Purification system of trichlorosilane and method for producing polysilicon

Abstract

The present invention relates to a purification system of trichlorosilane and a method for producing polysilicon. The present invention provides a purification technique of trichlorosilane, in which when high-purity trichlorosilane is purified from a chlorosilane fraction containing hydrocarbons, a large amount of chlorosilane is not discharged to the outside of the system, and reaction control can also be easily performed. In the present invention, in order to make separation of hydrocarbons contained in the chlorosilane fraction easy, a process of low-boiling by pyrolysis is provided in the purification system. Thus, in the purification cycle of trichlorosilane, low-boiling by pyrolysis based on hydrocarbons and separation are performed, without discharging a large amount of chlorosilane to the outside of the system. As a result, the production efficiency of trichlorosilane is improved, and there is also no problem of a decrease in the yield of polysilicon.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201710899771.2, filed on September 28, 2017, entitled "Trichlorosilane Purification System and Polycrystalline Silicon Manufacturing Method". Technical Field

[0002] This invention relates to a purification technique for trichlorosilane. Background Technology

[0003] Trichlorosilane is widely used as a raw material for manufacturing high-purity polycrystalline silicon of semiconductor grade. High-purity trichlorosilane is obtained, for example, by purifying crude trichlorosilane obtained by reacting metallurgical-grade metallic silicon with tetrachlorosilane and hydrogen or hydrogen chloride through processes such as distillation.

[0004] Polycrystalline silicon can be obtained by precipitating high-purity trichlorosilane using methods such as the Siemens process. However, tetrachlorosilane is produced as a byproduct in this precipitation reaction. This tetrachlorosilane byproduct can be reduced to form trichlorosilane, which can be purified and reused in the polycrystalline silicon precipitation reaction.

[0005] In the manufacturing of polycrystalline silicon, low cost is a primary requirement, but on the other hand, with the increasing integration of semiconductor devices, higher quality is also demanded. Specifically, there is a trend towards reducing the concentration of impurities (carbon, dopants, heavy metals, etc.) in polycrystalline silicon to the limit. Therefore, achieving high purity of trichlorosilane is of paramount importance in polycrystalline silicon manufacturing technology.

[0006] Most of the carbon impurities in trichlorosilane are hydrocarbons generated by the impurities in the metallic silicon used in the manufacture of crude trichlorosilane, as well as carbon byproducts from the inner wall materials of the reactor.

[0007] Therefore, in order to produce high-purity trichlorosilane, it is necessary to remove such hydrocarbons. Generally, the purification of trichlorosilane is carried out by distillation, but when the boiling points of the hydrocarbons contained as impurities are close to those of trichlorosilane, it is difficult to completely remove the hydrocarbons by distillation.

[0008] In particular, the boiling points of hydrocarbons with 5 carbon atoms and those close to 5 carbon atoms are extremely close to those of trichlorosilane. Therefore, in practice, separation by distillation is not easy. For example, isopentane (i-C5H), a branched alkane with 5 carbon atoms and classified as a hydrocarbon, is a case in point. 12 The boiling point of 27.7℃ is very close to that of trichlorosilane (31.8℃), making it one of the substances that is difficult to separate by distillation.

[0009] In view of this situation, the following method is proposed as a purification technique for trichlorosilane.

[0010] Patent document 1 (Japanese Patent Application Publication No. 2009-062212) proposes a method for using photochlorination to raise the boiling point of isopentane during the chlorination process, thereby making it easier to separate from trichlorosilane by distillation.

[0011] Furthermore, Patent Document 2 (DE1222481B) describes a method for introducing waste gas (exhaust gas) from a first precipitation reactor into a second precipitation reactor to produce polycrystalline silicon of higher purity. In this method, high-purity hydrogen is added to the second precipitation reactor to improve the yield.

[0012] Furthermore, Patent Document 3 (Japanese Patent Application Publication No. 2012-056836) discloses a method for manufacturing polycrystalline silicon in which purified condensate from a first precipitation process in a first reactor is supplied to a second reactor for a second precipitation process. In this method, hydrogen is circulated in both the first and second reactors, and any unused hydrogen is purified and reused.

[0013] However, these methods all have the following drawbacks: the reaction is difficult to control, and a large amount of chlorosilane is discharged from the system during purification, thus reducing the yield of polysilicon.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: Japanese Patent Application Publication No. 2009-062212

[0017] Patent Document 2: DE1222481B Publication

[0018] Patent Document 3: Japanese Patent Application Publication No. 2012-056836 Summary of the Invention

[0019] The problem that the invention aims to solve

[0020] The present invention was made in view of the above-mentioned problems, and its purpose is to provide a purification technique for trichlorosilane, which can purify high-purity trichlorosilane from chlorosilane fractions containing hydrocarbons without discharging a large amount of chlorosilane outside the system, and can also easily control the reaction.

[0021] Methods for solving problems

[0022] To solve the above problems, the trichlorosilane purification system of the present invention is a system for obtaining high-purity trichlorosilane from a chlorosilane fraction containing hydrocarbons, characterized in that it comprises: a pyrolysis reactor for pyrolyzing the hydrocarbons in the chlorosilane fraction to reduce their boiling point, and a distiller for separating the trichlorosilane contained in the chlorosilane fraction delivered from the pyrolysis reactor from other components.

[0023] Preferably, the above-mentioned pyrolysis reactor is capable of at least reducing the boiling point of isopentane, methyltrichlorosilane, and methyldichlorosilane.

[0024] In addition, the pyrolysis reactor described above is preferably capable of controlling the pressure during the low-boiling point process to a range of 0.01 to 2 MPa.

[0025] In addition, the pyrolysis reactor described above is preferably capable of controlling the temperature during the low-boiling point conversion to a range of 300 to 1200°C.

[0026] In addition, it is preferable that the iron content in the inner wall material of the above-mentioned pyrolysis reactor is 65% by weight or less, and more preferably 50% by weight or less.

[0027] In one embodiment, a gas pipeline is provided for introducing tetrachlorosilane and hydrogen into the aforementioned pyrolysis reactor.

[0028] In another method, the amount of hydrogen ([H2]) introduced from the gas pipeline into the pyrolysis reactor can be controlled in a ratio ([H2] / [STC]) of 1 to 6 with the amount of tetrachlorosilane ([STC]).

[0029] In another embodiment, the hydrogenation reactor is further provided in which tetrachlorosilane is reacted with hydrogen in the presence of metallic silicon to obtain crude trichlorosilane, and a gas pipeline is provided to transport chlorosilane containing the aforementioned low-boiling hydrocarbons to the hydrogenation reactor.

[0030] In the trichlorosilane purification method of the present invention, the above-described system is used to purify the trichlorosilane.

[0031] Furthermore, in the polycrystalline silicon manufacturing method of the present invention, trichlorosilane obtained by purification using the above-described system is used as a raw material.

[0032] Invention Effects

[0033] In this invention, to facilitate the separation of hydrocarbons contained in the chlorosilane fraction, a process of lowering the boiling point through pyrolysis is incorporated into the purification system. Thus, the lowering and separation of hydrocarbons based on pyrolysis are performed within the trichlorosilane purification cycle, eliminating the need to discharge large quantities of chlorosilanes outside the system. Consequently, the production efficiency of trichlorosilane is improved, and the problem of reduced polysilicon yield is avoided. Attached Figure Description

[0034] Figure 1 Block diagram (A) shows a system example of producing high-purity trichlorosilane by distilling and purifying crude trichlorosilane, and block diagram (B) shows a system example of a manufacturing process in which high-purity trichlorosilane is separated by distilling and purifying the gas generated in the polycrystalline silicon precipitation process and then supplied to the polycrystalline silicon manufacturing process again.

[0035] Figure 2 This is a block diagram of a system example in which the gas supplied from the crude trichlorosilane manufacturing process is purified to produce high-purity trichlorosilane and used as a gas for the manufacture of polycrystalline silicon, and the gas discharged from the polycrystalline silicon precipitation process is purified and then supplied back to the polycrystalline silicon precipitation process for use.

[0036] Figure 3 It is a block diagram illustrating a method for manufacturing crude trichlorosilane that includes at least one of a hydrogenation step and a chlorination step.

[0037] Figure 4 This is a block diagram illustrating the method of supplying a hydrocarbon-containing chlorosilane fraction separated by purification of crude trichlorosilane, along with tetrachlorosilane and hydrogen, to a pyrolysis process, and then supplying the resulting chlorosilane containing pyrolytic hydrocarbons to a hydrogenation process in the crude trichlorosilane manufacturing process.

[0038] Figure 5 This is a block diagram illustrating the method of supplying tetrachlorosilane recovered after the polycrystalline silicon precipitation reaction to the hydrogenation process via a pyrolysis process. Detailed Implementation

[0039] The trichlorosilane purification system of the present invention will now be described with reference to the accompanying drawings.

[0040] Regarding trichlorosilane (TCS) used in the manufacture of polycrystalline silicon, crude trichlorosilane obtained through a reaction accompanying the chlorination of metallic silicon is distilled and purified to achieve high purity before being supplied to the polycrystalline silicon manufacturing process. Alternatively, if the gas generated in the polycrystalline silicon precipitation process is distilled and purified to separate high-purity trichlorosilane, this high-purity trichlorosilane can be supplied again to the polycrystalline silicon manufacturing process.

[0041] However, in the crude trichlorosilane as described above, hydrocarbons byproducts generated from carbon impurities contained in the raw material metallic silicon are mixed in. Furthermore, hydrocarbons byproducts generated from carbon contained in the reaction apparatus are mixed in the gas generated during the polycrystalline silicon precipitation process. Among these hydrocarbons, isopentane and other hydrocarbons with approximately 5 carbon atoms have boiling points close to those of trichlorosilane, the target for purification, making separation from trichlorosilane difficult. In particular, isopentane has a boiling point of 27.7°C, which is extremely close to the boiling point of trichlorosilane (31.8°C).

[0042] Moreover, even trace amounts of hydrocarbons contained in the gas generated during the polycrystalline silicon precipitation process in such crude trichlorosilane will be gradually concentrated during the trichlorosilane purification process, thus becoming a reason that hinders the high-purity purification of trichlorosilane.

[0043] In this invention, the hydrocarbons contained in chlorosilanes are pyrolyzed to lower their boiling point, thereby increasing the boiling point difference with trichlorosilane and facilitating their separation from trichlorosilane. The pyrolysis products of the 5-carbon hydrocarbons yield alkanes and alkenes with 1 to 4 carbon atoms, whose boiling points are lower than those of trichlorosilane. The compound with the highest boiling point among these pyrolysis products is cis-2-butene with 4 carbon atoms, but its boiling point is only 3.7°C. Therefore, from a separation point, the boiling point difference with trichlorosilane (approximately 28°C) is sufficiently large. Thus, in this invention, the hydrocarbons contained in chlorosilanes are pyrolyzed to form hydrocarbons with 4 or fewer carbon atoms, thereby achieving lower boiling point. This allows for a boiling point difference of approximately 28°C or higher.

[0044] Therefore, the trichlorosilane purification system of the present invention includes a pyrolysis reactor for pyrolyzing hydrocarbons in a chlorosilane fraction to achieve a low boiling point, and a distiller for separating trichlorosilane contained in the chlorosilane fraction delivered from the pyrolysis reactor from other components, thereby enabling the production of high-purity trichlorosilane from a chlorosilane fraction containing hydrocarbons.

[0045] Figure 1 Block diagram (A) shows a system example of producing high-purity trichlorosilane by distilling and purifying crude trichlorosilane, and block diagram (B) shows a system example of a manufacturing process in which high-purity trichlorosilane is separated by distilling and purifying the gas generated in the polycrystalline silicon precipitation process and then supplied to the polycrystalline silicon manufacturing process again.

[0046] A chlorosilane containing hydrocarbons (e.g., isopentane, methyltrichlorosilane, methyldichlorosilane) is fed into a pyrolysis process (pyrolysis reactor). In the reactor, heated to 300°C–1200°C, the hydrocarbons are pyrolyzed and converted into substances with lower boiling points. This chlorosilane fraction containing the converted hydrocarbons is then transported to a production process (distillation apparatus) to separate the trichlorosilane from the other components.

[0047] As mentioned above, hydrocarbons with boiling points close to those of trichlorosilane are reduced to lower boiling points through a pyrolysis process, making them easy to separate and facilitating the purification of trichlorosilane to a high purity.

[0048] The pyrolysis reactor used in this invention is preferably capable of reducing the boiling points of at least isopentane, methyltrichlorosilane, and methyldichlorosilane. This is because these hydrocarbons have boiling points close to those of trichlorosilane, which is the target for purification, and are not easily separated by conventional methods.

[0049] Furthermore, the pyrolysis described above is carried out, for example, in a temperature range of 300 to 1200°C and a pressure range of 0.01 to 2 MPa. Therefore, the pyrolysis reactor is preferably capable of controlling the pressure during the deboiling process to a range of 0.01 to 2 MPa.

[0050] Figure 2 It is Figure 1 (A) and Figure 1 (B) is a block diagram of a circulating system example in which the gas supplied from the crude trichlorosilane manufacturing process is purified to produce high-purity trichlorosilane and used as a gas for the manufacture of polycrystalline silicon, and the gas discharged from the polycrystalline silicon precipitation process is purified and then supplied back to the polycrystalline silicon precipitation process for use.

[0051] It should be noted that, Figure 2 The manufacturing process of crude trichlorosilane shown is as follows: Figure 3 The method shown can include only one of the hydrogenation process (hydrogenation reactor) and the chlorination process (chlorination reactor), or it can include both processes. In this case, in the hydrogenation process, metallic silicon, tetrachlorosilane, and hydrogen are supplied. In the presence of metallic silicon, tetrachlorosilane reacts with hydrogen to obtain crude trichlorosilane containing trichlorosilane. A gas pipeline is provided to transport this crude trichlorosilane to the pyrolysis reactor. Meanwhile, in the chlorination process, metallic silicon and hydrogen chloride are supplied to obtain crude trichlorosilane containing trichlorosilane.

[0052] In addition, such as Figure 4As shown, it can also be configured as follows: a gas pipeline is provided to introduce tetrachlorosilane and hydrogen into the pyrolysis reactor; the hydrocarbon-containing chlorosilane fraction separated by purification of crude trichlorosilane is supplied to the pyrolysis process along with tetrachlorosilane and hydrogen; and the resulting chlorosilane containing pyrolytic hydrocarbons is supplied to the hydrogenation process of the crude trichlorosilane manufacturing process. It should be noted that, in this case, it is preferable to control the amount of hydrogen ([H2]) introduced into the pyrolysis reactor from the aforementioned gas pipeline in a ratio ([H2] / [STC]) of 1 to 6 to the amount of tetrachlorosilane ([STC]).

[0053] In addition, such as Figure 5 As shown, the process can also be configured such that the tetrachlorosilane recovered after the polycrystalline silicon precipitation reaction is supplied to the hydrogenation process via a pyrolysis process. It should be noted that, in this case, it is also preferable to control the amount of hydrogen ([H2]) introduced from the aforementioned gas pipeline into the pyrolysis reactor in a ratio ([H2] / [STC]) of 1 to 6 to the amount of tetrachlorosilane ([STC]).

[0054] [Example]

[0055] The following examples and comparative examples illustrate specific instances of using the system of the present invention to reduce the boiling point of isopentane by pyrolysis in a test gas containing a predetermined concentration of isopentane, a hydrocarbon, in a mixture of tetrachlorosilane and hydrogen.

[0056] (Example 1)

[0057] Under pyrolysis conditions of 450–650 °C, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube. The concentration of isopentane in the exhaust gas was determined using a gas chromatograph with a flame ionization detector (FID-GC) to investigate the decomposition rate of isopentane.

[0058] (Example 2)

[0059] Under pyrolysis conditions of 450–650 °C, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube with a pure nickel coating on its inner wall. The concentration of isopentane in the discharged gas was determined by FID-GC to investigate the decomposition rate of isopentane.

[0060] (Example 3)

[0061] Under pyrolysis conditions of 450–650 °C, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube with an inner wall coated with SUS316. The concentration of isopentane in the discharged gas was determined using FID-GC to investigate the decomposition rate of isopentane.

[0062] (Example 4)

[0063] Under pyrolysis conditions of 450–650 °C, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube with an inner wall coated with pure iron. The concentration of isopentane in the discharged gas was determined using FID-GC to investigate the decomposition rate of isopentane.

[0064] (Comparative Example 1)

[0065] With the pyrolysis temperature set to room temperature, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube. The concentration of isopentane in the discharged gas was measured using FID-GC to investigate the decomposition rate of isopentane.

[0066] (Comparative Example 2)

[0067] With the pyrolysis temperature set to room temperature, a test gas containing 5 ppm isopentane (tetrachlorosilane:hydrogen = 1:6) was passed through a quartz tube with an inner wall coated with SUS316. The concentration of isopentane in the discharged gas was measured using FID-GC to investigate the decomposition rate of isopentane.

[0068] The results of Examples 1 to 4 and Comparative Examples 1 to 2 are summarized in Table 1.

[0069] [Table 1]

[0070] Based on the results shown in Table 1, it can be confirmed that the pyrolysis of isopentane in chlorosilanes is promoted with increasing temperature. Furthermore, it can be confirmed that the lower the iron content of the material on the inner wall surface of the reactor, the easier the pyrolysis is to be promoted. The iron content of SUS316 is approximately 65% ​​by weight or less; therefore, the results shown in Table 1 indicate that at least when the iron content in the inner wall material of the pyrolysis reactor is 65% by weight or less, i-C5H is observed to promote pyrolysis. 12The decomposition rate is improved. For example, Incoloy (registered trademark) 800H is used as such a material, with an iron content of approximately 45% by weight. The inventors conducted experiments in a pyrolysis reactor using Incoloy (registered trademark) 800H as the inner wall material. The results showed an improved decomposition rate at 650°C compared to results in pyrolysis reactors using pure iron or SUS316 as the inner wall material. Therefore, it is considered that in practical applications, an inner wall material with an iron content of 65% by weight or less is preferred, and an inner wall material with an iron content of 50% by weight or less is more preferable.

[0071] The above system was used to purify high-purity trichlorosilane, which was then used as a raw material to manufacture polycrystalline silicon.

[0072] Industrial availability

[0073] This invention provides a purification technique for trichlorosilane, which can purify high-purity trichlorosilane from chlorosilane fractions containing hydrocarbons without discharging large amounts of chlorosilane outside the system and also allows for easy reaction control.

Claims

1. A method for purifying trichlorosilane, which is used to obtain high-purity trichlorosilane from a chlorosilane fraction containing hydrocarbons, comprising: The process of pyrolyzing isopentane in the chlorosilane fraction to achieve a lower boiling point in a pyrolysis reactor with an inner wall made of quartz or nickel, and... The process of separating trichlorosilane contained in the chlorosilane fraction delivered from the pyrolysis reactor from other components in a distiller.

2. The purification method for trichlorosilane according to claim 1, wherein, In the pyrolysis reactor, the pressure during the low-boiling point process is controlled within the range of 0.01 to 2 MPa.

3. The purification method for trichlorosilane according to claim 1 or 2, wherein, Tetrachlorosilane and hydrogen are introduced into the pyrolysis reactor via a gas pipeline.

4. The purification method for trichlorosilane according to claim 3, wherein, The amount of hydrogen [H2] introduced from the gas pipeline into the pyrolysis reactor is controlled such that the ratio of hydrogen to tetrachlorosilane [STC] is in the range of 1 to 6.

5. The purification method for trichlorosilane according to claim 1 or 2, wherein, have: The process of reacting tetrachlorosilane with hydrogen in the presence of metallic silicon within a hydrogenation reactor to obtain crude trichlorosilane, and... The process of conveying chlorosilanes containing the low-boiling-point hydrocarbons to the hydrogenation reactor.

6. A method for manufacturing polycrystalline silicon, using trichlorosilane obtained by purification using the method of claim 1 or 2 as a raw material.

7. The purification method for trichlorosilane according to claim 1 or 2, wherein, The process of pyrolyzing isopentane in the chlorosilane fraction to reduce its boiling point is carried out in a temperature range of 450–650°C.

Images