JP4279064B2 - Porous silica film and laminate having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous silica film having an inclined structure in the film thickness direction excellent in low reflectivity and mechanical durability, and a laminate having the porous silica film.
[0002]
[Prior art]
Fresnel at the time of light entering and exiting due to the difference in refractive index between optical elements or optical elements such as lenses, filters, prisms, antireflection films, transmissive films, solar cells, optical fibers, optical sensors, optical isolators, etc. It is known that reflection occurs. As countermeasures, it is conventionally known to use a multilayer interference film in which thin films having a high refractive index and a low refractive index are alternately laminated, or a refractive index gradient structure film in which the refractive index is changed in an inclined manner.
[0003]
The conventional multilayer interference film is designed with consideration of the phase of light to reduce the reflectivity and obtain a light transmission effect, but the transmittance varies depending on the wavelength of the light. There was a point. Furthermore, since it is necessary to form a number of transparent thin films with controlled film thickness and refractive index, there is a problem of lack of mass productivity and high cost.
[0004]
On the other hand, in order to form the refractive index gradient structure film, the apparent refractive index can be changed by changing the film composition, the surface shape of the film and the like in an inclined manner. For example, in Patent Document 1, a regular concave surface can be formed by transferring a surface composed of ultra particles. This method has an antireflection effect because the apparent refractive index has an inclined structure. However, the regular concave surface has a large wavelength dependency of the reflectance, and there is a problem in the above application. In addition, Patent Document 2 reports a method of performing etching using gas to form an aperiodic spongy microstructure on the surface. In this method, the wavelength dependence of the reflectance is somewhat reduced. Since any conventional material requires an uneven shape on the film surface, the coefficient of friction is large, and durability against mechanical wear and antifouling properties may be significantly reduced. Furthermore, this method is a multi-step process, and there are problems of high cost and mass productivity.
[0005]
Further, Patent Document 3 discloses that the refractive index distribution is controlled by changing the pore size and stacking with a spin coater. In this method, the target distribution structure can be easily obtained, but the surface roughness may change depending on the size of the pores existing on the outermost surface. Further, the same publication also reports a method of forming a gradient structure of porosity by sequentially changing the raw material composition in the CVD method and then removing the organic component by heat treatment. In this method, as described above, an inclined structure with a void ratio can be easily obtained. However, the CVD method often has a non-homogeneous film surface, and there is a problem in that a difference in mechanical strength depending on the location tends to occur. In addition, an organic component is always required, and there are not a few impurities in the finally remaining film.
[0006]
Therefore, some conventional materials have a continuous gradient structure of porosity, but there are problems in terms of wavelength dependency of reflectivity in the antireflection effect, surface properties, durability against mechanical wear, Further, the manufacturing method is costly because it requires a multi-step process and advanced coating technique, lacks mass productivity, and is not sufficiently satisfactory for the above applications.
[0007]
[Patent Document 1]
JP-A-8-274359
[Patent Document 2]
JP 2002-139601 A
[Patent Document 3]
JP 2001-272506 A
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a porous silica film excellent in low reflectivity with little wavelength dependency in the visible light region, easy laminating process, antifouling property, and mechanical strength, and an optical material and a semiconductor material using the same It is in providing a suitable laminated body.
[0009]
[Means for Solving the Problems]
  In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, the void ratio of the pores to be continuously changed in the film thickness direction is effective in optical materials and semiconductor materials. A porous silica film having performance has an extremely smooth surface property which has not been obtained conventionally. As a result, it has been found that the above-mentioned material excellent in not only low reflectivity with little wavelength dependency in the visible light region but also easy laminating process, antifouling property, and mechanical strength can be obtained, and the present invention is completed. It came to.
  The porous silica film of the present invention for achieving the above object has an average porosity of 35% or more.The average pore diameter is 0.5 to 100 nm, and the film thickness is 50 to 850 nm.Thus, the porosity within a depth of 100 nm from the surface is 24% or less, and the ten-point surface roughness Rz is 50 nm or less.
[0010]
  According to the present invention, since the porosity changes continuously in the film thickness direction, the wavelength dependence of Fresnel reflection and reflectance can be reduced, and an extremely excellent optical material can be provided. For example, when the porosity is reduced from the surface, since the pores are filled with air (refractive index 1), the refractive index of the porous silica film becomes smaller as the surface. Such a material has an ideal optical design as an antireflection film, and can be applied to optical applications such as solar cells, displays, and sensors.
  In the above applications, there may be a need for more severe environmental stability and chemical resistance. In this case, the porous silica film of the present invention is characterized in that the average porosity is 35% or more and the porosity within a depth of 100 nm from the surface is 24% or less. According to this invention, the mechanical strength is remarkably improved, the smoothness of the surface is improved, and the environmental stability and chemical resistance are improved.
[0011]
  Furthermore, the conventional porous silica film has a porous structure, and thus tends to have a rough surface due to the concave and convex portions. However, the porous silica film of the present invention has a ten-point surface roughness Rz.50It is characterized by being not more than nm. According to this invention, the friction coefficient of the surface is reduced, durability against mechanical wear is improved, and excellent antifouling properties are also exhibited. In optical material applications such as solar cells, displays, and sensors, the porous silica film of the present invention is often used in contact with the outside world, and the above performance is important.
[0012]
  The surface of the porous silica film of the present invention is extremely smooth and has an average surface roughness Ra.ButIt is preferable that it is 50 nm or less. According to the present invention, it is possible to facilitate a laminated structure that is absolutely necessary for the use of the optical material and the semiconductor material. For example, even when a transparent conductive layer such as ITO is laminated on the porous silica film of the present invention, the performance of the laminated transparent electrode layer is hardly impaired in order to prevent protrusions and depressions. In addition, when the smooth substrate is laminated via a resin or the like, the adhesion between the porous silica film and the smooth substrate is hardly impaired.
[0013]
  In the porous silica membrane of the present invention, it is preferable that the vacancies are continuous communication holes. According to the present invention, a porous silica film having excellent mechanical strength can be provided. Furthermore, the porous silica film of the present invention has a film thickness of 50 to 850 nm in terms of environmental stability in the above applications.The
[0014]
  The porous silica membrane of the present invention has an average pore diameter of 0.5 to 100 nm.TheThis is because the pores are nanometer-sized, and the transparency is improved as well as sufficient mechanical strength in the above applications. In addition, a porous silica film material having resistance to patterning can be obtained.
[0016]
A laminate for achieving the above object has the above-described porous silica film of the present invention on a substrate. The laminate of the present invention is characterized in that the substrate is transparent or a semiconductor substrate.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the actual situation of the present invention will be described.
The porosity of the porous silica film of the present invention is characterized by continuously changing in the film thickness direction. The change in porosity here may be the pore size or the number of pores, and means a change in the absolute amount occupied by the pores. Moreover, the porosity refers to the average porosity with respect to the film surface, and this continuously changes in the film thickness direction. Further, the change is not particularly limited, and may be linear or curvilinear. The continuous change means that there is a change in a region of 1/10 or less of the film thickness. In such a film structure, there is no clear interface in the film and it is accompanied by a continuous change in the optical constant. Therefore, Fresnel reflection in the antireflection material and the wavelength dependence of the reflectance are reduced, and the antireflection effect is maximized. Can contribute. In other words, it is an optimal material for optical applications such as solar cells, displays, and sensors.
[0018]
As a method for confirming the above structure, there are a transmission electron microscope (TEM) and a scanning electron microscope (SEM). In the case of observation with an electron microscope, it can be determined by taking an electron microscope photograph of an electron beam acceleration voltage of 5 kV and an observation magnification of 1000 to 10000 times and analyzing the cross-sectional image thereof. As a SEM observation sample, a laminate obtained by forming this porous silica film on a substrate was used as a sample, and mechanical shock was applied in a state where the sample was cooled and embrittled with liquid nitrogen. The brittle fracture surface was used. As this brittle fracture surface, a sample which was not deposited on a thin film of a conductive material such as metal or carbon, which is generally used for the purpose of improving the conductivity of the sample surface, was used. Further, as described above, since the porosity has a correlation with the refractive index, it could be evaluated by a spectroscopic ellipsometer. The change in the porosity can also be confirmed from the result of measurement by spectroscopic ellipsometry (manufactured by Sopra: GES-5) in which the wavelength range of the measurement light is 250 to 850 nm.
[0019]
Further, unlike a porous silica film having a conventional refractive index gradient structure, the porous silica film of the present invention having a homogeneous surface is characterized by a ten-point surface roughness (Rz) of 100 nm or less. The ten-point surface roughness (Rz) is preferably 50 nm or less, more preferably 30 nm or less, and most preferably 25 nm or less. Silica is formed from a fine regular structure, and the lower limit of the ten-point surface roughness (Rz) is 10 nm. Some conventional porous silica materials have sufficient antireflection performance, but there are many that cannot be put to practical use as an actual optical material application due to surface problems. However, the surface of the porous silica film of the present invention has an extremely small coefficient of friction due to the above surface properties, and is excellent in durability against mechanical wear. Furthermore, antifouling properties are also added. Specifically, it is important for optical materials such as solar cells, displays, and sensors that are often used in contact with the outside world, and can be said to be an optimal material for the above-mentioned applications.
[0020]
The ten-point surface roughness (Rz) used in the present invention is a ten-point average roughness defined in JIS B0601. That is, it is the difference between the average value of the Z data (height direction) from the maximum to the fifth peak on the specified surface and the Z data of the valley from the minimum to the fifth. There is a method using an atomic force microscope (AFM) to measure the ten-point surface roughness (Rz). The surface of a certain range is measured, and the ten-point surface roughness (Rz) in that region is calculated. For example, using a SPI 3800 manufactured by Seiko Electronics Co., Ltd., a surface image in the range of 5 um * 5 um is measured by the DFM mode, and the ten-point surface roughness (Rz) is calculated by software installed in the apparatus.
[0021]
The porous silica film of the present invention has an extremely smooth surface property in addition to the above surface property. The porous silica film has few concave portions often found in conventional porous silica films, and has a surface roughness Ra = 50 nm or less. The surface roughness Ra is preferably 10 nm or less, more preferably the surface roughness Ra is 5 nm or less, further preferably the surface roughness Ra is 3 nm or less, and most preferably the surface roughness Ra is 0.5 nm or less. As described above, since silica has a fine regular structure, it is difficult to obtain a surface roughness Ra of 0.1 nm or less. On the other hand, when the surface roughness Ra is larger than 50 nm, various troubles may be caused in the lamination process on the porous silica film of the present invention.
[0022]
The surface roughness (Ra) used in the present invention is a numerical value defined by JIS-B0601. For the measurement of the surface roughness (Ra), a stylus type step / surface roughness / fine shape measuring device (manufactured by KLA-Tencor Corporation: P-15) was used. Measurement conditions were such that the surface was not damaged, a stylus force (tactile pressure) of 0.2 mg to obtain an accurate surface roughness, a scanning speed of 20 μm / second, and a scanning distance of 500 μm to evaluate the smoothness as wide as possible. did. The calculation of the surface roughness (Ra) was performed by software installed in the apparatus. For the measurement of the surface roughness Ra, a method using an atomic force microscope (AFM) is also generally used. The surface of a certain range is measured, and the surface roughness Ra in that region is calculated. For example, an SPI 3800 manufactured by Seiko Electronics Co., Ltd. is used, a surface image in the range of 10 um * 10 um is measured by the DFM mode, and the entire average surface roughness (Ra) is calculated by software installed in the apparatus. The porous silica film described in the present invention shows a very smooth surface in this method as well.
[0023]
The pores of the porous silica film of the present invention are preferably continuous communication holes. The detailed hole structure is not particularly limited, and may be a tunnel shape or a connecting hole in which independent holes are connected. In terms of the homogeneity and mechanical strength of the porous silica film, a connecting hole in which independent pores are connected is preferable. Such a vacancy state is confirmed by the transmission electron microscope (TEM) or the scanning electron microscope (SEM) described above. In the case of the above-mentioned connecting holes, the average hole diameter described later is defined as an average value of their widths.
[0024]
According to the present invention, a porous silica film having excellent mechanical strength can be provided.
Furthermore, the porous silica film of the present invention preferably has a thickness of 50 to 2000 nm from the viewpoint of environmental stability in the above-mentioned applications. More preferably, the film thickness is 50 to 1000 nm, still more preferably 80 to 850 nm, and most preferably 200 to 700 nm. When the film thickness is smaller than 50 nm, the uneven surface composed of silica secondary particles appears, so that the surface smoothness of the porous silica film is impaired, and when the film thickness is larger than 2000 nm, the film is slightly wavy due to the three-dimensional network structure of silica. Similarly, the surface smoothness is impaired. The measurement was performed using a stylus type step, surface roughness, and fine shape measuring device (manufactured by KLA-Tencor Corporation: P-15). .
[0025]
The porous silica film of the present invention has pores filled with air or gas. Therefore, the physical constants such as the apparent density, dielectric constant, and refractive index of the porous silica film can be controlled by adjusting the average pore diameter and the average porosity (the amount of pores). By appropriately having an average pore diameter of 0.5 to 100 nm, it can be applied as a semiconductor material (such as a low dielectric constant material) excellent in mechanical strength and an optical material (such as a low refractive material or antireflection material). The average pore diameter is preferably 0.5 to 50 nm, more preferably the average pore diameter 1 to 20 nm, and most preferably the average pore diameter 3 to 20 nm. Conversely, if the average pore diameter is larger than 100 nm, the surface properties of the porous silica film are adversely affected. If the average pore diameter is smaller than 1 nm, the active groups on the pore wall surface approach each other, so that the stability of the porous silica film is impaired. And it becomes difficult to increase the porosity. Similarly, the average porosity of the entire porous silica film needs to be 25% or more in order to have an excellent function in applications such as semiconductor materials and optical materials. The average porosity is preferably 35% or more, more preferably the average porosity is 45% or more, and most preferably the average porosity is 55% or more. On the other hand, when the average porosity is 75% or more, the mechanical strength of the porous silica film is remarkably impaired, and the surface property is also deteriorated.
[0026]
The average pore diameter and the average porosity can be evaluated by a nitrogen adsorption method, TEM, or SEM. Specific measurement conditions are the same as the confirmation of the continuous change in the porosity described above. Further, as described above, since the average porosity has a correlation with the refractive index, it could be evaluated by a spectroscopic ellipsometer. The average porosity can be confirmed by a result of measurement by spectroscopic ellipsometry (manufactured by Sopra Co., Ltd .: GES-5) having a wavelength range of measurement light of 250 to 850 nm.
[0027]
In terms of mechanical strength and chemical resistance in optical material applications, it is preferable to have a dense layer within a depth of 300 nm from the surface of the porous silica film. More preferably, the depth is within 150 nm from the surface, more preferably within 100 nm, and most preferably within 50 nm. When the dense layer is deeper than 300 nm deep from the surface, the porous structure is impaired, and on the other hand, it is difficult to control the surface property uniformly within the depth of 10 nm. According to the present invention, the mechanical strength is remarkably improved, the surface smoothness and chemical resistance are also improved, and environmental stability under severe conditions can be obtained. In order to confirm this structure, it can be easily confirmed by TEM and SEM as described above.
[0028]
The laminate for achieving the above object can take a form characterized by having the above-described porous silica film of the present invention on a substrate. For example, in a semiconductor material application, it can be laminated on a semiconductor substrate. As a typical semiconductor substrate, there is a transparent conductive film, and a composite oxide thin film such as indium oxide added with tin or zinc oxide added with aluminum is preferable. In addition, a semiconductor such as silicon or germanium, a compound semiconductor such as gallium-arsenic or indium-antimony, a substrate such as ceramics or metal can be used, and a thin film of another material is formed on the surface thereof. Can also be used. Thin films in this case include aluminum, titanium, chromium, nickel, copper, silver, platinum, tantalum, tungsten, osmium, gold, and other metals, as well as polycrystalline silicon, alumina, titania, zirconia, silicon nitride, titanium nitride A thin film made of tantalum nitride, boron nitride, amorphous carbon, or fluorinated amorphous carbon may be used.
[0029]
In the optical material application, the substrate is preferably transparent, and more preferably has a refractive index of 1.15 to 2.2. This refractive index is an average refractive index in the entire depth direction determined by measurement with an ellipsometer based on ASTM D-542, and is represented by a value with respect to the sodium D line (589.3 nm) at 23 ° C. As the substrate having such a refractive index, a transparent substrate made of a general-purpose material can be used. For example, various shot glasses such as silicon dioxide, BK7, SF11, LaSFN9, BaK1, F2, etc., fluorinated glass, phosphorous glass, boron-phosphorus glass, borosilicate glass, synthetic fused silica glass, optical crown glass, low expansion borosilicate Glass, sapphire, soda glass, alkali-free glass, acrylic resin such as polymethyl methacrylate and cross-linked acrylate, aromatic polycarbonate resin such as bisphenol A polycarbonate, styrene resin such as polystyrene, amorphous polyolefin such as polycycloolefin Examples thereof include synthetic resins such as resins and epoxy resins.
[0030]
Of these, shot glass such as BK7 and BaK1, synthetic fused silica glass, optical crown glass, low expansion borosilicate glass, soda glass, alkali-free glass, acrylic resin, aromatic polycarbonate resin, and amorphous polyolefin resin are preferable. BK7 shot glass, synthetic fused silica glass, optical crown glass, low expansion borosilicate glass, soda glass, alkali-free glass, acrylic resin, and aromatic polycarbonate resin are most preferred. In addition, it can be laminated on an inorganic compound such as silsesquioxane hydroxide, methyl silsesquioxane, or porous silica.
[0031]
Although there is no restriction | limiting in particular in the thickness of a board | substrate, in an optical use, it is 0.1-10 mm normally. The lower limit of the substrate thickness is preferably 0.2 mm, more preferably 0.3 mm, from the viewpoint of mechanical strength and gas barrier properties. On the other hand, the upper limit value of the thickness of the substrate is preferably 5 mm, more preferably 3 mm, from the viewpoint of lightness and light transmittance.
[0032]
In addition, when the porous silica film of the present invention is developed on a substrate, the properties of the substrate surface may influence the properties of the produced film. Therefore, in addition to cleaning the substrate surface, in some cases, it is necessary to control the adsorption site on the substrate surface, and surface treatment may be performed. As a chemical method for substrate cleaning, immersion in acids such as hydrofluoric acid, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, alkanes such as aqueous sodium hydroxide, hydrogen peroxide and concentrated sulfuric acid, hydrochloric acid, ammonia, etc. Examples of physical methods include heat treatment in vacuum, ion sputtering, UV ozone treatment, and the like. In the surface treatment, heating and immersion in strong acids such as concentrated sulfuric acid, hydrochloric acid and nitric acid can be mentioned. Further, for a substrate having poor adhesion to the porous silica film, there is a method of adding an adsorption layer with a surfactant, a polymer electrolyte or the like. In particular, when a silicon substrate or a transparent glass substrate is used in terms of adhesion and productivity of the porous silica film of the present invention, cleaning with acids such as sulfuric acid and nitric acid and surface treatment are more preferable.
[0033]
The porous silica membrane of the present invention is composed of silicon oxide (SiO₂) The composition is mainly used. The porous silica film has a SiOx composition (provided that a silicon atom-carbon atom bond exists in a part of the silica composition by, for example, copolymerizing organic silanes in silica synthesis by a sol-gel method). , X is a positive number greater than 0 and less than 2.
[0034]
The porous silica film of the present invention may contain any chemical composition containing a positive element (may be abbreviated as additional composition). For example, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, titanium oxide, zirconium oxide, chromium oxide, manganese oxide, Transition metal oxide compositions such as iron oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, cadmium oxide, gallium oxide, indium oxide, germanium oxide, tin oxide, lead oxide; lithium oxide, sodium oxide, potassium oxide, oxide Alkali metal oxide compositions such as rubidium and cesium oxide; alkaline earth metal compositions such as magnesium oxide, calcium oxide, strontium oxide and barium oxide; boron oxide composition; aluminum oxide composition; It can be. In addition, known inorganic glass compositions such as a chalcogenide glass composition and a fluoride glass composition, and metal nanoparticles such as gold, silver, and copper can also be exemplified.
[0035]
The silicon oxide composition constituting the porous silica film is contained in such a ratio that the ratio of silicon to all positive elements including silicon is 50 to 100 mol%. When the silicon content is less than 50 mol%, the surface roughness of the porous silica film is extremely deteriorated, and the mechanical strength may be lowered. A preferable lower limit is 70 mol%, more preferably 80 mol%, and most preferably 90 mol%. A higher silica content results in a porous silica film having better surface smoothness.
[0036]
The porous silica film and the laminate having the same in the present invention are characterized by the above-described pore characteristics and surface smoothness, and the production method thereof is not particularly limited, but the laminate of the present invention can be efficiently and produced. An example of a method excellent in properties will be described in detail below.
[0037]
(Method for producing porous silica film and laminate)
The porous silica film is formed by the following process. (B) a step of preparing a raw material liquid for forming a porous silica film, (b) a step of forming a primary film from the raw material liquid, and (c) an intermediate film is formed by increasing the molecular weight of the formed primary film. (D) a step of promoting local hydrolysis reaction and dehydration condensation reaction in the intermediate film to form a gradient structure of porosity, and (e) a step of drying the porous silica film. Hereinafter, each step will be described.
[0038]
(A) preparing a raw material liquid for forming a porous silica film;
The raw material liquid for forming the porous silica film is a hydrous organic solution containing a raw material compound that is mainly composed of alkoxysilanes and can be increased in molecular weight by hydrolysis reaction and dehydration condensation reaction.
[0039]
The water-containing organic solution that is the raw material liquid for forming the porous silica film of the present invention contains alkoxysilanes, an organic solvent, water, and a catalyst that is added as necessary.
[0040]
Examples of alkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra (n-propoxy) silane, tetraisopropoxysilane, tetra (n-butoxy) silane, and the like, trimethoxysilane, triethoxysilane, and methyl. Trialkoxysilanes such as trimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dialkoxysilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, bis (Trimethoxysilyl) methane, bis (triethoxysilyl) methane, 1,2-bis (trimethoxysilyl) ethane, 1,2-bis (triethoxysilyl) ethane, 1,4-bis (tri Toxylsilyl) benzene, 1,4-bis (triethoxysilyl) benzene, 1,3,5-tris (trimethoxysilyl) benzene and the like, in which two or more trialkoxysilyl groups are bonded, 3- Aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3v glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3 -The thing which the alkyl group substituted by silicon atoms, such as carboxypropyl trimethoxysilane, has a reactive functional group is mentioned, Furthermore, these partial hydrolysates and oligomers may be sufficient.
[0041]
Among these, tetramethoxysilane, tetraethoxysilane, trimethoxysilane, triethoxysilane, tetramethoxysilane, or tetraethoxysilane oligomer is particularly preferable. In particular, tetramethoxysilane oligomers are most preferably used because of their reactivity and controllability of gelation.
[0042]
Furthermore, monoalkoxysilanes having 2 to 3 hydrogen, alkyl groups, or aryl groups on silicon atoms can be mixed with the alkoxysilanes. By mixing monoalkoxysilanes, the resulting porous silica membrane can be hydrophobized to improve water resistance. Examples of monoalkoxysilanes include triethylmethoxysilane, triethylethoxysilane, tripropylmethoxysilane, triphenylmethoxysilane, triphenylethoxysilane, diphenylmethylmethoxysilane, diphenylmethylethoxysilane, and the like. The mixing amount of monoalkoxysilanes is desirably 70 mol% or less of the total alkoxysilanes. If the mixing amount exceeds 70 mol%, ideal gelation may not occur.
[0043]
Further, fluorinated alkyls such as (3,3,3-trifluoropropyl) trimethoxysilane, (3,3,3-trifluoropropyl) triethoxysilane, pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane When an alkoxysilane having a group or a fluorinated aryl group is used in combination, excellent water resistance, moisture resistance, stain resistance and the like may be obtained.
[0044]
The shape of the oligomer in the raw material liquid is not particularly limited, and examples thereof include linear, cross-linked, cage-type molecules (silsesquioxane, etc.) and the like. In view of reactivity control at the time of coating, those having linear as the main component are preferable.
In addition, when applying the above-described raw material liquid, it is necessary that a certain degree of high molecular weight (that is, a state in which condensation has progressed to some extent) has already been achieved. It is preferable that high molecular weight is achieved to such an extent that insoluble matter cannot be formed. The reason for this is that if there are visible insolubles in the raw material solution before coating, large surface irregularities are formed and the film quality is deteriorated.
[0045]
As the organic solvent, those having the ability to mix alkoxysilanes constituting the raw material liquid, water, and a hydrophilic organic compound having a high boiling point described later are preferably used. Usable organic solvents include alcohols such as monohydric alcohols having 1 to 4 carbon atoms, dihydric alcohols having 1 to 4 carbon atoms, polyhydric alcohols such as glycerin and pentaerythritol; diethylene glycol, ethylene glycol monomethyl ether, ethylene Glycol dimethyl ether, 2-ethoxyethanol, propylene glycol monomethyl ether, propylene glycol methyl ether acetate and the like, ethers or esterified products of the above alcohols; ketones such as acetone and methyl ethyl ketone; formamide, N-methylformamide, N-ethylformamide, N , N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, N, N-di Tylacetamide, N-methylpyrrolidone, N-formylmorpholine, N-acetylmorpholine, N-formylpiperidine, N-acetylpiperidine, N-formylpyrrolidine, N-acetylpyrrolidine, N, N′-diformylpiperazine, N, N Amides such as' -diformylpiperazine and N, N'-diacetylpiperazine; Lactones such as γ-butyrolactone; Ureas such as tetramethylurea and N, N'-dimethylimidazolidine; Dimethylsulfoxide and the like . These organic solvents may be used alone or as a mixture. In order to form the porosity gradient structure of the porous silica film of the present invention, it is necessary to use a local hydrolysis reaction and dehydration condensation reaction after coating. is there. Therefore, a highly volatile organic solvent is preferable, and methanol, ethanol, n-propanol, isopropyl alcohol, and acetone are more preferable, and methanol or ethanol is most preferable.
[0046]
In order to form the porous structure of the present invention, a high-boiling hydrophilic organic compound may be contained in addition to the organic solvent described above. A high-boiling hydrophilic organic compound is an organic compound having a hydrophilic functional group such as a hydroxyl group, a carbonyl group, an ether bond, an ester bond, a carbonate bond, a carboxyl group, an amide bond, a urethane bond, or a urea bond in the molecular structure. That is. The hydrophilic organic compound may have a plurality of these hydrophilic functional groups in the molecular structure. The boiling point here is a boiling point under a pressure of 760 mmHg. The boiling point is preferably 80 ° C. or higher, and when a hydrophilic organic compound having a boiling point of less than 80 ° C. is used, the porosity of the porous silica film may be extremely reduced. Preferable examples of the hydrophilic organic compound having a boiling point of 80 ° C. or higher include alcohols having 3 to 8 carbon atoms, polyhydric alcohols having 2 to 6 carbon atoms, and phenols. More preferred hydrophilic organic compounds include alcohols having 3 to 8 carbon atoms, diols having 2 to 8 carbon atoms, triols having 3 to 8 carbon atoms, and tetraols having 4 to 8 carbon atoms. More preferable hydrophilic organic compounds include alcohols having 4 to 7 carbon atoms such as n-butanol, isobutyl alcohol, t-butyl alcohol, n-pentanol, cyclopentanol, n-hexanol, cyclohexanol, benzyl alcohol, C2-C4 diols such as ethylene glycol, propylene glycol, 1,4-butanediol, C3-C6 triols such as glycerol and trishydroxymethylethane, C4 such as erythritol and pentaerythritol -5 tetraols. In this hydrophilic organic compound, if the number of carbon atoms is too large, the hydrophilicity may decrease too much, and the dispersibility of the alkoxysilanes before the hydrolysis reaction may be destabilized.
[0047]
A catalyst is mix | blended as needed. Examples of the catalyst include substances that promote the hydrolysis and dehydration condensation reactions of the alkoxysilanes described above. Specific examples include acids such as hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid, oxalic acid and maleic acid; amines such as ammonia, butylamine, dibutylamine and triethylamine; bases such as pyridine; Lewis such as acetylacetone complex of aluminum Acids; and the like.
[0048]
Examples of the metal species of the metal chelate compound used as the catalyst include titanium, aluminum, zirconium, tin, and antimony. Specific examples of the metal chelate compound include the following.
[0049]
Examples of aluminum complexes include di-ethoxy mono (acetylacetonato) aluminum, di-n-propoxy mono (acetylacetonato) aluminum, di-isopropoxy mono (acetylacetonato) aluminum, di-n-butoxy. Mono (acetylacetonato) aluminum, di-sec-butoxy mono (acetylacetonato) aluminum, di-tert-butoxy mono (acetylacetonato) aluminum, monoethoxy bis (acetylacetonato) aluminum, mono-n -Propoxy bis (acetylacetonato) aluminum, monoisopropoxy bis (acetylacetonato) aluminum, mono-n-butoxy bis (acetylacetonato) aluminum, mono-sec-butoxy bi (Acetylacetonato) aluminum, mono-tert-butoxy bis (acetylacetonato) aluminum, tris (acetylacetonato) aluminum, diethoxy mono (ethylacetoacetate) aluminum, di-n-propoxy mono (ethylacetoacetate) ) Aluminum, diisopropoxy mono (ethyl acetoacetate) aluminum, di-n-butoxy mono (ethyl acetoacetate) aluminum, di-sec-butoxy mono (ethyl acetoacetate) aluminum, di-tert-butoxy mono (Ethyl acetoacetate) aluminum, monoethoxy bis (ethyl acetoacetate) aluminum, mono-n-propoxy bis (ethyl acetoacetate) aluminum, monoisoprop Xy-bis (ethyl acetoacetate) aluminum, mono-n-butoxy bis (ethyl acetoacetate) aluminum, mono-sec-butoxy bis (ethyl acetoacetate) aluminum, mono-tert-butoxy bis (ethyl acetoacetate) Examples thereof include aluminum chelate compounds such as aluminum and tris (ethylacetoacetate) aluminum.
[0050]
Titanium complexes include triethoxy mono (acetylacetonato) titanium, tri-n-propoxy mono (acetylacetonato) titanium, triisopropoxy mono (acetylacetonato) titanium, tri-n-butoxy mono (acetyl). Acetonato) titanium, tri-sec-butoxy mono (acetylacetonato) titanium, tri-tert-butoxy mono (acetylacetonato) titanium, diethoxy bis (acetylacetonato) titanium, di-n-propoxy bis (Acetylacetonato) titanium, diisopropoxy bis (acetylacetonato) titanium, di-n-butoxy bis (acetylacetonato) titanium, di-sec-butoxy bis (acetylacetonato) titanium, di-tert -Butoxy bis (ace Ruacetonate) titanium, monoethoxy tris (acetylacetonato) titanium, mono-n-propoxy tris (acetylacetonato) titanium, monoisopropoxy tris (acetylacetonato) titanium, mono-n-butoxy tris (acetyl) Acetonato) titanium, mono-sec-butoxy tris (acetylacetonate) titanium, mono-tert-butoxy tris (acetylacetonato) titanium, tetrakis (acetylacetonato) titanium, triethoxy mono (ethylacetoacetate) titanium , Tri-n-propoxy mono (ethyl acetoacetate) titanium, triisopropoxy mono (ethyl acetoacetate) titanium, tri-n-butoxy mono (ethyl acetoacetate) titanium, tri-sec-butyl Xy-mono (ethyl acetoacetate) titanium, tri-tert-butoxy mono (ethyl acetoacetate) titanium, diethoxy bis (ethyl acetoacetate) titanium, di-n-propoxy bis (ethyl acetoacetate) titanium, diiso Propoxy bis (ethyl acetoacetate) titanium, di-n-butoxy bis (ethyl acetoacetate) titanium, di-sec-butoxy bis (ethyl acetoacetate) titanium, di-tert-butoxy bis (ethyl acetoacetate) Titanium, monoethoxy tris (ethyl acetoacetate) titanium, mono-n-propoxy tris (ethyl acetoacetate) titanium, monoisopropoxy tris (ethyl acetoacetate) titanium, mono-n-butoxy tris (ethyl acetoacetate) Acetate) titanium, mono-sec-butoxy tris (ethyl acetoacetate) titanium, mono-tert-butoxy tris (ethyl acetoacetate) titanium, tetrakis (ethyl acetoacetate) titanium, mono (acetylacetonate) tris (ethyl aceto) Acetate) titanium, bis (acetylacetonato) bis (ethylacetoacetate) titanium, tris (acetylacetonato) mono (ethylacetoacetate) titanium and the like.
[0051]
In addition to these catalysts, weak alkaline compounds such as basic catalysts such as ammonia may be used. In this case, it is preferable to appropriately adjust the silica concentration, the organic solvent species, and the like. Moreover, when preparing a water-containing organic solution, it is preferable not to increase the catalyst concentration in a solution rapidly. Specific examples include a method of mixing alkoxysilanes and a part of an organic solvent, then mixing water, and finally mixing the remaining organic solvent and base.
[0052]
In order to proceed more optimally with the subsequent local hydrolysis and dehydration condensation reactions, the three-dimensional network structure of silica needs to be formed homogeneously. Therefore, it is preferable to adjust the addition amount of the catalyst so that the pH of the raw material liquid is 8 or less. More preferably, the pH is 3 to 7, and most preferably, the pH is adjusted to 4 to 6.
[0053]
The raw material liquid for forming the porous silica film of the present invention is formed by blending the above-mentioned raw materials. The blending ratio of the alkoxysilanes is preferably 10 to 60% by weight and more preferably 20 to 40% by weight with respect to the whole raw material liquid. When the blending ratio of alkoxysilanes exceeds 60% by weight, it is difficult to maintain the stability of the raw material liquid, and the porous silica film may be broken during film formation. On the other hand, when the compounding ratio of alkoxysilanes is less than 10% by weight, the hydrolysis reaction and the dehydration condensation reaction are extremely slow, and the film formability may be deteriorated (film unevenness).
[0054]
Water is necessary for hydrolysis of alkoxysilanes, and is important from the viewpoint of improving the film forming property of the target porous silica film. Therefore, when the preferable amount of water is defined by the molar ratio with respect to the amount of alkoxy groups, the amount is 0.1 to 1.6 mol times, especially 0.3 to 1.2 mol times with respect to 1 mol of alkoxy groups in alkoxysilane. The amount, particularly 0.5 to 0.7 mole times the amount is preferable.
[0055]
Water may be added at any time after the alkoxysilanes are dissolved in an organic solvent, but it is desirable to add water after sufficiently dispersing the alkoxysilanes, catalyst and other additives in the solvent. Most preferred. Although a hydrolysis reaction is caused by adding water, it can be added as an aqueous alcohol solution or as water vapor without being particularly limited. In addition, if water is added rapidly, depending on the type of alkoxysilane, the hydrolysis reaction and the dehydration condensation reaction occur too quickly, and precipitation may occur. Therefore, in order to prevent such precipitation, take sufficient time to add water, make the alcohol solvent coexist in a state where water is added uniformly, and add water at a low temperature. It is preferable to use means such as inhibiting the reaction alone or in combination.
[0056]
The purity of the water to be used may be one that has undergone either or both of ion exchange and distillation. When the porous silica film of the present invention is used in an application field that particularly dislikes minute impurities such as semiconductor materials and optical materials, a porous silica film with a higher purity is required, and thus distilled water is further ion-exchanged. It is desirable to use ultrapure water. In this case, for example, water passed through a filter having a pore size of 0.01 to 0.5 μm may be used.
[0057]
When a hydrophilic organic compound having a boiling point of 80 ° C. or higher is used in the water-containing organic solution, the content of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is equal to the total content of the organic solvent and the hydrophilic organic compound having a boiling point of 80 ° C. or higher. On the other hand, it is important that the amount is not more than a specific amount. The content of the hydrophilic organic compound having a boiling point of 80 ° C. or higher with respect to the total content is 90% by weight or less, preferably 85% by weight or less.
[0058]
If the blending ratio of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is too small, the porosity of the porous silica film becomes extremely small, and the film structure is fixed immediately after coating, thereby forming a gradient structure of porosity. May be difficult to do. On the other hand, even if the blending ratio of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is too large, the film immediately after coating does not have a stable structure, which may affect the surface properties and the gradient structure control. Generally, the blending ratio of the hydrophilic organic compound having a boiling point of 80 ° C. or higher is 10% by weight or more, particularly 30% by weight or more, particularly 55% by weight or more of the total content of the organic solvent and the hydrophilic organic compound having a boiling point of 80 ° C. or higher. It is preferable that
[0059]
The atmospheric temperature in the preparation of the raw material liquid and the mixing order are arbitrary, but in order to obtain a uniform structure formation in the raw material liquid, water is preferably mixed last. Further, in order to suppress extreme hydrolysis and dehydration condensation reaction of alkoxysilanes in the raw material liquid, the raw material liquid is usually adjusted at 0 to 60 ° C., particularly 15 to 40 ° C., particularly 15 to 30 ° C. It is preferable to carry out under wet conditions.
At the time of liquid preparation, the stirring operation of the raw material liquid is arbitrary, but it is more preferable to stir with a stirrer for each mixing.
[0060]
Furthermore, after the raw material solution is adjusted, the alkoxysilanes are preferably hydrolyzed and the dehydration condensation reaction proceeds, so that the solution is preferably aged. During this ripening period, it is preferable that the hydrolyzed condensate of the alkoxysilanes to be produced is in a state of being more uniformly dispersed in the raw material liquid, so that the liquid is preferably stirred.
[0061]
The temperature during the aging period is arbitrary, and in general, it may be heated at room temperature or continuously or intermittently. Among these, heat aging is preferable in order to form a uniform three-dimensional network structure by the hydrolysis condensate of alkoxysilanes. The specific temperature is not particularly limited as long as it is equal to or lower than the boiling point of the organic solvent to be used, and heat aging can be performed at a temperature equal to or higher than the boiling point of the organic solvent used under pressure. The heat aging time is appropriately adjusted depending on the temperature to be applied, but is preferably 15 hours or less, and more preferably 5 hours or less.
[0062]
(B) forming a primary film from the raw material liquid;
The primary film is formed by applying the raw material liquid prepared above onto a substrate. Examples of the substrate include semiconductors such as silicon and germanium, compound semiconductors such as gallium-arsenic and indium-antimony, substrates such as ceramics and metals, and transparent substrates such as glass substrates and synthetic resin substrates. In some cases, the substrate needs to be surface treated.
[0063]
Examples of means for applying the raw material liquid include a casting method in which the raw material liquid is extended onto the substrate using a bar coater, an applicator or a doctor blade, a dip method in which the substrate is immersed in the raw material liquid, and a spin coating method. Well known. Of these means, the casting method and the spin coating method are preferably employed because the raw material liquid can be uniformly applied. The spin coating method is particularly preferable for forming a homogeneous film.
[0064]
When the raw material liquid is applied by the casting method, the casting speed is 0.1 to 1000 m / min, preferably 0.5 to 700 m / min, and more preferably 1 to 500 m / min. The rotation speed in the place where the raw material liquid is applied and formed by the spin coating method is 10 to 100,000 rotations / minute, preferably 50 to 50,000 rotations / minute, and more preferably 100 to 10,000 rotations / minute.
[0065]
In the dip coating method, the substrate may be dipped in the raw material solution and pulled up at an arbitrary speed. The pulling speed at this time is preferably 0.01 to 50 mm / sec, more preferably 0.05 to 30 mm / sec, and particularly preferably 0.1 to 20 mm / sec. Although there is no restriction | limiting in the speed | rate which immerses a board | substrate in a raw material liquid, It may be preferable to immerse a board | substrate in a raw material liquid at a speed | rate comparable as a raising speed | rate. The substrate may be immersed for a suitable time until the substrate is immersed in the raw material solution and pulled up, and this duration is usually 1 second to 48 hours, preferably 3 seconds to 24 hours, more preferably 5 seconds to 12 hours. It's time.
[0066]
The atmosphere during coating may be air or an inert gas such as nitrogen or argon, and the temperature is usually 0 to 60 ° C., preferably 10 to 50 ° C., more preferably 20 to 40 ° C. The humidity is usually 5 to 90%, preferably 10 to 80%, more preferably 15 to 70%. The film forming temperature is 0 to 100 ° C., preferably 10 to 80 ° C., more preferably 20 to 70 ° C. There is a difference in the drying speed between the dip coating method and the spin coating method, and a slight difference may occur in the stable structure of the film immediately after coating. This can be adjusted by changing the atmosphere during application. In addition, it can be dealt with by surface treatment of the substrate.
[0067]
(C) a step in which the formed primary film is polymerized to form an intermediate film;
When the raw material liquid is applied onto the substrate, the molecular weight is increased by a sol-gel reaction, and an intermediate film is formed. The intermediate film obtained by this process has a stable structure in which an organic solvent is incorporated in a three-dimensional network structure.
[0068]
As the hydrolytic condensation reaction of alkoxysilanes by the sol-gel reaction proceeds, the condensation product of alkoxysilanes gradually increases in molecular weight. In the hydrolysis-condensation reaction, phase separation that may be caused by a change in phase equilibrium may occur. In the present invention, the composition of the raw material liquid, the alkoxysilanes used, and the hydrophilic organic compound having a boiling point of 80 ° C. or higher The phase separation is controlled to occur on the nanometer scale in consideration of the hydrophilicity of the liquid crystal. As a result, the separated phase of the hydrophilic organic compound is formed on the substrate while being retained in the three-dimensional network structure of the alkoxysilane condensate, and constitutes an intermediate film.
[0069]
In forming the intermediate film, for example, by pre-drying the coating film applied on the substrate, the solvent concentration in the outermost surface region of the film can be reduced and a partial condensation reaction of silica can be performed. Thereby, the smoothness of the film surface can be obtained.
[0070]
The pre-drying temperature of the intermediate film is usually 0 to 60 ° C., preferably 10 to 50 ° C., more preferably 20 to 40 ° C., and the relative humidity of the atmosphere is usually 5 to 95%, preferably 10 to 90%, More preferably, it is 15 to 80%, and most preferably 25 to 60%. The predrying time is usually 30 seconds to 60 minutes, preferably 1 to 30 minutes.
[0071]
(D) a step of promoting a local hydrolysis reaction and dehydration condensation reaction in the intermediate film to form a gradient gradient structure;
By promoting a local hydrolysis reaction and dehydration condensation reaction in the intermediate film, a gradient structure of porosity, that is, a continuous change in porosity is given. For example, a water-soluble organic solvent is brought into contact with the intermediate film, and a local hydrolysis reaction and dehydration condensation reaction can be advanced. By bringing a water-soluble organic solvent into contact with the intermediate film, the hydrophilic organic compound in the intermediate film is extracted and removed, and water in the intermediate film is removed. Since the water present in the intermediate film is not only dissolved in the organic solvent but also adsorbed on the inner wall of the film constituent material, it is necessary to effectively remove the water in the intermediate film. The degree of freedom of the three-dimensional structure of the atmospheric silica in contact with the water-soluble organic solvent is relatively high. Therefore, by allowing to stand at a temperature of 15 ° C. or higher for a certain period of time in this atmosphere, the local hydrolysis reaction and dehydration condensation reaction can be advanced with water contained in the organic solvent. Furthermore, the surface tension of the water-soluble organic solvent to be contacted is controlled by the amount of water, the degree of freedom of the three-dimensional structure of silica and the solvent penetration into the membrane can be controlled, and a gradient structure with the desired porosity can be obtained. Can do. Therefore, it is necessary to adjust the content of water in the organic solvent as appropriate. However, an excessive amount of water may cause water to remain in the film after the process, and in some cases, voids may disappear or become smaller in the subsequent heating or drying process of the film.
It is also possible to add a catalyst as described above to this water-soluble organic solvent.
[0072]
Examples of the means for contacting the hydrophilic organic compound in the intermediate film include immersing the intermediate film in a water-soluble organic solvent, washing the surface of the intermediate film with a water-soluble organic solvent, and the surface of the intermediate film. Examples thereof include spraying a water-soluble organic solvent on the surface, and spraying a vapor of the water-soluble organic solvent on the surface of the intermediate film. Of these, dipping means and cleaning means are preferred. Although the contact time between the intermediate film and the water-soluble organic solvent can be set in the range of 1 second to 24 hours, the upper limit of the contact time is preferably 12 hours and more preferably 6 hours from the viewpoint of productivity. On the other hand, the lower limit of the contact time is preferably 1 minute or longer because it is necessary to sufficiently advance the above reaction.
[0073]
As the contact treatment liquid, polar solvents are preferable, and among them, monohydric alcohols, polyhydric alcohols, ketones, ethers, esters, amides, or two or more hydrophilic solvents are preferable. When combining two or more kinds of hydrophilic solvents, they may be used in combination or may be combined by treating each solvent alone. Furthermore, the same kind of contact treatment liquid can be repeatedly acted on. Further, even when the surface tension of the target contact treatment liquid is different from the amount of water necessary for the reaction, it may be divided into two or more times.
[0074]
In addition, the following process can also be performed independently before the said process, after the said process, or simultaneously with the said process. In this step, the intermediate film is brought into contact with acids or bases under a constant humidity. Thereby, the hydrolysis reaction and dehydration condensation reaction of alkoxysilanes in the surface layer of the intermediate film can be promoted. As a result, not only the sloped structure of the porosity is formed, but also the surface region of the intermediate film can be increased in hardness. Preferable acids to be contacted include acids that are easily vaporized such as hydrogen chloride, formic acid, acetic acid, and trifluoroacetic acid. Preferred bases include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, isopropylamine, n-butylamine, cyclopentylamine, cyclohexylamine, and the like. 6 or less monoamines may be mentioned.
[0075]
As a method for bringing the intermediate film into contact with acids or bases, liquids or solutions or vapors of acids or bases are used. The humidity to be applied is preferably 10 to 80%, more preferably 18 to 70%. In addition, an inclined structure with a porosity can be formed by applying temperature to the intermediate film under the humidity. The heating may be performed not only from the surface of the intermediate film but also from the substrate surface. The temperature is preferably 20 ° C. or higher, and more preferably 35% or higher. The upper limit is 150 ° C. or lower, and if it is higher than that, the surface properties of the film may be impaired.
[0076]
(E) a step of drying the porous silica membrane;
The drying step is performed for the purpose of removing volatile components remaining in the porous silica membrane and / or for the purpose of maximizing the hydrolysis condensation reaction of alkoxysilanes. The drying temperature is 20 to 500 ° C., preferably 30 to 400 ° C., more preferably 50 to 350 ° C., and the drying time is 1 minute to 50 hours, preferably 3 minutes to 30 hours, more preferably 5 minutes to 15 hours.
[0077]
The drying method can be performed by a known method such as blow drying or drying under reduced pressure, and may be combined. After the blast drying, vacuum drying for the purpose of sufficiently removing volatile components can be added.
[0078]
In the post-drying, drying may be performed under any of pressure, reduced pressure, and normal pressure. The drying temperature is preferably less than the temperature at which the silica skeleton having the gradient structure of porosity formed in the above step is denatured, and is generally 0 to 100 ° C., more preferably 10 to 70 ° C., particularly 15 to 50. The drying time is usually 30 seconds to 60 minutes, preferably 1 minute to 30 minutes.
[0079]
The purpose of high-temperature drying is to remove unnecessary solvents and additives in the porous silica membrane and to cure the membrane. For example, an oven furnace, a vacuum dryer, a hot plate, or the like can be used for the heat drying. The drying time is usually 10 seconds to 48 hours, preferably 30 seconds to 24 hours, more preferably 1 minute to 12 hours, and the drying temperature is usually 100 to 370 ° C, preferably 130 to 350 ° C, more preferably. 150-320 ° C. High temperature drying may be performed under any of pressure, reduced pressure, and normal pressure.
[0080]
By treating the obtained porous silica film with a silylating agent, it is possible to make the surface more functional. By treating with a silylating agent, hydrophobicity is imparted to the porous silica film, and the pores can be prevented from being contaminated by impurities such as alkaline water. Examples of the silylating agent include trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethylethoxysilane, methyldiethoxysilane, dimethylvinylmethoxysilane, and dimethyl. Alkoxysilanes such as vinylethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, methyldichlorosilane, dimethylchlorosolane, dimethylvinylchlorosilane , Methyl vinyl dichlorosilane, methyl chloro disilane, triphenyl chloro silane, methyl diphenyl chloro Chlorosilanes such as silane, diphenyldichlorosilane, hexamethyldisilazane, N, N′-bis (trimethylsilyl) urea, N-trimethylsilylacetamide, dimethyltrimethylsilylamine, diethyltriethylsilylamine, trimethylsilylimidazole and other silazanes, (3, 3,3-trifluoropropyl) trimethoxysilane, (3,3,3-trifluoropropyl) triethoxysilane, pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane, etc. And alkoxysilanes having a group. Silylation is performed by applying a silylating agent to the porous silica film, immersing the porous silica film in the silylating agent, or exposing the porous silica film to the vapor of the silylating agent. Can do.
[0081]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
Example 1
Aluminum acetylacetonate was dissolved in a mixed solvent of methanol and n-butanol, and an oligomer of methoxysilane (MKC silicate MS51 manufactured by Mitsubishi Chemical Corporation) was added to a uniform solution of 30% by weight of the whole and stirred. . The mixing ratio of methanol and n-butanol here is 3: 7 by weight. Water exceeding the stoichiometric amount of hydrolysis and dehydration condensation reaction for the added methoxysilane oligomer was mixed with stirring to prepare a raw material solution. Prior to the coating step, the raw material liquid was stirred for a certain time at a temperature not higher than the boiling point of the organic solvent. Note that the pH of the prepared raw material liquid is applied to the substrate in the vicinity of neutrality.
[0082]
The above raw material liquid is spin-coated on a crown glass substrate at a speed of 3000 rpm for 30 seconds to form a primary film, and pre-dried under conditions of a humidity of 20 to 45% and a temperature of 25 to 30 ° C. Thus, an intermediate film was obtained.
The obtained intermediate film was immersed in ethanol (500 mL) containing less than 1% of water to remove the water in the film, and further allowed to stand in hydrous ethanol for 5 minutes. The humidity at this time is maintained in the range of 20 to 45%. As a result, an inclined structure having a porosity is formed. The taken-out membrane was dried in a drier kept at 150 ° C., and the reaction was terminated to obtain a porous silica membrane.
[0083]
When the cross section of the porous silica film thus obtained was observed with an SEM, the porosity was continuously changed. The porosity was 10% at the film surface to a depth of 50 nm, and the porosity was 24% at a depth of 50 nm to 100 nm. The porosity is 40% at a depth of 100 nm to 150 nm, 52% at a depth of 150 nm to 200 nm, 60% at a depth of 200 nm to 250 nm, 62% at a depth of 250 nm to 300 nm, and 62% at a depth of 300 nm to 350 nm. The porosity is 52%, the porosity is 48% when the depth is 350 nm to 400 nm, the porosity is 40% when the depth is 400 nm to 450 nm, the porosity is 28% when the depth is 450 nm to 500 nm, and the porosity is 36% when the depth is 500 nm to 500 nm. It can be seen that the gradient structure of the porosity is convex. Furthermore, it can also be confirmed from this measurement that the holes are communication holes. Moreover, as a result of evaluating the surface of the porous silica film with an atomic force microscope, the ten-point surface roughness Rz = 10 nm, and the result of measuring the stylus type step, surface roughness, and fine shape shows the average surface roughness. Ra = 0.7 nm and extremely smooth surface properties. Furthermore, it was found from the nitrogen adsorption method and the spectroscopic ellipsometer that the average pore diameter was 2.5 nm, the average porosity was 42%, and the film thickness was 573 nm, respectively.
[0084]
Since the porous silica film has a gradient structure of porosity, the refractive index of the material is also continuously changed. Such a material is useful as an optical material, and can be used specifically as a low reflection glass laminate for a solar cell. Some conventional antireflection materials for solar cells reduce the reflectance of sunlight by about 5% at the maximum, but they have a large wavelength dependency of the reflectance, and are not sufficient as solar cell efficiency. However, by using the porous silica film of the present invention, unprecedented antireflection performance can be obtained.
[0085]
For example, by scraping the surface of the porous silica film of the above example to a depth of 230 nm by sputtering or etching, the porosity is about 60% to 30% with respect to the film thickness direction which is impossible with the conventional multilayer structure. A porous silica film A that continuously changes and does not have the respective optical interfaces can be obtained. On the other hand, a silicon alkoxide obtained by adding a titanium alkoxide or a partial condensate thereof as described in Examples in JP-A-9-175840 to a glass substrate surface not having the porous silica film is used as an organic solvent. A titanium oxide / silicon film (thin film (1)) is formed from the raw material solution dissolved in the film, and tin oxide as described in the examples of JP 2001-36117 A is further formed on the thin film (1). A film (thin film (2)) is formed. Next, a conductive film is formed on the thin film (2) to obtain the solar cell low-reflection laminate shown in FIG.
[0086]
The reflectance was simulated with respect to visible light incident in the vertical direction of the solar cell low-reflection laminate. As a result, it can be seen that the reflectance is reduced by about 5% almost the same in the entire wavelength range of 350 to 850 nm as compared with the conventional glass substrate for solar cells, and the porous silica film of the present invention has a wavelength dependence of the reflectance. It can be said that it is an extremely excellent antireflection material with little property.
[0087]
There is a silicon-based material as a photoelectric conversion element of a solar cell that is currently most utilized. The wavelength dependence of the photoelectric conversion efficiency and the wavelength distribution of sunlight actually used are in a mutually contradictory relationship. Therefore, it is important to reduce the reflectance in the entire wavelength region of sunlight, and the fact that the wavelength dependency of the reflectance is small as described above can drastically improve the efficiency of the solar cell. That is, when the solar cell low-reflection laminate is used, the efficiency is improved by about 30%. Therefore, it can be estimated that an efficiency of nearly 20% can be obtained from the antireflection effect of the present invention with respect to the efficiency of about 15% of the conventional type. This epoch-making figure also contributes to the reduction of power generation cost, which is the biggest problem of solar cells.
[0088]
【The invention's effect】
The porous silica film of the present invention is characterized by a porous silica film whose porosity is continuously changed in the film thickness direction and having extremely excellent surface smoothness, and a laminate having the porous silica film. The porous silica film has the effects of 1) transparency and 2) antireflection properties, so that it can be applied to semiconductor materials and optical materials. Furthermore, according to the present invention, the wavelength dependence of Fresnel reflection and reflectance is reduced, which contributes to maximization of antireflection properties, and is an extremely excellent material particularly for optical materials. One example is the low-reflection laminate for solar cells. In addition, due to the extremely smooth surface properties of porous silica membranes, which were difficult for conventional porous silica membrane materials, 3) easy laminating process, 4) antifouling, 5) chemical resistance, 6) high machine The effect of strength can also be obtained, indicating that the porous silica film of the present invention is a very optimal material for the above-mentioned use.
[0089]
【The invention's effect】
The porous silica membrane of the present invention can be easily chemically modified on the surface and pore wall surface, and can be expected to expand the range of applications to separation adsorbents, catalyst materials, sensor materials, fuel cell electrolyte membranes, and the like. For example, since the pore wall surface of the porous silica film of the present invention has a large number of hydroxyl groups, the amount of water adsorbed is large, and there is an application development as a water adsorbent. In particular, since the porous silica film of the present invention has a sloped structure of porosity, it has specific adsorption characteristics and is expected to exhibit excellent performance in the above-mentioned applications.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a partially enlarged example of a low reflection laminated body for a solar cell using a porous silica film of the present invention.
[Explanation of symbols]
1 Porous silica membrane A
2 Glass substrate or transparent resin substrate
3 Thin film (1)
4 Thin film (2)
5 Conductive film

Claims (7)

The average porosity is 35% or more , the average pore diameter is 0.5 to 100 nm, the film thickness is 50 to 850 nm, the porosity within 100 nm from the surface is 24% or less, and the ten-point surface roughness Rz is A porous silica film having a thickness of 50 nm or less.   The porous silica film according to claim 1, which has a smooth surface having an average surface roughness Ra of 50 nm or less.   The porous silica film according to claim 1, wherein the pores are communication holes. An antireflection material comprising the porous silica film according to any one of claims 1 to 3 . A laminate having the porous silica film according to any one of claims 1 to 3 on a substrate. The laminate according to claim 5 , wherein the substrate is transparent. The laminate according to claim 5 , wherein the substrate is a semiconductor substrate.

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