JP4620851B2 - Method for producing hemispherical silica fine particles and hemispherical silica fine particles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing hemispherical silica fine particles and hemispherical silica fine particles.
More specifically, the present invention relates to a method for efficiently producing hemispherical silica fine particles suitable as an abrasive in a mirror polishing process such as a semiconductor substrate such as a silicon wafer or a memory hard disk substrate by the sol-gel method, and the above The present invention relates to hemispherical silica fine particles suitably used for applications.
[0002]
[Prior art]
In recent years, the progress of high-tech products such as computers has been remarkable, and the semiconductor elements, various devices and components used in these products have been increasing in functionality, such as higher integration, higher speed, higher capacity, and smaller size year by year. ing.
Along with this, the manufacturing accuracy of sub-micron and half-micron ultra-fine patterns is also required in the manufacture of semiconductor elements, and silicon wafers that are substrates are also required to have extremely high flatness and an intact surface. ing. In addition, a memory hard disk having a high surface flatness is required in order to reduce the size and increase the capacity.
[0003]
A material having such a surface is generally obtained by fine polishing called mirror polishing. For example, a silicon wafer having such a mirror surface used in the manufacture of a semiconductor device is obtained by cutting a single crystal silicon rod into a thin disk shape and then polishing the thin disk until it has a mirror surface shape. It is built by. Usually, the lapping process applied to the rough surface immediately after the cutting and the subsequent polishing process for precise polishing are employed for this polishing. In this polishing step, rough polishing and final polishing are performed to produce a silicon wafer having a mirror shape. Alumina powder or the like is mainly used in the lapping step, but in the rough polishing and final polishing, a slurry in which silica fine particles are dispersed in water as a main component is generally used.
[0004]
On the other hand, a substrate of a memory hard disk is used that has a surface-treated aluminum surface, and Ni-P deposited by chemical plating is generally used. For abrasives for aluminum substrates, a slurry in which alumina as a main component is dispersed in water is widely used. Recently, glass substrates are also becoming popular in order to cope with downsizing and large capacity, and a slurry in which cerium oxide, zirconium oxide, silica or the like is dispersed in water is used as an abrasive for the glass substrate. The The memory hard disk substrate is also required to have a high flatness and an intact surface as well as a high polishing rate in the same manner as the semiconductor substrate.
[0005]
In such mirror polishing treatment, silica fine particles used as an abrasive can be obtained by various methods such as a method of pulverizing and classifying baked silica gel, a method of hydrolyzing silicon tetrachloride at a high temperature, a sol-gel method, Among these methods, the method of pulverizing and classifying baked silica gel and the method of hydrolyzing silicon tetrachloride at high temperature may be mixed with impurities that adversely affect the semiconductor, and therefore, the sol-gel method is preferable.
[0006]
As for the properties of the silica fine particles, it is desirable to increase the particle size of the particles in order to increase the polishing rate. However, if the particle size is increased, the particles are more likely to settle and the specularity is reduced. It is important to select In addition, it is desirable to have a spherical surface from the viewpoint of intactness, but in the case of spherical particles, there is a problem that the particles are likely to roll during polishing and the polishing efficiency is not improved. Furthermore, if the particle size distribution is wide, coarse particles are bulky on the polishing surface, and the polishing pressure is intensively applied, so that the polishing surface is easily damaged.
[0007]
[Problems to be solved by the invention]
Under such circumstances, the present invention provides a substrate having an extremely high flatness and an intact surface when used as an abrasive in a mirror polishing process for a semiconductor substrate such as a silicon wafer or a memory hard disk substrate. An object of the present invention is to provide a method for efficiently producing silica fine particles having a high polishing rate and excellent dispersibility in an abrasive liquid by a sol-gel method, and silica fine particles having the above-described excellent functions. It is what.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors of the present invention have made spherical polyorganosiloxane particles having a specific particle size into the thermal decomposition temperature of organic groups contained therein in the presence of oxygen. It is found that what is obtained by dividing the particles into hemispheres by firing at the above temperature, pyrolyzing and oxidizing, has the above-mentioned excellent function. It came to be completed.
[0009]
That is, the present invention
(1) Spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm are pyrolyzed and oxidized by firing at a temperature equal to or higher than the thermal decomposition temperature of the organic group contained therein in the presence of oxygen, A method for producing hemispherical silica fine particles, characterized by splitting into hemispherical shapes,
(2) hemispherical silica fine particles formed by firing spherical polyorganosiloxane particles from the substantially central portion thereof, having an average diameter of 1 to 18 μm and a nitrogen adsorption specific surface area of 0.1 to 5 m. ² / g hemispherical silica fine particles, and (3) silica fine particles characterized by containing at least 30% of the above (2) hemispherical silica fine particles,
Is to provide.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing hemispherical silica fine particles of the present invention, first, spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm are prepared. Next, the spherical polyorganosiloxane particles are fired in the presence of oxygen to be thermally decomposed and oxidized, and split into hemispheres.
[0011]
The spherical polyorganosiloxane particles are preferably particles obtained by hydrolyzing and condensing an alkoxysilane compound having a non-hydrolyzable group, or particles obtained by growing particles using these particles as seed particles. . In particular, spherical polyorganosiloxane particles obtained by performing (A) seed particle liquid preparation step, (B) seed particle growth step, and (C) particle cleaning / drying step are suitable.
[0012]
Examples of the alkoxysilane compound having a non-hydrolyzable group used as a raw material include general formula (I)
R ¹ nSi (OR ² ) _4-n (I)
(In the formula, R ¹ is a non-hydrolyzable group having 1 to 20 carbon atoms, a (meth) acryloyloxy group or an epoxy group having 1 to 20 carbon atoms, or 2 to 20 carbon atoms). An alkenyl group, an aryl group having 6 to 20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms, R ² is an alkyl group having 1 to 6 carbon atoms, n is an integer of 1 to 3, and there are a plurality of R ¹ each R ¹ may be different from one another identical, if OR ² there are a plurality, each OR ² may be different even identical to each other.)
The alkoxysilane compound represented by these can be mentioned.
[0013]
In R ¹ in the general formula (I), the alkyl group having 1 to 20 carbon atoms is preferably an alkyl group having 1 to 10 carbon atoms, and the alkyl group may be linear, branched, or cyclic. Also good. Examples of this alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, octyl, and cyclopentyl. Group, cyclohexyl group and the like. As a C1-C20 alkyl group which has a (meth) acryloyloxy group or an epoxy group, the C1-C10 alkyl group which has the said substituent is preferable, and this alkyl group is linear, branched, Any of cyclic | annular form may be sufficient. Examples of the alkyl group having this substituent include γ-acryloyloxypropyl group, γ-methacryloyloxypropyl group, γ-glycidoxypropyl group, 3,4-epoxycyclohexyl group, and the like. The alkenyl group having 2 to 20 carbon atoms is preferably an alkenyl group having 2 to 10 carbon atoms, and the alkenyl group may be linear, branched or cyclic. Examples of the alkenyl group include vinyl group, allyl group, butenyl group, hexenyl group, octenyl group and the like. As a C6-C20 aryl group, a C6-C10 thing is preferable, for example, a phenyl group, a tolyl group, a xylyl group, a naphthyl group etc. are mentioned. As a C7-20 aralkyl group, a C7-10 thing is preferable, for example, a benzyl group, a phenethyl group, a phenylpropyl group, a naphthylmethyl group etc. are mentioned.
[0014]
On the other hand, the alkyl group having 1 to 6 carbon atoms represented by R ² may be linear, branched or cyclic, and examples thereof include a methyl group, an ethyl group, an n-propyl group, and isopropyl. Group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, cyclopentyl group, cyclohexyl group and the like.
[0015]
Examples of the alkoxysilane compound represented by the general formula (I) include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyl Triethoxysilane, butyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-acryloyloxypropyltrimethoxysilane, γ- Examples include methacryloyloxypropyltrimethoxysilane, dimethyldimethoxysilane, and methylphenyldimethoxysilane. Of these, methyltrimethoxysilane and vinyltrimethoxysilane are particularly preferred. These alkoxysilane compounds may be used individually by 1 type, and may be used in combination of 2 or more type.
[0016]
Next, each step will be described.
(A) Seed particle solution preparation step This (A) step is a step of preparing a seed particle solution by hydrolyzing and condensing the alkoxysilane compound represented by the general formula (I).
[0017]
In this step (A), the alkoxysilane compound represented by the general formula (I) is dissolved in an aqueous solution containing a nonionic surfactant as required, and ammonia and / or amine is added thereto, The alkoxysilane compound is hydrolyzed and condensed. The ammonia and amine are catalysts for hydrolysis and condensation of the alkoxysilane compound. Here, preferred examples of the amine include monomethylamine, dimethylamine, monoethylamine, diethylamine, and ethylenediamine. Ammonia and amine may be used alone or in combination of two or more. However, ammonia is preferred because it is less toxic, easy to remove, and inexpensive.
[0018]
Examples of the aqueous solution containing a nonionic surfactant include a solution obtained by dissolving a nonionic surfactant in water or a mixed solvent of water and a water-miscible organic solvent. Here, examples of the water-miscible organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone, dimethyl ketone and methyl ethyl ketone, and ethers such as diethyl ether and dipropyl ether. It is done. These may be mixed with water alone or in combination of two or more with water.
The amount of ammonia or amine used is not particularly limited, but is preferably selected so that the pH of the aqueous layer before starting the reaction is in the range of 7.5 to 11.0.
[0019]
In the present invention, as the nonionic surfactant used as desired, those having an HLB value in the range of 8 to 20 are preferably used. This HLB is an index representing the balance between hydrophilicity and lipophilicity, and the smaller the value, the higher the lipophilicity. When the HLB value deviates from the above range, the effect of the present invention is not sufficiently exhibited. In order to exhibit the effect of this invention better, what has a HLB value in the range of 10-17 is preferable.
[0020]
There is no particular limitation on the reaction format, and both a mixed homogeneous reaction and a two-layer reaction can be used. However, a particle size distribution variation coefficient (CV value) is small, and particles with good particle size accuracy are obtained. A mixed homogeneous reaction is more advantageous because the reaction operation is easy and the type of raw material is not limited by the specific gravity.
In this mixed homogeneous reaction, the alkoxysilane compound as a raw material is not particularly limited as long as it is miscible with an aqueous medium. The siliconized compound is preferable.
[0021]
First, this alkoxysilane compound is added to an aqueous solution having a nonionic surfactant and is usually stirred at a temperature of about 0 to 50 ° C. to obtain a uniform aqueous solution. While stirring this aqueous solution, preferably, ammonia and / or an amine-containing aqueous solution is added at a time as a catalyst, and the alkoxysilane compound is hydrolyzed and condensed to form seed particles to form a seed particle solution.
[0022]
(B) Seed particle growth step This (B) step is a step of growing the seed particles obtained in the above step (A). First, a separate build-up solution is prepared.
This build-up solution can be prepared by dissolving the alkoxysilane compound represented by the general formula (I) in an aqueous medium composed of water or a mixed solvent of water and the aforementioned water-miscible organic solvent. As a density | concentration of the alkoxysilane compound in this buildup solution, content of an alkoxysilane compound is preferable in 8-20 mol with respect to 1 liter of aqueous media. If the alkoxysilane compound concentration is lower than the above range, cracking of the particles may be difficult to occur during firing. On the other hand, if the alkoxysilane compound concentration is higher than the above range, the variation coefficient (CV value) of the particle size distribution exceeds 3%. It becomes difficult to obtain dispersed particles.
The coefficient of variation (CV value) is obtained by the following equation.
CV value (%) = (standard deviation of particle size / average particle size) × 100
[0023]
Next, while slowly stirring the built-up solution thus prepared, the seed particle liquid obtained in the step (A) is added thereto to grow particles. The reaction temperature at this time depends on the type of the alkoxysilane compound as a raw material, but is generally in the range of 0 to 60 ° C. In this growth reaction, the ammonia concentration (when ammonia is used as the catalyst) in the build-up solution after addition of the seed particle solution is preferably 0.001 mol / liter or less. If the ammonia concentration exceeds 0.001 mol / liter, cracking of particles is difficult to occur during firing.
[0024]
After confirming that the particle size growth has stopped after the seed particle solution is added, ammonia and / or an amine are added for aging.
The amount of ammonia or amine added is not particularly limited, but is preferably selected so that the pH of the reaction system is in the range of 9.0 to 12.0. The aging temperature may be carried out at the same temperature as in the above reaction, or may be carried out by slightly raising the temperature. The aging time depends on the reaction temperature, pH, etc., and cannot be determined generally, but usually about 1 to 20 hours is sufficient.
In this manner, true spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm are formed. These particles are monodisperse particles having a CV value of usually 3% or less.
[0025]
(C) Particle cleaning / drying step This (C) step is a step of washing and drying the polyorganosiloxane particles obtained in the above step (B).
There is no restriction | limiting in particular as washing | cleaning process of this particle | grain in this process, According to a conventional method, it wash | cleans sufficiently using lower alcohols, such as methanol.
After the washing treatment, if necessary, classification treatment may be performed to remove maximal particles or tiny particles, followed by drying treatment. Although there is no restriction | limiting in particular as a classification processing method, The wet classification method which classifies using the sedimentation speed changes with particle sizes is preferable. A drying process is normally performed at the temperature of the range of 100-200 degreeC.
[0026]
In the method for producing hemispherical silica fine particles of the present invention, the monodispersed true spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm thus obtained are fired to be thermally decomposed and oxidized, and split into hemispheres. Let
[0027]
In the firing treatment, firing is performed at a temperature equal to or higher than the thermal decomposition temperature of the organic group contained in the particles in the presence of oxygen, and the particles are thermally decomposed and oxidized. This calcination treatment is carried out in the presence of oxygen, but the oxygen concentration is preferably 10% by volume or more, and it is particularly advantageous to calcinate in air from the viewpoint of economy. The firing temperature is usually in the range of 300 to 1100 ° C. If this temperature is less than 300 ° C., firing is insufficient, and it is not necessary to perform firing at a temperature higher than 1100 ° C., and sufficient firing can be performed at a temperature of 1100 ° C. or less.
[0028]
When air is used for the firing process, it is preferable to flow 6% or more of the firing furnace capacity in one minute. Further, the higher the temperature rising rate, the higher the generation rate of cracked particles, and at least 0.5 ° C./min is desirable. There is no restriction | limiting in particular about a baking apparatus, An electric furnace, a rotary kiln, etc. can be used.
By this baking treatment, at least 30%, preferably 50% or more, more preferably 70% or more of the number of spherical polyorganosiloxane particles is usually divided into hemispheres.
[0029]
In the present invention, the polyorganosiloxane particles thus calcined are usually a mixture of true spherical particles and hemispherical particles, and may be used as they are, or classified by known means, and hemispherical. It is also possible to obtain only particles. When assuming the use of an abrasive used for mirror polishing of a semiconductor substrate such as a silicon wafer or a substrate for a memory hard disk, it is preferable to classify and use only hemispherical particles.
[0030]
The present invention also provides a hemispherical silica fine particle divided from the substantially central part of the spherical polyorganosiloxane particles by firing, having an average diameter of 1 to 18 μm and a nitrogen adsorption specific surface area of 0.1. In addition to providing hemispherical silica fine particles of ˜5 m ² / g, silica fine particles containing at least 30% of the hemispherical silica fine particles are also provided.
The nitrogen adsorption specific surface area is a value measured in accordance with ASTM D4820-93.
The hemispherical silica fine particles are particularly suitable as an abrasive in a mirror polishing process for a semiconductor substrate such as a silicon wafer or a memory hard disk substrate.
[0031]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0032]
Example 1
(1) Preparation of Seed Particle Liquid To 5000 g of ion-exchanged water, 500 g of methyltrimethoxysilane (hereinafter abbreviated as MTMS) and a polyoxyethylene alkyl ether nonionic surfactant “Neugen EA-137 (HLB13)” 5 ml of a 0.1 wt% aqueous solution (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added and stirred at 30 ° C. at 100 ppm. At the beginning of MTMS addition, it was dispersed in the form of oil droplets in the aqueous solution, but after about 3 hours, MTMS was completely dissolved and became a homogeneous solution.
[0033]
The stirring speed of the solution prepared above was lowered to 30 rpm, and 50 ml of 1 mol / liter ammonia water was added at once to this. Two minutes after adding the ammonia water, the particles grew and the solution became cloudy. The pH of the seed particle solution 30 minutes after the addition of aqueous ammonia was 9.47. The seed particle solution 0.2 ml 30 minutes after the addition of the ammonia water was added to 2 ml of a 0.1% by weight polyvinyl alcohol aqueous solution, and the particle diameter was immediately measured with a Coulter counter. As a result, the seed particles had an average particle size of 2.569 μm (CV value 1.49%).
[0034]
(2) Seed particle growth process 33,000 g of ion-exchanged water and 4950 g of MTMS were charged into a reaction vessel equipped with a stirrer and stirred at 30 ° C. at 100 rpm. After 3 hours, MTMS was completely dissolved in water and became a homogeneous solution. Subsequently, the stirring speed was lowered to 20 rpm, and 1450 g of the seed particle liquid obtained in the above (1) was added.
Ten minutes after the seed particle solution was added, the particle diameter was measured with an optical microscope video micrometer (Olympus Video Micrometer “VM-50”). After 2 hours 50 minutes and 3 hours after addition, it was determined that the particle size was about 9.5 μm and the growth of the particle size was completed, and 500 g of 25% by weight ammonia water was added dropwise with a metering pump and aged. Performed for 16 hours at room temperature.
The particle size of the particles thus obtained was measured with a Coulter counter, and it was found that the average particle size was 9.453 μm (CV value 1.74%).
[0035]
(3) Firing step The particles obtained in (2) above were separated from water by a centrifugal separator, then washed with methanol and dried. 400 g of the dried particles are put into a 40 liter muffle furnace (manufactured by Chugai Engineering Co., Ltd.), heated to 400 ° C. under the conditions of an air introduction rate of 4 liters / minute and a heating rate of 2 ° C./minute. Held for hours. Then, it heated up to 600 degreeC with the same temperature increase rate, and hold | maintained at this temperature for 9 hours.
When the particles after firing were observed with an optical microscope, particles split into hemispheres were observed. Observation with a Coulter counter revealed that the number of particles that were spherical (average particle size 7.8 μm) was 29%, whereas the number of particles that were split into hemispheres was 71%.
FIG. 1 shows a Coulter counter chart of the particles after firing, and FIG. 2 shows a scanning electron micrograph of hemispherical silica particles.
[0036]
Example 2
In the firing step of Example 1 (3), when the rate of temperature increase was changed from 2 ° C./min to 10 ° C./min and the firing was performed, the spherical particles were hemispherical with respect to 11% in number. The number of particles was 89%.
FIG. 3 shows a Coulter counter chart of the particles after firing.
[0037]
Example 3
In the firing step of Example 1 (3), when the firing rate was changed from 2 ° C./minute to 1 ° C./minute, the spherical particles were cracked in a hemisphere with respect to 41% in number. The number of particles was 59%.
[0038]
Comparative Example 1
In the firing step of Example 1 (3), when the firing rate was changed from 2 ° C./min to 0.2 ° C./min, all the particles were spherical particles and hemispherical cracked particles The occurrence of was not observed.
[0039]
Comparative Example 2
In the firing step of Example 1 (3), when firing was performed using nitrogen gas instead of air at the time of firing, all particles were true spherical particles, and no generation of hemispherical cracked particles was observed. .
[0040]
【The invention's effect】
According to the present invention, hemispherical silica fine particles that are split from the substantially central portion of the true spherical silica fine particles can be efficiently produced. This hemispherical silica fine particle is less contaminated with impurities and is suitable as a polishing agent in mirror polishing processing of semiconductor substrates such as silicon wafers and memory hard disk substrates. By using this, extremely high flatness and intactness are obtained. In addition to providing a substrate having the above surface, the polishing rate is high, and the particles are excellent in dispersibility in an abrasive liquid.
[Brief description of the drawings]
1 is a Coulter counter chart of particles after firing in Example 1. FIG.
2 is a scanning electron micrograph of hemispherical silica particles obtained in Example 1. FIG.
3 is a Coulter counter chart of particles after calcination in Example 2. FIG.

Claims (7)

Spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm are pyrolyzed and oxidized by firing at a temperature equal to or higher than the thermal decomposition temperature of the organic group contained in the presence of oxygen, and hemispherical. A method for producing hemispherical silica fine particles, comprising splitting. The method according to claim 1, wherein at least 30% of the number of spherical polyorganosiloxane particles is divided into hemispheres by a baking treatment. The method according to claim 1, wherein the temperature is increased to a temperature equal to or higher than the thermal decomposition temperature of the organic group at a temperature increase rate of 0.5 ° C./min or more, and the baking treatment is performed. The method according to claim 1, 2 or 3, wherein the baking treatment is performed in an atmosphere having an oxygen concentration of 10% by volume or more. Spherical polyorganosiloxane particles having an average particle diameter of 1 to 20 μm are represented by the general formula (I)
R ¹ nSi (OR ² ) _4-n (I)
(In the formula, R ¹ is a non-hydrolyzable group having 1 to 20 carbon atoms, a (meth) acryloyloxy group or an epoxy group having 1 to 20 carbon atoms, or 2 to 20 carbon atoms). An alkenyl group, an aryl group having 6 to 20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms, R ² is an alkyl group having 1 to 6 carbon atoms, n is an integer of 1 to 3, and there are a plurality of R ¹ each R ¹ may be different from one another identical, if OR ² there are a plurality, each OR ² may be different even identical to each other.)
The method according to any one of claims 1 to 4, wherein the particles are obtained by hydrolyzing and condensing the alkoxysilane compound represented by the formula (1) or particles obtained by growing particles using the particles as seed particles. . Spherical polyorganosiloxane particles are hemispherical silica fine particles that are split from substantially the center of the particles, and have an average diameter of 1 to 18 μm and a nitrogen adsorption specific surface area of 0.1 to ⁵ m ² / g. Hemispherical silica fine particles, characterized in that A silica fine particle comprising at least 30% of the hemispherical silica fine particles according to claim 6 in number.

Images