JP3665731B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents
Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は情報処理機器の記録媒体に用いられる情報記録媒体用ガラス基板の製造方法及び情報記録媒体の製造方法に関する。
【0002】
【従来の技術】
情報処理機器の記録媒体としての情報記録媒体の一つとして磁気ディスクがある。磁気ディスクは、基板上に磁性層等の薄膜を形成して構成されたものであり、その基板としてはアルミやガラス基板が用いられてきた。しかし、最近では、高記録密度化の追求に呼応して、アルミと比べて磁気ヘッドと磁気ディスクとの間隔をより狭くすることが可能なガラス基板の占める比率が次第に高くなってきている。また、ガラス基板表面は磁気ヘッドの浮上高さを極力下げることができるように、高精度に研磨して高記録密度化を実現している。
【0003】
上述したように高記録密度化にとって必要な低フライングハイト化のために磁気ディスク表面の高い平滑性は必要不可欠である。磁気ディスク表面の高い平滑性を得るためには、結局、高い平滑性の基板表面が求められるが、もはや、高精度に基板表面を研磨するだけでは、磁気ディスクの高記録密度化を実現できない段階まできている。つまり、いくら、高精度に研磨しても基板上に異物が付着していては高い平滑性は得られない。勿論、従来から異物の除去はなされていたが、従来では許容されていた基板上の異物が、今日の高密度化のレベルでは問題視される状況にある。
【0004】
一方、上述の高い平滑性を有するガラス基板は、酸化セリウムの研磨砥粒を使った精密研磨によって得ている。しかし、酸化セリウム砥粒による研磨工程の後、通常の洗浄では除去できない異物(研磨残り)が残ることで、表面粗さの低減ができないという問題があり、その解決策として、酸化セリウム研磨の後に、硫酸洗浄を行うことが提案されている(特願2000−93304号公報参照)。
【0005】
【発明が解決しようとする課題】
ところが、酸化セリウム研磨の後に、硫酸洗浄行う処理を実施した場合、研磨残りの除去には効果が認められたが、新たな問題が発生することがわかった。すなわち、上記処理をしたガラス基板には、凹欠陥がみられることがわかった。
【0006】
本発明は、上述の背景のもとでなされたものであり、強酸処理で研磨のこりを完全に除去すると同時に、強酸処理による表面粗れの発生を防止して欠陥のない高い平滑性を有する情報記録媒体用ガラス基板を製造可能な情報記録媒体用ガラス基板の製造方法及び情報記録媒体の製造方法を提供することを目的とする。
【0007】
【課題を解決するための手段】
上述の課題を解決するための手段として、第1の手段は、ガラス基板の主表面を研磨砥粒を用いて研磨した後、強酸処理を行う工程を有する磁気ディスク用ガラス基板の製造方法であって、前記ガラス基板は、少なくとも記録層が形成されて磁気ディスクとされるガラス基板であり、前記研磨砥粒として、前記強酸処理の際に用いる処理液成分と反応して、前記ガラス基板表面を浸蝕して凹部を形成する成分を生成する原因物質であって研磨砥粒に含まれる弗素又はリンの含有量が、前記磁気ディスクにおいてヘッドクラッシュまたは記録再生時のエラーの原因となる凹部の発生を防止できる量以下であるものを用いて、ガラス基板の研磨を行うことを特徴とする磁気ディスク用ガラス基板の製造方法である。第2の手段は、前記強酸処理を行う前に前記ガラス基板主表面に付着している研磨砥粒を除去する工程を有することを特徴とする第1の手段にかかる磁気ディスク用ガラス基板の製造方法である。第3の手段は、前記研磨砥粒を除去する工程は、水研磨、テープ研磨、スクラブ洗浄の中から選択される少なくとも1つであることを特徴とする第2の手段にかかる磁気ディスク用ガラス基板の製造方法である。第4の手段は、前記原因物質が弗素であり、その含有量が、5重量%以下であることを特徴とする第1乃至第3の何れか一の手段にかかる磁気ディスク用ガラス基板の製造方法である。第5の手段は、前記研磨砥粒は、酸化セリウムであることを特徴とする第1乃至第4の何れか一の手段にかかる磁気ディスク用ガラス基板の製造方法である。第6の手段は、前記強酸は、酸解離指数pKaが3以下のものであることを特徴とする第1乃至第5の何れか一の手段にかかる磁気ディスク用ガラス基板の製造方法である。第7の手段は、前記強酸は、硫酸であることを特徴とする第1乃至第6の何れかの手段にかかる磁気ディスク用ガラス基板の製造方法である。第8の手段は、前記硫酸の濃度は、30重量%以下(0重量%を除く)とすることを特徴とする第7の手段にかかる磁気ディスク用ガラス基板の製造方法である。第9の手段は、前記ガラス基板の主表面を強酸で処理した後、このガラス基板を強化する化学強化工程を行うことを特徴とする第1乃至第8の何れか一の手段にかかる磁気ディスク用ガラス基板の製造方法である。第10の手段は、第1乃至第9の何れか一の手段にかかる磁気ディスク用ガラス基板の製造方法で製造した磁気ディスク用ガラス基板上に少なくとも記録層を形成することを特徴とする磁気ディスクの製造方法である。
【0008】
上述の手段は、本発明者らの研究の結果はじめて解明された以下の事実に基づいてなされたものである。すなわち、本発明者らは、研磨剤を用いて研磨の後に、硫酸洗浄行う処理を実施した場合、ガラス基板に、凹欠陥による表面の粗れが生ずる現象を徹底的に調査した。その結果、研磨剤の種類によって凹欠陥による表面粗さが大きく左右されることが判明した。すなわち、ある種の研磨剤では凹欠陥の発生が著しく、他のある種の研磨剤では凹欠陥がほとんどみられないことが分かった。
【0009】
そこで、研磨剤の成分組成を微量成分まで詳細に調べた。なお、従来は、研磨剤の成分が問題になることは考えられなかったので、研磨剤の詳細な成分はほとんど不明であった。その結果、凹欠陥を生じさせる研磨剤には、共通して、強酸と反応してガラスを浸蝕する成分を生じさせる原因物質が含まれているという事実が判明した。例えば、一般的な研磨砥粒として知られている酸化セリウム研磨剤のある種のものには、弗素(弗化物)、リン(オキソ酸塩)などが含まれていることが判明した。
【0010】
このため、ガラス基板表面に研磨砥粒が付着した状態で硫酸洗浄を行うと、「弗化物+硫酸→フッ化水素+硫酸塩」又は「リンのオキソ酸塩+硫酸→リン酸+硫酸塩」という反応が起こり、研磨剤が付着した箇所にHF(フッ化水素)又はリン酸によるエッチング作用により、凹欠陥が形成され、表面が粗れるという事実が判明した。本発明は、この新規な解明事実に基づいてなされたものである。
【0011】
すなわち、第1の手段のように、使用する研磨砥粒として、強酸処理の際に用いる処理液成分と反応してガラス基板表面を浸蝕する成分を生成する原因物質の含有量が所定量以下であるものを使用することで、上記のエッチング作用による凹欠陥を阻止することができる。
【0012】
また、使用する研磨砥粒として、強酸処理の際に用いる処理液成分と反応してガラス基板表面を浸蝕する成分を生成する原因物質の含有量が所定量を超える場合には、強酸処理を行う前にガラス基板主表面に付着している研磨砥粒を除去する工程を設けることで、上記エッチング作用による凹欠陥を阻止することができる。
【0013】
ここでいう強酸とは、pKa(酸解離指数)が3以下のものをいい、例えば、塩酸(HCl)、硝酸(HNO3)、過塩素酸(HClO4)、硫酸(H2SO4)、亜塩素酸、塩素酸、臭化水素酸、ヨウ化水素酸、ヨウ素酸、チオシアン酸、アミド硫酸、クロム酸、ホスフィン酸、ホスホン酸、リン酸、二リン酸、トリポリリン酸、亜硫酸、二硫酸、セレン酸、亜セレン酸、ヒ酸、クロロ酢酸、ジクロロ酢酸、トリクロロ酢酸、トリフルオロ酢酸、ピクリン酸、マロン酸、シュウ酸などを指す。強酸処理とは、例えば、ガラス基板の洗浄、表面処理などを行う行為を言う。
【0014】
また、ここでいう所定量以下とは、研磨砥粒に含まれている原因物質が硫酸と反応してガラス基板が局所的にエッチングされないか、又はエッチングされてもグライドテストにおいて磁気ヘッドのクラッシュやヒットがなく、記録再生試験において、再生時の信号が読み取れないというエラーが発生しない範囲をいう。
【0015】
第2第3の手段のように、強酸処理前に、ガラス基板に付着している研磨砥粒を除去するので、研磨砥粒に含まれている弗素(弗化物)、リン(オキソ酸塩)等の原因物質と強酸(例えば、硫酸)とが反応して局所的にガラス基板がエッチングされることを確実に防止することができる。原因物質としては、弗素(F)、リン(P)等がある。
【0017】
研磨砥粒を使用した後のガラス基板に対する研磨砥粒は、強固に付着しているので、通常の洗浄方法(中性洗剤、水、IPA等による超音波洗浄)では取り除くことが難かしく、例えば、第4の手段にあるように、水研磨(研磨砥粒の濃度が0)、テープ研磨、スクラブ洗浄など機械的な作用によって研磨砥粒を除去する。これにより、強酸と研磨砥粒とが出会うことがなくなるので、凹欠陥の発生を確実に阻止することができる。
【0018】
ガラス基板に対してエッチング作用を有するものとしては、フッ化水素、リン酸、アルカリなどが挙げられる。フッ化水素、アルカリは、ガラス成分のSiーO、AlーO、BーO、P−Oのガラス網目形成酸化物を切る働きがあり、リン酸はリンの酸化物を含むガラスにおいてはガラス成分のP−Oのガラス網目形成酸化物を切る働きがある。
【0019】
酸化セリウム等研磨砥粒には、通常、5重量%を超える弗素が0.1重量%を超えるリンが含有されている。研磨工程の後、強酸処理を行う場合は、研磨砥粒に含まれるこのごく少量の弗素やリンでも強酸と反応することで、ガラス基板に対してつよいエッチングする作用を持つフッ化水素(HF)やリン酸が生成することになるので、局所的に研磨剤が残留した箇所でガラス基板がエッチングされる。
【0020】
上述のような理由から、研磨砥粒に含まれる弗素の含有量は、5重量%以下であることが望ましい。凹欠陥を防止するには、好ましくは、3重量%未満、さらに好ましくは弗素が含まれていない研磨砥粒を使用することが望ましい。但し、その場合、製造コスト等を考えると実用上、研磨砥粒に含まれる弗素の含有量は、1〜3重量%程度が好ましい。また、ガラス成分に、リンの酸化物が含まれる場合においては、上述の理由から、研磨砥粒に含まれるリンの含有量は0.1重量%以下であることが望ましい。
【0021】
ガラス基板の研磨工程で使用する研磨砥粒としては、酸化セリウム、酸化ジルコニウム、酸化アルミニウム、酸化マンガン、コロイダルシリカ等が挙げられる。中でも、研磨砥粒として酸化セリウムを使用する場合は、本発明の効果が顕著に表れる。
【0022】
また、第7の手段にあるように、強酸の中でも硫酸の場合、ガラス基板が腐食することがなく、研磨剤や異物の洗浄には適しているので好ましい。また、第8の手段にあるように、硫酸洗浄に使用する硫酸の濃度は、30重量%以下が好ましい。30重量%を超えると、弗素やリンと硫酸とが反応する確率が高くなり、凹欠陥の発生率が高くなるので好ましくない。硫酸の温度条件は、40℃以上沸点以下、好ましくは60℃以上120℃以下である。硫酸の温度が高くなるに従い洗浄効果が向上する。さらに好ましくは、15重量%以下が好ましい。
【0023】
強酸処理(特に、硫酸洗浄)する工程は、情報記録媒体用ガラス基板の製造工程中、特に、表面粗さRaを1.0nm以下に粗さを低減させることを目的とする主表面の精密研磨工程後に行うことが好ましい。これは、後述するように、精密研磨工程で使用する酸化セリウム等が研磨残り等の原因となりやすいからである。なお、硫酸洗浄する工程は、精密研磨工程以外の研磨工程の後に行っても研磨残り等の除去に効果がある。
【0024】
化学強化工程を伴う場合にあっては、強酸処理(特に、硫酸洗浄)する工程は、主表面の精密研磨工程後であって化学強化工程の前に行うことが好ましい。これは、硫酸洗浄によって精密研磨工程における研磨残り(突起)を溶解して除去することができるからである。研磨残りがガラス基板上に付着した状態で化学強化を行うと、化学強化処理液に化学強化に不必要な異物が混入されることになり、化学強化の際にガラス基板に異物が付着することにより膜下欠陥となる。化学強化工程後に精密研磨を行う場合にあっては、この化学強化工程後の精密研磨の後においても硫酸洗浄することが好ましい。
【0025】
上述の手段においては、硫酸洗浄を行う前に、アルカリによる前洗浄を行うことが好ましい。アルカリによる前洗浄を行うことにより、研磨工程で使用しガラス基板に付着した研磨剤を分散させ、緩やかなエッチング効果により研磨剤を効率的に除去することができる。アルカリ洗浄に使用する洗浄液としては、水酸化ナトリウム、水酸化カリウム、アンモニア等のアルカリ性を示す水溶液であれ
ば使用可能である。
【0026】
上述の手段において、ガラス基板の種類、サイズ、厚さ等は特に制限されない。ガラス基板の材質としては、例えば、アルミノシリケートガラス、ソーダライムガラス、ソーダアルミノ珪酸ガラス、アルミノボロシリケートガラス、ボロシリケートガラス、石英ガラス、チェーンシリケートガラス、又は、結晶化ガラス等のガラスセラミックなどが挙げられる。
【0027】
中でも硫酸に対して比較的耐性の強く、化学強化のしやすさなどから、アルミノシリケートガラスが良い。その中でも、アルミノシリケートガラスとしては、SiO2:58〜75重量%、Al2O3:5〜23重量%、Li2O:3〜10重量%、Na2O:4〜13重量%を主成分として含有する化学強化用ガラスや、TiO2:5〜30モル%、CaO:1〜45モル%、MgO+CaO:10〜45モル%、Na2O+Li2O:3〜30モル%、Al2O3:0〜15モル%、SiO2:35〜60モル%を含有する化学強化用ガラス等が好ましい。
【0028】
このような組成のアルミノシリケートガラス等は、珪フッ酸を用いた洗浄(エッチング作用あり)により異物の除去が可能であるが、この洗浄(エッチング作用)によりガラスの表面粗さが粗くなるので、このようなガラスに対して本発明の硫酸洗浄は適している。また、上記のような組成のアルミノシリケートガラス等は、化学強化することによって、抗折強度が増加し、圧縮応力層の深さも深く、ヌープ硬度にも優れる。
【0029】
上述の手段において、耐衝撃性や耐振動性等の向上を目的として、ガラス基板の表面に低温イオン交換法による化学強化処理を施すことがある。ここで、化学強化方法としては、従来より公知の化学強化法であれば特に制限されないが、例えば、ガラス転移点の観点から転移温度を超えない領域でイオン交換を行う低温型化学強化などが好ましい。化学強化に用いるアルカリ溶融塩としては、硝酸カリウム、硝酸ナトリウム、あるいは、それらを混合した硝酸塩などが挙げられる。化学強化する際のガラス基板の保持手段としては、種々の形態が考えられるが、要は、ガラス基板に化学強化処理液が所定の状態で接触することが可能であり、液ダレを起こさないものが好ましい。
【0030】
上述の手段にかかる情報記録媒体用ガラス基板は、磁気記録媒体用のガラス基板、光磁気ディスク用のガラス基板、光ディスクなどの電子光学用ディスク基板として利用できる。特に、磁気抵抗型ヘッド(巨大磁気抵抗型ヘッドも含む)で記録再生する磁気抵抗型ヘッド用の磁気ディスク基板として好適に利用できる。
【0031】
また、上述の手段にかかる情報記録媒体の製造方法においては、特に、磁気記録媒体の場合、ヘッドクラッシュや記録再生時のエラーの原因となる凹部の発生を防止できるので、ガラス基板上に磁性層等を形成した磁気記録媒体を高歩留まりで製造することができる。
【0032】
磁気記録媒体は、通常、所定の平坦度、表面粗さを有し、必要に応じ表面の化学強化処理を施した磁気ディスク用ガラス基板上に、下地層、磁性層、保護層、潤滑層を順次積層して製造する。
【0033】
磁気記録媒体における下地層は、磁性層に応じて選択される。下地層としては、例えば、Cr、Mo、Ta、Ti、W、V、B、Alなどの非磁性金属から選ばれる少なくとも一種以上の材料からなる下地層等が挙げられる。Coを主成分とする磁性層の場合には、磁気特性向上等の観点からCr単体やCr合金であることが好ましい。また、下地層は単層とは限らず、同一又は異種の層を積層した複数層構造とすることもできる。例えば、Cr/Cr、Cr/CrMo、Cr/CrV、CrV/CrV、NiAl/Cr、NiAl/CrMo、NiAl/CrV等の多層下地層等が挙げられる。
【0034】
磁気記録媒体における磁性層の材料は特に制限されない。磁性層としては、例えば、Coを主成分とするCoPt、CoCr、CoNi、CoNiCr、CoCrTa、CoPtCr、CoNiPtや、CoNiCrPt、CoNiCrTa、CoCrPtTa、CoCrPtB、CoCrPtSiOなどの磁性薄膜が挙げられる。磁性層は、磁性膜を非磁性膜(例えば、Cr、CrMo、CrVなど)で分割してノイズの低減を図った多層構成(例えば、CoPtCr/CrMo/CoPtCr、CoCrPtTa/CrMo/CoCrPtTaなど)としても良い。
【0035】
磁気抵抗型ヘッド(MRヘッド)又は巨大磁気抵抗型ヘッド(GMRヘッド)対応の磁性層としては、Co系合金に、Y、Si、希土類元素、Hf、Ge、Sn、Znから選択される不純物元素、又はこれらの不純物元素の酸化物を含有させたものなども含まれる。
【0036】
また、磁性層としては、上記の他、フェライト系、鉄−希土類系や、SiO2、BNなどからなる非磁性膜中にFe、Co、FeCo、CoNiPt等の磁性粒子が分散された構造のグラニュラーなどであっても良い。また、磁性層は、面内型、垂直型のいずれの記録形式であっても良い。
【0037】
磁気記録媒体における保護層は特に制限されない。保護層としては、例えば、Cr膜、Cr合金膜、カーボン膜、ジルコニア膜、シリカ膜等が挙げられる。これらの保護膜は、下地層、磁性層等とともにインライン型スパッタ装置で連続して形成できる。また、これらの保護膜は、単層としても良く、あるいは、同一又は異種の膜からなる多層構成としても良い。
【0038】
上述の手段では、上記保護層上に、あるいは上記保護層に替えて、他の保護層を形成しても良い。例えば、上記保護層に替えて、Cr膜の上にテトラアルコキシシランをアルコール系の溶媒で希釈した中に、コロイダルシリカ微粒子を分散して塗布し、さらに焼成して酸化ケイ素(SiO2)膜を形成しても良い。
【0039】
磁気記録媒体における潤滑層は特に制限されない。潤滑層は、例えば、液体潤滑剤であるパーフロロポリエーテルをフレオン系などの溶媒で希釈し、媒体表面にディップ法、スピンコート法、スプレイ法によって塗布し、必要に応じ加熱処理を行って形成する。
【0040】
【発明の実施の形態】
以下、実施例にかかる情報記録媒体用ガラス基板の製造方法及び情報記録媒体用ガラス基板並びに情報記録媒体の製造方法及び情報記録媒体を詳細に説明する。
(実施例1)
この実施例1にかかる情報記録媒体の製造方法は、(1)荒ずり工程、(2)端面鏡面研磨加工工程、(3)砂掛け(ラッピング)工程、(4)第一研磨工程、(5)第二研磨工程、(6)水研磨工程、(7)化学強化工程、(8)磁気ディスク製造工程、を有する。以下、これらの工程を詳細に説明する。
【0041】
(1)荒ずり工程
まず、ダウンドロー法で形成したシートガラスから、研削砥石で直径約100mmφ、厚さ3mmの円盤状に切り出したアルミノシリケートガラスからなるガラス基板を、比較的粗いダイヤモンド砥石で研削加工して、直径約100mmφ、厚さ1.5mmに成形した。この場合、ダウンドロー法の代わりに、溶融ガラスを、上型、下型、胴型を用いてダイレクトプレスして、円盤状のガラス体を得ても良い。また、フロート法で形成しても良い。
【0042】
なお、アルミノシリケートガラスとしては、SiO2:58〜75重量%、Al2O3:5〜23重量%、Li2O:3〜10重量%、Na2O:4〜13重量%を主成分として含有する化学強化用ガラス(ただし、P2O5のようなリンの酸化物を含まないアルミノシリケートガラス)を使用した。
【0043】
次いで、上記砥石よりも粒度の細かいダイヤモンド砥石で上記ガラス基板の両面を片面ずつ研削加工した。このときの荷重は100kg程度とした。これにより、ガラス基板両面の表面粗さをRmax(JISB0601で測定)で10μm程度に仕上げた。
【0044】
次に、円筒状の砥石を用いてガラス基板の中央部分に直径25mmφの孔を開けるとともに、外周端面も研削して直径を95mmφとした後、外周端面及び内周面に所定の面取り加工を施した。このときのガラス基板端面の表面粗さは、Rmaxで4μm程度であった。
【0045】
(2)端面鏡面加工工程
次いで、ブラシ研磨により、ガラス基板を回転させながらガラス基板の端面の表面粗さを、Rmaxで1μm、Raで0.3μm程度に研磨した。上記端面鏡面加工を終えたガラス基板の表面を水洗浄した。
【0046】
(3)砂掛け(ラッピング)工程
次に、ガラス基板に砂掛け加工を施した。この砂掛け工程は、寸法精度及び形状精度の向上を目的としている。砂掛け加工は、ラッピング装置を用いて行い、砥粒の粒度を#400、#1000と替えて2回行った。詳しくは、はじめに、粒度#400のアルミナ砥粒を用い、荷重Lを100kg程度に設定して、内転ギアと外転ギアを回転させることによって、キャリア内に収納したガラス基板の両面を面精度0〜1μm、表面粗さ(Rmax)6μm程度にラッピングした。
【0047】
次いで、アルミナ砥粒の粒度を#1000に替えてラッピングを行い、表面粗さ(Rmax)2μm程度とした。上記砂掛け加工を終えたガラス基板を、中性洗剤、水の各洗浄槽に順次浸漬して、洗浄した。
【0048】
(4)第一研磨工程
次に、第一研磨工程を施した。この第一研磨工程は、上述した砂掛け工程で残留した傷や歪みの除去を目的とするもので、研磨装置を用いて行った。詳しくは、ポリシャ(研磨粉)として硬質ポリシャ(セリウムパッドMHC15:ローデルニッタ社製)を用い、以下の研磨条件で第一研磨工程を実施した。
【0049】
研磨液:酸化セリウム(粒径1.3μm)(遊離砥粒)+水
荷重:300g/cm2(L=238kg)
研磨時間:15分
除去量:30μm
下定盤回転数:40rpm
上定盤回転数:35rpm
内ギア回転数:14rpm
外ギア回転数:29rpm
【0050】
上記第一研磨工程を終えたガラス基板を、中性洗剤、純水、純水、IPA(イソプロピルアルコール)、IPA(蒸気乾燥)の各洗浄槽に順次浸漬して、洗浄した。
【0051】
(5)第二研磨工程
次に、第一研磨工程で使用した研磨装置を用い、ポリシャを硬質ポリシャから軟質ポリシャ(ポリテックス:スピードファム社製)に替えて、第二研磨工程を実施した。この第二研磨工程は、上述した第一研磨工程で得られた平坦な表面を維持しつつ、例えば表面粗さRaが1.0〜0.3nm程度以下の粗さの低減を目的とするものである。研磨条件は、研磨液を酸化セリウム(粒径1.0μm、弗素含有量:6.3重量%、リン含有量:0.2重量%)+水とし、荷重を100g/cm2、研磨時間を5分、除去量を5μmとしたこと以外は、第一研磨工程と同様とした。
【0052】
(6)水研磨工程
次に、研磨液の供給から水に切り替えて2分間水研磨を行った。尚、使用する研磨パッドは、第二研磨工程と同じパッドを使用し、荷重は30g/cm2とした。
【0053】
(7)硫酸洗浄
次に、このガラス基板を温度70℃の硫酸(20重量%)で洗浄した。硫酸洗浄の方法は、洗浄槽に収容された硫酸に複数枚保持されたガラス基板を浸漬して(約3分)行った。このように、次工程の化学強化の前に研磨残りを確実に除去することにより、膜下欠陥を防止できる。特にこの硫酸洗浄を化学強化前に行うことは重要である。つまり、酸化セリウム研磨による研磨残りがガラス基板上に付着した状態で化学強化を行うと、化学強化処理液に化学強化に不必要な異物が混入されることになり、化学強化の際にガラス基板に異物が付着することにより膜下欠陥となる。このような膜下欠陥の発生を上述の硫酸洗浄で防止できる。
【0054】
上記硫酸による洗浄を終えたガラス基板を洗浄する。この洗浄工程は精密洗浄を意味し、ガラス基板に付着した有機成分からなる汚れや、パーティクルなどを除去することを目的とするものである。この洗浄工程からケースへの梱包に至るプロセスは、クリーンブースによって供給された清浄な空気の環境下で実施した。まず、最初の洗浄はガラス基板を、中性洗剤、中性洗剤、純水、純水、IPA(イソプロピルアルコール)、IPA(蒸気乾燥)の各洗浄槽に順次浸漬して、洗浄した。なお、各洗浄槽には超音波を印加した。
【0055】
(7)化学強化工程
次に、洗浄工程を終えたガラス基板に化学強化を施した。化学強化は、化学強化処理液を化学強化処理槽に入れ、保持部材で保持したガラス基板を化学強化処理液に浸漬して行う。なお、ガラス基板の保持部材は、ガラス基板の配列方向に等間隔でV溝を複数個形成した3本の支柱を、その両端面で連結部材で連結して形成されている。複数のガラス基板は、各ガラス基板が3本の支柱の同一平面内にあるV溝によって3点支持されて保持され、支柱の延在する方向に複数枚配列されている。
【0056】
本実施例の保持部材の各支柱と連結部材は化学強化の際必要となる高温域での耐食性に優れたオーステナイト系ステンレス合金であるSUS316で構成している。また、化学強化処理槽は,オーステナイト系ステンレス合金のSUS304で構成している。化学強化処理槽と保持手段の材料は、同種でも異種でも良い。他のステンレス合金としては、例えば、SUS316Lなどが好適である。また、本実施例の化学強化処理液は、フィルターを通して循環しているので、化学強化処理液が清浄に保たれている。
【0057】
化学強化の具体的方法は、硝酸カリウム(60%)と硝酸ナトリウム(40%)を混合した化学強化溶液を用意し、この化学強化溶液を400℃に加熱し、300℃に予熱された洗浄済みのガラス基板を約3時間浸漬して行った。この浸漬の際に、ガラス基板の表面全体が化学強化されるようにするため、複数のガラス基板が端面で保持されるように保持部材で保持して行った。
【0058】
このように、化学強化溶液に浸漬処理することによって、ガラス基板表層のリチウムイオン、ナトリウムイオンは、化学強化溶液中のナトリウムイオン、カリウムイオンにそれぞれ置換されガラス基板は強化される。ガラス基板の表層に形成された圧縮応力層の厚さは、約100〜200μmであった。
【0059】
上記化学強化を終えたガラス基板を、20℃の水槽に浸漬して急冷し約10分間維持した。これにより、微小クラックが入った不良品を除去できる。さらに化学強化を終えたガラス基板を、硫酸洗浄、中性洗剤、純水、IPA、IPA(蒸気乾燥)の洗浄・乾燥工程を行った。尚、これらの洗浄工程は、超音波を印加した超音波洗浄である。
【0060】
上記の工程を経て得られたガラス基板の主表面の表面粗さを原子間力顕微鏡(AFM)で測定したところ、Rmaxで6.5〜9.3nm、Raで0.6〜0.9nmであった。さらに、ガラス表面を精密検査したところ凹部の欠陥は観察されなかった(100枚観察して凹部欠陥が観察されたものが0枚)。
【0061】
(8)磁気ディスク製造工程
上述した工程を経て得られた磁気ディスク用ガラス基板の両面に、インライン型スパッタリング装置を用いて、NiAlのシード層、CrMo下地層、CoCrPtTa磁性層、水素化カーボン保護層を順次成膜し、ディップ法によりパーフルオロポリエーテル潤滑層を成膜して磁気ディスクを得た。
【0062】
得られた磁気ディスクについてグライドテストを実施したところ、ヒット(ヘッドが磁気ディスク表面の突起にかすること)やクラッシュ(ヘッドが磁気ディスク表面の突起に衝突すること)は認められなかった。(100枚中100枚OK)また、記録再生試験において、再生時の信号が読み取れなくなるというエラーも生じなかった(100枚中100枚OK)。
【0063】
(実施例2〜3)
また、上述の実施例における水研磨の変わりにスクラブ洗浄(条件:界面活性剤を用い、ローラー使用の枚葉式洗浄機にて洗浄)(実施例2)、テープ式テクスチャー装置を用いてテープ研磨(条件:ナイロン系テープを使用し、ダイヤモンド砥粒を供給しながら、回転した基板基板にテープを押し付ける枚葉式テープ式テクスチャー装置にて研磨(実施例3)を実施した他は、実施例と同様にして、ガラス基板を作製した。
【0064】
得られたガラス基板の主表面の表面粗さを原子間力顕微鏡(AFM)で測定したところ、上記実施例2では、Rmaxで6.6〜8.9nm、Raで0.6〜0.9nmであり、実施例3では、Rmaxで6.4〜9.2nm、Raで0.6〜0.8nmであった。また、ガラス基板表面を精密検査したところ、凹部の欠陥は観察されなかった(100枚観察して凹部欠陥が観察されたものが0枚)。
【0065】
得られた磁気ディスクについてグライドテストを実施したところ、ヒット(ヘッドが磁気ディスク表面の突起にかすること)やクラッシュ(ヘッドが磁気ディスク表面の突起に衝突すること)は認められなかった。(100枚中100枚OK)また、記録再生試験において、再生時の信号が読み取れなくなるというエラーも生じなかった(100枚中100枚OK)。
【0066】
(実施例4、5)
さらに、上記実施例の第二研磨工程で使用した酸化セリウム研磨砥粒を、高純度酸化セリウム(弗素含有量=0重量%)に変えたほかは、実施例2(スクラブ洗浄)と同様にして、ガラス基板を作製した(実施例4)。また、第二研磨工程で使用する研磨砥粒を高純度酸化セリウム(弗素含有量:0重量%)とし、強酸(硫酸)洗浄前にスクラブ洗浄を行わなかったこと以外は同様にしてガラス基板を作製した(実施例5)。
【0067】
得られたガラス基板の主表面の表面粗さを原子間力顕微鏡(AFM)で測定したところ、研磨速度が若干低下したものの実施例4、5ともに、Rmaxで5.3〜7.5nm、Raで0.5〜0.8nmであり、実施例2で得られたガラス基板の表面粗さよりも小さい結果となった。また、ガラス基板表面を精密検査したところ、凹部の欠陥は観察されなかった(100枚観察して凹部欠陥が観察されたものが0枚)。なお、実施例5に比べ、実施例4のように、強酸処理前にガラス基板の研磨剤の付着を強制的に除去する工程を入れた場合のほうが、洗浄性(洗浄時間や洗浄能力)が向上し、研磨剤残りも確実に防止することができる。
【0068】
得られた磁気ディスクについてグライドテストを実施したところ、ヒット(ヘッドが磁気ディスク表面の突起にかすること)やクラッシュ(ヘッドが磁気ディスク表面の突起に衝突すること)は認められなかった(100枚中100枚OK)。また、記録再生試験において、再生時の信号が読み取れなくなるというエラーも生じなかった(100枚中100枚OK)。
【0069】
(比較例1)
次に比較のために、硫酸洗浄前に水研磨を行わなかったこと、硫酸の洗浄条件を95℃、96重量%の濃硫酸を使用したこと以外は実施例1と同様にして、ガラス基板を作製した。得られたガラス基板の主表面の表面粗さを原子間力顕微鏡(AFM)で測定したところ、Rmaxで8.1〜11.3nm、Raで0.6〜0.9nmであった。また、ガラス基板表面を精密検査したところ、大きさが、数μm〜数mm程度で、深さ6〜10nm程度の凹部の欠陥が観察された(100枚中37枚)。
【0070】
次に、実施例1と同様の膜構成を有する磁気ディスクを作製し、グライドテスト及び記録再生試験を実施したところ、ヘッドの浮上不安定と思われるクラッシュが100枚中17枚、再生時の信号が読み取れなくなるというエラーが、100枚中19枚確認された。
【0071】
(実施例6)
実施例1で使用したアルミノシリケートガラスの代わりに、結晶化ガラスを用いたこと以外は実施例1と同様にして、ガラス基板及び磁気ディスクを作製した。なお、本実施例で使用した結晶化ガラスは、SiO2:65〜83重量%、Li2O:8〜13重量%、Al2O3:0〜7重量%、K2O:0〜7重量%、MgO:0.5〜3.5重量%、ZnO:0〜5重量%、P2O5:1〜4重量%、PbO:0〜5重量%の組成範囲のものを使用した。その結果、ガラス基板において実施例1と同様の表面粗さが得られ、ヘッドクラッシュを引き起こす、又は記録再生エラーを引き起こす凹部は観察されなかった。また、磁気ディスクについてのグライドテスト及び磁気抵抗型ヘッドによる再生試験においても、ヘッドクラッシュや、再生時のエラーは認められなかった。
【0072】
(比較例2)
次に、比較のために実施例6で用いた結晶化ガラスを用い、硫酸洗浄前に水研磨を行わなかったことと、硫酸の洗浄条件を95℃、96重量%の濃硫酸を使用したこと以外は実施例6と同様にしてガラス基板及び磁気ディスクを作製した。その結果、研磨剤に含まれる弗素やリンと硫酸との反応による凹部の欠陥が観察され、グライドテスト、記録再生試験でもクラッシュや再生時のエラーが確認された。
【0073】
【発明の効果】
以上説明したように本発明は、ガラス基板の主表面を研磨砥粒を用いて研磨した後、強酸処理を行う工程を有する磁気ディスク用ガラス基板の製造方法であって、前記研磨砥粒として、前記強酸処理の際に用いる処理液成分と反応して、前記ガラス基板表面を浸蝕する成分を生成する原因物質の含有量が所定量以下であるものを用いることを特徴とするもので、これにより、強酸処理で研磨のこりを完全に除去すると同時に、強酸処理による表面粗れの発生を防止して欠陥のない高い平滑性を有する磁気ディスク用ガラス基板を製造可能な磁気ディスク用ガラス基板の製造方法及び磁気ディスクの製造方法を提供することを可能にしているものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a glass substrate for an information recording medium used for a recording medium of information processing equipment, and a method for manufacturing an information recording medium.
[0002]
[Prior art]
One of information recording media as recording media for information processing equipment is a magnetic disk. A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum or glass substrate has been used as the substrate. However, recently, in response to the pursuit of higher recording density, the proportion of the glass substrate that can narrow the gap between the magnetic head and the magnetic disk as compared with aluminum is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible.
[0003]
As described above, high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height required for increasing the recording density. In order to obtain a high smoothness on the surface of the magnetic disk, a substrate surface with a high smoothness is ultimately required. However, it is no longer possible to achieve a high recording density of the magnetic disk by simply polishing the substrate surface with high precision. Well done. In other words, no matter how much the polishing is performed, if the foreign matter adheres to the substrate, high smoothness cannot be obtained. Needless to say, foreign substances have been removed from the past, but foreign substances on the substrate, which have been allowed in the past, are regarded as a problem at the level of high density today.
[0004]
On the other hand, the above-described glass substrate having high smoothness is obtained by precision polishing using cerium oxide abrasive grains. However, after the polishing process with cerium oxide abrasive grains, there is a problem that foreign matter (polishing residue) that cannot be removed by ordinary cleaning remains, so that the surface roughness cannot be reduced. It has been proposed to perform sulfuric acid cleaning (see Japanese Patent Application No. 2000-93304).
[0005]
[Problems to be solved by the invention]
However, it has been found that when a treatment for washing with sulfuric acid is performed after cerium oxide polishing, an effect has been recognized in removing the polishing residue, but a new problem occurs. That is, it was found that the glass substrate subjected to the above treatment has a concave defect.
[0006]
The present invention has been made under the above-mentioned background, and at the same time, the polishing residue is completely removed by the strong acid treatment, and at the same time, the occurrence of surface roughness due to the strong acid treatment is prevented and the information has high smoothness without defects. It is an object of the present invention to provide a method for producing a glass substrate for information recording medium and a method for producing an information recording medium capable of producing a glass substrate for recording medium.
[0007]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the first means includes a step of performing a strong acid treatment after polishing the main surface of the glass substrate using polishing abrasive grains. Glass substrate for magnetic disk A manufacturing method of The glass substrate is a glass substrate in which at least a recording layer is formed to be a magnetic disk, As the abrasive grains, the surface of the glass substrate is eroded by reacting with a treatment liquid component used in the strong acid treatment. The content of fluorine or phosphorus contained in the abrasive grains, which is a causative substance that generates a component that forms a recess, can prevent the occurrence of a recess that causes a head crash or an error during recording / reproduction in the magnetic disk. Glass substrate for magnetic disk, characterized by polishing glass substrate using less It is a manufacturing method. 2nd means has the process of removing the abrasive grain adhering to the said glass substrate main surface, before performing the said strong acid process, It concerns on 1st means characterized by the above-mentioned Glass substrate for magnetic disk It is a manufacturing method. The third means is The method for producing a glass substrate for a magnetic disk according to the second means is characterized in that the step of removing the abrasive grains is at least one selected from water polishing, tape polishing, and scrub cleaning. . A fourth means is the production of a glass substrate for a magnetic disk according to any one of the first to third means, wherein the causative substance is fluorine and the content thereof is 5% by weight or less. Is the method. A fifth means is a method for producing a glass substrate for a magnetic disk according to any one of the first to fourth means, wherein the abrasive grains are cerium oxide. The sixth means is The strong acid is a method for producing a glass substrate for a magnetic disk according to any one of the first to fifth means, wherein the acid dissociation index pKa is 3 or less. A seventh means is according to any one of the first to sixth means, wherein the strong acid is sulfuric acid. Glass substrate for magnetic disk It is a manufacturing method. The eighth means is that the concentration of sulfuric acid is 30% by weight or less. (Excluding 0% by weight) According to the seventh means characterized in that Glass substrate for magnetic disk It is a manufacturing method. According to a ninth means, according to any one of the first to eighth means, the main surface of the glass substrate is treated with a strong acid, and then a chemical strengthening step for strengthening the glass substrate is performed. Glass substrate for magnetic disk It is a manufacturing method. The tenth means is related to any one of the first to ninth means. Glass substrate for magnetic disk At least a recording layer is formed on a glass substrate for a magnetic disk manufactured by the manufacturing method of Magnetic disk It is a manufacturing method.
[0008]
The above-mentioned means has been made on the basis of the following facts that have been elucidated for the first time as a result of the study by the present inventors. That is, the present inventors have thoroughly investigated a phenomenon in which surface roughness due to a concave defect occurs in a glass substrate when a treatment for washing with sulfuric acid is performed after polishing with an abrasive. As a result, it was found that the surface roughness due to the concave defect is greatly influenced by the type of the abrasive. In other words, it was found that concave defects were remarkably generated with certain types of abrasives and almost no concave defects were observed with other types of abrasives.
[0009]
Therefore, the component composition of the abrasive was examined in detail up to a trace component. Heretofore, since it has not been considered that the components of the abrasive are problematic, the detailed components of the abrasive are almost unknown. As a result, it has been found that the abrasives that generate the concave defects commonly include a causative substance that generates a component that reacts with the strong acid to erode the glass. For example, it has been found that certain types of cerium oxide abrasives known as general abrasive grains contain fluorine (fluoride), phosphorus (oxoacid salt) and the like.
[0010]
For this reason, when sulfuric acid cleaning is performed with the abrasive grains adhering to the glass substrate surface, “fluoride + sulfuric acid → hydrogen fluoride + sulfate” or “phosphorous oxoacid salt + sulfuric acid → phosphoric acid + sulfate” It has been found that a concave defect is formed and the surface is roughened by an etching action of HF (hydrogen fluoride) or phosphoric acid at a place where the abrasive is attached. The present invention has been made on the basis of this new fact of elucidation.
[0011]
That is, as in the first means, the content of the causative substance that generates a component that erodes the glass substrate surface by reacting with the treatment liquid component used in the strong acid treatment as the abrasive grain to be used is a predetermined amount or less. By using a certain thing, the concave defect by said etching effect | action can be blocked | prevented.
[0012]
Also, If the content of the causative substance that generates a component that erodes the glass substrate surface by reacting with the treatment liquid component used in the strong acid treatment as the polishing abrasive to be used exceeds a predetermined amount, before performing the strong acid treatment By providing the step of removing the abrasive grains adhering to the main surface of the glass substrate, the concave defect due to the etching action can be prevented.
[0013]
The strong acid here means one having a pKa (acid dissociation index) of 3 or less, for example, hydrochloric acid (HCl), nitric acid (HNO Three ), Perchloric acid (HClO Four ), Sulfuric acid (H 2 SO Four ), Chlorous acid, chloric acid, hydrobromic acid, hydroiodic acid, iodic acid, thiocyanic acid, amidosulfuric acid, chromic acid, phosphinic acid, phosphonic acid, phosphoric acid, diphosphoric acid, tripolyphosphoric acid, sulfurous acid, two It refers to sulfuric acid, selenic acid, selenious acid, arsenic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, picric acid, malonic acid, oxalic acid and the like. The strong acid treatment refers to, for example, an action of cleaning a glass substrate, surface treatment, and the like.
[0014]
Further, the predetermined amount or less here means that the causative substance contained in the abrasive grains reacts with sulfuric acid and the glass substrate is not locally etched, or even if it is etched, the magnetic head crashes in the glide test. A range in which there is no hit and no error occurs in the recording / reproduction test that the signal at the time of reproduction cannot be read.
[0015]
Like the second and third means, the abrasive grains adhering to the glass substrate are removed before the strong acid treatment, so that fluorine (fluoride) and phosphorus (oxo acid salt) contained in the abrasive grains are removed. It is possible to reliably prevent the glass substrate from being locally etched due to the reaction of the causative substance such as the above and a strong acid (for example, sulfuric acid). Causative substances include fluorine (F) and phosphorus (P).
[0017]
Since the abrasive grains on the glass substrate after using the abrasive grains are firmly attached, it is difficult to remove them by a normal cleaning method (ultrasonic cleaning with neutral detergent, water, IPA, etc.). As in the fourth means, the abrasive grains are removed by mechanical action such as water polishing (polishing abrasive concentration is 0), tape polishing, scrub cleaning. As a result, the strong acid and the abrasive grains do not meet each other, so that the generation of the concave defect can be reliably prevented.
[0018]
Examples of those having an etching action on the glass substrate include hydrogen fluoride, phosphoric acid, and alkali. Hydrogen fluoride and alkali have a function to cut glass network-forming oxides of glass components Si—O, Al—O, B—O, and P—O, and phosphoric acid is glass in a glass containing an oxide of phosphorus. It serves to cut the glass network forming oxide of the component PO.
[0019]
Abrasive grains such as cerium oxide usually contain more than 5% by weight of fluorine and more than 0.1% by weight of phosphorus. When a strong acid treatment is performed after the polishing process, even a very small amount of fluorine or phosphorus contained in the polishing abrasive grains reacts with the strong acid, so that hydrogen fluoride (HF) has a function of performing a strong etching on the glass substrate. Since phosphoric acid is generated, the glass substrate is etched at locations where the abrasive remains locally.
[0020]
For the reasons described above, the fluorine content contained in the abrasive grains is preferably 5% by weight or less. In order to prevent concave defects, it is preferable to use abrasive grains that are preferably less than 3% by weight, more preferably fluorine-free. However, in that case, considering the manufacturing cost, the content of fluorine contained in the abrasive grains is preferably about 1 to 3% by weight in practice. In addition, when the glass component contains an oxide of phosphorus, the content of phosphorus contained in the abrasive grains is preferably 0.1% by weight or less for the reasons described above.
[0021]
Examples of the abrasive grains used in the glass substrate polishing step include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, and colloidal silica. Among these, when cerium oxide is used as the abrasive grains, the effects of the present invention are remarkably exhibited.
[0022]
Further, as described in the seventh means, sulfuric acid among strong acids is preferable because the glass substrate does not corrode and is suitable for cleaning abrasives and foreign matters. As in the eighth means, the concentration of sulfuric acid used for sulfuric acid cleaning is preferably 30% by weight or less. If it exceeds 30% by weight, the probability that fluorine, phosphorus and sulfuric acid react with each other increases, and the incidence of concave defects increases, which is not preferable. The temperature condition of sulfuric acid is 40 ° C. or higher and boiling point or lower, preferably 60 ° C. or higher and 120 ° C. or lower. The cleaning effect improves as the temperature of the sulfuric acid increases. More preferably, it is 15% by weight or less.
[0023]
The process of strong acid treatment (especially sulfuric acid cleaning) is a precision polishing of the main surface during the manufacturing process of a glass substrate for information recording media, particularly for the purpose of reducing the roughness to a surface roughness Ra of 1.0 nm or less. It is preferable to carry out after the process. This is because, as will be described later, cerium oxide or the like used in the precision polishing step tends to cause polishing residue and the like. In addition, even if it performs after the grinding | polishing processes other than a precision grinding | polishing process, the process wash | cleaned with sulfuric acid is effective in removal of grinding | polishing residue etc.
[0024]
When a chemical strengthening step is involved, it is preferable that the strong acid treatment (particularly, sulfuric acid cleaning) is performed after the main surface precision polishing step and before the chemical strengthening step. This is because the polishing residue (protrusions) in the precision polishing step can be dissolved and removed by washing with sulfuric acid. If chemical strengthening is performed with the polishing residue adhering to the glass substrate, foreign substances unnecessary for chemical strengthening are mixed in the chemical strengthening treatment solution, and foreign substances adhere to the glass substrate during chemical strengthening. Due to this, it becomes a subfilm defect. When precision polishing is performed after the chemical strengthening step, it is preferable to wash with sulfuric acid even after the precision polishing after the chemical strengthening step.
[0025]
In the above-mentioned means, it is preferable to perform pre-cleaning with alkali before performing sulfuric acid cleaning. By performing pre-cleaning with an alkali, the abrasive used in the polishing process and adhered to the glass substrate can be dispersed, and the abrasive can be efficiently removed by a gentle etching effect. The cleaning solution used for alkali cleaning may be an aqueous solution showing alkalinity such as sodium hydroxide, potassium hydroxide, ammonia, etc.
Can be used.
[0026]
In the above-described means, the type, size, thickness and the like of the glass substrate are not particularly limited. Examples of the material of the glass substrate include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or glass ceramic such as crystallized glass. It is done.
[0027]
Of these, aluminosilicate glass is preferable because of its relatively strong resistance to sulfuric acid and ease of chemical strengthening. Among these, as aluminosilicate glass, SiO 2 : 58 to 75% by weight, Al 2 O Three : 5 to 23% by weight, Li 2 O: 3 to 10% by weight, Na 2 O: Glass for chemical strengthening containing 4 to 13% by weight as a main component, TiO 2 : 5-30 mol%, CaO: 1-45 mol%, MgO + CaO: 10-45 mol%, Na 2 O + Li 2 O: 3 to 30 mol%, Al 2 O Three : 0 to 15 mol%, SiO 2 : The glass for chemical strengthening containing 35-60 mol% is preferable.
[0028]
The aluminosilicate glass having such a composition can remove foreign substances by cleaning with silicic acid (with etching action), but the surface roughness of the glass becomes rough by this cleaning (etching action). The sulfuric acid cleaning of the present invention is suitable for such glass. Further, the aluminosilicate glass having the above composition is chemically strengthened to increase the bending strength, the depth of the compressive stress layer, and the Knoop hardness.
[0029]
In the above-described means, the surface of the glass substrate may be subjected to a chemical strengthening process by a low temperature ion exchange method for the purpose of improving impact resistance, vibration resistance, and the like. Here, the chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. For example, low-temperature chemical strengthening in which ion exchange is performed in a region not exceeding the transition temperature from the viewpoint of the glass transition point is preferable. . Examples of the alkali molten salt used for chemical strengthening include potassium nitrate, sodium nitrate, and nitrates obtained by mixing them. Various means can be considered as the means for holding the glass substrate during chemical strengthening, but the point is that the chemical strengthening treatment liquid can contact the glass substrate in a predetermined state and does not cause dripping. Is preferred.
[0030]
The glass substrate for an information recording medium according to the above means can be used as a glass substrate for a magnetic recording medium, a glass substrate for a magneto-optical disk, an electro-optical disk substrate such as an optical disk. In particular, it can be suitably used as a magnetic disk substrate for a magnetoresistive head for recording / reproducing with a magnetoresistive head (including a giant magnetoresistive head).
[0031]
Further, in the method of manufacturing the information recording medium according to the above-mentioned means, particularly in the case of a magnetic recording medium, it is possible to prevent the occurrence of a concave portion that causes an error at the time of head crash or recording / reproduction, so that a magnetic layer is formed on the glass substrate. Etc. can be manufactured at a high yield.
[0032]
A magnetic recording medium usually has a predetermined flatness and surface roughness, and an underlayer, a magnetic layer, a protective layer, and a lubricating layer are provided on a glass substrate for a magnetic disk that has been subjected to chemical strengthening treatment on the surface as necessary. Produced by sequentially laminating.
[0033]
The underlayer in the magnetic recording medium is selected according to the magnetic layer. Examples of the underlayer include an underlayer made of at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the base layer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples thereof include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, CrV / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV.
[0034]
The material of the magnetic layer in the magnetic recording medium is not particularly limited. Examples of the magnetic layer include magnetic thin films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic layer may be a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV) to reduce noise. good.
[0035]
As a magnetic layer corresponding to a magnetoresistive head (MR head) or a giant magnetoresistive head (GMR head), a Co-based alloy, an impurity element selected from Y, Si, rare earth elements, Hf, Ge, Sn, and Zn Or those containing oxides of these impurity elements.
[0036]
As the magnetic layer, in addition to the above, ferrite, iron-rare earth, and SiO 2 Further, a granular structure in which magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of BN or the like may be used. Further, the magnetic layer may be either an in-plane type or a vertical type recording format.
[0037]
The protective layer in the magnetic recording medium is not particularly limited. Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed by an in-line sputtering apparatus together with an underlayer, a magnetic layer, and the like. These protective films may be a single layer, or may have a multilayer structure composed of the same or different films.
[0038]
In the above-described means, another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the above protective layer, colloidal silica fine particles are dispersed and coated in a tetraalkoxysilane diluted with an alcohol solvent on a Cr film, and then fired to form a silicon oxide (SiO2) film. You may do it.
[0039]
The lubricating layer in the magnetic recording medium is not particularly limited. The lubrication layer is formed by, for example, diluting perfluoropolyether, which is a liquid lubricant, with a solvent such as Freon, applying it to the surface of the medium by dipping, spin coating, or spraying, and performing heat treatment as necessary. To do.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the glass substrate for information recording media concerning the Example, the glass substrate for information recording media, the manufacturing method of an information recording medium, and an information recording medium are demonstrated in detail.
(Example 1)
The manufacturing method of the information recording medium according to Example 1 includes (1) a roughening process, (2) an end mirror polishing process, (3) a sanding (lapping) process, (4) a first polishing process, (5 ) A second polishing step, (6) a water polishing step, (7) a chemical strengthening step, and (8) a magnetic disk manufacturing step. Hereinafter, these steps will be described in detail.
[0041]
(1) Roughing process
First, a glass substrate made of aluminosilicate glass cut into a disk shape having a diameter of about 100 mmφ and a thickness of 3 mm from a sheet glass formed by the downdraw method is ground with a relatively rough diamond wheel, and the diameter is about Molded to 100 mmφ and 1.5 mm thickness. In this case, instead of the downdraw method, the molten glass may be directly pressed using an upper mold, a lower mold, and a body mold to obtain a disk-shaped glass body. Moreover, you may form by the float glass process.
[0042]
As aluminosilicate glass, SiO 2 : 58 to 75% by weight, Al 2 O Three : 5 to 23% by weight, Li 2 O: 3 to 10% by weight, Na 2 O: Glass for chemical strengthening containing 4 to 13% by weight as a main component (however, P 2 O Five Aluminosilicate glass that does not contain phosphorus oxides such as
[0043]
Next, both surfaces of the glass substrate were ground one by one with a diamond grindstone having a finer particle size than the grindstone. The load at this time was about 100 kg. Thereby, the surface roughness of both surfaces of the glass substrate was finished to about 10 μm by Rmax (measured by JISB0601).
[0044]
Next, a hole with a diameter of 25 mmφ is formed in the center portion of the glass substrate using a cylindrical grindstone, and the outer peripheral end face is ground to a diameter of 95 mmφ, and then the outer peripheral end face and the inner peripheral face are subjected to predetermined chamfering. did. The surface roughness of the end face of the glass substrate at this time was about 4 μm in Rmax.
[0045]
(2) End mirror finishing process
Next, the surface roughness of the end face of the glass substrate was polished to about 1 μm by Rmax and about 0.3 μm by Ra while rotating the glass substrate by brush polishing. The surface of the glass substrate after the end mirror processing was washed with water.
[0046]
(3) Sanding (wrapping) process
Next, the glass substrate was sanded. This sanding step aims to improve dimensional accuracy and shape accuracy. The sanding process was performed using a lapping apparatus, and the abrasive grain size was changed twice with # 400 and # 1000. Specifically, first, using alumina abrasive grains having a particle size of # 400, setting the load L to about 100 kg, and rotating the inner and outer rotation gears, the surface accuracy of both surfaces of the glass substrate housed in the carrier is improved. Lapping was performed to 0 to 1 μm and the surface roughness (Rmax) was about 6 μm.
[0047]
Next, lapping was performed by changing the particle size of the alumina abrasive grains to # 1000 to obtain a surface roughness (Rmax) of about 2 μm. The glass substrate that had been subjected to the sanding process was sequentially immersed in each washing tank of neutral detergent and water and washed.
[0048]
(4) First polishing process
Next, a first polishing step was performed. This first polishing step is intended to remove scratches and distortions remaining in the above-described sanding step, and was performed using a polishing apparatus. Specifically, a hard polisher (cerium pad MHC15: manufactured by Rodel Nitta) was used as the polisher (polishing powder), and the first polishing step was performed under the following polishing conditions.
[0049]
Polishing liquid: Cerium oxide (particle size 1.3 μm) (free abrasive grains) + water
Load: 300 g / cm 2 (L = 238kg)
Polishing time: 15 minutes
Removal amount: 30 μm
Lower platen rotation speed: 40rpm
Upper platen rotation speed: 35rpm
Inner gear speed: 14rpm
Outer gear speed: 29rpm
[0050]
The glass substrate that had been subjected to the first polishing step was sequentially immersed in cleaning baths of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) and washed.
[0051]
(5) Second polishing step
Next, using the polishing apparatus used in the first polishing process, the polisher was changed from a hard polisher to a soft polisher (Polytex: manufactured by Speedfam Co., Ltd.), and a second polishing process was performed. This second polishing step is intended to reduce the roughness of, for example, a surface roughness Ra of about 1.0 to 0.3 nm or less while maintaining the flat surface obtained in the first polishing step. It is. The polishing conditions were cerium oxide (particle size: 1.0 μm, fluorine content: 6.3 wt%, phosphorus content: 0.2 wt%) + water with a load of 100 g / cm. 2 The first polishing step was the same as the polishing step except that the polishing time was 5 minutes and the removal amount was 5 μm.
[0052]
(6) Water polishing process
Next, water polishing was performed for 2 minutes by switching from the supply of the polishing liquid to water. In addition, the polishing pad to be used is the same pad as the second polishing step, and the load is 30 g / cm. 2 It was.
[0053]
(7) Sulfuric acid cleaning
Next, this glass substrate was washed with sulfuric acid (20 wt%) at a temperature of 70 ° C. The sulfuric acid cleaning method was performed by immersing a plurality of glass substrates held in sulfuric acid accommodated in a cleaning tank (about 3 minutes). In this way, by removing the polishing residue without fail before chemical strengthening in the next step, subfilm defects can be prevented. In particular, it is important to perform this sulfuric acid washing before chemical strengthening. In other words, if chemical strengthening is performed with the cerium oxide polishing residue remaining on the glass substrate, foreign substances unnecessary for chemical strengthening are mixed in the chemical strengthening treatment solution, and the glass substrate is subjected to chemical strengthening. When a foreign substance adheres to the film, a subfilm defect occurs. Generation of such subfilm defects can be prevented by the above-described sulfuric acid cleaning.
[0054]
The glass substrate that has been cleaned with sulfuric acid is cleaned. This cleaning process means precision cleaning, and is intended to remove dirt, particles, and the like made of organic components adhering to the glass substrate. The process from the cleaning process to the packaging in the case was performed in an environment of clean air supplied by a clean booth. First, the first cleaning was performed by sequentially immersing the glass substrate in each cleaning bath of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.
[0055]
(7) Chemical strengthening process
Next, chemical strengthening was performed on the glass substrate after the cleaning process. Chemical strengthening is performed by placing the chemical strengthening treatment liquid in the chemical strengthening treatment tank and immersing the glass substrate held by the holding member in the chemical strengthening treatment liquid. Note that the glass substrate holding member is formed by connecting three support columns formed with a plurality of V-grooves at equal intervals in the glass substrate arrangement direction by connecting members at both end faces. The plurality of glass substrates are supported and held at three points by V-grooves in the same plane of the three support columns, and a plurality of glass substrates are arranged in the extending direction of the support columns.
[0056]
Each support column and connecting member of the holding member of the present embodiment are made of SUS316, which is an austenitic stainless alloy excellent in corrosion resistance in a high temperature range required for chemical strengthening. The chemical strengthening treatment tank is made of austenitic stainless alloy SUS304. The materials of the chemical strengthening treatment tank and the holding means may be the same or different. As another stainless alloy, for example, SUS316L is suitable. Moreover, since the chemical strengthening process liquid of the present embodiment is circulated through the filter, the chemical strengthening process liquid is kept clean.
[0057]
A specific method of chemical strengthening is to prepare a chemically strengthened solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed, and then heat the chemically strengthened solution to 400 ° C. and preheated to 300 ° C. The glass substrate was immersed for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, the plurality of glass substrates were held by holding members so as to be held at the end surfaces.
[0058]
Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions on the surface of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm.
[0059]
The glass substrate after the chemical strengthening was immersed in a 20 ° C. water bath, quenched, and maintained for about 10 minutes. Thereby, a defective product having a minute crack can be removed. Further, the glass substrate after chemical strengthening was subjected to washing / drying steps of sulfuric acid washing, neutral detergent, pure water, IPA, and IPA (steam drying). These cleaning steps are ultrasonic cleaning to which ultrasonic waves are applied.
[0060]
When the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), the Rmax was 6.5 to 9.3 nm, and the Ra was 0.6 to 0.9 nm. there were. Furthermore, when the glass surface was closely inspected, no defects in the recesses were observed (0 sheets in which the recess defects were observed after observing 100 sheets).
[0061]
(8) Magnetic disk manufacturing process
A NiAl seed layer, a CrMo underlayer, a CoCrPtTa magnetic layer, and a hydrogenated carbon protective layer are sequentially formed on both surfaces of the glass substrate for the magnetic disk obtained through the above-described process by using an in-line sputtering apparatus, and dip. A perfluoropolyether lubricating layer was formed by the method to obtain a magnetic disk.
[0062]
When a glide test was performed on the obtained magnetic disk, no hits (the head hitting the protrusion on the magnetic disk surface) or crash (the head collided with the protrusion on the magnetic disk surface) were not recognized. (100 out of 100 images were OK) In the recording / reproduction test, an error that the signal at the time of reproduction could not be read did not occur (100 out of 100 images were OK).
[0063]
(Examples 2-3)
Also, scrub cleaning instead of water polishing in the above-described embodiment (condition: cleaning using a surfactant and a single wafer cleaning machine using a roller) (Example 2), tape polishing using a tape-type texture device (Conditions: Example 3 except that polishing was carried out with a single-wafer type tape-type texture device that used nylon tape and pressed the tape against the rotated substrate substrate while supplying diamond abrasive grains. Similarly, a glass substrate was produced.
[0064]
When the surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope (AFM), in Example 2 above, Rmax was 6.6 to 8.9 nm, and Ra was 0.6 to 0.9 nm. In Example 3, Rmax was 6.4 to 9.2 nm, and Ra was 0.6 to 0.8 nm. Further, when the glass substrate surface was inspected closely, no defects in the recesses were observed (0 sheets in which the recess defects were observed by observing 100 sheets).
[0065]
When a glide test was performed on the obtained magnetic disk, no hits (the head hitting the protrusion on the magnetic disk surface) or crash (the head collided with the protrusion on the magnetic disk surface) were not recognized. (100 out of 100 images were OK) In the recording / reproduction test, an error that the signal at the time of reproduction could not be read did not occur (100 out of 100 images were OK).
[0066]
(Examples 4 and 5)
Further, the same procedure as in Example 2 (scrub cleaning) was performed except that the cerium oxide abrasive grains used in the second polishing step of the above example were changed to high-purity cerium oxide (fluorine content = 0% by weight). A glass substrate was prepared (Example 4). In addition, the glass substrate was formed in the same manner except that the polishing abrasive used in the second polishing step was high-purity cerium oxide (fluorine content: 0% by weight) and scrub cleaning was not performed before strong acid (sulfuric acid) cleaning. Prepared (Example 5).
[0067]
When the surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope (AFM), the polishing rate was slightly reduced, but in both Examples 4 and 5, Rmax was 5.3 to 7.5 nm, Ra 0.5 to 0.8 nm, which is smaller than the surface roughness of the glass substrate obtained in Example 2. Further, when the glass substrate surface was inspected closely, no defects in the recesses were observed (0 sheets in which the recess defects were observed by observing 100 sheets). In addition, as compared with Example 5, the cleaning property (cleaning time and cleaning ability) is higher when a process for forcibly removing the adhesion of the abrasive on the glass substrate is performed before the strong acid treatment as in Example 4. It is possible to improve and prevent the remaining abrasive.
[0068]
When the obtained magnetic disk was subjected to a glide test, no hit (the head hitting the protrusion on the magnetic disk surface) or crash (the head collided with the protrusion on the magnetic disk surface) was found (100 sheets). 100 sheets OK). In the recording / reproduction test, an error that the signal at the time of reproduction could not be read did not occur (100 out of 100 images were OK).
[0069]
(Comparative Example 1)
Next, for comparison, a glass substrate was prepared in the same manner as in Example 1 except that water polishing was not performed before washing with sulfuric acid and that the sulfuric acid washing conditions were 95 ° C. and 96 wt% concentrated sulfuric acid was used. Produced. When the surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope (AFM), Rmax was 8.1 to 11.3 nm and Ra was 0.6 to 0.9 nm. Further, when the surface of the glass substrate was closely inspected, defects of recesses having a size of about several μm to several mm and a depth of about 6 to 10 nm were observed (37 out of 100).
[0070]
Next, a magnetic disk having the same film configuration as in Example 1 was manufactured, and a glide test and a recording / reproducing test were performed. 19 errors out of 100 were confirmed.
[0071]
(Example 6)
A glass substrate and a magnetic disk were produced in the same manner as in Example 1 except that crystallized glass was used instead of the aluminosilicate glass used in Example 1. The crystallized glass used in this example is SiO. 2 : 65 to 83% by weight, Li 2 O: 8 to 13% by weight, Al 2 O Three : 0 to 7% by weight, K 2 O: 0 to 7% by weight, MgO: 0.5 to 3.5% by weight, ZnO: 0 to 5% by weight, P 2 O Five : 1 to 4 wt%, PbO: 0 to 5 wt% composition range. As a result, the same surface roughness as in Example 1 was obtained on the glass substrate, and no concave portion causing a head crash or a recording / reproducing error was observed. Also, in a glide test and a reproduction test using a magnetoresistive head for a magnetic disk, no head crash or reproduction error was observed.
[0072]
(Comparative Example 2)
Next, for comparison, the crystallized glass used in Example 6 was used, water polishing was not performed before sulfuric acid cleaning, and sulfuric acid was washed at 95 ° C. and 96 wt% concentrated sulfuric acid was used. A glass substrate and a magnetic disk were produced in the same manner as in Example 6 except for the above. As a result, defects in the recesses due to the reaction between fluorine and phosphorus contained in the abrasive and sulfuric acid were observed, and crashes and errors during reproduction were also confirmed in the glide test and recording / reproduction test.
[0073]
【The invention's effect】
As described above, the present invention includes a step of performing a strong acid treatment after polishing the main surface of the glass substrate using polishing abrasive grains. Magnetic disk A method for producing a glass substrate for use in the present invention, wherein the content of a causative substance that generates a component that erodes the surface of the glass substrate by reacting with the treatment liquid component used in the strong acid treatment as the abrasive grains is a predetermined amount. It is characterized by using the following, and by this, polishing residue is completely removed by strong acid treatment, and at the same time, surface roughness due to strong acid treatment is prevented and high smoothness without defects is obtained. Magnetic disk Glass substrates can be manufactured Magnetic disk Method for manufacturing glass substrate and Magnetic disk It is possible to provide a manufacturing method.
Claims (10)
前記ガラス基板は、少なくとも記録層が形成されて磁気ディスクとされるガラス基板であり、
前記研磨砥粒として、前記強酸処理の際に用いる処理液成分と反応して、前記ガラス基板表面を浸蝕して凹部を形成する成分を生成する原因物質であって研磨砥粒に含まれる弗素又はリンの含有量が、前記磁気ディスクにおいてヘッドクラッシュまたは記録再生時のエラーの原因となる凹部の発生を防止できる量以下であるものを用いて、ガラス基板の研磨を行うことを特徴とする磁気ディスク用ガラス基板の製造方法。A method for producing a glass substrate for a magnetic disk having a step of performing a strong acid treatment after polishing the main surface of the glass substrate using abrasive grains,
The glass substrate is a glass substrate in which at least a recording layer is formed to be a magnetic disk,
Fluorine contained in the polishing abrasive, which is a causative substance that reacts with the treatment liquid component used in the strong acid treatment to generate a component that erodes the glass substrate surface to form a recess as the polishing abrasive. A magnetic disk having a phosphorus content equal to or less than an amount capable of preventing the occurrence of a recess that causes a head crash or an error during recording / reproducing in the magnetic disk, and polishing a glass substrate Method for manufacturing glass substrate .
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US7384870B2 (en) | 2002-05-31 | 2008-06-10 | Hoya Corporation | Method for manufacturing glass substrate |
JP2004051455A (en) * | 2002-07-23 | 2004-02-19 | Furukawa Electric Co Ltd:The | Method of manufacturing optical fiber |
JP4041110B2 (en) * | 2004-09-29 | 2008-01-30 | Hoya株式会社 | Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk |
JP2009245467A (en) * | 2005-09-30 | 2009-10-22 | Hoya Corp | Process for producing glass substrate for magnetic disk, and process for producing magnetic disk |
JP5321168B2 (en) * | 2009-03-16 | 2013-10-23 | 東ソー株式会社 | Cleaning method for polished quartz glass substrate |
JP2011110637A (en) * | 2009-11-25 | 2011-06-09 | Asahi Glass Co Ltd | Method for manufacturing glass substrate for magnetic disk |
WO2012043214A1 (en) * | 2010-09-30 | 2012-04-05 | コニカミノルタオプト株式会社 | Manufacturing method for glass substrate for information recording medium, and information recording medium |
WO2013118648A1 (en) * | 2012-02-06 | 2013-08-15 | 旭硝子株式会社 | Method for producing glass product and method for producing magnetic disk |
JP7059794B2 (en) * | 2018-05-18 | 2022-04-26 | Agc株式会社 | Glass substrate and manufacturing method of glass substrate |
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