JP2004111016A - Phase transition optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase transition optical recording medium which has wide recording margin characteristics and has excellent recursive recording durability. <P>SOLUTION: (1) The phase transition optical recording medium is constituted by forming at least a lower protective layer/recording layer/upper interface layer/upper protective layer/reflection layer in this order or in reverse order on a transparent substrate, in which the upper interface layer consists of the oxides of one or more kinds of the elements (precluding Zr) selected from the groups 2 to 14 of the third period to sixth period of periodic table. (2) The phase transition optical recording medium has a lower interface layer consisting of the oxides of the one or more elements (precluding Zr) selected from the groups 2 to 14 of the third period to sixth period of periodic table between the lower protective layer and the recording layer. <P>COPYRIGHT: (C)2004,JPO

Description

【００２０】
次に、Ｚｒの酸化物及びこれと組み合わせる他の酸化物の物性及び組成について説明する。
Ｚｒの酸化物の代表例であるＺｒＯ_２は、室温では単斜晶であるが、約１０００℃前後で正方晶へ、更に、２３７０℃で立方晶へと相転移することが知られている。特に、１０００℃前後の相転移は大きな体積変化（４．０〜７．４％）を伴うため、記録中に大きな体積変化により膜剥がれ等を起こしてしまう可能性もある。また、スパッタリングターゲットの作成中に割れてしまうという問題も引き起こす。そこで低原子価酸化物を作る周期律表の第３周期〜第６周期の２Ａ族及び３Ａ族から選ばれる１種以上の酸化物をＺｒＯ_２に固溶し、部分安定化ジルコニア、或いは安定化ジルコニアとする。これにより、部分的又は全体的にＺｒＯ_２の最高温相である立方晶が室温まで安定相として存在することができ、相転移による大きな体積変化が回避され、ターゲット作成中の割れ、或いは、光記録媒体の膜剥がれを防止できる。ＺｒＯ_２に固溶させる周期律表の第３周期〜第６周期の２Ａ族及び３Ａ族の酸化物の好ましい具体例としては、ＭｇＯ、ＣａＯ、Ｓｃ_２Ｏ_３、Ｙ_２Ｏ_３、ＣｅＯ_２が挙げられる。固溶させる量は、酸化物の種類によっても異なるが、おおよそＺｒＯ_２に対し２〜１５モル％（α＝２〜１５）、より好ましくは、３〜１０モル％である。
【００２１】
更に、周期律表の第３周期〜第６周期の２族〜１４族から選ばれる１種以上の元素、より好ましくは第３周期〜第６周期の２族〜５族及び１２族〜１４族から選ばれる１種以上の元素の酸化物を混合しても良く、特に、ＴｉＯ_２、ＳｉＯ_２、Ａｌ_２Ｏ_３、ＭｇＯ、Ｔａ_２Ｏ_５、ＺｎＯが好ましい（ここで、ＭｇＯは、前記固溶させるＭｇＯとは別に混合させるものである）。これは、上記のようにＺｒＯ_２にＭｇＯ、ＣａＯ、Ｓｃ_２Ｏ_３、Ｙ_２Ｏ_３、ＣｅＯ_２を適量固溶し部分安定化ジルコニア、或いは、安定化ジルコニアとしただけでは、核形成促進効果が大きいため、繰り返し記録における結晶化促進効果が得られる反面、８０℃程度の高温における非晶質マークの保存安定性が損なわれてしまうためである。ＴｉＯ_２、ＳｉＯ_２、Ａｌ_２Ｏ_３、ＭｇＯ、Ｔａ_２Ｏ_５、ＺｎＯ等を混合することにより、結晶化促進効果はやや劣るものの、保存安定性には有利になる。
【００２２】
上記酸化物を混合させる割合は、記録層自身の保存安定性とも関連してくる。記録層の保存安定性が良く、ＺｒＯ_２にＭｇＯ、ＣａＯ、Ｓｃ_２Ｏ_３、Ｙ_２Ｏ_３、ＣｅＯ_２を適量固溶し部分安定化ジルコニア、或いは、安定化ジルコニアとしただけの材料を用いても特に問題が無い場合もある。しかし、記録層の保存安定性がそれ程よくない場合には、前記酸化物をある程度混合させるが、混合割合が６０モル％を越えるとＺｒＯ_２の結晶化促進効果が明確ではなくなるので、上限は６０モル％とする（γ＝０〜６０）。より好ましくは１０〜４０モル％である。
更にＺｎの硫化物であるＺｎＳを混合しても良い。ＺｒＯ_２は成膜速度が遅く、膜厚を厚くしたい場合には時間がかかり過ぎて基板変形を起したり、タクトが長くなりコスト高になってしまう。一方、ＺｎＳはＺｒＯ_２に比べると１０倍以上の速度で成膜が可能であり、これを混合することによってＺｒＯ_２の成膜速度も速くすることができる。但し、６０モル％を越えるとＺｒＯ_２の結晶化促進効果が明確ではなくなるので、上限は６０モル％（δ＝０〜６０）、より好ましくは２０モル％以下とする。
なお、ＺｒＯ_２の特性を活かすためには、ＺｒＯ_２にＭｇＯ、ＣａＯ、Ｓｃ_２Ｏ_３、Ｙ_２Ｏ_３、ＣｅＯ_２を適量固溶し部分安定化ジルコニア、或いは、安定化ジルコニアを少なくとも４０モル％（β＝４０〜１００）、より好ましくは６０モル％以上含有させる必要がある。
【００２３】
ＺｒＯ_２を含む層の膜厚は、１ｎｍより薄いと効果が明確でないため、１ｎｍ以上とする。上部界面層として用いる場合は上限を１８ｎｍ、より好ましくは２〜１４ｎｍとする。これより厚くなると記録層の到達温度が不足している分を上部保護層で補う場合に、反射層と記録層との間の上部界面層と上部保護層の合計膜厚が厚くなってしまい、反射率が低くなり過ぎてしまう。下部界面層として用いる場合には、光学特性のみを考慮すればよいが、１００ｎｍより厚いと成膜効率が悪く、膜の応力に起因する膜剥がれも起り易くなるので、１００ｎｍ以下、より好ましくは２〜２０ｎｍとする。
【００２４】
上部保護層材料としては前述したように、少なくともバルクの反射率が１０Ｗ／（ｍ・Ｋ）以下の材料を用いるが、中でもＺｎＳとＳｉＯ_２の混合物は低パワー側の記録特性を良好にする効果が大きい。ＺｎＳは屈折率ｎが大きいので光学的な調整効果が大きく、また、成膜速度も速いという利点があるが、単体では熱伝導率が大きく低パワー側の記録特性を良好にする効果が得られないため、熱伝導率の小さいＳｉＯ_２を混合して用いる。ＳｉＯ_２は１０モル％以上混合すれば、低パワー側の記録特性を良好にする効果が得られる。また、ＳｉＯ_２は単体で用いてもよい（ε：１０〜１００）。ＳｉＯ_２は屈折率ｎがＺｎＳ程は大きくないが、熱伝導率が小さいので低パワー側の記録特性を良好にする効果が得られる。また、Ｓを含まないため、反射層としてＡｇ又はＡｇ合金を用いた場合でも上部保護層と反射層との間に硫化防止層を設ける必要がない。
上部保護層の膜厚は、２ｎｍ以上とすることで低パワー側の記録特性を良好にする効果が得られる。上限は上部界面層との兼ね合いで決まるが、２０ｎｍより厚くすると冷却速度が遅くなり過ぎて、特に高線速で記録する場合には良好な記録が行えなくなり、また、再生光により劣化し易くなってしまうので、２０ｎｍ以下とする。
【００２５】
次に、記録層について説明する。
ここでは、記録層として原子比が３：１近傍のＳｂ−Ｔｅを母相とした材料について詳しく説明するが、モル比が２：１のＧｅＴｅ−Ｓｂ_２Ｔｅ_３の混合物を母相とした記録層にも適用できる。
記録・消去の際の結晶化は、前者の場合は非晶質との界面からの結晶成長により進行し、後者の場合は非晶質中の均一核形成により進行する。どちらの場合でも、界面相としてＺｒＯ_２を含む材料を用いることにより核生成が促進されるので、消し残りが生じ難くなり、繰り返し記録耐久性は向上する。
【００２６】
ＳｂとＴｅの原子比が３：１近傍のＳｂ−Ｔｅは繰り返し記録特性に優れた相変化記録材料である。ＳｂとＴｅの配合比を変えることにより、結晶化速度を調整することが可能であり、Ｓｂの比率を高くすると結晶化速度を速くすることができる。本発明者らの実験によれば、Ｓｂが６５原子％以上であれば、少なくともＣＤの１Ｘの線速（１．２ｍ／ｓ）で記録が可能である。Ｓｂがこれよりも少ないと、１．２ｍ／ｓでも繰り返し記録によるジッターの上昇が大きく、良好な記録を行えなかった。Ｓｂ比を高くしていくにつれて、結晶化速度も速くなり、より高線速で良好な記録が可能になっていく。評価装置等の制約により、どの程度の線速まで良好な記録が可能であるかの上限は確定できていないが、少なくともＤＶＤ５倍速（１７．５ｍ／ｓ）までは繰り返し記録が可能である。しかし、Ｓｂが８５原子％を越えると結晶化速度の上昇率が急激になり、非晶質マークの形成が殆どできなくなってしまった。従って、Ｓｂ−Ｔｅ二元系におけるＳｂの比率は６５原子％以上、８５原子％以下とすることが好ましい。
【００２７】
しかし、Ｓｂ−Ｔｅの二元系だけでは非晶質相の安定性が悪く、例えば、７０〜８０℃程度の高温環境下では５０時間以内に非晶質マークが結晶化してしまうという問題がある。そのため非晶質相の安定性を高められるような第３元素を１種類以上添加して用いる。
このような第３元素としては、Ｇｅが有効であり、少量の添加でも保存信頼性を飛躍的に向上できる。添加量は２原子％以上であれば、ＤＶＤ２倍速相当以上の結晶化速度の速い記録層においても非晶質安定性を向上させる効果が期待できる。添加量が増える程その効果は高くなるものの、特に結晶化速度が速く、高線速記録に適した記録層の場合、添加量が多すぎると、記録感度及び繰り返し記録特性の低下を招くため、多くても７原子％以下とすることが望ましい。
【００２８】
更に、Ｉｎ又はＧａを添加すると、結晶化速度を速くし、かつ、結晶化温度を上げることにより保存安定性を向上させることができる。
前述したＧｅは保存安定性向上に効果的ではあるが、結晶化速度を遅くしてしまうため、一定の結晶化速度を確保するためにはＧｅの添加に伴い、Ｓｂ比率を高くする必要がある。しかし、Ｓｂ比率が高くなると記録感度が低下する傾向がある。
これに対し、ＩｎやＧａを添加すれば、Ｓｂ比率を高くせずに結晶化速度を速くすることができ、記録感度に優れた記録層とすることができる。ＩｎやＧａの添加量は、１原子％より少ないと効果が明確でなく、多すぎると繰り返し記録特性及び再生光安定性が低下してしまうため７原子％以下とすることが望ましい。
【００２９】
その他に、結晶化速度の調整等の目的でＡｇ、Ｂｉ、Ｃ、Ｃａ、Ｃｒ、Ｃｕ、Ｄｙ、Ｍｇ、Ｍｎ、Ｓｅ、Ｓｉ、Ｓｎ等を添加しても良い。
以上のように、少なくともＧｅ、Ｉｎ又はＧａ、Ｓｂ、Ｔｅを適切に組み合わせて用いることにより所望の記録線速において繰り返し記録特性、記録感度、保存安定性に優れた記録層を形成することができる。
記録層の膜厚は、８ｎｍより薄いと変調度が小さく、また、再生光安定性も低下してしまうため８ｎｍ以上とし、２２ｎｍより厚いと繰り返し記録によるジッターの上昇が大きいため、２２ｎｍ以下とする。
【００３０】
反射層としては従来Ａｌを主成分とした合金が使用されている。Ａｌは反射率が高く、熱伝導率も高いことに加え、ディスク化した場合の経時安定性にも優れている。しかし、記録層材料の結晶化速度が速い場合には、反射層として従来よく使用されているＡｌ合金を用いたディスクでは、記録マークが細くなり易く、十分な変調度を有する記録を行うことは困難な場合があった。この理由としては、結晶化速度が速いと記録時に溶融領域の再結晶化領域が大きくなってしまい、形成される非晶質領域が小さくなってしまうことが挙げられる。
再結晶化領域を小さくするためには、上部保護層を薄くして急冷構造とすればよいが、単純に上部保護層を薄くしただけでは、記録層が十分に昇温されず、溶融領域が小さくなってしまうため、再結晶化領域を小さくできたとしても、結局、形成される非晶質領域は小さくなってしまう。
【００３１】
しかし、波長６５０〜６７０ｎｍにおける屈折率（ｎ＋ｉｋ）のｎ、ｋが共にＡｌより小さい金属を反射層に用いると、記録層の吸収率は向上し、変調度も大きくすることができる。
ｎ、ｋ共にＡｌより小さい金属としてはＡｕ、Ａｇ、Ｃｕ、及びそれらを主成分とした合金が挙げられる。ここで、主成分とするとは、９０原子％以上含有することを意味し、好ましくは９５原子％以上である。
これらの純金属について、λ＝６６０ｎｍにおけるスパッタ膜の屈折率の実測値、及び、熱伝導率の文献値（バルク）の値を表２に示す。
【表２】

【００３２】
表２より、Ａｕ、Ａｇ、Ｃｕは、何れもＡｌより熱伝導率が高いことが分る。従って、これらを反射層として用いると、記録層の光吸収率を向上させ、記録層の温度を上昇させて溶融領域を大きくする効果があると同時に、冷却速度も向上させるため冷却時の再結晶化領域が小さくなり、Ａｌ合金を用いた場合よりも大きな非晶質領域を形成することが可能になる。
記録マークの変調度は光学的な変調度とマークの大きさによって決まり、光学的な変調度が大きくマークが大きい程大きくなる。従って、記録層として、結晶化速度が速い材料を用いて、高線速記録を行う場合でも、上記反射層を用いれば、吸収率が大きく冷却速度が速いことから大きな記録マークが形成でき、また、結晶と非晶質の反射率差も大きいことから変調度の大きい記録が可能になる。
【００３３】
Ａｕ、Ａｇ、Ｃｕ、及びそれらを主成分とする合金の中でも、特に、Ａｇ及びＡｇ合金は比較的安価であり、また、同様に安価なＣｕ及びＣｕ合金に比べて酸化し難いため、経時安定性に優れた媒体を形成することができ、反射層として好ましい。但し、硫化には弱いため、上部保護層にＳを含むような材料を用いる場合には、硫化防止層が必要となる。
硫化防止層は、３ｎｍ以上の厚さがあれば、スパッタにより形成された膜はほぼ均一になり、硫化防止機能を発揮する。これより薄いと、部分的に欠陥を生じる確率が急に高くなってしまう。
【００３４】
硫化防止層の材料に要求される性質としては、Ｓを含まないこと、Ｓを透過しないこと等が挙げられる。
本発明者らが、種々の酸化膜や窒化膜等を硫化防止層として形成し、記録特性や保存信頼性の評価を行ったところ、ＳｉＣ、Ｓｉ、又はそれらの何れかを主成分とする材料が硫化防止層として優れた機能を持つことが分った。ここで、主成分とするとは、材料中にＳｉＣ又はＳｉを９０モル％以上含有することを意味し、好ましくは９５モル％以上である。
反射層の膜厚は９０ｎｍ以上であれば透過光が殆どなくなり、光を効率的に利用できるので、９０ｎｍ以上とする。膜厚は厚い程冷却速度が速くなり、結晶化速度の速い記録層を使用する場合には有利であるが、２００ｎｍ以下で冷却速度は飽和し、２００ｎｍより厚くしても記録特性に変化がなく、成膜に時間がかかるだけなので、２００ｎｍ以下とすることが好ましい。
【００３５】
下部保護層は耐熱性の保護膜としての役割の他に、光学的特性を調整する役割を担う。膜厚は４０ｎｍより薄いと耐熱性が悪く、繰り返し記録によるジッター上昇が大きくなってしまうため４０ｎｍ以上とする。また、２２０ｎｍより厚いと成膜効率が悪く、膜の応力に起因する膜剥がれ等も起り易くなるため好ましくない。よって、４０〜２２０ｎｍの範囲内、より好ましくは４０〜８０ｎｍの範囲内で、反射率及び変調度が大きく取れるような膜厚を選ぶ。
下部界面層を使用する場合には、下部界面層の分だけ、下部保護層の膜厚を減らすなど、全体で光学特性を満足するように調整する。
【００３６】
【実施例】
以下、実施例及び比較例により本発明を具体的に説明するが、本発明はこれらの実施例により限定されるものではない。なお、何れの実施例及び比較例の場合も、直径１２ｃｍ、厚さ０．６ｍｍ、トラックピッチ０．７４μｍの案内溝付きポリカーボネートディスク基板上に下部保護層、（下部界面層）、記録層、上部界面層、上部保護層、硫化防止層、反射層をこの順にスパッタにより成膜し、更に、反射層上にスピンコートで形成された有機保護膜を介して、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネートディスクを接着したものを、大口径ＬＤにより初期結晶化して試料として用いた。
評価は、基板側から波長６６０ｎｍ、ＮＡ０．６５のレーザー光を照射し、線密度０．２６７μｍ／ｂｉｔ、ＥＦＭ＋変調方式でランダムパターンを繰り返し記録することにより行った。
【００３７】
実施例１
下部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚６５ｎｍ、記録層としてＡｇ_１Ｉｎ_３Ｓｂ_７２Ｔｅ_２０Ｇｅ_４を膜厚１５ｎｍ、上部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）８０モル％（ＴｉＯ_２）２０モル％を膜厚２ｎｍ、上部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚１０ｎｍ、硫化防止層としてＳｉを膜厚４ｎｍ、反射層としてＡｇを膜厚１４０ｎｍ形成したディスクを初期結晶化した後、繰り返し記録特性を評価した。
図４に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００３８】
実施例２
上部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）４０モル％（ＴｉＯ_２）４０モル％（ＳｉＯ_２）２０モル％を膜厚２ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図５に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００３９】
実施例３
記録層としてＳｂ_７６Ｔｅ_２０Ｇｅ_４を膜厚１５ｎｍ形成した点以外は実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図６に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４０】
実施例４
下部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚６３ｎｍ、下部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）４０モル％（ＴｉＯ_２）４０モル％（ＳｉＯ_２）２０モル％を膜厚２ｎｍ、記録層としてＡｇ_１Ｉｎ_３Ｓｂ_７２Ｔｅ_２０Ｇｅ_４を膜厚１５ｎｍ、上部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）８０モル％（ＴｉＯ_２）２０モル％を膜厚２ｎｍ、上部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚１０ｎｍ、硫化防止層としてＳｉを膜厚４ｎｍ、反射層としてＡｇを膜厚１４０ｎｍ形成したディスクを初期結晶化した後、繰り返し記録特性を評価した。
図７に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４１】
比較例１
上部界面層を設けず、上部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚１２ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図８に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、Ｐｗ＝１５ｍＷと１７ｍＷの場合は、繰り返し記録１００００回までジッターが１０％以下であるが、Ｐｗ＝１９ｍＷの場合は、１００回を越えると１０％を越えてしまった。Ｐｗ＝１９ｍＷの場合には繰り返し記録によって１％程度の反射率低下も見られた。
【００４２】
実施例５
上部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）８０モル％（ＴｉＯ_２）２０モル％を膜厚１４ｎｍ、上部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚６ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図９に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４３】
比較例２〜３
下部保護層として（ＺｎＳ）８０モル％（ＳｉＯ_２）２０モル％を膜厚６５ｎｍ、記録層としてＡｇ_１Ｉｎ_３Ｓｂ_７２Ｔｅ_２０Ｇｅ_４を膜厚１５ｎｍ、上部保護層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）８０モル％（ＴｉＯ_２）２０モル％を膜厚１６ｎｍ（比較例２）、或いは膜厚１８ｎｍ（比較例３）、反射層としてＡｇを膜厚１４０ｎｍ形成したディスクを初期結晶化した後、繰り返し記録特性を評価した。
図１０、図１１に、それぞれ比較例２、比較例３のディスクに対し、線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図１０から分るように、比較例２の場合は、Ｐｗ＝１７ｍＷ、１９ｍＷと高パワー側では良好な繰り返し記録特性が得られたが、Ｐｗ＝１５ｍＷでは初回から良好な特性が得られなかった。
また、上部保護層の膜厚を厚くして記録層の到達温度を上げ、低パワー側の記録特性も良くしようとしたのが比較例３であるが、図１１から分るように、全体的にジッターが上昇してしまい、低パワー側の特性の改善効果も見られなかった。
【００４４】
実施例６
上部界面層として（ＺｒＯ_２−３モル％Ｙ_２Ｏ_３）８０モル％（ＴｉＯ_２）２０モル％を膜厚６ｎｍ、上部保護層としてＳｉＯ_２を膜厚８ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図１２に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４５】
実施例７
上部界面層として（ＺｒＯ_２−８モル％ＭｇＯ）８０モル％（ＴｉＯ_２）２０モル％を膜厚２ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図１３に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４６】
実施例８
上部界面層として（ＺｒＯ_２−８モル％ＭｇＯ）８０モル％（Ａｌ_２Ｏ_３）２０モル％を膜厚２ｎｍ形成した点以外は、実施例１と全く同様にしてディスクを作成し、繰り返し記録特性を評価した。
図１４に線速１４ｍ／ｓ、Ｐｗ＝１５ｍＷ、１７ｍＷ、１９ｍＷ、Ｐｅ＝４．４〜５．６ｍＷ、Ｐｂ＝０．１ｍＷで、１００００回まで繰り返し記録した場合のジッター（ｄａｔａ　ｔｏ　ｃｌｏｃｋジッター、クロストークなし）の変化の様子を示した。
図から分るように、何れもジッターは１０％以下であり、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を得ることができた。繰り返し記録による反射率低下も見られなかった。
【００４７】
【発明の効果】
本発明１〜１２によれば、広いパワー領域で繰り返し記録耐久性に優れた光記録媒体を提供できる。
本発明１３〜１６によれば、少なくともＣＤ１Ｘ（１．２ｍ／ｓ）〜ＤＶＤ５Ｘ（１７．５ｍ／ｓ）までの広い線速領域で良好な繰り返し記録特性、保存安定性を有する優れた光記録媒体を提供できる。
【図面の簡単な説明】
【図１】相変化型光ディスクに非晶質マークを記録する方法として通常使用されている方式を示す図。
【図２】非晶質マークにレーザーが照射され、結晶部との界面から結晶成長が進行し、結晶化していく様子を模式的に示す図。
【図３】温度と結晶成長速度の関係を示す図。
【図４】実施例１の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図５】実施例２の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図６】実施例３の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図７】実施例４の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図８】比較例１の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図９】実施例５の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１０】比較例２の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１１】比較例３の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１２】実施例６の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１３】実施例７の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１４】実施例８の光記録媒体に対し、１００００回まで繰り返し記録した場合のジッターの変化の様子を示す図。
【図１５】界面層がある場合とない場合のジッターの上昇の様子を比較した結果を示す図。
【符号の説明】
Ｐｗ　記録パワー
Ｐｅ　消去パワー
Ｐｂ　バイアスパワー
Ｔ　基準クロック[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase change type optical recording medium.
[0002]
[Prior art]
For an optical recording medium that can record, reproduce and erase information by irradiating a semiconductor laser beam, a magneto-optical recording method in which magnetization is reversed to record and erase information, and recording and erasing using a reversible phase change between crystal and amorphous. There is a phase change recording method. The latter is characterized by being capable of repeated recording with a single beam and having a simpler optical system on the drive side, and has been applied as a computer-related or audio-visual recording medium.
The phase-change optical recording medium heats the recording layer by irradiating the recording layer thin film on the substrate with laser light, and changes the disk reflectivity by changing the phase of the recording layer structure between crystalline and amorphous. Is recorded / erased. Normally, a state in which the entire surface is crystallized is set as an initial state, and data including an amorphous mark and a crystal space is recorded therein.
[0003]
FIG. 1 shows a method generally used for recording an amorphous mark on a phase change optical disk. The recording / erasing is performed by modulating the laser power into three values of recording power Pw, erasing power Pe, and bias power Pb (Pw>Pe> Pb). The mark section irradiates a pulse train composed of Pw and Pb. Since the recording layer is melted by Pw and then rapidly cooled by modulating to Pb, the melted region becomes an amorphous phase. By further modulating to Pe, the rear end of the amorphous portion is crystallized to form a mark of a predetermined length. When repeatedly recording, a previously modulated track is irradiated with a similarly modulated laser to crystallize and erase the already recorded amorphous mark and simultaneously place a new mark in a predetermined position. It is possible to perform direct repetitive recording formed on the recording medium.
[0004]
The simplest configuration of a phase-change optical recording medium is that a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are formed on a transparent substrate in this order or in reverse order. Recording and reproduction are performed by irradiating a laser from the layer side. As the upper and lower protective layers, ZnS and SiO ₂ The recording layer is made of Ag, In, Ge, Sb, Te or the like, and the reflective layer is made of Al alloy or Ag alloy. When an Ag alloy is used, a sulfuration preventing layer may be provided between the upper protective layer and the reflective layer. Although it differs depending on the composition of the recording layer, etc., if the recording is repeatedly performed on the optical recording medium having such a configuration, the jitter gradually increases in hundreds to thousands of repetitive recordings, and the recording medium cannot be used. .
[0005]
Therefore, in order to improve the repetitive recording durability, a part or all of the protective layer in contact with the recording layer is made of ZrO. ₂ It has been proposed to use materials containing These are ZrO ₂ It pays attention to its excellent heat resistance and mechanical strength. However, ZrO ₂ By simply using a material that contains a material containing a recording layer, it is not possible to exhibit sufficient repetitive recording durability in a wide recording power region. Particularly when the recording power is low, a sufficiently low jitter cannot be obtained.
For example, in the inventions disclosed in Patent Literatures 1 to 4, the optical conditions and the thermal conditions are not optimized, so that an optical recording medium having a repetitive recording durability with a wide recording power margin cannot be realized. ZrO ₂ Is also different from that of the present invention.
In the invention disclosed in Patent Document 5, ZrO ₂ Is used so as to be in contact with the recording layer, but is limited to the interface on the lower protective layer side.
[0006]
Patent Document 6 discloses an invention relating to an information recording medium in which a dielectric protective layer and a light absorbing protective layer are provided between a recording layer and a reflective layer. However, an object of the present invention is to improve an optical absorption difference between an amorphous state and a crystalline state of a recording layer to obtain an information recording medium suitable for high-density recording. different. Further, ZnS-SiO used as a material of the light absorbing protective layer in the examples ₂ Naturally, -W has a light-absorbing property, and is completely different from an oxide material having almost no light-absorbing property (which cannot be used in the invention of Patent Document 6) used in the interface layer in the present invention. different.
[0007]
[Patent Document 1]
JP-A-5-144085
[Patent Document 2]
JP-A-8-180458
[Patent Document 3]
JP 2000-348380 A
[Patent Document 4]
JP-A-2000-182277
[Patent Document 5]
JP-A-11-339314
[Patent Document 6]
JP-A-8-96411
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a phase-change optical recording medium having a wide recording power margin and excellent in repeated recording durability.
[0009]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 16).
1) At least a lower protective layer / recording layer / upper interface layer / upper protective layer / reflective layer is formed on a transparent substrate in this order or in reverse order, and the upper interface layer is composed of an oxide of Zr and A phase-change optical recording medium comprising an oxide of one or more elements (excluding Zr) selected from Groups 2 to 14 of the third to sixth periods.
2) Between the lower protective layer and the recording layer, an oxide of Zr and one or more elements selected from Groups 2 to 14 of the third to sixth periods of the periodic table (excluding Zr) The optical recording medium according to 1), further comprising a lower interface layer made of the oxide according to 1).
3) The upper interface layer or the lower interface layer is formed of a solid solution of a Zr oxide and an oxide of at least one element selected from Group 2 and Group 3 of the third to sixth periods of the periodic table. The phase-change-type optical recording medium according to 1) or 2), which is contained.
4) The upper interface layer or the lower interface layer is formed of one or more elements (excluding Zr) selected from Groups 2 to 5 and Groups 12 to 14 of the third to sixth periods of the periodic table. The phase-change optical recording medium according to any one of 1) to 3), further comprising an oxide.
5) The phase-change optical recording medium according to any one of 1) to 4), wherein the upper interface layer or the lower interface layer contains a sulfide of Zn.
6) The oxide of Zr is ZrO ₂ The optical recording medium according to any one of 1) to 5), wherein
7) The phase-change optical recording medium according to any one of 1) to 6), wherein the mixture containing a solid solution of Zr oxide is represented by the following formula.
[(ZrO ₂ ) 1-α (X) α] β (Z) γ (ZnS) δ
X: MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ Oxides of one or more elements selected from
Z: TiO ₂ , SiO ₂ , Al ₂ O ₃ , MgO, Ta ₂ O ₅ , One or more oxides selected from ZnO
α: 2 to 15 (mol%)
β: 40 to 100 (mol%)
γ: 0 to 60 (mol%)
δ: 0 to 60 (mol%)
β + γ + δ = 100 (mol%)
8) The phase-change optical recording medium according to any one of 1) to 7), wherein the thickness of the upper interface layer is 1 to 18 nm.
9) The phase-change optical recording medium according to any one of 2) to 8), wherein the thickness of the lower interface layer is 1 to 100 nm.
10) The phase-change optical recording medium according to any one of 1) to 9), wherein a material having a thermal conductivity of at least 10 W / (m · K) in a bulk state is used as an upper protective layer material. .
11) The phase-change optical recording medium according to any one of 1) to 10), wherein the material of the upper protective layer is made of a mixture of ZnS and Si oxide.
12) The phase-change optical recording medium according to 11), wherein the mixture of ZnS and Si oxide is represented by the following formula.
(ZnS) 100-ε (SiO ₂ ) Ε [ε: 10 to 100 (mol%)]
13) The phase-change optical recording medium according to any one of 1) to 12), wherein the thickness of the upper protective layer is 2 to 20 nm.
14) The recording layer contains at least Sb, Te and Ge, the atomic ratio Sb / (Sb + Te) of Sb and Te is 0.65 to 0.85, and the Ge content is 2 to 7 atomic%. The phase-change optical recording medium according to any one of 1) to 13).
15) The phase-change optical recording medium according to 14), wherein the recording layer further contains 1 to 7 atomic% of In or Ga.
16) The phase-change optical recording medium according to 14) or 15), wherein the recording layer has a thickness of 8 to 22 nm.
[0010]
Hereinafter, the present invention will be described in detail.
The present invention provides a phase-change optical recording medium having at least a lower protective layer / recording layer / upper protective layer / reflective layer in this order or reverse order, wherein an oxide of Zr is provided between the recording layer and the upper protective layer; An upper interface layer made of an oxide of one or more elements (excluding Zr) selected from Groups 2 to 14 of the third to sixth periods of the periodic table is provided. The term "family" in the present invention is based on IUPAC Inorganic Chemical Nomenclature Revised Edition (1989).
With this configuration, a phase-change optical recording medium having a wide recording power margin and excellent repetitive recording durability can be obtained.
Furthermore, between the lower protective layer and the recording layer, an oxide of Zr and one or more elements selected from the second to sixth groups of the third to sixth periods of the periodic table (excluding Zr) ), A lower interface layer made of an oxide may be provided. The composition of the oxide forming the upper interface layer and / or the lower interface layer is devised, or a layer configuration other than the interface layer is devised. For example, by using a material having at least a bulk thermal conductivity of 10 W / (m · K) or less as the upper protective layer, a more excellent phase-change optical recording medium can be obtained.
[0011]
In order to improve the repetitive recording durability, it is necessary to repeatedly and rapidly perform the phase transition between the crystal and the amorphous. When the jitter increases due to repetitive recording, a phenomenon that the reflectivity between marks and between short marks decreases is observed. This is presumed to be due to the fact that during repeated recording, erasure, that is, crystallization was not successfully performed, and a portion having a low reflectance which did not return to a part of the initial crystal state was accumulated.
By adopting the configuration of the present invention, a decrease in the reflectivity between marks and between short marks is not observed even by repeated recording, and an increase in jitter is suppressed. This is presumably because the layer containing the oxide of Zr has a nucleation promoting effect and promotes crystallization at a relatively low temperature.
[0012]
Crystallization proceeds through two processes of generation of crystal nuclei and crystal growth. In the case of a material having a Sb-Te binary system having an atomic ratio of Sb and Te of about 3: 1 as a base layer, recording / At the time of erasure, uniform nucleation hardly occurs, and crystallization of the amorphous portion proceeds due to crystal growth from the interface with the crystal portion. FIG. 2 schematically shows a state in which the amorphous mark is irradiated with a laser, crystal growth proceeds from the interface with the crystal part, and crystallization occurs.
FIG. 3 shows the relationship between the temperature and the crystal growth rate. As can be seen from FIG. 3, crystal growth proceeds at a high temperature in a specific temperature range immediately below the melting point. Therefore, when the end of the mark does not reach a temperature at which the crystal growth can proceed at a high speed, the erasure remains because the progress of the crystal growth is slow.
[0013]
If the area where the temperature is higher than the temperature at which crystal growth proceeds at a high speed when irradiated with a beam is sufficiently large with respect to the mark width, crystallization proceeds at a high speed from the end of the mark, but is about the same as the mark width. If the mark thickness is not uniform and partly thick, or if the recording beam tracking slightly deviates from the center, crystal growth is not necessarily performed at all the edges of the mark. In some cases, the temperature does not reach the temperature that progresses, so that the unerased portion is left.
When an interface layer made of the above-mentioned oxide of Zr or the like is used, the generation of crystal nuclei is promoted. It is presumed that crystallization proceeds due to crystal growth from the crystal nuclei generated, so that unerased portions are less likely to occur, and that the repeated recording durability is improved.
[0014]
Although it is not clear why crystal nucleus formation is promoted when an interface layer made of the above-mentioned oxide of Zr is used, it can be confirmed by the following experiment that crystal nucleus formation is promoted. That is, the optical recording medium on which the mark is recorded is rotated at a constant linear velocity, and a power slightly higher than the reproducing power is continuously applied. As a result, the mark portion becomes annealed at about 100 to 200 ° C., and a crystal nucleus is generated and crystallized inside the mark. When the jitter is monitored while continuously irradiating a power slightly higher than the reproducing power, a state in which the mark is crystallized can be measured as an increase in the jitter.
[0015]
An optical recording medium in which a lower protective layer / recording layer / upper protective layer / reflective layer is sequentially laminated on a substrate has a standard layer structure, and an interface layer having a thickness of about 2 nm is inserted between the lower protective layer and the recording layer. And how the jitter increases with the optical recording medium of FIG. The thickness of the lower protective layer is reduced by the amount of insertion of the interface layer so that the optical characteristics such as the reflectance are the same. The reason for inserting the interface layer on the lower interface layer side instead of the upper protective layer side is that if the interface layer is inserted on the upper protective layer side, the temperature changes even in the interface layer having a thickness of about 2 nm even if the optical characteristics are the same. However, when inserted into the lower protective layer, the temperature is hardly affected as long as the optical characteristics are the same. Most of the heat absorbed by the recording layer diffuses to the upper protective layer side where the reflective layer is located. Therefore, unless the conditions for heat diffusion on the upper protective layer side are the same, the temperature will change, and nucleation at the same temperature will occur. You will not be able to compare.
[0016]
FIG. 15 shows how jitter increases when such a comparison is made. The irradiation power is 1.4 mW and the rotational linear velocity is 3.5 m / s. From the figure, it can be confirmed that the jitter rises faster when the interface layer is provided, and that nucleation is promoted.
As described above, heat generated in the recording layer due to light absorption is mainly diffused to the reflective layer, and is cooled. Therefore, the recording layer is cooled from the upper protective layer side in the film thickness direction, and crystallization starts. For this reason, when an interface phase having a crystal nucleus generation promoting effect is provided on the upper protective layer side, crystallization is effectively promoted. Further, by providing an interface phase also on the lower protective layer side, crystallization is further promoted, so that the repetitive recording durability is further improved.
[0017]
A typical example of the oxide of Zr is ZrO. ₂ It is. ZrO ₂ Has a sufficiently high refractive index of about 2.2 at a wavelength of 660 nm and hardly absorbs. Optically, ZnS and SiO ₂ , It is not only used as the interface layer but also the upper protective layer is made of ZrO 2 ₂ A configuration including a layer containing However, this alone deteriorates the recording characteristics on the low power side as shown in a comparative example described later. This is because ZrO ₂ Having a thermal conductivity of ZnS-SiO ₂ This is probably because the temperature of the recording layer does not rise. Therefore, this disadvantage is reduced to ZrO ₂ Tried to compensate for this by increasing the film thickness of the layer containing Zr, but the overall jitter deteriorated, and the ZrO between the recording layer and the reflective layer. ₂ It was very difficult to obtain good characteristics in a wide power region by providing only a layer made of a mixture containing
[0018]
The oxides and nitrides shown in Table 1 having various thermal conductivities in a bulk state were converted to ZrO. ₂ When formed and confirmed as an upper protective layer between the upper interface layer made of a material containing ₂ Or (ZnS) 80 mol% (SiO ₂ It was found that when 20 mol% of the material was used as the upper protective layer, there was an effect of not deteriorating the recording characteristics on the low power side. These have relatively low thermal conductivity, and are all 10 W / (m · K) or less. Although it is difficult to measure the thermal conductivity of the thin film, it is considered that the properties of the thermal conductivity in a bulk state are reflected to some extent. However, ZrO ₂ In some cases, such as a material containing, the thermal conductivity of the bulk may be insufficient even if it is 10 W / (m · K) or less, and the thermal conductivity of the bulk state may vary depending on the structure of the formed thin film. It is important to note that not all relationships are directly applicable.
As described above, between the recording layer and the reflective layer, ZrO ₂ Is provided, and at least a bulk thermal conductivity is provided with an upper protective layer having a thermal conductivity of 10 W / (m · K) or less. A recording medium can be formed.
[0019]
[Table 1]

[0020]
Next, the physical properties and compositions of the oxide of Zr and other oxides combined therewith will be described.
ZrO which is a typical example of an oxide of Zr ₂ Is monoclinic at room temperature, but is known to undergo a phase transition to a tetragonal crystal at about 1000 ° C. and further to a cubic crystal at 2370 ° C. In particular, since the phase transition at around 1000 ° C. involves a large volume change (4.0 to 7.4%), a large volume change during recording may cause film peeling or the like. In addition, there is also a problem that the sputtering target is broken during production. Accordingly, one or more oxides selected from the 2A group and 3A group of the third to sixth periods of the periodic table for producing low-valent oxides are ZrO. ₂ To form a partially stabilized zirconia or a stabilized zirconia. As a result, ZrO is partially or entirely formed. ₂ The cubic crystal, which is the highest temperature phase, can exist as a stable phase up to room temperature, so that a large volume change due to phase transition can be avoided, and cracking during target production or film peeling of the optical recording medium can be prevented. ZrO ₂ Specific examples of the oxides of Group 2A and Group 3A in the third to sixth periods of the periodic table to be solid-dissolved in MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ Is mentioned. The amount of solid solution varies depending on the type of oxide, but is approximately ZrO ₂ 2 to 15 mol% (α = 2 to 15), more preferably 3 to 10 mol%.
[0021]
Further, at least one element selected from the 2nd to 14th groups of the 3rd to 6th periods of the periodic table, more preferably the 2nd to 5th groups and the 12th to 14th groups of the 3rd to 6th periods Oxides of at least one element selected from the group consisting of TiO. ₂ , SiO ₂ , Al ₂ O ₃ , MgO, Ta ₂ O ₅ , ZnO is preferable (here, MgO is mixed separately from the solid solution MgO). This is because ZrO ₂ MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ A solid solution of zirconia or partially stabilized zirconia or stabilized zirconia has a large nucleation promoting effect, so that a crystallization promoting effect in repeated recording can be obtained, but an amorphous mark at a high temperature of about 80 ° C. This is because the storage stability of the product is impaired. TiO ₂ , SiO ₂ , Al ₂ O ₃ , MgO, Ta ₂ O ₅ , ZnO and the like, the crystallization promotion effect is slightly inferior, but it is advantageous in storage stability.
[0022]
The mixing ratio of the oxide is related to the storage stability of the recording layer itself. The storage stability of the recording layer is good, and ZrO ₂ MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ There is a case where there is no particular problem even if a solid solution of the above is used as a partially stabilized zirconia or a material which is merely a stabilized zirconia. However, when the storage stability of the recording layer is not so good, the oxide is mixed to some extent, but when the mixing ratio exceeds 60 mol%, ZrO is mixed. ₂ Is not clear, the upper limit is set to 60 mol% (γ = 0 to 60). More preferably, it is 10 to 40 mol%.
Further, ZnS which is a sulfide of Zn may be mixed. ZrO ₂ However, if the film thickness is low, it takes too much time to increase the film thickness, and the substrate is deformed or the tact time is increased and the cost is increased. On the other hand, ZnS is ZrO ₂ It is possible to form a film at a speed of 10 times or more as compared with ₂ Can also be formed at a high speed. However, if it exceeds 60 mol%, ZrO ₂ Is not clear, the upper limit is 60 mol% (δ = 0 to 60), more preferably 20 mol% or less.
Note that ZrO ₂ To take advantage of the characteristics of ZrO ₂ MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ Must be dissolved in an appropriate amount to contain partially stabilized zirconia or at least 40 mol% (β = 40 to 100), more preferably 60 mol% or more of stabilized zirconia.
[0023]
ZrO ₂ If the thickness of the layer containing is less than 1 nm, the effect is not clear, so the thickness is set to 1 nm or more. When used as the upper interface layer, the upper limit is set to 18 nm, more preferably 2 to 14 nm. When the thickness is larger than this, when the temperature attained by the recording layer is compensated for by the upper protective layer, the total thickness of the upper interface layer and the upper protective layer between the reflective layer and the recording layer increases, The reflectance is too low. When used as the lower interface layer, only the optical characteristics need to be considered, but if it is thicker than 100 nm, the film formation efficiency is poor and the film is liable to peel off due to the stress of the film. ２０20 nm.
[0024]
As described above, as the material of the upper protective layer, a material having at least a bulk reflectance of 10 W / (m · K) or less is used. ₂ Has a great effect of improving the recording characteristics on the low power side. ZnS has a large refractive index n and therefore has a large optical adjustment effect, and has the advantage of a high film formation rate. However, ZnS alone has a large thermal conductivity and has an effect of improving the recording characteristics on the low power side. Because of this, SiO with low thermal conductivity ₂ Are mixed and used. SiO ₂ If 10 mol% or more is mixed, the effect of improving the recording characteristics on the low power side can be obtained. In addition, SiO ₂ May be used alone (ε: 10 to 100). SiO ₂ Although the refractive index n is not as large as that of ZnS, the effect of improving the recording characteristics on the low power side is obtained because the thermal conductivity is small. Further, since S is not contained, it is not necessary to provide an anti-sulfuration layer between the upper protective layer and the reflective layer even when Ag or an Ag alloy is used as the reflective layer.
When the thickness of the upper protective layer is 2 nm or more, an effect of improving the recording characteristics on the low power side can be obtained. The upper limit is determined by the balance with the upper interface layer. However, if the thickness is more than 20 nm, the cooling rate becomes too slow, and good recording cannot be performed, especially when recording is performed at a high linear velocity, and the recording medium is liable to be deteriorated by reproduction light. Therefore, the thickness is set to 20 nm or less.
[0025]
Next, the recording layer will be described.
Here, a material using Sb-Te having an atomic ratio of about 3: 1 as a mother phase as a recording layer will be described in detail, but GeTe-Sb having a molar ratio of 2: 1 will be described. ₂ Te ₃ Can be applied to a recording layer having a mixture of the above as a matrix.
Crystallization at the time of recording / erasing proceeds in the former case by crystal growth from the interface with the amorphous, and in the latter case, proceeds by uniform nucleation in the amorphous. In both cases, ZrO ₂ Since the nucleation is promoted by using the material containing, the unerased portion is less likely to occur, and the repeated recording durability is improved.
[0026]
Sb-Te having an atomic ratio of Sb to Te of about 3: 1 is a phase change recording material having excellent repetitive recording characteristics. The crystallization rate can be adjusted by changing the mixing ratio of Sb and Te, and the crystallization rate can be increased by increasing the ratio of Sb. According to the experiments by the present inventors, if Sb is 65 atomic% or more, recording can be performed at least at a linear velocity of 1 × of CD (1.2 m / s). When Sb was less than this, even at 1.2 m / s, the increase in jitter due to repeated recording was large, and good recording could not be performed. As the Sb ratio increases, the crystallization speed also increases, and good recording at a higher linear velocity becomes possible. Due to the limitations of the evaluation device and the like, the upper limit to which linear speed good recording is possible cannot be determined, but repetitive recording is possible at least up to DVD 5 × speed (17.5 m / s). However, when Sb exceeds 85 atomic%, the rate of increase in the crystallization rate becomes sharp, and the formation of amorphous marks becomes almost impossible. Therefore, it is preferable that the ratio of Sb in the Sb-Te binary system be 65 atomic% or more and 85 atomic% or less.
[0027]
However, the stability of the amorphous phase is poor only with the binary system of Sb—Te. For example, in a high temperature environment of about 70 to 80 ° C., there is a problem that the amorphous mark is crystallized within 50 hours. . Therefore, one or more third elements that can increase the stability of the amorphous phase are used.
Ge is effective as such a third element, and storage reliability can be drastically improved by adding a small amount. If the addition amount is 2 atomic% or more, an effect of improving the amorphous stability can be expected even in a recording layer having a high crystallization speed equivalent to DVD double speed or more. Although the effect increases as the amount of addition increases, the crystallization speed is particularly high, and in the case of a recording layer suitable for high linear velocity recording, if the amount of addition is too large, the recording sensitivity and the repetitive recording characteristics are reduced. It is desirable that the content be at most 7 atomic% or less.
[0028]
Further, when In or Ga is added, the crystallization speed can be increased, and the storage stability can be improved by increasing the crystallization temperature.
Although Ge described above is effective in improving storage stability, it slows down the crystallization rate, so that it is necessary to increase the Sb ratio with the addition of Ge in order to secure a constant crystallization rate. . However, as the Sb ratio increases, the recording sensitivity tends to decrease.
On the other hand, if In or Ga is added, the crystallization speed can be increased without increasing the Sb ratio, and a recording layer having excellent recording sensitivity can be obtained. If the amount of In or Ga is less than 1 atomic%, the effect is not clear, and if the amount is too large, the repetitive recording characteristics and the stability of the reproduction light are deteriorated.
[0029]
In addition, Ag, Bi, C, Ca, Cr, Cu, Dy, Mg, Mn, Se, Si, Sn, etc. may be added for the purpose of adjusting the crystallization speed.
As described above, by using at least Ge, In or Ga, Sb, and Te in an appropriate combination, a recording layer excellent in repetitive recording characteristics, recording sensitivity, and storage stability at a desired recording linear velocity can be formed. .
If the thickness of the recording layer is less than 8 nm, the modulation degree is small, and the stability of the reproduction light is reduced. Therefore, the thickness is set to 8 nm or more. If the thickness is more than 22 nm, the increase in jitter due to repeated recording is large. .
[0030]
Conventionally, an alloy containing Al as a main component has been used as the reflective layer. Al has a high reflectance and a high thermal conductivity, and also has excellent stability over time when formed into a disk. However, when the crystallization speed of the recording layer material is high, the recording mark tends to be thin on a disk using an Al alloy which is conventionally used as a reflection layer, and it is difficult to perform recording with a sufficient degree of modulation. Sometimes it was difficult. The reason for this is that if the crystallization speed is high, the recrystallized region of the molten region becomes large during recording, and the formed amorphous region becomes small.
In order to make the recrystallized area smaller, the upper protective layer may be made thinner to have a quenching structure.However, if the upper protective layer is simply made thinner, the temperature of the recording layer does not rise sufficiently and the molten area becomes smaller. Therefore, even if the recrystallized region can be made smaller, the formed amorphous region will eventually be smaller.
[0031]
However, when a metal in which n and k of the refractive index (n + ik) at wavelengths of 650 to 670 nm are both smaller than Al is used for the reflective layer, the absorptance of the recording layer is improved and the degree of modulation can be increased.
Examples of the metal in which both n and k are smaller than Al include Au, Ag, Cu, and alloys containing these as main components. Here, the term "main component" means that the content is 90 atomic% or more, and preferably 95 atomic% or more.
Table 2 shows the measured values of the refractive index of the sputtered film at λ = 660 nm and the values of the literature values (bulk) of the thermal conductivity for these pure metals.
[Table 2]

[0032]
Table 2 shows that Au, Ag, and Cu all have higher thermal conductivity than Al. Therefore, when these are used as the reflective layer, the light absorption of the recording layer is improved, and the temperature of the recording layer is increased to increase the melting area, and at the same time, the cooling rate is improved to recrystallize during cooling. Thus, it becomes possible to form a larger amorphous region than when an Al alloy is used.
The degree of modulation of a recording mark is determined by the degree of optical modulation and the size of the mark, and increases as the degree of optical modulation increases and the mark increases. Therefore, even in the case where high linear velocity recording is performed using a material having a high crystallization speed as the recording layer, a large recording mark can be formed because the absorption rate is large and the cooling rate is high if the reflective layer is used. Since the difference in reflectance between the crystal and the amorphous is large, recording with a large degree of modulation can be performed.
[0033]
Among Au, Ag, Cu, and alloys containing them as main components, Ag and Ag alloy are particularly inexpensive, and are hardly oxidized as compared with similarly inexpensive Cu and Cu alloy, so that they are stable with time. A medium having excellent properties can be formed, and is preferable as a reflective layer. However, since it is weak against sulfuration, when a material containing S is used for the upper protective layer, a sulfuration prevention layer is required.
If the anti-sulfuration layer has a thickness of 3 nm or more, the film formed by sputtering becomes substantially uniform, and exhibits an anti-sulfurization function. If the thickness is smaller than this, the probability of causing a partial defect suddenly increases.
[0034]
Properties required for the material of the anti-sulfuration layer include not containing S, not transmitting S, and the like.
The present inventors formed various oxide films and nitride films as anti-sulfuration layers and evaluated recording characteristics and storage reliability. As a result, SiC, Si, or a material containing any of them as a main component was used. Has an excellent function as an anti-sulfuration layer. Here, “main component” means that the material contains 90 mol% or more of SiC or Si, and preferably 95 mol% or more.
When the thickness of the reflective layer is 90 nm or more, almost no transmitted light is emitted, and light can be used efficiently. The larger the film thickness, the faster the cooling rate becomes, which is advantageous when using a recording layer with a high crystallization rate. However, the cooling rate is saturated at 200 nm or less, and there is no change in the recording characteristics even when the thickness is larger than 200 nm. Since it takes only a long time to form a film, the thickness is preferably 200 nm or less.
[0035]
The lower protective layer has a role of adjusting optical characteristics in addition to a role of a heat-resistant protective film. If the film thickness is less than 40 nm, the heat resistance is poor, and the jitter rise due to repeated recording becomes large. On the other hand, when the thickness is larger than 220 nm, the film forming efficiency is poor, and the film is liable to be peeled off due to the stress of the film. Therefore, a film thickness is selected so that the reflectance and the degree of modulation can be made large in the range of 40 to 220 nm, more preferably in the range of 40 to 80 nm.
When the lower interface layer is used, the thickness is adjusted so as to satisfy the optical characteristics as a whole by reducing the thickness of the lower protective layer by the lower interface layer.
[0036]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In each of the examples and comparative examples, a lower protective layer, a (lower interface layer), a recording layer, and an upper layer were formed on a polycarbonate disk substrate having a guide groove having a diameter of 12 cm, a thickness of 0.6 mm, and a track pitch of 0.74 μm. An interface layer, an upper protective layer, an anti-sulfuration layer, and a reflective layer are formed in this order by sputtering, and further, an organic protective film formed by spin coating on the reflective layer has a diameter of 12 cm and a thickness of 0.6 mm. The one to which the polycarbonate disk was bonded was initially crystallized by a large-diameter LD and used as a sample.
The evaluation was performed by irradiating a laser beam having a wavelength of 660 nm and NA of 0.65 from the substrate side and repeatedly recording a random pattern by a linear density of 0.267 μm / bit and an EFM + modulation method.
[0037]
Example 1
80 mol% of (ZnS) (SiO 2) ₂ ) 20 mol% of 65 nm in film thickness, Ag as recording layer ₁ In ₃ Sb ₇₂ Te ₂₀ Ge ₄ With a thickness of 15 nm as an upper interface layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 80 mol% (TiO ₂ ) 20 mol% in thickness of 2 nm, 80 mol% of (ZnS) (SiO 2) ₂ A) Initially crystallizing a disk in which 20 mol% was formed to a thickness of 10 nm, Si as an anti-sulfide layer to a thickness of 4 nm, and Ag as a reflective layer to a thickness of 140 nm, and the recording characteristics were repeatedly evaluated.
FIG. 4 shows the jitter (data to clock jitter, cross) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0038]
Example 2
As the upper interface layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 40 mol% (TiO ₂ ) 40 mol% (SiO ₂ A) A disc was prepared in exactly the same manner as in Example 1 except that 20 mol% was formed to a thickness of 2 nm, and the recording characteristics were repeatedly evaluated.
FIG. 5 shows the jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0039]
Example 3
Sb as recording layer ₇₆ Te ₂₀ Ge ₄ Was formed in the same manner as in Example 1 except that the film was formed to a thickness of 15 nm, and the recording characteristics were repeatedly evaluated.
FIG. 6 shows the jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0040]
Example 4
80 mol% of (ZnS) (SiO 2) ₂ ) 20 mol% as a lower interface layer with a film thickness of 63 nm (ZrO ₂ -3 mol% Y ₂ O ₃ ) 40 mol% (TiO ₂ ) 40 mol% (SiO ₂ ) 20 mol% of a film thickness of 2 nm, Ag as a recording layer ₁ In ₃ Sb ₇₂ Te ₂₀ Ge ₄ With a thickness of 15 nm as an upper interface layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 80 mol% (TiO ₂ ) 20 mol% in thickness of 2 nm, 80 mol% of (ZnS) (SiO 2) ₂ A) Initially crystallizing a disk in which 20 mol% was formed to a thickness of 10 nm, Si as an anti-sulfide layer to a thickness of 4 nm, and Ag as a reflective layer to a thickness of 140 nm, and the recording characteristics were repeatedly evaluated.
FIG. 7 shows the jitter (data to clock jitter, crossover) when recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0041]
Comparative Example 1
No upper interface layer is provided, and 80 mol% of (ZnS) (SiO ₂ A) A disk was prepared in exactly the same manner as in Example 1 except that a film thickness of 12 mol% was formed at 20 mol%, and repeated recording characteristics were evaluated.
FIG. 8 shows the jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figure, in the case of Pw = 15 mW and 17 mW, the jitter is 10% or less up to 10,000 times of repetitive recording. In the case of Pw = 19 mW, a decrease in reflectivity of about 1% was observed by repeated recording.
[0042]
Example 5
As the upper interface layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 80 mol% (TiO ₂ ) 20 mol% as a 14 nm-thick film and 80 mol% (ZnS) (SiO ₂ A disc was prepared in exactly the same manner as in Example 1 except that 20 mol% was formed to a thickness of 6 nm, and the recording characteristics were repeatedly evaluated.
FIG. 9 shows the jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0043]
Comparative Examples 2-3
80 mol% of (ZnS) (SiO 2) ₂ ) 20 mol% of 65 nm in film thickness, Ag as recording layer ₁ In ₃ Sb ₇₂ Te ₂₀ Ge ₄ With a film thickness of 15 nm as an upper protective layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 80 mol% (TiO ₂ ) A disk in which 20 mol% was formed to a thickness of 16 nm (Comparative Example 2) or 18 nm (Comparative Example 3), and a reflective layer formed of Ag having a thickness of 140 nm was subjected to initial crystallization, and then repeated recording characteristics were evaluated.
FIGS. 10 and 11 show the disks of Comparative Example 2 and Comparative Example 3 with a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. The state of change of jitter (data to clock jitter, no crosstalk) when recording was repeated up to 10,000 times is shown.
As can be seen from FIG. 10, in the case of Comparative Example 2, good repetitive recording characteristics were obtained on the high power side with Pw = 17 mW and 19 mW, but good characteristics were not obtained from the first time with Pw = 15 mW. .
Comparative Example 3 attempted to improve the recording characteristics on the low power side by increasing the temperature of the recording layer by increasing the thickness of the upper protective layer, but as shown in FIG. In addition, the jitter increased, and no effect of improving the characteristics on the low power side was observed.
[0044]
Example 6
As the upper interface layer (ZrO ₂ -3 mol% Y ₂ O ₃ ) 80 mol% (TiO ₂ ) 20 mol% of 6 nm in thickness, SiO as upper protective layer ₂ Was formed in the same manner as in Example 1 except that the film was formed to a thickness of 8 nm, and the recording characteristics were repeatedly evaluated.
FIG. 12 shows jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0045]
Example 7
As the upper interface layer (ZrO ₂ -8 mol% MgO) 80 mol% (TiO ₂ A) A disc was prepared in exactly the same manner as in Example 1 except that 20 mol% was formed to a thickness of 2 nm, and the recording characteristics were repeatedly evaluated.
FIG. 13 shows jitter (data to clock jitter, cross-talk) when recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0046]
Example 8
As the upper interface layer (ZrO ₂ -8 mol% MgO) 80 mol% (Al ₂ O ₃ A) A disc was prepared in exactly the same manner as in Example 1 except that 20 mol% was formed to a thickness of 2 nm, and the recording characteristics were repeatedly evaluated.
FIG. 14 shows the jitter (data to clock jitter, crossover) when the recording was repeated up to 10,000 times at a linear velocity of 14 m / s, Pw = 15 mW, 17 mW, 19 mW, Pe = 4.4 to 5.6 mW, and Pb = 0.1 mW. (Without talk).
As can be seen from the figures, the jitter was 10% or less in each case, and an optical recording medium excellent in repeated recording durability in a wide power range could be obtained. No decrease in reflectance due to repeated recording was observed.
[0047]
【The invention's effect】
According to the inventions 1 to 12, it is possible to provide an optical recording medium having excellent repetitive recording durability in a wide power range.
According to the inventions 13 to 16, an excellent optical recording medium having good repetitive recording characteristics and storage stability in a wide linear velocity region from at least CD1X (1.2 m / s) to DVD5X (17.5 m / s). Can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a method generally used as a method for recording an amorphous mark on a phase change optical disk.
FIG. 2 is a diagram schematically illustrating a state in which a laser is irradiated to an amorphous mark, crystal growth proceeds from an interface with a crystal part, and crystallization occurs.
FIG. 3 is a diagram showing a relationship between a temperature and a crystal growth rate.
FIG. 4 is a diagram illustrating a change in jitter when the optical recording medium of Example 1 is repeatedly recorded up to 10,000 times.
FIG. 5 is a diagram illustrating a state of a change in jitter when the optical recording medium of Example 2 is repeatedly recorded up to 10,000 times.
FIG. 6 is a diagram illustrating a change in jitter when the optical recording medium of Example 3 is repeatedly recorded up to 10,000 times.
FIG. 7 is a diagram showing a state of a change in jitter when the optical recording medium of Example 4 is repeatedly recorded up to 10,000 times.
FIG. 8 is a diagram showing a state of a change in jitter when the optical recording medium of Comparative Example 1 is repeatedly recorded up to 10,000 times.
FIG. 9 is a view showing a state of a change in jitter when the optical recording medium of Example 5 is repeatedly recorded up to 10,000 times.
FIG. 10 is a diagram showing a change in jitter when recording is repeatedly performed up to 10,000 times on the optical recording medium of Comparative Example 2.
FIG. 11 is a diagram illustrating a state of a change in jitter when the optical recording medium of Comparative Example 3 is repeatedly recorded up to 10,000 times.
FIG. 12 is a diagram illustrating a state of a change in jitter when the optical recording medium of Example 6 is repeatedly recorded up to 10,000 times.
FIG. 13 is a diagram showing a change in jitter when recording is repeatedly performed up to 10,000 times on the optical recording medium of Example 7.
FIG. 14 is a diagram showing a state of a change in jitter when the optical recording medium of Example 8 is repeatedly recorded up to 10,000 times.
FIG. 15 is a view showing a result of comparing a state of increase of jitter with and without an interface layer.
[Explanation of symbols]
Pw Recording power
Pe erase power
Pb bias power
T reference clock

Claims (16)

At least a lower protective layer / recording layer / upper interface layer / upper protective layer / reflective layer is formed on the transparent substrate in this order or in reverse order, and the upper interface layer is made of Zr oxide and A phase-change optical recording medium comprising an oxide of one or more elements (excluding Zr) selected from Groups 2 to 14 of the period to the sixth period. Between the lower protective layer and the recording layer, an oxide of Zr and one or more elements (excluding Zr) selected from Groups 2 to 14 of the third to sixth periods of the periodic table 2. The optical recording medium according to claim 1, further comprising a lower interface layer made of an oxide. The upper interface layer or the lower interface layer contains a solid solution of an oxide of Zr and an oxide of at least one element selected from Group 2 and Group 3 of the third to sixth periods of the periodic table. 3. The phase-change optical recording medium according to claim 1, wherein: The upper interface layer or the lower interface layer is an oxide of one or more elements (excluding Zr) selected from Groups 2 to 5 and Groups 12 to 14 of the third to sixth periods of the periodic table. The phase-change optical recording medium according to any one of claims 1 to 3, further comprising: The phase-change optical recording medium according to any one of claims 1 to 4, wherein the upper interface layer or the lower interface layer contains a sulfide of Zn. The optical recording medium according to claim 1, wherein the oxide of Zr is ZrO ₂ . 7. The phase-change optical recording medium according to claim 1, wherein the mixture containing the Zr oxide solid solution is represented by the following formula.
_{[(ZrO 2) 1-α (} X) α ] β (Z) γ (ZnS) δ
X: oxide of at least one element selected from MgO, CaO, Sc ₂ O ₃ , Y ₂ O ₃ , and CeO ₂ Z: TiO ₂ , SiO ₂ , Al ₂ O ₃ , MgO, Ta ₂ O ₅ , ZnO At least one oxide α selected from the group consisting of: 2 to 15 (mol%)
β: 40 to 100 (mol%)
γ: 0 to 60 (mol%)
δ: 0 to 60 (mol%)
β + γ + δ = 100 (mol%) 8. The phase-change optical recording medium according to claim 1, wherein the thickness of the upper interface layer is 1 to 18 nm. 9. The phase-change optical recording medium according to claim 2, wherein the lower interface layer has a thickness of 1 to 100 nm. 10. The phase-change optical recording medium according to claim 1, wherein a material having a thermal conductivity of at least 10 W / (m · K) in a bulk state is used as an upper protective layer material. 11. The phase-change optical recording medium according to claim 1, wherein the material of the upper protective layer comprises a mixture of ZnS and an oxide of Si. The phase-change optical recording medium according to claim 11, wherein the mixture of ZnS and Si oxide is represented by the following formula.
(ZnS) 100-ε (SiO 2) ε [epsilon: 10 to 100 (mol%)] 13. The phase-change optical recording medium according to claim 1, wherein the upper protective layer has a thickness of 2 to 20 nm. The recording layer contains at least Sb, Te and Ge, the atomic ratio Sb / (Sb + Te) of Sb and Te is 0.65 to 0.85, and the Ge content is 2 to 7 atomic%. A phase-change optical recording medium according to claim 1. The phase-change optical recording medium according to claim 14, wherein the recording layer further contains 1 to 7 atomic% of In or Ga. 16. The phase-change optical recording medium according to claim 14, wherein the recording layer has a thickness of 8 to 22 nm.

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