JP3797702B2

JP3797702B2 - Laser processing method for glass substrate, diffraction grating obtained by this method, and microlens array

Info

Publication number: JP3797702B2
Application number: JP06844096A
Authority: JP
Inventors: 正小山; 啓司常友
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 1996-03-25
Filing date: 1996-03-25
Publication date: 2006-07-19
Anticipated expiration: 2016-03-25
Also published as: JPH11216578A

Description

【０００１】
【発明の属する技術分野】
本発明は、ガラス基材に対するレーザ加工方法及びこの加工方法によって得られる回折格子及びマイクロレンズアレイに関する。
【０００２】
【従来の技術】
ガラスのうち特にＳiＯ₂を主成分とする珪酸塩ガラスは、透明度が高く、高温下で簡単に成形（変形）が可能なため、微細加工にて孔開けや凹凸を形成することで、光通信等に用いる光学部品やディスプレイ用のガラス基板等として広く用いられている。
【０００３】
上記の珪酸塩ガラスに微細加工を施すには、従来にあっては、フッ酸等のエッチャントを用いたウェットエッチング（化学エッチング）、或いはリアクティブイオンエッチング等のドライエッチング（物理エッチング）によるのが一般的である。
【０００４】
しかしながら、ウェットエッチングにあっては、エッチャントの管理と処理の問題があり、ドライエッチングにあっては真空容器等の設備が必要になり装置自体が大掛かりとなり、更に複雑なフォトリソグラフィー技術によってパターンマスク等を形成しなければならず効率的でない。
【０００５】
一方、レーザ光は強力なエネルギーを有し、照射された材料の表面温度を上げ、照射された部分をアブレーション（爆蝕）或いは蒸発せしめて種々の加工を施すことが従来から行われている。特にレーザ光は極めて小さなスポットに絞ることができるので、微細加工に適している。
【０００６】
そこで、特開昭５４−２８５９０号公報には、予め３００〜７００℃に加熱したガラス基板をテーブル上に固定し、このテーブルをＸ−Ｙ方向に移動させつつレーザ光を照射することで、ガラス基板表面を加工することが開示されている。
【０００７】
【発明が解決しようとする課題】
上述したように、ガラス基板を固定したテーブルをＸ−Ｙ方向に移動させることで、所望形状の凹凸をガラス基板に形成することができるのであるが、凹凸形状が例えば回折格子のような微細形状の場合、テーブルを移動させることで対処することはできない。
【０００８】
また、レーザ光にもＣＯ₂レーザ等の赤外線レーザ、Ｎd：ＹＡＧレーザ、Ｎd：ＹＡＧレーザと波長変換を組み合わせた近赤外領域から可視更には紫外領域に亘るレーザ、或いはＡrＦ、ＫrＦ等のエキシマレーザ等の紫外線レーザ等の種々のレーザ光があり、長波長のＣＯ₂ガスレーザを用いた場合には熱歪による割れが激しく起こる。また、紫外線域のＫrＦエキシマレーザ（波長２４８ｎｍ）を用いた場合でも照射痕周辺にはクラックが発生し、微細加工には適しない。そこで、ガラス加工に用いるレーザ光としては波長１９３ｎｍのＡrＦエキシマレーザの使用が最適となるが、このＡrＦエキシマレーザを使用した場合には空気による吸収があり、長い光軸を持たせるためにはＡr等の吸収のないガスと置換するか、真空にしなければならない。
【０００９】
【課題を解決するための手段】
上記課題を解決するため本発明に係るガラス基材のレーザ加工方法は、ガラス基材に対してレーザ光を照射し、レーザ光エネルギーをガラス基材に吸収させ、このエネルギーによる溶融、蒸発若しくはアブレーションによってガラスを除去するようにしたガラス基材のレーザ加工方法において、前記ガラス基材表面に照射されるレーザ光の光強度を部分的に異ならせ、光強度の強い部分のガラス除去量を多く、光強度の弱い部分のガラス除去量を少なくしてガラス基材表面に微細な凹凸を形成するようにした。
【００１０】
また、前記レーザ光として周期的若しくは規則的な光強度分布を有するレーザ光を用いることで、光結合器、偏光器、分波器、波長フィルタ、反射器或いはモード変換器等に組み込まれる回折格子或いはマイクロレンズアレイを製造することができる。
【００１１】
周期的な光強度分布を有するレーザ光は、フェイズマスク或いは２本のレーザ光を干渉せしめることによって得ることができ、ガラス基材表面に形成される周期的な凹凸の断面形状は、レーザ光のパルスエネルギーにて制御することができる。
また、規則的な光強度分布を有するレーザ光は、網目状マスク等を用いることで得ることができる。
【００１２】
更に、従来であれば、ガラス加工に用いることができるレーザ光は波長１９３ｎｍのＡrＦエキシマレーザに限定され、しかもＡr等の吸収のないガスと置換するか、真空にしなければならないので装置が大掛りになってしまうが、ガラスにＡg原子、ＡgコロイドまたはＡgイオンの形態で銀を導入することで、波長の長いレーザ光を使用しても割れや欠けを生じることなく照射痕も極めて平滑になることが実験の結果判明した。
【００１３】
ただし、従来の感光性ガラスや抗菌ガラスのように均一な濃度で銀が含有されている場合には、レーザ加工性の向上は見られず、加工が施される側の表面における銀の濃度が最も高く、徐々に他の面側に向かって銀の濃度が低下する濃度勾配となっていることが必要である。
【００１４】
これは、以下の図１に示す機構によるものと考えられる。
即ち、図１（ａ）に示すように、Ａgイオンの濃度が最も高い側の表面からレーザ光を照射する。すると、同図（ｂ）に示すように、最もＡgイオン濃度が高いガラス基材表面のＡgイオンが還元せしめられてコロイド（Ａgの超微粒子）となり、このコロイドがレーザ光エネルギーを吸収し、同図（ｃ）に示すように、このエネルギーによる溶融、蒸発若しくはアブレーションを生じ、表層部のガラスが除去される。そして、表層部のガラスが除去されるとその下層のガラスでも同様の現象が順次起こり、最終的には同図（ｄ）に示すように凹部若しくは貫通穴が形成される。
このように、ガラス基材の最表面から徐々にガラスが除去されてゆくので、割れや欠けが発生しにくい。これに対し、銀の濃度が均一であったり、銀が含まれていないガラス基材にあっては、ガラス基材内部でアブレーション等が生じ、割れや欠けが発生しやすい。
【００１５】
【発明の実施の形態】
以下に本発明の実施の形態を添付図面に基づいて説明する。
（実施例１）
図２に示す装置を用いてイオン交換を行った。加工用ガラス基材としては、ＳiＯ₂を主成分とし、これにＡl₂Ｏ₃、Ｂ₂Ｏ₃、Ｎa₂Ｏ、Ｆ等を含む厚さ２ｍｍの珪酸塩ガラスとし、石英容器内に満たす溶融塩としては硝酸銀と硝酸ナトリウムを５０mol%−５０mol%で混合したものを用いた。
【００１６】
上記の加工用ガラス基材を溶融塩を満たした石英容器内に１２分間浸漬した。尚、溶融塩の温度は電気炉中で２８５℃に保ち、反応雰囲気は空気とした。
以上の処理により、ガラス基材表面のＮaイオン（１価の陽イオン）を溶出せしめ、溶融塩中のＡgイオンをガラス中に拡散せしめた。Ａgが拡散した層の厚さをＸ線マイクロアナライザーで測定したところ約５μｍであった。
【００１７】
そして、図３に示す装置を用いて回折格子を製造した。具体的には、上記のガラス基板のイオン交換がなされた面に、スペーサを介して回折格子を形成したフェイズマスクを備えた基板を配置し、レーザ光を照射した。
フェイズマスクにレーザ光が入射すると、図４（ａ）に示すように、主として＋１次の回折光と−１次の回折光が出射し、これらの回折光の干渉によりフェイズマスクの出射側の極近傍に周期的な光の強度分布が得られる。そして、その周期は、入射側のレーザ光が平行光ならば、フェイズマスクの回折格子の周期に一致する。ここで、本実施例のフェイズマスクは回折格子周期：１０５５ｎｍ、回折格子深さ：約２５０ｎｍ、サイズ：１０ｍｍ×５ｍｍ（ＱＰＳ Technology Inc.製 Canada）を使用したので、１０５５ｎｍ程度の周期の光強度分布が形成される。
【００１８】
そして、この周期的な強度分布が形成された領域に、図４（ｂ）に示すように、ガラス基板をセットした。その結果、図４（ｃ）に示すように、当該周期的な光強度に応じてガラスが蒸発或いはアブレーションし、光強度の周期と同一の周期をもつ回折格子がガラス基板上に形成された。
【００１９】
尚、使用したレーザ光は、Ｎd：ＹＡＧレーザの第３高調波である３５５ｎｍの光とした。パルス幅は約１０ｎｓｅｃ、繰り返し周波数は５Ｈzであった。またレーザ光の１パルスあたりのエネルギーは、レーザのＱスイッチのタイミングを変えることで調整が可能であり、本実施例で用いたレーザの場合、最大のパルスエネルギーは約９０ｍＪであり、ビーム直径は約５ｍｍであった。
また、レーザ光による蒸発或いはアブレーションは、一般に非線形であり、ある強度以上になったとき、はじめて材料の蒸発が起きる。本実施例で使用したガラス基板の場合、３５５ｎｍの波長だと、３〜４Ｊ／ｃｍ²／pulse以上のエネルギー密度にならなければ、アブレーションは起きない。上述のように本実施例で使用したレーザのエネルギー密度は、約０．４６Ｊ／ｃｍ²であり、このままではガラスのアブレーションは起きないので、エネルギー密度を増大させるため、レーザ光を焦点距離２５０ｎｍのレンズで絞り込んでガラス基板上でのビームサイズが約２ｍｍになるようにした。
【００２０】
具体的な照射方法は、先ずレーザ光の強度を下げてレーザ光が図３に示すようにフェイズマスクの基板側からほぼ垂直に入射するように光軸の調整を行い、その後、レーザ光源のＱスイッチのタイミングを変えて、レーザ光のエネルギーを徐々に増加させた。レーザ光の光エネルギーが約８０ｍＪ／ｐｕｌｓｅになったときガラスのアブレーションが確認されたので、その状態のまま５パルスだけレーザ光を照射し、レーザ光の照射を停止した。
【００２１】
上記によって形成された回折格子の形状を図５及び図６に示す。ここで、図５（ａ）は回折格子の平面を走査型電子顕微鏡で観察した写真（10,000倍）、同図（ｂ）は同写真に基づいて作成した図、図６（ａ）は回折格子の断面を走査型電子顕微鏡で観察した写真（10,000倍）、同図（ｂ）は同写真に基づいて作成した図であり、これらの図から明らかなように、回折格子の周期は、使用したフェイズマスクの周期とほぼ一致しており、また回折格子の形状は光強度の周期構造の分布に従い曲面となっており、更に回折格子表面も非常に平滑であった。
【００２２】
尚、以上の測定は回折格子のほぼ中央で測定したものであるが、レーザビームの周辺部ではビーム中央部に比べて強度が低いので、中央部と異なる形状の回折格子が形成される。即ち、レーザビームの照射領域の中央部分（最も光強度が強い部分）では、光強度分布の凹部でもアブレーションが起きるので、作製された回折格子の凸部及び凹部は滑らかな曲面状になるのに対し、レーザビームの照射領域の周辺部（光強度の低い部分）では光強度分布の凸部のみでアブレーションが起きる結果、台形状の断面構造となる。このとき、回折格子の凸部上面はもともとガラス基板の表面であるので、それほど滑らかにならない。
【００２３】
上記したように、レーザビームの中央部分と周辺部分の光強度の違いによって形成される回折格子の形状が変化することを確かめたが、本実施例ではレーザ光の強度自体を変えても同様に回折格子の断面構造が変化することを確認した。
このようにして回折格子を製造すれば、特別な真空容器を必要とすることなく、非常に簡便に、しかも安価にガラス上に回折格子を作製できる。
【００２４】
ところで、本実施例にあってはスペーサによってフェイズマスクとガラス基板との間隔が約５０μｍとなるようにしている。これは、ガラス基板表面からの蒸発物がフェイズマスクに付着するのを極力防ぐためであり、この間隔自体は任意である。例えば＋１次光と−１次光とが重なっている範囲内ならば、フェイズマスクとガラス基板を密着させても回折格子は作製できるし、フェイズマスクとガラス基板との間に１５０μｍ程度の厚さの石英板を挟み密着させてレーザ照射を行った場合も、本実施例と同様に回折格子が作製できた。フェイズマスクは繰り返し使用されるものであり、その汚れを防ぐことは重要であり、したがってスペーサを介在させることは有効な手段である。
【００２５】
（実施例２）
本実施例にあっては、前記実施例のフェイズマスクを使用する代りに、２本のレーザ光の干渉を利用して周期的な強度分布を形成した。
即ち、図７に示すように、レーザ光をビームスプリッタにより２つに分け、ある角度を持たせて再び重ね合わせると、その重なり合った部分に周期的な光強度分布が形成される。その周期はレーザ光を重ね合せる角度により決まる。
本実施例では、２本のレーザビームの入射角を約２０°になるような光学系を構成した。このときの光強度分布の周期は約１０２０ｎｍになる。
そして、前記実施例１で使用したものと同種のレーザ加工性のあるガラスを、その２本レーザビームが重なり合った部分に設置し、レーザ光を照射した結果、アブレーションが起きた。図中のレンズはガラス面上でのエネルギー密度を上げるために使用したものであり、アブレーションが起きたときのエネルギー密度は、前記実施例と同様な値になった。
【００２６】
作製した回折格子の周期を測定したところ、予想された周期とほぼ一致した。断面形状を走査型電子顕微鏡で測定したところ、（実施例１）と同様に、曲面で表面の滑らかな回折格子が形成されていることが確かめられた。
【００２７】
ここで、（実施例１）と（実施例２）では、周期的な強度分布を形成する手段が異なり、それぞれに長所と短所がある。
即ち、フェイズマスクを利用した方法は、光学系の構成が簡単で周期の再現性もよいので、同一の周期の回折格子を生産する場合には有利である。一方、周期の変更を頻繁に行う場合には２本のレーザ光の干渉を利用する方法が有利である。
【００２８】
（実施例３）
図８に示すように、ガラス基板上にメッシュパターンを持つ銅製のマスクを密着し、レーザ光を焦点距離２５０ｍｍのレンズで絞り込み、ガラス基板上でのビームサイズが約２ｍｍになるようにして照射を行った。
使用したガラスは、前記実施例１で使用したものと同種のレーザ加工性のあるガラスを使用し、Ａgイオンのガラス内への導入条件は、溶融塩の温度を３００℃とした以外は実施例１と同様とし、使用するレーザ光はＮd：ＹＡＧレーザの第２高調波である５３２ｎｍの光とした。パルス幅は約１０ｎｓｅｃ、繰り返し周波数は５Ｈzであった。またレーザ光の１パルスあたりのエネルギーは、レーザのＱスイッチのタイミングを変えることで調整が可能であり、本実施例で用いたレーザの場合、最大のパルスエネルギーは約９０ｍＪであり、ビーム直径は約５ｍｍであった。
【００２９】
上記のガラス基板にレーザ加工を行うには、先ずレーザ光の強度を下げてレーザ光が図８に示すようにマスクの基板側からほぼ垂直に入射するように光軸の調整を行い、その後、レーザ光源のＱスイッチのタイミングを変えて、レーザ光のエネルギーを徐々に増加させた。レーザ光の光エネルギーが約４Ｊ／cm²／ｐｕｌｓｅになったときガラスのアブレーションが確認されたので、その状態のまま５パルスだけレーザ光を照射し、レーザ光の照射を停止した。
【００３０】
上記ガラス基板に形成された凹凸の形状を図９に示す。ここで、図９（ａ）は加工後のガラス基板の平面の写真、同図（ｂ）は同写真に基づいて作成した図であり、これらの図から明らかなように、ガラス基板にはメッシュ間隔５０μｍのマスクパターンが忠実に転写されていた。また、各凹部の周辺の割れは観察されなかった。尚、１μｍ前後の間隔で回折光の干渉光のパターンも観察された。このことは１μｍ前後の微細なオーダーでの転写も可能であることを示している。また本実施例では、５３２ｎｍのレーザ光を用いたが、３５５ｎｍの光でも同様の結果が得られた。更に、マスクの材料としては銅に限らず、アルミ、金等の熱伝導性に優れた材料、タングステン、ステンレス、タンタル等の高融点材料を使用することが可能である。
【００３１】
尚、上記の如きマスクパターンが転写されたガラス基板は、例えば凹部に高屈折率樹脂を充填する等の加工を施すことで、液晶ディスプレイ装置やプラズマディスプレイ装置等に組み込まれる平板型のマイクロレンズアレイ等として用いられる。
【００３２】
（実施例４）
この実施例にあっては、図１０に示すように、銅製のマスクをガラス基板上に密着させずに、レンズの光軸上に設置してレーザ光をガラス基板に照射した。
使用したガラス、Ａgイオンのガラス内への導入条件及び使用レーザ光は、前記実施例３と同様とした。
【００３３】
また図１０において、レンズ（焦点距離100mm）のレンズによってマスクの実像が結像する位置にガラスをセットした。そして、実施例３と同様に、ガラスがアブレーションするエネルギー密度である約４Ｊ／cm²／ｐｕｌｓｅになったときガラスのアブレーションが確認されたので、その状態のまま１０パルスだけレーザ光を照射し、レーザ光の照射を停止した。
【００３４】
上記ガラス基板に形成された凹凸の形状を図１１に示す。ここで、図１１（ａ）は加工後のガラス基板の平面の写真、同図（ｂ）は同写真に基づいて作成した図であり、これらの図から明らかなように、ガラス基板には実施例３と同一のマスクを用いて、実施例３よりも縮小されたサイズでメッシュが転写されていた。このように、レンズを用いることで、縮小転写及び拡大転写が可能となる。
【００３５】
また、上記にあってはマスクを用いて平板型のマイクロレンズアレイ用のガラス基板を製造する例を示したが、３本或いはそれ以上のレーザ光を干渉させることによって、図１２の（ａ）及び（ｂ）に示すように、マイクロレンズアレイ用のガラス基板を製造することが可能である。
【００３６】
尚、実施例にあってはＡl₂Ｏ₃−Ｂ₂Ｏ₃−Ｎa₂Ｏ−Ｆ系の珪酸塩ガラスにＡgイオン交換処理を施したものを示したが、他のガラスにＡgイオン交換処理を施したもの、或いはＡgイオン交換処理を施さないものであっても、レーザ加工性を有するものであれば本発明方法の実施対象として用いることができる。
また、本発明方法の実施対象となるガラス基材の形状としては板状のものに限らず、円柱状等任意である。
【００３７】
【発明の効果】
以上に説明したように本発明によれば、レーザ光によってガラスを加工するにあたり、ガラス表面に照射されるレーザ光の光強度を部分的に異ならせ、光強度の強い部分のガラス除去量を多く、光強度の弱い部分のガラス除去量を少なくしてガラス表面に微細な凹凸を形成するようにしたので、従来に比べ極めて微細なパターンを正確且つ短時間に形成することができる。
【００３８】
したがって、回折格子の製造或いは平板マイクロレンズアレイの基板の製造等に利用すれば、極めて有効である。
【００３９】
特に、使用するガラスとして銀が原子、コロイドまたはイオンの形態でガラス中に導入され、且つＡ銀の濃度が加工される表面において最も高濃度で、表面から内部に行くにしたがって徐々に濃度が低下するようにすれば、波長が比較的長いレーザ光を使用しても、割れや欠けが生じることがない。そして、波長の長いレーザ光を使用できれば、空気による吸収を考慮しなくてよいので、装置自体が簡単になる。
【図面の簡単な説明】
【図１】（ａ）〜（ｄ）は本発明に係るガラスのレーザ加工方法の基本的概念を説明した図
【図２】イオン交換に用いる装置の模式図
【図３】本発明方法で回折格子を製造する装置の概略図
【図４】（ａ）はフェイズマスクの作用を説明した図、（ｂ）は同フェイズマスクを介してガラス基板にレーザ光を照射している状態を示す図、（ｃ）はレーザ加工されたガラス基板を示す図
【図５】（ａ）は回折格子の平面を走査型電子顕微鏡で観察した写真（10,000倍）、（ｂ）は同写真に基づいて作成した図
【図６】（ａ）は回折格子の断面を走査型電子顕微鏡で観察した写真（10,000倍）、（ｂ）は同写真に基づいて作成した図
【図７】レーザ光に周期的な強度分布を形成する手段の別実施例を示す図
【図８】ガラス基板上にレーザ加工にてメッシュパターンを形成する装置の概略図
【図９】（ａ）はレーザ加工後のガラス基板の平面を走査型電子顕微鏡で観察した写真、（ｂ）は同写真に基づいて作成した図
【図１０】ガラス基板上にレーザ加工にてメッシュパターンを形成する装置の別実施例の概略図
【図１１】（ａ）はレーザ加工後のガラス基板の平面を走査型電子顕微鏡で観察した写真（10,000倍）、（ｂ）は同写真に基づいて作成した図
【図１２】（ａ）はレーザ加工後のガラス基板の平面を原子間力顕微鏡で観察した写真、（ｂ）は同写真に基づいて作成した図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method for a glass substrate, and a diffraction grating and a microlens array obtained by the processing method.
[0002]
[Prior art]
Among the glass, especially silicate glass mainly composed of SiO ₂ has high transparency and can be easily formed (deformed) at high temperature. It is widely used as an optical component for use in a glass substrate or a glass substrate for a display.
[0003]
In order to perform fine processing on the silicate glass, conventionally, wet etching (chemical etching) using an etchant such as hydrofluoric acid or dry etching (physical etching) such as reactive ion etching is used. It is common.
[0004]
However, in wet etching, there are problems in the management and processing of etchants. In dry etching, equipment such as a vacuum vessel is required, and the apparatus itself becomes large, and pattern masks and the like are made by more complicated photolithography technology. Must be formed and is not efficient.
[0005]
On the other hand, laser light has strong energy, and it has been conventionally performed to raise the surface temperature of the irradiated material and to perform various processing by ablating (evaporating) or evaporating the irradiated portion. In particular, since the laser beam can be focused to an extremely small spot, it is suitable for fine processing.
[0006]
Japanese Patent Application Laid-Open No. 54-28590 discloses that a glass substrate heated to 300 to 700 ° C. is fixed on a table and irradiated with laser light while moving the table in the XY direction. Processing a substrate surface is disclosed.
[0007]
[Problems to be solved by the invention]
As described above, by moving the table on which the glass substrate is fixed in the X-Y direction, irregularities with a desired shape can be formed on the glass substrate, but the irregular shape is a fine shape such as a diffraction grating, for example. In this case, it cannot be dealt with by moving the table.
[0008]
In addition, the laser beam is an infrared laser such as a CO ₂ laser, an Nd: YAG laser, an Nd: YAG laser and a laser ranging from the near infrared region to the visible or ultraviolet region, or an excimer such as ArF or KrF. There are various types of laser light such as an ultraviolet laser such as a laser, and when a long wavelength CO ₂ gas laser is used, cracking due to thermal strain occurs severely. Further, even when a KrF excimer laser (wavelength 248 nm) in the ultraviolet region is used, cracks are generated around the irradiation mark, which is not suitable for fine processing. Therefore, it is optimal to use an ArF excimer laser with a wavelength of 193 nm as a laser beam used for glass processing. However, when this ArF excimer laser is used, there is absorption by air, and in order to have a long optical axis, Ar is used. It must be replaced with a non-absorbing gas or a vacuum.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the glass substrate laser processing method according to the present invention irradiates the glass substrate with laser light, absorbs the laser beam energy into the glass substrate, and melts, evaporates or ablate by this energy. In the laser processing method of the glass substrate that is made to remove the glass by, by partially varying the light intensity of the laser light irradiated to the glass substrate surface, a large amount of glass removal of the portion where the light intensity is strong, The amount of glass removed in the portion with low light intensity was reduced to form fine irregularities on the surface of the glass substrate.
[0010]
Further, by using a laser beam having a periodic or regular light intensity distribution as the laser beam, a diffraction grating incorporated in an optical coupler, a polarizer, a duplexer, a wavelength filter, a reflector, a mode converter, or the like Alternatively, a microlens array can be manufactured.
[0011]
Laser light having a periodic light intensity distribution can be obtained by causing a phase mask or two laser lights to interfere with each other. The cross-sectional shape of the periodic irregularities formed on the surface of the glass substrate is It can be controlled by pulse energy.
Further, laser light having a regular light intensity distribution can be obtained by using a mesh mask or the like.
[0012]
Furthermore, conventionally, the laser beam that can be used for glass processing is limited to an ArF excimer laser with a wavelength of 193 nm, and it is necessary to replace it with a gas having no absorption such as Ar or to make a vacuum, so that the apparatus is large. However, by introducing silver into the glass in the form of Ag atoms, Ag colloids, or Ag ions, the irradiation traces become extremely smooth without cracking or chipping even when laser light having a long wavelength is used. It became clear as a result of the experiment.
[0013]
However, when silver is contained at a uniform concentration as in conventional photosensitive glass or antibacterial glass, the laser processability is not improved, and the silver concentration on the surface to be processed is It is necessary that the concentration gradient be the highest and the concentration of silver gradually decreases toward the other side.
[0014]
This is considered to be due to the mechanism shown in FIG.
That is, as shown in FIG. 1A, the laser beam is irradiated from the surface on the side where the Ag ion concentration is the highest. Then, as shown in FIG. 2B, Ag ions on the surface of the glass substrate having the highest Ag ion concentration are reduced to form colloids (Ag ultrafine particles), which absorb the laser beam energy, As shown in the figure (c), melting, evaporation or ablation is caused by this energy, and the glass in the surface layer portion is removed. Then, when the glass of the surface layer portion is removed, the same phenomenon sequentially occurs in the glass of the lower layer, and finally a recess or a through hole is formed as shown in FIG.
Thus, since glass is gradually removed from the outermost surface of a glass base material, it is hard to generate | occur | produce a crack and a chip. On the other hand, in the case of a glass base material having a uniform silver concentration or not containing silver, ablation or the like occurs within the glass base material, and cracks and chips are likely to occur.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Example 1
Ion exchange was performed using the apparatus shown in FIG. As a glass substrate for processing, a silicate glass having a thickness of 2 mm containing SiO ₂ as a main component and containing Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O, F and the like is melted to fill a quartz container. As the salt, a mixture of silver nitrate and sodium nitrate at 50 mol% to 50 mol% was used.
[0016]
The processing glass substrate was immersed in a quartz container filled with molten salt for 12 minutes. The temperature of the molten salt was kept at 285 ° C. in an electric furnace, and the reaction atmosphere was air.
Through the above treatment, Na ions (monovalent cations) on the surface of the glass substrate were eluted, and Ag ions in the molten salt were diffused into the glass. When the thickness of the layer in which Ag was diffused was measured with an X-ray microanalyzer, it was about 5 μm.
[0017]
And the diffraction grating was manufactured using the apparatus shown in FIG. Specifically, a substrate provided with a phase mask in which a diffraction grating was formed via a spacer was placed on the surface of the glass substrate on which ion exchange was performed, and laser light was irradiated.
When laser light is incident on the phase mask, as shown in FIG. 4A, + 1st order diffracted light and −1st order diffracted light are mainly emitted, and the output side pole of the phase mask is caused by interference of these diffracted lights. A periodic light intensity distribution is obtained in the vicinity. If the laser beam on the incident side is parallel light, the period coincides with the period of the diffraction grating of the phase mask. Here, since the phase mask of this example uses a diffraction grating period of 1055 nm, a diffraction grating depth of about 250 nm, and a size of 10 mm × 5 mm (Canada made by QPS Technology Inc.), the light intensity distribution having a period of about 1055 nm. Is formed.
[0018]
And the glass substrate was set to the area | region in which this periodic intensity distribution was formed, as shown in FIG.4 (b). As a result, as shown in FIG. 4C, the glass evaporated or ablated in accordance with the periodic light intensity, and a diffraction grating having the same period as the period of the light intensity was formed on the glass substrate.
[0019]
The laser beam used was 355 nm, which is the third harmonic of the Nd: YAG laser. The pulse width was about 10 nsec and the repetition frequency was 5 Hz. The energy per pulse of the laser beam can be adjusted by changing the timing of the Q switch of the laser. In the case of the laser used in this example, the maximum pulse energy is about 90 mJ, and the beam diameter is About 5 mm.
Also, evaporation or ablation by laser light is generally non-linear, and material evaporation occurs only when the intensity exceeds a certain level. In the case of the glass substrate used in this example, ablation does not occur unless the energy density is 3 to 4 J / cm ² / pulse or more at a wavelength of 355 nm. As described above, the energy density of the laser used in this example is about 0.46 J / cm ² , and glass ablation does not occur as it is. Therefore, in order to increase the energy density, the laser light is focused at a focal length of 250 nm. The lens size was reduced so that the beam size on the glass substrate was about 2 mm.
[0020]
Specifically, first, the intensity of the laser beam is lowered and the optical axis is adjusted so that the laser beam is incident substantially perpendicularly from the substrate side of the phase mask as shown in FIG. The energy of the laser beam was gradually increased by changing the switch timing. Since the ablation of the glass was confirmed when the light energy of the laser light reached about 80 mJ / pulse, the laser light was irradiated for 5 pulses in that state, and the laser light irradiation was stopped.
[0021]
The shape of the diffraction grating formed as described above is shown in FIGS. Here, FIG. 5A is a photograph (10,000 magnifications) obtained by observing the plane of the diffraction grating with a scanning electron microscope, FIG. 5B is a diagram created based on the photograph, and FIG. 6A is a diffraction grating. The photograph (10,000 times) which observed the cross section of this in a scanning electron microscope, the figure (b) is the figure created based on the photograph, and the period of a diffraction grating was used as evident from these figures. It almost coincided with the period of the phase mask, the shape of the diffraction grating was a curved surface according to the distribution of the periodic structure of light intensity, and the surface of the diffraction grating was very smooth.
[0022]
Although the above measurement is performed at substantially the center of the diffraction grating, the intensity of the peripheral portion of the laser beam is lower than that of the central portion of the beam, so that a diffraction grating having a shape different from that of the central portion is formed. That is, in the central part of the laser beam irradiation area (the part with the strongest light intensity), ablation occurs even in the concave part of the light intensity distribution, so that the convex part and concave part of the manufactured diffraction grating have a smooth curved surface. On the other hand, as a result of ablation occurring only at the convex portion of the light intensity distribution in the peripheral portion (low light intensity portion) of the laser beam irradiation region, a trapezoidal cross-sectional structure is obtained. At this time, since the upper surface of the convex portion of the diffraction grating is originally the surface of the glass substrate, it is not so smooth.
[0023]
As described above, it was confirmed that the shape of the diffraction grating formed due to the difference in the light intensity between the central part and the peripheral part of the laser beam changes. In this embodiment, the intensity of the laser light itself is changed in the same manner. It was confirmed that the sectional structure of the diffraction grating changed.
If the diffraction grating is manufactured in this manner, the diffraction grating can be produced on glass very easily and inexpensively without requiring a special vacuum vessel.
[0024]
By the way, in this embodiment, the distance between the phase mask and the glass substrate is set to about 50 μm by the spacer. This is to prevent evaporation from the glass substrate surface from adhering to the phase mask as much as possible, and this interval itself is arbitrary. For example, if the + 1st order light and the −1st order light overlap, the diffraction grating can be produced even if the phase mask and the glass substrate are brought into close contact with each other, and the thickness between the phase mask and the glass substrate is about 150 μm. In the case where laser irradiation was performed with a quartz plate sandwiched between and closely attached, a diffraction grating could be produced in the same manner as in this example. The phase mask is used repeatedly, and it is important to prevent the contamination of the phase mask. Therefore, interposing a spacer is an effective means.
[0025]
(Example 2)
In this example, instead of using the phase mask of the above example, a periodic intensity distribution was formed using interference of two laser beams.
That is, as shown in FIG. 7, when the laser light is divided into two by a beam splitter and overlapped again at a certain angle, a periodic light intensity distribution is formed in the overlapped portion. The period is determined by the angle at which the laser beams are superimposed.
In this embodiment, the optical system is configured such that the incident angles of the two laser beams are about 20 °. The period of the light intensity distribution at this time is about 1020 nm.
Then, the same kind of laser-workable glass as that used in Example 1 was placed in a portion where the two laser beams were overlapped, and as a result of laser irradiation, ablation occurred. The lens in the figure was used to increase the energy density on the glass surface, and the energy density when ablation occurred was the same value as in the previous example.
[0026]
When the period of the produced diffraction grating was measured, it almost coincided with the expected period. When the cross-sectional shape was measured with a scanning electron microscope, it was confirmed that a diffraction grating having a curved surface and a smooth surface was formed as in (Example 1).
[0027]
Here, (Example 1) and (Example 2) have different means for forming a periodic intensity distribution, and each has advantages and disadvantages.
That is, the method using a phase mask is advantageous when producing diffraction gratings having the same period because the configuration of the optical system is simple and the period is reproducible. On the other hand, when the cycle is frequently changed, a method using the interference of two laser beams is advantageous.
[0028]
Example 3
As shown in FIG. 8, a copper mask having a mesh pattern is closely attached to a glass substrate, and laser light is narrowed down with a lens having a focal length of 250 mm, and irradiation is performed so that the beam size on the glass substrate is about 2 mm. went.
The glass used was the same type of laser-workable glass as used in Example 1, and the conditions for introducing Ag ions into the glass were as follows except that the temperature of the molten salt was 300 ° C. 1 was used, and the laser beam used was 532 nm light, which is the second harmonic of the Nd: YAG laser. The pulse width was about 10 nsec and the repetition frequency was 5 Hz. The energy per pulse of the laser beam can be adjusted by changing the timing of the Q switch of the laser. In the case of the laser used in this example, the maximum pulse energy is about 90 mJ, and the beam diameter is About 5 mm.
[0029]
In order to perform laser processing on the glass substrate, first, the intensity of the laser beam is lowered and the optical axis is adjusted so that the laser beam is incident substantially perpendicularly from the substrate side of the mask as shown in FIG. The energy of the laser beam was gradually increased by changing the timing of the Q switch of the laser light source. Since the ablation of the glass was confirmed when the light energy of the laser light became about 4 J / cm ² / pulse, the laser light was irradiated for 5 pulses in that state, and the laser light irradiation was stopped.
[0030]
The shape of the unevenness formed on the glass substrate is shown in FIG. Here, FIG. 9A is a photograph of the plane of the glass substrate after processing, and FIG. 9B is a diagram created based on the photograph. As is clear from these figures, the glass substrate has a mesh. A mask pattern with an interval of 50 μm was faithfully transferred. Further, no cracks around each recess were observed. A pattern of interference light of diffracted light was also observed at intervals of about 1 μm. This indicates that transfer on a minute order of about 1 μm is also possible. In this example, 532 nm laser light was used, but similar results were obtained with 355 nm light. Furthermore, the material of the mask is not limited to copper, and materials having excellent thermal conductivity such as aluminum and gold, and high melting point materials such as tungsten, stainless steel, and tantalum can be used.
[0031]
The glass substrate to which the mask pattern as described above is transferred is a flat-type microlens array incorporated into a liquid crystal display device, a plasma display device or the like by performing processing such as filling a recess with a high refractive index resin, for example. Etc.
[0032]
(Example 4)
In this example, as shown in FIG. 10, the copper mask was placed on the optical axis of the lens without being in close contact with the glass substrate, and the glass substrate was irradiated with laser light.
The glass used, the conditions for introducing Ag ions into the glass, and the laser beam used were the same as in Example 3.
[0033]
In FIG. 10, glass was set at a position where a real image of the mask was formed by a lens (focal length 100 mm). As in Example 3, since the ablation of the glass was confirmed when the energy density at which the glass ablates was about 4 J / cm ² / pulse, the laser beam was irradiated for 10 pulses in that state, Laser light irradiation was stopped.
[0034]
FIG. 11 shows the shape of the irregularities formed on the glass substrate. Here, FIG. 11 (a) is a photograph of a plane of the glass substrate after processing, and FIG. 11 (b) is a diagram created based on the photograph. As is apparent from these figures, the glass substrate is implemented. Using the same mask as in Example 3, the mesh was transferred with a size smaller than that in Example 3. As described above, reduction transfer and enlargement transfer are possible by using the lens.
[0035]
Moreover, in the above, an example of manufacturing a glass substrate for a flat-type microlens array using a mask has been shown, but by interfering with three or more laser beams, (a) in FIG. And as shown to (b), it is possible to manufacture the glass substrate for micro lens arrays.
[0036]
In the examples, Al ₂ O ₃ —B ₂ O ₃ —Na ₂ O—F-based silicate glass was subjected to Ag ion exchange treatment, but other glass was subjected to Ag ion exchange treatment. Even those that have been subjected to the above treatment or those that are not subjected to the Ag ion exchange treatment can be used as targets for carrying out the method of the present invention as long as they have laser processability.
In addition, the shape of the glass substrate to be subjected to the method of the present invention is not limited to a plate shape, and may be any shape such as a columnar shape.
[0037]
【The invention's effect】
As described above, according to the present invention, when processing glass with laser light, the light intensity of the laser light irradiated on the glass surface is partially varied, and the amount of glass removed in a portion with high light intensity is increased. Since the glass removal amount of the portion with low light intensity is reduced and fine irregularities are formed on the glass surface, an extremely fine pattern can be formed accurately and in a short time compared to the conventional case.
[0038]
Therefore, it is extremely effective when used for manufacturing a diffraction grating or a flat microlens array substrate.
[0039]
In particular, as the glass used, silver is introduced into the glass in the form of atoms, colloids or ions, and the concentration of A silver is the highest on the surface to be processed, and the concentration gradually decreases from the surface to the inside. By doing so, even if a laser beam having a relatively long wavelength is used, cracks and chips are not generated. If a laser beam having a long wavelength can be used, it is not necessary to consider absorption by air, so that the apparatus itself is simplified.
[Brief description of the drawings]
FIGS. 1A to 1D are diagrams for explaining the basic concept of a glass laser processing method according to the present invention. FIG. 2 is a schematic diagram of an apparatus used for ion exchange. FIG. 4A is a diagram illustrating the operation of a phase mask, and FIG. 4B is a diagram illustrating a state in which a glass substrate is irradiated with laser light through the phase mask. (C) is a diagram showing a laser-processed glass substrate. FIG. 5 (a) is a photograph (10,000 magnifications) of the plane of the diffraction grating observed with a scanning electron microscope, and (b) is created based on the photograph. Fig. 6 (a) is a photograph (10,000x) of a cross section of a diffraction grating observed with a scanning electron microscope. (B) is a diagram created based on the photograph. Fig. 7 is a periodic intensity of laser light. FIG. 8 is a diagram showing another embodiment of the means for forming the distribution. FIG. 9A is a photograph of a plane of a glass substrate after laser processing observed with a scanning electron microscope, and FIG. 9B is a diagram created based on the photograph. Schematic of another embodiment of an apparatus for forming a mesh pattern by laser processing on a glass substrate. FIG. 11 (a) is a photograph (10,000 magnifications) of a plane of the glass substrate after laser processing observed with a scanning electron microscope. FIGS. 12A and 12B are diagrams created based on the photograph. FIGS. 12A and 12B are photographs in which the plane of the glass substrate after laser processing is observed with an atomic force microscope, and FIG. 12B is created based on the photograph. Figure

Claims

In the laser processing method for a glass substrate, the glass substrate is irradiated with laser light, the laser beam energy is absorbed by the glass substrate, and the glass is removed by melting, evaporation, or ablation by the energy. The light intensity of the laser light irradiated to the substrate surface is partially changed, the glass removal amount in the portion with high light intensity is increased, and the glass removal amount in the portion with weak light intensity is decreased to make the glass substrate surface fine. A glass substrate , wherein the laser beam is a laser beam having a periodic light intensity distribution, and the laser beam having the periodic light intensity distribution is obtained by a phase mask. laser processing method.

In the laser processing method for a glass substrate, the glass substrate is irradiated with laser light, the laser beam energy is absorbed by the glass substrate, and the glass is removed by melting, evaporation, or ablation by the energy. The light intensity of the laser light irradiated to the substrate surface is partially changed, the glass removal amount in the portion with high light intensity is increased, and the glass removal amount in the portion with weak light intensity is decreased to make the glass substrate surface fine. The laser beam is a laser beam having a periodic light intensity distribution, and the laser beam having the periodic light intensity distribution is obtained by causing two laser beams to interfere with each other. the cross-sectional shape of the periodic roughness formed in the surface of the glass base material, the laser of the glass substrate and controlling by laser beam pulse energy Engineering method.

3. The laser processing method for a glass substrate according to claim 1 , wherein the glass substrate to be laser processed has a form of Ag atoms, Ag colloids or Ag ions from the surface to a predetermined depth or over the entire surface. In this case, the silver concentration is the highest on the surface to be processed, and a concentration gradient is formed so that the concentration gradually decreases toward the other surface side. A laser processing method for a glass substrate.

In diffraction gratings incorporated in optical couplers, polarizers, demultiplexers, wavelength filters, reflectors, or mode converters, this diffraction grating has a periodic light intensity distribution on one side of a plate-shaped glass substrate. periodic roughness formed by the irradiation of the laser beam is provided with, it is irradiated with laser light for the one side of a glass substrate forming a plate-like, to absorb the laser light energy to the glass substrate, according to the energy Glass is removed by melting, evaporation, or ablation, and the light intensity of the laser light irradiated onto the glass substrate surface is partially changed, so that the glass removal amount in the portion with high light intensity is large and the light intensity is low. The glass removal amount of the portion is reduced to form fine irregularities on the glass substrate surface, and the laser beam is a laser beam having a periodic light intensity distribution, Laser beam having an intensity distribution, a diffraction grating obtained by the laser processing method of a glass substrate, characterized in that obtained by phase mask.

In diffraction gratings incorporated in optical couplers, polarizers, demultiplexers, wavelength filters, reflectors, or mode converters, this diffraction grating has a periodic light intensity distribution on one side of a plate-shaped glass substrate. periodic roughness formed by the irradiation of the laser beam is provided with, it is irradiated with laser light for the one side of a glass substrate forming a plate-like, to absorb the laser light energy to the glass substrate, according to the energy Glass is removed by melting, evaporation, or ablation, and the light intensity of the laser light irradiated onto the glass substrate surface is partially changed, so that the glass removal amount in the portion with high light intensity is large and the light intensity is low. The glass removal amount of the portion is reduced to form fine irregularities on the glass substrate surface, and the laser beam is a laser beam having a periodic light intensity distribution, Glass laser beam, which allowed the interference of two laser beams, the cross-sectional shape of the periodic roughness formed in the glass substrate surface, and controlling at the laser beam pulse energy having an intensity distribution A diffraction grating obtained by a laser processing method of a substrate .

6. The diffraction grating according to claim 4 or 5 , wherein the plate-like glass substrate constituting the diffraction grating is in the form of Ag atoms, Ag colloids or Ag ions from the surface to a predetermined depth or over the whole. This silver concentration is the highest on the surface where the diffraction grating is formed, and a concentration gradient is formed so that the concentration gradually decreases toward the other side. A diffraction grating characterized by

In a flat-type microlens array incorporated in a liquid crystal display element or the like, this flat-type microlens array is formed by irradiating a laser beam having a regular light intensity distribution on one side of a plate-like glass substrate. Regular concave portions are provided , and one side of the glass substrate that forms a plate is irradiated with laser light, the laser beam energy is absorbed by the glass substrate, and the glass is removed by melting, evaporation, or ablation by this energy. The light intensity of the laser light irradiated onto the glass substrate surface is partially changed, the glass removal amount of the portion with high light intensity is increased, and the glass removal amount of the portion with low light intensity is decreased. Fine irregularities are formed on the surface of the glass substrate, and the laser beam is a laser beam having a periodic light intensity distribution, and has the periodic light intensity distribution. That the laser beam is a microlens array obtained by the laser processing method of a glass substrate, characterized in that obtained by phase mask.

In a flat-type microlens array incorporated in a liquid crystal display element or the like, this flat-type microlens array is formed by irradiating a laser beam having a regular light intensity distribution on one side of a plate-like glass substrate. regular recess is provided is irradiated with laser light for the one side of a glass substrate forming a plate shape, the laser beam energy is absorbed by the glass substrate, the melt due to the energy, removing the glass by evaporation or ablation The light intensity of the laser light irradiated onto the glass substrate surface is partially changed, the glass removal amount of the portion with high light intensity is increased, and the glass removal amount of the portion with low light intensity is decreased. Fine irregularities are formed on the surface of the glass substrate, and the laser beam is a laser beam having a periodic light intensity distribution, and has the periodic light intensity distribution. That the laser light is caused to interfere with two laser beams, the cross-sectional shape of the periodic roughness formed in the surface of the glass base material, a glass substrate and controlling by laser beam pulse energy A microlens array obtained by a laser processing method.

9. The microlens array according to claim 7 or 8 , wherein the glass substrate constituting the microlens array is made of Ag atoms, Ag colloids or Ag ions from the surface to a predetermined depth or over the whole. Silver is contained in the form, and the concentration of this silver is the highest in the surface on the side where the diffraction grating is formed, and a concentration gradient is formed so that the concentration gradually decreases toward the other surface side A microlens array characterized by that.