JP5941774B2 - Synthetic silica glass powder and method for producing the same - Google Patents

Description

  Synthetic silica glass powder used as a raw material for a quartz glass crucible used as a container for molten silicon when a silicon wafer used for semiconductors and solar cells is manufactured by the single crystal pulling method (Czochralski method (CZ method)) About.

  With the recent increase in diameter of silicon wafers, a quartz crucible for pulling a silicon single crystal has adopted a two-layer structure. The outer layer is a silica layer made of natural quartz powder with excellent high-temperature strength, and the inner layer in contact with the silicon melt is a silica layer made of high-purity synthetic silica glass powder with few impurities (for example, Patent Document 1). See) used.

  In this two-layer crucible, it has been conventionally required that the inner layer has no bubbles (for example, see Patent Documents 2 to 4). When the transparent glass layer on the inner surface is substantially free of bubbles, there is an advantage that bubbles are not peeled off and the dislocation rate at the time of pulling up the silicon single crystal can be reduced.

  On the other hand, recently, at the time of pulling a silicon single crystal, in order to prevent the melt surface of the silicon melt in the crucible which has an adverse effect on the quality of the single crystal, the inner layer portion near the melt surface of the crucible has a volume of 0.01 to 0.2. In order to disperse external radiant heat in order to eliminate the temperature unevenness of the silicon melt (for example, refer to Patent Document 5) and 0.1% or more of the volume bubble content between the inner layer and the outer layer. A technique for providing a bubble-containing layer has been developed (see, for example, Patent Document 6). Thus, in recent years, there is a demand for a technique for partially creating bubbles of several tens of μm inside the crucible.

  A typical method for producing a two-layered crucible is by laminating natural quartz powder and synthetic silica glass powder in a rotating carbon mold (rotating mold) in layers and arc melting (see, for example, Patent Document 7). . In order to create bubbles by this method, the quartz powder deposited on the inner surface of the rotating mold is heated and melted from the mold space side, and air in the quartz powder deposition layer is sucked from the mold side during the heating and melting. A method of intermittently performing vacuuming and leakage to be removed is used (see Patent Document 6).

JP 2000-016896 A Japanese Patent Laid-Open No. 1-148883 JP 2001-002430 A JP-A-11-116388 JP 2004-250304 A JP 2009-084113 A JP 2008-162839 A

  However, the method described in Patent Document 6 has a problem that it is difficult to control the location where bubbles are generated and the bubble diameter.

  In addition to the above method, there is a method in which calcium carbonate or a carbon-containing substance (wood waste, etc.) is mixed with silica powder as a foaming agent in order to generate bubbles in the inner glass layer in contact with the silicon melt. There is a concern that these foaming agents themselves become impurities of silica and the adverse effect of becoming a starting point for crystallization of the glass layer.

  This invention is made | formed in view of said subject, The objective provides the high purity synthetic silica glass powder which can generate a bubble in the required location of a quartz crucible, and its manufacturing method. That is true.

  In order to solve such problems, the present inventors have synthesized various silica glass powders and examined them. When a specific synthetic silica glass powder is used, bubbles can be generated in the fused silica glass layer. The inventors have found that this is possible and have completed the present invention.

As a result of examining this specific synthetic silica glass powder in detail, it was found that a small amount of silica white particles (hereinafter referred to as “white particles”) was contained, and this was considered to be acting as a bubble generating agent. It was. The white grains are silica particles having the same purity as the particles of the synthetic silica glass powder in which the white grains are contained. Therefore, the inner surface of the crucible produced using the particles is kept at the same high purity as the raw silica.
That is, the gist of the present invention is as follows.

(1) particle diameter in the range of 10 to 1000 [mu] m, the median diameter of a synthetic silica glass powder is 700μm to 50, 1 to 600 pieces of silica white color particles child to the synthetic silica glass powder in / g A synthetic silica glass powder comprising: a silanol group having a concentration of 5 to 200 ppm by weight.
(2) The synthetic silica glass powder according to (1), wherein the number of white silica particles is 5 to 500 particles / g.
(3) The method for producing a synthetic silica glass powder according to (1) or (2), wherein the production is performed by a sol-gel method using alkoxysilane as a raw material.
(4) The sol-gel method, after pulverizing the wet gel to produce said alkoxysilane is hydrolyzed, the has been dried using a batch dryer wet gel crushing, the gel obtained after drying The method for producing a synthetic silica glass powder according to (3), which is a method of firing.
(5) A method of manufacturing synthetic silica glass powder according to (4), wherein the batch dryer is container rotating.
(6) The synthetic silica according to (5), wherein the charged amount of the pulverized wet gel relative to the inner wall area of the drying container of the batch dryer is 1 to 150 kg / m ² on a dry gel basis. Manufacturing method of glass powder.
(7) (1) or (2) the method for manufacturing a silicon single crystal for pulling a quartz crucible, characterized in that there use a synthetic silica glass powder as a starting material according to.

  The synthetic silica glass powder of the present invention can generate bubbles without reducing the purity of the fused silica glass layer. Also, when the synthetic silica glass powder of the present invention is used as a quartz crucible raw material for pulling up a silicon single crystal, it is possible to generate bubbles on the inner surface of the crucible produced using this, and more A quartz crucible capable of producing an excellent quality silicon single crystal can be produced.

An example of the flowchart for manufacturing the synthetic silica glass powder of this invention is shown. An example of the flowchart for manufacturing the synthetic silica glass powder of this invention is shown.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[1. Synthetic silica glass powder]
The synthetic silica glass powder of the present invention is amorphous silicon dioxide particles, and contains at least 1 to 600 silica white particles (hereinafter referred to as “white grains”) / g in the silica dioxide particles, and the concentration of silanol groups. Is 5 to 200 ppm by weight.
Below, the physical property which the synthetic silica glass powder of this invention shows is demonstrated in detail.

(1) Particle diameter, median diameter The particle diameter of the synthetic silica glass powder is 10 μm or more, preferably 50 μm or more, 1000 μm or less, preferably 500 μm or less, and its median diameter is 50 μm or more, preferably 100 μm or more. 700 μm or less, preferably 400 μm or less. The particle diameter used here is a particle diameter obtained by measuring synthetic silica glass powder containing white grains by a laser diffraction scattering method, and the median diameter means a particle diameter corresponding to 50% of the cumulative particle size distribution.

  By narrowing the particle size distribution of the synthetic silica glass powder within the above range, bubbles can be uniformly generated in the silica glass layer of the crucible inner layer, and by setting the median diameter within the above range, particles during arc melting can be produced. The balance between the melting rate of the gas and the desorption rate of the gas in the particles can be made favorable.

(2) Bulk density The bulk density of the synthetic silica glass powder is preferably 1.1 g / cm ³ or more, more preferably 1.2 g / cm ³ or more, preferably 1.5 g / cm ³ or less, more preferably The range is 1.4 g / cm ³ or less. The measurement of the bulk density is performed by, for example, a measurement method according to JIS-K-6720 for synthetic silica glass powder containing white grains.

  By setting the bulk density of the synthetic silica glass powder to be at least the lower limit of the above range, it is possible to reduce the occurrence of volume shrinkage when the synthetic silica glass powder is melted to form the silica glass layer. Moreover, it is possible to prevent the generation of coarse bubbles having a diameter of 1 mm or more due to the interparticle voids existing between the synthetic silica glass powders. By making the bulk density of the synthetic silica glass powder not more than the above upper limit, the melting rate can be made more uniform, and the generation of coarse bubbles due to melting unevenness can be prevented.

(3) a specific surface area of the specific surface area synthetic silica glass powder is preferably 0.003 m ² / g or more, more preferably, 0.01 m ² / g or more, preferably not more than 0.5 m ² / g, more preferably 0 It is a range of 1 m ² / g or less. The measurement of the specific surface area is performed on a synthetic silica glass powder containing white grains by a gas adsorption method such as a nitrogen adsorption method.

When the specific surface area of the synthetic silica glass powder exceeds 0.5 m ² / g, the properties of the porous gel derived from the dry gel of the raw material remain, causing coarse bubbles during crucible formation, On the other hand, if it is less than 0.003 m ² / g, the particle size of the synthetic silica glass powder usually exceeds 1000 μm, which is not preferable. By making the specific surface area within the above range, it is possible to produce a crucible with controlled bubble generation.

(4) Impurity content As the impurity content of the synthetic silica glass powder, the total content of metal elements is preferably 1 ppm by weight or less. The measurement of the impurity content is performed, for example, by ICP-MS (inductively coupled plasma mass spectrometry) on synthetic silica glass powder containing white grains.

When the impurity content of the synthetic silica glass powder is less than or equal to the upper limit of the above range, when a quartz crucible for pulling up a silicon single crystal is made using synthetic silica glass powder as a raw material, silicon Contamination can be prevented by suppressing elution of metal elements into the melt and silicon single crystal.
In addition, although the said impurity content is generally so preferable that there is little, the lower limit is about 10 weight ppb normally. Reducing impurities to less than 10 weight ppb is not very realistic and analysis at the 1 weight ppb level is very difficult.

(5) Content of silanol groups Further, the content of silanol groups (Si-OH) in the particles of the synthetic silica glass powder is 5 ppm by weight or more, preferably 20 ppm by weight or more, as the concentration of silanol groups. Weight ppm or less, preferably 100 ppm by weight or less. The concentration of silanol groups can be measured, for example, by infrared spectrophotometry (infrared spectroscopy) with respect to synthetic silica glass powder containing white grains, and is shown as a weight ratio of hydroxyl groups (OH groups) to particle weights.

  By making the content of silanol groups (Si-OH) in the particles of the synthetic silica glass powder above the lower limit of the above range, generation of bubbles based on water (water vapor) generated by dehydration condensation of silanol groups is made appropriate. While controlling, the baking time at the time of manufacturing synthetic silica glass powder can be prevented from becoming excessively long. By making the content of silanol groups (Si-OH) in the particles of the synthetic silica glass powder not more than the upper limit of the above range, excessive generation of bubbles is prevented, and durability such as crucible deformation at high temperatures is also achieved. Deterioration can be prevented.

[2. Silica white particles (white particles)]
The silica white particles (white particles) referred to in the present invention are amorphous silicon dioxide particles having the following characteristics (a) to (c).
(A) It looks white visually (b) The main component is SiO ₂ (c) The particle density is lower than 2.2 g / cm ³ Hereinafter, the silica white particles will be described in more detail.

  As for the appearance of white grains, the synthetic silica glass powder (hereinafter also referred to as “normal particles”) that does not contain the white grains is visually colorless and transparent, whereas white grains appear to be white visually. It is a feature. For this reason, it can be easily distinguished from normal particles with the naked eye. As for the shape, normal particles are spherical or massive, whereas white grains are mostly plate-like, and the thickness is usually about 5 to 50 μm. As the appearance, there are a case where the whole white grains are white and a case where the colorless and transparent particles are white partially or in the form of spots.

  The particle size distribution of white grains is almost the same as that of normal grains, and the particle diameter is in the range of 10 to 1000 μm. This is described in [4. This is because white grains are produced as a by-product in the production process of normal particles and pass through the same classification process as normal particles, as described in the method for producing synthetic silica glass powder and white grains.

The composition of white grains is the same high purity silica (silicon dioxide) as normal particles. The structure of the white grains is an agglomerated / sintered body of silica particles of 1 μm or less when one normal particle is a single non-porous silica particle while the white grains are observed with an electron microscope. The white grains have a structure in which a large number of bubbles having a size of submicron level exist, and the bubble volume fraction in the white grains is 0 to 18%. Since visible light is scattered by the bubbles, it is considered that the appearance looks white. Also because of the voids inside the white particle, particle density, amorphous silica (2.2g / cm ³⁾ lower than a 1.8~2.2g / cm ³ order.

In the present invention, the white grains are identified by confirming the color by visual observation, the particle composition is SiO ₂ by an X-ray spectroscopic analysis method such as SEM-EDX, and the liquid density is 2.2 g / cm. ^The white particles are put into a heavy liquid (specific gravity measuring liquid) adjusted to ³ or less, and the particle density is confirmed to be smaller than 2.2 g / cm ³ from the float and sink.

The reason why white particles generate bubbles in the fused silica layer is presumed to be due to the bubbles inside the white particles, but considering that bubbles larger than the volume are generated, white particles are melted during the melting of the silica powder. It is thought that water (water vapor) generated by dehydration condensation of SiOH groups (silanol groups) present at the ends of the SiO ₂ skeleton of the surrounding silica is aggregated with the bubbles of

  For the above reasons, the higher the silanol group concentration in the silica, the greater the amount of bubbles generated. Therefore, the amount of bubbles generated (number of generations) and the diameter of the bubbles when the synthetic silica glass powder is melted are the number of white grains. It can be controlled by the silanol group concentration. In the present invention, the content of white grains in the synthetic silica silica glass must be 1 to 600 / g. In order to significantly generate bubbles during melting, 5 g or more in 1 g of the synthetic silica glass is required. It is preferable that the number is 10 or more. On the other hand, if the number of white grains in 1 g of synthetic silica glass powder exceeds 600, huge bubbles of 1 mm or more are often generated. For example, for a crucible for pulling a silicon single crystal, It is necessary in terms of quality that the number of white grains is 600 or less. A more preferable upper limit of the white grain content is 500 / g.

  The silanol group concentration can be controlled by the time for heating to 1000 ° C. or higher in the firing step of synthetic silica glass powder production. The longer the heating time, the more the dehydration condensation reaction of the silanol groups in the raw material proceeds, and the silanol groups in the silica The concentration decreases.

For example, if the synthetic silica glass powder has a silanol group concentration of 5 to 200 ppm by weight, the bubble volume fraction in 1 g of molten glass per white grain is 10 ⁻⁵ to 10 ⁻³ volume. %. Moreover, although the magnitude | size of the bubble to generate | occur | produce depends on melting conditions, it is thought that it is about 0.01-1 mm in diameter, for example.

  In using the synthetic silica glass powder containing white grains of the present invention, a synthetic silica glass powder having a small white grain content or not containing white grains and another synthetic silica glass powder having a different white grain content are mixed. Can be used. In addition, white grains collected by visual extraction from a synthetic silica glass powder containing a large amount of white grains or separated by a method using the density difference between the normal grains and white grains described above, The number of white grains can be controlled by adding and mixing with synthetic silica glass powder having a small white grain content or no white grains.

  Furthermore, when using such synthetic silica glass powder, bubbles can be formed at a desired site by partially using the white particle-containing synthetic silica glass powder during crucible production.

[3. White grain detection / counting method]
The white grains can be detected visually, but the content of the white grains referred to in the present invention can be measured, for example, by the following analysis method (immersion light transmission method).

[Immersion transmitted light method]
2 g of synthetic silica glass powder is weighed into a glass container (weighing bottle) having a diameter of 3 cm and a depth of 3 cm, and 2 cc of a solvent (refractive liquid) whose refractive index is adjusted to 1.46, which is the same as that of amorphous silica, is added (refraction). As the liquid, for example, a mixed liquid of 65% by weight of metaxylene + 35% by weight of isobutanol can be used).

  The slurry is lightly stirred with a metal rod or the like to allow the powder and the refractive liquid to blend together. In this way, normal particles are completely invisible, and only white particles appear to float in the liquid. This is observed and counted with a stereomicroscope (several times magnification). This method is a well-known method used for observation of minerals and ceramic particles.

  The number of white grains defined in the present invention was calculated by converting the numerical value obtained by this method from the amount of the observation sample to the content per 1 g of synthetic silica glass powder, and averaging the measured values twice (n = 2). Is. Of course, three or more measurements may be performed, and the measured values in that case may be averaged.

[4. Method for producing synthetic silica glass powder and white grains]
The synthetic silica glass powder of the present invention is preferably produced by a sol-gel method using alkoxysilane as a raw material. The sol-gel method is known, for example, in the literature (Sakuo Sakuo “Science of the sol-gel method”), but as a specific production example, it is described in JP-A-5-246708 and JP-A-8-91822. A method is mentioned.
Basically, the hydrolysis reaction of alkoxysilane is performed using reaction (A) according to the following reaction formula (a).

As the raw material alkoxysilane, tetraalkoxysilane is preferable. In addition, it is preferable to use a raw material that has been purified by distillation in advance, whereby high-purity SiO ₂ can be produced.
_{(RO) 4 Si + 2H 2} O → SiO 2 + 4ROH (a)

  In the above reaction formula (a), R represents an alkyl group, and the number of carbon atoms is preferably 1 to 4. Particularly, the reaction (A) proceeds rapidly and the resulting alkoxy group has little residual alkoxy group in the silica. Groups are preferred.

An example of a production flow diagram of the synthetic silica glass powder of the present invention is shown in FIGS.
As shown in FIG. 1, the synthetic silica glass powder of the present invention comprises a hydrolysis step (step 1) for hydrolyzing alkoxysilane, a pulverization step (step 2) for pulverizing wet gel, and drying the pulverized wet gel. It is manufactured through a drying process (step 3) to be performed and a baking process (step 4) in which the dry gel is fired.

Alternatively, as shown in FIG. 2, the synthetic silica glass powder of the present invention comprises a hydrolysis step for hydrolyzing alkoxysilane (step 11), a pulverization step for pulverizing wet gel (step 12), and a wet gel after pulverization. After the drying process (step 13) for drying the above, and the firing process (step 14) for firing the dry gel, a classification process (step 15) for classifying the fired synthetic silica glass powder may be performed.
Hereinafter, each process will be described in detail. In the following description, a case where tetraalkoxysilane is used as the alkoxysilane will be described.

<Hydrolysis reaction (reaction (A))>
The hydrolysis reaction is a reaction in which the raw material tetraalkoxysilane is subjected to the hydrolysis reaction by the above-mentioned reaction (A), and can be performed by reacting tetraalkoxysilane with water according to a known method. Here, the hydrolyzate of tetraalkoxylane is referred to as “wet gel”.

  At this time, if necessary, an organic solvent such as alcohols, ethers, and ketones compatible with the by-produced alcohol may be mixed. For example, examples of alcohol include methanol, ethanol, propanol, etc., examples of ethers include diethyl ether, and examples of ketones include acetone.

  However, when the hydrolysis reaction proceeds, the alkoxy group bonded to silicon is released as an alcohol, so that the reaction solution becomes uniform before gelation (formation of wet gel), that is, the hydrolysis rate. In the case of a raw material containing a large alkoxy group (for example, methoxy group), it can be produced practically without any trouble without adding an alcohol or the like.

  In this reaction, a catalyst is not essential, but an acid such as hydrochloric acid, acetic acid, hydrofluoric acid or sulfuric acid, an alkali such as ammonia water, or the like may be used as a catalyst. The water used for the hydrolysis is preferably ultrapure water or the like in order to obtain the target synthetic silica glass powder with higher purity. The amount of water used is not particularly limited as long as the hydrolysis reaction proceeds, but in practice it is generally added in excess of the theoretical amount (2 times the mole of tetraalkoxysilane).

  In order to set the time required for gelation and the time required for coarse pulverization to an appropriate range, the molar ratio of tetraalkoxylane: water is 1: 2 to 1:10, preferably 1: 3 to 1: 8. More preferably, the range of 1: 4 to 1: 7 is practical. If the amount of water is extremely high, not only will gelation take a long time, but it will take time for the wet gel to become suitable for the grinding process after gelation, and in some cases excess water must be evaporated. In addition, there may be inconveniences such as the time required for the drying process described later. On the other hand, if the amount of water is too small, hydrolysis does not proceed sufficiently, and therefore gelation is not sufficiently performed. The hydrolysis reaction proceeds almost completely when a uniform solution of tetraalkoxylane and water is formed, and thereafter, the hydrolysis reaction may be allowed to stand until the solution gels and integrates.

  The conditions for the hydrolysis reaction and gelation vary depending on the raw materials used, but are usually about 20 minutes to 10 hours under conditions of a temperature of 20 to 100 ° C. and a pressure of normal pressure to 0.2 MPa. Gelation of the hydrolyzate proceeds in several hours even at room temperature and can be accelerated by heating. Therefore, the gelation time can be adjusted by adjusting the temperature conditions.

  In order to facilitate handling in the pulverization process, a coarse pulverization process in which the wet gel is roughly pulverized to a size of several cm may be performed after the hydrolysis reaction. There is no limitation on the method of coarse pulverization. For example, the wet gel in the hydrolysis container after the hydrolysis reaction is placed under reduced pressure to crack the gel, and the hydrolysis container containing the wet gel is rotated or rocked. By doing so, the gel can be pulverized.

<Crushing>
The wet gel obtained by hydrolysis of the above tetraalkoxylane contains by-product alcohol and unreacted water. In order to adjust the particle size of the final product, it is preferable to grind the wet gel at this stage. Here, what grind | pulverized the wet gel is called "grinding wet gel."

  During pulverization, since the wet gel is brittle, fine powder is likely to be generated. Therefore, in order to obtain the synthetic silica glass powder having a particle size of 10 to 1000 μm of the present invention with good yield, the residence time in the pulverizer is shortened and one-pass It is preferable to use a continuous pulverizer. The residence time is preferably within 1 minute, and the type of pulverizer is, for example, a high-speed rotating mill (hammer mill, pulverizer, etc.) of a type in which hammer, blade, pin, etc. are rotated at high speed and pulverized by impact and shear. Is preferably used. In particular, a screen mill in which a screen (perforated plate) for classifying the pulverized material is built in the pulverizer is preferable. The hole diameter of the perforated plate is 0.5 to 5 mm, more preferably 0.8 to 3 mm.

  The range of the final particle size distribution of the synthetic silica glass powder can be adjusted by sieving after firing, but the particle size distribution and median size within the particle size range are the screen pore size and mill rotation speed during wet gel grinding and It is preferable to control by the residence time.

  In addition, in order to reduce or prevent the mixing of metal components during the pulverization operation, use a net-type pulverizer that presses the wet gel against a net-like material made of synthetic resin, for example, and passes the mesh. Can do. Even when this type of pulverizer is used, the mesh size and residence time may be selected in the same manner as described above.

<Dry>
Next, the wet gel after pulverization is dried to remove alcohol and water contained in the gel. The pulverized wet gel is usually dried in a batch system. Here, what dried wet gel is called "dry gel."
The white grains of the present invention are usually produced by this drying process.
Specific drying methods can be exemplified as follows.

  The drying device used when producing the synthetic silica glass powder containing the specific white grains of the present invention is a conical dryer, a rotary dryer or the like, and a drying container having a jacket rotates to roll the powder inside. However, it is preferable that the powder is heated and dried through the inner wall surface of the container by circulating a heating medium such as steam (superheated steam) through the jacket.

As a drying device, for example, a type heated by hot air such as a fluidized bed dryer, a silica layer described later is difficult to form, and a continuous dryer usually has a short residence time in the drying device. Even if the layer is formed, it is often difficult to keep the number of white grains within the specific range of the present application.
As the material for the drying container, it is preferable to use a metal such as stainless steel in order to form white grains and prevent contamination of the wet gel.

  As drying conditions, it is preferable to reduce the pressure inside the container to, for example, about −20 to −95 kPa for promoting drying, and the drying temperature is 50 to 200 ° C., preferably 100 to 150 ° C. It is considered that white grains are generated on the inner wall surface of the drying container during this drying.

  As a white grain generation mechanism, 1 μm-sized silicon dioxide particles in the pulverized wet gel adhere to and deposit on the inner wall of the container, and this is pressed by the rolling gel particles to form a thin plate-like silica layer. Form. It is presumed that this silica layer repeats peeling and growth on the container wall surface, and the peeled portion is pulverized to become white grains and mixed into dried normal particles.

In order to set the white particle content in the synthetic silica glass powder to 1 to 600 / g, particularly 5 to 500 / g, which is within the preferred range of the present application, the amount of gel charged relative to the inner wall area of the drying container is set to On a dry gel basis, usually 1 kg / m ² or more, preferably 20 kg / m ² or more, more preferably 40 kg / m ² or more, usually 150 kg / m ² or less, preferably 100 kg / m ² or less, more preferably 80 kg / m. ^It should be ² or less. By making this charging amount 1 kg / m ² or more, it is possible to prevent the silica layer from being insufficiently formed because the gel charging amount with respect to the capacity of the dryer is extremely reduced, and industrially. It becomes efficient even if it sees. On the other hand, by making the charging amount 150 kg / m ² or less, it is possible to avoid that the drying operation becomes substantially difficult because the charging amount of the pulverized wet gel exceeds 50% of the dryer capacity. In addition, said preparation amount is the weight which represented the weight of the grinding | pulverization wet gel put into the drying apparatus of a drying apparatus at the time of drying with the dry gel base.

  The weight of the crushed wet gel expressed in dry gel base is calculated from the liquid content from the weight of the pulverized wet gel, for example, by measuring the liquid content (water content) of the pulverized wet gel by the loss on drying method. It can be obtained as the weight of the solid content obtained by subtracting the weight of the liquid content contained in the pulverized wet gel.

The residence time in the drying container is preferably 5 to 30 hours.
The rotational speed of the drying container is usually 0.01 m / s or more, preferably 0.05 m / s or more, and usually 5 m / s or less as a peripheral speed in order to form a white particle production / peeling cycle. Preferably it is 0.5 m / s or less. When the peripheral speed is not less than the lower limit of the above range, the tumbling and mixing of the gel becomes sufficient, and the drying time can be shortened. On the other hand, by setting the peripheral speed to be equal to or lower than the upper limit of the above range, it is possible to reduce wear of the wall surface due to the gel, and to prevent the silica layer from stably growing and the gel from being crushed.

  In addition, a certain number of drying batches are necessary before the formation / separation cycle of the silica layer adhering to the inner wall occurs stably, and the white grains reach the range specified in the present application. This is usually after drying about 3-4 batches. On the other hand, if the drying is repeated for a long period of time, the silica layer is firmly fixed and difficult to peel off. Usually, once in 50 to 200 batches, an alkaline aqueous solution such as an aqueous sodium hydroxide solution is charged into the dryer to form a silica layer. Is preferably dissolved and removed.

  The gel after drying (dry gel) is washed with pure water as necessary to remove the solvent and catalyst used for hydrolysis, and organic components derived from the alkoxy groups generated by hydrolysis. Can do.

  In order to facilitate the handling of the gel during the baking treatment, and for the purpose of suitably adjusting the final particle size distribution range by classification after the baking treatment, the dry gel is preliminarily applied after the drying treatment as necessary. You may classify them.

<Baking>
Since the dried dry gel is generally porous, it is not suitable as a raw material for forming a glass layer such as a crucible. Therefore, the obtained dry gel is preferably heated and fired to be densified to obtain a nonporous synthetic silica glass powder.

  The method of firing is not particularly limited, but in order to keep the purity as a synthetic silica glass powder high, it is possible to fill a quartz crucible with the powder and heat it in air or an inert gas atmosphere as necessary. preferable. The firing temperature is usually 1000 to 1300 ° C., and the firing time is generally about 10 to 100 hours.

  Since the silanol group concentration decreases as the firing time is lengthened, the firing temperature and time are adjusted according to the target concentration. In the firing step, the white particles are formed by agglomerating the fine silica particles from the initial aggregate of fine silica particles into one particle by sintering. At this time, although pores in individual fine silica particles disappear by firing, it is considered that voids between the original aggregated particles remain after firing to form white bubbles.

<Classification>
Synthetic silica glass powder containing a specific amount of white grains obtained through the drying and firing processes described above may be used as it is, but if necessary, it is classified by a sieve, an air classifier, etc. Is preferably adjusted. Classification can be performed using a screen having a pore size corresponding to an upper limit and a lower limit of a desired particle size of the synthetic silica glass powder.

  In addition, the manufacturing method based on the synthetic silica glass powder and the estimation mechanism of white grain formation described above is an example, and is not limited to this manufacturing method. For example, silica particles having a size of about submicron are granulated and fired as raw materials. It is also possible to separately manufacture only white grains and then mix a desired amount with normal particles.

[5. effect]
When the synthetic silica glass powder of the present invention is used, bubbles can be generated in the fused silica glass layer. Moreover, it is possible to generate a bubble in a desired location by including the synthetic silica glass powder of the present invention in a specific location.

  According to the method for producing a synthetic silica glass powder of the present invention, a synthetic silica glass powder containing white grains can be produced, and the amount of bubbles generated (number of occurrences) in the fused silica glass layer is suitable. A synthetic silica glass powder having the number of white grains and the silanol group concentration can be obtained.

  Furthermore, when the crucible is manufactured using the synthetic silica glass powder of the present invention, it is possible to generate bubbles at a site containing the synthetic silica glass powder of the present invention. It is possible to keep the used part at the same high purity as the raw silica. Thereby, for example, when the synthetic silica glass powder of the present invention is used for forming the inner surface of the crucible, it is possible to generate bubbles at a specific site without reducing the purity of the inner surface of the crucible.

[6. Quartz crucible for silicon single crystal pulling]
The synthetic silica glass powder of the present invention can be applied to a quartz crucible for pulling a silicon single crystal. A silica crucible for pulling a silicon single crystal having bubbles in the silica glass layer can be obtained by melting the silica glass powder during the production of the crucible using the synthetic silica glass powder containing white grains of the present invention.

  A quartz crucible for pulling a silicon single crystal is used, for example, for pulling a single crystal of silicon by the Czochralski method, and is used as a container for molten silicon in which polycrystalline silicon is put and heated and melted. .

  The synthetic silica glass powder of the present invention may be used for the whole (all parts) of the quartz crucible for pulling up the silicon single crystal, but in order to generate bubbles in a specific part of the quartz crucible for pulling up the silicon single crystal, The silica glass powder may be melted after filling the specific portion with the synthetic silica glass powder of the present invention together with the conventional raw silica glass powder not containing particles. The site where the synthetic silica glass powder of the present invention is used in a quartz crucible for pulling up a silicon single crystal is not particularly limited, and may be used as an inner layer of the inner surface of a crucible in contact with molten silicon, and heated by a heater. It may be used as an outer layer on the outer surface of the inner layer, may be used as an intermediate layer between the inner layer and the outer layer, or may be used at a specific position in each layer.

  When producing a quartz crucible for pulling up a silicon single crystal, bubbles can be formed at a desired site by partially using the synthetic silica glass powder of the present invention containing white grains. Thereby, the function according to the site | part where a bubble exists can be provided to the quartz crucible for silicon single crystal pulling, and the quartz crucible which can manufacture the silicon single crystal of the higher quality can be manufactured.

As an example, when filling the raw material silica glass powder on the inner surface of the mold, the synthetic silica glass powder of the present invention is filled at a position corresponding to the portion of the inner surface of the crucible that is in contact with the silicon melt surface. The powder can be melted. As a result, by containing bubbles on the inner surface of the inner surface of the crucible, which is the surface of the silicon melt, it is possible to suppress the surface vibration of the silicon melt compared to a crucible manufactured from a conventional synthetic silica glass powder. Can be expected.
Or when laminating and filling a plurality of silica glass powders containing conventional raw silica glass powder, the silica glass powder can be melted by laminating the synthetic silica glass powder of the present invention on the intermediate layer of the crucible. . Thereby, by having bubbles in the intermediate layer inside the crucible wall surface, compared to the conventional crucible having a two-layer structure in which the inner surface is a transparent glass layer and the outer surface is a bubble-containing layer, the external radiant heat during crucible heating is dispersed, Reduction of temperature unevenness of silicon melt can be expected.

[Measurement method of particle diameter and median diameter]
The particle diameter and median diameter of the synthetic silica glass powder were measured by a laser diffraction scattering method using a particle size distribution measuring device (Leeds & [Northrup, Microtrac FRA 9220). The particle diameter corresponding to 50% of the cumulative particle size distribution of the synthetic silica glass powder was defined as the median diameter.

[Method of measuring silanol group concentration]
The content of silanol groups in the synthetic silica glass powder is measured by using an infrared spectrophotometer (manufactured by JASCO, Fourier transform infrared spectrophotometer FT / IR-4100typeA) as the silanol group concentration. Was measured by measuring the peak height at a wave number of 3670 cm ⁻¹ after filling the void in the cell with carbon tetrachloride.

[Method of measuring the number of white grains]
The number of white particles of the synthetic silica glass powder is the above [3. It was measured by the immersion liquid transmission method described in “Detecting and Counting White Grains”.

<Production Example> Production of Synthetic Silica Glass Powder A stainless steel jacketed conical reactor with a capacity of 750 liters was charged with 180 kg of tetramethoxysilane and 106 kg of ultrapure water (5-fold molar amount), and hot water at 47 ° C. was added to the jacket. The reaction was carried out while rotating the reactor at a rotation speed of 6 rpm. When the internal temperature reached 80 ° C., the rotation was stopped and the gelation was allowed to proceed for 30 minutes. Thereafter, the inside of the reactor was decompressed to crack the gel and rotated again for 15 minutes to coarsely pulverize the gel to a size of several centimeters in the reactor.

This coarsely pulverized wet gel was taken out from the reactor, and then, using a high-speed rotating mill type pulverizer (Quadro, Comil (trade name)) having a mortar-shaped screen with a hole diameter of 1 mm and an anchor type blade inside. The coarsely pulverized wet gel was continuously pulverized to obtain a pulverized wet gel having a size of 1 mm or less. The liquid content of this gel was measured by the loss on drying method and found to be 69%. The remaining 31% is silica gel. (Hereinafter, this pulverized wet gel is referred to as “raw material wet gel”.)
This hydrolysis reaction and pulverization were repeated to produce a total of 1500 kg of raw material wet gel.

Subsequently, this raw material wet gel was placed in a 3000 liter stainless steel jacketed conical dryer (inner wall area 10.1 m ² ), which was previously dissolved and washed with a sodium hydroxide aqueous solution to remove the silica layer on the inner wall surface of the apparatus. 1420 kg was charged. At this time, the amount of silica gel in the raw material wet gel with respect to the inner wall area of the dry container (that is, the amount of raw material wet gel charged in the dry gel base) (hereinafter also referred to as “dry gel / inner wall area”) = 44 kg / m ² .

  Superheated steam is passed through the jacket of the dryer and dried at a reduced pressure of -90 kPa while rotating at a rotation speed of 1 rpm (peripheral speed = 0.16 m / s). When the gel temperature reaches 135 ° C, heating is stopped. Then, the pressure inside the dryer was restored.

  Next, 1000 L of ultrapure water was supplied to the dryer, and the apparatus was rotated for 10 minutes for washing, and then the aqueous phase portion above the gel was discharged out of the dryer. This washing of the gel with ultrapure water was further repeated twice.

  Thereafter, superheated steam was passed again through the jacket of the dryer, and drying was performed under reduced pressure while rotating at a rotation speed of 2 rpm. When the gel temperature reached 130 ° C., heating was stopped and the interior of the dryer was restored. The dry gel in the dryer was taken out and classified using screens of 125 μm and 630 μm to obtain 260 kg of dry gel having a particle size of 125 to 630 μm.

Next, this dry gel was baked as follows.
A quartz crucible having a capacity of 1 liter was charged with 800 g of dry gel, and the crucible was set in an electric furnace. Thereafter, the crucible was covered with a quartz disk having a hole in the center, and the quartz tube was inserted into the gel powder layer through the hole in the lid. Heating was performed while blowing dry air through the tube into the gel powder layer, and the gel powder layer was maintained at 1220 ° C. for 30 hours. After cooling, the fired gel was classified using screens of 100 μm and 450 μm to obtain synthetic silica glass powder having a particle size of 100 to 450 μm. As a result of measuring the particle size distribution, the median diameter was 190 μm. Moreover, when the silanol group density | concentration was measured, it was 48 ppm (weight ppm, hereafter the same).

  When the number of white grains of the obtained synthetic silica glass powder was measured, it was 1 / g. This indicates that the amount of white particles of the synthetic silica glass powder obtained in the first batch when a conical dryer is used is small.

<Reference example> Manufacture of synthetic silica glass powder without white grains ("silica powder A") 5 kg of raw material wet gel obtained in the above manufacturing example was separated into quartz bats, and left standing in a shelf-type vacuum dryer. did. The dried gel was transferred to a 5 liter beaker, and washed with ultrapure water and the supernatant aqueous phase separation was repeated three times in the same manner as in the above production example, and then dried again by standing.

The obtained dry gel was subjected to the operation of “classification-firing-classification” in the same manner as in the above production example, to obtain 600 g of synthetic silica glass powder. When the number of white grains was measured, no white grains were contained at 0 / g. Further, when the particle diameter, median diameter, and silanol group concentration of the obtained synthetic silica glass powder were measured, the particle diameter was 100 to 450 μm, the median diameter was 190 μm, and the median diameter was 48 ppm, as in the above production example.
Hereinafter, this synthetic silica glass powder not containing white grains is referred to as “silica powder A”.

<Example 1>
In the above production example, from the state where the inner wall surface of the dryer is clean, the raw material wet gel is dried continuously for 5 batches in the same manner as in the above production example without dissolving and removing the silica layer. The obtained dry gel was fired to produce a synthetic silica glass powder.

  When the particle diameter, median diameter, and silanol group concentration of the obtained synthetic quartz glass powder were measured, the particle diameter was 100 to 450 μm, the median diameter was 190 μm, and the silanol group concentration was 48 ppm as in the above production example. Moreover, it was 53 pieces / g when the number of contained white grains was measured.

  The white grains were picked up visually and subjected to elemental analysis with SEM / EDX (scanning electron microscope-energy dispersive X-ray spectroscopy). As a result, only silicon and oxygen were detected, and the white grains were highly pure silica. It was confirmed that. Further, when the white grains were divided with tweezers and the cross section was observed with an SEM, many holes having a size of 1 μm or less were present inside. Also, carbon tetrachloride (density 1.58 g / ml) and dibromomethane (density 2.48 g / ml) were mixed to prepare a solution (heavy liquid) with a density of 2.116 g / ml, and the white grains picked up As a result, all white grains floated on the surface of the heavy liquid, and it was confirmed that the density of white grains was lower than 2.2 g / ml of pure silica.

<Example 2>
Drying operations were carried out continuously for 5 batches in the same manner as in Example 1 except that the weight of the ground wet gel charged into the dryer was set to dry gel / inner wall area = 20 kg / m ² . A synthetic silica glass powder was produced by firing using the fifth batch of dry gel.

  When the number of white grains of the obtained synthetic silica glass powder was measured, it was 106 / g. Further, when the particle diameter, median diameter, and silanol group concentration of the obtained synthetic quartz glass powder were measured, the particle diameter was 100 to 450 μm, the median diameter was 190 μm, and the silanol group concentration was 48 ppm, as in the above production example. .

<Example 3>
In Example 2, the weight of charged wet gel in the dryer was set to dry gel / inner wall area = 10 kg / m ^2, and the dry gel of the fifth batch was similarly fired to produce a synthetic silica glass powder.

  When the number of white grains of the obtained synthetic silica glass powder was measured, it was 206 / g. Further, when the particle diameter, median diameter, and silanol group concentration of the obtained synthetic quartz glass powder were measured, the particle diameter was 100 to 450 μm, the median diameter was 190 μm, and the silanol group concentration was 48 ppm, as in the above production example. .

  The results are shown in Table 1. In addition, when the particle diameter, median diameter, and silanol concentration of the synthetic quartz silica glass powder of Examples 2 and 3 in Table 1 were measured, the particle diameter was 100 to 450 μm, the median diameter was 190 μm, as in the above production example, The silanol group concentration was 48 ppm. It can be seen from Table 1 that the number of white grains can be controlled by the amount of pulverized wet gel charged into the dryer.

[Method for measuring the number of bubbles in molten glass]
The silica powder A45g produced in the above reference example is weighed into a graphite crucible with a capacity of 50 cc, and the surface is flattened by tapping, and then a 2 g sample of the synthetic quartz silica glass powder to be measured is uniformly dispersed on the surface. Let

  The graphite crucible is heated at 1780 ° C. for 1 hour in a vacuum heating furnace and then cooled to obtain a cylindrical silica fused glass ingot. Bubbles in the obtained ingot were observed using a loupe, and the diameter was 0.1 mm or less in the surface layer (the layer derived from the dispersed synthetic quartz glass sample) formed on the transparent glass layer without bubbles. The number of bubbles is counted (unit: “pieces / g · sample”). It is considered that these bubbles are derived from water (water vapor) generated by dehydration condensation of white grains and silanol groups.

<Example 4>
White grains were picked up from the synthetic silica glass powder of Example 1 and added to the silica powder A to prepare a synthetic silica glass powder with 7 white grains / g. With respect to this glass powder, the number of bubbles was measured according to the above-described measurement method, and the number of bubbles having a diameter of 0.1 mm or less was 13 / g.

<Example 5>
In the same manner as in Example 4, a synthetic silica glass powder having the number of white grains = 22 / g was prepared and the number of bubbles was measured. As a result, the number of bubbles having a diameter of 0.1 mm or less was 44 / g.

<Example 6>
When the number of bubbles of the synthetic silica glass powder obtained in Example 1 was measured by the above method, the number of bubbles having a diameter of 0.1 mm or less was 105 / g.

<Examples 7 and 8>
The number of bubbles of the synthetic silica glass powder obtained in Examples 2 and 3 was measured in the same manner. The number of bubbles having a diameter of 0.1 mm or less was 203 and 398 / g, respectively.

<Example 9>
In the same manner as in Example 4, a synthetic silica glass powder having the number of white grains = 502 / g was prepared and the number of bubbles was measured. As a result, the number of bubbles having a diameter of 0.1 mm or less was 960 / g.

<Comparative Example 1>
The number of bubbles was measured using silica powder A (white particle content: 0 / g) as the silica powder dispersed and dispersed on the surface. No bubbles were observed in the surface layer, and the obtained ingot was transparent with no bubbles.

<Comparative Examples 2 and 3>
In the same manner as in Example 4, synthetic silica glass powder having white particles of 610 / g and 690 / g was prepared and the number of bubbles was measured. As a result, a large number of huge bubbles with a diameter of 1 mm or more were generated. The measurement was difficult.

  The results of Examples 4 to 9 and Comparative Examples 1 to 3 are summarized in Table 2. It can be seen that white grains are the cause of bubbles, and the number of bubbles can be controlled by the amount of white grains. It can also be seen that when the number of white grains exceeds 600 / g, giant bubbles having a diameter of 1 mm or more are generated.

  In addition, when the particle diameter and median diameter of the synthetic silica glass powder were measured for Examples 4 to 9 and Comparative Examples 1 to 3 shown in Table 2, the particle diameter was 100 to 450 μm and the median diameter was 190 μm as in the above production example. there were.

<Examples 10 to 14, Comparative Example 4>
Six types of synthetic silica glass powders (Examples 10 to 14 and Comparative Example 4) each having a silanol group concentration different from 10 ppm to 315 ppm were produced by changing the baking time of the dry gel in Example 1. The number of each white grain was 53 pieces / g, and there was no difference.

When the number of bubbles was measured by the above method, it was as shown in Table 3. The higher the silanol group concentration, the greater the number of bubbles.
In addition, when the particle diameter and median diameter of the synthetic silica glass powder used here were measured, the particle diameter was 100 to 450 μm and the median diameter was 190 μm as in the above production example.

Claims (7)

Ranges having a particle diameter of 10 to 1000 [mu] m, a synthetic silica glass powder which is a median diameter of 50-700 .mu.m, comprises the synthetic silica glass powder in the silica white particles child 1-600 pieces / g, and silanol A synthetic silica glass powder having a group concentration of 5 to 200 ppm by weight. 2. The synthetic silica glass powder according to claim 1, wherein the number of white silica particles is 5 to 500 particles / g.   3. The method for producing a synthetic silica glass powder according to claim 1, wherein the production is performed by a sol-gel method using alkoxysilane as a raw material. Wherein the sol-gel method, after pulverizing the wet gel to produce said alkoxysilane is hydrolyzed, which was dried with a dryer of the crushed wet gel batchwise, calcining the gel obtained after drying The method for producing a synthetic silica glass powder according to claim 3, wherein: Method for producing a synthetic silica glass powder according to claim 4, wherein the batch dryer is container rotating. The synthetic silica glass powder according to claim 5, wherein the charged amount of the pulverized wet gel with respect to the inner wall area of the drying container of the batch dryer is 1 to 150 kg / m ² on a dry gel basis. Production method. The method according to claim 1 or 2 for pulling up a silicon single crystal quartz crucible, characterized in that there use a synthetic silica glass powder as a starting material according to.

Images