WO2011118770A1 - 多結晶シリコンインゴットの製造方法及び多結晶シリコンインゴット - Google Patents
多結晶シリコンインゴットの製造方法及び多結晶シリコンインゴット Download PDFInfo
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- WO2011118770A1 WO2011118770A1 PCT/JP2011/057355 JP2011057355W WO2011118770A1 WO 2011118770 A1 WO2011118770 A1 WO 2011118770A1 JP 2011057355 W JP2011057355 W JP 2011057355W WO 2011118770 A1 WO2011118770 A1 WO 2011118770A1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
- B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/037—Purification
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
- C30B11/006—Controlling or regulating
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B28/00—Production of homogeneous polycrystalline material with defined structure
- C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
- C30B28/06—Production of homogeneous polycrystalline material with defined structure from liquids by normal freezing or freezing under temperature gradient
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
- C30B29/06—Silicon
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
- C30B35/002—Crucibles or containers
Definitions
- the present invention relates to a polycrystalline silicon ingot manufacturing method for manufacturing a polycrystalline silicon ingot by unidirectionally solidifying a silicon melt in a silica crucible, and a polycrystalline silicon ingot obtained by this manufacturing method.
- This application claims priority based on Japanese Patent Application No. 2010-071699 for which it applied to Japan on March 26, 2010, and uses the content here.
- a polycrystalline silicon ingot is used as a material for a substrate for a solar cell, as described in Patent Document 1, for example. That is, a polycrystalline silicon wafer is manufactured by slicing a polycrystalline silicon ingot to a predetermined thickness, and a solar cell substrate is manufactured by processing the polycrystalline silicon wafer.
- the characteristics of the polycrystalline silicon ingot which is the material of the substrate for the solar cell, greatly affect the performance such as the conversion efficiency.
- the amount of oxygen or impurities contained in polycrystalline silicon is large, the conversion efficiency of the solar cell is significantly reduced. Therefore, in order to keep the conversion efficiency of the solar cell high, it is necessary to reduce the amount of oxygen and the amount of impurities in the polycrystalline silicon serving as the solar cell substrate.
- the impurities are discharged from the solid phase toward the liquid phase because the solubility of the impurities in the solid phase is lower than that in the liquid phase. For this reason, the amount of impurities in the solid phase portion is reduced, but conversely, the amount of impurities is very high at the top of the polycrystalline ingot which is the solidification end portion.
- oxygen is mixed from the silica (SiO 2 ) into the silicon melt.
- Oxygen in the silicon melt is released from the liquid surface as SiO gas. Since oxygen is mixed from the bottom and side surfaces of the crucible at the start of solidification, the amount of oxygen in the silicon melt increases at the start of solidification. As solidification from the bottom side proceeds and the solid-liquid interface rises, oxygen starts to enter only from the side, so the amount of oxygen mixed into the silicon melt gradually decreases, and the amount of oxygen in the silicon melt Stabilizes at a constant value. For the reasons described above, the amount of oxygen is high at the bottom, which is the solidification start portion.
- Patent Document 2 there is provided a technique for suppressing the mixing of oxygen by using a crucible in which a Si 3 N 4 coating layer is formed on the inner surface (side surface and bottom surface) of a silica crucible.
- a polycrystalline silicon ingot is solidified in one direction, as described in Non-Patent Document 1, it has been solidified at a constant solidification rate of 0.2 mm / min (12 mm / h), for example. .
- An object of the present invention is to provide a method for producing a polycrystalline silicon ingot and a polycrystalline silicon ingot.
- the method for producing a polycrystalline silicon ingot according to the first aspect of the present invention is a method for producing a polycrystalline silicon ingot in which the silicon melt stored in the crucible is unidirectionally solidified upward from the bottom surface. Is made of silica, and a silicon nitride coating layer is formed on the inner surface of the side wall and the bottom surface of the silica.
- the solidification process in the crucible is a first from 0 mm to a height X on the basis of the bottom surface of the crucible. It is divided into a region, a second region from height X to height Y, and a third region greater than height Y.
- the height X is 10 mm ⁇ X ⁇ 30 mm
- the height Y is 30 mm ⁇ Y ⁇ .
- the solidification rate V1 in the first region is set within a range of 10 mm / h ⁇ V1 ⁇ 20 mm / h
- the solidification rate V2 in the second region is 1 mm / h ⁇ V2 ⁇ .
- a method for producing polycrystalline silicon ingot is set in the range of mm / h.
- the solidification process in the crucible is performed with the first region from 0 mm to height X and the height X to height Y with reference to the bottom surface of the crucible. And the solidification rate in the first region and the second region are defined.
- the height X of the first region is set to 10 mm ⁇ X ⁇ 30 mm, it is possible to reliably suppress oxygen from entering the silicon melt from the bottom surface of the crucible. If the solidification rate V1 is less than 10 mm / h, the generation of crystal nuclei is insufficient and smooth unidirectional solidification cannot be performed.
- the solidification speed V1 in the first region is set within a range of 10 mm / h ⁇ V1 ⁇ 20 mm / h.
- the solidification rate V2 in the second region is set within a range of 1 mm / h ⁇ V2 ⁇ 5 mm / h and is relatively slow, oxygen in the silicon melt is removed from the liquid surface in the second region. It becomes possible to release, and the amount of oxygen in the silicon melt can be greatly reduced. Since the height Y of the first region and the second region is 30 mm ⁇ Y ⁇ 100 mm, the length of the portion with a high oxygen content can be shortened, and the production yield of polycrystalline silicon as a product is greatly improved. Can be made. If the solidification rate V2 is less than 1 mm / h, the solid phase may be remelted.
- the solidification speed V2 in the second region is set within a range of 1 mm / h ⁇ V2 ⁇ 5 mm / h.
- the height YX of the second region is set in a range of 10 mm ⁇ YX ⁇ 40 mm.
- the height YX of the second region is YX ⁇ 10 mm, the time for releasing oxygen in the silicon melt to the outside is secured, and oxygen in the polycrystalline silicon ingot is secured. The amount can be reliably reduced.
- the height YX of the second region is YX ⁇ 40 mm, the length of the portion where the oxygen amount is high can be surely shortened.
- the solidification speed V3 in the third region is set in a range of 5 mm / h ⁇ V3 ⁇ 30 mm / h.
- the solidification rate V3 in the third region is set to V3 ⁇ 5 mm / h, the production efficiency of the polycrystalline silicon ingot can be ensured.
- the solidification speed V3 in the third region is V3 ⁇ 30 mm / h, the unidirectional solidification can be performed smoothly.
- a polycrystalline silicon ingot according to the second aspect of the present invention is a polycrystalline silicon ingot produced by the above-described polycrystalline silicon ingot producing method, and is high from the bottom of the polycrystalline silicon ingot that is in contact with the bottom surface of the crucible.
- This is a polycrystalline silicon ingot having an oxygen concentration of 4 ⁇ 10 17 atm / cm 3 or less at the center of the cross section of the 30 mm portion.
- the oxygen concentration in the central portion of the cross section at a height of 30 mm from the bottom of the polycrystalline silicon ingot that is in contact with the bottom of the crucible is 4 ⁇ 10 17 atm / cm 3 or less. Therefore, even a portion having a height of 30 mm from the bottom can be used as a product such as a polycrystalline silicon wafer.
- a method for manufacturing a polycrystalline silicon ingot and a polycrystalline silicon ingot capable of greatly improving the production yield of polycrystalline silicon by reducing the portion having a high oxygen concentration at the bottom. can do.
- the polycrystalline silicon ingot 1 according to this embodiment is a material for a polycrystalline silicon wafer used as a solar cell substrate.
- the polycrystalline silicon ingot 1 of the present embodiment has a quadrangular column shape, and its height H is set within a range of 200 mm ⁇ H ⁇ 350 mm. More specifically, in the present embodiment, the height H of the polycrystalline silicon ingot 1 is set to 300 mm. Further, the bottom surface of the quadrangular shape has a square shape with a side of about 680 mm.
- the bottom portion S1 of the polycrystalline silicon ingot 1 has a high oxygen concentration
- the top portion S2 of the polycrystalline silicon ingot 1 has a high impurity concentration. Therefore, the bottom portion S1 and the top portion S2 are cut and removed, and only the product portion S3 is commercialized as a polycrystalline silicon wafer.
- the polycrystalline silicon ingot 1 is configured such that the oxygen concentration at the center of the cross section at a height of 30 mm from the bottom is 4 ⁇ 10 17 atm / cm 3 or less.
- a 5 mm ⁇ 5 mm ⁇ 5 mm square measurement sample is taken from the center of the cross section, and the oxygen concentration is measured by infrared fluorescence analysis (IPS).
- IPS infrared fluorescence analysis
- the polycrystalline silicon ingot manufacturing apparatus 10 includes a crucible 20 in which a silicon melt L is stored, a chill plate 12 on which the crucible 20 is placed, an underfloor heater 13 that supports the chill plate 12 from below, and a crucible. 20 and a ceiling heater 14 disposed above 20.
- a heat insulating material 15 is provided around the crucible 20.
- the chill plate 12 has a hollow structure, and Ar gas is supplied to the inside through a supply pipe 16.
- the crucible 20 has a horizontal cross-sectional shape that is square (square) or round (circular), and in this embodiment, the crucible 20 is square (square).
- the crucible 20 includes a crucible main body 21 made of silica and a coating layer 22 provided inside the crucible main body 21.
- a coating layer 22 is formed on the entire inner surface of the crucible body 21 including the bottom surface and side surfaces of the crucible body 21.
- the coating layer 22 contains Si 3 N 4 (silicon nitride). More specifically, as shown in FIG. 3, this coating layer 22 is formed in a mixture base comprising Si 3 N 4 powder 24 of 0.2 to 4.0 ⁇ m and silica 25 containing 10 to 6000 ppm of sodium. Further, a fine fused silica sand 26 of 50 to 300 ⁇ m is dispersed. A mixture base made of Si 3 N 4 powder 24 and sodium-containing silica 25 is disposed on the outermost surface of the coating layer 22. Although not shown, a thermocouple for monitoring the height of the solidification interface is installed on the side surface of the crucible 20.
- Si 3 N 4 silicon nitride
- the polycrystalline silicon ingot 1 is manufactured using the polycrystalline silicon ingot manufacturing apparatus 10 described above.
- the silicon raw material is charged into the crucible 20 having the coating layer 22 formed on the inner surface.
- the silicon raw material a lump called “chunk” obtained by crushing high purity silicon of 11N (purity: 99.99999999999) is used.
- the particle size of the bulk silicon raw material is, for example, 30 mm to 100 mm.
- This silicon raw material is heated by energizing the ceiling heater 14 and the underfloor heater 13. Thereby, the silicon melt L is stored in the crucible 20.
- energization of the underfloor heater 13 is stopped, and Ar gas is supplied into the chill plate 12 through the supply pipe 16. Thereby, the bottom part of the crucible 20 is cooled. Further, by gradually reducing the energization to the ceiling heater 14, the silicon melt L in the crucible 20 is cooled from the bottom of the crucible 20 to become a solid phase C, and solidifies in one direction upward from the bottom.
- the solidification speed of the silicon melt L in the crucible 20 that is, the moving speed upward of the solid-liquid interface. Adjust.
- the solidification process of the silicon melt L in the crucible 20 is divided into three regions, and the solidification rate is set for each region.
- the solidification process in the crucible 20 is described with reference to the bottom surface 20a of the crucible 20 as a first area A1 from 0 mm to height X, a second area A2 from height X to height Y,
- the height X is set to be within a range of 10 mm ⁇ X ⁇ 30 mm and the height Y is within a range of 30 mm ⁇ Y ⁇ 100 mm.
- the height YX of the second region A2 is set to be within a range of 10 mm ⁇ YX ⁇ 40 mm.
- X 20 mm
- Y 40 mm
- the height YX of the second region A2 is 20 mm.
- the solidification rate in each region is set as follows.
- the solidification speed V1 in the first region A1 is set within a range of 10 mm / h ⁇ V1 ⁇ 20 mm / h.
- the solidification speed V2 in the second region A2 is set within a range of 1 mm / h ⁇ V2 ⁇ 5 mm / h.
- the solidification speed V1 in the third region A3 is set within a range of 5 mm / h ⁇ V1 ⁇ 30 mm / h. More specifically, as shown in FIG.
- the solidification rate V1 in the first region A1 from the bottom to 20 mm is 15 mm / h
- the solidification rate V2 in the second region A2 from 20 mm to 40 mm is 3 mm / h, 40 mm.
- the solidification speed V3 in the third region A3 is set to 5.8 mm / h.
- the average solidification rate of the entire polycrystalline silicon ingot 1 is 6.5 mm / h.
- the solid-liquid interface of silicon in the crucible has a flat shape. The height of the silicon solid-liquid interface from the bottom of the crucible is monitored by a thermocouple installed on the side of the crucible.
- the rectangular columnar polycrystalline silicon ingot 1 shown in FIG. 1 is formed by the unidirectional solidification method.
- the solidification process in the crucible 20 is performed from 0 mm to a height X with reference to the bottom surface 20a of the crucible 20. It is divided into a first region A1, a second region A2 from height X to height Y, and a third region A3 having height Y or higher, and the solidification rate in each region is defined.
- the solidification speed V1 in the first region A1 is set within the range of 10 mm / h ⁇ V1 ⁇ 20 mm / h and is relatively fast, the solid phase C is quickly formed on the bottom surface 20 a of the crucible 20.
- the mixing of oxygen from the bottom surface 20a of the crucible 20 into the silicon melt L can be suppressed.
- the solidification speed V1 in the first region A1 is set within a range of 10 mm / h ⁇ V1 ⁇ 20 mm / h.
- the solidification speed V2 in the second region A2 is set within a range of 1 mm / h ⁇ V2 ⁇ 5 mm / h, and is relatively slow.
- oxygen in the silicon melt L can be released from the liquid surface in the second region A2, and the amount of oxygen in the silicon melt L can be greatly reduced.
- the solidification speed V2 in the second region A2 is set within a range of 1 mm / h ⁇ V2 ⁇ 5 mm / h.
- the oxygen concentration at the center of the cross section of the portion 30 mm high from the bottom of the polycrystalline silicon ingot that is in contact with the bottom surface 20a of the crucible 20 is 4 ⁇ 10 17 atm / cm. Since it is 3 or less, even if it is a part 30 mm high from the bottom, a high-quality polycrystalline silicon ingot can be commercialized.
- the manufacturing method and polycrystalline silicon ingot of the polycrystalline silicon ingot which are embodiments of the present invention have been described, the present invention is not limited to this, and the design can be changed as appropriate.
- the polycrystalline silicon ingot manufacturing apparatus shown in FIG. 2 has been described as manufacturing a polycrystalline silicon ingot.
- the present invention is not limited to this, and the polycrystalline silicon ingot manufacturing apparatus having another structure can be used to manufacture polycrystalline silicon. An ingot may be manufactured.
- the size and shape of the polycrystalline silicon ingot are not limited to this embodiment, and the design may be changed as appropriate.
- a polycrystalline silicon ingot having a size of 680 mm square and a height of 300 mm was manufactured using the polycrystalline silicon ingot manufacturing apparatus described in the present embodiment.
- a polycrystalline silicon ingot was manufactured with a solidification rate constant at 12 mm / h. The time required for solidification was 25 hours.
- a polycrystalline silicon ingot was manufactured with a solidification rate constant at 5.1 mm / h. The time required for coagulation was 59 hours.
- a polycrystalline silicon ingot was manufactured by changing the solidification rate with the pattern described in the above embodiment. That is, as shown in FIG. 5, the solidification speed V1 in the first area A1 from the bottom to 20 mm is 15 mm / h, the solidification speed V2 in the second area A2 from 20 mm to 40 mm is 3 mm / h, from 40 mm to 300 mm. The solidification speed V3 in the third region A3 was set to 5.8 mm / h. The average solidification rate of the entire polycrystalline silicon ingot 1 was 6.5 mm / h, and the time required for solidification was 52.7 hours.
- the product yield R in the polycrystalline silicon ingot was calculated when the portion where the oxygen concentration was 4 ⁇ 10 17 atm / cm 3 or less was used as the product. Since the top of the polycrystalline silicon ingot has a large amount of impurities, the product yield R was calculated on the assumption that a portion 10 mm away from the top was cut off. The evaluation results are shown in Table 1.
- Comparative Example 1 As shown in FIG. 5, the oxygen concentration was very high in the vicinity of the bottom, and the oxygen concentration exceeded 4 ⁇ 10 17 atm / cm 3 even at a height of 100 mm from the bottom.
- Comparative Example 2 as shown in FIG. 5, the oxygen concentration was lower than that in Comparative Example 1, but the oxygen concentration exceeded 4 ⁇ 10 17 atm / cm 3 even at a height of 50 mm from the bottom.
- the oxygen concentration was high only in a small portion at the bottom, and the oxygen concentration was already 4 ⁇ 10 17 atm / cm 3 or less in the portion having a height of 20 mm.
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Abstract
Description
本願は、2010年3月26日に日本に出願された特願2010-071699号に基づき優先権を主張し、その内容をここに援用する。
特に、多結晶シリコンに含有される酸素量や不純物量が多いと、太陽電池の変換効率が大幅に低下する。したがって、太陽電池の変換効率を高く保つためには、太陽電池用基板となる多結晶シリコン中の酸素量や不純物量を低減する必要がある。
以下に、上記多結晶シリコンインゴットの底部および頂部において、それぞれ酸素量および不純物量が高くなる理由について詳しく説明する。
ルツボ内でシリコン融液を上方に向けて一方向凝固させた場合、固相での不純物の溶解度が液相よりも低いので、固相から液相に向けて不純物が排出される。このため、固相部分の不純物量は低くなるが、逆に凝固終了部分である上記多結晶インゴットの頂部においては、不純物量が非常に高くなる。
また、従来、多結晶シリコンインゴットを一方向凝固させる場合には、非特許文献1に記載されているように、例えば0.2mm/min(12mm/h)といった一定の凝固速度で凝固させていた。
従来の多結晶シリコンインゴット製造方法では、Si3N4コーティング層を形成したルツボを用いて、シリコン融液内への酸素の混入を抑制する事は出来ても、完全に防ぐことはできない。したがって、前述のように、凝固開始部である底部側の酸素濃度が高くなる。製品としての多結晶シリコンの酸素量の上限値を低く設定した場合、上記設定値を満足させるためには、多結晶シリコンインゴットの底部側の切断除去量を長くする必要がある。この場合、多結晶シリコンインゴット当たりから、製品化される多結晶シリコンの量が少なくなり、多結晶シリコンの生産効率が大幅に低減してしまうといった問題があった。
なお、凝固速度V1が10mm/h未満であると結晶核の発生が不十分となりスムーズに一方向凝固を行うことができなくなってしまう。また、凝固速度V1が20mm/hを超えると、第1領域の高さXを薄くすることができなくなる。このため、前記第1領域における凝固速度V1を10mm/h≦V1≦20mm/hの範囲内に設定している。
そして、第1領域及び第2領域の高さYが30mm≦Y<100mmとされているので、酸素量が高い部分の長さを短くでき、製品となる多結晶シリコンの生産歩留まりを大幅に向上させることができる。
なお、凝固速度V2が1mm/h未満であると固相が再溶融してしまう可能性がある。
また、凝固速度V2が5mm/hを超えると、酸素を十分に放出することができなくなる。このため、前記第2領域における凝固速度V2を1mm/h≦V2≦5mm/hの範囲内に設定している。
この場合、前記第2領域の高さY-Xが、Y-X≧10mmとされているので、シリコン融液内の酸素を外部へと放出する時間が確保され、多結晶シリコンインゴット内の酸素量を確実に低減することができる。一方、前記第2領域の高さY-Xが、Y-X≦40mmとされているので、酸素量が高い部分の長さを確実に短くすることができる。
この場合、前記第3領域における凝固速度V3が、V3≧5mm/hとされているので、多結晶シリコンインゴットの生産効率を確保することができる。一方、前記第3領域における凝固速度V3が、V3≦30mm/hとされているので、一方向凝固を円滑に実施することができる。
この構成の多結晶シリコンインゴットにおいては、前記ルツボの底面に接触していた多結晶シリコンインゴット底部から高さ30mmの部分の断面中心部における酸素濃度が4×1017atm/cm3以下とされているので、底部から高さ30mmの部分であっても、多結晶シリコンウェハ等の製品として使用することができる。
本実施形態である多結晶シリコンインゴット1は、太陽電池用基板として使用される多結晶シリコンウェハの素材となるものである。
この多結晶シリコンインゴット1の底部側部分S1は酸素濃度が高く、多結晶シリコンインゴット1の頂部側部分S2は不純物濃度が高い。そのため、これら底部側部分S1及び頂部側部分S2は切断除去され、製品部S3のみが多結晶シリコンウェハとして製品化される。
この多結晶シリコンインゴット製造装置10は、シリコン融液Lが貯留されるルツボ20と、このルツボ20が載置されるチルプレート12と、このチルプレート12を下方から支持する床下ヒータ13と、ルツボ20の上方に配設された天井ヒータ14と、を備えている。また、ルツボ20の周囲には、断熱材15が設けられている。
チルプレート12は、中空構造とされており、供給パイプ16を介して内部にArガスが供給される構成とされている。
このルツボ20は、図3に示すように、シリカからなるルツボ本体21と、このルツボ本体21の内側に設けられたコーティング層22と、を備えている。本実施形態では、図3に示すように、ルツボ本体21の底面および側面を含めてルツボ本体21の内面全体にコーティング層22が形成されている。
そして、コーティング層22の最表面にはSi3N4粉末24とナトリウム含有シリカ25とからなる混合体素地が配置されている。
また、図示しないが、凝固界面の高さをモニターするための熱電対が、ルツボ20の側面に設置されている。
次に、床下ヒータ13への通電を停止し、チルプレート12の内部に供給パイプ16を介してArガスを供給する。これにより、ルツボ20の底部を冷却する。さらに、天井ヒータ14への通電を徐々に減少させることにより、ルツボ20内のシリコン融液Lは、ルツボ20の底部から冷却されて固相Cとなり、底部から上方に向けて一方向凝固する。
そして、本実施形態では、ルツボ20内のシリコン融液Lの凝固過程を3つの領域に区分けし、それぞれの領域毎に凝固速度を設定している。
本実施形態では、X=20mm、Y=40mmとし、第2領域A2の高さY-Xを20mmとしている。
より具体的には、図5に示すように、底部から20mmまでの第1領域A1における凝固速度V1が15mm/h、20mmから40mmまでの第2領域A2における凝固速度V2が3mm/h、40mmから300mmまでの第3領域A3における凝固速度V3が5.8mm/hに設定されている。多結晶シリコンインゴット1全体の平均凝固速度は、6.5mm/hである。
一方向凝固時における、ルツボ内のシリコンの固液界面はフラットな形状をしている。シリコンの固液界面のルツボ底面からの高さは、ルツボ側面に設置した熱電対によりモニターする。
なお、凝固速度V1が10mm/h未満であると結晶核の発生が不十分となりスムーズに一方向凝固を行うことができなくなってしまう。また、凝固速度V1が20mm/hを超えると、第1領域A1の高さXを薄くすることができなくなる。このため、第1領域A1における凝固速度V1を10mm/h≦V1≦20mm/hの範囲内に設定している。
凝固速度V2が1mm/h未満であると固相が再溶融してしまう可能性がある。また、凝固速度V2が5mm/hを超えると、酸素を十分に放出することができなくなる。このため、第2領域A2における凝固速度V2を1mm/h≦V2≦5mm/hの範囲内に設定している。
例えば、図2に示す多結晶シリコンインゴット製造装置によって、多結晶シリコンインゴットを製造するものとして説明したが、これに限定されることはなく、他の構造の多結晶シリコンインゴット製造装置によって多結晶シリコンインゴットを製造してもよい。
また、多結晶シリコンインゴットの大きさや形状は、本実施形態に限定されることはなく、適宜設計変更してもよい。
比較例1として、凝固速度を12mm/hで一定として多結晶シリコンインゴットを製造した。なお、凝固に要した時間は25時間であった。
比較例2として、凝固速度を5.1mm/hで一定として多結晶シリコンインゴットを製造した。なお、凝固に要した時間は59時間であった。
また、比較例2では、図5に示すように、比較例1に比べると酸素濃度が低いが、底部から高さ50mmの部分でも酸素濃度が4×1017atm/cm3を超えていた。また、製品歩留まりRは、R=(300mm―(70mm+10mm))/300mm=73%であった。
このように、本発明によれば、製品として多結晶シリコンの歩留まりを大幅に向上させることができることが確認された。
20 ルツボ
20a 底面
22 コーティング層
Claims (4)
- ルツボ内に貯留したシリコン融液を、その底面から上方に向けて一方向凝固させる多結晶シリコンインゴットの製造方法であって、
前記ルツボは、シリカで構成され、その側壁内面及び底面内面に窒化珪素のコーティング層が形成されており、
前記ルツボ内における凝固過程を、前記ルツボの底面を基準として、0mmから高さXまでの第1領域と、高さXから高さYまでの第2領域と、高さY以上の第3領域と、に区分けし、この高さXが10mm≦X<30mm、高さYが30mm≦Y<100mmとされており、
前記第1領域における凝固速度V1が、10mm/h≦V1≦20mm/hの範囲内に設定され、前記第2領域における凝固速度V2が、1mm/h≦V2≦5mm/hの範囲内に設定されている多結晶シリコンインゴットの製造方法。 - 前記第2領域の高さY-Xが、10mm≦Y-X≦40mmの範囲内に設定されている請求項1に記載の多結晶シリコンインゴットの製造方法。
- 前記第3領域における凝固速度V3が、5mm/h≦V3≦30mm/hの範囲内に設定されている請求項1または請求項2に記載の多結晶シリコンインゴットの製造方法。
- 請求項1から請求項3のいずれか一項に記載の多結晶シリコンインゴットの製造方法によって製造された多結晶シリコンインゴットであって、
前記ルツボの底面に接触していた多結晶シリコンインゴット底部から高さ30mmの部分の断面中心部における酸素濃度が4×1017atm/cm3以下とされている多結晶シリコンインゴット。
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US13/636,490 US20130028825A1 (en) | 2010-03-26 | 2011-03-25 | Manufacturing method for polycrystalline silicon ingot, and polycrystalline silicon ingot |
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JP2004196577A (ja) * | 2002-12-18 | 2004-07-15 | Jfe Steel Kk | 多結晶シリコンの製造方法 |
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