JP2004273874A - Method for forming porous film and porous film formed thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a porous film for using various porous raw materials for forming the vacancy of a porous film regardless of the superiority/inferiority of its compatibility with super-critical fluid being extracted solvate, and increasing the degree of selective freedom of the vacancy size or skeletal structure. <P>SOLUTION: This method for forming a porous film comprises a primary film formation process for forming a primary film where skeletal materials and vacancy raw materials are contained in mixed states, a decomposing process for decomposing porous raw materials configuring the primary film, and an extraction process for extracting the porous raw materials decomposed by the decomposition process by using super-critical fluid. In the decomposition process, the porous raw materials can be decomposed by using the super-critical fluid containing decomposition promoting components for promoting the decomposition of the porous raw materials. The decomposition and extraction of the porous raw materials can be simultaneously carried out by one process(decomposition/extraction process) at the time of using the super-critical fluid. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a porous film having no firing process. In particular, it is suitable as a porous low dielectric constant film suitably used as a dielectric layer of a high frequency circuit or an interlayer insulating film of a semiconductor integrated circuit (LSI) and a method of forming the same.
[0002]
[Prior art]
A so-called spin-on-glass (SOG) film is used as an interlayer insulating film in a semiconductor device or the like. ₂ A coating-type insulating film containing as a main component is widely used. In addition, with the increase in the degree of integration of semiconductor elements, low dielectric constant interlayer insulating films containing organic components have been developed. However, with higher integration and multilayering of semiconductor devices and the like, a low dielectric constant interlayer insulating film material having a relative dielectric constant of 2 or less has been required.
[0003]
In order to realize a relative dielectric constant of 2 or less, it is essential to lower the density of the film itself, and for that purpose, it is necessary to use a porous material. However, if the density of the porous material is reduced to lower the dielectric constant, generally the mechanical strength of the material is significantly reduced. This is due to the fact that the vacancies introduced for lowering the density are unevenly dispersed. In order to maintain the strength as much as possible even when the density is lowered, it is effective to realize a highly regular structure such as a honeycomb structure.
[0004]
As a method for producing a porous material having a regular structure, JP-A-10-194720 (Patent Document 1) discloses a silica / surfactant composite by mixing and reacting an alkoxysilane, water and a surfactant. And then aging, drying and firing.
[0005]
As a method of obtaining a thin film from a porous material having a periodic structure, Japanese Patent Application Laid-Open No. 9-194298 (Patent Document 2) discloses that tetraalkoxysilane is hydrolyzed under an acidic condition and a surfactant is mixed with the hydrolyzed solution. A method of firing a silica-surfactant nanocomposite obtained by applying and drying a solution is disclosed.
[0006]
However, in these techniques, in order to realize a porous structure, a process of firing a surfactant, which is a pore source material that forms the pores of the porous structure, at a high temperature is required, and the temperature is high. Must be 500 ° C. or higher. Therefore, it cannot be used for the interlayer insulating film process of the semiconductor element.
[0007]
On the other hand, Japanese Patent Application Laid-Open No. 2001-55508 (Patent Literature 3) discloses a method of forming a porous material at a low temperature by converting a non-silicate material from a material comprising a silicate region and a non-silicate region by solvent exchange and fluid exchange. A method of extracting a porous silicate material by extraction is disclosed. Also, supercritical extraction is mentioned as an extraction means (claim 13). As is generally known, in a process using a supercritical fluid, no capillary contraction force is exerted, so that deformation of a target structure during solvent extraction can be extremely reduced. In the examples of this document, the use of supercritical fluid extraction of isopropanol alone is described.
[0008]
Although no specific example is disclosed, it is disclosed in Japanese Patent Application Laid-Open No. 2002-367984 (Patent Document 4) that it is possible to add another solvent having excellent compatibility with the component to be extracted to the supercritical medium. And Japanese Patent Application Laid-Open No. 2002-363286 (Patent Document 5).
[0009]
[Patent Document 1]
JP-A-10-194720 (Claims)
[Patent Document 2]
JP-A-9-194298 (Claims)
[Patent Document 3]
JP 2001-55508 A (Claims)
[Patent Document 4]
JP-A-2002-367984 (Claims)
[Patent Document 5]
JP-A-2002-363286 (Claims)
[0010]
[Problems to be solved by the invention]
However, it is difficult to remove all the materials in the non-silicate region by the technique of Patent Document 3. Before being made porous, the non-silicate region contains many substances such as photoinitiators and photocured organic substances in addition to surfactants, and supercritical fluids generally work as good solvents. This is because not all of these materials have miscibility and compatibility. Also, in the techniques of Patent Documents 4 and 5, since the extraction performance for the target component to be extracted, that is, the compatibility generally depends on the molecular weight, when the molecular weight becomes larger than a certain value, other solvents may be used. Can no longer be compatible.
That is, in the conventional method using a supercritical fluid as a means for removing a pore source material in the formation of a porous structure, the relative dielectric constant is used unless the pore source material used originally has good compatibility with the supercritical fluid. It is difficult to form a high quality porous film having a low quality. For this reason, there is a problem that the components of the pore source material extracted by the supercritical fluid are limited, and the pore size and skeleton structure of the finally formed porous membrane are limited.
[0011]
The present invention has been made in view of such a problem, and uses various materials as a pore source material for forming pores of a porous membrane, regardless of the degree of compatibility with a supercritical fluid as an extraction solvent. It is another object of the present invention to provide a method for forming a porous film having a high degree of freedom in selecting a pore size and a skeleton structure, and a porous film formed by the method.
[0012]
[Means for Solving the Problems]
The method for forming a porous film according to the present invention includes forming a primary film in which a skeletal material forming a skeleton of the porous film and a pore source material serving as a base of pores of the porous film are contained in a mixed state. A decomposition step of decomposing the porogen material constituting the primary membrane, and an extraction step of extracting the porogen material decomposed by the decomposition step using a supercritical fluid.
[0013]
According to this method for forming a porous membrane, after forming a primary membrane containing a skeleton material and a pore source material in a mixed state, a decomposition step for decomposing the pore source material of the primary membrane is provided, so that extraction with a supercritical fluid is performed. In the process, the supercritical fluid can be used to extract the pore source material that has been decomposed into low molecules by the decomposition process and has improved compatibility with the supercritical fluid. For this reason, at the stage of the primary film forming step, there is no limitation on the molecular weight and structure of the hole source material, and a wide variety of hole source materials can be used, and accordingly, various pore sizes and skeleton structures can be used. Can be formed. Moreover, in the stage of the extraction step using a supercritical fluid, the pore source material decomposed into low molecules can be extracted, so that the supercritical extraction can be performed efficiently and the productivity is excellent. Of course, since a supercritical fluid is used in the extraction step, processing at a low temperature is possible. For example, the present invention is suitably applied to formation of an interlayer insulating film of a semiconductor device.
[0014]
In the decomposition step, the hole source material can be decomposed using a supercritical fluid containing a decomposition promoting component for accelerating the decomposition of the hole source material. When such a supercritical fluid is used, the decomposition and extraction of the pore source material can be performed simultaneously in one step (decomposition / extraction step).
[0015]
As the decomposition promoting component, a component mainly composed of an oxidatively decomposable substance that oxidatively decomposes a pore source material (including a substance composed of only an oxidatively decomposable substance) can be used. When the decomposition promoting component containing the oxidatively decomposable substance as a main component is contained in a supercritical fluid, the decomposition promoting component is converted into a supercritical fluid together with a mixing promoting solvent having compatibility with the decomposition promoting component and the supercritical fluid. It can be contained. As the mixing promoting solvent, an organic solvent can be used, and the concentration of the decomposition promoting component with respect to the mixing promoting solvent is preferably 20 mass% or less. The supercritical fluid used in the extraction step, decomposition step or decomposition / extraction step is preferably one whose main component is carbon dioxide, alkyl alcohol or a mixture thereof.
[0016]
Further, as the skeleton material, an inorganic substance, particularly an inorganic substance containing silica as a main component, is preferable because a skeleton of the porous film has excellent insulating properties and stability, and a porous film having a lower dielectric constant can be obtained. Further, as the pore source material, an organic substance can be used. In particular, a surfactant is used at an appropriate concentration to form micelles, so that the pore source material can be regularly arranged, and Is preferred because it can form a regular skeleton.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for forming a porous film according to the present invention includes: (1) forming a primary film containing a skeleton material forming a skeleton of the porous film and a pore source material serving as a base of pores of the porous film in a mixed state; A primary film forming step, (2) a decomposition step of decomposing the pore source material constituting the primary film, and (3) an extraction step of extracting the pore source material decomposed in the decomposition step using a supercritical fluid. Is provided.
[0018]
In the decomposition step, it is preferable to decompose the hole source material using a supercritical fluid containing a decomposition promoting component for accelerating the decomposition of the hole source material. By using a supercritical fluid containing a decomposition promoting component, the decomposition treatment can be quickly performed with a high-density, high-diffusion fluid. For this reason, the decomposition promoting component can be efficiently brought into contact with the components in the minute space, so that good decomposition efficiency can be obtained. When a supercritical fluid containing the decomposition promoting component is used, the decomposition step and the extraction step can be performed simultaneously. The step of simultaneously performing the decomposition step and the extraction step is called a decomposition / extraction step.
[0019]
As the decomposition accelerating component, a component mainly containing an oxidatively decomposable substance that oxidatively decomposes the pore source material (including one composed of only the oxidatively decomposable substance) can be used. It is possible to reduce the molecular weight. For example, when a surfactant having a high molecular weight is used as a pore source material, large pores can be formed in accordance with the molecular weight of the surfactant. It is difficult to directly extract the surfactant with a supercritical fluid after forming a primary membrane containing the in a mixed state. Such a surfactant having a large molecular weight has a hydrophobic group consisting of a higher alkyl group bonded in a very long chain. This hydrophobic group is easily separated and decomposed by the oxidative decomposition substance. The hydrophobic group is decomposed in this way, and the low molecular weight surfactant is easily extracted by the supercritical fluid.
[0020]
When the oxidatively decomposable substance is used by being contained in a supercritical fluid, any substance that can be mixed with the supercritical fluid may be used. Specifically, O ₂ , O ₃ , N ₂ O, H ₂ O ₂ , HCl, HBr, Cl ₂ , BCl ₃ , HNO ₃ Such a gas can be used, and a protic solvent can also be used. Specific examples of the protic solvent include inorganic acids such as hydrochloric acid, perchloric acid, nitric acid, hydrofluoric acid, phosphoric acid, shelvic acid, and oxalic acid, organic acids such as acetic acid and formic acid, bromine trifluoride, and pentafluoride. Interhalogen compounds such as bromine can be used. These substances can be used alone or in combination of two or more.
[0021]
The oxidatively decomposable substance can be contained in the supercritical fluid together with a mixing promoting solvent having compatibility with both the oxidatively decomposable substance and the supercritical fluid. By using a mixing promoting solvent, it is possible to improve the compatibility between the supercritical fluid and the oxidatively decomposable substance even when the oxidatively decomposable substance alone is not compatible with or inferior to the supercritical fluid. Can be. In this case, the amount of the mixing accelerating solvent may be appropriately adjusted within a range in which the solvent can be compatible with the supercritical fluid without impairing the oxidative decomposability of the oxidative decomposable substance. As the concentration range to be adjusted, the amount of the oxidatively decomposable substance is set to 0.01% or more and 20% or less by mass% (wt%) with respect to the mixing promoting solvent contained in the supercritical fluid together with the oxidatively decomposable substance. Is preferred. More preferably, it is 0.05% or more and 10% or less. If the amount of the oxidatively decomposable substance is too small, the oxidatively decomposable substance is deteriorated, while if it is too large, it is difficult to be compatible with the supercritical fluid.
[0022]
It is preferable to use an organic solvent as the mixing promoting solvent. Examples of usable organic solvents include alcohol solvents, ketone solvents, and amide solvents.
[0023]
Specifically, as an alcohol solvent, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec- Pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol and 2-ethylbutanol can be mentioned.
[0024]
Further, as a ketone solvent, acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-n-butyl ketone, diethyl ketone, methyl-i-butyl ketone, methyl-n-pentyl ketone, ethyl-n-butyl ketone, methyl-n- Hexyl ketone and di-i-butyl ketone are exemplified.
[0025]
Examples of the amide-based solvent include formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylnermamide, acetamide, N-methylacetamide, N, N-dimethylacetamide, and N, N-dimethylacetamide. -Ethylacetamide, N, N-diethylacetamide, N-methylpropionamide, N-methylpyrrolidone.
[0026]
The supercritical fluid in which the decomposition promoting component and the mixing promoting solvent are dissolved is a carbon dioxide or an alkyl alcohol (the alkyl alcohol is methyl alcohol, ethyl alcohol, propyl One or a mixture of two or more of alcohols may be used, and these are collectively referred to as an alkyl alcohol.) Or a mixture of carbon dioxide and an alkyl alcohol is industrially preferable. This is because any of these supercritical fluids can be widely compatible with various substances.
[0027]
As the skeletal material serving as the skeleton of the porous structure, an inorganic material is excellent in terms of thermal stability, workability, and mechanical strength. For example, oxides such as titanium, silicon, aluminum, boron, germanium, lanthanum, magnesium, niobium, phosphorus, tantalum, tin, vanadium, and zirconium can be given. In particular, it is preferable to use these metal alkoxides as raw materials. This is because, in the film forming step, it is excellent in mixing with the hole source material described later.
[0028]
Specific metal alkoxides include:
Tetraethoxytitanium, tetraisopropoxytitanium, tetramethoxytitanium, tetranormal butoxytitanium,
Tetraethoxysilane, tetraisopropoxysilane, tetramethoxysilane, tetranormalbutoxysilane, triethoxyfluorosilane, triethoxysilane, triisopropoxyfluorosilane, trimethoxyfluorosilane, trimethoxysilane, trinormalbutoxyfluorosilane, trinormal Propoxyfluorosilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylchlorosilane, phenyltriethoxysilane, phenyldiethoxychlorosilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, Tris Methoxyethoxyvinylsilane,
Triethoxyaluminum, triisobutoxyaluminum, triisopropoxyaluminum, trimethoxyaluminum, trinormal butoxyaluminum, trinormal propoxyaluminum, trisecondary butoxyaluminum, tritertiary butoxyaluminum,
Triethoxy boron, triisobutoxy boron, triisopropoxy boron, trimethoxy boron, trinormal butoxy boron, tri secondary butoxy boron,
Tetraethoxygermanium, tetraisopropoxygermanium, tetramethoxygermanium, tetranormalbutoxygermanium,
Trismethoxyethoxysilanetan,
Bismethoxyethoxymagnesium,
Pentaethoxy niobium, pentaisopropoxy niobium, pentamethoxy niobium, penta normal butoxy niobium, penta normal propoxy niobium,
Triethyl phosphate, triethyl phosphite, triisopropoxy phosphate, triisopropoxy phosphite, trimethyl phosphate, trimethyl phosphite, tri-normal butyl phosphate, tri-normal butyl phosphite, tri-normal propyl phosphate, tri-normal propyl phosphate Fight,
Pentaethoxy tantalum, pentaisopropoxy tantalum, pentamethoxy tantalum,
Tetratertiary butoxy tin, tin acetate, triisopropoxy normal butyl tin,
Triethoxyvanadyl, trinormal propoxyoxyvanadyl, trisacetylacetonatovanadium,
Examples thereof include tetraisopropoxyzirconium, tetranormal butoxyzirconium, and tetratertiary butoxyzirconium.
[0029]
Among the metal alkoxides exemplified above, tetraisopropoxytitanium, tetranormalbutoxytitanium, tetraethoxysilane, tetraisopropoxysilane, tetramethoxysilane, tetranormalbutoxysilane, triisobutoxyaluminum, and triisopropoxyaluminum are preferable.
[0030]
In addition, among the above metal alkoxides, inorganic substances containing silica as a main component, for example, silicon alkoxides such as tetraethoxysilane and tetraisopropoxysilane are preferable because a porous film having a lower dielectric constant can be obtained.
[0031]
As the hole source material, it is preferable to use an organic substance that can be easily dispersed as a hole source in a skeleton material. Surfactants are suitable as such organic substances. Surfactants, when used at moderate concentrations, form micelles, which are aggregates of more surfactant molecules. Further, the micelles are arranged in a regular structure such as a cylinder or a layer according to the concentration. As a result, the framework material formed around each micelle also has an ordered structure. That is, since the micelles are formed in the skeleton, it is possible to arrange the pore sources regularly. By introducing a regular pore structure, the mechanical strength of the porous structure can be improved.
[0032]
As the surfactant, a nonionic surfactant, a cationic surfactant, or the like can be used.
[0033]
As the nonionic surfactant, an ethylene oxide derivative, a propylene oxide derivative, or the like can be used. Specifically, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene olein ether, polyoxyethylene coconut alcohol ether, polyoxyethylene purified coconut alcohol ether, polyoxyethylene 2-ethylhexyl Ether, polyoxyethylene synthetic alcohol ether, polyoxyethylene secondary alcohol ether, polyoxyethylene tridecyl ether, polyoxyethylene isostearyl ether, polyoxyethylene long chain alkyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl Ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene dinonyl phenyl ether Polyoxyethylene styrenated phenyl ether, polyoxyethylene phenyl ether, polyoxyethylene benzyl ether, polyoxyethylene β-naphthyl ether, polyoxyethylene bisphenol-A-ether, polyoxyethylene bisphenol-F-ether, polyoxy Ethylene laurylamine, polyoxyethylene tallowamine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene tallow propylenediamine, polyoxyethylene stearylpropylenediamine, polyoxyethylene N-cyclohexylamine, polyoxyethylene metaxylenediamine, Polyoxyethylene oleylamide, polyoxyethylene stearylamide, polyoxyethylene castor oil, Lioxyethylene hydrogenated castor oil, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monotallow oleate, polyoxyethylene monotol oil fatty acid ester, polyoxyethylene distearate, polyoxyethylene rosin ester, Polyoxyethylene wool grease ether, polyoxyethylene lanolin ether, polyoxyethylene lanolin alcohol ether, polyoxyethylene polyethylene glycol, polyoxyethylene glycerol ether, polyoxyethylene trimethylol propane ether, polyoxyethylene sorbitol ether, polyoxyethylene penta Erythritol dioleate ether, polyoxyethylene sorbitan mostate etherate, polyoxy Ethylene sorbitan monooleate ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxypropylene 2-ethylhexyl ether, polyoxyethylene polyoxypropylene isodecyl ether, polyoxyethylene polyoxypropylene synthetic alcohol ether, polyoxyethylene poly Oxypropylene tridecyl ether, polyoxyethylene polyoxypropylene nonyl phenyl ether, polyoxyethylene polyoxypropylene styrenated phenyl ether, polyoxyethylene polyoxypropylene laurylamine, polyoxyethylene polyoxypropylene tallowamine, polyoxyethylene polyoxy Propylene isodecyl ether, polyoxyethylene polyoxypropylene Ridecyl ether, polyoxyethylene polyoxypropylene lauryl ether, polyoxyethylene polyoxypropylene stearyl ether, polyoxyethylene polyoxypropylene glyceryl ether, polyoxypropylene 2-ethylhexyl ether, polyoxypropylene synthetic alcohol ether, polyoxypropylene butyl ether And polyoxypropylene bisphenol-A-ether, polyoxypropylene styrenated phenyl ether, polyoxypropylene meta-xylene diamine, and the like. These surfactants may be used alone or in combination of two or more.
[0034]
Examples of the cationic surfactant include C _n H _{2n + 1} (CH ₃ ) ₂ N ⁺ M ⁻ , C _n H _{2n + 1} (C ₂ H ₅ ) ₂ N ⁺ M ⁻ (M represents an element serving as an anion), C _n H _{2n + 1} NH ₂ , H ₂ N (CH ₂ ) _n NH ₂ A quaternary alkyl ammonium salt having an alkyl group having 8 to 24 carbon atoms, specifically,
Dodecanyltrimethylammonium chloride, tetradecanyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecanyltrimethylammonium chloride,
Dodecanyl trimethyl ammonium bromide, tetradecanyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, octadecanyl trimethyl ammonium bromide,
Dodecanyltriethylammonium chloride, tetradecanyltriethylammonium chloride, hexadecyltriethylammonium chloride, octadecanyltriethylammonium chloride,
Dodecanyltriethylammonium bromide, tetradecanyltriethylammonium bromide, hexadecyltriethylammonium bromide, octadecanyltriethylammonium bromide and the like can be mentioned.
[0035]
In addition to these surfactants, so-called gemini surfactants having a plurality of hydrophilic groups and a plurality of hydrophobic groups in one molecule, for example, C _n H _{2n + 1} X ₂ N ⁺ M ⁻ (CH ₂ ) _S N ⁺ M ⁻ X ₂ C _m H _{2m + 1} (N, m = 5 to 20, S = 1 to 10). Here, M is a hydrogen atom or a salt-forming anion (specifically, Cl ⁻ , Br ⁻ X is a hydrogen atom or a lower alkyl group (specifically, CH ₃ , C ₂ H ₅ Etc.). Specifically, C ₁₂ H ₂₅ (CH ₃ ) ₂ N ⁺ Cl ⁻ (CH ₂ ) ₄ N ⁺ Cl ⁻ (CH ₃ ) ₂ C ₁₂ H ₂₅ , C ₁₂ H ₂₅ (CH ₃ ) ₂ N ⁺ Br ⁻ (CH ₂ ) ₄ N ⁺ Br ⁻ (CH ₃ ) ₂ C ₁₂ H ₂₅ , C ₁₆ H ₃₃ (CH ₃ ) ₂ N ⁺ Cl ⁻ (CH ₂ ) ₄ N ⁺ Cl ⁻ (CH ₃ ) ₂ C ₁₆ H ₃₃ , C ₁₆ H ₃₃ (CH ₃ ) ₂ N ⁺ Br ⁻ (CH ₂ ) ₄ N ⁺ Br ⁻ (CH ₃ ) ₂ C ₁₆ H ₃₃ And the like.
[0036]
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not construed as being limited to such Examples.
[0037]
【Example】
Example 1
Tetraethoxysilane Si (C ₂ H ₅ O) ₄ And 1.9 g of hexadecyltrimethylammonium chloride as a pore source material and 0.45 g of water having a pH of 3 were mixed and stirred at room temperature for about 2 hours to obtain a transparent, uniform and viscous primary membrane. The forming solution was prepared. The obtained solution was spin-coated on a substrate by spin coating, and subsequently dried at 100 ° C. in the air to form a primary film. The primary membrane was subjected to a decomposition treatment of the pore source material using a supercritical extraction apparatus shown in FIG. 1 and then subjected to supercritical extraction.
[0038]
The supercritical extraction apparatus extracts a pore source material by a carbon dioxide cylinder 1 containing a carbon dioxide gas forming a supercritical fluid, an oxygen cylinder 2 containing an oxygen gas forming a decomposition promoting component, and a supercritical fluid. And a high-pressure container 3 for performing the operation. The carbon dioxide cylinder 1 is connected to the high-pressure vessel 3 via a pump 4 and an on-off valve 5, and the oxygen cylinder 2 is connected to the high-pressure vessel 3 via a regulator 6 and a check valve (not shown). A heater (not shown) is provided in a pipe downstream of the pump 4 and the regulator 6. Further, a pressure regulating valve 7 for adjusting the pressure in the high-pressure vessel 3 is provided in a downstream pipe line of the high-pressure vessel 3.
[0039]
Decomposition treatment and supercritical extraction of the hole source material were performed in the following manner. After disposing the base material in the high-pressure vessel 3, oxygen heated to 80 ° C. and held by the heater was introduced into the high-pressure vessel 3. The oxygen partial pressure in the high-pressure vessel 3 was set to a predetermined pressure (variably changed in the range of 0.1 to 5 MPa) by a regulator, and subsequently, carbon dioxide at 80 ° C. was introduced into the vessel 3, Was adjusted to raise the pressure in the high-pressure vessel 3 to 15 MPa to bring it into a supercritical state. After maintaining in this state for 10 minutes, 100 liters of carbon dioxide were passed as a gas conversion amount (amount of gas discharged from the outlet side of the pressure regulating valve). Thereafter, the pressure of the high-pressure container 3 was reduced, and then the substrate was taken out.
[0040]
As a result, a transparent film having a thickness of 2 μm was formed on the obtained base material. X-ray diffraction analysis was performed on the film formed on the substrate. FIG. 2 shows the result of the X-ray diffraction pattern. FIG. 2 shows a very sharp diffraction peak at a d value of about 3.0 nm, indicating that the obtained porous film has a periodic structure of about 3 nm.
[0041]
As a result of FTIR (Fourier transform infrared spectroscopy) analysis, when the oxygen partial pressure during supercritical treatment was less than 1 MPa, 2850 to 2950 cm ^-1 CH near ₃ , CH ₂ A peak attributable to stretching vibration was observed, and it was confirmed that hexadecyltrimethylammonium chloride remained and extraction was insufficient. On the other hand, those having a pressure of 1 MPa or more did not show these peaks, and it was confirmed that hexadecyltrimethylammonium chloride was completely removed.
[0042]
Further, after forming an Al electrode on the porous film obtained by the treatment at an oxygen partial pressure of 1 MPa or more, the capacitance was measured, and the relative dielectric constant was obtained. As a result, 1.5 was obtained. From this, it was found that an extremely porous film was formed.
[0043]
Example 2
In the same manner as in Example 1 above, a primary film forming solution was prepared, and a primary film was formed on a substrate using the solution. Using a supercritical extraction device shown in FIG. Decomposition and supercritical extraction were performed.
[0044]
The supercritical extraction apparatus shown in FIG. 3 used in this embodiment is basically the same as that of the first embodiment, and therefore, the same components are denoted by the same reference numerals and the description thereof will be omitted. The differences will be mainly described. In this apparatus, hydrogen peroxide (H ₂ O ₂ ) And ethanol as a solvent for dissolving the same. For this purpose, a hydrogen peroxide water container 12 and an ethanol container 13 are provided, and these containers are connected to the high-pressure container 3 via pumps 21, 23, on-off valves 22, 24, and a check valve (not shown), respectively. ing. Further, a heater (not shown) for heating the hydrogen peroxide solution and ethanol flowing through the pipeline is provided in the downstream flow path of the on-off valves 22 and 24. The concentration of the hydrogen peroxide solution is 31 mass% (wt%), and the flow rates of the hydrogen peroxide solution and ethanol are adjusted by the pumping amount of the pump.
[0045]
After disposing the base material in the high-pressure vessel 3, a mixture of a hydrogen peroxide solution and an ethanol mixture in supercritical carbon dioxide at a temperature of 80 ° C. and a pressure of 150 MPa was passed through the high-pressure vessel 3. Here, the mixed state in the high-pressure vessel was visually observed while changing the respective concentrations of the hydrogen peroxide solution, ethanol, and carbon dioxide. When these three kinds of substances are uniformly mixed, they are observed as colorless and transparent, while in an unevenly mixed state, the solution is observed as turbid. As a result, it was found that a specific concentration range exists in order to obtain a uniformly mixed supercritical fluid. The range is shown in FIG. In other words, oxidizing hydrogen peroxide alone cannot be uniformly mixed with supercritical carbon dioxide, but it is necessary to mix with ethanol at an appropriate ratio in order to form a uniform supercritical fluid. Therefore, as an embodiment, as shown in FIG. 5, the pumping speed (specified by the volume speed) of the pump is adjusted so that carbon dioxide (liquid conversion): ethanol: hydrogen peroxide solution = 94.5: 5: Using a supercritical fluid containing ethanol and hydrogen peroxide at a ratio (volume ratio) of 0.5, the primary membrane was simultaneously subjected to decomposition of the pore source material and supercritical extraction in the following manner. As a comparative example, supercritical extraction was performed using a supercritical fluid having a ratio of carbon dioxide (liquid conversion): ethanol = 90: 10.
[0046]
After flowing 100 liters of carbon dioxide as a gas equivalent at the above temperature, pressure and ratio, the inside of the vessel was flushed (washed) with a supercritical fluid consisting of carbon dioxide alone, and the high pressure vessel was depressurized. The material was taken out.
[0047]
As a result, a transparent film having a thickness of 2 μm was formed on the obtained base material. X-ray diffraction analysis was performed on the film formed on the substrate. The X-ray diffraction pattern was similar to that of FIG. 2, and the d value showed a very sharp diffraction peak at about 3.0 nm, indicating that the obtained porous film had a periodic structure of about 3 nm.
[0048]
In addition, as a result of FTIR analysis, no peak due to hexadecyltrimethylammonium chloride was observed in the examples, and it was confirmed that hexadecyltrimethylammonium chloride was completely extracted and removed. On the other hand, in the comparative example in which hydrogen peroxide was not introduced, 2850 to 2950 cm ^-1 CH near ₃ , CH ₂ A peak attributable to stretching vibration was observed, and hexadecyltrimethylammonium chloride remained, confirming that extraction was insufficient.
[0049]
After forming an Al electrode on the porous film of the example from which hexadecyltrimethylammonium chloride was completely extracted and removed, the capacitance was measured and the relative dielectric constant was obtained, and 1.5 was obtained. Was. From this, it was found that an extremely porous material was formed in the examples.
[0050]
【The invention's effect】
According to the method for forming a porous membrane of the present invention, since a step of decomposing a pore source material or a step of decomposing and extracting the pore source material is provided, the extraction of the pore source material can be performed efficiently and the productivity is excellent. Further, the type of application of the hole source material can be expanded, and a porous film having various pore sizes and skeleton structures can be easily formed. Of course, according to the present invention, since the hole source material can be extracted and removed at a low temperature, it can be suitably applied as a method for forming an interlayer insulating film in a manufacturing process of a semiconductor element or the like.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a supercritical extraction device used in Example 1.
FIG. 2 shows an X-ray diffraction pattern of a porous film in Example 1.
FIG. 3 is a schematic configuration diagram of a supercritical fluid extraction device used in Example 2.
FIG. 4 is a diagram illustrating a ternary mixed state showing a concentration range in which a mixture of carbon dioxide, ethanol, and hydrogen peroxide forms a uniform supercritical fluid.
FIG. 5 is an enlarged view of the vicinity of 100% of carbon dioxide in FIG. 4;

Claims (13)

A primary film forming step of forming a primary film in which a skeleton material forming a skeleton of a porous film and a pore source material serving as a base of pores of the porous film are contained in a mixed state, and a pore source forming the primary film A method for forming a porous membrane, comprising: a decomposition step of decomposing a material; and an extraction step of extracting the pore source material decomposed by the decomposition step using a supercritical fluid. The method for forming a porous film according to claim 1, wherein in the decomposition step, a supercritical fluid containing a decomposition promoting component for promoting the decomposition of the pore source material is used. A primary film forming step of forming a primary film in which a skeleton material forming a skeleton of a porous film and a pore source material serving as a base of pores of the porous film are contained in a mixed state, and a pore source forming the primary film A decomposition / extraction step of decomposing and extracting the pore source material using a supercritical fluid containing a decomposition promoting component for promoting the decomposition of the material. 4. The method for forming a porous film according to claim 2, wherein the decomposition promoting component is mainly composed of an oxidatively decomposable substance that oxidatively decomposes the pore source material. The method of forming a porous membrane according to claim 2, wherein the supercritical fluid contains the decomposition promoting component together with a mixing promoting solvent compatible with the decomposition promoting component and the supercritical fluid. The method for forming a porous film according to claim 5, wherein the mixing promoting solvent is an organic solvent. The method for forming a porous film according to claim 6, wherein the concentration of the decomposition promoting component with respect to the mixing promoting solvent is 20 mass% or less.
4 The method for forming a porous film according to any one of claims 1 to 7, wherein a main component of the supercritical fluid is carbon dioxide, an alkyl alcohol, or a mixture thereof. The method for forming a porous film according to any one of claims 1 to 8, wherein the skeleton material is an inorganic substance. The method for forming a porous film according to claim 9, wherein the inorganic substance is an inorganic substance containing silica as a main component. The method for forming a porous film according to any one of claims 1 to 10, wherein the hole source material is an organic substance. The method for forming a porous film according to claim 11, wherein the organic substance is a surfactant. A porous membrane formed by the method according to claim 1.

Images