JP2004018332A - Method for manufacturing silicon tetrafluoride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing high purity silicon tetrafluoride used in an electronics field or an optical field or the like. <P>SOLUTION: When silicon tetrafluoride gas is brought into contact with silicon to remove phosphorus and arsenic contained in the silicon tetrafluoride produced by the reaction of hydrogen fluoride with silicon, the contact of the silicon tetrafluoride gas with silicon is performed at 300-800°C under a condition of (V/Q)≥k. Where, V represents the volume (L) of a part of a vessel where silicon is filled; Q represents the flow rate (NL/min) of the produced silicon tetrafluoride gas; (k) is defined by k=18/(d-291)+0.04 and (d) represents a temperature (°C). <P>COPYRIGHT: (C)2004,JPO

Description

【００２０】
【発明の効果】
本発明により、低純度ＳｉとＨＦとの反応で、エレクトロニクス分野用途グレードの高純度ＳｉＦ_４を安価に製造することが可能となった。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing high-purity silicon tetrafluoride used in the fields of electronics, optics, and the like.
[0002]
2. Description of the Related Art
Silicon tetrafluoride (SiF ₄ ) is used as a fluorine dopant for quartz fibers, a raw material for a photomask material for semiconductor lithography, a CVD raw material gas for semiconductor production, and the like, and its usage is increasing year by year. The silicon tetrafluoride used for these applications is required to have a very high purity, but the phosphorus and arsenic components are harmful even in a very small amount. Strict. Therefore, there is a need for a technique for efficiently producing silicon tetrafluoride having a low phosphorus and arsenic component content.
[0003]
To obtain phosphorus and arsenic-free silicon tetrafluoride, high-purity phosphorus and arsenic-free silicon and hydrogen fluoride raw materials may be used, but such raw materials are expensive and disadvantageous in terms of production cost. It is. Therefore, when an inexpensive raw material with low purity is used, it is necessary to purify and remove impurities derived from the raw material from the reaction gas.
[0004]
Equation (1) is a reaction for producing silicon tetrafluoride by a reaction between silicon and hydrogen fluoride gas.
[0005]
Si (solid) + 4HF (gas) → SiF ₄ (gas) + 2H ₂ (gas) (1)
In this reaction, phosphorus and arsenic, which are impurities contained in silicon as a raw material, are fluorinated and PF ₃ (bp. = − 101.1 ° C.), PF ₅ (bp. = − 84.6 ° C.), AsF ₅ ( bp. =-52.9 ° C.), or a similar compound contained in the other material, hydrogen fluoride, is converted to a silicon tetrafluoride producing gas (formula (1) ), The volume ratio of SiF ₄ and H ₂ corresponding to the right side of (1) is mixed into the mixed gas having a ratio of 1: 2), so that it was difficult to obtain a high-purity product.
[0006]
[Means for Solving the Problems]
The present inventors have studied in detail the reaction of silicon tetrafluoride represented by the formula (1) using low-purity silicon and hydrogen fluoride as raw materials. The inventors have found that the coming phosphorus and arsenic compounds can be removed from the gas side by treating the silicon tetrafluoride gas with silicon heated to 300 ° C. or higher.
[0007]
That is, the present invention provides a method for removing phosphorus and arsenic contained in a silicon tetrafluoride gas generated by a reaction between silicon and hydrogen fluoride, when the silicon tetrafluoride gas is brought into contact with silicon to remove 300 to 800 ° C. A method for producing silicon tetrafluoride, wherein silicon and the silicon tetrafluoride gas are brought into contact with each other under the condition of (V / Q) ≧ k (where V is the volume of a vessel filled with silicon) [Liter], Q is the flow rate of the silicon tetrafluoride gas generating gas [N liter / min], k is defined as k = 18 / (d-291) +0.04, and d is the temperature [ ° C].).
[0008]
In the present invention, conditions required in the purification region will be described. The volume of the region filled with the heated silicon is V [liter] (V is the empty space volume of the container), and the flow rate of the silicon tetrafluoride producing gas for purifying phosphorus and arsenic is Q [N liter / min]. When the temperature of the purification region is d [° C.], the silicon tetrafluoride-producing gas must be brought into contact with silicon under the condition of V / Q ≧ k. Here, k is defined as k = 18 / (d-291) +0.04. Therefore, at 300 ° C., V / Q ≧ 2.04, at 400 ° C., V / Q ≧ 0.21, and at 600 ° C., V / Q ≧ 0.10. Therefore, if a V value and a Q value that are smaller than the k value at the set temperature are selected, the phosphorus and arsenic impurities cannot be removed.
[0009]
In the present invention, the same silicon as the raw material for producing silicon tetrafluoride may be used as the silicon used for the purification, and high-purity silicon is not necessarily required. For example, silicon having a purity of about 95 to 99% produced by reducing silica sand with carbon, which is industrially distributed in large quantities as a raw material for polysilicon, is sufficient. These low-purity silicon contain phosphorus and arsenic, which are the elements to be purified, and may seem seemingly unsuitable as a purifying agent. The concentration of these in the silicon tetrafluoride gas generated by gasification of phosphorus and arsenic contained therein does not increase. Similarly, impurities other than phosphorus and arsenic do not contaminate the silicon tetrafluoride gas. Approximately 66% by volume of the generated silicon tetrafluoride gas is hydrogen. By the action of this hydrogen and heated silicon, phosphorus and arsenic become compounds having a low vapor pressure and are equilibrium shifted toward the solid phase. However, since the abundances of phosphorus and arsenic are too small at the ppb level, the details of the mechanism have not been elucidated.
[0010]
Furthermore, it should be noted that the purification of phosphorus and arsenic significantly reduces the purification efficiency due to the presence of hydrogen fluoride. The reason for this can be understood from the assumption that hydrogen fluoride acts as a fluorinating agent for phosphorus and arsenic, so that the above-mentioned equilibrium shifts in the opposite direction and a phenomenon opposite to the purpose of purification occurs. For this reason, in the purification process, it is necessary to remove hydrogen fluoride as much as possible from the generated silicon tetrafluoride gas.
[0011]
Here, in the present invention, the method for purifying phosphorus and arsenic using heated silicon can be said to be particularly advantageous in this regard. This is because silicon, which acts as a purifier for phosphorus and arsenic, also reacts with hydrogen fluoride, an interfering component, to eliminate it, and only silicon tetrafluoride and hydrogen are generated as a result, resulting in the main component. This is because it has no influence on the production of silicon tetrafluoride as a flow.
[0012]
As a device for treating the generated silicon tetrafluoride gas with heated silicon to remove phosphorus and arsenic, a general packed tower equipped with a heater can be used. It is one embodiment of the present invention that the apparatus is installed downstream of the main reaction reactor. In addition, since the same type of reactor can be used for the reaction between silicon and hydrogen fluoride, which is the main reaction, the main reaction and the purification of phosphorus and arsenic are performed in order to simplify the series of operations in equipment. Can be continuously performed in a single container. In other words, by supplying hydrogen fluoride gas as a raw material from one side of a reaction vessel filled with silicon, flowing the gas phase in a so-called piston flow method in which back mixing does not occur, and discharging the gas from the other end, the upstream side portion of the vessel performs the main reaction. The region and the downstream portion act as a phosphorus and arsenic purification region.
[0013]
The main reaction shown in the formula (1) hardly progresses at room temperature, and when the temperature is increased, the reaction rate rapidly increases from around 250 ° C., and there is no particular upper limit in temperature. On the other hand, when the temperature is 300 ° C. or lower, phosphorus and arsenic are hardly removed, so that the required lower limit temperature is slightly higher in the case of purifying phosphorus and arsenic, but also there is no particular upper limit. Therefore, when the main reaction and purification are to be performed in the same vessel, there is no need to use a complicated structure such as providing a temperature distribution in the main reaction section and the purification section. Just match. In both processes, the higher the temperature, the higher the reaction rate. Therefore, it is advantageous in terms of efficiency to carry out the reaction at a temperature as high as possible up to the melting point of silicon (1420 ° C.). It is advantageous to carry out at a temperature of not more than ℃ for industrial applications. Practically, this temperature range that shows a sufficient reaction rate at 400 ° C. to 600 ° C. is optimal.
[0014]
In addition, the silicon tetrafluoride gas from which phosphorus and arsenic have been removed by the method of the present invention is then purified by a conventional separation method such as utilizing the vapor pressure difference between silicon tetrafluoride and hydrogen to remove pure hydrogen. Silicon fluoride can be obtained.
[0015]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
[0016]
Comparative Examples 1 to 5, Examples 1 to 5
Particulate silicon having a purity of 98% (crushed product having a particle size of 5 mmφ to 15 mmφ) produced by the carbon reduction method of silica sand was weighed and charged in a cylindrical vertical container. The container is made of Ni having an inner diameter of 80 mmφ and a height of 500 mm. The top plate has a nozzle for supplying gas and a thermometer stand, and the bottom plate has a nozzle for discharging gas. An electric heater is arranged on the outer periphery of the container so that the inside can be maintained at a predetermined temperature.
[0017]
From the top plate nozzle, a gas composed of silicon tetrafluoride = 33 vol%, P = 550 wtppb, As = 46 wtppb, and the balance hydrogen is supplied at a flow rate of 0.2 Nl / min to 4.4 Nl / min, and the Si filling portion is provided. While flowing from above to below in a piston flow system, was flowed at almost atmospheric pressure. It was brought into contact with silicon at a temperature condition of 250 to 600 ° C. The gas discharged from the lower nozzle was absorbed in pure water, and phosphorus was analyzed by ion chromatography, and arsenic was analyzed by ICP-MS. Table 1 shows the results and the experimental conditions.
[0018]
Examples 6 and 7
The processing was performed in the same manner as in Examples 1 and 3, except that the gas supplied from the top plate nozzle had a composition containing 1000 vol ppm of hydrogen fluoride. The results are shown in Table 1 as Example 6 and Example 7, respectively. These outlet gases were analyzed by FT-IR, and it was confirmed that hydrogen fluoride was not present (20 vol ppm or less).
[0019]
[Table 1]

[0020]
【The invention's effect】
According to the present invention, it has become possible to produce high-purity SiF _{4 of a} grade for use in the electronics field at low cost by the reaction between low-purity Si and HF.

Claims (1)

When the silicon tetrafluoride gas is contacted with silicon to remove phosphorus and arsenic contained in the silicon tetrafluoride gas generated by the reaction between silicon and hydrogen fluoride, (V) / Q) A method for producing silicon tetrafluoride, comprising bringing silicon into contact with the silicon tetrafluoride gas under the condition of ≧ k.
Here, V is the volume [liter] of the container filled with silicon,
Q is the flow rate [N liter / minute] of the silicon tetrafluoride gas generating gas,
k is defined as k = 18 / (d-291) +0.04;
d represents a temperature [° C.], respectively.