JP2004151493A - Apparatus for manufacturing dielectric multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric multilayer film manufacturing apparatus which can use a direct monitoring method with many kinds of monitor wavelengths by performing high-precision film thickness control and is suitably mass-produced. <P>SOLUTION: The apparatus equipped with a sputter cathode part 32 and an ion gun part 33 side by side opposite a rotating substrate 34 and manufactures a dielectric multilayer film in a vacuum chamber 31 is provided with variable openings 51a and 51b for restricting the deposition rate of the dielectric multilayer film to be deposited on the rotating substrate 34 and divided shutters 52 to 55 for correcting the film thickness of the dielectric multilayer film to be deposited on the rotating substrate 34 between the rotating substrate 34 and the sputter cathode part 32. Further, a digital signal processor 41 is provided which measures the intensity of monitoring monochromatic light received by a photodetector 38 after passing a plurality of monitor points 56a to 56h along a radius of the rotating substrate 34. Further, a computer 42 is provided which instructs the divided shutters 52 to 55 to block light according to variation in light intensity measured by the digital signal processor 41 when the monitoring monochromatic luminous flux consisting of one or more wavelengths passes through those monitor points 56a to 56h. <P>COPYRIGHT: (C)2004,JPO

Description

［式１］（（１）式）と表される。（ここで、Ｎは単層膜の屈折率、θは単層膜上の異なる界面における位相差を示す。）
このとき、単層膜の透過率Ｔは、
Ｔ＝４Ｙ／（Ｂ＋Ｃ）（Ｂ＋Ｃ）^＊ ・・・（２）
（ここで、＊は共役する複素数を示す。）
で表されるので、（１）式と（２）式とにより
Ｔ＝４Ｙ／［（１＋Ｙ）^２＋｛（Ｙ／Ｎ＋Ｎ）^２−（１＋Ｙ）^２｝ｓｉｎ^２θ］ ・・・（３）
となる。ただし、空気あるいは真空の屈折率は１としている。
【００２３】
本発明においては、さらに、付着成長中の最新表面層膜の光学膜厚Ｎｄ（Ｎは薄膜の屈折率、ｄは薄膜の物理的膜厚）を、
θ＝２πＮｄ／λ ・・・（４）
として、光学膜厚と単色光の波長とを算入して成る光学位相角として表す。
【００２４】
さらに、光学膜厚の増加に要する表面層膜の成長時間（ｔ）と逆透過率（１／Ｔ）との２変数の実測データ群を用いた最小二乗法により、実測データ群が極大または極小に到達する以前に二次関数回帰を行って、二次回帰関数
１／Ｔ＝Ａ_０＋Ｂ_０（ｔ−ｔ_ｐ）^２ ・・・（５）
として算出する。（ここで、Ａ_０及びＢ_０は定数、ｔ_ｐは極大または極小に到達するときの成長時間を表す。）
このとき、回帰関数の相関を高くするため、関数曲線の極大または極小に到達すべき表面層膜の光学膜厚が、この極大または極小まで残すところλ／４相当の光学膜厚のおおむね２５％から１０％となった時点からの実測データ群を用いて関数回帰することが望ましい。（λ：単色光の波長）
ところで、（３）式を変形して、
１／Ｔ＝（１＋Ｙ）^２／４Ｙ＋｛（Ｙ／Ｎ＋Ｎ）^２−（１＋Ｙ）^２｝ｓｉｎ^２θ／４Ｙ ・・・（６）
としたとき、最新表面層膜の成長開始時点の透過率をＴ_０と、最新表面層膜の光学膜厚がλ／４に達するときの成長時間経過時の透過率Ｔ_９０とは、
Ｔ_０＝４Ｙ／（１＋Ｙ）^２ ・・・（７）
Ｔ_９０＝４Ｙ／（Ｙ／Ｎ＋Ｎ）^２ ・・・（８）
として表される。
【００２５】
さらに、これらによりアドミッタンスＹが実数であるとき、
（１／Ｔ_０−１／Ｔ）／（１／Ｔ_０−１／Ｔ_９０）＝ｓｉｎ^２θ ・・・（９）
が得られ、逆透過率は光学位相角のみの関数で示すことができる。
【００２６】
上記したような干渉の原理に基づいて逆透過率は、単色光の波長の１／４に相当する光学膜厚間隔で周期分布する。そして、逆透過率の極大点及び極小点の近傍においては、（９）式を展開して得られる逆透過率の関数（θを変数とし、 ｓｉｎ^２θ項を含む関数）は二次関数に近似できる。したがって、極大点及び極小点における光学膜厚に到達するときの最新表面層膜の膜厚到達予測時間として、二次回帰関数上の極大点または極小点に対応する成長時間を用いることができる。そして、この膜厚到達予測時間に表面層膜に対する成膜を停止する。この際、相関の良好な二次回帰関数によるピーク制御をおこなうため、単色光の波長の１／４に相当する光学膜厚達成のための制御精度がさらに向上する。
【００２７】
この場合、表面層膜の光学膜厚は、上記のように（９）式を展開して得られる逆透過率の関数から算出できる。したがって、この時間微分または時間差分を最新表面層膜の成膜速度として算出し、この成膜速度により最新表面層膜が所定の光学膜厚に到達するために要する時間とすることができる。そして、これにより、所望の光学膜厚の膜厚制御が可能となる。即ち、制御すべき光学膜厚は、単色光の波長の１／４相当のものに限定されず、任意の光学膜厚に制御できることになる。
【００２８】
この際、上記の成膜源として、少なくとも２種類の異なる材質のスパッタターゲットを選択可能な状態で用いることにより、各ターゲット材質を選択して誘電体多層膜の各構成層の膜材料とすることができ、多層膜製造の利便性が向上する。
【００２９】
そして、スパッタターゲットの異なる材質種類として、Ｔａ金属とＳｉ金属とを用いることにより、例えば、ＢＰＦのような光学薄膜製品の高屈折率層材料として代表的なＴａ_２Ｏ_５などのタンタル化合物膜や、低屈折率層材料として代表的なＳｉＯ_２膜などのシリコン化合物膜の製造が可能となる。
【００３０】
このとき、上記の反応源を、中性ラジカル反応ガスを放出するものとすることにより、表面層膜において上記したような化合物膜の生成時に基板温度の上昇が抑制される。この結果、光学膜厚の制御精度の低下も抑制される。
【００３１】
【発明の実施の形態】
図３（ａ）は、本発明の誘電体多層膜製造装置の略断面図である。図３を参照して、真空チャンバ３１内に、成膜源たるスパッタターゲット部３２と反応源たるイオンガン部３３とがともに回転基板３４に対向して並置されている。さらに、チャンバ３１外の投光器３５が回転基板３４の上方位置に配置されており、８チャンネル投光器３５からの８本の平行単色光光束が上部光導入窓３６と回転基板３４と下部光導入窓３７とを介してチャンバ１外の８チャンネル受光器３８で受光される。
【００３２】
さらに、受光器３８で受光された８本の単色光光束は、図中点線で示す電気信号ラインを経由して８チャンネルプリアンプ３９、８チャンネルＡ／Ｄ変換器４０、ディジタルシグナルプロセッサ（ＤＳＰ）４１を介してコンピュータ４２に接続されており、このコンピュータ４２において、所望膜厚の到達予測時間を算出すると共に、算出された予測時間を成膜停止時点として成膜停止を指示して膜厚制御を行う。
【００３３】
スパッタターゲット部３２は、回転機構４３により上下逆転可能に設けたＴａターゲット４４とＳｉターゲット４５とを備えており、各ターゲット４４、４５にはそれぞれ防着板４４ａ、４５ａが覆設されるとともに、各防着板４４ａ、４５ａで包囲される空間内に、スパッタガス導入管４６が貫入する構造となっている。さらに、各ターゲット４４、４５が上面位置にあるときに、固定開口４７を介して回転基板３４と対向する。また、イオンガン部３３は、反応ガス導入管４８が貫入して成るＥＣＲイオンガン４９により構成されている。
【００３４】
回転基板３４は、駆動モータ５０の駆動により回転され、回転基板３４と成膜源３２との間には、成膜速度規制部材たる可変開口５１ａ、５１ｂと、膜厚補正部材たる分割シャッタ５２〜５５が設けられている。
【００３５】
回転基板３４と成膜源３２との間の構成をさらに詳説すると、基板３４とこれに近接して設けられた分割シャッタ５２〜５５とは、図３（ｂ）に示すように、８本の監視用単色光光束の基板３４上通過点（監視点）５６ａ〜５６ｈのそれぞれの軌跡が描く各同心円の円周に沿って、円弧帯状に形成される開口領域のそれぞれを独立の駆動軸５２ａ、５３ａ、５４ａ、５５ａにより開閉するものとして構成する。
【００３６】
さらに、基板３４と分割シャッタ５２〜５５とを含む装置３１の上面図を図３（ｃ）として示す。図中、図外のスパッタターゲット４４、４５を最下位置として、その上方に固定開口４７を穿設した平板４７ａを配置し、次にその上方に可変開口５１ａ、５１ｂを配置し、さらにその上方に分割シャッタ５２〜５５を配置し、最後に回転基板３４を配置した構成である。上記中、固定開口４７は、製品基板３４への蒸発分布を整えて広い範囲で光学特性を得るためのものであり、固定及び可変開口のいずれでも良い。また、可変開口５１ａ、５１ｂは、成膜終点付近で膜厚を精密に制御するために成膜速度を減速させるためのものであり、スパッタターゲット４４、４５の出力調整による減速では即効性が得られず時間がかかり生産性が悪くため、これに替るものである。即ち、当初は高い成膜速度で成膜を行い、成膜終点に近づいた時点で可変開口５１ａ、５１ｂの開度を減少することにより、成膜速度を減速させ、膜厚成長を精密制御するのである。さらに、分割シャッタ５２〜５５は、監視用単色光光束の基板３４上の通過点５６ａ〜５６ｈ（図示せず）のそれぞれの軌跡が描く各同心円の円周に沿って、円弧帯状に形成される開口領域のそれぞれを、独立の駆動シャフト５２ａ、５３ａ、５４ａ、５５ａを介して出し入れすることにより開閉し、これにより、上記開口領域における成膜を遮断するためのものである。また、可変開口５１ａ、５１ｂの開度調整や分割シャッタ５２〜５５の開閉は、受光器３８に連なるコンピュータ４２の指示により装置外部から制御される。
【００３７】
図３（ａ）に示す誘電体多層膜製造装置で膜厚制御を行うに際しては、まず、図外の真空ポンプの作動によりチャンバ３１内を所定の圧力状態に到達させる。そして、駆動モ−タ５０の駆動により製品基板３４を回転させ、次に、投光器３５から上部光導入窓３６と回転基板３４と下部光導入窓３７とを介して、８本の監視用単色光光束を受光部３８に通過させる。このとき、８本の監視用単色光は、２チャンネルずつ同一モニタ波長の単色光として計４種類のモニタ波長を用いる設計とした。さらに、可変開口５１ａ、５１ｂを所定の開度に保ち、また、分割シャッタ５２〜５５を全開にし、回転基板３４とＴａターゲット４４またはＳｉターゲット４５との間を遮断せずに両者を対向させる。そして、ターゲット４４または４５の近傍にスパッタガス導入管４３を介してアルゴンガスを導入し、所定のカソード電力を投入してスパッタ成膜を開始する。その際に、反応ガス導入管４８より酸素ガスとアルゴンガスとの混合ガスを導入しながらＥＣＲイオンガン４９から中性ラジカル酸素を発し、これにより、基板３４上に堆積するＴａまたはＳｉから成る金属種の酸化反応を行う。
さらに、Ｔａターゲット４４とＳｉターゲット４５とを選択的に作動させることにより、製品基板３４上に高屈折率層のＴａ_２Ｏ_５膜と、低屈折率層のＳｉＯ_２膜とから成る交互多層膜が形成されるが、上記したように交互多層膜の各構成層の光学膜厚を高精度で制御することが重要である。このため、上記のターゲット４４または４５によるスパッタ成膜開始時点を膜厚増加に要する成長時間の始点とする。
【００３８】
そして、上記４種類のモニタ波長を２本ずつ割り当てて計８本の平行光束とした監視用単色光が回転基板３４を通過した後に受光器３８で受光される。その後、各単色光は８チャンネルプリアンプ３９で電圧信号に変換され、さらに、８チャンネルＡ／Ｄ変換器４０でデジタル数値信号とされ、ＤＳＰ４１に入力されて、式（５）に基づき成長時間を定義域とする二次関数に回帰演算される。
【００３９】
そして、この二次回帰関数の極大または極小に対応する成長時間を膜厚到達予測時間として、これを、各モニタ波長の監視領域の成膜停止時点として、コンピュータ４２の指示により分割シャッタ５２〜５５を閉じることにより、円弧帯状の該当監視領域の成膜が遮断される。
【００４０】
すべてのモニタ波長の監視領域での成膜が停止した後に、ターゲット部３２において、次の最新表面層膜積層のため、下面で待機していたターゲット４５または４４を上面に逆転させ、上記と同様にして次の成膜工程に備える。そして、このような工程を繰り返すことにより、それぞれの監視領域における積層が独立に終了する。
【００４１】
さらに、以下各［実施例］において、本発明の誘電体多層膜製造装置により得られる光学薄膜製品の光学膜厚の制御精度を検討する。
【００４２】
【実施例】
［実施例１］
図３の誘電体多層膜製造装置を用い、Ｔａ_２Ｏ_５膜を高屈折率層とし、ＳｉＯ_２膜を低屈折率層とし、全構成層の光学膜厚がλ／４（λはモニタ波長）の整数倍である交互多層膜を積層形成して中帯域ＢＰＦを製作した。このときに用いるモニタ波長は、それぞれ１５５２．５２ｎｍ、１５５４．１２ｎｍ、１５５５．７２ｎｍ及び１５５７．３２ｎｍであり、光学薄膜設計は以下の通りである。
反射防止膜付きガラス製品基板（ＢＫ７）｜（ＨＬ）^３Ｌ（ＨＬ）^６Ｌ（ＨＬ）^６Ｌ（ＨＬ）^３｜空気
なお、屈折率の設計値は、低屈折率層において１．４４４、及び、高屈折率層において２．０８、製品基板（ＢＫ７）を１．５とした。
【００４３】
即ち、図３において、φ３００ｍｍの製品基板３４の外周縁から５ｍｍ内側の位置に監視用単色光通過路チャンネル１に対応する監視点を設定し、この監視点から回転円中心方向に１０ｍｍ間隔でチャンネル２〜８を設定した。
【００４４】
そして、図３の投光器３５に相当する波長可変レ−ザ−光源からの８本の単色光光束に対し、モニタ波長１５５２．５２ｎｍの単色光通過路としてチャンネル１及び２を割り当て、モニタ波長１５５４．１２ｎｍの単色光の光束路としてチャンネル３及び４を割り当て、モニタ波長１５５５．７２ｎｍの単色光の光束路としてチャンネル５及び６を割り当て、モニタ波長１５５７．３２ｎｍの単色光の光束路としてチャンネル７及び８を割り当てた。そして、受光部３８で受光されてＤＳＰ４１で計測される透過率を用いて、透過率曲線のピ−ク近傍で二次関数回帰を行い、各ピ−クに到達する到達予測時間を算出して成膜停止時点とした。この工程を繰り返した後の製品基板３４上の特性分布を図４に示す。図４に示すように、約１０ｍｍ程度の幅の環状帯領域５７〜６０においてそれぞれ同質の光学特性が分布することが分る。
【００４５】
また、図５は、チャンネル１〜８に対応する基板上監視領域の分光透過率特性であり、それぞれ中帯域ＢＰＦとして良好な光学製品が得られていることが分る。
【００４６】
［実施例２］
図３の誘電体多層膜製造装置を用い、Ｔａ_２Ｏ_５膜を高屈折率層とし、ＳｉＯ_２膜を低屈折率層とし、全構成層の光学膜厚がλ／４（λはモニタ波長）の整数倍である交互多層膜を積層形成して狭帯域ＢＰＦを製作した。このときに用いるモニタ波長は、それぞれ１５５２．５２ｎｍ、１５５３．３２ｎｍ、１５５４．１２ｎｍ及び１５５４．９２ｎｍであり、光学薄膜設計は以下の通りである。
反射防止膜付きガラス製品基板（ＢＫ７）｜（ＨＬ）^８Ｌ（ＨＬ）^１６Ｌ（ＨＬ）^１６Ｌ（ＨＬ）^８｜空気
なお、屈折率の設計値は、低屈折率層において１．４４４、及び、高屈折率層において２．０８、製品基板（ＢＫ７）を１．５とした。
【００４７】
即ち、図３において、φ３００ｍｍの製品基板３４の外周縁から５ｍｍ内側の位置に監視用単色光通過路チャンネル１に対応する監視点を設定し、この監視点から回転円中心方向に１０ｍｍ間隔でチャンネル２〜８を設定した。
【００４８】
そして、図３の投光器３５に相当する波長可変レ−ザ−光源からの８本の単色光光束に対し、モニタ波長１５５２．５２ｎｍの単色光通過路としてチャンネル１及び２を割り当て、モニタ波長１５５３．３２ｎｍの単色光の光束路としてチャンネル３及び４を割り当て、モニタ波長１５５４．１２ｎｍの単色光の光束路としてチャンネル５及び６を割り当て、モニタ波長１５５４．９２ｎｍの単色光の光束路としてチャンネル７及び８を割り当てた。そして、受光部３８で受光されてＤＳＰ４１で計測される透過率により逆透過率を算出し、これを用いて逆透過率曲線のピ−ク近傍で二次関数回帰を行い、各ピ−クに到達する到達予測時間を算出して成膜停止時点とした。
【００４９】
図６は、チャンネル１〜８に対応する基板上監視領域の分光透過率特性であり、それぞれ狭帯域ＢＰＦとして良好な光学製品が得られていることが分る。
【００５０】
［実施例３］
図３の誘電体多層膜製造装置を用い、Ｔａ_２Ｏ_５膜を高屈折率層とし、ＳｉＯ_２膜を低屈折率層とし、第１層及び第２層の光学膜厚はλ／４（λはモニタ波長）の整数倍とは異なるが、最終的な表面層（第２層）の成膜停止時点はピーク制御により予測した交互多層膜で反射防止膜膜を製作した。このときに用いるモニタ波長は、それぞれ１５５０ｎｍ、１５５５ｎｍ、１５６０ｎｍ、１５６５ｎｍであり、光学薄膜設計は以下の通りである。
反射防止膜付きガラス製品基板（ＢＫ７）｜０．３５Ｈ、１．２８８Ｌ｜空気
なお、屈折率の設計値は、低屈折率層において１．４４４、及び、高屈折率層において２．０８、製品基板（ＢＫ７）を１．５とした。
【００５１】
即ち、図３において、φ３００ｍｍの製品基板３４の外周縁から５ｍｍ内側の位置に監視用単色光通過路チャンネル１に対応する監視点を設定し、この監視点から回転円中心方向に１０ｍｍ間隔でチャンネル２〜８を設定した。
【００５２】
そして、図３の投光器３５に相当する波長可変レ−ザ−光源からの８本の単色光光束に対し、モニタ波長１５５０ｎｍの単色光通過路としてチャンネル１及び２を割り当て、モニタ波長１５５５ｎｍの単色光の光束路としてチャンネル３及び４を割り当て、モニタ波長１５６０ｎｍの単色光の光束路としてチャンネル５及び６を割り当て、モニタ波長１５６５ｎｍの単色光の光束路としてチャンネル７及び８を割り当てた。そして、受光部３８で受光されてＤＳＰ４１で計測される透過率により逆透過率を算出し、第１層においては、逆透過率を用いて０．３５Ｈに相当する成膜停止時点を予測し、また、第２層においては、逆透過率曲線のピ−ク近傍で二次関数回帰を行い、ピ−クに到達する到達予測時間を算出して成膜停止時点とした。
【００５３】
図７は、チャンネル１〜８に対応する基板上監視領域の分光反射率特性であり、それぞれ反射防止膜として良好な光学製品が得られていることが分る。
【００５４】
【発明の効果】
以上の説明から明らかなように、本発明によれば、透過率または逆透過率のピーク近傍で二次関数回帰したときの極大または極小に対応する成長時間を膜厚到達予測時間として用いることができるため、高精度で光学膜厚の膜厚成長を制御できる。また、多種類のモニタ波長による直接監視法を用い、良好な特性の誘電体薄膜が得られる監視領域を拡大することができる。このため、例えば狭帯域バンドパスフィルタなど、稠密波長多重通信システム用デバイスとして高品質の光学薄膜製品の量産化が可能となる。
【図面の簡単な説明】
【図１】（ａ）直接監視法を用いる従来の誘電体多層膜製造装置の略断面図
（ｂ）（ａ）の製造装置で得られる基板上の光学特性領域の概念図
【図２】従来の光学膜厚制御法による二次回帰関数の乖離を示すグラフ図
【図３】（ａ）本発明の誘電体誘電体多層膜製造装置の略断面図
（ｂ）（ａ）の製造装置中の基板と分割シャッタとを示す上面図
（ｃ）（ａ）の製造装置の上面図
【図４】［実施例１］で得られる基板上の光学特性領域の概念図
【図５】［実施例１］で得られる中帯域ＢＰＦの分光透過率特性を示すグラフ図
【図６】［実施例２］で得られる狭帯域ＢＰＦの分光透過率特性を示すグラフ図
【図７】［実施例３］で得られる反射防止膜の分光反射率特性を示すグラフ図
【符号の説明】
１ ３１ 真空チャンバ
２ 電子銃 ２ａ シャッタ
４ ３４ 回転基板
３２ スパッタターゲット部（成膜源）
３３ イオンガン部（反応源）
３５ 投光器
３６ 上部光導入窓
３７ 下部光導入窓
３８ 受光器（光強度計測手段）
３９ ８チャンネルプリアンプ
４０ ８チャンネルＡ／Ｄ変換器
４１ ディジタルシグナルプロセッサ（ＤＳＰ）
４２ コンピュータ
４４ Ｔａターゲット
４５ Ｓｉターゲット
４６ スパッタガス導入管
４７ 固定開口部
４８ 反応ガス導入管
４９ ＥＣＲイオンガン
５１ａ、５１ｂ 可変開口（成膜速度規制部材）
５２、５３、５４、５５ 分割シャッタ（膜厚補正部材）
５６ａ〜５６ｈ 監視点[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for producing a dielectric multilayer film, which mainly uses an optical thin film and can control the film thickness with high precision at the time of its formation. The use of optical thin films is expanding to various optical components and optical elements such as waveguides, diffraction gratings, light emission, display elements, optical memories, and solar cells. In particular, in the field of communication technology such as optical communication, in a dense wavelength division multiplexing communication (DWDM) system, there is a remarkable tendency to multilayer optical thin films for devices such as a multiplexer / demultiplexer. When manufacturing a thin film, it is required to control the optical film thickness of each constituent layer with high precision.
[0002]
[Prior art]
Film thickness measurement during thin film growth is important for controlling the deposition rate and film thickness, and in the case of optical thin films, the optical film thickness that determines optical properties such as reflectance and transmittance rather than physical film thickness (Product of refractive index and physical film thickness) is useful. For this reason, it is widely practiced to monitor the optical film thickness by measuring the optical properties during the growth of the thin film by a so-called optical film thickness control method for measuring the optical properties of the thin film. The optical film thickness control method includes a monochromatic photometric method, a two-color photometric method, a multicolor photometric method, and the like. Of these optical film thickness control methods, the monochromatic photometric method is the simplest.
[0003]
This is a peak (including the bottom and also synonymous with the maximum and the minimum, the same applies hereinafter) when the optical film thickness of the growing thin film is an integral multiple of λ / 4 (λ: wavelength of incident monochromatic light). Is used. Such a peak occurs when an adjacent layer on the substrate side on which the latest surface layer film being grown is laminated via the adhesion surface is formed with an optical film thickness that does not become an integral multiple of λ / 4. If the admittance of the system including the adjacent layer is not mathematically real, it does not always appear when the optical film thickness from the start of growth first reaches an integral multiple of λ / 4. However, even in these cases, the peak itself appears periodically at an optical film thickness interval corresponding to an integral multiple of λ / 4 after its appearance.
[0004]
However, in the case of using the monochromatic photometry, in the conventional method of performing peak control using the peak that appears as described above, the change in the amount of light with respect to the optical film thickness growing near the peak is small, and the control accuracy is deteriorated in principle. That is inevitable.
[0005]
In such a case, the accuracy can be improved by using an interference filter having a monitor wavelength slightly different from the desired wavelength to be controlled and stopping film formation at a large change in the amount of light other than near the peak. As this type of apparatus, an optical phase angle region is selected so as to obtain good control accuracy of an optical film thickness to be grown by measuring a light amount (reciprocal of transmittance) as an optical property, and determine a film forming stop point. There is something to do. (For example, Patent Document 1).
[0006]
On the other hand, for example, an apparatus disclosed in Patent Document 2 pursues a conventional monochromatic photometric method using a desired monitor wavelength as it is. In this method, the measured data immediately before forming a peak corresponding to the optical film thickness growth in which the measured light amount (transmittance) is an integral multiple of λ / 4 is subjected to a quadratic function regression by the least square method. , The point at which the peak on this regression function is reached. At this time, the prediction time itself is the most preferable, but when individual conditions need to be considered, the timing for stopping the film formation is determined using this as a reference time.
[0007]
By the way, the demand for a multilayer optical thin film is remarkable in the field of communication technology as described above, and in particular, an optical thin film of a device for a DWDM system (for example, a bandpass filter, hereinafter also referred to as a BPF) used for optical communication. May have more than 100 layers. Such a multilayer structure is composed of alternating layers of a high-refractive-index layer and a low-refractive-index layer each having an optical thickness of an odd multiple of λ / 4. (However, in the case of the BPF, the cavity layer may be formed by setting the optical film thickness of the high refractive index layer and the low refractive index layer in the alternating layers to an even multiple of the above λ / 4.) The usual method of controlling the film thickness while replacing the monitor substrate corresponding to each of the constituent thin films of the multilayer structure becomes complicated and impractical.
[0008]
Therefore, for an optical thin film having a multilayer structure, the film thickness is often controlled by a direct monitoring method that monitors a large number of alternating layers themselves formed on a product substrate. FIG. 1 shows an example of a film thickness control device using a direct monitoring method. In a vacuum chamber 1 shown in FIG. 1A, an electron gun 2 and an ion gun 3 are both juxtaposed so as to face a rotating substrate 4, and a light projecting unit 5 outside the chamber 1 is opposed to the rotating substrate 4. The light emitted from the light projector 5 to the rotation axis 4a of the rotating substrate 4 is received by the light receiver 8 outside the chamber 1 via the lower light introduction window 6 and the upper light introduction window 7. When the film thickness is controlled by the present apparatus, first, the product substrate 4 is rotated by driving the drive motor 9, and then one monitoring monochromatic light is transmitted from the light projector 5 through the lower light introducing window 6. The light beam passes along the rotation axis 4a. In this state, the shutter 2a is opened, and a vapor deposition film is formed on the product substrate 4 by the electron gun 2. At this time, a change in light intensity due to interference is observed by the light receiver 8 via the lower light introduction window 6 and the upper light introduction window 7. Further, the film thickness at the time of forming the vapor-deposited film is controlled based on this light intensity change, that is, the film forming stop time is determined by the film thickness control method disclosed in Patent Document 1 or Patent Document 2, for example, and the electron gun 2 is controlled by the shutter 2a. The film thickness growth is terminated by cutting off the film formation. In this way, a dielectric multilayer film having good spectral characteristics near the center of the product substrate is produced.
[0009]
However, in this case, as the lamination proceeds, the reflectance in the growing multilayer structure increases, that is, the transmittance gradually decreases, and the reliability of the measured value decreases. This effect is particularly serious in a narrow-band BPF formed by continuously laminating a large number of alternating layers each composed of a high-refractive-index λ / 4 film and a low-refractive-index λ / 4 film. Further, as the number of the alternating layers increases, the transmitted light amount change curve that changes with the film thickness growth deviates from the quadratic regression function near the peak and bottom, making it difficult to control the film thickness with high accuracy. FIG. 2 shows such a divergence of the quadratic regression function, in which the amount of transmitted light decreases (when the high refractive index layer H on the low refractive index layer L becomes the latest surface layer) and when it increases. (When the high refractive index layer H on the high refractive index layer H becomes the latest surface layer), the peak / bottom position predicted when the quadratic function regression is performed is greatly different, and the error varies. Thus, the point at which the film formation is stopped is predicted earlier when the amount of transmitted light decreases, and is predicted later when the amount of transmitted light increases.
[0010]
Further, in today's optical communication market, for example, ITU-T (International Telecommunication Union Telecommunications Co., Ltd.) has used narrow band BPFs used in multiplexers / demultiplexers of DWDM systems in 4, 8, 16,... A set of BPFs corresponding to various types of center wavelengths is required for each wavelength determined by the standardization sector. For this reason, it is demanded that filters having various types of center wavelengths be manufactured simultaneously and in large quantities.
[0011]
However, in the multilayer film manufacturing apparatus shown in FIG. 1, the direct monitoring method is effective because the monochromatic light beam for monitoring passes only along the rotation center axis. The optical thin film product obtained from the substrate region distant from the center indicated by 11 has wavelength characteristic fluctuation due to fluctuation of evaporation distribution, relative distance difference between the product substrate and the evaporation source, or uneven temperature of the product substrate surface. Due to the difference or the like, good characteristics corresponding to the monitor wavelength of the direct monitoring method are not shown.
[0012]
Therefore, the irradiation passage position of the monitoring monochromatic light beam is changed to a concentric position in the rotating substrate area instead of the rotation center axis, and the annular area formed in a belt shape on this circumference is an effective part of the direct monitoring method. However, only a slight improvement in the effective part area can be obtained. On the other hand, in the passing region of the monochromatic light beam for monitoring by the direct monitoring method, even if the control accuracy of the layer immediately before the latest surface layer is poor, the point at which the formation of the next latest layer is stopped is accurately determined by peak and bottom. , The error is naturally corrected, so that the error is reduced. Therefore, to obtain a good optical thin film product, the advantage of the monitoring area portion is remarkable, and it is important to expand this area.
[0013]
Patent Document 3 by the present inventors is an example of a dielectric multilayer film manufacturing apparatus having such an extended monitoring area. In this apparatus, a plurality of monitoring points are provided on a substrate rotating at a high speed, and a monitoring monochromatic light beam having the same wavelength is passed through the monitoring points to predictively control a film forming stop time and to be linked with a movable shutter. Then, good optical thin film products can be obtained from all of the monitoring areas enlarged corresponding to the monitoring points provided at multiple points. However, although this apparatus can mass-produce a dielectric multilayer film having one kind of wavelength characteristic, the disadvantage that an optical thin film product corresponding to various kinds of monitor wavelengths cannot be obtained remains. In addition, there remains a difficulty that a film thickness distribution that increases or decreases uniformly in the radial direction of the substrate is created.
[0014]
[Patent Document 1]
JP-A-58-140605 (pages 2-3, FIG. 1)
[Patent Document 2]
JP-A-63-28862 (pages 2 to 6, FIGS. 1 and 2)
[Patent Document 3]
Japanese Patent Application No. 2002-083260 (FIG. 1)
[0015]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and has been made in consideration of the above problems, and is capable of performing high-precision film thickness control, and is capable of using a direct monitoring method at a desired various kinds of monitor wavelengths. It is an object to provide a film manufacturing apparatus. In addition, it is assumed that this dielectric multilayer film can withstand narrow band BPF applications.
[0016]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an apparatus for manufacturing a dielectric multilayer film in a vacuum chamber including a film forming source and a reaction source arranged side by side opposite to a rotating substrate. Film-forming rate regulating member having an opening for regulating the film-forming speed of a dielectric multilayer film, and a film having an opening for correcting the film thickness of the dielectric multilayer film formed on the rotating substrate A thickness correcting member provided between the rotating substrate and the film forming source; and a light intensity measuring means for measuring the intensity of the monitoring monochromatic light passing through a plurality of monitoring points along the radius of the rotating substrate. A control system that enables the opening of the film thickness correction member to move in accordance with a change in light intensity measured by the light intensity measuring means when each of the monitoring monochromatic light beams having more than one type of wavelength passes through these monitoring points. It was provided with.
[0017]
According to this, the light intensity that changes in accordance with the increase in the thickness of the latest surface layer film of the dielectric multilayer film formed on the substrate is detected by the light intensity measuring means, and the thickness correction member of the film thickness correction member is accordingly detected. By moving the opening, an increase in the thickness of the dielectric multilayer film can be corrected. That is, it is possible to control the thickness of the latest surface layer film of the dielectric multilayer film with high accuracy. At this time, since monochromatic light of one or more wavelengths is used as a monitoring light flux, it is necessary to control the film thickness by a direct monitoring method corresponding to various monitor wavelengths to manufacture a dielectric multilayer film. Can be.
[0018]
Then, as a movable opening of the film thickness correcting member, a division for independently opening and closing each of the opening areas formed in the shape of an arc band along the circumference of each concentric circle drawn by each locus of the monitoring point when the rotating substrate is rotated. Use a shutter.
[0019]
This makes it possible to cut off the film formation under the same conditions for the same dielectric multilayer film formed in the shape of an arc band for each monochromatic light of a different wavelength when passing through the monitoring point. Therefore, it is possible to mass-produce a variety of high-quality dielectric multilayer films obtained in each of the arc-shaped monitoring regions.
[0020]
Further, the control system of the dielectric multilayer film manufacturing apparatus first transmits a monitoring monochromatic luminous flux having one or more wavelengths to each of a plurality of monitoring points over the period of forming the dielectric multilayer film on the rotating substrate. When the light passes through, the change in the light intensity measured by the light intensity measuring means is measured as the change in the transmittance of the dielectric multilayer film, and the reciprocal of this transmittance is calculated as the reverse transmittance.
[0021]
At this time, the admittance Y of the substrate can be calculated by using the characteristic matrix of the single-layer film according to the boundary conditions of the structure (the tangential components B and C of the electric field and the magnetic field are continuous).
[0022]
(Equation 1)

It is expressed as [Equation 1] (Equation (1)). (Here, N indicates the refractive index of the single-layer film, and θ indicates the phase difference at different interfaces on the single-layer film.)
At this time, the transmittance T of the single-layer film is
T = 4Y / (B + C) (B + C) ^* ... (2)
(Here, * indicates a conjugate complex number.)
T = 4Y / [(1 + Y) ² + ｛(Y / N + N) ² − (1 + Y) ² ｝ sin ² θ] (3) by the equations (1) and (2).
It becomes. However, the refractive index of air or vacuum is 1.
[0023]
In the present invention, the optical thickness Nd (N is the refractive index of the thin film, d is the physical thickness of the thin film) of the latest surface layer film during the adhesion growth is further defined as:
θ = 2πNd / λ (4)
Is expressed as an optical phase angle obtained by adding the optical film thickness and the wavelength of monochromatic light.
[0024]
Further, the least-square method using the measured data group of two variables of the growth time (t) of the surface layer film required for increasing the optical film thickness and the reverse transmittance (1 / T) makes the measured data group maximum or minimum. performing quadratic function regression prior to reaching the secondary regression function _{1 / T = a 0 + B} 0 (t-t p) 2 ··· (5)
Is calculated as (Wherein, _{A 0} and _{B 0} are constants, _{t p} represents the growth time when it reaches the maximum or minimum.)
At this time, in order to increase the correlation of the regression function, the optical film thickness of the surface layer film which should reach the maximum or minimum of the function curve is approximately 25% of the optical film thickness equivalent to λ / 4 where the maximum or minimum is left. It is desirable to perform a function regression using an actual measurement data group from the time point when the value becomes 10%. (Λ: wavelength of monochromatic light)
By the way, by transforming equation (3),
1 / T = (1 + Y) ² / 4Y + ｛(Y / N + N) ² − (1 + Y) ² ｝ sin ² θ / 4Y (6)
, The transmittance at the start of the growth of the latest surface layer film is T _0, and the transmittance T ₉₀ at the elapse of the growth time when the optical thickness of the latest surface layer film reaches λ / 4 is:
T ₀ = 4Y / (1 + Y) ² (7)
T ₉₀ = 4Y / (Y / N + N) ² (8)
It is expressed as
[0025]
Further, when admittance Y is a real number,
(1 / T ₀ −1 / T) / (1 / T ₀ −1 / T ₉₀ ) = sin ² θ (9)
Is obtained, and the reverse transmittance can be represented by a function of only the optical phase angle.
[0026]
Based on the principle of interference as described above, the reverse transmittance is periodically distributed at an optical film thickness interval corresponding to １ ／ of the wavelength of monochromatic light. In the vicinity of the maximum point and the minimum point of the reverse transmittance, the function of the reverse transmittance (a function including θ as a variable and a sin ² θ term) obtained by expanding Expression (9) becomes a quadratic function. Can be approximated. Therefore, the growth time corresponding to the maximum point or the minimum point on the quadratic regression function can be used as the estimated time to reach the film thickness of the latest surface layer film when reaching the optical film thickness at the maximum point and the minimum point. Then, the film formation on the surface layer film is stopped at the estimated film thickness reaching time. At this time, since peak control is performed by a quadratic regression function having a good correlation, control accuracy for achieving an optical film thickness equivalent to １ ／ of the wavelength of monochromatic light is further improved.
[0027]
In this case, the optical film thickness of the surface layer film can be calculated from the function of the reverse transmittance obtained by expanding Expression (9) as described above. Therefore, this time differential or time difference is calculated as the film formation speed of the latest surface layer film, and the film formation speed can be used as the time required for the latest surface layer film to reach a predetermined optical film thickness. This makes it possible to control the thickness of the desired optical film thickness. That is, the optical film thickness to be controlled is not limited to one equivalent to １ ／ of the wavelength of the monochromatic light, but can be controlled to an arbitrary optical film thickness.
[0028]
At this time, by using at least two types of sputter targets of different materials in a selectable state as the film forming source, each target material is selected and used as a film material of each constituent layer of the dielectric multilayer film. And the convenience of manufacturing a multilayer film is improved.
[0029]
By using Ta metal and Si metal as different material types of the sputter target, for example, a tantalum compound film such as Ta ₂ O ₅ or the like as a high refractive index layer material of an optical thin film product such as BPF, In addition, it is possible to manufacture a silicon compound film such as a typical SiO ₂ film as a low refractive index layer material.
[0030]
At this time, by raising the reaction source to emit a neutral radical reaction gas, an increase in the substrate temperature during the formation of the compound film as described above in the surface layer film is suppressed. As a result, a decrease in the control accuracy of the optical film thickness is suppressed.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3A is a schematic sectional view of a dielectric multilayer film manufacturing apparatus according to the present invention. Referring to FIG. 3, in a vacuum chamber 31, a sputter target portion 32 as a film formation source and an ion gun portion 33 as a reaction source are both arranged to face a rotating substrate 34. Further, a light projector 35 outside the chamber 31 is disposed above the rotating substrate 34, and eight parallel monochromatic light beams from the eight-channel light projector 35 are transmitted through the upper light introducing window 36, the rotating substrate 34, and the lower light introducing window 37. The light is received by the eight-channel light receiver 38 outside the chamber 1 via.
[0032]
Further, the eight monochromatic light beams received by the light receiver 38 are converted into eight-channel preamplifiers 39, eight-channel A / D converters 40, and digital signal processors (DSP) 41 via electric signal lines shown by dotted lines in the figure. Is connected to a computer 42 through which the predicted time to reach the desired film thickness is calculated, and the calculated predicted time is used as a film formation stop point to instruct film formation stop to control film thickness control. Do.
[0033]
The sputter target unit 32 includes a Ta target 44 and a Si target 45 provided so as to be able to be turned upside down by a rotating mechanism 43. The targets 44, 45 are covered with deposition prevention plates 44a, 45a, respectively. The structure is such that a sputter gas introduction pipe 46 penetrates into a space surrounded by the deposition-inhibiting plates 44a and 45a. Further, when each of the targets 44 and 45 is at the upper surface position, it faces the rotating substrate 34 via the fixed opening 47. The ion gun section 33 is constituted by an ECR ion gun 49 into which a reaction gas introduction pipe 48 penetrates.
[0034]
The rotating substrate 34 is rotated by the driving of a drive motor 50. Between the rotating substrate 34 and the film forming source 32, variable openings 51a and 51b serving as film forming speed regulating members, and divided shutters 52 to 51 serving as film thickness correcting members. 55 are provided.
[0035]
The configuration between the rotating substrate 34 and the film forming source 32 will be described in more detail. The substrate 34 and the divided shutters 52 to 55 provided in the vicinity of the substrate 34, as shown in FIG. Along the circumference of each concentric circle drawn by the respective trajectories of the monitoring monochromatic light beam passing points (monitoring points) 56a to 56h on the substrate 34, each of the opening regions formed in the shape of an arc band is formed by an independent drive shaft 52a. It is configured to be opened and closed by 53a, 54a, 55a.
[0036]
Further, a top view of the device 31 including the substrate 34 and the divided shutters 52 to 55 is shown in FIG. In the drawing, a flat plate 47a having a fixed opening 47 is disposed above the sputter targets 44, 45 (not shown) at the lowest position, and variable openings 51a, 51b are disposed above the sputter targets 44, 45. In this configuration, divided shutters 52 to 55 are arranged, and finally, a rotating substrate 34 is arranged. Among the above, the fixed opening 47 is for adjusting the evaporation distribution to the product substrate 34 to obtain optical characteristics in a wide range, and may be either a fixed or variable opening. The variable openings 51a and 51b are used to reduce the film forming speed in order to precisely control the film thickness near the film forming end point. This is an alternative because it takes time and productivity is low. That is, the film is initially formed at a high film forming speed, and the film forming speed is reduced by decreasing the opening degree of the variable openings 51a and 51b when approaching the film forming end point, thereby precisely controlling the film thickness growth. It is. Further, the divided shutters 52 to 55 are formed in an arc band along the circumference of each concentric circle drawn by each locus of passing points 56a to 56h (not shown) of the monitoring monochromatic light beam on the substrate 34. Each of the opening areas is opened and closed by moving in and out through independent drive shafts 52a, 53a, 54a, and 55a, thereby blocking film formation in the opening areas. The opening adjustment of the variable openings 51a and 51b and the opening and closing of the divided shutters 52 to 55 are controlled from the outside of the apparatus by instructions from a computer 42 connected to the light receiver 38.
[0037]
When controlling the film thickness by the dielectric multilayer film manufacturing apparatus shown in FIG. 3A, first, the inside of the chamber 31 is brought to a predetermined pressure state by operating a vacuum pump (not shown). Then, the product substrate 34 is rotated by driving the drive motor 50, and then eight monochromatic light beams for monitoring are transmitted from the projector 35 through the upper light introducing window 36, the rotating substrate 34, and the lower light introducing window 37. The light beam passes through the light receiving unit 38. At this time, the eight monitoring monochromatic lights were designed to use a total of four monitor wavelengths as monochromatic lights having the same monitor wavelength for each of two channels. Further, the variable openings 51a and 51b are kept at a predetermined opening degree, the divided shutters 52 to 55 are fully opened, and the rotating substrate 34 and the Ta target 44 or the Si target 45 are opposed to each other without being interrupted. Then, an argon gas is introduced into the vicinity of the target 44 or 45 through the sputtering gas introduction pipe 43, and a predetermined cathode power is applied to start sputtering film formation. At this time, neutral radical oxygen is emitted from the ECR ion gun 49 while introducing a mixed gas of oxygen gas and argon gas from the reaction gas introduction pipe 48, whereby the metal species of Ta or Si deposited on the substrate 34 is formed. Oxidation reaction.
Further, by selectively operating the Ta target 44 and the Si target 45, an alternating multilayer film composed of a high refractive index layer of Ta ₂ O ₅ film and a low refractive index layer of SiO ₂ film is formed on the product substrate. Is formed, but as described above, it is important to control the optical film thickness of each constituent layer of the alternating multilayer film with high accuracy. For this reason, the starting point of the sputtering film formation by the target 44 or 45 is set as the starting point of the growth time required for increasing the film thickness.
[0038]
The monochromatic light for monitoring, which is a total of eight parallel light beams by allocating the four types of monitor wavelengths two by two, is received by the light receiver 38 after passing through the rotating substrate 34. Thereafter, each monochromatic light is converted into a voltage signal by an 8-channel preamplifier 39, further converted into a digital numerical signal by an 8-channel A / D converter 40, input to a DSP 41, and defines a growth time based on the equation (5). A regression operation is performed on a quadratic function as a region.
[0039]
Then, the growth time corresponding to the maximum or the minimum of the quadratic regression function is set as the film thickness reaching prediction time, and this is set as the stop time of the film formation in the monitoring region of each monitor wavelength. Is closed, the film formation in the arc-shaped monitoring region is cut off.
[0040]
After the film formation in the monitoring areas of all monitor wavelengths is stopped, the target 45 or 44 waiting on the lower surface is reversed to the upper surface in the target portion 32 for the next latest surface layer film lamination, and the same as above. To prepare for the next film forming step. Then, by repeating such a process, the lamination in each monitoring area is independently finished.
[0041]
Further, in each of the following Examples, the control accuracy of the optical film thickness of the optical thin film product obtained by the dielectric multilayer film manufacturing apparatus of the present invention will be examined.
[0042]
【Example】
[Example 1]
3, the Ta ₂ O ₅ film is used as the high refractive index layer, the SiO ₂ film is used as the low refractive index layer, and the optical thickness of all the constituent layers is λ / 4 (where λ is the monitor wavelength). ) To form an intermediate multilayer BPF. The monitor wavelengths used at this time are 155.52 nm, 1554.12 nm, 1555.72 nm, and 1557.32 nm, respectively, and the optical thin film design is as follows.
Glass product substrate with antireflection film (BK7) | (HL) ³ L (HL) ⁶ L (HL) ⁶ L (HL) ³ | Air The design value of the refractive index is 1.444 in the low refractive index layer. Further, the high refractive index layer was set to 2.08, and the product substrate (BK7) was set to 1.5.
[0043]
That is, in FIG. 3, a monitoring point corresponding to the monitoring monochromatic light passage channel 1 is set at a position 5 mm inward from the outer peripheral edge of the product substrate 34 having a diameter of 300 mm, and the channels are spaced from the monitoring point by 10 mm toward the center of the rotating circle. 2 to 8 was set.
[0044]
Channels 1 and 2 are assigned to the eight monochromatic light beams from the wavelength variable laser light source corresponding to the light projector 35 in FIG. 3 as monochromatic light passages with a monitor wavelength of 1552.52 nm. Channels 3 and 4 are assigned as a light path of a monochromatic light of 12 nm, channels 5 and 6 are assigned as a light path of a monochromatic light of a monitor wavelength of 1555.72 nm, and channels 7 and 8 are assigned as a light path of a monochromatic light of a monitor wavelength of 1557.32 nm. Assigned. Then, using the transmittance received by the light receiving unit 38 and measured by the DSP 41, a quadratic function regression is performed in the vicinity of the peak of the transmittance curve to calculate a predicted arrival time at each peak. The time when the film formation was stopped was set. FIG. 4 shows the characteristic distribution on the product substrate 34 after repeating this process. As shown in FIG. 4, it can be seen that optical properties of the same quality are distributed in the annular band areas 57 to 60 having a width of about 10 mm.
[0045]
FIG. 5 shows the spectral transmittance characteristics of the monitoring area on the substrate corresponding to channels 1 to 8, and it can be seen that good optical products are obtained as the middle band BPFs.
[0046]
[Example 2]
3, the Ta ₂ O ₅ film is used as the high refractive index layer, the SiO ₂ film is used as the low refractive index layer, and the optical thickness of all the constituent layers is λ / 4 (where λ is the monitor wavelength). ) To form a narrow band BPF. The monitor wavelengths used at this time are 155.52 nm, 1553.32 nm, 1554.12 nm and 1554.92 nm, respectively, and the optical thin film design is as follows.
Glass product substrate with antireflection film (BK7) | (HL) ⁸ L (HL) ¹⁶ L (HL) ¹⁶ L (HL) ⁸ | Air The design value of the refractive index is 1.444 in the low refractive index layer. Further, the high refractive index layer was set to 2.08, and the product substrate (BK7) was set to 1.5.
[0047]
That is, in FIG. 3, a monitoring point corresponding to the monitoring monochromatic light passage channel 1 is set at a position 5 mm inward from the outer peripheral edge of the product substrate 34 having a diameter of 300 mm, and the channels are spaced from the monitoring point by 10 mm toward the center of the rotating circle. 2 to 8 was set.
[0048]
Channels 1 and 2 are assigned to the eight monochromatic light beams from the wavelength variable laser light source corresponding to the light projector 35 in FIG. Channels 3 and 4 are assigned as a light path of a monochromatic light of 32 nm, channels 5 and 6 are assigned as a light path of a monochromatic light of a monitor wavelength of 1554.12 nm, and channels 7 and 8 are assigned as a light path of a monochromatic light of a monitor wavelength of 1554.92 nm. Assigned. Then, a reverse transmittance is calculated based on the transmittance received by the light receiving unit 38 and measured by the DSP 41, and using this, a quadratic function regression is performed near the peak of the reverse transmittance curve, and each peak is calculated. The predicted arrival time was calculated and defined as the time point when the film formation was stopped.
[0049]
FIG. 6 shows the spectral transmittance characteristics of the monitoring area on the substrate corresponding to channels 1 to 8, and it can be seen that good optical products are obtained as narrow band BPFs.
[0050]
[Example 3]
3, the Ta ₂ O ₅ film is used as a high refractive index layer, the SiO ₂ film is used as a low refractive index layer, and the optical thickness of the first and second layers is λ / 4 ( Although [lambda] is different from an integral multiple of the monitor wavelength), the anti-reflection film was manufactured using an alternate multilayer film predicted by peak control at the final stop of the surface layer (second layer) film formation. The monitor wavelengths used at this time are 1550 nm, 1555 nm, 1560 nm, and 1565 nm, respectively, and the optical thin film design is as follows.
Glass product substrate with anti-reflection coating (BK7) | 0.35H, 1.288L | Air Note that the design value of the refractive index is 1.444 for the low refractive index layer and 2.08 for the high refractive index layer, and the product. The substrate (BK7) was set to 1.5.
[0051]
That is, in FIG. 3, a monitoring point corresponding to the monitoring monochromatic light passage channel 1 is set at a position 5 mm inward from the outer peripheral edge of the product substrate 34 having a diameter of 300 mm, and the channels are spaced from the monitoring point by 10 mm toward the center of the rotating circle. 2 to 8 was set.
[0052]
Channels 1 and 2 are assigned to the eight monochromatic light beams from the wavelength-tunable laser light source corresponding to the light projector 35 in FIG. Channels 3 and 4 were assigned as light flux paths, channels 5 and 6 were assigned as light flux paths for monochromatic light having a monitor wavelength of 1560 nm, and channels 7 and 8 were assigned as light flux paths for monochromatic light having a monitor wavelength of 1565 nm. Then, a reverse transmittance is calculated based on the transmittance received by the light receiving unit 38 and measured by the DSP 41, and in the first layer, a film formation stop time corresponding to 0.35H is predicted using the reverse transmittance, In the second layer, a quadratic function regression was performed in the vicinity of the peak of the reverse transmittance curve, and a predicted arrival time at which the peak was reached was determined as the film formation stop time.
[0053]
FIG. 7 shows the spectral reflectance characteristics of the monitoring area on the substrate corresponding to channels 1 to 8, and it can be seen that good optical products are obtained as antireflection films.
[0054]
【The invention's effect】
As apparent from the above description, according to the present invention, the growth time corresponding to the maximum or minimum when the quadratic function regression is performed in the vicinity of the peak of the transmittance or the inverse transmittance is used as the film thickness reaching prediction time. Therefore, the growth of the optical film thickness can be controlled with high accuracy. In addition, by using a direct monitoring method using various types of monitor wavelengths, it is possible to expand a monitoring region in which a dielectric thin film having good characteristics can be obtained. For this reason, it is possible to mass-produce high-quality optical thin film products as devices for dense wavelength division multiplexing communication systems such as narrow band pass filters.
[Brief description of the drawings]
FIG. 1A is a schematic cross-sectional view of a conventional dielectric multilayer film manufacturing apparatus using a direct monitoring method. FIG. 1B is a conceptual diagram of an optical characteristic region on a substrate obtained by the manufacturing apparatus of FIG. FIG. 3A is a graph showing the deviation of a quadratic regression function according to the optical film thickness control method. FIG. 3A is a schematic cross-sectional view of the dielectric / dielectric multilayer film manufacturing apparatus of the present invention. FIG. 4 is a top view of the manufacturing apparatus shown in FIGS. 4C and 4A showing a substrate and a divided shutter. FIG. 4 is a conceptual diagram of an optical characteristic region on a substrate obtained in [Example 1]. FIG. 6 is a graph showing the spectral transmittance characteristics of the middle band BPF obtained in [Example 2]. FIG. 7 is a graph showing the spectral transmittance characteristics of the narrow band BPF obtained in [Example 2]. A graph showing the spectral reflectance characteristics of the obtained anti-reflection film.
1 31 Vacuum chamber 2 Electron gun 2a Shutter 4 34 Rotating substrate 32 Sputter target unit (film formation source)
33 Ion gun part (reaction source)
35 Projector 36 Upper light introduction window 37 Lower light introduction window 38 Light receiver (light intensity measuring means)
39 8-channel preamplifier 40 8-channel A / D converter 41 Digital signal processor (DSP)
42 Computer 44 Ta target 45 Si target 46 Sputtering gas introduction pipe 47 Fixed opening 48 Reaction gas introduction pipe 49 ECR ion guns 51a, 51b Variable opening (film-forming speed regulating member)
52, 53, 54, 55 Divided shutter (film thickness correction member)
56a-56h Monitoring point

Claims (7)

In an apparatus for manufacturing a dielectric multilayer film in a vacuum chamber having a film forming source and a reaction source which are arranged side by side to face a rotating substrate, the film forming speed of the dielectric multilayer film formed on the rotating substrate is reduced. A film forming speed regulating member having an opening for regulating, and a film thickness correcting member having an opening for compensating a film thickness of a dielectric multilayer film formed on the rotating substrate; A light intensity measuring means for measuring the intensity of monochromatic light for monitoring passing through a plurality of monitoring points along the radius of the rotating substrate, and comprising one or more wavelengths. When each of the monochromatic light beams for monitoring passes through the monitoring point, a control system is provided that makes the opening of the film thickness correction member movable in accordance with a change in light intensity measured by the light intensity measuring means. Characteristic dielectric multilayer film manufacturing equipment. The movable opening of the film thickness correction member is formed by a divided shutter in which an opening area formed in an arc band along the circumference of each concentric circle by each locus of the monitoring point when the rotating substrate rotates is independently opened and closed. The apparatus for manufacturing a dielectric multilayer film according to claim 1, wherein: The control system, during the film formation period of the dielectric multilayer film on the rotating substrate, when passing the monitoring monochromatic light beam composed of the one or more wavelengths to each of the plurality of monitoring points, The light intensity change measured by the light intensity measuring means is measured as the transmittance change of the dielectric multilayer film, and the reciprocal of the transmittance is calculated as the reverse transmittance, and the thickness of the latest surface layer film during the adhesion growth is calculated. By the least squares method using the measured data group of the two variables of the growth time required for the increase and the reverse transmittance, a quadratic function regression is performed before the measured data group reaches the maximum or the minimum, and the principle of interference The thickness of the latest surface layer film when reaching the optical film thickness at the maximum and minimum of the reverse transmittance periodically distributed at an optical film thickness interval corresponding to １ ／ of the wavelength of the monochromatic light for monitoring As time, the quadratic regression function The dielectric multilayer film manufacturing apparatus according to claim 1 or 2, characterized in that a growth time corresponding to the maximum point or minimum point. As the thickness of the latest surface layer film grows, the latest surface layer film is formed into a predetermined optical film by an optical film thickness calculated from the reverse transmittance periodically distributed at an optical film thickness interval corresponding to the １ ／ wavelength. 3. The apparatus for manufacturing a dielectric multilayer film according to claim 1, wherein the control unit controls the film thickness growth by detecting that the thickness has reached. 5. The dielectric multilayer film according to claim 1, wherein the film forming source is made of at least two types of sputter targets of different materials, and the sputter targets are provided so as to be selectable. 6. manufacturing device. The apparatus according to claim 5, wherein Ta metal and Si metal are used as different material types of the sputtering target. The apparatus according to claim 1, wherein the reaction source emits a neutral radical reaction gas.

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