Polycrystalline silicon core cleaning method and system

Abstract

The invention discloses a polycrystalline silicon core cleaning method and system, relates to the technical field of polycrystalline silicon core production, and mainly aims to improve the cleaning quality of silicon cores. According to the main technical scheme, the polycrystalline silicon core cleaning method comprises the following steps: (1) mixed acid pickling; (2) spraying with pure water, bubbling and rinsing; (3) ultrasonic pure water washing; (4) wind cutting water removal; and (5) vacuum microwave drying.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline silicon core production technology, and in particular to a method and system for cleaning polycrystalline silicon cores. Background Technology

[0002] The main production process for polycrystalline silicon is the modified Siemens process. In this process, the silicon core serves as a crucial carrier material for polycrystalline silicon deposition, and its quality significantly impacts the quality of the rod-shaped silicon. During the growth of polycrystalline silicon, the surface of the silicon core is gradually covered by newly deposited silicon layers, forming polycrystalline silicon crystals, which primarily serve as the basis for the deposited silicon material. The entire process of silicon core production, from the pulling stage to furnace loading, can be divided into four stages: pulling, machining, cleaning and drying, and packaging. Cleaning the silicon core is a critical step, as the silicon core surface is the site of the reduction reaction, and surface characteristics (such as cleanliness and roughness) affect the deposition rate and the quality grade of the silicon material.

[0003] Silicon cores are produced by longitudinally slicing single-crystal wafers using a cutting machine, primarily used as heat carriers in the vapor deposition process for producing virgin polycrystalline silicon. During polycrystalline silicon production, the silicon core serves as the carrier for polycrystalline silicon deposition within the reduction furnace, and the cleanliness of its surface directly impacts the quality of the final polycrystalline silicon product. However, after undergoing a series of processes such as head and tail trimming, wire cutting, debinding, and conical grinding to meet specified dimensions and shapes, the silicon core may become contaminated with silicon sludge dust, organic matter, and metallic elements. Therefore, cleaning the silicon core is essential to avoid affecting subsequent use. Existing silicon core cleaning processes mainly include water washing, mixed acid washing, rinsing, ultrasonic cleaning, and drying, or manual wiping followed by the above steps. However, these methods all have certain drawbacks, such as poor cleaning effect, contamination of the silicon core during manual wiping, metal ion contamination, and residues of degreasing agents and acid. Summary of the Invention

[0004] In view of this, the present invention provides a polycrystalline silicon core cleaning method and system, the main purpose of which is to improve the cleaning quality of silicon cores.

[0005] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0006] On one hand, the present invention provides a method for cleaning polycrystalline silicon cores, the method comprising the following steps:

[0007] (1) Mixed acid pickling: The surface of the silicon core is cleaned in a pickling tank using a mixed solution of hydrofluoric acid and nitric acid. The cleaning time is 100-400s and the cleaning temperature is 18-35℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:(1-8):(25-80).

[0008] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank, spray pure water into the rinsing tank, stop spraying when the spray water level rises and overflows the rinsing tank, drain the spray water, spray pure water again after draining, repeat the spraying and drainage 1 to 5 times, and introduce nitrogen gas for bubbling while spraying and rinsing, the cumulative spraying and rinsing time is 100-500s;

[0009] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into an ultrasonic rinsing tank. The ultrasonic frequency is 20-60Hz, the ultrasonic rinsing time is 500-1000s, and the ultrasonic rinsing temperature is 20-45℃.

[0010] (4) Air removal water removal: Use clean air to blow the surface of the silicon core after rinsing in step (3) for 400-700 seconds;

[0011] (5) Vacuum microwave drying: Place the silicon core after purging in step (4) into a microwave drying oven. On the basis of evacuating the microwave drying oven, microwave dry the silicon core. The vacuum degree in the microwave drying oven is 70-120KPa, the microwave frequency range is 30-65Hz, and the drying time is 800-1500s.

[0012] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0013] Optionally, in step (1), the cleaning time is 240s, the cleaning temperature is 25℃, and the mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:(3-7):(35-50).

[0014] Optionally, in step (2), the spraying and drainage are repeated twice, and the cumulative time for spraying and rinsing is 200s.

[0015] Optionally, in step (3), the ultrasonic frequency is 40 Hz, the ultrasonic rinsing time is 700 s, and the ultrasonic rinsing temperature is 30 ℃.

[0016] Optionally, in step (4), the purging time is 500s.

[0017] Optionally, in step (5), the vacuum degree is 90 kPa, the microwave frequency is 40 Hz, and the drying time is 1200 s.

[0018] Optionally, the water after ultrasonic rinsing in step (3) can be drained out and used as the spray water in step (2).

[0019] On the other hand, the present invention provides a polycrystalline silicon core cleaning system, comprising:

[0020] The pickling tank, rinsing tank, ultrasonic rinsing tank, blower box and microwave drying oven are arranged in sequence.

[0021] The rinsing tank is equipped with a spray pipe, the bottom wall of the ultrasonic rinsing tank is connected to the top wall of the auxiliary water tank, the lower end of the auxiliary water tank is connected to the inlet of the spray pump, and the outlet of the spray pump is connected to the spray pipe.

[0022] Optionally, it also includes a chamber, in which the pickling tank, the rinsing tank, the ultrasonic rinsing tank, the blower box and the microwave drying box are arranged in sequence. The top wall of the chamber is connected to the exhaust gas treatment equipment, the bottom wall of the pickling tank is connected to the drain pipe, the drain pipe is equipped with a solenoid valve, the exhaust gas treatment equipment is electrically connected to the input terminal of the controller, and the output terminal of the controller is electrically connected to the solenoid valve.

[0023] By employing the above technical solution, the present invention has at least the following advantages:

[0024] By determining the cleaning process and parameters for polycrystalline silicon cores, the cleaning quality can be ensured to the greatest extent possible, meeting the requirements of the reduction reaction, and ultimately producing high-quality polycrystalline silicon cores. Furthermore, automated control and continuous production can be achieved, effectively reducing labor costs and safety risks.

[0025] Using automated control cleaning equipment to control the polycrystalline silicon core cleaning process and process parameters (cleaning temperature, cleaning time, mixed acid ratio, drying time) can not only reduce silicon core loss and save production costs, but also avoid or reduce the formation of acid spots on the silicon core surface and improve the appearance quality of the silicon core. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a polycrystalline silicon core cleaning system provided in an embodiment of the present invention.

[0027] The reference numerals in the accompanying drawings include: pickling tank 1, rinsing tank 2, ultrasonic rinsing tank 3, blower box 4, microwave drying oven 5, drain pipe 6, solenoid valve 7, temperature sensor 8, heat exchange tube 9, regulating valve 10, auxiliary water tank 11, spray pump 12, and spray pipe 13. Detailed Implementation

[0028] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0030] On the one hand, the present invention proposes a method for cleaning polycrystalline silicon cores, which is further described in detail through the following embodiments:

[0031] Example 1

[0032] Taking the cleaning of 18mm square silicon core as an example

[0033] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 200s and at a temperature of 25℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:5:40.

[0034] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, repeat the spraying and draining process twice, and introduce nitrogen gas for bubbling while spraying and rinsing, the cumulative spraying and rinsing time is 240s;

[0035] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products attached to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, nitrogen bubbling (bubbling is the use of air bubble impact) and rinsing.

[0036] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0037] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into the ultrasonic rinsing tank 3. The ultrasonic frequency is 40Hz, the ultrasonic rinsing time is 650s, and the ultrasonic rinsing temperature is 40℃.

[0038] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0039] (4) Air removal of water: Use clean air to blow away most of the water on the surface of the silicon core after rinsing in step (3) in a tangential direction. The blowing time is 500s.

[0040] (5) Vacuum microwave drying: The silicon core after being purged in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave after the microwave drying oven 5 is evacuated. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 85KPa, the microwave frequency range is 40Hz, and the drying time is 1200s.

[0041] After cleaning, the silicon core was observed to be free of oil stains, water stains, and oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the surface of the silicon core was 45.23 PPb, which was deemed a qualified product.

[0042] Example 2

[0043] Taking the cleaning of 18mm square silicon core as an example

[0044] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 240s and at a temperature of 25℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:5:50.

[0045] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, spraying and draining once, nitrogen gas is introduced for bubbling while spraying and rinsing, and the cumulative time of spraying and rinsing is 300s;

[0046] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products adhering to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, bubbling (bubbling is the use of air bubble impact) and rinsing.

[0047] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0048] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into the ultrasonic rinsing tank 3. The ultrasonic frequency is 40Hz, the ultrasonic rinsing time is 800s, and the ultrasonic rinsing temperature is 35℃.

[0049] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0050] (4) Air removal of water: Use clean air to blow the surface of the silicon core after rinsing in step (3) in a tangential direction for 600 seconds;

[0051] (5) Vacuum microwave drying: The silicon core after being purged in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave after the microwave drying oven 5 is evacuated. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 85KPa, the microwave frequency range is 40Hz, and the drying time is 1200s.

[0052] After cleaning, the product was observed to have no oil stains, water stains, or oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the silicon core surface was 15.67 PPb, which was deemed a qualified product.

[0053] Example 3

[0054] Taking the cleaning of a 14.7mm square silicon core as an example

[0055] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 240s and at a temperature of 30℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:6:50.

[0056] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, repeat the spraying and drainage twice, while spraying and rinsing, nitrogen gas is introduced for bubbling, the cumulative spraying and rinsing time is 200s;

[0057] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products adhering to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, bubbling (bubbling is the use of air bubble impact) and rinsing.

[0058] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0059] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into the ultrasonic rinsing tank 3. The ultrasonic frequency is 35Hz, the ultrasonic rinsing time is 700s, and the ultrasonic rinsing temperature is 35℃.

[0060] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0061] (4) Air removal of water: Use clean air to blow away most of the moisture on the silicon core surface after rinsing in step (3) in a tangential direction for 700 seconds.

[0062] (5) Vacuum microwave drying: The silicon core after purging in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave on the basis of vacuuming microwave drying oven 5. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 85KPa, the microwave frequency range is 40Hz, and the drying time is 1000s.

[0063] After cleaning, the silicon core was observed to be free of oil stains, water stains, and oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the surface of the silicon core was 33.67 PPb, which was deemed as a qualified product.

[0064] Example 4

[0065] Taking the cleaning of a 20mm square silicon core as an example

[0066] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 180s and at a temperature of 22℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:5:50.

[0067] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, repeat the spraying and drainage twice, while spraying and rinsing, nitrogen gas is introduced for bubbling, the cumulative spraying and rinsing time is 300s;

[0068] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products adhering to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, bubbling (bubbling is the use of air bubble impact) and rinsing.

[0069] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0070] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into ultrasonic rinsing tank 3. The ultrasonic frequency is 45Hz, the ultrasonic rinsing time is 800s, and the ultrasonic rinsing temperature is 30℃.

[0071] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0072] (4) Air removal of water: Use clean air to blow away most of the water on the surface of the silicon core after rinsing in step (3) in a tangential direction. The blowing time is 500s.

[0073] (5) Vacuum microwave drying: The silicon core after purging in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave on the basis of vacuuming microwave drying oven 5. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 90KPa, the microwave frequency range is 35Hz, and the drying time is 800s.

[0074] After cleaning, the silicon core was observed to be free of oil stains, water stains, and oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the surface of the silicon core was 49.31 PPb, which was deemed as a qualified product.

[0075] Example 5

[0076] Taking the cleaning of a 20mm square silicon core as an example

[0077] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 220s and at a temperature of 28℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:7:50.

[0078] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, repeat the spraying and draining process 3 times, and introduce nitrogen gas for bubbling while spraying and rinsing, the cumulative spraying and rinsing time is 300s;

[0079] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products adhering to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, bubbling (bubbling is the use of air bubble impact) and rinsing.

[0080] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0081] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into ultrasonic rinsing tank 3. The ultrasonic frequency is 45Hz, the ultrasonic rinsing time is 800s, and the ultrasonic rinsing temperature is 35℃.

[0082] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0083] (4) Air removal of water: Use clean air to blow away most of the moisture on the silicon core surface after rinsing in step (3) in a tangential direction for 650 seconds.

[0084] (5) Vacuum microwave drying: The silicon core after purging in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave on the basis of vacuuming microwave drying oven 5. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 90KPa, the microwave frequency range is 35Hz, and the drying time is 1200s.

[0085] After cleaning, the silicon core was observed to be free of oil stains, water stains, and oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the surface of the silicon core was 16.38 PPb, which was deemed as a qualified product.

[0086] Example 6

[0087] Taking the cleaning of 18mm square silicon core as an example

[0088] (1) Mixed acid pickling: The surface of the silicon core is cleaned in the pickling tank 1 with a mixed solution of hydrofluoric acid and nitric acid for 240s and at a temperature of 28℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:5:60.

[0089] (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank 2, spray pure water into the rinsing tank 2, stop spraying when the spray water level rises and overflows the rinsing tank 2, drain the spray water, spray pure water again after draining, repeat the spraying and draining process 3 times, and introduce nitrogen gas for bubbling while spraying and rinsing, the cumulative spraying and rinsing time is 280s;

[0090] Specifically, the purpose of step (2) is to remove the mixed acid and reaction products adhering to the surface of the silicon core after pickling, to prevent the silicon core from being in contact with the mixed acid for a long time and causing a deep oxidation reaction, which would affect the product quality and appearance. The mixed acid and reaction products on the surface of the silicon core are removed by ultrapure water spraying, bubbling (bubbling is the use of air bubble impact) and rinsing.

[0091] Specifically, nitrogen gas is used to isolate the bubbling process and prevent oxygen in the air from oxidizing the silicon core during pickling, which would lead to acid spots.

[0092] (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into the ultrasonic rinsing tank 3. The ultrasonic frequency is 40Hz, the ultrasonic rinsing time is 700s, and the ultrasonic rinsing temperature is 30℃.

[0093] Specifically, mixed acid is used to etch impurity metals on the surface of the silicon core and the silicon core itself. Spraying and rinsing cannot completely clean the deep-seated products and impurity metals. The cavitation effect of ultrasound in the liquid generates a powerful impact force to completely peel off the products and impurity metals on the surface of the silicon core.

[0094] (4) Air removal of water: Use clean air to blow away most of the water on the surface of the silicon core after rinsing in step (3) in a tangential direction. The blowing time is 500s.

[0095] (5) Vacuum microwave drying: The silicon core after purging in step (4) is placed in microwave drying oven 5. The silicon core is dried by microwave after vacuuming microwave drying oven 5. Vacuuming can effectively reduce the temperature required for microwave drying and shorten the drying time. The vacuum degree in microwave drying oven 5 is 100KPa, the microwave frequency range is 45Hz, and the drying time is 1200s.

[0096] After cleaning, the silicon core was observed to be free of oil stains, water stains, and oxidation marks. The sum of the metal content (trace metal elements including iron, chromium, nickel, copper, zinc, aluminum, potassium, sodium, calcium, tungsten, cobalt, titanium, manganese, lead, magnesium, molybdenum, and silver) on the surface of the silicon core was 22.56 PPb, which was deemed a qualified product.

[0097] The metal detection method for silicon core watches is as follows:

[0098] (1) Sampling: Weigh 30-50g of the purged silicon core sample;

[0099] (2) Pickling: The sample surface is rapidly rinsed with a mixture of nitric acid and hydrofluoric acid to obtain a pickling solution;

[0100] (3) Water washing: Rinse the acid-washed sample with water to obtain a water washing solution;

[0101] (4) Evaporation: Heat the pickling solution and the washing solution together until they are evaporated to dryness;

[0102] (5) Volume adjustment: Nitric acid is added to the residue after evaporation to dissolve it, and the solution is adjusted to volume to obtain the test sample;

[0103] (6) The metal impurity content of the prepared test sample was detected by inductively coupled plasma mass spectrometry.

[0104] Among them, the content of metallic impurities in silicon cores is less than 80 PPb, which is considered acceptable.

[0105] like Figure 1 As shown, on the other hand, the present invention also provides a polycrystalline silicon core cleaning system, comprising:

[0106] The pickling tank 1, rinsing tank 2, ultrasonic rinsing tank 3, blower box 4, and microwave drying box 5 are arranged in sequence.

[0107] The rinsing tank 2 is equipped with a spray pipe 13. The bottom wall of the ultrasonic rinsing tank 3 is connected to the top wall of the auxiliary water tank 11. The lower end of the auxiliary water tank 11 is connected to the inlet of the spray pump 12. The outlet of the spray pump 12 is connected to the spray pipe 13.

[0108] In this embodiment, the ultrasonic rinsing water is temporarily stored in the auxiliary water tank 11, and then pressurized by the spray pump 12 to be used as spray water for spraying and rinsing silicon cores, thereby improving the utilization rate of water resources and reducing the production cost of polysilicon.

[0109] In a specific embodiment, the system also includes a chamber, in which the pickling tank 1, the rinsing tank 2, the ultrasonic rinsing tank 3, the blower box 4, and the microwave drying box 5 are arranged sequentially. The top wall of the chamber is connected to the waste gas treatment equipment, the bottom wall of the pickling tank 1 is connected to the drain pipe 6, and the drain pipe 6 is equipped with a solenoid valve 7. The waste gas treatment equipment is electrically connected to the input terminal of the controller, and the output terminal of the controller is electrically connected to the solenoid valve 7.

[0110] In this embodiment, the waste gas treatment equipment consists of a fan and a scrubbing tower connected in sequence. As an emergency measure for the failure shutdown of the waste gas treatment equipment, when the fan or scrubbing tower stops abnormally and the acid mist in the chamber cannot be discharged or treated in time, the controller sends an opening command to the solenoid valve 7, and the mixed acid in the pickling tank 1 is discharged in time through the drain pipe 6 to avoid the acid mist in the chamber from escaping and causing an environmental accident.

[0111] Specifically, it also includes a temperature sensor 8 and a heat exchange tube 9, which are installed inside the pickling tank 1. One end of the heat exchange tube 9 is connected to the chilled water inlet pipe, and the other end is connected to the chilled water return pipe. A regulating valve 10 is installed on the chilled water return pipe. The temperature sensor 8 is electrically connected to the input terminal of the controller, and the output terminal of the controller is electrically connected to the regulating valve 10. Through integral feedback interlocking control, the temperature of the mixed acid solution in the pickling tank 1 is stably controlled within the process parameter range.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for cleaning polycrystalline silicon cores, characterized in that, Includes the following steps: (1) Mixed acid pickling: The surface of the silicon core is cleaned in a pickling tank using a mixed solution of hydrofluoric acid and nitric acid. The cleaning time is 100-400s and the cleaning temperature is 18-35℃. The mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:(1-8):(25-80). (2) Pure water spraying, bubbling and rinsing: Transfer the silicon core after acid washing in step (1) to the rinsing tank, spray pure water into the rinsing tank, stop spraying when the spray water level rises and overflows the rinsing tank, drain the spray water, spray pure water again after draining, repeat the spraying and drainage 1 to 5 times, and introduce nitrogen gas for bubbling while spraying and rinsing, the cumulative spraying and rinsing time is 100-500s; (3) Ultrasonic pure water rinsing: Immerse the silicon core after rinsing in step (2) into an ultrasonic rinsing tank. The ultrasonic frequency is 20-60Hz, the ultrasonic rinsing time is 500-1000s, and the ultrasonic rinsing temperature is 20-45℃. (4) Air removal water removal: Use clean air to blow the surface of the silicon core after rinsing in step (3) for 400-700 seconds; (5) Vacuum microwave drying: Place the silicon core after purging in step (4) into a microwave drying oven. On the basis of evacuating the microwave drying oven, microwave dry the silicon core. The vacuum degree in the microwave drying oven is 70-120KPa, the microwave frequency range is 30-65Hz, and the drying time is 800-1500s.

2. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, In step (1), the cleaning time is 240s, the cleaning temperature is 25℃, and the mass ratio of hydrofluoric acid, nitric acid and pure water in the mixed solution is 1:(3-7):(35-50).

3. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, In step (2), the spraying and drainage are repeated twice, and the cumulative time for spraying and rinsing is 200s.

4. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, In step (3), the ultrasonic frequency is 40 Hz, the ultrasonic rinsing time is 700 s, and the ultrasonic rinsing temperature is 30 ℃.

5. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, In step (4), the purging time is 500s.

6. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, In step (5), the vacuum degree is 90 kPa, the microwave frequency is 40 Hz, and the drying time is 1200 s.

7. The polycrystalline silicon core cleaning method according to claim 1, characterized in that, The water from the ultrasonic rinsing in step (3) is drained out and used as the spray water in step (2).

8. A polycrystalline silicon core cleaning system, characterized in that, include: The pickling tank, rinsing tank, ultrasonic rinsing tank, blower box and microwave drying oven are arranged in sequence. The rinsing tank is equipped with a spray pipe, the bottom wall of the ultrasonic rinsing tank is connected to the top wall of the auxiliary water tank, the lower end of the auxiliary water tank is connected to the inlet of the spray pump, and the outlet of the spray pump is connected to the spray pipe.

9. The polycrystalline silicon core cleaning system according to claim 8, characterized in that, It also includes a chamber, in which the pickling tank, the rinsing tank, the ultrasonic rinsing tank, the blower box and the microwave drying box are arranged in sequence. The top wall of the chamber is connected to the exhaust gas treatment equipment, the bottom wall of the pickling tank is connected to the drain pipe, the drain pipe is equipped with a solenoid valve, the exhaust gas treatment equipment is electrically connected to the input terminal of the controller, and the output terminal of the controller is electrically connected to the solenoid valve.

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