JPS63243174A - Coating liquid for forming high-purity silica coating film - Google Patents

Abstract

PURPOSE:To obtain the titled coating liquid giving a coating film having excellent crack resistance and suitable for insulation between wires on IC or surface- protection of IC, by compounding a polycondensation liquid of a specific tetraalkoxysilane compound and a polycondensation liquid of a specific dialkoxysilane compound. CONSTITUTION:The objective coating liquid having a crack-resistant film thickness of >=1mum can be produced by compounding (A) a reaction liquid (liquid A) obtained by polycondensation of a tetraalkoxysilane compound of formula I (R1-R4 are alkyl or aryl) or its low-condensation product (oligomer compound) in water and an organic solvent at 100-250 deg.C and (B) a reaction liquid (liquid B) produced by polycondensation of a dialkoxysilane compound of formula II (R5 and R6 are alkyl or aryl; R7 and R8 are H, alkyl or aryl; R7 and R8 are not H at the same time) in water and an organic solvent. The molar ratio of the Si in the liquid B to the Si in the liquid B is 0.1-1.3.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a coating liquid for forming a silica film.

More specifically, the present invention relates to a coating liquid for forming a novel silica film for insulation between wirings on an IC or for surface protection in semiconductor manufacturing, for example.

<Prior Art> Semiconductor technology is progressing rapidly -a>), and progress is being made in the development of high integration ratios and three-dimensional ICs through multilayer wiring. Against this background, the importance of flattening and smoothing technology has been highlighted. In particular, multilayer integration of interconnects and how to insulate between polysilicon and aluminum interconnects are important issues. Although it is necessary to manufacture it accurately, reliably, and at low cost, conventional vapor phase methods have drawbacks such as problems with flattening and reliability, and high costs. Regarding coating methods, polyimide, silica glass, and other materials have been proposed as materials, but polyimide-based materials have drawbacks in heat resistance, workability, etc., and reliability is a problem. Furthermore, it is known that silica glass-based materials generally use alkoxy silicates or condensates thereof (UK Patent No. 1076109). These alkoxysilicates are subjected to dehydration or dealcoholization using an acid or alkali catalyst. Later, as an improvement on these methods, a method using a reaction product of a halogenated silane, a carboxylic acid, and an alcohol (Japanese Patent Publication No. 1987-
16488, 52-20825), a method in which alkoxysilane is reacted in the presence of an acidic catalyst and acetic acids are used as a stabilizer for the product (JP-A-54-2
No. 4881) has been proposed. The maximum film thickness without cracking of the coating film obtained by these methods (hereinafter abbreviated as crack resistance) is at most 8°000 to 4.0°.
The limit is 0.00 Å, and if you try to obtain a film thicker than this by firing, cracks will occur in the film, so it is necessary to create a film with a crack resistance of 5.000 Å or more that is suitable as an interlayer insulating film or a surface protection film. It was difficult to obtain.

On the other hand, a method has been proposed in which a low condensate of trialkoxysilane is used as a seed to undergo condensation polymerization with dialkoxysilane or tetraalkoxysilane in the absence of a catalyst (Japanese Patent Publication No. 854/1985), but the final result is a gel It contains about 17% of acetic acid as a chemical inhibitor and cannot be used for the purposes of the present invention.

Under such circumstances, the inventors of the present application have already condensed a tetraalkoxysilane compound or a low condensate thereof at high temperature in the absence of a catalyst, thereby producing a highly pure film with a thickness of 5,000 Å.
A method for manufacturing the above coating liquid is provided. (Special application 1986
(No.-290848) However, it is still not completely satisfactory.

<Problems to be Solved by the Invention> Therefore, an object of the present invention is to provide a coating liquid for forming a silica film having a crack-resistant film thickness of 1 μtn or more, which has improved performance compared to the conventional one.

As a result of further research into the problems of the earlier application, the inventors of the present application have found that, in the presence or absence of a catalyst, without adding any components such as a stabilizer, It was discovered that a product obtained by condensation polymerization at high temperature is excellent as a coating solution for forming a silica film, and this led to the completion of the present invention.

That is, the present invention provides a tetraalkoxysilane compound represented by the general formula (a) OR+ R40-8i -OR2(a) Rs (wherein R1, R2, R3 and R4 represent an alkyl group or an aryl group) or a tetraalkoxysilane compound represented by the general formula (a) OR+ R40-8i -OR2(a) Low condensates (oligomer compounds),
from 100'C to 25°C without catalyst in the presence of water and organic solvents.
0'C! The reaction solution (hereinafter referred to as solution A) obtained by condensation polymerization is
) and the general formula (b) R50-8i-OR6(b) (In the formula, R5 and 16 represent an alkyl group or an aryl group. Also, R7 and R8 represent hydrogen, an alkyl group, or an aryl group. However, R7 and R8 are both hydrogen.) A reaction solution (hereinafter referred to as liquid B) obtained by condensation polymerization (hereinafter referred to as polymerization) of a dialkoxysilane compound represented by (except when R8 is hydrogen) in the presence of water and an organic solvent. The molar ratio of Si in liquid B to Si in liquid A is 0.1 to 1.8. This is a coating liquid for forming a silica film, characterized by containing the following:

The present invention will be specifically described below.

The alkoxysilicate compound represented by the general formula (a) used in the present invention refers to tetraalkoxysilane. That is, in the general formula (a), R1 to R4 represent an alkyl group or an aryl group, and the alkyl group has 1 carbon number.
-5 carbon atoms, and those having 1 to 8 carbon atoms are particularly preferred. R1 to R4 may be the same or different. Specifically, it represents a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, etc.

Preferred are methyl group, ethyl group, and isopropyl group.

Examples of the aryl group include phenyl group, tolyl group, and xylyl group. Preferably it is a phenyl group. General formula (a)
Examples of the alkoxysilicate compound represented by the above include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetrapentoxysilane, and tetraphenoxysilane.

Among these, tetramethoxysilane and tetraethoxysilane are particularly preferably used.

Low condensation products (oligomer compounds) of these tetraalkoxysilanes have an average degree of condensation n=5 to 6, such as MS-51 manufactured by Colcoat Co., Ltd., which is commercially available.
((Product name) Methyl silicate condensate), ES-40 (
(trade name) ethyl silicate condensate), etc. can be used.

In addition, the alkoxysilicate compound represented by the general formula (()) refers to dialkoxysilane. That is, the alkoxysilicate compound represented by the general formula (()
In the formula, R5 and R6 represent an alkyl group or an aryl group, and the alkyl group has 1 to 5 carbon atoms, and preferably has 1 to 3 carbon atoms. R5 and R
6 may be the same or different. Specifically, methyl group,
Represents an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, etc. Preferably a methyl group, an ethyl group,
It is an isopropyl group. Examples of the aryl group include phenyl, tolyl, and xylyl groups. Preferably it is a phenyl group. Further, R7 and R8 represent a hydrogen group, an alkyl group, or an aryl group, and the alkyl group has 1 to 5 carbon atoms, preferably one having 1 to 8 carbon atoms.

R7 and R8 may be the same or different.

However, the case where both R7 and R8 are hydrogen is excluded.

Specifically, it represents hydrogen, methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, etc. Preferred are hydrogen, methyl group, ethyl group, isopropyl group, and the like. Examples of the aryl group include phenyl group, tolyl group, xylyl group, etc., and phenyl group is preferable.

Examples of dialkoxysilicate compounds represented by general formula (b) include methyldimethoxysilane, dimethyldimethoxysilane, methylphenyldimethoxysilane, diphenyldimethoxysilane, methyljethoxysilane, dimethyljethoxysilane, methylphenyldimethoxysilane, and diphenyldimethoxysilane. Silane, methyldipropoxysilane, dimethyldipropoxysilane, methylphenyldipropoxysilane, diphenyldibutoxysilane,
Methyldiisopropoxysilane, dimethyldiisopropoxysilane, methylphenyldiisopropoxysilane,
Diphenyldiisopropoxysilane, methyldibutoxysilane, dimethyldibutoxysilane, methyldibutoxysilane, diphenyldibutoxysilane, methyldibentoxysilane, dimethyldibentoxysilane, methylphenyldipentoxysilane, Schifnil dibenoxysilane, methyldibutoxysilane, dimethylschiff,
Examples include tsukijisilane, methylphenyldiphenoxysilane, diphenyldiphenoxysilane, and the like. Among these, dimethyldimethoxysilane and dimethyljethoxysilane are particularly preferably used.

Next, if the amount of water used is small, the reaction will not proceed, and if it is large, problems such as gelation will occur. Generally, the molar ratio of both A liquid and B liquid to Si is 0.5 to 5, preferably 0.5 to 8.5. Since Part A is a polymer of tetraalkoxysilane, the molar ratio is preferably close to 2, and the organic solvent used may be any organic solvent in which the alkoxysilicate compound or its condensation polymer is soluble. Examples include alcohols such as methanol, ethanol, isolovanol, butanol, pentanol, hexanol, and cyclohexanol; THF; ethers such as ethyl ether and ethyl cellosolve; esters such as ethyl acetate;
Or aromatic hydrocarbons such as benzene and toluene.

Among these, alcohols such as isopropanol and ethanol are preferred. It is also possible to dilute with the above organic solvent after the nausea has stopped. The amount of organic solvent used is appropriately determined in relation to film thickness or flatness.

Generally, the mol is 3 to 8 times that of Si.

Hereinafter, a method for manufacturing liquid A and liquid B will be specifically explained.

The method for producing Solution A is to add predetermined amounts of alkoxysilane or its low condensate (oligomer), an organic solvent, and water to a glass or glass-lined stainless steel autoclave, and then heat and polymerize with stirring. The reaction temperature is 100~
250"C, preferably 120 to 200C.

If the temperature is below 100'C, the reaction rate is very slow and it is not preferred industrially. Furthermore, a high temperature of 250'C or higher is undesirable due to high pressure, which causes equipment problems.

The reaction time varies depending on the reaction temperature, but is usually preferably 4
It's around the time.

Next, the method for producing liquid B may be either a non-catalytic method or a catalytic method. The method carried out without a catalyst can be carried out in substantially the same manner as the method for producing liquid A.

On the other hand, in the method carried out under a catalyst, the production can be carried out in the same manner as in the case without a catalyst, except that the reaction temperature is 150°C or less, preferably θ~100"C. As the catalyst, an acid or alkali catalyst is used. Typical acid catalysts are hydrochloric acid, nitric acid, sulfuric acid, acetic acid, etc. Typical alkali catalysts are caustic soda, potassium hydroxide, ammonia,
These include tetramethylammonium hydroxide and pyridine. Although any catalyst can be used,
Since high purity is required for use in semiconductor applications, hydrochloric acid, acetic acid, ammonia, etc., which can be easily post-purified, are preferably used.

When a catalyst is used, in order to remove impurities such as chlorine mixed in from the catalyst, these are removed by general purification methods, such as distillation or ion exchange sesame oil, before use as B. is preferable. Note that it is more preferable to carry out the reaction without a catalyst from the viewpoint of preventing contamination of impurities from the catalyst.

The weight average molecular weight of the alkoxysilane polymer thus obtained (GPC method, standard polystyrene conversion) is 2.
,000 to 50,000, preferably a,oo
It is preferable that the alkoxysilane polymers of liquid A and liquid B, which are o to ao and ooo, have substantially the same M weight average molecule 1. If the weight average molecular weight is less than 2.000, it is not preferable because the film forming property deteriorates and the residual film rate decreases. 50
．． 000 or more, the viscosity of the coating liquid is too high to be practical.

Further, the degree of dispersion (weight average molecular weight/number average molecular weight) of the alkoxysilane polymer is preferably 20 or less. More preferably, it is 5 or less. More preferably it is 8 or less. If the degree of dispersion is 20 or more, it is unsuitable because it becomes difficult to obtain a uniform coating film.

Next, a method of mixing liquids A and B will be described.

Any mixing method may be used. For example, liquid A,
Solution B can be mixed by stirring at room temperature. Furthermore, since the B liquid does not solidify even if the organic solvent is removed, the organic solvent and catalyst may be removed by distillation and used as a liquid polymer (siloxane polymer).

The molar ratio of Si in liquid B and liquid A is as follows: the number of moles of Si in liquid A is 1
If it is smaller than 0.5.

When making a thick film of 1 μm or more, problems such as easy cracking occur. If it is larger than 1.8, a phenomenon similar to oil repelling occurs during film formation, making it difficult to obtain a clean film.

Therefore, preferably a range of 0.5 to 1.8 is used.

The coating solution for forming a silica film is the above alkoxysilane polymer, alcohols such as methanol, ethanol, isopropanol, butanol, pentanol, hexanol, cyclohexanol, ethers such as THF, diethyl ether, ethyl cellosolve, ethyl acetate, etc. or aromatic hydrocarbons such as benzene and toluene dissolved in an organic solvent. The concentration of the alkoxysilane polymer in the mixture of the organic solvent is appropriately determined so as to obtain the desired film thickness, but is generally 4% by weight or more, preferably 1% by weight or more. .

The film formation method is to apply the above coating solution by a commonly used spin code method or dipping method, then air dry or low temperature heating to sufficiently remove the solvent, and then heat to a temperature of 400'C or higher to remove unreacted alkoxy groups. In forming this film, which is carried out by decomposing the siloxane bond and forming a siloxane bond in this part, the heat treatment is carried out for 10 minutes or more, preferably 80 minutes or more, although it depends on the heat treatment temperature. At this time, it is preferable to perform the heat treatment in an atmosphere containing oxygen.

<Examples> The present invention will be specifically explained below using Examples, but the present invention is not limited to these in any way. The physical property values were measured as follows.

(1) Measurement of weight average molecular weight - The value measured by GPC (gel permeability chromatography) method was measured using Showa Denko Co., Ltd. (7) 5ho.
dex 5 standard S series (7) SL-
The measurement using the GPC method using IO2 expressed as a polystyrene (standard sphere) equivalent value was carried out using JASCO Corporation's TRI R (
JTAR-1 was used and Showa Denko Co., Ltd. was used as the column.
(D 5hodex A-80M (8φX500m)
And/or HaKF-802 (8φxa 00!!II
) was connected, RI was used as the extractor, and ethyl acetate was used as the eluent. Further, the flow rate was 1 m/min.

Based on a predetermined method, MN (number average molecule Q), Mw
(weight average molecular weight) and Q=lV1w/MN (dispersity) were determined.

(2) Method for measuring impurities The reaction product is placed in a platinum dish, the silicon is treated with an excess of 50 yen of hydrofluoric acid to convert it into silicon tetrafluoride, and then evaporated to dryness on a hot water bath. Dissolve the residue in water and take a predetermined amount of it in a flask and use it as a sample. For metal components, we used a high-frequency inductively coupled plasma (ICP) analyzer (ICPQ-1012) manufactured by Takashisha Co., Ltd.
The analysis was performed using

(8) Method for measuring film thickness The above reaction product was measured using Mikasa Spinner IH-
Drop a few drops onto a silicon wafer using an 860 model, and
A coating film was formed by spin coating at 0 to 8.50 Or pm for 15 seconds. This coated film was preliminarily baked at 100° C. for 10 minutes in a hot air circulation furnace, and then further baked at 450° C. for 80 minutes in a diffusion furnace. The film thickness was measured using a Talis chip manufactured by Rank Taylor and Bobson. Pinholes in the film formed in this way were measured using a pinhole detector manufactured by Atmel. After making scratches at the corners, a commercially available cellophane tape (registered trademark of Chiban Co., Ltd.) was applied and peeled off rapidly to determine the amount of peeling.

(5) Water used The water used was ultrapure water with a specific resistance of 15 megΩ-ω or more.

Example 1 (1) Liquid A synthesis method 208 g of tetraethyl orthosilicate (hereinafter abbreviated as TEO3) from which impurities were removed by distillation, 800 g of isopropanol (hereinafter abbreviated as IPA), and 86 f of water.
Place in an IL glass autoclave and warm. Reaction temperature 150℃! , under stirring for 4 hours at a reaction pressure of 1 s/- (400 r
pm) to polymerize.

After cooling, the polymer mixture was taken out from the reactor, and the molecular weight of the polymer was measured.

The molecular weight is Mw=6,100 MN=4,800 Q=
It was 1.27.

(2) Liquid B synthesis method 120 g of dimethyldimethoxysilane (hereinafter abbreviated as DMDMS) distilled to remove impurities, IPA 8
00g and 18g of water were placed in an IL glass autoclave and heated in the same manner. Reaction temperature 150℃ 1 reaction pressure IKg/
The mixture was heated under stirring (400 rpm) for 6 hours at d for polymerization. After cooling, the polymer mixture was taken out from the reactor, and the molecular weight of the polymer was measured. The molecular weight is lVLw 5.800,
MN: 4,100, Q = 1.41. The solvent was distilled off from this reaction solution at 50° C. under reduced pressure, and the solution was designated as Solution B.

(8) Preparation of coating liquid for film formation 100 parts by weight of liquid A and 15 parts by weight of liquid B (Si of liquid B and liquid A)
The molar ratio was 0.95') were stirred and mixed at room temperature.

(4) Measurement of physical properties The purity of this mixture was analyzed and the results are shown in Table 1. The viscosity of this mixture at this time was 3.2 CP, and the concentration of chloride ions was below the detection limit (ippm).

Table 1: Using this 1-coalescence mixture, a silicon wafer was spin-coded for 15 seconds at each bar rotation speed, then pre-fired for 200"0110 molecules, and further fired at 450°C for 80 minutes. Table 2 shows the measurement results of film thickness. The surface was a very smooth and homogeneous film. No cracks were observed, and the peeling test showed that the adhesion was good, and the pinhole measurement showed that the film had good adhesion.
As a result of the 5V withstand voltage test, no pinholes were observed.

Table 2 Example 2 (1) Liquid A synthesis method ES-40 ((trade name) ethyl silicate condensate, degree of condensation was calculated as a pentamer) 148.4 f, IP
800.5 fl of A and 21.6 F of water were placed in a 1 ton glass autoclave and heated. The reaction was carried out in the same manner as in Example 1 except for the reaction temperature: 120'C1, reaction pressure: 1 odor exposure. As a result of analyzing this solution, the viscosity was aCP, and the molecular weight was MW = 11.200 MN = 7,600 Q = 1.47
Met.

(2) B liquid synthesis method DMDMS 1201, IPA80ON, water 18f 1
Transfer to a T-glass autoclave and heat in the same manner. Reaction temperature: 150° C. Reaction pressure: 11 Q/m.

The mixture was heated and polymerized with stirring for 8 hours. Molecular weight Mw=12,
000 MN=8,700 Q=1.88. The solvent of this reaction solution was distilled off in the same manner as in Example 1, and the solution was designated as Solution B.

(8) Preparation of coating solution for film formation 100 parts by weight of solution A and 15 parts by weight of solution B (Si
The molar ratio was 0.95) were stirred and mixed at room temperature.

(4) Measurement of physical properties The purity of this mixture was analyzed and the results are shown in Table 8. Chlorine ions were below the detection limit (1p p ru ). The test results of the film formed in the same manner as in Example 1 are shown in the table.
4. The film surface was very smooth and homogeneous, no cracks were observed, and the adhesion and pinhole test results were also good.

Table-8 Table-4 Example 8 (1) Liquid A synthesis method MS-51 ((trade name) methyl silicate condensate) 11
5.2g (calculated as average pentamer χIPA800.5N
, 21.6N of water was taken into an autoclave, and the reaction temperature was 1.
The reaction was carried out in the same manner as in Example 1 at 20°C. Viscosity and molecule l are a, tcp%Mw=10,800 MN=7,80
0Q=1.88.

(2) B liquid synthesis method Methyldimethoxysilane (hereinafter abbreviated as MDMS)
), 800.5 g of IPA, and 18 g of water were added, and the mixture was heated and polymerized with stirring at a reaction temperature of 150° C. and a reaction pressure of 1 h/i for 8 hours. Molecular weight is Mw=11,000 MN
=7,800Q=1.41. The solvent of this reaction solution was distilled off under reduced pressure, and the solution was designated as Solution B.

(8) Preparation of Coating Solution for Film Formation Solution A 10 12.7 parts by weight of Solution B (81 mole ratio of Solution A and Solution B 1.0) were stirred and mixed at room temperature.

(4) Measurement of physical properties The results of purity analysis of this liquid mixture were as shown in Table 5. Chlorine ions were below the detection limit (ippm). Table 6 shows the test results of the film formed in the same manner as in Example 1. The film surface was very smooth and homogeneous, no cracks were observed, and the adhesion and pinhole test results were also good.

Table-5 Table-6 Actual 5ai Examples 4 to 6, Comparative Examples 1 to 8 Using liquids A and B of Example 2, B was added to 100Ii parts of liquid A.
Liquid 0.5, 10, 15, 25°801! Table 7 shows the results of a comparative study of the crack resistance of the film thickness when adding a certain amount.

Table-7 Example 7 (1) A liquid synthesis method Solution A synthesized in Example 2 was used.

(2) B liquid synthesis method DMDM5120g, I PA800Q and water 11F
and 0.1 cc of hydrochloric acid (86%) as a catalyst to IPA.
The 10-fold diluted solution was placed in a 1L glass autoclave and heated. Reaction temperature is 50″C1 Reaction pressure is IKt/
Polymerization was carried out by heating for 2 hours with stirring using clI.

After the reaction was completed, the solvent was repeatedly distilled off to remove the catalyst, hydrochloric acid. After the bath medium was distilled off five times, chloride ions were measured and found to be 199 m or less. Also, the molecular weight is Mw = 11
, 000 D, IN=7.400 Q=1.49
Met.

This reaction solution was designated as Solution B.

(8) Preparation of coating solution for film formation 100 parts by weight of liquid A and 1571 parts by weight of liquid B were stirred and mixed at room temperature. The Si molar ratio between liquid B and liquid A was 0.98.

(4) Measurement of physical properties The analysis result of the chloride ion concentration of this mixed solution was below the detection limit.

The test results for film formation are shown in Table 8.

The film surface was very smooth and homogeneous, no cracks were observed, and the results of the adhesion pinhole test were also good.

Table 8 <Effects of the Invention> The present invention provides coating liquid No. 444 for forming a silica film, which has extremely low impurities, good stability, less corrosion of the base material, and good crack resistance even in thick films. be done. This coating solution can be used not only as an insulating film but also as a protective film and a public base film.

Claims (7)

[Claims] (1) General formula (a) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (a) Tetraalkoxysilane compounds represented by (in the formula, R_1, R_2, R_3 and R_4 represent an alkyl group or an aryl group) or these A reaction solution obtained by condensing and polymerizing a low condensate (oligomer compound) at 100°C to 250°C in the presence of water and an organic solvent without a catalyst (hereinafter referred to as Solution A).
and general formula (b) ▲Mathematical formulas, chemical formulas, tables, etc.▼(b) (In the formula, R_5 and R_6 represent an alkyl group or an aryl group. Also, R_7 and R_8 represent hydrogen, an alkyl group, or an aryl group. However, this excludes the case where both R_7 and R_8 are hydrogen. S in liquid B relative to Si
A coating liquid for forming a silica film, characterized in that it contains i in a molar ratio of 0.1 to 1.8. (2) Liquid B contains dialkoxysilane compound without catalyst.
The coating liquid for forming a silica film according to claim 1, which is obtained by polycondensation at 00°C to 250°C. (3) The coating liquid for forming a silica film according to claim 1, wherein liquid B is obtained by polycondensing a dialkoxysilane compound at 0°C to 150°C in the presence of a catalyst. (4) The coating solution for forming a silica film according to claim 1, wherein the amount of water used relative to the tetraalkoxysilane compound is 0.5 to 5 in molar ratio relative to Si. (5) The coating liquid for forming a silica film according to claim 1, wherein R_1 to R_6 are alkyl groups having 1 to 5 carbon atoms. (6) The weight average molecular weight of liquid A and liquid B is 2,000 to 50
The coating liquid for forming a silica film according to claim 1, characterized in that it contains a siloxane-based polymer of . (7) The coating liquid for forming a silica film according to claim 6, wherein liquid A and liquid B contain a siloxane polymer having substantially the same weight average molecular weight.