JPH0761856B2 - Method for producing silicon dioxide powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a high-purity silicon dioxide powder that can be suitably used as a filler for a VLSI encapsulating material such as 4M-DRAM.

2. Description of the Related Art In recent years, an epoxy composition in which a large amount of silicon dioxide (silica) powder is filled in an epoxy resin is used as a VLSI sealing material.

However, some silica powder contains a large amount of radioactive elements such as uranium and thorium. Therefore, if the memory is sealed with an epoxy resin composition produced using this type of silica powder, the memory will be affected by alpha rays. There is a problem that it malfunctions. Therefore, conventionally, many methods for producing such silica powder containing no radioactive element have been proposed as follows.

For example, JP-A-60-81011 discloses a method for producing high-purity fused silica from natural high-purity quartz, and JP-A-61-190556 discloses a sol prepared from a high-purity silicon compound as a raw material. -Gel method, or a method for producing high-purity silica by hydrolysis / thermal oxidation, JP-A-58-168267 discloses a method for highly purifying natural high-purity silica by chemical treatment, and JP-A-60-168267 Japanese Patent Publication No. 42217-A discloses a method of producing high-purity silica by treating water glass as a raw material with an ion exchange resin, and then gelling and baking the raw material.

However, the following two types of high-purity silica production processes are currently in practical use.

[Sol-gel method]

Alkoxysilane → reaction step → gelation → drying → firing → pulverization [water glass method] water glass → reaction step → purification → gelling → drying → firing → pulverization Therefore, any method for producing high-purity silica powder is Since it involves a very complicated process, it requires a lot of man-hours and has a drawback that the operation is troublesome.

Further, in order to reduce the content of radioactive elements such as uranium in the silica powder, the raw material itself must be purified, so that the commercially available high-purity silica powder becomes very expensive. There was also the problem of being lost.

Therefore, it has been desired to develop an industrially advantageous method for producing high-purity silica powder.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for producing a silicon dioxide powder, which can inexpensively and easily produce a highly pure silica powder having a low content of radioactive elements. To aim.

Means and Actions for Solving the Problems The present inventor has conducted extensive studies in order to achieve the above-mentioned object, and after washing the metal silicon powder with an aqueous solution of mineral acid, the contents of uranium and thorium were each set to 1 ppb or less. By supplying this metallic silicon powder into an air stream containing oxygen and burning it, uranium and uranium with an average particle diameter of 0.01 to 10 microns can be easily obtained by a one-step method from an inexpensive raw material of metallic silicon powder washed with a mineral acid aqueous solution. A high-purity silicon dioxide powder having a thorium content of 0.5 ppb or less can be produced, and the silicon dioxide powder obtained by such a method is an epoxy resin composition synthesized by using this as a filler. Even if the memory is sealed with, there is no problem that the memory malfunctions due to alpha rays, and cutting-edge VLSI such as 4M-DRAM
It was found that it is the most suitable as a filler for the encapsulating material, and is therefore extremely useful in the field of the semiconductor industry, etc., and has completed the present invention.

Therefore, according to the present invention, the metal silicon powder is washed with an aqueous solution of mineral acid so that the uranium and thorium contents are each 1 ppb or less, and then the metal silicon powder is supplied into an air stream containing oxygen and burned to obtain an average particle size. And a uranium and thorium content of 0.5 ppb or less, respectively, for producing a high-purity silicon dioxide powder.

Hereinafter, the present invention will be described in more detail.

In the method for producing silicon dioxide powder (hereinafter referred to as silica powder) of the present invention, metal silicon powder is used as a starting material, and the metal silicon powder is washed with a mineral acid aqueous solution. In general, metallic silicon powder contains, in addition to iron, calcium, aluminum, magnesium, etc., radioactive elements such as uranium and thorium in an amount of about 5 to 15 ppb. When silica powder is manufactured using such metallic silicon powder as a raw material. Since silica powder contains uranium or thorium in an amount of about 2 to 10 ppb, it cannot be used as a filler for a sealing material for highly integrated ICs. However, in the present invention, metallic silicon powder should be washed with a mineral acid aqueous solution in advance. By this, the radioactive element in the metallic silicon powder can be sufficiently removed, and the uranium and thorium contents can each be reduced to 1 ppb or less.

Here, as the metallic silicon powder used as a raw material,
Any material may be used as long as the quality is 99.5% or more.

Further, the metallic silicon powder should be crushed beforehand with a ball mill, impact crusher, etc. in order to improve the cleaning efficiency with a mineral acid aqueous solution, to obtain a powder having a maximum particle size of 200 microns or less and an average particle size of 1 to 50 microns. In particular, in consideration of the combustion step, which is the next step, it is more preferable that the metal silicon powder has a maximum particle size of 100 μm or less and an average particle size of 1 to 30 μm.

As the aqueous solution of mineral acid, for example, an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid or the like is preferably used, and a mixed aqueous solution of these mineral acids may be used. Of these mineral acid aqueous solutions, nitric acid aqueous solutions are preferable. This is because even if nitric acid remains in the metallic silicon, it is exposed to a high temperature in the next combustion step and is oxidized and volatilized.

Furthermore, the acid concentration of the mineral acid aqueous solution is preferably 0.1 normal or more and 5 normal or less, and if it is less than 0.1 normal, radioactive elements such as uranium may not be removed. The powder yield may decrease.

In this case, the washing of the metallic silicon powder with the aqueous solution of mineral acid may be carried out by mixing the metallic silicon powder and the aqueous solution of the mineral acid at room temperature for reaction removal, but in order to remove radioactive elements efficiently with a low concentration of mineral acid. It is better to mix and stir at 50 ° C or higher to react. Although the reaction time depends on the temperature and the concentration of the metal silicon powder, the radioactive element in the metal silicon powder can be reduced to 1 ppb or less in 1 to 20 hours.

After treating the metallic silicon powder with the mineral acid aqueous solution, remove the mineral acid aqueous solution with a centrifuge or filtration, and then wash with ion-exchanged water or pure water. High-purity metallic silicon powder having a uranium and thorium content of 1 ppb or less can be obtained by a method such as drying with a dryer such as a dryer.

Next, in the present invention, the metal silicon powder thus obtained is supplied into an air stream containing oxygen and burned to directly produce silica powder.

Here, as the air flow containing oxygen, oxygen gas is usually used, but in some cases air can also be used.

The supply amount of the high-purity metallic silicon powder into the air flow containing oxygen is not particularly limited, but is substantially determined by the volume of the reaction chamber, and is usually 5 to 20 kg / hr, preferably 7 to It is 15 kg / hr.

In this case, combustion is started by supplying high-purity metallic silicon powder into an air stream containing oxygen and igniting it by an ignition source. When the metallic silicon powder is supplied into an air stream containing oxygen and burned in this way, the reaction flame has a temperature exceeding 2000 ° C. At such a high temperature, the element or compound having a low boiling point volatilizes preferentially. That is, compounds of uranium and thorium, which are slightly contained in the highly purified metal silicon powder, are also gasified at high temperature, and the silica powder formed by oxidizing the metal silicon powder is cooled to become a solid from a liquid. At this time, the compound of the radioactive element such as the above-mentioned volatile uranium compound is discharged and separated together with the gas without penetrating into the bulk of the silica particles, and in the method of the present invention, high purity is achieved even in this combustion step. Can be changed. In the present invention, in this combustion step, it is desirable to increase the amount of gas in or after the reaction flame so that the volatilized radioactive element compound is discharged together with the gas. This makes it possible to further reduce the amount of radioactive element attached to the obtained silica powder.

Effects of the Invention According to the production method of the present invention, it is possible to arbitrarily produce 0.01-10 micron spherical silica powder by a one-step method, using an inexpensive raw material called metallic silicon powder washed with a mineral acid aqueous solution. The high-purity silica powder can be produced industrially advantageously at low cost by a simple operation.

Therefore, the high-purity silica powder obtained by the production method of the present invention is extremely useful for the semiconductor industry and the like. For example, the obtained silica powders of various particle sizes can be combined and mixed so as to form a close-packed structure, and can be used as a filler such as an epoxy resin or a silicone resin. Such a composition is 4M-DRAM. It is most suitable as a sealing material for cutting-edge VLSI such as, and does not cause soft error and has low linear expansion. Further, it can be used more widely by using it together with a high-purity silica powder obtained by ordinary pulverization.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 4 and Comparative Example] Metallic silicon powder raw materials shown in Table 1 were washed with a mineral acid aqueous solution under the conditions shown in Table 1, and the metallic silicon powder was introduced into the apparatus shown in the drawings to produce silica.

Here, this apparatus is provided with a reaction vessel 1 having a reaction chamber 10, a combustor 2 provided on the upper side of the reaction vessel 1 and communicating with an upper portion of the reaction chamber 10, and a side of the reaction vessel 1, 10 A collection device 3 in communication with the lower part, a hopper 4 into which the metallic silicon powder washed with the mineral acid is put, and a powder supply device 5 for supplying the powder in the hopper 4 to the combustor 2. ing.

As shown in the enlarged view of FIG. 2, the combustor 2 is provided in the central portion, and is provided with a powder supply passage 20 that opens into the reaction chamber 10 and coaxially with the powder supply passage 20. A first oxygen supply path 21 opening in a ring shape, and a first L provided coaxially outside the first oxygen supply path 21 and opening in a ring shape in the reaction chamber 10.
The PG supply passage 2 and the first LPG supply passage 22 are coaxially provided outside the cooling water passage 23, and the cooling water passage 23 is provided coaxially outside the cooling water passage 23. A second LPG supply path 24 that opens in a ring shape in 10 and a second LPG supply path that is provided coaxially outside the second LPG supply path 24 and opens in a ring shape in the reaction chamber 10.
It is composed of an oxygen supply path 25.

Here, the metal silicon powder (B) sent from the hopper 4 through the powder supply device 5 is supplied from the powder supply path 20 together with the air (C). In this case, the air supply rate is ³ to 4 Nm ³ / hr, and the metal silicon powder supply rate is 6 to 7 kg.
/ hr. Further, from the first oxygen supply amount 21 and the second oxygen supply passage 25, oxygen gas (D) is supplied into the reaction chamber 10 by 17%, respectively.
Fed at a feed rate of Nm ³ / hr and 10 Nm ³ / hr. Also, the first L
From PG supply path 22 and the 2LPG supply passage 24 LPG (E) is supplied at a feed rate of each 1.5 Nm ³ / hr and 1.0 Nm ³ / hr.

In addition, the collecting device 3 has an exhaust pipe whose one end opens into the reaction chamber 10.
30 and a bag filter provided at the other end of the exhaust pipe 30
31 and a blower 32, the exhaust gas in the reaction chamber 10 is sucked and exhausted by driving the blower 32, and the generated silica powder (F) is collected. The suction of the blower 32 keeps the inside of the reaction chamber 10 at a negative pressure of 5 to 10 mmAq.

Using the apparatus configured as described above, a predetermined amount of oxygen gas and LPG was allowed to flow into the reaction chamber, and after forming an ignition flame,
Metal silicon powder was ejected from the powder supply passage 20 into the flame to form a reaction flame. Thereby, the metallic silicon powder was oxidized to form silica powder. The silica powder collected in the bag filter 31 was sampled to measure its particle size and radioactive element content. The measurement results are shown in Table 1.

From the results in Table 1, it was confirmed that according to the production method of the present invention (Examples 1 to 4), it is possible to obtain a high-purity silica powder having a uranium and thorium content of each radioactive element of 0.5 ppb or less. It was

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view of a silica manufacturing apparatus used in a manufacturing method according to an embodiment of the present invention, and FIG. 1 ... Reactor container, 2 ... Combustor 3 ... Collection device, 4 ... Hopper 5 ... Powder supply device, 20 ... Powder supply path 21,25 ... Oxygen supply unit 22, 24 ... LPG supply Channel 23 ... Cooling water channel

Claims (1)

[Claims] 1. A metal silicon powder is washed with an aqueous solution of mineral acid to reduce the uranium and thorium contents to 1 ppb or less, and then the metal silicon powder is supplied into an air stream containing oxygen and burned to obtain an average particle size. A method for producing a silicon dioxide powder, characterized in that a high-purity silicon dioxide powder having a uranium and thorium content of 0.01 to 10 microns and a uranium and thorium content of 0.5 ppb or less is produced.