JP2013189318A - Method for producing raw material for silicon-based solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a raw material for a silicon-based solar cell, capable of producing a melt raw material for a silicon-based solar cell in a short time from a silicon sludge generated in various types of silicon working processes and contaminated with metals in high concentrations.SOLUTION: Meal impurities of ≥1×10atoms/cmcontaminating a silicon powder in a silicon sludge are removed by cleaning; the silicon sludge after vacuum drying is charged in a vacuum chamber upstream of a melting chamber of an electron beam apparatus, and vacuum dried; then, the silicon sludge is moved to the melting chamber, and irradiated with electron beams and melted. Thereby, a melt raw material for a silicon-based solar cell can be produced in a short time from the silicon sludge generated in various silicon working processes and contaminated with metals in high concentrations.

Description

  The present invention relates to a method for producing a raw material for a silicon-based solar cell, specifically, silicon sludge generated in various silicon processing processes and contaminated with a high concentration of metal, and then vacuum-dried in an electron beam apparatus. It is related with the manufacturing method of the raw material for silicon type solar cells which can manufacture the melt | dissolution raw material for silicon type solar cells by melt | dissolving.

In manufacturing a silicon-based solar cell, a block-shaped raw material (melting raw material) made of silicon is put into a crucible and melted to cast a silicon ingot. Then, the silicon substrate for solar cells is obtained by slicing this silicon ingot.
By the way, a silicon wafer which is a formation substrate of an ultra-highly integrated device such as ULSI is manufactured by performing wafer processing on a single crystal silicon ingot pulled up by the Czochralski (CZ) method. Specifically, the single crystal silicon ingot is cut into blocks, and then the silicon block is subjected to peripheral grinding with a grinding wheel and slicing with a wire saw in order to obtain a large number of silicon wafers. Then, chamfering, lapping, etching, and polishing are sequentially performed on each silicon wafer to manufacture a product wafer for device formation.

In this wafer processing process, a large amount of silicon sludge, which is processing waste (silicon waste), is generated in the peripheral grinding step and the slicing step. Also, a large amount of silicon sludge is generated in the back grinding process of the device manufacturer. The silicon powder contained in the silicon sludge was contaminated with metal impurities such as Fe and Ni of 1 × 10 ¹⁵ atoms / cm ³ or more caused by the wafer processing apparatus, and the performance of the manufactured solar cell was significantly deteriorated. . In addition, since the property is sludge, it is difficult to handle, and most of them have been disposed of without being reused.

  Further, as a conventional technique for reusing silicon discarded from a wafer processing process, for example, “Crucible device and melting material solidification method using the crucible device” of Patent Document 1 is known. This is because the bulk scrap silicon is melted by irradiating an electron beam in an electron beam apparatus, thereby evaporating impurities (for example, phosphorus) contained in the scrap silicon to increase the purity of the silicon. By pouring into a crucible and solidifying it, a high-purity silicon-based solar cell material is obtained.

JP 2006-111519 A

However, in Patent Document 1, the property of waste silicon that is reused is a lump that can be easily handled and dissolved by an electron beam. Therefore, the prior art described in Patent Document 1 cannot be applied as it is to silicon sludge that the present invention intends to reuse. For example, metal impurities such as Fe and Ni having a high concentration of 1 × 10 ¹⁵ atoms / cm ³ or more are difficult to remove by electron beam irradiation because they do not evaporate in a vacuum. Silicon sludge contains a large amount of water, and if it is not vacuum-dried before melting, there is a risk of steam explosion during melting. Therefore, in order to avoid this, the silicon sludge needs to be naturally dried, for example, for about one week, and as a result, the processing time for reusing the waste silicon is prolonged.

Therefore, as a result of earnest research, the inventor adopted a method of cleaning silicon sludge with HF or HCl as a method for removing metal impurities of 1 × 10 ¹⁵ atoms / cm ³ or more that contaminate silicon powder contained in silicon sludge. In addition, if the silicon sludge is vacuum-dried using a high vacuum environment of 1 × 10 ⁻³ Pa or less that is secured in the electron beam apparatus when the electron beam is melted, all the above-mentioned problems can be solved. As a result, the present invention was completed.

  The present invention provides a silicon-based solar cell raw material that can be produced in a short period of time from a silicon sludge generated in various silicon processing processes and contaminated with a high concentration of metal. It aims to provide a method.

According to the first aspect of the present invention, a silicon sludge generated in a silicon processing process and containing silicon powder having a contamination concentration of metal impurities of 1 × 10 ¹⁵ atoms / cm ³ or more is treated with a cleaning liquid capable of removing the metal impurities. By cleaning, the metal impurities are removed from the silicon powder, the cleaned silicon sludge is put into a vacuum chamber of an electron beam apparatus, the silicon sludge is vacuum dried, and the silicon sludge after vacuum drying is removed. The vacuum-dried silicon is continuously charged in a melting chamber disposed downstream of the vacuum chamber in the electron beam apparatus, and the vacuum-dried silicon sludge is irradiated with an electron beam. The sludge is dissolved to form dissolved silicon, and then the dissolved silicon is put into a crucible for molding to By solidifying by cooling the con is a method for manufacturing a silicon-based material for a solar cell, a silicon-based solar cell material.

According to the first aspect of the present invention, first, silicon sludge generated in the silicon processing process is cleaned with a cleaning liquid capable of removing metal impurities. Thereby, a predetermined amount of metal impurities is removed from the silicon powder in the silicon sludge, and the metal impurity amount (metal contamination amount) of the silicon powder can be reduced to, for example, less than 1 × 10 ¹⁵ atoms / cm ³ . Next, the cleaned silicon sludge is put into a vacuum chamber of an electron beam apparatus, where the silicon sludge is vacuum dried. Thereby, the regeneration period of silicon sludge is shortened compared with the case where silicon sludge is naturally dried over about one week, for example.
The silicon sludge after vacuum drying is moved to a melting chamber, where the silicon sludge is irradiated with an electron beam to become dissolved silicon. Thereafter, the molten silicon is solidified by being put into a molding crucible to become a silicon-based solar cell material.

The “raw material for a silicon-based solar cell” is any of a raw material for a single crystal silicon-based solar cell, a raw material for a polycrystalline silicon-based solar cell, and a raw material for an amorphous silicon-based solar cell.
Silicon sludge is a cocoon in which silicon powder, impurities, and water are mixed in a mud. Impurities are, for example, alumina, silica, corundum, Cu, Fe, Ni, C, barium oxide, magnesium oxide, dust, etc. generated by wear of a grinding wheel.
Examples of the metal impurities contained in the silicon powder include Cu, Fe, Ni, C, alumina, barium oxide, and magnesium oxide.

  Examples of silicon processing processes involving generation of silicon sludge include block cutting of single crystal silicon ingots or polycrystalline silicon ingots, peripheral grinding of silicon blocks with a grinding wheel, orientation flat processing or notching of silicon blocks with a grinding wheel, silicon Each process such as chamfering of a wafer or lapping of a silicon wafer can be mentioned. Further, a back grinding process performed on the wafer after device formation is also included.

The average particle size of the solid content of the silicon sludge is 1 to 10 μm. In the peripheral grinding process of the ingot where a large amount of silicon sludge is generated and the back grinding process of the device manufacturer, coarse grinding using a rough grindstone and finish grinding using a dense grindstone are performed. The generated size is 1 to 10 μm.
As the cleaning liquid capable of removing metal impurities, for example, HF, HF / H ₂ O ₂ , HCl, HCl / H ₂ O ₂ , HF / HNO ₃ , and HF / ozone can be employed.
The silicon sludge after washing is generally rinsed with a rinsing liquid. As the rinsing liquid, for example, pure water or ultrapure water can be used. Pure water refers to highly purified water from which impurities have been removed by physical or chemical treatment. Specifically, 1 to 10 MΩ · cm or 1.0 to 0.1 μS / cm of water can be employed. Ultrapure water is one in which the amount of impurities contained in water is, for example, 0.01 μg / liter or less.

  The electron beam apparatus includes a vacuum chamber in which a vacuum pump is communicated to vacuum-dry the cleaned silicon sludge, a melting chamber disposed downstream of the vacuum chamber, and a hearth for storing the silicon sludge after vacuum drying. An electron gun that irradiates an electron beam onto the silicon sludge that has been vacuum-dried and is placed in the hearth chamber and is charged into the hearth, melts the electron beam, a crucible for molding into which the silicon melt is poured from the hearth, and a melting chamber A solidification chamber disposed downstream and containing a crucible. Note that the internal space of the electron beam apparatus is evacuated not only in the vacuum chamber but also in other space regions due to the negative pressure of the vacuum pump. Further, a temporary storage chamber storing a storage hopper for temporarily storing the silicon sludge after vacuum drying may be provided between the vacuum chamber and the melting chamber.

  During operation of the electron beam apparatus, first, the cleaned silicon sludge is put into a vacuum chamber, and then the vacuum chamber is evacuated by a vacuum pump to vacuum dry the silicon sludge. At this time, you may heat to 300 degreeC. Silicon sludge after vacuum drying in a vacuum chamber is continuously charged into a hearth, and the silicon sludge after vacuum drying is irradiated with an electron beam from an electron gun to obtain dissolved silicon. Next, melted silicon is poured into a crucible, which is cooled and solidified to obtain an ingot of a silicon-based solar cell material.

“The silicon sludge after vacuum drying is continuously fed into the melted dissolution chamber” means that the silicon sludge after vacuum drying is not taken out of the electron beam apparatus and is dissolved in a vacuum environment. Means that
Examples of the conditions for melting silicon sludge by an electron beam include a degree of vacuum of 0.01 Pa and a heating temperature of 1500 ° C.
As the crucible, for example, a copper crucible or a graphite crucible can be employed.
The silicon ingot taken out from the crucible becomes a melting raw material of the silicon-based solar cell after crushing. Then, this melt | dissolution raw material is thrown into the ingot casting apparatus for polycrystalline silicon type solar cells, for example, is melted, and a polycrystalline silicon ingot is cast. The polycrystalline silicon ingot after casting is processed into a wafer, and a PN junction is formed by a predetermined method to form a silicon-based solar cell.

The invention according to claim 2 is that the metal contaminant of the silicon powder is at least one of Fe and Ni, and the cleaning liquid is HF, HF / H ₂ O ₂ , HCl, HCl / H ₂ O _2. The method for producing a raw material for a silicon-based solar cell according to claim 1, which is a simple substance of HF / HNO ₃ or a combination thereof.

The metal contamination of the silicon powder in the invention described in claim 2 may be Fe alone, Ni alone, or both Fe and Ni.
The cleaning liquid may be HF only, HF / H ₂ O ₂ only, HCl only, HCl / H ₂ O ₂ only, or HF / HNO ₃ only. Alternatively, a combination of two or more of these may be used. Of these, HF is most preferable as the cleaning liquid. If it is HF, the removal capability of Fe is high, and it does not have an etching effect on silicon.

  According to a third aspect of the present invention, there is provided a sludge container for storing the cleaned silicon sludge in the vacuum chamber, and the sludge container is heated to 150 to 300 ° C. in the vacuum chamber. It is a manufacturing method of the raw material for silicon type solar cells of Claim 1 or Claim 2.

According to the invention described in claim 3, since the silicon sludge after cleaning is stored in the sludge container in the vacuum chamber, and then the sludge container is heated to 150 to 300 ° C. in the vacuum chamber, the drying time is shortened. .
As a method for heating the sludge container, for example, heater heating, infrared heating, or the like can be employed.

According to the first aspect of the present invention, since the silicon sludge generated in the silicon processing process is washed with a cleaning liquid capable of removing metal impurities, the metal impurities contained in the silicon sludge at a high concentration For example, it can be reduced to less than 1 × 10 ¹⁵ atoms / cm ³ . Moreover, since the silicon sludge after cleaning is vacuum-dried in the vacuum chamber of the electron beam apparatus, the regeneration period of the silicon sludge is shortened compared with, for example, the case where the silicon sludge is naturally dried over about one week. To do.
As described above, a melting raw material for a silicon-based solar cell can be produced in a short period of time from silicon sludge generated in various silicon processing processes and contaminated with a high concentration of metal.

  According to the invention described in claim 3, since the silicon sludge after cleaning is stored in the sludge container in the vacuum chamber, and then the sludge container is heated to 150 to 300 ° C. in the vacuum chamber, the drying time is shortened. .

It is a flow sheet which shows the manufacturing method of the raw material for silicon type solar cells which concerns on Example 1 of this invention. (A) is a longitudinal cross-sectional view which shows the state during washing | cleaning filtration of silicon sludge in the manufacturing method of the raw material for silicon-type solar cells which concerns on Example 1 of this invention. (B) is a longitudinal cross-sectional view which shows the state after washing | cleaning filtration of silicon sludge in the manufacturing method of the raw material for silicon | silicone solar cells which concerns on Example 1 of this invention. (C) is a longitudinal cross-sectional view which shows the state in the rinse of silicon sludge in the manufacturing method of the raw material for silicon type solar cells which concerns on Example 1 of this invention. (D) is a longitudinal cross-sectional view which shows the dehydrated state of the rinse liquid of silicon sludge in the manufacturing method of the raw material for silicon type solar cells which concerns on Example 1 of this invention. In the manufacturing method of the raw material for silicon-type solar cells which concerns on Example 1 of this invention, it is a longitudinal cross-sectional view which shows the discharge | emission state of the silicon sludge after rinse. It is a whole block diagram of the electron beam apparatus used with the manufacturing method of the raw material for silicon | silicone solar cells which concerns on Example 1 of this invention.

  Examples of the present invention will be specifically described below.

With reference to the flow sheet of FIG. 1, the manufacturing method of the raw material for silicon solar cells which concerns on Example 1 of this invention is demonstrated.
First, a polycrystalline silicon ingot having a specific resistance of 1 to 2 Ω · cm is cast using a mold (ingot casting apparatus) made of an electromagnetic cast furnace. Next, the top portion (upper end plate) of the polycrystalline silicon ingot, which is the final solidified portion, is required while supplying cutting water (water temperature 22 ° C.) made of pure water at 30 liters / minute to the polycrystalline silicon ingot. Cut to a suitable size. Since it is a final solidified portion, the concentration of metal impurities (Fe, Ni, etc.) in the end plate pieces may be 1 × 10 ¹⁵ atoms / cm ³ or more.

A large amount of silicon sludge is generated during end plate removal and block cutting. The term “silicon sludge” as used herein refers to a mold in which silicon powder having an average particle size (particle size distribution) of 2 to 3 μm, impurities, and pure water are mud. Impurities are, for example, alumina, silica, corundum, Cu, Fe, Ni, C, barium oxide, magnesium oxide, dust, etc. generated by wear of a grinding wheel. Among these, the contamination concentration of silicon sludge (silicon powder) due to metal impurities such as Fe and Ni is 1 × 10 ¹⁵ atoms / cm ³ or more, which is the same level as the end plate pieces.

Next, the silicon sludge is cleaned using a suction pump type cleaning device shown in FIGS.
As shown in FIGS. 2 and 3, the suction pump type cleaning device 10 has a suction tank (not shown) having an exhaust pipe with a suction pump communicated with an upper end surface opened. A support tray 11 having a lattice-like bottom plate is placed on the upper end portion of the suction tank so as to close the opening (FIG. 2A). In the support tray 11, a filtration container 12 made of a wire mesh having an opening of 1 to 30 μm is detachably stored.

At the time of sludge cleaning, first, silicon sludge a and HF cleaning liquid (HF concentration 0.5 to 5%) b are put into the filtration container 12, and a propeller type stirring device (not shown) is used. The mixture is stirred for a predetermined time so as to be dispersed therein. The amount of HF cleaning liquid b introduced is about 10 times the amount of silicon sludge a introduced. Thereby, metal impurities such as Fe and Ni are dissolved and removed from the silicon powder in the silicon sludge a, and the amount of contamination of the silicon powder such as Fe and Ni is reduced to less than 1 × 10 ¹⁴ atoms / cm ³ .

Next, the suction pump is operated to create a negative pressure in the suction tank, and through the hole in the bottom plate of the filtration container 12 and the hole in the bottom plate of the support tray 11, the HF cleaning liquid is sucked to dehydrate the silicon sludge a. (FIG. 2 (b)).
Next, a rinsing liquid c made of ultrapure water is injected into the filtration container 12 (FIG. 2 (c)). Similarly, the suction pump is operated to make the inside of the suction tank negative, and the rinsing liquid c is dehydrated. The water is forced to pass through the sludge a (FIG. 2 (d)). By repeating such a water flow operation a predetermined number of times, the cleaning of the silicon sludge a is completed.
After washing (including rinsing), the filtration container 12 is taken out from the support tray 11, and this is inverted, and the washed silicon sludge (water content 20%) a1 is discharged from the filtration container 12 (FIG. 3).

The cleaned silicon sludge a1 thus obtained is then transported to the electron beam apparatus shown in FIG. 4, where the silicon sludge a1 is vacuum dried, melted and solidified sequentially. Hereinafter, the electron beam apparatus will be described in detail.
As shown in FIG. 4, the electron beam apparatus 20 includes a vacuum chamber 21 arranged at the most upstream (upper stage) of the apparatus, a temporary storage chamber 22 for temporarily storing silicon sludge a2 vacuum-dried in the vacuum chamber 21, After the temporarily stored silicon sludge a2 is transferred to the hearth 30, the crucible into which the molten silicon a3 discharged from the melting chamber 23 is poured by irradiating an electron beam on the hearth 30 to form the molten silicon a3. And a discharge chamber 25 in which 24 is accommodated. The vacuum chamber 21, the temporary storage chamber 22, and the dissolution chamber 23 are continuously arranged substantially horizontally along the flow of the silicon sludges a1 to a3 in the electron beam apparatus 20. Further, the most downstream (lowermost) discharge chamber 25 is disposed immediately below the dissolution chamber 23.

  The vacuum chamber 21 is provided with a vacuum pump 26 for bringing the internal space of the vacuum chamber 21 into a vacuum state of 0.01 Pa, and a sludge container 27 for receiving silicon sludge a1 charged into the vacuum chamber 21 from outside the apparatus. Yes. The sludge container 27 incorporates a heater (not shown), and can be heated to 300 ° C. when the washed sludge is loaded. The temporary storage chamber 22 houses a temporary storage hopper 28 of silicon sludge a2 after vacuum drying. At the bottom of the temporary storage hopper 28, a cutting device 29 is provided for cutting out the stored silicon sludge a2 into the melting chamber 23 by a predetermined amount. The melting chamber 23 has a hearth 30 that receives the silicon sludge a2 cut out by the cutting device 29, and a pair disposed above the hearth 30 to irradiate the silicon sludge a2 in the hearth 30 with the silicon sludge a3. The electron gun 31 is disposed. The internal space of the discharge chamber 25 is divided into a standby stage S1, a molten silicon injection stage S2, and a cooling stage S3 for cooling the molten silicon. Each stage S1 to S3 includes quartz that can move between the stages. A crucible 24 made of metal is provided.

  The cleaned silicon sludge a1 is fed into the sludge container 27 from the raw material inlet of the vacuum chamber 21. Thereafter, the raw material inlet is closed, the vacuum pump 26 is operated, and further heated to 300 ° C. The vacuum chamber 21 and, consequently, the entire internal space of the electron beam apparatus 20 are set to a vacuum degree of 0.01 Pa. Thereby, the cleaned silicon sludge a1 stored in the sludge container 27 is vacuum-dried in a short time. As a result, for example, the drying time of the silicon sludge a1, and thus the regeneration period of the silicon sludge a can be shortened as compared with the case where the silicon sludge a1 is naturally dried over about one week.

  The silicon sludge a2 after vacuum drying is put into a temporary storage hopper 28 in the temporary storage chamber 22. After that, by operating the cutting device 29, the silicon sludge a2 after vacuum drying is cut out from the bottom of the temporary storage hopper 28 to the hearth 30 in the dissolution chamber 23 by a predetermined amount. In the melting chamber 23, an electron beam is irradiated from the two electron guns 31 to the silicon sludge a2 in the hearth 30, whereby the silicon sludge a2 is heated to become dissolved silicon a3.

  Thereafter, the molten silicon a <b> 3 in the hearth 30 flows down from the upper edge of the hearth 30 and is poured into the crucible 24 disposed in the injection stage S <b> 2 of the discharge chamber 25. After a predetermined amount of molten silicon a3 is stored in the crucible 24, the crucible 24 is carried out to the cooling stage S3, and a new crucible 24 is carried into the injection stage S2 from the standby stage S1. In the cooling stage S3, the molten silicon a3 is cooled and solidified to form a silicon ingot I. Thereafter, the silicon ingot I is taken out from the crucible 24, and then subjected to post-processing such as crushing to a required size, thereby becoming a silicon-based solar power raw material.

Here, the silicon sludge actually generated in the silicon processing process and containing silicon powder in the silicon powder when the ozone cleaning is performed after the HF cleaning (Test Example 1) and when not (Comparative Example 1). The contents of Fe, Ni and Co were measured and compared. The ozone cleaning conditions are a concentration of 20 ppm and a cleaning time of 5 minutes.
As for the measurement method of each metal impurity in silicon powder, in the case of Test Example 1, the silicon powder is first cleaned with ozone after HF cleaning, and the silicon powder is put into an electron beam device to be melted, then cooled and solidified for testing. The body was made. The content of each metal impurity was measured with respect to this test body by ICP-MS (ICP mass spectrometer, ELEMENT2 manufactured by Thermo Fisher Scientific Co., Ltd.). On the other hand, in the case of Comparative Example 1, unwashed silicon powder was put into an electron beam apparatus as it was, a test specimen was prepared in the same manner, and the content of each metal impurity of the test specimen was measured by ICP-MS. The specific conditions for producing the dissolved silicon are the same as in Example 1.

As a result, in the case of Comparative Example 1, the Fe content in the test specimen was 3 × 10 ¹⁷ atoms / cm ³ , the Ni content was 5 × 10 ¹⁶ atoms / cm ³ , and the Co content was 5 ×. Whereas it was 10 ¹⁶ atoms / cm ³ , in the case of Test Example 1, the Fe, Ni, and Co contents in the test specimen were all less than 1 × 10 ¹⁵ atoms / cm ^3. It was.

  The present invention is useful, for example, as a technique for utilizing silicon sludge that has been difficult to use as a raw material for solar cells.

20 electron beam device,
21 vacuum chamber,
23 dissolution chamber,
27 Sludge container,
a Silicon sludge,
a1 Silicon sludge after cleaning,
a2 Silicon sludge after vacuum drying,
a3 Dissolved silicon.

Claims (3)

By cleaning silicon sludge generated in a silicon processing process and containing silicon powder having a contamination concentration of metal impurities of 1 × 10 ¹⁵ atoms / cm ³ or more with a cleaning liquid capable of removing the metal impurities, Removing the metal impurities;
The silicon sludge after cleaning is put into a vacuum chamber of an electron beam apparatus, and the silicon sludge is vacuum-dried.
The silicon sludge after vacuum drying is continuously put into a melting chamber disposed downstream of the vacuum chamber in the electron beam apparatus, and here, the silicon sludge after vacuum drying is irradiated with an electron beam. Then, the silicon sludge after this vacuum drying is dissolved into dissolved silicon,
Next, a method for producing a silicon-based solar cell raw material, which is used as a silicon-based solar cell raw material, by charging the molten silicon into a molding crucible and cooling and solidifying the molten silicon. The metal contamination of the silicon powder is at least one of Fe and Ni,
_{2. The} raw material for a silicon-based solar cell according to claim 1, wherein the cleaning liquid is HF, HF / H ₂ O ₂ , HCl, HCl / H ₂ O ₂ , HF / HNO ₃ , HF / ozone alone or a combination thereof. Manufacturing method. In the vacuum chamber, a sludge container for storing the cleaned silicon sludge is disposed,
The method for producing a silicon-based solar cell material according to claim 1 or 2, wherein the sludge container is heated to 150 to 300 ° C in the vacuum chamber.

Images