CN114769219A - Method for cleaning electronic grade polysilicon with dry ice - Google Patents

Abstract

The invention discloses a method for cleaning electronic grade polycrystalline silicon by using dry ice. The method comprises the following steps: in the process of screening the crushed polysilicon material, taking protective gas or compressed air as carrier gas, and purging and cleaning the polysilicon material by using dry ice, wherein: the pressure of purging is 6-8 kilograms of force, and the flow rate of purging is 0.8-1.2 m/s. Therefore, the method is simple and convenient to operate, any wet chemical treatment is not needed, grease possibly introduced in each treatment process can be effectively removed, silicon powder, non-silicon objects and the silicon block attached to the surface of the silicon block can be effectively separated, particles on the surface of the silicon block are reduced, and pollutants brought into an acid washing machine are further reduced.

Description

Method for cleaning electronic grade polysilicon with dry ice

technical field

The invention relates to the technical field of polycrystalline silicon production, in particular to a method for cleaning electronic grade polycrystalline silicon by using dry ice.

Background technique

During the production and crushing of electronic grade polysilicon, a large amount of silicon powder will be produced near the crushing table, and these silicon powder will adhere to the surface of the silicon block. The probability will affect the cleaning effect of pickling. In addition, in the process of crushing, there are cases where people pick and choose, but because the edge of the silicon block is relatively sharp, the nitrile gloves worn by the personnel will be scratched and some fragments will fall off and adhere to the surface of the silicon block, and the attached nitrile fragments will It is a kind of high-carbon pollutant. After being brought into the crystal pulling furnace, it will cause local defects of the single crystal rod, and even lead to the failure of crystal pulling.

Therefore, the existing cleaning methods for electronic grade polysilicon still need to be further improved.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an object of the present invention is to propose a method for cleaning electronic grade polysilicon using dry ice, so as to effectively remove the grease that may be introduced in each treatment process, and to realize that the silicon powder, non-silicon matter and The effective separation of the silicon block reduces the particles on the surface of the silicon block, thereby reducing the pollutants brought into the pickling machine.

In one aspect of the present invention, the present invention proposes a method for cleaning electronic-grade polysilicon using dry ice. According to an embodiment of the present invention, the method includes: in the process of screening the polysilicon material obtained by crushing, Protective gas or compressed air is used as carrier gas, and dry ice is used to purge and clean the polysilicon material, wherein the purge pressure is 6-8 kgf, and the purge flow rate is 0.8-1.2 m/s. The inventor found that dry ice can be directly sublimated from solid state to gaseous state under the conditions of normal pressure and higher than -78.5°C (especially a temperature environment above 0°C, such as room temperature), and high-speed dry ice can be sprayed on the surface of polycrystalline silicon material, The sublimation of dry ice will take away a lot of heat near the surface of the silicon material, reduce the temperature of the grease attached to the surface of the silicon material, and cause it to be frozen and embrittled. The phenomenon of curling occurs and local cracking occurs. Under the purging of high-speed gas, the falling off is accelerated, thereby playing a role in decontamination. In addition, in the process of sieving the polysilicon material obtained by crushing, the generated silicon powder will be humidified and aggravated by the water vapor carried by the melting of dry ice. During the sieving process, the silicon powder particles and non-silicon materials are drawn out through the sieve holes, so as to remove the silicon powder and non-silicon materials. Therefore, the method is simple and convenient to operate, and does not require any wet chemical treatment. It can not only effectively remove the grease that may be introduced in each treatment process, but also realize the effective separation of silicon powder, non-silicon substances and silicon blocks attached to the surface of the silicon block. , reducing the particles on the surface of the silicon block, thereby reducing the pollutants brought into the pickling machine.

In addition, the method for cleaning electronic-grade polysilicon with dry ice according to the above embodiments of the present invention may also have the following additional technical features:

According to the embodiment of the present invention, the polycrystalline silicon material obtained by crushing is subjected to pre-screening and dust removal; the polycrystalline silicon material obtained by pre-screening and dust removal is screened again, and the polycrystalline silicon material is purged and cleaned with dry ice during the re-screening process. .

According to an embodiment of the present invention, the carrier gas is compressed air.

According to the embodiment of the present invention, the polysilicon material obtained by crushing is screened by a screening machine, the polycrystalline silicon material is blown and cleaned by a dry ice blower, and the dry ice blower is opened in advance before the screening machine is turned on. machine; after shutting down the screening machine, shut down the dry ice blower.

According to an embodiment of the present invention, the dry ice blower includes a dry ice injection hole, a carrier gas inlet line and a mixed gas outlet line, the dry ice injection hole is located on the upper part of the dry ice blower, and the carrier gas inlet line and the mixed gas outlet pipeline can withstand 6-10 kilograms of compressed air independently.

According to an embodiment of the present invention, the temperature of the purging and cleaning is not lower than 17°C, preferably performed in a temperature range from 17°C to room temperature.

According to an embodiment of the present invention, the purging and cleaning time is 5-10 minutes.

According to the embodiment of the present invention, in the process of sieving the polycrystalline silicon material obtained by crushing, the sieve plate used is inclined to the horizontal direction. big.

According to an embodiment of the present invention, the included angle between the sieve plate and the horizontal direction is 10 to 25 degrees; and/or the included angle between the purging and cleaning direction and the setting direction of the sieve plate is 90±10 degrees, preferably 90 degrees.

According to an embodiment of the present invention, when using a screening machine to screen the polysilicon material obtained by crushing, the screening machine is first turned on to work for a period of time, and then the polysilicon material is screened;

According to an embodiment of the present invention, the purge cleaning is performed in a clean environment.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic plan view of a dry ice blower according to an embodiment of the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

In one aspect of the present invention, the present invention proposes a method for cleaning electronic-grade polysilicon using dry ice. According to an embodiment of the present invention, the method includes: in the process of screening the polysilicon material obtained by crushing, Protective gas or compressed air is used as carrier gas, and dry ice is used to purge and clean the polysilicon material, wherein the purge pressure is 6-8 kgf, and the purge flow rate is 0.8-1.2 m/s. The inventor found that dry ice can be directly sublimated from solid state to gaseous state under the conditions of normal pressure and higher than -78.5°C (especially a temperature environment above 0°C, such as room temperature), and high-speed dry ice can be sprayed on the surface of polycrystalline silicon material, The sublimation of dry ice will take away a lot of heat near the surface of the silicon material, reduce the temperature of the grease attached to the surface of the silicon material, and cause it to be frozen and embrittled. The phenomenon of curling occurs and local cracking occurs. Under the purging of high-speed gas, the falling off is accelerated, thereby playing a role in decontamination. In addition, in the process of sieving the polysilicon material obtained by crushing, the generated silicon powder will be humidified and aggravated by the water vapor carried by the melting of dry ice. During the sieving process, the silicon powder particles and non-silicon materials are drawn out through the sieve holes, so as to remove the silicon powder and non-silicon materials. Therefore, the method is simple and convenient to operate, and does not require any wet chemical treatment. It can not only effectively remove the grease that may be introduced in each treatment process, but also realize the effective separation of silicon powder, non-silicon substances and silicon blocks attached to the surface of the silicon block. , reducing the particles on the surface of the silicon block, thereby reducing the pollutants brought into the pickling machine.

According to the embodiment of the present invention, the purging pressure of the carrier gas is 6-8 kgf, for example, it can be 6 kgf, 7 kgf, 8 kgf, etc., and the purging flow rate is 0.8-1.2 m/s, for example, it can be It is 0.8m/s, 0.9m/s, 1.0m/s, 1.2m/s, etc. The inventors found that if the carrier gas purging pressure or the purging flow rate is too small, it is difficult to obtain an effective dry ice purging force, The effect of purging and cleaning is poor; as the pressure of carrier gas purging or the flow rate of purging increases, the effect of purging and cleaning will also be improved, but when the pressure of carrier gas purging or the flow rate of purging increases to a certain level After the purging pressure of the carrier gas or the flow rate of the purging continues to increase, the effect of further improving the purging and cleaning effect is not obvious, and at the same time, the cost of purging and cleaning the bulk silicon material will be significantly increased; The purging pressure of the carrier gas is 6-8 kgf, and the purging flow rate is 0.8-1.2 m/s, which can better take into account the purging and cleaning effect of the bulk silicon material and the cost of purging and cleaning, and realize the block-shaped silicon material. A win-win for silicon cleanliness and economical cost.

According to the embodiment of the present invention, when there are many silicon powder or non-silicon impurities on the surface of the polysilicon material obtained by crushing, the polysilicon material obtained by crushing can be pre-screened and dedusted first; Screening again, in the process of re-screening, the polycrystalline silicon material is purged and cleaned with dry ice, so that part of the silicon powder or non-silicon impurities in the polycrystalline silicon material can be removed in advance, so as to not only avoid the silicon powder in the silicon material Too much or non-silicon impurities will affect the efficiency and effect of subsequent purging and cleaning of polysilicon materials, and at the same time, it can save the amount of dry ice, reduce the overall purging and cleaning costs, and achieve a win-win between the cleanliness of bulk silicon materials and economic costs.

According to the embodiment of the present invention, when purging and cleaning, either protective gas (such as inert gas or nitrogen) can be used as the carrier gas for dry ice purging, or compressed air with higher degree of purity can be used as the carrier gas for dry ice purging , thereby avoiding the introduction of new impurities. Preferably, compressed air can be used as the carrier gas for dry ice purging. The inventors found that the boiling point of dry ice is -78.5°C under normal pressure, that is, when the temperature is higher than -78.5°C, dry ice will sublimate and absorb the heat of surrounding objects, Reduce their temperature to close to -78.5°C. During the sublimation process of dry ice, the water vapor in the compressed air can be condensed, which is conducive to the condensation and shedding of silicon powder and non-silicon materials in the silicon material. Better removal of silicon powder and non-silicon.

According to the embodiment of the present invention, the polycrystalline silicon material obtained by crushing can be screened by a screening machine, and the polycrystalline silicon material can be blown and cleaned by a dry ice blower. Before turning on the screening machine, the dry ice can be turned on in advance. blower; after shutting down the sieving machine, shut down the dry ice blower. Therefore, in the whole process of sieving electronic grade polysilicon, it can be ensured that dry ice is used for purging and cleaning, so that the purging and cleaning of polysilicon material can be more thoroughly achieved, thereby obtaining block silicon with higher cleanliness. material.

According to an embodiment of the present invention, referring to FIG. 1 , the dry ice blower may include a dry ice injection hole 10 , a carrier gas inlet line 20 and a mixed gas outlet line 30 , and the dry ice injection hole 10 may be located in the dry ice blower On the upper part of the machine, the carrier gas inlet line 20 and the mixed gas outlet line 30 can independently withstand compressed air with a force of 6-10 kg. Specifically, the dry ice blower can be installed on the head of the screening machine, pour the silicon material into the screening machine, turn on the dry ice blower, spray high-speed dry ice on the surface of the polysilicon material, and the sublimation of the dry ice will take away the surface of the silicon material A large amount of heat nearby reduces the temperature of the grease attached to the surface of the silicon material, causing it to be frozen and embrittled. Because the thermal expansion coefficient of silicon is different from that of grease, after embrittlement, the grease will curl up and crack locally. Under the purging of the gas, the shedding is accelerated, so as to play a decontamination effect; in addition, the silicon powder produced by the screening machine during the shaking process will be humidified and aggravated by the water vapor carried by the melting of dry ice, and the PE wire and nitrile gloves on the surface of the silicon block Other non-silicon materials will be rapidly frozen, fall off, and be drawn out from the sieve holes with smaller apertures of the sieving machine, which can effectively separate silicon powder, non-silicon materials and silicon blocks. It can effectively remove the grease introduced in the process, and at the same time, it can also effectively separate the silicon powder, non-silicon matter and the silicon block attached to the surface of the silicon block, reduce the number of particles on the surface of the silicon block, and then reduce the particles brought into the pickling machine. quantity. According to some examples of the present invention, the diameter of the carrier gas inlet line and the mixed gas outlet line can be DN25, and a nozzle with a duckbill flat head can be selected, thereby further ensuring that the mixture of dry ice and carrier gas is sprayed out It can maintain high purge pressure and purge flow rate.

According to the embodiment of the present invention, the temperature of the purging and cleaning may not be lower than 17°C, for example, it may be 17°C, 19°C, 25°C, 30°C, etc. Control the ambient temperature, it can be carried out under normal temperature and pressure, and the dry ice can sublime directly from the solid state to the gaseous state more quickly, which can reduce the surface temperature of the silicon material more quickly, which is more conducive to improving the efficiency of purging and cleaning the silicon material. and effect. Preferably, the purging cleaning can be performed in a temperature range from 17° C. to room temperature, so that the efficiency and effect of the purging cleaning and the economic cost can be better taken into account.

According to the embodiment of the present invention, the time of the purging and cleaning can be 5-10 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc., thus, it can be ensured that a good cleaning effect can be obtained .

According to the embodiment of the present invention, in the process of sieving the polysilicon material obtained by crushing, the sieve plate used may be inclined to the horizontal direction. Gradually become larger, wherein the inclined sieve plate is more conducive to the movement and classification and screening of polycrystalline silicon material on the sieve plate. Therefore, in the sieving process, through the sieve plate vibration and multi-stage sieve sieving, small particles such as silicon powder and non-silicon can be removed first, and then the silicon blocks with smaller particle size can be removed, and finally a suitable particle size can be obtained. The required silicon block can further improve the purging effect of small particulate impurities such as silicon powder and non-silicon material, significantly reduce the number of particles on the surface of the silicon block, and obtain block silicon material with higher cleanliness.

According to the embodiment of the present invention, the angle between the sieve plate and the horizontal direction may be 10 to 25 degrees, specifically 10 degrees, 15 degrees, 20 degrees, 22 degrees, 25 degrees, etc., thus, not only can the particle size be convenient At the same time, the falling rate of the particles can also be controlled to ensure that the particles in the screening have a proper stay, avoiding the problem that the particles are difficult to maintain for a sufficient screening time and thus affect the separation effect; The included angle of the setting direction of the sieve plate can be 90±10 degrees, thereby, the purging and cleaning of the bulk silicon material can be further improved. Preferably, the included angle between the purging and cleaning direction and the setting direction of the sieve plate can be 90 degrees, which can make the purging and cleaning effect better.

According to the embodiment of the present invention, when using a screening machine to screen the polysilicon material obtained by crushing, the screening machine can be turned on for a period of time, and then the polysilicon material is screened, that is, the polysilicon material is screened. The screening machine can be preheated first, so that the screening machine can reach the normal working state, so as to further ensure the screening effect.

According to some examples of the present invention, the purging and cleaning can be performed in a clean environment, thereby effectively avoiding the introduction of new impurities, wherein an increasing device can be provided in the clean environment to facilitate the cleaning of the clean air in the clean environment. Boost for cleaner compressed air.

The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

The pre-screening process involved in the following examples is as follows:

Personnel wear dust respirators and sound-absorbing earplugs. Debug the particle size tester, and test the particle size blank value of the environment; in addition, the sieve plate in the sieving machine is set inclined, and in the direction from the top to the bottom, the sieve hole diameter of the sieve plate in the sieving machine gradually becomes larger, and the screen The hole diameter is 30-200mm. After opening the sieving machine for 5 minutes, pour 500 kg of polysilicon material into the sieving machine; Sample 2, Sample 3, Sample 4, Sample 5.

Example 1

Pour sample 1 into the sieving machine again, turn on the dry ice blower, adjust the purging pressure indicator to 6 kg, and stop the sieving machine after sieving for 5 minutes. Test with a particle size tester at the 30-200mm sieve hole of the sieving machine and 200-300mm above the sieve plate, and record the number of particles before 1min and after 1min, and record them as data 1 and data 2.

Example 2

The difference from Example 1 is that: the sample 2 is poured into the sieving machine again, the dry ice blowing machine is turned on, and the purging pressure indication is adjusted to 7 kg.

Example 3

The difference from Example 1 is: Pour the sample 3 into the sieving machine again, turn on the dry ice blowing machine, and adjust the blowing pressure indication to 8 kg.

Example 4

The difference from Example 1 is that: the sample 4 is poured into the sieving machine again, the dry ice blowing machine is turned on, and the purging pressure indication is adjusted to 9 kg.

Comparative ratio

Pour sample 5 into the sieving machine again, and after sieving for 5 minutes, stop the sieving machine. Use a particle size tester on the top of the sieve plate with a sieve aperture of 200-300 mm, and record the data of the number of particles before and after 1min, which are recorded as data 1 and data 2.

Table 1 is the test results of the total number of particles not larger than 0.5 μm in Examples 1 to 4 of the present invention and Comparative Example 1. Among them, the blank value is the number of particles not larger than 0.5 μm in the detection environment.

Table 1 Experimental record of the number of 0.5μm particles (counts/ft ³ )

Comparative ratio Example 1 Example 2 Example 3 Example 4 blank value 9854 7646 8716 5246 6489 Purge pressure/kg none 6 7 8 9 Data 1 (1min ago) 498713 16135 15497 14695 15962 Data 2 (after 1min) 327915 12894 14351 13689 11561

It can be seen from Table 1 that the particle numbers measured in the comparative example are 498,713 counts/ft ³ and 327,915 counts/ft ³ respectively, while the particle numbers measured in Examples 1 to 4 are significantly reduced. The silicon powder on the surface of the block is effectively separated from the silicon block, which can greatly reduce the particles on the surface of the silicon material. Among them, with the increase of the purging pressure, the number of particles on the surface of the finally obtained bulk silicon material generally showed a downward trend. The big reason is that the dry ice blower is located at the head of the sieving machine, and the purging direction is from top to bottom, while the particle size tester is located above the sieve plate downstream of the sieving machine for particle testing, including Two test points, the vibration drop time of the silicon material between the two test points is 1min. When the dry ice blower starts to blow, it has the effect of removing the silicon powder on the surface of the silicon block. The silicon material passes over the dry ice blower and vibrates. Going back, through the two points of the test, the number of particles generated by vibration at these two test points is detected by the particle size tester, that is to say, the particle size tester indirectly obtains silicon by measuring the number of particles in the environment. The number of particles on the surface of the material is measured as the number of particles above the falling direction of the silicon material. The more the number of particles measured in the environment, the less the amount of dust going downstream, and the higher the cleanliness of the obtained silicon material; In addition, at the head of the screening machine, the strong airflow direction provided by the dry ice blower is downward, which has a downward pressure on the dust particles. The higher the blowing pressure, the more obvious the downward pressure effect on the dust; After being hit on the silicon material, the surface of the silicon material actually has moisture regain, which can play a role in dust reduction. There will be wet silicon powder in some places on the sieve plate. Within a certain purging pressure range, the moisture regain will also increase with the increase of the dry ice purging pressure. It is relatively more obvious, but it is difficult to distinguish it from the naked eye. Although the wet silicon powder left on the sieve plate can reduce the amount of dust going downstream, this part of the silicon powder is located 200-300mm above the sieve plate. The probability of detection by the particle size tester is low, thus, although the cleanliness of the silicon material obtained in Examples 3 and 4 is higher, the number of particles measured after 1min is larger than that in Example 2. Phenomenon. To sum up, considering the economic cost and the effect of purging and cleaning, the pressure of purging and cleaning can be selected to be 6-8 kg.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (10)

1. A method for cleaning electronic grade polysilicon by using dry ice is characterized by comprising the following steps:

in the process of screening the crushed polycrystalline silicon material, protective gas or compressed air is used as carrier gas, and dry ice is used for purging and cleaning the polycrystalline silicon material, wherein: the pressure of the blowing is 6-8 kilograms of force, and the flow speed of the blowing is 0.8-1.2 m/s.

2. The method according to claim 1, characterized in that the polysilicon material obtained by crushing is subjected to pre-screening dust removal; and screening the polysilicon material obtained by pre-screening and dedusting again, and purging and cleaning the polysilicon material by using dry ice in the secondary screening process.

3. The method of claim 1, wherein the carrier gas is compressed air.

4. The method according to claim 1, characterized in that the crushed polysilicon material is screened by a screening machine, the polysilicon material is purged and cleaned by a dry ice purging machine, and the dry ice purging machine is started in advance before the screening machine is started; and after the sieving machine is closed, closing the dry ice purging machine.

5. The method as claimed in claim 1, wherein the dry ice purging machine comprises a dry ice charging hole, a carrier gas inlet line and a mixed gas outlet line, the dry ice charging hole is positioned at the upper part of the dry ice purging machine, and the carrier gas inlet line and the mixed gas outlet line can respectively and independently bear 6-10 kilograms of force of compressed air.

6. The method according to claim 1, wherein the temperature of the purge is not lower than 17 ℃, preferably in a temperature range from 17 ℃ to room temperature.

7. The method according to claim 1, wherein the time for the purge cleaning is 5-10 min.

8. The method according to any one of claims 1 to 7, wherein a sieve plate is used in the process of sieving the crushed polysilicon material, the sieve plate is arranged obliquely to the horizontal direction, and the pore diameter of the sieve plate is gradually increased from the top to the bottom.

9. The method according to claim 8, wherein the angle between the screen plate and the horizontal direction is 10-25 degrees; and/or the included angle between the purging and cleaning direction and the sieve plate setting direction is 90 +/-10 degrees, preferably 90 degrees.

10. The method according to claim 1, characterized in that when screening the crushed polysilicon material by using a screening machine, the screening machine is started to work for a period of time, and then the polysilicon material is screened;

optionally, the purging is performed in a clean environment.

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