JPH10226767A - Coating liquid for forming silica film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thick silica film which is free from cracks and smoothes the substrate with a good adhesion. SOLUTION: This coating liq. contains, as the essential ingredients, 8-30wt.% hydrotrialkoxysilane (A) represented by the formula: HSi(OR<1> )a (OR<2> )b (OR<3> )c (wherein R<1> , R<2> , and R<3> are each 1-4C alkyl; and a, b, and c are each an integer of 0-3 provided a+b+c=3), a polyalkoxysilane (B) represented by the formula: SiOd (OR<4> )e (wherein R<4> is methyl or ethyl; 0.4<=d<=1.2; and 1.6<=e<=3.2) in a molar ratio (in terms of Si) to ingredient A of 1 or lower, an org. solvent (C) boiling at 100-170 deg.C, an org. carboxylic acid (D), and a sulfonic acid catalyst (E).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating liquid for forming a silica film. This is a coating liquid that forms a silica coating that flattens the base with good adhesion and without cracks to substrates such as semiconductor substrates, glass, and ceramics. In particular, a silica coating which is suitably used for a flattening film or a protective film in a semiconductor element, a liquid crystal display element or the like is provided.

[0002]

2. Description of the Related Art In various fields, silica coatings are formed on various substrates using various silicates as raw materials by a sol-gel method. Among them, the method of forming a thin film by spin coating is an effective means in the manufacturing process because of its simplicity. Specifically, a method of obtaining a silica film by a spin coating method for a flattening film of a wiring step in a multilayer wiring process in a field of a VLSI manufacturing process, a protective film of a liquid crystal display element, and the like has been widely used (Japanese Patent Application Laid-Open No. Sho. 55-34258
No.). By the way, with the recent high integration and multifunctionalization of the VLSI, high demands have been made on these silica coatings. For example, in the flattening film application of semiconductor multilayer wiring devices, as the wiring becomes finer, a coating liquid with a sufficient film thickness is obtained in order to flatten the steps with different wiring widths in a single application. Is required. However, a method such as simply applying a liquid having a high silane concentration in the liquid has a disadvantage that cracks occur in the film due to shrinkage during curing, which leads to disconnection.

In order to improve this drawback, a coating solution using trifunctional alkyltrimethoxysilane as a silica source having a small shrinkage has been proposed (JP-A-63-241076).
No.). However, the resulting film has the disadvantage that it is unstable during the subsequent oxygen plasma treatment. Specifically, the energy of plasma
-C structure is susceptible to damage, and as a result, cracks occur, or outgases derived from organic substances are generated, or alkyl groups are damaged by oxygen plasma and cause moisture absorption, and aluminum wiring is likely to corrode. Since there is a problem, a process called etch back for selectively removing a portion irradiated with plasma after the film is formed is indispensable, and a decrease in productivity is inevitable.

As a coating solution having low shrinkage and not requiring etch back in a post-treatment step, a coating solution using hydrotrialkoxysilane having no organic functional group which causes outgassing as a silica source has been proposed ( Japanese Patent Application No. 7-25505
1). However, this solution has a problem that the potable time is short in order to exhibit performance because the condensation polymerization reaction of silane is fast. If the pot life can be extended, there is a method such as lowering the concentration of silane. However, a sufficient film thickness cannot be obtained from such a coating solution, and the flattening of the base is insufficient. There is a problem.

[0005]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned drawbacks of the prior art, and in particular, has a long pot life for exhibiting its performance, is capable of forming a thick film without cracks, and has a semiconductor, It has features such as good flatness of the base with good adhesion to various substrates such as glass and various ceramic substrates, and is particularly suitable for use as a flattening film or protective film in semiconductor devices and liquid crystal display devices. The purpose is to provide a coating solution for the silica coating to be obtained.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on these conventional problems, and as a result, have found that a silica film capable of forming a thick film without cracks and requiring no post-etch-back treatment is formed. In order to reduce the shrinkage during curing, it is preferable that the silica source used has a small number of alkoxy group functional groups, and S is easily decomposed in a later step.
After obtaining the knowledge that it is necessary to select a film having a structure in which an alkyl group is not directly bonded to a Si atom, in order to obtain a film containing no iC bond, a composition containing the following components as essential components was obtained. By using a composition containing the following components as essential components as a coating solution for forming a silica film, the composition has features such as a long pot life, no cracks even in a thick film, and excellent flattening of the base. A coating solution for forming a film was found. That is, the present invention provides: During the following general hydro birds formula alkoxysilane 8-30 ^{wt% HSi (OR 1) a (} OR 2) b (OR 3) c ( ^{wherein, R 1, R 2, R} 3 is an alkyl group of C1~4 , A,
b and c are each an integer of 0 to 3 and a + b + c
= 3) B. Polyalkoxysilane represented by the following chemical formula SiOd (OR ⁴ ) e (where R ⁴ is a methyl group or an ethyl group, and d and e are 0.4 ≦
d ≦ 1.2, 3.2 ≧ e ≧ 1.6) Organic solvent having a boiling point of 100 ° C. or more and 170 ° C. or less D. Organic carboxylic acid E. The coating liquid for forming a silica film has a sulfonic acid catalyst as an essential component, and the component B to the component A has a molar ratio of 1 or less in terms of Si.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below.
The component A used in the present invention is a hydrotrialkoxysilane represented by the following general formula. HSi (OR ¹ ) a (OR ² ) b (OR ³ ) c (wherein R ¹ , R ² and R ³ are a C1-4 alkyl group, a,
b and c are each an integer of 0 to 3 and a + b + c
= 3) Specifically, usually, trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane,
Hydrotrialkoxysilanes such as diethoxymonomethoxysilane and monomethoxydipropoxy are exemplified. Of these, trimethoxysilane, triethoxysilane, tripropoxysilane and tributoxysilane are preferred. The essential concentration of the component A in the entire coating liquid is from 8% by weight to 30% by weight. When the amount is less than 8% by weight, only a film having a small thickness can be obtained, and the flattening performance of the underlying step is low. Conversely, if it is more than 30% by weight,
A film with good in-plane uniformity of the film thickness cannot be obtained.

On the other hand, as a compound similar to the component A, an alkyl trialkoxysilane in which an alkyl group is directly bonded to a silicon element instead of H in a chemical structure is known, but when this is used instead of the component A, When the film obtained by coating is cured by heating, a clear heat loss is observed at 300 ° C. or higher. This is due to the thermal decomposition of the organic matter derived from the alkyl group bonded to the silicon element. In the later process of the device process, this causes corrosion of the metal of the wiring. Is preferably not contained. The component B of the present invention comprises:
It is a polyalkoxysilane represented by the following chemical formula. SiOd (OR ⁴ ) e (where R ⁴ is a methyl group or an ethyl group, and d and e are 0.4 ≦
d ≦ 1.2, 3.2 ≧ e ≧ 1.6)

The method for obtaining this compound is not particularly limited, and any one obtained by any of the methods is applicable. For example, a partial hydrolysis reaction of tetraalkoxysilane in the presence of an acid catalyst followed by a partial hydrolysis reaction And a method obtained by the above condensation reaction. In the above formula, d represents the average number of siloxane bonds formed by condensation per Si atom, and e represents the average number of alkoxy group residues per Si atom. If this method is used, d and e can be changed depending on the ratio of water to tetraalkoxysilane in the hydrolysis reaction, so that desired values of d and e can be selected according to the purpose. The component B exerts an effect on the development time of the performance of the coating liquid, that is, the extension of the pot life and the storage stability when used in combination with the component A. That is, the component B suppresses the high reactivity of the component A, particularly, the condensation polymerization reaction during storage of the liquid. In this case, it is necessary to suppress the reactivity of the B component itself, and therefore, it is effective to partially condense beforehand before mixing with other components to increase the molecular weight and reduce the number of functional groups. Required.

With respect to the values of the component B in the present invention, d is in the range of 0.4 ≦ d ≦ 1.2, and e is in the range of 1.6 ≦ e ≦ 3.2, and more preferably, d is in the range of 0.6 ≦ d ≦ 1.2. , E is
1.6 ≦ e ≦ 2.8. If a component having a value of d smaller than 0.4 and a value of e larger than 3.2 is used as the B component, the performance as a coating solution tends to change with the storage time of the solution, It lacks stability. Conversely, when the value of d is larger than 1.2 and the value of e is smaller than 1.6, defects due to the generation of foreign matter are likely to occur in the film obtained by coating, resulting in lack of uniformity. . A used together as an alkoxysilane in the present invention
In order not to reduce the effect of the component, the amount of the component B used is A
It is used in an amount equal to or less than equimolar in terms of mol based on the amount of Si atoms with respect to the use amount of the component. In general, a preferable concentration in the whole liquid is 3% by weight or more and 30% by weight or less. When the concentration of the component B is lower than this range, the storage stability of the coating solution is poor, and when the concentration is higher than this range, cracks easily occur in the film when the film is formed on an uneven base. The flattening of the step is likely to be incomplete.

The C component of the present invention has a boiling point of 100 ° C. or more and 17 ° C.
The organic solvent is not particularly limited as long as it is an organic solvent of 0 ° C. or less, more preferably 100 ° C. or more and 160 ° C. or less, as long as it can uniformly dissolve the components A, B, D, and E. Specifically, aliphatic alcohols such as 1-pentanol, 2-pentanol and 1-hexanol, butyl acetate, n-propyl propionate, ethyl n-butyrate, ethyl lactate, methyl valerate, and iso-ethyl valerate And the like; esters such as 2-hexanone, 3-hexanone and 2-heptanone; ether alcohols such as 2-methoxyethanol, 2-ethoxyethanol and 1-methoxy-2-propanol; propylene glycol-1-methyl. Ether esters such as ether-2-acetate and methyl 3-methoxypropionate, as well as toluene, xylene and the like can be used, and these solvents may be used as a mixture of two or more.

If the boiling point of these solvents is lower than 100 ° C., during spin coating, the solvent evaporates too quickly during the rotation of the substrate, so that the spreadability of the liquid on the substrate deteriorates, Coating with a large thickness becomes impossible. as a result,
Striation and in-plane non-uniformity of film thickness occur. Conversely, when a solvent having a boiling point higher than 170 ° C. is used, the solvent volatilizes slowly during rotation of the substrate during spin coating. Therefore, the reaction rate of the sol-gel reaction of the alkoxysilane, which proceeds with the volatilization of the solvent, becomes extremely low, and only a thin film can be obtained. From the viewpoint of such an effect, among the above solvents, 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-.
Propanol, 1-ethoxy-2-propanol is particularly preferred. Further, depending on the solubility of the components A, B, D and E, a solvent having a low boiling point such as methanol, ethanol or isopropyl alcohol may be mixed with the component C and used.
However, when these low-boiling solvents are used in combination, the content is desirably 20 parts by weight or less based on 100 parts by weight of the component C. If the amount is more than 20 parts by weight, volatilization of the solvent is accelerated, and it is difficult to obtain a film having a uniform thickness.

The amount of the component C can be determined according to the desired concentration of the silica component.
% By weight, preferably 35% by weight or more and 75% by weight or less. When the amount of the component C is 30% by weight or less, the spreadability of the liquid on the substrate during spin coating is poor, and the difference between the thickness of the coating at the center and the thickness of the periphery at the time of rotation is large.
The organic carboxylic acid of the component D of the present invention can be used in combination with the component E to form A
It is necessary for the acidolysis reaction of the alkoxy group of the alkoxysilanes of the component and the component B to proceed. Specifically, formic acid, oxalic acid, fumaric acid, maleic acid, glacial acetic acid,
Examples include acetic anhydride, propionic acid, and n-butyric acid.
Among them, oxalic acid, glacial acetic acid, and propionic acid are preferable from the viewpoint of the storage stability of the liquid, and the necessary amount is determined in the range of 0.2 to 1.5 equivalents of the sum of the alkoxy groups of the component A and the component B. Is 5% by weight or more and 30% by weight of the whole coating solution
It is used in the following range.

The component E is a catalyst necessary for the progress of the acid decomposition reaction between the alkoxy groups of the components A and B and the component D, and is used in combination with the component D. Specifically, in addition to inorganic acids such as sulfuric acid, organic sulfonic acids such as benzenesulfonic acid, paratoluenesulfonic acid, organic sulfonic acids such as naphthalene-1-sulfonic acid, and naphthalene-2-sulfonic acid are used. The addition amount is 0.1 to 5 parts by weight, based on 100 parts by weight of the total alkoxysilane to which the component A and the component b are added, and 0.01 to 2.5% by weight in all the components of the coating liquid.
Is necessary. Even when a liquid having a composition to which the amount of the component E is less than or not added is applied, no film is formed. Further, as a coating solution for a similar silica film, a coating solution obtained by hydrolyzing with alkoxysilane as a silica source and water is generally known. However, when water is used instead of component D, the reaction of component A is controlled. It is not practical, because it gels instantaneously at room temperature immediately after the addition of water. Therefore,
It is preferable that the water content of each component used is low or as low as possible, and the allowable water content is 0.5% by weight of the whole.
Preferably it is 0.1% by weight or less. When the content of water is larger than this range, problems such as a decrease in storage stability, a reduction in pot life, and a tendency to cause unevenness in film thickness at the time of application occur.

The present invention comprises the above-mentioned five components as main components. The compounding method is as follows. At room temperature, a lower carboxylic acid of component D and an acid of a reaction accelerator of component E are dissolved in a solvent containing component C.
It is common to add a trialkoxysilane of component A and a polyalkoxysilane of component B diluted with a solvent.
By stirring this mixture at room temperature for one day, a desired coating solution is obtained. The composition of the present invention thus obtained is applied to a substrate such as a ceramic or various metals by a spin coating method,
Next, after the solvent is volatilized, it is cured by heating at 400 ° C. or more, whereby a silica coating can be obtained. Hereinafter, the present invention will be described in more detail with reference to examples.

Synthesis Example 1 (Production of polymethoxysiloxane A) Tetramethoxysilane (Si (OC) was added to 37 g of methanol.
H ₃ ) ₄ ) 117 g were dissolved, and 0.05% hydrochloric acid 11.1 g was dissolved.
Was added to the mixture, and the mixture was heated at 65 ° C. for 2 hours to allow the hydrolysis and condensation reaction to proceed. Then, the temperature was further increased to 100 ° C., and the mixture was heated for 2 hours to remove methanol, thereby obtaining polymethoxysilane A. . The distribution of the number of siloxane bonds for the Si atom of A was measured by ²⁹ Si-NMR, and the average of the number of siloxane bonds per Si atom was determined from this.
Was 0.8. That is, the characteristic formula of A is SiO _0.8 (OC
H ₃ ) _2.4 . Based on this characteristic formula, the average molecular weight of A is defined as 115.7 in terms of 1 mol of Si atom,
It was applied to the calculation of the amount of raw materials charged in the following Examples and Comparative Examples.

Synthesis Example 2 (Production of Polymethoxysiloxane B) Tetramethoxysilane (Si (OC) was added to 37 g of methanol.
H _{3) 4)} was dissolved 117g of 0.05% hydrochloric acid 24.9
g was added and reacted under the same conditions as in Synthesis Example 1 to obtain polymethoxysilane B. The average of the number of siloxane bonds per Si atom was determined based on the measurement of the distribution of the number of siloxane bonds of Si atoms by ²⁹ Si-NMR.
It was 1.8. That is, the characteristic formula of B is SiO _1.8 (OC
H ₃ ) _0.4 . The average molecular weight of A was determined to be 69.7 in terms of 1 mol of Si atom based on this characteristic formula, and applied to the calculation of the raw material charge in the following Examples and Comparative Examples.

EXAMPLE 1 14.2 g of glacial acetic acid was added to 34.9 g of 2-ethoxyethanol.
And 0.1 g of concentrated sulfuric acid were added and stirred, 9.2 g (75 mmol) of hydrotrimethoxysilane and 6.9 g of polymethoxysiloxane A obtained in Synthesis Example 1 were added to 34.9 g of 2-ethoxyethanol ( 60 mmol) was added dropwise, and the mixture was stirred at room temperature for 1 day to obtain a coating solution. After the solution was further allowed to stand at room temperature for 2 days,
The solution was dropped on a silicon wafer substrate and spin-coated at a rotation speed of 3000 rotations / minute. 150 more soon
After volatilizing the solvent on a hot plate at 2 ° C. for 2 minutes, the mixture was heated and cured in an oven at 400 ° C. for 30 minutes. This liquid was applied to a siliceous stepped silicon substrate as shown in FIG. 1 under the same application and curing conditions. The characteristics of the obtained film, the step coverage characteristics, and the flattening performance were measured. The obtained coating solution was stored for 90 days in a low-temperature storage controlled at 4 to 7 ° C., and the solution after storage was applied under the same conditions as above, and the coating characteristics of the film thickness and the step were measured. The results are shown in the table.

Example 2 Glacial acetic acid 1 was added to 32.9 g of 1-methoxy-2-propanol.
While 8.1 g and 0.1 g of benzenesulfonic acid were added and stirred, 12.2 g (100 mm) of hydrotrimethoxysilane was added to 32.9 g of 1-methoxy-2-propanol.
ol) and 3.9 g (34 mmol) of polymethoxysilane A
A liquid obtained by diluting and mixing l) was added dropwise, and the mixture was stirred at room temperature for 1 day to obtain a coating liquid. Thereafter, the same type of substrate as in Example 1 was applied and cured by the same method to form a silica coating. The properties of the obtained film, the step coverage properties and the flattening performance are shown in the table.

Comparative Example 1 24.4 g of glacial acetic acid was added to 29.6 g of 2-ethoxyethanol.
And 0.1 g of concentrated sulfuric acid were added and stirred, and a solution obtained by diluting and mixing 16.5 g (135 mmol) of hydrotrimethoxysilane in 29.6 g of 2-ethoxyethanol was added dropwise, followed by stirring at room temperature for 1 day. To obtain a coating solution. Less than,
The same type of substrate as in Example 1 was applied and cured by the same method to form a silica coating. However, since the solution was gelled 5 days after the preparation of the solution, subsequent measurement of the film properties was impossible. The properties of the obtained film, the step coverage properties and the flattening performance are shown in the table.

Comparative Example 2 32.4 g of glacial acetic acid was added to 23.6 g of 2 -ethoxyethanol.
And 0.1 g of concentrated sulfuric acid were added and stirred, and 25.6 g of 2-ethoxyethanol was added to 20.5 g of tetramethoxysilane.
g (135 mmol) was added dropwise, and the mixture was stirred at room temperature for 1 day to obtain a coating solution. Hereinafter, Example 1
The same type of substrate was coated and cured in the same manner to form a silica coating. The properties of the obtained film, the step coverage properties and the flattening performance are shown in the table.

Comparative Example 3 Glacial acetic acid 1 was added to 36.3 g of 1-methoxy-2-propanol.
While 8.1 g and benzenesulfonic acid 0.1 g were added and stirred, 5.5 g (45 mmo) of hydrotrimethoxysilane was added to 36.3 g of 1-methoxy-2-propanol.
l) and 3.9 g (34 mmol) of polymethoxysilane A
A liquid obtained by diluting and mixing l) was added dropwise, and the mixture was stirred at room temperature for 1 day to obtain a coating liquid. Thereafter, the same type of substrate as in Example 1 was applied and cured by the same method to form a silica coating. The properties of the obtained film, the step coverage properties and the flattening performance are shown in the table.

Comparative Example 4 20.5 g of glacial acetic acid was added to 31.0 g of 2-ethoxyethanol.
And 0.1 g of paratoluenesulfonic acid, and stirred, and 12.2 g (100 mmol) of hydrotrimethoxysilane and 5.3 g (35 mmol) of tetramethoxysilane monomer were diluted and mixed with 31.0 g of 2-ethoxyethanol. The liquid was added dropwise, and the mixture was stirred at room temperature for one day to obtain a coating liquid. Thereafter, the same type of substrate as in Example 1 was applied and cured by the same method to form a silica coating. The properties of the obtained film, the step coverage properties and the flattening performance are shown in the table.

Comparative Example 5 14.2 g of glacial acetic acid was added to 36.2 g of 2-ethoxyethanol.
And 0.1 g of concentrated sulfuric acid, and stirred. Then, 9.2 g (75 mmol) of hydrotrimethoxysilane and 4.2 g of polymethoxysiloxane B obtained in Synthesis Example 2 were added to 36.2 g of 2-ethoxyethanol ( 60 mmol) was added dropwise, and the mixture was stirred at room temperature for 1 day to obtain a coating solution. Hereinafter, the same type of substrate was applied and cured in the same manner under the same conditions as in Example 1 to form a silica coating.
Since a large amount of foreign matter was generated, the characteristics of the film could not be measured.

[0025]

[Table 1]

(1) Using a film thickness meter Lambda Ace (manufactured by Dainippon Screen Mfg. Co., Ltd.), arbitrarily select nine places from the coating film on the substrate and measure the film thickness. Maximum value (or minimum value) of film thickness measurement data
Value obtained by dividing the absolute value of the difference between the average value and the average value (%) (3) After the film was formed on the SiO2 stepped substrate on the silicon wafer shown in the figure, the magnification was 10,000 times by SEM from the cross-sectional direction. Observation.
Number of cracks that can be recognized by observing the cross section of 10 irregularities having a width of 0.5 μm.

[0027]

As is clear from the table, according to the present invention, a coating film which forms a thick film without cracks and which flattens the base well and provides good storage stability is provided.

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[Procedure amendment]

[Submission date] April 16, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

FIG. 1 shows a siliceous stepped silicon substrate used in the examples.

Claims (1)

[Claims] 1. A. During the following general hydro birds formula alkoxysilane 8-30 ^{wt% HSi (OR 1) a (} OR 2) b (OR 3) c ( ^{wherein, R 1, R 2, R} 3 is an alkyl group of C1~4 , A, b, and c are all integers from 0 to 3, and a + b
+ C = 3) B. C. Polyalkoxysilane SiOd (OR ⁴ ) e represented by the following chemical formula (where R ⁴ represents a methyl group or an ethyl group, and d and e represent 0.4 ≦ d ≦ 1.2 and 3.2 ≧ e ≧ 1.6). Organic solvent having a boiling point of 100 ° C. or more and 170 ° C. or less D. Organic carboxylic acid E. A coating liquid for forming a silica film, comprising a sulfonic acid catalyst as an essential component, and a molar ratio of polyalkoxysilane of component B to hydrotrialkoxysilane of component A is 1 or less in terms of Si.