JP2005017461A

JP2005017461A - Forming method of anti-reflection film, and optical element

Info

Publication number: JP2005017461A
Application number: JP2003179375A
Authority: JP
Inventors: Tomokazu Taguchi; 智一田口; Kazuyuki Nishi; 和幸西
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 2003-06-24
Filing date: 2003-06-24
Publication date: 2005-01-20

Abstract

<P>PROBLEM TO BE SOLVED: To form an anti-reflection film which has superior anti-reflection performance and has less optical absorption in a blue color wavelength region of 420 to 500nm. <P>SOLUTION: In a vacuum deposition device, an S<SB>i</SB>O<SB>2</SB>film is formed under the pressure of 1.0×10<SP>-4</SP>to 1.3×10<SP>-4</SP>Torr, an Al<SB>2</SB>O<SB>3</SB>film is formed under the pressure of 1.4×10<SP>-4</SP>to 1.7×10<SP>-4</SP>Torr, and a T<SB>i</SB>O<SB>2</SB>film is formed under the pressure of 1.7×10<SP>-4</SP>to 2.9×10<SP>-4</SP>Torr. The first film is formed by temporarily controlling the pressure in the device to ≤2×10<SP>-5</SP>Torr, and then oxygen is injected and then controlling the pressure to the above prescribed pressure by charging oxygen. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、反射防止膜の形成方法およびこの方法によって反射防止膜が形成された光学素子に関するものである。
【０００２】
【従来の技術】
デジタルシネマ用プロジェクタなどの投影光学系はレンズやプリズムなどの複数個の光学素子で構成されている。このような光学素子の多い投影光学系では、反射光によるフレアやゴーストの発生を抑え、且つ透過光量損失による投影像の明るさ欠損を防ぐため、一連の光学素子には反射防止膜が施されている。
【０００３】
また、デジタルシネマ用プロジェクタなどの投影光学系では、現在１０，０００ルーメン程度の明るさが要求されるため、通常の光学部品よりも高い透過率が要求される。そこで、反射率を極限まで小さくすべく種々の反射防止膜がこれまでから提案されている（特許文献１〜６）。
【０００４】
【特許文献１】
特開２００２−１４２０３号公報（特許請求の範囲、図１〜図１１）
【特許文献２】
特開２００２−１４２０４号公報（特許請求の範囲、図４〜図６）
【特許文献３】
特開２００１−７４９０３号公報（特許請求の範囲）
【特許文献４】
特開平１０−２０１０２号公報（特許請求の範囲、図１〜図６）
【特許文献５】
特開平１−１３１５０１号公報（特許請求の範囲）
【特許文献６】
特開平２−１２６２０１号公報（特許請求の範囲、第１図、第２図）
【０００５】
【発明が解決しようとする課題】
ところが、従来の反射防止膜は分光反射率特性を専ら重視しているため、反射率を極限まで低下させたものであっても成膜条件如何によってはあまり透過光量が高くない。特に青色波長域は光学素子と反射防止膜の両方で吸収量が多く、透過光量の不足が大きな問題となっていた。
【０００６】
本発明はこのような従来の問題に鑑みてなされたものであり、その目的とするところは、優れた反射防止効果を有すると共に、青色波長域（本発明では４２０〜５００ｎｍの波長域をいう）の光吸収の少ない反射防止膜の形成方法およびこの方法で反射防止膜が形成された光学素子を提供することにある。
【０００７】
【課題を解決するための手段】
本発明によれば、ＳｉＯ_２を主成分とする膜（以下、単に「ＳｉＯ_２膜」と記すことがある）と、Ａｌ_２Ｏ_３を主成分とする膜（以下、単に「Ａｌ_２Ｏ_３膜」と記すことがある）と、ＴｉＯ_２を主成分とする膜（以下、単に「ＴｉＯ_２膜」と記すことがある）とを含む反射防止膜を、真空蒸着装置を用いて基材表面に形成する方法であって、ＳｉＯ_２膜は、１．０×１０^−４〜１．３×１０^−４Ｔｏｒｒの圧力下で形成し、Ａｌ_２Ｏ_３膜は、１．４×１０^−４〜１．７×１０^−４Ｔｏｒｒの圧力下で形成し、ＴｉＯ_２膜は、１．７×１０^−４〜２．０×１０^−４Ｔｏｒｒの圧力下で形成し、第１膜目は、装置内の圧力を一旦２×１０^−５Ｔｏｒｒ以下とした後、酸素を注入して前記所定圧力として形成することを特徴とする反射防止膜の形成方法が提供される。
【０００８】
ここで、前記圧力下で形成される蒸着膜の屈折率の低下を抑える観点から、ＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２膜の少なくとも１つの膜を、ＳｉＯ_２膜の場合には１０Å／ｓ以上、Ａｌ_２Ｏ_３膜の場合には５Å／ｓ以上、ＴｉＯ_２膜の場合には４．５Å／ｓ以上の形成速度で形成するのが好ましい。
【０００９】
生産効率などの観点から、膜形成時の設定圧力の低いものから順に膜形成を行うのが望ましい。
【００１０】
また本発明によれば、ＳｉＯ_２膜と、Ａｌ_２Ｏ_３膜と、ＴｉＯ_２膜とを含む反射防止膜が、真空蒸着装置を用いて光学素子本体に形成された光学素子であって、ＳｉＯ_２膜は、１．０×１０^−４〜１．３×１０^−４Ｔｏｒｒの圧力下で形成され、Ａｌ_２Ｏ_３膜は、１．４×１０^−４〜１．７×１０^−４Ｔｏｒｒの圧力下で形成され、ＴｉＯ_２膜は、１．７×１０^−４〜２．０×１０^−４Ｔｏｒｒの圧力下で形成され、第１膜目は、装置内の圧力を一旦２×１０^−５Ｔｏｒｒ以下とした後、酸素を注入して前記所定圧力として形成されたものであることを特徴とする光学素子が提供される。
【００１１】
ここで、前記圧力下で形成される蒸着膜を所定の屈折率とする観点から、ＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２膜の少なくとも１つの膜は、ＳｉＯ_２膜の場合は１０Å／ｓ以上、Ａｌ_２Ｏ_３膜の場合は５Å／ｓ以上、ＴｉＯ_２膜の場合は４．５Å／ｓ以上の形成速度で形成されたものが好ましい。
【００１２】
生産効率などの観点から、光学素子本体側から順にＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２膜が形成されているのが望ましい。
【００１３】
【発明の実施の形態】
本発明者等は、前記目的を達成すべく鋭意検討を重ねた結果、ＳｉＯ_２膜とＡｌ_２Ｏ_３膜、ＴｉＯ_２膜とを含む反射防止膜を、真空蒸着装置を用いて基材表面に形成する場合、酸素ガスを導入して、蒸着時の圧力を通常よりも高くすることによって、反射防止膜における少なくとも青色波長域の光吸収を小さくできるという知見を得て本発明をなすに至った。
【００１４】
このような効果が得られる機構については今のところ定かには解明されていないが、光を吸収しやすいＳｉ元素やＡｌ元素、Ｔｉ元素が、従来よりも多く存在する酸素と結合することによって、これらの元素による光吸収が抑えられるからであろうと推測している。
【００１５】
本発明の反射防止膜の形成方法について以下に詳述する。まず、本発明の形成方法の概略工程を図１に示す。図１は本発明に係る形成方法のフローチャートである。まず、光学素子本体などの基材を真空蒸着装置の真空室の所定位置に取り付ける。また同時に、ＳｉＯ_２やＡｌ_２Ｏ_３、ＴｉＯ_２などの蒸着材料も真空室の所定位置に配置する。そして、真空室を密閉した後、真空ポンプによって真空室内を２×１０^−５Ｔｏｒｒ以下の高真空とする（ステップＳ１）。次に、酸素ガスを真空室に注入して真空室を所定圧力とする（ステップＳ２）。
【００１６】
この所定圧力は蒸着材料の種類によって異なる。ＳｉＯ_２膜の場合は１．０×１０^−４〜１．３×１０^−４Ｔｏｒｒであり、Ａｌ_２Ｏ_３膜の場合は１．４×１０^−４〜１．７×１０^−４Ｔｏｒｒであり、ＴｉＯ_２膜の場合は１．７×１０^−４〜２．０×１０^−４Ｔｏｒｒである。真空室の圧力がこれらの圧力範囲の上限値より高い場合は、酸素ガスが膜中に取り込まれ膜の屈折率が低くなり所望の分光特性が得られなくなる。一方、真空室の圧力がこれらの圧力範囲の下限値より低い場合は、膜による青色波長域の光吸収を十分には抑えることができなくなる。より好ましい圧力は、ＳｉＯ_２膜の場合は１．１×１０^−４〜１．２×１０^−４Ｔｏｒｒであり、Ａｌ_２Ｏ_３膜の場合は１．５×１０^−４〜１．６×１０^−４Ｔｏｒｒであり、ＴｉＯ_２膜の場合は１．８×１０^−４〜１．９×１０^−４Ｔｏｒｒである。
【００１７】
このような圧力範囲で各膜を形成した場合であっても、通常よりも高い圧力下で蒸着を行っているため、蒸着膜内に気孔が不可避的に存在してしまい蒸着膜の屈折率が低くなることがある。そこで、屈折率の低下を抑えたい蒸着膜についてはその形成速度を従来よりも速くすることが推奨される。これにより、当該蒸着膜の密度が高くなる結果、蒸着膜内の気孔が圧縮され蒸着膜の屈折率の低下が抑えられるのである。形成速度としてはＳｉＯ_２膜の場合は１０Å／ｓ以上、Ａｌ_２Ｏ_３膜の場合は５Å／ｓ以上、ＴｉＯ_２膜の場合は４．５Å／ｓ以上とするのが好ましい。このような膜形成速度とするには、例えば電子ビームによって蒸着材料を加熱する場合には、電子ビームに流す電流を制御すればよい。この電流値としては、例えばドーム直径が約７２０ｍｍ、蒸着材料から基板までの距離が５８０〜８２０ｍｍの蒸着装置を用いた場合、上記形成速度にするには、ＳｉＯ_２膜の場合は５０〜６０ｍＡ、Ａｌ_２Ｏ_３膜の場合は１６０〜２２０ｍＡ、ＴｉＯ_２膜の場合は１８０〜２６０ｍＡの範囲に調整するのが好ましい。
【００１８】
図１を参照して、前記蒸着条件で蒸着膜を蒸着形成し（ステップＳ５）、膜厚モニターにより所定膜厚となったかどうかを判定し（ステップＳ６）、所定膜厚となったところで蒸着材料を入れた坩堝の上部を開閉自在に移動するシャターを閉じて第１膜目の蒸着を終了する（ステップＳ７）。そして、所定の積層膜構造になったかどうかを判定し（ステップＳ８）、所定の積層数に達していなければ、酸素ガスを注入または真空ポンプを駆動させて所定圧力とし（ステップＳ２）、蒸着材料および蒸着条件を変えて次の蒸着膜を前記と同様にして形成する（ステップＳ３〜Ｓ７）。この一連の処理を繰り返して所定の積層膜構造（ここではｍ層構造）の蒸着膜を形成する（ステップＳ８）。
【００１９】
生産効率の観点からは、蒸着処理時の設定圧力の低いものから順に蒸着膜を形成するのが好ましい。一旦高真空とした後は、順次酸素ガスを注入して真空室の圧力を高めて行けばよく、真空室内の雰囲気を真空ポンプで再度引く必要がないからである。これを前記３つの膜の場合に適用すれば、光学素子本体側から順にＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２膜とするのがよいことになる。
【００２０】
もちろん広帯域の光反射を防止するために、低屈折率膜および高屈折率膜を基体との間にさらに順次積層させた構造としても構わない。またＳｉＯ_２膜やＡｌ_２Ｏ_３膜、ＴｉＯ_２膜の各膜には、本発明の効果を害さない範囲において従来公知の添加物を添加しても構わない。
【００２１】
また光学素子本体と反射防止膜との密着性を一層向上させるために、エネルギー線照射処理や薬品処理などで光学素子本体の表面を表面改質処理してもよい。エネルギー線照射処理としては、コロナ放電処理、プラズマ処理、電子線照射処理、紫外線照射処理などが挙げられる。
【００２２】
反射防止膜を表面に形成する基材の材質としては、ガラス及びプラスチックのいずれであってもよい。プラスチックとしては、ポリメチルメタクリレート（ＰＭＭＡ）、ポリカーボネート、ポリスチレン、非晶質ポリオレフィンなどが挙げられる。またプラスチック基体の成形方法としては特に限定はなく、従来公知の成形方法、例えば注型法、射出成形法、プレス成形法などを用いることができる。
【００２３】
反射防止膜を表面に形成した本発明に係る光学素子の用途としては、例えばレンズやプリズムなどが挙げられる。特に、複数個の光学素子から構成される投影光学系に好適に用いられる。
【００２４】
【実施例】
以下、実施例に基づいて本発明をさらに詳細に述べる。なお、下記実施例は本発明を何ら制限するものではなく、前後記の趣旨を逸脱しない範囲で変更実施することは本発明の技術的範囲に包含される。
【００２５】
（実施例１）
真空蒸着装置を用いて、基材としてのホーヤ社製「ＦＣＤ１」の表面に、基材側から順にＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２を主成分とする膜、ＭｇＦ_２膜の４層構造からなる反射防止膜を形成した。反射防止膜の形成方法は次の通りである。
【００２６】
まず、基材を真空室に取り付け、真空室を密閉する。そして、真空ポンプを駆動させて真空室の圧力を２×１０^−５Ｔｏｒｒまで一旦下げた後、真空室に酸素ガスを注入して圧力を１．２×１０^−４Ｔｏｒｒとし、蒸着材料であるＳｉＯ_２を電子ビーム加熱法によって加熱蒸発させて基材に蒸着させた。このときの電子ビームの電流値は５５ｍＡで、ＳｉＯ_２膜の形成速度は１３．３Å／ｓであった。基材表面に形成されたＳｉＯ_２膜の膜厚が１０８．２ｎｍとなったところで第１膜目の蒸着処理を終了した。次に、酸素ガスを真空室に注入して真空室の圧力を１．５×１０^−４Ｔｏｒｒとした後、蒸着材料をＡｌ_２Ｏ_３として前記と同様に蒸着処理を行った。このときの電子ビームの電流値は２１０ｍＡで、Ａｌ_２Ｏ_３膜の形成速度は７．２Å／ｓであった。基材表面に形成されたＡｌ_２Ｏ_３膜の膜厚が７６．１ｎｍとなったところで第２膜目の蒸着処理を終了した。次いで、酸素ガスを真空室に注入して真空室の圧力を１．８×１０^−４Ｔｏｒｒに上げた後、蒸着材料をＴｉＯ_２を主成分とする材料として前記と同様に蒸着処理を行った。電子ビームの電流値は２００ｍＡで、ＴｉＯ_２を主成分とする膜の形成速度は５．３Å／ｓであった。基材表面に形成されたＴｉＯ_２膜の膜厚が１２０．２ｎｍとなったところで第３膜目の蒸着処理を終了した。そして最後に、真空ポンプを再び駆動させて真空室の圧力を２×１０^−５Ｔｏｒｒに下げた後、酸素ガスを注入することなく、ＭｇＦ_２を蒸着材料として前記と同様に蒸着処理を行った。ＭｇＦ_２膜の形成速度は９．６Å／ｓであった。基材表面に形成されたＭｇＦ_２膜の膜厚が８９．１ｎｍとなったところで第４膜目の蒸着処理を終了した。作製した反射防止膜の概略構成図を図２に示すと共に、上記蒸着条件を表１にまとめて示す。
【００２７】
【表１】

【００２８】
このようにして作製した光学素子の分光反射率特性および分光透過率特性を測定した。測定結果を図３及び図４に示す。図３によれば、形成された反射防止膜の反射率は可視光域において０．４％以下と優れたものであり、４２０〜５００ｎｍの青色波長域では０．２％以下と非常に低い値であった。また図４によれば、４２０〜５００ｎｍの青色波長域の平均透過率は９９．６１％と、従来に比べ格段に高い値であった。
【００２９】
（比較例１）
真空蒸着装置を用いて、基材としてのホーヤ社製「ＦＣＤ１」の表面に、基材側から順にＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２を主成分とする膜、ＭｇＦ_２膜の４層構造からなる反射防止膜を実施例１と同様にして形成した。蒸着条件を表２に示す。
【００３０】
【表２】

【００３１】
このようにして作製した光学素子の分光反射率特性および分光透過率特性を測定した。測定結果を図５及び図６に示す。図５によれば、形成された反射防止膜の反射率は可視光域において０．４％以下と優れたものであった。しかし、図６によれば、４２０〜５００ｎｍの青色波長域の平均透過率は９８．９３％と低い値であった。
【００３２】
（実施例２）
真空蒸着装置を用いて、基材としての「ＳＫ１０」の表面に、実施例１と同様にして、基材側から順にＡｌ_２Ｏ_３とＬａ_２Ｏ_３の混合物からなる膜、ＴｉＯ_２膜、ＳｉＯ_２膜の３層構造からなる反射防止膜を形成した。ここで、第１膜のＡｌ_２Ｏ_３とＬａ_２Ｏ_３の混合物からなる膜の屈折率が低下すると反射防止帯域が狭まるため、この第１膜の形成速度を５．８Å／ｓと通常よりも速くした。その他の蒸着条件を表３に示す。
【００３３】
【表３】

【００３４】
このようにして作製した光学素子の分光反射率特性および分光透過率特性を測定した。測定結果を図７及び図８に示す。図７によれば、４００〜４１０ｎｍの青色レーザ波長域において、形成された反射防止膜の反射率は平均０．１％以下と優れたものであり、また図８によれば、４００〜４１０ｎｍの青色レーザ波長域の平均透過率は９９．８９％と、従来に比べ格段に高い値であった。
【００３５】
（比較例２）
実施例２と同様にして真空蒸着装置を用いて、基材としての「ＳＫ１０」の表面に、基材側から順にＡｌ_２Ｏ_３とＬａ_２Ｏ_３の混合物からなる膜、ＴｉＯ_２膜、ＳｉＯ_２膜の３層構造からなる反射防止膜を形成した。蒸着条件を表４に示す。
【００３６】
【表４】

【００３７】
このようにして作製した光学素子の分光反射率特性および分光透過率特性を測定した。測定結果を図９及び図１０に示す。図９によれば、４００〜４１０ｎｍの青色レーザ波長域において、形成された反射防止膜の反射率は平均０．１％以下と実施例２の光学素子と同様に優れたものであった。しかし図１０によれば、４００〜４１０ｎｍの青色レーザ波長域の平均透過率は９９．１０％と低い値であった。
【００３８】
【発明の効果】
本発明に係る反射防止膜の形成方法では、真空蒸着装置を用いて基材表面に、１．０×１０^−４〜１．３×１０^−４Ｔｏｒｒの圧力下でＳｉＯ_２膜を形成し、１．４×１０^−４〜１．７×１０^−４Ｔｏｒｒの圧力下でＡｌ_２Ｏ_３膜を形成し、１．７×１０^−４〜２．０×１０^−４Ｔｏｒｒの圧力下でＴｉＯ_２膜を形成すると共に、第１膜目は、装置内の圧力を一旦２×１０^−５Ｔｏｒｒ以下とした後、酸素を注入して前記所定圧力として形成するので、優れた反射防止効果を奏すると共に、４２０〜５００ｎｍの青色波長域の光吸収の少ない反射防止膜を形成できる。
【００３９】
ＳｉＯ_２膜、Ａｌ_２Ｏ_３膜、ＴｉＯ_２膜の少なくとも１つの膜を、ＳｉＯ_２膜の場合には１０Å／ｓ以上、Ａｌ_２Ｏ_３膜の場合には５Å／ｓ以上、ＴｉＯ_２膜の場合には４．５Å／ｓ以上の形成速度で形成すると、各膜の屈折率の低下を抑えられる。
【００４０】
また、膜形成時の設定圧力の低いものから順に膜形成を行うと、蒸着処理の途中で真空室内の圧力を下げる操作が不要となり生産効率が向上する。
【００４１】
また本発明に係る光学素子では、前記形成方法で光学素子本体に反射防止膜が形成されているので、優れた反射防止効果を有すると共に、４２０〜５００ｎｍの青色波長域においても従来に比べ格段に高い透過率が得られる。
【図面の簡単な説明】
【図１】本発明に係る反射防止膜の形成方法の一例を示すフローチャート図である。
【図２】実施例１の反射防止膜の概略構成図である。
【図３】実施例１の光学素子の分光反射特性図である。
【図４】実施例１の光学素子の分光透過率特性図である。
【図５】比較例１の光学素子の分光反射特性図である。
【図６】比較例１の光学素子の分光透過率特性図である。
【図７】実施例２の光学素子の分光反射特性図である。
【図８】実施例２の光学素子の分光透過率特性図である。
【図９】比較例２の光学素子の分光反射特性図である。
【図１０】比較例２の光学素子の分光透過率特性図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming an antireflection film and an optical element having an antireflection film formed by this method.
[0002]
[Prior art]
Projection optical systems such as projectors for digital cinema are composed of a plurality of optical elements such as lenses and prisms. In such a projection optical system having many optical elements, a series of optical elements are provided with an antireflection film in order to suppress the occurrence of flare and ghost due to reflected light and to prevent the loss of brightness of the projected image due to loss of transmitted light amount. ing.
[0003]
In addition, since a projection optical system such as a projector for digital cinema currently requires a brightness of about 10,000 lumens, it requires a higher transmittance than a normal optical component. Therefore, various antireflection films have been proposed so far to reduce the reflectance to the limit (Patent Documents 1 to 6).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-14203 (Claims, FIGS. 1 to 11)
[Patent Document 2]
JP 2002-14204 (Claims, FIGS. 4 to 6)
[Patent Document 3]
JP 2001-74903 A (Claims)
[Patent Document 4]
Japanese Patent Laid-Open No. 10-20102 (Claims, FIGS. 1 to 6)
[Patent Document 5]
JP-A-1-131501 (Claims)
[Patent Document 6]
JP-A-2-126201 (Claims, FIGS. 1 and 2)
[0005]
[Problems to be solved by the invention]
However, since the conventional anti-reflection film focuses exclusively on the spectral reflectance characteristics, the amount of transmitted light is not so high depending on the film forming conditions even if the reflectance is lowered to the limit. In particular, the blue wavelength region has a large amount of absorption in both the optical element and the antireflection film, and a lack of transmitted light amount has been a serious problem.
[0006]
The present invention has been made in view of such a conventional problem, and the object thereof is to have an excellent antireflection effect and a blue wavelength region (in the present invention, a wavelength region of 420 to 500 nm). An object of the present invention is to provide a method for forming an antireflection film with little light absorption and an optical element having an antireflection film formed by this method.
[0007]
[Means for Solving the Problems]
According to the present invention, a film containing SiO ₂ as a main component (hereinafter sometimes simply referred to as “SiO ₂ film”) and a film containing Al ₂ O ₃ as a main component (hereinafter simply referred to as “Al ₂ O _3”). An antireflection film including a film mainly composed of TiO ₂ (hereinafter sometimes simply referred to as “TiO ₂ film”) using a vacuum deposition apparatus. The SiO ₂ film is formed under a pressure of 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr, and the Al ₂ O ₃ film is 1.4 × 10 ^−4. The film is formed under a pressure of ˜1.7 × 10 ⁻⁴ Torr, the TiO ₂ film is formed under a pressure of 1.7 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ Torr, and the first film is The pressure in the apparatus is temporarily set to 2 × 10 ⁻⁵ Torr or less, and then oxygen is injected to form the predetermined pressure. A method of forming an anti-reflection film is provided.
[0008]
Here, from the viewpoint of suppressing a decrease in the refractive index of the vapor deposition film formed under the pressure, at least one of the SiO ₂ film, the Al ₂ O ₃ film, and the TiO ₂ film is 10 には in the case of the SiO ₂ film. In the case of an Al ₂ O ₃ film, it is preferably formed at a rate of 5 Å / s or more, and in the case of a TiO ₂ film, it is preferably formed at a rate of 4.5 Å / s or more.
[0009]
From the viewpoint of production efficiency and the like, it is desirable to perform film formation in order from the lowest set pressure during film formation.
[0010]
According to the present invention, an antireflection film including a SiO ₂ film, an Al ₂ O ₃ film, and a TiO ₂ film is an optical element formed on an optical element body using a vacuum vapor deposition apparatus. _{The two} films are formed under a pressure of 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr, and the Al ₂ O ₃ film is formed of 1.4 × 10 ^{−4 to} 1.7 × 10 ⁻⁴ Torr. The TiO ₂ film is formed under a pressure of 1.7 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ Torr, and the first film has a pressure of 2 × 10 once in the apparatus. An optical element is provided which is formed at the predetermined pressure by injecting oxygen after the pressure is set to ⁻⁵ Torr or less.
[0011]
Here, from the viewpoint of setting the vapor deposition film formed under the pressure to a predetermined refractive index, at least one of the SiO ₂ film, the Al ₂ O ₃ film, and the TiO ₂ film is 10 Å / in the case of the SiO ₂ film. In the case of an Al ₂ O ₃ film, it is preferably 5 Å / s or more, and in the case of a TiO ₂ film, it is preferably formed at a formation rate of 4.5 Å / s or more.
[0012]
From the viewpoint of production efficiency and the like, it is desirable that a SiO ₂ film, an Al ₂ O ₃ film, and a TiO ₂ film are formed in order from the optical element body side.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a result of intensive studies to achieve the above object, the present inventors have applied an antireflection film including an SiO ₂ film, an Al ₂ O ₃ film, and a TiO ₂ film on the surface of a substrate using a vacuum deposition apparatus. In the case of forming, the present invention has been made by obtaining the knowledge that light absorption in at least the blue wavelength region in the antireflection film can be reduced by introducing oxygen gas and increasing the pressure during vapor deposition higher than usual. .
[0014]
Although the mechanism for obtaining such an effect has not been elucidated for now, Si elements, Al elements, and Ti elements that easily absorb light are combined with oxygen that is present more than before, It is speculated that light absorption by these elements can be suppressed.
[0015]
The method for forming the antireflection film of the present invention will be described in detail below. First, schematic steps of the forming method of the present invention are shown in FIG. FIG. 1 is a flowchart of a forming method according to the present invention. First, a base material such as an optical element main body is attached to a predetermined position in a vacuum chamber of a vacuum deposition apparatus. At the same time, vapor deposition materials such as SiO ₂ , Al ₂ O ₃ , and TiO ₂ are also arranged at predetermined positions in the vacuum chamber. Then, after the vacuum chamber is sealed, a high vacuum of 2 × 10 ⁻⁵ Torr or less is set in the vacuum chamber by a vacuum pump (step S1). Next, oxygen gas is injected into the vacuum chamber to bring the vacuum chamber to a predetermined pressure (step S2).
[0016]
This predetermined pressure varies depending on the type of vapor deposition material. In the case of the SiO ₂ film, 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr, and in the case of the Al ₂ O ₃ film, 1.4 × 10 ^{−4 to} 1.7 × 10 ⁻⁴ Torr. In the case of a TiO ₂ film, it is 1.7 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ Torr. When the pressure in the vacuum chamber is higher than the upper limit values of these pressure ranges, oxygen gas is taken into the film and the refractive index of the film is lowered, so that desired spectral characteristics cannot be obtained. On the other hand, when the pressure in the vacuum chamber is lower than the lower limit value of these pressure ranges, light absorption in the blue wavelength region by the film cannot be sufficiently suppressed. A more preferable pressure is 1.1 × 10 ^{−4 to} 1.2 × 10 ⁻⁴ Torr for the SiO ₂ film, and 1.5 × 10 ^{−4 to} 1.6 × for the Al ₂ O ₃ film. 10 ⁻⁴ Torr, and in the case of a TiO ₂ film, it is 1.8 × 10 ^{−4 to} 1.9 × 10 ⁻⁴ Torr.
[0017]
Even when each film is formed in such a pressure range, since vapor deposition is performed under a pressure higher than usual, pores inevitably exist in the vapor deposition film, and the refractive index of the vapor deposition film is low. May be lower. Therefore, it is recommended that the deposition rate of the deposited film for which the decrease in the refractive index is suppressed be higher than that of the conventional film. As a result, the density of the vapor deposition film increases, and as a result, the pores in the vapor deposition film are compressed, and the decrease in the refractive index of the vapor deposition film is suppressed. The formation rate is preferably 10 Å / s or more for the SiO ₂ film, 5 Å / s or more for the Al ₂ O ₃ film, and 4.5 Å / s or more for the TiO ₂ film. In order to achieve such a film formation speed, for example, when the vapor deposition material is heated by an electron beam, the current passed through the electron beam may be controlled. As this current value, for example, when a vapor deposition apparatus having a dome diameter of about 720 mm and a distance from the vapor deposition material to the substrate of 580 to 820 mm is used, in order to achieve the above formation speed, in the case of a SiO ₂ film, 50 to 60 mA, In the case of an Al ₂ O ₃ film, it is preferable to adjust to a range of 160 to 220 mA, and in the case of a TiO ₂ film, it is preferably adjusted to a range of 180 to 260 mA.
[0018]
Referring to FIG. 1, a deposited film is formed by vapor deposition under the above-described deposition conditions (step S5), and it is determined whether or not a predetermined film thickness is obtained by a film thickness monitor (step S6). The shutter that moves in an openable and closable manner is closed on the upper part of the crucible containing the metal, and the deposition of the first film is completed (step S7). Then, it is determined whether or not a predetermined laminated film structure is obtained (step S8). If the predetermined number of laminated layers has not been reached, oxygen gas is injected or a vacuum pump is driven to obtain a predetermined pressure (step S2), and the vapor deposition material Then, the next deposited film is formed in the same manner as described above by changing the deposition conditions (steps S3 to S7). This series of processes is repeated to form a deposited film having a predetermined laminated film structure (here, m-layer structure) (step S8).
[0019]
From the viewpoint of production efficiency, it is preferable to form the deposited film in order from the lowest set pressure during the deposition process. This is because once the high vacuum is achieved, oxygen gas is sequentially injected to increase the pressure in the vacuum chamber, and it is not necessary to draw the atmosphere in the vacuum chamber again with a vacuum pump. If this is applied to the case of the three films, it is preferable to sequentially form a SiO ₂ film, an Al ₂ O ₃ film, and a TiO ₂ film from the optical element body side.
[0020]
Of course, in order to prevent broadband light reflection, a structure in which a low refractive index film and a high refractive index film are further laminated in sequence with the substrate may be used. In addition, conventionally known additives may be added to the SiO ₂ film, Al ₂ O ₃ film, and TiO ₂ film as long as the effects of the present invention are not impaired.
[0021]
In order to further improve the adhesion between the optical element body and the antireflection film, the surface of the optical element body may be subjected to surface modification treatment by energy ray irradiation treatment, chemical treatment, or the like. Examples of the energy ray irradiation treatment include corona discharge treatment, plasma treatment, electron beam irradiation treatment, and ultraviolet ray irradiation treatment.
[0022]
The material of the base material on which the antireflection film is formed may be either glass or plastic. Examples of the plastic include polymethyl methacrylate (PMMA), polycarbonate, polystyrene, and amorphous polyolefin. The method for molding the plastic substrate is not particularly limited, and a conventionally known molding method such as a casting method, an injection molding method, a press molding method, or the like can be used.
[0023]
Examples of the use of the optical element according to the present invention in which an antireflection film is formed on the surface include a lens and a prism. In particular, it is suitably used for a projection optical system composed of a plurality of optical elements.
[0024]
【Example】
Hereinafter, the present invention will be described in more detail based on examples. It should be noted that the following examples do not limit the present invention in any way, and modifications and implementations without departing from the gist of the preceding and following descriptions are included in the technical scope of the present invention.
[0025]
(Example 1)
Using a vacuum deposition apparatus, on the surface of “FCD1” manufactured by Hoya as a base material, a SiO ₂ film, an Al ₂ O ₃ film, a film containing TiO ₂ as a main component, and an MgF ₂ film in order from the base material side. An antireflection film having a layer structure was formed. The method for forming the antireflection film is as follows.
[0026]
First, the substrate is attached to the vacuum chamber, and the vacuum chamber is sealed. Then, after the vacuum pump is driven to lower the pressure in the vacuum chamber to 2 × 10 ⁻⁵ Torr, oxygen gas is injected into the vacuum chamber to a pressure of 1.2 × 10 ⁻⁴ Torr. SiO ₂ was evaporated by heating by an electron beam heating method and deposited on the substrate. At this time, the current value of the electron beam was 55 mA, and the formation rate of the SiO ₂ film was 13.3 Å / s. When the film thickness of the SiO ₂ film formed on the substrate surface reached 108.2 nm, the first film deposition process was terminated. Next, oxygen gas was injected into the vacuum chamber to set the pressure in the vacuum chamber to 1.5 × 10 ⁻⁴ Torr, and then the evaporation material was Al ₂ O ₃ and vapor deposition was performed in the same manner as described above. The current value of the electron beam at this time was 210 mA, and the formation rate of the Al ₂ O ₃ film was 7.2 Å / s. When the film thickness of the Al ₂ O ₃ film formed on the substrate surface reached 76.1 nm, the second film deposition process was terminated. Next, after oxygen gas was injected into the vacuum chamber and the pressure in the vacuum chamber was increased to 1.8 × 10 ⁻⁴ Torr, the vapor deposition material was subjected to vapor deposition treatment in the same manner as described above using TiO ₂ as a main component. . The current value of the electron beam was 200 mA, and the film formation rate of TiO ₂ as a main component was 5.3 Å / s. When the film thickness of the TiO ₂ film formed on the substrate surface reached 120.2 nm, the third film deposition process was terminated. Finally, the vacuum pump was driven again to lower the vacuum chamber pressure to 2 × 10 ⁻⁵ Torr, and then the vapor deposition process was performed in the same manner as described above using MgF ₂ as the vapor deposition material without injecting oxygen gas. . The formation rate of the MgF ₂ film was 9.6 Å / s. When the film thickness of the MgF ₂ film formed on the substrate surface reached 89.1 nm, the fourth film deposition process was terminated. A schematic configuration diagram of the produced antireflection film is shown in FIG. 2, and the deposition conditions are summarized in Table 1.
[0027]
[Table 1]

[0028]
Spectral reflectance characteristics and spectral transmittance characteristics of the optical element thus fabricated were measured. The measurement results are shown in FIGS. According to FIG. 3, the reflectance of the formed antireflection film is excellent at 0.4% or less in the visible light region, and is a very low value of 0.2% or less in the blue wavelength region of 420 to 500 nm. Met. According to FIG. 4, the average transmittance in the blue wavelength region of 420 to 500 nm was 99.61%, which was a significantly higher value than before.
[0029]
(Comparative Example 1)
Using a vacuum deposition apparatus, on the surface of “FCD1” manufactured by Hoya as a base material, a SiO ₂ film, an Al ₂ O ₃ film, a film containing TiO ₂ as a main component, and an MgF ₂ film in order from the base material side. An antireflection film having a layer structure was formed in the same manner as in Example 1. The deposition conditions are shown in Table 2.
[0030]
[Table 2]

[0031]
Spectral reflectance characteristics and spectral transmittance characteristics of the optical element thus fabricated were measured. The measurement results are shown in FIGS. According to FIG. 5, the reflectance of the formed antireflection film was excellent at 0.4% or less in the visible light region. However, according to FIG. 6, the average transmittance in the blue wavelength range of 420 to 500 nm was a low value of 98.93%.
[0032]
(Example 2)
Using a vacuum deposition apparatus, a film made of a mixture of Al ₂ O ₃ and La ₂ O _{3 in} order from the substrate side, a TiO ₂ film, on the surface of “SK10” as the substrate in the same manner as in Example 1. An antireflection film having a three-layer structure of SiO ₂ film was formed. Here, when the refractive index of the film made of a mixture of Al ₂ O ₃ and La ₂ O ₃ of the first film is lowered, the antireflection band is narrowed. Was also faster. Other vapor deposition conditions are shown in Table 3.
[0033]
[Table 3]

[0034]
Spectral reflectance characteristics and spectral transmittance characteristics of the optical element thus fabricated were measured. The measurement results are shown in FIGS. According to FIG. 7, the reflectance of the formed antireflection film is excellent at an average of 0.1% or less in the blue laser wavelength region of 400 to 410 nm, and according to FIG. The average transmittance in the blue laser wavelength region was 99.89%, which was a significantly higher value than before.
[0035]
(Comparative Example 2)
Using a vacuum vapor deposition apparatus in the same manner as in Example 2, a film made of a mixture of Al ₂ O ₃ and La ₂ O _{3 in} order from the substrate side, a TiO ₂ film, and SiO ₂ on the surface of “SK10” as the substrate. _An antireflection film having a _two- layer three-layer structure was formed. The deposition conditions are shown in Table 4.
[0036]
[Table 4]

[0037]
Spectral reflectance characteristics and spectral transmittance characteristics of the optical element thus fabricated were measured. The measurement results are shown in FIGS. According to FIG. 9, in the blue laser wavelength region of 400 to 410 nm, the reflectance of the formed antireflection film was 0.1% or less on average, which was excellent as in the optical element of Example 2. However, according to FIG. 10, the average transmittance in the blue laser wavelength region of 400 to 410 nm was a low value of 99.10%.
[0038]
【The invention's effect】
In the method for forming an antireflection film according to the present invention, a SiO ₂ film is formed on a substrate surface using a vacuum deposition apparatus under a pressure of 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr, _{the Al} 2 _{O 3} film was formed under a pressure of ^{^{1.4 × 10 -4 ~1.7 × 10 -4}} Torr, TiO under a pressure of ^{^{1.7 × 10 -4 ~2.0 × 10 -4}} Torr _{In addition} to forming the _two films, the first film is formed at the predetermined pressure by injecting oxygen after the pressure in the apparatus is temporarily set to 2 × 10 ⁻⁵ Torr or less, so that an excellent antireflection effect is achieved. At the same time, an antireflection film with little light absorption in the blue wavelength region of 420 to 500 nm can be formed.
[0039]
SiO ₂ film, _Al 2 _{O 3} film, at least one layer of the TiO ₂ film, when the SiO ₂ film is 10 Å / s or more, _Al 2 _{O 3} in the case of the film 5 Å / s or more, of the TiO ₂ film In some cases, when the film is formed at a formation rate of 4.5 Å / s or more, a decrease in the refractive index of each film can be suppressed.
[0040]
In addition, when the films are formed in order from the lowest set pressure at the time of film formation, an operation for lowering the pressure in the vacuum chamber during the vapor deposition process is unnecessary, and the production efficiency is improved.
[0041]
Further, in the optical element according to the present invention, since the antireflection film is formed on the optical element body by the above-described forming method, it has an excellent antireflection effect and is also markedly superior in the blue wavelength region of 420 to 500 nm as compared with the conventional one. High transmittance can be obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a method for forming an antireflection film according to the present invention.
2 is a schematic configuration diagram of an antireflection film of Example 1. FIG.
3 is a spectral reflection characteristic diagram of the optical element of Example 1. FIG.
4 is a spectral transmittance characteristic diagram of the optical element of Example 1. FIG.
5 is a spectral reflection characteristic diagram of the optical element of Comparative Example 1. FIG.
6 is a spectral transmittance characteristic diagram of the optical element of Comparative Example 1. FIG.
7 is a spectral reflection characteristic diagram of the optical element according to Example 2. FIG.
8 is a spectral transmittance characteristic diagram of the optical element according to Example 2. FIG.
9 is a spectral reflection characteristic diagram of the optical element in Comparative Example 2. FIG.
10 is a spectral transmittance characteristic diagram of the optical element of Comparative Example 2. FIG.

Claims

A film composed mainly of SiO _2, a film composed mainly of Al ₂ O _3, an antireflection film and a film mainly composed of TiO _2, transparent substrate using a vacuum vapor deposition apparatus A method of forming on a surface,
The film mainly composed of SiO ₂ is formed under a pressure of 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr,
The film mainly composed of Al ₂ O ₃ is formed under a pressure of 1.4 × 10 ^{−4 to} 1.7 × 10 ⁻⁴ Torr,
The film mainly composed of TiO ₂ is formed under a pressure of 1.7 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ Torr,
The first film is formed with the predetermined pressure by injecting oxygen after the pressure in the apparatus is once set to 2 × 10 ⁻⁵ Torr or less.

Formation of SiO ₂ film containing as a main component, a film composed mainly of Al ₂ O _3, the anti-reflection film of claim 1 wherein at least one layer of a film mainly composed of TiO ₂ formed by the following formation speed Method.
Film having SiO ₂ as main component: 10 Å / s or more Film having Al ₂ O ₃ as main component: 5 Å / s or more Film having TiO ₂ as main component: 4.5 Å / s or more

The method of forming an antireflection film according to claim 1 or 2, wherein the film is formed in order from the lowest set pressure at the time of film formation.

A film composed mainly of SiO _2, a film composed mainly of Al ₂ O _3, an antireflection film including a film composed mainly of TiO ₂ is transparent optical element using a vacuum deposition apparatus An optical element formed on the body,
The film mainly composed of SiO ₂ is formed under a pressure of 1.0 × 10 ^{−4 to} 1.3 × 10 ⁻⁴ Torr,
The film mainly composed of Al ₂ O ₃ is formed under a pressure of 1.4 × 10 ^{−4 to} 1.7 × 10 ⁻⁴ Torr,
The film mainly composed of TiO ₂ is formed under a pressure of 1.7 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ Torr,
The first film is formed by setting the pressure in the apparatus to 2 × 10 ⁻⁵ Torr or less and then injecting oxygen to achieve the predetermined pressure.

5. The optical system according to claim 4, wherein at least one of a film containing SiO ₂ as a main component, a film containing Al ₂ O ₃ as a main component, and a film containing TiO ₂ as a main component is formed at the following formation rate. element.
Film having SiO ₂ as main component: 10 Å / s or more Film having Al ₂ O ₃ as main component: 5 Å / s or more Film having TiO ₂ as main component: 4.5 Å / s or more

The optical element according to claim 4, wherein a film mainly composed of SiO ₂ , a film mainly composed of Al ₂ O ₃ , and a film mainly composed of TiO ₂ are formed in order from the optical element body side.