JP4219609B2

JP4219609B2 - Method for manufacturing polarization separating element

Info

Publication number: JP4219609B2
Application number: JP2002105246A
Authority: JP
Inventors: 秀一曳地
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-04-08
Filing date: 2002-04-08
Publication date: 2009-02-04
Anticipated expiration: 2022-04-08
Also published as: JP2003294947A

Description

【０００１】
【発明の属する技術分野】
本発明は、生産性が良く、信頼性の高い偏光分離素子とその製造方法に関し、特に接着に特徴を有する偏光分離素子の製造方法に関する。
【０００２】
【従来の技術】
偏光分離素子に関する従来技術として、特開昭６３−３１４５０２号公報、特開２０００−７５１３０号公報では、簡単な工程で安価に作製できる偏光分離素子として、透明基板上、同一平面に回折格子を有する複屈折膜と、その上に等方性のオーバーコート層が被覆あるいは装荷されている構造のものが提案されている。これらの中には良好な光学的特性を得るために両面の平坦性の向上を目的とした構成となっているものがある。これはガラスやプラスチック等の透明基板上の同一平面に回折格子を形成し、接着剤により接着され、その複屈折膜が等方性のオーバーコート層で覆われ、このオーバーコート層が接着層も兼ねて透明基板と接着しているために、素子として強度があり、かつ生産性の高い構成となっているものである。
【０００３】
特開平９−９０２６３号公報記載の発明では、ホログラムディスク表面を予め上方に反った形状にプラスチック基板を成形加工し、組み付けた後に、重力によりホログラムディスクが下方に撓み反りを打ち消すことで、回折レーザー光の回折角の変動を低減している。
また、特許第２６３９６５９号公報記載の発明では、ガラス基板上にフォトエッチングで凹凸（回折格子）を形成し、もうひとつの面に真空蒸着法でＭｇＦ_２の無反射コーティングを施し、回折格子で反射されて直接に受光手段に入射したり、回折格子で反射された光が迷光となって受光手段に入射することを防止している。
【０００４】
１９９３年第４０回春季応用物理学会30a-B-1では、ＬｉＮｂＯ_３（ニオブ酸リチウム）を基板に用いた偏光分離素子を実現している。また、特開平１０−３３５４３３号公報記載の発明では、真空中で貼り付けを行い、貼り付け時の気泡の巻き込みを防止している。この場合、予め粘着剤を塗布しておいたフィルムを用いているように、蒸気圧成分を含む接着剤の使用には制限がある。
【０００５】
特開２０００−４７０１４号公報では、ニオブ酸リチウム基板の結晶のＸ面もしくはＹ面の所定の部分がプロトン交換されたプロトン交換層と、これによりニオブ酸リチウム基板に生じる応力を前記と同じ手法でプロトン交換されたプロトン交換層により応力を補正するプロトン交換層とを備えた光学素子の製造方法が記載されている。
【０００６】
【発明が解決しようとする課題】
直交する２つの偏光成分を分離するため、透明基板上に入射光の異なる振動面に対し屈折率が異なる有機複屈折膜を接着した構成の偏光分離素子では、前記有機複屈折膜の接着時において、有機複屈折膜が延伸した高分子材料であり、その後の微細加工プロセスにおけるフォトリソグラフィのレジスト硬化プロセスでかかる温度で、有機複屈折膜が熱収縮し、その結果、有機複屈折膜を接着した透明基板が、有機複屈折膜側に反るという問題がある。また、用いる接着剤も１〜１０％程度の硬化収縮があり、基板の反りが発生する問題がある。この有機複屈折膜接着基板の反りはフォトリソグラフィプロセスにおける露光時の焦点位置変動による焦点合わせ不良や、波面収差の低下等の問題となる。
【０００７】
また、有機複屈折膜のフィルム厚みは一般的に数十μｍ〜数百μｍと薄く、他の部材に接着する際、自重や気圧等により容易に変形し、透明基板上の接着剤と有機複屈折膜の接触点が面で接触し、気泡を巻込む問題がある。
さらに接着剤硬化後は透明基板と同等の屈折率が必要であり、また、光の吸収がない特性が要求される等、制約が多いという問題がある。また、ＬｉＮｂＯ_３のような材料を基板に用いて偏光分離素子を作成する方法では、高価な光学結晶が必要となり、材料コストが高く、また、プロセスも複雑になり製造コストも高くなる。
【０００８】
本発明は上記のような事情に鑑みなされたものであり、透明基板に有機複屈折膜を接着後、有機複屈折膜上への微細加工におけるプロセス時に発生する有機複屈折膜の熱収縮による基板の反りを低減することができる構成の偏光分離素子と、その製造方法を提供することを目的とする。
さらに本発明では、気泡の巻き込みの無い有機複屈折膜の接着を行なうことができ、これにより素子の信頼性向上を確保することのできる偏光分離素子の製造方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
上記目的を達成するための手段として、本発明では以下に示すような構成の偏光分離素子及びその製造方法を採用した。
(１)．直交する２つの偏光成分を分離するため、透明基板上に入射光の異なる振動面に対し屈折率が異なる有機複屈折膜を接着し、この有機複屈折膜に周期的な凹凸格子（以下、回折格子と記述する）を形成し、この回折格子の凹み部分に等方性の接着剤を充填し、該回折格子上に対向透明基板を接着した構成の偏光分離素子において、前記有機複屈折膜を接着する透明基板に応力を有するコーティング膜を設けた構成とする。
(２)．前記(１)に記載の偏光分離素子において、前記コーティング膜の応力は、引張り応力となるように構成する。
(３)．前記(１)または(２)に記載の偏光分離素子において、前記コーティング膜は、透明基板の屈折率と同等もしくはそれより小さい屈折率を有する単層または多層のコーティング膜、あるいは単層または透明基板より小さい屈折率と大きい屈折率との多層の反射防止膜からなる構成とする。
(４)．前記(１)，(２)または(３)に記載の偏光分離素子において、前記透明基板のコーティング膜を設けた面とは反対側の面に有機複屈折膜を接着した構成とする。
(５)．前記(４)に記載の偏光分離素子において、前記有機複屈折膜は、延伸により分子鎖を配向させた高分子膜からなる構成とする。
(６)．前記(１)〜(５)のいずれか一つに記載の偏光分離素子において、前記コーティング膜の応力を前記有機複屈折膜の熱収縮応力と均衡するよう制御した構成とする。
【００１０】
(７)．直交する２つの偏光成分を分離するため、透明基板上に入射光の異なる振動面に対し屈折率が異なる有機複屈折膜を接着し、この有機複屈折膜に周期的な凹凸格子（以下、回折格子と記述する）を形成し、この回折格子の凹み部分に等方性の接着剤を充填し、該回折格子上に対向透明基板を接着し、前記有機複屈折膜を接着する透明基板に応力を有するコーティング膜を設けた偏光分離素子の製造方法において、前記有機複屈折膜をＵ字形状に変形する工程と、該有機複屈折膜を透明基板に接着する際、ＣＣＤレーザー変位計を用いて前記有機複屈折膜のＵ字形状及び透明基板上の接着剤の凸形状の頂点位置情報を取得する工程と、前記有機複屈折膜のＵ字形状の頂点を接着剤の凸形状の頂点に位置合わせを行い、前記有機複屈折膜のＵ字形状の頂点と接着剤の凸形状の頂点との一つの接触点において接触させる工程と、前記接触点から全体に接触面を広げることにより接着する工程と、を含むことを特徴とする（請求項１）。
(８)．前記(７)に記載の偏光分離素子の製造方法において、前記コーティング膜の応力は引張り応力とし、該コーティング膜の応力により透明基板に反りを発生させる（請求項２）。
(９)．前記(７)または(８)に記載の偏光分離素子の製造方法において、前記コーティング膜として、透明基板の屈折率と同等もしくはそれより小さい屈折率を有する単層または多層のコーティング膜、あるいは単層または透明基板より小さい屈折率と大きい屈折率との多層の反射防止膜を形成する（請求項３）。
(１０)．前記(７)，(８)または(９)に記載の偏光分離素子の製造方法において、前記透明基板のコーティング膜を設けた面とは反対側の面に有機複屈折膜を接着する（請求項４）。
(１１)．前記(１０)に記載の偏光分離素子の製造方法において、前記有機複屈折膜は、延伸により分子鎖を配向させた高分子膜とする（請求項５）。
(１２)．前記(７)〜(１１)のいずれか一つに記載の偏光分離素子の製造方法において、前記コーティング膜の応力を前記有機複屈折膜の熱収縮応力と均衡するよう制御する（請求項６）。
(１３)．前記(７)〜(１２)のいずれか一つに記載の偏光分離素子の製造方法において、前記有機複屈折膜を透明基板に接着する工程では、紫外線を有機複屈折膜側から照射する（請求項７）。
尚、有機複屈折膜と透明基板とを接着する接着剤としては、光硬化型の接着剤（例えばアクリル系またはエポキシ系の光硬化型接着剤）などが好適に用いられる。
( １４ )．前記(７)〜(１３)のいずれか一つに記載の偏光分離素子の製造方法において、前記有機複屈折膜と透明基板とを接着する接着装置の透明基板を載置固定する装置形状を、透明基板のコーティング膜側表面形状と相似形とした（請求項８）。
(１５)．前記(７)〜(１３)のいずれか一つに記載の偏光分離素子の製造方法において、前記有機複屈折膜と透明基板とを接着する接着装置の有機複屈折膜を加圧する装置形状を、透明基板のコーティング膜とは反対側の表面形状と相似形とした（請求項９）。
【００１１】
【発明の実施の形態】
以下、本発明の実施形態を図面を参照して詳細に説明する。
図１は本発明の一実施例を示す偏光分離素子の概略断面図である。この偏光分離素子は、透明基板１上に入射光の異なる振動面に対し屈折率が異なる有機複屈折膜３を接着剤２により接着し、この有機複屈折膜３に周期的な凹凸格子（以下、回折格子と記述する）４を形成し、この回折格子４の凹み部分に等方性の接着剤５を充填し、該回折格子上に対向透明基板６を接着した構成であり、さらに、前記有機複屈折膜３を接着する透明基板１に引張り応力を有するコーティング膜７を設けた構成としたものである。
すなわち、この実施例では、透明基板１の片面に引張り応力を有する単層または多層の膜７をコーティングし、この透明基板１の反対の平面上に有機複屈折膜３を接着剤２で接着し、有機複屈折膜３に微細加工により回折格子４を形成し、その後、等方性接着剤５で対向透明基板６を接着し、偏光分離素子を構成している。以下、本発明の偏光分離素子とその製造方法の具体的な実施例を示す。
【００１２】
［実施例１］
本発明の第１の実施例を図２〜５を参照して説明する。図２に第１の実施例の透明基板及びコーティング膜の断面図を示した。本実施例では、透明基板１として、直径φ１００ｍｍ、板厚１．０ｍｍの石英ガラス基板を用い、この石英ガラス基板１の片面にコーティング膜７として真空蒸着法でＭｇＦ_２を１μｍの膜厚で形成した。真空蒸着は薄膜を形成する一般的な手法と同じ方法で形成しているので詳細な説明は省略する。
【００１３】
このようにしてＭｇＦ_２コーティング膜７が形成された石英ガラス基板１は、ＭｇＦ_２コーティング膜７の引張り応力により、ＭｇＦ_２コーティング膜７側に反っている。
また、望ましくはＭｇＦ_２コーティング膜７の引張り応力は１ＭＰａ〜１０ＧＰａになるように基板温度、膜厚、等のコーティング条件で応力を制御する。
尚、コーティング膜７の材質はＭｇＦ_２に限定するものではなく、石英ガラス基板１と屈折率が同等もしくはそれ以下の屈折率の材料、例えばＣａＦ_２、ＬｉＦ等の誘電体材料を用いてもよい。
【００１４】
次に図３は裏面側にコーティング膜を設けた基板上に有機複屈折膜を接着する際に用いられる接着装置の概略構成を示す図である。図３に示すように、Ｘ，Ｙ，Ｚ軸が移動可能な移動ステージ８上に固定された基板ホルダ９上に、ＭｇＦ_２膜面を下に石英ガラス基板１が載置され、図示しない真空吸着機構により固定される。この基板ホルダ９はＭｇＦ_２膜７をコーティングした石英ガラス基板１のコーティング膜側表面の反りとほぼ同じ形状を有する凸形状としている。基板ホルダ９及び石英ガラス基板１の上方には、図示しない接着剤滴下装置と、接着剤２の中心の特定と有機複屈折膜３の中心を測定するためのＸ，Ｙ方向に移動可能な測定系を設けてある。本実施例では測定系として、接着剤２、石英ガラス基板１及び有機複屈折膜３の表面からの反射光を検出し、変位量を読み取るＣＣＤレーザー変位計１１と、ＣＣＤレーザー変位計１１で位置検出し、位置情報をそれぞれの移動装置にフィードバックする回路（図示せず）と、有機複屈折膜３の両端部を保持するための保持装置１０を、基板ホルダ９に対し平行に配置し、これに図示しないモーメント力Ｍを発生する装置を配置している。
【００１５】
次に石英ガラス基板１の中心に、石英ガラス基板１とほぼ同じ屈折率１．５８のアクリル樹脂系の紫外線（ＵＶ）硬化型接着剤２を０．２ｍＬ滴下し、この上方に有機複屈折膜３を載置する。有機複屈折膜３は厚み０．１２ｍｍで１１０ｍｍ×１２０ｍｍの大きさに切断されており、保持装置１０により有機複屈折膜３の両端部が真空吸着により保持されている。そして、有機複屈折膜３の略中心位置を石英ガラス基板１の略中心位置に載置した後、図示しないモーメント発生装置により有機複屈折膜３をＵ字形状に変形する。再び、ＣＣＤレーザー変位計１１により有機複屈折膜３の表面形状を測定し、Ｕ字形状の中心位置を検出し、予め測定しておいた接着剤２の凸形状の頂点位置情報より移動量を演算し、Ｘ−Ｙ移動装置により有機複屈折膜３のＵ字形状の中心を接着剤２の凸中心に位置合わせを行う。そして、石英ガラス基板１−接着剤２−有機複屈折膜３の位置合わせを完了した後、移動ステージ８で基板ホルダ９を上昇し、接着剤２と有機複屈折膜３のそれぞれの頂点で接触する位置で停止し、その後、有機複屈折膜３のモーメント力Ｍを緩やかに解除しながら有機複屈折膜３を石英ガラス基板１上に載置する。
【００１６】
次に、図４に示すように、石英ガラス基板１のコーティング膜７とは反対側の面の反りとほぼ同じ凹み形状に加工した、直径φ１１０ｍｍ、厚み２０ｍｍの石英ガラス製押圧装置１２を有機複屈折膜３上に載せ、有機複屈折膜３の全面を均等に加圧し、接着剤２が石英ガラス基板１の全面に広がった時点で加圧を停止した後、押圧装置１２を通して図示しない紫外線照射装置（ＵＶ装置）で光強度３０ｍＷ／ｃｍ^２の紫外線を２００秒間照射し、接着剤２を硬化した。硬化後、直径φ１００ｍｍの外形に沿って、余分な有機複屈折膜３を切断した後、押圧装置１２を上昇し、基板ホルダ９の真空吸着を解除して石英ガラス基板１を取り出し、有機複屈折膜付き石英ガラス基板とした。
【００１７】
以上のように、接着工程時の位置合わせ方法として、有機複屈折膜３の中央から石英ガラス基板１に接触することで、面接触で接着する従来法では目視レベルで確認できる気泡の巻き込みが発生していたのに対し、本実施例の方法では気泡の巻き込みがない貼り合わせが実現できた。
【００１８】
尚、接着工程時の位置合わせは本実施例の方法の他、ＣＣＤカメラと画像処理装置により石英ガラス基板１と接着剤２の形状を認識し、中心を割り出し、位置合わせする方法等も実施可能である。また、ここでは接着剤としてアクリル樹脂系の光硬化型の接着剤を用いて接着したが、エポキシ樹脂系の光硬化型の接着剤を用いてもよい。
また、有機複屈折膜３はハンドリング性を考慮すると、厚みは０．０１ｍｍ以上が望ましいが、延伸により光学的特性を得ることを考慮すると、最大厚み０．５ｍｍの範囲で用いるのが好ましい。より望ましくは０．０５〜０．２ｍｍの範囲がよい。本実施例では厚み０．１２ｍｍの有機複屈折膜を用いた。
【００１９】
次に、石英ガラス基板１上に接着した有機複屈折膜３をイソプロピルアルコール等の有機溶媒と純水の順で洗浄する。その後、日本ゼオン化社製ＺＥＰ−５２０レジストをスピンコートにより０．５μｍ厚のレジスト膜を形成し、１００℃で３０分間ベークした。この時、有機複屈折膜３の熱収縮で石英ガラス基板１に引張り応力約７．５ＭＰａが発生するが、石英ガラス基板１の裏面にコーティングしたコーティング膜７の応力と均衡するため、石英ガラス基板１は平面性を保っている。その後、ステッパ装置を用い、有機複屈折膜３上のレジスト膜にライン＆スペース３μｍのパターンを８ｍｍピッチで３００周期繰り返し形成し、レジスト膜に周期的な凹凸格子（回折格子）のパターンを形成した素子を形成した。この回折格子のパターンは素子外形８×８ｍｍの中心に略形状１×２ｍｍで形成している。
【００２０】
この後、酸素ガスを主成分とするエッチングガス雰囲気中で、住友金属社製ＥＣＲ（Electron Cyclotron Resonance：電子サイクロトロン共鳴）エッチング装置でエッチングし、有機複屈折膜３に幅３μｍ、深さ５μｍのラインと３μｍ幅のスペースを３００周期繰り返した回折格子４を形成した。
尚、他のフォトリソ工程は一般に知られているプロセスを採用しており、詳細な説明は省略する。
【００２１】
次に、平面加工した直径φ２００ｍｍ、厚み５０ｍｍのステンレス台上に、有機複屈折膜３に回折格子４を形成した石英ガラス基板１を載置し、この回折格子面にアクリル樹脂系の光硬化型の等方性接着剤５をマイクロシリンジで０．２５ｍＬ計量滴下し、この等方性接着剤５を滴下した石英ガラス基板１の回折格子面に両面光学研磨した外径φ１００ｍｍ、厚み０．５ｍｍの対向透明基板６を載置し、さらにこの上に加圧部材として光学研磨した石英ガラスを載せ、対向透明基板６に１００ｇｆ／ｃｍ^２の圧力を印加し、等方性接着剤５を被接着面全面に広げた。尚、対向透明基板６の接着面と反対の面には入射波長の反射が最小となるよう反射防止膜を形成した。この状態で、図示しない紫外線照射装置で１５０ｍｍ上面から照射照度２０ｍＷ／ｃｍ^２の紫外光を対向透明基板６を通して１０分間照射し硬化接着した。このようにして製造した偏光分離素子の要部断面を図５に示す。
【００２２】
図５に示す偏光分離素子の等方性接着剤５は粘性や屈折率等の特性制御の容易さや接着力および透明性の点からアクリル系の接着剤を用いたが、エポキシ系でも同様なことが可能である。これらの接着剤は紫外線で硬化するので、加圧部材に石英ガラス等の透明部材を用いることにより加圧中硬化が可能であり、プロセスを簡略できる。
また、有機複屈折膜３としては、ポリエチレンテレフタレート（ＰＥＴ）等の高分子膜を布で擦ってラビング処理して配向膜を形成し、この配向膜上にポリジアセチレンモノマーを真空蒸着して配向させた後、紫外光を照射してポリマー化して異方性膜とする方法（参考文献：J.Appl.phys.,72,No,3,P938-947）があるが、工程が複雑でコスト高となるため、ここでは、分子鎖が配向した高分子膜で、特性の均一性を考慮して延伸された有機複屈折膜を用いた。
【００２３】
［実施例２］
次に本発明の第２の実施例について説明する。図６は本発明の第２の実施例を示す図であり、一方の面に多層コーティング膜を形成し、他方の面に有機複屈折膜を接着した透明基板の一例を示す要部断面図である。図中の符号２１は透明基板、２２は接着剤、２３は有機複屈折膜、２４は多層膜からなるコーティング膜である。尚、偏光分離素子の構成としては、図１、図５と同様に、有機複屈折膜２３上に周期的な凹凸格子（回折格子）４が形成され、その回折格子４の凹み部分には等方性接着剤５が充填され、該等方性接着剤で回折格子上に対向透明基板６が接着されるが、これらの図示は省略している。
【００２４】
本実施例では、透明基板２１として、直径φ１００ｍｍ、板厚０．５ｍｍのＢＫ−７基板を用い、このＢＫ−７基板２１の片面に、真空蒸着法でＳｉＯ_２膜２４ａ、ＴｉＯ_２膜２４ｂ、ＳｉＯ_２膜２４ｃの３層からなる多層コーティング膜２４を、ＳｉＯ_２／ＴｉＯ_２／ＳｉＯ_２がｎ1・ｔ1＝λ／４、ｎ2・ｔ2＝λ／４もしくはｎ2・ｔ2＝λ／２をとるように膜厚を制御し、引っ張り応力となるよう形成した。ここでｎ1はＳｉＯ_２の屈折率で、ｔ1はＳｉＯ_２の膜厚、ｎ2はＴｉＯ_２の屈折率で、ｔ2はＴｉＯ_２の膜厚、λは波長で６６０ｎｍである。尚、真空蒸着は薄膜を形成する一般的な手法と同じ方法で形成しているので詳細な説明は省略する。
【００２５】
このようにして多層コーティング膜２４が形成されたＢＫ−７基板２１は、多層のコーティング膜２４側からの入射光の反射率が０．５％以下と小さく、且つコーティング膜２４の引張り応力で膜側に反っている。尚、コーティング膜２４は、材質をＣａＦ_２やＳｉＯ_２等の他の誘電体の単層もしくは多層膜として構成してもよい。
【００２６】
次に図３と同様な構成の接着装置を用いた接着工程について説明するが、ここでは、図３の基板１、接着剤２、有機複屈折膜３を、本実施例のＢＫ−７基板２１、接着剤２２、有機複屈折膜２３に置き換えて説明する。Ｘ，Ｙ，Ｚ軸が移動可能な移動ステージ８上に固定された基板ホルダ９上に、本実施例のＢＫ−７基板２１をコーティング膜面を下にして載置し、図示しない真空吸着機構により固定する。この基板ホルダ９は多層コーティング膜２４をコーティングしたＢＫ−７基板２１のコーティング膜側表面の反りとほぼ同じ形状を有する凸形状としている。基板ホルダ９及びＢＫ−７基板２１の上方には、図示しない接着剤滴下装置と、接着剤の中心の特定と有機複屈折膜２３の中心を測定するためのＸ，Ｙ方向に移動可能な測定系を設けてある。本実施例では、図３と同様に測定系として、接着剤２２、ＢＫ−７基板２１及び有機複屈折膜２３の表面からの反射光を検出し、変位量を読み取るＣＣＤレーザー変位計１１と、ＣＣＤレーザー変位計１１で位置検出し、位置情報をそれぞれの移動装置にフィードバックする回路（図示せず）と、有機複屈折膜２３の両端部を保持するための保持装置１０を、基板ホルダ９に対し平行に配置し、これに図示しないモーメント力Ｍを発生する装置を配置している。
【００２７】
次に、ＢＫ−７基板２１の中心に、ＢＫ−７基板とほぼ同じ屈折率１．５８のアクリル樹脂系のＵＶ硬化型接着剤２２を０．２ｍＬ滴下し、この上方に有機複屈折膜２３を載置する。有機複屈折膜２３は厚み０．２ｍｍで１１０ｍｍ×１２０ｍｍの大きさに切断されており、図３と同様に保持装置１０により有機複屈折膜２３の両端部が真空吸着により保持されている。そして、有機複屈折膜２３の略中心位置をＢＫ−７基板の略中心位置に載置した後、図示しないモーメント発生装置により有機複屈折膜２３をＵ字形状に変形する。そして、再びＣＣＤレーザー変位計１１により有機複屈折膜２３の表面形状を測定し、Ｕ字形状の中心位置を検出し、予め測定しておいた接着剤２２の凸形状の頂点位置情報より移動量を演算し、Ｘ−Ｙ移動ステージ８により有機複屈折膜２３のＵ字形状の中心を接着剤２２の凸中心に位置合わせを行う。そして、ＢＫ−７基板−接着剤−有機複屈折膜の位置合わせを完了した後、移動ステージ８で基板ホルダを上昇し、接着剤２２と有機複屈折膜２３のそれぞれの頂点で接触する位置で停止し、その後、有機複屈折膜２３のモーメント力Ｍを緩やかに解除しながら有機複屈折膜２３をＢＫ−７基板２１上に載置する。
【００２８】
次に、図４と同様に、ＢＫ−７基板２１のコーティング膜とは反対側の面の反りとほぼ同じ形状を有する凹み形状に加工した、直径φ１１０ｍｍ、厚み２０ｍｍの石英ガラス製押圧装置１２を有機複屈折膜２３上に載せ、有機複屈折膜２３の全面を均等に加圧し、接着剤２２がＢＫ−７基板２１の全面に広がった時点で加圧を停止した後、押圧装置を通して紫外線照射装置（ＵＶ装置）で光強度３０ｍＷ／ｃｍ^２の紫外線を２００秒間照射し、接着剤２２を硬化した。硬化後、直径φ１００ｍｍの外形に沿って、余分な有機複屈折膜２３を切断した後、押圧装置を上昇し、基板ホルダの真空吸着を解除してＢＫ−７基板２３を取り出し、図６に示すような有機複屈折膜付きＢＫ−７基板とした。
【００２９】
以上のように、接着工程時の位置合わせ方法として、有機複屈折膜２３の中央から基板２１に接触することで、面接触で接着する従来法では目視レベルで確認できる気泡の巻き込みが発生していたのに対し、本実施例の方法では気泡の巻き込みがない貼り合わせが実現できた。
また、下記の表１に、有機複屈折膜側とコーティング膜（ＳｉＯ_２／ＴｉＯ_２／ＳｉＯ_２膜）側から紫外線を照射した時の光強度比を示すが、表１に示した通り、有機複屈折膜側から紫外線を入射することで、効率良く接着剤へ光照射できる。
【００３０】
【表１】

【００３１】
尚、接着工程時の位置合わせは本実施例の他、ＣＣＤカメラと画像処理装置によりＢＫ−７基板２１と接着剤２２の形状を認識し、中心を割り出し、位置合わせする方法等も実施可能である。また、ここではアクリル樹脂系の光硬化型の接着剤を用いて接着したが、エポキシ樹脂系の光硬化型の接着剤を用いてもよい。また、有機複屈折膜２３はハンドリング性を考慮すると、厚みは０．０１ｍｍ以上が望ましいが、延伸により光学的特性を得ることを考慮すると、最大厚み０．５ｍｍの範囲で用いるのが好ましい。より望ましくは０．０５〜０．２ｍｍの範囲がよい。本実施例では厚み０．２ｍｍの有機複屈折膜を用いた。
【００３２】
次に、ＢＫ−７基板２１上に接着した有機複屈折膜２３をイソプロピルアルコール等の有機溶媒と純水の順で洗浄する。その後、日本ゼオン化社製ＺＥＰ−５２０レジストを用い、スピンコートにより有機複屈折膜２３上に０．５μｍ厚のレジスト膜を形成し、１００℃で３０分間ベークした。この時、有機複屈折膜２３の熱収縮でＢＫ−７基板２１に引張り応力が発生するが、ＢＫ−７基板２１の裏面にコーティングしたコーティング膜２４の応力と均衡するためＢＫ−７基板２１は平面性を保っている。その後、ステッパ装置を用い、ライン＆スペース３μｍのパターンを８ｍｍピッチで３００周期繰り返し形成し、レジスト膜に周期的な凹凸格子（回折格子）のパターンを形成した素子を形成した。この回折格子のパターンは素子外形８×８ｍｍの中心に略形状１×２ｍｍで形成している。
【００３３】
この後、酸素ガスを主成分とするエッチングガス雰囲気中で、住友金属社製ＥＣＲ（Electron Cyclotron Resonance：電子サイクロトロン共鳴）エッチング装置でエッチングし、有機複屈折膜２３に幅３μｍ、深さ５μｍのラインと３μｍ幅のスペースを３００周期繰り返した回折格子を形成した。
尚、他のフォトリソ工程は一般に知られているプロセスを採用しており、詳細な説明は省略する。
【００３４】
次に平面加工した直径φ２００ｍｍ、厚み５０ｍｍのステンレス台上に、有機複屈折膜２３に回折格子を形成したＢＫ−７基板２１を載置し、この回折格子面にアクリル樹脂系の光硬化型の等方性接着剤をマイクロシリンジで０．２５ｍＬ計量滴下し、この等方性接着剤を滴下したＢＫ−７基板２１の回折格子面に両面光学研磨した外径φ１００ｍｍ、厚み０．５ｍｍの対向透明基板を載置し、さらにこの上に加圧部材として光学研磨した石英ガラスを載せ、対向透明基板に１００ｇｆ／ｃｍ^２の圧力を印加し、等方性接着剤を被接着面全面に広げた。尚、対向透明基板の接着面と反対の面には入射波長の反射が最小となるよう反射防止膜を形成した。この状態で、図示しない紫外線照射装置で１５０ｍｍ上面から照射照度２０ｍＷ／ｃｍ^２の紫外光を対向透明基板を通して１０分間照射し硬化接着した。このようにして製造した偏光分離素子の断面構造は図１や図５と略同様である。
【００３５】
以上のようにして製造された偏光分離素子の等方性接着剤は、粘性や屈折率等の特性制御の容易さや接着力および透明性の点からアクリル系の接着剤を用いたが、エポキシ系でも同様なことが可能である。これらの接着剤は紫外線で硬化するので、加圧部材に石英ガラス等の透明部材を用いることにより加圧中硬化が可能であり、プロセスを簡略できる。
また、有機複屈折膜２３としては、ポリエチレンテレフタレート（ＰＥＴ）等の高分子膜を布で擦ってラビング処理して配向膜を形成し、この配向膜上にポリジアセチレンモノマーを真空蒸着して配向させた後、紫外光を照射してポリマー化して異方性膜とする方法（参考文献：J.Appl.phys.,72,No,3,P938-947）があるが、工程が複雑でコスト高となるため、ここでは、分子鎖が配向した高分子膜で、特性の均一性を考慮して延伸された有機複屈折膜を用いた。
【００３６】
［実施例３］
次に本発明の第３の実施例について説明する。図７は本発明の第３の実施例の説明図であって、透明基板上に有機複屈折膜を接着する際に用いられる接着装置の概略構成を示す図である。
本実施例では図７に示すように、Ｘ，Ｙ，Ｚ軸が移動可能な移動ステージ８上に固定された基板ホルダ９上に、透明基板３１として、直径φ１００ｍｍ、板厚１．０ｍｍの透明なＢＫ−７基板が載置され、図示しない真空吸着機構により固定される。基板ホルダ９及びＢＫ−７基板３１の上方には、図示しない接着剤滴下装置と、接着剤３２の中心と有機複屈折膜３３の中心を測定するためのＸ，Ｙ方向に移動可能な測定系を設けてある。本実施例では、測定系として、接着剤３２、ＢＫ−７基板３１及び有機複屈折膜３３の表面からの反射光を検出し、変位量を読み取るＣＣＤレーザー変位計１１と、ＣＣＤレーザー変位計１１で位置検出し、位置情報をそれぞれの移動装置にフィードバックする回路（図示せず）と、有機複屈折膜３３の両端部を保持するための保持装置１０を、基板ホルダ９に対し平行に配置し、これに図示しないモーメント力Ｍを発生する装置を配置している。
【００３７】
次に、ＢＫ−７基板３１の中心に、ＢＫ−７基板３１とほぼ同じ屈折率１．５８のアクリル樹脂系のＵＶ硬化型接着剤３２を０．２ｍＬ滴下し、この上方に有機複屈折膜３３を載置する。有機複屈折膜３３は厚み０．２ｍｍで１１０ｍｍ×１２０ｍｍの大きさに切断されており、保持装置１０により有機複屈折膜３３の両端部が真空吸着により保持されている。そして、有機複屈折膜３３の略中心位置をＢＫ−７基板３１の略中心位置に載置した後、図示しないモーメント発生装置により有機複屈折膜３３をＵ字形状に変形する。そして、再びＣＣＤレーザー変位計１１により有機複屈折膜３３の表面形状を測定し、Ｕ字形状の中心位置を検出し、予め測定しておいた接着剤３２の凸形状の頂点位置情報より移動量を演算し、Ｘ−Ｙ移動装置により有機複屈折膜３３のＵ字形状の中心を接着剤３２の凸中心に位置合わせを行う。そして、ＢＫ−７基板−接着剤−有機複屈折膜の位置合わせを完了した後、移動ステージ８で基板ホルダ９を上昇し、接着剤３２と有機複屈折膜３３のそれぞれの頂点で接触する位置で停止し、その後、有機複屈折膜３３のモーメント力を緩やかに解除しながら有機複屈折膜３３をＢＫ−７基板３１上に載置する。
【００３８】
次に、ＢＫ−７基板３１の反りとほぼ同じ形状を有する凹み形状に加工した、直径φ１１０ｍｍ、厚み２０ｍｍの石英ガラス製押圧装置（図示せず）を有機複屈折膜上に載せ、有機複屈折膜３３の全面を均等に加圧し、接着剤３２がＢＫ−７基板３３の全面に広がった時点で加圧を停止した後、押圧装置を通して図示しない紫外線照射装置（ＵＶ装置）で光強度３０ｍＷ／ｃｍ^２の紫外線を２００秒間照射し、接着剤を硬化した。硬化後、直径φ１００ｍｍの外形に沿って、余分な有機複屈折膜３３を切断した後、押圧装置を上昇し、基板ホルダ９の真空吸着を解除してＢＫ−７基板３１を取り出し、有機複屈折膜付きＢＫ−７基板３１とした。図８（ａ）は以上のようにして有機複屈折膜が接着されたＢＫ−７基板の概略断面図である。
【００３９】
以上のように、接着工程時の位置合わせ方法として、有機複屈折膜３３の中央から基板３１に接触することで、面接触で接着する従来法では目視レベルで確認できる気泡の巻き込みが発生していたのに対し、本実施例の方法では気泡の巻き込みがない貼り合わせが実現できた。
【００４０】
尚、接着工程時の位置合わせは本実施例の他、ＣＣＤカメラと画像処理装置によりＢＫ−７基板２１と接着剤２２の形状を認識し、中心を割り出し、位置合わせする方法等も実施可能である。また、ここではアクリル樹脂系の光硬化型の接着剤を用いて接着したが、エポキシ樹脂系の光硬化型の接着剤を用いてもよい。また、有機複屈折膜３３はハンドリング性を考慮すると厚みは０．０１ｍｍ以上が望ましいが、延伸により光学的特性を得ることを考慮すると、最大厚み０．５ｍｍの範囲で用いるのが好ましい。より望ましくは０．０５〜０．２ｍｍの範囲がよい。本実施例では厚み０．２ｍｍの有機複屈折膜を用いた。
【００４１】
次に、図８（ａ）に示すＢＫ−７基板３１の有機複屈折膜３３を接着していない側の面に、真空蒸着法でＭｇＦ_２をｎ1・ｔ1＝λ／４、もしくはｎ1・ｔ1＝３λ／４となるように膜厚を制御してコーティング膜３４を形成した。図８（ｂ）はコーティング膜３４を形成したＢＫ−７基板の概略断面図である。ここでｎ1はＭｇＦ_２の屈折率で、ｔ1はＭｇＦ_２の膜厚、λは波長で６６０ｎｍを用いた。真空蒸着での基板温度は１００℃で実施した。真空蒸着プロセスは薄膜を形成する一般的な手法と同じ方法で形成しているので詳細な説明は省略する。
【００４２】
本実施例では、コーティング膜３４の引張り応力を有機複屈折膜３３の熱収縮による応力と均衡するよう０．１ＭＰａ〜１０ＧＰａで制御した。また、コーティング中の加熱により、有機複屈折膜３３の収縮が安定するため、その後のプロセスでの有機複屈折膜３３の収縮は極めて小さい。また、コーティング膜３４の構成を、ｎ1・ｔ1＝λ／４、もしくはｎ1・ｔ1＝３λ／４となるように膜厚を制御しているので、コーティング膜側からの入射光の反射率を低減できる。尚、コーティング膜３４のその他の膜構成としては、単層構成のＳｉＯ_２，ＣａＦ_２や、多層構成のＳｉＯ_２／ＴｉＯ_２／ＳｉＯ_２等でもよい。
【００４３】
次に、図８（ｂ）に示すＢＫ−７基板３１上の有機複屈折膜３３をイソプロピルアルコール等の有機溶媒と純水の順で洗浄する。その後、日本ゼオン化社製ＺＥＰ−５２０レジストを用い、スピンコートにより有機複屈折膜３３上に０．５μｍ厚のレジスト膜を形成し、１００℃で３０分間ベークした。この時、有機複屈折膜３３の熱収縮で基板３１に引張り応力が発生するが、ＢＫ−７基板３１の裏面にコーティングしたコーティング膜３４の引張り応力と均衡するためＢＫ−７基板３１は平面性を保っている。その後、ステッパ装置を用い、ライン＆スペース３μｍのパターンを８ｍｍピッチで３００周期繰り返し形成し、レジスト膜に周期的な凹凸格子（回折格子）のパターンを形成した素子を形成した。この回折格子のパターンは素子外形８×８ｍｍの中心に略形状１×２ｍｍで形成している。
【００４４】
この後、酸素ガスを主成分とするエッチングガス雰囲気中で、住友金属社製ＥＣＲ（Electron Cyclotron Resonance：電子サイクロトロン共鳴）エッチング装置でエッチングし、有機複屈折膜３３に幅３μｍ、深さ５μｍのラインと３μｍ幅のスペースを３００周期繰り返した回折格子を形成した。
尚、他のフォトリソ工程は一般に知られているプロセスを採用しており、詳細な説明は省略する。
【００４５】
次に、平面加工した直径φ２００ｍｍ、厚み５０ｍｍのステンレス台上に、回折格子を形成したＢＫ−７基板３１を載置し、この回折格子面にアクリル樹脂系の光硬化型の等方性接着剤をマイクロシリンジで０．２５ｍＬ計量滴下し、この等方性接着剤を滴下したＢＫ−７基板３１の回折格子面に両面光学研磨した外径φ１００ｍｍ、厚み０．５ｍｍの対向透明基板を載置し、さらにこの上に加圧部材として光学研磨した石英ガラスを載せ、対向透明基板に１００ｇｆ／ｃｍ^２の圧力を印加し、等方性接着剤５を被接着面全面に広げた。尚、対向透明基板の接着面と反対の面に入射波長の反射が最小となるよう反射防止膜を形成した。この状態で、図示しない紫外線照射装置で１５０ｍｍ上面から照射照度２０ｍＷ／ｃｍ^２の紫外光を対向透明基板を通して１０分間照射し硬化接着した。このようにして製造した偏光分離素子の断面構造は図１や図５と略同様である。
【００４６】
以上のようにして製造された偏光分離素子の等方性接着剤は、粘性や屈折率等の特性制御の容易さや接着力および透明性の点からアクリル系の接着剤を用いたが、エポキシ系でも同様なことが可能である。これらの接着剤は紫外線で硬化するので、加圧部材に石英ガラス等の透明部材を用いることにより加圧中硬化が可能であり、プロセスを簡略できる。
また、有機複屈折膜３３としては、ポリエチレンテレフタレート（ＰＥＴ）等の高分子膜を布で擦ってラビング処理して配向膜を形成し、この配向膜上にポリジアセチレンモノマーを真空蒸着して配向させた後、紫外光を照射してポリマー化して異方性膜とする方法（参考文献：J.Appl.phys.,72,No,3,P938-947）があるが、工程が複雑でコスト高となるため、ここでは、分子鎖が配向した高分子膜で、特性の均一性を考慮して延伸された有機複屈折膜を用いた。
【００４７】
以上、本発明の実施例１〜３について説明したが、本発明で作製した偏光分離素子の直径φ１００ｍｍの透明基板（石英ガラス基板またはＢＫ−７基板）の反りは３０μｍ以下であり、従来の基板の反りの１／５から１／１０と極めて小さい値であり、また、内包する気泡は従来は目視レベルで数個から数十個確認されていたのに対し、本発明の方法では気泡は確認できないほど低減できている。このように、本発明の偏光分離素子は、有機複屈折膜等を回折格子や位相差膜として用いた素子において、透明基板に有機複屈折膜を接着した有機複屈折膜の微細加工で発生する有機複屈折膜の収縮による基板の反りを、透明基板に形成したコーティング膜で相殺するので、露光時の焦点位置バラツキの低減による歩留まり向上と信頼性の高い偏光分離素子を実現することができる。
尚、実施例１〜３では、透明基板として石英ガラス基板またはＢＫ−７基板を用いた例を示したが、透明基板としてはこれらに限られるものではなく、その他の光学ガラス基板や、透明樹脂基板等、種々のものを用いることができる。
【００４８】
【発明の効果】
以上説明したように、本発明では、透明基板に引張り応力を有するコーティング膜を設け、透明基板のコーティング膜側とは反対側の面に有機複屈折膜を接着したことで、コーティング膜の応力を有機複屈折膜の熱収縮応力と均衡するように制御することにより、透明基板の反りを低減することができる。従って、基板の反りの発生を低減した偏光分離素子を実現することができる。
さらに本発明では、コーテイング膜を基板と同じ屈折率を有する単層または多層のコーテイング膜とすることにより、光学特性を低下することなく応力を発生することができ、また、コーテイング膜を単層または多層の反射防止膜とすることにより、光の入射効率を向上することができる。
さらに本発明では、有機複屈折膜を延伸により分子鎖を配向させた高分子膜とすることにより、低コスト化が達成できる。
さらに本発明では、有機複屈折膜と透明基板とを接着する接着剤として、光硬化型の接着剤（例えばアクリル系またはエポキシ系の光硬化型接着剤）を用いることにより、プロセスの簡略化とプロセスの低コスト化ができ、また、紫外線を有機複屈折膜側から照射することで、光反射が少なく、紫外線硬化時間を短縮できる。
さらに本発明では、有機複屈折膜をＵ字形状に変形して透明基板に１つの接触点において接触させ、接触点から全体に接触面を広げることにより、気泡の巻き込みが防止でき、信頼性の高い接着を行なうことができ、信頼性の高い偏光分離素子を提供することができる。
さらに本発明では、有機複屈折膜と透明基板とを接着する接着装置の透明基板を載置固定する装置形状を、透明基板のコーティング膜側表面形状と相似形としたことで、接着剤の厚みを均一にできる。
さらに本発明では、有機複屈折膜と透明基板とを接着する接着装置の有機複屈折膜を加圧する装置形状を、透明基板のコーティング膜とは反対側の表面形状と相似形としたことで、接着剤の厚みを均一にできる。
さらに本発明では、回折格子を分子鎖が配向した高分子としたことで、偏光分離素子の小型化、低コスト化が可能となる。
【図面の簡単な説明】
【図１】本発明の一実施例を示す偏光分離素子の概略断面図である。
【図２】引っ張り応力を有するコーティング膜を設けた透明基板の断面図である。
【図３】裏面側にコーティング膜を設けた基板上に有機複屈折膜を接着する際に用いられる接着装置の概略構成を示す図である。
【図４】図３に示す接着装置で基板上に有機複屈折膜を接着する際に用いられる押圧装置と接着断面の説明図である。
【図５】本発明の製造方法で作製された偏光分離素子の一例を示す要部断面図である。
【図６】一方の面に多層コーティング膜を形成し、他方の面に有機複屈折膜を接着した透明基板の一例を示す要部断面図である。
【図７】基板上に有機複屈折膜を接着する際に用いられる接着装置の概略構成を示す図である。
【図８】（ａ）は図７に示す接着装置で有機複屈折膜を接着した透明基板の一例を示す要部断面図であり、（ｂ）は有機複屈折膜の接着後にコーティング膜を形成した透明基板の一例を示す要部断面図である。
【符号の説明】
１：透明基板（石英ガラス基板）
２，２２，３２：接着剤
３，２３，３３：有機複屈折膜
４：回折格子
５：等方性接着剤
６：対向透明基板
７，３４：コーティング膜（ＭｇＦ_２膜）
８：移動ステージ
９：基板ホルダ
１０：保持装置
１１：ＣＣＤレーザー変位計
１２：押圧装置
２１，３１：透明基板（ＢＫ−７基板）
２４：多層コーティング膜
Ｍ：モーメント力[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a polarization separating element with good productivity and high reliability and a method for manufacturing the same, and in particular, a polarization separating element characterized by adhesion.ofIt relates to a manufacturing method.
[0002]
[Prior art]
As a conventional technique related to a polarization separation element, Japanese Patent Laid-Open Nos. 63-314502 and 2000-75130 have a diffraction grating on a transparent substrate on the same plane as a polarization separation element that can be manufactured at low cost with a simple process. A structure in which a birefringent film and an isotropic overcoat layer are coated or loaded thereon has been proposed. Some of these are designed to improve the flatness of both sides in order to obtain good optical characteristics. This forms a diffraction grating on the same plane on a transparent substrate such as glass or plastic, and is bonded with an adhesive, and the birefringent film is covered with an isotropic overcoat layer. In addition, since it is bonded to the transparent substrate, the element has strength and high productivity.
[0003]
In the invention described in Japanese Patent Laid-Open No. 9-90263, after a plastic substrate is molded into a shape in which the surface of the hologram disk is warped upward in advance and assembled, the hologram disk is bent downward by gravity to cancel the warpage, thereby diffracting laser. The fluctuation of the diffraction angle of light is reduced.
In the invention described in Japanese Patent No. 2639659, unevenness (diffraction grating) is formed on a glass substrate by photoetching, and MgF is formed on the other surface by vacuum deposition.₂The non-reflective coating is applied to prevent the light reflected by the diffraction grating and directly incident on the light receiving means, or the light reflected by the diffraction grating from entering the light receiving means as stray light.
[0004]
In 1993, the 40th Spring Society of Applied Physics 30a-B-1, LiNbO₃A polarization separation element using (lithium niobate) as a substrate is realized. Further, in the invention described in Japanese Patent Application Laid-Open No. 10-335433, pasting is performed in a vacuum to prevent entrainment of bubbles at the time of pasting. In this case, there is a limit to the use of an adhesive containing a vapor pressure component, as in the case of using a film that has been previously coated with a pressure-sensitive adhesive.
[0005]
In Japanese Patent Laid-Open No. 2000-47014, a proton exchange layer in which a predetermined portion of the X-plane or Y-plane of a lithium niobate substrate crystal is proton-exchanged, and stress generated thereby on the lithium niobate substrate by the same method as described above. A method of manufacturing an optical element including a proton exchange layer that corrects stress by a proton exchange layer subjected to proton exchange is described.
[0006]
[Problems to be solved by the invention]
In order to separate two polarization components orthogonal to each other, a polarization separation element having a structure in which an organic birefringent film having a different refractive index is bonded to a vibration surface of a different incident light on a transparent substrate is used when the organic birefringent film is bonded. The organic birefringent film is a stretched polymer material, and the organic birefringent film is thermally shrunk at the temperature applied in the resist curing process of photolithography in the subsequent microfabrication process, and as a result, the organic birefringent film is adhered. There is a problem that the transparent substrate warps to the organic birefringent film side. Further, the adhesive used also has a curing shrinkage of about 1 to 10%, which causes a problem of warping of the substrate. This warpage of the organic birefringent film adhesive substrate causes problems such as poor focusing due to focal position fluctuations during exposure in the photolithography process, and a reduction in wavefront aberration.
[0007]
In addition, the film thickness of the organic birefringent film is generally as thin as several tens of μm to several hundreds of μm, and when it is bonded to other members, it easily deforms due to its own weight, atmospheric pressure, etc. There is a problem that the contact point of the refracting film comes into contact with the surface and entrains bubbles.
Furthermore, after the adhesive is cured, there is a problem that there are many restrictions such as a refractive index equivalent to that of the transparent substrate and a requirement that light is not absorbed. LiNbO₃In the method of producing a polarization separation element using such a material for the substrate, an expensive optical crystal is required, the material cost is high, the process is complicated, and the manufacturing cost is also high.
[0008]
The present invention has been made in view of the above circumstances, and a substrate due to thermal contraction of an organic birefringent film generated during a process in microfabrication on an organic birefringent film after the organic birefringent film is bonded to a transparent substrate. An object of the present invention is to provide a polarization beam splitting element having a configuration capable of reducing the warpage and a manufacturing method thereof.
Furthermore, an object of the present invention is to provide a method of manufacturing a polarization separation element that can adhere an organic birefringent film without entrainment of bubbles, thereby ensuring improvement in element reliability.
[0009]
[Means for Solving the Problems]
  As means for achieving the above object, the present invention employs a polarization separation element having the following configuration and a method for manufacturing the same.
(1). In order to separate two orthogonal polarization components, an organic birefringent film with a different refractive index is bonded to a transparent substrate with different vibration surfaces of incident light, and a periodic concavo-convex grating (hereinafter referred to as diffraction) is attached to the organic birefringent film. In the polarization separating element having a configuration in which a concave portion of the diffraction grating is filled with an isotropic adhesive, and a counter transparent substrate is bonded onto the diffraction grating, the organic birefringent film is The transparent substrate to be bonded is provided with a stressed coating film.The
(2). In the polarization separation element according to (1), the stress of the coating film is configured to be a tensile stress.The
(3). In the polarized light separating element according to (1) or (2), the coating film is a single layer or multilayer coating film having a refractive index equal to or smaller than the refractive index of the transparent substrate, or a single layer or transparent substrate. It is composed of a multilayer antireflection film with a lower refractive index and a higher refractive index.The
(4). In the polarized light separating element according to (1), (2) or (3), an organic birefringent film is bonded to the surface of the transparent substrate opposite to the surface provided with the coating film.The
(5). In the polarization separation element according to (4), the organic birefringent film is composed of a polymer film in which molecular chains are oriented by stretching.The
(6). In the polarization separation element according to any one of (1) to (5), the stress of the coating film is controlled to be balanced with the heat shrinkage stress of the organic birefringent film.The
[0010]
(7). In order to separate two orthogonal polarization components, an organic birefringent film with a different refractive index is bonded to a transparent substrate with different vibration surfaces of incident light, and a periodic concavo-convex grating (hereinafter referred to as diffraction) is attached to the organic birefringent film. And isotropic adhesive is filled in the dents of the diffraction grating, the transparent substrate is adhered on the diffraction grating, and stress is applied to the transparent substrate to which the organic birefringent film is adhered. In a method for manufacturing a polarization separation element provided with a coating film having a shape, a step of deforming the organic birefringent film into a U-shape, and when adhering the organic birefringent film to a transparent substrate, a CCD laser displacement meter is used. Obtaining the vertex position information of the U-shape of the organic birefringent film and the convex shape of the adhesive on the transparent substrate; and positioning the U-shaped vertex of the organic birefringent film at the vertex of the convex shape of the adhesive The U-shaped organic birefringent film Apex of the convex shape of the apex of the adhesiveAt one point of contact withA step of contacting;Adhering by expanding the contact surface from the contact point to the whole;(Claim 1).
(8). In the method for manufacturing a polarization separation element according to (7), the stress of the coating film is a tensile stress, and the transparent substrate is warped by the stress of the coating film.
(9). In the method for manufacturing a polarization beam splitting element according to (7) or (8), the coating film is a single-layer or multi-layer coating film having a refractive index equal to or smaller than the refractive index of the transparent substrate, or a single layer Alternatively, a multilayer antireflection film having a refractive index smaller than that of the transparent substrate and a larger refractive index is formed.
(10). In the method of manufacturing a polarization separation element according to (7), (8), or (9), an organic birefringent film is adhered to a surface of the transparent substrate opposite to the surface on which the coating film is provided. 4).
(11). In the method for manufacturing a polarization beam splitting element according to (10), the organic birefringent film is a polymer film in which molecular chains are oriented by stretching.
(12). In the method for manufacturing a polarization separating element according to any one of (7) to (11), the stress of the coating film is controlled to be balanced with the heat shrinkage stress of the organic birefringent film. .
(13). In the method for manufacturing a polarization separation element according to any one of (7) to (12), in the step of bonding the organic birefringent film to a transparent substrate, ultraviolet light is irradiated from the organic birefringent film side (invoice) Item 7).
  As an adhesive for adhering the organic birefringent film and the transparent substrate, a photocurable adhesive (for example, an acrylic or epoxy photocurable adhesive) is preferably used.
( 14 ). (7) to (13), The device shape for mounting and fixing the transparent substrate of the bonding device for bonding the organic birefringent film and the transparent substrate is a coating film side surface of the transparent substrate. The shape is similar to the shape.8).
(15). (7) to (13In the method for manufacturing a polarization separating element according to any one of the above, the device shape for pressurizing the organic birefringent film of the bonding apparatus that bonds the organic birefringent film and the transparent substrate is the coating film of the transparent substrate. Similar to the surface shape on the opposite side.9).
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a polarization beam splitting element showing an embodiment of the present invention. In this polarization separation element, an organic birefringent film 3 having a different refractive index is bonded to a transparent substrate 1 with respect to different vibration surfaces of incident light by an adhesive 2, and a periodic concavo-convex grating (hereinafter referred to as “lattice grating”) , Which is described as a diffraction grating), and a concave portion of the diffraction grating 4 is filled with an isotropic adhesive 5, and an opposing transparent substrate 6 is bonded onto the diffraction grating. The transparent substrate 1 to which the organic birefringent film 3 is bonded is provided with a coating film 7 having a tensile stress.
That is, in this embodiment, a single-layer or multi-layer film 7 having a tensile stress is coated on one surface of the transparent substrate 1, and the organic birefringent film 3 is adhered to the opposite plane of the transparent substrate 1 with the adhesive 2. The diffraction grating 4 is formed on the organic birefringent film 3 by fine processing, and then the counter transparent substrate 6 is bonded with an isotropic adhesive 5 to constitute a polarization separation element. Specific examples of the polarized light separating element and the manufacturing method thereof according to the present invention will be described below.
[0012]
[Example 1]
A first embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows a sectional view of the transparent substrate and the coating film of the first embodiment. In this embodiment, a quartz glass substrate having a diameter of 100 mm and a plate thickness of 1.0 mm is used as the transparent substrate 1, and a coating film 7 is formed on one side of the quartz glass substrate 1 by a vacuum vapor deposition method.₂Was formed with a film thickness of 1 μm. Since vacuum deposition is formed by the same method as a general method for forming a thin film, detailed description thereof is omitted.
[0013]
In this way MgF₂The quartz glass substrate 1 on which the coating film 7 is formed is made of MgF.₂Due to the tensile stress of the coating film 7, MgF₂Warps to the coating film 7 side.
Desirably, MgF₂The stress is controlled under the coating conditions such as the substrate temperature and the film thickness so that the tensile stress of the coating film 7 is 1 MPa to 10 GPa.
The material of the coating film 7 is MgF₂The material having a refractive index equal to or lower than that of the quartz glass substrate 1, such as CaF.₂Alternatively, a dielectric material such as LiF may be used.
[0014]
Next, FIG. 3 is a diagram showing a schematic configuration of an adhesion apparatus used when an organic birefringent film is adhered on a substrate having a coating film on the back side. As shown in FIG. 3, on the substrate holder 9 fixed on the movable stage 8 in which the X, Y, and Z axes are movable, MgF₂The quartz glass substrate 1 is placed under the film surface and fixed by a vacuum suction mechanism (not shown). This substrate holder 9 is MgF₂The quartz glass substrate 1 coated with the film 7 has a convex shape having substantially the same shape as the warp of the coating film side surface. Above the substrate holder 9 and the quartz glass substrate 1, an adhesive dropping device (not shown), measurement that can be moved in the X and Y directions for specifying the center of the adhesive 2 and measuring the center of the organic birefringent film 3. There is a system. In this embodiment, as a measurement system, a reflected light from the surfaces of the adhesive 2, the quartz glass substrate 1 and the organic birefringent film 3 is detected, and a CCD laser displacement meter 11 for reading the displacement amount is used. A circuit (not shown) for detecting and feeding back position information to each moving device and a holding device 10 for holding both ends of the organic birefringent film 3 are arranged in parallel to the substrate holder 9. A device for generating a moment force M (not shown) is arranged.
[0015]
Next, 0.2 mL of an acrylic resin ultraviolet (UV) curable adhesive 2 having a refractive index of 1.58, which is substantially the same as that of the quartz glass substrate 1, is dropped at the center of the quartz glass substrate 1, and an organic birefringent film is formed thereon. 3 is placed. The organic birefringent film 3 has a thickness of 0.12 mm and is cut into a size of 110 mm × 120 mm, and both ends of the organic birefringent film 3 are held by vacuum holding by the holding device 10. Then, after placing the approximate center position of the organic birefringent film 3 at the approximately center position of the quartz glass substrate 1, the organic birefringent film 3 is deformed into a U shape by a moment generator (not shown). Again, the surface shape of the organic birefringent film 3 is measured by the CCD laser displacement meter 11, the center position of the U-shape is detected, and the movement amount is calculated from the vertex position information of the convex shape of the adhesive 2 measured in advance. The U-shaped center of the organic birefringent film 3 is aligned with the convex center of the adhesive 2 by the XY movement device. Then, after the alignment of the quartz glass substrate 1 -adhesive 2 -organic birefringent film 3 is completed, the substrate holder 9 is lifted by the moving stage 8 and contacted at the respective apexes of the adhesive 2 and the organic birefringent film 3 Then, the organic birefringent film 3 is placed on the quartz glass substrate 1 while gently releasing the moment force M of the organic birefringent film 3.
[0016]
Next, as shown in FIG. 4, a quartz glass pressing device 12 having a diameter of 110 mm and a thickness of 20 mm, which has been processed into a concave shape substantially the same as the curvature of the surface of the quartz glass substrate 1 opposite to the coating film 7, is organically mixed. Placed on the refraction film 3, pressurizes the entire surface of the organic birefringence film 3 evenly, stops the pressurization when the adhesive 2 spreads over the entire surface of the quartz glass substrate 1, and then irradiates ultraviolet rays (not shown) through the pressing device 12. Light intensity 30mW / cm with a device (UV device)²Was irradiated for 200 seconds to cure the adhesive 2. After curing, after cutting the excess organic birefringent film 3 along the outer diameter of φ100 mm, the pressing device 12 is raised, the vacuum adsorption of the substrate holder 9 is released, the quartz glass substrate 1 is taken out, and the organic birefringence is taken out. A quartz glass substrate with a film was used.
[0017]
As described above, as an alignment method at the time of the bonding process, by contacting the quartz glass substrate 1 from the center of the organic birefringent film 3, entrainment of bubbles that can be confirmed at a visual level occurs in the conventional method of bonding by surface contact. In contrast, in the method of this example, bonding without bubble entrainment could be realized.
[0018]
In addition to the method of the present embodiment, the alignment in the bonding process can be performed by recognizing the shapes of the quartz glass substrate 1 and the adhesive 2 by using a CCD camera and an image processing apparatus, determining the center, and aligning. It is. In addition, although an acrylic resin-based photocurable adhesive is used as an adhesive here, an epoxy resin-based photocurable adhesive may be used.
The organic birefringent film 3 is desirably 0.01 mm or more in consideration of handling properties, but is preferably used in a range of a maximum thickness of 0.5 mm in consideration of obtaining optical characteristics by stretching. A range of 0.05 to 0.2 mm is more desirable. In this example, an organic birefringent film having a thickness of 0.12 mm was used.
[0019]
Next, the organic birefringent film 3 adhered on the quartz glass substrate 1 is washed in order of an organic solvent such as isopropyl alcohol and pure water. Thereafter, a 0.5 μm thick resist film was formed by spin coating with ZEP-520 resist manufactured by Nippon Zeon Kabushiki Kaisha and baked at 100 ° C. for 30 minutes. At this time, a tensile stress of about 7.5 MPa is generated in the quartz glass substrate 1 due to the thermal contraction of the organic birefringent film 3, but the quartz glass substrate 1 is balanced with the stress of the coating film 7 coated on the back surface of the quartz glass substrate 1. 1 maintains flatness. After that, using a stepper device, a line and space pattern of 3 μm was repeatedly formed at a pitch of 8 mm for 300 periods on the resist film on the organic birefringent film 3, and a periodic uneven grating (diffraction grating) pattern was formed on the resist film. An element was formed. This diffraction grating pattern is formed in a substantially 1 × 2 mm shape at the center of the element outer shape of 8 × 8 mm.
[0020]
Thereafter, etching is performed with an ECR (Electron Cyclotron Resonance) etching apparatus manufactured by Sumitomo Metals in an etching gas atmosphere mainly containing oxygen gas, and a line having a width of 3 μm and a depth of 5 μm is formed on the organic birefringent film 3. And a diffraction grating 4 in which a space of 3 μm width was repeated for 300 periods.
The other photolithography process employs a generally known process, and a detailed description thereof is omitted.
[0021]
Next, the quartz glass substrate 1 in which the diffraction grating 4 is formed on the organic birefringent film 3 is placed on a flat-processed stainless steel plate having a diameter of 200 mm and a thickness of 50 mm, and an acrylic resin-based photocuring type is placed on the diffraction grating surface. 0.25 mL of the isotropic adhesive 5 was measured and dropped with a microsyringe, and the diffraction grating surface of the quartz glass substrate 1 onto which the isotropic adhesive 5 was dropped was optically polished on both sides with an outer diameter of φ100 mm and a thickness of 0.5 mm. A counter transparent substrate 6 is placed, and further, quartz glass optically polished as a pressure member is placed thereon, and 100 gf / cm is placed on the counter transparent substrate 6.²The isotropic adhesive 5 was spread over the entire adherend surface. An antireflection film was formed on the surface opposite to the bonding surface of the counter transparent substrate 6 so as to minimize the reflection of the incident wavelength. In this state, the irradiation illuminance is 20 mW / cm from the upper surface of 150 mm with an ultraviolet irradiation device (not shown).²Was irradiated for 10 minutes through the opposing transparent substrate 6 and cured and adhered. FIG. 5 shows a cross section of the main part of the polarization separation element manufactured in this way.
[0022]
The isotropic adhesive 5 of the polarization separation element shown in FIG. 5 uses an acrylic adhesive from the viewpoint of easy control of properties such as viscosity and refractive index, adhesive strength, and transparency. Is possible. Since these adhesives are cured by ultraviolet rays, curing during pressurization is possible by using a transparent member such as quartz glass as the pressurizing member, and the process can be simplified.
As the organic birefringent film 3, a polymer film such as polyethylene terephthalate (PET) is rubbed with a cloth to be rubbed to form an alignment film, and a polydiacetylene monomer is vacuum-deposited on the alignment film to be aligned. After that, there is a method of making an anisotropic film by irradiating with ultraviolet light (reference: J.Appl.phys., 72, No, 3, P938-947), but the process is complicated and expensive. Therefore, here, an organic birefringent film that is a polymer film with molecular chains oriented and stretched in consideration of uniformity of characteristics is used.
[0023]
[Example 2]
Next, a second embodiment of the present invention will be described. FIG. 6 is a diagram showing a second embodiment of the present invention, which is a cross-sectional view of the principal part showing an example of a transparent substrate in which a multilayer coating film is formed on one surface and an organic birefringence film is bonded to the other surface. is there. In the figure, reference numeral 21 denotes a transparent substrate, 22 denotes an adhesive, 23 denotes an organic birefringent film, and 24 denotes a coating film made of a multilayer film. As in the configuration of the polarization separating element, a periodic concavo-convex grating (diffraction grating) 4 is formed on the organic birefringent film 23 as in FIGS. An isotropic adhesive 5 is filled, and the counter transparent substrate 6 is bonded onto the diffraction grating with the isotropic adhesive, but these are not shown.
[0024]
In the present embodiment, a BK-7 substrate having a diameter of 100 mm and a thickness of 0.5 mm is used as the transparent substrate 21, and one side of the BK-7 substrate 21 is SiO 2 by vacuum deposition.₂Film 24a, TiO₂Film 24b, SiO₂A multilayer coating film 24 composed of three layers of the film 24c is made of SiO.₂/ TiO₂/ SiO₂The film thickness was controlled so that n1 · t1 = λ / 4, n2 · t2 = λ / 4, or n2 · t2 = λ / 2, and a tensile stress was formed. Where n1 is SiO₂Where t1 is SiO₂, N2 is TiO₂Where t2 is TiO₂The film thickness, λ, is 660 nm in wavelength. In addition, since vacuum deposition is formed by the same method as a general method for forming a thin film, detailed description thereof is omitted.
[0025]
The BK-7 substrate 21 on which the multilayer coating film 24 is formed in this manner has a small reflectance of incident light from the multilayer coating film 24 side of 0.5% or less, and is formed by the tensile stress of the coating film 24. Warped to the side. The coating film 24 is made of CaF.₂And SiO₂Other dielectrics such as a single layer or a multilayer film may be used.
[0026]
Next, the bonding process using the bonding apparatus having the same configuration as in FIG. 3 will be described. Here, the substrate 1, the adhesive 2, and the organic birefringent film 3 in FIG. 3 are replaced with the BK-7 substrate 21 of this embodiment. In the following description, the adhesive 22 and the organic birefringent film 23 are replaced. A BK-7 substrate 21 of this embodiment is placed on a substrate holder 9 fixed on a movable stage 8 capable of moving the X, Y, and Z axes, with the coating film side down, and a vacuum suction mechanism (not shown) To fix. The substrate holder 9 has a convex shape having substantially the same shape as the warp of the coating film side surface of the BK-7 substrate 21 coated with the multilayer coating film 24. Above the substrate holder 9 and the BK-7 substrate 21, an adhesive dropping device (not shown), measurement that can be moved in the X and Y directions for specifying the center of the adhesive and measuring the center of the organic birefringent film 23. There is a system. In the present embodiment, the CCD laser displacement meter 11 that detects the reflected light from the surfaces of the adhesive 22, the BK-7 substrate 21 and the organic birefringent film 23 and reads the displacement amount as a measurement system as in FIG. A circuit (not shown) for detecting the position by the CCD laser displacement meter 11 and feeding back the position information to each moving device and a holding device 10 for holding both ends of the organic birefringent film 23 are provided on the substrate holder 9. A device that generates a moment force M (not shown) is arranged in parallel with the device.
[0027]
Next, 0.2 mL of an acrylic resin-based UV curable adhesive 22 having a refractive index of 1.58, which is substantially the same as that of the BK-7 substrate, is dropped at the center of the BK-7 substrate 21, and the organic birefringent film 23 is disposed thereon. Is placed. The organic birefringent film 23 has a thickness of 0.2 mm and is cut into a size of 110 mm × 120 mm, and both ends of the organic birefringent film 23 are held by vacuum adsorption by the holding device 10 as in FIG. Then, after placing the approximate center position of the organic birefringent film 23 at the approximately center position of the BK-7 substrate, the organic birefringent film 23 is deformed into a U shape by a moment generator (not shown). Then, the surface shape of the organic birefringent film 23 is measured again by the CCD laser displacement meter 11, the center position of the U-shape is detected, and the movement amount is determined based on the convex vertex position information of the adhesive 22 measured in advance. And the center of the U shape of the organic birefringent film 23 is aligned with the convex center of the adhesive 22 by the XY moving stage 8. Then, after the alignment of the BK-7 substrate-adhesive-organic birefringent film is completed, the substrate holder is lifted by the moving stage 8, and at the positions where the adhesive 22 and the organic birefringent film 23 are in contact with each other. Thereafter, the organic birefringent film 23 is placed on the BK-7 substrate 21 while gently releasing the moment force M of the organic birefringent film 23.
[0028]
Next, as in FIG. 4, a quartz glass pressing device 12 having a diameter of 110 mm and a thickness of 20 mm, which has been processed into a concave shape having substantially the same shape as the warpage of the surface opposite to the coating film of the BK-7 substrate 21. Placed on the organic birefringent film 23, pressurizes the entire surface of the organic birefringent film 23 uniformly, stops the pressurization when the adhesive 22 spreads over the entire surface of the BK-7 substrate 21, and then irradiates with ultraviolet rays through a pressing device Light intensity 30mW / cm with a device (UV device)²Was irradiated for 200 seconds to cure the adhesive 22. After curing, after cutting the excess organic birefringent film 23 along the outer diameter of φ100 mm, the pressing device is raised, the vacuum adsorption of the substrate holder is released, and the BK-7 substrate 23 is taken out, as shown in FIG. Such a BK-7 substrate with an organic birefringent film was used.
[0029]
As described above, as an alignment method at the time of the bonding process, by bringing the organic birefringent film 23 into contact with the substrate 21 from the center, the conventional method of bonding by surface contact causes entrainment of bubbles that can be confirmed at the visual level. On the other hand, in the method of this example, it was possible to realize bonding without bubble entrainment.
Table 1 below shows the organic birefringent film side and the coating film (SiO 2₂/ TiO₂/ SiO₂The light intensity ratio when ultraviolet rays are irradiated from the (film) side is shown. As shown in Table 1, when the ultraviolet rays are incident from the organic birefringent film side, the adhesive can be efficiently irradiated with light.
[0030]
[Table 1]

[0031]
In addition to the present embodiment, the alignment in the bonding process can be performed by recognizing the shapes of the BK-7 substrate 21 and the adhesive 22 by using a CCD camera and an image processing apparatus, determining the center, and aligning the positions. is there. In addition, although an acrylic resin-based photo-curing adhesive is used here, an epoxy resin-based photo-curing adhesive may be used. The organic birefringent film 23 is preferably 0.01 mm or more in consideration of handling properties, but is preferably used in a range of a maximum thickness of 0.5 mm in consideration of obtaining optical characteristics by stretching. A range of 0.05 to 0.2 mm is more desirable. In this example, an organic birefringent film having a thickness of 0.2 mm was used.
[0032]
Next, the organic birefringent film 23 adhered on the BK-7 substrate 21 is washed in order of an organic solvent such as isopropyl alcohol and pure water. Thereafter, a 0.5 μm thick resist film was formed on the organic birefringent film 23 by spin coating using a ZEP-520 resist manufactured by Nippon Zeon Chemical Co., Ltd., and baked at 100 ° C. for 30 minutes. At this time, a tensile stress is generated in the BK-7 substrate 21 due to the thermal contraction of the organic birefringent film 23, but the BK-7 substrate 21 is balanced with the stress of the coating film 24 coated on the back surface of the BK-7 substrate 21. Maintains flatness. Thereafter, using a stepper device, a line and space pattern of 3 μm was repeatedly formed at a pitch of 8 mm for 300 periods, thereby forming an element in which a periodic uneven grating (diffraction grating) pattern was formed on the resist film. This diffraction grating pattern is formed in a substantially 1 × 2 mm shape at the center of the element outer shape of 8 × 8 mm.
[0033]
Thereafter, etching is performed with an ECR (Electron Cyclotron Resonance) etching apparatus manufactured by Sumitomo Metals in an etching gas atmosphere mainly containing oxygen gas, and a line having a width of 3 μm and a depth of 5 μm is formed on the organic birefringent film 23. And a diffraction grating in which a space of 3 μm width was repeated for 300 periods.
The other photolithography process employs a generally known process, and a detailed description thereof is omitted.
[0034]
Next, a BK-7 substrate 21 in which a diffraction grating is formed on the organic birefringent film 23 is placed on a stainless steel base having a diameter φ of 200 mm and a thickness of 50 mm. The acrylic resin-based photo-curing type is placed on the diffraction grating surface. 0.25 mL of isotropic adhesive was measured and dropped with a microsyringe, and the opposite transparent surface with an outer diameter of 100 mm and a thickness of 0.5 mm was optically polished on both sides of the diffraction grating surface of the BK-7 substrate 21 onto which this isotropic adhesive was dropped. A substrate is placed, and quartz glass optically polished as a pressure member is placed thereon, and 100 gf / cm is placed on the opposing transparent substrate.²Was applied to spread the isotropic adhesive over the entire surface to be bonded. An antireflection film was formed on the surface opposite to the bonding surface of the counter transparent substrate so as to minimize the reflection of the incident wavelength. In this state, the irradiation illuminance is 20 mW / cm from the upper surface of 150 mm with an ultraviolet irradiation device (not shown).²Was irradiated for 10 minutes through an opposing transparent substrate and cured and adhered. The cross-sectional structure of the polarization separation element thus manufactured is substantially the same as that shown in FIGS.
[0035]
As for the isotropic adhesive of the polarization separation element manufactured as described above, an acrylic adhesive was used from the viewpoint of easy control of properties such as viscosity and refractive index, adhesive strength, and transparency. But the same thing is possible. Since these adhesives are cured by ultraviolet rays, curing during pressurization is possible by using a transparent member such as quartz glass as the pressurizing member, and the process can be simplified.
Further, as the organic birefringent film 23, a polymer film such as polyethylene terephthalate (PET) is rubbed with a cloth to be rubbed to form an alignment film, and a polydiacetylene monomer is vacuum-deposited on the alignment film to be aligned. After that, there is a method of making an anisotropic film by irradiating with ultraviolet light (reference: J.Appl.phys., 72, No, 3, P938-947), but the process is complicated and expensive. Therefore, here, an organic birefringent film that is a polymer film with molecular chains oriented and stretched in consideration of uniformity of characteristics is used.
[0036]
[Example 3]
Next, a third embodiment of the present invention will be described. FIG. 7 is an explanatory view of a third embodiment of the present invention, and is a view showing a schematic configuration of an adhesion apparatus used when an organic birefringent film is adhered on a transparent substrate.
In this embodiment, as shown in FIG. 7, a transparent substrate 31 having a diameter φ of 100 mm and a plate thickness of 1.0 mm is formed on a substrate holder 9 fixed on a movable stage 8 in which X, Y, and Z axes can move. A BK-7 substrate is placed and fixed by a vacuum suction mechanism (not shown). Above the substrate holder 9 and the BK-7 substrate 31, an adhesive dripping device (not shown) and a measurement system movable in the X and Y directions for measuring the center of the adhesive 32 and the center of the organic birefringent film 33 are provided. Is provided. In this embodiment, as a measurement system, a CCD laser displacement meter 11 that detects reflected light from the surfaces of the adhesive 32, the BK-7 substrate 31, and the organic birefringent film 33 and reads the displacement amount, and a CCD laser displacement meter 11 The circuit (not shown) for detecting the position and feeding back the position information to each moving device and the holding device 10 for holding both ends of the organic birefringent film 33 are arranged in parallel to the substrate holder 9. In addition, a device for generating a moment force M (not shown) is disposed.
[0037]
Next, 0.2 mL of an acrylic resin-based UV curable adhesive 32 having a refractive index of 1.58, which is substantially the same as that of the BK-7 substrate 31, is dropped at the center of the BK-7 substrate 31, and an organic birefringent film is formed thereon. 33 is placed. The organic birefringent film 33 has a thickness of 0.2 mm and is cut into a size of 110 mm × 120 mm, and both ends of the organic birefringent film 33 are held by vacuum holding by the holding device 10. Then, after placing the approximate center position of the organic birefringent film 33 at the approximately center position of the BK-7 substrate 31, the organic birefringent film 33 is deformed into a U shape by a moment generator (not shown). Then, the surface shape of the organic birefringent film 33 is again measured by the CCD laser displacement meter 11, the center position of the U-shape is detected, and the movement amount is determined from the vertex position information of the convex shape of the adhesive 32 measured in advance. And the center of the U-shape of the organic birefringent film 33 is aligned with the convex center of the adhesive 32 by an XY moving device. Then, after the alignment of the BK-7 substrate-adhesive-organic birefringent film is completed, the substrate holder 9 is lifted by the moving stage 8, and the adhesive 32 and the organic birefringent film 33 are in contact with each vertex. Then, the organic birefringent film 33 is placed on the BK-7 substrate 31 while gradually releasing the moment force of the organic birefringent film 33.
[0038]
Next, a quartz glass pressing device (not shown) having a diameter of 110 mm and a thickness of 20 mm processed into a concave shape having substantially the same shape as the warp of the BK-7 substrate 31 is placed on the organic birefringence film. The entire surface of the film 33 is uniformly pressed, and when the adhesive 32 spreads over the entire surface of the BK-7 substrate 33, the pressing is stopped, and then the light intensity is 30 mW / with an ultraviolet irradiation device (UV device) (not shown) through the pressing device. cm²Was irradiated for 200 seconds to cure the adhesive. After curing, the excess organic birefringent film 33 is cut along the outer shape with a diameter of φ100 mm, and then the pressing device is raised, the vacuum adsorption of the substrate holder 9 is released, the BK-7 substrate 31 is taken out, and the organic birefringence is removed. A BK-7 substrate 31 with a film was obtained. FIG. 8A is a schematic cross-sectional view of a BK-7 substrate to which an organic birefringent film is bonded as described above.
[0039]
As described above, as an alignment method at the time of the bonding process, by bringing the organic birefringent film 33 into contact with the substrate 31 from the center, the conventional method of bonding by surface contact causes entrainment of bubbles that can be confirmed at the visual level. On the other hand, in the method of this example, it was possible to realize bonding without bubble entrainment.
[0040]
In addition to the present embodiment, the alignment in the bonding process can be performed by recognizing the shapes of the BK-7 substrate 21 and the adhesive 22 by using a CCD camera and an image processing apparatus, determining the center, and aligning the positions. is there. In addition, although an acrylic resin-based photo-curing adhesive is used here, an epoxy resin-based photo-curing adhesive may be used. The organic birefringent film 33 is preferably 0.01 mm or more in consideration of handling properties, but it is preferably used in the range of a maximum thickness of 0.5 mm in consideration of obtaining optical characteristics by stretching. A range of 0.05 to 0.2 mm is more desirable. In this example, an organic birefringent film having a thickness of 0.2 mm was used.
[0041]
Next, MgF is deposited on the surface of the BK-7 substrate 31 shown in FIG.₂The coating film 34 was formed by controlling the film thickness so that n1 · t1 = λ / 4 or n1 · t1 = 3λ / 4. FIG. 8B is a schematic cross-sectional view of the BK-7 substrate on which the coating film 34 is formed. Where n1 is MgF₂T1 is MgF₂The film thickness and λ were 660 nm in wavelength. The substrate temperature in vacuum deposition was 100 ° C. Since the vacuum deposition process is formed by the same method as a general method for forming a thin film, detailed description is omitted.
[0042]
In this example, the tensile stress of the coating film 34 was controlled at 0.1 MPa to 10 GPa so as to balance the stress due to the thermal contraction of the organic birefringent film 33. Further, since the shrinkage of the organic birefringent film 33 is stabilized by heating during coating, the shrinkage of the organic birefringent film 33 in the subsequent process is extremely small. Further, since the film thickness is controlled so that the structure of the coating film 34 is n1 · t1 = λ / 4 or n1 · t1 = 3λ / 4, the reflectance of incident light from the coating film side is reduced. it can. In addition, as another film configuration of the coating film 34, a single layer configuration of SiO₂, CaF₂And multi-layered SiO₂/ TiO₂/ SiO₂Etc.
[0043]
Next, the organic birefringent film 33 on the BK-7 substrate 31 shown in FIG. 8B is washed in order of an organic solvent such as isopropyl alcohol and pure water. Thereafter, a 0.5 μm thick resist film was formed on the organic birefringent film 33 by spin coating using ZEP-520 resist manufactured by Nippon Zeon Chemical Co., Ltd., and baked at 100 ° C. for 30 minutes. At this time, a tensile stress is generated in the substrate 31 due to the thermal contraction of the organic birefringent film 33, but the BK-7 substrate 31 is flat because it balances with the tensile stress of the coating film 34 coated on the back surface of the BK-7 substrate 31. Keep. Thereafter, using a stepper device, a line and space pattern of 3 μm was repeatedly formed at a pitch of 8 mm for 300 periods, thereby forming an element in which a periodic uneven grating (diffraction grating) pattern was formed on the resist film. This diffraction grating pattern is formed in a substantially 1 × 2 mm shape at the center of the element outer shape of 8 × 8 mm.
[0044]
Thereafter, etching is performed with an ECR (Electron Cyclotron Resonance) etching apparatus manufactured by Sumitomo Metals in an etching gas atmosphere mainly containing oxygen gas, and a line having a width of 3 μm and a depth of 5 μm is formed on the organic birefringent film 33. And a diffraction grating in which a space of 3 μm width was repeated for 300 periods.
The other photolithography process employs a generally known process, and a detailed description thereof is omitted.
[0045]
Next, a BK-7 substrate 31 on which a diffraction grating is formed is placed on a stainless steel base having a diameter φ of 200 mm and a thickness of 50 mm, and an acrylic resin photocurable isotropic adhesive is placed on the diffraction grating surface. 0.25 mL was measured and dropped with a microsyringe, and a counter transparent substrate having an outer diameter of φ100 mm and a thickness of 0.5 mm was placed on the diffraction grating surface of the BK-7 substrate 31 to which this isotropic adhesive was dropped. Further, an optically polished quartz glass is placed thereon as a pressure member, and 100 gf / cm is applied to the opposing transparent substrate.²The isotropic adhesive 5 was spread over the entire adherend surface. An antireflection film was formed on the surface opposite to the bonding surface of the counter transparent substrate so as to minimize the reflection of the incident wavelength. In this state, the irradiation illuminance is 20 mW / cm from the upper surface of 150 mm with an ultraviolet irradiation device (not shown).²Was irradiated for 10 minutes through an opposing transparent substrate and cured and adhered. The cross-sectional structure of the polarization separation element thus manufactured is substantially the same as that shown in FIGS.
[0046]
As for the isotropic adhesive of the polarization separating element manufactured as described above, an acrylic adhesive is used from the viewpoint of easy control of properties such as viscosity and refractive index, adhesive strength, and transparency. But the same thing is possible. Since these adhesives are cured by ultraviolet rays, curing during pressurization is possible by using a transparent member such as quartz glass as the pressurizing member, and the process can be simplified.
Further, as the organic birefringent film 33, a polymer film such as polyethylene terephthalate (PET) is rubbed with a cloth to be rubbed to form an alignment film, and a polydiacetylene monomer is vacuum-deposited on the alignment film to be aligned. After that, there is a method of making an anisotropic film by irradiating with ultraviolet light (reference: J.Appl.phys., 72, No, 3, P938-947), but the process is complicated and expensive. Therefore, here, an organic birefringent film that is a polymer film with molecular chains oriented and stretched in consideration of uniformity of characteristics is used.
[0047]
As mentioned above, although Examples 1-3 of this invention were demonstrated, the curvature of the transparent board | substrate (quartz glass board | substrate or BK-7 board | substrate) of diameter 100mm of the polarization separation element produced by this invention is 30 micrometers or less, and is a conventional board | substrate. In contrast, several to several tens of bubbles were included in the conventional visual inspection level, whereas in the method of the present invention, bubbles were confirmed. It can be reduced to the extent possible. As described above, the polarization separation element of the present invention is generated by microfabrication of an organic birefringent film in which an organic birefringent film is bonded to a transparent substrate in an element using an organic birefringent film or the like as a diffraction grating or a retardation film. Since the warpage of the substrate due to the shrinkage of the organic birefringent film is offset by the coating film formed on the transparent substrate, it is possible to realize a polarization separation element with improved yield and high reliability by reducing the focal position variation during exposure.
In Examples 1 to 3, an example using a quartz glass substrate or a BK-7 substrate as a transparent substrate was shown, but the transparent substrate is not limited to these, and other optical glass substrates and transparent resins are used. Various things, such as a board | substrate, can be used.
[0048]
【The invention's effect】
As described above, in the present invention, the coating film having a tensile stress is provided on the transparent substrate, and the organic birefringent film is adhered to the surface of the transparent substrate opposite to the coating film side, thereby reducing the stress of the coating film. By controlling the organic birefringent film so as to be balanced with the heat shrinkage stress, the warp of the transparent substrate can be reduced. Therefore, it is possible to realize a polarization separation element that reduces the occurrence of warping of the substrate.
Furthermore, in the present invention, by forming the coating film as a single layer or multilayer coating film having the same refractive index as that of the substrate, it is possible to generate stress without deteriorating the optical characteristics. By using a multilayer antireflection film, light incident efficiency can be improved.
Furthermore, in the present invention, cost reduction can be achieved by making the organic birefringent film a polymer film in which molecular chains are oriented by stretching.
Furthermore, in the present invention, by using a photocurable adhesive (for example, an acrylic or epoxy photocurable adhesive) as an adhesive for bonding the organic birefringent film and the transparent substrate, the process can be simplified. The cost of the process can be reduced, and by irradiating ultraviolet rays from the organic birefringent film side, light reflection is reduced and the ultraviolet curing time can be shortened.
Furthermore, in the present invention, the organic birefringent film is deformed into a U shape and brought into contact with the transparent substrate at one contact point, and the contact surface is expanded from the contact point to the whole, thereby preventing the entrainment of bubbles, and the reliability. It is possible to provide a highly reliable polarization separation element that can be bonded with a high degree of reliability.
Further, in the present invention, the thickness of the adhesive is obtained by changing the shape of the apparatus for mounting and fixing the transparent substrate of the bonding apparatus for bonding the organic birefringent film and the transparent substrate to the surface shape of the coating film side of the transparent substrate. Can be made uniform.
Furthermore, in the present invention, the device shape for pressing the organic birefringent film of the bonding apparatus for bonding the organic birefringent film and the transparent substrate is similar to the surface shape on the opposite side of the coating film of the transparent substrate, The thickness of the adhesive can be made uniform.
Furthermore, in the present invention, since the diffraction grating is made of a polymer in which molecular chains are oriented, the polarization separating element can be reduced in size and cost.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a polarization beam splitting element according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a transparent substrate provided with a coating film having tensile stress.
FIG. 3 is a diagram showing a schematic configuration of an adhesion apparatus used when an organic birefringent film is adhered on a substrate having a coating film on the back side.
4 is an explanatory view of a pressing device and a bonding cross section used when an organic birefringent film is bonded on a substrate with the bonding apparatus shown in FIG. 3; FIG.
FIG. 5 is a cross-sectional view of a principal part showing an example of a polarization beam splitting element manufactured by the manufacturing method of the present invention.
FIG. 6 is a cross-sectional view of an essential part showing an example of a transparent substrate in which a multilayer coating film is formed on one surface and an organic birefringent film is bonded to the other surface.
FIG. 7 is a diagram showing a schematic configuration of a bonding apparatus used when bonding an organic birefringent film on a substrate.
8A is a cross-sectional view of the main part showing an example of a transparent substrate to which an organic birefringent film is bonded by the bonding apparatus shown in FIG. 7, and FIG. 8B is a diagram illustrating a coating film formed after the organic birefringent film is bonded. It is principal part sectional drawing which shows an example of the made transparent substrate.
[Explanation of symbols]
1: Transparent substrate (quartz glass substrate)
2, 22, 32: Adhesive
3, 23, 33: Organic birefringent film
4: Diffraction grating
5: Isotropic adhesive
6: Opposing transparent substrate
7, 34: Coating film (MgF₂film)
8: Moving stage
9: Substrate holder
10: Holding device
11: CCD laser displacement meter
12: Pressing device
21, 31: Transparent substrate (BK-7 substrate)
24: Multilayer coating film
M: Moment force

Claims

In order to separate two orthogonal polarization components, an organic birefringent film with a different refractive index is bonded to a transparent substrate with different vibration surfaces of incident light, and a periodic concavo-convex grating (hereinafter referred to as diffraction) is attached to the organic birefringent film. And isotropic adhesive is filled in the dents of the diffraction grating, the transparent substrate is adhered on the diffraction grating, and stress is applied to the transparent substrate to which the organic birefringent film is adhered. In the method of manufacturing a polarization separation element provided with a coating film having
Transforming the organic birefringent film into a U-shape;
When adhering the organic birefringent film to the transparent substrate, obtaining a vertex position information of the U-shape of the organic birefringent film and the convex shape of the adhesive on the transparent substrate using a CCD laser displacement meter;
The U-shaped apex of the organic birefringent film is aligned with the convex apex of the adhesive, and one contact point between the U-shaped apex of the organic birefringent film and the convex apex of the adhesive a step of contacting at,
Adhering by expanding the contact surface from the contact point to the whole;
The manufacturing method of the polarization separation element characterized by including.

In the manufacturing method of the polarization splitting device according to claim 1,
The method of manufacturing a polarization separation element, wherein the stress of the coating film is a tensile stress, and the transparent substrate is warped by the stress of the coating film.

In the manufacturing method of the polarization separation element according to claim 1 or 2,
As the coating film, a single-layer or multilayer coating film having a refractive index equal to or smaller than that of the transparent substrate, or a multilayer antireflection film having a refractive index smaller than that of the single-layer or transparent substrate and a large refractive index. A method for manufacturing a polarization separation element, comprising: forming a polarization separation element.

In the manufacturing method of the polarization separation element according to claim 1, 2, or 3,
An organic birefringent film is adhered to a surface of the transparent substrate opposite to the surface on which the coating film is provided.

In the manufacturing method of the polarization separation element according to claim 4,
The method of manufacturing a polarization separation element, wherein the organic birefringent film is a polymer film in which molecular chains are oriented by stretching.

In the manufacturing method of the polarization splitting device according to any one of claims 1 to 5,
A method of manufacturing a polarization separation element, wherein the stress of the coating film is controlled to balance with the heat shrinkage stress of the organic birefringent film.

In the manufacturing method of the polarization separation element according to any one of claims 1 to 6,
In the step of bonding the organic birefringent film to the transparent substrate, ultraviolet light is irradiated from the organic birefringent film side.

In the manufacturing method of the polarization separation element according to any one of claims 1 to 7,
A method of manufacturing a polarization separation element, wherein the device shape for mounting and fixing the transparent substrate of the bonding device for bonding the organic birefringent film and the transparent substrate is similar to the coating film side surface shape of the transparent substrate .

In the manufacturing method of the polarization splitting device according to any one of claims 1 to 7 ,
Polarization separation characterized in that the shape of the device that presses the organic birefringent film of the bonding device that bonds the organic birefringent film and the transparent substrate is similar to the surface shape of the transparent substrate opposite to the coating film Device manufacturing method.