Polycrystalline silicon cleaning equipment

Abstract

While using hydrofluoric anhydride, the amount of hydrofluoric anhydride that needs to be recovered from exhaust gases should be kept to a minimum. [Solution] The polycrystalline silicon cleaning apparatus (1) comprises a cleaning tank (2) for cleaning polycrystalline silicon using an etching solution, a mixing tank (3) for storing the etching solution supplied to the cleaning tank in a mixed state with the etching solution recovered from the cleaning tank, a tank cooling device (4) for cooling the mixing tank, a first supply unit (11) for supplying an aqueous solution of mineral acid or hydrogen peroxide to the mixing tank, and a second supply unit (12) for supplying liquid hydrofluoric anhydride to the mixing tank. The second supply unit comprises a state-holding mechanism (25) for holding hydrofluoric anhydride in a liquid state, and an internal piping (26) arranged to be heat-exchangeable with the etching solution stored in the mixing tank, through which the liquid hydrofluoric anhydride, which has an opening into the stored etching solution, passes.

Description

Technical Field

[0001] The present invention relates to a method for mixing an etching solution for polycrystalline silicon, a method for manufacturing polycrystalline silicon, and a cleaning apparatus for polycrystalline silicon.

Background Art

[0002] Conventionally, as an etching solution for surface cleaning of polycrystalline silicon, an aqueous solution of a mineral acid such as nitric acid, hydrochloric acid, or sulfuric acid, or a mixed solution obtained by mixing hydrogen fluoride (HF) with an aqueous solution of hydrogen peroxide has been used. Hydrogen fluoride is mixed in the state of a 50% by weight aqueous solution of hydrogen fluoride (hydrofluoric acid).

[0003] Also, Patent Document 1 discloses that 99.9% hydrogen fluoride gas (anhydrous hydrofluoric acid) of hydrogen fluoride is mixed with an aqueous nitric acid solution having a concentration of 70% by weight or more to form a mixed acid solution, and a silicon compound is added to this mixed acid solution and reacted to produce an etching solution.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional method using 50% by weight hydrofluoric acid, as hydrogen fluoride consumed in cleaning is replenished, water having the same weight as the hydrofluoric acid is mixed into the etching solution. Therefore, the concentration of the mineral acid or hydrogen peroxide in the etching solution decreases, and replenishment of the mineral acid or hydrogen peroxide is separately required.

[0006] ​On the other hand, the method described in Patent Document 1 uses hydrofluoric anhydride rather than an aqueous solution, which makes it possible to suppress the decrease in nitric acid concentration associated with the replenishment of hydrogen fluoride. However, because hydrofluoric anhydride is mixed with the etching solution in a gaseous state, the amount of hydrogen fluoride that needs to be removed from the exhaust gas before discharge inevitably becomes large. This is because there is a limit to the amount of hydrogen fluoride gas that can dissolve in water, and the undissolved hydrogen fluoride gas is discharged outside the system. As a result, large-scale pollution control equipment is required to remove hydrogen fluoride from the exhaust gas.

[0007] One aspect of the present invention aims to propose an etching solution mixing method that can minimize the amount of hydrogen fluoride that needs to be recovered from exhaust gas while using hydrofluoric anhydride. [Means for solving the problem]

[0008] To solve the above problems, a polycrystalline silicon cleaning apparatus according to one aspect of the present invention includes: a cleaning tank for cleaning polycrystalline silicon using an etching solution which is a mixture of hydrogen fluoride and an aqueous solution of mineral acid, an aqueous solution which is a mixture of mineral acid and an organic acid, or an aqueous solution which is [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to realize an etching solution mixing method that uses hydrofluoric anhydride while minimizing the amount of hydrogen fluoride that needs to be recovered from exhaust gas. [Brief explanation of the drawing]

[0010] [Figure 1] This is a process diagram of the method for mixing the etching solution for polycrystalline silicon according to this embodiment 1. [Figure 2] This is a diagram illustrating the cleaning process of polycrystalline silicon in Embodiment 2. [Figure 3] This figure shows an example of the second supply unit in the above-mentioned cleaning device. [Figure 4] This figure shows an example of the configuration of the tank portion in the above-mentioned cleaning device. [Modes for carrying out the invention]

[0011] [Embodiment 1] One embodiment of the present invention will be described in detail below. In this embodiment, a method for mixing etching solutions for polycrystalline silicon and a method for manufacturing polycrystalline silicon will be described.

[0012] Figure 1 is a process diagram of the mixing method for the etching solution for polycrystalline silicon according to this embodiment. As shown in Figure 1, in the liquefaction step P1, hydrofluoric anhydride is made into a liquid state by controlling the pressure, temperature, or both. In the subsequent mixing step P2, the hydrofluoric anhydride, which has been made into a liquid state in P1, is mixed with an aqueous solution containing mineral acid, a mixed aqueous solution containing mineral acid and organic acid, or an aqueous solution containing hydrogen peroxide, with a water content of 45% by weight or less, thereby dissolving the hydrofluoric anhydride in the water of the aqueous solution containing mineral acid, the mixed aqueous solution containing mineral acid and organic acid, or the aqueous solution containing hydrogen peroxide.

[0013] In the above mixing method, hydrofluoric anhydride is mixed with the aqueous solution in a liquid state and dissolved in the water of the aqueous solution, resulting in a larger dissolution rate compared to when hydrofluoric anhydride is in a gaseous state. Therefore, the amount of hydrogen fluoride recovered from exhaust gas can be reduced.

[0014] In addition, since the water content of the above aqueous solution mixed with hydrofluoric anhydride is 45% by weight or less, the temperature rise of the etching solution due to the heat of hydration generated when hydrofluoric anhydride dissolves in the water of the above aqueous solution is not abrupt and can be suppressed to an acceptable level. By suppressing the temperature rise of the etching solution, the amount of hydrogen fluoride vaporized in the etching solution due to the heat of hydration can be minimized as much as possible.

[0015] In order to maintain the etching reaction rate, it is preferable that the water content of the above aqueous solution is 30% by weight or more. More preferably, the water content of the above aqueous solution is 35% by weight or more and 40% by weight or less.

[0016] The above mineral acid is, for example, nitric acid, and the above organic acid is, for example, acetic acid. The above mineral acid may be hydrochloric acid, sulfuric acid, or the like.

[0017] The method for producing polycrystalline silicon in this embodiment includes a step of cleaning the surface of polycrystalline silicon using an etching solution mixed by using such a method for mixing an etching solution for polycrystalline silicon. Thereby, large-scale decontamination equipment is not required, and the production cost of polycrystalline silicon can be reduced.

[0018] In the following Embodiment 2, a cleaning apparatus for polycrystalline silicon suitable for the method for mixing an etching solution for polycrystalline silicon in this embodiment and the method for producing polycrystalline silicon in this embodiment will be described.

[0019] 〔Embodiment 2〕 Other embodiments of the present invention will be described below.

[0020] In this embodiment, the cleaning apparatus 1 for polycrystalline silicon will be described. FIG. 2 is a diagram for explaining the cleaning process of polycrystalline silicon in Embodiment 2. In the following, the "cleaning apparatus for polycrystalline silicon" is referred to as the "cleaning apparatus".

[0021] The first etching solution is either only hydrofluoric acid (an aqueous solution of hydrogen fluoride) or an aqueous solution containing hydrogen fluoride and hydrogen peroxide (H2O2).

[0022] The second etching solution is mixed using the method for mixing the etching solution for polycrystalline silicon described in Embodiment 1, and is an aqueous solution containing hydrogen fluoride and nitric acid (HNO3).

[0023] Although details will be described later, in this embodiment, gaseous (liquefied gas) anhydrous hydrofluoric acid (anhydrous hydrogen fluoride, AHF) is used in the second etching solution, and anhydrous hydrofluoric acid is mixed into an aqueous solution of nitric acid (HNO3) to dissolve the anhydrous hydrofluoric acid in the water content of the aqueous solution of nitric acid (HNO3).

[0024] In the example of FIG. 2, the polycrystalline silicon PC is washed in the order of washing with the second etching solution → washing with the first etching solution → washing with the second etching solution, or washing with the first etching solution → washing with the second etching solution → washing with the first etching solution → washing with the second etching solution.

[0025] (State holding mechanism of the second supply unit) FIG. 3 is a diagram showing an example of the second supply unit 12 in the cleaning apparatus 1. The second supply unit 12 supplies anhydrous hydrofluoric acid (liquid) to a mixing tank 3, which will be described later, in the cleaning apparatus 1. The second supply unit 12 is a part of the cleaning apparatus 1 and includes a state holding mechanism 25 that holds anhydrous hydrofluoric acid in a liquid state and an in-tank pipe 26 (see FIG. 4), which will be described later.

[0026] In the example of FIG. 3, the second supply unit 12 includes a flow rate control unit 27 for controlling the flow rate during the supply of anhydrous hydrofluoric acid at the end portion of the path for supplying liquid anhydrous hydrofluoric acid to the mixing tank 3 corresponding to the mixing tank 3. The flow rate control unit 27 controls the flow rate of the anhydrous hydrofluoric acid supplied to the mixing tank 3 to, for example, 0.1 to 1.0 L / min.

[0027] The second supply unit 12 includes a storage tank 31, a pressurizing device 32, first to third cooling devices 33 to 35, a delivery pump 36, a thermometer 37, a first pressure gauge 38, a second pressure gauge 39, first to fourth valves 41 to 44, and the like.

[0028] The storage tank 31 stores hydrofluoric anhydride supplied from an external source in a liquid state. A first cooling device 33 is located in the supply path of hydrofluoric anhydride to the storage tank 31, and cooled hydrofluoric anhydride in a liquid state is supplied to the storage tank 31. Hereinafter, hydrofluoric anhydride in a liquid state will be referred to as hydrofluoric anhydride (liquid).

[0029] The pressurizing device 32 pressurizes hydrofluoric anhydride (liquid). Specifically, the pressurizing device 32 supplies nitrogen (gas) to the storage tank 31 to pressurize the storage tank 31 so that the pressure inside the storage tank 31 is within a predetermined range. The pressure inside the storage tank 31 is measured by the first pressure gauge 38, and the opening and closing of the first valve 41 and the second valve 42 are controlled based on the measured value.

[0030] When the pressure inside the storage tank 31 is high, the first valve 41, located in the path connecting the pressurizing device 32 and the storage tank 31, is controlled to close, and the second valve 42, located in the path connecting the pollution control equipment 45 and the storage tank 31, is controlled to open. This adjusts the pressure inside the storage tank 31 to stay within a predetermined range. The pressurizing device 32, along with the cooling mechanism described later, forms part of the state-maintaining mechanism 25.

[0031] The second cooling device 34 is located in the path connecting the storage tank 31 and the pollution control equipment 45. The second cooling device 34 is responsible for cooling the gas (exhaust gas) sent to the pollution control equipment 45 and returning the hydrogen fluoride, which is gaseous hydrofluoric acid (liquid) contained in the gas, back to the storage tank 31.

[0032] The discharge pump 36 sends the hydrofluoric anhydride (liquid) from the storage tank 31 to each path. The hydrofluoric anhydride (liquid) sent out by the discharge pump 36 returns to the storage tank 31 in a cooled state after passing through the cooling path 46 (thick line) where the third cooling device 35 is located.

[0033] The temperature of the hydrofluoric anhydride (liquid) in the storage tank 31 is measured by a thermometer 37, and based on the measured value, the opening and closing of the third valve 43 between the delivery pump 36 and the third cooling device 35 in the cooling path 46 is controlled. This adjusts the temperature of the hydrofluoric anhydride (liquid) in the storage tank 31 to be below a predetermined value, thereby maintaining the hydrofluoric anhydride in a liquid state.

[0034] The cooling mechanism is comprised of a delivery pump 36, a cooling path 46, a third cooling device 35, a thermometer 37, and a third valve 43, and this cooling mechanism functions as a state-holding mechanism 25 that controls the temperature of hydrofluoric anhydride to keep it in a liquid state. In other words, the state-holding mechanism 25 is equipped with a cooling mechanism that cools hydrofluoric anhydride.

[0035] The hydrofluoric anhydride (liquid) delivered by the delivery pump 36 is supplied to the mixing tank 3. The pressure in the path supplying the hydrofluoric anhydride (liquid) to the mixing tank 3 is measured by the second pressure gauge 39, and based on the measured value, the opening and closing of the fourth valve 44, which is located in the path connecting the delivery pump 36 and the storage tank 31, is controlled.

[0036] If the pressure in the supply path for hydrofluoric anhydride (liquid) to the mixing tank 3 is high, the fourth valve 44 is controlled to open. This allows hydrofluoric anhydride (liquid) to be supplied to the mixing tank 3 in a state that does not constitute high-pressure gas.

[0037] (Washing device using hydrofluoric anhydride) Figure 4 shows an example of the configuration of the tank portion in the cleaning apparatus 1 according to this embodiment. As shown in Figure 4, the cleaning apparatus 1 includes a second supply unit 12, a first supply unit 11, a cleaning tank 2, a mixing tank 3, a tank cooling device 4, a supply pump 5, a first supply pipe 6, a second supply pipe 7, a supply pipe 8, and a recovery pipe 9, etc.

[0038] The cleaning tank 2 cleans polycrystalline silicon PC using an etching solution which is a mixture of hydrogen fluoride and an aqueous solution of mineral acid, a mixed aqueous solution of mineral acid and organic acid, or an aqueous solution of hydrogen peroxide. The etching solution stored in the mixing tank 3 is supplied to the cleaning tank 2 via a supply pipe 8 equipped with a supply pump 5. The cleaning tank 2 is also provided with a recovery pipe 9 so that a portion of the etching solution used for cleaning is returned to the mixing tank 3 via the recovery pipe 9.

[0039] The mixing tank 3 is supplied with an aqueous solution of mineral acid, an aqueous solution of organic acid, or an aqueous solution of hydrogen peroxide from the first supply pipe 6, which is part of the first supply unit 11. The first supply unit 11 supplies an aqueous solution of mineral acid, a mixed aqueous solution of mineral acid and organic acid, or an aqueous solution of hydrogen peroxide.

[0040] Further, hydrofluoric anhydride (liquid) is supplied to the mixing tank 3 from the second supply pipe 7, which is part of the second supply unit 12 mentioned above. The mixing tank 3 stores the etching solution to be supplied to the cleaning tank 2 in a mixed state with the etching solution recovered from the cleaning tank 2. More specifically, the mixing tank 3 stores the etching solution stored in the mixing tank 3, a predetermined aqueous solution supplied from the first supply pipe 6, hydrofluoric anhydride (liquid) supplied from the second supply pipe 7, and the recovered etching solution returned from the recovery pipe 9, all mixed together.

[0041] The tank cooling device 4 cools the mixing tank 3 (the temperature of the liquid in the mixing tank 3) to a temperature lower than the boiling point of hydrogen fluoride. The tank cooling device 4 maintains the etching solution in the mixing tank 3 at a temperature lower than the boiling point of hydrogen fluoride. Preferably, the etching solution in the mixing tank 3 is kept at 15°C or lower. This allows the hydrofluoric anhydride (liquid) passing through the internal tank piping 26 to be sufficiently cooled.

[0042] The second supply unit 12 is further equipped with internal piping 26 through which hydrofluoric anhydride (liquid) provided in the mixing tank 3 passes. The internal piping 26 is arranged to exchange heat with the etching solution stored in the mixing tank 3 and opens into the etching solution stored in the mixing tank 3.

[0043] By providing the second supply unit 12 with such internal piping 26, the hydrofluoric anhydride (liquid) is cooled by heat exchange with the etching solution in the mixing tank 3, which is cooled by the tank cooling device 4, as it flows through the internal piping 26. As a result, the heat of hydration generated when the hydrofluoric anhydride (liquid) dissolves in the water in the etching solution (originally water contained in the aqueous solution of nitric acid, etc. supplied from the first supply unit 11) is offset, and the occurrence of bumping and other issues that are problems when using hydrofluoric anhydride can be effectively prevented (suppressed).

[0044] As mentioned above, the cleaning device 1 cleans the polycrystalline silicon PC using a second etching solution, which is an aqueous solution containing hydrofluoric acid and nitric acid. Therefore, the first supply unit 11 supplies an aqueous solution of nitric acid.

[0045] The internal piping 26 is 0.34m 2 It is preferable to have a heat exchange area of ​​the above size. This allows the hydrofluoric anhydride (liquid) to be sufficiently cooled to a temperature close to that of the etching solution as it passes through the piping 26 inside the tank. If the flow rate of hydrofluoric anhydride (liquid) during operation is, for example, in the range of 0.1 to 1.0 L / min, the hydrofluoric anhydride (liquid) can be sufficiently cooled even at the maximum flow rate of 1.0 L / min.

[0046] Furthermore, it is preferable that the internal piping 26 of the tank be made of fluororesin. Although aqueous solutions containing dissolved hydrofluoric acid are highly corrosive, corrosion of the internal piping 26 can be prevented by using fluororesin.

[0047] Furthermore, the mixing tank 3 is preferably made of PE (polyethylene resin), PP (polypropylene resin), or PVC (vinyl chloride resin), or a fluororesin such as PVDF, PFA, or PTFE. The mixing tank 3 may also be lined with the aforementioned PE, PP, PVC, PVDF, PFA, or PTFE.

[0048] This improves chemical resistance and prevents corrosion of the mixing tank 3. More preferably, in addition to the mixing tank 3, the storage tank 31 and the liquid delivery piping for hydrofluoric anhydride (liquid) in the second supply unit 12 are also lined. This prevents corrosion of the storage tank 31 and the liquid delivery piping, along with the mixing tank 3.

[0049] Furthermore, it is preferable that the pressurizing device 32 pressurizes the hydrofluoric anhydride (liquid) at the flow control unit 27, which is located at the end of the path supplying hydrofluoric anhydride (liquid) to the mixing tank 3, so that the pressure of the hydrofluoric anhydride (liquid) is 50 kPa or higher. This allows the hydrofluoric anhydride to be supplied to the mixing tank 3 in liquid form even when the ambient temperature is high. More preferably, the pressurizing device 32 pressurizes the flow control unit 27 so that the pressure is 70 kPa or higher.

[0050] (Additional notes) A method for mixing an etching solution for polycrystalline silicon according to one aspect of the present invention involves controlling the pressure, temperature, or both to make hydrofluoric anhydride liquid, mixing the liquid hydrofluoric anhydride with an aqueous solution containing a mineral acid, a mixed aqueous solution containing a mineral acid and an organic acid, or an aqueous solution containing hydrogen peroxide, with a water content of 45% by weight or less, thereby dissolving the hydrofluoric anhydride in the water of the aqueous solution containing the mineral acid, the mixed aqueous solution containing a mineral acid and an organic acid, or the aqueous solution containing hydrogen peroxide.

[0051] Furthermore, a method for producing polycrystalline silicon according to one aspect of the present invention includes a step of surface cleaning of polycrystalline silicon using an etching solution mixed using a method for mixing etching solutions for polycrystalline silicon according to one aspect of the present invention.

[0052] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0053] 1. Washing device 2. Washing tank 3 Mixing tank 4 tank cooling device 11 1st supply section 12 2nd supply section 25 State-holding mechanism 26 Internal piping 27 Flow Control Unit 32 Pressurizing device 35 Third cooling device (cooling mechanism) 36. Dispensing pump (cooling mechanism) 37 Thermometer (cooling mechanism) 45 Abatement equipment 46. ​​Cooling path (cooling mechanism) P1 Liquefaction process P2 Mixing process

Claims

1. A cleaning tank for cleaning polycrystalline silicon using an etching solution which is a mixture of hydrogen fluoride, an aqueous solution of mineral acid, a mixed aqueous solution of mineral acid and organic acid, or an aqueous solution of hydrogen peroxide, A mixing tank for storing the etching solution supplied to the cleaning tank in a state mixed with the etching solution recovered from the cleaning tank, The aforementioned mixing tank is cooled by a tank cooling device that cools the tank to a temperature lower than the boiling point of hydrogen fluoride, The mixing tank is provided with a first supply unit that supplies an aqueous solution of the mineral acid or an aqueous solution of hydrogen peroxide, The mixing tank is further equipped with a second supply unit for supplying liquid hydrofluoric anhydride. The second supply unit is, A state-holding mechanism that maintains hydrofluoric anhydride in a liquid state, A cleaning apparatus for polycrystalline silicon, comprising: an internal piping provided in the mixing tank through which liquid hydrofluoric anhydride passes; the internal piping being arranged to be heat exchangeable with the etching solution stored in the mixing tank and opening into the stored etching solution.

2. The cleaning apparatus for polycrystalline silicon according to claim 1, characterized in that the mineral acid is nitric acid.

3. The cleaning apparatus for polycrystalline silicon according to claim 1, characterized in that the organic acid is acetic acid.

4. The cleaning apparatus for polycrystalline silicon according to any one of claims 1 to 3, characterized in that the state-holding mechanism comprises a cooling mechanism for cooling hydrofluoric anhydride.

5. The piping inside the tank is 0.34 m ２ A cleaning apparatus for polycrystalline silicon according to any one of claims 1 to 3, characterized by having the above heat exchange area.

6. The polycrystalline silicon cleaning apparatus according to any one of claims 1 to 3, characterized in that the mixing tank is made of PE, PP, PVC, PVDF, PFA, or PTFE, or is lined with PE, PP, PVC, PVDF, PFA, or PTFE.

7. The state-holding mechanism includes a pressurizing device for pressurizing hydrofluoric anhydride, The second supply unit is, The end portion of the path for supplying the hydrofluoric anhydride to the mixing tank is provided with a flow control unit for controlling the flow rate of the hydrofluoric anhydride during supply. The flow rate control unit controls the flow rate to 0.1 to 1.0 L / min. The polycrystalline silicon cleaning apparatus according to any one of claims 1 to 3, characterized in that the pressurizing device pressurizes the hydrofluoric anhydride in the flow control unit to 50 kPa or more.

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