JPH069926A - Production of coating solution for forming silica film - Google Patents

Abstract

PURPOSE:To obtain the title soln. which can form a high-purity silica film excellent in etching processibility and crack resistance and useful as an insulation layer for a semiconductor by mixing a soln. contg. a specific silica-based condensate with a soln. contg. a specific silica-based compd. CONSTITUTION:The process comprises: step (1) wherein an alkyl silicate condensate of the formula wherein R1 to R5 are each independently alkyl or alkoxyalkyl; R6 is alkyl, alkoxy, etc.; m is an integer of 2 or higher; and 0<=n<m, is mixed with a 1-18C carboxylic acid in an amt. of from 0.2mol to 2-(<m+n>-1)/<m+n> mol wherein <m+n> is the mean degree of condensation, based on 1g atom of silicon in the condensate; step (2) wherein 1mol of a tetraalkoxysilane of the general formula: Si(OR7)4 wherein R7 is alkyl, etc., is mixed with 2mol or more of water; step (3) wherein two solns. obtd. in the steps (1) and (2) are each brought into contact with an ion exchange resin; and step (4) wherein both solns. obtd. in the step (3) are mixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a coating liquid for forming a silica film. More specifically, the present invention relates to a method for producing a coating liquid for forming a silica film of high purity, which is optimum for forming an insulating film for semiconductors by a coating film method.

[0002]

2. Description of the Related Art As a method of forming an insulating film for a semiconductor, a vapor phase growth method and a coating film method are known. By the way, in recent years, the degree of integration of semiconductors has become more sophisticated, and along with this, the line width of wiring has become narrower and the gap between them has become narrower.
In order to realize a fine wiring pattern, it is necessary to form an insulating film having a flat surface on a substrate having complicated irregularities. However, the vapor phase growth method has a problem that it is difficult to form a uniform and flat film when used on a surface having irregularities. On the other hand, the coating film method can be applied to a surface having irregularities and is an excellent method.

The important characteristics required for an insulating film for semiconductors are excellent etching processing characteristics and crack generation characteristics. Etching characteristics are characteristics relating to the denseness of the film, the film having poor denseness, in other words, the porous film becomes fragile, and the control during etching becomes ineffective because the etching progresses extremely rapidly, Precise etching becomes impossible. Further, in order to form an insulating film, it is necessary to apply a coating liquid for forming a silica film and then bake it. However, in order to flatten the surface irregularities and improve the insulating property, the film thickness should be thicker than about 4000 angstroms. Even in this case, it is necessary that cracks do not occur during firing, that is, the crack generation characteristics are excellent.

Japanese Unexamined Patent Publication No. 61-55164 discloses a method of using a silica-based condensate obtained by reacting a specific alkylsilicate condensate with a carboxylic acid as a coating liquid for forming a silica film. However, this method has a problem in that the etching processing characteristics are insufficient.

By the way, the silica coating forming coating liquid is required to have an extremely high purity. Among impurities that reduce purity, cationic substances mainly containing metal ions and anionic substances generated from acids are substances that should be removed with particular care. This is because the metal ions reduce the dielectric strength of the semiconductor insulating film, and the anionic substance corrodes aluminum on the semiconductor substrate, shortening the life of the semiconductor. However, in the coating liquid for forming a silica coating film obtained by the conventional method, in addition to the metal ions contained in the raw material, the metal ions eluted from the manufacturing apparatus material and the acid used during the manufacturing process are derived. There is a problem that the anionic substance is inevitably mixed and causes the above-mentioned inconvenience.

[0006]

In view of the present situation, the problem to be solved by the present invention is that it has excellent etching processing characteristics and does not cause cracks even when formed into a thick film of about 4000 angstroms or more. The present invention is to provide a high-purity coating liquid for forming a silica film, which can be used as an insulating film for semiconductors having excellent generation characteristics and which has an extremely low ionic substance content.

[0007]

The present inventors have arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention relates to a method for producing a coating liquid for forming a silica film, which includes the following steps (1) to (3). (1) Alkyl silicate condensate represented by the following general formula (A) and silicon 1 in the alkyl silicate condensate
0.2 mol or more per gram atom and (2-(<m + n
> -1) / <m + n>) moles (where <m + n>
Represents the average degree of condensation. (2) a tetraalkoxysilane represented by the general formula Si (OR ₇ ) ₄ (wherein R ₇ represents an alkyl group or a phenyl group) and the tetraalkoxy. Step of mixing 2 moles or more of water per mole of silane (3) Step of contact-treating the solution obtained in (1) above and the solution obtained in (2) above with an ion exchange resin (In the formula, R _{1 to} R ₅ are the same or different alkyl groups or alkoxyalkyl groups, R ₆ is an alkyl group, an alkoxy group or an alkoxyalkyl group, and m is an integer of 2 or more,
n represents an integer of 0 ≦ n <m. )

The details will be described below. In the step (1) of the present invention, the alkyl silicate condensate represented by the general formula (A) and 0.2 mol or more per gram atom of silicon in the alkyl silicate condensate and (2-(<m +
n> -1) / <m + n>) mol (where <m + n
> Represents the average degree of condensation. ) Is a step of mixing the carboxylic acid having 1 to 18 carbon atoms.

The alkyl silicate condensate represented by the general formula (A) is removed by hydrolyzing a tetraalkoxysilane monomer with water, or by hydrolyzing an alkoxychlorosilane monomer or a tetrachlorosilane monomer with water and then reacting with an alcohol. A method of carrying out a hydrogen chloride reaction, a tetraalkoxysilane monomer, obtained by a method of hydrolyzing by adding a smaller number of moles of a monoalkyltrialkoxysilane monomer, and a commercially available alkyl silicate condensate,
It may be used as it is or after being further condensed. In addition, R
The carbon number of _{1 to} R ₆ is usually 1 to 18, preferably 1
-10, most preferably 1-6.

Specific examples of the monomer used for producing the above alkyl silicate condensate include monoalkoxysilanes such as methyltrimethoxysilane, ethyltriethoxysilane and propyltriethoxysilane; methyltrichlorosilane and ethyl. Examples thereof include monoalkylchlorosilanes such as trichlorosilane; tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane; trialkoxychlorosilanes such as trimethoxychlorosilane and triethoxychlorosilane. In addition, you may mix and use 2 or more types of these compounds. The alkoxyalkyl group in the general formula (A) means a group represented by R'OR- (wherein R'and R are alkyl groups).

The carboxylic acid has 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and most preferably 2 to 6 carbon atoms.
What is used. If a carbon number of 19 or more is used, cissing is likely to occur when applied to the surface of the substrate.
Specific examples include formic acid, acetic acid, acetic anhydride, propionic acid, valeric acid, caproic acid, caprylic acid, benzoic acid and acrylic acid.

The amount of the carboxylic acid to be reacted with the alkyl silicate condensate is 0.2 mol or more per (1) gram atom of silicon in the alkyl silicate condensate and (2-(<m +
n> -1) / <m + n>) mol (where <m + n
> Represents the average degree of condensation. ), Preferably (1.3-
(<M + n> -1) / <m + n>) to (1.8-(<m
+ N> -1) / <m + n>) mol. If the amount of carboxylic acid is excessive, cracks are likely to occur in the resulting insulating film for semiconductors, while if the amount of carboxylic acid is insufficient, it is difficult to obtain a uniform film.

A solution containing a silica-based condensate by mixing an alkyl silicate condensate and a carboxylic acid (hereinafter referred to as "solution containing silica-based condensate").
Is obtained. In order to accelerate the progress of the reaction at the time of mixing, it is preferable to heat or add as a catalyst for a strong acid such as hydrochloric acid, sulfuric acid, or a sulfonic acid compound. The reaction is preferably carried out without a solvent or in the presence of an organic solvent having no hydroxyl group. A preferred specific reaction method is as follows.

In the alkyl silicate condensate, a mixed solution of a carboxylic acid and a catalyst is added dropwise or mixed at one time,
While stirring, the reaction is carried out at room temperature for 4 to 5 hours to 5 days or under heating under reflux for 0.5 to 8 hours. The reaction time is inversely proportional to the amount of the catalyst, and the reaction is extremely fast when a large amount of catalyst, for example, about 2 × 10 ⁻² mol times is added to silicon, while the reaction is slow at about 2 × 10 ⁻⁶ mol times or less. However, if a considerable amount of the strong acid that is the catalyst remains in the coating liquid,
It is not preferable to use a too large amount of catalyst because it corrodes the substrate and the metal on the substrate. Thus, a solution containing the silica-based condensate is obtained.

The step (2) of the present invention is carried out by the general formula Si (O
This is a step of mixing tetraalkoxysilane represented by R ₇ ) ₄ (wherein R ₇ alkyl group or phenyl group is represented) and 2 mol or more of water per 1 mol of the tetraalkoxysilane.

Specific examples of the tetraalkoxysilane represented by the general formula Si (OR ₇ ) ₄ include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and tetraphenoxysilane. The carbon number of R ₇ is usually 1-18, preferably 1-10, and most preferably 1-6.

The amount of water used is 2 mol or more, preferably 2 to 10 mol, and most preferably 2 to 6 mol, per 1 mol of tetraalkoxysilane. If the amount of water is too small, the denseness and chemical resistance of the obtained insulating film for a semiconductor will deteriorate. On the other hand, if the amount of water is too large, the storage stability of the obtained coating solution may be lowered, and gel may be generated,
Not preferable.

As the organic solvent, for example, methanol,
Alcohols such as ethanol and isopropanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone are used.

By mixing tetraalkoxysilane and water in an organic solvent, the tetraalkoxysilane is hydrolyzed, and at the same time, the decomposition product is condensed to give a solution containing a silica-based compound (hereinafter, referred to as "containing a silica-based compound"). Solution). In order to accelerate the progress of the reaction at the time of mixing, it is preferable to add it as a catalyst for strong acids such as hydrochloric acid, sulfuric acid and sulfonic acid compounds. The reaction temperature is room temperature to the boiling point of the solvent, and the reaction time is 0.5 hours to 5 days.

The step (3) of the present invention is a step of subjecting the solution obtained in the above (1) and the solution obtained in the above (2) to contact treatment with an ion exchange resin, and specifically, cation exchange. Examples include treatment with a resin and treatment with an anion exchange resin.

Specific examples of the cation exchange resin include strong acid cation exchange resins such as phenol sulfonic acid-formaldehyde resin and sulfonic acid derivative of styrene-divinylbenzene copolymer. Specific examples of the anion exchange resin include a quaternary ammonium salt type phenol resin, a strongly basic anion exchange resin such as a quaternary ammonium salt type styrene-divinylbenzene copolymer, an aromatic amine type resin, and an aliphatic resin. Examples thereof include weak base type anion exchange resins such as amine type resins and polyethylene-polyamine type resins. As the cation exchange resin and the anion exchange resin, commercially available products can be used. When the resin is used, it is necessary to convert it into an H type and an OH type by acid treatment or alkali treatment, respectively.

Ionic substances to be removed include sodium ion, calcium ion, iron ion, copper ion,
Examples thereof include metal ions such as aluminum ions and anions such as sulfate ions, nitrate ions and chloride ions derived from the acid used as the catalyst in the step (1). When the solution subjected to the treatment of the step (3) contains only one of the cationic impurities and the anionic impurities, the treatment with the cation exchange resin or the treatment with the anion exchange resin is performed depending on the case. However, only one of them needs to be implemented. When the solution contains both cationic impurities and anionic impurities, it is necessary to carry out both the treatment with the cation exchange resin and the treatment with the anion exchange resin.

A specific example of the treatment with the ion-exchange resin is a method in which the solution to be treated is passed through a column filled with the resin. Here, the cation exchange resin and the anion exchange resin may be packed in different columns for use, or both the exchange resins may be mixed and packed in one column for use. The specific condition of the treatment is the content of impurities,
The superficial velocity is usually ¹ to 20 hr ^-1 , though it depends on the target level to be removed and the performance of the exchange resin used.

The silica coating forming coating solution of the present invention is finally used by mixing a solution containing a silica-based condensate and a solution containing a silica-based compound. When the silica-based condensate is absent, crack generation characteristics are inferior, while when the silica-based compound is absent, etching processing characteristics are inferior. The amount ratio of the silica-based condensate and the silica-based compound is a ratio of silicon atoms in the silica-based condensate to the silicon atom of the silica-based compound, preferably in the range of 1 / 0.1 to 1 / 0.7, 1 /
0.2 to 1 / 0.5 is more preferable. If the amount of the silica-based condensate is too small, cracks may occur when the film thickness is set to about 4000 angstroms or more. On the other hand, if the amount of the silica-based compound is too small, the etching processing characteristics may be deteriorated, which is not preferable.

By the way, in carrying out the above step (3), a solution containing a silica-based condensate and a solution containing a silica-based compound are separately subjected to ion exchange treatment and then mixed. Alternatively, the solution containing the silica-based condensate and the solution containing the silica-based compound may be mixed in advance and then the mixed solution may be subjected to an ion exchange treatment. Upon mixing, for example, both solutions may be charged in a container that can be sealed and sufficiently mixed with a magnetic stirrer or a stirrer with a rotation motor.

The thus-obtained mixed solution is adjusted in concentration with an organic solvent, if necessary, and further filtered through a filter to obtain a final product, a silica film-forming coating liquid. As the organic solvent for adjusting the concentration, ethers such as ethyl cellosolve, isopropyl cellosolve and butyl cellosolve; esters such as ethyl acetate and butyl acetate; alcohols such as ethanol; ketones such as acetone are used.

In order to improve the film-forming property, a polymer compound such as polyvinyl acetate, polyvinyl formal, polyvinyl ether, polyethylene oxide, polypropylene glycol or ethyl cellulose may be added to the coating solution for forming a silica coating film of the present invention. Good. Further, in order to improve the film quality, boron compounds such as boron oxide, boric acid, and alkyl borate esters; phosphorus compounds such as phosphorus pentoxide, phosphoric acid, and alkyl phosphoric acid esters; arsenic oxide, arsenic acid, alkyl arsenic acid esters, and the like. Arsenic compound; antimony compounds such as antimony oxide, antimonic acid, and alkyl antimonic acid ester, and mixtures thereof, in an amount of 1% by weight or more and 50% by weight or less, based on SiO ₂ derived from silicon of the silica-based condensate and silica-based compound, It may be added preferably in a proportion of 2% by weight or more and 10% by weight or less. The above compound is preferably used in a state of being dissolved in the coating liquid.

The substrate to which the coating liquid for forming a silica film of the present invention is applied may be glass, metal, resin, ceramic or the like. As the coating method, a dipping method in which a substrate is immersed in a liquid and pulled up and the film thickness is changed by adjusting the pulling rate, or a spin coating method in which the substrate is rotated at a high speed for coating is used. After coating using these methods, the substrate is dried and then 350 ° C to 10 ° C.
By heating in the range of 00 ° C, a dense and smooth silica coating can be obtained.

The use of the coating liquid for forming a silica film of the present invention makes it possible to obtain a silica film having a thickness of 0.5 μm or more at a relatively low temperature of about 350 ° C., so that a high temperature process cannot be used for manufacturing a semiconductor. Also, it becomes possible to coat heat-resistant polymer ceramic molded bodies. Further, when treated at a high temperature, a film having excellent electrical and mechanical properties can be obtained. Furthermore, since the silica coating forming coating liquid of the present invention has an extremely low content of ionic impurities, it lowers the dielectric strength of the semiconductor insulating film or corrodes aluminum of the semiconductor substrate, thereby shortening the life of the semiconductor. There is no such problem. The coating liquid for forming a silica coating film of the present invention having such excellent characteristics is particularly suitable for use as an interlayer insulating film of a multi-layer wiring of electronic parts, a surface protective film, and the like.

[0030]

The present invention will be described below with reference to examples. Example 1 In a 1-liter flask, a commercially available alkyl silicate condensate (ethyl silicate 40, trade name ES-40, manufactured by Nippon Colcoat Co., Ltd .: R _{1 to} R ₅ in the general formula (A) is ethyl, and R ₆ is ethoxy. And n = 0, and the average degree of condensation is 4.63. 451 g and acetic acid 89 g (acetic acid / S).
i (molar ratio) = 0.5) was mixed, 0.53 g of 96% sulfuric acid was further added, and the mixture was stirred at a temperature of 70 ° C. for 5 hours to obtain a solution containing a silica-based condensate. The amount of silicon in the silica-based condensate contained in the solution was 3 mol.

Next, 312 g of tetraethoxysilane was dissolved in 240 g of ethanol, and 76 g of water (H ₂ O / H ₂ O /
Si molar ratio = 6.0) and 0.7 g of nitric acid were added, and the mixture was reacted in a 1 L flask under reflux for 2 hours to obtain a solution containing a silica compound. The amount of silicon in the silica compound contained in the solution was 1.50 mol. Then, a solution containing the above-mentioned silica-based condensate and a solution containing the silica-based compound are mixed so that the ratio of silicon contained in each solution is 1
It was mixed so that it would be /0.4. Then, a column filled with the styrene-divinylbenzene-based strong acid cation exchange resin and the styrene-divinylbenzene-based strongly basic anion exchange resin mixed and filled with the mixed solution had a superficial velocity of 3 h.
Passed at r ^-1 . Prior to use, styrene-
Divinylbenzene strong acid cation exchange resin and styrene-divinylbenzene strong basic anion exchange resin,
Each was treated with a 2N hydrochloric acid aqueous solution or a 1.5N caustic soda aqueous solution, washed with water, and then replaced with ethanol.

The solution after the treatment with the ion exchange resin was subjected to a qualitative test of sulfate ion with a 1 M (mol / l) aqueous barium chloride solution, and the sulfuric acid detected in the solution before the treatment with the ion exchange resin was detected. No white precipitate of barium was detected. In addition, when the metal ions were detected by the ICP-AES method (inductively coupled plasma atomic emission spectrometry), the results shown in Table 1 were obtained.

Further, the solution after the treatment with the ion exchange resin was diluted with butyrocellosolve and filtered through a 0.2 μ filter. The crack generation characteristics were evaluated using the obtained filtrate. The evaluation was carried out by spin coating several types of sample liquids having different concentrations on a silicon wafer having a diameter of 3 inches and baking at 450 ° C. for 30 minutes to form silica coatings of various thicknesses. The presence or absence of occurrence was visually observed. As a result, it was found that the minimum thickness of crack generation was 7,000 angstroms, which had extremely excellent crack generation characteristics.

Example 2 Example 1 was repeated except that the treatment with the styrene-divinylbenzene-based strongly acidic cation exchange resin was followed by the treatment with the styrene-divinylbenzene-based strongly basic anion exchange resin. I went the same way. The superficial velocity in each treatment was 5 hr ^-1 . A qualitative test of sulfate ion with a 1M aqueous solution of barium chloride was conducted on the solution after the treatment with the ion exchange resin, and no white precipitate of barium sulfate detected in the solution before the treatment with the ion exchange resin was detected. It was In addition, when metal ions were detected by the ICP-AES method, the results shown in Table 1 were obtained. Further, it was found that the minimum crack initiation thickness was 7,000 angstroms, which means that it had extremely excellent crack initiation characteristics.

[0035]

[Table 1] ------------- Post-treatment metal ion concentration ppb Sodium 240 <20 280 <20 Calcium 40 <10 50 <10 Iron 10 <10 15 <10 Potassium 20 <20 30 <20 Zinc 120 40 40 120 40 -------------. −−−−−−−−−−−−−−−−−−−−−−−−

[0036]

As described above, according to the present invention, cracks do not occur even when the film is excellent in etching processing characteristics and has a thickness of about 4000 angstroms or more.
It was possible to provide a high-purity coating liquid for forming a silica film, which can be used as an insulating film for a semiconductor excellent in crack generation characteristics and which has an extremely low ionic substance content.

Claims (1)

[Claims] 1. A method for producing a coating liquid for forming a silica film, which comprises the following steps (1) to (3). (1) Alkyl silicate condensate represented by the following general formula (A) and silicon 1 in the alkyl silicate condensate
0.2 mol or more per gram atom and (2-(<m + n
> -1) / <m + n>) moles (where <m + n>
Represents the average degree of condensation. (2) a tetraalkoxysilane represented by the general formula Si (OR ₇ ) ₄ (wherein R ₇ represents an alkyl group or a phenyl group) and the tetraalkoxy. Step of mixing 2 moles or more of water per mole of silane (3) Step of contact-treating the solution obtained in (1) above and the solution obtained in (2) above with an ion exchange resin (In the formula, R _{1 to} R ₅ are the same or different alkyl groups or alkoxyalkyl groups, R ₆ is an alkyl group, an alkoxy group or an alkoxyalkyl group, and m is an integer of 2 or more,
n represents an integer of 0 ≦ n <m. )