JPWO2011052657A1 - Precursor composition of porous film and method for forming porous film - Google Patents

Abstract

The precursor composition of the porous film is destroyed at a temperature higher than the temperature at which the first alkoxysilane compound, the second alkoxysilane compound, and the first alkoxysilane compound and the second alkoxysilane compound are copolymerized. And a nonionic surfactant micelle. Of these, the first alkoxysilane compound is tetraalkoxysilane, monoalkyltrialkoxysilane, dialkyldialkoxysilane, tetraalkoxysilane polymer, monoalkyltrialkoxysilane polymer, and dialkyldialkoxysilane polymer. The second alkoxysilane compound is at least one selected from the group consisting of trialkoxyphenylsilanes.

Description

  The present invention relates to a precursor composition for a porous film applied by a spin coating method to form a porous film, in particular, a precursor composition for a porous film made of an organosilicon oxide, and the precursor composition. The present invention relates to a method for forming a porous film to be used.

  In recent years, as devices equipped with semiconductor devices have been reduced in size, there has been an increasing demand for miniaturization and densification of elements and wirings constituting the semiconductor devices. Further, as the miniaturization of elements and wirings progresses, wiring delays become obvious. Therefore, a reduction in capacitance between wirings is also required in order to suppress a decrease in processing speed due to wiring delays. Therefore, conventionally, in order to reduce the capacitance between the wirings, for example, as described in Patent Document 1, the insulating film between the wirings is made of a porous organic silicon oxide film, that is, a porous silica film. Has been intensively studied.

  In the method of forming the porous silica film by spin coating, first, a precursor composition of the porous film is applied on the substrate. Next, the thermally decomposable organic compound contained in the precursor composition is decomposed by heating the substrate, and the space occupied by the thermally decomposable organic compound becomes a void, that is, a porous silicon A porous silica film is formed. And a hydrophobic functional group is introduce | transduced with respect to the whole surface of a porous silica membrane. The hydrophobic functional group is also introduced into the inner surface of the pores exposed on the surface of the porous silica film. According to the porous silica film thus formed, since the hydrophilic compound is suppressed from entering the pores, the increase in the dielectric constant by the hydrophilic compound is suppressed, and the porous silica film originally has the porous silica film. A low dielectric constant is maintained.

JP 2006-265350 A

  By the way, if the porous silica film is used as an insulating film between wirings, grooves and through holes for forming wirings, electrodes and the like are formed in the porous silica film. Since a dry etching process is generally used as a method for forming fine grooves and through-holes, the dry etching process is also performed on the porous silica film.

  On the other hand, plasma using an etching gas is induced in a gas phase in a reaction vessel in which dry etching is performed, and positive ions and radicals as etchants are generated. Then, the groove and the through hole are formed by etching the porous silica film physically or chemically with an etchant containing positive ions and radicals. At this time, vacancies formed inside the porous silica film, that is, vacancies into which the hydrophobic functional group is not introduced, are exposed on the inner surface of the through-hole. As a result, hydrophilic compounds such as water molecules in the atmosphere are adsorbed on the inner surface of the pores exposed to the outside through the through holes.

  That is, when a porous silica film is formed from the precursor composition described in Patent Document 1, the porous silica film has a low dielectric constant at the time of formation, but processing using a dry etching process is performed. After this time, the porous silica film may lose its low dielectric constant characteristics.

  The present invention has been made in view of the above-described conventional situation, and the purpose thereof is a precursor composition of a porous silica film capable of suppressing an increase in the relative dielectric constant of the porous film after the etching process, Another object of the present invention is to provide a method for forming a porous silica film using the same.

  The first aspect of the present disclosure is such that the first alkoxysilane compound, the second alkoxysilane compound, the first alkoxysilane compound, and the second alkoxysilane compound are destroyed at or above the temperature at which they are copolymerized. Provided is a porous membrane precursor composition comprising nonionic surfactant micelles. The first alkoxysilane compound comprises a tetraalkoxysilane, a monoalkyltrialkoxysilane, a dialkyldialkoxysilane, a tetraalkoxysilane polymer, a monoalkyltrialkoxysilane polymer, and a dialkyldialkoxysilane polymer. At least one selected from the group, and the second alkoxysilane compound is trialkoxyphenylsilane.

  According to the above configuration, an organic silicon oxide film having a polysiloxane skeleton as a main skeleton is formed under a condition in which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, and the organic silicon oxide Nonionic surfactant micelles are contained in the membrane. Then, above the temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, the nonionic surfactant micelles contained in the organic silicon oxide film are destroyed, and the space occupied by the micelles is destroyed. Holes are formed. Therefore, the porosity of the porous film having a polysiloxane skeleton as the main skeleton, that is, the relative dielectric constant, is defined by the content of the nonionic surfactant micelle.

  At this time, since the second alkoxysilane compound is trialkoxyphenylsilane, the surface layer of the porous film naturally includes a phenyl group in the three-dimensional polysiloxane skeleton. In other words, not only is the phenyl group added to the outer surface of the porous film, but the phenyl group is also added in a form surrounded by the polysiloxane skeleton constituting the porous film. A highly hydrophobic phenyl group is imparted throughout. As a result, even when dry etching is applied to the porous film, the inner surface of the void exposed through the recessed portion after etching has a highly hydrophobic phenyl group. In addition, since it is difficult for the etchant to reach the phenyl group surrounded by the polysiloxane skeleton, the above-described phenyl group can be held on the inner surface of the hole regardless of the shape after the etching.

  Here, when the hydrophobic functional group contained in the polysiloxane skeleton is an alkyl group, not only the bond between silicon and the hydrocarbon group is broken, but also the single bond between the carbons in the hydrocarbon group. Even when cleaved, the alkyl group is detached from the porous membrane. On the other hand, since the phenyl group has an arene structure including a single bond and a double bond, even if the carbon bond in the phenyl group is broken, the broken bond can be repaired. High nature.

  Furthermore, only one phenyl group is added to the silicon atom, and the number of carbon atoms bonded to the porous film can be increased by 6 times the number of the phenyl group. Here, in order to improve the plasma resistance, it is clear that improving the hydrophobicity is effective. For this purpose, it is necessary to increase the number of organic groups such as the hydrocarbon group. However, since such addition of organic groups causes a decrease in mechanical strength of the porous membrane, it is preferable that the number of organic groups added to the porous membrane is smaller.

  That is, the above-mentioned phenyltrimethoxysilane is an alkoxysilane compound that satisfies both the hydrophobicity and mechanical strength of the porous film, and consequently suppresses the increase in the dielectric constant of the porous film after the etching process. Can do.

  In addition, according to the above configuration, the porous membrane precursor composition contains the first alkoxysilane compound, the second alkoxysilane compound, and the nonionic surfactant. A polysiloxane skeleton that forms a skeleton of a porous film only by applying the precursor composition of the porous film to a substrate or the like that is a film formation target, and a hydrophobic functional group that is added to the polysiloxane skeleton; A porous film having the following can be formed. That is, as compared with the case where a hydrophobic functional group is added separately after forming the porous film as in the conventional technique, the number of steps required to form such a porous film can be reduced. Also become.

  When the number of carbon atoms of the alkoxy group or alkyl group of the alkoxysilane compound increases, the distance between the molecules of the alkoxysilane compound generally increases during the polymerization of the alkoxysilane compound. Therefore, the degree of polymerization in the porous film is low, and the densification of the film is difficult to be promoted in the portion excluding the pores. In the porous film as described above, since the porosity of the porous film, that is, the dielectric constant of the porous film is secured by the content of the nonionic surfactant micelle, the portion excluding the pores No additional holes are required for. Rather, from the viewpoint of securing the mechanical strength of the porous membrane or protecting the hydrophobic group in the membrane, a configuration that promotes densification of the membrane is preferable.

  Therefore, in one example, the first alkoxysilane compound is methyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, vinyltrimethoxysilane. Methyl silicate, dimethyldimethoxysilane, and dimethyldiethoxysilane which are polymers of ethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-glycidoxypropyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetramethoxysilane At least one selected from the group consisting of: In this case, since the first alkoxysilane compound is an alkoxysilane compound having an alkoxy group having 1 or 2 carbon atoms, the densification of the film is promoted in a portion excluding the vacancies. It is also possible to ensure the mechanical strength of the film and to more reliably protect the hydrophobic group in the film.

  As described above, when the number of carbon atoms of the alkoxy group of the alkoxysilane compound increases, the distance between the molecules of the alkoxysilane compound generally increases during the polymerization of the alkoxysilane compound, and in the portion excluding the vacancies, Densification is difficult to promote. From the viewpoint of securing the mechanical strength of the porous membrane or protecting the hydrophobic group in the membrane, a configuration that promotes densification of the membrane is preferable. Therefore, in one example, each alkoxy group of trialkoxyphenylsilane is an alkoxy group having 1 to 4 carbon atoms. In this case, since the densification of the membrane is promoted in the portion excluding the pores, it is possible to ensure the mechanical strength of the porous membrane and to more reliably protect the hydrophobic groups in the membrane. Also become.

  In order to suppress the increase in the dielectric constant of the porous film, it is effective to prevent the water film present in the atmosphere from having an affinity, that is, to increase the hydrophobicity of the porous film. It is. Since the phenyl group of the second alkoxysilane compound is hydrophobic, when it is introduced into the porous membrane, the porous membrane is imparted with hydrophobicity. In addition, as the number of phenyl groups introduced into the porous membrane increases, the degree of hydrophobicity of the porous membrane increases.

  On the other hand, it has been empirically known that the mechanical strength of the porous film decreases as the number of phenyl groups introduced into the porous film increases. This is because, for example, by adding a large number of hydrocarbon groups as side chains to the polysiloxane skeleton that becomes the skeleton of the porous film, the size per unit of the polysiloxane skeleton increases, that is, the skeleton becomes more sparse. It is thought to be. That is, a so-called trade-off relationship is established between the hydrophobicity of the porous film and the mechanical strength.

  Therefore, in one example, the substance amount of the second alkoxysilane compound is within a range that improves the hydrophobicity of the porous film and does not decrease the mechanical strength of the porous film, that is, the first alkoxysilane compound. It is adjusted to be in the range of more than 10 at% and less than 100 at% of the amount of silicon contained. Thereby, coexistence with ensuring the hydrophobicity provided to a porous membrane by a 2nd alkoxysilane compound and suppressing the fall of the mechanical strength of this porous membrane can be aimed at.

  When a mixture of a dialkyl dialkoxysilane and a tetraalkoxysilane was used as the first alkoxysilane compound, the porous film precursor composition was formed by two alkyl groups of the dialkylalkoxysilane. Hydrophobicity is imparted to the porous membrane. However, since the silicon atom of dialkyl dialkoxysilane has two of the four covalent bonds that can be used for bonding to the alkyl group, all of the above covalent bonds are bonded to the alkoxyl group. Compared to those used, it becomes easier to form a linear polysiloxane skeleton. That is, when the dialkyl dialkoxysilane is used, it is difficult to ensure the mechanical strength as the porous film.

  Therefore, in one example, the second alkoxysilane compound is adjusted to 3 to 5 times the amount of dialkyldialkoxysilane. As the second alkoxysilane compound having more alkoxy groups, a linear polysiloxane skeleton is hardly formed, and as a result, the mechanical strength as a porous film is ensured.

  Another aspect of the present disclosure is that the first alkoxysilane compound, the second alkoxysilane compound, the first alkoxysilane compound, and the second alkoxysilane compound are destroyed at a temperature higher than the copolymerization temperature. A method for forming a porous film using a porous film precursor composition containing ionic surfactant micelles, wherein the porous film precursor composition is applied to a substrate by spin coating And heating the substrate coated with the porous membrane precursor composition to a temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, and the nonionic property Disclosed is a method for forming a porous film, which includes a step of destroying a surfactant micelle and removing it from a copolymer of the first alkoxysilane compound and the second alkoxysilane compound. . The first alkoxysilane compound is composed of tetraalkoxysilane, monoalkyltrialkoxysilane, dialkyldialkoxysilane, tetraalkoxysilane polymer, monoalkyltrialkoxysilane polymer, and dialkyldialkoxysilane polymer. And the second alkoxysilane compound is trialkoxyphenylsilane.

  According to this method, the same effect as that of the first aspect can be obtained. Other aspects and advantages of the invention will become apparent from the following description.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment embodying a porous membrane precursor composition and a porous membrane forming method using the precursor composition according to the invention will be described.
The porous film formed using the precursor composition according to the present embodiment is a porous organosilicon oxide film, that is, a porous silica film, and the structural unit of this porous silica film is as follows. It is represented by chemical formula (1) (subscripts a, b and c are integers). Such a porous silica membrane is formed from a precursor composition comprising (a) a first alkoxysilane compound, (b) a second alkoxysilane compound, and (c) a nonionic surfactant micelle. .

(A) First alkoxysilane compound The first alkoxysilane compound is at least selected from the group consisting of tetraalkoxysilane, dialkyldialkoxysilane, tetraalkoxysilane polymer, and dialkyldialkoxysilane polymer. One is included. As an alkoxy group, it is preferable to employ | adopt a methoxy group, an ethoxy group, and a propoxy group, and these combinations are also arbitrary. As the alkyl group, a methyl group, an ethyl group, and a propyl group are preferably employed, and combinations thereof are also arbitrary. Such first alkoxysilane compounds include, for example, tetramethoxysilane, tetraethoxysilane, methyl silicate, dimethyldimethoxysilane, and dimethyldiethoxysilane, methyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyl. Examples include trimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-glycidoxypropyltriethoxysilane. The methyl silicate is a tetramethoxysilane multimer, for example, a tetramethoxysilane tetramer (see chemical formula (2)).

  In the first alkoxysilane compound, a polysiloxane skeleton represented as a part of the above chemical formula (1) is obtained by causing a silanol condensation polymerization reaction between two or more molecules of the monomer or polymer constituting the compound. The chemical formula (3) below is formed.

(B) a second alkoxysilane compound second alkoxysilane compound has three alkoxy groups (OR-) with one phenyl group (C 6 _{H 5 -)} and are trialkoxy phenylsilane bonded to silicon, It is represented by the following chemical formula (4).

  As for the number of carbon atoms which each alkoxy group has, 1-4 are preferable, and if it is this range, the combination of the said 3 alkoxy group is also arbitrary. Moreover, the 2nd alkoxysilane compound is used independently, and 2 or more types may be used together. Examples of such a second alkoxysilane compound include trimethoxyphenylsilane, triethoxyphenylsilane, tripropoxyphenylsilane, and tributoxyphenylsilane.

  In the second alkoxysilane compound, a dealcoholization polycondensation reaction occurs between two or more molecules, whereby a skeleton represented as a part of the chemical formula (1), that is, a skeleton containing a silicon and a phenyl group as a structural unit ( (See chemical formula (5) below). Then, a dealcohol alcohol condensation polymerization reaction occurs between two or more molecules between the first alkoxysilane compound and the second alkoxysilane compound, so that a skeleton having the chemical formula (1) as a structural unit is formed. It is formed.

(C) Nonionic surfactant micelle Nonionic surfactant, that is, a surfactant having a nonionic hydrophilic group, includes, for example, an alkyl polyoxyethylene ether, a fatty acid polyoxy, generally called polyethylene glycol type Ethylene ester, fatty acid polyoxyethylene sorbitan ester, polypropylene glycol polyoxyethylene adduct and the like are used. In addition, fatty acid sorbitan esters, fatty acid sucrose esters, fatty acid polyglycerol esters, and the like, which are generally called polyhydric alcohol types, can also be used.

  These nonionic surfactants are associated by hydrophobic interaction between molecules in a non-aqueous solvent in which (a) the first alkoxysilane compound, (b) the second alkoxysilane compound, etc. are dissolved, A micelle, which is a spherical structure that forms an outer surface with a hydrophilic group, is formed around the end of the molecule on the hydrophobic group side. The nonionic surfactant micelle has a temperature characteristic that it is structurally destroyed when the temperature exceeds the temperature at which the first alkoxysilane compound or the second alkoxysilane compound is copolymerized.

  If micelles are formed in the non-aqueous solvent in which the first alkoxysilane compound, the second alkoxysilane compound, etc. are dissolved, the first alkoxysilane compound and the second Two alkoxysilane compounds collect around the micelles. When the polycondensation reaction as described above proceeds with the first alkoxysilane compound and the second alkoxysilane compound gathered around the micelle in this way, the first alkoxysilane compound and the second alkoxysilane compound Is formed so as to surround the micelle. When micelles are removed from the copolymer of the first alkoxysilane compound and the second alkoxysilane compound, voids are formed in the region where the micelles are present. Therefore, since the diameter of the vacancies thus formed is proportional to the molecular weight of the nonionic surfactant, it is sufficient to select a surfactant having a higher molecular weight when it is desired to increase the vacancy diameter. On the other hand, when it is desired to reduce the pore diameter, a surfactant having a smaller molecular weight may be selected.

(D) Non-aqueous solvent In the precursor composition, in addition to the above-mentioned first alkoxysilane compound, second alkoxysilane compound, and nonionic surfactant micelle, a non-aqueous solvent for dissolving them Is used. Examples of the non-aqueous solvent include alcohol-based, acetone-based, ether-based, and ester-based solvents, and the non-aqueous solvent should be removed from the precursor composition before or when the above polymerization reaction proceeds. A solvent having a boiling point higher than 75 ° C. and lower than 130 ° C. can be used. Examples of such a solvent include ethanol (boiling point: 78.4 ° C.) belonging to alcohol, methyl ethyl ketone (boiling point: 79.6 ° C.), methyl isobutyl ketone (boiling point: 116.8 ° C.), and methyl-normal belonging to acetone. Butyl ketone (boiling point: 127 ° C.), 1,4-dioxane (boiling point: 101.1 ° C.) belonging to ether type, and isobutyl acetate (boiling point: 118 ° C.) and normal-propyl acetate (boiling point: 102 ° C.) belonging to ester type ), Normal-butyl acetate (boiling point: 125-126 ° C.).

(E) Reaction catalyst In the precursor composition, in addition to these various compounds, a catalyst for promoting a polycondensation reaction between the first alkoxysilane compound and the second alkoxysilane compound and a polymerization start temperature are adjusted. It is possible to use a catalyst for this as a reaction catalyst. As the reaction catalyst, an acid catalyst or a base catalyst can be used, and examples thereof include dilute nitric acid or triethylammonium hydroxide. In addition, you may make it neutralize the acidification of the precursor composition resulting from adding dilute nitric acid as a reaction catalyst by adding alkalis, such as a trimethyl ammonium hydroxide. The basification of the precursor composition resulting from the addition of triethylammonium hydroxide as a reaction catalyst may be neutralized by adding an acid such as dilute nitric acid.

  In the case of the precursor composition having the above structure, when the precursor composition is heated near the boiling point of the non-aqueous solvent, evaporation of the non-aqueous solvent contained in the precursor composition is promoted, and the first alkoxy The silane compound and the second alkoxysilane compound gather around the nonionic surfactant micelle. Further, when the precursor composition is heated to a temperature at which the first alkoxysilane compound and the second alkoxysilane compound start copolymerization, an organic silicon oxide film having a polysiloxane skeleton as a main skeleton is formed. Accordingly, nonionic surfactant micelles are included in the organic silicon oxide film. When the precursor composition is heated above the temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, the nonionic surfactant micelles contained in the organic silicon oxide film are destroyed. Thus, holes are formed in the space occupied by the micelle. Therefore, the porosity of the porous silica film having a polysiloxane skeleton as the main skeleton, that is, the relative dielectric constant, is defined by the content of the non-surfactant micelle.

  At this time, since an organic disilicon compound having a phenyl group is used as the second alkoxysilane compound, the surface layer of the porous silica film is naturally a polysiloxane skeleton which is a three-dimensional main skeleton. A phenyl group is also contained inside. That is, the phenyl group is added in such a manner as to be included in the polysiloxane skeleton constituting the porous silica film. And the highly hydrophobic phenyl group will be provided over the whole porous silica film. As a result, even when dry etching is applied to the porous silica film, the inner surface of the void exposed through the recessed portion after etching has a highly hydrophobic phenyl group. In addition, since it is difficult for the etchant to reach the phenyl group surrounded by the polysiloxane skeleton, the above-described phenyl group can be held on the inner surface of the hole regardless of the shape after the etching. Furthermore, even if the dissociation of the phenyl group by the etchant proceeds, since the hydrophobicity of the phenyl group is higher than the hydrophobicity of the alkyl group, the dissociation of the phenyl group proceeds to the same extent as the dissociation of the alkyl group. If it exists, it becomes easy to maintain the hydrophobicity of a porous membrane compared with the structure which uses an alkyl group as a hydrophobic group. Therefore, a decrease in hydrophobicity in the porous silica film can be suppressed, and an increase in the dielectric constant of the porous silica film after the processing can be suppressed.

  Incidentally, hexamethyldisiloxane may be added to the precursor composition in order to modify the alkoxy group bonded to the terminal of the polysiloxane skeleton that becomes the skeleton of the porous silica film. Further, in order to adjust the hydrophobicity of the porous silica film, for example, a cyclic molecule such as tetramethylcyclotetrasiloxane or octamethylcyclotetrasiloxane may be added. Since these molecules are included in the polysiloxane skeleton by ring-opening polymerization, it is possible to add 4 or 8 hydrocarbon groups per molecule to the polysiloxane skeleton. Can be improved.

  In addition, when the number of carbon atoms in the alkoxy group or alkyl group of the alkoxysilane compound increases, the intermolecular distance between the alkoxylsilane compounds generally becomes longer, and the densification of the film is promoted in the portion excluding the vacancies. It becomes difficult to be done. In the porous silica film as described above, since the porosity of the porous silica film, that is, the dielectric constant of the porous silica film is secured by the content of the non-surfactant micelles, the pores were excluded. No additional holes are required for the part. Rather, from the viewpoint of securing the hardness of the porous silica film or protecting the hydrophobic group in the film, a configuration in which the densification of the film is promoted is preferable. From this point, the first alkoxysilane compound is preferably tetramethoxysilane, tetraethoxysilane, or a polymer of tetramethoxysilane, methyl silicate, dimethyldimethoxysilane, or dimethyldiethoxysilane. The alkoxyl group in the second alkoxysilane compound is also preferably an alkoxyl group having 1 to 4 carbon atoms. According to these structures, since the densification of the film is promoted in the portion excluding the pores, the mechanical strength of the porous silica film can be ensured or the hydrophobic groups in the film can be more reliably protected. It becomes possible to do.

  In addition, the Si atom composition ratio percentage of the first alkoxysilane compound in the precursor composition has a large three-dimensional spread of the polysiloxane skeleton, which is the main skeleton, and is an indicator of the mechanical hardness of the porous silica film. From the viewpoint of increasing the Young's modulus, it is preferably 30 at% or more and 92 at% or less, and more preferably 44 at% or more and 87 at% or less.

  In addition, the Si atom composition percentage of the second alkoxysilane compound in the precursor composition is preferably 5 at% or more and 50 at% or less from the above viewpoint, and more preferably 8 at% or more and 46 at% or less.

  Further, when tetramethoxysilane is used as the first alkoxysilane compound and triethoxyphenylsilane is used as the second alkoxysilane compound, the Si atom composition percentage of tetramethoxysilane is 44 at% or more and 87 at% or less. And it is preferable that the Si atom composition percentage of triethoxyphenylsilane is 13 at% or more and 46 at% or less. This is because the difference between the polymerization initiation temperature between tetramethoxysilane, the polymerization initiation temperature between triethoxyphenylsilane, and the copolymerization initiation temperature between tetramethoxysilane and triethoxyphenylsilane is large, and the structure of the polysiloxane skeleton is This is extremely preferable from the viewpoint of adjustment by temperature.

Next, a method for producing a precursor composition of the porous silica film and a method for forming a porous silica film using the precursor composition will be described.
The ratio of (a) the first alkoxysilane compound, (b) the second alkoxysilane compound, and (c) the nonionic surfactant micelle is described above in any of the above (d) non-aqueous solvents. Mix in an appropriate ratio and stir at 25 ° C. for 30 minutes, for example. Next, (e) an acid catalyst or a base catalyst, which is a reaction catalyst, is added and, for example, stirred at 25 ° C. for 3 hours. Then, the precursor composition of the said porous membrane can be obtained by adding the alkali which neutralizes this acid catalyst, or the acid which neutralizes a base catalyst, and stirring for 24 hours, for example. The precursor composition is preferably liquid at room temperature.

  Next, the precursor composition thus prepared is applied to a film formation target. For example, the precursor composition is applied to a silicon substrate, which is a film formation target, by a spin coat method under the condition of 1200 rpm, for example. Nonionic surfactant micelles are formed in the film made of the precursor composition applied to the substrate, and the first alkoxysilane compound or the second alkoxysilane compound is formed around each micelle particle. Are gathering.

  Next, the non-aqueous solvent is removed from the precursor composition applied to the substrate. For example, the substrate coated with the precursor composition is heated in a vacuum atmosphere, and the temperature is raised to 350 ° C., for example, for 35 seconds to volatilize the non-aqueous solvent of the precursor composition. The time for heating the substrate may be set to a time during which the non-aqueous solvent contained in the precursor composition can be volatilized.

  Subsequently, with the evaporation of the non-aqueous solvent or after the evaporation of the non-aqueous solvent, the polymerization of the first alkoxysilane compound, the polymerization of the second alkoxysilane compound, and the first alkoxysilane compound and the second alkoxysilane compound Copolymerization with is started. For example, when heat is applied to the substrate from the outside and the temperature reaches about 350 ° C., heat energy is also given to the first alkoxysilane compound and the second alkoxysilane compound in the precursor composition, Polymerization of the first alkoxysilane compound, polymerization of the second alkoxysilane compound, and copolymerization of the first alkoxysilane compound and the second alkoxysilane compound proceed. Incidentally, in these reactions, the reaction catalyst promotes such reactions. When the non-aqueous solvent is completely evaporated by heating, the micelle surrounded by the organosilicon oxide composed of the polysiloxane skeleton remains at that position.

Then, with the start of polymerization of the alkoxysilane compound or after the polymerization of the alkoxysilane compound, removal of the nonionic surfactant micelles is started. For example, under the same temperature as the polymerization conditions and in a vacuum atmosphere, irradiation with, for example, 172 nm ultraviolet rays for 20 seconds is performed under conditions such as illuminance of 40 mW / cm ² to remove the nonionic surfactant applied on the substrate. . That is, as the ultraviolet irradiation time, a time during which the nonionic surfactant on the substrate can be removed can be set. When the substrate is irradiated with ultraviolet rays in this way, the association state of the nonionic surfactant or the nonionic surfactant itself is destroyed by the ultraviolet rays, so that the nonionic surfactant micelles are removed from the substrate. Removed. Note that these heat treatment and ultraviolet irradiation treatment are not limited to a vacuum atmosphere, and can be performed in a nitrogen atmosphere or an oxygen-containing atmosphere. In addition, after the porous silica film is formed by the completion of the ultraviolet irradiation treatment, the surface of the porous silica film is further silylated by exposing the surface of the porous silica film to vapor of hexamethyldisilazane. You may make it implement.

[Example]
A porous silica film precursor composition was prepared using the various compounds described above, and applied to the surface of the substrate to form the porous silica film of the example. Thereafter, the dielectric constant of the porous silica film of the example and the Young's modulus, which is an index of mechanical strength, were measured, and the dielectric constant after the reactive dry etching treatment was performed on the porous silica film was also measured.

  In preparing the precursor composition, first, the first alkoxysilane compound, the second alkoxysilane compound, and the nonionic surfactant were added to a non-aqueous solvent and stirred at 25 ° C. for 30 minutes. Next, an acid catalyst was added and stirred at 25 ° C. for 3 hours, and then an alkali neutralizing the acid catalyst was added and stirred for 24 hours.

When forming a porous silica film with the precursor composition thus prepared, first, the precursor composition was spin-coated on the surface of the silicon substrate under the condition of 1200 rpm. The substrate coated with this precursor composition was placed in a vacuum atmosphere, and the temperature was raised to 350 ° C. in 35 seconds. Next, ultraviolet rays having an illuminance of 40 mW / cm ² and a wavelength of 172 nm were irradiated at 350 ° C. for 20 seconds.

  The film thickness of the porous silica film thus formed was measured with an ellipsometer, and the relative dielectric constant was calculated from the CV characteristics measured using the mercury probe method. On the other hand, the Young's modulus of the porous silica film was measured with a nanoindenter (manufactured by Nanoinstrument).

And the said porous silica film | membrane was dry-etched on the conditions shown below. Note that an apparatus that performs plasma etching using inductively coupled plasma was used for the treatment.
Etching gas CF ₄ (90 sccm), Ar (10 sccm)
・ Total pressure of etching gas 1.0Pa
・ Antenna power 800W
・ Bias power 500W
After the dry etching process under the above conditions, the thickness of the porous silica film was measured and the non-dielectric constant was calculated. The method for measuring the thickness of the porous silica film and the method for calculating the relative dielectric constant were the same as those after the formation of the porous silica film.

[Example 1]
Various compounds shown in the above (a) to (e) and (f) a pH adjuster were mixed by blending as follows to prepare the precursor composition of the porous silica film.
(A) First alkoxysilane compound: tetraethoxysilane 0.024 mol
(B) Second alkoxysilane compound: trimethoxyphenylsilane 0.0036 mol
(C) Nonionic surfactant: Epan 450 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., see chemical formula (6)) 0.0007 mol

(D) Non-aqueous solvent: ethanol 22.0 ml
(E) Reaction catalyst: nitric acid solution (0.5%) 15.8 g
(F) pH adjuster: trimethylammonium hydroxide / propylene glycol monomethyl ether solution 0.00006 mol / 62.0 ml
In addition, while the Si atom composition ratio percentage of the said tetraethoxysilane in the said precursor composition is 87 at%, Si atom composition ratio percentage of the said trimethoxyphenylsilane in the same precursor composition is 13 at%.

  After forming a porous silica film using the precursor composition, the film thickness, relative dielectric constant, and Young's modulus were measured. The film thickness was 151 nm, the relative dielectric constant was 2.1, and the Young's modulus was 6 0.0 GPa. Further, when the porous silica film was dry-etched under the above conditions and the film thickness and relative dielectric constant were measured, the film thickness was 103 nm and the relative dielectric constant was 2.7. That is, it was recognized that the dielectric constant of the porous silica film was increased by 0.7 by performing the dry etching process.

[Example 2]
Various compounds shown in the above (a) to (e) and (f) a pH adjuster were mixed by blending as follows to prepare the precursor composition of the porous silica film.
(A-1) First alkoxysilane compound: tetraethoxysilane 0.0024 mol
(A-2) First alkoxysilane compound: methyl silicate 0.0084 mol
(B) Second alkoxysilane compound: triethoxyphenylsilane 0.0054 mol
(C) Nonionic surfactant: Epan 450 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., see chemical formula (6)) 0.0009 mol
(D) Non-aqueous solvent: ethanol 33.0 ml
(E) Reaction catalyst: nitric acid solution (0.5%) 8.31 g
(F) pH adjuster: trimethylammonium hydroxide / propylene glycol monomethyl ether solution 0.00009 mol / 93.0 ml
In addition, the Si atom composition ratio percentage of tetraethoxysilane is 15 at%, the Si atom composition ratio percentage of methyl silicate is 52 at%, and the Si atom composition ratio percentage of the triethoxyphenylsilane in the same precursor composition. Is 33 at%.

  After forming a porous silica film using the precursor composition, the film thickness, relative dielectric constant, and Young's modulus were measured. The film thickness was 202 nm, the relative dielectric constant was 2.0, and the Young's modulus was 5 It was 5 GPa. Further, when the porous silica film was dry-etched under the above conditions and the film thickness and relative dielectric constant were measured, the film thickness was 110 nm and the relative dielectric constant was 3.0. That is, the dielectric constant of the porous silica film increased by 1.0 due to the dry etching process.

[Example 3]
Various compounds shown in the above (a) to (e) and (f) a pH adjuster were mixed by blending as follows to prepare the precursor composition of the porous silica film.
(A-1) First alkoxysilane compound: tetraethoxysilane 0.019 mol
(A-2) First alkoxysilane compound: dimethyldiethoxysilane 0.005 mol (b) Second alkoxysilane compound: trimethoxyphenylsilane 0.015 mol
(C) Nonionic surfactant: Epan 450 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., see chemical formula (6)) 0.0010 mol
(D) Non-aqueous solvent: ethanol 30.8 ml
(E) Reaction catalyst: nitric acid solution (0.5%) 16.6 g
(F) pH adjuster: trimethylammonium hydroxide / propylene glycol monomethyl ether solution 0.00008 mol / 80.7 ml
In addition, the Si atom composition percentage of tetraethoxysilane is 49 at%, the Si atom composition percentage of dimethyldiethoxysilane is 13 at%, and the Si atom of the trimethoxyphenylsilane in the precursor composition. The composition ratio percentage is 38 at%.

  After forming a porous silica film using the precursor composition, the film thickness, relative dielectric constant, and Young's modulus were measured. The film thickness was 213 nm, the relative dielectric constant was 2.0, and the Young's modulus was 5 0.7 GPa. Further, when the porous silica film was dry-etched under the above conditions and the film thickness and relative dielectric constant were measured, the film thickness was 100 nm and the relative dielectric constant was 2.7. That is, the dielectric constant of the porous silica film increased by 0.7 due to the dry etching process.

[Example 4]
Various compounds shown in the above (a) to (e) and (f) a pH adjuster were mixed by blending as follows to prepare the precursor composition of the porous silica film.
(A-1) First alkoxysilane compound: tetraethoxysilane 0.0024 mol
(A-2) First alkoxysilane compound: methyl silicate 0.0134 mol
(B) Second alkoxysilane compound: trimethoxyphenylsilane 0.0014 mol
(Additive): Hexamethyldisiloxane 0.0014 mol
(C) Nonionic surfactant: Epan 450 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., see chemical formula (6)) 0.0015 mol
(D) Non-aqueous solvent: ethanol 47.0
(E) Reaction catalyst: nitric acid solution (0.5%) 10.90 g
(F) pH adjuster: trimethylammonium hydroxide / propylene glycol monomethyl ether solution 0.00012 mol / 139.4 ml
In addition, the Si atom composition ratio percentage of tetraethoxysilane is 13 at%, the Si atom composition ratio percentage of methyl silicate is 71 at%, and the Si atom composition ratio of the trimethoxyphenylsilane in the precursor composition. The percentage is 8 at%. Moreover, the Si atom composition ratio percentage of hexamethyldisiloxane as an additive is 8 at%.

[Comparative Example 1]
Among the various compounds shown in (a) to (f) of [Example 1], a precursor composition of a porous film was prepared without adding (b) the second alkoxysilane compound.
(A) First alkoxysilane compound: tetraethoxysilane 0.024 mol
(C) Nonionic surfactant: Epan 450 (trade name: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.006 mol
(D) Non-aqueous solvent: ethanol 34 ml
(E) Reaction catalyst: nitric acid solution (0.5%) 15 g
(F) pH adjuster: trimethylammonium hydroxide / propylene glycol monomethyl ether solution 0.00005 mol / 54 ml
After forming a porous silica film using the precursor composition, its film thickness, relative dielectric constant, and Young's modulus were measured. The film thickness was 191 nm, the relative dielectric constant was 2.0, and the Young's modulus was 6 It was 5 GPa. In addition, when the porous silica film was dry-etched under the above conditions and the film thickness and relative dielectric constant were measured, the film thickness was 102 nm and the relative dielectric constant was 3.8. That is, the relative dielectric constant of the porous silica film increased by 1.8 due to the dry etching process.

  Thus, the increase in relative dielectric constant after dry etching in the example was 0.7, while the increase in relative dielectric constant after dry etching in the comparative example was 1.8. That is, in the above example, the polysiloxane skeleton constituting the porous silica film contains a hydrophobic phenyl group, so that hydrocarbon group detachment is suppressed even after dry etching treatment, and the ratio is reduced. It can be said that the increase in dielectric constant was suppressed. In addition, the Young's modulus of the example was 6.0 GPa, and it was confirmed that the Young's modulus of the comparative example was substantially the same. Therefore, even if the phenyl group is added to the polysiloxane skeleton, the mechanical strength of the porous membrane is ensured if the number of carbon atoms of each alkoxy group of the trialkoxysilane group is 1 to 4. It is possible to protect the hydrophobic group in the film more reliably.

As described above, according to the above embodiment, the effects listed below can be obtained.
(1) The precursor composition of the porous silica film is equal to or higher than the temperature at which the first alkoxysilane compound, the second alkoxysilane compound, the first alkoxysilane compound, and the second alkoxysilane compound are copolymerized. And nonionic surfactant micelles that break down. As a result, under the conditions where the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, an organic silicon oxide film having a polysiloxane skeleton as a main skeleton is formed, and the organic silicon oxide film Nonionic surfactant micelles are included. Above the temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized, the nonionic surfactant micelles contained in the organic silicon oxide film are destroyed, and the spaces occupied by the micelles are destroyed. Holes are formed. Therefore, the porosity of the porous silica film having a polysiloxane skeleton as the main skeleton, that is, the relative dielectric constant, is defined by the content of the nonionic surfactant micelle.

  (2) Trialkoxyphenyl silane is used as the second alkoxysilane compound. Thereby, as a matter of course, the surface layer of the porous silica film includes phenyl groups in the three-dimensional polysiloxane skeleton. In other words, not only is the phenyl group added to the outer surface of the porous silica film, but the phenyl group is also added to the porous silica film surrounded by the polysiloxane skeleton. A highly hydrophobic phenyl group is imparted over the entire silica film. As a result, even when dry etching treatment is applied to the porous silica film, the inner surface of the void exposed through the etched surface has a highly hydrophobic phenyl group. In addition, since it is difficult for the etchant to reach the phenyl group surrounded by the polysiloxane skeleton, the above-described phenyl group can be held on the inner surface of the hole regardless of the shape after the etching. Furthermore, even if the dissociation of the phenyl group by the etchant proceeds, since the hydrophobicity of the phenyl group is higher than the hydrophobicity of the alkyl group, the dissociation of the phenyl group proceeds to the same extent as the dissociation of the alkyl group. If it exists, it becomes easy to maintain the hydrophobicity of a porous membrane compared with the structure which uses an alkyl group as a hydrophobic group. Therefore, it can suppress that the dielectric constant of a porous silica film increases after the process.

  (3) Since the precursor composition of the porous film contains the first alkoxysilane compound, the second alkoxysilane compound, and the nonionic surfactant, A porous film having a polysiloxane skeleton that forms a skeleton of the porous film only by applying the precursor composition of the porous film to a substrate or the like, and a hydrophobic functional group added to the polysiloxane skeleton. Can be formed. That is, as compared with the case where a hydrophobic functional group is added separately after forming the porous film as in the conventional technique, the number of steps required to form such a porous film can be reduced. Also become.

  (4) The first alkoxysilane compound is converted into methyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, vinyltriethoxy. From silane, 3-methacryloxypropyltriethoxysilane, 3-glycidoxypropyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetramethoxysilane, methyl silicate, dimethyldimethoxysilane, and dimethyldiethoxysilane At least one selected from the group consisting of: That is, the porous film is formed of an alkoxysilane compound having an alkoxy group having 1 or 2 carbon atoms. This promotes densification of the membrane in the area excluding the pores, so it is possible to ensure the mechanical strength of the porous silica membrane and to protect the hydrophobic groups in the membrane more reliably. It also becomes.

  (5) Each alkoxy group of trialkoxyphenylsilane is an alkoxy group having 1 to 4 carbon atoms. This promotes densification of the membrane in the area excluding the pores, so it is possible to ensure the mechanical strength of the porous silica membrane and to protect the hydrophobic groups in the membrane more reliably. It also becomes.

  (6) The substance amount of the second alkoxysilane compound is included in the first alkoxysilane compound in a range that improves the hydrophobicity of the porous film and does not reduce the mechanical strength of the porous film. The amount is adjusted to be greater than 10% and less than 100% of the amount of silicon. Thereby, coexistence with ensuring the hydrophobicity provided to a porous membrane by a 2nd alkoxysilane compound and suppressing the fall of the mechanical strength of this porous membrane can be aimed at.

  (7) When the first alkoxysilane compound is a dialkyl dialkoxysilane, the polysiloxane skeleton is formed by setting the second alkoxysilane compound to 3 to 5 times the amount of the first alkoxysilane compound. A polysiloxane skeleton is formed by the second alkoxysilane compound having more possible alkoxyl groups, and as a result, the mechanical strength as a porous film is secured.

  Although the embodiments of the present invention have been described, the present invention is not limited to the above, and may be modified within the scope of the appended claims and equivalents.

Claims (6)

A first alkoxysilane compound;
A second alkoxysilane compound;
A precursor composition of a porous membrane comprising: a nonionic surfactant micelle that breaks above a temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized;
The first alkoxysilane compound comprises a tetraalkoxysilane, a monoalkyltrialkoxysilane, a dialkyldialkoxysilane, a tetraalkoxysilane polymer, a monoalkyltrialkoxysilane polymer, and a dialkyldialkoxysilane polymer. At least one selected from the group;
The precursor composition of a porous film, wherein the second alkoxysilane compound is trialkoxyphenylsilane. In the precursor composition of the porous membrane according to claim 1,
The first alkoxysilane compound is
Methyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, A porous film characterized by being at least one selected from the group consisting of 3-glycidoxypropyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, methyl silicate, dimethyldimethoxysilane, and dimethyldiethoxysilane Precursor composition. In the precursor composition of the porous membrane according to claim 1 or 2,
The precursor composition of the porous film, wherein the number of carbon atoms of each alkoxy group in the trialkoxyphenylsilane is 1 to 4. In the precursor composition of the porous membrane according to any one of claims 1 to 3,
The number of silicon atoms contained in the second alkoxysilane compound in the precursor composition is greater than 10 at% and less than 100 at% of the number of silicon atoms contained in the first alkoxysilane compound in the precursor composition. A precursor composition of a porous membrane, characterized in that it exists. The first alkoxysilane compound is a mixture containing a dialkyldialkoxysilane, and the substance amount of the second alkoxysilane compound is 3 to 5 times the substance amount of the dialkyldialkoxysilane. The precursor composition of the porous membrane as described in any one of these. A first alkoxysilane compound, a second alkoxysilane compound, and a nonionic surfactant micelle that breaks above the temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized. A step of applying a porous film precursor composition comprising a substrate to a substrate by a spin coating method;
Raising the temperature of the substrate coated with the porous membrane precursor composition to a temperature at which the first alkoxysilane compound and the second alkoxysilane compound are copolymerized;
Destroying the nonionic surfactant micelle and removing it from the copolymer of the first alkoxysilane compound and the second alkoxysilane compound, comprising the steps of:
The first alkoxysilane compound is
At least one selected from the group consisting of tetraalkoxysilane, monoalkyltrialkoxysilane, dialkyldialkoxysilane, tetraalkoxysilane polymer, monoalkyltrialkoxysilane polymer, and dialkyldialkoxysilane polymer Yes,
The method for forming a porous film, wherein the second alkoxysilane compound is trialkoxyphenylsilane.