Polysilicon reduction furnace, and method of producing polysilicon

Abstract

To provide a polysilicon reduction furnace capable of suppressing the generation of a chlorosilane polymer and producing a high-purity polysilicon.SOLUTION: A polysilicon reduction furnace 1 reducing / depositing silicon onto a seed rod 5 by feeding reaction gas including chlorosilane into a furnace body 10 housing the electrified / heated seed rod 5, is characterized by comprising a temperature adjustment unit 20 adjusting an inner surface temperature of the furnace body 10 during a reduction reaction, in a range of 40°C or more and 200°C or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a polysilicon reduction furnace for reducing and depositing silicon on a seed rod by supplying a reaction gas containing chlorosilane into a furnace body containing an electrically heated seed rod, and a method for producing polysilicon using this polysilicon reduction furnace.

Background Art

[0002] Conventionally, when producing polysilicon, which is used as a raw material for semiconductors and solar cells, a polysilicon reduction furnace is used in which a reaction gas containing chlorosilane is supplied into a furnace body containing an electrically heated seed rod, and silicon is deposited on the seed rod by a reduction reaction. It is manufactured by the so-called Siemens method.

[0003] In this Siemens method, it is characteristic that the produced silicon is not brought into contact with a furnace body or the like that serves as a pollution source. Examples of the furnace body used include a metal bell jar made of stainless steel or the like. In addition, in polysilicon for semiconductors, extremely high purity has been required in recent years. Therefore, as shown in Patent Document 1, for example, the furnace body is sufficiently cooled so as not to generate any pollution.

[0004] However, when cooling the furnace body where the reduction reaction occurs, high-boiling compounds called "chlorosilane polymers" are likely to be generated and deposited, and there is a problem that the chlorosilane polymer accumulates in the exhaust gas pipe and blocks it. As a countermeasure, as shown in Non-Patent Document 1, for example, by heating the pipe, the generation of chlorosilane polymer in the pipe can be suppressed, and it has been found that blockage of the pipe due to deposition of chlorosilane polymer can be suppressed.

[0005] On the other hand, chlorosilane polymer is also generated on the inner surface of the furnace body, that is, at locations where the temperature has decreased due to cooling, in addition to the exhaust gas pipe. Here, for example, as shown in Non-Patent Document 2, it is known that chlorosilane polymers react with moisture in the air to generate harmful hydrogen chloride, while the hydrolysis products are known to exhibit explosive properties under certain conditions.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, the above-mentioned Siemens method is a batch-type manufacturing method. Usually, it takes about 3 to 7 days to deposit silicon on a seed rod to increase the diameter of the silicon rod, and then the furnace is opened to take out the silicon rod. At that time, the chlorosilane polymer generated inside the furnace body is released into the atmosphere and reacts with the moisture in the air, so hydrolysis products are generated and disasters such as explosions are likely to occur. Generating a large amount of chlorosilane polymer inside the furnace body should be avoided from the viewpoint of safety. Here, as described in Non-Patent Document 1, it is considered necessary to raise the inner wall temperature of the reactor in order to suppress the generation of chlorosilane polymer. However, as shown in Patent Document 1, if the temperature is raised excessively, metal contamination will occur, leading to deterioration of quality.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a polysilicon reduction furnace capable of suppressing the generation of chlorosilane polymer and producing high-purity polysilicon, and a method for producing polysilicon.

Means for Solving the Problems

[0010] In order to solve the above problems, the present inventors confirmed the relationship between the temperature of the reaction gas and the amount of impurities in the produced polysilicon. The reaction gas temperature was set at 30°C, 100°C, 150°C, 200°C, and 250°C, and the phosphorus concentrations of the produced polysilicon rods were compared. The results of the comparative experiment are shown in Table 1.

[0011]

Table 1

[0012] As shown in Table 1, an increase in the phosphorus concentration was confirmed when the temperature of the reaction gas was 200°C, and it was found that the phosphorus concentration would have an adverse effect on the semiconductor manufacturing process when the temperature reached 250°C.

[0013] The present invention has been made based on the above findings. The polysilicon reduction furnace according to Embodiment 1 of the present invention is a polysilicon reduction furnace in which a reaction gas containing chlorosilane is supplied into a furnace body containing a seed rod heated by energization, and silicon is reduced and deposited on the seed rod. It is characterized by having a temperature adjustment unit that adjusts the inner surface temperature of the furnace body during the reduction reaction within a range of 40°C or higher and 200°C or lower.

[0014] According to the polysilicon reduction furnace of Embodiment 1 of the present invention, since it is provided with a temperature adjustment unit that adjusts the inner surface temperature of the furnace body during the reduction reaction within a range of 40°C or higher and 200°C or lower, the generation of chloropolysilane can be suppressed, and high-purity polysilicon can be stably produced.

[0015] The polysilicon reduction furnace of Embodiment 2 of the present invention is the polysilicon reduction furnace of Embodiment 1 of the present invention, wherein the furnace body has an inner peripheral wall and an outer peripheral wall that covers the outside of this inner peripheral wall, and a refrigerant flow path through which refrigerant flows is formed between the inner peripheral wall and the outer peripheral wall, and the temperature adjustment unit is characterized in that it adjusts the inner surface temperature of the furnace body by controlling the inlet temperature of the refrigerant.

[0016] According to the polysilicon reduction furnace of Embodiment 2 of the present invention, the furnace body has a double-wall structure of an inner peripheral wall and an outer peripheral wall, a refrigerant flow path is formed between these inner peripheral wall and outer peripheral wall, and the temperature adjustment unit is configured to adjust the inner surface temperature of the furnace body by controlling the inlet temperature of the refrigerant. Therefore, it is possible to accurately adjust the inner surface temperature of the furnace body during the reduction reaction within a range of 40°C or higher and 200°C or lower.

[0017] The polysilicon reduction furnace of Embodiment 3 of the present invention is the polysilicon reduction furnace of Embodiment 2 of the present invention, characterized in that it has a reflux path for refluxing a part of the refrigerant discharged from the outlet of the refrigerant flow path back to the refrigerant flow path. According to the polysilicon reduction furnace of Embodiment 3 of the present invention, by refluxing a part of the refrigerant discharged from the outlet of the refrigerant flow path back to the refrigerant flow path, fluctuations in the inner surface temperature of the furnace body can be suppressed, and the inner surface temperature of the furnace body can be stably adjusted.

[0018] The polysilicon reduction furnace of Embodiment 4 of the present invention is the polysilicon reduction furnace of Embodiment 2 or Embodiment 3 of the present invention, characterized in that the temperature adjustment unit controls the difference between the inlet temperature and the outlet temperature of the refrigerant to be 10°C or less. According to the polysilicon reduction furnace of Embodiment 4 of the present invention, since the temperature adjustment unit is configured to control such that the difference between the inlet temperature and the outlet temperature of the refrigerant is 10°C or less, fluctuations in the inner surface temperature of the furnace body can be suppressed, and the inner surface temperature of the furnace body can be stably adjusted.

[0019] The polysilicon reduction furnace of Embodiment 5 of the present invention is the polysilicon reduction furnace according to any one of Embodiments 2 to 4 of the present invention, wherein the temperature adjustment unit is characterized by estimating and controlling the inner surface temperature of the furnace body from the heat quantity of the refrigerant taken out. According to the polysilicon reduction furnace of Embodiment 5 of the present invention, since the temperature adjustment unit is configured to estimate and control the inner surface temperature of the furnace body from the heat quantity of the refrigerant taken out, the cooling state by the refrigerant is grasped and the inner surface temperature of the furnace body is controlled, and the inner surface temperature of the furnace body can be stably adjusted.

[0020] The method for manufacturing polysilicon according to Embodiment 6 of the present invention is a method for manufacturing polysilicon using the polysilicon reduction furnace according to any one of Embodiments 1 to 5 of the present invention, characterized in that the inner surface temperature of the furnace body during the reduction reaction is adjusted within a range of 40°C or more and 200°C or less. According to the method for manufacturing polysilicon according to Embodiment 6 of the present invention, since it is provided with a temperature adjustment unit that adjusts the inner surface temperature of the furnace body during the reduction reaction within a range of 40°C or more and 200°C or less, the generation of chloropolysilane can be suppressed, and high-purity polysilicon can be stably manufactured.

Effects of the Invention

[0021] According to the present invention, it is possible to provide a polysilicon reduction furnace capable of suppressing the generation of chlorosilane polymer and manufacturing high-purity polysilicon, and a method for manufacturing polysilicon.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0023] Hereinafter, a polysilicon reduction furnace and a method for manufacturing polysilicon, which are embodiments of the present invention, will be described. In the polysilicon reduction furnace and the method for manufacturing polysilicon according to the present embodiment, polycrystalline silicon (polysilicon) used as a raw material for semiconductors and solar cells is manufactured. In these applications, those with particularly high purity are required.

[0024] As shown in FIG. 1, the polysilicon reduction furnace 1 according to the present embodiment includes a seed rod 5 that is energized and heated, a furnace body 10 that houses the seed rod 5, a gas supply unit 30 that supplies a reaction gas containing chlorosilane into the furnace body 10, a power supply unit 42 that energizes the seed rod 5, and a temperature adjustment unit 20 that adjusts the inner surface temperature of the furnace body 10.

[0025] As shown in FIG. 1, the furnace body 10 is composed of a plate portion 11 that forms the furnace bottom and a bell-shaped bell jar 16 that is detachably attached to the plate portion 11. The bell jar 16 that constitutes the furnace body 10 has a double-wall structure having an inner peripheral wall 17 and an outer peripheral wall 18 that covers the outside of the inner peripheral wall 17, and a refrigerant flow path 21 through which refrigerant flows is formed between the inner peripheral wall 17 and the outer peripheral wall 18. Further, the plate portion 11 that constitutes the furnace body 10 also has a double-wall structure having an inner peripheral wall 12 and an outer peripheral wall 13, and a refrigerant flow path 21 through which refrigerant flows is formed between the inner peripheral wall 12 and the outer peripheral wall 13.

[0026] In the bell jar 16, a refrigerant inlet 22 is formed at the lower end, and a refrigerant outlet 23 is formed at the top. A refrigerant supply pipe 26 is connected to the refrigerant inlet 22, and a refrigerant discharge pipe 27 is connected to the refrigerant outlet 23. Also, in the plate portion 11, a refrigerant inlet 22 is formed at the outer peripheral portion, and a refrigerant outlet 23 is formed at the central portion. A refrigerant supply pipe 26 is connected to the refrigerant inlet 22, and a refrigerant discharge pipe 27 is connected to the refrigerant outlet 23. In this way, the furnace body 10 is structured to be cooled by circulating a cooling medium (cooling water in this embodiment) through the bell jar 16 and the plate portion 11 that constitute the furnace body 10.

[0027] Inside the furnace body 10, seed rods 5 are arranged. An electrode portion 41 is formed on the upper surface of the plate portion 11, and the lower end of the seed rod 5 is inserted into this electrode portion 41. In this embodiment, two seed rods 5 are erected, and the upper end portions of the two seed rods 5, 5 are connected by a connecting member 6, and the seed rods 5 are arranged in an inverted U shape. That is, the two electrode portions 41, 41 are connected by the two seed rods 5, 5 and the connecting member 6. And the electrode portion 41 is connected to the power supply portion 42 and is energized and heated by the two seed rods 5, 5 and the connecting member 6 arranged in an inverted U shape.

[0028] Also, the plate portion 11 is provided with a gas jet outlet 31 for jetting a reaction gas containing chlorosilane and a gas discharge outlet 32 for discharging the gas after the reaction. A plurality of gas jet outlets 31 are formed on the upper surface of the plate portion 11, and each is connected to a gas supply pipe 33. A plurality of gas discharge outlets 32 are formed on the outer peripheral side of the plate portion 11, and each is connected to a gas discharge pipe 34. These gas jet outlets, gas supply pipes, gas discharge outlets, and gas discharge pipes constitute the above-described gas supply portion.

[0029] And in the polysilicon reduction furnace according to this embodiment, a temperature adjustment unit for adjusting the inner surface temperature of the furnace body is provided, and by this temperature adjustment unit, the inner surface temperature of the furnace body during the reduction reaction is configured to be adjusted within a range of 40°C or higher and 200°C or lower. In this embodiment, the temperature adjustment unit adjusts at least one of the inner surface temperature of the inner wall surface of the chamber or the inner surface temperature of the inner wall surface of the plate portion within a range of 40°C or higher and 200°C or lower.

[0030] By setting the inner surface temperature of the furnace body to 40°C or higher, the generation of chlorosilane polymer inside the furnace body can be suppressed. On the other hand, by setting the inner surface temperature of the furnace body to 200°C or lower, the amount of impurities in the produced polysilicon can be sufficiently reduced. Note that the lower limit of the inner surface temperature of the furnace body is preferably 45°C or higher, more preferably 65°C or higher, and even more preferably 85°C or higher. On the other hand, the upper limit of the inner surface temperature of the furnace body is preferably 200°C or lower, and more preferably 150°C or lower.

[0031] Here, in this embodiment, the temperature adjustment unit 20 is configured to adjust the inner surface temperature of the furnace body 10 by controlling the temperature of the refrigerant supplied to the refrigerant inlet 22 (the inlet temperature T1 of the refrigerant). In this embodiment, as shown in FIG. 1, a refrigerant reflux pipe 28 (reflux path) that branches from the refrigerant discharge pipe 27 connected to the refrigerant outlet 23 and is connected to the refrigerant supply pipe 26 is provided, and by refluxing a part of the refrigerant discharged from the refrigerant outlet 23, the temperature of the refrigerant supplied to the refrigerant inlet 22 (the inlet temperature T1 of the refrigerant) is configured to be adjusted.

[0032] Also, in this embodiment, thermometers are respectively disposed at the refrigerant inlet 22 and the refrigerant outlet 23, and the temperature adjustment unit 20 is configured to manage such that the difference between the temperature of the refrigerant supplied to the refrigerant inlet 22 (the inlet temperature T1 of the refrigerant) and the temperature of the refrigerant discharged from the refrigerant outlet 23 (the outlet temperature T2 of the refrigerant) is 10°C or lower. Furthermore, in the present embodiment, the temperature adjustment unit 20 is configured to estimate the inner surface temperature of the furnace body 10 from the heat amount carried out by the refrigerant and perform temperature control.

[0033] Here, the inner wall temperature can be calculated using the following formula for obtaining the heat transfer amount from the inlet temperature T1 and the outlet temperature T2 of the refrigerant. Q = λS(T2 - T1) / t (Q: Heat transfer amount [W], λ: Thermal conductivity [W / (m·K)], S: Cross-sectional area [m 2 , T1, T2: Temperature [K], t: Thickness [m])

[0034] Next, a method for manufacturing polysilicon using the polysilicon reduction furnace 1 according to the present embodiment will be described. First, the seed rod 5 is inserted into the electrode portion 41 formed on the plate portion 11 and arranged in an inverted U shape using the connecting member 6. Next, the bell jar 16 is placed above the plate portion 11 to form the furnace body 10, and the inside of the furnace body 10 is made into a sealed space. Then, an inert gas is introduced into the furnace body 10 and replaced.

[0035] Then, the temperature adjustment unit 20 adjusts the inner surface temperature of the furnace body 10 within a range of 40°C or higher and 200°C or lower. After adjusting the inner surface temperature of the furnace body 10 as described above, a reaction gas containing chlorosilane is supplied into the furnace body 10 to start the reduction reaction of silicon. Silicon generated by the reduction reaction is deposited on the surface of the seed rod 5 to increase the diameter of the silicon rod. At this time, during the reduction reaction, the temperature adjustment unit 20 maintains the inner surface temperature of the furnace body 10 within a range of 40°C or higher and 200°C or lower. When the silicon rod grows to a predetermined diameter, the furnace body 10 is opened and the silicon rod is taken out. As described above, polysilicon is manufactured.

[0036] According to the polysilicon reduction furnace 1 and the method for manufacturing polysilicon having the above-described configuration, since the inner surface temperature of the furnace body 10 during the reduction reaction is adjusted to 40°C or higher by the temperature adjustment unit 20, generation of chloropolysilane inside the furnace body 10 can be suppressed. Therefore, blockage of the gas discharge pipe 34 and generation of hydrolyzates of explosive chloropolysilane can be suppressed, and it becomes possible to stably manufacture polysilicon. Also, since the inner surface temperature of the furnace body 10 during the reduction reaction is adjusted to 200°C or lower by the temperature adjustment unit 20, the amount of impurities in the polysilicon can be sufficiently reduced, and it becomes possible to manufacture high-purity polysilicon.

[0037] Here, in the present embodiment, when the furnace body 10 (plate portion 11 and bell jar 16) has a double-wall structure of an inner peripheral wall 12, 17 and an outer peripheral wall 13, 18, and a refrigerant flow path 21 through which a refrigerant flows is formed between the inner peripheral wall 12, 17 and the outer peripheral wall 13, 18, and the temperature adjustment unit 20 is configured to adjust the inner surface temperature of the furnace body by controlling the inlet temperature of the refrigerant, the inner surface temperature of the furnace body 10 (plate portion 11 and bell jar 16) during the reduction reaction can be accurately adjusted within the range of 40°C or higher and 200°C or lower, and it becomes possible to more stably manufacture high-purity polysilicon.

[0038] Also, in the present embodiment, when a refrigerant reflux pipe 28 that branches from the refrigerant discharge pipe 27 connected to the refrigerant outlet 23 and is connected to the refrigerant supply pipe 26 is provided and is configured to reflux a part of the refrigerant discharged from the refrigerant outlet 23, fluctuations in the inner surface temperature of the furnace body 10 can be suppressed, and the inner surface temperature of the furnace body 10 can be stably adjusted.

[0039] Furthermore, in the present embodiment, when the temperature adjustment unit 20 is configured to control such that the difference between the temperature of the refrigerant supplied to the refrigerant inlet 22 (refrigerant inlet temperature T1) and the temperature of the refrigerant discharged from the refrigerant outlet 23 (refrigerant outlet temperature T2) is 10°C or lower, fluctuations in the inner surface temperature of the furnace body 10 can be suppressed, and the inner surface temperature of the furnace body 10 can be stably adjusted.

[0040] In addition, in the present embodiment, when the temperature adjustment unit 20 is configured to estimate the inner surface temperature of the furnace body 10 from the heat quantity of the refrigerant taken out and perform temperature control, the cooling state by the refrigerant is grasped to control the inner surface temperature of the furnace body 10, and the inner surface temperature of the furnace body 10 can be stably adjusted.

[0041] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.

Example

[0042] The results of the confirmation experiment conducted to confirm the effectiveness of the present invention will be described below.

[0043] <Examples 1 to 3 of the present invention> The temperature of the cooling water flowing into the reduction furnace was adjusted to 45°C (Example 1), 65°C (Example 2), and 85°C (Example 3) by merging it with the refluxed cooling water. The furnace was operated in that state, and the amount of chlorosilane polymer remaining inside the furnace body after the operation was visually confirmed. The evaluation results are shown in Table 2 and FIG. 3.

[0044] <Comparative example> The furnace was operated without merging the cooling water flowing into the reduction furnace with the refluxed cooling water, and the amount of chlorosilane polymer remaining inside the furnace body after the operation was visually confirmed. (The temperature of the cooling water at this time was 30°C.) The evaluation results are shown in Table 2 and FIG. 3.

[0045]

Table 2

[0046] Comparing the amount of chlorosilane polymer remaining inside the furnace body among Examples 1 to 3 of the present invention and Comparative Example 1 above, it was confirmed that the amount of chlorosilane polymer in Examples 1 to 3 of the present invention where temperature adjustment was performed (see FIGS. 3(b) to (d)) was reduced compared to the Comparative Example (see FIG. 3(a)).

[0047] In this example, a small polysilicon reduction furnace was used. However, in an actual polysilicon reduction furnace used in production, since the load changes during the reaction, when using cooling water with a fixed quantity and temperature, excessive cooling would occur during the low-load period at the initial stage of the reaction. Therefore, as shown in the section on the embodiment, it is preferable to estimate the inner wall temperatures of the plate and the bell jar using the heat transfer calculation formula and control the cooling water so as not to overcool.

[0048] As described above, according to the example of the present invention, it was confirmed that it is possible to provide a polysilicon reduction furnace capable of suppressing the generation of chlorosilane polymer and producing high-purity polysilicon, and a method for producing polysilicon.

Explanation of Signs

[0049] 1 Polysilicon reduction furnace 10 Furnace body 11 Plate part 12 Inner peripheral wall 13 Outer peripheral wall 16 Bell jar 17 Inner peripheral wall 18 Outer peripheral wall 20 Temperature adjustment part 21 Refrigerant flow path 22 Refrigerant inlet 23 Refrigerant outlet 26 Refrigerant supply pipe 27 Refrigerant discharge pipe 28 Refrigerant reflux pipe (reflux path)

Claims

1. A polysilicon reduction furnace for reducing and depositing silicon on a seed rod by supplying a reaction gas containing chlorosilane into a furnace body containing a seed rod heated by energization, characterized in that it is provided with a temperature adjustment unit for adjusting the inner surface temperature of the furnace body during the reduction reaction within a range of 40°C or higher and 200°C or lower.

2. The furnace body has an inner peripheral wall and an outer peripheral wall covering the outside of the inner peripheral wall, and a refrigerant flow path through which a refrigerant flows is formed between the inner peripheral wall and the outer peripheral wall, and the temperature adjustment unit adjusts the inner surface temperature of the furnace body by controlling the inlet temperature of the refrigerant. The polysilicon reduction furnace according to claim 1.

3. The polysilicon reduction furnace according to claim 2, characterized in that it has a reflux path for refluxing a part of the refrigerant discharged from the outlet of the refrigerant flow path into the refrigerant flow path.

4. The temperature adjustment unit controls the temperature adjustment unit such that the difference between the inlet temperature and the outlet temperature of the refrigerant is 10°C or less. The polysilicon reduction furnace according to claim 2.

5. The temperature adjustment unit estimates and controls the inner surface temperature of the furnace body from the heat carried out by the refrigerant. The polysilicon reduction furnace according to claim 2.

6. A method for producing polysilicon using the polysilicon reduction furnace according to any one of claims 1 to 5, characterized in that the inner surface temperature of the furnace body during the reduction reaction is adjusted within a range of 40°C or higher and 200°C or lower.

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