JP4837687B2 - Chemical treatment method of chlorosilanes - Google Patents

Description

The present invention relates to an analytical sample processing technique for analyzing impurity elements present in a trace amount in chlorosilanes. Examples of the chlorosilanes to be sample-treated in the present invention include one or a mixture of two or more chlorosilanes selected from tetrachlorosilane, trichlorosilane, and dichlorosilane.

Chlorosilanes, which are monosilane production raw materials used as production raw materials for semiconductor silicon and the like, or chlorosilanes, which are raw materials for dichlorosilane used as production raw materials for semiconductor silicon and the like, contain an extremely small amount of impurities. However, since the electrical characteristics of semiconductor silicon and the like are significantly adversely affected, ultra-high purity quality is required. For this reason, it is important to analyze impurities to verify manufacturing techniques and quality control methods for maintaining and managing impurity elements in chlorosilanes at a very low level.

  Conventionally, in the case of analysis of impurity elements in high-purity chlorosilanes, especially inorganic elements such as metal elements and boron, phosphorus, arsenic, etc., which are said to be dopant elements, for example, a method of directly introducing chlorosilanes into an analyzer for analysis (Patent Document 1), a method of reacting and hydrolyzing chlorosilanes with water (Non-Patent Documents 1 and 2), introducing vaporized chlorosilanes into an aqueous hydrofluoric acid solution and decomposing it, and by-product hydrochloric acid or A method for removing silicofluoride (Patent Document 2) is known.

However, when chlorosilanes are directly introduced into an analyzer, it is difficult to handle a large amount of sample, and there has been a problem that detection sensitivity cannot be increased in the analysis of an extremely small amount of impurities. On the other hand, the hydrolysis reaction of analytical samples of chlorosilanes is a vigorous reaction accompanied by generation of hydrogen chloride gas and heat generation, and it is a large-scale in order to decompose efficiently in a short time while ensuring the safety of work. It was necessary to create a dedicated reaction vessel with a cooling device and to carefully handle chlorosilanes and to carry out a long-time decomposition reaction operation.

Also, when the sample is vaporized, the gas concentration may enter the explosion range and there is a risk of ignition, explosion, etc., and it is dangerous to handle and it is necessary to handle a large amount of sample to detect trace impurities. There was a problem that it took a lot of time to decompose for that
Japanese Patent Laid-Open No. 2-110350 JP-A-1-302157 Journal of The Chinese Institute of Chemical Engineers, 5,99-105 (1974) Analyst, 115, 29-34 (1990)

  The present invention has been made for the purpose of avoiding the above-described problems during sample processing prior to analysis of impurities in chlorosilanes, and provides a chemical processing method for safely and gently decomposing a large amount of chlorosilanes in a short time. It is to provide.

  In the method of the present invention, high-purity chlorosilanes are cooled and solidified, and the cooled and solidified hydrofluoric acid aqueous solution is contacted with the cooled and solidified chlorosilanes, or the liquid hydrofluoric acid aqueous solution is cooled. The present invention relates to a chemical treatment for hydrolyzing by bringing it into contact with solidified chlorosilanes. By cooling and solidifying the analysis sample of chlorosilanes, the vapor pressure of highly reactive gas molecules can be kept extremely low, and the reaction heat can be kept low, so that the analysis sample can be handled safely. If necessary, decompose in contact with chlorosilanes and reagents in an inert gas atmosphere to avoid contact with highly reactive oxygen and moisture in the air and to avoid contamination of impurities from the environment. You can also.

Place the cooled and solidified hydrofluoric acid aqueous solution on the chlorosilane sample that has been cooled and solidified in advance, or drop the liquid hydrofluoric acid aqueous solution onto the chlorosilane sample that has been cooled and solidified in advance to allow it to solidify. By hydrofluoric acid reacting with the sample surface, hydrolysis proceeds in a stable manner at a very low temperature. The sample of chlorosilanes can be decomposed naturally while still standing, and the chlorosilanes can be handled safely as sample processing.

In addition, in order to avoid contamination of impurities from the environment, this decomposition solution is heated in an inert gas atmosphere to remove the main component silicon as a highly volatile fluoride, while concentrating impurities remaining in the decomposition solution. By doing so, a sample before analysis can be prepared. This operation facilitates the analysis of impurities in high-purity chlorosilanes.

  Specifically, the cooling and solidification of the sample is performed as follows. In the apparatus shown as an example in FIG. 1, the inside of the pipe is previously replaced with an inert gas such as argon gas or nitrogen gas, and chlorosilanes (samples) are made of polytetrafluoroethylene having an inner diameter of about 5 mm from a container such as a cylinder. Through a pipe, the sample is supplied to a sampling container having an internal volume of 200 ml that is similarly substituted with argon or nitrogen gas. The container is then cooled with liquid nitrogen and the sample is completely frozen.

By replacing the inside of the system with an inert gas such as argon gas, moisture and oxygen in the air with high reactivity can be shut off, and chlorosilanes can be handled safely. As shown in FIG. 1, it is preferable from the viewpoint of safety that the devices and pipes used for the decomposition reaction described above are connected to each other, a switching valve is disposed at a necessary location, and a mutual connection system is established.

Next, the hydrofluoric acid aqueous solution is similarly cooled and solidified in a separate container (with an internal volume of 200 ml) in advance, and then taken out and placed on the cooled and solidified sample, or the liquid hydrofluoric acid aqueous solution is cooled and solidified. While being gradually dissolved by the heat of reaction generated from the solid surface during the reaction with water or hydrogen fluoride, it is brought into contact with the solid surface of each cooled and solidified chlorosilane by dropping it onto the prepared sample. The hydrolysis reaction proceeds.

The generated silicon oxide further reacts with hydrogen fluoride to form silicon-soluble silicon fluoride or highly volatile fluoride. In this operation, it is desirable to carry out this decomposition reaction in an inert gas atmosphere in order to avoid contact with oxygen or moisture in the air that is highly reactive with chlorosilanes.

In the solid sample decomposition step, the concentration of hydrogen fluoride in the hydrofluoric acid aqueous solution used is preferably about 30 to 70% by mass. The amount of water and hydrogen fluoride to be used are calculated based on the following reaction formula, and the amount of water and fluoride to be actually used is used to complete the reaction. In order to stably dissolve the impurity compound in the acidic aqueous solution of hydrochloric acid or hydrofluoric acid generated at the time, it is preferable to use an excess amount, specifically 1.1 to 1.5 times the calculated amount.
However, in the hydrolysis reaction of chlorosilanes and the reaction with hydrofluoric acid, a plurality of reactions proceed as in the following reaction examples of dichlorosilane.
Silicic anhydride is produced in the reaction with water.
SiH ₂ Cl ₂ + 2H ₂ O → SiO ₂ + 2HCl + 3H ₂
In the reaction with hydrofluoric acid, volatile silicon tetrafluoride is generated by heating.
SiH ₂ Cl ₂ + 4HF → SiF ₄ + 2HCl + H ₂
In addition, in the presence of excess hydrofluoric acid, water-soluble hexafluorosilicon acid is generated, but changes to volatile silicon tetrafluoride by heating.
SiH ₂ Cl ₂ + 6HF → SiH ₂ F ₆ (water-soluble) + 2HCl + H ₂
On the other hand, the produced silicon anhydride is reacted with hydrofluoric acid, and becomes volatile silicon tetrafluoride by heating.
SiO ₂ + 4HF → SiF ₄ + 2H ₂ O
In this way, the silicon compound produced by each reaction, eventually evaporates disappeared as SiF ₄ by heat treatment.

  Further, in the above step, after the solid sample is decomposed to be in a solution state, it is preferably heated to a temperature of 100 ° C. to 120 ° C. to substantially evaporate the main component silicon fluoride from the decomposition solution. And remove. In the chemical treatment method of the present invention, in the above-described decomposition step, if necessary for analysis, a boron compound that easily volatilizes can be supplemented by adding a small amount of a complexing agent with boric acid such as mannitol. After obtaining the decomposition solution from which the silicon compound has been removed by the chemical treatment of the present invention, the remaining impurities can be heated and concentrated, and then an operation suitable for the analysis method employed can be performed to prepare a sample before measurement.

After heating and concentration, the residue and high-purity carbon powder can be mixed, molded into an electrode, and quantified by spark ion source mass spectrometry (hereinafter abbreviated as SSMS method), or after heating and concentrated, hydrochloric acid or Impurities concentrated with nitric acid can be redissolved to form a hydrochloric acid or nitric acid solution, which can be analyzed by inductively coupled plasma mass spectrometry, inductively coupled plasma emission spectroscopy, or by graphite furnace atomic absorption with elements.

  Since the SSMS method can detect trace impurities in a solid sample, it is used for analysis of high-purity materials. In this method, an element can be identified and quantified by performing a spark discharge in a vacuum using a sample as an electrode and mass analyzing ionized atoms. Using a photographic plate as a detector, the element is quantified using the carbon blackness as a standard. Concentration magnification can be easily increased by concentrating the sample in a small amount of high purity carbon powder. At the same time, it is possible to measure all elements in a solid including light elements. By further utilizing this excellent analytical means, the sample can be concentrated and shaped only at the tip of the electrode, and the amount of carbon mixed with the residue can be minimized, thereby increasing the required analytical sensitivity. it can.

On the other hand, a mixture of one or more chlorosilanes selected from tetrachlorosilane, trichlorosilane, and dichlorosilane is cooled and solidified. Similarly, a hydrofluoric acid aqueous solution is cooled and solidified, and these solids are brought into contact with each other to be decomposed. Alternatively, it is decomposed by bringing it into contact with an aqueous hydrofluoric acid solution, and then the resulting decomposition solution is heated to remove silicon, which is the main component, as a fluoride. Then, the remaining impurities are concentrated and then redissolved with an acid. Impurity analysis can be performed with high sensitivity using an inductively coupled plasma mass spectrometer.

Hereinafter, the present invention will be described in detail based on examples.

Example 1
Quantification of boron in the dichlorosilane sample before the purification step, which was taken out from the manufacturing facility step into a dedicated container, was performed using a spark ion source solid mass spectrometer (JEOL Ltd. JMS-01BM-2).
Open the valve of the argon gas cylinder container and fill the air (oxygen) or moisture in the system (container or pipe) with argon gas by switching the valve placed in the polytetrafluoroethylene pipe with an inner diameter of about 5 mm. Removed. Open the valve of the cylinder container that stores dichlorosilane, and store the chlorosilanes used for pipe cleaning (500 ml capacity) while co-washing liquid dichlorosilane by passing it through the valve with its own pressure at room temperature ) And flushed the amount necessary for co-washing. Next, the valve of the sampling container 4 is closed, the valve is switched, and 20 g of dichlorosilane for analysis is placed in the container 4 for sampling made of polytetrafluoroethylene shown in FIG. By filling the container with liquid nitrogen, dichlorosilane introduced into the container 4 was frozen and solidified.

The sampling container 4 containing chilled and solidified dichlorosilane is removed, and 0.2 ml of a 1% by mass aqueous mannitol solution is added to the container and frozen and solidified. The frozen dichlorosilane solid was transferred to a dedicated polytetrafluoroethylene reaction vessel (with an internal volume of 300 ml), and the solid fluoride previously frozen in the polytetrafluoroethylene vessel with an internal volume of 200 ml was transferred there. 20 g of an aqueous hydrogen acid solution (concentration: 50% by mass) was placed on the cooled and solidified dichlorosilane and allowed to stand until the decomposition reaction was completed. Two pipes for taking in and out the inert gas are arranged on the lid of the polytetrafluoroethylene container used for the decomposition reaction. A small amount of argon gas is flowed from one of the pipes to keep the reaction vessel in an inert atmosphere.

After completion of the decomposition, the reaction vessel was placed on a hot plate heated to 100 to 120 ° C., and hydrochloric acid, silicofluoride, excess hydrofluoric acid and water were removed by evaporation and dried. A small amount of ultrapure water is added dropwise to dissolve the concentrated components and adsorbed and concentrated on the carbon powder by mixing well with 40 mg of high-purity carbon powder (Hitachi Chemical Industry HSG-P2). After drying on a hot plate, the sample was scraped, formed into an electrode, and quantified by the SSMS method. A standard sample is prepared by diluting 50 mg of a standard sample for luminescence analysis (using G-Standards manufactured by Spex) with 450 mg of high-purity carbon powder (Hitachi Chemical Industry HSG-P2) and 25 mg of mannitol. Table 1 shows the analytical value (average value) and standard deviation of the boron (B) concentration obtained by repeating 5 times.

Example 2
Boron in the mixture of tetrachlorosilane and trichlorosilane taken out from the pre-distillation step of the production facility in a ratio of 7 to 3 was quantified in the same manner as in Example 1. The results are shown in Table 2.

Example 3
In the same manner as in Example 1, the high-purity dichlorosilane taken out from the distillation purification process of the production facility was transferred to a dedicated polytetrafluoroethylene reaction vessel in the same manner as in Example 1, and the solution was put into the decomposition-dedicated vessel. 20 ml of an aqueous hydrofluoric acid solution (concentration: 50% by mass) was added little by little and allowed to stand until the decomposition reaction was completed. Thereafter, as in Example 1, evaporation to dryness is performed. The remaining impurities were redissolved with 3 ml of nitric acid (concentration 0.6% by mass) to obtain an acidic aqueous solution, which was analyzed by an inductively coupled plasma mass spectrometer (HEWLETT PACKARD HP4500). The results are shown in Table 3. Sampling amounts were 31 g and 29.1 g, respectively, in two repeated analyses.

  Reaction in impurity analysis work for quality control of products that require high purity in the production of chlorosilanes used as raw materials for monosilane used in the semiconductor industry or in the production of chlorosilanes such as dichlorosilane used in semiconductor production Chlorosilanes can be safely and gently decomposed in a short period of time by bringing chlorosilanes with extremely high cooling properties into solid, and bringing them into contact with a hydrofluoric acid aqueous solution or liquid hydrofluoric acid aqueous solution that has been cooled and solidified in advance. Creating an analysis sample has a great effect on quality control of semiconductor gases.

Equipment for cooling and solidifying chlorosilanes. (Examples 1-3)

Explanation of symbols

1. 1. Argon gas cylinder Containers containing chlorosilanes (eg cylinders)
3. Storage container for chlorosilane after pipe cleaning 4. 4. Sample collection container Liquid nitrogen
6). Trap (cooled or liquefied or solidified so as not to be discharged outside the system)

Claims (2)

One or two or more chlorosilane mixtures selected from tetrachlorosilane, trichlorosilane, and dichlorosilane are cooled and solidified, the hydrofluoric acid aqueous solution is similarly cooled and solidified, and these solids are brought into contact with each other to be decomposed. A characteristic method for treating chlorosilanes. A method for treating chlorosilanes, comprising cooling and solidifying a mixture of one or more chlorosilanes selected from tetrachlorosilane, trichlorosilane, and dichlorosilane, and bringing the mixture into contact with a liquid hydrofluoric acid aqueous solution. .