JP4093472B2 - Phase change recording medium - Google Patents

Description

【００４３】
記録再生条件は４０５ｎｍ、ＮＡ＝０．８５、５．７ｍ／ｓ、記録線密度：０．１３μｍ／ｂｉｔ、記録パワーはジッタが最小となる記録パワー５．５ｍＷで記録、再生パワー：０．３ｍＷ、ジッタはσ／Ｔｗ（ウインドウ幅）、１−７変調でランダム信号を記録した。
表１に示すように、界面層があるほうがアーカイバル評価（８０℃、８５％）を行なってもジッタ変化がなく良好なメディアである。これは反射層として、第３保護層（７）としてＩＺＯを用いると、ＩＺＯは熱伝導率が高いので、第２記録層（１０）で記録される際に発生する熱がＡｇおよびＡｇ合金層を経由して、第３保護層（７）で放熱される。これによって、急激な冷却が必要とされる相変化材料ＳｂＴｅを主成分とする記録層は最適な急冷状態となり、小さなアモルファスマークが形成可能となる。
【００４４】
また、界面層（１４）として、Ｔｉ-Ｃ-Ｏ、あるいはＭｏ−Ｃ−Ｏ、あるいはＶ−Ｃ−Ｏ、あるいはＺｒ−Ｃ−ＯあるいはＣｒ−Ｃ−Ｏ、あるいはＮｂ−Ｃ−Ｏ、あるいはＭｎ−Ｃ−Ｏ、あるいはＳｉ−Ｃ−Ｏ、Ｔａ−Ｃ−Ｏで形成すると、上記材料の酸素量は１０％以下と少量でかつ安定であり、反射層にＡｇやＡｌ等の材料を使用しても、酸化され材料の変化がほとんど見受けられない。上記材料とＡｇ反射層の組み合わせのメディアではアーカイバル保存性（８０℃８５％、２００時間）も記録したマークのジッタが変化せず、良好な特性を示した。
【００４５】
しかし、第２の記録構成層（２００）の放熱性としては、前述のように第３保護層（７）の放熱性だけでは不充分でＡｇおよびＡｇ合金層（８）が熱の放熱性を改善して、特にＳｂＴｅをべースにした記録層では熱の最初の急冷性がアモルファスマークを形成するので、ＡｇおよびＡｇ合金層（８）と第３保護層（７）と界面層（１４）を組み合わせた構成とすることにより、高密度とＯ／Ｗ特性と保存性が改善される。
【００４６】
以下に、放熱機能を担う反射層（２）とＡｇまたはＡｇ合金層（８）についてそれぞれ説明する。
反射層（２）はとりわけ高熱伝導率の材料とすることにより、消去比および消去パワーマージンを改善できる。検討の結果、広い消去パワー範囲において本発明の記録層が持つ良好な消去特性を発揮させるには、単に膜厚方向の温度分布や時間変化のみならず膜面方向（記録ビーム走査方向に対して垂直方向）の温度分布をできるだけ平坦化できるような層構成を用いるのが好ましい。本発明においては、非常に高熱伝導率で３００ｎｍ以下の薄い反射層（２）を用いて、横方向の放熱効果を促進するのが特徴である。
一般には薄膜の熱伝導率はバルク状態の熱伝導率と大きく異なり、小さくなっているのが普通である。特に、４０ｎｍ未満の薄膜では成長初期の島状構造の影響で熱伝導率が１桁以上小さくなる場合があり好ましくない。さらに、成膜条件によって結晶性や不純物量が異なり、これによって同じ組成でも熱伝導率が異なる要因になる。
【００４７】
第１の記録構成層（１００）の反射層（２）における放熱は、反射層（２）の厚みを厚くしても達成できるが、反射層（２）の厚みが３００ｎｍを超えると第１記録層（４）膜面方向よりも膜厚方向の熱伝導が顕著になり、膜面方向の温度分布改善効果が得られない。また、反射層（２）自体の熱容量が大きくなり、反射層（２）ばかりでなく、ひいては第１記録層（４）の冷却に時間がかかるようになって非晶質マークの形成が阻害される。最も好ましいのは、高熱伝導率の反射層（２）を薄く設けて横方向への放熱を選択的に促進することである。従来用いられていた急冷構造は、膜厚方向の１次元的な熱の逃げにのみ注目し、第１記録層（４）から反射層（２）に早く熱を逃すことのみを意図しており、この平面方向の温度分布の平坦化に充分な留意が払われていなかった。
【００４８】
本発明に適した反射層（２）の材料としてはＡｇまたはＡｇ合金、Ｃｕ合金、Ａｌ合金等が挙げられる。
Ａｇ合金としては、後述のＡｇまたはＡｇ合金層（８）に用いられると同様のＡｇ合金が挙げられる。Ａｇ合金を反射層（２）として用いる場合、好ましい膜厚は３０ｎｍ以上、２００ｎｍ以下である。３０ｎｍ未満では純Ａｇでも放熱効果は不充分である。２００ｎｍを超えると熱が水平方向より垂直方向に逃げて水平方向の熱分布改善に寄与しないし、不必要な厚膜は生産性を低下させる。また、膜表面の微視的な平坦性も悪くなる。
【００４９】
Ｃｕ合金としては、例えばＣｕを０．３重量％以上、５．０重量％以下含有するＡｌ−Ｃｕ系合金がある。特に、ＺｎＳとＳｉＯ_２との混合系組成とＴａ_２Ｏ_５とを組み合わせた２層構成保護層とする場合には、Ｃｕを０．５重量％以上、４．０重量％以下含有するＡｌ−Ｃｕ系合金が耐食性、密着性、高熱伝導率の全てをバランス良く満足する反射層として望ましい。また、Ｓｉを０．３重量％以上、０．８重量％以下、Ｍｇを０．３重量％以上、１．２重量％以下含有するＡｌ−Ｍｇ−Ｓｉ系合金も有効である。
【００５０】
Ａｌ合金としては、例えばＡｌにＴａ、Ｔｉ、Ｃｏ、Ｃｒ、Ｓｉ、Ｓｃ、Ｈｆ、Ｐｄ、Ｐｔ、Ｍｇ、Ｚｒ、ＭｏあるいはＭｎを０．２原子％以上、２原子％以下含む合金などがあり、これらは添加元素濃度に比例して体積抵抗率が増加し、また耐ヒロック性が改善され、耐久性、体積抵抗率、成膜速度等考慮して用いることができる。Ａｌ合金に関しては、添加不純物量０．２原子％未満では成膜条件にもよるが、耐ヒロック性は不充分であることが多い。また、２原子％より多いと上記の低抵抗率が得られにくい。経時安定性をより重視する場合には添加成分としてはＴａが好ましい。
【００５１】
上記Ａｌ合金を反射層（２）として用いる場合、好ましい膜厚は１５０ｎｍ以上、３００ｎｍ以下である。１５０ｎｍ未満では純Ａｌでも放熱効果は不充分である。前記のように３００ｎｍを超えると熱が水平方向より垂直方向に逃げて水平方向の熱分布改善に寄与しないし、反射層そのものの熱容量が大きく、そのため記録層の冷却速度が遅くなってしまう。また、膜表面の微視的な平坦性も悪くなる。
【００５２】
次にＡｇまたはＡｇ合金層（８）について説明する。
本発明の第２記録層（１０）はＴｍ近傍での再凝固時の結晶成長が再結晶化の律速になっている。Ｔｍ近傍での冷却速度を極限まで大きくして非晶質マークおよびそのエッジの形成を確実かつ明確なものとするには、超急冷構造が有効であり、かつ膜面方向の温度分布の平坦化で、もともとＴｍ近傍で高速消去可能であったものがより高消去パワーまで確実に再結晶化による消去を確保できる。このため、いわゆる「第３保護層（７）での熱伝導遅延効果を考慮した超急冷構造」を本発明に係る第２の記録構成層（２００）に適用すると、従来のＧｅＴｅ−Ｓｂ_２Ｔｅ_３記録層に比べて一層効果がある。
【００５３】
このような超急冷のための放熱構成層としてＡｇまたはＡｇ合金層（８）が用いられる。ＡｇまたはＡｇ合金層（８）の形成する場合については製膜時のデポレート反射層（２）よりも遅くして膜厚不均一性をなくして形成する。ＡｇまたはＡｇ合金層（８）の膜厚は、５ｎｍ以上、２０ｎｍ以下が望ましい。５ｎｍ以下はデポレートを遅くしても不均一になる。
Ａｇ合金としては、ＡｇにＣｕ、Ｔｉ、Ｖ、Ｔａ、Ｎｂ、Ｗ、Ｃｏ、Ｃｒ、Ｓｉ、Ｇｅ、Ｓｎ、Ｓｃ、Ｈｆ、Ｐｄ、Ｒｈ、Ａｕ、Ｐｔ、Ｍｇ、Ｚｒ、ＭｏあるいはＭｎを０．２原子％以上、５原子％以下含む合金も望ましい。経時安定性をより重視する場合には添加成分としてはＴｉ、Ｍｇが好ましい。
【００５４】
本発明者らは前記反射層（２）およびＡｇまたはＡｇ合金層（８）における、Ａｌへの添加元素あるいはＡｇへの添加元素は、その添加元素濃度に比例して体積抵抗率が増加することを確認している。一方、不純物の添加は一般的に結晶粒径を小さくし、粒界の電子散乱を増加させて熱伝導率を低下させると考えられる。添加不純物量を調節することは、結晶粒径を大きくすることで材料本来の高熱伝導率を得るために必要である。
【００５５】
なお、反射層（２）およびＡｇまたはＡｇ合金層（８）は通常スパッタ法や真空蒸着法で形成されるが、ターゲットや蒸着材料そのものの不純物量もさることながら、成膜時に混入する水分や酸素量も含めて全不純物量を２原子％以下とする必要がある。このためにプロセスチャンバの到達真空度は１×１０^−３Ｐａ以下とすることが望ましい。また、１０^−４Ｐａより悪い到達真空度で成膜する場合には、成膜レートを１ｎｍ／秒以上、好ましくは１０ｎｍ／秒以上として不純物が取り込まれるのを防ぐことが望ましい。あるいは、意図的な添加元素を１原子％より多く含む場合は、成膜レートを１０ｎｍ／秒以上として付加的な不純物混入を極力防ぐことが望ましい。
【００５６】
成膜条件は不純物量とは無関係に結晶粒径に影響を及ぼす場合もある。例えば、ＡｌにＴａを２原子％程度混入した合金膜は、結晶粒の間に非晶質相が混在するが結晶相と非晶質相の割合は成膜条件に依存する。また、低圧でスパッタするほど結晶部分の割合が増え、体積抵抗率が下がり、熱伝導率が増加する。
膜中の不純物組成あるいは結晶性は、スパッタに用いる合金ターゲットの製法やスパッタガス（Ａｒ、Ｎｅ、Ｘｅ等）にも依存する。このように薄膜状態の体積抵抗率は、金属材料、組成のみによっては決まらない。高熱伝導率を得るためには、上記のように不純物量を少なくするのが望ましいが、一方でＡｌやＡｇの純金属は耐食性や耐ヒロック性に劣る傾向があるため、両者のバランスを考慮して最適組成を決める必要がある。
【００５７】
さらなる高熱伝導と高信頼性を得るために反射層（２）およびＡｇまたはＡｇ合金層（８）を多層化することも有効である。この場合、少なくとも１層は全層膜厚の５０％以上の膜厚を有する前記高熱伝導性材料（低体積抵抗率材料）からなり、実質的に放熱効果に寄与し、他の層が耐食性や保護層との密着性、耐ヒロック性の改善に寄与するように構成される。
より具体的には、金属中最も高熱伝導率および低体積抵抗率であるＡｇを用いた場合に、Ａｇに隣接する保護層中にＳ（硫化物等）を含むと相性が悪くて、硫化による腐食を起こしやすく、繰返しオーバーライト（Ｏ／Ｗ）した場合の劣化がやや速いという傾向がある。また、高温高湿の加速試験環境下で腐食を生じやすい傾向がある。そこで、低体積抵抗率材料としてＡｇまたはＡｇ合金を用いる際には、隣接保護層との間に界面層としてＡｌを主成分とする合金層を１ｎｍ以上、１００ｎｍ以下設けることも有効である。この厚さを５ｎｍ以上とすれば、層が島状構造とならず均一に形成されやすい。
【００５８】
上記Ａｌ合金としては前述と同様に、例えばＴａ、Ｔｉ、Ｃｏ、Ｃｒ、Ｓｉ、Ｓｃ、Ｈｆ、Ｐｄ、Ｐｔ、Ｍｇ、Ｚｒ、ＭｏまたはＭｎを０．２原子％以上、２原子％以下含むＡｌ合金が挙げられる。界面層の厚さは１ｎｍ未満では保護効果が不充分で、１００ｎｍを超えると放熱効果が犠牲になる。
【００５９】
さらに、Ａｇ合金反射層とＡｌ合金界面層を用いる場合、ＡｇとＡｌは比較的相互拡散しやすい組み合わせであるので、Ａｌ表面を１ｎｍより厚く酸化して界面酸化層を設けることが一層好ましい。なお、界面酸化層が５ｎｍ、特に１０ｎｍを越えるとそれが熱抵抗となり本来の趣旨である極めて放熱性の高い反射層としての機能が損なわれるので好ましくない。
【００６０】
本発明において良好な特性を示す高熱伝導率の反射層（２）、およびＡｇまたはＡｇ合金層（８）を規定するために、それぞれの熱伝導率を直接測定することも可能であるが、その熱伝導の良否を電気抵抗を利用して見積もることができる。金属膜のように電子が熱もしくは電気伝導を主として司る材料においては熱伝導率と電気伝導率は良好な比例関係があるためである。薄膜の電気抵抗は、その膜厚や測定領域の面積で規格化された抵抗率値で表わす。体積抵抗率と面積抵抗率は、通常の４探針法で測定でき、ＪＩＳ Ｎ ７１９４によって規定されている。本法により、薄膜の熱伝導率そのものを実測するよりもはるかに簡便かつ再現性の良いデータが得られる。
【００６１】
本発明において好ましい反射層（２）、およびＡｇまたはＡｇ合金層（８）の特性としては、体積抵抗率が２０ｎΩ・ｍ以上、１５０ｎΩ・ｍ以下であり、より好ましくは２０ｎΩ・ｍ以上、１００ｎΩ・ｍ以下である。体積抵抗率２０ｎΩ・ｍ未満の材料は薄膜状態では実質的に得にくい。体積抵抗率１５０ｎΩ・ｍより体積抵抗率が大きい場合でも、例えば３００ｎｍを超える厚膜とすれば面積抵抗率を下げることはできるが、本発明者らの検討によれば、このような高体積抵抗率材料で面積抵抗率のみ下げても充分な放熱効果は得られなかった。厚膜では単位面積当たりの熱容量が増大してしまうためと考えられる。また、このような厚膜では成膜に時間がかかり、材料費も増えるため製造コストの観点から好ましくないばかりでなく、さらに膜表面の微視的な平坦性も悪くなってしまう。膜厚３００ｎｍ以下で面積抵抗率０．２以上、０．９Ω／□以下が得られるような低体積抵抗率材料を用いるのが好ましく、０．５Ω／□が最も好ましい。ＡｇまたはＡｇ合金層（８）の場合は、透過率の関係から２０ｎｍ以下が望ましい。
【００６２】
反射層（２）あるいはＡｇまたはＡｇ合金層（８）の前記多層化については、高体積抵抗率材料と低体積抵抗率材料を組み合わせて所望の膜厚で所望の面積抵抗率を得るためにも有効である。合金化による体積抵抗率調節は、合金ターゲットの使用によりスパッタ工程を簡素化できるが、ターゲット製造コスト、ひいては媒体の原材料比を上昇させる要因にもなる。したがって、純Ａｌや純Ａｇの薄膜と上記添加元素そのものの薄膜を多層化して所望の体積抵抗率を得ることも有効である。層数が３層程度までであれば初期の装置コストは増加するものの、個々の媒体コストはかえって抑制できる場合がある。反射層（２）を複数の金属膜からなる多層反射層とし、全膜厚を４０ｎｍ以上、３００ｎｍ以下とし、多層反射層の厚さの５０％以上が体積抵抗率２０ｎΩ・ｍ以上、１５０ｎΩ・ｍ以下の金属薄膜層（多層であってもよい）とするのが好ましい。
【００６３】
次に、図１に示すようにカバー基板（１３）を設ける構成で、高ＮＡの対物レンズを用いる場合には、カバー基板（１３）の厚さは０．３ｍｍ以下、より好ましくは０．０６〜０．２０ｍｍの厚さが要求されるため、シート状であることが好ましい。材料としては、ポリカーボネート樹脂、アクリル樹脂、エポキシ樹脂、ポリスチレン樹脂、アクリロニトリル−スチレン共重合体樹脂、ポリエチレン樹脂、ポリプロピレン樹脂、シリコーン系樹脂、フッ素系樹脂、ＡＢＳ樹脂、ウレタン樹脂などが挙げられるが、光学特性、コストの点で優れるポリカーボネート樹脂、アクリル系樹脂が好ましい。上記透明シートを用いて薄型基板を形成する方法としては、紫外線硬化性樹脂あるいは透明な両面粘着シートを介して、透明シートを貼りつける方法が挙げられる。また、紫外線（ＵＶ）硬化性樹脂を保護層上に塗布してこれを硬化させて薄型基板を形成してもよい。
樹脂中間層も、接着層も上記樹脂を用いるが、ＵＶ硬化樹脂がコストの面で優れているので使用される。
【００６４】
【実施例】
以下、実施例により本発明を更に詳細に説明する。ただし、本発明はなんら実施例に限定されるものではない。
【００６５】
（実施例１）
図２に示す層構成で、ポリカーボネート製基板（２１）上に、反射層（２２）（ＡｇＣｕＰｔＰｄ）、界面層（３４）（Ｔｉ−Ｃ−Ｏ）、第１保護層（２３）（ＺｎＳＳｉＯ_２）、第１記録層（２４）（Ａｇ_５Ｉｎ_５Ｓｂ_６５Ｔｅ_２５）、第２保護層（２５）（ＺｎＳＳｉＯ_２）、樹脂中間層（２６）（ポリカーボネート）、第３保護層（２７）（ＩＺＯ）、ＡｇまたはＡｇ合金層（２８）（ＡｇＣｕＰｔＰｄ）、界面層（３４）（Ｔｉ−Ｃ−Ｏ）、第４保護層（２９）（ＺｎＳＳｉＯ_２）、第２記録層（３０）（Ｇｅ_５Ａｇ_２Ｓｂ_７０Ｔｅ_２３）、第５保護層（３１）（ＺｎＳＳｉＯ_２）、接着層（３２）（アクリル系両面接着）、カバー基板（３３）（ポリカーボネート）からなる各層を形成して評価用相変化型記録媒体を作製した。なお、ＵＶ硬化樹脂中間層（２６）とアクリル系両面接着層（３２）以外はスパッタ法により厚さを制御しながら基板（２１）側から順次各層を形成して作製した。
【００６６】
なお、各構成層の厚さは下記の通りに制御して作製した。
基板（２１）：１．１ｍｍ、反射層（２２）：１２０ｎｍ、界面層（３４）：４ｎｍ、第１保護層（２３）：７ｎｍ、第１記録層（２４）：１０ｎｍ、第２保護層（２５）：１００ｎｍ、樹脂中間層（２６）：３０μｍ、第３保護層（２７）：１２０ｎｍ、ＡｇまたはＡｇ合金層（２８）：１０ｎｍ、界面層（３４）：５ｎｍ、第４保護層（２９）：１０ｎｍ、第２記録層（３０）：６ｎｍ、第５保護層（３１）：１００ｎｍ、接着層（３２）：アクリル系両面粘着（３０μｍ）を使用、カバー基板（３３）：６０μｍ。
【００６７】
（実施例２）
実施例１において、界面層（３４）の材質をＴｉ-Ｃ-ＯからＺｒ−Ｃ−Ｏ組成に変えたほかは、実施例１の構成と厚さとを全く同様にして評価用相変化型記録媒体を作製した。
【００６８】
（実施例３）
実施例１において、界面層（３４）の材質をＴｉ−Ｃ−ＯからＣｒ−Ｃ−Ｏ組成に変えたほかは、実施例１の構成と厚さとを全く同様にして評価用相変化型記録媒体を作製した。
【００６９】
（実施例４）
実施例１において、界面層（３４）の材質をＴｉ−Ｃ−ＯからＮｂ−Ｃ−Ｏ組成に変えたほかは、実施例１の構成と厚さとを全く同様にして評価用相変化型記録媒体を作製した。
【００７０】
（実施例５）
実施例１において、界面層（３４）の材質をＴｉ−Ｃ−ＯのかわりにＴａ−Ｃ−Ｏ組成に変えたほかは、実施例１の構成と厚さとを全く同様にして評価用相変化型記録媒体を作製した。
【００７１】
（比較例１）
界面層がないこと以外実施例１に示す構成と厚さとを全く同様にして評価用相変化型記録媒体を作製した。
前記実施例１〜５および比較例１における評価用相変化型記録媒体の各層の構成材料をまとめて表２に示す。
【００７２】
【表２】

【００７３】
上記実施例におけるＴｉ−Ｃ−Ｏの組成は、（ＴｉＣ_２）_８０（ＴｉＯ_２）_２０）であり、許容範囲 （ＴｉＣ_２）x（ＴｉＯ_２）_{１００− x}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｚｒ−Ｃ−Ｏの組成は、（ＺｒＣ_２）_８０（ＺｒＯ_２）_２０であり、許容範囲 （ＺｒＣ_２）_ｘ（ＺｒＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｃｒ−Ｃ−Ｏの組成は、（ＣｒＣ_２）_８０（ＣｒＯ_２）_２０であり、許容範囲 （ＣｒＣ_２）_ｘ（ＣｒＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｎｂ−Ｃ−Ｏの組成は、（ＮｂＣ_２）_８０（ＮｂＯ_２）_２０であり、許容範囲 （ＮｂＣ_２）_ｘ（ＮｂＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｔａ−Ｃ−Ｏの組成は、（ＴａＣ_２）_８０（ＴａＯ_２）_２０であり、許容範囲 （ＴａＣ_２）_ｘ（ＴａＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
ＡｇＩｎＳｂＴｅの組成は、許容範囲（Ａｇ（１〜１０）、Ｉｎ（１〜１０）、Ｓｂ（６０〜９０）、Ｔｅ（１０〜３０）である。
ＧｅＳｂＴｅの組成は、許容範囲（Ｇｅ（１〜１０）、Ｓｂ（６０〜９０）、Ｔｅ（１０〜３０）である。
【００７４】
また、上記組成のものに代えて、以下のものを用いることができる。
Ｍｏ−Ｃ−Ｏの組成は、（ＭｏＣ_２）_８０（ＭｏＯ_２）_２０であり、許容範囲（ＭｏＣ_２）x（ＭｏＯ_２）_{１００− x}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｖ−Ｃ−Ｏの組成は、（ＶＣ_２）_８０（ＶＯ_２）_２０であり、許容範囲 （ＶＣ_２）ｘ（ＶＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｍｎ−Ｃ−Ｏの組成は、（ＭｎＣ_２）_８０（ＭｎＯ_２）_２０であり、許容範囲（ＭｎＣ_２）_ｘ（ＭｎＯ_２）１００−ｘの場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
Ｓｉ−Ｃ−Ｏの組成は、（ＳｉＣ_２）_８０（ＳｉＯ_２）_２０であり、許容範囲（ＳｉＣ_２）ｘ（ＳｉＯ_２）_{１００−ｘ}の場合、６０≦ｘ≦９０、好ましくは７０〜８０ａｔ％である。
【００７５】
＜評価＞
上記実施例１〜５および比較例１で作製した評価用相変化型記録媒体について、波長４０２ｎｍ、開口数ＮＡ０．８５の光学系を用いて集束光ビームを照射し、線速：５．７ｍ／ｓ、０．１３０μｍ／ｂｉｔの条件で、初期ジッタ（Ｊｉｔｔｅｒ）、記録パワー（ジッタ最小を示すパワー）、アーカイバル特性、Ｏ／Ｗ特性を評価した。第１の記録層構成、第２の記録層構成として結果を表３、表４に示す。
【００７６】
【表３】

【００７７】
【表４】

＊）記録パワー不足で記録不可能。
【００７８】
評価判断基準は下記による。
アーカイバル特性：８０℃、８５％（ＲＨ）の保存でジッタ（Ｊｉｔｔｅｒ）上昇が２０％以上となる時間（Ｈ）。
Ｏ／Ｗ特性：オーバーライト（Ｏ／Ｗ）によるジッタ（Ｊｉｔｔｅｒ）上昇が２０％に到達したオーバーライト（Ｏ／Ｗ）回数（回）。
記録パワー（記録感度）：ジッタ最小となるパワー。
【００７９】
上記評価試験の結果、実施例１〜５の本発明になる評価用相変化型記録媒体はいずれも優れたアーカイバル特性（１０００Ｈ〜２０００Ｈ）、Ｏ／Ｗ特性（１００００回〜２００００回）を示し、記録感度（８．５〜９．５ｍＷ）も良好で、比較例のそれぞれの特性１００Ｈ、３００Ｈ（アーカイバル特性）、１０００回（Ｏ／Ｗ特性）に較べてジッタ、アーカイバル特性は良好であった。
界面層がない比較例１は保存特性（アーカイバル特性）が悪く、界面層でＳｉＮを用いた比較例２では熱伝導率が高く、第２記録層の記録感度が悪く、記録ができなかった。
【００８０】
【発明の効果】
以上、詳細且つ具体的な説明により明らかなように、本発明の、基板上に少なくとも第１の記録構成層と樹脂中間層と第２の記録構成層とが順次設けられ、該第１の記録構成層は基板側から順に反射層、界面層、第１保護層、第１記録層、第２保護層から構成され、該第２の記録構成層は樹脂中間層側から順に第３保護層、ＡｇまたはＡｇ合金層、界面層、第４保護層、第２記録層、第５保護層から構成された相変化型記録媒体であって、第３保護層としてＩＺＯ、前記第１記録層と第２記録層が少なくともＳｂＴｅを含有し、前記界面層の光学定数の屈折率が波長３５０ｎｍから４２０ｎｍにおいて２．２以上２．５以下であることにより、光の干渉により第１の記録層構成の透過率を向上できるため、第２記録層の記録感度を良好にし、優れたＯ／Ｗ特性、アーカイバル特性、高密度記録性能を発揮する相変化型記録媒体が提供される。
また、本発明の界面層の形成成分をＴｉ−Ｃ−Ｏ、あるいはＭｏ−Ｃ−Ｏ、あるいはＶ−Ｃ−Ｏ、あるいはＺｒ−Ｃ−Ｏ、あるいはＣｒ−Ｃ−Ｏ、あるいはＮｂ−Ｃ−Ｏ、あるいはＭｎ−Ｃ−Ｏ、あるいはＳｉ−Ｃ−Ｏ、Ｔａ−Ｃ−Ｏで形成すると、光の干渉により、第１の記録層構成の光透過量が増え、第２記録層に到達する光量が増加し、第２記録層の記録感度を良好にし、また上記材料をもちいるとアーカイバル保存性（８０℃８５％、２００時間）も記録したマークのジッタが変化せず、良好な特性を示した。またＯ／Ｗ特性も良好なメディアを提供できるという優れた効果を奏する。
【図面の簡単な説明】
【図１】本発明の相変化型記録媒体を説明するための一例を示す層構成断面図である。
【図２】本発明の実施例における評価用相変化型記録媒体の層構成を示す断面図である。
【符号の説明】
１ 基板
２ 反射層
３ 第１保護層
４ 第１記録層
５ 第２保護層
６ 樹脂中間層
７ 第３保護層
８ ＡｇまたはＡｇ合金層
９ 第４保護層
１０ 第２記録層
１１ 第５保護層
１２ 接着層
１３ カバー基板
１４ 界面層
２１ 基板
２２ 反射層
２３ 第１保護層
２４ 第１記録層
２５ 第２保護層
２６ 樹脂中間層
２７ 第３保護層
２８ ＡｇまたはＡｇ合金層
２９ 第４保護層
３０ 第２記録層
３１ 第５保護層
３２ 接着層
３３ カバー基板
３４ 界面層
１００ 第１の記録構成層
２００ 第２の記録構成層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium (phase change type recording medium) for high density recording having a phase change type recording layer such as a rewritable DVD-R.
[0002]
[Prior art]
In general, a compact disc (CD) or DVD is performed by recording a binary signal and detecting a tracking signal by using a change in reflectance caused by light interference from the bottom and mirror surface of a concave pit. In recent years, phase-change-type rewritable compact discs (CD-RW: CD-Rewritable) are being widely used as media that have playback compatibility (compatibility) with CDs. Various possible DVDs have been proposed. Also, while the capacity of the DVD is 4.7 GB, the recording / reproducing wavelength is shortened to 350 nm to 420 nm, the numerical aperture NA (Numerical Aperture) is increased, and the system has a capacity of 20 GB or more. Has been proposed (see, for example, Non-Patent Document 1).
[0003]
These phase-changeable rewritable CDs, DVDs, and DVD-Rs detect a recorded information signal by using a reflectance difference and a phase difference change caused by a difference in refractive index between an amorphous state and a crystalline state. A typical phase change medium has a structure in which a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer are provided on a substrate, and reflectivity difference and phase difference using multiple interference of these constituent layers. Can be made compatible with CDs and DVDs. In the CD-RW, the compatibility of the CD with the recording signal and the groove signal can be ensured within the range where the reflectance is reduced to about 15 to 25%, and the CD drive with an amplification system that covers the low reflectance is added. Playback is possible. In the phase change recording medium, erasing and re-recording processes can be performed only by intensity modulation of one focused light beam. Therefore, in a phase change recording medium such as a CD-RW or a rewritable DVD, recording is recording. And overwrite (O / W) recording that simultaneously performs erasure.
[0004]
For recording information using phase change, crystalline, amorphous, or a mixed state thereof can be used. A plurality of crystal phases can be used, but a rewritable phase change recording medium that is currently in practical use In general, an unrecorded / erased state is set to a crystalline state, and an amorphous mark is formed and recorded.
[0005]
As the material for the phase change recording layer, chalcogen elements, that is, chalcogenide alloys containing S, Se, and Te are often used. For example, GeTe-Sb₂Te₃GeSbTe based on pseudo binary alloy, InTe-Sb₂Te₃InSbTe based on pseudo binary alloy, Sb_0.7Te_0.3Examples thereof include an AgInSbTe system and a GeSbTe system mainly composed of a eutectic alloy. Of these, GeTe-Sb₂Te₃A system in which excess Sb is added to a pseudo binary alloy, particularly Ge₁Sb₂Te₄Or Ge₂Sb₂Te₅The composition in the vicinity of intermetallic compounds such as is mainly put into practical use. These compositions are characterized by crystallization without phase separation peculiar to an intermetallic compound. Since the crystal growth rate is high, initialization is easy and recrystallization rate at the time of erasure is high. For this reason, conventionally, as a recording layer showing a practical overwrite (O / W) characteristic, a pseudo binary alloy system or a composition near an intermetallic compound has attracted attention (for example, see Non-Patent Document 2).
[0006]
Conventionally, a report has been made on a GeSbTe ternary composition or a recording layer composition containing an additive element based on this ternary composition (see, for example, Patent Documents 1 to 4). However, in order to apply a material having such a composition to an optical recording medium for high-density recording such as a rewritable DVD-R, development has just started, and there are many problems to be solved.
In particular, in the case of a short wavelength optical system such as a blue laser, the beam output is low, so that there is a drawback that noise is likely to occur in the recording layer, and it is difficult to satisfy both overwrite (O / W) characteristics and storage characteristics. This is a problem in high-speed and high-density recording.
In Patent Document 5, as a heat-resistant protective layer, paragraph [0017] shows a metal oxide such as ZnO or ZrO, a carbide such as TiC, or a mixture thereof. However, it is sulfide resistant and has no effect of satisfying the recording / reproducing characteristics while ensuring storage stability. In Japanese Patent Application No. 2002-334303, one recording layer is not two layers.
[0007]
[Patent Document 1]
JP 61-258787 A
[Patent Document 2]
Japanese Patent Laid-Open No. 62-152786
[Patent Document 3]
JP-A-1-63195
[Patent Document 4]
Japanese Patent Laid-Open No. 1-211249
[Patent Document 5]
Japanese Patent Laid-Open No. 6-60426 (page 3, right column, lines 26 to 33)
[Non-Patent Document 1]
ISO Technical Digest, '00 (2000), P.I. 210
[Non-Patent Document 2]
SPIE, vol. 2514 (1995), pp294-301
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and the object thereof is to generate noise and other overwrite (O / W) characteristics with respect to low output light with a short wavelength such as a blue laser. An object of the present invention is to provide a high-density recordable phase change recording medium having excellent archival characteristics.
[0009]
[Means for Solving the Problems]
That is, the above-described problem is (1) “at least a first recording structure layer, a resin intermediate layer, and a second recording structure layer are sequentially provided on a substrate, and the first recording structure layer is on the substrate side. In order from the reflective layer, the interface layer, the first protective layer, the first recording layer, and the second protective layer, and the second recording constituent layer is the third protective layer, Ag or Ag alloy layer in this order from the resin intermediate layer side. , An interface layer, a fourth protective layer, a second recording layer, and a fifth protective layer, wherein the phase change recording medium includes IZO as the third protective layer, and the first and second recording layers are at least A phase change recording medium comprising SbTe, wherein the refractive index of the optical constant of the interface layer is 2.2 or more and 2.5 or less at a wavelength of 350 nm to 420 nm, ”(2)“ of the interface layer The first component (1), wherein the forming component contains at least Ti—C—O. (3) “Phase change recording medium according to item (1), wherein the component forming the interface layer contains at least Mo—C—O”) (4) “Phase-change recording medium according to item (1) above, wherein the component for forming the interface layer contains at least V—C—O”, (5) “Formation of the interface layer” The phase change recording medium according to item (1), wherein the component contains at least Zr—C—O ”, (6)“ the component forming the interface layer contains at least Cr—C—O ” The phase change recording medium described in item (1) above, (7) “The formation component of the interface layer contains at least Nb—C—O. (1) (8) “The component forming the interface layer contains at least Mn—C—O”. The phase-change recording medium described in item (1) above, (9) “The formation component of the interface layer contains at least Si—C—O. (1) (10) “Phase change recording medium according to item (1), wherein the interface layer forming component contains at least Ta—C—O”) Solved by.
[0010]
  In order to solve the above problems, a phase change recording medium according to the present invention includes, on a substrate, at least a first recording constituent layer, a resin intermediate layer, and a second recording constituent layer, which are sequentially provided. The recording constituent layer is composed of a reflective layer, an interface layer, a first protective layer, a first recording layer, and a second protective layer in this order from the substrate side, and the second recording constituent layer is a third protective layer in order from the resin intermediate layer side. , An Ag or Ag alloy layer, an interface layer, a fourth protective layer, a second recording layer, and a fifth protective layer, the phase change type recording medium comprising IZO as the third protective layer, the first recording layer, The second recording layer contains at least SbTe, and the refractive index of the optical constant of the interface layer is 2.2 or more and 2.5 or less at a wavelength of 350 nm to 420 nm.2The light transmission amount of the recording layer configuration of the1The amount of light reaching the recording layer is increased, recording sensitivity is improved, noise such as jitter does not occur, and O / W characteristics, archival characteristics, and high-density recording performance are improved.
[0011]
That is, the first recording medium (1) is a phase change recording medium using a crystal and amorphous phase transition phenomenon caused by light irradiation, and the constituent layers are sequentially formed. For example, a reflective layer made of an Ag alloy is provided on a substrate on which a guide groove is formed, and an interface layer, a first protective layer, and a second protective layer having an optical constant of refractive index n of 2.2 to 2.5. Layers, for example ZnS and SiO₂As a first recording constituent layer for recording on the first recording layer from the so-called reflective layer to the second protective layer, the first recording layer containing SbTe as the main constituent element is laminated. ing. Then, an oxide layer is further provided on the second protective layer through an intermediate layer in which grooves are formed with a transparent resin such as a UV resin, and the third protective layer, IZO, is provided adjacent to the oxide layer. A film, an Ag or Ag alloy layer is provided, and the fourth protective layer and the fifth protective layer are made of, for example, ZnS and SiO₂The second recording constituent layer for recording on the second recording layer from the third protective layer to the fifth protective layer, in which the second recording layer containing SbTe as the main constituent element is laminated. It is the composition prepared as.
[0012]
As described above, the recording layer is composed of two layers, and each recording layer includes at least SbTe, thereby facilitating the formation of small marks to cope with high density recording. In the first recording layer configuration, the optical constant is An interface layer having a refractive index n of 2.2 or more and 2.5 or less is formed between the reflection layer and the first protective layer. To improve the recording sensitivity of the first recording layer. In the second recording layer structure, the IZO film and the Ag or Ag alloy layer, which is the third protective layer, are formed in the middle of the two recording layers with a thickness of 20 nm or less to improve the heat dissipation and the recording wavelength. By using Ag or Ag alloy having high light transmittance and thermal conductivity near 405 nm, heat dissipation is maintained at O / W, O / W characteristics are improved, and recording at high density is possible. is there.
[0013]
The reflective layer will be described. The present invention is characterized in that the heat radiation effect in the lateral direction is promoted by using a thin reflective layer (2) having a very high thermal conductivity and 300 nm or less. In general, the thermal conductivity of a thin film is greatly different from that of a bulk state and is usually small. In particular, a thin film having a thickness of less than 40 nm is not preferable because the thermal conductivity may be reduced by an order of magnitude or more due to the influence of an island-like structure at the initial stage of growth. Furthermore, the crystallinity and the amount of impurities differ depending on the film forming conditions, which causes the thermal conductivity to be different even with the same composition.
In order to define a high thermal conductivity reflective layer exhibiting good characteristics in the present invention, the thermal conductivity of the reflective layer (2) can be directly measured. Can be estimated. This is because in a material such as a metal film in which electrons mainly control heat or electric conduction, the thermal conductivity and electric conductivity have a good proportional relationship. The electric resistance of the thin film is represented by a resistivity value normalized by the film thickness or the area of the measurement region. The volume resistivity and the sheet resistivity can be measured by a normal four-probe method and are defined by JIS K 7194. This method provides data that is much simpler and more reproducible than actually measuring the thermal conductivity of a thin film.
[0014]
In the present invention, the reflective layer preferably has a volume resistivity of 20 nΩ · m to 150 nΩ · m, and more preferably 20 nΩ · m to 100 nΩ · m. A material having a volume resistivity of less than 20 nΩ · m is substantially difficult to obtain in a thin film state. Even if the volume resistivity is larger than 150 nΩ · m, the area resistivity can be lowered if, for example, a thick film exceeding 300 nm is used, but according to the study by the present inventors, such a high volume resistivity is obtained. Even if only the sheet resistivity was lowered with a rate material, a sufficient heat dissipation effect could not be obtained. This is probably because the heat capacity per unit area increases in the thick film. In addition, such a thick film is not preferable from the viewpoint of manufacturing cost because it takes time to form a film and increases the material cost. Furthermore, the microscopic flatness of the film surface is also deteriorated. Preferably, a low volume resistivity material is used so that a sheet resistivity of 0.2 to 0.9Ω / □ can be obtained with a film thickness of 300 nm or less. 0.5Ω / □ is most preferable.
[0015]
Suitable materials for the present invention are as follows. For example, an Ag—Cu alloy containing Cu in an amount of 0.3 wt% to 5.0 wt%. In particular, ZnS and SiO₂In the protective layer (3), (5), (7), (9), (11) of the layer made of (AlN layer), Cu is contained in an amount of 0.5 wt% to 4.0 wt%. An Ag—Cu-based alloy is desirable as a reflective layer that satisfies all of corrosion resistance, adhesion, and high thermal conductivity in a well-balanced manner.
An Ag—Pd—Cu alloy containing Si in an amount of 0.3 wt% to 0.8 wt% and Pd in an amount of 0.3 wt% to 1.2 wt% is also effective.
Further, although the Al alloy has good thermal conductivity, the surface property after film formation is poor and the Ag alloy is more suitable for high density recording.
[0016]
  Further, the component forming the interface layer in the phase change recording medium of the present invention is Ti—C—O (the item (2)), Mo—C—O (the item (3)), or V—C. -O (said (4) term), Zr-CO (said (5) term), Cr-CO (said (6) term), or Nb-CO (said (7)), or Mn—C—O (above (8)), or Si—C—O (above (9)) or Ta—C—O (above (10)). By doing so, n of the optical constant of the interface layer is 2.2 or more and 2.5 or less.Second recording layerIncreased transmittance1In this recording layer structure, the recording sensitivity is improved, noise such as jitter does not occur, and O / W characteristics, archival characteristics, and high-density recording performance are improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 schematically shows a cross-sectional view of a layer structure showing an example of a phase change recording medium of the present invention, and is a substrate (1) / reflective layer (2) / interface layer (14) / first protection. Layer (3) / first recording layer (4) / second protective layer (5) / resin intermediate layer (6) / third protective layer (7) / Ag or Ag alloy layer (8) / interface layer (14) / 4th protective layer (9) / second recording layer (10) / 5th protective layer (11) / adhesive layer (12) / cover substrate (13). The order of the layers as shown in FIG. 1 is suitable when each recording layer is irradiated with a focused light beam for recording / reproducing, for example, laser light, through the transparent cover substrate (13).
[0018]
As the material of the substrate (1) in the phase change recording medium of the present invention, a transparent resin such as polycarbonate, acrylic resin, polyolefin, or transparent glass can be used. Of these, polycarbonate resin is the most preferred material because it has a track record of being most widely used in CD and is inexpensive.
The substrate (1) is usually provided with grooves having a pitch of 0.8 μm or less for guiding the recording / reproducing light. However, the grooves are not necessarily geometrically rectangular or trapezoidal grooves. Alternatively, optical grooves may be formed by forming waveguides having different refractive indexes.
[0019]
Next, the material of the first recording layer (4) and the second recording layer (10) in the phase change recording medium of the present invention is a thin film mainly composed of an alloy containing Sb and Te as main constituent elements. Such alloys include, for example, those containing Ge, Sb, and Te as constituent elements. If necessary, other elements may be added to each recording layer made of such constituent elements up to a total of about 10 atomic%. Further, the optical constant of the recording layer can be finely adjusted by adding at least one element selected from O, N or S to each recording layer in an amount of 0.1 atomic% to 5 atomic%. However, it is not preferable to add more than 5 atomic% because the crystallization speed is lowered and the erasing performance is deteriorated.
[0020]
In addition, at least one selected from V, Nb, Ta, Cr, Co, Pt or Zr is added in an amount of 8 atomic% or less in order to increase the temporal stability without reducing the crystallization rate during overwrite (O / W). More preferably, it is 0.1 atomic% or more and 5 atomic% or less. The total amount of the additive element and Ge added to SbTe is preferably 15 atomic% or less. If it is contained in excess of 15 atomic%, phase separation other than Sb is induced. In particular, when the Ge content is 3 atomic% or more and 5 atomic% or less, the effect of addition is large.
[0021]
In order to improve stability over time and finely adjust the refractive index, it is preferable to add at least one of Si, Sn, or Pb in an amount of 5 atomic% or less. The total addition amount of these additive elements and Ge is preferably 15 atomic% or less. Each element of Si, Sn, or Pb is an element having a tetracoordinate network like Ge.
[0022]
Further, by adding 8 atomic% or less of Al, Ga, and In, there is an effect of increasing the crystallization temperature and simultaneously reducing jitter and improving the recording sensitivity, but segregation is likely to occur, so 6 atomic%. The following is preferable. Each addition amount of Al, Ga, In is 15 atomic% or less, preferably 13% or less as a total addition amount combined with Ge. Adding Ag in an amount of 8 atomic% or less is effective in improving the recording sensitivity, and the effect is particularly remarkable when it is used when the Ge atomic weight exceeds 5 atomic%. However, if the addition amount of Ag exceeds 8 atomic%, it is not preferable because it increases jitter and impairs the stability of the amorphous mark. Moreover, since it is easy to produce segregation when the total addition amount combined with Ge exceeds 15 atomic%, it is not preferable. The most preferable Ag content is 5 atomic% or less.
[0023]
The first recording layer (4) and the second recording layer (10) of the phase change recording medium of the present invention are phase change recording layers, and the thickness is generally preferably in the range of 5 nm to 100 nm. When the thickness of the first recording layer (4) and the second recording layer (10) is less than 5 nm, it is difficult to obtain sufficient contrast, and the crystallization rate tends to be slow, so that erasing in a short time is likely to be difficult. . On the other hand, if it exceeds 100 nm, it is difficult to obtain optical contrast, and cracks are likely to occur. The contrast needs to be compatible with a read-only disc such as a DVD.
[0024]
In high-density recording where the shortest mark length is 0.5 μm or less, the recording layer is preferably 5 nm or more and 25 nm or less. If the thickness is less than 5 nm, the reflectance is too low, and the influence of a non-uniform composition and a sparse film at the initial stage of film growth tends to appear. On the other hand, if it is thicker than 25 nm, the heat capacity becomes large and the recording sensitivity is deteriorated, and the crystal growth becomes three-dimensional, so that the edge of the amorphous mark tends to be disturbed and the jitter tends to increase. Furthermore, the volume change due to the phase change of the first recording layer (4) and the second recording layer (10) becomes remarkable, and the repeated overwrite (O / W) durability is deteriorated. From the viewpoint of jitter at the mark end and repeated overwriting (O / W) durability, the thickness is more preferably 20 nm or less.
[0025]
The density of each first recording layer (4) and second recording layer (10) is desirably 80% or more, more preferably 90% or more of the bulk density.
The density of the first recording layer (4) and the second recording layer (10) is such that, in the sputtering film forming method, the pressure of the sputtering gas (rare gas such as Ar) during film formation is lowered or close to the front of the target. Therefore, it is necessary to increase the amount of high energy Ar irradiated to the recording layer by arranging a substrate. The high energy Ar is one in which Ar ions irradiated to the target for sputtering are partially rebounded and reach the substrate side, or Ar ions in the plasma are accelerated by the sheath voltage over the entire surface of the substrate and reach the substrate. Either. Such an irradiation effect of a high energy rare gas is referred to as an “atomic peening effect”. In sputtering with Ar gas that is generally used, Ar is mixed into the sputtered film by an atomic peening effect. The atomic peening effect can be estimated from the amount of Ar in the mixed film. That is, if the amount of Ar is small, it means that the effect of irradiation with high energy Ar is small, and a film with a low density is easily formed. On the other hand, if the amount of Ar is large, irradiation with high energy Ar is intense and the density becomes high, but Ar taken into the film precipitates as void during repeated overwriting (O / W), and deteriorates repeated durability. Let An appropriate amount of Ar in the recording layer film is 0.1 atomic% or more and 1.5 atomic% or less. Furthermore, it is preferable to use high frequency sputtering rather than direct current sputtering because a high density film can be obtained by reducing the amount of Ar in the film.
[0026]
Further, the first recording layer (4) and the second recording layer (10) of the phase change recording medium of the present invention are usually amorphous after film formation. Therefore, it is necessary to crystallize the entire surface of each recording layer after film formation to obtain an initialized state (unrecorded state). As an initialization method, initialization by annealing in a solid phase is possible, but initialization by so-called melt recrystallization in which the recording layer is once melted and gradually cooled during resolidification to be crystallized is desirable. Each of the recording layers described above has few crystal growth nuclei immediately after film formation, and crystallization in the solid phase is difficult. However, according to melt recrystallization, a few crystal nuclei are formed and then melted. Recrystallization progresses at high speed mainly by crystal growth.
Since the crystal of the first recording layer (4) and the second recording layer (10) by the melt recrystallization and the crystal by the solid phase annealing have different reflectivities, if they are mixed, it causes noise. In actual overwrite (O / W) recording, since the erased portion becomes a crystal by melt recrystallization, initialization is preferably performed by melt recrystallization.
[0027]
During initialization by melt recrystallization, the recording layer is preferably melted locally and in a short time of about 1 millisecond or less. This is because if the melting region is wide, or if the melting time or the cooling time is too long, each layer is destroyed by heat or the surface of the plastic substrate is deformed. In order to provide a thermal history suitable for initialization, a high-power semiconductor laser beam having a wavelength of about 600 to 1000 nm is focused and irradiated on a long axis of 100 to 300 μm and a short axis of 1 to 3 μm. It is desirable to scan at a linear velocity of 10 m / s. Even if the same focused light is close to a circle, the melted region is too wide, re-amorphization is likely to occur, and damage to the multilayer structure and the substrate is not preferable.
[0028]
It can be confirmed as follows that the initialization was performed by melt recrystallization. That is, the recording medium having the recording power Pw, which melts the recording layer focused to a spot diameter smaller than about 1.5 μm, is applied to the medium after initialization at a constant linear velocity in a direct current. If there is a guide groove, the tracking servo and the focus servo are applied to the groove or the track formed between the grooves.
After that, if the reflectance in the erased state obtained by irradiating erasing light with the erasing power Pe (≦ Pw) on the same track is almost the same as the reflectance in the unrecorded initial state, the initialization is performed. The state can be confirmed as a melt recrystallization state. This is because the recording layer is once melted by irradiation with the recording light and completely recrystallized by irradiation with the erasing light, and then undergoes a process of melting by the recording light and recrystallization by the erasing light. This is because it is in a state of being converted into a state. Note that the reflectivity Rini in the initialized state and the reflectivity in the melt recrystallized state Rcry are substantially the same as the difference in reflectivity defined by (Rini−Rcry) / {(Rini + Rcry) / 2}. Say that it is 20% or less. Usually, the reflectance difference is larger than 20% only by solid phase crystallization such as annealing.
[0029]
As shown in FIG. 1, the first recording layer (4) and the second recording layer (10) of the present invention have the first recording layer (4), the first protective layer (3), and the second recording layer, respectively. The second recording layer (10) is sandwiched between the fourth protective layer (9) and the fifth protective layer (11) between the protective layer (5) and the substrate (1 ) Provided on the surface (groove forming surface).
[0030]
Each protective layer of the first protective layer (3), the second protective layer (5), the fourth protective layer (9), and the fifth protective layer (11) of the present invention will be described below.
The first protective layer (3) of the first recording constituent layer (100) prevents mutual diffusion of the first recording layer (4) and the reflective layer (2) and suppresses deformation of the first recording layer (4). However, it also has a function of efficiently releasing heat to the reflective layer (2). The second protective layer (5) is effective for preventing the deformation of the surface of the resin intermediate layer (6) mainly due to a high temperature during recording. The fourth protective layer (9) of the second recording constituent layer (200) releases heat to the second recording layer (10), the Ag or Ag alloy layer (8), the third protective layer (7), and the interface layer. And a function of preventing mutual diffusion of the second recording layer (10) and the Ag or Ag alloy layer (8). The fifth protective layer (11) is effective in adjusting the reflectance and preventing deformation of the adhesive layer (12) and the cover substrate (13) due to high temperatures during recording.
[0031]
The materials of the first protective layer (3), the second protective layer (5), the fourth protective layer (9), and the fifth protective layer (11) include refractive index, thermal conductivity, chemical stability, mechanical It is determined in consideration of strength or adhesion. As a material for forming each of the protective layers, it is desirable that the heat conduction characteristic is low.^-3pJ / (μm · N · nsec). In addition, it is difficult to directly measure the thermal conductivity of such a low thermal conductivity material in a thin film state, and a guideline can be obtained from a thermal simulation and an actual recording sensitivity measurement result as an alternative to the direct measurement.
[0032]
Examples of the above-mentioned protective layer materials having low thermal conductivity that give favorable results include ZnS, ZnO, and TaS.₂Alternatively, a composite dielectric containing at least one of rare earth sulfides in an amount of 50 mol% or more and 90 mol% or less, a high transparency, and a heat resistant compound having a melting point or decomposition point of 1000 ° C. or more is desirable. More specifically, a composite dielectric containing 60 mol% or more and 90 mol% or less of a rare earth sulfide such as La, Ce, Nd, or Y is desirable. Alternatively, the composition range of ZnS, ZnO or rare earth sulfide is desirably 70 to 90 mol%.
Examples of heat-resistant compound materials having a melting point or decomposition point of 1000 ° C. or higher to be mixed with these include Mg, Ca, Sr, Y, La, Ce, Ho, Er, Yb, Ti, Zr, Hf, V, Nb, Oxides such as Ta, Zn, Al, Si, Ge, and Pb, nitrides, carbides, and fluorides such as Ca, Mg, and Li can be used.
Note that the oxides, sulfides, nitrides, carbides, and fluorides do not necessarily have a stoichiometric composition, and it is also effective to control the composition or use a mixture for controlling the refractive index and the like. It is.
[0033]
As the protective layers of the first protective layer (3), the second protective layer (5), the fourth protective layer (9), and the fifth protective layer (11) of the present invention, Considering the consistency with the materials constituting the recording layer (4) and the second recording layer (10), ZnS and SiO₂And a mixed system composition is most preferable.
In the present invention, as described above, each protective layer has ZnS and SiO.₂However, using the same material in this way is advantageous from the viewpoint of cost reduction in manufacturing.
[0034]
The function and the like of each protective layer will be further described in detail.
The layer structure of the present invention belongs to a kind of layer structure called a rapid cooling structure. The rapid cooling structure employs a layer structure that promotes heat dissipation and increases the cooling rate at the time of re-solidification of the recording layer, thereby avoiding the problem of recrystallization during the formation of amorphous marks and increasing the speed by high-speed crystallization. Realize erasure ratio.
[0035]
The film thicknesses of the first protective layer (3) and the fourth protective layer (9) of the present invention greatly affect the durability in repeated overwriting (O / W), and are particularly important in suppressing the deterioration of jitter. is there. The film thickness is generally 5 nm or more and 30 nm or less. If it is less than 5 nm, the effect of delaying heat conduction in the protective layer is insufficient, and the recording sensitivity is significantly lowered, which is not preferable. If the film thickness is greater than 30 nm, a sufficient flattening effect of the temperature distribution in the mark width direction cannot be obtained, and each recording side and the reflective layer of the second protective layer (5) and the fifth protective layer (11) are recorded during recording. The temperature difference between the two sides increases, and the protective layer itself tends to deform asymmetrically due to the difference in thermal expansion between both sides of the protective layer. This repetition is not preferable because it accumulates microscopic plastic deformation inside the protective layer and causes an increase in noise.
The detailed thickness of the first protective layer (3) and the fourth protective layer (9) is preferably 15 nm to 25 nm when the wavelength of the recording laser light is 600 to 700 nm, and preferably 3 to 20 nm when the wavelength is 350 to 600 nm. More preferably, it is 3-15 nm.
[0036]
The film thickness of the second protective layer (5) and the fifth protective layer (11) needs to be 30 nm or more and 160 nm or less. When the thickness is less than 30 nm, the recording layer is easily broken due to deformation or the like, and the O / W characteristics are deteriorated. When the thickness is 160 nm or more, the reflectance variation is large and it is difficult to perform uniform recording. The O / W characteristic is more preferably 45 nm or more and 130 nm or less.
[0037]
When the phase change type recording layer material as described above is used, low jitter can be realized in high-density recording with a shortest mark length of 0.3 μm or less. However, according to the study by the present inventors, in order to realize high-density recording. When a short-wavelength laser diode (for example, a wavelength of 410 nm or less) is used, further attention needs to be paid to the layer structure of the rapid cooling structure. In particular, in the study of one-beam overwrite characteristics using a small focused light beam having a wavelength of 500 nm or less and a numerical aperture NA of 0.55 or more, it is possible to flatten the temperature distribution in the mark width direction to achieve a high erase ratio and erase power. It was found to be important for widening the margin. The same tendency applies to DVD-R compatible optical systems that use optical systems with wavelengths of 350 to 420 nm and NA = 0.85.
[0038]
The present inventors have studied an appropriate layer structure of a phase change recording medium having a two-layer recording structure so as to meet the above-described requirements, so as to have light transmission, heat dissipation, and high recording sensitivity. The interface layer (14) was constructed and designed to improve the recording sensitivity.
[0039]
In high-density mark length modulation recording using the optical system as described above, those having particularly low thermal conductivity are used as the first protective layer (3) and the fourth protective layer (9), preferably the film thickness thereof. Is 3 nm or more and 20 nm or less. For this reason, the interface layer (14) provided on the first protective layer (5) needs to have high thermal conductivity. With this configuration, heat does not escape rapidly during high-speed recording, and heat is applied to the reflective layer. High speed recording is possible.
Further, since the light reaching the first recording layer configuration is transmitted through the second recording layer configuration, the transmitted light is less than half of the incident light. Therefore, the incident light increases or the sensitivity of the first recording layer is better. good.
In the present invention, in the first recording layer configuration with a small amount of incident light, the first recording layer is sandwiched between layers having low thermal conductivity to improve recording sensitivity, and the first protective layer is formed thinly from 3 nm to 10 nm. By providing an interface layer having a refractive index n, which is an optical constant, of 2.2 or more and 2.4 or less between the layer and the reflective layer, heat can be easily absorbed and recording sensitivity is improved.
[0040]
In the above, when considering only thermal conductivity, the heat dissipation effect is promoted even if the thermal conductivity coefficient of the first protective layer (3) or the fourth protective layer (9) is increased, but the heat dissipation is promoted too much. If so, the irradiation power required for recording becomes high and the recording sensitivity is remarkably lowered. Therefore, it is necessary to have low thermal conductivity.
By using a thin-film protective layer with low thermal conductivity, a time delay is given to heat conduction from the recording layer to the reflective layer for several nsec to several tens of nsec from the start of recording power irradiation, and then heat dissipation to the reflective layer is promoted. Therefore, the recording sensitivity is not lowered more than necessary due to the heat conduction characteristics of the protective layer. For these reasons, the conventionally known SiO₂, Ta₂O₅, Al₂O₃The protective layer material mainly composed of AlN, SiN or the like is not preferable to be used alone because its own thermal conductivity is too high.
[0041]
As an example of the present invention, the recording sensitivity characteristics of the first recording layer (10) of the phase change recording medium having the structure of the present invention in which the interface layer (Ti—C—O) (14) is provided with a thickness of 4 nm are shown in Table 1. It was shown to.
Archival characteristics (80 ° C, 85%)
[0042]
[Table 1]

[0043]
Recording / reproducing conditions are 405 nm, NA = 0.85, 5.7 m / s, recording linear density: 0.13 μm / bit, recording power is recording at a recording power of 5.5 mW at which jitter is minimized, and reproducing power is 0.3 mW. The jitter was σ / Tw (window width), and a random signal was recorded with 1-7 modulation.
As shown in Table 1, the presence of the interface layer is a good medium with no jitter change even when archival evaluation (80 ° C., 85%) is performed. When IZO is used as the reflective layer and the third protective layer (7), the thermal conductivity of IZO is high. Therefore, the heat generated when the recording is performed on the second recording layer (10) generates Ag and Ag alloy layers. The heat is radiated by the third protective layer (7) via As a result, the recording layer mainly composed of the phase change material SbTe that requires rapid cooling is in an optimum rapid cooling state, and a small amorphous mark can be formed.
[0044]
Further, as the interface layer (14), Ti—C—O, Mo—C—O, V—C—O, Zr—C—O, Cr—C—O, Nb—C—O, or When formed with Mn—C—O, Si—C—O, or Ta—C—O, the amount of oxygen in the material is as small as 10% or less and is stable, and a material such as Ag or Al is used for the reflective layer. Even so, the material is oxidized and almost no change in material is observed. In the media of the combination of the above materials and the Ag reflection layer, the archival preservation (80 ° C., 85%, 200 hours) and the recorded mark jitter did not change and showed good characteristics.
[0045]
However, as described above, the heat dissipation of the second recording component layer (200) is not sufficient only by the heat dissipation of the third protective layer (7), and the Ag and Ag alloy layer (8) has a heat dissipation capability. Improved, especially in the recording layer based on SbTe, the first rapid cooling of the heat forms an amorphous mark, so the Ag and Ag alloy layer (8), the third protective layer (7) and the interface layer (14 ), The high density, the O / W characteristic, and the storage stability are improved.
[0046]
Below, the reflection layer (2) and Ag or Ag alloy layer (8) which bear a heat dissipation function are each demonstrated.
The reflective layer (2) can be improved in erasure ratio and erasure power margin by using a material having a particularly high thermal conductivity. As a result of investigation, in order to exhibit the good erasing characteristics of the recording layer of the present invention in a wide erasing power range, not only the temperature distribution in the film thickness direction and the time change but also the film surface direction (with respect to the recording beam scanning direction). It is preferable to use a layer structure that can flatten the temperature distribution in the vertical direction as much as possible. The present invention is characterized in that the heat radiation effect in the lateral direction is promoted by using a thin reflective layer (2) having a very high thermal conductivity and 300 nm or less.
In general, the thermal conductivity of a thin film is greatly different from that of a bulk state and is usually small. In particular, a thin film having a thickness of less than 40 nm is not preferable because the thermal conductivity may be reduced by an order of magnitude or more due to the influence of an island-like structure at the initial stage of growth. Furthermore, the crystallinity and the amount of impurities differ depending on the film forming conditions, which causes the thermal conductivity to be different even with the same composition.
[0047]
Heat dissipation in the reflective layer (2) of the first recording component layer (100) can be achieved even if the thickness of the reflective layer (2) is increased, but if the thickness of the reflective layer (2) exceeds 300 nm, the first recording is performed. Layer (4) The heat conduction in the film thickness direction becomes more significant than the film surface direction, and the effect of improving the temperature distribution in the film surface direction cannot be obtained. In addition, the heat capacity of the reflective layer (2) itself is increased, and it takes time to cool not only the reflective layer (2) but also the first recording layer (4), thereby inhibiting the formation of amorphous marks. The Most preferably, a thin reflective layer (2) having a high thermal conductivity is provided to selectively promote lateral heat dissipation. The conventional quenching structure focuses only on one-dimensional heat escape in the film thickness direction, and is intended only to release heat quickly from the first recording layer (4) to the reflective layer (2). However, sufficient attention has not been paid to the flattening of the temperature distribution in the planar direction.
[0048]
Examples of the material of the reflective layer (2) suitable for the present invention include Ag or Ag alloy, Cu alloy, Al alloy and the like.
Examples of the Ag alloy include the same Ag alloys when used for Ag or an Ag alloy layer (8) described later. When an Ag alloy is used as the reflective layer (2), the preferred film thickness is 30 nm or more and 200 nm or less. If it is less than 30 nm, the heat dissipation effect is insufficient even with pure Ag. If it exceeds 200 nm, the heat escapes in the vertical direction from the horizontal direction and does not contribute to the improvement of the heat distribution in the horizontal direction, and an unnecessary thick film decreases the productivity. Also, the microscopic flatness of the film surface is deteriorated.
[0049]
Examples of the Cu alloy include an Al—Cu alloy containing Cu in an amount of 0.3 wt% or more and 5.0 wt% or less. In particular, ZnS and SiO₂And mixed system composition with Ta₂O₅When a protective layer comprising two layers is combined, an Al—Cu alloy containing Cu in an amount of 0.5 wt% or more and 4.0 wt% or less balances corrosion resistance, adhesion, and high thermal conductivity. Desirable as a satisfactory reflective layer. Further, an Al—Mg—Si based alloy containing 0.3% by weight or more and 0.8% by weight or less of Si and 0.3% by weight or more and 1.2% by weight or less of Mg is also effective.
[0050]
Examples of the Al alloy include alloys containing 0.2 atomic% or more and 2 atomic% or less of Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo, or Mn. These increase in volume resistivity in proportion to the concentration of the added element, improve hillock resistance, and can be used in consideration of durability, volume resistivity, film formation rate, and the like. Regarding the Al alloy, when the amount of added impurities is less than 0.2 atomic%, although it depends on the film forming conditions, the hillock resistance is often insufficient. On the other hand, when the content is more than 2 atomic%, it is difficult to obtain the low resistivity. When importance is attached to stability over time, Ta is preferred as an additive component.
[0051]
When the Al alloy is used as the reflective layer (2), the preferred film thickness is 150 nm or more and 300 nm or less. If the thickness is less than 150 nm, the heat dissipation effect is insufficient even with pure Al. As described above, if it exceeds 300 nm, the heat escapes in the vertical direction from the horizontal direction and does not contribute to the improvement of the heat distribution in the horizontal direction, and the heat capacity of the reflective layer itself is large, so that the cooling rate of the recording layer becomes slow. Also, the microscopic flatness of the film surface is deteriorated.
[0052]
Next, the Ag or Ag alloy layer (8) will be described.
In the second recording layer (10) of the present invention, crystal growth at the time of resolidification in the vicinity of Tm is the rate-limiting factor for recrystallization. In order to increase the cooling rate in the vicinity of Tm as much as possible to ensure the formation of amorphous marks and their edges, the ultra-rapid cooling structure is effective, and the temperature distribution in the film surface direction is flattened. Thus, what can be erased at high speed in the vicinity of Tm can reliably ensure erasure by recrystallization up to a higher erasing power. For this reason, when the so-called “super quenching structure in consideration of the heat conduction delay effect in the third protective layer (7)” is applied to the second recording constituent layer (200) according to the present invention, the conventional GeTe-Sb is applied.₂Te₃More effective than the recording layer.
[0053]
Ag or an Ag alloy layer (8) is used as a heat dissipation constituent layer for such ultra-cooling. In the case of forming the Ag or Ag alloy layer (8), it is made slower than the depositing reflective layer (2) at the time of film formation to eliminate the film thickness non-uniformity. The film thickness of the Ag or Ag alloy layer (8) is preferably 5 nm or more and 20 nm or less. 5 nm or less becomes non-uniform even when the deposition rate is slowed down.
As an Ag alloy, Cu, Ti, V, Ta, Nb, W, Co, Cr, Si, Ge, Sn, Sc, Hf, Pd, Rh, Au, Pt, Mg, Zr, Mo, or Mn are 0 in Ag. An alloy containing 2 atomic% or more and 5 atomic% or less is also desirable. When importance is attached to stability over time, Ti and Mg are preferred as the additive component.
[0054]
In the reflective layer (2) and the Ag or Ag alloy layer (8), the present inventors show that the volume resistivity of the additive element to Al or the additive element to Ag increases in proportion to the concentration of the additive element. Have confirmed. On the other hand, the addition of impurities is generally considered to reduce the crystal grain size, increase the electron scattering at the grain boundaries, and lower the thermal conductivity. It is necessary to adjust the amount of added impurities in order to obtain the original high thermal conductivity of the material by increasing the crystal grain size.
[0055]
The reflective layer (2) and the Ag or Ag alloy layer (8) are usually formed by sputtering or vacuum vapor deposition, but not only the amount of impurities in the target or the vapor deposition material itself, The total amount of impurities including oxygen must be 2 atomic% or less. For this purpose, the ultimate vacuum of the process chamber is 1 × 10^-3It is desirable to set it to Pa or less. 10^-4In the case of film formation at an ultimate vacuum lower than Pa, it is desirable to prevent the incorporation of impurities by setting the film formation rate to 1 nm / second or more, preferably 10 nm / second or more. Alternatively, when the intentional additive element is included in an amount of more than 1 atomic%, it is desirable to prevent the addition of additional impurities as much as possible by setting the film formation rate to 10 nm / second or more.
[0056]
The film formation conditions may affect the crystal grain size regardless of the amount of impurities. For example, in an alloy film in which about 2 atomic% of Ta is mixed in Al, an amorphous phase is mixed between crystal grains, but the ratio between the crystalline phase and the amorphous phase depends on the film forming conditions. In addition, as the sputtering is performed at a lower pressure, the proportion of the crystal portion increases, the volume resistivity decreases, and the thermal conductivity increases.
The impurity composition or crystallinity in the film depends on the manufacturing method of the alloy target used for sputtering and the sputtering gas (Ar, Ne, Xe, etc.). Thus, the volume resistivity in the thin film state is not determined only by the metal material and the composition. In order to obtain high thermal conductivity, it is desirable to reduce the amount of impurities as described above. On the other hand, pure metals such as Al and Ag tend to be inferior in corrosion resistance and hillock resistance. It is necessary to determine the optimal composition.
[0057]
In order to obtain higher heat conduction and higher reliability, it is also effective to make the reflective layer (2) and the Ag or Ag alloy layer (8) multilayer. In this case, at least one layer is made of the high thermal conductivity material (low volume resistivity material) having a film thickness of 50% or more of the total film thickness, which substantially contributes to the heat dissipation effect, and the other layers have corrosion resistance and It is configured to contribute to improvement in adhesion to the protective layer and hillock resistance.
More specifically, when Ag having the highest thermal conductivity and low volume resistivity among metals is used, if S (sulfide or the like) is contained in the protective layer adjacent to Ag, the compatibility is poor, and due to sulfurization. Corrosion tends to occur, and there is a tendency for deterioration to be somewhat rapid when overwritten (O / W) repeatedly. In addition, corrosion tends to occur in an accelerated test environment of high temperature and high humidity. Therefore, when using Ag or an Ag alloy as the low volume resistivity material, it is also effective to provide an alloy layer containing Al as a main component as an interface layer between 1 nm and 100 nm between the adjacent protective layers. If this thickness is 5 nm or more, the layer does not have an island-like structure and is easily formed uniformly.
[0058]
As described above, the Al alloy includes, for example, Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo, or Mn in an amount of 0.2 atomic% to 2 atomic%. An alloy is mentioned. If the thickness of the interface layer is less than 1 nm, the protective effect is insufficient, and if it exceeds 100 nm, the heat dissipation effect is sacrificed.
[0059]
Further, when an Ag alloy reflective layer and an Al alloy interface layer are used, it is more preferable to provide an interface oxide layer by oxidizing the Al surface to a thickness greater than 1 nm because Ag and Al are relatively easy to interdiffuse. If the interfacial oxide layer exceeds 5 nm, particularly 10 nm, it becomes a thermal resistance, which is not preferable because the function as a reflective layer with extremely high heat dissipation, which is the original purpose, is impaired.
[0060]
In order to define the high thermal conductivity reflective layer (2) and the Ag or Ag alloy layer (8) exhibiting good characteristics in the present invention, it is possible to directly measure the respective thermal conductivity, The quality of heat conduction can be estimated using electrical resistance. This is because in a material such as a metal film in which electrons mainly control heat or electric conduction, the thermal conductivity and electric conductivity have a good proportional relationship. The electric resistance of the thin film is represented by a resistivity value normalized by the film thickness or the area of the measurement region. The volume resistivity and the area resistivity can be measured by a normal four-probe method and are defined by JIS N 7194. This method provides data that is much simpler and more reproducible than actually measuring the thermal conductivity of a thin film.
[0061]
In the present invention, the reflective layer (2) and the Ag or Ag alloy layer (8) preferably have a volume resistivity of 20 nΩ · m to 150 nΩ · m, more preferably 20 nΩ · m to 100 nΩ · m. m or less. A material having a volume resistivity of less than 20 nΩ · m is substantially difficult to obtain in a thin film state. Even if the volume resistivity is larger than 150 nΩ · m, the area resistivity can be lowered if, for example, a thick film exceeding 300 nm is used, but according to the study by the present inventors, such a high volume resistivity is obtained. Even if only the sheet resistivity was lowered with a rate material, a sufficient heat dissipation effect could not be obtained. This is probably because the heat capacity per unit area increases in the thick film. In addition, such a thick film takes a long time to form a film and increases material costs, which is not preferable from the viewpoint of manufacturing cost, and further, the microscopic flatness of the film surface is deteriorated. It is preferable to use a low volume resistivity material that provides a sheet resistivity of 0.2 or more and 0.9Ω / □ or less at a film thickness of 300 nm or less, and most preferably 0.5Ω / □. In the case of Ag or an Ag alloy layer (8), 20 nm or less is desirable from the viewpoint of transmittance.
[0062]
Regarding the multilayering of the reflective layer (2) or the Ag or Ag alloy layer (8), in order to obtain a desired sheet resistivity with a desired film thickness by combining a high volume resistivity material and a low volume resistivity material. It is valid. Although the volume resistivity adjustment by alloying can simplify the sputtering process by using an alloy target, it also causes an increase in target manufacturing cost and, consequently, the raw material ratio of the medium. Therefore, it is also effective to obtain a desired volume resistivity by multilayering a thin film of pure Al or pure Ag and a thin film of the additive element itself. If the number of layers is up to about 3, the initial apparatus cost increases, but the individual medium costs may be suppressed. The reflective layer (2) is a multilayer reflective layer made of a plurality of metal films, the total film thickness is 40 nm or more and 300 nm or less, and 50% or more of the thickness of the multilayer reflective layer is 20 nΩ · m or more and 150 nΩ · m or more. It is preferable to use the following metal thin film layer (may be a multilayer).
[0063]
Next, when a high NA objective lens is used in a configuration in which a cover substrate (13) is provided as shown in FIG. 1, the thickness of the cover substrate (13) is 0.3 mm or less, more preferably 0.06. Since a thickness of ˜0.20 mm is required, a sheet shape is preferable. Materials include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, etc. A polycarbonate resin and an acrylic resin, which are excellent in characteristics and cost, are preferable. Examples of a method for forming a thin substrate using the transparent sheet include a method of attaching a transparent sheet via an ultraviolet curable resin or a transparent double-sided pressure-sensitive adhesive sheet. Alternatively, an ultraviolet (UV) curable resin may be applied on the protective layer and cured to form a thin substrate.
Although the resin intermediate layer and the adhesive layer use the above-mentioned resin, the UV curable resin is used because of its excellent cost.
[0064]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples.
[0065]
Example 1
In the layer configuration shown in FIG. 2, on a polycarbonate substrate (21), a reflective layer (22) (AgCuPtPd), an interface layer (34) (Ti—C—O), a first protective layer (23) (ZnSSiO).₂), First recording layer (24) (Ag)₅In₅Sb₆₅Te₂₅), Second protective layer (25) (ZnSSiO₂), Resin intermediate layer (26) (polycarbonate), third protective layer (27) (IZO), Ag or Ag alloy layer (28) (AgCuPtPd), interface layer (34) (Ti—C—O), fourth Protective layer (29) (ZnSSiO₂), Second recording layer (30) (Ge₅Ag₂Sb₇₀Te₂₃), Fifth protective layer (31) (ZnSSiO₂), An adhesive layer (32) (acrylic double-sided adhesive), and a cover substrate (33) (polycarbonate) to form a phase change recording medium for evaluation. The layers other than the UV curable resin intermediate layer (26) and the acrylic double-sided adhesive layer (32) were formed by sequentially forming each layer from the substrate (21) side while controlling the thickness by a sputtering method.
[0066]
The thickness of each constituent layer was controlled as follows.
Substrate (21): 1.1 mm, reflective layer (22): 120 nm, interface layer (34): 4 nm, first protective layer (23): 7 nm, first recording layer (24): 10 nm, second protective layer ( 25): 100 nm, resin intermediate layer (26): 30 μm, third protective layer (27): 120 nm, Ag or Ag alloy layer (28): 10 nm, interface layer (34): 5 nm, fourth protective layer (29) : 10 nm, second recording layer (30): 6 nm, fifth protective layer (31): 100 nm, adhesive layer (32): acrylic double-sided adhesive (30 μm), cover substrate (33): 60 μm.
[0067]
(Example 2)
The phase change recording for evaluation was carried out in the same manner as in Example 1 except that the material of the interface layer (34) was changed from Ti—C—O to Zr—C—O composition in Example 1. A medium was made.
[0068]
(Example 3)
A phase change recording for evaluation was carried out in the same manner as in Example 1 except that the material of the interface layer (34) was changed from Ti—C—O to Cr—C—O composition in Example 1. A medium was made.
[0069]
Example 4
The phase change recording for evaluation was carried out in the same manner as in Example 1 except that the material of the interface layer (34) was changed from Ti—C—O to Nb—C—O composition in Example 1. A medium was made.
[0070]
(Example 5)
In Example 1, the material of the interface layer (34) was changed to a Ta—C—O composition instead of Ti—C—O. A mold recording medium was produced.
[0071]
(Comparative Example 1)
A phase change recording medium for evaluation was produced in the same manner as in Example 1 except that there was no interface layer.
Table 2 summarizes the constituent materials of each layer of the phase change recording medium for evaluation in Examples 1 to 5 and Comparative Example 1.
[0072]
[Table 2]

[0073]
  The composition of Ti—C—O in the above example is (TiC₂)₈₀(TiO₂)₂₀) And allowable range (TiC₂) X (TiO₂)_{100- x}In this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
  The composition of Zr—C—O is (ZrC₂)₈₀(ZrO₂)₂₀And allowable range (ZrC₂)_x(ZrO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
  The composition of Cr—C—O is (CrC₂)₈₀(CrO₂)₂₀And allowable range (CrC₂)_x(CrO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
  The composition of Nb—C—O is (NbC₂)₈₀(NbO₂)₂₀The allowable range (NbC₂)_x(NbO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
  The composition of Ta—C—O is (TaC₂)₈₀(TaO₂)₂₀And allowable range (TaC₂)_x(TaO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
  The composition of AgInSbTe is in an allowable range (Ag (1-10), In (1-10), Sb (60-90), Te (10-30).
  The composition of GeSbTe is within an allowable range (Ge (1-10), Sb (60-90), Te (10-30).The
[0074]
Moreover, the following can be used instead of the above composition.
The composition of Mo—C—O is (MoC₂)₈₀(MoO₂)₂₀And allowable range (MoC₂) X (MoO₂)_{100- x}In this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
The composition of V-C-O is (VC₂)₈₀(VO₂)₂₀And allowable range (VC₂) X (VO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
The composition of Mn—C—O is (MnC₂)₈₀(MnO₂)₂₀And the allowable range (MnC₂)_x(MnO₂) In the case of 100-x, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
The composition of Si—C—O is (SiC₂)₈₀(SiO₂)₂₀And allowable range (SiC₂) X (SiO₂)_100-xIn this case, 60 ≦ x ≦ 90, preferably 70 to 80 at%.
[0075]
<Evaluation>
The evaluation phase change recording media prepared in Examples 1 to 5 and Comparative Example 1 were irradiated with a focused light beam using an optical system having a wavelength of 402 nm and a numerical aperture NA of 0.85, and the linear velocity was 5.7 m / second. s, initial jitter (jitter), recording power (power indicating jitter minimum), archival characteristics, and O / W characteristics were evaluated under the conditions of 0.130 μm / bit. The results are shown in Tables 3 and 4 as the first recording layer configuration and the second recording layer configuration.
[0076]
[Table 3]

[0077]
[Table 4]

*) Recording is not possible due to insufficient recording power.
[0078]
Evaluation criteria are as follows.
Archival characteristics: Time (H) during which the jitter rises to 20% or more when stored at 80 ° C. and 85% (RH).
O / W characteristics: The number of overwriting (O / W) times when the jitter (Jitter) increase due to overwriting (O / W) reaches 20%.
Recording power (recording sensitivity): Power that minimizes jitter.
[0079]
As a result of the above evaluation tests, the phase change recording media for evaluation of Examples 1 to 5 of the present invention all exhibit excellent archival characteristics (1000H to 2000H) and O / W characteristics (10000 times to 20000 times). The recording sensitivity (8.5 to 9.5 mW) is also good, and the jitter and archival characteristics are better than those of the comparative examples 100H, 300H (archival characteristics), and 1000 times (O / W characteristics). there were.
Comparative Example 1 having no interface layer has poor storage characteristics (archival characteristics), and Comparative Example 2 using SiN in the interface layer has high thermal conductivity, recording sensitivity of the second recording layer is poor, and recording was not possible. .
[0080]
【The invention's effect】
As will be apparent from the detailed and specific description above, at least the first recording structure layer, the resin intermediate layer, and the second recording structure layer of the present invention are sequentially provided on the substrate, and the first recording The constituent layer is composed of a reflective layer, an interface layer, a first protective layer, a first recording layer, and a second protective layer in order from the substrate side, and the second recording constituent layer is a third protective layer in order from the resin intermediate layer side, A phase change type recording medium comprising an Ag or Ag alloy layer, an interface layer, a fourth protective layer, a second recording layer, and a fifth protective layer, wherein IZO as the third protective layer, the first recording layer and the first recording layer 2 When the recording layer contains at least SbTe and the refractive index of the optical constant of the interface layer is 2.2 or more and 2.5 or less at a wavelength of 350 nm to 420 nm, transmission of the first recording layer configuration due to light interference Since the rate can be improved, the recording sensitivity of the second recording layer is improved, O / W characteristics which, archival characteristic, a phase change type recording medium which exhibits high-density recording performance is provided.
Further, the component for forming the interface layer of the present invention is Ti—C—O, Mo—C—O, V—C—O, Zr—C—O, Cr—C—O, or Nb—C—. When it is formed of O, Mn—C—O, Si—C—O, or Ta—C—O, the light transmission amount of the first recording layer configuration increases due to light interference and reaches the second recording layer. The light intensity increases, the recording sensitivity of the second recording layer is improved, and when the above materials are used, the archival storability (80 ° C., 85%, 200 hours) does not change the jitter of the recorded mark, and it has good characteristics. showed that. In addition, an excellent effect of providing a medium having a good O / W characteristic is achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a layer structure showing an example for explaining a phase change recording medium of the present invention.
FIG. 2 is a cross-sectional view showing a layer structure of a phase change recording medium for evaluation in an example of the present invention.
[Explanation of symbols]
1 Substrate
2 Reflective layer
3 First protective layer
4 First recording layer
5 Second protective layer
6 Resin intermediate layer
7 Third protective layer
8 Ag or Ag alloy layer
9 Fourth protective layer
10 Second recording layer
11 Fifth protective layer
12 Adhesive layer
13 Cover substrate
14 Interface layer
21 Substrate
22 Reflective layer
23 First protective layer
24 First recording layer
25 Second protective layer
26 Resin intermediate layer
27 Third protective layer
28 Ag or Ag alloy layer
29 4th protective layer
30 Second recording layer
31 5th protective layer
32 Adhesive layer
33 Cover substrate
34 Interface layer
100 First recording composition layer
200 Second recording composition layer

Claims (10)

  At least a first recording configuration layer, a resin intermediate layer, and a second recording configuration layer are sequentially provided on the substrate, and the first recording configuration layer is sequentially formed from the substrate side with a reflective layer, an interface layer, a first protective layer, Consists of a first recording layer and a second protective layer. The second recording constituent layer is, in order from the resin intermediate layer side, a third protective layer, an Ag or Ag alloy layer, an interface layer, a fourth protective layer, and a second recording layer. And a phase change type recording medium comprising a fifth protective layer, wherein the third protective layer is IZO, the first recording layer and the second recording layer contain at least SbTe, and the optical constant of the interface layer is refracted. A phase change recording medium, wherein the rate is 2.2 or more and 2.5 or less at a wavelength of 350 nm to 420 nm.   The phase change recording medium according to claim 1, wherein the component forming the interface layer contains at least Ti—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer includes at least Mo—C—O.   The phase change recording medium according to claim 1, wherein the formation component of the interface layer includes at least V—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer contains at least Zr—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer includes at least Cr—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer includes at least Nb—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer contains at least Mn—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer contains at least Si—C—O.   The phase change recording medium according to claim 1, wherein the component forming the interface layer includes at least Ta—C—O.

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