JP6751578B2 - A coating liquid for forming a film and a base material with a coating using the coating liquid. - Google Patents

Description

The present invention relates to a coating liquid for forming a film capable of suppressing shrinkage during film formation, and a coated substrate using such a coating liquid.

In recent years, in the manufacturing industry of semiconductor devices, liquid crystal devices, sensor devices, display devices, etc., on semiconductor substrates, wiring layers of multi-layer wiring structures, element surfaces and / or on substrates provided with PN junctions, liquid crystal substrates, etc. In addition, a silica-based film is often formed as an insulating film. A CVD method or a coating method is used to form a silica-based film, but since it takes time to form a thick film in the CVD method, a film formation process by coating that can be formed in a short time is required.

As a liquid composition for forming such a silica-based coating film, for example, a coating film containing a reaction product of a silica sol obtained by hydrolyzing and polycondensing a specific alkoxysilane and a partial hydrolyzate of alkoxysilane. A coating liquid for forming has been proposed (see Patent Document 1). This coating liquid is obtained by first preparing a silica sol and then reacting the silica sol with a new alkoxysilane or a partial hydrolyzate thereof. Therefore, a bonding reaction between the silica particles and a new alkoxysilane occurs on the surface of the silica particles, and as a result, pinholes or voids are not generated, and the silica particles are dense, have good adhesion, and have mechanical strength. A coating liquid that is excellent in chemical resistance, moisture resistance, insulating property, etc. and forms a silica-based film having a low relative permittivity can be obtained.

Further, a coating liquid for forming a low dielectric constant silica-based coating film containing silica fine particles and a reaction product of a specific alkoxysilane and / or a specific halogenated silane or a hydrolyzate thereof has been proposed (Patent Documents). 2). In order to obtain this coating liquid, silica fine particles are reacted with at least a part of a specific alkoxysilane or a specific halogenated silane hydrolyzate. Therefore, the reaction between the silica fine particles and the alkoxysilane or the halogenated silane occurs on the surface of the silica fine particles. As a result, an insulating film having a small relative permittivity, excellent adhesion to the surface to be coated, mechanical strength, alkali resistance and other chemical resistance, and at the same time excellent crack resistance can be formed, and the surface to be coated can be formed. A coating liquid capable of highly flattening irregularities can be obtained.

Japanese Unexamined Patent Publication No. 3-263476 Japanese Unexamined Patent Publication No. 9-315812

The coating liquids described in Patent Documents 1 and 2 are those in which the polycondensation of alkoxysilane is further promoted and the inside of the silica fine particles is densified by performing heat treatment in the state of a dispersion liquid after preparing the silica fine particles. is there. However, at the boiling point of the dispersion liquid or the temperature of the treatment in an autoclave, the cross-linking reaction is not sufficient and uncross-linked silanol groups remain. Therefore, shrinkage occurs due to heat treatment during film formation, and the thickness is 2 μm or more. When trying to form the film, there was a problem that cracks were generated and a thick film could not be formed. Further, not only the silica fine particles but also the hydrolyzate portion of alkoxysilane which is a binder contained in the coating liquid also contains SiOR groups and SiOH groups, which causes film shrinkage and causes cracks. It was.
Further, when the heat treatment temperature at the time of film formation using the coating liquids described in Patent Documents 1 and 2 becomes high, shrinkage due to decomposition of SiR groups also occurs, so that cracks are more likely to occur when a high temperature process is used. There was also the problem.
As described above, it has been difficult to obtain a silica-based coating having excellent heat resistance and crack-free of 2 μm or more with the conventional coating liquid.

Therefore, an object of the present invention is to provide a coating liquid which can suppress shrinkage during film formation and is suitable for forming a thick film, and a substrate with a film using such a coating liquid.

As a method for forming a silica-based film on a semiconductor substrate or the like, the present inventors have focused on a coating method capable of forming a film in a short time and at a low cost as compared with a CVD method. As a result, it was found that by forming a film with a coating liquid using silica particles satisfying a specific requirement, it is possible to form a film in which cracks are unlikely to occur even when a thick film is formed. Furthermore, we have found that the coatings and coatings can withstand high temperature processes above 450 ° C.

That is, the coating liquid of the present invention contains silica particles and a dispersion medium that satisfy the following requirements (a) to (e).
(A) Average particle size is 10 to 500 nm
(B) Particle size coefficient of variation is 20% or less (c) SiO ₂ purity is 99.5% or more (d) Sphericality is 0.90 or more (e) Weight loss at 1000 ° C. based on 400 ° C. is 0 .5% or less

Further, in the coated base material of the present invention, a coating film mainly composed of silica particles satisfying the above requirements (a) to (e) is formed on the base material.
Further, the silica particles for film formation of the present invention are particles that satisfy the above requirements (a) to (e).

According to the coating liquid of the present invention, since the silica particles do not shrink during film formation, the obtained filmed substrate is less likely to crack and can form a thick film.

It is a schematic diagram explaining crushing. It is a schematic diagram explaining pulverization. It is a model diagram which shows one aspect of the crushing apparatus used in this invention.

[Coating liquid for forming a film]
The coating liquid of the present invention contains silica particles and a dispersion medium that satisfy the following requirements (a) to (e).

(A) Average particle size is 10 to 500 nm
(B) Particle size coefficient of variation (CV value) is 20% or less (c) SiO ₂ purity is 99.5% or more (d) Sphericality is 0.90 or more (e) At 1000 ° C. based on 400 ° C. Weight loss is 0.5% or less

(Silica particles)
The silica particles satisfying the above requirements (a) to (e) (hereinafter, may be referred to as high-density silica particles) are densified inside the particles. Therefore, when forming a film using a coating liquid containing high-density silica particles, shrinkage of the high-density silica particles is suppressed even if a high-temperature treatment such as a film-forming heat treatment (film drying step, film firing step) is performed. The occurrence of cracks can be suppressed, and the formed film becomes a low-stress film. Further, since the high-density silica particles have a uniform particle size, high packing at the time of particle arrangement is possible and a uniform film can be formed, which also suppresses the occurrence of cracks. ..

(A) Average particle size is 10 to 500 nm
The high-density silica particles have an average particle diameter of 10 to 500 nm. When the average particle size of the high-density silica particles is less than 10 nm, it becomes difficult to crush them to the primary particle size by coalescence and fusion in the crushing step after firing. Even if it can be crushed, the dispersibility may be insufficient. On the other hand, if it exceeds 500 nm, the adhesion to the underlying film deteriorates when the film is formed. From the viewpoint of crushing to the primary particle size and adhesion to the underlying film when formed into a film, the average particle size of the high-density silica is preferably 10 to 300 nm, more preferably 15 to 150 nm. preferable. The average particle size of the high-density silica particles was photographed with a scanning electron microscope (Hitachi High-Technologies Corporation: S-5500 type), and 250 particles in this image were photographed by an image analyzer (Asahi Kasei Co., Ltd.). Manufacture: It is a value calculated using IP-1000).

(B) Particle size coefficient of variation (CV value) is 20% or less High-density silica particles have a particle size coefficient of variation (CV value) of 20% or less, preferably 15% or less, preferably 10% or less. Is more preferable. If the coefficient of variation (CV value) of the high-density silica particles exceeds 20%, a uniform particle film cannot be obtained.

The coefficient of variation of particle size (CV value) can be calculated by the following formula. The individual particle size and the average particle size when calculating the coefficient of variation (CV value) of the particle size were calculated by the same method as described in the above section "(a) Average particle size is 10 to 500 nm". It is a thing.

(C) SiO ₂ purity of 99.5% or more The high-density silica particles have a SiO ₂ purity of 99.5% or more, preferably 99.7% or more, and preferably 99.9% or more. More preferred. When the purity of SiO ₂ of the high-density silica particles is less than 99.5%, since a large amount of impure content is contained, the fusion of the silica particles is promoted and the silica particles are redispersed (crushed) into the primary particles. It becomes a difficult secondary particle, and it becomes difficult to satisfy the requirement (b) regarding the particle size variation coefficient. Even if the requirement (b) is satisfied, when the film is formed from the coating liquid, the particles are fused to each other, the film shrinks, and cracks are likely to occur. Further, depending on the impure content contained, the insulating property becomes low when used as an insulating film. In order to obtain high-purity silica particles, it is preferable to use alkoxide as a raw material as a silica source, which makes it possible to apply it to the field of electronic devices such as semiconductors.

(D) The sphericity of the high-density silica particles is 0.90 or more, preferably 0.93 or more, and more preferably 0.95 or more. When the sphericity of the high-density silica particles is less than 0.90, a uniform particle film cannot be obtained. Incidentally, sphericity of such dense silica, and photographed by a scanning electron microscope, for any 50 particles, the minor axis orthogonal its maximum diameter respectively (D _L) and which (D _S) means the average value of the ratio of _(D S / D _L).

(E) Weight loss at 1000 ° C. based on 400 ° C. is 0.5% or less. High-density silica particles have a weight loss of 0.5% or less at 1000 ° C. based on 400 ° C., which is 0.3%. It is preferably less than or equal to, more preferably 0.2% or less. That is, it is preferable that there are few uncrosslinked silanol groups inside the particles. Therefore, the high-density silica particles are preferably calcined particles fired at 600 to 1200 ° C., preferably 800 to 1000 ° C. If the weight loss exceeds 0.5%, there is a problem that the film shrinkage becomes large when the film is fired, and cracks are likely to occur. In the present invention, the weight loss at 1000 ° C. based on 400 ° C. is defined based on 400 ° C., which is considered to remove all adsorbed water, and the substantially uncrosslinked silanol group amount is used as an index. This is because.

The particles that have been substantially converted to SiO ₂ are preferable not only in that they are difficult to shrink, but also in terms of high packing during particle arrangement during coating and film formation. Those treated at a relatively high temperature have fewer hydroxyl groups (-OH groups) on the surface that can be reactive groups, and interact with adjacent particles even during high concentration due to volatilization of the dispersion medium. This is because it tends to be arranged without any.

Further, for example, in order to effectively prevent the occurrence of cracks when the film is exposed to a high temperature process of 800 ° C. during firing, the high-density silica particles are heat-treated (baked) in advance above that temperature. It is preferable to have. That is, for example, the coating liquid containing the calcined particles fired at 800 ° C. is designated as a process-compatible coating liquid having an upper limit of 800 ° C. (including those labeled as 700 ° C. or lower or 800 ° C. or lower process-compatible coating liquid). A coating liquid having a temperature equal to or lower than the firing temperature as the corresponding process temperature can be used.

(F) Coarse particle amount is 5% by weight or less (other preferable requirements)
In the high-density silica particles, the proportion of coarse particles having a particle size of 4 times or more the average particle size is preferably 5% by weight or less, more preferably 3% by weight or less, and 1% by weight or less. It is more preferable, and it is particularly preferable that it is substantially not contained. By not containing coarse particles, a more uniform film can be obtained. When coarse particles are generated in the process of producing high-density silica, it is preferable to remove them by appropriately classifying them.

The coating liquid of the present invention may contain two or three or more particles that satisfy the above requirements (a) to (e). In particular, a mixture of two types is preferable. That is, the first silica particles having the first average particle size (first high-density silica particles) and the second silica particles having the second average particle size (second high-density silica particles) are mixed. Can be used. At this time, the first silica particles are particles (large diameter particles) having an average particle diameter of 50 to 500 nm, preferably 50 to 300 nm, and more preferably 50 to 150 nm, and the second silica particles are the first silica particles. It is desirable that the particles have an average particle diameter of 15 to 30%, preferably 20 to 25% (small diameter particles). By combining the large-diameter particles and the small-diameter particles, it is possible to form a more dense film. The mixing ratio of the large-diameter particles and the small-diameter particles is preferably 9: 1 to 6: 4 (weight ratio).

(Dispersion medium)
As the dispersion medium contained in the coating liquid of the present invention, a generally used organic dispersion medium can be used, and alcohols, glycolic acids, ethers, ketones and the like can be exemplified. The concentration of the high-density silica particles in the dispersion medium is preferably about 0.5 to 60% by weight, more preferably 10 to 50% by weight.
The amount of water contained in this dispersion medium is preferably 1% by weight or less, more preferably 0.5% by weight or less. This makes it possible to prevent the surface of the silica particles from becoming SiOH due to rehydration.

(Other ingredients)
The coating liquid for film formation of the present invention may contain other components in addition to the high-density silica particles and the dispersion medium. For example, additives such as a leveling agent can be added as needed.

(Preparation of coating liquid for film formation)
The coating liquid for film formation of the present invention can be produced by dispersing high-density silica particles in a dispersion medium using various dispersers such as an ultrasonic disperser and filtering the particles appropriately with a filter or the like.

[Base material with coating]
In the coated base material of the present invention, a coating film mainly composed of silica particles is directly or indirectly formed on the base material. The silica particles are high-density silica particles that satisfy the requirements (a) to (e) described above. The film thickness is, for example, about 1 to 20 μm. According to the present invention, since the high-density silica particles that are the main component of the film are densified, shrinkage in the heat treatment (film drying step, film firing step) during film formation is suppressed, and the thickness is preferably 2 μm or more. The occurrence of cracks is suppressed even with a thick film of 3 μm or more, more preferably 5 μm or more. Since the coating film of the present invention is dense even when fired at a low temperature of 200 ° C. or lower, it can be used for substrates and applications that cannot be fired at a high temperature.

Here, the coating film mainly composed of silica particles means a coating film in which silica particles are 50% by weight or more, preferably 70% or more, more preferably 90% by weight or more, and further preferably 95% by weight or more of the entire film. Particularly preferably, it is a film (a porous film composed of particles) substantially entirely composed of silica particles. Therefore, it is possible to obtain a film that does not cause cracks even when subjected to high temperature treatment.

The coating film may contain a binder component. The binder component can be contained, for example, in an amount of 0 to 30% by weight, preferably 0 to 10% by weight, based on the entire coating film. That is, the interparticle voids of the high-density silica particles are filled with a binder component, whereby a finer film can be obtained, and adhesion to the substrate, mechanical strength, chemical resistance, etc. can be improved. .. The binder component can be added in an appropriate manufacturing process according to the type and the like.

Here, as the binder component, a normally used inorganic binder or organic binder can be used. Examples of the inorganic binder include polysiloxane, polysilane, polycarbosilane, polysilazane, polycarbosilazane, polymetalloxane, and polyborosiloxane. Examples of the organic binder include thermoplastic resins such as polyester resin, polycarbonate resin, polyamide resin, polyphenylene oxide resin, thermoplastic acrylic resin, vinyl chloride resin, fluororesin, vinyl acetate resin, and silicone rubber, urethane resin, and melamine resin. , Butyral resin, phenol resin, epoxy resin, unsaturated polyester resin, thermosetting acrylic resin and other thermosetting resins, and UV curable acrylic resin and other photocurable resins.

(Manufacturing method of coated base material)
The method for producing a coated base material of the present invention includes a coating step of directly or indirectly applying the coating liquid for film formation described above onto the base material, and a dispersion medium by drying the base material to which the coating liquid is applied. It is provided with a film drying step for removing. Preferably, a film firing step is provided after the dispersion medium removing step. In addition, various steps may be further provided before and after each step, and for example, a base layer forming step and the like can be provided before the coating step.

As a coating method in the coating step, spin coating, slit coating, bar coating, squeegee coating, scan coating and the like can be appropriately selected according to the shape and type of the base material.

The membrane drying step is a step of drying the membrane at a temperature at which the dispersion medium can be removed, and is performed, for example, at a temperature of 300 ° C. or lower.

The film firing step is a step of heating and baking the film at a temperature higher than the drying temperature in order to achieve densification of the film. For example, 500 ° C. or higher, preferably 600 to 1200 ° C., more preferably 800 to It is carried out at about 1000 ° C. The film drying step and the film firing step may be performed as separate steps, but may be performed as a series of steps by continuously raising the temperature to, for example, 1000 ° C.

[Method for preparing high-density silica particles]
Hereinafter, a suitable method for producing the high-density silica particles of the present invention is shown.
(Mixing process)
An alkoxysilane (a hydrolyzable silicon-containing compound) represented by the following general formula (1) is hydrolyzed and polycondensed in the presence of a basic catalyst component to obtain a water-alcohol-based dispersion of silica fine particles. The average particle size of the silica fine particles is preferably in the range of 10 to 500 nm.
R _n Si (OR') _4-n ... (1)
(In the formula, R represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 8 carbon atoms, a fluorine-substituted alkyl group, an aryl group, or a vinyl group, and R'is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. , Aryl group, vinyl group. In addition, n is an integer of 0 to 3.)

Here, examples of the alkoxysilane include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraoctylsilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, and ethyltrimethoxy. Silane, ethyltriethoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, octyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethoxysilane, triethoxysilane , Triisopropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, dimethoxysilane, diethoxysilane, difluorodimethoxysilane, difluorodiethoxysilane, Examples thereof include trifluoromethyltrimethoxysilane, trifluoromethyltriethoxysilane, and a mixture containing two or more of these compounds, and among these, tetramethoxysilane and tetraethoxysilane are preferable.

The dispersion is preferably a water-alcohol-based dispersion containing water and alcohol. Examples of the alcohol used here include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, n-butyl alcohol and the like. Among these, it is preferable to use methyl alcohol, ethyl alcohol or a mixture thereof. Further, it is preferable that the dispersion liquid further contains a basic catalyst component.

Examples of the basic catalyst component include ammonia, ammonium hydroxide, quaternary ammonium compounds, organic amines and amine-based coupling agents. Among these, it is preferable to use ammonia, ammonium hydroxide or a quaternary ammonium compound.

(Refining process)
(Purification method 1)
The water-alcohol-based dispersion of the obtained silica fine particles is subjected to an ultrafiltration device to concentrate the volume until the volume is reduced to about one-half to about one-fifth, and the reaction contained in the dispersion is incomplete. It is preferable to prepare a water-alcohol-based dispersion of silica fine particles in which sufficient removal of the silicon-containing compound and adjustment of the content of the basic catalyst component are performed.

(Purification method 2)
In addition, silicon-containing compounds and sodium ions contained in the obtained dispersion liquid, which are insufficiently reacted, should be removed by treatment using an ion exchange resin which can be expected to have a separation and removal action such as adsorption as well as exchange of ion components. You can also. The unreacted product of alkoxysilane can be separated by using an anion exchange resin, but since sodium ions and the like can be removed by further using a cation exchange resin, both ion exchange resins are used. It is preferable to separate and remove.

The OH-type anion exchange resin is preferable as the anion exchange resin, and its form such as bead-like or fibrous is not limited. Further, as the treatment method, conventionally known methods such as a method in which the ion exchange resin is put into the dispersion liquid and treated by a batch method, a method in which the column is filled with the ion exchange resin and the liquid is passed, and the like can be used. ..
As the cation exchange resin, an H-type cation exchange resin is preferable, and its form such as bead-like or fibrous is not limited. Further, similarly to the above, as the treatment method, conventionally known methods such as a method of putting an ion exchange resin into the dispersion liquid and processing by a batch method, a method of filling a column with an ion exchange resin and passing the liquid, etc. are used. be able to.
By alternately performing the treatment of the cation exchange resin and the anion exchange resin a plurality of times, the alkali components such as the silicon-containing compound and the sodium ion can be separated and removed more effectively, and the silica particles can be fused more effectively. It becomes possible to suppress.

(Purification method 3)
Further, it is preferable to perform hydrothermal treatment after the treatments of the purification methods 1 and / or 2 or without performing the purification methods 1 and / or 2, and then perform a purification treatment using an ion exchange resin. By hydrothermal treatment, the silicon-containing compound existing inside the silica particles with insufficient reaction can be discharged to the outside of the particles (in the dispersion liquid), and then discharged into the dispersion liquid by the subsequent purification treatment using an ion exchange resin. Since the silicon-containing compound can be separated and removed, fusion of silica particles during firing can be suppressed. That is, if a silicon-containing compound having an insufficient reaction remains inside the silica particles, the silicon-containing compound appears on the particle surface during drying, and the silicon-containing compound is fused between the silica particles, that is, a neck. It is thought to promote the formation and growth of the part, but this can be suppressed.

Further, in the hydrothermal treatment, at the same time as the silicon-containing compound existing inside the silica particles and having insufficient reaction, the silicon-containing compound existing (adhering) to the surface of the silica particles is also discharged into the dispersion liquid. It is considered that this can be achieved, and in the subsequent purification treatment using the ion exchange resin, this is also separated and removed at the same time, so that the fusion of the silica particles during firing can be further suppressed. Further, since the silicon-containing compound that originally exists outside the silica particles (in the dispersion liquid) and has an insufficient reaction can be simultaneously separated and removed by the subsequent purification treatment using an ion exchange resin, the silica particles can also be separated from each other. Fusion can be suppressed. Further, an alkaline component such as sodium ion also causes the fusion of silica particles during firing to be promoted, but it is considered that this alkaline component can also be discharged from the inside of the silica particles at the same time, and subsequent ion exchange. By removing it by a purification treatment using a resin, fusion of silica particles can be suppressed more effectively.

The hydrothermal treatment conditions are not particularly limited as long as the silicon-containing compound existing inside the silica particles and having an insufficient reaction can be discharged to the outside of the particles, and even if the batch method is performed, a continuous method is used. You may go with. The temperature is preferably more than 100 ° C. and 300 ° C. or lower, more preferably 150 to 250 ° C. The pressure is usually the saturation pressure at each treatment temperature and may be further pressurized. The treatment time is preferably 1 to 24 hours, more preferably 3 to 15 hours. By performing the hydrothermal treatment under these conditions, the silicon-containing compound existing inside the silica particles and having an insufficient reaction can be more effectively discharged to the outside of the particles. The subsequent purification treatment using the ion exchange resin is the same as in the purification method 2.

The solvent of the dispersion may be replaced before the drying step of the next step. For example, it may be replaced with butanol or the like from the viewpoint of interaction with the surface hydroxyl group (−OH) and surface tension. Further, a solvent (NMP, PVA, etc.) that terminates the surface hydroxyl group may be blended.

(Drying process)
The dispersion medium is volatilized from the dispersion obtained in the purification step and dried to be distilled off. A general drying method such as heat drying or spray drying can be adopted, but surface interaction is suppressed to further suppress induction of silica particle coalescence, fusion, sintering, etc. in a subsequent step. Therefore, for example, in order to control the volatilization of the dispersion medium and the aggregation of particles, a treatment in the direction of reducing the Peclet number is preferable. Specifically, a method of drying at a low temperature of about 50 to 200 ° C. for a long time or a method of drying in several steps (step drying) is preferable. Further, the temperature may be gradually raised from room temperature to 20 to 400 ° C (for example, 350 ° C). It should be noted that in the drying step, chemical reactions such as hydrolysis and dehydration condensation occur at the same time as the dispersion medium volatilizes.

(Baking process)
In the firing step, the dried silica particles are fired at 600 to 1200 ° C. As a result, silanol (SiOH) becomes SiO ₂ , and densification occurs. In order to prevent non-uniformity inside the particles due to rapid heating, the temperature is raised from room temperature to 20 to 400 ° C (for example, 350 ° C), followed by a drying step of raising the temperature to 600 to 1200 ° C, preferably 800 to 1000 ° C. It is preferable to include a step (firing step). At the time of firing, the silica particles (primary particles) are fused (sintered) at the neck portion, and these are further aggregated to form aggregated particles. Here, when the firing temperature is less than 600 ° C., the obtained particles (calcined silica particles) are not sufficiently densified, and cracks are likely to occur when the film is formed. On the other hand, when the firing temperature exceeds 1200 ° C., the aggregate particles of silica particles are likely to be sintered. Therefore, it is difficult to crush (that is, return to the primary particles) until the original particle size is reached in the crushing step described later. In this way, firing causes sintering of the primary particles. In order to obtain particles of primary particle size even after firing, it is necessary not to sinter, or even if it is sintered, it must be redispersed (crushed) into primary particles afterwards. The product to which the above purification step is applied can be fired at a temperature of 800 to 1200 ° C., preferably 800 to 1000 ° C. to promote SiO ₂ conversion. Firing can be performed in an air atmosphere, but when cooling after firing, it is preferable to create a gas atmosphere with a dew point of 0 ° C. or lower in order to prevent moisture absorption due to dew condensation. A gas atmosphere with a dew point of −10 ° C. or lower is more preferable.

(Crushing process)
The crushing step is a step of redispersing (crushing) the primary particles sintered by firing into the primary particles, and may be a wet method or a dry method, but for crushing. A method of introducing gas into the container to generate a swirling flow and supplying the calcined silica particles obtained in the firing step into the swirling flow is preferable. As a result, the particles are crushed without being destroyed until the aggregated particles of the calcined silica particles have the particle size of the silica particles before firing. As a result, high-density silica particles can be obtained.

Here, the state of crushing is schematically shown in FIG. 1A. When the aggregate particles of the calcined silica particles 10 obtained in the firing step are supplied to a uniform swirling flow and crushed, the contact portions of the aggregate particles are separated by the contact between the aggregate particles, and the calcined silica particles 10 are obtained. Be done. Further, the neck portion 12 which is the fused portion of the calcined silica particles 10 is cleaved, and the high-density silica particles 13 dispersed in the primary particles are obtained.
As described above, the high-density silica particles 13 obtained by crushing using a uniform swirling flow are crushed not by collisions between particles but by shearing in the swirling flow, so that a fracture surface is unlikely to occur. Further, the separation surface 14 generated when the particles are cleaved at the fused portion (neck portion) has a smaller area than the fracture surface even if it becomes an active surface due to the crushing force. Therefore, according to the crushing in the swirling flow, the amount of SiOH newly generated on the particle surface is small, and the high-density silica particles 13 having excellent dispersibility can be easily obtained.

However, in the case where the fired silica particles 10 are crushed (crushed) by a conventionally used device that does not generate a swirling flow, for example, a crushing device such as a hammer mill, the fired silica particles are schematically shown in FIG. 1B. The particles may be destroyed by the collision between the 10 and the wall of the container or the collision between the particles to form a fracture surface 15 which is an active surface. Since the siloxane bond of the particles is cleaved on the fracture surface 15, silanol groups are easily generated. As a result, the fracture surface 15 becomes a hydrophilic surface, and the desired particles cannot be obtained.

FIG. 2 is a model diagram showing a crusher suitable for the present invention. The calcined silica particles are supplied into the crushing container 1 from the introduction port 3 provided in the crushing container 1. It is preferable that the introduction port 3 and the storage portion 4 for the calcined silica particles are in one closed space 5, and the closed space 5 is filled with the introduction gas. Further, the introduced gas flows into the container from the gas introduction unit 2.
Examples of the crushing device that crushes using the swirling flow generated by the high-pressure gas include the Nano Jetmizer series manufactured by Aisin Nano Technologies and the Nano Grinding Mill series manufactured by Sanlex Kogyo Co., Ltd. ..

Here, as the introduced gas, air, oxygen gas, inert gas or the like can be used. Air is recommended from the viewpoint of safety and economy.
Further, the dew point of the gas introduced into the crushing container is preferably 0 ° C. or lower. This is because when the dew point of the gas exceeds 0 ° C., silanol groups due to moisture are likely to be generated on the active surface that appears on the high-density silica particles by crushing. For this reason, the dew point of the introduced gas is preferably −10 ° C. or lower, more preferably −20 ° C. or lower. The introduced gas having a dew point of 0 ° C. or lower can be prepared by a known method such as a compressed gas, an air dryer, or an adsorption removal method using an adsorbent. The temperature at the time of crushing is not limited as long as it does not condense.

Further, the pressure of the introduced gas is preferably in the range of 0.1 to 1.5 MPa. If the pressure of the introduced gas is less than 0.1 MPa, the swirling speed of the gas may be insufficient and the crushing may be insufficient. If the pressure of the introduced gas exceeds 1.5 MPa, not only the crushing of the aggregated particles but also the collision between the particles increases, and the particles may be destroyed. Therefore, the range of 0.1 to 1.0 MPa with the high pressure side suppressed is more preferable. In addition, the Joule-Thomson effect due to the latent heat of expansion causes the temperature to become locally low, and water may be adsorbed from the active surface of the particles. As described above, if the pressure of the introduced gas is not appropriate, it becomes difficult to obtain high-density silica particles having few SiOH groups.
Further, the linear velocity of the introduced gas is preferably subsonic or higher, and more preferably transonic to supersonic. If the linear speed of the introduced gas is less than the subsonic speed, the turning speed may be insufficient and the crushing may be insufficient. Further, when the supersonic velocity is exceeded, not only the crushing of the aggregated particles but also the collision between the particles increases and the particles may be destroyed. The linear velocity of the introduced gas can be calculated from the pressure of the introduced gas.

Further, the amount ratio of the calcined silica particles and introducing the gas supplied to the swirling flow for a fixed grinding chamber volume (solid-gas ratio: g / ^{m 3)} is preferably from 4.4~36.3g / ^{m 3,} 6.6 ~ 30.3 g / m ³ is more preferable. If the solid-gas ratio is less than 4.4 g / m ³ , the supply amount of calcined silica particles may not be stable, and if it exceeds 36.3 g / m ³ , crushing may be insufficient. The solid-gas ratio is calculated by the ratio of the supply amount of calcined silica particles (solid) to the air volume of the introduced gas (gas) per unit time (solid (g / Hr) / gas (m ³ / Hr)). be able to. If the swirling flow is maintained and the crushing chamber volume / solid air ratio is maintained, the size of the crushing chamber is not limited.

Silicon carbide (SiC) is suitable as the surface material in the crushing container 1. In particular, it is preferable to use SiC fired at 900 ° C. or higher. When the crushing container 1 made of SiC is used, high-density silica particles containing no impurities such as zirconium (Zr), iron (Fe), uranium (U), and thorium (Th) can be obtained. Therefore, an electronic device having excellent reliability can be realized.

(Example 1)
[Preparation of silica particles]
(Mixing process)
1268 g of bedding water consisting of 508 g of methanol (manufactured by Kanto Chemical Co., Inc.) having a concentration of 99.9% by weight and 760 g of pure water was prepared. To prepare 24500 g of an ethyl silicate solution was stirred by adding 16048 g of methanol having a concentration of 99.9% by weight and 8452 g of ethyl silicate (manufactured by Tama Chemical Industry Co., Ltd.). Next, 1268 g of bedding water was heated and held at a temperature of 65 ° C., and 24500 g of an ethyl silicate solution and 9490 g of ammonia water having a concentration of 1.9% by weight were simultaneously added to the mixture over 5 hours with stirring. After completion of the addition, the aging operation was further carried out at 65 ° C. for 3 hours to obtain 35258 g of a water-methanol dispersion (hereinafter referred to as "water-methanol dispersion") containing 6.7% by weight of silica fine particles. ..
(Refining process)
Next, the obtained water-methanol dispersion was cooled to room temperature, and 20340 g of pure water was added to 31860 g of the water-methanol dispersion and stirred, and then an ultrafiltration filter (Asahi Kasei) was used under a temperature condition of 25 ° C. Using ACP-2013) manufactured by ACP Co., Ltd., the mixture was concentrated to a weight of 18711 g. As a result, 18711 g of a water-methanol dispersion (hereinafter referred to as "water-methanol purification solution") from which unreacted ethyl silicates and intermediate reactants contained in the water-methanol dispersion were removed was obtained. The particle size of the obtained silica fine particles was approximately 20 nm.
(Drying process)
The purified water-methanol solution was transferred to a SUS vat and dried in a dryer at 100 ° C.

(Baking process)
Next, the silica powder was placed in a SiC crucible (firing container) and fired at 900 ° C. for 10 hours using an electric furnace. This was cooled to obtain calcined silica particles.
(Crushing process)
Subsequently, the calcined silica particles are put into a crusher (manufactured by Aisin Nano Technologies, Inc .: Nanojetmizer NJ-100) in which a swirling flow due to a high-pressure gas is generated to crush the calcined silica particles to obtain a high density. Density silica particles (B1) were obtained. At this time, as the high-pressure gas, dry air controlled to a dew point of −10 ° C. (hereinafter referred to as “-10 ° C.”) was used when the pressure was 1.0 MPa by an air dryer. In addition, an enclosure was provided so as to seal the inlet of the calcined silica particles. Dry air with a dew point of −10 ° C. was introduced therein. The calcined silica particles were supplied from an environment having a dew point of −10 ° C., and the dry air introduced together with the calcined silica particles was also set to air having a dew point of −10 ° C.

The operating conditions of this device are: crushing pressure (swirl flow air pressure in the crushing part) 0.85 MPa, pressure in the calcined silica particle introduction part 1.0 MPa, raw material introduction speed 5 kg / Hr, swirling flow speed. (Linear speed) was set to 391 m / s, and the solid-state ratio was set to 22.6 g / m ³ .

[Evaluation method of high-density silica particles (B1)]
(A) Average particle size of silica fine particles The average particle size of high-density silica particles was photographed with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation: S-5500 type), and 250 particles in this image were taken. Was calculated using an image analyzer (manufactured by Asahi Kasei Co., Ltd .: IP-1000).

(B) Particle size coefficient of variation (CV value)
The coefficient of variation of particle size (CV value) was calculated by the following formula based on the measurement in "(a) Average particle size of silica fine particles".

(C) SiO ₂ purity (impurity content)
After 1 hour sintering at 1000 ° C. The dense silica particles, adding a few drops of a hydrofluoric acid sulphate and dryness on a sand bath, and burned for one hour at 1000 ° C., SiO ₂ from the difference before and after weight The purity was calculated.

(D) Measurement of sphericity Photographs were taken with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation: S-5500 type), and the maximum diameter ( _DL ) of any 50 high-density silica particles was taken. When, the average value of the ratio of the short diameter _{(D S) (D S /} D L) orthogonal thereto, which was used as a sphericity.

(E) Weight loss at 1000 ° C. based on 400 ° C. Using a differential thermal balance TG8120 manufactured by Rigaku Co., Ltd., the amount of weight loss was measured while raising the temperature from room temperature to 1000 ° C. at 1 ° C./min, and 400. The weight loss rate at 1000 ° C. based on the weight at ° C. was determined.

(F) Measurement of coarse particles When the distribution of particles with a large particle size is observed when measuring the average particle size, the proportion (weight ratio) of particles that is four times or more the average particle size is determined and the content of coarse particles is contained. The amount was taken.

[Preparation of coating liquid for film formation]
(Dispersion process)
1000 g of high-density silica particles were added to 2333 g of propylene glycol monopropyl ether and dispersed while applying ultrasonic waves.
(Filtration process)
The obtained high-density silica particle dispersion was filtered through a 0.5 μm filter to obtain a coating liquid 1 having a solid content concentration of 30% by weight.

[Preparation of coated substrate]
The coating liquid 1 is applied onto a silicon wafer by a spin coating method at a rotation speed of 300 to 700 rpm, dried at a temperature of 120 ° C. for 5 minutes, and then fired in a nitrogen atmosphere at a temperature of 900 ° C. for 30 minutes. , A coating film (coated substrate) having a thickness of 1 to 10 μm (in 1 μm increments) was formed. The film thickness was measured by a contact-type step film thickness measurement method (SURFCOM 1400D manufactured by ACCRETECH).

[Evaluation method for coated substrate]
(Crack resistance of silica-based coating)
The obtained coating film was observed with a microscope (magnification: 50 times) to confirm the presence or absence of cracks.

(Example 2)
A coating liquid 2 was obtained in the same manner as in Example 1 except that the water-methanol dispersion liquid containing silica fine particles obtained in the blending step of Example 1 was used as a seed and grown to a particle size of 100 nm. ..
(Example 3)
The coating liquid 1 and the coating liquid 2 were mixed at a solid content ratio of 3: 7 to obtain a coating liquid 3.
(Comparative Example 1)
Propylene glycol monomethyl ether was added to the water-methanol dispersion liquid containing silica fine particles obtained in the preparation step of Example 1, and the dispersion medium was replaced using a rotary evaporator. The solid content concentration was adjusted to 30% by weight to obtain a coating liquid 4.
(Comparative Example 2)
In the filtration step of Example 1, a coating liquid 5 was obtained in the same manner as in Example 1 except that a 3 μm filter was used.

1 Crushing container, 2 Gas inlet, 3 Inlet, 4 Storage, 5 Confined space, 10 Calcined silica particles, 11 Silica particles, 12 Neck, 13 High density silica particles, 14 Separation surface, 15 Fracture surface

Claims (5)

A coating liquid for forming a film containing silica particles and a dispersion medium.
The silica particles meets the following requirements (a) ~ (f), the coating liquid for film formation in which the silica particles and forming a 90% or more by weight of the coating of the entire film.
(A) Average particle size is 10 to 500 nm
(B) Particle size coefficient of variation is 20% or less (c) SiO ₂ purity is 99.5% or more (d) Sphericality is 0.90 or more (e) Weight loss at 1000 ° C. based on 400 ° C. is 0 .5% or less
(F) Coarse particle amount is 5% by weight or less A coated base material comprising a base material and a coating film mainly composed of silica particles formed on the base material.
The silica particles, Ri Oh in grains satisfying the following requirements (a) ~ (f), the film substrate with which the silica particles are characterized in that at least 90 wt% of the total film.
(A) Average particle size is 10 to 500 nm
(B) Particle size coefficient of variation is 20% or less (c) SiO ₂ purity is 99.5% or more (d) Sphericality is 0.90 or more (e) Weight loss at 1000 ° C. based on 400 ° C. is 0 .5% or less
(F) Coarse particle amount is 5% by weight or less The coated base material according to claim 2 , wherein the coating film has a film thickness of 2 μm or more. A coated base material comprising a coating step of applying the coating liquid according to claim 1 onto a base material and a film drying step of drying the base material to which the coating liquid is applied to remove a dispersion medium. Manufacturing method. The method for producing a film-coated base material according to claim 4 , wherein a film firing step is provided after the film drying step, and the heating temperature in the film firing step is 500 ° C. or higher.