JP4133468B2 - Method for forming porous film and porous film formed by the method - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
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 for a dielectric layer of a high frequency circuit and an interlayer insulating film of a semiconductor integrated circuit (LSI) and a method for forming the same.
[0002]
[Prior art]
SiO called spin-on-glass (SOG) film as an interlayer insulating film in semiconductor elements₂  A coating-type insulating film containing as a main component is widely used. Along with higher integration of semiconductor elements, interlayer dielectric films having a low dielectric constant containing organic components have been developed. However, with higher integration and multilayering of semiconductor elements and the like, a low dielectric constant interlayer insulating film material having a relative dielectric constant of 2 or less has been demanded.
[0003]
In order to realize a relative dielectric constant of 2 or less, it is indispensable to lower the density of the film itself. For this purpose, it is necessary to use a porous material. However, when the density of the porous material is lowered in order to reduce the dielectric constant, the mechanical strength generally decreases significantly. This is due to non-uniform dispersion of vacancies introduced for density reduction. 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, Japanese Patent Application Laid-Open No. 10-194720 (Patent Document 1) discloses that a silica / surfactant composite is prepared by mixing and reacting alkoxysilane, water and a surfactant. A method of aging, drying, and firing after forming the film is disclosed.
[0005]
Moreover, as a method for obtaining a thin film in a porous material having a periodic structure, Japanese Patent Laid-Open No. 9-194298 (Patent Document 2) includes hydrolyzing tetraalkoxysilane under an acidic condition and mixing a surfactant with this. A method for firing a silica-surfactant nanocomposite obtained by applying and drying a solution is disclosed.
[0006]
However, in these technologies, in order to realize a porous structure, a process of firing a surfactant, which is a pore source material that is a basis of pores of the porous structure, at a high temperature is required, and the temperature Needs to be 500 ° C. or higher. For this reason, it cannot be used for the interlayer insulation film process of a semiconductor element.
[0007]
On the other hand, as a method that can be made porous at a low temperature, Japanese Patent Laid-Open No. 2001-55508 (Patent Document 3) discloses a non-silicate material by solvent exchange and fluid exchange from a material composed of a silicate region and a non-silicate region. A method for producing a porous silicate material by extraction is disclosed. Further, supercritical extraction is also cited as an extraction means (claim 13). As is generally known, since the capillary contraction force does not work in the process using the supercritical fluid, the deformation of the target structure at the time of solvent extraction can be greatly reduced. In the examples of this document, it is stated to use supercritical fluid extraction of isopropanol alone.
[0008]
Although specific examples are not disclosed, it is possible to add another solvent having excellent compatibility with the target component to be extracted to the supercritical medium (Japanese Patent Application Laid-Open No. 2002-367984 (Patent Document 4)). And JP-A-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 2002-367984 A (Claims)
[Patent Document 5]
JP 2002-363286 A (Claims)
[0010]
[Problems to be solved by the invention]
However, in the technique of Patent Document 3, it is difficult to remove all the material in the non-silicate region. In the state before the formation of the porous structure, the non-silicate region contains many substances such as a surfactant, a photoinitiator and a photocured organic substance, and the supercritical fluid generally works as a good solvent. This is because they are not miscible or compatible with all these materials. Also, in the techniques of Patent Documents 4 and 5, the extraction performance for the component to be extracted, that is, the compatibility generally depends on the molecular weight, so that when the molecular weight becomes larger than a certain level, other solvents Even if it adds, it becomes impossible to make it compatible.
That is, in the formation of a porous structure, in the conventional method using a supercritical fluid as a means for removing the pore source material, the relative dielectric constant is used unless the pore source material originally has good compatibility with the supercritical fluid. It is difficult to form a low-quality and high-quality porous film. For this reason, the component of the hole source material extracted by the supercritical fluid is limited, and there is a problem that the pore size, the skeleton structure, and the like of the porous film to be finally formed are limited.
[0011]
The present invention has been made in view of such a problem, and various materials are used as the hole source material for forming the pores of the porous film regardless of the compatibility with the supercritical fluid as the extraction solvent. In other words, it is an object of the present invention to provide a method for forming a porous film having a large 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 is a method for forming a primary film in which a skeleton material that forms a skeleton of a porous film and a hole source material that is a base of pores of the porous film are included in a mixed state. A step, a decomposition step of decomposing the hole source material constituting the primary membrane, and an extraction step of extracting the hole source material decomposed by the decomposition step using a supercritical fluid.
[0013]
According to this method for forming a porous membrane, a primary membrane containing a skeleton material and a pore source material in a mixed state is formed, and then a decomposition process for decomposing the pore source material of the primary membrane is provided. In the process, extraction with a supercritical fluid can be performed on the pore source material that has been decomposed into low molecules by the decomposition process and improved in compatibility with the supercritical fluid. Therefore, at the stage of the primary film formation process, there is no restriction on the molecular weight and structure of the hole source material, and a wide variety of hole source materials can be used, and various pore sizes and skeletal structures can be used accordingly. The porous film can be formed. In addition, since the pore source material decomposed into low molecules can be extracted at the stage of the extraction process using the supercritical fluid, the supercritical extraction can be performed efficiently and the productivity is excellent. Of course, since a supercritical fluid is used in the extraction process, 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 element.
[0014]
  In the present invention,In the decomposition step, the hole source material is formed using a supercritical fluid containing a decomposition promoting component that promotes decomposition of the hole source material.Decompose. When the decomposition promoting component is contained in the supercritical fluid, a mixing promoting solvent composed of an organic solvent compatible with the decomposition promoting component and the supercritical fluid is used, and the concentration of the decomposition promoting component with respect to the mixing promoting solvent is set to 20. mass % Or less in the supercritical fluid together with the decomposition promoting component.When such a supercritical fluid is used, the hole source material can be decomposed and extracted simultaneously in one process (decomposition / extraction process).
[0015]
  As the decomposition accelerating component, a component containing an oxidatively decomposable substance that oxidizes and decomposes the pore source material as a main component (including an oxidatively decomposed substance only) is used.it can. AlsoAs the supercritical fluid used in the extraction step, the decomposition step, or the decomposition / extraction step, those whose main component is carbon dioxide, alkyl alcohol or a mixture thereof are preferable.
[0016]
As the skeleton material, an inorganic material, particularly an inorganic material mainly composed of silica, is preferable because it is excellent in insulation and stability as a skeleton of the porous film, and a porous film having a lower dielectric constant can be obtained. Further, as the hole source material, an organic substance can be used, and in particular, the surfactant is used in an appropriate concentration to form micelles. Therefore, the hole source material can be regularly arranged and pulled. Is preferable because it can form a regular skeleton.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The method for forming a porous film of the present invention includes: (1) forming a primary film containing a skeleton material forming a skeleton of a porous film and a pore source material that is a base of pores of the porous film in a mixed state. Three steps of a primary film forming step, (2) a decomposition step of decomposing the hole source material constituting the primary membrane, and (3) an extraction step of extracting the hole source material decomposed by the decomposition step using a supercritical fluid Is provided.
[0018]
  In the decomposition step, the hole source material is formed using a supercritical fluid containing a decomposition promoting component that promotes decomposition of the hole source material.Decompose. DisassemblyBy using a supercritical fluid containing an accelerating component, the decomposition treatment can be performed quickly with a high-density, highly diffusible fluid. For this reason, since the decomposition promoting component can be efficiently brought into contact with a component in a fine space, good decomposition efficiency can be obtained. When the supercritical fluid containing the decomposition promoting component is used, the decomposition step and the extraction step can be performed simultaneously. A process in which such a decomposition process and an extraction process are performed simultaneously is called a decomposition / extraction process.
[0019]
As the decomposition accelerating component, a component mainly composed of an oxidatively decomposable substance that oxidizes and decomposes the pore source material (including those composed only of an oxidatively decomposable substance) can be used. It becomes possible to reduce the molecular weight. For example, when a surfactant having a large molecular weight is used as the pore source material, large pores can be formed according to the molecular weight of the surfactant. It is difficult to directly extract the surfactant with a supercritical fluid after forming a primary film containing in a mixed state. Such a surfactant having a large molecular weight has a hydrophobic group composed of a higher alkyl group bonded in a very long chain. This hydrophobic group is easily fragmented and decomposed by an oxidative degradation substance. In this way, the hydrophobic group is decomposed and the low molecular weight surfactant is easily extracted by the supercritical fluid.
[0020]
The oxidatively decomposable substance may be any substance that can be mixed with the supercritical fluid when used in a supercritical fluid. Specifically, O₂, O_Three, N₂O, H₂O₂, HCl, HBr, Cl₂, BCl_Three, HNO_ThreeIn addition, a protic solvent can also be used. Specific examples of protic solvents include hydrochloric acid, perchloric acid, nitric acid, hydrofluoric acid, phosphoric acid, shelf acid, organic acid such as oxalic acid, organic acid such as acetic acid and formic acid, bromine trifluoride, pentafluoride, etc. 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 is compatible with both the oxidatively degradable substance and the supercritical fluid.Composed of organic solventContained in supercritical fluids with mixing-promoting solventsLet Mixing promotion solventBy using this, the compatibility between the supercritical fluid and the oxidatively decomposable substance can be improved even if the oxidatively decomposable substance alone is not compatible with the supercritical fluid or is inferior in compatibility. In this case, the amount of the mixing accelerating solvent may be appropriately adjusted as long as it is compatible with the supercritical fluid without impairing the oxidative decomposability of the oxidatively decomposable substance. As a concentration range to be adjusted, the amount of the oxidative decomposable substance is 0.01% or more and 20% or less in mass% (wt%) with respect to the mixing promoting solvent to be contained in the supercritical fluid together with the oxidative decomposable substance. It is preferable. More preferably, it is 0.05% or more and 10% or less. This is because if the amount of the oxidatively decomposable substance is too small, the oxidatively degradable property is deteriorated, while if it is too large, it is difficult to be compatible with the supercritical fluid.
[0022]
  As the mixing promoting solventExamples of the organic solvent that can be used include alcohol solvents, ketone solvents, and amide solvents.
[0023]
Specifically, as alcohol solvents, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec- Mention may be made of pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol.
[0024]
Also, as ketone solvents, 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- Examples include hexyl ketone and di-i-butyl ketone.
[0025]
Examples of amide solvents include formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylnermamide, acetamide, N-methylacetamide, N, N-dimethylacetamide, N -Ethylacetamide, N, N-diethylacetamide, N-methylpropionamide, N-methylpyrrolidone.
[0026]
The supercritical fluid in which the decomposition accelerating component and the mixing accelerating solvent are dissolved is carbon dioxide or alkyl alcohol (alkyl alcohol is methyl alcohol, ethyl alcohol, propyl, etc.) as in the supercritical fluid used in the extraction process. One or a mixture of two or more alcohols may be used, and these are collectively called alkyl alcohols.) It is industrially preferable to use a mixture of carbon dioxide and alkyl alcohol. This is because any of these supercritical fluids can be widely compatible with various substances.
[0027]
As the skeletal material that becomes 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, these metal alkoxides are preferably used as raw materials. This is because the film forming process is excellent in mixing with the hole source material described later.
[0028]
As a specific metal alkoxide,
Tetraethoxytitanium, tetraisopropoxytitanium, tetramethoxytitanium, tetranormalbutoxytitanium,
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, trinormalbutoxyaluminum, trinormalpropoxyaluminum, trisecondary butoxyaluminum, tritertiary butoxyaluminum,
Triethoxyboron, triisobutoxyboron, triisopropoxyboron, trimethoxyboron, trinormal butoxyboron, trisecondary butoxyboron,
Tetraethoxygermanium, tetraisopropoxygermanium, tetramethoxygermanium, tetranormalbutoxygermanium,
Trismethoxyethoxy lanthanum,
Bismethoxyethoxymagnesium,
Pentaethoxyniobium, pentaisopropoxyniobium, pentamethoxyniobium, pentanormalbutoxyniobium, pentanormalpropoxyniobium,
Triethyl phosphite, triethyl phosphite, triisopropoxy phosphite, triisopropoxy phosphite, trimethyl phosphite, trimethyl phosphite, trinormal butyl phosphate, trinormal butyl phosphite, trinormal propyl phosphate, trinormal propyl phosphite Fight,
Pentaethoxytantalum, pentaisopropoxytantalum, pentamethoxytantalum,
Tetra tertiary butoxy tin, tin acetate, triisopropoxy normal butyl tin,
Triethoxyvanadyl, trinormalpropoxyoxyvanadyl, 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]
Among the metal alkoxides, inorganic substances mainly composed of silica, 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 the skeleton material. As such an organic substance, a surfactant is suitable. When the surfactant is used at an appropriate concentration, it forms micelles that are aggregates of surfactant molecules. Further, the micelles are arranged in a regular structure such as a cylindrical shape or a layered shape according to the concentration. As a result, the skeleton material formed around each micelle also has an ordered structure. That is, since micelles are formed in the skeleton, the hole sources can be regularly arranged. 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 refined 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 octylphenyl ether, polyoxyethylene nonylphenyl 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, polyoxyethylene Laurylamine, polyoxyethylene beef tallow amine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene beef tallow propylene diamine, polyoxyethylene stearyl propylene diamine, polyoxyethylene N-cyclohexylamine, polyoxyethylene metaxylene diamine, poly Oxyethylene oleylamide, polyoxyethylene stearylamide, polyoxyethylene castor oil, polyoxyethylene Hydrogenated castor oil, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene mono tallow 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 trimethylolpropane ether, polyoxyethylene sorbitol ether, polyoxyethylene pentaerythritol diol Ate ether, polyoxyethylene sorbitan mostate ether, polyoxyethylene sol Tan monooleate ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene polyoxypropylene 2-ethylhexyl ether, polyoxyethylene polyoxypropylene isodecyl ether, polyoxyethylene polyoxypropylene synthetic alcohol ether, polyoxyethylene polyoxy Propylene tridecyl ether, polyoxyethylene polyoxypropylene nonylphenyl ether, polyoxyethylene polyoxypropylene styrenated phenyl ether, polyoxyethylene polyoxypropylene laurylamine, polyoxyethylene polyoxypropylene tallow amine, polyoxyethylene polyoxypropylene Isodecyl ether, polyoxyethylene polyoxypropylene tridecyl ether Polyoxyethylene polyoxypropylene lauryl ether, polyoxyethylene polyoxypropylene stearyl ether, polyoxyethylene polyoxypropylene glyceryl ether, polyoxypropylene 2-ethylhexyl ether, polyoxypropylene synthetic alcohol ether, polyoxypropylene butyl ether, polyoxypropylene Examples thereof include bisphenol-A-ether, polyoxypropylene styrenated phenyl ether, and polyoxypropylene metaxylenediamine. These surfactants can be used alone or in combination of two or more.
[0034]
Cationic surfactants include C_nH_{2n + 1}(CH_Three)₂N⁺M^-, C_nH_{2n + 1}(C₂H_Five)₂N⁺M^-(M represents an anion element), C_nH_{2n + 1}NH₂, H₂N (CH₂)_nNH₂A quaternary alkylammonium salt having an alkyl group having 8 to 24 carbon atoms represented by:
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,
Examples include dodecanyl triethyl ammonium bromide, tetradecanyl triethyl ammonium bromide, hexadecyl triethyl ammonium bromide, octadecanyl triethyl ammonium bromide and the like.
[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, such as C_nH_{2n + 1}X₂N⁺M^-(CH₂)_SN⁺M^-X₂C_mH_{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 represents a hydrogen atom or a lower alkyl group (specifically, CH_Three, C₂H_FiveEtc.) Specifically, C₁₂H_{twenty five}(CH_Three)₂N⁺Cl^-(CH₂)_FourN⁺Cl^-(CH_Three)₂C₁₂H_{twenty five}, C₁₂H_{twenty five}(CH_Three)₂N⁺Br^-(CH₂)_FourN⁺Br^-(CH_Three)₂C₁₂H_{twenty five}, C₁₆H₃₃(CH_Three)₂N⁺Cl^-(CH₂)_FourN⁺Cl^-(CH_Three)₂C₁₆H₃₃, C₁₆H₃₃(CH_Three)₂N⁺Br^-(CH₂)_FourN⁺Br^-(CH_Three)₂C₁₆H₃₃Etc.
[0036]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limitedly interpreted by this Example.
[0037]
【Example】
  First, a reference example in which a pore source material is decomposed and extracted using a supercritical fluid containing oxygen as a decomposition promoting component will be described.
  Tetraethoxysilane Si (C₂H_FiveO)_Four1.9 g, 1 g of hexadecyltrimethylammonium chloride as a pore source material, and 0.45 g of water of pH = 3 are mixed, stirred at room temperature for about 2 hours, and transparent, uniform and viscous primary membrane The forming solution was adjusted. The obtained solution was spin-coated on a substrate by a spin coating method, followed by drying at 100 ° C. in the atmosphere to form a primary film. The primary membrane was subjected to a supercritical extraction after the pore source material was decomposed using the supercritical extraction apparatus shown in FIG.
[0038]
The supercritical extraction device extracts a hole source material by a carbon dioxide cylinder 1 containing carbon dioxide gas forming a supercritical fluid, an oxygen cylinder 2 containing oxygen gas forming a decomposition promoting component, and a supercritical fluid. A high-pressure vessel 3. 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 attached to the downstream side of the pump 4 and the regulator 6. In addition, a pressure regulating valve 7 for adjusting the pressure in the high pressure vessel 3 is provided in the downstream pipe line of the high pressure vessel 3.
[0039]
The hole source material was decomposed and supercritical extraction was performed as follows. After the substrate was placed in the high-pressure vessel 3, oxygen heated and held at 80 ° C. by a heater was introduced into the high-pressure vessel 3. The oxygen partial pressure in the high-pressure vessel 3 is set to a predetermined pressure (variably changed in the range of 0.1 to 5 MPa) by a regulator, and then 80 ° C. carbon dioxide is introduced into the vessel 3 to adjust the pressure regulating valve. By adjusting the pressure, the pressure in the high-pressure vessel 3 was increased to 15 MPa to obtain a supercritical state. After holding in this state for 10 minutes, 100 liters of carbon dioxide was circulated as a gas conversion amount (amount of gas discharged from the outlet side of the pressure regulating valve). Then, after decompressing the high-pressure vessel 3, 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. The result of the X-ray diffraction pattern is shown in FIG. FIG. 2 shows a very sharp diffraction peak at a d value of about 3.0 nm, and it was found 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 processing is less than 1 MPa, 2850-2950 cm.^-1CH nearby_Three, CH₂It was confirmed that the peak due to stretching vibration was observed, hexadecyltrimethylammonium chloride remained, and extraction was insufficient. On the other hand, when the pressure was 1 MPa or more, these peaks were not observed, 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 with an oxygen partial pressure of 1 MPa or more, the capacitance was measured and the relative dielectric constant was obtained, and 1.5 was obtained. From this, it was found that a very porous film was formed.
[0043]
  Next, examples of the present invention will be described.
  In the same manner as in Example 1 above, a primary film forming solution was prepared, and a primary film was formed on the substrate using this solution, and the pore source material in the primary film was formed using the supercritical extraction apparatus 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. Therefore, the same components are denoted by the same reference numerals and the description thereof is omitted. The difference will be mainly described. In this device, hydrogen peroxide (H₂O₂) And ethanol as a solvent for dissolving the same. Therefore, a hydrogen peroxide solution container 12 and an ethanol container 13 are provided, and these containers are connected to the high-pressure container 3 through pumps 21 and 23, on-off valves 22 and 24, and check valves (not shown), respectively. ing. In addition, heaters (not shown) for heating the hydrogen peroxide solution and ethanol flowing through the pipes are attached to the downstream flow paths 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.
[0045]
After the substrate was placed in the high-pressure vessel 3, a mixture of hydrogen peroxide solution and ethanol mixed with supercritical carbon dioxide at a temperature of 80 ° C. and a pressure of 150 MPa was circulated in the high-pressure vessel 3. Here, each concentration of hydrogen peroxide solution, ethanol, and carbon dioxide was changed, and the mixed state in the high-pressure vessel was visually observed. When these three kinds of substances are uniformly mixed, they are observed as colorless and transparent, while in a non-uniform mixed state, the solution is observed as cloudy. As a result, it was found that there is a specific concentration range to obtain a uniformly mixed supercritical fluid. The range is shown in FIG. That is, the oxidizing hydrogen peroxide solution alone cannot be mixed with the supercritical carbon dioxide uniformly, and it is necessary to mix it with ethanol at an appropriate ratio in order to form a uniform supercritical fluid. Therefore, as an example, as shown in FIG. 5, the liquid feeding speed (specified by the volume speed) of the pump is adjusted, and carbon dioxide (liquid conversion): ethanol: hydrogen peroxide solution = 94.5: 5: Using a supercritical fluid containing ethanol and hydrogen peroxide water at a ratio (volume ratio) of 0.5, the pore source material was simultaneously decomposed and supercritical extracted in the following manner with respect to the primary membrane. As a comparative example, supercritical extraction was performed using a supercritical fluid in a ratio of carbon dioxide (liquid conversion): ethanol = 90: 10.
[0046]
After flowing 100 liters of carbon dioxide as a gas conversion amount at the above temperature, pressure, and ratio, the inside of the container was flushed (washed) using a supercritical fluid consisting of only carbon dioxide, the pressure of the high pressure container was reduced, The material was removed.
[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 is the same as that shown in FIG. 2, and the d value shows a very sharp diffraction peak at about 3.0 nm. The obtained porous film has 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, 2850-2950 cm.^-1CH nearby_Three, CH₂A peak due to stretching vibration was observed, hexadecyltrimethylammonium chloride remained, and it was confirmed 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, capacitance measurement was performed and the relative dielectric constant was obtained. As a result, 1.5 was obtained. It 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,Using a supercritical fluid containing a predetermined mixing-promoting solvent and decomposition-promoting componentSince there is a decomposition step or decomposition / extraction step for decomposing the hole source material, the hole source material can be extracted efficiently and the productivity is excellent. In addition, the application types of the hole source material can be expanded, and porous films 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 apparatus 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 extraction apparatus used in Example 2. FIG.
FIG. 4 is an explanatory diagram of 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 carbon dioxide in FIG. 4 near 100%.

Claims (9)

A primary film forming step for forming a primary film including a skeleton material for forming a skeleton of the porous film and a hole source material which is a base of pores of the porous film in a mixed state; and a hole source constituting the primary film A decomposition step of decomposing the material, and an extraction step of extracting the pore source material decomposed by the decomposition step using a supercritical fluid ,
In the decomposition step, the hole source material is decomposed using a supercritical fluid containing a decomposition promoting component that promotes decomposition of the hole source material;
The supercritical fluid includes a mixing promoting solvent composed of an organic solvent compatible with the decomposition promoting component and the supercritical fluid together with the decomposition promoting component, and the concentration of the decomposition promoting component with respect to the mixing promoting solvent is 20 mass %. A method for forming a porous film, which is as follows . A primary film forming step for forming a primary film including a skeleton material for forming a skeleton of the porous film and a hole source material which is a base of pores of the porous film in a mixed state; and a hole source constituting the primary film A decomposition / extraction step of decomposing and extracting the pore source material using a supercritical fluid containing a decomposition promoting component that promotes decomposition of the material ,
The supercritical fluid includes a mixing promoting solvent composed of an organic solvent compatible with the decomposition promoting component and the supercritical fluid together with the decomposition promoting component, and the concentration of the decomposition promoting component with respect to the mixing promoting solvent is 20 mass %. A method for forming a porous film, which is as follows . Porous film forming method of according to claim 1 or 2, wherein the decomposition accelerating component is mainly composed of pores source material oxidative decomposing oxidative degradation substances. The method for forming a porous film according to any one of claims 1 to 3 , wherein the main component of the supercritical fluid is carbon dioxide, alkyl alcohol, or a mixture thereof. The method for forming a porous film according to claim 1, wherein the skeleton material is an inorganic substance. The method for forming a porous film according to claim 5 , wherein the inorganic substance is an inorganic substance mainly composed of silica. The method for forming a porous film according to claim 1, wherein the pore source material is an organic substance. The method for forming a porous film according to claim 7 , wherein the organic substance is a surfactant. A porous membrane formed by the method according to claim 1 .

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