JP4279015B2 - Quartz glass crucible and method for producing quartz glass crucible - Google Patents

Description

【００６４】
表１に示すように、石英ガラスの仮想温度が１２００℃以上となるように製造され、３員環強度が０．２５以上の関連品例１及び関連品例２は、液面振動が発生しないことがわかった。また、単結晶化率もそれぞれ９９％、１００％と高率になり、これに対して、石英ガラスの仮想温度が１２００℃未満である１１６０℃となるように製造され、３員環強度が０．２０の従来例の場合は、液面振動が発生し、また、単結晶化率も９５％と低率になることがわかった。
【００６５】
また、石英ガラスの仮想温度を１１００℃となるように製造され、３員環強度が０．２３の比較例１は、液面振動が発生するが、単結晶化率は９９％と高率であることがわかった。
【００６６】
なお、従来例の場合、密度は２．２０１３であったのに対して、関連品例１の場合、密度は２．２０１９であった。
【００６７】
［試験２］
関連品及び本発明の石英ガラスルツボの製造方法により製造されたルツボの内表面特性を調べ、さらに、この石英ガラスルツボを用いて、シリコン単結晶の引上げを行い、結晶化率を調べた。
【００６８】
１．石英ガラスルツボの作製
（１）（関連品例３） 関連石英ガラスルツボであり、ルツボ形状型寸法が外径５６０ｍｍ、高さ５００ｍｍの型に堆積層厚さ２５ｍｍ（水晶原料で堆積厚さ１７ｍｍ＋内表面側：合成シリカ原料で第１合成シリカ粉末層堆積厚さ８ｍｍ）に充填した。上記ルツボ形状型の外面側から、真空ポンプを用いて３５０Ｔｏｒｒの溶融時圧力となるように減圧しながら、アルゴンガスを６０リットル／分の割合で成形体の中空部に供給した。アルゴンガスの供給開始から４分後、アーク電極に通電、継続し、成形体の内側からトータル５０分加熱した。アーク溶融開始から１０分後に溶融時圧力を７２０Ｔｏｒｒまで低減し、全アーク溶融時間５０分の約７０％経過後の３５分経過後（アーク停止１５分前）に、アルゴンガスの供給を停止して、同時に水素ガスを２００リットル／分の割合で成形体の中空部に供給した。水素ガスの供給１０分間経過後に、水素ガスの供給を停止して、アーク溶融を継続した。この時のルツボ内表面の温度は２３００℃であった。水素ガス停止５分後にアーク溶融を停止し、冷却のためにアルゴンガスを５００ｌ／ｍｉｎでルツボの中空部に供給することで、表２に示すような内表面特性を有する石英ガラスルツボを製造した。
【００６９】
（２）（実施例１） ルツボ形状型寸法が外径５６０ｍｍ、高さ５００ｍｍの型に堆積層厚さ２７ｍｍ（水晶原料で堆積厚さ１７ｍｍ＋内表面側：合成シリカ原料で第１合成シリカ粉末層堆積厚さ８ｍｍ＋最内表面側：開口部端部から２００ｍｍより下方のストレート部・円弧部・底部に合成シリカ原料で第２合成シリカ粉層堆積厚さ２ｍｍ）に充填した。上記ルツボ形状型の外面側から、上記関連品例３と同様にアルゴンガス、水素ガスを供給し、アーク溶融して、溶融ルツボを得た。この溶融ルツボの開口部端部から２００ｍｍより下方のストレート部・円弧部・底部を粒径８０メッシュのＳｉＣ砥粒でブラスト処理することで粗研削加工し、続いて、粒径４００メッシュのダイヤモンド砥石（ベルト）で再研削加工を行なった後、ルツボ溶融装置にて、上記アーク溶融時よりカーボン電極を下方に下げ５５０Ｔｏｒｒ減圧、水素ガスを２００リットル／分の割合で成形体の中空部に供給しつつ、５分間再アーク溶融を行ない、その後上記関連品例３と同様にアルゴンガスをルツボの中空部に供給し急冷を行なうことで、内表面に段差のなく、表２に示すような内表面特性を有する石英ガラスルツボを製造した。
【００７０】
（３）（比較例２） 関連品例３と同様の方法により、表２に示すような内表面特性を有するように製造工程を制御して、石英ガラスルツボを製造した。
【００７１】
２．内表面特性の測定方法
４部分（有気泡ストレート部、無気泡ストレート部、円弧部及び底部）の各々において、各１０個の試料を作製し、内表面から０．３ｍｍ位置の３員環強度を試験１と同様の方法で測定した。また、試験１と同じ測定装置、測定条件で、同様にして試料を作製し、ＳｉＨ基強度の測定を行なった。測定は上記３員環強度の測定と同様に４分割について各々１０個の試料の内表面から０．３ｍｍ位置のＳｉＨ基強度を測定した。さらに、上記４部分の内表面から１ｍｍの領域での単位体積当りの気泡個数、気泡占有率は厚さ１ｍｍの断面試料の拡大写真から実測した。
【００７２】
３．単結晶引上げ試験方法
実施例、関連品例及び比較例を各々１００個を用いて、初期シリコン融液面位置が、ルツボ開口部端部から約１００ｍｍとなるような条件にて、ＣＺ法によるシリコン単結晶の引上げを行なった。
【００７３】
４．結果
表２に示す。
【表２】

【００７４】
表２からもわかるように、関連品例３では、４部分（有気泡ストレート部、無気泡ストレート部、円弧部及び底部）の平均３員環強度は０．２５を上回っており、また、全体的に若干の気泡が内表面側に存在することが確認された。さらに、関連品例３を用いた単結晶引上げでは、液面振動の発生はなく、平均結晶化率も９３％と高い値であることがわかった。
【００７５】
また、実施例１は、４部分（有気泡ストレート部、無気泡ストレート部、円弧部及び底部）共、３員環強度は０．２５を上回っており、有気泡ストレート部には、他部に比べて気泡が多く存在しており、これに対して、他部は実質的に無気泡であることがわかった。また、有気泡ストレート部は、そのＳｉＨ基強度が１．０×１０^−４を上回っていることがわかった。さらに、実施例１を用いた単結晶引上げでは、液面振動の発生はなく、平均結晶化率も９８％と極めて高い値であることがわかった。
【００７６】
これに対して、比較例２は、４部分の平均３員環強度は０．２５に達せず、また、平均気泡個数も５と極めて少なく、その気泡含有率も小さいことがわかった。さらに、比較例２を用いた単結晶引上げでは、３５／１００の割合で液面振動が発生し、いくつかの石英ガラスルツボを用いた場合には、全く単結晶が引上げられない場合（単結晶化率＝０）があり、平均結晶化率も８５％と極めて低い値であることがわかった。
【００７７】
［試験３］
上記［試験２］の関連品例３の製造方法と同様の製造方法において、水素ガスの流量及び流出時間を調整することによって、内表面から０．２５ｍｍの表層領域のＯＨ基含有量が表３のような石英ガラスルツボを製造し（実施例２，３及び比較例３，４）、上記試験２と同様に液面振動頻度及び単結晶化率の測定を行った。なお、ＯＨ基含有量は、３７００ｃｍ^−１に検出されるＯＨピークと、８００ｃｍ^−１に検出されるＳｉ−Ｏピークとの面積強度の比を濃度換算することで算出する。
【００７８】
結果： 表３に示す。
【表３】

【００７９】
表３からもわかるように、実施例２では、３員環強度は０．２５であり、有気泡ストレート部には、他部に比べて気泡が多く存在していることがわかった。また、有気泡ストレート部は、そのＳｉＨ基強度が２．０×１０^−４、ＯＨ基含有量１００〜２５０ｐｐｍであることがわかった。さらに、実施例２を用いた単結晶引上げでは、液面振動の発生はなく、平均結晶化率も９５％と極めて高い値であることがわかった。
【００８０】
また、実施例３は、３員環強度は０．２６であり、有気泡ストレート部には、他部に比べて気泡が多く存在していることがわかった。また、有気泡ストレート部は、そのＳｉＨ基強度が３．０×１０^−５、ＯＨ基含有量１００〜２５０ｐｐｍであることがわかった。さらに、実施例３を用いた単結晶引上げでは、液面振動の発生はなく、平均結晶化率も９２％と極めて高い値であることがわかった。
【００８１】
これに対して、比較例３は、３員環強度は０．２６であるが、また、平均気泡個数も８と極めて少なく、その気泡含有率も小さく、ＳｉＨ基強度が−５．０×１０^−５、ＯＨ基含有量３０〜８０ｐｐｍあることがわかった。さらに、比較例３を用いた単結晶引上げでは、２５／１００の割合で液面振動が発生し、平均結晶化率も８６％と極めて低い値であることがわかった。
【００８２】
また、比較例４は、３員環強度は０．２３と０．２５以下であり、さらに、平均気泡個数も５と極めて少なく、その気泡含有率も小さく、ＳｉＨ基強度が−３．０×１０^−５、ＯＨ基含有量３５０〜４２０ｐｐｍであることがわかった。さらに、比較例４を用いた単結晶引上げでは、４０／１００の割合で液面振動が発生し、平均結晶化率も７５％と極めて低い値であることがわかった。
【００８３】
【発明の効果】
本発明に係わる石英ガラスルツボによれば、液面振動の発生を抑制できる内表面特性を持つ石英ガラスルツボを提供することができる。
【図面の簡単な説明】
【図１】 本発明の石英ガラスルツボに関連する石英ガラスルツボの概念図。
【図２】 図１のＡ部を拡大して示す概念図。
【図３】 石英ガラスのネットワークスペクトル図。
【図４】 本発明の石英ガラスルツボの製造方法に関連する石英ガラスルツボの製造方法の概念図。
【図５】 本発明の石英ガラスルツボの製造方法に関連する石英ガラスルツボの製造方法の製造工程図。
【図６】 本発明の石英ガラスルツボの製造方法により製造される石英ガラスルツボの概念図。
【図７】 図６のＡＡ部を拡大して示す概念図。
【図８】 図６のＢＡ部を拡大して示す概念図。
【図９】 本発明の一実施形態の石英ガラスルツボの製造方法の概念図。
【図１０】 本発明の一実施形態の石英ガラスルツボの製造方法の製造工程図。
【図１１】 本発明の一実施形態の石英ガラスルツボの製造方法におけるルツボ成形体の概念図。
【図１２】 本発明の一実施形態の石英ガラスルツボの製造方法の研削、研磨工程図。
【図１３】 本発明の一実施形態の石英ガラスルツボの製造方法に使用される研削装置の概念図。
【図１４】 本発明の一実施形態の石英ガラスルツボの製造方法に使用される研磨装置の概念図。
【符号の説明】
１ 石英ガラスルツボ
２ 内表面
３ 透明層（内層）
４ 外周面
５ 不透明層（外層）
１Ａ 石英ガラスルツボ
１Ａａ ストレート部
１Ａａ_１ 有気泡ストレート部
１Ａａ_２ 無気泡ストレート部
１Ａｂ 円弧部
１Ａｃ 底部
２Ａ 内表面
３Ａ 透明層（内層）
４Ａ 外周面
５Ａ 不透明層（外層）[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a quartz glass crucible used for pulling up a silicon single crystal and a method for producing a quartz glass crucible, and more particularly to a quartz glass crucible having improved inner surface characteristics and a method for producing a quartz glass crucible.
[0002]
[Prior art]
  Conventionally, quartz glass crucibles have been used for the production of silicon single crystals. This quartz glass crucible consists of an outer layer containing a large number of bubbles and a transparent inner layer. The inner layer includes a material using a natural siliceous material and a material using a synthetic siliceous material. The latter is advantageous in that it has few impurities and has a good single crystallization rate, so that the ratio of so-called synthetic quartz glass crucibles has gradually increased in recent years.
[0003]
  However, when a quartz glass crucible is used to melt the silicon and pull up the single crystal, waves are generated on the surface of the molten silicon and it is difficult to seed the seed crystal by proper immersion, and the silicon single crystal can be pulled up. Or a problem that single crystallization is hindered frequently occurred. This liquid surface vibration phenomenon is more likely to occur as the silicon crystal becomes larger in diameter. For this reason, it has become necessary to improve the inner surface characteristics of the inner surface of the quartz glass crucible.
[0004]
[Problems to be solved by the invention]
  Thus, there has been a demand for a quartz glass crucible having an inner surface characteristic capable of suppressing the occurrence of liquid level vibration and a method for producing the quartz glass crucible.
[0005]
  The present invention has been made in view of the above-described circumstances, and provides a quartz glass crucible having an inner surface characteristic capable of suppressing the occurrence of liquid level vibration and a method for producing a quartz glass crucible.Objective.
[0006]
[Means for Solving the Problems]
  In order to achieve the above object, according to one aspect of the present invention,A curved quartz glass crucible having an inner layer portion made of transparent quartz glass made of synthetic silica and having a straight portion, an arc portion and a bottom portion from the upper opening, and an inner layer portion at least 0.3 mm from the inner surface The strength of the three-membered ring is 0.25 or more, and the area of 1.0 mm from at least the inner surface of the straight portion having a predetermined length from the end of the opening is 100 / mm.³Having the above bubbles, the region has a SiH group strength of 3.0 × 10^-5There is provided a quartz glass crucible having a portion as described above and having a region of 1.0 mm or more from the inner surface except for the predetermined length substantially free of bubbles. As a result, the erosion (penetration) of the inner surface in contact with the Si melt is reduced, the generation of liquid surface vibration due to the SiO gas generated at the interface is suppressed, and the reduction in the amount of penetration results in the Si melt. Oxygen concentration in quartz increases, wettability between quartz glass and Si melt increases, and during the pulling of the single crystal, the Si melt partially crawls up the crucible straight part, and sudden liquid level vibration occurs due to this falling In particular, seeding at the initial stage of pulling up the single crystal can be performed accurately, and a silicon single crystal ingot having a high single crystallization rate can be manufactured. The SiH group strength at least in the region of 1.0 mm from the inner surface is 3.0 × 10^-5The above portions are preferably present in a layered manner substantially parallel to the inner surface of the quartz glass crucible and over the entire circumference. As a result, dislocations in the silicon single crystal can be prevented more reliably, and a higher single crystallization rate can be realized. Furthermore, the SiH group strength is 1.0 × 10 6.^-5More preferably.
[0007]
  In a suitable example, OH group content in the thickness of 0.05 mm or more of the surface layer of the said inner surface is 100-300 ppm. As a result, the Si melt partially crawls up on the inner surface of the crucible straight part, and sudden liquid level vibrations caused by the falling of the Si melt are prevented, and the erosion of the inner surface in contact with the Si melt is reduced. As a result, the occurrence of liquid level vibration due to the Si gas generated at the interface is suppressed.
[0008]
  According to another aspect of the invention,In the method for producing a quartz glass crucible in which raw material powder is supplied into a rotating mold and a crucible-shaped formed body is formed, and then this is arc-melted.The molded body is formed of a natural siliceous powder or a synthetic silica powder, and then provided with a first synthetic silica powder layer over the entire inner surface thereof. A second synthetic silica powder layer is provided on the surface,There is provided a method for producing a quartz glass crucible, characterized in that a fictive temperature of quartz is 1200 ° C. or higher and a cooling gas is sprayed on the inner surface of the quartz glass crucible immediately after the arc melting is stopped. This makes it possible to produce a quartz glass crucible having an inner surface that has a three-membered ring strength of 0.25 or more in the range of the surface layer of 0.5 mm on the inner surface of the quartz glass crucible and can suppress the occurrence of liquid level vibration. .Furthermore, the area of 1.0 mm from at least the inner surface of the straight portion having a predetermined length from the end of the opening is 100 / mm. ³ Having the above bubbles, the region has a SiH group strength of 3.0 × 10 ^-5 An area having 1.0 mm or more from the inner surface except for a predetermined length has substantially no bubbles.
[0009]
  In a preferred example, the second synthetic silica powder layer is removed after arc melting, and the surface after removal is heat-treated. Thereby, except for the predetermined length, a quartz glass crucible in which a region of 1.0 mm or more from the inner surface is substantially bubble-free is manufactured.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
  Less than,A quartz glass crucible related to the quartz glass crucible of the present invention (hereinafter referred to as a related quartz glass crucible).Will be described with reference to the accompanying drawings.
[0011]
  Figure 1RelationThe quartz glass crucible 1 has two layers having a transparent layer (inner layer) 3 on the inner surface 2 side of the quartz glass crucible 1 and an opaque layer (outer layer) 5 in which bubbles are present on the outer peripheral surface 4 side of the quartz glass crucible 1. It is formed with.
[0012]
  As shown in FIG. 2 in which the portion A of FIG. 1 is enlarged, the quartz glass crucible 1 has a three-membered ring strength of 0.25 or more in a surface layer range of 0.5 mm.
[0013]
  Since the liquid surface vibration phenomenon at the time of pulling the silicon single crystal is greatly influenced by the dissolution of the interface between the silicon melt and the quartz glass, the quartz glass crucible 1 according to the present invention having an inner surface layer having a predetermined glass structure is used as a liquid crystal. It is effective for suppressing surface vibration. Thereby, if a single crystal is pulled using the quartz glass crucible 1, a high single crystallization rate can be realized.
[0014]
  The three-membered ring strength is quartz glass (SiO₂) And is affected by the composition (OH, etc.) and thermal history of quartz glass, and the peak of the three-membered ring bond is shown in FIG. 3, and the network spectrum of quartz glass by laser Raman spectroscopy. Measure 600cm^-1Detected in the vicinity. Normally, when measuring the strength of a three-membered ring, 600 cm^-1The intensity area of the three-membered ring peak is divided by the intensity area of the SiO peak that is part of the quartz glass network spectrum. That is, 3-membered ring strength = strength area of 3-membered ring peak (565-650 cm^-1) / SiO peak intensity area (700-900 cm)^-1)
[0015]
  The aboveRelationFurthermore, in the quartz glass crucible, by setting the OH group content in the thickness region of 0.05 mm or more on the inner surface to 100 ppm or more, the inner surface of the crucible has a single polarity, and erosion by Si melt Since O which melts at least has one polarity in the Si melt, the inner surface of the crucible and the Si melt repel each other, so the Si melt partially crawls up the inner surface of the crucible straight part, It is possible to prevent the occurrence of sudden liquid level vibration due to this falling.
[0016]
  Further, by setting the OH group content in the thickness region of 0.05 mm or more on the inner surface of the quartz glass crucible to 300 ppm or less, erosion of the inner surface in contact with the Si melt is reduced, and SiO gas generated at the interface It is possible to suppress the occurrence of the liquid level vibration due to. It should be noted that the above effect can be realized when pulling up the actual single crystal because the thickness of the surface layer on the inner surface having the OH group content is at least 0.05 mm.
[0017]
  next,RelationA method for producing a quartz glass crucible will be described.
[0018]
  As shown in FIG. 4, the crucible molding die 12 of the quartz glass crucible manufacturing apparatus 11 is composed of a gas permeable member such as a die having a plurality of through holes or a highly purified porous carbon die. The inner member 13 is provided with a ventilation portion 14 on the outer periphery thereof, and a holding body 15 that holds the inner member 13.
[0019]
  A rotating shaft 16 connected to a rotating means (not shown) is fixed to the lower portion of the holding body 15 and supports the crucible forming die 12 so as to be rotatable. The ventilation part 14 is connected to an exhaust port 18 provided in the center of the rotary shaft 16 through an opening 17 provided in the lower part of the holding body 15, and the ventilation part 14 is connected to a decompression mechanism 19. Has been.
[0020]
  An arc electrode 20 for arc discharge, a raw material supply nozzle 21, an inert gas supply pipe 22, a hydrogen gas supply pipe 23, and a cooling gas supply pipe for supplying a cooling gas such as nitrogen gas are provided on the upper part facing the inner member 13. 24 and a shielding plate 25 that covers the opening of the crucible molding die 12 are further provided.
[0021]
  Therefore, in order to manufacture a crucible using the quartz glass crucible manufacturing apparatus 11 described above, a crucible molding die 12 is operated by operating a rotary drive source (not shown) and rotating the rotary shaft 16 in the direction of the arrow. Is rotated at a predetermined speed. High-purity silica powder is supplied into the crucible molding die 12 from above by a raw material supply nozzle 21. The supplied silica powder is pressed to the inner surface member 13 side of the crucible molding die 12 by centrifugal force to be molded as a crucible-shaped molded body 26. In addition, the said molded object 26 can also be shape | molded with an apparatus different from the quartz glass crucible apparatus which performs arc melting.
[0022]
  Further, in accordance with the manufacturing process diagram as shown in FIG. 5, the inside of the inner member 13 is depressurized by the operation of the depressurization mechanism 19, and further, argon gas is supplied from the inert gas supply pipe 22 at a certain rate. It supplies to the hollow part 26i. After a predetermined time has elapsed from the supply of the argon gas, the arc electrode 20 is energized and continued, heated from the inside of the molded body 26, and a molten layer is formed on the inner surface of the molded body 26.
[0023]
  After a predetermined time has elapsed, in order to appropriately form an opaque layer containing many bubbles on the outside of the crucible, the decompression mechanism 19 is adjusted or stopped to adjust or stop the decompression in the crucible molding die 12. Continue arcing during all arc melting with reduced pressure reduced or stopped, stop supplying argon gas after a certain time from the start of arc melting, stop supplying argon gas, for example, supply hydrogen gas simultaneously with stopping Hydrogen gas is supplied from the tube 23 to the hollow portion 26 i of the molded body 26 at a constant rate. The supply of hydrogen gas is started at the latest before a predetermined time before stopping the arc melting and after a certain percentage of the total arc melting time. After a predetermined time has elapsed from the start of arc melting, the arc energization is stopped, the supply of hydrogen gas is stopped, and a large amount of argon gas as a cooling gas is sprayed from the cooling gas supply pipe 24 onto the inner surface of the crucible to rapidly cool the inner surface. The crucible manufacturing process ends.
[0024]
  At this time, the fictive temperature of the quartz glass is set to 1200 ° C. or higher, more preferably 1230 ° C. or higher.
[0025]
  Note that the fictive temperature herein refers to the temperature at which the physical properties of quartz glass at room temperature vary depending on the thermal history at the time of manufacture, and those physical property values are set. In order to set the temperature to 1200 ° C. or higher, the arc melting temperature (for example, the crucible surface temperature 2000 ° C.), the melting time, and the cooling rate may be appropriately adjusted.
[0026]
  In particular, as a means for appropriately adjusting the cooling rate, it is preferable to perform rapid cooling by blowing a cooling gas onto the inner surface of the quartz glass crucible immediately after the arc melting is stopped.
[0027]
  The fictive temperature of quartz glass in a conventional quartz glass crucible is about 1100 ° C.
[0028]
  in this wayRelationThe method for producing a quartz glass crucible is a method in which the fictive temperature of quartz glass is set to 1200 ° C. or higher, and the cooling rate after arc melting is rapidly blown onto the inner surface of the quartz glass crucible immediately after the arc melting is stopped.coldBy doing this, the three-membered ring strength in the surface layer range of 0.5 mm is 0.25 or more.RelationA quartz glass crucible can be manufactured.
[0029]
  In addition, the present inventiononeThe quartz glass crucible of the embodiment will be described.
[0030]
  FIG. 6 shows the present invention.oneIn the quartz glass crucible 1A of the embodiment, an opaque layer (outer layer) having a transparent layer (inner layer) 3A on the inner surface 2A side of the quartz glass crucible 1A and a large number of bubbles on the outer peripheral surface 4A side of the quartz glass crucible 1A. It is formed of two layers having 5A.
[0031]
  The quartz glass crucible 1A is formed by a straight portion 1Aa having a straight cross section, an arcuate arc portion 1Ab connected to the straight portion 1Aa, and a bottom portion 1Ac connected to the arc portion 1Ab. Yes.
[0032]
  As shown in FIG. 7 showing the AA portion of FIG. 6 in an enlarged manner, the inner surface 2A of the quartz glass crucible 1A has the above-mentioned three-membered ring strength of 0.25 or more in a range of at least a surface layer of 0.3 mm.
[0033]
  Further, as shown in FIG. 8 showing an enlarged view of the BA portion in FIG. 6, a straight portion from the opening end portion to a predetermined length (depth) in the straight portion 1Aa of the quartz glass crucible 1A, that is, a bubbled straight portion. 1Aa₁The area of at least 1.0 mm from the inner surface 2A is 100 / mm³It has the above bubbles and SiH group strength is 3.0 × 10^-5(Preferably 1.0 × 10^-4) A transparent layer having the above portions in layers. The number of bubbles in this transparent layer is clearly less than the number of opaque layers.
[0034]
  In addition, bubbled straight part 1Aa₁Parts other than the above, that is, the straight part 1Aa, the non-bubble straight part 1Aa₂In the transparent layer of the arc portion 1Ab and the bottom portion 1Ac, an area of 1.0 mm or more from the inner surface is substantially bubble-free. Thereby, when pulling up the single crystal using the quartz glass crucible of the second embodiment, the erosion (penetration) of the inner surface 2A in contact with the Si melt is reduced, and the liquid surface vibration due to the SiO gas generated at the interface is reduced. Occurrence can be suppressed. Moreover, the oxygen concentration in the Si melt increases due to the reduction of the penetration amount, the wettability between the quartz glass and the Si melt increases, and during the pulling of the single crystal, the Si melt becomes the bubbled straight portion 1Aa.₁It is possible to prevent the occurrence of sudden liquid level vibration caused by partially climbing the inner surface of the liquid and dropping it. Thereby, in particular, seeding at the initial stage of pulling the single crystal can be performed accurately.
[0035]
  In addition, the present inventiononeIn the quartz glass crucible of the embodiment, the bubble-containing straight part 1Aa₁100 / mm in an area of 1.0 mm from at least the inner surface³It has the above bubbles, and the SiH group strength of quartz glass in the region is 3.0 × 10^-5(Preferably 1.0 × 10^-4) One of the characteristics is that it has a portion that is the above. Such a bubble is a bubbled straight portion 1Aa₁It is possible to provide a bubbled straight portion 1Aa by heating the heater from the outer surface of the crucible.₁By suppressing the heat radiation above the liquid surface via the crystal, the crystal pulling speed can be further increased and a stable single crystal can be obtained. In general, when bubbles exist in the transparent layer, the bubbles expand and rupture, and the Si single crystal is likely to undergo dislocation due to crystal dislocation. However, this treatment can be achieved by treating the inner surface 2A of the crucible with hydrogen. The SiH base strength is 3.0 × 10 approximately parallel to the inner surface and over the entire circumference of the region.^-5By forming the above portions in layers, the above dislocation can be prevented and a high single crystallization rate can be obtained.
[0036]
  The predetermined length from the end of the opening (the length of the bubbled straight portion) is preferably several tens of millimeters below the Si melt surface before seeding. In addition, the SiH group intensity was measured by irradiating a cross section of the silica glass crucible with ArF 514 nm laser light and detecting the scattered light from the side surface.^-1Differential strength and 2270-2300cm^-1About the difference from the differential intensity of 700-900cm^-1It is calculated by the method of taking the ratio with the height intensity of the Si—O peak. Specifically, it is as follows.
[0037]
  The SiH peak has a wavenumber of 2260 cm in the Raman spectrum obtained by excitation with an Ar ion laser of 514 nm.^-1Appears, but overlaps with the SiO band appearing over 1950-2550 nm. The SiO band is a wide peak with three peaks overlapped. The portion where the SiH peak appears hits the valley of the band, and it is difficult to remove (subtract) the base line processing or the SiO band, and obtain data with good S / N. Is difficult. Therefore, it is useful to employ a differential method as a method for obtaining the SiH peak intensity (SiH group intensity). Furthermore, 800cm^-1The intensity (peak height) of the SiO band is obtained, and the ratio with the SiH differential intensity is obtained. This method is (1) 1950-2550cm^-1Then, after smoothing (smoothing process) by the SAV-DOLAY method, differentiation is performed. (2) From the differential spectrum, 2225-2250 cm^-1And 2270-2300cm^-1The average value of each 13 points is obtained within the range of (the slopes of the left and right sides of the SiH peak are obtained). (3) The average value (slope) is D₁, D₂And D₁-D₂Asking for this D_SiHAnd (4) 800cm^-1After performing baseline processing in the same manner as when obtaining the three-membered ring strength for the SiO band, the peak height (maximum height) is obtained. This is H_SiOAnd (5) D_SiH/ H_SiOAnd this is taken as the SiH strength.
[0038]
  Furthermore, not only the specification of the number of bubbles but also the above effect can be further enhanced by setting the occupancy rate of the bubbles to 0.05 vol% or more. More preferably 200 pieces / mm³Or less and 0.1 vol% or less. If it is too much, the surface tends to be etched, the amount of penetration increases, and liquid surface vibration tends to be induced or a high oxygen concentration tends to occur.
[0039]
  In addition, the present inventiononeIn the quartz glass crucible of the embodiment, one feature is that 1.0 mm or more from the inner surfaces of the arc portion 1Ab and the bottom portion 1Ac is substantially bubble-free. Problems due to blistering and rupture can be solved. In particular, it is important that the arc portion 1Ab where the heater heat from the outer peripheral portion is most easily applied is substantially bubble-free.
[0040]
  In particular, the inner surface 2A is formed by polishing the entire inner surface of the arc-melted melting crucible, and heat-treating the polished surface with an oxyhydrogen burner, so that it is possible to ensure the absence of bubbles. In addition, substantially bubble-free means 10 / mm³Below, preferably 5 pieces / mm³It is as follows.
[0041]
  The aboveoneIn the embodiment silica glass crucible, the inner surface of the crucible has a single polarity by setting the OH group content in the thickness region of the inner surface of 0.05 mm or more to 100 ppm or more. O which melts at least by erosion has one polarity in the Si melt, so both repel each other, and the Si melt partially crawls up the inner surface of the crucible straight part, and this falls The occurrence of sudden liquid level vibration can be prevented more effectively.
[0042]
  Moreover, by setting the OH group content in the thickness region of the surface layer of 0.05 mm or more on the inner surface of the quartz glass crucible to 300 ppm or less, erosion of the inner surface in contact with the Si melt is more effectively reduced, and at the interface. Generation of liquid surface vibration due to the generated SiO gas can be more reliably suppressed. It should be noted that the above effect can be realized when pulling up the actual single crystal because the thickness of the surface layer on the inner surface having the OH group content is at least 0.05 mm.
[0043]
  Furthermore, the present inventiononeThe manufacturing method of the quartz glass crucible of the embodiment will be described.
[0044]
  BookThe manufacture of the silica glass crucible 1A of the embodiment has been described above.Related quartz glass crucible4, using a quartz glass crucible manufacturing apparatus as shown in FIG. 4, a raw material powder is supplied as shown in FIG. 9 to manufacture a molded body, and along the manufacturing process as shown in FIGS. 5 and 10. To manufacture. The same parts as those of the quartz glass crucible manufacturing apparatus shown in FIG.
[0045]
  For example, as shown in FIG. 9, a crucible molding die 12 of a quartz glass crucible manufacturing apparatus 11 is rotated at a predetermined speed, and a high-purity natural material is introduced into the crucible molding die 12 from above by a raw material supply nozzle 21. Supply siliceous (quartz) powder. The supplied silica powder is pressed against the inner surface member 13 side of the crucible molding die 12 by centrifugal force to form a crucible-shaped molded body 26A.
[0046]
  Further, the synthetic silica powder is supplied onto the molded body 26A to form the first synthetic silica powder layer 26A1 over the entire circumference of the inner surface 27A of the molded body 26A, and further, a predetermined length from the end of the opening. The air bubble straight part 26Aa₁The other inner surface except for the non-bubble portion 26Aa of the straight portion 26Aa₂Synthetic silica powder is supplied to the circular arc portion 26Ab and the bottom portion 26Ac, and the second synthetic silica powder layer 26A2 is formed over the entire inner surface of the first synthetic silica powder layer 26A1, and this is easily shown. In FIG. 11, a crucible molded body 1Ap indicated by a solid line is obtained.
[0047]
  Then, along with the manufacturing process diagram as shown in FIG.RelationThe same melting as that of the quartz glass crucible is performed to produce a melting crucible having the same shape as the crucible molded body 1Ap shown in FIG. Only the portion of the manufactured molten crucible where the second synthetic silica powder layer 26A2 is formed (shaded portion in FIG. 11) is subjected to grinding, polishing and heat treatment steps as shown in FIG.
[0048]
  The grinding process is performed in two stages, a rough grinding process and a regrinding process, using a process as shown in FIG. 12 and a handy type grinding apparatus (belt sander) 31 as shown in FIG.
[0049]
  In the rough grinding, the grinding belt 35 is rotated via a vane-type rotation mechanism 33 and a driving rotation roller 34 that are rotated by high-pressure air sent from a high-pressure air pipe 32 communicated with an air compressor (not shown). Grinding is performed while supplying water from the water supply nozzle 36 to the grinding belt 35 and the melted second synthetic silica powder layer (synthetic silica inner surface) 26A2.
[0050]
  The grinding belt 35 is a diamond grindstone (belt), and the diamond particle size in the rough grinding process is made finer than 80 mesh (#).
[0051]
  In the regrinding process, the diamond particle diameter of the grinding belt is reduced to 200 mesh or more, and grinding similar to rough grinding is performed. The arithmetic average roughness (Ra) (JIS B0601-1994) of the inner surface after the regrinding process is flattened to 3 μm or less. In this way, by making the roughness of Ra 3 μm or less, it becomes possible to perform a quicker polishing process in the next process, and it is possible to reliably remove microcrack damage generated in the grinding process in a shorter time. It becomes like this.
[0052]
  Further, according to the process as shown in FIG. 12, the ground inner surface of the melting crucible is polished in the polishing process.
[0053]
  For example, as shown in FIG. 14, the polishing process uses a handy type polishing apparatus 41, and between the polishing cloth 43 provided on the rotating roller 42 and the second synthetic silica powder layer (synthetic silica inner surface) 26A2 after melting. Abrasive is supplied for polishing. The inner surface thus polished can have a Ra of 1 μm or less, and the variation in surface roughness can be within a range of ± 0.1 μm over the entire inner surface. Since the abrasive cloth 35 has a fine diamond particle size of 800 mesh or more, microcrack damage that is harmful to the inner surface can be more reliably removed, and the uniformity is higher and Ra is more surely less than 1 μm. Can be small. When Ra is set to 1 μm or less, the heat treatment of the next step does not leave visible irregularities on the inner surface 2A, and does not adversely affect the pulled silicon single crystal. It is possible to leave no crack damage.
[0054]
  Next, according to a process as shown in FIG. 10, the polished inner surface of the molten crucible is heat-treated by a heat treatment process.
[0055]
  This heat treatment step (not shown) is performed by heating the entire inner surface by re-arc melting. At the time of re-arc melting, the carbon electrode is lowered downward, and the bubbled straight portion (thin non-hatched portion) 26Aa shown in FIG.₁To prevent remelting. Even when microbubbles exist only on a part of the inner surface of the melting crucible, the entire inner surface is ground and polished in the grinding process and polishing process, and the entire inner surface is heated at a high temperature using re-arc melting. 6, a crucible having a smooth inner surface with no step on the inner surface as shown in FIG. 6 is produced, and the three-membered ring strength of the inner layer portion at least 0.3 mm from the inner surface is 0.25 or more, 100 / mm area of 1.0 mm from at least the inner surface of the straight part with a predetermined length from the end of the opening.³Having the above bubbles, the region has a SiH group strength of 3.0 × 10^-5In addition to the above-described portion, the region having a thickness of 1.0 mm or more from the inner surface except for a predetermined length is substantially bubble-free, and has the inner surface characteristics capable of suppressing the occurrence of liquid level vibration.oneThe quartz glass crucible of the embodiment is manufactured.
[0056]
【Example】
  [Test 1]
  RelationA silicon single crystal was pulled up using a crucible produced by a method for producing a quartz glass crucible and having different three-membered ring strength, and the occurrence of liquid surface vibration and the single crystallization rate were examined.
[0057]
  The three-membered ring strength was measured as follows.
[0058]
  Laser Raman spectroscopyUse quartz glassMeasure the network spectrum.
[0059]
  Measuring apparatus: “RAMANOR S320 laser Raman spectroscopic analyzer” manufactured by Ehime Bussan Co., Ltd., an Ar laser (514 nm) is used as an incident laser, and a CCD detector is used as a detector.
[0060]
  Measurement conditions: Laser diameter: 100 μm, Laser output: 400 mW,
            Slit width: 250 μm, Slit height: 5 mm,
            Integration time: 1 second, laser incidence method: oblique incidence
[0061]
  sample:RelationCut out from the quartz glass crucible, and the incident surface and the scattered light detection surface are mirror-polished.
[0062]
  Result: A spectrum as shown in FIG. 3 was obtained. From the spectrum of each sample, the intensity area of the 3-membered ring peak (565-650 cm)^-1) And SiO peak intensity area (700-900 cm)^-1) And the three-membered ring strength was calculated from the three-membered ring strength area / SiO peak strength area.
[0063]
  Moreover, the result relevant to the three-membered ring strength as shown in Table 1 was obtained.
[Table 1]

[0064]
  As shown in Table 1, the quartz glass is manufactured so that the fictive temperature is 1200 ° C. or higher, and the three-membered ring strength is 0.25 or higher.Related product example 1as well asRelated product example 2It was found that liquid level vibration does not occur. In addition, the single crystallization ratios are as high as 99% and 100%, respectively. On the other hand, the fictive temperature of quartz glass is 1160 ° C., which is less than 1200 ° C., and the three-membered ring strength is 0. In the case of the conventional example of .20, liquid level vibration was generated, and the single crystallization rate was found to be as low as 95%.
[0065]
  Further, in Comparative Example 1 in which the fictive temperature of quartz glass is manufactured to 1100 ° C. and the three-membered ring strength is 0.23, liquid surface vibration occurs, but the single crystallization rate is as high as 99%. I found out.
[0066]
  In the case of the conventional example, the density was 2.2013,Related product example 1In this case, the density was 2.2019.
[0067]
[Test 2]
  A related product and a crucible manufactured by the method for manufacturing a quartz glass crucible of the present inventionThe inner surface characteristics of the silicon were investigated, and further, using this quartz glass crucible, the silicon single crystal was pulled up and the crystallization rate was examined.
[0068]
  1. Production of quartz glass crucible
  (1) (Related product example 3)RelationA quartz glass crucible, with a crucible shape mold size of outer diameter 560 mm, height 500 mm, deposition layer thickness 25 mm (deposition thickness 17 mm with quartz raw material + inner surface side: first synthetic silica powder layer deposition thickness with synthetic silica raw material 8 mm). Argon gas was supplied from the outer surface side of the crucible-shaped mold to the hollow portion of the molded body at a rate of 60 liters / min while reducing the pressure to a melting pressure of 350 Torr using a vacuum pump. Four minutes after the start of the supply of argon gas, the arc electrode was energized and continued, and heated from the inside of the compact for a total of 50 minutes. After 10 minutes from the start of arc melting, the pressure during melting is reduced to 720 Torr, and after 35 minutes have elapsed after about 70% of the total arc melting time has elapsed (15 minutes before the arc is stopped), the argon gas supply is stopped. Simultaneously, hydrogen gas was supplied to the hollow part of the molded body at a rate of 200 liters / minute. After the supply of hydrogen gas for 10 minutes, the supply of hydrogen gas was stopped and arc melting was continued. At this time, the temperature of the inner surface of the crucible was 2300 ° C. The quartz glass crucible having the inner surface characteristics as shown in Table 2 was manufactured by stopping arc melting 5 minutes after stopping hydrogen gas and supplying argon gas to the hollow part of the crucible at 500 l / min for cooling. .
[0069]
  (2) (Example)1) Crucible-shaped mold with outer diameter of 560 mm and height of 500 mm, deposited layer thickness 27 mm (crystal material deposited thickness 17 mm + inner surface side: synthetic silica material first synthetic silica powder layer deposited thickness 8 mm + innermost surface Side: A straight part, an arc part, and a bottom part below 200 mm from the end of the opening were filled with a synthetic silica raw material into a second synthetic silica powder layer deposition thickness of 2 mm). From the outer surface side of the crucible shape mold, the aboveRelated product example 3Similarly, argon gas and hydrogen gas were supplied, and arc melting was performed to obtain a melting crucible. Rough grinding is performed by blasting the straight part, arc part, and bottom part below 200 mm from the opening end of the melting crucible with SiC abrasive grains having a particle size of 80 mesh, followed by a diamond grinding stone having a particle size of 400 mesh (Belt) After regrinding with a crucible, the carbon electrode is lowered downward from the time of the arc melting with a crucible melting device, 550 Torr reduced pressure, and hydrogen gas is supplied to the hollow part of the molded body at a rate of 200 liters / minute While performing re-arc melting for 5 minutes,Related product examplesIn the same manner as in No. 3, a quartz glass crucible having inner surface characteristics as shown in Table 2 with no step on the inner surface was produced by supplying argon gas to the hollow portion of the crucible and performing rapid cooling.
[0070]
  (3) (Comparative Example 2)Related product example 3By the same method, the quartz glass crucible was manufactured by controlling the manufacturing process so as to have the inner surface characteristics as shown in Table 2.
[0071]
  2. Measuring method of inner surface characteristics
  In each of the four parts (bubbled straight part, bubbleless straight part, arc part, and bottom part), 10 samples each were prepared, and the strength of the three-membered ring at a position of 0.3 mm from the inner surface was the same as in Test 1. Measured with A sample was prepared in the same manner using the same measurement apparatus and measurement conditions as in Test 1, and the SiH group strength was measured. In the same manner as the measurement of the 3-membered ring strength, the SiH group strength at a position of 0.3 mm from the inner surface of 10 samples was measured for each of the four sections. Further, the number of bubbles per unit volume and the bubble occupancy in the region 1 mm from the inner surface of the four parts were measured from an enlarged photograph of a cross-sectional sample having a thickness of 1 mm.
[0072]
  3. Single crystal pulling test method
  Example,Related product examplesAnd using 100 each of the comparative examples, the silicon single crystal was pulled by the CZ method under the condition that the initial silicon melt surface position was about 100 mm from the end of the crucible opening.
[0073]
  4). result
  It shows in Table 2.
[Table 2]

[0074]
  As can be seen from Table 2,Related product example 3Then, the average three-membered ring strength of the four parts (the bubbled straight part, the bubbleless straight part, the arc part, and the bottom part) is higher than 0.25, and some bubbles exist on the inner surface side as a whole. It was confirmed. further,Related product example 3It was found that the single crystal pulling using, did not generate liquid surface vibration and the average crystallization rate was as high as 93%.
[0075]
  Examples1The three-membered ring strength exceeds 0.25 for all four parts (bubbled straight part, bubbleless straight part, arc part and bottom part), and the bubbled straight part has more bubbles than other parts. On the other hand, the other part was found to be substantially bubble-free. In addition, the bubbled straight portion has an SiH group strength of 1.0 × 10^-4I found out that Further examples1In the single crystal pulling using, no liquid surface vibration was generated, and the average crystallization rate was found to be an extremely high value of 98%.
[0076]
  In contrast, in Comparative Example 2, it was found that the average three-membered ring strength of the four portions did not reach 0.25, the average number of bubbles was as small as 5, and the bubble content was small. Further, in the single crystal pulling using the comparative example 2, the liquid level vibration is generated at a ratio of 35/100, and when several quartz glass crucibles are used, the single crystal cannot be pulled at all (single crystal It was found that the average crystallization rate was as low as 85%.
[0077]
  [Test 3]
  In [Test 2] aboveManufacturing method of related product example 3In the same manufacturing method, a quartz glass crucible having an OH group content in the surface layer region of 0.25 mm from the inner surface as shown in Table 3 was prepared by adjusting the flow rate and outflow time of hydrogen gas (Examples).2,3And Comparative Examples 3 and 4) and liquid surface vibration frequency and single crystallization rate were measured in the same manner as in Test 2 above. The OH group content is 3700 cm.^-1OH peak detected at 800 cm^-1The ratio of the area intensity to the Si—O peak detected at 1 is calculated by converting the concentration.
[0078]
  Results: Shown in Table 3.
[Table 3]

[0079]
  As can be seen from Table 3, the examples2Then, the three-membered ring strength was 0.25, and it was found that more bubbles were present in the bubbly straight portion than in other portions. In addition, the bubbled straight portion has an SiH group strength of 2.0 × 10^-4The OH group content was found to be 100 to 250 ppm. Further examples2In the single crystal pulling using, liquid surface vibration was not generated, and the average crystallization rate was found to be an extremely high value of 95%.
[0080]
  Examples3The three-membered ring strength was 0.26, and it was found that more bubbles were present in the bubbly straight part than in other parts. In addition, the bubbled straight portion has an SiH group strength of 3.0 × 10^-5The OH group content was found to be 100 to 250 ppm. Further examples3In the single crystal pulling using, liquid surface vibration was not generated, and the average crystallization rate was found to be an extremely high value of 92%.
[0081]
  In contrast, in Comparative Example 3, the three-membered ring strength was 0.26, but the average number of bubbles was as very small as 8, the bubble content was small, and the SiH group strength was -5.0 × 10^-5The OH group content was found to be 30 to 80 ppm. Furthermore, in the single crystal pulling using Comparative Example 3, it was found that liquid level vibration was generated at a ratio of 25/100, and the average crystallization rate was 86%, which was an extremely low value.
[0082]
  In Comparative Example 4, the three-membered ring strength is 0.23 and 0.25 or less, the average number of bubbles is very small as 5, the bubble content is small, and the SiH group strength is −3.0 ×. 10^-5The OH group content was found to be 350 to 420 ppm. Furthermore, in the single crystal pulling using Comparative Example 4, it was found that liquid level vibration was generated at a ratio of 40/100, and the average crystallization rate was 75%, which was an extremely low value.
[0083]
【The invention's effect】
  According to the quartz glass crucible according to the present invention, it is possible to provide a quartz glass crucible having an inner surface characteristic capable of suppressing the occurrence of liquid level vibration.
[Brief description of the drawings]
[Figure 1]Related to the quartz glass crucible of the present inventionConceptual diagram of quartz glass crucible.
FIG. 2 is an enlarged conceptual view of a part A in FIG.
FIG. 3 is a network spectrum diagram of quartz glass.
FIG. 4 of the present inventionRelated to quartz glass crucible manufacturing methodThe conceptual diagram of the manufacturing method of a quartz glass crucible.
FIG. 5 of the present inventionRelated to quartz glass crucible manufacturing methodThe manufacturing process figure of the manufacturing method of a quartz glass crucible.
FIG. 6 of the present inventionManufactured by quartz glass crucible manufacturing methodConceptual diagram of quartz glass crucible.
FIG. 7 is a conceptual diagram showing the AA part of FIG. 6 in an enlarged manner.
8 is a conceptual diagram showing an enlarged view of a BA portion in FIG. 6;
FIG. 9 shows the present invention.oneThe conceptual diagram of the manufacturing method of the quartz glass crucible of embodiment.
FIG. 10 shows the present invention.oneThe manufacturing process figure of the manufacturing method of the quartz glass crucible of embodiment.
FIG. 11 shows the present invention.oneThe conceptual diagram of the crucible molded object in the manufacturing method of the quartz glass crucible of embodiment.
FIG. 12 shows the present invention.oneThe grinding | polishing and grinding | polishing process drawing of the manufacturing method of the quartz glass crucible of embodiment.
FIG. 13 shows the present invention.oneThe conceptual diagram of the grinding device used for the manufacturing method of the quartz glass crucible of embodiment.
FIG. 14 shows the present invention.oneThe conceptual diagram of the grinding | polishing apparatus used for the manufacturing method of the quartz glass crucible of embodiment.
[Explanation of symbols]
1 Quartz glass crucible
2 Inner surface
3 Transparent layer (inner layer)
4 outer peripheral surface
5 Opaque layer (outer layer)
1A quartz glass crucible
1Aa Straight part
1Aa₁  Air bubble straight part
1Aa₂  Air-free straight section
1Ab Arc part
1Ac Bottom
2A inner surface
3A Transparent layer (inner layer)
4A outer peripheral surface
5A opaque layer (outer layer)

Claims (4)

A curved quartz glass crucible having an inner layer portion made of transparent quartz glass made of synthetic silica and having a straight portion, an arc portion and a bottom portion from the upper opening, and an inner layer portion at least 0.3 mm from the inner surface The strength of the three-membered ring is 0.25 or more, and at least 1.0 mm from the inner surface of the straight portion having a predetermined length from the end of the opening has 100 / mm ³ or more bubbles, and the region And a portion having a SiH group strength of 3.0 × 10 ⁻⁵ or more, and a region of 1.0 mm or more from the inner surface except for the predetermined length is substantially bubble-free. Glass crucible. 2. The quartz glass crucible according to claim 1, wherein the OH group content in a thickness of 0.05 mm or more on the surface of the inner surface is 100 to 300 ppm. In a method for producing a quartz glass crucible in which raw material powder is supplied into a rotating mold to form a crucible-shaped molded body and then arc-melted, the molded body is formed of natural siliceous powder or synthetic silica powder After the formation, a first synthetic silica powder layer is provided over the entire inner surface, and a second synthetic silica powder layer is provided on the inner surface other than a predetermined length from the end of the opening . A method for producing a quartz glass crucible, wherein a fictive temperature is 1200 ° C. or higher and a cooling gas is blown onto the inner surface of the quartz glass crucible immediately after the arc melting is stopped. 4. The method for producing a silica glass crucible according to claim 3 , wherein the second synthetic silica powder layer is removed after arc melting, and the surface after the removal is heat-treated.

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