A method for improving the shutdown of an electronic grade polysilicon reduction furnace

Abstract

The application provides a method for improving the shutdown of an electronic-grade polysilicon reduction furnace, which comprises the following steps: slowly reducing the feeding amount of the reduction furnace, reducing the running current of the reduction furnace, controlling the temperature balance in the reduction furnace, controlling the running temperature of the jacket water of the reduction furnace to remain unchanged, and then cutting off the power supply of the reduction furnace; after the power supply of the reduction furnace is cut off, the hydrogen purging flow is reduced again, and the jacket water flow of the reduction furnace is reduced to avoid the sharp cooling of the surface temperature of the silicon rod, so that the stress of the polysilicon rod can be slowly released after the power supply is cut off, the reduction furnace is prevented from being reversed, and the stability and economy of the electronic-grade polysilicon production can be ensured.

Description

Technical Field

[0001] This invention relates to the field of polysilicon reduction, and more specifically to a furnace shutdown method for improving the inverted rods in electronic-grade polysilicon reduction furnaces. Background Technology

[0002] In the field of electronic-grade polycrystalline silicon material preparation, the modified Siemens process remains the mainstream production process in China due to its mature process system and stable production capacity. As the core equipment in this process, the stability of the reduction furnace and the scientific nature of its shutdown operation are directly related to production efficiency and product quality.

[0003] Currently, the commonly used shutdown methods for reduction furnaces have significant technical shortcomings: the operation simply involves directly cutting off the material supply, followed by reducing the current slightly before directly shutting off the power. The entire process lacks systematic and precise control over the temperature of the silicon rods and the temperature of the water in the furnace jacket. This crude shutdown method causes a sharp drop in the temperature of the polycrystalline silicon rods after power is cut off. The stress generated inside the silicon rods due to the sudden temperature change cannot be effectively and evenly released, leading to rod collapse in the reduction furnace.

[0004] The problem of inverted silicon rods can lead to a series of serious production hazards and economic losses. On the one hand, inverted silicon rods can directly damage core equipment such as reduction furnaces and reactors, such as damage to the inner wall and chassis of the reduction furnace, damage to the electrodes of the reduction furnace, damage to the graphite parts used in production, and broken silicon blocks clogging the tail gas pipes. Moreover, after the reduction furnace is dismantled, it is necessary to repair the reduction furnace, chassis, and electrodes, and clean the tail gas pipes, which increases equipment maintenance costs and downtime, disrupts the normal production rhythm, and causes production delays. At the same time, more impurities will be introduced during the dismantling process, which will lead to a downgrade in the quality of polysilicon products and affect the market competitiveness of the products. There are certain safety risks in the dismantling process of the reduction furnace after inverted silicon rods, which may cause safety accidents. Moreover, high-density polycrystalline silicon rods (such as semiconductor-grade polycrystalline silicon rods and zone-melting-grade polycrystalline silicon rods) have a higher rate of tipping over. This is because, compared to ordinary polycrystalline silicon rods, high-density polycrystalline silicon rods have a more compact crystal structure, are more sensitive to temperature changes, exhibit more prominent stress concentration, and show more obvious uneven stress release within the silicon rod during furnace shutdown. Therefore, they are more prone to breakage or tipping over.

[0005] From the perspective of actual industry production, although there are many reasons for the collapse of the reduction furnace rods (such as substandard silicon core loading quality, silicon core height and curvature not meeting process requirements, unreasonable production process parameters and formulas, etc.), the stress release problem during the shutdown stage is most prominent in the production of high-density polycrystalline silicon rods, and has become a key bottleneck restricting the efficient and stable production of electronic-grade polycrystalline silicon. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an efficient, stable, and safe method for shutting down an electronic-grade polysilicon reduction furnace to prevent rod collapse. This method solves the stress release problem after power is cut off to the polysilicon rods in the reduction furnace, avoids rod collapse, and ensures that equipment, quality, and production cycle are not affected. In practical applications, it has achieved a good effect in reducing the rod collapse rate.

[0007] This invention is implemented by the following technical solution:

[0008] An improved shutdown method for inverting the ingots in an electronic-grade polycrystalline silicon reduction furnace includes the following stages:

[0009] (1) Material reduction stage: During the first execution cycle, the flow rate of trichlorosilane is uniformly reduced to the first preset value of trichlorosilane flow rate, the flow rate of hydrogen is reduced proportionally, and the operating current of the reduction furnace is reduced to the first preset value of current.

[0010] (2) Low material maintenance phase: During the second execution cycle, the flow rates of trichlorosilane and hydrogen, as well as the operating current of the reduction furnace, remain unchanged;

[0011] (3) Trichlorosilane interruption and heating stage: During the third execution cycle, the flow rate of trichlorosilane is reduced to 0KG / h, the flow rate of hydrogen is reduced to the second preset value of hydrogen flow rate, and the operating current of the reduction furnace remains unchanged.

[0012] After the third execution cycle ends, in the fourth execution cycle, the operating current of the reduction furnace is first increased to the second current preset value, and then the hydrogen flow rate and the operating current of the reduction furnace are kept unchanged; and the second current preset value is greater than the first current preset value.

[0013] (4) Reduction furnace power-off stage: During the fifth execution cycle, the operating current of the reduction furnace is uniformly reduced to 0A, and the reduction furnace is powered off; the hydrogen flow rate remains unchanged;

[0014] In the (1) material reduction stage, the (2) low material maintenance stage, the (3) trichlorosilane material cut-off and heating stage and the (4) reduction furnace power-off stage, the reduction furnace jacket water temperature is maintained within the specified deviation range of the jacket water temperature before shutdown by adjusting the water flow regulating valve of the reduction furnace jacket water.

[0015] (5) Hydrogen purging and cooling stage: During the sixth execution cycle, adjust the water flow regulating valve of the reduction furnace jacket water to reduce the water flow of the reduction furnace jacket to the first water flow preset value; the hydrogen flow remains unchanged or is reduced to the third hydrogen flow preset value.

[0016] (6) Shutdown and replacement stage: Use nitrogen to pressurize the reduction furnace to above 0.35MPa, and then depressurize. Each pressurization and depressurization takes more than 35 minutes. Repeat the pressurization and depressurization more than 6 times. Through this step, the flammable and explosive gases in the reduction furnace are fully replaced, so as to achieve the purpose of dismantling the furnace.

[0017] Furthermore, in the (1) material reduction stage, the first execution cycle is 20-60 min, the first current preset value is 560-980 A, and the first flow rate preset value of the trichlorosilane is 350-650 Kg / h.

[0018] Furthermore, in the (2) low material maintenance phase, the second execution cycle is 10-30 min.

[0019] Furthermore, in the trichlorosilane cutting-off heating stage (3), the third execution cycle is 10-20 min; the second hydrogen flow rate is preset to 12-20 kg / h; the fourth execution cycle is 35-80 min; and the second current is preset to 650-1020 A.

[0020] Furthermore, during the (4) reduction furnace power-off phase, the fifth execution cycle is 10-40 minutes.

[0021] Furthermore, in the hydrogen purging and cooling stage (5), the preset value of the first water flow rate is 2-5 m³ / h. 3 / h, the sixth execution cycle is 4-8h, and the preset value of the third hydrogen flow rate is 5-10Kg / h.

[0022] Furthermore, the specified deviation range is 0–2°C.

[0023] Advantages of this invention:

[0024] This invention controls the temperature inside the reduction furnace to remain balanced by gradually reducing the feed rate and decreasing the operating current, while simultaneously maintaining a constant operating temperature of the water in the furnace jacket until the furnace is powered off. After power is cut off, the hydrogen purging flow rate and the water flow rate in the furnace jacket are further reduced to prevent a rapid cooling of the silicon rod surface temperature. This allows the stress on the polycrystalline silicon rods to be released slowly after the furnace is shut down and the power is cut off, preventing the rods from collapsing. This ensures that the equipment, quality, and production cycle are not affected, avoiding risks such as equipment damage, product quality degradation, and production safety, and guaranteeing the stability and economy of electronic-grade polycrystalline silicon production. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] An improved shutdown method for inverting rods in an electronic-grade polycrystalline silicon reduction furnace, taking a 12-pair rod reduction furnace as an example, includes the following stages:

[0028] (1) Material reduction stage: Within 30 minutes, the flow rate of trichlorosilane is uniformly reduced to 500 kg / h, and the flow rate of hydrogen is reduced to 30 kg / h in the same proportion, so that the ratio of trichlorosilane and hydrogen is the same as that of trichlorosilane and hydrogen during the operation of the reduction furnace; and the operating current of the reduction furnace is reduced to 600A; by adjusting the water flow rate regulating valve of the reduction furnace jacket water, the temperature of the reduction furnace jacket water is maintained within the specified deviation range of the jacket water temperature (155℃) before the furnace shutdown; the specified deviation range is 0-2℃.

[0029] (2) Low material maintenance stage: maintain trichlorosilane flow rate of 500 kg / h, hydrogen flow rate of 30 kg / h, and reduction furnace operating current of 600 A; maintain for 20 min; maintain the reduction furnace jacket water temperature at a constant level during this stage;

[0030] (3) Trichlorosilane interruption and heating stage: Use 10 minutes to uniformly reduce the flow rate of trichlorosilane to 0 kg / h and the flow rate of hydrogen to 12 kg / h; During the trichlorosilane interruption process, the operating current of the reduction furnace is kept constant at 600 A; After the flow rates of trichlorosilane and hydrogen are adjusted, use 10 minutes to increase the current to 650 A and then maintain it for 40 minutes; During this stage, the temperature of the jacket water of the reduction furnace is kept constant.

[0031] (4) Power off stage of reduction furnace: Use 10 minutes to reduce the operating current of reduction furnace to 0A and power off reduction furnace; during this stage, maintain the temperature of reduction furnace jacket water at a constant level.

[0032] (5) Hydrogen purging and cooling stage: During the sixth execution cycle, adjust the water flow regulating valve of the reduction furnace jacket to reduce the water flow rate of the reduction furnace jacket to 2m. 3 / h; reduce hydrogen flow rate to 8Kg / h and maintain hydrogen purging for 6h;

[0033] (6) Shutdown and replacement stage: Nitrogen gas is used to pressurize the reduction furnace to above 0.40 MPa, and then depressurization is carried out. Each pressurization and depressurization takes 38 minutes. The pressurization and depressurization are repeated 6 times. This step ensures that the flammable and explosive gases in the reduction furnace are fully replaced, which improves the safety of production and achieves the purpose of dismantling the furnace.

[0034] Example 2

[0035] An improved shutdown method for inverting rods in an electronic-grade polycrystalline silicon reduction furnace, taking a 12-pair rod reduction furnace as an example, includes the following stages:

[0036] (1) Material reduction stage: Within 50 minutes, the flow rate of trichlorosilane is uniformly reduced to 600 kg / h, and the flow rate of hydrogen is reduced to 35 kg / h in the same proportion, so that the ratio of trichlorosilane and hydrogen is the same as that of trichlorosilane and hydrogen during the operation of the reduction furnace; and the operating current of the reduction furnace is reduced to 700 A; the temperature of the water in the jacket of the reduction furnace is maintained at 155℃ by adjusting the water flow regulating valve of the jacket water of the reduction furnace; the specified deviation range is 0-2℃.

[0037] (2) Low material maintenance stage: maintain trichlorosilane flow rate of 600 kg / h, hydrogen flow rate of 35 kg / h, and reduction furnace operating current of 700 A; maintain for 30 min; maintain the reduction furnace jacket water temperature at a constant level during this stage.

[0038] (3) Trichlorosilane interruption and heating stage: Use 20 minutes to uniformly reduce the flow rate of trichlorosilane to 0 kg / h and the flow rate of hydrogen to 15 kg / h; During the trichlorosilane interruption process, the operating current of the reduction furnace is kept constant at 700 A; After the flow rates of trichlorosilane and hydrogen are adjusted, first use 20 minutes to increase the current to 750 A, and then maintain it for 60 minutes; During this stage, the temperature of the jacket water of the reduction furnace is kept constant.

[0039] (4) Power-off stage of reduction furnace: Use 20 minutes to reduce the operating current of reduction furnace to 0A and power off reduction furnace; during this stage, maintain the temperature of reduction furnace jacket water at a constant level;

[0040] (5) Hydrogen purging and cooling stage: During the sixth execution cycle, adjust the water flow regulating valve of the reduction furnace jacket to reduce the water flow rate of the reduction furnace jacket to 3m³. 3 / h; reduce hydrogen flow rate to 10Kg / h and maintain hydrogen purging for 8h;

[0041] (6) Shutdown and replacement stage: Use nitrogen to fully replace the hydrogen in the reduction furnace. The specific method is to pressurize the nitrogen to 0.38MPa and then depressurize it. Repeat the pressurization and depressurization step 8 times. Each pressurization and depressurization lasts for 40 minutes.

[0042] Example 3

[0043] An improved shutdown method for inverting rods in an electronic-grade polycrystalline silicon reduction furnace, taking a 12-pair rod reduction furnace as an example, includes the following stages:

[0044] (2) Material reduction stage: Within 60 minutes, the flow rate of trichlorosilane is uniformly reduced to 600 kg / h, and the flow rate of hydrogen is reduced proportionally to 35 kg / h, so that the ratio of trichlorosilane and hydrogen is the same as that of trichlorosilane and hydrogen during the operation of the reduction furnace; and the operating current of the reduction furnace is reduced to 900 A; the temperature of the water in the jacket of the reduction furnace is maintained at 155℃ by adjusting the water flow regulating valve of the jacket water of the reduction furnace; the specified deviation range is 0-2℃.

[0045] (2) Low material maintenance stage: maintain trichlorosilane flow rate of 600 kg / h, hydrogen flow rate of 35 kg / h, and reduction furnace operating current of 900 A; maintain for 30 min; maintain the reduction furnace jacket water temperature at a constant level during this stage.

[0046] (3) Trichlorosilane interruption and heating stage: Use 20 minutes to uniformly reduce the flow rate of trichlorosilane to 0 kg / h and the flow rate of hydrogen to 15 kg / h; During the trichlorosilane interruption process, the operating current of the reduction furnace is kept constant at 900 A; After the flow rates of trichlorosilane and hydrogen are adjusted, first use 30 minutes to increase the current to 950 A, and then maintain it for 40 minutes; During this stage, the temperature of the jacket water of the reduction furnace is kept constant.

[0047] (4) Power-off stage of reduction furnace: Use 30 minutes to reduce the operating current of reduction furnace to 0A and power off reduction furnace; during this stage, maintain the temperature of reduction furnace jacket water at a constant level.

[0048] (5) Hydrogen purging and cooling stage: During the sixth execution cycle, adjust the water flow regulating valve of the reduction furnace jacket to reduce the water flow rate of the reduction furnace jacket to 5m³. 3 / h; reduce hydrogen flow rate to 10Kg / h and maintain hydrogen purging for 8h;

[0049] (6) Shutdown and replacement stage: Use nitrogen to fully replace the hydrogen in the reduction furnace. The specific method is to pressurize the nitrogen to above 0.42MPa and then depressurize it. Repeat the pressurization and depressurization step 10 times. Each pressurization and depressurization lasts for 40 minutes.

[0050] In Examples 1-3, no rod collapse occurred during the shutdown process, indicating that the improved shutdown method for preventing rod collapse in electronic-grade polysilicon reduction furnaces provided by this invention effectively solves the stress release problem after power failure of the polysilicon rods in the reduction furnace. This method exhibits good operability and stability in actual production and can significantly reduce the probability of rod collapse in the reduction furnace.

[0051] This invention, by refining the furnace shutdown method, enables the full release of silicon rod stress. Production verification shows that before using the technical solution of this invention, the rod failure rate was about 70%; after adopting the technical solution of this invention, the rod failure rate is about 5%, which can provide strong support for the production of electronic-grade polycrystalline silicon and has broad application prospects and significant economic benefits.

[0052] In this embodiment, during the material lowering stage, the operating current of the reduction furnace and the water flow regulating valve in the reduction furnace jacket can be reduced to maintain a constant temperature for the reduction furnace jacket water and the reduction furnace reaction temperature. During this stage, a certain amount of material is maintained in the reduction furnace for reaction, which can maintain consistency with the gas field and temperature field during the operation of the reduction furnace, avoiding the phenomenon of rapid material cutting causing a significant increase in the surface temperature of the silicon rod, resulting in melting of the silicon rod beam.

[0053] During the low-material maintenance stage, the flow rates of trichlorosilane and hydrogen are reduced, resulting in a decrease in the reaction temperature of the reduction furnace, while the temperature of the water in the reduction furnace jacket remains constant. The main purpose of this stage is to repair minor defects on the silicon rod surface. Maintaining a low flow rate allows for the repair of micro-cracks on the silicon rod surface, improving its surface morphology.

[0054] During the trichlorosilane cutting-off and heating stage, the trichlorosilane cutting-off is cut off, and the surface temperature of the silicon rod is increased by 20-50°C by increasing the operating current of the reduction furnace. By heating the silicon rod, the temperature from the center to the surface of the silicon rod is kept consistent, reducing the temperature difference.

[0055] During the power-off phase of the reduction furnace, the power to the reduction furnace is turned off, and the temperature is gradually reduced so that the temperature at the center and surface of the silicon rod decreases uniformly.

[0056] During the hydrogen purging and cooling stage, after the reduction furnace is powered off, hydrogen purging is maintained and the water flow rate in the reduction furnace jacket is reduced. During this stage, hydrogen purging can reduce external factors that interfere with the surface temperature of the silicon rod, and avoid the rod falling over due to excessively rapid temperature drop on the external surface of the silicon rod and internal and external temperature stress.

[0057] During the shutdown and replacement phase, nitrogen is used to fully replace the flammable and explosive gases in the reduction furnace in order to achieve safe furnace dismantling.

[0058] The above steps cover all operations during the shutdown phase. The trichlorosilane flow rate and hydrogen flow rate data are for a 12-pair rod reduction furnace. For larger reduction furnaces such as 24-pair rod reduction furnaces, 40-pair rod reduction furnaces, and 60-pair rod reduction furnaces, the trichlorosilane flow rate and hydrogen flow rate data can be increased by the corresponding ratios (2 times, 3.5 times, and 5 times, respectively) according to the steps in this embodiment. This can also solve the problem of rod collapse caused by stress release issues.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the shutdown process of an electronic-grade polycrystalline silicon reduction furnace, characterized in that, Includes the following stages: (1) Material reduction stage: During the first execution cycle, the flow rate of trichlorosilane is uniformly reduced to the first preset value of trichlorosilane flow rate, the flow rate of hydrogen is reduced proportionally, and the operating current of the reduction furnace is reduced to the first preset value of current. (2) Low material maintenance phase: During the second execution cycle, the flow rates of trichlorosilane and hydrogen, as well as the operating current of the reduction furnace, remain unchanged; (3) Trichlorosilane interruption and heating stage: During the third execution cycle, the flow rate of trichlorosilane is reduced to 0KG / h, the flow rate of hydrogen is reduced to the second preset value of hydrogen flow rate, and the operating current of the reduction furnace remains unchanged. After the third execution cycle ends, in the fourth execution cycle, the operating current of the reduction furnace is first increased to the second current preset value, and then the hydrogen flow rate and the operating current of the reduction furnace are kept unchanged. Furthermore, the second preset current value is greater than the first preset current value; (4) Reduction furnace power-off stage: During the fifth execution cycle, the operating current of the reduction furnace is uniformly reduced to 0A, and the reduction furnace is powered off; the hydrogen flow rate remains unchanged; In the (1) material reduction stage, the (2) low material maintenance stage, the (3) trichlorosilane material cut-off and heating stage and the (4) reduction furnace power-off stage, the reduction furnace jacket water temperature is maintained within the specified deviation range of the jacket water temperature before shutdown by adjusting the water flow regulating valve of the reduction furnace jacket water. (5) Hydrogen purging and cooling stage: During the sixth execution cycle, adjust the water flow regulating valve of the reduction furnace jacket water to uniformly reduce the water flow of the reduction furnace jacket to the first water flow preset value; the hydrogen flow remains unchanged or is reduced to the third hydrogen flow preset value. (6) Shutdown and replacement stage: Use nitrogen to pressurize the reduction furnace to above 0.35MPa, and then depressurize. Each pressurization and depressurization should last for more than 35 minutes; repeat the pressurization and depressurization process more than 6 times. In the trichlorosilane cutting-off heating stage (3), the third execution cycle is 10-20 min; the second hydrogen flow rate is preset to 12-20 kg / h; the fourth execution cycle is 35-80 min; and the second current is preset to 650-1020 A.

2. The furnace shutdown method for improving the tripping of the electronic-grade polycrystalline silicon reduction furnace according to claim 1, characterized in that, In the (1) material dropping stage, the first execution cycle is 20-60 min, the first current preset value is 560-980 A, and the first flow rate preset value of the trichlorosilane is 350-650 Kg / h.

3. The furnace shutdown method for improving the tipping of rods in an electronic-grade polycrystalline silicon reduction furnace according to claim 1, characterized in that, In the (2) low material maintenance phase, the second execution cycle is 10-30 min.

4. The furnace shutdown method for improving the tripping of the electronic-grade polycrystalline silicon reduction furnace according to claim 1, characterized in that, During the power outage phase of the reduction furnace in (4), the fifth execution cycle is 10-40 min.

5. The furnace shutdown method for improving the tipping of bars in an electronic-grade polycrystalline silicon reduction furnace according to claim 1, characterized in that, In the hydrogen purging and cooling stage (5), the preset value of the first water flow rate is 2-5 m³ / h. 3 / h, the sixth execution cycle is 4-8h, and the preset value of the third hydrogen flow rate is 5-10Kg / h.

6. The furnace shutdown method for improving the tipping of bars in an electronic-grade polycrystalline silicon reduction furnace according to claim 1, characterized in that, The specified deviation range is 0–2℃.