A light etching process for electronic grade polysilicon

Abstract

The present invention is a light etching process for electronic grade polysilicon. A light etching process for electronic grade polysilicon comprises: (1) washing the silicon block in tank No. 1 with high-purity water; (2) lightly etching the silicon block in tank No. 2 containing a mixed solution of hydrofluoric acid and hydrochloric acid; (3) washing the silicon block in tank No. 3 with high-purity water; (4) dehydrating the silicon block in tank No. 4 with clean inert gas; (5) pickling the silicon block in tank No. 5 containing a hydrochloric acid solution; (6) washing the silicon block in tank No. 6 with high-purity water; (7) passing the silicon block through tanks No. 7 and No. 8 in sequence and spraying with high-purity water; (8) washing the silicon block in tank No. 9 with high-purity water; (9) dehydrating the silicon block in tank No. 10 with clean inert gas. The light etching process for electronic grade polysilicon described in the present invention controls the metal impurity index on the surface of polysilicon to the minimum requirement of the national electronic polysilicon metal impurity surface while reducing the cost.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic-grade polysilicon, and in particular relates to a light etching process of electronic-grade polysilicon. Background Art

[0002] As one of the three main workshops for electronic-grade polysilicon, the post-processing workshop focuses on chemical cleaning. The silicon blocks from the crushing process are etched by the silicon material cleaning machine and then sent to the drying and packaging processes. Since electronic-grade polysilicon has extremely strict control over surface metal impurities, the silicon blocks need to be chemically cleaned to remove metal impurities attached to the surface to ensure product quality.

[0003] At present, the existing electronic-grade polysilicon chemical cleaning in China adopts a heavy etching process, which will cause waste of silicon materials with smooth surfaces and no spikes. In the future, electronic-grade polysilicon companies need to adopt a light etching process based on the conditions of the silicon materials themselves. In addition, chemical agents generally use UPS-grade acid. The cost of acid use is the main cost of post-processing, and how to reduce its cost is also a factor to be considered. According to the latest national electronic-grade polysilicon standard GB / T-12963-2022, the surface metal impurity content of electronic-grade polysilicon products must be at least less than 5ppbw, which provides a direction for the optimization of the silicon block cleaning process.

[0004] Prior art CN 112390259 B discloses a method for cleaning electronic-grade polysilicon. It uses a variety of chemical agents (NaOH, HNO3, HF, NH4OH, H2O2) in combination with acid washing and alkaline washing to significantly improve the cleaning effect of silicon blocks, making the silicon blocks more rounded as a whole, which is convenient for downstream processing.

[0005] Prior art CN 115815204 A discloses a method for cleaning electronic-grade polysilicon. The electronic-grade polysilicon is first washed with water for 100-800 seconds, then alkaline washed with NaOH ethanol solution of different concentrations for 180-200 seconds to remove organic matter on the silicon block, then washed with high-purity water, then etched with HNO3 and HF mixed solution of different concentration ratios for 100-800 seconds, and finally washed again with high-purity water to obtain electronic-grade polysilicon with higher purity.

[0006] Prior art CN214218196U discloses an electronic grade polysilicon cleaning system, comprising four cleaning tanks containing mixed solutions of HF, HNO3 and water in different concentration ratios and a water cleaning tank, with cleaning times independently ranging from 150 to 900 seconds, further improving the cleaning effect of silicon blocks and reducing the amount of cleaning solution used.

[0007] It can be seen from the above-mentioned existing technologies that the electronic-grade polysilicon cleaning processes currently published in the industry vary greatly, which is attributed to the different purposes of use of upstream electronic-grade polysilicon products by silicon wafer companies.

[0008] From the analysis of the etching thickness of silicon blocks, the average etching thickness of silicon blocks in China is about 15 microns, which requires the use of different chemical reagents and reasonable process cleaning tanks for optimization. This combination is inseparable from a large amount of multiple types of chemical reagents. Therefore, the electronic-grade polysilicon cleaning processes that have been published in China basically rely on high cost investment. For customers with relatively low requirements, using the same process is considered excessive cleaning, resulting in cost waste.

[0009] In view of this, the present invention proposes a new light etching process for electronic-grade polysilicon. When the silicon blocks crushed by the electronic-grade polysilicon enterprise are free of spikes and cracks, and the size is relatively regular and between 25mm-100mm, a small amount of chemical reagents can be used to meet the national minimum requirements for metal impurities on the surface of electronic polysilicon. Summary of the invention

[0010] The purpose of the present invention is to provide a light etching process for electronic grade polysilicon, which is suitable for polysilicon materials with no spikes, no cracks and a size between 25mm and 100mm. Different reagents are arranged in different concentrations and sequences, so that the metal impurity index on the surface of polysilicon can be controlled within the minimum requirements of the national electronic polysilicon surface metal impurities, and the purpose of reducing costs can be achieved.

[0011] In order to achieve the above purpose, the technical solution adopted is:

[0012] A light etching process for electronic grade polysilicon comprises the following steps:

[0013] (1) Place the silicon block in tank 1 and rinse with high-purity water;

[0014] (2) lightly etching the silicon block treated in step (1) in a No. 2 tank containing a mixed solution of hydrofluoric acid and hydrochloric acid;

[0015] (3) The silicon block treated in step (2) is rinsed in tank 3 with high-purity water;

[0016] (4) removing water from the silicon block treated in step (3) in tank No. 4 using clean inert gas;

[0017] (5) acid-washing the silicon block after the treatment in step (4) in a No. 5 tank containing a hydrochloric acid solution;

[0018] (6) The silicon block treated in step (5) is rinsed in tank 6 with high-purity water;

[0019] (7) passing the silicon block treated in step (6) through tanks 7 and 8 in sequence and spraying with high-purity water;

[0020] (8) The silicon block treated in step (7) is rinsed in tank No. 9 with high-purity water;

[0021] (9) The silicon block treated in step (8) is placed in tank No. 10 and dehydrated by using clean inert gas.

[0022] Furthermore, the silicon block has no peaks or cracks and has a size of 25 mm to 100 mm.

[0023] Furthermore, in the step (1), the water pressure is 0.4-0.6 MPa, and the flushing time is 180-300 s;

[0024] In the step (2), the light etching time is 300-600s and the temperature is 15-25°C;

[0025] In the step (3), the flushing time is 180-300s;

[0026] In the step (4), the air pressure is 0.4-0.6 MPa, the temperature is 25-30° C., and the time is 150-300 s;

[0027] In the step (5), the pickling time is 300-600s and the temperature is 15-25°C;

[0028] In the step (6), the flushing time is 180-300s;

[0029] In the step (7), the water pressure is 0.4-0.6 MPa and the flushing time is 180-300 s;

[0030] In the step (8), the temperature is 60-80° C. and the washing time is 180-300 s;

[0031] In the step (9), the temperature is 60-80°C, the air pressure is 0.4-0.6MPa, and the time is 180-300s.

[0032] Furthermore, in step (2), the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in tank No. 2 is 1:1:50-55;

[0033] In the step (5), the volume ratio of 36wt% hydrochloric acid to water in the hydrochloric acid solution is 1:50-55.

[0034] Furthermore, in step (2), the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in tank No. 2 is 1:1:50;

[0035] In the step (5), the volume ratio of 36wt% hydrochloric acid to water in the hydrochloric acid solution is 1:50.

[0036] Furthermore, the grooves 1, 3, 4, 6, 7 and 8 are made of PP material;

[0037] The grooves No. 2, 5, 9 and 10 are made of PVDF material.

[0038] Furthermore, the water after flushing in the No. 3 tank can be recycled to the No. 1 tank for use.

[0039] Furthermore, the water after flushing in tanks 6 and 7 can be recycled to tank 3 for use.

[0040] Furthermore, the water after flushing in the No. 8 tank can be recycled to the No. 6 tank for use.

[0041] Furthermore, the water after flushing in tank No. 9 can be recycled to tank No. 8 for use.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The light etching process of electronic-grade polysilicon described in the present invention is suitable for polysilicon materials with no spikes or cracks and a size between 25 mm and 100 mm, which can effectively avoid waste of silicon materials and reduce silicon material cleaning time; the use of HCl chemical agent can effectively reduce the cost of silicon material pickling; and a flushing water circulation system is set to achieve the purpose of saving water, increasing revenue, and circulating within the domain. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the flow chart of chemical cleaning of electronic grade polysilicon. DETAILED DESCRIPTION

[0045] In order to further explain the light etching process of electronic grade polysilicon of the present invention and achieve the intended purpose of the invention, the light etching process of electronic grade polysilicon proposed by the present invention, its specific implementation method, structure, characteristics and efficacy are described in detail below in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0046] The following will further introduce in detail a light etching process of electronic grade polysilicon according to the present invention in conjunction with specific embodiments:

[0047] The technical solution of the present invention is:

[0048] A light etching process for electronic grade polysilicon comprises the following steps:

[0049] (1) Place the silicon block in tank 1 and rinse with high-purity water;

[0050] (2) lightly etching the silicon block treated in step (1) in a No. 2 tank containing a mixed solution of hydrofluoric acid and hydrochloric acid;

[0051] (3) The silicon block treated in step (2) is rinsed in tank 3 with high-purity water;

[0052] (4) removing water from the silicon block treated in step (3) in tank No. 4 using clean inert gas;

[0053] (5) acid-washing the silicon block after the treatment in step (4) in a No. 5 tank containing a hydrochloric acid solution;

[0054] (6) The silicon block treated in step (5) is rinsed in tank 6 with high-purity water;

[0055] (7) passing the silicon block treated in step (6) through tanks 7 and 8 in sequence and spraying with high-purity water;

[0056] (8) The silicon block treated in step (7) is rinsed in tank No. 9 with high-purity water;

[0057] (9) The silicon block treated in step (8) is placed in tank No. 10 and dehydrated by using clean inert gas.

[0058] Preferably, the silicon block has no peaks or cracks and has a size of 25 mm to 100 mm.

[0059] Preferably, in the step (1), the water pressure is 0.4-0.6 MPa, and the flushing time is 180-300 s;

[0060] In the step (2), the light etching time is 300-600s and the temperature is 15-25°C;

[0061] In the step (3), the flushing time is 180-300s;

[0062] In the step (4), the air pressure is 0.4-0.6 MPa, the temperature is 25-30° C., and the time is 150-300 s;

[0063] In the step (5), the pickling time is 300-600s and the temperature is 15-25°C;

[0064] In the step (6), the flushing time is 180-300s;

[0065] In the step (7), the water pressure is 0.4-0.6 MPa and the flushing time is 180-300 s;

[0066] In the step (8), the temperature is 60-80° C. and the washing time is 180-300 s;

[0067] In the step (9), the temperature is 60-80°C, the air pressure is 0.4-0.6MPa, and the time is 180-300s.

[0068] Preferably, in step (2), the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in tank No. 2 is 1:1:50-55;

[0069] In the step (5), the volume ratio of 36wt% hydrochloric acid to water in the hydrochloric acid solution is 1:50-55.

[0070] Further preferably, in the step (2), the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in tank No. 2 is 1:1:50;

[0071] In the step (5), the volume ratio of 36wt% hydrochloric acid to water in the hydrochloric acid solution is 1:50.

[0072] Preferably, the grooves 1, 3, 4, 6, 7 and 8 are made of PP material;

[0073] The grooves No. 2, 5, 9 and 10 are made of PVDF material.

[0074] Preferably, the water after flushing in tank No. 3 can be recycled to tank No. 1 for use.

[0075] Preferably, the water after flushing in tanks 6 and 7 can be recycled to tank 3 for use.

[0076] Preferably, the water after flushing in tank No. 8 can be recycled to tank No. 6 for use.

[0077] Preferably, the water after flushing in tank No. 9 can be recycled to tank No. 8 for use.

[0078] Example 1.

[0079] Aiming at the cleaning process of electronic-grade polysilicon blocks with no spikes, no cracks and sizes between 25mm-100mm, this process consists of 6 water tanks, 2 acid tanks and 2 water removal tanks. High-purity water (UPW) is used in tanks 1#, 3#, 6#-9#, and the reagents used in tank 2# are hydrochloric acid (HCl) and hydrofluoric acid (HF). The reagent in tank 5# is HCl, and clean inert gas is used for water removal in tanks 4# and 10#.

[0080] Under the premise that the volume of each tank is 300L, the 1#-10# tanks are set as S1-S10 respectively, and the silicon blocks are cleaned in the S1-S10 tanks in sequence. Figure 1, the specific steps are as follows:

[0081] (1) The S1 tank is made of PP material and uses high-purity water to remove granular silicon and other particulate impurities on the surface of the silicon block. The water pressure requirement is 0.45MPa(G) and the flushing time is 190s.

[0082] (2) The S2 tank removes metal ions attached to the surface of the silicon block in the air by light etching with mixed acid solution. The material of the tank is PVDF, and the tank body is connected to a buffer tank. The volume ratio of 49wt% hydrofluoric acid, 36wt% hydrochloric acid and water in the tank is 1:1:55. The power is 1.2KW, the temperature is controlled at 18°C, and the light etching time is 400s.

[0083] (3) S3 tank uses high-purity water to rinse silicon blocks to remove residual mixed acid. The tank body is made of PP material, the power is 1.2KW, and the rinsing time is 190s.

[0084] (4) The S4 tank uses high-purity inert gas to remove residual water on the surface of the silicon block. The tank body is made of PP material, the air pressure is 0.45MPa(G), the temperature is 27°C, and the drying time is 170s.

[0085] (5) S5 tank further removes Al that may be attached to the surface of the silicon block through secondary pickling. 3+ 、Na + Mg 2+ , Fe 3+ The tank body is made of PVDF, the chemical agent is HCl, the volume ratio of 36wt% hydrochloric acid and high-purity water is 1:55, the temperature is controlled at 18°C, the power is 1.2KW, and the pickling time is 350s.

[0086] (6) S6 tank is used to clean residual acid. The tank body is made of PP material and the flushing time is 190s.

[0087] (7) S7 and S8 tanks are spray-flushing tanks. The tank body is made of PP material, the water pressure requirement is 0.45MPa(G), the power is 1.2KW, the spray time is 190s, and the tank body is connected to a water storage buffer tank and a water collection tank.

[0088] (8) S9 tank is washed again with water. The tank body is made of PVDF material, the temperature is controlled at 65°C, the power is 1.2KW, the flushing time is 190s, and the tank body is connected to a hot water buffer tank.

[0089] (9) S10 tank is a dewatering tank. The tank body is made of PVDF material, the medium is high-purity inert gas, the temperature is controlled at 65°C, the pressure is 0.45MPa(G), and the drying time is 170s.

[0090] The power in steps (1)-(9) refers to the power of the pump.

[0091] In addition, S1-S3, S5-S8, and S10 tanks are all equipped with flushing water circulation systems. S1 tank receives the cleaning water from S3 tank, and after filtration, it enters the screening system. It is necessary to detect the chloride ion concentration in the water and comprehensively consider the corrosion of the screening equipment. The pickling liquid from S2 tank is finally discharged into the waste acid treatment system. S3 tank receives the water filtered by S6 and S7 tanks, and after filtration, it enters S1 tank for silicon material pretreatment. The waste acid from S5 tank is finally discharged into the waste acid treatment system. S6 tank receives the cleaning water from S8 and enters S3 tank after filtration. The water in the water tank of S7 tank is filtered and enters S3 tank. The hot water after flushing S9 tank enters the water collection tank of S8 tank, and enters S6 tank after filtration. The gas in S10 tank enters the exhaust system, and the liquid enters the wastewater collection system.

[0092] Example 2.

[0093] The specific steps are as follows:

[0094] (1) Tank 1 is made of PP material and is cleaned with high-purity water at a water pressure of 0.5 MPa (G) and a flushing time of 250 seconds.

[0095] (2) The 2 tanks are made of PVDF material, and the tank body is connected to a buffer tank. The volume ratio of 49wt% hydrofluoric acid, 36wt% hydrochloric acid and water in the tank is 1:1:52, the power is 1.2KW, the temperature is controlled at 20°C, and the light etching time is 500s.

[0096] (3) Tank 3 uses high-purity water to rinse the silicon blocks to remove residual mixed acid. The tank body is made of PP material, the power is 1.2KW, and the rinsing time is 250s.

[0097] (4) 4 tanks use high-purity inert gas to remove residual water on the surface of the silicon block. The tank body is made of PP material, the air pressure is 0.5MPa(G), the temperature is 28℃, and the drying time is 250s.

[0098] (5) The tank body of the 5 tanks is made of PVDF material, and the chemical agent is HCl, the volume ratio of 36wt% hydrochloric acid and high-purity water is 1:52, the temperature is controlled at 20°C, the power is 1.2KW, and the pickling time is 500s.

[0099] (6) The 6 tanks are cleaned with high-purity water to remove residual acid. The tank body is made of PP material and the flushing time is 250s.

[0100] (7) Tanks 7 and 8 are spray-flushing tanks. The tank body is made of PP material, the water pressure requirement is 0.5 MPa (G), the power is 1.2 KW, the spray time is 250 s, and the tank body is connected to a water storage buffer tank and a water collection tank.

[0101] (8) The 9 tanks are washed again with water. The tank body is made of PVDF material, the temperature is controlled at 70°C, the power is 1.2KW, the flushing time is 250s, and the tank body is connected to a hot water buffer tank.

[0102] (9) Tank 10 is a dewatering tank. The tank body is made of PVDF, the medium is high-purity inert gas, the temperature is controlled at 70°C, the pressure is 0.5MPa(G), and the drying time is 250s.

[0103] Among them, a flushing circulation system is established through buffer tanks, pumps and other devices, and the water after flushing in tank No. 3 can be recycled to tank No. 1 for use, the water after flushing in tanks 6 and 7 can be recycled to tank No. 3 for use, the water after flushing in tank No. 8 can be recycled to tank No. 6 for use, and the water after flushing in tank No. 9 can be recycled to tank No. 8 for use.

[0104] Example 3.

[0105] The specific steps are as follows:

[0106] (1) Tank 1 is made of PP material and is cleaned with high-purity water at a water pressure of 0.4 MPa (G) and a flushing time of 300 seconds.

[0107] (2) The 2 tanks are made of PVDF material, and the tank body is connected to a buffer tank. The volume ratio of 49wt% hydrofluoric acid, 36wt% hydrochloric acid and water in the tank is 1:1:53, the power is 1.2KW, the temperature is controlled at 15°C, and the light etching time is 600s.

[0108] (3) Tank 3 uses high-purity water to rinse the silicon blocks to remove residual mixed acid. The tank body is made of PP material, the power is 1.2KW, and the rinsing time is 300s.

[0109] (4) 4 tanks use high-purity inert gas to remove residual water on the surface of the silicon block. The tank body is made of PP material, the air pressure is 0.4MPa(G), the temperature is 25℃, and the drying time is 300s.

[0110] (5) The tank body of the 5 tanks is made of PVDF material, and the chemical agent is HCl, the volume ratio of 36wt% hydrochloric acid and high-purity water is 1:53, the temperature is controlled at 15°C, the power is 1.2KW, and the pickling time is 600s.

[0111] (6) The 6 tanks are cleaned with high-purity water to remove residual acid. The tank body is made of PP material and the flushing time is 300s.

[0112] (7) Tanks 7 and 8 are spray-flushing tanks. The tank body is made of PP material, the water pressure requirement is 0.4MPa(G), the power is 1.2KW, the spray time is 300s, and the tank body is connected to a water storage buffer tank and a water collection tank.

[0113] (8) The 9 tanks are washed again with water. The tank body is made of PVDF material, the temperature is controlled at 60°C, the power is 1.2KW, the flushing time is 300s, and the tank body is connected to a hot water buffer tank.

[0114] (9) Tank 10 is a dewatering tank. The tank body is made of PVDF material, the medium is high-purity inert gas, the temperature is controlled at 60°C, the pressure is 0.4MPa(G), and the drying time is 300s.

[0115] Among them, a flushing circulation system is established through buffer tanks, pumps and other devices, and the water after flushing in tank No. 3 can be recycled to tank No. 1 for use, the water after flushing in tanks 6 and 7 can be recycled to tank No. 3 for use, the water after flushing in tank No. 8 can be recycled to tank No. 6 for use, and the water after flushing in tank No. 9 can be recycled to tank No. 8 for use.

[0116] Example 4.

[0117] The specific steps are as follows:

[0118] (1) Tank 1 is made of PP material and is cleaned with high-purity water at a water pressure of 0.6 MPa (G) and a flushing time of 180 seconds.

[0119] (2) The 2 tanks are made of PVDF material, and the tank body is connected to a buffer tank. The volume ratio of 49wt% hydrofluoric acid, 36wt% hydrochloric acid and water in the tank is 1:1:50, the power is 1.2KW, the temperature is controlled at 25°C, and the light etching time is 300s.

[0120] (3) Tank 3 uses high-purity water to rinse the silicon blocks to remove residual mixed acid. The tank body is made of PP material, the power is 1.2KW, and the rinsing time is 180s.

[0121] (4) 4 tanks use high-purity inert gas to remove residual water on the surface of the silicon block. The tank body is made of PP material, the air pressure is 0.6MPa(G), the temperature is 30℃, and the drying time is 150s.

[0122] (5) The tank body of the 5 tanks is made of PVDF material, and the chemical agent is HCl, the volume ratio of 36wt% hydrochloric acid and high-purity water is 1:50, the temperature is controlled at 25°C, the power is 1.2KW, and the pickling time is 300s.

[0123] (6) The 6 tanks are cleaned with high-purity water to clean the residual acid solution. The tank body is made of PP material and the flushing time is 180s.

[0124] (7) Tanks 7 and 8 are spray-flushing tanks. The tank body is made of PP material, the water pressure requirement is 0.6MPa(G), the power is 1.2KW, the spray time is 180s, and the tank body is connected to a water storage buffer tank and a water collection tank.

[0125] (8) The 9 tanks are washed again with water. The tank body is made of PVDF material, the temperature is controlled at 80°C, the power is 1.2KW, the flushing time is 180s, and the tank body is connected to a hot water buffer tank.

[0126] (9) Tank 10 is a dewatering tank. The tank body is made of PVDF, the medium is high-purity inert gas, the temperature is controlled at 80°C, the pressure is 0.6MPa(G), and the drying time is 150s.

[0127] Among them, a flushing circulation system is established through buffer tanks, pumps and other devices, and the water after flushing in tank No. 3 can be recycled to tank No. 1 for use, the water after flushing in tanks 6 and 7 can be recycled to tank No. 3 for use, the water after flushing in tank No. 8 can be recycled to tank No. 6 for use, and the water after flushing in tank No. 9 can be recycled to tank No. 8 for use.

[0128] Example 5.

[0129] The specific steps are as follows:

[0130] (1) Tank 1 is made of PP material and is cleaned with high-purity water at a water pressure of 0.5 MPa (G) and a flushing time of 200 seconds.

[0131] (2) The 2 tanks are made of PVDF material, and the tank body is connected to a buffer tank. The volume ratio of 49wt% hydrofluoric acid, 36wt% hydrochloric acid and water in the tank is 1:1:50-55, the power is 1.2KW, the temperature is controlled at 23°C, and the light etching time is 500s.

[0132] (3) Tank 3 uses high-purity water to rinse the silicon blocks to remove residual mixed acid. The tank body is made of PP material, the power is 1.2KW, and the rinsing time is 200s.

[0133] (4) 4 tanks use high-purity inert gas to remove residual water on the surface of the silicon block. The tank body is made of PP material, the air pressure is 0.5MPa(G), the temperature is 27℃, and the drying time is 200s.

[0134] (5) The tank body of the 5 tanks is made of PVDF material, and the chemical agent is HCl, the volume ratio of 36wt% hydrochloric acid and high-purity water is 1:50-55, the temperature is controlled at 25°C, the power is 1.2KW, and the pickling time is 400s.

[0135] (6) The 6 tanks are cleaned with high-purity water to remove residual acid. The tank body is made of PP material and the flushing time is 200s.

[0136] (7) Tanks 7 and 8 are spray-flushing tanks. The tank body is made of PP material, the water pressure requirement is 0.5 MPa (G), the power is 1.2 KW, the spray time is 200 s, and the tank body is connected to a water storage buffer tank and a water collection tank.

[0137] (8) The 9 tanks are washed again with water. The tank body is made of PVDF material, the temperature is controlled at 75°C, the power is 1.2KW, the flushing time is 200s, and the tank body is connected to a hot water buffer tank.

[0138] (9) Tank 10 is a dewatering tank. The tank body is made of PVDF, the medium is high-purity inert gas, the temperature is controlled at 75°C, the pressure is 0.5 MPa (G), and the drying time is 200 s.

[0139] Example 6.

[0140] The cleaned silicon blocks of Example 1-5 were tested, and the test results are shown in Table 1-2.

[0141] Table 1

[0142]

[0143] Table 2

[0144] Silicon block surface morphology Etching thickness Example 1 The surface is metallic, without spots or color difference. <1μm Example 2 The surface is metallic, without spots or color difference. <1μm Example 3 The surface is metallic, without spots or color difference. <1μm Example 4 The surface is metallic, without spots or color difference. <1μm Example 5 The surface is metallic, without spots or color difference. <1μm

[0145] As can be seen from Table 1-2, the light etching process of the present invention has good etching effect, can control the metal impurity index on the surface of polysilicon to the minimum requirement of the national electronic polysilicon surface metal impurities, and achieve the purpose of reducing costs.

[0146] The above is only a preferred embodiment of the embodiment of the present invention, and does not impose any form of limitation on the embodiment of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiment based on the technical essence of the embodiment of the present invention are still within the scope of the technical solution of the embodiment of the present invention.

Claims

1. A light etching process for electronic grade polysilicon, characterized in that: The following steps are involved: (1) Washing the silicon block in tank No. 1 with high-purity water; the silicon block has no spikes or cracks and has a size of 25 mm to 100 mm; (2) lightly etching the silicon block treated in step (1) in a No. 2 tank containing a mixed solution of hydrofluoric acid and hydrochloric acid; the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in the No. 2 tank is 1:1:50-55; (3) The silicon block treated in step (2) is rinsed in tank 3 with high-purity water; (4) removing water from the silicon block treated in step (3) in tank No. 4 using clean inert gas; (5) acid-washing the silicon block treated in step (4) in a No. 5 tank containing a hydrochloric acid solution; the volume ratio of 36 wt% hydrochloric acid to water in the hydrochloric acid solution is 1:50-55; (6) The silicon block treated in step (5) is rinsed in tank 6 with high-purity water; (7) passing the silicon block treated in step (6) through tanks 7 and 8 in sequence and spraying with high-purity water; (8) The silicon block treated in step (7) is rinsed in tank No. 9 with high-purity water; (9) The silicon block treated in step (8) is placed in tank No. 10 and dehydrated by using clean inert gas.

2. The light etching process according to claim 1, characterized in that: In the step (1), the water pressure is 0.4-0.6 MPa and the flushing time is 180-300 s; In the step (2), the light etching time is 300-600s and the temperature is 15-25°C; In the step (3), the flushing time is 180-300s; In the step (4), the air pressure is 0.4-0.6 MPa, the temperature is 25-30° C., and the time is 150-300 s; In the step (5), the pickling time is 300-600s and the temperature is 15-25°C; In the step (6), the flushing time is 180-300s; In the step (7), the water pressure is 0.4-0.6 MPa and the flushing time is 180-300 s; In the step (8), the temperature is 60-80° C. and the washing time is 180-300 s; In the step (9), the temperature is 60-80°C, the air pressure is 0.4-0.6MPa, and the time is 180-300s.

3. The light etching process according to claim 1, characterized in that: In the step (2), the volume ratio of 49 wt % hydrofluoric acid, 36 wt % hydrochloric acid and water in tank 2 is 1:1:50; In the step (5), the volume ratio of 36wt% hydrochloric acid to water in the hydrochloric acid solution is 1:

50.

4. The light etching process according to claim 1, characterized in that: The grooves 1, 3, 4, 6, 7 and 8 are made of PP material; The grooves No. 2, 5, 9 and 10 are made of PVDF material.

5. The light etching process according to claim 1, characterized in that: The water after flushing in the No. 3 tank can be recycled to the No. 1 tank for use.

6. The light etching process according to claim 1, characterized in that: The water after flushing in the No. 6 and No. 7 tanks can be recycled to the No. 3 tank for use.

7. The light etching process according to claim 1, characterized in that: The water after flushing in the No. 8 tank can be recycled to the No. 6 tank for use.

8. The light etching process according to claim 1, characterized in that: The water after flushing in the No. 9 tank can be recycled to the No. 8 tank for use.

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