JP2006182811A - Coating liquid for forming silica-based film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid for forming a silica-based film which gives an interlayer insulation film having a low dielectric constant. <P>SOLUTION: The coating liquid comprises a siloxane polymer, a basic compound and an organic solvent, where the basic compound is at least one selected from among organic ammonium salts and silazanes in an amount of 0.2-10 mass% based on the siloxane polymer and the siloxane polymer is a reaction product obtained by a hydrolysis reaction of at least one selected from among silane compounds represented by the formula: R<SB>4-n</SB>Si(OR')<SB>n</SB>(wherein R is a hydrogen atom, an alkyl group or a phenyl group and at least one of Rs is an alkyl group or a phenyl group; R' is an alkyl group or a phenyl group; and n is an integer of 2-4). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coating liquid for forming a silica-based film.

  Conventionally, silica-based coatings by the SOG (spin on glass) method are often used as planarization films and interlayer insulating films used in the manufacture of substrates for semiconductor elements and liquid crystal elements. This technique is a method in which a silica-based coating is formed by applying a coating solution containing a hydrolyzate of alkoxysilane or the like on a substrate by a spin coating method or the like, followed by heat treatment.

  Various proposals have been made regarding coating solutions (silica-based coating forming coating solutions) for forming a silica-based coating by the SOG method (for example, Patent Documents 1, 2, and 3 below).

JP 2001-131479 A JP 2001-115029 A JP 2004-96076 A

In recent years, in the field of semiconductor elements and liquid crystal elements, in order to meet the demands for higher integration, higher speed, more functions, etc., an interlayer insulating film having a lower dielectric constant is required.
However, a conventional silica-based film formed by applying a coating solution containing an alkoxysilane hydrolyzate or the like may not have a sufficiently low dielectric constant.
The present invention has been made to overcome the above-mentioned problems of the prior art and to solve the problems, and is capable of forming an interlayer insulating film having a lower dielectric constant than the conventional one. An object of the present invention is to provide an application liquid.

In order to achieve the above object, the coating liquid for forming a silica-based film of the present invention comprises a siloxane polymer, a basic compound, and an organic solvent.
As a result, during the heat treatment after applying the coating liquid, the basic compound promotes the condensation polymerization of the siloxane polymers, so that the organic component in the formed silica-based film is higher than that of the conventional one. It is presumed that the dielectric constant could be achieved.

  According to this invention, the dielectric constant of the silica-type film formed into a film can be made low enough by including a basic compound.

The basic compound contained in the coating solution for forming a silica-based film of the present invention is not particularly limited as long as there is no problem in compatibility with the siloxane polymer and the organic solvent to be used, but aliphatic amine, aromatic amine, Examples include organic amine compounds such as heterocyclic amines, organic ammonium salts such as quaternary ammonium hydroxides, and silazanes.
Specific examples of the aliphatic amine include monoethanolamine, triethanolamine, methylamine, ethylamine, propylamine, isopropylamine, butylamine, isobutylamine, tert-butylamine, pentylamine, isopentylamine, tert-pentylamine, Hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, trimethylamine, triethylamine, tripropylamine, triisopropylamine, tributylamine, triisobutylamine, tritert-butylamine, tripentylamine, tripentylamine Isopentylamine, tritert-pentylamine, trihexylamine, triheptylamine, trioctylamine, etc. It is below.

Specific examples of the aromatic amine include benzylamine, aniline, N-methylaniline, N, N-dimethylaniline, o-methylaniline, m-methylaniline, p-methylaniline, N, N-diethylaniline, diphenylamine, Examples thereof include di-p-tolylamine.
Specific examples of the heterocyclic amine include pyridine, o-methylpyridine, o-ethylpyridine, 2,3-dimethylpyridine, 4-ethyl-2-methylpyridine, and 3-ethyl-4-methylpyridine. .
Specific examples of the quaternary ammonium hydroxide include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethyl (hydroxyethyl) ammonium hydroxide, dimethyldi ( Hydroxyethyl) ammonium hydroxide and the like.
Examples of silazane include hexamethyldisilazane (HMDS).

Among these, tetramethylammonium hydroxide (TMAH) and hexamethyldisilazane (HMDS) are preferable.
These basic compounds may be used alone or in combination of two or more.
In the coating liquid for forming a silica-based film of the present invention, the basic compound is preferably 0.2 to 10% by mass, more preferably 1 to 10% by mass, and still more preferably based on the siloxane polymer. 2 to 10% by mass.
If the amount is less than 0.2% by mass, the effect of lowering the dielectric constant is too low, and by making it 10% by mass or less, gelation of the composition can be prevented.

  As the siloxane polymer contained in the coating solution for forming a silica-based film of the present invention, those known as a material for forming a silica-based film by the SOG method can be appropriately used. Preferably, a reaction product obtained by hydrolyzing at least one selected from silane compounds represented by the following general formula (I) is used.

R _4-n Si (OR ′) _n (I)

In general formula (I), R represents a hydrogen atom, an alkyl group or a phenyl group, R ′ represents an alkyl group or a phenyl group, and n represents an integer of 2 to 4. When a plurality of R are bonded to Si, the plurality of R may be the same or different. The plurality of (OR ′) groups bonded to Si may be the same or different.
The alkyl group as R is preferably a linear or branched alkyl group having 1 to 20 carbon atoms, and more preferably a linear or branched alkyl group having 1 to 4 carbon atoms. At least one of R is an alkyl group or a phenyl group.
The alkyl group as R ′ is preferably a linear or branched alkyl group having 1 to 5 carbon atoms. The alkyl group as R ′ preferably has 1 or 2 carbon atoms from the viewpoint of hydrolysis rate.

The reaction product obtained by hydrolyzing the silane compound includes a low molecular weight hydrolyzate and a condensate (siloxane oligomer) produced by causing a dehydration condensation reaction between molecules simultaneously with the hydrolysis reaction. Can be. When the siloxane polymer in the present invention includes such a hydrolyzate or condensate, it refers to the whole including these.
The mass average molecular weight (Mw) (polystyrene conversion standard by gel permeation chromatography, the same shall apply hereinafter) of the siloxane polymer contained in the coating solution for forming a silica-based film of the present invention is preferably 1000 to 3000. A more preferable range is 1200 to 2700, and a further preferable range is 1500 to 2000. When the Mw of the siloxane polymer is at least the lower limit of the above range, good film forming ability is obtained, and when the Mw is at most the upper limit of the above range, good embedding and flatness are obtained.

  The silane compound (i) when n in the general formula (I) is 4 is represented by the following general formula (II).

Si (OR ¹ ) _a (OR ² ) _b (OR ³ ) _c (OR ⁴ ) _d (II)

In the formula, R ¹ , R ² , R ³ and R ⁴ each independently represent the same alkyl group or phenyl group as the above R ′.
a, b, c and d are integers satisfying the condition of 0 ≦ a ≦ 4, 0 ≦ b ≦ 4, 0 ≦ c ≦ 4, 0 ≦ d ≦ 4 and a + b + c + d = 4.

  The silane compound (ii) when n in the general formula (I) is 3 is represented by the following general formula (III).

R ⁵ Si (OR ⁶ ) _e (OR ⁷ ) _f (OR ⁸ ) _g (III)

In the formula, R ⁵ represents the same alkyl group as the above R or a phenyl group. R ⁶ , R ⁷ , and R ⁸ each independently represent the same alkyl group or phenyl group as R ′ described above.
e, f, and g are integers that satisfy 0 ≦ e ≦ 3, 0 ≦ f ≦ 3, 0 ≦ g ≦ 3, and satisfy the condition of e + f + g = 3.

  The silane compound (iii) when n is 2 in the general formula (I) is represented by the following general formula (IV).

R ⁹ R ¹⁰ Si (OR ¹¹ ) _h (OR ¹² ) _i (IV)

In the formula, R ⁹ and R ¹⁰ represent a hydrogen atom, the same alkyl group as that of R, or a phenyl group. However, at least one of R ⁹ and R ¹⁰ represents the same alkyl group or phenyl group as R. R ¹¹ and R ¹² each independently represents the same alkyl group or phenyl group as the above R ′.
h and i are integers that satisfy 0 ≦ h ≦ 2, 0 ≦ i ≦ 2, and satisfy the condition of h + i = 2.

  Specific examples of the silane compound (i) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetrapentyloxysilane, tetraphenyloxysilane, trimethoxymonoethoxysilane, dimethoxydiethoxysilane, and triethoxy. Monomethoxysilane, trimethoxymonopropoxysilane, monomethoxytributoxysilane, monomethoxytripentyloxysilane, monomethoxytriphenyloxysilane, dimethoxydipropoxysilane, tripropoxymonomethoxysilane, trimethoxymonobutoxysilane, dimethoxydibutoxy Silane, triethoxymonopropoxysilane, diethoxydipropoxysilane, tributoxymonopropoxysilane, dimethoxymonoethoxymonobutyl Xysilane, diethoxymonomethoxymonobutoxysilane, diethoxymonopropoxymonobutoxysilane, dipropoxymonomethoxymonoethoxysilane, dipropoxymonomethoxymonobutoxysilane, dipropoxymonoethoxymonobutoxysilane, dibutoxymonomethoxymonoethoxysilane, Examples thereof include tetraalkoxysilanes such as dibutoxymonoethoxymonopropoxysilane and monomethoxymonoethoxymonopropoxymonobutoxysilane, among which tetramethoxysilane and tetraethoxysilane are preferable.

  Specific examples of the silane compound (ii) include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltripentyloxysilane, ethyltrimethoxysilane, ethyltripropoxysilane, ethyltripentyloxysilane, ethyltripentylsilane. Phenyloxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltripentyloxysilane, propyltriphenyloxysilane, butyltrimethoxysilane, butyltriethoxysilane, butyltripropoxysilane, butyltripentyloxysilane, butyltriphenyl Oxysilane, methylmonomethoxydiethoxysilane, ethylmonomethoxydiethoxysilane, propylmonomethoxydiethoxysilane, butylmonomethoxydie Xysilane, methylmonomethoxydipropoxysilane, methylmonomethoxydipentyloxysilane, methylmonomethoxydiphenyloxysilane, ethylmonomethoxydipropoxysilane, ethylmonomethoxydipentyloxysilane, ethylmonomethoxydiphenyloxysilane, propylmonomethoxydipropoxysilane , Propylmonomethoxydipentyloxysilane, propylmonomethoxydiphenyloxysilane, butylmonomethoxydipropoxysilane, butylmonomethoxydipentyloxysilane, butylmonomethoxydiphenyloxysilane, methylmethoxyethoxypropoxysilane, propylmethoxyethoxypropoxysilane, butylmethoxy Ethoxypropoxysilane, methyl monomethoxy monoethoxy monobut Examples include xyloxysilane, ethylmonomethoxymonoethoxymonobutoxysilane, propylmonomethoxymonoethoxymonobutoxysilane, and butylmonomethoxymonoethoxymonobutoxysilane. Among them, methyltrialkoxysilane (especially methyltrimethoxysilane, methyltriethoxysilane) Is preferred.

  Specific examples of the silane compound (iii) include methyldimethoxysilane, methylmethoxyethoxysilane, methyldiethoxysilane, methylmethoxypropoxysilane, methylmethoxypentyloxysilane, methylmethoxyphenyloxysilane, ethyldipropoxysilane, ethylmethoxypropoxy. Silane, ethyldipentyloxysilane, ethyldiphenyloxysilane, propyldimethoxysilane, propylmethoxyethoxysilane, propylethoxypropoxysilane, propyldiethoxysilane, propyldipentyloxysilane, propyldiphenyloxysilane, butyldimethoxysilane, butylmethoxyethoxysilane, Butyldiethoxysilane, Butylethoxypropoxysilane, Butyldipropoxysilane, Butylmethyl Dipentyloxysilane, butylmethyldiphenyloxysilane, dimethyldimethoxysilane, dimethylmethoxyethoxysilane, dimethyldiethoxysilane, dimethyldipentyloxysilane, dimethyldiphenyloxysilane, dimethylethoxypropoxysilane, dimethyldipropoxysilane, diethyldimethoxysilane, diethylmethoxy Propoxysilane, diethyldiethoxysilane, diethylethoxypropoxysilane, dipropyldimethoxysilane, dipropyldiethoxysilane, dipropyldipentyloxysilane, dipropyldiphenyloxysilane, dibutyldimethoxysilane, dibutyldiethoxysilane, dibutyldipropoxysilane, Dibutylmethoxypentyloxysilane, dibutylmethoxyphenyloxysilane , Methylethyldimethoxysilane, methylethyldiethoxysilane, methylethyldipropoxysilane, methylethyldipentyloxysilane, methylethyldiphenyloxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, methylbutyldimethoxysilane, methylbutyldi Ethoxysilane, methylbutyldipropoxysilane, methylethylethoxypropoxysilane, ethylpropyldimethoxysilane, ethylpropylmethoxyethoxysilane, dipropyldimethoxysilane, dipropylmethoxyethoxysilane, propylbutyldimethoxysilane, propylbutyldiethoxysilane, dibutylmethoxy Examples include ethoxysilane, dibutylmethoxypropoxysilane, dibutylethoxypropoxysilane, etc. Of these, methyldimethoxysilane and methyldiethoxysilane are preferred.

The silane compound used to obtain the reaction product can be appropriately selected from the silane compounds (i) to (iii).
A more preferred combination is a combination of silane compound (i) and silane compound (ii). When silane compound (i) and silane compound (ii) are used, these silane compounds (i) are preferably used in a range of 10 to 60 mol% and silane compound (ii) in a range of 90 to 40 mol%. More preferably, the silane compound (i) is 15 to 50 mol% and the silane compound (ii) is 85 to 50 mol%. The silane compound (ii) is more preferably one in which R ⁵ in the general formula (III) is an alkyl group or a phenyl group, preferably an alkyl group.

  The reaction product is prepared, for example, by a method in which one or more selected from the silane compounds (i) to (iii) are hydrolyzed and condensed in the presence of an acid catalyst, water, and an organic solvent. Can do.

As the acid catalyst, either an organic acid or an inorganic acid can be used.
As the inorganic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and the like can be used, among which phosphoric acid and nitric acid are preferable.
Examples of the organic acid include carboxylic acids such as formic acid, oxalic acid, fumaric acid, maleic acid, glacial acetic acid, acetic anhydride, propionic acid, and n-butyric acid, and organic acids having sulfur-containing acid residues. Examples of the organic acid having a sulfur-containing acid residue include organic sulfonic acids, and examples of esterified products thereof include organic sulfates and organic sulfites. Among these, organic sulfonic acids, for example, compounds represented by the following general formula (V) are particularly preferable.

R ¹³ -X (V)

(In the formula, R ¹³ is a hydrocarbon group which may have a substituent, and X is a sulfonic acid group.)

In the general formula (V), the hydrocarbon group as R ¹³ is preferably a hydrocarbon group having 1 to 20 carbon atoms, and this hydrocarbon group may be saturated or unsaturated, or linear. , May be branched or cyclic.
When the hydrocarbon group of R ¹³ is cyclic, an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, and an anthryl group is preferable, and a phenyl group is particularly preferable. One or more hydrocarbon groups having 1 to 20 carbon atoms may be bonded to the aromatic ring in the aromatic hydrocarbon group as a substituent. The hydrocarbon group as a substituent on the aromatic ring may be saturated or unsaturated, and may be linear, branched or cyclic.
Further, the hydrocarbon group as R ¹³ may have one or more substituents. Examples of the substituent include halogen atoms such as fluorine atoms, sulfonic acid groups, carboxyl groups, hydroxyl groups, amino Group, cyano group and the like.
The organic sulfonic acid represented by the general formula (V) is particularly nonafluorobutanesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, dodecylbenzenesulfonic acid or a mixture thereof from the viewpoint of the effect of improving the shape of the lower part of the resist pattern. Etc. are preferable.

The acid catalyst acts as a catalyst when the silane compound is hydrolyzed in the presence of water. The amount of the acid catalyst used is 1 to 1000 ppm, particularly 5 to 800 ppm, in the reaction system of the hydrolysis reaction. It is good to prepare so that it may become the range of.
The amount of water added is determined according to the hydrolysis rate to be obtained because the hydrolysis rate of the siloxane polymer changes accordingly.
In this specification, the hydrolysis rate of the siloxane polymer refers to the number of water molecules relative to the number of alkoxy groups (in moles) in the silane compound present in the reaction system of the hydrolysis reaction for synthesizing the siloxane polymer ( The number of moles) (unit:%).
In the present invention, the hydrolysis rate of the siloxane polymer is preferably 50 to 200%, and more preferably 75 to 180%. By setting the hydrolysis rate to be equal to or higher than the lower limit of the above range, good film quality in the silica-based film can be stably obtained. By making it to be not more than the upper limit of the above range, the storage stability of the coating solution for forming a silica-based film is improved.

Examples of the organic solvent in the reaction system of the hydrolysis reaction include methanol, ethanol, propanol, isopropanol (IPA), monohydric alcohols such as n-butanol, methyl-3-methoxypropionate, and ethyl-3-ethoxypropionate. Alkylcarboxylic acid esters such as ethylene glycol, diethylene glycol, propylene glycol, glycerin, trimethylolpropane, hexanetriol and other polyhydric alcohols, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether , Monoethers of polyhydric alcohols such as diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether or monoacetates thereof, methyl acetate, ethyl acetate, butyl acetate Esters such as acetone, methyl ethyl ketone, ketones such as methyl isoamyl ketone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, diethylene glycol dimethyl ether , Diethylene Recall diethyl ether, and the like diethylene glycol methyl ethyl polyhydric alcohol ethers which all alkyl-etherified hydroxyl of polyhydric alcohols such as ether.
The said organic solvent may be used independently and may be used in combination of 2 or more type.

  A siloxane polymer is obtained by performing a hydrolysis reaction in such a reaction system. The hydrolysis reaction is usually completed in about 5 to 100 hours, but in order to shorten the reaction time, it is preferable to heat in a temperature range not exceeding 80 ° C.

After completion of the reaction, a reaction solution containing the synthesized siloxane polymer and the organic solvent used for the reaction is obtained. The reaction solution can be made into the coating solution for forming a silica-based film of the present invention by adding or dissolving the above-mentioned basic compound. However, when adjusting to a preferable solid content concentration, a dilution solvent is further added. In addition, the diluted solution is used as a coating solution for forming a silica-based film.
As the diluting solvent, the same organic solvent used in the reaction system of the hydrolysis reaction for synthesizing the siloxane polymer can be used.
Moreover, when solid content concentration is low, you may concentrate and adjust solid content concentration.
Although SiO ₂ concentration in terms of the silica-based film-forming coating liquid of the present invention is not particularly limited, but is preferably about 1 to 30 wt%, more preferably about 5 to 25 wt%.

The silica-based coating-forming coating solution containing the reaction solution contains alcohol produced by the hydrolysis reaction of the silane compound. If the alcohol is excessively mixed, it may be removed by distillation under reduced pressure. The vacuum distillation has a degree of vacuum of 39.9 × 10 ^{2 to} 39.9 × 10 ³ Pa, preferably 66.5 × 10 ^{2 to} 26.6 × 10 ³ Pa, and a temperature of 20 to 50 ° C. within a range of 2 to 6 hours. It is better to do it.

  The coating liquid for forming a silica-based film of the present invention is suitably used for forming a silica-based film as a planarizing film or an interlayer insulating film. Examples of a method for forming a silica-based coating using the coating solution for forming a silica-based coating according to the present invention include a method in which the coating solution is applied onto a substrate and fired.

For example, first, a coating film is formed by applying a coating solution for forming a silica-based film on a substrate by a coating method such as spin coating, cast coating, or roll coating so as to have a predetermined film thickness. The thickness of the coating film is appropriately selected depending on the type of substrate to be applied.
It is then baked on a hot plate. The baking temperature at this time is about 80-500 degreeC, for example, More preferably, it is about 80-300 degreeC. Usually, the time required for this baking is 10 to 360 seconds, preferably 90 to 210 seconds. The baking process may be performed in a plurality of stages while changing the baking temperature.
Then, a silica-type film is obtained by baking at high temperature. The firing temperature is usually 350 ° C. or higher, preferably about 350 to 450 ° C.

  The coating liquid for forming a silica-based film of the present invention can form a silica-based film having a sufficiently low dielectric constant.

Example 1
170% 20% TMAH, 8.5 g of IPA, and 4.2 g of acetone were mixed and stirred to obtain a mixture A.
In a separate container, a solution (SiO ₂ ) obtained by hydrolytic condensation of CH ₃ Si (OCH ₃ ) ₃ : Si (OCH ₃ ) ₄ = 1: 1 (molar ratio) in a mixed solvent of IPA: acetone = 2: 1. 28% of 60% nitric acid was added to 47.1 g of the converted solid content (7%) and stirred. The aforementioned mixture A was added thereto with stirring. Thereafter, the mixture was further stirred for 3 hours to obtain a coating solution for forming a silica-based film.
The obtained coating liquid for forming a silica-based film was applied onto a silicon wafer by spin coating and heated on a hot plate at 80 to 150 to 200 ° C. for 1 minute each. Furthermore, it baked at 350 degreeC and formed the silica-type film.
The dielectric constant was measured and found to be 3.7.

(Example 2)
Hexamethyldisilazane (HMDS) 330 mg, IPA 8.2 g, and acetone 4.1 g were mixed and stirred to obtain a mixture B.
In another container, a solution obtained by hydrolytic condensation of CH ₃ Si (OCH ₃ ) ₃ : Si (OCH ₃ ) ₄ = 1: 1 in a mixed solvent of IPA: acetone = 2: 1 (SiO ₂ conversion solid content value 7 %) 160 μL of 60% nitric acid was added to 47.1 g and stirred. The above-mentioned mixture B was added thereto with stirring. Thereafter, the mixture was further stirred for 3 hours to obtain a coating solution for forming a silica-based film.
The obtained coating liquid for forming a silica-based film was applied onto a silicon wafer by spin coating and heated on a hot plate at 80 to 150 to 200 ° C. for 1 minute each. Furthermore, it baked at 350 degreeC and formed the silica-type film.
The dielectric constant was measured to be 4.7.

(Example 3)
Hexamethyldisilazane (HMDS) 66 mg, IPA 8.5 g, and acetone 4.2 g were mixed and stirred to obtain a mixture C.
In another container, a solution obtained by hydrolytic condensation of CH ₃ Si (OCH ₃ ) ₃ : Si (OCH ₃ ) ₄ = 1: 1 in a mixed solvent of IPA: acetone = 2: 1 (SiO ₂ conversion solid content value 7 %) 47.1 g of 60% nitric acid 32 μL was added and stirred. The above-mentioned mixture C was added there with stirring. Thereafter, the mixture was further stirred for 3 hours to obtain a coating solution for forming a silica-based film.
The obtained coating liquid for forming a silica-based film was applied onto a silicon wafer by spin coating and heated on a hot plate at 80 to 150 to 200 ° C. for 1 minute each. Furthermore, it baked at 350 degreeC and formed the silica-type film.
The dielectric constant was measured and found to be 5.2.

Example 4
Hexamethyldisilazane (HMDS) 33 mg, IPA 8.6 g, and acetone 4.3 g were mixed and stirred to obtain a mixture D.
In another container, a solution obtained by hydrolytic condensation of CH ₃ Si (OCH ₃ ) ₃ : Si (OCH ₃ ) ₄ = 1: 1 in a mixed solvent of IPA: acetone = 2: 1 (SiO ₂ conversion solid content value 7 %) 47.1 g of 60% nitric acid 16 μL was added and stirred. The above-mentioned mixture D was added there with stirring. Thereafter, the mixture was further stirred for 3 hours to obtain a coating solution for forming a silica-based film.
The obtained coating solution for forming a silica-based film was applied onto a silicon wafer by spin coating and heated on a hot plate at 80 to 150 to 200 ° C. for 1 minute each. Furthermore, it baked at 350 degreeC and formed the silica-type film.
The dielectric constant was measured to be 5.5.

(Comparative Example 1)
Spin a solution obtained by hydrolytic condensation of CH ₃ Si (OCH ₃ ) ₃ : Si (OCH ₃ ) ₄ = 1: 1 in a mixed solvent of IPA: acetone = 2: 1 (SiO ₂ conversion solid content value 7%) The coat was applied to a silicon wafer and heated on a hot plate at 80-150-200 ° C. for 1 minute each. Furthermore, it baked at 350 degreeC and formed the silica-type film.
The dielectric constant was measured and found to be 5.7.

[Thermal Desorption Spectroscopy (TDS)]
The organic components in the silica-based coatings formed by the silica-based coating forming coating solutions of Example 1 and Comparative Example 1 were detected and compared by TDS.
The results are shown in FIG. 1 and FIG. FIG. 1 shows the TDS analysis result of the silica-based coating formed with the coating solution of Example 1, and FIG. 2 shows the TDS analysis result of the silica-based coating formed with the coating solution of Comparative Example 1. is there.
As shown in FIG. 1 and FIG. 2, the silica-based film formed with the coating solution of Example 1 is M / z 28 (based on C ₂ H ₄ or the like) than the coating with the coating solution of Comparative Example 1. , 44 (based on C ₃ H ₈ etc.) increased, and M / z 17 (based on OH) and M / z 18 (based on H ₂ O) decreased.

FIG. 3 is a graph showing TDS results of a silica-based coating formed with the coating solution for forming a silica-based coating in Example 1. FIG. 4 is a diagram showing TDS results of a silica-based coating formed with a coating solution for forming a silica-based coating according to Comparative Example 1.

Claims (8)

  A coating liquid for forming a silica-based film, comprising a siloxane polymer, a basic compound, and an organic solvent.   The coating liquid for forming a silica-based film according to claim 1, wherein the basic compound is at least one selected from an organic ammonium salt and a silazane.   The said basic compound is 0.2-10 mass% with respect to a siloxane polymer, The coating liquid for silica type film formation of Claim 1 or 2 characterized by the above-mentioned. The siloxane polymer has the following general formula (I)
R _4-n Si (OR ′) _n (I)
Wherein R represents a hydrogen atom, an alkyl group or a phenyl group, at least one of R is an alkyl group or a phenyl group, R ′ represents an alkyl group or a phenyl group, and n is an integer of 2 to 4 Represents.)
The coating solution for forming a silica-based film according to any one of claims 1 to 3, which is a reaction product obtained by subjecting at least one selected from the silane compounds represented by the above to a hydrolysis reaction. The siloxane polymer is a hydrolyzate and / or a partial condensate of a mixture of RSi (OR ') ₃ and Si (OR') _4. 2. A coating solution for forming a silica-based film according to 1. It is RSi (OR ') ₃ : Si (OR') ₄ = 40: 60-90: 10 (molar ratio), The coating liquid for silica-type film formation of Claim 4 characterized by the above-mentioned.   The said siloxane polymer is 1000-3000 in mass mean molecular weight, The coating liquid for silica-type film formation in any one of Claims 1-6 characterized by the above-mentioned.   The coating liquid for forming a silica-based film according to any one of claims 1 to 7, wherein the siloxane polymer has a hydrolysis rate of 50 to 200%.

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