JP2005105281A - Silicious film-forming composition, silicious film and its forming method, and electronic part having silicious film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicious film-forming composition capable of forming a silicious film which is excellent in low dielectric property, exhibits sufficient mechanical strength and is curable at a lower temperature in a shorter time than conventional compositions. <P>SOLUTION: The silicious film-forming composition comprises a component (a): a siloxane resin obtained by hydrolytically condensing a compound represented by general formula (1): R<SP>1</SP><SB>n</SB>SiX<SB>4-n</SB>, a component (b): an organic solvent containing at least one aprotic solvent, a component (c): an onium salt and a component (d): a void-forming compound which is thermally decomposed or volatilized at a heating temperature of 250-500°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composition for forming a silica-based film, a silica-based film and a method for forming the same, and an electronic component including the silica-based film.

Conventionally, a SiO ₂ film formed by a CVD method and having a relative dielectric constant of about 4.2 has been used as a material for forming an interlayer insulating film. However, from the viewpoint of reducing the inter-wiring capacitance of the device and improving the operation speed of the LSI, a material capable of developing a further low dielectric constant has been desired.

  In response to this demand, a SiOF film having a relative dielectric constant of about 3.5 and formed by a CVD method has been developed. Furthermore, organic SOG (Spin On Glass), an organic polymer, etc. were developed as an insulating material which has a dielectric constant of 2.5-3.0. Furthermore, a porous material having voids in the coating is considered to be effective as an insulating material having a relative dielectric constant of 2.5 or less, and studies and developments for application to an interlayer insulating film of LSI are actively conducted. ing.

As a method for forming such a porous material, Patent Documents 1 and 2 below propose a method using organic SOG. In this method, a composition containing a hydrolyzed polycondensation product of a metal alkoxide and a polymer having volatilization or decomposition characteristics is heated to form a film, and then the film is heated to form pores in the film. To obtain a porous material.
JP-A-11-322992 JP-A-11-310411

  By the way, in electronic device parts such as semiconductor elements such as LSIs, an increase in signal delay time due to an increase in inter-wiring capacitance has become a problem with the miniaturization of wiring due to high integration. For this reason, in addition to heat resistance, mechanical characteristics, and the like, there is a demand for further reduction of the dielectric constant and heat treatment process for the insulating material of electronic device components.

  In general, there is a relationship represented by the equation: v = k / √ε between the signal propagation speed (v) of the wiring and the relative dielectric constant (ε) of the insulating material in contact with the wiring material (where k is a constant). That is, by increasing the frequency region to be used and reducing the relative dielectric constant (ε) of the insulating material, signal transmission speed can be increased.

  Here, the inventor has examined the above-described conventional method in detail, and in order to achieve a desired low dielectric constant required for the insulating film, an extremely large number of holes (voids) are formed in the insulating film. Found that it needs to be introduced in. Furthermore, the present inventors have found that when the mechanical film strength or film hardness of organic SOG as a film base material is inherently insufficient, the mechanical strength of the film is further reduced when the porosity is excessively increased. I found out that there is a tendency to end up. However, since the film strength tends to decrease as the dielectric constant of the insulating film decreases, it is a big problem to adapt the conventional process.

  Further, in order to cure the film forming composition and form a film, a high temperature atmosphere of 450 ° C. or higher is required. Moreover, it tends to take a long time of about one hour until the curing is finally completed. For this reason, when such a film is used as an interlayer insulating film, there is a concern about deterioration of other layers, particularly the wiring layer, due to the heat input (thermal budget) in the film forming process. Moreover, the problem that the curvature of a board | substrate becomes remarkable with the increase in the amount of heat inputs may also arise.

  Further, as described above, miniaturization of wiring due to high integration is accelerating, and thinning and multilayering of each member layer constituting a semiconductor device and change of materials such as wiring layers are progressing. Since the influence of material deterioration of each layer due to the amount of heat input is expected to increase more than ever, there is an urgent need to improve the thermal history by reducing the thermal load in each process.

  Therefore, the present invention has been made in view of such circumstances, and forms a silica-based coating that is excellent in low dielectric properties, has sufficient mechanical strength, and can be cured at a low temperature and in a short time compared to the prior art. An object of the present invention is to provide a composition for forming a silica-based film, a silica-based film comprising the composition, a method for forming the composition, and an electronic component including the silica-based film.

  In order to achieve the above object, the present inventors have conducted extensive research from the viewpoints of material components and composition thereof for obtaining a silica-based film suitable for an insulating film, and as a result, a composition containing a specific component is obtained. The present inventors have found that various conventional problems can be solved and have completed the present invention.

That is, the present invention comprises (a) component: the following general formula (1);
R ¹ _n SiX _4-n (1)
[Wherein R ¹ represents an H atom or an F atom, or a group containing a B atom, an N atom, an Al atom, a P atom, a Si atom, a Ge atom or a Ti atom, or an organic group having 1 to 20 carbon atoms, X represents a hydrolyzable group, and n represents an integer of 0 to 2. However, when n is 2, each R ¹ may be the same or different, and when n is 0 to 2, each X may be the same or different. ],
A siloxane resin obtained by hydrolytic condensation of a compound represented by the formula: (b) component: an organic solvent containing at least one aprotic solvent, (c) component: an onium salt, and (d) component: A composition for forming a silica-based film comprising a void-forming compound that thermally decomposes or volatilizes at a heating temperature of 250 to 500 ° C.

  The composition for forming a silica-based film of the present invention contains the siloxane resin having the above-described structure as a film-forming component, an aprotic solvent as an essential component as an organic solvent component for dissolving the siloxane resin, and further containing an onium salt. Silica that is excellent in low dielectric property, especially in high frequency region (high frequency region of 100 kHz or higher, for example, 1 MHz), has sufficient mechanical strength, and can be cured at a lower temperature and in a shorter time than conventional. A system film can be formed. Further, since the composition can be cured at a low temperature in a short time, the amount of heat input in the film forming process is also reduced. Therefore, problems such as deterioration of the wiring layer and the warp of the substrate can be solved. Furthermore, the uniformity of the film thickness can also be improved.

  The cause of the above effect is not necessarily clear, but the silica-based coating has low dielectric constant and sufficient mechanical strength mainly due to the use of the siloxane resin and aprotic solvent. The reason why the curing at a low temperature and in a short time is possible is mainly due to the use of an aprotic solvent and an onium salt. Moreover, it is thought that the improvement in the uniformity of the film thickness is mainly due to the use of an aprotic solvent.

  The composition for forming a silica-based film of the present invention further contains a void-forming compound that is thermally decomposed or volatilized at a heating temperature of 250 to 500 ° C. The composition for forming a silica-based film having such a configuration can form a silica-based film capable of achieving a low dielectric constant while suppressing a significant decrease in mechanical strength.

  The aprotic solvent preferably contains at least one aprotic solvent selected from the group consisting of ether solvents and ketone solvents, and dialkyl ethers of dihydric alcohols and alkyl ester ethers of dihydric alcohols. It is preferable to include at least one aprotic solvent selected from the group consisting of diesters of dihydric alcohols and cyclic ketones, and at least one of the aprotic solvents is an aprotic having a non-dielectric constant of 10 or more. It is preferable that it is an organic solvent. Furthermore, the content of the aprotic solvent having a relative dielectric constant of 10 or more is more preferably 50% by mass or more based on the weight of the component (b).

  The content of the aprotic solvent is preferably 80% by mass or more based on the weight of the component (b). When the content ratio of the aprotic solvent in the component (b) is small, there is a possibility that the temperature reduction and the time shortening at the time of curing of the composition may be hindered. Further, there is a risk of increasing the relative dielectric constant of the film and decreasing the mechanical strength.

  In particular, a composition for forming a silica-based film comprising an aprotic solvent having a non-dielectric constant of 10 or more as an organic solvent component contains a compound for forming voids described later and forms voids (holes). Tend to be narrower.

  The component (a) is selected from the group consisting of H atom, F atom, B atom, N atom, Al atom, P atom, Si atom, Ge atom, Ti atom and C atom with respect to 1 mol of Si atom. It is preferable that the total content of at least one atom is 0.65 mol or less.

  In the composition for forming a silica-based film having the above-described configuration, a decrease in adhesiveness with other films (layers) of the silica-based film and mechanical strength is suppressed. Therefore, it is possible to prevent the occurrence of interfacial delamination in a CMP (Chemical Mechanical Polish) process for a metal wiring layer such as Cu deposited on the silica-based film.

  The onium salt is preferably an ammonium salt. The composition for forming a silica-based film having such a configuration can improve the stability of the composition, and can further improve the electrical characteristics and mechanical properties of the silica-based film.

  Further, among the above ammonium salts, tetramethylammonium nitrate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium maleate and tetramethylammonium sulfate are used from the viewpoint of further improving the electrical properties of the silica-based coating. It is more preferable to use one or more ammonium salts selected from the group.

  The void-forming compound is a vinyl ether compound, a vinyl compound having a polyoxyethylene unit, a vinyl compound having a polyoxypropylene unit, a vinyl pyridine compound, a styrene compound, an alkyl ester vinyl compound, (meth) acrylate One or more compounds selected from the group consisting of an acid compound, a polymer having a polyoxyalkylene unit, and a polycarbonate polymer are preferred. The void-forming compound is more preferably a polymer having a polyoxyalkylene unit. Furthermore, the void forming compound is particularly preferably a polymer having a polyoxypropylene unit.

  The composition for forming a silica-based film in the case where the void-forming compound is the above compound can form a silica-based film that can further suppress a significant decrease in mechanical strength and can achieve a lower dielectric constant.

  Moreover, it is preferable that the said space | gap formation compound is what forms a micropore gradually in a silica-type film. By gradually forming micropores (voids, vacancies) in the silica-based coating, it is possible to further refine the pores and make the shape uniform during final curing.

  The present invention is also a method for forming a silica-based film on a substrate, wherein the composition for forming a silica-based film of the present invention is applied onto a substrate to form a coating film, and an organic contained in the coating film Provided is a method for forming a silica-based film, wherein after removing the solvent, the coating film is baked at a heating temperature of 250 to 500 ° C.

  The present invention further provides a silica-based coating provided on a substrate and formed by the above-described method for forming a silica-based coating, and in particular, the coating includes a plurality of such coatings provided on the substrate. Of these conductive layers, the conductive layer is useful as an insulating film formed between adjacent conductive layers, that is, an insulating film that needs to sufficiently reduce leakage current, for example, an interlayer insulating film.

  And this invention provides the electronic component by which the silica type coating film by this invention is formed on a board | substrate. Such an electronic component constitutes an electronic device such as a semiconductor device.

  As described above, according to the present invention, a low dielectric constant of 2.5 or less can be exhibited even in a high-frequency region of 100 kHz or more, it has sufficient mechanical strength, and has a lower temperature and a shorter time than conventional. There is provided a composition for forming a silica-based film capable of forming a silica-based film that can be cured at a low temperature. Moreover, the silica-type film which consists of this composition, its formation method, and an electronic component provided with this silica-type film are provided.

  Hereinafter, embodiments of the present invention will be described in detail. The composition for forming a silica-based film according to the present invention contains the components (a) to (c). What is characteristic in the present invention is that at least one aprotic solvent is used as the component (b). That is, it is to make the composition for forming a silica-based film containing a polar solvent having a high relative dielectric constant. Hereinafter, each component of the composition for forming a silica-based film of the present invention will be described in detail.

<(A) component>
In the present invention, the siloxane resin used as the component (a) functions as a film forming component of the silica-based film described later. In order to exhibit such a function, the composition for forming a silica-based film of the present invention contains a siloxane resin obtained by hydrolytic condensation of a compound represented by the following formula (1) as the component (a).
R ¹ _n SiX _4-n (1)
In the general formula (1), R ¹ is an H atom or F atom, or a group containing a B atom, an N atom, an Al atom, a P atom, a Si atom, a Ge atom, or a Ti atom, or a carbon number of 1 to 20 An organic group (preferably an organic group having 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms) is shown.

  In addition, H atom, F atom, B atom, N atom, Al atom, P atom, Si atom, Ge atom, Ti atom bonded to one atom of the Si atom forming the siloxane bond of the siloxane resin, and The total number (M) of at least one atom selected from the group consisting of C atoms (hereinafter referred to as “specific bonding atom”) is preferably 0.65 or less, more preferably 0.55 or less, and 0 .50 or less is particularly preferable, and 0.45 or less is extremely preferable. Further, the lower limit of M is preferably about 0.20.

  When the value of M exceeds 0.65, the adhesion of the finally obtained silica-based film to other films (layers), mechanical strength, etc. tend to be inferior. On the other hand, if the value of M is less than 0.20, the dielectric characteristics when used as an insulating film tend to be inferior. The siloxane resin contains at least one of H atom, F atom, N atom, Si atom, Ti atom, and C atom in terms of the film-forming property of the silica-based coating among the above specific bonding atoms. Among these, it is more preferable that at least one of H atom, F atom, N atom, Si atom and C atom is contained in terms of dielectric properties and mechanical strength.

In addition, the value of M can be calculated | required from the preparation amount of the compound represented by the said General formula (1) which is a raw material of siloxane resin. For example:
_{M = [M 1 + (M} 2/2) + (M 3/3)] / M Si
Can be used to calculate. In the formula, M ₁ represents the total number of atoms bonded to a single (only one) Si atom among specific bonding atoms, and M ₂ is shared by two silicon atoms among the specific bonding atoms. M ₃ represents the total number of atoms shared by three silicon atoms among the specific bonded atoms, and M _Si represents the total number of Si atoms.

  Returning to the general formula (1), X represents a hydrolyzable group. Examples of X include an alkoxy group, a halogen atom, an acetoxy group, an isocyanate group, and a hydroxyl group, and an alkoxy group is preferable. By making X an alkoxy group, the liquid stability and coating characteristics of the composition are improved.

  Examples of the compound represented by the general formula (1) when the hydrolyzable group X is an alkoxy group include tetraalkoxysilane, trialkoxysilane, and diorganodialkoxysilane. Tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-iso-propoxysilane, tetra-n-butoxysilane, tetra-sec-butoxysilane, tetra-tert-butoxysilane, tetra Examples thereof include phenoxysilane.

  Trialkoxysilanes include trimethoxysilane, triethoxysilane, tripropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltri-n-propoxysilane, methyltri-iso-propoxy. Silane, methyltri-n-butoxysilane, methyltri-iso-butoxysilane, methyltri-tert-butoxysilane, methyltriphenoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltri-n-propoxysilane, ethyltri-iso-propoxy Silane, ethyltri-n-butoxysilane, ethyltri-iso-butoxysilane, ethyltri-tert-butoxysilane, ethyltriphenoxysilane, n Propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltri-n-propoxysilane, n-propyltri-iso-propoxysilane, n-propyltri-n-butoxysilane, n-propyltri-iso-butoxy Silane, n-propyltri-tert-butoxysilane, n-propyltriphenoxysilane, iso-propyltrimethoxysilane, iso-propyltriethoxysilane, iso-propyltri-n-propoxysilane, iso-propyltri-iso- Propoxysilane, iso-propyltri-n-butoxysilane, iso-propyltri-iso-butoxysilane, iso-propyltri-tert-butoxysilane, iso-propyltriphenoxysilane, n-butyltrimethoxysilane N-butyltriethoxysilane, n-butyltri-n-propoxysilane, n-butyltri-iso-propoxysilane, n-butyltri-n-butoxysilane, n-butyltri-iso-butoxysilane, n-butyltri-tert -Butoxysilane, n-butyltriphenoxysilane, sec-butyltrimethoxysilane, sec-butyltriethoxysilane, sec-butyltri-n-propoxysilane, sec-butyltri-iso-propoxysilane, sec-butyltri-n-butoxy Silane, sec-butyltri-iso-butoxysilane, sec-butyltri-tert-butoxysilane, sec-butyltriphenoxysilane, t-butyltrimethoxysilane, t-butyltriethoxysilane, t-butyltri-n- Propoxysilane, t-butyltri-iso-propoxysilane, t-butyltri-n-butoxysilane, t-butyltri-iso-butoxysilane, t-butyltri-tert-butoxysilane, t-butyltriphenoxysilane, phenyltrimethoxysilane , Phenyltriethoxysilane, phenyltri-n-propoxysilane, phenyltri-iso-propoxysilane, phenyltri-n-butoxysilane, phenyltri-iso-butoxysilane, phenyltri-tert-butoxysilane, phenyltriphenoxysilane , Trifluoromethyltrimethoxysilane, pentafluoroethyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, etc. And the like.

  Diorganodialkoxysilanes include dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldi-n-propoxysilane, dimethyldi-iso-propoxysilane, dimethyldi-n-butoxysilane, dimethyldi-sec-butoxysilane, dimethyldi-tert-butoxy. Silane, dimethyldiphenoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldi-n-propoxysilane, diethyldi-iso-propoxysilane, diethyldi-n-butoxysilane, diethyldi-sec-butoxysilane, diethyldi-tert-butoxysilane Diethyldiphenoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, di-n-propyldi-n-propoxysilane, di n-propyldi-iso-propoxysilane, di-n-propyldi-n-butoxysilane, di-n-propyldi-sec-butoxysilane, di-n-propyldi-tert-butoxysilane, di-n-propyldiphenoxysilane Di-iso-propyldimethoxysilane, di-iso-propyldiethoxysilane, di-iso-propyldi-n-propoxysilane, di-iso-propyldi-iso-propoxysilane, di-iso-propyldi-n-butoxysilane Di-iso-propyldi-sec-butoxysilane, di-iso-propyldi-tert-butoxysilane, di-iso-propyldiphenoxysilane, di-n-butyldimethoxysilane, di-n-butyldiethoxysilane, di -N-Butyldi-n-propoxysilane Di-n-butyldi-iso-propoxysilane, di-n-butyldi-n-butoxysilane, di-n-butyldi-sec-butoxysilane, di-n-butyldi-tert-butoxysilane, di-n-butyldi Phenoxysilane, di-sec-butyldimethoxysilane, di-sec-butyldiethoxysilane, di-sec-butyldi-n-propoxysilane, di-sec-butyldi-iso-propoxysilane, di-sec-butyldi-n- Butoxysilane, di-sec-butyldi-sec-butoxysilane, di-sec-butyldi-tert-butoxysilane, di-sec-butyldiphenoxysilane, di-tert-butyldimethoxysilane, di-tert-butyldiethoxysilane Di-tert-butyldi-n-propoxysilane, di- tert-butyldi-iso-propoxysilane, di-tert-butyldi-n-butoxysilane, di-tert-butyldi-sec-butoxysilane, di-tert-butyldi-tert-butoxysilane, di-tert-butyldiphenoxysilane Diphenyldimethoxysilane, diphenyldiethoxysilane, diphenyldi-n-propoxysilane, diphenyldi-iso-propoxysilane, diphenyldi-n-butoxysilane, diphenyldi-sec-butoxysilane, diphenyldi-tert-butoxysilane, Examples include diphenyldiphenoxysilane, bis (3,3,3-trifluoropropyl) dimethoxysilane, and methyl (3,3,3-trifluoropropyl) dimethoxysilane.

  Moreover, as a compound (halogenated silane) represented by the general formula (1) when X is a halogen atom (halogen group), the alkoxy group in each alkoxysilane molecule described above is substituted with a halogen atom. A compound can be illustrated. Furthermore, examples of the compound (acetoxysilane) represented by the above formula (1) when X is an acetoxy group include compounds in which the alkoxy group in each alkoxysilane molecule described above is substituted with an acetoxy group. Furthermore, as a compound (isocyanate silane) represented by the said Formula (1) in case X is an isocyanate group, the compound by which the alkoxy group in each above-mentioned alkoxysilane molecule was substituted by the isocyanate group is mentioned. Furthermore, examples of the compound (hydroxysilane) represented by the above formula (1) when X is a hydroxyl group include compounds in which the alkoxy group in each alkoxysilane molecule described above is substituted with a hydroxyl group. . In addition, the compound represented by the said Formula (1) can be used individually or in combination of 2 or more types.

Returning to the general formula (1), n represents an integer of 0-2. However, when n is 2, each R ¹ may be the same or different. Further, when n is 0 to 2, the above Xs may be the same or different. In addition, it is preferable that n is 0-1, and the compound represented by the general formula (1) in which n is 0 and the compound represented by the general formula (1) in which n is 1 are used in combination. It is preferable to do. When a compound in which n is 0 and 1 is combined, the siloxane resin includes a unit represented by SiO ₂ and a unit represented by R ¹ SiO _3/2 . However, ^{R 1} is as defined above. Such a siloxane resin is obtained by cohydrolyzing and condensing the above-mentioned tetraalkoxysilane and trialkoxysilane having polyfunctionality. The unit represented by SiO ₂ is a unit derived from tetraalkoxysilane, and the unit represented by R ¹ SiO _3/2 is a unit derived from trialkoxysilane. Since the siloxane resin contains such a unit, the crosslink density is improved, so that the film characteristics can be improved.

  As a catalyst for promoting the hydrolysis and condensation of the compound represented by the general formula (1), formic acid, maleic acid, fumaric acid, acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, Nonanoic acid, decanoic acid, oxalic acid, adipic acid, sebacic acid, butyric acid, oleic acid, stearic acid, linoleic acid, linolenic acid, salicylic acid, benzoic acid, p-aminobenzoic acid, p-toluenesulfonic acid, phthalic acid, sulfone Organic acids such as acid, tartaric acid and trifluoromethanesulfonic acid, inorganic acids such as hydrochloric acid, phosphoric acid, nitric acid, boric acid, sulfuric acid and hydrofluoric acid can be used.

  It is preferable that the usage-amount of the said catalyst is the range of 0.0001-1 mol with respect to 1 mol of compounds represented by the said General formula (1). When the amount used exceeds 1 mol, gelation tends to be promoted at the time of hydrolytic condensation, and when it is less than 0.0001 mol, the reaction tends not to proceed substantially.

  In the hydrolysis-condensation reaction, alcohol produced as a by-product by hydrolysis of the compound represented by the general formula (1) is a protic solvent, and thus is preferably removed using an evaporator or the like. Moreover, although the quantity of the water used for a hydrolysis-condensation reaction can be determined suitably, as the quantity of this water, it is 0.5-20 mol with respect to 1 mol of compounds represented by the said General formula (1). It is preferable to set the value within the range. When the amount of water is less than 0.5 mol or more than 20 mol, the film-formability of the silica-based film is deteriorated and the storage stability of the composition itself tends to be lowered.

  The weight average molecular weight (Mw) of the siloxane resin is preferably 500 to 20,000, and preferably 1,000 to 10,000 from the viewpoints of solubility in a solvent, mechanical properties, moldability, and the like. More preferred. When this Mw is less than 500, the film formability of the silica-based film tends to be inferior. On the other hand, when this Mw exceeds 20,000, the compatibility with the solvent tends to decrease. In the present invention, Mw refers to a weight average molecular weight in terms of standard polystyrene by gel permeation chromatography (GPC).

<(B) component>
The component (b) is an organic solvent that makes it possible to simplify handling and the like by dissolving the siloxane resin that is the component (a) and reducing the viscosity thereof. Also, it has a function of narrowing the distribution of voids (holes) contained in the silica-based coating by increasing the relative dielectric constant of the aprotic solvent to a predetermined value or more.

  In order to exhibit such a function, the composition for forming a silica-based film of the present invention comprises an aprotic solvent based on the weight of the component (b) of 80% by mass or more, more desirably 90% by mass or more, and still more desirably 95%. It is preferable to contain it by mass% or more. When the content ratio of the aprotic solvent in the component (b) is small, there is a possibility that the temperature reduction and the time shortening at the time of curing of the composition may be hindered. Further, there is a risk of increasing the relative dielectric constant of the film and decreasing the mechanical strength.

  Furthermore, it is preferable that at least one of the aprotic solvents has a relative dielectric constant of 10 or more. By having such a relative dielectric constant, when a void is formed in the coating containing the void-forming compound described later, the distribution of voids in the coating tends to be narrow. The relative dielectric constant in the present invention refers to a value measured at 20 ° C. Further, the content of the aprotic solvent having a relative dielectric constant of 10 or more in the component (b) is preferably 50% by mass or more, and more preferably 60% by mass or more.

  Examples of the aprotic solvent include ketone solvents, ether solvents, ester solvents, ether acetate solvents, acetonitrile, amide solvents, sulfoxide solvents, and the like. Of these, ether solvents and ketone solvents are preferable, dialkyl ethers of dihydric alcohols, alkyl ester ethers of dihydric alcohols, diesters of dihydric alcohols and cyclic ketones are more preferable, and diethylene glycol dimethyl ether and cyclohexanone are particularly preferable. Among these suitable aprotic solvents, from the viewpoints of compatibility with the siloxane resin, the mechanical strength of the silica-based film, etc., ketone-based solvents are preferable, among which cyclic ketones are preferable, and cyclohexanone is particularly preferable.

  Examples of ketone solvents include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, Examples include diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, and acetonyl acetone.

  Examples of ether solvents include dioxane, dimethyl dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl mono-n-butyl ether. , Diethylene glycol di-n-butyl ether, diethylene glycol methyl mono-n-hexyl ether, tetraethylene glycol di-n-butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol diethyl ether, tetrahydrofuran, 2- Chill tetrahydrofuran.

  Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, and 3-acetate acetate. Methoxybutyl, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, γ-butyrolactone, γ-valerolactone, methyl acetoacetate, ethyl acetoacetate, diethylene glycol monomethyl acetate Ether, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, dipropylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, glycol diacetate, methyl acetate Toxic triglycol, ethyl propionate, n-butyl propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate and the like can be mentioned.

  Examples of ether acetate solvents include ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, acetate ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol methyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol-n- Examples include butyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, dipropylene glycol methyl ether acetate, and dipropylene glycol ethyl ether acetate.

  Examples of the amide solvent include N, N-dimethylformamide and N, N-dimethylacetamide, and examples of the sulfoxide solvent include N, N-dimethylsulfoxide.

  Examples of the aprotic solvent having a relative dielectric constant of 10 or more include ketone solvents, acetonitrile, amide solvents, sulfoxide solvents and the like. Examples of ketone solvents having a relative dielectric constant of 10 or more include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, and methyl-n-pentyl ketone. Methyl-n-hexyl ketone, diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone and the like. Examples of the amide solvent having a relative dielectric constant of 10 or more include N, N-dimethylformamide and N, N-dimethylacetamide. Examples of the sulfoxide solvent having a relative dielectric constant of 10 or more include N, N-dimethylsulfoxide. Etc. can be illustrated. These may be used alone or in combination of two or more.

  Furthermore, as the component (b), other protic solvent components can be included as necessary. Examples of such protic solvents include alcohol solvents, ether solvents, ester solvents and the like.

  Examples of alcohol solvents include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol, i-pentanol, 2-methylbutanol, sec -Pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol, Down benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, and the like.

  Examples of ether solvents include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, ethoxytriglycol, Examples include tetraethylene glycol mono-n-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and tripropylene glycol monomethyl ether.

  Examples of the ester solvent include methyl lactate, ethyl lactate, n-butyl lactate, and n-amyl lactate. These may be used alone or in combination of two or more with an aprotic solvent.

<(C) component>
The component (c) has a function of enhancing the stability of the composition for forming a silica-based film and further improving the electrical characteristics and mechanical properties of the silica-based film. Furthermore, the condensation reaction of the component (a) is accelerated to enable the curing temperature to be lowered and shortened, and the function of further suppressing the decrease in mechanical strength is also provided.

  In order to exhibit this function, the composition for forming a silica-based film of the present invention contains an onium salt as the component (c). Examples of the onium salt include ammonium salt, phosphonium salt, arsonium salt, stibonium salt, oxonium salt, sulfonium salt, selenonium salt, stannonium salt, iodonium salt and the like. Among these, ammonium salts are preferable because they are more excellent in the stability of the composition.

  As ammonium salt, tetramethylammonium oxide, tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium fluoride, tetrabutylammonium oxide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium fluoride, tetramethylammonium Examples thereof include nitrate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium maleate, and tetramethylammonium sulfate.

  Among these ammonium salts, tetramethylammonium nitrate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium maleate, tetramethylammonium sulfate from the viewpoint of improving the electrical properties of the silica-based coating Particularly preferred are ammonium salts such as

  In addition, although the details of the mechanism that is effective by containing the onium salt are still unclear, the dehydration condensation reaction is promoted by the onium salt to increase the density of the siloxane bond, and the remaining silanol group Therefore, it is estimated that the mechanical strength and dielectric characteristics are improved. However, the action is not limited to this.

<(D) component>
Moreover, it is preferable that the composition for silica-type film formation of this invention further contains the compound for void | space formation which thermally decomposes or volatilizes at the heating temperature of 250-500 degreeC as (d) component. The component (d) has a function of gradually forming fine pores (voids and vacancies) in the silica-based film, and further miniaturizing the pores and making the shape uniform at the time of final curing. In order to exhibit such a function, the component (d) preferably has a reduction rate in a nitrogen gas atmosphere at a temperature of 250 to 500 ° C. of 95% by mass or more, more preferably 97% by mass or more, and 99% by mass. % Or more is more preferable. When the reduction rate is less than 95% by mass, decomposition or volatilization of the compound tends to be insufficient when the silica-based film forming composition of the present invention is heated. That is, the (d) component, a part of the (d) component or the reaction product derived from the (d) component may remain in the finally obtained silica-based film. In this case, the electrical characteristics of the silica-based film may be deteriorated such as an increase in relative dielectric constant.

In addition, the “decrease rate” of the component (d) in the present invention is a value obtained by the following apparatus and conditions. That is, the “decrease rate” is a differential scanning calorimeter (10 mg / min) under the conditions that the temperature of the polymer 10 mg is 50 ° C., the temperature rising rate is 10 ° C./min, and the flow rate of nitrogen (N ₂ ) gas is 200 ml / min. Measured using Seiko Instruments Inc., TG / DTA6300). Note that α-alumina (manufactured by Seiko Instruments Inc.) is used as a reference, and a φ5 aluminum open sample pan (manufactured by Seiko Instruments Inc.) is used as a sample container.

  In addition, let the reference | standard mass before the decomposition | disassembly start of (d) component be the mass in 150 degreeC which is in the middle of temperature rising. This is because the decrease in mass at 150 ° C. or less is due to the removal of adsorbed moisture and the like, and it is estimated that the decomposition of the component (d) itself does not substantially occur. In the measurement of the “decrease rate”, when the component (d) cannot be directly measured because the component (d) is dissolved in the solution, the solution containing the component (d) For example, a residue obtained by taking about 2 g in a metal petri dish and drying at 150 ° C. for 3 hours in air at normal pressure is used as a sample.

  Specific examples of the component (d) include vinyl ether compounds, vinyl compounds having a polyoxyethylene unit, vinyl compounds having a polyoxypropylene unit, vinyl pyridine compounds, styrene compounds, alkyl ester vinyl compounds, (Meth) acrylate acid compounds, polymers having polyoxyalkylene units, polycarbonate polymers and the like can be mentioned. From the viewpoint of decomposition characteristics and mechanical strength of the film, the component (d) is preferably a polymer having a polyoxyalkylene unit, particularly preferably a polymer having a polyoxypropylene unit.

  Examples of the polyoxyalkylene unit include a polyoxyethylene unit, a polyoxypropylene unit, a polyoxytetramethylene unit, and a polyoxybutylene unit. Specifically, polyoxyethylene alkyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, ethylene oxide derivative of alkylphenol formalin condensate, polyoxyethylene polyoxypropylene block copolymer, polyoxypropylene alkyl ale, polyoxyethylene Ether type compounds such as polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitol fatty acid ester, ether ester type compounds such as polyoxyethylene fatty acid alkanolamide sulfate, polyethylene glycol fatty acid ester, ethylene glycol fatty acid ester, Fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, Ether ester type compounds such as propylene glycol fatty acid esters, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, glycol-type compounds such as polypropylene glycol, and the like.

  Examples of (meth) acrylate acid derivatives include acrylic acid alkyl esters, methacrylic acid alkyl esters, acrylic acid alkoxyalkyl esters, methacrylic acid alkyl esters, and methacrylic acid alkoxyalkyl esters. Examples of the alkyl acrylate ester include 1 to 6 carbon atoms such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, pentyl acrylate, and hexyl acrylate. Examples of the alkyl ester and alkyl methacrylate ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate and the like. -6 alkyl ester etc. are mentioned. Examples of the alkoxyalkyl acrylate include methoxymethyl acrylate, ethoxyethyl acrylate, and examples of the alkoxyalkyl methacrylate include methoxymethyl methacrylate, ethoxyethyl methacrylate, and the like.

  As the (meth) acrylate acid derivative, a copolymer with a compound having a hydroxyl group can be used. Specific examples of the compound include 2-hydroxyethyl acrylate, diethylene glycol acrylate, 2-hydroxypropyl acrylate, dipropylene glycol acrylate, methacrylic acid, 2-hydroxyethyl methacrylate, diethylene glycol methacrylate, 2-hydroxypropyl methacrylate, and dipropylene glycol methacrylate. Is mentioned.

  Examples of the polyester include a polycondensate of hydroxycarboxylic acid, a ring-opening polymer of lactone, and a polycondensate of an aliphatic polyol and an aliphatic polycarboxylic acid.

  Examples of the polycarbonate include polycondensates of carbonic acid and alkylene glycol such as polyethylene carbonate, polypropylene carbonate, polytrimethylene carbonate, polytetramethylene carbonate, polypentamethylene carbonate, and polyhexamethylene carbonate. Examples of the polyanhydride include polycondensates of dicarboxylic acids such as polymalonyl oxide, polyadipoyl oxide, polypimeyl oxide, polysuberoyl oxide, polyazelayl oxide, and polysebacoyl oxide.

  In addition, it is preferable that Mw of (d) component is 200-10,000 from points, such as the solubility to a solvent, compatibility with a siloxane resin, the mechanical property of a film | membrane, the moldability of a film | membrane, It is more preferably 5,000, and more preferably 400 to 2,000. When this Mw exceeds 100,000, the compatibility with the siloxane resin tends to decrease. On the other hand, if it is less than 200, void formation tends to be insufficient.

  Next, the content of each component of the composition for forming a silica-based film of the present invention will be described. The content of the component (a) in the composition for forming a silica-based film of the present invention is preferably 3 to 25% by mass. When the concentration of the component (a) exceeds 25% by mass, the amount of the organic solvent is too small, and the film formability of the silica-based film is deteriorated, and the stability of the composition itself tends to be lowered. On the other hand, when the concentration of the component (a) is less than 3% by mass, the amount of the solvent is excessive, and it is difficult to form a silica-based film having a desired film thickness.

  The content of the component (c) is preferably 0.001 ppm to 5% by mass, more preferably 0.01 ppm to 1% by mass, based on the total weight of the composition for forming a silica-based film of the present invention. More preferably, it is 0.1 ppm to 0.5 mass%. When this content is less than 0.001 ppm, the electrical properties and mechanical properties of the finally obtained silica-based coating tend to be inferior. On the other hand, when the content exceeds 5%, the stability of the composition, the film formability and the like tend to be inferior, and the electrical characteristics and process suitability of the silica-based film tend to be lowered. In addition, the onium salt which is (c) component can be added so that it may become a desired density | concentration, after melt | dissolving or diluting in water or a solvent as needed.

  The content of the component (d) is preferably 0.1 to 10% by mass and more preferably 1 to 5% by mass based on the total weight of the composition for forming a silica-based film of the present invention. When this content is less than 0.1% by mass, void formation tends to be insufficient. On the other hand, if it exceeds 10% by mass, the film strength may decrease.

  In addition, content of (b) component is the remainder remove | excluding the total weight of (a) component, (c) component, and (d) component from the weight of the said composition.

  In addition, it is desirable that the composition for forming a silica-based film of the present invention does not contain an alkali metal or an alkaline earth metal. Even when such a metal is contained, the metal ion concentration in the composition is preferably 100 ppb or less, and more preferably 20 ppb or less. When the metal ion concentration exceeds 100 ppb, the metal ions are liable to flow into a semiconductor element having a silica-based film obtained from the above composition, which may adversely affect the device performance itself. Therefore, it is effective to remove alkali metal or alkaline earth metal from the composition using an ion exchange filter or the like as necessary.

(Method for forming silica-based film, silica-based film and electronic component)
Next, preferred embodiments of the method for forming a silica-based film, the silica-based film, and the electronic component according to the present invention will be described.

  Using the composition for forming a silica-based film of the present invention, the silica-based film according to the present invention can be formed by, for example, the spin coating method described below. The spin coating method is suitable for forming the silica-based coating of the present invention because it is excellent in film forming properties and film uniformity.

  First, the composition for forming a silica-based film is spin-coated on a substrate such as a silicon wafer, preferably at 500 to 5000 rotations / minute, more preferably 1000 to 3000 rotations / minute, to form a coating film. At this time, if the rotational speed is less than 500 revolutions / minute, the film uniformity tends to deteriorate. On the other hand, when it exceeds 5000 rpm, the film formability may be deteriorated.

  Next, the organic solvent in the coating film is dried on a hot plate or the like preferably at 50 to 350 ° C., more preferably at 100 to 300 ° C. When this drying temperature is less than 50 ° C., the organic solvent tends to be not sufficiently dried. On the other hand, when the drying temperature exceeds 350 ° C., the component (d) for forming the porous layer is thermally decomposed before the siloxane skeleton of the siloxane resin is sufficiently formed, and the volatilization amount increases undesirably. It may be difficult to obtain a silica-based film having a high mechanical strength and low dielectric properties.

  Next, the coating film from which the organic solvent has been removed is baked at a heating temperature of 250 to 500 ° C. to perform final curing. In this manner, a silica-based film (Low-k film) that can exhibit a low dielectric constant even in a high-frequency region of 100 kHz or higher is formed. The “relative permittivity” in the present invention refers to a value measured in an atmosphere of 23 ° C. ± 2 ° C. and humidity of 40% ± 10%, and is preferably 2.5 or less. The relative dielectric constant is obtained, for example, by measuring the charge capacity between the Al metal and the N-type low resistivity substrate (Si wafer). The silica-based coating of the present invention has sufficient mechanical strength and can be cured at a lower temperature and in a shorter time than conventional. The final curing is preferably performed in an inert atmosphere such as nitrogen, argon, helium, etc. In this case, the oxygen concentration is preferably 1000 ppm or less. When the heating temperature is less than 250 ° C., sufficient curing tends not to be achieved, and decomposition and volatilization of the component (d) tend not to be promoted sufficiently. On the other hand, when the heating temperature exceeds 500 ° C., when there is a metal wiring layer, the amount of heat input may increase and the wiring metal may be deteriorated.

  In addition, the heating time during the curing is preferably 2 to 60 minutes, and more preferably 2 to 30 minutes. If this heating time exceeds 60 minutes, the amount of heat input may increase excessively and the wiring metal may deteriorate. As the heating device, it is preferable to use a heat treatment device such as a quartz tube furnace or other furnace, a hot plate, or rapid thermal annealing (RTA).

  The film thickness of the silica-based film thus formed is preferably 0.01 to 40 μm, and more preferably 0.1 to 2.0 μm. When the film thickness exceeds 40 μm, cracks are likely to occur due to stress. On the other hand, when the thickness is less than 0.01 μm, when metal wiring layers are present in the upper and lower layers of the silica-based film, the leakage characteristics between the upper and lower wiring layers tend to deteriorate.

  In addition, examples of the electronic component according to the present invention using the silica-based coating formed as described above include electronic devices having a silica-based coating such as a semiconductor element and a multilayer wiring board. The silica-based film of the present invention can be used as a surface protective film (passivation film), a buffer coat film, an interlayer insulating film, and the like in a semiconductor element. On the other hand, in a multilayer wiring board, it can be suitably used as an interlayer insulating film. When the silica-based coating of the present invention is used, for example, as a coating on a semiconductor element or a multilayer wiring board, it has excellent low dielectric properties.

  Specifically, as semiconductor elements, individual semiconductor elements such as diodes, transistors, compound semiconductors, thermistors, varistors, thyristors, DRAM (dynamic random access memory), SRAM (static random access memory), EPROM (Eraseable Programmable Read Only Memory), Mask ROM (Mask Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), Flash Memory, Memory Elements, Microprocessor, DSP , Theoretical circuit elements such as ASIC, integrated circuit elements such as compound semiconductors represented by MMIC (monolithic microwave integrated circuit), hybrid integrated circuits (hybrid IC), light emission Diode, etc. The photoelectric conversion element such as a charge coupled device and the like. Examples of the multilayer wiring board include a high-density wiring board such as MCM.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of an electronic component according to the present invention. The memory capacitor cell 8 (electronic component) functions as a gate electrode 3 (word line) provided via a gate insulating film 2B made of an oxide film on the silicon wafer 1 (substrate) on which the diffusion regions 1A and 1B are formed. )) And a counter electrode 8C provided thereabove, interlayer insulating films 5 and 7 (insulating films) having a two-layer structure are formed. Side wall oxide films 4A and 4B are formed on the side wall of the gate electrode 3, and a field oxide film 2A is formed in the diffusion region 1B on the side of the gate electrode to separate elements.

  The interlayer insulating film 5 is deposited on the gate electrode 3 and the field oxide film 2A, and is formed by spin coating the composition for forming a silica-based film of the present invention. Near the gate electrode 3 in the interlayer insulating film 5, a contact hole 5A in which an electrode 6 functioning as a bit line is embedded is formed. Further, a planarized interlayer insulating film 7 is deposited on the planarized interlayer insulating film 5, and a storage electrode 8A is embedded in a contact hole 7A formed so as to penetrate both. . The interlayer insulating film 7 is formed by spin-coating the silica-based film forming composition of the present invention in the same manner as the interlayer insulating film 5. A counter electrode 8C is provided on the storage electrode 8A via a capacitor insulating film 8B made of a high dielectric material. The interlayer insulating films 5 and 7 may have the same composition or different compositions.

  According to the electronic parts as exemplified above, the relative permittivity of the silica coating is sufficiently reduced compared to the conventional one, so that the wiring delay time in signal propagation can be sufficiently shortened and at the same time high reliability is realized. it can. It is also possible to improve the production yield and process margin of electronic parts. Furthermore, due to the excellent characteristics of the silica-based coating film comprising the composition for forming a silica-based coating film of the present invention, an electronic component having high density, high quality and excellent reliability can be provided.

  Hereinafter, the preferred embodiments of the present invention will be described in more detail, but the present invention is not limited to these embodiments.

(Example 1)
<Preparation of a composition for forming a silica-based film>
In a solution prepared by dissolving 154.6 g of tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g of cyclohexanone, 80.98 g of an aqueous solution in which 0.525 g of 70% nitric acid was dissolved was stirred for 30 minutes. It was dripped. After completion of the dropwise addition, the reaction was allowed to proceed for 5 hours. Subsequently, a portion of the produced ethanol and cyclohexanone was distilled off in a warm bath under reduced pressure to obtain 583.7 g of a polysiloxane solution. When the weight average molecular weight of the polysiloxane was measured by GPC, it was 1,350.

  Subsequently, 24.86 g of polypropylene glycol (manufactured by Aldrich, PPG725) 24.86 g, cyclohexanone 498.7 g, and 2.38% tetramethylammonium nitrate aqueous solution (PH3.6) 17 were added to 553.9 g of the polysiloxane solution. .89 g and 5.5 g of a maleic acid solution diluted to 1% were added and stirred and dissolved at room temperature for 30 minutes to prepare the composition for forming a silica-based film of the present invention. In addition, the weight loss rate at 350 ° C. of polypropylene glycol (manufactured by Aldrich, PPG725) used as the void forming compound was 99.9%.

(Example 2)
In a solution prepared by dissolving 154.6 g of tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g of cyclohexanone, 80.98 g of an aqueous solution in which 0.525 g of 70% nitric acid was dissolved was stirred for 30 minutes. It was dripped. After completion of the dropwise addition, the reaction was allowed to proceed for 5 hours. Subsequently, a portion of the produced ethanol and cyclohexanone was distilled off in a warm bath under reduced pressure to obtain 598.2 g of a polysiloxane solution. It was 1,280 when the weight average molecular weight of polysiloxane was measured by GPC method.

  Next, 514.5 g of a polysiloxane solution was added to 22.60 g of polypropylene glycol (manufactured by Aldrich, PPG725), 441.6 g of diethylene glycol dimethyl ether, and a 2.38% tetramethylammonium nitrate aqueous solution (PH 3.6). 16.26 g and 5.0 g of a maleic acid solution diluted to 1% were added and dissolved by stirring for 30 minutes at room temperature to prepare the silica-based film forming composition of the present invention. In addition, the weight loss rate at 350 ° C. of polypropylene glycol (manufactured by Aldrich, PPG725) used as the void forming compound was 99.9%.

(Comparative Example 1)
In a solution prepared by dissolving 154.6 g of tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g of ethanol, 80.98 g of an aqueous solution in which 0.525 g of 70% nitric acid was dissolved was stirred for 30 minutes. It was dripped. After completion of dropping, the reaction was allowed to proceed for 5 hours to obtain 819.0 g of a polysiloxane solution. It was 1,170 when the weight average molecular weight of polysiloxane was measured by GPC method.

  Next, 774.0 g of the polysiloxane solution was mixed with 22.60 g of polypropylene glycol (manufactured by Aldrich, PPG725), 182.1 g of ethanol, 2.38% tetramethylammonium nitrate aqueous solution (PH3.6) 16 as a void-forming compound. .26 g and 1 g of 1% diluted maleic acid aqueous solution 5.0 g were added and dissolved by stirring at room temperature for 30 minutes to prepare a silica-based film forming composition. In addition, the weight loss rate at 350 ° C. of polypropylene glycol (manufactured by Aldrich, PPG725) used as the void forming compound was 99.9%.

(Example 3)
<Manufacture of interlayer insulating film>
The composition for forming a silica-based film obtained in Examples 1 and 2 and Comparative Example 1 was spin-coated on a silicon wafer to form a coating film. In addition, rotation speed was adjusted so that the formation of a coating film might become a film which has a film thickness of 500 +/- 50nm after hardening. Next, after removing the organic solvent in the coating film at 250 ° C. over 3 minutes, the organic solvent was removed over 30 minutes at 400 ° C. using a quartz tube furnace in which the O ₂ concentration was controlled to around 100 ppm. The coating film was finally cured to produce a silica-based film as an interlayer insulating film. And the film thickness calculated | required from the phase difference produced by the light irradiation in wavelength 633nm was measured with the spectroscopic ellipsometer (the Gartner company make; ellipsometer L116B) by irradiating He-Ne laser beam on the obtained silica type coating film.

  Next, Al metal was vacuum-deposited on the silica-based coating using a vacuum deposition apparatus so as to have a thickness of about 0.1 μm in a circle having a diameter of 2 mm. As a result, an interlayer insulating film having a structure in which a silica-based film is disposed between an Al metal and a silicon wafer (low resistivity substrate) was manufactured.

[Specific permittivity measurement]
The charge capacity of the obtained interlayer insulating film was measured using a device in which a dielectric test fixture (Yokogawa Electric: HP16451B) was connected to an LF impedance analyzer (Yokogawa Electric: HP4192A) at a temperature of 23 ° C. The measurement was performed under conditions of ± 2 ° C., humidity 40% ± 10%, and operating frequency 1 MHz.

And the measured value of the charge capacity is given by the following formula:
Dielectric constant of interlayer insulating film = 3.597 × 10 ⁻² × charge capacity (pF) × film thickness of interlayer insulating film (μm)
And the relative dielectric constant of the interlayer insulating film was calculated. In addition, the value obtained by the film thickness measurement of the said silica-type film was used for the film thickness of an interlayer insulation film.

[Elastic modulus measurement]
Using nanoindenter SA2 (DCM, manufactured by MTS) (temperature: 23 ° C. ± 2 ° C., frequency: 75 Hz, elastic modulus measurement range: 1/10 or less of interlayer insulation film thickness, does not vary with indentation depth Range) The elastic modulus of the interlayer insulating film was measured.

Table 1 shows the measurement results of the electrical characteristics and elastic modulus (film strength) of the interlayer insulating film obtained in Example 3.

1 is a schematic cross-sectional view showing a preferred embodiment of an electronic component according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Silicon wafer (substrate), 1A, 1B ... Diffusion region, 2A ... Field oxide film, 2B ... Gate insulating film, 3 ... Gate electrode, 4A, 4B ... Side wall oxide film, 5, 7 ... Interlayer insulating film (insulating film) 5A, 7A ... contact hole, 6 ... bit line, 8 ... memory cell capacitor (electronic component), 8A ... storage electrode, 8B ... capacitor insulating film, 8C ... counter electrode.

Claims (17)

(A) component: the following general formula (1);
R ¹ _n SiX _4-n (1)
[Wherein R ¹ represents an H atom or an F atom, or a group containing a B atom, an N atom, an Al atom, a P atom, a Si atom, a Ge atom or a Ti atom, or an organic group having 1 to 20 carbon atoms, X represents a hydrolyzable group, and n represents an integer of 0 to 2. However, when n is 2, each R ¹ may be the same or different, and when n is 0 to 2, each X may be the same or different. ],
A siloxane resin obtained by hydrolytic condensation of a compound represented by:
(B) component: an organic solvent containing at least one aprotic solvent;
(C) component: onium salt,
(D) component: a void-forming compound that is thermally decomposed or volatilized at a heating temperature of 250 to 500 ° C .;
A composition for forming a silica-based film, comprising: The composition for forming a silica-based film according to claim 1, wherein the aprotic solvent contains at least one aprotic solvent selected from the group consisting of an ether solvent and a ketone solvent. The aprotic solvent comprises at least one aprotic solvent selected from the group consisting of dialkyl ethers of dihydric alcohols, alkyl ester ethers of dihydric alcohols, diesters of dihydric alcohols and cyclic ketones. Or the composition for silica-type film formation of 2 or 2. The composition for forming a silica-based film according to any one of claims 1 to 3, wherein at least one of the aprotic solvents is an aprotic solvent having a relative dielectric constant of 10 or more. The composition for forming a silica-based film according to claim 4, wherein the content of the aprotic solvent having a relative dielectric constant of 10 or more is 50% by mass or more based on the weight of the component (b). The composition for forming a silica-based film according to any one of claims 1 to 5, wherein the content of the aprotic solvent is 80% by mass or more based on the weight of the component (b). The component (a) is at least one selected from the group consisting of H atom, F atom, B atom, N atom, Al atom, P atom, Si atom, Ge atom, Ti atom and C atom with respect to 1 mol of Si atom. The composition for forming a silica-based film according to any one of claims 1 to 6, wherein the total content ratio of the atoms is 0.65 mol or less. The composition for forming a silica-based film according to any one of claims 1 to 7, wherein the onium salt is an ammonium salt. The ammonium salt is at least one ammonium salt selected from the group consisting of tetramethylammonium nitrate, tetramethylammonium acetate, tetramethylammonium propionate, tetramethylammonium maleate and tetramethylammonium sulfate. Item 9. The composition for forming a silica-based film according to Item 8. The void-forming compound is a vinyl ether compound, a vinyl compound having a polyoxyethylene unit, a vinyl compound having a polyoxypropylene unit, a vinyl pyridine compound, a styrene compound, an alkyl ester vinyl compound, (meth) acrylate. The composition for forming a silica-based film according to any one of claims 1 to 9, which is at least one compound selected from the group consisting of an acid-based compound, a polymer having a polyoxyalkylene unit, and a polycarbonate polymer. Stuff. The composition for forming a silica-based film according to any one of claims 1 to 9, wherein the void-forming compound is a polymer having a polyoxyalkylene unit. The composition for forming a silica-based film according to any one of claims 1 to 9, wherein the void-forming compound is a polymer having a polyoxypropylene unit. The composition for forming a silica-based film according to any one of claims 1 to 12, wherein the void-forming compound gradually forms micropores in the silica-based film. A method of forming a silica-based film on a substrate,
The composition for forming a silica-based film according to any one of claims 1 to 13 is applied on a substrate to form a coating film, and after removing the organic solvent contained in the coating film, the coating film is formed. A method for forming a silica-based coating, comprising firing at a heating temperature of 250 to 500 ° C. A silica-based coating film provided on a substrate and formed by the method for forming a silica-based coating film according to claim 14. 16. The silica-based coating according to claim 15, wherein the silica-based coating is formed between conductive layers adjacent to each other among a plurality of conductive layers provided on the substrate. . An electronic component comprising the substrate and the silica-based film according to claim 15 or 16 formed thereon.

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