JP4647131B2 - Method for forming thin film crystals - Google Patents

Method for forming thin film crystals Download PDF

Info

Publication number
JP4647131B2
JP4647131B2 JP2001136987A JP2001136987A JP4647131B2 JP 4647131 B2 JP4647131 B2 JP 4647131B2 JP 2001136987 A JP2001136987 A JP 2001136987A JP 2001136987 A JP2001136987 A JP 2001136987A JP 4647131 B2 JP4647131 B2 JP 4647131B2
Authority
JP
Japan
Prior art keywords
thin film
temperature
zno
crystal
present
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP2001136987A
Other languages
Japanese (ja)
Other versions
JP2002334874A (en
Inventor
仁 田畑
知二 川合
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Japan Science and Technology Agency
National Institute of Japan Science and Technology Agency
Original Assignee
Japan Science and Technology Agency
National Institute of Japan Science and Technology Agency
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Japan Science and Technology Agency, National Institute of Japan Science and Technology Agency filed Critical Japan Science and Technology Agency
Priority to JP2001136987A priority Critical patent/JP4647131B2/en
Priority to PCT/JP2002/002685 priority patent/WO2002101122A1/en
Publication of JP2002334874A publication Critical patent/JP2002334874A/en
Application granted granted Critical
Publication of JP4647131B2 publication Critical patent/JP4647131B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/02—Epitaxial-layer growth
    • C30B25/18—Epitaxial-layer growth characterised by the substrate
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/0242—Crystalline insulating materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02422—Non-crystalline insulating materials, e.g. glass, polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02469—Group 12/16 materials
    • H01L21/02472—Oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02551—Group 12/16 materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02551—Group 12/16 materials
    • H01L21/02554—Oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/0257—Doping during depositing
    • H01L21/02573—Conductivity type
    • H01L21/02581—Transition metal or rare earth elements

Description

【０００１】
【発明の属する技術分野】
本発明は、薄膜結晶の形成方法に係り、特に、２段階の薄膜形成手法による高品質薄膜の低温形成と、その薄膜結晶成長技術を利用して新しい機能を付加した半導体素子に関するものである。
【０００２】
【従来の技術】
最近、日亜化学工業（株）の中村修二等によって窒化ガリウム薄膜を用いた青色発光素子、レーザーダイオードの報告がなされ（特開平１０−２９４４９２号「窒化ガリウム系化合物半導体の結晶成長方法」等）、短波長発光の半導体レーザー開発が活発に進められている。
【０００３】
それによれば、薄膜結晶成長させる際、数百度以上の高温条件で形成する必要がある。また、高出力レーザー実現のためには、単結晶基板の使用が理想的であるが、現在は類似の基板としてサファイア基板が使用されている。また、これらの素子が発現可能な機能は発光機能のみに限定されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来技術によれば、
（１）高温での薄膜形成が必須のため、既存の半導体プロセス技術との整合性が難しい。
（２）高温での薄膜形成では、新しい機能を付与するため必須である第３元素の導入が難しい。このため、発現可能な物性が限定されている。
【０００５】
（３）高出力レーザー等への応用実現のために必須である、十分なサイズ（４インチ以上）の単結晶入手が極めて難しい。あるいは入手不可能である。
という問題があった。
比較的大きなサイズ（４インチ以上）の単結晶が入手可能な機能性材料として酸化物があり、その中でも酸化亜鉛（ＺｎＯ）は、下記に示すような多彩な物性を示す可能性を有する有望な材料である。
【０００６】
酸化物（例えばＺｎＯ）の場合、結晶性の良好な薄膜を形成するためには、高い温度（ＺｎＯ薄膜の場合６００℃以上）での作製が望ましい。つまり、図２に示した点線に対応するように、高温になるに従って高い品質のものを得ることができる。
一方、第３元素（ＺｎＯの場合、例えば、ｐ型伝導性を付与するためにＧａやＮ、磁性を発現させるためにはＶやＣｒ，Ｍｎ，Ｆｅ，Ｃｏ，Ｎｉ，他の遷移金属等）を、酸化物（例えば、ＺｎＯ）結晶格子中に導入するためには、非平衡条件である低温形成（ＺｎＯ薄膜の場合４００℃以下）が望ましい。
【０００７】
本発明は、上記した相反する２つの制約を満足することができ、高品質の酸化亜鉛薄膜を低温で形成することができる薄膜結晶の形成方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、上記目的を達成するために、
〔１〕薄膜結晶の形成方法において、基板上に６００℃〜１０００℃でテンプレート層としての高温バッファー層を厚さ５〜２０ｎｍ形成する工程と、この高温バッファー層上に４００℃以下で厚さ３００ｎｍ以上の酸化亜鉛（ＺｎＯ）の低温薄膜成長を行わせる工程とを施すことを特徴とする。
【０００９】
〔２〕上記〔１〕記載の薄膜結晶の形成方法において、２８０℃の低温を利用した非平衡薄膜形成により、Ｃｏ又はＶ磁性イオンを前記酸化亜鉛（ＺｎＯ）の低温薄膜に固溶させることを特徴とする。
本発明によれば、上記のように構成することにより、
（１）低温での高品質薄膜結晶成長
２段階薄膜形成法を用いた。第１段階は高温（６００〜１０００℃）で極薄く（５ｎｍ程度）種結晶を成長（第１段階成長）させた後、第２段階として低温（４００℃以下）で結晶を本成長（第２段階成長）させた（３００ｎｍ以上）。
【００１０】
これにより、６００℃以上の高温プロセスでのみ形成した薄膜と同程度の品質を示す薄膜が得られた。すなわち、テンプレート層としての「高温バッファー層」は、低温プロセスでの高品質薄膜結晶の実現に極めて有効であることを初めて発見した。
（２）新しい機能（磁性）の付与
上記（１）で確立した非平衡薄膜結晶形成方法により、従来の熱力学平衡条件では実現しなかった、高濃度の第３元素（特に、磁性イオンとして、ＣｏやＶ等の遷移金属）を導入し、新しい機能（室温磁性）の発現に成功した。
【００１１】
更に、ＺｎＯは透明であるため、ＺｎＯをベースにした透明室温強磁性体を初めて合成できた。
【００１２】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。
図１は本発明の実施例を示す半導体素子の断面模式図である。
この図において、１は基板（Ａｌ2 Ｏ3 又はガラス）、２はその基板１上に形成される高温バッファー層（テンプレート層：約５ｎｍ）、３はその高温バッファー層２上に形成される低温薄膜（ＺｎＯ膜）である。
【００１３】
図１に示すように、基板１上に第１段階として、高温プロセスにより種結晶層（極めて薄い層）としての高温バッファー層２を形成し、その上に第２段階として、低温での薄膜３の成長を行う。
なお、第１段階の高温バッファー層２は５ｎｍ以上の厚い膜であっても、第２層の結晶性改善には十分に効果を発揮する。要求される物性、使用方法次第で、第１段階のテンプレート層２は最適な厚さが決まる。例えば、第２段階の低温薄膜の電気特性や光学特性を効果的に利用したい場合は、テンプレート層２としては、５〜２０ｎｍ程度の薄い膜が望ましい。
【００１４】
図２は薄膜形成温度と品質を示す関係図であり、実線は、ＺｎＯへ第３元素を導入する効果を示しており、低温プロセス（非平衡状態）程、その品質が高いことを示す。一方、破線は結晶性（薄膜の品質）を示し、上記とは逆に高温プロセスでの合成ほど、高結晶性の薄膜が形成可能であることを示している。
ところで、本発明における対象材料とした酸化亜鉛（ＺｎＯ）は、バンドギャップが３．３ｅＶのワイドギャップ化合物であり、可視光に対して吸収特性がないため、透明な化合物である。また、第３元素の導入により、下記に示すような物性を示すことが期待される。すなわち、
（１）化学量論組成の場合、絶縁体（圧電体）であるが、
（２）Ｌｉ等の小さなイオンを導入することにより強誘電性に、
（３）ＡｌやＧａ等の３価のイオンを導入するとｎ型の半導体に、
（４）Ｎを導入するとｐ型の半導体に、
さらに、
（５）ＣｏやＶを導入すると強磁性にそれぞれなることが予測されてきたが、上記した（４）や（５）は実証されていなかった。
【００１５】
この実施例では、薄膜（ＺｎＯ膜）の形成に、紫外パルスレーザーであるＡｒＦエキシマレーザー（波長１９３ｎｍ）を利用しサファイア単結晶基板（ａ面）上にＺｎＯ薄膜を結晶成長させた。
形成条件は、
基板温度：２００〜７００℃
雰囲気：１×１０-3〜１０-7Ｔｏｒｒ
レーザー強度：０．５〜２ｊ／ｃｍ2
図３はＺｎＯ薄膜の蛍光強度を示す図であり、縦軸は蛍光強度（ｃｐｓ）、横軸はエネルギー（ｅＶ）である。
【００１６】
一例として、基板温度４００℃と６００℃で形成したＺｎＯ薄膜のフォトルミネッセンス（ＰＬ）を図３（ａ）および図３（ｂ）に示した。６００℃で形成したＺｎＯ薄膜〔図３（ｂ）〕には、良好な結晶性を示すエキシントンのピーク（３．３ｅＶ付近：Ａ印）が見られるのに対して、低温の４００℃で形成したサンプル〔図３（ａ）〕では、エキシントンピークは極めて弱く、２．５ｅＶ以下の格子欠陥起因のピーク（Ｂ印）が顕著に観察された。これにより、高品質結晶を得るためには、６００℃以上の高温プロセスが必須であることが分かる。
【００１７】
しかしながら、図１に示すように、基板１上に成長初期層（第１段階成長）として高温で（６００℃で）極薄く（５ｎｍ程度）種結晶である高温バッファー層２を成長させた後、低温（４００℃以下）で結晶を本成長（第２段階成長）させた（３００ｎｍ以上）ＺｎＯ薄膜３においては、図３（ｃ）に示すように、６００℃以上の高温プロセスでのみ形成した薄膜と同程度の品質を示すＰＬピークが得られた。つまり、テンプレート層としての高温バッファー層２は、低温プロセスでの高品質薄膜結晶の実現に極めて有効であることがわかった。
【００１８】
非平衡プロセスは、バルク体では合成できない化合物が形成可能であるという利点を有している。例えば、ＺｎＯに磁性を付与させるために、スピンを持つ元素Ｃｏ，Ｖ等の導入がこれまでに試みられてきた。しかし、これまでは、熱力学的な制約から、別の層が析出したり、また導入可能であった場合も、その固溶限は数％程度と極めて低かった。
【００１９】
しかし、本発明の高温バッファー層２を用いた２段階成膜法により、低温プロセスでの非平衡成膜（約２８０℃）を試みたところ、ＣｏやＶ磁性イオンを約１５％もＺｎＯに固溶させることが可能となり、ＺｎＯでの室温透明強磁性体を合成することに成功した。
図４および図５に各々ＣｏとＶを１５％導入したＺｎＯ薄膜の、磁化−温度特性と磁場−磁化特性を示す。
【００２０】
図４では、キュリー温度（磁性を示す限界温度）が約３７５Ｋ（約１００℃）の磁性体であることを示しており、３７５Ｋ付近と３００Ｋ付近で磁化の大きさが正方向に転移している。
この磁化−温度極性の形状は、強磁性に特有の傾向である。また、磁化の大きさが約１１ｅｍｕ／ｇであり、単位Ｃｏ当たりの磁化率に換算すると、３μＢ／Ｃｏ−ｓｉｔｅ以上に対応し、強磁性以外のメカニズム（スピングラスやキャントした反強磁性等）では説明が難しく、同物質が強磁性を示している証拠の一つである。
【００２１】
一方、図５では、ヒステリシス曲線が約１０００程度で飽和しており、さらに抗磁界が約２００−３００Ｇと十分に小さい。これは（Ｚｎ，Ｖ）Ｏ薄膜が強磁性を示していることの１つの実験的証拠である。応用的な見地からは、十分小さい磁場で磁化反転が可能なため、低消費エネルギーのメモリ素子やスイッチング素子に適用可能であることを示している。
【００２２】
このように、室温で明確なヒステリシス曲線が得られ、磁気メモリを有する強磁性体であることが、明確に示されている。
なお、本発明はＺｎＯに限らず、ＺｎＳ、ＺｎＳｅ、ＺｎＴｅ、ＣｓＳ、ＣｓＳｅ、ＣｄＴｅ等のII，VI族化合物（カルコゲナイド系等）に関して適用可能である。
【００２３】
図６は本発明にかかる（Ｚｎ，Ｖ）Ｏ薄膜の代表的なＸ線回折パターンを示す図であり、縦軸に蛍光強度（ｃｐｓ）、横軸に２θ−θ（度）が示され、縦軸は対数スケールで表示されている。対数スケールで表示することにより、微小な回折パターンも検出可能なように、拡大された表示方法となっている。このような条件で測定しても、基板であるサファイア（１１−２０）面からの回折ピークと、（Ｚｎ，Ｖ）Ｏ薄膜のｃ軸配向パターンのみが観察され、不純物や異相が存在していることが分かる。
【００２４】
図７は本発明にかかるＺｎサイトに置換したＶの量とＺｎＯ結晶のｃ軸長との関係を示す図である。
この図に示すように、Ｖ置換量を０から１５％まで増加させて行くに従い、ｃ軸長が系統的に増加していることがわかる。Ｖ原子が格子間位置を占有したり、粒界等に析出せずに、Ｚｎサイトに置換して導入されていることを示すデータである。
【００２５】
図８は本発明にかかる（Ｚｎ，Ｖ）Ｏ薄膜の磁化特性を示す図であり、図８（ａ）はその温度と磁化率との関係を示す図、図８（ｂ）はその室温（約３００Ｋ）における（Ｚｎ，Ｖ）Ｏ（Ｖ量１５％）の磁場−磁化率曲線を示す図、図８（ｃ）は本発明にかかる（Ｚｎ，Ｖ）Ｏ薄膜のＭ−Ｈ曲線のＶ濃度依存性を示す図である。
【００２６】
図８（ａ）において、Δは電気伝導性の悪い（絶縁体）サンプル、●は電気伝導性の良好なサンプルのデータを示している。電気伝導性が良い場合（●）は正磁化率を示し、強磁性であることが分かる。３５０Ｋまで正の値を示しているため、強磁性転移温度は３５０Ｋ以上であり、室温強磁性であることを示している。一方、電気伝導性の悪いサンプル（Δ）は磁化率が負の値を示している。これは、サファイア基板の反磁性に起因するものであり、（Ｚｎ，Ｖ）Ｏ薄膜が常磁性であることがわかる。
【００２７】
図８（ｂ）において、Δは電気伝導性の悪い（絶縁体）サンプル、●は電気伝導性の良好なサンプルのデータを示している。このデータにより、十分なキャリアが存在する場合（電気伝導性が良い場合）は、強磁性が発現されることが分かる。この結果は、室温キャリア誘起強磁性が実験的に示されたものであり、スピンエレクトロニクスの実用化において、その意義は大変大きい。
【００２８】
図８（ｃ）においは、１０Ｋにて測定を行った。Ｖ濃度は、▲は５％、◇は１０％、●は１５％を示しており、Ｖ濃度が増加するに伴い、強磁性が増大し安定している。吉田（阪大）らにより理論的に予想された傾向に合致している。
図９は本発明にかかる電気伝導性と磁性との関係を示す図である。
図９の左側に示す（ｎｏｎｍａｇｎｅｔｉｃと表示）ように、電気伝導性の低いサンプルは、磁性を示さない。一方、図９の右側に示す（ｆｅｒｒｏｍａｇｎｅｔｉｃと表示）ように、導電性の高いサンプルは強磁性を示す。これらの結果より、強磁性の発現機構は、２重交換相互作用による可能性が高い。
【００２９】
なお、本発明は上記実施例に限定されるものではなく、本発明の趣旨に基づいて種々の変形が可能であり、これらを本発明の範囲から排除するものではない。
【００３０】
【発明の効果】
以上、詳細に説明したように、本発明によれば、以下のような効果を奏することができる。
（Ａ）高品質の酸化亜鉛薄膜を低温で形成することができる。
（Ｂ）本発明を利用した非平衡プロセスにより、熱力学プロセスでは固溶できなかった高濃度まで第３元素を導入可能となり、従来存在しなかった新しい機能の付与、例えば、室温透明磁性薄膜を形成することができる。
【図面の簡単な説明】
【図１】 本発明の実施例を示す半導体素子の断面模式図である。
【図２】 薄膜形成温度と品質を示す関係図である。
【図３】 ＺｎＯ薄膜の蛍光強度を示す図である。
【図４】 Ｃｏを１５％導入したＺｎＯ薄膜の、磁化−温度特性を示す図である。
【図５】 Ｖを１５％導入したＺｎＯ薄膜の、磁場−磁化特性を示す図である。
【図６】 本発明にかかる（Ｚｎ，Ｖ）Ｏ薄膜の代表的なＸ線回折パターンを示す図である。
【図７】 本発明にかかるＺｎサイトに置換したＶの量とＺｎＯ結晶のｃ軸長との関係を示す図である。
【図８】 本発明にかかる（Ｚｎ，Ｖ）Ｏ薄膜の磁化特性を示す図である。
【図９】 本発明にかかる電気伝導性と磁性との関係を示す図である。
【符号の説明】
１ 基板（Ａｌ2 Ｏ3 又はガラス）
２ 高温バッファー層（テンプレート層：約５ｎｍ）
３ 低温薄膜（ＺｎＯ膜）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the formation how the thin-film crystal, and in particular the low temperature formation of a high-quality thin film by two-stage film forming method, a semiconductor device obtained by adding a new function using the thin-film crystal growth technology .
[0002]
[Prior art]
Recently, Shuji Nakamura of Nichia Chemical Co., Ltd. reported on a blue light emitting device and a laser diode using a gallium nitride thin film (Japanese Patent Laid-Open No. 10-294492 “Crystal growth method of gallium nitride compound semiconductor”, etc.) The development of short-wavelength light emitting semiconductor lasers has been actively promoted.
[0003]
According to this, when growing a thin film crystal, it is necessary to form it under a high temperature condition of several hundred degrees or more. In order to realize a high-power laser, it is ideal to use a single crystal substrate, but a sapphire substrate is currently used as a similar substrate. Further, the functions that can be expressed by these elements are limited to the light emitting function.
[0004]
[Problems to be solved by the invention]
However, according to the prior art,
(1) Since it is essential to form a thin film at a high temperature, consistency with existing semiconductor process technology is difficult.
(2) In forming a thin film at a high temperature, it is difficult to introduce a third element which is essential for providing a new function. For this reason, the physical property which can be expressed is limited.
[0005]
(3) It is extremely difficult to obtain a single crystal having a sufficient size (4 inches or more), which is essential for realizing an application to a high-power laser or the like. Or it is not available.
There was a problem.
There is an oxide as a functional material for which a single crystal having a relatively large size (4 inches or more) is available. Among them, zinc oxide (ZnO) is a promising material that may exhibit various physical properties as shown below. Material.
[0006]
In the case of an oxide (for example, ZnO), in order to form a thin film with good crystallinity, it is desirable to fabricate at a high temperature (600 ° C. or higher in the case of a ZnO thin film). That is, as the temperature rises, a higher quality can be obtained so as to correspond to the dotted line shown in FIG.
On the other hand, the third element (in the case of ZnO, for example, Ga or N for imparting p-type conductivity, V, Cr, Mn, Fe, Co, Ni, other transition metals or the like for manifesting magnetism) Is preferably formed at a low temperature (400 ° C. or lower in the case of a ZnO thin film), which is a non-equilibrium condition.
[0007]
The present invention is able to meet the two contradictory constraints described above, and an object thereof is to provide a form how a thin film crystal zinc oxide thin film of high quality can be formed at a low temperature.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In the method for forming a thin film crystal, a step of forming a high-temperature buffer layer as a template layer at 600 to 1000 ° C. on the substrate at a thickness of 5 to 20 nm, and a thickness of 300 nm at 400 ° C. or less on the high-temperature buffer layer And a step of performing low-temperature thin film growth of zinc oxide (ZnO) as described above.
[0009]
[2] In the method for forming the above-mentioned [1], wherein the thin-film crystal, the non-equilibrium film formed using a low temperature of 2 80 ° C., thereby solid solution of Co or V magnetic ions to the cold thin the zinc oxide (ZnO) It is characterized by.
According to the present invention, by configuring as described above,
(1) High quality thin film crystal growth at low temperature A two-stage thin film formation method was used. In the first stage, a seed crystal is grown extremely thin (about 5 nm) at a high temperature (600 to 1000 ° C.) (first stage growth), and then the crystal is grown as a second stage at a low temperature (400 ° C. or less) (second stage). Step growth) (300 nm or more).
[0010]
Thereby, the thin film which shows the quality comparable as the thin film formed only by the high temperature process of 600 degreeC or more was obtained. That is, it was discovered for the first time that a “high temperature buffer layer” as a template layer is extremely effective for realizing a high quality thin film crystal in a low temperature process.
(2) Addition of a new function (magnetism) By the non-equilibrium thin film crystal formation method established in (1) above, a high-concentration third element (especially as a magnetic ion, which was not realized under conventional thermodynamic equilibrium conditions) And introduced a new function (room temperature magnetism).
[0011]
Furthermore, since ZnO is transparent, a transparent room temperature ferromagnet based on ZnO could be synthesized for the first time.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a schematic sectional view of a semiconductor device showing an embodiment of the present invention.
In this figure, 1 is a substrate (Al 2 O 3 or glass), 2 is a high temperature buffer layer (template layer: about 5 nm) formed on the substrate 1, and 3 is a low temperature formed on the high temperature buffer layer 2. It is a thin film (ZnO film).
[0013]
As shown in FIG. 1, a high-temperature buffer layer 2 as a seed crystal layer (very thin layer) is formed on a substrate 1 as a first stage by a high-temperature process, and a thin film 3 at a low temperature is formed thereon as a second stage. Do growth.
Even if the high-temperature buffer layer 2 in the first stage is a thick film of 5 nm or more, it is sufficiently effective for improving the crystallinity of the second layer. The optimum thickness of the template layer 2 in the first stage is determined depending on the required physical properties and the method of use. For example, when it is desired to effectively use the electrical characteristics and optical characteristics of the second stage low temperature thin film, the template layer 2 is preferably a thin film of about 5 to 20 nm.
[0014]
FIG. 2 is a relational diagram showing the thin film formation temperature and quality, and the solid line shows the effect of introducing the third element into ZnO, and the lower the temperature process (non-equilibrium state), the higher the quality. On the other hand, the broken line indicates crystallinity (thin film quality), and contrary to the above, it indicates that the higher the crystalline film can be formed, the higher the synthesis by the high temperature process.
By the way, zinc oxide (ZnO) used as a target material in the present invention is a wide gap compound having a band gap of 3.3 eV, and has no absorption property with respect to visible light, and thus is a transparent compound. In addition, the introduction of the third element is expected to exhibit the following physical properties. That is,
(1) In the case of a stoichiometric composition, it is an insulator (piezoelectric material),
(2) Ferroelectricity by introducing small ions such as Li,
(3) When trivalent ions such as Al and Ga are introduced, the n-type semiconductor
(4) When N is introduced, it becomes a p-type semiconductor.
further,
(5) It has been predicted that when Co or V is introduced, each becomes ferromagnetic, but the above (4) and (5) have not been demonstrated.
[0015]
In this example, an ArF excimer laser (wavelength 193 nm), which is an ultraviolet pulse laser, was used to form a thin film (ZnO film), and a ZnO thin film was grown on a sapphire single crystal substrate (a-plane).
The formation conditions are
Substrate temperature: 200-700 ° C
Atmosphere: 1 × 10 −3 to 10 −7 Torr
Laser intensity: 0.5-2 j / cm 2
FIG. 3 is a diagram showing the fluorescence intensity of the ZnO thin film, where the vertical axis represents the fluorescence intensity (cps) and the horizontal axis represents the energy (eV).
[0016]
As an example, photoluminescence (PL) of a ZnO thin film formed at substrate temperatures of 400 ° C. and 600 ° C. is shown in FIGS. 3 (a) and 3 (b). The ZnO thin film formed at 600 ° C. [FIG. 3 (b)] shows an excinton peak (near 3.3 eV: mark A) showing good crystallinity, whereas it was formed at a low temperature of 400 ° C. In the sample [Fig. 3 (a)], the Exington peak was very weak, and a peak (mark B) due to lattice defects of 2.5 eV or less was remarkably observed. Thereby, in order to obtain a high quality crystal | crystallization, it turns out that the high temperature process of 600 degreeC or more is essential.
[0017]
However, as shown in FIG. 1, after growing a high temperature buffer layer 2 which is a seed crystal as a growth initial layer (first growth) on a substrate 1 at a high temperature (at 600 ° C.) and extremely thin (about 5 nm), In the ZnO thin film 3 (300 nm or more) in which crystals are grown (second stage growth) at a low temperature (400 ° C. or less), as shown in FIG. 3C, the thin film is formed only by a high temperature process of 600 ° C. or more. A PL peak showing the same quality as that obtained was obtained. That is, it was found that the high temperature buffer layer 2 as the template layer is extremely effective for realizing a high quality thin film crystal in a low temperature process.
[0018]
Non-equilibrium processes have the advantage that compounds that cannot be synthesized in bulk can be formed. For example, in order to impart magnetism to ZnO, attempts have been made so far to introduce spin elements such as Co and V. However, until now, due to thermodynamic limitations, even when another layer is deposited or can be introduced, its solid solubility limit is as low as several percent.
[0019]
However, when a non-equilibrium film formation (about 280 ° C.) in a low-temperature process was attempted by the two-step film formation method using the high-temperature buffer layer 2 of the present invention, about 15% of Co and V magnetic ions were fixed in ZnO. It was possible to dissolve it and succeeded in synthesizing a room temperature transparent ferromagnet with ZnO.
4 and 5 show the magnetization-temperature characteristics and the magnetic field-magnetization characteristics of a ZnO thin film into which 15% Co and V are introduced, respectively.
[0020]
FIG. 4 shows that the magnetic material has a Curie temperature (limit temperature indicating magnetism) of about 375 K (about 100 ° C.), and the magnitude of magnetization is shifted in the positive direction at around 375 K and 300 K. .
This shape of magnetization-temperature polarity is a tendency unique to ferromagnetism. In addition, the magnitude of the magnetization is about 11 emu / g, and when converted to the magnetic susceptibility per unit Co, it corresponds to 3 μB / Co-site or more, and a mechanism other than ferromagnetism (spin glass, canted antiferromagnetism, etc.) It is difficult to explain, and is one of the evidence that the substance shows ferromagnetism.
[0021]
On the other hand, in FIG. 5, the hysteresis curve is saturated at about 1000, and the coercive field is sufficiently small at about 200-300G. This is one experimental proof that the (Zn, V) O thin film exhibits ferromagnetism. From an applied point of view, it can be applied to a memory element or a switching element with low energy consumption because magnetization reversal is possible with a sufficiently small magnetic field.
[0022]
Thus, a clear hysteresis curve is obtained at room temperature, and it is clearly shown that the ferromagnetic body has a magnetic memory.
The present invention is not limited to ZnO, but can be applied to II and VI group compounds (chalcogenide-based compounds) such as ZnS, ZnSe, ZnTe, CsS, CsSe, and CdTe.
[0023]
FIG. 6 is a diagram showing a typical X-ray diffraction pattern of a (Zn, V) O thin film according to the present invention, where the vertical axis indicates fluorescence intensity (cps), and the horizontal axis indicates 2θ−θ (degrees). The vertical axis is displayed on a logarithmic scale. By displaying on a logarithmic scale, the display method is enlarged so that a minute diffraction pattern can be detected. Even when measured under such conditions, only the diffraction peak from the sapphire (11-20) plane as the substrate and the c-axis orientation pattern of the (Zn, V) O thin film are observed, and there are impurities and heterogeneous phases. I understand that.
[0024]
FIG. 7 is a graph showing the relationship between the amount of V substituted for the Zn site and the c-axis length of the ZnO crystal according to the present invention.
As shown in this figure, it can be seen that the c-axis length increases systematically as the V replacement amount is increased from 0 to 15%. This data shows that V atoms occupy interstitial positions or are not introduced into grain boundaries or the like but are substituted for Zn sites and introduced.
[0025]
8A and 8B are diagrams showing the magnetization characteristics of the (Zn, V) O thin film according to the present invention. FIG. 8A is a diagram showing the relationship between the temperature and the magnetic susceptibility, and FIG. FIG. 8C is a diagram showing a magnetic field-susceptibility curve of (Zn, V) O (V amount: 15%) at about 300 K), and FIG. 8C is a graph of V of the MH curve of the (Zn, V) O thin film according to the present invention. It is a figure which shows density | concentration dependence.
[0026]
In FIG. 8A, Δ represents data of a sample having poor electrical conductivity (insulator), and ● represents data of a sample having good electrical conductivity. When the electrical conductivity is good (●), it shows a positive magnetic susceptibility and is found to be ferromagnetic. Since the positive value is shown up to 350K, the ferromagnetic transition temperature is 350K or more, which indicates room temperature ferromagnetism. On the other hand, the sample (Δ) with poor electrical conductivity has a negative magnetic susceptibility. This is due to the diamagnetism of the sapphire substrate, and it can be seen that the (Zn, V) O thin film is paramagnetic.
[0027]
In FIG. 8B, Δ represents data of a sample having poor electrical conductivity (insulator), and ● represents data of a sample having good electrical conductivity. From this data, it can be seen that ferromagnetism is manifested when sufficient carriers are present (when electrical conductivity is good). This result experimentally shows room-temperature carrier-induced ferromagnetism, and its significance is very great in the practical application of spin electronics.
[0028]
In FIG. 8C, the measurement was performed at 10K. The V concentration is 5%, １０ is 10%, and ● is 15%. As the V concentration increases, ferromagnetism increases and is stable. It agrees with the trend predicted theoretically by Yoshida (Osaka Univ.) And others.
FIG. 9 is a diagram showing the relationship between electrical conductivity and magnetism according to the present invention.
As shown on the left side of FIG. 9 (indicated as nonmagnetic), the sample with low electrical conductivity does not exhibit magnetism. On the other hand, as shown on the right side of FIG. 9 (indicated as “ferromagnetic”), the highly conductive sample exhibits ferromagnetism. From these results, it is highly possible that the ferromagnetism expression mechanism is due to the double exchange interaction.
[0029]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0030]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
(A) A high-quality zinc oxide thin film can be formed at a low temperature.
(B) The non-equilibrium process using the present invention makes it possible to introduce the third element to a high concentration that could not be dissolved in the thermodynamic process, and to provide a new function that did not exist conventionally, for example, a room temperature transparent magnetic thin film Can be formed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a semiconductor element showing an embodiment of the present invention.
FIG. 2 is a relationship diagram showing thin film formation temperature and quality.
FIG. 3 is a diagram showing the fluorescence intensity of a ZnO thin film.
FIG. 4 is a diagram showing magnetization-temperature characteristics of a ZnO thin film into which 15% Co is introduced.
FIG. 5 is a diagram showing magnetic field-magnetization characteristics of a ZnO thin film into which V is introduced at 15%.
FIG. 6 is a diagram showing a typical X-ray diffraction pattern of a (Zn, V) O thin film according to the present invention.
FIG. 7 is a diagram showing the relationship between the amount of V substituted for Zn sites and the c-axis length of ZnO crystal according to the present invention.
FIG. 8 is a diagram showing the magnetization characteristics of a (Zn, V) O thin film according to the present invention.
FIG. 9 is a diagram showing the relationship between electrical conductivity and magnetism according to the present invention.
[Explanation of symbols]
1 Substrate (Al 2 O 3 or glass)
2 High temperature buffer layer (template layer: about 5 nm)
3 Low temperature thin film (ZnO film)

Claims (2)

（ａ）基板上に６００℃〜１０００℃でテンプレート層としての高温バッファー層を厚さ５〜２０ｎｍ形成する工程と、
（ｂ）該高温バッファー層上に４００℃以下で厚さ３００ｎｍ以上の酸化亜鉛（ＺｎＯ）の低温薄膜成長を行わせる工程とを施すことを特徴とする薄膜結晶の形成方法。(A) forming a high-temperature buffer layer as a template layer at a thickness of 5 to 20 nm on a substrate at 600 to 1000 ° C .;
And (b) performing a low-temperature thin film growth of zinc oxide (ZnO) having a thickness of 400 nm or less and a thickness of 300 nm or more on the high-temperature buffer layer. 請求項１記載の薄膜結晶の形成方法において、２８０℃の低温を利用した非平衡薄膜形成により、Ｃｏ又はＶ磁性イオンを前記酸化亜鉛（ＺｎＯ）の低温薄膜に固溶させることを特徴とする薄膜結晶の形成方法。 2. The method of forming a thin film crystal according to claim 1, wherein Co or V magnetic ions are dissolved in the low temperature thin film of zinc oxide (ZnO) by non-equilibrium thin film formation using a low temperature of 280 [deg.] C. Method for forming a thin film crystal.
JP2001136987A 2001-05-08 2001-05-08 Method for forming thin film crystals Expired - Fee Related JP4647131B2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP2001136987A JP4647131B2 (en) 2001-05-08 2001-05-08 Method for forming thin film crystals
PCT/JP2002/002685 WO2002101122A1 (en) 2001-05-08 2002-03-20 Method for forming thin film crystal and semiconductor element employing that method

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2001136987A JP4647131B2 (en) 2001-05-08 2001-05-08 Method for forming thin film crystals

Publications (2)

Publication Number Publication Date
JP2002334874A JP2002334874A (en) 2002-11-22
JP4647131B2 true JP4647131B2 (en) 2011-03-09

Family

ID=18984154

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2001136987A Expired - Fee Related JP4647131B2 (en) 2001-05-08 2001-05-08 Method for forming thin film crystals

Country Status (2)

Country Link
JP (1) JP4647131B2 (en)
WO (1) WO2002101122A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1302529C (en) * 2004-10-25 2007-02-28 中国科学院物理研究所 Three buffer layer method for preparing high quality zinc oxide monocrystalline film
JP4930933B2 (en) * 2006-03-31 2012-05-16 地方独立行政法人山口県産業技術センター Magneto-optic element
JP2011021270A (en) * 2009-06-16 2011-02-03 Central Glass Co Ltd Method for forming ceramic thin film
DE102009060547A1 (en) * 2009-12-23 2011-06-30 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 80686 Process for coating a substrate with aluminum-doped zinc oxide
KR101932576B1 (en) 2010-09-13 2018-12-26 가부시키가이샤 한도오따이 에네루기 켄큐쇼 Semiconductor device and method for manufacturing the same

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6278199A (en) * 1985-09-30 1987-04-10 Toshiba Corp Production of compound semiconductor crystal
JP2000244014A (en) * 1999-02-19 2000-09-08 Murata Mfg Co Ltd Semiconductor light emitting element and its manufacture

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2795226B2 (en) * 1995-07-27 1998-09-10 日本電気株式会社 Semiconductor light emitting device and method of manufacturing the same
JP3540275B2 (en) * 1998-10-09 2004-07-07 ローム株式会社 P-type ZnO single crystal and method for producing the same

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6278199A (en) * 1985-09-30 1987-04-10 Toshiba Corp Production of compound semiconductor crystal
JP2000244014A (en) * 1999-02-19 2000-09-08 Murata Mfg Co Ltd Semiconductor light emitting element and its manufacture

Also Published As

Publication number Publication date
WO2002101122A1 (en) 2002-12-19
JP2002334874A (en) 2002-11-22

Similar Documents

Publication Publication Date Title
Fu et al. A review of β-Ga2O3 single crystal defects, their effects on device performance and their formation mechanism
Ali et al. Influence of nickel doping on the energy band gap, luminescence, and magnetic order of spray deposited nanostructured ZnO thin films
Goktas et al. Physical properties of solution processable n-type Fe and Al co-doped ZnO nanostructured thin films: role of Al doping levels and annealing
Vijayaprasath et al. Characterization of dilute magnetic semiconducting transition metal doped ZnO thin films by sol–gel spin coating method
Lim et al. Observation of optical properties related to room-temperature ferromagnetism in co-sputtered Zn1− xCoxO thin films
Cao et al. Anomalous magnetic and transport behavior in the magnetic insulator Sr 3 Ir 2 O 7
EP1443130B1 (en) Natural superlattice homologous single crystal thin film, method for preparation thereof, and device using said single crystal thin film
Mandal et al. Microstructural, magnetic and optical properties of ZnO: Mn (0.01≤ x≤ 0.25) epitaxial diluted magnetic semiconducting films
Zhang et al. Structural, optical and electrical properties of sol-gel spin-coated Ga and F Co-doped ZnO films
JP4647131B2 (en) Method for forming thin film crystals
Kabilan et al. Annealing temperature enhanced visible absorption and magnetic properties of (Cu, Cr) co-doped ZnO diluted magnetic semiconductors
Fang et al. Structure and properties variations in Zn1− xCoxO nanorods prepared by microwave-assisted hydrothermal method
Baqiah et al. Effects of annealing temperature on the phase formation, optical, photoluminescence and magnetic properties of sol-gel YFeO3 films
Sato et al. Room temperature ferromagnetism in novel magnetic semiconductors based on II–IV–V2 chalcopyrite compounds
Riaz et al. Effect of Mn-doping concentration on the structural & magnetic properties of sol-gel deposited ZnO diluted magnetic semiconductor
Kumar et al. Epitaxial growth of terbium iron garnet thin films with out-of-plane axis of magnetization
Ma et al. The dilute magnetic and optical properties of Mn-doped ZnO nanowires
Xue-Chao et al. Difference in magnetic properties between Co-doped ZnO powder and thin film
KR100483318B1 (en) ferromagnetic - semiconductor single crystal and their manufacturing method
JP3773899B2 (en) Magnetic semiconductor material and manufacturing method thereof
Xu et al. Optimization of the pulsed laser deposition process of In 2 O 3 thin films for ferroelectric field effect device applications
Kundaliya et al. Large second-harmonic kerr rotation in GaFeO3 thin films on YSZ buffered silicon
Mahendran et al. Characterization of manganese doped ZnO (MZO) thin films by spin coating technique
Reddy et al. Structural and optical properties of sprayed Zn1− xMnxO films
Qing-Bo et al. Raman spectroscopy and magnetic properties of Mn-doped ZnO bulk single crystal

Legal Events

Date Code Title Description
A711 Notification of change in applicant

Free format text: JAPANESE INTERMEDIATE CODE: A712

Effective date: 20031031

RD03 Notification of appointment of power of attorney

Free format text: JAPANESE INTERMEDIATE CODE: A7423

Effective date: 20040129

A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20071127

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20100629

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20100826

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20101005

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20101019

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20101207

A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20101208

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20131217

Year of fee payment: 3

R150 Certificate of patent or registration of utility model

Free format text: JAPANESE INTERMEDIATE CODE: R150

LAPS Cancellation because of no payment of annual fees