System for cleaning trichlorosilane

Abstract

A system for purifying trichlorosilane comprising an impurity serving as a donor or acceptor in a silicon crystal, wherein the system includes an impurity conversion section which, in the presence of a distillation aid, converts an impurity contained in the trichlorosilane into a high-boiling-point compound, and a purification section which distills and purifies the trichlorosilane supplied by the impurity conversion section, wherein the impurity conversion section consists of a plurality of impurity conversion step sections, wherein the majority of impurity conversion step sections are connected in series, The majority of impurity conversion step sections comprise a first stage section and a second stage section connected in series with the first stage section. Ozone is added as a distillation aid in the first stage of the distillation process. In the second stage, aromatic aldehyde is added as a distillation aid, and The trichlorosilane treated in this way is evaporated in the second stage section using an evaporator, and the trichlorosilane, from which the high boiling point compounds are separated, is transported to the following stage section.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a process for producing high-purity trichlorosilane and in particular a process for obtaining high-purity trichlorosilane by removing donor and acceptor impurities from trichlorosilane containing these impurities. Description of the state of the art

[0002] High-purity polycrystalline silicon of semiconductor quality is generally produced using the Siemens process, employing a gas consisting primarily of trichlorosilane as the raw material. Therefore, extremely high purity is required for the trichlorosilane used as the raw material.

[0003] Of the impurities contained in the raw material trichlorosilane, elements such as phosphorus and arsenic (which act as donors) and boron and aluminum (which act as acceptors) are known to have a significant impact on the electrical properties of silicon crystals when present in polycrystalline silicon, even at very low concentrations. Therefore, it is extremely important and beneficial for practical applications to provide a method for the effective removal of donor and acceptor impurities from trichlorosilane.

[0004] Trichlorosilane for the production of polycrystalline silicon is generally obtained by purifying crude chlorosilanes of metallurgical quality (metallurgical silicon) containing a large amount of impurities, obtained by a prior art process, using methods such as distillation.

[0005] Metallurgical silicon contains the donor and acceptor impurities described above at levels of several hundred ppma relative to the atomic ratio. Such metallurgical silicon is purified to remove these impurities. However, if the removal of impurities during this purification step is insufficient, the impurities will remain in the resulting final trichlorosilane, leading to the incorporation of the remaining impurities into the polycrystalline silicon and a reduction in quality.

[0006] Donor and acceptor impurities contained in metallurgical silicon are hydrogenated, chlorinated, or otherwise reacted to form compounds with a variety of structures during the production of crude chlorosilanes and are mixed into the crude chlorosilanes. If the boiling points of such compounds are close to the boiling point of trichlorosilane, sufficient separation or removal of the aforementioned compounds by distillation is difficult.

[0007] Due to these circumstances, various methods have been proposed to reduce the levels of donor and acceptor impurities in chlorosilanes.

[0008] One such method is a method for removing donor and acceptor impurities from chlorosilanes by adsorbing the impurities onto aluminum oxide, silica gel, activated carbon, or similar materials.

[0009] US 3,252,752 A, for example, discloses a method for immobilizing a substance with an ion-electron pair on an adsorber such as activated carbon or silica gel and passing gaseous chlorosilanes over the immobilized substance to capture and remove impurities. DE 12 89 834 A further discloses a method for bringing chlorosilanes in a liquid or vaporous state into contact with activated aluminum oxide to remove impurities. JP 2010-269 994 A further discloses a method for removing impurities by bringing liquid chlorosilanes into contact with spherical activated carbon.

[0010] As an alternative method, a process is described for adding an organic substance to chlorosilanes as a distillation aid to generate adducts with donor and acceptor impurities and subsequently carrying out distillation and purification to obtain highly pure chlorosilanes.

[0011] For example, JP 2005-67979 A discloses a process for adding ethers to chlorosilanes and carrying out distillation and purification. Furthermore, JP 2009-62213 A discloses a process for treating chlorosilanes in the presence of aromatic aldehyde and oxygen to convert impurities into high-boiling-point compounds and subsequently carrying out distillation or similar processes on the treated chlorosilanes to separate the high-boiling-point impurity compound from the chlorosilanes.Furthermore, JP 2013-1632A discloses a method for providing an evaporator for the purpose of preventing recontamination due to the re-dissociation of high-boiling-point products from impurities between an impurity conversion process with a distillation aid and a distillation and purification step for separating the high-boiling-point products from impurities and the distillation aid of chlorosilanes.Furthermore, JP 2012-91960A discloses an invention of a process for purifying chlorosilanes comprising adding an aldehyde compound represented by the general formula Ar-R-CHO (where Ar is a replaced or non-replaced aryl group and R is an organic group with two or more carbon atoms) for converting donor and acceptor impurities contained in a chlorosilane distillate into high-boiling-point products in an impurity conversion step for removing the donor and acceptor impurities from the chlorosilane distillate to reduce their content and advancing the chlorosilane distillate after conversion into high-boiling-point products to a purification step.

[0012] The method for removing impurities contained in chlorosilanes by adsorbing the impurities onto aluminum oxide, silica gel, activated carbon, or similar materials, as described above, has the following problems: The method requires equipment such as an adsorption tower, which complicates factories, and handling the adsorbate after breakthrough and / or waste disposal are problematic. Furthermore, replacing the adsorber involves opening the system, thus causing corrosion within the equipment and potentially leading to chlorosilane contamination.

[0013] Furthermore, the process of adding an organic preparation as a distillation aid to chlorosilanes to generate adducts containing donor and acceptor impurities, followed by distillation and purification to obtain high-purity chlorosilanes, presents the following problem: If the generated adducts are unstable, they dissociate upon heating or similar processes during distillation and revert to compounds that are difficult to separate from the chlorosilanes. Another problem is that if the generation of the adducts is an equilibrium reaction, any impurity that is not converted to a high-boiling-point compound remains constant. US 2012 / 0121493A1 discloses a process for obtaining high-purity chlorosilanes from chlorosilanes containing boron and phosphorus impurities by adding a Lewis base with a masking effect to the chlorosilanes.

[0014] The present invention was developed to eliminate the previously described problems of prior art methods for purifying chlorosilanes, and one object of the present invention is to provide a system for purifying trichlorosilane that effectively removes donor and acceptor impurities from trichlorosilane by fully utilizing the action of a distillation aid and preventing recontamination by dissociation of an adduct occurring in connection with the conversion to a high-boiling-point compound or by impurity residues due to an equilibrium condition. SUMMARY OF THE INVENTION

[0015] To achieve the previously described objective, the system for purifying trichlorosilane according to the present invention is a system for purifying trichlorosilane comprising an impurity serving as a donor or acceptor in a silicon crystal, wherein the system comprises an impurity conversion section which, in the presence of a distillation aid, converts an impurity contained in the trichlorosilane into a high-boiling-point compound, and a purification section which distills and purifies the trichlorosilane supplied by the impurity conversion section, wherein the impurity conversion section consists of a plurality of impurity conversion step sections.

[0016] The majority of impurity conversion step sections are connected in series as defined in the claims and each of the impurity conversion step sections can comprise a receiving section for the trichlorosilane from the preceding stage section, an introduction section for the distillation aid, a conveying section for the trichlorosilane to the following stage section and a discharge section that discharges a residue from the impurity conversion step section.

[0017] Furthermore, the majority of impurity conversion step sections are connected in series, and each of the impurity conversion step sections may include a receiving section for the trichlorosilane from the preceding stage section, an introduction section for the distillation aid, and a conveying section for the trichlorosilane to the following stage section, and any impurity conversion step section other than a first impurity conversion step section may include a discharge section that discharges a residue to the preceding impurity conversion step section.

[0018] Furthermore, in a specific aspect, at least one of the majority of impurity conversion step sections integrates the receiving section for the trichlorosilane from the preceding step section and the introduction section for the distillation aid.

[0019] Furthermore, the trichlorosilane treated in this manner is evaporated in the second stage section using an evaporator, and the trichlorosilane from which the high-boiling-point compounds are separated is transferred to the following stage section as defined in the claims. Generally, one of the impurity conversion step sections can include an evaporator, and the trichlorosilane treated in the impurity conversion step section, from which the high-boiling-point compound is separated by evaporation with the evaporator, can be transferred to the following stage section.

[0020] Furthermore, in a certain aspect, at least one of the majority of impurity conversion step sections includes a distillation apparatus that separates the distillation aid and the high boiling point compound between the evaporator and the conveying section.

[0021] Furthermore, in a specific aspect, the trichlorosilane, from which the high-boiling-point compound is separated, is transported to the following stage in a state of condensation.

[0022] In the first stage, ozone is added as a distillation aid, and in the second stage, aromatic aldehyde is added as a distillation aid.

[0023] The amount of distillation aid supplied to each of the plurality of impurity conversion step sections is preferably 1 to 10 9 -times, better yet, 10 times 2 - up to 10 9 -times and even better, 10 times 4 - up to 10 9 -times the amount that enables the distillation aid to react with the total amount of impurities contained in the chlorosilane, thereby converting all of them into the high boiling point compound.

[0024] Furthermore, the reaction temperature is preferably set to 0 °C or more and 150 °C or less in a state in which the distillation aid is fed into the impurity conversion step sections.

[0025] A silicon crystal can be a silicon crystal comprising the donor impurity at a concentration of 2 ppta or less and the acceptor impurity at a concentration of 20 ppta or less, obtained from the trichlorosilane produced as a raw material by the system described above.

[0026] In the system according to the present invention, when purifying trichlorosilane, comprising an impurity serving as a donor or acceptor in a silicon crystal, an impurity conversion step is performed, which, in the presence of a distillation aid, converts an impurity contained in the trichlorosilane into a high-boiling-point compound. This conversion step consists of a plurality of impurity conversion step sections. Thus, recontamination by the dissociation of an adduct and / or the impurity residues can be prevented due to an equilibrium condition.

[0027] This prevents the mixing of donor and acceptor impurities into polycrystalline silicon when producing polycrystalline silicon using trichlorosilane purified by the system described above.

[0028] Furthermore, in one aspect of the system according to the present invention, the emptying of the distillation aid and the trichlorosilane from the system can be minimized, since the trichlorosilane residue containing the distillation aid is fed back to the preceding stage from the following stage section.

[0029] Furthermore, a system according to one aspect in which trichlorosilane is supplied from the preceding stage to the following stage in a gaseous state does not require any special equipment or electricity for liquefaction. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 shows a block diagram of an example of a system that separates high-purity trichlorosilane from trichlorosilane containing donor and acceptor impurities by a multi-stage impurity conversion step and a purification step, and uses the obtained high-purity trichlorosilane as raw material in a step to produce polycrystalline silicon. Fig. Figure 2 shows a block diagram illustrating a first configuration example of a multi-stage impurity conversion section that performs the multi-stage impurity conversion step. Fig. Figure 3 shows a block diagram illustrating a second example of the multi-stage impurity conversion section, which performs the multi-stage impurity conversion step. Fig.Figure 4 shows a block diagram illustrating a third example of the multi-stage impurity conversion section, which performs the multi-stage impurity conversion step. Fig. Figure 5 shows a block diagram illustrating the first and second configuration examples of the contamination conversion step section. Fig. Figure 6 shows a block diagram illustrating the third and fourth configuration examples of the contamination conversion step section. Fig. Figure 7 shows a block diagram illustrating further configuration examples of the contamination conversion step section. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0030] The system for purifying trichlorosilane according to the present invention is described below with reference to the drawings.

[0031] For example, high-purity trichlorosilane used in the production of polycrystalline silicon is obtained, as previously described, by purifying crude trichlorosilane obtained from metallurgical silicon containing a large amount of impurities by a prior art process, using a method such as distillation. Furthermore, if gas obtained from a step for the precipitation of polycrystalline silicon is distilled and purified to produce high-purity trichlorosilane, the high-purity trichlorosilane can be reused in a step for the production of polycrystalline silicon.

[0032] However, in crude trichlorosilane as described above, donor and acceptor impurities contained in metallurgical silicon used as raw material are mixed in, as is the element or similar used in a reactor for the precipitation of polycrystalline silicon.

[0033] It is not easy to separate such donor and acceptor impurities with boiling points close to that of the trichlorosilane to be purified.

[0034] As previously disclosed in JP 2005-67979A and JP 2009-62213A, processes for generating adducts containing donor and acceptor impurities using a distillation aid and separating these adducts by subsequent distillation to purify trichlorosilane have been widely used. In particular, when aromatic aldehyde is used as a distillation aid in the presence of oxygen, both donor and acceptor impurities can be removed simultaneously.

[0035] However, as already described, such methods present the following problem: When distilling and separating using a distillation aid, if the adducts contain donor and acceptor impurities and the distillation aid is unstable, the adducts dissociate through a process such as heating in the subsequent distillation step to return to the compounds, which are difficult to separate from chlorosilanes. A further problem is that if adduct generation is an equilibrium reaction, any impurity that is not converted to a high-boiling-point compound remains constant and impairs high-purity purification.

[0036] In the present invention, in the process for converting the donor and acceptor impurities contained in trichlorosilane to compounds with a high boiling point using a distillation aid in an impurity conversion step and subsequent distillation and separation of the impurities, the multi-stage impurity conversion step enables the obtaining of high-purity trichlorosilane, while the dissociation of the adducts and the impurity residues is prevented due to the equilibrium condition as previously described.

[0037] Fig.Figure 1 shows a block diagram of an example of a system that removes high-purity trichlorosilane (containing impurities TCS) comprising donor and acceptor impurities by a purification step consisting of a multi-stage impurity conversion step (S101) and a purification step (S102) and uses the obtained high-purity trichlorosilane as raw material in a step to produce polycrystalline silicon (S103).

[0038] Trichlorosilane comprising impurities that act as donors or acceptors in silicon crystals is subjected to a multi-stage impurity conversion step (S101). The impurities in this trichlorosilane are converted into high-boiling compounds in the presence of a distillation aid. The term "high-boiling compound" refers to a compound with a boiling point higher than that of trichlorosilane. The temperature difference between these boiling points is preferably 25 °C or more, better 50 °C or more, and even better 75 °C or more. After this treatment, the trichlorosilane is transferred to the purification step (S102), and high-purity trichlorosilane is separated. This high-purity trichlorosilane can be used as a feedstock in the step for producing polycrystalline silicon (S103).

[0039] Accordingly, the system for purifying trichlorosilane according to the present invention is a system for purifying trichlorosilane comprising an impurity serving as a donor or acceptor in a silicon crystal, wherein the system comprises an impurity conversion section which, in the presence of a distillation aid, converts an impurity contained in the trichlorosilane into a high-boiling-point compound, and a purification section which distills and purifies the trichlorosilane supplied by the impurity conversion section, wherein the impurity conversion section consists of a plurality of impurity conversion step sections.

[0040] Fig.Figure 2 shows a block diagram illustrating a first configuration example of a multi-stage impurity conversion section 100, which performs the multi-stage impurity conversion step (S101). A plurality of impurity conversion step sections (n ​​impurity conversion step sections from stage 1 to stage n: 10) 1 up to 10 n ) is connected in series and each of the impurity conversion step sections comprises a receiving section a for the trichlorosilane from a preceding stage section, an introduction section b for the distillation aid, a conveying section c for the trichlorosilane to the following stage section and a discharge section d which discharges a residue (the high boiling point compounds, the distillation aid, trichlorosilane residue) from the impurity conversion step section.

[0041] Fig.Figure 3 shows a block diagram illustrating a second configuration example of the multi-stage impurity conversion section 100, which executes the multi-stage impurity conversion step (S101). Also shown is a plurality of impurity conversion step sections (n ​​impurity conversion step sections from stage 1 to stage n: 10). 1 up to 10 n ) connected in series, and each of the impurity conversion step sections comprises a receiving section a for the trichlorosilane from a preceding stage section, an introduction section b for the distillation aid, and a transport section c for the trichlorosilane to the following stage section. In this respect, each of the impurity conversion step sections other than the first impurity conversion step section comprises 10 1a discharge section d, which discharges a residue (the high boiling point compounds, the distillation aid, trichlorosilane residue) to the preceding impurity conversion step section.

[0042] Fig. Figure 4 shows a block diagram illustrating a third configuration example of a multi-stage impurity conversion section 100, which performs the multi-stage impurity conversion step (S101). In this aspect, the receiving section a for a trichlorosilane from the preceding stage section and the introduction section b for the distillation aid in the Fig. 3 aspects shown are integrated. Although the receiving section a for trichlorosilane and the introduction section b for the distillation aid are integrated into each of the impurity conversion step sections in the Fig.The aspects shown in section 4 are integrated, they can be integrated in another aspect as described above in at least one of the majority of impurity conversion step sections.

[0043] Fig. 5(A) and Fig. Figure 5(B) shows block diagrams illustrating the first and second configuration examples of the aforementioned contamination conversion step sections. In the Fig. In the example shown in Figure 5(A), the impurity conversion step section comprises a reactor 20 and an evaporator 30 arranged downstream of the reactor 20. In the Fig. In the example shown in 5(B), there is no reactor 20.

[0044] In each of the previously described configuration examples, a distillation apparatus 40 for further separation of high-boiling-point compounds and the distillation aid can be arranged after the evaporator 30 as shown in Fig. 6(A) and Fig. 6(B) is shown.

[0045] This means that each of the impurity conversion step sections 10 includes an evaporator 30 and the trichlorosilane, from which high boiling point compounds are separated, is conveyed to the following stage section by evaporating the trichlorosilane treated in the impurity conversion step section 10 with the evaporator 30.

[0046] Reactor 20 serves to effectively convert impurities into high-boiling-point compounds, and if reactor 20 is present, the distillation aid is supplied to this reactor 20. Furthermore, oxygen is preferably supplied to effectively convert impurities into high-boiling-point compounds, while ozone is supplied as the distillation aid.

[0047] All of the majority of impurity conversion step sections can be combined into one of the four configurations described above or in a combination of these configurations. For example, in one aspect, at least one of the majority of impurity conversion step sections between the evaporator 30 and the conveying section can include a distillation apparatus 40 that separates the distillation aid and high-boiling-point compounds.

[0048] The transfer of the trichlorosilane, from which high-boiling-point compounds are separated, to the following stage can take place in an evaporated state or in a condensate state; however, the trichlorosilane is preferably transferred in a condensate state if the distillation aid used is liquid.

[0049] Furthermore, if a distillation aid is supplied, it can be introduced either into the liquid or onto the surface of the liquid; however, if the distillation aid used is a gas and is supplied to liquid trichlorosilane, the distillation aid is preferably introduced into the liquid. If, from the group comprising trichlorosilane and the distillation aid, one is gaseous and the other liquid, the distillation aid can be introduced in a state in which small air bubbles are generated in the liquid to increase the gas / liquid contact efficiency.

[0050] In the first stage, ozone is added as a distillation aid, and aromatic aldehyde is added as a distillation aid in the second stage. If the distillation aid is a combination of aromatic aldehyde and ozone, the aromatic aldehyde is preferably added first, followed by the ozone; however, other mixing methods may be used without restriction.

[0051] The amount of dopant impurity is measured beforehand by taking a sample of the trichlorosilane containing the impurities before treatment and performing a photoluminescence (PL) analysis of crystals precipitated in a small reactor. Using an existing reactor, the impurities in high-boiling-point compounds can be converted to each impurity conversion step by adding trichlorosilane, comprising the amount of impurities determined by the previously described measurement and the amount of distillation aid sufficient to react with the impurities. The amount of distillation aid added to each of the multiple impurity conversion step steps is preferably 1 to 10 9 -times, better yet, 10 times 2 - up to 10 9 -times and even better, 10 times 4 - up to 10 9- times the amount that allows the distillation aid to react with the total amount of impurities contained in the chlorosilane, thereby converting all of them into the high-boiling-point compound. The upper limit of these numerical ranges is 10 9 -times set because, if this numerical value is 10 9 If the amount of distillation aid added exceeds the -fold, it is on the order of %, resulting in an excess.

[0052] The reaction temperature in a state where the distillation aid is introduced in an impurity conversion step is 0 °C or more, preferably 10 °C or more or better 20 °C or more, because it is unlikely that the conversion reaction will proceed at a temperature that is too low and 150 °C or less, preferably 100 °C or less or better 50 °C or less, since a side reaction of the distillation aid may proceed at a temperature that is too high.

[0053] By using trichlorosilane produced by such a system as a raw material, polycrystalline silicon is obtained with donor impurities at a concentration of 2 ppta or less and acceptor impurities at a concentration of 20 ppta or less.

[0054] As previously described, in the system according to the present invention, for the purification of trichlorosilane, comprising an impurity serving as a donor or acceptor in a silicon crystal, an impurity conversion step, which converts an impurity contained in the trichlorosilane into a high-boiling-point compound in the presence of a distillation aid, consists of a plurality of impurity conversion step sections. Thus, recontamination by the dissociation of the adducts and / or the impurity residues can be prevented due to an equilibrium condition.

[0055] This prevents the mixing of donor and acceptor impurities into polycrystalline silicon when producing polycrystalline silicon using trichlorosilane purified by the system described above.

[0056] Furthermore, in one aspect of the system according to the present invention, the emptying of the distillation aid and the trichlorosilane from the system can be minimized, since the trichlorosilane residue containing the distillation aid is fed back to the preceding stage from the following stage section.

[0057] Furthermore, a system according to one aspect in which trichlorosilane is supplied from the preceding stage to the following stage in a gaseous state does not require any special equipment or electricity for liquefaction. Examples

[0058] The following examples and comparative examples describe specific examples in which trichlorosilane comprising 139 ppta phosphorus as a donor impurity and 387 ppta boron as an acceptor impurity is treated with a system according to the present invention. [Example 1]

[0059] In a system according to the block diagram of Fig. The two aspects shown were impurity conversion step sections as in Fig. 5(A) were formed and these two impurity conversion step sections (number of treatment stages = 2) were connected in series to form an impurity conversion section.

[0060] The trichlorosilane containing the aforementioned impurities was fed into the multi-stage impurity conversion section. Benzaldehyde, in an amount 24 million times the total amount of phosphorus and boron (1.6% by volume), and oxygen (1.6% by volume, nitrogen-based), in an amount 7.35 million times the total amount of boron, were added in each stage, and the trichlorosilane was treated to obtain 2.5 kg of trichlorosilane as a sample after the two-stage treatment. The obtained sample was subjected to silicon crystallization using a small reactor for the precipitation of polycrystalline silicon, and the phosphorus and boron concentrations were measured by photoluminescence (PL) analysis. The total amount of benzaldehyde and oxygen added was approximately 3.1 × 10⁻⁶ 7 - times the total amount of phosphorus and boron. This numerical value lies within the range of 1 to 10 9-fold", which was previously specified as the preferred range of the amount of distillation aid supplied to each of the plurality of impurity conversion step sections, wherein this amount of distillation aid enables the reaction with the total amount of impurities contained in the chlorosilane in order to convert all of these into high boiling point compounds. [Example 2]

[0061] The same treatment as in Example 1, but with three impurity conversion step sections (number of treatment stages = 3) linked in series to form one impurity conversion section, was carried out to obtain 2.5 kg of trichlorosilane as a sample. [Comparison example 1]

[0062] The same treatment as in Example 1, but using only one impurity conversion step section (number of treatment steps = 1) as the impurity conversion section, was carried out to obtain 2.5 kg of trichlorosilane as a sample.

[0063] The results of Example 1, Example 2 and Comparison Example 1 are summarized in Table 1. [Table 1] Number of treatment levels Phosphorus concentration Boron concentration Resistance Example 1 2 33 ppta 3.5 ppta 2888 Ω·cm Example 2 3 17 ppta <2 ppta 5018 Ω·cm Comparison example 1 1 46 ppta 6.5 ppta 2156 Ω·cm

[0064] The examples shown in Table 1 demonstrate that increasing the number of treatment stages lowers the phosphorus and boron concentrations of the polycrystalline silicon samples and increases their resistivity. In particular, in Example 2, with three treatment stages, a high resistivity value of more than 5000 Ω·cm was achieved for the silicon crystals, indicating that crystals with extremely low impurity concentrations were obtained. This suggests that the purity of trichlorosilane can be increased by increasing the number of treatment stages. [Example 3]

[0065] Fig. 7(A) and Fig. Figure 7(B) shows block diagrams illustrating further configuration examples of the Contamination Conversion Step Section 10. In the Fig.In the example shown in Figure 7(A), ozone is supplied to reactor 20 as a distillation aid, which forms the impurity conversion step section 10. Oxygen and a substance based on an aromatic aldehyde are used in combination as distillation aids according to the prior art, while ozone can effectively convert phosphorus impurities into compounds with high boiling points and facilitates the removal of phosphorus impurities because ozone is more oxidizing than oxygen. Furthermore, in such a configuration, the impurity conversion step section 10 is also effective in reducing the phosphorus impurity concentration alone, since no substance based on an aromatic aldehyde is supplied as a distillation aid. The concentration of supplied oxygen is preferably in the range of about 1 to 10 4 ppmv. An ozone concentration higher than 10 4ppmv also increases the risk of explosion, and an ozone concentration lower than 1 ppmv makes it more difficult to control the concentration.

[0066] In Fig. 7(B) is an impurity conversion step section 10A with the in Fig. The configuration shown in Figure 7(A) is arranged upstream of a contaminant conversion step section, and a contaminant conversion step section 10B with a reactor 20 and an evaporator 30 is arranged downstream of the contaminant conversion step section 10A. The configuration of the downstream contaminant conversion step section 10B itself is the same as in Figure 7(A). Fig. 5(A) shown; but oxygen and the aromatic aldehyde-based substance as distillation aids are supplied to reactor 20 simultaneously when impurity-containing TCS supplied from the preceding impurity conversion step section 10A is added.

[0067] In impurity conversion step sections with the in Fig. In the configuration shown in Figure 7(B), the impurity conversion treatment is divided into two stages: the earlier and the later stage. Ozone treatment takes place in the earlier stage, followed by the usual chemical treatment in the later stage. This is because the presence of ozone and benzaldehyde simultaneously poses a risk of byproduct generation. As previously described, such a configuration can effectively convert phosphorus impurities into high-boiling-point compounds and facilitates the removal of phosphorus impurities during the earlier stage treatment.

[0068] Likewise, in Fig.In the configuration example shown in 7(B) as described above, a distillation apparatus 40 for further separation of the distillation aid and high-boiling-point compounds is arranged downstream of the evaporator 30 as shown in Fig. 6(A) and Fig. 6(B) is shown.

[0069] A multi-stage impurity conversion step section 10 with a configuration as in Fig. 7(B) was used as an impurity conversion step section and distillation was carried out by adding trichlorosilane (3 kg) containing 139 ppta phosphorus as a donor impurity and 387 ppta boron as an acceptor impurity to this impurity conversion step section 10.

[0070] A helium gas mixture with an ozone concentration of 500 ppmv was passed through impurity conversion step 10A (the earlier stage) at a rate of 100 cc / min for 120 minutes. Conversely, an O₂ (1.6 vol%) / helium gas mixture was passed through impurity conversion step 10B (the later stage) at a rate of 100 cc / min for 120 minutes after the addition of 1 wt% benzaldehyde. The TCS obtained after distillation from impurity conversion step 10B was heated to allow for individual evaporation, and the condensate was collected. The TCS obtained from this sampling was used as raw material and subjected to silicon crystallization using a small reactor to precipitate polycrystalline silicon, and the phosphorus concentration was determined by photoluminescence (PL) analysis. [Comparative example 2]

[0071] The same treatment as in Example 3, except that a single step of impurity conversion step section 10B, but not impurity conversion step section 10A, was used for the impurity conversion step section, was carried out to obtain TCS after distillation as a sample. The TCS obtained by this sampling was used as raw material and subjected to silicon crystallization using a small reactor to precipitate polycrystalline silicon, and the phosphorus concentration was measured by photoluminescence (PL) analysis.

[0072] The results of the phosphorus concentration measurements in Example 3 and Comparative Example 2 are summarized in Table 2. [Table 2] Number of treatment levels Phosphorus concentration Example 3 2 21 ppta Comparative example 2 1 38 ppta

[0073] The present invention provides a system for purifying trichlorosilane, which effectively removes donor and acceptor impurities from trichlorosilane by fully utilizing the action of a distillation aid and preventing recontamination by dissociation of an adduct occurring in connection with the conversion of a high-boiling-point compound or the impurity residues due to an equilibrium condition.

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