JP2004315255A - Method for manufacturing fluoride crystal, fluoride crystal, optical system, and optical lithography device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a fluoride crystal, by which the amount of impurities mixed in a manufacturing process can be reduced, and the fluoride crystal having excellent internal transmittance can be easily manufactured. <P>SOLUTION: In the method for manufacturing the fluoride crystal, including crystallization processes 6, 2 for forming the crystal by melting a fluoride together with a scavenger and then solidifying, substitution processes 5, 7 for substituting impurities adsorbed on the surface with fluorine by bringing the fluoride into contact with gaseous fluorine at a temperature lower than the melting point of the fluoride are performed, and crystallization processes 6, 2 are performed continuously after the respective substitution processes 5, 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１１９】
実施例２
まず、図３に示す前処理炉１０にガス導入口１３を設けた表面処理炉兼前処理炉を用いて、原料粉末の容積を小さくし、原料粉末中の不純物を除去する前処理工程を行う。
【０１２０】
［フッ素置換工程５］
一般に販売されている高純度の人工合成フッ化カルシウム粉末５０ｋｇをベーキング済みで清浄な内径３００ｍｍのカーボン製のルツボ１６に充填した。このルツボ１６を表面置換と原料溶融を連続的に行うことのできる前処理炉１０にセットして、真空ポンプで内部を１０^−６Ｔｏｒｒまで真空排気を行った。
【０１２１】
真空容器１１内にＮＦ_３ガスを導入し、摂氏３５０℃まで昇温した。内部が３５０℃になった状態で５時間保持した。この過程で表面に吸着している酸素とフッ素との置換が行われ、表面がフッ素化される。
【０１２２】
［精製減容化工程６］
この後、引き続いて１０^−６ Ｔｏｒｒまで真空排気を行ったのち、昇温を行った。フッ化カルシウムの融点よりもやや低い１１００℃に達したところで昇温を停止し、スカベンジャとしてＮＦ_３ガスを導入した。
【０１２３】
原料とスカベンジャであるＮＦ_３ガスとを充分に反応させるため、１１００℃で１２時間保持した。この過程において、原料内部に含有している不純物、原料に混入している酸化カルシウムを除去することができる。
【０１２４】
スカベンジャとの反応を充分に進行させた後、さらに昇温し、フッ化カルシウムの融点である１４２０℃で２４時間保持した。この過程において、原料を溶融し、融液を均質化した。
【０１２５】
この後、温度を室温まで下げ、原料を固化した。この過程において、フッ化カルシウムの容積は小さくなり、単結晶育成炉２０のルツボ２６に充分な重量の原料を装填できた。こうして前処理工程が完了すると、多結晶のバルク原料を得ることができる。
【０１２６】
［フッ素置換工程７］
次に、図４の単結晶育成炉２０にガス導入口２３を設けた表面処理炉兼単結晶育成炉を用いて、フッ素置換工程７と単結晶育成工程８とを連続的に行う。
【０１２７】
まず、前処理工程でできたフッ化カルシウムの多結晶バルク取り出し、内径３００ｍｍのベーキング済みで清浄なカーボン製のルツボ２６に入れた。このルツボを表面置換と原料溶融を連続的に行うことのできる単結晶育成炉２０にセットして、真空ポンプで内部を１０^−６ Ｔｏｒｒまで真空排気をした。真空容器２１内にＮＦ_３のガスを導入し、摂氏３５０℃まで昇温した。内部が３５０℃になった状態で５時間保持した。この過程で表面に吸着している酸素とフッ素との置換が行われ、表面がフッ素化された。
【０１２８】
［単結晶育成工程８］
この後、引き続いて１０^−６ Ｔｏｒｒまで真空排気を行ったのち、昇温を行った。温度を制御しながら徐々に昇温し、１４２０℃に達したら２４時間維持して融液の均質化を行った。次にカーボンルツボを１ｍｍ／Ｈｒの速度で引き下げ、結晶化を行った。融液の全てが結晶化を完了したら、室温まで徐々に降下させた。
【０１２９】
［加工工程３］
取り出したインゴットから円盤状に素材を切り出し、熱処理炉でアニールを行った。
【０１３０】
［測定］
また、インゴットの残りの部分から、透過率測定用試料として、図５に示す位置のフッ化カルシウム単結晶の小片を６個切り出し、測定用サンプルとして直径３０ｍｍ、厚さ１０ｍｍに加工した。サンプルの紫外域および真空紫外域の透過率、１０ｍＪ／ｃｍ^２／ｐｕｌｓｅのＦ_２レーザーを１×１０^５パルス照射後の真空紫外域の透過率を分光光度計を用いて測定したところ、表２のとおりであった。
【０１３１】
このフッ化物結晶はインゴット全域に渡って透過率・Ｆ_２レーザー耐性が高く、光リソグラフィー用光学部材として素材を採取できる。
【０１３２】
【表２】

【０１３３】
実施例３
まず、図３に示す前処理炉１０にガス導入口１３を設けた表面処理炉兼前処理炉を用いて、原料粉末の容積を小さくし、原料粉末中の不純物を除去する前処理工程を行う。
【０１３４】
［フッ素置換工程５］
一般に販売されている高純度の人工合成フッ化カルシウム粉末５０ｋｇをベーキング済みで清浄な内径３００ｍｍのカーボン製のルツボ１６に充填した。このルツボ１６を表面置換と原料熔解を連続的に行うことのできる前処理炉１０にセットして、真空ポンプで内部を１０^−６ Ｔｏｒｒまで真空排気を行った。
【０１３５】
真空容器１１内にＣＦ_４ガスを導入し、摂氏７００℃まで昇温した。内部が７００℃になった状態で５時間保持した。この過程で表面に吸着している酸素とフッ素との置換が行われ、表面がフッ素化される。
【０１３６】
［精製減容化工程］
この後、引き続いて１０^−６ Ｔｏｒｒまで真空排気を行ったのち、昇温を行った。フッ化カルシウムの融点よりもやや低い１１００℃に達したところで昇温を停止し、スカベンジャとしてＣＦ_４ガスを導入した。
【０１３７】
原料とスカベンジャであるＣＦ_４ガスとを充分に反応させるため、１１００℃で１２時間保持した。この過程において、原料内部に含有している不純物、原料に混入している酸化カルシウムを除去することができた。
【０１３８】
スカベンジャとの反応を充分に進行させた後、さらに昇温し、フッ化カルシウムの融点である１４２０℃で２４時間保持した。この過程において、原料を溶融し、融液を均質化できた。この後、温度を室温まで下げ、原料を固化した。この過程において、フッ化カルシウムの容積は小さくなり、単結晶育成炉２０のルツボ２６に充分な重量の原料を装填できる。こうして前処理工程が完了すると、多結晶のバルク原料を得ることができた。
【０１３９】
［フッ素置換工程７］
次に、図４の単結晶育成炉２０にガス導入口２３を設けた表面処理炉兼単結晶育成炉を用いて、フッ素置換工程７と単結晶育成工程８とを連続的に行う。
【０１４０】
まず、前処理工程でできたフッ化カルシウムの多結晶バルクを取り出し、別の内径３００ｍｍのベーキング済みで清浄なカーボン製のルツボ２６に入れた。このルツボを表面置換と原料溶融を連続的に行うことのできる単結晶育成炉２０にセットして、真空ポンプで内部を１０^−６ Ｔｏｒｒまで真空排気をした。真空容器２１内にＣＦ_４のガスを導入し、摂氏７００℃まで昇温した。内部が７００℃になった状態で５時間保持した。この過程で表面に吸着している酸素とフッ素との置換が行われ、表面がフッ素化された。
【０１４１】
［単結晶育成工程８］
この後、引き続いて１０^−６ Ｔｏｒｒまで真空排気を行ったのち、昇温を行った。
【０１４２】
温度を制御しながら徐々に昇温し、１４２０℃に達したら２４時間維持して融液の均質化を行った。次にカーボン製のルツボ２６を１ｍｍ／Ｈｒの速度で引き下げ、結晶化を行った。融液の全てが結晶化を完了したら、室温まで徐々に降下させた。
【０１４３】
［加工工程３］
取り出したインゴットから円盤状に素材を切り出し、熱処理炉でアニールを行った。
【０１４４】
［測定］
また、インゴットの残りの部分から、透過率測定用試料として、図５に示す位置のフッ化カルシウム単結晶の小片を６個切り出し、測定用サンプルとして直径３０ｍｍ、厚さ１０ｍｍに加工した。サンプルの紫外域および真空紫外域の透過率、１０ｍＪ／ｃｍ^２／ｐｕｌｓｅのＦ_２レーザーを１×１０^５パルス照射後の真空紫外域の透過率を分光光度計を用いて測定したところ、表４のとおりであった。
【０１４５】
このフッ化物結晶はインゴット全域に渡って透過率・Ｆ^２レーザー耐性が高く、光リソグラフィー用光学部材として素材を採取できる。
【０１４６】
【表３】

【０１４７】
比較例
比較例として、従来の方法によるフッ化物単結晶の製造例を以下に示す。
【０１４８】
［前処理工程１］
まず、原料粉末の容積を小さくし、原料粉末中の不純物を除去する前処理工程を行った。
【０１４９】
一般に販売されている高純度の人工合成フッ化カルシウム粉末５０ｋｇにスカベンジャとしてフッ化鉛粉末を１ｍｏｌ／％を混合し、よく撹拌した後、ベーキング済みで清浄な内径３００ｍｍのカーボン製の前処理ルツボに充填した。このルツボを前処理炉にセットして、真空ポンプで内部を１０^−６ Ｔｏｒｒまで真空排気を行った。
【０１５０】
原料とスカベンジャであるＰｂＦ_２とを充分に反応させるため、１１００℃で６時間保持した。この過程において、原料内部に含有している不純物、原料に混入している酸化カルシウムを除去することができる。
【０１５１】
スカベンジャとの反応を充分に進行させた後、さらに昇温し、フッ化カルシウムの融点である１４２０℃で２４時間保持した。この過程において、原料を溶融し、融液を均質化できる。この後、温度を室温まで下げ、原料を固化した。この過程において、フッ化カルシウムの容積は小さくなり、育成ルツボに充分な重量の原料を充填できる。こうして前処理工程が完了すると、多結晶のバルク原料を得ることができる。
【０１５２】
［単結晶育成工程２］
次に、前処理工程でできたフッ化カルシウムの多結晶バルクを取り出し、別の内径３００ｍｍのベーキング済みで清浄なカーボン製の育成ルツボに入れた。このルツボを育成炉にセットして、真空ポンプで内部を１０^−６ Ｔｏｒｒまで真空排気をした。
【０１５３】
温度を制御しながら徐々に昇温し、１４２０℃に達したら２４時間維持して融液の均質化を行った。次にカーボンルツボを１ｍｍ／Ｈｒの速度で引き下げ、結晶化を行った。融液の全てが結晶化を完了したら、室温まで徐々に降下させた。
【０１５４】
［加工工程３］
取り出したインゴットから円盤状に素材を切り出し、熱処理炉でアニールを行った。
【０１５５】
［測定］
また、インゴットの残りの部分から、透過率測定用試料として、図５に示す位置のフッ化カルシウム単結晶の小片を６個切り出し、測定用サンプルとして直径３０ｍｍ、厚さ１０ｍｍに加工した。サンプルの紫外域および真空紫外域の透過率、１０ｍＪ／ｃｍ^２／ｐｕｌｓｅのＦ２レーザーを１×１０^５パルス照射後の真空紫外域の透過率を分光光度計を用いて測定したところ、表４のとおりであった。
【０１５６】
このフッ化物結晶はインゴット内に透過率・Ｆ^２レーザー耐性の分布が大きく、光リソグラフィー用光学部材としては、一部から少量を採取できるのみであった。
【０１５７】
【表４】

【０１５８】
【発明の効果】
以上詳述の通り、請求項１乃至３に記載の発明によれば、フッ化物の原料にフッ素含有ガスを接触させることにより、フッ化物の原料の表面に吸着された不純物をフッ素で置換するフッ素置換工程と、このフッ素置換工程の後、原料の表面に再度不純物が吸着される以前に、原料をスカベンジャと反応させるとともに溶融及び固化することにより結晶を形成する結晶化工程とを有するので、結晶化工程でフッ化物の原料を溶融させる前に、フッ素置換工程で原料の表面に吸着されている不純物を除去するため、表面に存在する不純物が内部に混入しにくく、不純物の除去が容易である。
【０１５９】
また、従来のように、表面から内部に混入された不純物を除去しようとすると、フッ化物を溶融させるのに大きな熱量を必要とするのに対し、この発明では別工程でまず表面のみの不純物を除去するようにしており、表面の不純物を除去する間はフッ化物を軟化或いは溶融する必要がないため、不純物を除去するために必要な熱量を従来に比べて大幅に少なくすることができる。しかも、結晶化工程では、スカベンジャにより原料の内部に存在する不純物だけを除去すればよく、内部に存在する不純物を除去し易い。そのため、優れた内部透過率を有するフッ化物結晶を製造し易い。
【０１６０】
また、請求項４に記載の発明によれば、精製減容化工程で形成された結晶バルクを用いて単結晶の育成を行うので、原料として粉末を用いていても、精製減容化工程により、原料粉末より体積を大幅に小さくしてから単結晶育成工程を行うことができ、製造に使用する装置やルツボの小型化を図り易く、大きなインゴットを製造し易い。
【０１６１】
更に、請求項５に記載の発明によれば、フッ素置換工程の処理温度より高い温度で、原料とスカベンジャとを結晶化工程で反応させるので、原料表面に吸着された不純物を除去する間、より確実に低い温度にすることができ、原料の不純物を除去するために必要な熱量をより確実に少なくすることができる。
【０１６２】
また、請求項６乃至１０に記載の発明によれば、各種のフッ素含有ガスを用いてフッ化物の原料の不純物をフッ素置換することができるので、より、容易に優れた内部透過率を有するフッ化物結晶が得られる。
【０１６３】
更に、請求項１１乃至１５に記載のフッ化物結晶によれば、紫外および真空紫外域において透過率・レーザー耐性の高いフッ化物結晶を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態のフッ化物結晶の製造方法を示すフローチャートである。
【図２】本発明の実施の形態のフッ化物結晶の製造方法に使用する表面処理炉の概略断面図である。
【図３】本発明の実施の形態のフッ化物結晶の製造方法に使用する前処理炉の概略断面図である。
【図４】本発明の実施の形態のフッ化物結晶の製造方法に使用する単結晶育成炉の概略断面図である。
【図５】実施例で製造したインゴットの縦断面図である。
【図６】従来の製造方法によるフッ化物結晶の製造方法を示すフローチャートである。
【符号の説明】
１０ 前処理炉
１１、２１、３１ 真空容器
１６、２６、３６ ルツボ
２０ 単結晶育成炉
３０ 表面処理炉[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ArF excimer laser or F₂A method for producing a fluoride crystal that can be suitably used in an optical system used for light having a wavelength in the ultraviolet or vacuum ultraviolet region, such as a photolithography apparatus using a laser, and a fluoride crystal obtained by using the same. Related devices.
[0002]
[Prior art]
In recent years, VLSIs have become highly integrated and highly functional, and fine processing technology on wafers has been required. As a processing method, a method using optical lithography has been used. The projection lens of the exposure apparatus, which is the key to this optical lithography technique, is required to have high imaging performance (resolution and depth of focus).
[0003]
Resolution and depth of focus are determined by the wavelength of light used for exposure and the NA (numerical aperture) of the lens. When the exposure wavelength λ is the same, the angle of the diffracted light becomes larger as the pattern becomes finer, so that the diffracted light cannot be taken unless the NA of the lens is large. Further, the shorter the exposure wavelength λ, the smaller the angle of the diffracted light in the same pattern, and thus the smaller the NA of the lens.
[0004]
The resolution and the depth of focus are expressed by the following equations.
[0005]
Resolution = k₁・ Λ / NA
Depth of focus = k₂・ Λ / (NA)²
(K₁, K₂Is a proportionality constant. )
From the above formula, in order to improve the resolution, it is only necessary to increase the lens diameter and increase the NA of the lens or shorten the exposure wavelength λ, and it is more advantageous to shorten λ in terms of the depth of focus. You can see that.
[0006]
In terms of shortening the wavelength of light, the exposure wavelength is becoming shorter and shorter, and an exposure apparatus using a KrF excimer laser light (wavelength 248 nm) or an ArF excimer laser light (wavelength 193 nm) as a light source has appeared on the market. . Very few optical materials can be used for photolithography at wavelengths below 250 nm, and most optical systems are designed with two types of materials: fluoride crystals and quartz glass.
[0007]
Further, the wavelength is further shortened and F₂Optical lithography using laser light (wavelength: 157 nm) is also in practical use. At this wavelength, it is considered difficult to use quartz glass anymore, and the usable materials are limited to some fluoride crystals such as strontium fluoride, barium fluoride and lithium fluoride in addition to calcium fluoride.
[0008]
Conventionally, the Bridgman method is generally performed as a method for producing a fluoride crystal. In some cases, fluoride crystals are grown by the usual Bridgman method and cut directly from the ingot to the target material size.However, after cutting the ingot into multiple blocks, a heat treatment step is added, and birefringence and refractive index are added. In some cases, internal quality such as homogeneity is improved.
[0009]
As an example, a method for producing a conventional calcium fluoride crystal by the Bridgman method (Stockberger method, crucible descent method) will be described. Note that other fluoride crystals can be manufactured in the same manner. FIG. 6 shows a conventional manufacturing process.
[0010]
In the case of calcium fluoride crystals used in the ultraviolet region or vacuum ultraviolet region, natural calcium fluoride is not used as a raw material, and it is common to use a high-purity powder raw material produced by chemical synthesis. is there.
[0011]
Here, in the pretreatment step 1, impurities contained in the raw material are removed by reacting the raw material with a fluorinated material called a scavenger at a temperature not lower than the melting point. At the same time, once melted and then solidified to form a polycrystalline bulk, the volume can be reduced by a factor of 2 to 3 compared to the original powder raw material, It is possible to increase the filling amount in the growth furnace.
[0012]
In Patent Document 1, the use of a scavenger causes contamination caused by the scavenger, so that a powder raw material capable of reducing the amount of the scavenger to be added is manufactured. Here, impurities such as oxides and carbon taken in the powder raw material are removed by a secondary treatment with a highly oxidizing fluorine gas.
[0013]
Next, the polycrystalline bulk obtained in the pretreatment step 1 is filled in a crucible of a growth apparatus, and a single crystal growth step as an intermediate treatment step 2 is performed. 10 in the growing device^-3-10^-4The temperature in the growing apparatus is maintained at a degree of vacuum of Pa or higher, and the raw material in the crucible is melted by raising the temperature in the growing apparatus to the melting point of calcium fluoride or higher. At this time, in order to minimize temporal fluctuations in the temperature inside the growing apparatus, control using a constant power output or highly accurate PID control is performed.
[0014]
Then, by lowering the crucible at a speed of about 0.1 to 5 mm / hour, the crystal is gradually crystallized from the lower part of the crucible. When the crystal is crystallized to the uppermost part of the melt, the crystal growth is completed, and simple slow cooling is performed avoiding rapid cooling so that the grown crystal (ingot) is not broken. When the temperature in the growing device has dropped to about room temperature, the device is opened to the atmosphere and the ingot is taken out.
[0015]
In the case of calcium fluoride used for small-sized optical parts and window materials that do not require homogeneity, in the processing step as post-processing step 3, after cutting the ingot, round it to a final product, etc. Processed. On the other hand, in the case of a calcium fluoride single crystal that is used for a projection lens of an optical lithography apparatus and requires high homogeneity, a simple heat treatment is performed in an ingot. Then, after being cut into an appropriate size for each target product in the processing step 3, further heat treatment is performed.
[0016]
A material satisfying desired performance among the thus obtained fluoride single crystal materials has been used as an optical member for an optical lithography apparatus.
[0017]
By the way, the optical system of the optical lithography apparatus has the highest resolution, the number of lenses is large for correcting various wavefront aberrations, and the optical path length is long. Therefore, if the optical material used in the optical system of the optical lithography apparatus absorbs even a small amount, the effect of a decrease in the amount of light becomes large in the entire optical system, and the illuminance on the wafer surface becomes insufficient. For example, with an optical path length of 1 m, even if the transmission loss is 0.5% / cm, the light intensity finally becomes 0.995.¹⁰⁰= 0.606, that is, 61%. Therefore, as for the optical member to be used, the internal transmittance is better as close to 100% / cm. Therefore, Patent Literature 2 below discloses an optical lithography apparatus including a calcium fluoride crystal having a wavelength of 185 nm or less and an internal transmittance of 99.5% / cm or more.
[0018]
Further, Patent Document 3 below discloses a method of measuring transmittance and a method of selecting a material from the transmittance. In the conventional manufacturing method, there is a distribution of transmittance in the ingot of the fluoride crystal, and in order to obtain a high transmittance, a part of the ingot must be selected and used. Understand from. At this time, if the required amount of the fluoride crystal is small, it is possible to sort, but F is expected to be mass-produced in the future.₂In a lithography apparatus using laser light, the wavelength of the light used is as short as 157 nm, and only a part of fluoride crystals such as calcium fluoride and barium fluoride can be considered as a material.₂It is said that the weight of a fluoride crystal required for a lithography apparatus is enormous, several tens kg to several hundred kg. In the method of selecting a portion having high transmittance, the yield is poor,₂Fluoride crystals for lithography are expensive, and₂The price of the lithography apparatus itself is also very expensive.
[0019]
On the other hand, in order to improve the internal transmittance of the fluoride crystal to the utmost or to improve the yield, it is conceivable to reduce impurities mixed in the manufacturing process.
[0020]
For example, Patent Documents 4 and 5 below propose that the purification step of a fluoride raw material and the single crystal growing step are performed in the same container.
[0021]
[Patent Document 1]
JP-A-2002-241196.
[0022]
[Patent Document 2]
JP-A-2000-227400.
[0023]
[Patent Document 3]
JP-A-2002-286913.
[0024]
[Patent Document 4]
JP-A-2001-240497.
[0025]
[Patent Document 5]
JP-A-2003-2789.
[0026]
[Problems to be solved by the invention]
However, as described above, since the optical characteristics with respect to the short-wavelength laser light are also deteriorated by a trace amount of impurities in the fluoride crystal, even a trace amount of impurities mixed in the manufacturing process must be reduced. No. However, the amount of impurities is extremely small, and it is not easy to further reduce the amount.
[0027]
Therefore, in Patent Literatures 4 and 5, by performing the two steps in the same container, the chance of contamination is reduced. However, in Patent Document 4, since the raw material powder is significantly larger in volume than a crystal having the same weight, there is a problem that a container such as a manufacturing apparatus and a crucible becomes significantly larger than the obtained crystal.
[0028]
More specifically, even if the crucible is filled with the powdered raw material, the crystal finally obtained is about half the size of the crucible, and the polycrystalline bulk formed in the pretreatment process is refilled into the growth crucible. Compared to the method, the productivity for the crucible volume is halved. In recent years, the size of fluorite for lithography has continued to expand, and the required diameter exceeds 250 mm at the maximum. In the case where the pretreatment step and the single crystal growth are performed in the same container, a huge crucible and a single crystal growth furnace are newly required to obtain fluorite having a diameter exceeding 250 mm with high productivity. Therefore, it was extremely difficult to produce large fluoride crystals.
[0029]
Therefore, the present invention proposes a method of manufacturing a fluoride crystal that can reduce the amount of impurities mixed during the manufacturing process and can easily manufacture a fluoride crystal having excellent internal transmittance. Another object of the present invention is to provide a fluoride crystal having excellent optical characteristics and an apparatus using the same.
[0030]
[Means for Solving the Problems]
The present inventor has conducted intensive studies and studies. As a result, when impurities such as oxygen and moisture are adsorbed on the surface of the raw material of fluoride in the storage stage of the raw material and intermediate, this is the ultraviolet / vacuum ultraviolet of the fluoride single crystal. It has been found that it greatly affects the transmittance of the region.
[0031]
That is, the raw material immediately after synthesis has high purity and its surface is clean. For example, as described in Patent Document 1, a raw material subjected to a secondary treatment with fluorine gas has a very high purity. However, even in the case of such a raw material, if very little impurity such as oxygen or moisture is present around the raw material in the storage stage, the impurity is adsorbed by the raw material, and the raw material is oxidized or oxidized during crystal growth. It remains as an impurity in the product and remains in the fluoride crystal material as the final product, causing the initial transmittance to decrease. Particularly, when the raw material is a powder, the surface area is large, so that impurities are easily adsorbed.
[0032]
Therefore, in the present invention, the above object is achieved by replacing the surface of the fluoride with fluorine before melting to remove impurities adsorbed on the fluoride surface without melting the fluoride.
[0033]
That is, the invention according to claim 1 includes a fluorine-substituting step of contacting a fluorine-containing gas with a fluorine-containing material to replace impurities adsorbed on the surface of the fluoride-containing material with fluorine. After the step, before the impurities are again adsorbed on the surface of the raw material, a crystallization step of forming a crystal by reacting the fluorine-substituted raw material with a scavenger and melting and solidifying the raw material. I do.
[0034]
Further, in the invention according to claim 2, in addition to the configuration according to claim 1, the raw material of the fluoride in the fluorine substitution step is a powder, and the crystallization step is substituted in the fluorine substitution step. The method is characterized in that it is a purification and volume reduction step of forming a crystal bulk by reacting the raw material powder with a scavenger and melting and solidifying the raw material powder.
[0035]
Further, in the invention according to claim 3, in addition to the configuration according to claim 1, the raw material of the fluoride in the fluorine substitution step is a crystal bulk, and the crystallization step is replaced in the fluorine substitution step. A single crystal growing step of growing a single crystal by causing the crystal bulk of the fluoride to react with a scavenger and melting and solidifying the single crystal.
According to a fourth aspect of the present invention, in addition to the configuration of the second aspect, by contacting the fluorine-containing gas with the crystal bulk formed in the purification and volume reduction step, the crystal bulk is reduced. A bulk fluorine replacement step of replacing impurities adsorbed on the surface with fluorine, and a single crystal growth step of growing a single crystal by melting and solidifying the crystal bulk, after the bulk fluorine replacement step, The single crystal growing step is performed before the impurities are again adsorbed on the surface of the crystal bulk.
[0036]
Further, in the invention according to claim 5, in addition to the configuration according to any one of claims 1 to 4, the raw material and the scavenger are crystallized at a temperature higher than a processing temperature of the fluorine substitution step. It is characterized by reacting in the process.
[0037]
According to a sixth aspect of the present invention, in addition to the configuration of any one of the first to fifth aspects, the fluorine-containing gas is a gas having fluorine as a molecular constituent element. .
[0038]
Furthermore, the invention according to claim 7 is a substance according to any one of claims 1 to 5, wherein the fluorine-containing gas has fluorine as a constituent element of a molecule and exists as a liquid at room temperature. And a gas generated by heating and / or decompression.
[0039]
The invention according to claim 8 is a liquid crystal display device according to any one of claims 1 to 5, wherein the fluorine-containing gas has fluorine as a molecular constituent element and exists as a solid at room temperature. , Characterized by being generated by heating and / or reduced pressure.
[0040]
Further, the invention according to a ninth aspect is characterized in that, in addition to the configuration according to any one of the first to eighth aspects, the fluorine-containing gas is a fluorine gas.
[0041]
According to a tenth aspect of the present invention, in addition to the configuration of the ninth aspect, the fluorine-containing gas is a mixed gas of the fluorine gas and an inert gas.
[0042]
Further, an invention according to claim 11 is a fluoride crystal produced by the production method according to any one of claims 1 to 10, wherein the internal transmittance at a wavelength of 190 nm or more and 250 nm or less is 99.8. % / Cm or more.
[0043]
According to a twelfth aspect of the present invention, there is provided a fluoride crystal manufactured by the manufacturing method according to any one of the first to tenth aspects, wherein the internal transmittance at a wavelength of 150 nm or more and less than 190 nm is 99.5. % / Cm or more.
[0044]
Furthermore, an invention according to claim 13 is a fluoride crystal produced by the production method according to any one of claims 1 to 10, wherein a pulsed laser having a wavelength of any of 150 nm to 250 nm is used. 10mJ / cm²/ Pulse intensity, 1 × 10⁵It is characterized in that the amount of decrease in transmittance after pulse irradiation is 0.5% / cm or less.
[0045]
Further, an invention according to claim 14 is a fluoride crystal produced by the production method according to any one of claims 1 to 10, wherein a plurality of positions inside the ingot at a wavelength of 190 nm or less are used. The difference in internal transmittance is 0.3% / cm or less.
[0046]
Further, the invention according to claim 15 is a fluoride crystal material cut out from the fluoride crystal produced by the production method according to any one of claims 1 to 10, wherein a plurality of positions inside the material are provided. Wherein the difference in internal transmittance at a wavelength of 190 nm or less is 0.3% / cm or less.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0048]
1 to 4 show a manufacturing process and a manufacturing apparatus according to this embodiment.
[0049]
In this embodiment, in order to produce a fluoride crystal, as shown in FIG. 1, a raw material powder of fluoride is substituted with fluorine in a fluorine substitution step 5, and then, in a purification and volume reduction step 6 as a crystallization step, a large amount of fluoride powder is produced. A crystal bulk is formed, and then the polycrystalline bulk is substituted with fluorine in a fluorine substitution step 7, and an ingot is formed in a single crystal growing step 8 as a crystallization step. It is manufactured by forming a material.
[0050]
In such a production method, as a fluoride raw material powder to be used, when producing a fluoride crystal used in the ultraviolet and vacuum ultraviolet regions, calcium fluoride, strontium fluoride, barium fluoride obtained by chemical synthesis, A high-purity raw material powder of a fluoride such as lithium fluoride is generally used.
[0051]
First, in the fluorine substitution step 5, impurities such as oxygen and moisture adsorbed on the surface of the raw material powder are replaced with fluorine by bringing a surface of the raw material powder into contact with a fluorine-containing gas.
[0052]
The surface of the raw material powder is not flat, and many small holes are present on the surface. In addition, since the surface itself is in a rough state, the surface area is very large, and oxygen and moisture are adsorbed on the surface. When crystal growth is performed using such a fluoride raw material powder as it is, oxygen remains in the fluoride crystal, resulting in low transmittance in the ultraviolet and vacuum ultraviolet regions. Therefore, by contacting a highly reactive fluorine-containing gas with the raw material powder, impurities such as oxygen molecules and water molecules adsorbed on the surface of the raw material powder are replaced with fluorine-containing gas molecules and removed.
[0053]
This fluorine substitution step 5 can be performed using a surface treatment furnace 30 as shown in FIG.
[0054]
The surface treatment furnace 30 includes a vacuum vessel 31. An exhaust port 32 to which a vacuum pump or the like is connected is connected to the vacuum vessel 31, and a fluorine-containing gas introduction port 33 capable of introducing a fluorine-containing gas is connected to the vacuum vessel 31. I have. Inside the vacuum vessel 31, a crucible 36 for filling the raw material powder is disposed in a space surrounded by the heat insulating material 34 and capable of being heated by the heater 35.
[0055]
In order to perform the fluorine substitution step 5 of the raw material using such a surface treatment furnace 30, first, the raw material powder is filled in a clean carbon crucible 36. This container is set in the surface treatment furnace 30, and the inside is evacuated. When the degree of vacuum is stabilized, a fluorine-containing gas is introduced into the inside from the fluorine-containing gas inlet 33. When the introduction of the fluorine-containing gas is completed, heating is performed, the temperature is raised to a processing temperature corresponding to the fluorine-containing gas, and the temperature is maintained at a constant temperature, thereby replacing the impurities adsorbed on the surface of the raw material powder with fluorine. I do.
[0056]
Here, as the fluorine-containing gas, F₂Gas itself, F₂A mixed gas obtained by mixing an inert gas with low reactivity such as Ar or He with a gas, NF₃, CF₄, C₂F₆, C₂F₄, ClF₃, SF₆, WF₆For example, a gas having fluorine as one of the constituent elements can be used. Of these, NF₃, CF₄Is preferred because it is easy to handle.₂A mixed gas of a gas and an inert gas is preferred because of its high reactivity at low temperatures.
[0057]
Note that a gas generated by vaporizing or decomposing a solid or liquid having fluorine as one of the constituent elements together with or in place of this gas, or a gas obtained by mixing a plurality of these gases can be used. .
[0058]
Here, as a solid having fluorine as one of the constituent elements, for example, AgF, CuF₂, AlF₃, FeF₂, MnF₂, PbF₂, ZnF₂, PTFE and the like, which are solid at normal temperature and pressure. Among them, it is preferable to use AgF, PTFE, or the like because the vaporization temperature is low.
[0059]
Examples of the liquid having fluorine as one of the constituent elements include a fluorine-containing substance that becomes liquid at normal temperature and normal pressure, such as hydrofluoric acid.
[0060]
When using these solids or liquids, a gas generator capable of controlling the temperature or the like and controlling the vaporization or decomposition of the fluorine-containing solids or liquids is provided outside the surface treatment furnace 30 so that the generated gas contains fluorine. The gas may be introduced from the gas inlet 33, or a gas may be generated inside by installing the above-described solid or liquid inside the vacuum vessel 31. Further, when the vaporization or decomposition temperature of the solid or liquid having a fluorine atom is as low as room temperature to about 300 ° C., a place for filling the corresponding solid or liquid in a furnace is provided, At the same time, only the relevant solid or liquid may be placed in the furnace.
[0061]
The processing temperature in the fluorine substitution step 5 does not need to be as high as in the conventional purification treatment using a scavenger. The heating in this step is not for the purpose of melting the raw material powder, but for promoting the substitution reaction of the impurities adsorbed on the surface of the raw material powder with fluorine. Therefore, it is not necessary to raise the temperature above the melting point of the fluoride crystal, which can be as high as 1000 ° C. or more.
[0062]
It is preferable that the fluorine treatment temperature be increased in order to increase the reactivity.₂Gas or F₂When a mixed gas of a gas and an inert gas is used, it is rich in reactivity, and therefore, it is preferably set to about 100 to 300 ° C. in consideration of furnace durability. In addition, as a fluorine-containing gas, relatively stable CF₄When NF is used, NF is about 700 to 800 ° C.₃In the case where is used, the temperature is preferably about 300 to 400 ° C.
[0063]
In addition, the fluorine substitution step 5 is performed by introducing the above-mentioned fluorine-containing gas into the vacuum vessel 31, and the pressure of the fluorine-containing gas in the vacuum vessel 31 is preferably 100 to 10000 Pa.
[0064]
Next, in the purification and volume reduction step 6, a scavenger, which is a fluorinating agent, is added to the fluorine-substituted raw material powder to react with impurities contained therein, and melt and solidify to obtain polycrystal. Form the bulk.
[0065]
The raw material powder usually contains an oxide with impurities mixed therein. Further, the oxide powder is often mixed as an impurity in the fluoride raw material powder. For this reason, in the case of the raw material powder in which the impurities on the surface are simply replaced in the fluorine replacement step 6, even if the single crystal is grown as it is, the obtained fluoride single crystal is colored due to the influence of the mixed impurities, It cannot be used as an optical member in the ultraviolet and vacuum ultraviolet regions. For this reason, in the purification and volume reduction step 6, the raw material powder is softened or melted, impurities such as oxides contained therein are reacted by a scavenger, and the raw material powder is converted into fluoride or the like to remove the powder. Is also highly purified.
[0066]
In the purification and volume reduction step 6, the powder raw material is melted and solidified,
A powder having a significantly higher volume per weight is made into a polycrystalline bulk having a lower volume per weight.
[0067]
For example, when forming a large ingot, a large amount of fluoride raw material is required. However, if this powder is used as it is, its volume becomes extremely large, and it cannot be manufactured unless a huge apparatus or crucible is used. Therefore, if a crystal bulk having a small volume is formed in the purification and volume reduction step 6, even when a large ingot is formed, it can be manufactured using a small apparatus or a crucible.
[0068]
This purification and volume reduction step 6 can be performed by a pretreatment furnace 10 as shown in FIG.
[0069]
The pretreatment furnace 10 includes a vacuum vessel 11, and an exhaust port 12 to which a vacuum pump or the like is connected is connected to the vacuum vessel 11. A crucible 16 for filling the raw material powder after the surface treatment is arranged in a space surrounded by the heat insulating material 14 and capable of being heated by the heater 15 inside the vacuum vessel 11. When gas is used as the scavenger, the gas inlet 13 is connected.
[0070]
First, a scavenger is added to the raw material powder whose surface has been replaced with fluorine, and the raw material powder is filled in a crucible 16 and placed in the pretreatment furnace 10.
[0071]
Next, the temperature is increased at a slow speed to a temperature higher than the processing temperature of the fluorine substitution step 5. Preferably, the scavenger is allowed to reach the boiling point over a sufficient time. This is because if the heating time is lengthened, the fluoride raw material and the scavenger can be sufficiently reacted at a temperature between the melting point and the boiling point of the scavenger.
[0072]
Thereafter, the temperature is raised to a temperature equal to or higher than the melting point of the fluoride to cause melting, and then the temperature is lowered to solidify the melt. In this way, a polycrystalline bulk of the fluoride is obtained in which the impurities are sufficiently removed and the volume is reduced.
[0073]
Here, the scavenger is an additive substance having an action of removing by reacting with impurities contained in the raw material powder, for example, metal fluoride such as lead fluoride, zinc fluoride, silver fluoride, and copper fluoride. Fluoride, organic compound of fluoride such as PTFE (polytetrafluoroethylene), CF₄, NF₃Gaseous fluoride such as F₂Mixed gas of gas and inert gas, F₂Gas itself or the like can be used.
[0074]
Here, as the element constituting the molecule used in the fluorine substitution step 5, the same substance as the substance having fluorine may be used, but it is preferable to use a solid or liquid substance. If a scavenger made of a solid or a liquid is used, it is not necessary to provide a facility for high-pressure gas in the pretreatment furnace 10, and handling is easier than a scavenger made of a gas.
[0075]
In the present invention, the purification and volume reduction step 6 is performed continuously after the fluorine substitution step 5 of the raw material powder. In other words, it is necessary to perform the step after the fluorine substitution step 5 and before the impurities such as oxygen and moisture existing in the atmosphere are adsorbed again due to leakage or the like on the surface of the raw material powder. Specifically, in this case, it is preferable to perform the purification and volume reduction step 6 within one day after the fluorine substitution step 5. The time before the impurity is re-adsorbed is within one day, but it is preferable that the amount of the impurity is appropriately selected because the amount of the impurity changes depending on storage conditions and the like.
[0076]
In order to continuously perform the fluorine substitution step 5 and the purification volume reduction step 6, after the surface of the raw material powder is substituted with fluorine, the raw material powder is taken out of the surface treatment furnace 30, mixed with a scavenger, and then melted in the pretreatment furnace 10. Alternatively, after the fluorine substitution step 5, the raw material powder can be continuously melted.
[0077]
In this case, for example, by providing the gas inlet 13 in the pretreatment furnace 10, it can be used as both a surface treatment furnace and a pretreatment furnace. The scavenger is introduced at a temperature of, or the scavenger is mixed with a commercially available raw material powder in advance, and after performing the fluorine substitution step 5 at a low temperature, the temperature is raised continuously to cause a reaction with the scavenger, thereby further melting the raw material. However, the effect of the present invention can be sufficiently obtained.
[0078]
Since the polycrystalline bulk obtained in this manner has a sufficiently reduced amount of impurities, it can be used as a fluoride raw material for forming a high-purity ingot.
[0079]
Therefore, in this embodiment, an ingot of a high-purity fluoride crystal is prepared using the polycrystalline bulk obtained in the purification and volume reduction step 6.
[0080]
In addition, as a raw material for forming an ingot, other than the polycrystalline bulk obtained in the fluorine substitution step 5 and the purification and volume reduction step 6, any other material can be used as appropriate. It is also possible to use a crystal bulk or a single crystal bulk.
[0081]
To form an ingot, first, in a fluorine substitution step 7, a fluorine-containing gas is brought into contact with the polycrystalline bulk to remove impurities such as oxygen and moisture adsorbed on the surface in the same manner as in the fluorine substitution step 5. Replace.
[0082]
The polycrystalline bulk obtained from the purification and volume reduction step 6 is sufficiently free of impurities, and its surface area is much smaller than that of the raw material powder of the same weight. However, when forming a large ingot, since a plurality of polycrystalline bulks are usually used, some polycrystalline bulks are often stored for a long time until a required number of bulks are created. Then, a small amount of impurities in the atmosphere are adsorbed again. This re-adsorbed impurity is trace, but if it remains during crystal growth, it causes a decrease in the transmittance of the fluoride single crystal in the ultraviolet and vacuum ultraviolet regions.
[0083]
Therefore, when an ingot is continuously formed after the purification and volume reduction step 6, the fluorine substitution step 7 is unnecessary.
[0084]
This fluorine substitution step 7 can be performed by a surface treatment furnace 30 having the same configuration as that of FIG.
[0085]
In order to perform the polycrystalline bulk fluorine substitution step 7 using the surface treatment furnace 30, similarly to the fluorine substitution step 5, first, one or more polycrystal bulks are filled in a clean crucible 36, and the surface treatment furnace 30 is charged. Set inside and evacuate the inside. When the degree of vacuum is stabilized, a fluorine-containing gas is introduced into the inside.
[0086]
As the fluorine-containing gas, a gas, a liquid or a solid having fluorine as the same molecular configuration as that used for the fluorine substitution of the raw material powder can be used. When a liquid or a solid having fluorine as a constituent element of a molecule is used, a gas can be generated and used in the same manner as described above.
[0087]
When the introduction of the fluorine-containing gas is completed, heating is performed and the temperature is maintained at a constant temperature to replace the impurities adsorbed on the surface of the polycrystalline bulk with fluorine. This heating is not for raising the temperature for the purpose of melting the polycrystalline bulk, but for heating the fluorine substitution reaction on the surface of the polycrystalline bulk. Therefore, it is not necessary to raise the fluorination temperature at this time to a temperature higher than the melting point of the fluoride crystal, which can be as high as 1000 ° C. or higher. The temperature may be lower than the temperature at which the raw material powder is melted.₂Gas or F₂When a mixed gas of a gas and an inert gas is used, the mixture is highly reactive. Therefore, the temperature is preferably set to about 100 to 300 ° C. in consideration of furnace durability. Further, as a fluorine-containing gas, relatively stable CF₄When NF is used, NF is about 700 to 800 ° C.₃In the case where is used, the temperature is preferably about 300 to 400 ° C.
[0088]
Next, the single crystal growing step 8 is performed by the single crystal growing furnace 20 using the polycrystalline bulk thus substituted with fluorine.
[0089]
The single crystal growing furnace 20 includes a vacuum vessel 21, and an exhaust port 22 to which a vacuum pump or the like is connected is connected to the vacuum vessel 21. Inside the vacuum vessel 21, a crucible 26 for filling the polycrystalline bulk is provided in a space surrounded by the heat insulating material 24 and provided with the heater 25, and the crucible 26 can be lowered by a pull-down rod 27. I have.
In a space surrounded by the heat insulating material 24, the heater 25 is configured to form a temperature gradient in which the upper part has a high temperature and the lower part has a low temperature.
[0090]
In the single crystal growing step 8, when the fluorine replacing step 7 is performed, the single crystal growing step 8 exists continuously after the fluorine replacing step 7, that is, in the atmosphere due to leakage or the like on the surface of the polycrystalline bulk of the raw material. It must be performed before impurities such as oxygen and moisture are re-adsorbed. Specifically, for example, it is preferable to perform the purification and volume reduction step 6 within one day after the fluorine substitution step 7.
[0091]
In order to perform the fluorine substitution step 7 and the single crystal growing step 8 continuously, after replacing the surface of the polycrystalline bulk with fluorine, the polycrystalline bulk is taken out from the crucible 36 of the surface treatment furnace 30 and charged into the crucible 26 of the single crystal growing furnace 20. Alternatively, the surface of the polycrystalline bulk may be replaced with fluorine, and subsequently, the temperature may be raised to melt.
In that case, for example, by providing the gas inlet 23 in the single crystal growing furnace 20, it can be used as a surface treatment furnace and a single crystal growing furnace.
[0092]
In order to perform the single crystal growing step 8 using the single crystal growing furnace 20 as shown in FIG. 4, first, a polycrystalline bulk is filled in a clean carbon crucible 26 and placed in the single crystal growing furnace 20. Then, after the inside of the single crystal growing furnace 20 is evacuated, heating is started. When the temperature reaches or exceeds the melting point of the fluoride to be produced, the state is maintained for a certain period of time in order to homogenize the melt. When the melt is sufficiently uniform, in the case of the vertical Bridgman method, the crucible is lowered by the pull-down rod 27 while controlling the speed, and a single crystal is gradually grown from the lower part of the ingot.
[0093]
When the growth of the single crystal is completed, a simple heat treatment is performed in the single crystal growing furnace 20 to take out the ingot. The ingot thus obtained is desirably a complete single crystal, but any ingot that can be used substantially as a single crystal may be used.
[0094]
Then, the ingot is taken out, and since the residual stress is large as it is, in processing step 3, the ingot is cut into a disk shape and annealed to obtain a fluoride crystal material having desired performance.
[0095]
When the fluoride is manufactured as described above, in the purification volume reduction step 6 and the single crystal growing step 8, the fluoride raw material powder is adsorbed on the surface of the raw material powder in the fluorine substitution steps 5 and 7 before being melted. Therefore, impurities present on the surface are less likely to be mixed into the raw material powder. Therefore, impurities adsorbed on the surface can be easily removed.
[0096]
Also, during the fluorine substitution steps 5 and 7, that is, while removing impurities adsorbed on the surface, it is necessary to soften or melt the fluoride as in the purification volume reduction step 6 and the single crystal growing step 8. And can be processed at low temperatures. Therefore, the amount of heat required to remove impurities is significantly reduced as compared with the conventional method of removing all impurities adsorbed on the surface of the raw material powder and impurities mixed therein by using a scavenger. Can be.
[0097]
Moreover, in the purification and volume reduction step 6, only the impurities present inside the raw material need to be intensively reacted and removed by the scavenger, so that the impurities existing inside the raw material powder can be more reliably removed more easily.
[0098]
In addition, since the raw material powder is converted into a polycrystalline bulk in the purification and volume reduction step 6 and the single crystal growing step 8 is performed using the polycrystalline bulk, even if powder is used as the raw material, the volume is significantly reduced. A single crystal can be grown, the single crystal growing furnace 20 and the crucible 26 can be easily reduced in size, and a large ingot can be easily manufactured.
[0099]
Furthermore, the fluoride crystal thus produced has a very low impurity concentration, and thus has high transmittance and laser resistance in the ultraviolet and vacuum ultraviolet regions.
[0100]
A fluoride crystal material obtained by processing such a fluoride crystal, an optical system in which one or a plurality of such optical materials are arranged in an optical path, and an optical lithography apparatus having such an optical system are KrF Excimer laser light (wavelength 248 nm), ArF excimer laser light (wavelength 193 nm), F₂The absorption of short-wavelength light such as laser light (wavelength 157 nm) is small, and a decrease in light amount can be suppressed.
[0101]
In the above-described embodiment, an example in which the vertical Bridgman method is used in the single crystal growing step 2 has been described. However, another crystal such as a vertical temperature gradient method (VGF method) or a Czochralski method (CZ method) is used. It goes without saying that the effect can be obtained even when applied to the breeding method. In the following examples, a manufacturing method is also exemplified, but the present invention is not limited to the method.
[0102]
Furthermore, in the above-described embodiment, an example was described in which fluoride powder was used as a raw material and polycrystalline bulk was used as a crystal bulk, but these are not particularly limited, and polycrystalline or single crystal raw materials may be used. May be used, and it is also possible to use a single crystal fluoride for the crystal bulk.
[0103]
【Example】
Hereinafter, examples will be described.
[0104]
Example 1
A calcium fluoride single crystal was manufactured using a furnace as shown in FIGS.
[0105]
[Fluorine substitution step 5]
50 kg of a commercially available high-purity artificial synthetic calcium fluoride powder was filled in a baked and clean carbon crucible 36. The crucible 36 is set in the surface treatment furnace 30 as shown in FIG.^-4Evacuation was performed to Torr.
[0106]
5% F in vacuum vessel 31₂A + 95% Ar mixed gas was introduced, and the temperature was raised to 150 ° C. The temperature was kept at 150 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface was replaced with fluorine, and the surface was fluorinated.
[0107]
Thereafter, the internal temperature was lowered to room temperature. At this stage, the oxygen, moisture and the like adsorbed on the surface of the powder have been replaced by fluorine, and the amount of impurities brought to the next step has been significantly reduced.
[0108]
[Purification volume reduction step 6]
Subsequently, within one day, the purification and volume reduction step 6 was performed using the pretreatment furnace 10 as shown in FIG. 1.0 mol% of a lead fluoride powder as a scavenger was added to the powder whose surface had been replaced with fluorine, and the mixture was thoroughly stirred and uniformly mixed, and then charged into a baked and clean carbon crucible 16 having an inner diameter of 300 mm. . 10 inside the device^-6After evacuating to Torr, the temperature was gradually raised. It was kept at 1100 ° C. for 6 hours in order to sufficiently react the calcium fluoride raw material with lead fluoride as a scavenger.
[0109]
In this process, impurities contained in the raw material and calcium oxide mixed in the raw material can be removed.
[0110]
After the reaction with the scavenger was sufficiently advanced, the temperature was further raised and kept at 1420 ° C., which is the melting point of calcium fluoride, for 24 hours. In this process, the raw materials were melted and the melt was homogenized. Thereafter, the temperature was lowered to room temperature, and the raw materials were solidified to form a polycrystalline bulk.
[0111]
In this process, the volume of the calcium fluoride becomes small, and the crucible 26 of the next single crystal growing furnace 20 can be loaded with a sufficient weight of the raw material. Thus, the pretreatment step was completed to obtain a polycrystalline bulk.
[0112]
[Fluorine substitution step 7]
Next, the polycrystalline bulk of calcium fluoride formed in the pretreatment step was placed in a baked and clean carbon crucible 36. The crucible 36 is set in the surface treatment furnace 30 and the inside is cooled to 10 by an oil-free dry vacuum pump.^-4Evacuated to Torr. 5% F in vacuum vessel 31₂A + 95% Ar mixed gas was introduced, and the temperature was raised to 150 ° C. The temperature was kept at 150 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface was replaced with fluorine, and the polycrystalline bulk surface was fluorinated.
[0113]
Thereafter, the internal temperature was lowered to room temperature. At this stage, impurities such as oxygen and moisture adsorbed on the surface of the polycrystalline bulk have been replaced by fluorine, and the amount of impurities brought to the next step is extremely small.
[0114]
[Single crystal growing step 8]
Then, within one day, using a single crystal growing furnace 20 as shown in FIG. 4, a calcium fluoride crystal single crystal growing step 8 was performed by the vertical Bridgman method. The polycrystalline bulk whose surface was replaced with fluorine was stored as a raw material bulk in a baked and clean carbon crucible 26 having an inner diameter of 300 mm and placed in a baked single crystal growing furnace 20. 10^-6After evacuating to Torr, the heater was heated and the temperature was raised. The temperature was gradually raised while controlling the temperature. When the temperature reached 1420 ° C., the temperature was maintained for 24 hours to homogenize the melt. Next, the carbon crucible was pulled down at a speed of 1 mm / Hr to perform crystallization. When all of the melt had completed crystallization, it was allowed to cool slowly to room temperature.
[0115]
[Processing process 3]
The material was cut out in a disk shape from the taken out ingot and annealed in a heat treatment furnace.
[0116]
[Measurement]
From the remaining portion 40 of the ingot, as a sample for transmittance measurement, six small pieces A to F of calcium fluoride crystals at positions shown in the longitudinal sectional view of the ingot in FIG. 5 were cut out, and the diameter of the sample for measurement was 30 mm and the thickness was 30 mm. It was processed to 10 mm. Sample transmittance in the ultraviolet region and vacuum ultraviolet region, 10 mJ / cm²/ Pulse F2 laser 1 × 10⁵The transmittance in the vacuum ultraviolet region after the pulse irradiation was measured using a spectrophotometer, and the results are as shown in Table 1.
[0117]
This fluoride crystal has a transmittance / F over the entire area of the ingot.₂The material has high laser resistance and can be used as an optical member for photolithography.
[0118]
[Table 1]

[0119]
Example 2
First, a pretreatment step of reducing the volume of the raw material powder and removing impurities in the raw material powder is performed using a surface treatment furnace and a pretreatment furnace provided with a gas inlet 13 in the pretreatment furnace 10 shown in FIG. .
[0120]
[Fluorine substitution step 5]
50 kg of a commercially available high-purity artificial synthetic calcium fluoride powder was filled in a baked and clean carbon crucible 16 having an inner diameter of 300 mm. The crucible 16 is set in the pretreatment furnace 10 capable of continuously performing the surface replacement and the raw material melting, and the inside of the crucible is controlled by a vacuum pump.^-6Evacuation was performed to Torr.
[0121]
NF in the vacuum vessel 11₃Gas was introduced and the temperature was raised to 350 ° C. The temperature was kept at 350 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface is replaced with fluorine, and the surface is fluorinated.
[0122]
[Purification volume reduction step 6]
After this, 10^-6  After evacuating to Torr, the temperature was raised. When the temperature reached 1100 ° C., which is slightly lower than the melting point of calcium fluoride, the temperature was stopped, and NF was used as a scavenger.₃Gas was introduced.
[0123]
Raw materials and scavenger NF₃In order to sufficiently react with the gas, the temperature was maintained at 1100 ° C. for 12 hours. In this process, impurities contained in the raw material and calcium oxide mixed in the raw material can be removed.
[0124]
After the reaction with the scavenger was sufficiently advanced, the temperature was further raised and kept at 1420 ° C., which is the melting point of calcium fluoride, for 24 hours. In this process, the raw materials were melted and the melt was homogenized.
[0125]
Thereafter, the temperature was lowered to room temperature, and the raw material was solidified. In this process, the volume of calcium fluoride was reduced, and the crucible 26 of the single crystal growing furnace 20 could be loaded with a sufficient weight of the raw material. When the pretreatment step is completed in this way, a polycrystalline bulk raw material can be obtained.
[0126]
[Fluorine substitution step 7]
Next, the fluorine substitution step 7 and the single crystal growing step 8 are continuously performed using a surface treatment furnace and a single crystal growing furnace provided with the gas inlet 23 in the single crystal growing furnace 20 of FIG.
[0127]
First, a polycrystalline bulk of calcium fluoride formed in the pretreatment step was taken out and placed in a baked and clean carbon crucible 26 having an inner diameter of 300 mm. The crucible is set in a single crystal growing furnace 20 capable of continuously performing surface replacement and raw material melting, and the inside is cooled to 10 by a vacuum pump.^-6  The chamber was evacuated to Torr. NF in the vacuum vessel 21₃Was introduced, and the temperature was raised to 350 ° C. The temperature was kept at 350 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface was replaced with fluorine, and the surface was fluorinated.
[0128]
[Single crystal growing step 8]
After this, 10^-6  After evacuating to Torr, the temperature was raised. The temperature was gradually raised while controlling the temperature. When the temperature reached 1420 ° C., the temperature was maintained for 24 hours to homogenize the melt. Next, the carbon crucible was pulled down at a speed of 1 mm / Hr to perform crystallization. When all of the melt had completed crystallization, it was allowed to cool slowly to room temperature.
[0129]
[Processing process 3]
The material was cut out in a disk shape from the taken out ingot and annealed in a heat treatment furnace.
[0130]
[Measurement]
In addition, six small pieces of calcium fluoride single crystal at the positions shown in FIG. 5 were cut out from the remaining portion of the ingot as a sample for transmittance measurement, and processed into a sample for measurement to a diameter of 30 mm and a thickness of 10 mm. Sample transmittance in the ultraviolet region and vacuum ultraviolet region, 10 mJ / cm²/ Pulse F₂1 × 10 laser⁵The transmittance in the vacuum ultraviolet region after the pulse irradiation was measured using a spectrophotometer.
[0131]
This fluoride crystal has a transmittance / F over the entire area of the ingot.₂It has high laser resistance and can be used as an optical member for photolithography.
[0132]
[Table 2]

[0133]
Example 3
First, a pretreatment step of reducing the volume of the raw material powder and removing impurities in the raw material powder is performed using a surface treatment furnace and a pretreatment furnace provided with a gas inlet 13 in the pretreatment furnace 10 shown in FIG. .
[0134]
[Fluorine substitution step 5]
50 kg of a commercially available high-purity artificial synthetic calcium fluoride powder was filled in a baked and clean carbon crucible 16 having an inner diameter of 300 mm. The crucible 16 is set in a pretreatment furnace 10 capable of continuously performing surface replacement and raw material melting, and the inside of the crucible is controlled by a vacuum pump.^-6  Evacuation was performed to Torr.
[0135]
CF in the vacuum vessel 11₄Gas was introduced and the temperature was raised to 700 ° C. The temperature was maintained at 700 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface is replaced with fluorine, and the surface is fluorinated.
[0136]
[Purification volume reduction step]
After this, 10^-6  After evacuating to Torr, the temperature was raised. When the temperature reached 1100 ° C., which is slightly lower than the melting point of calcium fluoride, the temperature was stopped, and CF was used as a scavenger.₄Gas was introduced.
[0137]
Raw materials and scavenger CF₄In order to sufficiently react with the gas, the temperature was maintained at 1100 ° C. for 12 hours. In this process, impurities contained in the raw material and calcium oxide mixed in the raw material could be removed.
[0138]
After the reaction with the scavenger was sufficiently advanced, the temperature was further raised and kept at 1420 ° C., which is the melting point of calcium fluoride, for 24 hours. In this process, the raw materials were melted and the melt was homogenized. Thereafter, the temperature was lowered to room temperature, and the raw material was solidified. In this process, the volume of calcium fluoride is reduced, and the crucible 26 of the single crystal growing furnace 20 can be loaded with a sufficient weight of the raw material. When the pretreatment step was completed in this way, a polycrystalline bulk raw material could be obtained.
[0139]
[Fluorine substitution step 7]
Next, the fluorine substitution step 7 and the single crystal growing step 8 are continuously performed using a surface treatment furnace and a single crystal growing furnace provided with the gas inlet 23 in the single crystal growing furnace 20 of FIG.
[0140]
First, the polycrystalline bulk of calcium fluoride formed in the pretreatment step was taken out and placed in another baked and clean carbon crucible 26 having an inner diameter of 300 mm. The crucible is set in a single crystal growing furnace 20 capable of continuously performing surface replacement and raw material melting, and the inside is cooled to 10 by a vacuum pump.^-6  The chamber was evacuated to Torr. CF in the vacuum vessel 21₄Was introduced, and the temperature was raised to 700 ° C. The temperature was maintained at 700 ° C. for 5 hours. In this process, the oxygen adsorbed on the surface was replaced with fluorine, and the surface was fluorinated.
[0141]
[Single crystal growing step 8]
After this, 10^-6  After evacuating to Torr, the temperature was raised.
[0142]
The temperature was gradually raised while controlling the temperature. When the temperature reached 1420 ° C., the temperature was maintained for 24 hours to homogenize the melt. Next, the crucible 26 made of carbon was lowered at a speed of 1 mm / Hr to perform crystallization. When all of the melt had completed crystallization, it was allowed to cool slowly to room temperature.
[0143]
[Processing process 3]
The material was cut out in a disk shape from the taken out ingot and annealed in a heat treatment furnace.
[0144]
[Measurement]
In addition, six small pieces of calcium fluoride single crystal at the positions shown in FIG. 5 were cut out from the remaining portion of the ingot as a sample for transmittance measurement, and processed into a sample for measurement to a diameter of 30 mm and a thickness of 10 mm. Sample transmittance in the ultraviolet region and vacuum ultraviolet region, 10 mJ / cm²/ Pulse F₂1 × 10 laser⁵The transmittance in the vacuum ultraviolet region after the pulse irradiation was measured using a spectrophotometer.
[0145]
This fluoride crystal has a transmittance / F over the entire area of the ingot.²It has high laser resistance and can be used as an optical member for photolithography.
[0146]
[Table 3]

[0147]
Comparative example
As a comparative example, an example of manufacturing a fluoride single crystal by a conventional method is shown below.
[0148]
[Pretreatment step 1]
First, a pretreatment step of reducing the volume of the raw material powder and removing impurities in the raw material powder was performed.
[0149]
1 mol /% of a lead fluoride powder is mixed as a scavenger with 50 kg of a commercially available high-purity artificial synthetic calcium fluoride powder, and the mixture is thoroughly stirred and then baked into a clean pre-treated crucible made of carbon having an inner diameter of 300 mm. Filled. This crucible is set in a pretreatment furnace, and the inside is^-6  Evacuation was performed to Torr.
[0150]
Raw material and PbF scavenger₂Was kept at 1100 ° C. for 6 hours in order to cause a sufficient reaction between In this process, impurities contained in the raw material and calcium oxide mixed in the raw material can be removed.
[0151]
After the reaction with the scavenger was sufficiently advanced, the temperature was further raised and kept at 1420 ° C., which is the melting point of calcium fluoride, for 24 hours. In this process, the raw materials can be melted and the melt can be homogenized. Thereafter, the temperature was lowered to room temperature, and the raw material was solidified. In this process, the volume of calcium fluoride becomes small, and the growing crucible can be filled with a sufficient weight of the raw material. When the pretreatment step is completed in this way, a polycrystalline bulk raw material can be obtained.
[0152]
[Single crystal growing step 2]
Next, the polycrystalline bulk of calcium fluoride formed in the pretreatment step was taken out and placed in another baked and clean carbon growth crucible having an inner diameter of 300 mm. This crucible is set in a growth furnace, and the inside is^-6  The chamber was evacuated to Torr.
[0153]
The temperature was gradually raised while controlling the temperature. When the temperature reached 1420 ° C., the temperature was maintained for 24 hours to homogenize the melt. Next, the carbon crucible was pulled down at a speed of 1 mm / Hr to perform crystallization. When all of the melt had completed crystallization, it was allowed to cool slowly to room temperature.
[0154]
[Processing process 3]
The material was cut out in a disk shape from the taken out ingot and annealed in a heat treatment furnace.
[0155]
[Measurement]
In addition, six small pieces of calcium fluoride single crystal at the positions shown in FIG. 5 were cut out from the remaining portion of the ingot as a sample for transmittance measurement, and processed into a sample for measurement to a diameter of 30 mm and a thickness of 10 mm. Sample transmittance in the ultraviolet region and vacuum ultraviolet region, 10 mJ / cm²/ Pulse F2 laser 1 × 10⁵The transmittance in the vacuum ultraviolet region after the pulse irradiation was measured using a spectrophotometer.
[0156]
This fluoride crystal has a transmittance and F in the ingot.²The laser resistance distribution was large, and only a small amount could be collected from a part of the optical member for photolithography.
[0157]
[Table 4]

[0158]
【The invention's effect】
As described in detail above, according to the first to third aspects of the present invention, a fluorine-containing gas is brought into contact with a fluoride raw material to replace impurities adsorbed on the surface of the fluoride raw material with fluorine. Since the replacement step and the fluorine replacement step, before the impurities are again adsorbed on the surface of the raw material, the raw material has a crystallization step of forming a crystal by reacting and melting and solidifying the raw material with the scavenger. Before the fluoride raw material is melted in the chemical conversion step, the impurities adsorbed on the surface of the raw material are removed in the fluorine substitution step, so that impurities present on the surface are hardly mixed into the inside, and the impurities can be easily removed. .
[0159]
In addition, as in the conventional case, when trying to remove impurities mixed in from the surface, a large amount of heat is required to melt the fluoride. In contrast, in the present invention, impurities only on the surface are first removed in a separate step. Since the fluoride is not required to be softened or melted while the impurities on the surface are removed, the amount of heat required for removing the impurities can be significantly reduced as compared with the conventional case. Moreover, in the crystallization step, only the impurities existing inside the raw material need to be removed by the scavenger, and the impurities existing inside can be easily removed. Therefore, it is easy to produce a fluoride crystal having excellent internal transmittance.
[0160]
According to the invention of claim 4, since the single crystal is grown using the crystal bulk formed in the purification and volume reduction step, even if powder is used as a raw material, the single crystal is grown by the purification and volume reduction step. In addition, the single crystal growing step can be performed after significantly reducing the volume of the raw material powder, making it easy to reduce the size of the apparatus and crucible used for the manufacture and to manufacture a large ingot.
[0161]
Furthermore, according to the invention as set forth in claim 5, the raw material and the scavenger are reacted in the crystallization step at a temperature higher than the processing temperature of the fluorine substitution step, so that the impurities adsorbed on the raw material surface can be removed more. The temperature can be reliably lowered, and the amount of heat required to remove impurities in the raw material can be reduced more reliably.
[0162]
Further, according to the inventions set forth in claims 6 to 10, since impurities of the raw material of the fluoride can be replaced with fluorine using various fluorine-containing gases, a fluorine having an excellent internal transmittance can be more easily obtained. Oxide crystals are obtained.
[0163]
Furthermore, according to the fluoride crystals according to claims 11 to 15, it is possible to provide a fluoride crystal having high transmittance and laser resistance in the ultraviolet and vacuum ultraviolet regions.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for producing a fluoride crystal according to an embodiment of the present invention.
FIG. 2 is a schematic sectional view of a surface treatment furnace used in the method for producing a fluoride crystal according to the embodiment of the present invention.
FIG. 3 is a schematic sectional view of a pretreatment furnace used in the method for producing a fluoride crystal according to the embodiment of the present invention.
FIG. 4 is a schematic sectional view of a single crystal growing furnace used in the method for producing a fluoride crystal according to the embodiment of the present invention.
FIG. 5 is a longitudinal sectional view of the ingot manufactured in the example.
FIG. 6 is a flowchart showing a method for manufacturing a fluoride crystal according to a conventional manufacturing method.
[Explanation of symbols]
10 Pretreatment furnace
11, 21, 31 Vacuum container
16, 26, 36 crucibles
20 Single crystal growing furnace
30 Surface treatment furnace

Claims (15)

A fluorine-containing gas is brought into contact with the fluoride raw material to replace the impurities adsorbed on the surface of the fluoride raw material with fluorine; and after the fluorine replacement step, the impurity is again added to the surface of the raw material. A step of reacting the fluorine-substituted raw material with a scavenger, and melting and solidifying the raw material before adsorption to form a crystal, thereby forming a crystal. The raw material of the fluoride in the fluorine substitution step is a powder, and the crystallization step is a step of reacting the raw material powder substituted in the fluorine substitution step with a scavenger and melting and solidifying to form a crystal bulk. The method for producing a fluoride crystal according to claim 1, which is a volume reduction step. The raw material of the fluoride in the fluorine substitution step is a crystal bulk, the crystallization step, the crystal bulk of the fluoride substituted in the fluorine substitution step is reacted with a scavenger and melted and solidified to form a single crystal The method for producing a fluoride crystal according to claim 1, wherein the method is a single crystal growing step for growing. Contacting the fluorine-containing gas with the crystal bulk formed in the purification and volume-reducing step to replace impurities adsorbed on the surface of the crystal bulk with fluorine; A single crystal growing step of growing a single crystal by melting and solidifying
The method for producing a fluoride crystal according to claim 2, wherein the single crystal growing step is performed before the impurities are again adsorbed on the surface of the crystal bulk after the bulk fluorine substitution step. The method for producing a fluoride crystal according to any one of claims 1 to 4, wherein the raw material and the scavenger are reacted in the crystallization step at a temperature higher than the processing temperature in the fluorine substitution step. . The method for producing a fluoride crystal according to any one of claims 1 to 5, wherein the fluorine-containing gas is a gas having fluorine as a constituent element of a molecule. 6. The gas according to claim 1, wherein the fluorine-containing gas is a gas generated by heating and / or depressurizing a substance having fluorine as a constituent element of a molecule and existing as a liquid at room temperature. 5. A method for producing a fluoride crystal according to any one of the above. The method according to claim 1, wherein the fluorine-containing gas is generated by heating and / or reducing pressure from a substance having fluorine as a constituent element of a molecule and existing as a solid at room temperature. 5. A method for producing a fluoride crystal according to any one of the above. The method for producing a fluoride crystal according to any one of claims 1 to 8, wherein the fluorine-containing gas is a fluorine gas. The method for producing a fluoride crystal according to claim 9, wherein the fluorine-containing gas is a mixed gas of the fluorine gas and an inert gas. A fluoride crystal produced by the production method according to any one of claims 1 to 10, wherein an internal transmittance at a wavelength of 190 nm or more and 250 nm or less is 99.8% / cm or more. Fluoride crystals. A fluoride crystal produced by the production method according to claim 1, wherein an internal transmittance at a wavelength of 150 nm or more and less than 190 nm is 99.5% / cm or more. Fluoride crystals. It is a fluoride crystal manufactured by the manufacturing method according to any one of claims 1 to 10, wherein a pulse laser having a wavelength of any of 150 nm to 250 nm is applied at an intensity of 10 mJ / cm ² / pulse, A fluoride crystal characterized in that the transmittance is reduced by 0.5% / cm or less after 1 × 10 ⁵ pulse irradiation. A fluoride crystal manufactured by the manufacturing method according to claim 1, wherein a difference in internal transmittance at a plurality of positions inside the ingot at a wavelength of 190 nm or less is 0.3%. / Cm or less. A fluoride crystal material cut out from the fluoride crystal manufactured by the manufacturing method according to claim 1, wherein internal transmittance at a plurality of positions inside the material at a wavelength of 190 nm or less. Is not more than 0.3% / cm.

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