JP4227278B2 - Information recording medium, manufacturing method thereof, and recording / reproducing method thereof - Google Patents

Description

【００６２】
表1に示すように、融点の点からは、結晶核供給層の材料としては、SnTeおよびPbTeが特に好ましいことがわかる。
【００６３】
結晶核供給層32は結晶状態で安定していることが好ましいため、結晶核供給層32の膜厚は、2nm以上であることが好ましく、さらに厚い方がより好ましい(薄いと結晶化に必要な原子数が不足するため)。しかしながら、結晶核供給層32の膜厚が厚いと、結晶核供給層32にエネルギービームが吸収されてしまい、相変態層33にエネルギービームが到達しなくなってしまう。したがって、結晶核供給層32の厚みは、2nm以上で4nm以下が好ましい。
【００６４】
結晶核供給層32は、ArガスまたはAr-N₂混合ガス雰囲気中で母材をスパッタリングすることによって形成できる。また、相変態層33は、ArガスまたはAr-N₂混合ガス雰囲気中で母材をスパッタリングすることによって形成できる。この際、相変態層３３が成膜後にas-depo非晶質であるためには、相変態層33の成膜速度は約30nm/分以上であることが好ましい。本発明者らの実験によれば、結晶化能向上層の膜厚が5nmで記録層の膜厚が10nmでは、記録層の成膜速度が5nm/分から20nm/分では記録層は成膜中に結晶化し、30nm/分から40nm/分ではas-depo非晶質と結晶相の混合状態となり、50nm/分以上ではas-depo非晶質となった。可逆的光学情報記録媒体10のように結晶核供給層32がある場合でも、相変態層33の成膜速度が遅いと相変態層33が成膜中に結晶化する場合がある。結晶核供給層32の膜厚と相変態層33の膜厚との組み合わせによって、相変態層33が成膜中に結晶化する成膜速度は異なるが、相変態層33の結晶化を防止するためには、相変態層33の成膜速度は30nm/分以上であることが好ましく、40nm/分以上であることがより好ましい。
【００６５】
情報記録媒体53では、結晶核供給層32として、SnTe,SnTe-M(ただし、Mは、N,Ag,Cu,Co,Ge,Mn,Nb,Ni,Pd,Pt,Sb,Se,Ti,V,ZrおよびPbTeから選ばれる少なくとも一つを含む),PbTe,Sb₂Te₃,Bi₂Te₃,Te,GeSbTe共晶,GeBiTe共晶のいずれを用いた場合も、相変態層33がas-depo非晶質の状態で情報を記録すること(as-depo記録)が可能であった。特に、融点が高いSnTeを含む材料、またはPbTeを含む材料を用いた場合に良好な結果が得られた。
【００６６】
また、相変態層33として、GeTe,GeSbTe,TeSnSe,InSbTe,GeBiTe,AgInSbTeおよびGeSbTeから選ばれる少なくとも一つを含み、且つAg,Sn,Cr,Pb,Bi,Pd,Se,In,Ti,Zr,Au,Pt,Al,MnおよびNから選ばれる少なくとも一つを添加した材料のいずれを用いた場合も、as-depo記録が可能であった。
【００６７】
以上のように、情報記録媒体53によれば、as-depo記録が可能となる。
【００６８】
図6は、本発明の情報記録媒体54の一構成例を示し、断面図を示す。図6を参照して、情報記録媒体54は、基板1と、基板1上に順次積層された保護層2、界面層10、記録層34、界面層11、保護層6および反射層7と、反射層7上に接着層8によって接着されたダミー基板9とを備える。そして、記録層34は、基板1側から順に積層された相変態層33と結晶核供給層35とを含む。なお、記録層34を除く部分については、図5で説明した情報記録媒体53と同様であるため、重複する説明は省略する。
【００６９】
記録層34、結晶核供給層35および相変態層33の機能は、それぞれ、図5で説明した記録層31、結晶核供給層32および相変態層33と同様である。すなわち、結晶核供給層35は、相変態層33の結晶化を容易にするための層である。また、相変態層33は、結晶状態と非晶質状態との間で可逆的に相変態を起こす層であり、この相変態によって情報を記録する層である。情報記録媒体54では、記録層34が上記構成を有するため、相変態層33は、結晶核供給層35との界面から結晶化が生じやすくなる。
【００７０】
情報記録媒体54では、図5の場合と異なり、記録層34は、基板1側から順に積層された相変態層33と結晶核供給層35とを備える。
【００７１】
相変態層33は、情報記録媒体53の相変態層33と同様である。
【００７２】
情報記録媒体53の結晶核供給層32と異なり、結晶核供給層35は、相変態層33に対してレーザ入射側と反対側に積層されている。したがって、結晶核供給層35には、相変態層33の融点よりも低い融点を有する材料も好適に使用できる。具体的には、図5で説明した結晶核供給層32の材料の他に、Teを含む材料として、SnTe,PbTeに加えて、Sb₂Te₃,Bi₂Te₃,Te,GeSbTe共晶組成,GeBiTe共晶組成も好適に使用できる。また、情報記録媒体54では、エネルギービームが相変態層33を通過してから結晶核供給層35に入射するため、情報記録媒体53と比較して結晶核供給層35の膜厚を厚くできる。具体的には、結晶核供給層35の膜厚は、約2nmから5nmが好ましい。また、相変態層33の成膜速度は、約30nm/分以上が好ましく、非晶質の状態で成膜される。
【００７３】
情報記録媒体54では、結晶核供給層35として、SnTe,SnTe-M(ただし、MはN,Ag,Cu,Co,Ge,Mn,Nb,Ni,Pd,Pt,Sb,Se,Ti,V,Zr及びPbTeから選ばれる少なくとも一つ),PbTe,Sb₂Te₃,Bi₂Te₃,Te,GeSbTe共晶，またはGeBiTe共晶のいずれを用いた場合も、相変態層33がas-depo非晶質の状態で情報の記録をすることが可能であった。情報記録媒体54では、いずれの材料を用いた場合にも良好な結果が得られた。
【００７４】
また、相変態層33として、GeTe,GeSbTe,TeSnSe,InSbTe,GeBiTe,AgInSbTe、またはGeSbTeを含んで且つAg,Sn,Cr,Pb,Bi,Pd,Se,In,Ti,Zr,Au,Pt,Al,MnおよびNから選ばれる少なくとも一つを添加した材料のいずれを用いた場合も、as-depo記録が可能であった。
【００７５】
以上のように、図6の情報記録媒体54によれば、情報記録媒体53と同様の効果が得られる。
【００７６】
図7では本発明の情報記録媒体について、一例を説明する。情報記録媒体55は、基板1と、基板1上に順次積層された保護層2、界面層10、記録層36、界面層11、保護層6および反射層7と、反射層7上に接着層8によって接着されたダミー基板9とを備える。そして、記録層36は、基板1側から順に積層された結晶核供給層32と相変態層33と結晶核供給層35とを含む。なお、記録層36を除く部分については、図5で説明した情報記録媒体53と同様であるため、重複する説明は省略する。
【００７７】
結晶核供給層32および35は、図5で説明した結晶核供給層32と同様の機能を有する。すなわち、結晶核供給層32および35は、相変態層33の結晶化を容易にするための層である。情報記録媒体55では、記録層36が上記構成を有するため、相変態層33は、結晶核供給層32または35との界面から結晶化が生じやすくなる。
【００７８】
情報記録媒体55では、図5の情報記録媒体53と異なり、相変態層33が結晶核供給層32と結晶核供給層35とによって挟まれている。
【００７９】
相変態層33は、図5で説明したものと同様の材料を用いる。
【００８０】
結晶核供給層32には、図5で説明した結晶核供給層32と同様の材料を用いることができる。結晶核供給層32は、Teを含む材料の中でも、融点が相変態層33よりも高い材料からなることが好ましい。
【００８１】
結晶核供給層35には、図6で説明した結晶核供給層35と同様の材料を用いることができる。結晶核供給層35には、Teを含む材料の中でも、融点が相変態層33の融点より低い材料も好適に用いることができる。
【００８２】
結晶核供給層32の材料と結晶核供給層35の材料とは、異なっていてもよい。たとえば、結晶核供給層32がSnTeからなり、結晶核供給層35がPbTeからなる場合でもよい。また、結晶核供給層32がPbTeからなり、結晶核供給層35がGeBiTe共晶組成からなる場合でもよい。なお、結晶核供給層32と結晶核供給層35とに同じ材料を用いた方が、成膜時に母材の数が少なくてすみ、また成膜装置をより簡素化できるという利点がある。
【００８３】
結晶核供給層32の膜厚と結晶核供給層35の膜厚とは、異なっていてもよいが、両膜厚の合計は5nm以下であることが好ましい。たとえば、結晶核供給層32の膜厚を1nmとし結晶核供給層35の膜厚を2nmとしてもよいし、あるいは、結晶核供給層32の膜厚を2nmとし結晶核供給層35の膜厚を3nmとしてもよい。
【００８４】
情報記録媒体55において、結晶核供給層32および35として、SnTe,SnTe-M(ただし、MはN,Ag,Cu,Co,Ge,Mn,Nb,Ni,Pd,Pt,Sb,Se,Ti,V,ZrおよびPbTeから選ばれる少なくとも一つ),PbTe,Sb₂Te₃,Bi₂Te₃,Te,GeSbTe共晶、またはGeBiTe共晶のいずれを用いた場合も、as-depo記録することが可能であった。特に、結晶核供給層32に融点が高いSnTeを含む材料またはPbTeを含む材料を用いた場合に良好な結果が得られた。
【００８５】
また、相変態層33としてGeTe,GeSbTe,TeSnSe,InSbTe,GeBiTe,AgInSbTe,またはGeSbTeを含んで且つAg,Sn,Cr,Pb,Bi,Pd,Se,In,Ti,Zr,Au,Pt,Al,MnおよびNから選ばれる少なくとも一つを添加した材料のいずれを用いた場合も、as-depo記録することが可能であった。
【００８６】
以上のように、図7の情報記録媒体55によれば、情報記録媒体53と同様の効果が得られる。
【００８７】
図5から7で説明した情報記録媒体は、Ra＞Rcに設計され、相変態層33がas-depo非晶質である状態のまま、初期化工程をすることなく信号が記録できる。
【００８８】
次に、本発明の情報記録媒体の製造方法について、一例を説明する。
【００８９】
本発明の情報記録媒体の製造方法は、記録層を備える情報記録媒体を製造する方法であって、結晶状態と非晶質状態との間で可逆的に相変態を起こす相変態層と、相変態層に積層され相変態層を結晶化しやすくする結晶核供給層とを含む記録層を形成する工程を含む。以下に、図5で説明した情報記録媒体53を製造する方法について、図5を参照しながら説明する。
【００９０】
まず、基板1上に、保護層2および界面層10を形成する。これらの層は、Arガスおよび反応ガス雰囲気中で材料となるターゲット(金属母材)を反応性スパッタリングするか、または、化合物母材をArガス雰囲気中かもしくはArガスおよび反応ガス雰囲気中でスパッタリングすることによって形成できる。
【００９１】
次に、界面層10上に結晶核供給層32と相変態層33とを積層する。結晶核供給層32及び相変態層33は、ArガスまたはAr-N₂混合ガス雰囲気中で母材をスパッタリングすることによって形成できる。なお、相変態層33は、非晶質となるような条件で形成される。相変態層33が成膜後にas-depo非晶質であるためには、図5で説明したように、相変態層33の成膜速度は約30nm/分以上であることが好ましい。
【００９２】
次に、相変態層33上に、界面層11と保護層6とを積層する。これらの層は、保護層2および界面層10と同様の方法によって形成できる。
【００９３】
次に、保護層6上に反射層7を形成する。反射層7は、スパッタリング法や蒸着法によって形成できる。
【００９４】
最後に、反射層7上に接着層8をスピンコート法によって塗布し、ダミー基板9を貼り合わせたのち、紫外線を照射して接着層8を硬化させた。このようにして、情報記録媒体53を製造できる。
【００９５】
なお、情報記録媒体54または55は、上記方法と同様の方法によって容易に製造できる。
【００９６】
上記の製造方法によれば、本発明の情報記録媒体を容易に製造できる。
【００９７】
次に、本発明の情報記録媒体の記録再生方法について一例を説明する。
【００９８】
本記録再生方法は、図5ないし7のいずれかに記載した本発明の情報記録媒体を用いる記録再生方法である。
【００９９】
具体的には、図5ないし7のいずれかに説明した情報記録媒体に変調したレーザビームを照射することによって、相変態層に非晶質域と結晶相域とを形成し、信号の記録を行う。レーザビームを低パワーにして相変態層の非晶質域に照射することによって、照射部分の非晶質域を結晶化できる。また、レーザビームを高パワーにして相変態層の結晶相域に照射することによって、照射部分の結晶相域を非晶質化できる。
【０１００】
本記録再生方法によれば、信頼性よく情報信号の記録を行うことができる。特に、図5ないし7に記載の情報記録媒体を用いることによって、as-depo記録が可能になる。
【０１０１】
【実施例】
次に、本発明の具体例を説明する。
【０１０２】
実施例1から13は、初期化不要を目的とし、成膜後に相変態層を結晶化させる発明についての実施例である。
【０１０３】
実施例14から26は、初期化不要を目的とし、相変態層がas-depo非晶質の状態で記録する発明についての実施例である。実施例26は信頼性に関する実施例である。
【０１０４】
(実施例1)
相変態層を成膜中に結晶化させるという結晶化能向上層としての機能には、結晶化能向上層自体が成膜後に結晶であることが必要条件と考えられる。結晶が構造的により安定である高速結晶化材料もしくは低融点材料を数種選び、それらの薄膜の成膜後の相構造を調べた。材料はBi₂Te₃,Sb₂Te₃,Sb,Te,SnTe,PbTe,GeSbTe共融，GeBiTe共融の8種類である。直径：100mm、厚み：6mm(以下、100mmφ×6mmtのように表示する)のスパッタリングタ−ゲットを、Ar雰囲気中でDCスパッタリングして、石英基板上に各々5nmの薄膜を形成した。得られた8種類の薄膜を、He-Neレ−ザで毎分50℃の速さで昇温しながら透過率を測定した。温度と透過率の関係を図４（ａ）〜（ｃ）に示す。成膜後の構造が非晶質であれば、図４（ａ）の様に相対的に室温での透過率が高く昇温中にある温度で、結晶相への相変態に伴う急激な透過率低下が観察される。この温度を結晶化温度と定義する。成膜後の構造が非晶質と結晶相の混合状態の場合、室温での透過率が図４（ａ）の場合より低く、図４（ｂ）の様に昇温中にわずかな透過率変化が観察される。また、結晶化温度は図４（ａ）の場合より低く、図4Aの状態より結晶化しやすくなっている。図４（ｂ）中のa,b,cのラインは、結晶状態と非晶質状態の割合が異なり、a,b,cの順に結晶相の含まれる割合が多くなる。成膜後の構造が結晶相であれば、相対的に室温での透過率は最も低く、図４（ｃ）の様に昇温しても透過率の変化はほとんど見られない。このような違いから相構造を判断することが可能である。8種類の薄膜の室温での構造を表2に示す。
【０１０５】
【表２】

【０１０６】
(実施例2)
実施例1の薄膜が結晶化能向上層としての機能を有するかを調べた。真空チャンバ−にて石英基板上に結晶化能向上層を成膜し、その上に相変態層を連続成膜した試料の、成膜後の相構造を調べた。膜厚は、石英｜結晶化能向上層(5nm)｜相変態層(10nm)である。結晶化能向上層のスパッタリング条件は実施例1と同様で、相変態層の材料はGe₂Sb₂Te₅である。相変態層の相構造は実施例1と同様に透過率測定で調べた。
【０１０７】
【表３】

【０１０８】
結晶化能向上層がない場合Ge₂Sb₂Te₅相変態層は成膜後は非晶質で図4Aの様な透過率変化を示した。結晶化温度は約200℃であった。結晶化能向上層にSbを使った場合、相変態層の結晶化温度は下がらず、結晶化および結晶核生成が認められなかった。結晶化能向上層にBi₂Te₃,Sb₂Te₃,Te,GeSbTe共融を使った場合、相変態層は非晶質と結晶相の混合状態となった。結晶化能向上層にSnTe,PbTe,GeBiTe共融を使った場合、図4Cの様な結果となり相変態層の結晶化が認められた。この結果から、Te化物を結晶化能向上層として使うと、相変態層の結晶化が促進されることがわかった。また、Te化物の中でも結晶構造が岩塩型である材料はより結晶化効果が大きいことも明らかになった。
【０１０９】
(実施例3)
結晶化能向上層にSnTeを使って膜厚と結晶化効果の関係を調べた。石英基板上にSnTeを1nmから20nmまで変えて成膜し、その上に相変態層を10nm成膜した。これらの試料の相変態層の構造を表4に示す。
【０１１０】
【表４】

【０１１１】
1nmでは非晶質と結晶の混合状態であったが、結晶化能向上層がない場合よりも結晶化が容易になるという効果が認められた。3nm以上あれば相変態層は結晶化した。
【０１１２】
(実施例4)
相変態層の成膜条件と結晶化効果を調べた。石英基板上にSnTeを5nm成膜し、その上に相変態層を10nm、成膜速度を変えて成膜した。これらの試料の相変態層の構造を表5に示す。
【０１１３】
【表５】

【０１１４】
結晶化能向上層が相変態層を結晶化させる効果は、相変態層の成膜速度に依存することがわかった。相変態層の成膜速度が5nm/分から20nm/分で結晶化し、30nm/分から40nm/分で非晶質と結晶相の混合状態になった。それ以上の速度では非晶質であった。相変態層の成膜速度が低速度の方が相変態層は結晶化しやすい。最も好ましい成膜速度は5nm/分から10nm/分であった。
【０１１５】
(実施例5)
SnTeの複素屈折率を実験的に求めたところ、屈折率n＝4.2,消衰係数k＝4.5であった。この複素屈折率から光学計算により、光学情報記録媒体の構成を決定し試作した。光学情報記録媒体の反射率を測定して相変態層が結晶化しているか調べた。
【０１１６】
図1に示すように、ポリカ−ボネート基板上に保護層を100nm,結晶化能向上層を5nm,相変態層を18nm,保護層を25nm,反射層を80nmこの順にバッチ式スパッタ装置を使用して、真空チャンバ−内で連続成膜した。各々の詳細な成膜条件は表6に示す。
【０１１７】
【表６】

【０１１８】
光学情報記録媒体の反射率は、パルステック製相変化光ディスク評価装置で測定した。光源は、波長660nm、NA0.6である。光学情報記録媒体を線速度8m/sで回転させ、半径40mm位置の鏡面部の反射率を測定した。その結果20%の反射率が得られた。
【０１１９】
完全に結晶化しているか調べるために、同位置に通常結晶化させるに十分なパワーで半導体レ−ザビームを照射した後、反射率を測定した。この場合20.3%の反射率が得られた。相変態層が成膜後にほぼ完全に結晶化していたことが検証できた。PbTe,GeBiTe共融についても同様の効果が認められた。
【０１２０】
(実施例6)
実施例5の多層膜構成で結晶化能向上層の膜厚のみを変えた場合、光学情報記録媒体の反射率と記録感度がどのように変化するか測定した。結晶化能向上層としてはSnTeを用いた。反射率測定条件は実施例5と同様で、記録感度は同装置で3T信号を溝間に1回記録し、CNR値が50dB得られる記録パワ−と定義した。結果を表7に示す。
【０１２１】
【表７】

【０１２２】
結晶化能向上層の膜厚が厚いほど多層膜の反射率は高くなるが、記録感度が低下し15nm以上の膜厚では、14mＷ以上の記録パワ−が必要であり実用困難である。この結果から結晶化能向上層の膜厚としては、1から10nmが好ましいことがわかった。
【０１２３】
(実施例7)
実施例5で試作した光学情報記録媒体のオーバーライトジッター特性を評価した。比較のため、結晶化能向上層のない従来構成で半導体レーザによる結晶化工程を経た光学情報記録媒体のオーバーライトジッター特性も評価した。3T信号を溝間に1回から20回まで記録してジッター値の変化を調べた。その結果を表8に示す。
【０１２４】
【表８】

【０１２５】
表中ジッター値は、記録マークの前端間ジッター値と後端間ジッター値の平均値である。
【０１２６】
尚、前端間ジッターと後端間ジッターの差は、記録回数に依らず0.5%以内であった。
【０１２７】
相変態層の結晶化が不十分で結晶相に非晶質が残っていると、2回目から4回目辺りの記録時にジッター値が増大する。本実施例では、結晶化能向上層を設けて成膜中に相変態層を結晶化させた光学情報記録媒体に記録を行っても2回目から4回目辺りでのジッタ−値の増大は認められなかった。従来の成膜後に半導体レーザビームを照射して結晶化させた記録膜とほぼ同等の結晶相が得られた。
【０１２８】
(実施例8)
図3の二層情報記録媒体の第一情報記録媒体の構成で、結晶化能向上層の効果を調べた。ポリカ−ボネート基板上に保護層を100nm,界面層を5nm,結晶化能向上層を3nm,相変態層を7nm,界面層を5nm,保護層を90nmとし、この順にバッチ式スパッタ装置を使用して、真空チャンバ−内で連続成膜した。結晶化能向上層材料の異なる7種類の情報記録媒体と結晶化能向上層がない情報記録媒体を試作した。同時に、石英基板上に同構成で多層膜を成膜した試料片も作製した。この試料片で成膜後の相変態層の相構造を調べた。Bi₂Te₃,Sb₂Te₃,Te,GeSbTe共融を使った場合は、非晶質と結晶相の混合であった。これらは、完全な非晶質ではないので結晶化しやすさを評価するため、光学情報記録媒体で半導体レ−ザビーム照射による結晶化をも試みた。結晶化能向上層がない場合は、初期化に要する半導体レーザのパワーは800mWであった。これはほぼレーザ出力上限であった。結晶化能向上層を使った場合の結果を表9に示す。
【０１２９】
【表９】

【０１３０】
相変態層が完全な結晶相にならなくても、結晶化能向上層を3nmでも設けることで初期化のパワ−がほぼ半減し、結晶化がより容易になることがわかった。結晶化能向上層1nmでも同様の効果が得られた。
【０１３１】
(実施例9)
図2に示すように光吸収層を有する構成についても、実施例5を行った。
【０１３２】
ポリカ−ボネート基板上に保護層のZnS−SiO₂を120nm,界面層のGeNを5nm,結晶化能向上層のSnTeを5nm,相変態層のGeSbTeを10nm,界面層のGeNを5nm,保護層のZnS-SiO₂を50nm,光吸収補正層のSi合金を30nm,反射層のAg合金を80nm成膜して、情報記録媒体を試作した。成膜後、結晶化能向上層の効果で相変態層は結晶化しており、17.0%の反射率が得られた。また、同位置に半導体レ−ザビームを照射した後、反射率を測定しても16.9%の反射率が得られ、成膜後完全に結晶化していることが検証できた。図2の構成でも結晶化能向上層の効果は認められた。
【０１３３】
(実施例10)
実施例9まではＴｅ化物を結晶化能向上層として採用し優れた効果が得られた。が、結晶化能向上層が光を吸収するため、膜厚範囲が5nm以下と極薄い範囲に限定される。そこで、光吸収が小さく且つ岩塩型構造の化合物も含むハロゲン化物についても結晶化能向上層としての機能があるか調べた。材料はZnF₂,AlF₃,KF,CaF₂,NaF,BaF₂,MgF₂,LaF₃,LiFの9種類のF化物である。各々100mmφ×6mmtの化合物スパッタリングタ−ゲットを、Ar雰囲気中でRFスパッタリングして、石英基板上に10nmの薄膜を形成した。引き続き、その上に相変態層を10nm連続成膜した試料の、成膜後の相変態層の相構造を調べた。実施例1と同様に、He-Neレ−ザで毎分50℃の速さで昇温しながら透過率を測定した。図4(a)-図4(c)から、9種類の試料の相構造を判断した結果、すべて非晶質と結晶相の混合状態であった。図4(b)の透過率変化を示したが、岩塩型構造の材料LiF,NaF,KFはbのラインに近く、他の材料はaのラインに近かった。岩塩型構造の材料を結晶化能向上層に用いた方が相変態層の結晶相の割合が増え、結晶化能向上層としての効果が高かった。
【０１３４】
(実施例11)
結晶化能向上層としてハロゲン化物を10nm形成して、実施例8を行った。その結果を表10に示す。
【０１３５】
【表１０】

【０１３６】
相変態層が非晶質と結晶相の混合状態でも、初期化レ−ザパワ−は結晶化能向上層がない場合に比べて大幅に低減した。ハロゲン化物の結晶化能向上層を設けることにより、結晶化に要するエネルギ−が小さくなっていることがわかる。ハロゲン化物の結晶化能向上層を設けた場合も、相変態層が結晶化しやすくなるという効果が得られた。
【０１３７】
(実施例12)
結晶化能向上層としての機能が高かったLiF,NaF,KFの複素屈折率を決定する。石英基板上に各々の結晶化能向上層を成膜し、段差計で膜厚を測定し、分光器で反射率と透過率を測定して複素屈折率を算出した。得られた複素屈折率を表11に示す。
【０１３８】
【表１１】

【０１３９】
これらの膜は、k＝0の透明膜であった。
【０１４０】
(実施例13)
実施例8の多層膜構成で結晶化能向上層の膜厚のみを変えた場合、光学情報記録媒体の反射率と記録感度がどのように変化するか測定した。結晶化能向上層としてはLiFを用いた。結果を表12に示す。
【０１４１】
【表１２】

【０１４２】
結晶化能向上層の膜厚が厚いほど多層膜の反射率は高くなる。1nmでは反射率が15%を下回った。また25nmを超える記録感度が14mW以上になる。この結果からハロゲン化物結晶化能向上層の膜厚としては、5nm以上20nm以下が好ましい。実施例６の結果と比較すると、結晶化能向上層自体のｋが小さい方が結晶化能向上層の膜厚をより厚く設定できることがわかる。
【０１４３】
尚、以上の実施例では図1,2,3の構成で結晶化能向上層の効果について述べたが、これらの構成に限られるものではなく、相変態層を成膜する事前に結晶化能向上層が成膜されていれば、その効果は保護層の膜厚や界面層の有無などに関係なく得られる。
【０１４４】
以上のように本発明によれば、相変態層の基板側界面に結晶化能向上層を成膜することにより、相変態層の成膜後の相構造が結晶相となり、熱的手段を必要とする結晶化工程が不要となるかもしくはより少ないパワ−で結晶化できるという結果が得られる。
【０１４５】
(実施例14)
実施例14では、結晶核供給層の材料について検討した結果を示す。
【０１４６】
相変態層を初期化せずにas-depoの状態で情報の記録を開始するためには、as-depo非晶質の部分を結晶化しながら記録しなければならないため、as-depo非晶質からなる相変態層に結晶核が生成されやすくなっていることが必要である。結晶核がより多く生成されると、非晶質から結晶相への転移温度(結晶化温度)がより低くなる。
【０１４７】
結晶核供給層の材料として、結晶相がNaCl型構造である材料、高速結晶化材料および低融点材料を数種類選び、これらの材料に相変態層を積層した場合の相変態層の結晶化温度を調べた。
【０１４８】
結晶核供給層の材料は、Bi₂Te₃,Sb₂Te₃,Sb,Te,SnTe,PbTe,SnTe-PbTe,SnTe-Ag,SnTe-Se,SnTeN,GeSbTe共晶，GeBiTe共晶、TiN,ZrNである。相変態層の材料はGeSbTeである。
【０１４９】
試料としては、石英基板/結晶核供給層(膜厚2nm)/相変態層(膜厚10nm)の層構成のものを用いた。SnTeN,TiNおよびZrN以外の結晶核供給層は、直径100mm×厚さ6mmのスパッタリングタ−ゲットを、Arガス雰囲気中でDCスパッタリングすることによって形成した。SnTeN,TiNまたはZrNからなる結晶核供給層は、SnTe,Ti,Zrの各々のスパッタリングタ−ゲットをAr-N₂混合ガス雰囲気中でRFスパッタリングすることによって形成した。GeSbTeからなる相変態層は、Arガス雰囲気中でターゲットをDCスパッタリングすることによって成膜した。
【０１５０】
また、結晶核供給層の無い試料も作製した。そして、結晶核供給層がある試料と無い試料とを、それぞれ、He-Neレーザで毎分50℃の速さで昇温しながら透過率を測定した。相変態層が結晶化温度に達すると試料の透過率が急激に低下するため、透過率の変化から結晶化温度が明らかになる。各試料の結晶化温度について、測定値を表13に示す。
【０１５１】
【表１３】

【０１５２】
結晶核供給層が無い場合には、相変態層であるGeSbTeの結晶化温度は192℃であった。Teを含む材料を結晶核供給層に使うと、相変態層の結晶化温度が下がり、結晶核生成に効果があると考えられる。TiNとZrNは結晶相がNaCl型構造であるが、結晶核生成には効果が見られなかった。Sbにも効果が見られなかった。
【０１５３】
(実施例15)
実施例15では、実施例14で結晶核生成に効果があった材料を用いて情報記録媒体53を製造し、as-depo記録を行った一例について説明する。
【０１５４】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂(80mol%ZnS-20mol%SiO₂。以下、同様である。)、界面層としてGeNを5nm、結晶核供給層を2nm、相変態層としてGeSbTeを10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。結晶核供給層の材料としては、Bi₂Te₃,Sb₂Te₃,Te,SnTe,SnTe-PbTe,SnTe-Ag,SnTe-Se,SnTeN,PbTe,GeSbTe共晶，またはGeBiTe共晶を用いた。
【０１５５】
次に、各材料の成膜条件について説明する。ZnS-20mol%SiO₂はZnS-20mol%SiO₂を母材としてArガス雰囲気中でRFスパッタリング法によって成膜した。GeNはGeを母材としてAr-N₂混合ガス雰囲気中でRFスパッタリング法によって成膜した。結晶核供給層は実施例1と同様の条件で成膜した。GeSbTeからなる相変態層は、GeSbTeを母材としてAr-N₂混合ガス雰囲気中でDCスパッタリング法によって成膜した。Ag合金からなる反射膜は、Ag合金を母材としてArガス雰囲気中でDCスパッタリング法によって成膜した。実施例15の情報記録媒体は、Raが約28%でRcが約10%になるように両保護層の膜厚を厳密に決定した。
【０１５６】
λ＝660nm、NA＝0.6のレーザを搭載した評価用ドライブを用いて、実施例2の可逆的光学情報記録媒体を評価した。評価項目は溝上の3T信号の振幅,ノイズレベル,CNRである。評価は、レーザビーム照射部分の線速度が8.2m/sの条件で行った。記録は、レーザビームを高パワーPp(mW)と低パワーPb(mW)で変調して行った。変調記録波形を図8に示す。元の状態に関係なく(as-depo非晶質、初期化した結晶相、記録状態)、レーザビームを変調することにより非晶質と結晶相が形成され、新たな情報が記録される。なお、Pr(mW)は再生パワーである。
【０１５７】
情報記録媒体の一部の環状領域を初期化することによって、as-depoのまま初期化を行っていないas-depo非晶質域と、初期化を行った結晶相域とを同一面内に形成した。そして、両状態域のCNRを比較することによって、as-depo記録が可能であるかどうかを判断した。各媒体とも、Raが約28%でRcが約10%あるので、両状態域においてアドレスの読みとりは良好であり、サーボは安定し、CNRの評価が可能であった。3T信号を溝上に1回記録した。評価結果を表14に示す。
【０１５８】
【表１４】

【０１５９】
表14から明らかなように、SnTeを含む材料またはPbTeを含む材料を用いた場合には、as-depo非晶質域のCNRと結晶相域のCNRとがほぼ同レベルであった。どちらかといえば、as-depo非晶質域の方が約1dBノイズレベルが低い分だけ、CNRは結晶相域より高かった。初期化によってわずかなノイズ上昇があると考えられる。Teを含む他の材料を用いた場合には、as-depo非晶質域でのCNRが結晶相域のCNRより約3dBから5dB低かったが45dB以上は得られた。以上の結果から、上記材料ではas-depo記録が可能であることがわかった。
【０１６０】
相変態層であるGeSbTeの融点は約620℃であり、SnTeおよびPbTe以外の結晶核供給層材料は融点が620℃以下である。そのため、記録時に相変態層に結晶核供給層が溶けて混ざり、光学的特性が変わってしまうためにCNRが数dB低いと考えられる。したがって、結晶核供給層の後に相変態層を成膜する構成では、結晶核供給層の材料として、SnTeを含む材料またはPbTeを含む材料がより好ましいことがわかった。
【０１６１】
(実施例16)
実施例16では、実施例14で結晶核生成に効果があった材料を用いて情報記録媒体54を製造し、as-depo記録を行った一例について説明する。
【０１６２】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、相変態層としてGeSbTeを10nm、結晶核供給層を2nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。結晶核供給層には、Bi₂Te₃,Sb₂Te₃,Te,SnTe,SnTe-PbTe,SnTe-Ag,SnTe-Se,SnTeN,PbTe,GeSbTe共晶，またはGeBiTe共晶を用いた。各層の成膜条件は、実施例15と同様である。
【０１６３】
情報記録媒体の一部の環状領域を初期化して、成膜後未初期化のas-depo非晶質域と初期化後の結晶相域とを同一面内に形成した。そして、両状態域のCNRを比較することにより、as-depo記録の可否を判断した。
【０１６４】
記録条件と評価条件は実施例2と同様である。評価結果を表15に示す。
【０１６５】
【表１５】

【０１６６】
表15から、結晶核供給層としていずれの材料も、as-depo非晶質域のCNRと結晶域のCNRとがほぼ同レベルであり、as-depo非晶質への記録が可能であることがわかった。このように、相変態層の後に結晶核供給層を成膜する構成において、結晶核供給層の材料として相変態層より融点が低い材料を用いてもas-depo記録ができることがわかった。
【０１６７】
(実施例17)
実施例17では、実施例15でas-depo記録ができることがわかったSnTeを用いて結晶核供給層を形成し、as-depo記録の結晶核供給層の膜厚依存性および記録回数依存性を調べた。実施例17では、実施例15と同様の方法で情報記録媒体53を作製した。この際、各サンプルごとに情報記録媒体の結晶核供給層の膜厚を、0nmから7nmまで、0.5nmごとに変えた。
【０１６８】
未初期化の非晶質状態に3T信号を1回、2回および10回記録した。評価条件は実施例15と同様である。評価結果を表16に示す。
【０１６９】
【表１６】

【０１７０】
表16から明らかなように、結晶核供給層の膜厚が2nm以上であれば、1回記録からほぼ飽和CNRが得られた。膜厚が1.5nm以下と薄い場合、1回記録では振幅が小さく、2回記録ではノイズレベルが高いために、CNRが低い。またノイズレベルは記録回数と共に下がるが、飽和CNRを得るには7回記録が必要であった。膜厚の厚い4.5nm以上では、記録パワー15mWで飽和CNRが得られなかった。結晶核供給層が厚いと、相変態層の記録感度が低下することがわかった。as-depo記録が可能で且つ、記録感度も良好である結晶核供給層の膜厚は、約2nmから約4nmであった。
【０１７１】
したがって、実施例17の情報記録媒体では、結晶核供給層の膜厚としては約2nmから約4nmが好ましいことがわかった。
【０１７２】
(実施例18)
実施例18では、実施例17と同様の実験を、情報記録媒体54について行った。
【０１７３】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、相変態層としてGeSbTeを10nm、結晶核供給層としてSnTeを、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。結晶核供給層であるSnTeの膜厚を、0nmから7nmまで、0.5nmごとに変えた。実施例17と同様の測定をした結果を、表17に示す。
【０１７４】
【表１７】

【０１７５】
表17から明らかなように、結晶核供給層の膜厚が2nm以上あれば1回記録からほぼ飽和CNRが得られた。5.5nm以上では、記録パワー15mＷで飽和CNRが得られなかった。実施例17の結果と同様に、結晶核供給層の膜厚が厚くなると、相変態層の記録感度が低下する。実施例18の情報記録媒体では、as-depo記録が可能で且つ、記録感度も良好である結晶核供給層の膜厚は、約2nmから約5nmであった。したがって、相変態層の後に結晶核供給層を積層する構成では、結晶核供給層の膜厚としては約2nmから約5nmが好ましい。
【０１７６】
(実施例19)
実施例19では、可逆的光学情報記録媒体55を作製した一例について説明する。
【０１７７】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層32としてSnTeを、相変態層としてGeSbTeを10nm、結晶核供給層35としてSnTeを、界面層としてGeNを5nm、第2の保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。結晶核供給層32,35の膜厚を変えて、実施例17と同様の条件でas-depo記録を行った。評価結果を表18に示す。
【０１７８】
【表１８】

【０１７９】
相変態層を結晶核供給層で挟む場合は、結晶核供給層32および35の膜厚がそれぞれ1nmでas-depo記録が可能であった。また、両結晶核供給層の膜厚をそれぞれ3nmとすると記録感度が不足した。相変態層の片側のみに結晶核供給層を設ける場合と比較して、相変態層の両側に結晶核供給層を設ける場合には、核生成効果が相乗されることが考えられる。したがって、相変態層の両側に結晶核供給層を形成する場合には、核結晶核供給層の膜厚は約半分でよく、約1nmから約2nmがより好ましい。
【０１８０】
(実施例20)
実施例20では、情報記録媒体53について、結晶核供給層の膜厚と、相変態層の成膜速度と相変態層の成膜後の状態との関係について調べた一例を説明する。
【０１８１】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO2、界面層としてGeNを5nm、結晶核供給層としてSnTe、相変態層としてGeSbTeを10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。
【０１８２】
各サンプルの情報記録媒体は、相変態層の成膜速度r(nm/分)が異なり、5nm/分から60nm/分まで変えた。結晶核供給層の膜厚d1は2nmと5nmである。d1＝2nmの情報記録媒体は、非晶質域の反射率Raが約28%で、結晶相域の反射率Rcが約10%となるように光学設計し、d1＝5nmの情報記録媒体は非晶質域の反射率Raが約30%で、結晶相域の反射率Rcが約12%となるように光学設計した。貼り合わせ後、情報記録媒体の一部の環状領域を初期化して、同一面内に成膜後に初期化していないas-depo非晶質域と初期化後の結晶相域を形成し、両状態域の反射率を測定した。
【０１８３】
反射率は、λ＝660nm、NA＝0.6のレーザを搭載した評価用ドライブを使って、線速度8.2m/sでフォーカスサーボを動作させた状態で、基板に形成されたミラー部分の反射率を測定した。相変態層の成膜速度と反射率との関係を表19に示す。
【０１８４】
【表１９】

【０１８５】
表19から、d1＝2nmの場合には、r≧20(nm/分)のときに未初期化域の反射率が約28%となっており、成膜後の状態が非晶質であると判定できる。一方、r＜20(nm/分)のときには反射率が10数%しか得られず、相変態層の少なくとも一部が成膜中に結晶化していることが考えられる。
【０１８６】
また、d1＝5nmの場合には、r≧50(nm/分)のときに未初期化域の反射率が約30%となっており、成膜後の状態が非晶質であると判定できる。一方、r＜50(nm/分)では、相変態層の少なくとも一部が成膜中に結晶化していることが考えられる。このように相変態層の成膜速度と結晶核供給層の膜厚とによって、相変態層の成膜後の状態が決まる。相変態層を非晶質の状態で成膜するには、結晶核供給層が厚いほど、相変態層の成膜速度を大きくすることが好ましい。
【０１８７】
(実施例21)
実施例21では、情報記録媒体53を用いて、Rcがほとんど0%である情報記録媒体でも、as-depo記録ができれば、ドライブでサーボの安定性と良好なアドレス読みとり性が得られるかを調べた。
【０１８８】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを2nm、相変態層としてGeSbTeを10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。
【０１８９】
両保護層の膜厚を厳密に決定して、Ra(相変態層が非晶質である場合の情報記録媒体の反射率)＞Rc(相変態層が結晶相である場合の情報記録媒体の反射率)の情報記録媒体を4種類作製した。
【０１９０】
情報記録媒体の一部の環状領域を初期化して、初期化していないas-depo非晶質域(Ra)と初期化後の結晶相域(Rc)とを同一面内に形成し、両状態域のサーボの安定性とアドレスの読みとり性およびCNRを評価した。評価結果を表20に示す。
【０１９１】
【表２０】

【０１９２】
表20に示すように、情報記録媒体のRcが5.3%の場合には、初期化した結晶相域ではアドレスが読み取りにくかった。また、Rcが0.9%の場合には、初期化した結晶相域では、トラッキングサーボが動作しにくかった。
【０１９３】
一方、Rc＞10(%)であれば、結晶相域でもサーボ特性が安定し、アドレス読み取り性も良好であった。このように、Ra＞Rcで光学設計した情報記録媒体を初期化してしまうと、Rcの下限値が制約される。これに対して、成膜後に初期化していないas-depo非晶質域では、Rcの値に関係なく、アドレス読みとり性は良好であった。初期化しなければアドレス部の反射率はRaで保存されるため、Rcの下限値は制約を受けない。このように、結晶核供給層と相変態層を積層した相変態層を使うと、as-depo記録が可能であり、Rcが0%に近くても、アドレス部分の反射率はRaで十分大きく保たれることから、情報記録媒体のアドレスが読みとれ、サーボも安定することが検証できた。また、良好なCNRも得られた。
【０１９４】
(実施例22)
実施例22では、実施例21と同様に情報記録媒体を作製し、λ＝405nmのレーザを使用して反射率の測定を行った一例について説明する。
【０１９５】
情報記録媒体53を作製するため、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを2nm、相変態層としてGeSbTeを12nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。
【０１９６】
保護層、界面層、結晶核供給層、相変態層、反射層は、λ＝405nmのレーザビームに対する複素屈折率をエリプソメトリで測定し、λ＝405nmの記録波長に対して△R(△R＝Rc-Ra)の絶対値が十分大きくなるように各層の膜厚を厳密に決定した。as-depo非晶質域と結晶相域の溝上に3T信号を1回記録し、CNRを測定した。測定結果を表21に示す。
【０１９７】
【表２１】

【０１９８】
λ＝405nmの短波長でもas-depo記録が可能であり、as-depo記録ができると、Rcが低くてもサーボが安定して、アドレス読みとり性も良好であった。このように、結晶核供給層と相変態層を積層した相変態層を使うと、短波長のレーザビームを用いたas-depo記録が可能であり、高密度化記録にも実施できることが検証された。
【０１９９】
(実施例23)
実施例23では、情報記録媒体53について、相変態層としてAgInSbTe使い、as-depo記録を行った一例について説明する。
【０２００】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを、相変態層としてAgInSbTeを10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。ZnS-20mol%SiO₂はZnS-20mol%SiO₂を母材としてArガス雰囲気中でRFスパッタリングすることによって成膜した。GeNはGeを母材としてAr-N₂混合ガス雰囲気中でRFスパッタリングすることによって成膜した。結晶核供給層は母材をArガス雰囲気中でDCスパッタリングすることによって成膜した。AgInSbTeはAgInSbTeを母材としてArガス雰囲気中でDCスパッタリングすることによって成膜した。Ag合金はAg合金を母材としてArガス雰囲気中でDCスパッタリングすることによって成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。各サンプルの情報記録媒体は、結晶核供給層の膜厚が異なる。膜厚は、0nmから7nmまで、0.5nmごとに変えた。また、3T信号をas-depo非晶質状態に1回、2回および10回記録した。結果を表22に示す。
【０２０１】
【表２２】

【０２０２】
表22に示すように、結晶核供給層の膜厚が2nm以上であれば1回記録からほぼ飽和CNRが得られることがわかった。結晶核供給層の膜厚が1.5nm以下と薄い場合、1回記録では振幅が小さく、2回記録ではノイズレベルが高いために、CNRが低いことがわかった。また、ノイズレベルは記録回数と共に下がるが、飽和CNRを得るには7回記録が必要であった。結晶核供給層の膜厚が4.5nm以上と厚い場合には、記録パワー15mWで飽和CNRが得られなかった。結晶核供給層の膜厚が厚いほど、相変態層の記録感度が低下する。as-depo記録が可能で、且つ記録感度も良好となる結晶核供給層の膜厚は、約2nmから約4nmであった。相変態層にAgInSbTeを使ってもas-depo記録は可能であり、結晶核供給層としてSnTeの効果が検証できた。
【０２０３】
AgInSbTeは、InSbとAgSbTe₂の混合物であることが報告されており、AgSbTe₂がNaCl型構造であるため、SnTeによる結晶核生成が促進されやすいのではないかと考えられる。
【０２０４】
(実施例24)
実施例24では、GeSbTeにAg,Sn,Cr,Pb,Bi,Pd,Se,In,Ti,Zr,Au,Pt,AlまたはMnのうちいずれかを添加したものを相変態層として用いて情報記録媒体53を作製した一例について説明する。
【０２０５】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを2nm、相変態層としてGeSbTe＋M(Mは、Ag,Sn,Cr,Pb,Bi,Pd,Se,In,Ti,Zr,Au,Pt,AlまたはMnのうちいずれか)を10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。
【０２０６】
上記サンプルについて、as-depoの状態で記録実験を行った結果を表23に示す。なお、表23中、(△CNR(dB))＝(10回目記録のCNR(dB))-(1回目記録のCNR(dB))である。
【０２０７】
【表２３】

【０２０８】
表23に示すように、GeSbTeにいずれの元素を添加しても、1回目からほぼ飽和CNRが得られた。したがって、相変態層として組成式GeSbTe＋Mで表される材料を使っても、as-depo記録が可能なことがわかった。
【０２０９】
(実施例25)
実施例25では、相変態層の膜厚が異なる情報記録媒体53を作製し、as-depo記録実験を行った一例について説明する。
【０２１０】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを2nm、相変態層としてGeSbTeを、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。相変態層の膜厚は、2nmから25nmまで変えた。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。貼り合わせ後、情報記録媒体の一部の環状領域を初期化して、成膜後に初期化していないas-depo非晶質域と初期化後の結晶相域とを同一面内に形成した。
【０２１１】
記録条件と評価条件は、実施例15と同様であり、両状態域に各々3T信号を溝上に1回記録してCNRを測定した。測定結果を表24に示す。
【０２１２】
【表２４】

【０２１３】
表24に示すように、相変態層の膜厚が2nmの場合には、結晶化しなかった。相変態層の膜厚が3nmからas-depo記録は可能であるが、25nmでは記録パワー15mWでCNRが飽和せず、記録感度不足であった。as-depo記録には、相変態層は3nmから20nmが実用可能であり、5nmから15nmが好ましい膜厚である。
【０２１４】
(実施例26)
実施例26では、情報記録媒体53について、結晶核供給層の記録特性信頼性への効果を調べた一例について説明する。
【０２１５】
案内溝を有するポリカ−ボネ−ト基板上に、保護層としてZnS-20mol%SiO₂、界面層としてGeNを5nm、結晶核供給層としてSnTeを2nm、相変態層としてGeSbTeを10nm、界面層としてGeNを5nm、保護層としてZnS-20mol%SiO₂、反射層としてAg合金をこの順で連続成膜した。成膜後、紫外線硬化樹脂をAg合金上にスピンコートしてダミー基板と貼り合わせた。実施例26の情報記録媒体は、Ra＞Rcになるように作製した。また、相変態層は、初期化しないでas-depo非晶質の状態で信号の記録を開始した。
【０２１６】
上記実施例26の情報記録媒体を作製したのち、90℃で20%RHの環境に24時間放置し、放置前後のジッター変化を測定した。測定は、試験1、試験2および試験3の3種類について行った。試験1では、放置前にas-depo記録して測定し、放置後は測定のみを行った。試験2では、放置前にas-depo記録して測定し、放置後に重ね書きし測定を行った。試験3では、放置前は未記録で、放置後にas-depo記録して測定を行った。
【０２１７】
λ＝660nm、NA＝0.6のレーザで、情報記録媒体を評価した。溝間および溝上の3T信号のジッター値を評価した。3T信号は1回記録した。線速度8.2m/sである。放置前後の溝間ジッター差を表25に示し、溝上ジッター差を表26に示す。なお、ここで、(ジッター差)＝(放置後のジッター値)-(放置前のジッター値)である。
【０２１８】
【表２５】

【０２１９】
【表２６】

【０２２０】
表25-26に示すように、溝間または溝上のいずれにおいても、試験1、試験2および試験3のジッター差は2%以下であり、as-depo非晶質へ記録した場合も信頼性は良好であった。このように結晶核供給層と相変態層(可逆的相変態を起こす部分)とを積層することによって、as-depo記録が可能で、オーバーライトの信頼性も確保できるという2つの効果が得られた。
【０２２１】
以上、本発明の実施形態について例を挙げて説明したが、本発明は、上記実施の形態に限定されず本発明の技術的思想に基づき他の実施形態に適用することができる。
【０２２２】
例えば、情報記録媒体については、上記実施形態の構成に限定されず、結晶核供給層と相変態層とが積層された相変態層を備える情報記録媒体であればよい。
【０２２３】
【発明の効果】
以上のように、本発明の情報記録媒体は、結晶核供給層と相変態層とが積層された相変態層を備えるため、情報の記録を信頼性よく容易に行うことができる。また、本発明の情報記録媒体は、初期化工程を必要とせずにas-depo記録が可能である。特に、Ra＞Rcである情報記録媒体において、Rcが0%に近くてもアドレスの読みとり性とサーボの安定性が良好であるという効果が得られる。
【０２２４】
また、本発明の情報記録媒体の製造方法は、本発明の情報記録媒体を容易に製造することができる。
【０２２５】
また、本発明の情報記録媒体の記録再生方法は、情報の記録を信頼性よく容易に行うことができる。
【図面の簡単な説明】
【図１】本発明の情報記録媒体の一構成例を示す部分断面図である。
【図２】本発明の情報記録媒体の別の一構成例を示す部分断面図である。
【図３】本発明の情報記録媒体の中の二層情報記録媒体の一構成例を示す部分断面図である。
【図４】（ａ）〜（ｃ）は、本発明の結晶化能向上層または結晶化能向上層上に積層した記録層の、相構造を判断するための、透過率の温度依存性を示すグラフである。横軸が温度で縦軸が透過率である。（ａ）は相構造が非晶質である場合のグラフである。（ｂ）は相構造が非晶質と結晶相の混合状態である場合のグラフである。（ｃ）は相構造が結晶相である場合のグラフである。
【図５】本発明の情報記録媒体の別の一構成例を示す部分断面図である。
【図６】本発明の情報記録媒体の別の一構成例を示す部分断面図である。
【図７】本発明の情報記録媒体の別の一構成例を示す部分断面図である。
【図８】本発明の情報記録媒体の記録再生方法について記録に用いるレーザビームの変調波形を示す図で、横軸が時間で、縦軸がレーザパワーである。
【符号の説明】
50,51,52,53,54,55,56 情報記録媒体
1 基板
2,6 保護層
3 結晶化能向上層
4 相変態層
5,31,34,36,38 記録層
7 反射層
8 接着層
9 ダミ−基板
10,11 界面層
12 光吸収補正層
13 第一の基板側
14,19 第一の保護層
15,18 第一の界面層
17 第一の記録層
20 第一情報記録媒体
21 分離層
22,26 第二の保護層
23,25 第二の界面層
27 レーザ光
28 第二の基板
29 第二情報記録媒体
32,35 結晶核供給層
33,37 相変態層[0001]
[Technical field to which the invention belongs]
The present invention relates to an information recording medium capable of optically recording, reproducing, erasing, and rewriting information, a manufacturing method thereof, and a recording / reproducing method thereof.
[0002]
[Prior art]
Conventionally, a phase change information recording medium includes a recording layer that causes a reversible phase transformation between a crystalline state and an amorphous state by a method such as sputtering on a transparent disk substrate in a film forming process. A multilayer film is formed. The structure of the recording layer after film formation is amorphous, and a phase change type is performed through a step (hereinafter referred to as an initialization step) of changing the entire recording layer from amorphous to a crystalline phase using optical or thermal means. An information recording medium is manufactured. (In this specification, the amorphous formed in this way is referred to as an as-depo amorphous, and the amorphous formed by being rapidly cooled after being melted by irradiation with a high power laser described below. To distinguish.)
The phase change information recording medium can record and rewrite a signal by irradiating the recording layer with a single laser beam modulated to high power and low power. When irradiated with a high power laser beam, the recording layer melts and rapidly cools to form an amorphous layer (recording state), and when a low power laser beam is irradiated and the recording layer rises in temperature and gradually cools, the crystalline phase (erased state) Is formed, and a recording mark of a level of about several μm (several hundred nm) is formed on the track. The signal reproduction is the difference ΔR (%) between the reflectance Rc (%) of the medium when the recording layer is in a crystalline phase and the reflectance Ra (%) of the medium when the recording layer is amorphous. (ΔR = | Rc-Ra |). Signals can be recorded and reproduced on any medium of Rc> Ra or Ra> Rc.
[0003]
In the initialization process described above, the reflectance of the medium changes from Ra to Rc. In particular, a medium optically designed such that Ra> Rc has a lower reflectivity, so that Rc is desirably 10% or more.
[0004]
The initialization process requires equipment equipped with optical or thermal means. For example, when a semiconductor laser is used as an optical means, the work of optimizing various conditions such as the shape of the laser beam, the laser irradiation power, the cooling speed, the rotation speed of the medium, and the required time for various media Cost. Further, it has been known that the recording layer undergoes a volume shrinkage of several percent when it is transformed from an amorphous state into a crystalline phase. Therefore, when the recording layer is crystallized after the multilayer film is formed, a new internal stress that is not present after the film formation occurs at least in the layer in contact with the recording layer due to the volume shrinkage of the recording layer. In addition, since a very thin recording layer of 10 nm or less has low light absorption and easily diffuses heat, crystallization requires a higher power density, and heat is applied to grooves and address pits previously transferred on the substrate. The initialization process has many problems, such as being loaded.
[0005]
If the initialization process can be eliminated, capital investment and development costs can be reduced, leading to a significant cost reduction of the medium. There are (1) Rc> Ra media, (2) Ra> Rc media, and different schemes that can eliminate the need for initialization. In order to obtain good servo characteristics, it is preferable to maintain a high reflectance.In the case of (1), the recording layer is in a crystalline phase after film formation (initial state Rc), and (2) In this case, the condition is that the recording layer is amorphous after the film formation (initial state Ra). (The initial state refers to the state of the medium prior to recording.) In order to implement these, a technique for crystallizing the recording layer during film formation and a technique for recording in an as-depo amorphous state are required.
[0006]
A method of crystallizing a recording layer of a phase change optical information recording medium during film formation is disclosed in International Publication No. WO98 / 47142. A manufacturing method for forming a recording layer directly on the crystallization promoting layer after providing a crystallization promoting layer made of a material whose crystal structure is a face-centered cubic lattice system or a rhombohedral lattice system, and a recording layer being formed The substrate temperature is 45 ° C to 110 ° C. Further, the material of the crystallization promoting layer contains at least one of Sb, Bi, Sb compound and Bi compound, and the recording layer of the phase change optical information recording medium manufactured by this manufacturing method is in a crystalline state. It is disclosed that a film is formed.
[0007]
In addition, as a method of manufacturing a phase change optical information recording medium configured to satisfy Ra> Rc, a manufacturing method in which the substrate temperature during film formation of the recording layer is 35 ° C. or higher and 150 ° C. or lower, and immediately before the recording layer is formed. A manufacturing method in which the substrate temperature is 35 ° C. or higher and 95 ° C. or lower is disclosed in International Publication No. WO98 / 38636. The phase change type optical information recording medium manufactured by this manufacturing method can obtain high recording characteristics from the initial recording even when recording is performed without performing an initialization process on an as-depo amorphous recording layer. It is disclosed.
[0008]
However, as for WO98 / 47142, Bi has a low melting point of about 271 ° C., and the sputtering power cannot be increased. As for WO98 / 38636, in order to heat the substrate and form the recording layer so as to be as-depo amorphous, it is necessary to uniformly raise the temperature of the entire surface of the substrate and maintain the temperature. Don't be. For example, when the substrate holder itself is heated, it is very difficult to raise the temperature uniformly unless the substrate holder and the substrate are in full contact with each other in order to conduct heat to the substrate. However, when the substrate is brought into full contact with the holder, there is a problem that scratches and dirt are easily generated on the substrate surface. In addition, when performing high-frequency induction, flash heating, etc., in addition to the complexity of the film-forming equipment for heating the substrate uniformly in a non-contact manner in a vacuum apparatus, the film-forming equipment is complicated. There is a problem that it is difficult to stably maintain a constant temperature. Furthermore, it is necessary to measure the temperature of the substrate in a vacuum device in a non-contact manner and monitor the temperature outside the device, and the complexity and size of the device cannot be avoided.
[0009]
Conventionally, it was difficult to record in as-depo amorphous because of the difference between as-depo amorphous and amorphous formed by irradiating the crystalline phase with laser. This is probably because of this. In general, amorphous materials have several metastable energy states, and when a medium is stored for a long period of time or under a high temperature condition, it may move to a different energy state before storage. For this reason, the optimum recording / reproducing conditions before and after storage are different, and recording / reproducing characteristics may change when recording / reproducing is performed under the same conditions. For example, when the recording mark of the recording layer shifts to a more stable energy state, the erasing sensitivity for crystallization of the recording layer is lowered, and thus the erasing rate at the time of overwriting the information signal may be lowered. is there.
[0010]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention solves the above problems, and provides an information recording medium that uses a material having a high melting point, does not warm the substrate, becomes a crystalline phase after film formation, and does not require an initialization process, and a method for manufacturing the same. It is a first object to provide an information recording medium that provides and reduces the energy required for crystallization.
[0011]
In addition, the present invention solves the above-mentioned problems, and it is not necessary to strictly control the temperature of the substrate immediately before and during film formation, and an initialization process is performed on an information recording medium optically designed with Ra> Rc. A second object of the present invention is to provide an information recording medium that can perform a recording operation in a state where the recording layer is in an as-depo amorphous state even if it is not performed.
[0012]
In addition, the present invention solves the above-described problems, does not require an initialization process, and can stably read an address and perform tracking servo control even when Rc is almost 0%, and its manufacture It is a third object to provide a method and a recording / reproducing method thereof.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an information recording medium having at least a recording layer formed on a substrate, the recording layer being reversible between a crystalline state and an amorphous state by irradiation with a light beam. A phase change layer for causing a phase change and a layer for improving the crystallization ability for improving the crystallization ability of the phase change layer, and forming the crystallization ability improvement layer before forming the phase change layer. By forming the film, the phase change layer causes crystal nucleation and crystal growth during film formation, and at least a part of the phase change layer is in a crystalline phase after film formation. At this time, the crystallization ability improving layer is preferably selected from telluride or halide. Specifically, tellurides are SnTe, PbTe, Te, Sb ₂ Te _Three , Bi ₂ Te _Three , GeSbTe, GeBiTe eutectic, and the film thickness is preferably 1 nm to 10 nm. Halide is ZnF ₂ , AlF _Three , KF, CaF ₂ , NaF, BaF ₂ , MgF ₂ , LaF _Three , LiF is selected, and the film thickness is preferably 1 nm to 20 nm. Further, the phase transformation layer is preferably made of a material having GeSbTe as a main component and having a crystal structure of a rock salt type, and the crystal structure of the crystallization ability improving layer is more preferably a rock salt type. The film formation rate when forming the phase change layer is preferably 5 nm / min to 20 nm / min. By using a material that is a telluride or a halide for the crystallization ability improving layer and forming the phase change layer at a low film formation rate, the phase change layer can be converted into a crystalline phase after the film formation.
[0014]
Further, the present invention provides the energy A for crystallization of the recording layer when the crystallization ability improving layer is formed, and the energy for crystallization of the recording layer when the crystallization ability improving layer is not formed. When − is B, A also has an effect of making B smaller than B.
[0015]
Further, the present invention provides a first information recording medium having at least a first recording layer formed on a first substrate and at least a second recording layer on a second substrate as means for solving the above-mentioned problems. Is a two-layer information recording medium in which a first information recording layer is reversible between a crystalline state and an amorphous state by irradiation with a light beam. A phase change layer for causing a phase change and a layer for improving the crystallization ability for improving the crystallization ability of the phase change layer, and forming the crystallization ability improvement layer before forming the phase change layer. By forming the film, the phase change layer causes crystal nucleation and crystal growth during film formation, and at least a part of the phase change layer is in a crystalline phase after film formation. With this configuration, the first recording layer has an effect of generating crystal nuclei and crystal growth during film formation, and at least a part of the first recording layer becomes a crystal phase after film formation.
[0016]
The present invention is also an information recording medium comprising at least a recording layer on a substrate, wherein the recording layer causes a reversible phase transformation between a crystalline state and an amorphous state by irradiation with a light beam. The transformation layer (here, the layer is not limited to being uniformly formed on one surface but also includes the case where it is formed in the shape of an island. The same applies to the crystal nucleus supply layer) and the phase transformation layer. And a crystal nucleus supply layer that is laminated and facilitates crystallization of the phase change layer. According to the information recording medium, recording can be started while the phase change layer remains in an as-depo amorphous state. Further, according to the information recording medium, an information recording medium having high reliability in recording and reproducing information signals with high density and high linear velocity can be obtained.
[0017]
In the information recording medium, it is preferable that the crystal nucleus supply layer and the phase change layer are laminated in this order from the substrate side. The information recording medium further includes a second crystal nucleus supply layer that facilitates crystallization of the phase change layer, and the phase change layer and the second crystal nucleus supply layer are arranged in this order from the substrate side. It is preferable that they are laminated. In the information recording medium, it is preferable that the phase change layer and the crystal nucleus supply layer are laminated in this order from the substrate side.
[0018]
In the information recording medium, the transition temperature from the amorphous state to the crystalline phase (hereinafter referred to as crystallization temperature) Tx1 (° C.) of the crystal nucleus supply layer and the crystallization temperature Tx2 (° C.) of the phase change layer. , Tx2> Tx1 is preferably satisfied. With the above configuration, crystallization of the phase change layer is facilitated. In the information recording medium, it is preferable that the melting point Tm1 (° C.) of the crystal nucleus supply layer and the melting point Tm2 (° C.) of the phase change layer satisfy the relationship of Tm1> Tm2. With the above configuration, even when the crystal nucleus supply layer is arranged on the laser beam incident side with respect to the phase change layer, an information recording medium with high stability of the crystal nucleus supply layer can be obtained.
[0019]
In the information recording medium, the crystal nucleus supply layer preferably contains Te. With the above structure, since Te functions as a crystal nucleus, the phase change layer can be easily crystallized. In the information recording medium, it is preferable that the crystal nucleus supply layer contains at least one selected from SnTe and PbTe. In the information recording medium, the crystal nucleus supply layer is SnTe-M (where M is N, Ag, Cu, Co, Ge, Mn, Nb, Ni, Pd, Pt, Sb, Se, Ti, V, Zr). And at least one selected from PbTe). Here, SnTe-M is obtained by adding M to SnTe without changing the abundance ratio of Te to Sn. For example, a compound of SnTe and M or a eutectic of SnTe and M is included. The M content is preferably at most 50%. A more preferable content of M is in the range of 0.5-50 atom%. SnTe is Sn ₅₀ Te ₅₀ A stoichiometric composition of (Sn: Te = 50: 50) is more preferred, but Sn ₄₅ Te ₅₅ (Sn: Te = 45: 55), Sn ₅₅ Te ₄₅ A tolerance of about ± 5%, such as (Sn: Te = 55: 45), is possible.
[0020]
In the information recording medium, it is preferable that the phase change layer is made of a chalcogen material. With the above configuration, an information recording medium capable of high density recording is obtained. In the information recording medium, it is preferable that the phase change layer includes at least one selected from GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, and AgInSbTe. In the information recording medium, the phase change layer is at least one selected from GeSbTe and Ag, Sn, Cr, Mn, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, Al, and N. It is preferable that an element is included.
[0021]
In the information recording medium, it is preferable that the thickness d1 (nm) of the crystal nucleus supply layer and the thickness d2 (nm) of the phase change layer satisfy a relationship of d2> d1. With the above configuration, it is possible to prevent the amount of laser beam incident on the phase change layer from being insufficient. In the information recording medium, it is preferable that the thickness d1 (nm) of the crystal nucleus supply layer satisfies a relationship of 0.3 <d1 ≦ 5. In the information recording medium, it is preferable that the thickness d2 (nm) of the phase change layer satisfies a relationship of 3 ≦ d2 ≦ 20.
[0022]
In the information recording medium, the reflectance Rc (%) of the information recording medium when the phase change layer is a crystalline phase, and the reflectance Ra (%) of the information recording medium when the phase change layer is amorphous. ) Preferably satisfies the relationship Ra> Rc. With the above configuration, it is possible to obtain an information recording medium in which grooves and addresses formed on the substrate are particularly easy to detect.
[0023]
The method for producing an information recording medium of the present invention is a method for producing an information recording medium comprising at least a recording layer, wherein the phase transformation layer causes a phase transformation reversibly between a crystalline state and an amorphous state. And a step of forming the recording layer including a crystal nucleus supply layer that is stacked on the phase change layer and facilitates crystallization of the phase change layer. According to the method for manufacturing the information recording medium, the information recording medium of the present invention can be easily manufactured. In the manufacturing method, it is preferable that the step of forming the phase change layer is performed under a condition that the phase change layer is amorphous. The above configuration enables as-depo recording.
[0024]
In the above production method, it is preferable that the film formation rate r (nm / min) of the phase change layer satisfies the relationship r ≧ 30. With the above structure, the phase change layer can be formed in an amorphous state.
[0025]
The information recording medium recording / reproducing method of the present invention is a method for recording information on an information recording medium comprising a recording layer, wherein the recording layer is reversibly between a crystalline state and an amorphous state. A phase change layer that causes a phase change; and a crystal nucleus supply layer that is stacked on the phase change layer and facilitates crystallization of the phase change layer, and irradiates the recording layer with a laser beam to thereby generate the phase change layer. Information is recorded by phase-transforming the layer. According to the recording / reproducing method of the information recording medium, information can be recorded with high reliability.
[0026]
In the recording / reproducing method, the crystal nucleus supply layer preferably contains at least one selected from SnTe and PbTe. According to the above configuration, information can be recorded particularly reliably.
[0027]
In the recording / reproducing method, the phase change layer preferably contains at least one selected from GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, and AgInSbTe. According to the above configuration, information can be recorded particularly reliably.
[0028]
In the recording / reproducing method, the phase change layer is preferably formed in an amorphous state, and recording of the information is preferably started in an amorphous state without being crystallized.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, FIGS. 1 to 3 illustrate an invention for crystallizing a phase change layer after film formation for the purpose of not requiring initialization.
[0030]
FIG. 1 shows an example of the configuration of an information recording medium 50 of the present invention, in which a protective layer 2, a crystallization ability improving layer 3, a phase change layer 4, a protective layer 6, and a reflective layer 7 are sequentially laminated on a substrate 1. In this structure, the adhesive layer 8 is bonded to the dummy substrate 9. The recording layer 5 includes two layers, a crystallization ability improving layer 3 and a phase change layer 4.
[0031]
As the substrate 1, a transparent disc-shaped polycarbonate resin, polymethyl methacrylate resin, polyolefin resin, norbornene resin, ultraviolet curable resin, glass, or the like can be used. The thickness of the substrate 1 is not particularly limited, but a substrate having a thickness of about 0.05 to 2.0 mm can be used. Further, a spiral or concentric guide groove for tracking the laser beam is provided on the surface of the substrate 1 on the side where the film is formed, as necessary. The surface on the side where the film is not formed is smooth.
[0032]
The protective layers 2 and 6 are dielectric thin films, and have a function of adjusting the optical distance to increase the light absorption efficiency to the recording layer, and increasing the amount of reflected light before and after recording to increase the signal amplitude. Further, the recording layer 5 is physically and chemically stable for the purpose of suppressing increase in noise due to thermal damage of the recording layer 5 and adjusting the reflectivity, absorptance, and phase of reflected light with respect to the laser beam 27, etc. It is preferable to use a material that has a melting point and a softening temperature higher than the melting point and does not dissolve in the recording layer material. For example, oxides such as Y, Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge, Sn, Pb, Sb, Bi, Te, Ti, Zr, Nb, Ta, Cr, Mo, Nitride such as W, B, Al, Ga, In, Si, Ge, Sn, Pb, carbide such as Ti, Zr, Nb, Ta, Cr, Mo, W, Si, sulfide such as Zn, Cd, selenium Dielectrics or tellurides, Mg, Ca and other fluorides, simple substances such as C, Si, Ge, etc., or mixtures thereof, or materials equivalent to dielectrics can be used. Among these, ZnS-SiO, which is a mixture ₂ Is a particularly excellent protective layer having a high refractive index, a high film forming rate, good mechanical properties and moisture resistance. The film thickness of the protective layer is calculated by, for example, the matrix method (for example, Hiroshi Kubota "Wave Optics" Iwanami Shinsho, 1971, see Chapter 3). It can be determined strictly so as to satisfy the condition that the change in the amount of reflected light in the state (after recording) is larger and the light absorption rate to the recording layer 5 is larger. The protective layers 2 and 6 may be made of different materials and compositions as necessary, or may be made of the same material and composition.
[0033]
The crystallizing ability improving layer 3 of the present invention causes crystal nucleation and crystal growth of the phase change layer 4 formed on the crystallizing ability improving layer 3, and crystallizes the phase change layer 4 during film formation. Has a function. If the crystallizing ability improving layer 3 itself has a crystal structure after film formation, its function becomes greater. In general, the structure of a thin film obtained by cooling the gas phase is easily affected by the structure of the substrate. It is considered that crystallization is promoted by providing a crystalline material layer before the phase change layer 4 is formed. The effect is considered to be greater when the crystal structure of the recording layer is the same. For example, in the case of the Ge—Sb—Te system, since it is of a rock salt type, the function of the crystallization ability improving layer 3 becomes larger if the crystal has a rock salt type structure. As the material of the crystallization ability improving layer 3, SnTe, PbTe of high speed crystallization material, Te, Sb of low melting point material ₂ Te _Three , Bi ₂ Te _Three , GeSbTe eutectic, GeBiTe eutectic and other Te compounds, or CaF ₂ , MgF ₂ , LaF, AlF _Three , NaF, BaF ₂ , KF, LiF, ZnF ₂ Halides such as have a crystallization effect. In particular, SnTe, PbTe, NaF, LiF, and KF were highly effective. In order to increase the light absorption to the phase change layer 4, in the case of Te compound, the crystallizing ability improving layer 3 itself has light absorption, so an extremely thin film thickness of 1 nm to 10 nm is preferable. Since the chemical conversion improving layer 3 itself hardly absorbs light, the film thickness can be set in the range of 1 nm to 20 nm.
[0034]
The phase change layer 4 is a material that undergoes a reversible phase transformation between a crystalline phase state and an amorphous state by irradiation with an optical beam, and whose optical constants (refractive index n, extinction coefficient k) change. Is preferably used. Ge-Sb-Te, Ge-Bi-Te based on Te, or any of these systems: Au, Ag, Cu, Al, Pd, Pt, Ce, Sn, Mn, Cr, Ti It is also possible to use a material to which is added. Nitrogen addition is also possible. Ge-Sb-Te is especially GeTe-Sb ₂ Te _Three The pseudo binary system composition can ensure good recording and erasing performance as a high-speed crystallization material. GeTe: Sb ₂ Te _Three = X: 1 (1.ltoreq.x.ltoreq.6) is a practically preferred composition with excellent phase stability. The phase change layer 4 containing nitrogen was formed by reactive sputtering in an Ar gas and N2 gas atmosphere using the material containing Te as a main component as a base material. The evaluation of the phase structure after the formation of the crystallizing ability improving layer 3 and the phase transformation layer 4 was performed by forming a thin film of about 10 nm on quartz glass and raising the temperature to about 350 ° C. with a He—Ne laser. The temperature at which the optical change occurs was examined. Further, the film thickness, reflectivity, and transmittance of the crystallization ability improving layer 3 were experimentally examined to calculate a complex refractive index for a predetermined laser wavelength. Using the obtained complex refractive index, optical calculation of the multilayer film by the matrix method was performed to determine the configuration of the information recording medium.
[0035]
The recording layer 5 of the present invention has a two-layer structure in which the phase change layer 4 is formed after the crystalline crystallization ability improving layer 3 is formed. With the two-layer structure, crystal nuclei are easily generated at the interface of the phase change layer 4 on the crystallization ability improving layer 3 side, and the phase change layer 4 causes crystal growth and enters a crystal state after film formation. Information recording / reproduction is performed by optical change of the phase change layer 4. Unless otherwise specified, the case where the phase change layer 4 is in a crystalline state or an amorphous state is expressed as the recording layer 5 being in a crystalline state or an amorphous state, respectively.
[0036]
The reflective layer 7 optically increases the amount of light absorbed by the recording layer 5, thermally diffuses the heat generated in the recording layer 5 quickly, and has a function of facilitating amorphousization. It also has the role of protecting the multilayer film from the usage environment. As the material of the reflective layer 7, for example, a single metal material having high thermal conductivity such as Al, Au, Ag, Cu, or one or more of these elements as a main component is used to improve moisture resistance or heat. Use an alloy material such as Al-Cr, Al-Ti, Ag-Pd, Ag-Pd-Cu, or Ag-Pd-Ti with one or more other elements added as appropriate to adjust conductivity. Can do. All of these materials are excellent materials having excellent corrosion resistance and satisfying rapid cooling conditions. Note that the reflective layer 7 may be easily made amorphous even without a quenching effect depending on recording conditions such as linear velocity or the composition of the phase change layer, and may be omitted.
[0037]
After the formation of the reflective layer 7 from the protective layer 2, the adhesive layer 8 was spin coated on the reflective layer 7 and bonded to the dummy substrate 9.
[0038]
As the adhesive layer 8, a material having high heat resistance and adhesiveness, for example, an adhesive resin such as an ultraviolet curable resin can be used, and a material mainly composed of an acrylic resin or a material mainly composed of an epoxy resin is used. be able to. Adhesive resin such as UV curable resin of the same material or different material, double-sided tape, dielectric film, or a combination of these as appropriate, and bonded to another dummy substrate as shown in Fig. 1 to form a single-sided structure disc Alternatively, the same film surfaces may be bonded face to face to form a double-sided structure disk.
[0039]
The dummy substrate 9 is for increasing the mechanical strength of the information recording medium 50 and protecting the laminated multilayer film. The material of the dummy substrate 9 can be selected from the materials of the substrate 1. It is important that the information recording medium 50 with the bonded structure does not have mechanical warping or distortion, and the dummy substrate 9 and the substrate 1 do not necessarily have to be made of the same material and also have the same thickness. Absent.
[0040]
FIG. 2 shows a configuration example of the information recording medium 51 of the present invention, on the substrate 1, the protective layer 2, the interface layer 10, the crystallization ability improving layer 3, the phase change layer 4, the interface layer 11, the protective layer 6, The light absorption correction layer 12 and the reflection layer 7 are sequentially laminated, and the dummy substrate 9 is bonded to the adhesive layer 8. This configuration is such that the light absorption rate Ac of the recording layer 5 when the recording layer 5 is in the crystalline state is larger than the light absorption rate Aa when the recording layer 5 is in the amorphous state. The light absorption correction layer 12 is provided between the layers 7 to achieve a light absorption balance. Even in this configuration, the crystallization of the phase change layer 4 was verified by forming the crystallization ability improving layer 3 in advance of the phase change layer 4.
[0041]
The substrate 1, the protective layers 2 and 6, the crystallization ability improving layer 3, the phase change layer 4, the reflective layer 7, the adhesive layer 8, and the dummy substrate 9 can be made of the same materials as in FIG.
[0042]
The interface layers 10 and 11 have a function of preventing mass transfer that occurs between the protective layer 2 and the recording layer 5 and the protective layer 6 and the recording layer 5 due to repeated recording, and Si, Al, Zr, Ti, Ge, Ta, A material mainly containing a nitride, oxide, nitride oxide, carbide, or a mixture thereof mainly containing Cr or the like is preferable. Further, the above function is exhibited only by providing either one of the interface layers 10 or 11, but it is more preferable to provide both, in which case, different materials / compositions may be used as necessary, or the same Materials and compositions can also be used. These interface layer materials can be formed by reactive sputtering of a metal base material in an Ar gas and reactive gas atmosphere, or by sputtering a compound base material in an Ar gas atmosphere. If the thickness of these interface layers is large, the reflectivity and absorptance of the multilayer structure are greatly changed and affect the recording / erasing performance. Therefore, the thickness is preferably 2 nm to 10 nm, and more preferably about 2 nm to 5 nm.
[0043]
The light absorption correction layer 12 adjusts the light absorptance ratio between when the recording layer 5 is in a crystalline state and when it is in an amorphous state, so that the mark shape is not distorted during overwriting, and recording For the purpose of increasing the difference in reflectance between when the layer 5 is in a crystalline state and when it is in an amorphous state and increasing the signal amplitude, a material that has a high refractive index and absorbs light appropriately is preferable. For example, a material having a refractive index n of 3 to 6 and an extinction coefficient k of 1 to 4 can be used. Specifically, Ge-Cr, Ge-Mo, Si-Cr, Si-Mo, Si-W and other amorphous Ge alloys and Si alloys, Te compounds, or Ti, Zr, Nb, Ta, Cr, It is preferable to use crystalline metals, metalloids and semiconductor materials such as Mo, W, SnTe and PbTe.
[0044]
FIG. 3 shows a configuration example of the double-layer information recording medium 52 of the present invention, which has a structure in which the first information recording medium 20 and the second information recording medium 29 are bonded together. Since the laser beam 27 is incident from the first substrate side 13 and both the information recording media 20 and 29 are recorded and reproduced from one side, there is no need to turn the media over and the recording / reproducing capacity is approximately doubled.
[0045]
For the first substrate 13 and the second substrate 28, the same material as that of the substrate 1 in FIG. 1 can be used.
[0046]
For the first protective layers 14 and 19 and the second protective layers 22 and 26, the same material as the protective layers 2 and 6 in FIG. 1 can be used.
[0047]
The first interface layers 15 and 18 and the second interface layers 23 and 25 can be made of the same material as the interface layers 10 and 11 in FIG.
[0048]
The crystallization ability improving layer 3 of the present invention is formed on the first optical information recording medium 20, and the same material as that in FIG. 1 is used.
[0049]
The second information recording medium 29 is optically designed so that the transmittance of the first information recording medium 20 is as high as possible because it is recorded and reproduced by the laser beam 27 incident through the first information recording medium 20. Therefore, the phase change layer 4 of the information medium 20 is set to an extremely thin film thickness of about 5 nm to about 8 nm. The crystallization ability improving layer 3 is also preferably as thin as 1 nm to 3 nm. Since the phase change layer 4 is thin, a larger laser energy is required in the initialization process. However, by forming the crystallization ability improving layer 3 even at 1 nm, the phase change layer 4 is easily crystallized, and the laser energy is increased. Was greatly reduced. Furthermore, by forming 3 nm, the phase change layer 4 was crystallized after the film formation.
[0050]
The second recording layer 24 is made of the same material as that of the phase change layer 4.
[0051]
The first recording layer 17 of the present invention has the same function as the recording layer 5 of FIG.
[0052]
The separation layer 21 is transparent, heat resistant and adhesive at the wavelength λ of the laser beam 27 in order to perform recording and reproduction with the laser beam 27 on each of the first information recording medium 20 and the second information recording medium 29. A high material is preferable. Specifically, for example, an adhesive resin such as an ultraviolet curable resin, a double-sided tape, a dielectric film, or a combination thereof can be used as appropriate. Further, the thickness of the separation layer 21 disturbs the signal information recorded on the other when recording or reproducing on either the first information recording medium 20 or the second information recording medium 29. In order to avoid leakage, it is necessary that the depth of focus is not less than 2 μm, for example, and that both the first information recording medium 20 and the second information recording medium 29 have laser light 27. It is also necessary that the total with the substrate thickness is within the range of the substrate thickness tolerance, for example, 100 μm or less.
[0053]
The reflective layer 7 is made of the same material as in FIG.
[0054]
In the following, FIGS. 5 to 7 illustrate the invention of recording in as-depo amorphous for the purpose of not requiring initialization.
[0055]
FIG. 5 shows one configuration example of the information recording medium 53 of the present invention. The protective layer 2, the interface layer 10, the crystal nucleus supply layer 32, the phase transformation layer 33, the interface layer 11, the protective layer 6, and the reflection are formed on the substrate 1. The layers 7 are sequentially stacked and bonded to the dummy substrate 9 with the adhesive layer 8. The recording layer 31 includes a crystal nucleus supply layer 32 and a phase change layer 33 that are sequentially stacked from the substrate 1 side. (The same applies to the following embodiments).
[0056]
The recording layer 31 includes a crystal nucleus supply layer 32 and a phase change layer 33 stacked above the substrate 1. The crystal nucleus supply layer 32 is a layer for facilitating crystallization of the phase change layer 33. The phase change layer 33 is a layer that reversibly undergoes a phase change between a crystalline state and an amorphous state, and is a layer that records information by this phase change. In the information recording medium 53, since the recording layer 31 has the above configuration, the phase change layer 33 is likely to be crystallized from the interface with the crystal nucleus supply layer 32.
[0057]
In order to facilitate the crystallization of the phase change layer 33, the crystal nucleus supply layer 32 has a lower crystallization temperature (transition temperature from amorphous to crystalline phase) than the phase change layer 33, and the crystal It is preferably made of a material that is stable. That is, it is preferable that the crystallization temperature Tx1 (° C.) of the crystal nucleus supply layer 32 and the crystallization temperature Tx2 (° C.) of the phase change layer 33 satisfy the relationship of Tx2> Tx1 (the same applies to the following embodiments). ).
[0058]
The phase change layer 33 is made of a material that causes a reversible phase change between a crystalline state and an amorphous state by irradiation with a light beam. The phase change layer 33 is made of, for example, a chalcogen material. Specifically, the phase change layer 33 preferably includes at least one selected from GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, and AgInSbTe among chalcogen-based materials. The phase transformation layer 33 includes GeSbTe and at least one element selected from Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, Al, Mn, Cu, and N. You may use the material containing these. Especially for Ge-Sb-Te materials, GeTe-Sb ₂ Te _Three A quasi-binary composition is preferable because it can ensure good recording and erasing performance as a high-speed crystallization material. In this case, GeTe: Sb ₂ Te _Three Since the composition range of = 1-6: 1 is excellent in phase stability, it is a practically preferable composition. The phase change layer 33 has a crystallization temperature of about 140 ° C. to about 240 ° C. and a melting point of about 600 ° C. to about 650 ° C. Further, the crystal structure of the phase change layer 33 is NaCl type in the case of crystallization by laser irradiation. In addition, the phase change layer 33 is in an amorphous state when formed, and as-depo recording is possible. The thickness of the phase change layer 33 is, for example, not less than 3 nm and not more than 20 nm.
[0059]
Therefore, a material containing Te is preferable as the material of the crystal nucleus supply layer 32, and a material containing at least one selected from SnTe and PbTe is particularly preferable.
[0060]
When the crystal nucleus supply layer 32 is formed on the laser incident side of the phase change layer 33 as in the information recording medium 53, the light beam reaches the crystal nucleus supply layer 32 and is absorbed first. The melting point of the layer 32 is preferably higher than the melting point of the phase change layer 33. That is, it is preferable that the melting point Tm1 (° C.) of the crystal nucleus supply layer 32 and the melting point Tm2 (° C.) of the phase change layer 33 satisfy the relationship of Tm1> Tm2. This is because when a signal is recorded by irradiating the phase change layer 33 with a high-power laser beam, in the process of melting and quenching, the crystal nucleus supply layer 32 is also melted at the same time and the function as the crystal nucleus supply layer is impaired. This is to prevent this. Here, Table 1 shows the crystallization temperature and melting point of a material containing Te as the material of the crystal nucleus supply layer 32.
[0061]
[Table 1]

[0062]
As shown in Table 1, it can be seen that SnTe and PbTe are particularly preferable as the material for the crystal nucleus supply layer from the viewpoint of the melting point.
[0063]
Since the crystal nucleus supply layer 32 is preferably stable in a crystalline state, the film thickness of the crystal nucleus supply layer 32 is preferably 2 nm or more, more preferably thicker (thinner is necessary for crystallization). Because the number of atoms is insufficient). However, if the film thickness of the crystal nucleus supply layer 32 is large, the energy beam is absorbed by the crystal nucleus supply layer 32, and the energy beam does not reach the phase change layer 33. Therefore, the thickness of the crystal nucleus supply layer 32 is preferably 2 nm or more and 4 nm or less.
[0064]
The crystal nucleus supply layer 32 is made of Ar gas or Ar-N. ₂ It can be formed by sputtering a base material in a mixed gas atmosphere. Further, the phase change layer 33 is formed of Ar gas or Ar-N. ₂ It can be formed by sputtering a base material in a mixed gas atmosphere. At this time, in order for the phase change layer 33 to be as-depo amorphous after film formation, the film formation rate of the phase change layer 33 is preferably about 30 nm / min or more. According to the experiments by the present inventors, when the film thickness of the crystallization ability improving layer is 5 nm and the film thickness of the recording layer is 10 nm, the recording layer is being formed when the film forming speed of the recording layer is 5 nm / min to 20 nm / min. Crystallized to 30 nm / min to 40 nm / min, and as-depo amorphous and crystalline phase were mixed, and at 50 nm / min and higher, it became as-depo amorphous. Even when the crystal nucleus supply layer 32 is present as in the reversible optical information recording medium 10, if the film formation rate of the phase change layer 33 is low, the phase change layer 33 may crystallize during film formation. Depending on the combination of the thickness of the crystal nucleus supplying layer 32 and the thickness of the phase change layer 33, the film formation rate at which the phase change layer 33 is crystallized during film formation varies, but the phase change layer 33 is prevented from being crystallized. For this purpose, the deposition rate of the phase change layer 33 is preferably 30 nm / min or more, and more preferably 40 nm / min or more.
[0065]
In the information recording medium 53, as the crystal nucleus supply layer 32, SnTe, SnTe-M (where M is N, Ag, Cu, Co, Ge, Mn, Nb, Ni, Pd, Pt, Sb, Se, Ti, (Including at least one selected from V, Zr and PbTe), PbTe, Sb ₂ Te _Three , Bi ₂ Te _Three In the case of using any one of Te, GeSbTe eutectic, and GeBiTe eutectic, it was possible to record information (as-depo recording) while the phase change layer 33 was in an as-depo amorphous state. In particular, good results were obtained when a material containing SnTe having a high melting point or a material containing PbTe was used.
[0066]
The phase change layer 33 includes at least one selected from GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, AgInSbTe, and GeSbTe, and Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr. As-depo recording was possible when any of the materials added with at least one selected from Au, Pt, Al, Mn and N was used.
[0067]
As described above, according to the information recording medium 53, as-depo recording is possible.
[0068]
FIG. 6 shows a configuration example of the information recording medium 54 of the present invention, and shows a cross-sectional view. Referring to FIG. 6, the information recording medium 54 includes a substrate 1, a protective layer 2, an interface layer 10, a recording layer 34, an interface layer 11, a protective layer 6, and a reflective layer 7 sequentially stacked on the substrate 1. And a dummy substrate 9 bonded on the reflective layer 7 with an adhesive layer 8. The recording layer 34 includes a phase change layer 33 and a crystal nucleus supply layer 35 that are sequentially stacked from the substrate 1 side. Since the portion excluding the recording layer 34 is the same as that of the information recording medium 53 described with reference to FIG.
[0069]
The functions of the recording layer 34, the crystal nucleus supply layer 35, and the phase change layer 33 are the same as those of the recording layer 31, the crystal nucleus supply layer 32, and the phase change layer 33 described in FIG. That is, the crystal nucleus supply layer 35 is a layer for facilitating crystallization of the phase change layer 33. The phase change layer 33 is a layer that reversibly undergoes a phase change between a crystalline state and an amorphous state, and is a layer that records information by this phase change. In the information recording medium 54, since the recording layer 34 has the above configuration, the phase change layer 33 is likely to be crystallized from the interface with the crystal nucleus supply layer 35.
[0070]
In the information recording medium 54, unlike the case of FIG. 5, the recording layer 34 includes a phase change layer 33 and a crystal nucleus supply layer 35 which are stacked in order from the substrate 1 side.
[0071]
The phase change layer 33 is the same as the phase change layer 33 of the information recording medium 53.
[0072]
Unlike the crystal nucleus supply layer 32 of the information recording medium 53, the crystal nucleus supply layer 35 is laminated on the opposite side of the laser incident side with respect to the phase change layer 33. Therefore, a material having a melting point lower than that of the phase change layer 33 can be suitably used for the crystal nucleus supply layer 35. Specifically, in addition to the material of the crystal nucleus supply layer 32 described in FIG. 5, as a material containing Te, in addition to SnTe and PbTe, Sb ₂ Te _Three , Bi ₂ Te _Three Te, GeSbTe eutectic composition and GeBiTe eutectic composition can also be preferably used. In the information recording medium 54, since the energy beam enters the crystal nucleus supply layer 35 after passing through the phase change layer 33, the crystal nucleus supply layer 35 can be made thicker than the information recording medium 53. Specifically, the film thickness of the crystal nucleus supply layer 35 is preferably about 2 nm to 5 nm. Further, the film formation rate of the phase change layer 33 is preferably about 30 nm / min or more, and is formed in an amorphous state.
[0073]
In the information recording medium 54, as the crystal nucleus supply layer 35, SnTe, SnTe-M (where M is N, Ag, Cu, Co, Ge, Mn, Nb, Ni, Pd, Pt, Sb, Se, Ti, V , At least one selected from Zr and PbTe), PbTe, Sb ₂ Te _Three , Bi ₂ Te _Three , Te, GeSbTe eutectic, or GeBiTe eutectic, it was possible to record information with the phase change layer 33 in an as-depo amorphous state. In the information recording medium 54, good results were obtained when any material was used.
[0074]
Further, the phase transformation layer 33 contains GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, AgInSbTe, or GeSbTe and Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, As-depo recording was possible when any of the materials added with at least one selected from Al, Mn and N was used.
[0075]
As described above, according to the information recording medium 54 of FIG. 6, the same effect as the information recording medium 53 can be obtained.
[0076]
FIG. 7 illustrates an example of the information recording medium of the present invention. The information recording medium 55 includes a substrate 1, a protective layer 2, an interface layer 10, a recording layer 36, an interface layer 11, a protective layer 6, and a reflective layer 7 sequentially laminated on the substrate 1, and an adhesive layer on the reflective layer 7. And a dummy substrate 9 bonded by 8. The recording layer 36 includes a crystal nucleus supply layer 32, a phase change layer 33, and a crystal nucleus supply layer 35, which are sequentially stacked from the substrate 1 side. Since the portion excluding the recording layer 36 is the same as the information recording medium 53 described with reference to FIG.
[0077]
The crystal nucleus supply layers 32 and 35 have the same function as the crystal nucleus supply layer 32 described with reference to FIG. That is, the crystal nucleus supply layers 32 and 35 are layers for facilitating crystallization of the phase change layer 33. In the information recording medium 55, since the recording layer 36 has the above configuration, the phase change layer 33 is likely to be crystallized from the interface with the crystal nucleus supply layer 32 or 35.
[0078]
In the information recording medium 55, unlike the information recording medium 53 of FIG. 5, the phase change layer 33 is sandwiched between the crystal nucleus supply layer 32 and the crystal nucleus supply layer 35.
[0079]
The phase change layer 33 is made of the same material as described in FIG.
[0080]
For the crystal nucleus supply layer 32, the same material as the crystal nucleus supply layer 32 described in FIG. 5 can be used. The crystal nucleus supply layer 32 is preferably made of a material having a higher melting point than the phase change layer 33 among materials containing Te.
[0081]
For the crystal nucleus supply layer 35, the same material as the crystal nucleus supply layer 35 described with reference to FIG. 6 can be used. Of the materials containing Te, a material having a melting point lower than that of the phase change layer 33 can be suitably used for the crystal nucleus supply layer 35.
[0082]
The material of the crystal nucleus supply layer 32 and the material of the crystal nucleus supply layer 35 may be different. For example, the crystal nucleus supply layer 32 may be made of SnTe and the crystal nucleus supply layer 35 may be made of PbTe. The crystal nucleus supply layer 32 may be made of PbTe, and the crystal nucleus supply layer 35 may be made of a GeBiTe eutectic composition. Note that the use of the same material for the crystal nucleus supply layer 32 and the crystal nucleus supply layer 35 is advantageous in that the number of base materials can be reduced during film formation and the film formation apparatus can be simplified.
[0083]
The film thickness of the crystal nucleus supply layer 32 and the film thickness of the crystal nucleus supply layer 35 may be different, but the total of both film thicknesses is preferably 5 nm or less. For example, the film thickness of the crystal nucleus supply layer 32 may be 1 nm and the film thickness of the crystal nucleus supply layer 35 may be 2 nm, or the film thickness of the crystal nucleus supply layer 32 may be 2 nm and the film thickness of the crystal nucleus supply layer 35 may be It may be 3 nm.
[0084]
In the information recording medium 55, as the crystal nucleus supply layers 32 and 35, SnTe, SnTe-M (where M is N, Ag, Cu, Co, Ge, Mn, Nb, Ni, Pd, Pt, Sb, Se, Ti, , V, Zr and PbTe), PbTe, Sb ₂ Te _Three , Bi ₂ Te _Three As-depo recording was possible when using any one of Te, Ge, GeSbTe, and GeBiTe eutectics. In particular, good results were obtained when a material containing SnTe or a material containing PbTe having a high melting point was used for the crystal nucleus supply layer 32.
[0085]
The phase change layer 33 contains GeTe, GeSbTe, TeSnSe, InSbTe, GeBiTe, AgInSbTe, or GeSbTe and Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, Al As-depo recording was possible when any of the materials added with at least one selected from Mn and N was used.
[0086]
As described above, according to the information recording medium 55 of FIG. 7, the same effect as that of the information recording medium 53 can be obtained.
[0087]
The information recording medium described in FIGS. 5 to 7 is designed such that Ra> Rc, and signals can be recorded without performing the initialization process while the phase change layer 33 is in an as-depo amorphous state.
[0088]
Next, an example of the method for producing the information recording medium of the present invention will be described.
[0089]
The method for producing an information recording medium of the present invention is a method for producing an information recording medium comprising a recording layer, wherein the phase transformation layer causes a phase transformation reversibly between a crystalline state and an amorphous state, and a phase Forming a recording layer including a crystal nucleus supply layer stacked on the transformation layer and facilitating crystallization of the phase transformation layer. Hereinafter, a method for manufacturing the information recording medium 53 described with reference to FIG. 5 will be described with reference to FIG.
[0090]
First, the protective layer 2 and the interface layer 10 are formed on the substrate 1. These layers can be formed by reactive sputtering of the target material (metal matrix) in an Ar gas and reactive gas atmosphere, or by sputtering a compound matrix in an Ar gas atmosphere or in an Ar gas and reactive gas atmosphere. Can be formed.
[0091]
Next, the crystal nucleus supply layer 32 and the phase change layer 33 are stacked on the interface layer 10. The crystal nucleus supply layer 32 and the phase change layer 33 are formed of Ar gas or Ar-N. ₂ It can be formed by sputtering a base material in a mixed gas atmosphere. Note that the phase change layer 33 is formed under conditions that make it amorphous. In order for the phase change layer 33 to be as-depo amorphous after film formation, as described with reference to FIG. 5, the film formation rate of the phase change layer 33 is preferably about 30 nm / min or more.
[0092]
Next, the interface layer 11 and the protective layer 6 are stacked on the phase change layer 33. These layers can be formed by the same method as the protective layer 2 and the interface layer 10.
[0093]
Next, the reflective layer 7 is formed on the protective layer 6. The reflective layer 7 can be formed by sputtering or vapor deposition.
[0094]
Finally, the adhesive layer 8 was applied on the reflective layer 7 by a spin coating method, and the dummy substrate 9 was bonded, and then the adhesive layer 8 was cured by irradiation with ultraviolet rays. In this way, the information recording medium 53 can be manufactured.
[0095]
The information recording medium 54 or 55 can be easily manufactured by a method similar to the above method.
[0096]
According to the above manufacturing method, the information recording medium of the present invention can be easily manufactured.
[0097]
Next, an example of the recording / reproducing method of the information recording medium of the present invention will be described.
[0098]
This recording / reproducing method is a recording / reproducing method using the information recording medium of the present invention described in any of FIGS.
[0099]
Specifically, by irradiating the information recording medium described in any of FIGS. 5 to 7 with a modulated laser beam, an amorphous region and a crystalline phase region are formed in the phase change layer, and signal recording is performed. Do. By irradiating the amorphous region of the phase change layer with a low laser beam power, the irradiated amorphous region can be crystallized. Further, by irradiating the crystal phase region of the phase change layer with a high power laser beam, the crystal phase region of the irradiated portion can be made amorphous.
[0100]
According to this recording / reproducing method, information signals can be recorded with high reliability. In particular, as-depo recording becomes possible by using the information recording medium shown in FIGS.
[0101]
【Example】
Next, specific examples of the present invention will be described.
[0102]
Examples 1 to 13 are examples of the invention for the purpose of not requiring initialization and for crystallizing the phase change layer after film formation.
[0103]
Examples 14 to 26 are examples relating to the invention in which the phase change layer is recorded in an as-depo amorphous state for the purpose of not requiring initialization. The embodiment 26 is an embodiment relating to reliability.
[0104]
(Example 1)
For the function as the crystallization ability improving layer to crystallize the phase change layer during film formation, it is considered that the crystallization ability improvement layer itself is a crystal after film formation. Several types of high-speed crystallization materials or low-melting-point materials whose crystals are structurally more stable were selected, and the phase structure after the film formation was investigated. The material is Bi ₂ Te _Three , Sb ₂ Te _Three , Sb, Te, SnTe, PbTe, GeSbTe eutectic, GeBiTe eutectic. A sputtering target having a diameter of 100 mm and a thickness of 6 mm (hereinafter referred to as 100 mmφ × 6 mmt) was DC-sputtered in an Ar atmosphere to form a 5 nm thin film on each quartz substrate. The transmittance of the obtained eight kinds of thin films was measured while increasing the temperature with a He—Ne laser at a rate of 50 ° C. per minute. The relationship between temperature and transmittance is shown in FIGS. If the structure after film formation is amorphous, as shown in FIG. 4 (a), the transmittance at room temperature is relatively high, and rapid transmission accompanying phase transformation to the crystalline phase occurs at a temperature during the temperature rise. A rate drop is observed. This temperature is defined as the crystallization temperature. When the structure after film formation is a mixed state of an amorphous phase and a crystalline phase, the transmittance at room temperature is lower than in the case of FIG. Changes are observed. Further, the crystallization temperature is lower than that in the case of FIG. 4A, and crystallization is easier than in the state of FIG. 4A. In the lines a, b, and c in FIG. 4B, the proportions of the crystalline state and the amorphous state are different, and the proportion of the crystalline phase increases in the order of a, b, and c. If the structure after film formation is a crystalline phase, the transmittance at room temperature is relatively lowest, and even when the temperature is raised as shown in FIG. It is possible to determine the phase structure from such differences. Table 2 shows the structures of the eight types of thin films at room temperature.
[0105]
[Table 2]

[0106]
(Example 2)
It was examined whether the thin film of Example 1 had a function as a crystallization ability improving layer. A crystallizing ability improving layer was formed on a quartz substrate in a vacuum chamber, and the phase structure after film formation of a sample in which a phase change layer was continuously formed thereon was examined. The film thickness is quartz | crystallizing ability improving layer (5 nm) | phase transformation layer (10 nm). The sputtering conditions for the crystallization ability improving layer were the same as in Example 1, and the material for the phase change layer was Ge. ₂ Sb ₂ Te _Five It is. The phase structure of the phase change layer was examined by transmittance measurement in the same manner as in Example 1.
[0107]
[Table 3]

[0108]
Ge if there is no crystallization-enhancing layer ₂ Sb ₂ Te _Five The phase change layer was amorphous after film formation and showed a change in transmittance as shown in FIG. 4A. The crystallization temperature was about 200 ° C. When Sb was used for the crystallization ability improving layer, the crystallization temperature of the phase change layer was not lowered, and crystallization and crystal nucleation were not observed. Bi in the crystallization ability improving layer ₂ Te _Three , Sb ₂ Te _Three When Te, GeSbTe eutectic is used, the phase change layer becomes a mixed state of amorphous and crystalline phases. When SnTe, PbTe, GeBiTe eutectic was used for the crystallization ability improving layer, the result shown in FIG. 4C was obtained, and crystallization of the phase change layer was observed. From this result, it was found that the crystallization of the phase change layer was promoted when Te compound was used as the crystallization ability improving layer. In addition, among the Te compounds, it was also clarified that the material having a crystal structure of rock salt type has a larger crystallization effect.
[0109]
(Example 3)
The relationship between the film thickness and the crystallization effect was investigated by using SnTe for the crystallization ability improvement layer. A film was formed on a quartz substrate by changing SnTe from 1 nm to 20 nm, and a phase change layer was formed thereon by 10 nm. Table 4 shows the structure of the phase change layer of these samples.
[0110]
[Table 4]

[0111]
At 1 nm, it was in a mixed state of amorphous and crystal. However, an effect that crystallization becomes easier than that in the case of no crystallization ability improving layer was recognized. If it was 3 nm or more, the phase change layer was crystallized.
[0112]
(Example 4)
The film formation conditions and the crystallization effect of the phase change layer were investigated. A 5 nm thick SnTe film was formed on a quartz substrate, and a 10 nm phase change layer was formed on the quartz substrate while changing the film forming speed. Table 5 shows the structure of the phase change layer of these samples.
[0113]
[Table 5]

[0114]
It was found that the effect of the crystallization ability improving layer to crystallize the phase change layer depends on the film formation rate of the phase change layer. The phase change layer was crystallized at a deposition rate of 5 nm / min to 20 nm / min, and became a mixed state of amorphous and crystalline phases at 30 nm / min to 40 nm / min. Above that, it was amorphous. When the film formation rate of the phase change layer is low, the phase change layer is more easily crystallized. The most preferable film formation rate was 5 nm / min to 10 nm / min.
[0115]
(Example 5)
When the complex refractive index of SnTe was experimentally determined, the refractive index n = 4.2 and the extinction coefficient k = 4.5. From this complex refractive index, the configuration of the optical information recording medium was determined by optical calculation and made as a prototype. The reflectance of the optical information recording medium was measured to check whether the phase change layer was crystallized.
[0116]
As shown in FIG. 1, a batch-type sputtering apparatus is used on a polycarbonate substrate with a protective layer of 100 nm, a crystallization ability improving layer of 5 nm, a phase change layer of 18 nm, a protective layer of 25 nm, and a reflective layer of 80 nm in this order. The film was continuously formed in a vacuum chamber. The detailed film forming conditions for each are shown in Table 6.
[0117]
[Table 6]

[0118]
The reflectance of the optical information recording medium was measured with a phase change optical disk evaluation apparatus manufactured by Pulstec. The light source has a wavelength of 660 nm and NA of 0.6. The optical information recording medium was rotated at a linear velocity of 8 m / s, and the reflectance of the mirror surface portion at a radius of 40 mm was measured. As a result, a reflectance of 20% was obtained.
[0119]
In order to investigate whether or not it was completely crystallized, the reflectivity was measured after irradiating the semiconductor laser beam at the same position with sufficient power for normal crystallization. In this case, a reflectance of 20.3% was obtained. It was verified that the phase change layer was almost completely crystallized after deposition. The same effect was observed for PbTe and GeBiTe eutectic.
[0120]
(Example 6)
When only the film thickness of the crystallization ability improving layer was changed in the multilayer film structure of Example 5, how the reflectance and recording sensitivity of the optical information recording medium were changed was measured. SnTe was used as the crystallization ability improving layer. The reflectance measurement conditions were the same as in Example 5, and the recording sensitivity was defined as a recording power at which a 3T signal was recorded once between grooves with the same apparatus and a CNR value of 50 dB was obtained. The results are shown in Table 7.
[0121]
[Table 7]

[0122]
The greater the thickness of the crystallization ability improving layer, the higher the reflectivity of the multilayer film. However, when the recording sensitivity is reduced and a film thickness of 15 nm or more, a recording power of 14 mW or more is required, which is difficult to put into practical use. From this result, it was found that the film thickness of the crystallization ability improving layer is preferably 1 to 10 nm.
[0123]
(Example 7)
The overwrite jitter characteristic of the optical information recording medium that was prototyped in Example 5 was evaluated. For comparison, an overwrite jitter characteristic of an optical information recording medium that has undergone a crystallization process using a semiconductor laser in a conventional configuration without a crystallization ability improving layer was also evaluated. 3T signal was recorded from 1 to 20 times between grooves, and the change of jitter value was examined. The results are shown in Table 8.
[0124]
[Table 8]

[0125]
The jitter value in the table is an average value of the jitter value between the front end and the rear end jitter of the recording mark.
[0126]
The difference between the front end jitter and the rear end jitter was within 0.5% regardless of the number of recordings.
[0127]
If the crystallization of the phase change layer is insufficient and amorphous remains in the crystal phase, the jitter value increases during the second to fourth recording. In this example, even when recording was performed on an optical information recording medium in which a crystallizing ability improving layer was provided and the phase change layer was crystallized during film formation, an increase in jitter value was recognized from the second time to the fourth time. I couldn't. A crystal phase almost equivalent to that of a recording film crystallized by irradiation with a semiconductor laser beam after conventional film formation was obtained.
[0128]
(Example 8)
With the configuration of the first information recording medium of the two-layer information recording medium of FIG. 3, the effect of the crystallization ability improving layer was investigated. On the polycarbonate substrate, the protective layer is 100 nm, the interface layer is 5 nm, the crystallization ability improving layer is 3 nm, the phase change layer is 7 nm, the interface layer is 5 nm, and the protective layer is 90 nm. The film was continuously formed in a vacuum chamber. Seven types of information recording media with different crystallization ability improving layer materials and information recording media without a crystallization ability improving layer were prototyped. At the same time, a sample piece in which a multilayer film was formed with the same structure on a quartz substrate was also produced. The phase structure of the phase change layer after film formation was examined using this sample piece. Bi ₂ Te _Three , Sb ₂ Te _Three When Te, GeSbTe eutectic was used, it was a mixture of amorphous and crystalline phases. Since these are not completely amorphous, in order to evaluate easiness of crystallization, crystallization by irradiation with a semiconductor laser beam was also attempted with an optical information recording medium. In the absence of the crystallization ability improving layer, the power of the semiconductor laser required for initialization was 800 mW. This was almost the upper limit of laser output. Table 9 shows the results when the crystallization ability improving layer was used.
[0129]
[Table 9]

[0130]
Even if the phase change layer did not become a complete crystal phase, it was found that the crystallization ability improving layer was provided even at 3 nm, the initialization power was almost halved and crystallization became easier. The same effect was obtained with the crystallization ability improving layer 1 nm.
[0131]
(Example 9)
Example 5 was also performed on a configuration having a light absorption layer as shown in FIG.
[0132]
ZnS-SiO protective layer on polycarbonate substrate ₂ 120 nm, GeN of interface layer 5 nm, SnTe of crystallization enhancement layer 5 nm, GeSbTe of phase change layer 10 nm, GeN of interface layer 5 nm, ZnS-SiO of protective layer ₂ An information recording medium was fabricated by depositing 50 nm of Si, 30 nm of Si alloy of the light absorption correction layer, and 80 nm of Ag alloy of the reflective layer. After the film formation, the phase change layer was crystallized due to the effect of the crystallization ability improving layer, and a reflectance of 17.0% was obtained. Further, even when the reflectance was measured after irradiating the semiconductor laser beam at the same position, a reflectance of 16.9% was obtained, and it was verified that the film was completely crystallized after film formation. In the configuration of FIG. 2, the effect of the crystallization ability improving layer was recognized.
[0133]
(Example 10)
Until Example 9, Te was used as the crystallization ability improving layer, and an excellent effect was obtained. However, since the crystallization ability improving layer absorbs light, the film thickness range is limited to an extremely thin range of 5 nm or less. Therefore, it was investigated whether a halide having a small light absorption and including a compound having a rock salt structure also has a function as a layer for improving the crystallization ability. Material is ZnF ₂ , AlF _Three , KF, CaF ₂ , NaF, BaF ₂ , MgF ₂ , LaF _Three There are 9 kinds of F compounds of LiF. Each compound sputtering target of 100 mmφ × 6 mmt was RF-sputtered in an Ar atmosphere to form a 10 nm thin film on a quartz substrate. Subsequently, the phase structure of the phase change layer after the film formation was examined for a sample in which a phase change layer was continuously formed thereon by 10 nm. In the same manner as in Example 1, the transmittance was measured with a He—Ne laser while the temperature was raised at a rate of 50 ° C. per minute. From FIG. 4 (a) to FIG. 4 (c), as a result of judging the phase structure of nine types of samples, all were in a mixed state of amorphous and crystalline phases. Fig. 4 (b) shows the change in transmittance. The rock salt structure materials LiF, NaF, and KF were close to the b line, and the other materials were close to the a line. The use of a rock salt type material for the crystallization ability improving layer increased the proportion of the crystalline phase in the phase transformation layer, and was more effective as a crystallization ability improving layer.
[0134]
(Example 11)
Example 8 was carried out by forming 10 nm of a halide as the crystallization ability improving layer. The results are shown in Table 10.
[0135]
[Table 10]

[0136]
Even when the phase change layer was in a mixed state of an amorphous phase and a crystalline phase, the initialization laser power was significantly reduced as compared with the case where the crystallizing ability improving layer was not provided. It can be seen that the energy required for crystallization is reduced by providing the layer for improving the crystallization ability of the halide. In the case of providing the halide crystallization ability improving layer, the effect that the phase change layer was easily crystallized was obtained.
[0137]
(Example 12)
The complex refractive index of LiF, NaF, KF, which has a high function as a crystallization ability improving layer, is determined. Each crystallization ability improving layer was formed on a quartz substrate, the film thickness was measured with a step meter, and the reflectance and transmittance were measured with a spectroscope to calculate the complex refractive index. Table 11 shows the obtained complex refractive index.
[0138]
[Table 11]

[0139]
These films were transparent films with k = 0.
[0140]
(Example 13)
When only the film thickness of the crystallization ability improving layer was changed in the multilayer film configuration of Example 8, how the reflectance and recording sensitivity of the optical information recording medium were changed was measured. LiF was used as the crystallization ability improving layer. The results are shown in Table 12.
[0141]
[Table 12]

[0142]
The thicker the crystallization ability improving layer, the higher the reflectance of the multilayer film. At 1 nm, the reflectivity was below 15%. In addition, the recording sensitivity exceeding 25 nm is 14 mW or more. From this result, the film thickness of the halide crystallization ability improving layer is preferably 5 nm or more and 20 nm or less. Compared with the results of Example 6, it can be seen that the smaller the k of the crystallization ability improving layer itself, the thicker the crystallization ability improving layer can be set.
[0143]
In the above embodiment, the effects of the crystallization ability improving layer are described in the configurations shown in FIGS. 1, 2 and 3. If the improvement layer is formed, the effect can be obtained regardless of the film thickness of the protective layer and the presence or absence of the interface layer.
[0144]
As described above, according to the present invention, by forming the crystallization ability improving layer at the substrate-side interface of the phase change layer, the phase structure after the phase change layer is formed becomes a crystalline phase, which requires thermal means. As a result, it is possible to obtain a result that the crystallization step is not necessary or can be crystallized with less power.
[0145]
(Example 14)
Example 14 shows the results of studying the material for the crystal nucleus supply layer.
[0146]
In order to start recording information in the as-depo state without initializing the phase change layer, the as-depo amorphous part must be recorded while being crystallized. It is necessary that crystal nuclei are easily generated in the phase transformation layer comprising When more crystal nuclei are generated, the transition temperature (crystallization temperature) from the amorphous phase to the crystalline phase becomes lower.
[0147]
As the material for the crystal nucleus supply layer, several types of materials with a crystal phase of NaCl type, a high-speed crystallization material, and a low-melting-point material are selected, and the crystallization temperature of the phase transformation layer when these materials are laminated with the phase transformation layer is set. Examined.
[0148]
The material of the crystal nucleus supply layer is Bi ₂ Te _Three , Sb ₂ Te _Three , Sb, Te, SnTe, PbTe, SnTe-PbTe, SnTe-Ag, SnTe-Se, SnTeN, GeSbTe eutectic, GeBiTe eutectic, TiN, ZrN. The material of the phase change layer is GeSbTe.
[0149]
A sample having a layer structure of quartz substrate / crystal nucleus supply layer (film thickness 2 nm) / phase transformation layer (film thickness 10 nm) was used. The crystal nucleus supply layer other than SnTeN, TiN and ZrN was formed by DC sputtering of a sputtering target having a diameter of 100 mm and a thickness of 6 mm in an Ar gas atmosphere. The crystal nucleus supply layer made of SnTeN, TiN, or ZrN is formed by using each of the sputtering targets of SnTe, Ti, and Zr as Ar-N. ₂ It was formed by RF sputtering in a mixed gas atmosphere. The phase change layer made of GeSbTe was formed by DC sputtering of the target in an Ar gas atmosphere.
[0150]
A sample without a crystal nucleus supply layer was also produced. And the transmittance | permeability was measured, heating up the sample with a crystal nucleus supply layer, and the sample without a crystal at a speed | rate of 50 degree-C with a He-Ne laser, respectively. When the phase change layer reaches the crystallization temperature, the transmittance of the sample rapidly decreases, and the crystallization temperature becomes clear from the change in transmittance. Table 13 shows the measured values for the crystallization temperature of each sample.
[0151]
[Table 13]

[0152]
When there was no crystal nucleus supply layer, the crystallization temperature of GeSbTe, which is a phase change layer, was 192 ° C. If a material containing Te is used for the crystal nucleus supply layer, the crystallization temperature of the phase transformation layer is lowered, and it is considered that the crystal nucleus generation is effective. Although TiN and ZrN have a NaCl-type crystal phase, they have no effect on crystal nucleation. Sb also had no effect.
[0153]
(Example 15)
In Example 15, an example will be described in which the information recording medium 53 was manufactured using the material that was effective in generating crystal nuclei in Example 14, and as-depo recording was performed.
[0154]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ (80mol% ZnS-20mol% SiO ₂ . The same applies hereinafter. ), 5 nm GeN as the interface layer, 2 nm crystal supply layer, 10 nm GeSbTe as the phase change layer, 5 nm GeN as the interface layer, ZnS-20 mol% SiO as the protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. As the material for the crystal nucleus supply layer, Bi ₂ Te _Three , Sb ₂ Te _Three Te, SnTe, SnTe-PbTe, SnTe-Ag, SnTe-Se, SnTeN, PbTe, GeSbTe eutectic, or GeBiTe eutectic were used.
[0155]
Next, film forming conditions for each material will be described. ZnS-20mol% SiO ₂ Is ZnS-20mol% SiO ₂ As a base material, a film was formed by RF sputtering in an Ar gas atmosphere. GeN is Ar-N with Ge as the base material ₂ A film was formed by RF sputtering in a mixed gas atmosphere. The crystal nucleus supply layer was formed under the same conditions as in Example 1. The phase transformation layer made of GeSbTe is made of Ar-N with GeSbTe as the base material. ₂ A film was formed by a DC sputtering method in a mixed gas atmosphere. The reflective film made of Ag alloy was formed by DC sputtering in an Ar gas atmosphere using Ag alloy as a base material. In the information recording medium of Example 15, the thicknesses of both protective layers were determined strictly so that Ra was about 28% and Rc was about 10%.
[0156]
The reversible optical information recording medium of Example 2 was evaluated using an evaluation drive equipped with a laser of λ = 660 nm and NA = 0.6. The evaluation items are the amplitude, noise level and CNR of 3T signal on the groove. The evaluation was performed under the condition that the linear velocity of the laser beam irradiated portion was 8.2 m / s. Recording was performed by modulating the laser beam with high power Pp (mW) and low power Pb (mW). The modulation recording waveform is shown in FIG. Regardless of the original state (as-depo amorphous, initialized crystal phase, recording state), the amorphous and crystalline phases are formed by modulating the laser beam, and new information is recorded. Note that Pr (mW) is the reproduction power.
[0157]
By initializing a part of the annular region of the information recording medium, the as-depo amorphous region that has not been initialized as-depo and the crystal phase region that has been initialized are in the same plane. Formed. Then, it was judged whether as-depo recording was possible or not by comparing the CNRs of both states. In each medium, Ra is about 28% and Rc is about 10%. Therefore, the address reading is good in both state areas, the servo is stable, and the CNR can be evaluated. A 3T signal was recorded once on the groove. The evaluation results are shown in Table 14.
[0158]
[Table 14]

[0159]
As is clear from Table 14, when the material containing SnTe or the material containing PbTe was used, the CNR in the as-depo amorphous region and the CNR in the crystalline phase region were almost the same level. If anything, the as-depo amorphous region had a higher CNR than the crystalline phase region due to the lower noise level of about 1 dB. It is thought that there is a slight noise rise due to initialization. When other materials including Te were used, the CNR in the as-depo amorphous region was about 3 dB to 5 dB lower than the CNR in the crystalline phase region, but more than 45 dB was obtained. From the above results, it was found that as-depo recording is possible with the above materials.
[0160]
The melting point of GeSbTe, which is a phase change layer, is about 620 ° C., and the crystal nucleus supply layer material other than SnTe and PbTe has a melting point of 620 ° C. or less. Therefore, it is considered that the CNR is lower by several dB because the crystal nucleus supply layer is melted and mixed in the phase change layer during recording and the optical characteristics are changed. Therefore, it was found that in the structure in which the phase change layer is formed after the crystal nucleus supply layer, a material containing SnTe or a material containing PbTe is more preferable as the material for the crystal nucleus supply layer.
[0161]
(Example 16)
In Example 16, an example will be described in which the information recording medium 54 was manufactured using the material that was effective in generating crystal nuclei in Example 14, and as-depo recording was performed.
[0162]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ , GeN 5 nm as interface layer, GeSbTe 10 nm as phase transformation layer, crystal nucleus supply layer 2 nm, GeN 5 nm as interface layer, ZnS-20 mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. Bi in the crystal nucleus supply layer ₂ Te _Three , Sb ₂ Te _Three Te, SnTe, SnTe-PbTe, SnTe-Ag, SnTe-Se, SnTeN, PbTe, GeSbTe eutectic, or GeBiTe eutectic were used. The film forming conditions for each layer are the same as in Example 15.
[0163]
A part of the annular region of the information recording medium was initialized, and an uninitialized as-depo amorphous region after film formation and a crystal phase region after initialization were formed in the same plane. Then, by comparing the CNR of both state areas, it was determined whether or not as-depo recording was possible.
[0164]
Recording conditions and evaluation conditions are the same as in Example 2. The evaluation results are shown in Table 15.
[0165]
[Table 15]

[0166]
From Table 15, the as-depo amorphous region CNR and the crystalline region CNR are almost the same level for any material for the crystal nucleus supply layer, and recording into as-depo amorphous is possible. I understood. Thus, it was found that as-depo recording can be performed even when a material having a melting point lower than that of the phase change layer is used as the material of the crystal nucleus supply layer in the configuration in which the crystal nucleus supply layer is formed after the phase change layer.
[0167]
(Example 17)
In Example 17, a crystal nucleus supply layer was formed using SnTe, which was found to be capable of as-depo recording in Example 15, and the film thickness dependency and recording frequency dependency of the crystal nucleus supply layer of as-depo recording were confirmed. Examined. In Example 17, the information recording medium 53 was produced by the same method as in Example 15. At this time, the thickness of the crystal nucleus supply layer of the information recording medium was changed every 0.5 nm from 0 nm to 7 nm for each sample.
[0168]
The 3T signal was recorded once, twice and ten times in an uninitialized amorphous state. Evaluation conditions are the same as in Example 15. The evaluation results are shown in Table 16.
[0169]
[Table 16]

[0170]
As apparent from Table 16, when the film thickness of the crystal nucleus supply layer was 2 nm or more, almost saturated CNR was obtained from one recording. When the film thickness is as thin as 1.5 nm or less, the CNR is low because the amplitude is small in the first recording and the noise level is high in the second recording. The noise level decreased with the number of recordings, but seven recordings were required to obtain a saturated CNR. When the film thickness was 4.5 nm or more, a saturated CNR could not be obtained at a recording power of 15 mW. It was found that when the crystal nucleus supply layer is thick, the recording sensitivity of the phase change layer decreases. The film thickness of the crystal nucleus supply layer capable of as-depo recording and good recording sensitivity was about 2 nm to about 4 nm.
[0171]
Therefore, it was found that in the information recording medium of Example 17, the film thickness of the crystal nucleus supply layer is preferably about 2 nm to about 4 nm.
[0172]
(Example 18)
In Example 18, the same experiment as in Example 17 was performed on the information recording medium 54.
[0173]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ GeN 5 nm as the interface layer, GeSbTe 10 nm as the phase change layer, SnTe as the crystal nucleus supply layer, GeN 5 nm as the interface layer, ZnS-20 mol% SiO as the protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. The film thickness of SnTe, the crystal nucleus supply layer, was changed from 0 nm to 7 nm by 0.5 nm. Table 17 shows the results of measurements similar to those of Example 17.
[0174]
[Table 17]

[0175]
As is apparent from Table 17, when the film thickness of the crystal nucleus supply layer was 2 nm or more, almost saturated CNR was obtained from one recording. Above 5.5 nm, a saturated CNR could not be obtained with a recording power of 15 mW. Similar to the result of Example 17, as the crystal nucleus supply layer becomes thicker, the recording sensitivity of the phase change layer decreases. In the information recording medium of Example 18, the thickness of the crystal nucleus supply layer capable of as-depo recording and good recording sensitivity was about 2 nm to about 5 nm. Therefore, in the structure in which the crystal nucleus supply layer is laminated after the phase change layer, the film thickness of the crystal nucleus supply layer is preferably about 2 nm to about 5 nm.
[0176]
(Example 19)
In Example 19, an example in which the reversible optical information recording medium 55 is produced will be described.
[0177]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ GeN 5 nm as interface layer, SnTe as crystal nucleus supply layer 32, 10 nm as GeSbTe as phase transformation layer, SnTe as crystal nucleus supply layer 35, GeN 5 nm as interface layer, ZnS-20 mol as second protective layer % SiO ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. As-depo recording was performed under the same conditions as in Example 17 by changing the film thickness of the crystal nucleus supply layers 32 and 35. The evaluation results are shown in Table 18.
[0178]
[Table 18]

[0179]
When the phase change layer was sandwiched between the crystal nucleus supply layers, as-depo recording was possible with the crystal nucleus supply layers 32 and 35 each having a thickness of 1 nm. Further, when the thicknesses of both crystal nucleus supply layers were 3 nm, the recording sensitivity was insufficient. Compared to the case where the crystal nucleus supply layer is provided only on one side of the phase change layer, the nucleation effect is considered to be synergistic when the crystal nucleus supply layer is provided on both sides of the phase change layer. Therefore, when forming a crystal nucleus supply layer on both sides of the phase change layer, the thickness of the nucleus crystal nucleus supply layer may be about half, and more preferably about 1 nm to about 2 nm.
[0180]
(Example 20)
In Example 20, an example in which the relationship between the thickness of the crystal nucleus supply layer, the deposition rate of the phase change layer, and the state after deposition of the phase change layer will be described for the information recording medium 53.
[0181]
On a polycarbonate substrate having guide grooves, ZnS-20 mol% SiO2 as a protective layer, GeN as an interface layer, 5 nm, SnTe as a crystal nucleus supply layer, GeSbTe as a phase change layer, 10 nm, GeN as an interface layer, 5 nm , ZnS-20mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate.
[0182]
The information recording medium of each sample was different in film formation rate r (nm / min) of the phase change layer, and varied from 5 nm / min to 60 nm / min. The film thickness d1 of the crystal nucleus supply layer is 2 nm and 5 nm. The information recording medium of d1 = 2 nm is optically designed so that the reflectance Ra of the amorphous region is about 28% and the reflectance Rc of the crystalline phase region is about 10%, and the information recording medium of d1 = 5 nm is The optical design was such that the reflectance Ra of the amorphous region was about 30% and the reflectance Rc of the crystalline phase region was about 12%. After bonding, some annular regions of the information recording medium are initialized, and an as-depo amorphous region that is not initialized after film formation and a crystal phase region after initialization are formed in the same plane. The reflectance of the area was measured.
[0183]
The reflectivity is the reflectivity of the mirror part formed on the substrate while the focus servo is operated at a linear velocity of 8.2 m / s using an evaluation drive equipped with a laser of λ = 660 nm and NA = 0.6. It was measured. Table 19 shows the relationship between the deposition rate of the phase change layer and the reflectance.
[0184]
[Table 19]

[0185]
From Table 19, when d1 = 2 nm, the reflectivity in the uninitialized region is about 28% when r ≧ 20 (nm / min), and the state after film formation is amorphous. Can be determined. On the other hand, when r <20 (nm / min), the reflectance is only 10% or more, and it is considered that at least a part of the phase change layer is crystallized during the film formation.
[0186]
In addition, when d1 = 5 nm, the reflectivity of the uninitialized region is about 30% when r ≧ 50 (nm / min), and the state after film formation is determined to be amorphous. it can. On the other hand, at r <50 (nm / min), it is considered that at least a part of the phase change layer is crystallized during film formation. Thus, the state after the phase change layer is formed is determined by the film formation rate of the phase change layer and the film thickness of the crystal nucleus supply layer. In order to form the phase change layer in an amorphous state, it is preferable to increase the film formation rate of the phase change layer as the crystal nucleus supply layer is thicker.
[0187]
(Example 21)
In Example 21, using the information recording medium 53, even if the information recording medium has an Rc of almost 0%, if as-depo recording can be performed, the drive can obtain servo stability and good address readability. It was.
[0188]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ , GeN 5 nm as interface layer, 2 nm SnTe as crystal nucleus supply layer, 10 nm GeSbTe as phase change layer, 5 nm GeN as interface layer, ZnS-20 mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate.
[0189]
The thickness of both protective layers is strictly determined, Ra (reflectance of the information recording medium when the phase change layer is amorphous)> Rc (information recording medium when the phase change layer is a crystalline phase) Four types of information recording media (reflectance) were produced.
[0190]
A part of the annular area of the information recording medium is initialized, and an uninitialized as-depo amorphous region (Ra) and a crystal phase region (Rc) after initialization are formed in the same plane, both states The servo stability and address readability and CNR were evaluated. The evaluation results are shown in Table 20.
[0191]
[Table 20]

[0192]
As shown in Table 20, when the Rc of the information recording medium was 5.3%, the address was difficult to read in the initialized crystal phase region. When Rc was 0.9%, the tracking servo was difficult to operate in the initialized crystal phase region.
[0193]
On the other hand, if Rc> 10 (%), the servo characteristics were stable even in the crystal phase region, and the address readability was good. Thus, if the information recording medium optically designed with Ra> Rc is initialized, the lower limit value of Rc is restricted. On the other hand, in the as-depo amorphous region that was not initialized after film formation, the address readability was good regardless of the value of Rc. If not initialized, the reflectance of the address portion is stored as Ra, so the lower limit value of Rc is not restricted. In this way, when using a phase change layer in which a crystal nucleus supply layer and a phase change layer are stacked, as-depo recording is possible, and even if Rc is close to 0%, the reflectance of the address portion is sufficiently large at Ra. From this, it was verified that the address of the information recording medium could be read and the servo was stable. A good CNR was also obtained.
[0194]
(Example 22)
In Example 22, an example in which an information recording medium was produced in the same manner as in Example 21 and the reflectance was measured using a laser with λ = 405 nm will be described.
[0195]
In order to produce the information recording medium 53, ZnS-20mol% SiO as a protective layer ₂ GeN 5 nm as interface layer, SnTe 2 nm as crystal nucleus supply layer, GeSbTe 12 nm as phase transformation layer, GeN 5 nm as interface layer, ZnS-20 mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate.
[0196]
The protective layer, the interface layer, the crystal nucleus supply layer, the phase change layer, and the reflection layer were measured by ellipsometry for the complex refractive index with respect to the laser beam of λ = 405 nm, and ΔR (ΔR for the recording wavelength of λ = 405 nm. = Rc-Ra) The film thickness of each layer was strictly determined so that the absolute value was sufficiently large. A 3T signal was recorded once on the grooves in the as-depo amorphous region and the crystalline phase region, and the CNR was measured. Table 21 shows the measurement results.
[0197]
[Table 21]

[0198]
As-depo recording was possible even at a short wavelength of λ = 405 nm. When as-depo recording was possible, even if Rc was low, the servo was stable and the address readability was good. As described above, it is verified that the use of a phase change layer in which a crystal nucleus supply layer and a phase change layer are stacked enables as-depo recording using a laser beam with a short wavelength and can be applied to high-density recording. It was.
[0199]
(Example 23)
In Example 23, an example in which as-depo recording is performed on the information recording medium 53 using AgInSbTe as a phase change layer will be described.
[0200]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ , GeN 5 nm as interface layer, SnTe as crystal nucleus supply layer, AgInSbTe 10 nm as phase change layer, GeN 5 nm as interface layer, ZnS-20mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. ZnS-20mol% SiO ₂ Is ZnS-20mol% SiO ₂ As a base material, a film was formed by RF sputtering in an Ar gas atmosphere. GeN is Ar-N with Ge as the base material ₂ A film was formed by RF sputtering in a mixed gas atmosphere. The crystal nucleus supply layer was formed by DC sputtering of the base material in an Ar gas atmosphere. AgInSbTe was formed by DC sputtering in an Ar gas atmosphere using AgInSbTe as a base material. The Ag alloy was formed by DC sputtering using an Ag alloy as a base material in an Ar gas atmosphere. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. Each sample information recording medium has a different crystal nucleus supply layer thickness. The film thickness was changed every 0.5 nm from 0 nm to 7 nm. In addition, 3T signals were recorded once, twice and ten times in an as-depo amorphous state. The results are shown in Table 22.
[0201]
[Table 22]

[0202]
As shown in Table 22, it was found that when the film thickness of the crystal nucleus supply layer was 2 nm or more, almost saturated CNR was obtained from one recording. When the film thickness of the crystal nucleus supply layer was as thin as 1.5 nm or less, it was found that the CNR was low because the amplitude was small in the first recording and the noise level was high in the second recording. Also, although the noise level decreases with the number of recordings, recording seven times was necessary to obtain a saturated CNR. When the film thickness of the crystal nucleus supply layer was as thick as 4.5 nm or more, saturation CNR was not obtained at a recording power of 15 mW. The greater the film thickness of the crystal nucleus supply layer, the lower the recording sensitivity of the phase change layer. The thickness of the crystal nucleus supply layer capable of as-depo recording and good recording sensitivity was about 2 nm to about 4 nm. As-depo recording is possible even when AgInSbTe is used for the phase change layer, and the effect of SnTe as the crystal nucleus supply layer was verified.
[0203]
AgInSbTe, InSb and AgSbTe ₂ A mixture of AgSbTe ₂ Is a NaCl-type structure, so it is thought that crystal nucleation by SnTe is likely to be promoted.
[0204]
(Example 24)
In Example 24, information obtained by adding any of Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, Al, or Mn to GeSbTe as a phase change layer. An example of producing the recording medium 53 will be described.
[0205]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ GeN as interface layer 5 nm, SnTe 2 nm as crystal nucleus supply layer, GeSbTe + M as phase transformation layer (M is Ag, Sn, Cr, Pb, Bi, Pd, Se, In, Ti, Zr, Au, Pt, (Al or Mn) 10nm, GeN 5nm as interface layer, ZnS-20mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate.
[0206]
Table 23 shows the results of recording experiments on the above samples in the as-depo state. In Table 23, (ΔCNR (dB)) = (CNR (dB) of 10th recording) − (CNR (dB) of 1st recording)).
[0207]
[Table 23]

[0208]
As shown in Table 23, even when any element was added to GeSbTe, almost saturated CNR was obtained from the first time. Therefore, it was found that as-depo recording was possible even when a material represented by the composition formula GeSbTe + M was used as the phase change layer.
[0209]
(Example 25)
In Example 25, an example in which an information recording medium 53 having a different phase change layer thickness was manufactured and an as-depo recording experiment was performed will be described.
[0210]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ GeN as the interface layer 5 nm, SnTe 2 nm as the crystal nucleus supply layer, GeSbTe as the phase change layer, GeN 5 nm as the interface layer, ZnS-20 mol% SiO as the protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. The thickness of the phase change layer was changed from 2 nm to 25 nm. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. After bonding, a part of the annular region of the information recording medium was initialized, and an as-depo amorphous region that was not initialized after film formation and a crystal phase region after initialization were formed in the same plane.
[0211]
The recording conditions and the evaluation conditions were the same as those in Example 15. Each time a 3T signal was recorded on the groove once in each state region, CNR was measured. Table 24 shows the measurement results.
[0212]
[Table 24]

[0213]
As shown in Table 24, when the film thickness of the phase change layer was 2 nm, it was not crystallized. As-depo recording is possible from the thickness of the phase change layer of 3 nm, but at 25 nm, the CNR was not saturated at a recording power of 15 mW, and the recording sensitivity was insufficient. For as-depo recording, the phase change layer is practically 3 nm to 20 nm, and preferably 5 nm to 15 nm.
[0214]
(Example 26)
In Example 26, an example in which the effect on the recording characteristic reliability of the crystal nucleus supply layer was examined for the information recording medium 53 will be described.
[0215]
ZnS-20mol% SiO as protective layer on polycarbonate substrate with guide groove ₂ , GeN 5 nm as interface layer, 2 nm SnTe as crystal nucleus supply layer, 10 nm GeSbTe as phase change layer, 5 nm GeN as interface layer, ZnS-20 mol% SiO as protective layer ₂ Then, an Ag alloy was continuously formed in this order as a reflective layer. After film formation, an ultraviolet curable resin was spin-coated on an Ag alloy and bonded to a dummy substrate. The information recording medium of Example 26 was manufactured so that Ra> Rc. The phase change layer was not initialized and signal recording was started in an as-depo amorphous state.
[0216]
After the information recording medium of Example 26 was prepared, it was left in an environment of 20% RH at 90 ° C. for 24 hours, and the jitter change before and after being left was measured. The measurement was performed for three types, Test 1, Test 2, and Test 3. In Test 1, as-depo recording was performed before leaving, and measurement was performed after leaving. In Test 2, as-depo recording was performed before leaving, and the measurement was overwritten after being left. In Test 3, the measurement was performed without recording before leaving, and recording as-depo after leaving.
[0217]
The information recording medium was evaluated with a laser of λ = 660 nm and NA = 0.6. The jitter value of 3T signal between and on the groove was evaluated. The 3T signal was recorded once. The linear velocity is 8.2m / s. Table 25 shows the inter-groove jitter difference before and after being left, and Table 26 shows the on-groove jitter difference. In this case, (jitter difference) = (jitter value after being left) − (jitter value before being left).
[0218]
[Table 25]

[0219]
[Table 26]

[0220]
As shown in Table 25-26, the jitter difference between Test 1, Test 2 and Test 3 is 2% or less, either between or on the grooves. It was good. By laminating the crystal nucleus supply layer and the phase transformation layer (the part that causes reversible phase transformation) in this way, as-depo recording is possible, and the two effects of securing the reliability of overwriting can be obtained. It was.
[0221]
The embodiments of the present invention have been described above by way of examples. However, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.
[0222]
For example, the information recording medium is not limited to the configuration of the above embodiment, and may be any information recording medium including a phase change layer in which a crystal nucleus supply layer and a phase change layer are stacked.
[0223]
【The invention's effect】
As described above, since the information recording medium of the present invention includes the phase change layer in which the crystal nucleus supply layer and the phase change layer are laminated, information can be recorded easily and reliably. The information recording medium of the present invention can perform as-depo recording without requiring an initialization process. In particular, in an information recording medium where Ra> Rc, even if Rc is close to 0%, the effect that the address readability and servo stability are good can be obtained.
[0224]
In addition, the information recording medium manufacturing method of the present invention can easily manufacture the information recording medium of the present invention.
[0225]
The information recording medium recording / reproducing method of the present invention can easily and reliably record information.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a configuration example of an information recording medium of the present invention.
FIG. 2 is a partial cross-sectional view showing another configuration example of the information recording medium of the present invention.
FIG. 3 is a partial cross-sectional view showing a configuration example of a two-layer information recording medium in the information recording medium of the present invention.
FIGS. 4A to 4C show the temperature dependence of the transmittance for determining the phase structure of the crystallization ability improving layer or the recording layer laminated on the crystallization ability improving layer of the present invention. It is a graph to show. The horizontal axis is temperature and the vertical axis is transmittance. (A) is a graph when the phase structure is amorphous. (B) is a graph when the phase structure is a mixed state of an amorphous phase and a crystalline phase. (C) is a graph when the phase structure is a crystalline phase.
FIG. 5 is a partial cross-sectional view showing another configuration example of the information recording medium of the present invention.
FIG. 6 is a partial cross-sectional view showing another configuration example of the information recording medium of the present invention.
FIG. 7 is a partial cross-sectional view showing another configuration example of the information recording medium of the present invention.
FIG. 8 is a diagram showing a modulation waveform of a laser beam used for recording in the information recording medium recording / reproducing method of the present invention, in which the horizontal axis represents time and the vertical axis represents laser power.
[Explanation of symbols]
50,51,52,53,54,55,56 Information recording medium
1 Board
2,6 Protective layer
3 Crystallization ability improvement layer
4 Phase transformation layer
5,31,34,36,38 Recording layer
7 Reflective layer
8 Adhesive layer
9 Dummy board
10,11 Interface layer
12 Light absorption correction layer
13 First board side
14,19 First protective layer
15,18 first interface layer
17 First recording layer
20 First information recording medium
21 Separation layer
22,26 Second protective layer
23,25 Second interface layer
27 Laser light
28 Second board
29 Second information recording medium
32,35 Crystal nucleus supply layer
33,37 Phase transformation layer

Claims (10)

An information recording medium having at least a recording layer formed on a substrate, the recording layer comprising a phase change layer that causes a reversible phase change between a crystalline state and an amorphous state by irradiation with a light beam; A crystallization ability improving layer that improves the crystallization ability of the phase change layer, the crystallization ability improvement layer is formed before forming the phase change layer, and the phase change layer is formed. occurred crystal nucleation and crystal growth in at least a portion of the phase change layer is formed on the crystalline phase after the formation, the crystallization ability improving layer is telluride material or Rannahli, the telluride is SnTe , GeTe-Sb ₂ Te ₃ eutectic compositions (hereinafter, referred to as GeSbTe eutectic) and GeTe-Bi ₂ Te ₃ eutectic compositions (hereinafter referred to GeBiTe eutectic) at least one der selected from is, the recording rewritable information recording mark is amorphous recorded in the layer Recording media. The energy for crystallizing the phase change layer when the crystallization ability improving layer is formed is A, and the energy for crystallizing the phase change layer when the crystallization ability improving layer is not formed is A. 2. The rewritable information recording medium according to claim 1, wherein B is A <B. The rewritable information recording medium according to claim 1, wherein a crystal structure of the phase change layer is a rock salt type. The rewritable information recording medium according to any one of claims 1 to 3, wherein the phase change layer includes GeSbTe. The rewritable information recording medium according to claim 1, wherein a crystal structure of the crystallization ability improving layer is a rock salt type. The rewritable information recording medium according to claim 1 or 2 , wherein a thickness dt (nm) of the crystallization ability improving layer selected from the telluride is 1≤dt≤10 . Rewritable information recording medium according to any one of claims 1-6 which does not require the initialization of the recording layer. The two-layer information recording medium in which the substrate is composed of two substrates, a first substrate and a second substrate, and the recording layer is formed on the two substrates, and the two substrates are bonded to each other. The rewritable information recording medium according to any one of claims 1 to 7 . The substrate is composed of two substrates, a first substrate and a second substrate, the recording layer is formed on the first substrate side, and the two substrates are bonded together with the two substrates facing outside. The rewritable information recording medium according to any one of claims 1 to 7 , which is a medium. In the method of any one of the information recording medium according to claim 1-9, when deposited the crystallization ability improving layer, and then depositing the phase change layer, during the formation of the phase change layer A method for producing a rewritable information recording medium, wherein the phase change layer is crystallized.

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