JP4339537B2 - Lithium calcium aluminum fluoride single crystal - Google Patents
Lithium calcium aluminum fluoride single crystal Download PDFInfo
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- JP4339537B2 JP4339537B2 JP2001367610A JP2001367610A JP4339537B2 JP 4339537 B2 JP4339537 B2 JP 4339537B2 JP 2001367610 A JP2001367610 A JP 2001367610A JP 2001367610 A JP2001367610 A JP 2001367610A JP 4339537 B2 JP4339537 B2 JP 4339537B2
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- 239000013078 crystal Substances 0.000 title claims description 56
- LQFSFEIKYIRLTN-UHFFFAOYSA-H aluminum;calcium;lithium;hexafluoride Chemical compound [Li+].[F-].[F-].[F-].[F-].[F-].[F-].[Al+3].[Ca+2] LQFSFEIKYIRLTN-UHFFFAOYSA-H 0.000 title claims description 44
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 description 77
- 238000010521 absorption reaction Methods 0.000 description 41
- 239000002994 raw material Substances 0.000 description 34
- 229910016569 AlF 3 Inorganic materials 0.000 description 22
- 229910004261 CaF 2 Inorganic materials 0.000 description 22
- 238000002834 transmittance Methods 0.000 description 13
- 230000003287 optical effect Effects 0.000 description 11
- -1 lithium calcium calcium aluminum Chemical compound 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 239000000843 powder Substances 0.000 description 6
- 229910016036 BaF 2 Inorganic materials 0.000 description 5
- 239000011812 mixed powder Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229910001634 calcium fluoride Inorganic materials 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000000206 photolithography Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- ULGYAEQHFNJYML-UHFFFAOYSA-N [AlH3].[Ca] Chemical compound [AlH3].[Ca] ULGYAEQHFNJYML-UHFFFAOYSA-N 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 238000003776 cleavage reaction Methods 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000007017 scission Effects 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は紫外および真空紫外で光学部材として使用されるフッ化リチウムカルシウムアルミニウム単結晶に関する。
【０００２】
【従来の技術】
半導体製造装置用のフォトリソグラフィーなどのレーザー加工の分野では、より精密に加工する必要から、紫外光を利用することが多くなってきている。しかしながら、レンズ、プリズム、ハーフミラー、窓材等の光学部材に用いられる硝材として従来使用されている石英ガラスでは、紫外光に対する内部透過率が低くなるなどの問題があるため石英ガラス以外の硝材が望まれるようになってきている。こうしたなか、波長が200nmよりも短い、いわゆる真空紫外光に対しては石英ガラス以外の硝材としてフッ化カルシウム（CaF2）やフッ化リチウム（LiF）の使用が検討されている。
【０００３】
しかしながら、フッ化リチウムは潮解性、劈開性が高く、各種光学部材に加工することが難しい。一方、フッ化カルシウムはフッ化リチウムに比べると潮解性はやや低くなるものの、依然として高い潮解性を持つことに変わりなく、また、劈開性も高いために各種光学部品への加工は決して容易ではない。
【０００４】
また、フッ化カルシウムの結晶を成長させるには原料を入れたるつぼを1400℃まで加熱・融解させる必要があり、そのため莫大なエネルギーが消費される。
【０００５】
これらの問題点を解決するために、フッ化リチウムカルシウムアルミニウム単結晶が検討されている。しかしながら、フッ化リチウムカルシウムアルミニウム単結晶に高エネルギー光を照射すると波長262nm付近にFセンターが形成される。これはフッ化リチウムカルシウムアルミニウム単結晶を紫外および真空紫外で光学部材として考えた場合には大きな問題となる。
【０００６】
【発明が解決しようとする課題】
本発明は、上記問題点を解決するためになされたもので、高エネルギー光を照射した場合でも、高い耐久性を有する紫外及び真空紫外領域用光学部材を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、フッ化リチウムカルシウムアルミニウム単結晶のドープ元素として、Li+のサイトにBe2+、Mg2+いずれか一方、あるいは同時に両方を0.05mol%<BeF2+MgF2<2.0mol%だけ導入した式Li1-x-yBexMgyCaAlF6+x+y (0.0005<x+y<0.020)で表されるフッ化リチウムカルシウムアルミニウム単結晶を紫外及び真空紫外領域用光学部材として用いることを特徴とする。
【０００８】
【発明の実施の形態】
以下に、本発明によるフッ化リチウムカルシウムアルミニウム単結晶の実施の形態について、より詳細に説明する。
【０００９】
本発明は、紫外および真空紫外での光学部材に有用であるフッ化リチウムカルシウムアルミニウム単結晶の組成を検討した結果、Li+のサイトにBe2+、Mg2+のいずれか一方、あるいは同時に両方を導入することで、高エネルギー光の照射により発生するカラーセンターを抑えることができることを見いだした。
【００１０】
高エネルギー光照射により発生するカラーセンターの原因はフッ化リチウムカルシウムアルミニウム単結晶中のF-サイト空孔によるものであり、高エネルギー光を照射することで価電子帯にある電子が導電帯に励起され、その電子が元の準位に戻ろうとする際にF-空孔にトラップされてしまうことによる。電子がF-空孔にトラップされるということは、バンドギャップ間に新しいエネルギー準位ができるということであり、これが高エネルギー光照射後の吸収に寄与するのである。即ち、高エネルギー光照射後の吸収を抑制するためには、このF-空孔を抑制すれば良いのである。
【００１１】
その１つの方法として、Li+のサイトをBe2+あるいはMg2+あるいは同時に両方で置換することが考えられる。Be2+あるいはMg2+はそのイオン半径の大きさからフッ化リチウムカルシウムアルミニウム結晶中ではLi+サイトを占有すると考えられるが、ここでLi+とBe2+, Mg2+のチャージが異なる所に注目する必要がある。Be2+とMg2+は単体の状態では２つのF-と結合しているのは明らかであるが、このBe2+とMg2+が単体の状態で１つのF-と結合しているLi+のサイトを占有した場合には、F-が１つ過剰になることが分かる。この過剰なF-がF-空孔を埋めるのである。つまり、高エネルギー光照射後の吸収の原因であるカラーセンターを抑制できる。
【００１２】
一方、Be2+, Mg2+の代わりに同じアルカリ土類金属であるSr2+, Ba2+を導入した場合には、Sr2+, Ba2+のイオン半径の大きさからフッ化リチウムカルシウムアルミニウム結晶のCa2+サイトを占有するため、過剰なF-によるF-空孔を埋める効果は得られず、高エネルギー光照射後の吸収を抑制することはできない。
【００１３】
フッ化リチウムカルシウムアルミニウム単結晶を真空紫外領域用光学部材として考えた場合には、X線照射後の波長262nmにおける誘導吸収がアンドープのフッ化リチウムカルシウムアルミニウム単結晶の誘導吸収の1/3以下である必要があるが、この点を考慮するとLi+のサイトへのBe2+、Mg2+導入の適正値は0.05mol%<BeF2+MgF2<2.0mol%程度となる。また、より好ましくは0.1mol%≦BeF2+MgF2≦1.0mol%のドープ量が必要となる。
【００１４】
［実施例１］
原料のLiF, CaF2, AlF3, MgF2の混合比がモル比で(LiF+ MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : MgF2 = 0.998 : 0.002となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察した。ここで、X線照射によって誘起される光吸収量を分かりやすく表現するために誘導吸収を導入した。
【００１５】
ある波長λ(nm)におけるX線照射前の透過率をT0(λ)とし、照射後の透過率をTirr(λ)とすると、X線によって誘起される誘導吸収μ(λ)は次式で表せる。
【００１６】
μ(λ) = ln［T0 (λ)/Tirr(λ)］
図１にこの式を用いて計算したLiF : MgF2 = 0.998 : 0.002の場合の結晶の誘導吸収を示す。また、比較のためMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶の値も示す。図１を見て明らかな通り、MgF2を0.2mol%導入することで、X線照射後の波長262nmにおける誘導吸収の値がMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に比較して約1/4程度と小さくなった。同様の効果が、LiF : MgF2 = 0.98〜0.9995 : 0.0005〜0.02の場合に得られた。
【００１７】
［実施例２］
原料のLiF, CaF2, AlF3, BeF2の混合比がモル比で(LiF+ BeF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2 = 0.98〜0.9995 : 0.0005〜0.02となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BeF2を0.05〜2.0mol%導入することで、X線照射後の波長262nmにおける誘導吸収の値がBeF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に比較して約1/4〜1/3程度と小さな値を示した。図２にBeF2を0.5mol%導入したフッ化リチウムカルシウムアルミニウム単結晶の誘導吸収を示す。
【００１８】
［実施例３］
原料のLiF, CaF2, AlF3, BeF2, MgF2の混合比がモル比で(LiF+ BeF2+MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2+MgF2 = 0.98〜0.9995 : 0.0005〜0.02となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BeF2とMgF2を0.05mol%<BeF2+MgF2<2.0mol%導入することで、X線照射後の波長262nmにおける誘導吸収の値がBeF2, MgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に比較して1/4〜1/3程度の値を示した。
【００１９】
［比較例１］
原料のLiF, CaF2, AlF3, BeF2の混合比がモル比で(LiF+ BeF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2 = 0.9998 : 0.0002となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。図３に結果を示す。BeF2を0.02mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はBeF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２０】
［比較例２］
原料のLiF, CaF2, AlF3, BeF2の混合比がモル比で(LiF+ BeF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2 = 0.97 : 0.03となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BeF2を3.0mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はBeF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２１】
［比較例３］
原料のLiF, CaF2, AlF3, MgF2の混合比がモル比で(LiF+ MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : MgF2 = 0.9998 : 0.0002となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、MgF2を0.02mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２２】
［比較例４］
原料のLiF, CaF2, AlF3, MgF2の混合比がモル比で(LiF+ MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : MgF2 = 0.97 : 0.030となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、MgF2を3.0mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２３】
［比較例５］
原料のLiF, CaF2, AlF3, BeF2, MgF2の混合比がモル比で(LiF+ BeF2+MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2+MgF2 =0.9998 : 0.0002となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BeF2＋MgF2を0.02mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はBeF2とMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２４】
［比較例６］
原料のLiF, CaF2, AlF3, BeF2, MgF2の混合比がモル比で(LiF+ BeF2+MgF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BeF2+MgF2 = 0.97: 0.03となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BeF2＋ MgF2を3.0mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はBeF2とMgF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の90%程度の値を示した。
【００２５】
［比較例７］
原料のLiF, CaF2, AlF3, SrF2の混合比がモル比で(LiF+ SrF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : SrF2 = 0.95〜0.9998 : 0.0002〜0.05となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、SrF2を0.02〜5.0mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はSrF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の95〜100%程度の値を示した。
【００２６】
［比較例８］
原料のLiF, CaF2, AlF3, BaF2の混合比がモル比で(LiF+ BaF2) : CaF2 : AlF3 = 1.10 : 1.00 : 1.10、かつLiF : BaF2 = 0.95〜0.9998 : 0.0002〜0.05となるように混合した粉末原料を準備し、原料を融解し、作製したフッ化リチウムカルシウムアルミニウム単結晶に1000 Gy相当のX線を照射し、照射前後で透過率の変化を観察し、X線照射による誘導吸収を計算した。結果、BaF2を0.02〜5.0mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線照射後の波長262nmにおける誘導吸収の値はBaF2を導入していないアンドープのフッ化リチウムカルシウムアルミニウム結晶に対する誘導吸収の95〜100%程度の値を示した。
【００２７】
以上の点を考慮すると、本発明によるフッ化リチウムカルシウムアルミニウム単結晶は、そのドープ元素として、Li+のサイトにBe2+、Mg2+の少なくとも一方を0.05mol%<BeF2+MgF2<2.0mol%だけ導入した式Li1-x-yBexMgyCaAlF6+x+y (0.0005<x+y<0.020)で表すことができると言える。なお、ｘ，ｙはそれぞれモル比を示す。
【００２８】
【発明の効果】
本発明にかかるBeF2、MgF2いずれか一つ、あるいは同時に両方をドープしたフッ化リチウムカルシウムアルミニウム単結晶は高エネルギー光を照射しても高い耐久性を有するため、半導体製造装置用のフォトリソグラフィーに使用するレンズ、プリズム、ハーフミラー、窓材等の光学部材、特に紫外及び真空紫外領域用光学部材としてこのフッ化リチウムカルシウムアルミニウム単結晶を提供できることが示された、重大な効果が認められた。
【図面の簡単な説明】
【図１】 MgF2を0.2mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線による誘導吸収を示す図である。
【図２】 BeF2を0.5mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線による誘導吸収を示す図である。
【図３】 BeF2を0.02mol%導入したフッ化リチウムカルシウムアルミニウム結晶のX線による誘導吸収を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium calcium aluminum fluoride single crystal used as an optical member in ultraviolet and vacuum ultraviolet.
[0002]
[Prior art]
In the field of laser processing such as photolithography for semiconductor manufacturing equipment, ultraviolet light is increasingly used because of the need for more precise processing. However, quartz glass that has been conventionally used as a glass material used for optical members such as lenses, prisms, half mirrors, and window materials has a problem such as low internal transmittance for ultraviolet light. It is becoming desirable. Under these circumstances, the use of calcium fluoride (CaF 2 ) or lithium fluoride (LiF) as a glass material other than quartz glass is being studied for so-called vacuum ultraviolet light having a wavelength shorter than 200 nm.
[0003]
However, lithium fluoride has high deliquescence and cleavage properties and is difficult to process into various optical members. Calcium fluoride, on the other hand, is slightly less deliquescent than lithium fluoride, but it still has high deliquescence and is highly cleaved, making it difficult to process various optical components. .
[0004]
In order to grow calcium fluoride crystals, it is necessary to heat and melt the crucible containing the raw material up to 1400 ° C, which consumes enormous energy.
[0005]
In order to solve these problems, lithium calcium aluminum fluoride single crystals have been studied. However, when high energy light is irradiated to a lithium calcium calcium aluminum single crystal, an F center is formed in the vicinity of a wavelength of 262 nm. This is a serious problem when a lithium calcium aluminum fluoride single crystal is considered as an optical member in the ultraviolet and vacuum ultraviolet.
[0006]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and an object thereof is to provide an ultraviolet and vacuum ultraviolet optical member having high durability even when irradiated with high energy light.
[0007]
[Means for Solving the Problems]
In the present invention, as a doping element of lithium calcium calcium aluminum single crystal, 0.05 mol% <BeF 2 + MgF 2 <2.0 mol% is added to either Be 2+ , Mg 2+ , or both at the Li + site. Lithium calcium aluminum fluoride single crystal represented by the introduced formula Li 1-xy Be x Mg y CaAlF 6 + x + y (0.0005 <x + y <0.020) is used as an optical member for the ultraviolet and vacuum ultraviolet regions. Features.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the lithium calcium aluminum fluoride single crystal according to the present invention will be described in more detail.
[0009]
The present invention, both the results of examining the composition of lithium fluoride calcium aluminum single crystal useful in the optical member in the ultraviolet and vacuum ultraviolet, Be 2+ in Li + site, either one of Mg 2+, or simultaneously It was found that the color center generated by the irradiation of high energy light can be suppressed by introducing.
[0010]
The cause of the color center generated by irradiation with high energy light is due to F - site vacancies in the lithium calcium aluminum fluoride single crystal, and electrons in the valence band are excited to the conduction band by irradiation with high energy light. is, F when the electrons to return to the original level - due to the fact that would be trapped in the pores. Electrons F - that is trapped in the pores is that it is a new energy level between the band gap, which is to contribute to the absorption after the high-energy irradiation. That is, in order to suppress the absorption after exposure to high-energy light, the F - is can I suppress pores.
[0011]
One method is to replace the Li + site with Be 2+ or Mg 2+ or both at the same time. Be 2+ or Mg 2+ is considered to occupy the Li + site in the lithium calcium aluminum fluoride crystal due to the size of its ionic radius, but where Li + is charged differently from Be 2+ and Mg 2+. It is necessary to pay attention to. Be 2+ and Mg 2+ is in the single state two F - While it is clear that combined with, one F at the Be 2+ and Mg 2+ are single state - it is bonded to when occupying li + sites, F - is seen to be a single excess. The excess F - is F - is fill the vacancies. That is, the color center that is the cause of absorption after irradiation with high energy light can be suppressed.
[0012]
On the other hand, when Sr 2+ and Ba 2+ , which are the same alkaline earth metals, are introduced instead of Be 2+ and Mg 2+ , lithium fluoride is used because of the ionic radius of Sr 2+ and Ba 2+. Since it occupies the Ca 2+ site of the calcium aluminum crystal, the effect of filling F − vacancies with excess F − cannot be obtained, and absorption after irradiation with high energy light cannot be suppressed.
[0013]
When a lithium calcium aluminum fluoride single crystal is considered as an optical member for the vacuum ultraviolet region, the induced absorption at a wavelength of 262 nm after X-ray irradiation is less than 1/3 of that of an undoped lithium calcium aluminum fluoride single crystal. In consideration of this point, the appropriate value for introducing Be 2+ and Mg 2+ into the Li + site is about 0.05 mol% <BeF 2 + MgF 2 <2.0 mol%. More preferably, a doping amount of 0.1 mol% ≦ BeF 2 + MgF 2 ≦ 1.0 mol% is required.
[0014]
[Example 1]
The mixing ratio of the raw materials LiF, CaF 2 , AlF 3 and MgF 2 is (LiF + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: MgF 2 = 0.998: 0.002 in molar ratio Mixed powder raw materials were prepared, the raw materials were melted, and the prepared lithium calcium calcium aluminum single crystal was irradiated with X-rays equivalent to 1000 Gy, and the change in transmittance was observed before and after irradiation. Here, in order to express the amount of light absorption induced by X-ray irradiation in an easy-to-understand manner, induced absorption was introduced.
[0015]
When the transmittance before X-ray irradiation at a certain wavelength λ (nm) is T 0 (λ) and the transmittance after irradiation is T irr (λ), the induced absorption μ (λ) induced by X-rays is It can be expressed by an expression.
[0016]
μ (λ) = ln [T 0 (λ) / T irr (λ)]
FIG. 1 shows the induced absorption of crystals when LiF: MgF 2 = 0.998: 0.002 calculated using this equation. For comparison, the value of an undoped lithium calcium aluminum fluoride crystal not introduced with MgF 2 is also shown. As can be seen in FIG. 1, by introducing 0.2 mol% of MgF 2 , the value of induced absorption at a wavelength of 262 nm after X-ray irradiation is compared with that of an undoped lithium calcium aluminum fluoride crystal without introducing MgF 2. And it became small with about 1/4. Similar effects were obtained when LiF: MgF 2 = 0.98 to 0.995: 0.0005 to 0.02.
[0017]
[Example 2]
The mixing ratio of the raw materials LiF, CaF 2 , AlF 3 , BeF 2 is molar ratio (LiF + BeF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2 = 0.98 to 0.995: 0.0005 to 0.02 Prepare powder raw materials mixed so as to become, melt the raw materials, irradiate the prepared lithium calcium aluminum fluoride single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, X-ray Induced absorption by irradiation was calculated. Result, the introduction of BeF 2 0.05 to 2.0 mol%, about as compared to the induction absorption value undoped lithium fluoride calcium aluminum crystals that do not introduce BeF 2 at wavelength after X-ray irradiation 262 nm 1 / A small value of about 4 to 1/3. FIG. 2 shows the induced absorption of lithium calcium aluminum fluoride single crystals into which 0.5 mol% of BeF 2 has been introduced.
[0018]
[Example 3]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 , BeF 2 , MgF 2 is molar ratio (LiF + BeF 2 + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2 + MgF 2 = 0.98 ~ 0.9995: Prepare powder raw material mixed so as to be 0.0005 ~ 0.02, melt the raw material, irradiate the prepared lithium calcium calcium aluminum single crystal with X-ray equivalent to 1000 Gy, and transmit before and after irradiation The change in rate was observed and the induced absorption by X-ray irradiation was calculated. As a result, by introducing BeF 2 and MgF 2 at 0.05 mol% <BeF 2 + MgF 2 <2.0 mol%, the induced absorption value at a wavelength of 262 nm after X-ray irradiation is undoped without BeF 2 and MgF 2 being introduced. Compared with the lithium calcium aluminum fluoride crystal, the value was about 1/4 to 1/3.
[0019]
[Comparative Example 1]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 , BeF 2 is (LiF + BeF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2 = 0.9998: 0.0002 in molar ratio Prepare mixed powder raw material, melt the raw material, irradiate the prepared lithium calcium calcium aluminum single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, induced absorption by X-ray irradiation Was calculated. The results are shown in FIG. The value of the induced absorption at a wavelength of 262nm after the X-ray irradiation of the BeF 2 0.02 mol% introduced lithium fluoride calcium aluminum crystals 90% of induced absorption for undoped lithium fluoride calcium aluminum crystals that do not introduce BeF 2 The value of was shown.
[0020]
[Comparative Example 2]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 , BeF 2 is (LiF + BeF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2 = 0.97: 0.03 in molar ratio Prepare mixed powder raw material, melt the raw material, irradiate the prepared lithium calcium calcium aluminum single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, induced absorption by X-ray irradiation Was calculated. A result, the value of the induced absorption at a wavelength of 262nm after the X-ray irradiation of the BeF 2 3.0 mol% introduced lithium fluoride calcium aluminum crystals induction absorption for undoped lithium fluoride calcium aluminum crystals that do not introduce BeF 2 90 A value of about% was shown.
[0021]
[Comparative Example 3]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 and MgF 2 is (LiF + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: MgF 2 = 0.9998: 0.0002 in molar ratio Prepare mixed powder raw material, melt the raw material, irradiate the prepared lithium calcium calcium aluminum single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, induced absorption by X-ray irradiation Was calculated. As a result, the value of induced absorption at a wavelength of 262 nm after X-ray irradiation of the lithium calcium aluminum fluoride crystal introduced with 0.02 mol% of MgF 2 is 90% of the induced absorption for the undoped lithium calcium aluminum fluoride crystal not introduced with MgF 2. A value of about% was shown.
[0022]
[Comparative Example 4]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 and MgF 2 is (LiF + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: MgF 2 = 0.97: 0.030 in molar ratio Prepare mixed powder raw material, melt the raw material, irradiate the prepared lithium calcium calcium aluminum single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, induced absorption by X-ray irradiation Was calculated. As a result, the value of the induced absorption at a wavelength of 262 nm after X-ray irradiation of the lithium calcium aluminum fluoride crystal introduced with 3.0 mol% of MgF 2 is 90% of the induced absorption for the undoped lithium calcium aluminum fluoride crystal not introduced with MgF 2. A value of about% was shown.
[0023]
[Comparative Example 5]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 , BeF 2 , MgF 2 is molar ratio (LiF + BeF 2 + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2+ MgF 2 = 0.9998: Prepare a powder raw material mixed so that it becomes 0.0002, melt the raw material, irradiate the produced lithium calcium aluminum fluoride single crystal with X-ray equivalent to 1000 Gy, and change the transmittance before and after irradiation Observed and calculated induced absorption by X-ray irradiation. As a result, the value of the induced absorption at a wavelength of 262 nm after X-ray irradiation of the lithium calcium aluminum fluoride crystal into which 0.02 mol% of BeF 2 + MgF 2 was introduced was an undoped lithium calcium aluminum fluoride crystal into which BeF 2 and MgF 2 were not introduced. A value of about 90% of the induced absorption was shown.
[0024]
[Comparative Example 6]
The mixing ratio of raw materials LiF, CaF 2 , AlF 3 , BeF 2 , MgF 2 is molar ratio (LiF + BeF 2 + MgF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10 and LiF: BeF 2 + MgF 2 = 0.97: Prepare powder raw material mixed so that 0.03, melt the raw material, irradiate the prepared lithium calcium aluminum fluoride single crystal with X-ray equivalent to 1000 Gy, and change the transmittance before and after irradiation Observed and calculated induced absorption by X-ray irradiation. As a result, the value of the stimulated absorption at a wavelength of 262 nm after X-ray irradiation of the lithium calcium aluminum fluoride crystal into which 3.0 mol% of BeF 2 + MgF 2 was introduced was undoped lithium calcium aluminum fluoride to which BeF 2 and MgF 2 were not introduced. A value of about 90% of the induced absorption for the crystal was shown.
[0025]
[Comparative Example 7]
Raw material LiF, in CaF 2, AlF 3, mixing ratio of the molar ratio of the SrF 2 (LiF + SrF 2) : CaF 2: AlF 3 = 1.10: 1.00: 1.10, and LiF: SrF 2 = 0.95~0.9998: 0.0002~0.05 Prepare powder raw materials mixed so as to become, melt the raw materials, irradiate the prepared lithium calcium aluminum fluoride single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, X-ray Induced absorption by irradiation was calculated. A result, the value of the induced absorption at a wavelength of 262nm after the X-ray irradiation of the SrF 2 0.02～5.0Mol% introduced lithium fluoride calcium aluminum crystals induced absorption of undoped lithium fluoride calcium aluminum crystals that do not introduce SrF 2 Value of about 95 to 100%.
[0026]
[Comparative Example 8]
The mixing ratio of the raw materials LiF, CaF 2 , AlF 3 , BaF 2 is molar ratio (LiF + BaF 2 ): CaF 2 : AlF 3 = 1.10: 1.00: 1.10, and LiF: BaF 2 = 0.95 to 0.9998: 0.0002 to 0.05 Prepare powder raw materials mixed so as to become, melt the raw materials, irradiate the prepared lithium calcium aluminum fluoride single crystal with X-ray equivalent to 1000 Gy, observe the change in transmittance before and after irradiation, X-ray Induced absorption by irradiation was calculated. A result, the value of the induced absorption at a wavelength of 262nm after the X-ray irradiation of the BaF 2 0.02～5.0Mol% introduced lithium fluoride calcium aluminum crystals induced absorption of undoped lithium fluoride calcium aluminum crystals that do not introduce BaF 2 Value of about 95 to 100%.
[0027]
Considering the above points, the lithium calcium aluminum fluoride single crystal according to the present invention has 0.05 mol% <BeF 2 + MgF 2 << at least one of Be 2+ and Mg 2+ at the Li + site as a doping element. It can be said that it can be expressed by the formula Li 1-xy Be x Mg y CaAlF 6 + x + y (0.0005 <x + y <0.020) introduced by 2.0 mol%. X and y each represents a molar ratio.
[0028]
【The invention's effect】
Since the lithium calcium aluminum fluoride single crystal doped with either one or both of BeF 2 and MgF 2 according to the present invention has high durability even when irradiated with high energy light, photolithography for semiconductor manufacturing equipment It was shown that this lithium calcium aluminum fluoride single crystal can be provided as an optical member such as lenses, prisms, half mirrors, window materials, etc., particularly as an optical member for the ultraviolet and vacuum ultraviolet region, and a significant effect was observed. .
[Brief description of the drawings]
FIG. 1 is a diagram showing X-ray induced absorption of lithium calcium aluminum fluoride crystals into which 0.2 mol% of MgF 2 has been introduced.
FIG. 2 is a diagram showing X-ray induced absorption of lithium calcium aluminum fluoride crystals into which 0.5 mol% of BeF 2 has been introduced.
FIG. 3 is a diagram showing X-ray induced absorption of lithium calcium calcium aluminum crystals into which 0.02 mol% of BeF 2 has been introduced.
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