Film forming composition, porous film and their preparation

[0001] The present invention relates to a film-forming composition capable of forming a porous film having excellent dielectric properties, adhesiveness, coating film uniformity, and mechanical strength, a method for producing the same, and a method for producing the same. The present invention relates to a method for forming a porous membrane and the formed porous membrane.

PROBLEM TO BE SOLVED: To solve an increase in wiring delay time due to an increase in inter-wiring capacitance, which is a parasitic capacitance between metal wiring, with the progress of high integration of semiconductor integrated circuits. This is an obstacle to improving the performance of semiconductor integrated circuits. The wiring delay time is the so-called RC delay, which is proportional to the product of the resistance of the metal wiring and the capacitance between the wirings.

[0003] Therefore, in order to reduce the wiring delay time, it is necessary to reduce the resistance of the metal wiring or the capacitance between the wirings.

[0004] By reducing the inter-wiring capacitance, the semiconductor device does not cause wiring delay even if it is highly integrated, so that it is possible to increase the speed and further reduce the power consumption.

[0005] As a method of reducing the capacitance between wirings, it is conceivable to reduce the relative permittivity of the interlayer insulating film formed between the metal wirings, and as an insulating film having a low relative permittivity, conventional silicon A porous film is being studied in place of the oxide film. It can be said that a porous film is almost the only film that can achieve a relative permittivity of 2.0 or less and is practical, and various methods for forming a porous film have been proposed there.

[0006] As a first method for forming a porous film, a precursor solution of a siloxane polymer containing a thermally unstable organic component is synthesized, and then the precursor solution is applied onto a substrate to form a coating film. There is a method of forming a large number of pores after the volatilized component by decomposing and volatilizing the organic component by performing heat treatment after that.

[0007] As a second method for forming the porous material, after forming a wet gel by applying a silica sol solution on a substrate or performing a CVD method, the evaporation rate of the solvent from the wet gel is controlled. , A method of forming a porous material by causing a condensation reaction of a silica sol while suppressing volume shrinkage is known.

[0008] As a third method for forming a porous film, a solution of silica fine particles is applied onto a substrate to form a coating film, and then the coating film is baked and hardened to form a large number of fine particles between the silica fine particles. A method of forming a hole is known.

[0009] As a fourth method, Japanese Patent Application Laid-Open No. 2000-38509 describes (A) R.¹_nSi (OR²)_4-n(R¹Is a monovalent organic group, n is an integer of 0 to 2), contains a polymer obtained by polymerizing a monomer containing (B) a metal chelate compound, (C) an acrylic acid ester and / or a methacrylic acid ester). Proposals have been made for a composition for forming a porous film, which is characterized by the above.

[0010] However, each of these methods has major drawbacks. That is, the first method for forming the porosity has a problem that the cost is high because it is necessary to synthesize a precursor solution of the siloxane polymer, and the precursor solution is applied to form a coating film. Since the amount of silanol groups remaining in the film increases, there are problems such as a degassing phenomenon in which water and the like evaporate in a heat treatment step performed later and deterioration of the film quality due to moisture absorption of the porous film.

[0011] Further, the second method for forming the porous film has a problem that the cost is high and is fine because a special coating device is required to control the evaporation rate of the solvent from the wet gel. A large amount of silanol remains on the surface of the pores, and if it is left as it is, it has high hygroscopicity and the film quality is significantly deteriorated. Therefore, it is necessary to silylate the silanol on the surface, which causes a problem that the process is complicated. When the wet gel is formed by the CVD method, a special CVD apparatus different from the plasma CVD apparatus usually used in the semiconductor process is required, so that the cost is also high.

[0012] In the third method of forming the porous film, the diameter of the pores formed between the silica fine particles is determined by the geometrically deposited structure of the silica fine particles. Since the diameter becomes very large, there is a problem that it is difficult to reduce the relative permittivity of the porous film to 2 or less.

[0013] In the case of the fourth method, the metal chelate compound of the component (B) among the three components (A), (B) and (C) improves the compatibility of the components (A) and (C). It is a necessary component and essential for making the thickness of the coating film uniform after curing, but it is not preferable because it complicates the component, complicates the manufacturing process, and increases the cost. That is, it is desired to develop a material that can form a uniform solution without a chelating component and that the coating film after curing is flat.

[0014] The present invention solves the above-mentioned problems at once, and a film-forming composition capable of forming a porous film having a relative permittivity of 2.0 or less in a simple process and at low cost, a method for producing the same, and a method for producing the same. It is an object of the present invention to provide a method for forming a porous membrane and a porous membrane.

[Means for Solving the Problems and Embodiments of the Invention] From conventional studies, the present inventors usually have low compatibility with the acrylic resin, and it is not possible to mix them uniformly as they are. He had the knowledge that it was difficult.

[0016] Further, according to the study by the present inventors, in the case of such a mixed solution, even if the solution is transparent and uniform in appearance, the compatibility is somewhat insufficient, and spin coating is performed. The applied thin film whitens, and streaky striations are violently generated. Therefore, in the case of a composite material, a very high degree of compatibility between materials is required for use in the application according to the present invention.

[0017] In the case of a mixed system of a silicone resin and an acrylic polymer, conventionally, it is not possible to prepare a uniform solution only with the silicone resin component and the acrylic resin component. For example, in the method of JP-A-2000-38509, In addition to the silicone component and the acrylic component, a metal chelate compound is listed as an essential component. Although there is no clear description, judging from the fact that it is desirable to react this chelate component with both silicone resin and acrylic resin components, it is possible to form a uniform solution for the first time by mediating the chelate component. it is conceivable that.

[0018] As a chelate component used to solve this problem, titanium, zirconium, aluminum, tin, antimony, tantalum, lead and the like are cited as examples, and such a component makes this material a semiconductor. When used in a device, there is a risk of causing unexpected problems, and there is also concern that it may cause hygroscopicity and deterioration of the film.

[0019] The present inventors have solved this problem by controlling the structure of the serialcon component, specifically, the following general formula (1) R.¹-SiZ₃ It contains 30 to 100 mol% of the structural unit (T unit) represented by (1), and of these T units, the following general formula (2) R¹-Si (OH) Z'₂ Contains 30 to 80 mol% of a structural unit (T-2 unit) containing one silanol group represented by (2) (however, R in the above formula).¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, Z is selected from an OH group, a hydrolyzable group and a siloxane residue, at least one indicates a siloxane residue, and Z'indicates a siloxane residue. ), When a silanol group-containing silicone resin having a number average molecular weight of 100 or more is used, an extremely uniform solution is formed in a mixed system with an acrylic polymer, and this solution is mottled even after being applied and heat-cured. We have found that it is possible to form a uniform and flat film that does not become, whiten, or cause striations.

[0020] Further, when the film formed in this manner is heated at a temperature at which the acrylic resin component decomposes, the acrylic resin component decomposes at the same time as the curing of the silicone resin component progresses, and the decomposition product evaporates. It was found that voids were formed in the film and eventually became a porous film, and as a result of measuring the relative permittivity, such a film showed a value much smaller than the original relative permittivity of the silicone resin, and the acrylic resin. The present invention has been completed by finding that a film having a dielectric constant of about 1.2 to 2.7 can be formed by adjusting compositions having different component contents.

[0021] Therefore, the present invention provides the following film-forming composition, a method for producing the same, a method for forming a porous film, and a porous film obtained thereby. Claim 1: (A) R¹SiX₃(However, R¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, and X indicates a hydrolyzable group. ) Is used to hydrolyze the hydrolyzable silane compound raw material containing 30 to 100 mol% of the total hydrolyzable silane compound under hydrophilic conditions that substantially do not contain an organic solvent. Obtained, the following general formula (1) R¹-SiZ₃ It contains 30 to 100 mol% of the structural unit (T unit) represented by (1), and of these T units, the following general formula (2) R¹-Si (OH) Z'₂ Contains 30 to 80 mol% of a structural unit (T-2 unit) containing one silanol group represented by (2) (however, R in the above formula).¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, Z is selected from an OH group, a hydrolyzable group and a siloxane residue, at least one indicates a siloxane residue, and Z'indicates a siloxane residue. ), A silanol group-containing silicone resin having a number average molecular weight of 100 or more, and (B) an acrylic acid ester, a methacrylate ester, or a mixture thereof, and a monomer having an alkoxysilyl group further constitutes an acrylic polymer. A silicone-containing film characterized in that a polymerization raw material containing 0.5 to 10 mol% of a monomer is dissolved in a solvent that dissolves a polymer obtained by polymerizing, and a uniform solution is formed without a chelating component. Composition for formation. 2. The composition according to claim 1, which is used for forming a coating film on a semiconductor substrate. 3. The composition according to claim 1, which is for forming an interlayer insulating film. Claim 4: (A) R¹SiX₃(However, R¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, and X indicates a hydrolyzable group. ) Is used to hydrolyze the hydrolyzable silane compound raw material containing 30 to 100 mol% of the total hydrolyzable silane compound under hydrophilic conditions that substantially do not contain an organic solvent. Obtained, the following general formula (1) R¹-SiZ₃ It contains 30 to 100 mol% of the structural unit (T unit) represented by (1), and of these T units, the following general formula (2) R¹-Si (OH) Z'₂ Contains 30 to 80 mol% of a structural unit (T-2 unit) containing one silanol group represented by (2) (however, R in the above formula).¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, Z is selected from an OH group, a hydrolyzable group and a siloxane residue, at least one indicates a siloxane residue, and Z'indicates a siloxane residue. ), A solution in a solvent of a silanol group-containing silicone resin having a number average molecular weight of 100 or more, (B) a polymerization monomer consisting of an acrylic acid ester, a methacrylate ester or a mixture thereof, or an oligomer thereof, and further alkoxysilyl Claims 1 and 2 or claim 1, which comprises a step of mixing a polymerization raw material containing a group-containing monomer containing 0.5 to 10 mol% of all the monomers constituting an acrylic polymer and polymerizing with a radical polymerization catalyst. 3. The method for producing a film-forming composition according to the above method. 5. A method for forming a porous film, which comprises applying the composition according to claim 1, 2 or 3 to a substrate and heating the formed film at a temperature equal to or higher than the decomposition temperature of the component (B). .. Claim 6: Porous membrane obtained by the method according to claim 5.

[0022] Hereinafter, the present invention will be described in detail. The silicone resin component (A) used in the present invention is defined as follows. The following general formula (1) R¹-SiZ₃ It contains 30 to 100 mol%, preferably 60 to 100 mol% of the structural unit (T unit) represented by (1), and of these T units, the following general formula (2) R¹-Si (OH) Z'₂ The structural unit (T-2 unit) containing one silanol group represented by (2) is contained in an amount of 30 to 80 mol%, preferably 40 to 70 mol% (however, R in the above formula).¹Indicates a substituted or unsubstituted monovalent hydrocarbon group, Z is selected from an OH group, a hydrolyzable group and a siloxane residue, at least one indicates a siloxane residue, and Z'indicates a siloxane residue. ), A silanol group-containing silicone resin having a number average molecular weight of 100 or more.

Here, the following general formula (1) R¹-SiZ₃ Among the structural units constituting this silicone resin represented by (1), R¹The monovalent hydrocarbon group preferably has 1 to 12 carbon atoms, such as an alkyl group, an aryl group, an aralkyl group, an alkenyl group, or a halogen atom in which some or all of these hydrogen atoms are fluorine atoms. Examples thereof include a group substituted with an epoxy-containing group such as a glycidyl group or a glycidyloxy group. Specific examples thereof include an alkyl group, an aryl group, and a glycidyl group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group, preferably having 1 to 5 carbon atoms. , These alkyl groups may be chained or branched, and the hydrogen atom may be further substituted with a fluorine atom. Examples of the aryl group include a phenyl group and a naphthyl group.

[0024] Further, Z represents an OH group, a hydrolyzable group or a siloxane residue, and specific examples of the hydrolyzable group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group and sec-. Examples thereof include an alkoxy group such as a butoxy group and a t-butoxy group, an alkenoxy group such as a vinyloxy group and a 2-propenoxy group, an asyloxy group such as a phenoxy group and an acetoxy group, an oxime group such as a butanoxim group, and an amino group. Of these, an alkoxy group is preferable, and a methoxy group, an ethoxy group, an isopropoxy group, and a butoxy group are particularly preferable because of ease of control during hydrolysis and condensation. Further, the siloxane residue means a substituent that is bonded to an adjacent silicon atom via an oxygen atom to form a siloxane bond, and is -O- (Si), but the oxygen atom. O to share with adjacent silicon atoms_1/2It can also be expressed as.

[0025] Further, in this silicone resin, the following general formula (2) R¹-Si (OH) Z'₂ It contains 30 to 80 mol% of a structural unit (T-2 unit) containing one silanol group represented by (2). Here, R¹Is defined as above, and Z'is a siloxane residue.

[0026] The silicone resin is the R of the above formula (1).¹-SiZ₃As a group other than R¹₃-SiZ (M unit), R¹₂-SiZ₂(D unit), SiZ₄(Q unit) may be included. In this case, the M unit is 0 to 30 mol%, especially 0 to 10 mol%, the D unit is 0 to 50 mol%, especially 0 to 20 mol%, and the Q unit is 0 to 30 mol%, especially 0 to 10 mol%. Can be the content of. However, at least one of Z in M unit, D unit, and Q unit is a siloxane residue.

[0027] Next, the molecular weight of the silanol group-containing silicone resin applied in the present invention will be described. When the silicone resin is applied to form a uniform film, the silicone resin has a molecular weight of a certain level or higher. It is desirable to form a uniform film. From this point, it is necessary to use a silicone resin having a number average molecular weight of 100 or more in the present invention. If it is less than 100, it is difficult to form a uniform film because an appropriate structure cannot be ensured, and the storage stability is also inferior. Preferably, the number average molecular weight is 500 to 100,000, particularly preferably 1000 to 5000.

[0028] The silicone resin applicable to the present invention preferably satisfies the above conditions and at the same time contains a certain amount or more of silanol groups, and is 5% by weight or more, particularly 6 to 20% by weight in the silicone resin. It is preferable to contain it. If the silanol group content is too low, the absolute amount of silanol groups that contribute to cross-linking is insufficient, and the hardness of the cured film may decrease.

[0029] The silicone resin may be produced by any method as long as the above conditions are satisfied. The specific manufacturing method will be described below.

[0030] As a raw material for production, a silane compound having a functional group such as an alkoxy group, an alkenyloxy group, an acyloxy group, a halogen atom, an amino group or an oxime group as a hydrolyzable group, or a partial hydrolysis / condensation thereof. You can use things. From the viewpoint of ease of control of the hydrolysis reaction, ease of treatment of hydrolysis by-products, and economic viewpoint, it is preferable to use an alkoxy group or a chlor atom, particularly an alkoxy group, as the hydrolyzable group. Good. When a chlor atom is used, it is preferable to completely hydrolyze the chlor atom so as not to leave a chlorine atom in the silicone resin. The number of hydrolyzable groups is 1, 2, 3, or 4 per silicon atom, and the organic substituent R satisfying the above conditions.¹Any silane compound having the above can be used, but the number of hydrolyzable groups X is 3, that is, R.¹SiX₃The hydrolyzable silane compound represented by is used in an amount of 30 to 100 mol%, particularly 50 to 100 mol%, of the total hydrolyzable silane compound. As another hydrolyzable silane compound, SiX₄, R¹₂SiX₂, R¹₃SiX can be used.

[0031] Specifically, tetrafunctional silanes (4 hydrolyzable groups) such as tetrachlorosilane, tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane: SiX.₄, Methyltrichlorosilane, Methyltrimethoxysilane, Methyltriethoxysilane, Methyltriisopropoxysilane, Methyltributoxysilane, Methyltriisopropenoxysilane, Ethyltrichlorosilane, Ethyltrimethoxysilane, Ppropyltrichlorosilane, Butyltrichlorosilane, Trifunctional silanes (hydrolytable groups) such as butyltrimethoxysilane, hexyltrichlorosilane, hexyltrimethoxysilane, decyltrichlorosilane, decyltrimethoxysilane, phenyltricrolsilane, phenyltrimethoxysilane, cyclohexyltrichlorosilane, cyclohexyltrimethoxysilane 3): R¹SiX₃, Dimethyldichlorosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldiisopropoxysilane, dimethyldibutoxysilane, dimethyldiisopropenoxysilane, propylmethyldichlorosilane, propylmethyldimethoxysilane, hexylmethyldichlorosilane, Bifunctional silanes such as hexylmethyldimethoxysilane, phenylmethyldichlorosilane, phenylmethyldimethoxysilane, diphenyldichlorosilane, diphenyldimethoxysilane (two hydrolyzable groups): R¹₂SiX₂, Trimethylchlorosilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylisopropenoxysilane, dimethylphenylchlorsilane and other monofunctional silanes (one hydrolyzable group): R¹₃SiX and so-called silane coupling agents having organic functional groups, such as vinyl trichlorosilane, vinyl trimethoxysilane, vinyl triethoxysilane, 5-hexenyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycid. Xypropyltriethoxysilane, 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxipropyltriethoxysilane, 4-vinylphenyltrimethoxysilane, 3- (4-vinylphenyl) propyltrimethoxysilane , 4-Vinylphenylmethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3- Mercaptopropyltriethoxysilane, vinylmethyldichlorosilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3- (meth) acrylic Loxypropylmethyldimethoxysilane, 3- (meth) acryloxipropylmethyldiethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldi Examples of silane compounds in which ethoxysilane and its partial hydrolyzate can be used are given.

[0032] It is more preferable to use an alkoxysilane, particularly methoxysilane or ethoxysilane, from the viewpoint of operability and ease of distilling off by-products. The organic silicon compounds that can be used are not limited to those described above. Further, one kind or a mixture of two or more kinds of these silane compounds may be used.

[0033] The silanol group-containing silicone resin according to the present invention is characterized in that it can be obtained by hydrolyzing the hydrolyzable silane compound in an aqueous solution. When hydrolysis is carried out under hydrophilic conditions containing substantially no organic solvent, a unique silicone resin having a structure containing a large amount of T-2 units, which characterizes the present invention, can be obtained. This silicone resin is prepared through the following steps.

[0034] First, the first step is a process of hydrolyzing and condensing the above-mentioned various hydrolyzable organic silane compounds in an aqueous solution having a pH of 1 to 7. The amount of water used for hydrolysis is preferably 50 to 5000 parts by weight with respect to 100 parts by weight of the silane compound or a mixture thereof blended in a composition satisfying the above conditions. If the amount is less than 50 parts by weight, the amount of water in the reaction system is small, so that it is difficult to control the reactivity of the silanol group described above, and it may not be possible to impart the structure. On the other hand, if it exceeds 5000 parts by weight, the silane concentration of the raw material may be too low and the condensation reaction may be delayed.

[0035] Hydrolysis is carried out by adding a silane compound to an aqueous solution and stirring the mixture. A hydrolysis catalyst may be added to promote hydrolysis, especially the initial hydrolysis. The hydrolysis catalyst may be added to the aqueous solution before the silane compound is added, or may be added to the dispersion liquid after the silane compound is dispersed. As the hydrolysis catalyst, a conventionally known catalyst can be used, and it is preferable to use a catalyst in which the added aqueous solution exhibits acidity of pH 1 to 7. In particular, acidic hydrogen halides, carboxylic acids, sulfonic acids, acidic or weakly acidic inorganic salts, solid acids such as ion exchange resins and the like are preferable. Specific examples include inorganic acids such as hydrofluoric acid, hydrochloric acid, nitrate and sulfuric acid, organic acids typified by acetic acid, maleic acid and trifluoroacetic acid, methanesulphonic acid, paratoluenesulphonic acid and trifluoromethanesulphonic acid. Examples thereof include sulphonic acids and cation exchange resins having a sulphonic acid group or a carboxylic acid group on the surface.

[0036] When a hydrolyzing catalyst is used, the amount added thereof is preferably in the range of 0.001 to 10 mol% with respect to 1 mol of the hydrolyzable group on the silicon atom. Under strong acid conditions below pH 1 or alkaline conditions above pH 7, silanol groups tend to be extremely unstable. More preferably, the pH of the aqueous solution used is 2-6. Since the amount of water is large in excess of the amount of hydrolyzable groups, the hydrolysis proceeds completely. Condensation of silanol groups easily proceeds by stirring under these conditions at room temperature or under heating.

[0037] At this stage, since a hydrolysis by-product is present in the system, the silane reaction mixture, which is a precursor of the silanol group-containing silicone resin, is dissolved in the solution and exists.

[0038] The second step is a process of removing the hydrolysis by-product from the solution containing the reaction mixture to the outside of the system to form a system mainly containing a silanol group-containing silicone resin and water.

[0039] That is, the solution containing the silane reaction mixture obtained in the first step is heated under normal pressure of 80 ° C. or lower, preferably about 30 to 70 ° C., or room temperature to 80 ° C. A system consisting of a silanol group-containing silicone resin and water by distilling off hydrolysis by-products such as alcohol by reducing the pressure to 20 mmHg to normal pressure at a temperature of ° C, preferably room temperature to 70 ° C. Convert to. In this process, the degree of condensation of the silicone resin further progresses.

[0040] The silicone resin hydrolyzed and condensed to some extent in the first step becomes polymerized as the condensation further progresses, and gradually loses its hydrophilicity. At the same time, most of the external environment in which the silicone resin is dissolved becomes water.

By removing 30 to 100% of the hydrolyzed by-product, the silanol group-containing silicone resin can no longer be dissolved in the solution, and the solution becomes slightly turbid or cloudy. When 50 to 100% of the by-products are removed, the silicone resin becomes insoluble in the aqueous layer and settles by standing.

[0042] The silicone resin separated from the aqueous layer in this way can be taken out by itself, but it can also be separated from the aqueous layer as a solution by adding an organic solvent that is not uniformly compatible with water. Is. Examples of such an organic solvent include diethyl ether, diisopropyl ether, methyl isobutyl ketone, ethyl acetate, n-butyl acetate, isobutyl acetate, benzene, toluene, xylene and the like.

[0043] The silicone resin used in the present invention can be produced in this way, but can be used by any production method within the range defined above, and is limited by the production method. It is not something that is done.

[0044] Next, a polymer obtained by polymerizing a monomer containing an acrylic acid ester, a methacrylic acid ester, or a mixture thereof, which are the components (B), will be described.

[0045] Examples of the acrylic acid ester and the methacrylic acid ester constituting the polymer in the present invention include an acrylic acid alkyl ester, a methacrylic acid alkyl ester, an acrylic acid alkoxyalkyl ester, a methacrylic acid alkyl ester, and a methacrylic acid alkoxyalkyl ester. be able to.

[0046] Examples of the alkyl acrylate ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, pentyl acrylate, and hexyl acrylate. As alkyl esters and alkyl methacrylates of ~ 6, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, butyl methacrylate, pentyl methacrylate, and methacrylic. Alkyl esters having 1 to 6 carbon atoms such as hexyl acid, methoxymethyl acrylate and ethoxyethyl acrylate as the acrylate alkoxyalkyl ester, and methoxymethyl methacrylate and ethoxyethyl methacrylate as the alkoxyalkyl methacrylate esters. Can be mentioned.

[0047] Among these, it is preferable to use an alkyl methacrylate ester, and it is particularly preferable to use methyl methacrylate, ethyl methacrylate, isobutyl methacrylate and the like.

[0048] In the present invention, the acrylic polymer is preferably formed by copolymerizing the above-mentioned monomer with a monomer having an alkoxysilyl group. Examples of the monomer having an alkoxysilyl group include 3- (trimethoxysilyl) propyl acrylate, 3- (triethoxysilyl) propyl acrylate, 3- [tri (methoxyethoxy) silyl] propyl acrylate, and 3- (tri (methoxyethoxy) silyl] acrylate. Methyldimethoxysilyl) propyl, 3- (methyldiethoxysilyl) propyl acrylate, 3- (trimethoxysilyl) propyl methacrylate, 3- (triethoxysilyl) propyl methacrylate, 3- [tri (methoxyethoxy) methacrylate) Examples thereof include silyl] propyl, 3- (methyldimethoxysilyl) propyl methacrylate, and 3- (methyldiethoxysilyl) propyl methacrylate.

[0049] The monomer having an alkoxysilyl group is preferably in a proportion of 0.5 to 10 mol%, particularly 1 to 7 mol%, in all the monomers constituting the acrylic polymer.

[0050] In the present invention, the acrylic polymer may be copolymerized with 40 mol% or less of a radically polymerizable monomer other than the above-mentioned acrylic acid ester, methacrylic acid ester and monomer having an alkoxysilyl group. Examples of the radically polymerizable monomer include unsaturated carboxylic acids such as acrylic acid and methacrylic acid, unsaturated amides such as N, N-dimethylacrylamide and N, N-dimethylmethacrylate, unsaturated nitriles such as acrylonitrile, and methylvinyl ketones. Examples include unsaturated ketones, styrene, and aromatic compounds such as α-methylstyrene.

[0051] In the present invention, the polystyrene-equivalent number average molecular weight of the acrylic polymer is preferably 1000 to 100,000, particularly preferably 1000 to 20000. The mixing ratio of the component (A) and the component (B) is 5:95 to 95: 5, especially 10:90 to 80:20 by weight.

[0052] Such an acrylic acid-based polymer can be mixed with a silicone resin component and subjected to a polymerization reaction in a state of being mixed with the following solvent to obtain the composition according to the present invention. When manufactured by such a method, the monomers are polymerized in the presence of the silicone resin, so that both resins form a mutual penetration network structure (IPN). As a result, even a mixture of a methyl-based silicone resin and an acrylic acid-based polymer, which is generally inferior in mutual solubility, is completely transparent and does not separate or become mottled even after application. A solution with much higher uniformity can be obtained as compared with the case of mixing.

[0053] The coating liquid according to the present invention is used in a state of being dissolved in a solvent that dissolves a silicone resin and an acrylic polymer. As the solvent used here, any ordinary coating solvent can be used, but methyl isobutyl ketone, butyl acetate, isobutyl acetate, ethyl lactate, cyclohexanone, diglime, ethyl cellosolve acetate, propylene glycol monomethyl Examples include, but are not limited to, ether acetate and anisole.

[0054] It is also possible to add a surfactant to this solution in order to improve the flatness when applied.

[0055] In order to form a film using the composition for forming a porous film of the present invention, first, the composition of the present invention is applied to a substrate to form a coating film. Here, examples of the substrate on which the composition of the present invention can be applied include semiconductors, glass, ceramics, metals, etc., and as the coating method, any method used in ordinary semiconductor device manufacturing can be used. However, examples thereof include spin coating, dipping, and roller blades. Here, the thickness of the coating film to be formed is usually 0.2 to 20 μm in the case of an interlayer insulating film. The formed coating film is then heated, which is usually aimed at evaporating the solvent in the coating solution in a step called prebaking to immobilize the shape of the coating film. The heating temperature at this time is a temperature sufficient to evaporate the solvent in the coating liquid.

[0056] The film thus formed can be heated to a temperature sufficient for the component (A) to be cured and the component (B) to be decomposed and evaporated to form a cured film having pores. it can.

[0057] As this heating method, it is preferable to heat at a temperature of 300 to 500 ° C., which results in a porous film having pores in the case of the present composition. The heating time is about 1 minute to 2 hours, but more preferably 5 minutes to 1 hour. If the heating temperature is too low, the curing of the component (A) and the decomposition and evaporation of the component (B) will not proceed, and only a film with insufficient curing and low mechanical strength can be formed. Temperatures of 350 to 450 ° C are more preferred as they may result in excessive decomposition of the components, also resulting in reduced film strength and incompatibility with semiconductor device manufacturing processes.

[0058] As the atmosphere at the time of this heating, there is a difference in the distribution of pores and the mechanical strength of the film between the case of performing in the atmosphere and the case of performing in an inert gas atmosphere. By controlling this, the film is used. The physical properties can be controlled, and any kind can be used and is not limited.

[0059] Examples of the inert gas include nitrogen gas and argon gas. In the present invention, the inert gas is preferably used so that the oxygen concentration is, for example, 5 ppm or less. By heating in the inert gas in this way, the influence of oxygen is eliminated and the obtained film is obtained. The permittivity of can be set to a lower value.

[0060] Further, in the method for producing a membrane of the present invention, by heating (reacting) the composition for forming a porous membrane under reduced pressure, the influence of oxygen is eliminated and the dielectric constant of the obtained membrane is lowered. Can be a value.

[0061] The film obtained by heating the composition of the present invention by the method of the present invention usually has pores of 100 nm or less and a porosity of 5 to 70%. The dielectric constant of the film is usually 2.7 to 1.2, preferably 2.5 to 1.2, and more preferably 2.2 to 1.2. Therefore, the film of the present invention is suitable as an insulating film, and is particularly suitable as an interlayer insulating film for highly integrated circuits.

[Examples] Hereinafter, the present invention will be specifically described with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited to the following Examples.

[Production Example 1] 408 g (3.0 mol) of methyltrimethoxysilane was charged in a 2 liter flask, and 800 g of water was added at 0 ° C. under a nitrogen atmosphere and mixed well. Under ice-cooling, 216 g of a 0.05 N aqueous hydrochloric acid solution was added dropwise over 40 minutes to carry out a hydrolysis reaction. After completion of the dropping, the mixture was stirred at 10 ° C. or lower for 1 hour and further at room temperature for 3 hours to complete the hydrolysis reaction. Then, methanol and water produced by hydrolysis were distilled off under reduced pressure for 1 hour under the condition of 70 ° C × 60 Torr to obtain 1136 g of a solution. The solution became cloudy, and when it was static for a whole day and night, it separated into two layers, and the silicone resin that became insoluble in water settled. After adding 200 g of methyl isobutyl ketone to this cloudy solution and stirring well, the solution was allowed to stand and separated from the aqueous layer. This gave 398 g of solution. Of this silanol group-containing silicone resin²⁹NMR analysis revealed that the T unit was 100 mol%, of which 2 mol% was T-1 unit, 42 mol% was T-2 unit, and 56 mol% was T-3 unit. This silicone resin The number average molecular weight of was 1800. However, T-1 unit: CH₃Si (OH)₂Z'T-2 unit: CH₃Si (OH) Z'₂T-3 unit: CH₃SiZ'₃[Production Example 2] The reaction was carried out in the same manner as in Production Example 1 except that 367 g of methyltrimethoxysilane and 41 g of dimethyldimethoxysilane were charged in a 2-liter flask, and 412 g of a methyl isobutyl ketone solution was obtained. .. The polystyrene-equivalent number average molecular weight by GPC was 2100. The obtained silicone resin has a T unit of 89 mol% and a D unit of 11 mol%, and of the T units, T-1 unit is 4 mol%, T-2 unit is 40 mol%, and T-3 unit is. It was 56 mol% (note that the T-1 to T-3 units are the same as above).

[Production Example 3] 17.95 g of ethyl methacrylate, 2.05 g of 3- (trimethoxysilyl) propyl methacrylate, 0.33 g of AIBN, 0.20 g of 2-mercaptoethanol and 30 g of 3-methoxymethylpropionate in a 100 ml flask. It was put in and dissolved. After replacing the inside of the system with nitrogen gas, a viscous polymer solution was obtained by stirring for 7 hours while heating in an oil bath at 80 ° C. When the average molecular weight in terms of polystyrene was measured by GPC, the number average molecular weight was 5200.

[Production Example 4] 19.0 g of isobutyl methacrylate, 1.0 g of 3- (trimethoxysilyl) propyl methacrylate, 0.33 g of AIBN, 0.20 g of 2-mercaptoethanol and 30 g of methyl isobutyl ketone are placed in a 100 ml flask and dissolved. It was. After placing a film in the system with nitrogen gas, a viscous polymer solution was obtained by stirring for 7 hours while heating in an oil bath at 80 ° C. When the average molecular weight in terms of polystyrene was measured by GPC, the number average molecular weight was 52000.

[Production Example 5] In a 2-liter flask, 498 g of the solution of Production Example 1, 37.8 g of methyl methacrylate (MMA), 16.2 g of butyl acrylate (BA), and 1.0 g of 3- (triethoxysilyl) propyl methacrylate. In addition, after stirring well, the inside of the system was replaced with nitrogen. This was heated to 95 ° C. and a 10 ml methyl isobutyl ketone solution of 1 g of AIBN was added over 2 hours. When the reaction solution was kept at the same temperature for another 3 hours, a viscous solution was obtained. When the average molecular weight in terms of polystyrene was measured by GPC, the number average molecular weight was 7890 and the weight average molecular weight was 14300.

[Production Example 6] In a 2-liter flask, 500 g of the silicone resin of Production Example 2, 37.8 g of ethyl methacrylate, 16.2 g of hexyl acrylate, and 1 g of 3- (methyldiethoxysilyl) propyl methacrylate are charged, and Production Example 5 The reaction was carried out in the same manner as in. The polystyrene-equivalent average molecular weight of the product was 19,500.

[Examples, Comparative Examples] A film spin-coated with a coating film solution of the components shown in Table 1 was heat-treated to obtain a porous film, which was evaluated. The coating solution was diluted with propylene glycol monomethyl ether acetate as needed to obtain a solution having a non-volatile residue of 30 to 40%, and spin coating was performed. The number of rotations at this time was 1500 to 3000 rotations for 60 seconds. After application, prebaking was performed at 100 ° C. for 60 seconds, and then heating was performed in the oven at 400 ° C. for 60 minutes in the air. The permittivity of the coating film was measured using an HP16451B electrode manufactured by Yokogawa Hewlett-Packard Co., Ltd. and an HP4284A Precision LCR meter at a frequency of 100 kHz. The results are shown in Table 1.

[0070] [Table 1]<img file="JP3654343B2_D0001.tif" />(Note) Flatness: Good, × Poor [0071] [Effect of the present invention] By using the composition of the present invention, the composition is porous and has a low dielectric constant, is flat and uniform, and has a small dielectric constant. Moreover, it has high mechanical strength and can form an optimum film as an interlayer insulating film when used in semiconductor device manufacturing.