JPH0761855B2 - Method for producing silicon dioxide powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silicon dioxide (hereinafter referred to as silica) powder. The silica powder obtained by the manufacturing method of the present invention can be used as a sealing material for the latest VLSI such as 4M-DRAM.

[Prior Art] In recent years, use of a composition in which a large amount of silica powder is filled in an epoxy resin has been studied as a sealing material for VLSI. However, when the silica powder used contains impurities, particularly radioactive elements such as uranium and thorium, there is a problem in that the memory element malfunctions due to α rays. Therefore, many methods for producing such a silica containing no radioactive element have been proposed.

For example, JP-A-60-81011 discloses a method for producing high-purity fused silica using natural high-purity quartz as a raw material. Further, Japanese Patent Laid-Open No. 61-190556 discloses a method of producing high-purity silica by a sol-gel method or hydrolysis and thermal oxidation using a high-purity silicon compound as a raw material. Further, JP-A-58-168267 discloses that
A method for highly purifying natural high-purity silica by chemical treatment is disclosed. Further, in JP-A-60-42217,
There is disclosed a method for producing high-purity silica by treating water glass as a raw material with an ion exchange resin, and then gelling and baking the same.

[Problems to be Solved by the Invention] The above-described conventional method for producing high-purity silica having an extremely small content of radioactive elements involves extremely complicated steps and requires a large number of steps. Further, in order to produce high-purity silica having a uranium content of 0.5 ppb or less, the raw material itself must be purified. For these reasons, high-purity silica that has hitherto been commercially available is very expensive. In addition, it has been difficult to freely control the particle size of the high-purity silica obtained by the above-mentioned conventional production method by a method other than the spherical silica produced by the sol-gel method.

The present invention has been made in view of such circumstances,
The purpose is to easily produce a high-purity silica powder having a low content of radioactive elements.

[Means and Actions for Solving the Problems] In the method for producing silica powder of the present invention, an average particle size of 0.01 to 10 μm is obtained by supplying metallic silicon powder into an air stream containing oxygen and burning it.
And a washing step of washing the silica powder to remove the radioactive element compound adhering to the surface.

In the burning step, metallic silicon powder is supplied into a stream containing oxygen,
This is the step of burning. The particle size of the metallic silicon powder is not particularly limited, but usually about 10 to 50 μm is suitable.
As the air flow containing oxygen, oxygen gas is usually used, but air may be used depending on the case. Then, the metallic silicon powder is supplied into an air flow containing oxygen and ignited by an ignition source, whereby combustion is started.

When such a metallic silicon powder is supplied into an air stream containing oxygen and burned, 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 radioactive elements such as uranium compounds and thorium compounds have a high vapor pressure at a relatively low temperature, and therefore are in a gasified state by volatilizing in a reaction flame. Then, when the silica formed by oxidizing the metallic silicon powder is cooled and becomes a solid from a liquid, the compounds of radioactive elements such as volatile uranium compounds adhere to the surface of the particles without penetrating into the bulk of the silica particles. Or is discharged together with the gas and separated. Therefore, in this combustion process, 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 compound attached to the silica powder obtained.

The washing step is a step of washing the silica powder obtained by the burning step to remove the radioactive element compound from the surface.
As described above, the radioactive element compound does not penetrate into the bulk of the silica powder, and most of the compound adheres to the surface. Therefore, the compound of the radioactive element adhering to the silica powder surface can be easily removed by washing with a suitable solvent. As the solvent, a low-concentration aqueous solution of mineral acid such as an aqueous solution of nitric acid can be used.

[Effects of the Invention] According to the production method of the present invention, spherical silica powder having an average particle size of 0.01 to 10 µm can be arbitrarily produced by a one-step method using an inexpensive raw material of metallic silicon. Further, by washing the obtained silica powder with a low-concentration aqueous solution of mineral acid or the like, high-purity silica powder having an extremely small content of radioactive elements can be obtained.

Therefore, the high-purity silica powder obtained by the production method of the present invention becomes extremely inexpensive and extremely useful for the semiconductor industry and the like. For example, the obtained silica powders having various particle sizes can be combined and mixed so as to have a close-packed structure, and used as a filler such as an epoxy resin or a silicone resin. Such a composition is most suitable as an encapsulant for a cutting-edge VLSI such as 4M-DRAM, does not cause a soft error, and has a low linear expansion. Further, when it is used together with sealing with an epoxy resin or the like, it is also characterized in that the composition can have a low viscosity or a filler can be highly filled. Then, by filling a silica resin having a particle size of 1 μm or less into a polyimide resin or the like for chip coating, it is possible to easily control the film thickness.

[Examples] Specific examples will be described below.

FIG. 1 shows a schematic configuration explanatory view of a manufacturing apparatus used for carrying out the manufacturing method of one embodiment of the present invention. This manufacturing apparatus includes a reaction container 1 having a reaction chamber 10, a combustor 2 provided at an upper portion of the reaction container 1 and opening to the reaction chamber 10, and a capture chamber provided at a lower side wall of the reaction container 1 and communicating with the reaction chamber 10. Collection device 3
And the hopper 4 and the raw material powder in the hopper 4 to the combustor 2
And a powder supply device 5 for supplying the powder.

The combustor 2, as shown in an enlarged view in FIG. 2, has a powder supply passage 20 provided at the center and opened to the reaction chamber 10, and a powder supply passage 20.
A ring-shaped opening that is provided coaxially with the reaction chamber 10
An oxygen supply passage 21 and a first LPG supply passage 22 coaxially provided outside the first oxygen supply passage 21 and opening in a ring shape in the reaction chamber 10.
A cooling water passage 23 coaxially provided outside the first LPG supply passage 22 for circulating cooling water, and a second LPG supply coaxially provided outside the cooling water passage 23 and opening in a ring shape in the reaction chamber 10. Road
24 and the reaction chamber provided coaxially outside the second LPG supply path 24.
It is composed of a second oxygen supply passage 25 that opens in a ring shape at 10.

From the powder supply path 20, metallic silicon powder is supplied together with nitrogen gas. Here, the supply amount of nitrogen gas is 4 Nm ³ / hr,
The supply amount of metallic silicon powder is 6 to 7 kg / hr. From the first oxygen supply passage 21 and the second oxygen supply path 25, oxygen gas is supplied to the supply amount of each 17 Nm ³ / hr and 10 Nm ³ / hr into the reaction chamber 10. In addition, LP is supplied from the first LPG supply path 22 and the second LPG supply path 24.
G is supplied at a supply rate of 1.5 Nm ³ / hr and 1.0 Nm ³ / hr, respectively.

The collection device 3 includes an exhaust pipe 30 opening to the reaction chamber 10 and an exhaust pipe.
It is composed of a dust collector 31 provided at the other end of 30 and a blower 32. By driving the blower 32, the combustion exhaust gas in the reaction chamber 10 is sucked and exhausted, and the generated silica powder is collected. By suction of the blower 32, the inside of the reaction chamber 10 is 5-10
It is maintained at a negative pressure of mmAq.

Metallic silicon powder pulverized to an average particle size of about 12 μm is put into the hopper 4, and the powder supply device 5 supplies a powder supply path.
Sent to 20.

[Combustion process] A predetermined amount of oxygen gas and LPG are caused to flow into the reaction chamber to form an ignition flame. Then, metallic silicon powder is ejected from the combustion supply passage 20 into the flame to form a reaction flame. As a result, the metallic silicon powder is oxidized to form silica powder. When the silica powder collected in the dust collector 31 was sampled and the particle size thereof was measured, the average particle size was 0.3 to 0.5 μm. Moreover, when the uranium analysis was performed by the fluorometric method, the obtained silica powder contained 3 ppb of uranium.

[Washing Step] 5 g of the silica powder obtained in the burning step was placed in a beaker, 50 ml of a 1N nitric acid aqueous solution was added, and the mixture was heated and mixed at 70 ° C. for 1 hour and 30 minutes. Thereafter, the silica powder was separated by filtration, washed with pure water, and dried to obtain high-purity silica powder. When the uranium content of this high-purity silica powder was measured by a fluorescence method, it was an extremely small amount of 0.3 ppb.

Since uranium can be easily removed by washing as described above, it is clear that uranium adheres to the surface portion of the silica powder obtained in the combustion step at a high concentration in the production method of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view of a manufacturing apparatus used in a manufacturing method of an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of an essential part of FIG. 1 ... Reaction vessel, 2 ... Combustor, 3 ... Collection device, 4 ... Hopper, 5 ... Powder supply device, 20 ... Powder supply path 21, 25 ... Oxygen supply path 22, 24 ... LPG supply Channel 23 ... Cooling water channel

Claims (1)

[Claims] 1. A combustion process in which metallic silicon powder is supplied into an air stream containing oxygen and burned to form a silicon dioxide powder having an average particle size of 0.01 to 10 μm; A method for producing silicon dioxide powder, which comprises a cleaning step for removing a compound of a radioactive element present therein.