JP4248323B2 - Phase change optical recording medium, manufacturing method thereof, and recording method - Google Patents

Description

【００１８】
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、ＧａαＳｂβ（α、βは原子％）として、５≦α≦２０、８０≦β≦９５の範囲がよい。
特許文献２の詳細な説明において、「Ｇａの組成は２０％以下になると気泡が原因と思われる膜の盛り上がりが出来るため、反射率の変化するレベルが不安定になり、実用上問題がある。」としており、本発明の光記録媒体と特許文献２の光記録媒体は本質的に異なるものであることが確認された。
この事実は、本発明のようにアモルファス−結晶間の相変化を用いる場合には、良好な記録特性が得られる組成範囲が、特許文献２に開示される結晶−結晶間の相変化を用いる場合と明らかに異なることを示している。
【００１９】
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ＧａＳｂ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】

【００２０】
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ＧａＳｂ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、ＧａαＳｂβ（５≦α≦２０、８０≦β≦９５、α、β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、Ｇａ_３Ｓｂ_９７ではアモルファス化することができず、Ｇａ_２５Ｓｂ_７５では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、５≦α≦１５、８５≦β≦９５であることが望ましい。
【００２１】
実施例３
記録層用の合金ターゲットを、Ｇａ_１２Ｓｂ_８８に対しＡｇ、Ｉｎ、Ｓｎ、Ｇｅ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４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ったところ、Ａｇ又はＩｎを添加した合金では、２８ｍ／ｓの記録速度条件において、Ｇａ_１２Ｓｂ_８８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を添加した合金で約１０％、Ｉｎを添加した合金で約１３％減少させることができた。但し、記録可能な線速範囲の判定基準をＣ／Ｎ比で４５ｄＢ以上として、Ｇａ_１２Ｓｂ_８８のみの場合は３６〜３８ｍ／ｓまで記録可能であったが、Ａｇを添加した合金では１０％低下し、Ｉｎを添加した合金では５％以内の低下が見られた。
Ｓｎを添加した合金では、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Ｇａ_１２Ｓｂ_８８のみの場合とほぼ同じであったが、記録可能な線速範囲は約７％早くなった。
Ｇｅを添加した合金では、記録線速範囲が約１０％低下し、記録パワーは約５％高くする必要があったが、８０℃８５％ＲＨの高温高湿下の保存信頼性テストを行ったところ、Ｇａ_１２Ｓｂ_８８のみの場合の５００時間後のジッタ上昇が約１．５％であったのに対し、０．５％以内に低減できることが分った。
同様に、Ｇａ_１２Ｓｂ_８８に対する添加元素をＡｕ、Ｃｕ、Ｂ、Ａｌ、Ｍｎ５原子％に変えた光記録媒体を作製したところ、ＡｇやＩｎと同様に記録パワーを下げることができた。また、Ｇａ_１２Ｓｂ_８８に対する添加元素をＺｎ、Ｓｉ、Ｂｉ、Ｐｂ５原子％に変えた光記録媒体を作製したところ、Ｓｎと同様に記録可能な線速が速くなった。また、Ｇａ_１２Ｓｂ_８８に対する添加元素をＮ２原子％に変えた光記録媒体を作製したところ、Ｇｅと同様にアモルファスマークの安定性が良くなった。
実際の組成設計においては、ＧａＳｂのみでも充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。
【００２２】
更に、Ｇａ_１２Ｓｂ_８８にＩｎを添加した合金を用いてＩｎの適正な添加量を評価したところ、１０原子％を超えると、記録線速範囲が１０ｍ／ｓ以下になってしまい、８０℃８５％ＲＨの高温高湿下の保存信頼性テストを行うと反射率変化が著しく悪化してしまうという不具合が見られ、本発明の目的である高速記録が出来なくなることが分った。この傾向はＡｇ、Ａｕ、Ｃｕ、Ｂ、Ａｌ、Ｉｎ、Ｍｎを添加した合金でも同様である。また、Ｓｎを添加した合金では、添加量が１０％を超えると５％添加した合金に比べて記録パワーを３０％大きくしても同じ変調度を得られなかった。このような場合には現状で想定される記録システムの最大記録パワーＰｗを用いても十分な信号が得られない恐れがある。この傾向はＺｎ、Ｂｉ、Ｐｂを添加した合金でも同様である。また、Ｇｅを添加した合金では添加量が１０％を超えると、記録線速範囲が、Ｉｎを添加した合金と同様に１０ｍ／ｓ以下となってしまうことと、記録パワーがＧａ_１２Ｓｂ_８８のみの場合に比べて３０％以上多く必要となった。
なお、Ｎは、記録層のスパッタ時の気相反応により合金中に取り込まれるが、５％以上の配合量とすることは困難であった。
【００２３】
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】

【００２４】
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＝６．３６、６．８７５、７．８０４、１０．７３７、１１．３３４°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＝３．７８、３．４９、３．０８、２．２４、２．１２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）
【００２５】
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。
【００２６】
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２．１２Å（２θ＝４２．６°）の格子面に強く配向している。
【００２７】
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、３００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。
【００２８】
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）、Ｇｅ_１６．７Ｓｂ_８３．３（参考例）、Ｇａ_１２Ｓｂ_８８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１１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１２）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】

【００２９】
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１３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。
【００３０】
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１４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。
【００３１】
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１５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_１２Ｓｂ_８８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。
【００３２】
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１６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１７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。
【００３３】
【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、Ｇｅ、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ＧａＳｂ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１２】ｈｅｘａｇｏｎａｌ構造の単位格子を示す図。
【図１３】格子定数ａと結晶化温度の関係を示す図。
【図１４】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１５】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１６】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１７】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]
BACKGROUND OF THE INVENTION
The present invention relates to a phase-change optical recording medium capable of optically changing a recording layer material by irradiating a light beam, recording and reproducing information, and rewritable, a manufacturing method thereof, and a recording method thereof. Is.
[0002]
[Prior art]
Patent Document 1 discloses that a recording material in which a metal or 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 crystallization speed is too high 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 slowed down, and information recording using a phase transition between crystal and amorphous can be performed. .
However, Ga ₅₀ Sb ₅₀ (Atom%) Alloys near the composition have a high melting point of 710 ° C. and a crystallization temperature of 350 ° C., and there is not enough power in the commercially available initialization devices, so even if initial crystallization is attempted, it is uniform within the circumference. A crystal state cannot be obtained and the reflectance becomes non-uniform. If a mark is recorded in a state where the reflectance is non-uniform, the noise of the signal is large, and it is difficult to record a signal at a high density, particularly as in a DVD.
[0003]
Patent Document 2 discloses a phase change 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 transmit information. Recording is performed, and the degree of modulation is 29% at most, which is problematic in practical use. In addition, “If Ga is less than 20%, the film may be swelled due to the occurrence of bubbles in the laser light irradiation part, so that the level at which the reflectivity changes becomes unstable, causing a problem in practical use. There is a description.
Furthermore, since the phase change between crystals uses the difference in reflectance due to the difference in crystal grain size, it is not suitable for high-density information recording that requires recording of minute marks. Information cannot be recorded at the same density as the DVD-ROM.
Non-Patent Document 1 describes the knowledge about an optical recording medium using a GeSb thin film capable of phase change at an ultra-high speed. However, the orientation of crystals that are regarded as important in the present invention is not observed in the electron diffraction pattern of FIG. In addition, the degree of modulation between the crystalline phase and the amorphous phase at this time is 15 to 20%, which is problematic in practice.
[0004]
Patent Document 3 discloses a phase change using a material whose main component is an alloy of (SbxGe1-x) 1-yIny (provided that 0.65 ≦ x ≦ 0.95, 0 <y ≦ 0.2) for the recording layer. Type optical recording media are disclosed.
However, the initialization conditions are 2.6 mW / μm in terms of laser power density. ² There is only a description that initial crystallization has occurred to a certain extent, and nothing is described about the high initialization laser power density required in the present invention.
It is presumed that a medium having a low crystal orientation and a low crystal reflectance can be obtained at a power density as low as described above. Also, the disclosed recording linear velocity range is a low linear velocity of 2.4 to 9.6 m / s, and no description is given regarding the correspondence to the high linear velocity recording as in the present invention.
[0005]
[Patent Document 1]
U.S. Pat. No. 4,818,666
[Patent Document 2]
JP 61-168145 A
[Patent Document 3]
JP 2001-39031 A
[Non-Patent Document 1]
“Appl. Phys. Lett.” 60 (25), 22 June 1992, p 3123-3125.
[0006]
[Problems to be solved by the invention]
The present invention enables recording / erasing by using a reversible phase change between an amorphous phase (amorphous phase) and a crystalline phase of a recording layer at a linear velocity of 10 m / s or more with the same capacity as a DVD-ROM. Another object of the present invention is to provide a phase change type optical recording medium having a large modulation degree and good stability of amorphous marks, a manufacturing method thereof, and a recording method.
[0007]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 15).
1) At least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer are provided on the substrate in this order, and the recording layer has GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atomic%) (provided that Including Te Recording and erasing utilizing 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. Phase change type optical recording medium.
2) The phase change optical recording medium according to 1), wherein 5 ≦ α ≦ 15 and 85 ≦ β ≦ 95.
3) The recording layer further comprises at least one selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Ge, Si, and N of 10 atomic% or less of the alloy. The phase change optical recording medium according to 1) or 2), which contains an element.
4) Any one of 1) to 3), wherein recording / erasing utilizing 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 claim 1.
5) The phase change type according to 4), wherein recording and erasing utilizing reversible phase change between the amorphous phase and the crystalline phase of the recording layer is possible even at a linear velocity of 28 m / s or more. Optical recording medium.
6) The phase change optical recording medium as described in any one of 1) to 5) above, 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 recording layer has a thickness in the range of 8 to 20 nm.
8) On the 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, and then the optical recording medium is 3 to 18 m / s. It is rotated at a constant linear velocity within the range, and the power density is 5 to 50 mW / μm. ² The phase-change optical recording medium according to any one of 1) to 7), wherein initial crystallization is performed by irradiating the optical recording medium while moving the laser beam at a constant speed in the radial direction. 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 8) The production method according to 8).
10) An alloy having a composition represented by GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atomic%) (where, Including Te A sputtering target for producing a phase change optical recording medium.
11) GaαSbβ (where 5 ≦ α ≦ 15, 85 ≦ β ≦ 95, where α and β are atomic%) (provided that Including Te A sputtering target for producing a phase change optical recording medium according to 10).
12) Mainly an alloy having a composition represented by GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atomic%) (where, Including Te Including at least one element selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Ge, Si, and N of 10 atomic% or less of the alloy) A sputtering target for producing a phase change optical recording medium.
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 20mW / μm ² The recording method for a phase change optical recording medium according to any one of 1) to 7), characterized in that it is as described above.
14) The recording linear velocity is set to 10 to 35 m / s, the light beam applied to the medium is formed by a single pulse or a plurality of pulse trains, and the ratio of the erasing power Pe to the recording power Pw is 0.10 ≦ Pe / The recording method for a phase change 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]
DETAILED DESCRIPTION OF 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 in this order on a substrate. This basic structure is shown in FIG. FIG. 1A is a perspective view of the medium, and FIG. 1B schematically shows a cross section (layer structure) of the notch portion of FIG.
In the first aspect of the invention, the description “recording / erasing using a reversible phase change between an amorphous phase (amorphous phase) and a crystalline phase of a recording layer is possible even at a linear velocity of 10 m / s or more” This means that it has the ability to record / erase at a linear velocity of 10 m / s or higher, and it may or may not have a recording / erasing capability at a linear velocity of less than 10 m / s.
Generally, glass, ceramics, or resin is used as the substrate material, but a resin substrate is preferable 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 fluorine resin, and the like, and a polycarbonate resin is preferable from the viewpoint of processability and optical characteristics. Further, the shape of the substrate may be any of a disk shape, a card shape, a sheet shape, and the like. Arbitrary things, such as 1.2 mm, 0.6 mm, and 0.1 mm, can be used for the thickness of a board | substrate.
[0009]
As materials used for the first intermediate layer and the second intermediate layer, SiO 2 ₂ TiO ₂ , ZnO, ZrO ₂ Metal oxide such as AlN, Si ₃ N ₄ Nitrides such as TiN; ZnS, In ₂ S ₃ , TaS ₃ Sulfides such as SiC; carbides such as SiC, TiC and ZrC; or a mixture thereof.
The first intermediate layer plays a role of protecting the recording layer so that impurities such as moisture are not mixed into 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 hardly permeates moisture, has good heat resistance, has a low absorption rate k, and a high refractive index n is preferable. The film thickness of the first intermediate layer is 40 to 500 nm, preferably 60 to 200 nm. If the thickness is less than 40 nm, the substrate is also heated at the same time when the recording layer is heated, so that the substrate is deformed. If the thickness exceeds 500 nm, peeling is likely to occur at the interface between the substrate and the first intermediate layer.
[0010]
The second intermediate layer serves to adjust the thermal characteristics of the recording layer. When the thickness of the second intermediate layer is reduced, heat is likely to escape, and when the thickness is increased, escape is difficult. The film thickness of the second intermediate layer is 5 to 100 nm, preferably 5 to 20 nm. If the thickness exceeds 100 nm, the heat is too high to form an amorphous phase, and if it is less than 5 nm, the recording sensitivity is deteriorated.
When speeding up a phase-change optical recording medium that can be rewritten using the phase change of the crystal-amorphous phase, a recording material with a high crystallization speed suitable for the recording linear velocity is used. There is a problem that the crystallization is easy to proceed and the mark becomes small and the modulation degree becomes small. For this reason, in order to shorten the recrystallization time as the recording material having a higher crystallization speed is used, it is preferable to make the second intermediate layer thin and to have a rapid cooling structure in which heat can easily escape. Further, the second intermediate layer may be composed of two or more layers so that heat can escape more easily.
[0011]
For the recording layer, an alloy having a composition represented by GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atomic%) is used (where, Including Te Except stuff). Preferred composition ranges are 5 ≦ α ≦ 15 and 85 ≦ β ≦ 95. Within this composition range, recording / erasing can be performed using a 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, and the degree of modulation is large. Thus, a phase change optical recording medium having good stability of amorphous marks can be obtained.
The AgInSbTe-based material used so far for CD-RW and DVD + RW is a material in which Ag and In are added as additive elements to the matrix phase material SbTe. Since the crystallization temperature of SbTe is as low as 120 ° C. and the amount of Sb is increased, the crystallization temperature is lowered, so that recording at 18 m / s, which is 5 times faster than DVD, is the limit. On the other hand, GaSb of the present invention has a high crystallization temperature of 194.5 ° C., and the stability of the amorphous mark is good even in a composition range where the crystallization speed is fast. This is because the GaSb lattice constant a is smaller than that of SbTe, so the force of the covalent bond is strong, and in order to thermally crystallize the amorphous phase, a large amount of energy is required to break the covalent bond and recombine the network. Because.
[0012]
Furthermore, at least one element selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Ge, Si, and N of 10 atomic% or less of the total alloy is included. By adding, it is possible to improve physical properties such as recording power, recordable linear velocity, and stability of amorphous marks.
If the film thickness of the recording layer is in the range of 5 to 25 nm, a modulation degree of 60% or more that satisfies the DVD standard can be obtained. Further, the desirable film thickness is 8 to 20 nm, and in this range, the modulation degree is 65% or more, and a more stable system can be obtained.
Various metals can be used for the reflective layer, but metal materials such as Al, Ag, Cu, and Au, or alloys obtained by adding Ti, Cr, Si, Pd, Cu, In, Mn, and the like to them are preferable. For high-speed recording, Ag, Cu, and Au, which have a particularly high thermal conductivity, are preferable. As a result, a rapid cooling structure in which heat can easily escape is obtained, so that a high degree of modulation can be obtained. The thickness of the reflective layer is preferably 60 to 300 nm. If the thickness is less than 60 nm, the heat dissipation effect cannot be obtained, and it is difficult to form an amorphization. If the thickness exceeds 300 nm, interface peeling tends to occur.
[0013]
The 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 the substrate, it is rotated at a constant linear velocity within a range of 3 to 18 m / s, and 5 to 50 mW / μm. ² Initial crystallization is performed by irradiating a laser beam having a power density of 1 mm while moving it at a constant speed in the radial direction. Preferred rotational linear velocities and power densities are 6-14 m / s and 15-40 mW / μm. ² It is.
When the initial crystallization is performed under the conditions of the present invention, a crystal having a strong orientation is obtained, and accordingly, an optical recording medium having a high reflectance can be provided.
In the recording method of the phase change optical recording medium of the present invention, 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. In addition, the power density at the recording power Pw of the pulse beam is 20 mW / μm. ² The above is preferable. This recording method enables stable recording at 28 m / s, which is equivalent to DVD 8 × speed.
Further, the recording linear velocity is set to 10 to 35 m / s, and the light beam applied to the medium is formed by a single pulse or a plurality of pulse trains, and the ratio of the erasing power Pe to the recording power Pw is 0.10 ≦ Pe / It is preferable to set so that Pw ≦ 0.65. A more preferable range is 0.13 ≦ Pe / Pw ≦ 0.60. By setting this recording condition, recording with a high C / N ratio can be performed at a recording linear velocity of 10 m / s or more.
[0014]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these Examples.
[0015]
Example 1
On a polycarbonate substrate having a thickness of 0.6 mm and a diameter of 120 mmφ having a guide groove with a track pitch of 0.74 μm and a groove depth of 400 mm, SiO 2 is formed by sputtering. ₂ 20 mol% ZnS-SiO ₂ Using a mixed target, the first intermediate layer is 75 nm thick, Ga ₁₂ Sb ₈₈ (Atom%) Recording layer 16 nm thick using alloy target, second intermediate layer 14 nm thick using the same target as the first intermediate layer, 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 preliminarily weighed and heated and melted in a glass ampoule, and then taken out and pulverized by a pulverizer. 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. For the ICP emission spectroscopic analysis method, a sequential type ICP emission spectroscopic analyzer SPS4000 manufactured by Seiko Instruments Inc. was used.
In the examples and comparative examples described later, the alloy composition of the recording layer and the alloy composition of the sputtering target are the same.
Next, a protective layer made of an acrylic resin is provided on the reflective layer by a spin coat 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 reflective layer with an ultraviolet curable resin. An example optical recording medium was prepared.
This optical recording medium is rotated at a constant linear velocity of 3 m / s, and the power density is 8 mW / μm. ² The initial crystallization was carried out by irradiating the laser beam in the radial direction while moving the laser beam at 36 μm / r.
[0016]
Recording and reproduction were performed on the optical recording medium using a pickup having a wavelength of 660 nm and NA of 0.65. Under the recording conditions of a recording linear velocity of 17 m / s, a recording linear density of 0.267 μm / bit having the same capacity as a DVD-ROM, a recording power Pw = 20 mW, and an erasing power Pe = 7 mW, the EFM + modulation method, which is a DVD modulation method, 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 with a short length in the laser beam scanning direction of about 0.4 .mu.m and long ones of about 1.8 .mu.m (gray portions where black and white contrast cannot be seen in the figure) are randomly. It was observed that it was recorded. As a result of examining the gray part by electron diffraction, it was a halo pattern indicating an amorphous phase. In the electron diffraction of the portion where the contrast between black and white is clear, a spot indicating a crystalline phase was observed.
In addition, when the recording layer after direct overwrite (DOW) 10 times was observed with a transmission electron microscope image, an image similar to the initial recording was observed, and it was confirmed that repeated recording could be performed by the phase change between the amorphous phase and the crystalline phase. It was done.
[0017]
In the same manner as described above, an optical recording medium with only the composition of the recording layer changed was produced, and the amorphous phase and the crystalline phase were confirmed by transmission electron microscopic images after initial recording at a recording linear velocity of 10 m / s and after 10 recordings of DOW. It was observed whether it was formed.
Table 1 shows the alloy composition and results. “◯” in the table indicates that a crystalline phase and an amorphous phase were observed. In “× (1)”, an amorphous phase was not observed under any recording condition. This is because the crystallization speed of the material is too high, and sufficient quenching conditions cannot be created within the range of recording conditions that can be set with the current recording apparatus, and all the materials are crystallized. Further, in “× (2)”, although an amorphous phase was observed, an amorphous phase was originally formed in a space portion that should be a crystalline phase.
[Table 1]

[0018]
In a rewritable optical recording medium, recording / erasing is generally performed by a recording strategy as shown in FIG. Normally, the recording power Pw (mW), the erasing power Pe, and the bias power Pb are three values from the higher power, and the recording layer is rapidly cooled by irradiating a pulse that suddenly decreases the power from Pw to Pb, thereby causing the amorphous phase. The recording layer is gradually cooled by irradiating with a constant power of Pe to form a space (crystal phase). The reason why the amorphous phase is formed in the space portion that should originally become the crystal phase is that the recording linear velocity is too high with respect to the crystallization speed of the material.
From these results, the alloy composition of the recording layer is preferably in the range of 5 ≦ α ≦ 20 and 80 ≦ β ≦ 95 as GaαSbβ (α and β are atomic%).
In the detailed description of Patent Document 2, “If the composition of Ga is 20% or less, the film that is thought to be caused by bubbles can swell, and the level at which the reflectance changes becomes unstable, causing a problem in practical use. It was confirmed that the optical recording medium of the present invention and the optical recording medium of Patent Document 2 are essentially different.
The fact is that when the phase change between amorphous and crystal is used as in the present invention, the composition range in which good recording characteristics can be obtained uses the phase change between crystal and crystal disclosed in Patent Document 2. It is clearly different.
[0019]
Example 2
An optical recording medium was produced and initially crystallized in the same manner as in Example 1 except that the recording layer alloy target was changed to a GaSb alloy having the same composition as the recording layer composition shown in Table 2.
C / N ratio when 3T was overwritten 10 times under the same recording conditions as in Example 1 for these optical recording media [noise (N) level and signal intensity (C: carrier) using spectrum analyzer] Are measured 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]

[0020]
Further, an optical recording medium was produced and initially crystallized in the same manner as in Example 1 except that the alloy target for the recording layer was changed to a GaSb alloy having the same composition as the recording layer composition shown in Table 3.
With respect to 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 10, 14, 28, and 35 m / s [spectrum analyzer. Table 3 shows the measurement of the ratio between the noise (N) level and the signal intensity (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 GaαSbβ (5 ≦ α ≦ 20, 80 ≦ β ≦ 95, where α and β are atomic%). However, Ga ₃ Sb ₉₇ Can not be amorphized, Ga ₂₅ Sb ₇₅ It was not possible to record repeatedly.
In order to reliably obtain a stable system with a C / N ratio of 45 dB or more, it is desirable that 5 ≦ α ≦ 15 and 85 ≦ β ≦ 95.
[0021]
Example 3
Alloy target for recording layer is Ga ₁₂ Sb ₈₈ On the other hand, an optical recording medium was produced and initially crystallized in the same manner as in Example 1 except that the alloy was changed to an alloy containing 5 atomic% of Ag, In, Sn, and Ge.
When the recording test was performed on the obtained four types of optical recording media in the same manner as in Example 1, the alloy to which Ag or In was added had Ga under the recording speed condition of 28 m / s. ₁₂ Sb ₈₈ In this case, the recording power required to obtain the same degree of modulation as that recorded at Pw = 30 mW could be reduced by about 10% for the alloy added with Ag and about 13% for the alloy added with In. . However, the criterion for the recordable linear velocity range is set to 45 dB or more in the C / N ratio, and Ga ₁₂ Sb ₈₈ In the case of only No. 1, it was possible to record up to 36 to 38 m / s. However, the alloy added with Ag was reduced by 10%, and the alloy added with In was reduced within 5%.
In the alloy added with Sn, the recording power at which the same degree of modulation can be obtained under the recording speed condition of 28 m / s is Ga. ₁₂ Sb ₈₈ However, the recordable linear velocity range was about 7% faster.
In the alloy with Ge added, the recording linear velocity range decreased by about 10% and the recording power had to be increased by about 5%. However, a storage reliability test at 80 ° C. and 85% RH under high temperature and high humidity was performed. However, Ga ₁₂ Sb ₈₈ It was found that the jitter increase after 500 hours in the case of only No. 1 was about 1.5%, but could be reduced within 0.5%.
Similarly, Ga ₁₂ Sb ₈₈ When an optical recording medium was prepared by changing the additive element to Au, Cu, B, Al, and Mn at 5 atomic%, the recording power could be lowered as in the case of Ag and In. Ga ₁₂ Sb ₈₈ When an optical recording medium was produced in which the additive element for Zn was changed to Zn, Si, Bi, and Pb 5 atomic%, the linear velocity that could be recorded was increased in the same manner as Sn. Ga ₁₂ Sb ₈₈ When an optical recording medium in which the additive element with respect to N2 was changed to N2 atomic% was produced, the stability of the amorphous mark was improved as in the case of Ge.
In actual composition design, sufficient recording characteristics can be obtained with GaSb alone, 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.
[0022]
Furthermore, Ga ₁₂ Sb ₈₈ When an appropriate addition amount of In was evaluated using an alloy added with In, if exceeding 10 atomic%, the recording linear velocity range became 10 m / s or less, and high temperature and high humidity of 80 ° C. and 85% RH. When the following storage reliability test was performed, it was found that the change in reflectance was remarkably deteriorated, and high-speed recording, which is the object of the present invention, could not be performed. This tendency is the same for alloys added with Ag, Au, Cu, B, Al, In, and Mn. Further, in the alloy added with Sn, when the added amount exceeds 10%, the same degree of modulation could not be obtained even when the recording power was increased by 30% compared to the alloy added with 5%. In such a case, there is a possibility that a sufficient signal cannot be obtained even if the maximum recording power Pw of the recording system assumed at present is used. This tendency is the same for alloys to which Zn, Bi, and Pb are added. In addition, when the addition amount exceeds 10% in the alloy to which Ge is added, the recording linear velocity range becomes 10 m / s or less like the alloy to which In is added, and the recording power is Ga. ₁₂ Sb ₈₈ More than 30% more than the case of only the case.
Note that N is taken into the alloy by a gas phase reaction during sputtering of the recording layer, but it has been difficult to achieve a compounding amount of 5% or more.
[0023]
Example 4
An optical recording medium was prepared in the same manner as in Example 1 except that the film thickness of the recording layer was changed to 3, 5, 8, 10, 15, 20, 25, and 30 nm. In the same manner as in Example 1, the C / N ratio and the modulation degree were evaluated. The results are shown in Table 4 and FIG.
When the film thickness of the recording layer was 5 to 25 nm, a modulation degree of 60% or more satisfying the DVD standard was obtained. The desirable film thickness of the recording layer is 8 to 20 nm. In this range, the modulation degree is 65% or more, and a more stable system can be obtained.
[Table 4]

[0024]
Example 5
The optical recording medium produced in Example 1 was rotated at a constant linear velocity of 9 m / s, and the power density was 18 mW / μm. ² The initial crystallization was carried out by irradiating the laser beam in the radial direction while moving the laser beam at 36 μm / r.
After physically peeling off the bonded portion of this optical recording medium, the (environmental) protective layer and the reflective layer are peeled off with an adhesive tape, and the substrate on which the recording layer remains is immersed in an organic solvent to remove the recording layer from the substrate. Stripped and filtered. The powder was filled in a capillary, and powder X-ray diffraction measurement was performed at a wavelength of 0.419 mm using radiation light with extremely high parallelism and brightness of the incident beam.
FIG. 6 shows a powder X-ray diffraction spectrum. The main diffraction spectrum peaks were 2θ = 6.36, 6.875, 7.804, 10.737, and 11.334 °. When the plane spacing of the lattice plane corresponding to each of these peaks was calculated according to the following Bragg equation, d = 3.78, 3.49, 3.08, 2.24, 2.12. 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 2 d sin θ = nλ
(D: interval between lattice planes, n: order of reflection, λ: wavelength of X-ray)
[0025]
Measured by In-plane X-ray diffraction (method of measuring a lattice plane perpendicular to the substrate surface of the sample) with the recording layer physically peeled off from the bonded portion of the same optical recording medium as described above. went. [Details of this measurement method are described in The Rigaku-Denki Journal 31 (1) 2000]. FIG. 7 shows a schematic diagram.
The apparatus used was X'pert MRD manufactured by Phillips, and copper Kα ray (wavelength λ = 1.54 mm) 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 ° about the portion where the X-rays hit as a rotation axis, and the X-ray diffraction spectrum is measured. Was done. According to this measurement method, since the penetration depth can be suppressed to several nm by making X-rays incident almost parallel to the substrate surface, the crystal structure of the thin recording layer can be accurately examined. .
A sample was set so that X-rays hit the vicinity of a radial position of 40 mm of the optical recording medium, and X-rays were incident parallel to the track direction of the optical recording medium. FIG. 8 shows a spectrum obtained by rotating the sample by 45 ° with the angle at this time set to 0 °, and the portion where the X-ray hits as the rotation axis, and measuring from 2θ = 20 to 70 °.
[0026]
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 in which the orientation of the crystal was removed by peeling the sample from the substrate to form powder, and the powder X-ray diffraction and in-plane diffraction (In-plane X-ray diffraction) ), The orientation of the crystal can be recognized more remarkably.
The result of converting the result of the powder X-ray diffraction into the wavelength λ = 1.54 mm is shown in FIG. When this is compared with the results of in-plane diffraction, the peak intensity around 2θ = 29 ° is the strongest in powder X-ray diffraction, whereas the peak at 29 ° is smaller 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 the lattice plane with a lattice spacing d of 2.12 mm (2θ = 42.6 °).
[0027]
Next, the power density is 3, 5, 7, 15, 25, 40, 50, 52 mW / μm. ² Table 5 shows the state after the initialization and the reflectivity when initialized at the optimum linear velocity. The evaluation criteria are “× (1)” when no crystal orientation is observed, “◯” when there is crystal orientation, “◎” when the crystal orientation is strong, “×” when film peeling occurs. (2) ".
[Table 5]

Line speed 3-18 m / s, power density 5-50 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 In this case, a strong orientation was observed, and a high reflectance was obtained accordingly.
An optical recording medium with crystal orientation and high reflectance exhibits 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 the environment of 85 ° C. and 85% RH was examined, it was confirmed that the jitter value did not change even after 300 hours and the stability of the amorphous mark was good (FIG. 10).
The jitter value is a value indicating the variation of the mark edge, and the smaller the value, the smaller the variation and the better the recording. It is known that when crystallization starts from the edge of the amorphous mark by the acceleration test, the jitter value deteriorates rapidly.
If the result of the acceleration test is roughly estimated as the lifetime at room temperature, it becomes 10 years or more, and the lifetime of the optical recording medium is sufficiently guaranteed. Therefore, it was confirmed that the above initialization conditions are suitable for obtaining a medium capable of high-speed recording at a recording linear velocity of 10 m / s or more, which is an object of the present invention.
[0028]
Alloy target for recording layer is Ag ₂ In ₅ Sb ₆₈ Te ₂₅ , Sb as the matrix material ₇₈ Te ₂₂ , Sb ₈₈ Te ₁₂ And In _31.7 Sb _68.3 (Comparative example above), Ge _16.7 Sb _83.3 (Reference example), Ga ₁₂ Sb ₈₈ An optical recording medium was fabricated in the same manner as in Example 1 except that the point was changed to.
These optical recording media are rotated at a constant linear velocity of 8 m / s, and the power density is 20 mW / μm. ² The initial crystallization was carried out by irradiating the laser beam in the radial direction while moving the laser beam at 36 μm / r.
These optical recording media were subjected to the same treatment as described above and subjected to powder X-ray diffraction. For comparison, powder X-ray diffraction was also performed on the powder Sb. The results are summarized in FIG. Ag ₂ In ₅ Sb ₆₈ Te ₂₅ , Sb ₇₈ Te ₂₂ , In _31.7 Sb _68.3 Each peak of can be indexed with a cubic structure and Sb ₈₈ Te ₁₂ , Ga ₁₂ Sb ₈₈ , Ge _16.7 Sb _83.3 Could be indexed with a hexagonal structure similar to the Sb structure.
In order to compare the crystal structures of the materials, the crystallization temperature Tc obtained by calculating the lattice constants a (Å) and c (Å) with reference to the unit cell (FIG. 12) of the hexagonal structure and the thermal analysis for all materials. (° C.) is shown in Table 6. When the c / a ratio is 2.45, it is equivalent to the cubic structure. The crystallization temperature is obtained by forming a single recording layer on glass and heating the amorphous film with 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 harder it is to crystallize.
[Table 6]

[0029]
Ag ₂ In ₅ Sb ₆₈ Te ₂₅ The system material is a material in which Ag and In are added as additive elements to the matrix phase material SbTe. It has been found that the crystallization speed of the material can be increased by increasing the amount of SbTe of the SbTe matrix material, but the material system with increased Sb has the disadvantage that the amorphous phase crystallizes even at low temperatures. It is estimated that 18 m / s recording, which is 5 times the speed, is the limit. Compared to the low crystallization temperatures of SbTe, 120.5 ° C and 79.5 ° C, GaSb and GeSb are 194.5 and 255.5 ° C, respectively, and the amorphous phase is very difficult to crystallize. 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 as a material system 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, in order to improve the stability of the amorphous phase, it is considered that the bonding force is strengthened by adding an element other than Sb.
The relationship between the lattice constant a and the crystallization temperature is shown in FIG. 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 recombine the network in order to thermally crystallize the amorphous phase. It is thought that there is.
[0030]
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 The initial crystallization was carried out by irradiating the laser beam in the radial direction while moving the laser beam at 36 μm / r.
In-plane diffraction (In-plane X-ray diffraction) was performed in the same manner as in Example 5 in a state where the bonded portion of the optical recording medium was physically peeled off and the recording layer became 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 45 °, and the X-ray diffraction spectrum was measured. FIG. 14 shows the results of measuring up to 135 ° by rotating the sample by 45 ° in increments of 0 ° when X-rays are incident in parallel to the track direction.
The optical recording medium subjected to the above initial crystallization was recorded under the same conditions as in Example 1 using the same recording / reproducing apparatus as in Example 1. As a result, the reflectance was as low as 17% and the modulation factor was as low as 55%. Since this material has low orientation and poor crystallinity, the reflectivity is low and the degree of modulation is small.
[0031]
Example 6
For the optical recording medium manufactured in Example 1, an LD (laser diode) with a wavelength of 660 nm and an optical system with NA of 0.65 were used, and at a recording linear velocity of 28 m / s, a pulse train laser beam as shown in FIG. FIG. 15 shows the result of the recording test performed by changing Pe / Pw to 0.2 and changing Pw.
The test was carried out by monitoring a C / N ratio of 10 times each of a single mark of 3T, 6T, 8T, and 14T in EFM + modulation which is a DVD modulation method. The 8T mark was also plotted together with the results when recording was performed only once (initial recording). The pulses used for recording were optimized for each T, and the number of pulses, the pulse width, and the Pb level width were optimized.
Ga ₁₂ Sb ₈₈ In a recording medium using a recording material, the recording power Pw is 15 mW or more to ensure a C / N ratio of 30 dB or more, and a recording characteristic 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 microns from the calculation, the power density of the beam at the recording power Pw required for recording is at least 20 mW / μm. ² , Preferably 30mW / μm ² It turns out that this is necessary.
[0032]
Example 7
Using the optical recording medium produced in Example 1, recording speeds were 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. This is shown in FIG. Further, the ratio of the erasing power Pe and the peak power Pw of the laser beam used for recording was optimized under the respective recording linear velocity conditions, and the power condition that maximized the C / N ratio was plotted against the recording linear velocity. This is shown in FIG.
As in Example 6, the number of pulses for each T was changed according to the respective linear velocity conditions, and the optimum number was used. The recording is a result of recording each T mark at random using an EFM + modulation system.
When Pe / Pw is changed under the recording linear velocity condition of 10 m / s, the range where the C / N ratio is good is 0.42 ≦ Pe / Pw ≦ 0.65, and in particular, the C / N ratio can be 50 dB. 0.47 ≦ Pe / Pw ≦ 0.60. Further, in the 35 m / s recording linear velocity condition, the range where the C / N ratio is good is 0.10 ≦ Pe / Pw ≦ 0.25, and in particular, the C / N ratio can be 50 dB, 0.13 ≦ Pe. /Pw≦0.22. The range between the recording linear velocity of 10 m / s and 35 m / s is filled with each linear velocity condition, so the range of the Pe / Pw ratio at which good recording characteristics can be obtained when the recording linear velocity is 10 to 35 m / s is 0.10 ≦ Pe / Pw ≦ 0.65, preferably 0.13 ≦ Pe / Pw ≦ 0.60.
[0033]
【The invention's effect】
According to the first aspect of the present invention, recording / erasing is performed using a reversible phase change between an amorphous phase (amorphous phase) and a crystalline phase of a recording layer at a linear velocity of 10 m / s or more with the same capacity as a DVD-ROM. It is possible to provide an optical recording medium that can
According to the present invention 2, an optical recording medium having a recording linear velocity of 10 m / s or more and a high C / N ratio can be provided.
According to the third aspect of the present 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 lowered, and when Sn, Si, Zn, Bi, and Pb are used, the recordable linear velocity is increased. If Ge and N are 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 repetitive recording at a recording linear velocity of 4 times the DVD (14 m / s) or higher.
According to the fifth aspect of the present invention, it is possible to provide an optical recording medium capable of repetitive recording at a recording linear speed of 8 times the speed (28 m / s) or more of DVD.
According to the sixth to seventh aspects of the present invention, an optical recording medium having a high modulation degree can be provided.
According to the present invention 8 to 9, it is possible to provide an optical recording medium manufacturing method capable of 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 invention 10 to 12, it is possible to provide a sputtering target for producing an optical recording medium capable of 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 of the present invention, a recording method for an optical recording medium capable of stable recording can be provided.
According to the fourteenth to fifteenth aspects of the present invention, it is possible to provide a recording method for an optical recording medium having a recording linear velocity of 10 m / s or higher and a high C / N ratio.
[Brief description of the drawings]
FIG. 1 is a view showing a basic structure of a phase change 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 view showing a transmission electron microscope image of a recording layer after the initial recording.
FIG. 3 is a diagram showing a recording strategy generally used in a rewritable optical recording medium.
4 is a graph showing the measurement result of the C / N ratio when using the GaSb alloy of Example 2. FIG.
FIG. 5 is a diagram showing the evaluation result of the degree of modulation when the film thickness of the recording layer of Example 4 is changed.
6 shows an X-ray powder diffraction spectrum of Example 5. FIG.
FIG. 7 is a diagram for explaining In-plane X-ray diffraction.
8 is a diagram showing a spectrum measured by In-plane X-ray diffraction for the optical recording medium of Example 5. FIG.
9 is a graph showing the result of converting the result of powder X-ray diffraction into a wavelength λ = 1.54 mm for the optical recording medium of Example 5. FIG.
FIG. 10 is a view showing a change in jitter value of the optical recording medium of Example 5 after storing the recorded medium in an environment of 80 ° C. and 85% RH.
FIG. 11 is a graph showing the results of powder X-ray diffraction of optical recording media of Example 5 and Comparative Example.
FIG. 12 shows a unit cell having a hexagonal structure.
FIG. 13 is a graph showing the relationship between the lattice constant a and the crystallization temperature.
14 is a diagram showing a spectrum measured by In-plane X-ray diffraction for the optical recording medium of Comparative Example 1. FIG.
FIG. 15 is a diagram showing a result of a recording test performed on the optical recording medium manufactured in Example 1;
16 is a graph plotting C / N ratios when recording is performed at different recording speeds using the optical recording medium manufactured in Example 1. FIG.
FIG. 17 uses the optical recording medium manufactured in Example 1 and records the power condition that maximizes the C / N ratio by optimizing the Pe / Pw of the laser beam used for recording under each recording linear velocity condition. The figure plotted with respect to the linear velocity.
[Explanation of symbols]
a Lattice constant
c Lattice constant

Claims (15)

The substrate has at least a first intermediate layer, a recording layer, a second intermediate layer, a reflective layer, and a protective layer in this order, and the recording layer is GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atoms%) (except for those containing Te ), and the recording layer has an amorphous phase (amorphous phase) and a crystalline phase even at a linear velocity of 10 m / s or more. A phase change optical recording medium capable of recording and erasing utilizing reversible phase change.   2. The phase change optical recording medium according to claim 1, wherein 5 ≦ α ≦ 15 and 85 ≦ β ≦ 95.   The recording layer further contains at least one element selected from Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Ge, Si, and N at 10 atomic% or less of the alloy. The phase change optical recording medium according to claim 1, wherein the phase change optical recording medium is contained.   4. Recording / erasing using a reversible phase change between an amorphous phase and a crystalline phase of a recording layer is possible even at a linear velocity of 14 m / s or more. The phase change optical recording medium described.   5. The phase change type light according to claim 4, wherein recording / erasing utilizing reversible phase change between an amorphous phase and a crystalline phase of the recording layer is possible 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 recording layer has a thickness in the range of 5 to 25 nm.   7. The phase change optical recording medium according to claim 6, wherein the thickness of the recording layer is in the range of 8 to 20 nm. An optical recording medium is produced 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, and then the optical recording medium is within a range of 3 to 18 m / s. The initial crystallization is performed by irradiating the optical recording medium while rotating the laser beam having a power density of 5 to 50 mW / μm ^{2 at} a constant speed in the radial direction. A method for producing a phase change optical recording medium according to claim 1. 9. The manufacturing method according to claim 8, wherein 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 / [mu] m < ² >. GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, where α and β are atomic%) (excluding those containing Te ), for producing phase change optical recording media Sputtering target. The phase change type according to claim 10, comprising an alloy having a composition represented by GaαSbβ (where 5 ≦ α ≦ 15, 85 ≦ β ≦ 95, α and β are atomic%) (excluding those containing Te ). Sputtering target for manufacturing optical recording media. An alloy having a composition represented by GaαSbβ (where 5 ≦ α ≦ 20, 80 ≦ β ≦ 95, α and β are atomic percent) (excluding those containing Te ), and 10 atomic percent of the alloy Phase change optical recording comprising at least one element selected from the following Ag, Au, Cu, B, Al, In, Mn, Sn, Zn, Bi, Pb, Ge, Si, N Sputtering target for medium production. 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 recording method is μm ² or more.   The recording linear velocity is set to 10 to 35 m / s, the light beam applied to the medium is formed by a single pulse or a plurality of pulse trains, and the ratio of the erasing power Pe to 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 recording method is set to 0.65.   15. The recording method for a phase change optical recording medium according to claim 14, wherein 0.13 ≦ Pe / Pw ≦ 0.60 is set.

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