond-containing organic polymer.
This is a method of heating for about an hour.

In the method of the present invention, since the hydrolysis and dehydration condensation of the tetraalkoxysilane are quickly completed, deterioration of the film quality due to evaporation of the solvent can be prevented, and a uniform porous film can be promptly obtained.

[0022]

Embodiments of the present invention will be described below. In addition, evaluation of the silicon oxide film obtained in the example was performed as follows. 1. Surface area (N2 BET) The surface area was measured using a nitrogen adsorption type surface area measuring device manufactured by Shimadzu Corporation. 2. Scanning Electron Microscope (SEM) A sample is cut into a square of about 5 mm, placed on a sample table on which a conductive tape is stuck, conduction is secured with a carbon paste, and platinum-palladium is vapor-deposited by about 1 nm, and a scanning electron microscope manufactured by Hitachi, Ltd. Measurements were taken with a microscope. Electron acceleration voltage is 1k
V was set.

[0023]

Example 1 0.6 g of tetraethoxysilane and 0.5 g of poly (N-vinylpyrrolidone) were added to 0.8 g of ethanol.
g and dimethylformamide (1.2 g), and the solution was added with 0.1N hydrochloric acid (0.05 g) and stirred at room temperature for 5 hours. To this solution was added 0.5 ml of a 0.1N ammonia aqueous solution, followed by stirring. The solution was immediately cast onto a glass substrate so as to have a thickness of 1 mm, and then left standing at room temperature for 1 hour in a closed container. The membrane had lost fluidity. The mixture was allowed to stand overnight, dried at 60 ° C. to 150 ° C. for 5 hours, and heated at 600 ° C. for 12 hours in nitrogen. It was found by a 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-coated on a silicon substrate, left for 3 minutes, washed with methanol, and dried at 60 ° C. for 10 minutes. 10ml
In a 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.
0.1 g of N hydrochloric acid was added, and the mixture was stirred at room temperature for 3 hours. 0.5 ml of a 0.1N ammonia aqueous solution was added to this solution, and the mixture was stirred and spin-coated on the silicon substrate at a speed of 1500 revolutions per second for 10 seconds so as to have a film thickness of 1 μm. Left for 1 hour. Allow to stand overnight, dry at 60 ° C. to 160 ° C. for 4 hours,
Heated at 0 ° C. for 8 hours. When the surface of the obtained silicon oxide film was observed with a scanning electron microscope, it was very uniform, and neither cracks nor giant particles were generated.

[0025]

Comparative Example 1 5.2 g of tetraethoxysilane and poly (N
-Vinylpyrrolidone) 1.5 g ethanol 2.5 g,
It was dissolved in 3.5 g of dimethylformamide, and 3.5 g of 0.08 N hydrochloric acid was added to this solution, followed by stirring at room temperature for 3 hours. This solution was applied on a glass substrate by casting so as to have a thickness of 1 mm, and then left at room temperature overnight in a closed container. However, the applied film was viscous and did not lose its fluidity.

[0026]

The porous silicon oxide thin film obtained according to the present invention is of good quality in spite of its extremely simple and rapid production method as compared with the conventional method. In addition, since the dielectric constant can be reduced because the pore diameter is small and the porosity can be increased, it can be used as an insulating film for LSI multilayer wiring. In addition, since it can be used as a carrier for a catalyst, it is very useful in industry.

Claims (1)

[Claims] 1. An alkoxysilane and an organic polymer containing an amide bond are dissolved in a solvent and partially hydrolyzed by adding an acid. A method for producing a porous silicon oxide film, comprising performing decomposition, dehydration condensation, and then evaporating a solvent to remove an organic polymer from a dried gel obtained.