JP2016005993A - Cleaning method of polycrystal silicon nugget - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of reducing a heat load to a resin-made container for housing a cleaning object to prevent degradation of the container and capable of shortening a cleaning process, in a field of cleaning technology of a silicon crystal.SOLUTION: A polycrystal silicon rod is crushed to obtain polycrystal silicon nuggets (S101), which are housed in a resin-made container (S102) and sent to subsequent cleaning steps (S103-S105). When a liquid temperature of a chemical agent in an etching step (S103), a pure water temperature in a rinsing step (S104), and a gas temperature of a blow gas supplied to a dryer in a drying step (S105) are referred to as T, T, and Trespectively, these temperatures are set so as not to fall in the progress of each step. In other words, the temperatures are set to gradually rise throughout the cleaning steps. The temperatures are preferably 85°C or lower in the cleaning steps.

Description

  The present invention relates to a method for cleaning a polycrystalline silicon lump.

For etching silicon crystal, an acid mixed solution of hydrofluoric acid (HF) and nitric acid (HNO ₃ ) or an acid mixed solution obtained by adding hydrogen peroxide (H ₂ O ₂ ) to this is generally used. The mixing ratio of these acid mixed solutions (etchants) is appropriately set according to the type and concentration of contaminants adhering to the surface of the silicon crystal to be cleaned, but is most commonly used. The mixed composition is a hydrofluoric acid solution having a volume ratio of HNO ₃ (70 wt%): HF (50 wt%) = 9: 1.

  After the silicon crystal is etched with the acid mixed solution, pure water cleaning (rinsing) is performed, and the chemical solution used in the etching is washed away until it reaches the ppb to ppt level, and then dried.

  Even when polycrystalline silicon grown by the Siemens method is crushed into a nugget-like crystalline silicon lump, the basic cleaning process is the same as described above, and various methods for cleaning have been proposed. (For example, refer to Patent Documents 1 to 3).

  When cleaning the polycrystalline silicon lump, the etching process with the chemical solution, the pure water rinsing process, and the gas blow drying process are performed in this order in a state where the polycrystalline silicon lump is accommodated in the resin container. Insufficient drying may cause stains on the surface of the polycrystalline silicon lump during storage, degrading quality.

  On the other hand, if the time of the drying process is lengthened, the generation of stains is suppressed, but not only the cleaning process time is lengthened and work efficiency is lowered, but also the container containing the polycrystalline silicon lump is reduced. The thermal load is increased and the deterioration is accelerated, and the smoothness of the surface is lowered, resulting in a “gritty” state.

  If the polycrystalline silicon lump is washed using a container having a rough surface, it will hinder automation of the pure water rinsing process. This is because, in the pure water rinsing process, the electrical conductivity of the pure water is monitored and the rinsing progress is automatically judged. As a result, the chemical components are strongly adsorbed on the rough surface, This is because the removal efficiency is greatly reduced, and the value of the electrical conductivity is extremely reduced.

JP 2011-68554 A JP 2012-211073 A JP 2012-224541 A

  Thus, in the field of silicon crystal cleaning technology, a technology that simultaneously realizes prevention of deterioration of a container accommodating a cleaning target and shortening of the cleaning process is desired.

  The present invention has been made in view of the above problems, and the object of the present invention is to reduce the thermal load on the resin container to prevent its deterioration and to enable a shortening of the cleaning process. It is to provide.

In order to solve the above-described problems, the method for cleaning a polycrystalline silicon lump according to the present invention includes an etching process using a chemical solution, a pure water rinsing process, and a gas blow drying process in this order while the polycrystalline silicon lump is contained in a container. In this method, the chemical temperature T ^{E in} the etching step, the pure water temperature T ^{R in the} rinsing step, and the gas temperature T ^D of the supply blow gas into the dryer in the drying step are: None of these decrease with the progress of each process, and the minimum chemical temperature (T ^E _min ) and the maximum chemical temperature (T ^E _max ) of the etching process, the minimum pure water temperature (T ^R ) of the rinsing process. _min ) and the maximum pure water temperature (T ^R _max ), the minimum gas temperature (T ^D _min ) and the maximum gas temperature (T ^D _max ) of the supply blow gas into the dryer in the drying step are T ^E _max ≦ T ^R _min ≦ T ^R _max ≦ Satisfy the relation of ^D _min, characterized in that.

  Preferably, the container for storing the polycrystalline silicon lump is made of any of the following materials. Polyethylene or its copolymer, polypropylene or its copolymer, polypropylene or its copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoroalkyl vinyl ether copolymer (FEP), tetrafluoroethylene perfluoro Alkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer (EPE), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / Chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF).

  Preferably, a plurality of holes are formed in the four side plates and the bottom plate of the container so that the aperture ratio is 28% or more and 50% or less.

  Preferably, the apparent specific gravity defined by W / V is 1.2 kg / liter or more, where W is the weight of the polycrystalline silicon mass accommodated in the container and V is the apparent volume. .

Preferably, when individual polycrystalline silicon chunks contained in the container are approximated to a sphere, the maximum value (D ^S _max ) and the minimum value (D ^S _min ) of the diameter (sphere equivalent diameter: D ^S ) The polycrystalline silicon block is selected so that the ratio (D ^S _max / D ^S _min ) is 6 or less.

Preferably, the maximum gas temperature (T ^D _max ) of the supply blow gas into the dryer in the drying step is 85 ° C. or lower, and the gas flow rate in the dryer is 0.5 m / sec or higher.

  Further, preferably, the total process time of the drying process is set to 0.77 minutes / kg or less in terms of the weight unit of the polycrystalline silicon lump accommodated in the container.

In the present invention, when the chemical temperature in the etching process is T ^E , the pure water temperature in the rinsing process is T ^R , and the gas temperature of the supply blow gas into the dryer in the drying process is T ^D , these temperatures are all It sets so that it may not fall with progress of each process. That is, the cleaning process is consistently set so that the temperature gradually increases. According to the present invention, the thermal load on the container in the drying process is reduced, and the drying time is shortened. As a result, it is possible to simultaneously prevent the deterioration of the container and shorten the cleaning process.

It is a figure for demonstrating notionally the process flow of the washing | cleaning method of the polycrystal silicon lump which concerns on this invention. It is a figure for demonstrating notionally the mode of the round hole provided in the bottom plate of a container.

  When a polycrystalline silicon lump (nugget) obtained by crushing a polycrystalline silicon rod grown by the Siemens method or the like is supplied as a raw material for semiconductor production, it is generally about 20 mm to 120 mm depending on the user's request. It is assumed to be of the diameter. In the manufacturing process of the polycrystalline silicon lump, products having the above-mentioned diameter range are finally selected and commercialized. However, in the crushing process, a small-sized polycrystalline silicon lump that is smaller than the above range is also generated.

  Naturally, the crushed polycrystalline silicon lump is cleaned, but the polycrystalline silicon lump having a size smaller than the above range is also accommodated in the cleaning container. In order to increase the processing amount per batch, as much polycrystalline silicon lump as possible will be accommodated in the container. However, the small-sized polycrystalline silicon lump has a large specific surface area. It takes a long time to dry.

  In order to shorten the drying time, it is effective to increase the temperature at the time of drying, but in that case, there is a problem that the thermal load of the container is increased and the life is shortened.

  Therefore, the inventors of the present invention, in a method for cleaning a polycrystalline silicon lump in which an etching process using a chemical solution, a rinsing process using pure water, and a drying process using gas blowing proceed in this order, the chemical temperature of the etching process and the purity of the rinsing process. The water temperature and the gas temperature of the blow gas supplied to the dryer in the drying process are set to gradually increase, and by eliminating sudden temperature changes, the drying process can be shortened and It was also decided to reduce the load on the resin of the container containing the crystalline silicon lump.

  FIG. 1 is a diagram for conceptually explaining the process flow of the method for cleaning a polycrystalline silicon lump according to the present invention. First, a polycrystalline silicon rod is crushed into a polycrystalline silicon lump (nugget) (S101), and these are accommodated in a resin container (S102) and flowed to the subsequent washing steps (S103 to S105).

If the chemical temperature in the etching step (S103) is T ^E , the pure water temperature in the rinsing step (S104) is T ^R , and the gas temperature of the blow gas supplied into the dryer in the drying step (S105) is T ^D , these temperatures Are set so that they do not decrease with the progress of the respective steps. That is, the cleaning process is consistently set so that the temperature gradually increases.

  The etching step (S103), the rinsing step (S104), and the drying step (S105) do not have to be a single step, but even if they are composed of two or more sub-steps, The temperature is set to be higher than the temperature in the previous sub-process. The drying step (S105) may include a step of drying the polycrystalline silicon lump in the dryer following the gas blowing step, but in this specification, the series of drying steps are collectively referred to as a gas blowing step. This is called a drying process.

Then, the minimum chemical temperature (T ^E _min ) and the maximum chemical temperature (T ^E _max ) in the etching step (S103), the minimum pure water temperature (T ^R _min ) and the maximum pure water temperature (T ^R _max ) in the rinsing step (S104). ), The minimum gas temperature (T ^D _min ) and the maximum gas temperature (T ^D _max ) of the blow gas supplied into the dryer in the drying step (S105) are set to T ^E _max ≦ T ^R _min ≦ T ^R _max ≦ T ^D _min Set conditions to satisfy the relationship.

That is, in the method for cleaning a polycrystalline silicon lump according to the present invention, the polycrystalline silicon lump in which the etching step with the chemical solution, the pure water rinsing step, and the gas blow drying step are performed in this order in a state where the polycrystalline silicon lump is accommodated in the container. In this cleaning method, the chemical temperature T ^{E in} the etching step, the pure water temperature T ^{R in the} rinsing step, and the gas temperature T ^D of the supply blow gas into the dryer in the drying step are all the respective steps. The minimum chemical solution temperature (T ^E _min ) and the maximum chemical solution temperature (T ^E _max ) in the etching process, the minimum pure water temperature (T ^R _min ), and the maximum pure water temperature in the rinse process are not reduced as the process proceeds. (T ^R _max ), the minimum gas temperature (T ^D _min ) and the maximum gas temperature (T ^D _max ) of the supply blow gas into the dryer in the drying step are T ^E _max ≦ T ^R _min ≦ T ^R _max ≦ T to satisfy the relationship of ^D _min To set the conditions so.

  In such a cleaning process, for example, when the rinsing process (S104) is performed in the first to third stages, the temperature of the ultrapure water in the third rinsing process performed immediately before the drying process (S105). Is set to 80 ° C, the rinse discharge liquid is reused in the second rinse process, and the rinse discharge liquid is reused in the first rinse process. This is advantageous because the water temperature gradually decreases.

  According to such reuse of the rinse liquid, the pure water temperature in the first-stage rinse tank is about 40 ° C., for example, and the pure water temperature gradually increases in the second and third stages. The heat load on the container is reduced.

  If the heat load on the container is large, the resin will deteriorate and the surface of the container will gradually become rough.If you continue to use it in this state, the polymer polymerization bonds will be broken due to the deterioration and the resin will be partially peeled off. Although it mixes in a product and causes a quality problem, according to the present invention, such a problem hardly occurs due to a reduction in heat load.

  The container used for such cleaning is made of the following resin, for example.

  Polyethylene or its copolymer, polypropylene or its copolymer, polypropylene or its copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoroalkyl vinyl ether copolymer (FEP), tetrafluoroethylene perfluoro Alkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer (EPE), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / Chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF).

  After the rinsing step, air or an inert gas is injected to dry the gas attached to the polycrystalline silicon lump to blow off the moisture. The gas temperature at that time is higher than that in the third rinsing step. The temperature is set to be higher than 80 ° C. which is the temperature of pure water, for example, 85 ° C. In addition to the method using a heat exchanger, there are various methods for raising the gas temperature, but an air heater system that can simultaneously obtain high-temperature air and low-temperature air by supplying compressed air is efficient. .

  In order to further reduce the thermal load, blow gas is effectively supplied to the individual polycrystalline silicon chunks in the drying process, and residual rinse components removed from the polycrystalline silicon chunks are quickly discharged from the container. It is effective to secure such a flow path.

  Therefore, according to a study by the present inventors, it is effective to form a plurality of holes in the four side plates and the bottom plate of the container so that the opening ratio is 28% or more and 50% or less. . If the aperture ratio is low, a sufficient flow path cannot be secured. On the other hand, if the aperture ratio is too high, a relatively small diameter of the accommodated polycrystalline silicon lump is dropped during the cleaning process.

  FIG. 2 is a diagram for conceptually explaining the state of the round hole provided in the bottom plate of the container. Such a round hole is a flow of pure water (linear velocity) near the surface of the polycrystalline silicon lump. And a flow path in which blow gas is effectively supplied to individual polycrystalline silicon chunks in the drying process and residual rinse components removed from the polycrystalline silicon chunks are quickly discharged from the container. Secure. Such holes are similarly formed in the four horizontal plates of the container.

  According to the study by the present inventors, the aperture ratio is in the above range, and the individual hole diameters are preferably 12 to 15 mm.

  When a drying experiment was conducted with an apparent specific gravity (bulk density) of 1.2 kg / liter accommodated in a 20 mm diameter polycrystalline silicon lump in such a container, a blow gas temperature of 85 ° C. and an air flow rate of 0.5 m / sec. It was confirmed that the drying was completed within 5 minutes under the above conditions. Here, the apparent specific gravity (bulk density) is defined as W / V, where W is the weight of the polycrystalline silicon block accommodated in the container and V is the apparent volume.

  In addition, when the size distribution of the polycrystalline silicon lump is narrow, the filling rate increases, and when the size distribution of the polycrystalline silicon lump is wide, the filling rate decreases. According to the study by the present inventors, in order to shorten the entire cleaning process and achieve productivity, it is preferable to set the filling rate to 1.2 kg / liter or more in terms of apparent specific gravity.

Further, in order to increase the filling rate, each of the polycrystalline silicon chunks accommodated in the container has a maximum value (D ^S _max ) of its diameter (sphere equivalent diameter: D ^S ) when approximated by a sphere. It is preferable to select the polycrystalline silicon lump so that the ratio (D ^S _max / D ^S _min ) of the minimum value (D ^S _min ) is 6 or less.

In order to reduce the thermal load on the container in the drying process and shorten the drying time, the supply blow gas into the dryer in the drying process has a maximum gas temperature (T ^D _max ) of 85 ° C. or less, and the dryer The gas flow rate inside is preferably 0.5 m / sec or more.

  In addition, it is preferable that the total process time of a drying process shall be 0.77 minutes / kg or less in conversion per weight unit of the polycrystal silicon lump accommodated in the container.

  Hereinafter, embodiments of the present invention will be described.

  A PP container having a volume of 16 liters was filled only with a silicon nugget having a sphere equivalent diameter of 20 mm. The filling weight at this time was 13 kg, the apparent volume was 10.8 liters, and the apparent specific gravity was 1.2 kg / liter.

  The opening ratio of the container used was 28%, and each of the four side plates was provided with 156 holes with a diameter of 12 mm and 63 holes with a diameter of 12 mm on the bottom. The upper surface of the container is opened on the entire surface.

Etching with a chemical solution was performed with a chemical solution of HNO ₃ (70 wt%): HF (50 wt%) = 9: 1 by volume ratio. The temperature of the chemical solution was controlled in the range of 20 to 30 ° C. by cooling the temperature rise due to the etching reaction with a chiller.

  After the etching with the chemical solution, rinsing consisting of four stages was performed. The temperature of the first-stage rinse layer is about 40 ° C., the temperature of the second-stage rinse tank is about 50 ° C., the temperature of the third-stage rinse tank is about 60 ° C., and the temperature of the final rinse tank is 80 ° C. (± 1 ° C.), and the temperature in the rinse layer was gradually increased.

  The cycle time of each rinse tank was 3 minutes, and the flow rate of rinse water in each tank was 20 liters / minute.

  The container was pulled up from the final rinsing tank (fourth rinse layer) and sprayed with high-pressure air just before it was put into the dryer to blow off water attached to the nugget and the surface of the container.

  The amount of jet air at the time of this gas blow was 4 liters / second at the outlet of the spray, and eight types of sprays of the same type were used in parallel. Immediately before spraying, the air temperature was increased by an air heater (high-temperature air generator TOHIN air heater AC-70W manufactured by Tohama Kogyo Co., Ltd.), and the temperature of the injection port was set to 80 ° C., the same as the temperature of the final rinse layer.

  Following the gas blowing step, the polycrystalline silicon lump was dried in a dryer. That is, the gas blow drying process includes a preceding gas blowing process and a subsequent dryer drying process.

  The dryer at this time was a ventilation type dryer, the inside temperature was set to 85 ° C. (± 1 ° C.), and the drying was performed for 5 minutes under the condition that the supply blow gas was ventilated at a flow rate of 0.5 m / sec. .

  The nugget in the container after the completion of the gas blow drying process showed no moisture and no uneven drying.

  Filling ratio (apparent specific gravity) of polycrystalline silicon lump to be stored in the container, sphericity of polycrystalline silicon lump (sphere equivalent diameter ratio), resin material and opening ratio of container, first stage of 4-stage rinse (first stage) The temperature of the rinsing tank and the final stage (fourth stage) rinsing tank, the blown gas temperature and the post-stage drying process of the pre-stage drying process when the gas blow drying process is a two-stage process of the pre-stage gas blow process and the post-stage dryer drying process. Eight examples and four comparative examples were carried out using the internal temperature, supply blow gas flow rate, and drying time as parameters, and the drying state and the number of repeated uses (life) of the container were examined.

  The results are summarized in Tables 1 and 2.

  In Comparative Example 1 and Comparative Example 2, drying is not sufficient because the opening ratio of the container is as low as 15%.

  The thing of the comparative example 3 is not fully dried since the supply blow gas flow velocity into the container in the latter drying process in the dryer is as low as 0.3 m / s.

  In Comparative Example 4, the opening ratio of the container is as low as 15%, so that drying is not sufficient, and the internal temperature in the latter drying process in the dryer is as high as 105 ° C., and the drying time is 30 minutes. Due to the influence of the heat load on the container due to its long length, the number of repeated use is remarkably reduced to 380 times.

  In contrast to these results, all of Examples 1 to 8 are in a good dry state, the number of repeated use of the container exceeds 1000 times, and the life of the container is extended. .

  In any of the containers used in Examples 1 to 8, a plurality of holes are formed in the four side plates and the bottom plate so that the opening ratio is 28% or more and 50% or less.

In addition, the apparent specific gravity of the polycrystalline silicon mass accommodated in the container is 1.2 kg / liter or more, and when the individual polycrystalline silicon mass accommodated in the container is approximated by a sphere, The ratio (sphere equivalent diameter ratio) between the maximum value (D ^S _max ) and the minimum value (D ^S _min ) of the diameter (sphere equivalent diameter: D ^S ) is 6 or less.

Furthermore, the maximum gas temperature (T ^D _max ) of the supply blow gas into the dryer in the drying process is 85 ° C. or less, and the gas flow rate in the dryer is 0.5 m / sec or more.

  As described above, according to the present invention, the thermal load on the container in the drying process is reduced, and the drying time is shortened. As a result, it is possible to simultaneously prevent the deterioration of the container and shorten the cleaning process.

Claims (7)

A method for cleaning a polycrystalline silicon lump in which a polycrystalline silicon lump is contained in a container, and an etching process using a chemical solution, a pure water rinsing process, and a gas blow drying process are performed in this order.
The chemical temperature T ^{E in} the etching process, the pure water temperature T ^{R in the} rinsing process, and the gas temperature T ^D of the supply blow gas into the dryer in the drying process all decrease as the processes progress. Not,
Minimum chemical solution temperature (T ^E _min ) and maximum chemical solution temperature (T ^E _max ) in the etching step, minimum pure water temperature (T ^R _min ) and maximum pure water temperature (T ^R _max ) in the rinsing step, The minimum gas temperature (T ^D _min ) and the maximum gas temperature (T ^D _max ) of the supply blow gas into the dryer satisfy the relationship of T ^E _max ≦ T ^R _min ≦ T ^R _max ≦ T ^D _min A method for cleaning a polycrystalline silicon lump. The method for cleaning a polycrystalline silicon lump according to claim 1, wherein the container containing the polycrystalline silicon lump is made of any of the following materials.
Polyethylene or its copolymer, polypropylene or its copolymer, polypropylene or its copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoroalkyl vinyl ether copolymer (FEP), tetrafluoroethylene perfluoro Alkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer (EPE), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / Chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF).   The method for cleaning a polycrystalline silicon lump according to claim 1 or 2, wherein a plurality of holes are formed in the four side plates and the bottom plate of the container so that the opening ratio is 28% or more and 50% or less. .   The apparent specific gravity defined by W / V is 1.2 kg / liter or more, where W is the weight of the polycrystalline silicon lump accommodated in the container and V is the apparent volume. 4. The method for cleaning a polycrystalline silicon lump according to any one of 3 above. When the individual polycrystalline silicon chunks contained in the container are approximated by a sphere, the ratio (D ^S _max ) of the maximum value (D ^S _max ) and the minimum value (D ^S _min ) of the diameter (sphere equivalent diameter: D ^S ) _The method for cleaning a polycrystalline silicon lump according to any one of claims 1 to 4, wherein the polycrystalline silicon lump is selected so that _max / D ^S _min is 6 or less. The maximum gas temperature (T ^D _max ) of the supply blow gas supplied into the dryer in the drying step is set to 85 ° C. or less, and the gas flow rate in the dryer is set to 0.5 m / second or more. 2. A method for cleaning a polycrystalline silicon lump according to item 1.   The total process time of the said drying process is 0.77 minutes / kg or less in conversion per weight unit of the polycrystalline silicon lump accommodated in the said container, The any one of Claims 1-6 Cleaning method for polycrystalline silicon lump.

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