KR100444650B1 - Substrate with a low dielectric constant coating film and low dielectric constant coating - Google Patents

Abstract

Relative dielectric constant of less than 3, excellent in chemical resistance such as adhesion to the surface of the substrate, mechanical strength, alkali resistance, etc., can form an insulating film excellent in crack resistance, and can evenly smooth the unevenness of the surface of the substrate Provided are a coating liquid for forming a low silica-based coating film and a silica-based coating film having a low dielectric constant.

The coating liquid for forming a low dielectric constant silica-based film contains a reaction product of silica fine particles and an alkoxysilane represented by the following formula and / or a halogenated silane represented by the following formula or hydrolyzate thereof.

X _n Si (OR) _4-n or

X _n SiX ' _4-n

(X represents H, F or an alkyl group, aryl group or vinyl group having 1 to 8 carbon atoms, R represents H or an alkyl group, aryl group or vinyl group having 1 to 8 carbon atoms, and X 'represents a halogen atom. It is an integer of 0-3.

Description

Substrate with a low dielectric constant coating liquid and a low dielectric constant coating film

The present invention can form an insulating film having a low relative dielectric constant, and excellent chemical resistance such as adhesion to the surface of the substrate, mechanical strength and alkali resistance, and at the same time, excellent crack resistance, and further, highly uneven surface of the substrate surface. The present invention relates to a coating liquid for forming a silica-based film having a low dielectric constant and a substrate on which a silica-based film having such a low dielectric constant is formed.

In the semiconductor device having a multilayer wiring with high integration of the semiconductor device, an interlayer insulating film is disposed between them in order to insulate between the semiconductor substrate and a metal wiring layer such as an aluminum wiring layer or between metal wiring layers.

If a metal wiring layer or the like is disposed on the semiconductor substrate, irregularities are generated on the semiconductor substrate by the metal wiring layer or the like, and disconnection occurs due to the uneven step even by further forming a metal wiring layer or the like on the uneven surface. In addition, when the uneven step is larger than the range of the exposure focal depth of the resist for forming the fine patterns, the fine pattern may not be formed. Therefore, it is necessary to highly planarize the uneven surface formed by the interlayer insulating film and various elements formed between the semiconductor substrate and the metal wiring layer and between the metal wiring layers.

Furthermore, in the structure having such a multilayer wiring, since the metal wiring interval is narrow in a semiconductor device of 0.3 µ rule or less, the impedance of the metal wiring is increased by electrostatic induction, which delays the response speed and consumes power. There is a risk of increase.

Therefore, it is necessary to make the relative dielectric constant of the interlayer insulating film disposed between the semiconductor substrate and the metal wiring layer such as the aluminum wiring layer or between the metal wiring layers as small as possible.

The interlayer insulating film used for the above-mentioned purpose generally uses a vapor phase growing method such as a plasma CVD method, a sputtering method or a coating liquid for film formation. It is formed on a substrate by a coating method for forming an insulating film.

However, in the gas phase growth method such as the plasma CVD method, the relative permittivity of the obtained film is known to be limited to 3.5 obtained by the silica film doped with fluorine, and it is difficult to form a film having a relative dielectric constant of 3 or less. In addition, the film formed by using a coating liquid made of a fluorinated polyimide resin or a fluorine-based resin has a relative dielectric constant of about 2, but has poor adhesion to the surface of the substrate, and also poor adhesion to a resist material used for micronization. There are also disadvantages such as poor chemical resistance and oxygen plasma resistance.

Although a coating film having a relative dielectric constant of 2.5 can be obtained as a coating liquid for forming a silica-based film formed from a partial hydrolyzate of an alkoxysilane that has been conventionally used, there is a disadvantage in that adhesion to the surface of a substrate is poor.

The present invention is to solve the problems of the prior art as described above, the relative dielectric constant is less than 3, and further excellent in chemical resistance, such as adhesion to the surface of the substrate, mechanical strength, alkali resistance, and at the same time excellent crack resistance An object of the present invention is to provide a coating liquid for forming a low dielectric constant silica-based coating film capable of forming an insulating film and further flattening irregularities on the surface of the substrate, and a substrate on which such a low dielectric constant silica-based coating film is formed.

Disclosure of the Invention

The coating liquid for forming a silica-based film having a low dielectric constant according to the present invention is a product of reacting a silica fine particle with an alkoxysilane represented by the following formula (1) and / or a halogenated silane represented by the following formula (2) or a hydrolyzate thereof. Wherein the silica fine particles are obtained by hydrolyzing at least one alkoxy silane represented by the following formula (1) at a temperature of 180 ° C. or higher and, optionally, aging at a temperature of 180 ° C. or higher.

X _n Si (OR) _4-n (1)

X _n SiX ' _4-n (2)

X is H, F, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group; R is H, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group; X 'represents a halogen atom; And n is an integer of 0-3.

Further, the coating liquid for forming a silica-based film having a low dielectric constant according to the present invention has an ion concentration of 1 mmol / lit. Is less than.

In addition, the substrate coated with the silica-based coating according to the present invention includes a silica-based coating having a low dielectric constant formed by using the coating liquid.

Best Mode for Carrying Out the Invention

Hereinafter, the coating liquid for forming a low dielectric constant silica-based film which concerns on this invention is demonstrated concretely.

Coating liquid for forming silica-based film with low dielectric constant

The coating liquid for forming a low dielectric constant silica-based film according to the present invention contains a reaction product of silica fine particles with an alkoxysilane represented by the following formula (1) and / or a halogenated silane represented by the following formula (2) or a hydrolyzate thereof It is characterized by that.

X _n Si (OR) _4-n (1)

X _n SiX ' _4-n (2)

(X is H, F, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group; R is H, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group; X 'is a halogen atom. Is an integer of ~ 3.)

Specific examples of the alkoxysilane represented by the formula X _n Si (OR) _4-n include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraoctylsilane, methyltrimethoxysilane, methyl Triethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, octyltriethoxysilane, vinyltrimethoxysilane, vinyl Triethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, dimethyldimethoxysilane, Dimethyl diethoxysilane, diethyldimethoxysilane, diethyl diethoxysilane, dimethoxysilane, diethoxysilane, difluorodimethoxysilane, difluoro diethoxysilane, trifluoromethyltrimethoxy As is, and trifluoromethyl may be mentioned such as a silane methyltrimethoxysilane.

Specific examples of the halogenated silane represented by the formula X _n SiX ′ _4-n include trichlorosilane, tribromosilane, fluorotrichlorosilane, methyltribromosilane, ethyltrichlorosilane, vinyltrichlorosilane, phenyltrichlorosilane, and the like. Can be mentioned.

Such coating liquid for low silica dielectric film formation can be prepared by the following method, for example.

First, silica fine particles can be obtained by hydrolyzing and polycondensing one or two or more alkoxysilanes represented by the above formula (1) in the presence of water, an organic solvent and a catalyst. Can be adopted.

Examples of the organic solvent include alcohols, ketones, ethers and esters, and more specifically, alcohols such as methanol, ethanol, propanol and butanol; Ketones such as methyl ethyl ketone and methyl isobutyl ketone; Glycol ethers such as methyl cellosolve, ethyl cellosolve and propylene glycol monopropyl ether; Glycols such as ethylene glycol, propylene glycol and hexylene glycol; Ester, such as methyl acetate, ethyl acetate, methyl lactate, and ethyl lactate, can be used.

As a catalyst, basic compounds, such as ammonia, an amine, an alkali metal compound, a quaternary ammonium compound, or an amine coupling agent, can be used.

The method for producing the silica fine particles will be described in more detail. For example, a basic compound catalyst such as alkoxysilane and ammonia water is added to the mixed solvent obtained by stirring the water-alcohol mixed solvent to react.

In this case, water may be used in an amount of 0.5 to 50 mol, preferably 1 to 25 mol, per mol of the Si-OR group constituting the alkoxysilane, and ammonia is, for example, 0.01 to 1 mol / SiO ₂ mol, Preferably then blended in an amount such as 0.05 to 0.8 mol / mol of SiO _2.

The alkoxysilane is preferably hydrolyzed at a temperature of 180 ° C. or higher, preferably 200 ° C. or higher, in a pressurized vessel such as an autoclave. In addition, it can then be aged at the same or higher temperatures. The higher the hydrolysis temperature and / or aging temperature, the more the polycondensation of the alkoxysilane is promoted and the more dense the internal structure of the silica fine particles is. In the present invention, when the hydrolysis and / or maturation is performed at this temperature, the silica fine particles become denser, the hygroscopicity of the fine particles themselves is lowered as well as the amount of residual functional groups on the particle surface is reduced. Therefore, the obtained film does not change with relative permittivity over time and is excellent in heat resistance.

For example, a high boiling point solvent such as ethylene glycol may be added to the water-alcohol mixed solvent while stirring to hydrolyze the alkoxysilane to generate and grow silica fine particles. When a high boiling point solvent is added when the alkoxysilane is hydrolyzed, transesterification of the alkoxy group may occur, and a high boiling point solvent may be trapped inside the silica fine particles to obtain porous silica fine particles having a low density.

As other silica fine particles, silica sol obtained by ion exchange, hydrolysis or the like of alkali metal silicate can also be used. In addition, fine particles made of porous zeolite from which aluminum is removed from the zeolite composed of aluminosilicate can also be used.

The silica fine particles that can be used in the present invention preferably have a particle diameter of about 30 to 1000 mm 3, preferably within the range of 50 to 500 mm 3. As long as it is the particle | grains of this range particle diameter, not only a thing with a uniform particle diameter but also a mixture of 2 or more types of microparticles from which a particle size differs may be sufficient. If the particle size is less than 30 mm 3, the dielectric constant of the obtained film becomes difficult to be lowered. On the other hand, if the particle size exceeds 1000 mm, defects are likely to occur during the miniaturization of photolithography.

The coating liquid for forming a silica-based film having a low dielectric constant used in the present invention comprises at least a part of the silica fine particles obtained according to the above, the alkoxysilane represented by the formula (1), the halogenated silane represented by the formula (2), or a hydrolyzate thereof. It is obtained by making it react. In this case, a mixture of the alkoxysilane and the halogenated silane may be used. The alkoxysilane reacted with the silica fine particles is preferably the same as that used for the production of the silica fine particles, or different. In this reaction, no growth of silica fine particles or generation of new silica fine particles occurs, and surface reactions of the silica fine particles with alkoxysilanes, halogenated silanes or their hydrolysates occur on the surfaces of the silica fine particles, and as a result, have excellent properties. A coating liquid providing a silica-based coating having a low dielectric constant is obtained.

Although the fine silica particles may be used as they are, it is preferable to solvent-exchange the water-organic solvent of the silica fine particle dispersion medium with only the organic solvent beforehand by ultrafiltration or the like before reacting them.

As an organic solvent used here, what was used at the time of the hydrolysis of said alkoxysilane can be mentioned.

When preparing the coating liquid, the alkoxysilane or halogenated silane reacted with the silica fine particles may be used without hydrolysis in advance, but it is preferable to use it as a hydrolyzate polymer obtained by hydrolysis in advance according to a known method. Aggregation and gelation of fine particles are less likely to occur, and a stable coating liquid tends to be obtained.

In this way, in the case of performing hydrolysis of the alkoxysilane or halogenated silane, water, an organic solvent and a catalyst are generally used. The organic solvent can select the above-mentioned thing. As a catalyst, in addition to the above-mentioned, an acid catalyst can be selected. Specifically, inorganic acids, such as hydrochloric acid, nitric acid, and sulfuric acid; Organic acids such as acetic acid, oxalic acid and toluenesulfonic acid; Or a compound showing acidity in an aqueous solution such as metal soap. Acid catalysts are particularly preferred.

Water is usually used in an amount of 0.1 to 5 mol, preferably 0.1 to 2 mol, per mol of the Si-OR group constituting the alkoxysilane or the Si-X 'group constituting the halogenated silane. The addition amount of the catalyst is generally used in an amount of 0.001 to 1 mol per mol of the alkoxysilane or halogenated silane.

The number average molecular weight of the hydrolyzate obtained by hydrolysis under the conditions described above is preferably 100 to 500,000, preferably 500 to 10000 (polystyrene equivalent molecular weight).

The coating liquid for forming a silica-based film having a low dielectric constant used in the present invention reacts by mixing the silica fine particles obtained as described above with an alkoxysilane, a halogenated silane or a hydrolyzate thereof, but the mixing ratio of both is at least a part of the silica fine particles. It is preferable that the surface of is a hydrolyzate in an amount sufficient to bind with the hydrolyzate.

In the present invention, the mixed amount of the alkoxysilane or halogenated silane hydrolyzate is preferably 0.01 parts by weight or more, preferably 0.02 parts by weight or more per 1 part by weight of the silica fine particles in terms of SiO ₂ .

When the amount of the alkoxysilane or halogenated silane hydrolyzate is less than 0.01 part by weight, the obtained silica-based coating becomes porous containing a large amount of intergranular voides of silica fine particles, but the dielectric constant can be expected to decrease, but with the surface of the substrate There exists a tendency for chemical-resistances, such as adhesiveness, mechanical strength, and alkali resistance, to fall, and the cracking resistance and the planarization performance of the base material surface also fall. In addition, the hydrolyzate of these alkoxysilanes or halogenated silanes also has a function as a binder for film formation, and unreacted hydrolyzate may exist in the coating liquid. However, if the amount is too large, the resulting film is filled with hydrolyzate of grain boundary pores of the silica fine particles, so that the dielectric constant of the film cannot be expected to decrease. Therefore, the hydrolyzate is preferably less than 10 parts by weight, preferably less than 1 part by weight, per 1 part by weight of silica fine particles.

Thus, after mixing such silica fine particles with hydrolyzates of alkoxysilanes or halogenated silanes, the temperature is usually about 100 ° C. or lower, preferably 80 ° C. or lower, and fluctuated depending on the temperature conditions and the like, and usually 0.5 to 5 hours, preferably Heats 0.5 to 3 hours.

Such a treatment yields a coating liquid for forming a low dielectric constant silica-based film in which a hydrolyzate of an alkoxysilane or a halogenated silane is bonded to at least part of the surface of the silica fine particles.

The silica-based film prepared using such a coating liquid has excellent characteristics. For example, the silica-based film thus obtained is calcined at 450 ° C. in nitrogen, and peaks due to OH groups appear in the FT-IR spectrum of the obtained film. Is not measured even after being left at room temperature for one week, and no moisture resorption is found, which is an important factor in increasing the dielectric constant.

Moreover, after manufacturing a coating liquid by the above-mentioned method, you may add alkoxysilane or a halogenated silane hydrolyzate further to a coating liquid. It is preferable that the hydrolyzate amount at this time is also the same range as the above.

The ion concentration in the coating liquid for forming a silica-based coating film according to the present invention is preferably 1.0 mmol / lit. Or less, preferably 0.5 mmol / lit. Or less. If the ion concentration exceeds 1.0 mmol / lit., The surface reactivity of the silica fine particles may be affected by the ions, resulting in insufficient surface treatment of the silica fine particles, resulting in a decrease in the planarization of the surface of the substrate. In addition, moisture reabsorption of the film is likely to occur.

In addition, the above problems are solved by lowering the ion concentration in the coating solution, and there are almost no voids, pinholes, etc., and the film having improved adhesion to the substrate, mechanical strength, chemical resistance, moisture resistance, and insulation is further improved. Obtained.

Ion concentration here means the total ion concentration of the cation and anion in a coating liquid, and is measured by the following method. That is, metal ions in cations are measured by atomic absorption method, and ammonium ions and anions are measured by ion chromatography.

Such a low ion coating liquid may be prepared by treating with a cation exchange resin and an anion exchange resin in any step of the manufacturing process.

For example, the method of mixing the hydrolyzate of an alkoxysilane or a halogenated silane after performing deionization of a silica fine particle dispersion, the method of deionizing after mixing both, etc. are mentioned.

In the deionization treatment, the cation exchange resin treatment and the anion exchange resin treatment may be performed respectively, or may be treated with two mixed resins.

Substrate coated with low dielectric constant silica coating

The base material coated with the film according to the present invention is obtained by applying a coating liquid for forming a silica-based film having a low dielectric constant obtained as described above to the surface of various base materials and then heating.

As the coating method, a conventional coating method such as a spray method, a spin coat method, a dipping method, a roll coater method or a transfer method can be used. . The heating temperature after application | coating is 300-450 degreeC normally, Preferably it is the range of 350-400 degreeC. This heating is preferably performed under an inert gas atmosphere such as nitrogen, and as a result, a film having a lower relative dielectric constant is obtained.

When the coating liquid is applied and dried on the substrate as described above, the film-forming component in the coating liquid is polymerized and cured, but the melt viscosity of the polymer decreases during the heating process, thereby increasing the reflowability of the film. The flatness of the obtained film is improved. When forming a film using the coating liquid for silica type film formation which concerns on this invention, the melt viscosity of the polymer by heating falls, and the reflowability by low viscosity is maintained by about 400 degreeC. . As a result, a film with further improved flatness is obtained.

The film thickness of the silica-based film having a low dielectric constant thus obtained varies depending on the substrate for forming the film, the purpose thereof, and the like. For example, on a silicon substrate in a semiconductor device, the film is usually 1000 to 2500 Å and an insulating film between multilayer wiring layers. In the case of, it is generally about 3000 ~ 5000Å.

As the base material coated with a low dielectric constant silica-based film according to the present invention, a semiconductor device, a liquid crystal display, a photomask with a phase shifter, etc. may be mentioned. In particular, in the semiconductor device, the above low dielectric constant film may be formed on the silicon substrate, between the wiring layers of the multi-layered wiring structure, the element surface, or the PN junction portion.

Effects of the Invention

The coating liquid for forming a silica-based film according to the present invention can form a film on the substrate having a low relative dielectric constant of 3 or less and excellent in adhesion to the surface of the substrate, mechanical strength, chemical resistance and crack resistance, and the like. The uneven surface of can be highly flattened.

In other words, when the silica-based coating is formed using the coating solution for forming a silica-based coating according to the present invention, the coating becomes porous by grain boundary pores between the silica fine particles contained as the film forming component, and as a result, the dielectric constant is higher than that of the conventional SOG film or the like. This reduced film is obtained. In addition, the hydrolyzate of the alkoxysilane or halogenated silane bound to the surface of the fine particles has the effect of preventing the reabsorption of water into the grain boundary pores, and the hygroscopicity of the fine particles themselves is also reduced by high temperature aging, so that the obtained film has a relative dielectric constant. It shows stable and low dielectric constant without change over time. In addition, since there are few organic groups remaining on the surface of silica fine particles, it is a film excellent in heat resistance. Moreover, adhesiveness with the surface of a base material surface also improves by the anchor effect of a silica fine particle.

The substrate coated with the low dielectric constant silica-based coating according to the present invention has a relative dielectric constant of 3 or less, and has a coating having excellent adhesion to the surface of the substrate, mechanical strength, chemical resistance, crack resistance and heat resistance, and the like. The uneven surface of the surface is highly planarized. Moreover, it is the base material surface which has a stable film with little change of a relative dielectric constant with time.

Hereinafter, although an Example demonstrates this invention, this invention is not limited to an Example.

Examples 1-6 and Comparative Examples 1 and 2

1. Preparation of Silica Fine Particles

A mixed liquid of 139.1 g of purified water and 169.9 g of methanol was kept at 60 ° C, and a tetra-ethoxysilane (ethyl silicate 28, manufactured by Tama Chemical Industry) was added to 2450 g of a water / methanol solution having a weight ratio of 2/8 to tetra 22.52.5 g of 0.25% aqueous ammonia and 596.4 g of 0.25% aqueous ammonia were added simultaneously over 52 hours. After the addition was terminated at this temperature for 3 hours. Thereafter, unreacted tetraethoxysilane, methanol, and ammonia were removed by ultrafiltration, followed by treatment with a zwitterion exchange resin (AG-501, manufactured by Bio-Rad) to give an impurity ion concentration of 0.5 mmol / lit. Silica fine particle dispersion (A) with an average particle diameter of 300 kPa was obtained.

Said dispersion (A) was aged at 300 degreeC by the autoclave for 3 hours, and the silica fine particle dispersion (B) of 250 micrometers of average particle diameters was obtained.

Except for using 139.1 g of purified water, 140 g of methanol, and 29.9 g of ethylene glycol, the mixture was prepared under the same conditions as the silica fine particle dispersion (A), and aged at 300 ° C. for 3 hours using an autoclave. The impurity ion concentration of 0.4 mmol / lit. The porous silica-based fine particle dispersion (C) with an average particle diameter of 250 kPa was obtained.

Ion concentration was measured by atomic absorption method and the concentration of ammonium and anion was measured by ion chromatography method.

2. Preparation of Hydrolysates of Alkoxysilanes and Halogenated Silanes

250 g of triethoxysilane was mixed with 750 g of methyl isobutyl ketone, 1000 g of 0.01 wt% aqueous hydrochloric acid solution was added, and reacted at 50 ° C for 1 hour while stirring. After it was left as it was, the upper methyl isobutyl ketone solution was aliquoted to obtain a hydrolyzate (A).

Hydrosilsesquioxane (HSQ, manufactured by Dow Corning), a hydrolyzate of trichlorosilane, was dissolved in methyl isobutyl ketone to a silica concentration of 10% by weight to obtain a hydrolyzate (B).

3. Production of coating liquid for film formation

The silica-based fine particle dispersion obtained as described above was distilled off from water and alcohol in a rotary evaporator, and solvent-substituted with methyl isobutyl ketone. The hydrolyzate of the alkoxysilane and halogenated silane obtained as described above was prescribed. Were mixed at a given ratio and heated at 50 ° C. for one hour. The solvent was then substituted with methyl isobutyl ketone again using a rotary evaporator to completely remove alcohol or water produced by heat treatment, and the coating liquid C-1 to C shown in Table 1 having a silica concentration of 20% by weight. -8 was prepared.

4. Silica-coated semiconductor device

The coating liquids C-1 to C-8 for film formation were each coated by a spin coat method on a semiconductor substrate provided with at least 0.25 micron ruled metal wiring, and dried at 250 ° C. for 3 minutes. Then, it baked at 450 degreeC for 30 minutes in nitrogen, and formed the silica type film. All of these silica coating films were 5000 kPa.

Furthermore, upper metal wiring was formed on these films, and the semiconductor device was manufactured.

The planarization characteristics and relative permittivity of the silica-based coating films of the semiconductor devices thus obtained were measured.

The relative permittivity was measured immediately after formation and after 1 week.

The results are shown in Table 2.

In Table 2, epsilon ₁ is the relative dielectric constant by firing in a nitrogen atmosphere immediately after film formation, and epsilon ₂ is the relative dielectric constant after one week of the film recorded on the left side.

In other words, the flatness was observed by SEM-type electron microscopy after the film formation, and the relative dielectric constant was measured by the mercury probe method.

Comparative Examples 3 and 4

The hydrolyzate (A) and (B) were each adjusted to a silica concentration of 20% by weight to prepare a coating liquid, and the same evaluation as above was performed after forming a silica-based coating film. The results are shown in Table 2.

From the results in Table 2, the silica-based coating obtained by using the coating liquid for forming a silica-based coating according to the present invention has a low relative dielectric constant and excellent flatness. Moreover, the film formed using the coating liquid (C-3-C-8) containing the high temperature aging silica fine particle hardly changes the relative dielectric constant even after one week, and is excellent in moisture resistance. On the other hand, the silica coating film obtained using the coating liquid which consists of hydrolyzate (A) and (B) has low moisture resistance.

Claims (6)

A coating liquid for forming a low dielectric constant silica film, comprising a reactant of silica fine particles with a halogenated silane represented by the following formula (2) or a hydrolyzate thereof: X _n SiX ' _4-n (2) X is H, F, a C1-C8 alkyl group, an aryl group, or a vinyl group; X 'is a halogen atom; n is an integer of 0-3. A coating liquid for forming a low dielectric constant silica film comprising a reactant of silica fine particles with a halogenated silane represented by formula (2) or a hydrolyzate thereof and an alkoxy silane represented by formula (1) or a hydrolyzate thereof: X _n Si (OR) _4-n (1) X is H, F, a C1-C8 alkyl group, an aryl group, or a vinyl group; R is H, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group; n is an integer of 0-3. The coating liquid for forming a low dielectric constant silica film according to claim 1 or 2, wherein silica fine particles are obtained by hydrolyzing and selectively aging at least one alkoxysilane represented by the formula (1). The coating liquid for forming a low dielectric constant silica film according to claim 3, wherein the hydrolysis or aging temperature is 180 ° C or higher. The ion concentration according to claim 1 or 2, wherein the ion concentration is 1 mmol / lit. Coating liquid for silica film formation with a low dielectric constant below. A substrate comprising a low dielectric constant silica film formed from the coating liquid of claim 1.