Patent Grant
9533279
Field of the Invention
The present invention relates to a method and an apparatus for manufacturing trichlorosilane by decomposing compounds (hereinbelow, referred to as “polymers”) containing high-boiling chlorosilane, which are generated in a polycrystalline silicon manufacturing process. In particular, the present invention relates to a method and an apparatus for manufacturing trichlorosilane by decomposing polymers that have been separated in a chlorination step or polymers that have been separated from an exhaust gas of a polycrystalline silicon manufacturing process.
Priority is claimed on Japanese Patent Application No. 2008-049229, filed Feb. 29, 2008, the content of which is incorporated herein by reference.
Description of Related Art
The high-purity polycrystalline silicon that can be used as a semiconductor material is mainly manufactured by the Siemens process in which, for example, trichlorosilane (SiHCl3; abbreviated “TCS”) and hydrogen are used as raw materials, a gas mixture thereof is introduced into a reactor and brought into contact with heated silicon rods, and silicon is deposited on the surfaces of the silicon rods due to the hydrogen reduction or thermal decomposition of the trichlorosilane at a high temperature.
The high purity trichlorosilane to be introduced into the reactor, for example, is manufactured by introducing metallurgical grade silicon and hydrogen chloride into a fluidized-bed chlorination furnace to react them, chlorinating the silicon to produce crude TCS (chlorination step), and purifying the crude TCS by distillation into high purity TCS.
In the manufacture of polycrystalline silicon, the reactor exhaust gas includes, in addition to unreacted trichlorosilane, hydrogen, and hydrogen chloride, by-products such as silicon tetrachloride (STC) and chlorosilanes including, for example, tetrachlorodisilane (Si2H2Cl4) and hexachlorodisilane (Si2Cl6). (Patent Document 1: PCT International Publication WO 02/012122) The chlorosilanes have boiling point higher than that of silicon tetrachloride, and they are referred to herein as “high boiling chlorosilanes”. Also, the gas produced in the chlorination reactor includes, in addition to trichlorosilane and unreacted hydrogen chloride, by-products such as silicon tetrachloride and high-boiling chlorosilanes.
Conventionally, when the gas that has been produced in the chlorination reactor is purified by distillation, separated polymers undergo a hydrolytic process and are then discarded. The exhaust gas of the reactor is introduced into a recovery distillation column, and after the polymers have been separated, the exhaust gas is returned to the distillation step of the chlorination step and recycled. However, the separated polymers undergo a hydrolytic process and are then discarded. Thus, there is problem in that the hydrolytic and the waste disposal processes are costly.
A method is known in which the polymers generated in the manufacture of polycrystalline silicon are returned to the fluidized-bed chlorination furnace and then decomposed and used in the manufacture of trichlorosilane (Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H01-188414). However, in this method, because the silicon powder and polymers supplied to the chlorination reactor are mixed, there is a problem that the fluidity of the silicon powder is reduced and the conversion rate of the silicon powder to chlorosilanes is lowered.
The present invention solves the above problems in the conventional polycrystalline silicon manufacture, and provides a manufacturing technology in which polymers separated from crude TCS in the chlorination step and polymers separated from the exhaust gas in the reactor are decomposed and converted to trichlorosilane.
The present invention relates to a method and an apparatus for manufacturing trichlorosilane that solves the problems described above by using the following features.
The method of the present invention is a method for manufacturing trichlorosilane by decomposing polymers, and for example, enables recovering trichlorosilane by decomposing polymers that have been separated in a polycrystalline silicon manufacturing process, enables significantly reducing the load incurred due to carrying out waste disposal by hydrolytic the polymers, increases the consumption efficiency of raw materials by recycling the recovered trichlorosilane, and enables the reduction of the polycrystalline silicon manufacturing cost.
Specifically, the manufacturing method of the present invention, for example, enables recovering trichlorosilane by decomposing at least one of a polymer that has been separated in a chlorination step in a polycrystalline silicon manufacturing process and a polymer that has been separated from an exhaust gas of a reactor. The recovered trichlorosilane can be recycled as a raw material for manufacturing polycrystalline silicon.
The manufacturing apparatus of the present invention is provided with a decomposition furnace that produces trichlorosilane by heating and decomposing polymers, and because trichlorosilane is manufactured by mixing the polymers and hydrogen chloride and reacting the mixture at a predetermined temperature, it is possible to manufacture trichlorosilane by using the polymers that have been separated in the chlorination step or the polymers that have been separated from the exhaust gas of the reactor.
In the case where at least a part of a supply pipe for the mixture is provided so as to pass through the inside of the decomposition furnace, the mixture is preheated while flowing through the supply pipe inside the furnace, and it is possible to react the mixture efficiently and to increase the yield of the trichlorosilane.
Below, the present invention will be explained concretely based on the embodiments.
The method of the present invention is a method for manufacturing trichlorosilane, wherein high-boiling chlorosilane-containing compounds (referred to herein as “polymers”), which have been generated in a polycrystalline silicon manufacturing process, are mixed with hydrogen chloride and introduced into a decomposition furnace, the polymers and the hydrogen chloride are reacted at a temperature of 450° C. or more, or preferably, of 450° C. or more and 700° C. or less, and the trichlorosilane is thereby manufactured.
For example, the decomposition process includes the following reactions.
Polymers may include other compounds such as pentachlorodisilane (Si2HCl5) and octachlorotrisilane (Si3Cl8). These compounds can also be decomposed by reacting with hydrogen chloride as well as the reactions (1) and (2).
The manufacturing method of the present invention can be applied to polymers that are separated in a manufacturing process for polycrystalline silicon. An example of a process for polycrystalline silicon manufacture is shown in
The metallurgical grade silicon and the hydrogen chloride are introduced into the fluidized-bed chlorination furnace 10, and, in a fluidized state, metallurgical grade silicon and hydrogen chloride are reacted to produce crude TCS. At this time, polymers are also generated. The produced chlorosilanes, which includes crude TCS, by-products, and unreacted hydrogen chloride and the like, is introduced into the distillation column 11 from the fluidized-bed chlorination furnace 10, and the crude TCS is purified by distillation. The purified TCS is introduced into the evaporator 12 from the distillation column 11, and at the same time, the distillation residue in the distillation column 11 is separated from the column bottom. The distillation residue includes polymers generated in the above process and the like, and distillation residue including the polymers are fed to the polymer decomposition step 30 according to an embodiment of the present invention.
The TCS, which has been introduced from the distillation column 11, and the hydrogen, STC, and TCS, which have been recovered from the downstream steps, are introduced into the evaporator 12, and a raw material gas in which these are mixed is prepared. This raw material gas is introduced into the reactor 13. Inside the reactor 13, plural silicon rods are stood, these silicon rods are heated to a temperature of 900° C. or more and 1200° C. or less, the raw material gas is brought into contact with surfaces of the heated silicon rods, and silicon is deposited thereon due to the hydrogen reduction and thermal decomposition of the TCS.
The exhaust gas of the reactor 13 contains, in addition to unreacted TCS, hydrogen, hydrogen chloride, and STC, high-boiling chlorosilanes such as tetrachlorodisilane and hexachlorodisilane that have been produced in the reactor 13. This exhaust gas is introduced into the condenser 14, cooled to a temperature of about −50° C., and the chlorosilanes, which include the polymers, are liquefied and thereby separated from the exhaust gas. The liquid that includes the chlorosilanes that have been separated by the condenser 14 is introduced into the distillation step 20. At the same time, hydrogen and hydrogen chloride and the like are included in the gas that has been extracted from the condenser 14, this gas is introduced into an absorption-adsorption step, and the hydrogen is thereby separated. This separated hydrogen is returned to the evaporator 12 and recycled as a raw material gas component.
In the distillation step 20, the TCS and the STC included in the liquid are stepwise distilled and separated from the polymers. The separated TCS and STC are returned to the evaporator 12 and recycled as a raw material gas component.
In the distillation step 20, a portion of the distilled chlorosilanes including the separated STC can be used as a raw material for generating TCS. For example, a portion of the distilled chlorosilanes including STC that has been separated in the distillation step 20 is introduced into the TCS conversion step 51 via the evaporator 50. In the TCS conversion step 51, STC (silicon tetrachloride) and hydrogen are reacted at a high temperature of 800° C. or more and 1300° C. or less to produce TCS (trichlorosilane). A gas including the produced TCS is introduced into a condenser 52, and cooled to a temperature of about −50° C. in the condenser 52. The TCS and STC and the like are liquefied and thereby separated from the gas. The separated liquid is returned to the distillation step 20. The TCS and STC that have been recovered in the distillation step 20 by distillation are returned to the evaporator 12 and recycled. In contrast, the gas that has been extracted from the condenser 52 is introduced into the absorption-adsorption step 53, and the hydrogen that is included in the gas is recovered. The recovered hydrogen is returned to the TCS conversion step 51 and recycled.
In this manner, in the process in which the TCS conversion step 51 is provided, polymers that are included in the exhaust gas of the reactor 13 and the polymers that have been generated in the TCS conversion process are included in the distillation residue that is separated in the distillation step 20, and these polymers (distillation residue) can be introduced into the polymer decomposition step 30 according to the embodiment of the present invention and decomposed.
The high-boiling chlorosilanes are generally included at about 20 to 50 mass % in the distillation residue that is separated by the distillation column 11 in the chlorination step and the distillation residue that is separated in the distillation step 20. Specifically, the distillation residue that is separated in the distillation step 20 includes, for example, about 1 to 3 mass % TCS, about 50 to 70 mass % STC, about 12 to 20 mass % Si2H2Cl4, about 13 to 22 mass % Si2Cl6, and about 3 to 6 mass % other high-boiling chlorosilanes. In the manufacturing method of this embodiment, these polymers are decomposed and converted to trichlorosilane (TCS).
The polymer decomposition step 30 for polymers is shown in
The gas including the TCS produced in the decomposition step 33 is fed to the condenser 34 through the discharge pipe 39, cooled to a temperature of about 30° C. to about 8° C., and a condensate that includes TCS is recovered. The recovered condensate is introduced into the distillation column 11 that purifies the crude TCS-containing gas of the chlorination step, the recovered TCS is purified with the crude TCS that was produced by the chlorination reactor 10, and this purified TCS can then be recycled. The STC that has been produced by the decomposition furnace 33 is recovered via the condenser 34, introduced into the polycrystalline silicon manufacturing step, and can thereby be recycled.
In the decomposition step shown in
In the polymer decomposition step 30 shown in
In the decomposition furnace 33, the polymers are reacted with hydrogen chloride at a high temperature of 450° C. or more and thereby converted to trichlorosilane (TCS). The reaction temperature in the reactor is 450° C. or more, and preferably 450° C. or more and 700° C. or less. When the temperature in the furnace is lower than 450° C., the decomposition of the polymers does not progress sufficiently. When the temperature in the furnace rises above 700° C., a reaction occurs in which the produced trichlorosilane reacts with the hydrogen chloride to produce silicon tetrachloride (STC), and this is not preferable because the recovery efficiency of the TCS will be decreased.
A schematic longitudinal cross-sectional view of the decomposition furnace 33 is shown in
In the decomposition furnace 33 shown in
In the decomposition furnace 33 shown in
In the decomposition furnace 33 shown in
The decomposition furnace 33 shown in
In the decomposition furnace 33 shown in
The polymers that have been separated in the chlorination step and the distillation step for the exhaust gas in the reactor are introduced into the polymer decomposition step shown in
The Comparative Example 1 is an example in which the decomposition temperature (300° C.) is lower than the range of the present invention; Example 9 is an example in which the decomposition temperature (900° C.) is higher than the preferred range of the present invention; and Example 10 is an example in which the supply rate (6 g/min) of the hydrogen chloride is lower than the preferred range of the present invention. Other than the above conditions, the polymers are decomposed to produce TCS in a manner similar to Examples 1 to 3. These results are shown in TABLE 3.
As shown in TABLE 1 and TABLE 2, according to the manufacturing method according to the present invention, because substantially all of the polymers present before processing takes place were decomposed and converted to trichlorosilane, the trichlorosilane yield was high. In contrast, as shown in TABLE 3, in the Comparative Example 1, the decomposition rate of the polymers was low and the amount of trichlorosilane was remarkably small. In Example 9, the produced amount of trichlorosilane was lower than those in Examples 1 to 8, and in Example 10, a large amount of precipitate is generated inside the furnace.
While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.
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