JPH0152326B2 - - Google Patents

Description

Claim 1 (A) To a silicon halide solution contaminated with a small amount of Lewis acid impurity, an excess of organosiloxane than the stoichiometric amount relative to the impurity concentration is added (provided that the organosiloxane is a cyclic siloxane, (B) at a temperature of about 25°C to 200°C until substantially all impurities form a non-volatile product;
A method for purifying silicon halide, comprising reacting impurities in a solution with the organosiloxane, and then (C) removing purified silicon halide by distillation. 2. The method according to claim 1, wherein the impurity contains boron. 3. The method according to claim 2, wherein the boron impurity is a boron halide. 4. The method of claim 1, wherein the silicon halide is selected from the group consisting of silicon tetrachloride, trichlorosilane, and dichlorosilane. 5. The method according to claim 4, wherein the silicon halide is trichlorosilane. 6. The method of claim 1, wherein the organosiloxane is selected from the group consisting of cyclotrisiloxane, cyclotetrasiloxane, polydimethylsiloxane oil, and dimethylmethylhydrogensiloxane copolymer. 7. The method according to claim 6, wherein the organosiloxane is cyclotrisiloxane. 8. The method of claim 7, wherein the cyclotrisiloxane is selected from the group consisting of alkyl, aryl, alkyl halide, aryl halide, or hydrogen-substituted alkyl or aryl cyclotrisiloxane. 9. The method of claim 8, wherein the cyclotrisiloxane is an alkylcyclotrisiloxane. 10 Claim 9, wherein the alkylcyclotrisiloxane is hexamethylcyclotrisiloxane
Section method. 11. The method of claim 6, wherein the organosiloxane is octamethyltetrasiloxane. 12. The method of claim 1, wherein the organosiloxane is added at a concentration of 5 to 100 times the molar concentration of the Lewis acid impurity. 13 The silicon halide is trichlorosilane, the Lewis acid impurity is mainly boron trichloride,
The organosiloxane is hexamethylcyclotrisiloxane and contains approximately 100% of the boron trichloride impurity.
The method according to claim 1, wherein the method is added at twice the concentration. 14 The silicon halide is chlorosilane, and the cyclic siloxane is alkyl, aryl,
alkyl halide, aryl halide or hydrogen-substituted alkyl or aryl selected from the group consisting of cyclotrisiloxane and cyclotetrasiloxane, wherein the non-volatile product formed in step (B) is a complex with said organosiloxane. The method described in paragraph 1. 15 In the process of manufacturing electronic equipment grade silicon from high-purity trichlorosilane, a compound that forms a complex or forms a bond with the low concentration Lewis acid impurity contained in such trichlorosilane is added to produce non-volatile silicon. A method for purifying trichlorosilane by forming a compound is characterized in that it takes the following steps: (A) adding a stoichiometric excess to the concentration of the impurity to a trichlorosilane solution contaminated with Lewis acid impurities; (B) wherein substantially all impurities are present in the non-volatile product; reacting impurities in the solution with the organosiloxane at a temperature of about 25°C to 200°C until the formation;
Then (C) purified trichlorosilane is removed by distillation. Description This invention relates to the preparation of trichlorosilane for electronic grade silicon, and more particularly, to the preparation of trichlorosilane for electronic grade silicon.
The present invention relates to a novel method for removing trace impurities that are proton donor contaminants, particularly boron and other Lewis acid or proton donor type impurities. Complex electronics applications such as semiconductors and transistors require very high purity silicon. It is well known that even trace amounts of impurities can significantly impair the performance of silicon-containing electronic components. Elemental silicon for semiconductors is generally made of silicon halides such as silicon tetrachloride (SiCl ₄ ), trichlorosilane (HSiCl ₃ ), and dichlorosilane (H ₂ SiCl ₂ ), and hydrogen, zinc, sodium, or metal hydrogen. Obtained by reduction with a compound. Silicon is also
It is also derived from the thermal decomposition of silane (SiH ₄ ),
The latter substances are difficult to handle because they burn explosively on contact with air. One of the most difficult impurities to remove from high purity silicon is boron. While other common impurities such as copper, iron and manganese are relatively easy to remove by conventional methods (e.g. zone purification, crystal pulling), boron has very similar physical properties to silicon. Due to its atomic nature, separation can only be achieved through repeated attempts. Furthermore, it is equally difficult to direct purification efforts on starting materials such as chlorosilanes, since boron forms corresponding compounds with similar properties. A variety of compounds have been used in the past to complex and bind impurities in substantially pure silicon halide solutions, such as phenols, triphenols, and nitrogen-containing compounds. For example, U.S. Pat. No. 3,403,003 (Morganthaler), no.
No. 3,126,248 (Pohl et al.) and No. 3,041,141 (Shoemaker et al.) describe these treatments. Commonly used methods for removing boron contaminants (U.S. Pat. No. 4,112,507 (Lang et al.)
(1999) discloses a method in which water vapor is introduced into a chlorosilane solution through silica gel. However, this is accompanied by problems of impurity regeneration and corrosion. It has now been discovered that boron chloride and other Lewis acids can be almost completely removed from the chlorosilane solution by introducing organosiloxane. Siloxanes react or complex with impurities and then react to form thermally stable compounds, namely borosiloxanes, which remain in the distillation of chlorosilanes. It is therefore an object of the present invention to provide a new method for purifying silicon halides. Another object of the present invention is to provide a method for removing boron halides, Lewis acids, and proton-donating compounds from silicon halide solutions. Another object of the invention is to provide an irreversible and non-corrosive purification process. Another object of the present invention is to provide a method for obtaining electronic grade silicon from high purity trichlorosilane. These and other objectives are: (A) adding a stoichiometric excess of organosiloxane relative to the impurity concentration to a silicon halide solution contaminated with Lewis acid impurities, and (B) eliminating almost all impurities. reacting the impurities in the solution with said siloxane at a temperature of about 25°C to 200°C until a non-volatile product is formed, and then (C) removing the purified silicon halide by distillation. This is achieved by a method of purifying silicon halide consisting of: DETAILED DESCRIPTION OF THE INVENTION The method of this invention involves contacting boron halide or other Lewis acid impurities present in a silicon halide solution with an excess molar amount of organosiloxane, and heating the solution to form a bond between the impurity and the siloxane. reaction to obtain a compound with a lower vapor pressure than the silicon halide, and then distilling off the pure silicon halide, leaving behind the impurities bound to the siloxane. This method is very effective in removing boron contaminants from silicon chloride solutions such as trichlorosilane. The boron concentration in the trichlorosilane solution is reduced to below 50 ppt by the treatment of the present invention. As used herein, a "Lewis acid" is any substance that accepts a pair of electrons and forms a covalent bond (ie, an "electron pair acceptor"). This includes the concept of a "proton donor" which is the Lowry-Brensted definition of an acid. From this it follows that boron trifluoride (BF ₃ ) is a typical Lewis acid because it has six electrons in the outermost part of the electron orbit. BF ₃ accepts a free electron pair,
Complete the eight electron orbits. Cyclotrisiloxane compounds suitable for this purpose are reacted with boron or other impurities present in the silicon halide so that a pure silicon-containing solution is distilled from the reaction vessel, followed by a non-volatile siloxane compound. What remains is any organosiloxane that forms a nonvolatile siloxane compound (eg, borosiloxane) that has a lower vapor pressure than the purified solution. These siloxanes include alkyl, aryl, alkyl halides, aryl halides or hydrogen-substituted alkyl or aryl cyclotrisiloxanes and cyclotetrasiloxanes, such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, polydimethylsiloxane oils. , dimethyl (methyl hydrogen) siloxane copolymers, and other cyclic siloxane monomers. Cyclotrisiloxane, alkylcyclotrisiloxane, halogenated alkylcyclotrisiloxane are preferred, and hexanemethylcyclotrisiloxane is most preferred. The siloxane is added to the impurity-contaminated silicon halide solution in an amount that ensures reaction between the siloxane and the Lewis acid impurity. The best results will be obtained if this amount is in large molar excess, for example 5 to 100 times, relative to the concentration of contaminants. However, any amount of siloxane suitable for effectively binding impurities in the solution may be used. After the siloxane is mixed into the solution, the mixture is heated to advance the reaction between the siloxane and the Lewis acid impurity. At very high temperatures, i.e. above 200°C, siloxane compounds undergo some decomposition and
Volatile borate is formed. at low temperatures
There is not enough reaction to effectively remove all the _BCl3 . For these reasons, the reaction temperature range is preferably from 25°C to about 200°C, and most preferably from about 80°C to about 130°C, although the reaction product is distilled to the same fraction as the silicon halide and purified. Higher temperatures may be used as long as they do not cause difficulties. Best results are obtained at approximately 100°C. As mentioned above, the reaction is continued until almost all impurities are bound to the siloxane compound.
Of course, the time will vary depending on the substance used, temperature, pressure, etc. By simple experimentation, the optimum reaction time for a given purification can easily be determined. The final step in the purification of the present invention is to distill the pure silicon halide from the reaction solution. The lower volatility of impurities bound to siloxane compared to silicon halides makes this final distillation possible. Distillation may be carried out at atmospheric pressure or at higher pressures if the temperature of the liquid material does not exceed the decomposition temperature of the borate formed during the process. Preferably, the temperature of the liquid is kept below about 200°C. To enable those skilled in the art to easily understand the practice of this invention, the following examples are presented by way of illustration and not by way of limitation. Example 1 Hexamethylcyclotrisiloxane (trimer)
7 parts by weight were mixed with 150 parts by weight of trichlorosilane (TCS) solution containing 5000 ppm boron trichloride, and 1
Stir periodically for a period of time. A sample of TCS distilled from the reaction mixture contained no BCl ₃ or borate as determined by infrared spectroscopy with a detection limit of 25 ppm. Example 2 A TCS solution containing 5 ppb BCl ₃ and 25 ppb trimer are mixed at 8.44 Kg/cm ² (120 psig) and 120°C. Spectroscopic analysis with a detection limit of 25 ppt on the distillate sample indicates that all BCl ₃ has been consumed. Example 3 200 ppm trimer is added to a TCS solution containing 2 ppm BCl ₃ . The mixture is heated to 130-135°C in an oil bath at ¹⁰⁰ psig for 4 hours. After standing overnight, four fractions are distilled out and analyzed for boron content using the colorimetric method used in Example 2.

Table: 2000 grams were added to the distiller, 99% of the material was recovered, and the presence of boron in each fraction was less than 50 ppt. Examples 4 and 5 The method of Example 3 was repeated twice and the following results were obtained.

[Table] Example 6 TCS solution containing 0.018 mol of BCl ₃ (5000 ppm)
400 parts by weight are placed in a reaction vessel along with enough trimer to make the solution 0.09 molar. The reaction mixture is stirred under pressure and a sample is periodically distilled for analysis by infrared spectroscopy as in Example 1.

[Table] Noh