JP4684619B2 - Method for preparing silica-based coating forming coating solution and silica-based coating forming coating solution - Google Patents

Description

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

There is an increasing demand for higher integration of semiconductor devices. For example, there is a high interest in technology for achieving high speed and low power consumption of ULSI (ultra super LSI). In particular, reduction of wiring resistance / capacitance is important, and therefore, development of an interlayer insulating film having a low dielectric constant is required.
In Patent Document 1 below, a silica system containing (a) a condensate obtained by hydrolyzing trialkoxysilane in an organic solvent under an acid catalyst, and (b) a polyalkylene glycol and / or a terminal alkylated product thereof. A technique for forming a silica-based film having a dielectric constant of 3.2 or less using a coating solution for forming a film is described.
JP 2002-319582 A

  However, the silica-based film formed using the silica-based film-forming coating solution described in Patent Document 1 described above includes a step of removing the photoresist layer with a stripping solution, and a step of removing the stripping solution after ashing the photoresist layer. There is a problem that when the film is contacted with the stripping solution in the process of using it, the silica-based film tends to decrease in film thickness or increase in dielectric constant.

  The present invention has been made in view of the above circumstances, and provides a coating solution for forming a silica-based coating film that has a low dielectric constant and can form a silica-based coating that is unlikely to cause film loss or increase in dielectric constant due to a stripping solution. The purpose is to provide.

To achieve the above object, a silica-based film-forming coating liquid of the present invention, the reaction product obtained by hydrolysis of a silane compound consisting of (A) an alkyltrialkoxysilane and trialkoxysilanes, (B 1) one or more selected from the group consisting of polyalkylene glycol and its terminal alkylated product , and (C) tetraalkylammonium hydroxide .
The method for preparing a coating solution for forming a silica-based film of the present invention includes a reaction product obtained by hydrolyzing a silane compound composed of alkyltrialkoxysilane and trialkoxysilane in the presence of water and an acid catalyst. After obtaining the reaction solution, one or more selected from the group consisting of polyalkylene glycol and its terminal alkylated product, and tetraalkylammonium hydroxide are added and mixed.

  According to the coating liquid for forming a silica-based film of the present invention, it is possible to form a silica-based film that has a low dielectric constant and is unlikely to cause film reduction or increase in dielectric constant due to the stripping solution.

<(A) component>
The coating solution for forming a silica-based film of the present invention contains, as the component (A), a reaction product obtained by hydrolyzing a silane compound composed of alkyltrialkoxysilane and trialkoxysilane.
A siloxane polymer is produced by the hydrolysis reaction. The reaction product includes a low molecular weight hydrolyzate and a condensate (siloxane oligomer) produced by a dehydration condensation reaction between molecules simultaneously with the hydrolysis reaction. May also be included. The component (A) in the present invention refers to the entire product including these hydrolysates or condensates in addition to the siloxane polymer.
Although the mass average molecular weight (Mw) (polystyrene conversion standard by gel permeation chromatography, the same applies hereinafter) of the reaction product is not particularly limited, 1000 to 10000 is preferable, and a more preferable range is 1000 to 5000.

As the alkyltrialkoxysilane, it is preferable to use one or more selected from alkyltrialkoxysilanes represented by the following general formula (I).
R ¹ Si (OR ² ) _a (OR ³ ) _b (OR ⁴ ) _c (I)
In the formula, R ¹ is a linear or branched alkyl group having 1 to 20 carbon atoms, preferably a linear or branched alkyl group having 1 to 4 carbon atoms.
R ² , R ³ , and R ⁴ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms. In particular, an alkyl group having 1 or 2 carbon atoms is preferred from the viewpoint of hydrolysis rate.
a, b, and c are integers that satisfy 0 ≦ a ≦ 3, 0 ≦ b ≦ 3, 0 ≦ c ≦ 3, and satisfy the condition of a + b + c = 3.

  Specific examples of the alkyltrialkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltripentyloxysilane, ethyltrimethoxysilane, ethyltripropoxysilane, ethyltripentyloxysilane, propyltrimethoxy Silane, propyltriethoxysilane, propyltripentyloxysilane, butyltrimethoxysilane, butyltriethoxysilane, butyltripropoxysilane, butyltripentyloxysilane, methylmonomethoxydiethoxysilane, ethylmonomethoxydiethoxysilane, propylmono Methoxydiethoxysilane, butylmonomethoxydiethoxysilane, methylmonomethoxydipropoxysilane, methylmonomethoxydipentyloxysilane , Ethyl monomethoxy dipropoxy silane, ethyl monomethoxy dipentyloxy silane, propyl monomethoxy dipropoxy silane, propyl monomethoxy dipentyl oxy silane, butyl monomethoxy dipropyloxy silane, butyl monomethoxy dipentyl oxy silane, methyl methoxy ethoxy propoxy silane , Propylmethoxyethoxypropoxysilane, butylmethoxyethoxypropoxysilane, methyl monomethoxymonoethoxymonobutoxysilane, ethylmonomethoxymonoethoxymonobutoxysilane, propylmonomethoxymonoethoxymonobutoxysilane, butylmonomethoxymonoethoxymonobutoxysilane, etc. Can be mentioned. Of these, methyltrimethoxysilane and methyltriethoxysilane are preferable from the viewpoint of hydrolysis rate.

As the trialkoxysilane, it is preferable to use one or more selected from trialkoxysilanes represented by the following general formula (II).
HSi (OR ⁵ ) _d (OR ⁶ ) _e (OR ⁷ ) _f (II)
R ⁵ , R ⁶ , and R ⁷ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms. In particular, an alkyl group having 1 or 2 carbon atoms is preferred from the viewpoint of hydrolysis rate.
d, e, and f are integers that satisfy 0 ≦ d ≦ 3, 0 ≦ e ≦ 3, and 0 ≦ f ≦ 3, and satisfy the condition of d + e + f = 3.

Specific examples of the trialkoxysilane include trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, tripentyloxysilane, dimethoxymonoethoxysilane, diethoxymonomethoxysilane, dipropoxymonomethoxysilane, dipropoxymono Ethoxysilane, dibutoxymonomethoxysilane, dipentyloxymonomethoxysilane, dipentyloxymonoethoxysilane, dipentyloxymonopropoxysilane, methoxyethoxypropoxysilane, butoxyethoxypropoxysilane,
Examples thereof include monopropoxydimethoxysilane, monopropoxydiethoxysilane, monobutoxydimethoxysilane, and monopentyloxydiethoxysilane. Of these, trimethoxysilane and triethoxysilane are preferable from the viewpoint of hydrolysis rate.

The reaction product can be obtained by a method in which a silane compound composed of one or more alkyltrialkoxysilanes and one or more trialkoxysilanes is hydrolyzed and condensed in the presence of an acid catalyst and water.
The ratio of alkyltrialkoxysilane and trialkoxysilane in the silane compound used for the hydrolysis reaction is preferably such that the molar ratio of alkyltrialkoxysilane / trialkoxysilane is in the range of 10/90 to 90/10. A preferred range is 20/80 to 80/20, and a more preferred range is 30/70 to 70/30.

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 such as compounds represented by the following general formula (III) are particularly preferable.

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

In the general formula (III), the hydrocarbon group as R is preferably a hydrocarbon group having 1 to 20 carbon atoms, and this hydrocarbon group may be saturated or unsaturated, linear, It may be either branched or annular.
When the hydrocarbon group of R is cyclic, for example, an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, and an anthryl group is preferable, and among them, a phenyl group is 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.
The hydrocarbon group as R may have one or more substituents, and examples of the substituent include halogen atoms such as fluorine atoms, sulfonic acid groups, carboxyl groups, hydroxyl groups, amino groups. And a cyano group.
As the organic sulfonic acid represented by the general formula (III), nonafluorobutanesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, in particular, from the viewpoint of the shape improvement effect at the bottom of the resist pattern formed on the silica-based film, Dodecylbenzenesulfonic acid or a mixture thereof is preferred.

The acid catalyst acts as a catalyst when hydrolyzing the silane compound in the presence of water. The amount of the acid catalyst to be used is, for example, 1 to 1000 ppm, particularly 5 in the reaction system of the hydrolysis reaction. What is necessary is just to prepare so that it may become in the range of -800 ppm.
The amount of water added is preferably in the range of 1.5 to 4.0 moles per mole of the total amount of silane compounds used. The acid catalyst may be added after adding water, or may be added as an acid aqueous solution obtained by previously mixing the acid catalyst and water.

The reaction system for the hydrolysis reaction may contain an organic solvent.
Specific examples of the organic solvent include methanol, ethanol, propanol, isopropyl alcohol, monohydric alcohols such as n-butanol, alkylcarboxylic acids such as methyl-3-methoxypropionate and ethyl-3-ethoxypropionate. Polyesters such as acid esters, ethylene glycol, diethylene glycol, propylene glycol, glycerin, trimethylolpropane, hexanetriol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol Monoethers of polyhydric alcohols such as monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether or the like, monoacetates thereof, methyl acetate, ethyl acetate, butyl acetate, etc. Esters, 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 glycol Diethyl A Le, and the like such as 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.

  Here, in order to improve the storage stability and film forming property of the coating solution, it is more preferable to use alkylene glycol dialkyl ether as the organic solvent.

<(B) component>
The coating liquid for forming a silica-based film of the present invention contains at least one selected from the group consisting of polyalkylene glycol and its terminal alkylated product as component (B).
1-5 are preferable and, as for carbon number of the alkylene group in polyalkylene glycol, 1-3 are more preferable. Specific examples include lower alkylene glycols such as polyethylene glycol and polypropylene glycol.
The terminal alkylated product of polyalkylene glycol is obtained by alkoxylating one or both hydroxyl groups of polyalkylene glycol with an alkyl group. The alkyl group used for terminal alkoxylation may be a linear or branched alkyl group, and the number of carbon atoms thereof is preferably 1 to 5, and more preferably 1 to 3. In particular, a linear alkyl group such as a methyl group, an ethyl group, or a propyl group is preferable.

(B) 100-10000 are preferable, as for the mass mean molecular weight (Mw) of a component, 200-5000 are more preferable, and 400-4000 are further more preferable. By making Mw of (B) component below the upper limit of the said range, favorable applicability | paintability is obtained without impairing the compatibility in a coating liquid, and the film thickness uniformity of a silica type coating improves. By setting it to be equal to or higher than the lower limit of the above range, the silica-based film can be made porous, and a low dielectric constant can be achieved.
The amount of component (B) used is preferably 25 to 200% by mass, more preferably 30 to 150% by mass, and more preferably 50 to 120% by mass with respect to the solid content (SiO ₂ equivalent mass) in the coating solution for forming a silica-based film. % Is more preferable. The dielectric constant of the silica-based coating can be lowered by setting the amount of component (B) used to be equal to or higher than the lower limit of the above range, and a silica-based coating having sufficient strength can be obtained by setting the amount to be lower than the upper limit of the above range. be able to.

<(C) component>
The coating liquid for forming a silica-based film of the present invention preferably contains tetraalkylammonium hydroxide as the component (C). Tetraalkylammonium hydroxide is represented by the following general formula (IV).
R ′ ₄ N ⁺ OH ⁻ (IV)
(In the formula, R ′ represents an alkyl group.)
The alkyl group as R ′ is preferably a linear or branched alkyl group having 1 to 5 carbon atoms, and more preferably 1 to 3 carbon atoms.
By including the component (C) in the coating liquid for forming a silica-based film, the formed silica-based film can be further reduced in dielectric constant.

Component (C) is preferably used in an amount of 0.0005 to 0.02 mass% (5-200 ppm), based on the solid content (SiO ₂ equivalent mass) in the coating solution for forming a silica-based film, 0.005 to 0.02 mass% (50-200 ppm) is more preferable, and 0.005-0.015 mass% (50-150 ppm) is still more preferable. (C) By making the usage-amount of a component more than the lower limit of the said range, the effect which reduces a dielectric constant is acquired, and the favorable temporal stability of a coating liquid is acquired by making it below the upper limit of the said range. .

  As a method for preparing a coating solution for forming a silica-based film of the present invention, for example, a silane compound comprising an alkyltrialkoxysilane and a trialkoxysilane is first added in the presence of water, the above acid catalyst, and preferably an organic solvent. By carrying out the decomposition reaction, a reaction solution containing the reaction product (A) is obtained. By adding the component (B) and preferably the component (C) to this reaction solution, and further adding a diluting solvent as necessary, a coating solution for forming a silica-based film is obtained.

The reaction solution containing the reaction product (A) can be used as it is for the preparation of a coating solution for forming a silica-based film, but the alcohol generated by hydrolysis is removed before adding any component other than the component (A). It is preferable. By removing the alcohol generated by the hydrolysis, storage stability and film formability can be improved. This alcohol is preferably removed by distillation under reduced pressure. The vacuum distillation is performed at a degree of vacuum of 39.9 × 10 ^{2 to} 39.9 × 10 ³ Pa (about 30 to 300 mmHg), preferably 66.5 × 10 ^{2 to} 26.6 × 10 ³ Pa (about 50 to 200 mmHg), It is preferable to carry out at a temperature of 20 to 80 ° C.

When the component (C) is added to the reaction solution, the component (C) may be added in a state of being dissolved in an appropriate solvent. Although the solvent in that case is not particularly limited, for example, an appropriate one can be used from those listed as the organic solvent to be included in the reaction system of the hydrolysis reaction.
Although the said dilution solvent is not specifically limited, For example, an appropriate thing can be used from what was mentioned as an organic solvent contained in the reaction system of the said hydrolysis reaction. In order to improve the storage stability and film formability of the coating solution, it is more preferable to use alkylene glycol dialkyl ether as a diluent solvent. It is preferable to adjust the usage-amount of this dilution solvent so that the solid content density | concentration of the coating liquid for silica-type film formation may become a preferable range.
The solid content of the silica-based film-forming coating solution (SiO ₂ concentration in terms) is not particularly limited, but is preferably about 1 to 30 wt%, more preferably about 5 to 25 wt%.

  The coating liquid for forming a silica-based film of the present invention is suitably used for forming a silica-based film as an interlayer insulating film. As a method of forming a silica-based film using the coating liquid for forming a silica-based film of the present invention, a normal SOG method can be used.

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. What is necessary is just to select the thickness of a coating film suitably.
It is then baked on a hot plate. By this baking treatment, the organic solvent in the coating film is volatilized, and further a reaction occurs between the molecules of the siloxane polymer to proceed the polymerization. The baking temperature at this time is about 80-500 degreeC, for example, More preferably, it is about 80-300 degreeC. 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.

According to the coating liquid for forming a silica-based film of the present invention, a silica-based film having a low dielectric constant can be formed. As one of the actions of decreasing the dielectric constant, it is conceivable that the silica-based film is made porous by containing the component (B).
According to the present invention, for example, it is possible to form a low dielectric constant silica-based film having a dielectric constant value of 3 or less, preferably 2.8 or less, measured by a measurement method described in Examples described later. .

In addition, the silica-based coating formed using the coating solution for forming a silica-based coating according to the present invention has good resistance to the stripping solution used for removing the resist film, and film thickness reduction or dielectric property due to contact with the stripping solution is good. An increase in rate is suppressed.
Among these stripping solutions, hydroxylamines, primary, secondary or tertiary aliphatic amines, alicyclic amines, aromatic amines, heterocyclic amines, aqueous ammonia, and lower alkyl quaternary ammoniums Good resistance to amine-based stripping solution containing salt, particularly amine-based stripping solution containing hydroxylamine.

Example 1
To 1432.8 g of propylene glycol dimethyl ether, 147.6 g of triethoxysilane and 122.4 g of methyltriethoxysilane were added and stirred. Subsequently, 97.2 g of pure water and 120 μl of nitric acid having a concentration of 60% by mass were added and stirred for 3 hours. Then, the reaction solution containing a reaction product was obtained by making it react at room temperature for 10 days. The mass average molecular weight (Mw) of the reaction product was 1600.
The obtained reaction solution was distilled under reduced pressure at 40 ° C. at 100 mmHg or less, and concentrated until the solid concentration was 12% by mass.
Next, 108 g (100% by mass with respect to the solid content in the reaction solution) of polypropylene glycol having a mass average molecular weight of 400 (product name; Newpol PP-400) manufactured by Sanyo Chemical Industries, Ltd. was added to the concentrated reaction solution.
Further, 12 g of a solution containing tetramethylammonium hydroxide (TMAH) having a concentration of 900 ppm in isopropyl alcohol (IPA) (TMAH concentration of 100 ppm relative to the solid content in the reaction solution) was added.
Further, 780 g of propylene glycol dimethyl ether was added and stirred to obtain a coating solution for forming a silica-based film.

The silica-based film-forming coating solution obtained above was applied onto a silicon wafer by spin coating, and baked on a hot plate. The heating conditions in the baking treatment were multi-stage baking at 80 ° C. for 3 minutes, then at 150 ° C. for 3 minutes, and then at 300 ° C. for 3 minutes. Then, it baked at 400 degreeC in the air (in nitrogen atmosphere), and obtained the silica type film with a film thickness of 2500cm.
When the dielectric constant of the obtained silica-based coating was measured using a mercury probe CV measuring apparatus (manufactured by SSM Japan, product name: SSM495), the dielectric constant was 2.30.
Furthermore, the silica-based film obtained above was immersed in a stripping solution containing hydroxylamines kept at 70 ° C. for 30 minutes. When the film reduction (difference between the film thickness before immersion and the film thickness after immersion) was examined, it was 331 mm. Moreover, after immersion, it was 5.67 when the dielectric constant was measured like the above.

(Comparative Example 1)
A coating solution for forming a silica-based film was prepared by changing the silane compound in Example 1 to triethoxysilane.
That is, 73.9 g of triethoxysilane was dissolved in 799.0 g of ethylene glycol dimethyl ether and stirred. Subsequently, 24.2 g of pure water and 3.2 μl of nitric acid having a concentration of 60% by mass were added and stirred for 3 hours. Then, the reaction solution containing a reaction product was obtained by making it react at room temperature for 6 days. The mass average molecular weight (Mw) of the reaction product was 1300.
The obtained reaction solution was distilled under reduced pressure at 120 to 140 mmHg or less at 40 ° C., and concentrated until the solid content concentration became 8% by mass.
Next, 100% by mass of both terminal methylated products of polyethylene glycol having a mass average molecular weight of 200 was added to the solid content in the reaction solution.
Further, by adding a solution containing tetramethylammonium hydroxide (TMAH) with a concentration of 50 ppm in isopropyl alcohol (IPA) so that the TMAH concentration with respect to the solid content in the reaction solution is 5.5 ppm, and stirring. A coating liquid for forming a silica-based film was obtained.

Using the obtained coating liquid for forming a silica-based film, a silica-based film having a film thickness of 2500 mm was formed on a silicon wafer in the same manner as in Example 1.
When the dielectric constant of the obtained silica-based coating was measured in the same manner as in Example 1, it was 2.5.
Further, this silica-based film was immersed in a stripping solution in the same manner as in Example 1. When the film reduction and dielectric constant after immersion were examined, the film reduction was 1004 mm and the dielectric constant was 10.

As shown in the above results, a silica-based film having a low dielectric constant was obtained in both Example 1 and Comparative Example 1.
The silica-based coating obtained in Example 1 has a smaller film loss when immersed in a stripping solution than the silica-based coating obtained in Comparative Example 1, and the dielectric constant due to immersion in the stripping solution is smaller. The rise was small.

Claims (6)

(A) a reaction product obtained by hydrolyzing a silane compound comprising alkyltrialkoxysilane and trialkoxysilane ;
(B) one or more selected from the group consisting of polyalkylene glycols and terminal alkylated products thereof , and
(C) A coating liquid for forming a silica-based film, comprising tetraalkylammonium hydroxide .   2. The coating liquid for forming a silica-based film according to claim 1, wherein the addition amount of the component (B) is 25 to 200 parts by mass with respect to 100 parts by mass of the solid content of the component (A).   The coating liquid for forming a silica-based film according to claim 1 or 2, wherein the component (B) has a mass average molecular weight of 100 to 10,000. The addition amount of the said (C) component is 5-200 ppm with respect to solid content of the said (A) component, The application | coating for silica-type film formation of any one of Claims 1-3 characterized by the above-mentioned. liquid. A reaction solution containing a reaction product is obtained by hydrolyzing a silane compound comprising alkyltrialkoxysilane and trialkoxysilane in the presence of water and an acid catalyst, and then comprising a polyalkylene glycol and its terminal alkylated product. A method for preparing a coating liquid for forming a silica-based film, comprising adding and mixing one or more selected from the group and tetraalkylammonium hydroxide. 6. The method for preparing a coating solution for forming a silica-based film according to claim 5, wherein the hydrolysis reaction is carried out in the presence of water, an acid catalyst, and an organic solvent.