JP3853543B2 - Optical information recording medium, manufacturing method thereof, recording / reproducing method, and recording / reproducing apparatus - Google Patents

Description

【０１０１】
（表１）の結果からも、Δｎ＝ｎ₁−ｎ₂は２以上が好ましく、３以上がより好ましいことがわかる。
【０１０２】
また、光吸収層３５の膜厚が薄すぎると、光吸収層３５の光学的効果が小さくなり、光吸収層３５の膜厚が厚すぎると、反射層３６の光学的効果が小さくなる。このため、光吸収層３５の膜厚は、入射光を適度に透過・吸収するような膜厚にする必要がある。光吸収層３５の膜厚ｄ₁は、後述する実施例などの実験結果から、入射光の波長をλとして、０．１λ／（ｎ₁・ｋ₁）≦ｄ₁≦１．０λ／（ｎ₁・ｋ₁）の範囲が好ましく、０．２λ／（ｎ₁・ｋ₁）≦ｄ₁≦０．８λ／（ｎ₁・ｋ₁）の範囲がより好ましいことが確認された。
【０１０３】
十分な冷却能を得るために、反射層３６として熱伝導率の大きい材料を用いており、マーク幅を均一にしてジッタを低減している。この反射層の熱伝導率としては、例えば３００Ｋ近傍の温度条件で５０Ｗ／ｍ・Ｋ以上であることが好ましく、１００Ｗ／ｍ・Ｋ以上、さらには１５０Ｗ／ｍ・Ｋ以上がより好ましい。さらに十分な冷却効果を得るためには、反射層３６の膜厚ｄ₂は、後述する実施例などの実験結果から、光吸収層３５の膜厚ｄ₁以上であることが好ましく、ｄ₁の１．５倍以上、さらには２倍以上がより好ましいことが確認された。
【０１０４】
本実施形態の光学情報記録媒体の製造方法、記録再生方法、記録再生装置は、第１の実施形態と同様とすればよい。
【０１０５】
なお、上記では、記録層の膜厚を１０ｎｍに設定したが、記録層の膜厚は必ずしもこの膜厚に限定されるものではない。
【０１０６】
（第３の実施形態）
本実施形態では、記録層を含む多層膜が２以上形成された光学的情報記録媒体について説明する。ここでは、各々が記録層を含む多層膜（情報層）が分離層を介して２層配置された形態について説明する。
【０１０７】
図８に示したように、本実施形態の光学的情報記録媒体では、透明基板４１上に、第１情報層４２、分離層４３、第２情報層４４および保護層４５がこの順に形成されている。第１情報層４２および第２情報層４３には、それぞれ記録層が含まれている。これらの記録層には、透明基板側から照射されるレーザ光により、情報が記録、再生される。
【０１０８】
本実施形態の第２情報層４４には、上記実施形態で説明した多層膜が適用される。また、第１情報層４２には、少なくとも、記録層と、この記録層の両側に配置された下側保護層および上側保護層とを含む多層膜を用いることが好ましい。これらの多層膜に含まれる各層および透明基板は、上記実施形態で説明した材料を用いて形成することができる。なお、第１情報層は、予め透明基板の表面上に凹凸パターンとして蓄積された情報を再生の対象とする、再生専用層であってもよい。
【０１０９】
また、第２情報層４４で情報の記録再生を行うため、第１情報層４２は照射されるレーザ光の少なくとも３０％を透過させることが好ましい。
【０１１０】
分離層４３としては、レーザ光の波長λにおいて透明であり、耐熱性および接着性に優れた材料であることが好ましく、具体的には、接着樹脂（例えば紫外線硬化性樹脂）、両面テープ、各種誘電体膜等を用いることができる。分離層４３の膜厚は、第１情報層４２および第２情報層４４のいずれか一方に情報の記録再生を行う際に、他方の情報層の情報が漏れ込まないように、２μｍ以上とすることが好ましい。一方、分離層４３の膜厚は、第１情報層４２と第２情報層４４のいずれにもレーザ光をフォーカシングするべく基板厚との合計が基板厚公差範囲となるように、１００μｍ以下とすることが好ましい。
【０１１１】
保護層４５は、第２の情報層４４を形成するための基板（保護基板）として利用してもよい。この場合は、第１の情報層４２を形成した透明基板４１と、第２の情報層４４を形成した保護基板とを、分離層４３を介して貼り合わせて光ディスクが製造される。保護基板の材料としては、透明基板４１と同様の材料を用いることができるが、必ずしも透明である必要はなく、その他の材料を用いてもよい。また、基板表面の形状も、透明基板表面の形状と同じである必要はなく、例えば、グルーブおよびランドを形成する案内溝の形状が異なっていてもよく、案内溝のスパイラル方向が逆であってもよい。さらに、分離層の第２情報層側の表面に、例えば２Ｐ法（photo-polymerization法）により案内溝を設けておけば、保護基板の表面は平面であっても構わない。また、保護層４５は、透明基板上に形成した第２情報層４４上に形成した層であってもよい。このような保護層は、例えば樹脂のスピンコートや接着剤による樹脂板の貼付により形成できる。
【０１１２】
本実施形態の製造方法の一例について説明する。それぞれに案内溝を形成した透明基板および保護基板の表面に、上記で説明したスパッタリング法などにより、各々、第１情報層および第２情報層を形成する。次いで、第１情報層または第２情報層の表面上に、紫外線硬化性樹脂を塗布して分離層とする。さらに、この分離層を介して第１情報層と第２情報層とが対向するように、透明基板と保護基板とを向かい合わせて加圧し、紫外線を照射して分離層を硬化させる。
【０１１３】
【実施例】
以下、実施例により本発明をさらに具体的に説明するが、以下の実施例は本発明を限定するものではない。
【０１１４】
（実施例１）
基板としては、厚さ０．６ｍｍのポリカーボネイト樹脂を用いた。この基板上には、ともに幅を０．６μｍとしたランドおよびグルーブを形成した。グルーブの深さは約７０ｎｍとした。
【０１１５】
この基板上に、ＺｎＳ−ＳｉＯ₂（分子数比ＺｎＳ：ＳｉＯ₂＝８０：２０）ターゲットを用いて約１２００ｎｍの下側保護層、Ｇｅ−Ｓｂ−Ｔｅ（原子数比Ｇｅ：Ｓｂ：Ｔｅ＝２２：２５：５３）ターゲットを用いて様々な膜厚の記録層、ＺｎＳ−ＳｉＯ₂（分子数比ＺｎＳ：ＳｉＯ₂＝８０：２０）ターゲットを用いて様々な膜厚の上側保護層、様々な材料のターゲットを用いて約４０ｎｍの中間層、様々な材料のターゲットを用いて約４０ｎｍの反射層を、いずれもスパッタリング法により順次積層した。いずれの層も直径１０ｃｍ、厚さ６ｍｍのスパッタリングターゲットを用い、記録層以外はＡｒガス中で、記録層はＡｒとＮ₂の混合ガス（全圧２ｍＴｏｒｒ、Ｎ₂ガス分圧は約５％）中で成膜した。
【０１１６】
こうして得られた光ディスクに紫外線硬化性樹脂でオーバーコートを施した後、レーザー光でアニールすることにより全面を初期結晶化し、No.1〜No.21の光ディスクとした。これらはクロスイレースの材料および膜厚構成に対する依存性を調べるために意図的に記録層、上側保護層の膜厚および中間層と反射層の材料を変えて作製したものである。
【０１１７】
表２に各光ディスクの記録層・上側保護層の膜厚、および中間層・反射層の材料を示す。
【０１１８】
これらの光ディスクを波長６６０ｎｍ、ＮＡ０．６の光学系を用い、線速６．０ｍ／ｓ（半径位置：約３２ｍｍ、回転数：約１８００ｒｐｍ）の条件でマークエッジ記録を行い、クロスイレースを測定した。
【０１１９】
具体的には、まず、グルーブに９．７ＭＨｚの３Ｔ信号を記録し、このトラックを再生して３Ｔ信号振幅Ａ₀をスペクトラムアナライザーで測定する。次に、そのグルーブの両隣のランドに２．６ＭＨｚの１１Ｔ信号を記録し、再びグルーブを再生して３Ｔ信号振幅Ａ₁をスペクトラムアナライザーで測定する。こうして測定した３Ｔ信号振幅の低下量ΔＡ＝Ａ₁−Ａ₀をクロスイレース評価の指標とする。これと同じことをランドとグルーブとを逆にして行い、同様に３Ｔ信号振幅低下量ΔＡ’を測定する。
【０１２０】
表２には各ディスクのΔＡの値による優劣を記載する。ただし、上記測定の結果、いずれのサンプルにおいても測定トラックをグルーブとした場合が３Ｔ信号振幅の低下量が大きくなったので（ΔＡ＞ΔＡ’）、その場合の結果（ΔＡ）のみで判定した。ΔＡの値が１ｄＢ未満のものは「Ａ」、１ｄＢ以上２ｄＢ未満のものは「Ｂ」、２ｄＢ以上５ｄＢ未満のものは「Ｃ」、５ｄＢ以上のものは「Ｄ」で示した。
【０１２１】
なお、信号を記録する際のレーザー変調波形は、３Ｔ信号の場合はパルス幅５１．３ｎｓ（パワーレベルＰ₁）の単一矩形パルスとし、１１Ｔ信号の場合は９個のパルスからなるパルス列（パワーレベルＰ₁）とし、その先頭は５１．３ｎｓ、２番目以降はすべて１７．１ｎｓのパルス幅で、各パルス間の幅も１７．１ｎｓ（パワーレベルＰ₃）とし、最終のパルスの直後に３４．２ｎｓの冷却区間（パワーレベルＰ₄）を設けた。マークを記録しない部分ではパワーレベルＰ₂の連続光（不変調光）とした。
【０１２２】
記録パワーレベルＰ₁は、３Ｔ信号を記録した場合にそのＣ／Ｎ比が４５ｄＢを超えるパワーの下限値の１．５倍とし、パワーレベルＰ₂は消去比、すなわち３Ｔ信号を記録した上に１１Ｔ信号をオーバーライトした際の３Ｔ信号振幅の減衰比が２５ｄＢを超えるパワー範囲の中央値とし、パワーレベルＰ₃およびＰ₄は、再生パワーレベルと同じ１ｍＷとした。
【０１２３】

【０１２４】
中間層および反射層に用いた各材料の熱伝導率は温度依存性があるが、おおよその値の範囲は以下のように特定できる。熱伝導率の大きい順に、Ａｌ（３０〜６００℃における熱伝導率は、約１５０〜２５０Ｗ／ｍ・ｋ）、Ｃｒ（５０〜１００Ｗ／ｍ・ｋ）、Ｔｉ（２０〜５０Ｗ／ｍ・ｋ）、ＷＳｉ₂（５〜２０Ｗ／ｍ・ｋ）、ＰｂＴｅ（１．０〜３．０Ｗ／ｍ・ｋ）、ＺｎＳ−ＳｉＯ₂（０．１〜０．５Ｗ／ｍ・ｋ）である。
【０１２５】
表２より、まず記録層膜厚の異なるNo.1〜No.5の光ディスクを比較すると、No.5ではクロスイレースが大きく、No.1およびNo.4ではクロスイレースがある程度改善され、No.3およびNo.4ではクロスイレースが十分小さかった。従って、クロスイレース低減の観点からは、記録層の膜厚は４ｎｍ以上１６ｎｍ以下が要求され、６ｎｍ以上１４ｎｍ以下が好ましい。
【０１２６】
次に、上側保護層の膜厚が異なるNo.3およびNo.6〜No.11の光ディスクを比較すると、上側保護層の膜厚が厚いほどクロスイレースが小さいことがわかる。これより上側保護層の膜厚は、クロスイレース低減の観点からは１０ｎｍ以上、さらには２０ｎｍ以上が好ましいことがわかる。
【０１２７】
さらに、中間層および反射層の材料が異なるNo.3およびNo.12〜No.21の光ディスクを比較する。この中で、No.3以外では、No.12〜No.14がクロスイレースが小さい。これらはいずれも反射層として、今回用いた材料の中で最も熱伝導率の高いＡｌを用いており、中間層は上側保護層と反射層の間の熱伝導率を有する材料である。一方、その他のNo.15〜No.21はいずれもクロスイレースが大きい。
【０１２８】
No.15〜No.19はいずれも中間層の熱伝導率が反射層のそれよりも高く、特にNo.17はNo.3の中間層と反射層の材料を入れ換えたものであるが、クロスイレースの点では大きな差が認められた。また、No.20および21は、中間層または反射層のどちらか一方を省いた構成であるが、両者ともクロスイレースは大きい。
【０１２９】
以上より、記録層上に複数の層が積層されている場合、記録層から近い順に熱伝導率が低い材料から高い材料へと段階的に変わっていく構成を採用すれば、クロスイレースを抑制できることが確認できた。これは、記録層から上側保護層、中間層を経て反射層へと熱が伝達していく過程で、その伝達速度が加速されるために、記録層の面内の熱伝導が低減されて隣接トラックへの影響も抑制されるからである。
【０１３０】
また、No.3として示した構成について、図３に示したように、記録層の上下に接してＧｅ、ＯおよびＮからなる約１０ｎｍの界面層を形成した光ディスクを作製した。ＧｅＯＮ膜は、Ｇｅターゲットを用い、Ａｒ、Ｎ₂およびＯ₂ガス中で反応性スパッタリングにより成膜した。この光ディスクの繰り返し特性を調べるために、３Ｔおよび１１Ｔ信号を交互に１万回あるいは１０万回記録し、１０回記録後と比べて３Ｔ信号の振幅変化を測定した。
【０１３１】
その結果、１万回記録後ではNo.3も、これに界面層を挿入した光ディスクも振幅低下は０．５ｄＢ以下の誤差範囲であったが、１０万回記録後ではNo.3の光ディスクは３ｄＢ程度振幅が低下したのに対し、これに界面層を挿入した光ディスクは依然として０．５ｄＢ以下の振幅低下であった。このことから、界面層を挿入することにより、クロスイレース低減に加え、繰り返し記録特性のさらなる向上が可能になることが確認された。
【０１３２】
なお、上記光ディスクの記録層の組成をオージェ電子分光法により分析した結果、Ｎ原子の占める割合は約２．２原子％であった。ここで、さらにNo.3と同じ構成の光ディスクを、記録層成膜時のＮ₂ガス分圧を変化させて複数成膜したところ、記録層中のＮ原子の占める割合が、分析の結果それぞれ約０．０、０．２、０．８、４．０、７．６原子％となった。
【０１３３】
これらの光ディスクの繰り返し特性を調べるために、３Ｔおよび１１Ｔ信号を交互に１万回または１０万回記録し、１０回記録後と比べての３Ｔ信号の振幅変化を測定した。その結果、１万回記録後ではいずれのディスクも振幅低下は０．５ｄＢ以下の誤差範囲であったが、１０万回記録後では記録層中のＮ原子の占める割合が約０．０原子％のものだけが、約２ｄＢ低下していたが、約０．２原子％のものは１ｄＢ程度、その他は０．５ｄＢ以内の誤差範囲の低下であった。また、これらのディスクに３Ｔ信号を記録して３Ｔ信号の振幅を測定し、次に９０℃相対湿度８０％の環境下で１００時間保存し、その後に３Ｔ信号振幅を測定して振幅変化を調べたところ、記録層中のＮ原子の占める割合が７．６原子％のディスクは５ｄＢ以上振幅が低下したが、４．０原子％のものは２ｄＢ程度の低下で、その他はほとんど低下しなかった。この結果より、繰り返し特性、耐湿性の観点からは、記録層中にＮ原子の占める割合は、０．０〜６．０原子％、さらには０．５〜４．０原子％が好ましいことが確認された。
【０１３４】
（実施例２）
基板としては、ポリカーボネイト樹脂からなり、厚さが０．６ｍｍ、グルーブおよびランドの幅がともに０．６μｍ、グルーブの深さが約７０ｎｍのものを用いた。この基板の上に、ＺｎＳ−ＳｉＯ₂（ＺｎＳ：ＳｉＯ₂＝８０：２０）ターゲットを用いて膜厚約１５０ｎｍの下側保護層、Ｇｅ−Ｓｂ−Ｔｅ（原子数比Ｇｅ：Ｓｂ：Ｔｅ＝２２：２５：５３）ターゲットを用いて膜厚約１０ｎｍの記録層、ＺｎＳ−ＳｉＯ₂（分子数比ＺｎＳ：ＳｉＯ₂＝８０：２０）ターゲットを用いて膜厚約３０ｎｍの上側保護層、様々な材料、例えばＰｂＴｅ（原子数比Ｐｂ：Ｔｅ＝５０：５０）ターゲットを用いて様々な膜厚の光吸収層、様々な材料、例えばＡｕターゲットを用いて様々な膜厚の反射層を、スパッタリング法によって順次積層した。いずれの場合においても直径１０ｃｍ、厚さ６ｍｍのターゲットを用い、記録層以外はＡｒガス中で、記録層はＡｒとＮ₂の混合ガス（全圧１ｍＴｏｒｒ中、Ｎ₂ガス分圧は約５％）中でスパッタした。
【０１３５】
このようにして得られたディスクの反射層の上に、紫外線硬化性樹脂を用いてオーバーコート層を形成した後、レーザービームによってアニールすることにより、全面を初期結晶化し、No.31〜47のディスクを得た。これらのディスクは、記録再生特性の材料および膜厚構成に対する依存性を調べるために、意図的に、光吸収層、反射層の材料および膜厚を変えて作製したものである。下記（表３）に、各ディスクの光吸収層、反射層の材料および膜厚を示す。
【０１３６】
ここで、実測によって求めた波長６６０ｎｍにおける各層の光学定数（屈折率ｎ、消衰係数ｋ）は、基板がｎ＝１．６、ｋ＝０．０、下側保護層および上側保護層としてのＺｎＳ−ＳｉＯ₂がｎ＝２．１、ｋ＝０．０、記録層としてのＧｅ−Ｓｂ−Ｔｅが非晶質状態でｎ＝４．１、ｋ＝１．６、結晶状態でｎ＝３．９、ｋ＝４．２、光吸収層および反射層としてのＰｂＴｅがｎ＝５．０、ｋ＝３．２、Ａｕがｎ＝０．３、ｋ＝３．６、Ａｌがｎ＝１．４、ｋ＝６．４、Ｐｄがｎ＝２．２、ｋ＝４．４、Ｃｒがｎ＝３．６、ｋ＝３．４、ＴｉＮがｎ＝２．５、ｋ＝１．２、ＰｄＴｅがｎ＝３．２、ｋ＝２．２、Ｇｅ₈₀Ｃｒ₂₀がｎ＝４．５、ｋ＝２．５、Ａｇ₉₈Ｐｄ₁Ｃｕ₁がｎ＝０．３、ｋ＝４．０であった。この値に基づいて光学計算を行って、算出されたＡcry／ＡamoおよびΔＲの値を（表３）に併せて示す。
【０１３７】
これらのディスクに、波長６６０ｎｍ、開口数（ＮＡ）０．６の光学系を用いて、線速６．０ｍ／ｓ（半径位置約３２ｍｍ、回転数約１８００ｒｐｍ）の条件でマークエッジ記録を行い、以下の測定を行った。まず、グルーブおよびランドに９．７ＭＨｚの３Ｔ信号と２．６ＭＨｚの１１Ｔ信号を交互に１１回記録し、３Ｔ信号が記録された状態でこのトラックを再生して、そのＣ／Ｎ比および消去率をスペクトラムアナライザーを用いて測定した。ここでは、消去率を、３Ｔ信号の振幅Ａ₃と１１Ｔ残留信号の振幅Ａ₁₁との差（Ａ₃−Ａ₁₁）として定義した。
【０１３８】
また、（８−１６）変調のランダム信号を１１回記録し、ジッタをタイムインターバルアナライザーを用いて測定した。ここで、ジッタとは、記録の原信号と再生信号の時間軸上のズレであり、３Ｔ〜１１Ｔの各信号の持つジッタの標準偏差の総和（σsum ）をとり、これを信号検出のウィンドウ幅（Ｔ）で割った値（σsum ／Ｔ）として表現される。例えば、ジッタが１２．８％以下であるということは、前記時間軸上のズレが正規分布になると仮定した場合、ビットエラー率が１０^-4以下であることに相当することが知られている。
【０１３９】
なお、信号を記録する際のレーザー変調波形は、ｎＴ（ｎは整数、３≦ｎ≦１１）信号の場合、（ｎ−２）個のパルスからなるパルス列（パワーレベルＰ₁）とし、その先頭は５１．３ｎｓ、２番目以降はすべて１７．１ｎｓのパルス幅で、各パルス間の幅も１７．１ｎｓ（パワーレベルＰ₃）とし、最終のパルスの直後に３４．２ｎｓの冷却区間（パワーレベルＰ₄）を設けた。マークを記録しない部分においては、パワーレベルＰ₂の連続光とした。記録パワーレベルＰ₁は、３Ｔ信号を記録した場合にそのＣ／Ｎ比が４５ｄＢを超えるパワーの下限値の１．５倍とし、パワーレベルＰ₂は消去率が最大となるパワーとし、パワーレベルＰ₃およびＰ₄は、再生パワーレベルと同じ１ｍＷとした。
【０１４０】
上記の条件で測定した結果を上記（表３）に示す。なお、表中の測定結果は、実用的な記録媒体として十分であるといえる結果を「Ｂ」、なかでも特に優れているものを「Ａ」、不十分であるが、密度・線速度・記録再生方式等の仕様によっては使用できる可能性のあるものを「Ｃ」、使用できる可能性のないものを「Ｄ」として表した。なお、さらに具体的には、Ｃ／Ｎ比について、「Ａ」は５３ｄＢ以上、「Ｂ」は５０ｄＢ以上５３ｄＢ未満、「Ｃ」は４７ｄＢ以上５０ｄＢ未満、「Ｄ」は４７ｄＢ未満にそれぞれ該当する。また、消去率については、「Ａ」は２４ｄＢ以上、「Ｂ」は２０ｄＢ以上２４ｄＢ未満、「Ｃ」は１６ｄＢ以上２０ｄＢ未満、「Ｄ」は１６ｄＢ未満にそれぞれ該当する。また、ジッタについては、「Ａ」は８％未満、「Ｂ」は８％以上１０％未満、「Ｃ」は１０％以上１３％未満、「Ｄ」は１３％以上にそれぞれ該当する。
【０１４１】

【０１４２】
ディスクNo.31〜No.38は、光吸収層としてｎの大きいＰｂＴｅ、反射層としてｎが小さく熱伝導率の大きいＡｕを用いたディスクであり、ディスクNo.31〜No.34は、反射層の膜厚を変化させたディスクであり、ディスクNo.34〜No.38は、光吸収層の膜厚を変化させたディスクである。
【０１４３】
ディスクNo.31〜No.34を比較すると、反射層のＡｕの膜厚が厚くなるほど冷却能が上がるために、ジッタが良好となっており、反射層の膜厚が光吸収層の膜厚以上となる辺りからジッタが１０％以下となっている。
【０１４４】
ディスクNo.34〜No.38を比較すると、ディスクNo.35のように光吸収層の膜厚が薄すぎるか、ディスクNo.37、No.38のように光吸収層の膜厚が厚すぎるディスクの場合、光学特性・評価結果ともに悪くなっている。一方、ディスクNo.34、No.36の場合には、光吸収層の膜厚が適当であるために、Ｃ／Ｎ比、消去率、ジッタともに良好な値が得られている。このように、光吸収層の適当な膜厚は、０．１λ／（ｎ₁・ｋ₁ ）以上１．０λ／（ｎ₁・ｋ₁）以下の範囲である。
【０１４５】
また、ディスクNo.39〜No.47は、光吸収層および反射層の材料を変えたディスクである。ディスクNo.34がΔｎ＝４．７であるのに対し、ディスクNo.40（Δｎ＝１．４）、ディスクNo.41（Δｎ＝１．１）、ディスクNo.42（Δｎ＝１．９）、ディスクNo.44（Δｎ＝１．４）、ディスクNo.45（Δｎ＝−４．７）などは、Δｎの値が２よりも小さいために光学特性が悪く、Ｃ／Ｎ比や消去率も低くなっており、当然ジッタも大きくなっている。ディスクNo.39（Δｎ＝２．８）、ディスクNo.43（Δｎ＝３．３）、ディスクNo.46（Δｎ＝２．２）、ディスクNo.47（Δｎ＝２．９）などは、Δｎが２以上で各特性も良好となってはいるが、やはりΔｎが小さいものほど記録再生特性は劣っており、Δｎは２．５以上、さらには３以上がより好ましいことがわかる。
【０１４６】
また、ディスクNo.34の構成について、図７に示すような、記録層３３の基板３１側および／または基板３１と反対側の面にＧｅＯＮ膜からなる膜厚約５ｎｍの界面層３９が形成されたディスクを作製した。ＧｅＯＮ膜は、Ｇｅターゲットを用い、Ａｒ、Ｎ₂およびＯ₂ガス中で反応性スパッタによって成膜した。これらのディスクに対し、ディスクNo.34と同様の測定を行った。その結果、いずれのディスクも、Ｃ／Ｎ比はディスクNo.34と変わらないものの、界面層３９（ＧｅＯＮ膜）を記録層３３の基板３１側のみ、基板３１と反対側のみ、基板３１側および基板３１と反対側に設けたディスクのそれぞれについて、消去率がディスクNo.34に対して、それぞれ約２ｄＢ、約４ｄＢ、約５ｄＢだけ向上し、ジッタ値についても８％未満の良好な値が得られた。このことから、界面層３９を挿入することにより、本実施形態の光学的情報記録媒体は消去特性がさらに向上することが明らかになった。
【０１４７】
【発明の効果】
以上説明したとおり、本発明によれば、クロスイレースが小さく、高密度の情報の記録再生に好適な光学的情報記録媒体を提供できる。また、本発明によれば、高密度・高線速度なオーバーライトにおいても消去率が高く、かつ、ジッタの小さい情報の記録再生が可能な光学的情報記録媒体を提供できる。また、本発明によれば、このような光学的情報記録媒体の製造方法とともに、上記媒体に好適な光学的情報記録媒体の記録再生方法、および光学的情報記録媒体の再生装置を提供するものである。
【図面の簡単な説明】
【図１】 本発明の光学的情報記録媒体の一形態（第１の実施形態）の部分断面図である。
【図２】 本発明の光学的情報記録媒体の一形態の部分斜視図である。
【図３】 本発明の光学的情報記録媒体の別の一形態（第１の実施形態）の部分断面図である。
【図４】 本発明の光学的情報記録再生装置の一形態の構成を示す図である。
【図５】 本発明の光学的情報記録媒体の記録再生方法に適用されるパルス波形の一例を示す波形図である。
【図６】 本発明の光学的情報記録媒体のまた別の一形態（第２の実施形態）の部分断面図である。
【図７】 本発明の光学的情報記録媒体のさらに別の一形態（第２の実施形態）の部分断面図である。
【図８】 本発明の光学的情報記録媒体のまた別の一形態（第３の実施形態）の部分断面図である。
【符号の説明】
１、３１ 透明基板
２、３２ 下側保護層
３、３３ 記録層
４、３４ 上側保護層
５ 中間層
３５ 光吸収層
６、３６ 反射層
７、３７ オーバーコート層
８ グルーブ
９ ランド
１０ レーザー光
１１ 記録マーク
１２、３９ 界面層
１３ 半導体レーザー
１４ コリメートレンズ
１５ ビームスプリッター
１６ λ／４波長板
１７ 対物レンズ
１８ 光ディスク
１９ ボイスコイル
２０ ターンテーブル
２１ モーター
２２ 検出器
２３ 再生信号
４１ 透明基板
４２ 第１情報層
４３ 分離層
４４ 第２情報層
４５ 保護層（保護基板）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording medium capable of recording and reproducing information signals with high signal quality by irradiating a thin film formed on a substrate with a high-energy light beam such as a laser beam, and its manufacture The present invention relates to a method, a recording / reproducing method thereof, and an optical recording / reproducing apparatus.
[0002]
[Prior art]
When a thin film such as a chalcogen material formed on a substrate is irradiated with a laser beam while adjusting the irradiation conditions and locally heated, the irradiated portion is amorphous with different optical constants (refractive index n, extinction coefficient k). It is possible to change the phase between the crystalline phase and the crystalline phase. A medium for performing high-speed and high-density information recording for detecting a difference in reflected light amount or transmitted light amount with respect to light of a specific wavelength as a signal by using such a phase change and a method for using the medium have been developed.
[0003]
In phase change recording, only a single laser beam is used and the laser output is modulated between the recording level and the erasing level according to the information signal and irradiated onto the information track. It becomes possible to record a signal (for example, JP-A-56-145530). This method is advantageous in that the magnetic circuit parts required for magneto-optical recording are not required and the head can be simplified, and the rewriting time can be shortened because erasing and recording can be performed simultaneously.
[0004]
In order to increase the density of phase change recording, a smaller recording mark is formed by shortening the wavelength of the light source used for recording, increasing the NA (numerical aperture) of the objective lens, and the like. A technique for improving the linear density in the direction and the track density in the radial direction is employed. Further, in order to improve the density in the circumferential direction, mark edge recording which gives information to the length of the recording mark is a groove which is a laser beam guiding groove provided on the substrate in order to improve the density in the radial direction. Land and groove recording, in which both the land between the guide groove and the land between the guide grooves, is proposed.
[0005]
In addition to increasing the density, it is also important to improve the information processing speed, that is, the speed of recording / reproducing information. For this reason, even if the disk is rotated at a high rotational speed even at the same radial position, the recording / reproducing speed is high. Studies are also underway on increasing the linear velocity.
[0006]
Furthermore, a plurality of recordable information layers are stacked via a separation layer, and a recording medium (for example, Japanese Patent Laid-Open No. 9-212917) with doubled capacity and any one of the plurality of information layers are selected. Thus, layer recognition means and layer switching means (for example, Japanese Patent Publication No. 10-505188) have been proposed for recording and reproduction.
[0007]
As recording density increases, overwriting distortion and repetitive degradation also become a problem. Especially, when recording marks are recorded on a track, the recording mark on the adjacent track is partially erased. (Hereinafter referred to as “cross erase”) is a problem. Cross erase becomes more prominent as the track interval is shortened in order to improve the recording density in the radial direction. In particular, in the land & groove recording, since the radial distance between the recording marks is approximately halved as compared with the case of recording only in one of the groove and the land, the influence becomes large.
[0008]
The cross erase occurs because the spot of the laser beam narrowed down during recording affects the track adjacent to the track to be recorded. Specifically, it is considered that the direct heating of the adjacent track by the laser beam and the indirect heating of the adjacent track by the heat conduction from the track to be recorded cause the cross erase.
[0009]
In addition, in the case of overwriting with a single beam, the light absorption rate is different between the amorphous part and the crystal part, and the crystal part requires latent heat of fusion. A difference in temperature reached when irradiated occurs, and the mark edge position is uneven due to the influence of the signal before overwriting at the time of overwriting. As a result, the error (jitter) in the time axis direction of the reproduction signal increases and the erasure rate decreases. This phenomenon becomes a serious problem when the recording linear velocity and density are increased, especially when the mark edge recording method is introduced.
[0010]
In order to solve this problem, it is necessary to equalize the ultimate temperatures when the beam of the same power is irradiated in the crystal part and the amorphous part. For that purpose, when the laser beam of wavelength λ is irradiated, the absorptance of the crystal part is Acry, the amorphous part is Aamo, and the light absorptivity ratio is used to compensate for the latent heat of fusion of the crystal part. Acry / Aamo must be greater than 1.0. In addition, the reflectance difference ΔR = Rcry−Ramo is obtained in order to obtain a high C / N ratio, where Rcry is the reflectance of the crystal part when the laser beam of wavelength λ is irradiated and Ramo is that of the amorphous part. Larger is desirable.
[0011]
Conventionally, as a technique for increasing both Acry / Aamo and ΔR as described above, a three-layer structure having no reflective layer (JP-A-3-113844, JP-A-5-298748), a material with low reflectivity A four-layer structure (Japanese Patent Laid-Open No. 4-102243, Japanese Patent Laid-Open No. 5-298747) or the like having a reflective layer using a thin film or a sufficiently thin reflective layer has been proposed.
[0012]
However, even if Acry / Aamo and ΔR are both increased using the above-described means, sufficient recording / reproducing characteristics are not always obtained. For example, when the thickness of the reflective layer is thin or the thermal conductivity of the reflective layer is low, the so-called cooling ability that releases heat generated from the light absorption of the recording layer to the reflective layer becomes insufficient, and the amorphous layer becomes amorphous. Hinder. This phenomenon is particularly noticeable in the front end portion of the mark that is amorphous, and an imbalance occurs in which the width of the front end portion of the mark is smaller than the width of the rear end portion of the mark. In addition, the mark edge position is not only physically deviated from the desired position, but the mark width is not uniform, so the edge position as an electric signal is further deviated, resulting in an increase in jitter. End up. This is a big problem in high density and high linear velocity recording.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to provide an optical information recording medium suitable for recording / reproducing high density information with small cross erase. It is another object of the present invention to provide an optical information recording medium capable of recording and reproducing information with a high erasure rate and low jitter even in high-density / high linear velocity overwrite. Furthermore, an object of the present invention is to provide a manufacturing method and a recording / reproducing method of these optical information recording media, and an optical information recording / reproducing apparatus using the optical information recording medium.
[0014]
[Means for Solving the Problems]
To achieve the above object, a first optical information recording medium of the present invention includes a transparent substrate and a multilayer film formed on the transparent substrate, and the multilayer film is closer to the transparent substrate. In order from the lower protective layer, including a recording layer, an upper protective layer, an intermediate layer and a reflective layer that reversibly change between two different states optically detectable by irradiation with a light beam, the upper protective layer, The thermal conductivity of the intermediate layer and the reflective layer is The level gradually increases from the layer closest to the recording layer, The film thickness of the recording layer is 4 nm or more and 16 nm or less, and at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer is further provided with an interface layer. It is characterized by that.
[0015]
By using such an optical information recording medium, heat conduction from the recording layer in the thickness direction of the multilayer film is promoted, and cross erase can be reduced. The film thickness of the recording layer is preferably 6 nm or more and 14 nm or less.
[0019]
Another of the present invention The optical information recording medium includes a transparent substrate and a multilayer film formed on the transparent substrate, and the multilayer film is optically irradiated by irradiation with a lower protective layer and a light beam in order from the side closer to the transparent substrate. Including a recording layer, an upper protective layer, an intermediate layer, and a reflective layer that reversibly change between two differently detectable states, wherein the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer is The level gradually increases from the layer closest to the recording layer, The thickness of the recording layer is 4 nm or more and 16 nm or less, and the track pitch of the transparent substrate is 0.6 μm or less.
[0020]
The optical information recording medium of the present invention may include a plurality of recording layers, and may include two or more information layers composed of a multilayer film including the recording layers. In this case, it is preferable that two or more information layers are laminated via a separation layer. Such an optical information recording medium includes, for example, a transparent substrate and a first information layer, a separation layer, and a second information layer formed on the transparent substrate in order from the side close to the transparent substrate.
[0021]
In the case where two information layers are provided as described above, the structure of the multilayer film described above is preferably applied to the second information layer, although not particularly limited. It is important that the second information layer far from the transparent substrate side on which the laser light is incident has high sensitivity. In the multilayer film, the intermediate layer or the light absorption layer absorbs the laser beam as in the case of the recording layer, so that the temperature of the recording layer is easily raised and good sensitivity is obtained. Moreover, in the multilayer film, heat generation is eliminated by rapid cooling by the reflective layer having high thermal conductivity. For this reason, thermal diffusion in the recording layer does not increase, and deterioration of the cross erase characteristic can be suppressed.
[0022]
The first manufacturing method of the optical information recording medium of the present invention is such that, on the transparent substrate, in order from the side close to the transparent substrate, the lower protective layer, between two different states optically detectable by light beam irradiation. Forming a multilayer film including a recording layer, an upper protective layer, an intermediate layer, and a reflective layer that reversibly change, and the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer Changes stepwise from the layer closest to the recording layer, The film thickness of the recording layer is 4 nm or more and 16 nm or less, and an interface layer is further provided on at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer. Features. By this manufacturing method, an optical information recording medium with reduced cross erase can be obtained.
[0025]
Each of the above manufacturing methods can also be applied to an optical information recording medium having two or more information layers. In this case, the step of forming the first information layer on the transparent substrate, the step of forming the second information layer on the protective substrate, and bonding the transparent substrate and the protective substrate through the separation layer, Preferably, the manufacturing method includes a step of forming the first information layer, the separation layer, and the second information layer in this order on the transparent substrate. In this case, the protective substrate functions as a layer that protects the information layer. Also in this case, it is preferable to form the second information layer on the protective substrate so that each configuration of the multilayer film described above is applied to the second information layer.
[0026]
The optical information recording medium recording / reproducing method of the present invention is a method for recording and reproducing information by making a light beam incident on the optical information recording medium of the present invention described above from the transparent substrate side, wherein the light beam Power level P that can instantaneously melt the irradiated part ₁ , Power level P that can not melt the irradiated part instantaneously ₂ And P _Three (However, P ₁ > P ₂ ≧ P _Three ≧ 0), and the power level P at which the optical state of the recording mark of the recording layer does not change and the reflectance sufficient for reproduction of the recording mark is obtained by irradiation. ₀ (However, P ₁ > P ₀ > 0)
At least one recording mark recorded on the recording layer is irradiated with a light beam at a power level P. ₁ And P _Three When a recording mark is not formed, a light beam is generated at a power level P. ₂ Hold on
Power level P ₀ The information recorded on the recording layer is reproduced by irradiating the light beam.
[0027]
Thus, by forming a recording mark with a pulse train generated by modulating the intensity, for example, when the first optical information recording medium is used, information can be recorded and reproduced while suppressing cross erase. Become. Further, for example, when the second or third optical information recording medium is used, the mark width can be made uniform except for excessive heat when a particularly long mark is formed.
[0028]
Each of the above recording / reproducing methods can also be applied to an optical information recording medium having two or more information layers. In this case, it is preferable to change the state of the recording layer included in the first information layer and the second information layer by making a light beam incident from the transparent substrate side.
[0029]
The optical information recording medium recording / reproducing apparatus of the present invention comprises the above-described optical information recording medium of the present invention, a light beam generating means for generating a light beam applied to the optical information recording medium, A light beam intensity modulating means for modulating the intensity of the light beam,
The intensity of the light beam is a power level P that can instantaneously melt the irradiated part. ₁ , Power level P that can not melt the irradiated part instantaneously ₂ And P _Three (However, P ₁ > P ₂ ≧ P _Three ≧ 0), and the power level P at which the optical state of the recording mark of the recording layer does not change and the reflection sufficient for reproduction of the recording mark is obtained by irradiation. ₀ (However, P ₁ > P ₀ > 0)
When the light beam intensity modulating means records information by forming a recording mark on the recording layer, the light beam is changed to a power level P ₁ And P _Three At least one of the recording marks is formed by a recording pulse train made up of a group of pulses generated by modulation between and the intensity of the light beam when the recording mark is not formed. ₂ Hold on to
When reproducing the information recorded on the recording layer, the intensity of the light beam is set to the power level P. ₀ It is characterized by holding.
[0030]
Each recording / reproducing apparatus can be applied to an optical information recording medium having two or more information layers. In this case, it is preferable to arrange the light beam generating means on the transparent substrate side of the recording medium so that the laser light is incident from the transparent substrate side.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
[0032]
(First embodiment)
In the present embodiment, the first optical information recording medium of the present invention will be mainly described. As a result of studying various layer configurations of the multilayer film formed on the substrate, the present inventor has found that the film thickness of the recording layer and the heat of the layer on the air side (opposite side of the substrate) from the recording layer are included in the cross erase. We found that the relationship of conductivity has a great influence and completed this form of media.
[0033]
In the optical information recording medium, the upper protective layer preferably has a thickness of 10 nm or more. If the upper protective layer is too thin, the distance between the recording layer and the intermediate layer becomes too short, and as a result, heat conduction from the recording layer to the intermediate layer is suppressed due to the heat of the intermediate layer itself. It is. The upper protective layer preferably has a thickness of 200 nm or less.
[0034]
The optical information recording medium preferably further includes an interface layer formed so as to be in contact with the recording layer. The interface layer is formed at least one interface between the upper protective layer and the recording layer and between the lower protective layer and the recording layer. The interface layer is preferably a layer containing Ge. This is because interdiffusion of atoms between the upper protective layer and / or the lower protective layer and the recording layer can be suppressed. The interface layer preferably contains at least one selected from Ge, Si, Cr, Ti and Al.
[0035]
In the optical information recording medium, the recording layer preferably contains Ge, Sb, and Te. This is because it is suitable as a material when erasing and recording are simultaneously performed in the recording layer. More preferably, the recording layer contains Ge, Sb, and Te as main components and further contains N of 6.0 atomic% or less. This is because it is effective in improving the repetition characteristics.
[0036]
In the optical information recording medium, the upper protective layer and / or the lower protective layer contains 60 to 100 mol% of ZnS, SiO 2 ₂ It is preferable to contain 40-0 mol%. This is because such a protective layer is excellent in heat resistance, has an appropriate thermal conductivity, and further has an appropriate refractive index for adjusting the optical characteristics of the medium.
[0037]
In the optical information recording medium, it is preferable that the reflective layer contains at least one selected from Au, Ag, Cu and Al. You may use the alloy containing these metals.
[0038]
In the optical information recording medium, the intermediate layer includes Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Os, Al, Ga, In, C, Si, Ge, Sn. It is preferable that at least one element selected from Pb, Sb and Bi is included. More specifically, it preferably comprises at least one compound selected from oxides, nitrides, carbides, sulfides, fluorides, selenides and tellurides containing at least one selected from the above elements. The intermediate layer is made of a material whose thermal conductivity has a value between the thermal conductivity of the upper protective layer and the thermal conductivity of the reflective layer.
[0039]
Moreover, it is preferable that an intermediate | middle layer consists of an interelement compound of the said element like Ge-Cr, Si-W, for example. In the present specification, a compound composed of two or more elements is referred to as an inter-element compound.
[0040]
In the optical information recording medium, when the recording layer is a crystalline phase, the reflectance, which is the ratio of the light beam reflected to the recording medium, and the absorption ratio, which is the ratio of absorption to the recording layer, respectively. When the recording layer is in an amorphous phase, Rcry and Aamo have a reflectance difference (Rcry-Ramo) of 5% or more (5 points or more in%) and an absorptivity ratio (Acry / Aamo) is preferably 1.0 or more.
[0041]
In this method for producing an optical information recording medium, it is preferable to form the recording layer at a speed of 200 nm / min or less. This is to ensure the film thickness accuracy of the recording layer.
[0042]
Further, the recording layer may be formed in an atmosphere containing an inert gas and a nitrogen gas, and the content of the nitrogen gas adjusted so that the recording layer contains not more than 6.0 atomic% of nitrogen atoms. preferable.
[0043]
In this optical information recording medium recording / reproducing method, it is preferable that at least a part of the recording pulse train is generated so that the pulse width and the interval between the pulses are substantially the same.
[0044]
In the recording / reproducing method of the optical information recording medium, the power level P immediately after the last pulse of the recording pulse train. _Four (However, P ₂ > P _Four It is preferable to provide a cooling section of ≧ 0).
[0045]
Hereinafter, the present embodiment will be specifically described with reference to the drawings.
1 and 2 are a partial cross-sectional view and a partial perspective view, respectively, of the optical disk of the present embodiment. As shown in FIG. 1, on this optical disk, a lower protective layer 2, a recording layer 3, an upper protective layer 4, an intermediate layer 5, and a reflective layer 6 are sequentially laminated on a transparent disk substrate 1 and further overcoated. A coat layer 7 is provided. Further, as shown in FIG. 2, since the groove 8 having a depth D is formed on the substrate 1, the surface of the laminated film 10 made of each of the above layers has concave and convex portions parallel to each other in the groove 8 and The land 9 is formed. The recording layer 3 is irradiated with laser light as a light beam from the substrate 1 side to form a recording mark 11. As shown in FIG. 2, for high density recording, it is preferable to form recording marks on both the groove 8 and the land 9 (land & groove recording).
[0046]
As the substrate 1, transparent materials such as polycarbonate resin, polymethyl methacrylate resin, polyolefin resin, arton resin, glass and the like can be used. The thickness of the substrate 1 is not particularly limited, but is preferably 0.1 mm to 2.0 mm.
[0047]
The lower protective layer 2 and the upper protective layer 4 suppress noise increase due to thermal damage to the substrate 1 or the recording layer 3 during laser light irradiation, and reflectivity, absorption rate, and phase adjustment of reflected light with respect to the laser light. Formed for. Examples of the protective layers 2 and 4 include Sc, Y, Ce, La, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Si, Te, and other oxides, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Zn, B, Al, Ga, In, Si, Ge, Sn, Pb, and other nitrides, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Carbides such as Zn, B, Al, Ga, In, Si, sulfides such as Zn, Cd, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, selenides or tellurides, Mg, Ca, etc. A dielectric material made of a simple substance such as fluoride, C, Si, Ge, or a mixture thereof can be used.
[0048]
The film thickness of the upper protective layer 4 is preferably 10 nm or more and 200 nm or less. If the upper protective layer 4 is too thin, heat escape from the recording layer 3 to the intermediate layer 5 becomes worse due to the influence of the heat of the intermediate layer 5 itself as described above. As described above, when the heat conduction in the thickness direction of the layer is lowered, the thermal diffusion in the surface of the recording layer 3 is increased, so that the cross erase may be increased. When the upper protective layer 4 is 10 nm or more, for example, the track pitch (average of the width of a pair of adjacent lands and grooves (1/2 of the groove pitch), the same as the groove pitch when recording only in the groove) is 0. Even if it is 6 μm, the cross erase is within the allowable range. The thicker the upper protective layer 4, the smaller the cross erase. However, since the optical characteristics repeat with a period of the film thickness λ / 2n (λ is the wavelength of the laser beam and n is the refractive index of the upper protective layer 4), the film thickness is necessary to obtain the desired optical characteristics of the medium. It is industrially disadvantageous to make it thicker. Therefore, although it depends on the wavelength λ and the refractive index n, the film thickness is preferably 200 nm or less. For the reasons described above, the thickness of the upper protective layer 4 is preferably 10 nm or more and 200 nm or less, and particularly preferably 20 nm or more and 200 nm or less.
[0049]
On the other hand, the thickness of the lower protective layer 2 is not particularly limited, but is preferably 10 nm or more and 200 nm or less. If the thickness of the lower protective layer is less than 10 nm, the substrate may be thermally deformed. The reason why the lower protective layer is preferably 200 nm or less is the same as that described above, where the upper protective layer is preferably 200 nm or less.
[0050]
As the recording layer 3, a chalcogenide based on Te or Se, for example, Ge—Sb—Te, Ge—Te, Pd—Ge—Sb—Te, In—Sb—Te, Sb—Te, Ag—In—Sb is used. -Te, Ge-Sb-Bi-Te, Ge-Sb-Se-Te, Ge-Sn-Te, Ge-Sn-Te-Au, Ge-Sb-Te-Cr, In-Se, In-Se-Co An alloy whose main component is etc. can be used. Alternatively, a material obtained by adding oxygen, nitrogen, or the like to these alloys may be used.
[0051]
The film thickness of the recording layer 3 is suitably 4 nm or more and 16 nm or less. Conventionally, in the case where the track pitch is so large that cross-erasing is not a problem, a film thickness of 20 nm or more has been advantageous in order to increase the optical contrast. However, when the recording layer is thick in this way, the heat conduction in the in-plane direction of the recording layer is large, and therefore, as the track pitch becomes shorter (for example, 0.6 μm or less), the cross erase becomes conspicuous. In order to reduce cross erase, it is advantageous that the recording layer is thin. By reducing the thickness of the recording layer, heat conduction in the in-plane direction of the layer can be reduced. For example, when the film thickness of the recording layer is 16 nm or less, the cross erase is within the allowable range even if the track pitch is 0.6 μm. However, if the film thickness of the recording layer is less than 4 nm, the optical contrast cannot be secured, and the influence of the film thickness fluctuation due to repeated recording becomes large and tracking becomes unstable, so that the cross erase becomes large. . Therefore, the film thickness of the recording layer is preferably 4 nm to 16 nm, and more preferably 6 nm to 14 nm.
[0052]
As the intermediate layer 5, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Al, Ga, In, C, Si, Ge, Sn, Pb, At least one element selected from Sb and Bi (in particular, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Os, Al, Ga, In, C, Si, Ge, Sn, Pb , At least one element selected from Sb and Bi), or at least one compound selected from oxides, nitrides, carbides, sulfides, fluorides, selenides, tellurides, and interelement compounds of these elements More specifically, Cr, Mo, W, Ti, Zr, Nb, Ta, Ge—Cr, Ge—Mo, Ge—W, Si—Cr, Si—Mo, Si are preferable. Use -W etc. It is possible.
[0053]
Although it does not specifically limit as a film thickness of the intermediate | middle layer 5, 5 nm or more and 100 nm or less are preferable.
[0054]
The reflective layer 6 is formed for the purpose of adjusting the reflectance, absorption rate, and phase of reflected light with respect to laser light, reducing the thermal load on the recording thin film, and the like. As described above, a metal material having a relatively high thermal conductivity such as Al, Au, Ag, or Cu, or an alloy material based on these can be used as the reflective layer.
[0055]
The thickness of the reflective layer 6 is not particularly limited, but is preferably 10 nm or more and 200 nm or less.
[0056]
The material used for each layer may be selected from the materials exemplified above, but the reflective layer 6, the intermediate layer 5 and the upper protective layer 4 have a higher thermal conductivity in this order. select. By setting the heat conductivity in this way, heat conduction from the recording layer 3 in the film thickness direction of the multilayer film is accelerated. Accordingly, the heat conduction in the in-plane direction of the recording layer 3 is relatively suppressed, and the adjacent tracks are hardly affected.
[0057]
The optical information recording medium can be provided with an interface layer 12 as shown in FIG. The interface layer 12 may be provided on both sides of the recording layer 3 as shown in FIG. 3, but may be provided only on one of them. When the interface layer 12 is provided, the atomic diffusion between the protective layers 2 and 4 and the recording layer 3 is suppressed, so that the repetitive characteristics of the recording medium can be improved. As the interface layer 12, a material having an anti-diffusion effect with respect to the material used for the protective layers 2 and 4 can be used, but a material containing Ge is preferable, and a material mainly containing a nitride of Ge is particularly preferable. Are better.
[0058]
The film thickness of the interface layer 12 is not particularly limited, but is preferably 1 nm or more and 50 nm or less.
[0059]
Each of the layers 2 to 6 and 12 can be formed by a vapor phase thin film deposition method such as a vacuum vapor deposition method, a sputtering method, an ion plating method, a CVD (Chemical Vapor Deposition) method, or an MBE (Molecular Beam Epitaxy) method. . However, the sputtering method has the best balance from the viewpoint of the film formation rate, the manufacturing cost, the quality of the obtained film, and the like. Each layer is generally formed while flowing an inert gas into a high vacuum chamber, but may be formed while oxygen, nitrogen, or the like is mixed in the inert gas. Thereby, O atoms, N atoms, etc. are mixed in the film, and the characteristics of the film can be adjusted. In particular, in the recording layer 3, mixing of these atoms (for example, mixing of nitrogen atoms of 6.0 atomic% or less) may be effective for improving the repetition characteristics of the medium and reducing cross erase.
[0060]
In addition, it is industrially advantageous for the optical information recording medium to sequentially form the layers 2 to 6 and 12 in parallel in separate chambers using a single-wafer film forming apparatus. When such a film forming method is employed, the recording layer does not affect the overall film forming efficiency even if the recording layer is formed at a relatively low speed. This is because the film thickness of the recording layer 3 is preferably 4 nm or more and 16 nm or less, and is, for example, about one digit thinner than the normal film thickness (100 nm or more) of the lower protective layer 2. Since accurately controlling the film thickness of the recording layer 3 is important for reducing cross erase as described above, it is preferable to secure a minimum film formation time of about 5 seconds. Accordingly, the recording layer deposition rate is preferably 200 nm / min or less.
[0061]
An overcoat layer 7 may be further provided on each layer formed as described above as shown in FIG. This layer 7 is preferably formed by applying an ultraviolet curable resin.
[0062]
However, the optical information recording medium of the present invention is not limited to the single-sided single-sided disk as shown in FIG. 1, and the recording layer is formed in the same manner as described above by using an ultraviolet curable resin and / or a hot melt type adhesive. It is good also as a double-sided disk by sticking together so that the board | substrate in which the multilayer film containing was formed and film surfaces oppose. In this case, it is preferable that the substrates are bonded via the separation layer so that the multilayer films, each of which serves as an information layer, do not directly contact each other. Alternatively, the surface on which the multilayer film is formed may be bonded to a dummy substrate with the adhesive to form a single-sided disk.
[0063]
FIG. 4 is a diagram showing an outline of an example of an apparatus for recording / reproducing an optical information recording medium. The laser beam 10 emitted from the semiconductor laser 13 in accordance with the input signal is condensed by the collimator lens 14 to become a parallel beam, and sequentially passes through the beam splitter 15, the quarter wavelength plate 16, and the objective lens 17. The light is irradiated onto the optical disk 18. The laser beam 10 is focused by moving the voice coil 19 up and down. The optical disk 18 is fixed on the turntable 20. Information signals are recorded and reproduced by irradiating the optical disk 18 rotating at a predetermined speed by the motor 21 with laser light.
[0064]
FIG. 5 is an example of a pulse waveform of laser light when recording an information signal. As shown in FIG. 5, the intensity of the laser beam is P ₁ , P ₂ , P _Three And P _Four Is modulated between. Where P ₁ Is a power level at which the irradiated part can be melted instantaneously, and the irradiated part can be instantaneously melted even when irradiation is performed while modulating the intensity below the power level as shown in FIG. P ₂ And P _Three Is a power level at which the irradiated part cannot be melted instantaneously, and preferably the irradiated part cannot be melted instantaneously even when irradiated without modulation. P _Four Is a power level for cooling the recording layer immediately after the last recording pulse train. In FIG. ₁ > P ₂ ≧ P _Three ≧ P _Four An example in which each power level is set so that ≧ 0 is shown. In order to modulate the intensity of the laser beam as described above, the drive current of the semiconductor laser may be modulated, but means such as an electro-optic modulator or an acousto-optic modulator may be used.
[0065]
However, it is not necessary to form all the recording marks by the recording pulse train as shown in FIG. 5, and for the pulse train having a short mark length, the power level P ₁ It may be formed by a single rectangular pulse. However, when a long mark is formed, the power level P as described above is used to improve the repetition characteristics and reduce the cross erase. ₁ It is preferable to suppress excessive heat by forming a pulse train that includes as a power peak.
[0066]
P ₂ Is a power level at which a recording mark cannot be formed even if the light beam is held at its intensity as shown in FIG. This power level may be a power level at which the recording mark cannot be formed but the recording mark can be erased. In this case, the power level P ₂ The recording mark is erased in the portion irradiated with the light beam.
[0067]
For example, in a phase change type optical disk, when the recording state is used corresponding to the amorphous state and the erasing state is used corresponding to the crystalline state, P ₁ Is a power level that can reversibly change the recording layer from the crystalline state to the amorphous state, P ₂ May be set as a power level that can reversibly change the recording layer from an amorphous state to a crystalline state.
[0068]
Immediately after the recording pulse train shown in FIG. _Four A cooling section is provided. Providing such a power level for cooling can remove heat of the mark rear end portion that is likely to be excessive in heat, and is effective in suppressing cross erase.
[0069]
Also, as in the recording pulse train shown in FIG. 5, if the pulse width and the length between each pulse are constant except for the first and last pulses, the modulation means can be simplified because the modulation can be performed at a single frequency. Can do.
[0070]
Note that each pattern such as the length of the recording mark, the length of the space before and after it, and the length of the adjacent mark, etc. may cause unevenness in the mark edge position, which may cause an increase in jitter. In the recording / reproducing method of the optical information recording medium, in order to prevent this and improve the jitter, the pulse position of the pulse train or the length of the pulse is adjusted as necessary so that the edge position is aligned for each pattern. It is preferable to compensate.
[0071]
When reproducing the recorded information signal, the power level P is such that the recording layer 3 does not change phase. ₀ The laser light (unmodulated light) is irradiated onto the optical disk, the reflected light is incident on the detector 22, and the reflected light amount change is detected as the reproduction signal 23.
[0072]
The change of the laser light power level as described above can be performed by controlling the drive current of the laser diode. Further, an electro-optic modulator or an acousto-optic modulator may be used as the light beam intensity modulating means.
[0073]
(Second Embodiment)
In the present embodiment, mainly the second and third optical information recording media of the present invention will be described.
[0074]
The optical information recording medium preferably further includes an interface layer at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer. According to this preferable example, the erasing characteristics can be improved. The interface layer preferably contains at least one selected from Ge, Si, Cr, Ti and Al.
[0075]
In the optical information recording medium, the thickness of the recording layer is preferably 4 nm or more and 16 nm or less. This is because if the recording layer is too thin, the optical contrast and the signal amplitude are reduced, and if it is too thick, thermal diffusion in the inner surface direction of the recording layer is increased and thermal interference between the marks is increased.
[0076]
In the optical information recording medium, the upper protective layer preferably has a thickness of 10 nm to 200 nm. If the upper protective layer is too thin, the heat generated by the light absorption of the light absorbing layer will affect the recording layer, increasing the thermal interference between the marks, and if it is too thick, the cooling effect by the reflective layer will be reduced. This is because the front and rear ends become unbalanced. Although not particularly limited, also in the present embodiment, the thickness of the lower protective layer is preferably 10 nm or more and 200 nm or less.
[0077]
In the optical information recording medium, the recording layer preferably contains Ge, Sb and Te, and further preferably contains Ge, Sb and Te as main components and further contains 6.0 atomic% N. .
[0078]
In the optical information recording medium, the upper protective layer and / or the lower protective layer is composed of 60 to 100 mol% ZnS and 40 to 0 mol% SiO. ₂ It is preferable to contain.
[0079]
In the optical information recording medium, it is preferable that the reflective layer contains at least one selected from Au, Ag, and Cu.
[0080]
In the optical information recording medium, the light absorption layer includes Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Al, Ga, In, At least one element selected from C, Si, Ge, Sn, Pb, Sb and Bi (in particular, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Os, Al, Ga, In , C, Si, Ge, Sn, Pb, Sb and Bi). More specifically, it is preferably composed of at least one compound selected from oxides, nitrides, carbides, sulfides, fluorides, selenides and tellurides containing at least one selected from the above elements. It is preferably an inter-element compound consisting of at least two selected from
[0081]
In the optical information recording medium, when the recording layer is a crystalline phase, the reflectance, which is the ratio of the light beam reflected to the recording medium, and the absorption ratio, which is the ratio of absorption to the recording layer, respectively. When the recording layer is in an amorphous phase, Rcry and Aamo have a reflectance difference (Rcry-Ramo) of 5% or more (5 points or more in%) and an absorptivity ratio (Acry / Aamo) is preferably 1.0 or more. According to this preferable example, the unevenness of the mark edge position at the time of overwriting can be eliminated.
[0082]
In the method for producing an optical information recording medium, the recording layer is preferably formed at a speed of 200 nm / min or less. This is to ensure the film thickness accuracy of the recording layer.
[0083]
Further, the recording layer may be formed in an atmosphere containing an inert gas and a nitrogen gas, and the content of the nitrogen gas adjusted so that the recording layer contains not more than 6.0 atomic% of nitrogen atoms. preferable.
[0084]
In this optical information recording medium recording / reproducing method, it is preferable that at least a part of the recording pulse train is generated so that the pulse width and the interval between the pulses are substantially the same.
[0085]
In the recording / reproducing method of the optical information recording medium, the power level P immediately after the last pulse of the recording pulse train. _Four (However, P ₂ > P _Four It is preferable to provide a cooling section of ≧ 0). According to this preferable example, the heat at the rear end portion of the mark, which is likely to be excessive in heat, can be removed, which is effective.
[0086]
Hereinafter, the present embodiment will be specifically described with reference to the drawings.
FIG. 6 is a partial sectional view showing the optical information recording medium of the present embodiment, and FIG. 7 is a partial sectional view of another example of the optical information recording medium of the present embodiment.
[0087]
As shown in FIG. 6, a lower protective layer 32, a recording layer 33, an upper protective layer 34, a light absorbing layer 35, and a reflective layer 36 are sequentially stacked on the substrate 31. Further, an overcoat layer 37 is provided. The disk is irradiated with a laser beam 38 from the substrate 31 side, whereby recording / reproduction of the disk is performed.
[0088]
As the material of the substrate 31, the lower protective layer 32, the recording layer 33, and the upper protective layer 34, the materials described in the first embodiment can be applied.
[0089]
The light absorption layer 35 is formed for the purpose of adjusting the reflectivity, the absorptance, and the phase of the reflected light with respect to the laser beam 38. Examples of the material constituting this layer include Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Al, Ga, In, C, Si, Ge, A material containing at least one selected from Sn, Pb, Sb and Bi, or at least one selected from oxides, nitrides, carbides, sulfides, fluorides, selenides, tellurides and interelement compounds of these elements A material comprising one compound is preferred. More specifically, Cr, Mo, W, Si, Ge, Te, Ge—Cr, Ge—Mo, Ge—W, Si—Cr, Si—Mo, Si—W, Ge—Te, Sn—Te, Pb-Te, Sb-Te, Bi-Te, or the like can be used.
[0090]
In addition, the said compound material may use the thing of the stoichiometric composition vicinity, and may use the thing of the composition shifted | deviated from the stoichiometric composition as needed. This also applies to the intermediate layer and the like in the first embodiment.
[0091]
The reflective layer 36 is formed for the purpose of adjusting the reflectance, absorption rate, and phase of reflected light with respect to the laser beam 38, reducing the thermal load on the recording thin film, and the like. As a material of the reflective layer, for example, a metal material having a relatively high thermal conductivity such as Al, Au, Ag, Cu, etc., among them, Au, Ag, Cu, or these having a refractive index of less than 0.5 at a wavelength of 600 nm. An alloy material based on is preferred. Among these, the Ag alloy is excellent in terms of thermal conductivity and optical constant, and is less expensive than Au having equivalent characteristics. In particular, a material in which an element such as Pd, Cu, Ti or the like is added to Ag within a range of 10 atomic% or less hardly corrodes, and is preferable from the viewpoint of environmental resistance and reliability.
[0092]
In the optical information recording medium, as shown in FIG. 7, the recording layer 33 is interposed between the lower protective layer 32 and the recording layer 33 and / or between the recording layer 33 and the upper protective layer 34. The interface layer 39 is preferably provided for the purpose of promoting crystallization. As the interface layer 39, there are some dielectric materials that play a role in the materials that can be used as the lower protective layer 32 and the upper protective layer 34, and these can be used. Is the most excellent. Further, by providing such an interface layer 39, the erasing characteristics can be improved.
[0093]
The lower protective layer 32, the recording layer 33, the upper protective layer 34, the light absorbing layer 35, the reflective layer 36, and the interface layer 39 can be formed by the same method as in the first embodiment.
[0094]
Further, as shown in FIG. 6, the optical information recording medium can be used as a single-sided single-sided disk by overcoating with an ultraviolet curable resin. Further, as described in the first embodiment, it can also be used as a double-sided disk. Furthermore, it can also be used as a single-sided disk by bonding the film surface facing the dummy substrate.
[0095]
The optical information recording medium of the present embodiment has a light absorption layer 35 (refractive index n ₁ , Extinction coefficient k ₁ , Film thickness d ₁ ) And the reflective layer 36 (refractive index n) ₂ , Extinction coefficient k ₂ , Film thickness d ₂ ) Is characterized by a combination of material and film thickness. Hereinafter, the role and effect of each layer will be described.
[0096]
Optically, the refractive index n of the light absorption layer 35 ₁ Is the refractive index n of the reflective layer 36. ₂ Acry / Aamo and ΔR can both be increased by appropriately increasing the ratio. Difference in refractive index Δn = n ₁ -N ₂ Is preferably 2 or more and 6 or less, more preferably 3 or more and 5 or less.
[0097]
The above range is supported by the following optical calculations. That is, the refractive index, extinction coefficient, and film thickness of each layer of the multilayer film are determined, and simultaneous equations for the optical energy balance at each interface are established and solved for all interfaces based on the energy conservation law. Thus, the reflectivity / transmittance of the entire multilayer film and the absorptance of each layer can be obtained. This technique itself is known, for example, as a matrix method (for example, Hiroshi Kubota et al. “Wave Optics” Iwanami Shoten, 1971). Here, substrate 31 / lower protective layer 32 (arbitrary film thickness) / recording layer 33 (10 nm) / upper protective layer 34 (arbitrary film thickness) / arranged in order from the incident side of the light beam (wavelength 660 nm) / Light absorption layer 35 (film thickness d ₁ ) / Acry / Aamo and ΔR values were calculated for a multilayered medium with a reflective layer 36 (80 nm).
[0098]
At that time, the refractive index n and the extinction coefficient k of each layer are as follows: the substrate 31 is n = 1.6, k = 0.0, the lower protective layer 32 is n = 2.1, k = 0.0, the recording layer In the amorphous state, n = 4.1, k = 1.6, in the crystalline state, n = 3.9, k = 4.2, and the upper protective layer 34 is n = 2.1, k = 0.0. The light absorption layer 35 is n = n ₁ , K = k ₁ The reflective layer 36 is n = n ₂ , K = k ₂ As calculated.
[0099]
Various n ₁ And n ₂ For a combination of k ₁ , K ₂ , D ₁ Was arbitrarily changed, and the maximum value of ΔR in the range of Acry / Aamo ≧ 1.0 was determined. The results are shown in (Table 1). In the following (Table 1), “A” and “B” are expected to have sufficient characteristics as a practical recording medium, and “C” is not sufficient, but density, linear velocity, recording / reproducing method, etc. Depending on the specifications, “D” indicates a material that may be used as a practical recording medium, and “D” indicates a material that is not suitable for practical use. More specifically, “A” indicates a case where there is a configuration in which the maximum value of ΔR satisfying the condition of Acry / Aamo ≧ 1.0 is 15% or more, and “B” indicates the same condition. The case where there is a configuration in which the maximum value of ΔR that satisfies the condition is 10% or more and less than 15% exists, and “C” indicates the case where there is a configuration in which the maximum value of ΔR that satisfies the condition satisfies 5% or more and less than 10%. “D” indicates a case where there is no configuration in which the maximum value of ΔR satisfying the same condition is 5% or more.
[0100]

[0101]
From the results of (Table 1), Δn = n ₁ -N ₂ 2 is preferably 2 or more, more preferably 3 or more.
[0102]
Moreover, when the film thickness of the light absorption layer 35 is too thin, the optical effect of the light absorption layer 35 will become small, and when the film thickness of the light absorption layer 35 is too thick, the optical effect of the reflection layer 36 will become small. For this reason, the film thickness of the light absorption layer 35 needs to be a film thickness that allows appropriate transmission and absorption of incident light. Film thickness d of light absorption layer 35 ₁ Is 0.1λ / (n from the experimental results of Examples and the like described later, where the wavelength of the incident light is λ. ₁ ・ K ₁ ) ≦ d ₁ ≦ 1.0λ / (n ₁ ・ K ₁ ) In the range of 0.2λ / (n ₁ ・ K ₁ ) ≦ d ₁ ≦ 0.8λ / (n ₁ ・ K ₁ ) Was confirmed to be more preferable.
[0103]
In order to obtain sufficient cooling ability, a material having a high thermal conductivity is used for the reflective layer 36, and the mark width is made uniform to reduce jitter. The thermal conductivity of the reflective layer is, for example, preferably 50 W / m · K or more, more preferably 100 W / m · K or more, and more preferably 150 W / m · K or more under a temperature condition in the vicinity of 300K. In order to obtain a sufficient cooling effect, the film thickness d of the reflective layer 36 is ₂ Is a film thickness d of the light absorption layer 35 based on experimental results such as examples described later. ₁ Or more, d ₁ It has been confirmed that 1.5 times or more, more preferably 2 times or more, is more preferable.
[0104]
The optical information recording medium manufacturing method, recording / reproducing method, and recording / reproducing apparatus of the present embodiment may be the same as those of the first embodiment.
[0105]
In the above description, the thickness of the recording layer is set to 10 nm, but the thickness of the recording layer is not necessarily limited to this thickness.
[0106]
(Third embodiment)
In this embodiment, an optical information recording medium in which two or more multilayer films including a recording layer are formed will be described. Here, a description will be given of a form in which two multilayer films (information layers) each including a recording layer are arranged via a separation layer.
[0107]
As shown in FIG. 8, in the optical information recording medium of the present embodiment, the first information layer 42, the separation layer 43, the second information layer 44, and the protective layer 45 are formed in this order on the transparent substrate 41. Yes. Each of the first information layer 42 and the second information layer 43 includes a recording layer. Information is recorded and reproduced on these recording layers by laser light irradiated from the transparent substrate side.
[0108]
The multilayer film described in the above embodiment is applied to the second information layer 44 of this embodiment. The first information layer 42 is preferably a multilayer film including at least a recording layer and a lower protective layer and an upper protective layer disposed on both sides of the recording layer. Each layer and transparent substrate included in these multilayer films can be formed using the materials described in the above embodiment. Note that the first information layer may be a reproduction-only layer that reproduces information stored in advance as a concavo-convex pattern on the surface of the transparent substrate.
[0109]
In addition, in order to record and reproduce information in the second information layer 44, the first information layer 42 preferably transmits at least 30% of the irradiated laser light.
[0110]
The separation layer 43 is preferably a material that is transparent at the wavelength λ of the laser beam and is excellent in heat resistance and adhesiveness. Specifically, an adhesive resin (for example, an ultraviolet curable resin), a double-sided tape, A dielectric film or the like can be used. The thickness of the separation layer 43 is set to 2 μm or more so that the information in the other information layer does not leak when information is recorded / reproduced in either the first information layer 42 or the second information layer 44. It is preferable. On the other hand, the thickness of the separation layer 43 is 100 μm or less so that the sum of the substrate thickness and the first information layer 42 and the second information layer 44 is within the substrate thickness tolerance range in order to focus the laser light on both. It is preferable.
[0111]
The protective layer 45 may be used as a substrate (protective substrate) for forming the second information layer 44. In this case, the transparent substrate 41 on which the first information layer 42 is formed and the protective substrate on which the second information layer 44 is formed are bonded together via the separation layer 43 to manufacture an optical disc. As the material of the protective substrate, the same material as that of the transparent substrate 41 can be used, but it is not necessarily transparent and other materials may be used. Also, the shape of the substrate surface need not be the same as the shape of the transparent substrate surface. For example, the shape of the guide groove forming the groove and the land may be different, and the spiral direction of the guide groove is reversed. Also good. Furthermore, if the guide groove is provided on the surface of the separation layer on the second information layer side by, for example, the 2P method (photo-polymerization method), the surface of the protective substrate may be flat. The protective layer 45 may be a layer formed on the second information layer 44 formed on the transparent substrate. Such a protective layer can be formed by, for example, resin spin coating or pasting a resin plate with an adhesive.
[0112]
An example of the manufacturing method of this embodiment is demonstrated. A first information layer and a second information layer are formed on the surfaces of the transparent substrate and the protective substrate, each having a guide groove, by the sputtering method described above, respectively. Next, an ultraviolet curable resin is applied on the surface of the first information layer or the second information layer to form a separation layer. Further, the transparent substrate and the protective substrate are pressed to face each other so that the first information layer and the second information layer face each other through the separation layer, and the separation layer is cured by irradiating ultraviolet rays.
[0113]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, a following example does not limit this invention.
[0114]
Example 1
As the substrate, a polycarbonate resin having a thickness of 0.6 mm was used. On this substrate, lands and grooves each having a width of 0.6 μm were formed. The groove depth was about 70 nm.
[0115]
On this substrate, ZnS-SiO ₂ (Molecular number ratio ZnS: SiO ₂ = 80: 20) A lower protective layer of about 1200 nm using a target, a Ge-Sb-Te (atomic ratio Ge: Sb: Te = 22: 25: 53) recording layer of various thicknesses using a target, ZnS-SiO ₂ (Molecular number ratio ZnS: SiO ₂ = 80: 20) Sputtering of an upper protective layer with various thicknesses using a target, an intermediate layer of about 40 nm using targets of various materials, and a reflective layer of about 40 nm using targets of various materials The layers were sequentially laminated by the method. Each layer used a sputtering target having a diameter of 10 cm and a thickness of 6 mm, except for the recording layer, in Ar gas, and the recording layers were Ar and N ₂ Gas mixture (total pressure 2 mTorr, N ₂ The film was formed in a gas partial pressure of about 5%.
[0116]
The optical disk thus obtained was overcoated with an ultraviolet curable resin, and then annealed with laser light, whereby the entire surface was initially crystallized to obtain No. 1 to No. 21 optical disks. These were produced by intentionally changing the thickness of the recording layer, the upper protective layer, and the materials of the intermediate layer and the reflective layer in order to investigate the dependency of the cross erase on the material and the film thickness configuration.
[0117]
Table 2 shows the film thickness of the recording layer / upper protective layer and the material of the intermediate layer / reflection layer of each optical disc.
[0118]
Mark edge recording was performed on these optical discs using an optical system with a wavelength of 660 nm and NA of 0.6 at a linear velocity of 6.0 m / s (radius position: about 32 mm, rotation speed: about 1800 rpm), and cross erase was measured. .
[0119]
Specifically, first, a 9.7 MHz 3T signal is recorded in the groove, and this track is reproduced to obtain a 3T signal amplitude A. ₀ Is measured with a spectrum analyzer. Next, an 11T signal of 2.6 MHz is recorded on both lands adjacent to the groove, and the groove is reproduced again to generate a 3T signal amplitude A. ₁ Is measured with a spectrum analyzer. 3A signal amplitude decrease ΔA = A measured in this way ₁ -A ₀ Is used as an index for cross erase evaluation. The same thing is performed by reversing the land and the groove, and the 3T signal amplitude decrease amount ΔA ′ is measured in the same manner.
[0120]
Table 2 lists the superiority or inferiority of each disk according to the value of ΔA. However, as a result of the above measurement, when the measurement track was a groove in any sample, the amount of decrease in the 3T signal amplitude was large (ΔA> ΔA ′), so the determination was made based only on the result (ΔA) in that case. A value of ΔA of less than 1 dB is indicated by “A”, 1 B or more and less than 2 dB is “B”, 2 dB or more and less than 5 dB is “C”, and 5 dB or more is indicated by “D”.
[0121]
Note that the laser modulation waveform when recording a signal is 51.3 ns (power level P) in the case of a 3T signal. ₁ ) In the case of an 11T signal, a pulse train consisting of 9 pulses (power level P) ₁ The first is 51.3 ns, the second and subsequent pulses are all 17.1 ns, and the width between each pulse is also 17.1 ns (power level P _Three ) And immediately after the last pulse, a cooling period of 34.2 ns (power level P _Four ). Power level P at the part where no mark is recorded ₂ Continuous light (unmodulated light).
[0122]
Recording power level P ₁ Is set to 1.5 times the lower limit of the power when the 3T signal is recorded and the C / N ratio exceeds 45 dB, and the power level P ₂ Is the median value of the power range in which the attenuation ratio of the 3T signal amplitude when the 11T signal is overwritten after the 3T signal is recorded and the 11T signal is overwritten, and the power level P _Three And P _Four Was 1 mW, the same as the reproduction power level.
[0123]

[0124]
The thermal conductivity of each material used for the intermediate layer and the reflective layer is temperature-dependent, but the approximate value range can be specified as follows. In descending order of thermal conductivity, Al (the thermal conductivity at 30 to 600 ° C. is about 150 to 250 W / m · k), Cr (50 to 100 W / m · k), Ti (20 to 50 W / m · k) , WSi ₂ (5 to 20 W / m · k), PbTe (1.0 to 3.0 W / m · k), ZnS—SiO ₂ (0.1 to 0.5 W / m · k).
[0125]
According to Table 2, first, when comparing No. 1 to No. 5 optical discs with different recording layer thicknesses, No. 5 has a large cross erase, No. 1 and No. 4 have improved to some extent, and No. In 3 and No. 4, the cross erase was small enough. Accordingly, from the viewpoint of reducing cross erase, the film thickness of the recording layer is required to be 4 nm to 16 nm, and preferably 6 nm to 14 nm.
[0126]
Next, comparing No. 3 and No. 6 to No. 11 optical discs having different upper protective layer thicknesses, it can be seen that the thicker the upper protective layer thickness, the smaller the cross erase. From this, it can be seen that the film thickness of the upper protective layer is preferably 10 nm or more, and more preferably 20 nm or more, from the viewpoint of reducing cross erase.
[0127]
Further, No. 3 and No. 12 to No. 21 optical discs having different materials for the intermediate layer and the reflective layer will be compared. Among these, except for No. 3, No. 12 to No. 14 have small cross erase. All of them use Al having the highest thermal conductivity among the materials used this time as the reflective layer, and the intermediate layer is a material having thermal conductivity between the upper protective layer and the reflective layer. On the other hand, the other No. 15 to No. 21 have large cross erase.
[0128]
No.15 to No.19 all have higher thermal conductivity of the intermediate layer than that of the reflective layer, especially No.17 is the one in which the materials of the No.3 intermediate layer and the reflective layer are interchanged. There was a big difference in terms of erasing. Nos. 20 and 21 have a configuration in which either the intermediate layer or the reflective layer is omitted, but both have large cross erase.
[0129]
From the above, when multiple layers are stacked on the recording layer, cross-erase can be suppressed by adopting a structure that gradually changes from a material with low thermal conductivity to a material with high thermal conductivity in the order from the recording layer. Was confirmed. This is because heat is transferred from the recording layer to the reflective layer through the upper protective layer and the intermediate layer, and the transfer speed is accelerated. This is because the influence on the track is also suppressed.
[0130]
In addition, as shown in FIG. 3, an optical disc having an interface layer of about 10 nm made of Ge, O, and N was formed in contact with the upper and lower sides of the recording layer as shown in FIG. The GeON film uses a Ge target, Ar, N ₂ And O ₂ Films were formed by reactive sputtering in gas. In order to investigate the repetitive characteristics of this optical disc, 3T and 11T signals were alternately recorded 10,000 times or 100,000 times, and the amplitude change of the 3T signal was measured as compared to after 10 times recording.
[0131]
As a result, after recording 10,000 times, both the No. 3 optical disc and the optical disc with the interface layer inserted therein had an amplitude drop of 0.5 dB or less, but after recording 100,000 times, the No. 3 optical disc While the amplitude was reduced by about 3 dB, the optical disc with the interface layer inserted therein still had an amplitude reduction of 0.5 dB or less. From this, it was confirmed that by inserting the interface layer, it is possible to further improve the repeated recording characteristics in addition to the reduction of the cross erase.
[0132]
As a result of analyzing the composition of the recording layer of the optical disk by Auger electron spectroscopy, the proportion of N atoms was about 2.2 atomic%. Here, an optical disk having the same configuration as No. 3 is used for the recording layer deposition. ₂ When a plurality of films were formed by changing the gas partial pressure, the proportion of N atoms in the recording layer was about 0.0, 0.2, 0.8, 4.0, and 7.6 atomic%, respectively, as a result of analysis. It became.
[0133]
In order to examine the repetitive characteristics of these optical discs, 3T and 11T signals were alternately recorded 10,000 times or 100,000 times, and the change in amplitude of the 3T signal compared to after 10 times recording was measured. As a result, after 10,000 recordings, the amplitude drop of each disk was within an error range of 0.5 dB or less, but after 100,000 recordings, the ratio of N atoms in the recording layer was about 0.0 atomic%. However, only about 0.2 atomic% was about 1 dB, and others were about 0.5 dB within the error range. Also, record the 3T signal on these discs and measure the amplitude of the 3T signal, and then store for 100 hours in an environment of 90 ° C. and 80% relative humidity, and then measure the amplitude of the 3T signal to examine the amplitude change. As a result, the disk in which the proportion of N atoms in the recording layer was 7.6 atomic% had an amplitude decrease of 5 dB or more, while that of 4.0 atomic% was about 2 dB, and the others were hardly decreased. . From these results, it is preferable that the ratio of N atoms in the recording layer is 0.0 to 6.0 atom%, more preferably 0.5 to 4.0 atom%, from the viewpoints of repeatability and moisture resistance. confirmed.
[0134]
(Example 2)
As the substrate, a substrate made of polycarbonate resin having a thickness of 0.6 mm, groove and land widths of 0.6 μm, and groove depth of about 70 nm was used. On this substrate, ZnS-SiO ₂ (ZnS: SiO ₂ = 80: 20) Lower protective layer with a film thickness of about 150 nm using a target, recording with a film thickness of about 10 nm using a Ge—Sb—Te (atomic ratio Ge: Sb: Te = 22: 25: 53) target Layer, ZnS-SiO ₂ (Molecular number ratio ZnS: SiO ₂ = 80: 20) Upper protective layer with a thickness of about 30 nm using a target, various materials, for example, a light absorbing layer with various thicknesses using a PbTe (atomic ratio Pb: Te = 50: 50) target, various Using various materials, for example, an Au target, reflective layers having various film thicknesses were sequentially laminated by a sputtering method. In either case, a target having a diameter of 10 cm and a thickness of 6 mm was used, and the recording layer other than the recording layer was in Ar gas. ₂ Mixed gas (N in total pressure of 1 mTorr, N ₂ Sputtering was performed in a gas partial pressure of about 5%.
[0135]
After forming an overcoat layer using an ultraviolet curable resin on the reflective layer of the disk thus obtained, the entire surface was initially crystallized by annealing with a laser beam, and No. 31 to 47 I got a disc. These discs were produced by intentionally changing the materials and film thicknesses of the light absorption layer and the reflective layer in order to investigate the dependency of the recording / reproducing characteristics on the material and the film thickness configuration. The following (Table 3) shows the material and film thickness of the light absorption layer and the reflection layer of each disk.
[0136]
Here, the optical constants (refractive index n, extinction coefficient k) of each layer at a wavelength of 660 nm obtained by actual measurement are as follows: the substrate is n = 1.6, k = 0.0, the lower protective layer and the upper protective layer. ZnS-SiO ₂ N = 2.1, k = 0.0, Ge—Sb—Te as the recording layer is in an amorphous state, n = 4.1, k = 1.6, in a crystalline state, n = 3.9, k = 4.2, PbTe as light absorbing layer and reflecting layer is n = 5.0, k = 3.2, Au is n = 0.3, k = 3.6, Al is n = 1.4, k = 6.4, Pd is n = 2.2, k = 4.4, Cr is n = 3.6, k = 3.4, TiN is n = 2.5, k = 1.2, PdTe is n = 3.2, k = 2.2, Ge ₈₀ Cr ₂₀ N = 4.5, k = 2.5, Ag ₉₈ Pd ₁ Cu ₁ N = 0.3 and k = 4.0. Optical calculation is performed based on this value, and the calculated values of Acry / Aamo and ΔR are also shown in (Table 3).
[0137]
Using these optical systems with a wavelength of 660 nm and a numerical aperture (NA) of 0.6 on these disks, mark edge recording was performed under the conditions of a linear velocity of 6.0 m / s (radius position: about 32 mm, rotation speed: about 1800 rpm), The following measurements were made. First, a 9.7 MHz 3T signal and a 2.6 MHz 11T signal are alternately recorded 11 times on the groove and land, and this track is reproduced with the 3T signal recorded, and its C / N ratio and erasure rate are recorded. Was measured using a spectrum analyzer. Here, the erasure rate is expressed by the amplitude A of the 3T signal. _Three And 11T residual signal amplitude A ₁₁ Difference from (A _Three -A ₁₁ ).
[0138]
A random signal of (8-16) modulation was recorded 11 times, and the jitter was measured using a time interval analyzer. Here, the jitter is a deviation on the time axis between the recording original signal and the reproduction signal, and the sum (σsum) of jitter standard deviations of each signal of 3T to 11T is taken, and this is used as the window width of the signal detection. It is expressed as a value (σsum / T) divided by (T). For example, the jitter of 12.8% or less means that the bit error rate is 10 when the deviation on the time axis is assumed to be a normal distribution. ^-Four It is known that it corresponds to the following.
[0139]
When the signal is recorded, the laser modulation waveform is an nT (n is an integer, 3 ≦ n ≦ 11) signal, and a pulse train (power level P) composed of (n−2) pulses. ₁ The first is 51.3 ns, the second and subsequent pulses are all 17.1 ns, and the width between each pulse is also 17.1 ns (power level P _Three ) And immediately after the last pulse, a cooling period of 34.2 ns (power level P _Four ). In the portion where no mark is recorded, power level P ₂ Of continuous light. Recording power level P ₁ Is set to 1.5 times the lower limit of the power when the 3T signal is recorded and the C / N ratio exceeds 45 dB, and the power level P ₂ Is the power that maximizes the erasure rate, and the power level P _Three And P _Four Was 1 mW, the same as the reproduction power level.
[0140]
The results measured under the above conditions are shown in the above (Table 3). The measurement results in the table are “B”, which is sufficient as a practical recording medium, and “A”, which is particularly excellent, and is insufficient, but the density, linear velocity, recording Depending on the specifications of the reproduction method, etc., those that may be usable are represented as “C”, and those that are not likely to be used are represented as “D”. More specifically, regarding the C / N ratio, “A” corresponds to 53 dB or more, “B” corresponds to 50 dB or more and less than 53 dB, “C” corresponds to 47 dB or more and less than 50 dB, and “D” corresponds to less than 47 dB. Regarding the erasure rate, “A” corresponds to 24 dB or more, “B” corresponds to 20 dB or more and less than 24 dB, “C” corresponds to 16 dB or more and less than 20 dB, and “D” corresponds to less than 16 dB. With respect to jitter, “A” corresponds to less than 8%, “B” corresponds to 8% or more and less than 10%, “C” corresponds to 10% or more and less than 13%, and “D” corresponds to 13% or more.
[0141]

[0142]
Discs No. 31 to No. 38 are discs using PbTe having a large n as a light absorption layer and Au having a small n and a large thermal conductivity as a reflection layer. Discs No. 31 to No. 34 are reflection layers. The disks No. 34 to No. 38 are disks in which the film thickness of the light absorption layer is changed.
[0143]
When comparing disks No. 31 to No. 34, the cooling performance increases as the Au film thickness of the reflective layer increases, so the jitter is good, and the reflective layer thickness is greater than or equal to the thickness of the light absorbing layer. Jitter is 10% or less from around.
[0144]
When comparing disks No. 34 to No. 38, the film thickness of the light absorbing layer is too thin as in disk No. 35, or the film thickness of the light absorbing layer is too thick as in disks No. 37 and No. 38. In the case of a disc, both optical characteristics and evaluation results are worse. On the other hand, in the case of the disks No. 34 and No. 36, since the film thickness of the light absorption layer is appropriate, good values are obtained for the C / N ratio, the erasure rate, and the jitter. Thus, an appropriate film thickness of the light absorption layer is 0.1λ / (n ₁ ・ K ₁ ) Or more 1.0λ / (n ₁ ・ K ₁ ) The following range.
[0145]
Disks No. 39 to No. 47 are disks in which the materials of the light absorption layer and the reflection layer are changed. While disk No. 34 is Δn = 4.7, disk No. 40 (Δn = 1.4), disk No. 41 (Δn = 1.1), disk No. 42 (Δn = 1.9) ), Disc No. 44 (Δn = 1.4), disc No. 45 (Δn = −4.7), etc. have a poor optical characteristic because the value of Δn is smaller than 2, and the C / N ratio and erasure The rate is also low, and of course the jitter is also large. Disc No. 39 (Δn = 2.8), Disc No. 43 (Δn = 3.3), Disc No. 46 (Δn = 2.2), Disc No. 47 (Δn = 2.9), etc. Although Δn is 2 or more and each characteristic is good, it is understood that the smaller the Δn is, the worse the recording / reproduction characteristic is, and Δn is 2.5 or more, and more preferably 3 or more.
[0146]
As for the configuration of the disk No. 34, as shown in FIG. 7, an interface layer 39 having a film thickness of about 5 nm made of a GeON film is formed on the surface of the recording layer 33 on the substrate 31 side and / or on the opposite side of the substrate 31. A disc was made. The GeON film uses a Ge target, Ar, N ₂ And O ₂ Films were formed by reactive sputtering in gas. Measurements similar to those of the disk No. 34 were performed on these disks. As a result, although the C / N ratio of all the disks is the same as that of the disk No. 34, the interface layer 39 (GeON film) is formed only on the substrate 31 side of the recording layer 33, only on the opposite side of the substrate 31, on the substrate 31 side, and For each of the disks provided on the opposite side of the substrate 31, the erasure rate is improved by about 2 dB, about 4 dB, and about 5 dB with respect to the disk No. 34, and a good jitter value of less than 8% is obtained. It was. From this, it became clear that the erasing characteristics of the optical information recording medium of this embodiment are further improved by inserting the interface layer 39.
[0147]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical information recording medium that is small in cross erase and suitable for recording and reproducing high-density information. Further, according to the present invention, it is possible to provide an optical information recording medium capable of recording / reproducing information with a high erasure rate and low jitter even in high-density / high linear velocity overwrite. The present invention also provides an optical information recording medium recording / reproducing method and an optical information recording medium reproducing apparatus suitable for the medium, as well as a method for producing such an optical information recording medium. is there.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view of an embodiment (first embodiment) of an optical information recording medium of the present invention.
FIG. 2 is a partial perspective view of an embodiment of the optical information recording medium of the present invention.
FIG. 3 is a partial cross-sectional view of another embodiment (first embodiment) of the optical information recording medium of the present invention.
FIG. 4 is a diagram showing a configuration of an embodiment of the optical information recording / reproducing apparatus of the present invention.
FIG. 5 is a waveform diagram showing an example of a pulse waveform applied to the recording / reproducing method of the optical information recording medium of the present invention.
FIG. 6 is a partial sectional view of still another embodiment (second embodiment) of the optical information recording medium of the present invention.
FIG. 7 is a partial cross-sectional view of still another embodiment (second embodiment) of the optical information recording medium of the present invention.
FIG. 8 is a partial cross-sectional view of still another embodiment (third embodiment) of the optical information recording medium of the present invention.
[Explanation of symbols]
1,31 Transparent substrate
2, 32 Lower protective layer
3, 33 Recording layer
4, 34 Upper protective layer
5 middle class
35 Light absorption layer
6, 36 Reflective layer
7, 37 Overcoat layer
8 Groove
9 Land
10 Laser light
11 Record mark
12, 39 Interface layer
13 Semiconductor laser
14 Collimating lens
15 Beam splitter
16 λ / 4 wave plate
17 Objective lens
18 Optical disc
19 Voice coil
20 Turntable
21 motor
22 Detector
23 Playback signal
41 Transparent substrate
42 First information layer
43 Separation layer
44 Second information layer
45 Protective layer (protective substrate)

Claims (23)

2 including a transparent substrate and a multilayer film formed on the transparent substrate, wherein the multilayer film is optically detectable by irradiation with a lower protective layer and a light beam in order from the side closer to the transparent substrate. Including a recording layer, an upper protective layer, an intermediate layer, and a reflective layer that reversibly change between states, and the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer is stepwise in order from the layer closest to the recording layer The thickness of the recording layer is 4 nm or more and 16 nm or less, and at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer is further interfaced. An optical information recording medium comprising a layer.   The optical information recording medium according to claim 1, wherein the recording layer has a thickness of 6 nm to 14 nm.   The optical information recording medium according to claim 1, wherein the reflective layer contains at least one selected from Au, Ag, Cu, and Al.   The intermediate layer is at least selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Os, Al, Ga, In, C, Si, Ge, Sn, Pb, Sb and Bi The optical recording information recording medium according to claim 1, comprising one element.   The optical recording information recording medium according to claim 4, wherein the intermediate layer is made of at least one compound selected from oxides, nitrides, carbides, sulfides, fluorides, selenides, and tellurium compounds.   The optical information recording medium according to claim 4, wherein the intermediate layer is made of an interelement compound. The optical information recording medium according to any one of claims 1 to 6 tracks pitch of the transparent substrate is 0.6μm or less.   The optical information recording medium according to claim 1, wherein the interface layer has a thickness of 1 nm to 50 nm and includes at least one selected from Ge, Si, Cr, Ti, and Al. The optical information recording medium according to any one of claims 1-8 film thickness of the upper protective layer is 10nm or more 200nm or less. The recording layer, Ge, optical information recording medium according to any one of claims 1 to 9 including Sb and Te. The optical information recording medium according to claim 10 , wherein the recording layer contains Ge, Sb, and Te as main components, and further contains 6.0 atomic% or less of N. Optical information according to one of claims 1 to 11 at least one layer selected from the upper protective layer and the lower protective layer contains 60 to 100 mol% ZnS and 40 to 0 mol% of SiO ₂ recoding media. The reflectance, which is the ratio at which the light beam is reflected by the recording medium, and the absorption ratio, which is the ratio at which the recording layer is absorbed, are Rcry and Acry, respectively, when the recording layer is in a crystalline phase, and the recording layer is amorphous. as Ramo and Aamo when a phase, reflectance difference (rCry-Ramo) is not less than 5%, and one of the claims 1 to 12 absorptance ratio (Acry / Aamo) is 1.0 or more An optical information recording medium according to claim 1. Including the first information layer, the separation layer, and the second information layer formed in order from the side close to the transparent substrate on the transparent substrate;
The first information layer and the second information layer each include a recording layer that reversibly changes between two different states that are optically detectable by irradiation with a light beam,
The optical information recording medium, wherein the second information layer is the multilayer film according to any one of claims 1 to 13 . On the transparent substrate, in order from the side close to the transparent substrate, a lower protective layer, a recording layer that reversibly changes between two different states optically detectable by irradiation with a light beam, an upper protective layer, an intermediate layer, and Including a step of forming a multilayer film including a reflective layer, wherein the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer changes stepwise from the layer closest to the recording layer, and the film thickness of the recording layer Is 4 nm or more and 16 nm or less,
A method for producing an optical information recording medium, further comprising an interface layer at at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer. A step of forming a first information layer on a transparent substrate; a step of forming a second information layer on a protective substrate; and bonding the transparent substrate and the protective substrate through a separation layer to thereby form the transparent substrate And forming the first information layer, the separation layer, and the second information layer in this order,
The second information layer includes a lower protective layer, a recording layer that reversibly changes between two different states that can be detected optically by irradiation with a light beam, an upper protective layer, and an intermediate layer from the side close to the transparent substrate. And the reflective layer in this order, the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer change in a stepwise manner from the layer close to the recording layer, and the film thickness of the recording layer is 4 nm or more and 16 nm or less The second information layer is formed on the protective substrate so that
A method for producing an optical information recording medium, further comprising an interface layer at at least one interface between the lower protective layer and the recording layer and between the recording layer and the upper protective layer. The method for producing an optical information recording medium according to claim 15 or 16 , wherein the recording layer is formed at a rate of 200 nm / min or less. The recording layer is formed in an atmosphere containing an inert gas and a nitrogen gas, wherein the content of the nitrogen gas is adjusted so that the recording layer contains 6.0 atom% or less of nitrogen atoms. The method for producing an optical information recording medium according to any one of 15 to 17 . A method for recording and reproducing information by causing a light beam to enter the optical information recording medium according to claim 1 from the transparent substrate side,
The intensity of the light beam is set to a power level P ₁ that can instantaneously melt the irradiated portion, and power levels P ₂ and P ₃ that cannot instantaneously melt the irradiated portion (where P ₁ > P ₂ ≧ P ₃ ≧ 0). ), And the power level P ₀ (where P ₁ > P ₀ > 0) at which the optical state of the recording mark of the recording layer does not change and the reflection sufficient to reproduce the recording mark is obtained by irradiation. sometimes,
At least one recording mark to be recorded on the recording layer is formed by a recording pulse train composed of a group of pulses generated by modulating a light beam between power levels P ₁ and P _3, and no recording mark is formed. In that case the light beam is held at power level P ₂ ,
A recording / reproducing method for an optical information recording medium, wherein information recorded on the recording layer is reproduced by irradiating a light beam having a power level P ₀ . The power level P _{4 (However, P 2> P 4 ≧ 0} ) immediately after the recording pulse train recording and reproducing method of the optical information recording medium according to claim 19 to provide a cooling section of the. 21. The recording / reproducing method for an optical information recording medium according to claim 19, wherein at least a part of the recording pulse train is generated so that a pulse width and an interval between the pulses are substantially the same. 15. The optical information recording medium according to claim 1 , a light beam generating means for generating a light beam irradiated on the optical information recording medium, and a light beam intensity for modulating the intensity of the light beam. Modulation means,
The intensity of the light beam is set to a power level P ₁ that can instantaneously melt the irradiated portion, and power levels P ₂ and P ₃ that cannot instantaneously melt the irradiated portion (where P ₁ > P ₂ ≧ P ₃ ≧ 0). ), And the power level P ₀ (where P ₁ > P ₀ > 0) at which the optical state of the recording mark of the recording layer does not change and the reflection sufficient to reproduce the recording mark is obtained by irradiation. sometimes,
When the light beam intensity modulating means records information by forming a recording mark, the recording is made of a group of pulses generated by modulating the light beam between power levels P ₁ and P _3. the pulse train to form at least one of the recording mark, holding the intensity of the light beam at the power level P ₂ when not forming a recording mark,
When reproducing the information recorded on the recording layer, the optical information recording medium recording / reproducing apparatus is characterized in that the intensity of the light beam is maintained at the power level P ₀ . 2 including a transparent substrate and a multilayer film formed on the transparent substrate, wherein the multilayer film is optically detectable by irradiation with a lower protective layer and a light beam in order from the side closer to the transparent substrate. Including a recording layer, an upper protective layer, an intermediate layer, and a reflective layer that reversibly change between states, and the thermal conductivity of the upper protective layer, the intermediate layer, and the reflective layer is stepwise in order from the layer closest to the recording layer high place, with a film thickness of the recording layer is 4nm or 16nm or less, the
An optical information recording medium, wherein the transparent substrate has a track pitch of 0.6 μm or less.

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