JP2004224041A - Phase change type optical recording medium, method for manufacturing the same and method for recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change type optical recording medium capable of recording/erasing by utilizing a reversible phase change between an amorphous phase and a crystalline phase of a recording layer at the same capacity as DVD-ROM and a linear velocity of ≥10 m/s and having a large modulation degree and a good stability of an amorphous mark, and a method for manufacturing it and a method for recording. <P>SOLUTION: The phase change type optical recording medium has at least a first intermediate layer, the recording layer, a second intermediate layer, a reflective layer and a protective layer in this order on a substrate. The recording layer comprises an alloy of a composition expressed by GeγSbδ (wherein 5≤γ≤25; 75≤δ≤95; and γ and δ are each atomic%). Recording/erasing by utilizing the reversible phase change between the amorphous phase and the crystalline phase of the recording layer is possible even at a linear velocity of ≥10 m/s. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００１６】
書換え型光記録媒体では、一般的に図３に示すような記録ストラテジにより記録・消去を行なう。通常、パワーが高い方から記録パワーＰｗ（ｍＷ）、消去パワーＰｅ、バイアスパワーＰｂの３値よりなり、ＰｗからＰｂに急激にパワーを落とすパルスを照射することにより記録層を急冷させてアモルファス相を形成させ、一定パワーのＰｅを照射することにより記録層を徐冷させてスペース（結晶相）を形成させる。本来結晶相となるべきスペース部分にアモルファス相が形成されてしまったのは、材料の結晶化速度に対して記録線速が速すぎるためである。
これらの結果から、記録層の合金組成は、ＧｅγＳｂδ（γ、δは原子％）として、５≦γ≦２５、７５≦δ≦９５の範囲がよい。
【００１７】
実施例２
記録層用の合金ターゲットを、表２に示した記録層組成と同一組成のＧｅＳｂ合金に変えた点以外は、実施例１と同様にして光記録媒体を作製し初期結晶化した。
これらの光記録媒体に対して、実施例１と同一の記録条件で３Ｔを１０回オーバーライトしたときのＣ／Ｎ比〔スペクトルアナライザを用いてノイズ（Ｎ）レベルと信号強度（Ｃ：キャリア）との比を測定〕を表２、図４に示す。
書換え型の光ディスクシステムを実現する場合、そのＣ／Ｎ比は、少なくとも４５ｄＢ必要であり、５０ｄＢ以上あれば更に安定したシステムを得ることができる。
【表２】

【００１８】
更に、記録層用の合金ターゲットを、表３に示した記録層組成と同一組成のＧｅＳｂ合金に変えた点以外は、実施例１と同様にして光記録媒体を作製し初期結晶化した。
これらの光記録媒体について、記録線速を１０、１４、２８、３５ｍ／ｓとした点以外は実施例１と同一の記録条件で３Ｔを１０回オーバーライトしたときのＣ／Ｎ比〔スペクトルアナライザを用いてノイズ（Ｎ）レベルと信号強度（Ｃ：キャリア）との比を測定〕を表３に示す。
【表３】

上記の結果から、ＧｅγＳｂδ（但し、５≦γ≦２５、７５≦δ≦９５、γ、δは原子％）の範囲ならば、記録線速１０〜３５ｍ／ｓでも記録可能であることが確かめられた。しかし、Ｇｅ_３Ｓｂ_９７では、アモルファス化することができなかった。また、Ｇｅ_３０Ｓｂ_７０では、本来結晶相となるべきスペース部分にアモルファス相が形成されてしまい繰り返し記録することができなかった。
確実にＣ／Ｎ比が４５ｄＢ以上の安定したシステムを得るには、１０≦γ≦２０、８０≦δ≦９０であることが望ましい。
【００１９】
実施例３
記録層用の合金ターゲットを、Ｇｅ_１６．７Ｓｂ_８３．３に対しＡｇ、Ａｕ、Ｃｕ、Ｂ、Ａｌ、Ｉｎ、Ｍｎをそれぞれ５原子％添加した合金に変えた点以外は、実施例１と同様にして光記録媒体を作製し初期結晶化した。
得られた８種類の光記録媒体について実施例１と同様にして記録試験を行なったところ、２８ｍ／ｓの記録速度条件において、Ｇｅ_１６．７Ｓｂ_８３．３のみの場合にＰｗ＝３０ｍＷで記録したのと同じ変調度を得るのに必要な記録パワーを、Ａｇ、Ａｕ、Ｃｕを添加した合金では約８％、Ｂ、Ａｌ、Ｉｎ、Ｍｎを添加した合金では約１２％減少させることができた。
同様にＳｎ、Ｓｉ、Ｚｎ、Ｂｉ、Ｐｂをそれぞれ５原子％添加した合金を用いて作製した光記録媒体では、２８ｍ／ｓの記録速度条件において同じ変調度が得られる記録パワーはＧｅ_１６．７Ｓｂ_８３．３のみの場合とほぼ同じであったが、Ｓｎの場合は記録可能な線速範囲が約５％速くなった。また、Ｓｉ、Ｚｎ、Ｂｉ、Ｐｂの場合は記録可能な線速範囲が約３％速くなった。
同様にＧｅ、Ｎをそれぞれ５原子％添加した合金を用いて作製した光記録媒体について８０℃８５％ＲＨの高温高湿下の保存信頼性テストを行なったところ、Ｇｅ_１６．７Ｓｂ_８３．３のみの場合の２００時間後のジッタ上昇が約２％であったのに対し、１．０％以内に低減できることが分った。
実際の組成設計においては、Ｇｅ_１６．７Ｓｂ_８３．３のみでも十分な記録特性が得られるが、更に使用目的に応じて上記の元素を単独で或いは複合して添加することにより、記録層材料の特性をコントロールできる。
【００２０】
実施例４
記録層の膜厚を３、５、８、１０、１５、２０、２５、３０ｎｍと変えた点以外は、実施例１と同様にして光記録媒体を作製し、初期結晶化した後、実施例１と同様にしてＣ／Ｎ比と変調度を評価した。結果を表４及び図５に示す。
記録層の膜厚が５〜２５ｎｍのときに、ＤＶＤの規格を満足する変調度６０％以上が得られた。望ましい記録層の膜厚は８〜２０ｎｍであり、この範囲では変調度が６５％以上であり、更に安定したシステムを得ることができる。
【表４】

【００２１】
実施例５
実施例１で作製した光記録媒体を一定線速９ｍ／ｓで回転させ、パワー密度が１８ｍＷ／μｍ^２のレーザー光を半径方向に送り３６μｍ／ｒで移動させながら照射することにより初期結晶化を行なった。
この光記録媒体の貼り合せ部分を物理的に剥がした後、粘着テープで（環境）保護層及び反射層を剥がし、記録層が残っている側の基板を有機溶剤に浸して記録層を基板から剥離させ、ろ過した。この粉末をキャピラリに充填し、入射ビームの平行性と輝度が極度に高い放射光を利用して波長０．４１９Åで粉末Ｘ線回折測定を行なった。
図６に粉末Ｘ線回折スペクトルを示す。主な回折スペクトルのピークは、２θ＝６．５１、６．９５３、８．０２１、１０．９７２、１１．７１°であった。これらの各ピークに対応する格子面の面間隔を下記のブラッグの式により計算すると、順に、ｄ＝３．６９、３．４６、３、２．１９、２．０６であった。これらのピークはＳｂ構造と同様の菱面体構造により指数付けすることができ、記録層は単相であることが分った。
ブラッグの式 ２ｄｓｉｎθ＝ｎλ
（ｄ：格子面の間隔、ｎ：反射の次数、λ：Ｘ線の波長）
【００２２】
上記と同じ光記録媒体の貼り合せ部分を物理的に剥がし記録層が最表面になった状態で、Ｉｎ−ｐｌａｎｅＸ線回折（試料の基板面に対し垂直な格子面を測定する方法）により測定を行った。〔この測定法の詳細は、Ｔｈｅ Ｒｉｇａｋｕ−Ｄｅｎｋｉ Ｊｏｕｒｎａｌ ３１（１）２０００に記述されている。〕図７に概略図を示す。
装置はフィリプス社製Ｘ′ｐｅｒｔ ＭＲＤ、Ｘ線の入射光源には銅のＫα線（波長λ＝１．５４Å）を用いた。基板面に対し殆ど平行にＸ線を入射（入射角０．２〜０．５°）し、Ｘ線が当っている部分を回転軸として試料を４５°ずつ回転させ、Ｘ線回折スペクトルの測定を行なった。この測定法によれば、基板面に対し殆ど平行にＸ線を入射することにより浸入深さを数ｎｍに抑えることができるので、膜厚が薄い記録層の結晶構造を正確に調べることができる。
光記録媒体の半径位置４０ｍｍ付近にＸ線が当るように試料をセットし、光記録媒体のトラック方向に平行にＸ線を入射させた。このときの角度を０°とし、Ｘ線が当っている部分を回転軸として４５°ずつ試料を回転させ、それぞれ２θ＝２０〜７０°まで測定したスペクトルを図８に示す。
【００２３】
多結晶の膜がある特定の方向に配向していると、該当のピークの強度が強くなるという関係がある。先に述べた粉末Ｘ線回折は、試料を基板から剥がし粉末化させたことによって結晶の配向性を取り除いた状態で測定したものであり、粉末Ｘ線回折と面内回折（Ｉｎ−ｐｌａｎｅＸ線回折）の結果を比較することにより、結晶の配向性がより顕著に判る。
粉末Ｘ線回折の結果を波長λ＝１．５４Åに換算した結果を図９に示す。これを面内回折の結果と比較すると、粉末Ｘ線回折では２θ＝２９°付近のピークの強度が最も強いのに対し、面内回折では２９°のピークが小さくなり、現れるピークの数も少なくなる。これは結晶が配向しているため、ブラッグの回折条件を満たさない格子面が出てくるためである。トラック方向に対し９０°にＸ線を入射したとき、格子間隔ｄが２．１０Å（２θ＝４３．１°）の格子面に強く配向している。
【００２４】
次に、パワー密度を３、５、７、１５、２５、４０、５０、５２ｍＷ／μｍ^２とし、それぞれ最適な線速で初期化したときの初期化後の状態及び反射率を表５に示す。評価基準は、結晶の配向性が見られないとき「×（１）」、結晶の配向性があるとき「○」、結晶の配向性が強いとき「◎」、膜剥がれが起きたとき「×（２）」とした。
【表５】

線速が３〜１８ｍ／ｓ、パワー密度が５〜５０ｍＷ／μｍ^２の範囲で結晶の配向性が見られ、特に線速が６〜１４ｍ／ｓ、パワー密度が１５〜４０ｍＷ／μｍ^２のとき強い配向性が見られ、それに伴って高い反射率が得られた。
結晶の配向性があり反射率が高い光記録媒体は、記録線速１０〜３５ｍ／ｓの記録条件において、Ｃ／Ｎ比４５ｄＢ以上の良好な記録特性を示し、記録後の光記録媒体を８０℃８５％ＲＨ環境下で保存した後のジッタ値の変化を調べたところ、４００時間後でもジッタ値は変化せず、アモルファスマークの安定性が良いことが確認された（図１０）。
ジッタ値は、マークエッジのばらつきを示す値であり、小さい程ばらつきが少なく良好な記録ができていることを示す。加速試験によりアモルファスマークのエッジから結晶化が始まると、ジッタ値は急激に悪くなることが分っている。
上記加速試験の結果を室温での寿命に概算すると１０年以上となり、光記録媒体の寿命は十分保証される。従って、本発明の目的とする１０ｍ／ｓ以上の記録線速での高速記録が可能な媒体を得るのに上記初期化条件が適していることも確かめられた。
【００２５】
記録層用の合金ターゲットをＧｅ_１７Ｓｂ_８３に変えた点以外は、実施例１と同様にして光記録媒体を作製した。
この光記録媒体を一定線速８ｍ／ｓで回転させ、パワー密度が２０ｍＷ／μｍ^２のレーザー光を半径方向に送り３６μｍ／ｒで移動させながら照射することにより初期結晶化を行なった。
この光記録媒体について、上記と同様の処理を行って測定した面内回折（Ｉｎ−ｐｌａｎｅＸ線回折）の結果を図１１に示す。この図から、トラック方向に対し垂直方向で格子間隔ｄ（Å）＝２．０９からのピーク回折強度が強く、配向性が良いことが分った。
この光記録媒体に対し、記録線速２８ｍ／ｓ、ＤＶＤ−ＲＯＭと同容量の記録密度でＥＦＭランダムパターンのＤＯＷを１０回、記録パワーＰｗ＝３０ｍＷ、消去パワーＰｅ＝６ｍＷで行なったところ、変調度６３％、反射率２４％であった。また、初回記録した記録媒体を８０℃８５％ＲＨ環境下で保存した後のジッタ値の変化を調べたところ、４００時間後でもジッタ値は変化せず、アモルファスマークの安定性が良いことが確認された。
【００２６】
記録層用の合金ターゲットをＡｇ_２Ｉｎ_５Ｓｂ_６８Ｔｅ_２５、その母相材料となるＳｂ_７８Ｔｅ_２２、Ｓｂ_８８Ｔｅ_１２及びＩｎ_３１．７Ｓｂ_６８．３（以上比較例）、Ｇａ_１２Ｓｂ_８８（参考例）、Ｇｅ_１６．７Ｓｂ_８３．３に変えた点以外は、実施例１と同様にして光記録媒体を作製した。
これらの光記録媒体を一定線速８ｍ／ｓで回転させ、パワー密度が２０ｍＷ／μｍ^２のレーザー光を半径方向に送り３６μｍ／ｒで移動させながら照射することにより初期結晶化を行なった。
これらの光記録媒体について、上記と同様の処理をして粉末Ｘ線回折を行った。比較のために粉末Ｓｂについても粉末Ｘ線回折を行なった。結果を纏めて図１２に示す。Ａｇ_２Ｉｎ_５Ｓｂ_６８Ｔｅ_２５、Ｓｂ_７８Ｔｅ_２２、Ｉｎ_３１．７Ｓｂ_６８．３のそれぞれのピークはｃｕｂｉｃ（正方晶）構造で指数付けすることができ、Ｓｂ_８８Ｔｅ_１２、Ｇａ_１２Ｓｂ_８８、Ｇｅ_１６．７Ｓｂ_８３．３はＳｂ構造と同様のｈｅｘａｇｏｎａｌ（六方晶）構造で指数付けすることができた。
材料の結晶構造を比較するため、全ての材料をｈｅｘａｇｏｎａｌ構造の単位格子（図１３）を基準として格子定数ａ（Å）、ｃ（Å）を計算した結果及び熱分析により求めた結晶化温度Ｔｃ（℃）を表６に示した。ｃ／ａ比が２．４５のときｃｕｂｉｃ構造と等価である。結晶化温度は、ガラス上に記録層の単膜を製膜し、アモルファス状態の膜を示差走査熱量測定器により昇温速度１０℃／分で昇温させ結晶化が起こる温度を結晶化温度とした。結晶化温度が高いほど、アモルファス相が安定で、結晶化し難いと言える。
【表６】

【００２７】
Ａｇ_２Ｉｎ_５Ｓｂ_６８Ｔｅ_２５系材料は、母相材料ＳｂＴｅに添加元素としてＡｇ、Ｉｎを入れた材料である。母相材料のＳｂＴｅのＳｂ量を増やすことにより材料の結晶化速度を速く出来ることが分っているが、Ｓｂを増やした材料系では低温でもアモルファス相が結晶化してしまうという欠点があり、ＤＶＤの５倍速である１８ｍ／ｓ記録が限界であると見積もっている。ＳｂＴｅの結晶化温度が、１２０．５℃、７９．５℃と低いのに比較して、ＧａＳｂ、ＧｅＳｂはそれぞれ１９４．５、２５５．５℃と高く、非常にアモルファス相が結晶化し難く、アモルファスマークの保存安定性が良いことが分る。これらの現象は、材料の構造から説明することができる。今回粉末Ｘ線回折を測定した材料は、全てＳｂに何かが添加されている材料系と考えることができる。Ｓｂ単独では結晶化速度は速いものの、室温でもすぐに結晶化してしまうほどアモルファス相の安定性が悪いため、光記録媒体の材料としては利用できない。そこで、アモルファス相の安定性を良くするために、Ｓｂ以外の元素を入れることにより結合力を強めていると考えられる。
格子定数ａと結晶化温度の関係を図１４に示す。格子定数ａが小さい材料は共有結合の力が強く、アモルファス相を熱的に結晶化させるために共有結合を切ってネットワークを組み替えるのに大きなエネルギーを必要とするため、結晶化温度が高くなっていると考えられる。
【００２８】
比較例１
実施例１で作製した光記録媒体を一定線速２ｍ／ｓで回転させ、パワー密度が４．５ｍＷ／μｍ^２のレーザー光を半径方向に送り３６μｍ／ｒで移動させながら照射することにより初期結晶化を行なった。
この光記録媒体の貼り合せ部分を物理的に剥がし記録層が最表面になった状態で、実施例５と同様にして面内回折（Ｉｎ−ｐｌａｎｅＸ線回折）を行った。即ち、基板面に対し殆ど平行にＸ線を入射（入射角０．２〜０．５°）し、試料を４５°ずつ回転させ、Ｘ線回折スペクトルの測定を行なった。トラック方向に平行にＸ線を入射させたときの角度を０°とし、４５°ずつ試料を回転させ１３５°まで測定した結果を図１５に示した。
上記初期結晶化を行なった光記録媒体を実施例１と同じ記録再生装置を用いて実施例１と同条件で記録したところ、反射率は１７％、変調度は５５％と低かった。この材料は配向性が小さく結晶性が悪いため反射率が低く、変調度が小さくなっている。
【００２９】
実施例６
実施例１で作製した光記録媒体に対し、波長６６０ｎｍのＬＤ（レーザーダイオード）とＮＡ０．６５の光学系を用い、記録線速度２８ｍ／ｓのときに図３に示すようなパルス列のレーザービームにより、Ｐｅ／Ｐｗを０．２とし、Ｐｗを変化させて記録テストを行った結果を図１６に示す。
テストはＤＶＤの変調方式であるＥＦＭ＋変調における３Ｔ、６Ｔ、８Ｔ、１４Ｔの単一マークをそれぞれ１０回ＤＯＷして、そのＣ／Ｎ比をモニターすることによって行った。８Ｔマークは、他に１回のみの記録（初回記録）を行ったときの結果も合わせてプロットした。記録に用いたパルスは、それぞれ各Ｔに最適化してそのパルス数とパルス幅、Ｐｂレベルの幅を最適化して用いた。
Ｇａ_１６Ｓｂ_８４を記録材料として用いた記録媒体において、Ｃ／Ｎ比を３０ｄＢ以上確保するためには記録パワーＰｗは１５ｍＷ以上、更に安定した記録が可能な４５ｄＢ以上の記録特性を得るには２０ｍＷ前後以上の記録パワーＰｗが必要である。
今回用いた光学系では、ビームパワーが１／ｅ^２となるビーム径は、計算から約０．９ミクロン程度であるため、記録に必要な記録パワーＰｗにおけるビームのパワー密度は少なくとも２０ｍＷ／μｍ^２、望ましくは３０ｍＷ／μｍ^２以上必要であることが分った。
【００３０】
実施例７
実施例１で作製した光記録媒体を用いて、記録速度を１０ｍ／ｓ、２８ｍ／ｓ、３５ｍ／ｓとし、図３記載のパルスビームを用いて記録を行い、そのＣ／Ｎ比をプロットしたのが図１７である。また、記録に用いるレーザー光の、消去パワーＰｅとピークパワーＰｗの比をそれぞれの記録線速条件下で最適化して、Ｃ／Ｎ比が最大となるパワー条件を記録線速に対してプロットしたのが図１８である。
実施例６と同様に各Ｔに対するパルス数は、それぞれの線速条件で変更し最適なものを用いた。記録はＥＦＭ＋変調方式を用い、各Ｔのマークをランダムに記録した場合の結果である。
１０ｍ／ｓ記録線速条件でＰｅ／Ｐｗを変えた場合にＣ／Ｎ比が良好な範囲は０．４２≦Ｐｅ／Ｐｗ≦０．６５であり、特にＣ／Ｎ比を５０ｄＢに出来るのは、０．４７≦Ｐｅ／Ｐｗ≦０．６０程度であった。また、３５ｍ／ｓ記録線速条件ではＣ／Ｎ比が良好な範囲は０．１０≦Ｐｅ／Ｐｗ≦０．２５であり、特にＣ／Ｎ比を５０ｄＢに出来るのは、０．１３≦Ｐｅ／Ｐｗ≦０．２２程度であった。記録線速１０ｍ／ｓと３５ｍ／ｓの条件の間は各線速条件で埋められるため、記録線速を１０〜３５ｍ／ｓとしたときに良好な記録特性が得られるＰｅ／Ｐｗ比の範囲は、０．１０≦Ｐｅ／Ｐｗ≦０．６５であり、望ましくは０．１３≦Ｐｅ／Ｐｗ≦０．６０である。
【００３１】
【発明の効果】
本発明１によれば、ＤＶＤ−ＲＯＭと同容量で１０ｍ／ｓ以上の線速度で記録層の非晶質相（アモルファス相）と結晶相との可逆的な相変化を利用して記録・消去が可能な光記録媒体を提供できる。
本発明２によれば、１０ｍ／ｓ以上の記録線速でＣ／Ｎ比が高い光記録媒体を提供できる。
本発明３によれば、使用目的に応じて記録層材料の特性をコントロールすることができる光記録媒体を提供できる。特に、Ａｇ、Ａｕ、Ｃｕ、Ｂ、Ａｌ、Ｉｎ、Ｍｎを用いると、必要とする記録パワーを下げることができ、Ｓｎ、Ｓｉ、Ｚｎ、Ｂｉ、Ｐｂを用いると、記録可能な線速を速くすることができ、Ｎを用いると、アモルファスマークの安定性を良くすることができる
本発明４によれば、ＤＶＤの４倍速（１４ｍ／ｓ）以上の記録線速で繰り返し記録が可能な光記録媒体を提供できる。
本発明５によれば、ＤＶＤの８倍速（２８ｍ／ｓ）以上の記録線速で繰り返し記録が可能な光記録媒体を提供できる。
本発明６〜７によれば、変調度が高い光記録媒体を提供できる。
本発明８〜９によれば、ＤＶＤ−ＲＯＭと同容量で１０ｍ／ｓ以上の記録線速で高速記録が可能な光記録媒体の製造方法を提供できる。
本発明１０〜１２によれば、ＤＶＤ−ＲＯＭと同容量で１０ｍ／ｓ以上の記録線速で高速記録が可能な光記録媒体製造用スパッタリングターゲットを提供できる。
本発明１３によれば、安定した記録が可能な光記録媒体の記録方法を提供できる。
本発明１４〜１５によれば、１０ｍ／ｓ以上の記録線速でＣ／Ｎ比が高い光記録媒体の記録方法を提供できる。
【図面の簡単な説明】
【図１】本発明の相変化型光記録媒体の基本的な構造を示す図。
（ａ） 斜視図
（ｂ） （ａ）の切り欠き部の断面（層構造）を模式的に示す図。
【図２】初回記録後の記録層の透過電子顕微鏡像を示す図。
【図３】書換え型光記録媒体で一般的に用いる記録ストラテジを示す図。
【図４】実施例２のＧｅＳｂ合金を用いた場合のＣ／Ｎ比の測定結果を示す図。
【図５】実施例４の記録層の膜厚を変化させた場合の変調度の評価結果を示す図。
【図６】実施例５の粉末Ｘ線回折スペクトルを示す図。
【図７】Ｉｎ−ｐｌａｎｅＸ線回折を説明するための図。
【図８】実施例５の光記録媒体について、Ｉｎ−ｐｌａｎｅＸ線回折により測定したスペクトルを示す図。
【図９】実施例５の光記録媒体について、粉末Ｘ線回折の結果を波長λ＝１．５４Åに換算した結果を示す図。
【図１０】実施例５の光記録媒体について、記録後の媒体を８０℃８５％ＲＨ環境下で保存した後のジッタ値の変化を示す図。
【図１１】実施例５の別の光記録媒体についてＩｎ−ｐｌａｎｅＸ線回折により測定したスペクトルを示す図。
【図１２】実施例５及び比較例の光記録媒体の粉末Ｘ線回折の結果を示す図。
【図１３】ｈｅｘａｇｏｎａｌ構造の単位格子を示す図。
【図１４】格子定数ａと結晶化温度の関係を示す図。
【図１５】比較例１の光記録媒体について、Ｉｎ−ｐｌａｎｅＸ線回折により測定したスペクトルを示す図。
【図１６】実施例１で作製した光記録媒体に対し、記録テストを行った結果を示す図。
【図１７】実施例１で作製した光記録媒体を用いて、記録速度を変えて記録を行ったときのＣ／Ｎ比をプロットした図。
【図１８】実施例１で作製した光記録媒体を用い、記録に用いるレーザー光のＰｅ／Ｐｗをそれぞれの記録線速条件下で最適化して、Ｃ／Ｎ比が最大となるパワー条件を記録線速に対してプロットした図。
【符号の説明】
ａ 格子定数
ｃ 格子定数[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase-change optical recording medium capable of recording, reproducing, and rewriting information by causing an optical change in a recording layer material by irradiating a light beam, and a method of manufacturing and recording the same. Things.
[0002]
[Prior art]
Patent Document 1 discloses that a recording material in which a metal or a chalcogenide element M is added to an alloy having a composition ratio of GaSb or InSb in the vicinity of 50:50 is used, and the crystallization speed is too fast with GaSb or InSb alone. Although it cannot be made amorphous, it is described that by adding a metal or chalcogenide element M to this, the crystallization speed can be reduced, and information recording using a crystal-amorphous phase transition can be performed. .
However, Ga ₅₀ Sb ₅₀ (Atomic%) Alloys near the composition have a high melting point of 710 ° C. and a crystallization temperature of 350 ° C., and the power is not sufficient with a commercially available initialization device. A crystalline state cannot be obtained, and the reflectance becomes non-uniform. When a mark is recorded with non-uniform reflectance, signal noise is large, and it is particularly difficult to record a signal at a high density like a DVD.
[0003]
Patent Document 2 discloses a phase change type optical recording medium using an alloy containing GaSb as a main component as a recording material. This optical recording medium uses a phase change between crystals to store information. The modulation is 29% at best, and there is a problem in practice. Also, "If the Ga content is less than 20%, the film may rise due to the formation of bubbles in the laser beam irradiation part, and the level at which the reflectance changes becomes unstable, which poses a practical problem. There is. "
Further, the phase change between crystal and crystal utilizes a difference in reflectance due to a difference in crystal grain size, and is not suitable for high-density information recording in which a minute mark needs to be recorded. Information cannot be recorded at the same density as a DVD-ROM.
Non-Patent Document 1 discloses knowledge about an optical recording medium using a GeSb thin film capable of phase change at an ultra-high speed. However, the electron diffraction pattern of FIG. However, the degree of modulation of the crystalline phase and the amorphous phase at this time is 15 to 20%, which poses a practical problem.
[0004]
Patent Document 3 discloses a phase change using a material whose main component is an alloy of (SbxGe1-x) 1-yIny (0.65 ≦ x ≦ 0.95, 0 <y ≦ 0.2) for a recording layer. A type optical recording medium is disclosed.
However, the initialization condition was 2.6 mW / μm in terms of laser power density. ² There is only description that initial crystallization has occurred to the extent, but nothing is described about the high initializing laser power density required in the present invention.
It is presumed that at a low power density as described above, only a medium having a low crystal orientation and a low crystal reflectivity can be obtained. Moreover, the disclosed linear recording speed range is a low linear velocity of 2.4 to 9.6 m / s, and does not describe correspondence to high linear velocity recording as in the present invention.
[0005]
[Patent Document 1]
U.S. Pat. No. 4,818,666
[Patent Document 2]
JP-A-61-168145
[Patent Document 3]
JP 2001-39031 A
[Non-patent document 1]
"Appl. Phys. Lett." 60 (25), 22 June 1992, p3123-3125.
[0006]
[Problems to be solved by the invention]
According to the present invention, recording and erasing can be performed using the reversible phase change between the amorphous phase (amorphous phase) and the crystalline phase of the recording layer at a linear velocity of 10 m / s or more with the same capacity as a DVD-ROM. An object of the present invention is to provide a phase-change optical recording medium having a high degree of modulation and a good stability of an amorphous mark, and a method for manufacturing and recording the same.
[0007]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 15).
1) On a substrate, at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer are provided in this order, and the recording layer is formed of GeγSbδ (provided that 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, γ, and δ are atomic%) and utilizes the reversible phase change between the amorphous phase (amorphous phase) and the crystalline phase of the recording layer even at a linear velocity of 10 m / s or more. A phase-change type optical recording medium characterized in that it is possible to perform recording and erasing.
2) The phase-change optical recording medium according to 1), wherein 10 ≦ γ ≦ 20 and 80 ≦ δ ≦ 90.
3) The recording layer further contains at least one element selected from the group consisting of Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Si, and N of 10 atomic% or less of the alloy. The phase-change-type optical recording medium according to 1) or 2), which is contained.
4) Recording / erasing using a reversible phase change between the amorphous phase and the crystalline phase of the recording layer is possible even at a linear velocity of 14 m / s or more. A phase-change optical recording medium according to any one of the above.
5) The phase change type according to 4), wherein recording and erasing can be performed using a reversible phase change between the amorphous phase and the crystalline phase of the recording layer even at a linear velocity of 28 m / s or more. Optical recording medium.
6) The phase-change optical recording medium according to any one of 1) to 5), wherein the thickness of the recording layer is in the range of 5 to 25 nm.
7) The phase-change optical recording medium according to 6), wherein the thickness of the recording layer is in the range of 8 to 20 nm.
8) On a substrate, at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer are laminated in this order to produce an optical recording medium. Rotated at a constant linear velocity within the range, power density is 5-50 mW / μm ² The initial phase crystallization by irradiating the laser beam at a constant speed in the radial direction to the optical recording medium to perform initial crystallization. Production method.
9) The rotational linear velocity of the recording medium is a constant linear velocity in the range of 6 to 14 m / s, and the power density of the laser beam is 15 to 40 mW / μm. ² The method according to 8), wherein:
10) A sputtering target for producing a phase-change optical recording medium, comprising an alloy having a composition represented by GeγSbδ (where 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%).
11) The sputtering target for producing a phase-change optical recording medium according to 10), comprising an alloy having a composition represented by GeγSbδ (where 10 ≦ γ ≦ 20, 80 ≦ δ ≦ 90, and γ and δ are atomic%).
12) An alloy having a composition represented by GeγSbδ (where 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%) as a main component, and 10% or less of Ag, Au, Cu, A sputtering target for producing a phase-change optical recording medium, comprising at least one element selected from the group consisting of B, Al, In, Mn, Sn, Zn, Bi, Pb, Si and N.
13) When the recording linear velocity is 28 m / s, a light beam for causing an optical change in the recording layer material is formed by a single pulse or a plurality of pulse trains, and the power density of the pulse beam at the recording power Pw is determined. 20mW / μm ² The recording method of a phase-change optical recording medium according to any one of 1) to 7), characterized in that:
14) The recording linear velocity is 10 to 35 m / s, the light beam irradiated on the medium is formed by a single pulse or a plurality of pulse trains, and the ratio between the erasing power Pe and the recording power Pw is 0.10 ≦ Pe / The recording method for a phase change type optical recording medium according to any one of 1) to 7), wherein Pw ≦ 0.65 is set.
15) The recording method for a phase-change optical recording medium according to 14), wherein 0.13 ≦ Pe / Pw ≦ 0.60 is set.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The phase-change optical recording medium of the present invention has at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer on a substrate in this order. This basic structure is shown in FIG. FIG. 1A is a perspective view of a medium, and FIG. 1B schematically shows a cross section (layer structure) of a cutout portion in FIG. 1A.
In the present invention 1, the description that “recording / erasing is possible using a reversible phase change between an amorphous phase (amorphous phase) and a crystalline phase of a recording layer even at a linear velocity of 10 m / s or more” is described. In other words, it has the capability of recording and erasing at a linear velocity of 10 m / s or more, and may or may not have the recording / erasing ability at a linear velocity of less than 10 m / s.
In general, glass, ceramics, or resin is used as the substrate material, but a resin substrate is desirable in terms of moldability and cost. Examples of the resin include a polycarbonate resin, an acrylic resin, an epoxy resin, a polystyrene resin, a polyethylene resin, a polypropylene resin, a silicone resin, a fluororesin, and the like, and a polycarbonate resin is preferable in view of workability, optical characteristics, and the like. Further, the shape of the substrate may be any of a disk shape, a card shape, a sheet shape and the like. Any thickness such as 1.2 mm, 0.6 mm, and 0.1 mm can be used for the thickness of the substrate.
[0009]
The material used for the first intermediate layer and the second intermediate layer is SiO 2 ₂ , TiO ₂ , ZnO, ZrO ₂ Metal oxides such as AlN, Si ₃ N ₄ , TiN and other nitrides; ZnS, In ₂ S ₃ , TaS ₃ And the like; carbides such as SiC, TiC and ZrC; and mixtures thereof.
The first intermediate layer has a role of protecting the recording layer so that impurities such as moisture do not enter the recording layer from the substrate, a role of preventing thermal damage to the substrate, a role of adjusting optical characteristics, and the like. Therefore, a material that does not easily transmit moisture, has good heat resistance, has a small absorption k, and has a large refractive index n is preferable. The thickness of the first intermediate layer is 40 to 500 nm, preferably 60 to 200 nm. When the thickness is less than 40 nm, the substrate is heated at the same time as the recording layer is heated, so that the substrate is deformed. When the thickness is more than 500 nm, peeling easily occurs at the interface between the substrate and the first intermediate layer, which is not preferable.
The second intermediate layer plays a role in adjusting the thermal characteristics of the recording layer. When the thickness of the second intermediate layer is reduced, heat is easily released, and when the thickness is increased, it is difficult to escape. The thickness of the second intermediate layer is 5 to 100 nm, preferably 5 to 20 nm. When the thickness exceeds 100 nm, heat is excessively absorbed and it is difficult to form an amorphous phase, and when the thickness is less than 5 nm, recording sensitivity is deteriorated.
[0010]
For the recording layer, an alloy having a composition represented by GeγSbδ (provided that 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%) is used. Preferred composition ranges are 10 ≦ γ ≦ 20 and 80 ≦ δ ≦ 90. In this composition range, recording / erasing can be performed at a linear velocity of 10 m / s or more by utilizing the reversible phase change between the amorphous phase (amorphous phase) and the crystalline phase of the recording layer, and the degree of modulation is large. As a result, a phase change type optical recording medium having good amorphous mark stability can be obtained.
Further, at least one element selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Si, and N is added to the alloy in an amount of 10 atomic% or less. Thereby, the physical properties such as the recording power, the linear velocity at which recording can be performed, and the stability of the amorphous mark can be improved.
If the thickness of the recording layer is in the range of 5 to 25 nm, a modulation factor of 60% or more that satisfies the DVD standard can be obtained. A more desirable film thickness is 8 to 20 nm. In this range, the degree of modulation is 65% or more, and a more stable system can be obtained.
Various metals can be used for the reflective layer, but a metal material such as Al, Ag, Cu, or Au or an alloy obtained by adding Ti, Cr, Si, Pd, Cu, In, or Mn to them is desirable. For high-speed recording, Ag, Cu, and Au having particularly high thermal conductivity are preferable. The thickness of the reflection layer is preferably from 60 to 300 nm. If the thickness is less than 60 nm, a heat radiation effect cannot be obtained, and it is difficult to form an amorphous state. If the thickness exceeds 300 nm, interface peeling tends to occur.
[0011]
Initial crystallization conditions are important for producing the phase-change optical recording medium of the present invention. Specifically, after laminating each of the above layers on a substrate, the layer is rotated at a constant linear velocity in a range of 3 to 18 m / s to obtain a 5 to 50 mW / μm ² The initial crystallization is performed by irradiating a laser beam having a power density of 2 while moving at a constant speed in the radial direction. Preferred rotational linear velocities and power densities are 6 to 14 m / s and 15 to 40 mW / μm ² It is.
In the recording method of the phase change type optical recording medium of the present invention, a light beam for causing an optical change in a recording layer material is formed by a single pulse or a plurality of pulse trains when a recording linear velocity is 28 m / s. At the same time, the power density of the pulse beam at the recording power Pw is set to 20 mW / μm. ² It is preferable to make the above.
Further, the recording linear velocity is set to 10 to 35 m / s, the light beam irradiated on the medium is formed by a single pulse or a plurality of pulse trains, and the ratio between the erasing power Pe and the recording power Pw is 0.10 ≦ Pe / It is preferable to set Pw ≦ 0.65. A more preferred range is 0.13 ≦ Pe / Pw ≦ 0.60.
[0012]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0013]
Example 1
On a polycarbonate substrate having a track pitch of 0.74 μm and a guide groove having a groove depth of 400 ° and a thickness of 0.6 mm and a diameter of 120 mmφ, a SiO2 film is formed by sputtering. ₂ 20 mol% ZnS-SiO ₂ Using a mixed target, the first intermediate layer is 75 nm thick, Ge ₁₆ Sb ₈₄ (Atomic%) The recording layer was 16 nm thick using an alloy target, the second intermediate layer was 14 nm thick using the same target as the first intermediate layer, and Ag-Pd (1 atomic%)-Cu (1 atomic%). Using a target, a reflective layer having a thickness of 140 nm was provided in this order.
The alloy target of the recording layer is weighed in advance, melted and heated in a glass ampule, then taken out, crushed by a crusher, and heated and sintered to obtain a disk-shaped target shape. did. When the composition ratio of the recording layer after film formation was measured by inductively coupled plasma (ICP) emission spectroscopy, the composition ratio was the same as the target charge amount. Sequential instruments: Sequential type ICP emission spectrometer SPS4000 was used for ICP emission spectroscopy. In Examples and Comparative Examples described later, the alloy composition of the recording layer is the same as the alloy composition of the sputtering target.
Next, a protective layer made of an acrylic resin is provided on the reflective layer by a spin coating method to a thickness of about 5 to 10 μm, and a substrate having a thickness of 0.6 mm, which is the same as the substrate, is adhered to the protective layer with an ultraviolet curable resin. Example optical recording media were produced.
This optical recording medium was rotated at a constant linear velocity of 3 m / s, and the power density was 8 mW / μm. ² Initial crystallization was performed by irradiating the laser beam while sending it in the radial direction while moving it at 36 μm / r.
[0014]
Recording and reproduction were performed on the optical recording medium using a pickup having a wavelength of 660 nm and an NA of 0.65. Under the recording conditions of a recording linear velocity of 17 m / s, a recording linear density of the same capacity as a DVD-ROM, 0.267 μm / bit, a recording power Pw = 20 mW, and an erasing power Pe = 7 mW, the EFM + modulation method which is a DVD modulation method is used. A random pattern was recorded.
FIG. 2 shows a transmission electron microscope image of the recording layer after the initial recording.
As can be seen from FIG. 2, marks of about 0.4 μm in the short direction in the laser beam scanning direction and about 1.8 μm in the long direction (gray portions where black and white contrast is not visible in the figure) are randomly arranged. It was observed to be recorded. As a result of examining the gray part by electron beam diffraction, a halo pattern indicating an amorphous phase (amorphous phase) was obtained. In electron beam diffraction of a portion where the contrast between black and white was clear, spots indicating a crystalline phase were observed.
Further, when the recording layer after 10 times of direct overwrite (DOW) was observed with a transmission electron microscope image, an image similar to that of the initial recording was observed, and it was confirmed that repeated recording could be performed due to a phase change between the amorphous phase and the crystalline phase. Was done.
[0015]
An optical recording medium in which only the composition of the recording layer was changed was prepared in the same manner as above, and the amorphous phase and the crystalline phase were determined by the transmission electron microscope images after the initial recording at a recording linear velocity of 10 m / s and the 10-time DOW recording. It was observed whether it was formed.
Table 1 shows the alloy composition and the results. “O” in the table indicates that a crystalline phase and an amorphous phase were observed. In “x (1)”, no amorphous phase was observed under any recording conditions. This is because the crystallization speed of the material is too high, and sufficient quenching conditions cannot be created within the range of the recording conditions that can be set by the current recording apparatus, and all the materials are crystallized. Further, in “× (2)”, although an amorphous phase was observed, the amorphous phase was originally formed in a space portion which should originally be a crystalline phase.
[Table 1]

[0016]
In a rewritable optical recording medium, recording / erasing is generally performed by a recording strategy as shown in FIG. Usually, the recording power Pw (mW), the erasing power Pe, and the bias power Pb consist of three values from the higher power, and the recording layer is rapidly cooled by irradiating a pulse for rapidly decreasing the power from Pw to Pb, thereby forming an amorphous phase. The recording layer is gradually cooled by irradiating Pe with a constant power to form a space (crystal phase). The amorphous phase was formed in the space that should originally be a crystalline phase because the recording linear velocity was too high relative to the crystallization speed of the material.
From these results, the alloy composition of the recording layer is preferably in the range of 5 ≦ γ ≦ 25 and 75 ≦ δ ≦ 95 as GeγSbδ (γ and δ are atomic%).
[0017]
Example 2
An optical recording medium was prepared and initially crystallized in the same manner as in Example 1 except that the alloy target for the recording layer was changed to a GeSb alloy having the same composition as the recording layer shown in Table 2.
For these optical recording media, the C / N ratio when 3T was overwritten 10 times under the same recording conditions as in Example 1 [Noise (N) level and signal intensity (C: carrier) using a spectrum analyzer) Is shown in Table 2 and FIG.
When realizing a rewritable optical disk system, the C / N ratio needs to be at least 45 dB, and if it is 50 dB or more, a more stable system can be obtained.
[Table 2]

[0018]
Further, an optical recording medium was produced and subjected to initial crystallization in the same manner as in Example 1 except that the alloy target for the recording layer was changed to a GeSb alloy having the same composition as the recording layer shown in Table 3.
For these optical recording media, the C / N ratio when 3T was overwritten 10 times under the same recording conditions as in Example 1 except that the recording linear velocity was set to 10, 14, 28, and 35 m / s [spectral analyzer Is used to measure the ratio between the noise (N) level and the signal strength (C: carrier)].
[Table 3]

From the above results, it was confirmed that recording was possible even at a recording linear velocity of 10 to 35 m / s within the range of GeγSbδ (where 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%). Was. But Ge ₃ Sb ₉₇ Could not be made amorphous. Also, Ge ₃₀ Sb ₇₀ In this case, an amorphous phase was formed in a space that should originally be a crystalline phase, and it was not possible to repeatedly record.
In order to surely obtain a stable system having a C / N ratio of 45 dB or more, it is desirable that 10 ≦ γ ≦ 20 and 80 ≦ δ ≦ 90.
[0019]
Example 3
The alloy target for the recording layer was Ge _16.7 Sb _83.3 On the other hand, an optical recording medium was prepared and initially crystallized in the same manner as in Example 1 except that an alloy containing 5 atomic% of each of Ag, Au, Cu, B, Al, In and Mn was used.
When a recording test was performed on the obtained eight types of optical recording media in the same manner as in Example 1, Ge recording was performed at a recording speed of 28 m / s. _16.7 Sb _83.3 The recording power required to obtain the same degree of modulation as that recorded at Pw = 30 mW in the case of only A was about 8% for an alloy containing Ag, Au, and Cu, and an alloy containing B, Al, In, and Mn. Reduced about 12%.
Similarly, in an optical recording medium manufactured using an alloy containing 5 atomic% of Sn, Si, Zn, Bi, and Pb, the recording power at which the same degree of modulation can be obtained at a recording speed of 28 m / s is Ge. _16.7 Sb _83.3 In the case of Sn, the recordable linear velocity range was increased by about 5%. In the case of Si, Zn, Bi, and Pb, the range of recordable linear velocity was increased by about 3%.
Similarly, a storage reliability test under high temperature and high humidity conditions of 80 ° C. and 85% RH was performed on an optical recording medium manufactured using an alloy containing 5 atomic% of Ge and N, respectively. _16.7 Sb _83.3 It was found that the rise in jitter after 200 hours in the case of only the above was about 2%, but could be reduced to within 1.0%.
In the actual composition design, Ge _16.7 Sb _83.3 Sufficient recording characteristics can be obtained with only the above, but the characteristics of the recording layer material can be controlled by adding the above elements alone or in combination depending on the purpose of use.
[0020]
Example 4
An optical recording medium was prepared in the same manner as in Example 1 except that the thickness of the recording layer was changed to 3, 5, 8, 10, 15, 20, 25, and 30 nm, and after initial crystallization, The C / N ratio and the degree of modulation were evaluated in the same manner as in Example 1. The results are shown in Table 4 and FIG.
When the thickness of the recording layer was 5 to 25 nm, a modulation factor of 60% or more satisfying the DVD standard was obtained. Desirable film thickness of the recording layer is 8 to 20 nm. In this range, the degree of modulation is 65% or more, and a more stable system can be obtained.
[Table 4]

[0021]
Example 5
The optical recording medium manufactured in Example 1 was rotated at a constant linear velocity of 9 m / s, and the power density was 18 mW / μm. ² Initial crystallization was performed by irradiating the laser beam while sending it in the radial direction while moving it at 36 μm / r.
After physically peeling the bonded portion of the optical recording medium, the (environment) protective layer and the reflective layer are peeled off with an adhesive tape, and the recording layer is immersed in an organic solvent to remove the recording layer from the substrate. Peeled off and filtered. This powder was filled in a capillary, and powder X-ray diffraction measurement was performed at a wavelength of 0.419 ° using synchrotron radiation having extremely high parallelism and luminance of the incident beam.
FIG. 6 shows a powder X-ray diffraction spectrum. The main diffraction spectrum peaks were at 2θ = 6.51, 6.953, 8.021, 10.972, and 11.71 °. When the lattice spacing corresponding to each of these peaks was calculated by the following Bragg formula, d = 3.69, 3.46, 3, 2.19, and 2.06 in this order. These peaks can be indexed by a rhombohedral structure similar to the Sb structure, and it was found that the recording layer was a single phase.
Bragg's equation 2dsinθ = nλ
(D: spacing between lattice planes, n: order of reflection, λ: wavelength of X-ray)
[0022]
In the state where the bonded portion of the same optical recording medium as above was physically peeled off and the recording layer became the outermost surface, measurement was performed by In-plane X-ray diffraction (a method of measuring a lattice plane perpendicular to the substrate surface of the sample). went. [Details of this measurement method are described in The Rigaku-Denki Journal 31 (1) 2000. FIG. 7 is a schematic diagram.
The apparatus was X'pert MRD manufactured by Philips, and a copper Kα ray (wavelength λ = 1.54 °) was used as an X-ray incident light source. X-rays are incident almost parallel to the substrate surface (incident angle: 0.2 to 0.5 °), and the sample is rotated by 45 ° with the portion where the X-rays are applied as a rotation axis, and the X-ray diffraction spectrum is measured. Was performed. According to this measuring method, since the penetration depth can be suppressed to several nm by irradiating the X-ray almost parallel to the substrate surface, the crystal structure of the recording layer having a small film thickness can be accurately examined. .
The sample was set so that the X-rays could hit near the radial position of 40 mm of the optical recording medium, and the X-rays were made incident parallel to the track direction of the optical recording medium. At this time, the angle was set to 0 °, the sample was rotated by 45 ° with the portion irradiated with X-rays as a rotation axis, and spectra measured from 2θ = 20 to 70 ° are shown in FIG. 8.
[0023]
When the polycrystalline film is oriented in a specific direction, there is a relationship that the intensity of the corresponding peak is increased. The powder X-ray diffraction described above was measured in a state where the crystal orientation was removed by peeling the sample from the substrate to form a powder, and the powder X-ray diffraction and in-plane X-ray diffraction (In-plane X-ray diffraction) were used. By comparing the results of (1) and (2), the orientation of the crystal is more remarkably determined.
FIG. 9 shows the result of converting the result of powder X-ray diffraction into a wavelength λ = 1.54 °. When this is compared with the result of in-plane diffraction, the peak intensity around 2θ = 29 ° is the strongest in powder X-ray diffraction, whereas the peak at 29 ° is small in in-plane diffraction, and the number of peaks that appear is small. Become. This is because the crystal is oriented, and a lattice plane that does not satisfy the Bragg diffraction condition appears. When X-rays are incident at 90 ° with respect to the track direction, they are strongly oriented on a lattice plane with a lattice spacing d of 2.10 ° (2θ = 43.1 °).
[0024]
Next, the power density was set to 3, 5, 7, 15, 25, 40, 50, 52 mW / μm. ² Table 5 shows the state and the reflectance after the initialization when each was initialized at the optimum linear velocity. The evaluation criteria were “× (1)” when no crystal orientation was observed, “「 ”when the crystal orientation was high,“ ◎ ”when the crystal orientation was strong, and“ × ”when the film was peeled. (2) ".
[Table 5]

Linear velocity 3 to 18 m / s, power density 5 to 50 mW / μm ² The crystal orientation is observed in the range of, particularly, the linear velocity is 6 to 14 m / s, and the power density is 15 to 40 mW / μm. ² At the time, a strong orientation was observed, and accordingly, a high reflectance was obtained.
An optical recording medium having crystal orientation and high reflectivity shows good recording characteristics with a C / N ratio of 45 dB or more under recording conditions of a recording linear velocity of 10 to 35 m / s. When the change in the jitter value after storage in an environment of 85 ° C. and 85% RH was examined, the jitter value did not change even after 400 hours, and it was confirmed that the stability of the amorphous mark was good (FIG. 10).
The jitter value is a value indicating the variation of the mark edge. The smaller the jitter value is, the smaller the variation is, indicating that a good recording is possible. It has been found that when the crystallization starts from the edge of the amorphous mark in the accelerated test, the jitter value rapidly deteriorates.
The result of the accelerated test is approximately 10 years or more when the life at room temperature is roughly estimated, and the life of the optical recording medium is sufficiently guaranteed. Therefore, it was also confirmed that the above-described initialization conditions were suitable for obtaining a medium capable of high-speed recording at a recording linear velocity of 10 m / s or more, which is the object of the present invention.
[0025]
Ge target for recording layer ₁₇ Sb ₈₃ An optical recording medium was manufactured in the same manner as in Example 1 except that the above-mentioned structure was changed.
This optical recording medium was rotated at a constant linear velocity of 8 m / s, and the power density was 20 mW / μm. ² Initial crystallization was performed by irradiating the laser beam while sending it in the radial direction while moving it at 36 μm / r.
FIG. 11 shows the results of in-plane diffraction (In-plane X-ray diffraction) of the optical recording medium measured by performing the same processing as described above. From this figure, it was found that the peak diffraction intensity from the lattice spacing d (Å) = 2.09 in the direction perpendicular to the track direction was strong and the orientation was good.
This optical recording medium was subjected to 10 EOW random pattern DOWs at a recording linear velocity of 28 m / s and the same recording density as a DVD-ROM at a recording power Pw = 30 mW and an erasing power Pe = 6 mW. The degree was 63% and the reflectance was 24%. In addition, when the change of the jitter value after storing the recording medium on which the initial recording was performed under the environment of 80 ° C. and 85% RH was examined, the jitter value did not change even after 400 hours, and it was confirmed that the stability of the amorphous mark was good. Was done.
[0026]
Ag target for recording layer ₂ In ₅ Sb ₆₈ Te ₂₅ , Sb as its matrix material ₇₈ Te ₂₂ , Sb ₈₈ Te ₁₂ And In _31.7 Sb _68.3 (Comparative example above), Ga ₁₂ Sb ₈₈ (Reference example), Ge _16.7 Sb _83.3 An optical recording medium was manufactured in the same manner as in Example 1 except that the above-mentioned structure was changed.
These optical recording media were rotated at a constant linear velocity of 8 m / s, and the power density was 20 mW / μm. ² Initial crystallization was performed by irradiating the laser beam while sending it in the radial direction while moving it at 36 μm / r.
These optical recording media were subjected to powder X-ray diffraction by performing the same treatment as described above. For comparison, powder X-ray diffraction was also performed on powder Sb. The results are shown in FIG. Ag ₂ In ₅ Sb ₆₈ Te ₂₅ , Sb ₇₈ Te ₂₂ , In _31.7 Sb _68.3 Can be indexed in a cubic (tetragonal) structure and Sb ₈₈ Te ₁₂ , Ga ₁₂ Sb ₈₈ , Ge _16.7 Sb _83.3 Could be indexed by a hexagonal (hexagonal) structure similar to the Sb structure.
In order to compare the crystal structures of the materials, the results of calculating the lattice constants a (Å) and c (Å) of all the materials based on the unit cell of the hexagonal structure (FIG. 13) and the crystallization temperature Tc obtained by thermal analysis (° C.) is shown in Table 6. When the c / a ratio is 2.45, it is equivalent to a cubic structure. The crystallization temperature is such that a single film of a recording layer is formed on glass, and the temperature of the amorphous film is raised by a differential scanning calorimeter at a heating rate of 10 ° C./min. did. It can be said that the higher the crystallization temperature, the more stable the amorphous phase and the more difficult it is to crystallize.
[Table 6]

[0027]
Ag ₂ In ₅ Sb ₆₈ Te ₂₅ The system material is a material in which Ag and In are added as an additive element to the matrix material SbTe. It has been found that the crystallization speed of the material can be increased by increasing the amount of SbTe in the SbTe matrix material. It is estimated that the recording speed of 18 m / s, which is 5 times faster than the above, is the limit. The crystallization temperature of SbTe is as low as 120.5 ° C. and 79.5 ° C., whereas that of GaSb and GeSb is as high as 194.5 and 255.5 ° C., respectively. It can be seen that the storage stability of the mark is good. These phenomena can be explained from the structure of the material. The materials for which powder X-ray diffraction was measured this time can be considered to be material systems in which something is added to Sb. Although Sb alone has a high crystallization speed, it cannot be used as a material for an optical recording medium because the stability of the amorphous phase is so poor that it crystallizes immediately even at room temperature. Therefore, it is considered that the bonding force is increased by adding an element other than Sb in order to improve the stability of the amorphous phase.
FIG. 14 shows the relationship between the lattice constant a and the crystallization temperature. A material having a small lattice constant a has a strong covalent bond, and requires a large amount of energy to break the covalent bond and rearrange the network in order to thermally crystallize the amorphous phase. It is thought that there is.
[0028]
Comparative Example 1
The optical recording medium produced in Example 1 was rotated at a constant linear velocity of 2 m / s, and the power density was 4.5 mW / μm. ² Initial crystallization was performed by irradiating the laser beam while sending it in the radial direction while moving it at 36 μm / r.
In-plane diffraction (In-plane X-ray diffraction) was performed in the same manner as in Example 5, with the bonded portion of the optical recording medium physically peeled off and the recording layer being the outermost surface. That is, X-rays were incident almost parallel to the substrate surface (incident angle: 0.2 to 0.5 °), the sample was rotated by 45 °, and the X-ray diffraction spectrum was measured. FIG. 15 shows the results obtained by setting the angle when the X-rays were incident parallel to the track direction to 0 °, rotating the sample by 45 ° in increments of 45 °, and measuring up to 135 °.
When the optical recording medium on which the above initial crystallization was performed was recorded under the same conditions as in Example 1 using the same recording / reproducing apparatus as in Example 1, the reflectance was 17% and the degree of modulation was as low as 55%. This material has low orientation and small crystallinity, and therefore has a low reflectance and a small degree of modulation.
[0029]
Example 6
An LD (laser diode) having a wavelength of 660 nm and an optical system having an NA of 0.65 were used for the optical recording medium manufactured in Example 1 and a laser beam having a pulse train as shown in FIG. 3 at a recording linear velocity of 28 m / s. , Pe / Pw is set to 0.2, and the result of a recording test performed by changing Pw is shown in FIG.
The test was performed by DOWing each single mark of 3T, 6T, 8T, and 14T in the EFM + modulation, which is a DVD modulation method, ten times and monitoring the C / N ratio. The 8T mark is also plotted together with the result of another one-time recording (initial recording). The pulses used for recording were optimized for each T, and the number of pulses, the pulse width, and the width of the Pb level were optimized and used.
Ga ₁₆ Sb ₈₄ In a recording medium using as a recording material, a recording power Pw of 15 mW or more is required to secure a C / N ratio of 30 dB or more, and a recording power of about 20 mW or more is required to obtain a recording characteristic of 45 dB or more that enables more stable recording. Power Pw is required.
In the optical system used this time, the beam power is 1 / e ² Since the calculated beam diameter is about 0.9 μm, the power density of the beam at the recording power Pw required for recording is at least 20 mW / μm. ² , Preferably 30 mW / μm ² It turns out that it is necessary.
[0030]
Example 7
Using the optical recording medium manufactured in Example 1, recording speed was set to 10 m / s, 28 m / s, and 35 m / s, recording was performed using the pulse beam shown in FIG. 3, and the C / N ratio was plotted. FIG. 17 shows this. Further, the ratio of the erasing power Pe to the peak power Pw of the laser beam used for recording was optimized under the respective recording linear velocity conditions, and the power condition at which the C / N ratio became maximum was plotted against the recording linear velocity. FIG. 18 shows this.
As in the case of the sixth embodiment, the optimal number of pulses for each T was changed under each linear velocity condition. The recording is a result of a case where each T mark is recorded randomly using the EFM + modulation method.
When Pe / Pw is changed under the condition of 10 m / s recording linear velocity, the range in which the C / N ratio is good is 0.42 ≦ Pe / Pw ≦ 0.65, and in particular, the C / N ratio can be set to 50 dB. , 0.47 ≦ Pe / Pw ≦ 0.60. Further, under the condition of the recording linear velocity of 35 m / s, the range in which the C / N ratio is favorable is 0.10 ≦ Pe / Pw ≦ 0.25, and particularly, the C / N ratio can be set to 50 dB only when 0.13 ≦ Pe / Pw ≦ approximately 0.22. Since the range between the recording linear velocities of 10 m / s and 35 m / s is filled with each linear velocity condition, the range of the Pe / Pw ratio at which good recording characteristics are obtained when the recording linear velocity is 10 to 35 m / s is as follows. , 0.10 ≦ Pe / Pw ≦ 0.65, and preferably 0.13 ≦ Pe / Pw ≦ 0.60.
[0031]
【The invention's effect】
According to the first aspect of the present invention, recording / erasing is performed at the same capacity as a DVD-ROM at a linear velocity of 10 m / s or more by utilizing a reversible phase change between an amorphous phase (amorphous phase) and a crystalline phase of a recording layer. And an optical recording medium capable of performing the above.
According to the second aspect, an optical recording medium having a high C / N ratio at a recording linear velocity of 10 m / s or more can be provided.
According to the third aspect of the invention, it is possible to provide an optical recording medium capable of controlling the characteristics of the recording layer material according to the purpose of use. In particular, when Ag, Au, Cu, B, Al, In, and Mn are used, the required recording power can be reduced, and when Sn, Si, Zn, Bi, and Pb are used, the recordable linear velocity increases. When N is used, the stability of the amorphous mark can be improved.
According to the fourth aspect of the present invention, it is possible to provide an optical recording medium capable of repeatedly recording at a recording linear velocity of 4 times or more (14 m / s) of DVD.
According to the fifth aspect of the present invention, it is possible to provide an optical recording medium capable of repeatedly recording at a recording linear velocity of 8 × speed (28 m / s) or more of DVD.
According to the present inventions 6 and 7, an optical recording medium having a high modulation degree can be provided.
According to the eighth and ninth aspects of the present invention, it is possible to provide a method of manufacturing an optical recording medium capable of performing high-speed recording at a recording linear velocity of 10 m / s or more with the same capacity as a DVD-ROM.
According to the present inventions 10 to 12, it is possible to provide a sputtering target for manufacturing an optical recording medium capable of performing high-speed recording at a recording linear velocity of 10 m / s or more with the same capacity as a DVD-ROM.
According to the thirteenth aspect, it is possible to provide a recording method for an optical recording medium capable of performing stable recording.
According to the inventions 14 and 15, a recording method for an optical recording medium having a high C / N ratio at a recording linear velocity of 10 m / s or more can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic structure of a phase change type optical recording medium of the present invention.
(A) Perspective view
(B) The figure which shows typically the cross section (layer structure) of the notch part of (a).
FIG. 2 is a diagram showing a transmission electron microscope image of a recording layer after initial recording.
FIG. 3 is a diagram showing a recording strategy generally used in a rewritable optical recording medium.
FIG. 4 is a view showing a measurement result of a C / N ratio when the GeSb alloy of Example 2 is used.
FIG. 5 is a diagram showing the evaluation results of the modulation degree when the thickness of the recording layer of Example 4 was changed.
FIG. 6 is a view showing a powder X-ray diffraction spectrum of Example 5.
FIG. 7 is a diagram for explaining In-plane X-ray diffraction.
FIG. 8 is a diagram showing a spectrum of the optical recording medium of Example 5 measured by In-plane X-ray diffraction.
FIG. 9 is a view showing the result of converting the result of powder X-ray diffraction into a wavelength λ = 1.54 ° for the optical recording medium of Example 5.
FIG. 10 is a diagram showing a change in jitter value of the optical recording medium of Example 5 after storing the medium after recording in an environment of 80 ° C. and 85% RH.
FIG. 11 is a view showing a spectrum of another optical recording medium of Example 5 measured by In-plane X-ray diffraction.
FIG. 12 is a view showing the results of powder X-ray diffraction of the optical recording media of Example 5 and Comparative Example.
FIG. 13 is a diagram showing a unit cell having a hexagonal structure.
FIG. 14 is a diagram showing a relationship between a lattice constant a and a crystallization temperature.
FIG. 15 is a diagram showing a spectrum of the optical recording medium of Comparative Example 1 measured by In-plane X-ray diffraction.
FIG. 16 is a diagram showing a result of performing a recording test on the optical recording medium manufactured in Example 1.
FIG. 17 is a diagram plotting the C / N ratio when recording is performed using the optical recording medium manufactured in Example 1 while changing the recording speed.
FIG. 18 is a graph showing the power conditions under which the C / N ratio is maximized by optimizing the Pe / Pw of the laser beam used for recording under the respective recording linear velocity conditions, using the optical recording medium produced in Example 1. The figure plotted with respect to linear velocity.
[Explanation of symbols]
a Lattice constant
c lattice constant

Claims (15)

On the substrate, at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer are provided in this order, and the recording layer is formed of GeγSbδ (provided that 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, γ and δ are alloys having the composition represented by atomic%) and recording utilizing the reversible phase change between the amorphous phase (amorphous phase) and the crystalline phase of the recording layer even at a linear velocity of 10 m / s or more. -A phase-change optical recording medium characterized by being erasable. 2. The phase change type optical recording medium according to claim 1, wherein 10 ≦ γ ≦ 20 and 80 ≦ δ ≦ 90. The recording layer further contains at least one element selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Si, and N in an amount of 10 atomic% or less of the alloy. 3. The phase-change optical recording medium according to claim 1, wherein: 4. A recording / erasing method using a reversible phase change between an amorphous phase and a crystalline phase of a recording layer even at a linear velocity of 14 m / s or more. The phase-change optical recording medium according to the above. 5. The phase change type light according to claim 4, wherein recording / erasing can be performed using a reversible phase change between the amorphous phase and the crystalline phase of the recording layer even at a linear velocity of 28 m / s or more. recoding media. 6. The phase-change optical recording medium according to claim 1, wherein the thickness of the recording layer is in the range of 5 to 25 nm. 7. The optical recording medium according to claim 6, wherein the thickness of the recording layer is in the range of 8 to 20 nm. After an optical recording medium is manufactured by laminating at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer in this order on a substrate, the optical recording medium is set in a range of 3 to 18 m / s. Rotating at a constant linear velocity, and irradiating the optical recording medium with laser light having a power density of 5 to 50 mW / μm ^{2 at} a constant speed in the radial direction to perform initial crystallization. A method for manufacturing a phase-change optical recording medium according to claim 1. 9. The method according to claim 8, wherein the linear velocity of rotation of the recording medium is a constant linear velocity within a range of 6 to 14 m / s, and the power density of the laser beam is 15 to 40 mW / [mu] m < ² >. A sputtering target for producing a phase-change optical recording medium, comprising an alloy having a composition represented by GeγSbδ (where 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%). The sputtering target for manufacturing a phase-change optical recording medium according to claim 10, comprising an alloy having a composition represented by GeγSbδ (where 10 ≦ γ ≦ 20, 80 ≦ δ ≦ 90, and γ and δ are atomic%). GeγSbδ (where 5 ≦ γ ≦ 25, 75 ≦ δ ≦ 95, and γ and δ are atomic%) as a main component, and Ag, Au, Cu, B, 10 atomic% or less of the alloy. A sputtering target for manufacturing a phase-change optical recording medium, comprising at least one element selected from the group consisting of Al, In, Mn, Sn, Zn, Bi, Pb, Si, and N. When the recording linear velocity is 28 m / s, a light beam for causing an optical change in the recording layer material is formed by a single pulse or a plurality of pulse trains, and the power density of the pulse beam at the recording power Pw is 20 mW / s. The recording method for a phase-change optical recording medium according to claim 1, wherein the thickness is at least ² μm. The recording linear velocity is 10 to 35 m / s, the light beam irradiated on the medium is formed by a single pulse or a plurality of pulse trains, and the ratio between the erasing power Pe and the recording power Pw is 0.10 ≦ Pe / Pw ≦ 8. The recording method for a phase-change optical recording medium according to claim 1, wherein the setting is made to be 0.65. 15. The recording method for a phase change type optical recording medium according to claim 14, wherein the setting is made so that 0.13 ≦ Pe / Pw ≦ 0.60.

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