Purification Method and Use of Ultra-High Purity Electronic Grade Polysilicon

Abstract

The present invention discloses a purification method and use of ultra-high purity electronic grade polysilicon. The method comprises the following steps: (1) heating a polysilicon rod to 1000-1200 °C and holding for not less than 4 h; (2) cooling the polysilicon rod after holding to 800-900 °C by an air cooling method, with a cooling rate of 20-30 °C / min; (3) continuing to cool the polysilicon rod to 500-600 °C by an air cooling method, with a cooling rate greater than 30 °C / min; (4) continuing to cool the polysilicon rod to room temperature by a natural cooling method or a water cooling method; (5) performing a crushing treatment on the polysilicon rod cooled to room temperature and cleaning the crushed product to obtain purified electronic grade polysilicon, wherein steps (1)-(3) are all carried out in an inert atmosphere. By using this method, the impurity content of polysilicon can be significantly reduced, the crystal structure defects of polysilicon can be reduced, and at the same time, it is easy to operate and convenient for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic-grade polysilicon, and more particularly, to a purification method and uses of ultra-high purity electronic-grade polysilicon. Background Art

[0002] Electronic-grade polysilicon is currently the industrial raw material with the highest purity manufactured by humans, with a purity of up to 13 nines. When the impurity content in electronic-grade polysilicon is too high, problems such as a decrease in resistance, which in turn affects the resistivity of single crystals and the minority carrier lifetime, will occur. In order to control the introduction of impurities in electronic-grade polysilicon, its production process has extremely strict requirements. Nevertheless, other elements besides silicon are still introduced in actual industrial production. Currently, non-metallic impurities (such as elements B, P, C, O, etc.) in electronic-grade polysilicon are generally detected by the zone melting method, that is, a cylindrical polysilicon rod is taken from a polysilicon rod produced by the improved Siemens method, then it is cleaned and zone melted to form a single crystal, sliced, and the impurities in the single crystal silicon are tested by infrared spectroscopy to evaluate the impurity content in electronic-grade polysilicon. Among them, before the taken polysilicon rod is cleaned, grinding is carried out, which is beneficial to maintaining the stability of the detection because for different surface morphologies, the residual impurities on the surface after cleaning are different.

[0003] In fact, the impurities in electronic-grade polysilicon are mainly divided into two categories: bulk impurities and surface impurities. Surface impurities can be removed through subsequent cleaning processes, but bulk impurities are difficult to remove once they are generated because they are located inside the silicon material. Currently, a lot of research has been carried out on reducing the introduction of bulk impurities, such as using multi-stage rectification to purify the raw material trichlorosilane and improving the equipment of the reduction furnace to reduce the possibility of introducing impurities. However, no matter how the probability of introducing impurities is reduced, it is impossible to introduce no impurities in the production process. Summary of the Invention

[0004] The present invention aims to solve at least to some extent the technical problems in the related art. To this end, an object of the present invention is to provide a purification method and uses of ultra-high purity electronic-grade polysilicon. By using this method, the impurity content of polysilicon can be significantly reduced, the crystal structure defects of polysilicon can be reduced, and at the same time, it is easy to operate and convenient for industrial production.

[0005] In one aspect of the present invention, the present invention provides a purification method of ultra-high purity electronic-grade polysilicon. According to an embodiment of the present invention, the method includes:

[0006] (1) Heating the polysilicon rod to 1000 - 1200 °C and holding for not less than 4 h;

[0007] (2) Cooling the polysilicon rod after holding to 800 - 900 °C by air cooling, and the cooling rate is 20 - 30 °C / min;

[0008] (3) The polysilicon rod is further cooled to 500 - 600 °C by air cooling, and the cooling rate is greater than 30 °C / min;

[0009] (4) The polysilicon rod is further cooled to room temperature by natural cooling or water cooling;

[0010] (5) The polysilicon rod cooled to room temperature is crushed, and the crushed product is washed to obtain purified electronic - grade polysilicon.

[0011] Among them, steps (1)-(3) are all carried out in an inert atmosphere.

[0012] The purification method of ultra - high - purity electronic - grade polysilicon in the above - mentioned embodiments of the present invention can convert at least part of the bulk impurities in the polysilicon into surface impurities for removal, improving the purity of the electronic - grade polysilicon, and having at least the following beneficial effects: 1) In step (1), controlling the holding time at high temperature within the above - mentioned range can ensure that various non - silicon impurities can obtain sufficient energy, so that as many impurities as possible can diffuse to grain boundaries and lattice defects; 2) Controlling the cooling rate in step (2) within the above - mentioned range, on the one hand, can make the thermal expansion coefficients of the surface and the interior of the polysilicon rod as consistent as possible, avoiding the polysilicon rod from being broken due to too large a difference in thermal expansion coefficients between the inside and outside of the polysilicon rod; on the other hand, at a relatively large cooling rate, the impurity elements diffused to grain boundaries and lattice defects can be fixed as soon as possible, so that as many non - silicon impurities as possible can be removed through subsequent crushing and washing; further, in step (3), through further rapid cooling, the obtained crystal structure can be made more stable, and the dislocation density in the polysilicon will not increase further during this cooling process, reducing the possibility of non - silicon elements continuing to diffuse into the crystal structure; 3) The inventor found that if direct quenching is used for temperature reduction after heat preservation, it will lead to too many dislocation densities in the silicon rod, which not only affects the subsequent use performance of the polysilicon, but also may reduce the recovery rate of polysilicon after the silicon rod is broken. Compared with water quenching for temperature reduction, by using air cooling for segmented cooling and controlling the above - mentioned cooling rate in the present invention, not only can the bulk impurities be converted into surface impurities as much as possible, but also the crystal structure can be prevented from being distorted, significantly reducing the dislocation density in the crystal and the structural defects of the electronic - grade polysilicon, ensuring its purification effect and use performance; 4) By carrying out heat preservation and air cooling in an inert atmosphere, the probability of introducing other impurities can also be reduced; 5) When the cooling temperature is reduced to 500 - 600 °C, the crystal structure of the polysilicon rod has been stabilized. Subsequently, choosing natural cooling or water cooling will not cause an increase in the crystal structure defects of the polysilicon. Further, after cooling, through crushing and washing, higher - purity electronic - grade polysilicon can be obtained.

[0013] In addition, the purification method of ultra - high - purity electronic - grade polysilicon according to the above - mentioned embodiments of the present invention may also have the following additional technical features:

[0014] In some embodiments of the present invention, in step (1), the heating rate of temperature rise is 40 - 60 °C / min; and / or, the heat preservation time is 4 - 18 h.

[0015] In some embodiments of the present invention, in step (1), the heat preservation time is 4 - 6 h.

[0016] In some embodiments of the present invention, the purity of the polysilicon rod is 6 - 13 N; and / or, the polysilicon rod is prepared by chemical vapor deposition, and the heat preservation treatment is directly carried out after the polysilicon rod is prepared.

[0017] In some embodiments of the present invention, in step (2), the polysilicon rod is cooled to 800 - 900 °C and then heat-preserved for 0.5 - 1 h.

[0018] In some embodiments of the present invention, in steps (2) - (3), an inert gas is used as the cooling medium in the air-cooling method.

[0019] In some embodiments of the present invention, in step (3), the cooling rate of the continued cooling is 40 - 50 °C / min.

[0020] In some embodiments of the present invention, in step (4), the natural cooling is carried out in an inert atmosphere, and high-purity water is used as the cooling medium in the water-cooling method.

[0021] In some embodiments of the present invention, in step (5), the cleaning includes pickling and water washing.

[0022] In yet another aspect of the present invention, the present invention provides the use of the above-mentioned purification method of ultra-high purity electronic-grade polysilicon in purifying polysilicon rods or massive polysilicon. Compared with the prior art, this use has all the technical features and effects of the above-mentioned purification method of ultra-high purity electronic-grade polysilicon, which will not be elaborated here. Generally speaking, it can not only significantly reduce the impurity content of polysilicon, but also reduce the crystal structure defects of polysilicon, and at the same time, it is easy to operate and convenient for industrial production.

[0023] The additional aspects and advantages of the present invention will be partly given in the following description, partly become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0025] Figure 1 is a schematic diagram of the impurity distribution of polysilicon according to an embodiment of the present invention;

[0026] Figure 2 It is a flowchart of a purification method for ultra-high purity electronic-grade polysilicon according to an embodiment of the present invention. Specific embodiments

[0027] The embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications.

[0028] In one aspect of the present invention, the present invention provides a purification method for ultra-high purity electronic-grade polysilicon. According to an embodiment of the present invention, the method includes: (1) heating a polysilicon rod to 1000-1200 °C and holding for no less than 4 h; (2) cooling the polysilicon rod after holding to 800-900 °C by air cooling, with a cooling rate of 20-30 °C / min; (3) continuing to cool the polysilicon rod to 500-600 °C by air cooling, with a cooling rate greater than 30 °C / min; (4) continuing to cool the polysilicon rod to room temperature by natural cooling or water cooling; (5) performing a crushing treatment on the polysilicon rod cooled to room temperature and cleaning the crushed product to obtain the purified ultra-high purity electronic-grade polysilicon, wherein steps (1)-(3) are all carried out in an inert atmosphere. In combination Figure 1 Understand that by controlling conditions such as the heating temperature, heating and cooling rates, holding time, and cooling method of the polysilicon, the distribution of non-silicon elements such as boron, phosphorus, carbon, and oxygen in the polysilicon changes, and some non-silicon elements transfer from the crystal interior to grain boundaries and lattice defects. When the polysilicon is crushed, the fracture surface is more likely to extend along the grain boundaries and lattice defects. Therefore, after the polysilicon is crushed, the non-silicon elements inside the polysilicon become surface non-silicon elements and can be removed by cleaning to obtain the purified electronic-grade polysilicon.

[0029] The following refers to Figure 2 The purification method for ultra-high purity electronic-grade polysilicon of the above embodiments of the present invention will be described in detail.

[0030] S100: Heat the polysilicon rod to 1000-1200 °C in an inert atmosphere and hold for no less than 4 h.

[0031] According to an embodiment of the present invention, by heating the polysilicon rod and holding it within the above temperature range, the silicon elements of the polysilicon rod can be rearranged, and various non-silicon impurities can obtain sufficient energy, so that as many impurities as possible can diffuse to grain boundaries and lattice defects.

[0032] According to an embodiment of the present invention, the heating rate of temperature rise can be 40 to 60 °C / min, for example, it can be 45 °C / min, 50 °C / min, or 55 °C / min, etc. The inventors found that if the heating rate of temperature rise is too low and the time for the temperature rise process is too long, the production efficiency will decrease; when the heating rate is too high, due to the time required for heat transfer, there will be a significant difference in the expansion coefficients inside and outside the polysilicon, which will lead to the fragmentation of the polysilicon. By controlling the heating rate within the above range, the present invention can obtain a higher heating rate on the premise of avoiding the fragmentation of the polysilicon, thereby improving the purification efficiency.

[0033] According to an embodiment of the present invention, the heat preservation time can be 4 to 18 h, for example, it can be 5 h, 8 h, 12 h, or 16 h, etc. The inventors found that the transfer and transition of non-silicon impurities in the polysilicon require a certain amount of time at high temperatures. During the heat preservation process, various non-silicon impurities can obtain sufficient energy to achieve the transfer of impurity molecules to grain boundaries and defects. In addition, silicon atoms will rearrange at high temperatures to achieve the growth of small grains, reducing the dislocation density and structural defects in the crystal. When the heat preservation time is too short, it is difficult to effectively achieve the above effects; if the heat preservation time is too long, it will not only cause a certain degree of waste of resources and a decrease in production efficiency, but also may increase the activity of impurity elements and the possibility of impurity elements continuing to diffuse into the crystal. By controlling the heat preservation time within the above range, the present invention can transfer as many impurity elements as possible to the grain boundaries and defects of the polysilicon rod on the basis of ensuring production efficiency, which is more conducive to improving the purification effect. Preferably, the heat preservation time can be 4 to 6 h, whereby a higher production efficiency and a better purification effect can be obtained simultaneously.

[0034] According to an embodiment of the present invention, the purity of the polysilicon rod in the present invention is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, the purity of the polysilicon rod can be 6 to 13 N, for example, it can be 7 N, 9 N, or 11 N. For another example, when the purity of electronic-grade polysilicon needs to reach 13 N, the purification method in the present invention can be used to purify the polysilicon rod with a purity lower than 13 N.

[0035] According to an embodiment of the present invention, the source or preparation method of the polysilicon rod in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, the polysilicon rod can be prepared by chemical vapor deposition (CVD). Preferably, the heat preservation treatment is directly carried out after the polysilicon rod is prepared. Among them, the polysilicon rod is prepared by chemical vapor deposition by carrying out a redox reaction between vaporized trichlorosilane and hydrogen on the surface of a silicon core at 1050 °C to 1100 °C, and crystalline silicon is produced and deposited on the surface of the silicon core. Directly carrying out the heat preservation treatment on the polysilicon rod obtained by vapor deposition can save the heating operation, thereby improving the production efficiency and saving energy consumption. For another example, the polysilicon rod can also be obtained by zone melting and drawing of massive polysilicon. Thus, purification of massive polysilicon (such as polysilicon powder, etc.) can also be achieved.

[0036] S200: Under an inert atmosphere, the heat-preserved polysilicon rod is cooled to 800 - 900 °C by air cooling, and the cooling rate is 20 - 30 °C / min.

[0037] According to an embodiment of the present invention, by controlling the cooling rate within the above range, on the one hand, the coefficient of thermal expansion on the surface and inside of the polysilicon rod can be kept as consistent as possible, avoiding the polysilicon rod from being broken due to too large a difference in the coefficient of thermal expansion inside and outside the polysilicon rod; on the other hand, the impurity elements diffused to grain boundaries and lattice defects can be fixed as soon as possible at a relatively large cooling rate, so that as many non-silicon impurities as possible can be removed by subsequent crushing and cleaning. In addition, by air-cooling the polysilicon rod to the above temperature range, the crystal structure can be prevented from being distorted, the dislocation density in the crystal can be significantly reduced, and the structural defects of electronic-grade polysilicon can be reduced, ensuring its structural performance and service performance.

[0038] According to an embodiment of the present invention, after the polysilicon rod is cooled to 800 - 900 °C, it can be further heat-preserved for 0.5 - 1 h. For example, it can be further heat-preserved for 0.6 h, 0.7 h or 0.8 h, etc. The inventors found that by heat-preserving the polysilicon rod, grain growth can be further achieved, the dislocation density and crystal defects can be reduced, and thus it is more beneficial to stabilize the crystal form and reduce internal stress. If the heat-preservation time is too short, the above effects cannot be achieved; if the heat-preservation time is too long, the production efficiency will be significantly reduced and the energy consumption will increase. By controlling the above heat-preservation conditions in the present invention, both the structural performance and service performance of the polysilicon material obtained after purification can be improved, and the production efficiency can be ensured.

[0039] According to an embodiment of the present invention, the gas cooling method may use an inert gas as a cooling medium, such as argon. Among them, by using an inert gas as a cooling medium, not only can the possibility of introducing foreign impurities be further reduced, but also it is beneficial to control the temperature, flow rate, and flux of the inert gas to flexibly regulate the cooling rate, so that the cooling process proceeds smoothly, thereby further realizing the controllability of the cooling effect and the purification effect. In addition, it should be noted that the temperature of the cooling medium is not particularly limited, and those skilled in the art can flexibly select according to actual needs. For example, a low-temperature cooling medium with a temperature below zero degrees Celsius or a normal-temperature cooling medium can be selected.

[0040] S300: Under an inert atmosphere, continue to cool the polysilicon rod to 500 - 600 °C by the gas cooling method, and the cooling rate is greater than 30 °C / min.

[0041] According to an embodiment of the present invention, by further rapidly cooling the polysilicon rod to 500 - 600 °C, the obtained crystal structure can be made more stable, and during this cooling process, the dislocation density in the polysilicon will not further increase, which can reduce the possibility of non-silicon elements continuing to diffuse into the crystal structure. In addition, by controlling the above cooling rate, the cooling efficiency can be further improved. Compared with water quenching for temperature reduction, in the present invention, by using the gas cooling method for segmented cooling, not only can as many bulk impurities as possible be converted into surface impurities, but also the crystal structure can be prevented from being distorted, the dislocation density in the crystal can be significantly reduced, the structural defects of electronic-grade polysilicon can be reduced, and its purification effect and service performance can be ensured;

[0042] According to an embodiment of the present invention, the cooling rate of the continued cooling can be 40 - 50 °C / min, thereby not only improving the cooling efficiency but also avoiding the polysilicon rod from being broken due to too large a difference in the expansion coefficients inside and outside the polysilicon rod.

[0043] S400: Continue to cool the polysilicon rod to room temperature by the natural cooling method or the water cooling method.

[0044] According to an embodiment of the present invention, after the cooling temperature is reduced to 500 - 600 °C, the crystal structure of the polysilicon rod has been stabilized, and subsequent selection of natural cooling or water cooling will not cause an increase in the crystal structure defects of the polysilicon.

[0045] According to an embodiment of the present invention, when the natural cooling method is used, it can be carried out under an inert atmosphere, thereby further avoiding the introduction of other impurities and ensuring the purification effect; when the water cooling method is used, high-purity water can be selected as the cooling medium, thereby further avoiding the introduction of other impurities and ensuring the purification effect. Preferably, the water cooling method can be used. When the temperature of the polysilicon is reduced to 500 - 600 °C, the dislocation density is controllable, and rapid cooling will not cause a further increase in the crystal dislocation density. Therefore, using the water cooling method can further improve the cooling efficiency while ensuring the purification effect.

[0046] S500: Crush the polysilicon rod cooled to room temperature, and clean the crushed product to obtain ultra-high purity electronic-grade polysilicon after purification.

[0047] According to an embodiment of the present invention, the cleaning preferably includes pickling and water washing, wherein pickling can further ensure the effective removal of impurity elements. After the cooling process, some non-silicon elements have been transferred from the crystal interior to grain boundaries and lattice defects. When the polysilicon is crushed, the fracture surface is more likely to extend along grain boundaries and lattice defects. Therefore, after the polysilicon is crushed, the non-silicon elements inside the polysilicon become surface non-silicon elements, and at this time, the impurity can be removed by pickling and water washing. It should be noted that the method of cleaning and removing impurities from the crushed polysilicon is a conventional operation in the art and will not be elaborated here.

[0048] In summary, the purification method of ultra-high purity electronic grade polysilicon in the above embodiments of the present invention controls conditions such as the heating temperature, heating and cooling rate, heat preservation time, and cooling method of polysilicon, so that the distribution of non-silicon elements such as boron, phosphorus, carbon, and oxygen in polysilicon changes, and some non-silicon elements transfer from the crystal interior to grain boundaries and lattice defects. When the polysilicon is broken, the fracture surface is more likely to extend along grain boundaries and lattice defects. Therefore, after the polysilicon is broken, the non-silicon elements inside the polysilicon become surface non-silicon elements and can be removed by cleaning to obtain purified electronic grade polysilicon. This method can convert at least part of the bulk impurities in polysilicon into surface impurities for removal, improving the purity of electronic grade polysilicon, and has at least the following beneficial effects: 1) In step (1), controlling the heat preservation time at a high temperature within the above range can ensure that various non-silicon impurities can obtain sufficient energy, so that as many impurities as possible can diffuse to grain boundaries and lattice defects; 2) Controlling the cooling rate in step (2) within the above range, on the one hand, can make the thermal expansion coefficients of the surface and the interior of the polysilicon rod as consistent as possible, avoiding the polysilicon rod from breaking due to too large a difference in thermal expansion coefficients between the inside and outside of the polysilicon rod; on the other hand, it can fix the impurity elements diffused to grain boundaries and lattice defects as soon as possible at a relatively large cooling rate, so that as many non-silicon impurities as possible can be removed by subsequent crushing and cleaning; further, in step (3), through further rapid cooling, the obtained crystal structure can be made more stable, and the dislocation density in the polysilicon will not increase further during this cooling process, reducing the possibility of non-silicon elements continuing to diffuse into the crystal structure; 3) The inventor found that if direct quenching is used for cooling after heat preservation, it will lead to too many dislocations in the silicon rod, which not only affects the subsequent use performance of polysilicon, but also may reduce the recovery rate of polysilicon after the silicon rod is broken. Compared with water quenching, by using air cooling for segmented cooling and controlling the above cooling rate in the present invention, not only can as many bulk impurities as possible be converted into surface impurities, but also the crystal structure can be prevented from being distorted, significantly reducing the dislocation density in the crystal and reducing the structural defects of electronic grade polysilicon to ensure its purification effect and use performance; 4) By heating, heat preserving, and air cooling in an inert atmosphere, the probability of introducing other impurities can also be reduced; 5) When the cooling temperature drops to 500-600 °C, the crystal structure of the polysilicon rod has been stabilized, and subsequent natural cooling or water cooling will not cause an increase in the crystal structure defects of the polysilicon. Therefore, after cooling, through crushing and cleaning, higher purity electronic grade polysilicon can be obtained.

[0049] In yet another aspect of the present invention, the present invention provides the use of the above purification method in purifying polysilicon rods or massive polysilicon. Compared with the prior art, this use has all the technical features and effects of the above ultra-high purity electronic-grade polysilicon purification method, which will not be elaborated here. Generally speaking, it can not only significantly reduce the impurity content of polysilicon, but also reduce the crystal structure defects of polysilicon, while being easy to operate and facilitating industrial production.

[0050] The embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention. For those not specified in the embodiments regarding specific techniques or conditions, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications.

[0051] Example 1

[0052] Purify polysilicon according to the following steps:

[0053] (1): Under an argon atmosphere, heat the polysilicon rod to a temperature T 1 of 1150 °C, with a heating rate v 1 of 50 °C / min and a holding time t 1 of 6 h;

[0054] (2): Under an argon atmosphere, cool the polysilicon rod after holding to T 2 of 850 °C by means of argon cooling, with a cooling rate v 2 of 25 °C / min;

[0055] (3): Under an argon atmosphere, continue to cool the above polysilicon rod to T 3 of 550 °C by means of argon cooling, with a cooling rate v 3 of 45 °C / min;

[0056] (4): Continue to cool the polysilicon rod in the above step to room temperature by means of water cooling;

[0057] (5): Crush the polysilicon rod cooled to room temperature to obtain polysilicon chunks with a particle size range mainly concentrated in 10 - 30 mm (the total mass accounts for about 40 - 60%), and wash the crushed product. Among them, the washing step specifically includes: pickling the crushed polysilicon material with an HF / HNO 3 system acid solution, then washing with high-purity water 3 - 5 times, drying, and finally obtaining purified electronic-grade polysilicon.

[0058] Examples 2 - 11

[0059] The differences from Example 1 are shown in Table 1, and the washing step is the same as that in Example 1.

[0060] Comparative Examples 1-13

[0061] The differences from Example 1 are shown in Table 1. The cleaning steps are the same as those in Example 1.

[0062] Table 1 Examples 1-11 and Comparative Examples 1-14

[0063]

[0064] Comparative Example 14

[0065] The polysilicon rod is crushed to obtain polysilicon chunks with a particle size range mainly concentrated in 10-30 mm (accounting for about 40-60% of the total mass), and the crushed product is cleaned. Among them, the cleaning steps specifically include: pickling the crushed polysilicon material with an HF / HNO 3 system acid solution, then washing with high-purity water 3-5 times, drying, and finally obtaining purified electronic-grade polysilicon.

[0066] Performance test:

[0067] Under the same conditions, the bulk impurity content of the purified polysilicon material is detected (detection method reference: GB / T37049-2018 Determination of Matrix Metal Impurities in Electronic-Grade Polysilicon - Inductively Coupled Plasma Mass Spectrometry), the yield of the polysilicon material

[0068] (Yield = total mass of silicon chunks after crushing / total mass of silicon rod) and the particle size distribution of the polysilicon material. The test results are shown in Table 2.

[0069] Table 2 Detection Results of Examples 1-11 and Comparative Examples 1-14

[0070]

[0071] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0072] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A purification method for ultra-high purity electronic grade polysilicon, characterized in that, it includes: (1) Heating the polysilicon rod to 1000 - 1200 °C and holding the temperature for not less than 4 h; (2) Cooling the polysilicon rod after heat preservation to 800 - 900 °C by air cooling method, and the cooling rate is 20 - 30 °C / min; (3) Continuing to cool the polysilicon rod to 500 - 600 °C by air cooling method, and the cooling rate is 40 - 50 °C / min; (4) Continuing to cool the polysilicon rod to room temperature by natural cooling method or water cooling method; (5) Crushing the polysilicon rod cooled to room temperature and cleaning the crushed product to obtain purified electronic grade polysilicon, wherein, steps (1) - (3) are all carried out in an inert atmosphere.

2. The purification method according to claim 1, characterized in that, in step (1), the heating rate of the heating is 40 - 60 °C / min; and / or, the holding time is 4 - 18 h.

3. The purification method according to claim 2, characterized in that, in step (1), the holding time is 4 - 6 h.

4. The purification method according to any one of claims 1 - 3, characterized in that, in step (1), the purity of the polysilicon rod is 6 - 13 N; and / or, the polysilicon rod is prepared by chemical vapor deposition method, and the holding treatment is directly carried out after the polysilicon rod is prepared.

5. The purification method according to any one of claims 1 - 3, characterized in that, in step (2), after the polysilicon rod is cooled to 800 - 900 °C, it is held for 0.5 - 1 h.

6. The purification method according to any one of claims 1 - 3, characterized in that, in steps (2) - (3), the air cooling method uses an inert gas as the cooling medium.

7. The purification method according to any one of claims 1 - 3, characterized in that, in step (4), the natural cooling is carried out in an inert atmosphere, and the water cooling method uses high-purity water as the cooling medium.

8. The purification method according to any one of claims 1 - 3, characterized in that, in step (5), the cleaning includes pickling and water washing.

9. Use of the purification method according to any one of claims 1 - 8 in purifying polysilicon rods or massive polysilicon.

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